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Zhengyu Liu - One of the best experts on this subject based on the ideXlab platform.
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hydroclimate footprint of pan asian monsoon water isotope during the Last Deglaciation
Science Advances, 2021Co-Authors: Zhengyu Liu, Bette L Ottobliesner, Peter U Clark, Esther C Brady, C Zhu, Robert A Tomas, Jiang Zhu, Alexandra JahnAbstract:Oxygen isotope speleothem records exhibit coherent variability over the pan-Asian summer monsoon (AM) region. The hydroclimatic representation of these oxygen isotope records for the AM, however, has remained poorly understood. Here, combining an isotope-enabled Earth system model in transient experiments with proxy records, we show that the widespread AM δ18Oc signal during the Last Deglaciation (20 to 11 thousand years ago) is accompanied by a continental-scale, coherent hydroclimate footprint, with spatially opposite signs in rainfall. This footprint is generated as a dynamically coherent response of the AM system primarily to meltwater forcing and secondarily to insolation forcing and is further reinforced by atmospheric teleconnection. Hence, widespread δ18Op depletion in the AM region is accompanied by a northward migration of the westerly jet and enhanced southwesterly monsoon wind, as well as increased rainfall from South Asia (India) to northern China but decreased rainfall in southeast China.
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asynchronous warming and δ18o evolution of deep atlantic water masses during the Last Deglaciation
Proceedings of the National Academy of Sciences of the United States of America, 2017Co-Authors: Jiaxu Zhang, Delia W Oppo, Zhengyu Liu, Peter U Clark, Shaun A Marcott, Esther C Brady, Alexandra Jahn, Keith LindsayAbstract:The large-scale reorganization of deep ocean circulation in the Atlantic involving changes in North Atlantic Deep Water (NADW) and Antarctic Bottom Water (AABW) played a critical role in regulating hemispheric and global climate during the Last Deglaciation. However, changes in the relative contributions of NADW and AABW and their properties are poorly constrained by marine records, including δ18O of benthic foraminiferal calcite (δ18Oc). Here, we use an isotope-enabled ocean general circulation model with realistic geometry and forcing conditions to simulate the deglacial water mass and δ18O evolution. Model results suggest that, in response to North Atlantic freshwater forcing during the early phase of the Last Deglaciation, NADW nearly collapses, while AABW mildly weakens. Rather than reflecting changes in NADW or AABW properties caused by freshwater input as suggested previously, the observed phasing difference of deep δ18Oc likely reflects early warming of the deep northern North Atlantic by ∼1.4 °C, while deep Southern Ocean temperature remains largely unchanged. We propose a thermodynamic mechanism to explain the early warming in the North Atlantic, featuring a strong middepth warming and enhanced downward heat flux via vertical mixing. Our results emphasize that the way that ocean circulation affects heat, a dynamic tracer, is considerably different from how it affects passive tracers, like δ18O, and call for caution when inferring water mass changes from δ18Oc records while assuming uniform changes in deep temperatures.
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coherent response of antarctic intermediate water and atlantic meridional overturning circulation during the Last Deglaciation reconciling contrasting neodymium isotope reconstructions from the tropical atlantic
Paleoceanography, 2017Co-Authors: Jiaxu Zhang, Zhengyu Liu, Johannes Rempfer, Fortunat Joos, Delia W OppoAbstract:Antarctic Intermediate Water (AAIW) plays important roles in the global climate system and the global ocean nutrient and carbon cycles. However, it is unclear how AAIW responds to global climate changes. In particular, neodymium isotopic composition (eNd) reconstructions from different locations from the tropical Atlantic, have led to a debate on the relationship between northward penetration of AAIW into the tropical Atlantic and the Atlantic Meridional Overturning Circulation (AMOC) variability during the Last Deglaciation. We resolve this controversy by studying the transient oceanic evolution during the Last Deglaciation using a neodymium-enabled ocean model. Our results suggest a coherent response of AAIW and AMOC: when AMOC weakens, the northward penetration and transport of AAIW decreases while its depth and thickness increase. Our study highlights that as part of the return flow of the North Atlantic Deep Water (NADW), the northward penetration of AAIW in the Atlantic is determined predominately by AMOC intensity. Moreover, the inconsistency among different tropical Atlantic eNd reconstructions is reconciled by considering their corresponding core locations and depths, which were influenced by different water masses in the past. The very radiogenic water from the bottom of the Gulf of Mexico and the Caribbean Sea, which was previously overlooked in the interpretations of deglacial eNd variability, can be transported to shallow layers during active AMOC, and modulates eNd in the tropical Atlantic. Changes in the AAIW core depth must also be considered. Thus, interpretation of eNd reconstructions from the tropical Atlantic is more complicated than suggested in previous studies.
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coherent changes of southeastern equatorial and northern african rainfall during the Last Deglaciation
Science, 2014Co-Authors: Bette L Ottobliesner, Jonathan T Overpeck, Zhengyu Liu, Peter U Clark, James M Russell, Bronwen Konecky, Peter B Demenocal, Sharon E NicholsonAbstract:During the Last Deglaciation, wetter conditions developed abruptly ~14,700 years ago in southeastern equatorial and northern Africa and continued into the Holocene. Explaining the abrupt onset and hemispheric coherence of this early African Humid Period is challenging due to opposing seasonal insolation patterns. In this work, we use a transient simulation with a climate model that provides a mechanistic understanding of deglacial tropical African precipitation changes. Our results show that meltwater-induced reduction in the Atlantic meridional overturning circulation (AMOC) during the early Deglaciation suppressed precipitation in both regions. Once the AMOC reestablished, wetter conditions developed north of the equator in response to high summer insolation and increasing greenhouse gas (GHG) concentrations, whereas wetter conditions south of the equator were a response primarily to the GHG increase.
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global climate evolution during the Last Deglaciation
Proceedings of the National Academy of Sciences of the United States of America, 2012Co-Authors: Peter U Clark, Hai Cheng, Anders E. Carlson, Jeremy D Shakun, Edward J Brook, Paul A Baker, Patrick J Bartlein, Simon Brewer, Darrell S Kaufman, Zhengyu LiuAbstract:Deciphering the evolution of global climate from the end of the Last Glacial Maximum approximately 19 ka to the early Holocene 11 ka presents an outstanding opportunity for understanding the transient response of Earth’s climate system to external and internal forcings. During this interval of global warming, the decay of ice sheets caused global mean sea level to rise by approximately 80 m; terrestrial and marine ecosystems experienced large disturbances and range shifts; perturbations to the carbon cycle resulted in a net release of the greenhouse gases CO2 and CH4 to the atmosphere; and changes in atmosphere and ocean circulation affected the global distribution and fluxes of water and heat. Here we summarize a major effort by the paleoclimate research community to characterize these changes through the development of well-dated, high-resolution records of the deep and intermediate ocean as well as surface climate. Our synthesis indicates that the superposition of two modes explains much of the variability in regional and global climate during the Last Deglaciation, with a strong association between the first mode and variations in greenhouse gases, and between the second mode and variations in the Atlantic meridional overturning circulation.
Peter U Clark - One of the best experts on this subject based on the ideXlab platform.
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hydroclimate footprint of pan asian monsoon water isotope during the Last Deglaciation
Science Advances, 2021Co-Authors: Zhengyu Liu, Bette L Ottobliesner, Peter U Clark, Esther C Brady, C Zhu, Robert A Tomas, Jiang Zhu, Alexandra JahnAbstract:Oxygen isotope speleothem records exhibit coherent variability over the pan-Asian summer monsoon (AM) region. The hydroclimatic representation of these oxygen isotope records for the AM, however, has remained poorly understood. Here, combining an isotope-enabled Earth system model in transient experiments with proxy records, we show that the widespread AM δ18Oc signal during the Last Deglaciation (20 to 11 thousand years ago) is accompanied by a continental-scale, coherent hydroclimate footprint, with spatially opposite signs in rainfall. This footprint is generated as a dynamically coherent response of the AM system primarily to meltwater forcing and secondarily to insolation forcing and is further reinforced by atmospheric teleconnection. Hence, widespread δ18Op depletion in the AM region is accompanied by a northward migration of the westerly jet and enhanced southwesterly monsoon wind, as well as increased rainfall from South Asia (India) to northern China but decreased rainfall in southeast China.
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asynchronous warming and δ18o evolution of deep atlantic water masses during the Last Deglaciation
Proceedings of the National Academy of Sciences of the United States of America, 2017Co-Authors: Jiaxu Zhang, Delia W Oppo, Zhengyu Liu, Peter U Clark, Shaun A Marcott, Esther C Brady, Alexandra Jahn, Keith LindsayAbstract:The large-scale reorganization of deep ocean circulation in the Atlantic involving changes in North Atlantic Deep Water (NADW) and Antarctic Bottom Water (AABW) played a critical role in regulating hemispheric and global climate during the Last Deglaciation. However, changes in the relative contributions of NADW and AABW and their properties are poorly constrained by marine records, including δ18O of benthic foraminiferal calcite (δ18Oc). Here, we use an isotope-enabled ocean general circulation model with realistic geometry and forcing conditions to simulate the deglacial water mass and δ18O evolution. Model results suggest that, in response to North Atlantic freshwater forcing during the early phase of the Last Deglaciation, NADW nearly collapses, while AABW mildly weakens. Rather than reflecting changes in NADW or AABW properties caused by freshwater input as suggested previously, the observed phasing difference of deep δ18Oc likely reflects early warming of the deep northern North Atlantic by ∼1.4 °C, while deep Southern Ocean temperature remains largely unchanged. We propose a thermodynamic mechanism to explain the early warming in the North Atlantic, featuring a strong middepth warming and enhanced downward heat flux via vertical mixing. Our results emphasize that the way that ocean circulation affects heat, a dynamic tracer, is considerably different from how it affects passive tracers, like δ18O, and call for caution when inferring water mass changes from δ18Oc records while assuming uniform changes in deep temperatures.
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coherent changes of southeastern equatorial and northern african rainfall during the Last Deglaciation
Science, 2014Co-Authors: Bette L Ottobliesner, Jonathan T Overpeck, Zhengyu Liu, Peter U Clark, James M Russell, Bronwen Konecky, Peter B Demenocal, Sharon E NicholsonAbstract:During the Last Deglaciation, wetter conditions developed abruptly ~14,700 years ago in southeastern equatorial and northern Africa and continued into the Holocene. Explaining the abrupt onset and hemispheric coherence of this early African Humid Period is challenging due to opposing seasonal insolation patterns. In this work, we use a transient simulation with a climate model that provides a mechanistic understanding of deglacial tropical African precipitation changes. Our results show that meltwater-induced reduction in the Atlantic meridional overturning circulation (AMOC) during the early Deglaciation suppressed precipitation in both regions. Once the AMOC reestablished, wetter conditions developed north of the equator in response to high summer insolation and increasing greenhouse gas (GHG) concentrations, whereas wetter conditions south of the equator were a response primarily to the GHG increase.
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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.
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ice sheet sources of sea level rise and freshwater discharge during the Last Deglaciation
Reviews of Geophysics, 2012Co-Authors: Anders E. Carlson, Peter U ClarkAbstract:We review and synthesize the geologic record that constrains the sources of sea level rise and freshwater discharge to the global oceans associated with retreat of ice sheets during the Last Deglaciation. The Last Glacial Maximum (∼26–19 ka) was terminated by a rapid 5–10 m sea level rise at 19.0–19.5 ka, sourced largely from Northern Hemisphere ice sheet retreat in response to high northern latitude insolation forcing. Sea level rise of 8–20 m from ∼19 to 14.5 ka can be attributed to continued retreat of the Laurentide and Eurasian Ice Sheets, with an additional freshwater forcing of uncertain amount delivered by Heinrich event 1. The source of the abrupt acceleration in sea level rise at ∼14.6 ka (meltwater pulse 1A, ∼14–15 m) includes contributions of 6.5–10 m from Northern Hemisphere ice sheets, of which 2–7 m represents an excess contribution above that derived from ongoing ice sheet retreat. Widespread retreat of Antarctic ice sheets began at 14.0–15.0 ka, which, together with geophysical modeling of far-field sea level records, suggests an Antarctic contribution to this meltwater pulse as well. The cause of the subsequent Younger Dryas cold event can be attributed to eastward freshwater runoff from the Lake Agassiz basin to the St. Lawrence estuary that agrees with existing Lake Agassiz outlet radiocarbon dates. Much of the early Holocene sea level rise can be explained by Laurentide and Scandinavian Ice Sheet retreat, with collapse of Laurentide ice over Hudson Bay and drainage of Lake Agassiz basin runoff at ∼8.4–8.2 ka to the Labrador Sea causing the 8.2 ka event.
Shaun A Marcott - One of the best experts on this subject based on the ideXlab platform.
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asynchronous warming and δ18o evolution of deep atlantic water masses during the Last Deglaciation
Proceedings of the National Academy of Sciences of the United States of America, 2017Co-Authors: Jiaxu Zhang, Delia W Oppo, Zhengyu Liu, Peter U Clark, Shaun A Marcott, Esther C Brady, Alexandra Jahn, Keith LindsayAbstract:The large-scale reorganization of deep ocean circulation in the Atlantic involving changes in North Atlantic Deep Water (NADW) and Antarctic Bottom Water (AABW) played a critical role in regulating hemispheric and global climate during the Last Deglaciation. However, changes in the relative contributions of NADW and AABW and their properties are poorly constrained by marine records, including δ18O of benthic foraminiferal calcite (δ18Oc). Here, we use an isotope-enabled ocean general circulation model with realistic geometry and forcing conditions to simulate the deglacial water mass and δ18O evolution. Model results suggest that, in response to North Atlantic freshwater forcing during the early phase of the Last Deglaciation, NADW nearly collapses, while AABW mildly weakens. Rather than reflecting changes in NADW or AABW properties caused by freshwater input as suggested previously, the observed phasing difference of deep δ18Oc likely reflects early warming of the deep northern North Atlantic by ∼1.4 °C, while deep Southern Ocean temperature remains largely unchanged. We propose a thermodynamic mechanism to explain the early warming in the North Atlantic, featuring a strong middepth warming and enhanced downward heat flux via vertical mixing. Our results emphasize that the way that ocean circulation affects heat, a dynamic tracer, is considerably different from how it affects passive tracers, like δ18O, and call for caution when inferring water mass changes from δ18Oc records while assuming uniform changes in deep temperatures.
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centennial scale changes in the global carbon cycle during the Last Deglaciation
Nature, 2014Co-Authors: Shaun A Marcott, Christo Buizert, T. J. Fudge, T K Bauska, Eric J Steig, Julia Rosen, Kurt M Cuffey, J P Severinghaus, Jinho Ahn, M KalkAbstract:Global climate and the concentration of atmospheric carbon dioxide (CO2) are correlated over recent glacial cycles. The combination of processes responsible for a rise in atmospheric CO2 at the Last glacial termination (23,000 to 9,000 years ago), however, remains uncertain. Establishing the timing and rate of CO2 changes in the past provides critical insight into the mechanisms that influence the carbon cycle and helps put present and future anthropogenic emissions in context. Here we present CO2 and methane (CH4) records of the Last Deglaciation from a new high-accumulation West Antarctic ice core with unprecedented temporal resolution and precise chronology. We show that although low-frequency CO2 variations parallel changes in Antarctic temperature, abrupt CO2 changes occur that have a clear relationship with abrupt climate changes in the Northern Hemisphere. A significant proportion of the direct radiative forcing associated with the rise in atmospheric CO2 occurred in three sudden steps, each of 10 to 15 parts per million. Every step took place in less than two centuries and was followed by no notable change in atmospheric CO2 for about 1,000 to 1,500 years. Slow, millennial-scale ventilation of Southern Ocean CO2-rich, deep-ocean water masses is thought to have been fundamental to the rise in atmospheric CO2 associated with the glacial termination, given the strong covariance of CO2 levels and Antarctic temperatures. Our data establish a contribution from an abrupt, centennial-scale mode of CO2 variability that is not directly related to Antarctic temperature. We suggest that processes operating on centennial timescales, probably involving the Atlantic meridional overturning circulation, seem to be influencing global carbon-cycle dynamics and are at present not widely considered in Earth system models.
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centennial scale changes in the global carbon cycle during the Last Deglaciation
Nature, 2014Co-Authors: Christo Buizert, T. J. Fudge, Shaun A Marcott, T K Bauska, Eric J Steig, Julia Rosen, Kurt M Cuffey, J P Severinghaus, M KalkAbstract:Carbon dioxide and methane records from a West Antarctic ice core show that although gradual variations in the concentration of atmospheric carbon dioxide during the Last glacial termination are linked to changes in Antarctic temperature, the concentration underwent three abrupt, centennial-scale changes related to sudden climate changes in the Northern Hemisphere. The underlying processes responsible for a rise in atmospheric carbon dioxide levels at the Last glacial termination, between 23,000 and 9,000 years ago, remain uncertain. This paper presents high-resolution carbon dioxide and methane records of the Last Deglaciation from the West Antarctic Ice Sheet Divide ice core. The authors find that a significant proportion of the direct radiative forcing associated with the rise in atmospheric carbon dioxide during the Last glacial–interglacial occurred in three abrupt steps during approximately four centuries. They suggest that this fast, centennial scale mode of carbon dioxide variability is closely linked to Northern Hemisphere climate potentially controlled by the strength of the Atlantic meridional overturning circulation. Global climate and the concentration of atmospheric carbon dioxide (CO2) are correlated over recent glacial cycles1,2. The combination of processes responsible for a rise in atmospheric CO2 at the Last glacial termination1,3 (23,000 to 9,000 years ago), however, remains uncertain1,2,3. Establishing the timing and rate of CO2 changes in the past provides critical insight into the mechanisms that influence the carbon cycle and helps put present and future anthropogenic emissions in context. Here we present CO2 and methane (CH4) records of the Last Deglaciation from a new high-accumulation West Antarctic ice core with unprecedented temporal resolution and precise chronology. We show that although low-frequency CO2 variations parallel changes in Antarctic temperature, abrupt CO2 changes occur that have a clear relationship with abrupt climate changes in the Northern Hemisphere. A significant proportion of the direct radiative forcing associated with the rise in atmospheric CO2 occurred in three sudden steps, each of 10 to 15 parts per million. Every step took place in less than two centuries and was followed by no notable change in atmospheric CO2 for about 1,000 to 1,500 years. Slow, millennial-scale ventilation of Southern Ocean CO2-rich, deep-ocean water masses is thought to have been fundamental to the rise in atmospheric CO2 associated with the glacial termination4, given the strong covariance of CO2 levels and Antarctic temperatures5. Our data establish a contribution from an abrupt, centennial-scale mode of CO2 variability that is not directly related to Antarctic temperature. We suggest that processes operating on centennial timescales, probably involving the Atlantic meridional overturning circulation, seem to be influencing global carbon-cycle dynamics and are at present not widely considered in Earth system models.
Delia W Oppo - One of the best experts on this subject based on the ideXlab platform.
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asynchronous warming and δ18o evolution of deep atlantic water masses during the Last Deglaciation
Proceedings of the National Academy of Sciences of the United States of America, 2017Co-Authors: Jiaxu Zhang, Delia W Oppo, Zhengyu Liu, Peter U Clark, Shaun A Marcott, Esther C Brady, Alexandra Jahn, Keith LindsayAbstract:The large-scale reorganization of deep ocean circulation in the Atlantic involving changes in North Atlantic Deep Water (NADW) and Antarctic Bottom Water (AABW) played a critical role in regulating hemispheric and global climate during the Last Deglaciation. However, changes in the relative contributions of NADW and AABW and their properties are poorly constrained by marine records, including δ18O of benthic foraminiferal calcite (δ18Oc). Here, we use an isotope-enabled ocean general circulation model with realistic geometry and forcing conditions to simulate the deglacial water mass and δ18O evolution. Model results suggest that, in response to North Atlantic freshwater forcing during the early phase of the Last Deglaciation, NADW nearly collapses, while AABW mildly weakens. Rather than reflecting changes in NADW or AABW properties caused by freshwater input as suggested previously, the observed phasing difference of deep δ18Oc likely reflects early warming of the deep northern North Atlantic by ∼1.4 °C, while deep Southern Ocean temperature remains largely unchanged. We propose a thermodynamic mechanism to explain the early warming in the North Atlantic, featuring a strong middepth warming and enhanced downward heat flux via vertical mixing. Our results emphasize that the way that ocean circulation affects heat, a dynamic tracer, is considerably different from how it affects passive tracers, like δ18O, and call for caution when inferring water mass changes from δ18Oc records while assuming uniform changes in deep temperatures.
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coherent response of antarctic intermediate water and atlantic meridional overturning circulation during the Last Deglaciation reconciling contrasting neodymium isotope reconstructions from the tropical atlantic
Paleoceanography, 2017Co-Authors: Jiaxu Zhang, Zhengyu Liu, Johannes Rempfer, Fortunat Joos, Delia W OppoAbstract:Antarctic Intermediate Water (AAIW) plays important roles in the global climate system and the global ocean nutrient and carbon cycles. However, it is unclear how AAIW responds to global climate changes. In particular, neodymium isotopic composition (eNd) reconstructions from different locations from the tropical Atlantic, have led to a debate on the relationship between northward penetration of AAIW into the tropical Atlantic and the Atlantic Meridional Overturning Circulation (AMOC) variability during the Last Deglaciation. We resolve this controversy by studying the transient oceanic evolution during the Last Deglaciation using a neodymium-enabled ocean model. Our results suggest a coherent response of AAIW and AMOC: when AMOC weakens, the northward penetration and transport of AAIW decreases while its depth and thickness increase. Our study highlights that as part of the return flow of the North Atlantic Deep Water (NADW), the northward penetration of AAIW in the Atlantic is determined predominately by AMOC intensity. Moreover, the inconsistency among different tropical Atlantic eNd reconstructions is reconciled by considering their corresponding core locations and depths, which were influenced by different water masses in the past. The very radiogenic water from the bottom of the Gulf of Mexico and the Caribbean Sea, which was previously overlooked in the interpretations of deglacial eNd variability, can be transported to shallow layers during active AMOC, and modulates eNd in the tropical Atlantic. Changes in the AAIW core depth must also be considered. Thus, interpretation of eNd reconstructions from the tropical Atlantic is more complicated than suggested in previous studies.
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paleoenvironmental change in the middle okinawa trough since the Last Deglaciation evidence from the sedimentation rate and planktonic foraminiferal record
Palaeogeography Palaeoclimatology Palaeoecology, 2007Co-Authors: Rong Xiang, Delia W Oppo, Youbin Sun, Muhong Chen, Fan ZhengAbstract:Well-dated, high-resolution records of planktonic foraminifera and oxygen isotopes from two sediment cores, A7 and E017, in the middle Okinawa Trough reveal strong and rapid millennial-scale climate changes since similar to 18 to 17 thousand years before present (kyr B.P.). Sedimentation rate shows a sudden drop at similar to 11.2 cal. kyr B.P. due to a rapid rise of sea level after the Younger Dryas (YD) and consequently submergence of the large continental shelf on the East China Sea (ECS) and the retreat of the estuary providing sediment to the basin. During the Last Deglaciation, the relative abundance of warm and cold species of planktonic foraminifera fluctuates strongly, consistent with the timing of sea surface temperature (SST) variations determined from Mg/Ca measurements of planktonic foraminifera from one of the two cores. These fluctuations are coeval with climate variation recorded in the Greenland ice cores and North Atlantic sediments, namely Heinrich event 1 (H1), Bolling-Allerod (B/A) and YD events. At about 9.4 kyr B.P., a sudden change in the relative abundance of shallow to deep planktonic species probably indicates a sudden strengthening of the Kuroshio Current in the Okinawa Trough, which was synchronous with a rapid sea-level rise at 9.5-9.2 kyr B.P. in the ECS, Yellow Sea (YS) and South China Sea (SCS). The abundance of planktonic foraminiferal species, together with Mg/Ca based SST, exhibits millennial-scale oscillations during the Holocene, with 7 cold events (at about 1.7, 2.3-4.6, 6.2, 7.3, 8.2, 9.6, 10.6 cal. kyr BP) superimposed on a Holocene warming trend. This Holocene trend, together with centennial-scale SST variations superimposed on the Last deglacial trend, suggests that both high and low latitude influences affected the climatology of the Okinawa Trough. (c) 2006 Elsevier B.V. All rights reserved.
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the amplitude and phasing of climate change during the Last Deglaciation in the sulu sea western equatorial pacific
Geophysical Research Letters, 2003Co-Authors: Yair Rosenthal, Delia W Oppo, Braddock K LinsleyAbstract:[1] Variations in tropical sea surface temperature patterns and the phasing relative to climate change in higher-latitudes provide insight into the mechanisms of climate change on both orbital and shorter time-scales. Here, we present well-dated, high-resolution records of planktonic foraminiferal δ18O and Mg/Ca-based SST spanning the Last Deglaciation from the Sulu Sea, located in the western equatorial Pacific. The results indicate that the Last glacial maximum was 2.3 ± 0.5°C cooler than present in the Sulu Sea with a concomitant decrease in sea surface salinity. The similarity between variations in surface salinity in the Sulu Sea, the western and eastern equatorial Pacific, and the Greenland ice-core record suggests that the observed changes in salinity reflect large-scale rearrangement of atmospheric patterns, which were coherent and synchronous throughout the Northern Hemisphere. The results suggest that the glacial equatorial Pacific climate was strongly influenced by both tropical, and extra-tropical forcing, although it is not clear whether interannual (ENSO) variability is a good analogue of glacial-interglacial climate change.
M Kalk - One of the best experts on this subject based on the ideXlab platform.
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centennial scale changes in the global carbon cycle during the Last Deglaciation
Nature, 2014Co-Authors: Shaun A Marcott, Christo Buizert, T. J. Fudge, T K Bauska, Eric J Steig, Julia Rosen, Kurt M Cuffey, J P Severinghaus, Jinho Ahn, M KalkAbstract:Global climate and the concentration of atmospheric carbon dioxide (CO2) are correlated over recent glacial cycles. The combination of processes responsible for a rise in atmospheric CO2 at the Last glacial termination (23,000 to 9,000 years ago), however, remains uncertain. Establishing the timing and rate of CO2 changes in the past provides critical insight into the mechanisms that influence the carbon cycle and helps put present and future anthropogenic emissions in context. Here we present CO2 and methane (CH4) records of the Last Deglaciation from a new high-accumulation West Antarctic ice core with unprecedented temporal resolution and precise chronology. We show that although low-frequency CO2 variations parallel changes in Antarctic temperature, abrupt CO2 changes occur that have a clear relationship with abrupt climate changes in the Northern Hemisphere. A significant proportion of the direct radiative forcing associated with the rise in atmospheric CO2 occurred in three sudden steps, each of 10 to 15 parts per million. Every step took place in less than two centuries and was followed by no notable change in atmospheric CO2 for about 1,000 to 1,500 years. Slow, millennial-scale ventilation of Southern Ocean CO2-rich, deep-ocean water masses is thought to have been fundamental to the rise in atmospheric CO2 associated with the glacial termination, given the strong covariance of CO2 levels and Antarctic temperatures. Our data establish a contribution from an abrupt, centennial-scale mode of CO2 variability that is not directly related to Antarctic temperature. We suggest that processes operating on centennial timescales, probably involving the Atlantic meridional overturning circulation, seem to be influencing global carbon-cycle dynamics and are at present not widely considered in Earth system models.
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centennial scale changes in the global carbon cycle during the Last Deglaciation
Nature, 2014Co-Authors: Christo Buizert, T. J. Fudge, Shaun A Marcott, T K Bauska, Eric J Steig, Julia Rosen, Kurt M Cuffey, J P Severinghaus, M KalkAbstract:Carbon dioxide and methane records from a West Antarctic ice core show that although gradual variations in the concentration of atmospheric carbon dioxide during the Last glacial termination are linked to changes in Antarctic temperature, the concentration underwent three abrupt, centennial-scale changes related to sudden climate changes in the Northern Hemisphere. The underlying processes responsible for a rise in atmospheric carbon dioxide levels at the Last glacial termination, between 23,000 and 9,000 years ago, remain uncertain. This paper presents high-resolution carbon dioxide and methane records of the Last Deglaciation from the West Antarctic Ice Sheet Divide ice core. The authors find that a significant proportion of the direct radiative forcing associated with the rise in atmospheric carbon dioxide during the Last glacial–interglacial occurred in three abrupt steps during approximately four centuries. They suggest that this fast, centennial scale mode of carbon dioxide variability is closely linked to Northern Hemisphere climate potentially controlled by the strength of the Atlantic meridional overturning circulation. Global climate and the concentration of atmospheric carbon dioxide (CO2) are correlated over recent glacial cycles1,2. The combination of processes responsible for a rise in atmospheric CO2 at the Last glacial termination1,3 (23,000 to 9,000 years ago), however, remains uncertain1,2,3. Establishing the timing and rate of CO2 changes in the past provides critical insight into the mechanisms that influence the carbon cycle and helps put present and future anthropogenic emissions in context. Here we present CO2 and methane (CH4) records of the Last Deglaciation from a new high-accumulation West Antarctic ice core with unprecedented temporal resolution and precise chronology. We show that although low-frequency CO2 variations parallel changes in Antarctic temperature, abrupt CO2 changes occur that have a clear relationship with abrupt climate changes in the Northern Hemisphere. A significant proportion of the direct radiative forcing associated with the rise in atmospheric CO2 occurred in three sudden steps, each of 10 to 15 parts per million. Every step took place in less than two centuries and was followed by no notable change in atmospheric CO2 for about 1,000 to 1,500 years. Slow, millennial-scale ventilation of Southern Ocean CO2-rich, deep-ocean water masses is thought to have been fundamental to the rise in atmospheric CO2 associated with the glacial termination4, given the strong covariance of CO2 levels and Antarctic temperatures5. Our data establish a contribution from an abrupt, centennial-scale mode of CO2 variability that is not directly related to Antarctic temperature. We suggest that processes operating on centennial timescales, probably involving the Atlantic meridional overturning circulation, seem to be influencing global carbon-cycle dynamics and are at present not widely considered in Earth system models.
