Pub Date : 2024-05-31DOI: 10.5194/egusphere-2024-865
Jennifer Scott, Douglas Coenen, Simon Jung
Abstract. The Asian monsoon system is a crucial part of the global climate system affecting a significant proportion of the world population. Understanding the controls for changes in the monsoon system is crucial for meaningful assessments of future climate change. The Arabian Sea is part of the wider Asian monsoon system and has been studied regarding controls of monsoon variability through time. In this study we present sea surface temperature data from 37–67 ka BP from sediment core NIOP 929 from the western Arabian Sea assessing the importance of northern/southern hemispheric climate change driving monsoon circulation in the Arabian Sea. Earlier work implies a straightforward link between monsoon variation in the Arabian Sea and northern hemisphere millennial scale climate change during glacial periods, as depicted in Greenland ice cores. We present a new millennial-scale Mg/Ca based sea surface temperature reconstruction based on the planktic foraminifera species G. bulloides and G. ruber. We use these data to calculate seasonal sea surface temperatures. The SST data are variable with a maximum short-term change of 8–9 °C. The variations in our SST records appear not related to change in either hemisphere in a straightforward fashion by not showing a phase-locked relation to millennial scale change in Greenland or Antarctic ice core records. We discuss these changes in the context of the Arabian Sea potentially being a “melting pot” with both the northern and the southern hemisphere exerting influence on a seasonal scale.
摘要亚洲季风系统是全球气候系统的重要组成部分，影响着世界上很大一部分人口。了解季风系统变化的控制因素对于对未来气候变化进行有意义的评估至关重要。阿拉伯海是更广泛的亚洲季风系统的一部分，人们一直在研究季风变化的控制因素。在这项研究中，我们展示了来自阿拉伯海西部沉积岩芯 NIOP 929 的公元前 37-67 ka 年的海面温度数据，评估了北半球/南半球气候变化对阿拉伯海季风环流的重要影响。早先的研究表明，阿拉伯海季风变化与北半球冰川期千年尺度气候变化之间存在直接联系，格陵兰冰芯中就有描述。我们根据浮游有孔虫物种 G. bulloides 和 G. ruber，提出了一种新的基于镁/钙的千年尺度海面温度重建方法。我们利用这些数据来计算季节性海表温度。海表温度数据是可变的，最大短期变化为 8-9 ℃。我们的海表温度记录的变化似乎与两个半球的变化没有直接关系，与格陵兰或南极冰芯记录中的千年尺度变化没有相锁关系。我们讨论这些变化的背景是，阿拉伯海可能是一个 "熔炉"，北半球和南半球都会产生季节性影响。
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Pub Date : 2024-05-30DOI: 10.5194/egusphere-2024-1396
Elisa Ziegler, Nils Weitzel, Jean-Philippe Baudouin, Marie-Luise Kapsch, Uwe Mikolajewicz, Lauren Gregoire, Ruza Ivanovic, Paul J. Valdes, Christian Wirths, Kira Rehfeld
<strong>Abstract.</strong> As of 2023, global mean temperature has risen by about 1.45 ± 0.12 °C with respect to the 1850–1900 pre-industrial baseline according to the World Meteorological Organization. This rise constitutes the first period of substantial global warming since the Last Deglaciation, when global temperatures rose over several millennia by about 4.0–7.0 °C according to proxy reconstructions. Similar levels of warming could be reached in the coming centuries considering current and possible future emissions. Such warming causes widespread changes in the climate system of which the mean state provides only an incomplete picture. Indeed, climate’s variability and the distributions of climate variables change with warming, impacting for example ecosystems and the frequency and intensity of extremes. However, climate variability during transition periods like the Last Deglaciation remains largely unexplored. Therefore, we investigate changes of climate variability on annual to millennial timescales in fifteen transient climate model simulations of the Last Deglaciation. This ensemble consists of models of varying complexity, from an energy balance model to Earth System Models and includes sensitivity experiments, which differ only in terms of their underlying ice sheet reconstruction, meltwater protocol, or consideration of volcanic forcing. While the ensemble simulates an increase of global mean temperature of 3.0–6.6 °C between the Last Glacial Maximum and Holocene, we examine whether common patterns of variability emerge in the ensemble. To this end, we compare the variability of surface climate during the Last Glacial Maximum, Deglaciation and Holocene by estimating and analyzing the distributions and power spectra of surface temperature and precipitation. For analyzing the distribution shapes, we turn to the higher order moments of variance, skewness and kurtosis. These show that the distributions cannot be assumed to be normal, a precondition for commonly used statistical methods. During the LGM and Holocene, they further reveal significant differences as most simulations feature larger variance during the LGM than Holocene, in-line with results from reconstructions. As a transition period, the Deglaciation stands out as a time of high variance of surface temperature and precipitation, especially on decadal and longer timescales. In general, this dependency on the mean state increases with model complexity, although there is a large spread between models of similar complexity. Some of that spread can be explained by differences in ice sheet, meltwater and volcanic forcings, revealing the impact of simulation protocols on simulated variability. The forcings affect variability not only on their characteristic timescales, rather, we find that they impact variability on all timescales from annual to millennial. The different forcing protocols further have a stronger imprint on the distributions of temperature than precipitation. A rea
{"title":"Patterns of changing surface climate variability from the Last Glacial Maximum to present in transient model simulations","authors":"Elisa Ziegler, Nils Weitzel, Jean-Philippe Baudouin, Marie-Luise Kapsch, Uwe Mikolajewicz, Lauren Gregoire, Ruza Ivanovic, Paul J. Valdes, Christian Wirths, Kira Rehfeld","doi":"10.5194/egusphere-2024-1396","DOIUrl":"https://doi.org/10.5194/egusphere-2024-1396","url":null,"abstract":"<strong>Abstract.</strong> As of 2023, global mean temperature has risen by about 1.45 ± 0.12 °C with respect to the 1850–1900 pre-industrial baseline according to the World Meteorological Organization. This rise constitutes the first period of substantial global warming since the Last Deglaciation, when global temperatures rose over several millennia by about 4.0–7.0 °C according to proxy reconstructions. Similar levels of warming could be reached in the coming centuries considering current and possible future emissions. Such warming causes widespread changes in the climate system of which the mean state provides only an incomplete picture. Indeed, climate’s variability and the distributions of climate variables change with warming, impacting for example ecosystems and the frequency and intensity of extremes. However, climate variability during transition periods like the Last Deglaciation remains largely unexplored. Therefore, we investigate changes of climate variability on annual to millennial timescales in fifteen transient climate model simulations of the Last Deglaciation. This ensemble consists of models of varying complexity, from an energy balance model to Earth System Models and includes sensitivity experiments, which differ only in terms of their underlying ice sheet reconstruction, meltwater protocol, or consideration of volcanic forcing. While the ensemble simulates an increase of global mean temperature of 3.0–6.6 °C between the Last Glacial Maximum and Holocene, we examine whether common patterns of variability emerge in the ensemble. To this end, we compare the variability of surface climate during the Last Glacial Maximum, Deglaciation and Holocene by estimating and analyzing the distributions and power spectra of surface temperature and precipitation. For analyzing the distribution shapes, we turn to the higher order moments of variance, skewness and kurtosis. These show that the distributions cannot be assumed to be normal, a precondition for commonly used statistical methods. During the LGM and Holocene, they further reveal significant differences as most simulations feature larger variance during the LGM than Holocene, in-line with results from reconstructions. As a transition period, the Deglaciation stands out as a time of high variance of surface temperature and precipitation, especially on decadal and longer timescales. In general, this dependency on the mean state increases with model complexity, although there is a large spread between models of similar complexity. Some of that spread can be explained by differences in ice sheet, meltwater and volcanic forcings, revealing the impact of simulation protocols on simulated variability. The forcings affect variability not only on their characteristic timescales, rather, we find that they impact variability on all timescales from annual to millennial. The different forcing protocols further have a stronger imprint on the distributions of temperature than precipitation. A rea","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"85 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-05-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141189750","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}
V. Holly L. Winton, Robert Mulvaney, Joel Savarino, Kyle R. Clem, Markus M. Frey
Abstract. Within the framework of the Isotopic Constraints on Past Ozone Layer in Polar Ice (ISOL-ICE) project, we present initial ice core results from the new ISOL-ICE ice core covering the last millennium from high-elevation Dronning Maud Land (DML) and discuss the implications for interpreting the stable isotopic composition of nitrogen in ice core nitrate (δ15N(NO3-)) as a surface ultra-violet radiation (UV) and total column ozone (TCO) proxy. In the quest to derive TCO using δ15N(NO3-), an understanding of past snow accumulation changes, as well as aerosol source regions and present-day drivers of their variability, is required. We therefore report here the ice core age–depth model, the snow accumulation and ice chemistry records, and correlation analysis of these records with climate variables over the observational era (1979–2016). The ISOL-ICE ice core covers the last 1349 years from 668 to 2017 CE ± 3 years, extending previous ice core records from the region by 2 decades towards the present and shows excellent reproducibility with those records. The extended ISOL-ICE record of last 2 decades showed a continuation of the methane sulfonate (MSA−) increase from ∼ 1800 to present while there were less frequent large deposition events of sea salts relative to the last millennium. While our chemical data do not allow us to distinguish the ultimate (sea ice or the open ocean) source of sea salt aerosols in DML winter aerosol, our correlation analysis clearly suggests that it is mainly the variability in atmospheric transport and not the sea ice extent that explains the interannual variability in sea salt concentrations in DML. Correlation of the snow accumulation record with climate variables over the observational era showed that precipitation at ISOL-ICE is predominately derived from the South Atlantic with onshore winds delivering marine air masses to the site. The snow accumulation rate was stable over the last millennium with no notable trends over the last 2 decades relative to the last millennium. Interannual variability in the accumulation record, ranging between 2 and 20 cm a−1 (w.e.), would influence the ice core δ15N(NO3-) record. The mean snow accumulation rate of 6.5±2.4 cm a−1 (w.e.) falls within the range suitable for reconstructing surface mass balance from ice core δ15N(NO3-), highlighting that the ISOL-ICE ice core δ15N(NO3-) can be used to reconstruct either the surface mass balance or surface UV if the ice core δ15N(NO3-) is corrected for the snow accumulation influence, thereby leaving the UV imprint in the δ15N(NO3-) ice core record to quantify natural ozone variability.
{"title":"Drivers of late Holocene ice core chemistry in Dronning Maud Land: the context for the ISOL-ICE project","authors":"V. Holly L. Winton, Robert Mulvaney, Joel Savarino, Kyle R. Clem, Markus M. Frey","doi":"10.5194/cp-20-1213-2024","DOIUrl":"https://doi.org/10.5194/cp-20-1213-2024","url":null,"abstract":"Abstract. Within the framework of the Isotopic Constraints on Past Ozone Layer in Polar Ice (ISOL-ICE) project, we present initial ice core results from the new ISOL-ICE ice core covering the last millennium from high-elevation Dronning Maud Land (DML) and discuss the implications for interpreting the stable isotopic composition of nitrogen in ice core nitrate (δ15N(NO3-)) as a surface ultra-violet radiation (UV) and total column ozone (TCO) proxy. In the quest to derive TCO using δ15N(NO3-), an understanding of past snow accumulation changes, as well as aerosol source regions and present-day drivers of their variability, is required. We therefore report here the ice core age–depth model, the snow accumulation and ice chemistry records, and correlation analysis of these records with climate variables over the observational era (1979–2016). The ISOL-ICE ice core covers the last 1349 years from 668 to 2017 CE ± 3 years, extending previous ice core records from the region by 2 decades towards the present and shows excellent reproducibility with those records. The extended ISOL-ICE record of last 2 decades showed a continuation of the methane sulfonate (MSA−) increase from ∼ 1800 to present while there were less frequent large deposition events of sea salts relative to the last millennium. While our chemical data do not allow us to distinguish the ultimate (sea ice or the open ocean) source of sea salt aerosols in DML winter aerosol, our correlation analysis clearly suggests that it is mainly the variability in atmospheric transport and not the sea ice extent that explains the interannual variability in sea salt concentrations in DML. Correlation of the snow accumulation record with climate variables over the observational era showed that precipitation at ISOL-ICE is predominately derived from the South Atlantic with onshore winds delivering marine air masses to the site. The snow accumulation rate was stable over the last millennium with no notable trends over the last 2 decades relative to the last millennium. Interannual variability in the accumulation record, ranging between 2 and 20 cm a−1 (w.e.), would influence the ice core δ15N(NO3-) record. The mean snow accumulation rate of 6.5±2.4 cm a−1 (w.e.) falls within the range suitable for reconstructing surface mass balance from ice core δ15N(NO3-), highlighting that the ISOL-ICE ice core δ15N(NO3-) can be used to reconstruct either the surface mass balance or surface UV if the ice core δ15N(NO3-) is corrected for the snow accumulation influence, thereby leaving the UV imprint in the δ15N(NO3-) ice core record to quantify natural ozone variability.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"41 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-05-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141165546","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract. The biological pump, defined as the marine biological production and sedimentation of particulate organic carbon (Corg), is a fundamental process to fix atmospheric carbon dioxide in the oceans, transfer carbon away from the atmosphere to the deep ocean, and maintain the CO2 level of the atmosphere. The level of carbon sequestration by the biological pump has varied throughout the last 50 million years, from particularly weak in the warm Eocene to much stronger in the Holocene. However, persistently warm climates in the more recent past, e.g., the Miocene Climate Optimum (MCO; 17 million years ago [Ma] to 13.8 Ma) also have affected the biological sequestration of carbon. A series of scientific ocean drill sites from the equatorial Pacific contain very low sedimentary Corg % in the period prior to 14 Ma but higher and much more variable Corg % afterward. Although lower absolute productivity may have contributed to the lower Corg burial at the MCO, higher relative Corg degradation also occurred. Ratios of Corg to other productivity indicators indicate higher relative loss of Corg. Temperature records imply that the higher Corg degradation occurred in the upper water column, and global cooling strengthened the biological pump but led to more variability in burial. Similar records of low Corg at the MCO can be found in the North Pacific, which suggest this was a global—rather than regional—change. A weakened biological pump during warm climate intervals helps to sustain periods of global warmth.
{"title":"Variations in the Biological Pump through the Miocene: Evidence from organic carbon burial in Pacific Ocean sediments","authors":"Mitchell Lyle, Annette Olivarez Lyle","doi":"10.5194/cp-2024-34","DOIUrl":"https://doi.org/10.5194/cp-2024-34","url":null,"abstract":"<strong>Abstract.</strong> The biological pump, defined as the marine biological production and sedimentation of particulate organic carbon (C<sub>org</sub>), is a fundamental process to fix atmospheric carbon dioxide in the oceans, transfer carbon away from the atmosphere to the deep ocean, and maintain the CO<sub>2 </sub>level of the atmosphere. The level of carbon sequestration by the biological pump has varied throughout the last 50 million years, from particularly weak in the warm Eocene to much stronger in the Holocene. However, persistently warm climates in the more recent past, e.g., the Miocene Climate Optimum (MCO; 17 million years ago [Ma] to 13.8 Ma) also have affected the biological sequestration of carbon. A series of scientific ocean drill sites from the equatorial Pacific contain very low sedimentary C<sub>org</sub> % in the period prior to 14 Ma but higher and much more variable C<sub>org</sub> % afterward. Although lower absolute productivity may have contributed to the lower C<sub>org</sub> burial at the MCO, higher relative C<sub>org</sub> degradation also occurred. Ratios of C<sub>org</sub> to other productivity indicators indicate higher relative loss of C<sub>org</sub>. Temperature records imply that the higher C<sub>org</sub> degradation occurred in the upper water column, and global cooling strengthened the biological pump but led to more variability in burial. Similar records of low C<sub>org</sub> at the MCO can be found in the North Pacific, which suggest this was a global—rather than regional—change. A weakened biological pump during warm climate intervals helps to sustain periods of global warmth.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"32 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-05-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141165597","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}
Dennis H.A. Vermeulen, Michiel L. J. Baatsen, Anna S. von der Heydt
Abstract. The Eocene-Oligocene Transition (EOT) is marked by a sudden δ18O excursion occurring in two distinct phases, ~500 ky apart. These phases signal a shift from the warm Middle- to Late-Eocene greenhouse climate to cooler conditions, with global surface air temperatures decreasing by 3–5 °C and the emergence of the first continent-wide Antarctic Ice Sheet (AIS). While ice-sheet modelling suggests that ice sheet growth can be triggered by declining pCO2, it still remains unclear how this transition has been initiated, in particular the first growth phase that seems to be related to oceanic and atmospheric cooling rather than ice sheet growth. Recent climate model simulations of the Late-Eocene show improved accuracy but depict climatic conditions that are not conducive to the survival of incipient ice sheets throughout the summer season. This study therefore examines whether it is plausible to develop ice sheets of sufficient scale to trigger the feedback mechanism(s) required to disrupt the atmospheric regime above the Antarctic continent during warm Late-Eocene summers and establish more favourable conditions for ice expansion. We thereby aim to assess the stability of an incipient AIS under varying radiative, orbital and cryospheric forcing. To do so, we evaluate Community Earth System Model 1.0.5 simulations, using a 38 Ma geo- and topographical reconstruction, considering different radiative (4 and 2 pre-industrial carbon) and orbital (present-day and low summer insolation) forcings. The climatic conditions prevailing during (the lead-up to) the EOT can be characterised as extremely seasonal and monsoonal, featuring a short yet intense summer period and contrasting cold winters — highly inhospitable to ice sheet growth for most of the continent, as limited snow accumulation is expected to survive the summer season. A narrow convergence zone with moist convection around the region where sub-cloud equivalent potential temperature is high is shown to exhibit a ring-like structure, advecting moist surface air advected from the Southern Ocean. This advection leads to high values of moist static energy and subsequent precipitation in these regions. To assess the influence of cryospheric forcing, we conducted another simulation, with regional, moderately-sized ice sheets imposed on the continent, to investigate their stability and influence on the atmospheric circulation. Regionally, these relatively small ice sheets respond strongly to radiative and orbital forcing, and demonstrate remarkably favourable self-sustaining and even expansion potential under 2 PIC and low summer insolation conditions. This emphasises a significant hysteresis effect for local and/or regional ice sheets on the Antarctic continent, suggesting the potential for a significant volume of ice on the Antarctic continent without an imminent full glaciation prior to the EOT.
{"title":"Response of Late-Eocene warmth to incipient glaciation on Antarctica","authors":"Dennis H.A. Vermeulen, Michiel L. J. Baatsen, Anna S. von der Heydt","doi":"10.5194/cp-2024-30","DOIUrl":"https://doi.org/10.5194/cp-2024-30","url":null,"abstract":"<strong>Abstract.</strong> The Eocene-Oligocene Transition (EOT) is marked by a sudden δ<sup>18</sup>O excursion occurring in two distinct phases, ~500 ky apart. These phases signal a shift from the warm Middle- to Late-Eocene greenhouse climate to cooler conditions, with global surface air temperatures decreasing by 3–5 °C and the emergence of the first continent-wide Antarctic Ice Sheet (AIS). While ice-sheet modelling suggests that ice sheet growth can be triggered by declining <em>p</em>CO<sub>2</sub>, it still remains unclear how this transition has been initiated, in particular the first growth phase that seems to be related to oceanic and atmospheric cooling rather than ice sheet growth. Recent climate model simulations of the Late-Eocene show improved accuracy but depict climatic conditions that are not conducive to the survival of incipient ice sheets throughout the summer season. This study therefore examines whether it is plausible to develop ice sheets of sufficient scale to trigger the feedback mechanism(s) required to disrupt the atmospheric regime above the Antarctic continent during warm Late-Eocene summers and establish more favourable conditions for ice expansion. We thereby aim to assess the stability of an incipient AIS under varying radiative, orbital and cryospheric forcing. To do so, we evaluate Community Earth System Model 1.0.5 simulations, using a 38 Ma geo- and topographical reconstruction, considering different radiative (4 and 2 pre-industrial carbon) and orbital (present-day and low summer insolation) forcings. The climatic conditions prevailing during (the lead-up to) the EOT can be characterised as extremely seasonal and monsoonal, featuring a short yet intense summer period and contrasting cold winters — highly inhospitable to ice sheet growth for most of the continent, as limited snow accumulation is expected to survive the summer season. A narrow convergence zone with moist convection around the region where sub-cloud equivalent potential temperature is high is shown to exhibit a ring-like structure, advecting moist surface air advected from the Southern Ocean. This advection leads to high values of moist static energy and subsequent precipitation in these regions. To assess the influence of cryospheric forcing, we conducted another simulation, with regional, moderately-sized ice sheets imposed on the continent, to investigate their stability and influence on the atmospheric circulation. Regionally, these relatively small ice sheets respond strongly to radiative and orbital forcing, and demonstrate remarkably favourable self-sustaining and even expansion potential under 2 PIC and low summer insolation conditions. This emphasises a significant hysteresis effect for local and/or regional ice sheets on the Antarctic continent, suggesting the potential for a significant volume of ice on the Antarctic continent without an imminent full glaciation prior to the EOT.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"73 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-05-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141153912","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 : 2024-05-24DOI: 10.5194/egusphere-2024-1003
Chloe A. Brashear, Tyler R. Jones, Valerie Morris, Bruce H. Vaughn, William H. G. Roberts, William B. Skorski, Abigail G. Hughes, Richard Nunn, Sune Olander Rasmussen, Kurt M. Cuffey, Bo M. Vinther, Todd Sowers, Christo Buizert, Vasileios Gkinis, Christian Holme, Mari F. Jensen, Sofia E. Kjellman, Petra M. Langebroek, Florian Mekhaldi, Kevin S. Rozmiarek, Jonathan W. Rheinlænder, Margit Simon, Giulia Sinnl, Silje Smith-Johnsen, James W. C. White
Abstract. During the Last Glacial Period (LGP), Greenland experienced approximately thirty abrupt warming phases, known as Dansgaard-Oeschger (D-O) Events, followed by cooling back to baseline glacial conditions. Studies of mean climate change across warming transitions reveal indistinguishable phase-offsets between shifts in temperature, dust, sea salt, accumulation and moisture source, thus preventing a comprehensive understanding of the “anatomy” of D-O cycles (Capron et al,. 2021). One aspect of abrupt change that has not been systematically assessed is how high-frequency, interannual-scale climatic variability surrounding mean temperature changes across D-O transitions. Here, we utilize the EGRIP ice core high-resolution water isotope record, a proxy for temperature and atmospheric circulation, to quantify the amplitude of 7–15 year isotopic variability for D-O events 2–13, the Younger Dryas and the Bølling-Allerød. On average, cold stadial periods consistently exhibit greater variability than warm interstadial periods. Most notably, we often find that reductions in the amplitude of the 7–15 year band led abrupt D-O warmings by hundreds of years. Such a large phase offset between two climate parameters in a Greenland ice core has never been documented for D-O cycles. However, similar centennial lead times have been found in proxies of Norwegian Sea ice cover relative to abrupt Greenland warming (Sadatzki et al., 2020). Using HadCM3, a fully coupled general circulation model, we assess the effects of sea ice on 7–15 year temperature variability at EGRIP. For a range of stadial and interstadial conditions, we find a strong relationship in line with our observations between colder simulated mean temperature and enhanced temperature variability at the EGRIP location. We also find a robust correlation between year-to-year North Atlantic sea-ice fluctuations and the strength of interannual-scale temperature variability at EGRIP. Thus, both paleoclimate proxy evidence and model simulations suggest that sea ice plays a substantial role in high-frequency climate variability prior to D-O warming. This provides a clue about the anatomy of D-O Events and should be the target of future sea-ice model studies.
{"title":"Shifts in Greenland interannual climate variability lead Dansgaard-Oeschger abrupt warming by hundreds of years","authors":"Chloe A. Brashear, Tyler R. Jones, Valerie Morris, Bruce H. Vaughn, William H. G. Roberts, William B. Skorski, Abigail G. Hughes, Richard Nunn, Sune Olander Rasmussen, Kurt M. Cuffey, Bo M. Vinther, Todd Sowers, Christo Buizert, Vasileios Gkinis, Christian Holme, Mari F. Jensen, Sofia E. Kjellman, Petra M. Langebroek, Florian Mekhaldi, Kevin S. Rozmiarek, Jonathan W. Rheinlænder, Margit Simon, Giulia Sinnl, Silje Smith-Johnsen, James W. C. White","doi":"10.5194/egusphere-2024-1003","DOIUrl":"https://doi.org/10.5194/egusphere-2024-1003","url":null,"abstract":"<strong>Abstract.</strong> During the Last Glacial Period (LGP), Greenland experienced approximately thirty abrupt warming phases, known as Dansgaard-Oeschger (D-O) Events, followed by cooling back to baseline glacial conditions. Studies of mean climate change across warming transitions reveal indistinguishable phase-offsets between shifts in temperature, dust, sea salt, accumulation and moisture source, thus preventing a comprehensive understanding of the “anatomy” of D-O cycles (Capron et al,. 2021). One aspect of abrupt change that has not been systematically assessed is how high-frequency, interannual-scale climatic variability surrounding mean temperature changes across D-O transitions. Here, we utilize the EGRIP ice core high-resolution water isotope record, a proxy for temperature and atmospheric circulation, to quantify the amplitude of 7–15 year isotopic variability for D-O events 2–13, the Younger Dryas and the Bølling-Allerød. On average, cold stadial periods consistently exhibit greater variability than warm interstadial periods. Most notably, we often find that reductions in the amplitude of the 7–15 year band led abrupt D-O warmings by hundreds of years. Such a large phase offset between two climate parameters in a Greenland ice core has never been documented for D-O cycles. However, similar centennial lead times have been found in proxies of Norwegian Sea ice cover relative to abrupt Greenland warming (Sadatzki et al., 2020). Using HadCM3, a fully coupled general circulation model, we assess the effects of sea ice on 7–15 year temperature variability at EGRIP. For a range of stadial and interstadial conditions, we find a strong relationship in line with our observations between colder simulated mean temperature and enhanced temperature variability at the EGRIP location. We also find a robust correlation between year-to-year North Atlantic sea-ice fluctuations and the strength of interannual-scale temperature variability at EGRIP. Thus, both paleoclimate proxy evidence and model simulations suggest that sea ice plays a substantial role in high-frequency climate variability prior to D-O warming. This provides a clue about the anatomy of D-O Events and should be the target of future sea-ice model studies.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"47 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-05-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141151888","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}
Nikita Kaushal, Carlos Perez-Mejias, Heather M. Stoll
<strong>Abstract.</strong> Glacial Terminations represent the largest amplitude climate changes of the last several million years. Several possible orbital-insolation triggers have been described to initiate and sustain glacial Terminations. Because of the availability of radiocarbon dating, the most recent Termination (TI) has been extensively characterized. Yet, it is widely discussed whether the sequence of feedbacks, millennial events and rates of change seen in TI is recurrent over previous Terminations. Beyond the limit of radiocarbon dating, records from the speleothem archive provide absolute age control through uranium-thorium dating and high-resolution proxy measurements. The PAGES SISALv3 global speleothem database allows us to synthesize the available speleothem records covering Terminations. However, speleothem climate signals are encoded in a number of proxies, and unlike proxies in other archives like ice or marine cores, the climatic interpretation of a given proxy can vary quite significantly among different regions. In this study, we <ul> <li>synthesize the available speleothem records providing climate information for Terminations: TII, TIIIA,TIII, TIV and TV,</li> <li>present the records based on the aspect of climate encoded in the available records,</li> <li>examine the effects of different ice volume corrections on the final climate proxy record,</li> <li>evaluate whether there are leads and lags in the manifestation of Terminations across different aspects of the climate systems and different regions,</li> <li>we suggest directions for future speleothem research covering Terminations, speculate on suitable tuning targets among marine and ice core proxies, and discuss what model outputs maybe most suitable for comparison.</li> </ul> We find that TII has the greatest number of globally distributed records followed by TIIA and TIII. The records covering TIV and TV are largely restricted to the East Asian and Southeast Asian monsoon regions. Modelling and data-model comparison studies have greatly increased our understanding of the interpretation of oxygen isotope records across Terminations. Ice volume corrections have the most significant impact on European speleothem records with moisture sourced directly from the North Atlantic region. Within each Termination, a sequence of events can be established between a sub-set of events and this sequence stays largely consistent across Terminations. However, improvements in dating and age-model uncertainties, higher resolution records and multi-proxy approaches are required to establish sequences within each sub-set of events. Beyond further research on targeted speleothem records, our recommendations for future directions include focusing on TII as a useful next target to understand climate dynamics, isotope-enabled transient simulations for better characterization of the other Terminations, and development of marine proxy records with signals common to speleothems to further impro
摘要冰川终结代表了过去几百万年中幅度最大的气候变化。已经描述了几种可能的轨道-日照触发因素来启动和维持冰川终结。由于可以进行放射性碳年代测定，最近的冰川终结（TI）已被广泛描述。然而，人们广泛讨论的是，在 TI 中看到的一系列反馈、千年事件和变化率是否在以前的终结中反复出现。在放射性碳测年的限制之外，通过铀-钍测年和高分辨率代用测量，来自岩浆档案的记录提供了绝对的年龄控制。通过 PAGES SISALv3 全球岩浆数据库，我们可以综合涵盖终结期的现有岩浆记录。然而，岩浆气候信号是由许多代用指标编码的，与冰或海洋岩芯等其他档案中的代用指标不同，不同地区对特定代用指标的气候解释可能有很大差异。在这项研究中，我们综合了提供 "终结点 "气候信息的现有岩浆记录：TII、TIIIA、TIII、TIV 和 TV 记录，根据现有记录所编码的气候方面来介绍这些记录，研究不同冰量校正对最终气候代用记录的影响，评估气候系统不同方面和不同地区的终结现象是否存在领先和滞后现象，提出未来涉及终结现象的岩浆研究方向，推测海洋和冰芯代用指标中合适的调整目标，并讨论哪些模型输出可能最适合进行比较。 我们发现 TII 有最多的全球分布记录，其次是 TIIA 和 TIII。涵盖 TIV 和 TV 的记录主要局限于东亚和东南亚季风区。建模和数据-模型对比研究大大提高了我们对各终端氧同位素记录解释的理解。冰量校正对欧洲岩浆记录的影响最大，其水分直接来自北大西洋地区。在每个终止点内，可以在一个子事件集之间建立一个事件序列，这个序列在各个终止点之间基本保持一致。然而，要在每个事件子集中确定序列，还需要改进年代测定和年龄模型的不确定性，提高记录的分辨率，并采用多代理方法。除了进一步研究有针对性的岩浆记录外，我们对未来方向的建议还包括：将 TII 作为了解气候动态的下一个有用目标；利用同位素进行瞬态模拟，以更好地描述其他终结点的特征；开发具有岩浆共同信号的海洋代用记录，以进一步改进终结点的年代学。
{"title":"Perspective on ice age Terminations from absolute chronologies provided by global speleothem records","authors":"Nikita Kaushal, Carlos Perez-Mejias, Heather M. Stoll","doi":"10.5194/cp-2024-37","DOIUrl":"https://doi.org/10.5194/cp-2024-37","url":null,"abstract":"<strong>Abstract.</strong> Glacial Terminations represent the largest amplitude climate changes of the last several million years. Several possible orbital-insolation triggers have been described to initiate and sustain glacial Terminations. Because of the availability of radiocarbon dating, the most recent Termination (TI) has been extensively characterized. Yet, it is widely discussed whether the sequence of feedbacks, millennial events and rates of change seen in TI is recurrent over previous Terminations. Beyond the limit of radiocarbon dating, records from the speleothem archive provide absolute age control through uranium-thorium dating and high-resolution proxy measurements. The PAGES SISALv3 global speleothem database allows us to synthesize the available speleothem records covering Terminations. However, speleothem climate signals are encoded in a number of proxies, and unlike proxies in other archives like ice or marine cores, the climatic interpretation of a given proxy can vary quite significantly among different regions. In this study, we <ul> <li>synthesize the available speleothem records providing climate information for Terminations: TII, TIIIA,TIII, TIV and TV,</li> <li>present the records based on the aspect of climate encoded in the available records,</li> <li>examine the effects of different ice volume corrections on the final climate proxy record,</li> <li>evaluate whether there are leads and lags in the manifestation of Terminations across different aspects of the climate systems and different regions,</li> <li>we suggest directions for future speleothem research covering Terminations, speculate on suitable tuning targets among marine and ice core proxies, and discuss what model outputs maybe most suitable for comparison.</li> </ul> We find that TII has the greatest number of globally distributed records followed by TIIA and TIII. The records covering TIV and TV are largely restricted to the East Asian and Southeast Asian monsoon regions. Modelling and data-model comparison studies have greatly increased our understanding of the interpretation of oxygen isotope records across Terminations. Ice volume corrections have the most significant impact on European speleothem records with moisture sourced directly from the North Atlantic region. Within each Termination, a sequence of events can be established between a sub-set of events and this sequence stays largely consistent across Terminations. However, improvements in dating and age-model uncertainties, higher resolution records and multi-proxy approaches are required to establish sequences within each sub-set of events. Beyond further research on targeted speleothem records, our recommendations for future directions include focusing on TII as a useful next target to understand climate dynamics, isotope-enabled transient simulations for better characterization of the other Terminations, and development of marine proxy records with signals common to speleothems to further impro","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"46 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-05-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141151967","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}
Benjamin Fredericks Petrick, Lars Reuning, Miriam Pfeiffer, Gerald Auer, Lorenz Schwark
Abstract. The Late Miocene Cooling (LMC) has been recognized as a global event in the climate record and posited as the start of modern ecosystems. Whereas shifts in modern terrestrial ecosystems around 7.0 – 5.5 Ma occur globally, little is known about changes in aquatic ecosystems. This is especially true of shallow water carbonate ecosystems, such as coral reefs, where few good proxy records exist. A “reef gap” existed during the Pliocene in the area of the Central Indo-Pacific, where reefs that had been present during the Messinian (7 – 5 Ma) drowned by the Early Pliocene (5 – 3 Ma). Here, we present a TEX86H-based sea surface temperature (SST) record for the Coral Sea, suggesting that the LMC was more pronounced than previously thought. During the LMC, the SSTs at ODP Site 811 declined by about 2 °C, and cooling lasted from 7 Ma to possibly as late as 5 Ma. This level of cooling has also been seen in other parts of the Central Indo-Pacific. Previous research showed that coral reefs across the Central Indo-Pacific experienced a major ecosystem change, leading to the collapse of the coral reefs by 5 Ma. This event led to a lack of coral reefs during the Pliocene, an event that has often been described as the “Pliocene reef gap.” The timing of the onset of this event matches the cooling in the records. This suggests that the LMC was a final stressor that provided a regional driver for the collapse of reefs and, therefore, a potential cause for the “Pliocene Coral Gap.” The relatively rapid and intense change in SST and other stressors associated with the cooling caused coral reef systems to collapse across the Central Indo-Pacific.
{"title":"Impact of the Late Miocene Cooling on the loss of coral reefs in the Central Indo-Pacific","authors":"Benjamin Fredericks Petrick, Lars Reuning, Miriam Pfeiffer, Gerald Auer, Lorenz Schwark","doi":"10.5194/cp-2024-28","DOIUrl":"https://doi.org/10.5194/cp-2024-28","url":null,"abstract":"<strong>Abstract.</strong> The Late Miocene Cooling (LMC) has been recognized as a global event in the climate record and posited as the start of modern ecosystems. Whereas shifts in modern terrestrial ecosystems around 7.0 – 5.5 Ma occur globally, little is known about changes in aquatic ecosystems. This is especially true of shallow water carbonate ecosystems, such as coral reefs, where few good proxy records exist. A “reef gap” existed during the Pliocene in the area of the Central Indo-Pacific, where reefs that had been present during the Messinian (7 – 5 Ma) drowned by the Early Pliocene (5 – 3 Ma). Here, we present a TEX<sub>86</sub><sup>H</sup>-based sea surface temperature (SST) record for the Coral Sea, suggesting that the LMC was more pronounced than previously thought. During the LMC, the SSTs at ODP Site 811 declined by about 2 °C, and cooling lasted from 7 Ma to possibly as late as 5 Ma. This level of cooling has also been seen in other parts of the Central Indo-Pacific. Previous research showed that coral reefs across the Central Indo-Pacific experienced a major ecosystem change, leading to the collapse of the coral reefs by 5 Ma. This event led to a lack of coral reefs during the Pliocene, an event that has often been described as the “Pliocene reef gap.” The timing of the onset of this event matches the cooling in the records. This suggests that the LMC was a final stressor that provided a regional driver for the collapse of reefs and, therefore, a potential cause for the “Pliocene Coral Gap.” The relatively rapid and intense change in SST and other stressors associated with the cooling caused coral reef systems to collapse across the Central Indo-Pacific.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"42 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-05-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140931676","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}
Suning Hou, Leonie Toebrock, Mart van der Linden, Fleur Rothstegge, Martin Ziegler, Lucas J. Lourens, Peter K. Bijl
Abstract. During the Pliocene, atmospheric CO2 concentrations (pCO2) were similar to today’s and global average temperature was ~3 °C higher. However, the relationships and phasing between variability in climate and pCO2 on orbital time scales are not well understood. Specifically, questions remain about the nature of a lag of pCO2 relative to benthic foraminiferal δ18O in the late-Pliocene Marine Isotope Stage M2 (3300 kiloannum ago, ka), which was longer than during the Pleistocene. Here, we present a multi-proxy paleoceanographic reconstruction of the late-Pliocene subantarctic zone, which is today one of the major ocean sinks of atmospheric CO2. New dinoflagellate cyst assemblage data is combined with previously published sea surface temperature reconstructions, to reveal past surface conditions, including latitudinal migrations of the subtropical front (STF) over the late-Pliocene at ODP Site 1168, offshore west Tasmania. We observe strong oceanographic variability at the STF over glacial-interglacial timescales, especially across the M2 (3320–3260 ka). By providing tight and independent age constraints from benthic foraminiferal δ18O, we find that, much more than benthic δ18O or local SST, latitudinal migrations of the STF are tightly coupled to pCO2 variations across the M2. Specifically, a northerly position of the STF during M2 deglaciation coincides with generally low pCO2. We postulate that the efficiency of the Southern Ocean carbon outgassing varied strongly with migrations of the STF, and that is in part accounted for the variability in pCO2 across M2.
{"title":"Southern Ocean control on atmospheric CO2 changes across late-Pliocene Marine Isotope Stage M2","authors":"Suning Hou, Leonie Toebrock, Mart van der Linden, Fleur Rothstegge, Martin Ziegler, Lucas J. Lourens, Peter K. Bijl","doi":"10.5194/cp-2024-33","DOIUrl":"https://doi.org/10.5194/cp-2024-33","url":null,"abstract":"<strong>Abstract.</strong> During the Pliocene, atmospheric CO<sub>2</sub> concentrations (<em>p</em>CO<sub>2</sub>) were similar to today’s and global average temperature was ~3 °C higher. However, the relationships and phasing between variability in climate and <em>p</em>CO<sub>2</sub> on orbital time scales are not well understood. Specifically, questions remain about the nature of a lag of <em>p</em>CO<sub>2</sub> relative to benthic foraminiferal δ<sup>18</sup>O in the late-Pliocene Marine Isotope Stage M2 (3300 kiloannum ago, ka), which was longer than during the Pleistocene. Here, we present a multi-proxy paleoceanographic reconstruction of the late-Pliocene subantarctic zone, which is today one of the major ocean sinks of atmospheric CO<sub>2</sub>. New dinoflagellate cyst assemblage data is combined with previously published sea surface temperature reconstructions, to reveal past surface conditions, including latitudinal migrations of the subtropical front (STF) over the late-Pliocene at ODP Site 1168, offshore west Tasmania. We observe strong oceanographic variability at the STF over glacial-interglacial timescales, especially across the M2 (3320–3260 ka). By providing tight and independent age constraints from benthic foraminiferal δ<sup>18</sup>O, we find that, much more than benthic δ<sup>18</sup>O or local SST, latitudinal migrations of the STF are tightly coupled to <em>p</em>CO<sub>2</sub> variations across the M2. Specifically, a northerly position of the STF during M2 deglaciation coincides with generally low <em>p</em>CO<sub>2</sub>. We postulate that the efficiency of the Southern Ocean carbon outgassing varied strongly with migrations of the STF, and that is in part accounted for the variability in <em>p</em>CO<sub>2</sub> across M2.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"39 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-05-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140931719","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract. The Southern Annular Mode (SAM) strongly influences climate variability in the Southern Hemisphere. The SAM index describes the phase and magnitude of the SAM and can be calculated by measuring the difference in mean sea level pressure (MSLP) between middle and high latitudes. This study investigates the effects of calculation methods and data resolution on the SAM index, and subsequent interpretations of SAM impacts and trends. We show that the normalisation step that is traditionally used in calculating the SAM index leads to substantial differences in the magnitude of the SAM index calculated at different temporal resolutions. Additionally, the equal weighting that the normalisation approach gives to MSLP variability at the middle and high southern latitudes artificially alters temperature and precipitation correlations and the interpretation of climate change trends in the SAM. These issues can be overcome by instead using a natural SAM index based on MSLP anomalies, resulting in consistent scaling and variability in the SAM index calculated at daily, monthly and annual data resolutions. The natural SAM index has improved representation of SAM impacts in the high southern latitudes, including the asymmetric (zonal wave-3) component of MSLP variability, whereas the increased weighting given to mid-latitude MSLP variability in the normalised SAM index incorporates a stronger component of tropical climate variability that is not directly associated with SAM variability. We conclude that an improved approach of calculating the SAM index from MSLP anomalies without normalisation would aid consistency across climate studies and avoid potential ambiguity in the SAM index, including SAM index reconstructions from palaeoclimate data, and thus enable more consistent interpretations of SAM trends and impacts.
摘要南环流模式（SAM）强烈影响着南半球的气候变率。南环流模式指数描述了南环流模式的相位和幅度，可通过测量中纬度和高纬度之间的平均海平面气压（MSLP）差来计算。本研究调查了计算方法和数据分辨率对萨姆指数的影响，以及随后对萨姆影响和趋势的解释。我们发现，传统上用于计算 SAM 指数的归一化步骤会导致在不同时间分辨率下计算出的 SAM 指数大小存在巨大差异。此外，归一化方法对中纬度和南纬高纬度的 MSLP 变率给予同等权重，人为地改变了温度和降水的相关性以及对 SAM 中气候变化趋势的解释。这些问题可以通过使用基于 MSLP 异常的自然 SAM 指数来解决，从而使按日、月和年数据分辨率计算的 SAM 指数具有一致的比例和变异性。自然 SAM 指数能更好地反映 SAM 对南部高纬度地区的影响，包括 MSLP 变率中的非对称（带状波-3）成分，而在归一化 SAM 指数中，中纬度 MSLP 变率的权重增加，纳入了热带气候变率中与 SAM 变率无直接关联的更强的成分。我们的结论是，通过 MSLP 异常值计算 SAM 指数而不进行归一化的改进方法将有助于气候研究的一致性，并避免 SAM 指数（包括根据古气候数据重建的 SAM 指数）中潜在的模糊性，从而使对 SAM 趋势和影响的解释更加一致。
{"title":"Technical note: An improved methodology for calculating the Southern Annular Mode index to aid consistency between climate studies","authors":"Laura Velasquez-Jimenez, Nerilie J. Abram","doi":"10.5194/cp-20-1125-2024","DOIUrl":"https://doi.org/10.5194/cp-20-1125-2024","url":null,"abstract":"Abstract. The Southern Annular Mode (SAM) strongly influences climate variability in the Southern Hemisphere. The SAM index describes the phase and magnitude of the SAM and can be calculated by measuring the difference in mean sea level pressure (MSLP) between middle and high latitudes. This study investigates the effects of calculation methods and data resolution on the SAM index, and subsequent interpretations of SAM impacts and trends. We show that the normalisation step that is traditionally used in calculating the SAM index leads to substantial differences in the magnitude of the SAM index calculated at different temporal resolutions. Additionally, the equal weighting that the normalisation approach gives to MSLP variability at the middle and high southern latitudes artificially alters temperature and precipitation correlations and the interpretation of climate change trends in the SAM. These issues can be overcome by instead using a natural SAM index based on MSLP anomalies, resulting in consistent scaling and variability in the SAM index calculated at daily, monthly and annual data resolutions. The natural SAM index has improved representation of SAM impacts in the high southern latitudes, including the asymmetric (zonal wave-3) component of MSLP variability, whereas the increased weighting given to mid-latitude MSLP variability in the normalised SAM index incorporates a stronger component of tropical climate variability that is not directly associated with SAM variability. We conclude that an improved approach of calculating the SAM index from MSLP anomalies without normalisation would aid consistency across climate studies and avoid potential ambiguity in the SAM index, including SAM index reconstructions from palaeoclimate data, and thus enable more consistent interpretations of SAM trends and impacts.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"30 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-05-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140931720","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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