Climate of The Past Discussions最新文献

{"title":"A 4000-year long Late Holocene climate record from Hermes Cave (Peloponnese, Greece)","authors":"T. Kluge, Tatjana S. Münster, N. Frank, E. Eiche, R. Mertz‐Kraus, D. Scholz, Martin Finné, I. Unkel","doi":"10.5194/cp-2020-47","DOIUrl":"https://doi.org/10.5194/cp-2020-47","url":null,"abstract":"Abstract. The societal and cultural development during the Bronze Age and the subsequent Iron Age was enormous in Greece, however interrupted by two significant transformations around 4200 years b2k (Early Helladic II/III; b2k refers to years before 2000 CE) and 3200 years b2k (end of Late Helladic III). Artefacts and building remains provide some insights into the cultural evolution, but only little is known about environmental and climatic changes on a detailed temporal and spatial scale. Here we present a 4000-year long stalagmite record (GH17-05) from Hermes Cave, Greece, located on Mount Ziria in the close vicinity of the Late Bronze Age citadel of Mycenae and the Classical-Hellenistic polis of Corinth. The cave was used in ancient times, as indicated by ceramic fragments in the entrance area and a pronounced soot layer in the stalagmite. 230Th-U dating provides age constraints for the growth of the stalagmite (continuous between ~ 800 and ~ 5300 years b2k) and the formation of a soot layer (2.5+0.5-0.65 ka b2k). Speleothem δ18O and δ13C values together with clumped isotopes and elemental ratios provide a detailed paleoclimate record of the Northern Peloponnese. The proxy data suggest significant centennial scale climate variability (i.e., wet vs. dry). Furthermore, carbonate δ18O values, calculated drip water δ18O values, 234U/238U activity ratios and elemental ratios suggest a long-term trend towards drier conditions from ca 3.7 to ~ 2.0 ka b2k. From 2.0 ka b2k towards growth stop of the stalagmite, a trend towards wetter conditions is observed. A high degree of correlation was found for isotope trends of different speleothems from the Peloponnese and partially with climate records from the Eastern Mediterranean, whereas speleothems and lake records with a larger distance to the Peloponnese show little correlation or even opposing trends.","PeriodicalId":263057,"journal":{"name":"Climate of The Past Discussions","volume":"12 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-05-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129693412","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}

{"title":"Holocene glaciation in the Rwenzori Mountains, Uganda","authors":"M. Jackson, M. Kelly, J. Russell, A. Doughty, J. A. Howley, S. Zimmerman, B. Nakileza","doi":"10.5194/cp-2020-61","DOIUrl":"https://doi.org/10.5194/cp-2020-61","url":null,"abstract":"Abstract. Tropical glaciers are retreating rapidly, threatening alpine ecosystems across the low latitudes. Understanding how tropical glaciers responded to past periods of warming is crucial for predicting and adapting to future climate change, yet relatively little is known about glacial fluctuations in tropical regions during the recent past (i.e., the Holocene Epoch). This is particularly true in the African tropics, where data constraining the timing and magnitude of Holocene glacial fluctuations in the region are sparse and where temperatures during the middle Holocene were perhaps as warm as or warmer than today. Here we present new beryllium-10 surface-exposure ages that constrain Holocene glacial extents in the equatorial Rwenzori Mountains, Uganda. These results document rapid Early Holocene (~11.7–8.2 ka) glacial retreat in two separate catchments and indicate that Late Holocene (~4.2 ka-present) deposits mark the greatest expansion of Rwenzori glaciers during the last ~11 ka. Holocene glacial fluctuations elsewhere in tropical Africa and in tropical South America are broadly similar to those in the Rwenzori, with most tropical glaciers retreating rapidly during the Early Holocene and remaining near or inboard of their Late Holocene positions through much of Holocene time. The similarity of Holocene glacial fluctuations across the tropics implies that low-latitude glaciers responded to a common forcing mechanism, most likely temperature. Although the drivers of Holocene temperature changes in the tropics remains enigmatic, these data help constrain the expression of tropical temperature changes in the low latitudes.","PeriodicalId":263057,"journal":{"name":"Climate of The Past Discussions","volume":"105 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-05-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131528240","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}

{"title":"Examining the role of varying surface pressure in the climate of early Earth","authors":"J. Xiong, Jun Yang","doi":"10.5194/cp-2020-55","DOIUrl":"https://doi.org/10.5194/cp-2020-55","url":null,"abstract":"Abstract. During the Archean Eon in 2.7 billion years ago, solar luminosity was about 75 % of the present-day level, but the surface temperature was suggested to similar to or even higher than modern. What mechanisms act to maintain the temperate climate of early Earth is not clearly known yet. Recent studies suggested that surface air pressure was different from the present level. How does varying surface air pressure influence the climate? Using an atmospheric general circulation model coupled to a slab ocean with specified oceanic heat transport, we show that decreasing (increasing) surface pressure acts to cool (warm) the surface mainly because the greenhouse effect of pressure broadening becomes weaker (stronger). The effect of halfing or doubling the surface pressure on the global-mean surface temperature is about 10 K or even larger when ice albedo feedback or water vapor feedback is strong. If the surface pressure was 0.5 bar, a combination of a CO2 partial pressure of about 0.04 bar and an oceanic heat transport of twice the present-day level or a combination of a CO2 partial pressure of about 0.10 bar and an oceanic heat transport of half the present-day level is required to maintain a climate similar to modern, under a given CH4 partial pressure of 1 mbar. Future work with fully coupled atmosphere-ocean models is required to explore the strength of oceanic heat transport and with cloud resolving models to examine the strength of cloud radiative effect under different surface air pressures.\u0000","PeriodicalId":263057,"journal":{"name":"Climate of The Past Discussions","volume":"126 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-04-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125220982","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}

{"title":"Synergy of the westerly winds and monsoons in lake evolution of global closed basins since the Last Glacial Maximum","authors":"Yu Li, Yuxin Zhang","doi":"10.5194/cp-2020-53","DOIUrl":"https://doi.org/10.5194/cp-2020-53","url":null,"abstract":"Abstract. Monsoon system and westerly circulation, to which climate change responds differently, are two important components of global atmospheric circulation, interacting with each other in the mid-to-low latitudes and having synergy effect to those regions. Relevant researches on global millennial-scale climate change in monsoon and westerlies regions are mostly devoted to multi-proxy analyses of lakes, stalagmites, ice cores, marine and eolian sediments. Different responses from these proxies to long-term environmental change make understanding climate change pattern in monsoonal and westerlies regions difficult. Accordingly, we disaggregated global closed basins into areas governed by monsoon and westerly winds and unified palaeoclimate indicators, as well as combined with the lake models and paleoclimate simulations for tracking millennial-scale evolution characteristics and mechanisms of global monsoon and westerly winds since the Last Glacial Maximum (LGM). Our results concluded that the effective moisture in most closed basins of the mid-latitudes Northern Hemisphere is mainly a trend on the decrease since the LGM, and of the low-latitudes is mainly a trend on the rise. Millennial-scale water balance change exhibits an obvious boundary between global westerlies and monsoon regions in closed basins, particularly in the Northern Hemisphere. In the monsoon dominated closed basins of the Northern Hemisphere, humid climate prevails in the early-mid Holocene and relative dry climate appears in the LGM and late Holocene. While in the westerly winds dominated closed basins of the Northern Hemisphere, climate is characterized by relative humid LGM and mid-Holocene (MH) compared with the dry early Holocene, which is likely to be connected with precipitation brought by the westerly circulation. This study provides insights into long-term evolution and synergy of monsoon and westerly wind systems and basis for projection of future hydrological balance in the low-to-mid latitudes.","PeriodicalId":263057,"journal":{"name":"Climate of The Past Discussions","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-04-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129592469","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}

{"title":"Human response to severe drought in Early Modern Catalonia. The case of Barcelona, Western Mediterranean (1620–1650)","authors":"Santiago Gorostiza, Maria Antònia Martí i Escayol, M. Barriendos","doi":"10.5194/cp-2020-33","DOIUrl":"https://doi.org/10.5194/cp-2020-33","url":null,"abstract":"Abstract. Combining historical climatology and environmental history, this article examines the diverse range of strategies deployed by the city government of Barcelona to confront the recurrent drought episodes experienced between 1626 and 1650. First, our reconstruction of drought episodes for the period 1525–1821, based on pro pluvia rogations as documentary proxy data, identifies the years 1625–1635 and 1640–1650 as the most significative drought events of the period 1521–1825 (highest Drought Frequency Weighted Index of the series). Throughout the article, we focus on human responses to drought and discuss how water scarcity was perceived and confronted by Barcelona city authorities. We present the ambitious water supply projects launched by the city government, together with the construction of windmills as an alternative to watermills in order to mill grain, as attempts to cope with diminishing water flows. The context was aggravated by political instability, related first to the tensions between the centralising efforts of the Spanish King Philip IV and later to the impact of the Thirty Years’ War in the border region between the French and Spanish Crowns (1635–1659). Finally, we interpret the efforts of the city government to codify and appropriate knowledge about urban water supply as an attempt to systematise historical information on infrastructure to improve institutional capacities to cope with water scarcity in the future. These efforts materialised in the elaboration of the Llibre de les Fonts de la Ciutat de Barcelona (“Book of Fountains of the City of Barcelona”), a manual compiling the knowledge of Barcelona’s water supply from source to tap, written by the Barcelona water city officer in 1650, after three decades of experience in his post.","PeriodicalId":263057,"journal":{"name":"Climate of The Past Discussions","volume":"82 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-04-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126169124","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}

{"title":"Rapid waxing and waning of Beringian ice sheet reconcile glacial climate records from around North Pacific","authors":"Zhongshi Zhang, Q. Yan, Ran Zhang, F. Colleoni, G. Ramstein, Gaowen Dai, M. Jakobsson, M. O’Regan, S. Liess, D. Rousseau, N. Wu, E. Farmer, C. Contoux, Chuncheng Guo, N. Tan, Zhengtang Guo","doi":"10.5194/cp-2020-38","DOIUrl":"https://doi.org/10.5194/cp-2020-38","url":null,"abstract":"Abstract. Throughout the Pleistocene the Earth has experienced pronounced glacial-interglacial cycles, which have been debated for decades. One concept widely held is that during most glacials only the Laurentide-Eurasian ice sheets across North America and Northwest Eurasia became expansive, while Northeast Siberia-Beringia remained ice-sheet-free. However, the recognition of glacial landforms and deposits on Northeast Siberia-Beringia and off the Siberian continental shelf is beginning to call into question this paradigm. Here, we combine climate and ice sheet modelling with well-dated paleoclimate records from the mid-to-high latitude North Pacific to demonstrate the episodic occurrences of an ice sheet across Northeast Siberia-Beringia. Our simulations first show that the paleoclimate records are irreconcilable with the established paradigm of Laurentide-Eurasia-only ice sheets, and then reveal that a Beringian ice sheet over Northeast Siberia-Beringia causes feedbacks between atmosphere and ocean, the result of which better explains these climate records from around the North Pacific during the past four glacial-interglacial cycles. Our simulations propose an alternative scenario for NH ice sheet evolution, which involves the rapid waxing and waning of the Beringian ice sheet alongside the growth of the Laurentide-Eurasian ice sheets. The new scenario settles the long-standing discrepancies between the direct glacial evidence and the climate evolution from around the mid-to-high latitude North Pacific. It depicts a high complexity in glacial climates and has important implications for our understanding of the dispersal of prehistoric humans through Beringia into North America.","PeriodicalId":263057,"journal":{"name":"Climate of The Past Discussions","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-04-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130035445","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}

{"title":"Testing Hypotheses About Glacial Dynamics and the Stage 11 Paradox Using a Statistical Model of Paleo-Climate","authors":"R. Kaufmann, F. Pretis","doi":"10.5194/cp-2020-58","DOIUrl":"https://doi.org/10.5194/cp-2020-58","url":null,"abstract":"Abstract. To test hypotheses about glacial dynamics, the Mid-Brunhes event, and the stage 11 paradox, we evaluate the ability of a statistical model to simulate climate during the previous ~800 000 years. Throughout this period, the model simulates the timing and magnitude of glacial cycles, including the saw-tooth pattern in which ice accumulates gradually and ablates rapidly, without nonlinearities or threshold effects. This suggests that nonlinearities and/or threshold effects do not play a critical role in glacial cycles. Furthermore, model accuracy throughout the previous ~800 000 years suggest that changes in glacial cycles associated with the Mid-Brunhes event, which occurs near the division between the out-of-sample period and the in-sample period, are not caused by changes in the dynamics of the climate system. Conversely, poor model performance during MIS stage 11 and Termination V is consistent with arguments that the stage 11 paradox represents a mismatch between orbital geometry and climate. Statistical orderings of simulation errors indicate that periods of reduced accuracy start with significant reductions in the model's ability to simulate carbon dioxide, non-sea-salt sodium, and non-sea-salt calcium. Their importance suggests that the stage 11 paradox is generated by changes in atmospheric and/or oceanic circulation that affect ocean ventilation of carbon dioxide.","PeriodicalId":263057,"journal":{"name":"Climate of The Past Discussions","volume":"40 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124791668","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}

{"title":"Large scale climate signals of a European oxygen isotope network from tree-rings – predominantly caused by ENSO teleconnections?","authors":"Daniel F. Balting, M. Ionita, M. Wegmann, G. Helle, G. Schleser, N. Rimbu, Mandy B. Freund, I. Heinrich, Diana E. Caldarescu, Gerrit Lohmann","doi":"10.5194/cp-2020-39","DOIUrl":"https://doi.org/10.5194/cp-2020-39","url":null,"abstract":"Abstract. We investigate the annual variability of δ18O tree ring records from sites distributed all over Europe covering the last 400 years. An Empirical Orthogonal Function (EOF) analysis reveals two distinct modes of variability on the basis of the existing δ18O tree ring records. The first mode of δ18O variability is associated with anomaly patterns of the El Nino-Southern Oscillation (ENSO) and reflects a multi-seasonal climatic signal. The ENSO signal is visible for the last 130 years, but is found weak during the period 1600 to 1850 suggesting that the relationship between ENSO and the European climate may not stable over time. The second mode of δ18O variability, which captures an out-of-phase variability between northwestern and southeastern European δ18O tree ring records, is related to a regional summer atmospheric circulation pattern revealing a pronounced centre over the North Sea. Locally, the δ18O anomalies associated with this mode show the same (opposite) sign with temperature (precipitation). We infer that the investigation of large-scale atmospheric circulation patterns and related teleconnections far beyond instrumental records can be done with oxygen isotopic signature derived from tree rings. However, the European δ18Ocel tree network needs to be consolidated and updated, as well as additional research on the stationarity of reconstructed climate signals and the stationarity of teleconnections is advisable.","PeriodicalId":263057,"journal":{"name":"Climate of The Past Discussions","volume":"13 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-03-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127456811","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}

{"title":"Sampling density and date influence spatial representation of tree ring reconstructions","authors":"Justin T. Maxwell, G. Harley, T. Matheus, B. Strange, Kayla Van Aken, Tsun Fung Au, J. Bregy","doi":"10.5194/cp-2020-31","DOIUrl":"https://doi.org/10.5194/cp-2020-31","url":null,"abstract":"Abstract. Our understanding of the natural variability of hydroclimate before the instrumental period (ca. 1900 in the United States; US) is largely dependent on tree-ring-based reconstructions. Large-scale soil moisture reconstructions from a network of tree-ring chronologies have greatly improved our understanding of the spatial and temporal variability in hydroclimate conditions, particularly extremes of both drought and pluvial (wet) events. However, certain regions within these large-scale reconstructions in the US have a sparse network of tree-ring chronologies. Further, several chronologies were collected in the 1980s and 1990s, thus our understanding of the sensitivity of radial growth to soil moisture in the US is based on a period that experienced multiple extremely severe droughts and neglects the impacts of recent, rapid global change. In this study, we expanded the tree-ring network of the Ohio River Valley in the US, a region with sparse coverage. We used a total of 72 chronologies across 15 species to examine how increasing the density of the tree-ring network influences the representation of reconstructing the Palmer Meteorological Drought Index (PMDI). Further, we tested how the sampling date influenced the reconstruction models by creating reconstructions that ended in the year 1980 and compared them to reconstructions ending in 2010 from the same chronologies. We found that increasing the density of the tree-ring network resulted in reconstructed values that better matched the spatial variability of instrumentally recorded droughts and to a lesser extent, pluvials. By sampling tree in 2010 compared to 1980, the sensitivity of tree rings to PMDI decreased in the southern portion of our region where severe drought conditions have been absent over recent decades. We emphasize the need of building a high-density tree-ring network to better represent the spatial variability of past droughts and pluvials. Further, chronologies on the International Tree-Ring Data Bank need updating regularly to better understand how the sensitivity of tree rings to climate may vary through time.","PeriodicalId":263057,"journal":{"name":"Climate of The Past Discussions","volume":"31 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129493851","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}

{"title":"Evaluation of isotopes and elements in planktonic foraminifera from the Mediterranean Sea as recorders of seawater oxygen isotopes and salinity","authors":"Linda K. Dämmer, L. D. de Nooijer, E. van Sebille, Jan G. Haak, G. Reichart","doi":"10.5194/cp-2020-26","DOIUrl":"https://doi.org/10.5194/cp-2020-26","url":null,"abstract":"Abstract. The Mediterranean Sea is characterized by a relatively strong west to east salinity gradient, which makes it an area suitable to test the effect of salinity on foraminiferal shell geochemistry. We collected living specimens of the planktonic foraminifer Globigerinoides ruber (white) to analyse the relation between element/Ca ratios, stable oxygen isotopes of their shells and surface seawater salinity, isotopic composition and temperature. The oxygen isotopes of sea surface water correlate with salinity in the Mediterranean also during winter, when sampled for this study. Sea water oxygen and hydrogen isotopes are positively correlated in both the eastern and western Mediterranean Sea, though especially in the eastern part the relationship differs from values reported previously for that area. The slope between salinity and seawater oxygen isotopes is lower than previously published. Still, despite the rather modest slope, seawater and foraminiferal carbonate oxygen isotopes are correlated in our dataset although with large residuals and high residual variability. This scatter can be due to either biological variability in vital effects or environmental variability. Numerical models backtracking particles show ocean current driven mixing of particles of different origin might dampen sensitivity and could result in an offset caused by horizontal transport. Results show that Na/Ca is positively correlated to salinity and independent of temperature. Foraminiferal Mg/Ca increases with temperature, as expected, and in line with earlier calibrations, also in the high salinity environment. By using living foraminifera during winter, the previously established Mg/Ca-temperature calibration is extended to temperatures below 18 °C, which is a fundamental prerequisite of using single foraminifera for reconstructing past seasonality.","PeriodicalId":263057,"journal":{"name":"Climate of The Past Discussions","volume":"59 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-03-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114956198","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}