Science.gov

Sample records for abrupt climate transitions

  1. Transition process of abrupt climate change based on global sea surface temperature over the past century

    NASA Astrophysics Data System (ADS)

    Yan, Pengcheng; Hou, Wei; Feng, Guolin

    2016-05-01

    A new detection method has been proposed to study the transition process of abrupt climate change. With this method, the climate system transiting from one stable state to another can be verified clearly. By applying this method to the global sea surface temperature over the past century, several climate changes and their processes are detected, including the start state (moment), persist time, and end state (moment). According to the spatial distribution, the locations of climate changes mainly have occurred in the Indian Ocean and western Pacific before the middle twentieth century, in the 1970s in the equatorial middle-eastern Pacific, and in the middle and southern Pacific since the end of the twentieth century. In addition, the quantitative relationship between the transition process parameters is verified in theory and practice: (1) the relationship between the rate and stability parameters is linear, and (2) the relationship between the rate and change amplitude parameters is quadratic.

  2. The role of oceanic heat transport in abrupt millennial-scale climate transitions

    NASA Astrophysics Data System (ADS)

    Arzel, Olivier; de Verdière, Alain Colin; England, Matthew H.

    2010-05-01

    The last glacial period was punctuated by rapid climate shifts, known as Dansgaard-Oeschger events, with strong imprint in the North Atlantic sector suggesting that they were linked with the Atlantic Meridional Overturning Circulation. Here an idealized single-hemisphere three-dimensional ocean-atmosphere-sea ice coupled model is used to explore the possible origin of the instability driving these abrupt events and to provide a plausible explanation for the relative stability of the Holocene. Focusing on the physics of noise-free millennial oscillations under steady external (solar) forcing, we show that cold climates become unstable, that is, exhibit abrupt millennial-scale transitions, for significantly lower freshwater fluxes than warm climates, in agreement with previous studies making use of zonally-averaged coupled models. This fundamental difference is a direct consequence of the weaker temperature stratification of the glacial ocean, mainly caused by upper ocean cooling. With similar overturning strengths between the cold and warm climates, this weaker temperature stratification implies a weaker baroclinic heat transport that ultimately leads to a weaker stabilization of the circulation by the negative temperature advection feedback. Using a two-hemisphere configuration of a coupled climate model of intermediate complexity, we show that this result is robust to the added presence of a bottom water mass of southern origin. The analysis reveals that under particular conditions, a pronounced interdecadal variability develops during warm interstadials, with maximum variance in the northern extension of the western boundary current in the North Atlantic. While the nature of the instability driving the millennial oscillations is identical to that found in ocean models under mixed boundary conditions, these interstadial-interdecadal oscillations share the same characteristics as those previously found in ocean models forced by fixed surface fluxes: they originate

  3. 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.

  4. Implications of abrupt climate change.

    PubMed

    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.

  5. Abrupt climate changes in northwestern Colombia during the Lateglacial and Holocene transition

    NASA Astrophysics Data System (ADS)

    Velasquez Ruiz, C.

    2013-05-01

    High resolution pollen/spores records from Paramo de Frontino (6, 29N, 76, 6W) and Paramo de Belmira (6,42'N, 75,40'W) in Colombia (Velásquez C. and H. Hooghiemstra, Paleobotany, 2012 in press; Velásquez C., et al., in preparation) spanning 17300 and 34000 cal yr BP; are studied for abrupt climatic change and compared with a La Cocha diatom record (Gonzalez, Z, et al., 2012), Frontino and Cariaco Basin (offshore Venezuela) titanium records and a Cariaco sea surface temperatures record (Gorin, G., et al, in preparation; Haug, et al., 2001; Lea D., et al., 2003; respectively); in reference to detected vegetation and climate variations. The most remarkable events occurred at 8200, 9300, 10400, 12000, 13500, 14.5-14.7, 16.2 and 21.4 cal yr BP. Low frequency cycles of 1500-2500 yr are present along the records suggesting that the North Atlantic Bond Cycles are also registered in northwestern South American terrestrial records. Some of these changes were dry while others wet, showing that both patterns "Cold poles, dry tropics" and "Cold poles, wet tropics" can be expressed. It was also found that the estimated temperatures from Paramo de Frontino (pollen based) and sea surface temperatures in Cariaco followed a similar trend during the the Late Glacial and Early Holocene. However, in the case of moisture, the Titanium record (indicative of rainfall) from the Cariaco Basin, the aquatic vegetation pollen and titanium records from Paramo de Frontino and diatoms record from La Cocha lake, showed a clear antiphase behavior during the same periods. Position and shape of Intertropical Convergence Zone are postulated as responsible for this variation. Keywords: palinology, Intertropical Convergence Zone, titanium, Colombia, climatic and vegetation changes.

  6. 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

  7. Revisiting Lake Hämelsee: reconstructing abrupt Lateglacial climate transitions using state- of-the-art palaeoclimatological proxies

    NASA Astrophysics Data System (ADS)

    Engels, Stefan; Hoek, Wim; Lane, Christine; Sachse, Dirk; Wagner-Cremer, Friederike

    2015-04-01

    Lake Hämelsee (Germany) is one of the northernmost sites in NW Europe that has varved sediments throughout large parts of its Lateglacial and Early Holocene sediment sequence. Previous research on this site has shown its potential, in terms of chronological resolution and palaeoecological reconstructions, for reconstructing the abrupt transitions into and out of the Younger Dryas, the last cold period of the last glacial. The site was revisited during a 1-week summer school for Early Stage Researchers (2013), within the INTIMATE Example training and research project, supported by EU Cost Action ES0907. Two overlapping sediment sequences were retrieved from the centre of the lake during the summer school. These sediments have since formed the basis for follow-up research projects, which have sparked the collaboration of around 30 researchers in 12 laboratories across Europe. A chronological framework for the core has been composed from a combination of varve counting, radiocarbon dating and tephrochronology. Tephrostratigraphic correlations allow direct correlation and precise comparison of the record to marine and ice core records from the North Atlantic region, and other terrestrial European archives. Furthermore, the core is has been subjected to multiple sedimentological (e.g. XRF, loss-on-ignition), geochemical (e.g. lipid biomarkers, GDGTs) and palaeoecological (e.g. pollen, chironomids) proxy-based reconstructions of past environmental and climatic conditions. The results provide important insights into the nature of the abrupt climate transitions of the Lateglacial and Early Holocene, both locally and on a continental scale. The INTIMATE Example participants: Illaria Baneschi, Achim Brauer, Christopher Bronk Ramsey, Renee de Bruijn, Siwan Davies, Aritina Haliuc, Katalin Hubay, Gwydion Jones, Meike Müller, Johanna Menges, Josef Merkt, Tom Peters, Francien Peterse, Anneke ter Schure, Kathrin Schuetrumpf, Richard Staff, Falko Turner, Valerie van den Bos.

  8. Abrupt climate change: Mechanisms, patterns, and impacts

    NASA Astrophysics Data System (ADS)

    Schultz, Colin

    2012-08-01

    In the span of only a few decades, the global temperature can soar by more than a dozen degrees Celsius, a feat that 20 years ago was considered improbable, if not impossible. But recent research in the nascent field of rapid climate change has upended the dominant views of decades past. Focusing primarily on events during and after the most recent glaciation, from 80,000 years ago, the AGU monograph Abrupt Climate Change: Mechanisms, Patterns, and Impacts, edited by Harunur Rashid, Leonid Polyak, and Ellen Mosley-Thompson, explores the transient climate transitions that were only recently uncovered in climate proxies around the world. In this interview, Eos talks to Harunur Rashid about piecing together ancient climes, the effect of abrupt change on historical civilizations, and why younger researchers may be more worried about modern warming than their teachers.

  9. Abrupt tropical climate change: past and present.

    PubMed

    Thompson, Lonnie G; Mosley-Thompson, Ellen; Brecher, Henry; Davis, Mary; León, Blanca; Les, Don; Lin, Ping-Nan; Mashiotta, Tracy; Mountain, Keith

    2006-07-11

    Three lines of evidence for abrupt tropical climate change, both past and present, are presented. First, annually and decadally averaged delta(18)O and net mass-balance histories for the last 400 and 2,000 yr, respectively, demonstrate that the current warming at high elevations in the mid- to low latitudes is unprecedented for at least the last 2 millennia. Second, the continuing retreat of most mid- to low-latitude glaciers, many having persisted for thousands of years, signals a recent and abrupt change in the Earth's climate system. Finally, rooted, soft-bodied wetland plants, now exposed along the margins as the Quelccaya ice cap (Peru) retreats, have been radiocarbon dated and, when coupled with other widespread proxy evidence, provide strong evidence for an abrupt mid-Holocene climate event that marked the transition from early Holocene (pre-5,000-yr-B.P.) conditions to cooler, late Holocene (post-5,000-yr-B.P.) conditions. This abrupt event, approximately 5,200 yr ago, was widespread and spatially coherent through much of the tropics and was coincident with structural changes in several civilizations. These three lines of evidence argue that the present warming and associated glacier retreat are unprecedented in some areas for at least 5,200 yr. The ongoing global-scale, rapid retreat of mountain glaciers is not only contributing to global sea-level rise but also threatening freshwater supplies in many of the world's most populous regions.

  10. Abrupt tropical climate change: Past and present

    PubMed Central

    Thompson, Lonnie G.; Mosley-Thompson, Ellen; Brecher, Henry; Davis, Mary; León, Blanca; Les, Don; Lin, Ping-Nan; Mashiotta, Tracy; Mountain, Keith

    2006-01-01

    Three lines of evidence for abrupt tropical climate change, both past and present, are presented. First, annually and decadally averaged δ18O and net mass-balance histories for the last 400 and 2,000 yr, respectively, demonstrate that the current warming at high elevations in the mid- to low latitudes is unprecedented for at least the last 2 millennia. Second, the continuing retreat of most mid- to low-latitude glaciers, many having persisted for thousands of years, signals a recent and abrupt change in the Earth’s climate system. Finally, rooted, soft-bodied wetland plants, now exposed along the margins as the Quelccaya ice cap (Peru) retreats, have been radiocarbon dated and, when coupled with other widespread proxy evidence, provide strong evidence for an abrupt mid-Holocene climate event that marked the transition from early Holocene (pre-5,000-yr-B.P.) conditions to cooler, late Holocene (post-5,000-yr-B.P.) conditions. This abrupt event, ≈5,200 yr ago, was widespread and spatially coherent through much of the tropics and was coincident with structural changes in several civilizations. These three lines of evidence argue that the present warming and associated glacier retreat are unprecedented in some areas for at least 5,200 yr. The ongoing global-scale, rapid retreat of mountain glaciers is not only contributing to global sea-level rise but also threatening freshwater supplies in many of the world’s most populous regions. PMID:16815970

  11. 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

  12. 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...

  13. Reconstruction of hydrologic responses to late-Glacial (9-33ka) abrupt climate transitions in the coastal southwest United States

    NASA Astrophysics Data System (ADS)

    Wu, M.; Feakins, S. J.; Kirby, M. E.

    2013-12-01

    A sediment core retrieved from Lake Elsinore, the largest natural freshwater lake in southern California, spans an age of 9 to 33ka BP. The period includes several late-Glacial abrupt climate transitions such as the Heinrich events (HEs) 1-3, the Bølling-Allerød (B-A), and the Younger Dryas (YD). This terrestrial site provides a unique opportunity to evaluate changes in hydrology in coastal southwest United States across these key abrupt climate transition events. Hydrogen isotopic ratios (δDwax) of the long-chain C28 alkanoic acid, a biomarker for terrestrial leaf wax, extracted from the sediments, were analyzed to reveal the δD of precipitation water in the past (δDprecip). In the modern climate, higher δDprecip values are associated with moisture sourced from the tropical Pacific, which brings a drier and warmer climate, whereas lower δDprecip values are associated with moisture sourced from north Pacific brought by polar jet stream, causing a wetter and colder climate. δDwax ranges from about -210‰ to -100‰ between late-Glacial HEs and the beginning of Holocene. The pattern generally correlates with Greenland ice core and regional speleothem records, with lower δDwax values corresponding to colder periods (HEs), and higher δDwax values corresponding to warmer periods (B-A and early Holocene). We infer cold and wet climate with north Pacific sourced moisture during the glacial, followed by gradual warming and drying into the B-A and Holocene, when the moisture sources shifted to the tropical Pacific. There is no substantive response to the YD. The fluctuations of δDwax into and out of the HEs can be as large as about 60‰, suggesting greatly variable hydrology across these late-Glacial abrupt climate transition events. The large shifts in δDwax signal during deglaciation and HEs indicate that hydrology in the coastal southwest US has responded sensitively to climate change, and therefore has important implications for water resources in this

  14. 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

  15. Can ice sheets trigger abrupt climatic change?

    SciTech Connect

    Hughes, T.

    1996-11-01

    The discovery in recent years of abrupt climatic changes in climate proxy records from Greenland ice cores and North Atlantic sediment cores, and from other sites around the world, has diverted attention from gradual insolation changes caused by Earth`s orbital variations to more rapid processes on Earth`s surface as forcing Quaternary climatic change. In particular, forcing by ice sheets has been quantified for a major ice stream that drained the Laurentide Ice Sheet along Hudson Strait. The history of these recent discoveries leading to an interest in ice sheets is reviewed, and a case is made that ice sheets may drive abrupt climatic change that is virtually synchronous worldwide. Attention is focused on abrupt inception and termination of a Quaternary glaciation cycle, abrupt changes recorded as stadials and interstadials within the cycle, abrupt changes in ice streams that trigger stadials and interstadials, and abrupt changes in the Laurentide Ice Sheet linked to effectively simultaneous abrupt changes in its ice streams. Remaining work needed to quantify further these changes is discussed. 90 refs., 14 figs.

  16. 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.

  17. 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

  18. The Nonlinear Response of the Equatorial Pacific Ocean-Atmosphere System to Periodic Variations in Insolation and its Association with the Abrupt Climate Transitions during the Quaternary.

    NASA Astrophysics Data System (ADS)

    Lopes, P. G.

    2015-12-01

    The evidences of climate changes during the Quaternary are abundant but the physical mechanisms behind the climate transitions are controversial. The theory of Milankovitch takes into account the periodic orbital variations and the solar radiation received by the Earth as the main explanation for the glacial-interglacial cycles. However, some gaps in the theory still remain. In this study, we propose elucidating some of these gaps by approaching the Equatorial Pacific Ocean as a large oscillator, capable of triggering climate changes in different temporal scales. A mathematical model representing El Ninõ-like phenomena, based on Duffing equation and modulated by the astronomical cycle of 100 ka, was used to simulate the variability of the equatorial Pacific climate system over the last 2 Ma. The physical configuration of the Pacific Ocean, expressed in the equation, explains the temporal limit of the glacial-interglacial cycles. According to the simulation results, consistent with paleoclimate records, the amplification of the effects of the gradual variation of the Earth's orbit eccentricity - another unclear question - is due to the feedback mechanism of the Pacific ocean-atmosphere system, which responds non-linearly to small variations in insolation forcing and determines the ENSO-like phase (warm or cold) at different time scales and different intensities. The approach proposed here takes into account that the abrupt transitions between the ENSO-like phases, and the consequent changes in the sea surface temperature (SST) along the Equatorial Pacific Ocean, produce reactions that act as secondary causes of the temperature fluctuations that result in a glaciation (or deglaciation) - as the drastic change on the rate of evaporation/precipitation around the globe, and the increase (or decrease) of the atmospheric CO2 absorption by the phytoplankton. The transitional behavior between the warm and the cold phases, according to the presented model, is enhanced as

  19. 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.

  20. Weird Weather: Large Abrupt Widespread Climate Changes

    SciTech Connect

    Alley, Richard B.

    2001-01-24

    Ice-core records and other paleoclimatic indicators show that large (up to 10 degrees C), abrupt (in about 10 years), widespread (hemispheric to global) climate changes have been common for much of the last 100,000 years and beyond, but rare during the most recent few millennia. Changes in the coupled ocean-atmosphere system with a center of activity in the north Atlantic probably have been important, but several hypotheses remain possible including solar influence and a stochastically resonant interaction with changing freshwater fluxes. Our current understanding does not allow us to exclude the possibility that human or natural processes could 'flip the switch' of another abrupt change in the future.

  1. Basic mechanism for abrupt monsoon transitions

    PubMed Central

    Levermann, Anders; Schewe, Jacob; Petoukhov, Vladimir; Held, Hermann

    2009-01-01

    Monsoon systems influence the livelihood of hundreds of millions of people. During the Holocene and last glacial period, rainfall in India and China has undergone strong and abrupt changes. Though details of monsoon circulations are complicated, observations reveal a defining moisture-advection feedback that dominates the seasonal heat balance and might act as an internal amplifier, leading to abrupt changes in response to relatively weak external perturbations. Here we present a minimal conceptual model capturing this positive feedback. The basic equations, motivated by observed relations, yield a threshold behavior, robust with respect to addition of other physical processes. Below this threshold in net radiative influx, R c, no conventional monsoon can develop; above R c, two stable regimes exist. We identify a nondimensional parameter l that defines the threshold and makes monsoon systems comparable with respect to the character of their abrupt transition. This dynamic similitude may be helpful in understanding past and future variations in monsoon circulation. Within the restrictions of the model, we compute R c for current monsoon systems in India, China, the Bay of Bengal, West Africa, North America, and Australia, where moisture advection is the main driver of the circulation. PMID:19858472

  2. Basic mechanism for abrupt monsoon transitions.

    PubMed

    Levermann, Anders; Schewe, Jacob; Petoukhov, Vladimir; Held, Hermann

    2009-12-08

    Monsoon systems influence the livelihood of hundreds of millions of people. During the Holocene and last glacial period, rainfall in India and China has undergone strong and abrupt changes. Though details of monsoon circulations are complicated, observations reveal a defining moisture-advection feedback that dominates the seasonal heat balance and might act as an internal amplifier, leading to abrupt changes in response to relatively weak external perturbations. Here we present a minimal conceptual model capturing this positive feedback. The basic equations, motivated by observed relations, yield a threshold behavior, robust with respect to addition of other physical processes. Below this threshold in net radiative influx, R(c), no conventional monsoon can develop; above R(c), two stable regimes exist. We identify a nondimensional parameter l that defines the threshold and makes monsoon systems comparable with respect to the character of their abrupt transition. This dynamic similitude may be helpful in understanding past and future variations in monsoon circulation. Within the restrictions of the model, we compute R(c) for current monsoon systems in India, China, the Bay of Bengal, West Africa, North America, and Australia, where moisture advection is the main driver of the circulation.

  3. 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

  4. 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.

  5. 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.

  6. 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

  7. 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.

  8. 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.

  9. 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.

  10. Wildfire responses to abrupt climate change in North America.

    PubMed

    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

    2009-02-24

    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.

  11. 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.

  12. Towards Greenland Glaciation: Cumulative or Abrupt Transition?

    NASA Astrophysics Data System (ADS)

    Tan, N.; Ramstein, G.; Contoux, C.; Ladant, J. B.; Dumas, C.; Donnadieu, Y.

    2014-12-01

    The insolation evolution [Laskar 2004] from 4 to 2.5 Ma depicts a series of three summer solstice insolation minima between 2.7 and 2.6 Ma, but there are other more important summer solstice minima notably around 3.82 and 3.05 Ma. On such a time span of more than 1 Ma, data shows that there are variations in the evolution of atmospheric CO2 concentration with a local maximum around 3 Ma [Seki et al.2010; Bartoli et al. 2011], before a decrease between 3 and 2.6 Ma. The latter, suggesting an abrupt ice sheet inception around 2.7 Ma, has been shown to be a major culprit for the full Greenland Glaciation [Lunt et al. 2008]. However, a recent study [Contoux et al. 2014, in review] suggests that a lowering of CO2 is not sufficient to initiate a glaciation on Greenland and must be combined to low summer insolation, with surviving ice during insolation maximum, suggesting a cumulative process in the first place, which could further lead to full glaciation at 2.7 Ma. Through a new tri-dimensional interpolation method implemented within the asynchronous coupling between an atmosphere ocean general circulation model (IPSL-CM5A) and an ice sheet model (GRISLI), we investigate the transient evolution of Greenland ice sheet during the Pliocene to diagnose whether the ice sheet inception is an abrupt event or rather a cumulative process, involving waxing and waning of the ice sheet during several orbital cycles. ReferencesBartoli, G., Hönisch, B., & Zeebe, R. E. (2011). Atmospheric CO2 decline during the Pliocene intensification of Northern Hemisphere glaciations. Paleoceanography, 26(4). Contoux C, Dumas C, Ramstein G, Jost A, Dolan A. M. (2014) Modelling Greenland Ice sheet inception and sustainability during the late Pliocene. (in review for Earth and Planetary Science Letters.).Laskar, J., Robutel, P., Joutel, F., Gastineau, M., Correia, A. C. M., & Levrard, B. (2004). A long-term numerical solution for the insolation quantities of the Earth. Astronomy & Astrophysics, 428

  13. Evidence for abrupt climate changes in annually laminated marine sediments.

    PubMed

    Kemp, Alan E S

    2003-09-15

    Annually laminated sediments from marine or lacustrine settings represent valuable high-resolution archives of climate change that record variation due to changing precipitation and run-off from land or variation in biological productivity and flux in the water column. Because of their annual resolution such sediments may capture abrupt changes of interannual to decadal scales rivaling corals and ice cores in resolution. Laminated sediments often occur intermittently in the sediment column, and the onset and cessation of laminae commonly record the abrupt crossing of thresholds related to climate change, for example, in the degree of oxygenation of bottom waters. Such records from marginal basins and continental margins have been pivotal in demonstrating that abrupt changes hitherto documented only in high-latitude ice cores are synchronous with climatic change at low latitudes. These insights into global teleconnections have improved our understanding of the mechanisms of rapid climate change. In deep-sea settings, the discovery of the episodic occurrence of laminated diatom-rich sediments in the Equatorial Pacific and Southern Ocean provides evidence for massive climate-related biogeochemical excursions tied to abrupt changes in the input, distribution and availability of nutrients in the oceans.

  14. 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.

  15. 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.

  16. 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.

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

    PubMed

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

    1993-03-01

    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.

  18. 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.

  19. 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

  20. 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.

  1. An interhemispheric mechanism for glacial abrupt climate change

    NASA Astrophysics Data System (ADS)

    Banderas, Rubén; Alvarez-Solas, Jorge; Robinson, Alexander; Montoya, Marisa

    2015-05-01

    The last glacial period was punctuated by abrupt climate changes that are widely considered to result from millennial-scale variability of the Atlantic meridional overturning circulation (AMOC). However, the origin of these AMOC reorganizations remains poorly understood. The climatic connection between both hemispheres indicated by proxies suggests that the Southern Ocean (SO) could regulate this variability through changes in winds and atmospheric CO concentration. Here, we investigate this hypothesis using a coupled climate model forced by prescribed CO and SO wind-stress variations. We find that the AMOC exhibits an oscillatory behavior between weak and strong circulation regimes which is ultimately caused by changes in the meridional density gradient of the Atlantic Ocean. The evolution of the simulated climatic patterns matches the amplitude and timing of the largest events that occurred during the last glacial period and their widespread climatic impacts. Our results suggest the existence of an internal interhemispheric oscillation mediated by the bipolar seesaw that could promote glacial abrupt climate changes through variations in atmospheric CO levels, the strength of the SO winds and AMOC reorganizations, and provide an explanation for the pervasive Antarctic-like climate signal found in proxy records worldwide.

  2. The Atlantic Meridional Overturning Circulation and Abrupt Climate Change

    NASA Astrophysics Data System (ADS)

    Lynch-Stieglitz, Jean

    2017-01-01

    Abrupt changes in climate have occurred in many locations around the globe over the last glacial cycle, with pronounced temperature swings on timescales of decades or less in the North Atlantic. The global pattern of these changes suggests that they reflect variability in the Atlantic meridional overturning circulation (AMOC). This review examines the evidence from ocean sediments for ocean circulation change over these abrupt events. The evidence for changes in the strength and structure of the AMOC associated with the Younger Dryas and many of the Heinrich events is strong. Although it has been difficult to directly document changes in the AMOC over the relatively short Dansgaard-Oeschger events, there is recent evidence supporting AMOC changes over most of these oscillations as well. The lack of direct evidence for circulation changes over the shortest events leaves open the possibility of other driving mechanisms for millennial-scale climate variability.

  3. The Atlantic Meridional Overturning Circulation and Abrupt Climate Change.

    PubMed

    Lynch-Stieglitz, Jean

    2017-01-03

    Abrupt changes in climate have occurred in many locations around the globe over the last glacial cycle, with pronounced temperature swings on timescales of decades or less in the North Atlantic. The global pattern of these changes suggests that they reflect variability in the Atlantic meridional overturning circulation (AMOC). This review examines the evidence from ocean sediments for ocean circulation change over these abrupt events. The evidence for changes in the strength and structure of the AMOC associated with the Younger Dryas and many of the Heinrich events is strong. Although it has been difficult to directly document changes in the AMOC over the relatively short Dansgaard-Oeschger events, there is recent evidence supporting AMOC changes over most of these oscillations as well. The lack of direct evidence for circulation changes over the shortest events leaves open the possibility of other driving mechanisms for millennial-scale climate variability.

  4. Simulating the response of glacial ice-sheets to past abrupt climate changes

    NASA Astrophysics Data System (ADS)

    Banderas, Rubén; Álvarez-Solas, Jorge; Robinson, Alexander; Montoya, Marisa

    2016-04-01

    Dansgaard-Oeschger (D/O) events were recurrent glacial abrupt climatic transitions between cold and warm conditions over Greenland with an approximate characteristic time of a thousand years. The uncertainties among the available sea level reconstructions hinder our understanding of the interactions between climate and global ice volume. In addition, only limited highly-resolved and continuous sea level records exist. Thus, the millennial time-scale response of glacial ice-sheets to past abrupt climate changes is not well known. Here, we use a hybrid ice sheet-ice shelf model in order to investigate the response of glacial ice-sheets to the influence of millennial-scale climate variability. An ensemble of simulations is performed by forcing the model with a wide range of time-varying climatologies derived from proxy data and from some of the currently available climate model simulations. The assessment of the resulting suite of transient simulations will contribute to constrain the inadequacies of sea level reconstructions in terms of amplitude and timing and will help to understand the implications of glacial abrupt climate changes in past sea level variability. Furthermore, our experiments could be useful to elucidate the mechanisms that involve the interactions between climate and ice sheets on millennial time scales, including future climate change.

  5. 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

  6. 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.

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

    PubMed

    Yasuhara, Moriaki; Cronin, Thomas M; Demenocal, Peter B; Okahashi, Hisayo; Linsley, Braddock K

    2008-02-05

    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-Allerød 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 approximately 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.

  8. Abrupt transitions of the top-down controlled Black Sea pelagic ecosystem during 1960 2000: Evidence for regime-shifts under strong fishery exploitation and nutrient enrichment modulated by climate-induced variations

    NASA Astrophysics Data System (ADS)

    Oguz, Temel; Gilbert, Denis

    2007-02-01

    Functioning of the Black Sea ecosystem has profoundly changed since the early 1970s under cumulative effects of excessive nutrient enrichment, strong cooling/warming, over-exploitation of pelagic fish stocks, and population outbreak of gelatinous carnivores. Applying a set of criteria to the long-term (1960-2000) ecological time-series data, the present study demonstrates that the Black Sea ecosystem was reorganised during this transition phase in different forms of top-down controlled food web structure through successive regime-shifts of distinct ecological properties. The Secchi disc depth, oxic-anoxic interface zone, dissolved oxygen and hydrogen sulphide concentrations also exhibit abrupt transition between their alternate regimes, and indicate tight coupling between the lower trophic food web structure and the biogeochemical pump in terms of regime-shift events. The first shift, in 1973-1974, marks a switch from large predatory fish to small planktivore fish-controlled system, which persisted until 1989 in the form of increasing small pelagic and phytoplankton biomass and decreasing zooplankton biomass. The increase in phytoplankton biomass is further supported by a bottom-up contribution due to the cumulative response to high anthropogenic nutrient load and the concurrent shift of the physical system to the "cold climate regime" following its ˜20-year persistence in the "warm climate regime". The end of the 1980s signifies the depletion of small planktivores and the transition to a gelatinous carnivore-controlled system. By the end of the 1990s, small planktivore populations take over control of the system again. Concomitantly, their top-down pressure when combined with diminishing anthropogenic nutrient load and more limited nutrient supply into the surface waters due to stabilizing effects of relatively warm winter conditions switched the "high production" regime of phytoplankton to its background "low production" regime. The Black Sea regime

  9. 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.

  10. Climate response to abrupt cessation of solar radiation management

    NASA Astrophysics Data System (ADS)

    McCusker, K. E.; Armour, K.; Bitz, C. M.; Battisti, D. S.

    2012-12-01

    Solar radiation management (SRM) as a means to reduce or cancel the effects of increased greenhouse gases may be regarded as effective to the extent that it broadly reduces warming and other related changes. Studies that have previously modeled SRM have focused on spatial inhomogeneities in the climate response, assuming that SRM is continued indefinitely and global climate is stabilized. In this study, we focus on the possible situation in which SRM is terminated (e.g. due to lack of funding, international governmental disorganization, technical failure, or unanticipated negative consequences) while greenhouse gases have continued rising. We use a global climate model (GCM) with a prescribed stratospheric sulfate burden that counteracts the Representative Concentration Pathway 8.5 (RCP8.5) - wherein the radiative forcing reaches 8.5 W/m2 above the preindustrial by 2100 - to show that upon termination of the sulfate burden, abrupt and sustained warming occurs that is well outside familiar 20th century bounds, especially on land. The GCM utilized has a climate sensitivity of 3.2 degrees Celsius, yet in reality climate sensitivity is unknown, its probability density distribution exhibiting a long tail at the high end of sensitivity. Using SRM to stabilize climate while greenhouse gases continue to rise has the effect of obscuring how the climate would respond to the additional gases given the opportunity - climate sensitivity would be masked. We use a simple upwelling-diffusion energy balance model to span the range of the observationally-constrained climate sensitivities to investigate the range of global mean rate of temperature rise following SRM termination, in addition to its sensitivity to termination year and background emissions scenario. We show that in fact, the distribution of temperature trends following termination could be far broader than those simulated by the GCM. These inherent dangers suggest that solar radiation management should only be

  11. Low-latitude mountain glacier evidence for abrupt climate changes

    NASA Astrophysics Data System (ADS)

    Thompson, L. G.; Mosley-Thompson, E. S.; Lin, P.; Davis, M. E.; Mashiotta, T. A.; Brecher, H. H.

    2004-12-01

    Clear evidence that a widespread warming of Earth's climate system is now underway comes from low latitude mountain glaciers. Proxy temperature histories reconstructed from ice cores, and the rapidly accelerating loss of both the total ice area and ice volume on a near global scale suggest that these glaciers responding to increasing rates of melting. In situ observations reveal the startling rates at which many tropical glaciers are disappearing. For example, the retreat of the terminus of the Qori Kalis Glacier in Peru is roughly 200 meters per year, 40 times faster than its retreat rate in 1978. Similarly, in 1912 the ice on Mount Kilimanjaro covered 12.1 km2, but today it covers only 2.6 km2. If the current rate of retreat continues, the perennial ice fields may disappear within the next few decades, making this the first time in the past 11,700 years that Kilimanjaro will be devoid of the ice that shrouds its summit. Tropical glaciers may be considered ``the canaries in the coal mine'' for the global climate system as they integrate and respond to key climatological variables, such as temperature, precipitation, cloudiness, humidity, and incident solar radiation. A composite of the decadally-averaged oxygen isotopic records from three Andean and three Tibetan ice cores extending back over the last two millennia shows an isotopic enrichment in the 20th century that suggests a large-scale warming is underway at lower latitudes. Multiple lines of evidence from Africa, the Middle East, Europe and South America indicate an abrupt mid-Holocene climate event in the low latitudes. If such an event were to occur now with a global human population of 6.3 billion people, the consequences could be severe. Clearly, we need to understand the nature and cause of abrupt climate events.

  12. 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

  13. 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.

  14. 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.

  15. Abrupt transition to complete congestion on complex networks and control.

    PubMed

    Wang, Wen-Xu; Wu, Zhi-Xi; Jiang, Rui; Chen, Guanrong; Lai, Ying-Cheng

    2009-09-01

    Previous works on traffic-flow dynamics on complex networks have mostly focused on continuous phase transition from a free-flow state to a locally congested state as a parameter, such as the packet-generating rate, is increased through a critical value. Above the transition point congestion occurs on a small subset of nodes. Utilizing a conventional traffic-flow model based on the packet birth-death process and more importantly, taking into account the fact that in realistic networks nodes have only finite buffers, we find an abrupt transition from free flow to complete congestion. Slightly below the transition point, the network can support the maximum amount of traffic for some optimal value of the routing parameter. We develop a mean-field theory to explain the surprising transition phenomenon and provide numerical support. Furthermore, we propose a control strategy based on the idea of random packet dropping to prevent/break complete congestion. Our finding provides insights into realistic communication networks where complete congestion can occur directly from a free-flow state without any apparent precursor, and our control strategy can be effective to restore traffic flow once complete congestion has occurred.

  16. Abrupt cooling over the North Atlantic in modern climate models

    PubMed Central

    Sgubin, Giovanni; Swingedouw, Didier; Drijfhout, Sybren; Mary, Yannick; Bennabi, Amine

    2017-01-01

    Observations over the 20th century evidence no long-term warming in the subpolar North Atlantic (SPG). This region even experienced a rapid cooling around 1970, raising a debate over its potential reoccurrence. Here we assess the risk of future abrupt SPG cooling in 40 climate models from the fifth Coupled Model Intercomparison Project (CMIP5). Contrary to the long-term SPG warming trend evidenced by most of the models, 17.5% of the models (7/40) project a rapid SPG cooling, consistent with a collapse of the local deep-ocean convection. Uncertainty in projections is associated with the models' varying capability in simulating the present-day SPG stratification, whose realistic reproduction appears a necessary condition for the onset of a convection collapse. This event occurs in 45.5% of the 11 models best able to simulate the observed SPG stratification. Thus, due to systematic model biases, the CMIP5 ensemble as a whole underestimates the chance of future abrupt SPG cooling, entailing crucial implications for observation and adaptation policy. PMID:28198383

  17. Abrupt cooling over the North Atlantic in modern climate models.

    PubMed

    Sgubin, Giovanni; Swingedouw, Didier; Drijfhout, Sybren; Mary, Yannick; Bennabi, Amine

    2017-02-15

    Observations over the 20th century evidence no long-term warming in the subpolar North Atlantic (SPG). This region even experienced a rapid cooling around 1970, raising a debate over its potential reoccurrence. Here we assess the risk of future abrupt SPG cooling in 40 climate models from the fifth Coupled Model Intercomparison Project (CMIP5). Contrary to the long-term SPG warming trend evidenced by most of the models, 17.5% of the models (7/40) project a rapid SPG cooling, consistent with a collapse of the local deep-ocean convection. Uncertainty in projections is associated with the models' varying capability in simulating the present-day SPG stratification, whose realistic reproduction appears a necessary condition for the onset of a convection collapse. This event occurs in 45.5% of the 11 models best able to simulate the observed SPG stratification. Thus, due to systematic model biases, the CMIP5 ensemble as a whole underestimates the chance of future abrupt SPG cooling, entailing crucial implications for observation and adaptation policy.

  18. Abrupt cooling over the North Atlantic in modern climate models

    NASA Astrophysics Data System (ADS)

    Sgubin, Giovanni; Swingedouw, Didier; Drijfhout, Sybren; Mary, Yannick; Bennabi, Amine

    2017-02-01

    Observations over the 20th century evidence no long-term warming in the subpolar North Atlantic (SPG). This region even experienced a rapid cooling around 1970, raising a debate over its potential reoccurrence. Here we assess the risk of future abrupt SPG cooling in 40 climate models from the fifth Coupled Model Intercomparison Project (CMIP5). Contrary to the long-term SPG warming trend evidenced by most of the models, 17.5% of the models (7/40) project a rapid SPG cooling, consistent with a collapse of the local deep-ocean convection. Uncertainty in projections is associated with the models' varying capability in simulating the present-day SPG stratification, whose realistic reproduction appears a necessary condition for the onset of a convection collapse. This event occurs in 45.5% of the 11 models best able to simulate the observed SPG stratification. Thus, due to systematic model biases, the CMIP5 ensemble as a whole underestimates the chance of future abrupt SPG cooling, entailing crucial implications for observation and adaptation policy.

  19. Abrupt climate shift in the Western Mediterranean Sea.

    PubMed

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

    2016-03-11

    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.

  20. 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.

  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. 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.

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

    USGS Publications Warehouse

    ,; 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.

  4. 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.

  5. Abrupt or not abrupt - biodiversity affects climate-vegetation interaction at the end of the African Humid Period

    NASA Astrophysics Data System (ADS)

    Claussen, Martin; Bathiany, Sebastian; Brovkin, Victor; Kleinen, Thomas

    2014-05-01

    Palaeo-climate and ecosystem data derived from the sediment record from Lake Yoa (Ounianga Kebir, North-East Tchad) have been interpreted as support for a weak interaction between climate and vegetation without abrupt changes in precipitation climate and vegetation coverage over the last 6000 years. However, interpretation of these data has neglected potential effects of plant diversity on the stability of the climate - vegetation system. Here, we use a conceptual model that represents plant diversity in terms of moisture requirement; some plant types are sensitive to changes in precipitation thereby leading to an unstable system with the possibility of abrupt changes, while other plant types are more resilient with gradual system changes. We demonstrate that plant diversity tends to attenuate the instability of the interaction between climate and sensitive plant types, while it reduces the stability of the interaction between climate and less sensitive plant types. Hence, despite large sensitivities of individual plant types to precipitation, a gradual decline in precipitation and mean vegetation cover can occur. The present study offers a new interpretation for reconstructed shifts in vegetation and climate in northern Africa at the end of the African Humid Period. It focusses on the ecosystems in semi-arid climate, but the principle that plant diversity can affect the stability of climate-vegetation interaction may generally apply.

  6. Abrupt transitions to tumor extinction: a phenotypic quasispecies model.

    PubMed

    Sardanyés, Josep; Martínez, Regina; Simó, Carles; Solé, Ricard

    2016-10-06

    The dynamics of heterogeneous tumor cell populations competing with healthy cells is an important topic in cancer research with deep implications in biomedicine. Multitude of theoretical and computational models have addressed this issue, especially focusing on the nature of the transitions governing tumor clearance as some relevant model parameters are tuned. In this contribution, we analyze a mathematical model of unstable tumor progression using the quasispecies framework. Our aim is to define a minimal model incorporating the dynamics of competition between healthy cells and a heterogeneous population of cancer cell phenotypes involving changes in replication-related genes (i.e., proto-oncogenes and tumor suppressor genes), in genes responsible for genomic stability, and in house-keeping genes. Such mutations or loss of genes result into different phenotypes with increased proliferation rates and/or increased genomic instabilities. Despite bifurcations in the classical deterministic quasispecies model are typically given by smooth, continuous shifts (i.e., transcritical bifurcations), we here identify a novel type of bifurcation causing an abrupt transition to tumor extinction. Such a bifurcation, named as trans-heteroclinic, is characterized by the exchange of stability between two distant fixed points (that do not collide) involving tumor persistence and tumor clearance. The increase of mutation and/or the decrease of the replication rate of tumor cells involves this catastrophic shift of tumor cell populations. The transient times near bifurcation thresholds are also characterized, showing a power law dependence of exponent [Formula: see text] of the transients as mutation is changed near the bifurcation value. These results are discussed in the context of targeted cancer therapy as a possible therapeutic strategy to force a catastrophic shift by simultaneously delivering mutagenic and cytotoxic drugs inside tumor cells.

  7. Abrupt reorganization of North Pacific and western North American climate during the last deglaciation

    NASA Astrophysics Data System (ADS)

    Lora, Juan M.; Mitchell, Jonathan L.; Tripati, Aradhna E.

    2016-11-01

    Dramatic hydroclimate shifts occurred in western North America during the last deglaciation, but the timing and mechanisms driving these changes are uncertain and debated, and previous modeling has largely relied on linear interpolations between equilibrium snapshot simulations. Using a published transient climate simulation and a range of proxy records, we analyze the region's climate evolution in order to identify the mechanisms governing hydroclimate shifts. A rapid loss of ice around 14,000 years ago causes an abrupt reorganization of the circulation, which precipitates drying and moistening of southwestern and northwestern North America, respectively. The atmospheric circulation transitions between two states on a timescale of decades to centuries, during which time the westerly jet shifts north by about 7°. In contrast to previous studies, we find that changes in the water budget of western North America prior to this event are not attributable to variations in the position of the jet, but rather to the intensity of moisture transport into the continent.

  8. Abrupt Holocene climate change as an important factor for human migration in West Greenland.

    PubMed

    D'Andrea, William J; Huang, Yongsong; Fritz, Sherilyn C; Anderson, N John

    2011-06-14

    West Greenland has had multiple episodes of human colonization and cultural transitions over the past 4,500 y. However, the explanations for these large-scale human migrations are varied, including climatic factors, resistance to adaptation, economic marginalization, mercantile exploration, and hostile neighborhood interactions. Evaluating the potential role of climate change is complicated by the lack of quantitative paleoclimate reconstructions near settlement areas and by the relative stability of Holocene temperature derived from ice cores atop the Greenland ice sheet. Here we present high-resolution records of temperature over the past 5,600 y based on alkenone unsaturation in sediments of two lakes in West Greenland. We find that major temperature changes in the past 4,500 y occurred abruptly (within decades), and were coeval in timing with the archaeological records of settlement and abandonment of the Saqqaq, Dorset, and Norse cultures, which suggests that abrupt temperature changes profoundly impacted human civilization in the region. Temperature variations in West Greenland display an antiphased relationship to temperature changes in Ireland over centennial to millennial timescales, resembling the interannual to multidecadal temperature seesaw associated with the North Atlantic Oscillation.

  9. 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

    2012-09-04

    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.

  10. 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

  11. 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

  12. Sensitivity and rapidity of vegetational response to abrupt climate change

    NASA Technical Reports Server (NTRS)

    Peteet, D.

    2000-01-01

    Rapid climate change characterizes numerous terrestrial sediment records during and since the last glaciation. Vegetational response is best expressed in terrestrial records near ecotones, where sensitivity to climate change is greatest, and response times are as short as decades.

  13. Sensitivity and rapidity of vegetational response to abrupt climate change.

    PubMed

    Peteet, D

    2000-02-15

    Rapid climate change characterizes numerous terrestrial sediment records during and since the last glaciation. Vegetational response is best expressed in terrestrial records near ecotones, where sensitivity to climate change is greatest, and response times are as short as decades.

  14. Multiple Equilibria and Abrupt Transitions in Arctic Summer Sea Ice Extent

    NASA Astrophysics Data System (ADS)

    Merryfield, W. J.; Holland, M. M.; Monahan, A. H.

    2006-12-01

    Some coupled model simulations of 21st century climate, including those of the third-generation Community Climate System Model (CCSM3), exhibit rapid and substantial decreases in Arctic summer sea ice extent leading to nearly ice-free summer Arctic conditions. Three factors have been identified as contributing to such behavior in CCSM3: (i) an inverse relationship between open water formed per cm of ice melt and the previous winter's mean ice thickness; (ii) relatively sudden increases or "pulses" of ocean heat transport into the Arctic, superimposed on a more gradual increase that occurs as the climate warms, and (iii) acceleration of melting due to the albedo feedback. This presentation describes a very simple mathematical treatment of these processes which models the response of yearly values of mean winter ice thickness and summer sea ice extent to changes on ocean heat transport, or OHT. The resulting equations are nonlinear, and in cases where the albedo feedback is sufficiently strong and early 20th century winter ice is not too thick, their solutions undergo a bifurcation to multiple equilibria as OHT increases. In this regime there are two stable states, one having finite summer ice extent and relatively thick winter ice, and the other having zero summer ice extent and thinner winter ice. If OHT increases gradually, there is a sudden, hysteretic transition to zero summer ice extent, whereas if fluctuations in OHT are superimposed on this increase the hysteretic transition becomes "blurred", with abrupt decreases in summer ice extent potentially occurring earlier. When parameters such as the strength of albedo feedback are calibrated to CCSM3 values, the system falls within the regime that exhibits multiple equilibria, whereas models having weaker albedo feedback or thicker initial winter ice would not. These results suggest that multiple sea-ice equilibria may play a role in the abrupt decreases in Arctic summer ice extent simulated by CCSM3, and that the

  15. 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.

  16. Ice-core evidence of abrupt climate changes.

    PubMed

    Alley, R B

    2000-02-15

    Ice-core records show that climate changes in the past have been large, rapid, and synchronous over broad areas extending into low latitudes, with less variability over historical times. These ice-core records come from high mountain glaciers and the polar regions, including small ice caps and the large ice sheets of Greenland and Antarctica.

  17. Atmospheric teleconnections between the tropics and the Southern Hemisphere westerly winds during abrupt climate change

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

    Abrupt, large amplitude climate oscillations occurred in the North Atlantic region during the last deglaciation and glacial period. Antarctic temperatures show a lagged and out-of-phase response, suggesting that these climate anomalies were propagated to the Southern Hemisphere high latitudes through changes in ocean circulation. Large changes in atmospheric circulation in the tropics accompanied abrupt North Atlantic climate change and modeling studies have predicted an atmospheric teleconnection between the tropics and the Southern Hemisphere westerly winds. However, consistent paleoclimate evidence for this tropical-high southern latitude atmospheric teleconnection has been lacking. Here we use a new high-resolution deuterium excess record from West Antarctica to show that moisture sources for Antarctic precipitation changed in phase with abrupt shifts in Northern Hemisphere climate, significantly before Antarctic temperature change. These results suggest that Southern Hemisphere mid-latitude storm tracks and westerly winds migrated north- and southwards within decades of rapid North Atlantic warming and cooling, respectively, and in parallel with the well-established migrations of the intertropical convergence zone. Both ocean and atmospheric processes, operating on different timescales, are critical to the global expression of abrupt climate change and this atmospheric link between the hemispheres may be important to the underlying dynamics.

  18. 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

  19. 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

    2015-09-02

    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.

  20. 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.

  1. 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

  2. Abrupt transitions between macrobenthic faunal assemblages across seagrass bed margins

    NASA Astrophysics Data System (ADS)

    Barnes, R. S. K.; Hamylton, S.

    2013-10-01

    The nature of the transition from one contrasting macrobenthic assemblage to another across interfaces between intertidal seagrass and unvegetated sand was investigated in the subtropical Moreton Bay Marine Park, eastern Australia, via six two-dimensional core lattices. The same pattern of transition was manifested in each lattice. Macrofaunal abundance, species density (both observed and estimated total) and assemblage composition did not vary with distance away from the interface within the 0.75 m wide marginal bands of each habitat type. Neither were there significant differences in assemblage metrics or composition between the marginal and non-edge regions of either habitat. There were, however, very marked differences in assemblage composition, abundance and species density across the 25 cm wide strip on either side of the actual interface, the interacting assemblages reacting symmetrically. All these differences therefore took place over an ecotone distance of only 0.5 m at most. Spatial trends in assemblage metrics across the boundary zone were captured accurately by second and third order polynomial regression models. It also appeared that edge effects on individual species within the seagrass were a variable local response not a consistent effect of closeness to the bare sand.

  3. Abrupt Climate Change: A Magnetic Coupling Model (MCM) Prediction.

    NASA Astrophysics Data System (ADS)

    Ely, John T. A.

    2002-04-01

    Recent findings [p.8 ISBN 0-309-07434-7] show major climate changes often occur in a decade. This is another of many MCM predictions (see refs). All of them tested from 1968 to date have been proven, including: Global warming is real and driven by fossil fuel (1970's); This CO2 forcing has ended Major Ice Ages; All Major and Minor Ice Ages are caused by decreases in existing (primarily subvisible and other thin, especially newly forming) cirrus at mid to high geomagnetic latitudes; Ionization of the atmosphere near 250 grams per square cm depth by GCR (galactic cosmic ray protons circa 1 gev) cause cirrus depression; Ice cores and other proxy records show ice ages exhibit increased beryllium-10, carbon-14, etc, due to GCR. As noted in the Mar and Apr abstracts, the MCM predictable climate ended in 2000, following over 30 yrs of our ignoring its easily testable warnings re fossil fuel. Hence, we now face the somber question of whether human intervention is still possible in a CO2 Runaway and sea level rise that may be on a decade time scale. [Ely, Session A8, APS Mtg, Seattle, Mar 01; Ely, Session H14.013, APS Mtg, Apr 01; MCM pub list http://faculty.washington.edu/ely/MCM.html

  4. Rounding of abrupt phase transitions in brain networks

    NASA Astrophysics Data System (ADS)

    Villa Martín, Paula; Moretti, Paolo; Muñoz, Miguel A.

    2015-01-01

    The observation of critical-like behavior in cortical networks represents a major step forward in elucidating how the brain manages information. Understanding the origin and functionality of critical-like dynamics, as well as its robustness, is a major challenge in contemporary neuroscience. Here, we present an extensive numerical study of a family of simple dynamical models, which describe activity propagation in brain networks through the integration of different neighboring spiking potentials, mimicking basic neural interactions. The requirement of signal integration may lead to discontinuous phase transitions in networks that are well described by the mean-field approximation, thus preventing the emergence of critical points in such systems. Brain networks, however, are finite dimensional and exhibit a heterogeneous hierarchical structure that cannot be encoded in mean-field models. Here we propose that, as a consequence of the presence of such a heterogeneous substrate with its concomitant structural disorder, critical-like features may emerge even in the presence of integration. These conclusions may prove significant in explaining the observation of traits of critical behavior in large-scale measurements of brain activity.

  5. High-resolution Greenland ice core data show abrupt climate change happens in few years.

    PubMed

    Steffensen, Jørgen Peder; Andersen, Katrine K; Bigler, Matthias; Clausen, Henrik B; Dahl-Jensen, Dorthe; Fischer, Hubertus; Goto-Azuma, Kumiko; Hansson, Margareta; Johnsen, Sigfús J; Jouzel, Jean; Masson-Delmotte, Valérie; Popp, Trevor; Rasmussen, Sune O; Röthlisberger, Regine; Ruth, Urs; Stauffer, Bernhard; Siggaard-Andersen, Marie-Louise; Sveinbjörnsdóttir, Arny E; Svensson, Anders; White, James W C

    2008-08-01

    The last two abrupt warmings at the onset of our present warm interglacial period, interrupted by the Younger Dryas cooling event, were investigated at high temporal resolution from the North Greenland Ice Core Project ice core. The deuterium excess, a proxy of Greenland precipitation moisture source, switched mode within 1 to 3 years over these transitions and initiated a more gradual change (over 50 years) of the Greenland air temperature, as recorded by stable water isotopes. The onsets of both abrupt Greenland warmings were slightly preceded by decreasing Greenland dust deposition, reflecting the wetting of Asian deserts. A northern shift of the Intertropical Convergence Zone could be the trigger of these abrupt shifts of Northern Hemisphere atmospheric circulation, resulting in changes of 2 to 4 kelvin in Greenland moisture source temperature from one year to the next.

  6. Causes and projections of abrupt climate-driven ecosystem shifts in the North Atlantic.

    PubMed

    Beaugrand, Grégory; Edwards, Martin; Brander, Keith; Luczak, Christophe; Ibanez, Frederic

    2008-11-01

    Warming of the global climate is now unequivocal and its impact on Earth' functional units has become more apparent. Here, we show that marine ecosystems are not equally sensitive to climate change and reveal a critical thermal boundary where a small increase in temperature triggers abrupt ecosystem shifts seen across multiple trophic levels. This large-scale boundary is located in regions where abrupt ecosystem shifts have been reported in the North Atlantic sector and thereby allows us to link these shifts by a global common phenomenon. We show that these changes alter the biodiversity and carrying capacity of ecosystems and may, combined with fishing, precipitate the reduction of some stocks of Atlantic cod already severely impacted by exploitation. These findings offer a way to anticipate major ecosystem changes and to propose adaptive strategies for marine exploited resources such as cod in order to minimize social and economic consequences.

  7. A Collaborative Proposal: Simulating and Understanding Abrupt Climate-Ecosystem Changes During Holocene with NCAR-CCSM3.

    SciTech Connect

    Zhengyu Liu, Bette Otto-Bliesner

    2013-02-01

    We have made significant progress in our proposed work in the last 4 years (3 years plus 1 year of no cost extension). In anticipation of the next phase of study, we have spent time on the abrupt changes since the last glacial maximum. First, we have performed further model-data comparison based on our baseline TRACE-21 simulation and made important progress towards the understanding of several major climate transitions. Second, we have made a significant effort in processing the model output of TRACE-21 and have put this output on a website for access by the community. Third, we have completed many additional sensitivity experiments. In addition, we have organized synthesis workshops to facilitate and promote transient model-data comparison for the international community. Finally, we have identified new areas of interest for Holocene climate changes.

  8. An astronomical correspondence to the 1470 year cycle of abrupt climate change

    NASA Astrophysics Data System (ADS)

    Kelsey, A. M.; Menk, F. W.; Moss, P. T.

    2015-10-01

    The existence of a ~ 1470 year cycle of abrupt climate change is well-established, manifesting in Bond ice-rafting debris (IRD) events, Dansgaard-Oeschger atmospheric temperature cycle, and cyclical climatic conditions precursory to increased El Niño/Southern Oscillation (ENSO) variability and intensity. This cycle is central to questions on Holocene climate stability and hence anthropogenic impacts on climate (deMenocal et al., 2000). To date no causal mechanism has been identified, although solar forcing has been previously suggested. Here we show that interacting combination of astronomical variables related to Earth's orbit may be causally related to this cycle and several associated key isotopic spectral signals. The ~ 1470 year climate cycle may thus be regarded as a high frequency extension of the Milankovitch precessional cycle, incorporating orbital, solar and lunar forcing through interaction with the tropical and anomalistic years and Earth's rotation.

  9. 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.

    2016-11-01

    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.

  10. 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.

  11. 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.

  12. 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.

  13. 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

    2013-12-03

    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.

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

    PubMed

    Broecker, W S

    2003-06-06

    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.

  15. Climatic and Societal Causes for Abrupt Environmental Change in the Mediterranean During the Common Era

    NASA Astrophysics Data System (ADS)

    Mensing, S. A.; Tunno, I.; Sagnotti, L.; Florindo, F.; Noble, P. J.; Archer, C.; Zimmerman, S. R. H.; Pavón-Carrasco, F. J.; Cifnani, G.; Passigli, S.; Piovesan, G.

    2015-12-01

    We compare climatic and societal causes for abrupt environmental change for the last 2000 years in the Rieti Basin, central Italy using high-resolution sedimentary paleoenvironmental proxies, historical documents, and annually resolved independent climate reconstructions of temperature and precipitation. Pollen zones, identified from temporally constrained cluster analysis, coincide with historic periods developed from well-established ceramic sequences corresponding to the Roman Imperial through Late Antique (1 to 600 CE) Early Medieval (600 to 875 CE), Medieval through Late Medieval (875 to 1400 CE), Renaissance and Modern (1400 to 1725 CE), and Contemporary periods (1725 CE to present). Non-metric dimensional scaling (NMDS) ordination showed that each temporal period occupied a unique ecologic space suggesting that a new landscape was created during each successive historic period. During Roman time, between 1 and 500 CE, a modest decline in forest coincides with a positive phase of the North Atlantic Oscillation (NAO) and drier climate; however mesophyllous forest is preserved. Steep decline in forest cover between 850 and 950 CE coincides with positive temperature anomalies in Europe and a positive NAO. Although this would seem to suggest climate as a cause, temperature and precipitation changes are modest and the magnitude and rapidity of the vegetation change suggests climate played a small role. Archaeological evidence from across Europe identifies socioeconomic factors that produced forest clearing. In contrast, cooler temperatures and a negative NAO (increased ppt) appears to have been a catalyst for land abandonment and forest recovery in the 13th to 14th centuries. The NAO produces opposite effects on societies in the eastern and western Mediterranean with the negative phase in 1400 CE leading to cool wet climate and land abandonment in central Italy but an abrupt shift to drier conditions and change from sedentary village life to nomadism in Syria.

  16. 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.

  17. Geometry Transition in the Cocos Plate, from Flat-Steep to Constant Dip: Smooth or Abrupt?

    NASA Astrophysics Data System (ADS)

    Perez-Campos, X.; Clayton, R. W.; Brudzinski, M. R.; Valdés-González, C. M.; Cabral-Cano, E.; Arciniega-Ceballos, A.; Córdoba-Montiel, F.

    2013-05-01

    Subduction of the Cocos Plate beneath North America has a variable and complex behavior along the Middle-American Trench. Initially, its geometry was delineated from regional seismicity. In the last 10 years, seismic experiments have illuminated some details in the geometry. They have reported, from NW to SE an abrupt dip transition, from 50 to 26°, as the result of a tear that splits Cocos North from Cocos South; then there is a smooth transition to a horizontal geometry under central Mexico. Further southeast, under the Isthmus of Tehuantepec, the Cocos plate shows a constant ~26° subduction dip. This last transition has been assumed to be smooth from the sparse seismicity in the region. A first glimpse of the slab geometry under Oaxaca, shows the slab continues to be flat at least until 97.5°W longitude, where the slab suddenly changes to a ~55° dip to the northeast. This occurs at a distance of ~75 km from the Pico de Orizaba volcano, which is a similar distance as the active Popocatepetl volcano from the place where the slab dives into the mantle along the Meso-American Subduction Experiment line, in central Mexico. East of this region, receiver function images show an abrupt change in the geometry and length of the slab.

  18. Slowing down of North Pacific climate variability and its implications for abrupt ecosystem change.

    PubMed

    Boulton, Chris A; Lenton, Timothy M

    2015-09-15

    Marine ecosystems are sensitive to stochastic environmental variability, with higher-amplitude, lower-frequency--i.e., "redder"--variability posing a greater threat of triggering large ecosystem changes. Here we show that fluctuations in the Pacific Decadal Oscillation (PDO) index have slowed down markedly over the observational record (1900-present), as indicated by a robust increase in autocorrelation. This "reddening" of the spectrum of climate variability is also found in regionally averaged North Pacific sea surface temperatures (SSTs), and can be at least partly explained by observed deepening of the ocean mixed layer. The progressive reddening of North Pacific climate variability has important implications for marine ecosystems. Ecosystem variables that respond linearly to climate forcing will have become prone to much larger variations over the observational record, whereas ecosystem variables that respond nonlinearly to climate forcing will have become prone to more frequent "regime shifts." Thus, slowing down of North Pacific climate variability can help explain the large magnitude and potentially the quick succession of well-known abrupt changes in North Pacific ecosystems in 1977 and 1989. When looking ahead, despite model limitations in simulating mixed layer depth (MLD) in the North Pacific, global warming is robustly expected to decrease MLD. This could potentially reverse the observed trend of slowing down of North Pacific climate variability and its effects on marine ecosystems.

  19. Decoupling of Northern North Atlantic Sea Surface Temperature and Deep Circulation during Abrupt Glacial Climate Change

    NASA Astrophysics Data System (ADS)

    Jonkers, L.; Barker, S.; Hall, I. R.

    2014-12-01

    Abrupt climate change is a prominent feature of the ice ages. The prevailing view is that these changes are related to fluctuations in ocean circulation, possibly triggered by changes in freshwater forcing as a result of ice-rafting events in the North Atlantic. Here we investigate this view by presenting results from a sediment core in the Northern North Atlantic (ODP 983 60.4°N, 23.6°W, 1984m depth, ~12-35 kyr), which is ideally positioned to monitor changes in the flow speed of Iceland-Scotland Overflow Waters. The mean size of silt (10-63 μm) has been proposed as a useful flow speed indicator, but can be influenced the presence of ice-rafted detritus (IRD). We present grain size data obtained using a Coulter counter as well as a laser diffraction particle sizer, which we compare to the proportion of Neogloboquadrina pachyderma (proxy for sea surface temperature) and manually counted coarse IRD. Grain size results are comparable for the two techniques and the influence of IRD is clearly visible in the mean size data. We use end-member modelling to derive an IRD-free estimate of flow speed variability and find clear reductions in the flow speed associated with IRD input. Sea surface temperature however, appears to vary independently from IRD input and hence deep circulation. In particular, IRD appears and current speed decreases after the onset of cooling and additional temperature variability is observed that is not associated with IRD events or changes in the deep circulation. These results question the classical view of freshwater forcing as the driver of abrupt climate change. We suggest that North Atlantic temperature variability may be related to shifts in position of the polar front and that, while IRD events may be coeval with changes in the deep circulation, these changes are not required to explain the abrupt temperature variability in the Northern North Atlantic.

  20. Abrupt Climate Events Recorded in Chinese and Central Asian Loess Sequences

    NASA Astrophysics Data System (ADS)

    Machalett, Bjoern; Oches, Eric A.; Haam, Eddie; Lai, Zhongping; Endlicher, Wilfried

    2013-04-01

    of suborbital global climate changes and an initiator of abrupt climate oscillations in the Northern Hemisphere.

  1. Abrupt Climate Events Recorded in Chinese and Central Asian Loess Sequences

    NASA Astrophysics Data System (ADS)

    Machalett, B.; Oches, E. A.; Haam, E. K.; Lai, Z.; Endlicher, W.

    2013-12-01

    of suborbital global climate changes and an initiator of abrupt climate oscillations in the Northern Hemisphere.

  2. 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).

  3. 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.

  4. Postglacial Response of Terrestrial Neotropical Vegetation to Abrupt Climate Change as Recorded by Pollen from a Marine Core, Cariaco Basin

    NASA Astrophysics Data System (ADS)

    Delusina, I.; Peterson, L. C.; Spero, H. J.

    2011-12-01

    The response of terrestrial vegetation to the climatic shift that followed the Last Glacial Maximum is a critical component of the Neotropical climate system: it is linked to the carbon cycle and makes it possible to trace the impact of climatic alterations. We analyzed fossil pollen from high-resolution marine core MD03-2620 from the anoxic Cariaco Basin, off the coast of Venezuela. The study covers the period from Last Glacial Maximum (LGM) to the mid-Holocene. Previous paleoreconstructions from Cariaco Basin sediments emphasized that the abrupt climatic change that followed the LGM was associated with a shift of the ITCZ, subsequent sea level oscillations and alteration in a thermohaline circulation. We maintain that pollen from the marine core reflects vegetation trends of a large regional area, which smooths out local peculiarities in vegetation and allows us to trace the Cold/Dry-Warm/Wet dynamic in the pollen assemblages of the Cariaco sediments. Our pollen analysis indicates an interval of clear dominance of C4-type plants between ca 19.0 - 17.5 kyr BP, representing the transition from salt-marshes to steppe/savanna on the lowland. The onset of the Mystery Interval MI (17.5 to ~14.5 kyr BP) caused the most dramatic changes in vegetation for all postglacial time and was characterized sequentially by both a wet and dry signal, resulting in the reduction of forest vegetation, and later with the expansion of salt marshes in the littoral zone. According to the pollen data, MI consisted of two clearly recognized parts with a bridge in the middle: 1) H1-a. Dry interval between ~17.5 and 16.5 kyr BP with gradually growing humidity, that reaches a plateau at ~16.6 kyr BP. 2) Middle of the MI: ~ 16.5 - 15.8 kyr BP, exhibiting warm, humid conditions. 3) H1-b. Dry period after ~15.8 kyr BP, to ~14.5 kyr BP. The largest abrupt change in the pollen record is the transition to the Bølling/Allerød Stade, where our results are well correlated with plant wax biomarker

  5. Nonlinearity in bacterial population dynamics: proposal for experiments for the observation of abrupt transitions in patches.

    PubMed

    Kenkre, V M; Kumar, Niraj

    2008-12-02

    An explicit proposal for experiments leading to abrupt transitions in spatially extended bacterial populations in a Petri dish is presented on the basis of an exact formula obtained through an analytic theory. The theory provides accurately the transition expressions despite the fact that the actual solutions, which involve strong nonlinearity, are inaccessible to it. The analytic expressions are verified through numerical solutions of the relevant nonlinear equation. The experimental setup suggested uses opaque masks in a Petri dish bathed in ultraviolet radiation [Lin A-L, et al. (2004) Biophys J 87:75-80 and Perry N (2005) J R Soc Interface 2:379-387], but is based on the interplay of two distances the bacteria must traverse, one of them favorable and the other adverse. As a result of this interplay feature, the experiments proposed introduce highly enhanced reliability in interpretation of observations and in the potential for extraction of system parameters.

  6. Abrupt thermal transition reveals hydrothermal boundary and role of seamounts within the Cocos Plate

    NASA Astrophysics Data System (ADS)

    Fisher, A. T.; Stein, C. A.; Harris, R. N.; Wang, K.; Silver, E. A.; Pfender, M.; Hutnak, M.; Cherkaoui, A.; Bodzin, R.; Villinger, H.

    2003-06-01

    New thermal data from 18-24 Ma lithosphere on the Cocos Plate delineate contrasting subsurface thermal conditions in adjacent sections of crust. Heat flow through seafloor created at the East Pacific Rise is generally suppressed by ~70% relative to conductive lithospheric cooling models, whereas heat flow through adjacent, similarly-aged lithosphere generated at the Cocos-Nazca Spreading Center is consistent with these models. The transition between thermal regimes is remarkably abrupt, only 2-5 km wide, indicating a shallow hydrothermal origin. The transition is more closely associated with differences in the distribution of basement outcrops than with tectonic boundaries, demonstrating the importance of the former in extracting heat from the lithosphere on a regional basis.

  7. Planet-wide volcanics correlated with Last Glacial abrupt climate changes

    NASA Astrophysics Data System (ADS)

    Bay, R. C.; Bramall, N.; Price, P. B.

    2004-12-01

    We recently reported a correlation in excess of 99.5% between volcanic ash layers recorded in the deep ice core site at Siple Dome, West Antarctica and millennium-timescale abrupt cold periods (Dansgaard-Oeschger events) recorded at Summit, Greenland (GISP2) during the last glacial period. These data, obtained with our deep borehole optical dust logger, are the best evidence yet for a causal connection between volcanism and millennial climate change on the planetary scale, and lead to possibilities of a direct causal relationship. We now present a comparison with other volcanic proxies which demonstrates that the heaviest ash layers we detected at Siple Dome, those sufficiently concentrated for detailed chemical analysis in the core, appear to have come from local sources in West Antarctica, whereas the majority correspond to volcanic events detected throughout the Antarctic continent that correlate strongly with millennial climate changes in the Northern Hemisphere. Excluding the several heaviest ash signals in the Siple Dome data set increases the correlation with climate above the 3-sigma level, more than 800-to-one rejection of the null hypothesis. In June 2004 we deployed a high-resolution logger in the GRIP borehole at Summit, Greenland. We detected of order ˜100 volcanic ash layers which correlate weakly if at all with millennial climate change, consistent with studies of other Greenlandic records of volcanism. This contrast may provide an important clue to understanding global volcano-climate interaction as well as the role of the Southern Hemisphere. Of interest is a scenario in which volcanic ash and sulfate abruptly increase the soluble iron in large surface areas of nutrient-limited oceans, particularly the Southern Ocean, and stimulate growth of phytoplankton which enhance cooling by altering ocean albedo and atmospheric chemistry through mechanisms not fully understood. Viewed from another perspective, crustal stresses from ice-sheet loading

  8. A steep-slope transistor based on abrupt electronic phase transition.

    PubMed

    Shukla, Nikhil; Thathachary, Arun V; Agrawal, Ashish; Paik, Hanjong; Aziz, Ahmedullah; Schlom, Darrell G; Gupta, Sumeet Kumar; Engel-Herbert, Roman; Datta, Suman

    2015-08-07

    Collective interactions in functional materials can enable novel macroscopic properties like insulator-to-metal transitions. While implementing such materials into field-effect-transistor technology can potentially augment current state-of-the-art devices by providing unique routes to overcome their conventional limits, attempts to harness the insulator-to-metal transition for high-performance transistors have experienced little success. Here, we demonstrate a pathway for harnessing the abrupt resistivity transformation across the insulator-to-metal transition in vanadium dioxide (VO2), to design a hybrid-phase-transition field-effect transistor that exhibits gate controlled steep ('sub-kT/q') and reversible switching at room temperature. The transistor design, wherein VO2 is implemented in series with the field-effect transistor's source rather than into the channel, exploits negative differential resistance induced across the VO2 to create an internal amplifier that facilitates enhanced performance over a conventional field-effect transistor. Our approach enables low-voltage complementary n-type and p-type transistor operation as demonstrated here, and is applicable to other insulator-to-metal transition materials, offering tantalizing possibilities for energy-efficient logic and memory applications.

  9. Adjustment of the global climate to an abrupt slowdown of the Atlantic meridional overturning circulation

    NASA Astrophysics Data System (ADS)

    Cheng, Wei; Bitz, Cecilia M.; Chiang, John C. H.

    We explore the adjustment of the global climate to an abrupt slowdown of the Atlantic Meridional Circulation (AMOC), with a particular focus on the energetics. The slowdown is induced by a sudden freshwater perturbation in the North Atlantic. Reduction in the AMOC decreases northward ocean heat transport (OHT) and leads to cooling in the northern high latitudes. This cooling results in a local reduction to the top of atmosphere (TOA) radiative heat loss and an increase in northward atmospheric heat transport (AHT). The energy for the increased northward AHT comes from a combination of increased downward radiative flux at the TOA in the southern tropics and anomalous heating from the ocean in the northern tropics, both of which are consequences of the southward shift in the Intertropical Convergence Zone. Hence, viewed in the energetics framework, the atmospheric response to an AMOC slowdown extends throughout the Northern Hemisphere and into the tropics, and suggests an intimate coupling between the two regions. The mechanisms for the high-latitude-tropical coupling are examined. When comparing freshwater perturbation experiments in modern and Last Glacial Maximum (LGM) background states, we found that the changes to the northward OHT, and the mechanisms of global adjustment to the AMOC slowdown, were qualitatively similar in both instances. The one major difference is that freshening in the LGM climate induces a significantly stronger sea ice feedback than in a modern climate, allowing greater local cooling of the North Atlantic, and causing a commensurately larger global climate adjustment.

  10. Gain control through divisive inhibition prevents abrupt transition to chaos in a neural mass model

    PubMed Central

    Papasavvas, Christoforos A.; Wang, Yujiang; Trevelyan, Andrew J.; Kaiser, Marcus

    2016-01-01

    Experimental results suggest that there are two distinct mechanisms of inhibition in cortical neuronal networks: subtractive and divisive inhibition. They modulate the input-output function of their target neurons either by increasing the input that is needed to reach maximum output or by reducing the gain and the value of maximum output itself, respectively. However, the role of these mechanisms on the dynamics of the network is poorly understood. We introduce a novel population model and numerically investigate the influence of divisive inhibition on network dynamics. Specifically, we focus on the transitions from a state of regular oscillations to a state of chaotic dynamics via period-doubling bifurcations. The model with divisive inhibition exhibits a universal transition rate to chaos (Feigenbaum behavior). In contrast, in an equivalent model without divisive inhibition, transition rates to chaos are not bounded by the universal constant (non-Feigenbaum behavior). This non-Feigenbaum behavior, when only subtractive inhibition is present, is linked to the interaction of bifurcation curves in the parameter space. Indeed, searching the parameter space showed that such interactions are impossible when divisive inhibition is included. Therefore, divisive inhibition prevents non-Feigenbaum behavior and, consequently, any abrupt transition to chaos. The results suggest that the divisive inhibition in neuronal networks could play a crucial role in keeping the states of order and chaos well separated and in preventing the onset of pathological neural dynamics. PMID:26465514

  11. Gain control through divisive inhibition prevents abrupt transition to chaos in a neural mass model

    NASA Astrophysics Data System (ADS)

    Papasavvas, Christoforos A.; Wang, Yujiang; Trevelyan, Andrew J.; Kaiser, Marcus

    2015-09-01

    Experimental results suggest that there are two distinct mechanisms of inhibition in cortical neuronal networks: subtractive and divisive inhibition. They modulate the input-output function of their target neurons either by increasing the input that is needed to reach maximum output or by reducing the gain and the value of maximum output itself, respectively. However, the role of these mechanisms on the dynamics of the network is poorly understood. We introduce a novel population model and numerically investigate the influence of divisive inhibition on network dynamics. Specifically, we focus on the transitions from a state of regular oscillations to a state of chaotic dynamics via period-doubling bifurcations. The model with divisive inhibition exhibits a universal transition rate to chaos (Feigenbaum behavior). In contrast, in an equivalent model without divisive inhibition, transition rates to chaos are not bounded by the universal constant (non-Feigenbaum behavior). This non-Feigenbaum behavior, when only subtractive inhibition is present, is linked to the interaction of bifurcation curves in the parameter space. Indeed, searching the parameter space showed that such interactions are impossible when divisive inhibition is included. Therefore, divisive inhibition prevents non-Feigenbaum behavior and, consequently, any abrupt transition to chaos. The results suggest that the divisive inhibition in neuronal networks could play a crucial role in keeping the states of order and chaos well separated and in preventing the onset of pathological neural dynamics.

  12. 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.

  13. A comparison of two methods for detecting abrupt changes in the variance of climatic time series

    NASA Astrophysics Data System (ADS)

    Rodionov, Sergei N.

    2016-06-01

    Two methods for detecting abrupt shifts in the variance - Integrated Cumulative Sum of Squares (ICSS) and Sequential Regime Shift Detector (SRSD) - have been compared on both synthetic and observed time series. In Monte Carlo experiments, SRSD outperformed ICSS in the overwhelming majority of the modeled scenarios with different sequences of variance regimes. The SRSD advantage was particularly apparent in the case of outliers in the series. On the other hand, SRSD has more parameters to adjust than ICSS, which requires more experience from the user in order to select those parameters properly. Therefore, ICSS can serve as a good starting point of a regime shift analysis. When tested on climatic time series, in most cases both methods detected the same change points in the longer series (252-787 monthly values). The only exception was the Arctic Ocean sea surface temperature (SST) series, when ICSS found one extra change point that appeared to be spurious. As for the shorter time series (66-136 yearly values), ICSS failed to detect any change points even when the variance doubled or tripled from one regime to another. For these time series, SRSD is recommended. Interestingly, all the climatic time series tested, from the Arctic to the tropics, had one thing in common: the last shift detected in each of these series was toward a high-variance regime. This is consistent with other findings of increased climate variability in recent decades.

  14. Antarctic Forcing of Abrupt Global Climate Change during Oxygen Isotope Stage 3.

    NASA Astrophysics Data System (ADS)

    Turney, C. S.; Palmer, J. G.

    2015-12-01

    Contrasting Greenland and Antarctic temperature trends during the late Pleistocene (60 to 11.5 ka) 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. Robustly testing this paradigm, however, requires a level of chronological precision currently lacking in terrestrial and marine records. Here we report a bidecadally-resolved New Zealand tree-ring sequence spanning two millennia that preserves a record of atmospheric radiocarbon (14C), allowing us to precisely align terrestrial, marine and ice sequences across a period encompassing ice-rafted debris event Heinrich 3 (H3) in the North Atlantic and Antarctic Isotope Maximum 4 (AIM4) in the Southern Hemisphere. We observe no significant difference in atmospheric and marine 14C records across H3 suggesting negligible impact on Atlantic Meridional Overturning Circulation (AMOC) but find that a climate downturn before AIM4 had a global impact, with warming in the North Atlantic (D-O 5.1) and a dramatic change in low latitude hydroclimate. Using the fully coupled CSIRO Mk3L climate system model we find that these trends are consistent with an Antarctic meltwater event propagated globally by atmospheric teleconnections. Our results suggest Southern Ocean dynamics played a significant role in driving global climate change across this period with implications for abrupt events through the late Pleistocene.

  15. Theoretical basis for predicting climate-induced abrupt shifts in the oceans

    PubMed Central

    Beaugrand, Gregory

    2015-01-01

    Among the responses of marine species and their ecosystems to climate change, abrupt community shifts (ACSs), also called regime shifts, have often been observed. However, despite their effects for ecosystem functioning and both provisioning and regulating services, our understanding of the underlying mechanisms involved remains elusive. This paper proposes a theory showing that some ACSs originate from the interaction between climate-induced environmental changes and the species ecological niche. The theory predicts that a substantial stepwise shift in the thermal regime of a marine ecosystem leads indubitably to an ACS and explains why some species do not change during the phenomenon. It also explicates why the timing of ACSs may differ or why some studies may detect or not detect a shift in the same ecosystem, independently of the statistical method of detection and simply because they focus on different species or taxonomic groups. The present theory offers a way to predict future climate-induced community shifts and their potential associated trophic cascades and amplifications.

  16. 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

  17. 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

  18. The Role of the Tropics in Last Glacial Abrupt Climate Change from a West Antarctic Ice Core

    NASA Astrophysics Data System (ADS)

    Jones, T. R.; White, J. W. C.; Steig, E. J.; Cuffey, K. M.; Vaughn, B. H.; Morris, V. A.; Vasileios, G.; Markle, B. R.; Schoenemann, S. W.

    2014-12-01

    Debate exists as to whether last glacial abrupt climate changes in Greenland, and associated changes in Antarctica, had a high-latitude or tropical trigger. An ultra high-resolution water isotope record from the West Antarctic Ice Sheet Divide (WAIS Divide) Ice Core Project has been developed with three key water isotope parameters that offer insight into this debate: δD, δ18O, and deuterium excess (dxs). δD and δ18O are a proxy for local temperature and regional atmospheric circulation, while dxs is primarily a proxy for sea surface temperature at the ice core's moisture source(s) (relative humidity and wind speed also play a role). We build on past studies that show West Antarctic climate is modulated by El Niño Southern Oscillation (ENSO) teleconnection mechanisms, which originate in the equatorial Pacific Ocean, to infer how past ENSO changes may have influenced abrupt climate change. Using frequency analysis of the water isotope data, we can reconstruct the amplitude of ENSO-scale climate oscillations in the 2-15 year range within temporal windows as low as 100 years. Our analysis uses a back diffusion model that estimates initial amplitudes before decay in the firn column. We combine δD, δ18O, and dxs frequency analysis to evaluate how climate variability at WAIS Divide is influenced by tropical climate forcing. Our results should ultimately offer insight into the role of the tropics in abrupt climate change.

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

    PubMed

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

    2009-12-08

    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-CO(2) 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 CO(2) emissions.

  20. 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

  1. 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.

  2. Continuous methane record of abrupt climate change 10-68 ka: sighting Heinrich events in the ice core record

    NASA Astrophysics Data System (ADS)

    Rhodes, Rachael; Brook, Edward; Chiang, John; Blunier, Thomas; Cheng, Hai; Edwards, R. Lawrence; Maselli, Olivia; McConnell, Joseph; Romanini, Daniele; Severinghaus, Jeffrey; Sowers, Todd; Stowasser, Christopher

    2014-05-01

    The Last Glacial period was punctuated by millennial scale abrupt climate changes - Dansgaard-Oeschger (D-O) cycles and Heinrich events. Controls on the magnitude and frequency of these climate perturbations, and how they may be inter-related, remain unclear. Specific problems include the difficulty of dating Heinrich sediment layers and local bias of key paleoclimate archives. We present a highly detailed and precise record of ice core methane (CH4), a globally integrated signal, which resolves climatic features in unprecedented resolution. Abrupt CH4 increases are resolved in Heinrich Stadials (HS) 1, 2, 4 and 5 where, in contrast to all D-O cycles, there are no concurrent abrupt changes in Greenland temperature. Using modern-day tropical rainfall variability as an analog, we propose that strong cooling in the North Atlantic severely restricted the northerly range of the Intertropical Convergence Zone (ITCZ), leading to an enhanced wet season over Southern Hemisphere tropical land areas, and consequently driving production of excess CH4 in tropical wetlands. Our findings place four Heinrich events firmly within ice core chronologies and suggest maximum durations of 778 to 1606 yr. CH4 anomalies are only associated with Heinrich events of Hudson Strait provenance, indicating that the tropical impacts of Heinrich events were not uniform.

  3. Insolation and Abrupt Climate Change Effects on the Western Pacific Maritime Monsoon

    NASA Astrophysics Data System (ADS)

    Partin, J. W.; Quinn, T. M.; Shen, C.; Cardenas, M.; Siringan, F. P.; Hori, M.; Okumura, Y.; Banner, J. L.; Lin, K.; Jiang, X.; Taylor, F. W.

    2013-12-01

    Many monsoon-sensitive paleoclimate archives capture the response of the Asian-Australian monsoon system to changes in summer insolation, as well as abrupt climate changes such as the Younger Dryas (YD). The response is commonly a direct one in Holocene and YD archives. In the case of insolation, increased summer insolation leads to increased monsoon rainfall over land, as captured in stalagmite δ18O records from Oman and China. We evaluate this direct response using maritime stalagmite records from the island of Palawan, Philippines (10 N, 119 E). The wet season in Palawan occurs over the same months (June-October) as in Oman, India and China. Therefore, we expected the Palawan stalagmite δ18O record, a proxy of rainfall, to have a similar response to changing insolation and hence, a trend of decreasing monsoon rainfall over the Holocene. However, the Holocene trend in two partially replicated stalagmite δ18O records is opposite to that expected: rainfall increases over the Holocene, despite the decrease of summer insolation over the Holocene. We interpret the Holocene trend observed at Palawan to be the result of an increase in the maritime monsoon that balances the reduction in the land monsoon; an interpretation that is consistent with previously published results from coupled ocean-atmosphere general circulation model runs. Seawater δ18O reconstructions from marine sediment cores in the western tropical Pacific contain a freshening trend over the Holocene, also supporting the hypothesis of increase maritime monsoon rainfall. The direct relationship between monsoon rainfall over land as recorded in the YD interval in Chinese stalagmite records is also observed in maritime monsoon rainfall during the YD at Palawan: both records get drier during the YD cold interval. This agreement between YD stalagmite records from China and Palawan contrasts sharply with the inverse relationship between these records over the Holocene. We further investigate the nature of

  4. The case of the global jitters - Even in seemingly stable times, climate can take an abrupt turn

    SciTech Connect

    Monastersky, R.

    1996-03-02

    Research in different parts of the world has recently revealed signs that climate has behaved erratically during the last few millennia. Conditions in various regions have shifted abruptly and repeatedly, perhaps even at the time of the collapse of the Akkadian civilization in 2200 B.C. This article discusses recent work of various scientists, who are trying to forecast future conditions, to understand what is causing these shifts and whether this rhythum has played a role in recent global warming. A side bar discusses signs of a solar link to climatic change.

  5. "What Controls the Structure and Stability of the Ocean Meridional Overturning Circulation: Implications for Abrupt Climate Change?"

    SciTech Connect

    Fedorov, Alexey

    2013-11-23

    The central goal of this research project is to understand the properties of the ocean meridional overturning circulation (MOC) – a topic critical for understanding climate variability and stability on a variety of timescales (from decadal to centennial and longer). Specifically, we have explored various factors that control the MOC stability and decadal variability in the Atlantic and the ocean thermal structure in general, including the possibility abrupt climate change. We have also continued efforts on improving the performance of coupled ocean-atmosphere GCMs.

  6. 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

  7. A Generalized Stability Analysis of the AMOC in Earth System Models: Implication for Decadal Variability and Abrupt Climate Change

    SciTech Connect

    Fedorov, Alexey V.

    2015-01-14

    The central goal of this research project was to understand the mechanisms of decadal and multi-decadal variability of the Atlantic Meridional Overturning Circulation (AMOC) as related to climate variability and abrupt climate change within a hierarchy of climate models ranging from realistic ocean models to comprehensive Earth system models. Generalized Stability Analysis, a method that quantifies the transient and asymptotic growth of perturbations in the system, is one of the main approaches used throughout this project. The topics we have explored range from physical mechanisms that control AMOC variability to the factors that determine AMOC predictability in the Earth system models, to the stability and variability of the AMOC in past climates.

  8. Transient Adjustment of the global climate to an abrupt Northern North Atlantic cooling

    NASA Astrophysics Data System (ADS)

    Tang, G.; Chang, P.; Panetta, R.; Saravanan, R.

    2013-12-01

    The Thermohaline Circulation (THC) is thought to play a key role in abrupt changes in Earth climate. In cold periods such as the Younger Dryas, the THC was much weaker than today. In an experiment with a fully coupled CCSM3 model an artificial freshwater flux is added to the Northern North Atlantic Ocean surface, which weakens the THC. The North Atlantic Ocean surface cools almost instantly after the freshwater flux onset. This cooling is subsequently spread throughout the Northern Hemisphere, resulting in the ITCZ moving southward. In the weakening THC, heat carried by the THC from Southern Hemisphere to the Northern Hemisphere is reduced, resulting in a cooler Northern Hemisphere. It is still questioned what role the atmosphere plays in this process. There are two possible ways the atmosphere may change the ocean surface temperature. One is that the wind changes the ocean surface wind-driven circulation, leading to a change to the ocean heat budget. Another is that the atmosphere changes the ocean-atmosphere heat flux directly. Here we look into the second possibility by comparing the effects of freshwater flux in a fully coupled model to the effects of the same flux in a model constructed by coupling an atmospheric general circulation model (CAM3) to a thermodynamic slab ocean model. With use of appropriate Q-fluxes, the coupled model with the slab ocean has the same climatology as the fully coupled CCSM3 model. Perturbation Q-fluxes are constructed for the fresh water flux experiments using a restoring technique. We find that the atmosphere interacting with a thermodynamic slab ocean can spread the cooling from the Northern North Atlantic and cause the ITCZ to move southward, and that there is a cooling front propagating southward with a speed depending on the mixed layer depth: a deeper mixed layer depth results in a slower propagation. By applying the Q-flux perturbation only in the Northern North Atlantic Ocean, the effect of the ocean circulation change on

  9. HIGH-PRESSURE PHYSICS. Direct observation of an abrupt insulator-to-metal transition in dense liquid deuterium.

    PubMed

    Knudson, M D; Desjarlais, M P; Becker, A; Lemke, R W; Cochrane, K R; Savage, M E; Bliss, D E; Mattsson, T R; Redmer, R

    2015-06-26

    Eighty years ago, it was proposed that solid hydrogen would become metallic at sufficiently high density. Despite numerous investigations, this transition has not yet been experimentally observed. More recently, there has been much interest in the analog of this predicted metallic transition in the dense liquid, due to its relevance to planetary science. Here, we show direct observation of an abrupt insulator-to-metal transition in dense liquid deuterium. Experimental determination of the location of this transition provides a much-needed benchmark for theory and may constrain the region of hydrogen-helium immiscibility and the boundary-layer pressure in standard models of the internal structure of gas-giant planets.

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

    NASA Astrophysics Data System (ADS)

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

    2016-12-01

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

  11. A climatic driver for abrupt mid-Holocene vegetation dynamics and the hemlock decline in New England.

    PubMed

    Foster, David R; Oswald, W Wyatt; Faison, Edward K; Doughty, Elaine D; Hansen, Barbara C S

    2006-12-01

    The mid-Holocene decline of eastern hemlock is widely viewed as the sole prehistorical example of an insect- or pathogen-mediated collapse of a North American tree species and has been extensively studied for insights into pest-host dynamics and the consequences to terrestrial and aquatic ecosystems of dominant-species removal. We report paleoecological evidence implicating climate as a major driver of this episode. Data drawn from sites across a gradient in hemlock abundance from dominant to absent demonstrate: a synchronous, dramatic decline in a contrasting taxon (oak); changes in lake sediments and aquatic taxa indicating low water levels; and one or more intervals of intense drought at regional to continental scales. These results, which accord well with emerging climate reconstructions, challenge the interpretation of a biotically driven hemlock decline and highlight the potential for climate change to generate major, abrupt dynamics in forest ecosystems.

  12. Abrupt Climate Change & Paleoindian Environments in western Colorado from 17-9 ka yr BP

    NASA Astrophysics Data System (ADS)

    Whitlock, C. L.; Briles, C.; Meltzer, D. J.

    2010-12-01

    The late-glacial period was characterized by rapid climate changes that resulted in significant ecosystem reorganizations worldwide. In western Colorado, one of the coldest locations in North American today, mountain environments during the late-glacial period are poorly known. Yet, archeological evidence indicates that Folsom-age Paleoindians were present in the region, perhaps even occasionally over-wintering in the Gunnison Basin during the Younger Dryas Chronozone (YDC; 12.9 to 11.5ka yr BP). To determine the climate, vegetation, and fire history during the late-glacial/early-Holocene transition, a 17-kyr-old sediment core from Lily Pond (38°56’06” N, 106°38’37”W, 3208m elevation) was analyzed for pollen and charcoal and compared with other high-resolution records from the region. The data suggest that, following deglaciation, the region supported an alpine parkland dominated by Artemisia and scattered Picea. Conditions warmed and became wetter than before during the Bølling-Allerød period (B/A; 14.7 to 12.9ka yr BP), when the region was covered by open Picea, Pinus, and Abies forest. Cooling during the YDC is inferred from abundant Picea, slightly more Artemisia and decreased Pinus, which indicate the presence of subalpine parkland. With the onset of the Holocene at ~11.5 ka yr BP, Pinus, Quercus, Artemisia, and Chenopodiaceae increased, suggesting an upslope expansion of xerophytic taxa in response to warmer and effectively drier summers than before or at present. Fire activity was absent prior to 14.7 ka yr BP, increased substantially during the B/A, decreased during the YDC, increased at the beginning of the Holocene, and declined in the early Holocene. The vegetation changes that occurred at Lily Pond are generally consistent with other high-resolution records in the Colorado Rockies in showing cooler-than-present YDC followed by rapid warming. The Lily Lake data provide new information that indicates substantial warming and establishment of

  13. The fluvial system response to abrupt climate change during the last cold stage: the Upper Pleistocene River Thames fluvial succession at Ashton Keynes, UK

    NASA Astrophysics Data System (ADS)

    Lewis, S. G.; Maddy, D.; Scaife, R. G.

    2001-02-01

    The last interglacial-glacial cycle (125-10 ka BP) is characterised by numerous rapid shifts in global climate on sub-Milankovitch timescales, recorded in the ocean and ice core records. These climatic fluctuations are clearly recorded in those European terrestrial sedimentary sequences that span this time period without interruption. In the UK, only fragmentary Upper Pleistocene sequences exist, mainly within the fluvial archive of the major river systems such as the Thames. The response of the upper River Thames to abrupt fluctuations in climate is documented in the fluvial sediments beneath the Floodplain Terrace (Northmoor Member of the Upper Thames Formation) at Ashton Keynes, Wiltshire. A number of criteria are set out by which significant changes in the fluvial system may be established from the sedimentological, palaeoecological and geochronological information contained within the succession. The sedimentary succession is divisible into four facies associations, on the basis of their sedimentology and bounding surface characteristics. These represent distinct phases of fluvial activity at the site and allow changes in fluvial style to be inferred. Palaeoecological reconstructions from pollen analysis of peats within the sequence provides an indication of the nature and direction of Late Glacial environmental change and optically stimulated luminescence and radiocarbon dating methods provide chronological control on the sequence. These data suggest that major changes in fluvial style are recorded within the succession, which can be related to the climatic fluctuations that took place on the oxygen isotope stage 5a/4 transition (approximately 70 ka BP) and the Devensian Late Glacial climatic warm-cold-warm oscillation (13-11 ka BP). The changes in fluvial style are a result of variations in sediment supply to the river resulting from changes in slope stability, vegetation cover and cold-climate mass movement processes and variations in discharge regime

  14. 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.

  15. Two Degrees of Separation: Abrupt Climate Change and the Adverse Impact to US National Security

    DTIC Science & Technology

    2009-04-01

    trend of increasing GHG emissions is marginally impacting or irrelevant altogether. “Other factors, including sun spots, solar winds, variations ...climate variations over a wide range of time scales, making it a natural sensor of climate variability and providing a visible expression of climate...many observed changes in phenology and distribution have been associated with rising water temperatures, as well as changes in salinity, oxygen levels

  16. Micropaleontological Record of Post-glacial History in Lake Champlain and Adjacent Regions: Implications for Glacial Lake Drainage and Abrupt Climate Events

    NASA Astrophysics Data System (ADS)

    Cronin, T. M.; Manley, P. L.; Guilbault, J.; Berke, M.; Rayburn, J. A.; Franzi, D. A.; Knuepfer, P. L.

    2005-12-01

    Post-glacial lacustrine and marine sediments of the Lake Champlain region range from 20 to >50 meters in thickness presenting an opportunity to assess the timing of North American glacial lake drainage at multidecadal timescales and evaluate its effect on North Atlantic salinity and abrupt climate events 13.5 to 10 kyr B.P. High-resolution analysis of foraminifera and ostracodes from cores taken onshore in the Plattsburgh, N.Y. vicinity and southern Quebec and offshore in southern Lake Champlain reveal complex changes in salinity during and after the transition from pro-glacial Lake Vermont (Lake Candona in Canada) to marine sedimentation in the Champlain Sea. The microfaunal sequence (bottom to top) includes: non-marine ostracodes ( Candona) in lacustrine varves, foraminiferal assemblages (common Cassidulina reniforme), another interval of Candona-bearing sediments (sometimes containing foraminifera), and, finally, sediments from the main phase of the Champlain sea episode containing diverse foraminiferal and marine ostracode assemblages. A decrease in salinity during the Champlain Sea is also in evidence from the shift in dominance of distinct variants of Elphidium in the deep basin. The marine episode ended with a progressive salinity decrease and the formation of Lake Champlain about 10 kyr B.P. Observed salinity changes could be caused by catastrophic fresh-water influx from large glacial lakes west of the Lake Champlain region, meltwater from the retreating Laurentide Ice Sheet margin, diminished influx of marine water from the St. Lawrence due to changes in the position of the ice sheet margin and isostatic adjustment, or a combination of factors. The ages of these events were determined by estimating the reservoir effect on radiocarbon dates on marine shells through comparison with AMS dates on plant material and palynology, and shed light on the hypothesis that glacial lake discharges catalyzed abrupt climate events.

  17. Percolation in interdependent and interconnected networks: Abrupt change from second- to first-order transitions

    NASA Astrophysics Data System (ADS)

    Hu, Yanqing; Ksherim, Baruch; Cohen, Reuven; Havlin, Shlomo

    2011-12-01

    Robustness of two coupled networks systems has been studied separately only for dependency coupling [Buldyrev , Nature (London)NATUAS0028-083610.1038/nature08932 464, 1025 (2010)] and only for connectivity coupling [Leicht and D’Souza, e-print arXiv:0907.0894]. Here we study, using a percolation approach, a more realistic coupled networks system where both interdependent and interconnected links exist. We find rich and unusual phase-transition phenomena including hybrid transition of mixed first and second order, i.e., discontinuities like in a first-order transition of the giant component followed by a continuous decrease to zero like in a second-order transition. Moreover, we find unusual discontinuous changes from second-order to first-order transition as a function of the dependency coupling between the two networks.

  18. Central European vegetation response to abrupt climate change at 8.2 ka

    NASA Astrophysics Data System (ADS)

    Tinner, Willy; Lotter, André F.

    2001-06-01

    Oxygen isotope records show a major climatic reversal at 8.2 ka in Greenland and Europe. Annually laminated sediments from two lakes in Switzerland and Germany were sampled contiguously to assess the response of European vegetation to climate change ca. 8.2 ka with time resolution and precision comparable to those of the Greenland ice cores. The pollen assemblages show pronounced and immediate responses (0 20 yr) of terrestrial vegetation to the climatic change at 8.2 ka. A sudden collapse of Corylus avellana (hazel) was accompanied by the rapid expansion of Pinus (pine), Betula (birch), and Tilia (linden), and by the invasion of Fagus silvatica (beech) and Abies alba (fir). Vegetational changes suggest that climatic cooling reduced drought stress, allowing more drought-sensitive and taller growing species to out-compete Corylus avellana by forming denser forest canopies. Climate cooling at 8.2 ka and the immediate reorganization of terrestrial ecosystems has gone unrecognized by previous pollen studies. On the basis of our data we conclude that the early Holocene high abundance of C. avellana in Europe was climatically caused, and we question the conventional opinion that postglacial expansions of F. silvatica and A. alba were controlled by low migration rates rather than by climate. The close connection between climatic change and vegetational response at a subcontinental scale implies that forecasted global warming may trigger rapid collapses, expansions, and invasions of tree species.

  19. Quantifying Climate Feedbacks from Abrupt Changes in High-Latitude Trace-Gas Emissions

    SciTech Connect

    Schlosser, Courtney Adam; Walter-Anthony, Katey; Zhuang, Qianlai; Melillo, Jerry

    2013-04-26

    Our overall goal was to quantify the potential for threshold changes in natural emission rates of trace gases, particularly methane and carbon dioxide, from pan-arctic terrestrial systems under the spectrum of anthropogenically forced climate warming, and the extent to which these emissions provide a strong feedback mechanism to global climate warming. This goal is motivated under the premise that polar amplification of global climate warming will induce widespread thaw and degradation of the permafrost, and would thus cause substantial changes in the extent of wetlands and lakes, especially thermokarst (thaw) lakes, over the Arctic. Through a coordinated effort of field measurements, model development, and numerical experimentation with an integrated assessment model framework, we have investigated the following hypothesis: There exists a climate-warming threshold beyond which permafrost degradation becomes widespread and thus instigates strong and/or sharp increases in methane emissions (via thermokarst lakes and wetland expansion). These would outweigh any increased uptake of carbon (e.g. from peatlands) and would result in a strong, positive feedback to global climate warming.

  20. 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.

  1. Atomic layer deposition and abrupt wetting transitions on nonwoven polypropylene and woven cotton fabrics.

    PubMed

    Hyde, G Kevin; Scarel, Giovanna; Spagnola, Joseph C; Peng, Qing; Lee, Kyoungmi; Gong, Bo; Roberts, Kim G; Roth, Kelly M; Hanson, Christopher A; Devine, Christina K; Stewart, S Michael; Hojo, Daisuke; Na, Jeong-Seok; Jur, Jesse S; Parsons, Gregory N

    2010-02-16

    Atomic layer deposition (ALD) of aluminum oxide on nonwoven polypropylene and woven cotton fabric materials can be used to transform and control fiber surface wetting properties. Infrared analysis shows that ALD can produce a uniform coating throughout the nonwoven polypropylene fiber matrix, and the amount of coating can be controlled by the number of ALD cycles. Upon coating by ALD aluminum oxide, nonwetting hydrophobic polypropylene fibers transition to either a metastable hydrophobic or a fully wetting hydrophilic state, consistent with well-known Cassie-Baxter and Wenzel models of surface wetting of roughened surfaces. The observed nonwetting/wetting transition depends on ALD process variables such as the number of ALD coating cycles and deposition temperature. Cotton fabrics coated with ALD aluminum oxide at moderate temperatures were also observed to transition from a natural wetting state to a metastable hydrophobic state and back to wetting depending on the number of ALD cycles. The transitions on cotton appear to be less sensitive to deposition temperature. The results provide insight into the effect of ALD film growth mechanisms on hydrophobic and hydrophilic polymers and fibrous structures. The ability to adjust and control surface energy, surface reactivity, and wettability of polymer and natural fiber systems using atomic layer deposition may enable a wide range of new applications for functional fiber-based systems.

  2. 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.

  3. Unity of Science: from High-Energy Neutrinos to Abrupt Climate Change and Life in Ice

    NASA Astrophysics Data System (ADS)

    Price, P. Buford

    2004-03-01

    These diverse topics exploit optical properties of micron-size particles in ice. AMANDA (Antarctic Muon and Neutrino Detector Array) searches for astrophysical sources of high-energy neutrinos by recording arrival times of Cherenkov light from their interaction products (muons and cascades) at phototubes in the 0.1 km^3 array in deep ice at the South Pole. Using pulsed lasers and LEDs in the array, we found that absorptivity and scattering of light in ice depend on dust concentration, which varies with depth due to dependence of dust concentration on global temperature at the time of deposition. Knowing dust concentration vs depth in AMANDA, we can fit muon tracks and locate neutrino sources to 1 arcdegree. As an AMANDA spinoff, we invented the Dust Logger, a new paleoclimatological instrument that emits laser light into glacial ice surrounding the borehole down which it is lowered. It records light that reenters the borehole after being partially absorbed and scattered by dust in the ice. This signal serves as an accurate proxy for global temperature as a function of time over a million years. The Dust Logger obtains a detailed time sequence of glacial and interglacial periods and of abrupt temperature changes that occur at millennial intervals. Occasional eruptions of nearby volcanoes punctuate the dust record with cm-thick ash layers in ice. We infer that strong volcanic eruptions lead to millennial-scale global coolings, most likely by dumping soluble iron- and acid-rich grains into nutrient-limited southern oceans, thus stimulating rapid growth of phytoplankton, which sequester carbon dioxide, a major greenhouse gas, from the atmosphere. Microbial cells are similar to dust in size and contain biomolecules that autofluoresce. We invented a BioSpectraLogger, which emits 224-nm laser light into ice and searches for fluorescence by microbes able to live in liquid veins in ice. It can be used in lakes, oceans, ice, and permafrost. A miniaturized version can search

  4. Abrupt transitions during sustained explosive eruptions: Examples from the 1912 eruption of Novarupta, Alaska

    USGS Publications Warehouse

    Adams, N.K.; Houghton, B.F.; Hildreth, W.

    2006-01-01

    Plinian/ignimbrite activity stopped briefly and abruptly 16 and 45 h after commencement of the 1912 Novarupta eruption defining three episodes of explosive volcanism before finally giving way after 60 h to effusion of lava domes. We focus here on the processes leading to the termination of the second and third of these three episodes. Early erupted pumice from both episodes show a very similar range in bulk vesicularity, but the modal values markedly decrease and the vesicularity range widens toward the end of Episode III. Clasts erupted at the end of each episode represent textural extremes; at the end of Episode II, clasts have very thin glass walls and a predominance of large bubbles, whereas at the end of Episode III, clasts have thick interstices and more small bubbles. Quantitatively, all clasts have very similar vesicle size distributions which show a division in the bubble population at 30 ??m vesicle diameter and cumulative number densities ranging from 107-109 cm-3. Patterns seen in histograms of volume fraction and the trends in the vesicle size data can be explained by coalescence signatures superimposed on an interval of prolonged nucleation and free growth of bubbles. Compared to experimental data for bubble growth in silicic melts, the high 1912 number densities suggest homogeneous nucleation was a significant if not dominant mechanism of bubble nucleation in the dacitic magma. The most distinct clast populations occurred toward the end of Plinian activity preceding effusive dome growth. Distributions skewed toward small sizes, thick walls, and teardrop vesicle shapes are indicative of bubble wall collapse marking maturation of the melt and onset of processes of outgassing. The data suggest that the superficially similar pauses in the 1912 eruption which marked the ends of episodes II and III had very different causes. Through Episode III, the trend in vesicle size data reflects a progressive shift in the degassing process from rapid magma ascent and

  5. The ocean's role in the transient response of climate to abrupt greenhouse gas forcing

    NASA Astrophysics Data System (ADS)

    Marshall, John; Scott, Jeffery R.; Armour, Kyle C.; Campin, J.-M.; Kelley, Maxwell; Romanou, Anastasia

    2015-04-01

    We study the role of the ocean in setting the patterns and timescale of the transient response of the climate to anthropogenic greenhouse gas forcing. A novel framework is set out which involves integration of an ocean-only model in which the anthropogenic temperature signal is forced from the surface by anomalous downwelling heat fluxes and damped at a rate controlled by a `climate feedback' parameter. We observe a broad correspondence between the evolution of the anthropogenic temperature () in our simplified ocean-only model and that of coupled climate models perturbed by a quadrupling of . This suggests that many of the mechanisms at work in fully coupled models are captured by our idealized ocean-only system. The framework allows us to probe the role of the ocean in delaying warming signals in the Southern Ocean and in the northern North Atlantic, and in amplifying the warming signal in the Arctic. By comparing active and passive temperature-like tracers we assess the degree to which changes in ocean circulation play a role in setting the distribution and evolution of . The background ocean circulation strongly influences the large-scale patterns of ocean heat uptake and storage, such that is governed by an advection/diffusion equation and weakly damped to the atmosphere at a rate set by climate feedbacks. Where warming is sufficiently small, for example in the Southern Ocean, changes in ocean circulation play a secondary role. In other regions, most noticeably in the North Atlantic, changes in ocean circulation induced by are central in shaping the response.

  6. Combined effect of soil erosion and climate change induces abrupt changes in soil and vegetation properties in semiarid Mediterranean shrublands.

    NASA Astrophysics Data System (ADS)

    Bochet, Esther; García-Fayos, Patricio

    2013-04-01

    Semiarid Mediterranean ecosystems are experiencing major alterations as a result of the complex interactions between climatic fluctuations and disturbances caused by human activities. Future scenarios of global change forecast a rapid degradation of these ecosystems, with a reduction of their functionality, as a result of changes in relevant vegetation and soil properties. Some theoretical models indicate that these ecosystems respond non-linearly to regular variations in the external conditions, with an abrupt shift when conditions approach a certain critical level or threshold. Considering these predictions, there is an urgent need to know the effects that these alterations might have on semi-arid ecosystems and their components. In this study, we aim at analyzing the consequences of climate change and increasing soil erosion on soil and vegetation properties and the functional dynamics of semiarid Mediterranean shrublands. We predict that the combined effect of both drivers will be additive or synergistic, increasing the negative effects of each one. We compared vegetation and soil properties of flat areas (low erosion) and steep hillslopes (high erosion) in two climatic areas (484 mm and 10.3°C, and 368mm and 11.9°C, respectively) that reproduce the predicted climate change in temperature and precipitation for the next 40 years. Species richness, vegetal cover, plant life-form composition were determined in 20 m2 plots and soil was sampled in the same plots to determine bulk density, aggregate stability, fertility and water holding capacity. All soil and vegetation properties were negatively affected by soil erosion and climate change. However, contrary to our hypothesis, the joined effect of both drivers on all soil and vegetation properties was antagonistic, except for the vegetal cover that showed an additive response to their interaction. Our results evidence that soil erosion affects more negatively the soil and vegetation properties in the cooler and

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

    PubMed

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

    2014-01-01

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

  8. Examining the potential impact of a warming ocean on food insecure Africa: concerns and mechanisms for abrupt climate change

    NASA Astrophysics Data System (ADS)

    Funk, C.; Dettinger, M.; Verdin, J.

    2007-12-01

    Given that more than 200 million sub-Saharan Africans are food insecure, abrupt climate change in Africa could be devastating. Recent observations for eastern and southern Africa suggest substantial declines in main growing season rainfall over the past 20 years. In this talk we present research from a multi-year study that examined the causes and implications of these drying trends. Our statistical and dynamic modeling results suggest that warming in the Indian Ocean has been linked to increased oceanic convection and disruptions in onshore moisture transports. These moisture transport disruptions, in turn, are probably associated with an increased frequency in agricultural drought in sub-tropical countries along Africa's eastern seaboard. This 'warm ocean-dry Africa' dipole appears to be a major driver of decadal variability. An evaluation of 11 climate change models suggests that increased tropical Indian Ocean precipitation, and the associated moisture transport disruptions, may in fact be anthropogenic, accounting for at least part of the regional drought tendencies in eastern and southern Africa over the past 20 years. These simulations also suggest continued increases in oceanic convection will be very likely over the next century. This diabatic forcing will likely produce continuing rainfall declines across 7 food insecure nations. These drying trends, combined with declining per capita agricultural capacity, are likely to contribute to a ~250 percent increase in food shortages over the next 30 years. Modest agricultural and market development, however, could alleviate the food problem substantially.

  9. Abrupt climate variability of eastern Anatolia vegetation during the last glacial

    NASA Astrophysics Data System (ADS)

    Pickarski, N.; Kwiecien, O.; Langgut, D.; Litt, T.

    2015-07-01

    Detailed analyses of the Lake Van pollen and stable oxygen isotope record allow the identification of millennial-scale vegetation and environmental changes in eastern Anatolia throughout the last glacial. The climate within the last glacial period (∼75-15 ka BP) was cold and dry, with low arboreal pollen (AP) levels. The driest and coldest period corresponds to Marine Isotope Stage (MIS) 2 (∼28-14.5 ka BP) dominated by the highest values of xerophytic steppe vegetation. Our high-resolution multi proxy record shows rapid expansions and contractions that mimic the stadial-interstadial pattern of the Dansgaard-Oeschger (DO) events as recorded in the Greenland ice cores, and thus, provide a linkage to North Atlantic climate oscillations. Periods of reduced moisture availability characterized at Lake Van by enhanced xerophytic species correlates well with increase in ice-rafted debris (IRD) and a decrease of sea surface temperature (SST) in the North Atlantic. Furthermore, comparison with the marine realm reveals that the complex atmosphere-ocean interaction can be recognized by the strength and position of the westerlies in eastern Anatolia. Influenced by rough topography at Lake Van, the expansion of temperate species (e.g. deciduous Quercus) was stronger during interstadials DO 19, 17-16, 14, 12 and 8. However, Heinrich events (HE), characterized by highest concentrations of ice-rafted debris in marine sediments, are identified in eastern Anatolia by AP values not lower and high steppe components not more abundant than during DO stadials. In addition, this work is a first attempt to establish a continuous microscopic charcoal record over the last glacial in the Near East, which documents an initial immediate response to millennial-scale climate and environmental variability and enables the shed light on the history of fire activity during the last glacial.

  10. Abrupt climate fluctuations in the tropics: the influence of Atlantic Ocean circulation

    NASA Astrophysics Data System (ADS)

    Street-Perrott, F. Alayne; Perrott, R. Alan

    1990-02-01

    Several prolonged droughts in the Sahel and tropical Mexico during the past 14,000 years were coincident with large injections of fresh water into the northern North Atlantic Ocean. The link between these phenomena lies in the thermohaline circulation of the oceans: input of fresh water decreases salinity leading to reduced North Atlantic Deep Water formation and anomalies of sea surface temperature of the kind associated with decreased rainfall in the northern tropics. Ice-sheet disintegration, the most important source of fresh-water input to the oceans, should therefore be considered explicitly in models of past and future climate.

  11. Abrupt climate oscillations during the last deglaciation in central north america

    PubMed

    Yu; Eicher

    1998-12-18

    Evidence from stable isotopes and a variety of proxies from two Ontario lakes demonstrate that many of the late glacial-to-early Holocene events that are well known from the North Atlantic seaboard, such as the Gerzensee-Killarney Oscillation (also known as the Intra-Allerod Cold Period), Younger Dryas, and Preboreal Oscillation, also occurred in central North America. These results thus imply that climatic forcing acted in the same manner in both regions and that atmospheric circulation played an important role in the propagation of these events.

  12. Abrupt onset of a second energy gap at the superconducting transition of underdoped Bi2212

    SciTech Connect

    Hussain, Zahid; Lee, W.S.; Vishik, I.M.; Tanaka, K.; Lu, D.H.; Sasagawa, T.; Nagaosa, N.; Devereaux, T.P.; Hussain, Z.; Shen, Z.-X.

    2007-05-26

    he superconducting gap--an energy scale tied to the superconducting phenomena--opens on the Fermi surface at the superconducting transition temperature (Tc) in conventional BCS superconductors. In underdoped high-Tc superconducting copper oxides, a pseudogap (whose relation to the superconducting gap remains a mystery) develops well above Tc (refs 1, 2). Whether the pseudogap is a distinct phenomenon or the incoherent continuation of the superconducting gap above Tc is one of the central questions in high-Tc research3, 4, 5, 6, 7, 8. Although some experimental evidence suggests that the two gaps are distinct9, 10, 11, 12, 13, 14, 15, 16, 17, 18, this issue is still under intense debate. A crucial piece of evidence to firmly establish this two-gap picture is still missing: a direct and unambiguous observation of a single-particle gap tied to the superconducting transition as function of temperature. Here we report the discovery of such an energy gap in underdoped Bi2Sr2CaCu2O8+delta in the momentum space region overlooked in previous measurements. Near the diagonal of Cu?O bond direction (nodal direction), we found a gap that opens at Tc and has a canonical (BCS-like) temperature dependence accompanied by the appearance of the so-called Bogoliubov quasi-particles, a classical signature of superconductivity. This is in sharp contrast to the pseudogap near the Cu?O bond direction (antinodal region) measured in earlier experiments19, 20, 21.

  13. Association between the transition from unemployment to re-employment after abrupt bankruptcy and the depressive symptoms.

    PubMed

    Nagatomi, Kaori; Ishitake, Tatsuya; Hara, Kunio; Shigemoto, Akira; Hoshiko, Michiko; Tsuji, Yoshiyasu; Yamaguchi, Yoshie; Tamaki, Hideki; Furumura, Mitsuyo; Muramoto, Junko

    2010-01-01

    The study aimed to examine the effects of long-term unemployment and the transition from unemployment to re-employment after abrupt bankruptcy on the mental health of unemployed Japanese. The cases of 96 men and 54 women who were laid off by a large shoemaking company because of sudden bankruptcy in 1998, were examined for one year. The mental health of these individuals was evaluated using a 'self-rating questionnaire for depression (SRQ-D)'. The respondents were categorized by employment transition status into four groups: (1) still employed full-time, (2) unemployment to full-time employment, (3) unemployment to part-time employment, and (4) still unemployed. The prevalence rate of depressive symptoms in the 'still unemployed' group was significantly higher (adjusted odds ratio (OR) = 4.33) than in the still employed group. Moreover, high levels of depressive symptoms were observed in the individuals in the 'unemployment to part-time employment' group (adjusted OR = 4.93). There was no significant risk of depressive tendency among individuals in the 'unemployment to full-time employment' group. The results suggest that the negative effect of re-employment to part-time employment on depressive symptoms is similar to that in long-term unemployment.

  14. Abrupt climate and vegetation variability of eastern Anatolia during the last glacial

    NASA Astrophysics Data System (ADS)

    Pickarski, N.; Kwiecien, O.; Langgut, D.; Litt, T.

    2015-11-01

    Detailed analyses of the Lake Van pollen, Ca / K ratio, and stable oxygen isotope record allow the identification of millennial-scale vegetation and environmental changes in eastern Anatolia throughout the last glacial (~ 111.5-11.7 ka BP). The climate of the last glacial was cold and dry, indicated by low arboreal pollen (AP) levels. The driest and coldest period corresponds to Marine Isotope Stage (MIS) 2 (~ 28-14.5 ka BP), which was dominated by highest values of xerophytic steppe vegetation. Our high-resolution multi-proxy record shows rapid expansions and contractions of tree populations that reflect variability in temperature and moisture availability. These rapid vegetation and environmental changes can be related to the stadial-interstadial pattern of Dansgaard-Oeschger (DO) events as recorded in the Greenland ice cores. Periods of reduced moisture availability were characterized by enhanced occurrence of xerophytic species and high terrigenous input from the Lake Van catchment area. Furthermore, the comparison with the marine realm reveals that the complex atmosphere-ocean interaction can be explained by the strength and position of the westerlies, which are responsible for the supply of humidity in eastern Anatolia. Influenced by the diverse topography of the Lake Van catchment, more pronounced DO interstadials (e.g., DO 19, 17-16, 14, 12 and 8) show the strongest expansion of temperate species within the last glacial. However, Heinrich events (HE), characterized by highest concentrations of ice-rafted debris (IRD) in marine sediments, cannot be separated from other DO stadials based on the vegetation composition in eastern Anatolia. In addition, this work is a first attempt to establish a continuous microscopic charcoal record for the last glacial in the Near East. It documents an immediate response to millennial-scale climate and environmental variability and enables us to shed light on the history of fire activity during the last glacial.

  15. Little Ice Age to modern climate transition of Meso-American climate derived from speleothems

    NASA Astrophysics Data System (ADS)

    Winter, A.; Miller, T.; Kushnir, Y.; Black, D. E.; Estrella, J.; Burnett, A.; Haug, G. H.; Breitenbach, S.; Beaufort, L.; Edwards, R.

    2011-12-01

    We present a high-resolution (annual) reconstruction of hydrological variability from a speleothem located in a cave under the Guatemala/Belize (G/B) border. Our age model is highly constrained by annual layering in the speleothem and nine U/Th MC ICPMS dates. Our δ18O record from 1640 to 2005 A.D. shows two large, abrupt decreases in inferred precipitation rates that appear to coincide with historical, large volcanic eruptions, superimposed on a general drying trend. The first abrupt increase in aridity occurred synchronously with the Tambora eruption in 1815, followed by another sharp decrease in Meso-American precipitation coincident with the eruption of Krakatau in 1883. Both drying events extend for thirty to forty years after the initial eruption, in good agreement with the 19th century drying and the "volcanic dust veil index" from Lamb (1970). Preliminary analysis indicates that the Meso-Americas may be highly sensitive to volcanic forcing because they receive considerable climate input from both Atlantic (primary) and Pacific (secondary) influences. Past volcanic aerosol model loading patterns from the Mt. Pinatubo eruption produced global and in particular, North Atlatic cooling. This could have moved the Atlantic ITCZ southwards and caused drying in Meso-America. Wavelet analysis of the speleothem data also shows ENSO scale variability. Our results highlight the need for better understanding of the consequences of volcanic eruptions and their patterns of climate variability, in particular during the transition from the Little Ice Age to the modern industrial era.

  16. Abrupt community transitions and cyclic evolutionary dynamics in complex food webs☆

    PubMed Central

    Takahashi, Daisuke; Brännström, Åke; Mazzucco, Rupert; Yamauchi, Atsushi; Dieckmann, Ulf

    2013-01-01

    Understanding the emergence and maintenance of biodiversity ranks among the most fundamental challenges in evolutionary ecology. While processes of community assembly have frequently been analyzed from an ecological perspective, their evolutionary dimensions have so far received less attention. To elucidate the eco-evolutionary processes underlying the long-term build-up and potential collapse of community diversity, here we develop and examine an individual-based model describing coevolutionary dynamics driven by trophic interactions and interference competition, of a pair of quantitative traits determining predator and prey niches. Our results demonstrate the (1) emergence of communities with multiple trophic levels, shown here for the first time for stochastic models with linear functional responses, and (2) intermittent and cyclic evolutionary transitions between two alternative community states. In particular, our results indicate that the interplay of ecological and evolutionary dynamics often results in extinction cascades that remove the entire trophic level of consumers from a community. Finally, we show the (3) robustness of our results under variations of model assumptions, underscoring that processes of consumer collapse and subsequent rebound could be important elements of understanding biodiversity dynamics in natural communities. PMID:23948552

  17. Abrupt climatic changes as triggering mechanisms of massive volcanic collapses: examples from Mexico (Invited)

    NASA Astrophysics Data System (ADS)

    Capra, L.

    2010-12-01

    Climate changes have been considered to be a triggering mechanism for large magmatic eruptions. However they can also trigger volcanic collapses, phenomena that cause the destruction of the entire sector of a volcano, including its summit. During the past 30 ka, major volcanic collapses occurred just after main glacial peaks that ended with a rapid deglaciation. Glacial debuttressing, load discharge and fluid circulation coupled with the post-glacial increase of humidity and heavy rains can activate the failure of unstable edifices. Looking at the synchronicity of the maximum glaciations during the late Pleistocene and Holocene in the northern and southern hemispheres it is evident that several volcanic collapses are absent during a glacial climax, but start immediately after it during a period of rapid retreat. Several examples can be detected around the world and Mexico is not an exception. The 28 ka Nevado de Toluca volcanic collapse occurred during an intraglacial stage, under humid conditions as evidenced by paleoclimatic studies on lacustrine sediments of the area. The debris avalanche deposit associated to this event clearly shows evidence of a large amount of water into the mass previous to the failure that enhanced its mobility. It also contains peculiar, plastically deformed, m-sized fragment of lacustrine sediments eroded from glacial berms. The 17 ka BP collapse of the Colima Volcano corresponds to the initial stage of glacial retreat in Mexico after the Last Glacial Maximum (22-17.5ka). Also in this case the depositional sequence reflects high humidity conditions with voluminous debris flow containing a large amount logs left by pine trees. The occurrence of cohesive debris flows originating from the failure of a volcanic edifice can also reflect the climatic conditions, indicating important hydrothermal alteration and fluid circulation from ice-melting at an ice-capped volcano, as observed for example at the Pico de Orizaba volcano for the Tetelzingo

  18. Climate, paleoecology and abrupt change during the Late Proterozoic: A consideration of causes and effects

    NASA Astrophysics Data System (ADS)

    McMenamin, Mark A. S.

    This chapter examines the influence of the biosphere on the initiation, and termination of, the glaciations of the late Proterozoic. Recent considerations suggest that the biosphere controlled the timing of the onset of glaciation and also controlled the timing of the end of glaciation. Massive carbonate accumulation and giant stromatolites of the Late Proterozoic, combined with major blooms of phytoplankton, led to significant drops in the carbon dioxide content of the atmosphere, and forced climate from greenhouse to icehouse conditions. Cryoconites and hyperscums, each with a distinctively adapted cryophilic microbiota, developed during the Proterozoic ice ages and may have been a factor in melting the ice. The Proterozoic Tindir Group, Alaska provides evidence for such a cryophilic microbiota. Only by invoking the activity of such organisms can we explain the rapidity of deglaciation. A propensity to accumulate massive carbonates was present before the glaciation as well as after the deposition of the cap carbonates. Substrate disturbance by burrowing metazoa after the ice ages disrupted the microbial mat component of Proterozoic carbonate sequestration. Stromatolites after the glaciation tend to have porous, clotted and thrombolitic textures instead of evenly laminated textures and would therefore be less effective at retaining carbon dioxide (as carbonate and organic matter) and keeping it out of marine circulation. Newly emergent, burrowing metazoa of the Late Proterozoic eventually halted the development of ice-age inducing conditions, and may have prevented even worse glaciations by releasing hydrocarbons sequestered in seafloor sediment.

  19. Abrupt State Change in Spatially-Patterned Subalpine Forests in Northern Colorado During the Medieval Climate Anomaly

    NASA Astrophysics Data System (ADS)

    Calder, W. J.; Shuman, B. N.

    2014-12-01

    Spatial patterns in many ecosystems arise from feedbacks associated with the potential for critical transitions and multiple stable states. Such systems may be susceptible to abrupt change, which could be indicated by early-warning signals, such as critical slowing down (increasingly long recovery from perturbation as a threshold approaches). Paleoecological data from ribbon forests, a type of subalpine parkland found in the Rocky Mountains, offer an opportunity to test these hypotheses. The forests consist of alternating strips of forest and meadow that form because bands of Picea and Abies trees act as snow fences with large snowdrifts forming on their lee sides. Drifts provide moisture for the adjacent trees, but also increase seedling mortality and shorten the growing season where drifts accumulate. The feedbacks between forest growth and snow accumulation maintain the ribbon forest-meadow pattern, and raise the potential for abrupt change if the feedbacks breakdown in response to factors like drought or fire. Our fossil pollen data from Summit Lake, located on the Continental Divide in the Park Range, northern Colorado, indicate that a closed forest transitioned rapidly to a ribbon forest state at ca. 1000 BP. Artemisia pollen increased (20 to 35%) and Picea and Abies pollen decreased (25 to 15%) within a century or less after a pair of charcoal peaks. Decreased charcoal influx (from 0.6 to 0.4 pieces/cm2/yr) and fire frequency (from 4.5 to 1.5 fires/ka) coincided with the pollen assemblage changes, and is consistent with decreased landscape biomass and fuel connectivity. Initial analyses show evidence of critical slowing down before the state change. After eight of eleven fires recorded by peaks in charcoal accumulation, Artemisia pollen percentages rise to a peak consistent with brief opening of the initially forested landscape. After 2000 BP, the magnitude and duration of the post-fire changes increases until no recovery is recorded after the shift at 1000

  20. Climate and Antartic Intermediate Water Covariations on Centennial-Millennial Timescales during MIS 3—Constraining the Role of the "Oceanic Tunnel" in Abrupt Climate Change.

    NASA Astrophysics Data System (ADS)

    Kleiven, H. F.; Ninnemann, U.

    2014-12-01

    The equatorward ventilation of Southern Hemisphere extratropical water masses to the low latitude thermocline has been proposed as a window through which the high latitude ocean can modulate tropical climate on anything from decadal to orbital timescales. This hypothesis is founded largely on the observation that tropical thermocline waters originate mostly in the Southern Hemisphere and that computer simulations suggest property anomalies in these source regions can advect through the intermediate ocean, "the ocean tunnel" to influence tropical SST. However, few observational records of extratropical ocean changes are available to assess their impacts on multi-decadal and longer timescales. Here we add to the observational record using new decadally resolved planktonic and benthic foraminiferal isotopic records spanning MIS 3 (20-50 ka) from the Chilean slope ODP Site 1233 that is located on the northern margin of the Antarctic Circumpolar Current and its seafloor lies in the core of Antarctic Intermediate Water (AAIW). Thus the site is ideally situated to reconstruct both near surface and AAIW variability in the high southern latitudes. On centennial to millennial timescales, changes in intermediate water properties track those in the near surface albeit with a reduced amplitude—confirming the idea that changes in the extratropical ocean effect the oceanic tunnel on these timescales. The new benthic and plantic foraminiferal isotope results demonstrate that variations in intermediate ocean properties and climate of the southeast Pacific closely align with those recorded in the EPICA ice core from Dronning Maud Land. Such abrupt, synoptic scale changes in Antarctic climate and dynamics will have potentially widespread climatic and biogeochemical consequences along the downstream flowpath of AAIW. The broad coherence of the observed Antarctic signal supports the concept of hemispheric thermal asynchrony on millennial timescales, and the extension of this climate

  1. 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.

  2. 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

  3. 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.

  4. Factors influencing doping control and abrupt metallurgical transitions during atmospheric pressure MOVPE growth of AlGaAs and GaAs

    NASA Astrophysics Data System (ADS)

    Roberts, J. S.; Mason, N. J.; Robinson, M.

    1984-09-01

    Atmospheric pressure MOVPE of GaAs and AlGaAs has been investigated using two gas handling systems and a conventional horizontal reactor. Initially a simple source/carrier gas manifold design was assessed but severe retention of reagents in the pipework resulted in poor control of doping and interface abruptness. However, integration of the reagent and carrier gas in a pressure balanced vent/run configuration gave a significant improvement. AlGaAs/GaAs multilayers and n +/n - GaAs transitions have been used to assess the performance of both systems. Abrupt p-type doping transitions using bis-cyclopentadienylmagnesium proved unsuccessful as long doping tails were observed.

  5. The significance of abrupt transitions in Lineweaver-Burk plots with particular reference to glutamate dehydrogenase. Negative and positive co-operativity in catalytic rate constants.

    PubMed

    Engel, P C; Ferdinand, W

    1973-01-01

    1. Lineweaver-Burk plots for glutamate dehydrogenase, glucose 6-phosphate dehydrogenase and several other enzymes show one or more abrupt transitions between apparently linear sections. These transitions correspond to abrupt increases in the apparent K(m) and V(max.) with increasing concentration of the varied substrate. 2. The generalized reciprocal initial-rate equation for a multi-site enzyme requires several restrictions to be put on it in order to generate such plots. These mathematical conditions are explored. 3. It is shown that the effective omission of a term in the denominator of the reciprocal initial-rate equation represents a minimal requirement for generation of abrupt transitions. This corresponds in physical terms to negative co-operativity followed by positive co-operativity affecting the catalytic rate constant for the reaction. 4. Previous models for glutamate dehydrogenase cannot adequately account for the results. On the other hand, the model based on both negative and positive co-operativity gives a good fit to the experimental points. 5. The conclusions are discussed in relation to current knowledge of the structure and mechanism of glutamate dehydrogenase.

  6. Climatic and human impacts on quasi-periodic and abrupt changes of sedimentation rate at multiple time scales in Lake Taihu, China

    NASA Astrophysics Data System (ADS)

    Liu, Huiyu; Xu, Xiaojuan; Lin, Zhenshan; Zhang, Mingyang; Mi, Ying; Huang, Changchun; Yang, Hao

    2016-12-01

    With the ensemble Empirical Mode Decomposition Method (EEMD) and the non-parametric Mann-Kendall Test, the quasi-periodic and abrupt changes of sedimentation rate at multiple time scales, and their relations to climate changes and human activities from 1951 to 2010 in Meiliang Bay of Lake Taihu (China) were studied. The results showed the following. (1) The change in sedimentation rate can be completely decomposed into three quasi-periodic changes on 3.7, 6.4, and 24-yr time scales, and a long-term trend. (2) The quasi-periodic changes in sedimentation rate are significantly and positively related to changes in annual average temperature at 6.4 and 24-yr time scales and human activities at 3.7-yr time scales, and not significantly related to precipitation at these time scales. The trend of sedimentation rate has a negative relation with temperature, but positive relations with precipitation and human activities. As a whole, the total variance contribution of climate changes to the quasi-periodic changes of sedimentation rate is close to that of human activities; (3) Temperature and precipitation are possibly related to the abrupt change of sedimentation rate as a whole. Floods have significant impacts on abrupt changes in the sedimentation rate at 3.7, 6.4 and 24-yr time scales. Moreover, some abrupt changes of sedimentation rate at 3.7- and 6.4-yr time scales are partly related to the changes of precipitation at 3.1-yr time scale and temperature at 5-yr time scale. The results of this study will help identify the impacts of climate change and human activities on lake sedimentation at different time scales, and will be available for use as a guide for reasonable development and effective protection of lake resources.

  7. Lateglacial/early Holocene fluvial reactions of the Jeetzel river (Elbe valley, northern Germany) to abrupt climatic and environmental changes

    NASA Astrophysics Data System (ADS)

    Turner, Falko; Tolksdorf, Johann Friedrich; Viehberg, Finn; Schwalb, Antje; Kaiser, Knut; Bittmann, Felix; von Bramann, Ullrich; Pott, Richard; Staesche, Ulrich; Breest, Klaus; Veil, Stephan

    2013-01-01

    Mechanisms of climatic control on river system development are still only partially known. Palaeohydrological investigations from river valleys often lack a precise chronological control of climatic processes and fluvial dynamics, which is why their specific forces remain unclear. In this multidisciplinary case study from the middle Elbe river valley (northern Germany) multiple dating of sites (palynostratigraphy, radiocarbon- and OSL-dating) and high-resolution analyses of environmental and climatological proxies (pollen, plant macro-remains and ostracods) reveal a continuous record of the environmental and fluvial history from the Lateglacial to the early Holocene. Biostratigraphical correlation to northwest European key sites shows that river system development was partially out of phase with the main climatic shifts. The transition from a braided to an incised channel system predated the main phase of Lateglacial warming (˜14.6 ka BP), and the meandering river did not change its drainage pattern during the cooling of the Younger-Dryas period. Environmental reconstructions suggest that river dynamics were largely affected by vegetation cover, as a vegetation cover consisting of herbs, dwarf-shrubs and a few larger shrubs seems to have developed before the onset of the main Lateglacial warming, and pine forests appear to have persisted in the river valley during the Younger Dryas. In addition, two phases of high fluvial activity and new channel incision during the middle part of the Younger Dryas and during the Boreal were correlated with changes from dry towards wet climatic conditions, as indicated by evident lake level rises. Lateglacial human occupation in the river valley, which is shown by numerous Palaeolithic sites, forming one of the largest settlement areas of that period known in the European Plain, is assigned to the specific fluvial and environmental conditions of the early Allerød.

  8. Climate change mitigation through livestock system transitions

    PubMed Central

    Havlík, Petr; Valin, Hugo; Herrero, Mario; Obersteiner, Michael; Schmid, Erwin; Rufino, Mariana C.; Mosnier, Aline; Thornton, Philip K.; Böttcher, Hannes; Conant, Richard T.; Frank, Stefan; Fritz, Steffen; Fuss, Sabine; Kraxner, Florian; Notenbaert, An

    2014-01-01

    Livestock are responsible for 12% of anthropogenic greenhouse gas emissions. Sustainable intensification of livestock production systems might become a key climate mitigation technology. However, livestock production systems vary substantially, making the implementation of climate mitigation policies a formidable challenge. Here, we provide results from an economic model using a detailed and high-resolution representation of livestock production systems. We project that by 2030 autonomous transitions toward more efficient systems would decrease emissions by 736 million metric tons of carbon dioxide equivalent per year (MtCO2e⋅y−1), mainly through avoided emissions from the conversion of 162 Mha of natural land. A moderate mitigation policy targeting emissions from both the agricultural and land-use change sectors with a carbon price of US$10 per tCO2e could lead to an abatement of 3,223 MtCO2e⋅y−1. Livestock system transitions would contribute 21% of the total abatement, intra- and interregional relocation of livestock production another 40%, and all other mechanisms would add 39%. A comparable abatement of 3,068 MtCO2e⋅y−1 could be achieved also with a policy targeting only emissions from land-use change. Stringent climate policies might lead to reductions in food availability of up to 200 kcal per capita per day globally. We find that mitigation policies targeting emissions from land-use change are 5 to 10 times more efficient—measured in “total abatement calorie cost”—than policies targeting emissions from livestock only. Thus, fostering transitions toward more productive livestock production systems in combination with climate policies targeting the land-use change appears to be the most efficient lever to deliver desirable climate and food availability outcomes. PMID:24567375

  9. Climate change mitigation through livestock system transitions.

    PubMed

    Havlík, Petr; Valin, Hugo; Herrero, Mario; Obersteiner, Michael; Schmid, Erwin; Rufino, Mariana C; Mosnier, Aline; Thornton, Philip K; Böttcher, Hannes; Conant, Richard T; Frank, Stefan; Fritz, Steffen; Fuss, Sabine; Kraxner, Florian; Notenbaert, An

    2014-03-11

    Livestock are responsible for 12% of anthropogenic greenhouse gas emissions. Sustainable intensification of livestock production systems might become a key climate mitigation technology. However, livestock production systems vary substantially, making the implementation of climate mitigation policies a formidable challenge. Here, we provide results from an economic model using a detailed and high-resolution representation of livestock production systems. We project that by 2030 autonomous transitions toward more efficient systems would decrease emissions by 736 million metric tons of carbon dioxide equivalent per year (MtCO2e⋅y(-1)), mainly through avoided emissions from the conversion of 162 Mha of natural land. A moderate mitigation policy targeting emissions from both the agricultural and land-use change sectors with a carbon price of US$10 per tCO2e could lead to an abatement of 3,223 MtCO2e⋅y(-1). Livestock system transitions would contribute 21% of the total abatement, intra- and interregional relocation of livestock production another 40%, and all other mechanisms would add 39%. A comparable abatement of 3,068 MtCO2e⋅y(-1) could be achieved also with a policy targeting only emissions from land-use change. Stringent climate policies might lead to reductions in food availability of up to 200 kcal per capita per day globally. We find that mitigation policies targeting emissions from land-use change are 5 to 10 times more efficient--measured in "total abatement calorie cost"--than policies targeting emissions from livestock only. Thus, fostering transitions toward more productive livestock production systems in combination with climate policies targeting the land-use change appears to be the most efficient lever to deliver desirable climate and food availability outcomes.

  10. Abrupt transition to heightened poliomyelitis epidemicity in England and Wales, 1947-1957, associated with a pronounced increase in the geographical rate of disease propagation.

    PubMed

    Smallman-Raynor, M R; Cliff, A D

    2014-03-01

    The abrupt transition to heightened poliomyelitis epidemicity in England and Wales, 1947-1957, was associated with a profound change in the spatial dynamics of the disease. Drawing on the complete record of poliomyelitis notifications in England and Wales, we use a robust method of spatial epidemiological analysis (swash-backwash model) to evaluate the geographical rate of disease propagation in successive poliomyelitis seasons, 1940-1964. Comparisons with earlier and later time periods show that the period of heightened poliomyelitis epidemicity corresponded with a sudden and pronounced increase in the spatial rate of disease propagation. This change was observed for both urban and rural areas and points to an abrupt enhancement in the propensity for the geographical spread of polioviruses. Competing theories of the epidemic emergence of poliomyelitis in England and Wales should be assessed in the light of this evidence.

  11. Neanderthal and Anatomically Modern Human interaction with Abrupt Late Pleistocene Environments - the data is finally good enough to talk about climate change!

    NASA Astrophysics Data System (ADS)

    Blockley, Simon; Schreve, Danielle

    2015-04-01

    The timing and nature of the appearance of Anatomically Modern Humans (AMH) in Europe, their interaction with, and eventual morphological replacement of Neanderthals (despite some shared genetic heritage) has been a matter of intense debate within archaeology for a generation. This period, often termed the Middle to Upper Palaeolithic transition occurs in the latter part of Marine Isotope Stage Three and in recent decades archaeological interest has been complemented by the input of palaeoclimate scientists, over the role of abrupt climate change in this process. This was due to the recognition from ice core and marine proxy archives, in particular, of periods if intense cooling, correlated to the marine record of Heinrich ice rafted debris layers from the Atlantic. As a result of these collaborations between the archaeological and palaeoenvironmental communities various drivers have been proposed for the Middle to Upper Palaeolithic Transition that include: (1) resource competition between two species occupying similar niches; (2) the impact of repeated cycles of Heinrich event cooling, leading to the decline and eventual disappearance of the Neanderthal populations, leaving a new region open for AMH exploitation; and (3) catastrophic impacts of large volcanic eruptions on Neanderthal populations. Attempts to address the above hypotheses have been dogged by the chronological precision available for a number of key archives. The accuracy of many of the radiocarbon ages that underpin the chronology for both Neanderthal and AMH archaeological sites has been questioned1. This has been exacerbated by uncertainties over the influence of variability in the radiocarbon marine reservoir effect on marine palaeoclimate records and a marine dominated radiocarbon calibration curve. Additionally, the counting uncertainties of the master Greenland palaeoclimate archives are also large by this time, meaning palaeoclimate interpretation can be equivocal. However, several research

  12. Climate-driven shifts in continental net primary production implicated as a driver of a recent abrupt increase in the land carbon sink

    NASA Astrophysics Data System (ADS)

    Buermann, Wolfgang; Beaulieu, Claudie; Parida, Bikash; Medvigy, David; Collatz, George J.; Sheffield, Justin; Sarmiento, Jorge L.

    2016-03-01

    The world's ocean and land ecosystems act as sinks for anthropogenic CO2, and over the last half century their combined sink strength grew steadily with increasing CO2 emissions. Recent analyses of the global carbon budget, however, have uncovered an abrupt, substantial ( ˜ 1 PgC yr-1) and sustained increase in the land sink in the late 1980s whose origin remains unclear. In the absence of this prominent shift in the land sink, increases in atmospheric CO2 concentrations since the late 1980s would have been ˜ 30 % larger than observed (or ˜ 12 ppm above current levels). Global data analyses are limited in regards to attributing causes to changes in the land sink because different regions are likely responding to different drivers. Here, we address this challenge by using terrestrial biosphere models constrained by observations to determine if there is independent evidence for the abrupt strengthening of the land sink. We find that net primary production significantly increased in the late 1980s (more so than heterotrophic respiration), consistent with the inferred increase in the global land sink, and that large-scale climate anomalies are responsible for this shift. We identify two key regions in which climatic constraints on plant growth have eased: northern Eurasia experienced warming, and northern Africa received increased precipitation. Whether these changes in continental climates are connected is uncertain, but North Atlantic climate variability is important. Our findings suggest that improved understanding of climate variability in the North Atlantic may be essential for more credible projections of the land sink under climate change.

  13. Six-decade temporal change and seasonal decomposition of climate variables in Lake Dianchi watershed (China): stable trend or abrupt shift?

    NASA Astrophysics Data System (ADS)

    Zhou, Jing; Liang, Zhongyao; Liu, Yong; Guo, Huaicheng; He, Dan; Zhao, Lei

    2015-01-01

    Meteorological trend analysis is a useful tool for understanding climate change and can provide useful information on the possibility of future change. Lake Dianchi is the sixth largest freshwater body in China with serious eutrophication. Algal blooms outbreak was proven to be closely associated with some climatic factors in Lake Dianchi. It is therefore essential to explore the trends of climatic time series to understand the mechanism of climate change on lake eutrophication. We proposed an integrated method of Mann-Kendall (MK) test, seasonal-trend decomposition using locally weighted regression (LOESS) (STL), and regime shift index (RSI) to decompose the trend analysis and identify the stable and abrupt changes of some climate variables from 1951 to 2009. The variables include mean air temperature (Tm), maximum air temperatures (Tmax), minimum air temperatures (Tmin), precipitation (Prec), average relative humidity (Hum), and average wind speed (Wind). The results showed that (a) annual Tm, Tmax, and Tmin have a significant increasing trend with the increasing rates of 0.26, 0.15and 0.43 °C per decade, respectively; (b) annual precipitation has an insignificant decreasing trend with the decreasing rate of 3.17 mm per decade; (c) annual Hum has a significant decreasing trend in all seasons; and (d) there are two turning points for temperature rise around 1980 and 1995 and two abrupt change periods for precipitation with the extreme points appearing in 1963 and 1976. Temperature rise and precipitation decline in summer and autumn as well as wind speed decrease after the 1990s may be an important reason for algal blooms outbreak in Lake Dianchi. This study was expected to provide foundation and reference for regional water resource management.

  14. Climate transition on Mars: a simple solution.

    NASA Astrophysics Data System (ADS)

    Shaw, G. H.

    2008-12-01

    Evidence for the presence of flowing water on the Martian surface at some time in the distant past is most persuasive. The current cold, dry climate and low atmospheric pressure precludes liquid surface water for any extended period of time, and these conditions seem to have generally prevailed since 1-2 Ga after Mars" formation. Water in unknown quantities (but presumably substantial) and CO2 in relatively small amounts are well established by many observations. The considerable difficulty of producing a warm, wet Mars under present solar output pales in comparison to producing these conditions when the sun was less luminous. Attempts to model such a climate using CO2 as the main greenhouse gas lead to very high atmospheric concentrations, which should have left an obvious signature. The absence of significant carbonate mineral deposits suggests that CO2 was not likely ever present in the atmosphere at the necessary concentrations. Alternative greenhouse gases, such as methane and ammonia, have met with the same objections applied to similar discussions of the early climate of Earth, namely the instability of these gases under ultraviolet light. This may be slightly less problematical for Mars given the greater distance from the sun. However, if the major reservoir for surface carbon on Mars was as organic compounds, the resolution to the climate problem could lie in the regeneration of methane (and perhaps ammonia) by volcanically-driven hydrothermal processing of these organics in the presence of water. Maintenance of sufficiently high levels of these potent greenhouse gases would have depended on continued thermal activity, especially early in Mars history when the faint young sun required especially high levels, and when thermal sources were undoubtedly greater than at present. The climate transition from warm and wet to cold and dry (in spite of the increasing luminosity of the sun) was the result of the exponential decay of thermal activity on the relatively

  15. Links between abrupt change in tropical hydroclimate, high-latitude climate change, and atmospheric greenhouse gases during the last ice age

    NASA Astrophysics Data System (ADS)

    Brook, E.; Rhodes, R.; Marcott, S. A.; Bauska, T. K.; Edwards, J. S.; Rosen, J. L.; Ahn, J.; Severinghaus, J. P.; Petrenko, V. V.; Menking, J. A.; Kalk, M.

    2015-12-01

    Development of very high-resolution data from polar ice cores over the last decade reveals a rich spectrum of greenhouse gas variability and its relationship to both tropical and subtropical hydroclimate and high-latitude abrupt climate change. The well-known atmospheric methane variations associated with Dansgaard-Oeschger events are now strongly linked to enhanced wetland emissions in the northern tropics based on recent work on the interpolar methane gradient. An increase in tropical rainfall associated with ITCZ migration is consistent with these observations. In addition, small, on order 5-10 ppm, changes in carbon dioxide accompany at least some Dansgaard-Oeschger events. Changes in terrestrial carbon storage, possibly in the tropics, are one explanation, but new stable isotope measurements indicate that this cannot be the only source for these events, and suggest that rising sea surface temperature must contribute. Very detailed recent data reveal variability during Greenlandic stadial periods that add to the potential links between greenhouse gases and tropical hydroclimate. During the last ice age and deglaciation, small, but rapid increases in atmospheric methane during some "Heinrich Stadials" suggest increases in methane emissions from the southern tropics associated with Heinrich events, possibly due to extreme southerly migration of rainfall belts associated with the ITCZ. Abrupt increases in carbon dioxide occur at precisely the same time as many of these Heinrich Stadial methane events. Stable isotopic data related to two of these abrupt carbon dioxide changes (during HS1 and preliminarily for HS 4) implicate an isotopically depleted source. Rapid release of terrestrial carbon (possibly due to drying in the northern tropics) is a possible explanation, although release of respiratory carbon dioxide from an ocean source (for example, due to increases in southern ocean upwelling) is another plausible alternative, albeit one that requires a fast oceanic

  16. Climate Transition on Mars: Solution and Implications

    NASA Astrophysics Data System (ADS)

    Shaw, G. H.

    2009-05-01

    Evidence for the presence of flowing water on the Martian surface is persuasive. The current cold, dry climate and low atmospheric pressure preclude liquid surface water for any extended period of time, and these conditions seem to have generally prevailed for the last 3+ billion years of Martian history. Water in unknown (but presumably substantial) quantities and CO2 in relatively small amounts, are well established by many observations. The considerable difficulty of explaining a warm, wet Mars under present solar output pales in comparison to explaining these conditions early in Martian history when the standard model of stellar evolution predicts that the sun was less luminous. Attempts to model such a climate using CO2 as the main greenhouse gas lead to very high atmospheric concentrations, which should have left an obvious signature. The absence of significant carbonate mineral deposits suggests that CO2 was not likely ever present in the atmosphere at the necessary concentrations. Alternative greenhouse gases, such as methane and ammonia, have met with the same objections applied to similar discussions of the early climate of Earth, but perhaps are slightly less problematical for Mars given the greater distance from the sun. However, if the major reservoir for surface carbon on Mars was as organic compounds, the resolution to the climate problem could lie in the regeneration of methane (and perhaps ammonia) by volcanically-driven hydrothermal processing of these organics in the presence of water. Maintenance of sufficiently high levels of these potent greenhouse gases would have depended on continued thermal activity, especially early in Mars' history when the faint young sun required extra high levels, and when thermal sources were undoubtedly greater than at present. The climate transition from warm and wet to cold and dry (in spite of increasing luminosity of the sun) was the result of the exponential decay of thermal activity on the relatively small

  17. Climate change, human health, and epidemiological transition.

    PubMed

    Barrett, Bruce; Charles, Joel W; Temte, Jonathan L

    2015-01-01

    The health of populations depends on the availability of clean air, water, food, and sanitation, exposure to pathogens, toxins and environmental hazards, and numerous genetic, behavioral and social factors. For many thousands of years, human life expectancy was low, and population growth was slow. The development of technology-based civilizations facilitated what Abdel Omran called "epidemiological transition," with increasing life expectancy and rapid population growth. To a large extent, the spectacular growth of human populations during the past two centuries was made possible by the energy extracted from fossil fuels. We have now learned, however, that greenhouse gases from fossil fuel combustion are warming the planet's surface, causing changes in oceanic and atmospheric systems, and disrupting weather and hydrological patterns. Climate change poses unprecedented threats to human health by impacts on food and water security, heat waves and droughts, violent storms, infectious disease, and rising sea levels. Whether or not humanity can reduce greenhouse gas emissions quickly enough to slow climate change to a rate that will allow societies to successfully adapt is not yet known. This essay reviews the current state of relevant knowledge, and points in a few directions that those interested in human health may wish to consider.

  18. Climate change, human health, and epidemiological transition

    PubMed Central

    Barrett, Bruce; Charles, Joel W.; Temte, Jonathan L.

    2015-01-01

    The health of populations depends on the availability of clean air, water, food, and sanitation, exposure to pathogens, toxins and environmental hazards, and numerous genetic, behavioral and social factors. For many thousands of years, human life expectancy was low, and population growth was slow. The development of technology-based civilizations facilitated what Abdel Omran called “epidemiological transition,” with increasing life expectancy and rapid population growth. To a large extent, the spectacular growth of human populations during the past two centuries was made possible by the energy extracted from fossil fuels. We have now learned, however, that greenhouse gases from fossil fuel combustion are warming the planet's surface, causing changes in oceanic and atmospheric systems, and disrupting weather and hydrological patterns. Climate change poses unprecedented threats to human health by impacts on food and water security, heat waves and droughts, violent storms, infectious disease, and rising sea levels. Whether or not humanity can reduce greenhouse gas emissions quickly enough to slow climate change to a rate that will allow societies to successfully adapt is not yet known. This essay reviews the current state of relevant knowledge, and points in a few directions that those interested in human health may wish to consider. PMID:25434735

  19. Evolution of ocean temperature and ice volume through the mid-Pleistocene climate transition.

    PubMed

    Elderfield, H; Ferretti, P; Greaves, M; Crowhurst, S; McCave, I N; Hodell, D; Piotrowski, A M

    2012-08-10

    Earth's climate underwent a fundamental change between 1250 and 700 thousand years ago, the mid-Pleistocene transition (MPT), when the dominant periodicity of climate cycles changed from 41 thousand to 100 thousand years in the absence of substantial change in orbital forcing. Over this time, an increase occurred in the amplitude of change of deep-ocean foraminiferal oxygen isotopic ratios, traditionally interpreted as defining the main rhythm of ice ages although containing large effects of changes in deep-ocean temperature. We have separated the effects of decreasing temperature and increasing global ice volume on oxygen isotope ratios. Our results suggest that the MPT was initiated by an abrupt increase in Antarctic ice volume 900 thousand years ago. We see no evidence of a pattern of gradual cooling, but near-freezing temperatures occur at every glacial maximum.

  20. What does the study of swamp ecological transition(s) tell us about past climatic conditions in East Africa?

    NASA Astrophysics Data System (ADS)

    Coffinet, Sarah; Huguet, Arnaud; Pedentchouk, Nikolai; Anquetil, Christelle; Kolaczek, Piotr; Kolaczek, Monika; Galka, Marius; Williamson, David; Bergonzini, Laurent; Majule, Amos; Laggoun-Défarge, Fatima; Wagner, Thomas; Derenne, Sylvie

    2016-04-01

    Peatlands represent only 3-5% of the total world land cover (Gorham, 1991) but approximately 20-30% of the total carbon storage of the world. However, they have so far been scarcely used as paleoclimate archives. The aim of this work was to reconstruct past climate and ecological changes through a high-resolution multi-proxy study of a 4 m peat core collected in the Kyambangunguru swamp (SW Tanzania). This core covers the last 4,000 years based on 14C dating of bulk organic matter and macro-remains. Microscopic observations ‒ macro-remains, micro-fossils, palynofacies and pollen ‒ and geochemical analyses ‒ organic carbon and nitrogen contents, branched glycerol dialkyl glycerol tetraethers (br GDGTs), n-alkanes and their H isotopic composition ‒ were combined to track potential ecological changes in the swamp and to relate them to climate forcings. This approach revealed an abrupt ecological transition ca. 2,300 yrs BP ago, when the ecosystem likely changed from a lake to a marsh. In addition, climate variations were investigated through the analysis of specific organic compounds, i.e. long chain n-alkanes and br GDGTs. On the one hand, the change in ecosystem functioning seems associated with an increase in mean annual air temperature of ca. 1 °C according to br GDGT-derived temperature estimates. On the other hand, the hydrogen isotopic composition of plant derived n-alkanes (δ²Hwax), which is related to the isotopic signature of precipitations and with hydrological regimes, did not show any abrupt shift at this period. In conclusion, high coherence between vegetation changes and climate modifications recorded by different proxies was observed along the core. They all indicate the transition from a lake to an acidic marsh ca. 2300 years ago. The onset of marsh formation may have been driven by hydroseral succession processes, i.e. the lake overgrowth by macrophytes, and may have been favoured by a warming climate and a long-term progressive trend

  1. Late second-early first millennium BC abrupt climate changes in coastal Syria and their possible significance for the history of the Eastern Mediterranean

    NASA Astrophysics Data System (ADS)

    Kaniewski, D.; Paulissen, E.; Van Campo, E.; Weiss, H.; Otto, T.; Bretschneider, J.; Van Lerberghe, K.

    2010-09-01

    The alluvial deposits near Gibala-Tell Tweini provide a unique record of environmental history and food availability estimates covering the Late Bronze Age and the Early Iron Age. The refined pollen-derived climatic proxy suggests that drier climatic conditions occurred in the Mediterranean belt of Syria from the late 13th/early 12th centuries BC to the 9th century BC. This period corresponds with the time frame of the Late Bronze Age collapse and the subsequent Dark Age. The abrupt climate change at the end of the Late Bronze Age caused region-wide crop failures, leading towards socio-economic crises and unsustainability, forcing regional habitat-tracking. Archaeological data show that the first conflagration of Gibala occurred simultaneously with the destruction of the capital city Ugarit currently dated between 1194 and 1175 BC. Gibala redeveloped shortly after this destruction, with large-scale urbanization visible in two main architectural phases during the Early Iron Age I. The later Iron Age I city was destroyed during a second conflagration, which is radiocarbon-dated at circa 2950 cal yr BP. The data from Gibala-Tell Tweini provide evidence in support of the drought hypothesis as a triggering factor behind the Late Bronze Age collapse in the Eastern Mediterranean.

  2. The abrupt climate change at the Eocene–Oligocene boundary and the emergence of South-East Asia triggered the spread of sapindaceous lineages

    PubMed Central

    Buerki, Sven; Forest, Félix; Stadler, Tanja; Alvarez, Nadir

    2013-01-01

    Background and Aims Paleoclimatic data indicate that an abrupt climate change occurred at the Eocene–Oligocene (E–O) boundary affecting the distribution of tropical forests on Earth. The same period has seen the emergence of South-East (SE) Asia, caused by the collision of the Eurasian and Australian plates. How the combination of these climatic and geomorphological factors affected the spatio-temporal history of angiosperms is little known. This topic is investigated by using the worldwide sapindaceous clade as a case study. Methods Analyses of divergence time inference, diversification and biogeography (constrained by paleogeography) are applied to a combined plastid and nuclear DNA sequence data set. Biogeographical and diversification analyses are performed over a set of trees to take phylogenetic and dating uncertainty into account. Results are analysed in the context of past climatic fluctuations. Key Results An increase in the number of dispersal events at the E–O boundary is recorded, which intensified during the Miocene. This pattern is associated with a higher rate in the emergence of new genera. These results are discussed in light of the geomorphological importance of SE Asia, which acted as a tropical bridge allowing multiple contacts between areas and additional speciation across landmasses derived from Laurasia and Gondwana. Conclusions This study demonstrates the importance of the combined effect of geomorphological (the emergence of most islands in SE Asia approx. 30 million years ago) and climatic (the dramatic E–O climate change that shifted the tropical belt and reduced sea levels) factors in shaping species distribution within the sapindaceous clade. PMID:23723259

  3. The complex behavior of the Cordilleran Ice Sheet and mountain glaciers to abrupt climate change during the latest Pleistocene

    NASA Astrophysics Data System (ADS)

    Menounos, Brian; Goehring, Brent; Osborn, Gerald; Clarke, Garry K. C.; Ward, Brent; Margold, Martin; Bond, Jeff; Clague, John J.; Lakeman, Tom; Schaefer, Joerg; Koch, Joe; Gosse, John; Stroeven, Arjen P.; Seguinot, Julien; Heyman, Jakob; Fulton, Robert

    2014-05-01

    Surficial mapping and more than 70 radiometric ages 10Be, 14C] constrain the evolution of the Cordilleran Ice Sheet (CIS) and associated mountain glaciers in western Canada during the latest Pleistocene. Our data suggest that: i) there is widespread evidence for the Younger Dryas (YD) throughout the mountains of western Canada; ii) late Pleistocene climate reconstructions based solely on alpine moraines may be misleading in regions with decaying ice sheets; iii) extensive interfluves in some mountain regions were ice-free between 16 ka and 13 ka (kilo calibrated yrs BP). Initial decay of the CIS from its maximum extent around 16 ka was likely due to a combination of climatic (surface melting) and dynamical factors. Climate amelioration during the Bølling-Allerød Warm Period [14.7-12.9 ka], likely the cause for the major phase of CIS decay, resulted in ice sheet equilibrium line altitudes (ELAs) ranging from 2500 m asl in southern BC to around 2000 m asl along the BC-Yukon border. Hence, before the onset of the Younger Dryas (YD) Cold Period [12.9-11.7 ka], the ice sheet shrank and became a labyrinth of individual and coalescing valley glaciers fed by major accumulation zones centered on the Coast Mountains and other high ranges of NW Canada. The response of remnant ice and cirque glaciers to the YD climate deterioration was highly variable. In some cases, small glaciers (0.5-2 km2) built YD moraines that were only hundreds of meters beyond those constructed during the Little Ice Age (LIA) [0.30-0.15 ka]. Our dating also reveals that much larger glaciers persisted in nearby valleys that lie hundreds of meters below the cirques. Hence, we infer that many cirques were completely deglaciated prior the YD, in contrast to low-lying valleys where ice sheet remnants persisted. Glaciers also advanced in north-central British Columbia during the YD, but here glaciers constructed large terminal and lateral moraines. In the Cassiar and northern Coast mountains, for example

  4. Structural, Magnetic, and Photomagnetic Studies of a Mononuclear Iron(II) Derivative Exhibiting an Exceptionally Abrupt Spin Transition. Light-Induced Thermal Hysteresis Phenomenon.

    PubMed

    Létard, Jean-François; Guionneau, Philippe; Rabardel, Louis; Howard, Judith A. K.; Goeta, Andres E.; Chasseau, Daniel; Kahn, Olivier

    1998-08-24

    The new spin-crossover compound Fe(PM-BiA)(2)(NCS)(2) with PM-BiA = N-(2-pyridylmethylene)aminobiphenyl has been synthesized. The temperature dependence of chi(M)T (chi(M) = molar magnetic susceptibility and T = temperature) has revealed an exceptionally abrupt transition between low-spin (LS) (S = 0) and high-spin (HS) (S = 2) states with a well-reproducible hysteresis loop of 5 K (T(1/2) downward arrow = 168 K and T(1/2) upward arrow = 173 K). The crystal structure has been determined both at 298 K in the HS state and at 140 K in the LS state. The spin transition takes place without change of crystallographic space group (Pccn with Z = 4). The determination of the intermolecular contacts in the LS and HS forms has revealed a two-dimensional structural character. The enthalpy and entropy variations, DeltaH and DeltaS, associated with the spin transition have been deduced from heat capacity measurements. DeltaS (= 58 J K(-)(1) mol(-)(1)) is larger than for other spin transition bis(thiocyanato) iron(II) derivatives. At 10 K the well-known LIESST (light-induced excited spin state trapping) effect has been observed within the SQUID cavity, by irradiating a single crystal or a powder sample with a Kr(+) laser coupled to an optical fiber. The magnetic behavior recorded under light irradiation in the warming and cooling modes has revealed a light-induced thermal hysteresis (LITH) effect with 35 < T(1/2) < 77 K. The HS --> LS relaxation after LIESST has been found to deviate from first-order kinetics. The kinetics has been investigated between 10 and 78 K. A thermally activated relaxation behavior at elevated temperatures and a nearly temperature independent tunneling mechanism at low temperatures have been observed. The slow rate of tunneling from the metastable HS state toward the ground LS state may be explained by the unusually large change in Fe-N bond lengths between these two states.

  5. Coccolithophore response to Abrupt and short-term climate changes in the Gulf of Lions (Western Mediterranean) during the last climatic cycle

    NASA Astrophysics Data System (ADS)

    Flores, J.; Gravalosa, J.; Colmenero-Hidalgo, E.; Sierro, F. J.; Canals, M.; Frigola, J.; Grimalt, J.; Berné, S.; Dannielou, B.

    2007-12-01

    Cores PRGL-1 (310 m long) and MD99-2348 (21.5 m long) were recovered in the Gulf of Lions (42.690N; 03.838 E) at 298.48 m water depth, during the PROMESS 1 campaign (SRV Bavenit drilling vessel) and IMAGES V (RV Marion Dufresne, Calypso piston core), respectively. The high sedimentation rates -estimated by robust 14C dating- have given us an excellent opportunity to perform high resolution analyses on these materials. In this study we present data from the last 25 kys. The retrieved sediments consist of silty-clay terrigenous material mixed with a small amount of calcareous microfossils. Quantitative analyses of coccolithophore assemblages allow us to identify significant changes in sea surface temperature in this period. Cold peaks are marked by increases in the proportion of Gephyrocapsa muellerae and large morphotypes of Emiliania huxleyi (>5 m); some of the most significant can be correlated with Heinrich events. The high sedimentation rates observed during most of the studied interval also allow us to identify an overprinted multicentennial scale pattern related to Dansgaard-Oeschger cycles. The combined analyses of coccolithophores and planktonic foraminifers permits to produce a sea surface temperature (SST) record in which sharp fluctuations of around 4º C in amplitude have been detected. These abrupt changes in SST are also linked to changes in surface productivity and in the deep and intermediate water dynamics, probably related with variations in the atmospheric pattern (NAO-like oscillations). PROMESS 1 is funded by the European Community (EVR1-T-40024).

  6. Abrupt climate changes and the effects of North Atlantic deepwater formation: Results from the GENESIS global climate model and comparison with data from the Younger Dryas event and the event at 8200 years bp and the present

    NASA Astrophysics Data System (ADS)

    Agustsdottir, Anna Maria

    1998-10-01

    Abrupt changes in climate towards glacial conditions have occurred several times during the last tens of thousands of years. A reduction in ocean heat transport to the high-latitude North Atlantic, associated with reduction, shutdown, or southward shift in formation of North Atlantic Deepwater, is hypothesized to have caused or amplified abrupt cooling events. The model-data comparisons reported here provide strong support for this hypothesis for the Younger Dryas interval and the cold event about 8200 years ago, and show likely changes were such an oceanic change to occur in the near future. Different levels of North Atlantic ocean heat transport were specified in age-appropriate simulations using the GENESIS GCM climate model. For the Younger Dryas, simulated reduction in GENESIS ocean heat transport (in versions 1.02A and 2.0) from modern levels produces climate-anomaly patterns, including many seasonal changes, that closely match observations, however, observed changes far from the North Atlantic are somewhat larger than modeled. Both model and data indicate stronger winds during cold times. Modeled cold-time winds produce about 10% more tropical-ocean Ekman divergence in regions and at times of prominent upwelling. The cooling associated with this, but not calculated for the mixed- layer GENESIS model ocean, probably is important in model-data differences. Because of the success of GENESIS in simulating Younger Dryas changes around the North Atlantic but underestimating those beyond this region, the large changes simulated for a modern reduction of North Atlantic ocean heat transport likely march or underestimate those that would occur if such a change occurred in the near future. Reduction in ocean heat transport for 8200 years ago form modern levels produces an anomaly pattern somewhat like observations, but reduction form heat transport higher than modern produces a much better match. Together with other evidence, this suggests that this cold climate event

  7. New insights for the Late Pleistocene to Mid Holocene landscape reconstruction in the Western part of the Thessaloniki Plain (Greece): evidence for an abrupt transition and consequences on the settling history

    NASA Astrophysics Data System (ADS)

    Psomiadis, D.; Ghilardi, M.; Demory, F.; Delanghe-Sabatier, D.

    2012-04-01

    The Neolithic site of Nea Nikomideia is located at the western limit of the Thessaloniki Plain, Northern Greece and the archaeological excavations conducted in the 1960s suggested that the settlement was located close to an ancient coastline during its early occupation. Recently published results indicated that palaeoenvironmental transitions in the area influenced the human occupation from the early Holocene (6000/5800 cal. B.C.). It was also established that a freshwater lake occupied the vicinity of the Neolithic settlement at the early stages (Ghilardi et al., under press). However, the Late Pleistocene landscape configuration has not been clearly established, despite of some attempts (Lykousis, 2001). This study presents new data, which are correlated with more densely dated proxies in order to thoroughly investigate the Late Pleistocene - Holocene transition as well as the impact of following environmental alterations on the settlement. Special attention is given on periods of soil coverage which are considered indicative of periods with favourable conditions for human occupation. A new sequence is used, based on 3 new boreholes, for laser grain size analysis, loss-on-ignition and carbonate content, magnetic susceptibility measurements, microfaunal inspection and radiocarbon datings (A.M.S.) and it is intercorrelated with other sequences from the area. The synthesis of the proxies reveals distinct events of palaeoenvironmental alterations in a very well constructed chronostratigraphic framework of more than 10.000 years. The Pleistocene subsurface is found in circa 9 meters deep and clearly indicates the presence of a large alluvial fan deposition (calm environment) from Aliakmon River. The abrupt transition with early Holocene sediments reveals that an important influx of fresh water helped in creating a limnic environment of deposition. From Neolithic times to the present day, the area turned into a marine bay and subsequently into a freshwater lake where

  8. Global cooling during the eocene-oligocene climate transition.

    PubMed

    Liu, Zhonghui; Pagani, Mark; Zinniker, David; Deconto, Robert; Huber, Matthew; Brinkhuis, Henk; Shah, Sunita R; Leckie, R Mark; Pearson, Ann

    2009-02-27

    About 34 million years ago, Earth's climate shifted from a relatively ice-free world to one with glacial conditions on Antarctica characterized by substantial ice sheets. How Earth's temperature changed during this climate transition remains poorly understood, and evidence for Northern Hemisphere polar ice is controversial. Here, we report proxy records of sea surface temperatures from multiple ocean localities and show that the high-latitude temperature decrease was substantial and heterogeneous. High-latitude (45 degrees to 70 degrees in both hemispheres) temperatures before the climate transition were approximately 20 degrees C and cooled an average of approximately 5 degrees C. Our results, combined with ocean and ice-sheet model simulations and benthic oxygen isotope records, indicate that Northern Hemisphere glaciation was not required to accommodate the magnitude of continental ice growth during this time.

  9. 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.

  10. 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 ...

  11. Circum-Mediterranean fire activity and climate changes during the mid Holocene environmental transition (8500-2500 cal yr BP)

    NASA Astrophysics Data System (ADS)

    Vannière, Boris; Power, Mitch J.; Roberts, Neil; Tinner, Willy; Carrión, José; Magny, Michel; Bartlein, Patrick

    2010-05-01

    In this contribution I will present a synthesis of mid- to late-Holocene fire activity from the Mediterranean basin and explore the linkages among fire, climate variability and seasonality, and people through several climatic and ecological transitions. Regional fire histories were created from 36 radiocarbon-dated sedimentary charcoal records, available from the Global Charcoal Database. During the mid-Holocene "Thermal Maximum", charcoal records from the northern Mediterranean suggest the region was more fire prone while records from the southern Mediterranean indicate a decrease in fire activity associated with wetter-than-present summers. A North-South partition at 40-43°N is apparent in the central and western Mediterranean. In the context of orbitally-induced summer insolation decrease, South Mediterranean wet conditions could be linked to the Afro-Asian summer monsoon which weakened after ca. 8000-6000 cal yr BP. Relatively abrupt changes in fire regime observed at ca. 5500-5000 cal yr BP may be associated to a threshold in this weakening influence of the orbitally-driven Afro-Asian monsoon strength. Charcoal records of past fire activity appear sensitive to both orbitally-forced climate changes and shorter lived excursions which may be related to cold events apparent in the North Atlantic record of ice-rafted debris. These results contradict former notions of gradual aridification of the entire region due to climatic forcing and/or human activities. In contrast, they suggest: 1) Teleconnections between the Mediterranean area and other climatic regions, in particular the North Atlantic and the low-latitude monsoon areas, influenced past fire regimes; 2) Gradual forcing, such as changes in orbital parameters, may have triggered more abrupt shifts in fire regime, either directly or indirectly through these teleconnections.

  12. Investigating the Climatic Transition Zone in Guyana, South America

    NASA Astrophysics Data System (ADS)

    Bovolo, C.; Pereira, R.; Parkin, G.; Kilsby, C. G.; Wagner, T.

    2010-12-01

    The climate of Guyana is influenced by the seasonal oscillation of the rain-bearing Inter-Tropical-Convergence Zone over the northern part of South America, producing two wet seasons on the coast and one wet season inland. The transition zone between the two climate regimes also corresponds to a distinct vegetation transition between intact and highly biodiverse rainforests in northern and central Guyana, and open, savannah type vegetation in the southwest. Coastal Guyana has been shown to be highly susceptible to El Niño Southern Oscillation (ENSO) events, with El-Niño conditions most likely to result in drought; however a brief analysis of available observations suggests that an opposite effect may exist inland. Geographically sparse meteorological records of variable quality (especially inland) have so far precluded detailed climatic studies of the Guianas. It is important therefore, to establish the climate regime of the area and to analyse the influence of ENSO on the region in order to derive baselines against which the impacts of any future landuse change or climate change can be measured. The impacts of climatic variations on the ecosystem services of the area can then also begin to be determined. This study compares the ECMWF ERA40 reanalysis dataset for the period 1957-2002 at a ~125 km2 (1.125 degree) resolution against available areally averaged meteorological observations in the Guyanas to determine if reanalysis data can be used to supplement observations in data-poor areas. Mean differences (biases) and correlations are examined comparing the seasonal cycles and the yearly, monthly and monthly anomaly time series. Results show that maps of average annual reanalysis precipitation for the region compare favourably against observations, although the model underestimates precipitation in some zones of higher elevation. ERA40 also appears slightly positively biased on the coast and negatively biased inland. Correlations between observed and modelled

  13. A 2400-year record of abrupt climate change from Almalou Crate Lake in NW Iran: Investigating the potential influence of solar variability on the climate of West Asia during late Holocene

    NASA Astrophysics Data System (ADS)

    Sharifi, A.; Pourmand, A.; Canuel, E. A.; Naderi Beni, A.; Lahijani, H. A.

    2013-12-01

    The Mediterranean climate of northwest Iran is influenced by mid-latitude Westerlies and the winter expansion of the Siberian Anticyclone. Given the significance of this region in development of human civilizations, high-resolution reconstructions of abrupt climate change are of particular interest during the Holocene. Almalou Crater Lake sustains the growth of plants inside the crater of a dormant volcanic cone on the eastern flank of the Sahand volcanic district in NW Iran. At an elevation of 2491 m.a.s.l., the crater is exclusively fed by rainfall during the spring and fall and snowfall during the winter. Preservation of organic matter within the crater can potentially record changes in atmospheric deposition and paleo-environmental conditions over this region. To reconstruct changes in atmospheric aeolian input, we present a high-resolution (sub-decadal) multi-proxy record of climate variability during the last 2400 years from a 3-m peat core recovered from the crater peat bog. Radiocarbon dates of eight samples along the core show a nearly constant rate of accumulation (7.7 mm yr-1, R2=0.98) since 2404×25 cal yr BP. Downcore X-ray fluorescence measurements of selected conservative lithogenic elements (e.g., Al, Si, and Ti) as well as redox-sensitive elements (e.g., Fe and Rb) at 10 mm intervals reveal several periods of elevated abundances related to enhanced atmospheric dust deposition. The co-variations between relative abundances of conservative and redox-sensitive elements as a function of time show significant agreement and attest to the ombrotrophic nature of the entire record. Intervals of enhanced dust deposition inferred from XRF data reveal three short episodes (~ 150-y) at 450-600, 1150-1300, and 1400-1550 cal yr BP, and one prolonged period (500 y) of dust accumulation from 1600 to 2070 cal yr BP. These intervals of high atmospheric dust coincide with historical records of drought and famine in Iran since 2000 BP. Wavelet analysis conducted on the

  14. Abruption-associated prematurity

    PubMed Central

    Han, Christina S.; Schatz, Frederick; Lockwood, Charles J.

    2011-01-01

    SYNOPSIS Chronic, subacute decidual hemorrhage (i.e., abruptio placenta and retrochorionic hematoma formation) is an important contributor to preterm parturition. Such hemorrhage induces thrombin from decidual tissue factor, which play a pivotal role in the development of preterm premature rupture of membranes and preterm delivery by acting through protease-activated receptors to promote the production of pro-inflammatory cytokines, and matrix-degrading metalloproteinases. Severe, acute abruption can lead to maternal and fetal mortality. Current management of abruption is individualized based on severity of disease, underlying etiology, and gestational age. PMID:21890016

  15. Atmospheric carbon dioxide through the Eocene-Oligocene climate transition.

    PubMed

    Pearson, Paul N; Foster, Gavin L; Wade, Bridget S

    2009-10-22

    Geological and geochemical evidence indicates that the Antarctic ice sheet formed during the Eocene-Oligocene transition, 33.5-34.0 million years ago. Modelling studies suggest that such ice-sheet formation might have been triggered when atmospheric carbon dioxide levels (pCO2atm) fell below a critical threshold of approximately 750 p.p.m.v., but the timing and magnitude of pCO2atm relative to the evolution of the ice sheet has remained unclear. Here we use the boron isotope pH proxy on exceptionally well-preserved carbonate microfossils from a recently discovered geological section in Tanzania to estimate pCO2atm before, during and after the climate transition. Our data suggest that are reduction in pCO2atm occurred before the main phase of ice growth,followed by a sharp recovery to pre-transition values and then a more gradual decline. During maximum ice-sheet growth, pCO2atm was between approximately 450 and approximately 1,500 p.p.m.v., with a central estimate of approximately 760 p.p.m.v. The ice cap survived the period of pCO2atm recovery,although possibly with some reduction in its volume, implying (as models predict) a nonlinear response to climate forcing during melting. Overall, our results confirm the central role of declining pCO2atm in the development of the Antarctic ice sheet (in broad agreement with carbon cycle modelling) and help to constrain mechanisms and feedbacks associated with the Earth's biggest climate switch of the past 65 Myr.

  16. Jurassic Paleolatitudes, Paleogeography, and Climate Transitions In the Mexican Subcontinen

    NASA Astrophysics Data System (ADS)

    Molina-Garza, R. S.; Geissman, J. W.; Lawton, T. F.

    2014-12-01

    Jurassic northward migration of Mexico, trailing the North America plate, resulted in temporal evolution of climate-sensitive depositional environments. Lower-Middle Jurassic rocks in central Mexico contain a record of warm-humid conditions, which are indicated by coal and compositionally mature sandstone deposited in continental environments. Preliminary paleomagnetic data indicate that these rocks were deposited at near-equatorial paleolatitudes. The Middle Jurassic (ca. 170 Ma) Diquiyú volcanic sequence in central Oaxaca give an overall mean of D=82.2º/ I= +4.1º (n=10; k=17.3, α95=12º). In the Late Jurassic, the Gulf of Mexico formed as a subsidiary basin of the Atlantic Ocean, when the supercontinent Pangaea ruptured. Upper Jurassic strata, including eolianite and widespread evaporite deposits, across Mexico indicate dry-arid conditions. Available paleomagnetic data (compaction-corrected) from eolianites in northeast Mexico indicate deposition at ~15-20ºN. As North America moved northward during Jurassic opening of the Atlantic, different latitudinal regions experienced coeval Late Jurassic climatic shifts. Climate transitions have been widely recognized in the Colorado plateau region. The plateau left the horse-latitudes in the late Middle Jurassic to reach temperate humid climates at ~40ºN in the latest Jurassic. In turn, the southern end of the North America plate (central Mexico) reached arid horse-latitudes in the Late Jurassic. At that time, epeiric platforms developed in the circum-Gulf region after a long period of margin extension. We suggest that Upper Jurassic hydrocarbon source rocks in the circum-Gulf region accumulated on these platforms as warm epeiric hypersaline seas and the Gulf of Mexico itself were fertilized by an influx of wind-blown silt from continental regions. Additional nutrients were brought to shallow zones of photosynthesis by ocean upwelling driven by changes in the continental landmass configuration.

  17. Understanding Abrupt, Natural Climate Variability Post-Industrial Revolution from the Subtropical Eastern Pacific: A Novel High Resolution Alkenone-derived Sea Surface Temperature Record

    NASA Astrophysics Data System (ADS)

    Kelly, C. S.; O'Mara, N. A.; Herbert, T.; Abella-Gutiérrez, J. L.; Herguera, J. C.

    2015-12-01

    Despite the ocean's importance in global biogeochemical feedbacks and heat storage, there is still a paucity of decadally-resolved sea surface temperature (SST) records to complement lacustrine and dendrological records of recent paleoclimate. Natural climate variability on multidecadal timescales is dominated by internal ocean circulation dynamics and feedbacks, and it is therefore imperative to employ marine proxies to reconstruct high resolution climate change. The timescales of this ocean-induced natural climate variability can be broken down into a few characteristic climate modes. Pressing questions about these modes include their stationarity in frequency and amplitude over time, in addition to the hypothesis that anthropogenic climate change has altered their behavior in comparison to natural variability. To pursue these questions, we must discern and analyze suitable climate archives in regions where modes of interest dominate modern climate variability. The region of Baja California, Mexico exhibits exceptional teleconnection to the El Niño Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO). Local, dramatic effects of ENSO and PDO on the marine biology and economy underline the importance of regional paleoclimate records from the Baja peninsula. Here, we present a high-resolution alkenone-derived SST reconstruction from the Industrial Revolution through the year 2000 by analysis of laminated box and Kasten sediment cores at Site PCM 00-78 (25.18°N, 112.66°W) in the subtropical eastern Pacific at a depth of 540 meters. Our SST record corresponds with NOAA extended reconstructed sea surface temperature, providing a robust basis for organic geochemical marine climatic reconstructions on timescales usually accessible only through speleothems, coral density bands, tree rings, and the like. Accordingly, based on this comparison to the historical data we expect our SST record may provide a more robust record of inter and multidecadal

  18. Heat waves connect abrupt polar climate changes during the past 67ka: evidence from sediment core GeoB3912-1

    NASA Astrophysics Data System (ADS)

    Yang, X.; Rial, J. A.

    2014-12-01

    According to the hypothesis of polar synchronization, climate variations of Earth's poles are connected with a persistent phase lock of π/2 throughout the last glacial period. However, it is not clear yet how the Earth's two poles communicate with each other, the Thermohaline circulation (THC) being a possible candidate for signal carrier. Here we present a possible way of climate variation propagation through the Atlantic Ocean - likely in the form of heat or thermal wave (Cattaneo's solution) - based on lagged correlation between an organic carbon climate proxy record from the tropical Atlantic and the south-north polar temperature gradient. We further demonstrate that the speed of such propagation is frequency dependent, of which the wave of the longest period travels the fastest at the speed of ~32 km/year consistent with the estimated speed of the THC. The observed speed - frequency relationship can be successfully modeled as resulting from a propagating dispersive thermal wave initiated by the polar temperature gradient maximum. We show that such heat wave propagation is a potential mechanism to couple and synchronize the polar climates during the last glacial period and to force the occurrence of Heinrich events. To summarize, the polar temperature gradient anomalies are consequence of the π/2 phase lock between the polar climates, which is caused by polar synchronization maintained by the coupling, which is, as the data suggest, in the form of thermal waves. The spikes in organic carbon and the Fe/Ca ratio records in the core GeoB3912-1 can be thought of as snapshots of the passage of strong meteorological wavefronts through the equatorial region. The results strongly suggest that each peak in the organic carbon recorded a half-hemisphere-delayed passage of a wave-like disturbance through the equator carrying the south-north temperature gradient maxima. And each of these occurs within timing error of the Heinrich events H0-H6.

  19. 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

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

    NASA Astrophysics Data System (ADS)

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

    2010-08-01

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

  1. Multiple abrupt climate changes in the western hemisphere during the past 50,000 years, and their implications concerning the response of vegetation to changing atmospheric chemistry

    SciTech Connect

    Jacobson, G.L. Jr.; Grimm, E.C.

    1995-06-01

    Independent evidence spanning the last 50,000 years from ice cores, ocean sediments, and detailed glacial-geologic investigations implies multiple. large warm/cool oscillations with a frequency of ca. 3000 years through much of the Western Hemisphere. Paleoecological studies at sites in North America and the west coast of South America reveal major, synchronous changes in vegetation corresponding to many of these high-frequency changes in climate. Sequences on both sides of the equator culminate in substantial warming at 14 ka BP and a brief cooling at ca. 11 ka BP just prior to the final onset of Holocene warming. The high-frequency climate oscillations are not explained by {open_quotes}Milankovitch{close_quotes} cycles in solar insolation or by changes in thermohaline ocean circulation. Rather, these changes in climate and the attendant synchronous, broad-scale responses of vegetation indicate a global atmospheric forcing. However, that forcing is apparently also distinct from changing concentrations of atmospheric CO2 (as represented in the Vostok ice-core data). High-resolution CO2 data, such as that from the new Greenland ice cores, will be required before critical assessments of plant-physiological responses to past atmospheric changes can be carried out.

  2. A stratigraphic framework for naming and robust correlation of abrupt climatic changes during the last glacial period based on three synchronized Greenland ice core records

    NASA Astrophysics Data System (ADS)

    Rasmussen, Sune O.

    2014-05-01

    Due to their outstanding resolution and well-constrained chronologies, Greenland ice core records have long been used as a master record of past climatic changes during 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 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. This is based on a combination of isotope ratios (δ18O, reflecting mainly local temperature) and calcium concentrations (reflecting mainly atmospheric dust loading). 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. This is a key step aimed at promoting unambiguous comparison and correlation between different proxy records, as well as a more secure basis for investigating the dynamics and fundamental causes of these climatic perturbations. The work presented is under review for publication in Quaternary Science Reviews. Author team: S

  3. The magnitude, timing and abruptness of changes in North African dust deposition over the last 20,000 years: Insights into regional atmospheric circulation and dust-related climate impacts

    NASA Astrophysics Data System (ADS)

    McGee, D.; deMenocal, P. B.; Winckler, G.; Stuut, J. W.; Bradtmiller, L. I.; Mahowald, N. M.; Albani, S.

    2012-12-01

    Reconstructions of eolian dust accumulation in West African margin sediments provide important continuous records of past changes in atmospheric circulation and aridity in the region. Existing records indicate dramatic changes in West African dust emissions over the last 20 ka, including high dust emissions during Heinrich Stadial 1 and the Younger Dryas and lower dust emissions during the African Humid Period, a period of enhanced monsoon precipitation from approximately 11.7-5 ka. The limited spatial extent of these records, as well as the lack of high-resolution flux data, do not allow us to determine whether changes in dust deposition occurred with similar timing, magnitude and abruptness throughout northwest Africa. Here we present new records from a meridional transect of cores stretching from 27°N to 19°N along the northwest African margin, as well as from cores in the western tropical Atlantic reflecting downwind deposition. By combining grain size endmember modeling with 230Th-normalized fluxes in these cores, we are able to document spatial and temporal changes in dust loads and grain size distributions within the North African dust plume throughout the last 20 ka. Our results provide quantitative estimates of the magnitude of dust flux changes associated with Heinrich Stadial 1, the Younger Dryas, and the AHP. Our data are consistent with abrupt, synchronous changes in dust fluxes in all cores at the beginning and end of the AHP. Using these new records to tune dust loadings in a fully coupled model of 6 ka climate, we find that low dust fluxes during the AHP may have had a substantial positive feedback on regional precipitation by amplifying the northward displacement of the Atlantic and West African ITCZ.

  4. Coincident exposure/drowning surfaces within Middle Cambrian Grand Cycles, East Tennessee: A model for abrupt limestone/shale transitions/sequence boundaries

    SciTech Connect

    Rankey, E.C.; Srinivasan, K.; Walker, K.R. . Dept. of Geological Science)

    1992-01-01

    Vertical transition from limestones to shales mark the boundaries of Cambrian Grand Cycles in Passive Margin Sequences over a wide geographic area. Field, petrographic, and geochemical evidence from near platform-edge mudstones and boundstones and platform-edge boundstones at the tops of the Craig Limestone and Maryville Limestone of the Conasauga Group in the southern Appalachians indicate platform death by subaerial exposure, followed by platform drowning and subsequent onlap of siliciclastic deposits. Physical evidence, in the form of scalloped truncation surfaces, as well as petrographic evidence consisting of wholesale and fabric-selective dissolution, internal brecciation, and vadose silt deposition indicate meteoric diagenesis following exposure. Depleted stable oxygen isotope compositions of inter- and intragranular blocky clear calcite spar of the Maryville Limestone have a mean delta O-18 composition of [minus]9.3[per thousand] (PDB) and a mean delta C-13 composition of +0.01[per thousand](PDB). Preliminary data from the Craig Limestone indicate similar delta C-13 values, but more depleted. Thus, the authors propose a common origin for the limestone-shale transitions at the top of these two units. Subaerial exposure during a sea-level fall at the top of these carbonate units terminated carbonate deposition. During exposure, a meteoric-water lens developed in the platform sediments leading to early diagenetic alteration. A rapid relative sea-level rise then drowned the platform, followed by subsidence and deepening during the lag-time before the onset of carbonate deposition. The deepening suppressed carbonate production and allowed fine siliciclastics characteristic of the adjacent basin to onlap the drowned platform.

  5. Characteristics of the deep ocean carbon system during the past 150,000 years: SigmaCO2 distributions, deep water flow patterns, and abrupt climate change.

    PubMed

    Boyle, E A

    1997-08-05

    Studies of carbon isotopes and cadmium in bottom-dwelling foraminifera from ocean sediment cores have advanced our knowledge of ocean chemical distributions during the late Pleistocene. Last Glacial Maximum data are consistent with a persistent high-SigmaCO2 state for eastern Pacific deep water. Both tracers indicate that the mid-depth North and tropical Atlantic Ocean almost always has lower SigmaCO2 levels than those in the Pacific. Upper waters of the Last Glacial Maximum Atlantic are more SigmaCO2-depleted and deep waters are SigmaCO2-enriched compared with the waters of the present. In the northern Indian Ocean, delta13C and Cd data are consistent with upper water SigmaCO2 depletion relative to the present. There is no evident proximate source of this SigmaCO2-depleted water, so I suggest that SigmaCO2-depleted North Atlantic intermediate/deep water turns northward around the southern tip of Africa and moves toward the equator as a western boundary current. At long periods (>15,000 years), Milankovitch cycle variability is evident in paleochemical time series. But rapid millennial-scale variability can be seen in cores from high accumulation rate series. Atlantic deep water chemical properties are seen to change in as little as a few hundred years or less. An extraordinary new 52.7-m-long core from the Bermuda Rise contains a faithful record of climate variability with century-scale resolution. Sediment composition can be linked in detail with the isotope stage 3 interstadials recorded in Greenland ice cores. This new record shows at least 12 major climate fluctuations within marine isotope stage 5 (about 70,000-130,000 years before the present).

  6. Abrupt changes in the southern extent of North Atlantic Deep Water during Dansgaard-Oeschger events

    NASA Astrophysics Data System (ADS)

    Gottschalk, Julia; Skinner, Luke C.; Misra, Sambuddha; Waelbroeck, Claire; Menviel, Laurie; Timmermann, Axel

    2015-12-01

    The glacial climate system transitioned rapidly between cold (stadial) and warm (interstadial) conditions in the Northern Hemisphere. This variability, referred to as Dansgaard-Oeschger variability, is widely believed to arise from perturbations of the Atlantic Meridional Overturning Circulation. Evidence for such changes during the longer Heinrich stadials has been identified, but direct evidence for overturning circulation changes during Dansgaard-Oeschger events has proven elusive. Here we reconstruct bottom water [CO32-] variability from B/Ca ratios of benthic foraminifera and indicators of sedimentary dissolution, and use these reconstructions to infer the flow of northern-sourced deep water to the deep central sub-Antarctic Atlantic Ocean. We find that nearly every Dansgaard-Oeschger interstadial is accompanied by a rapid incursion of North Atlantic Deep Water into the deep South Atlantic. Based on these results and transient climate model simulations, we conclude that North Atlantic stadial-interstadial climate variability was associated with significant Atlantic overturning circulation changes that were rapidly transmitted across the Atlantic. However, by demonstrating the persistent role of Atlantic overturning circulation changes in past abrupt climate variability, our reconstructions of carbonate chemistry further indicate that the carbon cycle response to abrupt climate change was not a simple function of North Atlantic overturning.

  7. Evidence for an abrupt transition in the mantle-derived source to the Long Valley Caldera rhyolites after the climactic eruption: from subduction-modified lithosphere to asthenosphere

    NASA Astrophysics Data System (ADS)

    Waters, L.; Lange, R. A.

    2014-12-01

    Shortly after the climactic eruption of ~600 km3 of Bishop Tuff zoned rhyolitic magma, ~100 km3 of crystal-poor Early Rhyolite erupted inside Long Valley Caldera between ~750-650 ka as domes, glassy lavas, and tuffs (Hildreth, 2004). Despite similarities in bulk composition (e.g., 73-75 wt% SiO2; ~100 ppm Sr), there are marked differences between the Late (≥ 790°C) Bishop Tuff and postcaldera Early Rhyolites. Although crystal-poor (<5%), the Early Rhyolites are often saturated with 7-8 mineral phases (plag + opx + ilm + tmte + biotite + apatite + zircon ± pyrrhotite), but without the quartz, sanidine, and cpx additionally found in the more crystal-rich (12-24%) Late Bishop Tuff. Pre-eruptive temperatures, on the basis of two Fe-Ti oxides, range from 720-860°C, and ∆NNO values range from-0.4 to -0.9 (consistent with abundant ilmenite). Thus the Early Rhyolites record fO2 values that are nearly two orders of magnitude lower than those in the Late Bishop Tuff (∆NNO = +1; Hildreth and Wilson, 2007). Application of the plagioclase-liquid hygrometer to Early Rhyolites gives pre-eruptive water contents ≤ 4.4 wt% H2O. The phenocrysts in Early Rhyolite obsidians often display euhedral and/or diffusion-limited growth textures, suggesting degassing-induced crystallization during rapid ascent. Isotopic data from the literature (e.g., Simon et al., 2014 and references therein) show that Long Valley rhyolites were derived from both crustal and mantle sources. We hypothesize that the drop in fO2 between the Late Bishop Tuff and Early Rhyolites may reflect a transition in their respective mantle source, from subduction-modified lithosphere to asthenosphere. Such a time-progressive transition in the mantle source of erupted basalts is seen throughout the Great Basin, occurring earliest in its central region and more recently toward its western margin (e.g. Cousens et al., 2012). Although the geochemistry of Quaternary basalts erupted around Long Valley indicate a

  8. 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.

  9. North Atlantic climate evolution through the Plio-Pleistocene climate transitions

    NASA Astrophysics Data System (ADS)

    Lawrence, K. T.; Sosdian, S.; White, H. E.; Rosenthal, Y.

    2010-12-01

    During the Plio-Pleistocene, the Earth witnessed the growth of large northern hemisphere ice sheets and profound changes in both North Atlantic and global climate. Here, we present a ~ 3.2 Myr long, orbitally-resolved alkenone sea surface temperature (SST) record from Deep Sea Drilling Project (DSDP) Site 607 (41°N, 33°W, water depth 3427 m) in the North Atlantic Ocean. We employ a multi-proxy approach comparing these new observations with existing bottom water temperature (BWT) and stable isotope time series from the same site and SST time series from other sites, shedding new light on Plio-Pleistocene climate change. North Atlantic temperature records show a long-term cooling with two major steps occurring during the late Pliocene (3.1 to 2.4 Ma) and the mid-Pleistocene (1.5 to 0.8 Ma), closely timed with intervals of major change in northern hemisphere ice sheets. Existing evidence suggests that the late Pliocene cooling may have been caused by a thresholded response to secular changes in atmospheric carbon dioxide (CO 2). While an explanation for the mid-Pleistocene cooling may involve glacial-interglacial changes in atmospheric CO 2, it seems to also require a change in the behavior of the ice sheets themselves. North Atlantic climate responses were closely phased with benthic oxygen isotope (δ 18O) changes during the "41 kyr world," indicating a strong common northern hemisphere high latitude imprint on North Atlantic climate signals. After the mid-Pleistocene transition (MPT), North Atlantic SST records and the Site 607 benthic carbon isotope (δ 13C) record are more closely phased with δ 18O, whereas BWT significantly leads δ 18O in the 100 kyr band, suggesting a shift from a northern to a southern hemisphere influence on North Atlantic BWT. We propose that the expansion of the West Antarctic ice sheet (WAIS) across the MPT increased the production and export of Antarctic Bottom Water from the Southern Ocean and subsequently controlled its incursion

  10. Stomatal proxy record of CO2 concentrations from the last termination suggests an important role for CO2 at climate change transitions

    NASA Astrophysics Data System (ADS)

    Steinthorsdottir, Margret; Wohlfarth, Barbara; Kylander, Malin E.; Blaauw, Maarten; Reimer, Paula J.

    2013-05-01

    A new stomatal proxy-based record of CO2 concentrations ([CO2]), based on Betula nana (dwarf birch) leaves from the Hässeldala Port sedimentary sequence in south-eastern Sweden, is presented. The record is of high chronological resolution and spans most of Greenland Interstadial 1 (GI-1a to 1c, Allerød pollen zone), Greenland Stadial 1 (GS-1, Younger Dryas pollen zone) and the very beginning of the Holocene (Preboreal pollen zone). The record clearly demonstrates that i) [CO2] were significantly higher than usually reported for the Last Termination and ii) the overall pattern of CO2 evolution through the studied time period is fairly dynamic, with significant abrupt fluctuations in [CO2] when the climate moved from interstadial to stadial state and vice versa. A new loss-on-ignition chemical record (used here as a proxy for temperature) lends independent support to the Hässeldala Port [CO2] record. The large-amplitude fluctuations around the climate change transitions may indicate unstable climates and that “tipping-point” situations were involved in Last Termination climate evolution. The scenario presented here is in contrast to [CO2] records reconstructed from air bubbles trapped in ice, which indicate lower concentrations and a gradual, linear increase of [CO2] through time. The prevalent explanation for the main climate forcer during the Last Termination being ocean circulation patterns needs to re-examined, and a larger role for atmospheric [CO2] considered.

  11. Could massive Arctic sea ice export to the North Atlantic be the real cause of abrupt climate change during the last deglaciation?

    NASA Astrophysics Data System (ADS)

    Coletti, A. J.; Condron, A.

    2015-12-01

    Using a coupled ocean-sea ice model (MITgcm), we investigate whether the break-up and mobilization of thick, multiyear, Arctic sea ice might have supplied enough freshwater to the Nordic Seas to reduce North Atlantic Deep Water (NADW) formation and weaken the Atlantic Meridional Overturning Circulation (AMOC). Numerical simulations of a Last Glacial Maximum (LGM) environment show the potential for sea ice to grow to ~30m thick, storing ~1.41x105 km3 of freshwater as sea ice in the Arctic (this is ~10 times the volume of freshwater stored in the modern-day Arctic). Releasing this volume of sea ice from the Arctic in 1-yr is equivalent to a high-latitude freshwater forcing of ~4.5 Sv, which is comparable (or larger) in magnitude to most meltwater floods emanating from land-based glacial lakes (e.g. Agassiz) during the last deglaciation. Opening of the Bering Strait and Barents Sea are two plausible mechanisms that may have initiated sea ice mobilization. Opening Bering Strait increases sea ice transport through the Fram Strait by 7% and results in a 22% weakening of AMOC for 2000 years and a >3°C warming in the Arctic basin at 800 m depth. Opening Barents Sea to simulate a collapse of the Fennoscandian ice sheet has little impact on Arctic sea ice and freshwater export to the North Atlantic, but weakens AMOC ~8%. In a simulation with both straits open there is a transition to near-modern sea ice circulation pattern and a 24% reduction in AMOC. Experiments with the Bering Strait open and sea ice artificially capped to 10 m show barely any difference to those when sea ice can grow to ~30m, suggesting that changes in topography have a much greater impact on AMOC than the freshwater forcing from sea ice melting in the Nordic Seas.

  12. Abruptness of Cascade Failures in Power Grids

    PubMed Central

    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

  13. Abruptness of cascade failures in power grids.

    PubMed

    Pahwa, Sakshi; Scoglio, Caterina; Scala, Antonio

    2014-01-15

    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".

  14. An abrupt change in ridge axis gravity with spreading rate

    NASA Technical Reports Server (NTRS)

    Small, Christopher; Sandwell, David T.

    1989-01-01

    A total of 44 Geosat profiles over ridges with spreading rates ranging from 14 to 155 mm/yr were analyzed. In agreement with previous studies, it is found that slow spreading ridges usually have high amplitude gravity troughs, while fast spreading ridges are characterized by low-amplitude ridge axis highs. Unexpectedly, it is found that the transition from axial trough to axial high occurs abruptly at a spreading rate of 60-70 mm/yr. Ridge axis gravity signatures are highly variable for rates less than 65 mm/yr and very uniform at higher rates. The transition of the gravity signature appears to get more abrupt than the transition of the topographic signature, suggesting an abrupt change in the style of isostatic compensation with spreading rate. Published models of ridge axis dynamics do not explain this sharp transition.

  15. Analysis of climatic conditions and preliminary assessment of alternative cooling strategies for houses in California transition climate zones

    SciTech Connect

    Huang, Y.J.; Zhang, H.

    1995-07-01

    This is a preliminary scoping study done as part of the {open_quotes}Alternatives to Compressive Cooling in California Transition Climates{close_quotes} project, which has the goal of demonstrating that houses in the transitional areas between the coast and the Central Valley of California do not require air-conditioning if they are properly designed and operated. The first part of this report analyzes the climate conditions within the transitional areas, with emphasis on design rather than seasonal conditions. Transitional climates are found to be milder but more variable than those further inland. The design temperatures under the most stringent design criteria, e.g. 0.1 % annual, are similar to those in the Valley, but significantly lower under more relaxed design criteria, e.g., 2% annual frequency. Transition climates also have large day-night temperature swings, indicating significant potential for night cooling, and wet-bulb depressions in excess of 25 F, indicating good potential for evaporative cooling. The second part of the report is a preliminary assessment using DOE-2 computer simulations of the effectiveness of alternative cooling and control strategies in improving indoor comfort conditions in two conventional Title-24 houses modeled in various transition climate locations. The cooling measures studied include increased insulation, light colors, low-emissivity glazing, window overhangs, and exposed floor slab. The control strategies studied include natural and mechanical ventilation, and direct and two-stage evaporative cooling. The results indicate the cooling strategies all have limited effectiveness, and need to be combined to produce significant improvements in indoor comfort. Natural and forced ventilation provide similar improvements in indoor conditions, but during peak cooling periods, these will still be above the comfort zone. Two-stage evaporative coolers can maintain indoor comfort at all hours, but not so direct evaporative coolers.

  16. TESTING THE LINK BETWEEN TERRESTRIAL CLIMATE CHANGE AND GALACTIC SPIRAL ARM TRANSIT

    SciTech Connect

    Overholt, Andrew C.; Melott, Adrian L.; Pohl, Martin E-mail: melott@ku.ed

    2009-11-10

    We re-examine past suggestions of a close link between terrestrial climate change and the Sun's transit of spiral arms in its path through the Milky Way galaxy. These links produced concrete fits, deriving the unknown spiral pattern speed from terrestrial climate correlations. We test these fits against new data on spiral structure based on CO data that do not make simplifying assumptions about symmetry and circular rotation. If we compare the times of these transits with changes in the climate of Earth, the claimed correlations not only disappear, but we also find that they cannot be resurrected for any reasonable pattern speed.

  17. RESTORING COASTAL ECOSYSTEMS: ABRUPT CLIMATE CHANGE

    EPA Science Inventory

    Consensus exists that U.S. coastal ecosystems are severely degraded due to a variety of human-factors requiring large financial expenditures to restore and manage. Yet, even as controversy surrounds human factors in ecosystem degradation in the Gulf of Mexico, Chesapeake Bay, an...

  18. Abrupt Climate Change Research Act of 2009

    THOMAS, 111th Congress

    Sen. Collins, Susan M. [R-ME

    2009-09-14

    09/14/2009 Read twice and referred to the Committee on Commerce, Science, and Transportation. (text of measure as introduced: CR S9330) (All Actions) Tracker: This bill has the status IntroducedHere are the steps for Status of Legislation:

  19. Abrupt warming of the Red Sea

    NASA Astrophysics Data System (ADS)

    Raitsos, D. E.; Hoteit, I.; Prihartato, P. K.; Chronis, T.; Triantafyllou, G.; Abualnaja, Y.

    2011-07-01

    Coral reef ecosystems, often referred to as “marine rainforests,” concentrate the most diverse life in the oceans. Red Sea reef dwellers are adapted in a very warm environment, fact that makes them vulnerable to further and rapid warming. The detection and understanding of abrupt temperature changes is an important task, as ecosystems have more chances to adapt in a slowly rather than in a rapid changing environment. Using satellite derived sea surface and ground based air temperatures, it is shown that the Red Sea is going through an intense warming initiated in the mid-90s, with evidence for an abrupt increase after 1994 (0.7°C difference pre and post the shift). The air temperature is found to be a key parameter that influences the Red Sea marine temperature. The comparisons with Northern Hemisphere temperatures revealed that the observed warming is part of global climate change trends. The hitherto results also raise additional questions regarding other broader climatic impacts over the area.

  20. Impacts of climate warming on atmospheric phase transition mechanisms

    NASA Astrophysics Data System (ADS)

    Varotsos, Costas A.; Ghosh, Satyajit

    2016-09-01

    Nowadays, climate change is a fact, and its impacts on heterogeneous chemistry mechanisms that take place in various atmospheric layers are of great interest. As an example, the uptake of atmospheric species on solid and liquid surfaces induces qualitative and quantitative changes from climatic alterations of the atmospheric thermal regime. We hereby present the experience gained on this subject by analysing real measurements of various atmospheric species and parameters conducted in Athens, Greece, exploring the atmospheric height region from the Earth's surface up to the lower stratosphere.

  1. From Abrupt Change to the Future (Hans Oeschger Medal Lecture)

    NASA Astrophysics Data System (ADS)

    Stocker, T.

    2009-04-01

    surface and many questions are still unresolved. A consistent simulation of ice age cycles including the remarkable transition from the 40 kyr to 100 kyr world is still missing. Evidence for interhemispheric connection, a persistent feature of the last ice age, remains circumstantial during earlier ice ages. Recent ice core analyses suggest extremely rapid climate change in the high latitude which is faster than any model has suggested. Sea ice changes must play an important role in that they may operate as an efficient accelerator. Modelling results are reviewed which suggest that instabilities in sea ice coverage can occur in response to relatively slow changes of the background climate. Such behaviour has been demonstrated in simulations of future climate, but it may well apply to past abrupt climate change. The paleoclimate record may therefore hold much more and more detailed information about instabilities and surprises if marine and atmospheric proxies are combined. However, only through the combination of highest-resolution paleoclimatic data and a clever hierarchy of models are we able to address and resolve these questions.

  2. Role of the Bering Strait on the hysteresis of the ocean conveyor belt circulation and glacial climate stability.

    PubMed

    Hu, Aixue; Meehl, Gerald A; Han, Weiqing; Timmermann, Axel; Otto-Bliesner, Bette; Liu, Zhengyu; Washington, Warren M; Large, William; Abe-Ouchi, Ayako; Kimoto, Masahide; Lambeck, Kurt; Wu, Bingyi

    2012-04-24

    Abrupt climate transitions, known as Dansgaard-Oeschger and Heinrich events, occurred frequently during the last glacial period, specifically from 80-11 thousand years before present, but were nearly absent during interglacial periods and the early stages of glacial periods, when major ice-sheets were still forming. Here we show, with a fully coupled state-of-the-art climate model, that closing the Bering Strait and preventing its throughflow between the Pacific and Arctic Oceans during the glacial period can lead to the emergence of stronger hysteresis behavior of the ocean conveyor belt circulation to create conditions that are conducive to triggering abrupt climate transitions. Hence, it is argued that even for greenhouse warming, abrupt climate transitions similar to those in the last glacial time are unlikely to occur as the Bering Strait remains open.

  3. Model Projections of an Imminent Transition to a More Arid Climate in Southwestern North America

    NASA Astrophysics Data System (ADS)

    Seager, Richard; Ting, Mingfang; Held, Isaac; Kushnir, Yochanan; Lu, Jian; Vecchi, Gabriel; Huang, Huei-Ping; Harnik, Nili; Leetmaa, Ants; Lau, Ngar-Cheung; Li, Cuihua; Velez, Jennifer; Naik, Naomi

    2007-05-01

    How anthropogenic climate change will affect hydroclimate in the arid regions of southwestern North America has implications for the allocation of water resources and the course of regional development. Here we show that there is a broad consensus among climate models that this region will dry in the 21st century and that the transition to a more arid climate should already be under way. If these models are correct, the levels of aridity of the recent multiyear drought or the Dust Bowl and the 1950s droughts will become the new climatology of the American Southwest within a time frame of years to decades.

  4. Model projections of an imminent transition to a more arid climate in southwestern North America.

    PubMed

    Seager, Richard; Ting, Mingfang; Held, Isaac; Kushnir, Yochanan; Lu, Jian; Vecchi, Gabriel; Huang, Huei-Ping; Harnik, Nili; Leetmaa, Ants; Lau, Ngar-Cheung; Li, Cuihua; Velez, Jennifer; Naik, Naomi

    2007-05-25

    How anthropogenic climate change will affect hydroclimate in the arid regions of southwestern North America has implications for the allocation of water resources and the course of regional development. Here we show that there is a broad consensus among climate models that this region will dry in the 21st century and that the transition to a more arid climate should already be under way. If these models are correct, the levels of aridity of the recent multiyear drought or the Dust Bowl and the 1950s droughts will become the new climatology of the American Southwest within a time frame of years to decades.

  5. Offset timing of climate oscillations during the last two glacial-interglacial transitions connected with large-scale freshwater perturbation

    NASA Astrophysics Data System (ADS)

    Jiménez-Amat, Patricia; Zahn, Rainer

    2015-06-01

    Multidecadal to centennial planktic δ18O and Mg/Ca records were generated at Ocean Drilling Program Site 976 (ODP976) in the Alboran Sea. The site is in the flow path of Atlantic inflow waters entering the Mediterranean and captured North Atlantic signals through the surface inflow and the atmosphere. The records reveal similar climatic oscillations during the last two glacial-to-interglacial transitions, albeit with a different temporal pacing. Glacial termination 1 (T1) was marked by Heinrich event 1 (H1), post-H1 Bølling/Allerød warming, and Younger Dryas (YD) cooling. During T2 the H11 δ18O anomaly was twice as high and lasted 30% longer than during H1. The post-H11 warming marked the start of MIS5e while the subsequent YD-style cooling occurred during early MIS5e. The post-H11 temperature increase at ODP976 matched the sudden Asian Monsoon Termination II at 129 ka B.P. Extending the 230Th-dated speleothem timescale to ODP976 suggests glacial conditions in the Northeast Atlantic region were terminated abruptly and interglacial warmth was reached in less than a millennium. The early-MIS5e cooling and freshening at ODP976 coincided with similar changes at North Atlantic sites suggesting this was a basin-wide event. By analogy with T1, we argue that this was a YD-type event that was shifted into the early stages of the last interglacial period. This scenario is consistent with evidence from northern North Atlantic and Nordic Sea sites that the continuing disintegration of the large Saalian Stage (MIS6) ice sheet in Eurasia delayed the advection of warm North Atlantic waters and full-strength convective overturn until later stages of MIS5e.

  6. 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.

  7. Teleconnections between the subtropical monsoons and high-latitude climates during the last deglaciation

    SciTech Connect

    Sirocko, F.; Schonberg, D.G.; McIntyre A.

    1996-04-26

    The major deglacial intensification of the southwest monsoon occurred at 11,450 {+-} 150 calendar years before present, synchronous with a major climate transition as recorded in Greenland ice. An earlier event of monsoon intensification at 16,000 {+-} 150 calendar years before present occurred at the end of Heinrich layer 1 in the Atlantic and parallels the initial rise in global atmospheric methane concentrations and the first abrupt climate changes in the Antarctic; thus, the evolution of the monsoonal and high-latitude climates show teleconnections but hemispheric asymmetries. Superimposed on abrupt events, the monsoonal climate shows high-frequency variability of 1785-, 1450-, and 1150-year oscillations, and abrupt climate change seems to occur when at least two of these oscillations are in phase. 40 refs., 5 figs.

  8. Parameterizing turbulence over abrupt topography

    NASA Astrophysics Data System (ADS)

    Klymak, Jody

    2016-11-01

    Stratified flow over abrupt topography generates a spectrum of propagating internal waves at large scales, and non-linear overturning breaking waves at small scales. For oscillating flows, the large scale waves propagate away as internal tides, for steady flows the large-scale waves propagate away as standing "columnar modes". At small-scales, the breaking waves appear to be similar for either oscillating or steady flows, so long as in the oscillating case the topography is significantly steeper than the internal tide angle of propagation. The size and energy lost to the breaking waves can be predicted relatively well from assuming that internal modes that propagate horizontally more slowly than the barotropic internal tide speed are arrested and their energy goes to turbulence. This leads to a recipe for dissipation of internal tides at abrupt topography that is quite robust for both the local internal tide generation problem (barotropic forcing) and for the scattering problem (internal tides incident on abrupt topography). Limitations arise when linear generation models break down, an example of which is interference between two ridges. A single "super-critical" ridge is well-modeled by a single knife-edge topography, regardless of its actual shape, but two supercritical ridges in close proximity demonstrate interference of the high modes that makes knife-edfe approximations invalid. Future direction of this research will be to use more complicated linear models to estimate the local dissipation. Of course, despite the large local dissipation, many ridges radiate most of their energy into the deep ocean, so tracking this low-mode radiated energy is very important, particularly as it means dissipation parameterizations in the open ocean due to these sinks from the surface tide cannot be parameterized locally to where they are lost from the surface tide, but instead lead to non-local parameterizations. US Office of Naval Research; Canadian National Science and

  9. The Impact of Near-term Climate Policy Choices on Technology and Emissions Transition Pathways

    SciTech Connect

    Eom, Jiyong; Edmonds, James A.; Krey, Volker; Johnson, Nils; Longden, Thomas; Luderer, Gunnar; Riahi, Keywan; Van Vuuren, Detlef

    2015-01-01

    This paper explores the implications of delays associated with currently formulated climate policies (compared to optimal policies) for long-term transition pathways to limit climate forcing to 450ppm CO2e on the basis of the AMPERE Work Package 2 model comparison study. The paper highlights the critical importance of the 2030-2050 period for ambitious mitigation strategies. In this period, the most rapid shift to non-greenhouse gas emitting technology occurs. In the delayed response emissions mitigation scenarios, an even faster transition rate in this period is required to compensate for the additional emissions before 2030. Our physical deployment measures indicate that, without CCS, technology deployment rates in the 2030-2050 period would become considerably high. Yet the presence of CCS greatly alleviates the challenges to the transition particularly after the delayed climate policies. The results also highlight the critical role that bioenergy and CO2 capture and storage (BECCS) could play. If this technology is available, transition pathways exceed the emissions budget in the mid-term, removing the excess with BECCS in the long term. Excluding either BE or CCS from the technology portfolio implies that emission reductions need to take place much earlier.

  10. NASA's Earth Observing System: The Transition from Climate Monitoring to Climate Change Prediction

    NASA Technical Reports Server (NTRS)

    King, Michael D.; Herring, David D.

    1998-01-01

    Earth's 4.5 billion year history is a study in change. Natural geological forces have been rearranging the surface features and climatic conditions of our planet since its beginning. There is scientific evidence that some of these natural changes have not only led to mass extinctions of species (e.g., dinosaurs), but have also severely impacted human civilizations. For instance, there is evidence that a relatively sudden climate change caused a 300-year drought that contributed to the downfall of Akkadia, one of the most powerful empires in the Middle-East region around 2200 BC. More recently, the "little ice age" from 1200-1400 AD forced the Vikings to abandon Greenland when temperatures there dropped by about 1.5 C, rendering it too difficult to grow enough crops to sustain the population. Today, there is compelling scientific evidence that human activities have attained the magnitude of a geological force and are speeding up the rate of global change. For example, carbon dioxide levels have risen 30 percent since the industrial revolution and about 40 percent of the world's land surface has been transformed by humans. We don't understand the cause-and-effect relationships among Earth's land, ocean, and atmosphere well enough to predict what, if any, impacts these rapid changes will have on future climate conditions. We need to make many measurements all over the world, over a long period of time, in order to assemble the information needed to construct accurate computer models that will enable us to forecast climate change. In 1988, the Earth System Sciences Committee, sponsored by NASA, issued a report calling for an integrated, long-term strategy for measuring the vital signs of Earth's climate system. The report urged that the measurements must all be intimately coupled with focused process studies, they must facilitate development of Earth system models, and they must be stored in an information system that ensures open access to consistent, long-term data

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

    NASA Astrophysics Data System (ADS)

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

    2009-12-01

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

  12. Global vegetation distribution and terrestrial climate evolution at the Eocene-Oligocene transition

    NASA Astrophysics Data System (ADS)

    Pound, Matthew; Salzmann, Ulrich

    2016-04-01

    The Eocene - Oligocene transition (EOT; ca. 34-33.5 Ma) is widely considered to be the biggest step in Cenozoic climate evolution. Geochemical marine records show both surface and bottom water cooling, associated with the expansion of Antarctic glaciers and a reduction in the atmospheric CO2 concentration. However, the global response of the terrestrial biosphere to the EOT is less well understood and not uniform when comparing different regions. We present new global vegetation and terrestrial climate reconstructions of the Priabonian (late Eocene; 38-33.9 Ma) and Rupelian (early Oligocene; 33.9-28.45 Ma) by synthesising 215 pollen and spore localities. Using presence/absence data of pollen and spores with multivariate statistics has allowed the reconstruction of palaeo-biomes without relying on modern analogues. The reconstructed palaeo-biomes do not show the equator-ward shift at the EOT, which would be expected from a global cooling. Reconstructions of mean annual temperature, cold month mean temperature and warm month mean temperature do not show a global cooling of terrestrial climate across the EOT. Our new reconstructions differ from previous global syntheses by being based on an internally consistent statistically defined classification of palaeo-biomes and our terrestrial based climate reconstructions are in stark contrast to some marine based climate estimates. Our results raise new questions on the nature and extent of terrestrial global climate change at the EOT.

  13. Empirical Validation of Conceptual Climate Models for the Mid-Pleistocene Transition

    NASA Astrophysics Data System (ADS)

    Gallatin, A.; Camp, C. D.

    2015-12-01

    Conceptual climate models are useful for testing hypotheses regarding the processes underlying observations; but they generally can only qualitatively match the empirical records. Models based on substantially different underlying physics can have comparable correlations with any given observation, thus robust model validation procedures are needed. The Mid-Pleistocene Transition (MPT) is an ideal test case for the development of such procedures because the character and cause of the transition from a dominant 41 kyr cycle in the early Pleistocene to a dominant 100 kyr cycle in the late Pleistocene is poorly understood. Using Ensemble Empirical Mode Decomposition, we analyze multiple conceptual models for the MPT which are based on differing physical hypotheses and show how modern time-series-analysis techniques can improve climate-model validation by extracting and comparing subtler features of both the observations and models.

  14. Livestock in a changing climate: production system transitions as an adaptation strategy for agriculture

    NASA Astrophysics Data System (ADS)

    Weindl, Isabelle; Lotze-Campen, Hermann; Popp, Alexander; Müller, Christoph; Havlík, Petr; Herrero, Mario; Schmitz, Christoph; Rolinski, Susanne

    2015-09-01

    Livestock farming is the world’s largest land use sector and utilizes around 60% of the global biomass harvest. Over the coming decades, climate change will affect the natural resource base of livestock production, especially the productivity of rangeland and feed crops. Based on a comprehensive impact modeling chain, we assess implications of different climate projections for agricultural production costs and land use change and explore the effectiveness of livestock system transitions as an adaptation strategy. Simulated climate impacts on crop yields and rangeland productivity generate adaptation costs amounting to 3% of total agricultural production costs in 2045 (i.e. 145 billion US). Shifts in livestock production towards mixed crop-livestock systems represent a resource- and cost-efficient adaptation option, reducing agricultural adaptation costs to 0.3% of total production costs and simultaneously abating deforestation by about 76 million ha globally. The relatively positive climate impacts on grass yields compared with crop yields favor grazing systems inter alia in South Asia and North America. Incomplete transitions in production systems already have a strong adaptive and cost reducing effect: a 50% shift to mixed systems lowers agricultural adaptation costs to 0.8%. General responses of production costs to system transitions are robust across different global climate and crop models as well as regarding assumptions on CO2 fertilization, but simulated values show a large variation. In the face of these uncertainties, public policy support for transforming livestock production systems provides an important lever to improve agricultural resource management and lower adaptation costs, possibly even contributing to emission reduction.

  15. Toward an understanding of the Middle Pleistocene Transition as a structural change in climate stability

    NASA Astrophysics Data System (ADS)

    Ditlevsen, Peter

    2016-04-01

    The Middle Pleistocene transition signifies a change approximately 1 Myr ago from a period with 40 kyr glacial cycles to a period of approximately 100 kyr cycles in response to the orbital forcing. This change from the "40 kyr world" to the "100 kyr world" is not reflected in noticeable changes in the forcing. To explain this we present a low order conceptual model for the oscillatory dynamics of the ice sheets in terms of a relaxation oscillator with multiple levels subject to the Milankovitch forcing. The model exhibits smooth transitions between three different climate states; an interglacial (i), a mild glacial (g) and a deep glacial (G) as proposed by Paillard (1998). The model suggests a dynamical explanation in terms of the structure of a slow manifold for the observed allowed and ``forbidden'' transitions between the three climate states. With the model, the pacing of the climate oscillations by the astronomical forcing is through the mechanism of phase-resetting of relaxation oscillations in which the internal phase of the oscillation is affected by the forcing.

  16. Transitional properties of droughts and related impacts of climate indices in the Pearl River basin, China

    NASA Astrophysics Data System (ADS)

    Xiao, Mingzhong; Zhang, Qiang; Singh, Vijay P.; Liu, Lin

    2016-03-01

    Drought is the natural hazard poorly understood so far due to various mechanisms behind. Moreover, disastrous effects of drought on human society necessitate accurate forecasting of drought behaviors. In this case, to improve forecasting of drought in the Pearl River basin, a trivariate copula model has been developed and used to include the El Nino Southern Oscillation (ENSO), North Atlantic Oscillation (NAO), Indian Ocean Dipole (IOD) and Pacific Decadal Oscillation (PDO) into model structure of Markov chain. The Standardized Precipitation Evapotranspiration Index (SPEI) has been used to monitor the drought in this study. Comparison with the preliminary correlation analysis between each month climate index and SPEI series indicated that the trivariate copula performs satisfactorily well in evaluation of influences of climate indices on the transition probabilities of drought. It is considered that the region with the negative vertical velocity is dominated by more precipitation and vice versa. Moreover, field patterns of 500 hPa vertical velocity anomalies related to each climate index have further corroborated the influences of climate indices on the drought behaviors. Besides, the mean extreme drought durations under different conditions of each climate index have also been investigated in this study. Results indicated that the mean extreme drought duration tends to be longer in the western part of the Pearl River basin during positive phase of ENSO while tends to be shorter during the positive phase of NAO and vice versa; in the central part of the Pearl River basin, the mean extreme drought duration tends to be shorter during the positive phase of ENSO, NAO and PDO while tends to be longer during the positive episode of IOD, and vice versa; in the eastern part of the Pearl River basin, the mean extreme drought duration tends to be shorter during the positive episode of ENSO and PDO, and vice versa. This study sheds new light on transitional behaviors of

  17. Climate change in the circum-North Atlantic region during the last deglaciation

    NASA Technical Reports Server (NTRS)

    Overpeck, Jonathan T.; Peterson, Larry C.; Kipp, Nilva; Imbrie, John; Rind, David

    1989-01-01

    A survey of new and published palaeoclimate data indicates that both the high- and low-latitude North Atlantic regions were characterized by at least three synchronous periods of abrupt climate change during the last glacial-to-interglacial transition. Climate model results suggest that changes in the melting history of the Laurentide Ice Sheet may explain much of this nonlinear response of the climate system to astronomical (Milankovitch) forcing.

  18. Climate change underlies global demographic, genetic, and cultural transitions in pre-Columbian southern Peru.

    PubMed

    Fehren-Schmitz, Lars; Haak, Wolfgang; Mächtle, Bertil; Masch, Florian; Llamas, Bastien; Cagigao, Elsa Tomasto; Sossna, Volker; Schittek, Karsten; Isla Cuadrado, Johny; Eitel, Bernhard; Reindel, Markus

    2014-07-01

    Several archaeological studies in the Central Andes have pointed at the temporal coincidence of climatic fluctuations (both long- and short-term) and episodes of cultural transition and changes of socioeconomic structures throughout the pre-Columbian period. Although most scholars explain the connection between environmental and cultural changes by the impact of climatic alterations on the capacities of the ecosystems inhabited by pre-Columbian cultures, direct evidence for assumed demographic consequences is missing so far. In this study, we address directly the impact of climatic changes on the spatial population dynamics of the Central Andes. We use a large dataset of pre-Columbian mitochondrial DNA sequences from the northern Rio Grande de Nasca drainage (RGND) in southern Peru, dating from ∼840 BC to 1450 AD. Alternative demographic scenarios are tested using Bayesian serial coalescent simulations in an approximate Bayesian computational framework. Our results indicate migrations from the lower coastal valleys of southern Peru into the Andean highlands coincident with increasing climate variability at the end of the Nasca culture at ∼640 AD. We also find support for a back-migration from the highlands to the coast coincident with droughts in the southeastern Andean highlands and improvement of climatic conditions on the coast after the decline of the Wari and Tiwanaku empires (∼1200 AD), leading to a genetic homogenization in the RGND and probably southern Peru as a whole.

  19. Climate change underlies global demographic, genetic, and cultural transitions in pre-Columbian southern Peru

    PubMed Central

    Fehren-Schmitz, Lars; Haak, Wolfgang; Mächtle, Bertil; Masch, Florian; Llamas, Bastien; Tomasto Cagigao, Elsa; Sossna, Volker; Schittek, Karsten; Isla Cuadrado, Johny; Eitel, Bernhard; Reindel, Markus

    2014-01-01

    Several archaeological studies in the Central Andes have pointed at the temporal coincidence of climatic fluctuations (both long- and short-term) and episodes of cultural transition and changes of socioeconomic structures throughout the pre-Columbian period. Although most scholars explain the connection between environmental and cultural changes by the impact of climatic alterations on the capacities of the ecosystems inhabited by pre-Columbian cultures, direct evidence for assumed demographic consequences is missing so far. In this study, we address directly the impact of climatic changes on the spatial population dynamics of the Central Andes. We use a large dataset of pre-Columbian mitochondrial DNA sequences from the northern Rio Grande de Nasca drainage (RGND) in southern Peru, dating from ∼840 BC to 1450 AD. Alternative demographic scenarios are tested using Bayesian serial coalescent simulations in an approximate Bayesian computational framework. Our results indicate migrations from the lower coastal valleys of southern Peru into the Andean highlands coincident with increasing climate variability at the end of the Nasca culture at ∼640 AD. We also find support for a back-migration from the highlands to the coast coincident with droughts in the southeastern Andean highlands and improvement of climatic conditions on the coast after the decline of the Wari and Tiwanaku empires (∼1200 AD), leading to a genetic homogenization in the RGND and probably southern Peru as a whole. PMID:24979787

  20. Transition to a climate state qualitatively different from modern in NCAR CCSM simulations of the Eocene

    NASA Astrophysics Data System (ADS)

    Caballero, R.; Huber, M.; Hanley, J.

    2012-04-01

    Recent paleoclimate proxy reconstructions indicate that global-mean surface temperatures in past warm climates may have been some 10-15°C higher than today. Little is known about atmospheric dynamics at temperatures this warm. In particular, is it possible that the general circulation may transition to a qualitatively different state at warm enough temperatures? We study this question in a set of simulations using NCAR's Community Climate System Model in both full- and slab-ocean configurations with a range of atmospheric CO2 concentrations extending from preindustrial values (280 ppm) up to 8960 ppm (5 doublings). We find that the simulation at 4480 ppm CO2 gives a remarkably good fit to recent surface temperature reconstructions of the early Eocene, and does not suffer from the classical 'low gradient' problem. We also find that the atmospheric general circulation in this and warmer simulations differs qualitatively from the modern regime in at least two major ways: 1) When equatorial surface temperatures exceed ~33°C, the model undergoes a transition to equatorial superrotation, a state with strong annual- and zonal-mean westerlies on the equator. The transition is driven by zonal momentum convergence due to large-amplitude transient eddies on the equator. These eddies have a structure similar to the observed Madden-Julian Oscillation (MJO). The model's MJO variability is weaker than observed when simulating the modern climate but increases sharply with temperature, coming to dominate the tropical variability and mean state of the warmest climates. 2) Poleward atmospheric moisture transport across midlatitudes decreases with increasing temperature, the opposite behaviour to that at temperatures close to modern. We account for this non-monotonic behaviour in terms of a simple diffusive model of the oceanic storm tracks which suggests that it is due mostly to the drop in mean eddy amplitudes as temperature increases.

  1. Stochastic variability and noise-induced generation of chaos in a climate feedback system including the carbon dioxide dynamics

    NASA Astrophysics Data System (ADS)

    Alexandrov, D. V.; Bashkirtseva, I. A.; Ryashko, L. B.

    2016-08-01

    In this work, a non-linear dynamics of a simple three-dimensional climate model in the presence of stochastic forcing is studied. We demonstrate that a dynamic scenario of mixed-mode stochastic oscillations of the climate system near its equilibrium can be formed. As this takes place, a growth of noise intensity increases the frequency of interspike intervals responsible for the abrupt climate changes. In addition, a certain enhancement of stochastic forcing abruptly increases the atmospheric carbon dioxide and decreases the Earth's ice mass. A transition from order to chaos occurring at a critical noise is shown.

  2. Similar Millennial Climate Variability on the Iberian Margin Before and After the Middle Pleistocene Transition

    NASA Astrophysics Data System (ADS)

    Skinner, L. C.; Birner, B.; Hodell, D. A.; Tzedakis, P. C.

    2015-12-01

    Although millennial-scale climate variability (<10 ka) has been well studied during the last glacial cycles, little is known about this important aspect of climate in the early Pleistocene, prior to the Middle Pleistocene Transition. Here we present a late early Pleistocene climate record at centennial resolution for two representative glaciations during the '41-ka world' (Marine Isotope Stages MIS 37-41, from 1235 to 1320 ka) from IODP Site U1385 ("Shackleton Site") on the southwest Iberian margin. Millennial-scale climate variability was suppressed during interglacial periods (MIS 37, MIS 39 and MIS 41) and was activated during glacial inceptions when benthic δ18O exceeded 3.2‰. Millennial variability during glacials MIS 38 and MIS 40 closely resembled Dansgaard-Oeschger events from the last glaciation (MIS 3) in amplitude, shape and pacing. The phasing of oxygen- and carbon-isotope variability is consistent with an active oceanic thermal bipolar see-saw between the Northern and Southern Hemispheres. Each of the prominent stadials in MIS 38 and MIS 40 was associated with a decrease in benthic carbon isotopes, indicating concomitant changes in meridional overturning circulation. A comparison to other North Atlantic records of ice-rafting in MIS 38 and MIS 40 suggests that freshwater forcing, as proposed for the late Pleistocene, triggered or amplified a slowdown of oceanic circulation and elicited the bipolar see-saw response. Our findings support similarities in the operation of the climate system occurring on millennial timescales both before and after the Middle Pleistocene Transition despite the increase in global ice volume and duration of the glacial cycles.

  3. Detecting abrupt dynamic change based on changes in the fractal properties of spatial images

    NASA Astrophysics Data System (ADS)

    Liu, Qunqun; He, Wenping; Gu, Bin; Jiang, Yundi

    2016-08-01

    Many abrupt climate change events often cannot be detected timely by conventional abrupt detection methods until a few years after these events have occurred. The reason for this lag in detection is that abundant and long-term observational data are required for accurate abrupt change detection by these methods, especially for the detection of a regime shift. So, these methods cannot help us understand and forecast the evolution of the climate system in a timely manner. Obviously, spatial images, generated by a coupled spatiotemporal dynamical model, contain more information about a dynamic system than a single time series, and we find that spatial images show the fractal properties. The fractal properties of spatial images can be quantitatively characterized by the Hurst exponent, which can be estimated by two-dimensional detrended fluctuation analysis (TD-DFA). Based on this, TD-DFA is used to detect an abrupt dynamic change of a coupled spatiotemporal model. The results show that the TD-DFA method can effectively detect abrupt parameter changes in the coupled model by monitoring the changing in the fractal properties of spatial images. The present method provides a new way for abrupt dynamic change detection, which can achieve timely and efficient abrupt change detection results.

  4. Plio-Pleistocene climatic transition and the lifting of the Teton Range, Wyoming

    NASA Astrophysics Data System (ADS)

    Leopold, Estella B.; Liu, Gengwu; Love, J. David; Love, David W.

    2007-01-01

    Fine-grained lacustrine, riverine and ash-fall sediments of the Shooting Iron Formation, whose late Pliocene age is established by Blancan gastropods and vertebrates, yield a pollen flora that is essentially similar in composition to the modern pollen rain in the Jackson Hole area. The Pliocene assemblage suggests a climate like that of the Jackson valley and foothills today. These spectra also resemble a Pliocene pollen flora from Yellowstone Park dated at ˜ 2.02 Ma. However, the underlying Miocene Teewinot sediments differ by containing pollen of four exotic deciduous hardwoods (Tertiary relicts) that suggest a summer-moist climate, unlike that of today. The Shooting Iron sediments lie with an angular unconformity on and above the Miocene lake sediments of the Teewinot Formation. Both of these deposits probably preceded the main uplift of the Teton Range based on the absence of Precambrian clasts in the Tertiary valley deposits. Because the Pliocene floras were modern in aspect, a Plio-Pleistocene transition would be floristically imperceptible here. The sequence denotes a protracted period of relative stability of climate during Teewinot time, and a shift in vegetational state (summer-wet trees drop out) sometime between the latest Miocene and latest Pliocene. The Pliocene spectra suggest a dry, cooler climate toward the end of Shooting Iron time.

  5. Plio-Pleistocene climatic transition and the lifting of the Teton Range, Wyoming

    USGS Publications Warehouse

    Leopold, E.B.; Liu, Gaisheng; Love, J.D.; Love, D.W.

    2007-01-01

    Fine-grained lacustrine, riverine and ash-fall sediments of the Shooting Iron Formation, whose late Pliocene age is established by Blancan gastropods and vertebrates, yield a pollen flora that is essentially similar in composition to the modern pollen rain in the Jackson Hole area. The Pliocene assemblage suggests a climate like that of the Jackson valley and foothills today. These spectra also resemble a Pliocene pollen flora from Yellowstone Park dated at ??? 2.02??Ma. However, the underlying Miocene Teewinot sediments differ by containing pollen of four exotic deciduous hardwoods (Tertiary relicts) that suggest a summer-moist climate, unlike that of today. The Shooting Iron sediments lie with an angular unconformity on and above the Miocene lake sediments of the Teewinot Formation. Both of these deposits probably preceded the main uplift of the Teton Range based on the absence of Precambrian clasts in the Tertiary valley deposits. Because the Pliocene floras were modern in aspect, a Plio-Pleistocene transition would be floristically imperceptible here. The sequence denotes a protracted period of relative stability of climate during Teewinot time, and a shift in vegetational state (summer-wet trees drop out) sometime between the latest Miocene and latest Pliocene. The Pliocene spectra suggest a dry, cooler climate toward the end of Shooting Iron time. ?? 2006 University of Washington.

  6. Rapid climate change did not cause population collapse at the end of the European Bronze Age.

    PubMed

    Armit, Ian; Swindles, Graeme T; Becker, Katharina; Plunkett, Gill; Blaauw, Maarten

    2014-12-02

    The impact of rapid climate change on contemporary human populations is of global concern. To contextualize our understanding of human responses to rapid climate change it is necessary to examine the archeological record during past climate transitions. One episode of abrupt climate change has been correlated with societal collapse at the end of the northwestern European Bronze Age. We apply new methods to interrogate archeological and paleoclimate data for this transition in Ireland at a higher level of precision than has previously been possible. We analyze archeological (14)C dates to demonstrate dramatic population collapse and present high-precision proxy climate data, analyzed through Bayesian methods, to provide evidence for a rapid climatic transition at ca. 750 calibrated years B.C. Our results demonstrate that this climatic downturn did not initiate population collapse and highlight the nondeterministic nature of human responses to past climate change.

  7. Rapid climate change did not cause population collapse at the end of the European Bronze Age

    PubMed Central

    Armit, Ian; Swindles, Graeme T.; Becker, Katharina; Plunkett, Gill; Blaauw, Maarten

    2014-01-01

    The impact of rapid climate change on contemporary human populations is of global concern. To contextualize our understanding of human responses to rapid climate change it is necessary to examine the archeological record during past climate transitions. One episode of abrupt climate change has been correlated with societal collapse at the end of the northwestern European Bronze Age. We apply new methods to interrogate archeological and paleoclimate data for this transition in Ireland at a higher level of precision than has previously been possible. We analyze archeological 14C dates to demonstrate dramatic population collapse and present high-precision proxy climate data, analyzed through Bayesian methods, to provide evidence for a rapid climatic transition at ca. 750 calibrated years B.C. Our results demonstrate that this climatic downturn did not initiate population collapse and highlight the nondeterministic nature of human responses to past climate change. PMID:25404290

  8. Abrupt Climate Change in the Atlantic Ocean During the Last 20,000 Years: Insights from Multi-Element Analyses of Benthic and Planktic Foraminifera and a Coupled OA-GCM

    DTIC Science & Technology

    2005-09-01

    paleoceanographic and terrestrial climate proxies . Greenland ice cores, in particular, provide evidence of large amplitude, very rapid climate change during...received the most attention because it is the largest Holocene excursion in the GISP2 810 record [Alley et al., 1997]. Multiple proxies in Greenland ice...latitude North Atlantic foraminiferal-based proxies such as modem analogue technique [Marchal et al., 2002; Risebrobakken et al., 2003], but

  9. Wave climate, sediment supply and the depth of the sand-mud transition: A global survey

    USGS Publications Warehouse

    George, D.A.; Hill, P.S.

    2008-01-01

    The influences of wave climate and sediment supply on the depths of sand-mud transitions (hSMT) are investigated. Depths of sand-mud transitions (SMT) are based on published granulometric data from surface samples gathered from 14 sites in different wave-dominated coastal environments with fluvial input, including high energy (Columbia, Eel, Russian, San Lorenzo, Copper, and Nepean rivers), moderate energy (Ebro, Nile, Santa Clara, Tseng-wen and Kao-ping rivers), and low energy (Po, Pescara and Tronto rivers) regimes. Geometric mean diameter (GMD) and mud percent are compiled from samples along shore-normal transects, and significant correlation is found between these two textural descriptors. Nominally, the SMT is defined as the transition from GMD > 63????m to 25% mud. This dual definition is applied to the 14 systems, and hSMT is tabulated for each system. Correlation is found between hSMT and the depth at which wave-induced bottom shear stress equals the critical erosion shear stress of the largest mud particles and also between hSMT and significant wave height. Lack of correlation between hSMT and sediment load of nearby rivers indicates either that the influence of sediment supply on depth of the sand-mud transition is small or is not adequately represented in this study. Shelf width and slope do not correlate with residuals from a formalized linear relationship between hSMT and significant wave height. The relationship between hSMT and wave climate is useful for calibration of numerical models of erosion and deposition in wave-dominated coastal environments, for prediction of seabed properties in remote or inaccessible areas, and for reconstruction of paleodepth based on facies changes from sand to mud in ancient rocks. ?? 2008.

  10. Effects of Atlantic warm pool variability over climate of South America tropical transition zone

    NASA Astrophysics Data System (ADS)

    Ricaurte Villota, Constanza; Romero-Rodríguez, Deisy; Andrés Ordoñez-Zuñiga, Silvio; Murcia-Riaño, Magnolia; Coca-Domínguez, Oswaldo

    2016-04-01

    Colombia is located in the northwestern corner of South America in a climatically complex region due to the influence processes modulators of climate both the Pacific and Atlantic region, becoming in a transition zone between phenomena of northern and southern hemisphere. Variations in the climatic conditions of this region, especially rainfall, have been attributed to the influence of the El Nino Southern Oscillation (ENSO), but little is known about the interaction within Atlantic Ocean and specifically Caribbean Sea with the environmental conditions of this region. In this work We studied the influence of the Atlantic Warm Pool (AWP) on the Colombian Caribbean (CC) climate using data of Sea Surface Temperature (SST) between 1900 - 2014 from ERSST V4, compared with in situ data SIMAC (National System for Coral Reef Monitoring in Colombia - INVEMAR), rainfall between 1953-2013 of meteorological stations located at main airports in the Colombian Caribbean zone, administered by IDEAM, and winds data between 2003 - 2014 from WindSat sensor. The parameters analyzed showed spatial differences throughout the study area. SST anomalies, representing the variability of the AWP, showed to be associated with Multidecadal Atlantic Oscillation (AMO) and with the index of sea surface temperature of the North-tropical Atlantic (NTA), the variations was on 3 to 5 years on the ENSO scale and of approximately 11 years possibly related to solar cycles. Rainfall anomalies in the central and northern CC respond to changes in SST, while in the south zone these are not fully engage and show a high relationship with the ENSO. Finally, the winds also respond to changes in SST and showed a signal approximately 90 days possibly related to the Madden-Julian Oscillation, whose intensity depends on the CC region being analyzed. The results confirm that region is a transition zone in which operate several forcing, the variability of climate conditions is difficult to attribute only one, as ENSO

  11. Rock Magnetic Record of the Middle Miocene Climatic Transition at ODP Site 747, Southern Ocean

    NASA Astrophysics Data System (ADS)

    Abrajevitch, A.; Roberts, A. P.; Kodama, K.

    2013-12-01

    ODP Site 747, located on the central Kerguelen Plateau, contains a compete record of the Middle Miocene Climatic Transition (MMCT) - a major cooling event that followed the warm mid-Miocene Climatic Optimum and culminated in an 'icehouse' climate regime. Because of its unusually well preserved and rich foraminiferal assemblages, the MMCT interval at Site 747 has been a focus of several high-resolution paleoclimatic studies that have effectively established this sequence as a reference for the Southern Ocean. Major changes in species abundances across the MMCT are conventionally interpreted to reflect changes in water temperature and salinity. Our XRF and rock magnetic study reveals a good correlation between terrigenous input (likely from local volcanic sources) and the abundances of the dominant planktonic foraminiferal species. Such a correlation suggests that nutrient flux (iron fertilization) played a significant role in controlling microplankton communities during the MMCT at Site 747. Concentration-dependent rock magnetic parameters appear to be a useful proxy for nutrient flux in this pelagic marine environment.

  12. 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.

  13. 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

    2016-07-20

    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.

  14. 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

  15. 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.

  16. The Arctic Holocene Transitions Proxy Climate Database — Principal Millennial-Scale Patterns

    NASA Astrophysics Data System (ADS)

    Kaufman, D. S.; McKay, N.

    2014-12-01

    The Arctic Holocene Transitions (AHT) Project is a community-based, PAGES-endorsed effort to investigate centennial-scale variability in the Arctic climate system during the Holocene, and to understand the feedbacks that lead to pronounced changes. The AHT project recently released a major database of Arctic Holocene proxy climate records (Clim. Past-Disc. 10:1). The systematic review of marine and terrestrial proxy climate time series is based on quantitative screening criteria with new approaches for assessing the geochronological accuracy of age models and for characterizing the climate variables represented by the proxies. Records from only 39% of the sites could be found in the primary paleoclimate data repositories, underscoring the importance of such community-based efforts to assembling a comprehensive product. The database authors, including representatives from six Arctic regions, considered published records from nearly 500 sites. Of these, time series from 170 sites met the criteria for inclusion in the database. Namely, the records are located north of 58°N, extend back at least to 6 cal ka (84% extend back > 8 ka), are resolved at sub-millennial scale (at least one value every 400 ± 200 yr) and have age models constrained by at least one age every 3000 yr. The database contains proxy records from lake sediment (60%), marine sediment (32%), glacier ice (5%), and other sources. Most (60%) reflect temperature (mainly summer warmth) and are primarily based on pollen, chironomid or diatom assemblages. Many (15%) reflect some aspect of hydroclimate as inferred from stable isotopes, pollen assemblages, and other indicators. Principal component (PC) analyses indicates that the predominant pattern of change in temperature-sensitive time series is a ramp between 5 and 3 ka that separates millennial-long intervals of less-pronounced change. This shift corresponds to cooling at most sites, but a substantial fraction of sites warm across this transition. Between

  17. Surface energy exchanges along a tundra-forest transition and feedbacks to climate

    USGS Publications Warehouse

    Beringer, J.; Chapin, F. S.; Thompson, Catharine Copass; McGuire, A.D.

    2005-01-01

    Surface energy exchanges were measured in a sequence of five sites representing the major vegetation types in the transition from arctic tundra to forest. This is the major transition in vegetation structure in northern high latitudes. We examined the influence of vegetation structure on the rates of sensible heating and evapotranspiration to assess the potential feedbacks to climate if high-latitude warming were to change the distribution of these vegetation types. Measurements were made at Council on the Seward Peninsula, Alaska, at representative tundra, low shrub, tall shrub, woodland (treeline), and boreal forest sites. Structural differences across the transition from tundra to forest included an increase in the leaf area index (LAI) from 0.52 to 2.76, an increase in canopy height from 0.1 to 6.1 m, and a general increase in canopy complexity. These changes in vegetation structure resulted in a decrease in albedo from 0.19 to 0.10 as well as changes to the partitioning of energy at the surface. Bulk surface resistance to water vapor flux remained virtually constant across sites, apparently because the combined soil and moss evaporation decreased while transpiration increased along the transect from tundra to forest. In general, sites became relatively warmer and drier along the transect with the convective fluxes being increasingly dominated by sensible heating, as evident by an increasing Bowen ratio from 0.94 to 1.22. The difference in growing season average daily sensible heating between tundra and forest was 21 W m-2. Fluxes changed non-linearly along the transition, with both shrubs and trees substantially enhancing heat transfer to the atmosphere. These changes in vegetation structure that increase sensible heating could feed back to enhance warming at local to regional scales. The magnitude of these vegetation effects on potential high-latitude warming is two to three times greater than suggested by previous modeling studies. ?? 2005 Elsevier B.V. All

  18. 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.

    2017-02-01

    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.

  19. Climatic and landscape controls on water transit times and silicate mineral weathering in the critical zone

    NASA Astrophysics Data System (ADS)

    Zapata-Rios, Xavier; McIntosh, Jennifer; Rademacher, Laura; Troch, Peter A.; Brooks, Paul D.; Rasmussen, Craig; Chorover, Jon

    2015-08-01

    The critical zone (CZ) can be conceptualized as an open system reactor that is continually transforming energy and water fluxes into an internal structural organization and dissipative products. In this study, we test a controlling factor on water transit times (WTT) and mineral weathering called Effective Energy and Mass Transfer (EEMT). We hypothesize that EEMT, quantified based on local climatic variables, can effectively predict WTT within—and mineral weathering products from—the CZ. This study tests whether EEMT or static landscape characteristics are good predictors of WTT, aqueous phase solutes, and silicate weathering products. Our study site is located around Redondo Peak, a rhyolitic volcanic resurgent dome, in northern New Mexico. At Redondo Peak, springs drain slopes along an energy gradient created by differences in terrain aspect. This investigation uses major solute concentrations, the calculated mineral mass undergoing dissolution, and the age tracer tritium and relates them quantitatively to EEMT and landscape characteristics. We found significant correlations between EEMT, WTT, and mineral weathering products. Significant correlations were observed between dissolved weathering products (Na+ and DIC), 3H concentrations, and maximum EEMT. In contrast, landscape characteristics such as contributing area of spring, slope gradient, elevation, and flow path length were not as effective predictive variables of WTT, solute concentrations, and mineral weathering products. These results highlight the interrelationship between landscape, hydrological, and biogeochemical processes and suggest that basic climatic data embodied in EEMT can be used to scale hydrological and hydrochemical responses in other sites.

  20. Mid-Pleistocene climate transition drives net mass loss from rapidly uplifting St. Elias Mountains, Alaska.

    PubMed

    Gulick, Sean P S; Jaeger, John M; Mix, Alan C; Asahi, Hirofumi; Bahlburg, Heinrich; Belanger, Christina L; Berbel, Glaucia B B; Childress, Laurel; Cowan, Ellen; Drab, Laureen; Forwick, Matthias; Fukumura, Akemi; Ge, Shulan; Gupta, Shyam; Kioka, Arata; Konno, Susumu; LeVay, Leah J; März, Christian; Matsuzaki, Kenji M; McClymont, Erin L; Moy, Chris; Müller, Juliane; Nakamura, Atsunori; Ojima, Takanori; Ribeiro, Fabiana R; Ridgway, Kenneth D; Romero, Oscar E; Slagle, Angela L; Stoner, Joseph S; St-Onge, Guillaume; Suto, Itsuki; Walczak, Maureen D; Worthington, Lindsay L; Bailey, Ian; Enkelmann, Eva; Reece, Robert; Swartz, John M

    2015-12-08

    Erosion, sediment production, and routing on a tectonically active continental margin reflect both tectonic and climatic processes; partitioning the relative importance of these processes remains controversial. Gulf of Alaska contains a preserved sedimentary record of the Yakutat Terrane collision with North America. Because tectonic convergence in the coastal St. Elias orogen has been roughly constant for 6 My, variations in its eroded sediments preserved in the offshore Surveyor Fan constrain a budget of tectonic material influx, erosion, and sediment output. Seismically imaged sediment volumes calibrated with chronologies derived from Integrated Ocean Drilling Program boreholes show that erosion accelerated in response to Northern Hemisphere glacial intensification (∼ 2.7 Ma) and that the 900-km-long Surveyor Channel inception appears to correlate with this event. However, tectonic influx exceeded integrated sediment efflux over the interval 2.8-1.2 Ma. Volumetric erosion accelerated following the onset of quasi-periodic (∼ 100-ky) glacial cycles in the mid-Pleistocene climate transition (1.2-0.7 Ma). Since then, erosion and transport of material out of the orogen has outpaced tectonic influx by 50-80%. Such a rapid net mass loss explains apparent increases in exhumation rates inferred onshore from exposure dates and mapped out-of-sequence fault patterns. The 1.2-My mass budget imbalance must relax back toward equilibrium in balance with tectonic influx over the timescale of orogenic wedge response (millions of years). The St. Elias Range provides a key example of how active orogenic systems respond to transient mass fluxes, and of the possible influence of climate-driven erosive processes that diverge from equilibrium on the million-year scale.

  1. Changes of the transitional climate zone in East Asia: past and future

    NASA Astrophysics Data System (ADS)

    Wang, Lin; Chen, Wen; Huang, Gang; Zeng, Gang

    2016-10-01

    The transitional climate zone (TCZ) between humid and arid regions in East Asia is characterized by sharp climate and biome gradients, interaction between the East Asian summer monsoon and the mid-latitude westerly winds and mixed agriculture-pasture activities. Consequently, it is highly vulnerable to natural disturbances and particularly human-driven global change. This study aims to illuminate the spatial and temporal variation of TCZ across both the retrospective and the prospective periods. In the historical period, both the front and rear edges of TCZ exhibit wide year-to-year excursions and have experienced coastward migration with increasing aridity throughout TCZ. Furthermore, precipitation fluctuation mainly contributes to interannual variability of TCZ whereas potential evaporation behavior dominates the long-term trends of TCZ. Models are capable of largely reproducing the shape and orientation of TCZ, although northwestward bias is apparent. In global warming scenario period, there will be continuing southeastward displacement for the front edge but the opposite northwestward movement is projected for the rear one, as a consequence of significant drying trends in the humid zone together with regime shifts towards humid conditions in the arid zone. Despite expanded TCZ sector, however, the available water resources inside it suffer little magnitude changes without preferential tendency towards either drier or wetter conditions, implying neither deleterious nor beneficial effects on the TCZ environment. Moreover, interannual variability of TCZ is expected to become stronger, resulting in more frequent occurrences of extreme swings. Finally, it is noted that uncertainty arising from climate models dominates in the TCZ than dispersed emission scenarios, in contrast to the situation in humid and arid zones.

  2. Mid-Pleistocene climate transition drives net mass loss from rapidly uplifting St. Elias Mountains, Alaska

    PubMed Central

    Jaeger, John M.; Mix, Alan C.; Asahi, Hirofumi; Bahlburg, Heinrich; Belanger, Christina L.; Berbel, Glaucia B. B.; Childress, Laurel; Cowan, Ellen; Drab, Laureen; Forwick, Matthias; Fukumura, Akemi; Ge, Shulan; Gupta, Shyam; Konno, Susumu; LeVay, Leah J.; März, Christian; McClymont, Erin L.; Moy, Chris; Müller, Juliane; Nakamura, Atsunori; Ojima, Takanori; Ribeiro, Fabiana R.; Ridgway, Kenneth D.; Romero, Oscar E.; Slagle, Angela L.; Stoner, Joseph S.; St-Onge, Guillaume; Suto, Itsuki; Walczak, Maureen D.; Worthington, Lindsay L.; Bailey, Ian; Enkelmann, Eva; Reece, Robert; Swartz, John M.

    2015-01-01

    Erosion, sediment production, and routing on a tectonically active continental margin reflect both tectonic and climatic processes; partitioning the relative importance of these processes remains controversial. Gulf of Alaska contains a preserved sedimentary record of the Yakutat Terrane collision with North America. Because tectonic convergence in the coastal St. Elias orogen has been roughly constant for 6 My, variations in its eroded sediments preserved in the offshore Surveyor Fan constrain a budget of tectonic material influx, erosion, and sediment output. Seismically imaged sediment volumes calibrated with chronologies derived from Integrated Ocean Drilling Program boreholes show that erosion accelerated in response to Northern Hemisphere glacial intensification (∼2.7 Ma) and that the 900-km-long Surveyor Channel inception appears to correlate with this event. However, tectonic influx exceeded integrated sediment efflux over the interval 2.8–1.2 Ma. Volumetric erosion accelerated following the onset of quasi-periodic (∼100-ky) glacial cycles in the mid-Pleistocene climate transition (1.2–0.7 Ma). Since then, erosion and transport of material out of the orogen has outpaced tectonic influx by 50–80%. Such a rapid net mass loss explains apparent increases in exhumation rates inferred onshore from exposure dates and mapped out-of-sequence fault patterns. The 1.2-My mass budget imbalance must relax back toward equilibrium in balance with tectonic influx over the timescale of orogenic wedge response (millions of years). The St. Elias Range provides a key example of how active orogenic systems respond to transient mass fluxes, and of the possible influence of climate-driven erosive processes that diverge from equilibrium on the million-year scale. PMID:26598689

  3. Heterogeneity in global vegetation and terrestrial climate change during the late Eocene to early Oligocene transition.

    PubMed

    Pound, Matthew J; Salzmann, Ulrich

    2017-02-24

    Rapid global cooling at the Eocene - Oligocene Transition (EOT), ~33.9-33.5 Ma, is widely considered to mark the onset of the modern icehouse world. A large and rapid drop in atmospheric pCO2 has been proposed as the driving force behind extinctions in the marine realm and glaciation on Antarctica. However, the global terrestrial response to this cooling is uncertain. Here we present the first global vegetation and terrestrial temperature reconstructions for the EOT. Using an extensive palynological dataset, that has been statistically grouped into palaeo-biomes, we show a more transitional nature of terrestrial climate change by indicating a spatial and temporal heterogeneity of vegetation change at the EOT in both hemispheres. The reconstructed terrestrial temperatures show for many regions a cooling that started well before the EOT and continued into the Early Oligocene. We conclude that the heterogeneous pattern of global vegetation change has been controlled by a combination of multiple forcings, such as tectonics, sea-level fall and long-term decline in greenhouse gas concentrations during the late Eocene to early Oligocene, and does not represent a single response to a rapid decline in atmospheric pCO2 at the EOT.

  4. Heterogeneity in global vegetation and terrestrial climate change during the late Eocene to early Oligocene transition

    NASA Astrophysics Data System (ADS)

    Pound, Matthew J.; Salzmann, Ulrich

    2017-02-01

    Rapid global cooling at the Eocene – Oligocene Transition (EOT), ~33.9–33.5 Ma, is widely considered to mark the onset of the modern icehouse world. A large and rapid drop in atmospheric pCO2 has been proposed as the driving force behind extinctions in the marine realm and glaciation on Antarctica. However, the global terrestrial response to this cooling is uncertain. Here we present the first global vegetation and terrestrial temperature reconstructions for the EOT. Using an extensive palynological dataset, that has been statistically grouped into palaeo-biomes, we show a more transitional nature of terrestrial climate change by indicating a spatial and temporal heterogeneity of vegetation change at the EOT in both hemispheres. The reconstructed terrestrial temperatures show for many regions a cooling that started well before the EOT and continued into the Early Oligocene. We conclude that the heterogeneous pattern of global vegetation change has been controlled by a combination of multiple forcings, such as tectonics, sea-level fall and long-term decline in greenhouse gas concentrations during the late Eocene to early Oligocene, and does not represent a single response to a rapid decline in atmospheric pCO2 at the EOT.

  5. Heterogeneity in global vegetation and terrestrial climate change during the late Eocene to early Oligocene transition

    PubMed Central

    Pound, Matthew J.; Salzmann, Ulrich

    2017-01-01

    Rapid global cooling at the Eocene – Oligocene Transition (EOT), ~33.9–33.5 Ma, is widely considered to mark the onset of the modern icehouse world. A large and rapid drop in atmospheric pCO2 has been proposed as the driving force behind extinctions in the marine realm and glaciation on Antarctica. However, the global terrestrial response to this cooling is uncertain. Here we present the first global vegetation and terrestrial temperature reconstructions for the EOT. Using an extensive palynological dataset, that has been statistically grouped into palaeo-biomes, we show a more transitional nature of terrestrial climate change by indicating a spatial and temporal heterogeneity of vegetation change at the EOT in both hemispheres. The reconstructed terrestrial temperatures show for many regions a cooling that started well before the EOT and continued into the Early Oligocene. We conclude that the heterogeneous pattern of global vegetation change has been controlled by a combination of multiple forcings, such as tectonics, sea-level fall and long-term decline in greenhouse gas concentrations during the late Eocene to early Oligocene, and does not represent a single response to a rapid decline in atmospheric pCO2 at the EOT. PMID:28233862

  6. Mid-Holocene climate transition in the Arctic: a database of multicentennial quality climate proxy data from 6 to 2 ka

    NASA Astrophysics Data System (ADS)

    Sundqvist, H. S.; Kaufman, D. S.; Balascio, N. L.

    2012-12-01

    A major goal of paleoclimatology is to reconstruct the spatial-temporal pattern of past climate changes. The spatial-temporal pattern of temperature variability reflects the dynamics of the climate system, including its response to known climate forcing mechanisms and thresholds that lead to rapid transitions. A large network of well-dated proxy climate records is needed to capture the details of past climate variability. We have embarked on major systematic compilation of previously published Holocene proxy climate records from the Arctic. The focus is on well-dated, highly resolved, continuous records that extend to at least 6 ka BP, thereby capturing the transition between the relatively warm conditions of the Holocene thermal maximum and the cooler Neoglaciation. We have identified 139 sites from north of 58° latitude where published proxy records are resolved at centennial scale (at least one value every 400 ± 200 years) and have timescales constrained by at least one radiometric age every 3000 years. We have assembled the metadata for the proxy records from all sites including information on their location, archive and proxy types, climate interpretation, quality of the record (sample resolution and geochronological control), and the data source. The database currently (August 2012) includes the numerical proxy records from most of the sites. We have also compiled the original geochronological data, with the future goal of revising the underlying age models and quantifying age uncertainties. The majority (73%) of the proxy records in the current metadatabase are from lake sediments, with the reminder from marine sediment (17%) and glacier ice (7%). Most of the paleo-temperature records (54%) are based on pollen spectra, and another 26% are based on chironomid assemblages. Many of the proxy records reflect changes in precipitation or hydrology (26%). A high proportion of the sites (35%) are from Fennoscandia, 22% are from the Canadian islands and Greenland

  7. Involuntary attentional capture by abrupt onsets

    NASA Technical Reports Server (NTRS)

    Remington, Roger W.; Johnston, James C.; Yantis, Steven

    1992-01-01

    Five experiments were carried out to examine the extent to which brief abrupt-onset visual stimuli involuntarily capture spatial attention. A fundumantal limitation on the conscious control of spatial attention is demonstrated. Data obtained reveal conditions under which the control of spatial attention is completely involuntary: attention is captured by an irrelevant event despite subjects' intentions to ignore the event. The paradigm used provided strong incentives to ignore the distracting abrupt onset, but these were insufficient to prevent capture. Results suggest that voluntary control of attention is limited to focusing attention in advance on locations, objects, or properties of interest. Under appropriate conditions, spatial attention can be involantarily drawn to abrupt-onset events despite the intention of subjects' to ignore them.

  8. Impact of subgrid-scale radiative heating variability on the stratocumulus-to-trade cumulus transition in climate models

    SciTech Connect

    Xiao, Heng; Gustafson, William I.; Wang, Hailong

    2014-04-29

    Subgrid-scale interactions between turbulence and radiation are potentially important for accurately reproducing marine low clouds in climate models. To better understand the impact of these interactions, the Weather Research and Forecasting (WRF) model is configured for large eddy simulation (LES) to study the stratocumulus-to-trade cumulus (Sc-to-Cu) transition. Using the GEWEX Atmospheric System Studies (GASS) composite Lagrangian transition case and the Atlantic Trade Wind Experiment (ATEX) case, it is shown that the lack of subgrid-scale turbulence-radiation interaction, as is the case in current generation climate models, accelerates the Sc-to-Cu transition. Our analysis suggests that in cloud-topped boundary layers subgrid-scale turbulence-radiation interactions contribute to stronger production of temperature variance, which in turn leads to stronger buoyancy production of turbulent kinetic energy and helps to maintain the Sc cover.

  9. 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.

  10. Refining our estimate of atmospheric CO2 across the Eocene-Oligocene climatic transition

    NASA Astrophysics Data System (ADS)

    Heureux, Ana M. C.; Rickaby, Rosalind E. M.

    2015-01-01

    The Eocene-Oligocene transition (EOT) followed by Oligocene isotope event 1 (Oi-1) is a dramatic global switch in climate characterized by deep-sea cooling and the first formation of permanent Antarctic ice. Models and proxy evidence suggest that declining partial pressure of atmospheric carbon dioxide (CO2atm) below a threshold may explain the onset of global cooling and associated ice formation at Oi-1. However, significant uncertainty remains in the estimated values and salient features of reconstructed CO2atm across this interval. In this study, we present novel carbon isotope records from size separated diatom associated organic matter (δ13Cdiatom) preserved in silica frustules. Physical preservation of this material allows concurrent investigation of isotopic and cell size information, providing two input parameters for biogeochemical models and the reconstruction of CO2atm. We estimate CO2atm in two ways; first we use size and reaction-diffusion kinetics of a cell to calculate a CO2atm threshold. Second we use the calibrated relationship between ɛp(diatom) and carbon dioxide from culture and field studies to create a record of CO2atm prior to and across the transition. Our study, from site 1090 in the Atlantic sector of the Southern Ocean, shows CO2atm values fluctuating between 900 and 1700 ± 100 p.p.m.v. across the EOT followed by a drop to values in the order of 700 to 800 ± 100 p.p.m.v. just prior to the onset of Oi-1. Our values and magnitude of CO2atm change differ from previous estimates, but confirm the overall trends inferred from boron isotopes and alkenones, including a marked rebound following Oi-1. Due to the intricate nature of the climate system and complexities in constraining paleo-proxies, this work emphasizes the importance of a multi-proxy approach to estimating of CO2atm in order to elucidate its role in the emplacement of Antarctic ice-sheets at the EOT.

  11. Abrupt onset of tongue deformation and phase space response of ions in magnetically-confined plasmas

    PubMed Central

    Ida, K.; Kobayashi, T.; Itoh, K.; Yoshinuma, M.; Tokuzawa, T.; Akiyama, T.; Moon, C.; Tsuchiya, H.; Inagaki, S.; Itoh, S.-I.

    2016-01-01

    An abrupt onset of the new tongue-shaped deformation of magnetic surface in magnetized plasmas, which was conjectured in since the 1960s but has not been observed, is experimentally identified just before an abrupt onset of a large-scale collapse event. Two novel properties of the event are identified. First, the transition of symmetry of perturbation (rather than a growth of linearly unstable MHD modes) was found to be a key for the onset of abrupt collapse, i.e., the transition of symmetry gives a new route to the collapse from stable state. Second, as a phase-space response of ions, the distortion from Maxwell-Boltzmann distribution of epithermal ions was observed for the first time. PMID:27796370

  12. Abrupt onset of tongue deformation and phase space response of ions in magnetically-confined plasmas

    NASA Astrophysics Data System (ADS)

    Ida, K.; Kobayashi, T.; Itoh, K.; Yoshinuma, M.; Tokuzawa, T.; Akiyama, T.; Moon, C.; Tsuchiya, H.; Inagaki, S.; Itoh, S.-I.

    2016-10-01

    An abrupt onset of the new tongue-shaped deformation of magnetic surface in magnetized plasmas, which was conjectured in since the 1960s but has not been observed, is experimentally identified just before an abrupt onset of a large-scale collapse event. Two novel properties of the event are identified. First, the transition of symmetry of perturbation (rather than a growth of linearly unstable MHD modes) was found to be a key for the onset of abrupt collapse, i.e., the transition of symmetry gives a new route to the collapse from stable state. Second, as a phase-space response of ions, the distortion from Maxwell-Boltzmann distribution of epithermal ions was observed for the first time.

  13. Spinal Surgery and Abrupt Intrathecal Baclofen Withdrawal.

    PubMed

    Zheng, Karl; Brodsky, Jay B

    2015-11-01

    Abrupt cessation of intrathecal baclofen can lead to a serious withdrawal syndrome. The anesthesiologist must be prepared to avoid intraoperative interruption of baclofen delivery before starting spinal surgery and to recognize and treat the symptoms of baclofen withdrawal in the immediate postoperative period.

  14. 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.

  15. Final Report for "Interdecadal climate regime transition and its interaction with climate change in CMIP5 simulations" (DOE Grant DE-SC0005344)

    SciTech Connect

    Huang, Huei-Ping

    2013-12-10

    Large-amplitude interdecadal shifts of atmospheric and ocean states from one climate regime to another have been observed several times in the 20th century. They include the 1976 transition from cool tropical Pacific SST to warm tropical SST and the post-1998 reversal back to a cooler state. The transition events affect both atmospheric circulation and global water cycle. Because on decadal-to-interdecadal time scale the amplitude of the climate shift is comparable to the trend induced by anthropogenic greenhouse gas forcing, understanding the structure, statistics, and predictability of those events is critical for near-term climate projection. This study analyzed the statistics and predictability of the transition events in the CMIP5 climate model simulations by using a set of climate indices, including atmospheric angular momentum (AAM) and regionally integrated hydrological variables. A significant improvement in the simulated 20th century climatology of AAM is found in CMIP5, compared to earlier simulations in CMIP3. Nevertheless, the improvement in the simulated decadal-to-interdecadal variability in AAM is relatively minor. Systematic biases in the regional water cycle that exist in CMIP3 are found to also exist in CMIP5, although with slight improvements in the latter. Climate shift events with an amplitude comparable to the observed 1976 or 1998 event are found to rarely occur in the CMIP5 20th century simulations. In the 21st century simulations with increasing GHG concentration, the upward trend superimposed to natural variability slightly increases the frequency of occurrences of the large-amplitude events. Even so, 1976-like events remain rare in those runs. In an additional analysis of the CMIP5 Decadal Runs for the 20th century, it is found that the decadal predictability in terms of AAM is generally weak, with useful predictability mainly restricted to within ENSO time scale. Overall, this study showed promises in the improved performance of CMIP5

  16. Timing, cause and consequences of mid-Holocene climate transition in the Arabian Sea

    NASA Astrophysics Data System (ADS)

    Saraswat, Rajeev; Naik, Dinesh Kumar; Nigam, Rajiv; Gaur, Anuruddh Singh

    2016-09-01

    We reconstruct centennial scale quantitative changes in surface seawater temperature (SST), evaporation-precipitation (from Mg/Ca and δ18O of surface dwelling planktic foraminifera), productivity (from relative abundance of Globigerina bulloides), carbon burial (from %CaCO3 and organic carbon [%Corg]) and dissolved oxygen at sediment-water interface, covering the entire Holocene, from a core collected from the eastern Arabian Sea. From the multi-proxy record, we define the timing, consequences and possible causes of the mid-Holocene climate transition (MHCT). A distinct shift in evaporation-precipitation (E-P) is observed at 6.4 ka, accompanied by a net cooling of SST. The shift in SST and E-P is synchronous with a change in surface productivity. A concurrent decrease is also noted in both the planktic foraminiferal abundance and coarse sediment fraction. A shift in carbon burial, as inferred from both the %CaCO3 and %Corg, coincides with a change in surface productivity. A simultaneous decrease in dissolved oxygen at the sediment-water interface, suggests that changes affected both the surface and subsurface water. A similar concomitant change is also observed in other cores from the Arabian Sea as well as terrestrial records, suggesting a widespread regional MHCT. The MHCT coincides with decreasing low-latitude summer insolation, perturbations in total solar intensity and an increase in atmospheric CO2.

  17. Signs of critical transition in the Everglades wetlands in response to climate and anthropogenic changes

    PubMed Central

    Foti, Romano; del Jesus, Manuel; Rinaldo, Andrea; Rodriguez-Iturbe, Ignacio

    2013-01-01

    The increasing pressure of climatic change and anthropogenic activities is predicted to have major effects on ecosystems around the world. With their fragility and sensitivity to hydrologic shifts and land-use changes, wetlands are among the most vulnerable of such ecosystems. Focusing on the Everglades National Park, we here assess the impact of changes in the hydrologic regime, as well as habitat loss, on the spatial configuration of vegetation species. Because the current structuring of vegetation clusters in the Everglades exhibits power-law behavior and such behavior is often associated with self-organization and dynamics occurring near critical transition points, the quantification and prediction of the impact of those changes on the ecosystem is deemed of paramount importance. We implement a robust model able to identify the main hydrologic and local drivers of the vegetation species spatial structuring and apply it for quantitative assessment. We find that shifts in the hydropatterns will mostly affect the relative abundance of species that currently colonize specific hydroperiod niches. Habitat loss or disruption, however, would have a massive impact on all plant communities, which are found to exhibit clear threshold behaviors when a given percentage of habitable habitat is lost. PMID:23576751

  18. Signs of critical transition in the Everglades wetlands in response to climate and anthropogenic changes.

    PubMed

    Foti, Romano; del Jesus, Manuel; Rinaldo, Andrea; Rodriguez-Iturbe, Ignacio

    2013-04-16

    The increasing pressure of climatic change and anthropogenic activities is predicted to have major effects on ecosystems around the world. With their fragility and sensitivity to hydrologic shifts and land-use changes, wetlands are among the most vulnerable of such ecosystems. Focusing on the Everglades National Park, we here assess the impact of changes in the hydrologic regime, as well as habitat loss, on the spatial configuration of vegetation species. Because the current structuring of vegetation clusters in the Everglades exhibits power-law behavior and such behavior is often associated with self-organization and dynamics occurring near critical transition points, the quantification and prediction of the impact of those changes on the ecosystem is deemed of paramount importance. We implement a robust model able to identify the main hydrologic and local drivers of the vegetation species spatial structuring and apply it for quantitative assessment. We find that shifts in the hydropatterns will mostly affect the relative abundance of species that currently colonize specific hydroperiod niches. Habitat loss or disruption, however, would have a massive impact on all plant communities, which are found to exhibit clear threshold behaviors when a given percentage of habitable habitat is lost.

  19. Gravel-rich layers from the Mid-Miocene Climate Transition near East Antarctica

    NASA Astrophysics Data System (ADS)

    Pierce, E. L.; van de Flierdt, T.; Hemming, S. R.; Williams, T.; Cook, C.; Passchier, S.

    2013-12-01

    A major step in the evolution of the East Antarctic ice sheet (EAIS) occurred ~14 million years ago during the Mid-Miocene Climate Transition (MMCT). This global climatic shift had a profound effect on Earth's climatic system, including a decrease in global temperatures and sea level, and an increase in global ice volume. Of particular interest during this transition is the growth of the EAIS; despite inferences on the total amount of ice growth on Antarctica as a whole, little is known of the temporal and spatial evolution of the East Antarctic ice sheet during this time. Here we present direct evidence of ice sheet dynamics during the MMCT from sediment in deep ocean cores close to the Antarctic continent. Between 14.2 and 13.8 Ma, coeval with the MMCT, unusually high concentrations of dropstones are found at IODP Site IODP Site U1356, Wilkes Land, and ODP Site 1165, Prydz Bay. Such concentrations of dropstones are found only in Neogene intervals within these cores, suggesting a particularly dynamic ice sheet during the MMCT. We interpret the IRD-rich layers to be caused by repeated, massive pulses of debris-laden icebergs. Taken together with evidence for global ice volume oscillations from seawater oxygen isotope records, our new records suggests that the MMCT featured repeated growth and collapse of the EAIS in at least two locations. At IODP Site U1356, we have obtained 40Ar/39Ar ages for all available ice-rafted hornblende grains (>150μm). Results suggest a consistent provenance from the nearby Mertz Shear Zone during at least six advance and retreat events of the EAIS within the Wilkes Subglacial Basin during the MMCT. While the ice margin probably sat along the extension of the Mertz Shear Zone at the western edge of the Wilkes Basin, variations in the ɛNd of the fine fraction of these sediments (<63μm) require significant changes in the overall provenance. The occurrence of radiogenic values during at least three times within the MMCT hints to supply

  20. 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.

  1. A recent and abrupt decline in the East African long rains

    NASA Astrophysics Data System (ADS)

    Lyon, Bradfield; DeWitt, David G.

    2012-01-01

    The successive failure of the East African short rains (typically October-December) and subsequent long rains (March-May) in 2010-11 plunged much of the region into severe drought, impacting millions of people and triggering a humanitarian crisis. While poor short rains in 2010 were generally anticipated given linkages with La Niña, the subsequent long rains do not exhibit similar predictability. Here we show the long rains failure in boreal spring of 2011 is consistent with a recurrent large-scale precipitation pattern that followed their abrupt decline around 1999. Using observations and climate model simulations, we show the abrupt decline in long rains precipitation is linked to similarly abrupt changes in sea surface temperatures, predominately in the tropical Pacific basin.

  2. Climate and Fuel Controls on North American Paleofires: Smoldering to Flaming in the Late-glacial-Holocene Transition.

    PubMed

    Han, Y M; Peteet, D M; Arimoto, R; Cao, J J; An, Z S; Sritrairat, S; Yan, B Z

    2016-02-10

    Smoldering and flaming fires, which emit different proportions of organic (OC) and black carbon (BC, in the form of char and soot), have long been recognized in modern wildfire observations but never in a paleo-record, and little is known about their interactions with climate. Here we show that in the late glacial-early Holocene transition period, when the climate was moist, relatively high quantities of char were deposited in Linsley Pond, Connecticut, USA while soot was more abundant during the warmer and drier early Holocene interval. The highest soot mass accumulation rates (MARs) occurred at the beginning of the Holocene as fuel availability increased through the climatic transition when boreal forests were locally extirpated. These variations with time are related to the different formation pathways of char and soot, which are governed by combustion efficiency. This study provides an approach for differentiating smoldering from flaming combustion in paleo-wildfire reconstructions. Our results suggest that climate and fuel loads control the occurrence of different wildfire types and precipitation may play a key role.

  3. Climate and Fuel Controls on North American Paleofires: Smoldering to Flaming in the Late-glacial-Holocene Transition

    PubMed Central

    Han, Y.M.; Peteet, D.M.; Arimoto, R.; Cao, J.J.; An, Z.S.; Sritrairat, S.; Yan, B.Z.

    2016-01-01

    Smoldering and flaming fires, which emit different proportions of organic (OC) and black carbon (BC, in the form of char and soot), have long been recognized in modern wildfire observations but never in a paleo-record, and little is known about their interactions with climate. Here we show that in the late glacial-early Holocene transition period, when the climate was moist, relatively high quantities of char were deposited in Linsley Pond, Connecticut, USA while soot was more abundant during the warmer and drier early Holocene interval. The highest soot mass accumulation rates (MARs) occurred at the beginning of the Holocene as fuel availability increased through the climatic transition when boreal forests were locally extirpated. These variations with time are related to the different formation pathways of char and soot, which are governed by combustion efficiency. This study provides an approach for differentiating smoldering from flaming combustion in paleo-wildfire reconstructions. Our results suggest that climate and fuel loads control the occurrence of different wildfire types and precipitation may play a key role. PMID:26860820

  4. Climate and Fuel Controls on North American Paleofires: Smoldering to Flaming in the Late-glacial-Holocene Transition

    NASA Astrophysics Data System (ADS)

    Han, Y. M.; Peteet, D. M.; Arimoto, R.; Cao, J. J.; An, Z. S.; Sritrairat, S.; Yan, B. Z.

    2016-02-01

    Smoldering and flaming fires, which emit different proportions of organic (OC) and black carbon (BC, in the form of char and soot), have long been recognized in modern wildfire observations but never in a paleo-record, and little is known about their interactions with climate. Here we show that in the late glacial-early Holocene transition period, when the climate was moist, relatively high quantities of char were deposited in Linsley Pond, Connecticut, USA while soot was more abundant during the warmer and drier early Holocene interval. The highest soot mass accumulation rates (MARs) occurred at the beginning of the Holocene as fuel availability increased through the climatic transition when boreal forests were locally extirpated. These variations with time are related to the different formation pathways of char and soot, which are governed by combustion efficiency. This study provides an approach for differentiating smoldering from flaming combustion in paleo-wildfire reconstructions. Our results suggest that climate and fuel loads control the occurrence of different wildfire types and precipitation may play a key role.

  5. Palaeoclimate: Climate's playground

    NASA Astrophysics Data System (ADS)

    Abram, Nerilie J.

    2017-01-01

    Abrupt climate changes in the glacial North Atlantic altered the position of wind systems in the Northern Hemisphere and tropics. Ice-core data show that this disruption also reached the southern westerlies.

  6. Forest elephant mitochondrial genomes reveal that elephantid diversification in Africa tracked climate transitions.

    PubMed

    Brandt, Adam L; Ishida, Yasuko; Georgiadis, Nicholas J; Roca, Alfred L

    2012-03-01

    Among elephants, the phylogeographic patterns of mitochondrial (mt) and nuclear markers are often incongruent. One hypothesis attributes this to sex differences in dispersal and in the variance of reproductive success. We tested this hypothesis by examining the coalescent dates of genetic markers within elephantid lineages, predicting that lower dispersal and lower variance in reproductive success among females would have increased mtDNA relative to nuclear coalescent dates. We sequenced the mitochondrial genomes of two forest elephants, aligning them to mitogenomes of African savanna and Asian elephants, and of woolly mammoths, including the most divergent mitogenomes within each lineage. Using fossil calibrations, the divergence between African elephant F and S clade mitochondrial genomes (originating in forest and savanna elephant lineages, respectively) was estimated as 5.5 Ma. We estimated that the (African) ancestor of the mammoth and Asian elephant lineages diverged 6.0 Ma, indicating that four elephantid lineages had differentiated in Africa by the Miocene-Pliocene transition, concurrent with drier climates. The coalescent date for forest elephant mtDNAs was c. 2.4 Ma, suggesting that the decrease in tropical forest cover during the Pleistocene isolated distinct African forest elephant lineages. For all elephantid lineages, the ratio of mtDNA to nuclear coalescent dates was much greater than 0.25. This is consistent with the expectation that sex differences in dispersal and in variance of reproductive success would have increased the effective population size of mtDNA relative to nuclear markers in elephantids, contributing to the persistence of incongruent mtDNA phylogeographic patterns.

  7. Millennial-scale climate variability in response to changing glacial and orbital boundary conditions during the Mid-Pleistocene transition

    NASA Astrophysics Data System (ADS)

    Ferretti, Patrizia; Crowhurst, Simon; Drysdale, Russell; Bajo, Petra; Barbante, Carlo

    2016-04-01

    The Mid-Pleistocene transition represents perhaps the most important climate transition in the Quaternary period, yet it is one of the most poorly understood. Although the exact timing and mechanism of the onset of the "100 kyr" regime remain a matter of debate, it is well established that the overall periodicity of the glacial-interglacial cycles changed from a dominant 41 kyr obliquity periodicity prior to ~0.9 Ma to a dominant late Pleistocene 100 kyr variance. This change in the frequency domain was associated with an increase in the amplitude of global ice volume variations that, superimposed on a long-term climatic trend towards more glacial conditions over millions of years, produced some of the most extreme glaciations recorded. This interval of time has often been considered to be important in relation to long-term Milankovitch-scale climate variability. In contrast, here, special emphasis will be placed on assessing the presence and the characteristics of the suborbital-scale variability, and reconstructing the evolution of millennial-scale climate variability as the average climate state evolve toward generally colder conditions with larger ice sheets, and the spectral character of climate variability shifted from dominantly 41 kyr to 100 kyr. Appealing evidence suggests that millennial-scale climate variability is amplified during times of intense forcing changes, but this rapid variability has not been thoroughly explored yet at the time when the major changes in climate periodicity occurred. To address these questions, we have examined the record of climatic conditions from Marine Isotope Stages 25 to 16 (~970-650 ka) using high-resolution stable isotope records from benthic and planktonic foraminifera from a sedimentary sequence in the North Atlantic (Integrated Ocean Drilling Program Expedition 306, Site U1313) in order to assess millennial-scale changes in sea-surface and deep-water conditions, the dynamics of thermohaline deep-water circulation

  8. 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

    2015-08-07

    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.

  9. 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

  10. Abrupt change of Antarctic moisture origin at the end of Termination II.

    PubMed

    Masson-Delmotte, V; Stenni, B; Blunier, T; Cattani, O; Chappellaz, J; Cheng, H; Dreyfus, G; Edwards, R L; Falourd, S; Govin, A; Kawamura, K; Johnsen, S J; Jouzel, J; Landais, A; Lemieux-Dudon, B; Lourantou, A; Marshall, G; Minster, B; Mudelsee, M; Pol, K; Röthlisberger, R; Selmo, E; Waelbroeck, C

    2010-07-06

    The deuterium excess of polar ice cores documents past changes in evaporation conditions and moisture origin. New data obtained from the European Project for Ice Coring in Antarctica Dome C East Antarctic ice core provide new insights on the sequence of events involved in Termination II, the transition between the penultimate glacial and interglacial periods. This termination is marked by a north-south seesaw behavior, with first a slow methane concentration rise associated with a strong Antarctic temperature warming and a slow deuterium excess rise. This first step is followed by an abrupt north Atlantic warming, an abrupt resumption of the East Asian summer monsoon, a sharp methane rise, and a CO(2) overshoot, which coincide within dating uncertainties with the end of Antarctic optimum. Here, we show that this second phase is marked by a very sharp Dome C centennial deuterium excess rise, revealing abrupt reorganization of atmospheric circulation in the southern Indian Ocean sector.

  11. Climate Literacy in the Classroom: Supporting Teachers in the Transition to NGSS

    NASA Astrophysics Data System (ADS)

    Rogers, M. J. B.; Merrill, J.; Harcourt, P.; Petrone, C.; Shea, N.; Mead, H.

    2014-12-01

    Meeting the challenge of climate change will clearly require 'deep learning' - learning that motivates a search for underlying meaning, a willingness to exert the sustained effort needed to understand complex problems, and innovative problem-solving. This type of learning is dependent on the level of the learner's engagement with the material, their intrinsic motivation to learn, intention to understand, and relevance of the material to the learner. Here, we present evidence for deep learning about climate change through a simulation-based role-playing exercise, World Climate. The exercise puts participants into the roles of delegates to the United Nations climate negotiations and asks them to create an international climate deal. They find out the implications of their decisions, according to the best available science, through the same decision-support computer simulation used to provide feedback for the real-world negotiations, C-ROADS. World Climate provides an opportunity for participants have an immersive, social experience in which they learn first-hand about both the social dynamics of climate change decision-making, through role-play, and the dynamics of the climate system, through an interactive computer simulation. Evaluation results so far have shown that the exercise is highly engaging and memorable and that it motivates large majorities of participants (>70%) to take action on climate change. In addition, we have found that it leads to substantial gains in understanding key systems thinking concepts (e.g., the stock-flow behavior of atmospheric CO2), as well as improvements in understanding of climate change causes and impacts. While research is still needed to better understand the impacts of simulation-based role-playing exercises like World Climate on behavior change, long-term understanding, transfer of systems thinking skills across topics, and the importance of social learning during the exercise, our results to date indicate that it is a

  12. Cool Science: Year 2 of Using Children's Artwork about Climate Change to Engage Riders on Mass Transit

    NASA Astrophysics Data System (ADS)

    Lustick, D. S.; Lohmeier, J.; Chen, R. F.

    2014-12-01

    A team of educators and scientists from the University of Massachusetts Lowell and the University of Massachusetts Boston will report on the second year of an informal science learning research project using mass transit spaces in Lowell, MA. Cool Science (CS) conducts a statewide art competition for K-12 students in the fall challenging them to express climate science understanding through the visual arts. An inter-disciplinary panel of judges evaluates entries and identifies the top 24 works of art. The best six student works of art are then put on public display throughout the spring on the Lowell Regional Transit Authority (LRTA). Displaying student artwork in Out of Home Multi-Media (OHMM) such as bus placards and posters is intended to engage riders with opportunities to learn informally. CS aims to promote and evaluate learning about climate change science among the general public and k-12 students/teachers. The goals of CS are: 1) Engage teachers, students, and parents in a climate change science communication competition. 2) Display the winning 6 artworks from K-12 students throughout the LRTA. 3) Assess the impact of Cool Science on the teaching and learning of climate science in K-12 formal education. 4) Assess the impact of Cool Science artwork on attitudes, awareness, and understanding of climate change among adult bus riders. A naturalistic inquiry employing a mixed methodology approach best describes our research design. The evaluation focuses on providing feedback regarding the potential learning outcomes for the K-12 students who create the media for the project and the general riding public who engage with the student artwork. To identify possible outcomes, data was collected in the several forms: survey, interviews, and online analytics. We see an urgent need to improve both the public's engagement with climate change science and to the profile of climate change science in formal education settings. The Cool Science (CS) project is an opportunity

  13. 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

  14. 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.

  15. 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.

  16. Mode transitions in Northern Hemisphere glaciation: co-evolution of millennial and orbital variability in Quaternary climate

    NASA Astrophysics Data System (ADS)

    Hodell, David A.; Channell, James E. T.

    2016-09-01

    We present a 3.2 Myr record of stable isotopes and physical properties at IODP Site U1308 (reoccupation of DSDP Site 609) located within the ice-rafted detritus (IRD) belt of the North Atlantic. We compare the isotope and lithological proxies at Site U1308 with other North Atlantic records (e.g., sites 982, 607/U1313, and U1304) to reconstruct the history of orbital and millennial-scale climate variability during the Quaternary. The Site U1308 record documents a progressive increase in the intensity of Northern Hemisphere glacial-interglacial cycles during the late Pliocene and Quaternary, with mode transitions at ˜ 2.7, 1.5, 0.9, and 0.65 Ma. These transitions mark times of change in the growth and stability of Northern Hemisphere ice sheets. They also coincide with increases in vertical carbon isotope gradients between the intermediate and deep ocean, suggesting changes in deep carbon storage and atmospheric CO2. Orbital and millennial climate variability co-evolved during the Quaternary such that the trend towards larger and thicker ice sheets was accompanied by changes in the style, frequency, and intensity of millennial-scale variability. This co-evolution may be important for explaining the observed patterns of Quaternary climate change.

  17. Instability of glacial climate in a model of the ocean- atmosphere-cryosphere system.

    PubMed

    Schmittner, Andreas; Yoshimori, Masakazu; Weaver, Andrew J

    2002-02-22

    In contrast to the relatively stable climate of the past 10,000 years, during glacial times the North Atlantic region experienced large-amplitude transitions between cold (stadial) and warm (interstadial) states. In this modeling study, we demonstrate that hydrological interactions between the Atlantic thermohaline circulation (THC) and adjacent continental ice sheets can trigger abrupt warming events and also limit the lifetime of the interstadial circulation mode. These interactions have the potential to destabilize the THC, which is already more sensitive for glacial conditions than for the present-day climate, thus providing an explanation for the increased variability of glacial climate.

  18. The Last Transition From Extreme Glacial to Extreme Interglacial Climate in NW Patagonia: Regional and Global Implications

    NASA Astrophysics Data System (ADS)

    Moreno, P. I.

    2004-12-01

    The study of interhemispheric climate linkages during and since the last ice age has benefited from the recent development of high-resolution ice core and marine records from the mid- and high latitudes of the Southern Hemisphere. Few paleoclimate records from terrestrial environments in these regions, however, have the temporal continuity, time resolution, and adequate chronologic control to allow a detailed examination of the timing, rates, direction, and phasing of climate change at millennial timescales. Stratigraphic, palynologic, and charcoal records from small, high-sediment accumulating lakes in the Chilean Lake District (41ºS) afford useful data for examining the interval between the LGM to the early Holocene (25-8 ka, ka=cal kyr BP). Millennial-scale changes in glacier extent and vegetation patterns within this interval match key events both in the Northern Hemisphere and Antarctic records, in particular the EPICA Dome C data, highlighting the role of an atmosphere-based conduit for the global propagation of abrupt climate changes. The onset of the last termination in NW Patagonia is marked by glacial collapse and the expansion of rainforest trees at 17.7 ka. An apparent antiphase relationship among the polar hemispheres between 17.7-14.7 ka, might reflect the hemispheric-scale effects of a quasi-total shut down of Atlantic Meridional Overturning circulation driven by Heinrich event 1. Extreme glacial and interglacial modes in the position/strength of the westerlies at multi-millennial timescales in the southern westerlies accompany important shifts in the abundance and composition of rainforest communities during the last termination and the early Holocene. At millennial timescales, this interval is characterised by successive warming pulses interrupted by a generalized reversal in trend with cooling events starting at 14.7 and 13.4 ka. Fires between 12.9-11.5 ka, i.e. Younger Dryas Chron (YDC), led to the expansion of opportunistic rainforest species

  19. Transition.

    ERIC Educational Resources Information Center

    Thompson, Sandy, Ed.; And Others

    1990-01-01

    This "feature issue" focuses on transition from school to adult life for persons with disabilities. Included are "success stories," brief program descriptions, and a list of resources. Individual articles include the following titles and authors: "Transition: An Energizing Concept" (Paul Bates); "Transition…

  20. 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.

  1. Climatology of extratropical transition for North Atlantic tropical cyclones in the high-resolution GFDL climate model

    NASA Astrophysics Data System (ADS)

    Liu, M.; Vecchi, G. A.; Smith, J. A.

    2015-12-01

    The extratropical transition (ET) process of tropical cyclones can lead to fundamental changes in hurricane structure and storms that continue to pose large threats to life and properties. Given the importance of ET, it is necessary to understand how ET changes under a warming climate. Towards this goal, the GFDL climate model (FLOR) is first used to understand the current-day ET climatology. The standard model and a flux-adjusted version of FLOR are both used to examine ET climatology. The operational cyclone phase space method is used to define the onset and completion times of ET. The ET climatology from the climate model is compared with those from two reanalysis data sets ranging from 1979 to 2012. Both models exhibit good skills at simulating the frequency map of phase space diagram. The flux-adjusted version shows much better skill in capturing the ET climatology in terms of ET track patterns, ET locations and monthly ET variations. The model is able to simulate the frequency ratio of reintensified tropical cyclones from all ET cases. Future work involves examining changes in the ET climatology under a changing climate.

  2. Scalariform-to-simple transition in vessel perforation plates triggered by differences in climate during the evolution of Adoxaceae

    PubMed Central

    Lens, Frederic; Vos, Rutger A.; Charrier, Guillaume; van der Niet, Timo; Merckx, Vincent; Baas, Pieter; Aguirre Gutierrez, Jesus; Jacobs, Bart; Chacon Dória, Larissa; Smets, Erik; Delzon, Sylvain; Janssens, Steven B.

    2016-01-01

    Background and Aims Angiosperms with simple vessel perforations have evolved many times independently of species having scalariform perforations, but detailed studies to understand why these transitions in wood evolution have happened are lacking. We focus on the striking difference in wood anatomy between two closely related genera of Adoxaceae, Viburnum and Sambucus, and link the anatomical divergence with climatic and physiological insights. Methods After performing wood anatomical observations, we used a molecular phylogenetic framework to estimate divergence times for 127 Adoxaceae species. The conditions under which the genera diversified were estimated using ancestral area reconstruction and optimization of ancestral climates, and xylem-specific conductivity measurements were performed. Key Results Viburnum, characterized by scalariform vessel perforations (ancestral), diversified earlier than Sambucus, having simple perforations (derived). Ancestral climate reconstruction analyses point to cold temperate preference for Viburnum and warm temperate for Sambucus. This is reflected in the xylem-specific conductivity rates of the co-occurring species investigated, showing that Viburnum lantana has rates much lower than Sambucus nigra. Conclusions The lack of selective pressure for high conductive efficiency during early diversification of Viburnum and the potentially adaptive value of scalariform perforations in frost-prone cold temperate climates have led to retention of the ancestral vessel perforation type, while higher temperatures during early diversification of Sambucus have triggered the evolution of simple vessel perforations, allowing more efficient long-distance water transport. PMID:27498812

  3. Noise-induced generation of saw-tooth type transitions between climate attractors and stochastic excitability of paleoclimate

    NASA Astrophysics Data System (ADS)

    Alexandrov, Dmitri V.; Bashkirtseva, Irina A.; Ryashko, Lev B.

    2015-11-01

    Motivated by important paleoclimate applications we study a three dimensional model of the Quaternary climatic variations in the presence of stochastic forcing. It is shown that the deterministic system exhibits a limit cycle and two stable system equilibria. We demonstrate that the closer paleoclimate system to its bifurcation points (lying either in its monostable or bistable zone) the smaller noise generates small or large amplitude stochastic oscillations, respectively. In the bistable zone with two stable equilibria, noise induces a complex multimodal stochastic regime with intermittency of small and large amplitude stochastic fluctuations. In the monostable zone, the small amplitude stochastic oscillations localized in the vicinity of unstable equilibrium appear along with the large amplitude oscillations near the stable limit cycle. For the analysis of these noise-induced effects, we develop the stochastic sensitivity technique and use the Mahalanobis metric in the three-dimensional case. To approximate the distribution of random trajectories in Poincare sections, we use a method of confidence ellipses. A spatial configuration of these ellipses is defined by the stochastic sensitivity and noise intensity. The glaciation/deglaciation transitions going between two polar Earth's states with the warm and cold climate become easier and quicker with increasing the noise intensity. Our stochastic analysis demonstrates a near 100 ky saw-tooth type climate self fluctuations known from paleoclimate records. In addition, the enhancement of noise intensity blurs the sharp climate cycles and reduces the glaciation-deglaciation periods of the Earth's paleoclimate.

  4. Staggering Changes in Mediterranean Sea Surface Temperatures Coincide with Global Climate and Evolution Transitions during the Late Miocene - Pliocene

    NASA Astrophysics Data System (ADS)

    Tzanova, A.; Herbert, T.; Peterson, L.

    2012-12-01

    The Late Miocene warmer-than-modern Earth is a time of important transitions such as the C3/C4 photosynthesis transition, the appearance of the Sahara and the hominin evolution. The interconnections and drivers for climate and evolutionary change during this time, such as pCO2, albedo, vegetation and temperatures, are still speculative. The causal relationships can be better understood via paleoproxy records from sensitive to climate shifts areas such as the Mediterranean Sea. The Mediterranean Sea is a largely enclosed mid-latitude basin on the cusp of the subtropical climate zone formed after the closure of the Tethys. The enclosed nature of the Mediterranean Sea makes it sensitive to continental climate and shifts in climate zones with the advantage of resolution, preservation and detail usually reserved for marine records Here we present a continuous 30 kyr resolution, sea surface temperature (SST) record for the Mediterranean Sea (Late Miocene - Pliocene) from the well-dated, uplifted marine sequences of Monte dei Corvi in Northern Italy and Rosello in Sicily, Italy. The Late Miocene portion of the record is from the pelagic, uplifted Monte dei Corvi land section. The data from two organic paleothermometers UK'37 and TEX86, establish the Mediterranean Sea as notably warmer than present. SSTs were equivalent and even higher than the warmest parts of the modern ocean. For the oldest samples, ~ 12.9 Ma to ~8.1 Ma, UK'37 derived temperatures hovered close to 28oC and possibly even higher. A distinct cooling trend takes over starting at ~8.1 Ma and superimposed upon it are prominent, high variability, cold episodes lasting from ~7 Ma to 6 Ma. During these extreme episodes, reconstructed SSTs reach values comparable the modern eastern Mediterranean annual average SST of 19.5oC. The variability during this colder period is substantial, with temperature swings of as much as ~6-8 oC over 40 kyr. Continuous pelagic sedimentation resumes after the Messinian Salinity

  5. The Dorsa Argentea Formation and the Noachian-Hesperian Transition: Climate and Glacial Flow Modeling

    NASA Astrophysics Data System (ADS)

    Scanlon, K. E.; Head, J. W.; Fastook, J. L.; Wordsworth, R. D.

    2016-09-01

    We used early Mars GCM and glacial flow model simulations to constrain climates allowing development, basal melting, and recession of an ice sheet consistent with the Noachian-Hesperian landforms and geologic units at the south pole of Mars.

  6. Perceived School Climate across the Transition from Elementary to Middle School

    ERIC Educational Resources Information Center

    Madjar, Nir; Cohen-Malayev, Maya

    2016-01-01

    The implications of the transition from elementary to middle school are of major concern for educators and researchers worldwide. Previous studies have yielded ambiguous findings; some have indicated negative outcomes of school transition, whereas others have demonstrated null or even positive effects. The aim of the current research was to…

  7. 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

  8. Noachian-Hesperian Transition and a Possible Climatic Optimum: Evidence from Landforms

    NASA Technical Reports Server (NTRS)

    Moore, J. M.; Howard, A. D.

    2004-01-01

    A climatic optimum? The often strong contrast between the pristine and degraded Noachian channels and craters might be due to a gradual climatic change superimposed upon an episode of mantling associated with early Hesperian volcanism. On the other hand, one or more episodes of volcanism or large impacts could have induced global warming and produced a relatively short-lived optimum for precipitation and runoff. The rapid cutoff of fluvial activity following the development of the later pristine fluvial features is consistent with this scenario. We discuss the changing style of erosion in the highlands during the Noachian and early Hesperian in a companion abstract to this workshop. Here we review the some of the morphologic evidence for a possible Noachian-Hesperian (N-H) climate optimum.

  9. 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.

  10. 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

  11. Indian monsoon variations during three contrasting climatic periods: the Holocene, Heinrich Stadial 2 and the last interglacial-glacial transition

    NASA Astrophysics Data System (ADS)

    Zorzi, Coralie; Fernanda Sanchez Goñi, Maria; Anupama, Krishnamurthy; Prasad, Srinivasan; Hanquiez, Vincent; Johnson, Joel; Giosan, Liviu

    2016-04-01

    In contrast to the East Asian and African monsoons the Indian monsoon is still poorly documented throughout the last climatic cycle (last 135,000 years). Pollen analysis from two marine sediment cores (NGHP-01-16A and NGHP-01-19B) collected from the offshore Godavari and Mahanadi basins, both located in the Core Monsoon Zone (CMZ) reveals changes in Indian summer monsoon variability and intensity during three contrasting climatic periods: the Holocene, the Heinrich Stadial (HS) 2 and the Marine Isotopic Stage (MIS) 5/4 during the ice sheet growth transition. During the first part of the Holocene between 11,300 and 4,200 cal years BP, characterized by high insolation (minimum precession, maximum obliquity), the maximum extension of the coastal forest and mangrove reflects high monsoon rainfall. This climatic regime contrasts with that of the second phase of the Holocene, from 4,200 cal years BP to the present, marked by the development of drier vegetation in a context of low insolation (maximum precession, minimum obliquity). The historical period in India is characterized by an alternation of strong and weak monsoon centennial phases that may reflect the Medieval Climate Anomaly and the Little Ice Age, respectively. During the HS 2, a period of low insolation and extensive iceberg discharge in the North Atlantic Ocean, vegetation was dominated by grassland and dry flora indicating pronounced aridity as the result of a weak Indian summer monsoon. The MIS 5/4 glaciation, also associated with low insolation but moderate freshwater fluxes, was characterized by a weaker reduction of the Indian summer monsoon and a decrease of seasonal contrast as recorded by the expansion of dry vegetation and the development of Artemisia, respectively. Our results support model predictions suggesting that insolation changes control the long term trend of the Indian monsoon precipitation, but its millennial scale variability and intensity are instead modulated by atmospheric

  12. Indian monsoon variations during three contrasting climatic periods: The Holocene, Heinrich Stadial 2 and the last interglacial-glacial transition

    NASA Astrophysics Data System (ADS)

    Zorzi, Coralie; Sanchez Goñi, Maria Fernanda; Anupama, Krishnamurthy; Prasad, Srinivasan; Hanquiez, Vincent; Johnson, Joel; Giosan, Liviu

    2015-10-01

    In contrast to the East Asian and African monsoons the Indian monsoon is still poorly documented throughout the last climatic cycle (last 135,000 years). Pollen analysis from two marine sediment cores (NGHP-01-16A and NGHP-01-19B) collected from the offshore Godavari and Mahanadi basins, both located in the Core Monsoon Zone (CMZ) reveals changes in Indian summer monsoon variability and intensity during three contrasting climatic periods: the Holocene, the Heinrich Stadial (HS) 2 and the Marine Isotopic Stage (MIS) 5/4 during the ice sheet growth transition. During the first part of the Holocene between 11,300 and 4200 cal years BP, characterized by high insolation (minimum precession, maximum obliquity), the maximum extension of the coastal forest and mangrove reflects high monsoon rainfall. This climatic regime contrasts with that of the second phase of the Holocene, from 4200 cal years BP to the present, marked by the development of drier vegetation in a context of low insolation (maximum precession, minimum obliquity). The historical period in India is characterized by an alternation of strong and weak monsoon centennial phases that may reflect the Medieval Climate Anomaly and the Little Ice Age, respectively. During the HS 2, a period of low insolation and extensive iceberg discharge in the North Atlantic Ocean, vegetation was dominated by grassland and dry flora indicating pronounced aridity as the result of a weak Indian summer monsoon. The MIS 5/4 glaciation, also associated with low insolation but moderate freshwater fluxes, was characterized by a weaker reduction of the Indian summer monsoon and a decrease of seasonal contrast as recorded by the expansion of dry vegetation and the development of Artemisia, respectively. Our results support model predictions suggesting that insolation changes control the long term trend of the Indian monsoon precipitation, but its millennial scale variability and intensity are instead modulated by atmospheric

  13. 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.

  14. 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

  15. Transitioning to a low-carbon climate-smart metropolitan America

    SciTech Connect

    Brown, Dr. Marilyn Ann; Southworth, Frank; Sarzynski, Andrea

    2010-01-01

    Meeting the climate challenge requires the leadership of metropolitan America. With two-thirds of the U.S. population and nearly three-quarters of the nation s economic activity residing in the nation s 100 largest metropolitan areas, urban centers account for much of the nation s greenhouse gas (GHG) emissions. At the same time, metropolitan America is the traditional locus of technological, entrepreneurial, and policy innovations. Its access to capital and a highly trained workforce have enabled metropolitan areas to play a pivotal role in expanding U.S. business opportunities while solving environmental challenges. With supportive federal policies, metropolitan areas can provide the low-carbon climate-smart leadership that is required to meet the nation s targets and timetables necessary to avoid dangerous levels of atmospheric greenhouse gases.

  16. The climate of HD 189733b from fourteen transits and eclipses measured by Spitzer

    SciTech Connect

    Agol, E.; Cowan, Nicolas B.; Knutson, Heather A.; Deming, Drake; Steffen, Jason H.; Henry, Gregory W.; Charbonneau, David; /Harvard-Smithsonian Ctr. Astrophys.

    2010-07-01

    We present observations of six transits and six eclipses of the transiting planet system HD 189733 taken with the Spitzer Space Telescope IRAC camera at 8 microns, as well as a re-analysis of previously published data. We use several novel techniques in our data analysis, the most important of which is a new correction for the detector 'ramp' variation with a double-exponential function which performs better and is a better physical model for this detector variation. Our main scientific findings are: (1) an upper limit on the variability of the day-side planet flux of 2.7% (68% confidence); (2) the most precise set of transit times measured for a transiting planet, with an average accuracy of 3 seconds; (3) a lack of transit-timing variations, excluding the presence of second planets in this system above 20% of the mass of Mars in low-order mean-motion resonance at 95% confidence; (4) a confirmation of the planet's phase variation, finding the night side is 64% as bright as the day side, as well as an upper limit on the night-side variability of 17% (68% confidence); (5) a better correction for stellar variability at 8 micron causing the phase function to peak 3.5 hours before secondary eclipse, confirming that the advection and radiation timescales are comparable at the 8 micron photosphere; (6) variation in the depth of transit, which possibly implies variations in the surface brightness of the portion of the star occulted by the planet, posing a fundamental limit on non-simultaneous multi-wavelength transit absorption measurements of planet atmospheres; (7) a measurement of the infrared limb-darkening of the star, which is in good agreement with stellar atmosphere models; (8) an offset in the times of secondary eclipse of 69 seconds, which is mostly accounted for by a 31 second light travel time delay and 33 second delay due to the shift of ingress and egress by the planet hot spot; this confirms that the phase variation is due to an offset hot spot on the

  17. The Climate of HD 189733b from Fourteen Transits and Eclipses Measured by Spitzer

    NASA Astrophysics Data System (ADS)

    Agol, Eric; Cowan, Nicolas B.; Knutson, Heather A.; Deming, Drake; Steffen, Jason H.; Henry, Gregory W.; Charbonneau, David

    2010-10-01

    We present observations of six transits and six eclipses of the transiting planet system HD 189733 taken with the Spitzer Space Telescope's Infrared Array Camera (IRAC) at 8 μm, as well as a re-analysis of previously published data. We use several novel techniques in our data analysis, the most important of which is a new correction for the detector "ramp" variation with a double-exponential function, which performs better and is a better physical model for this detector variation. Our main scientific findings are (1) an upper limit on the variability of the dayside planet flux of 2.7% (68% confidence); (2) the most precise set of transit times measured for a transiting planet, with an average accuracy of 3 s; (3) a lack of transit-timing variations, excluding the presence of second planets in this system above 20% of the mass of Mars in low-order mean-motion resonance at 95% confidence; (4) a confirmation of the planet's phase variation, finding the night side is 64% as bright as the day side, as well as an upper limit on the nightside variability of 17% (68% confidence); (5) a better correction for stellar variability at 8 μm causing the phase function to peak 3.5 hr before secondary eclipse, confirming that the advection and radiation timescales are comparable at the 8 μm photosphere; (6) variation in the depth of transit, which possibly implies variations in the surface brightness of the portion of the star occulted by the planet, posing a fundamental limit on non-simultaneous multi-wavelength transit absorption measurements of planet atmospheres; (7) a measurement of the infrared limb darkening of the star, which is in good agreement with stellar atmosphere models; (8) an offset in the times of secondary eclipse of 69 s, which is mostly accounted for by a 31 s light-travel time delay and 33 s delay due to the shift of ingress and egress by the planet hot spot; this confirms that the phase variation is due to an offset hot spot on the planet; (9) a

  18. Multiple equilibria, natural variability, and climate transitions in an idealized ocean-atmosphere model

    SciTech Connect

    Saravanan, R.; McWilliams, J.C.

    1995-10-01

    An idealized coupled ocean-atmosphere is constructed to study climatic equilibria and variability. The model focuses on the role of large-scale fluid motions in the climate system. The atmospheric component is an eddy-resolving two-level global primitive equation model with simplified physical parameterizations. The oceanic component is a zonally averaged sector model of the thermohaline circulation. The two components exchange heat and freshwater fluxes synchonously. Coupled integrations are carried out over periods of several centuries to identify the equilibrium states of the ocean-atmosphere system. It is shown that there exist at least three types of equilibria, which are distinguished by whether they have upwelling or downwelling in the polar regions. Each oceanic circulation in the coupled model exhibits natural variability on interdecadal and longer timescales. The dominant interdecadal mode of variability is associated with the advection of oceanic temperature anomalies in the sinking regions. The sensitivity of the coupled model to climatic perturbations is studied. A rapid increase in the greenhouse gas concentrations leads to a collapse of the meridional overtuning in the ocean. Introduction of a large positive surface freshwater anomaly in the high latitudes leads to a temporary suppression of the sinking motion, followed by a rapid recovery, due primarily to the high latitude cooling associated with the reduction of oceanic heat transport. In this evolution, the secondary roles played by the atmospheric heat transport and moisture transport in destablizing the thermohaline circulation are compared, and the former is found to be dominant.

  19. Arctic climate tipping points.

    PubMed

    Lenton, Timothy M

    2012-02-01

    There is widespread concern that anthropogenic global warming will trigger Arctic climate tipping points. The Arctic has a long history of natural, abrupt climate changes, which together with current observations and model projections, can help us to identify which parts of the Arctic climate system might pass future tipping points. Here the climate tipping points are defined, noting that not all of them involve bifurcations leading to irreversible change. Past abrupt climate changes in the Arctic are briefly reviewed. Then, the current behaviour of a range of Arctic systems is summarised. Looking ahead, a range of potential tipping phenomena are described. This leads to a revised and expanded list of potential Arctic climate tipping elements, whose likelihood is assessed, in terms of how much warming will be required to tip them. Finally, the available responses are considered, especially the prospects for avoiding Arctic climate tipping points.

  20. 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…

  1. 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.

  2. Late Glacial to Holocene abrupt temperature changes recorded by Crenarchaeota in Lake Lucerne (Vierwaldstättersee, Switzerland)

    NASA Astrophysics Data System (ADS)

    Blaga, Cornelia I.; Reichart, Gert-Jan; Lotter, André F.; Anselmetti, Flavio; Sinninghe Damsté, Jaap S.

    2010-05-01

    In this study we applied the TEX86 (TetraEther Index of 86 carbon atoms) temperature proxy to a sediment core from Lake Lucerne (Vierwaldstättersee) to reconstruct, in almost decadal resolution, temperature changes during the Younger Dryas and the Early Holocene (ca. 14600 to 10600 cal. BP). The TEX86 proxy suggests a sequence of shifts during the late glacial period that strongly resemble the shifts in δ18O values from the Greenland ice core record. The TEX86-reconstructed lake temperature record indicates a step-wise pattern of climate changes across the studied interval with a shift from colder to warmer temperatures at the onset of the late-glacial interstadial, followed by an abrupt cooling at the onset of Younger Dryas and a rapid warming from 5.5 to 9°C at the Younger Dryas/Holocene transition in less than 200 years. The temperature change associated with the Interstadial-Younger Dryas alternation is ca. 4 °C and is in line with previous temperature reconstructions based on different proxies. The rapid changes in temperature associated with the last deglaciation are reflected in the highest possible detail in the TEX86 record. It is thus clear that our proxy, based on the isoprenoidal GDGTs (Glycerol Dialkyl Glycerol Tetraethers), is capable to reflect high resolution records of rapid (decadal to century scale oscillations) environmental fluctuations comparable with those obtained from ice cores.

  3. 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.

  4. Modeling abrupt cultural regime shifts during the Palaeolithic and Stone Age.

    PubMed

    Aoki, Kenichi

    2014-12-07

    The coupled dynamics of the size and the mean cultural/technological level of a population, with positive feedback between these two variables, is modeled in the Malthusian-Boserupian framework. Bifurcation diagrams, with innovativeness or the cultureless carrying capacity as the parameter, show that abrupt transitions in the mean cultural level are possible. For example, a gradual evolutionary change toward greater innate innovativeness would produce an associated gradual increase in mean cultural level, until a threshold is crossed that triggers an abrupt cultural regime shift. Hence, the model may help explain the apparently sudden and dramatic efflorescences of Palaeolithic/Stone Age culture during the Late Pleistocene, without having to invoke major contemporaneous genetic changes in cognition. The results of statistical studies on the association between population size and toolkit diversity among ethnographic societies are also discussed.

  5. 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.

  6. A nonlinear dynamical 2D coupled mathematical model for phase transitions in methane gas hydrates within permafrost under climate change

    NASA Astrophysics Data System (ADS)

    Duxbury, N. S.; Romanovsky, V. E.; Romanovskii, N. N.; Garagulya, L. S.; Brouchkov, A. V.; Komarov, I. A.; Roman, L. T.; Tipenko, G. S.; Buldovich, S. N.; Maximova, L. N.

    2012-12-01

    We have developed coupled permafrost - carbon physical and numerical models, where carbon is in the form of methane clathrate hydrate ( CH4*6H2O ) in a porous subsurface environment. The driving force for the subsurface temperature field dynamics is climate variations on the Earth's surface. This is an upper boundary condition for the nonlinear evolutionary system of partial differential equations (PDEs) describing subsurface heat transfer (parabolic PDEs) in a generalized Stefan formulation. The developed numerical model is a valuable computational tool to quantitatively study nonlinear dynamical thermal processes with phase transitions in terrestrial and Martian subsurfaces. Our model is multifrontal and therefore allows one to perform computations for a problem with any number of emerging/vanishing phase transition interfaces (both in methane gas hydrate deposits and in permafrost), since the model treats these fronts implicitly in an enthalpy formulation and in corresponding finite-difference scheme. This model takes into account the pressure (and therefore the depth) dependence of the phase transition temperature for methane clathrate hydrate. We have performed model computations using the thermophysical characteristics (heat capacity, density/porosity, thermal conductivity) for the Siberian subsurface. It can be used as a terrestrial analog for the Martian subsurface (e.g., Duxbury et al., 2001). Also, thermophysical coefficients from laboratory experiments for methane clathrate hydrate were used in our model. In addition, our model takes into account the dependence of subsurface thermophysical characteristics on temperature and spatial coordinates. The results of our computations and their interpretation will be presented. References. N. S. Duxbury, I. A. Zotikov, K. H. Nealson, V. E. Romanovsky, F. D. Carsey (2001). A numerical model for an alternative origin of Lake Vostok and its exobiological implications for Mars, Journal of Geophysical Research

  7. Antarctic Ice Sheet variability across the Eocene-Oligocene boundary climate transition.

    PubMed

    Galeotti, Simone; DeConto, Robert; Naish, Timothy; Stocchi, Paolo; Florindo, Fabio; Pagani, Mark; Barrett, Peter; Bohaty, Steven M; Lanci, Luca; Pollard, David; Sandroni, Sonia; Talarico, Franco M; Zachos, James C

    2016-04-01

    About 34 million years ago, Earth's climate cooled and an ice sheet formed on Antarctica as atmospheric carbon dioxide (CO2) fell below ~750 parts per million (ppm). Sedimentary cycles from a drill core in the western Ross Sea provide direct evidence of orbitally controlled glacial cycles between 34 million and 31 million years ago. Initially, under atmospheric CO2 levels of ≥600 ppm, a smaller Antarctic Ice Sheet (AIS), restricted to the terrestrial continent, was highly responsive to local insolation forcing. A more stable, continental-scale ice sheet calving at the coastline did not form until ~32.8 million years ago, coincident with the earliest time that atmospheric CO2 levels fell below ~600 ppm. Our results provide insight into the potential of the AIS for threshold behavior and have implications for its sensitivity to atmospheric CO2 concentrations above present-day levels.

  8. The Campanian - Maastrichtian (Late Cretaceous) climate transition linked to a global carbon cycle perturbation

    NASA Astrophysics Data System (ADS)

    Voigt, S.; Friedrich, O.; Gale, A. S.

    2009-04-01

    The Late Cretaceous was a period of long-term climate cooling succeeding the extreme warmth of the mid-Cretaceous greenhouse world. The cooling is mainly considered as a result of changes in ocean circulation due to plate movements resulting in progressive deep-water exchange between the deep oceanic basins and a parallel drop in atmospheric carbon dioxide concentrations. In Campanian - Maastrichtian times, pronounced climate cooling is documented between 71 - 69 Ma, when distinct changes in foraminiferal oxygen and carbon isotope data at a global scale indicate substantial deep-water cooling and reduced rates of organic carbon burial. The causal mechanisms of this cooling period, however, are poorly understood to date. While some authors suggest mainly oceanographic changes, others supposed an ephemeral glaciation related to a eustatic sea-level fall. Mainly, the relative timing of oceanic oxygen and carbon isotope changes to eustatic sea-level changes is not proven yet. Likewise, the influence of plate tectonic changes as the opening of gateways or the subduction of mid-ocean ridges and/or of orbital forcing is poorly understood. A principle objection beside the sparse available data is the low temporal resolution of biostratigraphic zonations. Here, we present carbon isotope stratigraphies from Campanian-Maastrichtian Boundary sites in the Boreal and Tethyan shelf seas of Europe and from Shatsky Rise in the tropical Pacific in order to improve the resolution of stratigraphic correlation. Prominent features at that time are two negative carbon isotope excursions (CIEs) in the late Campanian and earliest Maastrichtian, which are well documented in the Lägerdorf-Kronsmoor section in N-Germany and the Campanian-Maastrichtian Boundary Stratotype at Tercis in SW France. These new carbon isotope records correlate well with the carbon isotope reference curve from the English Chalk (Jarvis et al., 2002, 2006). The new carbon isotope record at Site 305 in the tropical

  9. Antarctic Ice Sheet variability across the Eocene-Oligocene boundary climate transition

    NASA Astrophysics Data System (ADS)

    Galeotti, Simone; DeConto, Robert; Naish, Timothy; Stocchi, Paolo; Florindo, Fabio; Pagani, Mark; Barrett, Peter; Bohaty, Steven M.; Lanci, Luca; Pollard, David; Sandroni, Sonia; Talarico, Franco M.; Zachos, James C.

    2016-04-01

    About 34 million years ago, Earth’s climate cooled and an ice sheet formed on Antarctica as atmospheric carbon dioxide (CO2) fell below ~750 parts per million (ppm). Sedimentary cycles from a drillcore in the western Ross Sea provide direct evidence of orbitally controlled glacial cycles between 34 million and 31 million years ago. Initially, under atmospheric CO2 levels of ≥600 ppm, a smaller Antarctic Ice Sheet (AIS), restricted to the terrestrial continent, was highly responsive to local insolation forcing. A more stable, continental-scale ice sheet calving at the coastline did not form until ~32.8 million years ago, coincident with the earliest time that atmospheric CO2 levels fell below ~600 ppm. Our results provide insight into the potential of the AIS for threshold behavior and have implications for its sensitivity to atmospheric CO2 concentrations above present-day levels.

  10. Observational Evidence for a Decade-long climate optimum near the Hesperian/Amazonian Transition

    NASA Astrophysics Data System (ADS)

    Parsons, R.; Moore, J. M.; Howard, A. D.

    2012-12-01

    Hesperian to Amazonian-aged valleys (HAVs) are predominantly found in the southern equatorial and mid-latitudes of Mars and form parallel to dendritic networks. These features record a significant warming of the regional/global climate which may have been associated with outflow channel formation and/or a period of alluvial fan deposition in Margaritifer Terra [1]. HAVs are distinct from older valley networks in both their age and morphology and they provide a window into the past climate conditions and potential water sources which formed them. Using quantitative geomorphic analysis we calculate the expected range of timescales, water volumes, precipitation rates and atmospheric conditions which contributed to HAV formation. In Newton crater (40oS, -159oE) we measured valley widths, depths, slopes and alluvial fan volumes. These observations, when combined with a set of terrestrial sediment transport prediction functions [2,3,4,5], allow us to calculate an expected duration of fluvial activity ranging from 0.1 to 10 years for water-filled channel depths ranging between 20 and 130 cm, and median sediment grain size ranging from 1 mm to 10 cm. The water volume required to form a single HAV in Newton crater ranges between 1.8 and 5.7~km3 based on the Darcy-Weisbach equation [6] in combination with the aforementioned range in channel depths, grain sizes and formation timescales. These results imply water runoff rates of between 1 to 10~cm/day over a typical, 300~km2, drainage area. Such a high runoff rate and short formation time suggest a brief, dramatic regional to global climate excursion. The source of water which formed these features remains unclear, but it must have been released at the aforementioned rates, and was widely distributed within each drainage catchment, and regionally over Newton crater and the southern highlands. HAV formation was likely a two-step process involving, first, the deposition of a 10s of meters thick regional snowpack along

  11. Modeling Abrupt Change in Global Sea Level Arising from Ocean - Ice-Sheet Interaction

    SciTech Connect

    Holland, David M

    2011-09-24

    It is proposed to develop, validate, and apply a coupled ocean ice-sheet model to simulate possible, abrupt future change in global sea level. This research is to be carried out collaboratively between an academic institute and a Department of Energy Laboratory (DOE), namely, the PI and a graduate student at New York University (NYU) and climate model researchers at the Los Alamos National Laboratory (LANL). The NYU contribution is mainly in the area of incorporating new physical processes into the model, while the LANL efforts are focused on improved numerics and overall model development. NYU and LANL will work together on applying the model to a variety of modeling scenarios of recent past and possible near-future abrupt change to the configuration of the periphery of the major ice sheets. The project's ultimate goal is to provide a robust, accurate prediction of future global sea level change, a feat that no fully-coupled climate model is currently capable of producing. This proposal seeks to advance that ultimate goal by developing, validating, and applying a regional model that can simulate the detailed processes involved in sea-level change due to ocean ice-sheet interaction. Directly modeling ocean ice-sheet processes in a fully-coupled global climate model is not a feasible activity at present given the near-complete absence of development of any such causal mechanism in these models to date.

  12. Short-Term Test Results: Transitional Housing Energy Efficiency Retrofit in the Hot-Humid Climate

    SciTech Connect

    Sutherland, K.; Martin, E.

    2013-02-01

    This project evaluates the renovation of a 5,800 ft2, multi-use facility located in St. Petersburg, on the west coast of central Florida, in the hot humid climate. An optimal package of retrofit measures was designed to deliver 30-40% annual energy cost savings for this building with annual utility bills exceeding $16,000 and high base load consumption. Researchers projected energy cost savings for potential retrofit measures based on pre-retrofit findings and disaggregated, weather normalized utility bills as a basis for simulation true-up. A cost-benefit analysis was conducted for the seven retrofit measures implemented; adding attic insulation and sealing soffits, tinting windows, improving whole building air-tightness, upgrading heating and cooling systems and retrofitting the air distribution system, replacing water heating systems, retrofitting lighting, and replacing laundry equipment. The projected energy cost savings for the full retrofit package based on a post-retrofit audit is 35%. The building's architectural characteristics, vintage, and residential and commercial uses presented challenges for both economic projections and retrofit measure construction.

  13. Short-Term Test Results. Transitional Housing Energy Efficiency Retrofit in the Hot Humid Climate

    SciTech Connect

    Sutherland, K.

    2013-02-01

    This project evaluates the renovation of a 5,800 ft2, multi-use facility located in St. Petersburg, on the west coast of central Florida, in the hot humid climate. An optimal package of retrofit measures was designed to deliver 30%-40% annual energy cost savings for this building with annual utility bills exceeding $16,000 and high base load consumption. Researchers projected energy cost savings for potential retrofit measures based on pre-retrofit findings and disaggregated, weather normalized utility bills as a basis for simulation true-up. A cost-benefit analysis was conducted for the seven retrofit measures implemented; adding attic insulation and sealing soffits, tinting windows, improving whole building air-tightness, upgrading heating and cooling systems and retrofitting the air distribution system, replacing water heating systems, retrofitting lighting, and replacing laundry equipment. The projected energy cost savings for the full retrofit package based on a post-retrofit audit is 35%. The building's architectural characteristics, vintage, and residential and commercial uses presented challenges for both economic projections and retrofit measure construction.

  14. National climate change action plans: Interim report for developing and transition countries

    SciTech Connect

    Benioff, R.; Ness, E.; Hirst, J.

    1997-10-01

    Under its Support for National Action Plans (SNAP) initiative, the U.S. Country Studies Program is providing financial and technical assistance to 18 countries for the development of climate change action plans. Although most of the countries have not yet completed their plans, the important lessons learned thus far are valuable and should be shared with other countries and international institutions that have an interest in the process of action plan development. This interim report describes the experience of 11 countries that are the furthest along in their planning activity and who have offered to share their results to date with the larger community of interested nations. These action plans delineate specific mitigation and adaptation measures that the countries will implement and integrate into their ongoing development programs. This report focuses on the measures the countries have selected and the methods they used to prepare their action plans. This executive summary presents key lessons and common themes using a structure similar to that used in the individual country chapters.

  15. Abrupt temperature changes in the Western Mediterranean over the past 250,000 years.

    PubMed

    Martrat, Belen; Grimalt, Joan O; Lopez-Martinez, Constancia; Cacho, Isabel; Sierro, Francisco J; Flores, Jose Abel; Zahn, Rainer; Canals, Miquel; Curtis, Jason H; Hodell, David A

    2004-12-03

    A continuous high-resolution Western Mediterranean sea surface temperature (SST) alkenone record spanning the past 250,000 years shows that abrupt changes were more common at warming than at cooling. During marine isotope stage (MIS) 6, SST oscillated following a stadial-interstadial pattern but at lower intensities and rates of change than in the Dansgaard/Oeschger events of MIS 3. Some of the most prominent events occurred over MISs 5 and 7, after prolonged warm periods of high stability. Climate during the whole period was predominantly maintained in interglacial-interstadial conditions, whereas the duration of stadials was much shorter.

  16. Emerging climate-driven disturbance processes: widespread mortality associated with snow-to-rain transitions across 10° of latitude and half the range of a climate-threatened conifer.

    PubMed

    Buma, Brian; Hennon, Paul E; Harrington, Constance A; Popkin, Jamie R; Krapek, John; Lamb, Melinda S; Oakes, Lauren E; Saunders, Sari; Zeglen, Stefan

    2016-11-05

    Climate change is causing rapid changes to forest disturbance regimes worldwide. While the consequences of climate change for existing disturbance processes, like fires, are relatively well studied, emerging drivers of disturbance such as snow loss and subsequent mortality are much less documented. As the climate warms, a transition from winter snow to rain in high latitudes will cause significant changes in environmental conditions such as soil temperatures, historically buffered by snow cover. The Pacific coast of North America is an excellent test case, as mean winter temperatures are currently at the snow-rain threshold and have been warming for approximately 100 years post-Little Ice Age. Increased mortality in a widespread tree species in the region has been linked to warmer winters and snow loss. Here, we present the first high-resolution range map of this climate-sensitive species, Callitropsis nootkatensis (yellow-cedar), and document the magnitude and location of observed mortality across Canada and the United States. Snow cover loss related mortality spans approximately 10° latitude (half the native range of the species) and 7% of the overall species range and appears linked to this snow-rain transition across its range. Mortality is commonly >70% of basal area in affected areas, and more common where mean winter temperatures is at or above the snow-rain threshold (>0 °C mean winter temperature). Approximately 50% of areas with a currently suitable climate for the species (<-2 °C) are expected to warm beyond that threshold by the late 21st century. Regardless of climate change scenario, little of the range which is expected to remain suitable in the future (e.g., a climatic refugia) is in currently protected landscapes (<1-9%). These results are the first documentation of this type of emerging climate disturbance and highlight the difficulties of anticipating novel disturbance processes when planning for conservation and management.

  17. Placental Abruption Revealed by Hemoperitoneum: A Case Report

    PubMed Central

    Bertholdt, C.; Vincent-Rohfritsch, A.; Tsatsaris, V.; Goffinet, F.

    2016-01-01

    Background Hemoperitoneum is a life-threatening surgical emergency. Diagnosis of the cause is often difficult, in particular, during pregnancy when it may be either obstetric or nonobstetric. Case We report the case of a hemoperitoneum caused by the backflow of blood through a uterine tube, due to placental abruption. Conclusion Hemoperitoneum in pregnant women with no other signs can reveal placental abruption. The difficulty in identifying the cause may delay appropriate management. PMID:27994944

  18. « Younger-Dryas / African Humid Period »: a notable climatic transition over West Africa

    NASA Astrophysics Data System (ADS)

    Skonieczny, C.; Bory, A. J.; Bout-Roumazeilles, V.; Malaizé, B.; Grousset, F. E.; Abouchami, W.; Galer, S. J.; Francois, R. H.

    2013-05-01

    Every year, several hundreds teragrams of dust are emitted from the Sahara and Sahel regions. These mineral particles sensitively track variations in atmospheric circulation and continental aridity. Sediments of the Northeastern Atlantic Tropical Ocean (NEATO) are fed by this intense dust supply and comprise unique long-term archives of past dust emissions. Past modifications of dust characteristics in these sedimentary archives can provide precious information on changes in environmental conditions in source areas (aridity, weathering), as well as on changes in the characteristics of their atmospheric transport (pathways and strength). Over Africa, gradual increases in local insolation due to changes in the Earth's orbit are accompanied by a migration of the precipitation monsoon-system (associated with the InterTropical Convergence Zone, ITCZ) toward the North. This displacement leads to decrease in West African mineral dust emission. Consequently, Saharan and Sahelian dust deposited in the NEATO sedimentary archives represent an exceptional opportunity to document the environmental and climatic changes that have taken place in West Africa throughout the Quaternary and beyond (Rea, 1994). Here we document changes in the terrigenous supplies to the NETAO throughout the last deglaciation using the marine sediment core MD03-2705 located off Mauritania (18°05N; 21°09W; 3085m water depth) and retrieved from a bathymetric dome, 300 meters above the surrounding seafloor. Considering this particular environmental setting, the terrigenous fraction in this record is assumed to be predominantly of aeolian origin. Multi-proxy analyses of the carbonate-free fraction of the sediment were carried-out, including dust fluxes, grain-size, clay mineralogy and geochemical measurements (major and trace elements as well as Sr & Nd isotopes). We will discuss the most significant changes recorded over the studied period: levels dated from the Younger Dryas and the subsequent African

  19. Hesperian-Amazonian Transition Mid-Latitude Valleys: Markers of a Late Martian Climate Optima?

    NASA Technical Reports Server (NTRS)

    Moore, Jeffrey; Howard, A. D.; Parsons, Reid A.; Hobley, D. E.

    2012-01-01

    Recently the inventory of fluvial features that have been dated to the late Hesperian to early Amazonian epoch has increased dramatically, including a reassessment of the ages of the large alluvial fans and deltas (e.g., Eberswalde) to this time period. Mid-latitude Valleys (MLVs) are distinct from the older, more integrated Noachian-Hesperian Valley Networks which are deeply dissected, are generally of much larger spatial extent, and are more degraded. Although some MLVs involve rejuvenation of older Valley Networks, many MLVs are carved into smooth or rolling slopes and intercrater terrain. The MLVs range from a few meters to < 300 m in width, with nearly parallel valley walls and planforms that are locally sinuous. Although the MLVs in Newton and Gorgonum basins extend from the basin rims up to 75 km into the basin interior, most MLVs are shorter and often discontinuous. The occurrence of widespread MLVs suggest the possibility of their formation during one or perhaps more regional to global climatic episodes, possibly due to melting of seasonal to long-term accumulations of snow and ice. Temperatures warm enough to cause extensive melting may have occurred during optimal orbital and obliquity configurations, perhaps in conjunction with intensive volcanism releasing moisture and greenhouse gasses, or as a result of a brief episode of warming from a large impact. The concentration of MLVs to the northern and western basin slopes of Newton and Gorgonum basins suggests a possible aspect control to ice accumulation or melting. MLV activity occurred about at the same time as formation of the major outflow channels. A possible scenario is that delivery of water to the northern lowlands provided, through evaporation and sublimation, water that temporarily accumulated in the mid-southern latitudes as widespread ice deposits whose partial melting formed the MLVs and small, dominantly ice-covered lakes.

  20. Sensitivity of Ice and Climate Evolution Patterns to Modelling Uncertainties During the Last Glacial-Interglacial Transitions

    NASA Astrophysics Data System (ADS)

    Bahadory, T.; Tarasov, L.

    2015-12-01

    How did ice grow (volume, total area, extent) over North America (NA)and Eurasia (EA) during inception? Did the ice-sheets grow and shrinksimultaneously, or each had its own inception time and maximum extentand volume? How did the atmosphere respond to the changes in surfacealbedo, altitude, dust concentration, and other feedbacks in thesystem? And more interestingly, given the uncertainties in theclimate system, is there more than one way glacial inception anddeglaciation could happen? By exploring the sensitivity of the lastglacial inception and deglaciation to uncertainties in modelling suchas representation of radiative effect of clouds, initial state of theocean, downscaling and upscaling various climatic fields between theatmospheric and ice model, and albedo calculation, we try to answerthese questions. Therefore, we set up an ensemble of simulations for both inception anddeglaciation to investigate the extent to which such modellinguncertainties can affect ice volume, area, and regional thicknessevolution patterns, in addition to various climatic fields, such asthe Rossby number, jet-stream location and strength, and sea-iceexpansion, during these two periods of interest. We analyze theensemble results to 1. investigate how important the parameters weincluded in our ensemble can be in simulating glacial-interglacialtransitions, and 2. explore different possible patterns of the lastglacial inception and deglaciation. The ensemble is set up using a fully-coupled Earth Model ofIntermediate Complexity, LOVECLIM, previously used in severalpaleoclimate modelling studies, and a 3D thermo-mechanically coupledice sheet model. The coupled model is capable of simulating 1000years in about 24 hours using a single core, making it possible toaccomplish an ensemble of 1000s of runs for both transition periodswithin a few weeks.

  1. Warm climate transitions: A general circulation modeling study of the Late Paleocene Thermal Maximum (˜56 Ma)

    NASA Astrophysics Data System (ADS)

    Huber, Matthew; Sloan, L. Cirbus

    1999-07-01

    A unique opportunity to study rapid climate transitions in a warm climate world is provided by the Late Paleocene Thermal Maximum (LPTM), a ˜100,000 year interval during which high-latitude temperatures suddenly rose to their highest levels in the Cenozoic. In order to explore the processes and feedbacks which may have generated or limited this brief warming event, we model the atmosphere in equilibrium with sea surface temperatures (SSTs) derived for LPTM and for conditions more representative of the late Paleocene or early Eocene. Our model results suggest that conditions during the LPTM were more equable relative to the late Paleocene or early Eocene, with the mean annual temperature range reduced by more than 5°C over much of the continental interiors and precipitation over land increased by 5-10%. Nevertheless, despite specifying warm polar SSTs which exclude sea-ice, the model produces January continental interior temperatures less than -13°C, in contrast to proxy data estimates of higher temperatures. The zonal wind strength is drastically reduced during the LPTM, and during Northern Hemisphere winter, deep atmospheric convection over the Arctic Sea is generated owing to the specified warm SSTs. We calculate substantial wind-driven ocean circulation response to model-produced wind fields for these time intervals, including increases in inferred western boundary current strength of 8-28%. In general, our results are in agreement with deep-sea sediment-derived clay and eolian records which suggest warm, wet conditions with less vigorous atmospheric circulation during these time periods. However, major changes in the high-latitude hydrological cycle found in our LPTM experiment results raise important questions about high-latitude stable isotopic paleoclimate interpretations.

  2. Resilience, rapid transitions and regime shifts: fingerprinting the responses of Lake Żabińskie (NE Poland) to climate variability and human disturbance since 1000 AD

    NASA Astrophysics Data System (ADS)

    Tylmann, Wojciech; Hernández-Almeida, Iván; Grosjean, Martin; José Gómez Navarro, Juan; Larocque-Tobler, Isabelle; Bonk, Alicja; Enters, Dirk; Ustrzycka, Alicja; Piotrowska, Natalia; Przybylak, Rajmund; Wacnik, Agnieszka; Witak, Małgorzata

    2016-04-01

    Rapid ecosystem transitions and adverse effects on ecosystem services as responses to combined climate and human impacts are of major concern. Yet few quantitative observational data exist, particularly for ecosystems that have a long history of human intervention. Here, we combine quantitative summer and winter climate reconstructions, climate model simulations and proxies for three major environmental pressures (land use, nutrients and erosion) to explore the system dynamics, resilience, and the role of disturbance regimes in varved eutrophic Lake Żabińskie since AD 1000. Comparison between regional and global climate simulations and quantitative climate reconstructions indicate that proxy data capture noticeably natural forced climate variability, while internal variability appears as the dominant source of climate variability in the climate model simulations during most parts of the last millennium. Using different multivariate analyses and change point detection techniques, we identify ecosystem changes through time and shifts between rather stable states and highly variable ones, as expressed by the proxies for land-use, erosion and productivity in the lake. Prior to AD 1600, the lake ecosystem was characterized by a high stability and resilience against considerable observed natural climate variability. In contrast, lake-ecosystem conditions started to fluctuate at high frequency across a broad range of states after AD 1600. The period AD 1748-1868 represents the phase with the strongest human disturbance of the ecosystem. Analyses of the frequency of change points in the multi-proxy dataset suggests that the last 400 years were highly variable and flickering with increasing vulnerability of the ecosystem to the combined effects of climate variability and anthropogenic disturbances. This led to significant rapid ecosystem transformations.

  3. Ice-Sheet Dynamics and Millennial-Scale Climate Variability in the North Atlantic across the Middle Pleistocene Transition (Invited)

    NASA Astrophysics Data System (ADS)

    Hodell, D. A.; Nicholl, J.

    2013-12-01

    During the Middle Pleistocene Transition (MPT), the climate system evolved from a more linear response to insolation forcing in the '41-kyr world' to one that was decidedly non-linear in the '100-kyr world'. Smaller ice sheets in the early Pleistocene gave way to larger ice sheets in the late Pleistocene with an accompanying change in ice sheet dynamics. We studied Sites U1308 (49° 52.7'N, 24° 14.3'W; 3871 m) and U1304 (53° 3.4'N, 33° 31.8'W; 3024 m) in the North Atlantic to determine how ice sheet dynamics and millennial-scale climate variability evolved as glacial boundary conditions changed across the MPT. The frequency of ice-rafted detritus (IRD) in the North Atlantic was greater during glacial stages prior to 650 ka (MIS 16), reflecting more frequent crossing of an ice volume threshold when the climate system spent more time in the 'intermediate ice volume' window, resulting in persistent millennial scale variability. The rarity of Heinrich Events containing detrital carbonate and more frequent occurrence of IRD events prior to 650 ka may indicate the presence of 'low-slung, slippery ice sheets' that flowed more readily than their post-MPT counterparts (Bailey et al., 2010). Ice volume surpassed a critical threshold across the MPT that permitted ice sheets to survive boreal summer insolation maxima, thereby increasing ice volume and thickness, lengthening glacial cycles, and activating the dynamical processes responsible for Laurentide Ice Sheet instability in the region of Hudson Strait (i.e., Heinrich events). The excess ice volume during post-MPT glacial maxima provided a large, unstable reservoir of freshwater to be released to the North Atlantic during glacial terminations with the potential to perturb Atlantic Meridional Overtunring Circulation. We speculate that orbital- and millennial-scale variability co-evolved across the MPT and the interaction of processes on orbital and suborbital time scales gave rise to the changing patterns of glacial

  4. The mid-quarternary climatic transition as the free response of a three-variable dynamical model

    NASA Technical Reports Server (NTRS)

    Saltzman, Barry; Sutera, Alfonso

    1987-01-01

    A simplified version of a previously described dynamical model governing global ice mass, atmospheric carbon dioxide, and mean ocean temperature is shown to possess solutions, in a realistic parameter range, that can replicate the main features of the climatic variations implied by the full, two million years, Quaternary delta-O-18 record. These variations include a major 'transition' between a low-ice delta-O-18, low variance mode before roughly 900 kyr BP to a high-ice, high (near 100 kyr period) variance mode after that time to the present. The model contains only three free parameters in this simplified form. No external earth-orbital forcing is prescribed; i.e., the model represents only internal dynamics. From the previous studies it seems clear that additional variance representing such features as the 'rapid' deglaciation and the phase of the major Quaternary oscillation can be largely explained with no more than four additional parameters representing an internal asymmetry and the external perodic forcing. The present results, therefore, constitute a first-order account for the existence of the 'ice age' fluctuations over the last two million years, including the concomitant variations of atmospheric CO2.

  5. First dated human occupation of Italy at ~ 0.85 Ma during the late Early Pleistocene climate transition

    NASA Astrophysics Data System (ADS)

    Muttoni, Giovanni; Scardia, Giancarlo; Kent, Dennis V.; Morsiani, Enrico; Tremolada, Fabrizio; Cremaschi, Mauro; Peretto, Carlo

    2011-07-01

    A candidate for the oldest human occupation site in Italy is Monte Poggiolo where the lithic tool-bearing levels are currently dated to ~ 1 Ma based on electron spin resonance (ESR). The low analytical precision of ± 30% at 2σ makes it unclear whether the date actually conflicts with a recent reassessment of age constraints on key hominin sites from Italy, France, and Spain pointing to a uniformly young timing for the earliest habitation of southern Europe during the late Early Pleistocene climate transition within reverse magnetic polarity subchron C1r.1r (0.988-0.781 Ma). Our new magnetostratigraphic and biostratigraphic results show a sequence of stable normal and reverse polarities in a regional lithostratigraphic context that indicate the Monte Poggiolo tool-bearing site post-dates the Jaramillo normal polarity subchron, most probably occurring at ~ 0.85 Ma immediately after the pronounced cooling that culminated with marine isotope stage 22 when the associated regression may have opened new migration routes through the Po Valley for large mammals and hominins.

  6. Extrinsic regime shifts drive abrupt changes in regeneration dynamics at upper treeline in the Rocky Mountains, U.S.A.

    PubMed

    Elliott, Grant P

    2012-07-01

    Given the widespread and often dramatic influence of climate change on terrestrial ecosystems, it is increasingly common for abrupt threshold changes to occur, yet explicitly testing for climate and ecological regime shifts is lacking in climatically sensitive upper treeline ecotones. In this study, quantitative evidence based on empirical data is provided to support the key role of extrinsic, climate-induced thresholds in governing the spatial and temporal patterns of tree establishment in these high-elevation environments. Dendroecological techniques were used to reconstruct a 420-year history of regeneration dynamics within upper treeline ecotones along a latitudinal gradient (approximately 44-35 degrees N) in the Rocky Mountains. Correlation analysis was used to assess the possible influence of minimum and maximum temperature indices and cool-season (November-April) precipitation on regional age-structure data. Regime-shift analysis was used to detect thresholds in tree establishment during the entire period of record (1580-2000), temperature variables significantly Correlated with establishment during the 20th century, and cool-season precipitation. Tree establishment was significantly correlated with minimum temperature during the spring (March-May) and cool season. Regime-shift analysis identified an abrupt increase in regional tree establishment in 1950 (1950-1954 age class). Coincident with this period was a shift toward reduced cool-season precipitation. The alignment of these climate conditions apparently triggered an abrupt increase in establishment that was unprecedented during the period of record. Two main findings emerge from this research that underscore the critical role of climate in governing regeneration dynamics within upper treeline ecotones. (1) Regional climate variability is capable of exceeding bioclimatic thresholds, thereby initiating synchronous and abrupt changes in the spatial and temporal patterns of tree establishment at broad

  7. 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.

  8. Percolation-based precursors of transitions in extended systems

    PubMed Central

    Rodríguez-Méndez, Víctor; Eguíluz M, Víctor M.; Hernández-García, Emilio; Ramasco, José J.

    2016-01-01

    Abrupt transitions are ubiquitous in the dynamics of complex systems. Finding precursors, i.e. early indicators of their arrival, is fundamental in many areas of science ranging from electrical engineering to climate. However, obtaining warnings of an approaching transition well in advance remains an elusive task. Here we show that a functional network, constructed from spatial correlations of the system’s time series, experiences a percolation transition way before the actual system reaches a bifurcation point due to the collective phenomena leading to the global change. Concepts from percolation theory are then used to introduce early warning precursors that anticipate the system’s tipping point. We illustrate the generality and versatility of our percolation-based framework with model systems experiencing different types of bifurcations and with Sea Surface Temperature time series associated to El Niño phenomenon. PMID:27412567

  9. Percolation-based precursors of transitions in extended systems

    NASA Astrophysics Data System (ADS)

    Rodríguez-Méndez, Víctor; Eguíluz M, Víctor M.; Hernández-García, Emilio; Ramasco, José J.

    2016-07-01

    Abrupt transitions are ubiquitous in the dynamics of complex systems. Finding precursors, i.e. early indicators of their arrival, is fundamental in many areas of science ranging from electrical engineering to climate. However, obtaining warnings of an approaching transition well in advance remains an elusive task. Here we show that a functional network, constructed from spatial correlations of the system’s time series, experiences a percolation transition way before the actual system reaches a bifurcation point due to the collective phenomena leading to the global change. Concepts from percolation theory are then used to introduce early warning precursors that anticipate the system’s tipping point. We illustrate the generality and versatility of our percolation-based framework with model systems experiencing different types of bifurcations and with Sea Surface Temperature time series associated to El Niño phenomenon.

  10. Using Hydrated Salt Phase Change Materials for Residential Air Conditioning Peak Demand Reduction and Energy Conservation in Coastal and Transitional Climates in the State of California

    NASA Astrophysics Data System (ADS)

    Lee, Kyoung Ok

    The recent rapid economic and population growth in the State of California have led to a significant increase in air conditioning use, especially in areas of the State with coastal and transitional climates. This fact makes that the electric peak demand be dominated by air conditioning use of residential buildings in the summer time. This extra peak demand caused by the use of air conditioning equipment lasts only a few days out of the year. As a result, unavoidable power outages have occurred when electric supply could not keep up with such electric demand. This thesis proposed a possible solution to this problem by using building thermal mass via phase change materials to reduce peak air conditioning demand loads. This proposed solution was tested via a new wall called Phase Change Frame Wall (PCFW). The PCFW is a typical residential frame wall in which Phase Change Materials (PCMs) were integrated to add thermal mass. The thermal performance of the PCFWs was first evaluated, experimentally, in two test houses, built for this purpose, located in Lawrence, KS and then via computer simulations of residential buildings located in coastal and transitional climates in California. In this thesis, a hydrated salt PCM was used, which was added in concentrations of 10% and 20% by weight of the interior sheathing of the walls. Based on the experimental results, under Lawrence, KS weather, the PCFWs at 10% and 20% of PCM concentrations reduced the peak heat transfer rates by 27.0% and 27.3%, on average, of all four walls, respectively. Simulated results using California climate data indicated that PCFWs would reduce peak heat transfer rates by 8% and 19% at 10% PCM concentration and 12.2% and 27% at 20% PCM concentration for the coastal and transitional climates, respectively. Furthermore, the PCFWs, at 10% PCM concentration, would reduce the space cooling load and the annual energy consumption by 10.4% and 7.2%, on average in both climates, respectively.

  11. 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.

  12. 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.

  13. Characterization of a rapid climate shift at the MIS 8/7 transition in central Spain (Valdocarros II, Autonomous Region of Madrid) by means of the herpetological assemblages

    NASA Astrophysics Data System (ADS)

    Blain, Hugues-Alexandre; Panera, Joaquin; Uribelarrea, David; Rubio-Jara, Susana; Pérez-González, Alfredo

    2012-07-01

    Climate instability with high-amplitude and rapid shifts during the Middle Pleistocene is well known from pollen records and deep-ocean sediment cores. Although poorly correlatable with such long climate/environment records, the successive fossil amphibian and reptile assemblages from the Middle Pleistocene site of Valdocarros II (Autonomous Region of Madrid, central Spain) provide a unique opportunity to characterize the climatic and environmental features of such rapid (certainly less than 1000 years) shifts from cold to warm conditions in a terrestrial sequence. As the amphibians and reptiles do not differ at species level from the extant herpetofauna of the Iberian Peninsula, they can contribute to the reconstruction of the landscape and climate. In this paper, the mutual climatic range and habitat weighting methods are applied to the herpetofaunistic assemblages in order to estimate quantitative data. The difference in mean annual temperature between "cold" and "warm" periods is estimated at 3.2 °C, with a greater increase in temperature during winter (+3 °C) than during summer (+1 °C). During "cold" periods the climate was more Oceanic (although preserving some dryness during the summers), whereas during "warm" periods the climate became Mediterranean (with mild winters and a long period of dryness in the summer and early autumn). Though higher during cold periods, the continentality (or atmospheric temperature range) remained roughly similar, in accordance with the geographical location of the site in the centre of the Iberian Peninsula. A greater amount of open landscape occurred during "cold" periods, whereas during "warm" periods the wooded areas expanded from 20% to 40% of the landscape surface. Such climatic/environmental changes, together with the numeric datings of the site, suggest that this shift may correspond to the transition from MIS 8 to MIS 7, also called Termination III.

  14. Effects of land use/land cover and climate changes on surface runoff in a semi-humid and semi-arid transition zone in northwest China

    NASA Astrophysics Data System (ADS)

    Yin, Jing; He, Fan; Jiu Xiong, Yu; Qiu, Guo Yu

    2017-01-01

    Water resources, which are considerably affected by land use/land cover (LULC) and climate changes, are a key limiting factor in highly vulnerable ecosystems in arid and semi-arid regions. The impacts of LULC and climate changes on water resources must be assessed in these areas. However, conflicting results regarding the effects of LULC and climate changes on runoff have been reported in relatively large basins, such as the Jinghe River basin (JRB), which is a typical catchment (> 45 000 km2) located in a semi-humid and arid transition zone on the central Loess Plateau, northwest China. In this study, we focused on quantifying both the combined and isolated impacts of LULC and climate changes on surface runoff. We hypothesized that under climatic warming and drying conditions, LULC changes, which are primarily caused by intensive human activities such as the Grain for Green Program, will considerably alter runoff in the JRB. The Soil and Water Assessment Tool (SWAT) was adopted to perform simulations. The simulated results indicated that although runoff increased very little between the 1970s and the 2000s due to the combined effects of LULC and climate changes, LULC and climate changes affected surface runoff differently in each decade, e.g., runoff increased with increased precipitation between the 1970s and the 1980s (precipitation contributed to 88 % of the runoff increase). Thereafter, runoff decreased and was increasingly influenced by LULC changes, which contributed to 44 % of the runoff changes between the 1980s and 1990s and 71 % of the runoff changes between the 1990s and 2000s. Our findings revealed that large-scale LULC under the Grain for Green Program has had an important effect on the hydrological cycle since the late 1990s. Additionally, the conflicting findings regarding the effects of LULC and climate changes on runoff in relatively large basins are likely caused by uncertainties in hydrological simulations.

  15. Impacts of recent climate change on dry-land crop water consumption in the northern agro-pastoral transitional zone of China

    NASA Astrophysics Data System (ADS)

    Zhao, Lingyu; Liu, Yaling; Pan, Zhihua; An, Pingli; Pan, Xuebiao; Zhao, Peiyi

    2013-08-01

    Climate change has substantially impacted crop growth and development in the northern agro-pastoral transitional zone. Examination of the response of crop water consumption to climate change may provide a guide for adapting local agricultural production and ecological construction to new realities. The water consumption of three local crops (wheat, naked oats, and potatoes) is examined for Wuchuan County in the northern agro-pastoral transitional zone of China using meteorological data from 1960 to 2007 and soil moisture data from 1983 to 2007. The relationships between climate change and the crop water consumption are discussed. The results show that Wuchuan experienced both a warming trend and a reduction of precipitation between 1960 and 2007. The annual mean surface air temperature increased at a rate of 0.04°C yr-1 and the annual precipitation decreased at a rate of 0.7 mm yr-1. Both trends are particularly pronounced between 1983 and 2007, with an increase in annual mean temperature of 0.09°C yr-1 and a decrease in annual mean precipitation of 2.1 mm yr-1. Crop water consumption decreased between 1983 and 2007 for wheat (1.65 mm yr-1), naked oats (2.04 mm yr-1), and potatoes (3.85 mm yr-1). Potatoes and naked oats consume more water than wheat. Climate change has significantly impacted crop water consumption. Water consumption and rainfall during the growing season are positively correlated, while water consumption and active accumulated temperature are negatively correlated. Compared to precipitation, accumulated temperature has little impact on crop water consumption. Recent climate change has been detrimental for crop production in Wuchuan County. Adaptation to climate change should include efforts to breed drought-resistant crops and to develop drought-resistant cultivation techniques.

  16. East Antarctic Ice Sheet fluctuations during the Middle Miocene Climatic Transition inferred from faunal and biogeochemical data on planktonic foraminifera (ODP Hole 747A, Kerguelen Plateau)

    USGS Publications Warehouse

    Verducci, M.; Foresi, L.M.; Scott, G.H.; ,; Sprovieri, M.; Lirer, F.

    2007-01-01

    This research focuses on a detailed study of faunal and biogeochemical changes that occurred at ODP Hole 747A in the Kerguelen Plateau region of the Southern Ocean during the middle Miocene (14.8-11.8 Ma). Abundance fluctuations of several planktonic foraminiferal taxa, stable oxygen isotope and Mg/Ca ratios have been integrated as a multi-proxy approach to reach a better understanding of the growth modality and fluctuations of the East Antarctic Ice Sheet (EAIS) during this period. A 7°C decrease in Sea Surface Temperature (SST), an abrupt turnover in the planktonic foraminiferal assemblage, a 1.5‰ shift towards heavier δ18O values (Mi3 event) and a related shift towards heavier seawater δ118O values between 13.9 and 13.7 Ma, are interpreted to reflect rapid surface water cooling and EAIS expansion. Hole 747A data suggest a major change in the variability of the climate system fostered by EAIS expansion between 13.9 and 13.7 Ma. Ice sheet fluctuations were greater during the interval 14.8-13.9 Ma compared with those from 13.7 to 11.8 Ma, whereas the latter interval was characterized by a more stable EAIS. In our opinion, the middle Miocene ice sheet expansion in Antarctica represents a first step towards the development of the modern permanent ice sheet

  17. Paleobiogeography of scleractinian reef corals: Changing patterns during the Oligocene-Miocene climatic transition in the Mediterranean

    NASA Astrophysics Data System (ADS)

    Perrin, Christine; Bosellini, Francesca R.

    2012-02-01

    During the Oligocene-Miocene Greenhouse-to-Icehouse climatic transition, the biogeography of reef corals or zooxanthellate-like scleractinian corals was gradually changing from a pan-tropical Tethyan Province in the Eocene to three reef-coral Provinces of the Western Atlantic-Caribbean, Indo-Pacific and Mediterranean. Our REEFCORAL database encompasses updated and homogenized data on paleoenvironmental and systematics of scleractinian corals occurring in the Oligocene and Miocene outcrops from circum-Mediterranean regions, provided by most of relatively recently published data in the literature and by the study of published and unpublished collections of coral specimens from the same area, including the important collections housed at the MNHN (Paris) and our own collections. As there is no validated direct criterion for the identification of the coral-zooxanthellate symbiosis in the fossil record, and considering the difficulty to use the biogeochemical approaches in the context of this study, the subjectivity of the morphological criteria and the relative recent age of the fossil corals we are dealing with, a uniformitarian approach has been used for inferring the symbiotic status of scleractinian genera in REEFCORAL. Among the 158 genera included in our database, 93 can be considered as zooxanthellate and 10 have a doubtful zooxanthellate status. This relatively exhaustive database was used to reconstruct the temporal and spatial distribution of scleractinian corals in the Mediterranean during the Oligocene-Miocene time in order to discuss the interplaying effects of the global cooling at that time, the re-organization of the Tethyan realm resulting from the African, Arabian and Eurasian plate collision and the emergence of the Alpine chains, driving the gradual northward movement of the whole region outside the tropical/subtropical belt. It is shown that the structure of the Mediterranean z-coral Oligocene-Miocene paleobiodiversity was characterized by many

  18. Excitability, mixed-mode oscillations and transition to chaos in a stochastic ice ages model

    NASA Astrophysics Data System (ADS)

    Alexandrov, D. V.; Bashkirtseva, I. A.; Ryashko, L. B.

    2017-03-01

    Motivated by an important geophysical significance, we consider the influence of stochastic forcing on a simple three-dimensional climate model previously derived by Saltzman and Sutera. A nonlinear dynamical system governing three physical variables, the bulk ocean temperature, continental and marine ice masses, is analyzed in deterministic and stochastic cases. It is shown that the attractor of deterministic model is either a stable equilibrium or a limit cycle. We demonstrate that the process of continental ice melting occurs with a noise-dependent time delay as compared with marine ice melting. The paleoclimate cyclicity which is near 100 ky in a wide range of model parameters abruptly increases in the vicinity of a bifurcation point and depends on the noise intensity. In a zone of stable equilibria, the 3D climate model under consideration is extremely excitable. Even for a weak random noise, the stochastic trajectories demonstrate a transition from small- to large-amplitude stochastic oscillations (SLASO). In a zone of stable cycles, SLASO transitions are analyzed too. We show that such stochastic transitions play an important role in the formation of a mixed-mode paleoclimate scenario. This mixed-mode dynamics with the intermittency of large- and small-amplitude stochastic oscillations and coherence resonance are investigated via analysis of interspike intervals. A tendency of dynamic paleoclimate to abrupt and rapid glaciations and deglaciations as well as its transition from order to chaos with increasing noise are shown.

  19. Warm climate surprises

    SciTech Connect

    Overpeck, J.T.

    1996-03-29

    Over the last decade, paleoclimatic data from ice cores and sediments have shown that the climate system is capable of switching between significantly different modes, suggesting that climatic surprises may lie ahead. Most attention in the growing area of abrupt climatic change research continues to be focused on large changes observed during glacial periods. The weight of paleoclimatic evidence now suggests that conforting conclusions of benign warm climate variability may be incorrect. The article goes on to discuss the evidence for this. 17 refs.

  20. The Mid Pleistocene Climate Transition Recorded in a Hemipelagic Sediment Drift (ODP Leg 194): Implications for the Understanding of Continental Margin Sediment Sources and Sinks

    NASA Astrophysics Data System (ADS)

    Obrochta, S. P.; Hine, A. C.; Flower, B. P.; Locker, S. D.; Brooks, G. R.

    2002-12-01

    The Marion Plateau (NE Australia margin) provides an ideal setting to study continental margin paleoceanographic history. It is not significantly current scoured and is located at upper continental slope depths, freeing it from the influence of large sediment gravity flows. Atop the plateau, a hemipelagic sediment drift is perched and was drilled on Ocean Drilling Program Leg 194 (site 1198). The lithologic record and other shipboard-acquired data sets (physical properties, downhole logging), as well as the site-survey seismic data all suggest that cyclicity dominates this sedimentary section, which encompasses the Mid Pleistocene climate transition (0.9 to 0.92 Ma). This period contains the transition from a 41 k.y. cycle (ice volume and temperature) to 100 k.y. (ice volume and temperature) cycle dominated world. Preliminary results indicate that the basic stratigraphic units of this drift record terrestrial climate, continental margin, and pelagic processes. Mass accumulation rates of the siliciclastic, neritic carbonate, and pelagic carbonate components represent orbitally-forced cycles that form a predictable sedimentary architecture, and grain size variations are a proxy for fluctuations in bottom current strength. The terrigenous flux varies as a function of both aridity/humidity variation on the adjacent continent and sea-level fluctuations, while the carbonate flux varies as a function of paleoproductivity of the overlying water column plus lateral input from the developing Great Barrier Reef. Examination of the changing sedimentary architecture of this drift during the Mid Pleistocene climate transition will further the understanding of sedimentary sources and sinks along continental margins, including their sensitivity to sea level, climate, and circulation changes.

  1. Climate-driven ecosystem succession in the Sahara: the past 6000 years.

    PubMed

    Kröpelin, S; Verschuren, D; Lézine, A-M; Eggermont, H; Cocquyt, C; Francus, P; Cazet, J-P; Fagot, M; Rumes, B; Russell, J M; Darius, F; Conley, D J; Schuster, M; von Suchodoletz, H; Engstrom, D R

    2008-05-09

    Desiccation of the Sahara since the middle Holocene has eradicated all but a few natural archives recording its transition from a "green Sahara" to the present hyperarid desert. Our continuous 6000-year paleoenvironmental reconstruction from northern Chad shows progressive drying of the regional terrestrial ecosystem in response to weakening insolation forcing of the African monsoon and abrupt hydrological change in the local aquatic ecosystem controlled by site-specific thresholds. Strong reductions in tropical trees and then Sahelian grassland cover allowed large-scale dust mobilization from 4300 calendar years before the present (cal yr B.P.). Today's desert ecosystem and regional wind regime were established around 2700 cal yr B.P. This gradual rather than abrupt termination of the African Humid Period in the eastern Sahara suggests a relatively weak biogeophysical feedback on climate.

  2. 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)

  3. Help the climate, change your diet: A cross-sectional study on how to involve consumers in a transition to a low-carbon society.

    PubMed

    de Boer, Joop; de Witt, Annick; Aiking, Harry

    2016-03-01

    This paper explores how the transition to a low-carbon society to mitigate climate change can be better supported by a diet change. As climate mitigation is not the focal goal of consumers who are buying or consuming food, the study highlighted the role of motivational and cognitive background factors, including possible spillover effects. Consumer samples in the Netherlands (n = 527) and the United States (n = 556) were asked to evaluate food-related and energy-related mitigation options in a design that included three food-related options with very different mitigation potentials (i.e. eating less meat, buying local and seasonal food, and buying organic food). They rated each option's effectiveness and their willingness to adopt it. The outstanding effectiveness of the less meat option (as established by climate experts) was recognized by merely 12% of the Dutch and 6% of the American sample. Many more participants gave fairly positive effectiveness ratings and this was correlated with belief in human causation of climate change, personal importance of climate change, and being a moderate meat eater. Willingness to adopt the less meat option increased with its perceived effectiveness and, controlling for that, it was significantly related to various motivationally relevant factors. The local food option appealed to consumer segments with overlapping but partly different motivational orientations. It was concluded that a transition to a low carbon society can significantly benefit from a special focus on the food-related options to involve more consumers and to improve mitigation.

  4. 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

  5. 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.

  6. Abrupt Increases in Amazonian Tree Mortality Due to Drought-Fire Interactions

    NASA Technical Reports Server (NTRS)

    Brando, Paulo Monteiro; Balch, Jennifer K.; Nepstad, Daniel C.; Morton, Douglas C.; Putz, Francis E.; Coe, Michael T.; Silverio, Divino; Macedo, Marcia N.; Davidson, Eric A.; Nobrega, 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, longterm 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 x m(exp -1)). During the droughts of 2007 and 2010, regional forest fires burned 12 and 5% of southeastern Amazon forests, respectively, compared with less than 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.

  7. A novel method for detecting abrupt dynamic change based on the changing Hurst exponent of spatial images

    NASA Astrophysics Data System (ADS)

    He, Wen-Ping; Liu, Qun-Qun; Gu, Bin; Zhao, Shan-Shan

    2016-10-01

    The climate system is a classical spatiotemporal evolutionary dynamic system with spatiotemporal correlation characteristics. Based on this, two-dimensional detrended fluctuation analysis (TD-DFA) is used to estimate the Hurst exponent of two-dimensional images. Then, we monitored the change of the Hurst exponent of the images to identify an abrupt dynamic change. We tested the performance of this method with a coupled spatiotemporal dynamic model and found that it works well. The changes in the Hurst exponents of the spatial images are stable when there is no dynamic change in the system, but there will be a clear non-stationary change of the Hurst exponents; for example, the abrupt mean values change if the dynamics of the system change. Thus, the TD-DFA method is suitable for detecting an abrupt dynamic change from natural and artificial images. The spatial images of the NCEP reanalysis of the daily average temperature exhibited fractality. Based on this, we found three non-stationary changes in the Hurst exponents for the NCEP reanalysis of the daily average temperature or for the annual average temperature in the region (60°S-60°N). It can be concluded that the climate system may have incurred three dynamic changes since 1961 on decadal timescales, i.e., in approximately the mid-1970s, the mid-1980s, and between the late 1990s and the early 2000s.

  8. Abrupt response of chemical weathering to Late Quaternary hydroclimate changes in northeast Africa.

    PubMed

    Bastian, Luc; Revel, Marie; Bayon, Germain; Dufour, Aurélie; Vigier, Nathalie

    2017-03-14

    Chemical weathering of silicate rocks on continents acts as a major sink for atmospheric carbon dioxide and has played an important role in the evolution of the Earth's climate. However, the magnitude and the nature of the links between weathering and climate are still under debate. In particular, the timescale over which chemical weathering may respond to climate change is yet to be constrained at the continental scale. Here we reconstruct the relationships between rainfall and chemical weathering in northeast Africa for the last 32,000 years. Using lithium isotopes and other geochemical proxies in the clay-size fraction of a marine sediment core from the Eastern Mediterranean Sea, we show that chemical weathering in the Nile Basin fluctuated in parallel with the monsoon-related climatic evolution of northeast Africa. We also evidence strongly reduced mineral alteration during centennial-scale regional drought episodes. Our findings indicate that silicate weathering may respond as quickly as physical erosion to abrupt hydroclimate reorganization on continents. Consequently, we anticipate that the forthcoming hydrological disturbances predicted for northeast Africa may have a major impact on chemical weathering patterns and soil resources in this region.

  9. Abrupt response of chemical weathering to Late Quaternary hydroclimate changes in northeast Africa

    PubMed Central

    Bastian, Luc; Revel, Marie; Bayon, Germain; Dufour, Aurélie; Vigier, Nathalie

    2017-01-01

    Chemical weathering of silicate rocks on continents acts as a major sink for atmospheric carbon dioxide and has played an important role in the evolution of the Earth’s climate. However, the magnitude and the nature of the links between weathering and climate are still under debate. In particular, the timescale over which chemical weathering may respond to climate change is yet to be constrained at the continental scale. Here we reconstruct the relationships between rainfall and chemical weathering in northeast Africa for the last 32,000 years. Using lithium isotopes and other geochemical proxies in the clay-size fraction of a marine sediment core from the Eastern Mediterranean Sea, we show that chemical weathering in the Nile Basin fluctuated in parallel with the monsoon-related climatic evolution of northeast Africa. We also evidence strongly reduced mineral alteration during centennial-scale regional drought episodes. Our findings indicate that silicate weathering may respond as quickly as physical erosion to abrupt hydroclimate reorganization on continents. Consequently, we anticipate that the forthcoming hydrological disturbances predicted for northeast Africa may have a major impact on chemical weathering patterns and soil resources in this region. PMID:28290474

  10. Abrupt response of chemical weathering to Late Quaternary hydroclimate changes in northeast Africa

    NASA Astrophysics Data System (ADS)

    Bastian, Luc; Revel, Marie; Bayon, Germain; Dufour, Aurélie; Vigier, Nathalie

    2017-03-01

    Chemical weathering of silicate rocks on continents acts as a major sink for atmospheric carbon dioxide and has played an important role in the evolution of the Earth’s climate. However, the magnitude and the nature of the links between weathering and climate are still under debate. In particular, the timescale over which chemical weathering may respond to climate change is yet to be constrained at the continental scale. Here we reconstruct the relationships between rainfall and chemical weathering in northeast Africa for the last 32,000 years. Using lithium isotopes and other geochemical proxies in the clay-size fraction of a marine sediment core from the Eastern Mediterranean Sea, we show that chemical weathering in the Nile Basin fluctuated in parallel with the monsoon-related climatic evolution of northeast Africa. We also evidence strongly reduced mineral alteration during centennial-scale regional drought episodes. Our findings indicate that silicate weathering may respond as quickly as physical erosion to abrupt hydroclimate reorganization on continents. Consequently, we anticipate that the forthcoming hydrological disturbances predicted for northeast Africa may have a major impact on chemical weathering patterns and soil resources in this region.

  11. Role of Acclimatization in Weather-Related Human Mortality During the Transition Seasons of Autumn and Spring in a Thermally Extreme Mid-Latitude Continental Climate

    PubMed Central

    de Freitas, Christopher R.; Grigorieva, Elena A.

    2015-01-01

    Human mortality is closely related to natural climate-determined levels of thermal environmental stress and the resulting thermophysiological strain. Most climate-mortality research has focused on seasonal extremes during winter and summer when mortality is the highest, while relatively little attention has been paid to mortality during the transitional seasons of autumn and spring. The body acclimatizes to heat in the summer and cold in winter and readjusts through acclimatization during the transitions between the two during which time the body experiences the thermophysiological strain of readjustment. To better understand the influences of weather on mortality through the acclimatization process, the aim here is to examine the periods that link very cold and very warms seasons. The study uses the Acclimatization Thermal Strain Index (ATSI), which is a comparative measure of short-term thermophysiological impact on the body. ATSI centers on heat exchange with the body’s core via the respiratory system, which cannot be protected. The analysis is based on data for a major city in the climatic region of the Russian Far East characterized by very hot summers and extremely cold winters. The results show that although mortality peaks in winter (January) and is at its lowest in summer (August), there is not a smooth rise through autumn nor a smooth decline through spring. A secondary peak occurs in autumn (October) with a smaller jump in May. This suggests the acclimatization from warm-to-cold produces more thermophysiological strain than the transition from cold-to-warm. The study shows that ATSI is a useful metric for quantifying the extent to which biophysical adaptation plays a role in increased strain on the body during re-acclimatization and for this reason is a more appropriate climatic indictor than air temperature alone. The work gives useful bioclimatic information on risks involved in transitional seasons in regions characterized by climatic extremes. This

  12. Role of Acclimatization in Weather-Related Human Mortality During the Transition Seasons of Autumn and Spring in a Thermally Extreme Mid-Latitude Continental Climate.

    PubMed

    de Freitas, Christopher R; Grigorieva, Elena A

    2015-11-26

    Human mortality is closely related to natural climate-determined levels of thermal environmental stress and the resulting thermophysiological strain. Most climate-mortality research has focused on seasonal extremes during winter and summer when mortality is the highest, while relatively little attention has been paid to mortality during the transitional seasons of autumn and spring. The body acclimatizes to heat in the summer and cold in winter and readjusts through acclimatization during the transitions between the two during which time the body experiences the thermophysiological strain of readjustment. To better understand the influences of weather on mortality through the acclimatization process, the aim here is to examine the periods that link very cold and very warms seasons. The study uses the Acclimatization Thermal Strain Index (ATSI), which is a comparative measure of short-term thermophysiological impact on the body. ATSI centers on heat exchange with the body’s core via the respiratory system, which cannot be protected. The analysis is based on data for a major city in the climatic region of the Russian Far East characterized by very hot summers and extremely cold winters. The results show that although mortality peaks in winter (January) and is at its lowest in summer (August), there is not a smooth rise through autumn nor a smooth decline through spring. A secondary peak occurs in autumn (October) with a smaller jump in May. This suggests the acclimatization from warm-to-cold produces more thermophysiological strain than the transition from cold-to-warm. The study shows that ATSI is a useful metric for quantifying the extent to which biophysical adaptation plays a role in increased strain on the body during re-acclimatization and for this reason is a more appropriate climatic indictor than air temperature alone. The work gives useful bioclimatic information on risks involved in transitional seasons in regions characterized by climatic extremes. This

  13. 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

  14. Impacts of climate change on vegetation, hydrological and socio-economic droughts in a transitional wet-to-dry Mediterranean region

    NASA Astrophysics Data System (ADS)

    Nunes, João Pedro; Pulquério, Mário; Grosso, Nuno; Duarte Santos, Filipe; João Cruz, Maria

    2015-04-01

    The Tagus river basin is located in a transitional region between humid and semi-arid climate. The lower part of the basin is a strategic source of water for Portugal, providing water for agricultural irrigation, hydropower generation, and domestic water supplies for over 4 million people. Climate change in this region is expected to lead to higher temperatures and lower rainfall, therefore increasing climatic aridity. In this transitional region, this could lead to an increased frequency of severe droughts, threatening climatic support for current agricultural and forestry practices, as well as the sustainability of domestic water supplies. This work evaluated the impacts of climate change on drought frequency and severity for the Portuguese part of the Tagus river basin. Climate change scenarios for 2010-2100 (A2 greenhouse emission scenarios) were statistically downscaled for the study area. They were evaluated with the Soil and Water Assessment Tool (SWAT) eco-hydrological model, which simulated vegetation water demand and drought stress, soil water availability, irrigation abstraction, streamflow, reservoir storage and groundwater recharge. Water inflows from Spain were estimated using an empirical climate-based model. Drought occurrence and severity was analyzed in terms of: * meteorological drought, based on (i) the Standardized Precipitation Index and (ii) the Aridity Index; * vegetation/agricultural drought, based on plant water stress; * hydrological drought, based on (i) streamflow rates and (ii) reservoir storage; * socio-economic drought, based on (i) the capacity of the main reservoir in the system (Castelo de Bode) to sustain hydropower and domestic supplies, and (ii) the rate of groundwater extraction vs. irrigation demands for the cultures located in the intensive cultivation regions of the Lezírias near the Tagus estuary. The results indicate a trend of increasing frequency and severity of most drought types during the XXIst century, with a

  15. Abrupt reversal in ocean overturning during the Palaeocene/Eocene warm period.

    PubMed

    Nunes, Flavia; Norris, Richard D

    2006-01-05

    An exceptional analogue for the study of the causes and consequences of global warming occurs at the Palaeocene/Eocene Thermal Maximum, 55 million years ago. A rapid rise of global temperatures during this event accompanied turnovers in both marine and terrestrial biota, as well as significant changes in ocean chemistry and circulation. Here we present evidence for an abrupt shift in deep-ocean circulation using carbon isotope records from fourteen sites. These records indicate that deep-ocean circulation patterns changed from Southern Hemisphere overturning to Northern Hemisphere overturning at the start of the Palaeocene/Eocene Thermal Maximum. This shift in the location of deep-water formation persisted for at least 40,000 years, but eventually recovered to original circulation patterns. These results corroborate climate model inferences that a shift in deep-ocean circulation would deliver relatively warmer waters to the deep sea, thus producing further warming. Greenhouse conditions can thus initiate abrupt deep-ocean circulation changes in less than a few thousand years, but may have lasting effects; in this case taking 100,000 years to revert to background conditions.

  16. 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.

  17. Abrupt plant physiological changes in southern New Zealand at the termination of the Mi-1 event reflect shifts in hydroclimate and pCO2

    NASA Astrophysics Data System (ADS)

    Reichgelt, Tammo; D'Andrea, William J.; Fox, Bethany R. S.

    2016-12-01

    A rise in atmospheric CO2 is believed to be necessary for the termination of large-scale glaciations. Although the Antarctic Ice Sheet is estimated to have melted from ∼125% to ∼50% its modern size, there is thus far no evidence for an increase in atmospheric CO2 associated with the Mi-1 glacial termination in the earliest Miocene. Here, we present evidence from a high-resolution terrestrial record of leaf physiological change in southern New Zealand for an abrupt increase in atmospheric CO2 coincident with the termination of the Mi-1 glaciation and lasting approximately 20 kyr. Quantitative pCO2 estimates, made using a leaf gas exchange model, suggest that atmospheric CO2 levels may have doubled during this period, from 516 ± 111ppm to 1144 ± 410ppm, and subsequently returned back to 425 ± 53ppm. The 20-kyr interval with high pCO2 estimates is also associated with a period of increased moisture supply to southern New Zealand, inferred from carbon and hydrogen isotopes of terrestrial leaf waxes. The results provide the first high-resolution record of terrestrial environmental change at the Oligocene/Miocene boundary, document a ∼20 kyr interval of elevated pCO2 and increased local moisture availability, and provide insight into ecosystem response to a major orbitally driven climatic transition.

  18. From the Cover: Antarctic climate signature in the Greenland ice core record.

    PubMed

    Barker, Stephen; Knorr, Gregor

    2007-10-30

    A numerical algorithm is applied to the Greenland Ice Sheet Project 2 (GISP2) dust record from Greenland to remove the abrupt changes in dust flux associated with the Dansgaard-Oeschger (D-O) oscillations of the last glacial period. The procedure is based on the assumption that the rapid changes in dust are associated with large-scale changes in atmospheric transport and implies that D-O oscillations (in terms of their atmospheric imprint) are more symmetric in form than can be inferred from Greenland temperature records. After removal of the abrupt shifts the residual, dejumped dust record is found to match Antarctic climate variability with a temporal lag of several hundred years. It is argued that such variability may reflect changes in the source region of Greenland dust (thought to be the deserts of eastern Asia). Other records from this region and more globally also reveal Antarctic-style variability and suggest that this signal is globally pervasive. This provides the potential basis for suggesting a more important role for gradual changes in triggering more abrupt transitions in the climate system.

  19. Evidence from Ice-Rafted Debris and Sediment Provenance for a Dynamic East Antarctic Ice Sheet During the Mid-Miocene Climate Transition

    NASA Astrophysics Data System (ADS)

    Williams, T.; Pierce, E. L.; van de Flierdt, T.; Hemming, S. R.; Cook, C. P.; Passchier, S.; Sangiorgi, F.; Bijl, P.

    2015-12-01

    The Antarctic ice sheets underwent a major expansion during the Mid-Miocene Climate Transition, around 14 Ma, lowering eustatic sea level by perhaps 50m, based on evidence from benthic oxygen isotope records and sea level indicators. However, direct evidence of changes in the ice sheet is limited to sites in or close to the Transantarctic Mountains. Here we present evidence for ice sheet change from two widely separated sites offshore of East Antarctica, IODP Site U1356, Wilkes Land, and ODP Site 1165, Prydz Bay. Between 14.1 and 13.8 Ma at these sites, episodic pulses of ice-rafted debris (IRD), including dropstones, were deposited in concentrations exceeding those in the rest of the Miocene. These repeated pulses of IRD-bearing icebergs indicate large and repeated advances and retreats of the ice sheet during the course of the transition to a larger and relatively more stable ice sheet. We conducted provenance analyses on the mid-Miocene IRD and sediments. At Site U1356, 40Ar/39Ar ages of ice-rafted hornblende grains show that a major ice drainage was situated along the inland part of the Mertz Shear Zone and its southward extension along the west side of the Wilkes Subglacial Basin, while Nd isotope data from the terrigenous fine fraction show that the ice margin periodically expanded from high ground well into the Wilkes Subglacial Basin during periods of ice growth. At Site 1165, 40Ar/39Ar on dropstones indicate provenance from both the Lambert Glacier region and the part of Wilkes Land that contains the Aurora Subglacial Basin. The two sites provide a direct record of repeated collapse and re-growth of ice in at least two of East Antarctica's main drainage basins during the mid-Miocene climate transition. We will set our ice-rafted debris and provenance evidence for cryosphere change in the context of mid-Miocene climate records.

  20. Warm to cold polar climate transitions over the last 15,000 years: A paleoclimatology record from the raised beaches of northern Norway

    SciTech Connect

    Fletcher, C.H. ); Fairbridge, R.H. ); Moeller, J.K. ); Long, A.J. )

    1991-03-01

    Because of the strength of the cold, dry arctic high pressure vortex, and the absence of multiple air-mass sources, climate records from the polar region tend to display a cleaner signal than those from mid-latitude settings. The high arctic presents unique opportunities for the prediction of the natural background pattern of climate change prior to the disturbances generated by manmade atmospheric pollutants. The Varanger Peninsula of northernmost Norway was extensively depressed by an ice dome during the last glacial stage. Deglaciation was accompanied by isostatic recovery at a steady though exponentially decaying rate. Superimposed on the rising land is a discontinuous staircase of cobble beach ridges, deposited during the postglacial period by storms at the coast. The ridges are constructed during brief episodes of weather- and tide-related elevation of sea level and wave run-up. Storminess periods can only occur in the absence of sea ice associated with several decades of mild, relatively warm temperatures. A history of local relative sea level is constructed from over 70 radiocarbon dates of various water-level indicators. The sea-level history is used to construct a chronology of beach-ridge building that documents the cyclic, a periodic nature of arctic storminess conditions. The authors date a dynamic signal with multiple climate transitions from warm, stormy conditions to cool, calm conditions occurring roughly every 200 years between 15,000 years ago to 10,000 years ago. Throughout the Holocene the climate is more settled with longer periods separating the major warm to cool transitions.

  1. 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.

  2. 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.

  3. 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.

  4. Ultra-wideband horn antenna with abrupt radiator

    SciTech Connect

    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.

  5. 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.

  6. Hallucinations after abrupt withdrawal of oral and intrathecal baclofen.

    PubMed

    D'Aleo, Giangaetano; Cammaroto, Simona; Rifici, Carmela; Marra, Giuseppe; Sessa, Edoardo; Bramanti, Placido; Di Bella, Paolo

    2007-01-01

    Since 1977 several cases of hallucinations after abrupt withdrawal of oral baclofen have been described. There are no reports of hallucinations after gradual withdrawal of oral baclofen. No one has ever described visual hallucinations after abrupt interruption of intrathecal baclofen therapy. We describe five personally observed cases of visual hallucinations occurring after sudden interruption of baclofen (in two of these cases, intrathecal baclofen) therapy. The patients were immediately submitted to routine EEG, visual evoked potentials and standard brain magnetic resonance imaging (MRI). A few days later they also underwent polysomnography, fundus oculi examination and brain MRI of the temporal lobe. All these examinations were normal. We hypothesise that these symptoms could be due to biochemical and molecular changes, chiefly in glutamatergic n-methyl-d-aspartate, GABA-A, and GABA-B receptor response, leading to increased excitability and spontaneous activity as a result of chronic use of baclofen.

  7. Transition from the DMSP SSM/I to SSMIS sensors for NSIDC near-real-time snow and ice climate records

    NASA Astrophysics Data System (ADS)

    Gibbons, P.; Meier, W.; Scott, D.

    2010-12-01

    The National Snow and Ice Data Center (NSIDC) Distributed Active Archive Center (DAAC) distributes numerous satellite derived snow and ice data products that rely on the Defense Meteorological Satellite Program (DMSP) passive microwave SSM/I (Special Sensor Microwave/Imager) and SSMIS (Special Sensor Microwave Imager/Sounder) sensors. The SSM/I sensor started collecting data in 1987, providing a continuous record of snow and sea ice for over two decades. As capabilities developed to produce near-real-time products, interest in such products increased. As a result there are now expectations from both the scientific community and the general public to have continuous access to reasonably reliable near-real-time climate parameters (e.g., sea ice concentration). When sensors or satellites fail or are decommissioned, a transition must be made to continue the data time-series in a consistent manner. The recent failure of the F-13 SSM/I sensor created, for the first time, a need for NSIDC to transition its near-real-time snow and ice products to rely on a new sensor and platform (F-17 SSMIS). The process that surrounds such a transition is usually long and detail intensive, accomplished over several months. However, with demand high for immediate climate information, NSIDC was on a tight schedule to develop and implement a near-real-time inter-sensor calibration that would enable a seamless transition of its near-real-time snow and ice products, while maintaining a high-standard for data consistency and quality for scientific investigation of the cryosphere. This poster provides an overview of the process required and obstacles encountered, to continue the satellite data record for a highly popular and consistent line of products made available by NSIDC.

  8. Changes in the Rain-Snow Transition Elevation: The Impact of Climate Warming on the Spatial Variability of Snow and the Hydrology of Mountains Basins (Invited)

    NASA Astrophysics Data System (ADS)

    Marks, D. G.; Reba, M. L.; Winstral, A. H.; Kumar, M.

    2010-12-01

    The hydrology of mountain regions is determined by precipitation phase, volume and distribution. The complexities of precipitation volume and distribution are the result of a complex interplay between regional orographic effects, and local-scale wind field interaction with vegetation and topographic structure. Air-mass characteristics interact with the elevation range of mountain systems to determine the precipitation phase and the elevation of the rain-snow transition. The makeup of forest and river systems in mountain basins is a reflection of the stability of the rain-snow transition elevation over a long period of time. However, in a rapidly changing and warming climate, the rain-snow transition is no longer stable, and is moving to higher elevations. This will have a dramatic impact on mountain hydrology, streamflow, and our ability to predict water supplies from mountain regions. Detailed data on precipitation, snow, and meteorological conditions along an elevation gradient within the Reynolds Creek Experimental Watershed (RCEW) in the Owyhee Mountains of Idaho, USA are used to examine changes to the rain-snow transition elevation over the last 50 years. We present specific examples of how these changes have impacted snow distribution at watershed scales within the RCEW, including a reduction in redistribution, drifting and earlier melt-out, resulting in increased winter streamflow and decreased summer streamflow. We also show how these changes are likely to affect patterns of snow deposition across the northern Great Basin.

  9. Multistable states in the biosphere-climate system: towards conceptual models

    NASA Astrophysics Data System (ADS)

    Bartsev, S.; Belolipetskii, P.; Degermendzhi, A.

    2017-02-01

    Forecasting response of the biosphere and regional ecosystems to observed and expected climate change is the fundamental problem with obvious practical significance. Fundamental non-linearity of the climate system and biosphere makes feasible implementing multiple states and threshold processes in the biosphere-climate system (BCS) in response to gradually increasing influence factor (greenhouse gas concentrations growth). Really time series analysis of global temperature and other global and local parameters indicates the presence of abrupt transitions between stationary states. Identification of the switching mechanisms using general circulation models of the atmosphere and the ocean is associated with the obvious difficulties due to their complexity. Understanding the nature of such switches at qualitative level can be achieved by using a conceptual small-scale models. Some variants of possible mechanisms capable of generating these shifts and simultaneously supporting quasi-stationary periods between them are discussed.

  10. Holocene winter climate variability in mid-latitude western North America.

    PubMed

    Ersek, Vasile; Clark, Peter U; Mix, Alan C; Cheng, Hai; Edwards, R Lawrence

    2012-01-01

    Water resources in western North America depend on winter precipitation, yet our knowledge of its sensitivity to climate change remains limited. Similarly, understanding the potential for future loss of winter snow pack requires a longer perspective on natural climate variability. Here we use stable isotopes from a speleothem in southwestern Oregon to reconstruct winter climate change for much of the past 13,000 years. We find that on millennial time scales there were abrupt transitions between warm-dry and cold-wet regimes. Temperature and precipitation changes on multi-decadal to century timescales are consistent with ocean-atmosphere interactions that arise from mechanisms similar to the Pacific Decadal Oscillation. Extreme cold-wet and warm-dry events that punctuated the Holocene appear to be sensitive to solar forcing, possibly through the influence of the equatorial Pacific on the winter storm tracks reaching the US Pacific Northwest region.

  11. Jurassic climate mode governed by ocean gateway

    PubMed Central

    Korte, Christoph; Hesselbo, Stephen P.; Ullmann, Clemens V.; Dietl, Gerd; Ruhl, Micha; Schweigert, Günter; Thibault, Nicolas

    2015-01-01

    The Jurassic (∼201–145 Myr ago) was long considered a warm ‘greenhouse' period; more recently cool, even ‘icehouse' episodes have been postulated. However, the mechanisms governing transition between so-called Warm Modes and Cool Modes are poorly known. Here we present a new large high-quality oxygen-isotope dataset from an interval that includes previously suggested mode transitions. Our results show an especially abrupt earliest Middle Jurassic (∼174 Ma) mid-latitude cooling of seawater by as much as 10 °C in the north–south Laurasian Seaway, a marine passage that connected the equatorial Tethys Ocean to the Boreal Sea. Coincidence in timing with large-scale regional lithospheric updoming of the North Sea region is striking, and we hypothesize that northward oceanic heat transport was impeded by uplift, triggering Cool Mode conditions more widely. This extreme climate-mode transition provides a counter-example to other Mesozoic transitions linked to quantitative change in atmospheric greenhouse gas content. PMID:26658694

  12. Jurassic climate mode governed by ocean gateway.

    PubMed

    Korte, Christoph; Hesselbo, Stephen P; Ullmann, Clemens V; Dietl, Gerd; Ruhl, Micha; Schweigert, Günter; Thibault, Nicolas

    2015-12-11

    The Jurassic (∼201-145 Myr ago) was long considered a warm 'greenhouse' period; more recently cool, even 'icehouse' episodes have been postulated. However, the mechanisms governing transition between so-called Warm Modes and Cool Modes are poorly known. Here we present a new large high-quality oxygen-isotope dataset from an interval that includes previously suggested mode transitions. Our results show an especially abrupt earliest Middle Jurassic (∼174 Ma) mid-latitude cooling of seawater by as much as 10 °C in the north-south Laurasian Seaway, a marine passage that connected the equatorial Tethys Ocean to the Boreal Sea. Coincidence in timing with large-scale regional lithospheric updoming of the North Sea region is striking, and we hypothesize that northward oceanic heat transport was impeded by uplift, triggering Cool Mode conditions more widely. This extreme climate-mode transition provides a counter-example to other Mesozoic transitions linked to quantitative change in atmospheric greenhouse gas content.

  13. Jurassic climate mode governed by ocean gateway

    NASA Astrophysics Data System (ADS)

    Korte, Christoph; Hesselbo, Stephen P.; Ullmann, Clemens V.; Dietl, Gerd; Ruhl, Micha; Schweigert, Günter; Thibault, Nicolas

    2015-12-01

    The Jurassic (~201-145 Myr ago) was long considered a warm `greenhouse' period; more recently cool, even `icehouse' episodes have been postulated. However, the mechanisms governing transition between so-called Warm Modes and Cool Modes are poorly known. Here we present a new large high-quality oxygen-isotope dataset from an interval that includes previously suggested mode transitions. Our results show an especially abrupt earliest Middle Jurassic (~174 Ma) mid-latitude cooling of seawater by as much as 10 °C in the north-south Laurasian Seaway, a marine passage that connected the equatorial Tethys Ocean to the Boreal Sea. Coincidence in timing with large-scale regional lithospheric updoming of the North Sea region is striking, and we hypothesize that northward oceanic heat transport was impeded by uplift, triggering Cool Mode conditions more widely. This extreme climate-mode transition provides a counter-example to other Mesozoic transitions linked to quantitative change in atmospheric greenhouse gas content.

  14. Energy budget increases reduce mean streamflow more than snow-rain transitions: using integrated modeling to isolate climate change impacts on Rocky Mountain hydrology

    NASA Astrophysics Data System (ADS)

    Foster, Lauren M.; Bearup, Lindsay A.; Molotch, Noah P.; Brooks, Paul D.; Maxwell, Reed M.

    2016-04-01

    In snow-dominated mountain regions, a warming climate is expected to alter two drivers of hydrology: (1) decrease the fraction of precipitation falling as snow; and (2) increase surface energy available to drive evapotranspiration. This study uses a novel integrated modeling approach to explicitly separate energy budget increases via warming from precipitation phase transitions from snow to rain in two mountain headwaters transects of the central Rocky Mountains. Both phase transitions and energy increases had significant, though unique, impacts on semi-arid mountain hydrology in our simulations. A complete shift in precipitation from snow to rain reduced streamflow between 11% and 18%, while 4 °C of uniform warming reduced streamflow between 19% and 23%, suggesting that changes in energy-driven evaporative loss, between 27% and 29% for these uniform warming scenarios, may be the dominant driver of annual mean streamflow in a warming climate. Phase changes induced a flashier system, making water availability more susceptible to precipitation variability and eliminating the runoff signature characteristic of snowmelt-dominated systems. The impact of a phase change on mean streamflow was reduced as aridity increased from west to east of the continental divide.

  15. Abrupt switch to migratory night flight in a wild migratory songbird

    PubMed Central

    Zúñiga, Daniel; Falconer, Jade; Fudickar, Adam M.; Jensen, Willi; Schmidt, Andreas; Wikelski, Martin; Partecke, Jesko

    2016-01-01

    Every year, billions of wild diurnal songbirds migrate at night. To do so, they shift their daily rhythm from diurnality to nocturnality. In captivity this is observed as a gradual transition of daytime activity developing into nocturnal activity, but how wild birds prepare their daily rhythms for migration remains largely unknown. Using an automated radio-telemetry system, we compared activity patterns of free-living migrant and resident European blackbirds (Turdus merula) in a partially migratory population during the pre-migratory season. We found that activity patterns between migrant and resident birds did not differ during day and night. Migrants did not change their daily rhythm in a progressive manner as has been observed in captivity, but instead abruptly became active during the night of departure. The rapid shift in rhythmicity might be more common across migratory songbird species, but may not have been observed before in wild animals due to a lack of technology. PMID:27666200

  16. Tropical and Subtropical Cloud Transitions in Weather and Climate Prediction Models: The GCSS/WGNE Pacific Cross-Section Intercomparison (GPCI)

    NASA Technical Reports Server (NTRS)

    Teixeira, J.; Cardoso, S.; Bonazzola, M.; Cole, J.; DeGenio, A.; DeMott, C.; Franklin, C.; Hannay, C.; Jakob, C.; Jiao, Y.; Karlsson, J.; Kitagawa, H.; Kohler, M.; Kuwano-Yoshida, A.; LeDrian, C.; Turk, F. J.

    2011-01-01

    A model evaluation approach is proposed in which weather and climate prediction models are analyzed along a Pacific Ocean cross section, from the stratocumulus regions off the coast of California, across the shallow convection dominated trade winds, to the deep convection regions of the ITCZ the Global Energy and Water Cycle Experiment Cloud System Study/Working Group on Numerical Experimentation (GCSS/ WGNE) Pacific Cross-Section Intercomparison (GPCI). The main goal of GPCI is to evaluate and help understand and improve the representation of tropical and subtropical cloud processes in weather and climate prediction models. In this paper, a detailed analysis of cloud regime transitions along the cross section from the subtropics to the tropics for the season June July August of 1998 is presented. This GPCI study confirms many of the typical weather and climate prediction model problems in the representation of clouds: underestimation of clouds in the stratocumulus regime by most models with the corresponding consequences in terms of shortwave radiation biases; overestimation of clouds by the 40-yr ECMWF Re-Analysis (ERA-40) in the deep tropics (in particular) with the corresponding impact in the outgoing longwave radiation; large spread between the different models in terms of cloud cover, liquid water path and shortwave radiation; significant differences between the models in terms of vertical cross sections of cloud properties (in particular), vertical velocity, and relative humidity. An alternative analysis of cloud cover mean statistics is proposed where sharp gradients in cloud cover along the GPCI transect are taken into account. This analysis shows that the negative cloud bias of some models and ERA-40 in the stratocumulus regions [as compared to the first International Satellite Cloud Climatology Project (ISCCP)] is associated not only with lower values of cloud cover in these regimes, but also with a stratocumulus-to-cumulus transition that occurs too

  17. Tropical and subtropical cloud transitions in weather and climate prediction models: the GCSS/WGNE Pacific Cross-Section Intercomparison (GPCI)

    SciTech Connect

    Teixeira, J.; Cardoso, S.; Bonazzola, M.; Cole, Jason N.; DelGenio, Anthony D.; DeMott, C.; Franklin, A.; Hannay, Cecile; Jakob, Christian; Jiao, Y.; Karlsson, J.; Kitagawa, H.; Koehler, M.; Kuwano-Yoshida, A.; LeDrian, C.; Lock, Adrian; Miller, M.; Marquet, P.; Martins, J.; Mechoso, C. R.; Meijgaard, E. V.; Meinke, I.; Miranda, P.; Mironov, D.; Neggers, Roel; Pan, H. L.; Randall, David A.; Rasch, Philip J.; Rockel, B.; Rossow, William B.; Ritter, B.; Siebesma, A. P.; Soares, P.; Turk, F. J.; Vaillancourt, P.; Von Engeln, A.; Zhao, M.

    2011-11-01

    A model evaluation approach is proposed where weather and climate prediction models are analyzed along a Pacific Ocean cross-section, from the stratocumulus regions off the coast of California, across the shallow convection dominated trade-winds, to the deep convection regions of the ITCZ: the GCSS/WGNE Pacific Cross-section Intercomparison (GPCI). The main goal of GPCI is to evaluate, and help understand and improve the representation of tropical and sub-tropical cloud processes in weather and climate prediction models. In this paper, a detailed analysis of cloud regime transitions along the cross-section from the sub-tropics to the tropics for the season JJA of 1998 is presented. This GPCI study confirms many of the typical weather and climate prediction model problems in the representation of clouds: underestimation of clouds in the stratocumulus regime by most models with the corresponding consequences in terms of shortwave radiation biases; overestimation of clouds by the ECMWF Re-Analysis (ERA40) in the deep tropics (in particular) with the corresponding impact in the outgoing longwave radiation; large spread between the different models in terms of cloud cover, liquid water path and shortwave radiation; significant differences between the models in terms of vertical crosssections of cloud properties (in particular), vertical velocity and relative humidity. An alternative analysis of cloud cover mean statistics is proposed where sharp gradients in cloud cover along the GPCI transect are taken into account. This analysis shows that the negative cloud bias of some models and ERA40 in the stratocumulus regions (as compared to ISCCP) is associated not only with lower values of cloud cover in these regimes, but also with a stratocumulus-to-cumulus transition that occurs too early along the trade-wind Lagrangian trajectory. Histograms of cloud cover along the cross-section differ significantly between models. Some models exhibit a quasi-bimodal structure with cloud

  18. Projected Applications of a ``Climate in a Box'' Computing System at the NASA Short-term Prediction Research and Transition (SPoRT) Center

    NASA Astrophysics Data System (ADS)

    Jedlovec, G.; Molthan, A.; Zavodsky, B.; Case, J.; Lafontaine, F.

    2010-12-01

    The NASA Short-term Prediction Research and Transition (SPoRT) Center focuses on the transition of unique observations and research capabilities to the operational weather community, with a goal of improving short-term forecasts on a regional scale. Advances in research computing have lead to “Climate in a Box” systems, with hardware configurations capable of producing high resolution, near real-time weather forecasts, but with footprints, power, and cooling requirements that are comparable to desktop systems. The SPoRT Center has developed several capabilities for incorporating unique NASA research capabilities and observations with real-time weather forecasts. Planned utilization includes the development of a fully-cycled data assimilation system used to drive 36-48 hour forecasts produced by the NASA Unified version of the Weather Research and Forecasting (WRF) model (NU-WRF). The horsepower provided by the “Climate in a Box” system is expected to facilitate the assimilation of vertical profiles of temperature and moisture provided by the Atmospheric Infrared Sounder (AIRS) aboard the NASA Aqua satellite. In addition, the Moderate Resolution Imaging Spectroradiometer (MODIS) instruments aboard NASA’s Aqua and Terra satellites provide high-resolution sea surface temperatures and vegetation characteristics. The development of MODIS normalized difference vegetation index (NVDI) composites for use within the NASA Land Information System (LIS) will assist in the characterization of vegetation, and subsequently the surface albedo and processes related to soil moisture. Through application of satellite simulators, NASA satellite instruments can be used to examine forecast model errors in cloud cover and other characteristics. Through the aforementioned application of the “Climate in a Box” system and NU-WRF capabilities, an end goal is the establishment of a real-time forecast system that fully integrates modeling and analysis capabilities developed

  19. Projected Applications of a "Climate in a Box" Computing System at the NASA Short-Term Prediction Research and Transition (SPoRT) Center

    NASA Technical Reports Server (NTRS)

    Jedlovec, Gary J.; Molthan, Andrew L.; Zavodsky, Bradley; Case, Jonathan L.; LaFontaine, Frank J.

    2010-01-01

    The NASA Short-term Prediction Research and Transition (SPoRT) Center focuses on the transition of unique observations and research capabilities to the operational weather community, with a goal of improving short-term forecasts on a regional scale. Advances in research computing have lead to "Climate in a Box" systems, with hardware configurations capable of producing high resolution, near real-time weather forecasts, but with footprints, power, and cooling requirements that are comparable to desktop systems. The SPoRT Center has developed several capabilities for incorporating unique NASA research capabilities and observations with real-time weather forecasts. Planned utilization includes the development of a fully-cycled data assimilation system used to drive 36-48 hour forecasts produced by the NASA Unified version of the Weather Research and Forecasting (WRF) model (NU-WRF). The horsepower provided by the "Climate in a Box" system is expected to facilitate the assimilation of vertical profiles of temperature and moisture provided by the Atmospheric Infrared Sounder (AIRS) aboard the NASA Aqua satellite. In addition, the Moderate Resolution Imaging Spectroradiometer (MODIS) instruments aboard NASA s Aqua and Terra satellites provide high-resolution sea surface temperatures and vegetation characteristics. The development of MODIS normalized difference vegetation index (NVDI) composites for use within the NASA Land Information System (LIS) will assist in the characterization of vegetation, and subsequently the surface albedo and processes related to soil moisture. Through application of satellite simulators, NASA satellite instruments can be used to examine forecast model errors in cloud cover and other characteristics. Through the aforementioned application of the "Climate in a Box" system and NU-WRF capabilities, an end goal is the establishment of a real-time forecast system that fully integrates modeling and analysis capabilities developed within the NASA SPo

  20. Setting the Scene: Climate Risk and Resilience

    DTIC Science & Technology

    2011-10-01

    Adaptation partnerships opportunities Potential increase in Humanitarian Assistance/Disaster Response Wild-cards Ocean acidification Abrupt climate ...UNCLASSIFIED Setting the Scene: Climate Risk and Resilience RADM Dave Titley Director, Task Force Climate Change Oceanographer of the Navy October...ORGANIZATION NAME(S) AND ADDRESS(ES) Oceanographer of the Navy,Task Force Climate Change ,Washington,DC,20301 8. PERFORMING ORGANIZATION REPORT NUMBER

  1. Educating for Hope in Troubled Times: Climate Change and the Transition to a Post-Carbon Future

    ERIC Educational Resources Information Center

    Hicks, David

    2014-01-01

    This book explores three global issues--climate change, peak oil and the limits to growth. It sets out the facts about the inevitable yet still largely unknown changes, and examines the feelings and attitudes the coming changes engender. It offers teachers ways to engage with vital but too often avoided issues, and to share success stories and…

  2. The speed and timing of climate change: Detailed ice core stable isotope records from NorthGRIP, Greenland and Mt. Moulton, West Antarctica

    NASA Astrophysics Data System (ADS)

    Popp, Trevor J.

    Objective projections of future climate change require a detailed understanding of the natural variability and behavior of the climate system observed in the past. This dissertation endeavors to characterize the speed and timing of past climate changes on both orbital and extremely abrupt time scales from new high-resolution stable isotope time series from ice cores collected at NorthGRIP in Greenland and Mt. Moulton in West Antarctica. Greenland ice cores are uniquely suited for study of abrupt climate events because relatively high snow accumulation rates allow single years to be identified well into the last glacial period. Deuterium (deltaD) and deuterium excess time series at near annual resolution or better across the three major abrupt transitions of the last glacial termination are examined from the precisely dated NGRIP ice core. These records have been synchronized to within a few years or less to similar isotopic series developed from the GISP2 ice core which was collected 320 km SSE of the NGRIP site. 300-500 year time intervals were examined in detail at the end of the Younger Dryas (YD, 11.7 ka), the beginning of the YD (12.9 ka), and at the onset of Bolling (14.7 ka). Transition timing, duration and amplitudes were determined for each transition at both sites via a statistical ramp fitting approach. At each transition a complete mode shift between two climate states recorded by deltaD or excess, or both, was detected in as little as a single year with one exception at the cooling at the onset of the YD at GISP2. NGRIP and GISP2 share much common variance, sometimes in remarkable detail, in the timing and evolution of the climate transitions. Complete mode shifts in excess were synchronous to within a year or better between NGRIP and GISP2 for the two cold-to-warm transitions and represent a significant regional reorganization of atmospheric circulation delivering moisture from lower latitude source regions to the high latitudes of Greenland. At the

  3. Experimental study of gradual/abrupt dynamics of HfO2-based memristive devices

    NASA Astrophysics Data System (ADS)

    Brivio, S.; Covi, E.; Serb, A.; Prodromakis, T.; Fanciulli, M.; Spiga, S.

    2016-09-01

    The resistance switching dynamics of TiN/HfO2/Pt devices is analyzed in this paper. When biased with a voltage ramp of appropriate polarity, the devices experience SET transitions from high to low resistance states in an abrupt manner, which allows identifying a threshold voltage. However, we find that the stimulation with trains of identical pulses at voltages near the threshold results in a gradual SET transition, whereby the resistive state visits a continuum of intermediate levels as it approaches some low resistance state limit. On the contrary, RESET transitions from low to high resistance states proceed in a gradual way under voltage ramp stimulation, while gradual resistance changes driven by trains of identical spikes cover only a limited resistance window. The results are discussed in terms of the relations among the thermo-electrochemical effects of Joule heating, ion mobility, and resistance change, which provide positive and negative closed loop processes in SET and RESET, respectively. Furthermore, the effect of the competition between opposite tendencies of filament dissolution and formation at opposite metal/HfO2 interfaces is discussed as an additional ingredient affecting the switching dynamics.

  4. Lack of Critical Slowing Down Suggests that Financial Meltdowns Are Not Critical Transitions, yet Rising Variability Could Signal Systemic Risk.

    PubMed

    Guttal, Vishwesha; Raghavendra, Srinivas; Goel, Nikunj; Hoarau, Quentin

    2016-01-01

    Complex systems inspired analysis suggests a hypothesis that financial meltdowns are abrupt critical transitions that occur when the system reaches a tipping point. Theoretical and empirical studies on climatic and ecological dynamical systems have shown that approach to tipping points is preceded by a generic phenomenon called critical slowing down, i.e. an increasingly slow response of the system to perturbations. Therefore, it has been suggested that critical slowing down may be used as an early warning signal of imminent critical transitions. Whether financial markets exhibit critical slowing down prior to meltdowns remains unclear. Here, our analysis reveals that three major US (Dow Jones Index, S&P 500 and NASDAQ) and two European markets (DAX and FTSE) did not exhibit critical slowing down prior to major financial crashes over the last century. However, all markets showed strong trends of rising variability, quantified by time series variance and spectral function at low frequencies, prior to crashes. These results suggest that financial crashes are not critical transitions that occur in the vicinity of a tipping point. Using a simple model, we argue that financial crashes are likely to be stochastic transitions which can occur even when the system is far away from the tipping point. Specifically, we show that a gradually increasing strength of stochastic perturbations may have caused to abrupt transitions in the financial markets. Broadly, our results highlight the importance of stochastically driven abrupt transitions in real world scenarios. Our study offers rising variability as a precursor of financial meltdowns albeit with a limitation that they may signal false alarms.

  5. Lack of Critical Slowing Down Suggests that Financial Meltdowns Are Not Critical Transitions, yet Rising Variability Could Signal Systemic Risk

    PubMed Central

    Hoarau, Quentin

    2016-01-01

    Complex systems inspired analysis suggests a hypothesis that financial meltdowns are abrupt critical transitions that occur when the system reaches a tipping point. Theoretical and empirical studies on climatic and ecological dynamical systems have shown that approach to tipping points is preceded by a generic phenomenon called critical slowing down, i.e. an increasingly slow response of the system to perturbations. Therefore, it has been suggested that critical slowing down may be used as an early warning signal of imminent critical transitions. Whether financial markets exhibit critical slowing down prior to meltdowns remains unclear. Here, our analysis reveals that three major US (Dow Jones Index, S&P 500 and NASDAQ) and two European markets (DAX and FTSE) did not exhibit critical slowing down prior to major financial crashes over the last century. However, all markets showed strong trends of rising variability, quantified by time series variance and spectral function at low frequencies, prior to crashes. These results suggest that financial crashes are not critical transitions that occur in the vicinity of a tipping point. Using a simple model, we argue that financial crashes are likely to be stochastic transitions which can occur even when the system is far away from the tipping point. Specifically, we show that a gradually increasing strength of stochastic perturbations may have caused to abrupt transitions in the financial markets. Broadly, our results highlight the importance of stochastically driven abrupt transitions in real world scenarios. Our study offers rising variability as a precursor of financial meltdowns albeit with a limitation that they may signal false alarms. PMID:26761792

  6. Abrupt fiber taper based Michelson interferometric deflection sensor

    NASA Astrophysics Data System (ADS)

    Tian, Zhaobing; Yam, Scott S.-H.

    2008-06-01

    A new compact standard single mode fiber Michelson interferometer deflection sensor was proposed, tested and simulated. The new interferometer consists of a symmetrical abrupt 3 dB taper region with a 40 μm waist diameter, a 700 μm length and a 500nm thick gold layer coating. Compared with similar interferometric devices based on long period gratings that need microfabrication technology and photosensitive fibers, the proposed sensor uses a much simplified fabrication process and normal single mode fiber, and has a linear response of 1.1nm/mm.

  7. Clay mineral assemblages of terrestrial records (Xining Basin, China) during the Eocene-Oligocene climate Transition (EOT) and its environmental implications

    NASA Astrophysics Data System (ADS)

    Zhang, C.; Guo, Z.

    2013-12-01

    The Eocene-Oligocene Transition (EOT) between ~34.0 and 33.5 million years ago, where global climate cooled from 'greenhouse' to 'icehouse' at ~33.5 Ma ago, is one of the great events during Cenozoic climate deterioration. In contrast to the marine records of the EOT, significantly less research has focused on the continental climate change during this time, particularly in inner Asia. We present a comprehensive study of the upper Eocene to lower Oligocene succession with regular alternations of laterally continuous gypsum/gypsiferous layers and red mudstone beds in Tashan section of Xining Basin, which is located at the northeastern margin of the Tibetan Plateau. Clay minerals, which were extracted from this succession, were analyzed qualitatively and semi-quantitatively by using X-ray differaction (XRD). Base on detailed magnetostratigraphic time control, clay mineral compositions of this succession (33.1-35.5 Ma) are compared with open ocean marine records and Northern Hemisphere continental records to understand the process and characteristics of Asian climate change before, during and after EOT. Our results indicate that illite is the dominant clay mineral with less chlorite and variable smectite. Multi-parameter evidence suggests that the source areas of detrital inputs in Tashan have not changed and climate is the main control for the composition of the clay fraction. The characteristics of clay mineral concentrations suggest warm and humid fluctuations with cold and dry conditions and intense of seasonality during ~35.5-34.0 Ma in inner Asian. This changed to cold and dry condition at ~34 Ma and remained so from ~34-33.1 Ma. The comparisons between continental and marine records indicate that the climate changes experienced in the Xining basin region are more consistent with Northern Hemisphere rather than open oceans records. This indicates that paleoclimate changes for inner Asian before, during and after EOT was not controlled by Antarctic ice growth

  8. 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.

  9. Tropical African climate variability during the last glacial/interglacial transition: the molecular record from Lake Malawi

    NASA Astrophysics Data System (ADS)

    Castañeda, I. S.; Werne, J. P.; Johnson, T. C.

    2003-12-01

    In general, information regarding tropical African climate variability is relatively limited, especially in comparison with high-latitude studies. Unlike the high-latitudes where climate change is often expressed by fluctuations in temperature, low-latitude climate change is often expressed as variability in zonal circulation, which can result in hydrological fluctuations. Lake Malawi, situated in low-latitude tropical Africa (9-14° S), contains a continuous and high-resolution sedimentary record of the past 22ka BP and is anoxic below 250m, which enhances preservation of organic matter (OM). For these reasons, L. Malawi is an excellent location to examine the response of low-latitude African climate to global climate change. The climate of Malawi is strongly influenced by the position and seasonal migration of the ITCZ. During the rainy season from November to March, the ITCZ is positioned over L. Malawi (12-13° S) and the dominant winds are weak and northerly. Between April and May the ITCZ moves northward towards the equator and strong southerly winds prevail (Jury & Mwafulirwa, 2002). Previous studies of L. Malawi have shown responses to global climatic events, such as the Younger Dryas. Additionally, studies have demonstrated the response of L. Malawi to local or regional events, such as variability in the ITCZ. Based on BSi MAR, diatom, phosphorus, and trace metal data, Johnson et al. (2002) proposed that at times more frequent or stronger northerly winds promoted upwelling in the northern basin of L. Malawi, and suggested more southerly migrations of the ITCZ (reaching latitudes of >13\\deg S) as the cause of these increased winds. Additionally, a recent study of L. Malawi based on multiple bulk geochemical proxies provides evidence for both southward and northward displacements of the ITCZ during the past 23ka BP (Filippi and Talbot, submitted). In this study the molecular biomarker record of L. Malawi is examined. Previous studies of Lake Malawi have

  10. Climate change, adaptive cycles, and the persistence of foraging economies during the late Pleistocene/Holocene transition in the Levant

    PubMed Central

    Rosen, Arlene M.; Rivera-Collazo, Isabel

    2012-01-01

    Climatic forcing during the Younger Dryas (∼12.9–11.5 ky B.P.) event has become the theoretical basis to explain the origins of agricultural lifestyles in the Levant by suggesting a failure of foraging societies to adjust. This explanation however, does not fit the scarcity of data for predomestication cultivation in the Natufian Period. The resilience of Younger Dryas foragers is better illustrated by a concept of adaptive cycles within a theory of adaptive change (resilience theory). Such cycles consist of four phases: release/collapse (Ω); reorganization (α), when the system restructures itself after a catastrophic stimulus through innovation and social memory—a period of greater resilience and less vulnerability; exploitation (r); and conservation (K), representing an increasingly rigid system that loses flexibility to change. The Kebarans and Late Natufians had similar responses to cold and dry conditions vs. Early Natufians and the Pre-Pottery Neolithic A responses to warm and wet climates. Kebarans and Late Natufians (α-phase) shifted to a broader-based diet and increased their mobility. Early Natufian and Pre-Pottery Neolithic A populations (r- and K-phases) had a growing investment in more narrowly focused, high-yield plant resources, but they maintained the broad range of hunted animals because of increased sedentism. These human adaptive cycles interlocked with plant and animal cycles. Forest and grassland vegetation responded to late Pleistocene and early Holocene climatic fluctuations, but prey animal cycles reflected the impact of human hunting pressure. The combination of these three adaptive cycles results in a model of human adaptation, showing potential for great sustainability of Levantine foraging systems even under adverse climatic conditions. PMID:22371591

  11. 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.

  12. 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.

  13. Transitional changes in microfossil assemblages in the Japan Sea from the Late Pliocene to Early Pleistocene related to global climatic and local tectonic events

    NASA Astrophysics Data System (ADS)

    Itaki, Takuya

    2016-12-01

    Many micropaleontological studies based on data from on-land sections, oil wells, and deep-sea drilling cores have provided important information about environmental changes in the Japan Sea that are related to the global climate and the local tectonics of the Japanese Islands. Here, major changes in the microfossil assemblages during the Late Pliocene to Early Pleistocene are reviewed. Late Pliocene (3.5-2.7 Ma) surface-water assemblages were characterized mainly by cold-temperate planktonic flora and fauna (nannofossils, diatoms, radiolarians, and planktonic foraminifera), suggesting that nutrient-rich North Pacific surface waters entered the Japan Sea via northern straits. The common occurrence of Pacific-type deep-water radiolarians during this period also suggests that deep water from the North Pacific entered the Japan Sea via the northern straits, indicating a sill depth >500 m. A weak warm-water influence is recognized along the Japanese coast, suggesting a small inflow of warm water via a southern strait. Nannofossil and sublittoral ostracod assemblages record an abrupt cooling event at 2.75 Ma that correlates with the onset of the Northern Hemisphere glaciation. Subsequently, cold intermediate- and deep-water assemblages of ostracods and radiolarians increased in abundance, suggesting active ventilation and the formation of the Japan Sea Proper Water, associated with a strengthened winter monsoon. Pacific-type deep-water radiolarians also disappeared around 2.75 Ma, which is attributed to the intermittent occurrence of deep anoxic environments and limited migration from the North Pacific, resulting from the near-closure or shallowing of the northern strait by a eustatic fall in sea level and tectonic uplift of northeastern Japan. A notable reduction in primary productivity from 2.3 to 1.3 Ma also suggests that the nutrient supply from the North Pacific was restricted by the near-closure of the northern strait. An increase in the abundance of subtropical

  14. 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

    2014-07-03

    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

  15. The effect of abrupt permafrost thaw on the water table, vegetation and carbon feedback: results from a sub-arctic peatland

    NASA Astrophysics Data System (ADS)

    Malhotra, A.; Roulet, N. T.

    2015-12-01

    Uncertainty in estimating the carbon loss from thawing ice-rich permafrost is attributed, in part, to the abrupt changes in ecosystem structure and function after thaw. In a thawing peat plateau in the discontinuous permafrost zone (Stordalen, Mire, Sweden; ST), we tested for the occurrence of abrupt changes in hydrology and the effects of these changes on the water table and vegetation feedback. Using a chronosequence approach along three transects that capture several transitional thaw stages, we found abrupt hydrological changes following thaw, wherein adjacent areas (1 m apart) had unrelated water table depth (WTD) fluctuations. Despite these abrupt changes, surprisingly, the same Gaussian model of plant abundance explained by WTD could be applied to data from both ST and an undisturbed ombrotrophic peatland (Mer Bleue Bog, Canada; MB). However, the Gaussian model fit was better at MB than at ST. Furthermore, explanatory power of the model at ST decreased with increasing permafrost thaw. While water table and vegetation feedback in a thawing landscape is similar to that of a peatland without transitional land cover types, the vegetation and carbon feedback is complicated by non-linear shifts in the partitioning of gaseous effluxes between CO2 and CH4. These results will be presented along with key implications for modeling carbon loss from thawing landscapes.

  16. Cretaceous-Tertiary boundary in the Antarctic: Climatic cooling precedes biotic crisis

    NASA Technical Reports Server (NTRS)

    Stott, Lowell D.; Kennett, James P.

    1988-01-01

    Stable isotopic investigations were conducted on calcareous microfossils across two deep sea Cretaceous-Tertiary boundary sequences on Maud Rise, Weddell Sea, Antarctica. The boundary is taken at the level of massive extinctions in calcareous planktonic microfossils, and coincides with a sharp lithologic change from pure calcareous ooze to calcareous ooze with a large volcanic clay component. The uppermost Maestrichtian is marked by a long-term decrease in delta value of 0 to 18 which spans most of the lower and middle A. mayaroensis Zone and represents a warming trend which culminated in surface water temperatures of about 16 C. At approximately 3 meters below the K-T boundary this warming trend terminates abruptly and benthic and planktonic isotopic records exhibit a rapid increase in delta value of 0 to 18 that continues up to the K-T boundary. The trend towards cooler surface water temperatures stops abruptly at the K-T boundary and delta value of 0 to 18 values remain relatively stable through the Paleocene. Comparison of the Antarctic sequence with the previously documented deep sea records in the South Atlantic reveal shifts of similar magnitude in the latest Maestrichtian. It is indicated that the Southern Ocean underwent the most significant, and apparently permanent, climatic change. The latest Cretaceous oxygen isotopic shift recorded at Maud Rise and other deep sea sites is similar in magnitude to large positive delta valve of 0 to 18 shifts in the middle Eocene, at the Eocene/Oligocene boundary and in the middle Miocene that marked large scale climatic transitions which ultimately lead to cryospheric development of the Antarctic. The climatic shift at the end of the Cretaceous represents one of the most significant climatic transitions recorded in the latest Phanerozoic and had a profound effect on global climate as well as oceanic circulation.

  17. Infrastructure sufficiency in meeting water demand under climate-induced socio-hydrological transition in the urbanizing Capibaribe River Basin - Brazil

    NASA Astrophysics Data System (ADS)

    Ribeiro Neto, A.; Scott, C. A.; Lima, E. A.; Montenegro, S. M. G. L.; Cirilo, J. A.

    2014-03-01

    Water availability for a range of human uses will increasingly be affected by climate change especially in the arid and semi-arid tropics. This paper aims to evaluate the ability of reservoirs and related infrastructure to meet targets for water supply in the Capibaribe River Basin (CRB), in the state of Pernambuco, Brazil. The basin has experienced spatial and sectoral (agriculture-urban) reconfiguration of water demands. Human settlements that were once dispersed, relying on intermittent sources of surface water, are now increasingly experiencing water-scarcity effects. As a result, rural populations in the CRB are concentrating around infrastructural water supplies in a socio-hydrological transition process that results from (a) hydroclimatic variability, (b) investment and assistance programs that may enhance but can also supplant local adaptive capacity, and (c) demographic trends driving urbanization of the state capital, Recife, which mirror urban growth across Brazil. In the CRB, demands are currently composed of 69.1% urban potable water, 14.3% industrial, 16.6% irrigation (with ecosystem-service demands met by residual flow). Based on the application of linked hydrologic and water-resources models using precipitation and temperature projections of the IPCC SRES A1B scenario, a reduction in rainfall of 31.8% translated to streamflow reduction of 67.4% under present reservoir operations rules. The increasing demand due to population was also taken into account. This would entail severe water supply reductions for human consumption (-45.3%) and irrigation (-78.0%) by the end of the 21st century. This study demonstrates the vulnerabilities of the infrastructure system during socio-hydrological transition in response to hydroclimatic and demand variabilities in the CRB and also indicates the differential spatial impacts and vulnerability of multiple uses of water to changes over time. The paper concludes with a discussion of the broader implications of climate

  18. Salinization of Freshwater-Dependent Coastal Ecosystems: Understanding Landscapes in Transition Along the Leading Edge of Climate Change

    NASA Astrophysics Data System (ADS)

    Emanuel, R. E.; Bernhardt, E. S.; Ardón, M.; Wright, J. P.; BenDor, T.; Bhattachan, A.

    2015-12-01

    Climate change is transforming the outer edge of the Southern US coastal plain. Lower-lying parts of this region, characterized by extensive freshwater-dependent ecosystems, will be largely inundated by gradual sea level rise by the end of this century. In the interim, however, ocean waters are already penetrating and influencing freshwater-dependent coastal landscapes due to a combination of human and natural factors. This landward movement of salinity from the coast onto the coastal plain or "saltwater intrusion" is a critical water resource issue representing the leading edge of climate change for many coastal areas. The salinization of surface waters and adjacent lands has implications for crop and timber yields in managed ecosystems, ecosystem carbon sequestration in unmanaged ecosystems, and degradation of coastal water quality due to extraction of soil nutrients by seasalts. With this in mind, we seek to understand more broadly how vulnerability of coastal landscapes to saltwater intrusion shapes and is shaped by both natural and anthropogenic processes. We present a novel framework that couples intensive, in situ monitoring of hydrological and ecological conditions with a geospatial saltwater intrusion vulnerability index (SIVI). We discuss application of this framework to the Albemarle-Pamlico region of coastal North Carolina, where we are learning how climate, natural landscape structure, and human activities interact to mediate or exacerbate the vulnerability of freshwater-dependent lands to saltwater intrusion. We discuss the involvement of stakeholders and local knowledge in the research process as well. This work advances understanding of vulnerability to climate change in coastal regions by moving beyond simple inundation models to gain a more sophisticated understanding of the human and natural processes influencing salinization of surface waters and adjacent lands. As the Albemarle-Pamlico and similar regions worldwide transform in response to and

  19. The effects of future nationwide forest transition to discharge in the 21st century with regard to general circulation model climate change scenarios.

    PubMed

    Mouri, Goro; Nakano, Katsuhiro; Tsuyama, Ikutaro; Tanaka, Nobuyuki

    2016-08-01

    Catchment Simulator modelling frameworks based on the Minimal Advanced Treatments of Surface Interaction and Runoff (MATSIRO) model, which was expanded to estimate discharge by incorporating the effects of forest-type transition across the whole of Japan. The results indicated that, by the 2090s, annual runoff will increase above present-day values. Increases in annual variation in runoff by the 2090s was predicted to be around 14.1% when using the MRI-GCM data and 44.4% when using the HadGEM data. Analysis by long-term projection showed the largest increases in runoff in the 2090s were related to the type of forest, such as evergreen. Increased runoff can have negative effects on both society and the environment, including increased flooding events, worsened water quality, habitat destruction and changes to the forest moisture-retaining function. Prediction of the impacts of future climate change on water generation is crucial for effective environmental planning and management.

  20. Abrupt Bølling warming and ice saddle collapse contributions to the Meltwater Pulse 1a rapid sea level rise

    NASA Astrophysics Data System (ADS)

    Gregoire, Lauren J.; Otto-Bliesner, Bette; Valdes, Paul J.; Ivanovic, Ruza

    2016-09-01

    Elucidating the source(s) of Meltwater Pulse 1a, the largest rapid sea level rise caused by ice melt (14-18 m in less than 340 years, 14,600 years ago), is important for understanding mechanisms of rapid ice melt and the links with abrupt climate change. Here we quantify how much and by what mechanisms the North American ice sheet could have contributed to Meltwater Pulse 1a, by driving an ice sheet model with two transient climate simulations of the last 21,000 years. Ice sheet perturbed physics ensembles were run to account for model uncertainties, constraining ice extent and volume with reconstructions of 21,000 years ago to present. We determine that the North American ice sheet produced 3-4 m global mean sea level rise in 340 years due to the abrupt Bølling warming, but this response is amplified to 5-6 m when it triggers the ice sheet saddle collapse.

  1. Abrupt Bølling warming and ice saddle collapse contributions to the Meltwater Pulse 1a rapid sea level rise

    PubMed Central

    Otto‐Bliesner, Bette; Valdes, Paul J.; Ivanovic, Ruza

    2016-01-01

    Abstract Elucidating the source(s) of Meltwater Pulse 1a, the largest rapid sea level rise caused by ice melt (14–18 m in less than 340 years, 14,600 years ago), is important for understanding mechanisms of rapid ice melt and the links with abrupt climate change. Here we quantify how much and by what mechanisms the North American ice sheet could have contributed to Meltwater Pulse 1a, by driving an ice sheet model with two transient climate simulations of the last 21,000 years. Ice sheet perturbed physics ensembles were run to account for model uncertainties, constraining ice extent and volume with reconstructions of 21,000 years ago to present. We determine that the North American ice sheet produced 3–4 m global mean sea level rise in 340 years due to the abrupt Bølling warming, but this response is amplified to 5–6 m when it triggers the ice sheet saddle collapse. PMID:27773954

  2. Abrupt Bølling warming and ice saddle collapse contributions to the Meltwater Pulse 1a rapid sea level rise.

    PubMed

    Gregoire, Lauren J; Otto-Bliesner, Bette; Valdes, Paul J; Ivanovic, Ruza

    2016-09-16

    Elucidating the source(s) of Meltwater Pulse 1a, the largest rapid sea level rise caused by ice melt (14-18 m in less than 340 years, 14,600 years ago), is important for understanding mechanisms of rapid ice melt and the links with abrupt climate change. Here we quantify how much and by what mechanisms the North American ice sheet could have contributed to Meltwater Pulse 1a, by driving an ice sheet model with two transient climate simulations of the last 21,000 years. Ice sheet perturbed physics ensembles were run to account for model uncertainties, constraining ice extent and volume with reconstructions of 21,000 years ago to present. We determine that the North American ice sheet produced 3-4 m global mean sea level rise in 340 years due to the abrupt Bølling warming, but this response is amplified to 5-6 m when it triggers the ice sheet saddle collapse.

  3. Abrupt aridities in the Levant-Sahel linked with solar activities

    NASA Astrophysics Data System (ADS)

    Stein, M.; Kushnir, Y.

    2012-04-01

    Observations of 19th and 20th century precipitation in the Dead Sea watershed region display a multidecadal, anti-phase relationship to North Atlantic (NAtl) sea surface temperature (SST) variability, such that when the NAtl is relatively cold, Jerusalem experiences higher than normal precipitation and vice versa. This association is underlined by a negative correlation to precipitation in the sub-Saharan Sahel and a positive correlation to precipitation in western North America, areas that are also affected by multidecadal NAtl SST variability. These observations are consistent with broad range of Holocene hydroclimatic fluctuations from the epochal, to the millennial and centennial time scales, as displayed by the Dead Sea and Sahelian lake levels and by direct and indirect proxy indicators of NAtl SSTs. On the epochal time scale, the gradual cooling of NAtl SSTs throughout the Holocene in response to precession-driven reduction of summer insolation is associated with previously well-studied wet-to-dry transition in the Sahel and with a general increase in Dead Sea lake levels from low stands after the Younger Dryas to higher stands in the mid- to late-Holocene. On the millennial and centennial time scales there is also evidence for an antiphase relationship between Holocene variations in the Dead Sea and Sahelian lake levels and with proxy indicators of NAtl SSTs. However, the records are punctuated by abrupt lake-level drops and extensive expansion of the desert belt at ~8.1, 5.7, 3.3 and 1.4 ka cal BP, which appear to be in-phase and which occur during previously documented abrupt major cooling events in the Northern Hemisphere. We link these cooling to solar activity variations that were identified in the North Atlantic IRD and cosmogenic isotopes records.

  4. Tibetan plateau aridification linked to global cooling at the Eocene-Oligocene transition.

    PubMed

    Dupont-Nivet, Guillaume; Krijgsman, Wout; Langereis, Cor G; Abels, Hemmo A; Dai, Shuang; Fang, Xiaomin

    2007-02-08

    Continental aridification and the intensification of the monsoons in Asia are generally attributed to uplift of the Tibetan plateau and to the land-sea redistributions associated with the continental collision of India and Asia, whereas some studies suggest that past changes in Asian environments are mainly governed by global climate. The most dramatic climate event since the onset of the collision of India and Asia is the Eocene-Oligocene transition, an abrupt cooling step associated with the onset of glaciation in Antarctica 34 million years ago. However, the influence of this global event on Asian environments is poorly understood. Here we use magnetostratigraphy and cyclostratigraphy to show that aridification, which is indicated by the disappearance of playa lake deposits in the northeastern Tibetan plateau, occurred precisely at the time of the Eocene-Oligocene transition. Our findings suggest that this global transition is linked to significant aridification and cooling in continental Asia recorded by palaeontological and palaeoenvironmental changes, and thus support the idea that global cooling is associated with the Eocene-Oligocene transition. We show that, with sufficient age control on the sedimentary records, global climate can be distinguished from tectonism and recognized as a major contributor to continental Asian environments.

  5. CO2 and fire influence tropical ecosystem stability in response to climate change

    PubMed Central

    Shanahan, Timothy M.; Hughen, Konrad A.; McKay, Nicholas P.; Overpeck, Jonathan T.; Scholz, Christopher A.; Gosling, William D.; Miller, Charlotte S.; Peck, John A.; King, John W.; Heil, Clifford W.

    2016-01-01

    Interactions between climate, fire and CO2 are believed to play a crucial role in controlling the distributions of tropical woodlands and savannas, but our understanding of these processes is limited by the paucity of data from undisturbed tropical ecosystems. Here we use a 28,000-year integrated record of vegetation, climate and fire from West Africa to examine the role of these interactions on tropical ecosystem stability. We find that increased aridity between 28–15 kyr B.P. led to the widespread expansion of tropical grasslands, but that frequent fires and low CO2 played a crucial role in stabilizing these ecosystems, even as humidity changed. This resulted in an unstable ecosystem state, which transitioned abruptly from grassland to woodlands as gradual changes in CO2 and fire shifted the balance in favor of woody plants. Since then, high atmospheric CO2 has stabilized tropical forests by promoting woody plant growth, despite increased aridity. Our results indicate that the interactions between climate, CO2 and fire can make tropical ecosystems more resilient to change, but that these systems are dynamically unstable and potentially susceptible to abrupt shifts between woodland and grassland dominated states in the future. PMID:27427431

  6. CO2 and fire influence tropical ecosystem stability in response to climate change

    NASA Astrophysics Data System (ADS)

    Shanahan, Timothy M.; Hughen, Konrad A.; McKay, Nicholas P.; Overpeck, Jonathan T.; Scholz, Christopher A.; Gosling, William D.; Miller, Charlotte S.; Peck, John A.; King, John W.; Heil, Clifford W.

    2016-07-01

    Interactions between climate, fire and CO2 are believed to play a crucial role in controlling the distributions of tropical woodlands and savannas, but our understanding of these processes is limited by the paucity of data from undisturbed tropical ecosystems. Here we use a 28,000-year integrated record of vegetation, climate and fire from West Africa to examine the role of these interactions on tropical ecosystem stability. We find that increased aridity between 28–15 kyr B.P. led to the widespread expansion of tropical grasslands, but that frequent fires and low CO2 played a crucial role in stabilizing these ecosystems, even as humidity changed. This resulted in an unstable ecosystem state, which transitioned abruptly from grassland to woodlands as gradual changes in CO2 and fire shifted the balance in favor of woody plants. Since then, high atmospheric CO2 has stabilized tropical forests by promoting woody plant growth, despite increased aridity. Our results indicate that the interactions between climate, CO2 and fire can make tropical ecosystems more resilient to change, but that these systems are dynamically unstable and potentially susceptible to abrupt shifts between woodland and grassland dominated states in the future.

  7. Interhemispheric climate links revealed by late-glacial cooling episode in southern Chile.

    PubMed

    Moreno, P I; Jacobson, G L; Lowell, T V; Denton, G H

    2001-02-15

    Understanding the relative timings of climate events in the Northern and Southern hemispheres is a prerequisite for determining the causes of abrupt climate changes. But climate records from the Patagonian Andes and New Zealand for the period of transition from glacial to interglacial conditions--about 14.6-10 kyr before present, as determined by radiocarbon dating--show varying degrees of correlation with similar records from the Northern Hemisphere. It is necessary to resolve these apparent discrepancies in order to be able to assess the relative roles of Northern Hemisphere ice sheets and oceanic, atmospheric and astronomical influences in initiating climate change in the late-glacial period. Here we report pollen records from three sites in the Lake District of southern Chile (41 degrees S) from which we infer conditions similar to modern climate between about 13 and 12.2 14C kyr before present (BP), followed by cooling events at about 12.2 and 11.4 14C kyr BP, and then by a warming at about 9.8 14C kyr BP. These events were nearly synchronous with important palaeoclimate changes recorded in the North Atlantic region, supporting the idea that interhemispheric linkage through the atmosphere was the primary control on climate during the last deglaciation. In other regions of the Southern Hemisphere, where climate events are not in phase with those in the Northern Hemisphere, local oceanic influences may have counteracted the effects that propagated through the atmosphere.

  8. Northern host-parasite assemblages: history and biogeography on the borderlands of episodic climate and environmental transition.

    PubMed

    Hoberg, Eric P; Galbreath, Kurt E; Cook, Joseph A; Kutz, Susan J; Polley, Lydden

    2012-01-01

    Diversity among assemblages of mammalian hosts and parasites in northern terrestrial ecosystems was structured by a deep history of biotic and abiotic change that overlies a complex geographic arena. Since the Pliocene, Holarctic ecosystems assembled in response to shifting climates (glacial and interglacial stages). Cycles of episodic dispersal/isolation and diversification defined northern diversity on landscape to regional scales. Episodes of geographic expansion and colonisation linked Eurasia and North America across Beringia and drove macroevolutionary structure of host and parasite associations. Asynchronous dispersal from centres of origin in Eurasia into the Nearctic resulted in gradients in parasite diversity in the carnivoran, lagomorph, rodent and artiodactyl assemblages we reviewed. Recurrent faunal interchange and isolation in conjunction with episodes of host colonisation have produced a mosaic structure for parasite faunas and considerable cryptic diversity among nematodes and cestodes. Mechanisms of invasion and geographic colonisation leading to the establishment of complex faunal assemblages are equivalent in evolutionary and ecological time, as demonstrated by various explorations of diversity in these high-latitude systems. Our ability to determine historical responses to episodic shifts in global climate may provide a framework for predicting the cascading effects of contemporary environmental change.

  9. 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.

  10. Abrupt tectonics and rapid slab detachment with grain damage.

    PubMed

    Bercovici, David; Schubert, Gerald; Ricard, Yanick

    2015-02-03

    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.

  11. 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

  12. Atomically Abrupt Liquid-Oxide Interface Stabilized by Self-Regulated Interfacial Defects: The Case of Al/Al2O3 Interfaces

    SciTech Connect

    Kang, J.; Zhu, J. Y.; Curtis, C.; Blake, D.; Glatzmaier, G.; Kim, Y. H.; Wei, S. H.

    2012-06-01

    The atomic and electronic structures of the liquid Al/(0001) {alpha}-Al{sub 2}O{sub 3} interfaces are investigated by first-principles molecular dynamics simulations. Surprisingly, the formed liquid-solid interface is always atomically abrupt and is characterized by a transitional Al layer that contains a fixed concentration of Al vacancies ({approx}10 at.%). We find that the self-regulation of the defect density in the metal layer is due to the fact that the formation energy of the Al vacancies is readjusted in a way that opposes changes in the defect density. The negative-feedback effect stabilizes the defected transitional layer and maintains the atomic abruptness at the interface. The proposed mechanism is generally applicable to other liquid-metal/metal-oxide systems, and thus of significant importance in understanding the interface structures at high temperature.

  13. Paleoproductivity in the northwestern Pacific Ocean during the Pliocene-Pleistocene climate transition (3.0-1.8 Ma)

    NASA Astrophysics Data System (ADS)

    Venti, Nicholas L.; Billups, Katharina; Herbert, Timothy D.

    2017-02-01

    Alkenone mass accumulation rates (MARs) provide a proxy for export productivity in the northwestern Pacific (Ocean Drilling Program Site 1208) spanning the late Pliocene through early Pleistocene (3.0-1.8 Ma). We investigate changes in productivity associated with global cooling during the onset and expansion of Northern Hemisphere glaciation (NHG). Alkenone MARs vary on obliquity timescales throughout, but the amplitude increases at 2.75 Ma concurrent with the intensification of NHG and cooling of the sea surface by 3°C. The obliquity-scale variations in alkenone MARs parallel shipboard measurements of sediment color reflectance (%) with higher MARs significantly correlated (>95%) with darker (opal-rich) intervals. Variations in both lead benthic foraminiferal δ18O values by 1.5-2 kyr suggesting that export productivity may be a contributing factor, rather than a response, to the extent of continental glaciation. The biological pump is therefore a plausible mechanism for transferring atmospheric CO2 into the deep ocean during the onset of NHG and the ensuing obliquity-dominated climate regime. Obliquity-scale correlation between productivity and magnetic susceptibility is consistent with a link via westerly winds delivering terrigenous sediments and mixing the upper water column. Alkenone MARs also contain a 400 kyr modulation. Because this periodicity is a multiple of the residence time of carbon in the ocean, it may reflect inputs of new nutrients associated with eccentricity-forced changes in the terrestrial biosphere and weathering. We ascribe these findings to interactions between the East Asian winter monsoon and productivity in the North Pacific Ocean, perhaps contributing to Plio-Pleistocene climate change.

  14. Are treelines advancing? A global meta-analysis of treeline response to climate warming.

    PubMed

    Harsch, Melanie A; Hulme, Philip E; McGlone, Matt S; Duncan, Richard P

    2009-10-01

    Treelines are temperature sensitive transition zones that are expected to respond to climate warming by advancing beyond their current position. Response to climate warming over the last century, however, has been mixed, with some treelines showing evidence of recruitment at higher altitudes and/or latitudes (advance) whereas others reveal no marked change in the upper limit of tree establishment. To explore this variation, we analysed a global dataset of 166 sites for which treeline dynamics had been recorded since 1900 AD. Advance was recorded at 52% of sites with only 1% reporting treeline recession. Treelines that experienced strong winter warming were more likely to have advanced, and treelines with a diffuse form were more likely to have advanced than those with an abrupt or krummholz form. Diffuse treelines may be more responsive to warming because they are more strongly growth limited, whereas other treeline forms may be subject to additional constraints.

  15. The intensification of deep-water mass changes in the deep Atlantic Ocean throughout the Mid-Pleistocene climate transition

    NASA Astrophysics Data System (ADS)

    Poirier, R. K.; Billups, K.

    2012-12-01

    We examine the deep-water hydrography at Ocean Drilling Project (ODP) Site 1063 (subtropical North Atlantic, ~4600 meter water depth) using high-resolution benthic stable isotope (δ18O, δ13C) and grain size (% coarse, % Sortable Silt - SS, SS mean diameter) analyses from ~490 to 740 ka. The benthic foraminiferal δ13C record from Site 1063 provides a proxy for changes in the relative flux of lower North Atlantic Deep Water (NADW) through time. This record will refine the timing of increases in the formation of the densest components of NADW on the orbital and millennial-scale. We explore whether or not grain size analyses provide a proxy for changes in the relative velocity of the deep current. The new stable isotope data from Site 1063, when combined with the records of Poli et al. (2000), Ferretti et al. (2005), and Billups et al. (2011), tuned to the global benthic isotope stack (LR05) of Liesicki and Raymo (2004), provides a complete deep water record spanning Marine Isotope Stage (MIS) 25 to MIS 8 (~1020 to ~240 ka). Compiling published records from 16 additional sites, we use the Ocean Data View (ODV) program (Schlitzer, 2012) to map deep-water mass distributions through time. Results reveal an increasing distribution and influence of the NADW in relation to the Antarctic Bottom Water mass within interglacial periods beginning at MIS 15 continuing though the end of the Site 1063 record within MIS 9. Preliminary grain size analyses over a short interval of time reveal regular high frequency variations on the millennial scale. We anticipate having complete, high-resolution stable isotope and grain size records to discuss the hydrographic changes within the MIS 16/15 glacial/interglacial transition, as well as throughout the Mid-Pleistocene transition (MPT).

  16. Climatic stress events in the source region of modern man - Matching the last 20 ka of the Chew Bahir climate record with occupation history of adjacent refugia

    NASA Astrophysics Data System (ADS)

    Foerster, Verena; Vogelsang, Ralf; Junginger, Annett; Asrat, Asfawossen; Lamb, Henry F.; Viehberg, Finn; Trauth, Martin H.; Schaebitz, Frank

    2014-05-01

    A rapidly changing environment is considered an important driver not just for human evolution but also for cultural and technological innovation and migration. To evaluate the impact that climatic shifts on different timescales might have had on the living conditions of prehistoric humans is one of the cornerstones in current research, but continuous paleo-climate records in the vicinity of archaeological sites are still rare. As a contribution towards a better understanding of this human-climate interaction we here present a match between the last 20 ka of the just recently developed paleo-climate record from Chew Bahir in southern Ethiopia and the settlement history of adjacent possible refugia. The Chew Bahir basin, as a newly explored reliable climatic archive, lies in a biogeographically highly sensitive transition zone between the Main Ethiopian Rift and the Omo-Turkana basin and hence represents an ideal site to study climatic variability in the source region of modern man. The climatic history with a temporal resolution of up to 3 years is showing besides orbitally driven long-term transitions in and out of favourable living conditions several short abrupt excursions towards drier or wetter episodes. Comparing the frequency of archaeological findings as a parameter for human occupation to this close-by climate record that allows us to outline how complex the interplay between humans and environment during the last 20 ka really was, which dynamics might have been involved and which role the temporal dimension of environmental changes could have played for the adaption of humans.

  17. An fMRI study of abrupt-awake episodes during behavioral microsleeps.

    PubMed

    Chou, Yu-Hsiang; Chuang, Chun-Chao; Zao, John K; Ko, Li-Wei; Lin, Chin-Teng

    2011-01-01

    This paper reports the brain activation patterns of five subjects who were abruptly awakened from microsleeps in a simulated automotive driving experiment. By comparing the BOLD signals between behavioral microsleep (BM), abrupt awakening (AA) and post-abrupt awakening (post-AA) stages, we observed that visual area, frontal cortex, limbic lobe manifested more intense activation during the AA stage while frontal cortex, temporal cortex, primary motor area and insula were more activated during the post-AA stage. These results suggested that the subjects were likely in mental states differ from those associated with decision making processes as they went through and emerged from the abrupt awakening episodes.

  18. Cooling Mediterranean Sea surface temperatures during the Late Miocene provide a climate context for evolutionary transitions in Africa and Eurasia

    NASA Astrophysics Data System (ADS)

    Tzanova, Alexandrina; Herbert, Timothy D.; Peterson, Laura

    2015-06-01

    In the Late Miocene, grasslands proliferated, succulent plants diversified in the mid-latitudes, and the desert-like conditions appeared in the Sahara. Despite this major environmental change on land, the coeval deep-sea oxygen isotope record does not provide evidence for significant high latitude cooling or continental ice growth, making it difficult to relate widespread terrestrial environmental change to global climatic changes. A U37K‧ -derived sea surface temperature (SST) reconstruction spanning 13 to 6 Ma from uplifted hemipelagic sediments in Northern Italy provides the first continuous mid-latitude temperature record with which to compare the evolution of aridity and biotic events at similar latitudes in Northern Africa and Pakistan. Between 13 and 8.8 Ma, Mediterranean SST lay near the upper limit of the alkenone temperature proxy (∼28 °C), exceeding modern SST at the site by as much as 10 °C. Throughout the record, sapropel layers correspond to local SST maxima, suggesting that Late Miocene hydrological conditions in the Mediterranean responded to insolation forcing via mechanisms similar to those documented for the Plio-Pleistocene. Mediterranean SST cooled rapidly beginning at ∼8 Ma, with an episode of intense cooling to ∼19 °C between 7.2 Ma and 6.6 Ma, followed by a rebound to ∼25 °C preceding the Messinian Salinity Crisis at 5.9 Ma. These observations establish, for the first time, a direct relationship between increasing aridity in the Northern hemisphere mid-latitudes and significant cooling. Evidently, this cooling was not accompanied by significant growth in continental ice volume. The extreme warmth and subsequent cooling of the Mediterranean Sea are not well-represented in current Late Miocene climate models, which our results suggest underestimate regional warmth prior to the Late Miocene cooling. Evidence of secular cooling during the Late Miocene gives new support to the much-debated link between a possible decline in

  19. A life-cycle approach to technology, infrastructure, and climate policy decision making: Transitioning to plug-in hybrid electric vehicles and low-carbon electricity

    NASA Astrophysics Data System (ADS)

    Samaras, Constantine

    In order to mitigate the most severe effects of climate change, large global reductions in the current levels of anthropogenic greenhouse gas (GHG) emissions are required in this century to stabilize atmospheric carbon dioxide (CO2) concentrations at less than double pre-industrial levels. The Intergovernmental Panel on Climate Change (IPCC) fourth assessment report states that GHG emissions should be reduced to 50-80% of 2000 levels by 2050 to increase the likelihood of stabilizing atmospheric CO2 concentrations. In order to achieve the large GHG reductions by 2050 recommended by the IPCC, a fundamental shift and evolution will be required in the energy system. Because the electric power and transportation sectors represent the largest GHG emissions sources in the United States, a unique opportunity for coupling these systems via electrified transportation could achieve synergistic environmental (GHG emissions reductions) and energy security (petroleum displacement) benefits. Plug-in hybrid electric vehicles (PHEVs), which use electricity from the grid to power a portion of travel, could play a major role in reducing greenhouse gas emissions from the transport sector. However, this thesis finds that life cycle GHG emissions from PHEVs depend on the electricity source that is used to charge the battery, so meaningful GHG emissions reductions with PHEVs are conditional on low-carbon electricity sources. Power plants and their associated GHGs are long-lived, and this work argues that decisions made regarding new electricity supplies within the next ten years will affect the potential of PHEVs to play a role in a low-carbon future in the coming decades. This thesis investigates the life cycle engineering, economic, and policy decisions involved in transitioning to PHEVs and low-carbon electricity. The government has a vast array of policy options to promote low-carbon technologies, some of which have proven to be more successful than others. This thesis uses life

  20. Diverse types of percolation transitions

    NASA Astrophysics Data System (ADS)

    Lee, Deokjae; Cho, Y. S.; Kahng, B.

    2016-12-01

    Percolation has long served as a model for diverse phenomena and systems. The percolation transition, that is, the formation of a giant cluster on a macroscopic scale, is known as one of the most robust continuous transitions. Recently, however, many abrupt percolation transitions have been observed in complex systems. To illustrate such phenomena, considerable effort has been made to introduce models and construct theoretical frameworks for explosive, discontinuous, and hybrid percolation transitions. Experimental results have also been reported. In this review article, we describe such percolation models, their critical behaviors and universal features, and real-world phenomena.

  1. Climate Variability Drives Plankton Community Composition Changes: the 2010-2011 El Nino to La Nina Transition Around Australia

    NASA Technical Reports Server (NTRS)

    Thompson, Peter A.; Bonham, Pru; Thomson, Paul; Rochester, Wayne; Doblin, Martina A.; Waite, Anya M.; Richardson, Anthony; Rousseaux, Cecile S.

    2015-01-01

    The strong La Nina of 2010-2011 provided an opportunity to investigate the ecological impacts of El Nino-Southern Oscillation on coastal plankton communities using the nine national reference stations around Australia. Based on remote sensing and across the entire Australian region 2011 (La Nina) was only modestly different from 2010 (El Nino) with the average temperature declining 0.2 percent surface chlorophyll a up 3 percent and modelled primary production down 14 percent. Other changes included a poleward shift in Prochlorococcus and Synechococcus. Along the east coast, there was a reduction in salinity, increase in nutrients, Chlorophytes and Prasinophytes (taxa with chlorophyll b, neoxanthin and prasinoxanthin). The southwest region had a rise in the proportion of 19-hexoyloxyfucoxanthin; possibly coccolithophorids in eddies of the Leeuwin Current and along the sub-tropical front. Pennate diatoms increased, Ceratium spp. decreased and Scrippsiella spp. increased in 2011. Zooplankton biomass declined significantly in 2011. There was a reduction in the abundance of Calocalanus pavo and Temora turbinata and increases in Clausocalanus farrani, Oncaea scottodicarloi and Macrosetella gracilis in 2011. The changes in the plankton community during the strong La Nina of 2011 suggest that this climatic oscillation exacerbates the tropicalization of Australia.

  2. Impact of Climate Variability on Prevalence of Urinary Schistosomiasis over Sunyani in the Transition Belt of Ghana

    NASA Astrophysics Data System (ADS)

    Tay, S. K.; Amekudzi, L. K.; Tagoe, G.

    2012-04-01

    A study has been conducted to determine the impact of climate variability on Schistosoma haematobium infection among patients and school children in Sunyani between 2006 and 2009. Urine samples from the subjects were collected and examined in the laboratory using the filtration technique for the detection and quantification of Schistosomiasis haematobium eggs. The prevalence rate of urinary schistosomiasis at the Sunyani Regional Hospital for 2006, 2007, 2008 and 2009 were found to be 0.24%, 0.55%, 0.55% and 0.75% respectively while that for Methodist Junior High School in 2008 and 2009 were 60.1% and 60.3% respectively. A decrease in the relative humidity and average annual rainfall were identified as factors contributory to the increase in urinary Schistosomiasis prevalence rate. The temperature values obtained throughout the study period did not have any significant effect on the prevalence rate. The temperature values, however, were those that enhanced cercarial incubation (15-35˚C) with a resultant increase in shedding of cercariae leading to more infections among water contacts. The infection rate due to stream Amama was 20.1%, while that due to river Tano was 36.6%. The highest risk group was children aged 15-19 years. Praziquantel was administered to treat the infection, producing a cure rate of 93%. Recognition of urinary Schistosomiasis as a public health problem in Ghana is the main challenge to prevention and control of the disease.

  3. Distinguishing sources of variability in catchment transit time distributions: climate, water balance partitioning, and flow-path dynamics