Abstract. The Indian Summer Monsoon (ISM) with its rainfall is the lifeline for people living on the Indian subcontinent today and possibly was the driver of the rise and fall of early agricultural societies in the past. Intensity and position of the ISM have shifted in response to orbitally forced thermal land-ocean contrasts. At the northwestern monsoon margins, interactions between the subtropical westerly jet (STWJ) and the ISM constitute a tipping element in the Earth's climate system, because their non-linear interaction may be a first-order influence on rainfall. We reconstructed marine sea surface temperature (SST), supply of terrestrial material and vegetation changes from a very well-dated sediment core from the northern Arabian Sea to reconstruct the STWJ-ISM interaction. The Holocene record (from 11,000 years) shows a distinct, but gradual, southward displacement of the ISM in the Early to Mid-Holocene, increasingly punctuated by phases of intensified STWJ events that are coeval with interruptions of North Atlantic overturning circulation (Bond events). Effects of the non-linear interactions culminate between 4.6–3 ka BP, marking a climatic transition period during which the ISM shifted southwards and the influence of SWTJ became prominent. The lithogenic input shows an up to 4-fold increase after this time period signaling the strengthened influence of agricultural activities of the Indus civilization with enhanced erosion of soils amplifying the impact of Bond events and adding to the marine sedimentation rates adjacent to the continent.
摘要印度夏季季风(ISM)及其降雨是今天生活在印度次大陆上的人们的生命线，也可能是过去早期农业社会兴衰的驱动力。ISM的强度和位置随着轨道强迫的陆-海热对比而发生了变化。在西北季风边缘，副热带西风急流(STWJ)和ISM之间的相互作用构成了地球气候系统的一个引爆因素，因为它们之间的非线性相互作用可能是对降雨的一级影响。为了重建STWJ-ISM相互作用，我们重建了阿拉伯海北部一个年代非常精确的沉积物岩心的海表温度(SST)、陆源物质供应和植被变化。全新世记录(从11000年开始)显示，在全新世早期到中期，ISM有一个明显的、但逐渐向南移动的过程，与北大西洋翻转环流中断(Bond事件)同时发生的STWJ事件加剧的阶段越来越多。非线性相互作用的影响在4.6 ~ 3 ka BP之间达到顶峰，标志着ISM向南转移，SWTJ的影响变得突出的气候过渡期。在这一时期之后，岩石作用的输入增加了4倍，表明印度河文明农业活动的影响增强，土壤侵蚀加剧，放大了邦德事件的影响，并增加了与大陆相邻的海洋沉积速率。
{"title":"Holocene climatic changes in the Westerly-Indian Monsoon realm and\u0000its anthropogenic impact","authors":"Nicole Burdanowitz, T. Rixen, B. Gaye, K. Emeis","doi":"10.5194/cp-2020-141","DOIUrl":"https://doi.org/10.5194/cp-2020-141","url":null,"abstract":"Abstract. The Indian Summer Monsoon (ISM) with its rainfall is the lifeline for people living on the Indian subcontinent today and possibly was the driver of the rise and fall of early agricultural societies in the past. Intensity and position of the ISM have shifted in response to orbitally forced thermal land-ocean contrasts. At the northwestern monsoon margins, interactions between the subtropical westerly jet (STWJ) and the ISM constitute a tipping element in the Earth's climate system, because their non-linear interaction may be a first-order influence on rainfall. We reconstructed marine sea surface temperature (SST), supply of terrestrial material and vegetation changes from a very well-dated sediment core from the northern Arabian Sea to reconstruct the STWJ-ISM interaction. The Holocene record (from 11,000 years) shows a distinct, but gradual, southward displacement of the ISM in the Early to Mid-Holocene, increasingly punctuated by phases of intensified STWJ events that are coeval with interruptions of North Atlantic overturning circulation (Bond events). Effects of the non-linear interactions culminate between 4.6–3 ka BP, marking a climatic transition period during which the ISM shifted southwards and the influence of SWTJ became prominent. The lithogenic input shows an up to 4-fold increase after this time period signaling the strengthened influence of agricultural activities of the Indus civilization with enhanced erosion of soils amplifying the impact of Bond events and adding to the marine sedimentation rates adjacent to the continent.","PeriodicalId":263057,"journal":{"name":"Climate of The Past Discussions","volume":"24 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-11-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123603551","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Camilla K. Crockart, T. Vance, A. Fraser, N. Abram, A. Criscitiello, M. Curran, V. Favier, A. Gallant, H. Kjær, A. Klekociuk, Lenneke M. Jong, A. Moy, C. Plummer, P. Vallelonga, J. Wille, Lingwei Zhang
Abstract. Paleoclimate archives, such as high-resolution ice core records, provide a means to investigate long-term (multi-centennial) climate variability. Until recently, the Law Dome (Dome Summit South) ice core record remained one of few long-term high-resolution records in East Antarctica. A new ice core drilled in 2017/2018 at Mount Brown South, approximately 1000 km west of Law Dome, provides an additional high-resolution record that will likely span the last millennium in the Indian Ocean sector of East Antarctica. Here, we compare snowfall accumulation rates and sea salt concentrations in the upper portion (~21 m) of the Mount Brown South record, and an updated Law Dome record over the period 1975–2016. Annual sea salt concentrations from the Mount Brown South record preserves a stronger signal for the El Niño-Southern Oscillation (ENSO; in austral winter and spring, r = 0.521, p
摘要古气候档案，如高分辨率冰芯记录，提供了研究长期(多百年)气候变率的手段。直到最近，洛穹(南穹顶)冰芯记录仍然是东南极洲为数不多的长期高分辨率记录之一。2017/2018年，在Law Dome以西约1000公里的Mount Brown South钻取了一个新的冰芯，提供了一个额外的高分辨率记录，该记录可能跨越东南极洲印度洋地区的过去千年。在这里，我们比较了1975-2016年期间布朗山南部记录上部(~21 m)的降雪积累率和海盐浓度，以及更新的Law Dome记录。南布朗山记录的年海盐浓度为厄尔Niño-Southern涛动(ENSO;在南方冬春季，r = 0.521, p
{"title":"El Niño Southern Oscillation signal in a new East Antarctic ice core,\u0000Mount Brown South","authors":"Camilla K. Crockart, T. Vance, A. Fraser, N. Abram, A. Criscitiello, M. Curran, V. Favier, A. Gallant, H. Kjær, A. Klekociuk, Lenneke M. Jong, A. Moy, C. Plummer, P. Vallelonga, J. Wille, Lingwei Zhang","doi":"10.5194/cp-2020-134","DOIUrl":"https://doi.org/10.5194/cp-2020-134","url":null,"abstract":"Abstract. Paleoclimate archives, such as high-resolution ice core records, provide a means to investigate long-term (multi-centennial) climate variability. Until recently, the Law Dome (Dome Summit South) ice core record remained one of few long-term high-resolution records in East Antarctica. A new ice core drilled in 2017/2018 at Mount Brown South, approximately 1000 km west of Law Dome, provides an additional high-resolution record that will likely span the last millennium in the Indian Ocean sector of East Antarctica. Here, we compare snowfall accumulation rates and sea salt concentrations in the upper portion (~21 m) of the Mount Brown South record, and an updated Law Dome record over the period 1975–2016. Annual sea salt concentrations from the Mount Brown South record preserves a stronger signal for the El Niño-Southern Oscillation (ENSO; in austral winter and spring, r = 0.521, p \u0000","PeriodicalId":263057,"journal":{"name":"Climate of The Past Discussions","volume":"18 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-11-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132395683","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract. For previous glacial intervals, concomitant shifts in different proxy records from Greenland ice cores indicate repeated abrupt climate transitions comprising – among others – abrupt warming, a sudden reorganization of the atmospheric circulation, and a retreat of perannial sea ice. The physical mechanism underlying these so-called Dansgaard-Oeschger (DO) events remains debated. Former studies have made an effort to deduce the progression of temperature, circulation, and sea-ice changes at the onset of DO events from paleoclimate proxy records to constrain potential triggering mechanisms. In this context, recent research reports on systematically delayed transitions in Na+ concentrations and δ18O values compared to Ca2+ concentrations and the annual layer thickness by about one decade. This is interpreted as a temporal lag of sea ice retreat and Greenland warming with respect to atmospheric reorganization at the onset of DO-events. Here, we present a comprehensive statistical analysis of the relative phasing of DO transitions in Ca2+ and Na+ concentration records from the NGRIP ice core for the period 60–10 kyr BP. Regarding the time lags identified in this period as a sample generated from an unknown population, we derive probability density functions for the sample and population mean and test the null-hypothesis of a simultaneous transition. Special attention was paid to the uncertainties inherent to the transition onset detection in noisy data. Their rigorous propagation changes the test results from significant to non-significant and therefore a purely stochastic origin of the observed tendency for Ca2+ to lead the transition cannot be ruled out. In fact, we show that the data is very likely to comprise both: DO events that were led by a Ca2+ transition, as well as events led by a Na+ transition. Together, these findings clearly contradict a systematic lead or lag between the DO transitions in the two proxies, and the apparent Ca2+ lead should therefore not be interpreted as indication of a causal relationship. Under the assumption that all DO events followed the same physical mechanism and that the proxy interpretation holds true, the we conclude that at DO transition onsets, neither was the atmospheric reorganization caused by sea ice retreat, nor was the sea ice retreat triggered by atmospheric reorganization.
{"title":"A statistical approach to the phasing of atmospheric reorganization\u0000and sea ice retreat at the onset of Dansgaard-Oeschger events under\u0000rigorous treatment of uncertainties","authors":"Keno Riechers, N. Boers","doi":"10.5194/cp-2020-136","DOIUrl":"https://doi.org/10.5194/cp-2020-136","url":null,"abstract":"Abstract. For previous glacial intervals, concomitant shifts in different proxy records from Greenland ice cores indicate repeated abrupt climate transitions comprising – among others – abrupt warming, a sudden reorganization of the atmospheric circulation, and a retreat of perannial sea ice. The physical mechanism underlying these so-called Dansgaard-Oeschger (DO) events remains debated. Former studies have made an effort to deduce the progression of temperature, circulation, and sea-ice changes at the onset of DO events from paleoclimate proxy records to constrain potential triggering mechanisms. In this context, recent research reports on systematically delayed transitions in Na+ concentrations and δ18O values compared to Ca2+ concentrations and the annual layer thickness by about one decade. This is interpreted as a temporal lag of sea ice retreat and Greenland warming with respect to atmospheric reorganization at the onset of DO-events. Here, we present a comprehensive statistical analysis of the relative phasing of DO transitions in Ca2+ and Na+ concentration records from the NGRIP ice core for the period 60–10 kyr BP. Regarding the time lags identified in this period as a sample generated from an unknown population, we derive probability density functions for the sample and population mean and test the null-hypothesis of a simultaneous transition. Special attention was paid to the uncertainties inherent to the transition onset detection in noisy data. Their rigorous propagation changes the test results from significant to non-significant and therefore a purely stochastic origin of the observed tendency for Ca2+ to lead the transition cannot be ruled out. In fact, we show that the data is very likely to comprise both: DO events that were led by a Ca2+ transition, as well as events led by a Na+ transition. Together, these findings clearly contradict a systematic lead or lag between the DO transitions in the two proxies, and the apparent Ca2+ lead should therefore not be interpreted as indication of a causal relationship. Under the assumption that all DO events followed the same physical mechanism and that the proxy interpretation holds true, the we conclude that at DO transition onsets, neither was the atmospheric reorganization caused by sea ice retreat, nor was the sea ice retreat triggered by atmospheric reorganization.","PeriodicalId":263057,"journal":{"name":"Climate of The Past Discussions","volume":"30 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-11-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129757848","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
N. Scroxton, N. Scroxton, N. Scroxton, S. Burns, D. McGee, L. Godfrey, Lovasoa Ranivoharimanana, P. Faina
Abstract. The decline of the Mature Harappan period of the Harappan civilization in and around the Indus Valley between 4.3 and 3.9 kyr BP, its transition to the Late Harappan and subsequent abandonment by 3.0 kyr BP are frequently attributed to a reduction in summer monsoon rainfall associated with the 4.2 kyr event (4.26–3.97 kyr BP). Yet while the 4.2 kyr event is well documented in the Mediterranean and Middle East, its global footprint is undetermined, and its impact on monsoon rainfall largely unexplored. In this study we investigate the spatial and temporal variability of the tropical circum-Indian ocean hydroclimate in the mid to late Holocene. We conducted Monte-Carlo principal component analysis, taking into account full age uncertainty, on ten high-resolution, precisely dated paleohydroclimate records from the circum-Indian Ocean basin, all growing continuously or almost continuously between 5 and 3 kyr BP. The results indicate the dominant mode of variability in the region was a drying between 3.967 kyr BP (±0.095 kyr standard error) and 3.712 kyr BP (±0.092 kyr standard error) with dry conditions lasting for at least 300 years in some records, but a permanent change in others. We interpret PC1 and the drying event as a proxy of summer monsoon variability. A more abrupt event from 4.2 to 3.9 kyr BP is seen locally in individual records, but is often not of unusual magnitude, lacks regional coherence and is of minor importance to the principal component analysis. This result does not fit the prevailing narrative of a summer monsoon drought at the 4.2 kyr event contributing to the decline of Harappan civilisation. Instead we present the Double Drought Hypothesis . A comparison of existing Indian subcontinent paleoclimate records, modern climatology, the spatial and temporal evolution of Harappan archaeological sites, and upstream climatic variability in the Indian Ocean and Mediterranean and Middle East indicates two consecutive droughts were contributing factors in the decline of the Harappan. The first drought was an abrupt 300-year long winter rainfall drought between 4.26 and 3.97 kyr BP, associated with the 4.2 kyr event, propagated from the Mediterranean and Middle East. This led to Harappan site abandonment in the Indus valley and the end of Mature Harappan period. The second drought was a more gradual but longer lasting reduction in summer monsoon rainfall beginning 3.97 kyr BP leading to the further site abandonment at sites in Gujarat, a transition towards a more rural society, and the end of the Late Harappan. The consequences for the new mid to late Holocene Global Boundary Stratotype Section and Point in a stalagmite from Meghalaya are explored.
{"title":"Circum-Indian ocean hydroclimate at the mid to late Holocene\u0000transition: The Double Drought hypothesis and consequences for the\u0000Harappan","authors":"N. Scroxton, N. Scroxton, N. Scroxton, S. Burns, D. McGee, L. Godfrey, Lovasoa Ranivoharimanana, P. Faina","doi":"10.5194/cp-2020-138","DOIUrl":"https://doi.org/10.5194/cp-2020-138","url":null,"abstract":"Abstract. The decline of the Mature Harappan period of the Harappan civilization in and around the Indus Valley between 4.3 and 3.9 kyr BP, its transition to the Late Harappan and subsequent abandonment by 3.0 kyr BP are frequently attributed to a reduction in summer monsoon rainfall associated with the 4.2 kyr event (4.26–3.97 kyr BP). Yet while the 4.2 kyr event is well documented in the Mediterranean and Middle East, its global footprint is undetermined, and its impact on monsoon rainfall largely unexplored. In this study we investigate the spatial and temporal variability of the tropical circum-Indian ocean hydroclimate in the mid to late Holocene. We conducted Monte-Carlo principal component analysis, taking into account full age uncertainty, on ten high-resolution, precisely dated paleohydroclimate records from the circum-Indian Ocean basin, all growing continuously or almost continuously between 5 and 3 kyr BP. The results indicate the dominant mode of variability in the region was a drying between 3.967 kyr BP (±0.095 kyr standard error) and 3.712 kyr BP (±0.092 kyr standard error) with dry conditions lasting for at least 300 years in some records, but a permanent change in others. We interpret PC1 and the drying event as a proxy of summer monsoon variability. A more abrupt event from 4.2 to 3.9 kyr BP is seen locally in individual records, but is often not of unusual magnitude, lacks regional coherence and is of minor importance to the principal component analysis. This result does not fit the prevailing narrative of a summer monsoon drought at the 4.2 kyr event contributing to the decline of Harappan civilisation. Instead we present the Double Drought Hypothesis . A comparison of existing Indian subcontinent paleoclimate records, modern climatology, the spatial and temporal evolution of Harappan archaeological sites, and upstream climatic variability in the Indian Ocean and Mediterranean and Middle East indicates two consecutive droughts were contributing factors in the decline of the Harappan. The first drought was an abrupt 300-year long winter rainfall drought between 4.26 and 3.97 kyr BP, associated with the 4.2 kyr event, propagated from the Mediterranean and Middle East. This led to Harappan site abandonment in the Indus valley and the end of Mature Harappan period. The second drought was a more gradual but longer lasting reduction in summer monsoon rainfall beginning 3.97 kyr BP leading to the further site abandonment at sites in Gujarat, a transition towards a more rural society, and the end of the Late Harappan. The consequences for the new mid to late Holocene Global Boundary Stratotype Section and Point in a stalagmite from Meghalaya are explored.","PeriodicalId":263057,"journal":{"name":"Climate of The Past Discussions","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-11-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128814208","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
N. Scroxton, N. Scroxton, N. Scroxton, S. Burns, D. McGee, L. Godfrey, Lovasoa Ranivoharimanana, P. Faina
Abstract. The 4.2 kyr event is regarded as one of the largest and best documented abrupt climate disturbances of the Holocene. Drying across the Mediterranean and Middle East is well established and is linked to societal transitions in the Akkadian, Egyptian and Harappan civilizations. Yet the impacts of this regional drought are often extended to other regions and sometimes globally. In particular, the nature and spatial extent of the 4.2 kyr event in the tropics have not been established. Here, we present a new stalagmite stable isotope record from Anjohikely, northwest Madagascar. Growing between 5 and 2 kyr BP, stalagmite AK1 shows a hiatus between 4.32 and 3.83 kyr BP, replicating a hiatus in another stalagmite from nearby Anjohibe, and therefore indicating a significant drought around the time of the 4.2 kyr event. This result is the opposite to wet conditions at 8.2 kyr BP, suggesting fundamentally different forcing mechanisms. Elsewhere in the south-east African monsoon domain dry conditions are also recorded in sediment cores in Lake Malawi and Lake Masoko and the Taros Basin on Mauritius. However, at the peripheries of the monsoon domain, drying is not observed. At the northern (equatorial East Africa) and eastern (Rodrigues) peripheries, no notable event is record. At the southern periphery a wet event is recorded in stalagmites at Cold Air Cave and sediment cores at Lake Muzi and Mkhuze Delta. The spatial pattern is largely consistent with the modern rainfall anomaly pattern associated with weak Mozambique Channel Trough and a northerly austral summer Inter Tropical Convergence Zone position. Within age error, the observed peak climate anomalies are consistent with the 4.2 kyr event. However, outside Madagascar, regional hydrological change is consistently earlier than a 4.26 kyr BP event onset. Gradual hydrological change frequently begins at 4.6 kyr BP, raising doubt as to whether any coherent regional hydrological change is merely coincident with the 4.2 kyr event rather than part of a global climatic anomaly.
{"title":"Possible expression of the 4.2 kyr event in Madagascar and the south-east\u0000African monsoon","authors":"N. Scroxton, N. Scroxton, N. Scroxton, S. Burns, D. McGee, L. Godfrey, Lovasoa Ranivoharimanana, P. Faina","doi":"10.5194/cp-2020-137","DOIUrl":"https://doi.org/10.5194/cp-2020-137","url":null,"abstract":"Abstract. The 4.2 kyr event is regarded as one of the largest and best documented abrupt climate disturbances of the Holocene. Drying across the Mediterranean and Middle East is well established and is linked to societal transitions in the Akkadian, Egyptian and Harappan civilizations. Yet the impacts of this regional drought are often extended to other regions and sometimes globally. In particular, the nature and spatial extent of the 4.2 kyr event in the tropics have not been established. Here, we present a new stalagmite stable isotope record from Anjohikely, northwest Madagascar. Growing between 5 and 2 kyr BP, stalagmite AK1 shows a hiatus between 4.32 and 3.83 kyr BP, replicating a hiatus in another stalagmite from nearby Anjohibe, and therefore indicating a significant drought around the time of the 4.2 kyr event. This result is the opposite to wet conditions at 8.2 kyr BP, suggesting fundamentally different forcing mechanisms. Elsewhere in the south-east African monsoon domain dry conditions are also recorded in sediment cores in Lake Malawi and Lake Masoko and the Taros Basin on Mauritius. However, at the peripheries of the monsoon domain, drying is not observed. At the northern (equatorial East Africa) and eastern (Rodrigues) peripheries, no notable event is record. At the southern periphery a wet event is recorded in stalagmites at Cold Air Cave and sediment cores at Lake Muzi and Mkhuze Delta. The spatial pattern is largely consistent with the modern rainfall anomaly pattern associated with weak Mozambique Channel Trough and a northerly austral summer Inter Tropical Convergence Zone position. Within age error, the observed peak climate anomalies are consistent with the 4.2 kyr event. However, outside Madagascar, regional hydrological change is consistently earlier than a 4.26 kyr BP event onset. Gradual hydrological change frequently begins at 4.6 kyr BP, raising doubt as to whether any coherent regional hydrological change is merely coincident with the 4.2 kyr event rather than part of a global climatic anomaly.","PeriodicalId":263057,"journal":{"name":"Climate of The Past Discussions","volume":"31 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-11-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124927490","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract. The speleothems are an important source of paleoclimatic information in the land environment. The basic advantages of speleothems are the high potential of preservation; the possibility of precise dating by the U-series method; many different proxies like stable isotopes, trace elements, and microfabric which can be interpreted in the term of paleoclimate. The JS9 stalagmite was collected in Demanova Cave System (Slovakia). Presently this region of Europe is under influence of transitional and continental climate. However, in the past, it could be under stronger influence of the continental climate during cold glacial episodes and under wetter transitional climate during interglacial. The multiproxy record of the JS9 stalagmite represents ca. 60 ka period (143–83 ka). The multiproxy interpretation of the JS9 record shows that long time tendencies of δ18O have thermal nature while the short time δ18O signal reflects changes in humidity. In opposition to the records from the Alps and the northern Tatra mountains, the δ18O record of JS9 has instant decrease episodes during Termination II.
摘要洞穴主题是陆地环境古气候信息的重要来源。洞穴遗址的基本优势是具有较高的保存潜力;用u系列法精确定年的可能性;许多不同的代用品，如稳定同位素、微量元素和微结构，都可以用古气候的术语来解释。JS9石笋采集于斯洛伐克的Demanova洞穴系统。目前，欧洲的这一地区受到过渡性和大陆性气候的影响。而在过去，冷冰期受大陆气候的影响较大，间冰期受湿润过渡性气候的影响较大。JS9石笋的多代记录约为60 ka (143 ~ 83 ka)。JS9记录的多代理解释表明，长时间δ18O信号具有热性，短时间δ18O信号反映了湿度的变化。与阿尔卑斯山脉和北塔特拉山脉的记录相反，JS9的δ18O记录在终止II期间有瞬间减小的插曲。
{"title":"Speleothem oxygen record – thermal or moisture changes proxy? A\u0000case study of multiproxy record from MIS 5/MIS 6 age speleothems\u0000from Demänová Cave System","authors":"J. Pawlak","doi":"10.5194/cp-2020-125","DOIUrl":"https://doi.org/10.5194/cp-2020-125","url":null,"abstract":"Abstract. The speleothems are an important source of paleoclimatic information in the land environment. The basic advantages of speleothems are the high potential of preservation; the possibility of precise dating by the U-series method; many different proxies like stable isotopes, trace elements, and microfabric which can be interpreted in the term of paleoclimate. The JS9 stalagmite was collected in Demanova Cave System (Slovakia). Presently this region of Europe is under influence of transitional and continental climate. However, in the past, it could be under stronger influence of the continental climate during cold glacial episodes and under wetter transitional climate during interglacial. The multiproxy record of the JS9 stalagmite represents ca. 60 ka period (143–83 ka). The multiproxy interpretation of the JS9 record shows that long time tendencies of δ18O have thermal nature while the short time δ18O signal reflects changes in humidity. In opposition to the records from the Alps and the northern Tatra mountains, the δ18O record of JS9 has instant decrease episodes during Termination II.","PeriodicalId":263057,"journal":{"name":"Climate of The Past Discussions","volume":"25 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-10-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125797403","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
P. Strobel, M. Bliedtner, A. Carr, P. Frenzel, B. Klaes, G. Salazar, J. Struck, S. Szidat, R. Zech, T. Haberzettl
Abstract. South Africa is a key region for paleoclimate studies reconstructing and understanding past changes in atmospheric circulation, i.e., temperate Westerlies and tropical Easterlies. However, due to the scarcity of natural archives, the environmental evolution during the late Quaternary remains highly debated. Many archives that are available are peri-coastal lakes and wetlands and sea level changes during the Holocene often overprinted the paleoenvironmental signals in these archives. This study presents a new record from the coastal wetland Voёlvlei, which is an intermittent lake situated in the year-round rainfall zone (YRZ) of South Africa at the southern Cape coast. It presents an ideal archive to investigate both sea level and environmental changes. A 13 m-long sediment core was retrieved from Voёlvlei and analysed using a multi-proxy approach. The chronology reveals a basal age of 8,440+200/−250 cal BP. Paleoecological and elemental analyses indicate marine intrusions from 8,440 to 7,000 cal BP with a salinity optimum at 7,030+150/−190 cal BP. Since 6,000 cal BP, silting up has been causing an intermittent freshwater lake. Inferred from changes in allochthonous input, δ13Cn-alkane and δ2Hn-alkane increasing moisture is observed from 8,440+200/−250 cal BP. The δ2Hn-alkane record provides new evidence in contribution of different precipitation sources throughout the record with contributions from both Westerlies and Easterlies from 8,440 to 7,070 cal BP. Westerlies dominate from 7,070 to 6,420 cal BP followed by a distinct shift to an Easterly-dominance at 6,420 cal BP. An overall trend to a Westerly-lasting until 2,060 cal BP is followed by a trend towards an Easterlies-dominance, but both phases show several climatic spikes. Those spikes are also evident in other regional studies highlighting that the source and seasonality of precipitation has a mayor role for the hydrological balance. By comparing the Voёlvlei record with other regional studies, a similar trend in the overall moisture evolution along the southern Cape coast is inferred during the past 8.500 yrs.
摘要南非是古气候研究重建和理解过去大气环流变化的关键地区，即温带西风带和热带东风带。然而，由于自然档案的缺乏，晚第四纪的环境演变仍然存在很大的争议。现有的许多档案都是沿海湖泊和湿地，全新世的海平面变化往往叠加了这些档案中的古环境信号。本研究提出了沿海湿地Voёlvlei的新记录，这是一个位于南非南部开普海岸全年降雨带(YRZ)的间歇性湖泊。它是研究海平面和环境变化的理想资料。从Voёlvlei获取了一个13米长的沉积物岩心，并使用多代理方法进行了分析。年代学显示其基本年龄为8,440+200/ - 250 cal BP。古生态和元素分析表明，海相侵入范围为8,440 ~ 7,000 cal BP，盐度最佳值为7,030+150/ - 190 cal BP。从6000年前开始，淤积形成了一个间歇的淡水湖。从异源输入的变化推断，δ 13cn -烷烃和δ 2hn -烷烃在8,440+200/−250 cal BP开始增加水分。δ 2n -烷烃记录在8440 ~ 7070 cal BP期间提供了不同降水源贡献的新证据，其中西风带和东风都有贡献。在7070 ~ 6420 cal BP期间，西风带为主，在6420 cal BP期间，西风带明显转向东风为主。总体趋势是西风为主——持续到2060 cal BP，之后是东风为主的趋势，但这两个阶段都显示了几个气候尖峰。这些峰值在其他区域研究中也很明显，强调降水的来源和季节性对水文平衡起着重要作用。通过将Voёlvlei记录与其他区域研究进行比较，可以推断出在过去8500年里，南开普海岸的总体湿度演变趋势类似。
{"title":"Holocene sea level and environmental change at the southern Cape –\u0000an 8.5 kyr multi-proxy paleoclimate record from lake Voёlvlei, South\u0000Africa","authors":"P. Strobel, M. Bliedtner, A. Carr, P. Frenzel, B. Klaes, G. Salazar, J. Struck, S. Szidat, R. Zech, T. Haberzettl","doi":"10.5194/cp-2020-130","DOIUrl":"https://doi.org/10.5194/cp-2020-130","url":null,"abstract":"Abstract. South Africa is a key region for paleoclimate studies reconstructing and understanding past changes in atmospheric circulation, i.e., temperate Westerlies and tropical Easterlies. However, due to the scarcity of natural archives, the environmental evolution during the late Quaternary remains highly debated. Many archives that are available are peri-coastal lakes and wetlands and sea level changes during the Holocene often overprinted the paleoenvironmental signals in these archives. This study presents a new record from the coastal wetland Voёlvlei, which is an intermittent lake situated in the year-round rainfall zone (YRZ) of South Africa at the southern Cape coast. It presents an ideal archive to investigate both sea level and environmental changes. A 13 m-long sediment core was retrieved from Voёlvlei and analysed using a multi-proxy approach. The chronology reveals a basal age of 8,440+200/−250 cal BP. Paleoecological and elemental analyses indicate marine intrusions from 8,440 to 7,000 cal BP with a salinity optimum at 7,030+150/−190 cal BP. Since 6,000 cal BP, silting up has been causing an intermittent freshwater lake. Inferred from changes in allochthonous input, δ13Cn-alkane and δ2Hn-alkane increasing moisture is observed from 8,440+200/−250 cal BP. The δ2Hn-alkane record provides new evidence in contribution of different precipitation sources throughout the record with contributions from both Westerlies and Easterlies from 8,440 to 7,070 cal BP. Westerlies dominate from 7,070 to 6,420 cal BP followed by a distinct shift to an Easterly-dominance at 6,420 cal BP. An overall trend to a Westerly-lasting until 2,060 cal BP is followed by a trend towards an Easterlies-dominance, but both phases show several climatic spikes. Those spikes are also evident in other regional studies highlighting that the source and seasonality of precipitation has a mayor role for the hydrological balance. By comparing the Voёlvlei record with other regional studies, a similar trend in the overall moisture evolution along the southern Cape coast is inferred during the past 8.500 yrs.","PeriodicalId":263057,"journal":{"name":"Climate of The Past Discussions","volume":"12 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-10-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127004206","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
F. Pöppelmeier, J. Scheen, A. Jeltsch-Thömmes, T. Stocker
Abstract. The response of the Atlantic Meridional Overturning Circulation (AMOC) to freshwater perturbations critically depends on its mean-state. Large swaths of icebergs melting in the North Atlantic during the last deglaciation constituted such perturbations, and thus can provide important constraints on the stability of the AMOC. Yet, the mean AMOC state during the Last Glacial Maximum (LGM), preceding the rapid disintegration of the ice-sheets during the deglaciation, as well as its response to these perturbations remain debated. Here we investigate the evolution of the AMOC responding to freshwater perturbations under improved LGM boundary conditions in the Bern3D intermediate complexity model. Particularly, we consider the effect of an open versus a closed Bering Strait. The vigorous and deep AMOC under these glacial boundary conditions, consistent with previous simulations with different models, reacts more strongly to North Atlantic freshwater forcings than under pre-industrial conditions. This increased sensitivity is mostly related to the closed Bering Strait that cuts off the freshwater escape route through the Arctic into the Pacific, thus facilitating faster accumulation of freshwater in the North Atlantic halting deep water formation. Proxy reconstructions of the LGM AMOC instead indicate a weaker and possibly shallower AMOC than today, in conflict with the particularly strong and deep circulation states coherently simulated with ocean circulation models for the LGM. Simulations with reduced North Atlantic deep water formation, as a consequence of potentially increased continental runoff from ice-sheet melt and imposed changes in the hydrological cycle, more closely resemble the overturning circulation inferred from proxies. These circulation states also show bistable behavior, where the AMOC does not recover after North Atlantic freshwater hosing. However, no AMOC states are found here that either comprise an extreme shoaling or vigorous and concurrent shallow overturning as previously proposed based on paleoceanographic data.
{"title":"Simulated stability of the AMOC during the Last Glacial Maximum\u0000under realistic boundary conditions","authors":"F. Pöppelmeier, J. Scheen, A. Jeltsch-Thömmes, T. Stocker","doi":"10.5194/cp-2020-135","DOIUrl":"https://doi.org/10.5194/cp-2020-135","url":null,"abstract":"Abstract. The response of the Atlantic Meridional Overturning Circulation (AMOC) to freshwater perturbations critically depends on its mean-state. Large swaths of icebergs melting in the North Atlantic during the last deglaciation constituted such perturbations, and thus can provide important constraints on the stability of the AMOC. Yet, the mean AMOC state during the Last Glacial Maximum (LGM), preceding the rapid disintegration of the ice-sheets during the deglaciation, as well as its response to these perturbations remain debated. Here we investigate the evolution of the AMOC responding to freshwater perturbations under improved LGM boundary conditions in the Bern3D intermediate complexity model. Particularly, we consider the effect of an open versus a closed Bering Strait. The vigorous and deep AMOC under these glacial boundary conditions, consistent with previous simulations with different models, reacts more strongly to North Atlantic freshwater forcings than under pre-industrial conditions. This increased sensitivity is mostly related to the closed Bering Strait that cuts off the freshwater escape route through the Arctic into the Pacific, thus facilitating faster accumulation of freshwater in the North Atlantic halting deep water formation. Proxy reconstructions of the LGM AMOC instead indicate a weaker and possibly shallower AMOC than today, in conflict with the particularly strong and deep circulation states coherently simulated with ocean circulation models for the LGM. Simulations with reduced North Atlantic deep water formation, as a consequence of potentially increased continental runoff from ice-sheet melt and imposed changes in the hydrological cycle, more closely resemble the overturning circulation inferred from proxies. These circulation states also show bistable behavior, where the AMOC does not recover after North Atlantic freshwater hosing. However, no AMOC states are found here that either comprise an extreme shoaling or vigorous and concurrent shallow overturning as previously proposed based on paleoceanographic data.","PeriodicalId":263057,"journal":{"name":"Climate of The Past Discussions","volume":"94 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-10-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128968706","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
F. Lindau, J. Simões, R. R. Ribeiro, P. Ginot, B. Delmonte, G. Baccolo, S. Kutuzov, V. Maggi, E. Ramírez
Abstract. Understanding the mechanisms controlling glacial retreat in the tropical Andes can strengthen future predictions of ice cover in the region. As glaciers are a dominant freshwater source in these regions, accurate ice cover predictions are necessary for developing effective strategies to protect future water resources. In this study, we investigated a 97-year dust record from two Nevado Illimani ice cores to determine the dominant factors controlling particle concentration and size distribution. In addition, we measured the area of a Nevado Illimani glacier (glacier n°8) using aerial photographs from 1956 and 2009. We identified two dustier periods during the 20th century (1930s–1940s and 1980s–2016), which were linked to reduced moisture transport from the Amazon basin. This promoted an unprecedented increase in the percentage of coarse dust particles (CPPn, ∅ > 10 μm) during the 1990s, as drier local conditions favored the emission and deposition of coarse particles on the glacier. Moisture advection from the Amazon basin to Nevado Illimani was influenced by tropical North Atlantic sea surface temperatures (TNA), which was supported by the correlation between TNA and CPPn (r = 0.52). Furthermore, glacial retreat has been accelerating since the 1980s, and a notable relationship between CPPn and the freezing level height (FLH, r = 0.41) was observed. This suggests that higher FLHs promote glacial retreat, which exposes fresh glacial sediments and facilitates the transport of coarse dust particles to the Nevado Illimani summit. Therefore, both the area of glacier n°8 and the ice core record of coarse dust particles were found to respond to climate variability—particularly to the warmer conditions across the southern tropical Andes and drier conditions over the Amazon basin.
摘要了解控制热带安第斯山脉冰川退缩的机制可以加强对该地区未来冰盖的预测。由于冰川是这些地区的主要淡水来源，准确的冰盖预测对于制定有效的战略来保护未来的水资源是必要的。在这项研究中，我们研究了来自内华达州伊伊马尼州两个冰芯的97年尘埃记录，以确定控制颗粒浓度和大小分布的主导因素。此外，我们使用1956年和2009年的航空照片测量了内华达伊伊马尼冰川(冰川n°8)的面积。我们确定了20世纪两个尘土较多的时期(20世纪30年代至40年代和20世纪80年代至2016年)，这与亚马逊盆地的水分输送减少有关。这促使粗尘颗粒百分比(CPPn，∅> 10 μm)在20世纪90年代空前增加，因为干燥的当地条件有利于粗尘颗粒在冰川上的排放和沉积。热带北大西洋海表温度(TNA)与CPPn的相关关系(r = 0.52)支持热带北大西洋海表温度(TNA)对亚马逊盆地至内华达州的水汽平流的影响。此外，自20世纪80年代以来，冰川退缩加速，CPPn与冻结高度呈显著相关(FLH, r = 0.41)。这表明较高的FLHs促进了冰川退缩，暴露了新鲜的冰川沉积物，并促进了粗尘颗粒向内华达伊伊马尼山顶的运输。因此，8°冰川的面积和粗尘颗粒的冰芯记录都被发现对气候变化做出了反应，特别是对热带安第斯山脉南部的温暖条件和亚马逊盆地的干燥条件。
{"title":"Dust record in an ice core from tropical Andes (Nevado Illimani – Bolivia), potential for climate variability analyses in the Amazon basin","authors":"F. Lindau, J. Simões, R. R. Ribeiro, P. Ginot, B. Delmonte, G. Baccolo, S. Kutuzov, V. Maggi, E. Ramírez","doi":"10.5194/cp-2020-129","DOIUrl":"https://doi.org/10.5194/cp-2020-129","url":null,"abstract":"Abstract. Understanding the mechanisms controlling glacial retreat in the tropical Andes can strengthen future predictions of ice cover in the region. As glaciers are a dominant freshwater source in these regions, accurate ice cover predictions are necessary for developing effective strategies to protect future water resources. In this study, we investigated a 97-year dust record from two Nevado Illimani ice cores to determine the dominant factors controlling particle concentration and size distribution. In addition, we measured the area of a Nevado Illimani glacier (glacier n°8) using aerial photographs from 1956 and 2009. We identified two dustier periods during the 20th century (1930s–1940s and 1980s–2016), which were linked to reduced moisture transport from the Amazon basin. This promoted an unprecedented increase in the percentage of coarse dust particles (CPPn, ∅ > 10 μm) during the 1990s, as drier local conditions favored the emission and deposition of coarse particles on the glacier. Moisture advection from the Amazon basin to Nevado Illimani was influenced by tropical North Atlantic sea surface temperatures (TNA), which was supported by the correlation between TNA and CPPn (r = 0.52). Furthermore, glacial retreat has been accelerating since the 1980s, and a notable relationship between CPPn and the freezing level height (FLH, r = 0.41) was observed. This suggests that higher FLHs promote glacial retreat, which exposes fresh glacial sediments and facilitates the transport of coarse dust particles to the Nevado Illimani summit. Therefore, both the area of glacier n°8 and the ice core record of coarse dust particles were found to respond to climate variability—particularly to the warmer conditions across the southern tropical Andes and drier conditions over the Amazon basin.","PeriodicalId":263057,"journal":{"name":"Climate of The Past Discussions","volume":"44 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-10-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115656798","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
N. Young, A. Lesnek, J. Cuzzone, J. Briner, J. Badgeley, Alexandra Balter-Kennedy, B. Graham, A. Cluett, J. Lamp, R. Schwartz, T. Tuna, E. Bard, M. Caffee, S. Zimmerman, J. Schaefer
Abstract. During the middle to late Holocene (8.2 ka BP to present), the Greenland Ice Sheet (GrIS) was smaller than its current configuration. Determining the exact dimensions of the Holocene ice-sheet minimum and the duration that the ice margin rested inboard of its current position remains challenging. Contemporary retreat of the GrIS from its historical maximum extent in southwestern Greenland is exposing a landscape that holds clues regarding the configuration and timing of past ice-sheet minima. To quantify the duration of the time the GrIS margin was near its modern extent we develop a new technique on Greenland that utilizes in situ cosmogenic 10Be-14C-26Al in bedrock samples that have become ice free only in the last few decades by the retreating ice-sheet margin at Kangiata Nunaata Sermia (n = 12 sites; KNS), southwest Greenland. To maximize the utility of this approach, we refine the deglaciation history of the region with stand-alone 10Be measurements (n = 49) and traditional 14C ages from sedimentary deposits contained in proglacial-threshold lakes. We combine our reconstructed ice-margin history in the KNS region with additional geologic records from southwestern Greenland and recent model simulations of GrIS change, to constrain the timing of the GrIS minimum in southwest Greenland, the magnitude of Holocene inland GrIS retreat, and explore the regional climate history influencing Holocene ice-sheet behavior. Our 10Be-14C-26Al measurements reveal that 1) KNS retreated behind its modern margin just before 10 ka, but likely stabilized near the present GrIS margin for several thousand years before retreating farther inland, and 2) pre-Holocene 10Be detected in several of our sample sites is most easily explained by several thousand years of surface exposure during the Last Interglaciation. Moreover, our new results indicate that the minimum extent of the GrIS likely occurred after ~ 5 ka, and the GrIS margin may have approached its eventual historical maximum extent as early as ~ 2 ka. Recent simulations of GrIS change are able to match the geologic record of ice-sheet change in regions dominated by surface mass balance, but produce a poorer model-data fit in areas influenced by oceanic and dynamic processes. Simulations that achieve the best model-data fit suggest that inland retreat of the ice margin driven by early to middle Holocene warmth may have been mitigated by increased precipitation. Triple 10Be-14C-26Al measurements in recently deglaciated bedrock provide a new tool to help decipher the duration of smaller-than-present ice over multiple timescales. Modern retreat of the GrIS margin in southwest Greenland is revealing a bedrock landscape that was also exposed during the migration of the GrIS margin towards its Holocene minimum extent, but has yet to tap into a landscape that remained ice covered throughout the entire Holocene.
{"title":"Cosmogenic isotope measurements from recently deglaciated bedrock as a new tool to decipher changes in Greenland Ice Sheet size","authors":"N. Young, A. Lesnek, J. Cuzzone, J. Briner, J. Badgeley, Alexandra Balter-Kennedy, B. Graham, A. Cluett, J. Lamp, R. Schwartz, T. Tuna, E. Bard, M. Caffee, S. Zimmerman, J. Schaefer","doi":"10.5194/cp-2020-111","DOIUrl":"https://doi.org/10.5194/cp-2020-111","url":null,"abstract":"Abstract. During the middle to late Holocene (8.2 ka BP to present), the Greenland Ice Sheet (GrIS) was smaller than its current configuration. Determining the exact dimensions of the Holocene ice-sheet minimum and the duration that the ice margin rested inboard of its current position remains challenging. Contemporary retreat of the GrIS from its historical maximum extent in southwestern Greenland is exposing a landscape that holds clues regarding the configuration and timing of past ice-sheet minima. To quantify the duration of the time the GrIS margin was near its modern extent we develop a new technique on Greenland that utilizes in situ cosmogenic 10Be-14C-26Al in bedrock samples that have become ice free only in the last few decades by the retreating ice-sheet margin at Kangiata Nunaata Sermia (n = 12 sites; KNS), southwest Greenland. To maximize the utility of this approach, we refine the deglaciation history of the region with stand-alone 10Be measurements (n = 49) and traditional 14C ages from sedimentary deposits contained in proglacial-threshold lakes. We combine our reconstructed ice-margin history in the KNS region with additional geologic records from southwestern Greenland and recent model simulations of GrIS change, to constrain the timing of the GrIS minimum in southwest Greenland, the magnitude of Holocene inland GrIS retreat, and explore the regional climate history influencing Holocene ice-sheet behavior. Our 10Be-14C-26Al measurements reveal that 1) KNS retreated behind its modern margin just before 10 ka, but likely stabilized near the present GrIS margin for several thousand years before retreating farther inland, and 2) pre-Holocene 10Be detected in several of our sample sites is most easily explained by several thousand years of surface exposure during the Last Interglaciation. Moreover, our new results indicate that the minimum extent of the GrIS likely occurred after ~ 5 ka, and the GrIS margin may have approached its eventual historical maximum extent as early as ~ 2 ka. Recent simulations of GrIS change are able to match the geologic record of ice-sheet change in regions dominated by surface mass balance, but produce a poorer model-data fit in areas influenced by oceanic and dynamic processes. Simulations that achieve the best model-data fit suggest that inland retreat of the ice margin driven by early to middle Holocene warmth may have been mitigated by increased precipitation. Triple 10Be-14C-26Al measurements in recently deglaciated bedrock provide a new tool to help decipher the duration of smaller-than-present ice over multiple timescales. Modern retreat of the GrIS margin in southwest Greenland is revealing a bedrock landscape that was also exposed during the migration of the GrIS margin towards its Holocene minimum extent, but has yet to tap into a landscape that remained ice covered throughout the entire Holocene.","PeriodicalId":263057,"journal":{"name":"Climate of The Past Discussions","volume":"37 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-09-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114152659","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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