Science.gov

Sample records for abrupt millennial-scale climate

  1. Abrupt climate change: chaos and order at orbital and millennial scales

    NASA Astrophysics Data System (ADS)

    Rial, J. A.

    2004-04-01

    Successful prediction of future global climate is critically dependent on understanding its complex history, some of which is displayed in paleoclimate time series extracted from deep-sea sediment and ice cores. These recordings exhibit frequent episodes of abrupt climate change believed to be the result of nonlinear response of the climate system to internal or external forcing, yet, neither the physical mechanisms nor the nature of the nonlinearities involved are well understood. At the orbital (10 4-10 5 years) and millennial scales, abrupt climate change appears as sudden, rapid warming events, each followed by periods of slow cooling. The sequence often forms a distinctive saw-tooth shaped time series, epitomized by the deep-sea records of the last million years and the Dansgaard-Oeschger (D/O) oscillations of the last glacial. Here I introduce a simplified mathematical model consisting of a novel arrangement of coupled nonlinear differential equations that appears to capture some important physics of climate change at Milankovitch and millennial scales, closely reproducing the saw-tooth shape of the deep-sea sediment and ice core time series, the relatively abrupt mid-Pleistocene climate switch, and the intriguing D/O oscillations. Named LODE for its use of the logistic-delayed differential equation, the model combines simplicity in the formulation (two equations, small number of adjustable parameters) and sufficient complexity in the dynamics (infinite-dimensional nonlinear delay differential equation) to accurately simulate details of climate change other simplified models cannot. Close agreement with available data suggests that the D/O oscillations are frequency modulated by the third harmonic of the precession forcing, and by the precession itself, but the entrained response is intermittent, mixed with intervals of noise, which corresponds well with the idea that the climate operates at the edge between chaos and order. LODE also predicts a persistent

  2. 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.

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

    NASA Astrophysics Data System (ADS)

    Mitsui, Takahito; Crucifix, Michel

    2017-04-01

    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.

  4. 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

  5. Characterization of Millennial-Scale Climate Variability.

    NASA Astrophysics Data System (ADS)

    Roe, Gerard H.; Steig, Eric J.

    2004-05-01

    The oxygen isotope time series from ice cores in central Greenland [the Greenland Ice Sheet Project 2 (GISP2) and the Greenland Ice Core Project (GRIP)] and West Antarctica (Byrd) provide a basis for evaluating the behavior of the climate system on millennial time scales. These time series have been invoked as evidence for mechanisms such as an interhemispheric climate seesaw or a stochastic resonance process. Statistical analyses are used to evaluate the extent to which these mechanisms characterize the observed time series. Simple models in which the Antarctic record reflects the Greenland record or its integral are statistically superior to a model in which the two time series are unrelated. However, these statistics depend primarily on the large events in the earlier parts of the record (between 80 and 50 kyr BP). For the shorter, millennial-scale (Dansgaard Oeschger) events between 50 and 20 kyr BP, a first-order autoregressive [AR(1)] stochastic climate model with a physical time scale of τ = 600 ± 300 yr is a self-consistent explanation for the Antarctic record. For Greenland, AR(1) with τ = 400 ± 200 yr, plus a simple threshold rule, provides a statistically comparable characterization to stochastic resonance (though it cannot account for the strong 1500-yr spectral peak). The similarity of the physical time scales underlying the millennial-scale variability provides sufficient explanation for the similar appearance of the Greenland and Antarctic records during the 50 20-kyr BP interval. However, it cannot be ruled out that improved cross dating for these records may strengthen the case for an interhemispheric linkage on these shorter time scales. Additionally, the characteristic time scales for the records are significantly shorter during the most recent 10 kyr. Overall, these results suggest that millennial-scale variability is determined largely by regional processes that change significantly between glacial and interglacial climate regimes, with

  6. Holocene climate variability: interactions between orbital and century to millennial-scale climate forcing

    NASA Astrophysics Data System (ADS)

    Viau, A. E.; Gajewski, K.

    2006-12-01

    During the past 8,000 years, ice sheets had a lesser influence on the global climate system, and factors such as orbital-scale Milankovitch variations have apparently been the primary factors influencing the climate. A mean continental July temperature reconstruction based on pollen records from across North America quantifies temperature variations of several time scales. This temperature reconstruction shows similar features with several other Holocene climate records from around the world. Both orbital and millennial-scale variations in our temperature reconstruction appear coherent in structure and frequency with high-resolution ice, marine and other terrestrial paleoclimate records. Climate transitions in North America occurred at the same time as those identified in pollen diagrams from Europe. During the Holocene, climate in North America appears to have varied periodically every ~1100 years rather than the ~1500 year cycle found during the last glacial period. Coherence at frequencies between 900-1100 years between land, ice, and ocean records suggests a common forcing associated with widespread surface impacts during the Holocene. Several potential forcing mechanisms for century to millennial-scale climate variability during glacial and interglacial periods have been proposed. Which forcing or combination of them could cause this high-frequency climate variability during the Holocene? Part of the answer must reside in the varying amplitudes of millennial- scale climate changes during glacial, deglaciation and interglacials. Changes in ocean circulation (THC) and ice sheet dynamics are likely amplifiers of abrupt climate change during glacial and deglaciation regimes. However, during interglacials ice sheets are limited in extent and insolation variations dominate. In the absence of significant high-latitude ice-sheet forcing, one potential mechanism that could act as a "modulator" for Holocene climate variability is interactions between long-term changes

  7. Holocene Millennial-Scale Climate Variability in Western North America

    NASA Astrophysics Data System (ADS)

    Fawcett, P. J.; Castiglia, P. J.; Meyer, G. A.; Armour, J.

    2002-12-01

    We compare several high-resolution paleoclimatic records from western North America that indicate near-synchronous millennial-scale climate variability through much of the Holocene. A Holocene pluvial lake system in northern Chihuahua, Mexico alternates between lake highstands representing cooler and wetter conditions and dry playa conditions representing warmer, drier climates. Alpine lakes and bogs from the Sangre de Cristo Mountains of northern New Mexico record a series of glacial and periglacial events (colder, effectively wetter climates) that alternate with warmer, drier climates over the late Pleistocene and the Holocene. Forest fire-related sedimentation and alluvial activity from northeast Yellowstone National Park also shows a clear response to millennial-scale climate change during the Holocene. Pulses of fire-related debris flow activity occur during warmer, drier periods that are more prone to droughts. These alternate with cooler, effectively wetter conditions that produce more river discharge and form broad flood plains later preserved as terraces. Pluvial lake highstands in northern Mexico are centered at the following calendar ages: 230 yr B.P., 4.2 ka, 7.4 ka, and 9.3 ka. The northern New Mexico chronology shows cold, effectively wetter climates at the following calendar age midpoints: 200 yr B.P., 3.0 ka, 3.9 ka and 5.7 ka. The Yellowstone chronology shows cold, effectively wetter climates during the following age ranges: 300 to 600 yr B.P., 1.4 to 1.6 ka, 2.8 to 3.1 ka, 3.9 to 4.3 ka, and 5.5 to 6.0 ka. In the Rocky Mountain records, the millennial-scale events are more prominent during the late Holocene Neoglacial interval than during the early to middle Holocene. These climate events in western North America reflect widespread temperature anomalies and to a lesser extent, precipitation anomalies. The cold phases of these events correlate with a North Atlantic record of ice-rafting and cool events (Bond et al., 2001) and suggest that

  8. Millennial-scale climate variability through the Mid to Late Pleistocene

    NASA Astrophysics Data System (ADS)

    Barker, S.; Chen, J.; McManus, J. F.; Mokeddem, Z.; Theobald, M.; Thornalley, D. J.

    2013-12-01

    Millennial-scale climate variability has been pervasive throughout the last 800kyr at least. The global expression of such variability is epitomised by ice core temperature records from Greenland and Antarctica, with northern records revealing abrupt changes while southern records generally display more gradual changes that are approximately out of phase with their northern counterparts. One of the most intuitive mechanisms invoked to explain these opposing signals involves varying the northward heat transport associated with the Atlantic Meridional Overturning Circulation (AMOC). Additional evidence from a range of locations also highlights the importance of atmospheric shifts (e.g. rainfall and winds) in the global transmission of abrupt climate change. The (thermal) bipolar seesaw provides a simple means for transposing between the Antarctic and Greenland temperature records and has recently been exploited to produce a prediction of what Greenland records might look like if they extended back to 800ka. This exercise allowed an initial assessment of the potential interplay between millennial-scale variability and glacial-interglacial climate change (for example by confirming a link between seesaw oscillations and glacial terminations). However, the synthetic record is only a prediction and it is only 800kyr long. In order to place tighter constraints on the nature of millennial-scale variability through time and its relationship with the glacial cycles, we need to test and extend the prediction. Here we present the results from the first phase of a major effort to provide such a test. We present continuous high resolution (mean <200year) proxy SST records from ODP site 983 in the NE Atlantic spanning the last 400kyr (>2,200 samples - the final records will reach back to 1.7Ma and involve approximately 10,000 samples). Our results provide a vivid and revealing account of high latitude climate variability that can be compared directly with records from other sites

  9. Was millennial scale climate change during the Last Glacial triggered by explosive volcanism?

    PubMed Central

    Baldini, James U.L.; Brown, Richard J.; McElwaine, Jim N.

    2015-01-01

    The mechanisms responsible for millennial scale climate change within glacial time intervals are equivocal. Here we show that all eight known radiometrically-dated Tambora-sized or larger NH eruptions over the interval 30 to 80 ka BP are associated with abrupt Greenland cooling (>95% confidence). Additionally, previous research reported a strong statistical correlation between the timing of Southern Hemisphere volcanism and Dansgaard-Oeschger (DO) events (>99% confidence), but did not identify a causative mechanism. Volcanic aerosol-induced asymmetrical hemispheric cooling over the last few hundred years restructured atmospheric circulation in a similar fashion as that associated with Last Glacial millennial-scale shifts (albeit on a smaller scale). We hypothesise that following both recent and Last Glacial NH eruptions, volcanogenic sulphate injections into the stratosphere cooled the NH preferentially, inducing a hemispheric temperature asymmetry that shifted atmospheric circulation cells southward. This resulted in Greenland cooling, Antarctic warming, and a southward shifted ITCZ. However, during the Last Glacial, the initial eruption-induced climate response was prolonged by NH glacier and sea ice expansion, increased NH albedo, AMOC weakening, more NH cooling, and a consequent positive feedback. Conversely, preferential SH cooling following large SH eruptions shifted atmospheric circulation to the north, resulting in the characteristic features of DO events. PMID:26616338

  10. Was millennial scale climate change during the Last Glacial triggered by explosive volcanism?

    PubMed

    Baldini, James U L; Brown, Richard J; McElwaine, Jim N

    2015-11-30

    The mechanisms responsible for millennial scale climate change within glacial time intervals are equivocal. Here we show that all eight known radiometrically-dated Tambora-sized or larger NH eruptions over the interval 30 to 80 ka BP are associated with abrupt Greenland cooling (>95% confidence). Additionally, previous research reported a strong statistical correlation between the timing of Southern Hemisphere volcanism and Dansgaard-Oeschger (DO) events (>99% confidence), but did not identify a causative mechanism. Volcanic aerosol-induced asymmetrical hemispheric cooling over the last few hundred years restructured atmospheric circulation in a similar fashion as that associated with Last Glacial millennial-scale shifts (albeit on a smaller scale). We hypothesise that following both recent and Last Glacial NH eruptions, volcanogenic sulphate injections into the stratosphere cooled the NH preferentially, inducing a hemispheric temperature asymmetry that shifted atmospheric circulation cells southward. This resulted in Greenland cooling, Antarctic warming, and a southward shifted ITCZ. However, during the Last Glacial, the initial eruption-induced climate response was prolonged by NH glacier and sea ice expansion, increased NH albedo, AMOC weakening, more NH cooling, and a consequent positive feedback. Conversely, preferential SH cooling following large SH eruptions shifted atmospheric circulation to the north, resulting in the characteristic features of DO events.

  11. Was millennial scale climate change during the Last Glacial triggered by explosive volcanism?

    NASA Astrophysics Data System (ADS)

    Baldini, James U. L.; Brown, Richard J.; McElwaine, Jim N.

    2015-11-01

    The mechanisms responsible for millennial scale climate change within glacial time intervals are equivocal. Here we show that all eight known radiometrically-dated Tambora-sized or larger NH eruptions over the interval 30 to 80 ka BP are associated with abrupt Greenland cooling (>95% confidence). Additionally, previous research reported a strong statistical correlation between the timing of Southern Hemisphere volcanism and Dansgaard-Oeschger (DO) events (>99% confidence), but did not identify a causative mechanism. Volcanic aerosol-induced asymmetrical hemispheric cooling over the last few hundred years restructured atmospheric circulation in a similar fashion as that associated with Last Glacial millennial-scale shifts (albeit on a smaller scale). We hypothesise that following both recent and Last Glacial NH eruptions, volcanogenic sulphate injections into the stratosphere cooled the NH preferentially, inducing a hemispheric temperature asymmetry that shifted atmospheric circulation cells southward. This resulted in Greenland cooling, Antarctic warming, and a southward shifted ITCZ. However, during the Last Glacial, the initial eruption-induced climate response was prolonged by NH glacier and sea ice expansion, increased NH albedo, AMOC weakening, more NH cooling, and a consequent positive feedback. Conversely, preferential SH cooling following large SH eruptions shifted atmospheric circulation to the north, resulting in the characteristic features of DO events.

  12. Masked millennial-scale climate variations in South West Africa during the last glaciation

    NASA Astrophysics Data System (ADS)

    Hessler, I.; Dupont, L.; Handiani, D.; Paul, A.; Merkel, U.; Wefer, G.

    2011-10-01

    Large and abrupt shifts between extreme climatic conditions characterise the last glacial and deglacial period and are thought to be transmitted by the atmospheric and oceanic circulation. Millennial-scale climatic shifts associated with North Atlantic Heinrich Stadials (HSs) are thought to be closely related to a reduction of the Atlantic Meridional Overturning Circulation (AMOC), which lead to the accumulation of heat in the South Atlantic and a southward shift of the Intertropical Convergence Zone (ITCZ). Due to the linkage between the oceans and the atmosphere it is assumed that HSs also influence the vegetation composition in the African tropics. To address the connection between tropical African vegetation development and high-latitude climate change we present a high-resolution marine pollen record from ODP Site 1078 (off Angola) covering the period 50-10 ka BP. Although several tropical African vegetation and climate reconstructions indicate an impact of HSs on the African subcontinent, our vegetation record shows no response. Model simulations conducted with an Earth System Model of Intermediate Complexity (EMIC) including a dynamical vegetation component lead to the hypothesis that the vegetation response during HSs might have been muted by mechanisms that partly cancel each other.

  13. Smoothing of millennial scale climate variability in European Loess (and other records)

    NASA Astrophysics Data System (ADS)

    Zeeden, Christian; Obreht, Igor; Hambach, Ulrich; Veres, Daniel; Marković, Slobodan B.; Lehmkuhl, Frank

    2017-04-01

    Millennial scale climate variability is seen in various records of the northern hemisphere in the last glacial cycle, and their expression represents a correlation tool beyond the resolution of e.g. luminescence dating. Highest (correlative) dating accuracy is a prerequisite of comparing different geoarchives, especially when related to archaeological findings. Here we attempt to constrain the timing of loess geoarchives representing the environmental context of early humans in south-eastern Europe, and discuss the challenge of dealing with smoothed records. In this contribution, we present rock magnetic and grain size data from the Rasova loess record in the Lower Danube basin (Romania), showing millennial scale climate variability. Additionally, we summarize similar data from the Lower and Middle Danube Basins. A comparison of these loess data and reference records from Greenland ice cores and the Mediterranean-Black Sea region indicates a rather unusual expression of millennial scale climate variability recorded in loess. To explain the observed patterns, we experiment with low-pass filters of reference records to simulate a signal smoothing by natural processes such as e.g. bioturbation and pervasive diagenesis. Low-pass filters avoid high frequency oscillations and focus on the longer period (lower frequency) variability, here using cut-off periods from 1-15 kyr. In our opinion low-pass filters represent simple models for the expression of millennial scale climate variability in low sedimentation environments, and in sediments where signals are smoothed by e.g. bioturbation and/or diagenesis. Using different low-pass filter thresholds allows us to (a) explain observed patterns and their relation to millennial scale climate variability, (b) propose these filtered/smoothed signals as correlation targets for records lacking millennial scale recording, but showing smoothed climate variability on supra-millennial scales, and (c) determine which time resolution

  14. Evaluating the link between explosive volcanism and millennial scale climate change during the Last Glacial

    NASA Astrophysics Data System (ADS)

    Baldini, James U. L.; Brown, Richard; McElwaine, Jim

    2016-04-01

    Abrupt millennial scale climate change is one of the most characteristic features of the Last Glaciation. Despite its clear expression in a number of climate records worldwide, the mechanisms responsible for triggering these shifts remains elusive. Here we show that a strong statistically significant link exists between very large Northern Hemisphere (NH) eruptions and Greenland cooling over the interval 30 to 80 ka BP (>95% confidence). We hypothesise that following Last Glacial NH eruptions, the resulting aerosol veil cooled the NH preferentially, inducing an interhemispheric temperature imbalance, and forcing atmospheric circulation to the south. The initial aerosol-induced climate response may have been prolonged by a strong positive feedback involving NH glacier and sea ice expansion, increased NH albedo, and AMOC weakening. Regional effects of this reorganisation of atmospheric circulation included Greenland cooling, Antarctic warming, and a southward shifted ITCZ, all consistent with existing proxy evidence. Interestingly, previous research has suggested that a strong statistically significant link between evidence of Southern Hemisphere (SH) volcanism and Dansgaard-Oeschger (DO) events exists (>99% confidence), but did not propose a forcing mechanism (Bay et al., 2004). We suggest that SH eruptions occurring during the Last Glacial cooled the SH preferentially and forced atmospheric circulation to the north. A regional consequence of this was high latitude NH warming, followed by NH glacier and sea ice retreat, and AMOC strengthening. This initiated a positive feedback of NH warming, effectively amplifying the initial effects of the SH volcanic eruption, and resulting in the characteristic features of DO events.

  15. Millennial-scale climate instabilities in the subtropical Atlantic during MIS 6 and 7

    NASA Astrophysics Data System (ADS)

    Scheinwald, A.; Billups, K.

    2012-12-01

    We have constructed a high resolution (~200 year) planktonic foraminiferal stable isotope record spanning Marine Isotope Stages (MIS) 6 and 7 in the subtropical Atlantic (ODP Site 1059). The record fills a gap in a ~1 million year long time series of millennial-scale surface ocean hydrography in this region. Our ultimate goal is to test the hypothesis that millennial-scale climate signals in the northwestern subtropical Atlantic are linked to external driving factors such as the harmonics of precession. Results show that longer-term trends in the oxygen isotope data spanning MIS 6-7 closely follow precessional forcing allowing us to refine the original age model of Grützner et al. (2002). High frequency variations are superimposed on the long-term trend during both the glacial MIS 6 and the interglacial MIS 7. Spectral analyses indicate high concentration of power at millennial-scale periodicities of 10.9 kyr, 5.2 kyr, and 2.8 kyr. These periodicities are close to those expected from harmonics of precessional forcing during this interval of time (11.5 kyr, 5.8 kyr, 2.8 kyr). We will show the evolution of the millennial-scale periodicities in this region over the past 1 million years by splicing the record into published ones and unifying the age model.

  16. Sea ice and millennial-scale climate variability in the Nordic seas 90 kyr ago to present

    NASA Astrophysics Data System (ADS)

    Hoff, Ulrike; Rasmussen, Tine L.; Stein, Ruediger; Ezat, Mohamed M.; Fahl, Kirsten

    2016-07-01

    In the light of rapidly diminishing sea ice cover in the Arctic during the present atmospheric warming, it is imperative to study the distribution of sea ice in the past in relation to rapid climate change. Here we focus on glacial millennial-scale climatic events (Dansgaard/Oeschger events) using the sea ice proxy IP25 in combination with phytoplankton proxy data and quantification of diatom species in a record from the southeast Norwegian Sea. We demonstrate that expansion and retreat of sea ice varies consistently in pace with the rapid climate changes 90 kyr ago to present. Sea ice retreats abruptly at the start of warm interstadials, but spreads rapidly during cooling phases of the interstadials and becomes near perennial and perennial during cold stadials and Heinrich events, respectively. Low-salinity surface water and the sea ice edge spreads to the Greenland-Scotland Ridge, and during the largest Heinrich events, probably far into the Atlantic Ocean.

  17. Sea ice and millennial-scale climate variability in the Nordic seas 90 kyr ago to present.

    PubMed

    Hoff, Ulrike; Rasmussen, Tine L; Stein, Ruediger; Ezat, Mohamed M; Fahl, Kirsten

    2016-07-26

    In the light of rapidly diminishing sea ice cover in the Arctic during the present atmospheric warming, it is imperative to study the distribution of sea ice in the past in relation to rapid climate change. Here we focus on glacial millennial-scale climatic events (Dansgaard/Oeschger events) using the sea ice proxy IP25 in combination with phytoplankton proxy data and quantification of diatom species in a record from the southeast Norwegian Sea. We demonstrate that expansion and retreat of sea ice varies consistently in pace with the rapid climate changes 90 kyr ago to present. Sea ice retreats abruptly at the start of warm interstadials, but spreads rapidly during cooling phases of the interstadials and becomes near perennial and perennial during cold stadials and Heinrich events, respectively. Low-salinity surface water and the sea ice edge spreads to the Greenland-Scotland Ridge, and during the largest Heinrich events, probably far into the Atlantic Ocean.

  18. Mid-Pleistocene Orbital and Millennial Scale Climate Change in a 200 ky lacustrine sediment core from SW North America

    NASA Astrophysics Data System (ADS)

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

    2009-12-01

    progressive declines in cold boreal taxa pollen percentages (Picea, Abies), while others are characterized by abrupt warmings and decreases in boreal taxa pollen. Maximum interstadial temperatures are followed by abrupt coolings of as much as 6 to 7°C, and rapid increases in Picea and Abies pollen. These results show that the continental climate of SW North America had a strong response to millennial-scale climate change as well as to orbital forcing, even during a time of muted precessional cycles (MIS 11).

  19. Early Pleistocene sea level and millennial-scale climate fluctuations: a view from the tropical Pacific

    NASA Astrophysics Data System (ADS)

    Alix Jakob, Kim; Friedrich, Oliver; Pross, Jörg

    2015-04-01

    This project aims at deciphering the rate of sea level variability and its effect on millennial-scale climate fluctuations during the final phase of the intensification of northern hemisphere glaciation (NHG). Millennial-scale climate fluctuations appear to have changed significantly at glacial-interglacial time scales during the late Pliocene and Pleistocene. Thereby, millennial-scale climate fluctuations under a warmer climate during late Pliocene and early Pleistocene show markedly lower ampitudes compared to the fluctuations of the late Pleistocene. Numerous Pleistocene proxy records (e.g. McManus et al., 1999) suggest that this difference can be explained by an ice-volume/sea-level threshold that amplifies millennial-scale climate fluctuations and was not reached prior to the Mid-Pleistocene Transition (MPT). However, new records question the existence of this threshold (Bolton et al., 2010) and indicate that either the amplification of millennial-scale climate fluctuations before the MPT required a higher ice-volume threshold than in the late Pleistocene, that ice-volume had no significant effect on the amplitude of climate fluctuations, and/or the available sea level estimates for the early Pleistocene are inaccurate. For identifying the mechanisms underlying the dynamics of early Pleistocene ice sheets, material from the tropical Pacific Ocean (ODP Site 849) is studied over a time interval from 2.6 to 2.4 Ma (marine isotope stages 104 to 96). In summary, the main deliverables are (1) the establishment of a precise δ18O chemostratigraphy using the benthic foraminifera Cibicidoides wuellerstorfi by tuning the δ18O dataset to the LR04 benthic isotope stack (Lisiecki & Raymo, 2005), and (2) providing high-resolution (˜700 years) Mg/Ca and δ18O datasets using the benthic foraminifera Oridorsalis umbonatus and the planktonic foraminifera Globigerinoides ruber. This combined geochemical approach will be used to address the following research questions: (1

  20. Antarctic black carbon parallels insolation and millennial scale climate variation

    NASA Astrophysics Data System (ADS)

    Arienzo, M. M.; McConnell, J.; Goes, L. M.; Criscitiello, A. S.; Das, S. B.; Kipfstuhl, S.

    2016-12-01

    Biomass-burning and fossil-fuel combustion emit black carbon (BC) aerosols which impact climate directly by changing Earth's radiation budget and indirectly by reducing albedo when deposited on bright surfaces such as snow and ice. However quantification and predictive climate modeling have been hampered by limited understanding of the drivers of regional-scale biomass burning and few long-term burning records. In this work, we compare the Antarctic BC concentration and BC mass mean records to BC and biomass burning model simulation results and to low-latitude paleoclimate proxies to investigate a potential link between low latitude climate, biomass burning and BC emissions. We present the high-resolution record of BC concentration and BC particle mass (a proxy for size) from the West Antarctic Ice Sheet Divide (WAIS) ice core. This is the first long term record of BC aerosol deposition in Antarctica and it extends from 65,000 years before 1950 (yr BP) to 6,000 yr BP. To assess the spatial variability in BC deposition, we also compare previously published WAIS BC concentration measurements for the last 150 years to an array of new Antarctic ice core BC records as well as to published BC modeling results. BC and a wide range of trace elements were analyzed via a continuous melter system allowing for sub-annual resolution. For BC concentration determinations, we used the DRI continuous method for ice core analyses based on the Single Particle Soot Photometer (SP2; Droplet Measurement Technologies). Similarities in BC concentration and deposition in the ice core array for the last 150 years indicates that, as with industrial lead which must be transported long distances over the Southern Ocean from source areas, BC generally is well mixed in the Antarctic atmosphere, suggesting that the long term WAIS record is representative of much of Antarctica. The longer BC concentration and BC mass mean records from WD show variability with insolation changes and additional

  1. Millennial-Scale Climate Variability for the Last Glacial Cycle along the Iberian Margin based on Dinoflagellate Cysts

    NASA Astrophysics Data System (ADS)

    Datema, M.; Sangiorgi, F.; Reichart, G. J.; Lourens, L. J.; Sluijs, A.

    2014-12-01

    The Shackleton Site (IODP Expedition 339 Site U1385), located off the West-Portuguese Margin, preserves a continuous high-fidelity record of millennial-scale climate variability for the last several glacial cycles (~1.4 Myr) that can be correlated precisely to patterns observed in polar ice cores. In addition, rapid delivery of terrestrial material to the deep-sea environment allows the correlation of these marine records to European terrestrial climate records. This unique marine-ice-terrestrial linkage makes the Shackleton Site the ideal reference section for studying Quaternary abrupt climate change. The main objective of studying site U1385 is to establish a marine reference section of Pleistocene climate change. We generated millennial-scale dinoflagellate cyst (dinocyst) assemblage records from the Shackleton Site (IODP Expedition 339) to reconstruct upwelling, sea surface temperature (SST) and productivity across the last two glacial-interglacial cycles. We quantify the validity of dinocyst-based paleoenvironmental reconstructions based on multivariate statistics on dinocyst assemblages and multi-proxy data from regional core-tops and the last glacial cycle. This allows us to conclude that the strength of the West Iberian Margin upwelling system changed from relatively intense upwelling during the last glacial to upwelling relaxation during the Holocene as a result of reduced (strength of the) Portuguese trade winds. Secondly, SST, productivity/upwelling, strength of Portuguese trade winds and climate on the Iberian Peninsula co-vary on stadial-interstadial timescales and correspond to Greenland stadial-interstadial variability (δ18O). Finally, we will present a long-term paleoceanographic perspective down to ~120 ka.

  2. Glacial-Interglacial, Orbital and Millennial-Scale Climate Variability for the Last Glacial Cycle at Shackleton Site U1385 based on Dinoflagellate Cysts

    NASA Astrophysics Data System (ADS)

    Datema, M.

    2015-12-01

    The Shackleton Site (IODP Expedition 339 Site U1385), located off the West-Portuguese Margin, preserves a continuous high-fidelity record of millennial-scale climate variability for the last several glacial cycles (~1.4 Myr) that can be correlated precisely to patterns observed in polar ice cores. In addition, rapid delivery of terrestrial material to the deep-sea environment allows the correlation of these marine records to European terrestrial climate records. This unique marine-ice-terrestrial linkage makes the Shackleton Site the ideal reference section for studying Quaternary abrupt climate change. The main objective of studying Site U1385 is to establish a marine reference section of Pleistocene climate change. We generated (sub)millennial-scale (~600 year interval) dinoflagellate cyst (dinocyst) assemblage records from Shackleton Site U1385 (IODP Expedition 339) to reconstruct sea surface temperature (SST) and productivity/upwelling over the last 152 kyrs. In addition, our approach allows for detailed land-sea correlations, because we also counted assemblages of pollen and spores from higher plants. Dinocyst SST and upwelling proxies, as well as warm/cold pollen proxies from Site U1385 show glacial-interglacial, orbital and stadial-interstadial climate variability and correlate very well to Uk'37, planktic foraminifer δ18O and Ca/Ti proxies of previously drilled Shackleton Sites and Greenland Ice Core δ18O. The palynological proxies capture (almost) all Dansgaard-Oeschger events of the last glacial cycle, also before ~70 ka, where millennial-scale variability is overprinted by precession. We compare the performance and results of the palynology of Site U1385 to proxies of previously drilled Shackleton Sites and conclude that palynology strengthens the potential of this site to form a multi-proxy reference section for millennial scale climate variability across the Pleistocene-Holocene. Finally, we will present a long-term paleoceanographic perspective down

  3. Millennial-scale northern Hemisphere Atlantic-Pacific climate teleconnections in the earliest Middle Pleistocene.

    PubMed

    Hyodo, Masayuki; Bradák, Balázs; Okada, Makoto; Katoh, Shigehiro; Kitaba, Ikuko; Dettman, David L; Hayashi, Hiroki; Kumazawa, Koyo; Hirose, Kotaro; Kazaoka, Osamu; Shikoku, Kizuku; Kitamura, Akihisa

    2017-08-30

    Suborbital-scale climate variations, possibly caused by solar activity, are observed in the Holocene and last-glacial climates. Recently published bicentennial-resolution paleoceanic environmental records reveal millennial-scale high-amplitude oscillations postdating the last geomagnetic reversal in the Marine Isotope Stage (MIS) 19 interglacial. These oscillations, together with decoupling of post-reversal warming from maximum sea-level highstand in mid-latitudes, are key features for understanding the climate system of MIS 19 and the following Middle Pleistocene. It is unclear whether the oscillations are synchronous, or have the same driver as Holocene cycles. Here we present a high resolution record of western North Pacific submarine anoxia and sea surface bioproductivity from the Chiba Section, central Japan. The record reveals many oxic events in MIS 19, coincident with cold intervals, or with combined cold and sea-level fall events. This allows detailed correlations with paleoceanic records from the mid-latitude North Atlantic and Osaka Bay, southwest Japan. We find that the millennial-scale oscillations are synchronous between East and West hemispheres. In addition, during the two warmest intervals, bioproductivity follows the same pattern of change modulated by bicentennial cycles that are possibly related to solar activity.

  4. Millennial-scale climate variability in northwest Patagonia over the last 15 000 yr

    NASA Astrophysics Data System (ADS)

    Moreno, Patricio I.

    2004-01-01

    A pollen record from Lago Condorito (41°45'S, 73°07'W) shows prominent vegetation and climate changes at millennial time-scales, superimposed on multimillennial trends in temperature and westerly activity in northwest Patagonia during the past 15 000 yr. The record shows that evergreen temperate rainforests have dominated the landscape over this interval, with floristic changes ranging from cold-resistant North Patagonian forests with podocarp conifers to Valdivian forests with thermophilous, summer-drought resistant species. The long-term trend shows that cool-temperate and humid conditions prevailed between 15 000 and 11 000 cal. yr BP, followed by an extreme warm and dry phase between 11 000 and 7600 cal. yr BP, and subsequent cooling events and increase in precipitation that peaked at ca. 5000 cal. yr BP, when Southern Hemisphere alpine glaciers achieved their first Neoglacial maximum. Modern conditions were established at ca. 1800 cal. yr BP, following a warm and dry phase between ca. 2900 and 1800 cal.yrBP. These results suggest that millennial-scale climate variability during deglacial and post-glacial times also affected the mid-latitude region of the South Pacific, supporting the idea that changes in the tropical Pacific might be a key factor in the initiation and/or propagation of millennial-scale climate variability at regional, hemispheric and global scales. Copyright

  5. Coherent Resonant Millennial-Scale Climate Oscillations Triggered by Massive Meltwater Pulses.

    NASA Astrophysics Data System (ADS)

    Timmermann, Axel; Gildor, Hezi; Schulz, Michael; Tziperman, Eli

    2003-08-01

    The role of mean and stochastic freshwater forcing on the generation of millennial-scale climate variability in the North Atlantic is studied using a low-order coupled atmosphere-ocean-sea ice model. It is shown that millennial-scale oscillations can be excited stochastically, when the North Atlantic Ocean is fresh enough. This finding is used in order to interpret the aftermath of massive iceberg surges (Heinrich events) in the glacial North Atlantic, which are characterized by an excitation of Dansgaard-Oeschger events. Based on model results, it is hypothesized that Heinrich events trigger Dansgaard-Oeschger cycles and that furthermore the occurrence of Heinrich events is dependent on the accumulated climatic effect of a series of Dansgaard-Oeschger events. This scenario leads to a coupled ocean-ice sheet oscillation that shares many similarities with the Bond cycle. Further sensitivity experiments reveal that the timescale of the oscillations can be decomposed into stochastic, linear, and nonlinear deterministic components. A schematic bifurcation diagram is used to compare theoretical results with paleoclimatic data.

  6. A 0.6 million year record of millennial-scale climate variability in the tropics

    NASA Astrophysics Data System (ADS)

    Gibson, Kelly Ann; Peterson, Larry C.

    2014-02-01

    A ~600 kyr long scanning X-ray fluorescence record of redox variability from the Cariaco Basin, Venezuela, provides insight into rapid climate change in the tropics over the past five glacial-interglacial cycles. Variations in the sediment accumulation of the redox-sensitive element molybdenum (Mo) can be linked to changes in Intertropical Convergence Zone migration and reveal that millennial-scale variability is a persistent feature of tropical climate over the past 600 kyr, including during periods of interglacial warmth. This new record supports the idea that high-frequency tropical climate variability is not controlled solely by ice volume changes, with implications for the role of high-latitude forcing of Intertropical Convergence Zone position and tropical hydrology on millennial timescales.

  7. Centennial-to-millennial scale climate change during the last 100,000 years: a Southern Hemisphere perspective

    NASA Astrophysics Data System (ADS)

    van den Bos, Valerie; Rees, Andrew; Newnham, Rewi; Augustinus, Paul

    2017-04-01

    The response of past terrestrial ecosystems to abrupt climate change is central to the debate surrounding the consequences of future climate change. Many centennial-to-millennial scale episodes of rapid change over the past 117,000 years have been reported, notably the Dansgaard-Oeschger events of Greenland and the North Atlantic and Antarctic Isotope Maxima. Best expressed in past climate records from the polar and tropical regions, the timing, amplitude and duration of these changes are variable on a global scale, and it is unclear how the events are generated and transmitted to cause such asynchronous patterns. The southern mid-latitudes form a poorly understood piece of the puzzle. Our Marsden-funded project aims to increase understanding of the New Zealand climate system in relation to global patterns over the last 100 kyr by developing high-resolution climate records from the lake sediments contained within Auckland's maars. These crater lakes are unique, because their sediments are laminated throughout and the sedimentation rate is very high. Additionally, the numerous (>50) volcanic ash layers contained within the sediments act as anchor points in our chronologies. We have adopted a multiproxy approach that combines data from biotic, molecular biomarker isotope and geochemical analyses. The remit of my doctorate is to produce two independent, but complementary, temperature reconstructions from chironomid remains (mean summer temperatures) and pollen (mean annual temperatures) from Lake Pupuke sediments. This approach will eventually help us to address whether abrupt climate change events or changes in seasonality influenced climate and biota over the past 100,000 years in northern New Zealand, and whether these changes were driven by triggers from the North Atlantic, Antarctica or the tropics.

  8. Sea ice and millennial-scale climate variability in the Nordic seas 90 kyr ago to present

    PubMed Central

    Hoff, Ulrike; Rasmussen, Tine L.; Stein, Ruediger; Ezat, Mohamed M.; Fahl, Kirsten

    2016-01-01

    In the light of rapidly diminishing sea ice cover in the Arctic during the present atmospheric warming, it is imperative to study the distribution of sea ice in the past in relation to rapid climate change. Here we focus on glacial millennial-scale climatic events (Dansgaard/Oeschger events) using the sea ice proxy IP25 in combination with phytoplankton proxy data and quantification of diatom species in a record from the southeast Norwegian Sea. We demonstrate that expansion and retreat of sea ice varies consistently in pace with the rapid climate changes 90 kyr ago to present. Sea ice retreats abruptly at the start of warm interstadials, but spreads rapidly during cooling phases of the interstadials and becomes near perennial and perennial during cold stadials and Heinrich events, respectively. Low-salinity surface water and the sea ice edge spreads to the Greenland–Scotland Ridge, and during the largest Heinrich events, probably far into the Atlantic Ocean. PMID:27456826

  9. Origin of millennial-scale climate signals in the subtropical North Atlantic

    NASA Astrophysics Data System (ADS)

    Billups, K.

    2011-12-01

    In this study, I am testing the hypothesis that millennial-scale climate signals in the northwestern subtropical Atlantic are linked to external driving factors such as the harmonics of precession. The test is based on the observation that the precession period is not stationary through time. For example, between 900 and 340 Ka the time interval between successive precession minima (or maxima) ranges primarily from 17 kyr to 21 kyr with discrete intervals lasting up to ~30 kyr (spectral power centered on the 23 kyr and 19 kyr periodicities). After 340 Ka, however, precession minima (or maxima) consistently occur at longer intervals, between 21 kyr and 25 kyr (spectral power focused at the 23 kyr period). If in proxy records millennial-scale variations reflect the harmonics of precession, I expect that the millennial-scale periodicity associated with the 19 kyr precession period (e.g., the 4.8 kyr peak) loses power as the primary orbital peak loses power at 340 Ka. First order tests of this idea can be made using published planktic foraminiferal δ18O records from ODP Site 1059 (Hagen and Keigwin, 2002; Oppo et al., 2001) in the northwestern subtropical Atlantic spanning Marine Isotope Stages 2-6 (~20-150 Ka) and Site 1058 spanning MIS 12-22 (~450-900 Ka, Weirauch et al., 2008). After filtering the records to remove the 100 kyr cycle, the older time slice contains both precession peaks (23 and 19 kyr). Significant (95% confidence interval) suborbital peaks occur at 12 kyr, 5.7 kyr and 5.0 kyr, which are close to the periodicities of the expected harmonics. The younger time slice shows only one precession peak centered at ~23 kyr and significant (95% confidence interval) sub-orbital peaks at 11.2 kyr, and 5 kyr. Only the 11.2 kyr peak agrees with the expected period of the second harmonic of the 23 kyr precession peak. We are currently generating high resolution planktic foraminiferal stable isotope records in this region to span MIS 7, which, together with data from

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  11. Orbital- to millennial-scale abrupt hydrologic change in central Indonesia during the past 60,000 years

    NASA Astrophysics Data System (ADS)

    Russell, J. M.; Vogel, H.; Konecky, B.; Bijaksana, S.; King, J. W.; Cahyarini, S. Y.; Tamuntuan, G. H.; Noren, A. J.; Wattrus, N. J.

    2011-12-01

    convection over Indonesia. We observe substantial millennial-scale variability during MIS3 as well as the last glacial termination. For instance, Heinrich event 1 is a prominent arid event, as is the Younger Dryas. Aridity in central Indonesia during these North Atlantic stadials indicates that the "northern mode" of millennial climate variability observed in mainland Asia propagates south of the equator over maritime Indonesia, despite clear evidence for southward migration of the ITCZ. This suggests that water vapor content and convection within the ITCZ controls central Indonesian hydrology more than ITCZ position.

  12. Millennial Scale Variability of the AMOC and its Link to Climate During the Holocene

    NASA Astrophysics Data System (ADS)

    Thornalley, D. J.; Oppo, D.; Keigwin, L. D.; Hall, I. R.; Moffa Sanchez, P.

    2014-12-01

    Several proxy and modelling studies suggest that there may have been considerable change in the operation the Atlantic Meridional Overturning Circulation (AMOC) during the Holocene. Yet despite its importance for regional and global climate, the Holocene history of the AMOC is poorly constrained. Improving our knowledge of past AMOC variability will contribute to our general understanding of the dynamics of ocean circulation and the role it may play in causing or amplifying climate variability on millennial timescales. We present Holocene grain-size records in depth transects from Blake Outer Ridge and Cape Hatteras, sampling the full-depth range of the Deep Western Boundary Current (DWBC), the lower limb of the AMOC. These records will complement a depth-transect of grain-size records sampling the Iceland-Scotland (I-S) overflow, showing Holocene variations that reflect deglacial meltwater forcing in the early Holocene and insolation-forced trends from the middle-to-late Holocene (Thornalley et al., 2013, Climate of the Past). We will also present detailed grain-size records for the last 2,000 years, both in a depth transect of cores off Cape Hatteras, and from cores in the Iceland Basin, sampling the I-S overflow. Our extensive datasets enable us to provide a coherent synthesis of changes in the flow strength of key components of the AMOC on centennial-millennial and orbital timescales, which we can use to develop our understanding of past millennial-scale climate variability. Specific questions to be addressed include: How well coupled are Holocene trends in Iceland-Scotland overflow and the DWBC? How did I-S overflow and the AMOC vary during the last millennia, including the last ~150 years since the end of the Little Ice Age? Initial results suggest a long-term anti-phasing of the Nordic overflows, wherein mid-late Holocene weakening of the I-S overflow has been compensated for by a strengthening of Denmark Strait overflow. We will also report on pronounced

  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. Changes in interannual and interdecadal precipitation variability from millennial-scale climate model runs

    NASA Astrophysics Data System (ADS)

    Moyer, E. J.; Schwarzwald, K.; Chang, W.; McInerney, D.; Huang, W. K.; Zhorin, V.

    2016-12-01

    Understanding future changes in climate variability, which can impact human activities, is a current research priority. Changes in long-timescale variability are of particular concern, since droughts of multi-year duration can be devastating to human societies. These changes are however difficult to identify in the relatively short and non-stationary model runs of the CMIP5 archive and are best studied instead through millennial-scale climate simulations. We show here analysis of multi-millennial runs of the CCSM3 model in both pre-industrial and elevated CO2 conditions, using spectral analysis to describe the frequency dependence of variability differences in monthly precipitation. We find that in these runs, changes in precipitation variability largely scale with changes in means, both in individual locations and in the global mean, and that these changes show little frequency dependence. That is, interannual and multi-decadal variability show similar changes as are exhibited at sub-annual frequencies. The consistent response across frequencies suggests that changes in individual processes (e.g. ENSO) do not dominate projected changes in low-frequency precipitation variability.

  15. Geochemical proxies and millennial-scale climate variability during MIS 3 at Lake Chalco, central Mexico

    NASA Astrophysics Data System (ADS)

    Torres, E.; Lozano, S.; Roy, P.; Ortega, B.; Caballero, M.

    2013-05-01

    The Basin of Mexico (20N, 99W; 2240 m.a.s.l.) is present at the northern limit of the American tropics and is surrounded by up to 5400 m high mountains. The Lake Chalco is situated at the southern part of the basin and spreads over 120 km2. The precipitation in the modern era is influenced by the seasonal displacement of the Intertropical Convergence Zone and the high-pressure belt located at about 35 N. Five cores were drilled (up to 122.5 m depth) in order to document climate variability in paleohydrological conditions during the late Quaternary. The age model includes several 14C dates and tephra layers present in the upper 25 m of the core. We documented millennial-scale events during MIS 3 based on geochemical data (total organic carbon (TOC), total inorganic carbon (TIC), C/N ratio) and abundance of charcoal particles. By temporal correlation with GISP2 core we founded that Greenland interstadials match with TOC percentages suggesting wet conditions while stadials match with high TIC percentages and high charcoal concentrations suggesting dry conditions. We compared our data with speleothem records (δ18O) from Fort Station Cave (New Mexico) and Terciopelo Cave (Costa Rica), our preliminary results indicate that Chalco record has a similar climatic signal as Terciopelo Cave, both presented wet interstadials and dry stadials which appear to have been regulated by the seasonal migration of the ITCZ.

  16. Western North Atlantic evidence for millennial-scale changes in ocean circulation and climate

    NASA Astrophysics Data System (ADS)

    Keigwin, L. D.; Jones, G. A.

    1994-06-01

    Two late Quaternary series of high resolution percent carbonate data from western North Atlantic sediment drifts (Bermuda Rise and Bahama Outer Ridge) show millennial-scale oscillations superimposed on the familiar, longer-period oscillations of orbital origin. The dominant high-frequency oscillation in these records has a quasi-period of about 4000 years. These percent CaCO3 changes most likely result from the influence of climate change on the flux of terrigenous material from eastern Canada, the resuspension of continental margin sediment by deep eddy kinetic energy, and carbonate dissolution. Sediment is transported to the Bermuda Rise by deep recirculating gyres and to the Bahama Outer Ridge by the deep western boundary current system. Stable isotope results on foraminifera across several of these oscillations from interstadial climate conditions and from a glacial inception display variability similar to that of percent CaCO3. Oxygen isotope ratios of planktonic foraminifera suggest large variations in near-surface temperature and/or salinity, and carbon isotope ratios of benthic foraminifera indicate that there were significant oscillations in the flux of North Atlantic Deep Water (NADW). These data support models which couple surface ocean conditions in the North Atlantic, production of NADW, North Atlantic heat flux, and evidence for temperature oscillations in ice cores.

  17. 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

  18. Origin of millennial-scale climate instabilities in the subtropical Atlantic Ocean

    NASA Astrophysics Data System (ADS)

    Billups, K.; Scheinwald, A.; Dahl, P.

    2013-12-01

    We have generated a high resolution (~250-500 year) planktonic foraminiferal stable isotope record (Globigerinoides ruber white, senso lato) spanning Marine Isotope Stages (MIS) 6 through 8 in the northwestern subtropical Atlantic (Ocean Drilling Program Leg 172 Site 1059). The record fills a gap in an about 1.3 million year long time series of millennial-scale surface ocean hydrography in this region. We test the hypothesis that sub-orbital climate signals are linked to a response to precession forcing in tropical latitudes. Power spectra provide evidence for an increase in the length of half precession cycles as the 19 kyr precession period disappears from the insolation forcing at about 320 Ka in first order support of the hypothesis. In the time series, half precession (and quarter precession cycles when present) are evident as double (and quadruple) peaks within the given precession framework. However, in the time series there is no match between the amplitude modulation of the precession signal and its harmonics. During the time interval between 340-0 Ka (MIS 9-1) when the temporal resolution is high (250 year time step), the power spectra also contain significant peaks in the Dansgaard-Oeschger band (~1-8-1.5 kyr). Comparison of filter output with the time series, however, illustrates that there are only few instances where these types of variations are distinct in the foraminiferal δ18O record. We conclude that the evolution of half precession cycles over the time interval is largely consistent with a response to low latitude insolation, such as introduced by insolation maxima at the equinoxes and solstices (e.g., Short et al., 1991). Our analysis also shows that quarter precession cycles are present in the time series, at least intermittently, but we cannot uniquely tie them to changes in the primary precession signal. Our study highlights the importance of evaluating variations in the original time series to guide interpretations of significant peaks in

  19. 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

  20. Multi-millennial-scale climate variability in Antarctica during the past seven glacial periods

    NASA Astrophysics Data System (ADS)

    Kawamura, K.

    2009-12-01

    Climate variability on 1,000- to 10,000 -year timescales and associated interhemispheric seesaw during the last glacial period have been documented in a variety of paleoclimatic records. However, the frequency, magnitude, cause and prerequisites for the older glacial periods are still uncertain. We here present a new 720,000-year ice core record from Dome Fuji, East Antarctica. The agreement between the Dome Fuji and Dome C isotopic temperature records indicates homogeneous climate variability across the East Antarctic plateau throughout the past 720 kyr. By combining the two temperature proxy records, we identified persistent multi-millennial-scale Antarctic events over the past seven glacial periods. With a fully coupled atmosphere-ocean general circulation model, it is suggested that the prerequisite for the bipolar seesaw is the combination of a cold background climate and freshwater input into the northern North Atlantic. With our identification criteria, the mean repetition period of the large Antarctic events increased from 6 kyr in the older three glacial periods to 8 kyr in the younger four glacial periods. Low frequency variations (repetition period of >10 kyr) occur in the early parts of the last four glacial periods (i.e. after Mid-Brunhes climatic shift), suggesting a role of insolation forcing on the large bipolar events in the recent glacial periods. Dome Fuji Ice Core Project members (listed in alphabetical order): Ayako Abe-Ouchi, Yutaka Ageta, Shuji Aoki, Nobuhiko Azuma, Yoshiyuki Fujii, Koji Fujita, Shuji Fujita, Kotaro Fukui, Teruo Furukawa, Atsushi Furusaki, Kumiko Goto-Azuma, Ralf Greve, Motohiro Hirabayashi, Takeo Hondoh, Akira Hori, Shinichiro Horikawa, Kazuho Horiuchi, Makoto Igarashi, Yoshinori Iizuka, Takao Kameda, Kokichi Kamiyama, Hiroshi Kanda, Kenji Kawamura, Mika Kohno, Takayuki Kuramoto, Yuki Matsushi, Morihiro Miyahara, Takayuki Miyake, Atsushi Miyamoto, Hideaki Motoyama, Yasuo Nagashima, Yoshiki Nakayama, Takakiyo Nakazawa, Fumio

  1. Bering Sea millennial-scale climate variability during Marine Isotope Stages 22 and 21 (~900 ka): evidence for an active bipolar seesaw?

    NASA Astrophysics Data System (ADS)

    Kender, Sev; Hall, Ian R.; Becker, Julia; Aiello, Ivano W.; Radi, Taoufik; Asahi, Hirofumi

    2013-04-01

    The mid-Pleistocene transition (MPT), characterised by glacial intensification and lengthening, is marked by particularly abrupt ice sheet growth during the first ~100 ka glacial of Marine Isotope Stage (MIS) 22. Millennial-scale climate variability has been proposed to have become intensified during MPT glacials due to North American ice sheet growth beyond a critical size causing basal instability, but direct evidence for intensified millennial-scale climate variability during MIS 22 is so far lacking. In addition, evidence for an active 'bipolar seesaw' during the MPT has not yet been documented, despite this being a critical assumption in synthetically-produced Greenland ice core records. In this study we investigate MIS 22/21 (~910-840 ka) using high resolution (~0.3 ka) benthic foraminiferal oxygen isotopes (δ18O), ice-rafted debris (IRD) counts and lower resolution dinoflagellate cyst transfer functions for sea surface conditions, from Bering Sea Site U1343 (IODP Expedition 323, ~2 km water depth). During the transition from glacial MIS 22 to interglacial 21, surface water proxies indicate sea ice duration reduced, and productivity increased slightly, both indicative of warming sea surface temperatures during the deglacial. However, coincident with these shifts is a transient reversal (increase) in benthic δ18O, suggesting deep water briefly cooled. We suggest that the transient deglacial deep water cooling at Site U1343 implies a signal originating in the Southern Hemisphere (Ocean), as deep water in the Bering Sea is predominantly composed of Pacific Deep Water, which is sourced from Antarctic Bottom Water. Comparison with a similar resolution record from the North Atlantic (Site U1313) shows an equally transient increase in North Atlantic Deep Water (NADW) production occurred synchronously with the Bering Sea deep water cooling reversal. The coincident Bering Sea surface warming, Southern Ocean cooling, and NADW production increase is similar to the

  2. Masked millennial-scale climate variations in South West Africa during the last glaciation

    NASA Astrophysics Data System (ADS)

    Hessler, I.; Dupont, L.; Handiani, D.; Paul, A.; Merkel, U.; Wefer, G.

    2012-04-01

    To address the connection between tropical African vegetation development and high-latitude climate change we present a high-resolution pollen record from ODP Site 1078 (off Angola) covering the period 50-10 ka BP. Although several tropical African vegetation and climate reconstructions indicate an impact of Heinrich Stadials (HSs) in Southern Hemisphere Africa, our vegetation record shows no response. Model simulations conducted with an Earth System Model of Intermediate Complexity including a dynamical vegetation component provide one possible explanation. Because both precipitation and evaporation increased during HSs and their effects nearly cancelled each other, there was a negligible change in moisture supply. Consequently, the resulting climatic response to HSs might have been too weak to noticeably affect the vegetation composition in the study area. Our results also show that the response to HSs in southern tropical Africa neither equals nor mirrors the response to abrupt climate change in northern Africa.

  3. Investigating the impact of millennial scale Agulhas Current System variability on global ocean circulation and climate

    NASA Astrophysics Data System (ADS)

    Simon, M.; Hall, I. R.; Barker, S.; Ziegler, M.

    2012-04-01

    Around 4-5 times per year the Atlantic Ocean receives warm, saline waters from the Indo-Pacific Ocean through ring shedding events via the Agulhas Current (AC) around the southern tip of Africa. This transfer of heat and salt into the South Atlantic through the Indo-Atlantic Gateway, the so called 'Agulhas Leakage (AL)', constitutes the 'warm' upper return limb of the global oceans thermohaline circulation. As such AL is believed to have an important role in controlling the variability of the Atlantic meridional overturning circulation (AMOC). For example, recent modelling evidence suggests that AL actively stabilises our present climate, while palaeo-reconstructions highlight its important role as a potential driver for the rapid resumption of global interglacial climate change. Palaeo-reconstructions focussing on the upstream AC variability itself and its potential connection with the downstream AL, as well as its influence on the AMOC stability, are scarce. Thus the question of what ultimately drives variability of the AL on a range of timescales remains unclear. Here we present high-resolution (centennial-millennial scale) sea surface temperature (SST), salinity (SSS) and thermocline structure records from the "upstream" AC (Natal Valley) over the past 60,000 yrs. Results of surface (Globigerinoides ruber, sensu stricto) and thermocline (Pulleniatina obliquiloculata) planktonic δ18O and Mg/Ca-derived temperature records from the main flow path of the AC show modulation which match Antarctic warming events A1, A3, A4, which are more pronounced in the thermocline δ18O record. Mg/Ca derived SSTs suggest temperatures of 20-21°C at the Last Glacial Maximum (LGM), and show a progressive increase during Termination I (TI), which coincides with an increased abundance of subtropical planktonic foraminiferal marker species (Agulhas Leakage fauna, ALF) which indicates a progressive warming due to an increased influence of subtropical waters at the core site. Sortable

  4. Downslope strengthening millennial-scale climatic change signals deduced from high-resolution clay mineralogy during the last glaciation in the northern South China Sea

    NASA Astrophysics Data System (ADS)

    Zhao, S.; Liu, Z.; Wang, X.; Xie, X.; Shi, J.; Christophe, C.

    2015-12-01

    Clay mineralogy provides a powerful tool to reconstruct glacial-cyclic paleoceanographic and paleoclimatic changes in the South China Sea. However, whether the clay mineralogy could also reserve millennial-scale climatic change is still poorly understood, because clay minerals usually produced through the long-term chemical weathering are not sensitive to the fast environmental change. This study presents the high-resolution clay mineralogy of three high-quality sediment cores, which were retrieved from a transect on the continental slope of the northern South China Sea during the cruise of MD190 (2012). Our results show that time series changes of clay mineral assemblages display a clear occurrence of millennial-scale climatic change events, such as Younger Dryas, Bolling-Allerod, and Heinrich events 1-6. The reconstructed relative contributions of clay minerals from their source areas of Taiwan and Luzon are closely related to the millennial-scale climatic changes, while the clay mineral contribution from the source area of the Pearl River presents a relationship to the sea level change. Following the transect with increasing water depths, the Pearl River contribution decreases, whereas the Taiwan and Luzon contributions present more complex changes, and the millennial-scale climatic change signals are also gradually strengthened. The Luzon/Taiwan contribution ratio is used for the proxy of the millennial-scale paleoclimate evolution. The lower ratio presents colder events, while the high ratio indicates warmer periods. The distinct downslope strengthening millennial-scale climatic change indicates that deepwater sediments in the South China Sea could well reserve fast climatic change events that usually occurred in high latitudes.

  5. 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

  6. Persistent millennial-scale shifts in moisture regimes in western Canada during the past six millennia.

    PubMed

    Cumming, Brian F; Laird, Kathleen R; Bennett, Joseph R; Smol, John P; Salomon, Anne K

    2002-12-10

    Inferences of past climatic conditions from a sedimentary record from Big Lake, British Columbia, Canada, over the past 5,500 years show strong millennial-scale patterns, which oscillate between periods of wet and drier climatic conditions. Higher frequency decadal- to centennial-scale fluctuations also occur within the dominant millennial-scale patterns. These changes in climatic conditions are based on estimates of changes in lake depth and salinity inferred from diatom assemblages in a well dated sediment core. After periods of relative stability, abrupt shifts in diatom assemblages and inferred climatic conditions occur approximately every 1,220 years. The correspondence of these shifts to millennial-scale variations in records of glacial expansionrecession and ice-rafting events in the Atlantic suggest that abrupt millennial-scale shifts are important to understanding climatic variability in North America during the mid- to late Holocene. Unfortunately, the spatial patterns and mechanisms behind these large and abrupt swings are poorly understood. Similar abrupt and prolonged changes in climatic conditions today could pose major societal challenges for many regions.

  7. Southern Ocean Deep-Convection as a Driver of Centennial-to-Millennial-Scale Climate Variability at Southern High Latitudes

    NASA Astrophysics Data System (ADS)

    Pedro, J. B.; Martin, T.; Steig, E. J.; Jochum, M.; Park, W.; Rasmussen, S.

    2014-12-01

    Antarctic Isotope Maxima (AIM) are centennial-to-millennial scale warming events observed in Antarctic ice core records from the last glacial period and deglaciation. Mounting evidence links AIM events to parallel variations in atmospheric CO2, Southern Ocean (SO) sea surface temperatures and Antarctic Bottom Water production. According to the prevailing view, AIM events are forced from the North Atlantic by melt-water discharge from ice sheets suppressing the production of North Atlantic Deep Water and associated northward heat transport in the Atlantic. However observations and model studies increasingly suggest that melt-water fluxes have the wrong timing to be invoked as such a trigger. Here, drawing on results form the Kiel Climate Model, we present an alternative hypothesis in which AIM events are forced via internal oscillations in SO deep-convection. The quasi-periodic timescale of deep-convection events is set by heat (buoyancy) accumulation at SO intermediate depths and stochastic variability in sea ice conditions and freshening at the surface. Massive heat release from the SO convective zone drives Antarctic and large-scale southern hemisphere warming via a two-stage process involving changes in the location of Southern Ocean fronts, in the strength and intensity of the Westerlies and in meridional ocean and atmospheric heat flux anomalies. The potential for AIM events to be driven by internal Southern Ocean processes and the identification of time-lags internal to the southern high latitudes challenges conventional views on the North Atlantic as the pacemaker of millennial-scale climate variability.

  8. Southern Ocean Deep-Convection as a Driver of Centennial-to-Millennial-Scale Climate Variability at Southern High Latitudes

    NASA Astrophysics Data System (ADS)

    Pedro, J. B.; Martin, T.; Steig, E. J.; Jochum, M.; Park, W.; Rasmussen, S.

    2015-12-01

    Antarctic Isotope Maxima (AIM) are centennial-to-millennial scale warming events observed in Antarctic ice core records from the last glacial period and deglaciation. Mounting evidence links AIM events to parallel variations in atmospheric CO2, Southern Ocean (SO) sea surface temperatures and Antarctic Bottom Water production. According to the prevailing view, AIM events are forced from the North Atlantic by melt-water discharge from ice sheets suppressing the production of North Atlantic Deep Water and associated northward heat transport in the Atlantic. However observations and model studies increasingly suggest that melt-water fluxes have the wrong timing to be invoked as such a trigger. Here, drawing on results form the Kiel Climate Model, we present an alternative hypothesis in which AIM events are forced via internal oscillations in SO deep-convection. The quasi-periodic timescale of deep-convection events is set by heat (buoyancy) accumulation at SO intermediate depths and stochastic variability in sea ice conditions and freshening at the surface. Massive heat release from the SO convective zone drives Antarctic and large-scale southern hemisphere warming via a two-stage process involving changes in the location of Southern Ocean fronts, in the strength and intensity of the Westerlies and in meridional ocean and atmospheric heat flux anomalies. The potential for AIM events to be driven by internal Southern Ocean processes and the identification of time-lags internal to the southern high latitudes challenges conventional views on the North Atlantic as the pacemaker of millennial-scale climate variability.

  9. Carbon storage in the mid-depth Atlantic during millennial-scale climate events

    NASA Astrophysics Data System (ADS)

    Lacerra, Matthew; Lund, David; Yu, Jimin; Schmittner, Andreas

    2017-08-01

    Carbon isotope minima were a ubiquitous feature of the mid-depth Atlantic during Heinrich Stadial 1 (HS1, 14.5-17.5 kyr BP) and the Younger Dryas (YD, 11.5-12.9 kyr BP), yet their cause remains unclear. Recent evidence indicates that North Atlantic processes triggered the δ13C anomalies, with weakening of the Atlantic Meridional Overturning Circulation (AMOC) being the most likely driver. Model simulations suggest that slowing of the AMOC increases the residence time of mid-depth waters in the Atlantic, resulting in the accumulation of respired carbon. Here we assess ΣCO2 variability in the South Atlantic using benthic foraminiferal B/Ca, a proxy for [CO32-]. Using replicated high-resolution B/Ca records from 2 km water depth on the Brazil Margin, we show that [CO32-] decreased during HS1 and the YD, synchronous with apparent weakening of the AMOC. The [CO32-] response is smaller than in the tropical North Atlantic during HS1, indicating there was a north-south gradient in the [CO32-] signal similar to that for δ13C. The implied variability in ΣCO2 is consistent with model results, suggesting that carbon is temporarily sequestered in the mid-depth Atlantic during millennial-scale stadial events. Using a carbon isotope mass balance, we estimate that approximately 75% of the HS1 δ13C signal at the Brazil Margin was driven by accumulation of remineralized carbon, highlighting the nonconservative behavior of δ13C during the last deglaciation.

  10. Millennial-Scale Response and Impact of Climate Variability in the Gulf of California Across the LGM/Holocene Transition

    NASA Astrophysics Data System (ADS)

    McClymont, E. L.; Ganeshram, R.

    2008-12-01

    Within the modern climate system, the interannual variability in the tropical Pacific ocean-atmosphere circulation intensity, defined as the El Niño/Southern Oscillation (ENSO), has significant impacts both within and beyond the tropics. Despite evidence for past "ENSO-like" climate variability at a variety of timescales, the behaviour of the ENSO system under different climate boundary conditions continues to be debated. Here, we investigate the millennial-scale signature of ENSO-like variability across the transition from the Last Glacial Maximum to the early Holocene, testing the ENSO system response to changes in insolation, atmospheric CO2 and global ice volume. We have analysed a remarkable high resolution sediment core from the Gulf of California, MD02-2515 (IMAGES MONA expedition). The mm-scale (annually) laminated diatomaceous muds reflect seasonal variations in ocean and atmospheric circulation, driven in part by a monsoon climate, and interannual variability driven by ENSO. We address both the marine and terrestrial records of past ENSO-like variability using a variety of geochemical proxies. The UK37' and TEX86 indices for sea-surface temperature are combined with accumulation rates of chlorins, alkenones and diatom-specific sterols, alongside opal and organic carbon contents, to investigate the intensity of the upwelling system. We show that the transition from the LGM to the Holocene is marked by a slight warming (~ 2°C) and a reduction in the amplitude of millennial-scale SST variability (from ~ 5°C to ~ 3°C). SSTs differ between the UK37' and TEX86 proxies, reflecting production by different source organisms in different seasons and/or water depths. The difference between the two SST values is smallest when other proxies indicate reduced upwelling, consistent with a reduction in seasonal SST variability. Alkenone and chlorin concentrations detail highly variable coccolithophore and total primary production, but suggest reduced productivity and a

  11. 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.

  12. 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.

  13. Testing the Millennial-Scale Holocene Solar-Climate Connection in the Indo-Pacific Warm Pool

    NASA Astrophysics Data System (ADS)

    Khider, D.; Emile-Geay, J.; McKay, N.; Jackson, C. S.; Routson, C.

    2016-12-01

    The existence of 1000 and 2500-year periodicities found in reconstructions of total solar irradiance (TSI) and a number of Holocene climate records has led to the hypothesis of a causal relationship. However, attributing Holocene millennial-scale variability to solar forcing requires a mechanism by which small changes in total irradiance can influence a global climate response. One possible amplifier within the climate system is the ocean. If this is the case, then we need to know more about where and how this may be occurring. On the other hand, the similarity in spectral peaks could be merely coincidental, and this should be made apparent by a lack of coherence in how that power and phasing are distributed in time and space. The plausibility of the solar forcing hypothesis is assessed through a Bayesian model of the age uncertainties affecting marine sedimentary records that is propagated through spectral analysis of the climate and forcing signals at key frequencies. Preliminary work on Mg/Ca and alkenone records from the Indo-Pacific Warm Pool suggests that despite large uncertainties in the location of the spectral peaks within each individual record arising from age model uncertainty, sea surface variability on timescales of 1025±36 years and 2427±133 years (±standard error of the mean of the median periodicity in each record) are present in at least 95% and 70% of the ensemble spectra, respectively. However, we find a long phase delay between the peak in forcing and the maximum response in at least one of the records, challenging the solar forcing hypothesis and requiring further investigation between low- and high-latitude signals. Remarkably, all records suggest a periodicity near 1470±85 years, reminiscent of the cycles characteristic of Marine Isotope Stage 3; these cycles are absent from existing records of TSI, further questioning the millennial solar-climate connection.

  14. The Greening of the McGill Paleoclimate Model. Part II: Simulation of Holocene Millennial-Scale Natural Climate Variability

    NASA Astrophysics Data System (ADS)

    Mysak, L. A.; Wang, Y.; Wang, Z.; Brovkin, V.

    2003-12-01

    Multiple proxy data reveal that the middle Holocene (6 kyr BP) was warmer than the early Holocene (8 kyr BP) as well as the preindustrial period (1700 AD) in most regions of the Northern Hemisphere. This warmth is somewhat counterintuitive because the summer insolation was decreasing during this time. Cooling in the late Holocene (after 6 kyr BP) is hypothesized to be due mainly to the astronomical forcing. This cooling was also accompanied by significant changes in vegetation cover (i.e., treeline retreat from northern high latitudes; the desertification of the Sahara/Sahel region) and a small but gradual increase of atmospheric CO2 concentration (from 260 ppm to 280 ppm). The early-to-middle Holocene warming, on the other hand, is hypothesized to be due in part to ice-albedo feedback in Northern America, associated with decreases in the Laurentide ice sheet, which completely disappeared by 6 kyr BP. The snow-vegetation-albedo feedback is also hypothesized to have played a role in this early warming event. To test the above hypotheses, the earlier geophysical McGill Paleoclimate Model has been coupled to the vegetation model known as VECODE (VEgetation COntinuous DEscription, one of the simpler dynamic global vegetation models), and a number of sensitivity experiments have been performed. The model results illustrate the role that Northern Hemisphere land cover changes played in explaining the natural millennial-scale climate variability from the early Holocene (8 kyr BP) to the preindustrial period (1700 AD).

  15. Millennial Scale Rapid Climate Change Events of the last 60kya as Observed in Multiple Stalagmites from The Bahamas

    NASA Astrophysics Data System (ADS)

    Mehterian, S.; Arienzo, M. M.; Pourmand, A.; Broad, K.; Kakuk, B.; Swart, P. K.

    2016-12-01

    Nine stalagmites collected from various depths of a submerged cave system on the island of Abaco, Bahamas comprise a continuous record of oxygen isotopic variation between 7.3 to 63kyr. The depths from which the speleothems were collected range from 12m to 37m. The youngest age of the speleothems reflect the inundation of the cave system by rising sea level. Millennial scale rapid climate change events can be seen in the δ18O record of the Bahamian stalagmites as Heinrich Stadials H0 to H6 and Dansgaard Oeschger Events. This collection of stalagmites represents different depths in a cave in Abaco, and their collective geochemical record reflects the global climatic effects as experienced locally in the subtropical islands of the Bahamas. Separately, various stalagmites that grew during the same time periods reflect similar patterns in the δ18O values of their calcite mineralogy despite having been located at vastly different depth elevations relative to each other. In general, the average δ18O value for the stalagmites collected from this cave is -2.5‰ VPDB with a maximum and minimum δ18O value between 0.5 ‰ and -5.5‰ VPDB respectively during Heinrich stadials and D/O events. In addition to δ18O values measured in these stalagmites, ratios of Sr/Ca, Mg/Ca, and Ba/Ca are also compared with one another. This study attempts to elucidate differences, if any, that locations in a cave relative to sea level would have on recording the true climate signals of a region. Finally, results from this study are compared with stalagmites collected from Eleuthera, another Bahamian island with speleothems younger than those from Abaco in order to create a mostly continuous record of rapid climate change events dating back from present day to 63,000 years.

  16. 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.

  17. Millennial-scale vegetation dynamics in an estuary at the onset of the Miocene Climate Optimum

    PubMed Central

    Kern, Andrea; Harzhauser, Mathias; Mandic, Oleg; Roetzel, Reinhard; Ćorić, Stjepan; Bruch, Angela A.; Zuschin, Martin

    2010-01-01

    Pollen analyses have been proven to possess the possibility to decipher rapid vegetational and climate shifts in Neogene sedimentary records. Herein, a c. 21-kyr-long transgression–regression cycle from the Lower Austrian locality Stetten is analysed in detail to evaluate climatic benchmarks for the early phase of the Middle Miocene Climate Optimum and to estimate the pace of environmental change. Based on the Coexistence Approach, a very clear signal of seasonality can be reconstructed. A warm and wet summer season with c. 204–236 mm precipitation during the wettest month was opposed by a rather dry winter season with precipitation of c. 9–24 mm during the driest month. The mean annual temperature ranged between 15.7 and 20.8 °C, with about 9.6–13.3 °C during the cold season and 24.7–27.9 °C during the warmest month. In contrast, today’s climate of this area, with an annual temperature of 9.8 °C and 660 mm rainfall, is characterized by the winter season (mean temperature: −1.4 °C, mean precipitation: 39 mm) and a summer mean temperature of 19.9 °C (mean precipitation: 84 mm). Different modes of environmental shifts shaped the composition of the vegetation. Within few millennia, marshes and salt marshes with abundant Cyperaceae rapidly graded into Taxodiaceae swamps. This quick but gradual process was interrupted by swift marine ingressions which took place on a decadal to centennial scale. The transgression is accompanied by blooms of dinoflagellates and of the green alga Prasinophyta and an increase in Abies and Picea. Afterwards, the retreat of the sea and the progradation of estuarine and wetland settings were a gradual progress again. Despite a clear sedimentological cyclicity, which is related to the 21-kyr precessional forcing, the climate data show little variation. This missing pattern might be due to the buffering of the precessional-related climate signal by the subtropical vegetation. Another explanation could be the method

  18. Abrupt climate changes during Termination III in Southern Europe.

    PubMed

    Pérez-Mejías, Carlos; Moreno, Ana; Sancho, Carlos; Bartolomé, Miguel; Stoll, Heather; Cacho, Isabel; Cheng, Hai; Edwards, R Lawrence

    2017-09-19

    The Late Quaternary glacial-interglacial transitions represent the highest amplitude climate changes over the last million years. Unraveling the sequence of events and feedbacks at Termination III (T-III), including potential abrupt climate reversals similar to those of the last Termination, has been particularly challenging due to the scarcity of well-dated records worldwide. Here, we present speleothem data from southern Europe covering the interval from 262.7 to 217.9 kyBP, including the transition from marine isotope stage (MIS) 8 to MIS 7e. High-resolution δ(13)C, δ(18)O, and Mg/Ca profiles reveal major millennial-scale changes in aridity manifested in changing water availability and vegetation productivity. uranium-thorium dates provide a solid chronology for two millennial-scale events (S8.1 and S8.2) which, compared with the last two terminations, has some common features with Heinrich 1 and Heinrich 2 in Termination I (T-I).

  19. Abrupt climate changes during Termination III in Southern Europe

    NASA Astrophysics Data System (ADS)

    Pérez-Mejías, Carlos; Moreno, Ana; Sancho, Carlos; Bartolomé, Miguel; Stoll, Heather; Cacho, Isabel; Cheng, Hai; Edwards, R. Lawrence

    2017-09-01

    The Late Quaternary glacial–interglacial transitions represent the highest amplitude climate changes over the last million years. Unraveling the sequence of events and feedbacks at Termination III (T-III), including potential abrupt climate reversals similar to those of the last Termination, has been particularly challenging due to the scarcity of well-dated records worldwide. Here, we present speleothem data from southern Europe covering the interval from 262.7 to 217.9 kyBP, including the transition from marine isotope stage (MIS) 8 to MIS 7e. High-resolution δ13C, δ18O, and Mg/Ca profiles reveal major millennial-scale changes in aridity manifested in changing water availability and vegetation productivity. uranium–thorium dates provide a solid chronology for two millennial-scale events (S8.1 and S8.2) which, compared with the last two terminations, has some common features with Heinrich 1 and Heinrich 2 in Termination I (T-I).

  20. New Zealand maritime glaciation: millennial-scale southern climate change since 3.9 Ma.

    PubMed

    Carter, Robert M; Gammon, Paul

    2004-06-11

    Ocean Drilling Program Site 1119 is ideally located to intercept discharges of sediment from the mid-latitude glaciers of the New Zealand Southern Alps. The natural gamma ray signal from the site's sediment core contains a history of the South Island mountain ice cap since 3.9 million years ago (Ma). The younger record, to 0.37 Ma, resembles the climatic history of Antarctica as manifested by the Vostok ice core. Beyond, and back to the late Pliocene, the record may serve as a proxy for both mid-latitude and Antarctic polar plateau air temperature. The gamma ray signal, which is atmospheric, also resembles the ocean climate history represented by oxygen isotope time series.

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

    PubMed

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

    2014-08-21

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

  2. Fire-induced erosion and millennial-scale climate change in northern ponderosa pine forests.

    PubMed

    Pierce, Jennifer L; Meyer, Grant A; Jull, A J Timothy

    2004-11-04

    Western US ponderosa pine forests have recently suffered extensive stand-replacing fires followed by hillslope erosion and sedimentation. These fires are usually attributed to increased stand density as a result of fire suppression, grazing and other land use, and are often considered uncharacteristic or unprecedented. Tree-ring records from the past 500 years indicate that before Euro-American settlement, frequent, low-severity fires maintained open stands. However, the pre-settlement period between about ad 1500 and ad 1900 was also generally colder than present, raising the possibility that rapid twentieth-century warming promoted recent catastrophic fires. Here we date fire-related sediment deposits in alluvial fans in central Idaho to reconstruct Holocene fire history in xeric ponderosa pine forests and examine links to climate. We find that colder periods experienced frequent low-severity fires, probably fuelled by increased understory growth. Warmer periods experienced severe droughts, stand-replacing fires and large debris-flow events that comprise a large component of long-term erosion and coincide with similar events in sub-alpine forests of Yellowstone National Park. Our results suggest that given the powerful influence of climate, restoration of processes typical of pre-settlement times may be difficult in a warmer future that promotes severe fires.

  3. Origin of millennial-scale climate signals in the subtropical North Atlantic

    NASA Astrophysics Data System (ADS)

    Billups, Katharina; Scheinwald, Andre

    2014-06-01

    We present a high-resolution planktonic foraminiferal stable isotope record (Globigerinoides ruber) spanning marine oxygen isotope stages (MISs) 6 through 8 in the northwestern subtropical Atlantic Ocean (Ocean Drilling Program Leg 172 Site 1059). The record fills a gap to produce an about 1.3 Myr long continuous time series of high-frequency (> ~1/12 kyr) surface ocean hydrography, the first of this kind. We test the hypothesis that the suborbital climate signals (i.e., half and quarter precession cycles) are linked to precession forcing in tropical latitudes. Semiprecession cycles present between 0 and 320 ka are of the right periodicity to relate to the dominant precession forcing (23 kyr). These cycles are evident as double peaks within the given precession framework, and there is good match in the amplitude modulation of the filter output and the δ18O time series. Quarter precession cycles dominate the suborbital spectra between 320 ka and 1.3 Ma. Periodicities are close to those expected from the harmonics of the dominant precession peaks in the δ18O record, but present in the time series only intermittently, and their amplitude modulation does not match that of the primary precession period. Thus, only the half precession cycles evidence a response to low-latitude insolation such as that introduced by insolation maxima at the equinoxes or solstices during the course of a precession cycle. Additionally, we find well-defined, rapid (~1.5-2 kyr) variations across the first of the interglacial maxima of MIS 7 adding to evidence of non-ice sheet-related forcing factors in driving climate instabilities.

  4. Three climate cycles of millennial-scale vegetation change in Africa (Invited)

    NASA Astrophysics Data System (ADS)

    Dupont, L. M.

    2010-12-01

    Marine sediments can deliver long well-dated continuous sequences of environmental change, not only of the ocean but also of the continents. Vegetation records from these archives are often the only land-cover records to encompass several climate cycles. Comparing vegetation development during several cycles uncovers the structural and systematic differences between glacial and interglacial vegetation. Such data may help with the validation of the current earth system models including dynamic vegetation modules. A number of marine pollen records from the East Atlantic (ODP658, GIK16415, GIK16776, GIK16867, GeoB1016) and a new one from the Indian Ocean (MD96-2048) register the vegetation development in West and South Africa over a period of more than 300 thousand years covering at least three full glacial-interglacial cycles. From these dataset typical patterns of vegetation change in Africa are inferred and differences between cycles are discussed. Both latitudinal and altitudinal shifts in the vegetation have been recorded by pollen of e.g. Chenopods, Asteraceae (daisies), Ericaceae (heath), Podocarpus (yellow wood), Poaceae (grass), and lowland forest. While latitudinal shifts in the area of desert and savannah are typical in West Africa, altitudinal changes of the belt with mountainous forest and mountainous shrubs are more common in Southern Africa. During glacial times, vegetation includes ericaceous shrubs in Southern Africa, while desert shrubs expand in West Africa, and the area of the lowland forests is strongly reduced on the whole continent.

  5. 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.

  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. Impact of millennial-scale Holocene climate variability on eastern North American terrestrial ecosystems: Pollen-based climatic reconstruction

    USGS Publications Warehouse

    Willard, D.A.; Bernhardt, C.E.; Korejwo, D.A.; Meyers, S.R.

    2005-01-01

    We present paleoclimatic evidence for a series of Holocene millennial-scale cool intervals in eastern North America that occurred every ???1400 years and lasted ???300-500 years, based on pollen data from Chesapeake Bay in the mid-Atlantic region of the United States. The cool events are indicated by significant decreases in pine pollen, which we interpret as representing decreases in January temperatures of between 0.2??and 2??C. These temperature decreases include excursions during the Little Ice Age (???1300-1600 AD) and the 8 ka cold event. The timing of the pine minima is correlated with a series of quasi-periodic cold intervals documented by various proxies in Greenland, North Atlantic, and Alaskan cores and with solar minima interpreted from cosmogenic isotope records. These events may represent changes in circumpolar vortex size and configuration in response to intervals of decreased solar activity, which altered jet stream patterns to enhance meridional circulation over eastern North America. ?? 2004 Elsevier B.V. All rights reserved.

  8. Geochemical multielement signatures of glacial and interglacial facies of the Okhotsk Sea deepwater sediments during the past 350 kyr: A response to global climate changes at the orbital and millennial scales

    NASA Astrophysics Data System (ADS)

    Chebykin, Eugene P.; Gorbarenko, Sergey A.; Stepanova, Ol'ga G.; Panov, Vsevolod S.; Goldberg, Evgeny L.

    2015-03-01

    The previously dated deepwater sediment core MR06-04 PC-7R (length 1723 cm; 350 kyr) recovered from the central Okhotsk Sea (OS) was analyzed for biogenic compounds and for 63 chemical elements (using the inductively coupled plasma-mass spectrometry method) with a high resolution (1 cm; ~200 years). A one box model with two main members" and mathematical methods (based on multielemental composition of sediments) for the calculation of weight fractions (at each time slice) of two main types of geochemical facies that dominate during considerably diverse climatic periods (glacial maxima and interglacial optima) were proposed and tested. This model can be applied to other analogous natural systems whose sedimentation is driven by two main types of geochemical facies. The application of the developed model to the studied core revealed that variations of weight fractions of the typical interglacial and glacial geochemical facies in the sediments along the core depth (named as warm and cold "covariators," respectively) change synchronously with global and regional climate variability. Profiles of warm and inversed cold covariators coincide tightly, and their values increase during warm marine isotope stages and substages and decrease during cold ones over the last 350 kyr. Millennial scale changes in covariators had occurred simultaneously with abrupt variability in the OS productivity and sediment lithology and with millennial global climate variability. Some discrepancies in the warm and inversed cold covariators calculated using specific mathematical treatments revealed the episodic influence of volcanogenic matter presented in the core by visible tephra layers and cryptotephras.

  9. Dinoflagellate cysts as indicators of millennial scale climatic and oceanographic variability in Guaymas Basin, Gulf of California (Mexico) during the Late Quaternary

    NASA Astrophysics Data System (ADS)

    Price, Andrea M.; Mertens, Kenneth N.; Pospelova, *Vera; Pedersen, Thomas F.; Ganeshram, Raja S.

    2015-04-01

    A high-resolution record of organic-walled dinoflagellate cyst production in Guaymas Basin, Gulf of California (Mexico) reveals a complex paleoceanographic history over the last ~40 ka. Guaymas Basin is an excellent location to perform high resolution studies of changes in Late Quaternary climate and paleo-productivity because it is characterized by high primary productivity, high sedimentation rates, and low oxygen bottom waters. These factors contribute to the deposition and preservation of laminated sediments throughout large portions of core MD02-2515. This is one of the first studies in the Northeast Pacific to document dinoflagellate cyst production at a centennial to millennial scale throughout the Late Quaternary. Based on the cyst assemblages three major dinoflagellate cyst zones were established, and roughly correspond to Marine Isotope Stages 1 to 3. The most dominant dinoflagellate cyst taxa found throughout the core were Brigantedinium spp. and Operculodinium centrocarpum. Dansgaard-Oeschger event 8 is observed in the dinoflagellate cyst record, and is characterized by an increase in warm water taxa such as Spiniferites pachydermus. Other intervals of interest are the Younger Dryas where cooler sea-surface conditions are not recorded, and the Holocene which is characterized by the consistent presence of warm water species Stelladinium reidii, Tuberculodinidum vancampoae, Bitectatodinium spongium and an increase in Quinquecuspis concreta. Changes in cyst assemblages, concentrations and species diversity, along with geochemical data reflect major orbital to millennial-scale climatic and oceanographic changes. Keywords: Dansgaard-Oeschger events; dinoflagellate cyst; Gulf of California; late Quaternary climate change; upwelling; Younger Dryas.

  10. Millennial-scale climatic fluctuation in the fluvial record during MIS3: Very high-resolution seismic images from NE Hungary

    NASA Astrophysics Data System (ADS)

    Cserkész-Nagy, Ágnes; Sztanó, Orsolya

    2016-12-01

    Alluvial architectures of a meandering river existing in MIS3 were observed on very high-resolution (VHR) single-channel waterborne seismic profiles, 20-30 m below the Tisza River in the Pannonian Basin (Hungary). The study investigated the spatial and temporal variations of two, more than 2 km-long continuous series of inclined reflections interpreted as laterally accreted point bar complexes. The phases of natural meander migration were reconstructed in 3D based on the changes in the geometry and dip of the inclined reflections. A channel-forming discharge curve extending over approximately 2.5 ky was calculated by using paleo-width and depth data derived from the lateral accretion surfaces. Systematic analysis of the geometrical variations coupled with the discharge curve evaluation on each point bar complexes indicates millennial-scale discharge fluctuations 40-50 ky ago, to that the river responded principally by incision and infilling. The primary periodicity, comparable to the sub-Milankovitch cycles, is superimposed by shorter periods: ca. 500-year cycles reflect the phases of unidirectional meander development, while the smallest ones reflect the recurrence interval (150-200 years) of the highest floods. River-bed incisions happened step-by-step related to extreme floods, when the meander development also changed. The smaller-scale and more rapid fluctuations within a development unit were represented in variations of the channel width. Although the poor geochronology of the sandy fluvial deposits cannot allow any direct correlation to the climatostratigraphic events, the millennial-scale climate variations of MIS3 were pronouncedly characteristic in the discharge fluctuations.

  11. Climatically related millennial-scale fluctuations in strength of California margin oxygen-minimum zone during the past 60 k.y.

    SciTech Connect

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

    1999-11-01

    A strong oxygen-minimum zone (OMZ) currently exists along the California margin because of a combination of high surface-water productivity and poor intermediate-water ventilation. However, the strength of this OMZ may have been sensitive to late Quaternary ocean-circulation and productivity changes along the margin. Although sediment-lamination strength has been used to trace ocean-oxygenation changes in the past, oxygen levels on the open margin are not sufficiently low for laminations to form. In these regions, benthic foraminifera are highly sensitive monitors of OMZ strength, and their fossil assemblages can be used to reconstruct past fluctuations. Benthic foraminiferal assemblages from Ocean Drilling Program Site 1017, off Point Conception, exhibit major and rapid faunal oscillations in response to late Quaternary millennial-scale climate change (Dansgaard-Oeschger cycles) on the open central California margin. These faunal oscillations can be correlated to and are apparently synchronous with those reported from Santa Barbara Basin. Together they represent major fluctuations in the strength of the OMZ which were intimately associated with global climate change--weakening, perhaps disappearing, during cool periods and strengthening during warm periods. These rapid, major OMZ strength fluctuations were apparently widespread on the Northeast Pacific margin and must have influenced the evolution of margin biota and altered biogeochemical cycles with potential feedbacks to global climate change.

  12. 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.

  13. 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.

  14. Can uncertain landscape evolution models discriminate between landscape responses to stable and changing future climate? A millennial-scale test

    NASA Astrophysics Data System (ADS)

    Temme, A. J. A. M.; Baartman, J. E. M.; Schoorl, J. M.

    2009-10-01

    In the light of increasing societal interest in the effects of climate change, geomorphologists face the task of discriminating between natural landscape changes and landscape changes that result from human-induced climate change. Landscape Evolution Models (LEMs) are available for this purpose, but their application for prediction of future landscapes is problematic. Calibration of LEMs on a sufficiently long palaeo-record of landscape change solves some of these problems, but large uncertainties in input (e.g. climate) records and process descriptions remain. Using one of the few existing ka-scale LEM studies as starting point, this paper explores how uncertainty in the LEM LAPSUS (LandscApe ProcesS modelling at mUlti dimensions and scaleS, [Schoorl, J.M., Veldkamp, A. and Bouma, J., 2002. Modeling water and soil redistribution in a dynamic landscape context. Soil Science Society of America Journal, 66(5): 1610-1619]) affects its ability to discriminate future one-thousand year landscape change under stable climate from that under human-induced changed climate. Okhombe Valley in South Africa is used as a case study area. LEM uncertainty is characterized by different levels of parameter uncertainty. Results indicate that even under high levels of parameter uncertainty, LEM LAPSUS discriminates between responses to stable and changed climates for some zones in the landscape. Although confidence in model predictions remains limited, some explorative and relative conclusions about the effects of changed climate on future landscape evolution of Okhombe Valley are drawn. Finally, some possibilities and limitations of future studies on landscape evolution under changing climate are discussed.

  15. The Asian monsoon's role in atmospheric heat transport responses to orbital and millennial-scale climate change

    NASA Astrophysics Data System (ADS)

    McGee, D.; Green, B.; Donohoe, A.; Marshall, J.

    2015-12-01

    Recent studies have provided a framework for understanding the zonal-mean position of the tropical rain belt by documenting relationships between rain belt latitude and atmospheric heat transport across the equator (Donohoe et al., 2013). Modern seasonal and interannual variability in globally-averaged rain belt position (often referred to as 'ITCZ position') reflects the interhemispheric heat balance, with the rain belt's displacement toward the warmer hemisphere directly proportional to atmospheric heat transport into the cooler hemisphere. Model simulations suggest that rain belt shifts are likely to have obeyed the same relationship with interhemispheric heat transport in response to past changes in orbital parameters, ice sheets, and ocean circulation. This relationship implies that even small (±1 degree) shifts in the mean rain belt require large changes in hemispheric heat budgets, placing tight bounds on mean rain belt shifts in past climates. This work has primarily viewed tropical circulation in two dimensions, as a pair of zonal-mean Hadley cells on either side of the rain belt that are displaced north and south by perturbations in hemispheric energy budgets, causing the atmosphere to transport heat into the cooler hemisphere. Here we attempt to move beyond this zonal-mean perspective, motivated by arguments that the Asian monsoon system, rather than the zonal-mean circulation, plays the dominant role in annual-mean heat transport into the southern hemisphere in the modern climate (Heaviside and Czaja, 2012; Marshall et al., 2014). We explore a range of climate change experiments, including simulations of North Atlantic cooling and mid-Holocene climate, to test whether changes in interhemispheric atmospheric heat transport are primarily driven by the mean Hadley circulation, the Asian monsoon system, or other regional-scale atmospheric circulation changes. The scalings that this work identifies between Asian monsoon changes and atmospheric heat

  16. Toward a theory for millennial-scale climate variability through application of MEP in a simple dynamical model

    NASA Astrophysics Data System (ADS)

    Rial, J.; Noone, D.; Nordstrom, K.; Chase, T.; Gupta, V.

    2005-12-01

    Paleoclimate records contain a wealth of information about the character of climate variability and change. However, interpretation of these records is confounded by the lack of both a sufficient theory of climate system behavior and knowledge of those parameters that govern the character of the behavior. While one might argue that these concerns can be largely overcome by employing complex models of the climate system, interpretation of such models requires first a context for understanding simulation results. Further, it is yet to be demonstrated that indeed complex climate models can capture the internal and forced variability seen in proxy records. Specifically, it is not known if the ability to capture this variability has inadvertently been removed from the models range of possible behaviors due to the desire to tune parameterizations to closely reproduce contemporary climate. In view of these concerns, we use a simple model of the climate system that is sustained away from thermodynamic equilibrium by an energy flow. This model predicts the global mean temperature of the ocean from energy balance. Prediction of sea ice extent provides a nonlinear feedback the ocean temperature, thereby introducing into the model non-trivial internal oscillatory behavior. Such a simple model necessarily has a small number of tunable parameters. With selection of reasonable values for these parameters it has been shown to satisfactorily produce variability reminiscent of the Dansgaard-Oeschger variability observed in Northern Hemisphere proxy records. We take the view that the system should organize itself such that it will attain a regime that maximizes the production of entropy (MEP). By defining a thermodynamic entropy and maximizing it with respect to our free parameters, we determine an optimal parameter set. Here we examine how this selection differs from those estimated from physical arguments. In so doing, we show how the estimation of parameters can be used to argue

  17. 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).

  18. Multiple Speleothem Record of Orbital to Millennial-scale Climate Variability During MIS 21 to MIS 26

    NASA Astrophysics Data System (ADS)

    Hellstrom, J. C.; Bajo, P.; Drysdale, R.; Woodhead, J. D.; Ferretti, P.; Voelker, A. H. L.; Wolff, E. W.; Zanchetta, G.; Rodrigues, T.; Frisia, S.; Spoetl, C.; Fallick, A.

    2016-12-01

    Despite increasing interest in the study of orbital to millenial-scale climate variability during the Middle Pleistocene Transition our understanding of climate forcings as well as teleconnections is restricted in part by the lack of radiometrically-dated records. Furthermore, almost all high-resolution records have been recovered from marine setttings while continental archives remain highly under-represented. Here we present a multiple U-Pb radiometrically dated speleothem δ18O and δ13C record from Corchia Cave (Italy) which spans the Marine Isotope Stage (MIS) 21 to MIS 26 time interval. The record is based on four stalagmites and one subaqueous core. More than 100 U-Pb analyses secured a robust chronology and all climate events of interest were dated with a precision of 5ka or better. The speleothem chronology was transposed on to the marine benthic records through matching the speleothem δ18O and the SST records from the North Atlantic. Our results reveal that Terminations XII and X are separated by two obliquity cycles, and that Marine Isotope Stages 25 to 22 are not part of a 100-kyr cycle as previously thought. Furthermore, our time series reveal that precession also played an important role with each Termination occurring when summer insolation in either the Northern or Southern Hemisphere was high. This rules out the importance of an exclusively Northern Hemisphere summer insolation maximum in triggering the timing of these terminations and implicates obliquity as the major forcing parameter. Superimposed on the glacial-interglacial climate variability in our record we also recognise four interstadial periods during MIS 21. These millenial-scale events are in agreement with deep sea records distributed across the North Atlantic. The interstadials are recorded in both speleothem δ18O and δ13C proxies and are interpreted as reflective of a decrease in rainfall amount and temperature at the Corchia cave site probably as a response to precession

  19. Holocene multidecadal- to millennial-scale variations in Iceland-Scotland overflow and their relationship to climate

    NASA Astrophysics Data System (ADS)

    Mjell, Tor Lien; Ninnemann, Ulysses S.; Eldevik, Tor; Kleiven, Helga Kikki F.

    2015-05-01

    The Nordic Seas overflows are an important part of the Atlantic thermohaline circulation. While there is growing evidence that the overflow of dense water changed on orbital time scales during the Holocene, less is known about the variability on shorter time scales beyond the instrumental record. Here we reconstruct the relative changes in flow strength of Iceland-Scotland Overflow Water (ISOW), the eastern branch of the overflows, on multidecadal-millennial time scales. The reconstruction is based on mean sortable silt (SS>¯) from a sediment core on the Gardar Drift (60°19'N, 23°58'W, 2081 m). Our SS>¯ record reveals that the main variance in ISOW vigor occurred on millennial time scales (1-2 kyr) with particularly prominent fluctuations after 8 kyr. Superimposed on the millennial variability, there were multidecadal-centennial flow speed fluctuations during the early Holocene (10-9 kyr) and one prominent minimum at 0.9 kyr. We find a broad agreement between reconstructed ISOW and regional North Atlantic climate, where a strong (weak) ISOW is generally associated with warm (cold) climate. We further identify the possible contribution of anomalous heat and freshwater forcing, respectively, related to reconstructed overflow variability. We infer that ocean poleward heat transport can explain the relationship between regional climate and ISOW during the middle to late Holocene, whereas freshwater input provides a possible explanation for the reduced overflow during early Holocene (8-10 kyr).

  20. Millennial scale system impulse response of polar climates - deconvolution results between δ 18O records from Greenland and Antarctica

    NASA Astrophysics Data System (ADS)

    Reischmann, E.; Yang, X.; Rial, J. A.

    2013-12-01

    Deconvolution has long been used in science to recover real input given a system's impulse response and output. In this study, we applied spectral division deconvolution to select, polar, δ 18O time series to investigate the possible relationship between the climates of the Polar Regions, i.e. the equivalent to a climate system's ';impulse response.' While the records may be the result of nonlinear processes, deconvolution remains an appropriate tool because the two polar climates are synchronized, forming a Hilbert transform pair. In order to compare records, the age models of three Greenland and four Antarctica records have been matched via a Monte Carlo method using the methane-matched pair GRIP and BYRD as a basis for the calculations. For all twelve polar pairs, various deconvolution schemes (Wiener, Damped Least Squares, Tikhonov, Kalman filter) give consistent, quasi-periodic, impulse responses of the system. Multitaper analysis reveals strong, millennia scale, quasi-periodic oscillations in these system responses with a range of 2,500 to 1,000 years. These are not symmetric, as the transfer function from north to south differs from that of south to north. However, the difference is systematic and occurs in the predominant period of the deconvolved signals. Specifically, the north to south transfer function is generally of longer period than the south to north transfer function. High amplitude power peaks at 5.0ky to 1.7ky characterize the former, while the latter contains peaks at mostly short periods, with a range of 2.5ky to 1.0ky. Consistent with many observations, the deconvolved, quasi-periodic, transfer functions share the predominant periodicities found in the data, some of which are likely related to solar forcing (2.5-1.0ky), while some are probably indicative of the internal oscillations of the climate system (1.6-1.4ky). The approximately 1.5 ky transfer function may represent the internal periodicity of the system, perhaps even related to the

  1. 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

  2. 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.

  3. The role of atmosphere and ocean mechanisms in coupling millennial-scale climate variability between the hemispheres

    NASA Astrophysics Data System (ADS)

    Pedro, J. B.; Steig, E. J.; Ding, Q.; Bitz, C. M.

    2013-12-01

    Recent improvements in the dating of Antarctic and Greenland ice cores confirm an essentially synchronous onset of the Antarctic Cold Reversal (ACR) and Bølling-Allerød interstadial (DO1). Latest results also indicate zero phase lag through this period between Antarctic temperature and atmospheric CO2. Here we use these constraints and output from the first full transient general circulation model simulation of the last deglaciation (Community Climate System Model version 3; He et al, [2013]) to test existing hypotheses on the mechanisms of north-south climate coupling and CO2 ventilation from the deep Southern Ocean. The ocean bipolar seesaw hypothesis proposes that north-south coupling is explained by changes in the strength of northward heat transport in the Atlantic Ocean. An alternative (potentially complementary) mechanism suggests that the coupling results from atmospheric teleconnections in which temperature and sea ice changes in the North Atlantic force a shift in the position of the ITCZ, and in turn in the position and intensity of the southern hemisphere mid-latitude westerly winds. Both mechanisms can be linked to changes in atmospheric CO2 through their impacts on physical mixing and biogeochemical conditions in the Southern Ocean. The model run shows a two-stage response in southern high latitudes to the simulated DO1 warming. The first stage, lasting 200--300 years, sees an immediate northward shift in the ITCZ and a weakening of the westerlies. There is also an immediate increase in northward ocean heat transport, though this is confined to latitudes north of the Antarctic Circumpolar Current (ACC). The weaker westerlies would be expected to decrease wind-driven upwelling of warm circum-polar deep-waters, driving regional cooling. However strong cooling and expansion of Antarctic sea ice only begin in the second stage, which spans the next 300--400 years. During this interval the atmospheric fields return to their prior values. The increase in

  4. Episodic speleothem deposition tracks the terrestrial impact of millennial-scale last glacial climate variability in SW Ireland

    NASA Astrophysics Data System (ADS)

    Fankhauser, Adelheid; McDermott, Frank; Fleitmann, Dominik

    2016-11-01

    Eighty four new U-Th ages are presented for twenty randomly selected broken, displaced and reworked calcite speleothems retrieved from clastic sedimentary fill and from isolated bedding-plane shelves in Crag cave (SW Ireland). The dated pre-Holocene samples span much of the last glacial, ranging in age from 85.15 ± 0.60 to 23.45 ± 0.17 ka. Speleothem deposition requires the presence of liquid water, and because Crag cave is a shallow system, deposition is considered likely only when mean annual air temperatures (MAAT) exceed the freezing point of water. Deposition at this mid-latitude ocean-marginal site occurred episodically during MIS5a through to MIS2, synchronously within dating uncertainties, with the timing of Greenland Interstadials (GI). In the latter part of Marine Isotope Stage 3 (MIS3), deposition was particularly intense, consistent with regional scale climate amelioration inferred previously from radiocarbon ages for sparse MIS3 organic and freshwater surficial deposits in N. Ireland. A brief episode of speleothem deposition at c.23.40 ± 0.22 ka coincides with GI-2, demonstrating the sensitivity of the site to brief climate amelioration episodes in Greenland during MIS2. Conditions favourable for speleothem deposition occurred periodically during the last glacial, indicating temperature changes of at least 10 °C between stadials and interstadials at this mid-latitude site. Deposition ceased during Greenland Stadials (GS), including during periods of ice-rafting in the adjacent N. Atlantic Ocean (Heinrich events). Oxygen and carbon isotope ratios of the last glacial speleothems are generally elevated, reflecting non-equilibrium isotope fractionation effects. However, establishment of low δ13C values often occurred within a few decades of climate amelioration, indicating that biogenic CO2 production resumed rapidly at this site, particularly during MIS3. Speleothem δ18O variability was driven largely by long-term changes in the δ18O value of the

  5. Changes in U.S. Temperature Extremes under Increased CO2 in Millennial-scale Climate Simulations

    NASA Astrophysics Data System (ADS)

    Huang, W. K.; Stein, M.; Moyer, E. J.; Sun, S.; McInerney, D.

    2015-12-01

    Changes in extreme weather may produce some of the largest societal impacts from anthropogenic climate change: present-day weather damages are dominated by rare events that happen only every several decades or more. However, it is intrinsically difficult to estimate changes in those rare events from the short observational record. We therefore look for insight to climate models, where we can generate long simulations. In this work we use millennial runs from the Community Climate System Model version 3 (CCSM3) in equilibrated pre-industrial and future (700 and 1400 ppm CO2) conditions. We examine both how extremes change using 1000-year timeseries, and how well these changes can be estimated based on shorter pieces of these runs. We estimate changes to distributions of future annual temperature extremes (wintertime minima and summertime maxima) in the contiguous United States by fitting generalized extreme value (GEV) distributions using the block maxima approach. Our results show that the magnitude of summer warm extremes largely shifts in accordance with mean shifts in summertime temperatures, and their distribution does not otherwise change significantly. In contrast, winter cold extremes warm more than mean shifts in wintertime temperatures, with changes in spread and skewness at inland locations that lead to substantial changes in tail behavior. We then examine uncertainties that result from using shorter model runs. In principle, GEV modeling allows us to predict infrequent events using timeseries shorter than the recurrence frequency of those events. To investigate how well this approach works in practice, we estimate 20-, 50-, and 100-year extreme events, first in the full 1000-year model timeseries and then using segments of 20 and 50 years. We find that even with GEV modeling, timeseries that are of comparable length or shorter than the return period of interest can lead to very poor estimates. These results suggest caution when attempting to use short

  6. Changes in U.S. Temperature Extremes under Increased CO2 in Millennial-scale Climate Simulations

    NASA Astrophysics Data System (ADS)

    Horion, S.; Fensholt, R.; Verbesselt, J.; Tagesson, T.; Grogan, K.; Ehammer, A.; Tian, F.

    2014-12-01

    Changes in extreme weather may produce some of the largest societal impacts from anthropogenic climate change: present-day weather damages are dominated by rare events that happen only every several decades or more. However, it is intrinsically difficult to estimate changes in those rare events from the short observational record. We therefore look for insight to climate models, where we can generate long simulations. In this work we use millennial runs from the Community Climate System Model version 3 (CCSM3) in equilibrated pre-industrial and future (700 and 1400 ppm CO2) conditions. We examine both how extremes change using 1000-year timeseries, and how well these changes can be estimated based on shorter pieces of these runs. We estimate changes to distributions of future annual temperature extremes (wintertime minima and summertime maxima) in the contiguous United States by fitting generalized extreme value (GEV) distributions using the block maxima approach. Our results show that the magnitude of summer warm extremes largely shifts in accordance with mean shifts in summertime temperatures, and their distribution does not otherwise change significantly. In contrast, winter cold extremes warm more than mean shifts in wintertime temperatures, with changes in spread and skewness at inland locations that lead to substantial changes in tail behavior. We then examine uncertainties that result from using shorter model runs. In principle, GEV modeling allows us to predict infrequent events using timeseries shorter than the recurrence frequency of those events. To investigate how well this approach works in practice, we estimate 20-, 50-, and 100-year extreme events, first in the full 1000-year model timeseries and then using segments of 20 and 50 years. We find that even with GEV modeling, timeseries that are of comparable length or shorter than the return period of interest can lead to very poor estimates. These results suggest caution when attempting to use short

  7. North Atlantic millennial-scale climate variability 910 to 790 ka and the role of the equatorial insolation forcing

    NASA Astrophysics Data System (ADS)

    Ferretti, Patrizia; Crowhurst, Simon J.; Hall, Michael A.; Cacho, Isabel

    2010-04-01

    The Mid-Pleistocene transition (MPT) was the time when quasi-periodic (˜ 100 kyr), high-amplitude glacial variability developed in the absence of any significant change in the character of orbital forcing, leading to the establishment of the characteristic pattern of late Pleistocene climate variability. It has long been known that the interval around 900 ka stands out as a critical point of the MPT, when major glaciations started occurring most notably in the northern hemisphere. Here we examine the record of climatic conditions during this significant interval, using high-resolution stable isotope records from benthic and planktonic foraminifera from a sediment core in the North Atlantic (Integrated Ocean Drilling Program Expedition 306, Site U1313). We have considered the time interval from late in Marine Isotope Stage (MIS) 23 to MIS 20 (910 to 790 ka). Our data indicate that interglacial MIS 21 was a climatically unstable period and was broken into four interstadial periods, which have been identified and correlated across the North Atlantic region. These extra peaks tend to contradict previous studies that interpreted the MIS 21 variability as consisting essentially of a linear response to cyclical changes in orbital parameters. Cooling events in the surface record during MIS 21 were associated with low benthic carbon isotope excursions, suggesting a coupling between surface temperature changes and the strength of the Atlantic meridional overturning circulation. Time series analysis performed on the whole interval indicates that benthic and planktonic oxygen isotopes have significant concentrations of spectral power centered on periods of 10.7 kyr and 6 kyr, which is in agreement with the second and forth harmonic of precession. The excellent correspondence between the foraminifera δ18O records and insolation variations at the Equator in March and September suggests that a mechanism related to low-latitude precession variations, advected to the high

  8. Estimating changes in temperature extremes from millennial-scale climate simulations using generalized extreme value (GEV) distributions

    NASA Astrophysics Data System (ADS)

    Huang, Whitney K.; Stein, Michael L.; McInerney, David J.; Sun, Shanshan; Moyer, Elisabeth J.

    2016-07-01

    Changes in extreme weather may produce some of the largest societal impacts of anthropogenic climate change. However, it is intrinsically difficult to estimate changes in extreme events from the short observational record. In this work we use millennial runs from the Community Climate System Model version 3 (CCSM3) in equilibrated pre-industrial and possible future (700 and 1400 ppm CO2) conditions to examine both how extremes change in this model and how well these changes can be estimated as a function of run length. We estimate changes to distributions of future temperature extremes (annual minima and annual maxima) in the contiguous United States by fitting generalized extreme value (GEV) distributions. Using 1000-year pre-industrial and future time series, we show that warm extremes largely change in accordance with mean shifts in the distribution of summertime temperatures. Cold extremes warm more than mean shifts in the distribution of wintertime temperatures, but changes in GEV location parameters are generally well explained by the combination of mean shifts and reduced wintertime temperature variability. For cold extremes at inland locations, return levels at long recurrence intervals show additional effects related to changes in the spread and shape of GEV distributions. We then examine uncertainties that result from using shorter model runs. In theory, the GEV distribution can allow prediction of infrequent events using time series shorter than the recurrence interval of those events. To investigate how well this approach works in practice, we estimate 20-, 50-, and 100-year extreme events using segments of varying lengths. We find that even using GEV distributions, time series of comparable or shorter length than the return period of interest can lead to very poor estimates. These results suggest caution when attempting to use short observational time series or model runs to infer infrequent extremes.

  9. The greening of the McGill Paleoclimate Model. Part II: Simulation of Holocene millennial-scale natural climate changes

    NASA Astrophysics Data System (ADS)

    Wang, Yi; Mysak, Lawrence A.; Wang, Zhaomin; Brovkin, Victor

    2005-04-01

    Various proxy data reveal that in many regions of the Northern Hemisphere (NH), the middle Holocene (6 kyr BP) was warmer than the early Holocene (8 kyr BP) as well as the later Holocene, up to the end of the pre-industrial period (1800 AD). This pattern of warming and then cooling in the NH represents the response of the climate system to changes in orbital forcing, vegetation cover and the Laurentide Ice Sheet (LIS) during the Holocene. In an attempt to better understand these changes in the climate system, the McGill Paleoclimate Model (MPM) has been coupled to the dynamic global vegetation model known as VECODE (see Part I of this two-part paper), and a number of sensitivity experiments have been performed with the "green" MPM. The model results illustrate the following: (1) the orbital forcing together with the vegetation—albedo feedback result in the gradual cooling of global SAT from about 6 kyr BP to the end of the pre-industrial period; (2) the disappearance of the LIS over the period 8-6 kyr BP, associated with vegetation—albedo feedback, allows the global SAT to increase and reach its maximum at around 6 kyr BP; (3) the northern limit of the boreal forest moves northward during the period 8-6.4 kyr BP due to the LIS retreat; (4) during the period 6.4-0 kyr BP, the northern limit of the boreal forest moves southward about 120 km in response to the decreasing summer insolation in the NH; and (5) the desertification of northern Africa during the period 8-2.6 kyr BP is mainly explained by the decreasing summer monsoon precipitation.

  10. Sub-Millennial Scale Climatic and Hydrologic Variability in the Gulf of Mexico during the Early Holocene

    NASA Astrophysics Data System (ADS)

    Lodico, J. M.; Flower, B. P.; Quinn, T. M.

    2005-12-01

    Sediment core MD02-2550 from Orca Basin located in the northern Gulf of Mexico (GOM) provides a high-resolution early Holocene record of climatic and hydrologic changes from ~10.5 to 7 thousand calendar years before present (ka). Paired analyses of Mg/Ca and δ18O on the planktonic foraminifer Globigerinoides ruber (white variety, 250-355 μm) sampled at ~ 20 year resolution were used to generate proxy records of sea surface temperature (SST) and the δ18O of seawater in the GOM (δ18OGOM). The Mg/Ca-SST record contains an overall ~(~1.5 °C warming trend from 10.5 to 7 ka that appears to track the intensity of the annual insolation cycle and six temperature oscillations (~0.5-2 °C), the frequency of which are consistent with those found in records of solar variability. The δ18OGOM record contains five ~0.5 ‰ oscillations from 10.5 to 7 ka that bear some resemblance to regional hydrologic records from Haiti and the Cariaco Basin, plus a ~ -0.8 ‰ excursion that may be associated with the "8.2 ka event" recorded in Greenland air temperatures. The δ18OGOM record, if interpreted as a salinity proxy, suggest large salinity fluctuations (> 2 ‰) reflecting changes in evaporation-precipitation (E-P) and Mississippi River input to the GOM. Percent Globigerinoides sacculifer records from three cores in the GOM exhibit remarkably coherent changes, suggesting episodic centennial-scale incursions of Caribbean waters. Spectral analysis of the Mg/Ca-SST and the δ18OGOM time series indicate that surface water conditions may be influenced by solar variations because they share significant periods of variability with atmospheric Δ14C near 700, 200, and 80-70 years. Our results add to the growing body of evidence that the sub-tropics were characterized by significant decadal to centennial-scale climatic and hydrologic variability during the early Holocene.

  11. Reconstruction of Centennial and Millennial-scale Climate and Environmental Variability during the Holocene in the Central Canadian Arctic

    NASA Astrophysics Data System (ADS)

    Rolland, N.; Porinchu, D.; MacDonald, G.; Moser, K.

    2007-12-01

    The Arctic and sub-Arctic regions are experiencing dramatic changes in surface temperature, sea-ice extent, glacial melt, river discharge, soil carbon storage and snow cover. According to the IPCC high latitude regions are expected to warm between 4°C and 7°C over the next 100 years. The magnitude of warming and the rate at which it occurs will dwarf any previous warming episodes experienced by latitude regions over the last 11,000 years. It is critical that we improve our understanding of how the Arctic and sub-Arctic regions responded to past periods of warming, especially in light of the changes these regions will be experiencing over the next 100 years. One of the lines of evidence increasingly utilized in multi-proxy paleolimnological research is the Chironomidae (Insecta: Diptera). Also known as non-biting midge flies, chironomids are ubiquitous, frequently the most abundant insects found in freshwater ecosystems and very sensitive to environmental conditions. This research uses Chironomidae to quantitatively characterize climate and environmental conditions of the continental interior of Arctic Canada during the Holocene. Spanning four major vegetation zones (boreal forest, forest-tundra, birch tundra and herb tundra), the surface samples of 80 lakes recovered from the central Canadian Arctic were used to assess the relationship of 22 environmental variables with the chironomid distribution. Redundancy analysis (RDA) identified four variables, total Kjeldahl nitrogen (TKN), pH, summer surface water temperature (SSWT) and depth, which best explain the variance in the distribution of chironomids within these ecoregions. In order to provide new quantitative estimates of SSWT, a 1-component weighted average partial least square (WA-PLS) model was developed (r2jack = 0.76, RMSEP = 1.42°C) and applied downcore in two low arctic continental Nunavut lakes located approximately 50 km and 200 km north of modern treeline. This robust midge-inferred temperature

  12. The economics of abrupt climate change.

    PubMed

    Perrings, Charles

    2003-09-15

    The US National Research Council defines abrupt climate change as a change of state that is sufficiently rapid and sufficiently widespread in its effects that economies are unprepared or incapable of adapting. This may be too restrictive a definition, but abrupt climate change does have implications for the choice between the main response options: mitigation (which reduces the risks of climate change) and adaptation (which reduces the costs of climate change). The paper argues that by (i) increasing the costs of change and the potential growth of consumption, and (ii) reducing the time to change, abrupt climate change favours mitigation over adaptation. Furthermore, because the implications of change are fundamentally uncertain and potentially very high, it favours a precautionary approach in which mitigation buys time for learning. Adaptation-oriented decision tools, such as scenario planning, are inappropriate in these circumstances. Hence learning implies the use of probabilistic models that include socioeconomic feedbacks.

  13. Evidence for millennial-scale climatic events in the sedimentary infilling of a macrotidal estuarine system, the Seine estuary (NW France)

    NASA Astrophysics Data System (ADS)

    Sorrel, Philippe; Tessier, Bernadette; Demory, François; Delsinne, Nicolas; Mouazé, Dominique

    2009-03-01

    (MWP). In contrast, increased removal and transport of estuarine sediments occur when winter storm activity greatly intensified over northwestern France. We report four prominent centennial-scale periods of stronger storminess, occurring with a pacing of ˜1500 years, which are likely to be related to the last four Bond's Holocene cold events. Our results documenting a close link between coastal sedimentary dynamics, millennial-scale variations in Holocene climate and North Atlantic atmospheric circulation are fairly consistent with other records from Scandinavia, central Greenland and southern Europe.

  14. Centennial-millennial scale variations in Western Antarctic Ice Sheet discharge and their relationship to climate and ocean changes during the late Holocene

    NASA Astrophysics Data System (ADS)

    Snilstveit Hoem, Frida; Ninnemann, Ulysses S.; Kleiven, Helga (Kikki) F.; Irvali, Nil

    2017-04-01

    period of generally low IRD, coincides with Little Ice Age at 600 cal yr B.P. The local surface water hydrography appears relatively stable over the past 4000 years with the planktonic δ18O signal indicating centennial-millennial scale changes of typically ≤1˚ C (Δ0.22) and notably smaller in amplitude than the regional warming observed over the past century. The lack of correlation between surface water physical properties and IRD in the downcore records, suggests that IRD is not reflecting iceberg survival but rather changes in the supply (WAIS dynamics) or routing. Consistent with this interpretation, IRD covaries with climate on the Antarctic Peninsula (from JRI ice core) over the past 4 kyr with cooler conditions and lower amounts of IRD over much of the past two millennia than occurred earlier in the neoglaciation. Both records indicate a recovery with warming and increased IRD prior to industrialization. This relationship is consistent with the hypothesis that climate and specifically ocean temperatures were important for modulating WAIS discharge rates over the past few millennia.

  15. 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.

  16. 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.

  17. 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

  18. Millennial Scale Variability in Tropical South American Vegetation During the Last Glaciation

    NASA Astrophysics Data System (ADS)

    Hughen, K.; Drenzek, N.; Eglinton, T.; Bice, M.

    2005-12-01

    Millennial scale climate variability mirroring the Dansgaard-Oeschger events in Greenland ice cores has been recorded at locations around the globe. The forcing mechanisms responsible for these abrupt changes are hypothesized to originate at either high or low latitudes, but no evidence has yet confirmed either location. Detailed records of past shifts in the tropical hydrological cycle are needed to evaluate its potential role in causing abrupt global climate changes. The Cariaco Basin, off northern Venezuela, is situated along the northern margin of the seasonal range of the InterTropical Convergence Zone. Previously, vascular plant biomarkers have shown abrupt changes in terrestrial vegetation over northern South America, concurrent with rapid climate shifts of the last deglaciation. Carbon isotopes from long-chain n-alkanoic acids, a proxy for C3 versus C4 metabolic pathways, indicate that C3 plants predominated in the Cariaco watershed during warm/wet Bolling-Allerod and Holocene periods, and C4 plant biomass proliferated during cool/dry late Glacial and Younger Dryas intervals. The leaf wax data reveal that local vegetation biomass, although not necessarily entire biomes, shifted between arid grassland and wetter forest taxa on timescales of decades. Here we present new data from sediments of ODP Site 1002D in the Cariaco Basin that provide a record of terrestrial vegetation change and ITCZ variability over the past 60,000 years. Compound-specific carbon isotopes were measured on leaf waxes at about 500 year intervals, resolving millennial scale changes during Marine Isotope Stage 3. The complete record shows distinct isotopic shifts concurrent with D-O and Heinrich events in the high latitude N. Atlantic region. During D-O stadials and particularly Heinrich events, isotope ratios shift to enriched values, indicating increased C4 plant biomass and more arid conditions. The largest anomalies are seen during Heinrich events H0-H6, with isotopic shifts of up to

  19. 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

  20. 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.

  1. 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.

  2. Millennial-Scale Climate Variability during the Last 28 cal. ka BP in the Tyrrhenian Sea (central Sector of Mediterranean Sea)

    NASA Astrophysics Data System (ADS)

    Amore, F. Ornella; Palumbo, Eliana; Elderfield, Henry; Perugia, Carmen; Emanuele, Dario; Petrillo, Zaccaria

    2014-05-01

    High resolution reconstructions of coccolithophore assemblages and plankton carbon and oxygen stable isotope data from Ocean Drilling Project (ODP) Hole 974D have been studied to investigate climate variability in the Tyrrhenian Sea (Western Mediterranean) during the last 28 cal. ka BP. The main climatic signal is showed by coccolithophore assemblages and isotopic records at glacial/interglacial timescale. Through the application of statistical analyses, a possible role of half and fourth precession cycles was hypothesised, more likely linked to the influence of the Equator insolation on central sector of Western Mediterranean circulation. The occurrence of abrupt coolings, more likely connected to Northern Hemisphere global climatic changes, was hypothesised also in the Tyrrhenian Sea during the Last Glacial (LG) and the Holocene, highlighted by the occurrence of the subpolar species Coccolithus pelagicus pelagicus. The events of the LG occurred in correspondence of the Dansgaard/Oeschger (D/O) stadial at 28 cal. ka BP and Heinrich event 2. The Holocene events were quite synchronous with several Bond Cycles and Rapid Climate Changes. In addition, marine warm phases, coincident with the D/O interstadial 2 and the Bølling-Allerød interval, were recognised at ODP Hole 974D by increases of warm species. Furthermore, during the Younger Dryas, oxygen stable isotope record indicates the occurrence of a cooling while coccolithophore assemblages testify increased nutrient conditions, highlighted by the group of small Gephyrocapsa. During the transition to the Holocene a latitudinal warming was observed, through the comparison of available data from coccolithophore assemblages of other sites of the Tyrrhenian Sea (Sbaffi et al., 2001; Buccheri et al., 2002; Amore et al., 2004). The latitudinal warming moved northward versus the central part of the basin, reaching the maximum amplitude in correspondence of Tyrrhenian Holocene Climatic Optimum (Buccheri et al., 2002). Other

  3. Evidence for millennial-scale climate change during marine isotope stages 2 and 3 at Little Lake, Western Oregon, U.S.A.

    USGS Publications Warehouse

    Grigg, L.D.; Whitlock, C.; Dean, W.E.

    2001-01-01

    Pollen and geochemical data from Little Lake, western Oregon, suggest several patterns of millennial-scale environmental change during marine isotope stage (MIS) 2 (14,100-27,600 cal yr B.P.) and the latter part of MIS 3 (27,600-42,500 cal yr B.P.). During MIS 3, a series of transitions between warm- and cold-adapted taxa indicate that temperatures oscillated by ca. 2??-4??C every 1000-3000 yr. Highs and lows in summer insolation during MIS 3 are generally associated with the warmest and coldest intervals. Warm periods at Little Lake correlate with warm sea-surface temperatures in the Santa Barbara Basin. Changes in the strength of the subtropical high and the jet stream may account for synchronous changes at the two sites. During MIS 2, shifts between mesic and xeric subalpine forests suggest changes in precipitation every 1000-3000 yr. Increases in Tsuga heterophylla pollen at 25,000 and 22,000 cal yr B.P. imply brief warmings. Minimum summer insolation and maximum global ice-volumes during MIS 2 correspond to cold and dry conditions. Fluctuations in precipitation at Little Lake do not correlate with changes in the Santa Barbara Basin and may be explained by variations in the strength of the glacial anticyclone and the position of the jet stream. ?? 2001 University of Washington.

  4. 800,000 years of abrupt climate variability.

    PubMed

    Barker, Stephen; Knorr, Gregor; Edwards, R Lawrence; Parrenin, Frédéric; Putnam, Aaron E; Skinner, Luke C; Wolff, Eric; Ziegler, Martin

    2011-10-21

    We constructed an 800,000-year synthetic record of Greenland climate variability based on the thermal bipolar seesaw model. Our Greenland analog reproduces much of the variability seen in the Greenland ice cores over the past 100,000 years. The synthetic record shows strong similarity with the absolutely dated speleothem record from China, allowing us to place ice core records within an absolute timeframe for the past 400,000 years. Hence, it provides both a stratigraphic reference and a conceptual basis for assessing the long-term evolution of millennial-scale variability and its potential role in climate change at longer time scales. Indeed, we provide evidence for a ubiquitous association between bipolar seesaw oscillations and glacial terminations throughout the Middle to Late Pleistocene.

  5. A 50,000-year climatic record from the new coastal TALDICE ice core: consequences on millennial-scale variability features through the Antarctic continent

    NASA Astrophysics Data System (ADS)

    Buiron, Daphné; Stenni, Barbara; Frezzoti, Massimo; Chappellaz, Jerome; Lemieux, Benedicte; Masson-Delmotte, Valérie; Schilt, Adrian

    2010-05-01

    The TALDICE project retrieved a new ice core from a peripheral dome of East Antarctica. Talos Dome (72° 49' S, 159° 11' E; 2315 m; mean accumulation rate 80 kg m-2 yr-1; mean annual temp. -41°C) is located in the Northern Victoria Land, close to the Ross Sea. Back-trajectory analyses suggest that the site is mostly fed by air masses arriving both from the Pacific (and Ross Sea) and Indian Ocean sectors. The drilling team reached the depth of 1619.2 m in December 2007, covering more than 300,000 years of climatic records according to a preliminary age scale. Up to 50,000 years before present, the ice core dating is based on the use of a glaciological model and an inverse method, constrained by numerous and reliable age markers. They are defined from the synchronization of CH4 records of Talos Dome and Greenland ice cores, using in particular the rapid CH4 changes associated with the last termination and the D/O events. Measurements of the CH4 mixing ratio have been performed by LGGE and Bern laboratories using slightly different techniques, with a depth resolution ranging between 0.5 to 4 m. The comparison of water isotopic profiles from Talos Dome, EDC, EDML (Antarctica) and North-GRIP (Greenland) ice cores, once put on a common time scale deduced from CH4 and the optimisation from the inverse method, reveals that during the last deglaciation and the last glacial period, climatic changes at Talos Dome were essentially in phase with the Antarctic plateau, extending the bipolar seesaw sequence to this coastal site. This comparison also highlights different climatic behaviors between sites situated in the Indo/Pacific sector and in the Atlantic sector of the Southern Ocean, the latter showing more abrupt swings toward relatively warm conditions of the Antarctic Isotope Maxima. We will discuss this feature with respect to the bipolar seesaw model of Stocker (2003) and with respect to other climatic proxies.

  6. Abrupt North Atlantic circulation changes in response to gradual CO2 forcing in a glacial climate state

    NASA Astrophysics Data System (ADS)

    Zhang, Xu; Knorr, Gregor; Lohmann, Gerrit; Barker, Stephen

    2017-07-01

    Glacial climate is marked by abrupt, millennial-scale climate changes known as Dansgaard-Oeschger cycles. The most pronounced stadial coolings, Heinrich events, are associated with massive iceberg discharges to the North Atlantic. These events have been linked to variations in the strength of the Atlantic meridional overturning circulation. However, the factors that lead to abrupt transitions between strong and weak circulation regimes remain unclear. Here we show that, in a fully coupled atmosphere-ocean model, gradual changes in atmospheric CO2 concentrations can trigger abrupt climate changes, associated with a regime of bi-stability of the Atlantic meridional overturning circulation under intermediate glacial conditions. We find that changes in atmospheric CO2 concentrations alter the transport of atmospheric moisture across Central America, which modulates the freshwater budget of the North Atlantic and hence deep-water formation. In our simulations, a change in atmospheric CO2 levels of about 15 ppmv--comparable to variations during Dansgaard-Oeschger cycles containing Heinrich events--is sufficient to cause transitions between a weak stadial and a strong interstadial circulation mode. Because changes in the Atlantic meridional overturning circulation are thought to alter atmospheric CO2 levels, we infer that atmospheric CO2 may serve as a negative feedback to transitions between strong and weak circulation modes.

  7. 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.

  8. Millennial-scale fluctuations of the European Ice Sheet at the end of the last glacial, and their potential impact on global climate

    NASA Astrophysics Data System (ADS)

    Toucanne, Samuel; Soulet, Guillaume; Freslon, Nicolas; Silva Jacinto, Ricardo; Dennielou, Bernard; Zaragosi, Sébastien; Eynaud, Frédérique; Bourillet, Jean-François; Bayon, Germain

    2015-09-01

    Reconstructing Northern Hemisphere ice-sheet oscillations and meltwater routing to the ocean is important to better understand the mechanisms behind abrupt climate changes. To date, research efforts have mainly focused on the North American (Laurentide) ice-sheets (LIS), leaving the potential role of the European Ice Sheet (EIS), and of the Scandinavian ice-sheet (SIS) in particular, largely unexplored. Using neodymium isotopes in detrital sediments deposited off the Channel River, we provide a continuous and well-dated record for the evolution of the EIS southern margin through the end of the last glacial period and during the deglaciation. Our results reveal that the evolution of EIS margins was accompanied with substantial ice recession (especially of the SIS) and simultaneous release of meltwater to the North Atlantic. These events occurred both in the course of the EIS to its LGM position (i.e., during Heinrich Stadial -HS- 3 and HS2; ∼31-29 ka and ∼26-23 ka, respectively) and during the deglaciation (i.e., at ∼22 ka, ∼20-19 ka and from 18.2 ± 0.2 to 16.7 ± 0.2 ka that corresponds to the first part of HS1). The deglaciation was discontinuous in character, and similar in timing to that of the southern LIS margin, with moderate ice-sheet retreat (from 22.5 ± 0.2 ka in the Baltic lowlands) as soon as the northern summer insolation increase (from ∼23 ka) and an acceleration of the margin retreat thereafter (from ∼20 ka). Importantly, our results show that EIS retreat events and release of meltwater to the North Atlantic during the deglaciation coincide with AMOC destabilisation and interhemispheric climate changes. They thus suggest that the EIS, together with the LIS, could have played a critical role in the climatic reorganization that accompanied the last deglaciation. Finally, our data suggest that meltwater discharges to the North Atlantic produced by large-scale recession of continental parts of Northern Hemisphere ice sheets during HS, could

  9. 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.

  10. 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

  11. 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

  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. Assessing the persistence of millennial-scale oscillations during the penultimate glacial phase in southern Europe

    NASA Astrophysics Data System (ADS)

    Wilson, Graham; Frogley, Mick; Jones, Tim; Leng, Melanie

    2016-04-01

    There is growing evidence that millennial-scale climate oscillations are a pervasive feature of glacial intervals. During the last glaciation (Marine Isotope Stage (MIS) 2-4), incursions of cold water into the North Atlantic appeared to coincide with abrupt reductions in southern European tree populations (Tzedakis et al., 2004: Geology 32, 109-112), suggesting down-stream impacts on continental temperature and hydroclimate. Ice-rafting into the North Atlantic during the penultimate glacial (MIS 6) is thought to be less extensive than at times during MIS 2-4, perhaps resulting in more subdued climate oscillations. Published pollen data from Lake Ioannina core I-284 (Epirus, NW Greece) suggest pronounced oscillations in tree population extent during early MIS 6 (185-155 ka), followed by much-reduced tree populations and subdued oscillations throughout late MIS 6 (155-135 ka) (Roucoux et al., 2011: Journal of Quaternary Science 26, 616-626). Previous studies of the diatom and isotope records from the MIS 7/6, 6/5e and 2/1 transitions, and from MIS 5e and 1 in Lake Ioannina core I-284 demonstrate the sensitivity of these proxies to changes in regional climate. Here we apply a combined diatom and stable isotope (carbon and oxygen) approach to evaluate the influence of millennial-scale oscillations on southern Europe hydroclimate during MIS 6. The new isotope data from Lake Ioannina core I-284 demonstrates higher precipitation / evaporation (P/E) ratios between c. 178 and 164 ka, associated with peak insolation during MIS 6e, and episodes of planktonic diatom expansion likely reflecting the interstadials of the 6e complex. Close correspondence between diatom planktonic frequencies, arboreal pollen and regional sea-surface temperatures together provide strong evidence for millennial-scale oscillations in regional precipitation at times during the early‒mid MIS 6. The isotope data suggest overall cooler and drier conditions during the mid-late MIS 6, consistent with

  14. Centennial- to millennial-scale climate oscillations in the Central-Eastern Mediterranean Sea between 20,000 and 70,000 years ago: evidence from a high-resolution geochemical and micropaleontological record

    NASA Astrophysics Data System (ADS)

    Sprovieri, Mario; Di Stefano, Enrico; Incarbona, Alessandro; Salvagio Manta, Daniela; Pelosi, Nicola; Ribera d'Alcalà, Maurizio; Sprovieri, Rodolfo

    2012-07-01

    Here we present a high-resolution faunal, floral and geochemical (stable isotopes and trace elements) record from the sediments of Ocean Drilling Program Site 963 (central Mediterranean basin), which shows centennial/millennial-scale resemblance to the high-northern latitude rapid temperature fluctuations documented in the Greenland ice cores between 20 and 70 kyr BP. Oxygen and carbon isotopes, planktic foraminifera and calcareous nannofossil distributions suggest that Dansgaard-Oeschger (D/O) and Heinrich events (HE) are distinctly expressed in the Mediterranean climate record. Moreover, recurrent though subdued oscillations not previously identified in the Lateglacial Mediterranean sediments document a significant centennial-scale climate variability in the basin that is greater than previously thought. Alternations between climate regimes dominated by polar outbreaks during D/O stadials and warm D/O interstadials, with associated intensification of continental runoff, are well expressed in the ODP Site 963. These place the Mediterranean basin as an often overlooked recorder of the interplay between large- and regional- scale climate controls at intermediate latitudes, and of the possible interactions between different components of the climate system. Significant changes in Ba/Ca values measured in Globigerinoides ruber shells from a number of D/O stadials and interstadials suggest enhanced freshwater input from the north-eastern Mediterranean borderland during the D/O interstadials. However, the short duration of 3D stratification events never led to complete oxygen consumption along the water column, but clear effects of sluggish 3D circulation in the basin are testified to by negative excursions in δ13C measured in selected species of planktic and benthic foraminifera. HEs are constantly associated with lightening in the δ18O record of planktic foraminifera, possibly because of the impact of iceberg melting in the Iberian Margin on Mediterranean

  15. 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.

  16. 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.

  17. 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.

  18. Who is in the Driver's Seat? Millennial-Scale Records of Wildfire in the Western USA Reveal a Complex Interplay of Climate, Fire, and Vegetation

    NASA Astrophysics Data System (ADS)

    Pierce, J. L.; Meyer, G. A.; Bigio, E.; Nelson, N.; Poulos, M. J.; Jenkins, S.; Riley, K. E.; Weppner, K.; Svenson, L.; Fitch, E. P.; Frechette, J.

    2015-12-01

    A new synthesis of 10 study areas and >480 14C dates of Holocene fire and erosional response are recorded in alluvial fan sediments of the interior western US. Chronologies are from high elevation mixed conifer forests in the N. Rockies, ponderosa and Douglas-fir forests in the N. Rockies and SW, and low elevation sagebrush steppe and piñon-juniper woodlands near the Snake River Plain. Results are as follows: 1) Late Holocene arrivals of ponderosa, lodgepole and piñon pine at Northern Rockies sites correspond with increased fire severity, linking vegetation and fire regime changes. 2) Deposit types vary with environment; sheetfloods are more common in sparsely vegetated sites and in drier Holocene periods with open forests, whereas dense forests and infrequent severe fires often produce debris flows. 3) Climate variability drives ponderosa pine and Douglas-fir forests in both the SW and N. Rockies to burn 'at both ends of the spectrum', where frequent low-severity fires are typical, but higher-severity fires burn during severe droughts following fuel buildup over wet decades. 4) Fires in dry sage steppe are generally fuel-limited, but burn during prolonged wet and variable climates; grazing, land-use, and invasive species, particularly influence modern fires. 5) At moist high-elevation lodgepole and mixed conifer sites in Yellowstone and central Idaho, episodic large debris flows indicate high severity burns, often during severe multidecadal droughts. 6) Regionally coherent peaks exist ca. 200, 500, 900, 1700 and 2600 cal yr BP, but fire activity is not generally synchronous among sites. Differences in climate among sites likely account for some asynchroneity. 7) Recent severe fires have burned in 8 of 10 sites described; erosional response appears particularly anomalous in the SW, where impacts of fire suppression and land use are greatest. Widespread and severe modern fires may herald the arrival of a no-analog era of fire in the western US.

  19. Modeling dust emission response to North Atlantic millennial-scale climate variations from the perspective of East European MIS 3 loess deposits

    NASA Astrophysics Data System (ADS)

    Sima, A.; Kageyama, M.; Rousseau, D.-D.; Ramstein, G.; Balkanski, Y.; Antoine, P.; Hatté, C.

    2013-07-01

    European loess sequences of the Marine Isotope Stage 3 (~60-25 kyr BP) show periods of strong dust accumulation alternating with episodes of reduced sedimentation, favoring soil development. In the western part of the loess belt centered around 50° N, these variations appear to have been related to the North Atlantic rapid climate changes: the Dansgaard-Oeschger (DO) and Heinrich (H) events. It has been recently suggested that the North Atlantic climate signal can be detected further east, in loess deposits from Stayky (50°05.65' N, 30°53.92' E), Ukraine. Here we use climate and dust emission modeling to investigate this data interpretation. We focus on the areas north and northeast of the Carpathians, where loess deposits can be found, and the corresponding main dust sources must have been located as well. The simulations were performed with the LMDZ atmospheric general circulation model and the ORCHIDEE land surface model. They represent a reference "Greenland stadial" state and two perturbations, seen as sensitivity tests with respect to changes in the North Atlantic surface conditions between 30° and 63° N: a "Greenland interstadial" and an "H event". The main source for the loess deposits in the studied area is identified as a dust deflation band, with two very active spots located west-northwest from our reference site. Emissions only occur between February and June. Differences from one deflation spot to another, and from one climate state to another, are explained by analyzing the relevant meteorological and surface variables. Over most of the source region, the annual emission fluxes in the "interstadial" experiment are 30 to 50% lower than the "stadial" values; they would only be about 20% lower if the inhibition of dust uplift by the vegetation were not taken into account. Assuming that lower emissions result in reduced dust deposition leads us to the conclusion that the loess-paleosol stratigraphic succession in the Stayky area reflects indeed

  20. Millennial-scale climate variations in western Mediterranean during late Pleistocene-early Holocene: multi-proxy analyses from Padul peatbog (southern Iberian Peninsula)

    NASA Astrophysics Data System (ADS)

    Camuera, Jon; Jiménez-Moreno, Gonzalo; José Ramos-Román, María; García-Alix, Antonio; Jiménez-Espejo, Francisco; Toney, Jaime L.; Anderson, R. Scott; Kaufman, Darrell; Bright, Jordon; Sachse, Dirk

    2017-04-01

    Padul peatbog, located in southern Iberian Peninsula (western Mediterranean region) is a unique area for palaeoenvironmental studies due to its location, between arid and temperate climates. Previous studies showed that the Padul peatbog contains a continuous record of the last ca. 0.8-1 Ma, so it is an extraordinary site to identify glacial-interglacial phases as well as Heinrich and D-O events, linked to orbital- and suborbital-scale variations. In 2015, a new 42 m long core was taken from this area, providing an excellent sediment record probably for the last ca. 300,000 years. This study is focused on the paleoenvironmental and climatic reconstruction of the late Pleistocene and the early Holocene (ca. from 50,000 to 9,500 cal. yrs BP), using AMS 14C and AAR dating, high-resolution pollen analysis, lithology, continuous XRF-scanning, X-ray diffraction, magnetic susceptibility and organic geochemistry. These different proxies provide information not only about the regional environment change but also about local changes in the conditions of the Padul lake/peatbog due to variations in water temperature, pH or nutrients.

  1. Centennial- to millennial-scale climate oscillations in the Central-Eastern Mediterranean between 20,000 and 70,000 years ago: evidence from a high-resolution geochemical and micropaleontological record

    NASA Astrophysics Data System (ADS)

    Sprovieri, M.; di Stefano, E.; Incarbona, A.; Iudicone, D.; Pelosi, N.; Ribera D'Alcalà, M.; Sprovieri, R.

    2009-04-01

    Here we present a high-resolution faunal, floral and stable isotope record, from the sediments of ODP Site 963A (central Mediterranean basin), that evidence striking centennial/millennial-scale resemblance to the high-northern latitudes rapid temperature fluctuations documented in the Greenland ice cores. Oxygen and carbon isotopes, planktonic foraminifers and calcareous nannofossil distributions suggest that Dansgaard-Oeschger (D/O) and Heinrich events (HE) are distinctly expressed in the Mediterranean climate record. Moreover, recurrent although subdued oscillations not resolved before in the Late Glacial Mediterranean sediments among the well-known D/O events, document a relevant centennial-scale climate variability of the basin, higher than that generally thought. Alternations between climate regimes dominated by polar outbreaks during D/O stadials and seasonal northward displacement of the Intertropical Convergence Zone (ITCZ) during the D/O interstadials, with associated intensification of continental runoff and relevant changes in the evaporation/precipitation budgets of the Eastern Mediterranean basin, are well expressed in the ODP Site 963A and confirm the role of the Mediterranean basin as reliable recorder of the interplay between high-latitude and tropical climate control on the intermediate latitudes. The D/O interstadials warmer/humid phases induced short-term stratification of the water column, with associated relative declining of surface productivity. Though the relative short duration of the 3D stratification events never reached the threshold of complete oxygen consumption along the water column, evident effects of sluggish 3D circulation in the basin are clearly testified by negative excursions in the 13C values measured on selected species of planktonic and benthic foraminifers HEs are constantly associated to lighter 18O in planktonic foraminifera, suggesting an impact of the fresher Atlantic waters on the isotopic composition of

  2. Abrupt climate change around 4 ka BP: Role of the Thermohaline circulation as indicated by a GCM experiment

    NASA Astrophysics Data System (ADS)

    Wang, Shaowu; Zhou, Tianjun; Cai, Jingning; Zhu, Jinhong; Xie, Zhihui; Gong, Daoyi

    2004-04-01

    A great deal of palaeoenvironmental and palaeoclimatic evidence suggests that a predominant temperature drop and an aridification occurred at ca. 4.0 ka BP. Palaeoclimate studies in China support this dedution. The collapse of ancient civilizations at ca. 4.0 ka BP in the Nile Valley and Mesopotamia has been attributed to climate-induced aridification. A widespread alternation of the ancient cultures was also found in China at ca. 4.0 ka BP in concert with the collapse of the civilizations in the Old World. Palaeoclimatic studies indicate that the abrupt climate change at 4.0 ka BP is one of the realizations of the cold phase in millennial scale climate oscillations, which may be related to the modulation of the Thermohaline Circulation (THC) over the Atlantic Ocean. Therefore, this study conducts a numerical experiment of a GCM with SST forcing to simulate the impact of the weakening of the THC. Results show a drop in temperature from North Europe, the northern middle East Asia, and northern East Asia and a significant reduction of precipitation in East Africa, the Middle East, the Indian Peninsula, and the Yellow River Valley. This seems to support the idea that coldness and aridification at ca. 4.0 ka BP was caused by the weakening of the THC.

  3. Response of the Nile and its catchment to millennial-scale climatic change since the LGM from Sr isotopes and major elements of East Mediterranean sediments

    NASA Astrophysics Data System (ADS)

    Box, M. R.; Krom, M. D.; Cliff, R. A.; Bar-Matthews, M.; Almogi-Labin, A.; Ayalon, A.; Paterne, M.

    2011-02-01

    Changes in 87Sr/ 86Sr and major element geochemistry, from two sediment cores (9509 and 9501) in the Eastern Mediterranean (EM), were used to resolve changes in sediment provenance and, hence, determine climate changes in the Nile catchment and Eastern Sahara desert over the past 25 ka. The sediment was described by a three end-member system comprising Blue Nile (BN; 87Sr/ 86Sr = 0.7506; Sr = 210 ppm), White Nile (WN; 87Sr/ 86Sr = 0.7094; Sr = 72.5 ppm) and Saharan dust (SD; 87Sr/ 86Sr = 0.7183; Sr = 99 ppm). The sedimentary record of these cores represents the suspended load carried down the Nile river and discharged into the S.E. Levantine basin and thus records palaeoclimatically controlled changes in erosion and transport in the catchment. During arid periods (0-5 ka BP) and prior to 11 ka BP, fluxes of BN sediment at 9509 (˜6 g/cm 2/yr & 10-12 g/cm 2/yr, respectively) were greater than during the peak of the African Humid Period (AHP) from 5 to 11 ka BP (<2 g/cm 2/yr); this latter period witnessed the deposition of the youngest organic-rich sediment, termed sapropel (S-1), in the EM basin. By contrast the flux of WN increased during the AHP from ˜5 g/cm 2/yr at ˜13 ka BP to >15 g/cm 2/yr. In the Ethiopian Highlands (BN catchment) increases in the amount and duration of the monsoon during the AHP caused more vegetation to grow resulting in less soil erosion. In the WN catchment increased rainfall caused more catchment erosion and higher sediment flux through the Sudd marshes. The sedimentation rate in core 9509 increased during the AHP because of the greater importance of the WN sediment flux relative to the BN sediment flux. Saharan dust flux also decreased during the AHP reaching a minimum at ˜6 ka BP (core 9509) due to 'greening' of the Sahara desert. At the onset of S-1, the changes in Nile flow as determined by 87Sr/ 86Sr and climatic changes in the EM basin determined by δ 18O of planktonic foraminifera were simultaneous, confirming that such

  4. 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.

  5. 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

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

    PubMed Central

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

    2014-01-01

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

  7. Millennial Scale Cycles from Speleothems of the Gibraltar Caves

    NASA Astrophysics Data System (ADS)

    Boyd, Meighan; Mattey, Dave; Atkinson, Tim; Hoffmann, Dirk

    2016-04-01

    The Rock of Gibraltar contains many solution caves which initially formed near sea level and now span elevations to over 300m as a result of slow uplift over time. In the modern climate, Gibraltar holds an important position near the southern limit of the tracks taken by the depressions that deliver rainfall to Europe from the North Atlantic sector of the atmosphere. Monitoring in St. Michaels and Ragged Staff caves has been carried out since 2004 by monthly sampling and deployment of logging instruments which reveals that speleothem growth is most strongly influenced by seasonally reversing cave ventilation that permeates the entire rock. The results provide unprecedented insight into how cave environments respond to seasonal change, variations in sea level and neotectonic uplift and the ways that regional climate is recorded as chemical proxies in an evolving cave environment. We present an overview of the results of this proxy record of precipitation, sea level and environmental change, including new analysis within this 500ka record. A general mean isotopic composition of 1ka time slices have been stacked into a preliminary record from over twenty speleothems. Within this we look at higher resolution time slices to examine the occurrence of millennial scale cycles which occur within the Gibraltar record. During glacial maxima, the Gibraltar record shows elevated δ18O and associated higher δ13C caused by greater degassing or lower soil pCO2 from weakened vegetative activity during cool arid glacials. Highly resolved millennial scale warming events which seem to match the Greenland ice core record give insights into SST changes and atmospheric reorganization at Gibraltar.

  8. 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.

  9. 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.

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

    PubMed Central

    Marotzke, Jochem

    2000-01-01

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

  11. 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.

  12. Millennial-scale Asian summer monsoon variations in South China since the last deglaciation

    NASA Astrophysics Data System (ADS)

    Wang, Xisheng; Chu, Guoqiang; Sheng, Mei; Zhang, Shuqin; Li, Jinhua; Chen, Yun; Tang, Ling; Su, Youliang; Pei, Junling; Yang, Zhenyu

    2016-10-01

    Characterizing spatiotemporal variability of the Asian summer monsoon (ASM) is critical for full understanding of its behavior, dynamics, and future impacts. The present knowledge about ASM variations since the last glaciation in South China largely relies on several precisely-dated speleothem stable oxygen isotope (δ18 O) records. Although these speleothem δ18 O signals provide useful evidence for regional past environmental changes, their validity for denoting ASM intensity remains a great controversy. The Huguangyan Maar Lake (HML) provides one of the most complete archives of environmental and climatic changes in the tropical-subtropical South and East Asia since the last glaciation. Here we document a continuous centennial- to millennial-scale ASM record over the past 16 ky BP from the high-sedimentation-rate HML sediments. In contrast with the low-amplitude variations of Chinese speleothem-derived δ18 O signals and the Chinese loess-based monsoon precipitation proxy indexes, our multi-proxy records reveal a pattern of high-amplitude regional climatic fluctuations, including fine-scale oscillations during the Bølling-Allerød warming, the 8.2 ka cooling event, and an abrupt climate shift from 6.5-5.9 ka. The existence of Bond-like cold/dry events indicates a distinct influence of the North Atlantic circulation on low-latitude monsoon changes. The broad comparability between the HML paleo-proxies, Chinese speleothem δ18 O records, and the northern hemisphere summer insolation throughout the Holocene, suggests that solar insolation exerts a profound influence on ASM changes. These findings reinforce a model of combined insolation and glacial forcing of the ASM.

  13. New insights on the anatomy of abrupt climate changes based on high-resolution ice core records from NorthGRIP (Greenland)

    NASA Astrophysics Data System (ADS)

    Capron, E.; Rasmussen, S.; Popp, T. J.; Vaughn, B. H.; Gkinis, V.; Erhardt, T.; Fischer, H.; Blunier, T.; Landais, A.; Pedro, J. B.; Steffensen, J. P.; Svensson, A.; Vinther, B.

    2016-12-01

    The millennial-scale succession of Greenland Stadials (GS) and Greenland Interstadials (GI) illustrates the Greenland expression of the well-known sequence of Dansgaard-Oeschger (DO) events, within which we observe additional climate variations of decadal to centennial-scale duration. Various paradigms, mostly based on interactions between the cryosphere and the ocean, have been proposed to explain the existence and evolution of DO events. Annual to decadal scale records of environmental and climatic regional changes over the rapid transitions are needed to assess whether climate model outputs based on a particular mechanism are consistent with the observed spatial pattern and temporal phasing. Here we present new multiannual resolution stable water isotope measurements (ice δ18O and δD) and annually resolved ion chemistry records from the NorthGRIP ice core. Because these tracers imprint the signatures of different parts of the Northern Hemisphere climate system, we can map the anatomy - the spatial and temporal signature of climate and environmental changes - associated with abrupt transitions (from GS to GI and vice-versa) occurring during Marine Isotopic Stage (MIS) 4. We determine via a statistical approach the timing and duration of the transitions, along with the amplitude of the local and regional changes associated with each Greenland warming and cooling phase. We quantify similarities and differences in the sequences of events through a comparison with results obtained for MIS 3 abrupt transitions and results from the NEEM ice core for selected transitions. The anatomy of abrupt climate changes appears to be different from one event to the next, suggesting that the mechanisms at play are not identical for all of them. We discuss the possible influence of (1) the Heinrich Stadials (i.e. GS during which a Heinrich Event occurred) and of (2) the long term evolution of the climate system on the different decadal to centennial-scale sequences of events

  14. Atmospheric CO2 variations on millennial-scale during MIS 6

    NASA Astrophysics Data System (ADS)

    Shin, Jinhwa; Grilli, Roberto; Chappellaz, Jérôme; Teste, Grégory; Nehrbass-Ahles, Christoph; Schmidely, Loïc; Schmitt, Jochen; Stocker, Thomas; Fischer, Hubertus

    2017-04-01

    Understanding natural carbon cycle / climate feedbacks on various time scales is highly important for predicting future climate changes. Paleoclimate records of Antarctic temperatures, relative sea level and foraminiferal isotope and pollen records in sediment cores from the Portuguese margin have shown climate variations on millennial time scale over the Marine Isotope Stage 6 (MIS 6; from approximately 135 to 190 kyr BP). These proxy data suggested iceberg calving in the North Atlantic result in cooling in the Northern hemisphere and warming in Antarctica by changes in the Atlantic Meridional Overturning Circulation, which is explained by a bipolar see-saw trend in the ocean (Margari et al., 2010). Atmospheric CO2 reconstruction from Antarctic ice cores can provide key information on how atmospheric CO2 concentrations are linked to millennial-scale climate changes. However, existing CO2 records cannot be used to address this relationship because of the lack of suitable temporal resolution. In this work, we will present a new CO2 record with an improved time resolution, obtained from the Dome C ice core (75˚ 06'S, 123˚ 24'E) spanning the MIS 6 period, using dry extraction methods. We will examine millennial-scale features in atmospheric CO2, and their possible links with other proxies covering MIS 6. Margari, V., Skinner, L. C., Tzedakis, P. C., Ganopolski, A., Vautravers, M., and Shackleton, N. J.: The nature of millennial scale climate variability during the past two glacial periods, Nat.Geosci., 3, 127-131, 2010.

  15. 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.

  16. 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.

  17. 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

  18. Detecting abrupt climate changes on different time scales

    NASA Astrophysics Data System (ADS)

    Matyasovszky, István

    2011-10-01

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

  19. Millennial- and sub-millennial-scale shifts in moisture availability for western Mediterranean forest development during the Deglaciation and Holocene

    NASA Astrophysics Data System (ADS)

    Fletcher, W. J.; Sanchez Goñi, M. F.; Peyron, O.; Dormoy, I.

    2009-04-01

    Pollen data for temperate Mediterranean forest development from marine core MD95-2043 (Alborán Sea, western Mediterranean) and pollen-based climate reconstructions using the modern analogue technique (MAT) for annual precipitation (PANN) and mean temperatures of the coldest and warmest months (MTCO and MTWA) provide evidence for abrupt changes in western Mediterranean climate between 20 and 1 cal ka BP. During the Deglaciation period (20 -6 cal ka BP), major climatic shifts with parallel precipitation and temperature changes occurred at the onsets of Heinrich Event 1 (equivalent to the Oldest Dryas), the Bölling-Allerød (BA), and the Younger Dryas (YD). Multi-centennial-scale oscillations in forest development related to regional precipitation (PANN) variability occurred throughout the BA, YD, and early Holocene, with drier atmospheric conditions in phase with Lateglacial events of high-latitude cooling including GI-1d (Older Dryas), GI-1b (Intra-Allerød Cold Period) and GS-1 (YD), and during Holocene events associated with high-latitude cooling, meltwater pulses and N. Atlantic ice-rafting (events at 11.4, 10.1, 9.3, 8.2 and 7.4 cal ka BP). The forest record also indicates multi-centennial variability within the YD interval with an intra-YD episode of forest recovery. A possible climatic mechanism for the recurrence of sub-millennial-scale dry intervals and an opposed regional precipitation pattern with respect to western-central Europe relates to the dynamics of the jet stream and the prevalence of atmospheric blocking highs. Comparison of radiocarbon and ice-core ages for well-defined climatic transitions in the forest record suggests possible enhancement of marine reservoir ages in the Alborán Sea by approx. 200 years (surface water age approx. 600 years) during the Lateglacial. During the (mid- to late-) Holocene, a significant millennial-scale oscillation in forest development is detected, centred at around 1750 yrs, which may reflect low frequency

  20. 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.

  1. 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.

  2. Millennial-scale temperature variability during Marine Isotope Stages 19 and 31 in the continental Arctic

    NASA Astrophysics Data System (ADS)

    de Wet, G.; Castañeda, I. S.; Brigham-Grette, J.; Salacup, J. M.; Keisling, B. A.; Habicht, M. H.

    2014-12-01

    In light of predicted climate change, high-resolution paleoclimate records are essential to accurately contextualize future warming. The Arctic region in particular is currently lacking terrestrial paleoclimate reconstructions that extend beyond the last glacial period. A sediment core from Lake El'gygytgyn (Russia) provides a continuous record of Arctic climate spanning the past 3.6 Ma. Here we utilize molecular organic proxies to create millennial-scale paleotemperature reconstructions through Marine Isotope Stages (MIS) 19 and 31, two interglacial periods considered to be good analogs for the current interglacial and future climate change, respectively. MIS 31 has been previously identified a "super interglacial" period at Lake El'gygytgyn whereas MIS 19 provides an analog for the current MIS 1 interglacial, without anthropogenic influences, due to similar orbital forcing. Our paleotemperature reconstructions, based on the branched glycerol dialkyl glycerol tetraether (brGDGT) paleothermometer, demonstrate that Lake El'gygytgyn sediments capture glacial-interglacial climate variability noted in global climate records (Figure 1) and suggests close ties to Antarctic climate. We find that MIS 31 was the warmest interglacial period of the past ~ 1 Ma, in agreement with pollen-derived temperature estimates. Our cm-scale brGDGT temperature reconstruction, with an average time step of <500 years, to the best of our knowledge provides the highest resolution Arctic paleoclimate record of this "super interglacial" and reveals variability hitherto unobserved by lower resolution marine records. Our results are placed in context of paleotemperature reconstructions over the period of MIS 19-35. Remarkably, multiple proxies display a number of abrupt and short-lived temperature fluctuations of ca. 3-5°C occurring within MIS 19 and 31, as well as within other previous interglacials at Lake El'gygytgyn. We examine our results in the context of other biomarker records, existing

  3. 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

  4. 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.

  5. 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.

  6. 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

  7. 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.

  8. Variability of oceanic productivity in the North Atlantic during abrupt climate changes (Heinrich Events)

    NASA Astrophysics Data System (ADS)

    Nave, S.; Labeyrie, L.; Gherardi, J.; Cortijo, E.; Abrantes, F.; Kissel, C.

    2006-12-01

    Evidences of strong millennial-scale climate variability, especially marked during MIS3, have been reported worldwide in high-resolution records. These pronounced climate changes, known as Dansgaard-Oeschger cycles, are characterized by sudden shifts in temperature, dust content and concentration of methane. Some of the longest Dansgaard-Oescher stadials are closely related to massive iceberg surges, the Heinrich Events (HE), recognized by anomalous concentrations in ice-rafted debris in six peculiar layers in the North Atlantic. Besides the well-documented changes in hydrology, these iceberg discharges had probably a major impact on the marine ecosystem, but data to constrain this variability is lacking. In order to further our understanding on productivity feedbacks to massive iceberg discharges and associated hydrologic adjustments, we have done a high-resolution diatom and organic carbon analysis focused on 7 sedimentary sequences between 40ºN and 65ºN, each of them representative of a North Atlantic region. This study was conducted over two abrupt climate events of the last glacial period, Heinrich Event 1 (H1) and Heinrich Event 4 (H4). Our results show that during H4 event, productivity decreased drastically at all latitudes. No major blooms of siliceous phytoplankton were recorded during iceberg discharges, and hence production resulting from high nutrient supply does not seem to have occurred during HE as suggested by previous studies (Sancetta, 1992). Instead, the severe productivity decrease during H4 could be due to the establishment of a strong halocline and the consequent slowdown of the thermohaline circulation (reducing the mixed layer and therefore preventing the nutrient supply from deeper waters to the upper layer). However, during H1, although hydrologically similar, productivity was apparently not affected in northern latitudes, showing a progressive increase during the deglaciation period. Hence, our results suggest that the orbital forcing

  9. Wildfire responses to abrupt climate change in North America

    PubMed Central

    Marlon, J. R.; Bartlein, P. J.; Walsh, M. K.; Harrison, S. P.; Brown, K. J.; Edwards, M. E.; Higuera, P. E.; Power, M. J.; Anderson, R. S.; Briles, C.; Brunelle, A.; Carcaillet, C.; Daniels, M.; Hu, F. S.; Lavoie, M.; Long, C.; Minckley, T.; Richard, P. J. H.; Scott, A. C.; Shafer, D. S.; Tinner, W.; Umbanhowar, C. E.; Whitlock, C.

    2009-01-01

    It is widely accepted, based on data from the last few decades and on model simulations, that anthropogenic climate change will cause increased fire activity. However, less attention has been paid to the relationship between abrupt climate changes and heightened fire activity in the paleorecord. We use 35 charcoal and pollen records to assess how fire regimes in North America changed during the last glacial–interglacial transition (15 to 10 ka), a time of large and rapid climate changes. We also test the hypothesis that a comet impact initiated continental-scale wildfires at 12.9 ka; the data do not support this idea, nor are continent-wide fires indicated at any time during deglaciation. There are, however, clear links between large climate changes and fire activity. Biomass burning gradually increased from the glacial period to the beginning of the Younger Dryas. Although there are changes in biomass burning during the Younger Dryas, there is no systematic trend. There is a further increase in biomass burning after the Younger Dryas. Intervals of rapid climate change at 13.9, 13.2, and 11.7 ka are marked by large increases in fire activity. The timing of changes in fire is not coincident with changes in human population density or the timing of the extinction of the megafauna. Although these factors could have contributed to fire-regime changes at individual sites or at specific times, the charcoal data indicate an important role for climate, and particularly rapid climate change, in determining broad-scale levels of fire activity. PMID:19190185

  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. Millennial scale events during Terminations III and V and their role in shaping the deglaciation

    NASA Astrophysics Data System (ADS)

    Vazquez Riveiros, Natalia; Skinner, Luke; Waelbroeck, Claire; Roche, Didier; Bouttes, Nathaelle

    2017-04-01

    Marine Isotope Stage (MIS) 7, the interglacial period dated ca. 195 - 245 kyr ago, exemplifies the non-linearity subjacent in the astronomical theory of the ice ages. Despite the fact that it coincides with some of the strongest insolation increases over the last 500,000 years, MIS7 is a relatively mild interglacial. In comparison, MIS11, the interglacial period that took place 400 kyr ago, presents a major response of the climate system in most paleoclimatic records at a time of feeble orbital forcing. This mismatch between insolation forcing and climate response implies that if insolation is driving glacial-interglacial climate change, it can only be as a 'pace-maker' that triggers strong, positive feedbacks. Foremost among the mechanisms that may have amplified insolation-paced global change are millennial-scale ocean circulation perturbations, that have been linked to Antarctic temperature and atmospheric CO2 increases. This study investigates the influence of millennial-scale ocean perturbations in determining global climate during MIS7, by comparing marine sediment cores on a common time scale. New high-resolution data from core MD07-3077 in the Atlantic sector of the Southern Ocean, together with data from North Atlantic cores, indicate that the terminal seesaw events that took place during Terminations III and IIIa are of a different nature than those acting during Termination I or V. Their impact on global climate is not related in a simple way to their magnitude and duration, and they were probably influenced by the background state of the ocean during MIS8 and by the relative extent of European and North American ice sheets. The comparison of the records with simulations of the isotope-enabled Earth System Model of intermediate complexity iLOVECLIM sheds light on the respective roles of insolation and millennial scale events on the development of each interglacial.

  12. 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.

  13. 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

  14. 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.

  15. 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.

  16. 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.

  17. 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

  18. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

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

  20. 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.

  1. 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.

  2. 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

  3. The Late-Glacial and Holocene Marboré Lake sequence (2612 m a.s.l., Central Pyrenees, Spain): Testing high altitude sites sensitivity to millennial scale vegetation and climate variability

    NASA Astrophysics Data System (ADS)

    Leunda, Maria; González-Sampériz, Penélope; Gil-Romera, Graciela; Aranbarri, Josu; Moreno, Ana; Oliva-Urcia, Belén; Sevilla-Callejo, Miguel; Valero-Garcés, Blas

    2017-10-01

    This paper presents the environmental, climate and vegetation changes reconstructed for the last 14.6 kyr cal BP from the Marboré Lake sedimentary sequence, the highest altitude record (2612 m a.s.l.) in the Pyrenees studied up to date. We investigate the sensitivity of this high altitude site to vegetational and climate dynamics and altitudinal shifts during the Holocene by comparing palynological spectra of the fossil sequence and pollen rain content from current moss pollsters. We hypothesize that the input of sediments in lakes at such altitude is strongly controlled by ice phenology (ice-free summer months) and that during cold periods Pollen Accumulation Rate (PAR) and Pollen Concentration (PC) reflect changes in ice-cover and thus is linked to temperature changes. Low sedimentation rates and low PC and PAR occurred during colder periods as the Younger Dryas (GS-1) and the Holocene onset (12.6-10.2 kyr cal BP), suggesting that the lake-surface remained ice-covered for most of the year during these periods. Warmer conditions are not evident until 10.2 kyr cal BP, when an abrupt increase in sedimentation rate, PC and PAR occur, pointing to a delayed onset of the Holocene temperature increase at high altitude. Well-developed pinewoods and deciduous forest dominated the mid montane belt since 9.3 kyr cal BP until mid-Holocene (5.2 kyr cal BP). A downwards shift in the deciduous forest occurred after 5.2 kyr cal BP, in agreement with the aridity trend observed at a regional and Mediterranean context. The increase of herbaceous taxa during the late-Holocene (3.5 kyr cal BP-present) reflects a general trend to reduced montane forest, as anthropogenic disturbances were not evident until 1.3 kyr cal BP when Olea proportions from lowland areas and other anthropogenic indicators clearly expand. Our study demonstrates the need to perform local experimental approaches to check the effect of ice phenology on high altitude lakes sensitivity to vegetation changes to obtain

  4. 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.

  5. Millennial-scale variability during the last glacial in vegetation records from North America

    USGS Publications Warehouse

    Jiménez-Moreno, Gonzalo; Anderson, R. Scott; Desprat, S.; Grigg, L.D.; Grimm, E.C.; Heusser, L.E.; Jacobs, Brian F.; Lopez-Martinez, C.; Whitlock, C.L.; Willard, D.A.

    2010-01-01

    High-resolution pollen records from North America show that terrestrial environments were affected by Dansgaard-Oeschger (D-O) and Heinrich climate variability during the last glacial. In the western, more mountainous regions, these climate changes are generally observed in the pollen records as altitudinal movements of climate-sensitive plant species, whereas in the southeast, they are recorded as latitudinal shifts in vegetation. Heinrich (HS) and Greenland (GS) stadials are generally correlated with cold and dry climate and Greenland interstadials (GI) with warm-wet phases. The pollen records from North America confirm that vegetation responds rapidly to millennial-scale climate variability, although the difficulties in establishing independent age models for the pollen records make determination of the absolute phasing of the records to surface temperatures in Greenland somewhat uncertain. ?? 2009 Elsevier Ltd.

  6. Millennial-Scale ITCZ Variability in the Tropical Atlantic and Dynamics of Amazonian Rain Forest

    NASA Astrophysics Data System (ADS)

    Wang, X.; Auler, A. S.; Edwards, R. L.; Cheng, H.; Shen, C.; Smart, P. L.; Richards, D. A.

    2003-12-01

    Precipitation in the Amazon Basin is largely related to the intertropical convergence zone (ITCZ) in the tropical Atlantic which undergoes a regular seasonal migration. We chose a site south of the present day rainforest in semiarid northeastern Brazil, in order to study the timing of pluvial periods when the southern extend of the ITCZ would have been much further south than today. Shifts in the ITCZ position may have influenced the dynamics of rain forest and species diversity. We collected speleothems from northern Bahia state, located southeast of Amazonia. Age determinations with U-series dating methods show that samples grew rapidly during relatively short intervals (several hundreds of years) of glacial periods in the last 210 kyr. In addition, paleopluvial phases delineated by speleothem growth intervals show millennial-scale variations. Pluvial phases coincide with the timing of weak East Asian summer monsoon intensities (Wang et al., 2001, Science 294: 2345-2348), which have been correlated to the timing of stadials in Greenland ice core records and Heinrich events (Bond and Lotti, 1995, Science 267: 1005-1010). Furthermore, these intervals correspond to the periods of light color reflectance of Cariaco Basin sediments from ODP Hole 1002C (Peterson et al., 2000, Science, 290: 1947-1951), which was suggested to be caused by a southward shift of the northernmost position of the ITCZ and decreased rainfall in this region. Abrupt precipitation changes in northeastern Brazil may be due to the southward displacement of the southernmost position of the ITCZ associated with atmosphere-ocean circulation changes caused by (1) an increase in northern high latitude-tropical temperature gradient (Chiang et al., 2003, Paleoceanography, in press), and/or (2) the bipolar seesaw mechanism (Broecker et al., 1998, Paleoceanography 13: 119-121) during these Heinrich events. Pluvial phases are also coincident with higher insolation at 10° S during austral autumn. This

  7. The 9.2 ka event in Asian summer monsoon area: the strongest millennial scale collapse of the monsoon during the Holocene

    NASA Astrophysics Data System (ADS)

    Zhang, Wenchao; Yan, Hong; Dodson, John; Cheng, Peng; Liu, Chengcheng; Li, Jianyong; Lu, Fengyan; Zhou, Weijian; An, Zhisheng

    2017-06-01

    Numerous Holocene paleo-proxy records exhibit a series of centennial-millennial scale rapid climatic events. Unlike the widely acknowledged 8.2 ka climate anomaly, the likelihood of a significant climate excursion at around 9.2 cal ka BP, which has been notably recognized in some studies, remains to be fully clarified in terms of its magnitude and intensity, as well as its characteristics and spatial distributions in a range of paleoclimatic records. In this study, a peat sediment profile from the Dajiuhu Basin in central China was collected with several geochemical proxies and a pollen analysis carried out to help improve understanding of the climate changes around 9.2 cal ka BP. The results show that the peat development was interrupted abruptly at around 9.2 cal ka BP, when the chemical weathering strength decreased and the tree-pollen declined. This suggests that a strong drier regional climatic event occurred at around 9.2 cal ka BP in central China, which was, in turn, probably connected to the rapid 9.2 ka climate event co-developing worldwide. In addition, based on the synthesis of our peat records and the other Holocene hydrological records from Asian summer monsoon (ASM) region, we further found that the 9.2 ka event probably constituted the strongest abrupt collapse of the Asian monsoon system during the full Holocene interval. The correlations between ASM and the atmospheric 14C production rate, the North Atlantic drift ice records and Greenland temperature indicated that the weakened ASM event at around 9.2 cal ka BP could be interpreted by the co-influence of external and internal factors, related to the changes of the solar activity and the Atlantic Meridional Overturning Circulation (AMOC).

  8. Millennial-Scale Variability in the Indian Monsoon and Links to Ocean Circulation

    NASA Astrophysics Data System (ADS)

    DeLong, K. A.; Came, R. E.; Johnson, J. E.; Giosan, L.

    2014-12-01

    Millennial-scale variability in the Indian monsoon was temporally linked to changes in global ocean circulation during the last glacial period, as evidenced by planktic-benthic foraminiferal stable isotope and trace element results from an intermediate depth sediment core from the northwestern Bay of Bengal. Paired planktic foraminiferal Mg/Ca and δ18Oc constrain sea surface temperatures and isolate millennial-scale variations in the δ18O of surface waters (δ18Osw), which resulted from changes in river runoff in the northwestern Bay. Concurrently with low δ18Osw events, benthic foraminiferal δ13C decreased, suggesting an increased influence of an aged water mass at this intermediate depth site during the low salinity events. Benthic foraminiferal Cd/Ca results support the identification of this water mass as aged Glacial Antarctic Intermediate Water (GAAIW). Lagged correlation analysis (r= 0.41) indicates that changes in subsurface properties led changes in surface properties by an average of 380 years. The implication is that Southern Hemisphere climate exerted a controlling influence on the Indian monsoon during the last glacial period.

  9. East China Sea δ18O Record Detects Millennial-Scale Changes in the East Asian Summer Monsoon

    NASA Astrophysics Data System (ADS)

    Gleeman, E.; Clemens, S. C.; Lawman, A. E.; Kubota, Y.; Holbourn, A. E.; Martin, A.

    2015-12-01

    The East Asian Summer Monsoon (EASM) brings heavy summer rainfall to some of Asia's most densely-populated areas, impacting agricultural production and water resources. Sediment cores were recovered from International Ocean Drilling Program Site U1429 in the East China Sea (31° 37.04' N, 128° 59.50' E, 732 mbsl). This location receives runoff from the Yangtze River, which serves as a major drainage system for monsoon-induced precipitation. Hence, the δ18O record of planktonic foraminifera at Site U1429 reflects changes in regional, monsoon-driven salinity. The top 100 meters of core at Site U1429 were sampled at a preliminary resolution of 15 cm and processed to isolate the planktonic foraminifer Globigerinoides ruber for δ18O mass spectrometry analyses. Abrupt, millennial-scale regional climate variability in the EASM and its linkage to orbital forcings have been reconstructed using stratigraphic analysis of δ18O. The sub-orbital scale structure of the δ18O record over the past 400 kyr matches the structures of both the composite speleothem δ18O from eastern China (Sanbao and Hulu caves) and the planktonic δ18O record from northern South China Sea Site 1146. The similarities between these δ18O records indicate a strong regional response to monsoon forcing. Removal of the temperature component of the δ18O signal by using Mg/Ca (G. ruber) paleothermometry will provide a record of changes in the δ18O composition of seawater in response to Yangtze River runoff.

  10. Orbital and millennial-scale features of atmospheric CH4 over the past 800,000 years.

    PubMed

    Loulergue, Laetitia; Schilt, Adrian; Spahni, Renato; Masson-Delmotte, Valérie; Blunier, Thomas; Lemieux, Bénédicte; Barnola, Jean-Marc; Raynaud, Dominique; Stocker, Thomas F; Chappellaz, Jérôme

    2008-05-15

    Atmospheric methane is an important greenhouse gas and a sensitive indicator of climate change and millennial-scale temperature variability. Its concentrations over the past 650,000 years have varied between approximately 350 and approximately 800 parts per 10(9) by volume (p.p.b.v.) during glacial and interglacial periods, respectively. In comparison, present-day methane levels of approximately 1,770 p.p.b.v. have been reported. Insights into the external forcing factors and internal feedbacks controlling atmospheric methane are essential for predicting the methane budget in a warmer world. Here we present a detailed atmospheric methane record from the EPICA Dome C ice core that extends the history of this greenhouse gas to 800,000 yr before present. The average time resolution of the new data is approximately 380 yr and permits the identification of orbital and millennial-scale features. Spectral analyses indicate that the long-term variability in atmospheric methane levels is dominated by approximately 100,000 yr glacial-interglacial cycles up to approximately 400,000 yr ago with an increasing contribution of the precessional component during the four more recent climatic cycles. We suggest that changes in the strength of tropical methane sources and sinks (wetlands, atmospheric oxidation), possibly influenced by changes in monsoon systems and the position of the intertropical convergence zone, controlled the atmospheric methane budget, with an additional source input during major terminations as the retreat of the northern ice sheet allowed higher methane emissions from extending periglacial wetlands. Millennial-scale changes in methane levels identified in our record as being associated with Antarctic isotope maxima events are indicative of ubiquitous millennial-scale temperature variability during the past eight glacial cycles.

  11. Arctic Ocean freshwater as a trigger for abrupt climate change

    NASA Astrophysics Data System (ADS)

    Bradley, Raymond; Condron, Alan; Coletti, Anthony

    2016-04-01

    The cause of the Younger Dryas cooling remains unresolved despite decades of debate. Current arguments focus on either freshwater from Glacial Lake Agassiz drainage through the St Lawrence or the MacKenzie river systems. High resolution ocean modeling suggests that freshwater delivered to the North Atlantic from the Arctic Ocean through Fram Strait would have had more of an impact on Atlantic Meridional Overturning Circulation (AMOC) than freshwater from the St Lawrence. This has been interpreted as an argument for a MacKenzie River /Lake Agassiz freshwater source. However, it is important to note that although the modeling identifies Fram Strait as the optimum location for delivery of freshwater to disrupt the AMOC, this does not mean the freshwater source came from Lake Agassiz. Another potential source of freshwater is the Arctic Ocean ice cover itself. During the LGM, ice cover was extremely thick - many tens of meters in the Canada Basin (at least), resulting in a hiatus in sediment deposition there. Extreme ice thickness was related to a stagnant circulation, very low temperatures and continuous accumulation of snow on top of a base of sea-ice. This resulted in a large accumulation of freshwater in the Arctic Basin. As sea-level rose and a more modern circulation regime became established in the Arctic, this freshwater was released from the Arctic Ocean through Fram Strait, leading to extensive sea-ice formation in the North Atlantic (Greenland Sea) and a major reduction in the AMOC. Here we present new model results and a review of the paleoceanographic evidence to support this hypothesis. The bottom line is that the Arctic Ocean was likely a major player in causing abrupt climate change in the past, via its influence on the AMOC. Although we focus here on the Younger Dryas, the Arctic Ocean has been repeatedly isolated from the world ocean during glacial periods of the past. When these periods of isolation ended, it is probable that there were significant

  12. Have abrupt climate variations of the last glacial possibly been muted in the south-west African tropics by counteracting mechanisms?

    NASA Astrophysics Data System (ADS)

    Hessler, I.; Dupont, L.; Handiani, D.; Steinke, S.; Groeneveld, J.; Merkel, U.; Paul, A.

    2012-04-01

    The last glacial period including the last deglaciation (73.5-10 ka BP) is characterised by abrupt shifts between extreme climatic conditions. Millennial-scale climate variations associated with North Atlantic Heinrich Stadials (HSs) are thought to be transmitted by both the atmospheric and oceanic circulation resulting in a near-global footprint. It is further thought that HSs are closely related to a reduction or shut-down of the Atlantic Meridional Overturning Circulation, which, according to the bipolar-seesaw hypothesis, leads to the accumulation of heat in the South Atlantic. In addition, it is hypothesised that HSs result in a southward shift of the Intertropical Convergence Zone which then would likely influence the vegetation composition in the African tropics. To investigate the impact of HSs on the terrestrial African realm and the south-east Atlantic we reconstructed the vegetation development in Angola and the southern Congo Basin as well as the sea surface temperatures (SST) of the south-east Atlantic using marine sediments of ODP Site 1078 (11° 55'S, 13° 24'E, 427 m water depth). Two species of planktonic foraminifera were selected to reconstruct variations in surface water conditions in the south-east Atlantic. Due the ecological and seasonal preferences of Globigerinoides ruber (pink) this species provides a good tool to estimate SST variations during the southern hemisphere summer. In contrast, Globigerina bulloides is representing the Benguela Upwelling System during the southern hemisphere winter. While Mg/Ca-based SSTs of G. ruber (pink) were significantly higher by 1° -2° C during periods of abrupt climate change, the impact of HSs during southern hemisphere winter is less obvious. However, although there are several vegetation records that show an impact of HSs in the African tropics, our high-resolution pollen record from ODP Site 1078 reflects no vegetation changes during periods of HSs. Model simulations conducted with an Earth System

  13. 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

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. Stalagmite record of millennial-scale hydroclimate variability in Borneo during the last glacial period

    NASA Astrophysics Data System (ADS)

    Carolin, S. A.; Cobb, K.; Adkins, J. F.; Subhas, A.

    2011-12-01

    The role of the tropical Pacific in the chain of events associated with abrupt climate changes (ACC) remains uncertain. The reigning paradigm for explaining some important features of ACC events invokes a collapse of the Atlantic Ocean's thermohaline circulation (Broecker, 1998). However, as small changes in the tropics can potentially influence the global heat and water budgets, it is likely that teleconnections between the tropics and the north Atlantic play a key part in ACC mechanisms. Indeed, a cave stalagmite oxygen isotopic (δ18O) record from tropical China reveals that large tropical hydrological shifts accompany inferred shutdowns in the Atlantic thermohaline circulation (Wang et al., 2001). A continuous, high-resolution, well-dated record of hydroclimatic changes from the western tropical Pacific would provide additional insights into the mechanisms underlying millennial-scale ACC events. Here we present several high-resolution stalagmite δ18O records from northern Borneo (4N, 114E) spanning most of the last glacial period. Most tropical sites are characterized by an empirical inverse relationship between rainfall δ18O variations and regional precipitation (Dansgaard, 1964). This "amount effect" emerges from a site-specific rain and dripwater study conducted at our research site (Cobb et al., 2007). A previous study supports the idea that the rainwater δ18O signal is faithfully recorded in the stalagmite δ18O, under equilibrium precipitation conditions (Partin et al., 2007), such that stalagmite δ18O primarily reflects large-scale hydroclimate variability. The chronology of the new stalagmite δ18O records are determined using 32 U-Th disequilibrium dates that span from 30kybp to 70kybp. Dating errors range from a few hundred to a few thousand years, depending on the amount of detrital thorium contamination, which we correct using multiple isochrons. The sub-centennially-resolved δ18O records reveal several significant peaks in δ18O that represent

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

    USDA-ARS?s Scientific Manuscript database

    Amplification of the hydrologic cycle as a consequence of global warming is predicted to increase climate variability and the frequency and severity of droughts. Predicting how ecosystems will be affected by climate change requires not only reliable forecasts of future climate, but also observationa...

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

    SciTech Connect

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

    1998-02-27

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

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

    NASA Astrophysics Data System (ADS)

    Tierney, Jessica E.; Russell, James M.

    2007-08-01

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

  2. Millennial-scale variations of an East Antarctic outlet glacier during the Last Glaciation

    NASA Astrophysics Data System (ADS)

    Shevenell, A.; Guitard, M.; Rosenheim, B. E.; Leventer, A.; Yokoyama, Y.

    2016-12-01

    Antarctica's ice sheet response to ongoing climate change is the largest uncertainty in future sea-level projections. Recent warming has forced potentially irreversible retreat of the West Antarctic Ice Sheet. However, the vulnerability of marine-based portions of the East Antarctic Ice Sheet (EAIS), which contain 19 meters of sea-level-equivalent, remains uncertain due to a lack of data and long-held assumptions about EAIS stability. This uncertainty is concerning because numerical ice sheet models indicate that Antarctica's ice shelves and marine-terminating outlet glaciers respond rapidly to ocean perturbations (e.g., increased ocean heat flux, sea level rise), resulting in rapid regional ice mass loss. Ice-proximal marine geologic records are useful for informing and refining model outputs, yet few well-dated records of past East Antarctic marine-based outlet glacier response exist. Here we show that East Antarctica's largest marine-based outlet glacier system, the Lambert Glacier-Amery Ice Shelf system, experienced at least three millennial-scale advance and retreat cycles during the last glaciation. Because this system had retreated from the shelf edge before the Last Glacial Maximum, a late Quaternary ice-proximal sedimentary sequence is preserved in Prydz Channel. We have accurately dated these sediments using a newly established radiocarbon dating method that separates autochthonous marine from glacially reworked organic carbon. Three diatom-rich sedimentary units with elevated radiogenic beryllium-10 (10Be) concentrations reveal three open water intervals in inner Prydz Bay between 40 and 20 ka. Our sedimentologic and geochemical evidence indicates that the Lambert Glacier-Amery Ice shelf system had retreated landward of our study site coincident with millennial-scale atmospheric warm events and reduced Southern Ocean sea ice extent. The observed sensitivity of East Antarctica's largest outlet glacier system to climate forcing during the last glaciation

  3. Dynamics of climate and ecosystem coupling: abrupt changes and multiple equilibria.

    PubMed Central

    Higgins, Paul A T; Mastrandrea, Michael D; Schneider, Stephen H

    2002-01-01

    Interactions between subunits of the global climate-biosphere system (e.g. atmosphere, ocean, biosphere and cryosphere) often lead to behaviour that is not evident when each subunit is viewed in isolation. This newly evident behaviour is an emergent property of the coupled subsystems. Interactions between thermohaline circulation and climate illustrate one emergent property of coupling ocean and atmospheric circulation. The multiple thermohaline circulation equilibria that result caused abrupt climate changes in the past and may cause abrupt climate changes in the future. Similarly, coupling between the climate system and ecosystem structure and function produces complex behaviour in certain regions. For example, atmosphere-biosphere interactions in the Sahel region of West Africa lead to multiple stable equilibria. Either wet or dry climate equilibria can occur under otherwise identical forcing conditions. The equilibrium reached is dependent on past history (i.e. initial conditions), and relatively small perturbations to either climate or vegetation can cause switching between the two equilibria. Both thermohaline circulation and the climate-vegetation system in the Sahel are prone to abrupt changes that may be irreversible. This complicates the relatively linear view of global changes held in many scientific and policy communities. Emergent properties of coupled socio-natural systems add yet another layer of complexity to the policy debate. As a result, the social and economic consequences of possible global changes are likely to be underestimated in most conventional analyses because these nonlinear, abrupt and irreversible responses are insufficiently considered. PMID:12079526

  4. 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.

  5. Abrupt Climate Events in Britain and the North Atlantic during Marine Isotope Stage 11

    NASA Astrophysics Data System (ADS)

    Candy, I.; Tye, G.; Coxon, P.; Palmer, A.; Hardiman, M.; Matthews, I.; Loakes, K.; Ryves, D.; McClymont, E.

    2016-12-01

    The Holocene has been punctuated by numerous abrupt climatic events, whilst abrupt change may also occur in the future as ice-sheet decay interacts with ocean-circulation. It is unclear whether abrupt events are a common phenomenon in pre-Holocene interglacials and whether such events occur in association with terminal ice-sheet decay in the very early interglacial and/or in association with largescale melting of ice sheets, such as Greenland, during peak interglacial conditions. The best preserved abrupt climatic event in a pre-Holocene interglacial in western/central Europe comes from annually-laminated lake deposits of MIS 11c. These sequences are, however, fragmented and difficult to place into the context of the long/continuous benthic δ18O records of glacial interglacial cycles. This study presents; 1) a high-resolution record of an MIS 11c abrupt event from Britain and 2) the first high-precision correlation between European MIS11c deposits and the marine records of the North Atlantic (ODP 980) through the application of tephra chronology. Both the structure of this event and its position within the benthic δ18O stratigraphy of MIS11 implies that it is analogous to the 8.2ka event. However, the occurrence of other abrupt events later in MIS11c in Europe indicate the possibility that climatic instability occurred later in this interglacial too, possibly in association with the thermal maximum, and the ice volume minima, of this interglacial.

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

    PubMed Central

    Peteet, Dorothy

    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. PMID:10677467

  7. 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.

  8. 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.

  9. Extensive wildfires, climate change, and an abrupt state change in subalpine ribbon forests, Colorado.

    PubMed

    Calder, W John; Shuman, Bryan

    2017-10-01

    Ecosystems may shift abruptly when the effects of climate change and disturbance interact, and landscapes with regularly patterned vegetation may be especially vulnerable to abrupt shifts. Here we use a fossil pollen record from a regularly patterned ribbon forest (alternating bands of forests and meadows) in Colorado to examine whether past changes in wildfire and climate produced abrupt vegetation shifts. Comparing the percentages of conifer pollen with sedimentary δ(18) O data (interpreted as an indicator of temperature or snow accumulation) indicates a first-order linear relationship between vegetation composition and climate change with no detectable lags over the past 2,500 yr (r = 0.55, P < 0.001). Additionally, however, we find that the vegetation changed abruptly within a century of extensive wildfires, which were recognized in a previous study to have burned approximately 80% of the surrounding 1,000 km(2) landscape 1,000 yr ago when temperatures rose ~0.5°C. The vegetation change was larger than expected from the effects of climate change alone. Pollen assemblages changed from a composition associated with closed subalpine forests to one similar to modern ribbon forests. Fossil pollen assemblages then remained like those from modern ribbon forests for the following ~1,000 yr, providing a clear example of how extensive disturbances can trigger persistent new vegetation states and alter how vegetation responds to climate. © 2017 by the Ecological Society of America.

  10. Millennial-scale sea-level control on avulsion events on the Amazon Fan

    NASA Astrophysics Data System (ADS)

    Maslin, Mark; Knutz, Paul C.; Ramsay, Tony

    2006-12-01

    The Late Quaternary Amazon deep-sea fan provides a modern analogue to ancient fan systems containing coarse-grained hydrocarbon reservoirs. Sand lenses deposited within the Amazon Fan, due to abrupt shifts in channel pathways called avulsion events, were drilled as part of ODP Leg 155. The hemipelagic sediment directly on top of the avulsion sands was dated using primarily AMS radio carbon dating. This dating shows that these large sand lobes (˜1 km 3) are triggered by relatively small, millennial scale changes in marine transgression and regression (±5-10 m). Relative sea level also controls the architecture of the Channel-levee distributive systems within the Amazon Fan. For example prior to 22 k calendar years BP there is a tripartite channel system. After 22 ka there is only one active Channel-levee system. Transitions between the multi-channel and single channel configurations are related to variations in the volume of sediment supply resulting in aggradation or erosion of channel floor and levee growth in the canyon-channel transition area. The sensitivity of the Amazon deep-sea Fan sedimentation to relatively small changes in sea level supports one of the central assumptions of the theory of Sequence Stratigraphy. In addition this study demonstrates how traps for hydrocarbons may have been formed in ancient fan systems.

  11. 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

  12. 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.

  13. 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.

  14. The effect of millennial-scale changes in Arabian Sea denitrification on atmospheric CO2.

    PubMed

    Altabet, Mark A; Higginson, Matthew J; Murray, David W

    2002-01-10

    Most global biogeochemical processes are known to respond to climate change, some of which have the capacity to produce feedbacks through the regulation of atmospheric greenhouse gases. Marine denitrification-the reduction of nitrate to gaseous nitrogen-is an important process in this regard, affecting greenhouse gas concentrations directly through the incidental production of nitrous oxide, and indirectly through modification of the marine nitrogen inventory and hence the biological pump for CO2. Although denitrification has been shown to vary with glacial-interglacial cycles, its response to more rapid climate change has not yet been well characterized. Here we present nitrogen isotope ratio, nitrogen content and chlorin abundance data from sediment cores with high accumulation rates on the Oman continental margin that reveal substantial millennial-scale variability in Arabian Sea denitrification and productivity during the last glacial period. The detailed correspondence of these changes with Dansgaard-Oeschger events recorded in Greenland ice cores indicates rapid, century-scale reorganization of the Arabian Sea ecosystem in response to climate excursions, mediated through the intensity of summer monsoonal upwelling. Considering the several-thousand-year residence time of fixed nitrogen in the ocean, the response of global marine productivity to changes in denitrification would have occurred at lower frequency and appears to be related to climatic and atmospheric CO2 oscillations observed in Antarctic ice cores between 20 and 60 kyr ago.

  15. 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

  16. Millennial-scale Atlantic/East Pacific sea surface temperature linkages during the last 100,000 years

    NASA Astrophysics Data System (ADS)

    Dubois, Nathalie; Kienast, Markus; Kienast, Stephanie S.; Timmermann, Axel

    2014-06-01

    Amplifying both internally generated variability and remote climate signals from the Atlantic Ocean via coupled air-sea instabilities, the eastern tropical Pacific (ETP) is well situated to detect past climate changes and variations in Central American wind systems that dynamically link the Atlantic and the Pacific. Here we compare new and previously published alkenone-based sea surface temperature (SST) reconstructions from diverse environments within the ETP, i.e. the Eastern Pacific Warm Pool (EPWP), the equatorial and the northern Peruvian Upwelling regions over the past 100,000 yr. Over this time period, a fairly constant meridional temperature gradient across the region is observed, indicating similar hydrographic conditions during glacial and interglacial periods. The data further reveal that millennial-scale cold events associated with massive iceberg surges in the North Atlantic (Heinrich events) generate cooling in the ETP from ∼8°N to ∼2°S. Data from Heinrich event 1, however, indicate that the response changes sign south of 2°S. These millennial-scale alterations of the SST pattern across diverse environments of the ETP support previous climate modeling experiments that suggested an Atlantic-Pacific connection caused by the intensification of the Central American gap winds, enhanced upwelling and mixing north of the equator and supported by positive air-sea feedbacks in the eastern tropical Pacific.

  17. Millennial-scale ocean acidification and late Quaternary

    SciTech Connect

    Riding, Dr Robert E; Liang, Liyuan; Braga, Dr Juan Carlos

    2014-01-01

    Ocean acidification by atmospheric carbon dioxide has increased almost continuously since the last glacial maximum (LGM), 21 000 years ago. It is expected to impair tropical reef development, but effects on reefs at the present day and in the recent past have proved difficult to evaluate. We present evidence that acidification has already significantly reduced the formation of calcified bacterial crusts in tropical reefs. Unlike major reef builders such as coralline algae and corals that more closely control their calcification, bacterial calcification is very sensitive to ambient changes in carbonate chemistry. Bacterial crusts in reef cavities have declined in thickness over the past 14 000 years with largest reduction occurring 12 000 10 000 years ago. We interpret this as an early effect of deglacial ocean acidification on reef calcification and infer that similar crusts were likely to have been thicker when seawater carbonate saturation was increased during earlier glacial intervals, and thinner during interglacials. These changes in crust thickness could have substantially affected reef development over glacial cycles, as rigid crusts significantly strengthen framework and their reduction would have increased the susceptibility of reefs to biological and physical erosion. Bacterial crust decline reveals previously unrecognized millennial-scale acidification effects on tropical reefs. This directs attention to the role of crusts in reef formation and the ability of bioinduced calcification to reflect changes in seawater chemistry. It also provides a long-term context for assessing anticipated anthropogenic effects.

  18. Millennial-Scale Subsurface Temperature Change in the Niger Delta Linked to Atlantic Meridional Overturning Circulation Variability During the Last Deglacial

    NASA Astrophysics Data System (ADS)

    Schmidt, M. W.; Parker, A. O.; Chang, P.

    2015-12-01

    Understanding how Atlantic Meridional Overturning Circulation (AMOC) variability influenced the abrupt climatic changes that characterized the last deglacial has become a fundamental topic in Paleoceanography. Both modern observations and modeling simulations suggest that subsurface temperatures between 300-600 m across the Tropical North Atlantic warm when AMOC weakens, providing a possible fingerprint for reconstructing past AMOC variability (Schmidt et al., 2012). Furthermore, this AMOC-induced subsurface warming has the potential to impact the West African Monsoon, possibly providing an important high-latitude / tropical climate teleconnection (Chang et al., 2008). Here, we present a new high-resolution Mg/Ca record of subsurface (~300 m water depth) temperature variability across the last deglacial from sediment core Fan 17 (4.81oN, 4.41oE, 1178 m depth) recovered from the Niger Delta based on the deep-dwelling planktonic foraminifera Globorotalia crassaformis. Our G. crassaformis Mg/Ca record suggests an increase in subsurface temperatures up to 4oC from 17.2 to 14.8 kyr, consistent with previously published proxy data suggesting AMOC was in a reduced state during Heinrich Event 1 and the subsequent Mystery Interval (McManus et al., 2004). The G. crassaformis Mg/Ca record then shows a cooling associated with the onset of the Bølling Allerød interstadial, followed by a second warming at the start of the Younger Dryas. These millennial-scale warming events are nearly synchronous with a similar record of subsurface temperature change from the Bonaire Basin in the Southern Caribbean (Schmidt et al., 2012) and may provide important evidence for the rapid adjustment of tropical Atlantic subsurface temperatures in response to a weakened AMOC state.

  19. Millennial-scale temperature change velocity in the continental northern Neotropics.

    PubMed

    Correa-Metrio, Alexander; Bush, Mark; Lozano-García, Socorro; Sosa-Nájera, Susana

    2013-01-01

    Climate has been inherently linked to global diversity patterns, and yet no empirical data are available to put modern climate change into a millennial-scale context. High tropical species diversity has been linked to slow rates of climate change during the Quaternary, an assumption that lacks an empirical foundation. Thus, there is the need for quantifying the velocity at which the bioclimatic space changed during the Quaternary in the tropics. Here we present rates of climate change for the late Pleistocene and Holocene from Mexico and Guatemala. An extensive modern pollen survey and fossil pollen data from two long sedimentary records (30,000 and 86,000 years for highlands and lowlands, respectively) were used to estimate past temperatures. Derived temperature profiles show a parallel long-term trend and a similar cooling during the Last Glacial Maximum in the Guatemalan lowlands and the Mexican highlands. Temperature estimates and digital elevation models were used to calculate the velocity of isotherm displacement (temperature change velocity) for the time period contained in each record. Our analyses showed that temperature change velocities in Mesoamerica during the late Quaternary were at least four times slower than values reported for the last 50 years, but also at least twice as fast as those obtained from recent models. Our data demonstrate that, given extremely high temperature change velocities, species survival must have relied on either microrefugial populations or persistence of suppressed individuals. Contrary to the usual expectation of stable climates being associated with high diversity, our results suggest that Quaternary tropical diversity was probably maintained by centennial-scale oscillatory climatic variability that forestalled competitive exclusion. As humans have simplified modern landscapes, thereby removing potential microrefugia, and climate change is occurring monotonically at a very high velocity, extinction risk for tropical

  20. Millennial-Scale Temperature Change Velocity in the Continental Northern Neotropics

    PubMed Central

    Correa-Metrio, Alexander; Bush, Mark; Lozano-García, Socorro; Sosa-Nájera, Susana

    2013-01-01

    Climate has been inherently linked to global diversity patterns, and yet no empirical data are available to put modern climate change into a millennial-scale context. High tropical species diversity has been linked to slow rates of climate change during the Quaternary, an assumption that lacks an empirical foundation. Thus, there is the need for quantifying the velocity at which the bioclimatic space changed during the Quaternary in the tropics. Here we present rates of climate change for the late Pleistocene and Holocene from Mexico and Guatemala. An extensive modern pollen survey and fossil pollen data from two long sedimentary records (30,000 and 86,000 years for highlands and lowlands, respectively) were used to estimate past temperatures. Derived temperature profiles show a parallel long-term trend and a similar cooling during the Last Glacial Maximum in the Guatemalan lowlands and the Mexican highlands. Temperature estimates and digital elevation models were used to calculate the velocity of isotherm displacement (temperature change velocity) for the time period contained in each record. Our analyses showed that temperature change velocities in Mesoamerica during the late Quaternary were at least four times slower than values reported for the last 50 years, but also at least twice as fast as those obtained from recent models. Our data demonstrate that, given extremely high temperature change velocities, species survival must have relied on either microrefugial populations or persistence of suppressed individuals. Contrary to the usual expectation of stable climates being associated with high diversity, our results suggest that Quaternary tropical diversity was probably maintained by centennial-scale oscillatory climatic variability that forestalled competitive exclusion. As humans have simplified modern landscapes, thereby removing potential microrefugia, and climate change is occurring monotonically at a very high velocity, extinction risk for tropical

  1. 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.

  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. Millennial-scale ocean current intensity changes off southernmost Chile and implications for Drake Passage throughflow

    NASA Astrophysics Data System (ADS)

    Lamy, F.; Arz, H. W.; Kilian, R.; Baeza Urrea, O.; Caniupan, M.; Kissel, C.; Lange, C.

    2012-04-01

    The Antarctic Circumpolar Current (ACC) plays an essential role in the thermohaline circulation and global climate. Today a large volume of ACC water passes through the Drake Passage, a major geographic constrain for the circumpolar flow. Satellite tracked surface drifters have shown that Subantarctic Surface water of the ACC is transported northeastward across the Southeast Pacific from ~53°S/100°W towards the Chilean coast at ~40°S/75°W where surface waters bifurcate and flow northward into the Peru Chile Current (PCC) finally reaching the Eastern Tropical Pacific, and southwards into the Cape Horn Current (CHC). The CHC thus transports a significant amount of northern ACC water towards the Drake Passage and reaches surface current velocities of up to 35 cm/s within a narrow belt of ~100-150 km width off the coast. Also at deeper water levels, an accelerated southward flow occurs along the continental slope off southernmost South America that likewise substantially contributes to the Drake Passage throughflow. Here we report on high resolution geochemical and grain-size records from core MD07-3128 (53°S; 1032 m water depth) which has been retrieved from the upper continental slope off the Pacific entrance of the Magellan Strait beneath the CHC. Magnetic grain-sizes and grain-size distributions of the terrigenous fraction reveal large amplitude changes between the Holocene and the last glacial, as well as millennial-scale variability (most pronounced during Marine Isotope Stage). Magnetic grain-sizes, silt/clay ratios, fine sand contents, sortable silt contents, and sortable silt mean grain-sizes are substantially higher during the Holocene suggesting strongly enhanced current activity. The high absolute values imply flow speeds larger than 25 cm/s as currently observed in the CHC surface current. Furthermore, winnowing processes through bottom current activity and changes in the availability of terrigenous material (ice-sheet extension and related supply of

  5. Millennial-Scale Variability in the Asian Monsoon from Chinese Cave Records (Invited)

    NASA Astrophysics Data System (ADS)

    Edwards, R.; Cheng, H.

    2013-12-01

    Over the past 15 years a number of key climate records based upon the oxygen isotopic cave calcite have been published. Such records reflect changes in the oxygen isotopic composition of rainfall at the cave sites. Among the strengths of the cave records are the possibility of precise dating using the Th-230 dating method, high resolution oxygen isotope values (typically a few years to several decades), the possibility of long records (hundreds of thousands of years), and the possibility of wide geographic coverage. Records from caves (mainly from Hulu, Dongge, and Sanbao) in SE China now cover much of the past 400,000 with an average oxygen isotope resolution of several decades. The Chinese record follows summer solar insolation and also exhibits millennial-scale variability. For the last glacial cycle, virtually every significant millennial and centennial-scale event observed in Greenland is also observed in the Hulu and/or Dongge Cave records, with inferred higher monsoon rainfall correlating with inferred higher temperature in Greenland. We have established cave-based chronologies for the NGRIP and GISP2 records based correlations of these events. Using these timescales, none of the records (cave or ice) exhibit precisely timed jumps into interstadial conditions at intervals of 1470 to 1500 years as required by some versions of the stochastic resonance model. However, all have significant spectral power at ~1500 years, suggesting that a version of the model that does not require exact timing may be viable. In addition to millennial-scale events, Heinrich Stadial Events are observed in the Chinese records as times of unusually low inferred monsoon rainfall, which we term 'Weak Monsoon Intervals'. All of the Heinrich Stadial Events of the last glacial period are found in the Chinese record. Furthermore, major Weak Monsoon Intervals (WMIs) or sequences of WMIs are found on each of the last five ice age terminations. On each termination, the WMIs correlate with ice

  6. The role of sea ice in abrupt climate changes following the last glacial maximum

    NASA Astrophysics Data System (ADS)

    Nisancioglu, Kerim; Dokken, Trond

    2017-04-01

    Climate changes following the last glacial maximum ( 21-10ka BP) are considered some of the most dramatic and wide reaching abrupt events of the geological past. On Greenland the transition from the last glacial maximum to the Bølling-Allerød (BA) warm period was extremely abrupt, as is the transitions in and out of the Younger Dryas (YD) cold period. In terms of ocean changes, there are indications from proxy records that the large scale Atlantic Meridional Overturning Circulation (AMOC) was significantly reduced a few thousand years before the BA and again at the start of the YD. However, the link between changes in AMOC and climate in the Northern Hemisphere and in particular on Greenland is unclear. Here, we study changes to climate and circulation in the North Atlantic across these key climate transitions based on a sediment core from the Nordic Seas as well as sensitivity studies with a global climate model. Preliminary results suggest that changes in sea ice and stratification of the Nordic Seas played a key role in the observed climate changes during and preceding the deglaciation of the large land based ice sheets. In particular the cold period following Heinrich Event 1 (H1) and ending at the BA as well as the cold YD are associated with expansions of Arctic sea ice into the Nordic Seas region.

  7. 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.

  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. Millennial-scale cyclicity in the Pliocene: Evidence from the East African Rift Valley

    NASA Astrophysics Data System (ADS)

    Wilson, K. E.; Leng, M. J.; Edgar, R. K.; Deino, A. L.; Kingston, J. D.; Maslin, M. A.; Mackay, A. W.

    2010-12-01

    Superimposed on the long-term trend of aridification in East Africa were a series of humid episodes, coincident with major transitions in global climate during the Plio-Pleistocene. The period of climatic variability between 2.7 and 2.5 Ma is coeval with the amplification of ice sheet growth and cooling in the Northern Hemisphere, however climate change in the low latitudes remains poorly understood. In the Tugen Hills, a well-dated package of fluviolacustrine sediments, characterised by five diatomite units, records the precessionally-driven cycling of a major freshwater lake system in the Baringo-Bogoria basin within the Central Kenyan Rift between 2.68 and 2.55 Ma. We use stable oxygen isotope measurements of diatom silica (δ18Odiatom), combined with the analysis of whole-sample geochemistry by x-ray fluorescence, to investigate potential palaeoenvironmental signals recorded in the best dated of these diatomite deposits spanning the period between 2.606 Ma and 2.617 Ma (40Ar/39Ar chronology normalised to Astronomical Polarity Time Scale). Geochemical results were modelled using multivariate statistics, and mass-balance calculations were applied to the isotope values to correct for the effects of residual contamination within the purified diatom samples. The modelled δ18Odiatom values, coupled with diatom assemblage counts, reveal a series of millennial-scale climate oscillations throughout the period of diatomite deposition. Six negative excursions in the δ18Odiatom signal of up to 5 per mil represent periods of enhanced precipitation and indicate that wet-dry cycles occur, on average, every 1,400 years. Such high-resolution cycles are rarely found in records from this time, thus giving a valuable insight to the nature of short-term fluctuations in Pliocene climate.

  10. The role of stochastic noise in the abrupt climatic transitions of the pleistocene

    SciTech Connect

    Matteucci, G.

    1991-01-01

    Analyses of marine [delta][sup 18]O records suggest that the variations of the Earth's orbital parameters have induced and provided the timing of the Pleistocene climatic oscillations. This dissertation analyses some statistical properties of the Pleistocene climate by estimating the Probability Density Function (PDF) of the [delta][sup 18]O record. The results allow to define statistically what were the [open quotes]typical conditions[close quotes] (in a probabilistic sense) of the Quaternary, to identify the modes of the PDF as the mean glacial and interglacial climatic states, and to clarify the meaning and the abruptness of the climatic transitions. A zero-dimensional Energy Balance Model is developed. The nonlinearity of the ice albedo-temperature feedback leads to multiple steady-state equilibria. The role of stochastic perturbations and their interaction with the orbital forcing in producing the periodic and abrupt climatic transitions of the late Pleistocene are illustrated. A stochastic sensitivity analysis is used to clarify the results, especially the selective amplification of the orbitally-induced 100 kyr cycle, and the predictability of the system on the time scales of the orbital cycles. From the analysis of GCM simulations and observational zonally- averaged data a one-dimensional EBM is then developed. The strong nonlinearity of this model and the occurrence of multiple equilibria is caused by the presence of the Thin Ice Cap Instability. A discussion of the features that stochastic perturbations would introduce, follows. Finally a GCM sensitivity study to atmospheric CO[sub 2] shows how the effects of varying CO[sub 2] concentrations can be included in simple EBMs. The role that stochastic perturbations, orbital forcing, and the known past concentrations of atmospheric CO[sub 2] have played in producing the abrupt climatic transitions of the late Pleistocene is discussed.

  11. Deglacial Millennial-scale Calcium Carbonate Spikes in the North Pacific Ocean

    NASA Astrophysics Data System (ADS)

    Chikamoto, M. O.; Timmermann, A.; Harada, N.; Okazaki, Y.

    2015-12-01

    Numerous paleoproxy records from the subarctic Pacific Ocean show two very pronounced deglacial peaks in calcium carbonate content for the Heinrich 1/ Bolling-Allerod (H1-BA) transition (at 14 ka) and for the Younger Dryas/Preboreal transition (at 11 ka). Focusing on the H1-BA transition, some model simulations capture the North Pacific shift from ventilated to stratified conditions and from cooling to warming conditions via oceanic and atmospheric connections between Atlantic and Pacific Oceans. To test the impact of these physical scenarios (variations in ocean stratification and temperature during the H1-BA transition) on calcite production or preservation, we conduct a series of idealized experiments using the Earth System Model Intermediate Complexity LOVECLIM. The variations in North Pacific Ocean stratification by anomalous freshwater forcing show low calcite productivity in associated with the subsurface nutrient decline. On the other hand, the rapid H1-BA warming of the North Pacific Ocean induced by anomalous heat forcing in turn increases calcite productivity due to the temperature-dependent growth rate of phytoplankton. These results suggest the possibility that the millennial-scale calcium carbonate peaks are the result of surface biogeochemical responses to the climate transition, not by the deep circulation response.

  12. The "MIS 11 paradox" and ocean circulation: Role of millennial scale events

    NASA Astrophysics Data System (ADS)

    Vázquez Riveiros, Natalia; Waelbroeck, Claire; Skinner, Luke; Duplessy, Jean-Claude; McManus, Jerry F.; Kandiano, Evgenia S.; Bauch, Henning A.

    2013-06-01

    The role of millennial scale climate variability in supplementing the astronomical forcing of glacial-interglacial transitions remains a major unresolved question. Here we compare the occurrence and character of "terminal" ice rafting events in both the North and South Atlantic during the last deglaciation (Termination I, TI) and during the transition between Marine Isotope Stages (MIS) 12 and 11 (or Termination V, TV). We show that TV experienced a massive terminal ice rafting event in the North Atlantic that was more intense and longer lasting than Heinrich event 1 (H1) of the last deglaciation. This massive ice rafting event was linked to cold stadial conditions and reduced deep water formation in the North Atlantic, in parallel with warming at high southern latitudes, similar to the bipolar seesaw pattern exhibited during H1 over the last deglaciation. We propose that the particular intensity and duration of the TV ice rafting event resulted from the especially large volume of Northern Hemisphere ice sheets during MIS12. In turn, the unusually long duration and large amplitude of TV likely resulted from the exceptionally prolonged collapse of the AMOC during the TV Heinrich stadial, and from a subsequent transient AMOC "overshoot" with respect to later MIS11 interglacial circulation. Furthermore, we suggest that the intense Heinrich stadial of TV contributed to the deglaciation primarily via meridional heat transport anomalies that would have enhanced the incipient warming arising from relatively weak insolation forcing, and only secondarily via CO2 release.

  13. Glacial reduction and millennial-scale variations in Drake Passage throughflow

    PubMed Central

    Lamy, Frank; Arz, Helge W.; Kilian, Rolf; Lange, Carina B.; Lembke-Jene, Lester; Wengler, Marc; Kaiser, Jérôme; Baeza-Urrea, Oscar; Hall, Ian R.; Harada, Naomi; Tiedemann, Ralf

    2015-01-01

    The Drake Passage (DP) is the major geographic constriction for the Antarctic Circumpolar Current (ACC) and exerts a strong control on the exchange of physical, chemical, and biological properties between the Atlantic, Pacific, and Indian Ocean basins. Resolving changes in the flow of circumpolar water masses through this gateway is, therefore, crucial for advancing our understanding of the Southern Ocean’s role in global ocean and climate variability. Here, we reconstruct changes in DP throughflow dynamics over the past 65,000 y based on grain size and geochemical properties of sediment records from the southernmost continental margin of South America. Combined with published sediment records from the Scotia Sea, we argue for a considerable total reduction of DP transport and reveal an up to ∼40% decrease in flow speed along the northernmost ACC pathway entering the DP during glacial times. Superimposed on this long-term decrease are high-amplitude, millennial-scale variations, which parallel Southern Ocean and Antarctic temperature patterns. The glacial intervals of strong weakening of the ACC entering the DP imply an enhanced export of northern ACC surface and intermediate waters into the South Pacific Gyre and reduced Pacific–Atlantic exchange through the DP (“cold water route”). We conclude that changes in DP throughflow play a critical role for the global meridional overturning circulation and interbasin exchange in the Southern Ocean, most likely regulated by variations in the westerly wind field and changes in Antarctic sea ice extent. PMID:26417070

  14. Glacial reduction and millennial-scale variations in Drake Passage throughflow.

    PubMed

    Lamy, Frank; Arz, Helge W; Kilian, Rolf; Lange, Carina B; Lembke-Jene, Lester; Wengler, Marc; Kaiser, Jérôme; Baeza-Urrea, Oscar; Hall, Ian R; Harada, Naomi; Tiedemann, Ralf

    2015-11-03

    The Drake Passage (DP) is the major geographic constriction for the Antarctic Circumpolar Current (ACC) and exerts a strong control on the exchange of physical, chemical, and biological properties between the Atlantic, Pacific, and Indian Ocean basins. Resolving changes in the flow of circumpolar water masses through this gateway is, therefore, crucial for advancing our understanding of the Southern Ocean's role in global ocean and climate variability. Here, we reconstruct changes in DP throughflow dynamics over the past 65,000 y based on grain size and geochemical properties of sediment records from the southernmost continental margin of South America. Combined with published sediment records from the Scotia Sea, we argue for a considerable total reduction of DP transport and reveal an up to ∼ 40% decrease in flow speed along the northernmost ACC pathway entering the DP during glacial times. Superimposed on this long-term decrease are high-amplitude, millennial-scale variations, which parallel Southern Ocean and Antarctic temperature patterns. The glacial intervals of strong weakening of the ACC entering the DP imply an enhanced export of northern ACC surface and intermediate waters into the South Pacific Gyre and reduced Pacific-Atlantic exchange through the DP ("cold water route"). We conclude that changes in DP throughflow play a critical role for the global meridional overturning circulation and interbasin exchange in the Southern Ocean, most likely regulated by variations in the westerly wind field and changes in Antarctic sea ice extent.

  15. Postglacial Human resilience and susceptibility to abrupt climate change new insights from Star Carr

    NASA Astrophysics Data System (ADS)

    Blockley, Simon; Abrook, Ashley; Bayliss, Alex; Candy, Ian; Conneller, Chantal; Darvill, Chris; Deeprose, Laura; Kearney, Rebecca; Langdon, Pete; Langdon Langdon, Cath; Lincoln, Paul; Macleod, Alison; Matthews, Ian; Palmer, Adrian; Schreve, Danielle; Taylor, Barry; Milner, Nicky

    2017-04-01

    We know little about the lives of the early humans who lived during the early Postglacial period (the Lateglacial and Early Holocene), a time characterised by abrupt climate change after 16,000, which includes a series of abrupt climatic transitions linked to the reorganisation of the global environment after the glacial maximum and the last major global warming event at the onset of the Holocene. The hunter-gatherers who lived during the early Postglacial have been characterised as highly mobile, dispersed and living within small groups, and there is much debate as to how they adapted to climatic and environmental change: did they move in response to climatic transitions (and if so what was the climatic threshold), or instead adapt their lifeways to the new environmental conditions? A key area for examining these ideas is the British Isles as it sits on the Atlantic fringe of Northwest Europe with a climate that is highly responsive to the wider climate forcing experienced in the northern Hemisphere. Furthermore, in this period, Britain is directly linked to continental Europe due to lowered global sea levels allowing for the ease of human migration in and out of this region. In general the British record has been seen as being dominated by abandonment and reoccupation in the Postglacial during periods of climatic transition with hunter-gatherer mobility being closely linked to the prevailing environment. Recent discoveries at the Early Mesolithic site of Star Carr and surrounding area, linked to local and regional climate records, based on isotopic, chironomid and pollen proxy data and dated at high chronological resolution, offer a new picture. Postglacial human occupation of the area commences at the Pleistocene/Holocene transition but is short lived and appears to end close to the Pre-Boreal Oscillation, However, this is followed by a period where hunter-gatherers occupy Star Carr and settle and invest time and effort into building huts and large scale wooden

  16. Decadal to millennial scale archaeointensity variations in the Levant

    NASA Astrophysics Data System (ADS)

    Shaar, R.; Tauxe, L.; Ron, H.; Agnon, A.; Ben-Yosef, E.; Finkelstein, I.

    2013-12-01

    Recovering the absolute intensity of the past geomagnetic field (paleointensity) is a fundamental effort in the paleomagnetic research, but it is a complicated task. Paleointensity experiments should be carefully designed using sufficient number of specimens, and accurate correction for remanence anisotropy, cooling rate effects, and non-linear TRM (NLT). In addition, the basic assumption of the paleointensity method - a stable thermoremanent magnetization carried by single domain like particles - is hard to test using non-destructive methods. As a result, the interpretation of the paleointensity experiments can be non-unique and ambiguous. Moreover, the experimental difficulties compound with dating uncertainties related to the studied materials. We address each of these difficulties in an effort to construct a high resolution paleointensity curve of the Levant on archaeological time scales (archaeointensity). To address the experimental issues we apply the Thellier-type IZZI protocol with additional anisotropy, cooling rate, and NLT corrections. To ensure consistency, comparability, and objectivity of the interpretations we apply an automatic data analysis technique using an open code computer program (PmagPy Thellier GUI). To account for ambiguous interpretations we make the raw data, which include thousands of specimens, available in the MagIC database to allow other researchers to re-interpret and compile the datasets. Here we present the current status of the Levantine archaeointensity curve, and discuss its implication on our understanding of geomagnetic secular variations. The Levantine dataset includes mostly data from slag deposits - industrial heaps of metallurgic slag, and archaeological mounds ('Tel') - stratified sites created by cities rebuilt on top of others. The two types of records complement each other in a constructive fashion. The slag deposits provide records in a decadal resolution, while the mounds offer centennial to millennial scale

  17. 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.

  18. 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.

  19. 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.

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

    PubMed Central

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

    2013-01-01

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

  1. 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.

  2. Linear trend and abrupt changes of climate indices in the arid region of northwestern China

    NASA Astrophysics Data System (ADS)

    Wang, Huaijun; Pan, Yingping; Chen, Yaning; Ye, Zhengwei

    2017-11-01

    In recent years, climate extreme events have caused increasing direct economic and social losses in the arid region of northwestern China. Based on daily temperature and precipitation data from 1960 to 2010, this paper discussed the linear trend and abrupt changes of climate indices. The general evolution was obtained by the empirical orthogonal function (EOF), the Mann-Kendall test, and the distribution-free cumulative sum chart (CUSUM) test. The results are as follows: (1) climate showed a warming trend at annual and seasonal scale, with all temperature indices exhibiting statistically significant changes. The warm indices have increased, with 1.37%days/decade of warm days (TX90p), 0.17 °C/decade of warmest days (TXx) and 1.97 days/decade of warm spell duration indicator (WSDI), respectively. The cold indices have decreased, with - 1.89%days/decade, 0.65 °C/decade and - 0.66 days/decade for cold nights (TN10p), coldest nights (TNn) and cold spell duration indicator (CSDI), respectively. The precipitation indices have also increased significantly, coupled with the changes of magnitude (max 1-day precipitation amount (RX1day)), frequency (rain day (R0.1)), and duration (consecutive dry days (CDD)). (2) Abrupt changes of the annual regional precipitation indices and the minimum temperature indices were observed around 1986, and that of the maximum temperature indices were observed in 1996. (3) The EOF1 indicated the overall coherent distribution for the whole study area, and its principal component (PC1) was also observed, showing a significant linear trend with an abrupt change, which were in accordance with the regional observation results. EOF2 and EOF3 show contrasts between the southern and northern study areas, and between the eastern and western study areas, respectively, whereas no significant tendency was observed for their PCs. Hence, the climate indices have changed significantly, with linear trends and abrupt changes noted for all climate indices

  3. 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.

  4. 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.

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

    PubMed Central

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

    2006-01-01

    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 10Be and dust) and wetland methane emissions. The simulations produce a short period of significantly diminished North Atlantic Deep Water and are able to quantitatively match paleoclimate observations, including the lack of isotopic signal in the North Atlantic. This direct comparison with multiple proxy records provides compelling evidence that changes in ocean circulation played a major role in this abrupt climate change event. PMID:16415159

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

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

    PubMed Central

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

    2011-01-01

    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. PMID:21628586

  13. 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.

  14. Asian Monsoon Variations on Orbital-Millennial Scales and the `100 Thousand Year Problems'

    NASA Astrophysics Data System (ADS)

    Cheng, H.; Edwards, R. L.; Sinha, A.; Spoetl, C.; Yi, L.; Li, X.; Kathayat, G.

    2016-12-01

    Speleothem oxygen isotope records from China characterize changes in the Asian monsoon and global climate. We have now extended our Chinese record to cover the full uranium/thorium dating range: the last 640,000 years. The record's length, temporal precision, and correlations with both ice core and marine records allow us to further probe the enduring `100 ka problem'—i.e., why do large-amplitude ice age cycles and changes in eccentricity share common spectral power although the latter generates negligible change in insolation? Based on our record's timing, the ice age terminations are separated by 4 or 5 precession cycles, supporting the idea that the 100 ka ice age cycle is an average of discrete numbers of precession cycles. Furthermore, the suborbital component of monsoon rainfall variability exhibits power in precession and obliquity bands, and is nearly anti-phased with June 21 boreal insolation. These observations indicate that insolation, in part, paces the occurrence of millennial-scale events, including those associated with ice age terminations and `unfinished terminations'. In the East Asian summer monsoon (EASM) domain, Loess magnetic susceptibility records from the Chinese Loess Plateau (CLP) show that the EASM is dominated by 100 ka cycles, which is in contrast to the conventional notion that insolation changes caused by the 20 ka precession cycle are the primary driver of summer monsoon. These observations present another paradox, which we dub here as the `Chinese 100 ka problem'. The existing and new speleothem records from both China and India reinforce the idea that precession, rather than glacial-interglacial, cycles, is the dominant driver of both EASM and Indian summer monsoon variations. The lack of precession signals in the loess records from the CLP might stem partially from its unique climatological settings and complex nature of loess magnetic susceptibility proxy.

  15. Millennial-scale interaction between ice sheets and ocean circulation during marine isotope stage 100

    NASA Astrophysics Data System (ADS)

    Ohno, Masao; Hayashi, Tatsuya; Sato, Masahiko; Kuwahara, Yoshihiro; Mizuta, Asami; Kita, Itsuro; Sato, Tokiyuki; Kano, Akihiro

    2016-05-01

    Waxing/waning of the ice sheets and the associated change in thermohaline circulation have played an important role in global climate change since major continental ice sheets appeared in the northern hemisphere about 2.75 million years ago. In the earliest glacial stages, however, establishment of the linkage between ice sheet development and ocean circulation remain largely unclear. Here we show new high-resolution records of marine isotope stage 100 recovered from deep-sea sediments on the Gardar Drift, in the subpolar North Atlantic. Results of a wide range of analyses clearly reveal the influence of millennial-scale variability in iceberg discharge on ocean surface condition and bottom current variability in the subpolar North Atlantic during marine isotope stage 100. We identified eight events of ice-rafted debris, which occurred mostly with decreases in sea surface temperature and in current components indicating North Atlantic Deep Water. These decreases are interpreted by weakened deep water formation linked to iceberg discharge, similarly to observations from the last glacial period. Dolomite fraction of the ice-rafted events in early MIS 100 like the last glacial Heinrich events suggests massive collapse of the Laurentide ice sheet in North America. At the same time, our early glacial data suggest differences from the last glacial period: absence of 1470-year periodicity in the interactions between ice sheets and ocean, and northerly shift of the ice-rafted debris belt. Our high-resolution data largely improve the picture of ice-sheet/ocean interactions on millennial time scales in the early glacial period after major Northern Hemisphere glaciation.

  16. Northern Hemisphere millennial-scale ice discharges as a response to oceanic forcing simulated with a hybrid ice-sheet/ice-shelf model

    NASA Astrophysics Data System (ADS)

    Alvarez-Solas, J.; Montoya, M.; Robinson, A. J.; Banderas-Carreño, R.; Ritz, C.; Ganopolski, A.

    2012-04-01

    Marine and continental records and ice core data have revealed the existence of pronounced millennial time-scale climate variability during the last glacial cycle. Greenland ice core records show abrupt transitions known as Dansgaard-Oeschger (DO) events within decades from cold (stadial) to relatively warm (interstadial) conditions, followed by slow cooling that lasts several centuries and more rapid cooling through stadial conditions. Two types of explanation have been suggested: periodic external forcing and internal oscillations in the climate system, for which ocean circulation is the main candidate. On the other hand, six periods of extreme cooling registered in the Northern Hemisphere, known as Heinrich events, have been found to be coeval with increased deposition of ice-rafted debris, which is interpreted as enhanced discharge of icebergs into the North Atlantic Ocean. Recently, the coupled effects between ocean circulation and ice-sheets dynamics have been suggested to play a major role in triggering Heinrich events. This interpretation of Heinrich events responding to changes in the oceanic patterns (or at least not being purely internal and spontaneous manifestations of ice sheets), allows the possibility to provide an explicit relationship between DO events and the periodic iceberg surges. Here this hypothesis is reassessed within a more realistic modeling framework by forcing a 3D state-of-the-art ice-sheet model with the output of abrupt climate change simulations carried out with a coupled climate model of intermediate complexity. These show the main expected characteristics of such events: an abrupt warming of the North Atlantic and Atlantic Meridional Overturning Circulation (AMOC) intensification followed by a progressive cooling and AMOC reduction, as well as a more drastic fall into a stadial condition. Interestingly, stadial periods are characterized by the occurrence of subsurface oceanic warming of up to 3 K in regions where deep water

  17. Millennial-scale variability in dust deposition, marine export production, and nutrient consumption in the glacial subantarctic ocean (Invited)

    NASA Astrophysics Data System (ADS)

    Martinez-Garcia, A.; Sigman, D. M.; Anderson, R. F.; Ren, H. A.; Hodell, D. A.; Straub, M.; Jaccard, S.; Eglinton, T. I.; Haug, G. H.

    2013-12-01

    Based on the limitation of modern Southern Ocean phytoplankton by iron and the evidence of higher iron-bearing dust fluxes to the ocean during ice ages, it has been proposed that iron fertilization of Southern Ocean phytoplankton contributed to the reduction in atmospheric CO2 during ice ages. In the Subantarctic zone of the Atlantic Southern Ocean, glacial increases in dust flux and export production have been documented, supporting the iron fertilization hypothesis. However, these observations could be interpreted alternatively as resulting from the equatorward migration of Southern Ocean fronts during ice ages if the observed productivity rise was not accompanied by an increase in major nutrient consumption. Here, new 230Th-normalized lithogenic and opal fluxes are combined with high-resolution biomarker measurements to reconstruct millennial-scale changes in dust deposition and marine export production in the subantarctic Atlantic over the last glacial cycle. In the same record foraminifera-bound nitrogen isotopes are used to reconstruct ice age changes in surface nitrate utilization, providing a comprehensive test of the iron fertilization hypothesis. Elevation in foraminifera-bound δ15N, indicating more complete nitrate consumption, coincides with times of surface cooling and greater dust flux and export production. These observations indicate that the ice age Subantarctic was characterized by iron fertilized phytoplankton growth. The resulting strengthening of the Southern Ocean's biological pump can explain the ~40 ppm lowering of CO2 that characterizes the transitions from mid-climate states to full ice age conditions as well as the millennial-scale atmospheric CO2 fluctuations observed within the last ice age

  18. 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

  19. 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.

  20. Abrupt climate changes of the last deglaciation detected in a western Mediterranean forest record

    NASA Astrophysics Data System (ADS)

    Fletcher, W. J.; Sanchez Goñi, M. F.; Peyron, O.; Dormoy, I.

    2009-01-01

    Evidence for abrupt changes in western Mediterranean climate between 20 and 6 cal ka BP is examined in marine core MD95-2043 (Alborán Sea), using pollen data for temperate Mediterranean forest development and pollen-based climate reconstructions using the modern analogue technique (MAT) for annual precipitation (Pann) and mean temperatures of the coldest and warmest months (MTCO and MTWA). Major climatic shifts with parallel temperature and precipitation changes occurred at the onsets of Heinrich Event 1 (equivalent to the Oldest Dryas), the Bölling-Allerød (BA), and the Younger Dryas (YD). Multi-centennial-scale oscillations in forest development related to regional precipitation (Pann) variability occurred throughout the BA, YD, and early Holocene, with drier atmospheric conditions in phase with Lateglacial events of high-latitude cooling including GI-1d (Older Dryas), GI-1b (Intra-Allerød Cold Period) and GS-1 (YD), and during Holocene events associated with high-latitude cooling, meltwater pulses and N. Atlantic ice-rafting (events at 11.4, 10.1, 9.3, 8.2 and 7.4 cal ka BP). The forest record also indicates multi-centennial variability within the YD interval and multiple Preboreal climate oscillations. A possible climatic mechanism for the recurrence of dry intervals and an opposed regional precipitation pattern with respect to western-central Europe relates to the dynamics of the jet stream and the prevalence of atmospheric blocking highs. Comparison of radiocarbon and ice-core ages for well-defined climatic transitions in the forest record suggests possible enhancement of marine reservoir ages in the Alborán Sea by ~200 years (surface water age ~600 years) during the Lateglacial.

  1. 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.

  2. 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.

  3. 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.

  4. 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

  5. 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

  6. Sub-millennial Scale Hydrographic Variation on the New Jersey Margin

    NASA Astrophysics Data System (ADS)

    Bauska, T.; Sommerfield, C.; Martin, P.; Billups, K.

    2006-12-01

    This study presents first results of an attempt to resolve millennial and sub-millennial scale climate variations on the New Jersey Margin (ODP Site 1073, 650 m water depth). We use oxygen isotope analysis of planktonic foraminifera (Globorotalia inflata) to explore the potential of this site to resolve rapid paleoenvironmental change at a location near the paleo ice margin and in the path of freshwater discharge from the Hudson River. We also examine variations in the mean grain size of the sortable silt (10-63 μm) to explore the potential for resolving concurrent changes in bottom water currents. Thus far, we have sampled a 30 m sediment section representing the Last Glacial Maximum radiocarbon dated to between 14.4 ka and 23.3 ka. With the exception of one barren interval between 16.4 and 17.8 ka, the average time step of the foraminiferal record is ~90 years; the sedimentological record is continuous at a 90-180 yr resolution. Results from the grain size analysis indicate a gradual coarsening trend from 20 ka to 14.4 ka, suggesting relatively stronger bottom currents during the early part of the deglaciation or an influx of coarse sediment from the shelf as sea level rose. The foraminiferal d18O record is very different from pelagic records spanning this time interval as it lacks a clear trend toward decreasing values reflective of ice volume changes during the deglaciation. Rather, the d18O record is dominated by large variations on the order of 1 per mil with maxima recurrent every 500 to 700 years. We interpret these rapid variations to either reflect variations in surface water temperature on the order of 4-5 ° C or freshwater water input through the Hudson River. These two scenarios will be tested using foraminiferal Mg/Ca ratios to construct an independent surface water temperature record and Ba/Ca ratios to qualitatively identify fresh water influx events. We conclude that it is possible to derive meaningful paleoenvironmental information from this

  7. What Forced Holocene Millennial-Scale Variability? A Tale from the Western Tropical Pacific

    NASA Astrophysics Data System (ADS)

    Khider, D.; Stott, L. D.; Jackson, C.; Huerta, G.

    2014-12-01

    A number of climate archives have documented millennial-scale variability during the Holocene. It is not currently known whether these variations are forced or unforced. A solar forcing hypothesis has been put forward to explain the 1000 and 2500-year periodicities because of similarities between the spectral peaks in the proxy records and reconstructions of solar variability. Our work on a marine record of Mg/Ca-based sea surface temperatures (SSTs) within the Indo-Pacific Warm Pool (core MD98-2181) challenges the solar hypothesis because there is no coherence between the amplitude of changes in solar forcing and in the proxy SSTs. There is also a long phase delay between the peak in forcing and the maximum response. On the other hand, there exists the possibility that the deep ocean can drive some of the Holocene variability, especially at the 1500-year timescale. This periodicity is reminiscent of the Marine Isotope Stage 3 (MIS3) cycles. To evaluate whether the Holocene and MIS3 variability does in fact arise from the same mechanism, we start with the premise that climate variability from different parts of the globe should have similar relationships in the Holocene as they did in MIS3. However, this comparison is difficult because of the poor chronologic constraints inherent to proxy records. We circumvented this problem by using the benthic foraminifera δ18O from the same MD81 samples, which provides a record of deep ocean temperature and salinities. Since these conservative properties are acquired in the Southern Ocean, the MD81 benthic δ18O is a record of high southern latitude variability. Thus, MD81 allows us to investigate the relative timing of tropical and southern ocean variability from a single location. A time series analysis of the MD81 record shows that although the 1,500-year cycle is present during both the Holocene and MIS3, the phasing of tropical Pacific and Southern Ocean variability is different. During the Holocene, tropical Pacific

  8. Millennial-scale provenance changes of aeolian dust in the Japan Sea sediments during the last glacial period (Invited)

    NASA Astrophysics Data System (ADS)

    Nagashima, K.; Tada, R.; Isozaki, Y.; Toyoda, S.; Tani, A.; Sun, Y.

    2009-12-01

    It is generally accepted that East Asian Summer Monsoon (EASM) intensity varies with Dansgaard-Oeschger (D-O) cycles based on the oxygen isotope ratio of stalagmites in China [Wang et al., 2001, 2008], which in turn suggest a connection between the climates in subtropical Asia and North Atlantic on a millennial-scale. However, the dynamics of such connection are still unsolved. Here we demonstrate the temporal changes in the provenance of aeolian dust in the Japan Sea sediments, which is interpreted as reflecting changes in the westerly jet path over East Asia. We further discuss the role of the westerly jet in linking the EASM to the North Atlantic climate on a millennial-scale. At present, a substantial amount of aeolian dust is emitted from the large dry areas in the East Asia, typically the Taklimakan Desert and the Gobi Desert in southern Mongolia (hereafter, Mongolian Gobi) [Sun et al., 2001; Zhao et al., 2006]. Since the Japan Sea is located on the eastern margin of the Eurasian continent under the influence of Asian winter monsoon wind and the westerly jet that passes over the Mongolian Gobi and the Taklimakan Desert, respectively, it should have been receiving significant amount of aeolian dust emitted from these deserts, in various proportions depending on the prevailing wind and the extents of the source areas [Nagashima et al., 2007]. If correct, the wind system changes over East Asia should have been recorded as the provenance changes of the aeolian dust in Japan Sea sediments. In our previous study, the Electron Spin Resonance (ESR) intensity and the Crystallinity Index (CI) of silt size quartz in the Japan Sea sediments were proved to be a good indicator of dust provenance [Nagashima et al., 2007]. We have focused on quartz because it is the major component of aeolian dust and resistant to alteration during weathering, transport, and diagenesis. So, we conducted ESR and CI analyses using the silt size quartz in Japan Sea sediments. The results show

  9. 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

  10. 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

  11. Ice Sheet Forcing of Abrupt Climate Change: Lessons from the Last Deglaciation

    NASA Astrophysics Data System (ADS)

    Clark, P. U.; Weaver, A. J.; Mitrovica, J. X.

    2003-04-01

    Ice sheets are known to influence climate through their impact on the hydrological cycle and attendant changes in the thermohaline circulation. Large and rapid releases of freshwater from ice sheets to sensitive areas of deepwater formation may arise from several mechanisms. The last deglaciation provides the level of preservation necessary to identify specific mechanisms of ice-sheet forcing and attendant climatic responses. Here, we discuss the primary mechanisms and how they have contributed to the abrupt climate changes of the last deglaciation. Sea level records suggest that the start of the deglacial sea-level rise began 19 ka with an abrupt 10--15 m sea-level rise occurring over less than 500 years. We suggest that warming that began >21 ka led to the abrupt collapse of a part of the Northern Hemisphere ice sheet system at 19 ka, perhaps through destabilizing ice shelves. A number of climate records reveal responses at this time that are consistent with this 19-ka meltwater pulse being released into the North Atlantic and disrupting North Atlantic deepwater formation. Subsequent cooling and reduced Atlantic thermohaline circulation caused the Oldest Dryas cold interval that was sustained by Heinrich event 1 at 17.7 ka. During this interval, global sea level rose at ˜2.3 mm yr-1. Subsequently, during mwp-1A, sea level rose at rates exceeding 40 mm yr-1. We suggest that mwp-1A occurred in response to a prolonged interval of Southern Hemisphere warming that began ˜19 ka. Some of this warming may have originated in response to a bipolar seesaw triggered by the large reduction in Atlantic thermohaline circulation that caused the Oldest Dryas. The rise in CO_2 and methane beginning at ˜17.5 ka may have amplified Southern Hemisphere warming prior to mwp-1A. In any event, this warming may have triggered a partial collapse of the Antarctic ice sheet, perhaps by destabilizing ice shelves. By freshening the AAIW formation region, our model results show that mwp-1A

  12. 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.

  13. Connecting the records: exploiting tephra deposits to help understand abrupt climate change

    NASA Astrophysics Data System (ADS)

    Davies, S. M.; Abbott, P. M.; Bourne, A. J.; Chapman, M.; Pearce, N. J. G.; Griggs, A. J.; Cook, E.

    2016-12-01

    The causal mechanism of abrupt climate change during the last glacial period remains a key challenge. Although these events are well-documented in a wide range of proxy records, the triggers and drivers remain poorly understood, largely due to the dating uncertainties that prevent the integration of different archives. Unravelling the lead/lag responses (hence cause and effect) between the Earth's climate components is limited by the challenges of synchronising palaeoclimate records on a common timescale. Here we present the potential and the challenges of optimising the use of cryptotephra deposits to precisely correlate the Greenland ice-cores with North Atlantic marine records. A series of new cryptotephra deposits have been identified in Greenland, increasing the scope of identifying coeval isochrons in the marine environment. This new framework, however, brings new challenges in the search for unique and robust geochemical fingerprints for unequivocal tephra correlations. As such, some tephra deposits are proposed to be more valuable than others and underpin key snapshots in time during the last glacial period. The North Atlantic Ash Zone II, for instance, represents the most widespread isochron and constrains the cooling of GI-15. Some tephra deposits in the ice-core record originate from ultra-distal sources beyond the North Atlantic region and we also explore the potential for establishing North Pacific linkages.

  14. Abrupt Climate Transitions in an unforced Integration of CESM (Community Earth System Model)

    NASA Astrophysics Data System (ADS)

    Kleppin, H.; Jochum, M.; Shields, C. A.; Otto-Bliesner, B. L.

    2014-12-01

    In a pre-industrial control simulation of CESM changes of Greenland temperature show an asymmetric pattern that is a slow decrease at centennial timescales and an abrupt increase at decadal timescales, resembling the pattern of Dansgaard-Oeschger-cycles. A strong influence of equatorial Pacific SST anomalies on the pressure state above the North Atlantic and hence the wind forcing of the Labrador Sea gyre is found. The cooling is triggered by a stochastic anomalous pressure pattern over the North Atlantic that weakens the wind forcing of the Labrador gyre, slowing down and advecting less warm and saline subtropical waters to high latitudes. Then sea ice growth commences in the Labrador Sea due to locally reduced warm water transport. The sea ice anomaly above the Labrador Sea enhances the anomalous atmospheric circulation and eventually causes a cold core anticyclonic high pressure anomaly to persist during the entire 300 years that the cold North Atlantic phase lasts. Furthermore the decreased salinity transport towards the Labrador Sea induces a positive feedback that weakens the gyre circulation further and causes a reduced deep water convection. This leads to a reduced Atlantic meridional overturning circulation of about 4 Sverdrup, and eventually a reduced northward heat transport. After a 30 year period of prevailing cold SST anomalies in the east Pacific the disturbed atmospheric circulation above the North Atlantic slowly disappears, the Labrador Sea gyre circulation and deep water convection resume, melting the additional sea ice away and eventually causing an abrupt increase of Greenland temperatures. First ocean-sea ice only simulations forced with the anomalous atmospheric fluxes extracted from the original simulation reproduce the climate transition and the changed ocean circulation , even if starting from background ocean conditions that differ from the original ones.

  15. Abrupt climate changes of the last deglaciation detected in a Western Mediterranean forest record

    NASA Astrophysics Data System (ADS)

    Fletcher, W. J.; Sanchez Goñi, M. F.; Peyron, O.; Dormoy, I.

    2010-04-01

    Abrupt changes in Western Mediterranean climate during the last deglaciation (20 to 6 cal ka BP) are detected in marine core MD95-2043 (Alboran Sea) through the investigation of high-resolution pollen data and pollen-based climate reconstructions by the modern analogue technique (MAT) for annual precipitation (Pann) and mean temperatures of the coldest and warmest months (MTCO and MTWA). Changes in temperate Mediterranean forest development and composition and MAT reconstructions indicate major climatic shifts with parallel temperature and precipitation changes at the onsets of Heinrich stadial 1 (equivalent to the Oldest Dryas), the Bölling-Allerød (BA), and the Younger Dryas (YD). Multi-centennial-scale oscillations in forest development occurred throughout the BA, YD, and early Holocene. Shifts in vegetation composition and (Pann reconstructions indicate that forest declines occurred during dry, and generally cool, episodes centred at 14.0, 13.3, 12.9, 11.8, 10.7, 10.1, 9.2, 8.3 and 7.4 cal ka BP. The forest record also suggests multiple, low-amplitude Preboreal (PB) climate oscillations, and a marked increase in moisture availability for forest development at the end of the PB at 10.6 cal ka BP. Dry atmospheric conditions in the Western Mediterranean occurred in phase with Lateglacial events of high-latitude cooling including GI-1d (Older Dryas), GI-1b (Intra-Allerød Cold Period) and GS-1 (YD), and during Holocene events associated with high-latitude cooling, meltwater pulses and N. Atlantic ice-rafting. A possible climatic mechanism for the recurrence of dry intervals and an opposed regional precipitation pattern with respect to Western-central Europe relates to the dynamics of the westerlies and the prevalence of atmospheric blocking highs. Comparison of radiocarbon and ice-core ages for well-defined climatic transitions in the forest record suggests possible enhancement of marine reservoir ages in the Alboran Sea by 200 years (surface water age 600 years

  16. Millennial-scale dynamics of southern Amazonian rain forests.

    PubMed

    Mayle, F E; Burbridge, R; Killeen, T J

    2000-12-22

    Amazonian rain forest-savanna boundaries are highly sensitive to climatic change and may also play an important role in rain forest speciation. However, their dynamics over millennial time scales are poorly understood. Here, we present late Quaternary pollen records from the southern margin of Amazonia, which show that the humid evergreen rain forests of eastern Bolivia have been expanding southward over the past 3000 years and that their present-day limit represents the southernmost extent of Amazonian rain forest over at least the past 50,000 years. This rain forest expansion is attributed to increased seasonal latitudinal migration of the Intertropical Convergence Zone, which can in turn be explained by Milankovitch astronomic forcing.

  17. 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.

  18. Middle East coastal ecosystem response to middle-to-late Holocene abrupt climate changes.

    PubMed

    Kaniewski, D; Paulissen, E; Van Campo, E; Al-Maqdissi, M; Bretschneider, J; Van Lerberghe, K

    2008-09-16

    The Holocene vegetation history of the northern coastal Arabian Peninsula is of long-standing interest, as this Mediterranean/semiarid/arid region is known to be particularly sensitive to climatic changes. Detailed palynological data from an 800-cm alluvial sequence cored in the Jableh plain in northwest Syria have been used to reconstruct the vegetation dynamics in the coastal lowlands and the nearby Jabal an Nuşayriyah mountains for the period 2150 to 550 B.C. Corresponding with the 4.2 to 3.9 and 3.5 to 2.5 cal kyr BP abrupt climate changes (ACCs), two large-scale shifts to a more arid climate have been recorded. These two ACCs had different impacts on the vegetation assemblages in coastal Syria. The 3.5 to 2.5 cal kyr BP ACC is drier and lasted longer than the 4.2 to 3.9 cal kyr BP ACC, and is characterized by the development of a warm steppe pollen-derived biome (1100-800 B.C.) and a peak of hot desert pollen-derived biome at 900 B.C. The 4.2 to 3.9 cal kyr BP ACC is characterized by a xerophytic woods and shrubs pollen-derived biome ca. 2050 B.C. The impact of the 3.5 to 2.5 cal kyr BP ACC on human occupation and cultural development is important along the Syrian coast with the destruction of Ugarit and the collapse of the Ugarit kingdom at ca. 1190 to 1185 B.C.

  19. Middle East coastal ecosystem response to middle-to-late Holocene abrupt climate changes

    PubMed Central

    Kaniewski, D.; Paulissen, E.; Van Campo, E.; Al-Maqdissi, M.; Bretschneider, J.; Van Lerberghe, K.

    2008-01-01

    The Holocene vegetation history of the northern coastal Arabian Peninsula is of long-standing interest, as this Mediterranean/semiarid/arid region is known to be particularly sensitive to climatic changes. Detailed palynological data from an 800-cm alluvial sequence cored in the Jableh plain in northwest Syria have been used to reconstruct the vegetation dynamics in the coastal lowlands and the nearby Jabal an Nuşayriyah mountains for the period 2150 to 550 B.C. Corresponding with the 4.2 to 3.9 and 3.5 to 2.5 cal kyr BP abrupt climate changes (ACCs), two large-scale shifts to a more arid climate have been recorded. These two ACCs had different impacts on the vegetation assemblages in coastal Syria. The 3.5 to 2.5 cal kyr BP ACC is drier and lasted longer than the 4.2 to 3.9 cal kyr BP ACC, and is characterized by the development of a warm steppe pollen-derived biome (1100–800 B.C.) and a peak of hot desert pollen-derived biome at 900 B.C. The 4.2 to 3.9 cal kyr BP ACC is characterized by a xerophytic woods and shrubs pollen-derived biome ca. 2050 B.C. The impact of the 3.5 to 2.5 cal kyr BP ACC on human occupation and cultural development is important along the Syrian coast with the destruction of Ugarit and the collapse of the Ugarit kingdom at ca. 1190 to 1185 B.C. PMID:18772385

  20. Monsoon variability in the northeastern Arabian Sea on orbital- and millennial scale during the past 200,000 years

    NASA Astrophysics Data System (ADS)

    Lückge, Andreas; Groeneveld, Jeroen; Steinke, Stephan; Mohtadi, Mahyar; Westerhold, Thomas; Schulz, Hartmut

    2016-04-01

    The Dansgaard-Oeschger oscillations and Heinrich events described in the Greenland ice cores and in North Atlantic and Western Mediterranean sediments are also expressed in the climate of the tropics, for example, as documented in Arabian Sea sediments. However, little is known about these fluctuations beyond the reach of the Greenland ice cores. Here, we present high-resolution geochemical, sedimentological as well as micropaleontological data from two cores (SO130-283KL, 987m water depth and SO130-289KL, 571m) off the coast of Pakistan, extending the monsoon record on orbital and millennial scales to the past 200,000 years. The stable oxygen isotope record of the surface-dwelling planktonic foraminifer G. ruber shows a strong correspondence to Greenland ice core δ18O, whereas the deepwater δ18O signal of benthic foraminifera (U. peregrina and G. affinis) reflects patterns recorded in ice cores from Antarctica. Strong shifts in benthic δ18O during stadials/Heinrich events are interpreted to show frequent advances of oxygen-rich intermediate water masses into the Arabian Sea originating from the southern ocean. Alkenone-derived SSTs varied between 23 and 28° C. Highest temperatures were encountered during interglacial MIS 5. Rapid SST changes of 2° C magnitude on millennial scale are overlain by long-term SST fluctuations. Interstadials (of glacial phases) and the cold phases of interglacials are characterized by sediments enriched in organic carbon (up to 4 % TOC) whereas sediments with low TOC contents (< 1 % TOC) appear during stadials and Heinrich events. Shifts at climate transitions, such as onsets of interstadials, were coeval with changes in productivity-related and anoxia-indicating proxies. Interstadial inorganic elemental data consistently show that enhanced fluxes of terrestrial-derived sediments are paralleled by productivity maxima, and are characterized by an increased fluvial contribution from the Indus River. In contrast, stadials are

  1. Quality assessment of chronologies in Latin American pollen records: a contribution to centennial to millennial scale studies of environmental change

    NASA Astrophysics Data System (ADS)

    Flantua, S. G. A.; Hooghiemstra, H.; Blaauw, M.

    2015-04-01

    The newly updated inventory of the Latin American Pollen Database (LAPD) offers an important overview of data available for multi-proxy and multi-site purposes. However, heterogeneous paleoecological databases are not suitable to be integrated without an uncertainty assessment of existing chronologies. Therefore, we collected all chronological control points and age model metadata from the LAPD literature to create a complementary chronological database of 5116 dates from 1097 pollen records. We start with an overview on chronological dating and reporting in Central and South America. Specific problems and recommendations for chronology reporting are discussed. Subsequently, we implement a temporal quality assessment of pollen records from northwest South-America to support research on climate forcers and responses at a centennial-millennial time-scale. New chronologies are generated for 233 pollen records based on updated calibration curves. Different time windows are discussed on sample resolution and temporal uncertainty. Approximately one in four pollen diagrams depicts < 500 years resolution data at the Younger Dryas/Holocene transition. Overall, our analyses suggest that the temporal resolution of multi-site syntheses of late Pleistocene fossil pollen records in the northwest South-America is ca. 240 years, a resolution which allows analysis of ecological responses to centennial-millennial-scale climate change during the last deglaciation.

  2. Biological and physical controls in the Southern Ocean on past millennial-scale atmospheric CO2 changes

    PubMed Central

    Gottschalk, Julia; Skinner, Luke C.; Lippold, Jörg; Vogel, Hendrik; Frank, Norbert; Jaccard, Samuel L.; Waelbroeck, Claire

    2016-01-01

    Millennial-scale climate changes during the last glacial period and deglaciation were accompanied by rapid changes in atmospheric CO2 that remain unexplained. While the role of the Southern Ocean as a 'control valve' on ocean–atmosphere CO2 exchange has been emphasized, the exact nature of this role, in particular the relative contributions of physical (for example, ocean dynamics and air–sea gas exchange) versus biological processes (for example, export productivity), remains poorly constrained. Here we combine reconstructions of bottom-water [O2], export production and 14C ventilation ages in the sub-Antarctic Atlantic, and show that atmospheric CO2 pulses during the last glacial- and deglacial periods were consistently accompanied by decreases in the biological export of carbon and increases in deep-ocean ventilation via southern-sourced water masses. These findings demonstrate how the Southern Ocean's 'organic carbon pump' has exerted a tight control on atmospheric CO2, and thus global climate, specifically via a synergy of both physical and biological processes. PMID:27187527

  3. Biological and physical controls in the Southern Ocean on past millennial-scale atmospheric CO2 changes.

    PubMed

    Gottschalk, Julia; Skinner, Luke C; Lippold, Jörg; Vogel, Hendrik; Frank, Norbert; Jaccard, Samuel L; Waelbroeck, Claire

    2016-05-17

    Millennial-scale climate changes during the last glacial period and deglaciation were accompanied by rapid changes in atmospheric CO2 that remain unexplained. While the role of the Southern Ocean as a 'control valve' on ocean-atmosphere CO2 exchange has been emphasized, the exact nature of this role, in particular the relative contributions of physical (for example, ocean dynamics and air-sea gas exchange) versus biological processes (for example, export productivity), remains poorly constrained. Here we combine reconstructions of bottom-water [O2], export production and (14)C ventilation ages in the sub-Antarctic Atlantic, and show that atmospheric CO2 pulses during the last glacial- and deglacial periods were consistently accompanied by decreases in the biological export of carbon and increases in deep-ocean ventilation via southern-sourced water masses. These findings demonstrate how the Southern Ocean's 'organic carbon pump' has exerted a tight control on atmospheric CO2, and thus global climate, specifically via a synergy of both physical and biological processes.

  4. Biological and physical controls in the Southern Ocean on past millennial-scale atmospheric CO2 changes

    NASA Astrophysics Data System (ADS)

    Gottschalk, Julia; Skinner, Luke C.; Lippold, Jörg; Vogel, Hendrik; Frank, Norbert; Jaccard, Samuel L.; Waelbroeck, Claire

    2016-05-01

    Millennial-scale climate changes during the last glacial period and deglaciation were accompanied by rapid changes in atmospheric CO2 that remain unexplained. While the role of the Southern Ocean as a 'control valve' on ocean-atmosphere CO2 exchange has been emphasized, the exact nature of this role, in particular the relative contributions of physical (for example, ocean dynamics and air-sea gas exchange) versus biological processes (for example, export productivity), remains poorly constrained. Here we combine reconstructions of bottom-water [O2], export production and 14C ventilation ages in the sub-Antarctic Atlantic, and show that atmospheric CO2 pulses during the last glacial- and deglacial periods were consistently accompanied by decreases in the biological export of carbon and increases in deep-ocean ventilation via southern-sourced water masses. These findings demonstrate how the Southern Ocean's 'organic carbon pump' has exerted a tight control on atmospheric CO2, and thus global climate, specifically via a synergy of both physical and biological processes.

  5. 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.

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

    PubMed Central

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

    2009-01-01

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

  7. Lake-Level Responses to Abrupt Climate Changes in North-Central Pennsylvania since >16 ka

    NASA Astrophysics Data System (ADS)

    Halstead, T. M.; Shuman, B. N.

    2016-12-01

    Water levels in small lakes and ponds have widely responded to late-Quaternary climate changes, and we use a combination of geophysical surveys and sediment cores to reconstruct the hydrologic history of Sunfish Pond near Leroy, Pennsylvania (41°38'N 76°41'W). The small lake sits atop Barclay Mountain, a narrow ridge of the Appalachian Mountains near the southern limit of the Wisconsin glaciation. Ground-penetrating radar (GPR) profiles and a transect of three sediment cores indicate that the shoreline position of the lake has shifted over time with sandy littoral sediments extending outward into the lake stratigraphy, which is primarily composed of organic-rich muds. Calibrated radiocarbon ages from a sediment core collected in 2.25 m of water indicate that the lake formed by ca. 16.1 ka. Deposition of organic-rich muds in the near-shore core indicates moderately high water levels during the period of Heinrich Event 1, the Younger Dryas, and portions of the early Holocene. Sand layers and exceptionally low sediment accumulation rates indicate low water, however, from <16-12.5 ka and again from 5.5-2.8 ka. The water level has been near its modern high level since 2.8 ka based on extensive deposition of rapidly accumulating, organic-rich muds across the basin. The changes coincide with major changes in regional pollen records, and confirm the hydrologic significance of late-Pleistocene abrupt events in the Mid-Atlantic region.

  8. Abrupt Climate Change in the Southern Great Plains during the Last Glacial Interval

    NASA Astrophysics Data System (ADS)

    Housson, A. L.; Maupin, C. R.; Roark, B.; Shen, C. C.; Baykara, O.; White, K.; Kampen-Lewis, S. V.; McChesney, C. L.

    2016-12-01

    Understanding how the climate of the North American Great Plains may change in the future is of tremendous socioeconomic importance, yet the regional response to previous abrupt global climate events, such as the Dansgaard-Oeschger (DO) cycles of the last glacial interval, are poorly known. Here we present two absolutely dated (U/Th), partially replicated oxygen isotope (δ18O) records from calcite speleothems in central Texas (30° N, 98° W) that grew during marine isotope stage 3 (MIS 3) (31 to 49 ky BP). The study site experiences boreal spring and fall maxima in precipitation with rainfall moisture sourced almost exclusively from the Gulf of Mexico. The two samples exhibit reproducible δ18O means and variability during overlapping growth intervals. Weak correlations between paired oxygen and carbon isotopic values coupled with reproducible δ18O strongly suggest that dripwater δ18O and calcite formation temperatures are the primary drivers of speleothem δ18O variations through time. We interpret more depleted (enriched) δ18O values to reconstruct warmer and wetter (cooler and drier) conditions based on observations of modern rainfall stable isotope variations at the study site. We find that warmer and wetter conditions in the Southern Plains are contemporaneous with MIS 3 DO interstadials, while cooler and more arid conditions prevail during stadials and Heinrich Events 4 and 5. Our results show a response opposite that of hydrologic reconstructions from the American Southwest, where wetter conditions occur with stadial conditions. Future work includes exploration of paleoclimate model results to examine potential mechanisms responsible for this opposite phasing. Our speleothem data indicate that further intensification of rainy seasons in the Southern Plains should not be ruled out as a response to anthropogenic global warming.

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  10. Orbital- and Millennial-Scale Changes in the Australasian Monsoon Through the Late Pleistocene

    NASA Astrophysics Data System (ADS)

    Gagan, M. K.; Ayliffe, L. K.; Scroxton, N. G.; Krause, C. E.; Kimbrough, A. K.; Hantoro, W. S.; Drysdale, R.; Hellstrom, J.; Cheng, H.; Edwards, R.; Zhao, J.; Griffiths, M. L.

    2012-12-01

    Speleothem 18O/16O records from China and Borneo have revealed changes in Asian monsoon rainfall over the last ~570,000 years (e.g. Wang et al. 2008, Cheng et al. 2010, Meckler et al. 2012), yet little is known about orbital- and millennial-scale climate change in the 'southern half' of the Australasian monsoon domain. To fill this gap, we aim to build speleothem 18O/16O records for the seasonal monsoon rainfall belt of south-central Indonesia. Between 2006 and 2011, we sampled speleothems in Flores and southwest Sulawesi (latitudes 5-9oS) with U-series ages extending to 92,000 yBP and ~470,000 yBP, respectively. Development of the 18O/16O records for Sulawesi is in progress, but the basal ages of the speleothems (onset of stalagmite growth) are intriguing because they cluster around glacial terminations, when the East Asian monsoon is known to have been weak (Cheng et al. 2010). There is clear antiphasing of the Flores and China speleothem 18O/16O records on precession time-scales over the last ~90,000 years. A distinct maximum in monsoon rainfall in Flores occurred ~21,000 yBP, suggesting the ITCZ moved south during the Last Glacial Maximum in response to the southern hemisphere summer insolation maximum. This finding indicates that ITCZ positioning in tropical Australasia, through its influence on large-scale oceanic-atmospheric circulation, could have played a key role in the rapid rise of atmospheric CO2 and global warming that ultimately led to the demise of the last ice age, as summarised by Denton et al. (2010) and others. The new Flores speleothem 18O/16O records also show that climate change in the North Atlantic region and Australasian monsoon rainfall are inextricably linked on millennial timescales (Griffiths et al. 2009, Lewis et al. 2011). For example, rapid warming in the North Atlantic region during Dansgaard-Oeschger Event 21 (~86,000 yBP) was linked to a synchronous northward shift of the Australasian ITCZ, marking the final demise of MIS 5b. In

  11. Ocean circulation, ice sheet growth and interhemispheric coupling of millennial climate variability during the mid-Pleistocene (ca 800-400 ka)

    NASA Astrophysics Data System (ADS)

    Alonso-Garcia, M.; Sierro, F. J.; Kucera, M.; Flores, J. A.; Cacho, I.; Andersen, N.

    2011-11-01

    Stable carbon and oxygen isotopes from benthic and planktic foraminifers, planktic foraminifer assemblages and ice rafted debris from the North Atlantic Site U1314 (Integrated Ocean Drilling Program Expedition 306) were examined to investigate orbital and millennial-scale climate variability in the North Atlantic and its impact on global circulation focusing on the development of glacial periods during the mid-Pleistocene (ca 800-400 ka). Glacial initiations were characterized by a rapid cooling (6-10 °C in less than 7 kyr) in the mean annual sea surface temperature (SST), increasing benthic δ 18O values and high benthic δ 13C values. The continuous increase in benthic δ 18O suggests a continuous ice sheet growth whereas the positive benthic δ 13C values indicate that the flow of the Iceland Scotland Overflow water (ISOW) was vigorous. Strong deep water formation in the Norwegian Greenland Sea promoted a high transfer of freshwater from the ocean to the continents. However, low SSTs at Site U1314 suggest a subpolar gyre cooling and freshening that may have reduced deep water formation in the Labrador Sea during glacial initiations. Once the 3.5‰ threshold in the benthic δ 18O record was exceeded, ice rafting started and ice sheet growth was punctuated by millennial-scale waning events which returned to the ocean part of the freshwater accumulated on the continents. Ice-rafting events were associated with a rapid reduction in the ISOW (benthic δ 13C values dropped 0.5-1‰) and followed by millennial-scale warmings. The first two millennial-scale warm intervals of each glacial period reached interglacial temperatures and were particularly abrupt (6-10 °C in ˜3 kyr). Subsequent millennial-scale warm events were cooler probably because the AMOC was rather reduced as suggested by the low benthic δ 13C values. These two abrupt warming events that occurred at early glacial periods were also observed in the Antarctic temperature and CO 2 records, suggesting a

  12. Bayesian comparison of conceptual models of abrupt climate changes during the last glacial period

    NASA Astrophysics Data System (ADS)

    Boers, Niklas; Ghil, Michael; Rousseau, Denis-Didier

    2017-04-01

    Records of oxygen isotope ratios and dust concentrations from the North Greenland Ice Core Project (NGRIP) provide accurate proxies for the evolution of Arctic temperature and atmospheric circulation during the last glacial period (12ka to 100ka b2k) [1]. The most distinctive feature of these records are sudden transitions, called Dansgaard-Oeschger (DO) events, during which Arctic temperatures increased by up to 10 K within a few decades. These warming events are consistently followed by more gradual cooling in Antarctica [2]. The physical mechanisms responsible for these transitions and their out-of-phase relationship between the northern and southern hemisphere remain unclear. Substantial evidence hints at variations of the Atlantic Meridional Overturning Circulation as a key mechanism [2,3], but also other mechanisms, such as variations of sea ice extent [4] or ice shelf coverage [5] may play an important role. Here, we intend to shed more light on the relevance of the different mechanisms suggested to explain the abrupt climate changes and their inter-hemispheric coupling. For this purpose, several conceptual differential equation models are developed that represent the suggested physical mechanisms. Optimal parameters for each model candidate are then determined via maximum likelihood estimation with respect to the observed paleoclimatic data. Our approach is thus semi-empirical: While a model's general form is deduced from physical arguments about relevant climatic mechanisms — oceanic and atmospheric — its specific parameters are obtained by training the model on observed data. The distinct model candidates are evaluated by comparing statistical properties of time series simulated with these models to the observed statistics. In particular, Bayesian model selection criteria like Maximum Likelihood Ratio tests are used to obtain a hierarchy of the different candidates in terms of their likelihood, given the observed oxygen isotope and dust time series

  13. The Paleoceanography of Cariaco Basin and its Relationship to Deglacial and Abrupt Climate Change

    NASA Astrophysics Data System (ADS)

    Peterson, L. C.; Yurco, L. N.; Gibson, K.; Haug, G. H.; Deplazes, G.; Black, D. E.; Thunell, R.

    2011-12-01

    Sediments of the anoxic Cariaco Basin have produced important high-resolution records of climate and oceanographic change in the southern Caribbean over the last glacial-interglacial cycle. For example, the well-known Dansgaard-Oeschger (D-O) excursions of Greenland ice core fame are recorded in Cariaco Basin by alternating dark and light sediment intervals which reflect climatically-driven oscillations between anoxic and oxygenated deep basin conditions, changes in biological productivity at the surface, and rapid oscillations in the input of siliciclastic muds from local rivers. These oscillations can be related to past changes in the average position of the Intertropical Convergence Zone (ITCZ). Periods of high input of continental sediment and elevated organic carbon (OC) contents are in phase with the warm interstadials and indicate higher regional precipitation and productivity and a more northerly position of the ITCZ; periods of low siliciclastic input and low OC contents during the colder stadials are evidence of dry and less productive regional conditions and southerly displacement of the ITCZ. This now well-known pattern of change in Cariaco Basin is consistent with a mechanism driven by changes in the Atlantic's Meridional Overturning Circulation (AMOC), with a weakened AMOC leading to cooler North Atlantic sea surface temperatures, an enhanced meridional temperature gradient, and a southward shift of the ITCZ. Though every D-O excursion can be identified in Cariaco sediments, the time intervals corresponding to Heinrich ice-rafting episodes in the North Atlantic record the most arid conditions, presumably reflecting an ITCZ response to periods of most severely curtailed AMOC. This talk will review these changes as well as other lines of paleo-evidence for regional changes in the Caribbean-Gulf of Mexico system, with a particular focus on the Late Glacial and Deglacial intervals. In Cariaco Basin, evidence will be presented for a previously unidentified

  14. 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

  15. Rapid interhemispheric climate links via the Australasian monsoon during the last deglaciation.

    PubMed

    Ayliffe, Linda K; Gagan, Michael K; Zhao, Jian-xin; Drysdale, Russell N; Hellstrom, John C; Hantoro, Wahyoe S; Griffiths, Michael L; Scott-Gagan, Heather; St Pierre, Emma; Cowley, Joan A; Suwargadi, Bambang W

    2013-01-01

    Recent studies have proposed that millennial-scale reorganization of the ocean-atmosphere circulation drives increased upwelling in the Southern Ocean, leading to rising atmospheric carbon dioxide levels and ice age terminations. Southward migration of the global monsoon is thought to link the hemispheres during deglaciation, but vital evidence from the southern sector of the vast Australasian monsoon system is yet to emerge. Here we present a 230thorium-dated stalagmite oxygen isotope record of millennial-scale changes in Australian-Indonesian monsoon rainfall over the last 31,000 years. The record shows that abrupt southward shifts of the Australian-Indonesian monsoon were synchronous with North Atlantic cold intervals 17,600-11,500 years ago. The most prominent southward shift occurred in lock-step with Heinrich Stadial 1 (17,600-14,600 years ago), and rising atmospheric carbon dioxide. Our findings show that millennial-scale climate change was transmitted rapidly across Australasia and lend support to the idea that the 3,000-year-long Heinrich 1 interval could have been critical in driving the last deglaciation.

  16. "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.

  17. 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.

  18. 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.

  19. 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

  20. High-Resolution Greenland Ice Core Data Show Abrupt Climate Change Happens in Few Years

    NASA Astrophysics Data System (ADS)

    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, Árný 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.

  1. 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.

  2. Millennial-scale variability in the local radiocarbon reservoir age of the Florida Keys reef tract during the Holocene

    NASA Astrophysics Data System (ADS)

    Ashe, E.; Toth, L. T.; Cheng, H.; Edwards, R. L.; Richey, J. N.

    2016-12-01

    The oceanic passage between the Florida Keys and Cuba, known as the Straits of Florida, provides a critical connection between the tropics and northern Atlantic. Changes in the character of water masses transported through this region may ultimately have important impacts on high-latitude climate variability. Although recent studies have documented significant changes in the density of regional surface waters over millennial timescales, little is known about the contribution of local- to regional-scale changes in circulation to surface-water variability. Local variability in the radiocarbon age, ΔR, of surface waters can be used to trace changes in local water-column mixing and/or changes in regional source water over a variety of spatial and temporal scales. We reconstructed "snapshots" of ΔR variability across the Florida Keys reef tract during the last 10,000 years by dating 68 unaltered corals collected from Holocene reef cores with both U-series and radiocarbon techniques. We combined the snapshots of ΔR into a semi-empirical model to develop a robust statistical reconstruction of millennial-scale variability in ΔR on the Florida Keys reef tract. Our model demonstrates that ΔR varied significantly during the Holocene, with relatively high values during the early Holocene and around 3000 years BP and relatively low values around 7000 years BP and at present. We compare the trends in ΔR to existing paleoceanographic reconstructions to evaluate the relative contribution of local upwelling versus changes in source water to the region as a whole in driving local radiocarbon variability, and discuss the importance of these results to our understanding of regional-scale oceanographic and climatic variability during the Holocene. We also discuss the implications of our results for radiocarbon dating of marine samples from south Florida and present a model of ΔR versus 14C age that can be used to improve the accuracy of radiocarbon calibrations from this region.

  3. Century to millennial-scale temperature variations for the last two thousand years indicated from glacial geologic records of Southern Alaska

    NASA Astrophysics Data System (ADS)

    Wiles, Gregory C.; Barclay, David J.; Calkin, Parker E.; Lowell, Thomas V.

    2008-01-01

    Comparisons of temperature sensitive climate proxy records with tree-ring, lichen and radiocarbon dated histories from land-terminating, non-surging glaciers for the last two millennia from southern Alaska identify summer temperature as a primary driver of glacial expansions. Two major intervals in the Alaskan chronology of glaciation, during the First Millennium AD (FMA) and again during the Little Ice Age (LIA), are evident as broad times of cooling and ice expansion. These two intervals are respectively followed by ice retreat coincident with the Medieval Warm Period (MWP) and contemporary warming, and together correspond with millennial-scale variations recognized in the North Atlantic. The FMA advance appears to be of similar extent as the subsequent LIA expansions indicating a uniformity of forcing over the past two millennia.

  4. 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.

  5. Atmospheric CO2 and climate on millennial time scales during the last glacial period.

    PubMed

    Ahn, Jinho; Brook, Edward J

    2008-10-03

    Reconstructions of ancient atmospheric carbon dioxide (CO2) variations help us better understand how the global carbon cycle and climate are linked. We compared CO2 variations on millennial time scales between 20,000 and 90,000 years ago with an Antarctic temperature proxy and records of abrupt climate change in the Northern Hemisphere. CO2 concentration and Antarctic temperature were positively correlated over millennial-scale climate cycles, implying a strong connection to Southern Ocean processes. Evidence from marine sediment proxies indicates that CO2 concentration rose most rapidly when North Atlantic Deep Water shoaled and stratification in the Southern Ocean was reduced. These increases in CO2 concentration occurred during stadial (cold) periods in the Northern Hemisphere, several thousand years before abrupt warming events in Greenland.

  6. Late Pleistocene climate drivers of early human migration

    NASA Astrophysics Data System (ADS)

    Timmermann, Axel; Friedrich, Tobias

    2016-10-01

    On the basis of fossil and archaeological data it has been hypothesized that the exodus of Homo sapiens out of Africa and into Eurasia between ~50-120 thousand years ago occurred in several orbitally paced migration episodes. Crossing vegetated pluvial corridors from northeastern Africa into the Arabian Peninsula and the Levant and expanding further into Eurasia, Australia and the Americas, early H. sapiens experienced massive time-varying climate and sea level conditions on a variety of timescales. Hitherto it has remained difficult to quantify the effect of glacial- and millennial-scale climate variability on early human dispersal and evolution. Here we present results from a numerical human dispersal model, which is forced by spatiotemporal estimates of climate and sea level changes over the past 125 thousand years. The model simulates the overall dispersal of H. sapiens in close agreement with archaeological and fossil data and features prominent glacial migration waves across the Arabian Peninsula and the Levant region around 106-94, 89-73, 59-47 and 45-29 thousand years ago. The findings document that orbital-scale global climate swings played a key role in shaping Late Pleistocene global population distributions, whereas millennial-scale abrupt climate changes, associated with Dansgaard-Oeschger events, had a more limited regional effect.

  7. Late Pleistocene climate drivers of early human migration.

    PubMed

    Timmermann, Axel; Friedrich, Tobias

    2016-10-06

    On the basis of fossil and archaeological data it has been hypothesized that the exodus of Homo sapiens out of Africa and into Eurasia between ~50-120 thousand years ago occurred in several orbitally paced migration episodes. Crossing vegetated pluvial corridors from northeastern Africa into the Arabian Peninsula and the Levant and expanding further into Eurasia, Australia and the Americas, early H. sapiens experienced massive time-varying climate and sea level conditions on a variety of timescales. Hitherto it has remained difficult to quantify the effect of glacial- and millennial-scale climate variability on early human dispersal and evolution. Here we present results from a numerical human dispersal model, which is forced by spatiotemporal estimates of climate and sea level changes over the past 125 thousand years. The model simulates the overall dispersal of H. sapiens in close agreement with archaeological and fossil data and features prominent glacial migration waves across the Arabian Peninsula and the Levant region around 106-94, 89-73, 59-47 and 45-29 thousand years ago. The findings document that orbital-scale global climate swings played a key role in shaping Late Pleistocene global population distributions, whereas millennial-scale abrupt climate changes, associated with Dansgaard-Oeschger events, had a more limited regional effect.

  8. Internal ice - Sheet variability as source for the multi-century and millennial-scale iceberg events during the Holocene? A model study

    NASA Astrophysics Data System (ADS)

    Bügelmayer-Blaschek, Marianne; Roche, Didier M.; Renssen, Hans; Andrews, John T.

    2016-04-01

    The climate of the Holocene, the current interglacial covering the past 11,700 years, has been relatively stable compared to previous periods. Nevertheless, repeating occurrence of rapid natural climate changes that challenged human society are seen in proxy reconstructions. Ocean sediment cores for example display prominent peaks of enhanced ice rafted debris (IRD) during the Holocene with a multi-decadal to millennial scale periodicity. Different mechanisms were proposed that caused these enhanced IRD events, for example variations in the incoming total solar irradiance (TSI), volcanic eruptions and the combination of internal climate variability and external forcings. We investigate the probable mechanisms causing the occurrence of IRD-events over the past 6000 years using a fully coupled climate - ice-sheet - iceberg model (iLOVECLIM). We performed 19 experiments that differ in the applied forcings (TSI, volcanic) and the initial atmospheric conditions. To explore internal ice sheet variability one further experiment was done with fixed climate conditions. All the model runs displayed prominent peaks of enhanced iceberg melt flux (IMF), independent of the chosen experimental set-up. The spectral analysis of the experiments with the ice-sheet - climate model coupled displays significant peaks at 2000, 1000 years in all the experiments and at 500 years in most runs. The experiment with fixed climate conditions displays one significant peak of about 1500 years related to internal ice sheet variability. This frequency is modulated to 2000 and 1000 years in all the experiments with a coupled climate - ice sheet due to interactions between the climate components. We further investigate the impact of minimum TSI events on the timing and occurrence of enhanced IMF. In the experimental set-up that was forced with idealized sinusoidal TSI variations (±4 Wm-2), we find a significant occurrence of an increased iceberg melt flux about 60 years after the minimum TSI value

  9. Millennial-scale oscillations between sea ice and convective deep water formation

    NASA Astrophysics Data System (ADS)

    Saha, Raj

    2015-11-01

    During the last ice age there were several quasiperiodic abrupt warming events. The climatic effects of the so-called Dansgaard-Oeschger (D-O) events were felt globally, although the North Atlantic experienced the largest and most abrupt temperature anomalies. Similar but weaker oscillations also took place during the interglacial period. This paper proposes an auto-oscillatory mechanism between sea ice and convective deep water formation in the North Atlantic as the source of the persistent cycles. A simple dynamical model is constructed by coupling and slightly modifying two existing models of ocean circulation and sea ice. The model exhibits mixed mode oscillations, consisting of decadal-scale small-amplitude oscillations and a large-amplitude relaxation fluctuation. The decadal oscillations occur due to the insulating effect of sea ice and leads to periodic ventilation of heat from the polar ocean. Gradually, an instability builds up in the polar column and results in an abrupt initiation of convection and polar warming. The unstable convective state relaxes back to the small-amplitude oscillations from where the process repeats in a self-sustained manner. Freshwater pulses mimicking Heinrich events cause the oscillations to be grouped into packets of progressively weaker fluctuations, as observed in proxy records. Modulation of this stable oscillation mechanism by freshwater and insolation variations could account for the distribution and pacing of D-O and Bond events. Physical aspects of the system such as sea ice extent and oceanic advective flow rates could determine the characteristic 1500 year time scale of D-O events. The model results with respect to the structure of the water column in the Nordic seas during stadial and interstadial phases are in agreement with paleoproxy observations.

  10. Millennial-scale instability of the antarctic ice sheet during the last glaciation

    PubMed

    Kanfoush; Hodell; Charles; Guilderson; Mortyn; Ninnemann

    2000-06-09

    Records of ice-rafted detritus (IRD) concentration in deep-sea cores from the southeast Atlantic Ocean reveal millennial-scale pulses of IRD delivery between 20,000 and 74,000 years ago. Prominent IRD layers correlate across the Polar Frontal Zone, suggesting episodes of Antarctic Ice Sheet instability. Carbon isotopes (delta(13)C) of benthic foraminifers, a proxy of deepwater circulation, reveal that South Atlantic IRD events coincided with strong increases in North Atlantic Deep Water (NADW) production and inferred warming (interstadials) in the high-latitude North Atlantic. Sea level rise or increased NADW production associated with strong interstadials may have resulted in destabilization of grounded ice shelves and possible surging in the Weddell Sea region of West Antarctica.

  11. Millennial-scale variability in Southern Hemisphere westerly wind activity over the last 5000 years in SW Patagonia

    NASA Astrophysics Data System (ADS)

    Moreno, P. I.; François, J. P.; Villa-Martínez, R. P.; Moy, C. M.

    2009-01-01

    Here we report results from a high-resolution palynological record and stratigraphic/geochronologic data related to a Neoglacial event in Torres del Paine National Park, southern Chile (51°S, 71°W), to investigate climatic variations in Southwest Patagonia during the last 5000 years. The record reveals a stepwise expansion of Nothofagus-dominated woodlands and forests with discrete pulses at 4400, 2900, 1300, and 570 cal yr BP. Superimposed upon this trend we identify a relative opening of the woodlands between 4100-2900 and 2300-1300 cal yr BP. Closed-canopy forests dominated the landscape between 570-60 cal yr BP, followed by a rapid decline at the end of the 19th century that coincided with intense fire activity and the appearance of Rumex cf. acetocella, an exotic species introduced by European settlers. We interpret these changes as variations in the intensity and/or position of the southern margin of the westerly winds, which culminated with a net eastward shift of the forest-steppe ecotone during the Little Ice Age. We propose that millennial-scale changes in either the latitudinal position and/or the overall strength of the southern westerlies may be responsible for vegetation changes, fire occurrence, and the dynamic behavior of Patagonian glaciers during the last 5000 years. Because the modern maximum in near-surface wind velocities and precipitation is located between 48° and 50°S, we suggest that the core of the southern westerlies may have achieved this modern position ˜570 years ago.

  12. North Atlantic forcing of millennial-scale Indo-Australian monsoon dynamics during the Last Glacial period

    NASA Astrophysics Data System (ADS)

    Denniston, Rhawn F.; Wyrwoll, Karl-Heinz; Asmerom, Yemane; Polyak, Victor J.; Humphreys, William F.; Cugley, John; Woods, David; LaPointe, Zachary; Peota, Julian; Greaves, Elizabeth

    2013-07-01

    Recent studies of the Last Glacial period Indo-Australian summer monsoon (IASM) have revealed links to both northern and southern hemisphere high latitude climate as well as to regional ocean conditions. Particular interest has been paid to the monsoon response to Heinrich events, with variability explained by meridional shifts in positioning of the intertropical convergence zone (ITCZ), but this model has not been adequately tested. In addition, the shorter-lived Dansgaard/Oeschger (D/O) events have not been detected (beyond D/O-1, the Bølling/Allerød) in land-based records from the Indo-Pacific, despite their prominent expression in stalagmites from southern Asia, raising questions about the sensitivity of the IASM to these events. Here we present a Southern Hemisphere stalagmite oxygen isotopic time series from Ball Gown Cave (BGC), tropical northern Australia, located on the margins of the modern austral summer ITCZ, that spans 40-31 and 27-8 ka. Elevated IASM rainfall coincides with Heinrich stadials and the Younger Dryas, while decreased rainfall characterizes D/O interstadials, a response that is anti-phased with sites spanning the Indo-Pacific Warm Pool and with Chinese records of the East Asian summer monsoon. The BGC time series thus reveals a precipitation dipole consistent with a southward (northward) migration of the ITCZ during periods of high northern latitude cooling (warming) as the primary driver of millennial-scale IASM variability during the Last Glacial period. Our record indicates a strengthening of the IASM after the Younger Dryas period, likely as a result of rising sea level and sea surface temperatures, breaking the link with the high latitudes.

  13. The role of oceanic variability on millennial-scale iceberg discharges: focus on Heinrich events

    NASA Astrophysics Data System (ADS)

    Alvarez-Solas, J.; Montoya, M.; Banderas, R.; Dumas, C.; Ritz, C.

    2011-12-01

    Ice core data and marine and continental records reveal the existence of pronounced millennial time-scale climate variability during the last glacial cycle. Greenland ice core records show abrupt transitions known as Dansgaard-Oeschger (DO) events within decades from cold (stadial) to relatively warm (interstadial) conditions, followed by a slow cooling lasting several centuries and a more rapid fall through stadial conditions. Two types of explanation have been suggested: periodic external forcing and internal oscillations, for which ocean circulation is the main candidate. On the other hand, six periods of extreme cooling registered in the Northern Hemisphere, known as Heinrich events (HEs), have been found to be coeval with increased deposition of ice-rafted debris, which is interpreted as enhanced discharge of icebergs into the North Atlantic Ocean. Recently, the coupled effects between ocean circulation and ice-sheets dynamics have been suggested to play a major role in triggering HEs. This interpretation of HEs being responding to changes in the oceanic patterns, takes the advantage to provide an explicit relationship between DO events and the periodic iceberg surges. In particular, it has been shown in a box model that a series of DO events favors the occurrence of a HE through a resonance phenomenon, giving an explanation to the denominated Bond cycle. Here this hypothesis is reassessed within a more realistic modeling framework by forcing a 3D ice-sheet/shelf model with the output of abrupt climate change simulations carried out with a coupled climate model. These show the main expected characteristics of such events: an abrupt warming of the North Atlantic and Atlantic Meridional Overturning Circulation (AMOC) intensification followed by a progressive cooling and AMOC reduction and a more drastic fall into a stadial condition. Interestingly, stadial periods are characterized by the occurrence of a subsurface warming up to 3 K in regions where deep water

  14. Abrupt shifts of the Sahara-Sahel boundary during Heinrich Stadials

    NASA Astrophysics Data System (ADS)

    Collins, J. A.; Govin, A.; Mulitza, S.; Heslop, D.; Zabel, M.; Hartmann, J.; Röhl, U.; Wefer, G.

    2013-01-01

    Relict dune fields that are found at 14° N in the modern-day African Sahel are testament to equatorward expansions of the Sahara desert during the late Pleistocene. However, difficulties of dating dune formation mean that abrupt millennial-scale climate events are not always resolved in these records. High-resolution marine core studies have identified Heinrich Stadials as the dustiest periods of the last glacial, although no studies have mapped the spatio-temporal evolution of dust export from West Africa. We use the major-element composition of four marine sediment cores to reconstruct the spatial extent of Saharan-dust versus river-sediment input to the continental margin from West Africa over the last 60 ka. This allows us to map the position of the sediment composition corresponding to the Sahara-Sahel boundary. Our records indicate that the Sahara-Sahel boundary reached its most southerly position (13° N) during Heinrich Stadials, suggesting that these were the periods when the sand dunes formed at 14° N on the continent, rather than at the Last Glacial Maximum. We find that SSB position was closely linked to North Atlantic sea surface temperatures, which during Heinrich Stadials triggered abrupt increases of aridity and wind strength in the Sahel, exposing new dust sources. This result illustrates the influence of the Atlantic meridional overturning circulation on the southerly extent of the Sahara desert and has implications for global atmospheric dust loading.

  15. Millennial-scale versus long-term dynamics in the surface and subsurface of the western North Atlantic Subtropical Gyre during Marine Isotope Stage 5

    NASA Astrophysics Data System (ADS)

    Bahr, André; Nürnberg, Dirk; Karas, Cyrus; Grützner, Jens

    2013-12-01

    Subtropical Gyres are an important constituent of the ocean-atmosphere system due to their capacity to store vast amounts of warm and saline waters. Here we decipher the sensitivity of the (sub)surface North Atlantic Subtropical Gyre with respect to orbital and millennial scale climate variability between ~ 140 and 70 ka, Marine Isotope Stage (MIS) 5. Using (isotope) geochemical proxy data from surface and thermocline dwelling foraminifers from Blake Ridge off the west coast of North America (ODP Site 1058) we show that the oceanographic development at subsurface (thermocline) level is substantially different from the surface ocean. Most notably, surface temperatures and salinities peak during the penultimate deglaciation (Termination II) and early MIS 5e, implying that subtropical surface ocean heat and salt accumulation might have resulted from a sluggish northward heat transport. In contrast, maximum thermocline temperatures are reached during late MIS 5e when surface temperatures are already declining. We argue that the subsurface warming originated from intensified Ekman downwelling in the Subtropical Gyre due to enhanced wind stress. During MIS 5a-d a tight interplay of the subtropical upper ocean hydrography to high latitude millennial-scale cold events can be observed. At Blake Ridge, the most pronounced of these high latitude cold events are related to surface warming and salt accumulation in the (sub)surface. Similar to Termination II, heat accumulated in the Subtropical Gyre probably due to a reduced Atlantic Meridional Overturning Circulation. Additionally, a southward shift and intensification of the subtropical wind belts lead to a decrease of on-site precipitation and enhanced evaporation, coupled to intensified gyre circulation. Subsequently, the northward advection of this warm and saline water likely contributed to the fast resumption of the overturning circulation at the end of these high latitude cold events.

  16. Coherent Sea Ice Variations in the Nordic Seas and Abrupt Greenland Climate Changes over Dansgaard-Oeschger Cycles

    NASA Astrophysics Data System (ADS)

    Sadatzki, H.; Berben, S.; Dokken, T.; Stein, R.; Fahl, K.; Jansen, E.

    2016-12-01

    Rapid changes in sea ice extent in the Nordic Seas may have played a crucial role in controlling the abruptness of ocean circulation and climate changes associated with Dansgaard-Oeschger (D-O) cycles during the last glacial (Li et al., 2010; Dokken et al., 2013). To investigate the role of sea ice for abrupt climate changes, we produced a sea ice record from the Norwegian Sea Core MD99-2284 at a temporal resolution approaching that of ice core records, covering four D-O cycles at ca. 32-41 ka. This record is based on the sea ice diatom biomarker IP25, open-water phytoplankton biomarker dinosterol and semi-quantitative phytoplankton-IP25 (PIP25) estimates. A detailed tephrochronology of MD99-2284 corroborates the tuning-based age model and independently constrains the GS9/GIS8 transition, allowing for direct comparison between our sediment and ice core records. For cold stadials we find extremely low fluxes of total organic carbon, dinosterol and IP25, which points to a general absence of open-water phytoplankton and ice algae production under a near-permanent sea ice cover. For the interstadials, in turn, all biomarker fluxes are strongly enhanced, reflecting a highly productive sea ice edge situation and implying largely open ocean conditions for the eastern Nordic Seas. As constrained by three tephra layers, we observe that the stadial-interstadial sea ice decline was rapid and may have induced a coeval abrupt northward shift in the Greenland precipitation moisture source as recorded in ice cores. The sea ice retreat also facilitated a massive heat release through deep convection in the previously stratified Nordic Seas, generating atmospheric warming of the D-O events. We thus conclude that rapid changes in sea ice extent in the Nordic Seas amplified oceanic reorganizations and were a key factor in controlling abrupt Greenland climate changes over D-O cycles. Dokken, T.M. et al., 2013. Paleoceanography 28, 491-502 Li, C. et al., 2010. Journ. Clim. 23, 5457-5475

  17. 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.

  18. Emergence and evolution of millennial-scale variability in the East Asian summer monsoon over the last 3 Ma recorded in hemipelagic sediments of the Japan Sea recovered by IODP Expedition 346

    NASA Astrophysics Data System (ADS)

    Tada, R.; Irino, T.; Ikeda, M.; Ikehara, K.; Karasuda, A.; Lu, S.; Seki, A.; Sugisaki, S.; Itaki, T.; Sagawa, T.; Kubota, Y.; Xuan, C.; Murray, R. W.; Alvarez Zarikian, C. A.; Scientists, E.

    2016-12-01

    It has been well established the East Asian summer monsoon (EASM) varied on millennial timescales associated with abrupt climatic changes in Greenland known as Dansgaard-Oeschger cycles (DOC). Variations in EASM intensity can now be traced back to 640 ka based on a stalagmite-derived d18O record from South China (Cheng et al., 2016), but no high-resolution EASM records stretch beyond 640 ka. In contrast, millennial-scale oceanic variation has been traced back to 1.45 Ma in the North Atlantic on the Iberian Margin (Hodell et al., 2015), based on scanning XRF Ca/Ti ratios, and the Greenland temperature record has been extended back to 800 ka by the generation of a synthetic temperature record constructed based on the bipolar see-saw relationship between the Greenland and Antarctic temperatures recorded in ice cores (GLT_syn_hi; Baker et al., 2011). The hemipelagic sediments of the Japan Sea offer the potential to reconstruct milllennial-scale climate variability in the NW Pacific because it is characterized by centimeter- to decimeter-scale alternation of dark and light layers with dark (light) layers that correspond to DO interstadials (stadials) (Tada et al., 1999). The dark sediment color reflects Corg content, and deposition of dark layers results from nutrient influx through the southern strait modulated by Yangtze discharge, which reflects EASM precipitation in South China. IODP Exp. 346 drilled six sites in the deeper part of the Japan Sea, and recovered continuous pelagic sequences back to more than 3 Ma. Here, we present a basin-wide correlation of dark and light layers across all six sites back to 3 Ma. The first onset of alternating dark and light layers occurs at 2.6 Ma, but their occurrence is rather irregular. The occurrence becomes more frequent from 2.2 Ma, and then they occur in every glacial periods since 1.3 Ma. The temporal changes in amplitude and frequency, as well as detailed comparison with other high-resolution records will be presented.

  19. Synchronous interhemispheric Holocene climate trends in the tropical Andes

    PubMed Central

    Polissar, Pratigya J.; Abbott, Mark B.; Wolfe, Alexander P.; Vuille, Mathias; Bezada, Maximiliano

    2013-01-01

    Holocene variations of tropical moisture balance have been ascribed to orbitally forced changes in solar insolation. If this model is correct, millennial-scale climate evolution should be antiphased between the northern and southern hemispheres, producing humid intervals in one hemisphere matched to aridity in the other. Here we show that Holocene climate trends were largely synchronous and in the same direction in the northern and southern hemisphere outer-tropical Andes, providing little support for the dominant role of insolation forcing in these regions. Today, sea-surface temperatures in the equatorial Pacific Ocean modulate rainfall variability in the outer tropical Andes of both hemispheres, and we suggest that this mechanism was pervasive throughout the Holocene. Our findings imply that oceanic forcing plays a larger role in regional South American climate than previously suspected, and that Pacific sea-surface temperatures have the capacity to induce abrupt and sustained shifts in Andean climate. PMID:23959896

  20. Synchronous interhemispheric Holocene climate trends in the tropical Andes.

    PubMed

    Polissar, Pratigya J; Abbott, Mark B; Wolfe, Alexander P; Vuille, Mathias; Bezada, Maximiliano

    2013-09-03

    Holocene variations of tropical moisture balance have been ascribed to orbitally forced changes in solar insolation. If this model is correct, millennial-scale climate evolution should be antiphased between the northern and southern hemispheres, producing humid intervals in one hemisphere matched to aridity in the other. Here we show that Holocene climate trends were largely synchronous and in the same direction in the northern and southern hemisphere outer-tropical Andes, providing little support for the dominant role of insolation forcing in these regions. Today, sea-surface temperatures in the equatorial Pacific Ocean modulate rainfall variability in the outer tropical Andes of both hemispheres, and we suggest that this mechanism was pervasive throughout the Holocene. Our findings imply that oceanic forcing plays a larger role in regional South American climate than previously suspected, and that Pacific sea-surface temperatures have the capacity to induce abrupt and sustained shifts in Andean climate.

  1. 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.

  2. 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

  3. The Long and the Short of it: Millennial-Scale and Contemporary Sediment Yields of Eastern Grand Canyon

    NASA Astrophysics Data System (ADS)

    Nichols, K. K.; Webb, R.; Cleveland, K. M.; Bierman, P. R.; Finkel, R.; Larsen, J.

    2007-05-01

    Dams on the Colorado River were constructed to regulate and store water for irrigation and domestic consumption, but flow regulation has had major impacts on hydrological and ecological processes within the watershed. Intrinsic to understanding these impacts requires a quantitative knowledge of the sediment yields in regulated reaches. Unfortunately, little is known about the long-term sediment yields, and contemporary data were either estimated or measured over only a few decades and only at only a few locations and therefore may not reflect the longer cycles of erosion and aggradation within the mainstem Colorado River or within the tributary basins. Here, we present data that compares contemporary sediment yield derived from models of ungaged tributaries in eastern Grand Canyon with millennial-scale sediment yield data derived from cosmogenic 10Be to highlight the sediment delivery processes over the past several thousand years. Models of the contemporary sediment yield of eastern Grand Canyon suggest 349 Mg km-2 y-1 of sediment. Cosmogenic 10Be estimates of long-term (104 yr) yields are 227 Mg ky-2 y-1, only 65% of the contemporary estimates. The difference in these estimates most likely reflects a change in process during the effective range of cosmogenic 10Be (>10 ky). Hanks and Webb (2006) suggest that the bed of the Colorado River in this reach may have aggraded approximately 10 m as a result of a high debris-flow frequency from tributary canyons potentially related to the Pleistocene-Holocene climate change. Conversely, the cosmogenic 10Be data average the high contemporary yields with potentially lower yields of the early- Holocene and late-Pleistocene. If the contemporary sediment yields are extrapolated for the entirety of the Holocene, then the cosmogenic data suggest much lower average sediment yields prior to the Pleistocene- Holocene transition. If correct, these data suggest that Pleistocene-Holocene climate change increased sediment yields several

  4. 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.

  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. 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.

  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. Atmospheric CO2 and abrupt climate change in Antarctic warming events 3 and 4 (65 ~ 48 kyrBP)

    NASA Astrophysics Data System (ADS)

    Ahn, J.; Brook, E. J.

    2006-12-01

    Understanding phase relationship between atmospheric CO2 and abrupt climate change (e.g., Dansgaard- Oeschger [D-O] and Heinrich events) in the last glacial period has been hampered by uncertain chronology of CO2 records from Antarctic ice cores. We developed a new extraction/analytical system to measure CO2 in ice cores, and are using it to examine millennial variations of atmospheric CO2 in the Byrd ice core, which has an age scale well synchronized to Greenland cores using CH4 records. Duplicate measurements of the Byrd ice show average standard error of the mean and pooled standard deviation of 1.55 and 1.98 ppm CO2, respectively. Our preliminary data cover Antarctic warming events A3 and A4, the onset of which precedes D-O events 14 and 17. For A3 and A4 the initial CO2 rise precedes the corresponding D-O events by 2 and 4 kyrs, respectively. CO2 reaches final interstadial levels during A4 approximately 2 kyrs before the onset of D-O 17, but the CO2 rise during A3 is more abrupt, with over half of the ~17 ppm change occurring in a <600 year step immediately preceding D-O event 14. Further high time-resolution measurements of CO2 concentration in the Byrd ice core are in progress and may help us understand the carbon cycle, teleconnection of climate-related factors such as CH4 and biological productivity recorded in marine sediments and temperatures in northern and southern hemispheres, and the chronology of other Antarctic ice cores using CO2 as a correlation tool.

  9. 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.

  10. 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.

  11. 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

  12. Millennial-scale ocean acidification and late Quaternary decline of cryptic bacterial crusts in tropical reefs.

    PubMed

    Riding, R; Liang, L; Braga, J C

    2014-09-01

    Ocean acidification by atmospheric carbon dioxide has increased almost continuously since the last glacial maximum (LGM), 21,000 years ago. It is expected to impair tropical reef development, but effects on reefs at the present day and in the recent past have proved difficult to evaluate. We present evidence that acidification has already significantly reduced the formation of calcified bacterial crusts in tropical reefs. Unlike major reef builders such as coralline algae and corals that more closely control their calcification, bacterial calcification is very sensitive to ambient changes in carbonate chemistry. Bacterial crusts in reef cavities have declined in thickness over the past 14,000 years with largest reduction occurring 12,000-10,000 years ago. We interpret this as an early effect of deglacial ocean acidification on reef calcification and infer that similar crusts were likely to have been thicker when seawater carbonate saturation was increased during earlier glacial intervals, and thinner during interglacials. These changes in crust thickness could have substantially affected reef development over glacial cycles, as rigid crusts significantly strengthen framework and their reduction would have increased the susceptibility of reefs to biological and physical erosion. Bacterial crust decline reveals previously unrecognized millennial-scale acidification effects on tropical reefs. This directs attention to the role of crusts in reef formation and the ability of bioinduced calcification to reflect changes in seawater chemistry. It also provides a long-term context for assessing anticipated anthropogenic effects. © 2014 John Wiley & Sons Ltd.

  13. Millennial-scale projection of oceanic oxygen change due to global warming

    NASA Astrophysics Data System (ADS)

    Yamamoto, Akitomo; Abe-Ouchi, Ayako; Shigemitsu, Masahito; Oka, Akira; Takahashi, Kunio; Ohgaito, Rumi; Yamanaka, Yasuhiro

    2016-04-01

    Global warming is expected to globally decrease ocean oxygen concentrations by sea surface warming and ocean circulation change. Oxygen reduction is expected to persist for a thousand years or more, even after atmospheric carbon dioxide stops rising. However, long-term changes in ocean oxygen and circulation are still unclear. Here we simulate multimillennium changes in ocean circulation and oxygen under doubling and quadrupling of atmospheric carbon dioxide, using GCM (MIROC) and an offline biogeochemical model. In the first 500 years, global oxygen concentration decreases, consistent with previous studies. Thereafter, however, the oxygen concentration in the deep ocean globally recovers and overshoots at the end of the simulations, despite surface oxygen decrease and weaker AMOC. This is because, after the initial cessation, the recovery and overshooting of deep ocean convection in the Weddell Sea enhance ventilation and supply oxygen-rich surface waters to deep ocean. Another contributor to deep ocean oxygenation is seawater warming, which reduces the export production and shifts the organic matter remineralization to the upper water column. Our results indicate that the change in ocean circulation in the Southern Ocean potentially drives millennial-scale oxygenation in deep ocean, which is opposite to the centennial-scale global oxygen reduction and general expectation.

  14. Iceberg discharges and oceanic circulation changes during glacial abrupt climate changes

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

    Proxy data reveal the existence of episodes of increased deposition of ice-rafted debris in the North Atlantic Ocean during the last glacial period. These are interpreted as massive iceberg discharges mainly from the Laurentide Ice Sheet. Although these have long been attributed to self-sustained ice sheet oscillations, growing evidence points to an active role of the oceanic circulation. Here we will present simulations of the last glacial period carried out with a hybrid ice sheet-ice shelf model. Two mechanisms producing iceberg discharges are compared. First, we reproduce the classic binge-purge by which the iceberg surges are produced thanks to the existence of an internal thermo-mechanical feedback that allows the ice sheet to behave under an oscillatory regime. Second, our ice-sheet model is forced by an oceanic warming index derived from proxy data that accounts for the impact of past ocean circulation changes on ocean temperatures. In this case, the model generates a time series of iceberg calving that agrees with ice-rafted debris records over the past 80 ka. We compare the two theories and discuss their advantages and weaknesses in terms of both the robustness of the physics on which they are based and their comparison with proxies. This comparison highlights the importance of considering past oceanic circulation changes in order to understand the ice-sheet dynamics. However, the ultimate processes determining abrupt changes in the Atlantic Meridional Overturning Circulation (AMOC) remain elusive. Therefore we will also analyze several proposed mechanisms that aims to explain such AMOC reorganizations, focusing on those that do not require freshwater flux forcing.

  15. 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.

  16. Abrupt climate transition of icy worlds from snowball to moist or runaway greenhouse

    NASA Astrophysics Data System (ADS)

    Yang, Jun; Ding, Feng; Ramirez, Ramses M.; Peltier, W. R.; Hu, Yongyun; Liu, Yonggang

    2017-08-01

    Ongoing and future space missions aim to identify potentially habitable planets in our Solar System and beyond. Planetary habitability is determined not only by a planet's current stellar insolation and atmospheric properties, but also by the evolutionary history of its climate. It has been suggested that icy planets and moons become habitable after their initial ice shield melts as their host stars brighten. Here we show from global climate model simulations that a habitable state is not achieved in the climatic evolution of those icy planets and moons that possess an inactive carbonate-silicate cycle and low concentrations of greenhouse gases. Examples for such planetary bodies are the icy moons Europa and Enceladus, and certain icy exoplanets orbiting G and F stars. We find that the stellar fluxes that are required to overcome a planet's initial snowball state are so large that they lead to significant water loss and preclude a habitable planet. Specifically, they exceed the moist greenhouse limit, at which water vapour accumulates at high altitudes where it can readily escape, or the runaway greenhouse limit, at which the strength of the greenhouse increases until the oceans boil away. We suggest that some icy planetary bodies may transition directly to a moist or runaway greenhouse without passing through a habitable Earth-like state.

  17. Millennial-scale fluctuations in Saharan dust supply across the decline of the African Humid Period

    NASA Astrophysics Data System (ADS)

    Zielhofer, Christoph; von Suchodoletz, Hans; Fletcher, William J.; Schneider, Birgit; Dietze, Elisabeth; Schlegel, Michael; Schepanski, Kerstin; Weninger, Bernhard; Mischke, Steffen; Mikdad, Abdeslam

    2017-09-01

    The Sahara is the world's largest dust source with significant impacts on trans-Atlantic terrestrial and large-scale marine ecosystems. Contested views about a gradual or abrupt onset of Saharan aridity at the end of the African Humid Period dominate the current scientific debate about the Holocene Saharan desiccation. In this study, we present a 19.63 m sediment core sequence from Lake Sidi Ali (Middle Atlas, Morocco) at the North African desert margin. We reconstruct the interaction between Saharan dust supply and Western Mediterranean hydro-climatic variability during the last 12,000 yr based on analyses of lithogenic grain-sizes, XRF geochemistry and stable isotopes of ostracod shells. A robust chronological model based on AMS 14C dated pollen concentrates supports our multi-proxy study. At orbital-scale there is an overall increase in southern dust supply from the Early Holocene to the Late Holocene, but our Northern Saharan dust record indicates that a gradual Saharan desiccation was interrupted by multiple abrupt dust increases before the 'southern dust mode' was finally established at 4.7 cal ka BP. The Sidi Ali record features millennial peaks in Saharan dust increase at about 11.1, 10.2, 9.4, 8.2, 7.3, 6.6, 6.0, and 5.0 cal ka BP. Early Holocene Saharan dust peaks coincide with Western Mediterranean winter rain minima and North Atlantic cooling events. In contrast, Late Holocene dust peaks correspond mostly with prevailing positive phases of the North Atlantic Oscillation. By comparing with other North African records, we suggest that increases in Northern Saharan dust supply do not solely indicate sub-regional to regional aridity in Mediterranean Northwest Africa but might reflect aridity at a trans-Saharan scale. In particular, our findings support major bimillennial phases of trans-Saharan aridity at 10.2, 8.2, 6.0 and 4.2 cal ka BP. These phases coincide with North Atlantic cooling and a weak African monsoon.

  18. Abrupt transition from natural to anthropogenic aerosol radiative forcing: Observations at the ABC-Maldives Climate Observatory

    NASA Astrophysics Data System (ADS)

    Ramana, M. V.; Ramanathan, V.

    2006-10-01

    Using aerosol-radiation observations over the north Indian Ocean, we show how the monsoon transition from southwest to northeast flow gives rise to a similar transition in the direct aerosol radiative forcing from natural to anthropogenic forcing. These observations were taken at the newly built aerosol-radiation-climate observatory at the island of Hanimaadhoo (6.776°N, 73.183°E) in the Republic of Maldives. This observatory is established as a part of Project Atmospheric Brown Clouds (ABC) and is referred to as the ABC-Maldives Climate Observatory at Hanimaadhoo (ABC_MCOH). The transition from the southwest monsoon during October to the northeast monsoon flow during early November occurs abruptly over a period of few weeks over ABC-MCOH and reveals a dramatic contrast between the natural marine aerosols transported from the south Indian Ocean by the southwest monsoon and that of the polluted aerosols transported from the south and Southeast Asian region by the northeast monsoon. We document the change in the microphysical properties and the irradiance at the surface, to identify the human signature on aerosol radiative forcing. We first establish the precision of surface radiometric observations by comparing simultaneous observations using calibrated Kipp & Zonen and Eppley pyrheliometers and pyranometers for direct, diffuse and global solar radiation. We show that the direct, diffuse and global radiation can be measured within a precision of about 3 to 5 Wm-2. Furthermore, when we include the observed aerosol optical properties as input into the Monte Carlo Aerosol Cloud Radiation (MACR) model (developed by us using Indian Ocean Experiment data), the simulated fluxes agree with the observed direct, diffuse and global fluxes within the measurement accuracy. A steady southwest monsoon flow of about 5 to 7 ms-1 persists until middle of October which switches to an abrupt change in direction to northeast flow of similar speeds bringing in polluted air from south

  19. 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

  20. Transitions between multiple equilibria of paleo climate: a glimpse in to the dynamics of abrupt climate change

    NASA Astrophysics Data System (ADS)

    Ferreira, David; Marshall, John; Ito, Takamitsu; McGee, David; Moreno-Chamarro, Eduardo

    2017-04-01

    The dynamics regulating large climatic transitions such as glacial-interglacial cycles or DO events remains a puzzle. Forcings behind these transitions are not robustly identified and potential candidates (e.g. Milankovitch cycles, freshwater perturbations) often appear too weak to explain such dramatic transitions. A potential solution to this long-standing puzzle is that Earth's climate is endowed with multiple equilibrium states of global extent. Such states are commonly found in low-order or conceptual climate models, but it is unclear whether a system as complex as Earth's climate can sustain multiple equilibrium states. Here we report that multiple equilibrium states of the climate system are also possible in a complex, fully dynamical coupled ocean-atmosphere-sea ice GCM with idealized Earth-like geometry, resolved weather systems and a hydrological cycle. In our model, two equilibrium states coexist for the same parameters and external forcings: a Warm climate with a small Northern hemisphere sea ice cap and a large southern one and a Cold climate with large ice caps at both poles. The dynamical states of the Warm and Cold solutions exhibit striking similarities with our present-day climate and the climate of the Last Glacial Maximum, respectively. A carbon cycle model driven by the two dynamical states produces an atmospheric pCO2 draw-down of about 110 pm between the Warm and Cold states, close to Glacial-Interglacial differences found in ice cores. Mechanism controlling the existence of the multiple states and changes in the atmospheric CO2 will be briefly presented. Finally we willdescribe transition experiments from the Cold to the Warm state, focusing on the lead-lags in the system, notably between the Northern and Southern Hemispheres climates.

  1. 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.

  2. A high-resolution record of Holocene millennial-scale oscillations of surface water, foraminiferal paleoecology and sediment redox chemistry in the SE Brazilian margin

    NASA Astrophysics Data System (ADS)

    Dias, B. B.; Barbosa, C. F.; Albuquerque, A. L.; Piotrowski, A. M.

    2014-12-01

    Holocene millennial-scale oscillations and Bond Events (Bond et al. 1997) are well reported in the North Atlantic as consequence of fresh water input and weaking of the Atlantic Meridional Overturning Circulation (AMOC). It has been hypothesized that the effect of weaking of AMOC would lead to warming in the South Atlantic due to "heat piracy", causing surface waters to warm and a reorganization of surface circulation. There are few reconstructions of AMOC strength in the South Atlantic, and none with a high resolution Holocene record of changes of productivity and the biological pump. We reconstruct past changes in the surface water mass hydrography, productivity, and sediment redox changes in high-resolution in the core KCF10-01B, located 128 mbsl water depth off Cabo Frio, Brazil, a location where upwelling is strongly linked to surface ocean hydrography. We use Benthic Foraminiferal Accumulation Rate (BFAR) to reconstruct productivity, which reveals a 1.3kyr cyclicity during the mid- and late-Holocene. The geochemistry of trace and rare earth elements on foraminiferal Fe-Mn oxide coatings show changes in redox-sensitive elements indicating that during periods of high productivity there were more reducing conditions in sediment porewaters, producing a Ce anomaly and reduction and re-precipitation of Mn oxides. Bond events 1-7 were identified by a productivity increase along with reducing sediment conditions which was likely caused by Brazil Current displacement offshore allowing upwelling of the nutritive bottom water South Atlantic Central Waters (SACW) to the euphotic zone and a stronger local biological pump. In a global context, correlation with other records show that this occurred during weakened AMOC and southward displacement of the ITCZ. We conclude that Bond climatic events and millennial-scale variability of AMOC caused sea surface hydrographic changes off the Brazilian Margin leading to biological and geochemical changes recorded in coastal records

  3. Abrupt climate change in the Black Sea basin during the last glacial period (10-60 kyr)

    NASA Astrophysics Data System (ADS)

    Arz, H. W.; Lamy, F.; Kwiecien, O.; Nowaczyk, N.; Plessen, B.; Röhl, U.; Ganopolski, A.

    2009-04-01

    As the most distant arm of the Atlantic Ocean, the Black Sea demonstrates an unparalleled feature: it oscillates between lacustrine and marine stages following, respectively, glacial-interglacial sea level changes. Today, the Black Sea is the world's largest anoxic basin. Coring efforts during the last years rather suggested an extensive glacial sediment cover on most of the Black Sea slope areas not reachable with conventional gravity and piston coring devices. Here we present new sediment cores retrieved from the tectonically formed Archangelsky Ridge in the southeastern Black Sea during the 2007 RV Meteor cruise M72/5, which provide a first view into a complete and undisturbed section of the last glacial period. Different independent stratigraphic approaches (radiocarbon dating, tephrochronology, paleomagnetics, tuning to Greenland ice cores) lead to a consistent age-depth model for the last glacial period. Various proxies from cores 24/25-GC1 suggest strong and immediate responses of the glacial Black Sea freshwater lake to the abrupt D-O climate oscillations of the last glacial period. Each abrupt warming initiated, like during Termination I, inorganic carbonate precipitation in the lake system. Subsequent stadials are marked by increasing IRD input suggesting more abundant coastal ice formation likely reflecting colder winter temperatures. Ostracod stable oxygen isotopes record the precipitation/runoff signal of the drainage basin but show a strongly smoothed signal characteristic to an 1-2 kyr mixing-time in the Black Sea basin with striking similarities to the Antarctic temperature and global ice volume records (Arz et al. 2007).

  4. 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.

  5. 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.

  6. Millennial-scale variability of marine productivity and terrigenous matter supply in the western Bering Sea over the past 180 kyr

    NASA Astrophysics Data System (ADS)

    Riethdorf, J.-R.; Nürnberg, D.; Max, L.; Tiedemann, R.; Gorbarenko, S. A.; Malakhov, M. I.

    2012-12-01

    We used piston cores recovered in the western Bering Sea to reconstruct millennial-scale changes in marine productivity and terrigenous matter supply over the past ~180 kyr. Based on a geochemical multi-proxy approach our results indicate closely interacting processes controlling marine productivity and terrigenous matter supply comparable to the situation in the Okhotsk Sea. Overall, terrigenous inputs were high, whereas primary production was low. Minor increases in marine productivity occurred during warm intervals of stage 5 and interstadials, but pronounced maxima were recorded during interglacials and Termination I. Seasonal sea-ice is suggested to act as the dominant transport agent for terrigenous material. From our results we propose glacial, deglacial, and interglacial scenarios for environmental change in the Bering Sea. These changes seem to be primarily controlled by insolation and sea-level forcing which affect the strength of atmospheric pressure systems and sea-ice growth. The opening history of the Bering Strait and the Aleutian passes is considered to have had an additional impact. Sea-ice dynamics are thought to drive changes in surface productivity, terrigenous inputs, and upper-ocean stratification. High-resolution core logging data (color b*, XRF scans) strongly correspond to the Dansgaard-Oeschger climate variability registered in the NGRIP ice core and support an atmospheric coupling mechanism of Northern Hemisphere climates.

  7. Millennial-scale variability of marine productivity and terrigenous matter supply in the western Bering Sea over the past 180 kyr

    NASA Astrophysics Data System (ADS)

    Riethdorf, J.-R.; Nürnberg, D.; Max, L.; Tiedemann, R.; Gorbarenko, S. A.; Malakhov, M. I.

    2013-06-01

    We used piston cores recovered in the western Bering Sea to reconstruct millennial-scale changes in marine productivity and terrigenous matter supply over the past ~180 kyr. Based on a geochemical multi-proxy approach, our results indicate closely interacting processes controlling marine productivity and terrigenous matter supply comparable to the situation in the Okhotsk Sea. Overall, terrigenous inputs were high, whereas export production was low. Minor increases in marine productivity occurred during intervals of Marine Isotope Stage 5 and interstadials, but pronounced maxima were recorded during interglacials and Termination I. The terrigenous material is suggested to be derived from continental sources on the eastern Bering Sea shelf and to be subsequently transported via sea ice, which is likely to drive changes in surface productivity, terrigenous inputs, and upper-ocean stratification. From our results we propose glacial, deglacial, and interglacial scenarios for environmental change in the Bering Sea. These changes seem to be primarily controlled by insolation and sea-level forcing which affect the strength of atmospheric pressure systems and sea-ice growth. The opening history of the Bering Strait is considered to have had an additional impact. High-resolution core logging data (color b*, XRF scans) strongly correspond to the Dansgaard-Oeschger climate variability registered in the NGRIP ice core and support an atmospheric coupling mechanism of Northern Hemisphere climates.

  8. Millennial Scale Geomagnetic and Environmental Change in the West Iberian Margin during Late Quaternary

    NASA Astrophysics Data System (ADS)

    Xuan, C.; Richter, C.; Acton, G.; Stoner, J. S.; Li, B.; Hodell, D. A.; Ducassou, E.; MacLachlan, S. E.; Voelker, A. H. L.

    2015-12-01

    Paleomagnetic and environmental magnetic studies were performed on u-channel samples collected continuously from the top ~20 to 50 m of sediments recovered during Integrated Ocean Drilling Program (IODP) Expedition 339 to the west Iberian Margin at Sites U1385, U1390, and U1391. Natural remanent magnetization (NRM) and various laboratory-induced magnetizations of the u-channel samples were measured at every 1 cm interval on a 2G Enterprises u-channel pass-through superconducting rock magnetometer, before and after a minimum of 13 step alternating field (AF) demagnetization routine at 5 or 10 mT spacing between steps, up to a maximum peak field of 100 mT. NRM demagnetization data reveal a stable and well-defined primary magnetization for samples from all three sites. Maximum angular deviation (MAD) values associated with the component direction calculations using principal component analysis (PCA) are mostly < 2°. We use a combination of radiocarbon dating, benthic and planktic oxygen isotope stratigraphy, and correlation of natural gamma radiation and X-ray fluorescence data to those of nearby well-dated piston cores, to construct reliable age models for the studied sediments. Studied samples from the three sites cover the last ~40 to over 100 kyrs, with mean sediment accumulation rates ranging from ~10 cm/kyr to over 70 cm/kyr. Occasional sandy layers in the sediments appear to correspond to significantly lower intensities of NRM and ARM, but have little influence on NRM directions. Relative paleointensity (RPI) variations at the three sites estimated using the slopes of best-fit lines of the NRM and anhysteretic remanent magnetization (ARM) data and mean NRM/ARM ratios placed on the acquired age models, show detailed (sub-) millennial scale variabilities and apparently resemble each other and RPI records from other North Atlantic regions at least on time scales of a few thousand years.

  9. Slow Onsets, Abrupt Changes, and Fast Reflexes: Learning from Climate Hazards in a Changing World

    NASA Astrophysics Data System (ADS)

    Pulwarty, R. S.

    2016-12-01

    Adaptation is higher than ever before on the global agenda. Awareness of risks across the weather-climate continuum has increased pressure for information to support planning under changing rates and emergence of multiple hazards (e.g. drought, heat waves, floods). In recognition of this demand, the global community is developing a Global Framework for Climate Services, implementing the Sendai Framework on disaster risk reduction, and formulating climate-sensitive development and research initiatives aimed at nations and communities. The gap between conceptual feasibility and practical implementation remains immense. One of Gilbert White's many important contributions was in developing a framework for structuring adjustment decisions in the context of longer-term risks. The physical environment at a given stage of technology sets the theoretical range of choice while the practical range of choice is set by culture, capacity and institutions. These factors facilitate or impede efficient and equitable responses, with the latter being key in the underestimation of the complexities of adaptation. This presentation will focus on the scientific research, monitoring and information needed to address challenges in (1) Understanding thresholds in the relationship between physical and social changes, including those in connected systems such as water, food and energy, (2) Designing and diffusion of decision support tools and smart practices, and (3) Understanding the links between capacity-building and implementation, including the need to focus researchers and institutions on improving decision quality (not just meeting "user needs"). The author will engage the audience in a discussion of the drivers of social transitions and transformations, drawing on cases from around the world. Key questions, include "What leads to proactive collaboration and action?"; "How often should we revise our assumptions about the direction and magnitude of changes as events unfold?"; and "What

  10. Millennial-scale Surface and Subsurface Dynamics in the Caribbean Sea from LGM to Holocene

    NASA Astrophysics Data System (ADS)

    Reißig, S.; Nuernberg, D.; Poggemann, D. W.

    2016-12-01

    The Caribbean Sea is an important source of warm and saline water that is transported into the North Atlantic, and therefore plays a key role in the global thermohaline circulation. Today, waters from the (sub-) tropical Atlantic enter the Caribbean through a variety of passages. The water masses flow through the Caribbean into the Gulf of Mexico via the Yucatan Strait, forming the Gulf Stream which represents the northward flowing branch of the Atlantic Meridional Overturning Circulation (AMOC). The AMOC is intimately linked to abrupt northern hemisphere climate change and is a key player for the transport of tropical heat to high northern latitudes. A reduced AMOC during the deglacial resulted in sea-surface cooling in wide areas of the tropical North Atlantic, while the subsurface ocean experienced regional warming by several degrees due to the reorganization of ocean circulation at intermediate depths. Based on stable isotope compositions (δ13C, δ18O) and elemental (Mg/Ca) ratios of a surface dwelling (Globigerinoides ruber) and deep dwelling (Globorotalia truncatulinoides) planktonic foraminifera, we reconstruct surface and subsurface temperature, thermocline variation and salinity changes during the past 24 thousand years, to evaluate the role of a weakened AMOC on the main inflow areas of Equatorial Current waters into the Caribbean. This study reveals new information about water mass inflow into the Caribbean basin and is compared to an unpublished record of the water masses exiting the Caribbean from a core located at the flow-through of the Caribbean into the Gulf of Mexico (Campeche Bank).

  11. Synchronous climate changes in Antarctica and the North Atlantic

    USGS Publications Warehouse

    Steig, E.J.; Brook, E.J.; White, J.W.C.; Sucher, C.M.; Bender, M.L.; Lehman, S.J.; Morse, D.L.; Waddington, E.D.; Clow, G.D.

    1998-01-01

    Central Greenland ice cores provide evidence of abrupt changes in climate over the past 100,000 years. Many of these changes have also been identified in sedimentary and geochemical signatures in deep-sea sediment cores from the North Atlantic, confirming the link between millennial-scale climate variability and ocean thermohaline circulation. It is shown here that two of the most prominent North Atlantic events - the rapid warming that makes the end of the last glacial period and the Bolling/Allerod-Younger Dryas oscillation - are also recorded in an ice core from Taylor Dome, in the western Ross Sea sector of Antarctica. This result contrasts with evidence from ice cores in other regions of Antarctica, which show an asynchronous response between the Northern and Southern Hemispheres.

  12. Synchronous climate changes in antarctica and the north atlantic

    PubMed

    Steig; Brook; White; Sucher; Bender; Lehman; Morse; Waddington; Clow

    1998-10-02

    Central Greenland ice cores provide evidence of abrupt changes in climate over the past 100,000 years. Many of these changes have also been identified in sedimentary and geochemical signatures in deep-sea sediment cores from the North Atlantic, confirming the link between millennial-scale climate variability and ocean thermohaline circulation. It is shown here that two of the most prominent North Atlantic events-the rapid warming that marks the end of the last glacial period and the Bolling/Allerod-Younger Dryas oscillation-are also recorded in an ice core from Taylor Dome, in the western Ross Sea sector of Antarctica. This result contrasts with evidence from ice cores in other regions of Antarctica, which show an asynchronous response between the Northern and Southern Hemispheres.

  13. 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

  14. 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

  15. 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.

  16. Millennial scale oscillations in bulk δ15N and δ13C over the Mid- to Late Holocene seen in proteinaceous corals from the North Pacific Subtropical Gyre

    NASA Astrophysics Data System (ADS)

    Glynn, D. S.; Mccarthy, M. D.; McMahon, K.; Guilderson, T. P.

    2014-12-01

    The North Pacific Subtropical Gyre (NPSG) is the largest continuous ecosystem on this planet and is an important regulator of biogeochemical cycling and carbon sequestration. With evidence of its expansion in a warming climate, it is necessary to develop a more complete understanding of the variability in productivity and nutrient dynamics in this important ecosystem through time. We constructed a long-term, high resolution record of bulk record of stable nitrogen (δ15N) and carbon isotopes (δ13C) from multiple proteinaceous deep sea corals around Hawaii extending back ~5300 years with few gaps. Our data confirms the decreasing trend in δ15N since the Little Ice Age (1850s), which matches previously published results in part attributed to anthropogenic climate change (e.g. Sherwood et al. 2014). However, while the rate of change since the Little Ice Age (δ15N declines ~1‰ over ~150yrs) remains by far the most rapid throughout the longer record, there also appear to be longer-term (near-millennial scale) climatic oscillations of even greater magnitude (δ15N shifts ~1.5-2‰ over ~1000yrs). After removal of the Seuss Effect, δ13C values also declined ~1.5‰ since the Little Ice Age. Furthermore, there also appear to be oscillations in δ13C of ~1-2‰ over millennial timescales. These results reveal the existence of previously unrecognized long-term oscillations in NPSG biogeochemical cycles, which are likely linked to changes in phytoplankton species composition, food web dynamics, and/or variability in source nutrients and productivity possibly caused by changes in climate. This study provides insight into nutrient dynamics in the NPSG over the past five millennia, and offers a historical baseline to better analyze the effects of current anthropogenic climate forcing.

  17. Holocene climate less stable than previously thought

    NASA Astrophysics Data System (ADS)

    deMenocal, Peter; Bond, Gerard

    Until recently, Holocene climate was thought to be extremely stable with none of the abrupt variations that characterize the cold climates of glacial times [Dansgaard et al., 1993]. New terrestrial, marine, and ice core data, however, document abrupt changes during the warm interglacial climate of the last 12,000 years. These newly developed Holocene paleoclimate records indicate that the Holocene was punctuated by a series of millennial-scale (1000-2000 year) cooling events, the most recent of which was the Little Ice Age (LIA) between approximately 1500 and 1800 A.D. Historical evidence indicates that the estimated ˜1°-2°C LIA ooling was ufficient to choke European ports with sea ice, freeze European rivers (as graphically recorded in the 1565 painting “Winter Landscape” by Pieter Bruegel), force abandonment of Viking colonies in Greenland, and cause glaciers to overrun alpine villages [Bradley and Jones, 1995]. Although these Holocene cooling events were not as large as the well-known glacial Heinrich events and Dansgaard-Oeschger climate instabilities [Bond et al., 1996; Dansgaard et al., 1993], they nonetheless document dramatic climate swings during the “climatically stable” Holocene.

  18. Development of Middle Stone Age innovation linked to rapid climate change

    PubMed Central

    Ziegler, Martin; Simon, Margit H.; Hall, Ian R.; Barker, Stephen; Stringer, Chris; Zahn, Rainer

    2013-01-01

    The development of modernity in early human populations has been linked to pulsed phases of technological and behavioural innovation within the Middle Stone Age of South Africa. However, the trigger for these intermittent pulses of technological innovation is an enigma. Here we show that, contrary to some previous studies, the occurrence of innovation was tightly linked to abrupt climate change. Major innovational pulses occurred at times when South African climate changed rapidly towards more humid conditions, while northern sub-Saharan Africa experienced widespread droughts, as the Northern Hemisphere entered phases of extreme cooling. These millennial-scale teleconnections resulted from the bipolar seesaw behaviour of the Atlantic Ocean related to changes in the ocean circulation. These conditions led to humid pulses in South Africa and potentially to the creation of favourable environmental conditions. This strongly implies that innovational pulses of early modern human behaviour were climatically influenced and linked to the adoption of refugia. PMID:23695699

  19. Development of Middle Stone Age innovation linked to rapid climate change.

    PubMed

    Ziegler, Martin; Simon, Margit H; Hall, Ian R; Barker, Stephen; Stringer, Chris; Zahn, Rainer

    2013-01-01

    The development of modernity in early human populations has been linked to pulsed phases of technological and behavioural innovation within the Middle Stone Age of South Africa. However, the trigger for these intermittent pulses of technological innovation is an enigma. Here we show that, contrary to some previous studies, the occurrence of innovation was tightly linked to abrupt climate change. Major innovational pulses occurred at times when South African climate changed rapidly towards more humid conditions, while northern sub-Saharan Africa experienced widespread droughts, as the Northern Hemisphere entered phases of extreme cooling. These millennial-scale teleconnections resulted from the bipolar seesaw behaviour of the Atlantic Ocean related to changes in the ocean circulation. These conditions led to humid pulses in South Africa and potentially to the creation of favourable environmental conditions. This strongly implies that innovational pulses of early modern human behaviour were climatically influenced and linked to the adoption of refugia.

  20. Do Quercus ilex woodlands undergo abrupt non-linear functional changes in response to human disturbance along a climatic gradient?

    NASA Astrophysics Data System (ADS)

    Bochet, Esther; García-Fayos, Patricio; José Molina, Maria; Moreno de las Heras, Mariano; Espigares, Tíscar; Nicolau, Jose Manuel; Monleon, Vicente

    2017-04-01

    Theoretical models predict that drylands are particularly prone to suffer critical transitions with abrupt non-linear changes in their structure and functions as a result of the existing complex interactions between climatic fluctuations and human disturbances. However, so far, few studies provide empirical data to validate these models. We aim at determining how holm oak (Quercus ilex) woodlands undergo changes in their functions in response to human disturbance along an aridity gradient (from semi-arid to sub-humid conditions), in eastern Spain. For that purpose, we used (a) remote-sensing estimations of precipitation-use-efficiency (PUE) from enhanced vegetation index (EVI) observations performed in 231x231 m plots of the Moderate Resolution Imaging Spectroradiometer (MODIS); (b) biological and chemical soil parameter determinations (extracellular soil enzyme activity, soil respiration, nutrient cycling processes) from soil sampled in the same plots; (c) vegetation parameter determinations (ratio of functional groups) from vegetation surveys performed in the same plots. We analyzed and compared the shape of the functional change (in terms of PUE and soil and vegetation parameters) in response to human disturbance intensity for our holm oak sites along the aridity gradient. Overall, our results evidenced important differences in the shape of the functional change in response to human disturbance between climatic conditions. Semi-arid areas experienced a more accelerated non-linear decrease with an increasing disturbance intensity than sub-humid ones. The proportion of functional groups (herbaceous vs. woody cover) played a relevant role in the shape of the functional response of the holm oak sites to human disturbance.

  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. 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

  3. Patterns and Impacts of millennial-scale hydroclimatic change in North American during the Holocene

    NASA Astrophysics Data System (ADS)

    Shuman, B. N.

    2012-12-01

    A new database of >100 lake-level reconstructions spanning the Holocene from the United States and Canada reveals that long-term patterns of hydroclimatic change in the mid-latitudes were punctuated by a series of abrupt events, particularly at ca. 8 and 5.5 ka. New detailed reconstructions from the Rocky Mountains and the northeast U.S. show that the abrupt changes produced important changes in the gradient of moisture availability across the continent with the mid-continent drying and the Atlantic coast becoming wet at ca 8 ka, and then a reversal of this pattern at 5.5 ka. Both changes are associated with important abrupt changes in North American vegetation, including abrupt shifts in the boundaries of the Great Plains grasslands and including the classic collapse of eastern hemlock (Tsuga) species. Regression analyses indicate that the area of the Laurentide Ice Sheet and Atlantic sea surface temperatures drove the abrupt changes. Archeological data also reveal societal importance of the hydroclimatic changes, which included probably severe reductions in mid-continent river flows.

  4. 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

  5. Eolian sediment responses to late Quaternary climate changes: Temporal and spatial patterns in the Sahara

    USGS Publications Warehouse

    Swezey, C.

    2001-01-01

    This paper presents a compilation of eolian-based records of late Quaternary climate changes in the Sahara. Although the data are relatively sparse, when viewed as a whole, they reveal a general pattern of widespread eolian sediment mobilization prior to 11,000 cal. years BP, eolian sediment stabilization from 11,000 to 5000 cal. years BP, and a return to widespread eolian sediment mobilization after 5000 cal. years BP. Furthermore, an eolian-based record from southern Tunisia reveals the existence of millennial-scale changes in eolian sediment behavior. These millennial-scale variations provide examples of eolian sediment responses to climate changes at a scale intermediate between seasonal and orbital ('Milankovitch') changes, and they are also coincident with abrupt atmospheric and oceanic changes. The general synchroneity of the eolian stratigraphic records and their coincidence with various oceanic and atmospheric changes suggest that global forcing mechanisms have influenced late Quaternary eolian sediment behavior in the Sahara. ?? 2001 Elsevier Science B.V.

  6. 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.

  7. Northern Hemisphere Controls on Tropical Southeast African Climate During the Past 60,000 Years

    NASA Astrophysics Data System (ADS)

    Tierney, Jessica E.; Russell, James M.; Huang, Yongsong; Damsté, Jaap S. Sinninghe; Hopmans, Ellen C.; Cohen, Andrew S.

    2008-10-01

    The processes that control climate in the tropics are poorly understood. We applied compound-specific hydrogen isotopes (δD) and the TEX86 (tetraether index of 86 carbon atoms) temperature proxy to sediment cores from Lake Tanganyika to independently reconstruct precipitation and temperature variations during the past 60,000 years. Tanganyika temperatures follow Northern Hemisphere insolation and indicate that warming in tropical southeast Africa during the last glacial termination began to increase ~3000 years before atmospheric carbon dioxide concentrations. δD data show that this region experienced abrupt changes in hydrology coeval with orbital and millennial-scale events recorded in Northern Hemisphere monsoonal climate records. This implies that precipitation in tropical southeast Africa is more strongly controlled by changes in Indian Ocean sea surface temperatures and the winter Indian monsoon than by migration of the Intertropical Convergence Zone.

  8. Linkages between rapid climate variability and deep-sea benthic foraminifera in the deep Subantarctic South Atlantic during the last 95 kyr

    NASA Astrophysics Data System (ADS)

    Diz, Paula; Barker, Stephen

    2015-06-01

    We present a high-resolution record of benthic foraminifera fauna from a sediment core retrieved from the South Cape Basin (Subantarctic South Atlantic) spanning the last glacial cycle (95 kyr). Information provided by benthic foraminiferal assemblages together with paleoclimate proxies from the same core allow us to interpret changes in the style of primary production (episodic versus sustained) in relation to abrupt climate oscillations. Our results indicate that fluctuations in the abundance of the phytodetritus-related species, Epistominella exigua, are concomitant with millennial-scale high-latitude climate perturbations. Episodic phytoplankton blooms increased during a negative mode of the bipolar seesaw, irrespective of the magnitude of the perturbation (i.e., Heinrich stadial versus non-Heinrich stadial events). We provide a hypothesis linking the frequency and intensity of these events to atmospheric perturbations, interhemispheric climate variability, and millennial-scale changes in atmospheric CO2. A notable exception to the overall pattern is the generally high abundance of E. exigua across the globally synchronous onset of glacial marine oxygen isotope stage (MIS) 4, a period generally characterized by increased dustiness and low-quality organic carbon as inferred by the percentage of the nonphytodetritus species. This highlights the special characteristics governing the onset of MIS 4 in the Subantarctic.

  9. The Enigma of Millennial-scale Rainfall Variations in the Southeast African Tropics: a Breakdown of the ITCZ Paradigm

    NASA Astrophysics Data System (ADS)

    Tierney, J.; Russell, J.; Huang, Y.; Sinninghe Damste, J.; Hopmans, E.; Cohen, A.

    2008-12-01

    A high-resolution, continuous, compound-specific D/H isotope and TEX86 record from Lake Tanganyika spanning the last 60 ka affords us a definitive look at past rainfall and temperature variations in the southeast African tropics. From this record, it is evident that this region experienced abrupt and dramatic episodes of aridity co-eval with known high-latitude millennial climate coolings, such as the Younger Dryas and Heinrich Events 1 and 4. Yet lithogenic and biological proxy evidence from Southeast Africa suggests that the Intertropical Convergence Zone (ITCZ) shifted south and northerly winds intensified during these events, per predictions from General Circulation Model experiments. A southward shift in the ITCZ should make the southern tropics, including Lake Tanganyika, wet, so why then is southeast Africa dry, and thus in- phase with the Northern Hemisphere? The explanation behind this "breakdown" in the ITCZ paradigm likely involves Indian Ocean dynamics, including SST variability, monsoon dynamics, and zonal reconfigurations of Walker circulation in the Indian Ocean basin - all of which modulate the amount of moisture transported into continental Africa and the strength of convergence within the ITCZ itself. These Indian Ocean dynamics may be teleconnected to the North Atlantic, thus serving as a conduit for the transmission of high-latitude abrupt climate change to continental Africa.

  10. 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.

  11. An 8700 Year Record of Holocene Climate Variability from the Yucatan Peninsula

    NASA Astrophysics Data System (ADS)

    Wahl, D.; Byrne, R.; Anderson, L.

    2013-12-01

    Our understanding of Holocene climate change in the Maya lowlands of Central America has improved significantly during the last several decades thanks to the development of proxy climate records from lake cores and speleothems. One important finding is that longer-term climate changes (i.e., millennial scale) were driven primarily by precessional forcing; less clear, however, are the causes of abrupt shifts and higher frequency (centennial to decadal) change recognized in many Holocene climate reconstructions. The mechanisms driving climate change on these time scales have been difficult to identify in the region, in part because the Yucatan peninsula is influenced by climatic conditions linked to both the tropical Atlantic and Pacific oceans. Additional complications arise from the development of dense human populations following the initial introduction of agriculture ~5000 cal yr BP, which had significant impact on the environment as a whole. Here we present the results of analyses (stable isotope, pollen, magnetic susceptibility, and physical properties) of a 7.25 m sediment core from Lago Puerto Arturo, a closed basin lake in the northern Peten, Guatemala. An age-depth model, based on 6 AMS radiocarbon determinations and created using CLAM, indicates the record extends to 8700 cal yr BP. Proxy data suggest that, similar to other low latitude sites, millennial scale climate at Lago Puerto Arturo was driven by changes in insolation. Higher frequency variability is associated with El Niño/Southern Oscillation (ENSO) and North Atlantic Oscillation (NAO) dynamics, reflecting latitudinal shifts in the Intertropical Convergence Zone in both the tropical North Atlantic and North Pacific. Solar forcing may also play a role in short-term climate change. The pollen and isotope records show that the entire period of prehispanic settlement and agricultural activity, i.e. ~5000-1000 cal yr B.P., was characterized by relatively dry conditions compared to before or after.

  12. 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

  13. Millennial-scale variability in Atlantic water advection to the Nordic Seas derived from Holocene coccolith concentration records

    NASA Astrophysics Data System (ADS)

    Giraudeau, J.; Grelaud, M.; Solignac, S.; Andrews, J. T.; Moros, M.; Jansen, E.

    2010-05-01

    Abundance patterns of coccolith species in two Holocene marine cores retrieved off Norway and northern Iceland are indicative of millennial-scale modulations in the flow of the main (Norwegian Atlantic Current) and secondary (North Iceland Irminger Current) branches of the North Atlantic Drift to the Nordic Seas. Long-term trends in coccolith abundance changes reflect major Holocene steps in Atlantic Water transfer to the Nordic Seas at orbital scale with important constraints on the convective activity of the Nordic Seas that leads to the formation of the precursor water mass of North Atlantic Deep Water. Millennial-scale Holocene episodes of increased advection of Atlantic waters off Norway are associated with enhanced winter precipitation over Scandinavia, increased sea-salt fluxes over Greenland, and strengthened wind over Iceland, thereby suggesting a common atmospheric forcing: the location and intensity of the westerlies and the associated changes in mid- to high-latitude pressure gradients. Our biotic data indicate an opposite pattern of Atlantic water inflow at suborbital scale between the western (Denmark) and eastern (Iceland-Scotland) straits of the northern Atlantic throughout the Holocene. This, as supported by present observational and simulated data, further highlights the role of atmospheric oscillations in the recent history of the North Atlantic-Nordic Seas water mass exchanges across the Greenland-Scotland Ridge. Such atmospheric processes are thought to explain the observed coupling between periods of excess export of arctic sea-ice to the Nordic Seas and intervals of maximum inflow of Atlantic water to the Norwegian Sea throughout the last 11 000 years.

  14. 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

  15. 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.

  16. Evidence of abrupt climate changes in the Near East - half a million years of environmental conditions captured in Lake Van's subsurface

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

    Varved sedimentary records have shown their high potential to reconstruct abrupt and global climate change within the marine realm (e.g. Cariaco Basin, Santa Barbara Basin). Continental counterparts, consisting of long and varved lacustrine sediments, can be found in the subsurface of some deep lakes such as Lake Van in Eastern Anatolia (Turkey). This lake is a 440 m deep terminal soda lake situated in a climatically sensitive semiarid and tectonically active region. Through the ICDP project Paleovan, its complete 220 m long sedimentary succession was recovered in 2010. Lithological descriptions, XRF-scanning and sampling for multi-proxy studies are underway since spring 2011. The lithostratigraphic framework of the composite profile, consisting of carbonaceous clayey silt intercalated by ~300 tephra layers, is overprinted by dozens of seismic-related microdeformations. This partially annually-resolved continental sediment sequence is ideal to reconstruct climate, tectonic and volcanic activity in the mid-latitudes over the past 500'000 years. Distinct color transitions and repetitive sedimentary patterns are the expression of sudden and periodic environmental changes. They are also mirrored in high-resolution color data and variations in total organic carbon concentrations, both reflecting lake productivity. First results of absolute age control is provided by single-crystal Ar/Ar dating of tephra layers. It is confirmed by an excellent match of proxy data to marine isotope stages and substages. The abrupt changes observed in the record suggest that climatic, hydrological and environmental conditions prevailing in Eastern Anatolia were synchronous to the Dansgaard-Oeschger (D/O) cycles recorded in ice and marine sediment cores as well as in speleothems from the last glacial period. The presence of this signal in the Lake Van archive indicates a wide-reaching effect of N-Atlantic-controlled climate. Furthermore, analogous evidence of identical sub

  17. 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.

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

    NASA Astrophysics Data System (ADS)

    Weiss, H.

    2003-12-01

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

  19. Millennial-scale plankton regime shifts in the subtropical North Pacific Ocean.

    PubMed

    McMahon, Kelton W; McCarthy, Matthew D; Sherwood, Owen A; Larsen, Thomas; Guilderson, Thomas P

    2015-12-18

    Climate change is predicted to alter marine phytoplankton communities and affect productivity, biogeochemistry, and the efficacy of the biological pump. We reconstructed high-resolution records of changing plankton community composition in the North Pacific Ocean over the past millennium. Amino acid-specific δ(13)C records preserved in long-lived deep-sea corals revealed three major plankton regimes corresponding to Northern Hemisphere climate periods. Non-dinitrogen-fixing cyanobacteria dominated during the Medieval Climate Anomaly (950-1250 Common Era) before giving way to a new regime in which eukaryotic microalgae contributed nearly half of all export production during the Little Ice Age (~1400-1850 Common Era). The third regime, unprecedented in the past millennium, began in the industrial era and is characterized by increasing production by dinitrogen-fixing cyanobacteria. This picoplankton community shift may provide a negative feedback to rising atmospheric carbon dioxide concentrations.

  20. Millennial-scale plankton regime shifts in the subtropical North Pacific Ocean

    NASA Astrophysics Data System (ADS)

    McMahon, Kelton W.; McCarthy, Matthew D.; Sherwood, Owen A.; Larsen, Thomas; Guilderson, Thomas P.

    2015-12-01

    Climate change is predicted to alter marine phytoplankton communities and affect productivity, biogeochemistry, and the efficacy of the biological pump. We reconstructed high-resolution records of changing plankton community composition in the North Pacific Ocean over the past millennium. Amino acid-specific δ13C records preserved in long-lived deep-sea corals revealed three major plankton regimes corresponding to Northern Hemisphere climate periods. Non-dinitrogen-fixing cyanobacteria dominated during the Medieval Climate Anomaly (950-1250 Common Era) before giving way to a new regime in which eukaryotic microalgae contributed nearly half of all export production during the Little Ice Age (~1400-1850 Common Era). The third regime, unprecedented in the past millennium, began in the industrial era and is characterized by increasing production by dinitrogen-fixing cyanobacteria. This picoplankton community shift may provide a negative feedback to rising atmospheric carbon dioxide concentrations.

  1. Climate variability of Central Asia on orbital to millennial timescales

    NASA Astrophysics Data System (ADS)

    Cheng, H.; Spoetl, C.; Breitenbach, S. F. M.; Sinha, A.; Wassenburg, J. A.; Li, X.; Yi, L.; Jochum, K. P.; Scholz, D.; Peng, Y.; Kathayat, G.; Edwards, R. L.

    2016-12-01

    It remains a longstanding question to which extent the climate variability in Westerly Central Asia is causally linked to large-scale changes in Asian monsoon on a wide range of timescales. Here we present high-resolution and precisely dated speleothem oxygen-carbon isotope and trace element records of Central Asia's hydroclimate variability from Tonnel'naya cave, Uzbekistan, and Kesang cave, western China, covering the last 136 and 500 ka, respectively. On orbital timescales, the supra-regional climate variability, inferred from our oxygen isotope records, exhibit a precession rhythm, punctuated by millennial-scale abrupt climate events. This supra-regional climate mode is indeed coherent with the Asian monsoon variability, supporting previous modeling results, which persistently indicate a close coupling relationship between the Asian monsoon and the Westerly climates. However, the local hydroclimatic variability at the two cave sites, as inferred from carbon isotope and trace element records, shows climate variations that are distinctly different from their supra-regional modes. Particularly, hydroclimatic changes in both cave areas during the Holocene are consistent with the Holocene lake proxy records from the region, and lag behind the supra-regional climate variability by several thousand years. Our multi-proxy data may reconcile the paradox of an apparent out-of-phase hydroclimatic variability between Westerly Central Asia and monsoon Asia by identifying different Central Asia climate modes on different tempo-spatial scales.

  2. 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

  3. 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.

  4. Millennial-scale sustainability of the Chesapeake Bay Native American oyster fishery

    PubMed Central

    Rick, Torben C.; Reeder-Myers, Leslie A.; Hofman, Courtney A.; Breitburg, Denise; Lockwood, Rowan; Henkes, Gregory; Kellogg, Lisa; Lowery, Darrin; Luckenbach, Mark W.; Mann, Roger; Ogburn, Matthew B.; Southworth, Melissa; Wah, John; Wesson, James; Hines, Anson H.

    2016-01-01

    Estuaries around the world are in a state of decline following decades or more of overfishing, pollution, and climate change. Oysters (Ostreidae), ecosystem engineers in many estuaries, influence water quality, construct habitat, and provide food for humans and wildlife. In North America’s Chesapeake Bay, once-thriving eastern oyster (Crassostrea virginica) populations have declined dramatically, making their restoration and conservation extremely challenging. Here we present data on oyster size and human harvest from Chesapeake Bay archaeological sites spanning ∼3,500 y of Native American, colonial, and historical occupation. We compare oysters from archaeological sites with Pleistocene oyster reefs that existed before human harvest, modern oyster reefs, and other records of human oyster harvest from around the world. Native American fisheries were focused on nearshore oysters and were likely harvested at a rate that was sustainable over centuries to millennia, despite changing Holocene climatic conditions and sea-level rise. These data document resilience in oyster populations under long-term Native American harvest, sea-level rise, and climate change; provide context for managing modern oyster fisheries in the Chesapeake Bay and elsewhere around the world; and demonstrate an interdisciplinary approach that can be applied broadly to other fisheries. PMID:27217572

  5. Millennial-scale sustainability of the Chesapeake Bay Native American oyster fishery.

    PubMed

    Rick, Torben C; Reeder-Myers, Leslie A; Hofman, Courtney A; Breitburg, Denise; Lockwood, Rowan; Henkes, Gregory; Kellogg, Lisa; Lowery, Darrin; Luckenbach, Mark W; Mann, Roger; Ogburn, Matthew B; Southworth, Melissa; Wah, John; Wesson, James; Hines, Anson H

    2016-06-07

    Estuaries around the world are in a state of decline following decades or more of overfishing, pollution, and climate change. Oysters (Ostreidae), ecosystem engineers in many estuaries, influence water quality, construct habitat, and provide food for humans and wildlife. In North America's Chesapeake Bay, once-thriving eastern oyster (Crassostrea virginica) populations have declined dramatically, making their restoration and conservation extremely challenging. Here we present data on oyster size and human harvest from Chesapeake Bay archaeological sites spanning ∼3,500 y of Native American, colonial, and historical occupation. We compare oysters from archaeological sites with Pleistocene oyster reefs that existed before human harvest, modern oyster reefs, and other records of human oyster harvest from around the world. Native American fisheries were focused on nearshore oysters and were likely harvested at a rate that was sustainable over centuries to millennia, despite changing Holocene climatic conditions and sea-level rise. These data document resilience in oyster populations under long-term Native American harvest, sea-level rise, and climate change; provide context for managing modern oyster fisheries in the Chesapeake Bay and elsewhere around the world; and demonstrate an interdisciplinary approach that can be applied broadly to other fisheries.

  6. 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

  7. Constraining millennial scale dynamics of a Greenland tidewater glacier for the verification of a calving criterion based numerical model

    NASA Astrophysics Data System (ADS)

    Lea, J.; Mair, D.; Rea, B.; Nick, F.; Schofield, E.

    2012-04-01

    The ability to successfully model the behaviour of Greenland tidewater glaciers is pivotal to understanding the controls on their dynamics and potential impact on global sea level. However, to have confidence in the results of numerical models in this setting, the evidence required for robust verification must extend well beyond the existing instrumental record. Perhaps uniquely for a major Greenland outlet glacier, both the advance and retreat dynamics of Kangiata Nunata Sermia (KNS), Nuuk Fjord, SW Greenland over the last ~1000 years can be reasonably constrained through a combination of geomorphological, sedimentological and archaeological evidence. It is therefore an ideal location to test the ability of the latest generation of calving criterion based tidewater models to explain millennial scale dynamics. This poster presents geomorphological evidence recording the post-Little Ice Age maximum dynamics of KNS, derived from high-resolution satellite imagery. This includes evidence of annual retreat moraine complexes suggesting controlled rather than catastrophic retreat between pinning points, in addition to a series of ice dammed lake shorelines, allowing detailed interpretation of the dynamics of the glacier as it thinned and retreated. Pending ground truthing, this evidence will contribute towards the calibration of results obtained from a calving criterion numerical model (Nick et al, 2010), driven by an air temperature reconstruction for the KNS region determined from ice core data.

  8. A New Holocene Lake Sediment Archive from Samoa (Tropical South Pacific) Reveals Millennial Scale Changes in Hydroclimate.

    NASA Astrophysics Data System (ADS)

    Sear, D. A.; Hassall, J. D.; Langdon, P. G.; Croudace, I. W. C.; Maloney, A. E.; Sachs, J. P.

    2015-12-01

    El Niño-Southern Oscillation (ENSO) is the strongest source of interannual climate variability on the planet. Its behaviour leads to major hydro-climate impacts around the world, including flooding, drought, and altering cyclone frequency. Simulating ENSO behaviour is difficult using climate models, as it is a complex non-linear system, and hence predicting its future variability under changing climate is challenging. Using palaeoclimate data thus allows an insight into long-term ENSO behaviour against a range of different forcings throughout the Holocene. To date long, coherent, high resolution records from lake sediment archives have been limited to the Pacific Rim. We present new data from the closed crater Lake Lanoto'o, on Upolu Island, Samoa, located within the tropical South Pacific. The lake sediment record extends back into the early Holocene with an average sedimentation rate 0.4mm a-1. We demonstrate a strong correspondence between precipitation at the study site and measures of the Southern Oscillation Index (SOI)1. We compare geochemical proxies of precipitation to a long-term reconstruction of the SOI2. The resulting proxy SOI record extends over the last 9000 years, revealing scales of change in ENSO that match those recorded from sites located on the Pacific rim3,4. A major period of La-Nina dominance occurs around 4.5ka BP before abruptly switching to El-Nino dominance around 3.2ka. Thereafter, phases of El-Nino - La Nina dominance, alternate every c. 400yrs. The results point to prolonged phases of enhanced or reduced precipitation - conditions that may influence future population resilience to climate change, and may also have been triggers for the colonisation of more remote eastern Polynesia. 1. http://www.cgd.ucar.edu/cas/catalog/climind/SOI.signal.annstd.ascii. 2. Yan, H. et al. (2011) Nature Geoscience, 4, p.611. 3. Conroy J. L. et al. (2008) Quaternary Science Reviews, 27, p.1166 4. Moy, C. M. et al. (2002) Nature, 420, p.162

  9. Holocene millennial-scale productivity variations in the Sicily Channel (Mediterranean Sea)

    NASA Astrophysics Data System (ADS)

    Incarbona, Alessandro; di Stefano, Enrico; Patti, Bernardo; Pelosi, Nicola; Bonomo, Sergio; Mazzola, Salvatore; Sprovieri, Rodolfo; Tranchida, Giorgio; Zgozi, Salem; Bonanno, Angelo

    2008-09-01

    The calcareous nannofossil assemblages of Ocean Drilling Program Hole 963D from the central Mediterranean Sea have been investigated to document oceanographic changes in surface waters. The studied site is located in an area sensitive to large-scale atmospheric and climatic systems and to high- and low-latitude climate connection. It is characterized by a high sedimentation rate (the achieved mean sampling resolution is <70 years) that allowed the Sicily Channel environmental changes to be examined in great detail over the last 12 ka BP. We focused on the species Florisphaera profunda that lives in the lower photic zone. Its distribution pattern shows repeated abundance fluctuations of about 10-15%. Such variations could be related to different primary production levels, given that the study of the distribution of this species on the Sicily Channel seafloor demonstrates the significant correlation to productivity changes as provided by satellite imagery. Productivity variations were quantitatively estimated and were interpreted on the basis of the relocation of the nutricline within the photic zone, led by the dynamics of the summer thermocline. Productivity changes were compared with oceanographic, atmospheric, and cosmogenic nuclide proxies. The good match with Holocene master records, as with ice-rafted detritus in the subpolar North Atlantic, and the near-1500-year periodicity suggest that the Sicily Channel environment responded to worldwide climate anomalies. Enhanced Northern Hemisphere atmospheric circulation, which has been reported as one of the most important forcing mechanisms for Holocene coolings in previous Mediterranean studies, had a remarkable impact on the water column dynamics of the Sicily Channel.

  10. Calcification response of a key phytoplankton family to millennial-scale environmental change.

    PubMed

    McClelland, H L O; Barbarin, N; Beaufort, L; Hermoso, M; Ferretti, P; Greaves, M; Rickaby, R E M

    2016-09-28

    Coccolithophores are single-celled photosynthesizing marine algae, responsible for half of the calcification in the surface ocean, and exert a strong influence on the distribution of carbon among global reservoirs, and thus Earth's climate. Calcification in the surface ocean decreases the buffering capacity of seawater for CO2, whilst photosynthetic carbon fixation has the opposite effect. Experiments in culture have suggested that coccolithophore calcification decreases under high CO2 concentrations ([CO2(aq)]) constituting a negative feedback. However, the extent to which these results are representative of natural populations, and of the response over more than a few hundred generations is unclear. Here we describe and apply a novel rationale for size-normalizing the mass of the calcite plates produced by the most abundant family of coccolithophores, the Noëlaerhabdaceae. On average, ancient populations subjected to coupled gradual increases in [CO2(aq)] and temperature over a few million generations in a natural environment become relatively more highly calcified, implying a positive climatic feedback. We hypothesize that this is the result of selection manifest in natural populations over millennial timescales, so has necessarily eluded laboratory experiments.

  11. Calcification response of a key phytoplankton family to millennial-scale environmental change

    PubMed Central

    McClelland, H. L. O.; Barbarin, N.; Beaufort, L.; Hermoso, M.; Ferretti, P.; Greaves, M.; Rickaby, R. E. M.

    2016-01-01

    Coccolithophores are single-celled photosynthesizing marine algae, responsible for half of the calcification in the surface ocean, and exert a strong influence on the distribution of carbon among global reservoirs, and thus Earth’s climate. Calcification in the surface ocean decreases the buffering capacity of seawater for CO2, whilst photosynthetic carbon fixation has the opposite effect. Experiments in culture have suggested that coccolithophore calcification decreases under high CO2 concentrations ([CO2(aq)]) constituting a negative feedback. However, the extent to which these results are representative of natural populations, and of the response over more than a few hundred generations is unclear. Here we describe and apply a novel rationale for size-normalizing the mass of the calcite plates produced by the most abundant family of coccolithophores, the Noëlaerhabdaceae. On average, ancient populations subjected to coupled gradual increases in [CO2(aq)] and temperature over a few million generations in a natural environment become relatively more highly calcified, implying a positive climatic feedback. We hypothesize that this is the result of selection manifest in natural populations over millennial timescales, so has necessarily eluded laboratory experiments. PMID:27677230

  12. Does peatland restoration make a difference to the millennial scale carbon balance?

    NASA Astrophysics Data System (ADS)

    Quillet, Anne; Roulet, Nigel; Wu, Jianghua

    2017-04-01

    Millennial peatland carbon balance is of crucial importance to assess the past and future forcing of peatlands carbon sequestration on climate. However drainage and exploitation of peatlands over the last and current centuries greatly affect the carbon balance of 25% of the global peatlands (Parish et al. 2008). Moreover, the impact of drainage is likely to remain for unforeseeable time, modifying the hydrology and the ecology of peatlands. The aim of this study is to assess the influence on the long-term carbon balance of restoration practices over abandonment on vacuum-extracted peatlands. We modified the Holocene Peat Model (Frolking et al. 2010) to simulate peat extraction as well as different post-extraction management strategies: abandonment, drainage blocking and restoration. Simulation results enable the comparison of the response of the system to different management strategies. The carbon balance is estimated for the millennia following extraction for different management strategies and different climate conditions. The difference between restoration practices and abandonment allows the assessment of the net carbon gain associated with restoration. Although it is expected that successful restoration practices are beneficial to the carbon budget of the ecosystem, it will take millennia to restore what has been extracted. In cases where the site is left abandoned, it is estimated that peat would degrade within centuries. The management strategies and the duration of the period of latency between extraction and restoration are key factors controlling the magnitude of the future carbon loss or gain of a peatland.

  13. Calcification response of a key phytoplankton family to millennial-scale environmental change

    NASA Astrophysics Data System (ADS)

    McClelland, H. L. O.; Barbarin, N.; Beaufort, L.; Hermoso, M.; Ferretti, P.; Greaves, M.; Rickaby, R. E. M.

    2016-09-01

    Coccolithophores are single-celled photosynthesizing marine algae, responsible for half of the calcification in the surface ocean, and exert a strong influence on the distribution of carbon among global reservoirs, and thus Earth’s climate. Calcification in the surface ocean decreases the buffering capacity of seawater for CO2, whilst photosynthetic carbon fixation has the opposite effect. Experiments in culture have suggested that coccolithophore calcification decreases under high CO2 concentrations ([CO2(aq)]) constituting a negative feedback. However, the extent to which these results are representative of natural populations, and of the response over more than a few hundred generations is unclear. Here we describe and apply a novel rationale for size-normalizing the mass of the calcite plates produced by the most abundant family of coccolithophores, the Noëlaerhabdaceae. On average, ancient populations subjected to coupled gradual increases in [CO2(aq)] and temperature over a few million generations in a natural environment become relatively more highly calcified, implying a positive climatic feedback. We hypothesize that this is the result of selection manifest in natural populations over millennial timescales, so has necessarily eluded laboratory experiments.

  14. Decadal to millennial-scale variability in sea ice, primary productivity, and Pacific-Water inflow in the Chukchi/East Siberian Sea area (Arctic Ocean)

    NASA Astrophysics Data System (ADS)

    Stein, Ruediger; Fahl, Kirsten; Matthiessen, Jens; Méheust, Marie; Nam, Seung-il; Niessen, Frank; Schade, Inka; Schreck, Michael; Wassmuth, Saskia; Xiao, Xiaotong

    2014-05-01

    Sea-ice is an essential component of the global climate system and, especially, the Polar Oceans. An alarming decrease in term of sea-ice concentration, thickness and duration, has been observed in the Arctic Ocean and its marginal seas over the last 30 years. Thus, understanding the processes controlling modern sea-ice variability and reconstructing paleo-sea-ice extent and variability in polar regions have become of great interest for the international scientific community during the last years. Here, we present new proxy records determined in sediment cores from the East Siberian Sea (RV Polarstern Expedition ARK-XXIII/3 in 2008; Core PS72/350) and from the Chukchi Sea (RV Araon Expedition ARA2B in 2011; Core ARA2B-1A, -1B). These records, including organic-geochemical bulk parameters, specific biomarkers (IP25 and sterols; PIP25; for recent reviews see Stein et al., 2012; Belt and Müller, 2013), biogenic opal, mineralogical data as well as high-resolution XRF scanning data, give new insight into the short-term (decadal-, centennial- to millennial-scale) variability in sea-ice, primary productivity and Pacific-Water inflow during Holocene times. Maximum concentrations of phytoplankton biomarkers and biogenic opal were determined between 8.5 and 4 kyrs. BP, suggesting enhanced primary productivity triggered by increased inflow of nutrient-rich Pacific Water (and/or an increased nutrient input due to an ice-edge position). Short-lived peak values in productivity might be related to strong pulses of Pacific-Water input during this time period (cf., Ortiz et al., 2009). A seasonal sea-ice cover was present in the Chukchi Sea throughout the last 10 kyrs. During the last 3-4 kyrs. BP, the sea-ice cover significantly extended. References Belt, S.T. and Müller, J., 2013. The Arctic sea ice biomarker IP25: a review of current understanding, recommendations for future research and applications in palaeo sea ice reconstructions. Quaternary Science Review 73, 9-25. Ortiz

  15. Stalagmite reconstructions of western tropical Pacific climate from the last glacial maximum to present

    NASA Astrophysics Data System (ADS)

    Partin, Judson Wiley

    The West Pacific Warm Pool (WPWP) plays an important role in the global heat budget and global hydrologic cycle, so knowledge about its past variability would improve our understanding of global climate. Variations in WPWP precipitation are most notable during El Nino-Southern Oscillation events, when climate changes in the tropical Pacific impact rainfall not only in the WPWP, but around the globe. The stalagmite records presented in this dissertation provide centennial-to-millennial-scale constraints of WPWP precipitation during three distinct climatic periods: the Last Glacial Maximum (LGM), the last deglaciation, and the Holocene. In Chapter 2, the methodologies associated with the generation of U/Th-based absolute ages for the stalagmites are presented. In the final age models for the stalagmites, dates younger than 11,000 years have absolute errors of +/-400 years or less, and dates older than 11,000 years have a relative error of +/-2%. Stalagmite-specific 230Th/ 232Th ratios, calculated using isochrons, are used to correct for the presence of unsupported 230Th in a stalagmite at the time of formation. Hiatuses in the record are identified using a combination of optical properties, high 232Th concentrations, and extrapolation from adjacent U/Th dates. In Chapter 3, stalagmite oxygen isotopic composition (delta18O) records from N. Borneo are presented which reveal millennial-scale rainfall changes that occurred in response to changes in global climate boundary conditions, radiative forcing, and abrupt climate changes. The stalagmite delta18O records detect little change in inferred precipitation between the LGM and the present, although significant uncertainties are associated with the impact of the Sunda Shelf on rainfall delta 18O during the LGM. A millennial-scale drying in N. Borneo, inferred from an increase in stalagmite delta18O, peaks at ˜16.5ka coeval with timing of Heinrich event 1, possibly related to a southward movement of the Intertropical

  16. Millennial-scale variability in Antarctic ice-sheet discharge during the last deglaciation.

    PubMed

    Weber, M E; Clark, P U; Kuhn, G; Timmermann, A; Sprenk, D; Gladstone, R; Zhang, X; Lohmann, G; Menviel, L; Chikamoto, M O; Friedrich, T; Ohlwein, C

    2014-06-05

    Our understanding of the deglacial evolution of the Antarctic Ice Sheet (AIS) following the Last Glacial Maximum (26,000-19,000 years ago) is based largely on a few well-dated but temporally and geographically restricted terrestrial and shallow-marine sequences. This sparseness limits our understanding of the dominant feedbacks between the AIS, Southern Hemisphere climate and global sea level. Marine records of iceberg-rafted debris (IBRD) provide a nearly continuous signal of ice-sheet dynamics and variability. IBRD records from the North Atlantic Ocean have been widely used to reconstruct variability in Northern Hemisphere ice sheets, but comparable records from the Southern Ocean of the AIS are lacking because of the low resolution and large dating uncertainties in existing sediment cores. Here we present two well-dated, high-resolution IBRD records that capture a spatially integrated signal of AIS variability during the last deglaciation. We document eight events of increased iceberg flux from various parts of the AIS between 20,000 and 9,000 years ago, in marked contrast to previous scenarios which identified the main AIS retreat as occurring after meltwater pulse 1A and continuing into the late Holocene epoch. The highest IBRD flux occurred 14,600 years ago, providing the first direct evidence for an Antarctic contribution to meltwater pulse 1A. Climate model simulations with AIS freshwater forcing identify a positive feedback between poleward transport of Circumpolar Deep Water, subsurface warming and AIS melt, suggesting that small perturbations to the ice sheet can be substantially enhanced, providing a possible mechanism for rapid sea-level rise.

  17. Millennial scale displacement of the subarctic boundary during the last deglaciation in the northwestern Pacific

    NASA Astrophysics Data System (ADS)

    Sagawa, T.; Murayama, M.; Oba, T.; Ikehara, K.

    2006-12-01

    We have generated millennial time scale records of sea surface temperature and salinity in the northwestern Pacific for the last 25 kyr. Paleo-sea surface temperature was estimated by planktonic foraminfieral Mg/Ca paleothermometry for two sediment cores. GH02-1030 (42 14N, 144 13E, 1212 m water depth) and MD01-2420 (36 04N, 141 49E, 2101 m water depth) were taken from north and south of the subarctic boundary (SAB), respectively. Several anomalous high Mg/Ca values were detected in glacial portion of core GH02-1030, and these high Mg/Ca peaks were accompanied by negative carbon isotopic anomalies. Previous studies in this region suggested that the foraminiferal negative carbon isotope anomaly was a evidence of methane release from seafloor (Uchida et al., 2004; Ohkushi et al., 2005). Therefore, the foraminiferal Mg/Ca anomalies in GH02-1030 were possibly caused by authigenic carbonate formation as a result of methane release in the sediment. Reconstructed SST from north of the SAB, eliminated high Mg/Ca anomalies, showed small variations through the last deglaciation, suggesting that surface temperature of the Oyashio Current has been little changed. On the other hand, SST from south of the SAB (MD01-2420) showed large fluctuations in response to millennial time scale climate changes. As a result, SST difference between two sites was minimized in cold period. The large fluctuations seen only in south of the SAB and small SST difference during cold periods suggest that the subarctic boundary displaced equaterward such as LGM and YD in responce to Northern Hemispheric millennial climate changes.

  18. 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

  19. 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.

  20. 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

  1. 100,000-year-long terrestrial record of millennial-scale linkage between eastern North American mid-latitude paleovegetation shifts and Greenland ice-core oxygen isotope trends

    NASA Astrophysics Data System (ADS)

    Litwin, Ronald J.; Smoot, Joseph P.; Pavich, Milan J.; Markewich, Helaine W.; Brook, George; Durika, Nancy J.

    2013-09-01

    We document frequent, rapid, strong, millennial-scale paleovegetation shifts throughout the late Pleistocene, within a 100,000+ yr interval (~ 115-15 ka) of terrestrial sediments from the mid-Atlantic Region (MAR) of North America. High-resolution analyses of fossil pollen from one core locality revealed a continuously shifting sequence of thermally dependent forest assemblages, ranging between two endmembers: subtropical oak-tupelo-bald cypress-gum forest and high boreal spruce-pine forest. Sedimentary textural evidence indicates fluvial, paludal, and loess deposition, and paleosol formation, representing sequential freshwater to subaerial environments in which this record was deposited. Its total age-depth model, based on radiocarbon and optically stimulated luminescence ages, ranges from terrestrial oxygen isotope stages (OIS) 6 to 1. The particular core sub-interval presented here is correlative in trend and timing to that portion of the oxygen isotope sequence common among several Greenland ice cores: interstades GI2 to GI24 (≈ OIS2-5 d). This site thus provides the first evidence for an essentially complete series of 'Dansgaard-Oeschger' climate events in the MAR. These data reveal that the ~ 100,000 yr preceding the Late Glacial and Holocene in the MAR of North America were characterized by frequently and dynamically changing climate states, and by vegetation shifts that closely tracked the Greenland paleoclimate sequence.

  2. Centennial and millennial-scale hydroclimate changes in northwestern Patagonia since 16,000 yr BP

    NASA Astrophysics Data System (ADS)

    Moreno, Patricio I.; Videla, Javiera

    2016-10-01

    We examine hydroclimate changes at centennial/millennial timescales since 16,000 yr BP in northwestern Patagonia based on the pollen and charcoal record from Lago El Salto, a small closed-basin lake located in the Chilean Lake District (41°38‧48.02″S, 73° 5‧48.42″W). We observe cold/wet conditions between 14,500-16,000 yr BP, followed by further cooling with increased precipitation until 13,000 yr BP, enhanced precipitation seasonality and/or variability between 11,600-13,000 yr BP, and an extended warm-and-dry interval between 7600 and 11,300 yr BP with peak paleofire activity. Colder-and-wetter than present conditions and muted paleofire activity prevail between 5300 and 7600 yr BP, followed by alternating cold/wet and centennial-scale warm/dry phases starting at 5300 yr BP with three conspicuous megadroughts since 2500 yr BP. The most recent megadrought occurred during the Medieval Climate Anomaly. We identify a cold reversal that spans the Antarctic Cold Reversal (ACR) and the Younger Dryas (YD) chrons with stronger-than-present westerly influence during the former and enhanced variability during the latter. These results extend the northern limit of strong cooling and increase in precipitation during the ACR and the southern limit of influence of strong hydrologic variations during the YD in terrestrial environments, suggesting an overlap in the spheres of influence of processes originating from southern and northern polar latitudes. An extended warm southern westerly wind (SWW)-minimum interval is evident between 7600 and 11,300 yr BP, followed by a rapid shift to cool-moist conditions between 5300 and 7600 yr BP brought by a mid-Holocene SWW maximum. Since then we observe centennial-scale hydroclimate variability, which has driven biodiversity and fire-regime shifts of evergreen temperate rainforests.

  3. 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.

  4. Synchronous volcanic eruptions and abrupt climate change ∼17.7 ka plausibly linked by stratospheric ozone depletion

    PubMed Central

    McConnell, Joseph R.; Burke, Andrea; Dunbar, Nelia W.; Köhler, Peter; Thomas, Jennie L.; Chellman, Nathan J.; Maselli, Olivia J.; Sigl, Michael; Adkins, Jess F.; Baggenstos, Daniel; Burkhart, John F.; Brook, Edward J.; Buizert, Christo; Cole-Dai, Jihong; Fudge, T. J.; Knorr, Gregor; Graf, Hans-F.; Grieman, Mackenzie M.; Iverson, Nels; McGwire, Kenneth C.; Mulvaney, Robert; Paris, Guillaume; Rhodes, Rachael H.; Saltzman, Eric S.; Steffensen, Jørgen Peder; Taylor, Kendrick C.; Winckler, Gisela

    2017-01-01

    Glacial-state greenhouse gas concentrations and Southern Hemisphere climate conditions persisted until ∼17.7 ka, when a nearly synchronous acceleration in deglaciation was recorded in paleoclimate proxies in large parts of the Southern Hemisphere, with many changes ascribed to a sudden poleward shift in the Southern Hemisphere westerlies and subsequent climate impacts. We used high-resolution chemical measurements in the West Antarctic Ice Sheet Divide, Byrd, and other ice cores to document a unique, ∼192-y series of halogen-rich volcanic eruptions exactly at the start of accelerated deglaciation, with tephra identifying the nearby Mount Takahe volcano as the source. Extensive fallout from these massive eruptions has been found >2,800 km from Mount Takahe. Sulfur isotope anomalies and marked decreases in ice core bromine consistent with increased surface UV radiation indicate that the eruptions led to stratospheric ozone depletion. Rather than a highly improbable coincidence, circulation and climate changes extending from the Antarctic Peninsula to the subtropics—similar to those associated with modern stratospheric ozone depletion over Antarctica—plausibly link the Mount Takahe eruptions to the onset of accelerated Southern Hemisphere deglaciation ∼17.7 ka. PMID:28874529

  5. Synchronous volcanic eruptions and abrupt climate change ∼17.7 ka plausibly linked by stratospheric ozone depletion.

    PubMed

    McConnell, Joseph R; Burke, Andrea; Dunbar, Nelia W; Köhler, Peter; Thomas, Jennie L; Arienzo, Monica M; Chellman, Nathan J; Maselli, Olivia J; Sigl, Michael; Adkins, Jess F; Baggenstos, Daniel; Burkhart, John F; Brook, Edward J; Buizert, Christo; Cole-Dai, Jihong; Fudge, T J; Knorr, Gregor; Graf, Hans-F; Grieman, Mackenzie M; Iverson, Nels; McGwire, Kenneth C; Mulvaney, Robert; Paris, Guillaume; Rhodes, Rachael H; Saltzman, Eric S; Severinghaus, Jeffrey P; Steffensen, Jørgen Peder; Taylor, Kendrick C; Winckler, Gisela

    2017-09-19

    Glacial-state greenhouse gas concentrations and Southern Hemisphere climate conditions persisted until ∼17.7 ka, when a nearly synchronous acceleration in deglaciation was recorded in paleoclimate proxies in large parts of the Southern Hemisphere, with many changes ascribed to a sudden poleward shift in the Southern Hemisphere westerlies and subsequent climate impacts. We used high-resolution chemical measurements in the West Antarctic Ice Sheet Divide, Byrd, and other ice cores to document a unique, ∼192-y series of halogen-rich volcanic eruptions exactly at the start of accelerated deglaciation, with tephra identifying the nearby Mount Takahe volcano as the source. Extensive fallout from these massive eruptions has been found >2,800 km from Mount Takahe. Sulfur isotope anomalies and marked decreases in ice core bromine consistent with increased surface UV radiation indicate that the eruptions led to stratospheric ozone depletion. Rather than a highly improbable coincidence, circulation and climate changes extending from the Antarctic Peninsula to the subtropics-similar to those associated with modern stratospheric ozone depletion over Antarctica-plausibly link the Mount Takahe eruptions to the onset of accelerated Southern Hemisphere deglaciation ∼17.7 ka.

  6. Synchronous volcanic eruptions and abrupt climate change ˜17.7 ka plausibly linked by stratospheric ozone depletion

    NASA Astrophysics Data System (ADS)

    McConnell, Joseph R.; Burke, Andrea; Dunbar, Nelia W.; Köhler, Peter; Thomas, Jennie L.; Arienzo, Monica M.; Chellman, Nathan J.; Maselli, Olivia J.; Sigl, Michael; Adkins, Jess F.; Baggenstos, Daniel; Burkhart, John F.; Brook, Edward J.; Buizert, Christo; Cole-Dai, Jihong; Fudge, T. J.; Knorr, Gregor; Graf, Hans-F.; Grieman, Mackenzie M.; Iverson, Nels; McGwire, Kenneth C.; Mulvaney, Robert; Paris, Guillaume; Rhodes, Rachael H.; Saltzman, Eric S.; Severinghaus, Jeffrey P.; Steffensen, Jørgen Peder; Taylor, Kendrick C.; Winckler, Gisela

    2017-09-01

    Glacial-state greenhouse gas concentrations and Southern Hemisphere climate conditions persisted until ˜17.7 ka, when a nearly synchronous acceleration in deglaciation was recorded in paleoclimate proxies in large parts of the Southern Hemisphere, with many changes ascribed to a sudden poleward shift in the Southern Hemisphere westerlies and subsequent climate impacts. We used high-resolution chemical measurements in the West Antarctic Ice Sheet Divide, Byrd, and other ice cores to document a unique, ˜192-y series of halogen-rich volcanic eruptions exactly at the start of accelerated deglaciation, with tephra identifying the nearby Mount Takahe volcano as the source. Extensive fallout from these massive eruptions has been found >2,800 km from Mount Takahe. Sulfur isotope anomalies and marked decreases in ice core bromine consistent with increased surface UV radiation indicate that the eruptions led to stratospheric ozone depletion. Rather than a highly improbable coincidence, circulation and climate changes extending from the Antarctic Peninsula to the subtropics—similar to those associated with modern stratospheric ozone depletion over Antarctica—plausibly link the Mount Takahe eruptions to the onset of accelerated Southern Hemisphere deglaciation ˜17.7 ka.

  7. The ACER pollen and charcoal database: a global resource to document vegetation and fire response to abrupt climate changes during the last glacial period

    NASA Astrophysics Data System (ADS)

    Sánchez Goñi, María Fernanda; Desprat, Stéphanie; Daniau, Anne-Laure; Bassinot, Frank C.; Polanco-Martínez, Josué M.; Harrison, Sandy P.; Allen, Judy R. M.; Anderson, R. Scott; Behling, Hermann; Bonnefille, Raymonde; Burjachs, Francesc; Carrión, José S.; Cheddadi, Rachid; Clark, James S.; Combourieu-Nebout, Nathalie; Mustaphi, Colin. J. Courtney; Debusk, Georg H.; Dupont, Lydie M.; Finch, Jemma M.; Fletcher, William J.; Giardini, Marco; González, Catalina; Gosling, William D.; Grigg, Laurie D.; Grimm, Eric C.; Hayashi, Ryoma; Helmens, Karin; Heusser, Linda E.; Hill, Trevor; Hope, Geoffrey; Huntley, Brian; Igarashi, Yaeko; Irino, Tomohisa; Jacobs, Bonnie; Jiménez-Moreno, Gonzalo; Kawai, Sayuri; Kershaw, A. Peter; Kumon, Fujio; Lawson, Ian T.; Ledru, Marie-Pierre; Lézine, Anne-Marie; Liew, Ping Mei; Magri, Donatella; Marchant, Robert; Margari, Vasiliki; Mayle, Francis E.; Merna McKenzie, G.; Moss, Patrick; Müller, Stefanie; Müller, Ulrich C.; Naughton, Filipa; Newnham, Rewi M.; Oba, Tadamichi; Pérez-Obiol, Ramón; Pini, Roberta; Ravazzi, Cesare; Roucoux, Katy H.; Rucina, Stephen M.; Scott, Louis; Takahara, Hikaru; Tzedakis, Polichronis C.; Urrego, Dunia H.; van Geel, Bas; Valencia, B. Guido; Vandergoes, Marcus J.; Vincens, Annie; Whitlock, Cathy L.; Willard, Debra A.; Yamamoto, Masanobu

    2017-09-01

    Quaternary records provide an opportunity to examine the nature of the vegetation and fire responses to rapid past climate changes comparable in velocity and magnitude to those expected in the 21st-century. The best documented examples of rapid climate change in the past are the warming events associated with the Dansgaard-Oeschger (D-O) cycles during the last glacial period, which were sufficiently large to have had a potential feedback through changes in albedo and greenhouse gas emissions on climate. Previous reconstructions of vegetation and fire changes during the D-O cycles used independently constructed age models, making it difficult to compare the changes between different sites and regions. Here, we present the ACER (Abrupt Climate Changes and Environmental Responses) global database, which includes 93 pollen records from the last glacial period (73-15 ka) with a temporal resolution better than 1000 years, 32 of which also provide charcoal records. A harmonized and consistent chronology based on radiometric dating (14C, 234U/230Th, optically stimulated luminescence (OSL), 40Ar/39Ar-dated tephra layers) has been constructed for 86 of these records, although in some cases additional information was derived using common control points based on event stratigraphy. The ACER database compiles metadata including geospatial and dating information, pollen and charcoal counts, and pollen percentages of the characteristic biomes and is archived in Microsoft AccessTM at https://doi.org/10.1594/PANGAEA.870867.

  8. 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

  9. 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

  10. Climate variations of Central Asia on orbital to millennial timescales

    PubMed Central

    Cheng, Hai; Spötl, Christoph; Breitenbach, Sebastian F. M.; Sinha, Ashish; Wassenburg, Jasper A.; Jochum, Klaus Peter; Scholz, Denis; Li, Xianglei; Yi, Liang; Peng, Youbing; Lv, Yanbin; Zhang, Pingzhong; Votintseva, Antonina; Loginov, Vadim; Ning, Youfeng; Kathayat, Gayatri; Edwards, R. Lawrence

    2016-01-01

    The extent to which climate variability in Central Asia is causally linked to large-scale changes in the Asian monsoon on varying timescales remains a longstanding question. Here we present precisely dated high-resolution speleothem oxygen-carbon isotope and trace element records of Central Asia’s hydroclimate variability from Tonnel’naya cave, Uzbekistan, and Kesang cave, western China. On orbital timescales, the supra-regional climate variance, inferred from our oxygen isotope records, exhibits a precessional rhythm, punctuated by millennial-scale abrupt climate events, suggesting a close coupling with the Asian monsoon. However, the local hydroclimatic variability at both cave sites, inferred from carbon isotope and trace element records, shows climate variations that are distinctly different from their supra-regional modes. Particularly, hydroclimatic changes in both Tonnel’naya and Kesang areas during the Holocene lag behind the supra-regional climate variability by several thousand years. These observations may reconcile the apparent out-of-phase hydroclimatic variability, inferred from the Holocene lake proxy records, between Westerly Central Asia and Monsoon Asia. PMID:27833133

  11. Climate variations of Central Asia on orbital to millennial timescales.

    PubMed

    Cheng, Hai; Spötl, Christoph; Breitenbach, Sebastian F M; Sinha, Ashish; Wassenburg, Jasper A; Jochum, Klaus Peter; Scholz, Denis; Li, Xianglei; Yi, Liang; Peng, Youbing; Lv, Yanbin; Zhang, Pingzhong; Votintseva, Antonina; Loginov, Vadim; Ning, Youfeng; Kathayat, Gayatri; Edwards, R Lawrence

    2016-11-11

    The extent to which climate variability in Central Asia is causally linked to large-scale changes in the Asian monsoon on varying timescales remains a longstanding question. Here we present precisely dated high-resolution speleothem oxygen-carbon isotope and trace element records of Central Asia's hydroclimate variability from Tonnel'naya cave, Uzbekistan, and Kesang cave, western China. On orbital timescales, the supra-regional climate variance, inferred from our oxygen isotope records, exhibits a precessional rhythm, punctuated by millennial-scale abrupt climate events, suggesting a close coupling with the Asian monsoon. However, the local hydroclimatic variability at both cave sites, inferred from carbon isotope and trace element records, shows climate variations that are distinctly different from their supra-regional modes. Particularly, hydroclimatic changes in both Tonnel'naya and Kesang areas during the Holocene lag behind the supra-regional climate variability by several thousand years. These observations may reconcile the apparent out-of-phase hydroclimatic variability, inferred from the Holocene lake proxy records, between Westerly Central Asia and Monsoon Asia.

  12. Climate variations of Central Asia on orbital to millennial timescales

    NASA Astrophysics Data System (ADS)

    Cheng, Hai; Spötl, Christoph; Breitenbach, Sebastian F. M.; Sinha, Ashish; Wassenburg, Jasper A.; Jochum, Klaus Peter; Scholz, Denis; Li, Xianglei; Yi, Liang; Peng, Youbing; Lv, Yanbin; Zhang, Pingzhong; Votintseva, Antonina; Loginov, Vadim; Ning, Youfeng; Kathayat, Gayatri; Edwards, R. Lawrence

    2016-11-01

    The extent to which climate variability in Central Asia is causally linked to large-scale changes in the Asian monsoon on varying timescales remains a longstanding question. Here we present precisely dated high-resolution speleothem oxygen-carbon isotope and trace element records of Central Asia’s hydroclimate variability from Tonnel’naya cave, Uzbekistan, and Kesang cave, western China. On orbital timescales, the supra-regional climate variance, inferred from our oxygen isotope records, exhibits a precessional rhythm, punctuated by millennial-scale abrupt climate events, suggesting a close coupling with the Asian monsoon. However, the local hydroclimatic variability at both cave sites, inferred from carbon isotope and trace element records, shows climate variations that are distinctly different from their supra-regional modes. Particularly, hydroclimatic changes in both Tonnel’naya and Kesang areas during the Holocene lag behind the supra-regional climate variability by several thousand years. These observations may reconcile the apparent out-of-phase hydroclimatic variability, inferred from the Holocene lake proxy records, between Westerly Central Asia and Monsoon Asia.

  13. Differential Millennial-scale Responses of Terrestrial Carbon Cycling Dynamics to Warming from two Contrasting Lake Catchments in Arctic Alaska

    NASA Astrophysics Data System (ADS)

    Longo, W. M.; Huang, Y.; Russell, J. M.; Giblin, A. E.; McNichol, A. P.; Xu, L.; Daniels, W.

    2016-12-01

    Earth's permafrost carbon (C) reservoir is more than twice as large as global atmospheric C and its vulnerability to warming makes it a significant potential feedback to climate change. Predicted rates of warming could result in the release of 5 to 15% of permafrost C to the atmosphere by 2100 (Schuur et al., 2015); however the uncertainty around this estimate hinders our ability to quantify the arctic temperature-carbon feedback. To elucidate the long-term response of terrestrial C to warming in regions underlain by continuous permafrost, we present geologic records of changes in temperature and terrestrial C cycling dynamics from sediment cores from two contrasting lake catchments in arctic Alaska. The sediment records feature independent chronologies, biomarker-based temperature reconstructions, and geochemical measurements of vascular plant biomarkers (lignin phenols) that provide insight into terrestrial carbon quality, its release from permafrost soils and its transit time on the landscape. Our results indicate that both abrupt and sustained increases in temperature over the past 20,000 years resulted in increased carbon normalized yields of lignin phenols (Λ8, Λ6), which indicate increased mobilization of terrestrial organic carbon from permafrost soils. Lignin phenol indicators of terrestrial carbon quality (Ad:Al(s), Ad:Al(v)), indicated that carbon quality decreased with increasing temperature. These results demonstrate covariation between temperature and both the decay of terrestrial organic matter and lignin alteration resulting from dissolution and sorption processes. Compound specific radiocarbon analyses of lignin phenols and their offsets from depositional ages quantify transit times of terrestrial carbon on the landscape. These measurements revealed the presence of a persistent "pre-aged" terrestrial organic carbon pool, which is likely sourced from degrading permafrost. We also observe different responses of terrestrial organic carbon cycling to

  14. Millennial-scale records of North American Monsoon in time and space during the last glacial period: reconstructions from arid northern Mexico

    NASA Astrophysics Data System (ADS)

    Roy, P.; Quiroz-Jiménez, D.; Charles-Polo, M.; Lozano-Santacruz, R.

    2013-05-01

    The arid northern Mexico is part of the Sonora and Chihuahua Deserts and both the deserts belong to the North American Desert system. The North American Monsoon (NAM) or Mexican Monsoon refers to the system that brings summer precipitation to arid northern Mexico and southwestern USA. It contributes ca. 70-80% of total annual precipitation along the western slopes of the Sierra Madre Occidental (northern Mexico) and ca. 40-50% of total precipitation in Arizona and New Mexico (southwest USA). High-resolution geochemical data from lacustrine deposits located between 23°N and 31°N (paleolakes La Salada, Babicora and San Felipe) provide spatio-temporal and millennial-scale paleohydrological records related to the dynamics of summer precipitation as well as westerly winter storms over the last glacial period. The inverse relationship between proxy records of runoff into lacustrine basins of northern Mexico and winter precipitation over the southwestern USA indicate that the westerly winter storms had minimal influence south of 30°N and the paleohydrological changes are mainly summer precipitation controlled. The variation in summer season precipitation between 20 and 60 cal. kyr BP was driven by long term changes in summer insolation. During an interval of lower summer insolation (i.e. >60 cal. kyr BP), the higher summer precipitation could be related to the NAM expansion as a result of reduced north hemisphere ice sheets. On a millennial-scale, the region received more than average precipitation during the warm interstadials and vice versa.

  15. Strong hemispheric coupling of glacial climate through freshwater discharge and ocean circulation.

    PubMed

    Knutti, R; Flückiger, J; Stocker, T F; Timmermann, A

    2004-08-19

    The climate of the last glacial period was extremely variable, characterized by abrupt warming events in the Northern Hemisphere, accompanied by slower temperature changes in Antarctica and variations of global sea level. It is generally accepted that this millennial-scale climate variability was caused by abrupt changes in the ocean thermohaline circulation. Here we use a coupled ocean-atmosphere-sea ice model to show that freshwater discharge into the North Atlantic Ocean, in addition to a reduction of the thermohaline circulation, has a direct effect on Southern Ocean temperature. The related anomalous oceanic southward heat transport arises from a zonal density gradient in the subtropical North Atlantic caused by a fast wave-adjustment process. We present an extended and quantitative bipolar seesaw concept that explains the timing and amplitude of Greenland and Antarctic temperature changes, the slow changes in Antarctic temperature and its similarity to sea level, as well as a possible time lag of sea level with respect to Antarctic temperature during Marine Isotope Stage 3.

  16. 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).

  17. North Atlantic forcing of tropical Indian Ocean climate.

    PubMed

    Mohtadi, Mahyar; Prange, Matthias; Oppo, Delia W; De Pol-Holz, Ricardo; Merkel, Ute; Zhang, Xiao; Steinke, Stephan; Lückge, Andreas

    2014-05-01

    The response of the tropical climate in the Indian Ocean realm to abrupt climate change events in the North Atlantic Ocean is contentious. Repositioning of the intertropical convergence zone is thought to have been responsible for changes in tropical hydroclimate during North Atlantic cold spells, but the dearth of high-resolution records outside the monsoon realm in the Indian Ocean precludes a full understanding of this remote relationship and its underlying mechanisms. Here we show that slowdowns of the Atlantic meridional overturning circulation during Heinrich stadials and the Younger Dryas stadial affected the tropical Indian Ocean hydroclimate through changes to the Hadley circulation including a southward shift in the rising branch (the intertropical convergence zone) and an overall weakening over the southern Indian Ocean. Our results are based on new, high-resolution sea surface temperature and seawater oxygen isotope records of well-dated sedimentary archives from the tropical eastern Indian Ocean for the past 45,000 years, combined with climate model simulations of Atlantic circulation slowdown under Marine Isotope Stages 2 and 3 boundary conditions. Similar conditions in the east and west of the basin rule out a zonal dipole structure as the dominant forcing of the tropical Indian Ocean hydroclimate of millennial-scale events. Results from our simulations and proxy data suggest dry conditions in the northern Indian Ocean realm and wet and warm conditions in the southern realm during North Atlantic cold spells.

  18. Millennial-scale vegetation changes in the north-eastern Russian Arctic during the Pliocene/Pleistocene transition (2.7-2.5 Ma) inferred from the pollen record of Lake El'gygytgyn

    NASA Astrophysics Data System (ADS)

    Andreev, Andrei A.; Tarasov, Pavel E.; Wennrich, Volker; Melles, Martin

    2016-09-01

    The sediment record of Lake El'gygytgyn (67°30‧N, 172°05‧E) spans the past 3.6 Ma and provides unique opportunities for qualitative and quantitative reconstructions of the regional paleoenvironmental history of the terrestrial Arctic. Millennial-scale pollen studies of the sediments that accumulated during the Late Pliocene and Early Pleistocene (ca. 2.7 to 2.5 Ma) demonstrate orbitally-driven vegetation and climate changes during this transitional interval. Pollen spectra show a significant vegetation shift at the Pliocene/Pleistocene boundary that is, however, delayed by a few thousand years compared to lacustrine response. About 2.70-2.68 Ma the vegetation at Lake El'gygytgyn, currently a tundra area was mostly dominated by larch forests with some shrub pine, shrub alder and dwarf birch in understory. During the marine isotope stages G3 and G1, ca. 2.665-2.647 and 2.625-2.617 Ma, some spruce trees grew in the local larch-pine forests, pointing to relatively warm climate conditions. At the beginning of the Pleistocene, around 2.588 Ma, a prominent climatic deterioration led to a change from larch-dominated forests to predominantly treeless steppe- and tundra-like habitats. Between ca. 2.56-2.53 Ma some climate amelioration is reflected by the higher presence of coniferous taxa (mostly pine and larch, but probably also spruce) in the area. After 2.53 Ma a relatively cold and dry climate became dominant again, leading to open steppe-like and shrubby environments followed by climate amelioration between ca. 2.510 and 2.495 Ma, when pollen assemblages show that larch forests with dwarf birch and shrub alder still grew in the lake's vicinity. Increased contents of green algae colonies (Botryococcus) remains and Zygnema cysts around 2.691-2.689, 2.679-2.677, 2.601-2.594, 2.564-2.545, and 2.532-2.510 Ma suggest a spread of shallow-water environments most likely due to a lake-level lowering. These events occurred simultaneously with dry climate conditions inferred

  19. 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

  20. Precise dating of Dansgaard-Oeschger climate oscillations in western Europe from stalagmite data.

    PubMed

    Genty, D; Blamart, D; Ouahdi, R; Gilmour, M; Baker, A; Jouzel, J; Van-Exter, Sandra

    2003-02-20

    The signature of Dansgaard-Oeschger events--millennial-scale abrupt climate oscillations during the last glacial period--is well established in ice cores and marine records. But the effects of such events in continental settings are not as clear, and their absolute chronology is uncertain beyond the limit of (14)C dating and annual layer counting for marine records and ice cores, respectively. Here we present carbon and oxygen isotope records from a stalagmite collected in southwest France which have been precisely dated using 234U/230Th ratios. We find rapid climate oscillations coincident with the established Dansgaard-Oeschger events between 83,000 and 32,000 years ago in both isotope records. The oxygen isotope signature is similar to a record from Soreq cave, Israel, and deep-sea records, indicating the large spatial scale of the climate oscillations. The signal in the carbon isotopes gives evidence of drastic and rapid vegetation changes in western Europe, an important site in human cultural evolution. We also find evidence for a long phase of extremely cold climate in southwest France between 61.2 +/- 0.6 and 67.4 +/- 0.9 kyr ago.

  1. Annual proxy data from Lago Grande di Monticchio (southern Italy) contributing to chronological constraints and abrupt climatic oscillations between 76 and 112 ka

    NASA Astrophysics Data System (ADS)

    Martin-Puertas, C.; Brauer, A.; Wulf, S.; Ott, F.; Lauterbach, S.; Dulski, P.

    2014-06-01

    We present annual sedimentological proxies and sub-annual element scanner data from the Lago Grande di Monticchio (MON) sediment record for the sequence 76-112 ka, which, combined with the decadal to centennial resolved pollen assemblage, allow a comprehensive reconstruction of six major abrupt cold and relatively humid spells (MON 1-6) in the central Mediterranean during early phase of the last glaciation. These climatic oscillations are defined by intervals of thicker varves and high Ti-counts and coincide with episodes of forest depletion interpreted as cold and wet oscillations. Based on the independent and slightly revised MON-2014 varve chronology (76-112 ka), a detailed comparison with the Greenland ice-core δ18O record (NGRIP) and northern Alps speleothem δ18O data (NALPS) is presented. Based on visual inspection of major changes in the proxy data, MON 2-6 are suggested to correlate with GS 25-20. MON 1 (Woillard event), the first and shortest cooling spell in the Mediterranean after a long phase of stable interglacial conditions, has no counterpart in the Greenland ice core, but coincides with the lowest isotope values at the end of the gradual decrease in δ18O in NGRIP during the second half of the GI 25. MON 3 is the least pronounced cold spell and shows gradual transitions, whereas its NGRIP counterpart GS 24 is characterized by sharp changes in the isotope records. MON 2 and MON 4 are the longest most pronounced oscillations in the MON sediments in good agreement with their counterparts in the ice and spelethem records. The length of MON 4 (correlating with GS 22) support the duration of this stadial proposed by the NALPS timescales and suggests ca. 500 yr longer duration than calculated by GICC05 and AICC2012, which would confirm a~possible underestimation in the ice-core. Absolute dating of the cold spells occurring from 112 to 100 ka (MON 1-3) in the MON-2014 chronology is in good agreement with the GICC05 and NALPS timescales but the younger

  2. 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

  3. Paleoceanographic Synthesis of Abrupt Sea Ice and Temperature Changes in the Subarctic Pacific and Marginal Seas through the Past 20,000 Years

    NASA Astrophysics Data System (ADS)

    Davis, C. V.; Myhre, S. E.; Borreggine, M. J.; Caissie, B.; Praetorius, S. K.; Katsuki, K.; Moffitt, R.; Deutsch, C.

    2016-12-01

    Substantial efforts have been concentrated over the last half-century on the paleoceaongraphy of the North Pacific. Here we synthesize existing paleoceanographic records of temperature and sea ice extent across the Subarctic Pacific and marginal seas, including the Bering Sea, Alaskan Gyre, and Sea of Okhotsk. We focus on 26 cores collected between 1988-2009 and from 36-60°N with well-developed chronologies to reconstruct the abrupt climate transitions of the last 20,000 years, including the abrupt warming events of the Northern Hemisphere glacial terminations (Termination IA, IB). Specifically, we utilize foraminiferal (δ18O & Mg/Ca) and coccolithophore (Uk'37) derived proxies for near-surface temperature reconstructions, and diatom assemblages and indicator species to reconstruct sea ice extent and marginal sea ice environments. Sea-ice associated diatom species peaked in compositional dominance mid-way through the deglaciation from the mid-Bølling ( 14.5 ka) to the early Allerød ( 13.8 ka). Even at the lowest latitude site (36°01.4'N, core MD01-2421), sea-ice affiliated diatoms peak in the Last Glacial Maximum ( 18 ka) and the early Bølling ( 13.8 ka). Biogeochemical proxies for late-spring to late-summer temperatures across the Subarctic Pacific indicate surface ocean warming between the Last Glacial Maximum ( 6°) and the Holocene (12-18°C) at all sites. However, region-specific, latitudinal differences in the timing and magnitude of warming and millennial scale deglacial oscillations are evident. For example, in the Western Subarctic Pacific the higher-latitude sites show lower amplitude warming through the deglaciation, but greater expression of ephemeral mid-Bølling cooling than lower latitude sites. Sea ice and temperature are important primary metrics for understanding the rate and magnitude of surface ocean response to abrupt warming events, including the response of subpolar environments to warming in the modern ocean.

  4. 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

  5. Coherent millennial-scale patterns in U37k‧ and TEX86H temperature records during the penultimate interglacial-to-glacial cycle in the western Mediterranean

    NASA Astrophysics Data System (ADS)

    Huguet, Carme; Martrat, Belen; Grimalt, Joan O.; Sinninghe Damsté, Jaap S.; Schouten, Stefan

    2011-06-01

    The TEX86H temperature proxy is a relatively new proxy based on crenarchaeotal lipids and has rarely been applied together with other temperature proxies. In this study, we applied the TEX86H on a sediment core from the Alboran Sea (western Mediterranean, core ODP-977A) covering the penultimate climate cycle, that is, from 244 to 130 ka, and compared this with previously published sea surface temperatures derived from the U37k' of alkenones of haptophyta and Mg/Ca records of planktonic foraminifera. The TEX86H temperature record shows remarkably similar stadial-interstadial patterns and abrupt temperature changes to those observed with the U37k' palaeothermometer. Absolute TEX86H temperature estimates are generally higher than those of U37k', though this difference (<3°C in 81% of the data points) is mainly within the temperature calibration error for both proxies, suggesting that crenarchaeota and haptophyta experienced similar temperature variations. During occasional events (<5% of the analyzed time span), however, the TEX86H exhibits considerably higher absolute temperature estimates than the U37k'. Comparison with Mg/Ca records of planktonic foraminifera as well as other Mediterranean TEX86 and U37k' records suggests that part of this divergence may be attributed to seasonal differences, that is, with TEX86H reflecting mainly the warm summer season while U37k' would show annual mean. Biases in the global calibration of both proxies or specific biases in the Mediterranean are an alternative, though less likely, explanation. Despite differences between absolute TEX86H and U37k' temperatures, the correlation between the two proxies (r2 = 0.59, 95% significance) provides support for the occurrence of abrupt temperature variations in the western Mediterranean during the penultimate interglacial-to-glacial cycle.

  6. Millennial-scale variations in western Sierra Nevada precipitation during the last glacial cycle MIS 4/3 transition

    NASA Astrophysics Data System (ADS)

    Oster, Jessica L.; Montañez, Isabel P.; Mertz-Kraus, Regina; Sharp, Warren D.; Stock, Greg M.; Spero, Howard J.; Tinsley, John; Zachos, James C.

    2014-07-01

    Dansgaard-Oeschger (D-O) cycles had far-reaching effects on Northern Hemisphere and tropical climate systems during the last glacial period, yet the climatic response to D-O cycles in western North America is controversial, especially prior to 55 ka. We document changes in precipitation along the western slope of the central Sierra Nevada during early Marine Oxygen Isotope Stages (MIS) 3 and 4 (55-67 ka) from a U-series dated speleothem record from McLean's Cave. The timing of our multi-proxy geochemical dataset is coeval with D-O interstadials (15-18) and stadials, including Heinrich Event 6. The McLean's Cave stalagmite indicates warmer and drier conditions during Greenland interstadials (GISs 15-18), signified by elevated δ18O, δ13C, reflectance, and trace element concentrations, and less radiogenic 87Sr/86Sr. Our record extends evidence of a strong linkage between high-latitude warming and reduced precipitation in western North America to early MIS 3 and MIS 4. This record shows that the linkage persists in diverse global climate states, and documents the nature of the climatic response in central California to Heinrich Event 6.

  7. Stratigraphic evidence for millennial-scale temporal clustering of earthquakes on a continental-interior fault: Holocene Mississippi River floodplain deposits, New Madrid seismic zone, USA

    NASA Astrophysics Data System (ADS)

    Holbrook, John; Autin, Whitney J.; Rittenour, Tammy M.; Marshak, Stephen; Goble, Ronald J.

    2006-07-01

    The earthquake cycles that characterize continental-interior areas that are far from active plate boundaries have proven highly cryptic and difficult to resolve. We used a novel paleoseismic proxy to address this issue. Namely, we reconstructed Holocene Mississippi River channels from maps of floodplain strata in order to identify channel perturbations reflective of major displacement events on the high-hazard and mid-plate Reelfoot thrust fault, New Madrid seismic zone, U.S.A. Only three discrete slip events are currently documented for the Reelfoot fault (˜ AD 900, ˜ AD 1450, and AD 1812). This study extends this record and, thus, illustrates the utility of stratigraphic proxies as paleoseismic tools. We concurrently offer here some of the first quantified response times for tectonically induced channel pattern changes in large alluvial rivers. We identified at least two cycles of pervasive meandering that were interrupted by channel-straightening responses occurring upstream of the Reelfoot fault scarp. These straightening responses initiated at 2244 BC +/- 269 to 1620 BC +/- 220 and ˜ AD 900, respectively, and each records initiation of a period of Reelfoot fault slip after millennia of relative tectonic quiescence. The second (or New Madrid) straightening response was triggered by the previously known ˜ AD 900 fault slip event, and this initial low sinuosity has been protracted until the modern day by the latter ˜ AD 1450 and AD 1812 events. The first (or Bondurant) straightening response began a period of several hundred to ˜ 1400 years of low river sinuosity which evidences a similar period of multiple recurrent displacement events on the Reelfoot fault. These Bondurant events predate the existing paleoseismic record for the Reelfoot fault. These data offer initial evidence that slip events on the Reelfoot fault were temporally clustered on millennial scales and, thus, offers the first direct evidence for millennial-scale clustering of earthquakes on a

  8. A 400-kyr record of millennial-scale carbonate preservation events in the Southern Ocean: Implications for Atlantic Meridional Overturning Circulation and atmospheric CO2

    NASA Astrophysics Data System (ADS)

    Hodell, D. A.; Vautravers, M. J.; Barker, S.; Charles, C.; Crowhurst, S.

    2014-12-01

    Hodell et al. (2001) suggested that carbonate preservation in the deep Cape Basin represented a qualitative, high-resolution record of the temporal evolution of the carbonate saturation state of the deep sea. The carbonate signal reflects both transient events in the redistribution of alkalinity and DIC in the deep ocean and steady-state mass balance processes. Here we re-analyzed the carbonate records of Sites 1089/TN057-21 using an Avaatech XRF core scanner and measured elemental variations at 2.5-mm resolution for the past 400 kyrs. Log Ca/Ti is highly correlated to weight percent carbonate content and other dissolution proxies and resolves millennial-scale events in carbonate preservation. A high-pass filter removes the low-frequency (orbital) variability in carbonate preservation, which is attributed mainly to steady-state mass balance processes. The high-frequency (suborbital) component reflects transient responses to the redistribution of carbonate ion that is related mainly to changing deep-water circulation. During the last glacial period, distinct millennial-scale increases in carbonate preservation in piston core TN057-21 occurred during times of enhanced Atlantic Meridional Overtunring Circulation (AMOC) (Barker et al., 2010; Barker and Diz, 2014), as supported by increases in benthic δ13C and less radiogenic ɛNd values. Carbonate preservation peaked particularly during long, warm interstadials in Greenland when a deep water mass with high carbonate ion concentration was formed in the North Atlantic. Export of NADW may have been greater than the Holocene during some of these events ("overshoots") and/or preformed carbonate ion concentrations in North Atlantic source areas may have been higher owing to lower atmospheric CO2 and less carbonate production in surface water. Each South Atlantic carbonate peak is associated with the start of Antarctic cooling and declining or leveling of atmospheric CO2, reflecting the signature of a thermal bipolar seesaw

  9. 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

  10. High Resolution, Millennial-Scale Patterns of Bed Compensation on a Sand-Rich Submarine Lobe, Western Niger Delta Slope

    NASA Astrophysics Data System (ADS)

    Jobe, Z. R.

    2014-12-01

    Existing facies models of submarine lobes suggest a thick, sand-rich proximal and axial part and thin, muddy distal and lateral fringes. This model was developed from observations in many areas where turbidity flows encounter a decrease in slope and collapse, depositing sand proximally and mud distally. This facies model is commonly used to explain stacking patterns encountered in outcrops and wellbores as well as to build reservoir models of lobe deposits. A submarine lobe on the modern seafloor of the western Niger Delta slope imaged with three-dimensional seismic data and sampled with 28 piston cores suggests that the traditional lobe facies model is not applicable. Fed by a single channel, the roughly symmetrical (9 km x 8 km) sand body occurs on a low gradient 'step' on the slope. The feeder channel ends abruptly at the apex of the lobe as the gradient decreases, and the lobe is not channelized. Seismic amplitudes are high across the lobe, and piston cores validate that these amplitudes correspond to sand. There is no significant change in sand percentage across the lobe, either parallel to or across flow direction. Bed thickness and grain size data do not show a decreasing trend downdip or laterally from the feeder channel. Radiocarbon age dating demonstrates bed-scale compensation across the lobe, with progressively younger turbidite sand beds stepping from north to south during a 2,000 year time interval (15,000-13,000 years before present) before lobe abandonment at 12,000 years before present. This progressive compensation, however, does not result in any facies change or any channelization on the lobe. At the downdip edge of the lobe, steeper gradients led to the development of a knickpoint and associated channel that continues downslope. The even sand distribution, lack of channelization, and downdip knickpoint suggest that the depositing turbidity flows must have been much larger than the accommodation, leading to sand deposition across the entire lobe

  11. Millennial-scale northwest African droughts related to Heinrich events and Dansgaard-Oeschger cycles: Evidence in marine sediments from offshore Senegal

    NASA Astrophysics Data System (ADS)

    Itambi, A. C.; von Dobeneck, T.; Mulitza, S.; Bickert, T.; Heslop, D.

    2009-03-01

    We present a suite of new high-resolution records (0-135 ka) representing pulses of aeolian, fluvial, and biogenic sedimentation along the Senegalese continental margin. A multiproxy approach based on rock magnetic, element, and color data was applied on three cores enclosing the present-day northern limit of the ITCZ. A strong episodic aeolian contribution driven by stronger winds and dry conditions and characterized by high hematite and goethite input was revealed north of 13°N. These millennial-scale dust fluxes are synchronous with North Atlantic Heinrich stadials. Fluvial clay input driven by the West African monsoon predominates at 12°N and varies at Dansgaard-Oeschger time scales while marine productivity is strongly enhanced during the African humid periods and marine isotope stage 5. From latitudinal signal variations, we deduce that the last glacial ITCZ summer position was located between core positions at 12°26' and 13°40'N. Furthermore, this work also shows that submillennial periods of aridity over northwest Africa occurred more frequently and farther south than previously thought.

  12. Freshwater impacts recorded in tetraunsaturated alkenones and alkenone sea surface temperatures from the Okhotsk Sea across millennial-scale cycles

    NASA Astrophysics Data System (ADS)

    Harada, Naomi; Sato, Miyako; Sakamoto, Tatsuhiko

    2008-09-01

    We present records of phytoplankton-produced alkenones down a long piston core, which reveal changes of sea surface temperature (SST) and sea surface salinity (SSS) in the southwestern Okhotsk Sea over the past 120 ka. Between 20 and 60 ka B.P., alkenone-derived temperatures typically increased by 6°C-8°C from periods corresponding, within a few hundred years, to stadials to those corresponding to interstadials recorded in Greenland ice cores. The abundance of C37:4 alkenone relative to total C37 alkenones (percent C37:4), a possible proxy for salinity, indicated that during most low SSS was associated with high SST. The warm freshwater events might be related to (1) a decline in the supply of saline water entering the Okhotsk Sea through the Soya Strait; (2) strengthening of the freshwater supply from the Amur River and precipitation over the Okhotsk Sea, associated mainly with increased Asian summer monsoon activity; and (3) the effect of melting sea ice. These findings increase our understanding of the close linkage between high and low latitudes in relation to climate change and the synchronicity of climate changes within a few centuries between the Pacific and the Atlantic sides of the Northern Hemisphere.

  13. A Millennial Scale Tree-Ring Based Summer Temperature Reconstruction for Northern Mongolia (931-2005 C.E.)

    NASA Astrophysics Data System (ADS)

    Davi, N. K.; D'Arrigo, R.; Cook, E. R.; Baatarbileg, N.; Jacoby, G. C.; Anchukaitis, K. J.; Pederson, N.

    2013-12-01

    Warming over Mongolia and adjacent Central Asia has been unusually rapid over the past few decades, with surface temperature anomalies higher than for much of the globe. With few meteorological records available in this remote region prior to the 1950s, longer, paleoclimatic time series must be used to understand annual-centennial climate variability, potential forcing mechanisms (e.g. volcanism, increasing greenhouse gases) and the significance of such major features of the past millennium as the Medieval Climate Anomaly and Little Ice Age. In this study we use an unusually extensive collection of living and subfossil wood samples from temperature-sensitive larch trees to produce the first millennial-length, well-calibrated and verified reconstruction of summer temperatures for Mongolia and vicinity. The reconstruction shows a very cold mid-900s, rapid and sustained warming during the MCA, cooling during the LIA epoch LIA (1350-1850), and warming during the 20th century. There is very rapid tree growth found in 2004-2005, which may result from very warm temperatures and melting permafrost. The recent warming exceeds that of the MCA. Extreme cooling in several years is attributed to several major volcanic eruptions over the past millennium.

  14. Rapid climate change and no-analog vegetation in lowland Central America during the last 86,000 years

    NASA Astrophysics Data System (ADS)

    Correa-Metrio, Alexander; Bush, Mark B.; Cabrera, Kenneth R.; Sully, Shannon; Brenner, Mark; Hodell, David A.; Escobar, Jaime; Guilderson, Tom

    2012-03-01

    Glacial-interglacial climate cycles are known to have triggered migrations and reassortments of tropical biota. Although long-term precessionally-driven changes in temperature and precipitation have been demonstrated using tropical sediment records, responses to abrupt climate changes, e.g. the cooling of Heinrich stadials or warmings of the deglaciation, are poorly documented. The best predictions of future forest responses to ongoing warming will rely on evaluating the influences of both abrupt and long-term climate changes on past ecosystems. A sedimentary sequence recovered from Lake Petén-Itzá, Guatemalan lowlands, provided a natural archive of environmental history. Pollen and charcoal analyses were used to reconstruct the vegetation and climate history of the area during the last 86,000 years. We found that vegetation composition and air temperature were strongly influenced by millennial-scale changes in the North Atlantic Ocean. Whereas Greenland warm interstadials were associated with warm and relatively wet conditions in the Central American lowlands, cold Greenland stadials, especially those associated with Heinrich events, caused extremely dry and cold conditions. Even though the vegetation seemed to have been highly resilient, plant associations without modern analogs emerged mostly following sharp climate pulses of either warmth or cold, and were paralleled by exceptionally high rates of ecological change. Although pulses of temperature change are evident in this 86,000-year record none matched the rates projected for the 21st Century. According to our findings, the ongoing rapid warming will cause no-modern-analog communities, which given the improbability of returning to lower-than-modern CO2 levels, anthropogenic barriers to migration, and increased anthropogenic fires, will pose immense threats to the biodiversity of the region.

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  16. Forest fire and climate change in western North America: insights from sediment charcoal records.

    Treesearch

    Daniel G Gavin; Douglas J Hallett; Feng Sheng Hu; Kenneth P Lertzman; Susan J Prichard; Kendrick J Brown; Jason A Lynch; Patrick Bartlein; David L. Peterson

    2007-01-01

    Millennial-scale records of forest fire provide important baseline information for ecosystem management, especially in regions with too few recent fires to describe the historical range of variability. Charcoal records from lake sediments and soil profiles are well suited for reconstructing the incidence of past fire and its relationship to changing climate and...

  17. Tracking millennial-scale Holocene glacial advance and retreat using osmium isotopes: Insights from the Greenland ice sheet

    NASA Astrophysics Data System (ADS)

    Rooney, Alan D.; Selby, David; Lloyd, Jeremy M.; Roberts, David H.; Lückge, Andreas; Sageman, Bradley B.; Prouty, Nancy G.

    2016-04-01

    High-resolution Os isotope stratigraphy can aid in reconstructing Pleistocene ice sheet fluctuation and elucidating the role of local and regional weathering fluxes on the marine Os residence time. This paper presents new Os isotope data from ocean cores adjacent to the West Greenland ice sheet that have excellent chronological controls. Cores MSM-520 and DA00-06 represent distal to proximal sites adjacent to two West Greenland ice streams. Core MSM-520 has a steadily decreasing Os signal over the last 10 kyr (187Os/188Os = 1.35-0.81). In contrast, Os isotopes from core DA00-06 (proximal to the calving front of Jakobshavn Isbræ) highlight four stages of ice stream retreat and advance over the past 10 kyr (187Os/188Os = 2.31; 1.68; 2.09; 1.47). Our high-resolution chemostratigraphic records provide vital benchmarks for ice-sheet modelers as we attempt to better constrain the future response of major ice sheets to climate change. Variations in Os isotope composition from sediment and macro-algae (seaweed) sourced from regional and global settings serve to emphasize the overwhelming effect weathering sources have on seawater Os isotope composition. Further, these findings demonstrate that the residence time of Os is shorter than previous estimates of ∼104 yr.

  18. Tracking millennial-scale Holocene glacial advance and retreat using Osmium isotopes: Insights from the Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    Rooney, Alan; Selby, David; Lloyd, Jeremy; Roberts, David; Lückge, Andreas; Sageman, Bradley; Prouty, Nancy

    2016-04-01

    Using new high-resolution osmium (Os) isotope stratigraphy from cores adjacent to the Greenland ice sheet we highlight the potential for chemostratigraphy to contribute to our understanding of ice sheet dynamics. This study utilizes sediment cores that have excellent chronological controls and demonstrates the role of local and regional weathering fluxes on the marine Os residence time. Distal to the Greenland ice streams core MSM-520 displays a steady lowering of the Os isotope composition during the Holocene. In contrast, proximal to the calving front of Jakobshavn Isbræ (core DA00-06), the Os isotope stratigraphy highlights four stages of ice stream retreat and advance. Our chemostratigraphic records provide vital benchmarks as we attempt to better constrain the future response of major ice sheets to climate change. Variations in Os isotope composition from sediment and macro-algae (seaweed) sourced from both near-field and far-field settings emphasize the overwhelming effect local weathering sources have on seawater Os isotope composition.

  19. Tracking millennial-scale Holocene glacial advance and retreat using osmium isotopes: Insights from the Greenland ice sheet

    USGS Publications Warehouse

    Rooney, Alan D.; Selby, David; Llyod, Jeremy M.; Roberts, David H.; Luckge, Andreas; Sageman, Bradley B.; Prouty, Nancy G.

    2016-01-01

    High-resolution Os isotope stratigraphy can aid in reconstructing Pleistocene ice sheet fluctuation and elucidating the role of local and regional weathering fluxes on the marine Os residence time. This paper presents new Os isotope data from ocean cores adjacent to the West Greenland ice sheet that have excellent chronological controls. Cores MSM-520 and DA00-06 represent distal to proximal sites adjacent to two West Greenland ice streams. Core MSM-520 has a steadily decreasing Os signal over the last 10 kyr (187Os/188Os = 1.35–0.81). In contrast, Os isotopes from core DA00-06 (proximal to the calving front of Jakobshavn Isbræ) highlight four stages of ice stream retreat and advance over the past 10 kyr (187Os/188Os = 2.31; 1.68; 2.09; 1.47). Our high-resolution chemostratigraphic records provide vital benchmarks for ice-sheet modelers as we attempt to better constrain the future response of major ice sheets to climate change. Variations in Os isotope composition from sediment and macro-algae (seaweed) sourced from regional and global settings serve to emphasize the overwhe