Science.gov

Sample records for glacial maximum climate

  1. Mediterranean Ocean Climate for the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Mikolajewicz, Uwe

    2010-05-01

    To correctly reproduce past climate changes is one of the prerequistes for reliably predicting anthropogenic climate change. Here, results from an attempt to simulate the climate of the Last Glacial Maximum (LGM, 21.000 years ago) for the Mediterranean Sea are pesented. For this time slice, precompiled proxy data sets exist. One key problem in regional ocean modelling for past time slices is to obtain atmospheric forcing data. A multi-step approach is used. A coarse resolution earth system model consisting of coupled atmospheric-oceanic general circulation models (ECHAM5_T31/MPIOM_GR3) with a dynamical vegetation model (LPJ) was integrated for several thousand years to steady state. The surface conditions derived from these model simulations (sea surface temperature (SST), sea ice and vegetation) were used as lower boundary conditions for a short (20 years plus 9 years of spinup) simulation with a high resolution stand-alone atmosphere model (ECHAM5_T106). The continental runoff was calculated using a hydrological discharge model. This procedure was performed both for the Last Glacial Maximum as well as for a preindustrial control simulation. Atmospheric composition, earth orbital parameters, topography and ice sheet distribution were prescribed following the protocol for the PMIP2 project. The simulations of the Mediterranean ocean climate were performed with a regional version of MPIOM. The model has a horizontal resolution of approximately 25 km and 29 levels. The surface heat fluxes are calculated with bulk fomulas using the model SST. Freshwater forcing consists of evaporation (calculated from the latent heat flux), precipitation and river runoff. The model uses daily forcing for the atmospheric input derived from the high resolution atmosphere model. In the Atlantic box a restoring to observed hydrography is applied. For the LGM the anomalies from the coupled model are added to observations. This model has been integrated in each of the cases for more than

  2. Carbon-biosphere-climate interactions in the last glacial maximum climate

    SciTech Connect

    Friedlingstein, P.; Prentice, K.C.; Fung, I.Y.

    1995-04-20

    The total carbon inventory in the terrestrial biosphere in the last glacial maximum (LGM), 18 kyr ago, is analyzed in a series of experiments that examine the sensitivity of the inventory to vegetation distribution and carbon dynamics. The results show that for most forest vegetation types, carbon densities for the LGM are within 10% of their present-day values. Discrepancies between vegetation distributions simulated by two bioclimatic schemes are attributable to the assignation of vegetation types to climates with rare or no present-day analog. The model experiments, combined with palynogical data for regions with no present-day analog climate, yield to a decrease of 612{+-}105 Gt C compared to present day. 47 refs., 12 figs., 3 tabs.

  3. Effect of altered boundary conditions on GCM studies of the climate of the last glacial maximum

    SciTech Connect

    Hyde, W.T.; Peltier, W.R.

    1993-05-21

    The authors address a problem discovered recently with global climate model results for the last glacial maximum. Bard, et. al. pointed out a mismatch in boundary conditions entered into the model. Ice sheet conditions were derived from CLIMAP based on a time 18000 radiocarbon years ago. It was assumed that radiocarbon and sidereal dates coincide. However it was recently shown that the sidereal data of the last glacial maximum is nearer 21kbp. The authors perform model calculations to attempt to evaluate the seriousness of this mismatch in terms of calculated results from the global climate model runs for the last glacial maximum. The authors find that one result of the timing mismatch is a sizable difference in northern hemisphere summer and Eurasian winter climates. These changes should have a major impact on circulation patterns in the GCM simulations. In addition new ice sheet model programs are available now which appear to improve on CLIMAP models. The authors urge that these GCM simulations be rerun.

  4. Dust fluxes and iron fertilization in Holocene and Last Glacial Maximum climates

    NASA Astrophysics Data System (ADS)

    Lambert, Fabrice; Tagliabue, Alessandro; Shaffer, Gary; Lamy, Frank; Winckler, Gisela; Farias, Laura; Gallardo, Laura; De Pol-Holz, Ricardo

    2015-07-01

    Mineral dust aerosols play a major role in present and past climates. To date, we rely on climate models for estimates of dust fluxes to calculate the impact of airborne micronutrients on biogeochemical cycles. Here we provide a new global dust flux data set for Holocene and Last Glacial Maximum (LGM) conditions based on observational data. A comparison with dust flux simulations highlights regional differences between observations and models. By forcing a biogeochemical model with our new data set and using this model's results to guide a millennial-scale Earth System Model simulation, we calculate the impact of enhanced glacial oceanic iron deposition on the LGM-Holocene carbon cycle. On centennial timescales, the higher LGM dust deposition results in a weak reduction of <10 ppm in atmospheric CO2 due to enhanced efficiency of the biological pump. This is followed by a further ~10 ppm reduction over millennial timescales due to greater carbon burial and carbonate compensation.

  5. The influence of climate on peatland extent in Western Siberia since the Last Glacial Maximum.

    PubMed

    Alexandrov, G A; Brovkin, V A; Kleinen, T

    2016-04-20

    Boreal and subarctic peatlands are an important dynamical component of the earth system. They are sensitive to climate change, and could either continue to serve as a carbon sink or become a carbon source. Climatic thresholds for switching peatlands from sink to source are not well defined, and therefore, incorporating peatlands into Earth system models is a challenging task. Here we introduce a climatic index, warm precipitation excess, to delineate the potential geographic distribution of boreal peatlands for a given climate and landscape morphology. This allows us to explain the present-day distribution of peatlands in Western Siberia, their absence during the Last Glacial Maximum, their expansion during the mid-Holocene, and to form a working hypothesis about the trend to peatland degradation in the southern taiga belt of Western Siberia under an RCP 8.5 scenario for the projected climate in year 2100.

  6. The influence of climate on peatland extent in Western Siberia since the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Alexandrov, G. A.; Brovkin, V. A.; Kleinen, T.

    2016-04-01

    Boreal and subarctic peatlands are an important dynamical component of the earth system. They are sensitive to climate change, and could either continue to serve as a carbon sink or become a carbon source. Climatic thresholds for switching peatlands from sink to source are not well defined, and therefore, incorporating peatlands into Earth system models is a challenging task. Here we introduce a climatic index, warm precipitation excess, to delineate the potential geographic distribution of boreal peatlands for a given climate and landscape morphology. This allows us to explain the present-day distribution of peatlands in Western Siberia, their absence during the Last Glacial Maximum, their expansion during the mid-Holocene, and to form a working hypothesis about the trend to peatland degradation in the southern taiga belt of Western Siberia under an RCP 8.5 scenario for the projected climate in year 2100.

  7. The influence of climate on peatland extent in Western Siberia since the Last Glacial Maximum

    PubMed Central

    Alexandrov, G. A.; Brovkin, V. A.; Kleinen, T.

    2016-01-01

    Boreal and subarctic peatlands are an important dynamical component of the earth system. They are sensitive to climate change, and could either continue to serve as a carbon sink or become a carbon source. Climatic thresholds for switching peatlands from sink to source are not well defined, and therefore, incorporating peatlands into Earth system models is a challenging task. Here we introduce a climatic index, warm precipitation excess, to delineate the potential geographic distribution of boreal peatlands for a given climate and landscape morphology. This allows us to explain the present-day distribution of peatlands in Western Siberia, their absence during the Last Glacial Maximum, their expansion during the mid-Holocene, and to form a working hypothesis about the trend to peatland degradation in the southern taiga belt of Western Siberia under an RCP 8.5 scenario for the projected climate in year 2100. PMID:27095029

  8. Climate Sensitivity of the Last Glacial Maximum from Paleoclimate Simulations and Observations

    NASA Astrophysics Data System (ADS)

    Otto-Bliesner, B. L.; Brady, E.; Kothavala, Z.

    2004-12-01

    Global coupled climate models run for future scenarios of increasing atmospheric CO2 give a range of response of the global average surface temperature. Regional responses, including the North Atlantic overturning circulation and tropical Pacific ENSO, also vary significantly among models. The second phase of the Paleoclimate Modeling Intercomparison Project (PMIP 2) is coordinating simulations and data syntheses for the Last Glacial Maximum (21,000 years before present) to allow another assessment of climate sensitivity. Atmospheric CO2 concentrations at the Last Glacial Maximum (LGM) have been estimated using measurements from ice cores to be 185 ppmv, approximately 50% of present-day values. Global, annual mean surface temperature simulated by the slab ocean version of the National Center for Atmospheric Research (NCAR) Community Climate System Model (CCSM3) shows a cooling of -2.8°C for LGM CO2 levels and a warming of 2.5°C for a doubling of CO2. Slab and coupled CCSM3 simulations that include the reductions of the other atmospheric trace gases and the large ice sheets covering North America and Eurasia at LGM give cooling in agreement with proxy inferences and indicate that LGM CO2 explains about half of the global cooling at LGM. Regional signatures of the climate system to changed LGM forcing are also an important measure of climate sensitivity and results from the fully coupled version of CCSM3 will be shown.

  9. Climate sensitivity estimated from temperature reconstructions of the Last Glacial Maximum.

    PubMed

    Schmittner, Andreas; Urban, Nathan M; Shakun, Jeremy D; Mahowald, Natalie M; Clark, Peter U; Bartlein, Patrick J; Mix, Alan C; Rosell-Melé, Antoni

    2011-12-09

    Assessing the impact of future anthropogenic carbon emissions is currently impeded by uncertainties in our knowledge of equilibrium climate sensitivity to atmospheric carbon dioxide doubling. Previous studies suggest 3 kelvin (K) as the best estimate, 2 to 4.5 K as the 66% probability range, and nonzero probabilities for much higher values, the latter implying a small chance of high-impact climate changes that would be difficult to avoid. Here, combining extensive sea and land surface temperature reconstructions from the Last Glacial Maximum with climate model simulations, we estimate a lower median (2.3 K) and reduced uncertainty (1.7 to 2.6 K as the 66% probability range, which can be widened using alternate assumptions or data subsets). Assuming that paleoclimatic constraints apply to the future, as predicted by our model, these results imply a lower probability of imminent extreme climatic change than previously thought.

  10. A brief history of climate - the northern seas from the Last Glacial Maximum to global warming

    NASA Astrophysics Data System (ADS)

    Eldevik, Tor; Risebrobakken, Bjørg; Bjune, Anne E.; Andersson, Carin; Birks, H. John B.; Dokken, Trond M.; Drange, Helge; Glessmer, Mirjam S.; Li, Camille; Nilsen, Jan Even Ø.; Otterå, Odd Helge; Richter, Kristin; Skagseth, Øystein

    2014-12-01

    The understanding of climate and climate change is fundamentally concerned with two things: a well-defined and sufficiently complete climate record to be explained, for example of observed temperature, and a relevant mechanistic framework for making closed and consistent inferences concerning cause-and-effect. This is the case for understanding observed climate, as it is the case for historical climate as reconstructed from proxy data and future climate as projected by models. The present study offers a holistic description of northern maritime climate - from the Last Glacial Maximum through to the projected global warming of the 21st century - in this context. It includes the compilation of the most complete temperature record for Norway and the Norwegian Sea to date based on the synthesis of available terrestrial and marine paleoclimate reconstructions into continuous times series, and their continuation into modern and future climate with the instrumental record and a model projection. The scientific literature on a variable northern climate is reviewed against this background, and with a particular emphasis on the role of the Norwegian Atlantic Current - the Gulf Stream's extension towards the Arctic. This includes the introduction of an explicit and relatively simple diagnostic relation to quantify the change in ocean circulation consistent with reconstructed ocean temperatures. It is found that maritime climate and the strength of the Norwegian Atlantic Current are closely related throughout the record. The nature of the relation is however qualitatively different as one progresses from the past, through the present, and into the future.

  11. The last glacial maximum

    USGS Publications Warehouse

    Clark, P.U.; Dyke, A.S.; Shakun, J.D.; Carlson, A.E.; Clark, J.; Wohlfarth, B.; Mitrovica, J.X.; Hostetler, S.W.; McCabe, A.M.

    2009-01-01

    We used 5704 14C, 10Be, and 3He ages that span the interval from 10,000 to 50,000 years ago (10 to 50 ka) to constrain the timing of the Last Glacial Maximum (LGM) in terms of global ice-sheet and mountain-glacier extent. Growth of the ice sheets to their maximum positions occurred between 33.0 and 26.5 ka in response to climate forcing from decreases in northern summer insolation, tropical Pacific sea surface temperatures, and atmospheric CO2. Nearly all ice sheets were at their LGM positions from 26.5 ka to 19 to 20 ka, corresponding to minima in these forcings. The onset of Northern Hemisphere deglaciation 19 to 20 ka was induced by an increase in northern summer insolation, providing the source for an abrupt rise in sea level. The onset of deglaciation of the West Antarctic Ice Sheet occurred between 14 and 15 ka, consistent with evidence that this was the primary source for an abrupt rise in sea level ???14.5 ka.

  12. The simulated climate of the Last Glacial Maximum and insights into the global marine carbon cycle

    NASA Astrophysics Data System (ADS)

    Buchanan, Pearse J.; Matear, Richard J.; Lenton, Andrew; Phipps, Steven J.; Chase, Zanna; Etheridge, David M.

    2016-12-01

    The ocean's ability to store large quantities of carbon, combined with the millennial longevity over which this reservoir is overturned, has implicated the ocean as a key driver of glacial-interglacial climates. However, the combination of processes that cause an accumulation of carbon within the ocean during glacial periods is still under debate. Here we present simulations of the Last Glacial Maximum (LGM) using the CSIRO Mk3L-COAL (Carbon-Ocean-Atmosphere-Land) earth system model to test the contribution of physical and biogeochemical processes to ocean carbon storage. For the LGM simulation, we find a significant global cooling of the surface ocean (3.2 °C) and the expansion of both minimum and maximum sea ice cover broadly consistent with proxy reconstructions. The glacial ocean stores an additional 267 Pg C in the deep ocean relative to the pre-industrial (PI) simulation due to stronger Antarctic Bottom Water formation. However, 889 Pg C is lost from the upper ocean via equilibration with a lower atmospheric CO2 concentration and a global decrease in export production, causing a net loss of carbon relative to the PI ocean. The LGM deep ocean also experiences an oxygenation ( > 100 mmol O2 m-3) and deepening of the calcite saturation horizon (exceeds the ocean bottom) at odds with proxy reconstructions. With modifications to key biogeochemical processes, which include an increased export of organic matter due to a simulated release from iron limitation, a deepening of remineralisation and decreased inorganic carbon export driven by cooler temperatures, we find that the carbon content of the glacial ocean can be sufficiently increased (317 Pg C) to explain the reduction in atmospheric and terrestrial carbon at the LGM (194 ± 2 and 330 ± 400 Pg C, respectively). Assuming an LGM-PI difference of 95 ppm pCO2, we find that 55 ppm can be attributed to the biological pump, 28 ppm to circulation changes and the remaining 12 ppm to solubility. The biogeochemical

  13. Climate, CO2, and the history of North American grasses since the Last Glacial Maximum.

    PubMed

    Cotton, Jennifer M; Cerling, Thure E; Hoppe, Kathryn A; Mosier, Thomas M; Still, Christopher J

    2016-03-01

    The spread of C4 grasses in the late Neogene is one of the most important ecological transitions of the Cenozoic, but the primary driver of this global expansion is widely debated. We use the stable carbon isotopic composition (δ(13)C) of bison and mammoth tissues as a proxy for the relative abundance of C3 and C4 vegetation in their grazing habitat to determine climatic and atmospheric CO2 controls on C4 grass distributions from the Last Glacial Maximum (LGM) to the present. We predict the spatial variability of grass δ(13)C in North America using a mean of three different methods of classification and regression tree (CART) machine learning techniques and nine climatic variables. We show that growing season precipitation and temperature are the strongest predictors of all single climate variables. We apply this CART analysis to high-resolution gridded climate data and Coupled Model Intercomparison Project (CMIP5) mean paleoclimate model outputs to produce predictive isotope landscape models ("isoscapes") for the current, mid-Holocene, and LGM average δ(13)C of grass-dominated areas across North America. From the LGM to the present, C4 grass abundances substantially increased in the Great Plains despite concurrent increases in atmospheric CO2. These results suggest that changes in growing season precipitation rather than atmospheric CO2 were critically important in the Neogene expansion of C4 grasses.

  14. Climate, CO2, and the history of North American grasses since the Last Glacial Maximum

    PubMed Central

    Cotton, Jennifer M.; Cerling, Thure E.; Hoppe, Kathryn A.; Mosier, Thomas M.; Still, Christopher J.

    2016-01-01

    The spread of C4 grasses in the late Neogene is one of the most important ecological transitions of the Cenozoic, but the primary driver of this global expansion is widely debated. We use the stable carbon isotopic composition (δ13C) of bison and mammoth tissues as a proxy for the relative abundance of C3 and C4 vegetation in their grazing habitat to determine climatic and atmospheric CO2 controls on C4 grass distributions from the Last Glacial Maximum (LGM) to the present. We predict the spatial variability of grass δ13C in North America using a mean of three different methods of classification and regression tree (CART) machine learning techniques and nine climatic variables. We show that growing season precipitation and temperature are the strongest predictors of all single climate variables. We apply this CART analysis to high-resolution gridded climate data and Coupled Model Intercomparison Project (CMIP5) mean paleoclimate model outputs to produce predictive isotope landscape models (“isoscapes”) for the current, mid-Holocene, and LGM average δ13C of grass-dominated areas across North America. From the LGM to the present, C4 grass abundances substantially increased in the Great Plains despite concurrent increases in atmospheric CO2. These results suggest that changes in growing season precipitation rather than atmospheric CO2 were critically important in the Neogene expansion of C4 grasses. PMID:27051865

  15. Sensitivity of Last Glacial Maximum climate to uncertainties in tropical and subtropical ocean temperatures

    USGS Publications Warehouse

    Hostetler, S.; Pisias, N.; Mix, A.

    2006-01-01

    The faunal and floral gradients that underlie the CLIMAP (1981) sea-surface temperature (SST) reconstructions for the Last Glacial Maximum (LGM) reflect ocean temperature gradients and frontal positions. The transfer functions used to reconstruct SSTs from biologic gradients are biased, however, because at the warmest sites they display inherently low sensitivity in translating fauna to SST and they underestimate SST within the euphotic zones where the pycnocline is strong. Here we assemble available data and apply a statistical approach to adjust for hypothetical biases in the faunal-based SST estimates of LGM temperature. The largest bias adjustments are distributed in the tropics (to address low sensitivity) and subtropics (to address underestimation in the euphotic zones). The resulting SSTs are generally in better agreement than CLIMAP with recent geochemical estimates of glacial-interglacial temperature changes. We conducted a series of model experiments using the GENESIS general atmospheric circulation model to assess the sensitivity of the climate system to our bias-adjusted SSTs. Globally, the new SST field results in a modeled LGM surface-air cooling relative to present of 6.4 ??C (1.9 ??C cooler than that of CLIMAP). Relative to the simulation with CLIMAP SSTs, modeled precipitation over the oceans is reduced by 0.4 mm d-1 (an anomaly -0.4 versus 0.0 mm d-1 for CLIMAP) and increased over land (an anomaly -0.2 versus -0.5 mm d-1 for CLIMAP). Regionally strong responses are induced by changes in SST gradients. Data-model comparisons indicate improvement in agreement relative to CLIMAP, but differences among terrestrial data inferences and simulated moisture and temperature remain. Our SSTs result in positive mass balance over the northern hemisphere ice sheets (primarily through reduced summer ablation), supporting the hypothesis that tropical and subtropical ocean temperatures may have played a role in triggering glacial changes at higher latitudes.

  16. Climatic controls of western U.S. glaciers at the last glacial maximum

    USGS Publications Warehouse

    Hostetler, S.W.; Clark, P.U.

    1997-01-01

    We use a nested atmospheric modeling strategy to simulate precipitation and temperature of the western United States 18,000 years ago (18 ka). The high resolution of the nested model allows us to isolate the regional structure of summer temperature and winter precipitation that is crucial to determination of the net mass balance of late-Pleistocene mountain glaciers in this region of diverse topography and climate. Modeling results suggest that climatic controls of these glaciers varied significantly over the western U.S. Glaciers in the northern Rocky Mountains existed under relatively cold July temperatures and low winter accumulation, reflecting anticyclonic, easterly wind flow off the Laurentide Ice Sheet. In contrast, glaciers that existed under relatively warmer and wetter conditions are located along the Pacific coast south of Oregon, where enhanced westerlies delivered higher precipitation than at present. Between these two groupings lie glaciers that were controlled by a mix of cold and wet conditions attributed to the convergence of cold air from the ice sheet and moisture derived from the westerlies. Sensitivity tests suggest that, for our simulated 18 ka climate, many of the glaciers exhibit a variable response to climate but were generally more sensitive to changes in temperature than to changes in precipitation, particularly those glaciers in central Idaho and the Yellowstone Plateau. Our results support arguments that temperature depression generally played a larger role in lowering equilibrium line altitudes in the western U.S. during the last glacial maximum than did increased precipitation, although the magnitude of temperature depression required for steady-state mass balance varied from 8-18??C. Only the Sierra Nevada glaciers required a substantial increase in precipitation to achieve steady-state mass balance, while glaciers in the Cascade Range existed with decreased precipitation.

  17. Impact of CO2 and climate on Last Glacial Maximum vegetation - a factor separation

    NASA Astrophysics Data System (ADS)

    Claussen, M.; Selent, K.; Brovkin, V.; Raddatz, T.; Gayler, V.

    2012-11-01

    Differences between glacial and pre-industrial potential vegetation patterns can conceptually be attributed to two factors: firstly to differences in the climate, caused by a strong increase in ice masses and the radiative effect of lower greenhouse gas concentrations, and secondly to differences in the ecophysiological effect of lower glacial atmospheric CO2 concentrations. The synergy emerging from these effects when operating simultaneously can be interpreted as sensitivity of the effect of enhancing physiologically available CO2 on shifting vegetation to climate warming. Alternatively and equally valid, it can be viewed as sensitivity of climatically induced vegetation changes to differences in physiologically available CO2. A first complete factor separation based on simulations with the MPI Earth System Model indicates that the pure climate effect mainly leads to a contraction or a shift in vegetation patterns when comparing glacial with pre-industrial simulation vegetation patterns. Globally, a reduction in fractional coverage of most plant functional types is seen - except for raingreen shrubs which strongly benefit from the colder and drier climate. The ecophysiological effect of CO2 appears to be stronger than the pure climate contribution for many plant functional types - in line with previous simulations. The ecophysiological effect of lower CO2 mainly yields a reduction in fractional coverage, a thinning of vegetation and a strong reduction in net primary production. The synergy appears to be as strong as each of the pure contributions locally. For tropical evergreen trees, the synergy appears strong also on global average. Hence this modelling study suggests that for tropical forests, an increase in CO2 has, on average, a stronger ecophysiological effect in warmer climate than in glacial climate. Alternatively, areal differences in tropical forests induced by climate warming can, on average, be expected to be larger with increasing concentration of

  18. Impact of CO2 and climate on Last Glacial maximum vegetation - a factor separation

    NASA Astrophysics Data System (ADS)

    Claussen, M.; Selent, K.; Brovkin, V.; Raddatz, T.; Gayler, V.

    2013-06-01

    The factor separation of Stein and Alpert (1993) is applied to simulations with the MPI Earth system model to determine the factors which cause the differences between vegetation patterns in glacial and pre-industrial climate. The factors firstly include differences in the climate, caused by a strong increase in ice masses and the radiative effect of lower greenhouse gas concentrations; secondly, differences in the ecophysiological effect of lower glacial atmospheric CO2 concentrations; and thirdly, the synergy between the pure climate effect and the pure effect of changing physiologically available CO2. It is has been shown that the synergy can be interpreted as a measure of the sensitivity of ecophysiological CO2 effect to climate. The pure climate effect mainly leads to a contraction or a shift in vegetation patterns when comparing simulated glacial and pre-industrial vegetation patterns. Raingreen shrubs benefit from the colder and drier climate. The pure ecophysiological effect of CO2 appears to be stronger than the pure climate effect for many plant functional types - in line with previous simulations. The pure ecophysiological effect of lower CO2 mainly yields a reduction in fractional coverage, a thinning of vegetation and a strong reduction in net primary production. The synergy appears to be as strong as each of the pure contributions locally, but weak on global average for most plant functional types. For tropical evergreen trees, however, the synergy is strong on global average. It diminishes the difference between glacial and pre-industrial coverage of tropical evergreen trees, due to the pure climate effect and the pure ecophysiological CO2 effect, by approximately 50 per cent.

  19. Responses of Amazonian ecosystems to climatic and atmospheric carbon dioxide changes since the last glacial maximum.

    PubMed

    Mayle, Francis E; Beerling, David J; Gosling, William D; Bush, Mark B

    2004-03-29

    The aims of this paper are to review previously published palaeovegetation and independent palaeoclimatic datasets together with new results we present from dynamic vegetation model simulations and modern pollen rain studies to: (i) determine the responses of Amazonian ecosystems to changes in temperature, precipitation and atmospheric CO2 concentrations that occurred since the last glacial maximum (LGM), ca. 21 000 years ago; and (ii) use this long-term perspective to predict the likely vegetation responses to future climate change. Amazonia remained predominantly forested at the LGM, although the combination of reduced temperatures, precipitation and atmospheric CO2 concentrations resulted in forests structurally and floristically quite different from those of today. Cold-adapted Andean taxa mixed with rainforest taxa in central areas, while dry forest species and lianas probably became important in the more seasonal southern Amazon forests and savannahs expanded at forest-savannah ecotones. Net primary productivity (NPP) and canopy density were significantly lower than today. Evergreen rainforest distribution and NPP increased during the glacial-Holocene transition owing to ameliorating climatic and CO2 conditions. However, reduced precipitation in the Early-Mid-Holocene (ca. 8000-3600 years ago) caused widespread, frequent fires in seasonal southern Amazonia, causing increased abundance of drought-tolerant dry forest taxa and savannahs in ecotonal areas. Rainforests expanded once more in the Late Holocene owing to increased precipitation caused by greater austral summer insolation, although some of this forest expansion (e.g. in parts of the Bolivian Beni) is clearly caused by palaeo Indian landscape modification. The plant communities that existed during the Early-Mid-Holocene may provide insights into the kinds of vegetation response expected from similar increases in temperature and aridity predicted for the twenty-first century. We infer that ecotonal areas

  20. Responses of Amazonian ecosystems to climatic and atmospheric carbon dioxide changes since the last glacial maximum.

    PubMed Central

    Mayle, Francis E; Beerling, David J; Gosling, William D; Bush, Mark B

    2004-01-01

    The aims of this paper are to review previously published palaeovegetation and independent palaeoclimatic datasets together with new results we present from dynamic vegetation model simulations and modern pollen rain studies to: (i) determine the responses of Amazonian ecosystems to changes in temperature, precipitation and atmospheric CO2 concentrations that occurred since the last glacial maximum (LGM), ca. 21 000 years ago; and (ii) use this long-term perspective to predict the likely vegetation responses to future climate change. Amazonia remained predominantly forested at the LGM, although the combination of reduced temperatures, precipitation and atmospheric CO2 concentrations resulted in forests structurally and floristically quite different from those of today. Cold-adapted Andean taxa mixed with rainforest taxa in central areas, while dry forest species and lianas probably became important in the more seasonal southern Amazon forests and savannahs expanded at forest-savannah ecotones. Net primary productivity (NPP) and canopy density were significantly lower than today. Evergreen rainforest distribution and NPP increased during the glacial-Holocene transition owing to ameliorating climatic and CO2 conditions. However, reduced precipitation in the Early-Mid-Holocene (ca. 8000-3600 years ago) caused widespread, frequent fires in seasonal southern Amazonia, causing increased abundance of drought-tolerant dry forest taxa and savannahs in ecotonal areas. Rainforests expanded once more in the Late Holocene owing to increased precipitation caused by greater austral summer insolation, although some of this forest expansion (e.g. in parts of the Bolivian Beni) is clearly caused by palaeo Indian landscape modification. The plant communities that existed during the Early-Mid-Holocene may provide insights into the kinds of vegetation response expected from similar increases in temperature and aridity predicted for the twenty-first century. We infer that ecotonal areas

  1. A Short Guide to the Climatic Variables of the Last Glacial Maximum for Biogeographers.

    PubMed

    Varela, Sara; Lima-Ribeiro, Matheus S; Terribile, Levi Carina

    2015-01-01

    Ecological niche models are widely used for mapping the distribution of species during the last glacial maximum (LGM). Although the selection of the variables and General Circulation Models (GCMs) used for constructing those maps determine the model predictions, we still lack a discussion about which variables and which GCM should be included in the analysis and why. Here, we analyzed the climatic predictions for the LGM of 9 different GCMs in order to help biogeographers to select their GCMs and climatic layers for mapping the species ranges in the LGM. We 1) map the discrepancies between the climatic predictions of the nine GCMs available for the LGM, 2) analyze the similarities and differences between the GCMs and group them to help researchers choose the appropriate GCMs for calibrating and projecting their ecological niche models (ENM) during the LGM, and 3) quantify the agreement of the predictions for each bioclimatic variable to help researchers avoid the environmental variables with a poor consensus between models. Our results indicate that, in absolute values, GCMs have a strong disagreement in their temperature predictions for temperate areas, while the uncertainties for the precipitation variables are in the tropics. In spite of the discrepancies between model predictions, temperature variables (BIO1-BIO11) are highly correlated between models. Precipitation variables (BIO12-BIO19) show no correlation between models, and specifically, BIO14 (precipitation of the driest month) and BIO15 (Precipitation Seasonality (Coefficient of Variation)) show the highest level of discrepancy between GCMs. Following our results, we strongly recommend the use of different GCMs for constructing or projecting ENMs, particularly when predicting the distribution of species that inhabit the tropics and the temperate areas of the Northern and Southern Hemispheres, because climatic predictions for those areas vary greatly among GCMs. We also recommend the exclusion of BIO14

  2. A Short Guide to the Climatic Variables of the Last Glacial Maximum for Biogeographers

    PubMed Central

    Varela, Sara; Lima-Ribeiro, Matheus S.; Terribile, Levi Carina

    2015-01-01

    Ecological niche models are widely used for mapping the distribution of species during the last glacial maximum (LGM). Although the selection of the variables and General Circulation Models (GCMs) used for constructing those maps determine the model predictions, we still lack a discussion about which variables and which GCM should be included in the analysis and why. Here, we analyzed the climatic predictions for the LGM of 9 different GCMs in order to help biogeographers to select their GCMs and climatic layers for mapping the species ranges in the LGM. We 1) map the discrepancies between the climatic predictions of the nine GCMs available for the LGM, 2) analyze the similarities and differences between the GCMs and group them to help researchers choose the appropriate GCMs for calibrating and projecting their ecological niche models (ENM) during the LGM, and 3) quantify the agreement of the predictions for each bioclimatic variable to help researchers avoid the environmental variables with a poor consensus between models. Our results indicate that, in absolute values, GCMs have a strong disagreement in their temperature predictions for temperate areas, while the uncertainties for the precipitation variables are in the tropics. In spite of the discrepancies between model predictions, temperature variables (BIO1-BIO11) are highly correlated between models. Precipitation variables (BIO12- BIO19) show no correlation between models, and specifically, BIO14 (precipitation of the driest month) and BIO15 (Precipitation Seasonality (Coefficient of Variation)) show the highest level of discrepancy between GCMs. Following our results, we strongly recommend the use of different GCMs for constructing or projecting ENMs, particularly when predicting the distribution of species that inhabit the tropics and the temperate areas of the Northern and Southern Hemispheres, because climatic predictions for those areas vary greatly among GCMs. We also recommend the exclusion of BIO14

  3. 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

  4. Synchronicity of Kuroshio Current and climate system variability since the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Zheng, Xufeng; Li, Anchun; Kao, ShuhJi; Gong, Xun; Frank, Martin; Kuhn, Gerhard; Cai, Wenju; Yan, Hong; Wan, Shiming; Zhang, Honghai; Jiang, Fuqing; Hathorne, Edmund; Chen, Zhong; Hu, Bangqi

    2016-10-01

    The Kuroshio Current (KC) is the northward branch of the North Pacific subtropical gyre (NPG) and exerts influence on the exchange of physical, chemical, and biological properties of downstream regions in the Pacific Ocean. Resolving long-term changes in the flow of the KC water masses is, therefore, crucial for advancing our understanding of the Pacific's role in global ocean and climate variability. Here, we reconstruct changes in KC dynamics over the past 20 ka based on grain-size spectra, clay mineral, and Sr-Nd isotope constraints of sediments from the northern Okinawa Trough. Combined with published sediment records surrounding the NPG, we suggest that the KC remained in the Okinawa Trough throughout the Last Glacial Maximum. Together with Earth-System-Model simulations, our results additionally indicate that KC intensified considerably during the early Holocene (EH). The synchronous establishment of the KC ;water barrier; and the modern circulation pattern during the EH highstand shaped the sediment transport patterns. This is ascribed to the precession-induced increase in the occurrence of La Niña-like state and the strength of the East Asian summer monsoon. The synchronicity of the shifts in the intensity of the KC, Kuroshio extension, and El Niño/La Niña-Southern Oscillation (ENSO) variability may further indicate that the western branch of the NPG has been subject to basin-scale changes in wind stress curl over the North Pacific in response to low-latitude insolation. Superimposed on this long-term trend are high-amplitude, large century, and millennial-scale variations during last 5 ka, which are ascribed to the advent of modern ENSO when the equatorial oceans experienced stronger insolation during the boreal winter.

  5. Wetland methane emissions during the Last Glacial Maximum estimated from PMIP2 simulations: Climate, vegetation, and geographic controls

    NASA Astrophysics Data System (ADS)

    Weber, S. L.; Drury, A. J.; Toonen, W. H. J.; van Weele, M.

    2010-03-01

    It is an open question to what extent wetlands contributed to the interglacial-glacial decrease in atmospheric methane concentration. Here we estimate methane emissions from glacial wetlands, using newly available PMIP2 simulations of the Last Glacial Maximum (LGM) climate from coupled atmosphere-ocean and atmosphere-ocean-vegetation models. These simulations apply improved boundary conditions resulting in better agreement with paleoclimatic data than earlier PMIP1 simulations. Emissions are computed from the dominant controls of water table depth, soil temperature, and plant productivity, and we analyze the relative role of each factor in the glacial decline. It is found that latitudinal changes in soil moisture, in combination with ice sheet expansion, cause boreal wetlands to shift southward in all simulations. This southward migration is instrumental in maintaining the boreal wetland source at a significant level. The mean emission temperature over boreal wetlands drops by only a few degrees, despite the strong overall cooling. The temperature effect on the glacial decline in the methane flux is therefore moderate, while reduced plant productivity contributes equally to the total reduction. Model results indicate a relatively small boreal and large tropical source during the LGM, with wetlands on the exposed continental shelves mainly contributing to the tropical source. This distribution in emissions is consistent with the low interpolar difference in glacial methane concentrations derived from ice core data.

  6. The Occurrence and Climatic Implications of a Rapid Regression of Lake Elsinore, CA, During the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Markle, B. R.; Kirby, M.; Carrasco, J.

    2008-12-01

    Southern California is a densely populated region, highly sensitive to climate change and prone to potentially devastating hydrologic variability (e.g. droughts, floods, etc). In the interest of characterizing past climatic and hydrologic variability, this study analyzes a sediment core from Lake Elsinore, California with a particular focus on a possible rapid regression event at the height of the Last Glacial Maximum (LGM) (between 19,330 and 21,070 calendar yr BP). Sediment analyses (grain size, magnetic susceptibility, and total organic matter) and geochemical analyses (δ13C and molar C/N) are used to characterize and identify this event (hereafter referred to as the Last Glacial Maximum Regression Event or LGMRE). The combination of sediment characteristics of the LGMRE is not observed elsewhere in sediment core LESS02-09 suggesting that the event is unique over the period of observation. This rapid drying event is superimposed on a longer, orbital scale transgressive/regressive cycle. Given the generally wet climate of the LGM, the presence of the LGMRE is unexpected and indicates that Southern California is susceptible to rapid climate change. Evidence suggests synchrony at both orbital and centennial time scales between the Lake Elsinore climate record of the LGM and other terrestrial and marine climate records from southern California as well as the Great Basin region. Furthermore, evidence is presented for synchrony between the Lake Elsinore sediment core and the GISP 2 ice core record from Greenland, at both orbital the centennial time scales, suggesting climatic teleconnections between Southern California and the North Atlantic. It is possible that these two geographically distant areas are linked via dynamics of the altered Last Glacial Maximum jet stream.

  7. The effect of a dynamic soil scheme on the climate of the mid-Holocene and the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Stärz, M.; Lohmann, G.; Knorr, G.

    2016-01-01

    In order to account for coupled climate-soil processes, we have developed a soil scheme which is asynchronously coupled to a comprehensive climate model with dynamic vegetation. This scheme considers vegetation as the primary control of changes in physical soil characteristics. We test the scheme for a warmer (mid-Holocene) and colder (Last Glacial Maximum) climate relative to the preindustrial climate. We find that the computed changes in physical soil characteristics lead to significant amplification of global climate anomalies, representing a positive feedback. The inclusion of the soil feedback yields an extra surface warming of 0.24 °C for the mid-Holocene and an additional global cooling of 1.07 °C for the Last Glacial Maximum. Transition zones such as desert-savannah and taiga-tundra exhibit a pronounced response in the model version with dynamic soil properties. Energy balance model analyses reveal that our soil scheme amplifies the temperature anomalies in the mid-to-high northern latitudes via changes in the planetary albedo and the effective longwave emissivity. As a result of the modified soil treatment and the positive feedback to climate, part of the underestimated mid-Holocene temperature response to orbital forcing can be reconciled in the model.

  8. The effect of a dynamic soil scheme on the climate of the mid-Holocene and the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Stärz, Michael; Lohmann, Gerrit; Knorr, Gregor

    2016-04-01

    In order to account for coupled climate-soil processes, we have developed a soil scheme, which is asynchronously coupled to a comprehensive climate model with dynamic vegetation. This scheme considers vegetation as the primary control of changes in physical soil characteristics. We test the scheme for a warmer (mid-Holocene) and colder (Last Glacial Maximum) climate relative to the preindustrial climate. We find that the computed changes of physical soil characteristics lead to significant amplification of global climate anomalies, representing a positive feedback. The inclusion of the soil feedback yields an extra surface warming of 0.24°C for the mid-Holocene and an additional global cooling of 1.07°C for the Last Glacial Maximum. Transition zones such as desert/savannah and taiga/tundra exhibit a pronounced response in the model version with dynamic soil properties. Energy balance model analyses reveal that our soil scheme amplifies the temperature anomalies in the mid-to-high northern latitudes via changes in the planetary albedo and the effective longwave emissivity. As a result of the modified soil treatment and the positive feedback on climate, part of the underestimated mid-Holocene temperature response to orbital forcing can be reconciled in the model.

  9. Lake-levels, vegetation and climate in Central Asia during the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Amosov, Mikhail

    2014-05-01

    Central Asian region is bounded in the east corner of the Greater Khingan Range and the Loess Plateau, and to the west - the Caspian Sea. This representation of region boundaries is based on classical works of A.Humboldt and V.Obruchev. Three typical features of Central Asia nature are: climate aridity, extensive inland drainage basins with numerous lakes and mountain systems with developed glaciation. Nowadays the extensive data is accumulated about lake-levels during the Last Glacial Maximum (LGM) in Central Asia. Data compilation on 20 depressions, where lakes exist now or where they existed during LGM, shows that most of them had usually higher lake-level than at present time. This regularity could be mentioned for the biggest lakes (the Aral Sea, the Balkhash, the Ysyk-Kol etc.) and for small ones that located in the mountains (Tien Shan, Pamir and Tibet). All of these lake basins get the precipitation due to westerlies. On the other hand lakes, which are located in region's east rimland (Lake Qinghai and lakes in Inner Mongolia) and get the precipitation due to summer East Asian monsoons, do not comply with the proposed regularity. During LGM these lake-levels were lower than nowadays. Another exception is Lake Manas, its lake-level was also lowered. Lake Manas is situated at the bottom of Junggar Basin. There are many small rivers, which come from the ranges and suffer the violent fluctuation in the position of its lower channel. It is possible to assume that some of its runoff did not get to Lake Manas during LGM. Mentioned facts suggest that levels of the most Central Asian lakes were higher during LGM comparing to their current situation. However, at that period vegetation was more xerophytic than now. Pollen data confirm this information for Tibet, Pamir and Tien Shan. Climate aridization of Central Asia can be proved by data about the intensity of loess accumulation during LGM. This evidence received for the east part of region (the Loess Plateau) and

  10. Global connections between aeolian dust, climate and ocean biogeochemistry at the present day and at the last glacial maximum

    NASA Astrophysics Data System (ADS)

    Maher, B. A.; Prospero, J. M.; Mackie, D.; Gaiero, D.; Hesse, P. P.; Balkanski, Y.

    2010-04-01

    Palaeo-dust records in sediments and ice cores show that wind-borne mineral aerosol ('dust') is strongly linked with climate state. During glacial climate stages, for example, the world was much dustier, with dust fluxes two to five times greater than in interglacial stages. However, the influence of dust on climate remains a poorly quantified and actively changing element of the Earth's climate system. Dust can influence climate directly, by the scattering and absorption of solar and terrestrial radiation, and indirectly, by modifying cloud properties. Dust transported to the oceans can also affect climate via ocean fertilization in those regions of the world's oceans where macronutrients like nitrate are abundant but primary production and nitrogen fixation are limited by iron scarcity. Dust containing iron, as fine-grained iron oxides/oxyhydroxides and/or within clay minerals, and other essential micronutrients (e.g. silica) may modulate the uptake of carbon in marine ecosystems and, in turn, the atmospheric concentration of CO 2. Here, in order to critically examine past fluxes and possible climate impacts of dust in general and iron-bearing dust in particular, we consider present-day sources and properties of dust, synthesise available records of dust deposition at the last glacial maximum (LGM); evaluate the evidence for changes in ocean palaeo-productivity associated with, and possibly caused by, changes in aeolian flux to the oceans at the LGM; and consider the radiative forcing effects of increased LGM dust loadings.

  11. Tropical climate at the last glacial maximum inferred from glacier mass-balance modeling

    USGS Publications Warehouse

    Hostetler, S.W.; Clark, P.U.

    2000-01-01

    Model-derived equilibrium line altitudes (ELAs) of former tropical glaciers support arguments, based on other paleoclimate data, for both the magnitude and spatial pattern of terrestrial cooling in the tropics at the last glacial maximum (LGM). Relative to the present, LGM ELAs were maintained by air temperatures that were 3.5??to 6.6 ??C lower and precipitation that ranged from 63% wetter in Hawaii to 25% drier on Mt. Kenya, Africa. Our results imply the need for a ~3 ??C cooling of LGM sea surface temperatures in the western Pacific warm pool. Sensitivity tests suggest that LGM ELAs could have persisted until 16,000 years before the present in the Peruvian Andes and on Papua, New Guinea.

  12. Impacts of climatic change on carbon storage in the Sahara?Gobi desert belt since the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Lioubimtseva, E.; Simon, B.; Faure, H.; Faure-Denard, L.; Adams, J. M.

    1998-05-01

    Reconstructions of palaeolandscapes for intervals with different climatic conditions help define regional trends in palaeobiomass and carbon storage due to global climatic change. The Sahara-Gobi desert belt stretches for about 15,000 km from the Atlantic coast to Northern China. Natural vegetation zones have undergone a number of significant shifts and complex qualitative changes under the contrasting climatic conditions of the Last Glacial Maximum (LGM) and the Holocene Climatic Optimum (HCO). The results presented here are based on palynological, pedological and sedimentological evidence, which indicate that the amount of carbon stored in vegetation and soils would have been much smaller during the Glacial Maximum than in the interglacial and post glacial times. Comparison of a set of palaeogeographic maps of this region for the chosen time-slices (ca. 20-18 ka, 9-8 ka and the present) allows us to discuss land biomass changes. Dry and cool conditions during the LGM resulted in the spread of arid and semi-arid ecosystems at northern and southern margins of the desert belt. The southern limit of the Sahara migrated southward at least 400 km relative to its present position, and almost 1000 km south compared to the mid-Holocene. The northern margin of the temperate deserts and dry steppes of Central Asia shifted northward for not less than 200-300 km over Kazakhstan, southern Siberia and Mongolia. In this study we have quantified variations of the main ecosystems from the LGM to the HCO in terms of changes in carbon storage. Each vegetation zone has been assigned a carbon density for living and dead (soil) organic matter. During the last world deglaciation, the Sahara-Gobi desert belt was a sink for approximately 200 Gt of atmospheric carbon, but since the mid-Holocene, it has been a source of carbon.

  13. Gridded climate data from 5 GCMs of the Last Glacial Maximum downscaled to 30 arc s for Europe

    NASA Astrophysics Data System (ADS)

    Schmatz, D. R.; Luterbacher, J.; Zimmermann, N. E.; Pearman, P. B.

    2015-06-01

    Studies of the impacts of historical, current and future global change require very high-resolution climate data (≤ 1 km) as a basis for modelled responses, meaning that data from digital climate models generally require substantial rescaling. Another shortcoming of available datasets on past climate is that the effects of sea level rise and fall are not considered. Without such information, the study of glacial refugia or early Holocene plant and animal migration are incomplete if not impossible. Sea level at the last glacial maximum (LGM) was approximately 125 m lower, creating substantial additional terrestrial area for which no current baseline data exist. Here, we introduce the development of a novel, gridded climate dataset for LGM that is both very high resolution (1 km) and extends to the LGM sea and land mask. We developed two methods to extend current terrestrial precipitation and temperature data to areas between the current and LGM coastlines. The absolute interpolation error is less than 1 and 0.5 °C for 98.9 and 87.8 %, respectively, of all pixels within two arc degrees of the current coastline. We use the change factor method with these newly assembled baseline data to downscale five global circulation models of LGM climate to a resolution of 1 km for Europe. As additional variables we calculate 19 "bioclimatic" variables, which are often used in climate change impact studies on biological diversity. The new LGM climate maps are well suited for analysing refugia and migration during Holocene warming following the LGM.

  14. Mid-Holocene and last glacial maximum climate simulations with the IPSL model: part II: model-data comparisons

    NASA Astrophysics Data System (ADS)

    Kageyama, Masa; Braconnot, Pascale; Bopp, Laurent; Mariotti, Véronique; Roy, Tilla; Woillez, Marie-Noëlle; Caubel, Arnaud; Foujols, Marie-Alice; Guilyardi, Eric; Khodri, Myriam; Lloyd, James; Lombard, Fabien; Marti, Olivier

    2013-05-01

    The climates of the mid-Holocene (MH, 6,000 years ago) and the Last Glacial Maximum (LGM, 21,000 years ago) have been extensively documented and as such, have become targets for the evaluation of climate models for climate contexts very different from the present. In Part 1 of the present work, we have studied the MH and LGM simulations performed with the last two versions of the IPSL model: IPSL_CM4, run for the PMIP2/CMIP3 (Coupled Model Intercomparion Project) projects and IPSL_CM5A, run for the most recent PMIP3/CMIP5 projets. We have shown that not only are these models different in their simulations of the PI climate, but also in their simulations of the climatic anomalies for the MH and LGM. In the Part 2 of this paper, we first examine whether palaeo-data can help discriminate between the model performances. This is indeed the case for the African monsoon for the MH or for North America south of the Laurentide ice sheet, the South Atlantic or the southern Indian ocean for the LGM. For the LGM, off-line vegetation modelling appears to offer good opportunities to distinguish climate model results because glacial vegetation proves to be very sensitive to even small differences in LGM climate. For other cases such as the LGM North Atlantic or the LGM equatorial Pacific, the large uncertainty on the SST reconstructions, prevents model discrimination. We have examined the use of other proxy-data for model evaluation, which has become possible with the inclusion of the biogeochemistry morel PISCES in the IPSL_CM5A model. We show a broad agreement of the LGM-PI export production changes with reconstructions. These changes are related to the mixed layer depth in most regions and to sea-ice variations in the high latitudes. We have also modelled foraminifer abundances with the FORAMCLIM model and shown that the changes in foraminifer abundance in the equatorial Pacific are mainly forced by changes in SSTs, hence confirming the SST-foraminifer abundance relationship

  15. The climate of the Last Glacial Maximum in south-eastern Australia

    NASA Astrophysics Data System (ADS)

    Shulmeister, J.; Cohen, T.; Kiernan, K.; Woodward, C.; Barrows, T.; Fitzsimmons, K.; Kemp, J.; Haworth, R.; Clark, D. H.; Gontz, A. M.; Chang, J.; Mueller, D.; Slee, A.; Ellerton, D.

    2015-12-01

    The Last Glaciation Maximum (c. 25-18 kyr) in south-eastern Australia has traditionally been regarded as both significantly colder than the present and much more arid. This was based on a variety of evidence including the dramatic reduction in tree pollen and dune activity in currently humid areas such as the Blue Mountains of NSW. Maintaining arid conditions under significantly lower temperatures is quite challenging and not all lines of evidence supported strong aridity. Over the last four years an ARC project has worked to develop new lines of evidence to test these inferences. Outcomes from the project indicate that winter temperatures were significantly colder than at present (an 8-11 C decrease) while summer temperatures were cooler but not as extreme (4-6.5 C). Moisture balances appear to have been more positive than present along the eastern highlands, while areas to the west were comparatively drier. The humid zone along the divide maintained at least seasonally stronger flows in the major rivers, meaning that water was more available in western districts than under modern climates. I will summarise the evidence for this new pattern and highlight the climatological patterns that would be consistent with the reconstruction. I will conclude by speculating on the implications for both human landscape use and what happened to the vegetation.

  16. Numerical Modeling of Rocky Mountain Paleoglaciers - Insights into the Climate of the Last Glacial Maximum and the Subsequent Deglaciation

    NASA Astrophysics Data System (ADS)

    Leonard, E. M.; Laabs, B. J. C.; Plummer, M. A.

    2014-12-01

    Numerical modeling of paleoglaciers can yield information on the climatic conditions necessary to sustain those glaciers. In this study we apply a coupled 2-d mass/energy balance and flow model (Plummer and Phillips, 2003) to reconstruct local last glacial maximum (LLGM) glaciers and paleoclimate in ten study areas along the crest of the U.S. Rocky Mountains between 33°N and 49°N. In some of the areas, where timing of post-LLGM ice recession is constrained by surface exposure ages on either polished bedrock upvalley from the LLGM moraines or post-LLGM recessional moraines, we use the model to assess magnitudes and rates of climate change during deglaciation. The modeling reveals a complex pattern of LLGM climate. The magnitude of LLGM-to-modern climate change (temperature and/or precipitation change) was greater in both the northern (Montana) Rocky Mountains and southern (New Mexico) Rocky Mountains than in the middle (Wyoming and Colorado) Rocky Mountains. We use temperature depression estimates from global and regional climate models to infer LLGM precipitation from our glacier model results. Our results suggest a reduction of precipitation coupled with strongly depressed temperatures in the north, contrasted with strongly enhanced precipitation and much more modest temperature depression in the south. The middle Rocky Mountains of Colorado and Wyoming appear to have experienced a reduction in precipitation at the LLGM without the strong temperature depression of the northern Rocky Mountains. Preliminary work on modeling of deglaciation in the Sangre de Cristo Range in southern Colorado suggests that approximately half of the LLGM-to-modern climate change took place during the initial ~2400 years of deglaciation. If increasing temperature and changing solar insolation were the sole drivers of this initial deglaciation, then temperature would need to have risen by slightly more than 1°C/ky through this interval to account for the observed rate of ice recession.

  17. Last glacial maximum climate inferences from cosmogenic dating and glacier modeling of the western Uinta ice field, Uinta Mountains, Utah

    NASA Astrophysics Data System (ADS)

    Refsnider, Kurt A.; Laabs, Benjamin J. C.; Plummer, Mitchell A.; Mickelson, David M.; Singer, Bradley S.; Caffee, Marc W.

    2008-01-01

    During the last glacial maximum (LGM), the western Uinta Mountains of northeastern Utah were occupied by the Western Uinta Ice Field. Cosmogenic 10Be surface-exposure ages from the terminal moraine in the North Fork Provo Valley and paired 26Al and 10Be ages from striated bedrock at Bald Mountain Pass set limits on the timing of the local LGM. Moraine boulder ages suggest that ice reached its maximum extent by 17.4 ± 0.5 ka (± 2σ). 10Be and 26Al measurements on striated bedrock from Bald Mountain Pass, situated near the former center of the ice field, yield a mean 26Al/ 10Be ratio of 5.7 ± 0.8 and a mean exposure age of 14.0 ± 0.5 ka, which places a minimum-limiting age on when the ice field melted completely. We also applied a mass/energy-balance and ice-flow model to investigate the LGM climate of the western Uinta Mountains. Results suggest that temperatures were likely 5 to 7°C cooler than present and precipitation was 2 to 3.5 times greater than modern, and the western-most glaciers in the range generally received more precipitation when expanding to their maximum extent than glaciers farther east. This scenario is consistent with the hypothesis that precipitation in the western Uintas was enhanced by pluvial Lake Bonneville during the last glaciation.

  18. Climate sensitivity estimated from temperature reconstructions of the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Schmittner, A.; Urban, N.; Shakun, J. D.; Mahowald, N. M.; Clark, P. U.; Bartlein, P. J.; Mix, A. C.; Rosell-Melé, A.

    2011-12-01

    In 1959 IJ Good published the discussion "Kinds of Probability" in Science. Good identified (at least) five kinds. The need for (at least) a sixth kind of probability when quantifying uncertainty in the context of climate science is discussed. This discussion brings out the differences in weather-like forecasting tasks and climate-links tasks, with a focus on the effective use both of science and of modelling in support of decision making. Good also introduced the idea of a "Dynamic probability" a probability one expects to change without any additional empirical evidence; the probabilities assigned by a chess playing program when it is only half thorough its analysis being an example. This case is contrasted with the case of "Mature probabilities" where a forecast algorithm (or model) has converged on its asymptotic probabilities and the question hinges in whether or not those probabilities are expected to change significantly before the event in question occurs, even in the absence of new empirical evidence. If so, then how might one report and deploy such immature probabilities in scientific-support of decision-making rationally? Mature Probability is suggested as a useful sixth kind, although Good would doubtlessly argue that we can get by with just one, effective communication with decision makers may be enhanced by speaking as if the others existed. This again highlights the distinction between weather-like contexts and climate-like contexts. In the former context one has access to a relevant climatology (a relevant, arguably informative distribution prior to any model simulations), in the latter context that information is not available although one can fall back on the scientific basis upon which the model itself rests, and estimate the probability that the model output is in fact misinformative. This subjective "probability of a big surprise" is one way to communicate the probability of model-based information holding in practice, the probability that the

  19. Synchronous decadal changes between Asian monsoon and Greenland climates during the last glacial maximum

    NASA Astrophysics Data System (ADS)

    Wu, J. Y.; Wang, Y. J.; Cheng, H.; Edwards, R.

    2008-12-01

    An annually laminated stalagmite from Hulu Cave in Southern China grew for about 3000 years starting at 21345 aBP (±85 a) as determined by lamina counting and U-Th dating. The stalagmite δ 18O time series provides a continuous history of the Asian monsoon precipitation and δ 13C may reflect the soil biogenic production, which is linked to climatic factors such as temperature and humidity. The annual layer thickness (LT) from this stalagmite can not be regarded as a direct indicator of precipitation. LT and gray level (GL) may indicate the changes in the relative humidity of the cave environment. The δ 18O record with average 3.7-year resolution precisely anchored the timing of IS2 event which was well expressed in the Greenland ice core δ 18O records. The timing of IS2 in GISP2 is close to the chronology of the stalagmite records within the uncertainty of U/Th dates. Our record, in combination with the previously-published record between 17 and 15 kaBP also from Hulu Cave, indicated that the monsoon events (H1 and H2), in terms of their structure, are quite different from the cold events in North Atlantic, which were well presented in the Greenland ice core δ 18O records. For both of the H1 and H2, the monsoon precipitation records show a rapid transition from dry to wet conditions, followed by a stepwise increasing trend, with a total duration of more than 600 years. In contrast, the Greenland δ 18O records display abrupt changes either into or out of the events. The H98 δ 18O record shows a teleconnection between the density of East Asia monsoon and polar temperature on centennial to multi-decade scales during the LGM. However, the different structure of climatic events between the low and high latitude areas also suggests that changes of East Asian monsoon were triggered not only by the North Atlantic themorhaline circulation but also by some other factors. The coupled oceanic- atmospheric circulation from tropical Pacific may be a possible forcing, it

  20. PALEOCLIMATE: Glacial Climate Instability.

    PubMed

    Labeyrie, L

    2000-12-08

    Throughout the last glacial period, rapid climatic changes called Dansgaard-Oeschger (D-O) events occurred in the Northern Hemisphere. As Labeyrie discusses in his Perspective, these events are ideal targets for testing our understanding of climate change and developing climatic change models. Important steps toward understanding D-O events, particularly regarding the role of the low latitudes, are now reported by Hughen et al. and Peterson et al.

  1. The influence of continental ice, atmospheric CO2, and land albedo on the climate of the last glacial maximum

    NASA Astrophysics Data System (ADS)

    Broccoli, A. J.; Manabe, S.

    1987-02-01

    The contributions of expanded continental ice, reduced atmospheric CO2, and changes in land albedo to the maintenance of the climate of the last glacial maximum (LGM) are examined. A series of experiments is performed using an atmosphere-mixed layer ocean model in which these changes in boundary conditions are incorporated either singly or in combination. The model used has been shown to produce a reasonably realistic simulation of the reduced temperature of the LGM (Manabe and Broccoli 1985b). By comparing the results from pairs of experiments, the effects of each of these environmental changes can be determined. Expanded continental ice and reduced atmospheric CO2 are found to have a substantial impact on global mean temperature. The ice sheet effect is confined almost exclusively to the Northern Hemisphere, while lowered CO2 cools both hemispheres. Changes in land albedo over ice-free areas have only a minor thermal effect on a global basis. The reduction of CO2 content in the atmosphere is the primary contributor to the cooling of the Southern Hemisphere. The model sensitivity to both the ice sheet and CO2 effects is characterized by a high latitude amplification and a late autumn and early winter maximum. Substantial changes in Northern Hemisphere tropospheric circulation are found in response to LGM boundary conditions during winter. An amplified flow pattern and enhanced westerlies occur in the vicinity of the North American and Eurasian ice sheets. These alterations of the tropospheric circulation are primarily the result of the ice sheet effect, with reduced CO2 contributing only a slight amplification of the ice sheet-induced pattern.

  2. Marine palynological record for tropical climate variations since the late last glacial maximum in the northern South China Sea

    NASA Astrophysics Data System (ADS)

    Dai, Lu; Weng, Chengyu

    2015-12-01

    The upper part (191-1439 cm) of the marine sediment core MD05-2906 from the northern South China Sea (SCS) was palynologically investigated. The chronology suggested that it covered the record since ~19 calendar kiloyears before present (cal ka BP) and revealed a detailed environmental change history since the late last glacial maximum (LGM). During the late LGM, due to the lowered sea level (~100 m lower) and the shortened distance from the shore to the study site, the pollen concentration was very high. The pollen assemblages were dominated by non-arboreal taxa, especially Artemisia pollen, before ~15 cal ka BP. Abundant subtropical and tropical pollen taxa were still important components and a south subtropical climate prevailed during the late LGM. The coexistent rich Artemisia pollen possibly was not derived from near shores, but was derived mainly from the northern exposed continental shelf in the East China Sea (ECS). After ~15 cal ka BP, with the rise in the sea level and enhanced distance from the pollen source areas to the core site, pollen concentrations started to decline gradually. However, during the late deglaciation and early Holocene, the higher concentrations of many pollen taxa reoccurred, which cannot be attributed to the sea level changes. Pinus pollen deposited in the core, which is considered to be mostly water-carried based on many modern pollen surveys, also started to dramatically increase at the same time. Therefore, the higher pollen concentration, with more Pinus and Typha (an aquatic plant) pollen indicated a notably enhanced terrestrial runoff and precipitation during the last deglaciation/Holocene transition (~11.3-9.4 cal ka BP). We inferred that a strong summer monsoon occurred at this time. During the late LGM/deglaciation transition period, the pollen assemblage reflected a gradually warming climate, and the climate fluctuations derived from the high-latitudes were not well-identified. This study suggests that solar insolation

  3. Topographic and climatic influences on accelerated loess accumulation since the last glacial maximum in the Palouse, Pacific Northwest, USA

    NASA Astrophysics Data System (ADS)

    Sweeney, Mark R.; Busacca, Alan J.; Gaylord, David R.

    2005-05-01

    Topographic and climatic influences have controlled thick loess accumulation at the southern margin of the Palouse loess in northern Oregon. Juniper and Cold Springs Canyons, located on the upwind flank of the Horse Heaven Hills, are oriented perpendicular to prevailing southwesterly winds. These canyons are topographic traps that separate eolian sand on the upwind side from thick accumulations (nearly 8 m) of latest Pleistocene to Holocene L1 loess on the downwind side. Silt- and sand-rich glacial outburst flood sediment in the Umatilla Basin is the source of eolian sand and loess for the region. Sediment from this basin also contributes to loess accumulations across much of the Columbia Plateau to the northeast. Downwind of Cold Springs Canyon, Mt. St. Helens set S and Glacier Peak tephras bracket 4 m of loess, demonstrating that approximately 2500 g m -2 yr -1 of loess accumulated between about 15,400-13,100 cal yr B.P. Mass accumulation rates decreased to approximately 250 g m -2 yr -1 from 13,100 cal yr B.P. to the present. Tephrochronology suggests that the bulk of near-source Palouse loess accumulated in one punctuated interval in the latest Pleistocene characterized by a dry and windy climate.

  4. Vegetation and environmental responses to climate forcing during the Last Glacial Maximum and deglaciation in the East Carpathians: attenuated response to maximum cooling and increased biomass burning

    NASA Astrophysics Data System (ADS)

    Magyari, E. K.; Veres, D.; Wennrich, V.; Wagner, B.; Braun, M.; Jakab, G.; Karátson, D.; Pál, Z.; Ferenczy, Gy; St-Onge, G.; Rethemeyer, J.; Francois, J.-P.; von Reumont, F.; Schäbitz, F.

    2014-12-01

    The Carpathian Mountains were one of the main mountain reserves of the boreal and cool temperate flora during the Last Glacial Maximum (LGM) in East-Central Europe. Previous studies demonstrated Lateglacial vegetation dynamics in this area; however, our knowledge on the LGM vegetation composition is very limited due to the scarcity of suitable sedimentary archives. Here we present a new record of vegetation, fire and lacustrine sedimentation from the youngest volcanic crater of the Carpathians (Lake St Anne, Lacul Sfânta Ana, Szent-Anna-tó) to examine environmental change in this region during the LGM and the subsequent deglaciation. Our record indicates the persistence of boreal forest steppe vegetation (with Pinus, Betula, Salix, Populus and Picea) in the foreland and low mountain zone of the East Carpathians and Juniperus shrubland at higher elevation. We demonstrate attenuated response of the regional vegetation to maximum global cooling. Between ˜22,870 and 19,150 cal yr BP we find increased regional biomass burning that is antagonistic with the global trend. Increased regional fire activity suggests extreme continentality likely with relatively warm and dry summers. We also demonstrate xerophytic steppe expansion directly after the LGM, from ˜19,150 cal yr BP, and regional increase in boreal woodland cover with Pinus and Betula from 16,300 cal yr BP. Plant macrofossils indicate local (950 m a.s.l.) establishment of Betula nana and Betula pubescens at 15,150 cal yr BP, Pinus sylvestris at 14,700 cal yr BP and Larix decidua at 12,870 cal yr BP. Pollen data furthermore support population genetic inferences regarding the regional presence of some temperate deciduous trees during the LGM (Fagus sylvatica, Corylus avellana, Fraxinus excelsior). Our sedimentological data also demonstrate intensified aeolian dust accumulation between 26,000 and 20,000 cal yr BP.

  5. Changes in the intermediate water mass formation rates in the global ocean for the Last Glacial Maximum, mid-Holocene and pre-industrial climates

    NASA Astrophysics Data System (ADS)

    Wainer, I.; Goes, M.; Murphy, L. N.; Brady, E.

    2012-09-01

    The paleoclimate version of the National Center for Atmospheric Research Community Climate System Model version 3 (NCAR-CCSM3) is used to analyze changes in the water formation rates in the Atlantic, Pacific, and Indian Oceans for the Last Glacial Maximum (LGM), mid-Holocene (MH) and pre-industrial (PI) control climate. During the MH, CCSM3 exhibits a north-south asymmetric response of intermediate water subduction changes in the Atlantic Ocean, with a reduction of 2 Sv in the North Atlantic and an increase of 2 Sv in the South Atlantic relative to PI. During the LGM, there is increased formation of intermediate water and a more stagnant deep ocean in the North Pacific. The production of North Atlantic Deep Water (NADW) is significantly weakened. The NADW is replaced in large extent by enhanced Antarctic Intermediate Water (AAIW), Glacial North Atlantic Intermediate Water (GNAIW), and also by an intensified of Antarctic Bottom Water (AABW), with the latter being a response to the enhanced salinity and ice formation around Antarctica. Most of the LGM intermediate/mode water is formed at 27.4 <σθ < 29.0 kg/m3, while for the MH and PI most of the subduction transport occurs at 26.5 < σθ < 27.4 kg/m3. The simulated LGM Southern Hemisphere winds are more intense by 0.2-0.4 dyne/cm2. Consequently, increased Ekman transport drives the production of intermediate water (low salinity) at a larger rate and at higher densities when compared to the other climatic periods.

  6. The response of the Okhotsk Sea environment to the orbital-millennium global climate changes during the Last Glacial Maximum, deglaciation and Holocene

    NASA Astrophysics Data System (ADS)

    Gorbarenko, Sergey A.; Artemova, Antonina V.; Goldberg, Evgeniy L.; Vasilenko, Yuriy P.

    2014-05-01

    Reconstruction of regional climate and the Okhotsk Sea (OS) environment for the Last Glacial Maximum (LGM), deglaciation and Holocene was performed on the basis of high-resolution records of ice rafted debris (IRD), СаСО3, opal, total organic carbon (TOС), biogenic Ba (Ba_bio) and redox sensitive element (Mn, Mo) content, and diatom and pollen results of four cores that form a north-southern transect. Age models of the studied cores were earlier established by AMS 14C data, oxygen-isotope chronostratigraphy and tephrochronology. According to received results, since 25 ka the regional climate and OS environmental conditions have changed synchronously with LGM condition, cold Heinrich event 1, Bølling-Allerød (BA) warming, Younger Dryas (YD) cooling and Pre-Boreal (PB) warming recorded in the Greenland ice core, North Atlantic sediment, and China cave stalagmites. Calculation of IRD MAR in sediment of north-south transect cores indicates an increase of sea ice formation several times in the glacial OS as compared to the Late Holocene. Accompanying ice formation, increased brine rejection and the larger potential density of surface water at the north shelf due to a drop of glacial East Asia summer monsoon precipitation and Amur River run off, led to strong enhancement of the role of the OS in glacial North Pacific Intermediate Water (NPIW) formation. The remarkable increase in OS productivity during BA and PB warming was probably related with significant reorganisation of the North Pacific deep water ventilation and nutrient input into the NPIW and OS Intermediate Water (OSIW). Seven Holocene OS millennial cold events based on the elevated values of the detrended IRD stack record over the IRD broad trend in the sediments of the studied cores have occurred synchronously with cold events recorded in the North Atlantic, Greenland ice cores and China cave stalagmites after 9 ka. Diatom production in the OS was mostly controlled by sea ice cover changes and surface

  7. Relative timing of last glacial maximum and late-glacial events in the central tropical Andes

    NASA Astrophysics Data System (ADS)

    Bromley, Gordon R. M.; Schaefer, Joerg M.; Winckler, Gisela; Hall, Brenda L.; Todd, Claire E.; Rademaker, Kurt M.

    2009-11-01

    Whether or not tropical climate fluctuated in synchrony with global events during the Late Pleistocene is a key problem in climate research. However, the timing of past climate changes in the tropics remains controversial, with a number of recent studies reporting that tropical ice age climate is out of phase with global events. Here, we present geomorphic evidence and an in-situ cosmogenic 3He surface-exposure chronology from Nevado Coropuna, southern Peru, showing that glaciers underwent at least two significant advances during the Late Pleistocene prior to Holocene warming. Comparison of our glacial-geomorphic map at Nevado Coropuna to mid-latitude reconstructions yields a striking similarity between Last Glacial Maximum (LGM) and Late-Glacial sequences in tropical and temperate regions. Exposure ages constraining the maximum and end of the older advance at Nevado Coropuna range between 24.5 and 25.3 ka, and between 16.7 and 21.1 ka, respectively, depending on the cosmogenic production rate scaling model used. Similarly, the mean age of the younger event ranges from 10 to 13 ka. This implies that (1) the LGM and the onset of deglaciation in southern Peru occurred no earlier than at higher latitudes and (2) that a significant Late-Glacial event occurred, most likely prior to the Holocene, coherent with the glacial record from mid and high latitudes. The time elapsed between the end of the LGM and the Late-Glacial event at Nevado Coropuna is independent of scaling model and matches the period between the LGM termination and Late-Glacial reversal in classic mid-latitude records, suggesting that these events in both tropical and temperate regions were in phase.

  8. A cosmogenic 10Be chronology for the local last glacial maximum and termination in the Cordillera Oriental, southern Peruvian Andes: Implications for the tropical role in global climate

    NASA Astrophysics Data System (ADS)

    Bromley, Gordon R. M.; Schaefer, Joerg M.; Hall, Brenda L.; Rademaker, Kurt M.; Putnam, Aaron E.; Todd, Claire E.; Hegland, Matthew; Winckler, Gisela; Jackson, Margaret S.; Strand, Peter D.

    2016-09-01

    Resolving patterns of tropical climate variability during and since the last glacial maximum (LGM) is fundamental to assessing the role of the tropics in global change, both on ice-age and sub-millennial timescales. Here, we present a10Be moraine chronology from the Cordillera Carabaya (14.3°S), a sub-range of the Cordillera Oriental in southern Peru, covering the LGM and the first half of the last glacial termination. Additionally, we recalculate existing 10Be ages using a new tropical high-altitude production rate in order to put our record into broader spatial context. Our results indicate that glaciers deposited a series of moraines during marine isotope stage 2, broadly synchronous with global glacier maxima, but that maximum glacier extent may have occurred prior to stage 2. Thereafter, atmospheric warming drove widespread deglaciation of the Cordillera Carabaya. A subsequent glacier resurgence culminated at ∼16,100 yrs, followed by a second period of glacier recession. Together, the observed deglaciation corresponds to Heinrich Stadial 1 (HS1: ∼18,000-14,600 yrs), during which pluvial lakes on the adjacent Peruvian-Bolivian altiplano rose to their highest levels of the late Pleistocene as a consequence of southward displacement of the inter-tropical convergence zone and intensification of the South American summer monsoon. Deglaciation in the Cordillera Carabaya also coincided with the retreat of higher-latitude mountain glaciers in the Southern Hemisphere. Our findings suggest that HS1 was characterised by atmospheric warming and indicate that deglaciation of the southern Peruvian Andes was driven by rising temperatures, despite increased precipitation. Recalculated 10Be data from other tropical Andean sites support this model. Finally, we suggest that the broadly uniform response during the LGM and termination of the glaciers examined here involved equatorial Pacific sea-surface temperature anomalies and propose a framework for testing the viability

  9. The anatomy of Last Glacial Maximum climate variations in south Westland, New Zealand, derived from pollen records

    NASA Astrophysics Data System (ADS)

    Vandergoes, Marcus J.; Newnham, Rewi M.; Denton, George H.; Blaauw, Maarten; Barrell, David J. A.

    2013-08-01

    We present pollen records from three sites in south Westland, New Zealand, that document past vegetation and inferred climate change between approximately 30,000 and 15,000 cal. yr BP. Detailed radiocarbon dating of the enclosing sediments at one of those sites, Galway tarn, provides a more robust chronology for the structure and timing of climate-induced vegetation change than has previously been possible in this region. The Kawakawa/Oruanui tephra, a key isochronous marker, affords a precise stratigraphic link across all three pollen records, while other tie points are provided by key pollen-stratigraphic changes which appear to be synchronous across all three sites. Collectively, the records show three episodes in which grassland, interpreted as indicating mostly cold subalpine to alpine conditions, was prevalent in lowland south Westland, separated by phases dominated by subalpine shrubs and montane-lowland trees, indicating milder interstadial conditions. Dating, expressed as a Bayesian-estimated single 'best' age followed in parentheses by younger/older bounds of the 95% confidence modelled age range, indicates that a cold stadial episode, whose onset was marked by replacement of woodland by grassland, occurred between 28,730 (29,390-28,500) and 25,470 (26,090-25,270) cal. yr BP (years before AD, 1950), prior to the deposition of the Kawakawa/Oruanui tephra. Milder interstadial conditions prevailed between 25,470 (26,090-25,270) and 24,400 (24,840-24,120) cal. yr BP and between 22,630 (22,930-22,340) and 21,980 (22,210-21,580) cal. yr BP, separated by a return to cold stadial conditions between 24,400 and 22,630 cal. yr BP. A final episode of grass-dominated vegetation, indicating cold stadial conditions, occurred from 21,980 (22,210-21,580) to 18,490 (18,670-17,950) cal. yr BP. The decline in grass pollen, indicating progressive climate amelioration, was well advanced by 17,370 (17,730-17,110) cal. yr BP, indicating that the onset of the termination in south

  10. Climate-driven changes to dune activity during the Last Glacial Maximum and deglaciation in the Mu Us dune field, north-central China

    NASA Astrophysics Data System (ADS)

    Xu, Zhiwei; Lu, Huayu; Yi, Shuangwen; Vandenberghe, Jef; Mason, Joseph A.; Zhou, Yali; Wang, Xianyan

    2015-10-01

    One significant change of terrestrial landscapes in response to past climate change has been the transformation between activity and stability of extensively distributed wind-blown sand dunes. The relations between the dynamics of the aeolian landscape and its drivers are not yet completely understood, however. Evidence of aeolian sand deposition during the Last Glacial Maximum (LGM) is scarce in many mid-latitude dune fields, whereas abundant evidence exists for aeolian sand accumulation during the deglaciation, i.e. after about 15 ka. Whether this contrast actually reflects changes in dune activity is still unclear, making paleoclimatic interpretation uncertain. Comprehensive field investigation and luminescence dating in the Mu Us dune field, north-central China, demonstrates that aeolian sands deposited during the LGM are preserved as fills in periglacial sand wedges and beneath loess deposits near the downwind dune field margin. The scarcity of LGM dune sand elsewhere in the dune field is interpreted as the result of intensive aeolian activity without substantial net sand accumulation. Increasing sand accumulation after 15 ka, reflected by much more extensive preservation, signals a change in sand supply relative to sand transportation through the dune field. Reduced wind strength and other environmental changes including regional permafrost degradation after 15 ka transformed the dune field state from net erosion to net accumulation; the dunes, however, remained largely mobile as they were in the LGM. Similar diverging patterns of dune sand accumulation and preservation before and after 15 ka in many mid-latitude dune fields imply broad climatic controls linked to the changes in high-northern-latitude forcing.

  11. Modeling glacial climates

    NASA Technical Reports Server (NTRS)

    North, G. R.; Crowley, T. J.

    1984-01-01

    Mathematical climate modelling has matured as a discipline to the point that it is useful in paleoclimatology. As an example a new two dimensional energy balance model is described and applied to several problems of current interest. The model includes the seasonal cycle and the detailed land-sea geographical distribution. By examining the changes in the seasonal cycle when external perturbations are forced upon the climate system it is possible to construct hypotheses about the origin of midlatitude ice sheets and polar ice caps. In particular the model predicts a rather sudden potential for glaciation over large areas when the Earth's orbital elements are only slightly altered. Similarly, the drift of continents or the change of atmospheric carbon dioxide over geological time induces radical changes in continental ice cover. With the advance of computer technology and improved understanding of the individual components of the climate system, these ideas will be tested in far more realistic models in the near future.

  12. Human population dynamics in Europe over the Last Glacial Maximum

    PubMed Central

    Tallavaara, Miikka; Luoto, Miska; Korhonen, Natalia; Järvinen, Heikki; Seppä, Heikki

    2015-01-01

    The severe cooling and the expansion of the ice sheets during the Last Glacial Maximum (LGM), 27,000–19,000 y ago (27–19 ky ago) had a major impact on plant and animal populations, including humans. Changes in human population size and range have affected our genetic evolution, and recent modeling efforts have reaffirmed the importance of population dynamics in cultural and linguistic evolution, as well. However, in the absence of historical records, estimating past population levels has remained difficult. Here we show that it is possible to model spatially explicit human population dynamics from the pre-LGM at 30 ky ago through the LGM to the Late Glacial in Europe by using climate envelope modeling tools and modern ethnographic datasets to construct a population calibration model. The simulated range and size of the human population correspond significantly with spatiotemporal patterns in the archaeological data, suggesting that climate was a major driver of population dynamics 30–13 ky ago. The simulated population size declined from about 330,000 people at 30 ky ago to a minimum of 130,000 people at 23 ky ago. The Late Glacial population growth was fastest during Greenland interstadial 1, and by 13 ky ago, there were almost 410,000 people in Europe. Even during the coldest part of the LGM, the climatically suitable area for human habitation remained unfragmented and covered 36% of Europe. PMID:26100880

  13. Human population dynamics in Europe over the Last Glacial Maximum.

    PubMed

    Tallavaara, Miikka; Luoto, Miska; Korhonen, Natalia; Järvinen, Heikki; Seppä, Heikki

    2015-07-07

    The severe cooling and the expansion of the ice sheets during the Last Glacial Maximum (LGM), 27,000-19,000 y ago (27-19 ky ago) had a major impact on plant and animal populations, including humans. Changes in human population size and range have affected our genetic evolution, and recent modeling efforts have reaffirmed the importance of population dynamics in cultural and linguistic evolution, as well. However, in the absence of historical records, estimating past population levels has remained difficult. Here we show that it is possible to model spatially explicit human population dynamics from the pre-LGM at 30 ky ago through the LGM to the Late Glacial in Europe by using climate envelope modeling tools and modern ethnographic datasets to construct a population calibration model. The simulated range and size of the human population correspond significantly with spatiotemporal patterns in the archaeological data, suggesting that climate was a major driver of population dynamics 30-13 ky ago. The simulated population size declined from about 330,000 people at 30 ky ago to a minimum of 130,000 people at 23 ky ago. The Late Glacial population growth was fastest during Greenland interstadial 1, and by 13 ky ago, there were almost 410,000 people in Europe. Even during the coldest part of the LGM, the climatically suitable area for human habitation remained unfragmented and covered 36% of Europe.

  14. Comparing lake and soil records to climate model simulations of hydrologic conditions across the western United States at the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Ibarra, D. E.; Maher, K.; Oster, J. L.; Egger, A. E.; Harris, C.; Horton, D. E.; Weaver, K. L.

    2012-12-01

    Motivated by the potential for dramatic future hydrologic changes, studies that investigate the transitions between Earth's different climate states have the potential to enhance our understanding of the modern climate system and potential future variability. The interval surrounding the Last Glacial Maximum (LGM) represents a period when Earth's boundary conditions, greenhouse gas concentrations and orbital parameters were substantially different than today, and thus reconstruction of climate at the LGM provides a key test for climate models. Our study synthesizes multi-proxy geochemical analyses and examines Paleoclimate Model Intercomparison Project 3 (PMIP3) simulations in an effort to reconstruct changes in the hydrologic cycle over the western United States during the LGM. To enhance the spatial coverage of lake level records, we investigated the timing and magnitude of the most recent pluvial lake cycle at Surprise Valley, California by combining the 230Th-U ages and the δ18O and δ13C of shoreline tufa deposits. This new lake record, spanning 31.2 to 4.6 ka, places lake level 180 and 100 meters above present day playa, at 13.9 ± 1.2 and 22.5 ± 4.6 ka respectively. Combined isotopic and hydrologic modeling of Lake Surprise indicates that annual evaporation may have decreased by as much as 62% (at 13.9 ka) and 20% (at 22.5 ka) during the lake highstand and the LGM. Alternatively, annual precipitation may have increased by as much as 164% and 25% during the lake highstand and the LGM, respectively. Regionally, uranium isotopic variations in dated soil opal are used to constrain net infiltration (~P-ET) along a north-south transect (34.9 to 43.2 °N) in western North America between 10 and 60 ka. Leading up to the LGM, P-ET in soils increased by about 30 to 80% in the valleys of the Great Basin and Mojave deserts, peaking between 24 to 30 ka. A comparison of lake record highstands to changes in P-ET recorded in soil opal found that increases in P-ET precede

  15. Climate change and Arctic ecosystems: 1. Vegetation changes north of 55°N between the last glacial maximum, mid-Holocene, and present

    USGS Publications Warehouse

    Bigelow, N.H.; Brubaker, L.B.; Edwards, M.E.; Harrison, S.P.; Prentice, I.C.; Anderson, P.M.; Andreev, A.A.; Bartlein, P.J.; Christensen, T.R.; Cramer, W.; Kaplan, J.O.; Lozhkin, A.V.; Matveyeva, N.V.; Murray, D.F.; McGuire, A.D.; Razzhivin, V.Y.; Ritchie, J.C.; Smith, B.; Walker, D.A.; Gajewski, K.; Wolf, V.; Holmqvist, B.H.; Igarashi, Y.; Kremenetskii, K.; Paus, A.; Pisaric, M.F.J.; Volkova, V.S.

    2003-01-01

    A unified scheme to assign pollen samples to vegetation types was used to reconstruct vegetation patterns north of 55??N at the last glacial maximum (LGM) and mid-Holocene (6000 years B.P.). The pollen data set assembled for this purpose represents a comprehensive compilation based on the work of many projects and research groups. Five tundra types (cushion forb tundra, graminoid and forb tundra, prostrate dwarf-shrub tundra, erect dwarf-shrub tundra, and low- and high-shrub tundra) were distinguished and mapped on the basis of modern pollen surface samples. The tundra-forest boundary and the distributions of boreal and temperate forest types today were realistically reconstructed. During the mid-Holocene the tundra-forest boundary was north of its present position in some regions, but the pattern of this shift was strongly asymmetrical around the pole, with the largest northward shift in central Siberia (???200 km), little change in Beringia, and a southward shift in Keewatin and Labrador (???200 km). Low- and high-shrub tundra extended farther north than today. At the LGM, forests were absent from high latitudes. Graminoid and forb tundra abutted on temperate steppe in northwestern Eurasia while prostrate dwarf-shrub, erect dwarf-shrub, and graminoid and forb tundra formed a mosaic in Beringia. Graminoid and forb tundra is restricted today and does not form a large continuous biome, but the pollen data show that it was far more extensive at the LGM, while low- and high-shrub tundra were greatly reduced, illustrating the potential for climate change to dramatically alter the relative areas occupied by different vegetation types.

  16. The Last Glacial Maximum experiment in PMIP4-CMIP6

    NASA Astrophysics Data System (ADS)

    Kageyama, Masa; Braconnot, Pascale; Abe-Ouchi, Ayako; Harrison, Sandy; Lambert, Fabrice; Peltier, W. Richard; Tarasov, Lev

    2016-04-01

    The Last Glacial Maximum (LGM), around 21,000 years ago, is a cold climate extreme. As such, it has been the focus of many studies on modelling and climate reconstruction, which have brought knowledge on the mechanisms explaining this climate, in terms of climate on the continents and of the ocean state, and in terms relationships between climate changes over land, ice sheets and oceans. It is still a challenge for climate or Earth System models to represent the amplitude of climate changes for this period, under the following forcings: - Ice sheets, which represent perturbations in land surface type, altitude and land/ocean distribution - Atmospheric composition - Astronomical parameters Feedbacks from the vegetation and dust are also known to have played a role in setting up the LGM climate but have not been accounted for in previous PMIP experiments. In this poster, we will present the experimental set-up of the PMIP4 LGM experiment, which is presently being discussed and will be finalized for March 2016. For more information and discussion of the PMIP4-CMIP6 experimental design, please visit: https://wiki.lsce.ipsl.fr/pmip3/doku.php/pmip3:cmip6:design:index

  17. North Atlantic Deep Water Production during the Last Glacial Maximum.

    PubMed

    Howe, Jacob N W; Piotrowski, Alexander M; Noble, Taryn L; Mulitza, Stefan; Chiessi, Cristiano M; Bayon, Germain

    2016-06-03

    Changes in deep ocean ventilation are commonly invoked as the primary cause of lower glacial atmospheric CO2. The water mass structure of the glacial deep Atlantic Ocean and the mechanism by which it may have sequestered carbon remain elusive. Here we present neodymium isotope measurements from cores throughout the Atlantic that reveal glacial-interglacial changes in water mass distributions. These results demonstrate the sustained production of North Atlantic Deep Water under glacial conditions, indicating that southern-sourced waters were not as spatially extensive during the Last Glacial Maximum as previously believed. We demonstrate that the depleted glacial δ(13)C values in the deep Atlantic Ocean cannot be explained solely by water mass source changes. A greater amount of respired carbon, therefore, must have been stored in the abyssal Atlantic during the Last Glacial Maximum. We infer that this was achieved by a sluggish deep overturning cell, comprised of well-mixed northern- and southern-sourced waters.

  18. Contrasting scaling properties of interglacial and glacial climates

    PubMed Central

    Shao, Zhi-Gang; Ditlevsen, Peter D.

    2016-01-01

    Understanding natural climate variability is essential for assessments of climate change. This is reflected in the scaling properties of climate records. The scaling exponents of the interglacial and the glacial climates are fundamentally different. The Holocene record is monofractal, with a scaling exponent H∼0.7. On the contrary, the glacial record is multifractal, with a significantly higher scaling exponent H∼1.2, indicating a longer persistence time and stronger nonlinearities in the glacial climate. The glacial climate is dominated by the strong multi-millennial Dansgaard–Oeschger (DO) events influencing the long-time correlation. However, by separately analysing the last glacial maximum lacking DO events, here we find the same scaling for that period as for the full glacial period. The unbroken scaling thus indicates that the DO events are part of the natural variability and not externally triggered. At glacial time scales, there is a scale break to a trivial scaling, contrasting the DO events from the similarly saw-tooth-shaped glacial cycles. PMID:26980084

  19. Contrasting scaling properties of interglacial and glacial climates.

    PubMed

    Shao, Zhi-Gang; Ditlevsen, Peter D

    2016-03-16

    Understanding natural climate variability is essential for assessments of climate change. This is reflected in the scaling properties of climate records. The scaling exponents of the interglacial and the glacial climates are fundamentally different. The Holocene record is monofractal, with a scaling exponent H∼0.7. On the contrary, the glacial record is multifractal, with a significantly higher scaling exponent H∼1.2, indicating a longer persistence time and stronger nonlinearities in the glacial climate. The glacial climate is dominated by the strong multi-millennial Dansgaard-Oeschger (DO) events influencing the long-time correlation. However, by separately analysing the last glacial maximum lacking DO events, here we find the same scaling for that period as for the full glacial period. The unbroken scaling thus indicates that the DO events are part of the natural variability and not externally triggered. At glacial time scales, there is a scale break to a trivial scaling, contrasting the DO events from the similarly saw-tooth-shaped glacial cycles.

  20. The Southern Glacial Maximum 65,000 years ago and its Unfinished Termination

    NASA Astrophysics Data System (ADS)

    Schaefer, Joerg M.; Putnam, Aaron E.; Denton, George H.; Kaplan, Michael R.; Birkel, Sean; Doughty, Alice M.; Kelley, Sam; Barrell, David J. A.; Finkel, Robert C.; Winckler, Gisela; Anderson, Robert F.; Ninneman, Ulysses S.; Barker, Stephen; Schwartz, Roseanne; Andersen, Bjorn G.; Schluechter, Christian

    2015-04-01

    Glacial maxima and their terminations provide key insights into inter-hemispheric climate dynamics and the coupling of atmosphere, surface and deep ocean, hydrology, and cryosphere, which is fundamental for evaluating the robustness of earth's climate in view of ongoing climate change. The Last Glacial Maximum (LGM, ∼26-19 ka ago) is widely seen as the global cold peak during the last glacial cycle, and its transition to the Holocene interglacial, dubbed 'Termination 1 (T1)', as the most dramatic climate reorganization during this interval. Climate records show that over the last 800 ka, ice ages peaked and terminated on average every 100 ka ('100 ka world'). However, the mechanisms pacing glacial-interglacial transitions remain controversial and in particular the hemispheric manifestations and underlying orbital to regional driving forces of glacial maxima and subsequent terminations remain poorly understood. Here we show evidence for a full glacial maximum in the Southern Hemisphere 65.1 ± 2.7 ka ago and its 'Unfinished Termination'. Our 10Be chronology combined with a model simulation demonstrates that New Zealand's glaciers reached their maximum position of the last glacial cycle during Marine Isotope Stage-4 (MIS-4). Southern ocean and greenhouse gas records indicate coeval peak glacial conditions, making the case for the Southern Glacial Maximum about halfway through the last glacial cycle and only 15 ka after the last warm period (MIS-5a). We present the hypothesis that subsequently, driven by boreal summer insolation forcing, a termination began but remained unfinished, possibly because the northern ice sheets were only moderately large and could not supply enough meltwater to the North Atlantic through Heinrich Stadial 6 to drive a full termination. Yet the Unfinished Termination left behind substantial ice on the northern continents (about 50% of the full LGM ice volume) and after another 45 ka of cooling and ice sheet growth the earth was at inter

  1. The tropical lapse rate steepened during the Last Glacial Maximum

    PubMed Central

    Loomis, Shannon E.; Russell, James M.; Verschuren, Dirk; Morrill, Carrie; De Cort, Gijs; Sinninghe Damsté, Jaap S.; Olago, Daniel; Eggermont, Hilde; Street-Perrott, F. Alayne; Kelly, Meredith A.

    2017-01-01

    The gradient of air temperature with elevation (the temperature lapse rate) in the tropics is predicted to become less steep during the coming century as surface temperature rises, enhancing the threat of warming in high-mountain environments. However, the sensitivity of the lapse rate to climate change is uncertain because of poor constraints on high-elevation temperature during past climate states. We present a 25,000-year temperature reconstruction from Mount Kenya, East Africa, which demonstrates that cooling during the Last Glacial Maximum was amplified with elevation and hence that the lapse rate was significantly steeper than today. Comparison of our data with paleoclimate simulations indicates that state-of-the-art models underestimate this lapse-rate change. Consequently, future high-elevation tropical warming may be even greater than predicted. PMID:28138544

  2. The tropical lapse rate steepened during the Last Glacial Maximum.

    PubMed

    Loomis, Shannon E; Russell, James M; Verschuren, Dirk; Morrill, Carrie; De Cort, Gijs; Sinninghe Damsté, Jaap S; Olago, Daniel; Eggermont, Hilde; Street-Perrott, F Alayne; Kelly, Meredith A

    2017-01-01

    The gradient of air temperature with elevation (the temperature lapse rate) in the tropics is predicted to become less steep during the coming century as surface temperature rises, enhancing the threat of warming in high-mountain environments. However, the sensitivity of the lapse rate to climate change is uncertain because of poor constraints on high-elevation temperature during past climate states. We present a 25,000-year temperature reconstruction from Mount Kenya, East Africa, which demonstrates that cooling during the Last Glacial Maximum was amplified with elevation and hence that the lapse rate was significantly steeper than today. Comparison of our data with paleoclimate simulations indicates that state-of-the-art models underestimate this lapse-rate change. Consequently, future high-elevation tropical warming may be even greater than predicted.

  3. Range persistence during the last glacial maximum: Carex macrocephala was not restricted to glacial refugia.

    PubMed

    King, Matthew G; Horning, Matthew E; Roalson, Eric H

    2009-10-01

    The distribution of many species inhabiting northwestern North America has been heavily influenced by the climatic changes during the late Pleistocene. Several studies have suggested that species were restricted to glacial refugia north and/or south of the continental ice sheet front. It is also hypothesized that the coast of northwestern North America could have been a prime location for glacial refugia because of the lowering of the eustatic sea level and the concomitant rise of the continental shelf because of tectonic rebound. Alternatively, some coastal species distributions and demographics may have been unaffected in the long-term by the last glacial maximum (LGM). We tested the glacial refugium hypothesis on an obligate coastal plant species, Carex macrocephala by sampling 600 individuals from 41 populations with 11 nuclear microsatellite loci and the rpL16 plastid intragenic spacer region. The microsatellite data sets suggest a low level of population differentiation with a standardized G'(ST) = 0.032 and inbreeding was high with an F = 0.969. The homogenization of the populations along the coast was supported by a principal coordinate analysis, amovas and samova analyses. Analyses using the rpL16 data set support the results of the microsatellite analyses, with a low F(ST) of 0.042. Coalescent and mismatch analyses using rpL16 suggest that C. macrocephala has not gone through a significant bottleneck within the past 100,000 years, although a much earlier population expansion was indicated by the mismatch analysis. Carex macrocephala exhibits the characteristics of metapopulation dynamics and on the basis of these results, we concluded that it was not restricted to glacial refugia during the LGM, but that it existed as a large metapopulation.

  4. Reconstruction of past climate variability and ENSO-like fluctuations in the southern Gulf of California (Alfonso Basin) since the last glacial maximum

    NASA Astrophysics Data System (ADS)

    Staines-Urías, Francisca; González-Yajimovich, Oscar; Beaufort, Luc

    2015-05-01

    Nannofossil assemblages from core MD02-2510 provide a 22 ka record of past oceanographic variability in Alfonso Basin (Gulf of California, east subtropical Pacific). In this area, environmental conditions depend on a monsoonal system heavily influenced by changes in the location of the ITCZ and nearby atmospheric pressure centers. To reconstruct nutricline depth and ENSO-like variability, two ecological indexes were calculated based on the relative abundance of the three dominant coccolith species. The late glacial period is characterized by intensified wind-driven upwelling, high primary productivity and La Niña-like conditions. An environmental shift occurs during the glacial-interglacial transition, El Niño-like conditions intensify, nutricline deepens and surface productivity declines. The late Holocene is characterized by a persistent increase in nutricline depth and dominance of El Niño-like conditions. The fluctuations in the composition of the coccolith assemblages can be related to orbital-scale fluctuations in the average position of the ITCZ. However, while the ENSO-like signal that overprints the record varies in response to orbital forcing, on suborbital time scales the relation between ENSO-like conditions and the average position of the ITCZ and the North Pacific High changes, suggesting that the development of persistent El Niño-like conditions is strongly dependent on the specific climatic background.

  5. North Atlantic Deep Water Production during the Last Glacial Maximum

    PubMed Central

    Howe, Jacob N. W.; Piotrowski, Alexander M.; Noble, Taryn L.; Mulitza, Stefan; Chiessi, Cristiano M.; Bayon, Germain

    2016-01-01

    Changes in deep ocean ventilation are commonly invoked as the primary cause of lower glacial atmospheric CO2. The water mass structure of the glacial deep Atlantic Ocean and the mechanism by which it may have sequestered carbon remain elusive. Here we present neodymium isotope measurements from cores throughout the Atlantic that reveal glacial–interglacial changes in water mass distributions. These results demonstrate the sustained production of North Atlantic Deep Water under glacial conditions, indicating that southern-sourced waters were not as spatially extensive during the Last Glacial Maximum as previously believed. We demonstrate that the depleted glacial δ13C values in the deep Atlantic Ocean cannot be explained solely by water mass source changes. A greater amount of respired carbon, therefore, must have been stored in the abyssal Atlantic during the Last Glacial Maximum. We infer that this was achieved by a sluggish deep overturning cell, comprised of well-mixed northern- and southern-sourced waters. PMID:27256826

  6. First results from IODP Expedition 325 to the Great Barrier Reef: unlocking climate and sea level secrets since the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Webster, J. M.; Yokoyama, Y.; Cotterill, C.; Expedition 325 Scientists

    2010-12-01

    ages from >30 to 9 ka. This chronology, combined with their recovered depths, clearly demonstrates that Exp. 325 recovered coral reef material from key periods of interest for sea level change and environmental reconstruction, including the Last Glacial Maximum, Heinrich Events 1 and 2, 19ka-MWP, Bølling-Allerød, MWP1A, the Younger Dryas and MWPB. The new Exp. 325 cores are especially important because few fossil coral records span these intervals, and even fewer are from stable, passive margin settings far from the confounding influences of ice sheets or tectonic activity. This paper summarizes Exp. 325’s first results and their broader implications for understanding global sea-level and paleoclimate changes, and provides a first interpretation of how these reefs responded to environmental stress.

  7. Early Circum-Arctic Glacial Decay Following the Last Glacial Maximum?

    NASA Astrophysics Data System (ADS)

    Snow, T.; Alonso-Garcia, M.; Flower, B. P.; Shevenell, A.; Roehl, U.; Goddard, E.

    2012-12-01

    Recent rapid warming, glacial retreat, and sea ice reduction observed in the Arctic suggest extreme regional environmental sensitivity to ongoing anthropogenic climate change. To place these recent environmental changes in context and better understand the forcings and feedbacks involved in Arctic climate change, regional studies of past intervals of rapid warming are required. Paleoceanographic studies from the high-latitude North Atlantic indicate close relationships between meltwater discharges from circum-Arctic ice sheets, perturbations of Atlantic Meridional Overturning Circulation (AMOC), and global climate variations on sub-orbital timescales during the Late Quaternary. During the last glacial-interglacial transition (25-10 ka), when atmospheric temperatures over Greenland warmed 10-15°C and the AMOC experienced millennial-scale variability, low-resolution stable isotope studies from Fram Strait sediment cores indicate that the circum-Arctic ice sheets began to melt earlier than lower latitude Northern Hemisphere ice sheets, discharging their meltwater into the high latitude North Atlantic. Fram Strait, located at the gateway between the Atlantic and Arctic Oceans, is the only region where Arctic meltwater can exchange with the world oceans on both glacial and interglacial timescales. Thus, high-resolution paleoceanographic studies of Fram Strait sediments are critically required for understanding changes in Arctic meltwater flux to the North Atlantic on sub-orbital timescales. Here we present the first high-resolution (<100 yr) multi-proxy dataset from Fram Strait (ODP Site 986; 77°20.43'N, 9°04.66'E; water depth: 2063 m) to assess the timing of circum-Arctic ice sheet decay since the Last Glacial Maximum. Foraminiferal isotopic and elemental, scanning X-Ray Fluorescence, and ice-rafted debris records are used to isolate Arctic meltwater and iceberg discharge signals. Sharp increases in productivity and changes in water mass ventilation are inferred

  8. Interhemispheric ice-sheet synchronicity during the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Weber, M. E.; Clark, P. U.; Ricken, W.; Mitrovica, J. X.; Hostetler, S. W.; Kuhn, G.

    2012-04-01

    The timing of the last maximum extent of the Antarctic ice sheets relative to those in the Northern Hemisphere remains poorly understood because only a few findings with robust chronologies exist for Antarctic ice sheets. We developed a chronology for the Weddell Sea sector of the East Antarctic ice sheet that, combined with ages from other Antarctic ice-sheet sectors, indicates the advance to their maximum extent at 29 -28 ka, and retreat from their maximum extent at 19 ka was nearly synchronous with Northern Hemisphere ice sheets (Weber, M.E., Clark, P. U., Ricken, W., Mitrovica, J. X., Hostetler, S. W., and Kuhn, G. (2011): Interhemispheric ice-sheet synchronicity during the Last Glacial Maximum. - Science, 334, 1265-1269, doi: 10.1126:science.1209299). As for the deglaciation, modeling studies suggest a late ice-sheet retreat starting around 14 ka BP and ending around 7 ka BP with a large impact of an unstable West Antarctic Ice Sheet (WAIS) and a small impact of a stable East Antarctic Ice Sheet (EAIS). However, the Weddell Sea sites studied here, as well as sites from the Scotia Sea, provide evidence that specifically the EAIS responded much earlier, possibly provided a significant contribution to the last sea-level rise, and was much more dynamic than previously thought. Using the results of an atmospheric general circulation we conclude that surface climate forcing of Antarctic ice mass balance would likely cause an opposite response, whereby a warming climate would increase accumulation but not surface melting. Furthermore, our new data support teleconnections involving a sea-level fingerprint forced from Northern Hemisphere ice sheets as indicated by gravitational modeling. Also, changes in North Atlantic Deepwater formation and attendant heat flux to Antarctic grounding lines may have contributed to synchronizing the hemispheric ice sheets.

  9. Early local last glacial maximum in the tropical Andes.

    PubMed

    Smith, Jacqueline A; Seltzer, Geoffrey O; Farber, Daniel L; Rodbell, Donald T; Finkel, Robert C

    2005-04-29

    The local last glacial maximum in the tropical Andes was earlier and less extensive than previously thought, based on 106 cosmogenic ages (from beryllium-10 dating) from moraines in Peru and Bolivia. Glaciers reached their greatest extent in the last glacial cycle approximately 34,000 years before the present and were retreating by approximately 21,000 years before the present, implying that tropical controls on ice volumes were asynchronous with those in the Northern Hemisphere. Our estimates of snowline depression reflect about half the temperature change indicated by previous widely cited figures, which helps resolve the discrepancy between estimates of terrestrial and marine temperature depression during the last glacial cycle.

  10. Glacial history of Tranquilo glacier (Central Patagonia) since the Last Glacial Maximum through to the present.

    NASA Astrophysics Data System (ADS)

    Sagredo, E. A.; Araya, P. S.; Schaefer, J. M.; Kaplan, M. R.; Kelly, M. A.; Lowell, T. V.; Aravena, J. C.

    2014-12-01

    Deciphering the timing and the inter-hemispheric phasing of former glacial fluctuations is critical for understanding the mechanisms and climate signals underlying these glacial events. Here, we present a detailed chronology of glacial fluctuations for Río Tranquilo glacier (47°S), since the LGM, including up to the present. Río Tranquilo is a small glacial valley located on the northern flank of Monte San Lorenzo, an isolated granitic massif, ~70 km to the east of the southern limit of the Northern Patagonian Icefield. Although Mt. San Lorenzo is located on the leeward side of the Andes, it is one of the most glacierized mountains in the region, with an ice surface area of ~140 km2. Geomorphic evidence suggests that during past episodes of climate change several small glaciers that today occupy the headwalls of Río Tranquilo valley expanded and coalesced, depositing a series of moraines complexes along the flanks and bottom of the valley. We used two independent dating techniques to constrain the age of the glacial history of the area. 10Be surface exposure ages from boulders located atop moraine ridges reveal that Río Tranquilo valley underwent glacial expansion/stabilization during at least the LGM (late LGM?), Late glacial (ACR and Younger Dryas) and Mid-Holocene. Within the Mid-Holocene limits, tree-ring based chronology indicates that Río Tranquilo glacier expanded during the Late Holocene as well. Our results are the first detailed chronology of glacial fluctuations from a single valley glacier, spanning the entire period from the (end of the) LGM up to the present, in southern South America. By identifying different glacial episodes within a single alpine valley, this study provides baseline data for studying the relative magnitude of the climate events responsible for these glacial events.

  11. Constraints on the magnitude and patterns of ocean cooling at the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Margo Project Members; Waelbroeck, C.; Paul, A.; Kucera, M.; Rosell-Melé, A.; Weinelt, M.; Schneider, R.; Mix, A. C.; Abelmann, A.; Armand, L.; Bard, E.; Barker, S.; Barrows, T. T.; Benway, H.; Cacho, I.; Chen, M.-T.; Cortijo, E.; Crosta, X.; de Vernal, A.; Dokken, T.; Duprat, J.; Elderfield, H.; Eynaud, F.; Gersonde, R.; Hayes, A.; Henry, M.; Hillaire-Marcel, C.; Huang, C.-C.; Jansen, E.; Juggins, S.; Kallel, N.; Kiefer, T.; Kienast, M.; Labeyrie, L.; Leclaire, H.; Londeix, L.; Mangin, S.; Matthiessen, J.; Marret, F.; Meland, M.; Morey, A. E.; Mulitza, S.; Pflaumann, U.; Pisias, N. G.; Radi, T.; Rochon, A.; Rohling, E. J.; Sbaffi, L.; Schäfer-Neth, C.; Solignac, S.; Spero, H.; Tachikawa, K.; Turon, J.-L.

    2009-02-01

    Observation-based reconstructions of sea surface temperature from relatively stable periods in the past, such as the Last Glacial Maximum, represent an important means of constraining climate sensitivity and evaluating model simulations. The first quantitative global reconstruction of sea surface temperatures during the Last Glacial Maximum was developed by the Climate Long-Range Investigation, Mapping and Prediction (CLIMAP) project in the 1970s and 1980s (refs 2, 3). Since that time, several shortcomings of that earlier effort have become apparent. Here we present an updated synthesis of sea surface temperatures during the Last Glacial Maximum, rigorously defined as the period between 23 and 19 thousand years before present, from the Multiproxy Approach for the Reconstruction of the Glacial Ocean Surface (MARGO) project. We integrate microfossil and geochemical reconstructions of surface temperatures and include assessments of the reliability of individual records. Our reconstruction reveals the presence of large longitudinal gradients in sea surface temperature in all of the ocean basins, in contrast to the simulations of the Last Glacial Maximum climate available at present.

  12. The early rise and late demise of New Zealand’s last glacial maximum

    PubMed Central

    Rother, Henrik; Fink, David; Shulmeister, James; Mifsud, Charles; Evans, Michael; Pugh, Jeremy

    2014-01-01

    Recent debate on records of southern midlatitude glaciation has focused on reconstructing glacier dynamics during the last glacial termination, with different results supporting both in-phase and out-of-phase correlations with Northern Hemisphere glacial signals. A continuing major weakness in this debate is the lack of robust data, particularly from the early and maximum phase of southern midlatitude glaciation (∼30–20 ka), to verify the competing models. Here we present a suite of 58 cosmogenic exposure ages from 17 last-glacial ice limits in the Rangitata Valley of New Zealand, capturing an extensive record of glacial oscillations between 28–16 ka. The sequence shows that the local last glacial maximum in this region occurred shortly before 28 ka, followed by several successively less extensive ice readvances between 26–19 ka. The onset of Termination 1 and the ensuing glacial retreat is preserved in exceptional detail through numerous recessional moraines, indicating that ice retreat between 19–16 ka was very gradual. Extensive valley glaciers survived in the Rangitata catchment until at least 15.8 ka. These findings preclude the previously inferred rapid climate-driven ice retreat in the Southern Alps after the onset of Termination 1. Our record documents an early last glacial maximum, an overall trend of diminishing ice volume in New Zealand between 28–20 ka, and gradual deglaciation until at least 15 ka. PMID:25071171

  13. The early rise and late demise of New Zealand's last glacial maximum.

    PubMed

    Rother, Henrik; Fink, David; Shulmeister, James; Mifsud, Charles; Evans, Michael; Pugh, Jeremy

    2014-08-12

    Recent debate on records of southern midlatitude glaciation has focused on reconstructing glacier dynamics during the last glacial termination, with different results supporting both in-phase and out-of-phase correlations with Northern Hemisphere glacial signals. A continuing major weakness in this debate is the lack of robust data, particularly from the early and maximum phase of southern midlatitude glaciation (∼30-20 ka), to verify the competing models. Here we present a suite of 58 cosmogenic exposure ages from 17 last-glacial ice limits in the Rangitata Valley of New Zealand, capturing an extensive record of glacial oscillations between 28-16 ka. The sequence shows that the local last glacial maximum in this region occurred shortly before 28 ka, followed by several successively less extensive ice readvances between 26-19 ka. The onset of Termination 1 and the ensuing glacial retreat is preserved in exceptional detail through numerous recessional moraines, indicating that ice retreat between 19-16 ka was very gradual. Extensive valley glaciers survived in the Rangitata catchment until at least 15.8 ka. These findings preclude the previously inferred rapid climate-driven ice retreat in the Southern Alps after the onset of Termination 1. Our record documents an early last glacial maximum, an overall trend of diminishing ice volume in New Zealand between 28-20 ka, and gradual deglaciation until at least 15 ka.

  14. Glacial onset predated Late Ordovician climate cooling

    NASA Astrophysics Data System (ADS)

    Pohl, Alexandre; Donnadieu, Yannick; Le Hir, Guillaume; Ladant, Jean-Baptiste; Dumas, Christophe; Alvarez-Solas, Jorge; Vandenbroucke, Thijs R. A.

    2016-06-01

    The Ordovician glaciation represents the acme of one of only three major icehouse periods in Earth's Phanerozoic history and is notorious for setting the scene for one of the "big five" mass extinction events. Nevertheless, the mechanisms that drove ice sheet growth remain poorly understood and the final extent of the ice sheet crudely constrained. Here using an Earth system model with an innovative coupling method between ocean, atmosphere, and land ice accounting for climate and ice sheet feedback processes, we report simulations portraying for the first time the detailed evolution of the Ordovician ice sheet. We show that the emergence of the ice sheet happened in two discrete phases. In a counterintuitive sequence of events, the continental ice sheet appeared suddenly in a warm climate. Only during the second act, and set against a background of decreasing atmospheric CO2, followed steeply dropping temperatures and extending sea ice. The comparison with abundant sedimentological, geochemical, and micropaleontological data suggests that glacial onset may have occurred as early as the Middle Ordovician Darriwilian, in agreement with recent studies reporting third-order glacioeustatic cycles during the same period. The second step in ice sheet growth, typified by a sudden drop in tropical sea surface temperatures by ˜8°C and the further extension of a single, continental-scale ice sheet over Gondwana, marked the onset of the Hirnantian glacial maximum. By suggesting the presence of an ice sheet over Gondwana throughout most of the Middle and Late Ordovician, our models embrace the emerging paradigm of an "early Paleozoic Ice Age."

  15. The Antarctic Circumpolar Current during the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Lynch-Stieglitz, J.; Ito, T.

    2014-12-01

    The circulation and climate of the modern Southern Ocean is dominated by the Antarctic Circumpolar Current (ACC) and associated frontal structures that separate the cold, nutrient-rich Antarctic water masses from the subantarctic and subtropical waters of northern basins. The structure in seawater density across the ACC puts strong constraints on the intensity of the eastward flow. Here we investigate the density structure across the ACC during the Last Glacial Maximum (LGM). We explore the relationship between the lateral density contrast across the ACC and the vertical density stratification north of the ACC in General Circulation Models (GCMs). We employ a compilation of paleoceanographic constraints from the literature, including the oxygen isotopic composition of benthic foraminifera and the chlorinity and oxygen isotopic composition of pore waters in order to reconstruct these vertical and lateral density contrasts south of Australia during the LGM. We infer that the density contrast across the ACC is slightly reduced relative today's. While some model simulations produce a density stratification and ACC much stronger than today's during the LGM, we find the bulk of the paleoceanographic data do not support such a scenario.

  16. Speleothem Paleoclimatology of the Last Glacial Maximum and Deglaciation in Yucatan, Mexico

    NASA Astrophysics Data System (ADS)

    Gentry, C. L.; Hodell, D. A.; Curtis, J. H.; Brenner, M.; Gallup, C.; Endsley, E.

    2006-12-01

    Two speleothems were collected in August 2005 from Columnas Cave near Tzucacab, Yucatan, Mexico. Both stalagmites have basal ages placing the initial growth during the Last Glacial Maximum (LGM). The first sample, Hobo 3, has a basal U/Th age of 21,089 +/- 221 years and the second sample, Hobo 4, has a basal U/Th age of 21,823 +/- 261 years. Oxygen isotopes were measured on calcite samples drilled every 0.5mm along the growth axis of these speleothems. Oxygen isotope values are relatively low at the base of both Hobo 3 and 4 during the LGM, and increase during the period inferred to represent the Late Glacial. Lower oxygen isotopic values during the LGM suggest a cold, wet climate in Yucatan followed by more arid conditions during the Late Glacial. This interpretation is consistent with recent findings from sediment cores from Lake Peten Itza, Guatemala (Hodell et al., 2006). We speculate that a cold, wet LGM may have been caused by increased winter precipitation related to polar outbreaks and "Norte" winds, which bring rain to Yucatan today during the dry season. Arid conditions during the Late Glacial may coincide with delivery of glacial meltwater to the Gulf of Mexico via the Mississippi River. Although additional U/Th dates are needed to constrain the chronology, our preliminary results suggest that Hobo 3 and 4 stalagmites will provide a detailed history of climate change for the northern Yucatan Peninsula during the last glacial cycle.

  17. Paleodust variability since the Last Glacial Maximum and implications for iron inputs to the ocean

    NASA Astrophysics Data System (ADS)

    Albani, S.; Mahowald, N. M.; Murphy, L. N.; Raiswell, R.; Moore, J. K.; Anderson, R. F.; McGee, D.; Bradtmiller, L. I.; Delmonte, B.; Hesse, P. P.; Mayewski, P. A.

    2016-04-01

    Changing climate conditions affect dust emissions and the global dust cycle, which in turn affects climate and biogeochemistry. In this study we use observationally constrained model reconstructions of the global dust cycle since the Last Glacial Maximum, combined with different simplified assumptions of atmospheric and sea ice processing of dust-borne iron, to provide estimates of soluble iron deposition to the oceans. For different climate conditions, we discuss uncertainties in model-based estimates of atmospheric processing and dust deposition to key oceanic regions, highlighting the large degree of uncertainty of this important variable for ocean biogeochemistry and the global carbon cycle. We also show the role of sea ice acting as a time buffer and processing agent, which results in a delayed and pulse-like soluble iron release into the ocean during the melting season, with monthly peaks up to ~17 Gg/month released into the Southern Oceans during the Last Glacial Maximum (LGM).

  18. Obliquity Control On Southern Hemisphere Climate During The Last Glacial

    PubMed Central

    Fogwill, C.J.; Turney, C.S.M.; Hutchinson, D.K.; Taschetto, A.S.; England, M.H.

    2015-01-01

    Recent paleoclimate reconstructions have challenged the traditional view that Northern Hemisphere insolation and associated feedbacks drove synchronous global climate and ice-sheet volume during the last glacial cycle. Here we focus on the response of the Patagonian Ice Sheet, and demonstrate that its maximum expansion culminated at 28,400 ± 500 years before present (28.4 ± 0.5 ka), more than 5,000 years before the minima in 65°N summer insolation and the formally-defined Last Glacial Maximum (LGM) at 21,000 ± 2,000 years before present. To investigate the potential drivers of this early LGM (eLGM), we simulate the effects of orbital changes using a suite of climate models incorporating prescribed and evolving sea-ice anomalies. Our analyses suggest that Antarctic sea-ice expansion at 28.5 ka altered the location and intensity of the Southern Hemisphere storm track, triggering regional cooling over Patagonia of 5°C that extends across the wider mid-southern latitudes. In contrast, at the LGM, continued sea-ice expansion reduced regional temperature and precipitation further, effectively starving the ice sheet and resulting in reduced glacial expansion. Our findings highlight the dominant role that orbital changes can play in driving Southern Hemisphere glacial climate via the sensitivity of mid-latitude regions to changes in Antarctic sea-ice extent. PMID:26115344

  19. Obliquity Control On Southern Hemisphere Climate During The Last Glacial.

    PubMed

    Fogwill, C J; Turney, C S M; Hutchinson, D K; Taschetto, A S; England, M H

    2015-06-26

    Recent paleoclimate reconstructions have challenged the traditional view that Northern Hemisphere insolation and associated feedbacks drove synchronous global climate and ice-sheet volume during the last glacial cycle. Here we focus on the response of the Patagonian Ice Sheet, and demonstrate that its maximum expansion culminated at 28,400 ± 500 years before present (28.4 ± 0.5 ka), more than 5,000 years before the minima in 65 °N summer insolation and the formally-defined Last Glacial Maximum (LGM) at 21,000 ± 2,000 years before present. To investigate the potential drivers of this early LGM (eLGM), we simulate the effects of orbital changes using a suite of climate models incorporating prescribed and evolving sea-ice anomalies. Our analyses suggest that Antarctic sea-ice expansion at 28.5 ka altered the location and intensity of the Southern Hemisphere storm track, triggering regional cooling over Patagonia of 5 °C that extends across the wider mid-southern latitudes. In contrast, at the LGM, continued sea-ice expansion reduced regional temperature and precipitation further, effectively starving the ice sheet and resulting in reduced glacial expansion. Our findings highlight the dominant role that orbital changes can play in driving Southern Hemisphere glacial climate via the sensitivity of mid-latitude regions to changes in Antarctic sea-ice extent.

  20. Ocean Cooling Pattern at the Last Glacial Maximum

    DOE PAGES

    Zhuang, Kelin; Giardino, John R.

    2012-01-01

    Ocean temperature and ocean heat content change are analyzed based on four PMIP3 model results at the Last Glacial Maximum relative to the prehistorical run. Ocean cooling mostly occurs in the upper 1000 m depth and varies spatially in the tropical and temperate zones. The Atlantic Ocean experiences greater cooling than the rest of the ocean basins. Ocean cooling is closely related to the weakening of meridional overturning circulation and enhanced intrusion of Antarctic Bottom Water into the North Atlantic.

  1. Meltwater input to the southern ocean during the last glacial maximum

    SciTech Connect

    Shemesh, A.; Burckle, L.H.; Hays, J.D.

    1994-12-02

    Three records of oxygen isotopes in biogenic silica from deep-sea sediment cores from the Atlantic and Indian sectors of the Southern Ocean reveal the presence of isotopically depleted diatomaceous opal in sediment from the last glacial maximum. This depletion is attributed to the presence of lids of meltwater that mixed with surface water along certain trajectories in the Southern Ocean. An increase in the drainage from Antarctica or extensive northward transport of icebergs are among the main mechanisms that could have produced the increase in meltwater input to the glacial Southern Ocean. Similar isotopic trends were observed in older climatic cycles at the same cores.

  2. Glacial climate in the tropics

    SciTech Connect

    Broecker, W.

    1996-06-28

    New findings have caused ideas about the Earth`s climate during the Pleistocene glaciation to change. A consensus seems to be forming that during times of glaciation, climatic conditions in the tropics were quite different from those today. However still to be explained is why strontium-calcium measurements on corals and moble gas measurements of ground water suggest a tropical cooling of 4-6 C while foraminiferal speciation, oxygen isotope, and alkenone results suggest a cooling of no more than 3 C. This article discusses different aspects of the debate. 9 refs., 1 fig.

  3. Reconstruction of North American drainage basins and river discharge since the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Wickert, Andrew D.

    2016-11-01

    Over the last glacial cycle, ice sheets and the resultant glacial isostatic adjustment (GIA) rearranged river systems. As these riverine threads that tied the ice sheets to the sea were stretched, severed, and restructured, they also shrank and swelled with the pulse of meltwater inputs and time-varying drainage basin areas, and sometimes delivered enough meltwater to the oceans in the right places to influence global climate. Here I present a general method to compute past river flow paths, drainage basin geometries, and river discharges, by combining models of past ice sheets, glacial isostatic adjustment, and climate. The result is a time series of synthetic paleohydrographs and drainage basin maps from the Last Glacial Maximum to present for nine major drainage basins - the Mississippi, Rio Grande, Colorado, Columbia, Mackenzie, Hudson Bay, Saint Lawrence, Hudson, and Susquehanna/Chesapeake Bay. These are based on five published reconstructions of the North American ice sheets. I compare these maps with drainage reconstructions and discharge histories based on a review of observational evidence, including river deposits and terraces, isotopic records, mineral provenance markers, glacial moraine histories, and evidence of ice stream and tunnel valley flow directions. The sharp boundaries of the reconstructed past drainage basins complement the flexurally smoothed GIA signal that is more often used to validate ice-sheet reconstructions, and provide a complementary framework to reduce nonuniqueness in model reconstructions of the North American ice-sheet complex.

  4. Changing amounts and sources of moisture in the U.S. southwest since the Last Glacial Maximum in response to global climate change

    NASA Astrophysics Data System (ADS)

    Feng, Weimin; Hardt, Benjamin F.; Banner, Jay L.; Meyer, Kevin J.; James, Eric W.; Musgrove, MaryLynn; Edwards, R. Lawrence; Cheng, Hai; Min, Angela

    2014-09-01

    The U.S. southwest has a limited water supply and is predicted to become drier in the 21st century. An improved understanding of factors controlling moisture sources and availability is aided by reconstruction of past responses to global climate change. New stable isotope and growth-rate records for a central Texas speleothem indicate a strong influence of Gulf of Mexico (GoM) moisture and increased precipitation from 15.5 to 13.5 ka, which includes the majority of the Bølling-Allerød warming (BA: 14.7-12.9 ka). Coeval speleothem records from 900 and 1200 km to the west allow reconstruction of regional moisture sources and atmospheric circulation. The combined isotope and growth-rate time series indicates 1) increased GoM moisture input during the majority of the BA, producing greater precipitation in Texas and New Mexico; and 2) a retreat of GoM moisture during Younger Dryas cooling (12.9-11.5 ka), reducing precipitation. These results portray how late-Pleistocene atmospheric circulation and moisture distribution in this region responded to global changes, providing information to improve models of future climate.

  5. Changing amounts and sources of moisture in the U.S. southwest since the Last Glacial Maximum in response to global climate change

    USGS Publications Warehouse

    Feng, Weimin; Hardt, Benjamin F.; Banner, Jay L.; Meyer, Kevin J.; James, Eric W.; Musgrove, MaryLynn; Edwards, R. Lawrence; Cheng, Hai; Min, Angela

    2014-01-01

    The U.S. southwest has a limited water supply and is predicted to become drier in the 21st century. An improved understanding of factors controlling moisture sources and availability is aided by reconstruction of past responses to global climate change. New stable isotope and growth-rate records for a central Texas speleothem indicate a strong influence of Gulf of Mexico (GoM) moisture and increased precipitation from 15.5 to 13.5 ka, which includes the majority of the Bølling–Allerød warming (BA: 14.7–12.9 ka). Coeval speleothem records from 900 and 1200 km to the west allow reconstruction of regional moisture sources and atmospheric circulation. The combined isotope and growth-rate time series indicates 1) increased GoM moisture input during the majority of the BA, producing greater precipitation in Texas and New Mexico; and 2) a retreat of GoM moisture during Younger Dryas cooling (12.9–11.5 ka), reducing precipitation. These results portray how late-Pleistocene atmospheric circulation and moisture distribution in this region responded to global changes, providing information to improve models of future climate.

  6. The glaciers of Sierra Segundera (Zamora, NW Spain) during their Maximum Ice Extent: area, volume, Glacial Equilibrium Line Altitude and paleo-climatic implications

    NASA Astrophysics Data System (ADS)

    María Fernández, Jose; Ubeda, Jose; Palacios, David

    2015-04-01

    The aim of this paper is to reconstruct the Quaternary glaciers which formed the eastern sector of the Sierra Segundera ice-cap (NW Iberian Peninsula) during its Maximum Ice Extent (MIE) local phase (33 ka) in a surface area of 165 km2, to estimate the ice volumes and Equilibrium Line Altitudes (ELAs). The study area presents a wide altimetric range of approx. 1200 m, from the Tera glacier front to the Peña Trevinca (42°14'33'' N, 6°47'46'' W; 2127 m) and Peña Negra (42°14'58'' N, 6°47'39'' W; 2121 m) horns, covering a wide plateau at an altitude of over 1700 m. The reconstruction of the MIE paleoglaciers used a combination of various tools: a rheological numerical model which describes the ice flow, GIS and geomorphological field work to validate the results. The model used here allowed the reconstruction of the surface topography of the paleoglacial ice, even though there is no existing geomorphologic evidence to reveal the thickness of the ice at that time. The GIS enabled the creation of Digital Elevation Models (DEMs) and the estimation of thicknesses and volumes. The reconstructed topography and the delimitation of the geomorphologic features were used to estimate the ELA using the following methods: Area x Altitude Balance Ratio (AABR), Accumulation Area Ratio (AAR), Terminus Headwall Altitude Ratio (THAR) and Maximum Elevation of Lateral Moraines (MELM). The DEM reconstructed for the surface of the paleoglaciers obtained an estimated maximum ice thickness of over 450 m during the MIE, and a total ice volume of 2.63 x 10(10)m3 for the eastern half of the ice-cap. When estimating the paleo-ELAs, the AABR and AAR methods obtain more logical values. The AABR method obtains BR=1, which questions the BR=2 assumed as representative for medium latitude glaciers with oceanic influence; the paleo-ELA AABR was 1739 m. Applying the AAR method with the ratio 0.65 gives the result 1735 m. The THAR and MELM methods give values of 1637 m and 1651 m respectively for

  7. North Pacific atmospheric rivers and their influence on western North America at the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

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

    2017-01-01

    Southwestern North America was wetter than present during the Last Glacial Maximum. The causes of increased water availability have been recently debated, and quantitative precipitation reconstructions have been underutilized in model-data comparisons. We investigate the climatological response of North Pacific atmospheric rivers to the glacial climate using model simulations and paleoclimate reconstructions. Atmospheric moisture transport due to these features shifted toward the southeast relative to modern. Enhanced southwesterly moisture delivery between Hawaii and California increased precipitation in the southwest while decreasing it in the Pacific Northwest, in agreement with reconstructions. Coupled climate models that are best able to reproduce reconstructed precipitation changes simulate decreases in sea level pressure across the eastern North Pacific and show the strongest southeastward shifts of moisture transport relative to a modern climate. Precipitation increases of ˜1 mm d-1, due largely to atmospheric rivers, are of the right magnitude to account for reconstructed pluvial conditions in parts of southwestern North America during the Last Glacial Maximum.

  8. Last Glacial Maximum and deglaciation of the Iberian Central System.

    NASA Astrophysics Data System (ADS)

    Palacios, D.; Andrés, N.; Vieira, G.; Marcos, J.; Vázquez-Selem, L.

    2012-04-01

    The Central System runs E-W across the centre of the Iberian Peninsula and is composed mainly of crystalline rocks. A glacial morphology is well preserved on many of its most important summit areas especially towards the Atlantic. Research has recently been carried out in three of the sierras of this mountain system, with the aim of establishing the absolute chronology of the maximum glacial advance and of the deglaciation in the whole system. The method used is cosmogenic 36Cl surface exposure dating of moraine boulders and glacially polished outcrops. The selected areas are the Sierra de Guadarrama (Palacios et al. 2012) close to Peñalara Peak (40°51'N, 3°57'W; 2428 m), the Sierra de Gredos (Palacios et al. 2011) close to Almanzor Peak (40°14'N, 5°17'W; 2592 m), and the Sierra de la Estrela (Vieira and Palacios, 2010) close to Alto de la Torre summit (40°20'N, 7°34'W; 1993 m). These areas are representative of the whole Central System from west to east. The results are highly homogeneous. Moraines dating from earlier than the last glaciation were not found in any of the sierras. On the contrary, in all cases the oldest moraines from the last glaciation rest on intensely weathered crystalline surfaces. The oldest moraines date from between 31 and 26 ka. In most cases, the deposition of these moraine ridges was followed by minor advances and retreats which left a sequence of ridges very close together, lasting until 18-16 ka. A fast retreat occurred after 16-15 ka, when glaciers completely abandoned the valleys, disappearing in most cases by 13-14 ka. The ice lasted until 11-10 ka, but only in small cirques found on sheltered rock-walls below the highest peaks.

  9. Paleoecology of central Kentucky since the last glacial maximum

    NASA Astrophysics Data System (ADS)

    Wilkins, Gary R.; Delcourt, Paul A.; Delcourt, Hazel R.; Harrison, Frederick W.; Turner, Manson R.

    1991-09-01

    Pollen grains and spores, plant macrofossils, and sponge spicules from a 7.2-m sediment core from Jackson Pond dating back to 20,000 yr B.P. are the basis for new interpretations of vegetational, limnological, and climatic changes in central Kentucky. During the full-glacial interval (20,400 to 16,800 yr B.P.) upland vegetation was closed spruce forest with jack pine as a subdominant. Aquatic macrophyte and sponge assemblages indicate that the site was a relatively deep, open pond with low organic productivity. During late-glacial time (16,800 to 11,300 yr B.P.) spruce populations continued to dominate while jack pine declined and sedge increased as the vegetation became a more open, taiga-like boreal woodland. Between 11,300 and 10,000 yr B.P., abundances of spruce and oak pollen oscillated reciprocally, possibly reflecting the Younger Dryas oscillation as boreal taxa underwent a series of declines and increases at the southern limit of their ranges before becoming extirpated and replaced by deciduous forest. In the early Holocene (10,000 to 7300 yr B.P.) a mesic deciduous woodland developed; it was replaced by xeric oak-hickory forest during the middle Holocene between 7300 and 3900 yr B.P. Grass increased after 3900 yr B.P., indicating that the presettlement vegetation mosaic of mixed deciduous forest and prairie (the "Kentucky Barrens") became established in central Kentucky after the Hypsithermal interval. Sponge spicules increased in number during the Holocene, reflecting reduced water depths in the pond. Sediment infilling, as well as climatic warming and the expansion of fringing shrub thickets, increased nutrient and habitat availability for freshwater sponges.

  10. Interannual physiological responses of glacial trees to changes in atmospheric [CO2] since the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Gerhart, L. M.; Harris, J. M.; Ward, J. K.

    2009-12-01

    During the Last Glacial Maximum, atmospheric [CO2] were as low as 180 ppm and have currently risen to a modern value of 385 ppm as a result of fossil fuel combustion and deforestation. In order to understand how changing [CO2] influenced the physiology of trees over the last 50,000 years, we analyzed carbon isotope ratios of individual tree rings from juniper wood specimens from the Rancho La Brea tar pits in southern California and kauri wood specimens from peat bogs in New Zealand (North Island). Modern trees from different altitudes were compared to account for changes in precipitation and temperature through time in order to isolate the effects of changing [CO2]. We hypothesized that over the last 50,000 years, the ratio of ci (intracellular [CO2]) to ca (atmospheric [CO2]) would be maintained within each species. Consequently, ci values would be significantly lower in glacial trees due to lower ca levels during the LGM. In addition, we hypothesized that low [CO2] (which does not vary between years during the LGM) dominated tree physiology during the LGM as evidenced by low levels of inter-annual variation in ci/ca ratios relative to modern trees (which are known to respond to high frequency variation in water and temperature between years). In both kauri and juniper trees, mean ci/ca values remained constant throughout 50,000 years despite major climatic and [CO2] changes, indicating that there is a long-term physiological set point in these species. Limitations on the ci values of glacial junipers suggest that 90 ppm CO2 represents a survival compensation point for this species. In addition, glacial trees showed very low inter-annual variation in ci/ca values compared to modern trees. This suggests that glacial tree physiology may have been dominated by low CO2 that was constant between years, whereas modern trees may be dominated by climatic factors that vary substantially between years. Consequently, while each species maintained mean ci/ca values over time

  11. Reconstruction of the glacial maximum recorded in the central Cantabrian Mountains (N Iberia)

    NASA Astrophysics Data System (ADS)

    Rodríguez-Rodríguez, Laura; Jiménez-Sánchez, Montserrat; José Domínguez-Cuesta, María

    2014-05-01

    The Cantabrian Mountains is a coastal range up to 2648 m altitude trending parallel to northern Iberian Peninsula edge at a maximum distance of 100 km inland (~43oN 5oW). Glacial sediments and landforms are generally well-preserved at altitudes higher than 1600 m, evidencing the occurrence of former glaciations. Previous research supports a regional glacial maximum prior to ca 38 cal ka BP and an advanced state of deglaciation by the time of the global Last Glacial Maximum (Jiménez-Sánchez et al., 2013). A geomorphological database has been produced in ArcGIS (1:25,000 scale) for an area about 800 km2 that partially covers the Redes Natural Reservation and Picos de Europa Regional Park. A reconstruction of the ice extent and flow pattern of the former glaciers is presented for this area, showing that an ice field was developed on the study area during the local glacial maximum. The maximum length of the ice tongues that drained this icefield was remarkably asymmetric between both slopes, recording 1 to 6 km-long in the northern slope and up to 19 km-long in southern one. The altitude difference between the glacier fronts of both mountain slopes was ca 100 m. This asymmetric character of the ice tongues is related to geologic and topo-climatic factors. Jiménez-Sánchez, M., Rodríguez-Rodríguez, L., García-Ruiz, J.M., Domínguez-Cuesta, M.J., Farias, P., Valero-Garcés, B., Moreno, A., Rico, M., Valcárcel, M., 2013. A review of glacial geomorphology and chronology in northern Spain: timing and regional variability during the last glacial cycle. Geomorphology 196, 50-64. Research funded by the CANDELA project (MINECO-CGL2012-31938). L. Rodríguez-Rodríguez is a PhD student with a grant from the Spanish national FPU Program (MECD).

  12. Grassland Vegetation in the Southern Great Plains during the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Hall, Stephen A.; Valastro, Salvatore

    1995-09-01

    New pollen records from White Lake in the Southern High Plains and from Friesenhahn Cave on the southeastern Edwards Plateau of Texas indicate that the glacial-age vegetation of the southern Great Plains was a grassland. The High Plains was a treeless Artemisia grassland and the Edwards Plateau, at the south edge of the Great Plains, was a grassland with pinyon pines and deciduous trees in canyons and riparian habitats. The glacial-age grasslands differ from modern shortgrass and tallgrass prairies and may have no modern analog. The dominance of prairie vegetation during the last glacial maximum is compatible with late Pleistocene mammalian faunas and late-glacial grassland pollen records from the region. Earlier interpretations of a pine-spruce forest on the High Plains were based on pollen assemblages that are here shown to have been altered by postdepositional deterioration, resulting in differential preservation of conifer pollen grains. Accordingly, the "Tahoka Pluvial" and other "climatic episodes" defined by High Plains pollen records are abandoned.

  13. Craniometric analysis of European Upper Palaeolithic and Mesolithic samples supports discontinuity at the Late Glacial Maximum

    PubMed Central

    Brewster, Ciarán; Meiklejohn, Christopher; von Cramon-Taubadel, Noreen; Pinhasi, Ron

    2014-01-01

    The Last Glacial Maximum (LGM) represents the most significant climatic event since the emergence of anatomically modern humans (AMH). In Europe, the LGM may have played a role in changing morphological features as a result of adaptive and stochastic processes. We use craniometric data to examine morphological diversity in pre- and post-LGM specimens. Craniometric variation is assessed across four periods—pre-LGM, late glacial, Early Holocene and Middle Holocene—using a large, well-dated, dataset. Our results show significant differences across the four periods, using a MANOVA on size-adjusted cranial measurements. A discriminant function analysis shows separation between pre-LGM and later groups. Analyses repeated on a subsample, controlled for time and location, yield similar results. The results are largely influenced by facial measurements and are most consistent with neutral demographic processes. These findings suggest that the LGM had a major impact on AMH populations in Europe prior to the Neolithic. PMID:24912847

  14. Constraint on the penultimate glacial maximum Northern Hemisphere ice topography (≈140 kyrs BP)

    NASA Astrophysics Data System (ADS)

    Colleoni, Florence; Wekerle, Claudia; Näslund, Jens-Ove; Brandefelt, Jenny; Masina, Simona

    2016-04-01

    The penultimate glacial maximum (PGM, ≈140 kyrs BP), is known to be the most extensive glaciation on record that occurred during the last 400 kyrs over Eurasia. We used a coupled Atmosphere-Ocean-Sea-Ice-Land model to simulate the climate of the PGM accounting for a reconstruction of the large PGM Eurasian ice sheet. Due to uncertainties in the PGM Laurentide ice-sheet topography, two simulations with different ice-sheet topographies over North America (large as for the Last Glacial Maximum, LGM and small as for 13 kyrs BP) are performed. Results show that the simulated PGM glacial maximum climates are of comparable magnitude with previous simulations of the LGM in both cases. Assuming a small Laurentide ice-sheet instead of the LGM one in our PGM simulations results in a shift in the planetary waves. This causes an increase in storm track activity over the North Atlantic as well as higher temperatures and precipitation rates over North America, North Atlantic and over the Eurasian ice sheet. In addition, it induces a negative temperature anomaly over East Siberia yielding a thick snow cover, which seems to be in agreement with data from recent Arctic campaigns suggesting that an ice cap developed over Beringia during the PGM. All together, the changes in large-scale circulation and regional climate simulated using a small Laurentide ice sheet match the proxies well. Based on our findings, we suggest that the Laurentide ice sheet might have been smaller during the PGM than during the LGM, in turn also implying a larger Eurasian ice sheet than during the LGM, which is supported by various geological evidence of the PGM.

  15. Interhemispheric ice-sheet synchronicity during the last glacial maximum

    USGS Publications Warehouse

    Weber, M.E.; Clark, P.U.; Ricken, W.; Mitrovica, J.X.; Hostetler, S.W.; Kuhn, G.

    2011-01-01

    The timing of the last maximum extent of the Antarctic ice sheets relative to those in the Northern Hemisphere remains poorly understood. We develop a chronology for the Weddell Sea sector of the East Antarctic Ice Sheet that, combined with ages from other Antarctic ice-sheet sectors, indicates that the advance to and retreat from their maximum extent was within dating uncertainties synchronous with most sectors of Northern Hemisphere ice sheets. Surface climate forcing of Antarctic mass balance would probably cause an opposite response, whereby a warming climate would increase accumulation but not surface melting. Our new data support teleconnections involving sea-level forcing from Northern Hemisphere ice sheets and changes in North Atlantic deep-water formation and attendant heat flux to Antarctic grounding lines to synchronize the hemispheric ice sheets.

  16. Interhemispheric ice-sheet synchronicity during the Last Glacial Maximum.

    PubMed

    Weber, Michael E; Clark, Peter U; Ricken, Werner; Mitrovica, Jerry X; Hostetler, Steven W; Kuhn, Gerhard

    2011-12-02

    The timing of the last maximum extent of the Antarctic ice sheets relative to those in the Northern Hemisphere remains poorly understood. We develop a chronology for the Weddell Sea sector of the East Antarctic Ice Sheet that, combined with ages from other Antarctic ice-sheet sectors, indicates that the advance to and retreat from their maximum extent was within dating uncertainties synchronous with most sectors of Northern Hemisphere ice sheets. Surface climate forcing of Antarctic mass balance would probably cause an opposite response, whereby a warming climate would increase accumulation but not surface melting. Our new data support teleconnections involving sea-level forcing from Northern Hemisphere ice sheets and changes in North Atlantic deep-water formation and attendant heat flux to Antarctic grounding lines to synchronize the hemispheric ice sheets.

  17. Shortwave forcing and feedbacks in Last Glacial Maximum and Mid-Holocene PMIP3 simulations.

    PubMed

    Braconnot, Pascale; Kageyama, Masa

    2015-11-13

    Simulations of the climates of the Last Glacial Maximum (LGM), 21 000 years ago, and of the Mid-Holocene (MH), 6000 years ago, allow an analysis of climate feedbacks in climate states that are radically different from today. The analyses of cloud and surface albedo feedbacks show that the shortwave cloud feedback is a major driver of differences between model results. Similar behaviours appear when comparing the LGM and MH simulated changes, highlighting the fingerprint of model physics. Even though the different feedbacks show similarities between the different climate periods, the fact that their relative strength differs from one climate to the other prevents a direct comparison of past and future climate sensitivity. The land-surface feedback also shows large disparities among models even though they all produce positive sea-ice and snow feedbacks. Models have very different sensitivities when considering the vegetation feedback. This feedback has a regional pattern that differs significantly between models and depends on their level of complexity and model biases. Analyses of the MH climate in two versions of the IPSL model provide further indication on the possibilities to assess the role of model biases and model physics on simulated climate changes using past climates for which observations can be used to assess the model results.

  18. Patterns and mechanisms of warm pool hydroclimate change at the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    DiNezio, Pedro; Tierney, Jessica; Otto-Bliesner, Bette; Timmermann, Axel

    2016-04-01

    A definitive answer on the mechanisms driving glacial-interglacial changes in tropical hydroclimate is lacking, particularly regarding the importance of greenhouse gases. We address this issue by evaluating mechanisms and patterns of rainfall change over the Indo-Pacific warm pool (IPWP) in climate model simulations and proxy data of the Last Glacial Maximum (LGM). Our simulations show two mechanisms explaining the proxy data. Exposure of the Sunda and Sahul shelves due to lowered sea level drives a weakening of the Walker circulation explaining the dipole of drier IPWP center and wetter eastern Indian Ocean. Ice sheet albedo alters the inter-hemispheric temperature gradient driving changes in the Asian monsoon that explain the dry condition over India and the northern IPWP. Proxy and model data show consistent patterns of cooling over the Indian Ocean and Arabian Sea, providing independent evidence for the proposed mechanisms. Together these results demonstrate that ice sheets are a first order driver of tropical climate on glacial-interglacial timescales. Greenhouse gases drive a response that is relatively negligible and therefore cannot be detected using the available proxy data.

  19. Ground movement at Somma-Vesuvius from Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Marturano, Aldo; Aiello, Giuseppe; Barra, Diana; Fedele, Lorenzo; Morra, Vincenzo

    2012-01-01

    Detailed micropalaeontological and petrochemical analyses of rock samples from two boreholes drilled at the archaeological excavations of Herculaneum, ~ 7 km west of the Somma -Vesuvius crater, allowed reconstruction of the Late Quaternary palaeoenvironmental evolution of the site. The data provide clear evidence for ground uplift movements involving the studied area. The Holocenic sedimentary sequence on which the archaeological remains of Herculaneum rest has risen several meters at an average rate of ~ 4 mm/yr. The uplift has involved the western apron of the volcano and the Sebeto-Volla Plain, a populous area including the eastern suburbs of Naples. This is consistent with earlier evidence for similar uplift for the areas of Pompeii and Sarno valley (SE of the volcano) and the Somma -Vesuvius eastern apron. An axisimmetric deep source of strain is considered responsible for the long-term uplift affecting the whole Somma -Vesuvius edifice. The deformation pattern can be modeled as a single pressure source, sited in the lower crust and surrounded by a shell of Maxwell viscoelastic medium, which experienced a pressure pulse that began at the Last Glacial Maximum.

  20. Precipitation Isotopes Reveal Intensified Indonesian Monsoon Circulation During the Dry Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Konecky, B. L.; Russell, J. M.; Vogel, H.; Bijaksana, S.; Huang, Y.

    2014-12-01

    The Indo-Pacific Warm Pool (IPWP) invigorates the oceanic-atmospheric circulation in the tropics, with far-reaching climate impacts that extend into the high latitudes. A growing number of deglacial proxy reconstructions from the region have revealed the importance of both high- and low-latitude climate processes to IPWP rainfall during the late Pleistocene. Many of these proxies reconstruct the oxygen and hydrogen isotopic composition of rainfall (δ18Oprecip, δDprecip), a powerful tool for understanding changes in climate. However, an increasing number of studies from the region have highlighted the tendency for δ18Oprecip and δDprecip to reflect regional and/or remote circulation processes rather than local rainfall amounts, complicating the reconstruction of IPWP hydroclimate. To better understand high- and low-latitude drivers of late Pleistocene hydroclimate in the IPWP, precipitation isotopic reconstructions must be constrained with both modern observations and independent proxies for rainfall amount. We present a reconstruction of δDprecip using leaf wax compounds preserved in the sediments of Lake Towuti, Sulawesi, from 60,000 years before present to today. We interpret our proxy record with the aid of a new precipitation isotopic dataset from our study site, with daily rainfall isotope measurements to constrain the processes controlling δDprecip. Our Lake Towuti δDwax record is strikingly similar to a speleothem δ18O record from southern Indonesia (Ayliffe et al., 2013) and shares features with other nearby records spanning the Last Glacial Maximum to present. Together, these records indicate that monsoon circulation was intensified in central and southern Indonesia during the glacial period. However, other independent rainfall proxies from Lake Towuti indicate that dry conditions accompanied the intensified monsoon. Regional-scale isotopic depletion during the dry glacial period may have arisen from dynamical and other fractionating processes that

  1. Paleometeorology: High resolution Northern Hemisphere wintertime mid-latitude dynamics during the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Unterman, M. B.; Crowley, T. J.; Hodges, K. I.; Kim, S.-J.; Erickson, D. J.

    2011-12-01

    Hourly winter weather of the Last Glacial Maximum (LGM) is simulated using the Community Climate Model version 3 (CCM3) on a globally resolved T170 (˜75 km) grid. Results are compared to a longer LGM climatological run with the same boundary conditions and monthly saves. Hourly-scale animations are used to enhance interpretations. The purpose of the study is to explore whether additional insights into ice age conditions can be gleaned by going beyond the standard employment of monthly average model statistics to infer ice age weather and climate. Results for both LGM runs indicate a decrease in North Atlantic and increase in North Pacific cyclogenesis. Storm trajectories react to the mechanical forcing of the Laurentide Ice Sheet, with Pacific storms tracking over middle Alaska and northern Canada, terminating in the Labrador Sea. This result is coincident with other model results in also showing a significant reduction in Greenland wintertime precipitation - a response supported by ice core evidence. Higher-temporal resolution puts in sharper focus the close tracking of Pacific storms along the west coast of North America. This response is consistent with increased poleward heat transport in the LGM climatological run and could help explain “early” glacial warming inferred in this region from proxy climate records. Additional analyses shows a large increase in central Asian surface gustiness that support observational inferences that upper-level winds associated with Asian-Pacific storms transported Asian dust to Greenland during the LGM.

  2. Reduced El Niño-Southern Oscillation during the Last Glacial Maximum.

    PubMed

    Ford, Heather L; Ravelo, A Christina; Polissar, Pratigya J

    2015-01-16

    El Niño-Southern Oscillation (ENSO) is a major source of global interannual variability, but its response to climate change is uncertain. Paleoclimate records from the Last Glacial Maximum (LGM) provide insight into ENSO behavior when global boundary conditions (ice sheet extent, atmospheric partial pressure of CO2) were different from those today. In this work, we reconstruct LGM temperature variability at equatorial Pacific sites using measurements of individual planktonic foraminifera shells. A deep equatorial thermocline altered the dynamics in the eastern equatorial cold tongue, resulting in reduced ENSO variability during the LGM compared to the Late Holocene. These results suggest that ENSO was not tied directly to the east-west temperature gradient, as previously suggested. Rather, the thermocline of the eastern equatorial Pacific played a decisive role in the ENSO response to LGM climate.

  3. Reduced El Niño-Southern Oscillation during the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Ford, Heather L.; Ravelo, A. Christina; Polissar, Pratigya J.

    2015-01-01

    El Niño-Southern Oscillation (ENSO) is a major source of global interannual variability, but its response to climate change is uncertain. Paleoclimate records from the Last Glacial Maximum (LGM) provide insight into ENSO behavior when global boundary conditions (ice sheet extent, atmospheric partial pressure of CO2) were different from those today. In this work, we reconstruct LGM temperature variability at equatorial Pacific sites using measurements of individual planktonic foraminifera shells. A deep equatorial thermocline altered the dynamics in the eastern equatorial cold tongue, resulting in reduced ENSO variability during the LGM compared to the Late Holocene. These results suggest that ENSO was not tied directly to the east-west temperature gradient, as previously suggested. Rather, the thermocline of the eastern equatorial Pacific played a decisive role in the ENSO response to LGM climate.

  4. Cooling of tropical Brazil (5{degrees}C) during the last glacial maximum

    SciTech Connect

    Stute, M.; Forster, M.; Frischkom, H.

    1995-07-21

    A 30,000-year paleotemperature record derived from noble gases dissolved in carbon-14-dated ground water indicates that the climate in lowland Brazil (Piaui Province, 7{degrees}S, 41.5{degrees}W; altitude, 400 meters) was 5.4{degrees} {+-} 0.6{degrees}C cooler during the last glacial maximum than today. This result suggests a rather uniform cooling of the Americas between 40{degrees}S and 40{degrees}N. A 5.4{degrees}C cooling of tropical South America is consistent with pollen records, snow line reconstructions, and strontium/calcium ratios and {delta}{sup 18}O coral records but is inconsistent with the sea-surface temperature reconstruction of CLIMAP (Climate: Long-Range investigation, Mapping and Prediction). On the basis of these results, it appears that the tropical Americas are characterized by a temperature sensitivity comparable to that found in higher latitudes. 36 refs., 4 figs., 2 tabs.

  5. Reversed flow of Atlantic deep water during the Last Glacial Maximum.

    PubMed

    Negre, César; Zahn, Rainer; Thomas, Alexander L; Masqué, Pere; Henderson, Gideon M; Martínez-Méndez, Gema; Hall, Ian R; Mas, José L

    2010-11-04

    The meridional overturning circulation (MOC) of the Atlantic Ocean is considered to be one of the most important components of the climate system. This is because its warm surface currents, such as the Gulf Stream, redistribute huge amounts of energy from tropical to high latitudes and influence regional weather and climate patterns, whereas its lower limb ventilates the deep ocean and affects the storage of carbon in the abyss, away from the atmosphere. Despite its significance for future climate, the operation of the MOC under contrasting climates of the past remains controversial. Nutrient-based proxies and recent model simulations indicate that during the Last Glacial Maximum the convective activity in the North Atlantic Ocean was much weaker than at present. In contrast, rate-sensitive radiogenic (231)Pa/(230)Th isotope ratios from the North Atlantic have been interpreted to indicate only minor changes in MOC strength. Here we show that the basin-scale abyssal circulation of the Atlantic Ocean was probably reversed during the Last Glacial Maximum and was dominated by northward water flow from the Southern Ocean. These conclusions are based on new high-resolution data from the South Atlantic Ocean that establish the basin-scale north to south gradient in (231)Pa/(230)Th, and thus the direction of the deep ocean circulation. Our findings are consistent with nutrient-based proxies and argue that further analysis of (231)Pa/(230)Th outside the North Atlantic basin will enhance our understanding of past ocean circulation, provided that spatial gradients are carefully considered. This broader perspective suggests that the modern pattern of the Atlantic MOC-with a prominent southerly flow of deep waters originating in the North Atlantic-arose only during the Holocene epoch.

  6. Antarctic density stratification and the strength of the circumpolar current during the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Lynch-Stieglitz, Jean; Ito, Takamitsu; Michel, Elisabeth

    2016-05-01

    The interaction between ocean circulation and biological processes in the Southern Ocean is thought to be a major control on atmospheric carbon dioxide content over glacial cycles. A better understanding of stratification and circulation in the Southern Ocean during the Last Glacial Maximum (LGM) provides information that will help us to assess these scenarios. First, we evaluate the link between Southern Ocean stratification and circulation states in a suite of climate model simulations. While simulated Antarctic Circumpolar Current (ACC) transport varies widely (80-350 Sverdrup (Sv)), it co-varies with horizontal and vertical stratification and the formation of the southern deep water. We then test the LGM simulations against available data from paleoceanographic proxies, which can be used to assess the density stratification and ACC transport south of Australia. The paleoceanographic data suggest a moderate increase in the Southern Ocean stratification and the ACC strength during the LGM. Even with the relatively large uncertainty in the proxy-based estimates, extreme scenarios exhibited by some climate models with ACC transports of greater than 250 Sv and highly saline Antarctic Bottom Water are highly unlikely.

  7. Large Scale Anthropogenic Reduction of Forest Cover in Last Glacial Maximum Europe

    PubMed Central

    Pfeiffer, Mirjam; Kolen, Jan C. A.; Davis, Basil A. S.

    2016-01-01

    Reconstructions of the vegetation of Europe during the Last Glacial Maximum (LGM) are an enigma. Pollen-based analyses have suggested that Europe was largely covered by steppe and tundra, and forests persisted only in small refugia. Climate-vegetation model simulations on the other hand have consistently suggested that broad areas of Europe would have been suitable for forest, even in the depths of the last glaciation. Here we reconcile models with data by demonstrating that the highly mobile groups of hunter-gatherers that inhabited Europe at the LGM could have substantially reduced forest cover through the ignition of wildfires. Similar to hunter-gatherers of the more recent past, Upper Paleolithic humans were masters of the use of fire, and preferred inhabiting semi-open landscapes to facilitate foraging, hunting and travel. Incorporating human agency into a dynamic vegetation-fire model and simulating forest cover shows that even small increases in wildfire frequency over natural background levels resulted in large changes in the forested area of Europe, in part because trees were already stressed by low atmospheric CO2 concentrations and the cold, dry, and highly variable climate. Our results suggest that the impact of humans on the glacial landscape of Europe may be one of the earliest large-scale anthropogenic modifications of the earth system. PMID:27902716

  8. Large Scale Anthropogenic Reduction of Forest Cover in Last Glacial Maximum Europe.

    PubMed

    Kaplan, Jed O; Pfeiffer, Mirjam; Kolen, Jan C A; Davis, Basil A S

    2016-01-01

    Reconstructions of the vegetation of Europe during the Last Glacial Maximum (LGM) are an enigma. Pollen-based analyses have suggested that Europe was largely covered by steppe and tundra, and forests persisted only in small refugia. Climate-vegetation model simulations on the other hand have consistently suggested that broad areas of Europe would have been suitable for forest, even in the depths of the last glaciation. Here we reconcile models with data by demonstrating that the highly mobile groups of hunter-gatherers that inhabited Europe at the LGM could have substantially reduced forest cover through the ignition of wildfires. Similar to hunter-gatherers of the more recent past, Upper Paleolithic humans were masters of the use of fire, and preferred inhabiting semi-open landscapes to facilitate foraging, hunting and travel. Incorporating human agency into a dynamic vegetation-fire model and simulating forest cover shows that even small increases in wildfire frequency over natural background levels resulted in large changes in the forested area of Europe, in part because trees were already stressed by low atmospheric CO2 concentrations and the cold, dry, and highly variable climate. Our results suggest that the impact of humans on the glacial landscape of Europe may be one of the earliest large-scale anthropogenic modifications of the earth system.

  9. Numerical Modeling of the Last Glacial Maximum Yellowstone Ice Cap Captures Asymmetry in Moraine Ages

    NASA Astrophysics Data System (ADS)

    Anderson, L. S.; Wickert, A. D.; Colgan, W. T.; Anderson, R. S.

    2014-12-01

    The Last Glacial Maximum (LGM) Yellowstone Ice Cap was the largest continuous ice body in the US Rocky Mountains. Terminal moraine ages derived from cosmogenic radionuclide dating (e.g., Licciardi and Pierce, 2008) constrain the timing of maximum Ice Cap extent. Importantly, the moraine ages vary by several thousand years around the Ice Cap; ages on the eastern outlet glaciers are significantly younger than their western counterparts. In order to interpret these observations within the context of LGM climate in North America, we perform two numerical glacier modeling experiments: 1) We model the initiation and growth of the Ice Cap to steady state; and 2) We estimate the range of LGM climate states which led to the formation of the Ice Cap. We use an efficient semi-implicit 2-D glacier model coupled to a fully implicit solution for flexural isostasy, allowing for transient links between climatic forcing, ice thickness, and earth surface deflection. Independent of parameter selection, the Ice Cap initiates in the Absaroka and Beartooth mountains and then advances across the Yellowstone plateau to the west. The Ice Cap advances to its maximum extent first to the older eastern moraines and last to the younger western and northwestern moraines. This suggests that the moraine ages may reflect the timescale required for the Ice Cap to advance across the high elevation Yellowstone plateau rather than the timing of local LGM climate. With no change in annual precipitation from the present, a mean summer temperature drop of 8-9° C is required to form the Ice Cap. Further parameter searches provide the full range of LGM paleoclimate states that led to the Yellowstone Ice Cap. Using our preferred parameter set, we find that the timescale for the growth of the complete Ice Cap is roughly 10,000 years. Isostatic subsidence helps explain the long timescale of Ice Cap growth. The Yellowstone Ice Cap caused a maximum surface deflection of 300 m (using a constant effective elastic

  10. Change in atmospheric mineral aerosols in response to climate: Last glacial period, preindustrial, modern, and doubled carbon dioxide climates

    USGS Publications Warehouse

    Mahowald, N.M.; Muhs, D.R.; Levis, S.; Rasch, P.J.; Yoshioka, M.; Zender, C.S.; Luo, C.

    2006-01-01

    Desert dust simulations generated by the National Center for Atmospheric Research's Community Climate System Model for the current climate are shown to be consistent with present day satellite and deposition data. The response of the dust cycle to last glacial maximum, preindustrial, modern, and doubled-carbon dioxide climates is analyzed. Only natural (non-land use related) dust sources are included in this simulation. Similar to some previous studies, dust production mainly responds to changes in the source areas from vegetation changes, not from winds or soil moisture changes alone. This model simulates a +92%, +33%, and -60% change in dust loading for the last glacial maximum, preindustrial, and doubled-carbon dioxide climate, respectively, when impacts of carbon dioxide fertilization on vegetation are included in the model. Terrestrial sediment records from the last glacial maximum compiled here indicate a large underestimate of deposition in continental regions, probably due to the lack of simulation of glaciogenic dust sources. In order to include the glaciogenic dust sources as a first approximation, we designate the location of these sources, and infer the size of the sources using an inversion method that best matches the available data. The inclusion of these inferred glaciogenic dust sources increases our dust flux in the last glacial maximum from 2.1 to 3.3 times current deposition. Copyright 2006 by the American Geophysical Union.

  11. Stable water isotope behavior during the last glacial maximum: A general circulation model analysis

    NASA Technical Reports Server (NTRS)

    Jouzel, Jean; Koster, Randal D.; Suozzo, Robert J.; Russell, Gary L.

    1994-01-01

    Global water isotope geochemisty during the last glacial maximum (LGM) is simulated with an 8 deg x 10 deg atmospheric general circulation model (GCM). The simulation results suggest that the spatial delta O-18/temperature relationships observed for the present day and LGM climates are very similar. Furthermore, the temporal delta O-18/temperature relationship is similar to the present-day spatial relationship in regions for which the LGM/present-day temperature change is significant. This helps justify the standard practice of applying the latter to the interpretation of paleodata, despite the possible influence of other factors, such as changes in the evaportive sources of precipitation or in the seasonality of precipitation. The model suggests, for example, that temperature shifts inferred from ice core data may differ from the true shifts by only about 30%.

  12. Deepwater circulation variation in the South China Sea since the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Zheng, Xufeng; Kao, ShuhJi; Chen, Zhong; Menviel, Laurie; Chen, Han; Du, Yan; Wan, Shiming; Yan, Hong; Liu, Zhonghui; Zheng, Liwei; Wang, Shuhong; Li, Dawei; Zhang, Xu

    2016-08-01

    Deepwater circulation plays a central role in global climate. Compared with the Atlantic, the Pacific deepwater circulation's history remains unclear. The Luzon overflow, a branch of the North Pacific deep water, determines the ventilation rate of the South China Sea (SCS) basin. Sedimentary magnetic properties in the SCS reflect millennial-scale fluctuations in deep current intensity and orientation. The data suggest a slightly stronger current at the Last Glacial Maximum compared to the Holocene. But, the most striking increase in deep current occurred during Heinrich stadial 1 (H1) and to a lesser extent during the Younger Dryas (YD). Results of a transient deglacial experiment suggest that the northeastern current strengthening at the entrance of the SCS during H1 and the YD, times of weak North Atlantic Deep Water formation, could be linked to enhanced formation of North Pacific Deep Water.

  13. The Last Glacial Maximum and Termination in the Torres del Paine Region, Southern South America

    NASA Astrophysics Data System (ADS)

    Garcia, J.; Hall, B. L.; Kaplan, M. R.; Vega, R. M.; Binnie, S.; Gómez, G.; Santana, F.

    2012-12-01

    Deciphering the timing, structure and termination of the local last glacial maximum (LGM) throughout Patagonia (42-55 S) remains one of the key unsolved paleoclimate questions in Quaternary sciences. During the last glaciation, the Patagonian ice sheet formed one ice body along the Patagonian Andes (42-55 S) in southern South America, but previous work has revealed different spatiotemporal ice dynamics along the eastern and western ice margins. The Patagonian Andes is the only landmass that exists at this latitude confronting the southern westerly wind belt, which seems to have played a key role in past glacial and climate changes. Therefore, reconstructing southern Andes glacier history constitutes a key element for understanding the causes of glaciations in the Southern Hemisphere. Major progress has been made to document the local Late-Pleistocene glacier history, particularly in response to recent application of exposure-cosmogenic dating technique in the region, although only sparse well-dated paleoclimate records exist in this vast area. LGM moraine-based records in south Patagonia (~48-55 S) have been developed for the Strait of Magellan area, where full glacial conditions seems to have occurred between ~28.0 - 17.5 ka. Despite that these data seem to confirm previous glacial chronologies developed in north Patagonia and the Chilean Lake District (40-42 S), recent works in Torres del Paine and Última Esperanza basins (50-51 S), suggest that glacial maximum conditions may have occurred earlier (i.e., during Marine Isotope Stage 3) and that ice extent could have been twice the size of previously thought. Here, we discuss paleoclimatological implications from our 10Be and 26Al-dating program of moraines in the Torres del Paine region in southern Patagonia. We focused our efforts in the previously undated Río de las Viscachas (RV) I and II moraines, which occur distal to the late-glacial TDP II, III and IV moraines that enclose present lake bodies at the

  14. Hydrological and vegetation shifts in the Wallacean region of central Indonesia since the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Wicaksono, Satrio A.; Russell, James M.; Holbourn, Ann; Kuhnt, Wolfgang

    2017-02-01

    Precipitation is the most important variable of Indonesian climate, yet there are substantial uncertainties about past and future hydroclimate dynamics over the region. This study explores vegetation and rainfall and associated changes in atmospheric circulation during the past 26,000 years in Wallacea, a biogeographical area in central Indonesia, wedged between the Sunda and Sahul shelves and known for its exceptionally high rainforest biodiversity. We use terrestrial plant biomarkers from sediment cores retrieved from Mandar Bay, off west Sulawesi, to reconstruct changes in Wallacean vegetation and climate since the Last Glacial Maximum (LGM). Enriched leaf wax carbon isotope (δ13Cwax) values recorded in Mandar Bay during the LGM, together with other regional vegetation records, document grassland expansion, implying a regionally dry, and possibly more seasonal, glacial climate. Depleted leaf wax deuterium isotope (δDwax) values in Mandar Bay during the LGM, and low reconstructed precipitation isotope compositions from nearby sites, reveal an intensified Austral-Asian summer monsoon circulation and a southward shift of the mean position of the Intertropical Convergence Zone, likely due to strong southern hemisphere summer insolation and the presence of large northern hemisphere ice sheets. Mandar Bay δ13Cwax was anti-correlated with δDwax during the LGM and the last deglaciation, but was positively correlated during most of the Holocene, indicating time-varying controls on the isotopic composition of rainfall in this region. The inundation event of the Sunda Shelf and in particular the opening of the Java Sea and Karimata Strait between 9.4 and 11.1 thousand years ago might have provided new moisture sources for regional convection and/or influenced moisture source trajectories, providing the trigger for shifts in atmospheric circulation and the controls on precipitation isotope compositions from the LGM to the Holocene.

  15. The vegetation cover of New Zealand at the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Newnham, Rewi; McGlone, Matt; Moar, Neville; Wilmshurst, Janet; Vandergoes, Marcus

    2013-08-01

    A new reconstruction of the vegetation cover for New Zealand at the Last Glacial Maximum (LGM) is presented, based primarily on a database of 66 pollen site records and a more limited range of plant macrofossil and coleopteran records. Extensive forest is evident only from Auckland northwards. Conifer-broadleaf forest similar to that in the region today, but with Agathis australis scarce, persisted in the far north, whilst Nothofagus trees and a range of shrub taxa characterised the more open forests elsewhere in Northland. Survival of Nothofagus-dominated forest in coastal and exposed continental shelf locations to the southwest of Auckland and northwestern South Island is also indicated. Beyond these regions, vegetation cover comprised shrubland- and grassland-dominant communities, with the latter more prominent in eastern areas, to the south and presumably at higher altitudes. Nevertheless the survival of forest trees is indicated unambiguously in most regions apart from the eastern South Island. Thus the concept of 'micro glacial forest refugia' in New Zealand remains supported by this latest glacial vegetation reconstruction and we draw possible parallels with the developing but contentious concept of 'northern cryptic refugia' in Europe. Recent assertions that pollen and beetle reconstructions of the New Zealand LGM vegetation patterns diverge significantly are not supported by this analysis. Rather, the two proxies are readily reconciled if the term 'woody' as indicated by coleoptera is not restricted to tall forest trees but extended to the widespread woody shrub and small tree elements of the New Zealand flora. Regional distinctions in the LGM vegetation reconstruction concur broadly with the contemporary vegetation pattern, suggesting that, along with temperature depression and likely drier growing conditions, a zonal circulation regime with prominent southern westerly winds was important at 21 ka, as it is today. Pollen-climate modelling of the extent of

  16. Arctic Dinoflagellate Migration Marks the Oligocene Glacial Maximum: Implications for the Rupelian-Chattian Boundary

    NASA Astrophysics Data System (ADS)

    van Simaeys, S.; Brinkhuis, H.; Pross, J.; Williams, G. L.; Zachos, J. C.

    2004-12-01

    Various geochemical and biotic climate proxies, and notably deep-sea benthic foraminiferal δ 18O records indicate that the Eocene 'greenhouse' state of the Earth gradually evolved towards an earliest Oligocene 'icehouse' state, eventually triggering the abrupt appearance of large continental ice-sheets on Antarctic at ˜33.3 Ma (Oi-1 event). This, however, was only the first of two major glacial events in the Oligocene. Benthic foraminiferal δ 18O records show a second positive excursion in the mid Oligocene, consistent with a significant ice-sheet expansion and/or cooling at 27.1 Ma (Oi-2b) coincident with magnetosubchron C9n. Here, we report on a mid Oligocene, globally synchronous, Arctic dinoflagellate migration event, calibrated against the upper half of C9n. A sudden appearance, and abundance increases of the Arctic taxon Svalbardella at lower-middle latitudes coincides with the so-called Oi-2b benthic δ 18O event, dated at ˜27.1 Ma. This phenomenon is taken to indicate significant high-latitude surface water cooling, concomitant Antarctic ice-sheet growth, and sea level lowering. The duration of the Svalbardella migrations, and the episode of profound cooling is estimated as ˜500 ka, and is here termed the Oligocene Glacial Maximum (OGM). Our records suggest a close link between the OGM, sea-level fall, and the classic Rupelian-Chattian boundary, magnetostratigraphically dating this boundary as ˜27.1 Ma.

  17. Dynamical downscaling of tropical cyclones from CCSM4 simulations of the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Yoo, Jinwoong; Galewsky, Joseph; Camargo, Suzana J.; Korty, Robert; Zamora, Ryan

    2016-09-01

    Dynamical downscaling of simulations of the Last Glacial Maximum (LGM) and late twentieth century (20C) were conducted using the Weather Research and Forecasting (WRF) model with the aim of (1) understanding how the downscaled kinematic and thermodynamic variables influence simulated tropical cyclone (TC) activity over the western North Pacific during the LGM and the 20C periods and (2) to test the relevance of TC genesis factors for the colder LGM climate. The results show that, despite the lower temperatures during the LGM, the downscaled TC climatology over the western North Pacific in the LGM simulation does not differ significantly from that in the 20C simulation. Among the TC environmental factors, the TC potential intensity, mid-tropospheric entropy deficit, and vertical wind shear during the LGM were consistent with previous analyses of TC genesis factors in LGM global climate model simulations. Changes in TC genesis density between the LGM and the 20C simulations seem to be well represented by the ventilation index, a nondimensional measure of the combined effects of vertical wind shear, and thermodynamic properties, suggesting the potential applicability of those factors for TC activity evaluation during the LGM and possibly other climates.

  18. Variations in tree cover in North America since the last glacial maximum

    NASA Astrophysics Data System (ADS)

    Williams, John W.

    2003-01-01

    Accurate reconstructions of late-Quaternary land-cover change are needed to better understand past interactions of the terrestrial biosphere with other components of the earth system. This paper presents a sequence of reconstructed needleleaved and broadleaved tree-cover densities for North America since the last glacial maximum, generated from fossil-pollen data and present-day tree-cover estimates derived from the Advanced Very High Resolution Radiometer (AVHRR). For this study, a refined form of the modern analog technique was developed, called the hierarchical analog technique, which can constrain paleoenvironmental properties even for fossil-pollen assemblages without close analogs in the modern-pollen record. Pollen taxa from samples that are compositionally unlike any modern-pollen samples are regrouped into plant functional categories based upon phenology, life form, leaf shape, and climatic tolerances, and the analog analysis rerun. Reclassifying individual pollen taxa into broader functional categories enables analogs to be found when no compositional analogs exist, but at a cost of increased uncertainties in the analog estimates. Tests of the hierarchical analog technique shows that it accurately reconstructs present-day tree-cover densities. The median standard deviation for each individual estimate is <10%. Tree-cover densities during the last glacial maximum were low relative to present, and have increased since. Lower-than-present tree-cover densities at the last glacial maximum were likely due to a combination of low temperatures, low precipitation, and low atmospheric CO 2 concentrations. By 14 ka, broadleaved tree-cover densities had begun to rise in the southeastern US and needleleaved forests grew in the western US, southeastern US, and as a belt along the southern margin of the Laurentide Ice Sheet. By the mid-Holocene, the northern and western needleleaved forests had joined. Needleleaved and broadleaved tree densities continued to increase

  19. High resolution record of the Last Glacial Maximum in eastern Australia

    NASA Astrophysics Data System (ADS)

    Petherick, Lynda; Moss, Patrick; McGowan, Hamish

    2010-05-01

    time than traditionally accepted, and was not uniformly cool and dry. Alloway, B. V., D. J. Lowe, D. J. A. Barrell, R. M. Newnham, P. C. Almond, P. C. Augustinus, N. A. N. Bertler, L. Carter, N. J. Litchfield, M. S. McGlone, J. Shulmeister, M. J. Vandergoes, P. W. Williams and N.-I. members (2007). Towards a climate event stratigraphy for New Zealand over the past 30 000 years (NZ-INTIMATE project). Journal of Quaternary Science 22(1): 9-35. Denton, G. H., T. V. Lowell, C. J. Heusser, C. Schluchter, B. G. Andersen, L. E. Heusser, P. I. Moreno and D. R. Marchant (1999). Geomorrphology, stratigraphy, and radiocarbon chronology of Llanquihe Drift in the area of the Southern Lake District, Seno Reloncavi, and Isal Grande de Chiloe, Chile. Geografiska Annaler 81A: 167-229. EPICA (2006). One-to-one coupling of glacial climate variability in Greenland and Antarctica. Nature 444: 195-198. Kershaw, A. P., G. M. McKenzie, N. Porch, R. G. Roberts, J. Brown, H. Heijnis, M. L. Orr, G. Jacobsen and P. R. Newall (2007). A high-resolution record of vegetation and climate through the last glacial cycles from Caledonia Fen, southeastern highlands of Australia. Journal of Quaternary Science 22(5): 481-500. Newnham, R. M., D. J. Lowe, T. Giles and B. V. Alloway (2007). Vegetation and climate of Auckland, New Zealand, since ca. 32 000 cal. yr ago: support for an extended LGM Journal of Quaternary Science 22(5): 517-534. Petherick, L. M., H. A. McGowan and P. T. Moss (2008). Climate variability during the Last Glacial Maximum in eastern Australia: Evidence of two stadials? Journal of Quaternary Science 23(8): 787-802. Röthlisberger, R., R. Mulvaney, E. W. Wolff, M. A. Hutterli, M. Bigler, S. Sommer and J. Jouzel (2002). Dust and sea salt variability in central East Antarctica (Dome C) over the last 45 kyr and its implications for southern high latitude climate. Geophysical Research Letters 29(20): Art # 1963. Smith, M. A. (2009). Late Quaternary landscapes in Central Australia: sedimentary

  20. Glacial and climatic evolution from the Little Ice Age last Maximum to the present in Tröllaskagi Peninsula (North Iceland): the case of Gljúlfurárjökull

    NASA Astrophysics Data System (ADS)

    María Fernández, Jose; Andres, Nuria; Tanarro, Luis Miguel; Palacios, David

    2015-04-01

    This paper presents the evolution of the Gljúlfurárjökull glacier (65°42'48'' N, 18°39'13'' W; 980 m), located at the headwall of the Skiðadalur valley, on the Tröllaskagi peninsula (N. Iceland). This is one of many small glaciers situated on the bottom of the Tröllaskagi valleys. This glacier is one of the few "clean" glaciers, i.e. not covered with boulders, as is the case with most of the glaciers on this peninsula. This makes the glacier especially sensitive to climate change, and it has retreated and advanced many times since its last maximum during the Little Ice Age (LIA) maximum in the mid- 19th century (Caseldine and Stötter, 1993), leaving a large number of moraine ridges. This paper analyses the change in this glacier from the LIA up to the present day, with reference to the variations in the surface, ELA and volume. Lichenometry and geomorphological field analysis were used to establish the exact limits of the glacier during the LIA last maximum. An aerial photo from 1946 and two orthophotos from 2000 and 2013 were also used. Using photointerpretation and Geographical Information Systems (GIS), the aerial photos were georeferenced to delimit the glacier in different years, analyse the surface and volume variations, and calculate the ELA for each date. The ELA analysis was carried out using the method: Accumulation Area Ratio (AAR 0.67). The results obtained with this method are: Little Ice Age Maximum: 945 m a.s.l. (almost the same ELA proposed by Caseldine and Stötter, 1993) 1946: 970 m a.s.l. 2000: 980 m a.s.l. 2013: 990 m a.s.l. The ice volume lost from LIA to 2000 was: 111.68 hm3 Reference Caseldine, C., Stötter, J., 1993. "Little Ice Age" glaciation of Tröllaskagi Peninsula, northern Iceland: Climatic implications for reconstructed equilibrium line altitudes (ELAs). Holocene 3: 357-366. Research funded by Cryocrisis project (CGL2012-35858), Government of Spain, and Nils Mobility projects (EEA GRANTS)

  1. Decadal-scale climate drivers for glacial dynamics in Glacier National Park, Montana, USA

    USGS Publications Warehouse

    Pederson, G.T.; Fagre, D.B.; Gray, S.T.; Graumlich, L.J.

    2004-01-01

    Little Ice Age (14th-19th centuries A.D.) glacial maxima and 20th century retreat have been well documented in Glacier National Park, Montana, USA. However, the influence of regional and Pacific Basin driven climate variability on these events is poorly understood. We use tree-ring reconstructions of North Pacific surface temperature anomalies and summer drought as proxies for winter glacial accumulation and summer ablation, respectively, over the past three centuries. These records show that the 1850's glacial maximum was likely produced by ???70 yrs of cool/wet summers coupled with high snowpack. Post 1850, glacial retreat coincides with an extended period (>50 yr) of summer drought and low snowpack culminating in the exceptional events of 1917 to 1941 when retreat rates for some glaciers exceeded 100 m/yr. This research highlights potential local and ocean-based drivers of glacial dynamics, and difficulties in separating the effects of global climate change from regional expressions of decadal-scale climate variability. Copyright 2004 by the American Geophysical Union.

  2. 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.

  3. Carbon storage in Amazonia during the last glacial maximum: secondary data and uncertainties.

    PubMed

    Turcq, Bruno; Cordeiro, Renato C; Sifeddine, Abdefettah; Simões Filho, Francisco F L; Albuquerque, Ana Luisa S; Abrão, Jorge J

    2002-12-01

    The Amazonian forest is, due to its great size, carbon storage capacity and present-day variability in carbon uptake and release, an important component of the global carbon cycle. Paleo-environmental reconstruction is difficult for Amazonia due to the scarcity of primary palynological data and the mis-interpretation of some secondary data. Studies of lacustrine sediment records have shown that Amazonia has known periods in which the climate was drier than it is today. However, not all geomorphological features such as dunes, and slope erosion, which are thought to indicate rainforest regression, date from the time of the Late Glacial Maximum (LGM) and these features do not necessarily correspond to episodes of forest regression. There is also uncertainty concerning LGM carbon storage due to rainforest soils and biomass estimates. Soil carbon content may decrease moderately during the LGM, whereas rainforest biomass may change considerably in response to changes in the global environment. Biomass per unit area in Amazonia has probably been reduced by the cumulative effects of low CO2 concentration, a drier climate and lower temperatures. As few paleo-vegetation data are available, there is considerable uncertainty concerning the amount of carbon stored in Amazonia during the LGM, which may have corresponded to 44-94% of the carbon currently stored in biomass and soils.

  4. Palaeodistribution modelling of European vegetation types at the Last Glacial Maximum using modern analogues from Siberia: Prospects and limitations

    NASA Astrophysics Data System (ADS)

    Janská, Veronika; Jiménez-Alfaro, Borja; Chytrý, Milan; Divíšek, Jan; Anenkhonov, Oleg; Korolyuk, Andrey; Lashchinskyi, Nikolai; Culek, Martin

    2017-03-01

    We modelled the European distribution of vegetation types at the Last Glacial Maximum (LGM) using present-day data from Siberia, a region hypothesized to be a modern analogue of European glacial climate. Distribution models were calibrated with current climate using 6274 vegetation-plot records surveyed in Siberia. Out of 22 initially used vegetation types, good or moderately good models in terms of statistical validation and expert-based evaluation were computed for 18 types, which were then projected to European climate at the LGM. The resulting distributions were generally consistent with reconstructions based on pollen records and dynamic vegetation models. Spatial predictions were most reliable for steppe, forest-steppe, taiga, tundra, fens and bogs in eastern and central Europe, which had LGM climate more similar to present-day Siberia. The models for western and southern Europe, regions with a lower degree of climatic analogy, were only reliable for mires and steppe vegetation, respectively. Modelling LGM vegetation types for the wetter and warmer regions of Europe would therefore require gathering calibration data from outside Siberia. Our approach adds value to the reconstruction of vegetation at the LGM, which is limited by scarcity of pollen and macrofossil data, suggesting where specific habitats could have occurred. Despite the uncertainties of climatic extrapolations and the difficulty of validating the projections for vegetation types, the integration of palaeodistribution modelling with other approaches has a great potential for improving our understanding of biodiversity patterns during the LGM.

  5. Reconstructing Oceanographic Conditions From the Holocene to the Last Glacial Maximum in the Bay of Bengal

    NASA Astrophysics Data System (ADS)

    Miller, J.; Dekens, P. S.; Weber, M. E.; Spiess, V.; France-Lanord, C.

    2015-12-01

    The International Ocean Discovery Program (IODP) Expedition 354 drilled 7 sites in the Bay of Bengal, providing a unique opportunity to improve our understanding of the link between glacial cycles, tropical oceanographic changes, and monsoon strength. Deep-sea sediment cores of the Bengal Fan fluctuate between sand, hemipelagic and terrestrial sediment layers. All but one of the sites (U1454) contain a layer of calcareous clay in the uppermost part of the core that is late Pleistocene in age. During Expedition 354 site U1452C was sampled at high resolution (every 2cm) by a broad group of collaborators with the goal of reconstructing monsoon strength and oceanographic conditions using a variety of proxies. The top 480 cm of site U1452C (8ºN, 87ºE, 3671m water depth) contains primarily nannofossil rich calcareous clay. The relatively high abundance of foraminifera will allow us to generate a high resolution record of sea surface temperature (SST) and sea surface salinity (SSS) using standard foraminifera proxies. We will present oxygen isotopes (δ18O) and Mg/Ca data of mixed layer planktonic foraminifera from the top 70cm of the core, representing the Holocene to the last glacial maximum. δ18O of planktonic foraminifera records global ice volume and local SST and SSS, while Mg/Ca of foraminifera is a proxy for SST. The paired Mg/Ca and δ18O measurements on the same samples of foraminifera, together with published estimates with global ocean δ18O, can be used to reconstruct both SST and local δ18O of seawater, which is a function of the evaporation/precipitation balance. In future work, the local SSS and SST during the LGM will be paired with terrestrial and other oceanic proxies to increase our understanding of how global climate is connected to monsoon strength.

  6. Timing of maximum glacial extent and deglaciation from HualcaHualca volcano (southern Peru), obtained with cosmogenic 36Cl.

    NASA Astrophysics Data System (ADS)

    Alcalá, Jesus; Palacios, David; Vazquez, Lorenzo; Juan Zamorano, Jose

    2015-04-01

    Andean glacial deposits are key records of climate fluctuations in the southern hemisphere. During the last decades, in situ cosmogenic nuclides have provided fresh and significant dates to determine past glacier behavior in this region. But still there are many important discrepancies such as the impact of Last Glacial Maximum or the influence of Late Glacial climatic events on glacial mass balances. Furthermore, glacial chronologies from many sites are still missing, such as HualcaHualca (15° 43' S; 71° 52' W; 6,025 masl), a high volcano of the Peruvian Andes located 70 km northwest of Arequipa. The goal of this study is to establish the age of the Maximum Glacier Extent (MGE) and deglaciation at HualcaHualca volcano. To achieve this objetive, we focused in four valleys (Huayuray, Pujro Huayjo, Mollebaya and Mucurca) characterized by a well-preserved sequence of moraines and roches moutonnées. The method is based on geomorphological analysis supported by cosmogenic 36Cl surface exposure dating. 36Cl ages have been estimated with the CHLOE calculator and were compared with other central Andean glacial chronologies as well as paleoclimatological proxies. In Huayuray valley, exposure ages indicates that MGE occurred ~ 18 - 16 ka. Later, the ice mass gradually retreated but this process was interrupted by at least two readvances; the last one has been dated at ~ 12 ka. In the other hand, 36Cl result reflects a MGE age of ~ 13 ka in Mollebaya valley. Also, two samples obtained in Pujro-Huayjo and Mucurca valleys associated with MGE have an exposure age of 10-9 ka, but likely are moraine boulders affected by exhumation or erosion processes. Deglaciation in HualcaHualca volcano began abruptly ~ 11.5 ka ago according to a 36Cl age from a polished and striated bedrock in Pujro Huayjo valley, presumably as a result of reduced precipitation as well as a global increase of temperatures. The glacier evolution at HualcaHualca volcano presents a high correlation with

  7. The concept of global monsoon applied to the last glacial maximum: A multi-model analysis

    NASA Astrophysics Data System (ADS)

    Jiang, Dabang; Tian, Zhiping; Lang, Xianmei; Kageyama, Masa; Ramstein, Gilles

    2015-10-01

    The last glacial maximum (LGM, ca. 21,000 years ago) has been extensively investigated for better understanding of past glacial climates. Global-scale monsoon changes, however, have not yet been determined. In this study, we examine global monsoon area (GMA) and precipitation (GMP) as well as GMP intensity (GMPI) at the LGM using the experiments of 17 climate models chosen from the Paleoclimate Modelling Intercomparison Project (PMIP) according to their ability to reproduce the present global monsoon climate. Compared to the reference period (referring to the present day, ca. 1985, for three atmospheric plus two atm-slab ocean models and the pre-industrial period, ca. 1750, for 12 fully coupled atmosphere-ocean or atmosphere-ocean-vegetation models), the LGM monsoon area increased over land and decreased over the oceans. The boreal land monsoon areas generally shifted southward, while the northern boundary of land monsoon areas retreated southward over southern Africa and South America. Both the LGM GMP and GMPI decreased in most of the models. The GMP decrease mainly resulted from the reduced monsoon precipitation over the oceans, while the GMPI decrease was derived from the weakened intensity of monsoon precipitation over land and the boreal ocean. Quantitatively, the LGM GMP deficit was due to, first, the GMA reduction and, second, the GMPI weakening. In response to the LGM large ice sheets and lower greenhouse gas concentrations in the atmosphere, the global surface and tropospheric temperatures cooled, the boreal summer meridional temperature gradient increased, and the summer land-sea thermal contrast at 40°S - 70°N decreased. These are the underlying dynamic mechanisms for the LGM monsoon changes. Qualitatively, simulations agree with reconstructions in all land monsoon areas except in the western part of northern Australia where disagreements occur and in South America and the southern part of southern Africa where there is uncertainty in reconstructions

  8. Last Glacial Maximum Dated by Means of 10Be in the Maritime Alps (Italy)

    NASA Astrophysics Data System (ADS)

    Granger, D. E.; Spagnolo, M.; Federici, P.; Pappalardo, M.; Ribolini, A.; Cyr, A. J.

    2006-12-01

    Relatively few exposure dates of LGM moraines boulders are available for the European Alps, and none on the southern flank. Ponte Murato (PM) is a frontal moraine at 860 m asl in the Gesso Basin (Maritime Alps, SW European Alps). The PM moraine dams the 157 km2 Gesso della Barra Valley and it represents the lowermost frontal moraine of the entire Gesso Valley, near the outlet of the valley in the Po Plain. Its ELA, determined from the paleo- shape of the supposed Gesso della Barra glacier, is 1746 m asl. Tetti Bandito (TB) is a small and badly preserved glacial deposit, tentatively attributed to a lateral-frontal moraine, that is positioned 5 km downvalley from the PM deposit at 800 m asl. There are no other glacial deposits downvalley from the TB moraine in the Gesso Basin or farther NE in the piedmont region of the upper Po Plain. Boulders sampled on the PM and on the TB moraine crests gave a 10Be cosmogenic age of respectively 16300 ± 880 ka (average value) and 18798 ± 973 ka. This result constrains the PM frontal moraine within the LGM interval but also suggests that the maximum expansion of the Gesso Basin glacier was more downvalley at some point during the last glaciation. If the TB is a lateral-frontal moraine as supposed, the two TB and PM moraines would represent the outer and inner moraine crests of the same LGM stadial, with the outer moraine much less pronounced than the inner moraine, similarly to the maximalstand and the hochstand described in the Eastern Alps (Van Husen, 1997). Within this perspective, the PM and TB dates are consistent with a European Alps LGM corresponding to MIS 2 (Ivy-Ochs et al., 2004). This study of the Maritime Alps moraines is also in agreement with the Upper Würm climatic theory (Florineth and Schlüchter, 2000) of a stronger influence of the W and SW incoming humid airflows in the European Alps, differently from the nearby Vosges and Pyrenees mountain chains where more dry conditions were probably responsible for a very

  9. Upward Altitudinal Shifts in Habitat Suitability of Mountain Vipers since the Last Glacial Maximum.

    PubMed

    Yousefi, Masoud; Ahmadi, Mohsen; Nourani, Elham; Behrooz, Roozbeh; Rajabizadeh, Mehdi; Geniez, Philippe; Kaboli, Mohammad

    2015-01-01

    We determined the effects of past and future climate changes on the distribution of the Montivipera raddei species complex (MRC) that contains rare and endangered viper species limited to Iran, Turkey and Armenia. We also investigated the current distribution of MRC to locate unidentified isolated populations as well as to evaluate the effectiveness of the current network of protected areas for their conservation. Present distribution of MRC was modeled based on ecological variables and model performance was evaluated by field visits. Some individuals at the newly identified populations showed uncommon morphological characteristics. The distribution map of MRC derived through modeling was then compared with the distribution of protected areas in the region. We estimated the effectiveness of the current protected area network to be 10%, which would be sufficient for conserving this group of species, provided adequate management policies and practices are employed. We further modeled the distribution of MRC in the past (21,000 years ago) and under two scenarios in the future (to 2070). These models indicated that climatic changes probably have been responsible for an upward shift in suitable habitats of MRC since the Last Glacial Maximum, leading to isolation of allopatric populations. Distribution will probably become much more restricted in the future as a result of the current rate of global warming. We conclude that climate change most likely played a major role in determining the distribution pattern of MRC, restricting allopatric populations to mountaintops due to habitat alterations. This long-term isolation has facilitated unique local adaptations among MRC populations, which requires further investigation. The suitable habitat patches identified through modeling constitute optimized solutions for inclusion in the network of protected areas in the region.

  10. Upward Altitudinal Shifts in Habitat Suitability of Mountain Vipers since the Last Glacial Maximum

    PubMed Central

    Yousefi, Masoud; Ahmadi, Mohsen; Nourani, Elham; Behrooz, Roozbeh; Rajabizadeh, Mehdi; Geniez, Philippe; Kaboli, Mohammad

    2015-01-01

    We determined the effects of past and future climate changes on the distribution of the Montivipera raddei species complex (MRC) that contains rare and endangered viper species limited to Iran, Turkey and Armenia. We also investigated the current distribution of MRC to locate unidentified isolated populations as well as to evaluate the effectiveness of the current network of protected areas for their conservation. Present distribution of MRC was modeled based on ecological variables and model performance was evaluated by field visits. Some individuals at the newly identified populations showed uncommon morphological characteristics. The distribution map of MRC derived through modeling was then compared with the distribution of protected areas in the region. We estimated the effectiveness of the current protected area network to be 10%, which would be sufficient for conserving this group of species, provided adequate management policies and practices are employed. We further modeled the distribution of MRC in the past (21,000 years ago) and under two scenarios in the future (to 2070). These models indicated that climatic changes probably have been responsible for an upward shift in suitable habitats of MRC since the Last Glacial Maximum, leading to isolation of allopatric populations. Distribution will probably become much more restricted in the future as a result of the current rate of global warming. We conclude that climate change most likely played a major role in determining the distribution pattern of MRC, restricting allopatric populations to mountaintops due to habitat alterations. This long-term isolation has facilitated unique local adaptations among MRC populations, which requires further investigation. The suitable habitat patches identified through modeling constitute optimized solutions for inclusion in the network of protected areas in the region. PMID:26367126

  11. Radiocarbon evidence for enhanced respired carbon storage in the Atlantic at the Last Glacial Maximum

    PubMed Central

    Freeman, E.; Skinner, L. C.; Waelbroeck, C.; Hodell, D.

    2016-01-01

    The influence of ocean circulation changes on atmospheric CO2 hinges primarily on the ability to alter the ocean interior's respired nutrient inventory. Here we investigate the Atlantic overturning circulation at the Last Glacial Maximum and its impact on respired carbon storage using radiocarbon and stable carbon isotope data from the Brazil and Iberian Margins. The data demonstrate the existence of a shallow well-ventilated northern-sourced cell overlying a poorly ventilated, predominantly southern-sourced cell at the Last Glacial Maximum. We also find that organic carbon remineralization rates in the deep Atlantic remained broadly similar to modern, but that ventilation ages in the southern-sourced overturning cell were significantly increased. Respired carbon storage in the deep Atlantic was therefore enhanced during the last glacial period, primarily due to an increase in the residence time of carbon in the deep ocean, rather than an increase in biological carbon export. PMID:27346723

  12. Thermocline Structure and ENSO Variability in the eastern equatorial Pacific during the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Clark, S.; Koutavas, A.; Lynch-Stieglitz, J.; Rustic, G.

    2015-12-01

    The mean state and variability of the eastern equatorial Pacific (EEP) during the Last Glacial Maximum (LGM) are of great interest because of the region's role in the El Niño-Southern Oscillation (ENSO) and global climate. We investigated changes in thermocline structure between the Late Holocene (LH) and LGM with stable isotopes of planktonic foraminifera in sediment cores from the Galápagos. We measured δ18O in two species—Globigerinoides ruber, inhabiting the surface mixed layer, and Neogloboquadrina dutertrei, inhabiting the deep thermocline—in order to evaluate the vertical temperature contrast between the two species. We also measured δ18O of individual N. dutertrei from modern (late 20th century) and LGM sediments in order to assess thermocline temperature variability related to ENSO activity. Our data indicate a reduced vertical contrast in the upper ocean during the LGM, which is most consistent with a deeper thermocline and thicker mixed layer. Additionally, δ18O of individual N. dutertrei shells shows 2.5 times greater population variance in the LGM than in the modern sample. This large variance indicates that thermocline temperatures were more variable during the LGM than today, consistent with more active ENSO. Together, these results imply that the mean state of the EEP was characterized by a deeper thermocline and greater ENSO variability. The results further show the potential for reconstructing ENSO variability from deep-sea sediments of the EEP, where other geological archives of ENSO are currently extremely limited.

  13. Sensitivity of palaeotidal models of the northwest European shelf seas to glacial isostatic adjustment since the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Ward, Sophie L.; Neill, Simon P.; Scourse, James D.; Bradley, Sarah L.; Uehara, Katsuto

    2016-11-01

    The spatial and temporal distribution of relative sea-level change over the northwest European shelf seas has varied considerably since the Last Glacial Maximum, due to eustatic sea-level rise and a complex isostatic response to deglaciation of both near- and far-field ice sheets. Because of the complex pattern of relative sea level changes, the region is an ideal focus for modelling the impact of significant sea-level change on shelf sea tidal dynamics. Changes in tidal dynamics influence tidal range, the location of tidal mixing fronts, dissipation of tidal energy, shelf sea biogeochemistry and sediment transport pathways. Significant advancements in glacial isostatic adjustment (GIA) modelling of the region have been made in recent years, and earlier palaeotidal models of the northwest European shelf seas were developed using output from less well-constrained GIA models as input to generate palaeobathymetric grids. We use the most up-to-date and well-constrained GIA model for the region as palaeotopographic input for a new high resolution, three-dimensional tidal model (ROMS) of the northwest European shelf seas. With focus on model output for 1 ka time slices from the Last Glacial Maximum (taken as being 21 ka BP) to present day, we demonstrate that spatial and temporal changes in simulated tidal dynamics are very sensitive to relative sea-level distribution. The new high resolution palaeotidal model is considered a significant improvement on previous depth-averaged palaeotidal models, in particular where the outputs are to be used in sediment transport studies, where consideration of the near-bed stress is critical, and for constraining sea level index points.

  14. Ice-sheet configuration in the CMIP5/PMIP3 Last Glacial Maximum experiments

    NASA Astrophysics Data System (ADS)

    Abe-Ouchi, A.; Saito, F.; Kageyama, M.; Braconnot, P.; Harrison, S. P.; Lambeck, K.; Otto-Bliesner, B. L.; Peltier, W. R.; Tarasov, L.; Peterschmitt, J.-Y.; Takahashi, K.

    2015-06-01

    We describe the creation of boundary conditions related to the presence of ice sheets, including ice sheet extent and height, ice shelf extent, and the distribution and altitude of ice-free land, at the Last Glacial Maximum (LGM) for use in LGM experiments conducted as part of the fifth phase of the Coupled Modelling Intercomparison Project (CMIP5) and the third phase of the Palaeoclimate Modelling Intercomparison Project (PMIP3). The CMIP5/PMIP3 data sets were created from reconstructions made by three different groups, which were all obtained using a model-inversion approach but differ in the assumptions used in the modelling and in the type of data used as constraints. The ice sheet extent, and thus the albedo mask, for the Northern Hemisphere (NH) does not vary substantially between the three individual data sources. The difference in the topography of the NH ice sheets is also moderate, and smaller than the differences between these reconstructions (and the resultant composite reconstruction) and ice-sheet reconstructions used in previous generations of PMIP. Only two of the individual reconstructions provide information for Antarctica. The discrepancy between these two reconstructions is larger than the difference for the NH ice sheets although still less than the difference between the composite reconstruction and previous PMIP ice-sheet reconstructions. Differences in the climate response to the individual LGM reconstructions, and between these reconstructions and the CMIP5/PMIP3 composite, are largely confined to the ice-covered regions, but also extend over North Atlantic Ocean and Northern Hemisphere continents through atmospheric stationary waves. There are much larger differences in the climate response to the latest reconstructions (or the derived composite) and ice-sheet reconstructions used in previous phases of PMIP.

  15. Glacial wetland distribution and methane emissions estimated from PMIP2 climate simulations

    NASA Astrophysics Data System (ADS)

    Weber, Nanne; Drury, Annajoy; Toonen, Willem; van Weele, Michiel

    2010-05-01

    It is an open question to what extent wetlands contributed to the interglacial-glacial decrease in atmospheric methane concentration. Here we estimate methane emissions from glacial wetlands, using newly available PMIP2 simulations of the Last Glacial Maximum (LGM) climate from coupled atmosphere-ocean and atmosphere-ocean-vegetation models. Emissions are computed from the dominant controls of water table depth, soil temperature and plant productivity and we analyse the relative role of each factor in the glacial decline. It is found that latitudinal changes in soil moisture, in combination with ice-sheet expansion, cause boreal wetlands to shift southward in all simulations. This southward migration is instrumental in maintaining the boreal wetland source at a significant level. The temperature effect is found to be moderate, while reduced plant productivity contributes equally to the total reduction. Model results indicate a relatively small boreal and large tropical source during the LGM, consistent with the low interpolar difference in glacial methane concentrations derived from ice-core data.

  16. Pollen record from Ka'au Crater, Oahu, Hawaii: Evidence for a dry glacial maximum

    SciTech Connect

    Hotchkiss, S.C.; Juvik, J.O. Univ. of Hawaii, Hilo )

    1993-06-01

    Fossil pollen from a 3.5 m-long core from Ka'au Crater, Hawaii (elev. 460 m), yields a ca. 23,000-year record of regional vegetation history. Results indicate a full-glacial period drier and possibly cooler than present, a warmer and wetter early Holocene, and a somewhat drier late Holocene; this sequence agrees with earlier work by Selling (1948) on other islands. The oldest zone is donated by pollen of Chenopodium oahuense, Acacia koa, and Dodonaea viscosa; post-glacial pollen assemblages feature high percentages of Myrsine and Coprosma, followed by increases in Lycopodium cernuum Ilex anomala. Freycinetia arborea and Pritchardia. After about 8000 years ago, Chenopodium, Acacia, and Dodonaea increase, suggesting a return to drier conditions. Abundant pollen of Chenopodium oahuense, a plant of dry regions, during the last glacial maximum implies that neither the trade winds nor cyclonic storms were delivering as much moisture to the regional vegetation as they presently do. This suggests that the ocean surface temperature during the last glacial maximum may have been cooler than present, a finding contradictory to the reconstructions of the CLIMAP (1981) group, which show temperatures near Hawaii equal to or even warmer than present.

  17. The role of glacial cycles in promoting genetic diversity in the Neotropics: the case of cloud forests during the Last Glacial Maximum

    PubMed Central

    Ramírez-Barahona, Santiago; Eguiarte, Luis E

    2013-01-01

    The increasing aridity during the Last Glacial Maximum (LGM) has been proposed as a major factor affecting Neotropical species. The character and intensity of this change, however, remains the subject of ongoing debate. This review proposes an approach to test contrasting paleoecological hypotheses by way of their expected demographic and genetic effects on Neotropical cloud forest species. We reviewed 48 paleoecological records encompassing the LGM in the Neotropics. The records show contrasting evidence regarding the changes in precipitation during this period. Some regions remained fairly moist and others had a significantly reduced precipitation. Many paleoecological records within the same region show apparently conflicting evidence on precipitation and forest stability. From these data, we propose and outline two demographic/genetic scenarios for cloud forests species based on opposite precipitation regimes: the dry refugia and the moist forests hypotheses. We searched for studies dealing with the population genetic structure of cloud forest and other montane taxa and compared their results with the proposed models. To date, the few available molecular studies show insufficient genetic evidence on the predominance of glacial aridity in the Neotropics. In order to disentangle the climatic history of the Neotropics, the present study calls for a general multi-disciplinary approach to conduct future phylogeographic studies. Given the contradictory paleoecological information, population genetic data on Neotropical cloud forest species should be used to explicitly test the genetic consequences of competing paleoecological models. PMID:23531632

  18. The Northern Extent of the Southern Hemisphere Westerly Wind Belt since the Last Glacial Maximum Tracked via Sediment Provenance

    NASA Astrophysics Data System (ADS)

    Franzese, A. M.; Goldstein, S. L.; Hemming, S. R.

    2015-12-01

    The Southern Hemisphere Westerlies are known to be important for climate due to their effects on the global carbon cycle and on the global thermohaline circulation. Many proxy records suggest that the strength and position of the Southern Hemisphere westerly winds have changed significantly since the Last Glacial Maximum (LGM) at ~21,000 years BP. However, a recent compilation of all available evidence for Southern Hemisphere westerly wind changes during the Last Glacial Maximum (LGM) led to the conclusion that "their strength and position in colder and warmer climates relative to today remain a wide open question" (Kohfeld et al. (2013) Quaternary Science Reviews, 68). This paper finds that an equatorward displacement of the glacial winds is consistent with observations, but cannot rule out other, competing hypotheses. Using the geochemical characteristics of deep-sea sediments deposited along the Mid-Atlantic Ridge, I test the hypothesis that the LGM Southern Hemisphere Westerlies were displaced northward. In the central South Atlantic, dust can be delivered from South America via the Westerlies, or from Africa via the Trade Winds. The continental sources of South America and Africa have very different geochemical signatures, making it possible to distinguish between eolian transport via the Westerlies vs. the Trade Winds. Any northward shift in the Southern Hemisphere Westerlies would increase the northward extent of a South American provenance in sediments dominated by eolian sources. I will present geochemical provenance data (radiogenic isotope ratios; major and trace element concentrations) in a latitudinal transect of cores along the Mid-Atlantic Ridge that document whether, in fact, such a shift occurred, and put an important constraint on how far north the wind belts shifted during the LGM.

  19. Fast Vegetational Responses to Late-Glacial Climate Change

    NASA Astrophysics Data System (ADS)

    Williams, J. W.; Post, D. M.; Cwynar, L. C.; Lotter, A. F.; Levesque, A. J.

    2001-12-01

    How rapidly can natural ecosystems respond to rapid climate change? This question can be addressed by studying paired paleoecological and paleoclimatological records spanning the last deglaciation. Between 16 and 10 ka, abrupt climatic oscillations (e.g. Younger Dryas, Gerzensee/Killarney Oscillations) interrupted the general warming trend. Rates of climate change during these events were as fast or faster than projected rates of change for this century. We compiled a dozen high-resolution lacustrine records in North America and Europe with a pollen record and independent climatic proxy, a clear Younger Dryas signal, and good age control. Cross-correlation analysis suggests that vegetation responded rapidly to late-glacial climate change, with significant changes in vegetation composition occurring within the lifespan of individual trees. At all sites, vegetation lagged climate by less than 200 years, and at two-thirds of the sites, the initial vegetational response occurred within 100 years. The finding of rapid vegetational responses is consistent across sites and continents, and is similar to the 100-200 year response times predicted by gap-scale forest models. Likely mechanisms include 1) increased susceptibility of mature trees to disturbances such as fire, wind, and disease, thereby opening up gaps for colonization, 2) the proximity of these sites to late-glacial treeline, where climate may directly control plant population densities and range limits, 3) the presence of herbaceous taxa with short generation times in these plant communities, and 4) rapid migration due to rare long-distance seed dispersals. Our results are consistent with reports that plant ranges are already shifting in response to recent climate change, and suggest that these shifts will persist for the next several centuries. Widespread changes in plant distributions may affect surface-atmosphere interactions and will challenge attempts to manage ecosystems and conserve biodiversity.

  20. Loop Current variability due to wind stress and reduced sea level during the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Mildner, T. C.; Eden, C.; Nuernberg, D.; Schoenfeld, J.

    2011-12-01

    One of the most prominent features of the circulation in the Gulf of Mexico is the Loop Current (LC). It is of special interest as it influences not only the climate in the Gulf of Mexico. Although causation is not well understood yet, dynamical relationships between LC retraction and extension, seasonal migrations of the Intertropical Convergence Zone (ITCZ) and the related wind stress curl over the subtropical North Atlantic, and changes in the thermohaline circulation are indicated by model simulations. A characteristic feature of the LC is the shedding of anticyclonic eddies. These eddies can have depth signatures of up to 1000 m and are of special interest as they supply heat and moisture into the western and northern Gulf. The eddies are generated aperiodically every 3 to 21 months, with an average shedding time of 9.5 months. Eddy shedding appears to be related to a suite of oceanographic forcing fields such as the Yucatan Channel throughflow, the Florida Current and North Brazil Current variability, as well as synoptic meteorological forcing variability. By combining state-of-the-art paleoceanographic and meso-scale eddy-resolving numerical modeling techniques, we examined the Loop Current dynamics and hydrographic changes in the Gulf going back in time up to ~21,000 years. To assess the impact of Last Glacial Maximum (LGM) wind stress and reduced sea level we have re-configured an existing hierarchy of models of the North Atlantic Ocean (FLAME) with a horizontal grid resolution of ca. 30 km (wind stress was taken from the PMIP-II database). The sea level was lowered compared to the CONTROL run by 110 m and 67 m. These sea level changes have been chosen according to the cold-deglacial periods Heinrich I and Younger Dryas. The result of our model simulations is a continuous increase in eddy shedding from the LGM to the Holocene. This increase is predominantly controlled by the continuous deglacial sea level rise. Changes in wind stress curl related to the

  1. Dust: A diagnostic of the hydrologic cycle during the last glacial maximum

    SciTech Connect

    Yuk L. Yung; Typhoon Lee; Chung-Ho Wang; Ying-Tzung Shieh

    1996-02-16

    Dust concentrations in ice of the last glacial maximum (LGM) are high in ice cores from Greenland and Antarctica. The magnitude of the enhancements can be explained if the strength of the hydrologic cycle during the LGM was about half of that at present. This notion is consistent with a large decrease (5{degrees}C) in ocean temperature during the LGM, as recently deduced from measurements of strontium and calcium in corals. 24 refs., 1 fig.

  2. Dust: a diagnostic of the hydrologic cycle during the last glacial maximum.

    PubMed

    Yung, Y L; Lee, T; Wang, C H; Shieh, Y T

    1996-02-16

    Dust concentrations in ice of the last glacial maximum (LGM) are high in ice cores from Greenland and Antarctica. The magnitude of the enhancements can be explained if the strength of the hydrologic cycle during the LGM was about half of that at present. This notion is consistent with a large decrease (5 degrees Celsius) in ocean temperature during the LGM, as recently deduced from measurements of strontium and calcium in corals.

  3. Dust: a diagnostic of the hydrologic cycle during the last glacial maximum

    NASA Technical Reports Server (NTRS)

    Yung, Y. L.; Lee, T.; Wang, C. H.; Shieh, Y. T.

    1996-01-01

    Dust concentrations in ice of the last glacial maximum (LGM) are high in ice cores from Greenland and Antarctica. The magnitude of the enhancements can be explained if the strength of the hydrologic cycle during the LGM was about half of that at present. This notion is consistent with a large decrease (5 degrees Celsius) in ocean temperature during the LGM, as recently deduced from measurements of strontium and calcium in corals.

  4. Global monsoon change during the Last Glacial Maximum: a multi-model study

    NASA Astrophysics Data System (ADS)

    Yan, Mi; Wang, Bin; Liu, Jian

    2016-07-01

    Change of global monsoon (GM) during the Last Glacial Maximum (LGM) is investigated using results from the multi-model ensemble of seven coupled climate models participated in the Coupled Model Intercomparison Project Phase 5. The GM changes during LGM are identified by comparison of the results from the pre-industrial control run and the LGM run. The results show (1) the annual mean GM precipitation and GM domain are reduced by about 10 and 5 %, respectively; (2) the monsoon intensity (demonstrated by the local summer-minus-winter precipitation) is also weakened over most monsoon regions except Australian monsoon; (3) the monsoon precipitation is reduced more during the local summer than winter; (4) distinct from all other regional monsoons, the Australian monsoon is strengthened and the monsoon area is enlarged. Four major factors contribute to these changes. The lower greenhouse gas concentration and the presence of the ice sheets decrease air temperature and water vapor content, resulting in a general weakening of the GM precipitation and reduction of GM domain. The reduced hemispheric difference in seasonal variation of insolation may contribute to the weakened GM intensity. The changed land-ocean configuration in the vicinity of the Maritime Continent, along with the presence of the ice sheets and lower greenhouse gas concentration, result in strengthened land-ocean and North-South hemispheric thermal contrasts, leading to the unique strengthened Australian monsoon. Although some of the results are consistent with the proxy data, uncertainties remain in different models. More comparison is needed between proxy data and model experiments to better understand the changes of the GM during the LGM.

  5. Last glacial maximum constraints on the Earth System model HadGEM2-ES

    NASA Astrophysics Data System (ADS)

    Hopcroft, Peter O.; Valdes, Paul J.

    2015-09-01

    We investigate the response of the atmospheric and land surface components of the CMIP5/AR5 Earth System model HadGEM2-ES to pre-industrial (PI: AD 1860) and last glacial maximum (LGM: 21 kyr) boundary conditions. HadGEM2-ES comprises atmosphere, ocean and sea-ice components which are interactively coupled to representations of the carbon cycle, aerosols including mineral dust and tropospheric chemistry. In this study, we focus on the atmosphere-only model HadGEM2-A coupled to terrestrial carbon cycle and aerosol models. This configuration is forced with monthly sea surface temperature and sea-ice fields from equivalent coupled simulations with an older version of the Hadley Centre model, HadCM3. HadGEM2-A simulates extreme cooling over northern continents and nearly complete die back of vegetation in Asia, giving a poor representation of the LGM environment compared with reconstructions of surface temperatures and biome distributions. The model also performs significantly worse for the LGM in comparison with its precursor AR4 model HadCM3M2. Detailed analysis shows that the major factor behind the vegetation die off in HadGEM2-A is a subtle change to the temperature dependence of leaf mortality within the phenology model of HadGEM2. This impacts on both snow-vegetation albedo and vegetation dynamics. A new set of parameters is tested for both the pre-industrial and LGM, showing much improved coverage of vegetation in both time periods, including an improved representation of the needle-leaf forest coverage in Siberia for the pre-industrial. The new parameters and the resulting changes in global vegetation distribution strongly impact the simulated loading of mineral dust, an important aerosol for the LGM. The climate response in an abrupt 4× pre-industrial CO2 simulation is also analysed and shows modest regional impacts on surface temperatures across the Boreal zone.

  6. Extensive glaciations in Anatolian Mountains during the global Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Akçar, Naki; Yavuz, Vural; Ivy-Ochs, Susan; Yeşilyurt, Serdar; Reber, Regina; Tikhomirov, Dmitry; Kubik, Peter; Vockenhuber, Christof; Schlüchter, Christian

    2014-05-01

    As a response to the changes in the atmospheric circulation at the beginning of the Last Glacial Maximum (LGM), equilibrium line altitude commenced to decrease and, thus, also Anatolian glaciers started to expand. Depending on the altitude of the mountains and size of the accumulation area, the advance began earlier in the eastern Black Sea Mountains prior to 27 ka. In the Kavron, Verçenik, Başyayla and Çoruh valleys, glaciers terminated at an altitude of 1600 m with a length of > 10 km. In eastern Anatolia, 15 km-long glaciers descended to 1400 m from the extensive ice-fields of the Munzır Mountains. In central and western Anatolia, glaciers were smaller (ca. 6 km-long) except for Dedegöl Mountains. There, a glacier length of around 9 km and an advance down to 1450 m were mapped. At Mount Erciyes glaciers began to advance down to 2150 m prior to 25 ka. In southwestern Anatolia, beginning of the LGM advance was documented at ca. 22 ka at Mount Sandıras, where a 1.5 km-long cirque glacier terminated at an altitude of 1900 m. Meanwhile, valley glaciers descended to 2050 m at Mount Akdaǧ, 6 km down from the peak. In northwestern Anatolia, one paleoglacier commenced to grow prior to ca. 25 ka at Uludaǧ and it reached a length of 5 km and an altitude 1600 m. In brief, Anatolian glaciers reached their maximum extent between 27 and 21 ka during the global LGM. The LGM deglaciation resulted in the collapse of Anatolian glaciers. The deglaciation was almost synchronous in all mountains. Climatic fluctuations at the end of LGM have produced only small glaciers, which are much more sensitive to temperature and/or precipitation changes than larger glaciers. Our recent study at Uludaǧ revealed that the glaciers re-advanced at least three times until 19 ka after their maximum extent at around 21 ka. We explain this dynamic behaviour as a response mechanism to different phases of the winter indices of the North Atlantic Oscillation, which resulted in an enhanced

  7. Glacial meltwater cooling of the Gulf of Mexico - GCM implications for Holocene and present-day climates

    NASA Technical Reports Server (NTRS)

    Oglesby, Robert J.; Maasch, Kirk A.; Saltzman, Barry

    1989-01-01

    The NCAR Community Climate Model GCM is presently used to investigate the possible effects on regional and hemispheric climates of reduced SSTs in the Gulf of Mexico, in view of delta-O-18 records and terrestrial evidence for at least two major glacial meltwater discharges after the last glacial maximum. Three numerical experiments have been conducted with imposed gulfwide SST coolings of 3, 6, and 12 C; in all cases, significant reductions arise in the North Atlantic storm-track intensity, together with a strong decrease in transient eddy water vapor transport out of the Gulf of Mexico. Other statistically significant changes occur across the Northern Hemisphere.

  8. High regional climate sensitivity over continental China constrained by glacial-recent changes in temperature and the hydrological cycle

    PubMed Central

    Eagle, Robert A.; Risi, Camille; Mitchell, Jonathan L.; Eiler, John M.; Seibt, Ulrike; Neelin, J. David; Li, Gaojun; Tripati, Aradhna K.

    2013-01-01

    The East Asian monsoon is one of Earth’s most significant climatic phenomena, and numerous paleoclimate archives have revealed that it exhibits variations on orbital and suborbital time scales. Quantitative constraints on the climate changes associated with these past variations are limited, yet are needed to constrain sensitivity of the region to changes in greenhouse gas levels. Here, we show central China is a region that experienced a much larger temperature change since the Last Glacial Maximum than typically simulated by climate models. We applied clumped isotope thermometry to carbonates from the central Chinese Loess Plateau to reconstruct temperature and water isotope shifts from the Last Glacial Maximum to present. We find a summertime temperature change of 6–7 °C that is reproduced by climate model simulations presented here. Proxy data reveal evidence for a shift to lighter isotopic composition of meteoric waters in glacial times, which is also captured by our model. Analysis of model outputs suggests that glacial cooling over continental China is significantly amplified by the influence of stationary waves, which, in turn, are enhanced by continental ice sheets. These results not only support high regional climate sensitivity in Central China but highlight the fundamental role of planetary-scale atmospheric dynamics in the sensitivity of regional climates to continental glaciation, changing greenhouse gas levels, and insolation. PMID:23671087

  9. High regional climate sensitivity over continental China constrained by glacial-recent changes in temperature and the hydrological cycle.

    PubMed

    Eagle, Robert A; Risi, Camille; Mitchell, Jonathan L; Eiler, John M; Seibt, Ulrike; Neelin, J David; Li, Gaojun; Tripati, Aradhna K

    2013-05-28

    The East Asian monsoon is one of Earth's most significant climatic phenomena, and numerous paleoclimate archives have revealed that it exhibits variations on orbital and suborbital time scales. Quantitative constraints on the climate changes associated with these past variations are limited, yet are needed to constrain sensitivity of the region to changes in greenhouse gas levels. Here, we show central China is a region that experienced a much larger temperature change since the Last Glacial Maximum than typically simulated by climate models. We applied clumped isotope thermometry to carbonates from the central Chinese Loess Plateau to reconstruct temperature and water isotope shifts from the Last Glacial Maximum to present. We find a summertime temperature change of 6-7 °C that is reproduced by climate model simulations presented here. Proxy data reveal evidence for a shift to lighter isotopic composition of meteoric waters in glacial times, which is also captured by our model. Analysis of model outputs suggests that glacial cooling over continental China is significantly amplified by the influence of stationary waves, which, in turn, are enhanced by continental ice sheets. These results not only support high regional climate sensitivity in Central China but highlight the fundamental role of planetary-scale atmospheric dynamics in the sensitivity of regional climates to continental glaciation, changing greenhouse gas levels, and insolation.

  10. Chronology of the last glacial maximum in the upper Bear River Basin, Utah

    USGS Publications Warehouse

    Laabs, B.J.C.; Munroe, Jeffrey S.; Rosenbaum, J.G.; Refsnider, K.A.; Mickelson, D.M.; Singer, B.S.; Caffee, M.W.

    2007-01-01

    The headwaters of the Bear River drainage were occupied during the Last Glacial Maximum (LGM) by outlet glaciers of the Western Uinta Ice Field, an extensive ice mass (???685 km2) that covered the western slope of the Uinta Mountains. A well-preserved sequence of latero-frontal moraines in the drainage indicates that outlet glaciers advanced beyond the mountain front and coalesced on the piedmont. Glacial deposits in the Bear River drainage provide a unique setting where both 10Be cosmogenic surface-exposure dating of moraine boulders and 14C dating of sediment in Bear Lake downstream of the glaciated area set age limits on the timing of glaciation. Limiting 14C ages of glacial flour in Bear Lake (corrected to calendar years using CALIB 5.0) indicate that ice advance began at 32 ka and culminated at about 24 ka. Based on a Bayesian statistical analysis of cosmogenic surface-exposure ages from two areas on the terminal moraine complex, the Bear River glacier began its final retreat at about 18.7 to 18.1 ka, approximately coincident with the start of deglaciation elsewhere in the central Rocky Mountains and many other alpine glacial localities worldwide. Unlike valleys of the southwestern Uinta Mountains, deglaciation of the Bear River drainage began prior to the hydrologie fall of Lake Bonneville from the Provo shoreline at about 16 ka. ?? 2007 Regents of the University of Colorado.

  11. Multiple evolutionary units and demographic stability during the last glacial maximum in the Scytalopus speluncae complex (Aves: Rhinocryptidae).

    PubMed

    Pulido-Santacruz, Paola; Bornschein, Marcos Ricardo; Belmonte-Lopes, Ricardo; Bonatto, Sandro L

    2016-09-01

    The Atlantic Forest (AF) of South America harbors one of the world's highest bird species richness, but to date there is a deficient understanding of the spatial patterns of genetic diversity and the evolutionary history of this biome. Here we estimated the phylogenetic and populational history of the widespread Mouse-colored Tapaculo (Scytalopus speluncae) complex across the Brazilian AF, using data from two mitochondrial genes and 12 microsatellite loci. Both markers uncovered several cryptic, mostly allopatric and well-supported lineages that may represent distinct species-level taxa. We investigated whether diversification in S. speluncae is compatible with the Carnaval-Moritz model of Pleistocene refugia. We found that northern lineages have high levels of genetic diversity, agreeing with predictions of more stable forest refugia in these areas. In contrast, southern lineages have lower levels of mtDNA diversity with a signature of population expansion that occurred earlier (∼0.2Mya) than the last glacial maximum. This result suggests that the AF may be stable enough to maintain endemic taxa through glacial cycles. Moreover, we propose that the "mid-Pleistocene climate transition" between 1.2 and 0.7million years ago, from a warmer to a colder climate, may have played an important but mostly overlooked role in the evolution of AF montane taxa.

  12. Climatic implications of correlated upper Pleistocene glacial and fluvial deposits on the Cinca and Gallego rivers, NE Spain

    SciTech Connect

    Lewis, Claudia J; Mcdonald, Eric; Sancho, Carlos; Pena, Jose- Luis

    2008-01-01

    We correlate Upper Pleistocene glacial and fluvial deposits of the Cinca and Gallego River valleys (south central Pyrenees and Ebro basin, Spain) using geomorphic position, luminescence dates, and time-related trends in soil development. The ages obtained from glacial deposits indicate glacial periods at 85 {+-} 5 ka, 64 {+-} 11 ka, and 36 {+-} 3 ka (from glacial till) and 20 {+-} 3 ka (from loess). The fluvial drainage system, fed by glaciers in the headwaters, developed extensive terrace systems in the Cinca River valley at 178 {+-} 21 ka, 97 {+-} 16 ka, 61 {+-} 4 ka, 47 {+-} 4 ka, and 11 {+-} 1 ka, and in the Gallego River valley at 151 {+-} 11 ka, 68 {+-} 7 ka, and 45 {+-} 3 ka. The times of maximum geomorphic activity related to cold phases coincide with Late Pleistocene marine isotope stages and heinrich events. The maximum extent of glaciers during the last glacial occurred at 64 {+-} 11 ka, and the terraces correlated with this glacial phase are the most extensive in both the Cinca (61 {+-} 4 ka) and Gallego (68 {+-} 7 ka) valleys, indicating a strong increase in fluvial discharge and availability of sediments related to the transition to deglaciation. The global Last Glacial Maximum is scarcely represented in the south central Pyrenees owing to dominantly dry conditions at that time. Precipitation must be controlled by the position of the Iberian Peninsula with respect to the North Atlantic atmospheric circulation system. The glacial systems and the associated fluvial dynamic seem sensitive to (1) global climate changes controlled by insolation, (2) North Atlantic thermohaline circulation influenced by freshwater pulses into the North Atlantic, and (3) anomalies in atmospheric circulation in the North Atlantic controlling precipitation on the Iberian peninsula. The model of glacial and fluvial evolution during the Late Pleistocene in northern Spain could be extrapolated to other glaciated mountainous areas in southern Europe.

  13. Basal conditions and flow dynamics of the Rhine glacier, Alps, at the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Cohen, Denis; Gillet-Chaulet, Fabien; Zwinger, Thomas; Machguth, Horst; Haeberli, Wilfried; Fischer, Urs H.

    2016-04-01

    The safe disposal of radioactive wastes in deep geological repositories requires their containment and isolation for up to one million years. In Switzerland, repositories are planned in the northern Swiss lowlands near the marginal zone of the former Rhine glacier that repeatedly formed two extensive piedmont lobes (the Rhine and Linth lobes) over the Swiss Plateau. Future ice-age conditions may thus impact the repositories due to erosion by glaciers, permafrost conditions, and changes in groundwater fluxes. We use the Last Glacial Maximum (LGM) as a representative future ice-age scenario over northern Switzerland and model the Rhine glacier at the LGM using a full three-dimensional, thermo-mechanical model that solves Stokes flow in ice and the heat equation in both ice and rock. Permafrost in rocks and sediments is implemented using an effective heat capacity formulation. The Rhine glacier at the LGM is one of the best studied paleo-glacier with geomorphic reconstructions of terminal moraines, equilibrium lines, provenance of erratics, till extent and provenance, and evidences of cold vs warm subglacial environments. These data are compared with modeled ice ice thickness, cold vs warm basal condition, and flow paths. Numerical results indicate that LGM modeled ice extent and ice thickness are not fully consistent with geomorphic reconstructions and known climate proxies: ice is either too thick in the accumulation zone or summer temperatures are too cold at the terminus. Simulations with different climate parameters all indicate, however, that the beds of the Rhine and Linth lobes were at the melting temperature except above local topographic highs and along a thin marginal zone. Sliding speed was highest along topographic lows with ice moving at 20 to 80 m a-1 depending on mass balance gradients. Basal shear stress was low (< 30 kPa). Melt water was probably abundant due to above-freezing temperatures in summer. Thus, melt water was likely routed over large

  14. Glacial landscape evolution on Hall Peninsula, Baffin Island, since the Last Glacial Maximum: insights into switching glacial dynamics and thermo-mechanical conditions

    NASA Astrophysics Data System (ADS)

    Johnson, C. L.; Ross, M.

    2012-12-01

    Ice cover in north central Hall Peninsula, Baffin Island has evolved from full Laurentide Ice Sheet (LIS) cover during the Last Glacial Maximum (LGM) to a thin ice cap that now covers about 800 km2 in the northeast sector. The exposed subglacial landscape consists of contrasting geomorphological zones which allude to complex spatial and temporal changes in basal ice dynamics and thermal regime since LGM. We used satellite imagery, field observations, a large till geochemical database, and terrestrial cosmogenic isotopes to get new insights into subglacial erosion intensity, ice flow dynamics, and glacial history. Fields of streamlined bedrock-cored ridges (e.g. drumlins) have been mapped and their elongation ratios calculated. The density of bedrock-controlled lakes, which has traditionally been used as a proxy for subglacial erosion intensity on Baffin Island, has been re-examined using modern GIS techniques. This work has revealed a mosaic of glacial terrain zones each consisting of characteristics that are distinct from the other zones. Five glacial terrain zones (GTZ) have been recognized. One zone (GTZ 1) is characterized by a broad flowset of northeast trending streamlined hills and parallel paleo-flow indicators. It also has the highest streamlined hill density, longest elongation ratios, and the highest lake density of the study area. This northeast flowset is crosscut locally by ice flow indicators that converge into troughs that now form a series of fjords. Landforms and ice flow indicators of this younger system (GTZ 2) are traced inland showing propagation of the channelized system into this portion of the LIS. The central area of the peninsula contains a zone of thicker till and rolling topography (GTZ 3) as well as a zone consisting of southeast trending features and associated perpendicular moraines (GTZ 4). The modern ice cap and its past extension form the last zone (GTZ 5). The preservation of the northeast system (GTZ 1) outside of the

  15. Geoarchaeological response to landscape changes of the Greek continental shelf since the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Kapsimalis, Vasilios; Pavlopoulos, Kosmas; Panagiotopoulos, Ioannis

    2010-05-01

    An overview of geological, sedimentological, palaeoclimatic, archaeological and mythological data is presented in order to detect the geomorphological changes of the Aegean and Ionian shelves during the last sea-level transgression, and comprehend the consequent prehistoric human adaptations. The irregular rise of sea level since the Last Glacial Maximum forced the Palaeolithic human to abandon its settlements located near the old (lower) coastlines and to move landward in new positions. Commonly, the coastline movement was very slow causing no significant impact on human activities; however in some cases, the transgression was very prompt causing human migration towards highlands. In some very gentle-dipped and wide regions, e.g. the North Aegean plateau, the sea-level rise caused a rapid coastline retreat (in some extreme case as fast as 10 m/yr) and inundation of an extended surface area. However, at the same time, in the steep parts of the Greek shelf, e.g. the Kyparissiakos Gulf and Crete, the coastline advanced landwards with a slow motion (commonly, a few cm/yr) covering small areas. In addition, coastal regions with particular geomorphologic characteristics, e.g. coastal paleo-lakes protected by a sill (gulfs of Corinth, Amvrakikos, Pagasitikos Evvoikos, Saronikos), were deluged by the sea during different periods and under different intensity, depending on the elevation of the sill and the manner of its overflow. Although the presence of Palaeolithic human in the Greek mainland has been confirmed by several archaeological excavations, there is no certain evidence for human settlement in the deep parts of Greek shelf. However, many archaeologists have suggested that some of Palaeolithic people lived on the shelf, when the sea level was lower than its present position. Nevertheless, some potential Palaeolithic migration routes can be indicated taking into account (a) the palaeogeographic reconstruction of Greek shelf over the Last Quaternary; (b

  16. Modelling of mineral dust for interglacial and glacial climate conditions with a focus on Antarctica

    SciTech Connect

    Sudarchikova, Natalia; Mikolajewicz, Uwe; Timmreck, C.; O'Donnell, D.; Schurgers, G.; Sein, Dmitry; Zhang, Kai

    2015-05-19

    The mineral dust cycle responds to climate variations and plays an important role in the climate system by affecting the radiative balance of the atmosphere and modifying biogeochemistry. Polar ice cores provide unique information about deposition of aeolian dust particles transported over long distances. These cores are a palaeoclimate proxy archive of climate variability thousands of years ago. The current study is a first attempt to simulate past interglacial dust cycles with a global aerosol–climate model ECHAM5-HAM. The results are used to explain the dust deposition changes in Antarctica in terms of quantitative contribution of different processes, such as emission, atmospheric transport and precipitation, which will help to interpret palaeodata from Antarctic ice cores. The investigated periods include four interglacial time slices: the pre-industrial control (CTRL), mid-Holocene (6000 yr BP; hereafter referred to as \\"6 kyr\\"), last glacial inception (115 000 yr BP; hereafter \\"115 kyr\\") and Eemian (126 000 yr BP; hereafter \\"126 kyr\\"). One glacial time interval, the Last Glacial Maximum (LGM) (21 000 yr BP; hereafter \\"21 kyr\\"), was simulated as well to be a reference test for the model. Results suggest an increase in mineral dust deposition globally, and in Antarctica, in the past interglacial periods relative to the pre-industrial CTRL simulation. Approximately two-thirds of the increase in the mid-Holocene and Eemian is attributed to enhanced Southern Hemisphere dust emissions. Slightly strengthened transport efficiency causes the remaining one-third of the increase in dust deposition. The moderate change in dust deposition in Antarctica in the last glacial inception period is caused by the slightly stronger poleward atmospheric transport efficiency compared to the pre-industrial. Maximum dust deposition in Antarctica was simulated for the glacial period. LGM dust deposition in Antarctica is substantially increased due to 2.6 times higher

  17. Modelling of mineral dust for interglacial and glacial climate conditions with a focus on Antarctica

    DOE PAGES

    Sudarchikova, Natalia; Mikolajewicz, Uwe; Timmreck, C.; ...

    2015-05-19

    The mineral dust cycle responds to climate variations and plays an important role in the climate system by affecting the radiative balance of the atmosphere and modifying biogeochemistry. Polar ice cores provide unique information about deposition of aeolian dust particles transported over long distances. These cores are a palaeoclimate proxy archive of climate variability thousands of years ago. The current study is a first attempt to simulate past interglacial dust cycles with a global aerosol–climate model ECHAM5-HAM. The results are used to explain the dust deposition changes in Antarctica in terms of quantitative contribution of different processes, such as emission,more » atmospheric transport and precipitation, which will help to interpret palaeodata from Antarctic ice cores. The investigated periods include four interglacial time slices: the pre-industrial control (CTRL), mid-Holocene (6000 yr BP; hereafter referred to as \\"6 kyr\\"), last glacial inception (115 000 yr BP; hereafter \\"115 kyr\\") and Eemian (126 000 yr BP; hereafter \\"126 kyr\\"). One glacial time interval, the Last Glacial Maximum (LGM) (21 000 yr BP; hereafter \\"21 kyr\\"), was simulated as well to be a reference test for the model. Results suggest an increase in mineral dust deposition globally, and in Antarctica, in the past interglacial periods relative to the pre-industrial CTRL simulation. Approximately two-thirds of the increase in the mid-Holocene and Eemian is attributed to enhanced Southern Hemisphere dust emissions. Slightly strengthened transport efficiency causes the remaining one-third of the increase in dust deposition. The moderate change in dust deposition in Antarctica in the last glacial inception period is caused by the slightly stronger poleward atmospheric transport efficiency compared to the pre-industrial. Maximum dust deposition in Antarctica was simulated for the glacial period. LGM dust deposition in Antarctica is substantially increased due to 2.6 times

  18. Last Glacial vegetation and climate change in the southern Levant

    NASA Astrophysics Data System (ADS)

    Miebach, Andrea; Chen, Chunzhu; Litt, Thomas

    2015-04-01

    Reconstructing past climatic and environmental conditions is a key task for understanding the history of modern mankind. The interaction between environmental change and migration processes of the modern Homo sapiens from its source area in Africa into Europe is still poorly understood. The principal corridor of the first human dispersal into Europe and also later migration dynamics crossed the Middle East. Therefore, the southern Levant is a key area to investigate the paleoenvironment during times of human migration. In this sense, the Last Glacial (MIS 4-2) is particularly interesting to investigate for two reasons. Firstly, secondary expansions of the modern Homo sapiens are expected to occur during this period. Secondly, there are ongoing discussions on the environmental conditions causing the prominent lake level high stand of Lake Lisan, the precursor of the Dead Sea. This high stand even culminated in the merging of Lake Lisan and Lake Kinneret (Sea of Galilee). To provide an independent proxy for paleoenvironmental reconstructions in the southern Levant during the Last Glacial, we investigated pollen assemblages of the Dead Sea/Lake Lisan and Lake Kinneret. Located at the Dead Sea Transform, the freshwater Lake Kinneret is nowadays connected via the Jordan with the hypersaline Dead Sea, which occupies Earth's lowest elevation on land. The southern Levant is a transition area of three different vegetation types. Therefore, also small changes in the climate conditions effect the vegetation and can be registered in the pollen assemblage. In contrast to the Holocene, our preliminary results suggest another vegetation pattern during the Last Glacial. The vegetation belt of the fragile Mediterranean biome did no longer exist in the vicinity of Lake Kinneret. Moreover, the vegetation was rather similar in the whole study area. A steppe vegetation with dwarf shrubs, herbs, and grasses predominated. Thermophilous elements like oaks occurred in limited amounts. The

  19. Climatic Instability and Regional Glacial Advances in the Late Ediacaran

    NASA Astrophysics Data System (ADS)

    Hannah, J. L.; Stein, H. J.; Marolf, N.; Bingen, B.

    2014-12-01

    The Ediacaran Period closed out the environmentally raucous Neoproterozoic Era with the last of multiple glacial events and the first ephemeral glimmer of multicellular life. As such, evolution of Earth's biosphere and the marine environments that nurtured this nascent biota are of particular interest. Because the Ediacaran biota appear in the stratigraphic record just above tillites in many localities, inferences are naturally drawn to link glaciation to bioevolution. Here we review known controls on the timing and extent of the late Ediacaran Gaskier and Varanger glacial events, bolstered by new constraints on the Moelv tillite of South Norway. The elusive mid-Ediacaran glacial strata are poorly dated, patchy in distribution, and relatively limited in thickness. The type Gaskier glaciogenic units in Newfoundland are 582 to 584 Ma, based on U-Pb zircon ages from intercalated ash beds [1]. The Varanger glaciogenic deposits in northern Norway, in contrast, remain only roughly constrained to ca. 630 to 560 Ma. Post-Gaskier negative carbon isotope excursions (CIEs) have been reported from multiple localities in both China and SW United States, suggesting climatic instability in the late Ediacaran. Although most localities lack solid geochronology, paleontologic constraints place the Hongtiegou glacial diamictite and accompanying CIE in the Chaidam Basin, NW China, in the latest Ediacaran, ca. 555 Ma [2]. We previously suggested that the Moelv tillite in south Norway was roughly equivalent to the Gaskier, based on an imprecise Re-Os age of ~560 Ma [3] for the underlying Biri shale. Reanalysis of these data shows that the upper part of the shale section was disturbed by a redox front during the Caledonian orogeny. The undisturbed lower part of the section yields a more precise Model 1 isochron age of 559.5 ± 6.2 Ma, clearly post-dating the Gaskier event well outside analytical uncertainty. These new results bolster arguments that the Gaskier glaciation was not a global

  20. Vegetation responses to climate changes during the penultimate glacial period (marine isotope stage 6) in southern Europe

    NASA Astrophysics Data System (ADS)

    Roucoux, Katy; Margari, V.; Lawson, I. T.; Tzedakis, P. C.

    2010-05-01

    Like the last glacial, the penultimate glacial interval (MIS 6, 185,000 to 132,000 years before present) was characterised by increasing continental ice volume and decreasing concentrations of atmospheric greenhouse gases. However, greater orbital eccentricity during MIS 6 resulted in precessional-scale insolation changes of higher amplitude. This led to some unexpected combinations of climatic boundary conditions such as the high northern hemisphere summer insolation but relatively large ice volume and low atmospheric carbon dioxide concentrations of marine isotopic event 6.5. Records of regional climatic responses to different combinations of climatic forcing factors, in the form of pollen records of vegetation change, can contribute to our understanding of which factors determine conditions at the Earth's surface. Few palaeoecological records cover the penultimate glacial in detail and hence environmental and climatic responses during this interval are not yet well known. At Lake Ioannina, NW Greece, records of the last two glacial intervals are preserved at the same site enabling comparisons of vegetation responses to be made between periods with differing orbital configurations while keeping site variables constant. Our new palynological record spans the penultimate glacial interval at centennial scale resolution and represents the most detailed terrestrial record of this interval to date. Vegetation development throughout the glacial period indicates long-term cooling and drying reflecting the overall decline of northern hemisphere summer insolation and accumulation of large-northern hemisphere ice sheets, as expected. Conditions in NW Greece at the penultimate glacial maximum (PGM) appear to have been colder and drier than during the Last Glacial Maximum, consistent with records of lower Mediterranean sea surface temperature and greater extent of the European ice sheet at the PGM. During the early part of MIS 6, however, it appears that the high amplitude

  1. Model Comparison of Subantarctic Mode and Antarctic Intermediate Water In The Southeast Pacific During The Present And Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Hartin, C. A.; Fine, R. A.; Clement, A. C.; Kamenkovich, I. V.; Peterson, L. C.

    2009-12-01

    Subantarctic Mode Water (SAMW) and Antarctic Intermediate Water (AAIW) are large volume mid-depth (400-1200 m) water masses, which transport heat, freshwater and CO2 into the Southern Hemisphere subtropical gyres and to the equatorial thermoclines. This study investigates variations in SAMW and AAIW properties and circulation in the southeast Pacific between the present and Last Glacial Maximum (LGM). Observations from the 1990s and 2000s and model output from NCAR CCSM3 climate model are compared. Under present climate conditions, some of the coldest SAMW and freshest AAIW are formed in the southeast Pacific Ocean. Presently, SAMW is formed equatorward of the Subantarctic Front (SAF) within deep mixed layers, while AAIW is formed just poleward of the SAF. During the LGM there was a fundamental reorganization of the ocean circulation. The model simulates an equatorward shift in the location of formation by approximately 7° between present day and the LGM. The model also simulates a fresher SAMW during the LGM, while AAIW is saltier by up to 1.5 psu. In addition, depth, equatorward extent and thickness have varied between the LGM and present. Comparisons of SAMW and AAIW under present day conditions and under extreme climate conditions (i.e. the LGM), can be used to shed light on how these important water masses will vary with future climate change.

  2. Controls on Last Glacial Maximum ice extent in the Weddell Sea embayment, Antarctica

    NASA Astrophysics Data System (ADS)

    Whitehouse, Pippa L.; Bentley, Michael J.; Vieli, Andreas; Jamieson, Stewart S. R.; Hein, Andrew S.; Sugden, David E.

    2017-01-01

    The Weddell Sea sector of the Antarctic Ice Sheet is hypothesized to have made a significant contribution to sea-level rise since the Last Glacial Maximum. Using a numerical flowline model we investigate the controls on grounding line motion across the eastern Weddell Sea and compare our results with field data relating to past ice extent. Specifically, we investigate the influence of changes in ice temperature, accumulation, sea level, ice shelf basal melt, and ice shelf buttressing on the dynamics of the Foundation Ice Stream. We find that ice shelf basal melt plays an important role in controlling grounding line advance, while a reduction in ice shelf buttressing is found to be necessary for grounding line retreat. There are two stable positions for the grounding line under glacial conditions: at the northern margin of Berkner Island and at the continental shelf break. Global mean sea-level contributions associated with these two scenarios are 50 mm and 130 mm, respectively. Comparing model results with field evidence from the Pensacola Mountains and the Shackleton Range, we find it unlikely that ice was grounded at the continental shelf break for a prolonged period during the last glacial cycle. However, we cannot rule out a brief advance to this position or a scenario in which the grounding line retreated behind present during deglaciation and has since re-advanced. Better constraints on past ice sheet and ice shelf geometry, ocean temperature, and ocean circulation are needed to reconstruct more robustly past behavior of the Foundation Ice Stream.

  3. Tree ring and glacial records of Holocene climate change, northern Gulf of Alaska region

    NASA Astrophysics Data System (ADS)

    Barclay, David J.

    1998-11-01

    Tree-ring cross-dates of glacially overrun trees at eight sites around western Prince William Sound show ice margins advanced in the early (late 12th through 13th centuries AD) and middle (17th to early 18th centuries) Little Ice Age. Tree-ring dates of 22 moraines at 13 glaciers in the same region indicate an early period of moraine stabilization in the early 18th century. This overlaps with the second period of glaciers overrunning trees and marks culmination of this middle Little Ice Age advance. Moraine stabilization on nine of the study forefields in the latter 19th century delineates a third interval of Little Ice Age glacial expansion. These intervals of land-terminating glacier advance are synchronous with other tree-ring dated glacial histories from around the northern Gulf of Alaska, suggesting common climatic forcing across this region. Ring-widths in a 1119-year long tree-ring-width chronology developed from subfossil and living trees on glacial forefields around western Prince William Sound are primarily controlled by May through July temperatures of the growth year. Multi-decadal length warm periods in western Prince William Sound during the past 750 years were centered on 1300, 1440, 1730 and 1950 AD. Major cool periods were centered on 1400, 1660 and 1870 AD. Surficial mapping and 52 radiocarbon ages enable reconstruction of the Holocene glacial history of Yakutat Bay and Russell Fiord. Following an early to middle Holocene non-glacial interval, Hubbard Glacier began an advance at ~5600 cal. BP that culminated between ~4300 and 3474 cal. BP. Retreat by ~3200 cal. BP preceded readvance to Holocene maxima in Yakutat Bay and Russell Fiord at ~725 cal. BP (1225 cal. AD). The Hubbard ice margin in Yakutat Bay retreated by 1245 cal. AD, and was behind its modern position by 1791 AD. Ice from the Brabazon Range kept the Russell Fiord glacier lobe at its maximum until retreat during the late 18th and 19th centuries AD. The extent and timing of specific

  4. Equatorial Moisture Transport in the Asia-Australia Region During the Last Glacial Maximum - Evidence from Paleoceanographic Observations and Modelling Results

    NASA Astrophysics Data System (ADS)

    Mueller, A.; Hope, P.

    2007-05-01

    The Last Glacial Maximum (LGM), about 20,000 years ago, was on average cooler and also drier across the globe. Northern Australia, however, has few appropriate sites from which to gain proxy evidence of the climatic conditions during the culmination of the last glacial. The sediment blown off the continent and deposited in marine cores can begin to provide such evidence. In Australia there are two preferred off-shore dust paths - one of which is to the north-west. Sediment cores from the Timor Trough show higher elemental ratios of Mg/Al, K/Al, and Ti/Al and the presence of an inorganic nitrogen fraction during the late glacial compared to the Holocene (the last 10,000 years). These changes indicate both greater amounts of material off the continent during glacial times and a weathering regime more common in arid, cold climates at the source region of the sediment. To complement the proxy evidence, the results from GCMs forced with LGM sea surface temperatures, ice-sheets and lower atmospheric CO2, were examined. They show cold and dry conditions across northern Australia and stronger off-shore winds in the north-west, conditions that match the climate reconstructions based on the sediment in the marine cores. Cross-equatorial moisture transport during this time does not extend as far south as in the present day, contributing to these dry conditions. However, further north there was limited change in that transport. The LGM sea surface temperature grids used to force these GCMs were based upon temperature reconstructions from cores such as the ones examined here. The fact that the proxy reconstructions of the continental climate from the marine cores matches the GCM simulations based on the surface temperatures reconstructed from such cores provides a consistent picture of the climate of northern Australia during glacial times. This provides evidence where there are few appropriate sites for direct proxy evidence to be obtained.

  5. The atmospheric CH4 increase since the Last Glacial Maximum. I - Source estimates

    NASA Technical Reports Server (NTRS)

    Chappellaz, Jerome A.; Fung, Inez Y.; Thompson, Anne M.

    1993-01-01

    An estimate of the distribution of wetland area and associated CH4 emission is presented for the Last Glacial Maximum (LGM, 18 kyr BP, kiloyear Before Present) and the Pre-Industrial Holocene (PIH, 9000-200 years BP). The wetland source, combined with estimates of the other biogenic sources and sink, yields total source strengths of 120 and 180 Tg CH4/yr for LGM and PIH respectively. These source strengths are shown to be consistent with source estimates inferred from a photochemical model, and point to changes in wetland CH4 source as a major factor driving the atmospheric CH4 increase from LGM to PIH.

  6. The narrow endemic Norwegian peat moss Sphagnum troendelagicum originated before the last glacial maximum

    PubMed Central

    Stenøien, H K; Shaw, A J; Stengrundet, K; Flatberg, K I

    2011-01-01

    It is commonly found that individual hybrid, polyploid species originate recurrently and that many polyploid species originated relatively recently. It has been previously hypothesized that the extremely rare allopolyploid peat moss Sphagnum troendelagicum has originated multiple times, possibly after the last glacial maximum in Scandinavia. This conclusion was based on low linkage disequilibrium in anonymous genetic markers within natural populations, in which sexual reproduction has never been observed. Here we employ microsatellite markers and chloroplast DNA (cpDNA)-encoded trnG sequence data to test hypotheses concerning the origin and evolution of this species. We find that S. tenellum is the maternal progenitor and S. balticum is the paternal progenitor of S. troendelagicum. Using various Bayesian approaches, we estimate that S. troendelagicum originated before the Holocene but not before c. 80 000 years ago (median expected time since speciation 40 000 years before present). The observed lack of complete linkage disequilibrium in the genome of this species suggests cryptic sexual reproduction and recombination. Several lines of evidence suggest multiple origins for S. troendelagicum, but a single origin is supported by approximate Bayesian computation analyses. We hypothesize that S. troendelagicum originated in a peat-dominated refugium before last glacial maximum, and subsequently immigrated to central Norway by means of spore flow during the last thousands of years. PMID:20717162

  7. The Growth Response of Two Diatom Species to Atmospheric Dust from the Last Glacial Maximum

    PubMed Central

    Hoffmann, Linn J.; Breitbarth, Eike; Strzepek, Robert F.; Wolff, Eric W.

    2016-01-01

    Relief of iron (Fe) limitation in the surface Southern Ocean has been suggested as one driver of the regular glacial-interglacial cycles in atmospheric carbon dioxide (CO2). The proposed cause is enhanced deposition of Fe-bearing atmospheric dust to the oceans during glacial intervals, with consequent effects on export production and the carbon cycle. However, understanding the role of enhanced atmospheric Fe supply in biogeochemical cycles is limited by knowledge of the fluxes and ‘bioavailability’ of atmospheric Fe during glacial intervals. Here, we assess the effect of Fe fertilization by dust, dry-extracted from the Last Glacial Maximum portion of the EPICA Dome C Antarctic ice core, on the Antarctic diatom species Eucampia antarctica and Proboscia inermis. Both species showed strong but differing reactions to dust addition. E. antarctica increased cell number (3880 vs. 786 cells mL-1), chlorophyll a (51 vs. 3.9 μg mL-1) and particulate organic carbon (POC; 1.68 vs. 0.28 μg mL-1) production in response to dust compared to controls. P. inermis did not increase cell number in response to dust, but chlorophyll a and POC per cell both strongly increased compared to controls (39 vs. 15 and 2.13 vs. 0.95 ng cell-1 respectively). The net result of both responses was a greater production of POC and chlorophyll a, as well as decreased Si:C and Si:N incorporation ratios within cells. However, E, antarctica decreased silicate uptake for the same nitrate and carbon uptake, while P. inermis increased carbon and nitrate uptake for the same silicate uptake. This suggests that nutrient utilization changes in response to Fe addition could be driven by different underlying mechanisms between different diatom species. Enhanced supply of atmospheric dust to the surface ocean during glacial intervals could therefore have driven nutrient-utilization changes which could permit greater carbon fixation for lower silica utilization. Additionally, both species responded more

  8. Antarctic ice dynamics and southern ocean surface hydrology during the last glacial maximum

    SciTech Connect

    Labeyrie, L.D.; Burckle, L.; Labracherie, M.; Pichon, J.J.; Ippolito, P.; Grojean, M.C.; Duplessy, J.C.

    1985-01-01

    Eight high sedimentation rate cores located between 61/sup 0/S and 43/sup 0/S in the Atlantic and Indian sectors of the Southern Ocean have been studied in detail for foraminifera and diatom /sup 18/O//sup 16/O ratios, and changes in radiolarian and diatom specific abundance. Comparison of these different parameters permits a detailed description of the surface water hydrology during the last glacial maximum. The authors demonstrate that from 25 kyr BP to 15 kyr BP a large number of icebergs formed around the Antarctic continent. Melting along the Polar Front decreased surface salinity by approximately 1.5 per thousand between 43/sup 0/S and 50/sup 0/S. They propose that an increase of snow accumulation at the Antarctic periphery and downdraw during maximum ice extension are primary causes for this major discharge of icebergs.

  9. Evolutionary history underlies plant physiological responses to global change since the last glacial maximum.

    PubMed

    Becklin, Katie M; Medeiros, Juliana S; Sale, Kayla R; Ward, Joy K

    2014-06-01

    Assessing family- and species-level variation in physiological responses to global change across geologic time is critical for understanding factors that underlie changes in species distributions and community composition. Here, we used stable carbon isotopes, leaf nitrogen content and stomatal measurements to assess changes in leaf-level physiology in a mixed conifer community that underwent significant changes in composition since the last glacial maximum (LGM) (21 kyr BP). Our results indicate that most plant taxa decreased stomatal conductance and/or maximum photosynthetic capacity in response to changing conditions since the LGM. However, plant families and species differed in the timing and magnitude of these physiological responses, and responses were more similar within families than within co-occurring species assemblages. This suggests that adaptation at the level of leaf physiology may not be the main determinant of shifts in community composition, and that plant evolutionary history may drive physiological adaptation to global change over recent geologic time.

  10. Assessing the Impact of Laurentide Ice-sheet Topography on Glacial Climate

    NASA Technical Reports Server (NTRS)

    Ullman, D. J.; LeGrande, A. N.; Carlson, A. E.; Anslow, F. S.; Licciardi, J. M.

    2014-01-01

    Simulations of past climates require altered boundary conditions to account for known shifts in the Earth system. For the Last Glacial Maximum (LGM) and subsequent deglaciation, the existence of large Northern Hemisphere ice sheets caused profound changes in surface topography and albedo. While ice-sheet extent is fairly well known, numerous conflicting reconstructions of ice-sheet topography suggest that precision in this boundary condition is lacking. Here we use a high-resolution and oxygen-isotopeenabled fully coupled global circulation model (GCM) (GISS ModelE2-R), along with two different reconstructions of the Laurentide Ice Sheet (LIS) that provide maximum and minimum estimates of LIS elevation, to assess the range of climate variability in response to uncertainty in this boundary condition.We present this comparison at two equilibrium time slices: the LGM, when differences in ice-sheet topography are maximized, and 14 ka, when differences in maximum ice-sheet height are smaller but still exist. Overall, we find significant differences in the climate response to LIS topography, with the larger LIS resulting in enhanced Atlantic Meridional Overturning Circulation and warmer surface air temperatures, particularly over northeastern Asia and the North Pacific. These up- and downstream effects are associated with differences in the development of planetary waves in the upper atmosphere, with the larger LIS resulting in a weaker trough over northeastern Asia that leads to the warmer temperatures and decreased albedo from snow and sea-ice cover. Differences between the 14 ka simulations are similar in spatial extent but smaller in magnitude, suggesting that climate is responding primarily to the larger difference in maximum LIS elevation in the LGM simulations. These results suggest that such uncertainty in ice-sheet boundary conditions alone may significantly impact the results of paleoclimate simulations and their ability to successfully simulate past climates

  11. Climate driven thresholds for post-glacial soil development (Invited)

    NASA Astrophysics Data System (ADS)

    Dixon, J. L.; Chadwick, O.

    2013-12-01

    We explore thresholds in soil development along a strong climate gradient in the South Island of New Zealand. Soils are developed in thin (~1m) loess deposits that mantle LGM and post LGM moraines and outwash in the Waitaki catchment, extending from Lake Benmore in the south to just below the Tasman glacier in the north. We sampled 28 soil profiles across a strong precipitation gradient spanning 400-4000 mm/yr. Base cations in soils are increasingly leached as rainfall increases and soil pH decreases along the climate gradient. The pools of exchangeable iron and aluminum increase with rainfall while pools of plant available nutrients decrease. Several soil processes are nonlinearly affected by rainfall and we identify two important thresholds for soil development in these loessal soils. The first occurs at approximately 800 mm/yr where the soil leaching intensity increases markedly with rainfall, likely associated with the transition to a positive water balance. The second occurs at high rainfall (~2000 mm/yr) where soils become depleted in labile nutrients and base cations, and extractable Al and Fe concentrations no longer increase with increasing rainfall. Together these data identify nonlinear changes in weathering intensity with rainfall, and show clear climate control on relatively young, post-glacial soil development.

  12. Phylogenetic assemblage structure of North American trees is more strongly shaped by glacial-interglacial climate variability in gymnosperms than in angiosperms.

    PubMed

    Ma, Ziyu; Sandel, Brody; Svenning, Jens-Christian

    2016-05-01

    How fast does biodiversity respond to climate change? The relationship of past and current climate with phylogenetic assemblage structure helps us to understand this question. Studies of angiosperm tree diversity in North America have already suggested effects of current water-energy balance and tropical niche conservatism. However, the role of glacial-interglacial climate variability remains to be determined, and little is known about any of these relationships for gymnosperms. Moreover, phylogenetic endemism, the concentration of unique lineages in restricted ranges, may also be related to glacial-interglacial climate variability and needs more attention. We used a refined phylogeny of both angiosperms and gymnosperms to map phylogenetic diversity, clustering and endemism of North American trees in 100-km grid cells, and climate change velocity since Last Glacial Maximum together with postglacial accessibility to recolonization to quantify glacial-interglacial climate variability. We found: (1) Current climate is the dominant factor explaining the overall patterns, with more clustered angiosperm assemblages toward lower temperature, consistent with tropical niche conservatism. (2) Long-term climate stability is associated with higher angiosperm endemism, while higher postglacial accessibility is linked to to more phylogenetic clustering and endemism in gymnosperms. (3) Factors linked to glacial-interglacial climate change have stronger effects on gymnosperms than on angiosperms. These results suggest that paleoclimate legacies supplement current climate in shaping phylogenetic patterns in North American trees, and especially so for gymnosperms.

  13. Testing a dynamic global vegetation model for pre-industrial and Last Glacial Maximum boundary conditions

    NASA Astrophysics Data System (ADS)

    Handiani, Dian N.; Rachmayani, Rima; Paul, André; Dupont, Lydie M.

    2010-05-01

    Achieving better comparison between dynamic global vegetation models (DGVM) with pollen or plant data is important for the climate-vegetation modeling community. Our study tried to find a scheme that can be applied consistently to compare DGVMs with pollen data sets. We tested two models, the Top-down Representation of Interactive Foliage and Flora Including Dynamics (TRIFFID) and the Community Land Model's Dynamic Global Vegetation Model (CLM-DGVM), which we both ran for pre-industrial boundary conditions. In addition, we ran the TRIFFID model using boundary conditions for the Last Glacial Maximum (LGM, ~19,000- 23,000 years before present). For comparisons, we used the modern vegetation of the BIOME4 model and the reconstruction for the year 18000 after pollen data from the BIOME6000 (Version 4.2) project. Differences in the number of PFTs in each DGVMs lead to different results of the biome distribution even if models and data qualitatively agree. In the CLM-DGVM pre-industrial run, northern South America is covered by savanna or desert biome, which is associated with more growing degree days and lower rates of precipitation. Meanwhile, the TRIFFID model simulated a tropical forest in northern South America and a desert biome in Australia, probably because of higher values of growing degree days and different precipitation rates, which is lower in South America and higher in Australia. The climate parameters from both models show a similar pattern as in the BIOME4 model, but the values are higher in the DGVMs. Biome distributions of the pre-industrial simulation show similarities and differences between dynamic vegetation modeling and data reconstructions. Both models reveal a fair agreement simulating savanna and desert biomes around the Sahel, tropical forest in western Africa, boreal forest in eastern North America and in Siberia, and tundra in northern Canada. Some discrepancies appear in South America and Africa, where pollen data indicate a combination of

  14. Effects of fire and CO2 on biogeography and primary production in glacial and modern climates.

    PubMed

    Martin Calvo, Maria; Prentice, Iain Colin

    2015-11-01

    Dynamic global vegetation models (DGVMs) can disentangle causes and effects in the control of vegetation and fire. We used a DGVM to analyse climate, CO2 and fire influences on biome distribution and net primary production (NPP) in last glacial maximum (LGM) and pre-industrial (PI) times. The Land surface Processes and eXchanges (LPX) DGVM was run in a factorial design with fire 'off' or 'on', CO2 at LGM (185 ppm) or PI (280 ppm) concentrations, and LGM (modelled) or recent climates. Results were analysed by Stein-Alpert decomposition to separate primary effects from synergies. Fire removal causes forests to expand and global NPP to increase slightly. Low CO2 greatly reduces forest area (dramatically in a PI climate; realistically under an LGM climate) and global NPP. NPP under an LGM climate was reduced by a quarter as a result of low CO2 . The reduction in global NPP was smaller at low temperatures, but greater in the presence of fire. Global NPP is controlled by climate and CO2 directly through photosynthesis, but also through biome distribution, which is strongly influenced by fire. Future vegetation simulations will need to consider the coupled responses of vegetation and fire to CO2 and climate.

  15. Ploidy race distributions since the Last Glacial Maximum in the North American desert shrub, Larrea tridentata

    USGS Publications Warehouse

    Hunter, K.L.; Betancourt, J.L.; Riddle, B.R.; Van Devender, T. R.; Cole, K.L.; Geoffrey, Spaulding W.

    2000-01-01

    1 A classic biogeographic pattern is the alignment of diploid, tetraploid and hexaploid races of creosote bush (Larrea tridentata) across the Chihuahuan, Sonoran and Mohave Deserts of western North America. We used statistically robust differences in guard cell size of modern plants and fossil leaves from packrat middens to map current and past distributions of these ploidy races since the Last Glacial Maximum (LGM). 2 Glacial/early Holocene (26-10 14C kyr BP or thousands of radiocarbon years before present) populations included diploids along the lower Rio Grande of west Texas, 650 km removed from sympatric diploids and tetraploids in the lower Colorado River Basin of south-eastern California/south-western Arizona. Diploids migrated slowly from lower Rio Grande refugia with expansion into the northern Chihuahuan Desert sites forestalled until after ???4.0 14C kyr BP. Tetraploids expanded from the lower Colorado River Basin into the northern limits of the Sonoran Desert in central Arizona by 6.4 14C kyr BP. Hexaploids appeared by 8.5 14C kyr BP in the lower Colorado River Basin, reaching their northernmost limits (???37??N) in the Mohave Desert between 5.6 and 3.9 14C kyr BP. 3 Modern diploid isolates may have resulted from both vicariant and dispersal events. In central Baja California and the lower Colorado River Basin, modern diploids probably originated from relict populations near glacial refugia. Founder events in the middle and late Holocene established diploid outposts on isolated limestone outcrops in areas of central and southern Arizona dominated by tetraploid populations. 4 Geographic alignment of the three ploidy races along the modern gradient of increasingly drier and hotter summers is clearly a postglacial phenomenon, but evolution of both higher ploidy races must have happened before the Holocene. The exact timing and mechanism of polyploidy evolution in creosote bush remains a matter of conjecture. ?? 2001 Blackwell Science Ltd.

  16. Ploidy race distributions since the Last Glacial Maximum in the North American desert shrub, Larea tridentata

    USGS Publications Warehouse

    Hunter, Kimberly L.; Betancourt, Julio L.; Riddle, Brett R.; Van Devender, Thomas R.; Cole, K.L.; Spaulding, W.G.

    2001-01-01

    1. A classic biogeographic pattern is the alignment of diploid, tetraploid and hexaploid races of creosote bush (Larrea tridentata) across the Chihuahuan, Sonoran and Mohave Deserts of western North America. We used statistically robust differences in guard cell size of modern plants and fossil leaves from packrat middens to map current and past distributions of these ploidy races since the Last Glacial Maximum (LGM). 2 Glacial/early Holocene (26a??10 14C kyr bp or thousands of radiocarbon years before present) populations included diploids along the lower Rio Grande of west Texas, 650 km removed from sympatric diploids and tetraploids in the lower Colorado River Basin of south-eastern California/south-western Arizona. Diploids migrated slowly from lower Rio Grande refugia with expansion into the northern Chihuahuan Desert sites forestalled until after ~4.0 14C kyr bp. Tetraploids expanded from the lower Colorado River Basin into the northern limits of the Sonoran Desert in central Arizona by 6.4 14C kyr bp. Hexaploids appeared by 8.5 14C kyr bp in the lower Colorado River Basin, reaching their northernmost limits (~37A?N) in the Mohave Desert between 5.6 and 3.9 14C kyr bp. 3 Modern diploid isolates may have resulted from both vicariant and dispersal events. In central Baja California and the lower Colorado River Basin, modern diploids probably originated from relict populations near glacial refugia. Founder events in the middle and late Holocene established diploid outposts on isolated limestone outcrops in areas of central and southern Arizona dominated by tetraploid populations. 4 Geographic alignment of the three ploidy races along the modern gradient of increasingly drier and hotter summers is clearly a postglacial phenomenon, but evolution of both higher ploidy races must have happened before the Holocene. The exact timing and mechanism of polyploidy evolution in creosote bush remains a matter of conjecture.

  17. Constraints on soluble aerosol iron flux to the Southern Ocean at the Last Glacial Maximum

    PubMed Central

    Conway, T.M.; Wolff, E.W.; Röthlisberger, R.; Mulvaney, R.; Elderfield, H.E.

    2015-01-01

    Relief of iron (Fe) limitation in the Southern Ocean during ice ages, with potentially increased carbon storage in the ocean, has been invoked as one driver of glacial–interglacial atmospheric CO2 cycles. Ice and marine sediment records demonstrate that atmospheric dust supply to the oceans increased by up to an order of magnitude during glacial intervals. However, poor constraints on soluble atmospheric Fe fluxes to the oceans limit assessment of the role of Fe in glacial–interglacial change. Here, using novel techniques, we present estimates of water- and seawater-soluble Fe solubility in Last Glacial Maximum (LGM) atmospheric dust from the European Project for Ice Coring in Antarctica (EPICA) Dome C and Berkner Island ice cores. Fe solubility was very variable (1–42%) during the interval, and frequently higher than typically assumed by models. Soluble aerosol Fe fluxes to Dome C at the LGM (0.01–0.84 mg m−2 per year) suggest that soluble Fe deposition to the Southern Ocean would have been ≥10 × modern deposition, rivalling upwelling supply. PMID:26204562

  18. Mite dispersal among the Southern Ocean Islands and Antarctica before the last glacial maximum

    PubMed Central

    Mortimer, E.; Jansen van Vuuren, B.; Lee, J. E.; Marshall, D. J.; Convey, P.; Chown, S. L.

    2011-01-01

    It has long been maintained that the majority of terrestrial Antarctic species are relatively recent, post last glacial maximum, arrivals with perhaps a few microbial or protozoan taxa being substantially older. Recent studies have questioned this ‘recolonization hypothesis’, though the range of taxa examined has been limited. Here, we present the first large-scale study for mites, one of two dominant terrestrial arthropod groups in the region. Specifically, we provide a broad-scale molecular phylogeny of a biologically significant group of ameronothroid mites from across the maritime and sub-Antarctic regions. Applying different dating approaches, we show that divergences among the ameronothroid mite genera Podacarus, Alaskozetes and Halozetes significantly predate the Pleistocene and provide evidence of independent dispersals across the Antarctic Polar Front. Our data add to a growing body of evidence demonstrating that many taxa have survived glaciation of the Antarctic continent and the sub-Antarctic islands. Moreover, they also provide evidence of a relatively uncommon trend of dispersals from islands to continental mainlands. Within the ameronothroid mites, two distinct clades with specific habitat preferences (marine intertidal versus terrestrial/supralittoral) exist, supporting a model of within-habitat speciation rather than colonization from marine refugia to terrestrial habitats. The present results provide additional impetus for a search for terrestrial refugia in an area previously thought to have lacked ice-free ground during glacial maxima. PMID:20943685

  19. Ancient DNA supports southern survival of Richardson's collared lemming (Dicrostonyx richardsoni) during the last glacial maximum.

    PubMed

    Fulton, Tara L; Norris, Ryan W; Graham, Russell W; Semken, Holmes A; Shapiro, Beth

    2013-05-01

    Collared lemmings (genus Dicrostonyx) are circumpolar Arctic arvicoline rodents associated with tundra. However, during the last glacial maximum (LGM), Dicrostonyx lived along the southern ice margin of the Laurentide ice sheet in communities comprising both temperate and boreal species. To better understand these communities and the fate of these southern individuals, we compare mitochondrial cytochrome b sequence data from three LGM-age Dicrostonyx fossils from south of the Laurentide ice sheet to sequences from modern Dicrostonyx sampled from across their present-day range. We test whether the Dicrostonyx populations from LGM-age continental USA became extinct at the Pleistocene-Holocene transition ~11000 years ago or, alternatively, if they belong to an extant species whose habitat preferences can be used to infer the palaeoclimate along the glacial margin. Our results indicate that LGM-age Dicrostonyx from Iowa and South Dakota belong to Dicrostonyx richardsoni, which currently lives in a temperate tundra environment west of Hudson Bay, Canada. This suggests a palaeoclimate south of the Laurentide ice sheet that contains elements similar to the more temperate shrub tundra characteristic of extant D. richardsoni habitat, rather than the very cold, dry tundra of the Northern Arctic. While more data are required to determine whether or not the LGM southern population is ancestral to extant D. richardsoni, it seems most probable that the species survived the LGM in a southern refugium.

  20. Polar front shift and atmospheric CO2 during the glacial maximum of the Early Paleozoic Icehouse.

    PubMed

    Vandenbroucke, Thijs R A; Armstrong, Howard A; Williams, Mark; Paris, Florentin; Zalasiewicz, Jan A; Sabbe, Koen; Nõlvak, Jaak; Challands, Thomas J; Verniers, Jacques; Servais, Thomas

    2010-08-24

    Our new data address the paradox of Late Ordovician glaciation under supposedly high pCO(2) (8 to 22x PAL: preindustrial atmospheric level). The paleobiogeographical distribution of chitinozoan ("mixed layer") marine zooplankton biotopes for the Hirnantian glacial maximum (440 Ma) are reconstructed and compared to those from the Sandbian (460 Ma): They demonstrate a steeper latitudinal temperature gradient and an equatorwards shift of the Polar Front through time from 55 degrees -70 degrees S to approximately 40 degrees S. These changes are comparable to those during Pleistocene interglacial-glacial cycles. In comparison with the Pleistocene, we hypothesize a significant decline in mean global temperature from the Sandbian to Hirnantian, proportional with a fall in pCO(2) from a modeled Sandbian level of approximately 8x PAL to approximately 5x PAL during the Hirnantian. Our data suggest that a compression of midlatitudinal biotopes and ecospace in response to the developing glaciation was a likely cause of the end-Ordovician mass extinction.

  1. Polar front shift and atmospheric CO2 during the glacial maximum of the Early Paleozoic Icehouse

    PubMed Central

    Vandenbroucke, Thijs R. A.; Armstrong, Howard A.; Williams, Mark; Paris, Florentin; Zalasiewicz, Jan A.; Sabbe, Koen; Nõlvak, Jaak; Challands, Thomas J.; Verniers, Jacques; Servais, Thomas

    2010-01-01

    Our new data address the paradox of Late Ordovician glaciation under supposedly high pCO2 (8 to 22× PAL: preindustrial atmospheric level). The paleobiogeographical distribution of chitinozoan (“mixed layer”) marine zooplankton biotopes for the Hirnantian glacial maximum (440 Ma) are reconstructed and compared to those from the Sandbian (460 Ma): They demonstrate a steeper latitudinal temperature gradient and an equatorwards shift of the Polar Front through time from 55°–70° S to ∼40° S. These changes are comparable to those during Pleistocene interglacial-glacial cycles. In comparison with the Pleistocene, we hypothesize a significant decline in mean global temperature from the Sandbian to Hirnantian, proportional with a fall in pCO2 from a modeled Sandbian level of ∼8× PAL to ∼5× PAL during the Hirnantian. Our data suggest that a compression of midlatitudinal biotopes and ecospace in response to the developing glaciation was a likely cause of the end-Ordovician mass extinction. PMID:20696937

  2. The Influence of Glacial Ice Sheets on Atlantic Meridional Overturning Circulation Through Atmospheric Circulation Change under Glacial Climate

    NASA Astrophysics Data System (ADS)

    Sherriff-Tadano, S.; Abe-Ouchi, A.; Yoshimori, M.; Oka, A.; Chan, W. L.

    2014-12-01

    It is well known that glacial ice sheets (Laurentide, Fennoscandian and Antarctic ice sheets) exert a large influence on the climate including the atmospheric circulation. Moreover, recent climate modeling studies suggest that glacial ice sheets have a large impact on the Atlantic meridional overturning circulation (AMOC). However, the process by which the ice sheets impact on the AMOC is not yet fully understood. On the other hand, recent studies showed that surface wind changes play a crucial role on changes to the AMOC under glacial climate. Therefore, in this study, we investigate in detail, the process by which the ice sheet modifies the AMOC through surface wind change. Here we conduct numerical experiments using an atmospheric general circulation model (AGCM) and an ocean general circulation model (OGCM) separately. Our method consists of 2 steps. First, from AGCM experiments, we evaluate the effect of glacial ice sheets on the surface wind. Second, from OGCM experiments, we evaluate the influence of the wind stress change on the AMOC by applying the surface wind change as a boundary condition, while leaving other boundary conditions (surface heat and water fluxes) unchanged. In addition, we conduct several sensitivity experiments. Using the AGCM, we explore individual ice sheet effect, ice sheet topography effect and albedo effect on surface wind change. Moreover, using the OGCM, we change the surface wind gradually or apply the surface wind change only at a specific region in order to explore the wind change effect in detail. We find that glacial ice sheets largely intensify the AMOC by surface wind change under glacial climate. Compare to other regions, it reveals that the wind change at the North Atlantic (NA) is a key region. There, the northern glacial ice sheet topography intensifies the Icelandic Low and anti-cyclonic circulation over the Laurentide ice sheet. However, this wind effect is effective only when the NA is not widely covered by sea ice

  3. Erosion and transport by Byrd Glacier, Antarctica during the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Licht, K. J.; Palmer, E. F.

    2013-02-01

    Glacial till samples from seven, modern-Holocene Byrd Glacier moraines were characterized using particle size analysis, sand petrography and detrital zircon geochronology and compared to Ross Sea tills deposited during the Last Glacial Maximum. The goal was to identify the paleoflow path for Byrd Glacier and assess the use of multiple provenance techniques. The coarse sand fraction of Byrd Glacier tills is dominated by lithic fragments of adjacent bedrock outcrops, except samples from the Lonewolf Nunataks, which have a higher proportion of mineral to lithic fragments, as well as a recognizable exotic component. Cluster analysis shows that Byrd Glacier tills, with the exception of the two Lonewolf Nunataks sites, do not cluster strongly with Ross Sea samples because they have a higher proportion of lithic fragments. This indicates that comminution must be an active subglacial process beneath East Antarctic outlet glaciers. Byrd Glacier tills are also typically coarser grained that Ross Sea tills and their maturity is a reflection of both glacial processes and rock type. Measured U/Pb ages of detrital zircons from Byrd Glacier tills range from Triassic to Archean (240-3540 Ma) with a dominance of grains 530-600 Ma. Ross Sea till samples show spatial variability in U/Pb age distributions, with the core sites west of the 180° longitude line showing similarity to most Byrd Glacier tills, whereas core NBP9407-39, east of 180° long., is dominated by ˜100 Ma grains. Ross Sea tills also contain a recognizable detrital zircon fraction eroded inland of the Transantarctic Mountains. Both provenance methods indicate that the ice flow line for Byrd Glacier during the LGM was to the east of Ross Island and extended on either side of Ross Bank, with the majority of ice flowing to the Ross Sea's Central Basin. Our analysis shows that sand petrography and detrital zircon U/Pb age spectra provide complementary datasets that produce similar ice flow reconstructions and reveal

  4. Linking microbial assemblages to paleoenvironmental conditions from the Holocene and Last Glacial Maximum times in Laguna Potrok Aike sediments, Argentina

    NASA Astrophysics Data System (ADS)

    Vuillemin, Aurele; Ariztegui, Daniel; Leavitt, Peter R.; Bunting, Lynda

    2014-05-01

    Laguna Potrok Aike is a closed basin located in the southern hemisphere's mid-latitudes (52°S) where paleoenvironmental conditions were recorded as temporal sedimentary sequences resulting from variations in the regional hydrological regime and geology of the catchment. The interpretation of the limnogeological multiproxy record developed during the ICDP-PASADO project allowed the identification of contrasting time windows associated with the fluctuations of Southern Westerly Winds. In the framework of this project, a 100-m-long core was also dedicated to a detailed geomicrobiological study which aimed at a thorough investigation of the lacustrine subsurface biosphere. Indeed, aquatic sediments do not only record past climatic conditions, but also provide a wide range of ecological niches for microbes. In this context, the influence of environmental features upon microbial development and survival remained still unexplored for the deep lacustrine realm. Therefore, we investigated living microbes throughout the sedimentary sequence using in situ ATP assays and DAPI cell count. These results, compiled with pore water analysis, SEM microscopy of authigenic concretions and methane and fatty acid biogeochemistry, provided evidence for a sustained microbial activity in deep sediments and pinpointed the substantial role of microbial processes in modifying initial organic and mineral fractions. Finally, because the genetic material associated with microorganisms can be preserved in sediments over millennia, we extracted environmental DNA from Laguna Potrok Aike sediments and established 16S rRNA bacterial and archaeal clone libraries to better define the use of DNA-based techniques in reconstructing past environments. We focused on two sedimentary horizons both displaying in situ microbial activity, respectively corresponding to the Holocene and Last Glacial Maximum periods. Sequences recovered from the productive Holocene record revealed a microbial community adapted to

  5. Retreat history of the East Antarctic Ice Sheet since the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Mackintosh, Andrew N.; Verleyen, Elie; O'Brien, Philip E.; White, Duanne A.; Jones, R. Selwyn; McKay, Robert; Dunbar, Robert; Gore, Damian B.; Fink, David; Post, Alexandra L.; Miura, Hideki; Leventer, Amy; Goodwin, Ian; Hodgson, Dominic A.; Lilly, Katherine; Crosta, Xavier; Golledge, Nicholas R.; Wagner, Bernd; Berg, Sonja; van Ommen, Tas; Zwartz, Dan; Roberts, Stephen J.; Vyverman, Wim; Masse, Guillaume

    2014-09-01

    The East Antarctic Ice Sheet (EAIS) is the largest continental ice mass on Earth, and documenting its evolution since the Last Glacial Maximum (LGM) is important for understanding its present-day and future behaviour. As part of a community effort, we review geological evidence from East Antarctica that constrains the ice sheet history throughout this period (˜30,000 years ago to present). This includes terrestrial cosmogenic nuclide dates from previously glaciated regions, 14C chronologies from glacial and post-glacial deposits onshore and on the continental shelf, and ice sheet thickness changes inferred from ice cores and continental-scale ice sheet models. We also include new 14C dates from the George V Land - Terre Adélie Coast shelf. We show that the EAIS advanced to the continental shelf margin in some parts of East Antarctica, and that the ice sheet characteristically thickened by 300-400 m near the present-day coastline at these sites. This advance was associated with the formation of low-gradient ice streams that grounded at depths of >1 km below sea level on the inner continental shelf. The Lambert/Amery system thickened by a greater amount (800 m) near its present-day grounding zone, but did not advance beyond the inner continental shelf. At other sites in coastal East Antarctica (e.g. Bunger Hills, Larsemann Hills), very little change in the ice sheet margin occurred at the LGM, perhaps because ice streams accommodated any excess ice build up, leaving adjacent, ice-free areas relatively unaffected. Evidence from nunataks indicates that the amount of ice sheet thickening diminished inland at the LGM, an observation supported by ice cores, which suggest that interior ice sheet domes were ˜100 m lower than present at this time. Ice sheet recession may have started ˜18,000 years ago in the Lambert/Amery glacial system, and by ˜14,000 years ago in Mac.Robertson Land. These early pulses of deglaciation may have been responses to abrupt sea-level rise

  6. The atmospheric CH4 increase since the Last Glacial Maximum. II - Interactions with oxidants

    NASA Technical Reports Server (NTRS)

    Thompson, Anne M.; Chappellaz, Jerome A.; Fung, Inez Y.; Kucsera, T. L.

    1993-01-01

    Results of two studies of the effect of changing CH4 fluxes on global tropospheric oxidant levels, O3, OH, and H2O2, performed with a multibox photochemical model, are presented. A sensitivity study is conducted by scaling back CH4, CO, and NO emissions relative to the present-day budget. When the CH4 ice core record is compared to calculated CH4 abundances, corresponding CH4 fluxes for the preindustrial Holocene (PIH) and Last Glacial Maximum (LGM) are fairly well-constrained: 175-225 Tg CH/4/yr for PIH and 100-130 Tg CH4/yr for LGM. Specific scenarios for CH4/CO/NO are selected to represent sources for the PIH and LGM. The CH4 budget is taken from an evaluation of wetlands and other natural sources.

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

    PubMed

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

    2002-02-22

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

  8. First Global Climate Model Simulations of the M2 Pliocene Glacial

    NASA Astrophysics Data System (ADS)

    Dolan, A.; Haywood, A.; Hunter, S. J.; Tindall, J.; Valdes, P. J.

    2013-12-01

    The Pliocene Epoch (5.2 to 2.6 Ma) and specifically the PRISM interval (3.0 to 3.3 Ma) have frequently been targeted to investigate warm intervals in Earth history (e.g. Haywood et al., 2013). However, climate variability within the Pliocene is often overlooked. Although not as dramatic as the glacial and interglacial cycles that typified the Pleistocene, the Pliocene also exhibited climate variability and periods which were apparently cooler than modern (Lisiecki and Raymo, 2005). Of particular interest is the major cooling event that occurred around 3.3 Ma during Marine Isotope Stage (MIS) M2. This 'Pliocene glacial' punctuates an otherwise relatively warm background climate and has been referred to as a failed attempt of the climate to reach a full glacial state (De Schepper et al., 2009; Haug and Tiedemann, 1998). The onset of full Northern Hemisphere (NH) glaciation finally occurred at the end of the Pliocene (~ 2.75 Ma). Although numerous temperature reconstructions from around the world's oceans tend to capture the MIS M2 cooling event, the exact nature of M2 remains enigmatic. Sea level records vary but suggest a maximum sea level drop of ~65 m compared to modern, which in itself is significant enough to necessitate the growth of a NH ice sheet (Dwyer and Chandler, 2009). Previous ice sheet modelling suggests that ~8 m sea level equivalent (SLE) ice could be stored on Antarctica (Pollard and DeConto, 2009) and this larger ice sheet (compared to modern) is potentially supported by the increase in ice-rafted debris (IRD) found offshore of East Antarctica during this time (Passchier, 2011). IRD in the North Atlantic would suggest the presence of an ice sheet on Greenland (e.g. Kleiven et al., 2002), but the locations of other ice caps in the NH are not determined due to the destructive nature of subsequent Pleistocene ice sheet advances. Moreover, recent evidence questions whether the climate in the NH was favourable at all for the initiation of ice sheets

  9. Deepwater redox changes in the southern Okinawa Trough since the last glacial maximum

    NASA Astrophysics Data System (ADS)

    Dou, Yanguang; Yang, Shouye; Li, Chao; Shi, Xuefa; Liu, Jihua; Bi, Lei

    2015-06-01

    In this study, rare earth element (REE) was treated as a paleo-redox proxy to investigate the changes of depositional environment in the southern Okinawa Trough since the last glacial maximum. The acid-leachable fraction (leachate) of the sediments recovered from the ODP Site 1202B is dominated by biogenic and authigenic components while detrital contamination is minor. The significant enrichment of middle REE suggests a large contribution from authigenic Mn oxyhydroxides and cerium (Ce) anomaly can indicate deepwater redox change. The REE parameters including Ce anomaly in the leachate exhibit remarkable and abrupt changes in the early Holocene (∼9.5 ka) and during LGM (∼20 ka). An increase of Ce anomaly at 28-22 ka implies the suboxic deepwater condition probably caused by increased primary productivity. Weak positive Ce anomalies during the last glacial maximum and deglaciation suggest an oxic depositional environment responding to the enhanced deepwater ventilation with the advection of the North Pacific Intermediate Water and/or South China Sea Intermediate Water into the trough. A decrease of Ce anomaly in the early Holocene might be caused by the intrusion and strengthening of the Kuroshio Current in the trough that enhanced the water stratification and induced a gradual development of suboxic depositional condition. Furthermore, an abrupt change of chemical composition at ca. 4 ka probably indicates a decrease of dissolved oxygen in deepwater and a weakening of ventilation in the Okinawa Trough. This study suggests that REE proxy can provide new insights into the linkage among surface current, deepwater circulation and sediment record in the continental margin where terrigenous input dominates.

  10. Reaching and abandoning the furthest ice extent during the Last Glacial Maximum in the Alps

    NASA Astrophysics Data System (ADS)

    Ivy-Ochs, Susan; Wirsig, Christian; Zasadni, Jerzy; Hippe, Kristina; Christl, Marcus; Akçar, Naki; Schluechter, Christian

    2016-04-01

    During the Last Glacial Maximum (LGM) in the European Alps (late Würm) local ice caps and extensive ice fields in the high Alps fed huge outlet glaciers that occupied the main valleys and extended onto the forelands as piedmont lobes. Records from numerous sites suggest advance of glaciers beyond the mountain front by around 30 ka (Ivy-Ochs 2015 and references therein). Reaching of the maximum extent occurred by about 27-26 ka, as exemplified by dates from the Rhein glacier area (Keller and Krayss, 2005). Abandonment of the outermost moraines at sites north and south of the Alps was underway by about 24 ka. In the high Alps, systems of transection glaciers with transfluences over many of the Alpine passes dominated, for example, at Grimsel Pass in the Central Alps (Switzerland). 10Be exposure ages of 23 ± 1 ka for glacially sculpted bedrock located just a few meters below the LGM trimline in the Haslital near Grimsel Pass suggest a pulse of ice surface lowering at about the same time that the foreland moraines were being abandoned (Wirsig et al., 2016). Widespread ice surface lowering in the high Alps was underway by no later than 18 ka. Thereafter, glaciers oscillated at stillstand and minor re-advance positions on the northern forelands for several thousand years forming the LGM stadial moraines. Final recession back within the mountain front took place by 19-18 ka. Recalculation to a common basis of all published 10Be exposure dates for boulders situated on LGM moraines suggests a strong degree of synchrony for the timing of onset of ice decay both north and south of the Alps. Ivy-Ochs, S., 2015, Cuadernos de investigación geográfica 41: 295-315. Keller, O., Krayss, E., 2005, Vierteljahrschr. Naturforsch. Gesell. Zürich 150: 69-85. Wirsig, C. et al., 2016, J. Quat. Sci. 31: 46-59.

  11. Quantifying the change in equilibrium-line altitude during the Last Glacial Maximum in the Subtropical Andes using a mass-balance model

    NASA Astrophysics Data System (ADS)

    Vargo, L.; Galewsky, J.

    2014-12-01

    Quantifying changes in equilibrium-line altitude (ELA) can be used to better understand past regional climates. We use a glacial mass-balance model in conjunction with global climate model (GCM) output data to calculate the change in ELA between modern and Last Glacial Maximum (LGM; 21 ka) climates in the presently hyper-arid subtropical Andes. The region is currently unglaciated, despite cold enough temperatures, as there is too little moisture to sustain glaciers. Previous studies suggest this area was glaciated during the LGM, however, little is known about the extent of the glaciation or the climate required to sustain it. The mass-balance model used in this study calculates the change in ELA using the positive degree-day (PDD) sum, the sum of daily mean air temperatures that are above zero. The PDD sum is used to calculate ablation, which is then assumed to be proportional to temperature, in order to calculate the change in ELA. Using output from several GCM simulations, we compare the change in ELA between LGM and modern climates across the different models for the subtropical Andes. These simulations suggest that the changes in climate resulted in a lowering of ELAs to the extent that parts of the subtropical Andes were glaciated during the LGM.

  12. The climate response of the Indo-Pacific warm pool to glacial sea level

    NASA Astrophysics Data System (ADS)

    Di Nezio, Pedro N.; Timmermann, Axel; Tierney, Jessica E.; Jin, Fei-Fei; Otto-Bliesner, Bette; Rosenbloom, Nan; Mapes, Brian; Neale, Rich; Ivanovic, Ruza F.; Montenegro, Alvaro

    2016-06-01

    Growing climate proxy evidence suggests that changes in sea level are important drivers of tropical climate change on glacial-interglacial timescales. These paleodata suggest that rainfall patterns over the Indo-Pacific warm pool (IPWP) are highly sensitive to the landmass configuration of the Maritime Continent and that lowered sea level contributed to large-scale drying during the Last Glacial Maximum (LGM, approximately 21,000 years B.P.). Using the Community Earth System Model Version 1.2 (CESM1), we investigate the mechanisms by which lowered sea level influenced the climate of the IPWP during the LGM. The CESM1 simulations show that, in agreement with previous hypotheses, changes in atmospheric circulation are initiated by the exposure of the Sunda and Sahul shelves. Ocean dynamical processes amplify the changes in atmospheric circulation by increasing the east-west sea surface temperature (SST) gradient along the equatorial Indian Ocean. The coupled mechanism driving this response is akin to the Bjerknes feedback and results in a large-scale climatic reorganization over the Indian Ocean with impacts extending from east Africa to the western tropical Pacific. Unlike exposure of the Sunda shelf, exposure of Sahul shelf and the associated changes in surface albedo play a key role because of the positive feedback. This mechanism could explain the pattern of dry (wet) eastern (western) Indian Ocean identified in climate proxies and LGM simulations. However, this response also requires a strengthened SST gradient along the equatorial Indian Ocean, a pattern that is not evident in marine paleoreconstructions. Strategies to resolve this issue are discussed.

  13. Sea-surface temperatures around the Australian margin and Indian Ocean during the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Barrows, Timothy T.; Juggins, Steve

    2005-04-01

    We present new last glacial maximum (LGM) sea-surface temperature (SST) maps for the oceans around Australia based on planktonic foraminifera assemblages. To provide the most reliable SST estimates we use the modern analog technique, the revised analog method, and artificial neural networks in conjunction with an expanded modern core top database. All three methods produce similar quality predictions and the root mean squared error of the consensus prediction (the average of the three) under cross-validation is only ±0.77 °C. We determine LGM SST using data from 165 cores, most of which have good age control from oxygen isotope stratigraphy and radiocarbon dates. The coldest SST occurred at 20,500±1400 cal yr BP, predating the maximum in oxygen isotope records at 18,200±1500 cal yr BP. During the LGM interval we observe cooling within the tropics of up to 4 °C in the eastern Indian Ocean, and mostly between 0 and 3 °C elsewhere along the equator. The high latitudes cooled by the greatest degree, a maximum of 7-9 °C in the southwest Pacific Ocean. Our maps improve substantially on previous attempts by making higher quality temperature estimates, using more cores, and improving age control.

  14. North American paleoclimate reconstructions for the Last Glacial Maximum using an inverse modeling through iterative forward modeling approach applied to pollen data

    NASA Astrophysics Data System (ADS)

    Izumi, Kenji; Bartlein, Patrick J.

    2016-10-01

    The inverse modeling through iterative forward modeling (IMIFM) approach was used to reconstruct Last Glacial Maximum (LGM) climates from North American fossil pollen data. The approach was validated using modern pollen data and observed climate data. While the large-scale LGM temperature IMIFM reconstructions are similar to those calculated using conventional statistical approaches, the reconstructions of moisture variables differ between the two approaches. We used two vegetation models, BIOME4 and BIOME5-beta, with the IMIFM approach to evaluate the effects on the LGM climate reconstruction of differences in water use efficiency, carbon use efficiency, and atmospheric CO2 concentrations. Although lower atmospheric CO2 concentrations influence pollen-based LGM moisture reconstructions, they do not significantly affect temperature reconstructions over most of North America. This study implies that the LGM climate was very cold but not very much drier than present over North America, which is inconsistent with previous studies.

  15. Bundled turbidite deposition in the central Pandora Trough (Gulf of Papua) since Last Glacial Maximum: Linking sediment nature and accumulation to sea level fluctuations at millennial timescale

    NASA Astrophysics Data System (ADS)

    Jorry, StéPhan J.; Droxler, André W.; Mallarino, Gianni; Dickens, Gerald R.; Bentley, Sam J.; Beaufort, Luc; Peterson, Larry C.; Opdyke, Bradley N.

    2008-03-01

    Since Last Glacial Maximum (23-19 ka), Earth climate warming and deglaciation occurred in two major steps (Bølling-Allerød and Preboreal), interrupted by a short cooling interval referred to as the Younger Dryas (12.5-11.5 ka B.P.). In this study, three cores (MV-33, MV-66, and MD-40) collected in the central part of Pandora Trough (Gulf of Papua) have been analyzed, and they reveal a detailed sedimentary pattern at millennial timescale. Siliciclastic turbidites disappeared during the Bølling-Allerød and Preboreal intervals to systematically reoccur during the Younger Dryas interval. Subsequent to the final disappearance of the siliciclastic turbidites a calciturbidite occurred during meltwater pulse 1B. The Holocene interval was characterized by a lack of siliciclastic turbidites, relatively high carbonate content, and fine bank-derived aragonitic sediment. The observed millennial timescale sedimentary variability can be explained by sea level fluctuations. During the Last Glacial Maximum, siliciclastic turbidites were numerous when the lowstand coastal system was located along the modern shelf edge. Although they did not occur during the intervals of maximum flooding of the shelf (during meltwater pulses 1A and 1B), siliciclastic turbidites reappear briefly during the Younger Dryas, an interval when sea level rise slowed, stopped, or perhaps even fell. The timing of the calciturbidite coincides with the first reflooding of Eastern Fields Reef, an atoll that remained exposed for most of the glacial stages.

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

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

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

  17. Quantifying the stability of planktic foraminiferal physical niches between the Holocene and Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Waterson, A. M.; Edgar, K. M.; Schmidt, D. N.; Valdes, P. J.

    2017-01-01

    The application of transfer functions on fossil assemblages to reconstruct past environments is fundamentally based on the assumption of stable environmental niches in both space and time. We quantitatively test this assumption for six dominant planktic foraminiferal species (Globigerinoides ruber (pink), G. ruber (white), Trilobatus sacculifer, Truncorotalia truncatulinoides, Globigerina bulloides, and Neogloboquadrina pachyderma) by contrasting reconstructions of species realized and optimum distributions in the modern and during the Last Glacial Maximum (LGM) using an ecological niche model (ENM; MaxEnt) and ordination framework. Global ecological niche models calibrated in the modern ocean have high predictive performance when projected to the LGM for subpolar and polar species, indicating that the environmental niches of these taxa are largely stable at the global scale across this interval. In contrast, ENMs had much poorer predictive performance for the optimal niche of tropical-dwelling species, T. sacculifer and G. ruber (pink). This finding is supported by independent metrics of niche margin change, suggesting that niche stability in environmental space was greatest for (sub)polar species, with greatest expansion of the niche observed for tropical species. We find that globally calibrated ENMs showed good predictions of species occurrences globally, whereas models calibrated in either the Pacific or Atlantic Oceans only and then projected globally performed less well for T. sacculifer. Our results support the assumption of environmental niche stability over the last 21,000 years for most of our focal planktic foraminiferal species and, thus, the application of transfer function techniques for palaeoenvironmental reconstruction during this interval. However, the lower observed niche stability for (sub)tropical taxa T. sacculifer and G. ruber (pink) suggests that (sub)tropical temperatures could be underestimated in the glacial ocean with the strongest

  18. Anatomy of Some Non-Heinrich Events During The Last Glacial Maximum on Laurentian Fan

    NASA Astrophysics Data System (ADS)

    Gil, I. M.; Keigwin, L. D.

    2013-12-01

    High-resolution diatom assemblage analyses coupled with oxygen and carbon isotopic records from a new 28 m piston core on Laurentian Fan reveal significant sedimentological and marine productivity changes related to variability of the nearby Laurentide Ice Sheet during the Last Glacial Maximum. Between 21.0 and 19.7 ka and between 18.8 and 18.6 ka, olive-grey clays intervals interrupt the usual glacial red-clays sedimentation. The timing of these two intervals corresponds to reported occurrence of layers low in detrital carbonate (LDC, considered as non-Heinrich events) that occurred between Heinrich Event 1 and 2. Diatoms are only abundant during those LDC - olive-grey clay intervals and suggest ice retreat (allowing light penetration necessary to diatoms). The species succession reveals also different environmental conditions. The 21.0 to 19.7 ka interval is divisible to two main periods: the first was characterized by environmental conditions dominated by ice, while the second period (starting at 20.2 ka) was warmer than the first. During the shorter 18.8 to 18.6 ka interval, conditions were even warmer than during the 20.2 to 19.7 ka sub-interval. Finally, the comparison of the interpreted oceanographic conditions with changes in Ice Rafted Debris and other records from the North Atlantic will bring a new insight into those episodes that precede the transition to deglaciation beginning ~18.2 ka on Laurentian Fan (based on δ18-O in N. pachyderma (s.)).

  19. Carbonate chemistry of intermediate waters in the Southwest Pacific Ocean since the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Allen, K. A.; Sikes, E. L.; Elmore, A.; Hoenisch, B.; deMenocal, P. B.; Rosenthal, Y.

    2013-12-01

    Shifts in ocean circulation and marine carbon storage likely played an important role in the termination of the last ice age, but the mechanisms driving these changes have not yet been fully explained. It has been suggested that a greater amount of CO2 was stored in the deep sea during glacial periods via the biologic pump and/or increased uptake by a more alkaline ocean. To quantify the relative roles of such processes, more constraints on past deep ocean alkalinity are needed. Here, we present a new record of deep water carbonate chemistry for the last 30,000 years derived from a sediment core located at 1,627 meters depth in New Zealand's Bay of Plenty. Today, this core site lies at the boundary between relatively fresh Antarctic/Tasman Intermediate Water (above), and Circumpolar Deep Water (below) with more corrosive Pacific Deep Water also intruding from the north. Trace element and stable isotopic composition of foraminiferal calcite (the epibenthic species Cibicidoides wuellerstorfi) reveal changes in bottom water carbonate chemistry during periods of atmospheric CO2 change. The boron to calcium ratio (B/Ca) in these shells indicates that deep water saturation (ΔCO32-) during the last glacial maximum (LGM) was only 5 μmol kg-1 less than the modern value of ~ 20 μmol/kg, consistent with previous work identifying the Pacific as a 'well-buffered' ocean basin on long timescales. However, reconstructed ΔCO32- values fluctuated by as much as 30 μmol/kg across the deglaciation, exhibiting the most pronounced changes between 17 and 13 ka. Together with shifts in carbon isotopes, these results imply changes in circulation and/or respired CO2 storage, and support a series of events in which major oceanographic changes are intimately linked with shifts in atmospheric circulation.

  20. Migration Patterns of Subgenus Alnus in Europe since the Last Glacial Maximum: A Systematic Review

    PubMed Central

    Douda, Jan; Doudová, Jana; Drašnarová, Alena; Kuneš, Petr; Hadincová, Věroslava; Krak, Karol; Zákravský, Petr; Mandák, Bohumil

    2014-01-01

    Background/Aims Recently, new palaeoecological records supported by molecular analyses and palaeodistributional modelling have provided more comprehensive insights into plant behaviour during the last Quaternary cycle. We reviewed the migration history of species of subgenus Alnus during the last 50,000 years in Europe with a focus on (1) a general revision of Alnus history since the Last Glacial Maximum (LGM), (2) evidence of northern refugia of Alnus populations during the LGM and (3) the specific history of Alnus in particular European regions. Methodology We determined changes in Alnus distribution on the basis of 811 and 68 radiocarbon-dated pollen and macrofossil sites, respectively. We compiled data from the European Pollen Database, the Czech Quaternary Palynological Database, the Eurasian Macrofossil Database and additional literature. Pollen percentage thresholds indicating expansions or retreats were used to describe patterns of past Alnus occurrence. Principal Findings An expansion of Alnus during the Late Glacial and early Holocene periods supports the presence of alders during the LGM in southern peninsulas and northerly areas in western Europe, the foothills of the Alps, the Carpathians and northeastern Europe. After glaciers withdrew, the ice-free area of Europe was likely colonized from several regional refugia; the deglaciated area of Scandinavia was likely colonized from a single refugium in northeastern Europe. In the more northerly parts of Europe, we found a scale-dependent pattern of Alnus expansion characterised by a synchronous increase of Alnus within individual regions, though with regional differences in the times of the expansion. In southern peninsulas, the Alps and the Carpathians, by contrast, it seems that Alnus expanded differently at individual sites rather than synchronously in whole regions. Conclusions Our synthesis supports the idea that northern LGM populations were important sources of postglacial Alnus expansion. The

  1. Millenial-scale lag times in vegetation response to glacial climate in Siberia

    NASA Astrophysics Data System (ADS)

    Herzschuh, Ulrike; Birks, John H.; Andreev, Andrei; Melles, Martin; Brigham-Grette, Julie

    2016-04-01

    Vegetation change on all relevant temporal scales is assumed to be primarily driven by contemporary climate change, which would imply that vegetation-climate feedbacks become effective without long-term delay. However, our results from multivariate analyses of pollen assemblages from Lake Eĺgygytgyn (NE Siberia) and other data covering the Mid-Pliocene-Warm-Period and the Plio-Pleistocene-Transition challenge this concept of broad-scale vegetation-climate equilibrium. Our results indicate that interglacial vegetation during the Plio-Pleistocene transition mainly reflects the condition of the preceding glacial instead of contemporary interglacial climate. We assume that the observed vegetation-climate disequilibrium, in particular the absence of pine and spruce in interglacials following strong glacial stages, originates from the combined effects of permafrost persistence, distant glacial refugia, and fire plus possible interactions. Our results imply that today's widespread larch ecosystem on permafrost is not in climate-equilibrium but rather represents a transient vegetation type which is still responding to the extreme glacial condition of the last glacial. This also implies that feedback between vegetation and climate and between permafrost and climate in northern mid- and high latitudes becomes active with long-term delay, which is of relevance for global climate change.

  2. The Environment Changes in the Southwestern Taiwan Since the Last Glacial Maximum Epoch

    NASA Astrophysics Data System (ADS)

    Yang, Yung-Jan; Chen, Wen-Shan

    2015-04-01

    We use 31 boreholes to reconstruct the depositional environments in the southwestern Taiwan. Based on the sedimentary structures, it is divided into eight facies associations that is important to reconstruct depositional environment. Based on the depositional environment, sequence stratigraphy and radiocarbon dating data, it can be implied significant environment and shoreline changes. (1) The southwestern Taiwan is characterized by a subaerial environment and formed two incised valleys during the sea-level fall in the last glacial maximum epoch. (2) The shoreline was migrated to the landward and close to the frontal foothills, and the environment changed deepen into tidal flat and lagoon during 18,000-10,000 years ago. (3) The area occurred the deepest environment from shoreface to offshore transition during 8,000-7,000 years ago. (4) The shoreline was retreated to the seaward. The environment changed shallowen into barrier island, lagoon, and coastal plain since 7,000 years ago. This study confirm the decreasing accommodation space in this area result from huge sediment inputs and decreased eustatic sea-level rise, which cause the maximum flooding epoch appear earlier.

  3. North Atlantic storm track changes during the Last Glacial Maximum recorded by Alpine speleothems.

    PubMed

    Luetscher, Marc; Boch, R; Sodemann, H; Spötl, C; Cheng, H; Edwards, R L; Frisia, S; Hof, F; Müller, W

    2015-02-27

    The European Alps are an effective barrier for meridional moisture transport and are thus uniquely placed to record shifts in the North Atlantic storm track pattern associated with the waxing and waning of Late-Pleistocene Northern Hemisphere ice sheets. The lack of well-dated terrestrial proxy records spanning this time period, however, renders the reconstruction of past atmospheric patterns difficult. Here we present a precisely dated, continuous terrestrial record of meteoric precipitation in Europe between 30 and 14.7 ka. In contrast to present-day conditions, our speleothem data provide strong evidence for preferential advection of moisture from the South across the Alps supporting a southward shift of the storm track during the local Last Glacial Maximum (that is, 26.5-23.5 ka). Moreover, our age control indicates that this circulation pattern preceded the Northern Hemisphere precession maximum by ~3 ka, suggesting that obliquity may have played a considerable role in the Alpine ice aggradation.

  4. North Atlantic storm track changes during the Last Glacial Maximum recorded by Alpine speleothems

    PubMed Central

    Luetscher, Marc; Boch, R.; Sodemann, H.; Spötl, C.; Cheng, H.; Edwards, R. L.; Frisia, S.; Hof, F.; Müller, W.

    2015-01-01

    The European Alps are an effective barrier for meridional moisture transport and are thus uniquely placed to record shifts in the North Atlantic storm track pattern associated with the waxing and waning of Late-Pleistocene Northern Hemisphere ice sheets. The lack of well-dated terrestrial proxy records spanning this time period, however, renders the reconstruction of past atmospheric patterns difficult. Here we present a precisely dated, continuous terrestrial record of meteoric precipitation in Europe between 30 and 14.7 ka. In contrast to present-day conditions, our speleothem data provide strong evidence for preferential advection of moisture from the South across the Alps supporting a southward shift of the storm track during the local Last Glacial Maximum (that is, 26.5–23.5 ka). Moreover, our age control indicates that this circulation pattern preceded the Northern Hemisphere precession maximum by ~3 ka, suggesting that obliquity may have played a considerable role in the Alpine ice aggradation. PMID:25724008

  5. Reconstruction of glacial changes on HualcaHualca volcano (southern Peru) from the Maximum Glacier Extent to present.

    NASA Astrophysics Data System (ADS)

    Alcalá, Jesus; Palacios, David; Juan Zamorano, Jose

    2015-04-01

    Little is known about glacial area changes in the Peruvian glaciers and how responds to climate fluctuations especially in the arid region where ice masses represent the major water supply. In this research, we present the results related to glacier area, volume and minimum glacier altitude evolution from the Maximum Glacier Extent (MGE) to 2000 on HualcaHualca volcano (15° 43' S; 71° 52' W; 6,025 masl), a large andesitic stratovolcano located in the south-western Peruvian Andes approximately 70 km north-west of Arequipa. We focused the study in four valleys (Huayuray, Pujro Huayjo, Mollebaya and Mucurca) because preserved a complete and well-defined sequence of glacial deposits. Moreover, these valleys, with the exception of Mucurca, still retain ice masses relegated to active cirques on summits areas so has been possible to reconstruct glacier recent dynamics. To reconstruct former glaciers, we used frontal and lateral moraines while delimitation of recent ice masses was based on the analysis of aerial photographs (1955) as well as Landsat satellite scene (2000). Geographical Information System (GIS) allowed map and quantify with high accuracy glacier spatial parameters. The magnitude of glacial expansion was highest during MEG in Huayuray, where the glacier reached 22.7 km2 of extension and the front ice was situated at 3,650 masl, than in Pujro Huayjo (23.8 km2; 4,300 masl), Mollebaya (17.8 km2; 4,315 masl) and Mucurca (8.0 km2; 4,350 masl). The cause of this difference has been associated to the control exercised by topography. Glacier of Huayuray flowed by a steep slope while mass ices of Pujro Huayjo, Mollebaya and Mucurca slipped to the Altiplano. In the other hand, the data from 2000 show that the intensity of deglaciation was more drastic in Mucurca, where glacier has already disappeared, than in Huayuray (1.2 km2; 5,800 masl), Pujro Huayjo (1.8 km2; 5,430 masl) or Mollebaya (0.95 km2; 5,430 masl) as a consequence of it's lesser glacier entity. Research

  6. Models and the paleo record of biome responses to glacial climate and CO2

    SciTech Connect

    Prentice; Colin, I.; Haxeltine

    1995-06-01

    Continental-scale reconstructions of the distribution of biomes at the last glacial maximum (LGM) indicate big changes, which can primarily be explained by climate. The climate was different from today mainly because of a combination of low concentrations of CO{sub 2} and other greenhouse gases and the presence of large continental ice sheets. Atmospheric general circulation model (AGCM) simulations, driven by these factors and linked to simple biome models in {open_quotes}diagnostic{close_quotes} mode, account for the broad outlines of the changes in vegetation patterns, including encroachment of C4 grasslands and savannas on what are now tropical forests. Physiological effects of low CO{sub 2} might also have played a role by altering the partitioning of precipitation to evapotranspiration and runoff, and altering the competitive balance of C3 and C4 plants. Such effects have not been quantified until recently, with the development of integrated biome/biochemistry models like those used in the VEMAP project. In these models, vegetation composition affects the coupled C and H{sub 2}O fluxes, which in turn influence the competitive balance of the constituent plant types. The relative importance of climatic and physiological effects of CO{sub 2} on biome distributions is a key issue for the future. This is gives added impetus to research that aims to exploit the potential of palaeo, data, through global data synthesis projects like BIOME 6000, to provide objective benchmarks against which to test models of the biosphere and climate.

  7. Simulating the effect of glacial sea level changes on Indo-Pacific climate

    NASA Astrophysics Data System (ADS)

    Di Nezio, P. N.; Tierney, J. E.; Timmermann, A.; Otto-Bliesner, B. L.; Mapes, B. E.

    2014-12-01

    Lowered sea level during the Last Glacial Maximum (LGM) altered the geography of the Maritime Continent exposing the Sunda shelf. Multi-proxy evidence indicates that the exposure of the Sunda shelf has a first-order effect on the climate of the Indo-Pacific warm pool. The climate response involves changes in the Walker circulation driven by a massive reduction in atmospheric deep convection over the Sunda shelf. Few climate models participating in the Paleo Model Intercomparison Project (PMIP) are capable of simulating this response. Using the Community Earth System Model Version 1 (CESM1) we show that a models ability of to simulate this response depends on the formulation of the atmospheric deep convection scheme. Using CESM1 we also find that the Indian Ocean amplifies the response via the Bjerknes feedback. This results in a large reorganization of the climate of the Indian Ocean, which during the LGM resembles the Pacific, with a cold tongue and dry conditions in the east, and warmer SSTs and wetter conditions in the west. Ideas for testing these mechanisms using proxy data will be discussed.

  8. Ice-age Ice-sheet Rheology: Constraints from the Last Glacial Maximum Form of the Laurentide Ice Sheet

    NASA Technical Reports Server (NTRS)

    Peltier, W. Richard; Goldsby, David L.; Kohlstedt, David L.; Tarasov, Lev

    2000-01-01

    State-ot-the-art thermomechanical models of the modern Greenland ice and the ancient Laurenticle ice sheet that covered Canada at the Last Glacial Maximum (LGM) are not able to explain simultaneously the observed forms of these cryospheric structures when the same, anisotropy-enhanced, version of the conventional Glen flow law is employed to describe their rheology. The LGM Laurenticle ice sheet. predicted to develop in response to orbital climate forcing, is such that the ratio of its thickness to its horizontal extent is extremely large compared to the aspect ratio inferred on the basis of surface-geomorphological and solid-earth-geophysical constraints. We show that if the Glen flow law representation of the rheology is replaced with a new rheology based upon very high quality laboratory measurements of the stress-strain-rate relation, then the aspect ratios of both the modern Greenland ice sheet and the Laurenticle ice sheet, that existed at the LGM, are simultaneously explained with little or no retuning of the flow law.

  9. The vegetation and climate during the Last Glacial Cold Period, northern South Island, New Zealand

    NASA Astrophysics Data System (ADS)

    Callard, S. Louise; Newnham, Rewi M.; Vandergoes, Marcus J.; Alloway, Brent V.; Smith, Carol

    2013-08-01

    Pollen assemblages from Howard Valley, South Island, New Zealand, were used to reconstruct the palaeovegetation and infer past climate during the period ca 38-21 cal. ka, which encompasses the Marine Isotope Stage (MIS) 3/2 transition and Last Glacial Cold Period (LGCP). A glacier occupied the upper Howard Valley during the Last Glacial, whilst extensive glaciofluvial outwash surfaces were constructed in the lower valley. Episodic periods of fluvial aggradation and incision have produced a complex sequence of terraces flanking the main Howard River and its tributaries. Sedimentary sequences from three exposed valley fills, sampled for palynological analysis and radiocarbon dating, consist of a complex vertical and lateral arrangement of coarse textured cobbly sandy gravels interbedded with organic-rich silt deposits. Palynology of these organic-rich horizons was directly compared to an existing beetle record from these same horizons. During late MIS 3 the site was dominated by marshy shrubland vegetation interspersed with mixed beech forest, indicating temperatures ˜2-3 °C cooler than present. Climate cooling began as early as 35.7 cal. ka and coincides with evidence of cooling from other sites in New Zealand, South America and with an Antarctic cooling signature. A three phase vegetation and inferred climate pattern occurs at the site during the LGCP beginning with a transition to an alpine/sub-alpine grassland comparable to communities growing near treeline today marking the change to glacial conditions before 31 cal. ka. A small increase in tree abundance between ca 25.8 and 22.7 cal. ka suggests minor climate amelioration during the mid-LGCP. During this phase, a possible volcanically induced vegetation disruption caused by the deposition of the Kawakawa Tephra at 25 cal. ka is evident in the pollen record. This is followed by a further decline in tree pollen and increase in alpine grassland and herb pollen indicating further deterioration of conditions and a

  10. Extent and Timing of the Last Glacial Maximum in Southwestern Alaska

    NASA Astrophysics Data System (ADS)

    Mann, Daniel H.; Peteet, Dorothy M.

    1994-09-01

    A glacier complex composed of confluent alpine glaciers, island ice caps, and piedmont lobes covered much of the Alaska Peninsula and Kodiak Island during the last glacial maximum (LGM). Because this glacier complex formed the southeastern border of Beringia, its dynamics may have been important in the timing and feasibility of the northwest coast route for human migration into lower-latitude North America. Radiocarbon dates from stratigraphic sections on Kodiak Island and in the Bristol Bay lowlands bracket the LGM in southwestern Alaska between 23,000 and 14,700 yr B.P. Reconstruction of ice thickness based on glacier trimlines, moraines, and calculations of basal-shear stress depict the Alaska Peninsula Glacier Complex flowing to the outer edge of the continental shelf in the Gulf of Alaska. Equilibrium-line altitudes (ELAs) were 300 to 700 m lower than today and approached sea level on the southwestern Alaska Peninsula. In northeastern areas where ELAs were higher, bedrock topography largely controlled ice flow except where ice saddles bridged straits and inlets.

  11. Paleolithic human exploitation of plant foods during the last glacial maximum in North China.

    PubMed

    Liu, Li; Bestel, Sheahan; Shi, Jinming; Song, Yanhua; Chen, Xingcan

    2013-04-02

    Three grinding stones from Shizitan Locality 14 (ca. 23,000-19,500 calendar years before present) in the middle Yellow River region were subjected to usewear and residue analyses to investigate human adaptation during the last glacial maximum (LGM) period, when resources were generally scarce and plant foods may have become increasingly important in the human diet. The results show that these tools were used to process various plants, including Triticeae and Paniceae grasses, Vigna beans, Dioscorea opposita yam, and Trichosanthes kirilowii snakegourd roots. Tubers were important food resources for Paleolithic hunter-gatherers, and Paniceae grasses were exploited about 12,000 y before their domestication. The long tradition of intensive exploitation of certain types of flora helped Paleolithic people understand the properties of these plants, including their medicinal uses, and eventually led to the plants' domestication. This study sheds light on the deep history of the broad spectrum subsistence strategy characteristic of late Pleistocene north China before the origins of agriculture in this region.

  12. Simulation of the global bio-geophysical interactions during the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Kubatzki, C.; Claussen, M.

    The bio-geophysical feedbacks during the Last Glacial Maximum (LGM, 21000 yBP) are investigated by use of an asynchronously coupled global atmosphere-biome model. It is found that the coupled model improves on the results of an atmosphere-only model especially for the Siberian region, where the inclusion of vegetation-snow-albedo interaction leads to a better agreement with geological reconstructions. Furthermore, it is shown that two stable solutions of the coupled model are possible under LGM boundary conditions. The presence of bright sand desert at the beginning of a simulation leads to more extensive subtropical deserts, whereas an initial global vegetation cover with forest, steppe, or dark desert results in a northward spread of vegetation of up to some 1000 km, mainly in the western Sahara. These differences can be explained in the framework of Charney's theory of a ``self-induction'' of deserts through albedo enhancement. Moreover, it is found that the tropical easterly jet is strengthened in the case of the ``green'' Sahara, which in turn leads to a modification of the Indian summer monsoon.

  13. Last glacial maximum environments in northwestern Patagonia revealed by fossil small mammals

    NASA Astrophysics Data System (ADS)

    Tammone, Mauro N.; Hajduk, Adan; Arias, Pablo; Teta, Pablo; Lacey, Eileen A.; Pardiñas, Ulyses F. J.

    2014-07-01

    Comparisons of historical and modern assemblages of mammals can yield important insights into patterns and processes of environmental change. Here, we present the first analyses of small mammal assemblages present in northern Patagonia during the last glacial maximum (LGM). Using remains obtained from owl pellets excavated from an archeological cave site (Arroyo Corral I, levels VII-V, carbon dates of 22,400-21,530 cal yr BP), we generate estimates of the minimum number of individuals for all species detected; these estimates, in turn are used to determine relative species abundances. Comparisons of these data with similar analyses of small mammal remains obtained from a second archeological site (ACoII, levels IV-V, carbon dates of 10,010-9220 cal yr BP) as well as from modern owl pellets reveal pronounced changes in relative species abundance since the LGM. In particular, Euneomys chinchilloides and Ctenomys sociabilis - the predominant species during the LGM - declined markedly, suggesting a change from open, bare habitat punctuated by patches of wet meadows and shrubs to the more densely vegetated mosaic of ecotone habitats found in this region today. These data provide important new insights into the environmental changes that have occurred in northern Patagonia over the last 20,000 years.

  14. Remote forcing at the Last Glacial Maximum in the Tropical Pacific Ocean

    NASA Astrophysics Data System (ADS)

    Andreasen, Dyke H.; Ravelo, A. Christina; Broccoli, Anthony J.

    2001-01-01

    We present results of a Last Glacial Maximum (LGM) wind stress sensitivity experiment using a high-resolution ocean general circulation model of the tropical Pacific Ocean. LGM wind stress, used to drive the ocean model, was generated using an atmospheric general circulation model simulation forced by LGM boundary conditions as part of the Paleoclimate Modeling Intercomparison Project (PMIP) [Broccoli, 2000]. LGM wind stress anomalies were large in the western half of the basin, yet there was a significant hydrographic response in the eastern half. This ocean model experiment hind casts changes that are in close agreement with paleoceanographic data from the entire region, even without the explicit modeling of the air-sea interactions. Data and model both predict that the annual average thermocline tilt across the basin was enhanced. Data and model are consistent with a stronger equatorial undercurrent which shoaled to the west of where it does today, and stronger advection of water from the Peru Current into the east equatorial Pacific and across the equator. Paleoproductivity and sea surface temperature (SST) data are interpreted in light of the modeling results, indicating that paleoproductivity changes were related to wind-forced dynamical changes resulting from LGM boundary conditions, while SST changes were related to independent, possibly radiative, forcing. Overall, our results imply that much of the dynamic response of the tropical Pacific during the LGM can be explained by wind field changes resulting from global LGM boundary conditions.

  15. Across-shelf sediment transport since the Last Glacial Maximum, southern California margin

    USGS Publications Warehouse

    Sommerfield, C.K.; Lee, H.J.

    2004-01-01

    Correlation of continental shelf-slope stratigraphy in Santa Monica Bay (southern California) with Ocean Drilling Program records for nearby slope-basin sites has illuminated the timing and scale of terrigenous sediment dispersal on margin since the Last Glacial Maximum (LGM). Marine flooding surfaces preserved in a transgressive sequence on the Santa Monica Shelf provide a key link between base-level elevation and sediment transport across shelf. Sediment-accumulation rates at slope-basin sites were maximal ca. 15-10 ka, well after the LGM, decreased during the 12-9 ka transition from fluvial-estuarine to fully marine conditions on the shelf, and decelerated throughout the Holocene to 30%-75% of their values at the LGM. The deceleration is interpreted to manifest a landward shift in the margin depocenter with the onset of transgressive sedimentation beginning when sea level surmounted the shelf edge ca. 13 ka, as predicted by sequence-stratigraphic models. However, the records make clear that factors other than base level modulated slope-basin accumulation rates during the deglaciation. ?? 2004 Geological Society of America.

  16. Last Glacial Maximum cirque glaciation in Ireland and implications for reconstructions of the Irish Ice Sheet

    NASA Astrophysics Data System (ADS)

    Barth, Aaron M.; Clark, Peter U.; Clark, Jorie; McCabe, A. Marshall; Caffee, Marc

    2016-06-01

    Reconstructions of the extent and height of the Irish Ice Sheet (IIS) during the Last Glacial Maximum (LGM, ∼19-26 ka) are widely debated, in large part due to limited age constraints on former ice margins and due to uncertainties in the origin of the trimlines. A key area is southwestern Ireland, where various LGM reconstructions range from complete coverage by a contiguous IIS that extends to the continental shelf edge to a separate, more restricted southern-sourced Kerry-Cork Ice Cap (KCIC). We present new 10Be surface exposure ages from two moraines in a cirque basin in the Macgillycuddy's Reeks that provide a unique and unequivocal constraint on ice thickness for this region. Nine 10Be ages from an outer moraine yield a mean age of 24.5 ± 1.4 ka while six ages from an inner moraine yield a mean age of 20.4 ± 1.2 ka. These ages show that the northern flanks of the Macgillycuddy's Reeks were not covered by the IIS or a KCIC since at least 24.5 ± 1.4 ka. If there was more extensive ice coverage over the Macgillycuddy's Reeks during the LGM, it occurred prior to our oldest ages.

  17. Changes in North African dust deposition: 35 ka through the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Kinsley, C. W.; McGee, D.; Winckler, G.; deMenocal, P. B.; Stuut, J. W.; Bradtmiller, L. I.

    2013-12-01

    Past changes in atmospheric circulation and aridity in the North African region can be explored by examining continuous records of reconstructed eolian dust accumulation in West African margin sediments. Recent high-resolution reconstructions of dust deposition by McGee et al. (2013) from a meridional transect of cores stretching from 27°N to 19°N along the northwest African margin indicate dramatic changes in North African dust emissions over the last 20 ka. Times of high dust emissions were documented during Heinrich Stadial 1 and the Younger Dryas, and lower dust emissions during the African Humid Period. Here we present a continuation of these records, combining grain size endmember modeling with 230Th-normalized fluxes in these cores to document spatial and temporal changes in dust loads and grain size distributions within the North African dust plume from 20 to ~35 ka. Our results provide quantitative estimates of the magnitude of dust flux changes associated with previous Heinrich Stadials, and lend insight to the nature of the North African dust plume through the entirety of the Last Glacial Maximum. References: McGee, D., deMenocal, P.B., Winckler, G., Stuut, J.B.W., Bradtmiller, L.I., 2013. The magnitude, timing and abruptness of changes in North African dust deposition over the last 20,000 yr. Earth And Planetary Science Letters 371-372, 163-176.

  18. Paleolithic human exploitation of plant foods during the last glacial maximum in North China

    PubMed Central

    Liu, Li; Bestel, Sheahan; Shi, Jinming; Song, Yanhua; Chen, Xingcan

    2013-01-01

    Three grinding stones from Shizitan Locality 14 (ca. 23,000–19,500 calendar years before present) in the middle Yellow River region were subjected to usewear and residue analyses to investigate human adaptation during the last glacial maximum (LGM) period, when resources were generally scarce and plant foods may have become increasingly important in the human diet. The results show that these tools were used to process various plants, including Triticeae and Paniceae grasses, Vigna beans, Dioscorea opposita yam, and Trichosanthes kirilowii snakegourd roots. Tubers were important food resources for Paleolithic hunter–gatherers, and Paniceae grasses were exploited about 12,000 y before their domestication. The long tradition of intensive exploitation of certain types of flora helped Paleolithic people understand the properties of these plants, including their medicinal uses, and eventually led to the plants' domestication. This study sheds light on the deep history of the broad spectrum subsistence strategy characteristic of late Pleistocene north China before the origins of agriculture in this region. PMID:23509257

  19. A 3000-yr annually laminated stalagmite record of the Last Glacial Maximum from Hulu Cave, China

    NASA Astrophysics Data System (ADS)

    Duan, Fucai; Wu, Jiangying; Wang, Yongjin; Edwards, R. Lawrence; Cheng, Hai; Kong, Xinggong; Zhang, Weihong

    2015-03-01

    A high-resolution, annual layer-counted and 230Th-dated multi-proxy record is constructed from a stalagmite in Hulu Cave, China. These proxies, including δ18O, annual layer thickness (ALT), gray level (GL) and Sr/Ca, cover a time span of ~ 3000 yr from 21 to 24 ka. The physical proxies (ALT and GL) and the geochemical index (Sr/Ca), all primarily reflecting karst hydrological processes, vary in concert and their coherence is supported by wavelet analyses. Variations in the δ18O data agree with fluctuations in the ALT and Sr/Ca records on multi-decadal to centennial scales, suggesting that the Hulu δ18O signal is strongly associated with varying local rainfall amounts on short timescales. A monsoon failure event at ~ 22.2 ka correlates with a decrease in tropical rainfall, a reduction in global CH4 and an ice-rafted event in the North Atlantic. This correlation highlights roles of the Asian monsoon and tropical hydrological cycle in modulating global CH4, because the high-latitude emission was inhibited during the Last Glacial Maximum (LGM). Spectral analysis of the δ18O record displays peaks at periodicities of 139, 59, 53, 43, 30, 23 and 19-15 yr. The absence of typical centennial solar cycles may be related to muted changes in ocean circulation during the LGM.

  20. Indo-Pacific Warm Pool variability during the Holocene and Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Xu, Jian; Kuhnt, Wolfgang; Holbourn, Ann; Regenberg, Marcus; Andersen, Nils

    We measured oxygen isotopes and Mg/Ca ratios in the surface-dwelling planktonic foraminifer Globigerinoides ruber (white s.s.) and the thermocline dweller Pulleniatina obliquiloculata to investigate upper ocean spatial variability in the Indo-Pacific Warm Pool (IPWP). We focused on three critical time intervals: the Last Glacial Maximum (LGM; 18-21.5 ka), the early Holocene (8-9 ka), and the late Holocene (0-2 ka). Our records from 24 stations in the South China Sea, Timor Sea, Indonesian seas, and western Pacific indicate overall dry and cool conditions in the IPWP during the LGM with a low thermal gradient between surface and thermocline waters. During the early Holocene, sea surface temperatures increased by ˜3°C over the entire region, indicating intensification of the IPWP. However, in the eastern Indian Ocean (Timor Sea), the thermocline gradually shoaled from the LGM to early Holocene, reflecting intensification of the subsurface Indonesian Throughflow (ITF). Increased surface salinity in the South China Sea during the Holocene appears related to northward displacement of the monsoonal rain belt over the Asian continent together with enhanced influx of saltier Pacific surface water through the Luzon Strait and freshwater export through the Java Sea. Opening of the freshwater portal through the Java Sea in the early Holocene led to a change in the vertical structure of the ITF from surface- to thermocline-dominated flow and to substantial freshening of Timor Sea thermocline waters.

  1. Antarctic sea ice control on ocean circulation in present and glacial climates.

    PubMed

    Ferrari, Raffaele; Jansen, Malte F; Adkins, Jess F; Burke, Andrea; Stewart, Andrew L; Thompson, Andrew F

    2014-06-17

    In the modern climate, the ocean below 2 km is mainly filled by waters sinking into the abyss around Antarctica and in the North Atlantic. Paleoproxies indicate that waters of North Atlantic origin were instead absent below 2 km at the Last Glacial Maximum, resulting in an expansion of the volume occupied by Antarctic origin waters. In this study we show that this rearrangement of deep water masses is dynamically linked to the expansion of summer sea ice around Antarctica. A simple theory further suggests that these deep waters only came to the surface under sea ice, which insulated them from atmospheric forcing, and were weakly mixed with overlying waters, thus being able to store carbon for long times. This unappreciated link between the expansion of sea ice and the appearance of a voluminous and insulated water mass may help quantify the ocean's role in regulating atmospheric carbon dioxide on glacial-interglacial timescales. Previous studies pointed to many independent changes in ocean physics to account for the observed swings in atmospheric carbon dioxide. Here it is shown that many of these changes are dynamically linked and therefore must co-occur.

  2. Sea level and global ice volumes from the Last Glacial Maximum to the Holocene.

    PubMed

    Lambeck, Kurt; Rouby, Hélène; Purcell, Anthony; Sun, Yiying; Sambridge, Malcolm

    2014-10-28

    The major cause of sea-level change during ice ages is the exchange of water between ice and ocean and the planet's dynamic response to the changing surface load. Inversion of ∼1,000 observations for the past 35,000 y from localities far from former ice margins has provided new constraints on the fluctuation of ice volume in this interval. Key results are: (i) a rapid final fall in global sea level of ∼40 m in <2,000 y at the onset of the glacial maximum ∼30,000 y before present (30 ka BP); (ii) a slow fall to -134 m from 29 to 21 ka BP with a maximum grounded ice volume of ∼52 × 10(6) km(3) greater than today; (iii) after an initial short duration rapid rise and a short interval of near-constant sea level, the main phase of deglaciation occurred from ∼16.5 ka BP to ∼8.2 ka BP at an average rate of rise of 12 m⋅ka(-1) punctuated by periods of greater, particularly at 14.5-14.0 ka BP at ≥40 mm⋅y(-1) (MWP-1A), and lesser, from 12.5 to 11.5 ka BP (Younger Dryas), rates; (iv) no evidence for a global MWP-1B event at ∼11.3 ka BP; and (v) a progressive decrease in the rate of rise from 8.2 ka to ∼2.5 ka BP, after which ocean volumes remained nearly constant until the renewed sea-level rise at 100-150 y ago, with no evidence of oscillations exceeding ∼15-20 cm in time intervals ≥200 y from 6 to 0.15 ka BP.

  3. Sea level and global ice volumes from the Last Glacial Maximum to the Holocene

    PubMed Central

    Lambeck, Kurt; Rouby, Hélène; Purcell, Anthony; Sun, Yiying; Sambridge, Malcolm

    2014-01-01

    The major cause of sea-level change during ice ages is the exchange of water between ice and ocean and the planet’s dynamic response to the changing surface load. Inversion of ∼1,000 observations for the past 35,000 y from localities far from former ice margins has provided new constraints on the fluctuation of ice volume in this interval. Key results are: (i) a rapid final fall in global sea level of ∼40 m in <2,000 y at the onset of the glacial maximum ∼30,000 y before present (30 ka BP); (ii) a slow fall to −134 m from 29 to 21 ka BP with a maximum grounded ice volume of ∼52 × 106 km3 greater than today; (iii) after an initial short duration rapid rise and a short interval of near-constant sea level, the main phase of deglaciation occurred from ∼16.5 ka BP to ∼8.2 ka BP at an average rate of rise of 12 m⋅ka−1 punctuated by periods of greater, particularly at 14.5–14.0 ka BP at ≥40 mm⋅y−1 (MWP-1A), and lesser, from 12.5 to 11.5 ka BP (Younger Dryas), rates; (iv) no evidence for a global MWP-1B event at ∼11.3 ka BP; and (v) a progressive decrease in the rate of rise from 8.2 ka to ∼2.5 ka BP, after which ocean volumes remained nearly constant until the renewed sea-level rise at 100–150 y ago, with no evidence of oscillations exceeding ∼15–20 cm in time intervals ≥200 y from 6 to 0.15 ka BP. PMID:25313072

  4. Glacier advances in northeastern Turkey before and during the global Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Reber, Regina; Akçar, Naki; Yesilyurt, Serdar; Yavuz, Vural; Tikhomirov, Dmitry; Kubik, Peter W.; Schlüchter, Christian

    2014-10-01

    Our study in the Başyayla Valley in northeastern Anatolia showed evidence of four glacier advances that built terminal and lateral moraines. Surface exposure dating of boulders on these moraines showed that the Maximum Ice Extent (MIE) was asynchronous with the global Last Glacial Maximum (LGM; 22.1 ± 4.3 thousand years; ka). The local MIE took place at least 57.0 ± 3.5 ka ago. The extent of the Başyayla Glacier during this advance is not known exactly because the boulders are only preserved on a lateral moraine. The next advance was prior to 41.5 ± 2.5 ka, and it descended down the valley to approximately 2320 m above sea level (m a.s.l.), with a glacier length of 5.3 km. During the early global LGM, the Başyayla Glacier extended for a distance of 4.9 km down to approx. 2430 m a.s.l. The last recorded advance occurred during the global LGM. This extension was 0.7 km smaller than the local MIE and its terminus reached 2490 m a.s.l. only. The exposure ages of boulders in a retreat position at an altitude of approx. 3045 m a.s.l. indicate that the valley has remained ice-free since the Lateglacial period. Therefore, the Lateglacial extent was limited to the cirque system in the uppermost part of the catchment. Furthermore, Holocene glacier oscillations seem to be either absent or restricted to solifluction in the whole catchment and to rock glacier movements in the southern tributary of the Başyayla Valley system.

  5. Satsurblia: New Insights of Human Response and Survival across the Last Glacial Maximum in the Southern Caucasus

    PubMed Central

    Pinhasi, Ron; Meshveliani, Tengiz; Matskevich, Zinovi; Bar-Oz, Guy; Weissbrod, Lior; Miller, Christopher E.; Wilkinson, Keith; Lordkipanidze, David; Jakeli, Nino; Kvavadze, Eliso; Higham, Thomas F. G.; Belfer-Cohen, Anna

    2014-01-01

    The region of western Georgia (Imereti) has been a major geographic corridor for human migrations during the Middle and Upper Palaeolithic (MP/UP). Knowledge of the MP and UP in this region, however, stems mostly from a small number of recent excavations at the sites of Ortvale Klde, Dzudzuana, Bondi, and Kotias Klde. These provide an absolute chronology for the Late MP and MP–UP transition, but only a partial perspective on the nature and timing of UP occupations, and limited data on how human groups in this region responded to the harsh climatic oscillations between 37,000–11,500 years before present. Here we report new UP archaeological sequences from fieldwork in Satsurblia cavein the same region. A series of living surfaces with combustion features, faunal remains, stone and bone tools, and ornaments provide new information about human occupations in this region (a) prior to the Last Glacial Maximum (LGM) at 25.5–24.4 ka cal. BP and (b) after the LGM at 17.9–16.2 ka cal. BP. The latter provides new evidence in the southern Caucasus for human occupation immediately after the LGM. The results of the campaigns in Satsurblia and Dzudzuana suggest that at present the most plausible scenario is one of a hiatus in the occupation of this region during the LGM (between 24.4–17.9 ka cal. BP). Analysis of the living surfaces at Satsurblia offers information about human activities such as the production and utilisation of lithics and bone tools, butchering, cooking and consumption of meat and wild cereals, the utilisation of fibers, and the use of certain woods. Microfaunal and palynological analyses point to fluctuations in the climate with consequent shifts in vegetation and the faunal spectrum not only before and after the LGM, but also during the two millennia following the end of the LGM. PMID:25354048

  6. Rapid climate and environmental changes in the western Iberian Peninsula since the last glacial period

    NASA Astrophysics Data System (ADS)

    Etourneau, Johan; Kim, Jung-Hyun; Kang, Sujin; Oliveira, Dulce; Gal, Jong-Ku; Choi, Bohyung; Shin, Kyung-Hoon; Penaud, Aurélie; Fernanda Sanchez Goni, Maria

    2016-04-01

    The warm and saline Mediterranean Outflow Waters (MOW) affect density structure of the North Atlantic current, thereby altering the Atlantic Meridional Overturning circulation and thus global climate. Previous studies on southwestern European margin sequences have demonstrated their capability to reconstruct past changes in atmospheric and oceanic conditions at orbital and millennial time scales. However, the detailed evolution of the climate and environmental variability during the last climatic transition, especially during the last major abrupt climate events (e.g. the Dansgaard-Oeschger, Heinrich and 8.2 kyr events), is not well documented. Furthermore, the potential impact of changes in the Mediterranean Outflow Waters (MOW) on the North Atlantic and climate are far from being understood. Here we scrutinize changes in MOW over the last 25 kyrs by investigating sediment core MD99-2339 (35.89°N, 7.53°W, 1170 m water depth) collected in the Gulf of Cadiz. We analyzed alkenones (UK'37) to gain information on the sea surface temperatures. We also analyzed n-alkanes and their associated carbon (d13C) isotopes that we combined to pollen assemblages to reconstruct vegetation and humidity changes. We find that the cold alkenone-derived SST periods (Last Glacial Maximum (LGM), Younger Dryas (YD) and Heinrich Stadial 1 (HS1)) might be associated to a regional increase in the upwelling activity driven by stronger coastal off-shore winds that supply this area by cold deep waters. Stronger upwelling intensity may be linked to a greater export of MOW. In comparison, the d13C n-alkanes indicate drier conditions during HS1 and YD, and wetter conditions during the LGM and Holocene, which is opposite to the recorded precipitation signal by pollen assemblages. This inverse relationship suggest an opposite trend in seasonal precipitation (summer vs winter) which might imply a distinct forcing since the last glacial period. Alternatively, the signals of d13C n-alkanes might

  7. Last Glacial - Holocene climate variability in the Atlantic sector of the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Xiao, Wenshen; Esper, Oliver; Gersonde, Rainer

    2016-03-01

    The Southern Ocean plays a major role in the glacial/interglacial global carbon cycle. However, there is a substantial lack of information from its Antarctic Zone south of the Polar Front (PF) to understand key climate processes (e.g., sea ice variability, productivity changes, CO2 source region, shifts of the Southern Westerly Wind) active in this region during the glacial/interglacial transition, due to the limited high-resolution sediment records from this area. To close this gap, we investigated high resolution diatom records from a series of sediment cores from the Atlantic and Western Indian sectors of the Southern Ocean between the modern PF and the Winter Sea Ice (WSI) edge. Summer Sea Surface Temperature (SSST) and sea ice information spanning the past 30 thousand years were derived from diatom transfer functions and indicators, which augment comprehensive information on past surface ocean conditions and related ocean and atmospheric circulation, as well as opal deposition. These complementary lines of evidences also provide important environmental boundary conditions for climate simulations understanding the past climate development in the high latitudes Southern Ocean. Our reconstructions show that the Last Glacial (LG) SSSTs south of the modern PF are 1-3 °C colder than modern conditions, WSI expanded to the modern PF. Our data suggests effective carbon export in the Antarctic Zone during the LG. Deglacial two steps of warming support the bipolar seesaw mechanism. Antarctic Zone is an important source region for the CO2 deglacial increase. The warming was more suppressed towards south, due to continuous ice discharge from Antarctica. The SSSTs exceeded modern values during the early Holocene optimum, when WSI extent probably retreated south of its modern position. The southern boundary of maximum opal deposition zone may have shifted to south of 55°S in the Bouvet Island area at this time. The mid-late Holocene cooling with WSI re-expanding to the

  8. Millennial climatic fluctuations are key to the structure of last glacial ecosystems.

    PubMed

    Huntley, Brian; Allen, Judy R M; Collingham, Yvonne C; Hickler, Thomas; Lister, Adrian M; Singarayer, Joy; Stuart, Anthony J; Sykes, Martin T; Valdes, Paul J

    2013-01-01

    Whereas fossil evidence indicates extensive treeless vegetation and diverse grazing megafauna in Europe and northern Asia during the last glacial, experiments combining vegetation models and climate models have to-date simulated widespread persistence of trees. Resolving this conflict is key to understanding both last glacial ecosystems and extinction of most of the mega-herbivores. Using a dynamic vegetation model (DVM) we explored the implications of the differing climatic conditions generated by a general circulation model (GCM) in "normal" and "hosing" experiments. Whilst the former approximate interstadial conditions, the latter, designed to mimic Heinrich Events, approximate stadial conditions. The "hosing" experiments gave simulated European vegetation much closer in composition to that inferred from fossil evidence than did the "normal" experiments. Given the short duration of interstadials, and the rate at which forest cover expanded during the late-glacial and early Holocene, our results demonstrate the importance of millennial variability in determining the character of last glacial ecosystems.

  9. 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.

  10. Surface Velocities of Himalayan Glaciers: Implications for Glacial Erosion Potential During Climatic Change

    NASA Astrophysics Data System (ADS)

    Scherler, D.; Bookhagen, B.; Strecker, M. R.

    2007-12-01

    Mountain glaciers in the high elevations (> 3.5 km) of the Himalaya are very efficient erosion agents. Glacier size and thus the area affected by glacial erosion are controlled by climatic conditions. Understanding the impact of climate change and variability on glacial budgets and erosion requires knowledge of the erosive potential of glaciers, which is inferred to scale with ice flux. Here, we use ASTER satellite imagery in combination with the orthorectification and correlation tool COSI-Corr to derive horizontal surface velocities of glaciers from several regions across the Himalayan-Karakoram domain. Our results show that glaciers in the Eastern and Central Himalaya, where precipitation is mainly supplied by the Indian Summer Monsoon, are relatively slow, with velocities usually below 50-60 m/a. In contrast, glaciers in the Western Himalaya and Karakoram, receive a significant amount of precipitation during the winter months and are considerably faster with velocities often exceeding 80-100 m/a. This discrepancy is visible among glaciers of different size and orientation although local slope and catchment area effects may cause velocity excursions. A relatively sharp gradient appears to exist in the catchment area of the Sutlej River in the NW Himalaya of India at approximately 79°E. To the east, glaciers in the Garhwal Himalaya - among them Gangotri glacier, the largest in the Indian Himalaya - have mean velocities of around 20-40 m/a, whereas glaciers in the much drier Lahul region to the west attain mean velocities of around 30-60 m/a. Importantly, the Sutlej River valley marks a climatic transition zone from an annual summer-rainfall maximum (more than 75% of annual rainfall during the summer) to the east to a winter-rainfall maximum (more than 60% of annual rainfall during the winter) to the west. These observations corroborate the notion of a significant climatic boundary in this part of the Himalaya, which may have shifted west- and northward during

  11. Dynamics of the last glacial maximum Antarctic ice-sheet and its response to ocean forcing.

    PubMed

    Golledge, Nicholas R; Fogwill, Christopher J; Mackintosh, Andrew N; Buckley, Kevin M

    2012-10-02

    Retreat of the Last Glacial Maximum (LGM) Antarctic ice sheet is thought to have been initiated by changes in ocean heat and eustatic sea level propagated from the Northern Hemisphere (NH) as northern ice sheets melted under rising atmospheric temperatures. The extent to which spatial variability in ice dynamics may have modulated the resultant pattern and timing of decay of the Antarctic ice sheet has so far received little attention, however, despite the growing recognition that dynamic effects account for a sizeable proportion of mass-balance changes observed in modern ice sheets. Here we use a 5-km resolution whole-continent numerical ice-sheet model to assess whether differences in the mechanisms governing ice sheet flow could account for discrepancies between geochronological studies in different parts of the continent. We first simulate the geometry and flow characteristics of an equilibrium LGM ice sheet, using pan-Antarctic terrestrial and marine geological data for constraint, then perturb the system with sea level and ocean heat flux increases to investigate ice-sheet vulnerability. Our results identify that fast-flowing glaciers in the eastern Weddell Sea, the Amundsen Sea, central Ross Sea, and in the Amery Trough respond most rapidly to ocean forcings, in agreement with empirical data. Most significantly, we find that although ocean warming and sea-level rise bring about mainly localized glacier acceleration, concomitant drawdown of ice from neighboring areas leads to widespread thinning of entire glacier catchments-a discovery that has important ramifications for the dynamic changes presently being observed in modern ice sheets.

  12. Shoreline reconstructions for the Persian Gulf since the last glacial maximum

    NASA Astrophysics Data System (ADS)

    Lambeck, Kurt

    1996-07-01

    Sea-level change in the Persian Gulf since the time of the last maximum glaciation at about 18 000 yr BP is predicted to exhibit considerable spatial variability, because of the response of the Earth to glacial unloading of the distant ice sheets and to the meltwater loading of the Gulf itself and the adjacent ocean. Models for these glacio-hydro-isostatic effects have been compared with observations of sea-level change and palaeoshoreline reconstructions of the Gulf have been made. From the peak of the glaciation until about 14 000 yr BP the Gulf is free of marine influence out to the edge of the Biaban Shelf. By 14 000 yr BP the Strait of Hormuz had opened up as a narrow waterway and by about 12 500 years ago the marine incursion into the Central Basin had started. The Western Basin flooded about 1000 years later. Momentary stillstands may have occurred during the Gulf flooding phase at about 11 300 and 10 500 yr BP. The present shorelines was reached shortly before 6000 yr ago and exceeded as relative sea level rose 1-2 m above its present level, inundating the low-lying areas of lower Mesopotamia. These reconstructions have implications for models of the evolution of the Euphrates-Tigris-Karun delta, as well as for the movements of people and the timing of the earliest settlements in lower Mesopotamia. For example, the early Gulf floor would have provided a natural route for people moving westwards from regions to the east of Iran from the late Palaeolithic to early Neolithic.

  13. Dynamics of the last glacial maximum Antarctic ice-sheet and its response to ocean forcing

    PubMed Central

    Golledge, Nicholas R.; Fogwill, Christopher J.; Mackintosh, Andrew N.; Buckley, Kevin M.

    2012-01-01

    Retreat of the Last Glacial Maximum (LGM) Antarctic ice sheet is thought to have been initiated by changes in ocean heat and eustatic sea level propagated from the Northern Hemisphere (NH) as northern ice sheets melted under rising atmospheric temperatures. The extent to which spatial variability in ice dynamics may have modulated the resultant pattern and timing of decay of the Antarctic ice sheet has so far received little attention, however, despite the growing recognition that dynamic effects account for a sizeable proportion of mass-balance changes observed in modern ice sheets. Here we use a 5-km resolution whole-continent numerical ice-sheet model to assess whether differences in the mechanisms governing ice sheet flow could account for discrepancies between geochronological studies in different parts of the continent. We first simulate the geometry and flow characteristics of an equilibrium LGM ice sheet, using pan-Antarctic terrestrial and marine geological data for constraint, then perturb the system with sea level and ocean heat flux increases to investigate ice-sheet vulnerability. Our results identify that fast-flowing glaciers in the eastern Weddell Sea, the Amundsen Sea, central Ross Sea, and in the Amery Trough respond most rapidly to ocean forcings, in agreement with empirical data. Most significantly, we find that although ocean warming and sea-level rise bring about mainly localized glacier acceleration, concomitant drawdown of ice from neighboring areas leads to widespread thinning of entire glacier catchments—a discovery that has important ramifications for the dynamic changes presently being observed in modern ice sheets. PMID:22988078

  14. Paleosecular variations of geomagnetic field from the Last Glacial Maximum to the Holocene in the north of South China Sea

    NASA Astrophysics Data System (ADS)

    Yang, X.; Huang, W.; Liu, Q.

    2012-12-01

    The high-resolution geomagnetic field records from the Last Glacial Maximum to the Holocene, which possessed of a notable climate change, were scarce in the global area. In this abstract, two gravity piston cores ZSQD2 (114.16oE, 19.58oN, ~190 cm in length, water depth 681m) and ZSQD34 (114.74oE, 19.05oN, ~184 cm in length, water depth 1820 m), situated in the north of South China Sea, were selected to study the secular variations of geomagnetic field in this area. Radiocarbon ages of G.sacculifer suggest that the deposition rate varied with 56.1 cm/kyr and 3.7 cm/kyr during the Last Glacial and the Holocene, respectively. Rock magnetic results indicate that the pseudo-single domain magnetite with low coercivity dominate the properties of sediments. The characteristic remanent magnetization (ChRM) values are evaluated using the 5-8 AF steps when MAD values are generally <5. Constrained by the radiocarbon chronology, the secular variation curves since ~18 cal. kyr can be constructed using the ChRM directions and NRM/ARM ratios (as a proxy of relative intensity). Comparing the Holocene SV with that from terrestrial lakes in Southern China, similar shape corroborates the reliability of records and uniform pattern of non-dipole magnetic field. Two significant features on SV curves present the geomagnetic field characteristics from ~17 cal. kyr to the early Holocene. One is that the direction variations lag behind the relative intensity on the millennium time scale. Such as a major direction shift occurred around 13 cal. kyr while the relative intensity low was about 14 cal. kyr. Another feature is the fast and frequent wiggles both in direction and intensity between ~17 to ~14.5 cal. kyr. During this period, two significant negative inclination anomalies occurred at ~16.4 and ~15.4 cal. kyr associated with low intensity, respectively. Nevertheless, the corresponding declinations did not show the reversed features although they had also some slight fluctuations. The

  15. Late glacial climate estimates for southern Nevada: The ostracode fossil record

    SciTech Connect

    Forester, R.M.; Smith, A.J.

    1995-10-01

    Climate change plays an important role in determining as possible long term hydrological performance of the potential high level nuclear waste repository within Yucca Mountain, Nevada. Present-day global circulation results in this region having an arid to semi-arid climate characterized by hot and relatively dry summers. Global circulation during the late glacial (about 14 to 20 ka) was very different from the present-day. Preliminary study of late-glacial fossil ostracodes from {open_quotes}marsh deposits{close_quotes} in the upper Las Vegas Valley suggests mean annual precipitation may have been four times higher, while mean annual temperature may have been about 10{degrees}C cooler than today. A major difference between present-day and late-glacial climate was likely the existence of cooler, cloudier, and wetter summers in the past.

  16. The cold climate geomorphology of the Eastern Cape Drakensberg: A reevaluation of past climatic conditions during the last glacial cycle in Southern Africa

    NASA Astrophysics Data System (ADS)

    Mills, S. C.; Barrows, T. T.; Telfer, M. W.; Fifield, L. K.

    2017-02-01

    Southern Africa is located in a unique setting for investigating past cold climate geomorphology over glacial-interglacial timescales. It lies at the junction of three of the world's major oceans and is affected by subtropical and temperate circulation systems, therefore recording changes in Southern Hemisphere circulation patterns. Cold climate landforms are very sensitive to changes in climate and thus provide an opportunity to investigate past changes in this region. The proposed existence of glaciers in the high Eastern Cape Drakensberg mountains, together with possible rock glaciers, has led to the suggestion that temperatures in this region were as much as 10-17 °C lower than present. Such large temperature depressions are inconsistent with many other palaeoclimatic proxies in Southern Africa. This paper presents new field observations and cosmogenic nuclide exposure ages from putative cold climate landforms. We discuss alternative interpretations for the formation of the landforms and confirm that glaciers were absent in the Eastern Cape Drakensberg during the last glaciation. However, we find widespread evidence for periglacial activity down to an elevation of 1700 m asl, as illustrated by extensive solifluction deposits, blockstreams, and stone garlands. These periglacial deposits suggest that the climate was significantly colder ( 6 °C) during the Last Glacial Maximum, in keeping with other climate proxy records from the region, but not cold enough to initiate or sustain glaciers or rock glaciers.

  17. Oxygen isotopic composition of the Mediterranean Sea since the Last Glacial Maximum: constraints from pore water analyses

    NASA Astrophysics Data System (ADS)

    Paul, Hilary A.; Bernasconi, Stefano M.; Schmid, Daniel W.; McKenzie, Judith A.

    2001-09-01

    Interstitial waters recovered from Ocean Drilling Program, Leg 161, site 976 in the western Mediterranean Sea are used in conjunction with a numerical model to constrain the δ 18O of seawater in the basin since the Last Glacial Maximum, including Sapropel Event 1. To resolve the oxygen isotopic composition of the deep Mediterranean, we use a model that couples fluid diffusion with advective transport, thus producing a profile of seawater δ 18O variability that is unaffected by glacial-interglacial variations in marine temperature. Comparing our reconstructed seawater δ 18O to recent determinations of 1.0‰ for the mean ocean change in glacial-interglacial δ 18O due to the expansion of global ice volume, we calculate an additional 0.2‰ increase in Mediterranean δ 18O caused by local evaporative enrichment. This estimate of δ 18O change, due to salinity variability, is smaller than previous studies have proposed and demonstrates that Mediterranean records of foraminiferal calcite δ 18O from the last glacial period include a strong temperature component. Paleotemperatures determined in combination with a stacked record of foraminiferal calcite depict almost 9°C of regional cooling for the Last Glacial Maximum. Model results suggest a decrease of ˜1.1‰ in seawater δ 18O relative to the modern value caused by increased freshwater input and reduced salinity accompanying the formation of the most recent sapropel. The results additionally indicate the existence of isotopically light water circulating down to bottom water depths, at least in the western Mediterranean, supporting the existence of an 'anti-estuarine' thermohaline circulation pattern during Sapropel Event 1.

  18. The hierarchical structure of glacial climatic oscillations: Interactions between ice-sheet dynamics and climate

    SciTech Connect

    Paillard, D.

    1995-04-01

    Abrupt climatic oscillations around the North Atlantic have been identified recently in Greenland ice cores as well as in North Atlantic marine sediment cores. The good correlation between the {open_quote}Dansgaard Oeschger events{close_quote} in the ice and the {open_quote}Heinrich events{close_quote} in the ocean suggests climate, in the North Atlantic region, underwent several massive reorganizations in the last glacial period. A characteristic feature seems to be their hierarchical structure. Every 7 to 10-thousand years, when the temperature is close to its minimum, the ice-sheet undergoes a massive iceberg discharge. This Heinrich event is followed by an abrupt warming. then by other oscillations, each lasting between one and two thousand years. These secondary oscillations do not have a clear signature in marine sediments but constitute most of the{open_quote} Dansgaard-Oeschger events{close_quote} found in the ice. A simplified model coupling an ice-sheet and an ocean basin, to illustrate how the interactions between these two components can lead to such a hierarchical structure. The ice-sheet model exhibits internal oscillations composed of growing phases and basal ice melting phases that induce massive iceberg discharges. These fresh water inputs in the ocean stop for a moment the thermohaline circulation, enhancing the temperature contrast between low- and high-latitudes. Just after this event, the thermohaline circulation restarts and an abrupt warming of high-latitude regions is observed. For some parameter values, these warmer temperatures have some influence on the ice-sheet, inducing secondary oscillations similar to those found in paleoclimatic records. Although the mechanism presented here may be too grossly simplified. it nevertheless underlines the potential importance of the coupling between ice-sheet dynamics and oceanic thermohaline circulation on the structure of the climatic records during the last glacial period. 33 refs., 14 figs., 1 tab.

  19. Heinrich-type glacial surges in a low-order dynamical climate model

    SciTech Connect

    Verbitsky, M.; Saltzman, B.

    1994-07-01

    Recent studies suggest the occurrence of sporadic episodes during which the ice streams that discharge ice sheets become enormously active, producing large numbers of icebergs (reflected in North Atlantic sea cores as {open_quotes}Heinrich events{close_quotes}) and possibly causing the partial collapse of the ice sheets. To simulate the mechanism of implied internal thermo-hydrodynamical instability in the context of a more general paleoclimate dynamics model (PDM), a new sliding-catastrophe function that can account for ice-sheet surges in terms of the thickness, density, viscosity, heat-capacity. and heat-conductivity of ice is introduced. Analysis suggests these events might be of three possible kinds: the first occurs in periods of glacial maximum when temperature conditions on the ice surface are extremely cold, but internal friction within bottom boundary layer is also at its maximum and is strong enough to melt ice and cause its surge. The second may happen during an interglacial, when the ice thickness is small but relatively warm climate conditions on the upper surface of ice can be easily advected with the flow of ice to the bottom where even a small additional heating due to friction may cause melting. The third and, perhaps, most interesting type is one that may occur during ice sheet growth: in this period particles of ice reaching the bottom {open_quotes}remember{close_quotes} the warm temperature conditions of the previous interglacial and additional heating due to increasing friction associated with the growing ice sheet may again cause melting. This third introduces the interesting possibility that earlier CO{sub 2} concentrations may be as important for the present-day climate as its current value. According to our model the climate system seems more vulnerable to surges during the penultimate interglacial period than in present one contributing to an explanation of the recent results of the Greenland Ice Core Project. 18 refs., 3 figs., 1 tab.

  20. Tropical Ice Core Isotopes Reveal Changes in Convection from the Last Glacial Maximum to the Present

    NASA Astrophysics Data System (ADS)

    Lawrence, J. R.; Gedzelman, S. D.

    2002-12-01

    The oxygen isotopic composition of water vapors over the tropical oceans has been measured. Samples were collected at three locations: 8.4N 167.6E, 16.0N 97.2W, and 24.5N 81.6W over 3 to 8 week periods two to three times per day. Isotope values varied from -10 to -24 per mil. Dew points varied from 20 to 28 degrees centigrade. The lowering of isotope values below isotopic equilibrium with seawater was caused by exposure of air parcels to rainfall upwind of the sampling location. The higher the intensity and the better the organization of tropical rain systems the lower were the isotope values. This isotopic variation is transferred to tropical ice cores such as those in the Andes Mountains. Raleigh Distillation model curves along the moist adiabat show how isotopes in water vapor and precipitation vary from the ocean surface to the ice core site. Isotope values of precipitation today at the ice core site are lower than those predicted from the Raleigh model assuming that the oxygen isotopic composition of the starting vapor was in near isotopic equilibrium with the sea surface. Simply by lowering the isotopic composition of water vapor over the oceans in the source region it is possible to achieve overlap of model results with measured values. The average oxygen isotope value of ice over the range of present-day measured temperatures matches the model-calculated values if we assume that the initial oxygen isotope value for the source water vapor is about -17 per mil. The average oxygen isotope value of ice at the Last Glacial Maximum (LGM) over the range of estimated temperatures overlaps Raleigh model calculated values. The closer proximity of this data field to the model calculated values can be explained by a higher oxygen isotope value for the source water vapor. Less intense and less organized convection over the tropical oceans at LGM would have resulted in higher oxygen isotope values for the source vapors. In addition, examination of cloud top echoes from

  1. Similar millennial climate variability on the Iberian margin during two early Pleistocene glacials and MIS 3

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

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

  2. Paleobotanical evidence of the history of summer precipitation in the American Southwest since the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Thompson, R. S.

    2012-12-01

    Changes in the spatial patterns in paleoclimatic proxy data provide evidence of changing levels of effective moisture in the Southwest since the Last Glacial Maximum. These patterns may reflect changes in the North American Monsoon, in concert with other climatic and environmental influences. For paleobotanical data, the past distributions of plant species in the Southwest were probably influenced by changes in several factors, including warm-season and cool-season precipitation and the extremes of summer and winter temperatures. Paleobotanical changes were likely to have been strongly influenced by changes in the monsoon, but may not provide an unambiguous history of the monsoon. Macrofossil assemblages from packrat middens provide evidence that plant species in the Southwest lived farther south and at lower elevations than today at the Last Glacial Maximum (~21 ka). Woodland plants lived in areas that now host species of hot and dry desert environments, and it appears that cool-season precipitation was dominant. However, seasonality was less pronounced than today, and although there may have been some component of summer precipitation, it was probably not associated with the monsoon. By ~15 ka, plants of the current deserts began to arrive, indicating increasing warmth. However, woodland plants persisted at lower and southerly locations (relative to today) until ~12.5 ka, when most of these species were extricated from the present-day Sonoran and Chihuahuan deserts. The warming of the continent, decay of the Laurentide ice sheet, and concomitant changes in the surrounding oceans would certainly caused a northward shift in atmospheric circulation and established the conditions necessary for the monsoon. However, the patterning of spatial and temporal changes in the paleobotanical data confounds simple interpretations. Significant changes occurred at the beginning of the Holocene (~11 to 10 ka), with the establishment of near-modern desert and steppe plant

  3. Reconstructing ecological niches and geographic distributions of caribou ( Rangifer tarandus) and red deer ( Cervus elaphus) during the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Banks, William E.; d'Errico, Francesco; Peterson, A. Townsend; Kageyama, Masa; Colombeau, Guillaume

    2008-12-01

    A variety of approaches have been used to reconstruct glacial distributions of species, identify their environmental characteristics, and understand their influence on subsequent population expansions. Traditional methods, however, provide only rough estimates of past distributions, and are often unable to identify the ecological and geographic processes that shaped them. Recently, ecological niche modeling (ENM) methodologies have been applied to these questions in an effort to overcome such limitations. We apply ENM to the European faunal record of the Last Glacial Maximum (LGM) to reconstruct ecological niches and potential ranges for caribou ( Rangifer tarandus) and red deer ( Cervus elaphus), and evaluate whether their LGM distributions resulted from tracking the geographic footprint of their ecological niches (niche conservatism) or if ecological niche shifts between the LGM and present might be implicated. Results indicate that the LGM geographic ranges of both species represent distributions characterized by niche conservatism, expressed through geographic contraction of the geographic footprints of their respective ecological niches.

  4. Investigating vegetation-climate interactions during glacial times using the IPSL GCM

    NASA Astrophysics Data System (ADS)

    Woillez, Marie-Noelle; Kageyama, Masa; Krinner, Gerhard

    2010-05-01

    Vegetation plays an important role in the climate system, through its impact on albedo, rugosity and water fluxes. Only few GCM studies have investigated the climatic impact of vegetation changes in glacial times, some using a fixed glacial vegetation based on pollinic reconstructions (e.g. Crowley & Baum 1997; Wyputta & McAvaney 2001) and some others using vegetation models ( Kubatzki & Claussen 1998; Levis & Foley 1999; Crucifix & Hewitt 2005), but seldom with a full atmosphere-vegetation coupling. Moreover, most of these simulations have been run with fixed sea surface temperatures, thus inhibiting potential oceanic retroactions. Here we force two different vegetation models, ORCHIDEE and BIOME4, with outputs from the IPSL_CM4 Atmosphere-Ocean General Circulation Model (AOGCM). Two different glacial climates are used: with and without collapsed Atlantic Meridional Overturning Circulation (AMOC).The state with a collapsed AMOC results from an imposed additional freshwater flux in the North Atlantic ocean. Then, the different resulting vegetations are used to force the AOGCM. The new climatic states are compared with data and with results from other simulations performed in the PMIP2 project. If time allows we will also show the results from a fully coupled glacial simulation IPSL_CM4-ORCHIDEE and compare the results to those obtained in forced mode.

  5. Atlantic Ocean Circulation at the Last Glacial Maximum: Inferences from Data and Models

    DTIC Science & Technology

    2012-09-01

    vector and gradients. A prescribed correlation length scale determines the dif- fusion coefficient . This new tool provides (1) an improved ability to...Chappell. Australian dust storms : temporal trends and relationships with synoptic pressure distributions (1960-99). Int. J. Climatology, 24 (12):1581–1599...uncertain (see Figure 2-2). The majority of available dust records show glacial periods to have been generally dustier and interglacials to have been more

  6. Late Glacial and Early Holocene Climatic Changes Based on a Multiproxy Lacustrine Sediment Record from Northeast Siberia

    SciTech Connect

    Kokorowski, H D; Anderson, P M; Sletten, R S; Lozhkin, A V; Brown, T A

    2008-05-20

    Palynological (species assemblage, pollen accumulation rate), geochemical (carbon to nitrogen ratios, organic carbon and biogenic silica content), and sedimentological (particle size, magnetic susceptibility) data combined with improved chronology and greater sampling resolution from a new core from Elikchan 4 Lake provide a stronger basis for defining paleoenvironmental changes than was previously possible. Persistence of herb-dominated tundra, slow expansion of Betula and Alnus shrubs, and low percentages of organic carbon and biogenic silica suggest that the Late-Glacial transition (ca. 16,000-11,000 cal. yr BP) was a period of gradual rather than abrupt vegetation and climatic change. Consistency of all Late-Glacial data indicates no Younger Dryas climatic oscillation. A dramatic peak in pollen accumulation rates (ca. 11,000-9800 cal. yr BP) suggests a possible summer temperature optimum, but finer grain-sizes, low magnetic susceptibility, and greater organic carbon and biogenic silica, while showing significant warming at ca. 11,000 cal. yr BP, offer no evidence of a Holocene thermal maximum. When compared to trends in other paleo-records, the new Elikchan data underscore the apparent spatial complexity of climatic responses in Northeast Siberia to global forcings between ca. 16,000-9000 cal. yr BP.

  7. Variability of neodymium isotopes associated with planktonic foraminifera in the Pacific Ocean during the Holocene and Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Hu, Rong; Piotrowski, Alexander M.; Bostock, Helen C.; Crowhurst, Simon; Rennie, Victoria

    2016-08-01

    The deep Pacific Ocean holds the largest oceanic reservoir of carbon which may interchange with the atmosphere on climatologically important timescales. The circulation of the deep Pacific during the Last Glacial Maximum (LGM), however, is not well understood. Neodymium (Nd) isotopes of ferromanganese oxide coatings precipitated on planktonic foraminifera are a valuable proxy for deep ocean water mass reconstruction in paleoceanography. In this study, we present Nd isotope compositions (εNd) of planktonic foraminifera for the Holocene and the LGM obtained from 55 new sites widely distributed in the Pacific Ocean. The Holocene planktonic foraminiferal εNd results agree with the proximal seawater data, indicating that they provide a reliable record of modern bottom water Nd isotopes in the deep Pacific. There is a good correlation between foraminiferal εNd and seawater phosphate concentrations (R2 = 0.80), but poorer correlation with silicate (R2 = 0.37). Our interpretation is that the radiogenic Nd isotope is added to the deep open Pacific through particle release from the upper ocean during deep water mass advection and aging. The data thus also imply the Nd isotopes in the Pacific are not likely to be controlled by silicate cycling. In the North Pacific, the glacial Nd isotopic compositions are similar to the Holocene values, indicating that the Nd isotope composition of North Pacific Deep Water (NPDW) remained constant (-3.5 to -4). During the LGM, the southwest Pacific cores throughout the water column show higher εNd corroborating previous studies which suggested a reduced inflow of North Atlantic Deep Water to the Pacific. However, the western equatorial Pacific deep water does not record a corresponding radiogenic excursion, implying reduced radiogenic boundary inputs during the LGM probably due to a shorter duration of seawater-particle interaction in a stronger glacial deep boundary current. A significant negative glacial εNd excursion is evident in

  8. Poorly ventilated deep ocean at the Last Glacial Maximum inferred from carbon isotopes: A data-model comparison study

    NASA Astrophysics Data System (ADS)

    Menviel, L.; Yu, J.; Joos, F.; Mouchet, A.; Meissner, K. J.; England, M. H.

    2017-01-01

    Atmospheric CO2 was ˜90 ppmv lower at the Last Glacial Maximum (LGM) compared to the late Holocene, but the mechanisms responsible for this change remain elusive. Here we employ a carbon isotope-enabled Earth System Model to investigate the role of ocean circulation in setting the LGM oceanic δ13C distribution, thereby improving our understanding of glacial/interglacial atmospheric CO2 variations. We find that the mean ocean δ13C change can be explained by a 378 ± 88 Gt C(2σ) smaller LGM terrestrial carbon reservoir compared to the Holocene. Critically, in this model, differences in the oceanic δ13C spatial pattern can only be reconciled with a LGM ocean circulation state characterized by a weak (10-15 Sv) and relatively shallow (2000-2500 m) North Atlantic Deep Water cell, reduced Antarctic Bottom Water transport (≤10 Sv globally integrated), and relatively weak (6-8 Sv) and shallow (1000-1500 m) North Pacific Intermediate Water formation. This oceanic circulation state is corroborated by results from the isotope-enabled Bern3D ocean model and further confirmed by high LGM ventilation ages in the deep ocean, particularly in the deep South Atlantic and South Pacific. This suggests a poorly ventilated glacial deep ocean which would have facilitated the sequestration of carbon lost from the terrestrial biosphere and atmosphere.

  9. Future Implications of Climate-driven Vegetation Change in North America Since the Last Glacial Period

    NASA Astrophysics Data System (ADS)

    Nolan, C.; Jackson, S. T.; Overpeck, J. T.; Betancourt, J. L.

    2013-12-01

    Climate projections for the next century include increases in average global temperature that are likely to cause changes in plant community composition and structure across the globe. Characterizing the magnitude of impending climate-driven vegetation changes is important for conservation planning and adaptation, but difficult because climate-driven vegetation change is the result of interacting processes operating on multiple spatial and temporal scales. Paleoecological records from all the vegetated continents offer a proxy record of the vegetation during the last glacial period (defined here as 14,000 to 21,000 years before present). Assessment of the degree of change between glacial-age and modern vegetation provides a metric for assessing impacts of future climate change. A global comparison is underway, in which regional experts are compiling all available pollen and plant macrofossil records with coverage during the last glacial period, and comparing glacial-age vegetation with modern (or late Holocene) vegetation, assessing the magnitude of compositional and structural change. Here we present results from North America (excepting Beringia). Nearly all sites assessed show large changes in composition and structure, all attributable to climate change associated with a sub-continental annual surface air warming of ca. 4 to 10+ °C. Current rates of atmospheric greenhouse gas emissions promise comparable magnitudes of climate change over the next one to two centuries, and at a rate much faster than over the last deglaciation. Our results thus suggest that this future climate change will drive major changes in vegetation distributions everywhere in North America.

  10. Antarctic sea ice control on ocean circulation in present and glacial climates

    PubMed Central

    Ferrari, Raffaele; Jansen, Malte F.; Adkins, Jess F.; Burke, Andrea; Stewart, Andrew L.; Thompson, Andrew F.

    2014-01-01

    In the modern climate, the ocean below 2 km is mainly filled by waters sinking into the abyss around Antarctica and in the North Atlantic. Paleoproxies indicate that waters of North Atlantic origin were instead absent below 2 km at the Last Glacial Maximum, resulting in an expansion of the volume occupied by Antarctic origin waters. In this study we show that this rearrangement of deep water masses is dynamically linked to the expansion of summer sea ice around Antarctica. A simple theory further suggests that these deep waters only came to the surface under sea ice, which insulated them from atmospheric forcing, and were weakly mixed with overlying waters, thus being able to store carbon for long times. This unappreciated link between the expansion of sea ice and the appearance of a voluminous and insulated water mass may help quantify the ocean’s role in regulating atmospheric carbon dioxide on glacial–interglacial timescales. Previous studies pointed to many independent changes in ocean physics to account for the observed swings in atmospheric carbon dioxide. Here it is shown that many of these changes are dynamically linked and therefore must co-occur. PMID:24889624

  11. A high-resolution history of the South American Monsoon from Last Glacial Maximum to the Holocene

    PubMed Central

    Novello, Valdir F.; Cruz, Francisco W.; Vuille, Mathias; Stríkis, Nicolás M.; Edwards, R. Lawrence; Cheng, Hai; Emerick, Suellyn; de Paula, Marcos S.; Li, Xianglei; Barreto, Eline de S.; Karmann, Ivo; Santos, Roberto V.

    2017-01-01

    The exact extent, by which the hydrologic cycle in the Neotropics was affected by external forcing during the last deglaciation, remains poorly understood. Here we present a new paleo-rainfall reconstruction based on high-resolution speleothem δ18O records from the core region of the South American Monsoon System (SAMS), documenting the changing hydrological conditions over tropical South America (SA), in particular during abrupt millennial-scale events. This new record provides the best-resolved and most accurately constrained geochronology of any proxy from South America for this time period, spanning from the Last Glacial Maximum (LGM) to the mid-Holocene. PMID:28281650

  12. A high-resolution history of the South American Monsoon from Last Glacial Maximum to the Holocene.

    PubMed

    Novello, Valdir F; Cruz, Francisco W; Vuille, Mathias; Stríkis, Nicolás M; Edwards, R Lawrence; Cheng, Hai; Emerick, Suellyn; de Paula, Marcos S; Li, Xianglei; Barreto, Eline de S; Karmann, Ivo; Santos, Roberto V

    2017-03-10

    The exact extent, by which the hydrologic cycle in the Neotropics was affected by external forcing during the last deglaciation, remains poorly understood. Here we present a new paleo-rainfall reconstruction based on high-resolution speleothem δ(18)O records from the core region of the South American Monsoon System (SAMS), documenting the changing hydrological conditions over tropical South America (SA), in particular during abrupt millennial-scale events. This new record provides the best-resolved and most accurately constrained geochronology of any proxy from South America for this time period, spanning from the Last Glacial Maximum (LGM) to the mid-Holocene.

  13. A high-resolution history of the South American Monsoon from Last Glacial Maximum to the Holocene

    NASA Astrophysics Data System (ADS)

    Novello, Valdir F.; Cruz, Francisco W.; Vuille, Mathias; Stríkis, Nicolás M.; Edwards, R. Lawrence; Cheng, Hai; Emerick, Suellyn; de Paula, Marcos S.; Li, Xianglei; Barreto, Eline De S.; Karmann, Ivo; Santos, Roberto V.

    2017-03-01

    The exact extent, by which the hydrologic cycle in the Neotropics was affected by external forcing during the last deglaciation, remains poorly understood. Here we present a new paleo-rainfall reconstruction based on high-resolution speleothem δ18O records from the core region of the South American Monsoon System (SAMS), documenting the changing hydrological conditions over tropical South America (SA), in particular during abrupt millennial-scale events. This new record provides the best-resolved and most accurately constrained geochronology of any proxy from South America for this time period, spanning from the Last Glacial Maximum (LGM) to the mid-Holocene.

  14. Last Glacial Maximum sea surface temperature and sea-ice extent in the Pacific sector of the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Benz, Verena; Esper, Oliver; Gersonde, Rainer; Lamy, Frank; Tiedemann, Ralf

    2016-08-01

    Sea surface temperatures and sea-ice extent are most critical variables to evaluate the Southern Ocean paleoceanographic evolution in relation to the development of the global carbon cycle, atmospheric CO2 and ocean-atmosphere circulation. Here we present diatom transfer function-based summer sea surface temperature (SSST) and winter sea-ice (WSI) estimates from the Pacific sector of the Southern Ocean to bridge a gap in information that has to date hampered a well-established reconstruction of the last glacial Southern Ocean at circum-Antarctic scale. We studied the Last Glacial Maximum (LGM) at the EPILOG time slice (19,000-23,000 calendar years before present) in 17 cores and consolidated our LGM picture of the Pacific sector taking into account published data from its warmer regions. Our data display a distinct east-west differentiation with a rather stable WSI edge north of the Pacific-Antarctic Ridge in the Ross Sea sector and a more variable WSI extent over the Amundsen Abyssal Plain. The zone of maximum cooling (>4 K) during the LGM is in the present Subantarctic Zone and bounded to its south by the 4 °C isotherm. The isotherm is in the SSST range prevailing at the modern Antarctic Polar Front, representing a circum-Antarctic feature, and marks the northern edge of the glacial Antarctic Circumpolar Current (ACC). The northward deflection of colder than modern surface waters along the South American continent led to a significant cooling of the glacial Humboldt Current surface waters (4-8 K), which affected the temperature regimes as far north as tropical latitudes. The glacial reduction of ACC temperatures may also have resulted in significant cooling in the Atlantic and Indian Southern Ocean, thus enhancing thermal differentiation of the Southern Ocean and Antarctic continental cooling. The comparison with numerical temperature and sea-ice simulations yields discrepancies, especially concerning the estimates of the sea-ice fields, but some simulations

  15. Lack of deep air convection in firn at Dome Fuji in the last glacial maximum from precise measurements of krypton isotopes

    NASA Astrophysics Data System (ADS)

    Kawamura, K.; Severinghaus, J. P.

    2012-12-01

    Polar ice cores and occluded air provide records of past climate, atmospheric composition and glaciological conditions. In order to establish the age difference between ice and gas records (e.g. Antarctic temperature and CO2), firn densification models with reconstructed temperature and accumulation rate are generally employed for estimating the past firn thickness. However, nitrogen and argon isotopes (15N/14N and 40Ar/36Ar) from the Antarctic interior (Vostok, Dome Fuji, Dome C) for glacial periods have shown significantly smaller gravitational fractionation (equivalent to 30-40 m of firn thickness) than predicted by densification models (e.g. Caillon et al., 2003). This discrepancy may be explained if a deep air convection, which eliminates isotopic fractionation at the top part of firn, was extremely well developed during glacial periods. A modern Antarctic site having deep convective zone (23 m) has been found at a near-zero accumulation area (leeward face of Megadunes) with deep cracks (Severinghaus et al., 2010), although the magnitude is still smaller than hypothesized for the deep ice core sites in glacial maxima. Here we show, by measuring isotopic ratios of krypton (Kr) as well as argon and nitrogen from Dome Fuji ice core, that a thick convective zone was not developed during the last glacial maximum (LGM) at this site. Because heavy noble gases such as Kr and Xe have smaller diffusivities than N2 and Ar, they are less fractionated in deep firn if strong convective mixing exists. We developed a method to simultaneously measure 15N/14N, 40Ar/36Ar and 86Kr/82Kr in ice-core air and applied it to Dome Fuji ice core over the last ~30,000 years including the LGM and current interglacial period (Holocene). When normalized to unit mass difference and corrected for thermal signal by using N2 and Ar isotopic records, the differences between N2 and Kr isotopic ratios are similar for the Holocene and LGM, suggesting that convection zone in LGM was similar to today

  16. The Paleoclimate of the Dead Sea Basin from the Last Glacial Maximum to the Holocene

    DTIC Science & Technology

    2001-11-01

    The purpose of this study was to determine the late glacial paleoclimate of the Southern Levant. A study of delta 13C and delta 18O in carbonates...derived from carbon and oxygen isotopes provide insight into the paleoclimate of the Southern Levant. The period from 20-14.6 kya was dry and cool, with...organic matter into the basin. The results of this study agree with other studies based on paleolake levels, pollen levels and paleoclimate studies from the Dead Sea Basin.

  17. A 33,000-Year-Old Incipient Dog from the Altai Mountains of Siberia: Evidence of the Earliest Domestication Disrupted by the Last Glacial Maximum

    PubMed Central

    Ovodov, Nikolai D.; Crockford, Susan J.; Kuzmin, Yaroslav V.; Higham, Thomas F. G.; Hodgins, Gregory W. L.; van der Plicht, Johannes

    2011-01-01

    Background Virtually all well-documented remains of early domestic dog (Canis familiaris) come from the late Glacial and early Holocene periods (ca. 14,000–9000 calendar years ago, cal BP), with few putative dogs found prior to the Last Glacial Maximum (LGM, ca. 26,500–19,000 cal BP). The dearth of pre-LGM dog-like canids and incomplete state of their preservation has until now prevented an understanding of the morphological features of transitional forms between wild wolves and domesticated dogs in temporal perspective. Methodology/Principal Finding We describe the well-preserved remains of a dog-like canid from the Razboinichya Cave (Altai Mountains of southern Siberia). Because of the extraordinary preservation of the material, including skull, mandibles (both sides) and teeth, it was possible to conduct a complete morphological description and comparison with representative examples of pre-LGM wild wolves, modern wolves, prehistoric domesticated dogs, and early dog-like canids, using morphological criteria to distinguish between wolves and dogs. It was found that the Razboinichya Cave individual is most similar to fully domesticated dogs from Greenland (about 1000 years old), and unlike ancient and modern wolves, and putative dogs from Eliseevichi I site in central Russia. Direct AMS radiocarbon dating of the skull and mandible of the Razboinichya canid conducted in three independent laboratories resulted in highly compatible ages, with average value of ca. 33,000 cal BP. Conclusions/Significance The Razboinichya Cave specimen appears to be an incipient dog that did not give rise to late Glacial – early Holocene lineages and probably represents wolf domestication disrupted by the climatic and cultural changes associated with the LGM. The two earliest incipient dogs from Western Europe (Goyet, Belguim) and Siberia (Razboinichya), separated by thousands of kilometers, show that dog domestication was multiregional, and thus had no single place of origin (as

  18. Invertebrate Metacommunity Structure and Dynamics in an Andean Glacial Stream Network Facing Climate Change

    PubMed Central

    Cauvy-Fraunié, Sophie; Espinosa, Rodrigo; Andino, Patricio; Jacobsen, Dean; Dangles, Olivier

    2015-01-01

    Under the ongoing climate change, understanding the mechanisms structuring the spatial distribution of aquatic species in glacial stream networks is of critical importance to predict the response of aquatic biodiversity in the face of glacier melting. In this study, we propose to use metacommunity theory as a conceptual framework to better understand how river network structure influences the spatial organization of aquatic communities in glacierized catchments. At 51 stream sites in an Andean glacierized catchment (Ecuador), we sampled benthic macroinvertebrates, measured physico-chemical and food resource conditions, and calculated geographical, altitudinal and glaciality distances among all sites. Using partial redundancy analysis, we partitioned community variation to evaluate the relative strength of environmental conditions (e.g., glaciality, food resource) vs. spatial processes (e.g., overland, watercourse, and downstream directional dispersal) in organizing the aquatic metacommunity. Results revealed that both environmental and spatial variables significantly explained community variation among sites. Among all environmental variables, the glacial influence component best explained community variation. Overland spatial variables based on geographical and altitudinal distances significantly affected community variation. Watercourse spatial variables based on glaciality distances had a unique significant effect on community variation. Within alpine catchment, glacial meltwater affects macroinvertebrate metacommunity structure in many ways. Indeed, the harsh environmental conditions characterizing glacial influence not only constitute the primary environmental filter but also, limit water-borne macroinvertebrate dispersal. Therefore, glacier runoff acts as an aquatic dispersal barrier, isolating species in headwater streams, and preventing non-adapted species to colonize throughout the entire stream network. Under a scenario of glacier runoff decrease, we

  19. Quaternary fluvial response to climate change in glacially influenced river systems

    NASA Astrophysics Data System (ADS)

    Cordier, Stéphane; Adamson, Kathryn; Delmas, Magali; Calvet, Marc; Harmand, Dominique

    2016-04-01

    Over the last few decades, many studies in Europe and other continents have focused on the fluvial response to climate forcing in unglaciated basins. However, glacial activity may have a profound impact on the behaviour of the fluvial systems located downstream. In comparison to ice-free basins, these systems are characterised by distinctive hydrological and sediment supply regimes. Over Quaternary timescales, the fluvial records are influenced by periglacial (in non-glaciated areas), proglacial, and paraglacial processes. Understanding the impacts of these processes on the formation and preservation of the Quaternary geomorphological and sedimentary archives is key for our understanding of glacial-fluvial interactions. We investigate the impact of Quaternary glacial activity on fluvial sediment transfer, deposition, and preservation. Using existing studies from across Europe, we create a database of glaciofluvial geomorphology, sedimentology, and geochronology. This is used to examine how glacial forcing of fluvial systems varies spatially in different basin settings, and temporally over successive Milankovitch cycles. In particular, we focus on the ways in which the primary glacial-fluvial depositional signal could be distinguished from periglacial and paraglacial reworking and redeposition.

  20. Polar Climate Connections of the Last Glacial Period

    NASA Astrophysics Data System (ADS)

    Yang, X.; Rial, J. A.

    2015-12-01

    Ever since the cross-core chronology became available, the connection between the Earth's polar regions - or the lack of such [Wunsch, 2003; 2006] - has been an on-going debate in the paleoclimate community. While the inverse relationship inferred from the bipolar seesaw model [Crowley, 1992] could not account for the difference in signal shape of the polar records, integration/differentiation (I/D) has been proposed as the linkage between them [Schmittner et al., 2003; Huybers, 2004; Roe and Steig, 2004; Schmittner et al., 2004]. Stoker and Johnsen [2003] have proposed a revised (thermal) bipolar seesaw model (TBS), demonstrating that the climate record from Antarctic is that of the Greenland convolved with an exponential decaying function, which represents the heat reservoir of the Southern Ocean. More recently, Rial [2012] has proposed phase synchronization (PS) as the polar climate connection from which polar climate records can be treated approximately as a Hilbert transform pair. All three models (I/D, TBS, and PS) have been used to reconstruct past climate of the north from the longer climate record of the south [Siddall et al., 2006; Barker et al., 2011; Oh et al., 2014]. However, no comparison has been made to test and analyze these models against one another for their performance and stabilities. Here we investigated the aforementioned models with polar climate data on the recent AICC2012 chronology to derive the similarities and differences among them in both time and frequency domains. Most importantly we discussed how such differences translate to the discrepancies in reconstructions of the northern climate and possible physical mechanism(s) of connection each model limits and allows. ReferencesBarker et al., 2011, Science, 334(6054), 347-351. Crowley, 1992, Paleoceanography, 7(4), 489-497. Huybers, 2004, QSR, 23(1-2), 207-210. Oh et al., 2014, QSR, 83, 129-142. Rial, 2012, Am J Sci, 312(4), 417-448. Roe & Steig, 2004, Journal of Climate, 17(10), 1929

  1. 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

  2. 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

  3. 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.

  4. 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.

  5. Interhemispheric climate links revealed by late-glacial cooling episode in southern Chile.

    PubMed

    Moreno, P I; Jacobson, G L; Lowell, T V; Denton, G H

    2001-02-15

    Understanding the relative timings of climate events in the Northern and Southern hemispheres is a prerequisite for determining the causes of abrupt climate changes. But climate records from the Patagonian Andes and New Zealand for the period of transition from glacial to interglacial conditions--about 14.6-10 kyr before present, as determined by radiocarbon dating--show varying degrees of correlation with similar records from the Northern Hemisphere. It is necessary to resolve these apparent discrepancies in order to be able to assess the relative roles of Northern Hemisphere ice sheets and oceanic, atmospheric and astronomical influences in initiating climate change in the late-glacial period. Here we report pollen records from three sites in the Lake District of southern Chile (41 degrees S) from which we infer conditions similar to modern climate between about 13 and 12.2 14C kyr before present (BP), followed by cooling events at about 12.2 and 11.4 14C kyr BP, and then by a warming at about 9.8 14C kyr BP. These events were nearly synchronous with important palaeoclimate changes recorded in the North Atlantic region, supporting the idea that interhemispheric linkage through the atmosphere was the primary control on climate during the last deglaciation. In other regions of the Southern Hemisphere, where climate events are not in phase with those in the Northern Hemisphere, local oceanic influences may have counteracted the effects that propagated through the atmosphere.

  6. High-elevation amplification of warming since the Last Glacial Maximum in East Africa: New perspectives from biomarker paleotemperature reconstructions

    NASA Astrophysics Data System (ADS)

    Loomis, S. E.; Russell, J. M.; Kelly, M. A.; Eggermont, H.; Verschuren, D.

    2013-12-01

    Tropical lapse rate variability on glacial/interglacial time scales has been hotly debated since the publication of CLIMAP in 1976. Low-elevation paleotemperature reconstructions from the tropics have repeatedly shown less warming from the Last Glacial Maximum (LGM) to present than reconstructions from high elevations, leading to widespread difficulty in estimating the true LGM-present temperature change in the tropics. This debate is further complicated by the fact that most paleotemperature estimates from high elevations in the tropics are derived from pollen- and moraine-based reconstructions of altitudinal shifts in vegetation belts and glacial equilibrium line altitudes (ELAs). These traditional approaches rely on the assumption that lapse rates have remained constant through time. However, this assumption is problematic in the case of the LGM, when pervasive tropical aridity most likely led to substantial changes in lapse rates. Glycerol dialkyl glycerol tetraethers (GDGTs) can be used to reconstruct paleotemperatures independent of hydrological changes, making them the ideal proxy to reconstruct high elevation temperature change and assess lapse rate variability through time. Here we present two new equatorial paleotemperature records from high elevations in East Africa (Lake Rutundu, Mt. Kenya and Lake Mahoma, Rwenzori Mountains, Uganda) based on branched GDGTs. Our record from Lake Rutundu shows deglacial warming starting near 17 ka and a mid-Holocene thermal maximum near 5 ka. The overall amplitude of warming in the Lake Rutundu record is 6.8×1.0°C from the LGM to the present, with mid-Holocene temperatures 1.6×0.9°C warmer than modern. Our record from Lake Mahoma extends back to 7 ka and shows similar temperature trends to our record from Lake Rutundu, indicating similar temporal resolution of high-elevation temperature change throughout the region. Combining these new records with three previously published GDGT temperature records from different

  7. Simulation of glacial ocean biogeochemical tracer and isotope distributions based on the PMIP3 suite of climate models

    NASA Astrophysics Data System (ADS)

    Khatiwala, Samar; Muglia, Juan; Kvale, Karin; Schmittner, Andreas

    2016-04-01

    In the present climate system, buoyancy forced convection at high-latitudes together with internal mixing results in a vigorous overturning circulation whose major component is North Atlantic Deep Water. One of the key questions of climate science is whether this "mode" of circulation persisted during glacial periods, and in particular at the Last Glacial Maximum (LGM; 21000 years before present). Resolving this question is both important for advancing our understanding of the climate system, as well as a critical test of numerical models' ability to reliably simulate different climates. The observational evidence, based on interpreting geochemical tracers archived in sediments, is conflicting, as are simulations carried out with state-of-the-art climate models (e.g., as part of the PMIP3 suite), which, due to the computational cost involved, do not by and large include biogeochemical and isotope tracers that can be directly compared with proxy data. Here, we apply geochemical observations to evaluate the ability of several realisations of an ocean model driven by atmospheric forcing from the PMIP3 suite of climate models to simulate global ocean circulation during the LGM. This results in a wide range of circulation states that are then used to simulate biogeochemical tracer and isotope (13C, 14C and Pa/Th) distributions using an efficient, "offline" computational scheme known as the transport matrix method (TMM). One of the key advantages of this approach is the use of a uniform set of biogeochemical and isotope parameterizations across all the different circulations based on the PMIP3 models. We compare these simulated distributions to both modern observations and data from LGM ocean sediments to identify similarities and discrepancies between model and data. We find, for example, that when the ocean model is forced with wind stress from the PMIP3 models the radiocarbon age of the deep ocean is systematically younger compared with reconstructions. Changes in

  8. Glacial morphology in the Chinese Pamir: Connections among climate, erosion, topography, lithology and exhumation

    NASA Astrophysics Data System (ADS)

    Schoenbohm, Lindsay M.; Chen, Jie; Stutz, Jamey; Sobel, Edward R.; Thiede, Rasmus C.; Kirby, Benjamin; Strecker, Manfred R.

    2014-09-01

    Modification of the landscape by glacial erosion reflects the dynamic interplay of climate through temperature, precipitation, and prevailing wind direction, and tectonics through rock uplift and exhumation rate, lithology, and range and fault geometry. We investigate these relationships in the northeast Pamir Mountains using mapping and dating of moraines and terraces to determine the glacial history. We analyze modern glacial morphology to determine glacier area, spacing, headwall relief, debris cover, and equilibrium line altitude (ELA) using the area x altitude balance ratio (AABR), toe-to-headwall altitude ratio (THAR) and toe-to-summit altitude method (TSAM) for 156 glaciers and compare this to lithologic, tectonic, and climatic data. We observe a pronounced asymmetry in glacial ELA, area, debris cover, and headwall relief that we interpret to reflect both structural and climatic control: glaciers on the downwind (eastern) side of the range are larger, more debris covered, have steeper headwalls, and tend to erode headward, truncating the smaller glaciers of the upwind, fault-controlled side of the range. We explain this by the transfer of moisture deep into the range as wind-blown or avalanched snow and by limitations imposed on glacial area on the upwind side of the range by the geometry of the Kongur extensional system (KES). The correspondence between rapid exhumation along the KES and maxima in glacier debris cover and headwall relief and minimums in all measures of ELA suggest that taller glacier headwalls develop in a response to more rapid exhumation rates. However, we find that glaciers in the Muji valley did not extend beyond the range front until at least 43 ka, in contrast to extensive glaciation since 300 ka in the south around the high peaks, a pattern which does not clearly reflect uplift rate. Instead, the difference in glacial history and the presence of large peaks (Muztagh Ata and Kongur Shan) with flanking glaciers likely reflects

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

    PubMed

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

    2012-04-24

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

  10. Analysis of the global atmospheric methane budget using ECHAM-MOZ simulations for present-day, pre-industrial time and the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Basu, A.; Schultz, M. G.; Schröder, S.; Francois, L.; Zhang, X.; Lohmann, G.; Laepple, T.

    2014-01-01

    Atmospheric methane concentrations increased considerably from pre-industrial (PI) to present times largely due to anthropogenic emissions. However, firn and ice core records also document a notable rise of methane levels between the Last Glacial Maximum (LGM) and the pre-industrial era, the exact cause of which is not entirely clear. This study investigates these changes by analyzing the methane sources and sinks at each of these climatic periods. Wetlands are the largest natural source of methane and play a key role in determining methane budget changes in particular in the absence of anthropogenic sources. Here, a simple wetland parameterization suitable for coarse-scale climate simulations over long periods is introduced, which is derived from a high-resolution map of surface slopes together with various soil hydrology parameters from the CARAIB vegetation model. This parameterization was implemented in the chemistry general circulation model ECHAM5-MOZ and multi-year time slices were run for LGM, PI and present-day (PD) climate conditions. Global wetland emissions from our parameterization are 72 Tg yr-1 (LGM), 115 Tg yr-1 (PI), and 132 Tg yr-1 (PD). These estimates are lower than most previous studies, and we find a stronger increase of methane emissions between LGM and PI. Taking into account recent findings that suggest more stable OH concentrations than assumed in previous studies, the observed methane distributions are nevertheless well reproduced under the different climates. Hence, this is one of the first studies where a consistent model approach has been successfully applied for simulating methane concentrations over a wide range of climate conditions.

  11. Climate change and evolving human diversity in Europe during the last glacial.

    PubMed Central

    Gamble, Clive; Davies, William; Pettitt, Paul; Richards, Martin

    2004-01-01

    A link between climate change and human evolution during the Pleistocene has often been assumed but rarely tested. At the macro-evolutionary level Foley showed for hominids that extinction, rather than speciation, correlates with environmental change as recorded in the deep sea record. Our aim is to examine this finding at a smaller scale and with high-resolution environmental and archaeological archives. Our interest is in changing patterns of human dispersal under shifting Pleistocene climates during the last glacial period in Europe. Selecting this time frame and region allows us to observe how two hominid taxa, Neanderthals and Crô-Magnons, adapted to climatic conditions during oxygen isotope stage 3. These taxa are representative of two hominid adaptive radiations, termed terrestrial and aquatic, which exhibited different habitat preferences but similar tolerances to climatic factors. Their response to changing ecological conditions was predicated upon their ability to extend their societies in space and time. We examine this difference further using a database of all available radiocarbon determinations from western Europe in the late glacial. These data act as proxies for population history, and in particular the expansion and contraction of regional populations as climate changed rapidly. Independent assessment of these processes is obtained from the genetic history of Europeans. The results indicate that climate affects population contraction rather than expansion. We discuss the consequences for genetic and cultural diversity which led to the legacy of the Ice Age: a single hominid species, globally distributed. PMID:15101580

  12. Climate change and evolving human diversity in Europe during the last glacial.

    PubMed

    Gamble, Clive; Davies, William; Pettitt, Paul; Richards, Martin

    2004-02-29

    A link between climate change and human evolution during the Pleistocene has often been assumed but rarely tested. At the macro-evolutionary level Foley showed for hominids that extinction, rather than speciation, correlates with environmental change as recorded in the deep sea record. Our aim is to examine this finding at a smaller scale and with high-resolution environmental and archaeological archives. Our interest is in changing patterns of human dispersal under shifting Pleistocene climates during the last glacial period in Europe. Selecting this time frame and region allows us to observe how two hominid taxa, Neanderthals and Crô-Magnons, adapted to climatic conditions during oxygen isotope stage 3. These taxa are representative of two hominid adaptive radiations, termed terrestrial and aquatic, which exhibited different habitat preferences but similar tolerances to climatic factors. Their response to changing ecological conditions was predicated upon their ability to extend their societies in space and time. We examine this difference further using a database of all available radiocarbon determinations from western Europe in the late glacial. These data act as proxies for population history, and in particular the expansion and contraction of regional populations as climate changed rapidly. Independent assessment of these processes is obtained from the genetic history of Europeans. The results indicate that climate affects population contraction rather than expansion. We discuss the consequences for genetic and cultural diversity which led to the legacy of the Ice Age: a single hominid species, globally distributed.

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

    NASA Astrophysics Data System (ADS)

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

    2009-12-01

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

  14. Orbital control of western North America atmospheric circulation and climate over two glacial cycles

    NASA Astrophysics Data System (ADS)

    Lachniet, Matthew S.; Denniston, Rhawn F.; Asmerom, Yemane; Polyak, Victor J.

    2014-05-01

    The now arid Great Basin of western North America hosted expansive late Quaternary pluvial lakes, yet the climate forcings that sustained large ice age hydrologic variations remain controversial. Here we present a 175,000 year oxygen isotope record from precisely-dated speleothems that documents a previously unrecognized and highly sensitive link between Great Basin climate and orbital forcing. Our data match the phasing and amplitudes of 65°N summer insolation, including the classic saw-tooth pattern of global ice volume and on-time terminations. Together with the observation of cold conditions during the marine isotope substage 5d glacial inception, our data document a strong precessional-scale Milankovitch forcing of southwestern paleoclimate. Because the expansion of pluvial lakes was associated with cold glacial conditions, the reappearance of large lakes in the Great Basin is unlikely until ca. 55,000 years into the future as climate remains in a mild non-glacial state over the next half eccentricity cycle.

  15. Orbital control of western North America atmospheric circulation and climate over two glacial cycles.

    PubMed

    Lachniet, Matthew S; Denniston, Rhawn F; Asmerom, Yemane; Polyak, Victor J

    2014-05-02

    The now arid Great Basin of western North America hosted expansive late Quaternary pluvial lakes, yet the climate forcings that sustained large ice age hydrologic variations remain controversial. Here we present a 175,000 year oxygen isotope record from precisely-dated speleothems that documents a previously unrecognized and highly sensitive link between Great Basin climate and orbital forcing. Our data match the phasing and amplitudes of 65°N summer insolation, including the classic saw-tooth pattern of global ice volume and on-time terminations. Together with the observation of cold conditions during the marine isotope substage 5d glacial inception, our data document a strong precessional-scale Milankovitch forcing of southwestern paleoclimate. Because the expansion of pluvial lakes was associated with cold glacial conditions, the reappearance of large lakes in the Great Basin is unlikely until ca. 55,000 years into the future as climate remains in a mild non-glacial state over the next half eccentricity cycle.

  16. Migration of the subtropical front as a modulator of glacial climate.

    PubMed

    Bard, Edouard; Rickaby, Rosalind E M

    2009-07-16

    Ice cores extracted from the Antarctic ice sheet suggest that glacial conditions, and the relationship between isotopically derived temperatures and atmospheric PCO(2) have been constant over the last 800,000 years of the Late Pleistocene epoch. But independent lines of evidence, such as the extent of Northern Hemisphere ice sheets, sea level and other temperature records, point towards a fluctuating severity of glacial periods, particularly during the more extreme glacial stadials centred around 340,000 and 420,000 years ago (marine isotope stages 10 and 12). Previously unidentified mechanisms therefore appear to have mediated the relationship between insolation, CO(2) and climate. Here we test whether northward migration of the subtropical front (STF) off the southeastern coast of South Africa acts as a gatekeeper for the Agulhas current, which controls the transport of heat and salt from the Indo-Pacific Ocean to the Atlantic Ocean. Using a new 800,000-year record of sea surface temperature and ocean productivity from ocean sediment core MD962077, we demonstrate that during cold stadials (particularly marine isotope stages 10 and 12), productivity peaked and sea surface temperature was up to 6 degrees C cooler than modern temperatures. This suggests that during these cooler stadials, the STF moved northward by up to 7 degrees latitude, nearly shutting off the Agulhas current. Our results, combined with faunal assemblages from the south Atlantic show that variable northwards migration of the Southern Hemisphere STF can modulate the severity of each glacial period by altering the strength of the Agulhas current carrying heat and salt to the Atlantic meridional overturning circulation. We show hence that the degree of northwards migration of the STF can partially decouple global climate from atmospheric partial pressure of carbon dioxide, P CO(2), and help to resolve the long-standing puzzle of differing glacial amplitudes within a consistent range of atmospheric

  17. 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.

  18. Deep lakes in the Polar Urals - unique archives for reconstructing the Quaternary climate and glacial history in the Russian Arctic

    NASA Astrophysics Data System (ADS)

    Svendsen, J.; Gyllencreutz, R.; Henriksen, M.; Lohne, O. S.; Mangerud, J.; Nazarov, D.

    2009-12-01

    A lake coring campaign in the Polar Urals is carried out within the framework of the Norwegian-Russian IPY-project “The Ice Age Development and Human Settlement in Northern Eurasia” (ICEHUS). The overall aim of the project is to improve the description and understanding of the Late Quaternary environmental and climate changes in the Russian Arctic and how these changes may have affected the early human occupation. In order to obtain a continuous record of climate variability back in time seismic records and sediment cores have been collected from selected mountain lakes. The summer of 2009 we cored two lakes situated near the water shed in the interior northernmost Urals. Seismic profiles show that both these glacially eroded basins contain thick sequences of Quaternary sediments. The thickest strata were found in Bolshoye Shuchye, the largest and deepest lake in the Ural Mountains. This lake is 13 km long and 140 m deep and contains more than 130 m of acoustically laminated sediments. These strata probably accumulated over a rather long time span, possibly covering several interglacial-glacial cycles. Up to 24 m long cores were obtained from the lake floors. We anticipate that they will provide unique high resolution records of the climate and glacial history during the last Ice Age. The seismic records and the sediment cores will form a well-founded basis for assessing the potential and possibilities to core also the deeper strata that could not be reached with the applied coring equipment. In view of the obtained results from the investigated basins, as well as other geological and geochronological data from the surrounding areas, we find it highly unlikely that any glaciers extended into these lakes during the Last Glacial Maximum (LGM), supporting our current hypothesis that the local glaciers in the Polar Urals remained small during the LGM. Our observations indicate that the mountain valleys have been essentially ice free since Marine Isotope Stage 4, at

  19. Genetic Signals of Demographic Expansion in Downy Woodpecker (Picoides pubescens) after the Last North American Glacial Maximum

    PubMed Central

    Pulgarín-R, Paulo C.; Burg, Theresa M.

    2012-01-01

    The glacial cycles of the Pleistocene have been recognized as important, large-scale historical processes that strongly influenced the demographic patterns and genetic structure of many species. Here we present evidence of a postglacial expansion for the Downy Woodpecker (Picoides pubescens), a common member of the forest bird communities in North America with a continental distribution. DNA sequences from the mitochondrial tRNA-Lys, and ATPase 6 and 8 genes, and microsatellite data from seven variable loci were combined with a species distribution model (SDM) to infer possible historical scenarios for this species after the last glacial maximum. Analyses of Downy Woodpeckers from 23 geographic areas suggested little differentiation, shallow genealogical relationships, and limited population structure across the species’ range. Microsatellites, which have higher resolution and are able to detect recent differences, revealed two geographic groups where populations along the eastern edge of the Rocky Mountains (Montana, Utah, Colorado, and southern Alberta) were genetically isolated from the rest of the sampled populations. Mitochondrial DNA, an important marker to detect historical patterns, recovered only one group. However, populations in Idaho and southeast BC contained high haplotype diversity and, in general were characterized by the absence of the most common mtDNA haplotype. The SDM suggested several areas in the southern US as containing suitable Downy Woodpecker habitat during the LGM. The lack of considerable geographic structure and the starburst haplotype network, combined with several population genetic tests, suggest a scenario of demographic expansion during the last part of Pleistocene and early Holocene. PMID:22792306

  20. Saharan Wind Regimes Traced by the Sr-Nd Isotopic Composition of Subtropical Atlantic Sediments: Last Glacial Maximum vs Today

    NASA Astrophysics Data System (ADS)

    Grousset, F. E.; Parra, M.; Bory, A.; Martinez, P.; Bertrand, P.; Shimmield, G.; Ellam, R. M.

    New Nd-Sr isotopic data on the <30 μm lithic particles of surface and Last Glacial Maximum sediments recovered along the African margin between the Equator and the Gibraltar Strait are presented in combination with grain-size measurements. This <30 μm size fraction allows us to eliminate any hemipelagic contribution that could occur in the coarser fractions. In the eolian fraction, both Sr and Nd isotopic tracers reveal the same major northwestern origin (Mauritania, Mali, southern Algeria and Morocco). The Archaean formations of the western Saharan shield could be the source of the very unradiogenic ratios observed here. The more southern regions (Senegal, Guinea) act only as secondary sources. A similar pattern is observed for the LGM. Lithic particles are mostly transported by both Trade and Saharan Air Layer (SAL) winds, along an approximate NE-SW axis; this main feature matches the 'southern plume', characterizing the dust transport observed during winter. No significant latitudinal shift of the belt winds is observed between the LGM and today. At the LGM, however, dust fluxes were 2-4 times higher than today, leading to a more 'Archaean-type' imprint in the deposits. We do not observe any clear relationship between the latitudinal variability of the upwelling systems identified in this region at the LGM and the location of the major wind systems. Both enhanced aridity on the continent and increased wind speed probably occurred together over western tropical Africa during the Last Glacial period.

  1. Flow of the West Antarctic Ice Sheet on the continental margin of the Bellingshausen Sea at the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Ó Cofaigh, Colm; Larter, Rob D.; Dowdeswell, Julian A.; Hillenbrand, Claus-Dieter; Pudsey, Carol J.; Evans, Jeffrey; Morris, Peter

    2005-11-01

    Geophysical data show that during the last glaciation the West Antarctic Ice Sheet (WAIS) drained to the continental shelf edge of the Bellingshausen Sea through a cross-shelf bathymetric trough (Belgica Trough) as a grounded, fast flowing, ice stream. The drainage basin feeding this ice stream probably encompassed southwestern Palmer Land, parts of southern Alexander Island, and the Bryan Coast of Ellsworth Land, with an area exceeding 200,000 km2. On the inner continental shelf, streamlined bedrock and drumlins mapped by swath bathymetry show that the ice stream was fed by convergent ice flow draining from Eltanin Bay and bays to the east, as well as by ice draining the southern part of the Antarctic Peninsula Ice Sheet through the Ronne Entrance. The presence of a paleoice stream in Belgica Trough is indicated by megascale glacial lineations formed in soft till and a trough mouth fan on the continental margin. Grounding zone wedges on the inner and midshelf record ice marginal stillstands during deglaciation and imply a staggered pattern of ice sheet retreat. These new data indicate an extensive WAIS at the Last Glacial Maximum (LGM) on the Bellingshausen Sea continental margin, which advanced to the shelf edge. In conjunction with ice sheet reconstructions from the Antarctic Peninsula and Pine Island Bay, this implies a regionally extensive ice sheet configuration during the LGM along the Antarctic Peninsula, Bellingshausen Sea, and Amundsen Sea margins, with fast flowing ice streams draining the WAIS and Antarctic Peninsula Ice Sheet to the continental shelf edge.

  2. Genetic signals of demographic expansion in Downy Woodpecker (Picoides pubescens) after the last North American glacial maximum.

    PubMed

    Pulgarín-R, Paulo C; Burg, Theresa M

    2012-01-01

    The glacial cycles of the Pleistocene have been recognized as important, large-scale historical processes that strongly influenced the demographic patterns and genetic structure of many species. Here we present evidence of a postglacial expansion for the Downy Woodpecker (Picoides pubescens), a common member of the forest bird communities in North America with a continental distribution. DNA sequences from the mitochondrial tRNA-Lys, and ATPase 6 and 8 genes, and microsatellite data from seven variable loci were combined with a species distribution model (SDM) to infer possible historical scenarios for this species after the last glacial maximum. Analyses of Downy Woodpeckers from 23 geographic areas suggested little differentiation, shallow genealogical relationships, and limited population structure across the species' range. Microsatellites, which have higher resolution and are able to detect recent differences, revealed two geographic groups where populations along the eastern edge of the Rocky Mountains (Montana, Utah, Colorado, and southern Alberta) were genetically isolated from the rest of the sampled populations. Mitochondrial DNA, an important marker to detect historical patterns, recovered only one group. However, populations in Idaho and southeast BC contained high haplotype diversity and, in general were characterized by the absence of the most common mtDNA haplotype. The SDM suggested several areas in the southern US as containing suitable Downy Woodpecker habitat during the LGM. The lack of considerable geographic structure and the starburst haplotype network, combined with several population genetic tests, suggest a scenario of demographic expansion during the last part of Pleistocene and early Holocene.

  3. Imaging Evidence for Hubbard Glacier Advances and Retreats since the Last Glacial Maximum in Disenchantment and Yakutat Bays, Alaska

    NASA Astrophysics Data System (ADS)

    Zurbuchen, J.; Gulick, S. P.; Levoir, M. A.; Goff, J. A.; Haeussler, P. J.

    2013-12-01

    confirms at least two of these advances to be during the Holocene while the oldest may represent the Last Glacial Maximum. The most recent advance likely reached its terminal position at the mouth of Disenchantment Bay, never entering Yakutat Bay. Our interpretation suggests that the Hubbard Glacier has repeatedly advanced around the east side of Yakutat Bay in Knight Island Channel, possibly due to the presence of Malaspina Glacier cutting off access to the central Yakutat Bay during a time of mutual advance. Within the range of the seismic data available for the area, it seems unlikely that the Hubbard Glacier fills all of Yakutat Bay when it advances.

  4. The last glacial termination: targets for climate modelling and proxy-based reconstructions

    NASA Astrophysics Data System (ADS)

    Renssen, Hans; Blockley, Simon P.; Rasmussen, Sune O.; Roche, Didier M.; Valdes, Paul J.; Nisancioglu, Kerim M.; Working Group 3 Members Of Intimate

    2013-04-01

    During the last glacial termination, the climate system experienced a major reorganisation, making this time interval a crucial period for our understanding of climate change. Despite a basic understanding of these changes and a reasonable level of agreement between data and model simulations, a deeper understanding of the last glacial termination remains a long standing goal: we are still faced with the dual challenge of reconstructing the climate history from incomplete and uncertain proxy data, and accurately simulating the climate history with physics-based climate models. There are, however, significant advantages in attempting to reliably integrate palaeoclimate data with model simulations, not least because it is necessary to examine the limitations of both current models and palaeoclimate records before testing possible forcing mechanisms. For the model studies, palaeodata play a crucial role, both as a source of (1) climate forcings for the modelling experiments and (2) palaeoclimate information that is required for model evaluation. Therefore, interaction between the modelling and data communities is essential. For this purpose, and with the last termination as a target, a working group has been set up within the INTIMATE (INTegration of Ice core, MArine and TErrestrial records of the last termination) COST Action (http://cost-es0907.geoenvi.org). We report on the outcome of a workshop of this working group, discussing the state of knowledge of the forcings and various aspects of climate variability during the last termination. We focus in particular on the main uncertainties in the climate signals and the forcings. We discuss the major problems that must be solved to make further progress in our understanding. This requires a joint effort of paleodata, chronology, and climate modelling communities. A number of specific targets for these communities are identified.

  5. 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.

  6. Stable isotopes of fossil teeth corroborate key general circulation model predictions for the Last Glacial Maximum in North America

    NASA Astrophysics Data System (ADS)

    Kohn, Matthew J.; McKay, Moriah

    2010-11-01

    Oxygen isotope data provide a key test of general circulation models (GCMs) for the Last Glacial Maximum (LGM) in North America, which have otherwise proved difficult to validate. High δ18O pedogenic carbonates in central Wyoming have been interpreted to indicate increased summer precipitation sourced from the Gulf of Mexico. Here we show that tooth enamel δ18O of large mammals, which is strongly correlated with local water and precipitation δ18O, is lower during the LGM in Wyoming, not higher. Similar data from Texas, California, Florida and Arizona indicate higher δ18O values than in the Holocene, which is also predicted by GCMs. Tooth enamel data closely validate some recent models of atmospheric circulation and precipitation δ18O, including an increase in the proportion of winter precipitation for central North America, and summer precipitation in the southern US, but suggest aridity can bias pedogenic carbonate δ18O values significantly.

  7. Climate change as the dominant control on glacial-interglacial variations in C3 and C4 plant abundance.

    PubMed

    Huang, Y; Street-Perrott, F A; Metcalfe, S E; Brenner, M; Moreland, M; Freeman, K H

    2001-08-31

    Although C4 plant expansions have been recognized in the late Miocene, identification of the underlying causes is complicated by the uncertainties associated with estimates of ancient precipitation, temperature, and partial pressure of atmospheric carbon dioxide (PCO2). Here we report the carbon isotopic compositions of leaf wax n-alkanes in lake sediment cores from two sites in Mesoamerica that have experienced contrasting moisture variations since the last glacial maximum. Opposite isotopic trends obtained from these two sites indicate that regional climate exerts a strong control on the relative abundance of C3 and C4 plants and that in the absence of favorable moisture and temperature conditions, low PCO2 alone is insufficient to drive an expansion of C4 plants.

  8. Mediterranean Sea surface radiocarbon reservoir age changes since the last glacial maximum.

    PubMed

    Siani, G; Paterne, M; Michel, E; Sulpizio, R; Sbrana, A; Arnold, M; Haddad, G

    2001-11-30

    Sea surface reservoir ages must be known to establish a common chronological framework for marine, continental, and cryospheric paleoproxies, and are crucial for understanding ocean-continent climatic relationships and the paleoventilation of the ocean. Radiocarbon dates of planktonic foraminifera and tephra contemporaneously deposited over Mediterranean marine and terrestrial regions reveal that the reservoir ages were similar to the modern one (approximately 400 years) during most of the past 18,000 carbon-14 years. However, reservoir ages increased by a factor of 2 at the beginning of the last deglaciation. This is attributed to changes of the North Atlantic thermohaline circulation during the massive ice discharge event Heinrich 1.

  9. Maximum glacial advance and deglaciation of the Pinar Valley (Sierra de Gredos, Central Spain) and its significance in the Mediterranean context

    NASA Astrophysics Data System (ADS)

    Palacios, David; Andrés, Nuria; Marcos, Javier; Vázquez-Selem, Lorenzo

    2012-12-01

    Pinar Valley is located on the north side of Galana Peak (40° 15‧ 21″ N; 5° 18‧ 00″ W; 2564 m a.s.l.), Sierra de Gredos, in the center of the Iberian Peninsula. Surface exposure ages based on the in situ accumulation of 36Cl were obtained from six moraine boulders and from three bedrock outcrops to investigate the timing of both the last local glacial maximum and the deglaciation. The oldest moraines, which probably overrode older glacial deposits, are coeval to the global Last Glacial Maximum. Subsequently the Pinar glacier underwent minor pulsations close to its maximum position, followed by general glacier retreat after ~ 17-16 ka. Small cirque glaciers probably remained during the terminal Pleistocene but they had completely disappeared by 10 ka.

  10. Moisture supply for northern ice-sheet growth during the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Hebbeln, Dierk; Dokken, Trond; Andersen, Espen S.; Hald, Morten; Elverhøi, Anders

    1994-08-01

    DURING the last ice age, the Barents Sea ice sheet began to grow 22 kyr ago1, only 8 kyr before it began to disintegrate2. This implies that the ice must have grown very rapidly from the coast to the edge of the continental shelf. Such rapid growth of a large ice sheet requires significant amounts of moisture3, but the origin of this moisture has been unclear, particularly as the CLIMAP climate reconstruction suggests4,5 that the Greenland-Iceland-Norwegian (GIN) seas were perennially ice-covered during this period. Here we present data from deep-sea sediment cores from the Fram Strait, which suggest that relatively warm water from the North Atlantic Ocean was advected into the GIN seas in two short-term events (27-22.5 and 19.5-14.5 kyr ago). We suggest that the resulting seasonally ice-free waters were an important regional moisture source for the Barents Sea ice sheet, and that the GIN seas played a much more active role in climate during the last glaciation than has previously been supposed.

  11. Nearly synchronous climate change in the Northern Hemisphere during the last glacial termination

    USGS Publications Warehouse

    Benson, L.; Burdett, J.; Lund, S.; Kashgarian, Michaele; Mensing, S.

    1997-01-01

    The climate of the North Atlantic region underwent a series of abrupt cold/warm oscillations when the ice sheets of the Northern Hemisphere retreated during the last glacial termination (17.711.5 kyr ago). Evidence for these oscillations, which are recorded in European terrestrial sediments as the Oldest Dryas/Bolling/Older Dryas/Allerod/Younger Dryas vegetational sequence, has been found in Greenland ice cores. The geographical extent of many of these oscillations is not well known, but the last major cold event (the Younger Dryas) seems to have been global in extent. Here we present evidence of four major oscillations in the hydrological balance of the Owens basin, California, that occurred during the last glacial termination. Dry events in western North America occurred at approximately the same time as cold events recorded in Greenland ice, with transitions between climate regimes in the two regions taking place within a few hundred years of each other. Our observations thus support recent climate simulations which indicate that cooling of the North Atlantic Ocean results in cooling of the North Pacific Ocean which, in turn, leads to a drier climate in western North America.

  12. Geodetic measurements reveal similarities between post-Last Glacial Maximum and present-day mass loss from the Greenland ice sheet.

    PubMed

    Khan, Shfaqat A; Sasgen, Ingo; Bevis, Michael; van Dam, Tonie; Bamber, Jonathan L; Wahr, John; Willis, Michael; Kjær, Kurt H; Wouters, Bert; Helm, Veit; Csatho, Beata; Fleming, Kevin; Bjørk, Anders A; Aschwanden, Andy; Knudsen, Per; Munneke, Peter Kuipers

    2016-09-01

    Accurate quantification of the millennial-scale mass balance of the Greenland ice sheet (GrIS) and its contribution to global sea-level rise remain challenging because of sparse in situ observations in key regions. Glacial isostatic adjustment (GIA) is the ongoing response of the solid Earth to ice and ocean load changes occurring since the Last Glacial Maximum (LGM; ~21 thousand years ago) and may be used to constrain the GrIS deglaciation history. We use data from the Greenland Global Positioning System network to directly measure GIA and estimate basin-wide mass changes since the LGM. Unpredicted, large GIA uplift rates of +12 mm/year are found in southeast Greenland. These rates are due to low upper mantle viscosity in the region, from when Greenland passed over the Iceland hot spot about 40 million years ago. This region of concentrated soft rheology has a profound influence on reconstructing the deglaciation history of Greenland. We reevaluate the evolution of the GrIS since LGM and obtain a loss of 1.5-m sea-level equivalent from the northwest and southeast. These same sectors are dominating modern mass loss. We suggest that the present destabilization of these marine-based sectors may increase sea level for centuries to come. Our new deglaciation history and GIA uplift estimates suggest that studies that use the Gravity Recovery and Climate Experiment satellite mission to infer present-day changes in the GrIS may have erroneously corrected for GIA and underestimated the mass loss by about 20 gigatons/year.

  13. Geodetic measurements reveal similarities between post–Last Glacial Maximum and present-day mass loss from the Greenland ice sheet

    PubMed Central

    Khan, Shfaqat A.; Sasgen, Ingo; Bevis, Michael; van Dam, Tonie; Bamber, Jonathan L.; Wahr, John; Willis, Michael; Kjær, Kurt H.; Wouters, Bert; Helm, Veit; Csatho, Beata; Fleming, Kevin; Bjørk, Anders A.; Aschwanden, Andy; Knudsen, Per; Munneke, Peter Kuipers

    2016-01-01

    Accurate quantification of the millennial-scale mass balance of the Greenland ice sheet (GrIS) and its contribution to global sea-level rise remain challenging because of sparse in situ observations in key regions. Glacial isostatic adjustment (GIA) is the ongoing response of the solid Earth to ice and ocean load changes occurring since the Last Glacial Maximum (LGM; ~21 thousand years ago) and may be used to constrain the GrIS deglaciation history. We use data from the Greenland Global Positioning System network to directly measure GIA and estimate basin-wide mass changes since the LGM. Unpredicted, large GIA uplift rates of +12 mm/year are found in southeast Greenland. These rates are due to low upper mantle viscosity in the region, from when Greenland passed over the Iceland hot spot about 40 million years ago. This region of concentrated soft rheology has a profound influence on reconstructing the deglaciation history of Greenland. We reevaluate the evolution of the GrIS since LGM and obtain a loss of 1.5-m sea-level equivalent from the northwest and southeast. These same sectors are dominating modern mass loss. We suggest that the present destabilization of these marine-based sectors may increase sea level for centuries to come. Our new deglaciation history and GIA uplift estimates suggest that studies that use the Gravity Recovery and Climate Experiment satellite mission to infer present-day changes in the GrIS may have erroneously corrected for GIA and underestimated the mass loss by about 20 gigatons/year. PMID:27679819

  14. Sequence stratigraphy of the subaqueous Changjiang (Yangtze River) delta since the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Xu, Taoyu; Wang, Guoqing; Shi, Xuefa; Wang, Xin; Yao, Zhengquan; Yang, Gang; Fang, Xisheng; Qiao, Shuqing; Liu, Shengfa; Wang, Xuchen; Zhao, Quanhong

    2016-01-01

    This study focuses on sedimentary research at the subaqueous Changjiang (Yangtze River) delta, based on five high-resolution seismic profiles and seven borehole cores with accurate AMS 14C datings. Three distinct seismic units were identified from the seismic profiles according to seismic reflection characteristics, and five sedimentary facies were recognized from borehole cores. These facies constituted a fining upward sedimentary sequence in relation to postglacial sea-level transgression. Three sequence surfaces (sequence boundary (SB), transgressive surface (TS), and maximum flooding surface (MFS)) demarcate the boundaries between early transgressive system tract (E-TST), late transgressive system tract (L-TST), early highstand system tract (E-HST) and late highstand system tract (L-HST), which constitute the sixth order sequence. These system tracts were developed coevally with postglacial sea-level rise. E-TST (~ 19-12 ka BP) corresponds to an incised-valley infilling in the early stages of postglacial transgression whereas L-TST (~ 12-7.5 ka BP) was formed during the last stage of postglacial transgression. The progradational structure of L-TST reflected in seismic profiles is possibly related to the intensification of the East Asian summer monsoon. E-HST (~ 7.5-2 ka BP) was deposited in response to the highstand after maximum postglacial transgression was reached, while L-HST (~ 2 ka BP-present) was initiated by accelerated progradation of the Changjiang delta.

  15. Climate change since the last glacial period in Lebanon and the persistence of Mediterranean species

    NASA Astrophysics Data System (ADS)

    Cheddadi, R.; Khater, C.

    2016-10-01

    In this study, we quantified the mean January temperature (Tjan) and both winter (Pw) and summer (Ps) precipitation from three fossil pollen records from Lebanon. Tjan showed a strong correlation with the global temperature changes retrieved in the NGRIP Greenland ice core. The amplitude of ca. 8 °C between the Younger Dryas (YD) period and the Holocene is coherent with climate reconstructions from the Eastern Mediterranean. The overall amount of precipitation was also lower during the YD than during the Holocene but the contrast between Pw and Ps was much more reduced (less than 2 times) during the YD than during the Holocene (up to 8 times). Such different seasonal contrast compare to the present day is coherent with some climate proxies from the Levant that tend to indicate the presence of moisture during the last glacial period. In effect, the low Pw during the YD reflects the replacement of the forest ecosystem by a more shrubby or herbaceous vegetation. Concomitantly, the occurrence of an amount of precipitation higher than the current one during the summer season, along with a reduced evaporation, due to lower temperature, may have contributed to some local observed high lake levels in the area. During the last glacial period, Lebanon was not under a typical Mediterranean climate such as the one we know today, i.e. with a strong precipitation and temperature contrast between summer and winter seasons, but rather under a less contrasted climate. Mediterranean species persisted in this area due to the low amplitude of temperature change between the last glacial period and the Holocene as well as to an availability of moisture throughout the year instead of an occurrence mainly during the winter season as is the case today.

  16. Modeling of depth to base of Last Glacial Maximum and seafloor sediment thickness for the California State Waters Map Series, eastern Santa Barbara Channel, California

    USGS Publications Warehouse

    Wong, Florence L.; Phillips, Eleyne L.; Johnson, Samuel Y.; Sliter, Ray W.

    2012-01-01

    Models of the depth to the base of Last Glacial Maximum and sediment thickness over the base of Last Glacial Maximum for the eastern Santa Barbara Channel are a key part of the maps of shallow subsurface geology and structure for offshore Refugio to Hueneme Canyon, California, in the California State Waters Map Series. A satisfactory interpolation of the two datasets that accounted for regional geologic structure was developed using geographic information systems modeling and graphics software tools. Regional sediment volumes were determined from the model. Source data files suitable for geographic information systems mapping applications are provided.

  17. Estimating maximum global wind power availability and associated climatic consequences

    NASA Astrophysics Data System (ADS)

    Miller, Lee; Gans, Fabian; Kleidon, Axel

    2010-05-01

    Estimating maximum global wind power availability and associated climatic consequences Wind speed reflects the continuous generation of kinetic energy and its dissipation, primarily in the atmospheric boundary layer. When wind turbines extract kinetic wind energy, less kinetic energy remains in the atmosphere in the mean state. While this effect does not play a significant role for a single turbine, it becomes a critical factor for the estimation of large-scale wind power availability. This extraction of kinetic energy by turbines also competes with the natural processes of kinetic energy dissipation, thus setting fundamental limits on extractability that are not considered in previous large-scale studies [1,2,3]. Our simple momentum balance model using ECMWF climate data illustrates a fundamental limit to global wind power extractability and thereby electricity potential (93TW). This is independent of engineering advances in turbine design and wind farm layout. These results are supported by similar results using a global climate model of intermediate complexity. Varying the surface drag coefficient with different simulations allows us to directly relate changes in atmospheric and boundary layer dissipation with resulting climate indices and wind power potential. These new estimates of the maximum power generation by wind turbines are well above the currently installed capacity. Hence, present day installations are unlikely to have a global impact. However, when compared to the current human energy demand of 17TW combined with plans by the US and EU to drastically increase onshore and offshore wind turbine installations [4,5,6], understanding the climatic response and ultimate limitations of wind power as a large-scale renewable energy source is critical. [1] Archer, C., and M.Z. Jacobson, (2005) Evaluation of global wind power, J. Geophys. Res. 110:D12110. [2] Lu, X., M.B. McElroy, and J. Kiviluoma, (2009) Global potential for wind-generated electricity, Proc

  18. Sea ice led to poleward-shifted winds at the Last Glacial Maximum: the influence of state dependency on CMIP5 and PMIP3 models

    NASA Astrophysics Data System (ADS)

    Sime, Louise C.; Hodgson, Dominic; Bracegirdle, Thomas J.; Allen, Claire; Perren, Bianca; Roberts, Stephen; de Boer, Agatha M.

    2016-12-01

    Latitudinal shifts in the Southern Ocean westerly wind jet could drive changes in the glacial to interglacial ocean CO2 inventory. However, whilst CMIP5 model results feature consistent future-warming jet shifts, there is considerable disagreement in deglacial-warming jet shifts. We find here that the dependence of pre-industrial (PI) to Last Glacial Maximum (LGM) jet shifts on PI jet position, or state dependency, explains less of the shifts in jet simulated by the models for the LGM compared with future-warming scenarios. State dependence is also weaker for intensity changes, compared to latitudinal shifts in the jet. Winter sea ice was considerably more extensive during the LGM. Changes in surface heat fluxes, due to this sea ice change, probably had a large impact on the jet. Models that both simulate realistically large expansions in sea ice and feature PI jets which are south of 50° S show an increase in wind speed around 55° S and can show a poleward shift in the jet between the PI and the LGM. However, models with the PI jet positioned equatorwards of around 47° S do not show this response: the sea ice edge is too far from the jet for it to respond. In models with accurately positioned PI jets, a +1° difference in the latitude of the sea ice edge tends to be associated with a -0.85° shift in the 850 hPa jet. However, it seems that around 5° of expansion of LGM sea ice is necessary to hold the jet in its PI position. Since the Gersonde et al. (2005) data support an expansion of more than 5°, this result suggests that a slight poleward shift and intensification was the most likely jet change between the PI and the LGM. Without the effect of sea ice, models simulate poleward-shifted westerlies in warming climates and equatorward-shifted westerlies in colder climates. However, the feedback of sea ice counters and reverses the equatorward trend in cooler climates so that the LGM winds were more likely to have also been shifted slightly poleward.

  19. Reconstruction of changes in the Weddell Sea sector of the Antarctic Ice Sheet since the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Hillenbrand, Claus-Dieter; Bentley, Michael J.; Stolldorf, Travis D.; Hein, Andrew S.; Kuhn, Gerhard; Graham, Alastair G. C.; Fogwill, Christopher J.; Kristoffersen, Yngve; Smith, James. A.; Anderson, John B.; Larter, Robert D.; Melles, Martin; Hodgson, Dominic A.; Mulvaney, Robert; Sugden, David E.

    2014-09-01

    The Weddell Sea sector is one of the main formation sites for Antarctic Bottom Water and an outlet for about one fifth of Antarctica's continental ice volume. Over the last few decades, studies on glacial-geological records in this sector have provided conflicting reconstructions of changes in ice-sheet extent and ice-sheet thickness since the Last Glacial Maximum (LGM at ca 23-19 calibrated kiloyears before present, cal ka BP). Terrestrial geomorphological records and exposure ages obtained from rocks in the hinterland of the Weddell Sea, ice-sheet thickness constraints from ice cores and some radiocarbon dates on offshore sediments were interpreted to indicate no significant ice thickening and locally restricted grounding-line advance at the LGM. Other marine geological and geophysical studies concluded that subglacial bedforms mapped on the Weddell Sea continental shelf, subglacial deposits and sediments over-compacted by overriding ice recovered in cores, and the few available radiocarbon ages from marine sediments are consistent with major ice-sheet advance at the LGM. Reflecting the geological interpretations, different ice-sheet models have reconstructed conflicting LGM ice-sheet configurations for the Weddell Sea sector. Consequently, the estimated contributions of ice-sheet build-up in the Weddell Sea sector to the LGM sea-level low-stand of ˜130 m vary considerably. In this paper, we summarise and review the geological records of past ice-sheet margins and past ice-sheet elevations in the Weddell Sea sector. We compile marine and terrestrial chronological data constraining former ice-sheet size, thereby highlighting different levels of certainty, and present two alternative scenarios of the LGM ice-sheet configuration, including time-slice reconstructions for post-LGM grounding-line retreat. Moreover, we discuss consistencies and possible reasons for inconsistencies between the various reconstructions and propose objectives for future research. The aim

  20. Vegetation of Eurasia from the last glacial maximum to present: Key biogeographic patterns

    NASA Astrophysics Data System (ADS)

    Binney, Heather; Edwards, Mary; Macias-Fauria, Marc; Lozhkin, Anatoly; Anderson, Patricia; Kaplan, Jed O.; Andreev, Andrei; Bezrukova, Elena; Blyakharchuk, Tatiana; Jankovska, Vlasta; Khazina, Irina; Krivonogov, Sergey; Kremenetski, Konstantin; Nield, Jo; Novenko, Elena; Ryabogina, Natalya; Solovieva, Nadia; Willis, Kathy; Zernitskaya, Valentina

    2017-02-01

    Continental-scale estimates of vegetation cover, including land-surface properties and biogeographic trends, reflect the response of plant species to climate change over the past millennia. These estimates can help assess the effectiveness of simulations of climate change using forward and inverse modelling approaches. With the advent of transient and contiguous time-slice palaeoclimate simulations, vegetation datasets with similar temporal qualities are desirable. We collated fossil pollen records for the period 21,000-0 cal yr BP (kyr cal BP; calibrated ages) for Europe and Asia north of 40°N, using extant databases and new data; we filtered records for adequate dating and sorted the nomenclature to conform to a consistent yet extensive taxon list. From this database we extracted pollen spectra representing 1000-year time-slices from 21 kyr cal BP to present and used the biomization approach to define the most likely vegetation biome represented. Biomes were mapped for the 22 time slices, and key plant functional types (PFTs, the constituents of the biomes) were tracked though time. An error matrix and index of topographic complexity clearly showed that the accuracy of pollen-based biome assignments (when compared with modern vegetation) was negatively correlated with topographic complexity, but modern vegetation was nevertheless effectively mapped by the pollen, despite moderate levels of misclassification for most biomes. The pattern at 21 ka is of herb-dominated biomes across the whole region. From the onset of deglaciation (17-18 kyr cal BP), some sites in Europe record forest biomes, particularly the south, and the proportion of forest biomes gradually increases with time through 14 kyr cal BP. During the same period, forest biomes and steppe or tundra biomes are intermixed across the central Asian mountains, and forest biomes occur in coastal Pacific areas. These forest biome occurrences, plus a record of dated plant macrofossils, indicate that some tree

  1. Late Glacial climate and palaeoenvironment in the Southern Carpathian Mountains inferred by chironomid and pollen analyses

    NASA Astrophysics Data System (ADS)

    Tóth, M.; Heiri, O.; Magyari, E.; Braun, M.; Buczkó, K.; Bálint, M.; Jakab, G.

    2009-04-01

    The Southern Carpathian Mountains have several glacial lakes with their sediments extending back to the Late Glacial period (ca. 11,500-14,700 calibrated radiocarbon years BP). This area has so far missed quantitative palaeoclimate records that are however much needed in order to obtain a continental-scale picture of ecosystem reorganization in response to rapid climatic changes during the Late Glacial. High-resolution chironomid and pollen analyses can both provide such records. In this study these two methods are applied to the sediment sequence of a small sub-alpine lake, Taul dintre Brazi (Retezat Mts, 1740 m a.s.l., 0.5 ha). The lake is situated on base-poor, granite bedrock, within the Picea abies forest belt. Our aim was (1) to study changes in the chironomid fauna, (2) to obtain summer temperature estimates using a chironomid-mean July air temperature inference model, and finally (3) to compare the chironomid-inferred climate record with a pollen-based quantitative climate record (plant functional type method). Here we provide first results from this multi-proxy study. The Late Glacial and Early Holocene part of this core was analysed at 100-200 yr resolution. During the Oldest Dryas the chironomid fauna was dominated by Pseudodiamesa and Tanytarsini species; the start of the Lateglacial interstadial was marked by the diversification of Tanytarsini (Tanytarsus lugens-type, Tanytarsus pallidicornis-type, Paratanytarsus sp, Micropsectra insignilobus-type) and the disappearance of Pseudodiamesa suggesting a distinct increase in summer temperature. At the same time afforestation by Larix, Pinus cembra, Pinus mugo and Picea abies was signaled by the pollen, stomatal and plant macrofossil records. During the Younger Dryas reversal the chironomid fauna showed increasing abundance of Micropsectra insignilobus-type, a chironomid typical for cool, nutrient poor lakes whereas the pollen, plant macrofossil and stomatal records pointed to a decrease of Picea abies

  2. Variations in Organic Matter Burial and Composition in Sediments from the Indian Ocean Continental Margin Off SW Indonesia (Sumatra - Java - Flores) Since the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Jennerjahn, T. C.; Gesierich, K.; Schefuß, E.; Mohtadi, M.

    2014-12-01

    Global climate change is a mosaic of regional changes to a large extent determined by region-specific feedbacks between climate and ecosystems. At present the ocean is forming a major sink in the global carbon cycle. Organic matter (OM) storage in sediments displays large regional variations and varied over time during the Quaternary. Upwelling regions are sites of high primary productivity and major depocenters of organic carbon (OC), the least understood of which is the Indian Ocean upwelling off Indonesia. In order to reconstruct the burial and composition of OM during the Late Quaternary, we analyzed five sediment cores from the Indian Ocean continental margin off the Indonesian islands Sumatra to Flores spanning the last 20,000 years (20 kyr). Sediments were analyzed for bulk composition, stable carbon and nitrogen isotopes of OM, amino acids and hexosamines and terrestrial plant wax n-alkanes and their stable carbon isotope composition. Sedimentation rates hardly varied over time in the western part of the transect. They were slightly lower in the East during the Last Glacial Maximum (LGM) and deglaciation, but increased strongly during the Holocene. The amount and composition of OM was similar along the transect with maximum values during the deglaciation and the late Holocene. High biogenic opal covarying with OM content indicates upwelling-induced primary productivity dominated by diatoms to be a major control of OM burial in sediments in the East during the past 20 kyr. The content of labile OM was low throughout the transect during the LGM and increased during the late Holocene. The increase was stronger and the OM less degraded in the East than in the West indicating that continental margin sediments off Java and Flores were the major depocenter of OC burial along the Indian Ocean margin off SW Indonesia. Temporal variations probably resulted from changes in upwelling intensity and terrestrial inputs driven by variations in monsoon strength.

  3. Tropical cooling at the last glacial maximum and extratropical ocean ventilation1

    CCR contribution number: 780.

    NASA Astrophysics Data System (ADS)

    Liu, Zhengyu; Shin, Sang-Ik; Otto-Bliesner, Bette; Kutzbach, John E.; Brady, Esther C.; Lee, DongEun

    2002-05-01

    The NCAR CSM is used to simulate the climate at Last Glacial Maximum. The CSM simulates a tropical SST cooling of 2.1°C. It is shown that about half of this tropical cooling is associated with the upper ocean circulation, especially the ventilation of thermocline and intermediate waters from the mid/high latitude South Pacific.

  4. Validation of climate model-inferred regional temperature change for late-glacial Europe

    PubMed Central

    Heiri, Oliver; Brooks, Stephen J.; Renssen, Hans; Bedford, Alan; Hazekamp, Marjolein; Ilyashuk, Boris; Jeffers, Elizabeth S.; Lang, Barbara; Kirilova, Emiliya; Kuiper, Saskia; Millet, Laurent; Samartin, Stéphanie; Toth, Monika; Verbruggen, Frederike; Watson, Jenny E.; van Asch, Nelleke; Lammertsma, Emmy; Amon, Leeli; Birks, Hilary H.; Birks, H. John B.; Mortensen, Morten F.; Hoek, Wim Z.; Magyari, Enikö; Sobrino, Castor Muñoz; Seppä, Heikki; Tinner, Willy; Tonkov, Spassimir; Veski, Siim; Lotter, André F.

    2014-01-01

    Comparisons of climate model hindcasts with independent proxy data are essential for assessing model performance in non-analogue situations. However, standardized paleoclimate datasets for assessing the spatial pattern of past climatic change across continents are lacking for some of the most dynamic episodes of Earth's recent past. Here we present a new chironomid-based paleotemperature dataset designed to assess climate model hindcasts of regional summer temperature change in Europe during the late-glacial and early Holocene. Latitudinal and longitudinal patterns of inferred temperature change are in excellent agreement with simulations by the ECHAM-4 model, implying that atmospheric general circulation models like ECHAM-4 can successfully predict regionally diverging temperature trends in Europe, even when conditions differ significantly from present. However, ECHAM-4 infers larger amplitudes of change and higher temperatures during warm phases than our paleotemperature estimates, suggesting that this and similar models may overestimate past and potentially also future summer temperature changes in Europe. PMID:25208610

  5. Validation of climate model-inferred regional temperature change for late-glacial Europe.

    PubMed

    Heiri, Oliver; Brooks, Stephen J; Renssen, Hans; Bedford, Alan; Hazekamp, Marjolein; Ilyashuk, Boris; Jeffers, Elizabeth S; Lang, Barbara; Kirilova, Emiliya; Kuiper, Saskia; Millet, Laurent; Samartin, Stéphanie; Toth, Monika; Verbruggen, Frederike; Watson, Jenny E; van Asch, Nelleke; Lammertsma, Emmy; Amon, Leeli; Birks, Hilary H; Birks, H John B; Mortensen, Morten F; Hoek, Wim Z; Magyari, Enikö; Muñoz Sobrino, Castor; Seppä, Heikki; Tinner, Willy; Tonkov, Spassimir; Veski, Siim; Lotter, André F

    2014-09-11

    Comparisons of climate model hindcasts with independent proxy data are essential for assessing model performance in non-analogue situations. However, standardized palaeoclimate data sets for assessing the spatial pattern of past climatic change across continents are lacking for some of the most dynamic episodes of Earth's recent past. Here we present a new chironomid-based palaeotemperature dataset designed to assess climate model hindcasts of regional summer temperature change in Europe during the late-glacial and early Holocene. Latitudinal and longitudinal patterns of inferred temperature change are in excellent agreement with simulations by the ECHAM-4 model, implying that atmospheric general circulation models like ECHAM-4 can successfully predict regionally diverging temperature trends in Europe, even when conditions differ significantly from present. However, ECHAM-4 infers larger amplitudes of change and higher temperatures during warm phases than our palaeotemperature estimates, suggesting that this and similar models may overestimate past and potentially also future summer temperature changes in Europe.

  6. Post-glacial landscape response to climate variability in the southeastern San Juan Mountains of Colorado, USA

    NASA Astrophysics Data System (ADS)

    Johnson, Bradley G.; Eppes, Martha Cary; Diemer, John A.; Jiménez-Moreno, Gonzalo; Layzell, Anthony L.

    2011-11-01

    Geomorphic mapping in the upper Conejos River Valley of the San Juan Mountains has shown that three distinct periods of aggradation have occurred since the end of the last glacial maximum (LGM). The first occurred during the Pleistocene-Holocene transition (~ 12.5-9.5 ka) and is interpreted as paraglacial landscape response to deglaciation after the LGM. Evidence of the second period of aggradation is limited but indicates a small pulse of sedimentation at ~ 5.5 ka. A third, more broadly identifiable period of sedimentation occurred in the late Holocene (~ 2.2-1 ka). The latest two periods of aggradation are concurrent with increases in the frequency of climate change in the region suggesting that Holocene alpine and sub-alpine landscapes respond more to rapid changes in climate than to large singular climatic swings. Soil development and radiocarbon dating indicate that hillslopes were stable during the Holocene even while aggradation was occurring in valley bottoms. Thus, we can conclude that erosion does not occur equally throughout the landscape but is focused upslope of headwater streams, along tributary channels, or on ridge tops. This is in contrast to some models which assume equal erosion in headwater basins.

  7. Glacial to Holocene climate changes in the SE Pacific. The Raraku Lake sedimentary record (Easter Island, 27°S)

    NASA Astrophysics Data System (ADS)

    Sáez, Alberto; Valero-Garcés, Blas L.; Giralt, Santiago; Moreno, Ana; Bao, Roberto; Pueyo, Juan J.; Hernández, Armand; Casas, David

    2009-12-01

    Easter Island (SE Pacific, 27°S) provides a unique opportunity to reconstruct past climate changes in the South Pacific region based on terrestrial archives. Although the general climate evolution of the south Pacific since the Last Glacial Maximum (LGM) is coherent with terrestrial records in southern South America and Polynesia, the details of the dynamics of the shifting Westerlies, the South Pacific Convergence Zone and the South Pacific Anticyclone during the glacial-interglacial transition and the Holocene, and the large scale controls on precipitation in tropical and extratropical regions remain elusive. Here we present a high-resolution reconstruction of lake dynamics, watershed processes and paleohydrology for the last 34 000 cal yrs BP based on a sedimentological and geochemical multiproxy study of 8 cores from the Raraku Lake sediments constrained by 22 AMS radiocarbon dates. This multicore strategy has reconstructed the sedimentary architecture of the lake infilling and provided a stratigraphic framework to integrate and correlate previous core and vegetation studies conducted in the lake. High lake levels and clastic input dominated sedimentation in Raraku Lake between 34 and 28 cal kyr BP. Sedimentological and geochemical evidences support previously reported pollen data showing a relatively open forest and a cold and relatively humid climate during the Glacial period. Between 28 and 17.3 cal kyr BP, including the LGM period, colder conditions contributed to a reduction of the tree coverage in the island. The coherent climate patterns in subtropical and mid latitudes of Chile and Eastern Island for the LGM (more humid conditions) suggest stronger influence of the Antarctic circumpolar current and an enhancement of the Westerlies. The end of Glacial Period occurred at 17.3 cal kyr BP and was characterized by a sharp decrease in lake level conducive to the development of major flood events and erosion of littoral sediments. Deglaciation (Termination

  8. 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

  9. 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.

  10. Climate and vegetation since the Last Interglacial (MIS 5e) in a putative glacial refugium, northern Idaho, USA

    NASA Astrophysics Data System (ADS)

    Herring, Erin M.; Gavin, Daniel G.

    2015-06-01

    There are very few terrestrial sediment records from North America that contain a nearly continuous sequence spanning from the Last Interglacial period to the present. We present stratigraphic records of pollen and several other proxies from a Carex-dominated wetland, Star Meadows, located 140 km south of the maximum extent of the Cordilleran Ice Sheet and near the current southern extent of interior mesic forests in northern Idaho. Many species in this region are disjunct by 160 km of arid steppe and dry forest from their more extensive distribution along the Pacific Northwest coast and may have survived in an interior refugium. The chronology for the upper 251 cm was determined by six radiocarbon dates and one tephra deposit, and the age of the remainder of the core (251-809 cm) was estimated by correlation with SPECMAP δ18O. Fluctuating water levels were inferred from alternating peat, biogenic silica, and aquatic pollen types. During MIS 5e the region was warmer and drier than today and was dominated by Pinus (likely Pinus contorta) mixed conifer forest surrounding a Carex meadow. A cool-moist climate (MIS 5b-5d) soon developed, and the site was inundated with deep water. Pollen indicated wetland vegetation (Betula glandulosa, Typhaceae, and Salix) developed around a lake with a Pseudotsuga/Larix and Picea forest on the surrounding slopes. During MIS 5a, a warmer climate supported a Pseudotsuga/Larix, Abies, and Picea forest on the surrounding hillsides and a Carex-dominated environment within a dry meadow. From MIS 4 to MIS 3, a cool and wet Pinus and Picea forest predominated. Water levels rose, enabling Nuphar to persist within a perennial lake while a sedge fen established along the lake margin. As climate transitioned into MIS 2, a cooler and drier climate supported a Pinus and Picea subalpine parkland, though water levels remained high enough to support Nuphar. During the Last Glacial Maximum the sediment was mainly silt and clay with high Artemisia and

  11. Climate versus geological controls on glacial meltwater micronutrient production in southern Greenland

    NASA Astrophysics Data System (ADS)

    Aciego, S. M.; Stevenson, E. I.; Arendt, C. A.

    2015-08-01

    Low concentrations of micronutrients in subarctic North Atlantic surface waters limit phytoplankton growth. Iron, phosphorous, and silicon are all potentially bio-limiting nutrients; iron is the most well documented in the subarctic North Atlantic. Manganese, nickel, copper and zinc are also essential trace metals for phytoplankton cell function. However, the spatial and temporal variability in the flux of these elements to the subarctic North Atlantic is undercharacterized. Here we show new data from the meltseason peak in 2013 indicating that glacial meltwater from the southern tip of Greenland has elevated dissolved major and trace metal concentrations compared to glacial meltwater draining shorter melt season glacial catchments to the north. Fe concentrations range from 0.13 to 6.97 μM, Zn from 4 to 95 μM, and Si from 4 to 36 μM, all higher than the depleted surface waters of the subarctic North Atlantic. Measured hydrochemical data modeled by PHREEQC indicates meltwater is undersaturated in pyrite and silicate phases but supersaturated with respect to oxyhydroxides, hematite and goethite, all phases that precipitate Fe as colloids, of which the nanoparticle phases should remain biologically available. The variability in geologic units between the sites indicates that subglacial lithology is a minor but not the dominant control on meltwater chemistry. The disparity in concentrations is directly correlated with climate, and an extended melt season, suggesting that future warming in Greenland will lead to increased trace element, and potential micronutrient, flux to the subarctic North Atlantic surface waters.

  12. Palynology of the northeastern Fram Strait since the Last Glacial Maximum : evidence for large amplitude changes in sea-surface conditions

    NASA Astrophysics Data System (ADS)

    Falardeau, Jade; de Vernal, Anne; Spielhagen, Robert

    2016-04-01

    species leads us to reconstruct relatively high summer temperatures (up to 11°C) in a context of high seasonality due to low surface salinity and to strong stratification. After 12.5 ka BP, important changes in species relative abundance reflect the development of modern-like dinocyst assemblages. A lowering of summer SST and increased salinity are recorded from 12.5 to 10.5 ka, after which the data indicates an early Holocene thermal optimum followed by a cooling trend accompanied by increase in sea ice cover. The palynological results from the Fram Strait area are generally consistent with biomarker data suggesting late glacial variations in sea ice cover and Holocene cooling trend (Müller et al, 2012, 2014). References: de Vernal et al., 2005. Reconstruction of sea-surface conditions at middle to high latitudes of the Northern Hemisphere during the Last Glacial Maximum (LGM) based on dinoflagellate cyst assemblages. Quaternary Science Reviews 24, p. 897-924 Müller, J., Werner, K., Stein, R., Fahl, K., Moros, M., Jansen, E., 2012. Holocene cooling culminates in sea ice oscillations in Fram Strait. Quaternary Science Reviews 47, 1-14 Müller, J., Stein, R., 2014. High-resolution record of late glacial and deglacial sea ice changes in Fram Strait corroborates ice-ocean interactions during abrupt climate shifts. Earth and Planetary Science Letters 403, 446-455

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

    NASA Astrophysics Data System (ADS)

    Bahadory, T.; Tarasov, L.

    2015-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2005-12-01

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

  15. Not so deserted…paleoecology and human subsistence in Central Iberia (Guadalajara, Spain) around the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Yravedra, José; Julien, Marie-Anne; Alcaraz-Castaño, Manuel; Estaca-Gómez, Verónica; Alcolea-González, Javier; de Balbín-Behrmann, Rodrigo; Lécuyer, Christophe; Marcel, Claude Hillaire; Burke, Ariane

    2016-05-01

    In contrast to the coastal areas of the Iberian Peninsula, the Upper Palaeolithic settlement of central Iberia, dominated by the Spanish plateau, is poorly known. Traditional models assume a total or virtual depopulation of the interior of the Iberian Peninsula during the Last Glacial. In this paper we present a detailed investigation of human-environment interactions through the first zooarchaeological, taphonomic and isotopic study of the key site of Peña Capón, a rock shelter located in the south-eastern foothills of the Central System range that contains a multi-layered deposit dated to marine isotope stage 2 (MIS 2). Analyses of the faunal assemblages of the Proto-Solutrean (3) and Middle Solutrean (2) layers show that human preferentially hunted horse, deer and iberian ibex living in the vicinity of the rock shelter. Isotope geochemistry of the animal remains of Peña Capón provides us with the first detailed intra-tooth multi-proxy analysis for this time period in south-western Europe, providing estimates of climatic conditions, seasonal flucturation of diet, as well as patterns of seasonal mobility. Our results indicate that human presence at Peña Capón was apparently restricted to relatively warm intervals around the LGM or reflects the presence of an ecological refuge, and provide us with evidence of recurrent human presence in the Iberian interior during the Upper Paleolithic prior to the Magdalenian.

  16. Debris flow sensitivity to glacial-interglacial climate change - supply vs transport

    NASA Astrophysics Data System (ADS)

    D'Arcy, Mitch; Roda Boluda, Duna C.; Whittaker, Alexander C.

    2016-04-01

    Numerical models suggest that small mountain catchment-alluvial fan systems might be sensitive to climate changes over glacial-interglacial cycles, and record these palaeoclimate signals in the sedimentology of their deposits. However, these models are still largely untested, and the propagation of climate signals through simple sediment routing systems remains contentious. Here, we present detailed sedimentological records from 8 debris flow fan systems in Owens Valley, California, that capture the past ~ 120 ka of deposition. We identify a strong and sustained relationship between deposit grain size and palaeoclimate records over a full glacial-interglacial cycle, with significantly coarser-grained deposits found in warm and dry periods. Our data show that these systems are highly sensitive to climate with a rapid response timescale of < 10ka, which we attribute to rapid transfer from source to sink. This sensitive record might be explained by changes in sediment supply and/or changes in sediment mobilisation, and we evaluate these mechanisms quantitatively. We find little evidence that changes in catchment hypsometry, weathering patterns, past glaciation or sediment production can explain the grain size changes we observe on the fans. However we do find that grain size has increased exponentially with rising temperatures, at a rate that matches the intensification of storms with warming. As these debris flows are triggered by surface runoff during intense storms, we interpret that enhanced runoff rates in warm and stormy conditions are responsible for entraining larger clasts during debris flow initiation. This implies that debris flow fans might record signals of past storm intensity. Our study utilises field sedimentology and focuses on short transport distances (~ 10 km) and climate changes over ~ 1-100 ka timespans, but could additionally have important implications for how eroding landscapes might respond to future warming scenarios. We address the

  17. 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

  18. Response of Terrestrial Vegetation to Variations in Temperature and Aridity Since the Last Glacial Maximum in Lake Chalco, Mexico

    NASA Astrophysics Data System (ADS)

    Werne, J. P.; Halbur, J.; Rubesch, M.; Brown, E. T.; Ortega, B.; Caballero, M.; Correa-Metrio, A.; Lozano, S.

    2013-05-01

    The water balance of the Southwestern United States and most of Mexico is dependent on regional climate systems, including the Mexican (or North American) Monsoon. The Mexican Monsoon leads to significant summer rainfall across a broad swath of the continent, which constitutes the major source of annual precipitation over much of this region. The position of the ITCZ and the strength of the accompanying monsoon are affected by variability in insolation. Stronger northern hemisphere summer insolation shifts the ITCZ northward, bringing about a more intense monsoon. Here we discuss a new geochemical climate record from Lake Chalco, Mexico, which couples inorganic (X-ray fluorescence) and organic (biomarkers and stable isotopes) geochemical proxies to reconstruct temperature and aridity over the past 45,000 years, as well as the response of terrestrial vegetation to such climate changes. The Basin of Mexico is a high altitude closed lacustrine basin (20°N, 99°W; 2240 m.a.s.l.) in the Trans Mexican Volcanic Belt. The plain of Lake Chalco, located near Mexico City in the southern sub-basin, has an area of 120 km2 and a catchment of 1100 km2. Though the present-day lake has been reduced to a small marsh due to historic diversion of its waters, over longer timescales the lake has been a sensitive recorder of hydroclimatic variations. Low Ca concentrations indicate more arid periods during the late glacial (34 - 15 kybp) compared to the last interstadial or early Holocene. This observation is supported by the ratio of terrestrial to aquatic lipid biomarkers (long vs. short chain n-alkanes), which indicate greater relative inputs of aquatic biomarkers during wetter periods. The changes in aridity as shown in these geochemical proxies are compared with temperature as reflected in glycerol dialkyl glycerol tetraether (GDGT) based paleotemperature proxies to assess the extent to which insolation may have driven aridity variations, and with terrestrial and aquatic biomarker

  19. Reconstructing the Last Glacial Maximum ice sheet in the Weddell Sea embayment, Antarctica, using numerical modelling constrained by field evidence

    NASA Astrophysics Data System (ADS)

    Le Brocq, A. M.; Bentley, M. J.; Hubbard, A.; Fogwill, C. J.; Sugden, D. E.; Whitehouse, P. L.

    2011-09-01

    The Weddell Sea Embayment (WSE) sector of the Antarctic ice sheet has been suggested as a potential source for a period of rapid sea-level rise - Meltwater Pulse 1a, a 20 m rise in ˜500 years. Previous modelling attempts have predicted an extensive grounding line advance in the WSE, to the continental shelf break, leading to a large equivalent sea-level contribution for the sector. A range of recent field evidence suggests that the ice sheet elevation change in the WSE at the Last Glacial Maximum (LGM) is less than previously thought. This paper describes and discusses an ice flow modelling derived reconstruction of the LGM ice sheet in the WSE, constrained by the recent field evidence. The ice flow model reconstructions suggest that an ice sheet consistent with the field evidence does not support grounding line advance to the continental shelf break. A range of modelled ice sheet surfaces are instead produced, with different grounding line locations derived from a novel grounding line advance scheme. The ice sheet reconstructions which best fit the field constraints lead to a range of equivalent eustatic sea-level estimates between approximately 1.4 and 3 m for this sector. This paper describes the modelling procedure in detail, considers the assumptions and limitations associated with the modelling approach, and how the uncertainty may impact on the eustatic sea-level equivalent results for the WSE.

  20. The California current of the last glacial maximum: reconstruction at 42°N based on multiple proxies

    USGS Publications Warehouse

    Ortiz, Joseph D.; Mix, Alan C.; Hostetler, Steven W.; Kashgarian, Michaele

    1997-01-01

    Multiple paleoceanographic proxies in a zonal transect across the California Current near 42°N record modern and last glacial maximum (LGM) thermal and nutrient gradients. The offshore thermal gradient, derived from foraminiferal species assemblages and oxygen isotope data, was similar at the LGM to that at present (warmer offshore), but average temperatures were 3.3° ±1.5°C colder. Observed gradients require that the sites remained under the southward flow of the California Current, and thus that the polar front remained north of 42°N during the LGM. Carbon isotopic and foraminiferal flux data suggests enhanced nutrients and productivity of foraminfera in the northern California Current up to 650 km offshore. In contrast, marine organic carbon and coastal diatom burial rates decreased during the LGM. These seemingly contradictory results are reconciled by model simulations of the LGM wind- field, which suggest that wind stress curl at 42°N (and thus open-ocean upwelling) increased, while offshore Ekman transport (and thus coastal upwelling) decreased during the last ice age. The ecosystem of the northern California Current during the LGM approximated that of the modern Gulf of Alaska. Cooling and production in this region was thus driven by stronger open-ocean upwelling and/or southward flow of high-latitude water masses, rather than by coastal upwelling.

  1. Earliest Human Presence in North America Dated to the Last Glacial Maximum: New Radiocarbon Dates from Bluefish Caves, Canada

    PubMed Central

    Bourgeon, Lauriane; Burke, Ariane; Higham, Thomas

    2017-01-01

    The timing of the first entry of humans into North America is still hotly debated within the scientific community. Excavations conducted at Bluefish Caves (Yukon Territory) from 1977 to 1987 yielded a series of radiocarbon dates that led archaeologists to propose that the initial dispersal of human groups into Eastern Beringia (Alaska and the Yukon Territory) occurred during the Last Glacial Maximum (LGM). This hypothesis proved highly controversial in the absence of other sites of similar age and concerns about the stratigraphy and anthropogenic signature of the bone assemblages that yielded the dates. The weight of the available archaeological evidence suggests that the first peopling of North America occurred ca. 14,000 cal BP (calibrated years Before Present), i.e., well after the LGM. Here, we report new AMS radiocarbon dates obtained on cut-marked bone samples identified during a comprehensive taphonomic analysis of the Bluefish Caves fauna. Our results demonstrate that humans occupied the site as early as 24,000 cal BP (19,650 ± 130 14C BP). In addition to proving that Bluefish Caves is the oldest known archaeological site in North America, the results offer archaeological support for the “Beringian standstill hypothesis”, which proposes that a genetically isolated human population persisted in Beringia during the LGM and dispersed from there to North and South America during the post-LGM period. PMID:28060931

  2. The modern and Last Glacial Maximum hydrological cycles of the Eastern Mediterranean and the Levant from a water isotope perspective

    NASA Astrophysics Data System (ADS)

    Goldsmith, Y.; Polissar, P. J.; Ayalon, A.; Bar-Matthews, M.; deMenocal, P. B.; Broecker, W. S.

    2017-01-01

    The isotopic composition of precipitation (δP) is one of the most widely used and informative terrestrial paleoclimate proxies. δP integrates a series of hydrological processes; therefore, any interpretation of paleohydrology using δP requires a thorough understanding and quantification of the full hydrological cycle. In this paper, we use modern data to analytically model the full isotopic hydrological cycle of the Eastern Mediterranean and the Southern Levant, including oceanic evaporation, distillation during transport and precipitation over land. This model allows us to determine the important factors controlling this system. The model results underscore the significance of the isotopic distillation process driven by the land-sea temperature gradient as a significant factor controlling the long-term average isotopic composition of precipitation across Israel. Based on the understanding of the processes that govern the modern system, we model the isotopic composition of precipitation from the Last Glacial Maximum (LGM) using published data for speleothem oxygen isotopes in calcite, oxygen and hydrogen isotopes in fluid inclusions and clumped isotope values from Soreq Cave and the isotopic composition of East Mediterranean planktonic foraminifera G. ruber. The data and model results indicate two plausible scenarios for the LGM that entail changes in the magnitude of distillation over Israel, in normalized humidity over the Mediterranean and possible shifts of the moisture trajectories over the Mediterranean. The results presented in the paper illustrate the importance of understanding the full local hydrological cycle when reconstructing and interpreting the isotopic composition of precipitation.

  3. Earliest Human Presence in North America Dated to the Last Glacial Maximum: New Radiocarbon Dates from Bluefish Caves, Canada.

    PubMed

    Bourgeon, Lauriane; Burke, Ariane; Higham, Thomas

    2017-01-01

    The timing of the first entry of humans into North America is still hotly debated within the scientific community. Excavations conducted at Bluefish Caves (Yukon Territory) from 1977 to 1987 yielded a series of radiocarbon dates that led archaeologists to propose that the initial dispersal of human groups into Eastern Beringia (Alaska and the Yukon Territory) occurred during the Last Glacial Maximum (LGM). This hypothesis proved highly controversial in the absence of other sites of similar age and concerns about the stratigraphy and anthropogenic signature of the bone assemblages that yielded the dates. The weight of the available archaeological evidence suggests that the first peopling of North America occurred ca. 14,000 cal BP (calibrated years Before Present), i.e., well after the LGM. Here, we report new AMS radiocarbon dates obtained on cut-marked bone samples identified during a comprehensive taphonomic analysis of the Bluefish Caves fauna. Our results demonstrate that humans occupied the site as early as 24,000 cal BP (19,650 ± 130 14C BP). In addition to proving that Bluefish Caves is the oldest known archaeological site in North America, the results offer archaeological support for the "Beringian standstill hypothesis", which proposes that a genetically isolated human population persisted in Beringia during the LGM and dispersed from there to North and South America during the post-LGM period.

  4. Upper Ocean Variability in the Indo-Pacific Warm Pool during the Late Holocene, Early Holocene and Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Xu, J.; Kuhnt, W.; Holbourn, A. E.; Andersen, N.

    2009-12-01

    We analyzed oxygen isotopes and Mg/Ca ratios in the surface dwelling planktonic foraminifer Globigerinoides ruber (white s.s.) and the thermocline dweller Pulleniatina obliquiloculata to improve understanding of upper ocean spatial variability in the Indo-Pacific Warm Pool (IPWP). We focused on three critical time intervals: the Last Glacial Maximum (LGM; 18-21.5 ka), the early Holocene (8-9 ka) and the late Holocene (0-2 ka). Our records from twenty-four stations in the South China Sea, Timor Sea, Indonesian seas and western Pacific indicate overall dry and cool conditions in the IPWP during the LGM with a low thermal gradient between surface and thermocline waters. Warm surface waters (>28 Celsius degree) spread over the entire region during the early Holocene, indicating substantial expansion of the IPWP. However in the eastern Indian Ocean (Timor Sea), the thermocline gradually shoaled from the LGM to early Holocene, reflecting intensification of the subsurface Indonesian Throughflow. Increased precipitation over the South China Sea appears related to an intensified summer monsoon and northward displacement of the Intertropical Convergence Zone. Increased freshwater export from the South China Sea through the Java Sea also contributed to a change in the vertical structure of the Indonesian Throughflow from surface- to thermocline-dominated flow and a freshening of Timor Sea waters during the early Holocene.

  5. Responses of ocean circulation and carbon cycle to changes in the position of the Southern Hemisphere westerlies at Last Glacial Maximum.

    PubMed

    Völker, Christoph; Köhler, Peter

    2013-12-01

    We explore the impact of a latitudinal shift in the westerly wind belt over the Southern Ocean on the Atlantic meridional overturning circulation (AMOC) and on the carbon cycle for Last Glacial Maximum background conditions using a state-of-the-art ocean general circulation model. We find that a southward (northward) shift in the westerly winds leads to an intensification (weakening) of no more than 10% of the AMOC. This response of the ocean physics to shifting winds agrees with other studies starting from preindustrial background climate, but the responsible processes are different. In our setup changes in AMOC seemed to be more pulled by upwelling in the south than pushed by downwelling in the north, opposite to what previous studies with different background climate are suggesting. The net effects of the changes in ocean circulation lead to a rise in atmospheric pCO2 of less than 10 μatm for both northward and southward shift in the winds. For northward shifted winds the zone of upwelling of carbon- and nutrient-rich waters in the Southern Ocean is expanded, leading to more CO2outgassing to the atmosphere but also to an enhanced biological pump in the subpolar region. For southward shifted winds the upwelling region contracts around Antarctica, leading to less nutrient export northward and thus a weakening of the biological pump. These model results do not support the idea that shifts in the westerly wind belt play a dominant role in coupling atmospheric CO2 rise and Antarctic temperature during deglaciation suggested by the ice core data.

  6. Timing of advance and basal condition of the Laurentide Ice Sheet during the last glacial maximum in the Richardson Mountains, NWT

    NASA Astrophysics Data System (ADS)

    Lacelle, Denis; Lauriol, Bernard; Zazula, Grant; Ghaleb, Bassam; Utting, Nicholas; Clark, Ian D.

    2013-09-01

    This study presents new ages for the northwest section of the Laurentide Ice Sheet (LIS) glacial chronology from material recovered from two retrogressive thaw slumps exposed in the Richardson Mountains, Northwest Territories, Canada. One study site, located at the maximum glacial limit of the LIS in the Richardson Mountains, had calcite concretions recovered from aufeis buried by glacial till that were dated by U/Th disequilibrium to 18,500 cal yr BP. The second site, located on the Peel Plateau to the east yielded a fossil horse (Equus) mandible that was radiocarbon dated to ca. 19,700 cal yr BP. These ages indicate that the Peel Plateau on the eastern flanks of the Richardson Mountains was glaciated only after 18,500 cal yr BP, which is later than previous models for the global last glacial maximum (LGM). As the LIS retreated the Peel Plateau around 15,000 cal yr BP, following the age of the Tutsieta phase, we conclude that the presence of the northwestern margin of the LIS at its maximum limit was a very short event in the western Canadian Arctic.

  7. Basal conditions of the Rhine Glacier at the Last Glacial Maximum: insights from high-resolution transient numerical models

    NASA Astrophysics Data System (ADS)

    Cohen, Denis; Gillet-Chaulet, Fabien; Haeberli, Wilfried; Fischer, Urs H.

    2014-05-01

    Questions about the safety of nuclear waste repositories during future ice ages in previously glaciated landscapes have lent impetus to new numerical model simulations concerning past ice conditions. In Switzerland, all potential sites investigated for these repositories have been affected during LGM or earlier ice ages by large piedmont glaciers and/or peri-/subglacial permafrost under cold-dry conditions. First quantitative reconstructions and analysis using steady-state approaches were carried out in the 1980s. Recent advances in ice flow numerical models and code parallelization make it now possible to run transient thermo-mechanical full-Stokes models at high resolution. These models couple ice flow to temperature-dependent sliding at the bed and climate parameterization (temperature, mass balance gradients) at the surface. Starting from the reconstruction of the Alpine ice field in Switzerland, we model the transient flow of the Rhine Glacier from its source in the Alps to its terminus that formed a large polythermal piedmont lobe in the northern Swiss plateau and in southern Germany. Results indicate that basal conditions are strongly dependent on initial temperature parameterization and climate conditions that lead to the LGM. The models indicate that much of the substrate below the ice lobe was at the melting temperature, opening possibilities for fast erosion and overdeepening formation. Other areas in alpine valleys were also at the melting temperature when the basal ice originating from high up in the Alps had sufficient time to reach the melting temperature at the bed of thick valley glaciers. Cold climate conditions kept marginal ice and ice up valley cold. High sliding speed and basal shear stress, two other parameters that promote erosion, indicate that erosion was potentially high in some portions of the main trunks of the Rhine Glacier but less so in more marginal parts of the flat piedmont lobe. Results from these transient full thermo

  8. Dynamics of the North American Ice Sheet Complex during its inception and build-up to the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Stokes, Chris R.; Tarasov, Lev; Dyke, Arthur S.

    2012-09-01

    The North American Ice Sheet Complex played a major role in global sea level fluctuations during the Late Quaternary but our knowledge of its dynamics is based mostly on its demise from the Last Glacial Maximum (LGM), a period characterised by non-linear behaviour in the form of punctuated ice margin recession, episodic ice streaming and major shifts in the location of ice divides. In comparison, knowledge of the pre-LGM ice complex is poorly constrained, largely because of the fragmentary nature of the evidence relating to ice sheet build-up. In this paper, we explore the inception and growth of ice (120-20 ka) using a glacial systems model which has been calibrated against a large and diverse set of data relating to the deglacial interval. We make use of calibration data prior to the LGM but its scarcity introduces greater uncertainty, which is partly alleviated by our large ensemble analysis. Results suggest that, following the last interglaciation (Oxygen Isotope Stage: OIS 5e), the ice complex initiated over the north-eastern Canadian Arctic and in the Cordillera within a few thousand years. It then underwent rapid growth to an OIS 5 maximum at ˜110 ka (5d) and covered ˜70% of the area occupied by the LGM ice cover (although only 30% by volume). An OIS 5 minimum is modelled at ˜80 ka (5a), before a second phase of rapid growth at the start of OIS 4, which culminated in a large ice complex at ˜65 ka (almost as large as at the LGM). Subsequent deglaciation was rapid (maximum modelled sea level contribution of >16 cm per century) and resulted in an OIS 3 minimum between ca 55-60 ka. Thereafter, the ice complex grew towards its LGM configuration, interrupted by several phases of successively less significant mass loss. Our results support and extend previous inferences based on geological evidence and reinforce the notion of a highly dynamic pre-LGM ice complex (e.g. with episodes of ±10 s m of eustatic sea level equivalent in <5 ka). Consistent with previous

  9. Groundwater flow modeling of periods with periglacial and glacial climate conditions for the safety assessment of the proposed high-level nuclear waste repository site at Forsmark, Sweden

    NASA Astrophysics Data System (ADS)

    Vidstrand, Patrik; Follin, Sven; Selroos, Jan-Olof; Näslund, Jens-Ove

    2014-09-01

    The impact of periglacial and glacial climate conditions on groundwater flow in fractured crystalline rock is studied by means of groundwater flow modeling of the Forsmark site, which was recently proposed as a repository site for the disposal of spent high-level nuclear fuel in Sweden. The employed model uses a thermal-hydraulically coupled approach for permafrost modeling and discusses changes in groundwater flow implied by the climate conditions found over northern Europe at different times during the last glacial cycle (Weichselian glaciation). It is concluded that discharge of particles released at repository depth occurs very close to the ice-sheet margin in the absence of permafrost. If permafrost is included, the greater part discharges into taliks in the periglacial area. During a glacial cycle, hydraulic gradients at repository depth reach their maximum values when the ice-sheet margin passes over the site; at this time, also, the interface between fresh and saline waters is distorted the most. The combined effect of advances and retreats during several glaciations has not been studied in the present work; however, the results indicate that hydrochemical conditions at depth in the groundwater flow model are almost restored after a single event of ice-sheet advance and retreat.

  10. The Influence of True Polar Wander on Climate and Glacial Inception in North America

    NASA Astrophysics Data System (ADS)

    Daradich, A.; Huybers, P. J.; Mitrovica, J. X.; Chan, N. H.

    2014-12-01

    While plate tectonic motions and dynamic topography of continents each reflect an active mantle convective regime, excursions of the Earth's rotation axis relative to a fixed hotspot reference frame are remarkably muted. Early studies of paleomagnetically inferred pole positions suggested excursions of less than a few degrees [Jurdy and Van Der Voo, 1975]. For this reason, long-term changes in Earth's rotation, or true polar wander (TPW), were thought to have a negligible role in the observed long-term secular cooling of Earth's climate through the Tertiary [Donn and Shaw, 1977]. This gradual cooling over the past 65 million years began at a time when much of Earth's climate was relatively warm and quiescent and culminated in dramatic glacial cycles of the Pleistocene. In contrast to earlier studies, recent reanalyses of paleomagnetic pole positions suggest a secular drift in Earth's rotation axis of greater than ten degrees in the last 40 million years [Torsvik et al., 2012; Doubrovine et al., 2012]. The direction of this drift brings North America, a site of advancing and retreating ice sheets throughout the Pleistocene, to increasingly higher latitudes. Using an orbital solution valid for the last 50 million years [Laskar et al., 2004], we compute the effect of TPW on insolation quantities for sites in Greenland and the Canadian Arctic Archipelago. Our results indicate that a three degree shift in latitude driven by TPW is comparable to a two degree change in obliquity in terms of its impact on summer energy (i.e. the total energy for the year on days surpassing a given insolation threshold; Huybers, 2006). In addition, we explore climatological gradients using modern climatological data and employ simple climate models to characterize reductions in positive degree days for the North American Arctic over the last 40 million years. We find that TPW and continental drift that moved arctic North America poleward could have driven cooling that contributed to glacial

  11. Expansion dating: calibrating molecular clocks in marine species from expansions onto the Sunda Shelf Following the Last Glacial Maximum.

    PubMed

    Crandall, Eric D; Sbrocco, Elizabeth J; Deboer, Timery S; Barber, Paul H; Carpenter, Kent E

    2012-02-01

    The rate of change in DNA is an important parameter for understanding molecular evolution and hence for inferences drawn from studies of phylogeography and phylogenetics. Most rate calibrations for mitochondrial coding regions in marine species have been made from divergence dating for fossils and vicariant events older than 1-2 My and are typically 0.5-2% per lineage per million years. Recently, calibrations made with ancient DNA (aDNA) from younger dates have yielded faster rates, suggesting that estimates of the molecular rate of change depend on the time of calibration, decaying from the instantaneous mutation rate to the phylogenetic substitution rate. aDNA methods for recent calibrations are not available for most marine taxa so instead we use radiometric dates for sea-level rise onto the Sunda Shelf following the Last Glacial Maximum (starting ∼18,000 years ago), which led to massive population expansions for marine species. Instead of divergence dating, we use a two-epoch coalescent model of logistic population growth preceded by a constant population size to infer a time in mutational units for the beginning of these expansion events. This model compares favorably to simpler coalescent models of constant population size, and exponential or logistic growth, and is far more precise than estimates from the mismatch distribution. Mean rates estimated with this method for mitochondrial coding genes in three invertebrate species are elevated in comparison to older calibration points (2.3-6.6% per lineage per million years), lending additional support to the hypothesis of calibration time dependency for molecular rates.

  12. Late quaternary distribution of the Cycladophora davisiana radiolarian species: Reflection of possible ventilation of the North Pacific intermediate water during the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Matul, A. G.; Abelmann, A.; Gersonde, R.; Nürnberg, D.; Tiedemann, R.; Kruglikova, S. B.

    2015-02-01

    A comparison of micropaleontological data on the distribution of the Cycladophora davisiana radiolarian species in the surface sediment layer and the Late Quaternary sediments from the Subarctic Pacific and Far East marginal seas allowed conclusions concerning the possible conditions and occurrence of intermediate waters during the last glacial maximum. We used the modern data on the C. davisiana species, which is a micro-paleontological indicator of the cold oxygen-rich upper intermediate water mass, which is now forming only in the Sea of Okhotsk. The high amount of C. davisiana in sediments of the last glacial maximum may point to the possible formation and expansion of the ventilated intermediate water in the most part of the Subarctic paleo-Pacific: the Bering Sea, the Sea of Okhotsk, within the NW Gyre, and in the Gulf of Alaska.

  13. Glacial records of global climate: A 1500-year tropical ice core record of climate

    SciTech Connect

    Thompson, L.G.; Davis, M.E.; Mosley-Thompson, E. )

    1994-03-01

    A general discussion is given of climate variability over the last 1500 years as interpreted from two ice cores from the Quelccaya ice cap, Peru. The possible role of climatic variability in prehistory over this period is discussed with emphases on (1) relationships between climate and the rise and decline of coastal and highland cultures; (2) the possible causes of two major dust events recorded in the quelccaya ice cores around AD 920 and AD 600; (3) implications of climatic variation for the occupation and abandonment of the Gran Pajaten area. The remarkable similarity between changes in highland and coastal cultures and changes in accumulation as determined from the Quelccaya ice cores implies a strong connection between human activities and climate in this region of the globe. Two ice cores drilled to bedrock from the 6047 masl col of Huascaran in the Cordillera Blanca, Peru in 1993 offer the potential of an annual to decadal climatic and environmental record which should allow the study of human-climate and human-environmental relationships over 10,000+ years. The 1991 and 1993 evidence from the Quelccaya ice cap indicates that recent and rapid warming is currently underway in the tropical Andes. Thus, many of the unique glacier archives are in imminent danger of being lost forever.

  14. Climatic Forcings of the Last Major Glacial Inception: A GCM Simulation of 115.5 Ka

    NASA Astrophysics Data System (ADS)

    Essig, M.; Oglesby, R.; Otieno, F.; Bromwich, D.

    2007-12-01

    The onset of Northern Hemisphere glaciation at around 115.5 Ka is thought to have been caused by a number of factors. Two of the most important of these are a reduction in atmospheric CO2 from approximately 380 ppm to 180 ppm, and changes in the earth's eccentricity, precession, and obliquity due to Milankovitch orbital cycles. We used the NCAR CCSM3 GCM in fully coupled mode to simulate the climate at 115.5 ka B.P. The fully-coupled mode includes dynamical atmospheric and oceanic components, as well as sophisticated land surface and sea ice schemes. Sea level and the distribution of the continents were held at present-day values, since they changed little between 0 Ka and 115.5 Ka. Thus, our model simulation can also be thought of as examining the roles of lowered CO2 and orbital configuration in driving glacial inception. In particular, we hypothesize that these climatic forcings will lead to a succession of cool summers and warm wet winters in key regions of the high latitude Northern Hemisphere. In turn, we expect this will be conducive to building the perennial snow pack that is an essential precursor to the Laurentide and Fenno-Scandinavian ice sheets. Though the simulation is still underway at this writing, preliminary results from the first 100 years of the run suggest that this does indeed take place. Key results from the completed run will be presented at the meeting, along with an assessment of how they differ from a present-day CCSM3 control run. Furthermore, in glacial inception regions the performance of both the control run and an existing CCSM3 preindustrial simulation are being compared to ERA40 reanalyses as an additional test of model fidelity. The model simulation is also being verified using all available data from geologic record for the time around 115.5 Ka.

  15. Leaf Dynamics of Panicum maximum under Future Climatic Changes

    PubMed Central

    Britto de Assis Prado, Carlos Henrique; Haik Guedes de Camargo-Bortolin, Lívia; Castro, Érique; Martinez, Carlos Alberto

    2016-01-01

    Panicum maximum Jacq. ‘Mombaça’ (C4) was grown in field conditions with sufficient water and nutrients to examine the effects of warming and elevated CO2 concentrations during the winter. Plants were exposed to either the ambient temperature and regular atmospheric CO2 (Control); elevated CO2 (600 ppm, eC); canopy warming (+2°C above regular canopy temperature, eT); or elevated CO2 and canopy warming (eC+eT). The temperatures and CO2 in the field were controlled by temperature free-air controlled enhancement (T-FACE) and mini free-air CO2 enrichment (miniFACE) facilities. The most green, expanding, and expanded leaves and the highest leaf appearance rate (LAR, leaves day-1) and leaf elongation rate (LER, cm day-1) were observed under eT. Leaf area and leaf biomass were higher in the eT and eC+eT treatments. The higher LER and LAR without significant differences in the number of senescent leaves could explain why tillers had higher foliage area and leaf biomass in the eT treatment. The eC treatment had the lowest LER and the fewest expanded and green leaves, similar to Control. The inhibitory effect of eC on foliage development in winter was indicated by the fewer green, expanded, and expanding leaves under eC+eT than eT. The stimulatory and inhibitory effects of the eT and eC treatments, respectively, on foliage raised and lowered, respectively, the foliar nitrogen concentration. The inhibition of foliage by eC was confirmed by the eC treatment having the lowest leaf/stem biomass ratio and by the change in leaf biomass-area relationships from linear or exponential growth to rectangular hyperbolic growth under eC. Besides, eC+eT had a synergist effect, speeding up leaf maturation. Therefore, with sufficient water and nutrients in winter, the inhibitory effect of elevated CO2 on foliage could be partially offset by elevated temperatures and relatively high P. maximum foliage production could be achieved under future climatic change. PMID:26894932

  16. Lizards on Ice: Evidence for Multiple Refugia in Liolaemus pictus (Liolaemidae) during the Last Glacial Maximum in the Southern Andean Beech Forests

    PubMed Central

    Vera-Escalona, Iván; D'Elía, Guillermo; Gouin, Nicolás; Fontanella, Frank M.; Muñoz-Mendoza, Carla; Sites, Jack W.; Victoriano, Pedro F.

    2012-01-01

    Historical climate changes and orogenesis are two important factors that have shaped intraspecific biodiversity patterns worldwide. Although southern South America has experienced such complex events, there is a paucity of studies examining the effects on intraspecific diversification in this part of the world. Liolaemus pictus is the southernmost distributed lizard in the Chilean temperate forest, whose genetic structure has likely been influenced by Pleistocene glaciations. We conducted a phylogeographic study of L. pictus in Chile and Argentina based on one mitochondrial and two nuclear genes recovering two strongly divergent groups, Northern and Southern clades. The first group is distributed from the northernmost limit of the species to the Araucanía region while the second group is distributed throughout the Andes and the Chiloé archipelago in Southern Chile. Our results suggest that L. pictus originated 751 Kya, with divergence between the two clades occurring in the late Pleistocene. Demographic reconstructions for the Northern and Southern clades indicate a decrease in effective population sizes likely associated with Pleistocene glaciations. Surprisingly, patterns of genetic variation, clades age and historical gene flow in populations distributed within the limits of the Last Glacial Maximum (LGM) are not explained by recent colonization. We propose an “intra-Andean multiple refuge” hypothesis, along with the classical refuge hypothesis previously proposed for the biota of the Chilean Coastal range and Eastern Andean Cordillera. Our hypothesis is supported by niche modelling analysis suggesting the persistence of fragments of suitable habitat for the species within the limits of the LGM ice shield. This type of refuge hypothesis is proposed for the first time for an ectothermic species. PMID:23209552

  17. Comment on "Last glacial maximum cirque glaciation in Ireland and implications for reconstructions of the Irish ice sheet. Quaternary Science Reviews 141, 85-93"

    NASA Astrophysics Data System (ADS)

    Knight, Jasper

    2016-10-01

    Southwest Ireland is a critical location to examine the sensitivity of late Pleistocene glaciers to climate variability in the northeast Atlantic, because of its proximal location to Atlantic moisture sources and the presence of high mountains in the Macgillycuddy's Reeks range which acted as a focus for glacierization (Harrison et al., 2010). The extent of Last Glacial Maximum (LGM) glaciers in southwest Ireland and their link to the wider British-Irish Ice Sheet (BIIS), however, is under debate. Some models suggest that during the LGM the region was wholly inundated by ice from the larger BIIS (Warren, 1992; Sejrup et al., 2005), whereas others suggest north-flowing ice from the semi-independent Cork-Kerry Ice Cap (CKIC) was diverted around mountain peaks, resulting in exposed nunataks in the Macgillycuddy's Reeks (Anderson et al., 2001; Ballantyne et al., 2011). Cirque glaciers may also have been present on mountain slopes above this regional ice surface (Warren, 1979; Rea et al., 2004). More recently, investigations have focused on the extent and age of cirque glaciers in the Reeks, based on the mapped distribution of end moraines (Warren, 1979; Harrison et al., 2010), and on cosmogenic dates on boulders on these moraines (Harrison et al., 2010) and on associated scoured bedrock surfaces across the region (Ballantyne et al., 2011). The recent paper by Barth et al. (2016) contributes to this debate by providing nine cosmogenic 10Be ages on boulders from two moraines from one small (∼1.7 km2) and low (373 m elevation of the cirque floor) cirque basin at Alohart (52°00‧50″N, 9°40‧30″W) within the Reeks range. These dates are welcomed because they add to the lengthening list of age constraints on geomorphic activity in the region that spans the time period from the LGM to early Holocene.

  18. Long-Distance Dispersal after the Last Glacial Maximum (LGM) Led to the Disjunctive Distribution of Pedicularis kansuensis (Orobanchaceae) between the Qinghai-Tibetan Plateau and Tianshan Region

    PubMed Central

    Li, Wen-Jun; Sui, Xiao-Lin; Kuss, Patrick; Liu, Yan-Yan; Li, Ai-Rong; Guan, Kai-Yun

    2016-01-01

    Quaternary climate fluctuations have profoundly affected the current distribution patterns and genetic structures of many plant and animal species in the Qinghai-Tibetan Plateau (QTP) and adjacent mountain ranges, e.g. Tianshan (TSR), Altay, etc. In this greater area disjunct distributions are prominent but have nevertheless received little attention with respect to the historical processes involved. Here, we focus on Pedicularis kansuensis to test whether the current QTP and TSR disjunction is the result of a recent Holocene range expansion involving dispersal across arid land bridge(s) or a Pleistocene range fragmentation involving persistence in refugia. Two chloroplast DNA spacers were sequenced for 319 individuals from 34 populations covering the entire distribution range of this species in China. We found a total of 17 haplotypes of which all occurred in the QTP, and only five in the TSR. Overall genetic diversity was high (HT = 0.882, HS = 0.559) and higher in the QTP than in the TSR. Genetic differentiation among regions and populations was relatively low (GST = 0.366) and little evidence for a phylogeographic pattern emerged. The divergence times for the four main lineages could be dated to the early Pleistocene. Surprisingly, the two ubiquitous haplotypes diverged just before or around the Last Glacial Maximum (LGM) and were found in different phylogenetic lineages. The Species Distribution Model suggested a disappearance of P. kansuensis from the TSR during the LGM in contrast to a relatively constant potential distribution in the QTP. We conclude that P. kansuensis colonized the TSR after the LGM. The improbable long-distance dispersal by wind or water across arid land seed flow may well have had birds or men as vector. PMID:27806090

  19. Lizards on ice: evidence for multiple refugia in Liolaemus pictus (Liolaemidae) during the last glacial maximum in the Southern Andean beech forests.

    PubMed

    Vera-Escalona, Iván; D'Elía, Guillermo; Gouin, Nicolás; Fontanella, Frank M; Muñoz-Mendoza, Carla; Sites, Jack W; Victoriano, Pedro F

    2012-01-01

    Historical climate changes and orogenesis are two important factors that have shaped intraspecific biodiversity patterns worldwide. Although southern South America has experienced such complex events, there is a paucity of studies examining the effects on intraspecific diversification in this part of the world. Liolaemus pictus is the southernmost distributed lizard in the Chilean temperate forest, whose genetic structure has likely been influenced by Pleistocene glaciations. We conducted a phylogeographic study of L. pictus in Chile and Argentina based on one mitochondrial and two nuclear genes recovering two strongly divergent groups, Northern and Southern clades. The first group is distributed from the northernmost limit of the species to the Araucanía region while the second group is distributed throughout the Andes and the Chiloé archipelago in Southern Chile. Our results suggest that L. pictus originated 751 Kya, with divergence between the two clades occurring in the late Pleistocene. Demographic reconstructions for the Northern and Southern clades indicate a decrease in effective population sizes likely associated with Pleistocene glaciations. Surprisingly, patterns of genetic variation, clades age and historical gene flow in populations distributed within the limits of the Last Glacial Maximum (LGM) are not explained by recent colonization. We propose an "intra-Andean multiple refuge" hypothesis, along with the classical refuge hypothesis previously proposed for the biota of the Chilean Coastal range and Eastern Andean Cordillera. Our hypothesis is supported by niche modelling analysis suggesting the persistence of fragments of suitable habitat for the species within the limits of the LGM ice shield. This type of refuge hypothesis is proposed for the first time for an ectothermic species.

  20. Possible solar origin of the 1,470-year glacial climate cycle demonstrated in a coupled model.

    PubMed

    Braun, Holger; Christl, Marcus; Rahmstorf, Stefan; Ganopolski, Andrey; Mangini, Augusto; Kubatzki, Claudia; Roth, Kurt; Kromer, Bernd

    2005-11-10

    Many palaeoclimate records from the North Atlantic region show a pattern of rapid climate oscillations, the so-called Dansgaard-Oeschger events, with a quasi-periodicity of approximately 1,470 years for the late glacial period. Various hypotheses have been suggested to explain these rapid temperature shifts, including internal oscillations in the climate system and external forcing, possibly from the Sun. But whereas pronounced solar cycles of approximately 87 and approximately 210 years are well known, a approximately 1,470-year solar cycle has not been detected. Here we show that an intermediate-complexity climate model with glacial climate conditions simulates rapid climate shifts similar to the Dansgaard-Oeschger events with a spacing of 1,470 years when forced by periodic freshwater input into the North Atlantic Ocean in cycles of approximately 87 and approximately 210 years. We attribute the robust 1,470-year response time to the superposition of the two shorter cycles, together with strongly nonlinear dynamics and the long characteristic timescale of the thermohaline circulation. For Holocene conditions, similar events do not occur. We conclude that the glacial 1,470-year climate cycles could have been triggered by solar forcing despite the absence of a 1,470-year solar cycle.

  1. Antarctic climate cooling and response of diatoms in glacial meltwater streams

    USGS Publications Warehouse

    Esposito, R.M.M.; Horn, S.L.; McKnight, Diane M.; Cox, M.J.; Grant, M.C.; Spaulding, S.A.; Doran, P.T.; Cozzetto, K.D.

    2006-01-01

    To understand biotic responses to an Antarctic cooling trend diatom samples from glacial meltwater streams in the McMurdo Dry Valleys, the largest ice-free area in Antarctica. Diatoms are abundant in these streams, and 24 of 40 species have only been found in the Antarctic. The percentage of these Antarctic diatom species increased with decreasing annual stream flow and increasing harshness of the stream habitat. The species diversity of assemblages reached a maximum when the Antarctic species accounted for 40-60% of relative diatom abundance. Decreased solar radiation and air-temperatures reduce annual stream flow, raising the dominance of these Antarctic species to levels above 60%. Thus, cooling favors the Antarctic species, and lowers diatom species diversity in this region. Copyright 2006 by the American Geophysical Union.

  2. Vegetation, climate and fire-dynamics in East Africa inferred from the Maundi crater pollen record from Mt Kilimanjaro during the last glacial-interglacial cycle

    NASA Astrophysics Data System (ADS)

    Schüler, Lisa; Hemp, Andreas; Zech, Wolfgang; Behling, Hermann

    2012-04-01

    The pollen, charcoal and sedimentological record from the Maundi crater, located at 2780 m elevation on the south-eastern slope of Mt Kilimanjaro, is one of the longest terrestrial records in equatorial East Africa, giving an interesting insight into the vegetation and climate dynamics back to the early last Glacial period. Our sediment record has a reliable chronology until 42 ka BP. An extrapolation of the age-depth model, as well as matching with other palaeo-records from tropical East Africa, suggest a total age of about 90 ka BP at the bottom of the record. During the last Glacial the distribution as well as the composition of the vegetation belts classified as colline savanna, submontane woodland, montane forest, ericaceous belt, and alpine vegetation changed. The early last Glacial is characterized by high amounts of Poaceae and Asteraceae pollen suggesting a climatically dry but stable phase. Based on the absence of pollen grains in samples deposited around 70 ka BP, we assume the occurrence of distinct drought periods. During the pre-LGM (Last Glacial Maximum) a higher taxa diversity of the ericaceous and montane zone is recorded and suggests a spread of forest and shrub vegetation, thus indicating a more humid period. The taxa diversity increases steadily during the recorded time span. The decent of vegetation zones indicate dry and cold conditions during the LGM and seem to have been detrimental for many taxa, especially those of the forest vegetation; however, the early last Glacial seems to have been markedly drier than the LGM. The reappearance of most of the taxa (most importantly Alchemilla, Araliaceae, Dodonea, Hagenia, Ilex, Myrsine, Moraceae, Piperaceae) during the deglacial and Holocene period suggest a shift into humid conditions. An increase in ferns and the decrease in grasses during the Holocene also indicate increasing humidity. Fire played an important role in controlling the development and elevation of the ericaceous zone and the tree

  3. The effect of greenhouse gas concentrations and ice sheets on the glacial AMOC in a coupled climate model

    NASA Astrophysics Data System (ADS)

    Klockmann, Marlene; Mikolajewicz, Uwe; Marotzke, Jochem

    2016-09-01

    Simulations with the Max Planck Institute Earth System Model (MPI-ESM) are used to study the sensitivity of the AMOC and the deep-ocean water masses during the Last Glacial Maximum to different sets of forcings. Analysing the individual contributions of the glacial forcings reveals that the ice sheets cause an increase in the overturning strength and a deepening of the North Atlantic Deep Water (NADW) cell, while the low greenhouse gas (GHG) concentrations cause a decrease in overturning strength and a shoaling of the NADW cell. The effect of the orbital configuration is negligible. The effects of the ice sheets and the GHG reduction balance each other in the deep ocean so that no shoaling of the NADW cell is simulated in the full glacial state. Experiments in which different GHG concentrations with linearly decreasing radiative forcing are applied to a setup with glacial ice sheets and orbital configuration show that GHG concentrations below the glacial level are necessary to cause a shoaling of the NADW cell with respect to the pre-industrial state in MPI-ESM. For a pCO2 of 149 ppm, the simulated overturning state and the deep-ocean water masses are in best agreement with the glacial state inferred from proxy data. Sensitivity studies confirm that brine release and shelf convection in the Southern Ocean are key processes for the shoaling of the NADW cell. Shoaling occurs only when Southern Ocean shelf water contributes significantly to the formation of Antarctic Bottom Water.

  4. Isotopic Evidence for C4 Grass Expansion During the Last Glacial Maximum and Younger Dryas in Northern Australia

    NASA Astrophysics Data System (ADS)

    Johnson, B. J.; Wakeham, S.; Gelinas, Y.; Luly, J.; Miller, G.

    2004-12-01

    In northern and central Australia, late Quaternary records of terrestrial environmental change are rare due to generally poor preservation of pollen grains and a derth of long-term, continuous lacustrine sedimentary deposits. The Wombe mound spring in the Keep River National Park, Northern Territory, is an organic mound and isolated patch of monsoon vine thicket thought to have formed tens of thousands of years ago. In an effort to obtain a record of paleovegetation and fire history from northern Australia, a 3.4 m sediment core was recovered from the Wombe mound spring and subject to multiple types of analyses. The core represents a continuous depositional sequence with radiocarbon ages spanning the last 35 ka cal years (hereafter referred to as 35 ka). Paleovegetation was reconstructed using a combination of pollen and carbon isotopes in bulk sediment and higher plant leaf wax (HPLW) lipid biomarkers. The fire history was reconstructed from paired graphitic black carbon (GBC) and polycyclic aromatic hydrocarbon (PAH) analyses of the core sediments. Between 35 and 11 ka, the bulk organic carbon (OC) isotope data fluctuate between -22 and -15%, with the most isotopically enriched values measured at 11.4 ka. Between 12.3 and 6.8 ka, OC isotope values decrease by 13%, and remain steady from 6.8 ka to the present at -28%. There are two distinct peaks of isotopic enrichment in the higher plant leaf wax biomarkers. These two peaks coincide with the Last Glacial Maximum (LGM; 21 ka) and the Younger Dryas (YD; 11.4 ka) and represent maximum increases in C4 grasses relative to C3 plants. Relative increases in C4 grasses during the LGM in other parts of the tropics (i.e., Sacred Lake, Mt. Kenya) have been attributed to the competitive advantage of C4 plants relative to C3 plants under reduced atmospheric pCO2 and is likely the cause for C4 expansion in northern Australia. The increase in C4 grasses during the YD is reflected in the bulk sediment and HPLW isotope data and is

  5. Post-Last Glacial Maximum (Latest Pleistocene to Holocene) geology of the Santa Barbara shelf, southern California

    NASA Astrophysics Data System (ADS)

    Johnson, S. Y.; Ritchie, A. C.; Conrad, J. E.; Dartnell, P.; Phillips, E.; Sliter, R. W.

    2011-12-01

    High-resolution bathymetric and seismic-reflection data collected for the California Seafloor Mapping Program (http://walrus.wr.usgs.gov/mapping/csmp/) provide new insights for understanding the post-Last Glacial Maximum (LGM) evolution of the Santa Barbara shelf, highlighting relationships between tectonics, eustasy, and sediment supply. The west-trending shelf extends offshore for 5 to 7 km and is bounded on the south by the deep Santa Barbara basin and on the north by a narrow coastal zone and the steep, rapidly uplifting Santa Ynez Mountains. The active, west-trending, north-dipping Ventura-Pitas Point-North Channel and Red Mountain fault systems form the structural boundary between two distinct shelf domains. The smooth, gently sloping, southern shelf is flooded by thick (35 to 40 m), prograding Santa Clara and Ventura River deltaic deposits. These thick strata drape the shelfbreak and fill the accommodation space created by rising sea level, largely masking the influence of active tectonics. In contrast, the northern shelf has complex bathymetry and a well-defined, sharp shelfbreak at ~90 m water depth. The northern shelf is relatively sediment starved (mean sediment thickness is 3 to 4 m), with thickest accumulations (up to ~18 m) forming shallow (< 30 m), discontinuous to laterally coalescing, inner-shelf bars that are best developed at the mouths of steep coastal watersheds. These watersheds also feed several distinct, coarse-grained sediment lobes (as large as ~1.5 km2, extending to 3 km offshore and depths of 70 m) that probably formed during massive flood events. The relative lack of offshore deposits on the northern shelf suggests sediment transport is dominated by easterly nearshore drift. Faulting and folding on the northern shelf are significant controls on sediment distribution and thickness, the occurrence of bedrock uplifts, and common hydrocarbon-associated seeps, pockmarks, and mounds. Bedrock, typically "soft" Neogene strata, is especially

  6. Multi-proxies study on the paleoceanography and terrigenous input in the polar Nodic Sea since the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Liu, Yanguang

    2016-04-01

    The polar Nodic Sea (NS) lies between the Arctic and Antlantic Oceans and the poleward-directed Atlantic heat and water transfer system plays a key role in affecting the ocean changes and sediments input. A suite of well-proven proxy methods for sediment core ARC5-BB03 (72°26.606'N, 7°35.890'E, water depth 2598 m) are used to address issues that are critical to the understanding of paleoceanographic conditions and sediments supplies over the Last Glacial Maximum (LGM) in this region. The methods include grain size analysis, AMS14C dating, color reflectance, high-resolution XRF scanning, oxygen isotope of planktic foraminifera and organic geochemistry measuring. The principal component analysis of the XRF data is applied for identification of sedimentary sources. Variations of grain size and elements' content indicate that the sedimentary sources of the polar NS have undergone dramatic changes over the past 26 ka BP. Changes of terrigenous input in the polar NS show close relationship with the variations of the North Atlantic Current (NAC), the melting of sea ice and ice sheet, the establishment of the Thermohaline Circulation (TC) and the forming of the North Atlantic Deep Water. The coarse grain size sediments before 21.5 ka BP implies different source from those in the later period because the terrigenous input is dominant in this period and occupied by an orderly layer of expandable minerals (OLEM). Strengthened sea ice extension is deemed to the main reason for the high terrigenous input in the polar NS before 21.5 ka BP. Between 21.5~16.5 cal. ka BP, biogenic materials increase accompanied with the decrease of terrigenous contribution indicates the impact of northward intrusion of NAC and the strenghthen of water ventilaiton in polar NS. The decrease of biogenic substance and the increase of terrigenous input during 16.5~10 cal. ka BP is consistent with the fluctuation in the melting of ice sheet and intensity of NAC during the last deglaciation. Compare

  7. How many seals were there? The global shelf loss during the last glacial maximum and its effect on the size and distribution of grey seal populations.

    PubMed

    Boehme, Lars; Thompson, Dave; Fedak, Mike; Bowen, Don; Hammill, Mike O; Stenson, Garry B

    2012-01-01

    Predicting how marine mammal populations respond to habitat changes will be essential for developing conservation management strategies in the 21st century. Responses to previous environmental change may be informative in the development of predictive models. Here we describe the likely effects of the last ice age on grey seal population size and distribution. We use satellite telemetry data to define grey seal foraging habitat in terms of the temperature and depth ranges exploited by the contemporary populations. We estimate the available extent of such habitat in the North Atlantic at present (between 1.42 · 10(6) km(2) and 2.07 · 10(6) km(2)) and at the last glacial maximum (between 4.74 · 10(4) km(2) and 2.11 · 10(5) km(2)); taking account of glacial and seasonal sea-ice coverage, estimated reductions of sea-level (123 m) and sea surface temperature hind-casts. Most of the extensive continental shelf waters (North Sea, Baltic Sea and Scotian Shelf), currently supporting >95% of grey seals, were unavailable during the last glacial maximum. A combination of lower sea-level and extensive ice-sheets, massively increased seasonal sea-ice coverage and southerly extent of cold water would have pushed grey seals into areas with no significant shelf waters. The habitat during the last glacial maximum might have been as small as 3% of today's extent and grey seal populations may have fallen to similarly low numbers. An alternative scenario involving a major change to a pelagic or bathy-pelagic foraging niche cannot be discounted. However, hooded seals currently dominate that niche and may have excluded grey seals from such habitat. If as seems likely, the grey seal population fell to very low levels it would have remained low for several thousand years before expanding into current habitats over the past 12,000 years or so.

  8. How Many Seals Were There? The Global Shelf Loss during the Last Glacial Maximum and Its Effect on the Size and Distribution of Grey Seal Populations

    PubMed Central

    Boehme, Lars; Thompson, Dave; Fedak, Mike; Bowen, Don; Hammill, Mike O.; Stenson, Garry B.

    2012-01-01

    Predicting how marine mammal populations respond to habitat changes will be essential for developing conservation management strategies in the 21st century. Responses to previous environmental change may be informative in the development of predictive models. Here we describe the likely effects of the last ice age on grey seal population size and distribution. We use satellite telemetry data to define grey seal foraging habitat in terms of the temperature and depth ranges exploited by the contemporary populations. We estimate the available extent of such habitat in the North Atlantic at present (between 1.42·106 km2 and 2.07·106 km2) and at the last glacial maximum (between 4.74·104 km2 and 2.11·105 km2); taking account of glacial and seasonal sea-ice coverage, estimated reductions of sea-level (123 m) and sea surface temperature hind-casts. Most of the extensive continental shelf waters (North Sea, Baltic Sea and Scotian Shelf), currently supporting >95% of grey seals, were unavailable during the last glacial maximum. A combination of lower sea-level and extensive ice-sheets, massively increased seasonal sea-ice coverage and southerly extent of cold water would have pushed grey seals into areas with no significant shelf waters. The habitat during the last glacial maximum might have been as small as 3% of today's extent and grey seal populations may have fallen to similarly low numbers. An alternative scenario involving a major change to a pelagic or bathy-pelagic foraging niche cannot be discounted. However, hooded seals currently dominate that niche and may have excluded grey seals from such habitat. If as seems likely, the grey seal population fell to very low levels it would have remained low for several thousand years before expanding into current habitats over the past 12,000 years or so. PMID:23300843

  9. A loess-paleosol record of climate and glacial history over the past two glacial-interglacial cycles (~140 ka), southern Jackson Hole, Wyoming

    USGS Publications Warehouse

    Pierce, Kenneth L.; Muhs, Daniel R.; Fosberg, Maynard A.; Mahan, Shannon; Rosenbaum, Joseph G.; Licciardi, Joseph M.; Pavich, Milan J.

    2011-01-01

    Loess accumulated on a Bull Lake outwash terrace of Marine Oxygen Isotope Stage 6 (MIS 6) age in southern Jackson Hole, Wyoming. The 9 m section displays eight intervals of loess deposition (Loess 1 to Loess 8, oldest), each followed by soil development. Our age-depth model is constrained by thermoluminescence, meteoric Be-10 accumulation in soils, and cosmogenic Be-10 surface exposure ages. We use particle size, geochemical, mineral-magnetic, and clay mineralogical data to interpret loess sources and pedogenesis. Deposition of MIS 6 loess was followed by a tripartite soil/thin loess complex (Soils 8,7, and 6) apparently reflecting the large climatic oscillations of MIS 5. Soil 8 (MIS 5e) shows the strongest development. Loess 5 accumulated during a glacial interval (similar to 76-69 ka; MIS 4) followed by soil development under conditions wetter and probably colder than present. Deposition of thick Loess 3 (similar to 43-51 ka, MIS 3) was followed by soil development comparable with that observed in Soil 1. Loess 1 (MIS 2) accumulated during the Pinedale glaciation and was followed by development of Soil 1 under a semiarid climate. This record of alternating loess deposition and soil development is compatible with the history of Yellowstone vegetation and the glacial flour record from the Sierra Nevada. Published by Elsevier Inc. on behalf of University of Washington.

  10. Integration of ice-core, marine and terrestrial records for the Australian Last Glacial Maximum and Termination: a contribution from the OZ INTIMATE group

    NASA Astrophysics Data System (ADS)

    Turney, C. S. M.; Haberle, S.; Fink, D.; Kershaw, A. P.; Barbetti, M.; Barrows, T. T.; Black, M.; Cohen, T. J.; Corrège, T.; Hesse, P. P.; Hua, Q.; Johnston, R.; Morgan, V.; Moss, P.; Nanson, G.; van Ommen, T.; Rule, S.; Williams, N. J.; Zhao, J.-X.; D'Costa, D.; Feng, Y.-X.; Gagan, M.; Mooney, S.; Xia, Q.

    2006-10-01

    The degree to which Southern Hemisphere climatic changes during the end of the last glacial period and early Holocene (30-8 ka) were influenced or initiated by events occurring in the high latitudes of the Northern Hemisphere is a complex issue. There is conflicting evidence for the degree of hemispheric teleconnection and an unresolved debate as to the principle forcing mechanism(s). The available hypotheses are difficult to test robustly, however, because the few detailed palaeoclimatic records in the Southern Hemisphere are widely dispersed and lack duplication. Here we present climatic and environmental reconstructions from across Australia, a key region of the Southern Hemisphere because of the range of environments it covers and the potentially important role regional atmospheric and oceanic controls play in global climate change. We identify a general scheme of events for the end of the last glacial period and early Holocene but a detailed reconstruction proved problematic. Significant progress in climate quantification and geochronological control is now urgently required to robustly investigate change through this period. Copyright

  11. 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

  12. The Dynamics of Greenland's Glacial Fjords and Their Role in Climate.

    PubMed

    Straneo, Fiamma; Cenedese, Claudia

    2015-01-01

    Rapid mass loss from the Greenland Ice Sheet has sparked interest in its glacial fjords for two main reasons: Increased submarine melting of glaciers terminating in fjords is a plausible trigger for glacier retreat, and the anomalous freshwater discharged from Greenland is transformed by fjord processes before being released into the large-scale ocean. Knowledge of the fjords' dynamics is thus key to understanding ice sheet variability and its impact on climate. Although Greenland's fjords share some commonalities with other fjords, their deep sills and deeply grounded glaciers, the presence of Atlantic and Polar Waters on the continental shelves outside the fjords' mouths, and the seasonal discharge at depth of large amounts of surface melt make them unique systems that do not fit existing paradigms. Major gaps in understanding include the interaction of the buoyancy-driven circulation (forced by the glacier) and shelf-driven circulation, and the dynamics in the near-ice zone. These must be addressed before appropriate forcing conditions can be supplied to ice sheet and ocean/climate models.

  13. Late-Glacial to Early Holocene Climate Changes from a Central Appalachians Pollen and Macrofossil Record

    NASA Technical Reports Server (NTRS)

    Kneller, Margaret; Peteet, Dorothy

    1997-01-01

    A Late-glacial to early Holocene record of pollen, plant macrofossils and charcoal, based on two cores, is presented for Browns Pond in the central Appalachians of Virginia. An AMS radiocarbon chronology defines the timing of moist and cold excursions, superimposed upon the overall warming trend from 14,200 to 7,500 C-14 yr B.P. This site shows cold, moist conditions from approximately 14,200 to 12,700 C-14 yr B.P., with warming at 12,730, 11,280 and 10,050 C-14 yr B.P. A decrease in deciduous broad-leaved tree taxa and Pinus strobus (haploxylon) pollen, simultaneous with a re-expansion of Abies denotes a brief, cold reversal from 12,260 to 12,200 C-14 yr B.P. A second cold reversal, inferred from increases in montane conifers, is centered at 7,500 C-14 yr B.P. The cold reversals at Browns Pond may be synchronous with climate change in Greenland, and northwestern Europe. Warming at 11,280 C-14 yr B.P. shows the complexity of regional climate responses during the Younger Dryas chronozone.

  14. 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.

  15. Climate Change Adaptation Decision Making for Glacial Lake Outburst Floods From Palcacocha Lake in Peru

    NASA Astrophysics Data System (ADS)

    Cuellar, A. D.; McKinney, D. C.

    2014-12-01

    Climate change has accelerated glacial retreat in high altitude glaciated regions of Peru leading to the growth and formation of glacier lakes. Glacial lake outburst floods (GLOF) are sudden events triggered by an earthquake, avalanche into the lake or other shock that causes a sudden outflow of water. These floods are catastrophic because of their sudden onset, the difficulty predicting them, and enormous quantity of water and debris rapidly flooding downstream areas. Palcacocha Lake in the Peruvian Andes has experienced accelerated growth since it burst in 1941 and threatens the major city of Huaraz and surrounding communities. Since the 1941 flood stakeholders have advocated for projects to adapt to the increasing threat posed by Palcacocha Lake. Nonetheless, discussions surrounding projects for Palcacocha have not included a rigorous analysis of the potential consequences of a flood, probability of an event, or costs of mitigation projects. This work presents the first step to rationally analyze the risks posed by Palcacocha Lake and the various adaptation projects proposed. In this work the authors use decision analysis to asses proposed adaptation measures that would mitigate damage in downstream communities from a GLOF. We use an existing hydrodynamic model of the at-risk area to determine how adaptation projects will affect downstream flooding. Flood characteristics are used in the HEC-FIA software to estimate fatalities and injuries from an outburst flood, which we convert to monetary units using the value of a statistical life. We combine the monetary consequences of a GLOF with the cost of the proposed projects and a diffuse probability distribution for the likelihood of an event to estimate the expected cost of the adaptation plans. From this analysis we found that lowering the lake level by 15 meters has the least expected cost of any proposal despite uncertainty in the effect of lake lowering on flooding downstream.

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

    NASA Astrophysics Data System (ADS)

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

    2010-05-01

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

  17. Differences in ice retreat across Pine Island Bay, West Antarctica, since the Last Glacial Maximum: Indications from multichannel seismic reflection data

    USGS Publications Warehouse

    Uenzelmann-Neben, G.; Gohl, K.; Larter, R.D.; Schlüter, P.

    2007-01-01

    An understanding of the glacial history of Pine Island Bay (PIB) is essential for refining models of the future stability of the West Antarctic Ice Sheet (WAIS). New multichannel seismic reflection data from inner PIB are interpreted in context of previously published reconstructions for the retreat history in this area since the Last Glacial Maximum. Differences in the behavior of the ice sheet during deglaciation are shown to exist for the western and eastern parts of PIB. While we can identify only a thin veneer of sedimentary deposits in western PIB, eastern PIB shows sedimentary layers ≤ 400 msTWT. This is interpreted as a result of differences in ice retreat: a fast ice retreat in western PIB accompanied by rapid basal melting led to production of large meltwater streams, a slower ice retreat in eastern PIB is most probably the result of smaller drainage basins resulting in less meltwater production.

  18. Modelling large-scale ice-sheet-climate interactions following glacial inception

    NASA Astrophysics Data System (ADS)

    Gregory, J. M.; Browne, O. J. H.; Payne, A. J.; Ridley, J. K.; Rutt, I. C.

    2012-10-01

    We have coupled the FAMOUS global AOGCM (atmosphere-ocean general circulation model) to the Glimmer thermomechanical ice-sheet model in order to study the development of ice-sheets in north-east America (Laurentia) and north-west Europe (Fennoscandia) following glacial inception. This first use of a coupled AOGCM-ice-sheet model for a study of change on long palæoclimate timescales is made possible by the low computational cost of FAMOUS, despite its inclusion of physical parameterisations similar in complexity to higher-resolution AOGCMs. With the orbital forcing of 115 ka BP, FAMOUS-Glimmer produces ice caps on the Canadian Arctic islands, on the north-west coast of Hudson Bay and in southern Scandinavia, which grow to occupy the Keewatin region of the Canadian mainland and all of Fennoscandia over 50 ka. Their growth is eventually halted by increasing coastal ice discharge. The expansion of the ice-sheets influences the regional climate, which becomes cooler, reducing the ablation, and ice accumulates in places that initially do not have positive surface mass balance. The results suggest the possibility that the glaciation of north-east America could have begun on the Canadian Arctic islands, producing a regional climate change that caused or enhanced the growth of ice on the mainland. The increase in albedo (due to snow and ice cover) is the dominant feedback on the area of the ice-sheets and acts rapidly, whereas the feedback of topography on SMB does not become significant for several centuries, but eventually has a large effect on the thickening of the ice-sheets. These two positive feedbacks are mutually reinforcing. In addition, the change in topography perturbs the tropospheric circulation, producing some reduction of cloud, and mitigating the local cooling along the margin of the Laurentide ice-sheet. Our experiments demonstrate the importance and complexity of the interactions between ice-sheets and local climate.

  19. Aspects of the Glacial-deglacial Climate of Western North America

    NASA Astrophysics Data System (ADS)

    Hostetler, S. W.; Alder, J. R.; Bartlein, P. J.; Cuzzone, J. K.; Wettstein, J. J.; Clark, P. U.

    2014-12-01

    We have completed a series of global climate simulations from the LGM (21 ka) to present at 3-ky increments with GENMOM, a coupled A/OGCM with a nominal horizontal resolution of 3.75°. Each time segment was forced by appropriate boundary conditions (insolation, GHGs, ice sheets, sea level,) and run out for 1100 years to ensure minimal drift in the temperature of the deep ocean. GENMOM produces LGM and mid-Holocene (6 ka) climates consistent with paleoenvironmental data and the PMIP2 and CMIP5/PMIP3 simulations. The climate sensitivity is attributed to the interplay of various boundary conditions changes throughout the deglaciation as the ice sheets melt, the seasonality of insolation increases and GHG concentrations rise. Given the dominance of the Laurentide Ice Sheet and insolation-driven continental heating during the deglaciation and MH, these controls are particularly evident in the hydroclimate of NA. We use our simulations alone and combined with the PMIP simulations to explore aspects of the evolution of the glacial-Holocene hydroclimate of Western North America related to changes in storm tracks and the strength of the monsoon circulation. We find variable agreement and disagreement among the models, particularly in the Southwest monsoon regions. We also find that, while the LGM moisture climatologies of the models may be locally consistent with paleoenvironmental data, the precipitation and temperature fields from the models produce substantial variability in simulations of the LIS as modeled by the CISM-GLIMMER ice sheet model, suggesting deficiencies in modeled regional and hemispheric circulation, moisture transport, or the surface energy balance over the ice.

  20. 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.

  1. The impact of glacial/interglacial climate changes on fluvial and mass-wasting processes in the Taiwan's mountains

    NASA Astrophysics Data System (ADS)

    Li, W. L.; Hsieh, M. L.; Tsui, H. K.; Hsiao, Y. T.

    2014-12-01

    The Taiwan orogenic belt, located in Southeastern Asia, is under monsoon climate, frequently attacked by tropical typhoons, and characterized by rapid tectonic uplift with high seismicity. Researchers have been linking the Taiwan's landscapes to active tectonic uplift. In this study, we show the significance of glacial/interglacial climate changes in shaping the landscapes. We focus on the mountain areas that have never been glaciated. Based on >400 radiocarbon dates (70 of which >12 ka), we find that both the slope and fluvial activities were generally low during the glacial time. Still, extensive alluviation had occurred at certain time periods, forming large debris slopes or alluvial fans (typically along mountain fronts), and causing significant aggradation along some major rivers. In contrast, with numerous landslides and debris flows, river incision has dominated during the postglacial time. Episodic river aggradation with alluvial-terrace development (typically at tributary mouths) also occurred during this time period, but was less extensive than previously. Some huge postglacial alluvial terraces have been proved sourced from the colluviums deposited in the glacial time. We attribute the low landscape activities of the glacial period to the dryness during the period. However, even in this time rare but severe rainfall events must have occurred to trigger some extensive alluviation. In contrast, the increase in both rainfall and typhoon frequency during the postglacial time drastically increased the slope instability and sediment yield. The great stream power, along with the sufficient coarse debris acting as erosion tools, ensured the rapid river incision during this time.

  2. Tropical Climate Variability From the Last Glacial Maximum to the Present

    DTIC Science & Technology

    2005-09-01

    whole or in part is permitted for any purpose of the United States Government . This thesis should be cited as: Kristina Ariel Dahl, 2005. Tropical...southwestern Europe Iberian Pen- Keigwin LD, Curry WB, Lehman SJ, Johnson GS (1994) The role insula, Pyrenees , Massif Central, Northern Appenines. J Qua- of the... Government Rahmstorf S (1995) Bifurcations of the Atlantic thermohaline cir- Printing Office, Washington DC culation in response to changes in the

  3. Exposure dating and glacial reconstruction at Mt. Field, Tasmania, Australia, identifies MIS 3 and MIS 2 glacial advances and climatic variability

    NASA Astrophysics Data System (ADS)

    Mackintosh, A. N.; Barrows, T. T.; Colhoun, E. A.; Fifield, L. K.

    2006-05-01

    Tasmania is important for understanding Quaternary climatic change because it is one of only three areas that experienced extensive mid-latitude Southern Hemisphere glaciation and it lies in a dominantly oceanic environment at a great distance from Northern Hemisphere ice sheet feedbacks. We applied exposure dating using 36Cl to an extensive sequence of moraines from the last glacial at Mt. Field, Tasmania. Glaciers advanced at 41-44 ka during Marine oxygen Isotope Stage (MIS) 3 and at 18 ka during MIS 2. Both advances occurred in response to an ELA lowering greater than 1100 m below the present-day mean summer freezing level, and a possible temperature reduction of 7-8°C. Deglaciation was rapid and complete by ca. 16 ka. The overall story emerging from studies of former Tasmanian glaciers is that the MIS 2 glaciation was of limited extent and that some glaciers were more extensive during earlier parts of the last glacial cycle. Copyright

  4. Modelling Glacial Lake Outburst Floods: Key Considerations and Challenges Posed By Climatic Change

    NASA Astrophysics Data System (ADS)

    Westoby, M.

    2014-12-01

    The number and size of moraine-dammed supraglacial and proglacial lakes is increasing as a result of contemporary climatic change. Moraine-dammed lakes are capable of impounding volumes of water in excess of 107 m3, and often represent a very real threat to downstream communities and infrastructure, should the bounding moraine fail and produce a catastrophic Glacial Lake Outburst Flood (GLOF). Modelling the individual components of a GLOF, including a triggering event, the complex dam-breaching process and downstream propagation of the flood is incredibly challenging, not least because direct observation and instrumentation of such high-magnitude flows is virtually impossible. We briefly review the current state-of-the-art in numerical GLOF modelling, with a focus on the theoretical and computational challenges associated with reconstructing or predicting GLOF dynamics in the face of rates of cryospheric change that have no historical precedent, as well as various implications for researchers and professionals tasked with the production of hazard maps and disaster mitigation strategies.

  5. Late-glacial vegetation and climate at the Manis Mastodon site, Olympic Peninsula, Washington

    NASA Astrophysics Data System (ADS)

    Petersen, Kenneth L.; Mehringer, Peter J.; Gustafson, Carl E.

    1983-09-01

    As the late Wisconsin Cordilleran Ice Sheet retreated, sediment accumulated in shallow depressions at the Manis Mastodon Archaeological site on the Olympic Peninsula, near Sequim, Washington. Pollen, plant macrofossils, and bones of mastodon, caribou, and bison occur within the lower 47 cm of these deposits. The fossil pollen and seed assemblages indicate persistence for 1000 yr (11,000-12,000 yr B.P.) of an herb-and-shrub-dominated landscape at a time when forest species appear elsewhere in Washington and in adjacent British Columbia. At present, Sequim is near the northern coastal limits of both Cactaceae and Ceratophyllum. Mean annual precipitation is 42.7 cm and summer temperatures average 15°-16°C in July. The absence of coniferous trees and the presence of cactus and Ceratophyllum in late-glacial sediments are explained by a regional climate that was drier and at least as warm as today. These conditions persisted in the rain shadow of the Olympic Mountains until at least 11,000 yr B.P.

  6. Northern hemisphere climate control on the environmental dynamics in the glacial Black Sea "Lake"

    NASA Astrophysics Data System (ADS)

    Wegwerth, Antje; Kaiser, Jérôme; Dellwig, Olaf; Shumilovskikh, Lyudmila S.; Nowaczyk, Norbert R.; Arz, Helge W.

    2016-03-01

    The Marine Isotope Stage (MIS) 3 stands out due to its abrupt changes from cold and dry stadials to warm and humid interstadials, the so-called Dansgaard-Oeschger cycles that also affected temperature and rainfall in the Black Sea region. This study is based on a gravity core from the southeastern (SE) Black Sea that covers the last glacial lake stage from 64 to 20 ka BP. By using the composition of major and trace elements in the sediments, terrestrial plant-derived n-alkane flux, and Sr/Ca from benthic ostracods, we reconstruct the variability of riverine and aeolian input, salinity, and productivity in the SE Black Sea region in response to the Northern Hemisphere climate oscillations. During colder and drier stadials, the aeolian input increased relative to the riverine discharge, potentially due to southward shifted and/or stronger westerly winds and due to changes in the vegetation cover. An evaporation exceeding freshwater supply by rainfall and rivers possibly caused higher salinity and a lower lake level. The environmental status during MIS 4 and 2 is very much comparable with the stadial conditions during MIS 3. During warmer and more humid interstadials, lower salinity and presumably positive lake level changes most likely resulted from increased precipitation and river discharge. This likely increased primary productivity through an augmented nutrient supply. Lowest average salinities are suggested for the middle part of MIS 3 in response to enhanced meltwater from the disintegrating Fennoscandian Ice Sheet and/or by generally more humid conditions.

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  8. Glacier changes since Local Last Glacial Maximum in the South-West slope of Nevado Hualcán, Cordillera Blanca, Peru, deduced from moraine mapping and GIS-based analysis

    NASA Astrophysics Data System (ADS)

    Giráldez, Claudia; Palacios, David; Haeberli, Wilfried; Úbeda, Jose; Schauwecker, Simone; Torres, Judith

    2014-05-01

    Area x Altitude Balance Ratio (AABR). The results show a decrease in surface area with respect to Hualcán-III-LLGM of 16% for Hualcán-II-YD; 50% for Hualcán-I-LIA; and 74% for 2003. With respect to 2003, ELAs shifted ~520 m since the Local Last Glacial Maximum (LLGM), ~470 m since a marked late-glacial stage (YD?), ~130 m since the Little Ice Age (LIA) and about ~100 m since 1962. If the changes are exclusively attributed to temperature effects, warming since LLGM can be estimated at some 3°C and since the maximum glacier extent of LIA at about 0.8°C. Such values are rather close to mean global temperature change during the corresponding intervals. Most of the ELA shift since LIA appears to have taken place during recent decades characterized by very rapid glacier shrinkage, although air temperature does not seem to have risen considerably during the last 30 years. These results along with other environmental and social approaches will contribute to a better understanding of impacts from climate change and glacier shrinkage in order to develop adaptation, mitigation and disaster risk reduction strategies in the Peruvian Andes.

  9. High-amplitude, centennial-scale climate oscillations during the last glacial in the western Third Pole as recorded in the Guliya ice cap

    NASA Astrophysics Data System (ADS)

    Thompson, L. G.; Yao, T.; Mosley-Thompson, E.; Wu, G.; Davis, M. E.; Tian, L.; Lin, P. N.

    2015-12-01

    The Guliya ice cap, located in the Kunlun Mountains in the western Third Pole (TP) region near the northern limit of the southwest monsoon influence, may be the only non-polar ice field that provides detailed histories of climate and environment over the last glacial cycle. A continuous climate record from an ice core drilled in 1992 contains Eemian ice, and basal temperatures measured that year confirmed that the record was not being removed from the bottom. The δ18O record throughout Marine Isotope Stage 2 (MIS2) displays the occurrence of high-amplitude (~20‰) episodes of ~200-year periodicity, and the aerosol records suggest snow cover, regional vegetation and fire frequency that vary in synchrony. These oscillations might reflect the movement of the northernmost penetration of the monsoon precipitation through the Late Glacial Stage, which is restricted by the topographic barrier posed by the Kunlun range, and might also reflect solar-driven nonlinearities in the climate system such as sudden shifts in the jet stream. Recent model simulations suggest that glacial cooling over China was significantly amplified by stationary waves, and the Guliya MIS2 oscillations could reflect cyclical variability in these waves. These results are supported by clumped isotope thermometry of carbonates from the Chinese Loess Plateau, which indicate a 6 to 7oC decrease in Last Glacial Maximum summer temperatures. These studies will lead to a better understanding of the mechanisms driving such high-frequency, high-amplitude oscillations. A review of the 2015 Sino-American cooperative ice core drilling program on Guliya is presented. This program will serve as a flagship for the TP Environment Program, an international, multidisciplinary collaboration among professionals and students in 14 countries designed to investigate environmental changes across the TP. The rapidly warming TP contains ~46,000 glaciers that collectively hold one of Earth's largest stores of fresh water that

  10. Glacial to Holocene climate changes in Easter Island (SE Pacific, 27

    NASA Astrophysics Data System (ADS)

    Sáez, A.; Giralt, S.; Valero-Garcés, B. L.; Moreno, A.; Bao, R.; Pueyo, J. J.; Hernández, A.

    2009-04-01

    Sedimentary architecture and paleoclimate for the last 34 000 cal years BP and human activity during the last 850 years have been reconstructed from the Raraku Lake sediments in Easter Island (SE Pacific, 27°S) using a high-resolution multiproxy study of 8 cores, 36 AMS radiocarbon dates and correlation with previous core studies. The Last Glacial period was characterized by cold and relatively humid conditions between 34 to 28 cal kyr BP. High lake levels and clastic input dominated sedimentation in Raraku Lake and a relatively open forest developed at that time. Between 28 and 17.3 cal kyr BP, including LGM period, colder conditions contributed to a reduction of the tree coverage in the island. The end of Glacial Period occurred at 17.3 cal kyr BP and was characterized by a sharp decrease in lake level conducive to the development of major floods due to the erosion of littoral sediments. The Deglaciation Period (Termination 1) occurred between 17.3 and 12.5 cal kyr BP, characterized by an increase in lake productivity, a decrease in the terrigenous input and a rapid lake level recovery inaugurating a period of intermediate lake levels. During this period, the dominance of algal lamination is interpreted as a warmer climate. The timing and duration of this warming trend in Easter Island broadly agrees with other mid- and low latitude circum South Pacific terrestrial records. The early Holocene was characterized by low lake levels. The lake level dropped during the early Holocene (ca. 9.5 cal kyr BP) and peatbog and shallow lake conditions dominated till mid Holocene, partially caused by the colmatation of the lacustrine basin. During the mid Holocene an intense drought occurred that led to a persistent low water table period, subaerial exposure and erosion of some of the sediments, generating a sedimentary gap in the Raraku sequence, from 4.2 to 0.8 cal kyr BP. The palm deforestation of the Easter Island, attributed to the human colonization at about 850 cal yr

  11. Killer whale nuclear genome and mtDNA reveal widespread population bottleneck during the last glacial maximum.

    PubMed

    Moura, Andre E; Janse van Rensburg, Charlene; Pilot, Malgorzata; Tehrani, Arman; Best, Peter B; Thornton, Meredith; Plön, Stephanie; de Bruyn, P J Nico; Worley, Kim C; Gibbs, Richard A; Dahlheim, Marilyn E; Hoelzel, Alan Rus

    2014-05-01

    Ecosystem function and resilience is determined by the interactions and independent contributions of individual species. Apex predators play a disproportionately determinant role through their influence and dependence on the dynamics of prey species. Their demographic fluctuations are thus likely to reflect changes in their respective ecological communities and habitat. Here, we investigate the historical population dynamics of the killer whale based on draft nuclear genome data for the Northern Hemisphere and mtDNA data worldwide. We infer a relatively stable population size throughout most of the Pleistocene, followed by an order of magnitude decline and bottleneck during the Weichselian glacial period. Global mtDNA data indicate that while most populations declined, at least one population retained diversity in a stable, productive ecosystem off southern Africa. We conclude that environmental changes during the last glacial period promoted the decline of a top ocean predator, that these events contributed to the pattern of diversity among extant populations, and that the relatively high diversity of a population currently in productive, stable habitat off South Africa suggests a role for ocean productivity in the widespread decline.

  12. Imaging evidence for Hubbard Glacier advances and retreats since the last glacial maximum in Yakutat and Disenchantment Bays, Alaska

    NASA Astrophysics Data System (ADS)

    Zurbuchen, Julie M.; Gulick, Sean P. S.; Walton, Maureen A. L.; Goff, John A.

    2015-06-01

    High-resolution 2-D multichannel seismic data, collected during the 2012 UTIG-USGS National Earthquake Hazards Reduction Program survey of Disenchantment and Yakutat Bays in southeast Alaska, provide insight into their glacial history. These data show evidence of two unconformities, appearing in the form of channels, and are interpreted to be advance pathways for Hubbard Glacier. The youngest observable channel, thought to have culminated near the main phase of the Little Ice Age (LIA), is imaged in Disenchantment Bay and ends at a terminal moraine near Blizhni Point. An older channel, thought to be from an advance that culminated in the early phase of the LIA, extends from Disenchantment Bay into the northeastern edge of Yakutat Bay, turning southward at Knight Island and terminating on the southeastern edge of Yakutat Bay. Our interpretation is that Hubbard Glacier has repeatedly advanced around the east side of Yakutat Bay in Knight Island Channel, possibly due to the presence of Malaspina Glacier cutting off access to central Yakutat Bay during times of mutual advance. We observe two distinct erosional surfaces and retreat sequences of Hubbard Glacier in Yakutat Bay, supporting the hypothesis that minor glacial advances in fjords do not erode all prior sediment accumulations. Interpretation of chaotic seismic facies between these two unconformities suggests that Hubbard Glacier exhibits rapid retreats and that Disenchantment Bay is subject to numerous episodes of outburst flooding and morainal bank collapse. These findings also suggest that tidewater glaciers preferentially reoccupy the same channels in bay and marine settings during advances.

  13. Glacial to Holocene changes in trans-Atlantic Saharan dust transport and dust-climate feedbacks.

    PubMed

    Williams, Ross H; McGee, David; Kinsley, Christopher W; Ridley, David A; Hu, Shineng; Fedorov, Alexey; Tal, Irit; Murray, Richard W; deMenocal, Peter B

    2016-11-01

    Saharan mineral dust exported over the tropical North Atlantic is thought to have significant impacts on regional climate and ecosystems, but limited data exist documenting past changes in long-range dust transport. This data gap limits investigations of the role of Saharan dust in past climate change, in particular during the mid-Holocene, when climate models consistently underestimate the intensification of the West African monsoon documented by paleorecords. We present reconstructions of African dust deposition in sediments from the Bahamas and the tropical North Atlantic spanning the last 23,000 years. Both sites show early and mid-Holocene dust fluxes 40 to 50% lower than recent values and maximum dust fluxes during the deglaciation, demonstrating agreement with records from the northwest African margin. These quantitative estimates of trans-Atlantic dust transport offer important constraints on past changes in dust-related radiative and biogeochemical impacts. Using idealized climate model experiments to investigate the response to reductions in Saharan dust's radiative forcing over the tropical North Atlantic, we find that small (0.15°C) dust-related increases in regional sea surface temperatures are sufficient to cause significant northward shifts in the Atlantic Intertropical Convergence Zone, increased precipitation in the western Sahel and Sahara, and reductions in easterly and northeasterly winds over dust source regions. Our results suggest that the amplifying feedback of dust on sea surface temperatures and regional climate may be significant and that accurate simulation of dust's radiative effects is likely essential to improving model representations of past and future precipitation variations in North Africa.

  14. Glacial to Holocene changes in trans-Atlantic Saharan dust transport and dust-climate feedbacks

    PubMed Central

    Williams, Ross H.; McGee, David; Kinsley, Christopher W.; Ridley, David A.; Hu, Shineng; Fedorov, Alexey; Tal, Irit; Murray, Richard W.; deMenocal, Peter B.

    2016-01-01

    Saharan mineral dust exported over the tropical North Atlantic is thought to have significant impacts on regional climate and ecosystems, but limited data exist documenting past changes in long-range dust transport. This data gap limits investigations of the role of Saharan dust in past climate change, in particular during the mid-Holocene, when climate models consistently underestimate the intensification of the West African monsoon documented by paleorecords. We present reconstructions of African dust deposition in sediments from the Bahamas and the tropical North Atlantic spanning the last 23,000 years. Both sites show early and mid-Holocene dust fluxes 40 to 50% lower than recent values and maximum dust fluxes during the deglaciation, demonstrating agreement with records from the northwest African margin. These quantitative estimates of trans-Atlantic dust transport offer important constraints on past changes in dust-related radiative and biogeochemical impacts. Using idealized climate model experiments to investigate the response to reductions in Saharan dust’s radiative forcing over the tropical North Atlantic, we find that small (0.15°C) dust-related increases in regional sea surface temperatures are sufficient to cause significant northward shifts in the Atlantic Intertropical Convergence Zone, increased precipitation in the western Sahel and Sahara, and reductions in easterly and northeasterly winds over dust source regions. Our results suggest that the amplifying feedback of dust on sea surface temperatures and regional climate may be significant and that accurate simulation of dust’s radiative effects is likely essential to improving model representations of past and future precipitation variations in North Africa. PMID:28138515

  15. Holocene climate and glacial history of the northeastern Antarctic Peninsula: the marine sedimentary record from a long SHALDRIL core

    NASA Astrophysics Data System (ADS)

    Michalchuk, Bradley R.; Anderson, John B.; Wellner, Julia S.; Manley, Patricia L.; Majewski, Wojciech; Bohaty, Steve

    2009-12-01

    A high-resolution record of Holocene deglacial and climate history was obtained from a 77 m sediment core from the Firth of Tay, Antarctic Peninsula, as part of the SHALDRIL initiative. This study provides a detailed sedimentological record of Holocene paleoclimate and glacial advance and retreat from the eastern side of the peninsula. A robust chronostratigraphy was derived from thirty-three radiocarbon dates on carbonate material. This chronostratigraphic framework was used to establish the timing of glacial and climate events derived from multiple proxies including: magnetic susceptibility, electric resistivity, porosity, ice-rafted debris content, organic carbon content, nitrogen content, biogenic silica content, and diatom and foraminiferal assemblages. The core bottomed-out in a stiff diamicton interpreted as till. Gravelly and sandy mud above the till is interpreted as proximal glaciomarine sediment that represents decoupling of the glacier from the seafloor circa 9400 cal. yr BP and its subsequent landward retreat. This was approximately 5000 yr later than in the Bransfield Basin and South Shetland Islands, on the western side of the peninsula. The Firth of Tay core site remained in a proximal glaciomarine setting until 8300 cal. yr BP, at which time significant glacial retreat took place. Deposition of diatomaceous glaciomarine sediments after 8300 cal. yr BP indicates that an ice shelf has not existed in the area since this time. The onset of seasonally open marine conditions between 7800 and 6000 cal. yr BP followed the deglacial period and is interpreted as the mid-Holocene Climatic Optimum. Open marine conditions lasted until present, with a minor cooling having occurred between 6000 and 4500 cal. yr BP and a period of minor glacial retreat and/or decreased sea ice coverage between 4500 and 3500 cal. yr BP. Finally, climatic cooling and variable sea ice cover occurred from 3500 cal. yr BP to near present and it is interpreted as being part of the

  16. Late glacial to Holocene climatic and oceanographic record of sediment facies from the South Scotia Sea off the northern Antarctic Peninsula

    NASA Astrophysics Data System (ADS)

    Yoon, H. I.; Khim, B. K.; Yoo, K.-C.; Bak, Y. S.; Lee, J. I.

    2007-10-01

    Two gravity cores were collected from the South Scotia Sea located off the northern Antarctic Peninsula during the 2002/2003 Korea Antarctic Research Program (KARP) expedition to determine the late Quaternary climatic and oceanographic history. Reassessment of previous sedimentological, geochemical and micropaleontological analyses combined with established age model of AMS 14C dates represent the reliable record of late Pleistocene climatic/oceanographic change for the Scotia Sea region of Antarctica. During the Last Glacial Maximum (LGM), the South Scotia Sea received large amounts of sorted terrigenous sediments and some of the reworked diatom fossils emplaced by bottom currents from an extensively glaciated Weddell Sea continental margin. Drifting icebergs calved from the glacial fronts have dispersed glacial dropstones throughout the study area. The bottom current deposits during the glacial phase comprise two lithologic units: (1) bioturbated gravelly sandy mud (Facies 1), formed by sluggish bottom current caused by reduced dense-water production originated from the ice sheet on the Weddell Shelf, (2) indistinctly layered diatomaceous mud as shown by total organic carbon (TOC) highs in the Facies 1, deposited by sporadic bottom currents caused by intensified sea-ice formation in polynya during the glacial stage. The LGM is characterized by greater and longer sea-ice coverage and a restricted Weddell/Scotia summer communication, as evidenced by a relative decrease in percentage Thalssiosira antarctica and Chaetoceros resting spores, which are more abundant close to the Weddell Ice Shelf. Deglaciation (about 13,000-9000 14C yr BP) in the South Scotia Sea was characterized by increasing TOC, diatom abundance, and decreasing magnetic susceptibility and sand contents up core. At this time, subglacial meltwater streams began to emanate from the Weddell Ice Sheet with peak of ice rafting. Sediment-laden turbid plumes from melting glacier and deglaciated Weddell

  17. Post-glacial landform evolution in the middle Satluj River valley, India: Implications towards understanding the climate tectonic interactions

    NASA Astrophysics Data System (ADS)

    Sharma, Shubhra; Bartarya, S. K.; Marh, B. S.

    2016-04-01

    Late Quaternary landform evolution in monsoon-dominated middle Satluj valley is reconstructed using the fragmentary records of fluvial terraces, alluvial fans, debris flows, paleo-flood deposits, and epigenetic gorges. Based on detailed field mapping, alluvial stratigraphy, sedimentology and optical chronology, two phases of fluvial aggradations are identified. The older aggradation event dated between ˜13 and 11 ka (early-Holocene), occurred in the pre-existing topography carved by multiple events of erosion and incision. Climatically, the event corresponds to the post-glacial strengthened Indian summer monsoon (ISM). The younger aggradation event dated between ˜5 and 0.4 ka (mid- to late-Holocene), was during the declining phase of ISM. The terrain witnessed high magnitude floods during transitional climate (˜6.5-7 ka). The fluvial sedimentation was punctuated by short-lived debris flows and alluvial fans during the LGM (weak ISM), early to mid-Holocene transition climate and mid- to late-Holocene declining ISM. Based on the terrace morphology, an event of relatively enhanced surface uplift is inferred after late Holocene. The present study suggests that post-glacial landforms in the middle Satluj valley owe their genesis to the interplay between the climate variability and local/regional tectonic interactions.

  18. Climate Change, Glacier Retreat and Sediment Waves: Evidences from Fans in the Fox Glacial valley (New Zealand) and Analogical Modeling

    NASA Astrophysics Data System (ADS)

    Gomez, C. A.; Purdie, H.

    2015-12-01

    As global climate continues warm, mountain environments are changing, and rates of glacial retreat are unprecedented. The hydrologic implications of this rapid ice retreat and changing climate conditions have been the focus of numerous studies, but the consequent effects on the sediment cascade in valleys and tributaries has received considerably less attention. In the present study, we investigated the role of glacial recession on sediment mobilization and deposition in a mountain valley catchment at Fox Glacier, New Zealand. In particular, we analyze the role of glacier recession on the formation of sediment fans in the main valley. Emphasis was put on the role of sediment, impounded by the glacier in side tributaries, becoming rapidly available for remobilization as the glacier retreats. The method is based on field observations, and measurements using high resolution GNSS (Trimble R8 survey grade differential GNSS) and photogrammetric methods using Structure from Motion based on ground-, helicopter- and UAV- photographs. Field observations were conducted in the period 2014 - 2015, and have been complimented with analogic modeling in the laboratory, in order to comprehend the processes driving rapid fan formation. The analogic model reproduced the retreat of the glacier and the response of a tributary, with simulations for both glaciated and de-glaciated conditions. For similar hydrologic and slope parameters, the fans created after glacial retreat have shown an acceleration in their formation of up to 12 times compared to fanes created without glacial influence. Field observations within the period 2013 - 2015 of Straight Creek Fan (Fox Valley, New Zealand) have confirmed laboratory simulations, with the fan growing to a radius superior to 200 m and a valley-long width superior to 450 m. As glaciers continue to retreat, it can be expected that sediment surges will occur in affected valleys, without the requirements of other forcing like earthquake or extreme

  19. Changes in productivity and redox conditions during the Last Glacial Maximum as recorded in high-resolution geochemical records from Alfonso Basin, Gulf of California

    NASA Astrophysics Data System (ADS)

    Choumiline, K.; Lyons, T. W.; Carriquiry, J. D.; Perez-Cruz, L. L.; Beaufort, L.

    2015-12-01

    The Last Glacial Maximum represents the most recent major sea level low stand in Earth history. Such changes in eustatic sea level impacted the oxygenation of marine basins, yet the characteristics and mechanisms of those impacts remain poorly known. Specific basin conditions are needed to develop, record, and preserve those paleoredox changes through time most effectively, including rapid sedimentation rates and silled basin morphologies. The anoxic Alfonso Basin, partially separated from the Gulf of California by a bathymetric sill, is such a place. The basin is located in a dry semiarid region dominated by dust inputs and only occasional tropical cyclone-induced fluvial contributions. We present the first multi-proxy reconstruction of southern Gulf of California paleoredox that covers an uninterrupted timespan from the Late Pleistocene to the present, with an emphasis on the Last Glacial Maximum. In this research we contrast geochemical data from a 47-meter-long sediment core (collected with the giant CALYPSO corer aboard the R/V Marion Dufresne) with the solid phase and pore water chemical data from a shorter but very detailed box core (collected on the R/V El Puma), both from Alfonso Basin. Our results show that during the Late Pleistocene and throughout the Holocene several paleoredox shifts occurred, often accompanied by differences in lamination (laminated/massive alternations) and trace element (Mo, V, U) compositions; detailed Fe chemistry (FeHR/FeTand Fe/Al ratios); as well as carbon and sulfur concentrations and isotope ratios. For example, FeHR/FeT ratios indicate values of roughly 0.15 during the Last Glacial Maximum (lower than theoretic threshold of 0.2 between oxic and anoxic), suggesting more oxic conditions, in comparison to 0.25 and higher in the Holocene. Most of the variability seen in these proxies is related to global sea level change, while some variability is instead related to local variations in paleoproductivity, often connected to

  20. Intensification of the meridional temperature gradient in the Great Barrier Reef following the Last Glacial Maximum - Results from IODP Expedition 325

    NASA Astrophysics Data System (ADS)

    Felis, Thomas; McGregor, Helen V.; Linsley, Braddock K.; Tudhope, Alexander W.; Gagan, Michael K.; Suzuki, Atsushi; Inoue, Mayuri; Thomas, Alexander L.; Esat, Tezer M.; Thompson, William G.; Tiwari, Manish; Potts, Donald C.; Mudelsee, Manfred; Yokoyama, Yusuke; Webster, Jody M.

    2015-04-01

    Tropical south-western Pacific temperatures are of vital importance to the Great Barrier Reef (GBR), but the role of sea surface temperatures (SSTs) in the growth of the GBR since the Last Glacial Maximum remains largely unknown. Here we present records of Sr/Ca and δ18O for Last Glacial Maximum and deglacial corals that were drilled by Integrated Ocean Drilling Program (IODP) Expedition 325 along the shelf edge seaward of the modern GBR. The Sr/Ca and δ18O records of the precisely U-Th dated fossil shallow-water corals show a considerably steeper meridional SST gradient than the present day in the central GBR. We find a 1-2 ° C larger temperature decrease between 17° S and 20° S about 20,000 to 13,000 years ago. The result is best explained by the northward expansion of cooler subtropical waters due to a weakening of the South Pacific gyre and East Australian Current. Our findings indicate that the GBR experienced substantial and regionally differing temperature change during the last deglaciation, much larger temperature changes than previously recognized. Furthermore, our findings suggest a northward contraction of the Western Pacific Warm Pool during the LGM and last deglaciation, and serve to explain anomalous drying of northeastern Australia at that time. Overall, the GBR developed through significant SST change and, considering temperature alone, may be more resilient than previously thought. Webster, J. M., Yokoyama, Y. & Cotteril, C. & the Expedition 325 Scientists. Proceedings of the Integrated Ocean Drilling Program Vol. 325 (Integrated Ocean Drilling Program Management International Inc., 2011). Felis, T., McGregor, H. V., Linsley, B. K., Tudhope, A. W., Gagan, M. K., Suzuki, A., Inoue, M., Thomas, A. L., Esat, T. M., Thompson, W. G., Tiwari, M., Potts, D. C., Mudelsee, M., Yokoyama, Y., Webster, J. M. Intensification of the meridional temperature gradient in the Great Barrier Reef following the Last Glacial Maximum. Nature Communications 5, 4102

  1. Running hotter, faster, shallower: acceleration of the marine nitrogen cycle from the Last Glacial Maximum to the pre-industrial, and implications for the future

    NASA Astrophysics Data System (ADS)

    Galbraith, E. D.

    2015-12-01

    Biologically-available nitrogen is the primary limiting nutrient in the global ocean. The complex physical-biological interdependencies of nitrogen fixation and denitrification, the source and sink of bioavailable nitrogen, have led to uncertainty over their future trajectories under higher CO2. Sedimentary nitrogen isotope evidence suggests that the global rate of denitrification was on the order of 50% lower during the last glacial maximum, and reveals that significant changes in denitrification have occurred on a decadal-centennial timescale. Coupled atmosphere-ocean-biogeochemistry models simulate similar changes, through physically-driven changes in anoxia, which then feed back on nitrogen fixation through the availability of phosphorus to diazotrophs. In addition, diazotroph culture experiments suggest that nitrogen fixation was further limited during glacial maxima by low CO2, causing an additional slowdown of the nitrogen cycle. The emergent picture suggests that deglaciation accelerated both sides of the N cycle, with more rapid loss encouraged by expanded shallow anoxia, and more rapid gain encouraged by higher CO2. It will be argued that the net effect on the nitrogen inventory can be approximated by knowing the distribution of surface ocean PO4, given the observed correlation of surface PO4 concentrations on the P:C ratio of exported organic matter.

  2. Too much of a good thing: sea ice extent may have forced emperor penguins into refugia during the last glacial maximum.

    PubMed

    Younger, Jane L; Clucas, Gemma V; Kooyman, Gerald; Wienecke, Barbara; Rogers, Alex D; Trathan, Philip N; Hart, Tom; Miller, Karen J

    2015-06-01

    The relationship between population structure and demographic history is critical to understanding microevolution and for predicting the resilience of species to environmental change. Using mitochondrial DNA from extant colonies and radiocarbon-dated subfossils, we present the first microevolutionary analysis of emperor penguins (Aptenodytes forsteri) and show their population trends throughout the last glacial maximum (LGM, 19.5-16 kya) and during the subsequent period of warming and sea ice retreat. We found evidence for three mitochondrial clades within emperor penguins, suggesting that they were isolated within three glacial refugia during the LGM. One of these clades has remained largely isolated within the Ross Sea, while the two other clades have intermixed around the coast of Antarctica from Adélie Land to the Weddell Sea. The differentiation of the Ross Sea population has been preserved despite rapid population growth and opportunities for migration. Low effective population sizes during the LGM, followed by a rapid expansion around the beginning of the Holocene, suggest that an optimum set of sea ice conditions exist for emperor penguins, corresponding to available foraging area.

  3. 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.

  4. The interaction of climate and glacial landforms on subsurface and surface hydrology and chemistry across a heterogeneous boreal plain landscape

    NASA Astrophysics Data System (ADS)

    Hokanson, Kelly; Carrera-Hernández, Jaime; Devito, Kevin; Mendoza, Carl

    2016-04-01

    The Boreal Plains (BP) region of Canada is experiencing high levels of anthropogenic activity and may be susceptible to climate change to various degrees. The BP is characterized by heterogeneous glacial landforms, with large contrasts in storage and transmissivity, which when coupled with wet-dry climate cycles, results in complex groundwater-surface water interactions. Predicting the impacts of land use change, climate change, and the future performance of constructed and reclaimed landscapes is currently not possible due to our limited knowledge regarding the natural variability of water table fluctuations, geochemistry, and salinity across the various glacial landforms in the BP. We compare isotopes, EC, chemistry (DOC, Ca, Mg, SO4) and water table position between a drought (2003) and a wet (2013) year to examine the interactions between climate, landform, and geology on the variation in landscape connectivity and overall salinity distribution. Data were collected from surface waters to a depth of 40 m, along a 50 km transect encompassing pond-wetland-forestland sequences across the major glacial depositional types typical of the BP (coarse textured glaciofluvial outwash, fine textured stagnant ice moraine, and lacustrine clay plain). Within each landform, sites range from isolated local flow systems to large intermediate scale flow systems. High spatial variability of water table fluctuations and salinity illustrate the strong regional controls that climate and geology exerts over scales of groundwater flow between landforms and surface water bodies across the BP, reinforcing the need to link surface water and groundwater processes when developing conceptual models. Additionally, when coupled with a strong, physical hydrogeologic conceptual model, synoptic chemical and isotopic surveys can be used to confirm scales and directions of flow; however, without an understanding of the climatic and geologic influence of the region, such data cannot be used as a

  5. The de-correlation of westerly winds and westerly-wind stress over the Southern Ocean during the Last Glacial Maximum

    SciTech Connect

    Liu, Wei; Lu, Jian; Leung, Lai-Yung R.; Xie, Shang-Ping; Liu, Zhengyu; Zhu, Jiang

    2015-02-22

    This paper investigates the changes of the Southern Westerly Winds (SWW) and Southern Ocean (SO) upwelling between the Last Glacial Maximum (LGM) and preindustrial (PI) in the PMIP3/CMIP5 simulations, highlighting the role of the Antarctic sea ice in modulating the wind stress effect on the ocean. Particularly, a discrepancy may occur between the changes in SWW and westerly wind stress, caused primarily by an equatorward expansion of winter Antarctic sea ice that undermines the wind stress in driving the liquid ocean. Such discrepancy may reflect the LGM condition in reality, in view of that the model simulates this condition has most credible simulation of modern SWW and Antarctic sea ice. The effect of wind stress on the SO upwelling is further explored via the wind-induced Ekman pumping, which is reduced under the LGM condition in all models, in part by the sea-ice “capping” effect present in the models.

  6. Constant wind regimes during the Last Glacial Maximum and early Holocene: evidence from Little Llangothlin Lagoon, New England Tablelands, eastern Australia

    NASA Astrophysics Data System (ADS)

    Shulmeister, James; Kemp, Justine; Fitzsimmons, Kathryn E.; Gontz, Allen

    2016-07-01

    Here we present the results of a multi-proxy investigation - integrating geomorphology, ground-penetrating radar, and luminescence dating - of a high-elevation lunette and beach berm in northern New South Wales, eastern Australia. The lunette occurs on the eastern shore of Little Llangothlin Lagoon and provides evidence for a lake high stand combined with persistent westerly winds at the Last Glacial Maximum (LGM - centring on 21.5 ka) and during the early Holocene (ca. 9 and 6 ka). The reconstructed atmospheric circulation is similar to the present-day conditions, and we infer no significant changes in circulation at those times, as compared to the present day. Our results suggest that the Southern Hemisphere westerlies were minimally displaced in this sector of Australasia during the latter part of the last ice age. Our observations also support evidence for a more positive water balance at the LGM and early Holocene in this part of the Australian sub-tropics.

  7. The Last Glacial Maximum in the Northern European loess belt: Correlations between loess-paleosol sequences and the Dehner Maar core (Eifel Mountains)

    NASA Astrophysics Data System (ADS)

    Zens, Joerg; Krauß, Lydia; Römer, Wolfgang; Klasen, Nicole; Pirson, Stéphane; Schulte, Philipp; Zeeden, Christian; Sirocko, Frank; Lehmkuhl, Frank

    2016-04-01

    The D1 project of the CRC 806 "Our way to Europe" focusses on Central Europe as a destination of modern human dispersal out of Africa. The paleo-environmental conditions along the migration areas are reconstructed by loess-paleosol sequences and lacustrine sediments. Stratigraphy and luminescence dating provide the chronological framework for the correlation of grain size and geochemical data to large-scale climate proxies like isotope ratios and dust content of Greenland ice cores. The reliability of correlations is improved by the development of precise age models of specific marker beds. In this study, we focus on the (terrestrial) Last Glacial Maximum of the Weichselian Upper Pleniglacial which is supposed to be dominated by high wind speeds and an increasing aridity. Especially in the Lower Rhine Embayment (LRE), this period is linked to an extensive erosion event. The disconformity is followed by an intensive cryosol formation. In order to support the stratigraphical observations from the field, luminescence dating and grain size analysis were applied on three loess-paleosol sequences along the northern European loess belt to develop a more reliable chronology and to reconstruct paleo-environmental dynamics. The loess sections were compared to newest results from heavy mineral and grain size analysis from the Dehner Maar core (Eifel Mountains) and correlated to NGRIP records. Volcanic minerals can be found in the Dehner Maar core from a visible tephra layer at 27.8 ka up to ~25 ka. They can be correlated to the Eltville Tephra found in loess section. New quartz luminescence ages from Romont (Belgium) surrounding the tephra dated the deposition between 25.0 + 2.3 ka and 25.8 + 2.4 ka. In the following, heavy minerals show an increasing importance of strong easterly winds during the second Greenland dust peak (~24 ka b2k) correlating with an extensive erosion event in the LRE. Luminescence dating on quartz bracketing the following soil formation yielded ages of

  8. New insights on Late Quaternary Asian palaeomonsoon variability and the timing of the Last Glacial Maximum in southwestern China

    NASA Astrophysics Data System (ADS)

    Cook, Charlotte G.; Jones, Richard T.; Langdon, Peter G.; Leng, Melanie J.; Zhang, Enlou

    2011-04-01

    A ˜6.35 m core (06SD) was retrieved from Lake Shudu, Yunnan Province, China. The sediments spanning the period ˜22.6-10.5 kcal. yr BP (6.35-1.44 m) were analysed using a combination of variables including pollen, charcoal, particle size, magnetic susceptibility and loss-on-ignition. The resulting palaeorecord provides a high-resolution reconstruction of Late Pleistocene to Early Holocene climatic and environmental changes in southwestern China. Our findings indicate that from c. 22.6 to 17.7 kcal. yr BP, vegetation assemblages were primarily aligned to sparse xerophytic grassland/tundra or cold-tolerant boreal Pinus forest, indicating that climatic conditions in southwestern China were cold and dry. However, from c. 17.7 to 17.4 kcal. yr BP, the Lake Shudu record is punctuated by marked environmental changes. These include the establishment of denser vegetation cover, a marked expansion of boreal Pinus forest and enhanced hydrological activity in the catchment over centennial timescales, perhaps suggesting that stepwise variations in the Asian Monsoon were triggering fundamental environmental changes over sub-millennial timescales. Thereafter, the pollen record captures a period of environmental instability reflected in fluctuations across all of the variables, which persists until c. 17.1 kcal. yr BP. After c. 17.1 kcal. yr BP, the expansion of steppe vegetation cover and cold-cool mixed forest consisting of mesophilous vegetation such as Tsuga and Picea, thermophilous trees including Ulmus and deciduous Quercus inferred from the Lake Shudu pollen record point to the establishment of warmer, wetter and perhaps more seasonal conditions associated with a strengthening Asian Summer Monsoon during the shift from Pleistocene to Holocene climatic conditions.

  9. Climatic control of sediment transport from the Himalayas to the proximal NE Bengal Fan during the last glacial-interglacial cycle

    NASA Astrophysics Data System (ADS)

    Joussain, Ronan; Colin, Christophe; Liu, Zhifei; Meynadier, Laure; Fournier, Léa; Fauquembergue, Kelly; Zaragosi, Sébastien; Schmidt, Frédéric; Rojas, Virginia; Bassinot, Franck

    2016-09-01

    Clay mineralogy, siliciclastic grain-size, major elements, 87Sr/86Sr, and εNd analyses of deep-sea sediments cored in the north-eastern Bay of Bengal are used to reconstruct evolution of detrital sources and sediment transport to the proximal part of the Bengal deep-sea fan during the last climatic cycle. εNd values (-13.3 to -9.7) and 87Sr/86Sr ratios (0.721-0.733) indicate a mixture of sediments originating from the Ganges-Brahmaputra rivers and the Indo-Burman ranges. Interglacial Marine Isotopic Stages (MIS) 5 and 1 are associated with a higher contribution of sediments from the Ganges-Brahmaputra river system than is the case for glacial MIS 6, 4, 3, and 2. Siliciclasitic grain-size combined with Si/Al and Si/Fe ratios indicate coarser glacial sediments with numerous turbidite layers. Glacial turbidite layers display similar clay mineralogical compositions to hemipelagic sediments. Only few of turbidite layers (MIS 6, 4, and 2) are slightly unradiogenic (εNd -13.3), suggesting a higher contribution of Ganges-Brahmaputra river sediments. Independently of changes in the sedimentary sources, the smectite/(illite + chlorite) ratio of cores located on the NE Bengal Fan indicates higher inputs of primary minerals (illite and chlorite) from the highlands of the river basins (relief) during glacial MIS 6, 4, 3, and 2 and an increased contribution of pedogenic minerals (smectite and kaolinite) during interglacial MIS 5 and 1. Maximum smectite/(illite + chlorite) ratios during the warm sub-stages of MIS 5 suggest an intensification of summer monsoon rainfall associated with higher rates of physical erosion of the Indo-Gangetic flood-plain and/or dominant summer hydrological conditions transporting a higher proportion of sediments deriving from the Ganges-Brahmaputra rivers to the NE Bengal Fan. In addition, a higher production of smectite in soils of the Indo-Gangetic flood-plain during periods of intensification of monsoon rainfall cannot be excluded.

  10. Fast Deposition of Small River Particles on the NE South China Sea Slope Basin Since the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Lin, S.; Cheng, W. Y.; Hsieh, I. C.

    2015-12-01

    Huge quantities of small rivers derived suspended particles are exporting to the ocean from oceanic islands at the present time. Depending on location and proportion of shelf/slope area, a major fraction of small river particles may by-pass the shelf region, transport and deposit on the deep ocean basin. Major mechanisms driving those huge quantities of small river derived particles to the ocean are quantity of precipitation from monsoon and those from short period of tropical cyclone. Although data demonstrate that deeper part of the South China Sea, SCS, is the major final burial location of the river derived particles from the island of Taiwan, it is not sure if this was the same during the glaciation when monsoon and climatic conditions were drastic different from the present time. The purpose of this study is to understand history of small river derived sediment export and deposition during climatic change. A long piston core with length of ~35 meter was taken on r/v Marion DuFresne on a slope basin offshore SW Taiwan. We have measured density, magnetic susceptibility with multi-sensor core logger, MSCL, and organic, inorganic carbon, C/N ratio, biogenic silica as well as grain sizes. Foraminifera (Orbulina universa, Globigerinoides sacculifer and Globigerinoides conglobatus) were picked and measured carbon 14 for age determination. Two different types of processes control sediment deposition in our study site, steady state and event driven sedimentation. Our results demonstrated that sedimentation rates were consistent during each major periods, the Holocene (present to 10k year) and the transition (10-20 k year) period, but, difference existed in between the two. Sedimentation rate was about twice faster during the transition period (20-10k year) than that at the Holocene (10-present time) at our study site. A number of spikes existed in our study site, probably a result of turbidite overflow from the adjacent canyon. Frequency and total thickness of event

  11. Altitudinal dynamics of glacial lakes under changing climate in the Hindu Kush, Karakoram, and Himalaya ranges

    NASA Astrophysics Data System (ADS)

    Ashraf, Arshad; Naz, Rozina; Iqbal, Muhammad Bilal

    2017-04-01

    The environmental challenges posed by global warming in the Himalayan region include early and rapid melting of snow and glaciers, creation of new lakes, and expansion of old ones posing a high risk of glacial lakes outburst flood (GLOF) hazard for downstream communities. According to various elevation ranges, 3044 lakes were analyzed basinwide in the Hindu Kush-Karakoram-Himalaya (HKH) ranges of Pakistan using multisensor remote sensing data of the 2001-2013 period. An overall increase in glacial lakes was observed at various altitudinal ranges between 2500 and 5500, m out of which noticeable change by number was within the 4000-4500 m range. The analysis carried out by glacial-fed lakes and nonglacial-fed lakes in different river basins indicated variable patterns depending on the geographic location in the HKH region. The correlation analysis of parameters like lake area, expansion rate, and elevation was performed with 617 glacial lakes distributed in various river basins of the three HKH ranges. Lake area (2013) and elevation showed a negative relationship for all basins except Hunza, Shigar, and Shyok. The correlation between the expansion rate of lakes and elevation was on the positive side for Swat, Gilgit, Shigar, and Shingo basins-a situation that may be attributed to the variable altitudinal pattern of temperature and precipitation. In order to explore such diverse patterns of lake behavior and relationship with influential factors in the HKH, detailed studies based on using high resolution image data coupled with in situ information are a prerequisite. Although an increase in lake area observed below 3500 m would be favorable for water resource management, but could be alarming in context of glacial flood hazards that need to be monitored critically on a long-term basis.

  12. High resolution dating of moraines on Kodiak Island, Alaska links Atlantic and North Pacific climatic changes during the late glacial

    SciTech Connect

    Mann, D.H. . Alaska Quaternary Center)

    1992-01-01

    Much less is known about the paleoclimate and paleoceanography of the North Pacific than the North Atlantic despite the North Pacific's important role in the global ocean-climate system. Kodiak Island lies in the northwestern Gulf of Alaska astride the eastern end of the Aleutian Low. On southwestern Kodiak Island, coastal bluffs section a series of moraines, kettle ponds, and bogs formed between 15 and 9 ka BP. Distinctive tephras from volcanoes on the Alaska Peninsula provide time-lines within the stratigraphy. Deformation events recorded in sediment stacks from basins within glaciotectonic landforms allows precise dating of glacial events. An ice cap occupied the Kodiak archipelago during the last glaciation. Three glacial advances of the southwestern margin of this ice cap occurred after 15 ka BP. At 13.4 ka, piedmont ice lobes formed large push moraines extending into Shelikof Strait during the Low Cape Advance. The less-extensive Tundra Advance culminated between 12 and 11.7 ka BP followed by glacier retreat then readvance to form the prominent Olga Moraine system between 11 and 10 ka BP. The timing of the Tundra and Olga Advances correlates closely with that of the Older and Younger Dryas cold episodes in northwestern Europe suggesting that these climatic oscillations were synchronous throughout the northern hemisphere.

  13. Impacts of climate and humans on the vegetation in northwestern Turkey: palynological insights from Lake Iznik since the Last Glacial

    NASA Astrophysics Data System (ADS)

    Miebach, Andrea; Niestrath, Phoebe; Roeser, Patricia; Litt, Thomas

    2016-03-01

    The Marmara region in northwestern Turkey provides a unique opportunity for studying the vegetation history in response to climate changes and anthropogenic impacts because of its location between different climate and vegetation zones and its long settlement history. Geochemical and mineralogical investigations of the largest lake in the region, Lake Iznik, already registered climate-related changes of the lake level and the lake mixing. However, a palynological investigation encompassing the Late Pleistocene to Middle Holocene was still missing. Here, we present the first pollen record of the last ca. 31 ka cal BP (calibrated kilo years before 1950) inferred from Lake Iznik sediments as an independent proxy for paleoecological reconstructions. Our study reveals that the vegetation in the Iznik area changed generally between (a) steppe during glacials and stadials indicating dry and cold climatic conditions, (b) forest-steppe during interstadials indicating milder and moister climatic conditions, and (c) oak-dominated mesic forest during interglacials indicating warm and moist climatic conditions. Moreover, a pronounced succession of pioneer trees, cold temperate, warm temperate, and Mediterranean trees appeared since the Lateglacial. Rapid climate changes, which are reflected by vegetation changes, can be correlated with Dansgaard-Oeschger (DO) events such as DO-4, DO-3, and DO-1, the Younger Dryas, and probably also the 8.2 event. Since the mid-Holocene, the vegetation was influenced by anthropogenic activities. During early settlement phases, the distinction between climate-induced and human-induced changes of the vegetation is challenging. Still, evidence for human activities consolidates since the Early Bronze Age (ca. 4.8 ka cal BP): cultivated trees, crops, and secondary human indicator taxa appeared, and forests were cleared. Subsequent fluctuations between extensive agricultural uses and regenerations of the natural vegetation become apparent.

  14. Warming-induced northwestward migration of the East Asian monsoon rain belt from the Last Glacial Maximum to the mid-Holocene.

    PubMed

    Yang, Shiling; Ding, Zhongli; Li, Yangyang; Wang, Xu; Jiang, Wenying; Huang, Xiaofang

    2015-10-27

    Glacial-interglacial changes in the distribution of C3/C4 vegetation on the Chinese Loess Plateau have been related to East Asian summer monsoon intensity and position, and could provide insights into future changes caused by global warming. Here, we present δ(13)C records of bulk organic matter since the Last Glacial Maximum (LGM) from 21 loess sections across the Loess Plateau. The δ(13)C values (range: -25‰ to -16‰) increased gradually both from the LGM to the mid-Holocene in each section and from northwest to southeast in each time interval. During the LGM, C4 biomass increased from <5% in the northwest to 10-20% in the southeast, while during the mid-Holocene C4 vegetation increased throughout the Plateau, with estimated biomass increasing from 10% to 20% in the northwest to >40% in the southeast. The spatial pattern of C4 biomass in both the LGM and the mid-Holocene closely resembles that of modern warm-season precipitation, and thus can serve as a robust analog for the contemporary East Asian summer monsoon rain belt. Using the 10-20% isolines for C4 biomass in the cold LGM as a reference, we derived a minimum 300-km northwestward migration of the monsoon rain belt for the warm Holocene. Our results strongly support the prediction that Earth's thermal equator will move northward in a warmer world. The southward displacement of the monsoon rain belt and the drying trend observed during the last few decades in northern China will soon reverse as global warming continues.

  15. Loess and floods: High-resolution multi-proxy data of Last Glacial Maximum (LGM) slackwater deposition in the Flinders Ranges, semi-arid South Australia

    NASA Astrophysics Data System (ADS)

    Haberlah, David; Williams, Martin A. J.; Halverson, Galen; McTainsh, Grant H.; Hill, Steven M.; Hrstka, Tomas; Jaime, Patricio; Butcher, Alan R.; Glasby, Peter

    2010-09-01

    Terrace remnants of late Pleistocene fine-grained valley-fill deposits (Silts) deeply entrenched by ephemeral traction load streams in arid areas remain a puzzle. They have been attributed to a variety of origins ranging from lacustrine to alluvial floodplains. We here report a centimetre-scale multi-proxy study of a 7 m section of Silts in the semi-arid Flinders Ranges of South Australia, which span the lead-up to and peak of the Last Glacial Maximum (LGM). The results of detailed lithostratigraphic mapping, high-resolution parametric particle-size analysis, Automated Mineralogy, induced magnetic susceptibility, carbon stable isotope geochemistry, and a chronostratigraphy based on 27 AMS radiocarbon and 6 luminescence ages are discussed in terms of sediment provenance, depositional environment and weathering history with the aim of reconstructing the regional palaeo-environment. The data are consistent with a fluctuating aeolian-fluvial interplay dominating the extended LGM environment with a greater impact on the landscape than all combined geomorphic processes since then. Accordingly, weathered slope mantles and loess accessions were eroded and entrained by numerous small and at least a dozen large-scale flood events, and trapped in an intra-montane floodplain extending into Brachina Gorge. Upstream of this narrow constriction, recurrent backflooding is discussed resulting in a thick sequence of layered to laminated slackwater couplets. Aggradation and degradation of valley-fills appear to be largely controlled by fine-sediment supply from the valley slopes, replenished by wind-blown dust from upwind playa lakes and source-bordering dunefields. In conclusion, this study demonstrates how dust storms and flooding rains can account for 'pluvial' features previously explained by the opposing effects of reduced precipitation and evaporation in the colder more arid glacial landscape of southern Australia.

  16. Glacial refugia in a maritime temperate climate: cicada (Kikihia subalpina) mtDNA phylogeography in New Zealand.

    PubMed

    Marshall, David C; Hill, Kathy B R; Fontaine, Kathryn M; Buckley, Thomas R; Simon, Chris

    2009-05-01

    Understanding the biological significance of Pleistocene glaciations requires knowledge of the nature and extent of habitat refugia during glacial maxima. An opportunity to examine evidence of glacial forest refugia in a maritime, Southern Hemisphere setting is found in New Zealand, where the extent of Pleistocene forests remains controversial. We used the mitochondrial phylogeography of a forest-edge cicada (Kikihia subalpina) to test the hypothesis that populations of this species survived throughout South Island during the Last Glacial Maximum. We also compared mitochondrial DNA phylogeographic patterns with male song patterns that suggest allopatric divergence across Cook Strait. Cytochrome oxidase I and II sequences were analyzed using network analysis, maximum-likelihood phylogenetic estimation, Bayesian dating and Bayesian skyline plots. K. subalpina haplotypes from North Island and South Island form monophyletic clades that are concordant with song patterns. Song divergence corresponds to approximately 2% genetic divergence, and Bayesian dating suggests that the North Island and South Island population-lineages became isolated around 761,000 years BP. Almost all South Island genetic variation is found in the north of the island, consistent with refugia in Marlborough Sounds, central Nelson and northwest Nelson. All central and southern South Island and Stewart Island haplotypes are extremely similar to northern South Island haplotypes, a 'northern richness/southern purity' pattern that mirrors genetic patterns observed in many Northern Hemisphere taxa. Proposed southern South Island forest habitat fragments may have been too small to sustain populations of K. subalpina, and/or they may have harboured ecological communities with no modern-day analogues.

  17. The influence of climate during and after a glacial surge - A comparison of the last two surges of Fridtjovbreen, Svalbard

    NASA Astrophysics Data System (ADS)

    Lønne, Ida

    2014-02-01

    Glacial surges are periods of fast flow, often limited in space and time, and driven by internal conditions which are not fully explained. The quantity and variety of documented case-studies and settings demonstrate that the critical variables are difficult to isolate. In an alternative approach, two surges from the same basin were compared at Fridtjovhamna; one of the few known sites where this is possible. Fridtjovbreen is a polythermal glacier that has been through two recent surges: the last event (1991-2002) occurred during an unusually warm period in the high Arctic, whereas the previous surge culminated in 1861, around the Little Ice Age when many Svalbard-glaciers had their maximum Holocene extent. Based on a multi-disciplinary study, processes and landforms from the two episodes were compared with respect to ice-front movement rates, formation and decay of ice-cored moraines and glacial meltwater drainage patterns. The study demonstrates that moraines and meltwater traces from the oldest surge, locally well preserved, provide excellent opportunities for reconstructing the behavior of the ice-mass. The last surge, however, took place during a period with ablation rates never seen at this latitude, and 10 years after the maximum extent, the deglaciated areas onshore hardly show traces from the event.

  18. The Thermal History of the East African Rift Lakes Region Since the Last Glacial Maximum Using TEX86 Paleothermometry

    NASA Astrophysics Data System (ADS)

    Berke, M. A.; Johnson, T. C.; Werne, J. P.; Schouten, S.; Sinninghe Damsté, J. S.

    2008-12-01

    We present preliminary results from a study using the TEX86 temperature proxy from sediments of East African Rift Lakes (including Lakes Turkana, Albert, and Malawi) to reconstruct the thermal history of tropical Africa for the last ~ 20,000 years at a subcentennial to multicentennial resolution. The TEX86 proxy, based on tetraether membrane lipids produced by lacustrine Crenarchaeota, has been shown to be successful at recording lake surface temperatures of some large lakes, including Lakes Malawi and Tanganyika, while providing unreasonable surface temperatures for lakes that receive a large input of soil material. The East African Rift Lakes are climatically sensitive, with the majority of water loss due to evaporation rather than outflow. Thus, they are useful for paleoclimate studies, being sensitive to even small changes in aridity. Temperature records from the northern and central basins of Lake Malawi agree well and fall within modern surface lake temperatures. A 2.5°C cooling is evident during the Younger Dryas in the northern basin record, with no response seen in the central basin. We are currently investigating mechanisms to explain why both records show a gradual cooling of 3°C during the late Holocene. Lake Albert shows an intriguing two-step cooling during the Younger Dryas, reaching temperatures 2.5°C lower than temperatures preceding or following this interval. The temperature record of Lake Turkana shows an interesting ~ 500 year cyclicity of low temperatures punctuated by abrupt warming events. Lakes Turkana and Albert show TEX86 paleotemperatures considerably lower (8°C cooler in Lake Albert and ~ 4°C cooler in Lake Turkana) than modern surface water temperatures. Although these records appear to fall in the range of temporal variability, these temperature discrepancies may indicate varying Crenarcheotal populations between lakes or other influencing factors.

  19. Glacial History of Southernmost South America and Implications for Movement of the Westerlies and Antarctic Frontal Zone

    NASA Astrophysics Data System (ADS)

    Kaplan, M. R.; Fogwill, C. J.; Hulton, N. R.; Sugden, D. E.; Peter, K. W.

    2004-12-01

    The ~1 Myr glacial geologic record in southern South American is one of the few available terrestrial paleoclimate proxies at orbital and suborbital time scales in the middle latitudes of the Southern Hemisphere. Presently, southernmost Patagonia lies about 3\\deg north of the Antarctic frontal zone and within the middle latitude westerlies and the climate is controlled by the surrounding maritime conditions. Thus, the long-term glacial record provides insight into the history of climatic boundaries over the middle and high latitude southern ocean, including the upwind SE Pacific Ocean, tectonic-glacial evolution of the Andes, and global climate. To date, cosmogenic nuclide and 14C dating have focused on glacial fluctuations between 51 and 53\\deg S (Torres del Paine to northern Tierra del Fuego) during the last glacial cycle, including the late glacial period. At least 4 advances occurred between ca. 25 and 17 ka, with the maximum expansion of ice ca. 25-24 ka. Major deglaciation commenced after ca. 17.5 ka, which was interrupted by a major glacial-climate event ca. 14-12 ka. Modelling experiments suggest that the ice mass needed to form the glacial maximum moraines required about a 6\\deg cooling and a slight drying relative to the present. Such a fundamental temperature reduction, despite high summer isolation, strongly suggests northward movement of the westerlies and the polar front on millennial timescales. The Patagonian record also indicates that on orbital timescales equatorward movement of climate boundaries and glacial growth was in phase with major Northern Hemisphere ice volume change, despite high local summer insolation. At suborbital timescales, the picture is more complex. While major facets of the last glacial maximum appear to be in phase between the hemispheres, at least some late glacial events may be in step with Antarctic climate change. Present and future research will further constrain the timing of glacial events over the last 1 Myr and

  20. Sedimentary record on the Indian Summer Monsoon since the Last Glacial Maximum: Evidence from the southeastern Andaman Sea

    NASA Astrophysics Data System (ADS)

    Shi, Xuefa; Liu, Shengfa; Cao, Peng; Khokiattiwong, Somkiat; Kornkanitnan, Narumol

    2016-04-01

    The Indian Summer Monsoon (ISM) generated by across-equatorial pressure gradient between the Asian continent and the southern Indian Ocean is a major component of the Asian monsoon system and establishes interactions among the ocean, land and atmosphere. Provenance and paleoclimate changes in the Andaman Sea during the last 26 ka were reconstructed from high-resolution records of grain-size, major elements and Sr-Nd isotopes in core ADM-9. The values of ɛNd(0) and 87Sr/86Sr were in good agreement with those of Irrawaddy River sediments, indicating a common source of origin. Two sensitive grain-size intervals (3.4-7.5 and 16.8-21.2 μm) were identified; the former was controlled primarily by sea-level change, whereas the latter was related to Irrawaddy River discharge and South-west Current transport driven by the ISM. Proxies of chemical weathering (K/Al) and terrigenous input (Ti/Ca) coupled with sensitive grain-size interval (16.8-21.2 μm population) revealed that the ISM was weak during ~15-26 ka BP and then strengthened gradually to a maximum during ~7-9 ka BP; subsequently, the ISM exhibited a generally declining trend to ~2 ka BP. The variation of the ISM recorded in this work is consistent with ISM variations observed in an open area in the northern Indian Ocean and in adjacent continents, implying the evolution of the Asia summer monsoon since 26 ka.

  1. Collapse of the California Current during glacial maxima linked to climate change on land.

    PubMed

    Herbert, T D; Schuffert, J D; Andreasen, D; Heusser, L; Lyle, M; Mix, A; Ravelo, A C; Stott, L D; Herguera, J C

    2001-07-06

    Time series of alkenone unsaturation indices gathered along the California margin reveal large (4 degrees to 8 degrees C) glacial-interglacial changes in sea surface temperature (SST) over the past 550,000 years. Interglacial times with SSTs equal to or exceeding that of the Holocene contain peak abundances in the pollen of redwood, the distinctive component of the temperate rainforest of the northwest coast of California. In the region now dominated by the California Current, SSTs warmed 10,000 to 15,000 years in advance of deglaciation at each of the past five glacial maxima. SSTs did not rise in advance of deglaciation south of the modern California Current front. Glacial warming along the California margin therefore is a regional signal of the weakening of the California Current during times when large ice sheets reorganized wind systems over the North Pacific. Both the timing and magnitude of the SST estimates suggest that the Devils Hole (Nevada) calcite record represents regional but not global paleotemperatures, and hence does not pose a fundamental challenge to the orbital ("Milankovitch") theory of the Ice Ages.

  2. Effect of low glacial atmospheric CO{sub 2} on tropical African montane vegetation

    SciTech Connect

    Jolly, D.; Haxeltine, A.

    1997-05-02

    Estimates of glacial-interglacial climate change in tropical Africa have varied widely. Results from a process-based vegetation model show how montane vegetation in East Africa shifts with changes in both carbon dioxide concentration and climate. For the last glacial maximum, the change in atmospheric carbon dioxide concentration alone could explain the observed replacement of tropical montane forest by a scrub biome. This result implies that estimates of the last glacial maximum tropical cooling based on tree-line shifts must be revised. 30 refs., 2 figs.

  3. Calibrating a Glaciological Model of the Greenland Ice Sheet From the Last Glacial Maximum to Present-day Using Field Observations of Relative sea Level and ice Extent

    NASA Astrophysics Data System (ADS)

    Simpson, M. J.; Milne, G. A.; Huybrechts, P.; Long, A. J.

    2008-12-01

    We constrain a three-dimensional thermomechnical model of Greenland Ice Sheet evolution from the Last Glacial Maximum (LGM, 21 ka BP) to the present-day using primarily observations of relative sea level as well as data on past ice extent. Our new model (Huy2) fits the majority of the observations and is characterised by a number of key features: (i) The ice sheet had a LGM excess volume (relative to present) of 4.1 m ice- equivalent sea-level which increased to a maximum value of 4.6 m at 16.5 ka BP; (ii) retreat from the continental shelf was not continuous around the entire margin (there was a readvance during the Younger Dryas) and the final episode of marine retreat was rapid and relatively late (c. 12 ka BP), leaving the ice sheet land based by 10 ka BP; (iii) in response to the Holocene Thermal Maximum the ice margin retreated behind its present-day position by up to 80 km in the southwest, 20 km in the south and 80 km in the northeast. As a result of this retreat, the modelled ice sheet reaches a minimum volume between 5 - 4 ka BP which corresponds to a rise of 0.17 m ice-equivalent sea-level since this time. Our results suggest that remaining discrepancies between the model and observations are likely associated with non-Greenland ice load, differences between modelled and observed present-day ice elevation around the margin, lateral variations in Earth structure and/or a diachronous ice margin retreat.

  4. Calibrating a glaciological model of the Greenland ice sheet from the Last Glacial Maximum to present-day using field observations of relative sea level and ice extent

    NASA Astrophysics Data System (ADS)

    Simpson, Matthew J. R.; Milne, Glenn A.; Huybrechts, Philippe; Long, Antony J.

    2009-08-01

    We constrain a three-dimensional thermomechanical model of Greenland ice sheet (GrIS) evolution from the Last Glacial Maximum (LGM, 21 ka BP) to the present-day using, primarily, observations of relative sea level (RSL) as well as field data on past ice extent. Our new model (Huy2) fits a majority of the observations and is characterised by a number of key features: (i) the ice sheet had an excess volume (relative to present) of 4.1 m ice-equivalent sea level at the LGM, which increased to reach a maximum value of 4.6 m at 16.5 ka BP; (ii) retreat from the continental shelf was not continuous around the entire margin, as there was a Younger Dryas readvance in some areas. The final episode of marine retreat was rapid and relatively late (c. 12 ka BP), leaving the ice sheet land based by 10 ka BP; (iii) in response to the Holocene Thermal Maximum (HTM) the ice margin retreated behind its present-day position by up to 80 km in the southwest, 20 km in the south and 80 km in a small area of the northeast. As a result of this retreat the modelled ice sheet reaches a minimum extent between 5 and 4 ka BP, which corresponds to a deficit volume (relative to present) of 0.17 m ice-equivalent sea level. Our results suggest that remaining discrepancies between the model and the observations are likely associated with non-Greenland ice load, differences between modelled and observed present-day ice elevation around the margin, lateral variations in Earth structure and/or the pattern of ice margin retreat.

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

    PubMed

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

    2016-02-10

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

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

    PubMed Central

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

    2016-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

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

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

    NASA Astrophysics Data System (ADS)

    Jiménez-Amat, Patricia; Zahn, Rainer

    2015-06-01

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

  9. Climate control on soil age and weathering thresholds in young, post-glacial soils of New Zealand

    NASA Astrophysics Data System (ADS)

    Dixon, J. L.; Chadwick, O.; Vitousek, P.

    2014-12-01

    Climate is often invoked as a major driver of soil and landscape evolution. But a coherent story has failed to emerge for how climate controls soil properties and weathering rates - partially due to competing influences of mineral residence times and supply rates in eroding landscapes. Here, we combine insights and methods across the related fields of geomorphology, soil science and geochemistry, to explore weathering thresholds in non-eroding, young soils along a strong precipitation gradient (400-4000 mm/yr) in the South Island of New Zealand. We studied ~30 soil profiles developed in thin (~1m) loess deposits that mantle LGM and post LGM moraines and outwash in the Waitaki catchment, extending from Lake Benmore to just below the Tasman glacier in the north. We find repeated thresholds (sharp, non-linear transitions) in soil chemistry, including exchangeable cations, pH and total elemental abundances. Abundance of pedogenic iron and aluminum increase with precipitation, stabilizing at ~2000 mm/yr. Plant-available phosphorous and exchangeable Ca and Mg are rapidly depleted as precipitation exceeds 1000 mm/yr. However total elemental abundances show up to 50% of major cations are retained at wetter sites, likely in less labile minerals. Preliminary numerical modeling of cation weathering kinetics provides some support for this interpretation. Together our data identify nonlinear changes in weathering intensity with rainfall, and show clear climate control on relatively young, post-glacial soil development. Additionally, we measured profiles and inventories of meteoric 10Be to quantify soil residence times across the climate gradient. This nuclide is cosmogenically produced in the atmosphere and binds strongly to reactive surfaces in soil following fallout. Exchangeable beryllium does not decrease with rainfall, despite decreasing pH along the climate gradient. Therefore we are confident that nuclide concentrations do not reflect leaching. Instead, these

  10. Convergence rates vs Exhumation rates: An indirect test of exhumation rates during the last glacial maximum in the St. Elias Orogen

    NASA Astrophysics Data System (ADS)

    Pavlis, T. L.; Serpa, L.; Bruhn, R. L.; Plafker, G.

    2002-12-01

    full P-Y convergence (which requires that GPS data are recording a strain transient that is not representative of long-term motion) or the undeformed deep-sea fan imaged in seismic data is too young to have accumulated sufficient deformation to produce finite structures visible in the seismic data. If the latter is true, the undeformed sediment must have accumulated entirely during the last glacial maximum, when glaciers dumped their sediment load directly off the continental shelf onto the deep sea fans. Drilling is ultimately needed to determine the age of the sediments, but if this hypothesis is correct, this observation would indicate erosion rates during the last glacial maximum that are comparable to Holocene rates.

  11. Evidence For The Role of Deep Sea Temperature In Glacial Climate and Carbon Cycles

    NASA Astrophysics Data System (ADS)

    Martin, P.; Archer, D.; Lea, D. W.

    Measurements of benthic foraminiferal Mg/Ca from the deep tropical Pacific (cores TR163-31P and 20B, 3.2 km water depth) provide a baseline for evaluating changes in deep sea temperature during the last glacial period. Mg/Ca variations of >50% (1.3 to 0.6 mmol/mol) imply temperature changes of ~4 deg. C. The most extreme and prolonged cold period was at the start of the last glacial (~80,000 BP), with near freezing bottom water temperatures marking the onset of continental glaciation. A second brief but pronounced cooling near ~35,000 BP coincides with the beginning of a second phase of glaciation. Millennial-scale variability in benthic Mg/Ca in the 20,000 year period between the two major episodes of ice growth is direct evidence for millennial-scale oscillations in deep water temperature. Over the last 90,000 years, oscillations in deep sea temperature show a clear correlation with Antarctic air temper- atures and atmospheric CO2. Throughout 5ky-long oscillations evident in Stage III, the paleodata show a relationship between CO2 and deep ocean T of~10 ppm/deg. C, consistent with new ocean GCM CO2 solubility results. However, to explain the full glacial-interglacial CO2 change, we still require external forcing (changes in ocean biology or pH, for example), or alternatively a mechanism to enhance the solubility sensitivity to global mean T in the ocean.

  12. Reconstructing the contribution of the Weddell Sea sector, Antarctica, to sea level rise since the last glacial maximum, using numerical modelling constrained by field evidence.

    NASA Astrophysics Data System (ADS)

    Le Brocq, A.; Bentley, M.; Hubbard, A.; Fogwill, C.; Sugden, D.

    2008-12-01

    A numerical ice sheet model constrained by recent field evidence is employed to reconstruct the Last Glacial Maximum (LGM) ice sheet in the Weddell Sea Embayment (WSE). Previous modelling attempts have predicted an extensive grounding line advance (to the continental shelf break) in the WSE, leading to a large equivalent sea level contribution for the sector. The sector has therefore been considered as a potential source for a period of rapid sea level rise (MWP1a, 20 m rise in ~500 years). Recent field evidence suggests that the elevation change in the Ellsworth mountains at the LGM is lower than previously thought (~400 m). The numerical model applied in this paper suggests that a 400 m thicker ice sheet at the LGM does not support such an extensive grounding line advance. A range of ice sheet surfaces, resulting from different grounding line locations, lead to an equivalent sea level estimate of 1 - 3 m for this sector. It is therefore unlikely that the sector made a significant contribution to sea level rise since the LGM, and in particular to MWP1a. The reduced ice sheet size also has implications for the correction of GRACE data, from which Antarctic mass balance calculations have been derived.

  13. Chlorine-36 and 14C chronology support a limited last glacial maximum across central Chukotka, northeastern Siberia, and no Beringian ice sheet

    USGS Publications Warehouse

    Brigham-Grette, J.; Gualtieri, L.M.; Glushkova, O.Y.; Hamilton, T.D.; Mostoller, D.; Kotov, A.

    2003-01-01

    The Pekulney Mountains and adjacent Tanyurer River valley are key regions for examining the nature of glaciation across much of northeast Russia. Twelve new cosmogenic isotope ages and 14 new radiocarbon ages in concert with morphometric analyses and terrace stratigraphy constrain the timing of glaciation in this region of central Chukotka. The Sartan Glaciation (Last Glacial Maximum) was limited in extent in the Pekulney Mountains and dates to ???20,000 yr ago. Cosmogenic isotope ages > 30,000 yr as well as non-finite radiocarbon ages imply an estimated age no younger than the Zyryan Glaciation (early Wisconsinan) for large sets of moraines found in the central Tanyurer Valley. Slope angles on these loess-mantled ridges are less than a few degrees and crest widths are an order of magnitude greater than those found on the younger Sartan moraines. The most extensive moraines in the lower Tanyurer Valley are most subdued implying an even older, probable middle Pleistocene age. This research provides direct field evidence against Grosswald's Beringian ice-sheet hypothesis. ?? 2003 Elsevier Science (USA). All rights reserved.

  14. Phylogeography of Littorina sitkana in the northwestern Pacific Ocean: evidence of eastward trans-Pacific colonization after the Last Glacial Maximum.

    PubMed

    Azuma, Noriko; Zaslavskaya, Nadezhda I; Yamazaki, Tomoyasu; Nobetsu, Takahiro; Chiba, Susumu

    2017-04-01

    We investigated genetic diversity and population structure of the Sitka periwinkle Littorina sitkana along the coastlines of the northwestern Pacific (NWP) to evaluate the possibility of trans-Pacific colonization of this species from the NWP to the northeastern Pacific (NEP) after the Last Glacial Maximum. We sampled L. sitkana from 32 populations in the NWP, and sequenced a region of the mitochondrial cytochrome b oxidase gene for population genetic analyses. The results were compared with those of previous reports from the NEP. The genetic diversity of L. sitkana was much higher in the NWP than in the NEP. Genetic connectivity between the NWP and NEP populations was indicated by an extremely abundant haplotype in the NEP that was also present in eastern Hokkaido and the Kuril Islands. To confirm these results, we compared sequences of the longest intron of the aminopeptidase N gene (APN54) in the nuclear genome in four populations of L. sitkana in the NWP with previous results from the NEP. Again, much higher genetic diversity was found in the NWP than in the NEP and genetic connectivity was supported between the Kuril Islands and the NEP. These results imply postglacial colonization of this species from the NWP to the NEP, probably along the Kuril and Aleutian Island chains. This study is the first report of possible trans-Pacific postglacial colonization of a direct-developing gastropod, inferred from genetic data.

  15. Qualitative assessment of PMIP3 rainfall simulations across the eastern African monsoon domains during the mid-Holocene and the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Chevalier, Manuel; Brewer, Simon; Chase, Brian M.

    2017-01-01

    In this paper we compare a compilation of multiproxy records spanning the eastern African margin with general circulation model simulations of seasonal precipitation fields for the mid-Holocene and the Last Glacial Maximum (LGM) carried out as part of the third phase of the Paleoclimate Modelling Intercomparison Project (PMIP3). Results show good agreement during the mid-Holocene (the '6K experiment'), with palaeodata and model outputs correlating well and indicating that changes in insolation drove a stronger northern African monsoon (north of ∼0-5°S) during the terminal "African Humid Period" and a weaker southeast African monsoon. For the LGM (the '21K experiment'), however, significant discrepancies exist both between model simulations, and between existing palaeodata and simulated conditions, both in terms of direction and amplitude of change. None of the PMIP3 simulations reflect the pattern inferred from the palaeodata. Two major discrepancies have been identified to explain this: 1) the limited sensitivity of the southern monsoon domain to the colder temperatures of the Indian Ocean (-2 °C), and 2) the absence of changes in the dynamic of the Indian Ocean Walker circulation over the entire basin, despite the exposure of the Sahul and Sunda shelves that weakened convection over the Indo-Pacific Warm Pool during the LGM. These results indicate that some major features of the atmospheric and oceanic teleconnections between the different monsoon regions require further consideration as models evolve.

  16. The silicon isotope composition of Ethmodiscus rex laminated diatom mats from the tropical West Pacific: Implications for silicate cycling during the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Xiong, Zhifang; Li, Tiegang; Algeo, Thomas; Doering, Kristin; Frank, Martin; Brzezinski, Mark A.; Chang, Fengming; Opfergelt, Sophie; Crosta, Xavier; Jiang, Fuqing; Wan, Shiming; Zhai, Bin

    2015-07-01

    The cause of massive blooms of Ethmodiscus rex laminated diatom mats (LDMs) in the eastern Philippine Sea (EPS) during the Last Glacial Maximum (LGM) remains uncertain. In order to better understand the mechanism of formation of E. rex LDMs from the perspective of dissolved silicon (DSi) utilization, we determined the silicon isotopic composition of single E. rex diatom frustules (δ30SiE. rex) from two sediment cores in the Parece Vela Basin of the EPS. In the study cores, δ30SiE. rex varies from -1.23‰ to -0.83‰ (average -1.04‰), a range that is atypical of marine diatom δ30Si and that corresponds to the lower limit of reported diatom δ30Si values of any age. A binary mixing model (upwelled silicon versus eolian silicon) accounting for silicon isotopic fractionation during DSi u