1
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Li T, Robinson LF, MacGilchrist GA, Chen T, Stewart JA, Burke A, Wang M, Li G, Chen J, Rae JWB. Enhanced subglacial discharge from Antarctica during meltwater pulse 1A. Nat Commun 2023; 14:7327. [PMID: 37957152 PMCID: PMC10643554 DOI: 10.1038/s41467-023-42974-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2023] [Accepted: 10/27/2023] [Indexed: 11/15/2023] Open
Abstract
Subglacial discharge from the Antarctic Ice Sheet (AIS) likely played a crucial role in the loss of the ice sheet and the subsequent rise in sea level during the last deglaciation. However, no direct proxy is currently available to document subglacial discharge from the AIS, which leaves significant gaps in our understanding of the complex interactions between subglacial discharge and ice-sheet stability. Here we present deep-sea coral 234U/238U records from the Drake Passage in the Southern Ocean to track subglacial discharge from the AIS. Our findings reveal distinctively higher seawater 234U/238U values from 15,400 to 14,000 years ago, corresponding to the period of the highest iceberg-rafted debris flux and the occurrence of the meltwater pulse 1A event. This correlation suggests a causal link between enhanced subglacial discharge, synchronous retreat of the AIS, and the rapid rise in sea levels. The enhanced subglacial discharge and subsequent AIS retreat appear to have been preconditioned by a stronger and warmer Circumpolar Deep Water, thus underscoring the critical role of oceanic heat in driving major ice-sheet retreat.
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Affiliation(s)
- Tao Li
- State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing, China.
- School of Earth Sciences, University of Bristol, Bristol, UK.
- Department of Earth and Planetary Sciences, Nanjing University, Nanjing, China.
| | - Laura F Robinson
- School of Earth Sciences, University of Bristol, Bristol, UK
- Department of Environment and Geography, University of York, York, UK
| | - Graeme A MacGilchrist
- Program in Atmospheric and Oceanic Science, Princeton University, Princeton, NJ, USA
- School of Earth and Environmental Sciences, University of St Andrews, St Andrews, UK
| | - Tianyu Chen
- Department of Earth and Planetary Sciences, Nanjing University, Nanjing, China
| | | | - Andrea Burke
- School of Earth and Environmental Sciences, University of St Andrews, St Andrews, UK
| | - Maoyu Wang
- Department of Earth and Planetary Sciences, Nanjing University, Nanjing, China
| | - Gaojun Li
- Department of Earth and Planetary Sciences, Nanjing University, Nanjing, China
| | - Jun Chen
- Department of Earth and Planetary Sciences, Nanjing University, Nanjing, China
| | - James W B Rae
- School of Earth and Environmental Sciences, University of St Andrews, St Andrews, UK
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2
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Rapid northern hemisphere ice sheet melting during the penultimate deglaciation. Nat Commun 2022; 13:3819. [PMID: 35780147 PMCID: PMC9250507 DOI: 10.1038/s41467-022-31619-3] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2022] [Accepted: 06/27/2022] [Indexed: 11/17/2022] Open
Abstract
The rate and consequences of future high latitude ice sheet retreat remain a major concern given ongoing anthropogenic warming. Here, new precisely dated stalagmite data from NW Iberia provide the first direct, high-resolution records of periods of rapid melting of Northern Hemisphere ice sheets during the penultimate deglaciation. These records reveal the penultimate deglaciation initiated with rapid century-scale meltwater pulses which subsequently trigger abrupt coolings of air temperature in NW Iberia consistent with freshwater-induced AMOC slowdowns. The first of these AMOC slowdowns, 600-year duration, was shorter than Heinrich 1 of the last deglaciation. Although similar insolation forcing initiated the last two deglaciations, the more rapid and sustained rate of freshening in the eastern North Atlantic penultimate deglaciation likely reflects a larger volume of ice stored in the marine-based Eurasian Ice sheet during the penultimate glacial in contrast to the land-based ice sheet on North America as during the last glacial. Stalagmites from NW Iberia record the rapid demise of large ice sheets during the penultimate deglaciation, and reveal decadal-scale feedbacks between warming and ice melting.
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3
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The timing, duration and magnitude of the 8.2 ka event in global speleothem records. Sci Rep 2022; 12:10542. [PMID: 35732793 PMCID: PMC9217811 DOI: 10.1038/s41598-022-14684-y] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2022] [Accepted: 05/06/2022] [Indexed: 11/09/2022] Open
Abstract
Abrupt events are a feature of many palaeoclimate records during the Holocene. The best example is the 8.2 ka event, which was triggered by a release of meltwater into the Labrador Sea and resulted in a weakening of poleward heat transport in the North Atlantic. We use an objective method to identify rapid climate events in globally distributed speleothem oxygen isotope records during the Holocene. We show that the 8.2 ka event can be identified in >70% of the speleothem records and is the most coherent signal of abrupt climate change during the last 12,000 years. The isotopic changes during the event are regionally homogenous: positive oxygen isotope anomalies are observed across Asia and negative anomalies are seen across Europe, the Mediterranean, South America and southern Africa. The magnitude of the isotopic excursions in Europe and Asia are statistically indistinguishable. There is no significant difference in the duration and timing of the 8.2 ka event between regions, or between the speleothem records and Greenland ice core records. Our study supports a rapid and global climate response to the 8.2 ka freshwater pulse into the North Atlantic, likely transmitted globally via atmospheric teleconnections.
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4
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Abstract
The peopling of Siberia and the Americas is intriguing for archaeologists, linguists, and human geneticists, but despite significant recent developments, many details remain controversial. Here, we provide insights based on genetic diversity within Helicobacter pylori, a bacterium that infects 50% of all humans. H. pylori strains were collected from across eastern Eurasia and the Americas. Sequence analyses indicated that Siberia contains both anciently diverged and recently admixed bacteria, supporting both human persistence over the last glacial maximum and more recent human recolonization. We inferred a single migration across the Bering land bridge, accompanied by a dramatic reduction in effective population size, followed by bidirectional Holocene gene flow between Asia and the Americas. The gastric bacterium Helicobacter pylori shares a coevolutionary history with humans that predates the out-of-Africa diaspora, and the geographical specificities of H. pylori populations reflect multiple well-known human migrations. We extensively sampled H. pylori from 16 ethnically diverse human populations across Siberia to help resolve whether ancient northern Eurasian populations persisted at high latitudes through the last glacial maximum and the relationships between present-day Siberians and Native Americans. A total of 556 strains were cultivated and genotyped by multilocus sequence typing, and 54 representative draft genomes were sequenced. The genetic diversity across Eurasia and the Americas was structured into three populations: hpAsia2, hpEastAsia, and hpNorthAsia. hpNorthAsia is closely related to the subpopulation hspIndigenousAmericas from Native Americans. Siberian bacteria were structured into five other subpopulations, two of which evolved through a divergence from hpAsia2 and hpNorthAsia, while three originated though Holocene admixture. The presence of both anciently diverged and recently admixed strains across Siberia support both Pleistocene persistence and Holocene recolonization. We also show that hspIndigenousAmericas is endemic in human populations across northern Eurasia. The evolutionary history of hspIndigenousAmericas was reconstructed using approximate Bayesian computation, which showed that it colonized the New World in a single migration event associated with a severe demographic bottleneck followed by low levels of recent admixture across the Bering Strait.
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5
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Lin Y, Hibbert FD, Whitehouse PL, Woodroffe SA, Purcell A, Shennan I, Bradley SL. A reconciled solution of Meltwater Pulse 1A sources using sea-level fingerprinting. Nat Commun 2021; 12:2015. [PMID: 33795667 PMCID: PMC8016857 DOI: 10.1038/s41467-021-21990-y] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2020] [Accepted: 02/17/2021] [Indexed: 02/01/2023] Open
Abstract
The most rapid global sea-level rise event of the last deglaciation, Meltwater Pulse 1A (MWP-1A), occurred ∼14,650 years ago. Considerable uncertainty regarding the sources of meltwater limits understanding of the relationship between MWP-1A and the concurrent fast-changing climate. Here we present a data-driven inversion approach, using a glacio-isostatic adjustment model to invert for the sources of MWP-1A via sea-level constraints from six geographically distributed sites. The results suggest contributions from Antarctica, 1.3 m (0-5.9 m; 95% probability), Scandinavia, 4.6 m (3.2-6.4 m) and North America, 12.0 m (5.6-15.4 m), giving a global mean sea-level rise of 17.9 m (15.7-20.2 m) in 500 years. Only a North American dominant scenario successfully predicts the observed sea-level change across our six sites and an Antarctic dominant scenario is firmly refuted by Scottish isolation basin records. Our sea-level based results therefore reconcile with field-based ice-sheet reconstructions.
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Affiliation(s)
- Yucheng Lin
- Department of Geography, Durham University, Durham, UK.
- Research School of Earth Sciences, Australian National University, ACT, Canberra, Australia.
| | - Fiona D Hibbert
- Research School of Earth Sciences, Australian National University, ACT, Canberra, Australia
- Department of Environment and Geography, University of York, York, UK
| | | | | | - Anthony Purcell
- Research School of Earth Sciences, Australian National University, ACT, Canberra, Australia
| | - Ian Shennan
- Department of Geography, Durham University, Durham, UK
| | - Sarah L Bradley
- Department of Geography, The University of Sheffield, Sheffield, UK
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6
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Aguiar W, Meissner KJ, Montenegro A, Prado L, Wainer I, Carlson AE, Mata MM. Magnitude of the 8.2 ka event freshwater forcing based on stable isotope modelling and comparison to future Greenland melting. Sci Rep 2021; 11:5473. [PMID: 33750824 PMCID: PMC7943769 DOI: 10.1038/s41598-021-84709-5] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2020] [Accepted: 02/17/2021] [Indexed: 11/10/2022] Open
Abstract
The northern hemisphere experienced an abrupt cold event ~ 8200 years ago (the 8.2 ka event) that was triggered by the release of meltwater into the Labrador Sea, and resulting in a weakening of the poleward oceanic heat transport. Although this event has been considered a possible analogue for future ocean circulation changes due to the projected Greenland Ice Sheet (GIS) melting, large uncertainties in the amount and rate of freshwater released during the 8.2 ka event make such a comparison difficult. In this study, we compare sea surface temperatures and oxygen isotope ratios from 28 isotope-enabled model simulations with 35 paleoproxy records to constrain the meltwater released during the 8.2 ka event. Our results suggest that a combination of 5.3 m of meltwater in sea level rise equivalent (SLR) released over a thousand years, with a short intensification over ~ 130 years (an additional 2.2 m of equivalent SLR) due to routing of the Canadian river discharge, best reproduces the proxy anomalies. Our estimate is of the same order of magnitude as projected future GIS melting rates under the high emission scenario RCP8.5.
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Affiliation(s)
- Wilton Aguiar
- Laboratório de Estudos dos Oceanos e Clima, Instituto de Oceanografia, Universidade Federal do Rio Grande-FURG, Rio Grande, RS, 96203-900, Brazil.
| | - Katrin J Meissner
- Climate Change Research Center and ARC Centre of Excellence for Climate Extremes, University of New South Wales, Sydney, Australia
| | - Alvaro Montenegro
- Department of Geography, The Ohio State University, Columbus, OH, 43210, USA
| | - Luciana Prado
- Instituto Oceanográfico, Universidade de São Paulo, São Paulo, 05508-120, Brazil.,Instituto de Geociências, Universidade de Brasília, Brasília, 70297-400, Brazil
| | - Ilana Wainer
- Instituto Oceanográfico, Universidade de São Paulo, São Paulo, 05508-120, Brazil
| | | | - Mauricio M Mata
- Laboratório de Estudos dos Oceanos e Clima, Instituto de Oceanografia, Universidade Federal do Rio Grande-FURG, Rio Grande, RS, 96203-900, Brazil
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7
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Pico T, Mitrovica JX, Mix AC. Sea level fingerprinting of the Bering Strait flooding history detects the source of the Younger Dryas climate event. SCIENCE ADVANCES 2020; 6:eaay2935. [PMID: 32133400 PMCID: PMC7043918 DOI: 10.1126/sciadv.aay2935] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/06/2019] [Accepted: 12/06/2019] [Indexed: 06/10/2023]
Abstract
During the Last Glacial Maximum, expansive continental ice sheets lowered globally averaged sea level ~130 m, exposing a land bridge at the Bering Strait. During the subsequent deglaciation, sea level rose rapidly and ultimately flooded the Bering Strait, linking the Arctic and Pacific Oceans. Observational records of the Bering Strait flooding have suggested two apparently contradictory scenarios for the timing of the reconnection. We reconcile these enigmatic datasets using gravitationally self-consistent sea-level simulations that vary the timing and geometry of ice retreat between the Laurentide and Cordilleran Ice Sheets to the southwest of the Bering Strait to fit observations of a two-phased flooding history. Assuming the datasets are robust, we demonstrate that their reconciliation requires a substantial melting of the Cordilleran and western Laurentide Ice Sheet from 13,000 to 11,500 years ago. This timing provides a freshwater source for the widely debated Younger Dryas cold episode (12,900 to 11,700 years ago).
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Affiliation(s)
- T. Pico
- Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138, USA
- Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA
| | - J. X. Mitrovica
- Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138, USA
| | - A. C. Mix
- College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, OR 97331, USA
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8
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Labrador Sea freshening at 8.5 ka BP caused by Hudson Bay Ice Saddle collapse. Nat Commun 2019; 10:586. [PMID: 30718573 PMCID: PMC6362222 DOI: 10.1038/s41467-019-08408-6] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2018] [Accepted: 01/03/2019] [Indexed: 11/20/2022] Open
Abstract
A significant reduction in the Atlantic Meridional Overturning Circulation and rapid northern Hemisphere cooling 8200 years ago have been linked to the final melting of the Laurentide Ice Sheet. Although many studies associated this cold event with the drainage of Lake Agassiz-Ojibway, recent model simulations have shown that the Hudson Bay Ice Saddle collapse would have had much larger effects on the Atlantic Meridional Overturning Circulation than the lake outburst itself. Based on a combination of Mg/Ca and oxygen isotope ratios of benthic foraminifera, this study presents the first direct evidence of a major Labrador shelfwater freshening at 8.5 ka BP, which we associate with the Hudson Bay Ice Saddle collapse. The freshening is preceded by a subsurface warming of the western Labrador Sea, which we link to the strengthening of the West Greenland Current that could concurrently have accelerated the ice saddle collapse in Hudson Bay. The exact freshwater scenario that caused the 8.2 ka cold event is still debated. This study presents new evidence for a severe Labrador shelfwater freshening 8500 years ago that was caused by the Hudson Bay Ice Saddle collapse following a warming in subsurface waters.
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9
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Neil K, Gajewski K. An 11,000‐yr record of diatom assemblage responses to climate and terrestrial vegetation changes, southwestern Québec. Ecosphere 2018. [DOI: 10.1002/ecs2.2505] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Affiliation(s)
- Karen Neil
- Laboratory of Paleoclimatology and Climatology Department of Geography Environment and Geomatics University of Ottawa Ottawa Ontario K1N6N5 Canada
| | - Konrad Gajewski
- Laboratory of Paleoclimatology and Climatology Department of Geography Environment and Geomatics University of Ottawa Ottawa Ontario K1N6N5 Canada
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10
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Hawkings JR, Hatton JE, Hendry KR, de Souza GF, Wadham JL, Ivanovic R, Kohler TJ, Stibal M, Beaton A, Lamarche-Gagnon G, Tedstone A, Hain MP, Bagshaw E, Pike J, Tranter M. The silicon cycle impacted by past ice sheets. Nat Commun 2018; 9:3210. [PMID: 30097566 PMCID: PMC6086862 DOI: 10.1038/s41467-018-05689-1] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2017] [Accepted: 06/11/2018] [Indexed: 11/17/2022] Open
Abstract
Globally averaged riverine silicon (Si) concentrations and isotope composition (δ30Si) may be affected by the expansion and retreat of large ice sheets during glacial−interglacial cycles. Here we provide evidence of this based on the δ30Si composition of meltwater runoff from a Greenland Ice Sheet catchment. Glacier runoff has the lightest δ30Si measured in running waters (−0.25 ± 0.12‰), significantly lower than nonglacial rivers (1.25 ± 0.68‰), such that the overall decline in glacial runoff since the Last Glacial Maximum (LGM) may explain 0.06–0.17‰ of the observed ocean δ30Si rise (0.5–1.0‰). A marine sediment core proximal to Iceland provides further evidence for transient, low-δ30Si meltwater pulses during glacial termination. Diatom Si uptake during the LGM was likely similar to present day due to an expanded Si inventory, which raises the possibility of a feedback between ice sheet expansion, enhanced Si export to the ocean and reduced CO2 concentration in the atmosphere, because of the importance of diatoms in the biological carbon pump. The role ice sheets play in the silica cycle over glacial−interglacial timescales remains unclear. Here, based on the measurement of silica isotopes in Greenland meltwater and a nearby marine sediment core, the authors suggest expanding ice sheets considerably increased isotopically light silica in the oceans.
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Affiliation(s)
- Jon R Hawkings
- Bristol Glaciology Centre, School of Geographical Sciences, University Road, Bristol, BS8 1SS, UK.
| | - Jade E Hatton
- Bristol Glaciology Centre, School of Geographical Sciences, University Road, Bristol, BS8 1SS, UK
| | | | - Gregory F de Souza
- Institute of Geochemistry and Petrology, ETH Zurich, Clausiusstrasse 25, 8092, Zürich, Switzerland
| | - Jemma L Wadham
- Bristol Glaciology Centre, School of Geographical Sciences, University Road, Bristol, BS8 1SS, UK
| | - Ruza Ivanovic
- School of Earth and Environment, University of Leeds, Leeds, LS2 9JT, UK
| | - Tyler J Kohler
- Department of Ecology, Charles University, Viničná 7, 12844, Prague 2, Czech Republic
| | - Marek Stibal
- Department of Ecology, Charles University, Viničná 7, 12844, Prague 2, Czech Republic
| | - Alexander Beaton
- National Oceanography Centre, University of Southampton Waterfront Campus, European Way, Southampton, SO14 3ZH, UK
| | | | - Andrew Tedstone
- Bristol Glaciology Centre, School of Geographical Sciences, University Road, Bristol, BS8 1SS, UK
| | - Mathis P Hain
- Earth and Planetary Sciences, University of California, Santa Cruz, CA, 95064, USA.,Ocean and Earth Science, National Oceanography Centre Southampton, University of Southampton Waterfront Campus, European Way, Southampton, SO14 3ZH, UK
| | - Elizabeth Bagshaw
- School of Earth and Ocean Sciences, Cardiff University, Main Building, Park Place, Cardiff, CF10 3AT, UK
| | - Jennifer Pike
- School of Earth and Ocean Sciences, Cardiff University, Main Building, Park Place, Cardiff, CF10 3AT, UK
| | - Martyn Tranter
- Bristol Glaciology Centre, School of Geographical Sciences, University Road, Bristol, BS8 1SS, UK
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11
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Mey J, Scherler D, Wickert AD, Egholm DL, Tesauro M, Schildgen TF, Strecker MR. Glacial isostatic uplift of the European Alps. Nat Commun 2016; 7:13382. [PMID: 27830704 PMCID: PMC5109590 DOI: 10.1038/ncomms13382] [Citation(s) in RCA: 50] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2016] [Accepted: 09/28/2016] [Indexed: 11/15/2022] Open
Abstract
Following the last glacial maximum (LGM), the demise of continental ice sheets induced crustal rebound in tectonically stable regions of North America and Scandinavia that is still ongoing. Unlike the ice sheets, the Alpine ice cap developed in an orogen where the measured uplift is potentially attributed to tectonic shortening, lithospheric delamination and unloading due to deglaciation and erosion. Here we show that ∼90% of the geodetically measured rock uplift in the Alps can be explained by the Earth’s viscoelastic response to LGM deglaciation. We modelled rock uplift by reconstructing the Alpine ice cap, while accounting for postglacial erosion, sediment deposition and spatial variations in lithospheric rigidity. Clusters of excessive uplift in the Rhône Valley and in the Eastern Alps delineate regions potentially affected by mantle processes, crustal heterogeneity and active tectonics. Our study shows that even small LGM ice caps can dominate present-day rock uplift in tectonically active regions. For half a century, the cause for recent uplift of the European Alps has been debated. Here, the authors show that ∼90% of the geodetically measured rock uplift in the Alps can be explained by the Earth’s viscoelastic response to ice melting after the Last Glacial Maximum.
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Affiliation(s)
- Jürgen Mey
- Institut für Erd- und Umweltwissenschaften, Universität Potsdam, 14476 Potsdam, Germany
| | - Dirk Scherler
- Helmholtz Centre Potsdam, GFZ German Research Centre for Geosciences, Telegrafenberg, 14473 Potsdam, Germany.,Institute of Geological Sciences, Freie Universität Berlin, 12249 Berlin, Germany
| | - Andrew D Wickert
- Department of Earth Sciences and Saint Anthony Falls Laboratory, University of Minnesota, Minneapolis, 55455 Minnesota, USA
| | - David L Egholm
- Department of Geoscience, Aarhus University, 8000 Aarhus, Denmark
| | - Magdala Tesauro
- Department of Earth Sciences, Utrecht University, 3508 Utrecht, Netherlands
| | - Taylor F Schildgen
- Institut für Erd- und Umweltwissenschaften, Universität Potsdam, 14476 Potsdam, Germany.,Helmholtz Centre Potsdam, GFZ German Research Centre for Geosciences, Telegrafenberg, 14473 Potsdam, Germany
| | - Manfred R Strecker
- Institut für Erd- und Umweltwissenschaften, Universität Potsdam, 14476 Potsdam, Germany
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12
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Chen T, Robinson LF, Beasley MP, Claxton LM, Andersen MB, Gregoire LJ, Wadham J, Fornari DJ, Harpp KS. Ocean mixing and ice-sheet control of seawater 234U/238U during the last deglaciation. Science 2016; 354:626-629. [PMID: 27811276 DOI: 10.1126/science.aag1015] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2016] [Accepted: 09/22/2016] [Indexed: 11/02/2022]
Abstract
Seawater 234U/238U provides global-scale information about continental weathering and is vital for marine uranium-series geochronology. Existing evidence supports an increase in 234U/238U since the last glacial period, but the timing and amplitude of its variability has been poorly constrained. Here we report two seawater 234U/238U records based on well-preserved deep-sea corals from the low-latitude Atlantic and Pacific Oceans. The Atlantic 234U/238U started to increase before major sea-level rise and overshot the modern value by 3 per mil during the early deglaciation. Deglacial 234U/238U in the Pacific converged with that in the Atlantic after the abrupt resumption of Atlantic meridional overturning. We suggest that ocean mixing and early deglacial release of excess 234U from enhanced subglacial melting of the Northern Hemisphere ice sheets have driven the observed 234U/238U evolution.
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Affiliation(s)
- Tianyu Chen
- Bristol Isotope Group, School of Earth Sciences, University of Bristol, Bristol, UK
| | - Laura F Robinson
- Bristol Isotope Group, School of Earth Sciences, University of Bristol, Bristol, UK
| | - Matthew P Beasley
- Bristol Isotope Group, School of Earth Sciences, University of Bristol, Bristol, UK
| | - Louis M Claxton
- Bristol Isotope Group, School of Earth Sciences, University of Bristol, Bristol, UK
| | - Morten B Andersen
- Institute of Geochemistry and Petrology, Department of Earth Sciences, ETH Zürich, Zürich, Switzerland.,School of Earth and Ocean Sciences, Cardiff University, Cardiff, UK
| | | | - Jemma Wadham
- Bristol Glaciology Centre, School of Geographical Sciences, University of Bristol, Bristol, UK
| | - Daniel J Fornari
- Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA
| | - Karen S Harpp
- Department of Geology, Colgate University, 13 Oak Drive, Hamilton, NY 13346, USA
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13
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Gregoire LJ, Otto‐Bliesner B, Valdes PJ, Ivanovic R. Abrupt Bølling warming and ice saddle collapse contributions to the Meltwater Pulse 1a rapid sea level rise. GEOPHYSICAL RESEARCH LETTERS 2016; 43:9130-9137. [PMID: 27773954 PMCID: PMC5053285 DOI: 10.1002/2016gl070356] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/11/2016] [Revised: 08/11/2016] [Accepted: 08/19/2016] [Indexed: 06/06/2023]
Abstract
Elucidating the source(s) of Meltwater Pulse 1a, the largest rapid sea level rise caused by ice melt (14-18 m in less than 340 years, 14,600 years ago), is important for understanding mechanisms of rapid ice melt and the links with abrupt climate change. Here we quantify how much and by what mechanisms the North American ice sheet could have contributed to Meltwater Pulse 1a, by driving an ice sheet model with two transient climate simulations of the last 21,000 years. Ice sheet perturbed physics ensembles were run to account for model uncertainties, constraining ice extent and volume with reconstructions of 21,000 years ago to present. We determine that the North American ice sheet produced 3-4 m global mean sea level rise in 340 years due to the abrupt Bølling warming, but this response is amplified to 5-6 m when it triggers the ice sheet saddle collapse.
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Affiliation(s)
| | | | | | - Ruza Ivanovic
- School of Earth and EnvironmentUniversity of LeedsLeedsUK
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14
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Ice stream activity scaled to ice sheet volume during Laurentide Ice Sheet deglaciation. Nature 2016; 530:322-6. [PMID: 26887494 DOI: 10.1038/nature16947] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2015] [Accepted: 12/16/2015] [Indexed: 11/08/2022]
Abstract
The contribution of the Greenland and West Antarctic ice sheets to sea level has increased in recent decades, largely owing to the thinning and retreat of outlet glaciers and ice streams. This dynamic loss is a serious concern, with some modelling studies suggesting that the collapse of a major ice sheet could be imminent or potentially underway in West Antarctica, but others predicting a more limited response. A major problem is that observations used to initialize and calibrate models typically span only a few decades, and, at the ice-sheet scale, it is unclear how the entire drainage network of ice streams evolves over longer timescales. This represents one of the largest sources of uncertainty when predicting the contributions of ice sheets to sea-level rise. A key question is whether ice streams might increase and sustain rates of mass loss over centuries or millennia, beyond those expected for a given ocean-climate forcing. Here we reconstruct the activity of 117 ice streams that operated at various times during deglaciation of the Laurentide Ice Sheet (from about 22,000 to 7,000 years ago) and show that as they activated and deactivated in different locations, their overall number decreased, they occupied a progressively smaller percentage of the ice sheet perimeter and their total discharge decreased. The underlying geology and topography clearly influenced ice stream activity, but--at the ice-sheet scale--their drainage network adjusted and was linked to changes in ice sheet volume. It is unclear whether these findings can be directly translated to modern ice sheets. However, contrary to the view that sees ice streams as unstable entities that can accelerate ice-sheet deglaciation, we conclude that ice streams exerted progressively less influence on ice sheet mass balance during the retreat of the Laurentide Ice Sheet.
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15
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Dutton A, Carlson AE, Long AJ, Milne GA, Clark PU, DeConto R, Horton BP, Rahmstorf S, Raymo ME. SEA-LEVEL RISE. Sea-level rise due to polar ice-sheet mass loss during past warm periods. Science 2015; 349:aaa4019. [PMID: 26160951 DOI: 10.1126/science.aaa4019] [Citation(s) in RCA: 86] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Interdisciplinary studies of geologic archives have ushered in a new era of deciphering magnitudes, rates, and sources of sea-level rise from polar ice-sheet loss during past warm periods. Accounting for glacial isostatic processes helps to reconcile spatial variability in peak sea level during marine isotope stages 5e and 11, when the global mean reached 6 to 9 meters and 6 to 13 meters higher than present, respectively. Dynamic topography introduces large uncertainties on longer time scales, precluding robust sea-level estimates for intervals such as the Pliocene. Present climate is warming to a level associated with significant polar ice-sheet loss in the past. Here, we outline advances and challenges involved in constraining ice-sheet sensitivity to climate change with use of paleo-sea level records.
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Affiliation(s)
- A Dutton
- Department of Geological Sciences, University of Florida,Gainesville, FL 32611, USA.
| | - A E Carlson
- College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, OR 97331, USA
| | - A J Long
- Department of Geography, Durham University, Durham, UK
| | - G A Milne
- Department of Earth Sciences, University of Ottawa, Ottawa, Canada
| | - P U Clark
- College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, OR 97331, USA
| | - R DeConto
- Department of Geosciences, University of Massachusetts, Amherst, MA 01003, USA
| | - B P Horton
- Department of Marine and Coastal Sciences, Rutgers University, New Brunswick, NJ 08901, USA. Earth Observatory of Singapore, Nanyang Technological University, Singapore, 639798
| | - S Rahmstorf
- Potsdam Institute for Climate Impact Research, Potsdam, Germany
| | - M E Raymo
- Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964, USA
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Wickert AD, Mitrovica JX, Williams C, Anderson RS. Gradual demise of a thin southern Laurentide ice sheet recorded by Mississippi drainage. Nature 2013; 502:668-71. [PMID: 24172978 DOI: 10.1038/nature12609] [Citation(s) in RCA: 59] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2013] [Accepted: 08/28/2013] [Indexed: 11/10/2022]
Abstract
At the Last Glacial Maximum (LGM), about 21,000 years before present, land-based ice sheets held enough water to reduce global mean sea level by 130 metres. Yet after decades of study, major uncertainties remain as to the distribution of that ice. Here we test four reconstructions of North American deglacial ice-sheet history by quantitatively connecting them to high-resolution oxygen isotope (δ(18)O) records from the Gulf of Mexico using a water mixing model. For each reconstruction, we route meltwater and seasonal runoff through the time-evolving Mississippi drainage basin, which co-evolves with ice geometry and changing topography as ice loads deform the solid Earth and produce spatially variable sea level in a process known as glacial isostatic adjustment. The δ(18)O records show that the Mississippi-drained southern Laurentide ice sheet contributed only 5.4 ± 2.1 metres to global sea level rise, of which 0.66 ± 0.07 metres were released during the meltwater pulse 1A event 14,650-14,310 years before present, far less water than previously thought. In contrast, the three reconstructions based on glacial isostatic adjustment overpredict the δ(18)O-based post-LGM meltwater volume by a factor of 1.6 to 3.6. The fourth reconstruction, which is based on ice physics, has a low enough Mississippi-routed meltwater discharge to be consistent with δ(18)O constraints, but also contains the largest LGM North American ice volume. This suggests that modelling based on ice physics may be the best way of matching isotopic records while also sequestering enough water in the North American ice sheets to match the observed LGM sea level fall.
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Affiliation(s)
- Andrew D Wickert
- Institute of Arctic and Alpine Research and Department of Geological Sciences, University of Colorado, 1560 30th Street, Boulder, Colorado 80303, USA
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Abe-Ouchi A, Saito F, Kawamura K, Raymo ME, Okuno J, Takahashi K, Blatter H. Insolation-driven 100,000-year glacial cycles and hysteresis of ice-sheet volume. Nature 2013; 500:190-3. [PMID: 23925242 DOI: 10.1038/nature12374] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2013] [Accepted: 06/10/2013] [Indexed: 11/09/2022]
Abstract
The growth and reduction of Northern Hemisphere ice sheets over the past million years is dominated by an approximately 100,000-year periodicity and a sawtooth pattern (gradual growth and fast termination). Milankovitch theory proposes that summer insolation at high northern latitudes drives the glacial cycles, and statistical tests have demonstrated that the glacial cycles are indeed linked to eccentricity, obliquity and precession cycles. Yet insolation alone cannot explain the strong 100,000-year cycle, suggesting that internal climatic feedbacks may also be at work. Earlier conceptual models, for example, showed that glacial terminations are associated with the build-up of Northern Hemisphere 'excess ice', but the physical mechanisms underpinning the 100,000-year cycle remain unclear. Here we show, using comprehensive climate and ice-sheet models, that insolation and internal feedbacks between the climate, the ice sheets and the lithosphere-asthenosphere system explain the 100,000-year periodicity. The responses of equilibrium states of ice sheets to summer insolation show hysteresis, with the shape and position of the hysteresis loop playing a key part in determining the periodicities of glacial cycles. The hysteresis loop of the North American ice sheet is such that after inception of the ice sheet, its mass balance remains mostly positive through several precession cycles, whose amplitudes decrease towards an eccentricity minimum. The larger the ice sheet grows and extends towards lower latitudes, the smaller is the insolation required to make the mass balance negative. Therefore, once a large ice sheet is established, a moderate increase in insolation is sufficient to trigger a negative mass balance, leading to an almost complete retreat of the ice sheet within several thousand years. This fast retreat is governed mainly by rapid ablation due to the lowered surface elevation resulting from delayed isostatic rebound, which is the lithosphere-asthenosphere response. Carbon dioxide is involved, but is not determinative, in the evolution of the 100,000-year glacial cycles.
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Affiliation(s)
- Ayako Abe-Ouchi
- Atmosphere and Ocean Research Institute, The University of Tokyo, Kashiwa 277-8568, Japan.
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