Abstract. Noise in Holocene paleoclimate reconstructions can hamper the detection of centennial to millennial climate variations and diagnoses of the dynamics involved. This paper uses multiple ensembles of reconstructions to separate signal and noise and determine what, if any, centennial to millennial variations influenced North America during the past 7000 years. To do so, ensembles of temperature and moisture reconstructions were compared across four different spatial scales: multi-continent, regional, sub-regional, and local. At each scale, two independent multi-record ensembles were compared to detect any centennial to millennial departures from the long Holocene trends, which correlate more than expected from random patterns. In all cases, the potential centennial to millennial variations had small magnitudes. However, at least two patterns of centennial to millennial variability appear evident. First, large-scale variations included a prominent Mid-Holocene anomaly from 5600–5000 yr BP that increased mean effective moisture and produced temperature anomalies of different signs in different regions. The changes shifted the north–south temperature gradient in mid-latitude North America with a pattern similar to that of the North Atlantic Oscillation (NAO). Second, correlated multi-century (∼ 350 years) variations produce a distinct spectral signature in temperature and hydroclimate records along the western Atlantic margin. Both patterns differ from random variations, but they express distinct spatiotemporal characteristics consistent with separate controlling dynamics.
{"title":"Patterns of centennial to millennial Holocene climate variation in the North American mid-latitudes","authors":"Bryan N. Shuman","doi":"10.5194/cp-20-1703-2024","DOIUrl":"https://doi.org/10.5194/cp-20-1703-2024","url":null,"abstract":"Abstract. Noise in Holocene paleoclimate reconstructions can hamper the detection of centennial to millennial climate variations and diagnoses of the dynamics involved. This paper uses multiple ensembles of reconstructions to separate signal and noise and determine what, if any, centennial to millennial variations influenced North America during the past 7000 years. To do so, ensembles of temperature and moisture reconstructions were compared across four different spatial scales: multi-continent, regional, sub-regional, and local. At each scale, two independent multi-record ensembles were compared to detect any centennial to millennial departures from the long Holocene trends, which correlate more than expected from random patterns. In all cases, the potential centennial to millennial variations had small magnitudes. However, at least two patterns of centennial to millennial variability appear evident. First, large-scale variations included a prominent Mid-Holocene anomaly from 5600–5000 yr BP that increased mean effective moisture and produced temperature anomalies of different signs in different regions. The changes shifted the north–south temperature gradient in mid-latitude North America with a pattern similar to that of the North Atlantic Oscillation (NAO). Second, correlated multi-century (∼ 350 years) variations produce a distinct spectral signature in temperature and hydroclimate records along the western Atlantic margin. Both patterns differ from random variations, but they express distinct spatiotemporal characteristics consistent with separate controlling dynamics.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"27 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141866170","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}
Lucy Timbrell, James Blinkhorn, Margherita Colucci, Michela Leonardi, Manuel Chevalier, Matt Grove, Eleanor Scerri, Andrea Manica
Abstract.Both proxies and models provide key resources to explore how palaeoenvironmental changes may have impacted diverse biotic communities and cultural processes. Whilst proxies provide the gold standard in reconstructing the local environment, they only provide point estimates for a limited number of locations; on the other hand, models have the potential to afford more extensive and standardised geographic coverage. A key decision when using model outputs is the appropriate geographic resolution to adopt; models are coarse scale, in the order of several arc degrees, and so their outputs are usually downscaled to a higher resolution. Most publicly available model time-series have been downscaled to 30 or 60 arc-minutes, but it is unclear whether such resolution is sufficient, or whether this may homogenise environments and mask the spatial variability that is often the primary subject of analysis. Here, we explore the impact of further downscaling model outputs from 30 to 5 arc-minutes using the delta method, which uses the difference between past and present model data sets to increase spatial resolution of simulations, in order to determine to what extent further downscaling captures climatic trends at the site-level, through direct comparison with proxy reconstructions. We use the output from the HadCM3 Global Circulation model for annual temperature, mean temperature of the warmest quarter, and annual precipitation, which we evaluated against a large empirical dataset of pollen-based reconstructions from across the Northern Hemisphere. Our results demonstrate that, overall, models tend to provide broadly similar accounts of past climate to that obtained from proxy reconstructions, with coherence tending to decline with age. However, our results imply that downscaling to a very fine scale has minimal to no effect on the coherence of model data with pollen records. Optimal spatial resolution is therefore likely to be highly dependent on specific research contexts and questions, with careful consideration required regarding the trade-off between highlighting local-scale variation and increasing potential error.
{"title":"More is not always better: downscaling climate model outputs from 30 to 5-minute resolution has minimal impact on coherence with Late Quaternary proxies","authors":"Lucy Timbrell, James Blinkhorn, Margherita Colucci, Michela Leonardi, Manuel Chevalier, Matt Grove, Eleanor Scerri, Andrea Manica","doi":"10.5194/cp-2024-53","DOIUrl":"https://doi.org/10.5194/cp-2024-53","url":null,"abstract":"<strong>Abstract.</strong> <span>Both proxies and models provide key resources to explore how palaeoenvironmental changes may have impacted diverse biotic communities and cultural processes. Whilst proxies provide the gold standard in reconstructing the local environment, they only provide point estimates for a limited number of locations; on the other hand, models have the potential to afford more extensive and standardised geographic coverage. A key decision when using model outputs is the appropriate geographic resolution to adopt; models are coarse scale, in the order of several arc degrees, and so their outputs are usually downscaled to a higher resolution. Most publicly available model time-series have been downscaled to 30 or 60 arc-minutes, but it is unclear whether such resolution is sufficient, or whether this may homogenise environments and mask the spatial variability that is often the primary subject of analysis. Here, we explore the impact of further downscaling model outputs from 30 to 5 arc-minutes using the delta method, which uses the difference between past and present model data sets to increase spatial resolution of simulations, in order to determine to what extent further downscaling captures climatic trends at the site-level, through direct comparison with proxy reconstructions. We use the output from the HadCM3 Global Circulation model for annual temperature, mean temperature of the warmest quarter, and annual precipitation, which we evaluated against a large empirical dataset of pollen-based reconstructions from across the Northern Hemisphere. Our results demonstrate that, overall, models tend to provide broadly similar accounts of past climate to that obtained from proxy reconstructions, with coherence tending to decline with age. However, our results imply that downscaling to a very fine scale has minimal to no effect on the coherence of model data with pollen records. Optimal spatial resolution is therefore likely to be highly dependent on specific research contexts and questions, with careful consideration required regarding the trade-off between highlighting local-scale variation and increasing potential error. </span><span></span>","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"203 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-07-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141866200","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 : 2024-07-30DOI: 10.5194/egusphere-2024-2156
Jonathan Ortved Melcher, Sune Halkjær, Peter Ditlevsen, Peter L. Langen, Guido Vettoretti, Sune Olander Rasmussen
Abstract. This study introduces a novel dynamical systems model designed to capture the highly non-periodic nature of Dansgaard-Oeschger (DO) events. Such events are difficult to model adequately due to their variable durations — some lasting around a century, while others span multiple millennia — and the occurrence of short precursor events that precede the longer DO events despite similar boundary climate conditions. Utilizing a simplified two-equation framework derived from the Stommel model, our approach integrates an internal control parameter which acts as a feedback parameter on the Antarctic Bottom Water (AABW) formation. Through both analytical and numerical methods, we establish a suitable parameter domain within which the newly adjusted models can accurately replicate the paleoclimatic records of DO events as described by summary statistics derived from ice-core data. The analysis also shows that without the novel control parameter, the model does not have a suitable parameter domain in which it can reproduce the wide range of event characteristics seen in the ice-core record. The study provides new insights into the underlying mechanisms driving these highly significant climate phenomena and the necessary timescale in which they are forced, by allowing the new model's parameters to vary through time. This allows our model to achieve unprecedented precision in capturing a realistic sequence of DO events with timing characteristics matching those of the observational record. This refined model not only enhances our understanding of the DO cycles but also demonstrates the potential of simple dynamical systems to simulate complex climate interactions.
摘要本研究介绍了一种新的动力系统模式，旨在捕捉丹斯加德-奥斯赫格（Dansgaard-Oeschger，DO）事件的高度非周期性。由于此类事件的持续时间长短不一，有的持续一个世纪左右，有的则长达数千年，而且尽管边界气候条件相似，但在较长 DO 事件之前会出现一些短的前兆事件，因此很难对其进行充分建模。我们的方法利用从斯托梅尔（Stommel）模型中推导出的简化二方程框架，整合了一个内部控制参数，作为南极底层水（AABW）形成的反馈参数。通过分析和数值方法，我们建立了一个合适的参数域，在这个参数域内，新调整的模型可以准确地复制冰芯数据汇总统计所描述的溶解氧事件的古气候记录。分析还表明，如果没有新的控制参数，模型就没有一个合适的参数域来再现冰芯记录中的各种事件特征。这项研究通过允许新模型的参数随时间变化，对驱动这些极为重要的气候现象的基本机制以及迫使它们发生变化的必要时间尺度提供了新的见解。这使得我们的模型能够前所未有地精确捕捉到一系列真实的 DO 事件，其时间特征与观测记录相吻合。这个完善的模型不仅增强了我们对溶解氧循环的理解，而且还展示了简单动力系统模拟复杂气候相互作用的潜力。
{"title":"Advances in conceptual modelling of the variable nature of Dansgaard-Oeschger events","authors":"Jonathan Ortved Melcher, Sune Halkjær, Peter Ditlevsen, Peter L. Langen, Guido Vettoretti, Sune Olander Rasmussen","doi":"10.5194/egusphere-2024-2156","DOIUrl":"https://doi.org/10.5194/egusphere-2024-2156","url":null,"abstract":"<strong>Abstract.</strong> This study introduces a novel dynamical systems model designed to capture the highly non-periodic nature of Dansgaard-Oeschger (DO) events. Such events are difficult to model adequately due to their variable durations — some lasting around a century, while others span multiple millennia — and the occurrence of short precursor events that precede the longer DO events despite similar boundary climate conditions. Utilizing a simplified two-equation framework derived from the Stommel model, our approach integrates an internal control parameter which acts as a feedback parameter on the Antarctic Bottom Water (AABW) formation. Through both analytical and numerical methods, we establish a suitable parameter domain within which the newly adjusted models can accurately replicate the paleoclimatic records of DO events as described by summary statistics derived from ice-core data. The analysis also shows that without the novel control parameter, the model does not have a suitable parameter domain in which it can reproduce the wide range of event characteristics seen in the ice-core record. The study provides new insights into the underlying mechanisms driving these highly significant climate phenomena and the necessary timescale in which they are forced, by allowing the new model's parameters to vary through time. This allows our model to achieve unprecedented precision in capturing a realistic sequence of DO events with timing characteristics matching those of the observational record. This refined model not only enhances our understanding of the DO cycles but also demonstrates the potential of simple dynamical systems to simulate complex climate interactions.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"50 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-07-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141865958","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. Atmospheric circulation changes, their driving mechanisms, and interactions are important topics in global change research. Local changes in the East Asian summer monsoon (EASM) and the midlatitude westerlies will inevitably affect the climate and ecology of the arid zone of northwestern China. Hence, it is important to study these regional changes. While previous studies in this area are all single-point climate reconstruction studies, there is a lack of research on the interaction areas and driving mechanisms of the two major circulations. Dendroclimatology can provide high-resolution, long-term, and reliable multi-point proxies for the study of interannual and interdecadal climate change. We chose to observe these changes in the Alxa Plateau using dendrochronological methods. We assembled ring-width records of Qinghai spruce (Picea crassifolia) in the mountain regions surrounding the Alxa Plateau: the Helan Mountains, Changling Mountain, and Dongda Mountain. The results show that radial growth was indeed affected by changes in the monsoon and westerlies. The heterogeneity of precipitation and climatic wet–dry changes in different regions is primarily influenced by the interactions between atmospheric circulation systems, each with its own dominant controlling factors. In the case of the Helan Mountains, both of these major atmospheric circulation systems play a significant role in shaping climate changes. Changling Mountain in the southern part of the Alxa Plateau is mainly influenced by the EASM. Dongda Mountain is mainly influenced by the westerlies. Understanding these local conditions will help us predict climate changes in northwestern China.
{"title":"Interaction between the East Asian summer monsoon and westerlies as shown by tree-ring records","authors":"Shengchun Xiao, Xiaomei Peng, Quanyan Tian, Aijun Ding, Jiali Xie, Jingrong Su","doi":"10.5194/cp-20-1687-2024","DOIUrl":"https://doi.org/10.5194/cp-20-1687-2024","url":null,"abstract":"Abstract. Atmospheric circulation changes, their driving mechanisms, and interactions are important topics in global change research. Local changes in the East Asian summer monsoon (EASM) and the midlatitude westerlies will inevitably affect the climate and ecology of the arid zone of northwestern China. Hence, it is important to study these regional changes. While previous studies in this area are all single-point climate reconstruction studies, there is a lack of research on the interaction areas and driving mechanisms of the two major circulations. Dendroclimatology can provide high-resolution, long-term, and reliable multi-point proxies for the study of interannual and interdecadal climate change. We chose to observe these changes in the Alxa Plateau using dendrochronological methods. We assembled ring-width records of Qinghai spruce (Picea crassifolia) in the mountain regions surrounding the Alxa Plateau: the Helan Mountains, Changling Mountain, and Dongda Mountain. The results show that radial growth was indeed affected by changes in the monsoon and westerlies. The heterogeneity of precipitation and climatic wet–dry changes in different regions is primarily influenced by the interactions between atmospheric circulation systems, each with its own dominant controlling factors. In the case of the Helan Mountains, both of these major atmospheric circulation systems play a significant role in shaping climate changes. Changling Mountain in the southern part of the Alxa Plateau is mainly influenced by the EASM. Dongda Mountain is mainly influenced by the westerlies. Understanding these local conditions will help us predict climate changes in northwestern China.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"45 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-07-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141866199","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}
Naroa Martinez-Braceras, Aitor Payros, Jaume Dinarès-Turell, Idoia Rosales, Javier Arostegi, Roi Silva-Casal
Abstract. Lower Pliensbachian hemipelagic successions from the northern Iberian palaeomargin are characterized by the occurrence of organic-rich calcareous rhythmites of decimetre-thick limestone and marl beds as well as thicker black shale intervals. Understanding the genetic mechanisms of the cyclic lithologies and processes involved along with the nature of the carbon cycle is of primary interest. This cyclostratigraphic study, carried out in one of the black shale intervals exposed in Santiurde de Reinosa (Basque–Cantabrian Basin), reveals that the calcareous rhythmites responded to periodic environmental variations in the Milankovitch-cycle band and were likely driven by eccentricity-modulated precession. The main environmental processes that determined the formation of the rhythmite were deduced on the basis of the integrated sedimentological, mineralogical, and geochemical study of an eccentricity bundle. The formation of precession couplets was controlled by variations in carbonate production and dilution by terrigenous supplies, along with periodic changes in bottom-water oxygenation. Precessional configurations with marked annual seasonality increased terrigenous input (by rivers or wind) to marine areas and boosted organic productivity in surface water. The great accumulation of organic matter on the seabed eventually decreased bottom-water oxygenation, which might also be influenced by reduced ocean ventilation. Thus, deposition of organic-rich marls and shales occurred when annual seasonality was maximal. On the contrary, a reduction in terrestrial inputs at precessional configurations with minimal seasonality diminished shallow organic productivity, which, added to an intensification of vertical mixing, contributed to increasing the oxidation of organic matter. These conditions also favoured greater production and basinward export of carbonate mud in shallow marine areas, causing the formation of limy hemipelagic beds. Short eccentricity cycles modulated the amplitude of precession-driven variations in terrigenous input and oxygenation of bottom seawater. Thus, the amplitude of the contrast between successive precessional beds increased when the Earth's orbit was elliptical and diminished when it was circular. The data also suggest that short eccentricity cycles affected short-term sea level changes, probably through orbitally modulated aquifer eustasy.
摘要伊比利亚古边缘北部的下更新统半沉积层的特点是，在十厘米厚的石灰岩和泥灰岩床以及较厚的黑色页岩层中出现富含有机质的钙质韵律岩。了解循环岩性的成因机制、相关过程以及碳循环的性质是人们最感兴趣的问题。这项循环地层学研究是在 Santiurde de Reinosa（巴斯克-坎塔布里亚盆地）出露的一个黑色页岩岩层中进行的，研究结果表明，钙质韵律岩对米兰科维奇周期带的周期性环境变化做出了反应，很可能是由偏心调制的前向驱动的。在对偏心率束进行沉积学、矿物学和地球化学综合研究的基础上，推断出了决定节律岩形成的主要环境过程。碳酸盐生成量的变化和土著物质的稀释作用，以及底层水含氧量的周期性变化控制着节律对偶的形成。具有明显年度季节性的前向构造增加了（河流或风）对海洋区域的土著输入，提高了表层水的有机生产力。海底有机物的大量积累最终降低了底层水的含氧量，这也可能受到海洋通风减少的影响。因此，富含有机质的泥灰岩和页岩沉积发生在年季节性最强的时候。相反，在季节性最小的前向配置中，陆地输入的减少降低了浅层有机生产力，再加上垂直混合的加强，有助于增加有机物的氧化。这些条件还有利于浅海区碳酸盐泥的大量生产和向海盆输出，从而形成了含石灰质的半沉积床。短偏心率周期调节了前震驱动的陆源输入和底层海水含氧量变化的幅度。因此，当地球轨道为椭圆形时，连续前向海床之间的对比振幅增大，而当地球轨道为圆形时，对比振幅减小。数据还表明，短偏心率周期影响了短期海平面变化，这可能是通过轨道调节含水层的膨胀作用实现的。
{"title":"Orbitally forced environmental changes during the accumulation of a Pliensbachian (Lower Jurassic) black shale in northern Iberia","authors":"Naroa Martinez-Braceras, Aitor Payros, Jaume Dinarès-Turell, Idoia Rosales, Javier Arostegi, Roi Silva-Casal","doi":"10.5194/cp-20-1659-2024","DOIUrl":"https://doi.org/10.5194/cp-20-1659-2024","url":null,"abstract":"Abstract. Lower Pliensbachian hemipelagic successions from the northern Iberian palaeomargin are characterized by the occurrence of organic-rich calcareous rhythmites of decimetre-thick limestone and marl beds as well as thicker black shale intervals. Understanding the genetic mechanisms of the cyclic lithologies and processes involved along with the nature of the carbon cycle is of primary interest. This cyclostratigraphic study, carried out in one of the black shale intervals exposed in Santiurde de Reinosa (Basque–Cantabrian Basin), reveals that the calcareous rhythmites responded to periodic environmental variations in the Milankovitch-cycle band and were likely driven by eccentricity-modulated precession. The main environmental processes that determined the formation of the rhythmite were deduced on the basis of the integrated sedimentological, mineralogical, and geochemical study of an eccentricity bundle. The formation of precession couplets was controlled by variations in carbonate production and dilution by terrigenous supplies, along with periodic changes in bottom-water oxygenation. Precessional configurations with marked annual seasonality increased terrigenous input (by rivers or wind) to marine areas and boosted organic productivity in surface water. The great accumulation of organic matter on the seabed eventually decreased bottom-water oxygenation, which might also be influenced by reduced ocean ventilation. Thus, deposition of organic-rich marls and shales occurred when annual seasonality was maximal. On the contrary, a reduction in terrestrial inputs at precessional configurations with minimal seasonality diminished shallow organic productivity, which, added to an intensification of vertical mixing, contributed to increasing the oxidation of organic matter. These conditions also favoured greater production and basinward export of carbonate mud in shallow marine areas, causing the formation of limy hemipelagic beds. Short eccentricity cycles modulated the amplitude of precession-driven variations in terrigenous input and oxygenation of bottom seawater. Thus, the amplitude of the contrast between successive precessional beds increased when the Earth's orbit was elliptical and diminished when it was circular. The data also suggest that short eccentricity cycles affected short-term sea level changes, probably through orbitally modulated aquifer eustasy.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"56 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-07-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141866172","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}
Xiaodong Zhang, Brett J. Tipple, Jiang Zhu, William D. Rush, Christian A. Shields, Joseph B. Novak, James C. Zachos
Abstract. The effects of anthropogenic warming on the hydroclimate of California are becoming more pronounced with the increased frequency of multi-year droughts and flooding. As a past analog for the future, the Paleocene–Eocene Thermal Maximum (PETM) is a unique natural experiment for assessing global and regional hydroclimate sensitivity to greenhouse gas warming. Globally, extensive evidence (i.e., observations and climate models with high pCO2) demonstrates hydrological intensification with significant variability from region to region (i.e., drier or wetter, greater frequency, and/or intensity of extreme events). Central California (paleolatitude ∼ 42° N), roughly at the boundary between dry subtropical highs and mid-latitude low-pressure systems, would have been particularly susceptible to shifts in atmospheric circulation and precipitation patterns/intensity. Here, we present new observations and climate model output on regional/local hydroclimate responses in central California during the PETM. Our findings, based on multi-proxy evidence within the context of model outputs, suggest a transition to an overall drier climate punctuated by increased precipitation during summer months along central coastal California during the PETM.
{"title":"Response of coastal California hydroclimate to the Paleocene–Eocene Thermal Maximum","authors":"Xiaodong Zhang, Brett J. Tipple, Jiang Zhu, William D. Rush, Christian A. Shields, Joseph B. Novak, James C. Zachos","doi":"10.5194/cp-20-1615-2024","DOIUrl":"https://doi.org/10.5194/cp-20-1615-2024","url":null,"abstract":"Abstract. The effects of anthropogenic warming on the hydroclimate of California are becoming more pronounced with the increased frequency of multi-year droughts and flooding. As a past analog for the future, the Paleocene–Eocene Thermal Maximum (PETM) is a unique natural experiment for assessing global and regional hydroclimate sensitivity to greenhouse gas warming. Globally, extensive evidence (i.e., observations and climate models with high pCO2) demonstrates hydrological intensification with significant variability from region to region (i.e., drier or wetter, greater frequency, and/or intensity of extreme events). Central California (paleolatitude ∼ 42° N), roughly at the boundary between dry subtropical highs and mid-latitude low-pressure systems, would have been particularly susceptible to shifts in atmospheric circulation and precipitation patterns/intensity. Here, we present new observations and climate model output on regional/local hydroclimate responses in central California during the PETM. Our findings, based on multi-proxy evidence within the context of model outputs, suggest a transition to an overall drier climate punctuated by increased precipitation during summer months along central coastal California during the PETM.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"78 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141778419","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 : 2024-07-25DOI: 10.5194/egusphere-2024-2229
Cécile Figus, Or M. Bialik, Andrey Yu. Gladenkov, Tatyana V. Oreshkina, Johan Renaudie, Pavel Smirnov, Jakub Witkowski
Abstract. Diatoms play a major role in the carbon and silicon cycles, and thus diatom-bearing sediments represent an archive of past climatic and environmental settings. In shallow marine and freshwater environments, the accumulation of diatom frustules forms a sedimentary rock called diatomite. However, most global scale studies of diatom-bearing sediments focus on deep-sea sites, whereas shallow marine and freshwater diatomites are studied mainly at a regional level. To address this problem, we present a global scale compilation of diatomite occurrences spanning the Palaeogene (~66 to ~23 Ma). This period was characterized by initial extreme warmth followed by a prolonged cooling, disrupted by short-term climatic events called hyperthermals, and by a number of palaeoceanographic and palaeogeographic changes. The aim of this compilation is to determine the response of diatom production to Palaeogene environmental fluctuations, by examining the influence of climate, tectonic activity and ocean circulation on diatomite deposition. Although climatic factors appear to have had an indirect impact, our study suggests that palaeogeographic and palaeoceanographic changes were key drivers of diatomite deposition during the Palaeogene, particularly from the Early Eocene Climatic Optimum (~53 to ~49 Ma) onwards. In fact, our compilation suggests the absence of diatomite deposition in epicontinental seas between ~46 and ~43 Ma, while diatomites do not begin to accumulate in open ocean environments until ~43.5 Ma. Moreover, we observe that regional climate and volcano–tectonic activity have had an impact on the deposition of freshwater diatomites.
摘要硅藻在碳和硅的循环中发挥着重要作用，因此含硅藻的沉积物是过去气候和环境背景的档案。在浅海和淡水环境中，硅藻颗粒的堆积形成了一种叫做硅藻土的沉积岩。然而，对含硅藻沉积物的全球尺度研究大多集中在深海地点，而对浅海和淡水硅藻土的研究主要集中在区域层面。为了解决这个问题，我们汇编了古近纪（约 66 至约 23 Ma）硅藻土的全球分布情况。这一时期的特点是最初极度温暖，随后是长期冷却，并被称为高热的短期气候事件以及一系列古海洋学和古地理学变化所打断。本资料汇编旨在通过研究气候、构造活动和海洋环流对硅藻土沉积的影响，确定硅藻生产对古近纪环境波动的反应。虽然气候因素似乎有间接影响，但我们的研究表明，古地理和古海洋学变化是古近纪硅藻土沉积的主要驱动因素，特别是从早始新世气候最适宜期（约 53 至约 49 Ma）开始。事实上，我们的汇编表明，在 ~46 Ma 到 ~43 Ma 之间，大陆海域没有硅藻土沉积，而硅藻土直到 ~43.5 Ma 才开始在开阔洋环境中积累。此外，我们还观察到区域气候和火山构造活动对淡水硅藻土的沉积产生了影响。
{"title":"Climatic and tectonic controls on shallow marine and freshwater diatomite deposition through the Palaeogene","authors":"Cécile Figus, Or M. Bialik, Andrey Yu. Gladenkov, Tatyana V. Oreshkina, Johan Renaudie, Pavel Smirnov, Jakub Witkowski","doi":"10.5194/egusphere-2024-2229","DOIUrl":"https://doi.org/10.5194/egusphere-2024-2229","url":null,"abstract":"<strong>Abstract.</strong> Diatoms play a major role in the carbon and silicon cycles, and thus diatom-bearing sediments represent an archive of past climatic and environmental settings. In shallow marine and freshwater environments, the accumulation of diatom frustules forms a sedimentary rock called diatomite. However, most global scale studies of diatom-bearing sediments focus on deep-sea sites, whereas shallow marine and freshwater diatomites are studied mainly at a regional level. To address this problem, we present a global scale compilation of diatomite occurrences spanning the Palaeogene (~66 to ~23 Ma). This period was characterized by initial extreme warmth followed by a prolonged cooling, disrupted by short-term climatic events called hyperthermals, and by a number of palaeoceanographic and palaeogeographic changes. The aim of this compilation is to determine the response of diatom production to Palaeogene environmental fluctuations, by examining the influence of climate, tectonic activity and ocean circulation on diatomite deposition. Although climatic factors appear to have had an indirect impact, our study suggests that palaeogeographic and palaeoceanographic changes were key drivers of diatomite deposition during the Palaeogene, particularly from the Early Eocene Climatic Optimum (~53 to ~49 Ma) onwards. In fact, our compilation suggests the absence of diatomite deposition in epicontinental seas between ~46 and ~43 Ma, while diatomites do not begin to accumulate in open ocean environments until ~43.5 Ma. Moreover, we observe that regional climate and volcano–tectonic activity have had an impact on the deposition of freshwater diatomites.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"25 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141778422","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}
Dominique K. L. L. Jenny, Tammo Reichgelt, Charlotte L. O'Brien, Xiaoqing Liu, Peter K. Bijl, Matthew Huber, Appy Sluijs
Abstract. The Oligocene (33.9–23.03 Ma) had warm climates with flattened meridional temperature gradients, while Antarctica retained a significant cryosphere. These may pose imperfect analogues to distant future climate states with unipolar icehouse conditions. Although local and regional climate and environmental reconstructions of Oligocene conditions are available, the community lacks synthesis of regional reconstructions. To provide a comprehensive overview of marine and terrestrial climate and environmental conditions in the Oligocene, and a reconstruction of trends through time, we review marine and terrestrial proxy records and compare these to numerical climate model simulations of the Oligocene. Results, based on the present relatively sparse data, suggest temperatures around the Equator that are similar to modern temperatures. Sea surface temperatures (SSTs) show patterns similar to land temperatures, with warm conditions at mid- and high latitudes (∼60–90°), especially in the Southern Hemisphere (SH). Vegetation-based precipitation reconstructions of the Oligocene suggest regionally drier conditions compared to modern times around the Equator. When compared to proxy data, climate model simulations overestimate Oligocene precipitation in most areas, particularly the tropics. Temperatures around the mid- to high latitudes are generally underestimated in models compared to proxy data and tend to overestimate the warming in the tropics. In line with previous proxy-to-model comparisons, we find that models underestimate polar amplification and overestimate the Equator-to-pole temperature gradient suggested from the available proxy data. This further stresses the urgency of solving this widely recorded problem for past warm climates, such as the Oligocene.
{"title":"Climate variability, heat distribution, and polar amplification in the warm unipolar “icehouse” of the Oligocene","authors":"Dominique K. L. L. Jenny, Tammo Reichgelt, Charlotte L. O'Brien, Xiaoqing Liu, Peter K. Bijl, Matthew Huber, Appy Sluijs","doi":"10.5194/cp-20-1627-2024","DOIUrl":"https://doi.org/10.5194/cp-20-1627-2024","url":null,"abstract":"Abstract. The Oligocene (33.9–23.03 Ma) had warm climates with flattened meridional temperature gradients, while Antarctica retained a significant cryosphere. These may pose imperfect analogues to distant future climate states with unipolar icehouse conditions. Although local and regional climate and environmental reconstructions of Oligocene conditions are available, the community lacks synthesis of regional reconstructions. To provide a comprehensive overview of marine and terrestrial climate and environmental conditions in the Oligocene, and a reconstruction of trends through time, we review marine and terrestrial proxy records and compare these to numerical climate model simulations of the Oligocene. Results, based on the present relatively sparse data, suggest temperatures around the Equator that are similar to modern temperatures. Sea surface temperatures (SSTs) show patterns similar to land temperatures, with warm conditions at mid- and high latitudes (∼60–90°), especially in the Southern Hemisphere (SH). Vegetation-based precipitation reconstructions of the Oligocene suggest regionally drier conditions compared to modern times around the Equator. When compared to proxy data, climate model simulations overestimate Oligocene precipitation in most areas, particularly the tropics. Temperatures around the mid- to high latitudes are generally underestimated in models compared to proxy data and tend to overestimate the warming in the tropics. In line with previous proxy-to-model comparisons, we find that models underestimate polar amplification and overestimate the Equator-to-pole temperature gradient suggested from the available proxy data. This further stresses the urgency of solving this widely recorded problem for past warm climates, such as the Oligocene.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"62 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141778420","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}
Nora Farina Specht, Martin Claussen, Thomas Kleinen
Abstract. During the early Holocene to mid-Holocene, about 11 500 to 5500 years ago, lakes expanded across the Sahel and Sahara in response to enhanced summer monsoon precipitation. To investigate the effect of these lakes on the West African summer monsoon, previous simulation studies prescribed mid-Holocene lakes from reconstructions. By prescribing mid-Holocene lakes, however, the terrestrial water balance is inconsistent with the size of the lakes. In order to close the terrestrial water cycle, we construct a dynamic endorheic lake (DEL) model and implement it into the atmosphere–land model ICON-JSBACH4. For the first time, this allows us to investigate the dynamic interaction between climate, lakes, and vegetation across northern Africa. Additionally, we investigate the effect of lake depth changes on mid-Holocene precipitation, a neglected aspect in previous simulation studies. A pre-industrial control simulation shows that the DEL model realistically simulates the lake extent across northern Africa. Only in the Ahnet and Chotts basins is the lake area slightly overestimated, which is likely related to the coarse resolution of the simulations. The mid-Holocene simulations reveal that both the lake expansion and the vegetation expansion cause a precipitation increase over northern Africa. The sum of these individual contributions to the precipitation is, however, larger than the combined effect that is generated when lake and vegetation dynamics interact. Thus, the lake–vegetation interaction causes a relative drying response across the entire Sahel. The main reason for this drying response is that the simulated vegetation expansion cools the land surface more strongly than the lake expansion, which is dominated by the expansion of Lake Chad. Accordingly, the surface temperature increases over the region of Lake Chad and causes local changes in the meridional surface-temperature gradient. These changes in the meridional surface-temperature gradient are associated with reduced inland moisture transport from the tropical Atlantic into the Sahel, which causes a drying response in the Sahel. An idealized mid-Holocene experiment shows that a similar drying response is induced when the depth of Lake Chad is decreased by about 1–5 m, without changing the horizontal lake area. By reducing the depth of Lake Chad, the heat storage capacity of the lake decreases, and the lake warms faster during the summer months. Thus, in the ICON-JSBACH4 model, the lake depth significantly influences the simulated surface temperature and the simulated meridional surface-temperature gradient between the simulated lakes and vegetation, thereby affecting mid-Holocene precipitation over northern Africa.
{"title":"Dynamic interaction between lakes, climate, and vegetation across northern Africa during the mid-Holocene","authors":"Nora Farina Specht, Martin Claussen, Thomas Kleinen","doi":"10.5194/cp-20-1595-2024","DOIUrl":"https://doi.org/10.5194/cp-20-1595-2024","url":null,"abstract":"Abstract. During the early Holocene to mid-Holocene, about 11 500 to 5500 years ago, lakes expanded across the Sahel and Sahara in response to enhanced summer monsoon precipitation. To investigate the effect of these lakes on the West African summer monsoon, previous simulation studies prescribed mid-Holocene lakes from reconstructions. By prescribing mid-Holocene lakes, however, the terrestrial water balance is inconsistent with the size of the lakes. In order to close the terrestrial water cycle, we construct a dynamic endorheic lake (DEL) model and implement it into the atmosphere–land model ICON-JSBACH4. For the first time, this allows us to investigate the dynamic interaction between climate, lakes, and vegetation across northern Africa. Additionally, we investigate the effect of lake depth changes on mid-Holocene precipitation, a neglected aspect in previous simulation studies. A pre-industrial control simulation shows that the DEL model realistically simulates the lake extent across northern Africa. Only in the Ahnet and Chotts basins is the lake area slightly overestimated, which is likely related to the coarse resolution of the simulations. The mid-Holocene simulations reveal that both the lake expansion and the vegetation expansion cause a precipitation increase over northern Africa. The sum of these individual contributions to the precipitation is, however, larger than the combined effect that is generated when lake and vegetation dynamics interact. Thus, the lake–vegetation interaction causes a relative drying response across the entire Sahel. The main reason for this drying response is that the simulated vegetation expansion cools the land surface more strongly than the lake expansion, which is dominated by the expansion of Lake Chad. Accordingly, the surface temperature increases over the region of Lake Chad and causes local changes in the meridional surface-temperature gradient. These changes in the meridional surface-temperature gradient are associated with reduced inland moisture transport from the tropical Atlantic into the Sahel, which causes a drying response in the Sahel. An idealized mid-Holocene experiment shows that a similar drying response is induced when the depth of Lake Chad is decreased by about 1–5 m, without changing the horizontal lake area. By reducing the depth of Lake Chad, the heat storage capacity of the lake decreases, and the lake warms faster during the summer months. Thus, in the ICON-JSBACH4 model, the lake depth significantly influences the simulated surface temperature and the simulated meridional surface-temperature gradient between the simulated lakes and vegetation, thereby affecting mid-Holocene precipitation over northern Africa.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"9 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141778421","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. Temperature and mineral dust records serve as valuable palaeoclimatic indicators for studying atmospheric variability across different temporal scales. In this study, we employed Haar fluctuations to analyse global spatiotemporal atmospheric variability over the Last Glacial Cycle, capturing both high- and low-frequency information within the records, regardless of uniform or non-uniform sampling. Furthermore, we utilised Haar fluctuations to compute fluctuation correlations, thereby enhancing our understanding of palaeoclimate dynamics. Our findings reveal a latitudinal dependency in the transition from macroweather to climate regimes (τc), with polar regions experiencing shorter transitions compared to the tropics and mid-latitudes. These transitions occur at approximately 1/100th of glacial cycle length scales, suggesting a dominant forcing mechanism beyond Milankovitch cycles. Additionally, our analysis shows that polar regions have larger fluctuation amplitudes than lower latitudes as a consequence of the polar amplification effect. Furthermore, fluctuation correlations demonstrate faster synchronisation between the poles themselves compared to lower-latitude sites, achieving high correlation values within 10 kyr. Therefore, our findings suggest a consistent climate signal propagating from the poles to the Equator, representing the first empirical evidence supporting the hypothesis that the poles play a pivotal role as climate change drivers, influencing the variability in climatic transitions worldwide.
{"title":"Geographic variability in dust and temperature in climate scaling regimes over the Last Glacial Cycle","authors":"Nicolás Acuña Reyes, Elwin van't Wout, Shaun Lovejoy, Fabrice Lambert","doi":"10.5194/cp-20-1579-2024","DOIUrl":"https://doi.org/10.5194/cp-20-1579-2024","url":null,"abstract":"Abstract. Temperature and mineral dust records serve as valuable palaeoclimatic indicators for studying atmospheric variability across different temporal scales. In this study, we employed Haar fluctuations to analyse global spatiotemporal atmospheric variability over the Last Glacial Cycle, capturing both high- and low-frequency information within the records, regardless of uniform or non-uniform sampling. Furthermore, we utilised Haar fluctuations to compute fluctuation correlations, thereby enhancing our understanding of palaeoclimate dynamics. Our findings reveal a latitudinal dependency in the transition from macroweather to climate regimes (τc), with polar regions experiencing shorter transitions compared to the tropics and mid-latitudes. These transitions occur at approximately 1/100th of glacial cycle length scales, suggesting a dominant forcing mechanism beyond Milankovitch cycles. Additionally, our analysis shows that polar regions have larger fluctuation amplitudes than lower latitudes as a consequence of the polar amplification effect. Furthermore, fluctuation correlations demonstrate faster synchronisation between the poles themselves compared to lower-latitude sites, achieving high correlation values within 10 kyr. Therefore, our findings suggest a consistent climate signal propagating from the poles to the Equator, representing the first empirical evidence supporting the hypothesis that the poles play a pivotal role as climate change drivers, influencing the variability in climatic transitions worldwide.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"64 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-07-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141778423","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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