Abstract. Saltgiants, although well studies, still offer some unsolved questions. One example is the Messinian Saltgiant which formed during the Messinian Salinity Crisis (MSC, 5.97 to 5.33 Ma) in the Mediterranean Sea. While a common assumption is that gypsum precipitated in the marginal parts of the basin before halite formed in the deeper part of the basin, this could be not yet been confirmed. Indeed, it has also been suggested that, while the primary lower gypsum was forming, the deep basins was already accumulating halite. In this study we use box modeling to investigate the distribution of halite and gypsum deposits for different configurations. Due to a dimensionless description of basin restriction, our results can be transferred to other basins. With this approach we find that under the right conditions all configurations lead to a simultaneous but spatially separated precipitation of gypsum and halite. They would, however, not lead to the spatial pattern that is observed in the Mediterranean, i.e. halite deposition in the deep basins while gypsum is deposited in the margins. Based on those results we propose a timeline for a salinifying basin. For an average salinity above gypsum but below halite saturation, halite is first formed in a sufficiently restricted margin, and only once the average salinity approaches the one of halite saturation can it also form in open areas of the basin due to horizontal salinity gradients. Once the whole basin has reached halite saturation, gypsum only forms in margins with a positive local freshwater budget. Such a mechanism would produce less than 1 m of gypsum within 25 kyr. We thus conclude that a simultaneous, yet spatially separated precipitation of gypsum and halite within a one basin is possible, but unlikely to have led to the massive primary lower gypsum outcrops in the Mediterranean, while halite formed in the deeper parts of the same sub-basin.
{"title":"A question of time and space: A model approach to the synchronicity of gypsum and halite during the Messinian Salinity Crisis","authors":"Ronja Monika Ebner, Paul Meijer","doi":"10.5194/cp-2024-58","DOIUrl":"https://doi.org/10.5194/cp-2024-58","url":null,"abstract":"<strong>Abstract.</strong> Saltgiants, although well studies, still offer some unsolved questions. One example is the Messinian Saltgiant which formed during the Messinian Salinity Crisis (MSC, 5.97 to 5.33 Ma) in the Mediterranean Sea. While a common assumption is that gypsum precipitated in the marginal parts of the basin before halite formed in the deeper part of the basin, this could be not yet been confirmed. Indeed, it has also been suggested that, while the primary lower gypsum was forming, the deep basins was already accumulating halite. In this study we use box modeling to investigate the distribution of halite and gypsum deposits for different configurations. Due to a dimensionless description of basin restriction, our results can be transferred to other basins. With this approach we find that under the right conditions all configurations lead to a simultaneous but spatially separated precipitation of gypsum and halite. They would, however, not lead to the spatial pattern that is observed in the Mediterranean, i.e. halite deposition in the deep basins while gypsum is deposited in the margins. Based on those results we propose a timeline for a salinifying basin. For an average salinity above gypsum but below halite saturation, halite is first formed in a sufficiently restricted margin, and only once the average salinity approaches the one of halite saturation can it also form in open areas of the basin due to horizontal salinity gradients. Once the whole basin has reached halite saturation, gypsum only forms in margins with a positive local freshwater budget. Such a mechanism would produce less than 1 m of gypsum within 25 kyr. We thus conclude that a simultaneous, yet spatially separated precipitation of gypsum and halite within a one basin is possible, but unlikely to have led to the massive primary lower gypsum outcrops in the Mediterranean, while halite formed in the deeper parts of the same sub-basin.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"24 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-09-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142190494","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}
Javier Blasco, Ilaria Tabone, Daniel Moreno-Parada, Alexander Robinson, Jorge Alvarez-Solas, Frank Pattyn, Marisa Montoya
Abstract. Tipping elements, including the Antarctic Ice Sheet (AIS), are Earth system components that could reach critical thresholds due to anthropogenic emissions. Increasing our understanding of past warm climates can help to elucidate the future contribution of the AIS to emissions. The mid-Pliocene Warm Period (mPWP; ∼ 3.3–3.0 million years ago) serves as an ideal benchmark experiment. During this period, CO2 levels were similar to the present day (PD; 350–450 ppmv), but global mean temperatures were 2.5–4.0 K higher. Sea level reconstructions from that time indicate a rise of 5–25 m compared to the present, highlighting the potential crossing of tipping points in Antarctica. In order to achieve a sea level contribution far beyond 10 m, not only the West Antarctic Ice Sheet (WAIS) needs to largely decrease, but a significant response in the East Antarctic Ice Sheet (EAIS) is also required. A key question in reconstructions and simulations is therefore which of the AIS basins retreated during the mPWP. In this study, we investigate how the AIS responds to climatic and bedrock conditions during the mPWP. To this end, we use the Pliocene Model Intercomparison Project, Phase 2 (PlioMIP2), general circulation model ensemble to force a higher-order ice sheet model. Our simulations reveal that the WAIS experiences collapse with a 0.5 K oceanic warming. The Wilkes Basin shows retreat at 3 K oceanic warming, although higher precipitation rates could mitigate such a retreat. Totten Glacier shows slight signs of retreats only under high-oceanic warming conditions (greater than 4 K oceanic anomaly). If only the WAIS collapses, we simulate a mean contribution of 2.7 to 7.0 ms.l.e. (metres of sea level equivalent). If, in addition, the Wilkes Basin retreats, our simulations suggest a mean contribution of 6.0 to 8.9 ms.l.e. Besides uncertainties related to the climate forcing, we also examine other sources of uncertainty related to initial ice thickness and ice dynamics. We find that the climatologies yield a higher uncertainty than the dynamical configuration if parameters are constrained with PD observations and that starting from Pliocene reconstructions leads to smaller ice sheet configurations due to the hysteresis behaviour of marine bedrocks. Ultimately, our study concludes that marine ice cliff instability is not a prerequisite for the retreat of the Wilkes Basin. Instead, a significant rise in oceanic temperatures can initiate such a retreat.
{"title":"Antarctic tipping points triggered by the mid-Pliocene warm climate","authors":"Javier Blasco, Ilaria Tabone, Daniel Moreno-Parada, Alexander Robinson, Jorge Alvarez-Solas, Frank Pattyn, Marisa Montoya","doi":"10.5194/cp-20-1919-2024","DOIUrl":"https://doi.org/10.5194/cp-20-1919-2024","url":null,"abstract":"Abstract. Tipping elements, including the Antarctic Ice Sheet (AIS), are Earth system components that could reach critical thresholds due to anthropogenic emissions. Increasing our understanding of past warm climates can help to elucidate the future contribution of the AIS to emissions. The mid-Pliocene Warm Period (mPWP; ∼ 3.3–3.0 million years ago) serves as an ideal benchmark experiment. During this period, CO2 levels were similar to the present day (PD; 350–450 ppmv), but global mean temperatures were 2.5–4.0 K higher. Sea level reconstructions from that time indicate a rise of 5–25 m compared to the present, highlighting the potential crossing of tipping points in Antarctica. In order to achieve a sea level contribution far beyond 10 m, not only the West Antarctic Ice Sheet (WAIS) needs to largely decrease, but a significant response in the East Antarctic Ice Sheet (EAIS) is also required. A key question in reconstructions and simulations is therefore which of the AIS basins retreated during the mPWP. In this study, we investigate how the AIS responds to climatic and bedrock conditions during the mPWP. To this end, we use the Pliocene Model Intercomparison Project, Phase 2 (PlioMIP2), general circulation model ensemble to force a higher-order ice sheet model. Our simulations reveal that the WAIS experiences collapse with a 0.5 K oceanic warming. The Wilkes Basin shows retreat at 3 K oceanic warming, although higher precipitation rates could mitigate such a retreat. Totten Glacier shows slight signs of retreats only under high-oceanic warming conditions (greater than 4 K oceanic anomaly). If only the WAIS collapses, we simulate a mean contribution of 2.7 to 7.0 ms.l.e. (metres of sea level equivalent). If, in addition, the Wilkes Basin retreats, our simulations suggest a mean contribution of 6.0 to 8.9 ms.l.e. Besides uncertainties related to the climate forcing, we also examine other sources of uncertainty related to initial ice thickness and ice dynamics. We find that the climatologies yield a higher uncertainty than the dynamical configuration if parameters are constrained with PD observations and that starting from Pliocene reconstructions leads to smaller ice sheet configurations due to the hysteresis behaviour of marine bedrocks. Ultimately, our study concludes that marine ice cliff instability is not a prerequisite for the retreat of the Wilkes Basin. Instead, a significant rise in oceanic temperatures can initiate such a retreat.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"14 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-09-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142190517","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}
Murat Aydin, Melinda R. Nicewonger, Gregory L. Britten, Dominic Winski, Mary Whelan, John D. Patterson, Erich Osterberg, Christopher F. Lee, Tara Harder, Kyle J. Callahan, David Ferris, Eric S. Saltzman
Abstract. Carbonyl sulfide (COS) is the most abundant sulfur gas in the atmosphere with links to terrestrial and oceanic productivity. We measured COS in ice core air from an intermediate-depth ice core from the South Pole using both dry and wet extraction methods, recovering a 52 500-year record. We find evidence for COS production in the firn, altering the atmospheric signal preserved in the ice core. Mean sea salt aerosol concentrations from the same depth are a good proxy for the COS production, which disproportionately impacts the measurements from glacial period ice with high sea salt aerosol concentrations. The COS measurements are corrected using sea salt sodium (ssNa) as a proxy for the excess COS resulting from the production. The ssNa-corrected COS record displays substantially less COS in the glacial period atmosphere than the Holocene and a 2 to 4-fold COS rise during the deglaciation synchronous with the associated climate signal. The deglacial COS rise was primarily source driven. Oceanic emissions in the form of COS, carbon disulfide (CS2), and dimethylsulfide (DMS) are collectively the largest natural source of atmospheric COS. A large increase in ocean COS emissions during the deglaciation suggests enhancements in emissions of ocean sulfur gases via processes that involve ocean productivity, although we cannot quantify individual contributions from each gas.
摘要。羰基硫化物（COS）是大气中最丰富的硫气体，与陆地和海洋的生产力息息相关。我们使用干法和湿法提取方法测量了南极中深冰芯空气中的 COS，恢复了 52 500 年的记录。我们发现有证据表明，COS 在杉林中产生，改变了冰芯中保存的大气信号。来自同一深度的平均海盐气溶胶浓度是 COS 生成的良好替代物，它对来自海盐气溶胶浓度较高的冰川期冰层的测量结果产生了不成比例的影响。利用海盐钠（ssNa）对 COS 测量值进行了校正，以替代因 COS 生成而产生的过量 COS。海盐钠校正后的 COS 记录显示，冰川期大气中的 COS 远远少于全新世，而在褪冰期，COS 上升了 2 到 4 倍，与相关的气候信号同步。冰川期 COS 上升主要是源驱动的。海洋排放的 COS、二硫化碳（CS2）和二甲基硫化物（DMS）是大气中 COS 的最大天然来源。降冰期海洋 COS 排放量的大幅增加表明，通过涉及海洋生产力的过程，海洋硫化气体的排放量有所增加，尽管我们无法量化每种气体的单独贡献。
{"title":"Carbonyl sulfide measurements from a South Pole ice core and implications for atmospheric variability since the last glacial period","authors":"Murat Aydin, Melinda R. Nicewonger, Gregory L. Britten, Dominic Winski, Mary Whelan, John D. Patterson, Erich Osterberg, Christopher F. Lee, Tara Harder, Kyle J. Callahan, David Ferris, Eric S. Saltzman","doi":"10.5194/cp-20-1885-2024","DOIUrl":"https://doi.org/10.5194/cp-20-1885-2024","url":null,"abstract":"Abstract. Carbonyl sulfide (COS) is the most abundant sulfur gas in the atmosphere with links to terrestrial and oceanic productivity. We measured COS in ice core air from an intermediate-depth ice core from the South Pole using both dry and wet extraction methods, recovering a 52 500-year record. We find evidence for COS production in the firn, altering the atmospheric signal preserved in the ice core. Mean sea salt aerosol concentrations from the same depth are a good proxy for the COS production, which disproportionately impacts the measurements from glacial period ice with high sea salt aerosol concentrations. The COS measurements are corrected using sea salt sodium (ssNa) as a proxy for the excess COS resulting from the production. The ssNa-corrected COS record displays substantially less COS in the glacial period atmosphere than the Holocene and a 2 to 4-fold COS rise during the deglaciation synchronous with the associated climate signal. The deglacial COS rise was primarily source driven. Oceanic emissions in the form of COS, carbon disulfide (CS2), and dimethylsulfide (DMS) are collectively the largest natural source of atmospheric COS. A large increase in ocean COS emissions during the deglaciation suggests enhancements in emissions of ocean sulfur gases via processes that involve ocean productivity, although we cannot quantify individual contributions from each gas.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"19 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-08-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142190519","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}
Matias Romero, Shanti B. Penprase, Maximillian S. Van Wyk de Vries, Andrew D. Wickert, Andrew G. Jones, Shaun A. Marcott, Jorge A. Strelin, Mateo A. Martini, Tammy M. Rittenour, Guido Brignone, Mark D. Shapley, Emi Ito, Kelly R. MacGregor, Marc W. Caffee
Abstract. Determining the timing and extent of Quaternary glaciations around the globe is critical to understanding the drivers behind climate change and glacier fluctuations. Evidence from the southern mid-latitudes indicates that local glacial maxima preceded the global Last Glacial Maximum (LGM), implying that feedbacks in the climate system or ice dynamics played a role beyond the underlying orbital forcings. To shed light on these processes, we investigated the glacial landforms shaped and deposited by the Lago Argentino glacier (50° S), an outlet lobe of the former Patagonian Ice Sheet, in southern Argentina. We mapped geomorphological features on the landscape and dated moraine boulders and outwash sediments using 10Be cosmogenic nuclides and feldspar infrared stimulated luminescence (IRSL) to constrain the chronology of glacial advance and retreat. We report that the Lago Argentino glacier lobe reached more extensive limits prior to the global LGM, advancing during the middle to late Pleistocene between 243–132 ka and during Marine Isotope Stage 3 (MIS 3), culminating at 44.5 ± 8.0 and at 36.6 ± 1.0 ka. Our results indicate that the most extensive advance of the last glacial cycle occurred during MIS 3, and we hypothesize that this was a result of longer and colder winters, as well as increased precipitation delivered by a latitudinal migration of the Southern Westerly Winds belt, highlighting the role of local and regional climate feedbacks in modulating ice mass changes in the southern mid-latitudes.
摘要确定全球第四纪冰川的时间和范围对于了解气候变化和冰川波动背后的驱动因素至关重要。来自南半球中纬度地区的证据表明，当地冰川最大值出现在全球末次冰川最盛期（LGM）之前，这意味着气候系统或冰动力学的反馈作用超出了基本的轨道作用力。为了揭示这些过程，我们调查了阿根廷湖冰川（南纬 50°）塑造和沉积的冰川地貌，该冰川是阿根廷南部前巴塔哥尼亚冰原的一个出口裂片。我们绘制了地貌特征图，并利用 10Be 宇宙成因核素和长石红外激发发光（IRSL）测定了冰碛巨石和冲刷沉积物的年代，以确定冰川前进和后退的年代学。我们报告说，阿根廷湖冰川叶在全球大冰期之前达到了更大的范围，在 243-132 ka 之间的中更新世晚期和海洋同位素阶段 3（MIS 3）期间前进，在 44.5 ± 8.0 ka 和 36.6 ± 1.0 ka 达到顶峰。我们的研究结果表明，上一个冰川周期最大规模的前进发生在 MIS 3 期间，我们假设这是冬季更长、更冷以及南西风带纬度迁移带来的降水量增加的结果，突出了当地和区域气候反馈在调节南中纬度地区冰量变化中的作用。
{"title":"Late Quaternary glacial maxima in southern Patagonia: insights from the Lago Argentino glacier lobe","authors":"Matias Romero, Shanti B. Penprase, Maximillian S. Van Wyk de Vries, Andrew D. Wickert, Andrew G. Jones, Shaun A. Marcott, Jorge A. Strelin, Mateo A. Martini, Tammy M. Rittenour, Guido Brignone, Mark D. Shapley, Emi Ito, Kelly R. MacGregor, Marc W. Caffee","doi":"10.5194/cp-20-1861-2024","DOIUrl":"https://doi.org/10.5194/cp-20-1861-2024","url":null,"abstract":"Abstract. Determining the timing and extent of Quaternary glaciations around the globe is critical to understanding the drivers behind climate change and glacier fluctuations. Evidence from the southern mid-latitudes indicates that local glacial maxima preceded the global Last Glacial Maximum (LGM), implying that feedbacks in the climate system or ice dynamics played a role beyond the underlying orbital forcings. To shed light on these processes, we investigated the glacial landforms shaped and deposited by the Lago Argentino glacier (50° S), an outlet lobe of the former Patagonian Ice Sheet, in southern Argentina. We mapped geomorphological features on the landscape and dated moraine boulders and outwash sediments using 10Be cosmogenic nuclides and feldspar infrared stimulated luminescence (IRSL) to constrain the chronology of glacial advance and retreat. We report that the Lago Argentino glacier lobe reached more extensive limits prior to the global LGM, advancing during the middle to late Pleistocene between 243–132 ka and during Marine Isotope Stage 3 (MIS 3), culminating at 44.5 ± 8.0 and at 36.6 ± 1.0 ka. Our results indicate that the most extensive advance of the last glacial cycle occurred during MIS 3, and we hypothesize that this was a result of longer and colder winters, as well as increased precipitation delivered by a latitudinal migration of the Southern Westerly Winds belt, highlighting the role of local and regional climate feedbacks in modulating ice mass changes in the southern mid-latitudes.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"37 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-08-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142190518","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}
Meike D. W. Scherrenberg, Constantijn J. Berends, Roderik S. W. van de Wal
Abstract. During the Mid-Pleistocene transition (MPT) the dominant periodicity of glacial cycles increased from 41 thousand years (kyr) to an average of 100 kyr, without any appreciable change in the orbital pacing. As the MPT is not a linear response to orbital forcing, it must have resulted from feedback processes in the Earth system. However, the precise mechanisms underlying the transition are still under debate. In this study, we investigate the MPT by simulating the Northern Hemisphere ice sheet evolution over the past 1.5 million years. The transient climate forcing of the ice-sheet model was obtained using a matrix method, by interpolating between two snapshots of global climate model simulations. Changes in climate forcing are caused by variations in CO2, insolation, as well as implicit climate–ice sheet feedbacks. Using this method, we were able to capture glacial-interglacial variability during the past 1.5 million years and reproduce the shift from 41 kyr to 100 kyr cycles without any additional drivers. Instead, the modelled frequency change results from the prescribed CO2 combined with orbital forcing, and ice sheet feedbacks. Early Pleistocene terminations are initiated by insolation maxima. After the MPT, low CO2 levels can compensate insolation maxima which favour deglaciation, leading to an increasing glacial cycle periodicity. These deglaciations are also prevented by a relatively small North American ice sheet, which, through its location and feedback processes, can generate a relatively stable climate. Larger North American ice sheets become more sensitive to small temperature increases. Therefore, Late Pleistocene terminations are facilitated by the large ice-sheet volume, were small changes in temperature lead to self-sustained melt instead. This concept is confirmed by experiments using constant insolation or CO2. The constant CO2 experiments generally capture only the Early Pleistocene cycles, while those with constant insolation only capture Late Pleistocene cycles. Additionally, we find that a lowering of CO2concentrations leads to an increasing number of insolation maxima that fail to initiate terminations. These results therefore suggest a regime shift, where during the Early Pleistocene, glacial cycles are dominated by orbital oscillations, while Late Pleistocene cycles tend to be more dominated by CO2. This implies that the MPT can be explained by a decrease in glacial CO2 concentration superimposed on orbital forcing.
{"title":"CO2 and summer insolation as drivers for the Mid-Pleistocene transition","authors":"Meike D. W. Scherrenberg, Constantijn J. Berends, Roderik S. W. van de Wal","doi":"10.5194/cp-2024-57","DOIUrl":"https://doi.org/10.5194/cp-2024-57","url":null,"abstract":"<strong>Abstract.</strong> During the Mid-Pleistocene transition (MPT) the dominant periodicity of glacial cycles increased from 41 thousand years (kyr) to an average of 100 kyr, without any appreciable change in the orbital pacing. As the MPT is not a linear response to orbital forcing, it must have resulted from feedback processes in the Earth system. However, the precise mechanisms underlying the transition are still under debate. In this study, we investigate the MPT by simulating the Northern Hemisphere ice sheet evolution over the past 1.5 million years. The transient climate forcing of the ice-sheet model was obtained using a matrix method, by interpolating between two snapshots of global climate model simulations. Changes in climate forcing are caused by variations in CO<sub>2</sub>, insolation, as well as implicit climate–ice sheet feedbacks. Using this method, we were able to capture glacial-interglacial variability during the past 1.5 million years and reproduce the shift from 41 kyr to 100 kyr cycles without any additional drivers. Instead, the modelled frequency change results from the prescribed CO<sub>2</sub> combined with orbital forcing, and ice sheet feedbacks. Early Pleistocene terminations are initiated by insolation maxima. After the MPT, low CO<sub>2</sub> levels can compensate insolation maxima which favour deglaciation, leading to an increasing glacial cycle periodicity. These deglaciations are also prevented by a relatively small North American ice sheet, which, through its location and feedback processes, can generate a relatively stable climate. Larger North American ice sheets become more sensitive to small temperature increases. Therefore, Late Pleistocene terminations are facilitated by the large ice-sheet volume, were small changes in temperature lead to self-sustained melt instead. This concept is confirmed by experiments using constant insolation or CO<sub>2</sub>. The constant CO<sub>2</sub> experiments generally capture only the Early Pleistocene cycles, while those with constant insolation only capture Late Pleistocene cycles. Additionally, we find that a lowering of CO<sub>2</sub>concentrations leads to an increasing number of insolation maxima that fail to initiate terminations. These results therefore suggest a regime shift, where during the Early Pleistocene, glacial cycles are dominated by orbital oscillations, while Late Pleistocene cycles tend to be more dominated by CO<sub>2</sub>. This implies that the MPT can be explained by a decrease in glacial CO<sub>2</sub> concentration superimposed on orbital forcing.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"10 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-08-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142190406","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 : 2024-08-20DOI: 10.5194/egusphere-2024-2499
Karl Purcell, Margit H. Simon, Ellie J. Pryor, Simon J. Armitage, Jeroen van der Lubbe, Eystein Jansen
Abstract. During the late Quaternary the past climatic conditions of southern South Africa underwent fluctuations, influenced by various climatic factors, such as the impacts of both the Indian and Atlantic Oceans, as well as the effects of the southeasterly trade winds and Southern Hemisphere Westerlies (SHW), influenced by changes in orbital parameters. At the same time, this region exhibits some of the most abundant Middle Stone Age (MSA) archaeological sites containing records of Homo sapiens behavioural and technological evolution. Consequently, there is a pressing need for precise climatic reconstructions that can provide climate constraints during the MSA in this area. However, there is a lack of continuous high-resolution climate records covering the majority of the MSA, which spans from ~300 to ~60 ka. In this study, we present data obtained from a marine sediment core (MD20-3592) that spans approximately the last 260,000 (from m8 to 1) aiming to expand the spatial and temporal coverage of available climate archives. This marine sediment core documents both terrestrial and ocean hydroclimate variability because it is strategically positioned close to the South African coastline receiving terrestrial sediments via riverine input as well as being located under the marine influence of the Agulhas Current at the same time. X-ray fluorescence (XRF) core scanning, calibrated with discrete samples analyzed by XRF spectroscopy, was used to determine the variability of the bulk elemental composition of the core over time. Principal component analysis was performed to facilitate the interpretation of the data. Statistical analyses including frequency analysis, gaussian filtering, and wavelet analysis reveal that the regional hydroclimate was affected mostly by local insolation changes caused by orbital precession, and high latitude forcing that varies on timescales associated with orbital obliquity and eccentricity. Increased fluvial input was associated with a high precession index, during times of high local insolation, due to the effects of precession on local convergence and seasonal rainfall. Comparison with regional climate archives confirmed the dominant influence of precession on precipitation in southern South Africa. On glacial-interglacial timescales, lower precipitation observed during glacial intervals could be explained by a northward shift of the Southern Hemisphere Westerlies (SHW) and South Indian Ocean convergence zone (SIOCZ). Finally, the data from core MD20-3592 can provide a climatic context for the appearance of behavioral complexity in South Africa between ~ 120 ka and ~ 50 ka. Humid conditions in the river catchments going through the south coast and south-east coast of South Africa were present at approximately 117 ka, 93 ka, and 72 ka, alternating with dry conditions at approximately 105 ka, 83 ka, and 60–50 ka.
摘要在第四纪晚期，受各种气候因素的影响，如印度洋和大西洋的影响，以及受轨道参数变化影响的东南信风和南半球西风（SHW）的影响，南非南部过去的气候条件发生了波动。与此同时，该地区拥有一些最丰富的中石器时代（MSA）考古遗址，记录着智人的行为和技术演变。因此，该地区迫切需要精确的气候重建，以提供中石器时代的气候约束。然而，目前还缺乏涵盖澳门星际娱乐网址大部分地区（约 300 至约 60 ka）的连续高分辨率气候记录。在本研究中，我们展示了从海洋沉积物岩芯（MD20-3592）获得的数据，其时间跨度约为过去 26 万年（从 m8 到 1），旨在扩大现有气候档案的时空覆盖范围。该海洋沉积物岩芯同时记录了陆地和海洋的水文气候变异性，因为它位于南非海岸线附近，既能通过河流输入接收陆地沉积物，又能同时受到阿古哈斯海流的海洋影响。使用 X 射线荧光 (XRF) 岩心扫描，并用 XRF 光谱分析的离散样本进行校准，以确定岩心大量元素组成随时间的变化情况。为便于解释数据，进行了主成分分析。包括频率分析、高斯滤波和小波分析在内的统计分析显示，区域水文气候主要受轨道前移引起的当地日照变化以及与轨道斜度和偏心率相关的时标变化的高纬度强迫的影响。在当地日照较高的时期，由于偏前对当地辐合和季节性降雨的影响，河流输入量的增加与偏前指数较高有关。与区域气候档案的比较证实，南非南部的降水主要受前向影响。在冰川-间冰期的时间尺度上，冰川期降水量较低的原因可能是南半球西风带（SHW）和南印度洋辐合带（SIOCZ）的北移。最后，来自岩芯 MD20-3592 的数据可以为南非在约 120 ka 至约 50 ka 之间出现的行为复杂性提供气候背景。在大约 117 ka、93 ka 和 72 ka 时，流经南非南海岸和东南海岸的河流集水区气候潮湿，而在大约 105 ka、83 ka 和 60-50 ka 时，气候干燥。
{"title":"Climate variability off Africa’s southern Cape over the past 260, 000 years","authors":"Karl Purcell, Margit H. Simon, Ellie J. Pryor, Simon J. Armitage, Jeroen van der Lubbe, Eystein Jansen","doi":"10.5194/egusphere-2024-2499","DOIUrl":"https://doi.org/10.5194/egusphere-2024-2499","url":null,"abstract":"<strong>Abstract.</strong> During the late Quaternary the past climatic conditions of southern South Africa underwent fluctuations, influenced by various climatic factors, such as the impacts of both the Indian and Atlantic Oceans, as well as the effects of the southeasterly trade winds and Southern Hemisphere Westerlies (SHW), influenced by changes in orbital parameters. At the same time, this region exhibits some of the most abundant Middle Stone Age (MSA) archaeological sites containing records of <em>Homo sapiens</em> behavioural and technological evolution. Consequently, there is a pressing need for precise climatic reconstructions that can provide climate constraints during the MSA in this area. However, there is a lack of continuous high-resolution climate records covering the majority of the MSA, which spans from ~300 to ~60 ka. In this study, we present data obtained from a marine sediment core (MD20-3592) that spans approximately the last 260,000 (from m8 to 1) aiming to expand the spatial and temporal coverage of available climate archives. This marine sediment core documents both terrestrial and ocean hydroclimate variability because it is strategically positioned close to the South African coastline receiving terrestrial sediments via riverine input as well as being located under the marine influence of the Agulhas Current at the same time. X-ray fluorescence (XRF) core scanning, calibrated with discrete samples analyzed by XRF spectroscopy, was used to determine the variability of the bulk elemental composition of the core over time. Principal component analysis was performed to facilitate the interpretation of the data. Statistical analyses including frequency analysis, gaussian filtering, and wavelet analysis reveal that the regional hydroclimate was affected mostly by local insolation changes caused by orbital precession, and high latitude forcing that varies on timescales associated with orbital obliquity and eccentricity. Increased fluvial input was associated with a high precession index, during times of high local insolation, due to the effects of precession on local convergence and seasonal rainfall. Comparison with regional climate archives confirmed the dominant influence of precession on precipitation in southern South Africa. On glacial-interglacial timescales, lower precipitation observed during glacial intervals could be explained by a northward shift of the Southern Hemisphere Westerlies (SHW) and South Indian Ocean convergence zone (SIOCZ). Finally, the data from core MD20-3592 can provide a climatic context for the appearance of behavioral complexity in South Africa between ~ 120 ka and ~ 50 ka. Humid conditions in the river catchments going through the south coast and south-east coast of South Africa were present at approximately 117 ka, 93 ka, and 72 ka, alternating with dry conditions at approximately 105 ka, 83 ka, and 60–50 ka.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"34 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-08-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142190520","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}
Serena Lagorio, Barbara Delmonte, Dieter Tetzner, Elisa Malinverno, Giovanni Baccolo, Barbara Stenni, Massimo Frezzotti, Valter Maggi, Nancy Bertler
Abstract. The pattern of atmospheric and climate changes recorded by coastal Antarctic ice core sites, and the processes they illustrate, highlight the importance of multiproxy studies on ice cores drilled from such peripheral areas, where regional to local-scale processes can be documented. Here, we present a 2000 year long record of aeolian mineral dust and diatoms windblown to the Roosevelt Island obtained from the RICE (Roosevelt Island Climate Evolution project) ice core. Mineral dust and diatoms are highly complementary at RICE since they are related to the large-scale South Pacific atmospheric circulation regime, carrying dust-rich air masses that travelled above the marine boundary layer, and local oceanic aerosol transport by low-level marine air masses, respectively. The 550–1470 CE period is characterized by enhanced mineral dust transport originating from the Southern Hemisphere continents, reduced sea-ice extent in the Eastern Ross and Amundsen Seas, and more frequent penetration of humid air masses responsible for the relative increase in snow accumulation. Around 1300 CE, in particular, in concomitance with marked El Niño-like conditions, the Ross Sea dipole reaches its maximum expression. After 1470 CE, relatively lower dust and snow deposition at RICE suggests an increase in pack ice. This period is characterized by episodes of unprecedented peaks of aeolian diatom deposition, indicating a rapid reorganization of atmospheric circulation linked to the eastward enlargement of the Ross Sea polynya, likely culminating with the opening of the proposed Roosevelt Island polynya, and to an increased influence of low-level marine air masses to the site during the Little Ice Age.
{"title":"Aeolian dust and diatoms at Roosevelt Island (Ross Sea, Antarctica) over the last two millennia reveal the local expression of climate changes and the history of the Ross Sea polynya","authors":"Serena Lagorio, Barbara Delmonte, Dieter Tetzner, Elisa Malinverno, Giovanni Baccolo, Barbara Stenni, Massimo Frezzotti, Valter Maggi, Nancy Bertler","doi":"10.5194/cp-2024-56","DOIUrl":"https://doi.org/10.5194/cp-2024-56","url":null,"abstract":"<strong>Abstract.</strong> The pattern of atmospheric and climate changes recorded by coastal Antarctic ice core sites, and the processes they illustrate, highlight the importance of multiproxy studies on ice cores drilled from such peripheral areas, where regional to local-scale processes can be documented. Here, we present a 2000 year long record of aeolian mineral dust and diatoms windblown to the Roosevelt Island obtained from the RICE (Roosevelt Island Climate Evolution project) ice core. Mineral dust and diatoms are highly complementary at RICE since they are related to the large-scale South Pacific atmospheric circulation regime, carrying dust-rich air masses that travelled above the marine boundary layer, and local oceanic aerosol transport by low-level marine air masses, respectively. The 550–1470 CE period is characterized by enhanced mineral dust transport originating from the Southern Hemisphere continents, reduced sea-ice extent in the Eastern Ross and Amundsen Seas, and more frequent penetration of humid air masses responsible for the relative increase in snow accumulation. Around 1300 CE, in particular, in concomitance with marked El Niño-like conditions, the Ross Sea dipole reaches its maximum expression. After 1470 CE, relatively lower dust and snow deposition at RICE suggests an increase in pack ice. This period is characterized by episodes of unprecedented peaks of aeolian diatom deposition, indicating a rapid reorganization of atmospheric circulation linked to the eastward enlargement of the Ross Sea polynya, likely culminating with the opening of the proposed Roosevelt Island polynya, and to an increased influence of low-level marine air masses to the site during the Little Ice Age.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"9 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-08-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142190521","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 : 2024-08-20DOI: 10.5194/egusphere-2024-1874
Knut Lehre Seip, Øyvind Grøn, Hui Wang
Abstract. Volcanism is known to be an instigating factor for the Late Antique Little Ice Age (LALIA, 536–660) and the Little Ice Age (LIA, 1250–1850), but little is known about when the effect of volcanism ends, and which other mechanisms prolong a cold period that includes the ice-ages’ cold periods, but also continued periods with persistent cooling. Here we show, with a high-resolution lead-lag method, where the stratospheric aerosol optical depth (SAOD) generated by volcanic emissions ceases to precede the Northern Hemisphere summer temperature (NHST). We find that five climate mechanisms cool the Northern Hemisphere (percentage time in parentheses): SAOD (51 %), total solar irradiance (TSI, 2 %), the North Atlantic oscillation (NAO, 11 %), the interdecadal Pacific oscillation (IPO, 28 %) and CO2 (16 %). The last four variables overlap, and altogether the five climate variables cover 89 % of the cold period that includes LALIA and LIA. In contrast, we find an increase in atmospheric CO2 over a brief period just after large volcanic eruptions. During the cold period, the five variables lead NHST, are in a cooling mode, and have sufficient strength to cool the Northern Hemisphere.
摘要。众所周知，火山爆发是古代晚期小冰河时期（LALIA，536-660 年）和小冰河时期（LIA，1250-1850 年）的诱发因素，但人们对火山爆发的影响何时结束，以及哪些其他机制延长了包括冰河时期在内的寒冷时期，以及持续冷却的时期知之甚少。在这里，我们用一种高分辨率的前导-滞后方法展示了火山排放产生的平流层气溶胶光学深度（SAOD）在什么情况下不再先于北半球夏季温度（NHST）。我们发现有五种气候机制使北半球降温（括号内为时间百分比）：SAOD（51%）、太阳总辐照度（TSI，2%）、北大西洋涛动（NAO，11%）、太平洋年代际涛动（IPO，28%）和二氧化碳（16%）。后四个变量相互重叠，这五个气候变量共覆盖了包括 LALIA 和 LIA 的寒冷时期的 89%。相比之下，我们发现大气中的二氧化碳在火山大爆发后的短暂时期内有所增加。在寒冷时期，这五个变量领先于 NHST，处于冷却模式，并有足够的强度冷却北半球。
{"title":"Identifying climate variables that interchange with volcanic eruptions as cooling forces during the Common Era’s ice ages","authors":"Knut Lehre Seip, Øyvind Grøn, Hui Wang","doi":"10.5194/egusphere-2024-1874","DOIUrl":"https://doi.org/10.5194/egusphere-2024-1874","url":null,"abstract":"<strong>Abstract.</strong> Volcanism is known to be an instigating factor for the Late Antique Little Ice Age (LALIA, 536–660) and the Little Ice Age (LIA, 1250–1850), but little is known about when the effect of volcanism ends, and which other mechanisms prolong a cold period that includes the ice-ages’ cold periods, but also continued periods with persistent cooling. Here we show, with a high-resolution lead-lag method, where the stratospheric aerosol optical depth (SAOD) generated by volcanic emissions ceases to precede the Northern Hemisphere summer temperature (NHST). We find that five climate mechanisms cool the Northern Hemisphere (percentage time in parentheses): SAOD (51 %), total solar irradiance (TSI, 2 %), the North Atlantic oscillation (NAO, 11 %), the interdecadal Pacific oscillation (IPO, 28 %) and CO<sub>2</sub> (16 %). The last four variables overlap, and altogether the five climate variables cover 89 % of the cold period that includes LALIA and LIA. In contrast, we find an increase in atmospheric CO<sub>2</sub> over a brief period just after large volcanic eruptions. During the cold period, the five variables lead NHST, are in a cooling mode, and have sufficient strength to cool the Northern Hemisphere.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"77 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-08-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142190522","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}
Carlo Mologni, Marie Revel, Eric Chaumillon, Emmanuel Malet, Thibault Coulombier, Pierre Sabatier, Pierre Brigode, Gwenael Hervé, Anne-Lise Develle, Laure Schenini, Medhi Messous, Gourguen Davtian, Alain Carré, Delphine Bosch, Natacha Volto, Clément Ménard, Lamya Khalidi, Fabien Arnaud
Abstract. Understanding past and present hydrosystem feedbacks to global ocean–atmospheric interactions represents one of the main challenges to preventing droughts, extreme events, and related human catastrophes in the face of global warming, especially in arid and semiarid environments. In eastern Africa, the El Niño–Southern Oscillation (ENSO) was identified as one of the primary drivers of precipitation variability affecting water availability. However, the northern East African Rift System (EARS) still suffers from the underrepresentation of predictive and ENSO teleconnection models because of the scarcity of local to regional historical or palaeo-data. In this paper, we provide a 50-year seasonal flood and drought chronicle of the Awash River catchment from the study of laminated sediment from Gemeri and Afambo lakes (central Afar region, Ethiopia) with the aim of reconstructing the magnitude of regional hydroclimatic events. Pluricentimetric micro-laminated lithogenic facies alternating with plurimillimetric carbonate-enriched facies are investigated in both lakes. We couple dating methods including radiocarbon, short-lived radionuclides, palaeomagnetic field variations, and varve counting on both lake deposits to build a high-resolution age model and to discuss the regional hydrosedimentary dynamics of the Awash River over the last ∼ 700 years with a focus on the last 50 years. Using a multiproxy approach, we observe that following a multicentennial enhanced hydrological period, the two lakes have experienced a gradual decrease in river load inflow since 1979 CE, attaining extreme drought and high evaporative conditions between 1991 and 1997 CE. In 2014, the construction of a dam and increased agricultural water management in the lower Awash River plain impacted the erodibility of local soils and the hydrosedimentary balance of the lake basins, as evidenced by a disproportionate sediment accumulation rate. Comparison of our quantitative reconstruction with (i) lake water surface evolution, (ii) the interannual Awash River flow rates, and (iii) the El Niño 3.4 model highlights the intermittent connections between ENSO sea surface temperature anomalies, regional droughts, and hydrological conditions in the northern EARS.
{"title":"50-year seasonal variability in East African droughts and floods recorded in central Afar lake sediments (Ethiopia) and their connections with the El Niño–Southern Oscillation","authors":"Carlo Mologni, Marie Revel, Eric Chaumillon, Emmanuel Malet, Thibault Coulombier, Pierre Sabatier, Pierre Brigode, Gwenael Hervé, Anne-Lise Develle, Laure Schenini, Medhi Messous, Gourguen Davtian, Alain Carré, Delphine Bosch, Natacha Volto, Clément Ménard, Lamya Khalidi, Fabien Arnaud","doi":"10.5194/cp-20-1837-2024","DOIUrl":"https://doi.org/10.5194/cp-20-1837-2024","url":null,"abstract":"Abstract. Understanding past and present hydrosystem feedbacks to global ocean–atmospheric interactions represents one of the main challenges to preventing droughts, extreme events, and related human catastrophes in the face of global warming, especially in arid and semiarid environments. In eastern Africa, the El Niño–Southern Oscillation (ENSO) was identified as one of the primary drivers of precipitation variability affecting water availability. However, the northern East African Rift System (EARS) still suffers from the underrepresentation of predictive and ENSO teleconnection models because of the scarcity of local to regional historical or palaeo-data. In this paper, we provide a 50-year seasonal flood and drought chronicle of the Awash River catchment from the study of laminated sediment from Gemeri and Afambo lakes (central Afar region, Ethiopia) with the aim of reconstructing the magnitude of regional hydroclimatic events. Pluricentimetric micro-laminated lithogenic facies alternating with plurimillimetric carbonate-enriched facies are investigated in both lakes. We couple dating methods including radiocarbon, short-lived radionuclides, palaeomagnetic field variations, and varve counting on both lake deposits to build a high-resolution age model and to discuss the regional hydrosedimentary dynamics of the Awash River over the last ∼ 700 years with a focus on the last 50 years. Using a multiproxy approach, we observe that following a multicentennial enhanced hydrological period, the two lakes have experienced a gradual decrease in river load inflow since 1979 CE, attaining extreme drought and high evaporative conditions between 1991 and 1997 CE. In 2014, the construction of a dam and increased agricultural water management in the lower Awash River plain impacted the erodibility of local soils and the hydrosedimentary balance of the lake basins, as evidenced by a disproportionate sediment accumulation rate. Comparison of our quantitative reconstruction with (i) lake water surface evolution, (ii) the interannual Awash River flow rates, and (iii) the El Niño 3.4 model highlights the intermittent connections between ENSO sea surface temperature anomalies, regional droughts, and hydrological conditions in the northern EARS.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"2 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-08-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142190523","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}
Judit Torner, Isabel Cacho, Heather Stoll, Ana Moreno, Joan O. Grimalt, Francisco J. Sierro, Hai Cheng, R. Lawrence Edwards
Abstract. The full understanding of climate feedbacks responsible for the amplification of deglaciations requires robust chronologies for these climate transitions, but, in the case of marine records, radiocarbon chronologies are possible only for the last glacial termination. Although the assumed relationships between the marine isotopic record and the orbital parameters provide a first order chronology for the previous terminations, an independent chronological control allows the relationships between orbital forcing and the climate response to be assessed over multiple previous terminations. Here we present new geochemical records of Marine Isotope Stages 11 to 7 from a western Mediterranean speleothem, establishing a new long terrestrial climate record for this region. Its absolute U/Th dates provide an exceptional chronology for the glacial terminations IV, III, and III.a. The onset of these three glacial terminations was marked by rapid δ18O depletions, reflecting ocean freshening by ice melting, thus providing an excellent tie point for regional marine records also sensitive to such freshening. These new chronologies reveal an earlier onset of the deglacial melting for the TIV and TIII.a in contrast to the generally accepted marine chronologies and indicate that the duration of these deglaciations was variable, with TIV particularly longer (~20 kyr). This study also supports that the onset of deglacial melting always occurred during declining precession index while a nonunique relation occurred with the obliquity parameter.
{"title":"New age constraints for glacial terminations IV, III, and III.a based on Western Mediterranean speleothem records","authors":"Judit Torner, Isabel Cacho, Heather Stoll, Ana Moreno, Joan O. Grimalt, Francisco J. Sierro, Hai Cheng, R. Lawrence Edwards","doi":"10.5194/cp-2024-54","DOIUrl":"https://doi.org/10.5194/cp-2024-54","url":null,"abstract":"<strong>Abstract.</strong> The full understanding of climate feedbacks responsible for the amplification of deglaciations requires robust chronologies for these climate transitions, but, in the case of marine records, radiocarbon chronologies are possible only for the last glacial termination. Although the assumed relationships between the marine isotopic record and the orbital parameters provide a first order chronology for the previous terminations, an independent chronological control allows the relationships between orbital forcing and the climate response to be assessed over multiple previous terminations. Here we present new geochemical records of Marine Isotope Stages 11 to 7 from a western Mediterranean speleothem, establishing a new long terrestrial climate record for this region. Its absolute U/Th dates provide an exceptional chronology for the glacial terminations IV, III, and III.a. The onset of these three glacial terminations was marked by rapid δ<sup>18</sup>O depletions, reflecting ocean freshening by ice melting, thus providing an excellent tie point for regional marine records also sensitive to such freshening. These new chronologies reveal an earlier onset of the deglacial melting for the TIV and TIII.a in contrast to the generally accepted marine chronologies and indicate that the duration of these deglaciations was variable, with TIV particularly longer (~20 kyr). This study also supports that the onset of deglacial melting always occurred during declining precession index while a nonunique relation occurred with the obliquity parameter.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"1 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-08-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142190525","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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