S. Boulila, G. Dupont‐Nivet, B. Galbrun, H. Bauer, J. Chateauneuf
Abstract. The Eocene-Oligocene Transition (EOT) marks the onset of the Antarctic glaciation and the switch from greenhouse to icehouse climates. However, the driving mechanisms and the precise timing of the EOT remain controversial mostly due to the lack of well-dated stratigraphic records, especially in continental environments. Here we present a cyclo-magnetostratigraphic and sedimentological study of a ∼7.6 Myr-long lacustrine record spanning the late Eocene to the earliest Oligocene, from a drill-core in the Rennes Basin (France). Time-series analysis of natural gamma-ray (NGR) log data shows evidence of Milankovitch cycle bands. In particular, the 405 kyr stable eccentricity is expressed with strong amplitudes. Astronomical calibration to this 405 kyr periodicity yields duration estimates of Chrons C12r through C16n.1n, providing additional constraints on the middle–early Eocene timescale. Correlations between the orbital eccentricity curve and the 405 kyr tuned NGR time series and assumptions on their phase relationships, enable to test previously proposed ages for the EO boundary, indicating that 33.71 and 34.10 Ma are the most likely. Additionally, the 405 kyr tuning calibrates the most pronounced NGR cyclicity to a period of ∼1 Myr matching the g1-g5 eccentricity term. Such cyclicity has been recorded in other continental records, pointing to its significant expression in continental depositional environments. The record of g1-g5 and sometimes g2-g5 eccentricity terms in previously acquired sedimentary facies proxies in CDB1 core led us to hypothesize that the paleolake level may have behaved as a lowpass filter for orbital forcing. Two prominent changes in the sedimentary facies were detected across the EOT, which are temporally equivalent to the two main climatic steps, EOT-1 and Oi-1. Combined with previously acquired geochemical (δ15Norg, TOC), mineralogical (Quartz, clays) and pollen assemblage proxies from CDB1, we suggest that these two facies changes reflect the two major Antarctic cooling/glacial phases via the hydrological cycle, as significant shifts to drier and cooler climate conditions, thus supporting the stepwise nature of the EOT. Remarkably, a strongly dominant obliquity expressed in the latest Eocene corresponds in time to the interval from the EOT precursor glacial event till the EOT-1. We interpret the obliquity dominance as reflecting preconditioning phases for the onset of the major Antarctic glaciation, either from its direct impact on the formation/(in)stability of the incipient Antactic Ice Sheet (AIS), or through its modulation of the North Atlantic Deep Water production given the North Atlantic coastal location of the CDB1 site.
{"title":"Age and driving mechanisms of the Eocene-Oligocene Transition from astronomical tuning of a lacustrine record (Rennes Basin, France)","authors":"S. Boulila, G. Dupont‐Nivet, B. Galbrun, H. Bauer, J. Chateauneuf","doi":"10.5194/CP-2021-46","DOIUrl":"https://doi.org/10.5194/CP-2021-46","url":null,"abstract":"Abstract. The Eocene-Oligocene Transition (EOT) marks the onset of the Antarctic glaciation and the switch from greenhouse to icehouse climates. However, the driving mechanisms and the precise timing of the EOT remain controversial mostly due to the lack of well-dated stratigraphic records, especially in continental environments. Here we present a cyclo-magnetostratigraphic and sedimentological study of a ∼7.6 Myr-long lacustrine record spanning the late Eocene to the earliest Oligocene, from a drill-core in the Rennes Basin (France). Time-series analysis of natural gamma-ray (NGR) log data shows evidence of Milankovitch cycle bands. In particular, the 405 kyr stable eccentricity is expressed with strong amplitudes. Astronomical calibration to this 405 kyr periodicity yields duration estimates of Chrons C12r through C16n.1n, providing additional constraints on the middle–early Eocene timescale. Correlations between the orbital eccentricity curve and the 405 kyr tuned NGR time series and assumptions on their phase relationships, enable to test previously proposed ages for the EO boundary, indicating that 33.71 and 34.10 Ma are the most likely. Additionally, the 405 kyr tuning calibrates the most pronounced NGR cyclicity to a period of ∼1 Myr matching the g1-g5 eccentricity term. Such cyclicity has been recorded in other continental records, pointing to its significant expression in continental depositional environments. The record of g1-g5 and sometimes g2-g5 eccentricity terms in previously acquired sedimentary facies proxies in CDB1 core led us to hypothesize that the paleolake level may have behaved as a lowpass filter for orbital forcing. Two prominent changes in the sedimentary facies were detected across the EOT, which are temporally equivalent to the two main climatic steps, EOT-1 and Oi-1. Combined with previously acquired geochemical (δ15Norg, TOC), mineralogical (Quartz, clays) and pollen assemblage proxies from CDB1, we suggest that these two facies changes reflect the two major Antarctic cooling/glacial phases via the hydrological cycle, as significant shifts to drier and cooler climate conditions, thus supporting the stepwise nature of the EOT. Remarkably, a strongly dominant obliquity expressed in the latest Eocene corresponds in time to the interval from the EOT precursor glacial event till the EOT-1. We interpret the obliquity dominance as reflecting preconditioning phases for the onset of the major Antarctic glaciation, either from its direct impact on the formation/(in)stability of the incipient Antactic Ice Sheet (AIS), or through its modulation of the North Atlantic Deep Water production given the North Atlantic coastal location of the CDB1 site.\u0000","PeriodicalId":263057,"journal":{"name":"Climate of The Past Discussions","volume":"17 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-05-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115541207","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract. Scania (sw. Skåne), southern Sweden, offers a particularly interesting case for studying the historical relationship between climate variability and grain production, given the favourable natural conditions in terms of climate and soils for grain production, as well as the relative lack of heat-sensitive grain varieties like wheat in its production composition. In this article, I combine a contextual understanding of historical grain production in Scania, including historical, phenological and natural geographic aspects, with quantitative analysis of available empirical sources to estimate the relationship between climate variability and grain production between the years c. 1702–1911. The main result of this study is that grain production in Scania was primarily sensitive to climate variability during the high summer months of June and July, preferring relatively cool and humid conditions, and to some extent precipitation during the winter months, preferring relatively dry conditions. Furthermore, grain production was relatively insensitive to climate variability during the spring, autumn and harvest seasons. At the end of the study period, these relationships were shifting as the so-called early improved cultivars were being imported from other parts of Europe. Finally, I also shed new light on the climate history of the region, especially for the late 18th century, previously argued to be a particularly cold period, through homogenization of the early instrumental series from Lund (1753–1870).
{"title":"Climate variability and grain production in Scania, c. 1702–1911","authors":"Martin K Skoglund","doi":"10.5194/CP-2021-52","DOIUrl":"https://doi.org/10.5194/CP-2021-52","url":null,"abstract":"Abstract. Scania (sw. Skåne), southern Sweden, offers a particularly interesting case for studying the historical relationship between climate variability and grain production, given the favourable natural conditions in terms of climate and soils for grain production, as well as the relative lack of heat-sensitive grain varieties like wheat in its production composition. In this article, I combine a contextual understanding of historical grain production in Scania, including historical, phenological and natural geographic aspects, with quantitative analysis of available empirical sources to estimate the relationship between climate variability and grain production between the years c. 1702–1911. The main result of this study is that grain production in Scania was primarily sensitive to climate variability during the high summer months of June and July, preferring relatively cool and humid conditions, and to some extent precipitation during the winter months, preferring relatively dry conditions. Furthermore, grain production was relatively insensitive to climate variability during the spring, autumn and harvest seasons. At the end of the study period, these relationships were shifting as the so-called early improved cultivars were being imported from other parts of Europe. Finally, I also shed new light on the climate history of the region, especially for the late 18th century, previously argued to be a particularly cold period, through homogenization of the early instrumental series from Lund (1753–1870).\u0000","PeriodicalId":263057,"journal":{"name":"Climate of The Past Discussions","volume":"8 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-05-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130198614","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Xiaodan Zhang, G. Ren, Yuda Yang, H. Bing, Z. Hao, Panfeng Zhang
Abstract. The major droughts and floods in the Hanjiang River basin have a significant impact on the flood prevention and control in the middle reaches of the Yangtze River and water resources management in the areas of the South-North Water Diversion Middle Line Project of China. However, there is a lack of understanding of the multi-decadal to century-scale patterns of droughts and floods in the Hanjiang River Basin. Applying the yearly drought and flood grades reconstructed based on historical documents, and the criteria developed for identifying extreme droughts and floods in historical periods, this paper constructs a time series of extreme droughts and floods (i.e., the event with occurrence probability less than 10 % from 1951–2017) in the Hanjiang River basin from 1426–2017. The possible linkages of the extreme droughts and floods with Asian monsoon (i.e., East Asian monsoon and South Asian monsoon), strong ENSO (i.e., El Nino and La Nina) and large volcanic eruptions are also discussed. The results show that there were 45 extreme droughts and 51 extreme floods in the Hanjiang River basin over the past 592 years. The frequency of extreme droughts was high during the 15th century, early 16th century, the 17th, and the 20th centuries, with the 20th century being the highest. For extreme floods, the frequency was high in the 16th century, the 17th century, the 19th century, and the 20th century, with the 19th to 20th centuries being the highest. The 18th century was a common low period of extreme droughts and floods, while the 20th century saw a high frequency of both. When the Asian monsoon is weak, extreme droughts were more likely to occur; and when the Asian monsoon is strong, extreme floods were more likely to occur. Furthermore, on multi-decadal scale, extreme floods were found to become more frequent with the increase in numbers of strong El Nino events and large volcanic eruptions. These results are informative for the study of mechanisms and predictability of decadal to century scale variability of extreme hydro-climatic events in the Hanjiang River basin.
{"title":"Reconstruction and analysis of extreme drought and flood events in the Hanjiang River basin since 1426","authors":"Xiaodan Zhang, G. Ren, Yuda Yang, H. Bing, Z. Hao, Panfeng Zhang","doi":"10.5194/CP-2021-43","DOIUrl":"https://doi.org/10.5194/CP-2021-43","url":null,"abstract":"Abstract. The major droughts and floods in the Hanjiang River basin have a significant impact on the flood prevention and control in the middle reaches of the Yangtze River and water resources management in the areas of the South-North Water Diversion Middle Line Project of China. However, there is a lack of understanding of the multi-decadal to century-scale patterns of droughts and floods in the Hanjiang River Basin. Applying the yearly drought and flood grades reconstructed based on historical documents, and the criteria developed for identifying extreme droughts and floods in historical periods, this paper constructs a time series of extreme droughts and floods (i.e., the event with occurrence probability less than 10 % from 1951–2017) in the Hanjiang River basin from 1426–2017. The possible linkages of the extreme droughts and floods with Asian monsoon (i.e., East Asian monsoon and South Asian monsoon), strong ENSO (i.e., El Nino and La Nina) and large volcanic eruptions are also discussed. The results show that there were 45 extreme droughts and 51 extreme floods in the Hanjiang River basin over the past 592 years. The frequency of extreme droughts was high during the 15th century, early 16th century, the 17th, and the 20th centuries, with the 20th century being the highest. For extreme floods, the frequency was high in the 16th century, the 17th century, the 19th century, and the 20th century, with the 19th to 20th centuries being the highest. The 18th century was a common low period of extreme droughts and floods, while the 20th century saw a high frequency of both. When the Asian monsoon is weak, extreme droughts were more likely to occur; and when the Asian monsoon is strong, extreme floods were more likely to occur. Furthermore, on multi-decadal scale, extreme floods were found to become more frequent with the increase in numbers of strong El Nino events and large volcanic eruptions. These results are informative for the study of mechanisms and predictability of decadal to century scale variability of extreme hydro-climatic events in the Hanjiang River basin.","PeriodicalId":263057,"journal":{"name":"Climate of The Past Discussions","volume":"39 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-05-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133600065","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Raffaello Nardin, M. Severi, A. Amore, S. Becagli, F. Burgay, L. Caiazzo, V. Ciardini, G. Dreossi, M. Frezzotti, S. Hong, Ishaq Khan, B. Narcisi, M. Proposito, C. Scarchilli, E. Selmo, A. Spolaor, B. Stenni, R. Traversi
Abstract. Ice core dating is the first step for a correct interpretation of climatic and environmental changes. In this work, we release a stratigraphic dating of the uppermost 197 m of the 250 m deep GV7(B) ice core (drilling site, 70°41’S, 158°52’E, 1950 m a.s.l.) with a sub-annual resolution. Chemical stratigraphies of NO3−, MSA (methanesulfonic acid), non-sea salt SO42−, sea-salt ions and the oxygen isotopic composition (δ18O) were used in the annual layer counting upon the identification of a seasonal profile in their records. Different procedures were tested and thanks to the volcanic history of the core, obtained in previous works, an accurate age-depth correlation was obtained for the period 1179–2009 CE. Once the dating of the core was finalized, the annual mean accumulation rate was evaluated throughout the analyzed 197 m of the core, obtaining an annually resolved history of the snow accumulation on site in the last millennium. A small, yet consistent, rise in accumulation rate was found for the last 830 years since the middle of the 18th century.
摘要冰芯测年是正确解释气候和环境变化的第一步。在这项工作中，我们发布了250 m深GV7(B)冰芯(钻探地点，70°41'S, 158°52'E, 1950 m a.s.l)最上层197 m的次年分辨率地层测年结果。通过对年层NO3−、MSA(甲磺酸)、非海盐SO42−、海盐离子和氧同位素组成(δ18O)的化学地层学分析，确定了它们的季节剖面。研究人员测试了不同的程序，并根据之前的工作获得的岩心火山历史，获得了公元1179年至2009年期间的准确年龄-深度相关性。一旦确定了岩心的年代，在分析的岩心197米范围内评估年平均积累率，获得了过去一千年来现场积雪的年分解历史。自18世纪中叶以来的830年里，积累率出现了小幅但持续的上升。
{"title":"Dating of an East Antarctic ice core (GV7) by high resolution chemical stratigraphies","authors":"Raffaello Nardin, M. Severi, A. Amore, S. Becagli, F. Burgay, L. Caiazzo, V. Ciardini, G. Dreossi, M. Frezzotti, S. Hong, Ishaq Khan, B. Narcisi, M. Proposito, C. Scarchilli, E. Selmo, A. Spolaor, B. Stenni, R. Traversi","doi":"10.5194/CP-2021-44","DOIUrl":"https://doi.org/10.5194/CP-2021-44","url":null,"abstract":"Abstract. Ice core dating is the first step for a correct interpretation of climatic and environmental changes. In this work, we release a stratigraphic dating of the uppermost 197 m of the 250 m deep GV7(B) ice core (drilling site, 70°41’S, 158°52’E, 1950 m a.s.l.) with a sub-annual resolution. Chemical stratigraphies of NO3−, MSA (methanesulfonic acid), non-sea salt SO42−, sea-salt ions and the oxygen isotopic composition (δ18O) were used in the annual layer counting upon the identification of a seasonal profile in their records. Different procedures were tested and thanks to the volcanic history of the core, obtained in previous works, an accurate age-depth correlation was obtained for the period 1179–2009 CE. Once the dating of the core was finalized, the annual mean accumulation rate was evaluated throughout the analyzed 197 m of the core, obtaining an annually resolved history of the snow accumulation on site in the last millennium. A small, yet consistent, rise in accumulation rate was found for the last 830 years since the middle of the 18th century.","PeriodicalId":263057,"journal":{"name":"Climate of The Past Discussions","volume":"6 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-05-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127124943","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
D. Karger, M. Nobis, S. Normand, C. Graham, N. Zimmermann
Abstract. High resolution, downscaled climate model data are used in a wide variety of applications in environmental sciences. Here we present the CHELSA-TraCE21k downscaling algorithm to create global monthly climatologies for temperature and precipitation at 30 arcsec spatial resolution in 100 year time steps for the last 21,000 years. Paleo orography at high spatial resolution and at each timestep is created by combining high resolution information on glacial cover from current and Last Glacial Maximum (LGM) glacier databases with the interpolation of a dynamic ice sheet model (ICE6G) and a coupling to mean annual temperatures from CCSM3-TraCE21k. Based on the reconstructed paleo orography, mean annual temperature and precipitation was downscaled using the CHELSA V1.2 algorithm. The data were validated by comparisons with the glacial extent of the Laurentide ice shield based on expert delineations, proxy data from Greenland ice cores, historical climate data from meteorological stations, and a dynamic simulation of species a distribution throughout the Holocene. Validations show that CHELSA TraCE21k output creates a reasonable representation of the distribution of temperature and precipitation through time at a high spatial resolution, and simulations based on the data are capable of detecting effective LGM refugia of species.
{"title":"CHELSA-TraCE21k v1.0. Downscaled transient temperature and precipitation data since the last glacial maximum","authors":"D. Karger, M. Nobis, S. Normand, C. Graham, N. Zimmermann","doi":"10.5194/CP-2021-30","DOIUrl":"https://doi.org/10.5194/CP-2021-30","url":null,"abstract":"Abstract. High resolution, downscaled climate model data are used in a wide variety of applications in environmental sciences. Here we present the CHELSA-TraCE21k downscaling algorithm to create global monthly climatologies for temperature and precipitation at 30 arcsec spatial resolution in 100 year time steps for the last 21,000 years. Paleo orography at high spatial resolution and at each timestep is created by combining high resolution information on glacial cover from current and Last Glacial Maximum (LGM) glacier databases with the interpolation of a dynamic ice sheet model (ICE6G) and a coupling to mean annual temperatures from CCSM3-TraCE21k. Based on the reconstructed paleo orography, mean annual temperature and precipitation was downscaled using the CHELSA V1.2 algorithm. The data were validated by comparisons with the glacial extent of the Laurentide ice shield based on expert delineations, proxy data from Greenland ice cores, historical climate data from meteorological stations, and a dynamic simulation of species a distribution throughout the Holocene. Validations show that CHELSA TraCE21k output creates a reasonable representation of the distribution of temperature and precipitation through time at a high spatial resolution, and simulations based on the data are capable of detecting effective LGM refugia of species.","PeriodicalId":263057,"journal":{"name":"Climate of The Past Discussions","volume":"44 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-05-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122111093","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Rebekah A. Stein, N. Sheldon, S. E. Allen, M. Smith, Rebecca M. Dzombak, B. Jicha
Abstract. As increasing atmospheric carbon dioxide (CO2) and temperatures accompany modern climate change, ancient hothouse periods become a focal point for understanding ecosystem function under similar conditions. The early Eocene exhibited high temperatures, high CO2 levels, and similar tectonic plate configuration to today, so it has been invoked as an analog to modern climate change. During the early Eocene, the greater Green River Basin (GGRB) of southwest Wyoming was covered by an ancient hypersaline lake (Lake Gosiute; Green River Formation) and associated fluvial and floodplain systems (Wasatch and Bridger Formations). The volcaniclastic Bridger Formation was deposited by an inland delta that drained from the northwest into freshwater Lake Gosiute and is known for its vast paleontological assemblages. The Blue Rim escarpment exposes approximately 100 meters of the lower Bridger Formation, which includes plant and mammal fossils, paleosols and organic remains suitable for geochemical analyses, as well as ash beds and volcaniclastic sandstone beds suitable for radioisotopic dating. New 40Ar/39Ar ages from the middle and top of the Blue Rim escarpment constrain age of its strata to ~49.5–48.5 Ma ago, during the “falling limb” of the early Eocene climatic optimum. Using several geochemical tools, we reconstructed provenance and parent material in both the paleosols and the associated sediments and found no change in sediment input source despite significant variation in sedimentary facies and organic carbon burial. We also reconstructed environmental conditions at the time, including temperature and precipitation (from paleosols) and the isotopic composition of CO2 from plants found in the floral assemblages, before comparing them to reconstructions for the same time made using leaf physiognomic techniques and marine proxies. The paleosol-based reconstructions (near the base of the section) of precipitation (608–1167 mm yr−1) and temperature (10.4 to 12.0 °C) were within error of, although lower than, those based on floral assemblages, which were stratigraphically higher in the section. Geochemistry and detrital feldspar geochronology indicate a consistent provenance for Blue Rim sediments, sourcing predominantly from the Idaho paleoriver, which drained the active Challis volcanic field. Thus, because there was neither significant climatic change nor significant provenance change, variation in sedimentary facies and organic carbon burial likely reflected localized geomorphic controls, and the relative height of the water table. The ecosystem can be characterized as a wet, subtropical forest throughout the interval based upon the floral humidity province and Holdridge life zone schemes. Given the mid-paleolatitude position of the Blue Rim Escarpment, those results are consistent with marine proxies that indicate that globally warm climatic conditions continued beyond the peak warm conditions of the early Eocene climatic optimum. The reconstru
{"title":"Climate & Ecology in the Rocky Mountain Interior After the Early Eocene Climatic Optimum","authors":"Rebekah A. Stein, N. Sheldon, S. E. Allen, M. Smith, Rebecca M. Dzombak, B. Jicha","doi":"10.5194/CP-2021-45","DOIUrl":"https://doi.org/10.5194/CP-2021-45","url":null,"abstract":"Abstract. As increasing atmospheric carbon dioxide (CO2) and temperatures accompany modern climate change, ancient hothouse periods become a focal point for understanding ecosystem function under similar conditions. The early Eocene exhibited high temperatures, high CO2 levels, and similar tectonic plate configuration to today, so it has been invoked as an analog to modern climate change. During the early Eocene, the greater Green River Basin (GGRB) of southwest Wyoming was covered by an ancient hypersaline lake (Lake Gosiute; Green River Formation) and associated fluvial and floodplain systems (Wasatch and Bridger Formations). The volcaniclastic Bridger Formation was deposited by an inland delta that drained from the northwest into freshwater Lake Gosiute and is known for its vast paleontological assemblages. The Blue Rim escarpment exposes approximately 100 meters of the lower Bridger Formation, which includes plant and mammal fossils, paleosols and organic remains suitable for geochemical analyses, as well as ash beds and volcaniclastic sandstone beds suitable for radioisotopic dating. New 40Ar/39Ar ages from the middle and top of the Blue Rim escarpment constrain age of its strata to ~49.5–48.5 Ma ago, during the “falling limb” of the early Eocene climatic optimum. Using several geochemical tools, we reconstructed provenance and parent material in both the paleosols and the associated sediments and found no change in sediment input source despite significant variation in sedimentary facies and organic carbon burial. We also reconstructed environmental conditions at the time, including temperature and precipitation (from paleosols) and the isotopic composition of CO2 from plants found in the floral assemblages, before comparing them to reconstructions for the same time made using leaf physiognomic techniques and marine proxies. The paleosol-based reconstructions (near the base of the section) of precipitation (608–1167 mm yr−1) and temperature (10.4 to 12.0 °C) were within error of, although lower than, those based on floral assemblages, which were stratigraphically higher in the section. Geochemistry and detrital feldspar geochronology indicate a consistent provenance for Blue Rim sediments, sourcing predominantly from the Idaho paleoriver, which drained the active Challis volcanic field. Thus, because there was neither significant climatic change nor significant provenance change, variation in sedimentary facies and organic carbon burial likely reflected localized geomorphic controls, and the relative height of the water table. The ecosystem can be characterized as a wet, subtropical forest throughout the interval based upon the floral humidity province and Holdridge life zone schemes. Given the mid-paleolatitude position of the Blue Rim Escarpment, those results are consistent with marine proxies that indicate that globally warm climatic conditions continued beyond the peak warm conditions of the early Eocene climatic optimum. The reconstru","PeriodicalId":263057,"journal":{"name":"Climate of The Past Discussions","volume":"61 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-04-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123820711","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
S. Sherriff-Tadano, A. Abe‐Ouchi, A. Oka, Takahito Mitsui, F. Saito
Abstract. Glacial periods undergo frequent climate shifts between warm interstadials and cold stadials on a millennial time-scale. Recent studies have shown that the duration of these climate modes varies with the background climate; a colder background climate and lower CO2 generally results in a shorter interstadial and a longer stadial through its impact on the Atlantic Meridional Overturning Circulation (AMOC). However, the duration of stadials was shorter during the Marine Isotope Stage 3 (MIS3) compared with MIS5, despite the colder climate in MIS3, suggesting potential control from other climate factors on the duration of stadials. In this study, we investigated the role of glacial ice sheets. For this purpose, freshwater hosing experiments were conducted with an atmosphere–ocean general circulation model under MIS5a, MIS3 and MIS3 with MIS5a ice sheet conditions. The impact of ice sheet differences on the duration of the stadials was evaluated by comparing recovery times of the AMOC after freshwater forcing was reduced. Hosing experiments showed a slightly shorter recovery time of the AMOC in MIS3 compared with MIS5a, which was consistent with ice core data. We found that larger glacial ice sheets in MIS3 shortened the recovery time. Sensitivity experiments showed that stronger surface winds over the North Atlantic shortened the recovery time by increasing the surface salinity and decreasing the sea ice amount in the deepwater formation region, which set favourable conditions for oceanic convection. In contrast, we also found that surface cooling by larger ice sheets tended to increase the recovery time of the AMOC by increasing the sea ice thickness over the deepwater formation region. Thus, this study suggests that the larger ice sheet in MIS3 compared with MIS5a could have contributed to the shortening of stadials in MIS3, despite the climate being colder than that of MIS5a, when the effect of surface wind played a larger role.
{"title":"Does a difference in ice sheets between Marine Isotope Stages 3 and 5a affect the duration of stadials?","authors":"S. Sherriff-Tadano, A. Abe‐Ouchi, A. Oka, Takahito Mitsui, F. Saito","doi":"10.5194/CP-2021-47","DOIUrl":"https://doi.org/10.5194/CP-2021-47","url":null,"abstract":"Abstract. Glacial periods undergo frequent climate shifts between warm interstadials and cold stadials on a millennial time-scale. Recent studies have shown that the duration of these climate modes varies with the background climate; a colder background climate and lower CO2 generally results in a shorter interstadial and a longer stadial through its impact on the Atlantic Meridional Overturning Circulation (AMOC). However, the duration of stadials was shorter during the Marine Isotope Stage 3 (MIS3) compared with MIS5, despite the colder climate in MIS3, suggesting potential control from other climate factors on the duration of stadials. In this study, we investigated the role of glacial ice sheets. For this purpose, freshwater hosing experiments were conducted with an atmosphere–ocean general circulation model under MIS5a, MIS3 and MIS3 with MIS5a ice sheet conditions. The impact of ice sheet differences on the duration of the stadials was evaluated by comparing recovery times of the AMOC after freshwater forcing was reduced. Hosing experiments showed a slightly shorter recovery time of the AMOC in MIS3 compared with MIS5a, which was consistent with ice core data. We found that larger glacial ice sheets in MIS3 shortened the recovery time. Sensitivity experiments showed that stronger surface winds over the North Atlantic shortened the recovery time by increasing the surface salinity and decreasing the sea ice amount in the deepwater formation region, which set favourable conditions for oceanic convection. In contrast, we also found that surface cooling by larger ice sheets tended to increase the recovery time of the AMOC by increasing the sea ice thickness over the deepwater formation region. Thus, this study suggests that the larger ice sheet in MIS3 compared with MIS5a could have contributed to the shortening of stadials in MIS3, despite the climate being colder than that of MIS5a, when the effect of surface wind played a larger role.\u0000","PeriodicalId":263057,"journal":{"name":"Climate of The Past Discussions","volume":"13 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-04-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128741705","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
O. Ukhvatkina, A. Omelko, D. Kislov, A. Zhmerenetsky, T. Epifanova, J. Altman
Abstract. Here, we present precipitation reconstructions based on tree rings from Pinus koraiensis (Korean pine) from three sites placed along latitudinal (330 km) gradient in Sikhote-Alin mountains, Russian Far East. The tree-ring width chronologies were built using standard tree-ring procedures. We reconstructed the April–June precipitation for the southern Sikhote-Alin (SSA), March–June precipitation for the central Sikhote-Alin (CSA) and March–July precipitation for the northwestern Sikhote-Alin (NSA) over the 1609 to 2013, 1804 to 2009 and 1858 to 2013, respectively. We found that an important limiting factor for Korean pine growth was precipitation within the period when the air current coming from the continent during the cold period is replaced with the impact of the wet ocean air current. We identified common wet years for SSA, CSA and NSA occurred in 1805, 1853, 1877, 1903, 1906, 1927, 1983, 2009 and common dry years occurred in 1821, 1869, 1919, 1949 and 2003. Our reconstructions have 3, 15 and 60 year periods and corresponds to influence of the El Nino-Southern Oscillation and Pacific Decadal Oscillation on the region's climate and relevant processes, respectively. Despite the impact of various global processes, the main contribution to precipitation formation in study area is still made by the Pacific Ocean, which determines their amount and periodicity.
{"title":"Tree-ring based spring precipitation reconstruction in the Sikhote-Alin Mountain Range","authors":"O. Ukhvatkina, A. Omelko, D. Kislov, A. Zhmerenetsky, T. Epifanova, J. Altman","doi":"10.5194/cp-2020-49","DOIUrl":"https://doi.org/10.5194/cp-2020-49","url":null,"abstract":"Abstract. Here, we present precipitation reconstructions based on tree rings from Pinus koraiensis (Korean pine) from three sites placed along latitudinal (330 km) gradient in Sikhote-Alin mountains, Russian Far East. The tree-ring width chronologies were built using standard tree-ring procedures. We reconstructed the April–June precipitation for the southern Sikhote-Alin (SSA), March–June precipitation for the central Sikhote-Alin (CSA) and March–July precipitation for the northwestern Sikhote-Alin (NSA) over the 1609 to 2013, 1804 to 2009 and 1858 to 2013, respectively. We found that an important limiting factor for Korean pine growth was precipitation within the period when the air current coming from the continent during the cold period is replaced with the impact of the wet ocean air current. We identified common wet years for SSA, CSA and NSA occurred in 1805, 1853, 1877, 1903, 1906, 1927, 1983, 2009 and common dry years occurred in 1821, 1869, 1919, 1949 and 2003. Our reconstructions have 3, 15 and 60 year periods and corresponds to influence of the El Nino-Southern Oscillation and Pacific Decadal Oscillation on the region's climate and relevant processes, respectively. Despite the impact of various global processes, the main contribution to precipitation formation in study area is still made by the Pacific Ocean, which determines their amount and periodicity.","PeriodicalId":263057,"journal":{"name":"Climate of The Past Discussions","volume":"9 5 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-04-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123568198","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A. Quiquet, D. Roche, C. Dumas, N. Bouttes, F. Lhardy
Abstract. The last deglaciation offers an unique opportunity to understand the climate – ice sheet interactions in a global warming context. In this paper, to tackle this question, we use an Earth system model of intermediate complexity coupled to an ice sheet model covering the Northern Hemisphere to simulate the last deglaciation and the Holocene (26–0 ka BP). We use a synchronous coupling every year between the ice sheet and the rest of the climate system and we ensure a closed water cycle considering the release of freshwater flux to the ocean due to ice sheet melting. Our reference experiment displays a gradual warming in response to the forcings, with no abrupt changes. In this case, while the amplitude of the freshwater flux to the ocean induced by ice sheet retreat is realistic, it is sufficient to shut down the Atlantic meridional overturning from which the model does not recover within the time period simulated. However, with reduced freshwater flux we are nonetheless able to obtain different oceanic circulation evolutions, including some abrupt transitions between shut-down and active circulation states in the course of the deglaciation. The fast oceanic circulation recoveries lead to abrupt warming phases in Greenland. Our simulated ice sheet geometry evolution is in overall good agreement with available global reconstructions, even though the abrupt sea level rise at 14.6 kaBP is underestimated, possibly because the climate model underestimates the millenial- scale temperature variability. In the course of the deglaciation, large-scale grounding line instabilities are simulated both for the Eurasian and North American ice sheets. The first instability occurs in the Barents-Kara seas for the Eurasian ice sheet at 14.5 kaBP. A second grounding line instability occurs circa 12 kaBP in the proglacial lake that formed at the southern margin of the North American ice sheet. With additional asynchronously coupled experiments, we assess the sensitivity of our results to different ice sheet model choices related to surface and sub-shelf mass balance, ice deformation and grounding line representation. While the ice sheet evolutions differ within this ensemble, the global climate trajectory is only weakly affected by these choices. In our experiments, only the abrupt shifts in the oceanic circulation due to freshwater fluxes are able to produce some millenial-scale variability since no self-generating abrupt transitions are simulated without these fluxes.
摘要最后一次冰川消融为了解全球变暖背景下的气候-冰盖相互作用提供了一个独特的机会。为了解决这个问题，我们使用了一个中等复杂程度的地球系统模型和一个覆盖北半球的冰盖模型来模拟末次消冰和全新世(26-0 ka BP)。我们每年在冰盖和气候系统的其余部分之间使用同步耦合，我们确保一个封闭的水循环，考虑到由于冰盖融化而向海洋释放的淡水通量。我们的参考实验显示，随着这些强迫的变化，气温逐渐变暖，没有突然的变化。在这种情况下，虽然由冰盖退缩引起的流入海洋的淡水通量的振幅是真实的，但它足以阻止大西洋经向翻转，而模式在模拟的时间内无法恢复这种翻转。然而，在淡水通量减少的情况下，我们仍然能够得到不同的海洋环流演变，包括在消冰过程中在停止和活跃环流状态之间的一些突变。快速的海洋环流恢复导致格陵兰岛的突然变暖阶段。我们模拟的冰盖几何演变总体上与现有的全球重建结果一致，尽管14.6 kaBP的海平面突然上升被低估了，这可能是因为气候模式低估了千年尺度的温度变化。在消冰过程中，模拟了欧亚和北美冰盖大尺度接地线的不稳定性。第一次不稳定发生在欧亚冰盖的巴伦支-喀拉海，时间为14.5 kaBP。第二次接地线不稳定发生在北美冰盖南缘形成的前冰湖大约12kabp。通过额外的异步耦合实验，我们评估了我们的结果对与地表和亚冰架质量平衡、冰变形和接地线表示相关的不同冰盖模型选择的敏感性。虽然在这个组合中，冰盖的演变是不同的，但这些选择对全球气候轨迹的影响很小。在我们的实验中，只有淡水通量引起的海洋环流突变才能够产生一些千年尺度的变率，因为没有这些通量就无法模拟自生突变。
{"title":"Climate and ice sheet evolutions from the last glacial maximum to the pre-industrial period with an ice sheet – climate coupled model","authors":"A. Quiquet, D. Roche, C. Dumas, N. Bouttes, F. Lhardy","doi":"10.5194/CP-2021-39","DOIUrl":"https://doi.org/10.5194/CP-2021-39","url":null,"abstract":"Abstract. The last deglaciation offers an unique opportunity to understand the climate – ice sheet interactions in a global warming context. In this paper, to tackle this question, we use an Earth system model of intermediate complexity coupled to an ice sheet model covering the Northern Hemisphere to simulate the last deglaciation and the Holocene (26–0 ka BP). We use a synchronous coupling every year between the ice sheet and the rest of the climate system and we ensure a closed water cycle considering the release of freshwater flux to the ocean due to ice sheet melting. Our reference experiment displays a gradual warming in response to the forcings, with no abrupt changes. In this case, while the amplitude of the freshwater flux to the ocean induced by ice sheet retreat is realistic, it is sufficient to shut down the Atlantic meridional overturning from which the model does not recover within the time period simulated. However, with reduced freshwater flux we are nonetheless able to obtain different oceanic circulation evolutions, including some abrupt transitions between shut-down and active circulation states in the course of the deglaciation. The fast oceanic circulation recoveries lead to abrupt warming phases in Greenland. Our simulated ice sheet geometry evolution is in overall good agreement with available global reconstructions, even though the abrupt sea level rise at 14.6 kaBP is underestimated, possibly because the climate model underestimates the millenial- scale temperature variability. In the course of the deglaciation, large-scale grounding line instabilities are simulated both for the Eurasian and North American ice sheets. The first instability occurs in the Barents-Kara seas for the Eurasian ice sheet at 14.5 kaBP. A second grounding line instability occurs circa 12 kaBP in the proglacial lake that formed at the southern margin of the North American ice sheet. With additional asynchronously coupled experiments, we assess the sensitivity of our results to different ice sheet model choices related to surface and sub-shelf mass balance, ice deformation and grounding line representation. While the ice sheet evolutions differ within this ensemble, the global climate trajectory is only weakly affected by these choices. In our experiments, only the abrupt shifts in the oceanic circulation due to freshwater fluxes are able to produce some millenial-scale variability since no self-generating abrupt transitions are simulated without these fluxes.\u0000","PeriodicalId":263057,"journal":{"name":"Climate of The Past Discussions","volume":"87 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-04-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125919838","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
C. Williams, A. Sellar, Xin Ren, A. Haywood, P. Hopcroft, S. Hunter, W. Roberts, Robin S. Smith, E. Stone, J. Tindall, D. Lunt
Abstract. Here we present the experimental design and results from a new mid-Pliocene simulation using the latest version of the UK’s physical climate model, HadGEM3-GC31-LL, conducted under the auspices of CMIP6/PMIP4/PlioMIP2. Although two other paleoclimate simulations have been recently run using this model, they both focused on more recent periods within the Quaternary and therefore this is the first time this version of the UK model has been run this far back in time. The mid-Pliocene Warm Period, ~3 Ma, is of particular interest because it represents a time period when the Earth was in equilibrium with CO2 concentrations roughly equivalent to those of today, providing a possible analogue for current and future climate change. The implementation of the Pliocene boundary conditions is firstly described in detail, based on the PRISM4 dataset, including CO2, ozone, orography, ice mask, lakes, vegetation fractions and vegetation functional types. These were incrementally added into the model, to change from a preindustrial setup to Pliocene conditions. The results of the simulation are then presented, which are firstly compared with the model’s pre-industrial simulation, secondly with previous versions of the same model and with available proxy data, and thirdly with all other models included in PlioMIP2. Firstly, the comparison with preindustrial suggests that the Pliocene simulation is consistent with current understanding and existing work, showing warmer and wetter conditions, and with the greatest warming occurring over high latitude and polar regions. The global mean surface air temperature anomaly at the end of the Pliocene simulation is 5.1 °C, which is the 2nd highest of all models included in PlioMIP2 and is consistent with the fact that HadGEM3-GC31-LL has one of the highest Effective Climate Sensitivities of all CMIP6 models. Secondly, the comparison with previous generation models and with proxy data suggests a clear increase in global sea surface temperatures as the model has undergone development. Up to a certain level of warming, this results in a better agreement with available proxy data, and the “sweet spot” appears to be the previous CMIP5 generation of the model, HadGEM2-AO. The most recent simulation presented here, however, appears to show poorer agreement with the proxy data compared with HadGEM2, and may be overly sensitive to the Pliocene boundary conditions resulting in a climate that is too warm. Thirdly, the comparison with other models from PlioMIP2 further supports this conclusion, with HadGEM3-GC31-LL being one of the warmest and wettest models in all of PlioMIP2 and, if all the models are ordered according to agreement with proxy data, HadGEM3-GC31-LL ranks approximately halfway among them.
{"title":"Simulation of the mid-Pliocene Warm Period using HadGEM3: Experimental design and results from model-model and model-data comparison","authors":"C. Williams, A. Sellar, Xin Ren, A. Haywood, P. Hopcroft, S. Hunter, W. Roberts, Robin S. Smith, E. Stone, J. Tindall, D. Lunt","doi":"10.5194/CP-2021-40","DOIUrl":"https://doi.org/10.5194/CP-2021-40","url":null,"abstract":"Abstract. Here we present the experimental design and results from a new mid-Pliocene simulation using the latest version of the UK’s physical climate model, HadGEM3-GC31-LL, conducted under the auspices of CMIP6/PMIP4/PlioMIP2. Although two other paleoclimate simulations have been recently run using this model, they both focused on more recent periods within the Quaternary and therefore this is the first time this version of the UK model has been run this far back in time. The mid-Pliocene Warm Period, ~3 Ma, is of particular interest because it represents a time period when the Earth was in equilibrium with CO2 concentrations roughly equivalent to those of today, providing a possible analogue for current and future climate change. The implementation of the Pliocene boundary conditions is firstly described in detail, based on the PRISM4 dataset, including CO2, ozone, orography, ice mask, lakes, vegetation fractions and vegetation functional types. These were incrementally added into the model, to change from a preindustrial setup to Pliocene conditions. The results of the simulation are then presented, which are firstly compared with the model’s pre-industrial simulation, secondly with previous versions of the same model and with available proxy data, and thirdly with all other models included in PlioMIP2. Firstly, the comparison with preindustrial suggests that the Pliocene simulation is consistent with current understanding and existing work, showing warmer and wetter conditions, and with the greatest warming occurring over high latitude and polar regions. The global mean surface air temperature anomaly at the end of the Pliocene simulation is 5.1 °C, which is the 2nd highest of all models included in PlioMIP2 and is consistent with the fact that HadGEM3-GC31-LL has one of the highest Effective Climate Sensitivities of all CMIP6 models. Secondly, the comparison with previous generation models and with proxy data suggests a clear increase in global sea surface temperatures as the model has undergone development. Up to a certain level of warming, this results in a better agreement with available proxy data, and the “sweet spot” appears to be the previous CMIP5 generation of the model, HadGEM2-AO. The most recent simulation presented here, however, appears to show poorer agreement with the proxy data compared with HadGEM2, and may be overly sensitive to the Pliocene boundary conditions resulting in a climate that is too warm. Thirdly, the comparison with other models from PlioMIP2 further supports this conclusion, with HadGEM3-GC31-LL being one of the warmest and wettest models in all of PlioMIP2 and, if all the models are ordered according to agreement with proxy data, HadGEM3-GC31-LL ranks approximately halfway among them. \u0000","PeriodicalId":263057,"journal":{"name":"Climate of The Past Discussions","volume":"4 5 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-04-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123421861","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：