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Jerry X Mitrovica - One of the best experts on this subject based on the ideXlab platform.
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was the laurentide ice sheet significantly reduced during Marine Isotope Stage 3
Geology, 2019Co-Authors: Tamara Pico, April S Dalton, Peter J Barnett, Sarah A Finkelstein, Steven L Forman, Jerry X MitrovicaAbstract:Accurately reconstructing the paleogeography of the Laurentide Ice Sheet (LIS) during Marine Isotope Stage 3 (MIS 3; ca. 57,000 to ca. 29,000 yr B.P.) is critical for understanding glacial growth toward the Last Glacial Maximum (LGM), refining sea-level histories, and studying the Earth system response to rapid climate change events. Here, we present a geochronological data set useful for testing hypotheses of global sea level and refining ice sheet configuration through this interval. Data (n = 735) span the entire MIS 3 interval and consist of 14C determinations (n = 651), cosmogenic exposure ages (n = 52), and optically stimulated luminescence dates (n = 32). On that basis, we hypothesize that the central region of the LIS underwent a dramatic reduction in ice from ca. 52 to 40 ka. Key to this hypothesis are geological records at sites in the Hudson Bay Lowlands (east central Canada) that suggest a Marine incursion and development of terrestrial landscapes. We show that these landscapes are consistent with recently published glacial isostatic adjustment predictions that include widespread deglaciation of the eastern (Labrador) sector of the LIS with ice buildup over the western (Keewatin) sector at 42 ka. Ice growth from this minimum toward the LGM is likely to have been rapid. The agreement between this data set and modeling predictions prompts the reassessment of key Late Pleistocene records, including Heinrich events, loess deposition in the continental United States, and sedimentological records from the Gulf of Mexico.
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sensitivity of last interglacial sea level high stands to ice sheet configuration during Marine Isotope Stage 6
Quaternary Science Reviews, 2017Co-Authors: Jacqueline Austermann, S Dendy, Jessica R Creveling, Jerry X MitrovicaAbstract:Abstract Estimates of peak global mean sea level (GMSL) during the Last Interglacial (LIG, ∼129-116 ka) based on geological sea level high-stand markers require a correction for the contaminating influence of glacial isostatic adjustment (GIA). This correction is obtained by calculating the viscoelastic response of the Earth to changes in the ice and ocean load prior to and following the LIG. While ice retreat over the last deglaciation is relatively well constrained, changes in ice cover prior to the LIG are more uncertain. We investigate the sensitivity of numerical predictions of GIA during the LIG to variations in the geometry of pre-LIG ice cover and the timing of the deglaciation into the LIG, with a particular focus on Marine Isotope Stage (MIS) 6 (∼190-130 ka). We demonstrate that reconstructing the pre-LIG ice history by replicating the last glacial cycle back in time, rather than using ice volume approximations based on oxygen Isotope records, can introduce errors in LIG high-stand predictions of ∼5 m at sites on the peripheral bulge of major ice complexes, and up to ∼2 m at far-field sites. We also demonstrate that predictions of LIG sea level are more sensitive to the geographic distribution of ice cover during MIS 6 than previously recognized. Adopting simulations which vary the relative size of Late Pleistocene ice cover over North America and Eurasia can yield a change in predicted high-stand elevations of ∼5 m in both the near and far field of northern hemisphere ice sheets. This far-field sensitivity arises, in part, from the reorientation of Earth's rotation axis during MIS 6, which in turn drives sea-level changes with a distinct geographic signature. In future work we will apply the insights gained here to re-evaluate the observed geographic variability in geological high-stand markers of LIG age and estimates of GMSL based upon them.
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collapse of polar ice sheets during the Stage 11 interglacial
Nature, 2012Co-Authors: Maureen E Raymo, Jerry X MitrovicaAbstract:The magnitude of sea level rise during Marine Isotope Stage 11 (about 400,000 years ago) is shown to have been probably only 6 to 13 metres, in contrast to some earlier estimates of up to 20 metres. The ice sheets in Greenland and West Antarctica are known to be susceptible to climate warming, and both are losing mass. How the East Antarctic Ice Sheet will respond to warming is less clear. Recent evidence from shoreline features in Bermuda and the Bahamas suggested that during Marine Isotope Stage 11 — a period of warming that occurred about 400,000 years ago — the sea level was 20 metres higher than it is today, which pointed to significant melting of the East Antarctic Ice Sheet. Now, an estimate that takes into account post-glacial crustal subsidence of the shoreline sites during an anomalously long interglacial period puts the sea level during Stage 11 at 6–13 metres higher than today. That can be explained by the collapse of the Greenland and West Antarctic ice sheets, with only a small contribution from the East Antarctic Ice Sheet. Contentious observations of Pleistocene shoreline features on the tectonically stable islands of Bermuda and the Bahamas have suggested that sea level about 400,000 years ago was more than 20 metres higher than it is today1,2,3,4. Geochronologic and geomorphic evidence indicates that these features formed during interglacial Marine Isotope Stage (MIS) 11, an unusually long interval of warmth during the ice age1,2,3,4. Previous work has advanced two divergent hypotheses for these shoreline features: first, significant melting of the East Antarctic Ice Sheet, in addition to the collapse of the West Antarctic Ice Sheet and the Greenland Ice Sheet1,2,3; or second, emplacement by a mega-tsunami during MIS 11 (ref. 4, 5). Here we show that the elevations of these features are corrected downwards by ∼10 metres when we account for post-glacial crustal subsidence of these sites over the course of the anomalously long interglacial. On the basis of this correction, we estimate that eustatic sea level rose to ∼6–13 m above the present-day value in the second half of MIS 11. This suggests that both the Greenland Ice Sheet and the West Antarctic Ice Sheet collapsed during the protracted warm period while changes in the volume of the East Antarctic Ice Sheet were relatively minor, thereby resolving the long-standing controversy over the stability of the East Antarctic Ice Sheet during MIS 11.
Richard G Roberts - One of the best experts on this subject based on the ideXlab platform.
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the nubian complex of dhofar oman an african middle stone age industry in southern arabia
PLOS ONE, 2011Co-Authors: Jeffrey I Rose, Vitaly I Usik, Anthony E Marks, Yamandu H Hilbert, Christopher S Galletti, Ash Parton, Jean Marie Geiling, Viktor Cerný, Mike W Morley, Richard G RobertsAbstract:Despite the numerous studies proposing early human population expansions from Africa into Arabia during the Late Pleistocene, no archaeological sites have yet been discovered in Arabia that resemble a specific African industry, which would indicate demographic exchange across the Red Sea. Here we report the discovery of a buried site and more than 100 new surface scatters in the Dhofar region of Oman belonging to a regionally-specific African lithic industry - the late Nubian Complex - known previously only from the northeast and Horn of Africa during Marine Isotope Stage 5, ∼128,000 to 74,000 years ago. Two optically stimulated luminescence age estimates from the open-air site of Aybut Al Auwal in Oman place the Arabian Nubian Complex at ∼106,000 years ago, providing archaeological evidence for the presence of a distinct northeast African Middle Stone Age technocomplex in southern Arabia sometime in the first half of Marine Isotope Stage 5.
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middle paleolithic occupation on a Marine Isotope Stage 5 lakeshore in the nefud desert saudi arabia
Quaternary Science Reviews, 2011Co-Authors: Michael D Petraglia, Abdullah Alsharekh, Remy Crassard, Nicholas Drake, Huw S Groucutt, Adrian G Parker, Richard G RobertsAbstract:Major hydrological variations associated with glacial and interglacial climates in North Africa and the Levant have been related to Middle Paleolithic occupations and dispersals, but suitable archaeological sites to explore such relationships are rare on the Arabian Peninsula. Here we report the discovery of Middle Paleolithic assemblages in the Nefud Desert of northern Arabia associated with stratified deposits dated to 75,000 years ago. The site is located in close proximity to a substantial relict lake and indicates that Middle Paleolithic hominins penetrated deeply into the Arabian Peninsula to inhabit landscapes vegetated by grasses and some trees. Our discovery supports the hypothesis of range expansion by Middle Paleolithic populations into Arabia during the final humid phase of Marine Isotope Stage 5, when environmental conditions were still favorable.
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late acheulean hominins at the Marine Isotope Stage 6 5e transition in north central india
Quaternary Research, 2011Co-Authors: Michael Haslam, Jacqueline L Fenwick, Ceri Shipton, Peter Ditchfield, M.c. Gupta, Richard G Roberts, Nicole Boivin, Atul Dubey, Michael D PetragliaAbstract:Single-grain optically stimulated luminescence dating was applied to Late Quaternary sediments at two sites in the Middle Son Valley, Madhya Pradesh, India. Designated Bamburi 1 and Patpara, these sites contain Late Acheulean stone tool assemblages, which we associate with non-modern hominins. Age determinations of 140–120 ka place the formation of these sites at around the Marine Oxygen Isotope Stage 6–5 transition, placing them among the youngest Acheulean sites in the world. We present here the geochronology and sedimentological setting of these sites, and consider potential implications of Late Pleistocene archaic habitation in north-central India for the initial dispersal of modern humans across South Asia.
Malcolm T. Mcculloch - One of the best experts on this subject based on the ideXlab platform.
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phasing and amplitude of sea level and climate change during the penultimate interglacial
Nature Geoscience, 2009Co-Authors: Andrea Dutton, Tezer M Esat, Kurt Lambeck, Edouard Bard, Fabrizio Antonioli, Malcolm T. MccullochAbstract:The penultimate interglacial period was punctuated by three sea-level highstands. Uranium–thorium ages obtained from speleothems in Italian caves show that the relationship between the timing of the peaks in sea level and Northern Hemisphere insolation is dependent on the previous extent of continental ice sheets. Earth’s climate has oscillated between short-lived interglacial and extended glacial periods for the past million years. Before the last interglacial, absolutely dated markers of sea level become increasingly rare; hence, our knowledge of sea-level change driven by the waxing and waning of continental ice sheets before that time is largely based on proxy records from deep-sea cores1,2,3 that lack direct age control. Here we present precise U–Th ages for a remarkable collection of submerged speleothems4,5 from Italy, which record three sea-level highstands during the penultimate interglacial period, Marine Isotope Stage 7, from 245,000 to 190,000 years ago. We find that sea level rose above −18 m (relative to modern sea level) several thousand years before maximum Northern Hemisphere insolation during the first and third highstands. In contrast, the second highstand, Marine Isotope Stage 7.3, is essentially synchronous with the insolation maximum, and sea level during this highstand only peaked at about −18 m, even though the concurrent insolation forcing was the strongest of the three highstands. We attribute the different phasing and amplitude of the Marine Isotope Stage 7.3 highstand to the extensive continental glaciation that preceded it. This finding highlights the significance of cryosphere response time to the climate system.
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orbital forcing of the Marine Isotope Stage 9 interglacial
Science, 2001Co-Authors: Claudine H Stirling, Tezer M Esat, Steve G Blake, Kurt Lambeck, Malcolm T. Mcculloch, Alex N HallidayAbstract:Milankovitch orbital forcing theory has been used to assign time scales to many paleoclimate records. However, the validity of this theory remains uncertain, and independent sea-level chronologies used to test its applicability have been restricted largely to the past ∼135,000 years. Here, we report U-series ages for coral reefs formed on Henderson Island during sea-level high-stands occurring at ∼630,000 and ∼330,000 years ago. These data are consistent with the hypothesis that interglacial climates are forced by Northern Hemisphere summer solar insolation centered at 65°N latitude, as predicted by Milankovitch theory.
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Orbital forcing of the Marine Isotope Stage 9 interglacial.
Science, 2001Co-Authors: Claudine H Stirling, Tezer M Esat, Steve G Blake, Kurt Lambeck, Malcolm T. Mcculloch, Alex N HallidayAbstract:Milankovitch orbital forcing theory has been used to assign time scales to many paleoclimate records. However, the validity of this theory remains uncertain, and independent sea-level chronologies used to test its applicability have been restricted largely to the past approximately 135,000 years. Here, we report U-series ages for coral reefs formed on Henderson Island during sea-level high-stands occurring at approximately 630,000 and approximately 330,000 years ago. These data are consistent with the hypothesis that interglacial climates are forced by Northern Hemisphere summer solar insolation centered at 65 degrees N latitude, as predicted by Milankovitch theory.
Renato Spahni - One of the best experts on this subject based on the ideXlab platform.
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glacial interglacial and millennial scale variations in the atmospheric nitrous oxide concentration during the last 800 000 years
Quaternary Science Reviews, 2010Co-Authors: Adrian Schilt, Matthias Baumgartner, Thomas Blunier, Jakob Schwander, Renato Spahni, Hubertus FischerAbstract:We present records of atmospheric nitrous oxide obtained from the ice cores of the European Project for Ice Coring in Antarctica (EPICA) Dome C and Dronning Maud Land sites shedding light on the concentration of this greenhouse gas on glacial–interglacial and millennial time scales. The extended EPICA Dome C record covers now all interglacials of the last 800,000 years and reveals nitrous oxide variations in concert with climate. Highest mean interglacial nitrous oxide concentrations of 280 parts per billion by volume are observed during the interglacial corresponding to Marine Isotope Stage 11 around 400,000 years before present, at the same time when carbon dioxide and methane reach maximum mean interglacial concentrations. The temperature reconstruction at Dome C indicates colder interglacials between 800,000 and 440,000 years before present compared to the interglacials of the last 440,000 years. In contrast to carbon dioxide and methane, which both respond with lower concentrations at lower temperatures, nitrous oxide shows mean interglacial concentrations of 4–19 parts per billion by volume higher than the preindustrial Holocene value during the interglacials corresponding to Marine Isotope Stage 9–19. At the end of most interglacials, nitrous oxide remains substantially longer on interglacial levels than methane. Nevertheless, nitrous oxide shows millennial-scale variations at the same time as methane throughout the last 800,000 years. We suggest that these millennial-scale variations have been driven by a similar mechanism as the Dansgaard/Oeschger events known from the last glacial. Our data lead to the hypothesis that emissions from the low latitudes drive past variations of the atmospheric nitrous oxide concentration.
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Isotope calibrated greenland temperature record over Marine Isotope Stage 3 and its relation to ch4
Earth and Planetary Science Letters, 2006Co-Authors: Christof Huber, Jakob Schwander, Renato Spahni, Markus Leuenberger, Jacqueline Fluckiger, Thomas F Stocker, Sigfus J Johnsen, Amaelle Landais, Jean JouzelAbstract:Large temperature variations on millennial time scales in Greenland characterised the last ice age. Abrupt warmings, known as Dansgaard–Oeschger (DO) events, can be traced in the δ18Oice record of Greenland ice cores. However, it has been shown that δ18Oice is not a direct temperature proxy. Measurements of the isotopic composition of gases trapped in the ice can be used to calibrate the paleothermometer. Here we present a continuous temperature record based on high resolution δ15N measurements and firn model studies. It covers a sequence of 9 DO events (9–17) during the time period from 38 to 64 kyr BP for which temperature changes of 8 to 15 °C were estimated. The difference between the modern and the glacial δ18Oice–T relationship can be explained by a combination of source temperature changes and changes in the annual distribution of precipitation. A detailed comparison of the temperature evolution with reconstructions of the atmospheric methane (CH4) concentration shows that CH4 rises lag temperature increases at the onset of DO events by 25 to 70 yr within data resolution. The strong correlation between Greenland temperature and CH4 on millennial and submillennial time scales suggests that variations on these time scales were probably of hemispheric extent.
Jakob Schwander - One of the best experts on this subject based on the ideXlab platform.
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glacial interglacial and millennial scale variations in the atmospheric nitrous oxide concentration during the last 800 000 years
Quaternary Science Reviews, 2010Co-Authors: Adrian Schilt, Matthias Baumgartner, Thomas Blunier, Jakob Schwander, Renato Spahni, Hubertus FischerAbstract:We present records of atmospheric nitrous oxide obtained from the ice cores of the European Project for Ice Coring in Antarctica (EPICA) Dome C and Dronning Maud Land sites shedding light on the concentration of this greenhouse gas on glacial–interglacial and millennial time scales. The extended EPICA Dome C record covers now all interglacials of the last 800,000 years and reveals nitrous oxide variations in concert with climate. Highest mean interglacial nitrous oxide concentrations of 280 parts per billion by volume are observed during the interglacial corresponding to Marine Isotope Stage 11 around 400,000 years before present, at the same time when carbon dioxide and methane reach maximum mean interglacial concentrations. The temperature reconstruction at Dome C indicates colder interglacials between 800,000 and 440,000 years before present compared to the interglacials of the last 440,000 years. In contrast to carbon dioxide and methane, which both respond with lower concentrations at lower temperatures, nitrous oxide shows mean interglacial concentrations of 4–19 parts per billion by volume higher than the preindustrial Holocene value during the interglacials corresponding to Marine Isotope Stage 9–19. At the end of most interglacials, nitrous oxide remains substantially longer on interglacial levels than methane. Nevertheless, nitrous oxide shows millennial-scale variations at the same time as methane throughout the last 800,000 years. We suggest that these millennial-scale variations have been driven by a similar mechanism as the Dansgaard/Oeschger events known from the last glacial. Our data lead to the hypothesis that emissions from the low latitudes drive past variations of the atmospheric nitrous oxide concentration.
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Isotope calibrated greenland temperature record over Marine Isotope Stage 3 and its relation to ch4
Earth and Planetary Science Letters, 2006Co-Authors: Christof Huber, Jakob Schwander, Renato Spahni, Markus Leuenberger, Jacqueline Fluckiger, Thomas F Stocker, Sigfus J Johnsen, Amaelle Landais, Jean JouzelAbstract:Large temperature variations on millennial time scales in Greenland characterised the last ice age. Abrupt warmings, known as Dansgaard–Oeschger (DO) events, can be traced in the δ18Oice record of Greenland ice cores. However, it has been shown that δ18Oice is not a direct temperature proxy. Measurements of the isotopic composition of gases trapped in the ice can be used to calibrate the paleothermometer. Here we present a continuous temperature record based on high resolution δ15N measurements and firn model studies. It covers a sequence of 9 DO events (9–17) during the time period from 38 to 64 kyr BP for which temperature changes of 8 to 15 °C were estimated. The difference between the modern and the glacial δ18Oice–T relationship can be explained by a combination of source temperature changes and changes in the annual distribution of precipitation. A detailed comparison of the temperature evolution with reconstructions of the atmospheric methane (CH4) concentration shows that CH4 rises lag temperature increases at the onset of DO events by 25 to 70 yr within data resolution. The strong correlation between Greenland temperature and CH4 on millennial and submillennial time scales suggests that variations on these time scales were probably of hemispheric extent.