Abstract. An unusually severe hurricane (Louisbourg Storm) struck Nova Scotia, Canada, in 1757. Historic records describing storm conditions as well as damage to ships and coastal fortifications indicate an intensity beyond any modern (post-1851) Atlantic cyclones striking the same region, yet this storm struck during a cold climate period known as the Little Ice Age (LIA). Its track and timing coincided with a British naval blockade of a French fleet at Fortress Louisbourg during the Seven Years' War (1756–1763). This provides a unique opportunity to explore growing scientific evidence of heightened storminess in the North Atlantic despite a colder climate expected to suppress hurricane intensification but which research is increasingly showing to have supported North Atlantic storms of exceptional strength. Weather attributes extracted from the logs of naval vessels scattered by the Louisbourg Storm provided multiple hourly observations recorded at different locations. Wave height and wind force estimates at ship locations were compared to extreme storm surge heights calculated for Louisbourg Harbour and a shipwreck site south of Fortress Louisbourg. Comparing these metrics to those of modern analogues that crossed the same bathymetry reflects landfall intensity consistent with a powerful major hurricane. Historical records show this storm originated as a tropical cyclone at the height of hurricane season and intensified into the northern midlatitudes along the Gulf Stream. Its intensity at landfall is consistent with established seasonal climatological models where highly baroclinic westerlies driven by autumn continental cooling encounter intensifying north-tracking tropical cyclones fuelled by sea surface temperatures that peak in autumn. Stronger seasonal contrasts from earlier and colder continental westerlies in the Little Ice Age (LIA) may have triggered explosive extratropical transition from a large hurricane resulting in a more severe strike. It suggests that tropical cyclones lasting days to weeks and the conditions that generate them are likely masked by cooler historic mean annual to multi-decadal LIA climate reconstructions.
{"title":"A major midlatitude hurricane in the Little Ice Age","authors":"John Dickie, Grant Wach","doi":"10.5194/cp-20-1141-2024","DOIUrl":"https://doi.org/10.5194/cp-20-1141-2024","url":null,"abstract":"Abstract. An unusually severe hurricane (Louisbourg Storm) struck Nova Scotia, Canada, in 1757. Historic records describing storm conditions as well as damage to ships and coastal fortifications indicate an intensity beyond any modern (post-1851) Atlantic cyclones striking the same region, yet this storm struck during a cold climate period known as the Little Ice Age (LIA). Its track and timing coincided with a British naval blockade of a French fleet at Fortress Louisbourg during the Seven Years' War (1756–1763). This provides a unique opportunity to explore growing scientific evidence of heightened storminess in the North Atlantic despite a colder climate expected to suppress hurricane intensification but which research is increasingly showing to have supported North Atlantic storms of exceptional strength. Weather attributes extracted from the logs of naval vessels scattered by the Louisbourg Storm provided multiple hourly observations recorded at different locations. Wave height and wind force estimates at ship locations were compared to extreme storm surge heights calculated for Louisbourg Harbour and a shipwreck site south of Fortress Louisbourg. Comparing these metrics to those of modern analogues that crossed the same bathymetry reflects landfall intensity consistent with a powerful major hurricane. Historical records show this storm originated as a tropical cyclone at the height of hurricane season and intensified into the northern midlatitudes along the Gulf Stream. Its intensity at landfall is consistent with established seasonal climatological models where highly baroclinic westerlies driven by autumn continental cooling encounter intensifying north-tracking tropical cyclones fuelled by sea surface temperatures that peak in autumn. Stronger seasonal contrasts from earlier and colder continental westerlies in the Little Ice Age (LIA) may have triggered explosive extratropical transition from a large hurricane resulting in a more severe strike. It suggests that tropical cyclones lasting days to weeks and the conditions that generate them are likely masked by cooler historic mean annual to multi-decadal LIA climate reconstructions.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"65 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-05-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140931722","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 : 2024-05-08DOI: 10.5194/egusphere-2024-1211
Andrew L. Lowry, Hamish A. McGowan
Abstract. The mid-Holocene climate of Australia and the equatorial tropics of the Indonesian–Australian monsoon region is investigated using the Community Earth System Model (CESM) and the Weather Research and Forecasting (WRF) model. Each model is used to simulate the pre-industrial (1850) and the mid-Holocene (6000 years before 1950) climate. The results of these four simulations are compared to existing bioclimatic modelling of temperature and precipitation. The finer resolution WRF simulations reduce the bias between the model and bioclimatic data results for three of the four variables available in the proxy dataset. The model results show that temperatures over southern Australia at the mid-Holocene and pre-industrial period were similar, and temperatures were slightly warmer during the mid-Holocene over northern Australia and into the tropics, compared to the pre-industrial. During the mid-Holocene precipitation was generally reduced over northern Australia and in the Indonesian–Australian monsoon region, particularly during summertime. The results highlight the improved value of using finer resolution models such as WRF to simulate the palaeoclimate.
{"title":"Insights into the Australian mid-Holocene climate using downscaled climate models","authors":"Andrew L. Lowry, Hamish A. McGowan","doi":"10.5194/egusphere-2024-1211","DOIUrl":"https://doi.org/10.5194/egusphere-2024-1211","url":null,"abstract":"<strong>Abstract.</strong> The mid-Holocene climate of Australia and the equatorial tropics of the Indonesian–Australian monsoon region is investigated using the Community Earth System Model (CESM) and the Weather Research and Forecasting (WRF) model. Each model is used to simulate the pre-industrial (1850) and the mid-Holocene (6000 years before 1950) climate. The results of these four simulations are compared to existing bioclimatic modelling of temperature and precipitation. The finer resolution WRF simulations reduce the bias between the model and bioclimatic data results for three of the four variables available in the proxy dataset. The model results show that temperatures over southern Australia at the mid-Holocene and pre-industrial period were similar, and temperatures were slightly warmer during the mid-Holocene over northern Australia and into the tropics, compared to the pre-industrial. During the mid-Holocene precipitation was generally reduced over northern Australia and in the Indonesian–Australian monsoon region, particularly during summertime. The results highlight the improved value of using finer resolution models such as WRF to simulate the palaeoclimate.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"40 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-05-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140931824","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 : 2024-05-07DOI: 10.5194/egusphere-2024-1261
Qinggang Gao, Emilie Capron, Louise C. Sime, Rachael H. Rhodes, Rahul Sivankutty, Xu Zhang, Bette L. Otto-Bliesner, Martin Werner
Abstract. Given relatively abundant paleo proxies, the study of the Last Interglacial (LIG, ~129-116 thousand years ago, ka) is valuable to understanding natural variability and feedback in a warmer-than-preindustrial climate. The Paleoclimate Modelling Intercomparison Project Phase 4 (PMIP4) coordinated LIG model simulations which focus on 127 ka. Here we evaluate 12 PMIP4 127-ka Tier 1 model simulations against four recent paleoclimate syntheses of LIG sea and air temperatures and sea ice concentrations. The four syntheses include 99 reconstructions and show considerable variations, some but not all of which are attributable to the different sites included in each synthesis. All syntheses support the presence of a warmer Southern Ocean, with reduced sea ice, and a warmer Antarctica at 127 ka compared to the preindustrial. The PMIP4 127-ka Tier 1 simulations, forced solely by orbital parameters and greenhouse gas concentrations, do not capture the magnitude of this warming. Here we follow up on previous work that suggests the importance of preceding deglaciation meltwater release into the North Atlantic. We run a 3000-year 128-ka simulation using HadCM3 with a 0.25 Sv North Atlantic freshwater hosing, which approximates the PMIP4 127-ka Tier 2 H11 (Heinrich event 11) simulation. The hosed 128-ka HadCM3 simulation captures much of the warming and sea ice loss shown in the four data syntheses at 127 ka relative to preindustrial: south of 40° S, modelled annual sea surface temperature (SST) rises by 1.3±0.6 °C, while reconstructed average anomalies range from 2.2 °C to 2.7 °C; modelled summer SST increases by 1.1±0.7 °C, close to 1.2–2.2 °C reconstructed average anomalies; September sea ice area (SIA) reduces by 40 %, similar to reconstructed 40 % reduction of sea ice concentration (SIC); over the Antarctic ice sheet, modelled annual surface air temperature (SAT) increases by 2.6±0.4 °C, even larger than reconstructed average anomalies 2.2 °C. Our results suggest that the impacts of deglaciation ice sheet meltwater need to be considered to simulate the Southern Ocean and Antarctic changes at 127 ka.
{"title":"Assessment of the southern polar and subpolar warming in the PMIP4 Last Interglacial simulations using paleoclimate data syntheses","authors":"Qinggang Gao, Emilie Capron, Louise C. Sime, Rachael H. Rhodes, Rahul Sivankutty, Xu Zhang, Bette L. Otto-Bliesner, Martin Werner","doi":"10.5194/egusphere-2024-1261","DOIUrl":"https://doi.org/10.5194/egusphere-2024-1261","url":null,"abstract":"<strong>Abstract.</strong> Given relatively abundant paleo proxies, the study of the Last Interglacial (LIG, ~129-116 thousand years ago, ka) is valuable to understanding natural variability and feedback in a warmer-than-preindustrial climate. The Paleoclimate Modelling Intercomparison Project Phase 4 (PMIP4) coordinated LIG model simulations which focus on 127 ka. Here we evaluate 12 PMIP4 127-ka Tier 1 model simulations against four recent paleoclimate syntheses of LIG sea and air temperatures and sea ice concentrations. The four syntheses include 99 reconstructions and show considerable variations, some but not all of which are attributable to the different sites included in each synthesis. All syntheses support the presence of a warmer Southern Ocean, with reduced sea ice, and a warmer Antarctica at 127 ka compared to the preindustrial. The PMIP4 127-ka Tier 1 simulations, forced solely by orbital parameters and greenhouse gas concentrations, do not capture the magnitude of this warming. Here we follow up on previous work that suggests the importance of preceding deglaciation meltwater release into the North Atlantic. We run a 3000-year 128-ka simulation using HadCM3 with a 0.25 <em>Sv</em> North Atlantic freshwater hosing, which approximates the PMIP4 127-ka Tier 2 H11 (Heinrich event 11) simulation. The hosed 128-ka HadCM3 simulation captures much of the warming and sea ice loss shown in the four data syntheses at 127 ka relative to preindustrial: south of 40° S, modelled annual sea surface temperature (SST) rises by 1.3±0.6 °C, while reconstructed average anomalies range from 2.2 °C to 2.7 °C; modelled summer SST increases by 1.1±0.7 °C, close to 1.2–2.2 °C reconstructed average anomalies; September sea ice area (SIA) reduces by 40 %, similar to reconstructed 40 % reduction of sea ice concentration (SIC); over the Antarctic ice sheet, modelled annual surface air temperature (SAT) increases by 2.6±0.4 °C, even larger than reconstructed average anomalies 2.2 °C. Our results suggest that the impacts of deglaciation ice sheet meltwater need to be considered to simulate the Southern Ocean and Antarctic changes at 127 ka.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"26 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-05-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140886001","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 : 2024-05-03DOI: 10.5194/egusphere-2024-979
Viktoria Larsson, Simon Jung
Abstract. Mg/Ca ratios measured in benthic foraminifera have been explored as a potential palaeothermometry proxy for bottom water temperatures (BWT). Mg/Ca-BWT calibrations from the Indian Ocean are rare and comprise conflicting results. Inconsistencies between studies suggest that calibrations may need to be region specific. The aim of this study was to develop benthic foraminifera (Uvigerina peregrina, Cibicidoides wuellerstorfi and Cibicidoides mundulus) based Mg/Ca – BWT calibrations in the tropical western Indian Ocean. Testing variations of existing analytical protocols, aimed at optimising cleaning of the foraminifera while avoiding sample loss in the process, entailed that a previously established protocol by Barker et al. (2003) was the most suitable for our study. The majority of samples of Cibicidoides mundulus and Uvigerina peregrina, however, remained contaminated, rendering those data unusable for Mg/Ca core-top calibrations. Only Mg/Ca ratios in Cibicidoides wuellerstorfi allowed a tentative Mg/Ca - BWT calibration with the relationship being: Mg/Ca = 0.19 ± 0.02 ∗ BWT + 1.07 ± 0.03, 𝑟2 = 0.87. While this result differs to some degree from previous studies it principally suggests that existing core-top calibrations from the wider Indian Ocean can be applied to core-tops in the western Indian Ocean. The agreement of Mg/Ca ratios at lower temperatures in Cibicidoides wuellerstorfi, Cibicidoides mundulus and Uvigerina peregrina with Mg/Ca ratios reported for these species at low temperatures in other studies supports this conclusion. Many uncertainties surrounding the Mg/Ca proxy exist and more calibration studies are required to improve this method.
{"title":"Western Indian Ocean bottom water temperature calibration – are benthic foraminiferal Mg/Ca ratios a reliable palaeothermometry proxy?","authors":"Viktoria Larsson, Simon Jung","doi":"10.5194/egusphere-2024-979","DOIUrl":"https://doi.org/10.5194/egusphere-2024-979","url":null,"abstract":"<strong>Abstract.</strong> Mg/Ca ratios measured in benthic foraminifera have been explored as a potential palaeothermometry proxy for bottom water temperatures (BWT). Mg/Ca-BWT calibrations from the Indian Ocean are rare and comprise conflicting results. Inconsistencies between studies suggest that calibrations may need to be region specific. The aim of this study was to develop benthic foraminifera (<em>Uvigerina peregrina</em>, <em>Cibicidoides wuellerstorfi</em> and <em>Cibicidoides mundulus</em>) based Mg/Ca – BWT calibrations in the tropical western Indian Ocean. Testing variations of existing analytical protocols, aimed at optimising cleaning of the foraminifera while avoiding sample loss in the process, entailed that a previously established protocol by Barker et al. (2003) was the most suitable for our study. The majority of samples of <em>Cibicidoides mundulus</em> and <em>Uvigerina peregrina</em>, however, remained contaminated, rendering those data unusable for Mg/Ca core-top calibrations. Only Mg/Ca ratios in <em>Cibicidoides wuellerstorfi</em> allowed a tentative Mg/Ca - BWT calibration with the relationship being: Mg/Ca = 0.19 ± 0.02 ∗ BWT + 1.07 ± 0.03, 𝑟<sup>2</sup> = 0.87. While this result differs to some degree from previous studies it principally suggests that existing core-top calibrations from the wider Indian Ocean can be applied to core-tops in the western Indian Ocean. The agreement of Mg/Ca ratios at lower temperatures in <em>Cibicidoides wuellerstorfi</em>, <em>Cibicidoides mundulus</em> and <em>Uvigerina peregrina</em> with Mg/Ca ratios reported for these species at low temperatures in other studies supports this conclusion. Many uncertainties surrounding the Mg/Ca proxy exist and more calibration studies are required to improve this method.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"31 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-05-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140829936","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}
Julia E. Weiffenbach, Henk A. Dijkstra, Anna S. von der Heydt, Ayako Abe-Ouchi, Wing-Le Chan, Deepak Chandan, Ran Feng, Alan M. Haywood, Stephen J. Hunter, Xiangyu Li, Bette L. Otto-Bliesner, W. Richard Peltier, Christian Stepanek, Ning Tan, Julia C. Tindall, Zhongshi Zhang
Abstract. During the mid-Pliocene warm period (mPWP; 3.264–3.025 Ma), atmospheric CO2 concentrations were approximately 400 ppm, and the Antarctic Ice Sheet was substantially reduced compared to today. Antarctica is surrounded by the Southern Ocean, which plays a crucial role in the global oceanic circulation and climate regulation. Using results from the Pliocene Model Intercomparison Project (PlioMIP2), we investigate Southern Ocean conditions during the mPWP with respect to the pre-industrial period. We find that the mean sea surface temperature (SST) warming in the Southern Ocean is 2.8 °C, while global mean SST warming is 2.4 °C. The enhanced warming is strongly tied to a dramatic decrease in sea ice cover over the mPWP Southern Ocean. We also see a freshening of the ocean (sub)surface, driven by an increase in precipitation over the Southern Ocean and Antarctica. The warmer and fresher surface leads to a highly stratified Southern Ocean that can be related to weakening of the deep abyssal overturning circulation. Sensitivity simulations show that the decrease in sea ice cover and enhanced warming is largely a consequence of the reduction in the Antarctic Ice Sheet. In addition, the mPWP geographic boundary conditions are responsible for approximately half of the increase in mPWP SST warming, sea ice loss, precipitation, and stratification increase over the Southern Ocean. From these results, we conclude that a strongly reduced Antarctic Ice Sheet during the mPWP has a substantial influence on the state of the Southern Ocean and exacerbates the changes that are induced by a higher CO2 concentration alone. This is relevant for the long-term future of the Southern Ocean, as we expect melting of the western Antarctic Ice Sheet in the future, an effect that is not currently taken into account in future projections by Coupled Model Intercomparison Project (CMIP) ensembles.
{"title":"Highly stratified mid-Pliocene Southern Ocean in PlioMIP2","authors":"Julia E. Weiffenbach, Henk A. Dijkstra, Anna S. von der Heydt, Ayako Abe-Ouchi, Wing-Le Chan, Deepak Chandan, Ran Feng, Alan M. Haywood, Stephen J. Hunter, Xiangyu Li, Bette L. Otto-Bliesner, W. Richard Peltier, Christian Stepanek, Ning Tan, Julia C. Tindall, Zhongshi Zhang","doi":"10.5194/cp-20-1067-2024","DOIUrl":"https://doi.org/10.5194/cp-20-1067-2024","url":null,"abstract":"Abstract. During the mid-Pliocene warm period (mPWP; 3.264–3.025 Ma), atmospheric CO2 concentrations were approximately 400 ppm, and the Antarctic Ice Sheet was substantially reduced compared to today. Antarctica is surrounded by the Southern Ocean, which plays a crucial role in the global oceanic circulation and climate regulation. Using results from the Pliocene Model Intercomparison Project (PlioMIP2), we investigate Southern Ocean conditions during the mPWP with respect to the pre-industrial period. We find that the mean sea surface temperature (SST) warming in the Southern Ocean is 2.8 °C, while global mean SST warming is 2.4 °C. The enhanced warming is strongly tied to a dramatic decrease in sea ice cover over the mPWP Southern Ocean. We also see a freshening of the ocean (sub)surface, driven by an increase in precipitation over the Southern Ocean and Antarctica. The warmer and fresher surface leads to a highly stratified Southern Ocean that can be related to weakening of the deep abyssal overturning circulation. Sensitivity simulations show that the decrease in sea ice cover and enhanced warming is largely a consequence of the reduction in the Antarctic Ice Sheet. In addition, the mPWP geographic boundary conditions are responsible for approximately half of the increase in mPWP SST warming, sea ice loss, precipitation, and stratification increase over the Southern Ocean. From these results, we conclude that a strongly reduced Antarctic Ice Sheet during the mPWP has a substantial influence on the state of the Southern Ocean and exacerbates the changes that are induced by a higher CO2 concentration alone. This is relevant for the long-term future of the Southern Ocean, as we expect melting of the western Antarctic Ice Sheet in the future, an effect that is not currently taken into account in future projections by Coupled Model Intercomparison Project (CMIP) ensembles.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"47 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-05-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140829869","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}
Nicolò Ardenghi, David J. Harning, Jonathan H. Raberg, Brooke R. Holman, Thorvaldur Thordarson, Áslaug Geirsdóttir, Gifford H. Miller, Julio Sepúlveda
Abstract. Paleoclimate reconstructions across Iceland provide a template for past changes in climate across the northern North Atlantic, a crucial region due to its position relative to the global northward heat transport system and its vulnerability to climate change. The roles of orbitally driven summer cooling, volcanism, and human impact as triggers of local environmental changes in the Holocene of Iceland remain debated. While there are indications that human impact may have reduced environmental resilience during late Holocene summer cooling, it is still difficult to resolve to what extent human and natural factors affected Iceland's late Holocene landscape instability. Here, we present a continuous Holocene fire record of northeastern Iceland from proxies archived in Stóra Viðarvatn sediment. We use pyrogenic polycyclic aromatic hydrocarbons (pyroPAHs) to trace shifts in fire regimes, paired with continuous biomarker and bulk geochemical records of soil erosion, lake productivity, and human presence. The molecular composition of pyroPAHs and a wind pattern reconstruction indicate a naturally driven fire signal that is mostly regional. Generally low fire frequency during most of the Holocene significantly increased at 3 ka and again after 1.5 ka BP before known human settlement in Iceland. We propose that shifts in vegetation type caused by cooling summers over the past 3 kyr, in addition to changes in atmospheric circulation, such as shifts in North Atlantic Oscillation (NAO) regime, led to increased aridity and biomass flammability. Our results show no evidence of faecal biomarkers associated with human activity during or after human colonisation in the 9th century CE. Instead, faecal biomarkers follow the pattern described by erosional proxies, pointing toward a negligible human presence and/or a diluted signal in the lake's catchment. However, low post-colonisation levels of pyroPAHs, in contrast to an increasing flux of erosional bulk proxies, suggest that farming and animal husbandry may have suppressed fire frequency by reducing the spread and flammability of fire-prone vegetation (e.g. heathlands). Overall, our results describe a fire frequency heavily influenced by long-term changes in climate through the Holocene. They also suggest that human colonisation had contrasting effects on the local environment by lowering its resilience to soil erosion while increasing its resilience to fire.
摘要。冰岛的古气候重建为北大西洋北部过去的气候变化提供了一个模板，由于其相对于全球向北热量输送系统的位置及其对气候变化的脆弱性，冰岛是一个至关重要的地区。在冰岛全新世，由轨道驱动的夏季降温、火山活动和人类活动对当地环境变化的影响仍存在争议。虽然有迹象表明人类的影响可能降低了全新世晚期夏季降温时的环境复原力，但人类和自然因素对冰岛全新世晚期地貌不稳定性的影响程度仍难以确定。在这里，我们从 Stóra Viðarvatn 沉积物中存档的代用指标中获得了冰岛东北部全新世火灾的连续记录。我们利用热源多环芳烃（pyroPAHs）来追溯火灾机制的转变，并与土壤侵蚀、湖泊生产力和人类存在的连续生物标志物和大体积地球化学记录相配合。热释PAHs的分子组成和风型重建表明，自然驱动的火灾信号主要是区域性的。在冰岛已知人类定居之前的公元前 3 ka 和公元前 1.5 ka 后，全新世大部分时期的火灾频率普遍较低。我们认为，除了大气环流的变化（如北大西洋涛动（NAO）机制的变化）外，过去 3 千年夏季的降温也导致了植被类型的变化，从而增加了干旱程度和生物量的易燃性。我们的研究结果表明，在公元 9 世纪人类殖民期间或之后，没有证据表明粪便生物标志物与人类活动有关。相反，粪便生物标志物遵循侵蚀代用指标所描述的模式，表明湖泊集水区的人类存在可以忽略不计和/或信号被稀释。然而，与侵蚀性大量代用指标流量不断增加形成对比的是，殖民化后的火致多环芳香烃含量较低，这表明农耕和畜牧业可能通过减少火灾易发植被（如荒地）的蔓延和易燃性而抑制了火灾频率。总之，我们的研究结果描述了全新世时期受长期气候变化严重影响的火灾频率。这些结果还表明，人类的殖民活动对当地环境产生了截然不同的影响，降低了当地环境对水土流失的抵御能力，同时提高了当地环境对火灾的抵御能力。
{"title":"A Holocene history of climate, fire, landscape evolution, and human activity in northeastern Iceland","authors":"Nicolò Ardenghi, David J. Harning, Jonathan H. Raberg, Brooke R. Holman, Thorvaldur Thordarson, Áslaug Geirsdóttir, Gifford H. Miller, Julio Sepúlveda","doi":"10.5194/cp-20-1087-2024","DOIUrl":"https://doi.org/10.5194/cp-20-1087-2024","url":null,"abstract":"Abstract. Paleoclimate reconstructions across Iceland provide a template for past changes in climate across the northern North Atlantic, a crucial region due to its position relative to the global northward heat transport system and its vulnerability to climate change. The roles of orbitally driven summer cooling, volcanism, and human impact as triggers of local environmental changes in the Holocene of Iceland remain debated. While there are indications that human impact may have reduced environmental resilience during late Holocene summer cooling, it is still difficult to resolve to what extent human and natural factors affected Iceland's late Holocene landscape instability. Here, we present a continuous Holocene fire record of northeastern Iceland from proxies archived in Stóra Viðarvatn sediment. We use pyrogenic polycyclic aromatic hydrocarbons (pyroPAHs) to trace shifts in fire regimes, paired with continuous biomarker and bulk geochemical records of soil erosion, lake productivity, and human presence. The molecular composition of pyroPAHs and a wind pattern reconstruction indicate a naturally driven fire signal that is mostly regional. Generally low fire frequency during most of the Holocene significantly increased at 3 ka and again after 1.5 ka BP before known human settlement in Iceland. We propose that shifts in vegetation type caused by cooling summers over the past 3 kyr, in addition to changes in atmospheric circulation, such as shifts in North Atlantic Oscillation (NAO) regime, led to increased aridity and biomass flammability. Our results show no evidence of faecal biomarkers associated with human activity during or after human colonisation in the 9th century CE. Instead, faecal biomarkers follow the pattern described by erosional proxies, pointing toward a negligible human presence and/or a diluted signal in the lake's catchment. However, low post-colonisation levels of pyroPAHs, in contrast to an increasing flux of erosional bulk proxies, suggest that farming and animal husbandry may have suppressed fire frequency by reducing the spread and flammability of fire-prone vegetation (e.g. heathlands). Overall, our results describe a fire frequency heavily influenced by long-term changes in climate through the Holocene. They also suggest that human colonisation had contrasting effects on the local environment by lowering its resilience to soil erosion while increasing its resilience to fire.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"18 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-05-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140829864","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 : 2024-05-02DOI: 10.5194/egusphere-2024-1072
Jan Maier, Nicole Burdanowitz, Gerhard Schmiedl, Birgit Gaye
Abstract. In this study, we present the first well-dated, high-resolution alkenone-based sea surface temperature (SST) record (SL167) from the northeastern Oman Margin (Gulf of Oman) in the northwestern Arabian Sea. The SST reconstructions spanning the last 43 kyr reveal fluctuations of approximately 7 °C (20.1 °C to 27.4 °C) and demonstrate a higher sensitivity to climate variations compared to similar core locations in the Arabian Sea. SSTs remained low during Heinrich events (H2, H3, H4), the Younger Dryas, early and late Holocene, and were high during Dansgaard-Oeschger interstadials (D-O 11, D-O 4 - 9, Bølling-Allerød (B-A), and mid-Holocene. SST was predominantly influenced by the SW monsoon during warmer periods and the NE monsoon during cold intervals. The dynamics of strengthening and weakening monsoon periods were likely controlled by shifts in the Intertropical Convergence Zone prompted by changes in solar radiation in the Northern Hemisphere. The last glacial maximum exhibited no intense cooling probably due to stronger NW winds and an eastward shift of the SST gradient in the Gulf of Oman, resulting in a brief and moderate cooling period. Strong SW winds during the early Holocene transported cold water masses from Oman upwelling into the Gulf of Oman, lowering SSTs. A rapid temperature increase of approx. 2 °C during the mid-Holocene was induced by an abrupt eastward shift of the SST gradient.
{"title":"Spatial and temporal variability of sea surface temperatures and monsoon dynamics in the northwestern Arabian Sea during the last 43 kyr","authors":"Jan Maier, Nicole Burdanowitz, Gerhard Schmiedl, Birgit Gaye","doi":"10.5194/egusphere-2024-1072","DOIUrl":"https://doi.org/10.5194/egusphere-2024-1072","url":null,"abstract":"<strong>Abstract.</strong> In this study, we present the first well-dated, high-resolution alkenone-based sea surface temperature (SST) record (SL167) from the northeastern Oman Margin (Gulf of Oman) in the northwestern Arabian Sea. The SST reconstructions spanning the last 43 kyr reveal fluctuations of approximately 7 °C (20.1 °C to 27.4 °C) and demonstrate a higher sensitivity to climate variations compared to similar core locations in the Arabian Sea. SSTs remained low during Heinrich events (H2, H3, H4), the Younger Dryas, early and late Holocene, and were high during Dansgaard-Oeschger interstadials (D-O 11, D-O 4 - 9, Bølling-Allerød (B-A), and mid-Holocene. SST was predominantly influenced by the SW monsoon during warmer periods and the NE monsoon during cold intervals. The dynamics of strengthening and weakening monsoon periods were likely controlled by shifts in the Intertropical Convergence Zone prompted by changes in solar radiation in the Northern Hemisphere. The last glacial maximum exhibited no intense cooling probably due to stronger NW winds and an eastward shift of the SST gradient in the Gulf of Oman, resulting in a brief and moderate cooling period. Strong SW winds during the early Holocene transported cold water masses from Oman upwelling into the Gulf of Oman, lowering SSTs. A rapid temperature increase of approx. 2 °C during the mid-Holocene was induced by an abrupt eastward shift of the SST gradient.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"82 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-05-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140829859","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}
Livia Manser, Tyler Kukla, Jeremy K. C. Rugenstein
Abstract. The Great Plains of North America host a stark climatic gradient, separating the humid and well-watered eastern US from the semi-arid and arid western US, and this gradient shapes the region's water availability, its ecosystems, and its economies. This climatic boundary is largely set by the influence of two competing atmospheric circulation systems that meet over the Great Plains – the wintertime westerlies bring dominantly dry air that gives way to moist, southerly air transported by the Great Plains low-level jet in the warmer months. Climate model simulations suggest that, as CO2 rises, this low-level jet will strengthen, leading to greater precipitation in the spring but less in the summer and, thus, no change in mean annual precipitation. Combined with rising temperatures that will increase potential evapotranspiration, semi-arid conditions will shift eastward, with potentially large consequences for the ecosystems and inhabitants of the Great Plains. We examine how hydroclimate in the Great Plains varied in the past in response to warmer global climate by studying the paleoclimate record within the Ogallala Formation, which underlies nearly the entire Great Plains and provides a spatially resolved record of hydroclimate during the globally warmer late Miocene. We use the stable isotopes of oxygen (δ18O) as preserved in authigenic carbonates hosted within the abundant paleosol and fluvial successions that comprise the Ogallala Formation as a record of past hydroclimate. Today, and coincident with the modern aridity gradient, there is a sharp meteoric water δ18O gradient with high (−6 ‰ to 0 ‰) δ18O in the southern Great Plains and low (−12 ‰ to −18 ‰) δ18O in the northern plains. We find that the spatial pattern of reconstructed late Miocene precipitation δ18O is indistinguishable from the spatial pattern of modern meteoric water δ18O. We use a recently developed vapor transport model to demonstrate that this δ18O spatial pattern requires air mass mixing over the Great Plains between dry westerly and moist southerly air masses in the late Miocene – consistent with today. Our results suggest that the spatial extents of these two atmospheric circulation systems have been largely unchanged since the late Miocene and any strengthening of the Great Plains low-level jet in response to warming has been isotopically masked by proportional increases in westerly moisture delivery. Our results hold implications for the sensitivity of Great Plains climate to changes in global temperature and CO2 and also for our understanding of the processes that drove Ogallala Formation deposition in the late Miocene.
{"title":"Stable isotope evidence for long-term stability of large-scale hydroclimate in the Neogene North American Great Plains","authors":"Livia Manser, Tyler Kukla, Jeremy K. C. Rugenstein","doi":"10.5194/cp-20-1039-2024","DOIUrl":"https://doi.org/10.5194/cp-20-1039-2024","url":null,"abstract":"Abstract. The Great Plains of North America host a stark climatic gradient, separating the humid and well-watered eastern US from the semi-arid and arid western US, and this gradient shapes the region's water availability, its ecosystems, and its economies. This climatic boundary is largely set by the influence of two competing atmospheric circulation systems that meet over the Great Plains – the wintertime westerlies bring dominantly dry air that gives way to moist, southerly air transported by the Great Plains low-level jet in the warmer months. Climate model simulations suggest that, as CO2 rises, this low-level jet will strengthen, leading to greater precipitation in the spring but less in the summer and, thus, no change in mean annual precipitation. Combined with rising temperatures that will increase potential evapotranspiration, semi-arid conditions will shift eastward, with potentially large consequences for the ecosystems and inhabitants of the Great Plains. We examine how hydroclimate in the Great Plains varied in the past in response to warmer global climate by studying the paleoclimate record within the Ogallala Formation, which underlies nearly the entire Great Plains and provides a spatially resolved record of hydroclimate during the globally warmer late Miocene. We use the stable isotopes of oxygen (δ18O) as preserved in authigenic carbonates hosted within the abundant paleosol and fluvial successions that comprise the Ogallala Formation as a record of past hydroclimate. Today, and coincident with the modern aridity gradient, there is a sharp meteoric water δ18O gradient with high (−6 ‰ to 0 ‰) δ18O in the southern Great Plains and low (−12 ‰ to −18 ‰) δ18O in the northern plains. We find that the spatial pattern of reconstructed late Miocene precipitation δ18O is indistinguishable from the spatial pattern of modern meteoric water δ18O. We use a recently developed vapor transport model to demonstrate that this δ18O spatial pattern requires air mass mixing over the Great Plains between dry westerly and moist southerly air masses in the late Miocene – consistent with today. Our results suggest that the spatial extents of these two atmospheric circulation systems have been largely unchanged since the late Miocene and any strengthening of the Great Plains low-level jet in response to warming has been isotopically masked by proportional increases in westerly moisture delivery. Our results hold implications for the sensitivity of Great Plains climate to changes in global temperature and CO2 and also for our understanding of the processes that drove Ogallala Formation deposition in the late Miocene.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"47 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-04-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140830050","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}
Rudolf Brázdil, Jan Lhoták, Kateřina Chromá, Petr Dobrovolný
Abstract. Grain prices in early modern Europe reflected the effects of weather and climate on crop yields and a complex array of societal and socio-economic factors. This study presents a newly developed series of grain prices for Sušice (southwestern Bohemia, Czech Republic) for the period 1725–1824 CE, based on various archival sources. It aims to analyse their relationships with weather and climate, represented by temperature, precipitation, and drought (self-calibrated Palmer Drought Severity Index, scPDSI) reconstructions, as well as particular weather extremes and anomalies reported in documentary evidence. Wheat, rye, barley, and oats series in Sušice showed high mutual correlations. The mean highest prices during the year typically occurred from May to July before the harvest, while prices usually declined afterwards. Wheat, rye, and barley prices were significantly negatively correlated with spring temperatures and positively correlated with scPDSI from winter to summer. This indicates that wetter winters, cooler and wetter springs, and wetter summers contributed to higher prices. The extremely high grain prices in the years 1746, 1771–1772, 1802–1806, and 1816–1817 were separately analysed with respect to weather and climate patterns and other socio-economic and political factors. The results obtained were discussed in relation to data uncertainty, factors influencing grain prices, and the broader European context.
{"title":"Effects of weather and climate on fluctuations of grain prices in southwestern Bohemia, 1725–1824 CE","authors":"Rudolf Brázdil, Jan Lhoták, Kateřina Chromá, Petr Dobrovolný","doi":"10.5194/cp-20-1017-2024","DOIUrl":"https://doi.org/10.5194/cp-20-1017-2024","url":null,"abstract":"Abstract. Grain prices in early modern Europe reflected the effects of weather and climate on crop yields and a complex array of societal and socio-economic factors. This study presents a newly developed series of grain prices for Sušice (southwestern Bohemia, Czech Republic) for the period 1725–1824 CE, based on various archival sources. It aims to analyse their relationships with weather and climate, represented by temperature, precipitation, and drought (self-calibrated Palmer Drought Severity Index, scPDSI) reconstructions, as well as particular weather extremes and anomalies reported in documentary evidence. Wheat, rye, barley, and oats series in Sušice showed high mutual correlations. The mean highest prices during the year typically occurred from May to July before the harvest, while prices usually declined afterwards. Wheat, rye, and barley prices were significantly negatively correlated with spring temperatures and positively correlated with scPDSI from winter to summer. This indicates that wetter winters, cooler and wetter springs, and wetter summers contributed to higher prices. The extremely high grain prices in the years 1746, 1771–1772, 1802–1806, and 1816–1817 were separately analysed with respect to weather and climate patterns and other socio-economic and political factors. The results obtained were discussed in relation to data uncertainty, factors influencing grain prices, and the broader European context.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"37 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-04-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140811251","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 : 2024-04-25DOI: 10.5194/egusphere-2024-940
Christophe Sturm
Abstract. The Swedish Meteorology and Hydrology Institute (SMHI) provides a national aggregated climate indicator from 1860 to present. We present a new method to compute the national climate indicator based on Empirical Orthogonal Functions (EOF). EOF are computed during the1961–2018 calibration period, and later applied to the full experiment period 1860–2020. This study focuses the climate indicator for precipitation; it follows the same methodology as for the national climate indicator for temperature, described in the companion article (Sturm, 2024a). The new method delivers results in good overall agreement with the reference method (i.e. arithmetic mean from selected stations in the reference network). Discrepancies are found prior to 1900, primarily related to the reduced number of active stations: the robustness of the indicator estimation is assessed by an ensemble computation with added random noise, which confirms that the ensemble spread increases significantly prior to 1880. The present study establishes that the 10-year running averaged precipitation indicator rose from -8.37 mm.month-1 in 1903 to 4.08 mm.month-1 in 2010 (with respect to the mean value of 54.18 mm.month-1 for the 1961–2018 calibration period), i.e. a 27 % increase over a century. Winter (DJF) precipitation rose by +20 mm.month-1 between 1890–2010, summer precipitation by +25 mm.month-1. The leading EOF patterns illustrate the spatial modes of variability for climate variability. For precipitation, the first EOF pattern displays more pronounced regional features (maximum over the West coast), which is completed by a north-south seesaw pattern for the second EOF. We illustrate that EOF patterns calculated from observation data reproduce the major features of EOF calculated from GridClim, a gridded dataset over Sweden, for annual and seasonal averages. The leading EOF patterns vary significantly for seasonal averages (DJF, MAM, JJA, SON) for precipitation. Finally, future developments of the EOF-method are discussed for calculating regional aggregated climate indicators, their relationship to synoptic circulation patterns and the benefits of homogenisation of observation series. The EOF-based method to compute a spatially aggregated indicator for temperature is presented in a companion article (Sturm, 2024a), which includes a detailed description of the datasets and methods used in this study. The code and data for this study is available on Zenodo (Sturm, 2024b).
{"title":"Spatially aggregated climate indicators over Sweden (1860–2020), part 2: Precipitation","authors":"Christophe Sturm","doi":"10.5194/egusphere-2024-940","DOIUrl":"https://doi.org/10.5194/egusphere-2024-940","url":null,"abstract":"<strong>Abstract.</strong> The Swedish Meteorology and Hydrology Institute (SMHI) provides a national aggregated climate indicator from 1860 to present. We present a new method to compute the national climate indicator based on Empirical Orthogonal Functions (EOF). EOF are computed during the1961–2018 calibration period, and later applied to the full experiment period 1860–2020. This study focuses the climate indicator for precipitation; it follows the same methodology as for the national climate indicator for temperature, described in the companion article (Sturm, 2024a). The new method delivers results in good overall agreement with the reference method (i.e. arithmetic mean from selected stations in the reference network). Discrepancies are found prior to 1900, primarily related to the reduced number of active stations: the robustness of the indicator estimation is assessed by an ensemble computation with added random noise, which confirms that the ensemble spread increases significantly prior to 1880. The present study establishes that the 10-year running averaged precipitation indicator rose from -8.37 mm.month<sup>-1</sup> in 1903 to 4.08 mm.month<sup>-1</sup> in 2010 (with respect to the mean value of 54.18 mm.month<sup>-1</sup> for the 1961–2018 calibration period), i.e. a 27 % increase over a century. Winter (DJF) precipitation rose by +20 mm.month<sup>-1 </sup>between 1890–2010, summer precipitation by +25 mm.month<sup>-1</sup>. The leading EOF patterns illustrate the spatial modes of variability for climate variability. For precipitation, the first EOF pattern displays more pronounced regional features (maximum over the West coast), which is completed by a north-south seesaw pattern for the second EOF. We illustrate that EOF patterns calculated from observation data reproduce the major features of EOF calculated from GridClim, a gridded dataset over Sweden, for annual and seasonal averages. The leading EOF patterns vary significantly for seasonal averages (DJF, MAM, JJA, SON) for precipitation. Finally, future developments of the EOF-method are discussed for calculating regional aggregated climate indicators, their relationship to synoptic circulation patterns and the benefits of homogenisation of observation series. The EOF-based method to compute a spatially aggregated indicator for temperature is presented in a companion article (Sturm, 2024a), which includes a detailed description of the datasets and methods used in this study. The code and data for this study is available on Zenodo (Sturm, 2024b).","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"1 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-04-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140800412","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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