Abstract. It has been previously proposed that glacial inception represents a bifurcation transition between interglacial and glacial states and is governed by the nonlinear dynamics of the climate–cryosphere system. To trigger glacial inception, the orbital forcing (defined as the maximum of summer insolation at 65° N and determined by Earth’s orbital parameters) must be lower than a critical level, which depends on the atmospheric CO2 concentration. While paleoclimatic data do not provide a strong constraint on the dependence between CO2 and critical insolation, its accurate estimation is of fundamental importance for predicting future glaciations and the effect that anthropogenic CO2 emissions might have on them. In this study, we use the novel Earth system model of intermediate complexity CLIMBER-X with interactive ice sheets to produce a new estimation of the critical insolation–CO2 relationship for triggering glacial inception. We perform a series of experiments in which different combinations of orbital forcing and atmospheric CO2 concentration are maintained constant in time. We analyze for which combinations of orbital forcing and CO2 glacial inception occurs and trace the critical relationship between them, separating conditions under which glacial inception is possible from those where glacial inception is not materialized. We also provide a theoretical foundation for the proposed critical insolation–CO2 relation. We find that the use of the maximum summer insolation at 65° N as a single metric for orbital forcing is adequate for tracing the glacial inception bifurcation. Moreover, we find that the temporal and spatial patterns of ice sheet growth during glacial inception are not always the same but depend on the critical insolation and CO2 level. The experiments evidence the fact that during glacial inception, ice sheets grow mostly in North America, and only under low CO2 conditions are ice sheets also formed over Scandinavia. The latter is associated with a weak Atlantic Meridional Overturning Circulation (AMOC) for low CO2. We find that the strength of AMOC also affects the rate of ice sheet growth during glacial inception.
{"title":"New estimation of critical insolation–CO2 relationship for triggering glacial inception","authors":"Stefanie Talento, Matteo Willeit, Andrey Ganopolski","doi":"10.5194/cp-20-1349-2024","DOIUrl":"https://doi.org/10.5194/cp-20-1349-2024","url":null,"abstract":"Abstract. It has been previously proposed that glacial inception represents a bifurcation transition between interglacial and glacial states and is governed by the nonlinear dynamics of the climate–cryosphere system. To trigger glacial inception, the orbital forcing (defined as the maximum of summer insolation at 65° N and determined by Earth’s orbital parameters) must be lower than a critical level, which depends on the atmospheric CO2 concentration. While paleoclimatic data do not provide a strong constraint on the dependence between CO2 and critical insolation, its accurate estimation is of fundamental importance for predicting future glaciations and the effect that anthropogenic CO2 emissions might have on them. In this study, we use the novel Earth system model of intermediate complexity CLIMBER-X with interactive ice sheets to produce a new estimation of the critical insolation–CO2 relationship for triggering glacial inception. We perform a series of experiments in which different combinations of orbital forcing and atmospheric CO2 concentration are maintained constant in time. We analyze for which combinations of orbital forcing and CO2 glacial inception occurs and trace the critical relationship between them, separating conditions under which glacial inception is possible from those where glacial inception is not materialized. We also provide a theoretical foundation for the proposed critical insolation–CO2 relation. We find that the use of the maximum summer insolation at 65° N as a single metric for orbital forcing is adequate for tracing the glacial inception bifurcation. Moreover, we find that the temporal and spatial patterns of ice sheet growth during glacial inception are not always the same but depend on the critical insolation and CO2 level. The experiments evidence the fact that during glacial inception, ice sheets grow mostly in North America, and only under low CO2 conditions are ice sheets also formed over Scandinavia. The latter is associated with a weak Atlantic Meridional Overturning Circulation (AMOC) for low CO2. We find that the strength of AMOC also affects the rate of ice sheet growth during glacial inception.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"26 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141513571","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-06-14DOI: 10.5194/egusphere-2024-1648
Jingjing Guo, Martin Ziegler, Louise Fuchs, Youbin Sun, Francien Peterse
Abstract. Variations in the oxygen isotope composition (δ18O) of cave speleothems and numerous proxy records from loess-paleosol sequences have revealed past variations in East Asian monsoon (EAM) intensity. However, challenges persist in reconstructing precipitation changes quantitatively. Here, we use the positive relationship between the degree of cyclization (DC) of branched glycerol dialkyl glycerol tetraethers (brGDGTs) in modern surface soils from the Chinese loess Plateau (CLP) and mean annual precipitation (MAP) to quantify past monsoon precipitation changes on the CLP. We present a new ~130,000-year long DC-based MAP record for the Yuanbao section on the western edge of CLP, which closely tracks the orbital- and millennial-scale variations in both the speleothem δ18O record and the hydrogen isotope composition of plant waxes (δ2Hwax) from the same section. Combing our new data with existing brGDGT records from other CLP sites reveals a spatial gradient in MAP that is most pronounced during glacials, when the western CLP experiences more arid conditions and receives up to ~250 mm less precipitation than in the southeast, whereas MAP is ~850 mm across the CLP during the Holocene optimum. Furthermore, the DC records show that precipitation amount on the CLP varies at the precession as well as obliquity scale, as opposed to the primarily precession scale variations in speleothem δ18O and δ2Hwax at Yuanbao, and the 100-kyr cycle in other loess proxies such as magnetic susceptibility, which rather indicates the relative intensity of the EAM. At the precession scale, the DC record is in phase with δ2Hwax from same section as well as the speleothem δ18O record, which supports the hypothesis that monsoon precipitation is driven by northern hemisphere summer insolation.
{"title":"Quantitative reconstruction of past monsoon precipitation based on tetraether membrane lipids in Chinese loess","authors":"Jingjing Guo, Martin Ziegler, Louise Fuchs, Youbin Sun, Francien Peterse","doi":"10.5194/egusphere-2024-1648","DOIUrl":"https://doi.org/10.5194/egusphere-2024-1648","url":null,"abstract":"<strong>Abstract.</strong> Variations in the oxygen isotope composition (δ<sup>18</sup>O) of cave speleothems and numerous proxy records from loess-paleosol sequences have revealed past variations in East Asian monsoon (EAM) intensity. However, challenges persist in reconstructing precipitation changes quantitatively. Here, we use the positive relationship between the degree of cyclization (DC) of branched glycerol dialkyl glycerol tetraethers (brGDGTs) in modern surface soils from the Chinese loess Plateau (CLP) and mean annual precipitation (MAP) to quantify past monsoon precipitation changes on the CLP. We present a new ~130,000-year long DC-based MAP record for the Yuanbao section on the western edge of CLP, which closely tracks the orbital- and millennial-scale variations in both the speleothem δ<sup>18</sup>O record and the hydrogen isotope composition of plant waxes (δ<sup>2</sup>H<sub>wax</sub>) from the same section. Combing our new data with existing brGDGT records from other CLP sites reveals a spatial gradient in MAP that is most pronounced during glacials, when the western CLP experiences more arid conditions and receives up to ~250 mm less precipitation than in the southeast, whereas MAP is ~850 mm across the CLP during the Holocene optimum. Furthermore, the DC records show that precipitation amount on the CLP varies at the precession as well as obliquity scale, as opposed to the primarily precession scale variations in speleothem δ<sup>18</sup>O and δ<sup>2</sup>H<sub>wax</sub> at Yuanbao, and the 100-kyr cycle in other loess proxies such as magnetic susceptibility, which rather indicates the relative intensity of the EAM. At the precession scale, the DC record is in phase with δ<sup>2</sup>H<sub>wax</sub> from same section as well as the speleothem δ<sup>18</sup>O record, which supports the hypothesis that monsoon precipitation is driven by northern hemisphere summer insolation.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"27 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-06-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141513576","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-06-12DOI: 10.5194/egusphere-2024-1707
Jade Margerum, Julia Homann, Stuart Umbo, Gernot Nehrke, Thorsten Hoffmann, Anton Vaks, Aleksandr Kononov, Alexander Osintsev, Alena Giesche, Andrew Mason, Franziska A. Lechleitner, Gideon M. Henderson, Ola Kwiecien, Sebastian F. M. Breitenbach
Abstract. Wildfires are a rapidly increasing threat to boreal forests. While our understanding of the drivers behind wildfires and their environmental impact is growing, it is mostly limited to the observational period. Here we focus on the boreal forests of southern Siberia, and exploit a U-Th dated stalagmite from Botovskaya cave (55.2994° N, 105.4445° E), located in the upper Lena region of southern Siberia, to document wildfire activity and vegetation dynamics during parts of two warm periods; the last interglacial (124.1 – 118.8 ka BP) and the Holocene (10 – 0 ka BP). Our record is based on levoglucosan (Lev), a biomarker sensitive to biomass burning, and on lignin oxidation products (LOPs) that discriminate between open and closed forest and hard- or softwood vegetation. In addition, we used carbon stable isotope ratios (δ13C) to evaluate soil respiration and local infiltration changes. While the δ13C record reflects a dominant control of the host rock, the Lev and LOP time series show fire pattern and vegetation type differences between the last interglacial and the Holocene. Our LOP data suggest that during the last interglacial, the region around Botovskaya cave was characterised by open forest, which by ca. 121.5 ka BP underwent a transition from fire-resistant hardwood to fire-prone softwood. The Lev record indicates that fire activity was high and increased towards the end of last interglacial just before 119 ka BP. In contrast, the Holocene was characterised by a closed-forest environment with mixed hard- and softwood vegetation. Holocene fire activity varied but at a much lower level than during the last interglacial. We attribute the changes in wildfire activity during the intervals of interest to the interplay between vegetation and climate. The open forests of the last interglacial were more likely to ignite than their closed Holocene equivalents, and their flammability was aided by warmer and drier summers and a stronger seasonal temperature contrast compared to the Holocene. Our comparison of the last two interglacial intervals suggests that with increasing global temperatures the boreal forest of southern Siberia becomes progressively more vulnerable to higher wildfire activity.
{"title":"Reconstruction of Holocene and Last Interglacial vegetation dynamics and wildfire activity in southern Siberia","authors":"Jade Margerum, Julia Homann, Stuart Umbo, Gernot Nehrke, Thorsten Hoffmann, Anton Vaks, Aleksandr Kononov, Alexander Osintsev, Alena Giesche, Andrew Mason, Franziska A. Lechleitner, Gideon M. Henderson, Ola Kwiecien, Sebastian F. M. Breitenbach","doi":"10.5194/egusphere-2024-1707","DOIUrl":"https://doi.org/10.5194/egusphere-2024-1707","url":null,"abstract":"<strong>Abstract.</strong> Wildfires are a rapidly increasing threat to boreal forests. While our understanding of the drivers behind wildfires and their environmental impact is growing, it is mostly limited to the observational period. Here we focus on the boreal forests of southern Siberia, and exploit a U-Th dated stalagmite from Botovskaya cave (55.2994° N, 105.4445° E), located in the upper Lena region of southern Siberia, to document wildfire activity and vegetation dynamics during parts of two warm periods; the last interglacial (124.1 – 118.8 ka BP) and the Holocene (10 – 0 ka BP). Our record is based on levoglucosan (Lev), a biomarker sensitive to biomass burning, and on lignin oxidation products (LOPs) that discriminate between open and closed forest and hard- or softwood vegetation. In addition, we used carbon stable isotope ratios (δ<sup>13</sup>C) to evaluate soil respiration and local infiltration changes. While the δ<sup>13</sup>C record reflects a dominant control of the host rock, the Lev and LOP time series show fire pattern and vegetation type differences between the last interglacial and the Holocene. Our LOP data suggest that during the last interglacial, the region around Botovskaya cave was characterised by open forest, which by ca. 121.5 ka BP underwent a transition from fire-resistant hardwood to fire-prone softwood. The Lev record indicates that fire activity was high and increased towards the end of last interglacial just before 119 ka BP. In contrast, the Holocene was characterised by a closed-forest environment with mixed hard- and softwood vegetation. Holocene fire activity varied but at a much lower level than during the last interglacial. We attribute the changes in wildfire activity during the intervals of interest to the interplay between vegetation and climate. The open forests of the last interglacial were more likely to ignite than their closed Holocene equivalents, and their flammability was aided by warmer and drier summers and a stronger seasonal temperature contrast compared to the Holocene. Our comparison of the last two interglacial intervals suggests that with increasing global temperatures the boreal forest of southern Siberia becomes progressively more vulnerable to higher wildfire activity.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"51 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-06-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141513572","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract. This study investigates a sediment core (RS15-LC47) from the Ross Sea continental rise to elucidate the sea-ice interaction and resulting paleodepositional changes over the past 800 ka. By integrating whole-core Magnetic Susceptibility (MS), sediment biogenic components (TOC, CaCO3, and biogenic silica), sedimentological features, and the isotopic ratio of authigenic beryllium (10Be/9Be)reac, we unravel the paleoenvironmental changes and their influence on the sedimentary processes. The lower segment of the investigated interval (750–550 ka) exhibits distinct lithological characteristics, including parallel and cross laminations, along with millimeter-scale faults, suggestive of contourite depositional processes. This section also displays irregular trends in MS values due to poorly sorted sediments, characteristics feature of sediment slumping. The lowest (10Be/9Be)reac ratio in this interval suggests reduced Circumpolar Deep Water (CDW) inflow due to strengthened Antarctic Slope Current (ASC). Although the Total Organic Carbon (TOC) is highest in this interval, high Carbon-to-Nitrogen (C/N) ratio and low Barium excess (Baex) suggests reduced marine productivity due to increased terrestrial input likely from advancing ice sheets. Following the Mid-Pleistocene Transition (MPT), MS values remain consistently low until MIS 8 (~250 ka) and (10Be/9Be)reac relatively increases, indicating persistent lukewarm condition. We hypothesize this timeframe favorable for ice-shelf disintegration and possible collapse of the West Antarctic Ice Sheet (WAIS). Between 550 and 250 ka, TOC/TN levels resemble those observed in the euphotic layer of the Ross Sea, with relatively higher Baex and TOC, indicating higher productivity during an extended lukewarm condition. During the late Pleistocene (> 250 ka), coarser grain size and IRD-rich layers suggest strengthening of bottom currents. The upwelling of CDW facilitated a drastic increase in the (10Be/9Be)reac ratio during the late Pleistocene. OpalMAR and TOC % exhibit positive trends with (10Be/9Be)reac during the late Pleistocene interglacials, suggesting increased productivity during warmer periods.
摘要本研究调查了罗斯海大陆隆起的沉积岩芯（RS15-LC47），以阐明过去 800 ka 年间海冰相互作用及其导致的古沉积变化。通过整合整个岩芯的磁感应强度（MS）、沉积物生物成份（TOC、CaCO3 和生物硅）、沉积学特征以及自生铍同位素比值（10Be/9Be）reac，我们揭示了古环境变化及其对沉积过程的影响。调查区间的下段（750-550 ka）表现出明显的岩性特征，包括平行层理和交叉层理，以及毫米尺度的断层，表明了等高线沉积过程。由于沉积物分选较差，该区段的 MS 值也呈现出不规则的趋势，这是沉积物坍塌的特征。该区间的最低（10Be/9Be）reac 比率表明，由于南极坡流（ASC）增强，环极深水（CDW）流入量减少。虽然总有机碳（TOC）在这一区间最高，但高碳氮比（C/N）和低钡过量（Baex）表明，由于陆地输入的增加，海洋生产力降低了，而陆地输入可能来自不断推进的冰盖。在中更新世过渡（MPT）之后，MS 值一直保持在较低水平，直到 MIS 8（约 250 ka），（10Be/9Be）reac 相对增加，表明温热状态持续存在。我们假设这一时间段有利于冰架解体和南极西部冰原（WAIS）的可能崩溃。在 550 ka 到 250 ka 之间，TOC/TN 水平类似于在罗斯海的透光层中观测到的水平，Baex 和 TOC 相对较高，表明在较长时间的温热条件下生产力较高。在晚更新世（250 ka）期间，粒度较粗且富含 IRD 的海层表明底层海流增强。在晚更新世，CDW 的上涌促进了（10Be/9Be）reac 比率的急剧上升。在晚更新世间冰期，乳白层厚度（OpalMAR）和总有机碳（TOC）%与（10Be/9Be）reac呈正相关趋势，表明在温暖时期生产力提高。
{"title":"Drastic changes in Depositional Environments at the Ross Sea Continental Margin since the Mid-Pleistocene: More evidence for West Antarctic Ice Sheet collapse","authors":"Chinmay Dash, Yeong Bae Seong, Ajay Kumar Singh, Min Kyung Lee, Jae Il Lee, Kyu-Cheul Yoo, Hyun Hee Rhee, Byung Yong Yu","doi":"10.5194/cp-2024-38","DOIUrl":"https://doi.org/10.5194/cp-2024-38","url":null,"abstract":"<strong>Abstract.</strong> This study investigates a sediment core (RS15-LC47) from the Ross Sea continental rise to elucidate the sea-ice interaction and resulting paleodepositional changes over the past 800 ka. By integrating whole-core Magnetic Susceptibility (MS), sediment biogenic components (TOC, CaCO<sub>3</sub>, and biogenic silica), sedimentological features, and the isotopic ratio of authigenic beryllium (<sup>10</sup>Be/<sup>9</sup>Be)<sub>reac</sub>, we unravel the paleoenvironmental changes and their influence on the sedimentary processes. The lower segment of the investigated interval (750–550 ka) exhibits distinct lithological characteristics, including parallel and cross laminations, along with millimeter-scale faults, suggestive of contourite depositional processes. This section also displays irregular trends in MS values due to poorly sorted sediments, characteristics feature of sediment slumping. The lowest (<sup>10</sup>Be/<sup>9</sup>Be)<sub>reac </sub>ratio in this interval suggests reduced Circumpolar Deep Water (CDW) inflow due to strengthened Antarctic Slope Current (ASC). Although the Total Organic Carbon (TOC) is highest in this interval, high Carbon-to-Nitrogen (C/N) ratio and low Barium excess (Ba<sub>ex</sub>) suggests reduced marine productivity due to increased terrestrial input likely from advancing ice sheets. Following the Mid-Pleistocene Transition (MPT), MS values remain consistently low until MIS 8 (~250 ka) and (<sup>10</sup>Be/<sup>9</sup>Be)<sub>reac</sub> relatively increases, indicating persistent lukewarm condition. We hypothesize this timeframe favorable for ice-shelf disintegration and possible collapse of the West Antarctic Ice Sheet (WAIS). Between 550 and 250 ka, TOC/TN levels resemble those observed in the euphotic layer of the Ross Sea, with relatively higher Ba<sub>ex</sub> and TOC, indicating higher productivity during an extended lukewarm condition. During the late Pleistocene (> 250 ka), coarser grain size and IRD-rich layers suggest strengthening of bottom currents. The upwelling of CDW facilitated a drastic increase in the (<sup>10</sup>Be/<sup>9</sup>Be)<sub>reac</sub> ratio during the late Pleistocene. Opal<sub>MAR</sub> and TOC % exhibit positive trends with (<sup>10</sup>Be/<sup>9</sup>Be)<sub>reac</sub> during the late Pleistocene interglacials, suggesting increased productivity during warmer periods.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"2016 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-06-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141508147","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract. Weather systems in the southern Indian Ocean influence East Antarctic precipitation variability and surface mass balance. However, long term variability in synoptic-scale weather systems in this region is not well understood due to short instrumental records that are mostly limited to the satellite era (post 1979). Ice core records from coastal East Antarctica suggest significant decadal variability in snowfall accumulation, indicating that data from the satellite era alone is not enough to characterise climate variability in the high southern latitudes. It is therefore challenging to contextualise recent precipitation trends and extremes in relation to climate change in this area. We used synoptic typing of daily 500 hPa geopotential height anomalies and the Law Dome ice core (East Antarctica) annual snowfall accumulation record to investigate whether the Twentieth Century Reanalysis project can represent the synoptic conditions associated with increased precipitation at Law Dome prior to the satellite era. Twelve synoptic types were identified using self-organising maps based on their dominant pressure anomaly patterns over the southern Indian Ocean, with four types associated with above average daily precipitation at Law Dome. Our results indicate that the Twentieth Century Reanalysis project can reliably represent the meridional synoptic conditions associated with increased precipitation at Law Dome from 1948, aligning with the assimilation of consistent surface pressure data from weather stations in the southern Indian Ocean. This extends the time period available to contextualise recent trends and extremes in precipitation and synoptic weather conditions by up to three decades beyond the satellite era. These results will help contextualise East Antarctic surface mass balance variability prior to the satellite era, with implications for improved understanding of the largest source of potential sea level rise.
摘要南印度洋的天气系统影响着南极东部的降水变化和地表质量平衡。然而，由于仪器记录较短，且大多仅限于卫星时代（1979 年以后），人们对该地区同步尺度天气系统的长期变异性了解不多。南极洲东部沿海地区的冰芯记录表明，降雪累积量存在显著的十年变异性，这表明仅凭卫星时代的数据不足以描述南部高纬度地区的气候变异性特征。因此，将最近的降水趋势和极端降水与这一地区的气候变化联系起来具有挑战性。我们利用每日 500 hPa 位势高度异常的天气类型和 Law Dome 冰芯（南极洲东部）的年降雪量累积记录，研究二十世纪再分析项目能否代表卫星时代之前与 Law Dome 降水量增加相关的天气条件。根据南印度洋上空的主要气压异常模式，利用自组织地图确定了 12 种天气类型，其中 4 种类型与劳穹顶高于平均日降水量有关。我们的研究结果表明，二十世纪再分析项目可以可靠地代表自 1948 年以来与劳穹顶降水量增加相关的经向合流条件，这与南印度洋气象站提供的一致的表面气压数据同化一致。这将可用于分析近期降水趋势和极端天气情况的时间段延长了三十年，超过了卫星时代。这些结果将有助于了解卫星时代之前南极东部地表质量平衡变化的背景，对更好地了解潜在海平面上升的最大来源具有重要意义。
{"title":"Evaluating the Twentieth Century Reanalysis Version 3 with synoptic typing and East Antarctic ice core accumulation","authors":"Max T. Nilssen, Danielle G. Udy, Tessa R. Vance","doi":"10.5194/cp-2024-39","DOIUrl":"https://doi.org/10.5194/cp-2024-39","url":null,"abstract":"<strong>Abstract.</strong> Weather systems in the southern Indian Ocean influence East Antarctic precipitation variability and surface mass balance. However, long term variability in synoptic-scale weather systems in this region is not well understood due to short instrumental records that are mostly limited to the satellite era (post 1979). Ice core records from coastal East Antarctica suggest significant decadal variability in snowfall accumulation, indicating that data from the satellite era alone is not enough to characterise climate variability in the high southern latitudes. It is therefore challenging to contextualise recent precipitation trends and extremes in relation to climate change in this area. We used synoptic typing of daily 500 hPa geopotential height anomalies and the Law Dome ice core (East Antarctica) annual snowfall accumulation record to investigate whether the Twentieth Century Reanalysis project can represent the synoptic conditions associated with increased precipitation at Law Dome prior to the satellite era. Twelve synoptic types were identified using self-organising maps based on their dominant pressure anomaly patterns over the southern Indian Ocean, with four types associated with above average daily precipitation at Law Dome. Our results indicate that the Twentieth Century Reanalysis project can reliably represent the meridional synoptic conditions associated with increased precipitation at Law Dome from 1948, aligning with the assimilation of consistent surface pressure data from weather stations in the southern Indian Ocean. This extends the time period available to contextualise recent trends and extremes in precipitation and synoptic weather conditions by up to three decades beyond the satellite era. These results will help contextualise East Antarctic surface mass balance variability prior to the satellite era, with implications for improved understanding of the largest source of potential sea level rise.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"13 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-06-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141513574","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Jérôme Lopez-Saez, Christophe Corona, Lenka Slamova, Matthias Huss, Valérie Daux, Kurt Nicolussi, Markus Stoffel
Abstract. Glacier mass balance reconstructions provide a means of placing relatively short observational records into a longer-term context. Here, we use multiple proxies from Pinus cembra trees from God da Tamangur, combining tree ring anatomy and stable isotope chronologies to reconstruct seasonal glacier mass balance (i.e., winter, summer, and annual mass balance) for the nearby Silvretta Glacier over the last 2 centuries. The combination of tree ring width, radial diameter of earlywood cell lumina, and latewood radial cell wall thickness provides a highly significant reconstruction for summer mass balance, whereas for the winter mass balance, the correlation was less significant but still robust when radial cell lumina were combined with δ18O records. A combination of the reconstructed winter and summer mass balances allows the quantification of the annual mass balance of the Silvretta Glacier for which in situ measurements date back to 1919. Our reconstruction indicates a substantial increase in glacier mass during the first half of the 19th century and an abrupt termination of this phase after the end of the Little Ice Age. Since the 1860s, negative glacier mass balances have been dominant and mass losses accelerate as anthropogenic warming picks up in the Alps.
{"title":"Multiproxy tree ring reconstruction of glacier mass balance: insights from Pinus cembra trees growing near Silvretta Glacier (Swiss Alps)","authors":"Jérôme Lopez-Saez, Christophe Corona, Lenka Slamova, Matthias Huss, Valérie Daux, Kurt Nicolussi, Markus Stoffel","doi":"10.5194/cp-20-1251-2024","DOIUrl":"https://doi.org/10.5194/cp-20-1251-2024","url":null,"abstract":"Abstract. Glacier mass balance reconstructions provide a means of placing relatively short observational records into a longer-term context. Here, we use multiple proxies from Pinus cembra trees from God da Tamangur, combining tree ring anatomy and stable isotope chronologies to reconstruct seasonal glacier mass balance (i.e., winter, summer, and annual mass balance) for the nearby Silvretta Glacier over the last 2 centuries. The combination of tree ring width, radial diameter of earlywood cell lumina, and latewood radial cell wall thickness provides a highly significant reconstruction for summer mass balance, whereas for the winter mass balance, the correlation was less significant but still robust when radial cell lumina were combined with δ18O records. A combination of the reconstructed winter and summer mass balances allows the quantification of the annual mass balance of the Silvretta Glacier for which in situ measurements date back to 1919. Our reconstruction indicates a substantial increase in glacier mass during the first half of the 19th century and an abrupt termination of this phase after the end of the Little Ice Age. Since the 1860s, negative glacier mass balances have been dominant and mass losses accelerate as anthropogenic warming picks up in the Alps.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"26 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-06-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141256565","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Stefan Brönnimann, Janusz Filipiak, Siyu Chen, Lucas Pfister
Abstract. The winter 1739/40 is known as one of the coldest winters in Europe since early instrumental measurements began. Many contemporary sources discuss the cold waves and compare the winter to that of 1708/09. It is less well known that the year 1740 remained cold until August and again in October, and that negative temperature anomalies are also found over Eurasia and North America. The 1737/40 cold season over northern midlatitude land areas was perhaps the coldest in 300 years, and 1740 was the coldest year in Central Europe in 600 years. New monthly, global climate reconstructions allow addressing this momentous event in greater detail, while daily observations and weather reconstructions give insight into the synoptic situations. Over Europe, we find that the event was initiated by a strong Scandinavian blocking in early January, allowing the advection continental cold air. From February until June, high pressure dominated over Ireland, arguably associated with frequent East Atlantic blocking. This led to cold air advection from the cold northern North Atlantic. During the summer, cyclonic weather dominated over Central Europe, associated with cold and wet air from the Atlantic. The possible role of oceanic influences (El Niño) and external forcings (eruption of Mount Tarumae in 1739) are discussed. While a possible El Niño event might have contributed to the winter cold spells, the East Atlantic blocking is arguably unrelated to either El Niño or the volcanic eruption. In all, the cold year of 1740 marks one of the strongest, arguably unforced excursions in European temperature.
{"title":"The weather of 1740, the coldest year in Central Europe in 600 years","authors":"Stefan Brönnimann, Janusz Filipiak, Siyu Chen, Lucas Pfister","doi":"10.5194/cp-2024-40","DOIUrl":"https://doi.org/10.5194/cp-2024-40","url":null,"abstract":"<strong>Abstract.</strong> The winter 1739/40 is known as one of the coldest winters in Europe since early instrumental measurements began. Many contemporary sources discuss the cold waves and compare the winter to that of 1708/09. It is less well known that the year 1740 remained cold until August and again in October, and that negative temperature anomalies are also found over Eurasia and North America. The 1737/40 cold season over northern midlatitude land areas was perhaps the coldest in 300 years, and 1740 was the coldest year in Central Europe in 600 years. New monthly, global climate reconstructions allow addressing this momentous event in greater detail, while daily observations and weather reconstructions give insight into the synoptic situations. Over Europe, we find that the event was initiated by a strong Scandinavian blocking in early January, allowing the advection continental cold air. From February until June, high pressure dominated over Ireland, arguably associated with frequent East Atlantic blocking. This led to cold air advection from the cold northern North Atlantic. During the summer, cyclonic weather dominated over Central Europe, associated with cold and wet air from the Atlantic. The possible role of oceanic influences (El Niño) and external forcings (eruption of Mount Tarumae in 1739) are discussed. While a possible El Niño event might have contributed to the winter cold spells, the East Atlantic blocking is arguably unrelated to either El Niño or the volcanic eruption. In all, the cold year of 1740 marks one of the strongest, arguably unforced excursions in European temperature.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"70 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-06-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141256638","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Markus Adloff, Frerk Pöppelmeier, Aurich Jeltsch-Thömmes, Thomas F. Stocker, Fortunat Joos
Abstract. Variations in the Atlantic Meridional Overturning Circulation (AMOC) are associated with Northern Hemispheric and global climate shifts. Thermal thresholds of the AMOC have been found in a hierarchy of numerical circulation models, and there is an increasing body of evidence for the existence of highly sensitive AMOC modes where small perturbations can cause disproportionately large circulation and hence climatic changes. We discovered such thresholds in simulations with the intermediate-complexity Earth system model Bern3D, which is highly computationally efficient, allowing for studying this non-linear behaviour systematically over entire glacial cycles. By simulating the AMOC under different magnitudes of orbitally paced changes in radiative forcing over the last 788 000 years, we show that up to three thermal thresholds are crossed during glacial cycles in Bern3D and that thermal forcing could have destabilised the AMOC repeatedly. We present the circulation and sea ice patterns that characterise the stable circulation modes between which this model oscillates during a glacial cycle and assess how often and when thermal forcing could have preconditioned the Bern3D AMOC for abrupt shifts over the last 788 kyr.
{"title":"Multiple thermal Atlantic Meridional Overturning Circulation thresholds in the intermediate complexity model Bern3D","authors":"Markus Adloff, Frerk Pöppelmeier, Aurich Jeltsch-Thömmes, Thomas F. Stocker, Fortunat Joos","doi":"10.5194/cp-20-1233-2024","DOIUrl":"https://doi.org/10.5194/cp-20-1233-2024","url":null,"abstract":"Abstract. Variations in the Atlantic Meridional Overturning Circulation (AMOC) are associated with Northern Hemispheric and global climate shifts. Thermal thresholds of the AMOC have been found in a hierarchy of numerical circulation models, and there is an increasing body of evidence for the existence of highly sensitive AMOC modes where small perturbations can cause disproportionately large circulation and hence climatic changes. We discovered such thresholds in simulations with the intermediate-complexity Earth system model Bern3D, which is highly computationally efficient, allowing for studying this non-linear behaviour systematically over entire glacial cycles. By simulating the AMOC under different magnitudes of orbitally paced changes in radiative forcing over the last 788 000 years, we show that up to three thermal thresholds are crossed during glacial cycles in Bern3D and that thermal forcing could have destabilised the AMOC repeatedly. We present the circulation and sea ice patterns that characterise the stable circulation modes between which this model oscillates during a glacial cycle and assess how often and when thermal forcing could have preconditioned the Bern3D AMOC for abrupt shifts over the last 788 kyr.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"22 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-06-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141256559","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-06-03DOI: 10.5194/egusphere-2024-1387
Jean-Philippe Baudouin, Nils Weitzel, Maximilian May, Lukas Jonkers, Andrew M. Dolman, Kira Rehfeld
Abstract. Reconstructing past variations of the global mean surface temperature is used to characterise the Earth system response to perturbations as well as validate Earth system simulations. Reconstructing GMST beyond the instrumental period relies on algorithms aggregating local proxy temperature records. Here, we propose to establish standards for the evaluation of the performance of such reconstruction algorithms. Our framework relies on pseudo-proxy experiments. That is, we test the ability of the algorithm to reconstruct a simulated GMST, using artificially generated proxy data created from the same simulation. We apply the framework to an adapted version of the GMST reconstruction algorithm used in Snyder (2016), and the synthesis of marine proxy records for temperature of the last 130 kyr from Jonkers et al. (2020). We use an ensemble of 4 transient simulations of the last glacial cycle or the last 25 kyr for the pseudo-proxy experiments. We find the algorithm to be able to reconstruct timescales longer than 4 kyr over the last 25 kyr. However, beyond 40 kyr BP, age uncertainty limits the algorithm capability to timescales longer than 15 kyr. The main sources of uncertainty are a factor, that rescales near global mean sea surface temperatures to GMST, the proxy measurement, the specific set of record locations, and potential seasonal bias. Increasing the number of records significantly reduces all sources of uncertainty but the scaling. We also show that a trade-off exists between the inclusion of a large number of records, which reduces the uncertainty on long time scales, and of only records with low age uncertainty, high accumulation rate, and high resolution, which improves the reconstruction of the short timescales. Finally, the method and the quantitative results presented here can serve as a basis for future evaluations of reconstructions. We also suggest future avenues to improve reconstruction algorithms and discuss the key limitations arising from the proxy data properties.
{"title":"Testing the reliability of global surface temperature reconstructions of the last glacial cycle","authors":"Jean-Philippe Baudouin, Nils Weitzel, Maximilian May, Lukas Jonkers, Andrew M. Dolman, Kira Rehfeld","doi":"10.5194/egusphere-2024-1387","DOIUrl":"https://doi.org/10.5194/egusphere-2024-1387","url":null,"abstract":"<strong>Abstract.</strong> Reconstructing past variations of the global mean surface temperature is used to characterise the Earth system response to perturbations as well as validate Earth system simulations. Reconstructing GMST beyond the instrumental period relies on algorithms aggregating local proxy temperature records. Here, we propose to establish standards for the evaluation of the performance of such reconstruction algorithms. Our framework relies on pseudo-proxy experiments. That is, we test the ability of the algorithm to reconstruct a simulated GMST, using artificially generated proxy data created from the same simulation. We apply the framework to an adapted version of the GMST reconstruction algorithm used in Snyder (2016), and the synthesis of marine proxy records for temperature of the last 130 kyr from Jonkers et al. (2020). We use an ensemble of 4 transient simulations of the last glacial cycle or the last 25 kyr for the pseudo-proxy experiments. We find the algorithm to be able to reconstruct timescales longer than 4 kyr over the last 25 kyr. However, beyond 40 kyr BP, age uncertainty limits the algorithm capability to timescales longer than 15 kyr. The main sources of uncertainty are a factor, that rescales near global mean sea surface temperatures to GMST, the proxy measurement, the specific set of record locations, and potential seasonal bias. Increasing the number of records significantly reduces all sources of uncertainty but the scaling. We also show that a trade-off exists between the inclusion of a large number of records, which reduces the uncertainty on long time scales, and of only records with low age uncertainty, high accumulation rate, and high resolution, which improves the reconstruction of the short timescales. Finally, the method and the quantitative results presented here can serve as a basis for future evaluations of reconstructions. We also suggest future avenues to improve reconstruction algorithms and discuss the key limitations arising from the proxy data properties.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"20 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-06-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141256557","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-06-03DOI: 10.5194/egusphere-2024-1322
Lauren R. Marshall, Anja Schmidt, Andrew P. Schurer, Nathan Luke Abraham, Lucie J. Lücke, Rob Wilson, Kevin Anchukaitis, Gabriele Hegerl, Ben Johnson, Bette L. Otto-Bliesner, Esther C. Brady, Myriam Khodri, Kohei Yoshida
Abstract. Climate variability in the last millennium (past 1000 years) is dominated by the effects of large-magnitude volcanic eruptions; however, a long-standing mismatch exists between model-simulated and tree-ring derived surface cooling. Accounting for the self-limiting effects of large sulfur dioxide (SO2) injections and the limitations in tree-ring records such as lagged responses due to biological memory reconciles some of the discrepancy, but uncertainties remain particularly for the largest tropical eruptions. The representation of volcanic forcing in the latest generation of climate models has improved significantly, but most models prescribe the aerosol optical properties rather than using SO2 emissions directly and including interactions between the aerosol, chemistry and dynamics. Here, we use the UK Earth System Model (UKESM) to simulate the climate of the last millennium (1250–1850) using volcanic SO2 emissions. Averaged across all large-magnitude eruptions, we find similar Northern Hemisphere (NH) summer cooling compared with other last millennium climate simulations from the Paleo Model Intercomparison Project Phase 4, run with both SO2 emissions and prescribed forcing, and a continued overestimation of surface cooling compared with tree-ring reconstructions. However, for the largest-magnitude tropical eruptions in 1257 (Mt. Samalas) and 1815 (Mt. Tambora), some models including UKESM1 suggest a smaller NH summer cooling that is in better agreement with tree-ring records. In UKESM1, we find that the simulated volcanic forcing differs considerably from the PMIP4 dataset used in models without interactive aerosol schemes, with marked differences in the hemispheric spread of the aerosol, resulting in lower forcing in the NH when SO2 emissions are used. Our results suggest that for the largest tropical eruptions, the spatial distribution of aerosol can account for some of the discrepancies between model-simulated and tree-ring derived cooling. Further work should therefore focus on better resolving the spatial distribution of aerosol forcing for past eruptions.
{"title":"Last Millennium Volcanic Forcing and Climate Response using SO2 Emissions","authors":"Lauren R. Marshall, Anja Schmidt, Andrew P. Schurer, Nathan Luke Abraham, Lucie J. Lücke, Rob Wilson, Kevin Anchukaitis, Gabriele Hegerl, Ben Johnson, Bette L. Otto-Bliesner, Esther C. Brady, Myriam Khodri, Kohei Yoshida","doi":"10.5194/egusphere-2024-1322","DOIUrl":"https://doi.org/10.5194/egusphere-2024-1322","url":null,"abstract":"<strong>Abstract.</strong> Climate variability in the last millennium (past 1000 years) is dominated by the effects of large-magnitude volcanic eruptions; however, a long-standing mismatch exists between model-simulated and tree-ring derived surface cooling. Accounting for the self-limiting effects of large sulfur dioxide (SO<sub>2</sub>) injections and the limitations in tree-ring records such as lagged responses due to biological memory reconciles some of the discrepancy, but uncertainties remain particularly for the largest tropical eruptions. The representation of volcanic forcing in the latest generation of climate models has improved significantly, but most models prescribe the aerosol optical properties rather than using SO<sub>2</sub> emissions directly and including interactions between the aerosol, chemistry and dynamics. Here, we use the UK Earth System Model (UKESM) to simulate the climate of the last millennium (1250–1850) using volcanic SO<sub>2</sub> emissions. Averaged across all large-magnitude eruptions, we find similar Northern Hemisphere (NH) summer cooling compared with other last millennium climate simulations from the Paleo Model Intercomparison Project Phase 4, run with both SO<sub>2</sub> emissions and prescribed forcing, and a continued overestimation of surface cooling compared with tree-ring reconstructions. However, for the largest-magnitude tropical eruptions in 1257 (Mt. Samalas) and 1815 (Mt. Tambora), some models including UKESM1 suggest a smaller NH summer cooling that is in better agreement with tree-ring records. In UKESM1, we find that the simulated volcanic forcing differs considerably from the PMIP4 dataset used in models without interactive aerosol schemes, with marked differences in the hemispheric spread of the aerosol, resulting in lower forcing in the NH when SO<sub>2</sub> emissions are used. Our results suggest that for the largest tropical eruptions, the spatial distribution of aerosol can account for some of the discrepancies between model-simulated and tree-ring derived cooling. Further work should therefore focus on better resolving the spatial distribution of aerosol forcing for past eruptions.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"127 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-06-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141256364","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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