Sebastian Steinig, Wolf Dummann, Peter Hofmann, Martin Frank, Wonsun Park, Thomas Wagner, Sascha Flögel
Abstract. Black shale sediments from the Barremian to Aptian South Atlantic document the intense and widespread burial of marine organic carbon during the initial stages of seafloor spreading between Africa and South America. The enhanced sequestration of atmospheric CO2 makes these young ocean basins potential drivers of the Early Cretaceous carbon cycle and climate perturbations. The opening of marine gateways between initially restricted basins and related circulation and ventilation changes are a commonly invoked explanation for the transient formation and disappearance of these regional carbon sinks. However, large uncertainties in palaeogeographic reconstructions limit the interpretation of available palaeoceanographic data and prevent any robust model-based quantifications of the proposed circulation and carbon burial changes. Here, we present a new approach to assess the principal controls on the Early Cretaceous South Atlantic and Southern Ocean circulation changes under full consideration of the uncertainties in available boundary conditions. Specifically, we use a large ensemble of 36 climate model experiments to simulate the Barremian to Albian progressive opening of the Falkland Plateau and Georgia Basin gateways with different configurations of the proto-Drake Passage, the Walvis Ridge, and atmospheric CO2 concentrations. The experiments are designed to complement available geochemical data across the regions and to test circulation scenarios derived from them. All simulations show increased evaporation and intermediate water formation at subtropical latitudes that drive a meridional overturning circulation whose vertical extent is determined by the sill depth of the Falkland Plateau. The densest water masses formed in the southern Angola Basin and potentially reached the deep Cape Basin as Walvis Ridge Overflow Water. Palaeogeographic uncertainties are as important as the lack of precise knowledge of atmospheric CO2 levels for the simulated temperature and salinity spread in large parts of the South Atlantic. Overall temperature uncertainties reach up to 15 °C and increase significantly with water depth. The ensemble approach reveals temporal changes in the relative importance of geographic and radiative forcings for the simulated oceanographic conditions and, importantly, nonlinear interactions between them. The progressive northward opening of the highly restricted Angola Basin increased the sensitivity of local overturning and upper-ocean stratification to atmospheric CO2 concentrations due to large-scale changes in the hydrological cycle, while the chosen proto-Drake Passage depth is critical for the ocean dynamics and CO2 response in the southern South Atlantic. Finally, the simulated processes are integrated into a recent carbon burial framework to document the principal control of the regional gateway evolution on the progressive shift from the prevailing saline and oxygen-depleted subtropical water masses to the dominance o
{"title":"Controls on Early Cretaceous South Atlantic Ocean circulation and carbon burial – a climate model–proxy synthesis","authors":"Sebastian Steinig, Wolf Dummann, Peter Hofmann, Martin Frank, Wonsun Park, Thomas Wagner, Sascha Flögel","doi":"10.5194/cp-20-1537-2024","DOIUrl":"https://doi.org/10.5194/cp-20-1537-2024","url":null,"abstract":"Abstract. Black shale sediments from the Barremian to Aptian South Atlantic document the intense and widespread burial of marine organic carbon during the initial stages of seafloor spreading between Africa and South America. The enhanced sequestration of atmospheric CO2 makes these young ocean basins potential drivers of the Early Cretaceous carbon cycle and climate perturbations. The opening of marine gateways between initially restricted basins and related circulation and ventilation changes are a commonly invoked explanation for the transient formation and disappearance of these regional carbon sinks. However, large uncertainties in palaeogeographic reconstructions limit the interpretation of available palaeoceanographic data and prevent any robust model-based quantifications of the proposed circulation and carbon burial changes. Here, we present a new approach to assess the principal controls on the Early Cretaceous South Atlantic and Southern Ocean circulation changes under full consideration of the uncertainties in available boundary conditions. Specifically, we use a large ensemble of 36 climate model experiments to simulate the Barremian to Albian progressive opening of the Falkland Plateau and Georgia Basin gateways with different configurations of the proto-Drake Passage, the Walvis Ridge, and atmospheric CO2 concentrations. The experiments are designed to complement available geochemical data across the regions and to test circulation scenarios derived from them. All simulations show increased evaporation and intermediate water formation at subtropical latitudes that drive a meridional overturning circulation whose vertical extent is determined by the sill depth of the Falkland Plateau. The densest water masses formed in the southern Angola Basin and potentially reached the deep Cape Basin as Walvis Ridge Overflow Water. Palaeogeographic uncertainties are as important as the lack of precise knowledge of atmospheric CO2 levels for the simulated temperature and salinity spread in large parts of the South Atlantic. Overall temperature uncertainties reach up to 15 °C and increase significantly with water depth. The ensemble approach reveals temporal changes in the relative importance of geographic and radiative forcings for the simulated oceanographic conditions and, importantly, nonlinear interactions between them. The progressive northward opening of the highly restricted Angola Basin increased the sensitivity of local overturning and upper-ocean stratification to atmospheric CO2 concentrations due to large-scale changes in the hydrological cycle, while the chosen proto-Drake Passage depth is critical for the ocean dynamics and CO2 response in the southern South Atlantic. Finally, the simulated processes are integrated into a recent carbon burial framework to document the principal control of the regional gateway evolution on the progressive shift from the prevailing saline and oxygen-depleted subtropical water masses to the dominance o","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"27 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-07-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141778425","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. During the Last Glacial Maximum (LGM, ∼ 23 000 to 19 000 years ago), the Patagonian Ice Sheet (PIS) covered the central chain of the Andes between ∼ 38 to 55° S. Existing paleoclimate evidence – mostly derived from glacial landforms – suggests that maximum ice sheet expansions in the Southern Hemisphere and Northern Hemisphere were not synchronized. However, large uncertainties still exist in the timing of the onset of regional deglaciation and its major drivers. Here we present an ensemble of numerical simulations of the PIS during the LGM. We assess the skill of paleoclimate model products in reproducing the range of atmospheric conditions needed to enable an ice sheet growth in concordance with geomorphological and geochronological evidence. The resulting best-fit climate product is then combined with records from southern South America offshore sediment cores and Antarctic ice cores to drive transient simulations throughout the last 70 ka using a glacial index approach. Our analysis suggests a strong dependence of the PIS geometry on near-surface air temperature forcing. Most ensemble members underestimate the ice cover in the northern part of Patagonia, while tending to expand beyond its constrained eastern boundaries. We largely attribute these discrepancies between the model-based ice geometries and geological evidence to the low resolution of paleoclimate models and their prescribed ice mask. In the southernmost sector, evidence suggests full glacial conditions during marine isotope stage 3 (MIS3, ∼ 59 400 to 27 800 years ago), followed by a warming trend towards MIS2 (∼ 27 800 to 14 700 years ago). However, in northern Patagonia, this deglacial trend is absent, indicating a relatively consistent signal throughout MIS3 and MIS2. Notably, Antarctic cores do not reflect a glacial history consistent with the geochronological observations. Therefore, investigations of the glacial history of the PIS should take into account southern midlatitude records to capture effectively its past climatic variability.
摘要在末次冰川极盛时期（LGM，距今23000至19000年），巴塔哥尼亚冰盖（PIS）覆盖了南纬38至55°之间的安第斯山脉中心链。现有的古气候证据（主要来自冰川地貌）表明，南半球和北半球冰盖的最大扩张时间并不同步。然而，区域性冰川消融开始的时间及其主要驱动因素仍然存在很大的不确定性。在这里，我们展示了对远古至近古时期 PIS 的一系列数值模拟。我们评估了古气候模式产品在再现冰盖增长所需的大气条件范围方面的技能，这些条件与地貌学和地质年代学证据是一致的。然后，将得到的最佳拟合气候产品与南美洲南部近海沉积岩芯和南极冰芯的记录结合起来，利用冰川指数方法对整个过去 70 ka 年进行瞬态模拟。我们的分析表明，PIS 的几何形状与近地面气温强迫有很大关系。大多数集合成员低估了巴塔哥尼亚北部的冰盖，而倾向于扩大到其受限的东部边界之外。我们将这些基于模型的冰盖几何图形与地质证据之间的差异主要归因于古气候模型的低分辨率及其规定的冰盖。在最南端，有证据表明在海洋同位素阶段 3（MIS3，距今 59400 年至 27800 年）期间是完全冰川期，随后在海洋同位素阶段 2（距今 27800 年至 14700 年）出现变暖趋势。然而，在巴塔哥尼亚北部，这种退冰趋势并不存在，表明在整个MIS3和MIS2期间信号相对一致。值得注意的是，南极岩心没有反映出与地质年代观测结果一致的冰川历史。因此，在研究太平洋岛国的冰川历史时，应考虑到南部中纬度的记录，以有效捕捉其过去的气候变异。
{"title":"Climate and ice sheet dynamics in Patagonia throughout marine isotope stages 2 and 3","authors":"Andrés Castillo-Llarena, Franco Retamal-Ramírez, Jorge Bernales, Martín Jacques-Coper, Matthias Prange, Irina Rogozhina","doi":"10.5194/cp-20-1559-2024","DOIUrl":"https://doi.org/10.5194/cp-20-1559-2024","url":null,"abstract":"Abstract. During the Last Glacial Maximum (LGM, ∼ 23 000 to 19 000 years ago), the Patagonian Ice Sheet (PIS) covered the central chain of the Andes between ∼ 38 to 55° S. Existing paleoclimate evidence – mostly derived from glacial landforms – suggests that maximum ice sheet expansions in the Southern Hemisphere and Northern Hemisphere were not synchronized. However, large uncertainties still exist in the timing of the onset of regional deglaciation and its major drivers. Here we present an ensemble of numerical simulations of the PIS during the LGM. We assess the skill of paleoclimate model products in reproducing the range of atmospheric conditions needed to enable an ice sheet growth in concordance with geomorphological and geochronological evidence. The resulting best-fit climate product is then combined with records from southern South America offshore sediment cores and Antarctic ice cores to drive transient simulations throughout the last 70 ka using a glacial index approach. Our analysis suggests a strong dependence of the PIS geometry on near-surface air temperature forcing. Most ensemble members underestimate the ice cover in the northern part of Patagonia, while tending to expand beyond its constrained eastern boundaries. We largely attribute these discrepancies between the model-based ice geometries and geological evidence to the low resolution of paleoclimate models and their prescribed ice mask. In the southernmost sector, evidence suggests full glacial conditions during marine isotope stage 3 (MIS3, ∼ 59 400 to 27 800 years ago), followed by a warming trend towards MIS2 (∼ 27 800 to 14 700 years ago). However, in northern Patagonia, this deglacial trend is absent, indicating a relatively consistent signal throughout MIS3 and MIS2. Notably, Antarctic cores do not reflect a glacial history consistent with the geochronological observations. Therefore, investigations of the glacial history of the PIS should take into account southern midlatitude records to capture effectively its past climatic variability.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"15 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-07-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141778424","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 : 2024-07-22DOI: 10.5194/egusphere-2024-1959
Calla N. Gould-Whaley, Russell N. Drysdale, Pauline C. Treble, Jan-Hendrik May, Stacey C. Priestley, John C. Hellstrom, Clare Buswell
Abstract. As anthropogenic climate change enhances aridity across vast regions of the globe, understanding drivers of aridification is more important than ever before. Unfortunately, arid regions globally tend to exhibit a paucity of palaeoclimate records, and the archives that are available typically comprise unconsolidated sediments prone to reworking, large dating uncertainties, and ambiguous climatic interpretations. This is certainly true of Australia’s vast continental interior, which is dominated by harsh, arid conditions. Mairs Cave, in the southern Ikara-Flinders Ranges (South Australia), is located on the southern margin of the arid zone. In the present day the cave is largely dry and there is limited evidence of active speleothem growth. However, historical records and observations throughout the cave indicate that it has been periodically flooded, suggesting the local water balance was once much more positive than it is today. The cave contains a curtain of hanging speleothems known as pendulites, which grow subaqueously when submerged in water that is saturated with respect to calcite. Geochemical evidence, including trace element concentrations, uranium isotope ratios, and Dead Carbon Fractions, all indicate that rising of the local groundwater during periods of enhanced groundwater recharge is the cause of the cave flooding events that trigger pendulite growth. Uranium-thorium dating of a pendulite retrieved from Mairs Cave has revealed two multi-millennial growth phases (68.5 to 65.4 kyr and 51.2 to 42.3 kyr) and two short bursts of growth (18.9 kyr and 16.4 kyr) during the Last Glacial Period. The absence of subsequent pendulite growth suggests that strong water deficits under warm Holocene interglacial conditions give rise to episodic, rather than persistent, cave flooding.
{"title":"Subaqueous speleothems as archives of groundwater recharge on Australia’s southern arid margin","authors":"Calla N. Gould-Whaley, Russell N. Drysdale, Pauline C. Treble, Jan-Hendrik May, Stacey C. Priestley, John C. Hellstrom, Clare Buswell","doi":"10.5194/egusphere-2024-1959","DOIUrl":"https://doi.org/10.5194/egusphere-2024-1959","url":null,"abstract":"<strong>Abstract.</strong> As anthropogenic climate change enhances aridity across vast regions of the globe, understanding drivers of aridification is more important than ever before. Unfortunately, arid regions globally tend to exhibit a paucity of palaeoclimate records, and the archives that are available typically comprise unconsolidated sediments prone to reworking, large dating uncertainties, and ambiguous climatic interpretations. This is certainly true of Australia’s vast continental interior, which is dominated by harsh, arid conditions. Mairs Cave, in the southern Ikara-Flinders Ranges (South Australia), is located on the southern margin of the arid zone. In the present day the cave is largely dry and there is limited evidence of active speleothem growth. However, historical records and observations throughout the cave indicate that it has been periodically flooded, suggesting the local water balance was once much more positive than it is today. The cave contains a curtain of hanging speleothems known as pendulites, which grow subaqueously when submerged in water that is saturated with respect to calcite. Geochemical evidence, including trace element concentrations, uranium isotope ratios, and Dead Carbon Fractions, all indicate that rising of the local groundwater during periods of enhanced groundwater recharge is the cause of the cave flooding events that trigger pendulite growth. Uranium-thorium dating of a pendulite retrieved from Mairs Cave has revealed two multi-millennial growth phases (68.5 to 65.4 kyr and 51.2 to 42.3 kyr) and two short bursts of growth (18.9 kyr and 16.4 kyr) during the Last Glacial Period. The absence of subsequent pendulite growth suggests that strong water deficits under warm Holocene interglacial conditions give rise to episodic, rather than persistent, cave flooding.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"215 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-07-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141742140","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}
Paul Töchterle, Anna Baldo, Julian B. Murton, Frederik Schenk, R. Lawrence Edwards, Gabriella Koltai, Gina E. Moseley
Abstract. The Younger Dryas stadial was characterised by a rapid shift towards cold-climate conditions in the North Atlantic realm during the last deglaciation. While some climate parameters including atmospheric temperature and glacier extent are widely studied, empirical constraints on permafrost temperature and snow thickness are limited. To address this, we present a regional dataset of cryogenic cave carbonates (CCCs) from three caves in Great Britain that formed at temperatures between −2 and 0 °C. Our CCC record indicates that these permafrost temperatures persisted for most of the Younger Dryas. By combining ground temperatures with surface temperatures from high-resolution ground-truthed model simulations, we demonstrate that ground temperatures were approximately 6.6 ± 2.3 °C warmer than the mean annual air temperature. Our results suggest that the observed temperature offset between permafrost and the atmosphere can be explained by an average snow thickness between 0.2 and 0.9 m, which persisted for 233 ± 54 d per year. By identifying modern analogues from climate reanalysis data, we demonstrate that the inferred temperature and snow cover characteristics for the British Isles during the Younger Dryas are best explained by extreme temperature seasonality, comparable to continental parts of today's Arctic Archipelago. Such a climate for the British Isles necessitates a winter sea ice margin at approximately 45° N in the North Atlantic Ocean.
{"title":"Reconstructing Younger Dryas ground temperature and snow thickness from cave deposits","authors":"Paul Töchterle, Anna Baldo, Julian B. Murton, Frederik Schenk, R. Lawrence Edwards, Gabriella Koltai, Gina E. Moseley","doi":"10.5194/cp-20-1521-2024","DOIUrl":"https://doi.org/10.5194/cp-20-1521-2024","url":null,"abstract":"Abstract. The Younger Dryas stadial was characterised by a rapid shift towards cold-climate conditions in the North Atlantic realm during the last deglaciation. While some climate parameters including atmospheric temperature and glacier extent are widely studied, empirical constraints on permafrost temperature and snow thickness are limited. To address this, we present a regional dataset of cryogenic cave carbonates (CCCs) from three caves in Great Britain that formed at temperatures between −2 and 0 °C. Our CCC record indicates that these permafrost temperatures persisted for most of the Younger Dryas. By combining ground temperatures with surface temperatures from high-resolution ground-truthed model simulations, we demonstrate that ground temperatures were approximately 6.6 ± 2.3 °C warmer than the mean annual air temperature. Our results suggest that the observed temperature offset between permafrost and the atmosphere can be explained by an average snow thickness between 0.2 and 0.9 m, which persisted for 233 ± 54 d per year. By identifying modern analogues from climate reanalysis data, we demonstrate that the inferred temperature and snow cover characteristics for the British Isles during the Younger Dryas are best explained by extreme temperature seasonality, comparable to continental parts of today's Arctic Archipelago. Such a climate for the British Isles necessitates a winter sea ice margin at approximately 45° N in the North Atlantic Ocean.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"38 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-07-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141742142","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 : 2024-07-22DOI: 10.5194/egusphere-2024-1998
Kirstin Koepnick, Minmin Fu, Eli Tziperman
Abstract. In spite of decades of research, the role of climate feedbacks in the Pleistocene glacial cycles is still not fully understood. Here, we calculate the surface mass balance (SMB) of the Laurentide Ice Sheet (LIS) throughout the last deglaciation using the isotope-enabled transient climate model experiment (iTraCE). A surface energy balance framework is used to calculate yearly melt, and a parameterization of the refreezing of snow melt and liquid precipitation is incorporated. The SMB calculated from iTraCE overestimates the total ice mass loss rate in comparison to the ICE-6G reconstruction from the Last Glacial Maximum (LGM; 21 ka) until about 15–14 ka; subsequently, the fully forced climate model experiment better fits the ICE-6G ice volume loss rate. We find the melt rate for the LIS to be primarily set by the small residual of large net shortwave and longwave radiative fluxes. The melt, and hence the SMB, are very sensitive to small changes in the albedo and downwelling longwave radiation. By increasing albedo by a mere 1.9 % or by decreasing downwelling longwave radiation by only 1.45 % (well within the uncertainty range of these variables), the large overestimation of the rate of mass loss deduced from the SMB compared to reconstructed rates of mass loss from 19–15 ka can be eliminated. The inconsistency of the climate model-derived, offline SMB calculation and the ice mass reconstructions exists irrespective of the role of ablation caused by ice flow, which cannot be calculated using this analysis. The extreme sensitivity of the melt rate suggests that General Circulation Models (GCMs) still struggle to reliably calculate the SMB, presenting a significant roadblock in our attempt to understand the Pleistocene ice ages.
{"title":"Investigating the surface mass balance of the Laurentide Ice Sheet during the last deglaciation","authors":"Kirstin Koepnick, Minmin Fu, Eli Tziperman","doi":"10.5194/egusphere-2024-1998","DOIUrl":"https://doi.org/10.5194/egusphere-2024-1998","url":null,"abstract":"<strong>Abstract.</strong> In spite of decades of research, the role of climate feedbacks in the Pleistocene glacial cycles is still not fully understood. Here, we calculate the surface mass balance (SMB) of the Laurentide Ice Sheet (LIS) throughout the last deglaciation using the isotope-enabled transient climate model experiment (iTraCE). A surface energy balance framework is used to calculate yearly melt, and a parameterization of the refreezing of snow melt and liquid precipitation is incorporated. The SMB calculated from iTraCE overestimates the total ice mass loss rate in comparison to the ICE-6G reconstruction from the Last Glacial Maximum (LGM; 21 ka) until about 15–14 ka; subsequently, the fully forced climate model experiment better fits the ICE-6G ice volume loss rate. We find the melt rate for the LIS to be primarily set by the small residual of large net shortwave and longwave radiative fluxes. The melt, and hence the SMB, are very sensitive to small changes in the albedo and downwelling longwave radiation. By increasing albedo by a mere 1.9 % or by decreasing downwelling longwave radiation by only 1.45 % (well within the uncertainty range of these variables), the large overestimation of the rate of mass loss deduced from the SMB compared to reconstructed rates of mass loss from 19–15 ka can be eliminated. The inconsistency of the climate model-derived, offline SMB calculation and the ice mass reconstructions exists irrespective of the role of ablation caused by ice flow, which cannot be calculated using this analysis. The extreme sensitivity of the melt rate suggests that General Circulation Models (GCMs) still struggle to reliably calculate the SMB, presenting a significant roadblock in our attempt to understand the Pleistocene ice ages.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"161 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-07-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141742141","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 : 2024-07-18DOI: 10.5194/egusphere-2024-2194
Catherine M. Collins, Nicolas Perdrial, Pierre-Henri Blard, Nynke Keulen, William C. Mahaney, Halley Mastro, Juliana Souza, Donna M. Rizzo, Yves Marrocchi, Paul C. Knutz, Paul R. Bierman
Abstract. In 1966, drilling at Camp Century, Greenland, recovered 3.44 meters of sub-glacial material from beneath 1350 meters of ice. Although prior analysis of this material showed that the core includes glacial sediment, ice, and sediment deposited during an interglacial, the sub-glacial material had never been thoroughly studied. To better characterize this material, we analyzed 26 of the 30 core samples remaining in the archive. We performed a multi-scale analysis including X-ray diffraction, micro-computed tomography, and scanning electron microscopy to delineate stratigraphic units and assign facies based on inferred depositional processes. At the macro-scale, quantitative X-ray diffraction revealed that quartz and feldspar dominated the sediment and that there was insignificant variation in relative mineral abundance between samples. Meso-scale evaluation of the frozen material using micro-computed tomography scans showed clear variations in the stratigraphy of the core characterized by the presence of bedding, grading, and sorting. Micro-scale grain size and shape analysis, conducted using scanning electron microscopy, showed an abundance of fine-grained materials in the lower part of the core and no correspondence between grain shape parameters and sedimentary structures. These multiscale data define 5 distinct stratigraphic units within the core based on sedimentary process; K-means clustering analysis supports this proposed unit delineation. Our observations suggest that ice retreat uncovered the Camp Century region exposing basal till, covered with a remnant of basal ice or firn (Units 1 and 2). Continued ice-free conditions led to till disruption by liquid water causing a slump deposit (Unit 3) and the development of a small fluvial system of increasing energy up core (Units 4–5). Analysis of the Camp Century sub-glacial material indicates a diverse stratigraphy preserved below the ice that recorded episodes of glaciated and deglaciated conditions in northwestern Greenland. Our physical, geochemical, and mineralogic analyses reveal a history of deposition, weathering, and sediment transport preserved under the ice and show the promise of sub-glacial materials to increase our knowledge of past ice sheet behavior over time.
摘要1966 年，在格陵兰世纪营进行的钻探从 1350 米的冰层下发现了 3.44 米的亚冰川物质。尽管之前对这些物质的分析表明，岩芯包括冰川沉积物、冰和间冰期沉积物，但从未对亚冰川物质进行过深入研究。为了更好地描述这些材料的特征，我们对档案中剩余的 30 个岩心样本中的 26 个进行了分析。我们进行了包括 X 射线衍射、微型计算机断层扫描和扫描电子显微镜在内的多尺度分析，以划分地层单元，并根据推断的沉积过程分配面层。在宏观尺度上，定量 X 射线衍射显示石英和长石在沉积物中占主导地位，不同样本之间的相对矿物丰度差异不大。利用微型计算机断层扫描技术对冻结物质进行的中尺度评估显示，岩芯的地层有明显的变化，其特点是存在层理、分级和分选。利用扫描电子显微镜进行的微尺度粒度和粒形分析表明，岩心下部有大量细粒物质，而粒形参数与沉积结构之间没有对应关系。这些多尺度数据根据沉积过程在岩芯中定义了 5 个不同的地层单元；K-均值聚类分析支持这一单元划分建议。我们的观测结果表明，冰川退缩揭开了 Camp Century 地区的冰层，露出了覆盖着基底冰或冷杉残余的基底萌蘖（第 1 和第 2 单元）。持续的无冰条件导致了液态水对基底的破坏，造成了坍塌沉积（第 3 单元），并形成了一个能量不断增加的小型河道系统（第 4-5 单元）。对坎普世纪冰川下物质的分析表明，冰层下保存了多种多样的地层，记录了格陵兰岛西北部冰川和冰川消融的情况。我们的物理、地球化学和矿物学分析揭示了保存在冰层下的沉积、风化和沉积物迁移的历史，并表明亚冰川材料有望增加我们对过去冰盖随时间变化的行为的了解。
{"title":"Characterization of the 1966 Camp Century Sub-Glacial Core: A Multiscale Analysis","authors":"Catherine M. Collins, Nicolas Perdrial, Pierre-Henri Blard, Nynke Keulen, William C. Mahaney, Halley Mastro, Juliana Souza, Donna M. Rizzo, Yves Marrocchi, Paul C. Knutz, Paul R. Bierman","doi":"10.5194/egusphere-2024-2194","DOIUrl":"https://doi.org/10.5194/egusphere-2024-2194","url":null,"abstract":"<strong>Abstract.</strong> In 1966, drilling at Camp Century, Greenland, recovered 3.44 meters of sub-glacial material from beneath 1350 meters of ice. Although prior analysis of this material showed that the core includes glacial sediment, ice, and sediment deposited during an interglacial, the sub-glacial material had never been thoroughly studied. To better characterize this material, we analyzed 26 of the 30 core samples remaining in the archive. We performed a multi-scale analysis including X-ray diffraction, micro-computed tomography, and scanning electron microscopy to delineate stratigraphic units and assign facies based on inferred depositional processes. At the macro-scale, quantitative X-ray diffraction revealed that quartz and feldspar dominated the sediment and that there was insignificant variation in relative mineral abundance between samples. Meso-scale evaluation of the frozen material using micro-computed tomography scans showed clear variations in the stratigraphy of the core characterized by the presence of bedding, grading, and sorting. Micro-scale grain size and shape analysis, conducted using scanning electron microscopy, showed an abundance of fine-grained materials in the lower part of the core and no correspondence between grain shape parameters and sedimentary structures. These multiscale data define 5 distinct stratigraphic units within the core based on sedimentary process; K-means clustering analysis supports this proposed unit delineation. Our observations suggest that ice retreat uncovered the Camp Century region exposing basal till, covered with a remnant of basal ice or firn (Units 1 and 2). Continued ice-free conditions led to till disruption by liquid water causing a slump deposit (Unit 3) and the development of a small fluvial system of increasing energy up core (Units 4–5). Analysis of the Camp Century sub-glacial material indicates a diverse stratigraphy preserved below the ice that recorded episodes of glaciated and deglaciated conditions in northwestern Greenland. Our physical, geochemical, and mineralogic analyses reveal a history of deposition, weathering, and sediment transport preserved under the ice and show the promise of sub-glacial materials to increase our knowledge of past ice sheet behavior over time.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"63 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-07-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141742143","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 : 2024-07-18DOI: 10.5194/egusphere-2024-2123
Alice Paine, Joost Frieling, Timothy Shanahan, Tamsin Mather, Nicholas McKay, Stuart Robinson, David Pyle, Isabel Fendley, Ruth Kiely, William Gosling
Abstract. Changing hydrology impacts the biogeochemical cycling of elements such as mercury (Hg), whose transport and transformation in the environment appear linked to hydroclimate on diverse timescales. Key questions remain about how these processes manifest over different timescales and their potential environmental consequences. For example, millennial-scale Hg-hydroclimate interactions in the terrestrial realm are poorly understood, as few sedimentary records have sufficient length and/or resolution to record abrupt and long-lasting changes in Hg cycling, and the relative roles of depositional processes on these changes. Here, we present a high-resolution sedimentary Hg record from tropical Lake Bosumtwi (Ghana, West Africa) since ~96 ka. A coupled response is observed between Hg flux and shifts in sediment composition, the latter reflecting changes in lake level. Specifically, we find that the amplitude and frequency of Hg peaks increase as the lake level rises, suggesting that Hg burial was enhanced in response to an insolation-driven increase in precipitation at ~73 ka. A more transient, threefold increase in Hg concentration and accumulation rate is also recorded between ~13 and 4 ka, coinciding with a period of distinctly higher rainfall across North Africa known as the African Humid Period. Two mechanisms, likely working in tandem, could explain this correspondence: (1) an increase in wet deposition of Hg by precipitation and (2) efficient sequestration of organic-hosted Hg. Taken together, our results reaffirm that changes in hydroclimate, directly and/or indirectly, can be linked to millennial-scale changes in tropical Hg cycling, and that these signals can be recorded in lake sediments.
摘要水文的变化影响着汞（Hg）等元素的生物地球化学循环，其在环境中的迁移和转化似乎与不同时间尺度的水文气候有关。关于这些过程在不同时间尺度上的表现形式及其潜在的环境后果，仍然存在一些关键问题。例如，由于很少有沉积记录具有足够的长度和/或分辨率来记录汞循环的突然和持久变化，以及沉积过程在这些变化中的相对作用，因此人们对陆地领域千年尺度的汞-水文气候相互作用知之甚少。在这里，我们展示了自约 96 ka 年以来热带博苏姆特维湖（西非加纳）的高分辨率沉积汞记录。我们观察到汞通量与沉积物成分变化之间的耦合反应，后者反映了湖泊水位的变化。具体来说，我们发现随着湖泊水位的上升，汞峰的振幅和频率也在增加，这表明在约 73 ka 时，由于日照驱动的降水量增加，汞的埋藏量也随之增加。在约 13 至 4 ka 期间，汞浓度和积累率也出现了更短暂的三倍增长，这与整个北非降雨量明显增加的时期（即非洲湿润期）相吻合。有两种机制可以解释这种对应关系：(1) 降水造成的汞湿沉积增加；(2) 有机态汞的有效固存。总之，我们的研究结果再次证明，水文气候的变化（直接和/或间接）与热带汞循环的千年尺度变化有关，这些信号可以记录在湖泊沉积物中。
{"title":"New evidence for millennial-scale interactions between Hg cycling and hydroclimate from Lake Bosumtwi, Ghana","authors":"Alice Paine, Joost Frieling, Timothy Shanahan, Tamsin Mather, Nicholas McKay, Stuart Robinson, David Pyle, Isabel Fendley, Ruth Kiely, William Gosling","doi":"10.5194/egusphere-2024-2123","DOIUrl":"https://doi.org/10.5194/egusphere-2024-2123","url":null,"abstract":"<strong>Abstract.</strong> Changing hydrology impacts the biogeochemical cycling of elements such as mercury (Hg), whose transport and transformation in the environment appear linked to hydroclimate on diverse timescales. Key questions remain about how these processes manifest over different timescales and their potential environmental consequences. For example, millennial-scale Hg-hydroclimate interactions in the terrestrial realm are poorly understood, as few sedimentary records have sufficient length and/or resolution to record abrupt and long-lasting changes in Hg cycling, and the relative roles of depositional processes on these changes. Here, we present a high-resolution sedimentary Hg record from tropical Lake Bosumtwi (Ghana, West Africa) since ~96 ka. A coupled response is observed between Hg flux and shifts in sediment composition, the latter reflecting changes in lake level. Specifically, we find that the amplitude and frequency of Hg peaks increase as the lake level rises, suggesting that Hg burial was enhanced in response to an insolation-driven increase in precipitation at ~73 ka. A more transient, threefold increase in Hg concentration and accumulation rate is also recorded between ~13 and 4 ka, coinciding with a period of distinctly higher rainfall across North Africa known as the African Humid Period. Two mechanisms, likely working in tandem, could explain this correspondence: (1) an increase in wet deposition of Hg by precipitation and (2) efficient sequestration of organic-hosted Hg. Taken together, our results reaffirm that changes in hydroclimate, directly and/or indirectly, can be linked to millennial-scale changes in tropical Hg cycling, and that these signals can be recorded in lake sediments.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"16 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-07-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141742035","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 : 2024-07-18DOI: 10.5194/egusphere-2024-1596
Mark Vinz Elbertsen, Erik van Sebille, Peter Kristian Bijl
Abstract. The Eocene-Oligocene Transition is characterised by the inception of the large-scale Antarctic ice sheet. However, evidence of earlier glaciation during the Eocene has been found, including the presence of ice-rafted debris at Ocean Drilling Program Leg 113 Site 696 on the South Orkney Microcontinent (Carter et al., 2017). This suggests marine-terminating glaciers should have been present in the southern Weddell Sea region during the late Eocene, generating sufficiently large icebergs to South Orkney to survive the high Eocene ocean temperatures. Here, we use Lagrangian iceberg tracing in a high-resolution eddy-resolving ocean model of the late Eocene (Nooteboom et al., 2022) to show that icebergs released from offshore the present-day Filchner Ice Shelf region and Dronning Maud Land could reach the South Orkney Microcontinent during the late Eocene. The high melt rates under the Eocene warm climate require a minimum initial iceberg mass on the order of 100 Mt and an iceberg thickness of several tens of metres to be able to reach the South Orkney Microcontinent. Although these sizes are at the larger end of the present-day range of common iceberg sizes around Antarctica, the minimum estimates are not unfeasible and, hence, the present study confirms previous findings suggesting glaciation and iceberg calving were possible in the late Eocene.
{"title":"Possible provenance of IRD by tracing late Eocene Antarctic iceberg melting using a high-resolution ocean model","authors":"Mark Vinz Elbertsen, Erik van Sebille, Peter Kristian Bijl","doi":"10.5194/egusphere-2024-1596","DOIUrl":"https://doi.org/10.5194/egusphere-2024-1596","url":null,"abstract":"<strong>Abstract.</strong> The Eocene-Oligocene Transition is characterised by the inception of the large-scale Antarctic ice sheet. However, evidence of earlier glaciation during the Eocene has been found, including the presence of ice-rafted debris at Ocean Drilling Program Leg 113 Site 696 on the South Orkney Microcontinent (Carter et al., 2017). This suggests marine-terminating glaciers should have been present in the southern Weddell Sea region during the late Eocene, generating sufficiently large icebergs to South Orkney to survive the high Eocene ocean temperatures. Here, we use Lagrangian iceberg tracing in a high-resolution eddy-resolving ocean model of the late Eocene (Nooteboom et al., 2022) to show that icebergs released from offshore the present-day Filchner Ice Shelf region and Dronning Maud Land could reach the South Orkney Microcontinent during the late Eocene. The high melt rates under the Eocene warm climate require a minimum initial iceberg mass on the order of 100 Mt and an iceberg thickness of several tens of metres to be able to reach the South Orkney Microcontinent. Although these sizes are at the larger end of the present-day range of common iceberg sizes around Antarctica, the minimum estimates are not unfeasible and, hence, the present study confirms previous findings suggesting glaciation and iceberg calving were possible in the late Eocene.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"46 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-07-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141742036","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 : 2024-07-16DOI: 10.5194/egusphere-2024-2093
Armelle Ballian, Maud J. M. Meijers, Isabelle Cojan, Damien Huyghe, Miguel Bernecker, Katharina Methner, Mattia Tagliavento, Jens Fiebig, Andreas Mulch
Abstract. During the Middle Miocene, the Earth shifted from a warm state, the Miocene Climatic Optimum (MCO, 16.9–14.7 Ma), to a colder state associated with the formation of extensive and permanent ice sheets on Antarctica. This climatic shift, the Middle Miocene Climatic Transition (MMCT, 14.7–13.8 Ma) strongly affected the composition and structure of major biomes, ocean circulation, as well as precipitation patterns. Although Middle Miocene climate dynamics are well documented in marine records, our knowledge of terrestrial climate change is not well constrained. Here we present a long-term (23–13 Ma) stable (𝛿13C, 𝛿18O) and clumped (∆47) isotope record of soil carbonates from a northern Mediterranean Alpine foreland basin (Digne-Valensole Basin, France). ∆47-derived soil carbonate formation temperatures indicate a highly dynamic dry season temperature pattern that is consistent with multiple periods of reorganization of atmospheric circulation during the MCO. We propose that changes in atmospheric circulation patterns modified the seasonality of precipitation and, ultimately, the timing of pedogenic carbonate formation. Consequently, ∆47 soil carbonate temperature data record the combined effects of long-term regional temperature and carbonate formation seasonality change. The data are consistent with the existence of a proto-Mediterranean climate already during certain MCO time intervals. Following the MMCT, the stable and clumped isotope record displays pronounced cooling after 13.8 Ma accompanied by a rather large (-5.0 %) decrease in soil water 𝛿18O values. Our northern Mediterranean foreland basin climate record shares strong similarities with time-equivalent records from the terrestrial European mid-latitudes and the global oceans and enhances our understanding of the circum-Alpine Middle Miocene terrestrial climate dynamics.
{"title":"Middle Miocene climate evolution in the Northern Mediterranean region (Digne-Valensole basin, SE France)","authors":"Armelle Ballian, Maud J. M. Meijers, Isabelle Cojan, Damien Huyghe, Miguel Bernecker, Katharina Methner, Mattia Tagliavento, Jens Fiebig, Andreas Mulch","doi":"10.5194/egusphere-2024-2093","DOIUrl":"https://doi.org/10.5194/egusphere-2024-2093","url":null,"abstract":"<strong>Abstract.</strong> During the Middle Miocene, the Earth shifted from a warm state, the Miocene Climatic Optimum (MCO, 16.9–14.7 Ma), to a colder state associated with the formation of extensive and permanent ice sheets on Antarctica. This climatic shift, the Middle Miocene Climatic Transition (MMCT, 14.7–13.8 Ma) strongly affected the composition and structure of major biomes, ocean circulation, as well as precipitation patterns. Although Middle Miocene climate dynamics are well documented in marine records, our knowledge of terrestrial climate change is not well constrained. Here we present a long-term (23–13 Ma) stable (𝛿<sup>13</sup>C, 𝛿<sup>18</sup>O) and clumped (∆<sub>47</sub>) isotope record of soil carbonates from a northern Mediterranean Alpine foreland basin (Digne-Valensole Basin, France). ∆<sub>47</sub>-derived soil carbonate formation temperatures indicate a highly dynamic dry season temperature pattern that is consistent with multiple periods of reorganization of atmospheric circulation during the MCO. We propose that changes in atmospheric circulation patterns modified the seasonality of precipitation and, ultimately, the timing of pedogenic carbonate formation. Consequently, ∆<sub>47</sub> soil carbonate temperature data record the combined effects of long-term regional temperature and carbonate formation seasonality change. The data are consistent with the existence of a proto-Mediterranean climate already during certain MCO time intervals. Following the MMCT, the stable and clumped isotope record displays pronounced cooling after 13.8 Ma accompanied by a rather large (-5.0 %) decrease in soil water 𝛿<sup>18</sup>O values. Our northern Mediterranean foreland basin climate record shares strong similarities with time-equivalent records from the terrestrial European mid-latitudes and the global oceans and enhances our understanding of the circum-Alpine Middle Miocene terrestrial climate dynamics.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"7 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-07-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141717823","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 : 2024-07-15DOI: 10.5194/egusphere-2024-1771
Dael Sassoon, Nathalie Combourieu-Nebout, Odile Peyron, Adele Bertini, Francesco Toti, Vincent Lebreton, Marie-Hélène Moncel
Abstract. Pleistocene interglacials, specifically MIS 19, 11 and 5, have been suggested as analogues of MIS 1 due to similar solar forcing patterns, greenhouse gas concentrations and sea levels. There has been substantial debate regarding which of these is the most suitable analogue and so far there has been no consensus, although what really emerges from recent work is the high variation in regional climate during these periods. One of the limiting factors in our understanding of these potential analogues is the fact that very few long-sequences cover the entire duration of these interglacials at high resolution. In this study, a multi-method approach is used to produce climatic reconstructions for MIS 19, 11, 5 and 1, using pollen data derived from a single long marine core from ODP Site 976. This represents the first study which attempts to use pollen-based climatic reconstructions to compare MIS 1 with its analogues, representing a necessary contribution to the debate with a focus on the relationships between vegetation and climate in the southwestern Mediterranean. Three methods of quantitative climate reconstruction have been adopted: the more widely used methods Modern Analogues Technique (MAT) and Weighted Average Partial Least Squares regression (WA-PLS), and a more recent machine-learning method known as Boosted Regression Trees (BRT). The reconstructions show consistent changes in temperature and precipitation during MIS 19, 11, 5 and 1, which correlate well with climatic changes observed in other regional and global proxies, and highlight distinct climatic characteristics of each interglacial period in the southwestern Mediterranean. MIS 19 exhibits high variability and colder temperatures compared to subsequent interglacials and the MIS 1. Conversely, MIS 11 displays warmer temperatures and greater stability, which makes it a useful analogue to understand prolonged interglacials, crucial considering the anthropogenic impacts on the duration of warm climate during the Holocene. MIS 5 exhibits overall warmer conditions, and its higher temperature coupled with fluctuations in solar forcing makes it a less suitable MIS 1 analogue. Although past interglacials do not offer direct predictions for the Holocene's future, they provide essential insights into Earth's responses to various forcing factors, serving as crucial benchmarks for understanding the Mediterranean's sensitivity to global changes.
摘要由于类似的太阳强迫模式、温室气体浓度和海平面，更新世间冰期，特别是 MIS 19、11 和 5 被认为是 MIS 1 的类似期。关于哪个时期是最合适的类比期，人们一直争论不休，至今尚未达成共识，不过从最近的研究中可以看出，这些时期的区域气候变化很大。限制我们了解这些潜在类似期的因素之一是，很少有长序列能够高分辨率地涵盖这些间冰期的整个持续时间。在本研究中，利用从 ODP 976 号站点获取的单个长海洋岩芯的花粉数据，采用多种方法重建了 MIS 19、11、5 和 1 的气候。这是首次尝试使用基于花粉的气候重建来比较 MIS 1 与其类似物的研究，是对以地中海西南部植被与气候关系为重点的讨论的必要贡献。研究采用了三种定量气候重建方法：应用较广的现代类比技术（MAT）和加权平均最小二乘法回归（WA-PLS），以及一种较新的机器学习方法，即增强回归树（BRT）。重建结果表明，在 MIS 19、11、5 和 1 期间，气温和降水量发生了一致的变化，这与其他地区和全球代用指标观测到的气候变化密切相关，并凸显了地中海西南部每个间冰期的独特气候特征。与随后的间冰期和间冰期 1 相比，间冰期 19 表现出较高的可变性和较低的温度；相反，间冰期 11 表现出较高的温度和较强的稳定性，这使其成为了解长期间冰期的一个有用类比，考虑到人类活动对全新世温暖气候持续时间的影响，这一点至关重要。MIS 5 显示出总体较暖的条件，其较高的温度加上太阳强迫的波动，使其不太适合作为 MIS 1 的类似物。虽然过去的间冰期不能直接预测全新世的未来，但它们提供了地球对各种强迫因素反应的重要见解，是了解地中海对全球变化敏感性的重要基准。
{"title":"Pollen-based climatic reconstructions for the interglacial analogues of MIS 1 (MIS 19, 11 and 5) in the Southwestern Mediterranean: insights from ODP Site 976","authors":"Dael Sassoon, Nathalie Combourieu-Nebout, Odile Peyron, Adele Bertini, Francesco Toti, Vincent Lebreton, Marie-Hélène Moncel","doi":"10.5194/egusphere-2024-1771","DOIUrl":"https://doi.org/10.5194/egusphere-2024-1771","url":null,"abstract":"<strong>Abstract.</strong> Pleistocene interglacials, specifically MIS 19, 11 and 5, have been suggested as analogues of MIS 1 due to similar solar forcing patterns, greenhouse gas concentrations and sea levels. There has been substantial debate regarding which of these is the most suitable analogue and so far there has been no consensus, although what really emerges from recent work is the high variation in regional climate during these periods. One of the limiting factors in our understanding of these potential analogues is the fact that very few long-sequences cover the entire duration of these interglacials at high resolution. In this study, a multi-method approach is used to produce climatic reconstructions for MIS 19, 11, 5 and 1, using pollen data derived from a single long marine core from ODP Site 976. This represents the first study which attempts to use pollen-based climatic reconstructions to compare MIS 1 with its analogues, representing a necessary contribution to the debate with a focus on the relationships between vegetation and climate in the southwestern Mediterranean. Three methods of quantitative climate reconstruction have been adopted: the more widely used methods Modern Analogues Technique (MAT) and Weighted Average Partial Least Squares regression (WA-PLS), and a more recent machine-learning method known as Boosted Regression Trees (BRT). The reconstructions show consistent changes in temperature and precipitation during MIS 19, 11, 5 and 1, which correlate well with climatic changes observed in other regional and global proxies, and highlight distinct climatic characteristics of each interglacial period in the southwestern Mediterranean. MIS 19 exhibits high variability and colder temperatures compared to subsequent interglacials and the MIS 1. Conversely, MIS 11 displays warmer temperatures and greater stability, which makes it a useful analogue to understand prolonged interglacials, crucial considering the anthropogenic impacts on the duration of warm climate during the Holocene. MIS 5 exhibits overall warmer conditions, and its higher temperature coupled with fluctuations in solar forcing makes it a less suitable MIS 1 analogue. Although past interglacials do not offer direct predictions for the Holocene's future, they provide essential insights into Earth's responses to various forcing factors, serving as crucial benchmarks for understanding the Mediterranean's sensitivity to global changes.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"36 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-07-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141717824","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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