1
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Lu F, Pausata FSR, Mohtadi M. Reconstruct the intertropical convergence zone over the Indo-Pacific Warm Pool with extended records and empirical orthogonal function. Proc Natl Acad Sci U S A 2024; 121:e2408502121. [PMID: 38913901 DOI: 10.1073/pnas.2408502121] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/26/2024] Open
Affiliation(s)
- Fuzhi Lu
- School of Geography and Ocean Science, Nanjing University, Nanjing 210023, China
| | - Francesco S R Pausata
- Department of Earth and Atmospheric Sciences, University of Quebec in Montreal, Montreal H2L 2C4, Canada
| | - Mahyar Mohtadi
- Marine Umweltwissenschaften-Center for Marine Environmental Sciences, University of Bremen, Bremen 28359, Germany
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2
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Yuan S, Chiang HW, Liu G, Bijaksana S, He S, Jiang X, Imran AM, Wicaksono SA, Wang X. The strength, position, and width changes of the intertropical convergence zone since the Last Glacial Maximum. Proc Natl Acad Sci U S A 2023; 120:e2217064120. [PMID: 38033310 PMCID: PMC10666097 DOI: 10.1073/pnas.2217064120] [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: 10/06/2022] [Accepted: 09/18/2023] [Indexed: 12/02/2023] Open
Abstract
The intertropical convergence zone (ITCZ) plays a key role in regulating tropical hydroclimate and global water cycle through changes in its convection strength, latitudinal position, and width. The long-term variability of the ITCZ, along with the corresponding driving mechanisms, however, remains obscure, mainly because it is difficult to separate different ITCZ variables in paleoclimate proxy records. Here, we report a speleothem oxygen isotope (δ18O) record from southwestern Sulawesi, Indonesia, and compile it with other speleothem records from the Maritime Continent. Using the spatial gradient of speleothem δ18O along a transect across the ITCZ, we constrain ITCZ variabilities over the Maritime Continent during the past 30,000 y. We find that ITCZ convection strength overall intensified from the last glacial period to the Holocene, following changes in climate boundary conditions. The mean position of the regional ITCZ has moved latitudinally no more than 3° in the past 30,000 y, consistent with the deduction from the atmospheric energy framework. However, different from modern observations and model simulations for future warming, the ITCZ appeared narrower during both the late Holocene and most part of the last glacial period, and its expansion occurred during Heinrich stadials and the early-to-mid Holocene. We also find that during the last glacial and deglacial period, prominent millennial-scale ITCZ changes were closely tied to the variability of the Atlantic meridional overturning circulation (AMOC), whereas during the Holocene, they were predominantly modulated by the long-term variability of the Walker circulation.
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Affiliation(s)
- Shufang Yuan
- Earth Observatory of Singapore, Nanyang Technological University, Singapore639798, Singapore
- Asian School of Environment, Nanyang Technological University, 639798, Singapore
| | - Hong-Wei Chiang
- Department of Geosciences, National Taiwan University, Taipei10617, Taiwan
| | - Guangxin Liu
- Department of Atmospheric Science, Yunnan University, Kunming650500, China
| | - Satria Bijaksana
- Faculty of Mining and Petroleum Engineering, Institut Teknologi Bandung, Bandung40132, Indonesia
| | - Shaoneng He
- Earth Observatory of Singapore, Nanyang Technological University, Singapore639798, Singapore
- Asian School of Environment, Nanyang Technological University, 639798, Singapore
| | - Xiuyang Jiang
- School of Geographical Sciences, Fujian Normal University, Fuzhou350007, China
| | - Andi M. Imran
- Department of Geological Engineering, Hasanuddin University, Makassar90245, Indonesia
| | - Satrio A. Wicaksono
- Department of Earth, Environmental, and Planetary Sciences, Brown University, Providence, RI02912
| | - Xianfeng Wang
- Earth Observatory of Singapore, Nanyang Technological University, Singapore639798, Singapore
- Asian School of Environment, Nanyang Technological University, 639798, Singapore
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3
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Wolf A, Ersek V, Braun T, French AD, McGee D, Bernasconi SM, Skiba V, Griffiths ML, Johnson KR, Fohlmeister J, Breitenbach SFM, Pausata FSR, Tabor CR, Longman J, Roberts WHG, Chandan D, Peltier WR, Salzmann U, Limbert D, Trinh HQ, Trinh AD. Deciphering local and regional hydroclimate resolves contradicting evidence on the Asian monsoon evolution. Nat Commun 2023; 14:5697. [PMID: 37709741 PMCID: PMC10502020 DOI: 10.1038/s41467-023-41373-9] [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: 11/30/2022] [Accepted: 09/01/2023] [Indexed: 09/16/2023] Open
Abstract
The winter and summer monsoons in Southeast Asia are important but highly variable sources of rainfall. Current understanding of the winter monsoon is limited by conflicting proxy observations, resulting from the decoupling of regional atmospheric circulation patterns and local rainfall dynamics. These signals are difficult to decipher in paleoclimate reconstructions. Here, we present a winter monsoon speleothem record from Southeast Asia covering the Holocene and find that winter and summer rainfall changed synchronously, forced by changes in the Pacific and Indian Oceans. In contrast, regional atmospheric circulation shows an inverse relation between winter and summer controlled by seasonal insolation over the Northern Hemisphere. We show that disentangling the local and regional signal in paleoclimate reconstructions is crucial in understanding and projecting winter and summer monsoon variability in Southeast Asia.
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Affiliation(s)
- Annabel Wolf
- Department of Earth System Science, University of California, Irvine, CA, 92697, USA.
- Department of Geography and Environmental Sciences, Northumbria University Newcastle, Newcastle-upon-Tyne, NE1 8ST, UK.
| | - Vasile Ersek
- Department of Geography and Environmental Sciences, Northumbria University Newcastle, Newcastle-upon-Tyne, NE1 8ST, UK.
| | - Tobias Braun
- Potsdam Institute for Climate Impact Research, 14473, Potsdam, Germany
| | - Amanda D French
- Environmental Research Institute, Waikato University, Hamilton, 3240, New Zealand
| | - David McGee
- Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, 02139-4307, USA
| | | | - Vanessa Skiba
- Potsdam Institute for Climate Impact Research, 14473, Potsdam, Germany
| | - Michael L Griffiths
- Department of Environmental Science, William Paterson University, Wayne, NJ, 07470, USA
| | - Kathleen R Johnson
- Department of Earth System Science, University of California, Irvine, CA, 92697, USA
| | - Jens Fohlmeister
- Federal Office for Radiations Protection, 10318, Berlin, Germany
| | - Sebastian F M Breitenbach
- Department of Geography and Environmental Sciences, Northumbria University Newcastle, Newcastle-upon-Tyne, NE1 8ST, UK
| | - Francesco S R Pausata
- Department of Earth and Atmospheric Sciences, Centre ESCER (Étude et la Simulation du Climat à l'Échelle Régionale) and GEOTOP (Research Center on the dynamics of the Earth System), University of Quebec in Montreal, Montréal, QC, Canada
| | - Clay R Tabor
- Department of Earth Sciences, University of Connecticut, Storrs, CT, 06269, USA
| | - Jack Longman
- Department of Geography and Environmental Sciences, Northumbria University Newcastle, Newcastle-upon-Tyne, NE1 8ST, UK
- Institute for Chemistry and Biology of the Marine Environment (ICBM), University of Oldenburg, Oldenburg, 26129, Germany
| | - William H G Roberts
- Department of Geography and Environmental Sciences, Northumbria University Newcastle, Newcastle-upon-Tyne, NE1 8ST, UK
| | - Deepak Chandan
- Department of Physics, University of Toronto, 60 St. George Street, Toronto, ON, M5S1A7, Canada
| | - W Richard Peltier
- Department of Physics, University of Toronto, 60 St. George Street, Toronto, ON, M5S1A7, Canada
| | - Ulrich Salzmann
- Department of Geography and Environmental Sciences, Northumbria University Newcastle, Newcastle-upon-Tyne, NE1 8ST, UK
| | | | - Hong Quan Trinh
- Institute of Chemistry, Vietnam Academy of Science and Technology, Ha Noi, 10072, Viet Nam
| | - Anh Duc Trinh
- Nuclear Training Center, Vietnam Atomic Energy Institute, 140 Nguyen Tuan, Thanh Xuan, Ha Noi, 11416, Viet Nam
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4
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Wright KT, Johnson KR, Marks GS, McGee D, Bhattacharya T, Goldsmith GR, Tabor CR, Lacaille-Muzquiz JL, Lum G, Beramendi-Orosco L. Dynamic and thermodynamic influences on precipitation in Northeast Mexico on orbital to millennial timescales. Nat Commun 2023; 14:2279. [PMID: 37080955 PMCID: PMC10119167 DOI: 10.1038/s41467-023-37700-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2021] [Accepted: 03/28/2023] [Indexed: 04/22/2023] Open
Abstract
The timing and mechanisms of past hydroclimate change in northeast Mexico are poorly constrained, limiting our ability to evaluate climate model performance. To address this, we present a multiproxy speleothem record of past hydroclimate variability spanning 62.5 to 5.1 ka from Tamaulipas, Mexico. Here we show a strong influence of Atlantic and Pacific sea surface temperatures on orbital and millennial scale precipitation changes in the region. Multiple proxies show no clear response to insolation forcing, but strong evidence for dry conditions during Heinrich Stadials. While these trends are consistent with other records from across Mesoamerica and the Caribbean, the relative importance of thermodynamic and dynamic controls in driving this response is debated. An isotope-enabled climate model shows that cool Atlantic SSTs and stronger easterlies drive a strong inter-basin sea surface temperature gradient and a southward shift in moisture convergence, causing drying in this region.
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Affiliation(s)
- Kevin T Wright
- Dept. of Earth System Science, University of California, Irvine, 3200 Croul Hall, Irvine, CA, USA.
| | - Kathleen R Johnson
- Dept. of Earth System Science, University of California, Irvine, 3200 Croul Hall, Irvine, CA, USA.
| | - Gabriela Serrato Marks
- Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - David McGee
- Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA
| | | | - Gregory R Goldsmith
- Schmid College of Science and Technology, Chapman University, Orange, CA, USA
| | - Clay R Tabor
- Department of Geosciences, University of Connecticut, Storrs, CT, USA
| | | | - Gianna Lum
- Dept. of Earth System Science, University of California, Irvine, 3200 Croul Hall, Irvine, CA, USA
| | - Laura Beramendi-Orosco
- Instituto de Geología, Universidad Nacional Autónoma de México, Ciudad Universitaria, Ciudad de, México, México
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5
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Bagniewski W, Rousseau DD, Ghil M. The PaleoJump database for abrupt transitions in past climates. Sci Rep 2023; 13:4472. [PMID: 36934110 PMCID: PMC10024733 DOI: 10.1038/s41598-023-30592-1] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2022] [Accepted: 02/27/2023] [Indexed: 03/20/2023] Open
Abstract
Tipping points (TPs) in Earth's climate system have been the subject of increasing interest and concern in recent years, given the risk that anthropogenic forcing could cause abrupt, potentially irreversible, climate transitions. Paleoclimate records are essential for identifying past TPs and for gaining a thorough understanding of the underlying nonlinearities and bifurcation mechanisms. However, the quality, resolution, and reliability of these records can vary, making it important to carefully select the ones that provide the most accurate representation of past climates. Moreover, as paleoclimate time series vary in their origin, time spans, and periodicities, an objective, automated methodology is crucial for identifying and comparing TPs. To address these challenges, we introduce the open-source PaleoJump database, which contains a collection of carefully selected, high-resolution records originating in ice cores, marine sediments, speleothems, terrestrial records, and lake sediments. These records describe climate variability on centennial, millennial and longer time scales and cover all the continents and ocean basins. We provide an overview of their spatial distribution and discuss the gaps in coverage. Our statistical methodology includes an augmented Kolmogorov-Smirnov test and Recurrence Quantification Analysis; it is applied here, for illustration purposes, to selected records in which abrupt transitions are automatically detected and the presence of potential tipping elements is investigated. These transitions are shown in the PaleoJump database along with other essential information about the records, including location, temporal scale and resolution, as well as temporal plots. This open-source database represents, therefore, a valuable resource for researchers investigating TPs in past climates.
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Affiliation(s)
- Witold Bagniewski
- Department of Geosciences and Laboratoire de Météorologie Dynamique (CNRS and IPSL), École Normale Supérieure, PSL University, Paris, France.
| | - Denis-Didier Rousseau
- Geosciences Montpellier, CNRS, University of Montpellier, Montpellier, France
- Institute of Physics - CSE, Division of Geochronology and Environmental Isotopes, Silesian University of Technology, Gliwice, Poland
- Lamont-Doherty Earth Observatory, Columbia University, New York, USA
| | - Michael Ghil
- Department of Geosciences and Laboratoire de Météorologie Dynamique (CNRS and IPSL), École Normale Supérieure, PSL University, Paris, France
- Department of Atmospheric and Oceanic Sciences, University of California at Los Angeles, Los Angeles, USA
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6
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Antiphase response of the Indonesian-Australian monsoon to millennial-scale events of the last glacial period. Sci Rep 2022; 12:20214. [PMID: 36424387 PMCID: PMC9691635 DOI: 10.1038/s41598-022-21843-8] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2022] [Accepted: 10/04/2022] [Indexed: 11/27/2022] Open
Abstract
Antiphase behaviour of monsoon systems in alternate hemispheres is well established at yearly and orbital scales in response to alternating sensible heating of continental landmasses. At intermediate timescales without a sensible heating mechanism both in-phase and antiphase behaviours of northern and southern hemisphere monsoon systems are recorded at different places and timescales. At present, there is no continuous, high resolution, precisely dated record of millennial-scale variability of the Indonesian-Australian monsoon during the last glacial period with which to test theories of paleomonsoon behaviour. Here, we present an extension of the Liang Luar, Flores, speleothem δ18O record of past changes in southern hemisphere summer monsoon intensity back to 55.7 kyr BP. Negative δ18O excursions (stronger monsoon) occur during Heinrich events whereas positive excursions (weaker monsoon) occur during Dansgaard-Oeschger interstadials-a first order antiphase relationship with northern hemisphere summer monsoon records. An association of negative δ18O excursions with speleothem growth phases in Liang Luar suggests that these stronger monsoons are related to higher rainfall amounts. However, the response to millennial-scale variability is inconsistent, including a particularly weak response to Heinrich event 3. We suggest that additional drivers such as underlying orbital-scale variability and drip hydrology influence the δ18O response.
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7
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Hapsari KA, Jennerjahn T, Nugroho SH, Yulianto E, Behling H. Sea level rise and climate change acting as interactive stressors on development and dynamics of tropical peatlands in coastal Sumatra and South Borneo since the Last Glacial Maximum. GLOBAL CHANGE BIOLOGY 2022; 28:3459-3479. [PMID: 35312144 DOI: 10.1111/gcb.16131] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/06/2021] [Revised: 12/15/2021] [Accepted: 01/18/2022] [Indexed: 06/14/2023]
Abstract
Southeast Asian peatlands, along with their various important ecosystem services, are mainly distributed in the coastal areas of Sumatra and Borneo. These ecosystems are threatened by coastal development, global warming and sea level rise (SLR). Despite receiving growing attention for their biodiversity and as massive carbon stores, there is still a lack of knowledge on how they initiated and evolved over time, and how they responded to past environmental change, that is, precipitation, sea level and early anthropogenic activities. To improve our understanding thereof, we conducted multi-proxy paleoecological studies in the Kampar Peninsula and Katingan peatlands in the coastal area of Riau and Central Kalimantan, Indonesia. The results indicate that the initiation timing and environment of both peatlands are very distinct, suggesting that peat could form under various vegetation as soon as there is sufficient moisture to limit organic matter decomposition. The past dynamics of both peatlands were mainly attributable to natural drivers, while anthropogenic activities were hardly relevant. Changes in precipitation and sea level led to shifts in peat swamp forest vegetation, peat accumulation rates and fire regimes at both sites. We infer that the simultaneous occurrence of El Niño-Southern Oscillation (ENSO) events and SLR resulted in synergistic effects which led to the occurrence of severe fires in a pristine coastal peatland ecosystem; however, it did not interrupt peat accretion. In the future, SLR, combined with the projected increase in frequency and intensity of ENSO, can potentially amplify the negative effects of anthropogenic peatland fires. This prospectively stimulates massive carbon release, thus could, in turn, contribute to worsening the global climate crisis especially once an as yet unknown threshold is crossed and peat accretion is halted, that is, peatlands lose their carbon sink function. Given the current rapid SLR, coastal peatland managements should start develop fire risk reduction or mitigation strategies.
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Affiliation(s)
- K Anggi Hapsari
- Department of Palynology and Climate Dynamics, University of Goettingen, Goettingen, Germany
| | - Tim Jennerjahn
- Department of Biogeochemistry and Geology, Leibniz Centre for Tropical Marine Research (ZMT), Bremen, Germany
- Faculty of Geoscience, University of Bremen, Bremen, Germany
| | - Septriono Hari Nugroho
- Research Center for Geotechnology, National Research and Innovation Agency (BRIN), Bandung, Indonesia
| | - Eko Yulianto
- Research Center for Geotechnology, National Research and Innovation Agency (BRIN), Bandung, Indonesia
| | - Hermann Behling
- Department of Palynology and Climate Dynamics, University of Goettingen, Goettingen, Germany
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8
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Huang E, Wang P, Wang Y, Yan M, Tian J, Li S, Ma W. Dole effect as a measurement of the low-latitude hydrological cycle over the past 800 ka. SCIENCE ADVANCES 2020; 6:6/41/eaba4823. [PMID: 33028516 PMCID: PMC7541075 DOI: 10.1126/sciadv.aba4823] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/20/2019] [Accepted: 08/20/2020] [Indexed: 06/11/2023]
Abstract
The quest of geological proxies to evaluate low-latitude hydrological changes at a planetary scale remains an ongoing issue. The Dole effect is such a potential proxy owing to its global character. We propose a new approach to recalculate the fluctuation of the Dole effect (∆DE*) over the past 800 thousand years (ka). The ∆DE* calculated this way is dominated by precession cycles alone, with lesser variance in the obliquity bands and almost no variance in the eccentricity bands. Moreover, the ∆DE* is notably correlated with Chinese stalagmite δ18O record over the past 640 ka; simulated terrestrial rainfall changes between 30°N and 30°S over the past 300 ka. Our findings highlight the predominant role of the low-latitude hydroclimate in governing the ∆DE* on orbital time scales, while high-latitude climate impacts are negligible. In turn, we argue that the ∆DE* can be used to indicate low-latitude hydrological changes at a global extent.
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Affiliation(s)
- Enqing Huang
- State Key Laboratory of Marine Geology, Tongji University, Shanghai 200092, China.
| | - Pinxian Wang
- State Key Laboratory of Marine Geology, Tongji University, Shanghai 200092, China
| | - Yue Wang
- State Key Laboratory of Marine Geology, Tongji University, Shanghai 200092, China
| | - Mi Yan
- Key Laboratory for Virtual Geographic Environment, School of Geography, Nanjing Normal University, Nanjing 210023, China
| | - Jun Tian
- State Key Laboratory of Marine Geology, Tongji University, Shanghai 200092, China
| | - Shihan Li
- State Key Laboratory of Marine Geology, Tongji University, Shanghai 200092, China
| | - Wentao Ma
- State Key Laboratory of Marine Geology, Tongji University, Shanghai 200092, China
- State Key Laboratory of Satellite Ocean Environment Dynamics, Second Institute of Oceanography, Hangzhou 310012, China
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9
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Dang H, Jian Z, Wang Y, Mohtadi M, Rosenthal Y, Ye L, Bassinot F, Kuhnt W. Pacific warm pool subsurface heat sequestration modulated Walker circulation and ENSO activity during the Holocene. SCIENCE ADVANCES 2020; 6:6/42/eabc0402. [PMID: 33055161 PMCID: PMC7556771 DOI: 10.1126/sciadv.abc0402] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/02/2020] [Accepted: 08/25/2020] [Indexed: 06/11/2023]
Abstract
Dynamics driving the El Niño-Southern Oscillation (ENSO) over longer-than-interannual time scales are poorly understood. Here, we compile thermocline temperature records of the Indo-Pacific warm pool over the past 25,000 years, which reveal a major warming in the Early Holocene and a secondary warming in the Middle Holocene. We suggest that the first thermocline warming corresponds to heat transport of southern Pacific shallow overturning circulation driven by June (austral winter) insolation maximum. The second thermocline warming follows equatorial September insolation maximum, which may have caused a steeper west-east upper-ocean thermal gradient and an intensified Walker circulation in the equatorial Pacific. We propose that the warm pool thermocline warming ultimately reduced the interannual ENSO activity in the Early to Middle Holocene. Thus, a substantially increased oceanic heat content of the warm pool, acting as a negative feedback for ENSO in the past, may play its role in the ongoing global warming.
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Affiliation(s)
- Haowen Dang
- State Key Laboratory of Marine Geology, Tongji University, Shanghai 200092, China
| | - Zhimin Jian
- State Key Laboratory of Marine Geology, Tongji University, Shanghai 200092, China.
| | - Yue Wang
- State Key Laboratory of Marine Geology, Tongji University, Shanghai 200092, China
| | - Mahyar Mohtadi
- MARUM-Center for Marine Environmental Sciences, University of Bremen, 28359 Bremen, Germany
| | - Yair Rosenthal
- Department of Marine and Coastal Science and Department of Earth and Planetary Sciences, Rutgers University, New Brunswick, NJ 08901, USA
| | - Liming Ye
- Key Laboratory of Submarine Geosciences, Second Institute of Oceanography, Ministry of Natural Resources of China, Hangzhou 310012, China
| | - Franck Bassinot
- Laboratoire des Sciences du Climat et de l'Environnement/IPSL, CEA-CNRS-UVSQ, University Paris-Saclay, 91198 Gif-sur-Yvette, France
| | - Wolfgang Kuhnt
- Institute of Geosciences, Christian-Albrechts-University, D-24118 Kiel, Germany
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10
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Initiation of a stable convective hydroclimatic regime in Central America circa 9000 years BP. Nat Commun 2020; 11:716. [PMID: 32024832 PMCID: PMC7002718 DOI: 10.1038/s41467-020-14490-y] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2018] [Accepted: 12/16/2019] [Indexed: 11/08/2022] Open
Abstract
Many Holocene hydroclimate records show rainfall changes that vary with local orbital insolation. However, some tropical regions display rainfall evolution that differs from gradual precessional pacing, suggesting that direct rainfall forcing effects were predominantly driven by sea-surface temperature thresholds or inter-ocean temperature gradients. Here we present a 12,000 yr continuous U/Th-dated precipitation record from a Guatemalan speleothem showing that Central American rainfall increased within a 2000 yr period from a persistently dry state to an active convective regime at 9000 yr BP and has remained strong thereafter. Our data suggest that the Holocene evolution of Central American rainfall was driven by exceeding a temperature threshold in the nearby tropical oceans. The sensitivity of this region to slow changes in radiative forcing is thus strongly mediated by internal dynamics acting on much faster time scales.
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11
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Abstract
Glacial-interglacial cycles have constituted a primary mode of climate variability over the last 2.6 million years of Earth's history. While glacial periods cannot be seen simply as a reverse analogue of future warming, they offer an opportunity to test our understanding of the response of precipitation patterns to a much wider range of conditions than we have been able to directly observe. This review explores key features of precipitation patterns associated with glacial climates, which include drying in large regions of the tropics and wetter conditions in substantial parts of the subtropics and midlatitudes. I describe the evidence for these changes and examine the potential causes of hydrological changes during glacial periods. Central themes that emerge include the importance of atmospheric circulation changes in determining glacial-interglacial precipitation changes at the regional scale, the need to take into account climatic factors beyond local precipitation amount when interpreting proxy data, and the role of glacial conditions in suppressing the strength of Northern Hemisphere monsoon systems.
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Affiliation(s)
- David McGee
- Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA;
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12
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Abstract
We present a high-resolution, replicated speleothem δ18O record from Klang Cave in southern Thailand that characterizes rainfall variation in NCIP over the past 2,700 y. This record reveals notable dry climate conditions during the current and past warm periods, similar to the observations in SCIP, which resemble enhanced El Niño-like conditions. Using a newly developed ITCZ shift index, we find a southward shifted ITCZ during the early MWP and the CWP. Our results suggest that detecting changes in rainfall due to anthropogenic forcing still remains indistinguishable from natural variability in the northern tropics. Tropical rainfall variability is closely linked to meridional shifts of the Intertropical Convergence Zone (ITCZ) and zonal movements of the Walker circulation. The characteristics and mechanisms of tropical rainfall variations on centennial to decadal scales are, however, still unclear. Here, we reconstruct a replicated stalagmite-based 2,700-y-long, continuous record of rainfall for the deeply convective northern central Indo-Pacific (NCIP) region. Our record reveals decreasing rainfall in the NCIP over the past 2,700 y, similar to other records from the northern tropics. Notable centennial- to decadal-scale dry climate episodes occurred in both the NCIP and the southern central Indo-Pacific (SCIP) during the 20th century [Current Warm Period (CWP)] and the Medieval Warm Period (MWP), resembling enhanced El Niño-like conditions. Further, we developed a 2,000-y-long ITCZ shift index record that supports an overall southward ITCZ shift in the central Indo-Pacific and indicates southward mean ITCZ positions during the early MWP and the CWP. As a result, the drying trend since the 20th century in the northern tropics is similar to that observed during the past warm period, suggesting that a possible anthropogenic forcing of rainfall remains indistinguishable from natural variability.
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13
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Wurster CM, Rifai H, Zhou B, Haig J, Bird MI. Savanna in equatorial Borneo during the late Pleistocene. Sci Rep 2019; 9:6392. [PMID: 31024024 PMCID: PMC6483998 DOI: 10.1038/s41598-019-42670-4] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2018] [Accepted: 04/02/2019] [Indexed: 12/01/2022] Open
Abstract
Equatorial Southeast Asia is a key region for global climate change. Here, the Indo-Pacific Warm Pool (IPWP) is a critical driver of atmospheric convection that plays a dominant role in global atmospheric circulation. However, fluctuating sea-levels during the Pleistocene produced the most drastic land-sea area changes on Earth, with the now-drowned continent of Sundaland being exposed as a contiguous landmass for most of the past 2 million years. How vegetation responded to changes in rainfall that resulted from changing shelf exposure and glacial boundary conditions in Sundaland remains poorly understood. Here we use the stable carbon isotope composition (δ13C) of bat guano and High Molecular Weight n-alkanes, from Saleh Cave in southern Borneo to demonstrate that open vegetation existed during much the past 40,000 yrs BP. This location is at the southern equatorial end of a hypothesized ‘savanna corridor’ and the results provide the strongest evidence yet for its existence. The corridor would have operated as a barrier to east-west dispersal of rainforest species, and a conduit for north-south dispersal of savanna species at times of lowered sea level, explaining many modern biogeographic patterns. The Saleh Cave record also exhibits a strong correspondence with insolation and sea surface temperatures of the IPWP, suggesting a strong sensitivity of vegetation to tropical climate change on glacial/interglacial timeframes.
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Affiliation(s)
- Christopher M Wurster
- College of Science and Engineering, James Cook University, Cairns, Queensland, 4870, Australia. .,ARC Centre of Excellence for Australian Biodiversity and Heritage, James Cook University, Cairns, Queensland, 4870, Australia. .,Centre of Tropical Environmental and Sustainability Sciences, James Cook University, Cairns, Queensland, 4870, Australia.
| | - Hamdi Rifai
- Department of Physics Faculty of Mathematics and Natural Sciences, Universitas Negeri Padang, Padang, 25131, Indonesia
| | - Bin Zhou
- Key Laboratory of Surficial Geochemistry (Ministry of Education), School of Earth Sciences and Engineering, Nanjing University, Nanjing, China
| | - Jordahna Haig
- College of Science and Engineering, James Cook University, Cairns, Queensland, 4870, Australia.,ARC Centre of Excellence for Australian Biodiversity and Heritage, James Cook University, Cairns, Queensland, 4870, Australia.,Centre of Tropical Environmental and Sustainability Sciences, James Cook University, Cairns, Queensland, 4870, Australia
| | - Michael I Bird
- College of Science and Engineering, James Cook University, Cairns, Queensland, 4870, Australia.,ARC Centre of Excellence for Australian Biodiversity and Heritage, James Cook University, Cairns, Queensland, 4870, Australia.,Centre of Tropical Environmental and Sustainability Sciences, James Cook University, Cairns, Queensland, 4870, Australia
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14
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DiNezio PN, Tierney JE, Otto-Bliesner BL, Timmermann A, Bhattacharya T, Rosenbloom N, Brady E. Glacial changes in tropical climate amplified by the Indian Ocean. SCIENCE ADVANCES 2018; 4:eaat9658. [PMID: 30547084 PMCID: PMC6291310 DOI: 10.1126/sciadv.aat9658] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/23/2018] [Accepted: 11/14/2018] [Indexed: 05/26/2023]
Abstract
The mechanisms driving glacial-interglacial changes in the climate of the Indo-Pacific warm pool are poorly understood. Here, we address this question by combining paleoclimate proxies with model simulations of the Last Glacial Maximum climate. We find evidence of two mechanisms explaining key patterns of ocean cooling and rainfall change interpreted from proxy data. Exposure of the Sahul shelf excites a positive ocean-atmosphere feedback involving a stronger surface temperature gradient along the equatorial Indian Ocean and a weaker Walker circulation-a response explaining the drier/wetter dipole across the basin. Northern Hemisphere cooling by ice sheet albedo drives a monsoonal retreat across Africa and the Arabian Peninsula-a response that triggers a weakening of the Indian monsoon via cooling of the Arabian Sea and associated reductions in moisture supply. These results demonstrate the importance of air-sea interactions in the Indian Ocean, amplifying externally forced climate changes over a large part of the tropics.
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Affiliation(s)
- Pedro N. DiNezio
- Institute for Geophysics, Jackson School of Geosciences, University of Texas at Austin, J.J. Pickle Research Campus, Building 196 10100 Burnet Road (R2200), Austin, TX 78758, USA
| | - Jessica E. Tierney
- Department of Geosciences, The University of Arizona, 1040 E 4th Street, Tucson, AZ 85721, USA
| | - Bette L. Otto-Bliesner
- National Center for Atmospheric Research, Climate and Global Dynamics Laboratory, 1850 Table Mesa Drive, Boulder, CO 80305, USA
| | - Axel Timmermann
- Center for Climate Physics, Institute for Basic Science, Busandaehak-ro 63beon-gil 2, Geumjeong-gu, Busan 46241, South Korea
- Pusan National University, Busandaehak-ro 63beon-gil 2, Geumjeong-gu, Busan 46241, South Korea
| | - Tripti Bhattacharya
- Department of Earth Science, Syracuse University, 204 Heroy Geology Laboratory, Syracuse, NY 13244-1070, USA
| | - Nan Rosenbloom
- National Center for Atmospheric Research, Climate and Global Dynamics Laboratory, 1850 Table Mesa Drive, Boulder, CO 80305, USA
| | - Esther Brady
- National Center for Atmospheric Research, Climate and Global Dynamics Laboratory, 1850 Table Mesa Drive, Boulder, CO 80305, USA
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15
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Who were the Nataruk people? Mandibular morphology among late Pleistocene and early Holocene fisher-forager populations of West Turkana (Kenya). J Hum Evol 2018; 121:235-253. [PMID: 29857967 DOI: 10.1016/j.jhevol.2018.04.013] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2017] [Revised: 04/24/2018] [Accepted: 04/25/2018] [Indexed: 01/27/2023]
Abstract
Africa is the birthplace of the species Homo sapiens, and Africans today are genetically more diverse than other populations of the world. However, the processes that underpinned the evolution of African populations remain largely obscure. Only a handful of late Pleistocene African fossils (∼50-12 Ka) are known, while the more numerous sites with human fossils of early Holocene age are patchily distributed. In particular, late Pleistocene and early Holocene human diversity in Eastern Africa remains little studied, precluding any analysis of the potential factors that shaped human diversity in the region, and more broadly throughout the continent. These periods include the Last Glacial Maximum (LGM), a moment of extreme aridity in Africa that caused the fragmentation of population ranges and localised extinctions, as well as the 'African Humid Period', a moment of abrupt climate change and enhanced connectivity throughout Africa. East Africa, with its range of environments, may have acted as a refugium during the LGM, and may have played a critical biogeographic role during the heterogene`ous environmental recovery that followed. This environmental context raises a number of questions about the relationships among early Holocene African populations, and about the role played by East Africa in shaping late hunter-gatherer biological diversity. Here, we describe eight mandibles from Nataruk, an early Holocene site (∼10 Ka) in West Turkana, offering the opportunity of exploring population diversity in Africa at the height of the 'African Humid Period'. We use 3D geometric morphometric techniques to analyze the phenotypic variation of a large mandibular sample. Our results show that (i) the Nataruk mandibles are most similar to other African hunter-fisher-gatherer populations, especially to the fossils from Lothagam, another West Turkana locality, and to other early Holocene fossils from the Central Rift Valley (Kenya); and (ii) a phylogenetic connection may have existed between these Eastern African populations and some Nile Valley and Maghrebian groups, who lived at a time when a Green Sahara may have allowed substantial contact, and potential gene flow, across a vast expanse of Northern and Eastern Africa.
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16
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Southern Hemisphere climate variability forced by Northern Hemisphere ice-sheet topography. Nature 2018; 554:351-355. [DOI: 10.1038/nature24669] [Citation(s) in RCA: 34] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2017] [Accepted: 10/19/2017] [Indexed: 11/09/2022]
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17
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Extensive wet episodes in Late Glacial Australia resulting from high-latitude forcings. Sci Rep 2017; 7:44054. [PMID: 31004127 PMCID: PMC5341032 DOI: 10.1038/srep44054] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2016] [Accepted: 02/03/2017] [Indexed: 11/08/2022] Open
Abstract
Millennial-scale cooling events termed Heinrich Stadials punctuated Northern Hemisphere climate during the last glacial period. Latitudinal shifts of the intertropical convergence zone (ITCZ) are thought to have rapidly propagated these abrupt climatic signals southward, influencing the evolution of Southern Hemisphere climates and contributing to major reorganisation of the global ocean-atmosphere system. Here, we use neodymium isotopes from a marine sediment core to reconstruct the hydroclimatic evolution of subtropical Australia between 90 to 20 thousand years ago. We find a strong correlation between our sediment provenance proxy data and records for western Pacific tropical precipitations and Australian palaeolakes, which indicates that Northern Hemisphere cooling phases were accompanied by pronounced excursions of the ITCZ and associated rainfall as far south as about 32°S. Comparatively, however, each of these humid periods lasted substantially longer than the mean duration of Heinrich Stadials, overlapping with subsequent warming phases of the southern high-latitudes recorded in Antarctic ice cores. In addition to ITCZ-driven hydroclimate forcing, we infer that changes in Southern Ocean climate also played an important role in regulating late glacial atmospheric patterns of the Southern Hemisphere subtropical regions.
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18
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Johnson CN, Alroy J, Beeton NJ, Bird MI, Brook BW, Cooper A, Gillespie R, Herrando-Pérez S, Jacobs Z, Miller GH, Prideaux GJ, Roberts RG, Rodríguez-Rey M, Saltré F, Turney CSM, Bradshaw CJA. What caused extinction of the Pleistocene megafauna of Sahul? Proc Biol Sci 2017; 283:rspb.2015.2399. [PMID: 26865301 DOI: 10.1098/rspb.2015.2399] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
During the Pleistocene, Australia and New Guinea supported a rich assemblage of large vertebrates. Why these animals disappeared has been debated for more than a century and remains controversial. Previous synthetic reviews of this problem have typically focused heavily on particular types of evidence, such as the dating of extinction and human arrival, and have frequently ignored uncertainties and biases that can lead to misinterpretation of this evidence. Here, we review diverse evidence bearing on this issue and conclude that, although many knowledge gaps remain, multiple independent lines of evidence point to direct human impact as the most likely cause of extinction.
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Affiliation(s)
- C N Johnson
- School of Biological Sciences, University of Tasmania, Private Bag 55, Hobart, Tasmania 7001, Australia
| | - J Alroy
- Department of Biological Sciences, Macquarie University, New South Wales 2109, Australia
| | - N J Beeton
- School of Biological Sciences, University of Tasmania, Private Bag 55, Hobart, Tasmania 7001, Australia
| | - M I Bird
- Centre for Tropical Environmental and Sustainability Studies, College of Science Technology and Engineering, James Cook University, Cairns, Queensland 4878, Australia
| | - B W Brook
- School of Biological Sciences, University of Tasmania, Private Bag 55, Hobart, Tasmania 7001, Australia
| | - A Cooper
- Australian Centre for Ancient DNA, School of Biological Sciences, The University of Adelaide, Adelaide, South Australia 5005, Australia
| | - R Gillespie
- Centre for Archaeological Science, School of Earth and Environmental Sciences, University of Wollongong, New South Wales 2522, Australia Archaeology and Natural History, School of Culture, History and Language, Australian National University, Canberra, Australian Capital Territory 0200, Australia
| | - S Herrando-Pérez
- The Environment Institute, School of Biological Sciences, The University of Adelaide, Adelaide, South Australia 5005, Australia Department of Biogeography and Global Change, National Museum of Natural Sciences-Spanish Research Council (CSIC) c/ José Gutiérrez Abascal 2, 28006 Madrid, Spain
| | - Z Jacobs
- Centre for Archaeological Science, School of Earth and Environmental Sciences, University of Wollongong, New South Wales 2522, Australia
| | - G H Miller
- Institute of Arctic and Alpine Research, Geological Sciences, University of Colorado, Boulder, CO 80309-0450, USA Environment and Agriculture, Curtin University, Perth, Western Australia 6102, Australia
| | - G J Prideaux
- School of Biological Sciences, Flinders University, Bedford Park, South Australia 5042, Australia
| | - R G Roberts
- Centre for Archaeological Science, School of Earth and Environmental Sciences, University of Wollongong, New South Wales 2522, Australia
| | - M Rodríguez-Rey
- The Environment Institute, School of Biological Sciences, The University of Adelaide, Adelaide, South Australia 5005, Australia
| | - F Saltré
- The Environment Institute, School of Biological Sciences, The University of Adelaide, Adelaide, South Australia 5005, Australia
| | - C S M Turney
- Climate Change Research Centre, University of New South Wales, Sydney, New South Wales 2052, Australia
| | - C J A Bradshaw
- The Environment Institute, School of Biological Sciences, The University of Adelaide, Adelaide, South Australia 5005, Australia
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19
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Mirazón Lahr M. The shaping of human diversity: filters, boundaries and transitions. Philos Trans R Soc Lond B Biol Sci 2016; 371:20150241. [PMID: 27298471 PMCID: PMC4920297 DOI: 10.1098/rstb.2015.0241] [Citation(s) in RCA: 48] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/25/2016] [Indexed: 01/21/2023] Open
Abstract
The evolution of modern humans was a complex process, involving major changes in levels of diversity through time. The fossils and stone tools that record the spatial distribution of our species in the past form the backbone of our evolutionary history, and one that allows us to explore the different processes-cultural and biological-that acted to shape the evolution of different populations in the face of major climate change. Those processes created a complex palimpsest of similarities and differences, with outcomes that were at times accelerated by sharp demographic and geographical fluctuations. The result is that the population ancestral to all modern humans did not look or behave like people alive today. This has generated questions regarding the evolution of human universal characters, as well as the nature and timing of major evolutionary events in the history of Homo sapiens The paucity of African fossils remains a serious stumbling block for exploring some of these issues. However, fossil and archaeological discoveries increasingly clarify important aspects of our past, while breakthroughs from genomics and palaeogenomics have revealed aspects of the demography of Late Quaternary Eurasian hominin groups and their interactions, as well as those between foragers and farmers. This paper explores the nature and timing of key moments in the evolution of human diversity, moments in which population collapse followed by differential expansion of groups set the conditions for transitional periods. Five transitions are identified (i) at the origins of the species, 240-200 ka; (ii) at the time of the first major expansions, 130-100 ka; (iii) during a period of dispersals, 70-50 ka; (iv) across a phase of local/regional structuring of diversity, 45-25 ka; and (v) during a phase of significant extinction of hunter-gatherer diversity and expansion of particular groups, such as farmers and later societies (the Holocene Filter), 15-0 ka.This article is part of the themed issue 'Major transitions in human evolution'.
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Affiliation(s)
- Marta Mirazón Lahr
- Leverhulme Centre for Human Evolutionary Studies, Department of Archaeology and Anthropology, University of Cambridge, Fitzwilliam Street, Cambridge CB2 1QH, UK
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20
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Was millennial scale climate change during the Last Glacial triggered by explosive volcanism? Sci Rep 2015; 5:17442. [PMID: 26616338 PMCID: PMC4663491 DOI: 10.1038/srep17442] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2015] [Accepted: 10/29/2015] [Indexed: 11/24/2022] Open
Abstract
The mechanisms responsible for millennial scale climate change within glacial time
intervals are equivocal. Here we show that all eight known radiometrically-dated
Tambora-sized or larger NH eruptions over the interval 30 to 80 ka BP
are associated with abrupt Greenland cooling (>95% confidence). Additionally,
previous research reported a strong statistical correlation between the timing of
Southern Hemisphere volcanism and Dansgaard-Oeschger (DO) events (>99%
confidence), but did not identify a causative mechanism. Volcanic aerosol-induced
asymmetrical hemispheric cooling over the last few hundred years restructured
atmospheric circulation in a similar fashion as that associated with Last Glacial
millennial-scale shifts (albeit on a smaller scale). We hypothesise that following
both recent and Last Glacial NH eruptions, volcanogenic sulphate injections into the
stratosphere cooled the NH preferentially, inducing a hemispheric temperature
asymmetry that shifted atmospheric circulation cells southward. This resulted in
Greenland cooling, Antarctic warming, and a southward shifted ITCZ. However, during
the Last Glacial, the initial eruption-induced climate response was prolonged by NH
glacier and sea ice expansion, increased NH albedo, AMOC weakening, more NH cooling,
and a consequent positive feedback. Conversely, preferential SH cooling following
large SH eruptions shifted atmospheric circulation to the north, resulting in the
characteristic features of DO events.
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21
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Ozken I, Eroglu D, Stemler T, Marwan N, Bagci GB, Kurths J. Transformation-cost time-series method for analyzing irregularly sampled data. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2015; 91:062911. [PMID: 26172776 DOI: 10.1103/physreve.91.062911] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/20/2015] [Indexed: 06/04/2023]
Abstract
Irregular sampling of data sets is one of the challenges often encountered in time-series analysis, since traditional methods cannot be applied and the frequently used interpolation approach can corrupt the data and bias the subsequence analysis. Here we present the TrAnsformation-Cost Time-Series (TACTS) method, which allows us to analyze irregularly sampled data sets without degenerating the quality of the data set. Instead of using interpolation we consider time-series segments and determine how close they are to each other by determining the cost needed to transform one segment into the following one. Using a limited set of operations-with associated costs-to transform the time series segments, we determine a new time series, that is our transformation-cost time series. This cost time series is regularly sampled and can be analyzed using standard methods. While our main interest is the analysis of paleoclimate data, we develop our method using numerical examples like the logistic map and the Rössler oscillator. The numerical data allows us to test the stability of our method against noise and for different irregular samplings. In addition we provide guidance on how to choose the associated costs based on the time series at hand. The usefulness of the TACTS method is demonstrated using speleothem data from the Secret Cave in Borneo that is a good proxy for paleoclimatic variability in the monsoon activity around the maritime continent.
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Affiliation(s)
- Ibrahim Ozken
- Department of Physics, Ege University, 35100 Izmir, Turkey
- Potsdam Institute for Climate Impact Research (PIK), 14473 Potsdam, Germany
| | - Deniz Eroglu
- Potsdam Institute for Climate Impact Research (PIK), 14473 Potsdam, Germany
- Department of Physics, Humboldt University, 12489 Berlin, Germany
| | - Thomas Stemler
- School of Mathematics and Statistics, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia
| | - Norbert Marwan
- Potsdam Institute for Climate Impact Research (PIK), 14473 Potsdam, Germany
| | - G Baris Bagci
- Department of Materials Science and Nanotechnology Engineering, TOBB University of Economics and Technology, 06560 Ankara, Turkey
| | - Jürgen Kurths
- Potsdam Institute for Climate Impact Research (PIK), 14473 Potsdam, Germany
- Department of Physics, Humboldt University, 12489 Berlin, Germany
- Institute for Complex Systems and Mathematical Biology, University of Aberdeen, Aberdeen AB24 3UE, United Kingdom
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22
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Rhodes RH, Brook EJ, Chiang JCH, Blunier T, Maselli OJ, McConnell JR, Romanini D, Severinghaus JP. Paleoclimate. Enhanced tropical methane production in response to iceberg discharge in the North Atlantic. Science 2015; 348:1016-9. [PMID: 26023138 DOI: 10.1126/science.1262005] [Citation(s) in RCA: 92] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
The causal mechanisms responsible for the abrupt climate changes of the Last Glacial Period remain unclear. One major difficulty is dating ice-rafted debris deposits associated with Heinrich events: Extensive iceberg influxes into the North Atlantic Ocean linked to global impacts on climate and biogeochemistry. In a new ice core record of atmospheric methane with ultrahigh temporal resolution, we find abrupt methane increases within Heinrich stadials 1, 2, 4, and 5 that, uniquely, have no counterparts in Greenland temperature proxies. Using a heuristic model of tropical rainfall distribution, we propose that Hudson Strait Heinrich events caused rainfall intensification over Southern Hemisphere land areas, thereby producing excess methane in tropical wetlands. Our findings suggest that the climatic impacts of Heinrich events persisted for 740 to 1520 years.
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Affiliation(s)
- Rachael H Rhodes
- College of Earth, Ocean, and Atmospheric Sciences, 104 CEOAS Administration, Oregon State University, Corvallis, OR 97331, USA.
| | - Edward J Brook
- College of Earth, Ocean, and Atmospheric Sciences, 104 CEOAS Administration, Oregon State University, Corvallis, OR 97331, USA
| | - John C H Chiang
- Department of Geography and Berkeley Atmospheric Sciences Center, University of California, Berkeley, CA, USA
| | - Thomas Blunier
- Center for Ice and Climate, Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark
| | - Olivia J Maselli
- Division of Hydrologic Sciences, Desert Research Institute, 2215 Raggio Parkway, Reno, NV 89512, USA
| | - Joseph R McConnell
- Division of Hydrologic Sciences, Desert Research Institute, 2215 Raggio Parkway, Reno, NV 89512, USA
| | - Daniele Romanini
- Joseph Fourier University-Grenoble 1/CNRS, LIPhy UMR 5588, Grenoble, F-38041, France
| | - Jeffrey P Severinghaus
- Scripps Institution of Oceanography, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0244, USA
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23
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Migrations and dynamics of the intertropical convergence zone. Nature 2014; 513:45-53. [PMID: 25186899 DOI: 10.1038/nature13636] [Citation(s) in RCA: 113] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2013] [Accepted: 07/01/2014] [Indexed: 11/08/2022]
Abstract
Rainfall on Earth is most intense in the intertropical convergence zone (ITCZ), a narrow belt of clouds centred on average around six degrees north of the Equator. The mean position of the ITCZ north of the Equator arises primarily because the Atlantic Ocean transports energy northward across the Equator, rendering the Northern Hemisphere warmer than the Southern Hemisphere. On seasonal and longer timescales, the ITCZ migrates, typically towards a warming hemisphere but with exceptions, such as during El Niño events. An emerging framework links the ITCZ to the atmospheric energy balance and may account for ITCZ variations on timescales from years to geological epochs.
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24
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Rapid interhemispheric climate links via the Australasian monsoon during the last deglaciation. Nat Commun 2014; 4:2908. [PMID: 24309539 DOI: 10.1038/ncomms3908] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2013] [Accepted: 11/08/2013] [Indexed: 11/08/2022] Open
Abstract
Recent studies have proposed that millennial-scale reorganization of the ocean-atmosphere circulation drives increased upwelling in the Southern Ocean, leading to rising atmospheric carbon dioxide levels and ice age terminations. Southward migration of the global monsoon is thought to link the hemispheres during deglaciation, but vital evidence from the southern sector of the vast Australasian monsoon system is yet to emerge. Here we present a 230thorium-dated stalagmite oxygen isotope record of millennial-scale changes in Australian-Indonesian monsoon rainfall over the last 31,000 years. The record shows that abrupt southward shifts of the Australian-Indonesian monsoon were synchronous with North Atlantic cold intervals 17,600-11,500 years ago. The most prominent southward shift occurred in lock-step with Heinrich Stadial 1 (17,600-14,600 years ago), and rising atmospheric carbon dioxide. Our findings show that millennial-scale climate change was transmitted rapidly across Australasia and lend support to the idea that the 3,000-year-long Heinrich 1 interval could have been critical in driving the last deglaciation.
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25
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North Atlantic forcing of tropical Indian Ocean climate. Nature 2014; 509:76-80. [PMID: 24784218 DOI: 10.1038/nature13196] [Citation(s) in RCA: 160] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2013] [Accepted: 02/28/2014] [Indexed: 11/09/2022]
Abstract
The response of the tropical climate in the Indian Ocean realm to abrupt climate change events in the North Atlantic Ocean is contentious. Repositioning of the intertropical convergence zone is thought to have been responsible for changes in tropical hydroclimate during North Atlantic cold spells, but the dearth of high-resolution records outside the monsoon realm in the Indian Ocean precludes a full understanding of this remote relationship and its underlying mechanisms. Here we show that slowdowns of the Atlantic meridional overturning circulation during Heinrich stadials and the Younger Dryas stadial affected the tropical Indian Ocean hydroclimate through changes to the Hadley circulation including a southward shift in the rising branch (the intertropical convergence zone) and an overall weakening over the southern Indian Ocean. Our results are based on new, high-resolution sea surface temperature and seawater oxygen isotope records of well-dated sedimentary archives from the tropical eastern Indian Ocean for the past 45,000 years, combined with climate model simulations of Atlantic circulation slowdown under Marine Isotope Stages 2 and 3 boundary conditions. Similar conditions in the east and west of the basin rule out a zonal dipole structure as the dominant forcing of the tropical Indian Ocean hydroclimate of millennial-scale events. Results from our simulations and proxy data suggest dry conditions in the northern Indian Ocean realm and wet and warm conditions in the southern realm during North Atlantic cold spells.
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Abstract
The Indo-Pacific warm pool houses the largest zone of deep atmospheric convection on Earth and plays a critical role in global climate variations. Despite the region's importance, changes in Indo-Pacific hydroclimate on orbital timescales remain poorly constrained. Here we present high-resolution geochemical records of surface runoff and vegetation from sediment cores from Lake Towuti, on the island of Sulawesi in central Indonesia, that continuously span the past 60,000 y. We show that wet conditions and rainforest ecosystems on Sulawesi present during marine isotope stage 3 (MIS3) and the Holocene were interrupted by severe drying between ∼33,000 and 16,000 y B.P. when Northern Hemisphere ice sheets expanded and global temperatures cooled. Our record reveals little direct influence of precessional orbital forcing on regional climate, and the similarity between MIS3 and Holocene climates observed in Lake Towuti suggests that exposure of the Sunda Shelf has a weaker influence on regional hydroclimate and terrestrial ecosystems than suggested previously. We infer that hydrological variability in this part of Indonesia varies strongly in response to high-latitude climate forcing, likely through reorganizations of the monsoons and the position of the intertropical convergence zone. These findings suggest an important role for the tropical western Pacific in amplifying glacial-interglacial climate variability.
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