The Experts below are selected from a list of 330 Experts worldwide ranked by ideXlab platform
James W C White - One of the best experts on this subject based on the ideXlab platform.
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southern hemisphere climate variability forced by northern hemisphere ice sheet topography
Nature, 2018Co-Authors: Tyler R Jones, Eric J Steig, William H G Roberts, Kurt M Cuffey, B R Markle, James W C WhiteAbstract:The presence of large Northern Hemisphere ice sheets and reduced greenhouse gas concentrations during the Last Glacial Maximum fundamentally altered global ocean-atmosphere climate dynamics. Model simulations and palaeoclimate records suggest that glacial boundary conditions affected the El Nino-Southern Oscillation, a dominant source of short-term global climate variability. Yet little is known about changes in short-term climate variability at mid- to high latitudes. Here we use a high-resolution water isotope record from West Antarctica to demonstrate that interannual to decadal climate variability at high southern latitudes was almost twice as large at the Last Glacial Maximum as during the ensuing Holocene Epoch (the past 11,700 years). Climate model simulations indicate that this increased variability reflects an increase in the teleconnection strength between the tropical Pacific and West Antarctica, owing to a shift in the mean location of tropical convection. This shift, in turn, can be attributed to the influence of topography and albedo of the North American ice sheets on atmospheric circulation. As the planet deglaciated, the largest and most abrupt decline in teleconnection strength occurred between approximately 16,000 years and 15,000 years ago, followed by a slower decline into the early Holocene.
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southern hemisphere climate variability forced by northern hemisphere ice sheet topography
Nature, 2018Co-Authors: Tyler R Jones, Eric J Steig, William H G Roberts, Kurt M Cuffey, B R Markle, James W C WhiteAbstract:An Antarctic ice core reveals that, during the last ice age, the topography of Northern Hemisphere ice sheets shifted tropical Pacific convection eastward, increasing climate variability in the high southern latitudes. During glacial maxima, ice covered vast areas of the Northern Hemisphere and had a broad influence across the global climate system. Tyler Jones and colleagues show that climate variability in the Southern Hemisphere was influenced by these large Northern Hemisphere ice sheets and was about twice as high during the Last Glacial Maximum than in the warmer Holocene that followed. The ice sheets created more elevated and brighter surfaces than at present and this altered the location of tropical convection and the atmospheric pathways that link the tropics to West Antarctica. The results reveal the intimate climatic link between the high latitudes, and the key role of the tropics as an interhemispheric mediator. The presence of large Northern Hemisphere ice sheets and reduced greenhouse gas concentrations during the Last Glacial Maximum fundamentally altered global ocean–atmosphere climate dynamics1. Model simulations and palaeoclimate records suggest that glacial boundary conditions affected the El Nino–Southern Oscillation2,3, a dominant source of short-term global climate variability. Yet little is known about changes in short-term climate variability at mid- to high latitudes. Here we use a high-resolution water isotope record from West Antarctica to demonstrate that interannual to decadal climate variability at high southern latitudes was almost twice as large at the Last Glacial Maximum as during the ensuing Holocene Epoch (the past 11,700 years). Climate model simulations indicate that this increased variability reflects an increase in the teleconnection strength between the tropical Pacific and West Antarctica, owing to a shift in the mean location of tropical convection. This shift, in turn, can be attributed to the influence of topography and albedo of the North American ice sheets on atmospheric circulation. As the planet deglaciated, the largest and most abrupt decline in teleconnection strength occurred between approximately 16,000 years and 15,000 years ago, followed by a slower decline into the early Holocene.
Michael E Weber - One of the best experts on this subject based on the ideXlab platform.
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centennial scale Holocene climate variations amplified by antarctic ice sheet discharge
Nature, 2017Co-Authors: Pepijn Johannes Bakker, Peter U Clark, Nicholas R Golledge, Andreas Schmittner, Michael E WeberAbstract:Proxy-based indicators of past climate change show that current global climate models systematically underestimate Holocene-Epoch climate variability on centennial to multi-millennial timescales, with the mismatch increasing for longer periods. Proposed explanations for the discrepancy include ocean-atmosphere coupling that is too weak in models, insufficient energy cascades from smaller to larger spatial and temporal scales, or that global climate models do not consider slow climate feedbacks related to the carbon cycle or interactions between ice sheets and climate. Such interactions, however, are known to have strongly affected centennial- to orbital-scale climate variability during past glaciations, and are likely to be important in future climate change. Here we show that fluctuations in Antarctic Ice Sheet discharge caused by relatively small changes in subsurface ocean temperature can amplify multi-centennial climate variability regionally and globally, suggesting that a dynamic Antarctic Ice Sheet may have driven climate fluctuations during the Holocene. We analysed high-temporal-resolution records of iceberg-rafted debris derived from the Antarctic Ice Sheet, and performed both high-spatial-resolution ice-sheet modelling of the Antarctic Ice Sheet and multi-millennial global climate model simulations. Ice-sheet responses to decadal-scale ocean forcing appear to be less important, possibly indicating that the future response of the Antarctic Ice Sheet will be governed more by long-term anthropogenic warming combined with multi-centennial natural variability than by annual or decadal climate oscillations.
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millennial scale variability in antarctic ice sheet discharge during the last deglaciation
Nature, 2014Co-Authors: Michael E Weber, Gerrit Lohmann, Peter U Clark, Gerhard Kuhn, Axel Timmermann, Daniela Sprenk, Rupert Gladstone, Xu Zhang, Laurie Menviel, M O ChikamotoAbstract:Two well-dated, high-resolution records of iceberg-rafted debris are presented that document variability in Antarctic Ice Sheet discharge during the last deglaciation. Global sea levels have risen by more than 100 metres since the last glacial maximum around 20,000 years ago, with several meltwater pulses of several metres or more. In the most dramatic of these — meltwater pulse 1A — sea level rose by about 16 metres at 14,600 years ago. This magnitude of sea level rise strongly suggests major Antarctica contributions, but to date there has been no firm physical evidence. Now Michael Weber and colleagues present a record of iceberg rafted debris from the Scotia Sea and show clear signals of pulsed iceberg release from Antarctica as early as 19,000 years ago. The largest iceberg release occurred during meltwater pulse 1A, providing the long-sought confirmation of Antarctic contributions to this major jump in sea-level rise. Our understanding of the deglacial evolution of the Antarctic Ice Sheet (AIS) following the Last Glacial Maximum (26,000–19,000 years ago)1 is based largely on a few well-dated but temporally and geographically restricted terrestrial and shallow-marine sequences2,3,4. This sparseness limits our understanding of the dominant feedbacks between the AIS, Southern Hemisphere climate and global sea level. Marine records of iceberg-rafted debris (IBRD) provide a nearly continuous signal of ice-sheet dynamics and variability. IBRD records from the North Atlantic Ocean have been widely used to reconstruct variability in Northern Hemisphere ice sheets5, but comparable records from the Southern Ocean of the AIS are lacking because of the low resolution and large dating uncertainties in existing sediment cores. Here we present two well-dated, high-resolution IBRD records that capture a spatially integrated signal of AIS variability during the last deglaciation. We document eight events of increased iceberg flux from various parts of the AIS between 20,000 and 9,000 years ago, in marked contrast to previous scenarios which identified the main AIS retreat as occurring after meltwater pulse 1A3,6,7,8 and continuing into the late Holocene Epoch. The highest IBRD flux occurred 14,600 years ago, providing the first direct evidence for an Antarctic contribution to meltwater pulse 1A. Climate model simulations with AIS freshwater forcing identify a positive feedback between poleward transport of Circumpolar Deep Water, subsurface warming and AIS melt, suggesting that small perturbations to the ice sheet can be substantially enhanced, providing a possible mechanism for rapid sea-level rise.
Pippa L Whitehouse - One of the best experts on this subject based on the ideXlab platform.
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extensive retreat and re advance of the west antarctic ice sheet during the Holocene
Nature, 2018Co-Authors: Jonathan Kingslake, Reed P Scherer, Torsten Albrecht, Ross D Powell, Ronja Reese, Nathan D Stansell, Slawek Tulaczyk, Martin Wearing, J J Coenen, Pippa L WhitehouseAbstract:To predict the future contributions of the Antarctic ice sheets to sea-level rise, numerical models use reconstructions of past ice-sheet retreat after the Last Glacial Maximum to tune model parameters 1 . Reconstructions of the West Antarctic Ice Sheet have assumed that it retreated progressively throughout the Holocene Epoch (the past 11,500 years or so)2-4. Here we show, however, that over this period the grounding line of the West Antarctic Ice Sheet (which marks the point at which it is no longer in contact with the ground and becomes a floating ice shelf) retreated several hundred kilometres inland of today's grounding line, before isostatic rebound caused it to re-advance to its present position. Our evidence includes, first, radiocarbon dating of sediment cores recovered from beneath the ice streams of the Ross Sea sector, indicating widespread Holocene marine exposure; and second, ice-penetrating radar observations of englacial structure in the Weddell Sea sector, indicating ice-shelf grounding. We explore the implications of these findings with an ice-sheet model. Modelled re-advance of the grounding line in the Holocene requires ice-shelf grounding caused by isostatic rebound. Our findings overturn the assumption of progressive retreat of the grounding line during the Holocene in West Antarctica, and corroborate previous suggestions of ice-sheet re-advance 5 . Rebound-driven stabilizing processes were apparently able to halt and reverse climate-initiated ice loss. Whether these processes can reverse present-day ice loss 6 on millennial timescales will depend on bedrock topography and mantle viscosity-parameters that are difficult to measure and to incorporate into ice-sheet models.
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extensive retreat and re advance of the west antarctic ice sheet during the Holocene
Nature, 2018Co-Authors: Jonathan Kingslake, Reed P Scherer, Torsten Albrecht, Jason Coenen, Ross D Powell, Ronja Reese, Nathan D Stansell, Slawek Tulaczyk, Martin Wearing, Pippa L WhitehouseAbstract:To predict the future contributions of the Antarctic ice sheets to sea-level rise, numerical models use reconstructions of past ice-sheet retreat after the Last Glacial Maximum to tune model parameters 1 . Reconstructions of the West Antarctic Ice Sheet have assumed that it retreated progressively throughout the Holocene Epoch (the past 11,500 years or so)2–4. Here we show, however, that over this period the grounding line of the West Antarctic Ice Sheet (which marks the point at which it is no longer in contact with the ground and becomes a floating ice shelf) retreated several hundred kilometres inland of today’s grounding line, before isostatic rebound caused it to re-advance to its present position. Our evidence includes, first, radiocarbon dating of sediment cores recovered from beneath the ice streams of the Ross Sea sector, indicating widespread Holocene marine exposure; and second, ice-penetrating radar observations of englacial structure in the Weddell Sea sector, indicating ice-shelf grounding. We explore the implications of these findings with an ice-sheet model. Modelled re-advance of the grounding line in the Holocene requires ice-shelf grounding caused by isostatic rebound. Our findings overturn the assumption of progressive retreat of the grounding line during the Holocene in West Antarctica, and corroborate previous suggestions of ice-sheet re-advance 5 . Rebound-driven stabilizing processes were apparently able to halt and reverse climate-initiated ice loss. Whether these processes can reverse present-day ice loss 6 on millennial timescales will depend on bedrock topography and mantle viscosity—parameters that are difficult to measure and to incorporate into ice-sheet models. Radiocarbon dating of sediment cores and ice-penetrating radar observations are used to demonstrate that the West Antarctic Ice Sheet has not retreated progressively during the Holocene Epoch, but has instead showed periods of retreat and re-advance.
Eric J Steig - One of the best experts on this subject based on the ideXlab platform.
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southern hemisphere climate variability forced by northern hemisphere ice sheet topography
Nature, 2018Co-Authors: Tyler R Jones, Eric J Steig, William H G Roberts, Kurt M Cuffey, B R Markle, James W C WhiteAbstract:An Antarctic ice core reveals that, during the last ice age, the topography of Northern Hemisphere ice sheets shifted tropical Pacific convection eastward, increasing climate variability in the high southern latitudes. During glacial maxima, ice covered vast areas of the Northern Hemisphere and had a broad influence across the global climate system. Tyler Jones and colleagues show that climate variability in the Southern Hemisphere was influenced by these large Northern Hemisphere ice sheets and was about twice as high during the Last Glacial Maximum than in the warmer Holocene that followed. The ice sheets created more elevated and brighter surfaces than at present and this altered the location of tropical convection and the atmospheric pathways that link the tropics to West Antarctica. The results reveal the intimate climatic link between the high latitudes, and the key role of the tropics as an interhemispheric mediator. The presence of large Northern Hemisphere ice sheets and reduced greenhouse gas concentrations during the Last Glacial Maximum fundamentally altered global ocean–atmosphere climate dynamics1. Model simulations and palaeoclimate records suggest that glacial boundary conditions affected the El Nino–Southern Oscillation2,3, a dominant source of short-term global climate variability. Yet little is known about changes in short-term climate variability at mid- to high latitudes. Here we use a high-resolution water isotope record from West Antarctica to demonstrate that interannual to decadal climate variability at high southern latitudes was almost twice as large at the Last Glacial Maximum as during the ensuing Holocene Epoch (the past 11,700 years). Climate model simulations indicate that this increased variability reflects an increase in the teleconnection strength between the tropical Pacific and West Antarctica, owing to a shift in the mean location of tropical convection. This shift, in turn, can be attributed to the influence of topography and albedo of the North American ice sheets on atmospheric circulation. As the planet deglaciated, the largest and most abrupt decline in teleconnection strength occurred between approximately 16,000 years and 15,000 years ago, followed by a slower decline into the early Holocene.
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southern hemisphere climate variability forced by northern hemisphere ice sheet topography
Nature, 2018Co-Authors: Tyler R Jones, Eric J Steig, William H G Roberts, Kurt M Cuffey, B R Markle, James W C WhiteAbstract:The presence of large Northern Hemisphere ice sheets and reduced greenhouse gas concentrations during the Last Glacial Maximum fundamentally altered global ocean-atmosphere climate dynamics. Model simulations and palaeoclimate records suggest that glacial boundary conditions affected the El Nino-Southern Oscillation, a dominant source of short-term global climate variability. Yet little is known about changes in short-term climate variability at mid- to high latitudes. Here we use a high-resolution water isotope record from West Antarctica to demonstrate that interannual to decadal climate variability at high southern latitudes was almost twice as large at the Last Glacial Maximum as during the ensuing Holocene Epoch (the past 11,700 years). Climate model simulations indicate that this increased variability reflects an increase in the teleconnection strength between the tropical Pacific and West Antarctica, owing to a shift in the mean location of tropical convection. This shift, in turn, can be attributed to the influence of topography and albedo of the North American ice sheets on atmospheric circulation. As the planet deglaciated, the largest and most abrupt decline in teleconnection strength occurred between approximately 16,000 years and 15,000 years ago, followed by a slower decline into the early Holocene.
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millennial scale storminess variability in the northeastern united states during the Holocene Epoch
Nature, 2002Co-Authors: Anders Noren, Paul R Bierman, Eric J Steig, Andrea Lini, John SouthonAbstract:For the purpose of detecting the effects of human activities on climate change, it is important to document natural change in past climate1. In this context, it has proved particularly difficult to study the variability in the occurrence of extreme climate events, such as storms with exceptional rainfall1. Previous investigations have established storm chronologies using sediment cores from single lakes2,3,4,5,6,7,8, but such studies can be susceptible to local environmental bias. Here we date terrigenous inwash layers in cores from 13 lakes, which show that the frequency of storm-related floods in the northeastern United States has varied in regular cycles during the past 13,000 years (13 kyr), with a characteristic period of about 3 kyr. Our data show four peaks in storminess during the past 14 kyr, approximately 2.6, 5.8, 9.1 and 11.9 kyr ago. This pattern is consistent with long-term changes in the average sign of the Arctic Oscillation9, suggesting that modulation of this dominant atmospheric mode may account for a significant fraction of Holocene climate variability in North America and Europe.
Tyler R Jones - One of the best experts on this subject based on the ideXlab platform.
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southern hemisphere climate variability forced by northern hemisphere ice sheet topography
Nature, 2018Co-Authors: Tyler R Jones, Eric J Steig, William H G Roberts, Kurt M Cuffey, B R Markle, James W C WhiteAbstract:The presence of large Northern Hemisphere ice sheets and reduced greenhouse gas concentrations during the Last Glacial Maximum fundamentally altered global ocean-atmosphere climate dynamics. Model simulations and palaeoclimate records suggest that glacial boundary conditions affected the El Nino-Southern Oscillation, a dominant source of short-term global climate variability. Yet little is known about changes in short-term climate variability at mid- to high latitudes. Here we use a high-resolution water isotope record from West Antarctica to demonstrate that interannual to decadal climate variability at high southern latitudes was almost twice as large at the Last Glacial Maximum as during the ensuing Holocene Epoch (the past 11,700 years). Climate model simulations indicate that this increased variability reflects an increase in the teleconnection strength between the tropical Pacific and West Antarctica, owing to a shift in the mean location of tropical convection. This shift, in turn, can be attributed to the influence of topography and albedo of the North American ice sheets on atmospheric circulation. As the planet deglaciated, the largest and most abrupt decline in teleconnection strength occurred between approximately 16,000 years and 15,000 years ago, followed by a slower decline into the early Holocene.
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southern hemisphere climate variability forced by northern hemisphere ice sheet topography
Nature, 2018Co-Authors: Tyler R Jones, Eric J Steig, William H G Roberts, Kurt M Cuffey, B R Markle, James W C WhiteAbstract:An Antarctic ice core reveals that, during the last ice age, the topography of Northern Hemisphere ice sheets shifted tropical Pacific convection eastward, increasing climate variability in the high southern latitudes. During glacial maxima, ice covered vast areas of the Northern Hemisphere and had a broad influence across the global climate system. Tyler Jones and colleagues show that climate variability in the Southern Hemisphere was influenced by these large Northern Hemisphere ice sheets and was about twice as high during the Last Glacial Maximum than in the warmer Holocene that followed. The ice sheets created more elevated and brighter surfaces than at present and this altered the location of tropical convection and the atmospheric pathways that link the tropics to West Antarctica. The results reveal the intimate climatic link between the high latitudes, and the key role of the tropics as an interhemispheric mediator. The presence of large Northern Hemisphere ice sheets and reduced greenhouse gas concentrations during the Last Glacial Maximum fundamentally altered global ocean–atmosphere climate dynamics1. Model simulations and palaeoclimate records suggest that glacial boundary conditions affected the El Nino–Southern Oscillation2,3, a dominant source of short-term global climate variability. Yet little is known about changes in short-term climate variability at mid- to high latitudes. Here we use a high-resolution water isotope record from West Antarctica to demonstrate that interannual to decadal climate variability at high southern latitudes was almost twice as large at the Last Glacial Maximum as during the ensuing Holocene Epoch (the past 11,700 years). Climate model simulations indicate that this increased variability reflects an increase in the teleconnection strength between the tropical Pacific and West Antarctica, owing to a shift in the mean location of tropical convection. This shift, in turn, can be attributed to the influence of topography and albedo of the North American ice sheets on atmospheric circulation. As the planet deglaciated, the largest and most abrupt decline in teleconnection strength occurred between approximately 16,000 years and 15,000 years ago, followed by a slower decline into the early Holocene.