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Ayako Abeouchi - One of the best experts on this subject based on the ideXlab platform.
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ice sheet configuration in the cmip5 pmip3 Last Glacial Maximum experiments
Geoscientific Model Development, 2015Co-Authors: Kurt Lambeck, W R Peltier, Masa Kageyama, Bette L Ottobliesner, Ayako Abeouchi, Fuyuki Saito, Pascale Braconnot, Sandy P Harrison, Lev TarasovAbstract:Abstract. We describe the creation of a data set describing changes related to the presence of ice sheets, including ice-sheet extent and height, ice-shelf extent, and the distribution and elevation of ice-free land at the Last Glacial Maximum (LGM), which were used 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 in 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. Although largely confined to the ice-covered regions, differences between the climate response to the individual LGM reconstructions extend over the North Atlantic Ocean and Northern Hemisphere continents, partly through atmospheric stationary waves. Differences between the climate response to the CMIP5/PMIP3 composite and any individual ice-sheet reconstruction are smaller than those between the CMIP5/PMIP3 composite and the ice sheet used in the Last phase of PMIP (PMIP2).
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modelling the antarctic marine cryosphere at the Last Glacial Maximum
Annals of Glaciology, 2015Co-Authors: Kazuya Kusahara, Ayako Abeouchi, Tatsuru Sato, Takashi Obase, Ralf Greve, Hiroyasu HasumiAbstract:We estimate the sea-ice extent and basal melt of Antarctic ice shelves at the Last Glacial Maximum (LGM) using a coupled ice-shelf-sea-ice-ocean model. The shape of Antarctic ice shelves, ocean conditions and atmospheric surface conditions at the LGM are different from those in the present day; these are derived from an ice-shelf-ice-sheet model, a sea-ice-ocean model and a climate model for Glacial simulations, respectively. The winter sea ice in the LGM is shown to extend up to ∼7° of latitude further equatorward than in the present day. For the LGM summer, the model shows extensive sea-ice cover in the Atlantic sector and little sea ice in the other sectors. These modelled sea-ice features are consistent with those reconstructed from sea-floor sedimentary records. Total basal melt of Antarctic ice shelves in the LGM was ∼2147 Gt a –1 , which is much larger than the present-day value. More warm waters originating from Circumpolar Deep Water could be easily transported into ice-shelf cavities during the LGM because the full Glacial grounding line extended to shelf break regions and ice shelves overhung continental slopes. This increased transport of warm water masses underneath an ice shelf and into their basal cavities led to the high basal melt of ice shelves in the LGM.
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the southern westerlies during the Last Glacial Maximum in pmip2 simulations
Climate Dynamics, 2009Co-Authors: Maisa Rojas, Masa Kageyama, Esther C Brady, Michel Crucifix, Ayako Abeouchi, Patricio I Moreno, Chris Hewitt, Rumi Ohgaito, Pandora HopeAbstract:The Southern Hemisphere westerly winds are an important component of the climate system at hemispheric and global scales. Variations in their intensity and latitudinal position through an ice-age cycle have been proposed as important drivers of global climate change due to their influence on deep-ocean circulation and changes in atmospheric CO2. The position, intensity, and associated climatology of the southern westerlies during the Last Glacial Maximum (LGM), however, is still poorly understood from empirical and modelling standpoints. Here we analyse the behaviour of the southern westerlies during the LGM using four coupled ocean-atmosphere simulations carried out by the Palaeoclimate Modelling Intercomparison Project Phase 2 (PMIP2). We analysed the atmospheric circulation by direct inspection of the winds and by using a cyclone tracking software to indicate storm tracks. The models suggest that changes were most significant during winter and over the Pacific ocean. For this season and region, three out four models indicate decreased wind intensities at the near surface as well as in the upper troposphere. Although the LGM atmosphere is colder and the equator to pole surface temperature gradient generally increases, the tropospheric temperature gradients actually decrease, explaining the weaker circulation. We evaluated the atmospheric influence on the Southern Ocean by examining the effect of wind stress on the Ekman pumping. Again, three of the models indicate decreased upwelling in a latitudinal band over the Southern Ocean. All models indicate a drier LGM than at present with a clear decrease in precipitation south of 40°S over the oceans. We identify important differences in precipitation anomalies over the land masses at regional scale, including a drier climate over New Zealand and wetter over NW Patagonia.
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Last Glacial Maximum ocean thermohaline circulation pmip2 model intercomparisons and data constraints
Geophysical Research Letters, 2007Co-Authors: Bette L Ottobliesner, Esther C Brady, Michel Crucifix, C D Hewitt, Thomas M Marchitto, Ayako Abeouchi, Shingo Murakami, S L WeberAbstract:The ocean thermohaline circulation is important for transports of heat and the carbon cycle. We present results from PMIP2 coupled atmosphere-ocean simulations with four climate models that are also being used for future assessments. These models give very different Glacial thermohaline circulations even with comparable circulations for present. An integrated approach using results from these simulations for Last Glacial Maximum (LGM) with proxies of the state of the Glacial surface and deep Atlantic supports the interpretation from nutrient tracers that the boundary between North Atlantic Deep Water and Antarctic Bottom Water was much shallower during this period. There is less constraint from this integrated reconstruction regarding the strength of the LGM North Atlantic overturning circulation, although together they suggest that it was neither appreciably stronger nor weaker than modern. Two model simulations identify a role for sea ice in both hemispheres in driving the ocean response to Glacial forcing.
Yusuke Yokoyama - One of the best experts on this subject based on the ideXlab platform.
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rapid glaciation and a two step sea level plunge into the Last Glacial Maximum
Nature, 2018Co-Authors: Yusuke Yokoyama, Tezer M Esat, William G Thompson, Alexander L Thomas, Jody M Webster, Yosuke Miyairi, Chikako Sawada, Takahiro Aze, Hiroyuki MatsuzakiAbstract:The approximately 10,000-year-long Last Glacial Maximum, before the termination of the Last ice age, was the coldest period in Earth’s recent climate history1. Relative to the Holocene epoch, atmospheric carbon dioxide was about 100 parts per million lower and tropical sea surface temperatures were about 3 to 5 degrees Celsius lower2,3. The Last Glacial Maximum began when global mean sea level (GMSL) abruptly dropped by about 40 metres around 31,000 years ago4 and was followed by about 10,000 years of rapid deglaciation into the Holocene1. The masses of the melting polar ice sheets and the change in ocean volume, and hence in GMSL, are primary constraints for climate models constructed to describe the transition between the Last Glacial Maximum and the Holocene, and future changes; but the rate, timing and magnitude of this transition remain uncertain. Here we show that sea level at the shelf edge of the Great Barrier Reef dropped by around 20 metres between 21,900 and 20,500 years ago, to −118 metres relative to the modern level. Our findings are based on recovered and radiometrically dated fossil corals and coralline algae assemblages, and represent relative sea level at the Great Barrier Reef, rather than GMSL. Subsequently, relative sea level rose at a rate of about 3.5 millimetres per year for around 4,000 years. The rise is consistent with the warming previously observed at 19,000 years ago1,5, but we now show that it occurred just after the 20-metre drop in relative sea level and the related increase in global ice volumes. The detailed structure of our record is robust because the Great Barrier Reef is remote from former ice sheets and tectonic activity. Relative sea level can be influenced by Earth’s response to regional changes in ice and water loadings and may differ greatly from GMSL. Consequently, we used glacio-isostatic models to derive GMSL, and find that the Last Glacial Maximum culminated 20,500 years ago in a GMSL low of about −125 to −130 metres.
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microfacies and diagenesis of older pleistocene pre Last Glacial Maximum reef deposits great barrier reef australia iodp expedition 325 a quantitative approach
Sedimentology, 2013Co-Authors: Eberhard Gischler, Yusuke Yokoyama, Alexander L Thomas, Jody M Webster, Andre W Droxler, Bernd R SchoneAbstract:During Integrated Ocean Drilling Program Expedition 325, 34 holes were drilled along five transects in front of the Great Barrier Reef of Australia, penetrating some 700 m of late Pleistocene reef deposits (post-Glacial; largely 20 to 10 kyr bp) in water depths of 42 to 127 m. In seven holes, drilled in water depths of 42 to 92 m on three transects, older Pleistocene (older than Last Glacial Maximum, >20 kyr bp) reef deposits were recovered from lower core sections. In this study, facies, diagenetic features, mineralogy and stable isotope geochemistry of 100 samples from six of the latter holes were investigated and quantified. Lithologies are dominated by grain-supported textures, and were to a large part deposited in high-energy, reef or reef slope environments. Quantitative analyses allow 11 microfacies to be defined, including mixed skeletal packstone and grainstone, mudstone-wackestone, coral packstone, coral grainstone, coralline algal grainstone, coral-algal packstone, coralline algal packstone, Halimeda grainstone, microbialite and caliche. Microbialites, that are common in cavities of younger, post-Glacial deposits, are rare in pre-Last Glacial Maximum core sections, possibly due to a lack of open framework suitable for colonization by microbes. In pre-Last Glacial Maximum deposits of holes M0032A and M0033A (>20 kyr bp), marine diagenetic features are dominant; samples consist largely of aragonite and high-magnesium calcite. Holes M0042A and M0057A, which contain the oldest rocks (>169 kyr bp), are characterized by meteoric diagenesis and samples mostly consist of low-magnesium calcite. Holes M0042A, M0055A and M0056A (>30 kyr bp), and a horizon in the upper part of hole M0057A, contain both marine and meteoric diagenetic features. However, only one change from marine to meteoric pore water is recorded in contrast with the changes in diagenetic environment that might be inferred from the sea-level history. Values of stable isotopes of oxygen and carbon are consistent with these findings. Samples from holes M0032A and M0033A reflect largely positive values (δ18O: −1 to +1‰ and δ13C: +1 to +4‰), whereas those from holes M0042A and M0057A are negative (δ18O: −4 to +2‰ and δ13C: −8 to +2‰). Holes M0055A and M0056A provide intermediate values, with slightly positive δ13C, and negative δ18O values. The type and intensity of meteroric diagenesis appears to have been controlled both by age and depth, i.e. the time available for diagenetic alteration, and reflects the relation between reef deposition and sea-level change.
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timing of the Last Glacial Maximum from observed sea level minima
Nature, 2000Co-Authors: Yusuke Yokoyama, Kurt Lambeck, Patrick De Deckker, Paul Johnston, Keith L FifieldAbstract:During the Last Glacial Maximum, ice sheets covered large areas in northern latitudes, and global temperatures were significantly lower than today. But few direct estimates exist of the volume of the ice sheets, or the timing and rates of change during their advance and retreat. Here we analyze four distinct sediment facies in the shallow, tectonically stable Bonaparte Gulf, Australia - each of which is characteristic of a distinct range in sea level - to estimate the Maximum volume of land-based ice during the Last glaciation and the timing of the initial melting phase. We use faunal assemblages and preservation status of the sediments to distinguish open marine, shallow marine, marginal marine and brackish conditions, and estimate the timing and the mass of the ice sheets using radiocarbon dating and glacio-hydroisostatic modelling. Our results indicate that from at least 22,000 to 19,000 (calendar) years before present, land-based ice volume was at its Maximum, exceeding today's grounded ice sheets by 52.5 x 10 exp 6 cu km. A rapid decrease in ice volume by about 10 percent within a few hundred years terminated the Last Glacial Maximum at 19,000 +/- 250 years.
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refining the eustatic sea level curve since the Last Glacial Maximum using far and intermediate field sites
Earth and Planetary Science Letters, 1998Co-Authors: Kevin Fleming, Yusuke Yokoyama, Kurt Lambeck, Paul Johnston, Dan Zwartz, John ChappellAbstract:The eustatic component of relative sea-level change provides a measure of the amount of ice transferred between the continents and oceans during Glacial cycles. This has been quantified for the period since the Last Glacial Maximum by correcting observed sea-level change for the glacio-hydro-isostatic contributions using realistic ice distribution and earth models. During the Last Glacial Maximum (LGM) the eustatic sea level was 125±5 m lower than the present day, equivalent to a land-based ice volume of (4.6–4.9)×107 km3. Evidence for a non-uniform rise in eustatic sea level from the LGM to the end of the deglaciation is examined. The initial rate of rise from ca. 21 to 17 ka was relatively slow with an average rate of ca. 6 m ka−1, followed by an average rate of ca. 10 m ka−1 for the next 10 ka. Significant departures from these average rates may have occurred at the time of the Younger Dryas and possibly also around 14 ka. Most of the decay of the large ice sheets was completed by 7 ka, but 3–5 m of water has been added to the oceans since that time.
David S Battisti - One of the best experts on this subject based on the ideXlab platform.
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the partitioning of meridional heat transport from the Last Glacial Maximum to co2 quadrupling in coupled climate models
Journal of Climate, 2020Co-Authors: Aaron Donohoe, David S Battisti, Kyle C Armour, Gerard H Roe, Lily HahnAbstract:AbstractMeridional heat transport (MHT) is analyzed in ensembles of coupled climate models simulating climate states ranging from the Last Glacial Maximum (LGM) to quadrupled CO2. MHT is partitione...
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sensitivity of the atlantic intertropical convergence zone to Last Glacial Maximum boundary conditions
Paleoceanography, 2003Co-Authors: John C H Chiang, Michela Biasutti, David S BattistiAbstract:[1] Recent paleoproxy records suggest that the mean latitude of the Atlantic Intertropical Convergence Zone (ITCZ) varied synchronously with North Atlantic climate over a range of timescales throughout the Holocene and Last Glacial Maximum. We show that the present-day “meridional mode” of atmosphere-ocean variability in the tropical Atlantic is a potentially useful model for understanding these paleoclimate changes. The tropical Atlantic in a coupled atmospheric general circulation and slab ocean model responds to Last Glacial Maximum conditions with a southward displacement of the ITCZ. This response arises primarily through the land ice sheet that forces increased North Atlantic trades analogous to the forcing on the present-day meridional mode. Changes to sea ice coverage and to ocean heat transport associated with a weakened Atlantic thermohaline circulation also cause a meridional mode response, though through different mechanisms. Our results highlight the potential for tropical Atlantic paleoclimate to be driven from the high latitude influences, in particular, land ice on Glacial-interGlacial timescales.
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the importance of tropical sea surface temperature patterns in simulations of Last Glacial Maximum climate
Journal of Climate, 2001Co-Authors: Jeffrey H Yin, David S BattistiAbstract:Abstract Prescribed SST experiments are performed using the National Center for Atmospheric Research’s Community Climate Model version 3 general circulation model to isolate the contribution of the tropical SSTs reconstructed by the Climate, Long-range Investigation, Mapping and Prediction study (CLIMAP) to the modeled global atmospheric circulation anomalies at the Last Glacial Maximum (LGM). The changes in tropical SST patterns cause changes in tropical convection that force large (>300 m in 500-mb geopotential height) changes in Northern Hemisphere wintertime circulation. These midlatitude circulation changes occur despite the small (1°C) change in the mean tropical SST between the present and the CLIMAP reconstruction. In fact, the midlatitude circulation changes due to the difference in the tropical SST pattern between the present and the CLIMAP reconstruction are greater than the circulation changes due to a uniform tropical SST cooling of 3°C or those due to the presence of the LGM ice sheets. The ...
W R Peltier - One of the best experts on this subject based on the ideXlab platform.
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ice sheet configuration in the cmip5 pmip3 Last Glacial Maximum experiments
Geoscientific Model Development, 2015Co-Authors: Kurt Lambeck, W R Peltier, Masa Kageyama, Bette L Ottobliesner, Ayako Abeouchi, Fuyuki Saito, Pascale Braconnot, Sandy P Harrison, Lev TarasovAbstract:Abstract. We describe the creation of a data set describing changes related to the presence of ice sheets, including ice-sheet extent and height, ice-shelf extent, and the distribution and elevation of ice-free land at the Last Glacial Maximum (LGM), which were used 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 in 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. Although largely confined to the ice-covered regions, differences between the climate response to the individual LGM reconstructions extend over the North Atlantic Ocean and Northern Hemisphere continents, partly through atmospheric stationary waves. Differences between the climate response to the CMIP5/PMIP3 composite and any individual ice-sheet reconstruction are smaller than those between the CMIP5/PMIP3 composite and the ice sheet used in the Last phase of PMIP (PMIP2).
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on eustatic sea level history Last Glacial Maximum to holocene
Quaternary Science Reviews, 2002Co-Authors: W R PeltierAbstract:Abstract This paper addresses the question of the magnitude and time dependence of the globally averaged (eustatic) rise of sea level that occurred subsequent to the time of Last Glacial Maximum (LGM) at approximately 21,000 calendar years before present. Through the analysis of relative sea level (RSL) histories predicted by a realistic mass conserving and gravitationally self-consistent theory of postGlacial sea level change, it is demonstrated that there are preferred oceanic locations at which this eustatic function is well approximated by local sea level history. One such location is the Island of Barbados in the Caribbean Sea, a site from which a coral based record exists that extends from mid-Holocene to LGM. Because of the sea level ambiguity that is inherent to coral based records, however, it is important that the global ice-equivalent eustatic sea level curve inferred on the basis of the Barbados data be tested against observations at other locations from which similarly extensive records are also available but which are derived on the basis of sea level indicators which are not subject to the ambiguities inherent to corals. It is shown that, when the eustatic function employed in the global theoretical model is tuned so as to enable the model to fit the Barbados observations, where the Maximum relative sea level (RSL) depression is assumed to be near 120 m, then the theory misfits the record from the Sunda Shelf in the Indonesian Archipelago as well as the record from J. Bonaparte Gulf in northern Australia. Both of these recently published records appear to constrain the LGM low stand of RSL to a value above 120 m. The implications of these results for interpretation of the long coral derived records from the Huon Peninsula of Papua, New Guinea and the island of Tahiti are also discussed.
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global water balance and atmospheric water vapour transport at Last Glacial Maximum climate simulations with the canadian climate centre for modelling and analysis atmospheric general circulation model
Canadian Journal of Earth Sciences, 2000Co-Authors: G Vettoretti, W R Peltier, N A McfarlaneAbstract:A series of new simulations of the climate state at Last Glacial Maximum has been performed using the Canadian second-generation atmospheric general circulation model and are described herein. The ...
Simon T Belt - One of the best experts on this subject based on the ideXlab platform.
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nordic seas polynyas and their role in preconditioning marine productivity during the Last Glacial Maximum
Nature Communications, 2018Co-Authors: Jochen Knies, Denizcan Koseoglu, Leif Rise, Nicole J Baeten, Valerie K Bellec, Reidulv Boe, Martin Klug, Giuliana Panieri, Patrycja E Jernas, Simon T BeltAbstract:Arctic and Antarctic polynyas are crucial sites for deep-water formation, which helps sustain global ocean circulation. During Glacial times, the occurrence of polynyas proximal to expansive ice sheets in both hemispheres has been proposed to explain limited ocean ventilation and a habitat requirement for marine and higher-trophic terrestrial fauna. Nonetheless, their existence remains equivocal, not least due to the hitherto paucity of sufficiently characteristic proxy data. Here we demonstrate polynya formation in front of the NW Eurasian ice sheets during the Last Glacial Maximum (LGM), which resulted from katabatic winds blowing seaward of the ice shelves and upwelling of warm, sub-surface Atlantic water. These polynyas sustained ice-sheet build-up, ocean ventilation, and marine productivity in an otherwise Glacial Arctic desert. Following the catastrophic meltwater discharge from the collapsing ice sheets at ~17.5 ka BP, polynya formation ceased, marine productivity declined dramatically, and sea ice expanded rapidly to cover the entire Nordic Seas.
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Nordic Seas polynyas and their role in preconditioning marine productivity during the Last Glacial Maximum
Nature Publishing Group, 2018Co-Authors: Jochen Knies, Denizcan Koseoglu, Leif Rise, Valerie K Bellec, Reidulv Boe, Martin Klug, Giuliana Panieri, Patrycja E Jernas, Nicole Baeten, Simon T BeltAbstract:Polynyas potentially played a role in sustaining marine life during the Last Glacial, yet their presence and importance remains equivocal. This multi-proxy study reconstructs a corridor of polynyas in the Nordic Seas during the Last Glacial Maximum, and reveals a strong association with biological productivity
