Abstracts / Quaternary International 279-280 (2012) 121–232172
a continuous lacustrine section of the past several hundred thousand yearsis expected to be accumulated. The drilling project funded by ICDP iscurrently (November–December 2010) underway. The team aims toestablish the environmental and paleoseismic history of the Levant Regionduring the past several hundred thousand years.
FINE-GRID SIMULATION OF ANTARCTIC ICE-STREAM DYNAMICS AT THELAST GLACIAL MAXIMUM
Nicholas R. Golledge. Antarctic Research Centre, Victoria University, NewZealandE-mail address: [email protected]
Until recently, numerical models were generally incapable of properlyresolving ice streams and other fine-scale (<10 km) glaciodynamic char-acteristics for entire continental-scale ice sheets, due to the computationalexpense of solving discretised flow equations across domains of >1e06(x, y) unknowns. The Parallel Ice Sheet Model (PISM - Bueler et al., 2010),however, now specifically fills that gap, and lends itself to the use of highperformance computing (HPC) facilities. We use the BlueFern supercom-puter (University of Canterbury, New Zealand) to implement PISM at 5 kmresolution across a domain of 2.8e07 km2 using 100 vertical layers, withthe aim of simulating the dynamical complexity of the expanded LGM icesheet in Antarctica. Using a sliding law that combines weighted solutionsto equations of both the shallow ice and shallow shelf approximations(SIA / SSA), our model predicts the magnitude of ice stream dischargesunder a range of scenarios representing contrasting basal sliding, internaldeformation, and oceanic conditions. The primary empirical constraintswe use to guide experimentation are cosmogenic surface exposure agesfrom locations around the periphery of the continent, and from a smallnumber of inland sites. Implicitly we also constrain the model with marinegeological data. Model results indicate that the present embayments of theBellingshausen, Amundsen, Ross and Weddell seas were instrumental indischarging large volumes of ice at the LGM, in accordance with geologicalevidence such as the distribution of mega-scale glacial lineations acrossthe continental shelf. Critically, our model demonstrates that these fociwere supplied with ice from extensive inland catchments via persistentfast-flowing conduits, in a manner analogous to that of present-dayAntarctic ice streams.
HIGH-RESOLUTION MODELLING OF PAST AND PRESENT GLACIER-CLIMATE SENSITIVITY IN THE NEW ZEALAND SOUTHERN ALPS
Nicholas R. Golledge. Antarctic Research Centre, Victoria University, NewZealandE-mail address: [email protected]
We use a three-dimensional thermomechanical ice-sheet model tonumerically simulate geologically mapped ice extents from the Last GlacialMaximum (LGM) to the present-day, in order to investigate the climaticcontrols on Southern Alps glaciation. To achieve the fine grid spacingsnecessary to accurately resolve small-scale glaciological flow features, weuse an ice sheet model that is specifically optimised for the parallel pro-cessing capability of high-performance computing facilities. Overa domain of c. 250000 km2 we achieve x, y resolution of 500 m witha vertical grid-spacing of 25 m. By iteratively tuning glaciological modelparameters to give consistent results under a range of climate scenarios(precipitation / temperature combinations), our experiments isolate theenvironmental changes necessary for each glacial episode. At LGM, ourmodel best replicates empirical limits when forced with a 7 K cooling and35 % reduction in precipitation. Under these conditions we simulatea linear mountain icefield extending much of the length of the MainDivide, feeding outlet glaciers that extend onto the lowland plains throughtopographic troughs. At their most extensive, modelled glaciers havesurface velocities up to c. 2.5 km/a, and are characterised by steep massbalance gradients. The modelled LGM glacier system is therefore highlydynamic, and responds sensitively to mass balance perturbations arisingfrom changes in forcing climate. These findings concur with previous
southern hemisphere modelling studies, and thus together may providea useful insight into mid-latitude climate sensitivity over the last c. 25 kyr.
CHARACTERIZING THE ROLE OF INTERNAL VARIABILITY IN REGIONALCLIMATE PALEOSIMULATIONS
Juan Jose Gómez-Navarro. University of Murcia, SpainE-mail address: [email protected]
The climate system fluctuates naturally over a large frequency range, fromdays to millions of years. In addition, it can also be affected by anthropo-genic greenhouse gasses emissions at multi-decadal scale. Understandingthe natural variability at multi centennial scale would help in assessinghow much of the recent warming is attributable to human activities.Efforts to assess the role of natural variability belong to two categories:climate reconstructions based on proxy indicators and climate modelsimulations. In this last respect, the use of Regional Climate Models, drivenby global simulations, may reduce the scale gap between both approachesand improve many aspects of the simulations performed with globalmodels. However, the models are affected by a strong chaotic internalvariability over a brad band of time scales, which may difficult thecomparison between them and proxy records. In this contribution wepresent a comparison of two simulations performedwith a climate versionof the mesoscalar model MM5 driven by the AOGCM ECHO-G over the lastmillennium (1001–1990) for a domain encompassing the Iberian Penin-sula. The only difference between the two runs is the initial conditions, andthus these experiments allow us to investigate the role of the externalforcing in influencing the evolution of several climate variables, comparedwith the magnitude of the internal variability. Results indicate that thelong-term evolution of temperature is largely governed by the externalforcings over all the domain. Precipitation is nevertheless much lessstrongly driven by the external forcings. The comparison of both runsallows us to identify areas over the IP where the evolution of precipitationis not significantly driven by random variability. In areas other than these(most part of the domain), comparison exercises with proxy reconstruc-tions are difficult, since this variable is does not clearly respond to externalforcing.
DID WARM INTERSTADIALS IN THE NORTH ATLANTIC ALWAYSCOINCIDE WITH HUMID INTERVALS IN NORTHERN SOUTH AMERICA?
Catalina González. Universidad de Los Andes, ColombiaE-mail address: [email protected]
Laminated sediments from the Cariaco Basin that have accumulated underanoxic conditions preserve an almost continuous record of unparalleltemporal resolution showing evidence for abrupt climate changes interrestrial and marine systems from northern South America. Thecomparison of pollen and spores (terrestrial proxies) with dinoflagellatescysts (marine proxy) provides important information on land-sea inter-actions. Back through marine isotope stage (MIS) 4 the palynologicalrecord displays a clear North Atlantic climatic variability. Here, northAtlantic warm periods are characterized by low reflectance values,enhancedmarine productivity, increased precipitation and river discharge,and expanded semi-deciduous forests, which are related to a northwardshift in themean latitudinal position of the Intertropical Convergence Zone(ITCZ). During cold stadial periods the opposite trend reveals a southwardmigration of the ITCZ. However, palynological results from core MD03-2622 suggest an opposite pattern for MIS 5. Dinocyst assemblages changeat around 70 ka from a more autotrophic–dominated towards a moreupwelling-dominated phytoplankton community. During MIS 5 light-coloured intervals, high percentages of runoff indicators and lowpercentages of upwelling dinocysts suggest that colder intervals duringMIS5 coincided with more humid conditions, opposed to what happensfromMIS 4 on. These sudden changes in phytoplankton communities seemto be related to reorganizations of the local-regional hydrography, whichhas a tight relationship with regional climate. By comparing these resultsto pollen data from the same core and to other available data we discuss
