Pub Date : 2024-09-18DOI: 10.5194/egusphere-2024-2660
Helen J. Shea, Ailie Gallant, Ariaan Purich, Tessa R. Vance
Abstract. The Mount Brown South (MBS) ice core in East Antarctica (69° S, 86° E) has produced records of sea salt concentration and snow accumulation for examining past climate. In a previous study, the sea salt concentration, but not snow accumulation, showed a significant, positive relationship with the El Niño-Southern Oscillation (ENSO) from June to November. Here, we use observations and reanalysis data to provide insights into the mechanisms modulating this previously identified relationship for the austral winter season (June-August). A teleconnection between the tropical Pacific and high-latitude winds in the vicinity of MBS is identified. Specifically, El Niño events are related to strengthened westerly winds ∼60° S, leading to more local sea ice via anomalous Ekman transport in an area to the northeast of the MBS site. Impacts from La Niña are less obvious, showing that there is a non-linear component to this relationship. MBS is a wet deposition site, and we show that sea salt is likely transported from northeast of MBS via synoptic-scale storms that accompany high precipitation events. These storms and their associated precipitation, show no substantial differences between years of high and low sea salt concentration, so we suggest it is the source of sea salt that differs, rather than the transport mechanism. El Niño-associated strengthened westerly winds in the MBS region could enhance sea salt availability by increasing ocean aerosol spray and/or by increasing sea ice formation, both of which can act as sources of sea salt. This may explain why sea salt concentration, rather than snow accumulation, is most closely related to ENSO variability in the ice core record. Identifying the mechanisms modulating key variables such as sea salts and snow accumulation at ice core sites provides further insights into what these valuable records can decipher about climate variability in the pre-instrumental period.
{"title":"Climate influences on sea salt variability at Mount Brown South, East Antarctica","authors":"Helen J. Shea, Ailie Gallant, Ariaan Purich, Tessa R. Vance","doi":"10.5194/egusphere-2024-2660","DOIUrl":"https://doi.org/10.5194/egusphere-2024-2660","url":null,"abstract":"<strong>Abstract.</strong> The Mount Brown South (MBS) ice core in East Antarctica (69° S, 86° E) has produced records of sea salt concentration and snow accumulation for examining past climate. In a previous study, the sea salt concentration, but not snow accumulation, showed a significant, positive relationship with the El Niño-Southern Oscillation (ENSO) from June to November. Here, we use observations and reanalysis data to provide insights into the mechanisms modulating this previously identified relationship for the austral winter season (June-August). A teleconnection between the tropical Pacific and high-latitude winds in the vicinity of MBS is identified. Specifically, El Niño events are related to strengthened westerly winds ∼60° S, leading to more local sea ice via anomalous Ekman transport in an area to the northeast of the MBS site. Impacts from La Niña are less obvious, showing that there is a non-linear component to this relationship. MBS is a wet deposition site, and we show that sea salt is likely transported from northeast of MBS via synoptic-scale storms that accompany high precipitation events. These storms and their associated precipitation, show no substantial differences between years of high and low sea salt concentration, so we suggest it is the source of sea salt that differs, rather than the transport mechanism. El Niño-associated strengthened westerly winds in the MBS region could enhance sea salt availability by increasing ocean aerosol spray and/or by increasing sea ice formation, both of which can act as sources of sea salt. This may explain why sea salt concentration, rather than snow accumulation, is most closely related to ENSO variability in the ice core record. Identifying the mechanisms modulating key variables such as sea salts and snow accumulation at ice core sites provides further insights into what these valuable records can decipher about climate variability in the pre-instrumental period.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"10 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142254018","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}
Mateo Duque-Villegas, Martin Claussen, Thomas Kleinen, Jürgen Bader, Christian H. Reick
Abstract. Over the last hundreds of millennia natural rhythms in Earth's astronomical motions triggered large-scale climate changes and led periodically to humid conditions in much of North Africa. Known as African humid periods (AHPs), such times sustained river networks, vegetation, wildlife and prehistoric settlements. Mechanisms, extent and timing of the changes still cannot be completely outlined. Although AHPs along glacial cycles are recognizable in long marine sediment records, the related land cover changes are difficult to reconstruct due to scarcity of proxy data over the continent. Moreover, most available information covers only the latest AHP during the Holocene. Here we use a comprehensive Earth system model to look at additional, much earlier, possible cases of AHPs. We simulate the full last glacial cycle, aiming to reproduce the last four AHPs as seen in available proxies. The simulated AHPs seem in broad agreement with geological records, especially in terms of timing and relative strength. We focus on the simulated vegetation coverage in North Africa and we detect a dominant change pattern that seems to scale linearly with known climate forcing variables. We use such scaling to approximate North African vegetation fractions over the last eight glacial cycles. Although the simple linear estimation is based on a single mode of vegetation variability (that explains about 70 % of the variance), it helps to discuss some broad-scale spatial features that had been only considered for the Holocene AHP. Extending the climate simulation several millennia into the future reveals that such pattern scaling breaks when greenhouse gases become a stronger climate change driver.
{"title":"Pattern scaling of simulated vegetation change in North Africa during glacial cycles","authors":"Mateo Duque-Villegas, Martin Claussen, Thomas Kleinen, Jürgen Bader, Christian H. Reick","doi":"10.5194/cp-2024-61","DOIUrl":"https://doi.org/10.5194/cp-2024-61","url":null,"abstract":"<strong>Abstract.</strong> Over the last hundreds of millennia natural rhythms in Earth's astronomical motions triggered large-scale climate changes and led periodically to humid conditions in much of North Africa. Known as African humid periods (AHPs), such times sustained river networks, vegetation, wildlife and prehistoric settlements. Mechanisms, extent and timing of the changes still cannot be completely outlined. Although AHPs along glacial cycles are recognizable in long marine sediment records, the related land cover changes are difficult to reconstruct due to scarcity of proxy data over the continent. Moreover, most available information covers only the latest AHP during the Holocene. Here we use a comprehensive Earth system model to look at additional, much earlier, possible cases of AHPs. We simulate the full last glacial cycle, aiming to reproduce the last four AHPs as seen in available proxies. The simulated AHPs seem in broad agreement with geological records, especially in terms of timing and relative strength. We focus on the simulated vegetation coverage in North Africa and we detect a dominant change pattern that seems to scale linearly with known climate forcing variables. We use such scaling to approximate North African vegetation fractions over the last eight glacial cycles. Although the simple linear estimation is based on a single mode of vegetation variability (that explains about 70 % of the variance), it helps to discuss some broad-scale spatial features that had been only considered for the Holocene AHP. Extending the climate simulation several millennia into the future reveals that such pattern scaling breaks when greenhouse gases become a stronger climate change driver.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"18 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142254020","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 circumnavigations of Cook (second voyage, 1772–1775) and Bellingshausen (1819–1821) were attempts to find any great southern land mass poleward of ∼ 50° S and consequently involved sailing for three or two summers, respectively, in polar latitudes around Antarctica. Extensive sea ice eventually blocked each voyage's southern probes, although Bellingshausen, unknowingly at the time, saw the Antarctic continent. However, these attempts meant sea ice and iceberg records from the early historical period were collected nearly simultaneously from around much of Antarctica. Here, these records are extracted from journals, analysed, and compared to each other and the modern satellite record of both forms of marine ice. They generally show an early historical period with a more northerly record of both forms of marine ice than normal for today, but to a geographically varying degree. However, the early historical period in the Pacific sector of the Southern Ocean saw marine ice generally within the range of modern observations for the same time of year, but the Weddell Sea and Indian Ocean marine ice, particularly on Cook's voyage, then extended several degrees further north than in today's extreme ice years.
{"title":"The Southern Ocean marine ice record of the early historical, circum-Antarctic voyages of Cook and Bellingshausen","authors":"Grant R. Bigg","doi":"10.5194/cp-20-2045-2024","DOIUrl":"https://doi.org/10.5194/cp-20-2045-2024","url":null,"abstract":"Abstract. The circumnavigations of Cook (second voyage, 1772–1775) and Bellingshausen (1819–1821) were attempts to find any great southern land mass poleward of ∼ 50° S and consequently involved sailing for three or two summers, respectively, in polar latitudes around Antarctica. Extensive sea ice eventually blocked each voyage's southern probes, although Bellingshausen, unknowingly at the time, saw the Antarctic continent. However, these attempts meant sea ice and iceberg records from the early historical period were collected nearly simultaneously from around much of Antarctica. Here, these records are extracted from journals, analysed, and compared to each other and the modern satellite record of both forms of marine ice. They generally show an early historical period with a more northerly record of both forms of marine ice than normal for today, but to a geographically varying degree. However, the early historical period in the Pacific sector of the Southern Ocean saw marine ice generally within the range of modern observations for the same time of year, but the Weddell Sea and Indian Ocean marine ice, particularly on Cook's voyage, then extended several degrees further north than in today's extreme ice years.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"313 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142254016","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. Arctic permafrost stores vast amounts of terrestrial organic matter (terrOM). Under warming climate conditions, Arctic permafrost thaws, releasing aged carbon and potentially impacting the modern carbon cycle. We investigated the characteristics of terrestrial biomarkers, including n-alkanes, fatty acids, and lignin phenols, in marine sediment cores to understand how the sources of terrOM transported to the ocean change in response to varying environmental conditions such as sea-level rise, sea ice coverage, inland climate warming, and freshwater input. We examined two sediment records from the western Laptev Sea (PS51/154 and PS51/159) covering the past 17.8 kyr. Our analyses reveal three periods with high mass accumulation rates (MARs) of terrestrial biomarkers, from 14.1 to 13.2, 11.6 to 10.9, and 10.9 to 9.5 kyr BP. These MAR peaks revealed distinct terrOM sources, likely in response to changes in shelf topography, rates of sea-level rise, and inland warming. By comparing periods of high terrOM MAR in the Laptev Sea with published records from other Arctic marginal seas, we suggest that enhanced coastal erosion driven by rapid sea-level rise during meltwater pulse 1A (mwp-1A) triggered elevated terrOM MAR across the Arctic. Additional terrOM MAR peaks coincided with periods of enhanced inland warming, prolonged ice-free conditions, and freshwater flooding, which varied between regions. Our results highlight regional environmental controls on terrOM sources, which can either facilitate or preclude regional terrOM fluxes in addition to global controls.
{"title":"Environmental controls of rapid terrestrial organic matter mobilization to the western Laptev Sea since the last deglaciation","authors":"Tsai-Wen Lin, Tommaso Tesi, Jens Hefter, Hendrik Grotheer, Jutta Wollenburg, Florian Adolphi, Henning Bauch, Alessio Nogarotto, Juliane Müller, Gesine Mollenhauer","doi":"10.5194/cp-2024-60","DOIUrl":"https://doi.org/10.5194/cp-2024-60","url":null,"abstract":"<strong>Abstract.</strong> Arctic permafrost stores vast amounts of terrestrial organic matter (terrOM). Under warming climate conditions, Arctic permafrost thaws, releasing aged carbon and potentially impacting the modern carbon cycle. We investigated the characteristics of terrestrial biomarkers, including <em>n</em>-alkanes, fatty acids, and lignin phenols, in marine sediment cores to understand how the sources of terrOM transported to the ocean change in response to varying environmental conditions such as sea-level rise, sea ice coverage, inland climate warming, and freshwater input. We examined two sediment records from the western Laptev Sea (PS51/154 and PS51/159) covering the past 17.8 kyr. Our analyses reveal three periods with high mass accumulation rates (MARs) of terrestrial biomarkers, from 14.1 to 13.2, 11.6 to 10.9, and 10.9 to 9.5 kyr BP. These MAR peaks revealed distinct terrOM sources, likely in response to changes in shelf topography, rates of sea-level rise, and inland warming. By comparing periods of high terrOM MAR in the Laptev Sea with published records from other Arctic marginal seas, we suggest that enhanced coastal erosion driven by rapid sea-level rise during meltwater pulse 1A (mwp-1A) triggered elevated terrOM MAR across the Arctic. Additional terrOM MAR peaks coincided with periods of enhanced inland warming, prolonged ice-free conditions, and freshwater flooding, which varied between regions. Our results highlight regional environmental controls on terrOM sources, which can either facilitate or preclude regional terrOM fluxes in addition to global controls.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"17 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142254019","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 : 2024-09-18DOI: 10.5194/egusphere-2024-2675
Bartholomé Duboc, Katrin J. Meissner, Laurie Menviel, Nicholas K. H. Yeung, Babette Hoogakker, Tilo Ziehn, Matthew Chamberlain
Abstract. Recent studies investigating future warming scenarios have shown that the ocean oxygen content will continue to decrease over the coming century due to ocean warming and changes in oceanic circulation. However, significant uncertainties remain regarding the magnitude and patterns of future ocean deoxygenation. Here, we simulate ocean oxygenation with the ACCESS ESM1.5 model during two past interglacials that were warmer than the preindustrial climate, the Last Interglacial (Marine Isotope Stage (MIS) 5e, ~ 129–115 ka) and MIS 9e (~ 336–321 ka). While orbital parameters were similar during MIS 5e and MIS 9e, with lower precession, higher eccentricity and higher obliquity than pre-industrial, greenhouse gas radiative forcing was highest during MIS 9e. We find that the global ocean is overall less oxygenated in the MIS 5e and MIS 9e simulations compared to the preindustrial control run and that oxygen concentrations are more sensitive to changes in the distribution of incoming solar radiation than to differences in greenhouse gas concentrations. Large regions in the Mediterranean Sea are hypoxic in the MIS 5e simulation, and to a lesser extent in the MIS 9e simulation, due to an intensification and expansion of the African Monsoon, enhanced river run-off and resulting freshening of surface waters and stratification. Upwelling zones off the coast of North America and North Africa are weaker in both simulations compared to the preindustrial control run, leading to less primary productivity and export production. Antarctic Bottom Water is less oxygenated, while North Atlantic Deep Water and the North Pacific Ocean at intermediate depths are higher in oxygen content. All changes in oxygen concentrations are primarily caused by changes in ocean circulation and export production and secondarily by changes in temperature and solubility.
摘要最近对未来变暖情景的调查研究表明，由于海洋变暖和大洋环流的变化，海洋含氧量在下个世纪将继续下降。然而，未来海洋脱氧的程度和模式仍存在很大的不确定性。在此，我们利用 ACCESS ESM1.5 模型模拟了过去两个比工业化前气候更温暖的间冰期（末次间冰期（海洋同位素阶段（MIS）5e，约 129-115 ka）和 MIS 9e（约 336-321 ka）期间的海洋含氧量。虽然 MIS 5e 和 MIS 9e 期间的轨道参数相似，与工业化前相比，前向度更低、偏心率更高、倾角更大，但 MIS 9e 期间的温室气体辐射强迫最大。我们发现，与工业化前的对照运行相比，在 MIS 5e 和 MIS 9e 模拟中，全球海洋的含氧量总体较低，氧气浓度对太阳辐射入射分布的变化比对温室气体浓度的差异更为敏感。在 MIS 5e 模拟中，地中海大面积缺氧，在 MIS 9e 模拟中缺氧程度较轻，原因是非洲季风增强并扩大，河流径流增强，导致表层水变清和分层。与工业化前的对照运行相比，两种模拟中北美和北非沿岸的上升流区都较弱，导致初级生产力和出口生产减少。南极底层海水含氧量较低，而北大西洋深层海水和北太平洋中层海水含氧量较高。氧气浓度的所有变化主要是由海洋环流和出口生产的变化引起的，其次是由温度和溶解度的变化引起的。
{"title":"Simulated ocean oxygenation during the interglacials MIS 5e and MIS 9e","authors":"Bartholomé Duboc, Katrin J. Meissner, Laurie Menviel, Nicholas K. H. Yeung, Babette Hoogakker, Tilo Ziehn, Matthew Chamberlain","doi":"10.5194/egusphere-2024-2675","DOIUrl":"https://doi.org/10.5194/egusphere-2024-2675","url":null,"abstract":"<strong>Abstract.</strong> Recent studies investigating future warming scenarios have shown that the ocean oxygen content will continue to decrease over the coming century due to ocean warming and changes in oceanic circulation. However, significant uncertainties remain regarding the magnitude and patterns of future ocean deoxygenation. Here, we simulate ocean oxygenation with the ACCESS ESM1.5 model during two past interglacials that were warmer than the preindustrial climate, the Last Interglacial (Marine Isotope Stage (MIS) 5e, ~ 129–115 ka) and MIS 9e (~ 336–321 ka). While orbital parameters were similar during MIS 5e and MIS 9e, with lower precession, higher eccentricity and higher obliquity than pre-industrial, greenhouse gas radiative forcing was highest during MIS 9e. We find that the global ocean is overall less oxygenated in the MIS 5e and MIS 9e simulations compared to the preindustrial control run and that oxygen concentrations are more sensitive to changes in the distribution of incoming solar radiation than to differences in greenhouse gas concentrations. Large regions in the Mediterranean Sea are hypoxic in the MIS 5e simulation, and to a lesser extent in the MIS 9e simulation, due to an intensification and expansion of the African Monsoon, enhanced river run-off and resulting freshening of surface waters and stratification. Upwelling zones off the coast of North America and North Africa are weaker in both simulations compared to the preindustrial control run, leading to less primary productivity and export production. Antarctic Bottom Water is less oxygenated, while North Atlantic Deep Water and the North Pacific Ocean at intermediate depths are higher in oxygen content. All changes in oxygen concentrations are primarily caused by changes in ocean circulation and export production and secondarily by changes in temperature and solubility.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"240 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142254021","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. Understanding orbital-scale changes in East Asian summer monsoon (EASM) precipitation is a fundamental issue in paleoclimate research as it helps assess the response of the East Asian monsoon to different climatic forcings, such as insolation, ice volume, and greenhouse gases. However, due to inconsistencies between different proxies, the fundamental driving force for EASM variability remains controversial. The present study simulated the global climate under given insolation changes over the past 450 kyr using a climate model, version 2.3 of the Meteorological Research Institute's Coupled General Circulation Model (MRI-CGCM2.3). Changes in summer insolation over East Asia resulted in distinct climatic responses in China and Japan: an increase in summer insolation led to increased summer precipitation in China and decreased summer precipitation in Japan. Composite analyses of simulated climate under strong boreal-summer insolation suggest that warming of the Indian Ocean occurs under intense insolation, resulting in the intensification of the North Pacific subtropical high (sub-high). The northern shift in the monsoon front, associated with the intensified sub-high, leads to an increase in rainfall in the coastal area of China. In contrast, the intensity of the EASM around Japan is affected by the strength of the North Pacific High. Under strong insolation, the increase in thermal contrast between the North American continent and the North Pacific Ocean intensifies the North Pacific High, decreasing summer precipitation around Japan. Thus, strong regional differences in the effects of solar-insolation variability on summer precipitation in East Asia exist due to interactions with different ocean basins.
{"title":"Contrasting responses of summer precipitation to orbital forcing in Japan and China over the past 450 kyr","authors":"Taiga Matsushita, Mariko Harada, Hiroaki Ueda, Takeshi Nakagawa, Yoshimi Kubota, Yoshiaki Suzuki, Youichi Kamae","doi":"10.5194/cp-20-2017-2024","DOIUrl":"https://doi.org/10.5194/cp-20-2017-2024","url":null,"abstract":"Abstract. Understanding orbital-scale changes in East Asian summer monsoon (EASM) precipitation is a fundamental issue in paleoclimate research as it helps assess the response of the East Asian monsoon to different climatic forcings, such as insolation, ice volume, and greenhouse gases. However, due to inconsistencies between different proxies, the fundamental driving force for EASM variability remains controversial. The present study simulated the global climate under given insolation changes over the past 450 kyr using a climate model, version 2.3 of the Meteorological Research Institute's Coupled General Circulation Model (MRI-CGCM2.3). Changes in summer insolation over East Asia resulted in distinct climatic responses in China and Japan: an increase in summer insolation led to increased summer precipitation in China and decreased summer precipitation in Japan. Composite analyses of simulated climate under strong boreal-summer insolation suggest that warming of the Indian Ocean occurs under intense insolation, resulting in the intensification of the North Pacific subtropical high (sub-high). The northern shift in the monsoon front, associated with the intensified sub-high, leads to an increase in rainfall in the coastal area of China. In contrast, the intensity of the EASM around Japan is affected by the strength of the North Pacific High. Under strong insolation, the increase in thermal contrast between the North American continent and the North Pacific Ocean intensifies the North Pacific High, decreasing summer precipitation around Japan. Thus, strong regional differences in the effects of solar-insolation variability on summer precipitation in East Asia exist due to interactions with different ocean basins.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"13 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-09-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142254022","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}
Rachael H. Rhodes, Yvan Bollet-Quivogne, Piers Barnes, Mirko Severi, Eric W. Wolff
Abstract. To extract climatically relevant chemical signals from the deepest, oldest Antarctic ice, we must first investigate the degree to which chemical ions diffuse within solid ice. Volcanic sulfate peaks are an ideal target for such an investigation because they are high-amplitude, short-duration (∼3 years) events with a quasi-uniform structure. Here we present an analysis of the EPICA Dome C sulfate record over the last 450 kyr. We identify volcanic peaks and isolate them from the non-sea-salt sulfate background to reveal the effects of diffusion: amplitude damping and broadening of peaks in the time domain with increasing depth and age. Sulfate peak shape is also altered by the thinning of ice layers with depth that results from ice flow. Both processes must be simulated to derive effective diffusion rates. This is achieved by running a forward model to diffuse idealised sulfate peaks at different rates while also accounting for ice thinning. Our simulations suggest a median effective diffusion rate of sulfate ions of 2.4±1.7×10-7 m2 yr−1 in Holocene ice, slightly faster than suggested by previous work. The effective diffusion rate observed in deeper ice is significantly lower, and Holocene ice shows the highest rate of the last 450 kyr. Beyond the Holocene, there is no systematic difference between the effective diffusion rates of glacial and interglacial periods despite variations in soluble ion concentrations, dust loading, and ice grain radii. Effective diffusion rates for 40 to 200 ka are relatively constant and of the order 1×10-8 m2 yr−1. Our results suggest that the diffusion of sulfate ions within volcanic peaks is relatively fast initially, perhaps through an interconnected vein network, but slows significantly after 40 kyr. In the absence of clear evidence for a controlling influence of temperature on sulfate diffusivity with depth and age, we hypothesise that the rapid decrease in effective diffusion rate from the time of deposition to ice of 50 ka age may be due to a switch in the mechanism of diffusion resulting from the changing location of sulfate ions within the ice microstructure and/or interconnectedness of veins and grain boundaries.
摘要要从最深、最古老的南极冰中提取与气候相关的化学信号，我们必须首先研究化学离子在固体冰中的扩散程度。火山硫酸盐峰是这种研究的理想目标，因为它们是高振幅、短持续时间（3 年）的事件，具有准均匀结构。在此，我们对过去 450 千年的 EPICA 圆顶 C 硫酸盐记录进行了分析。我们确定了火山峰值，并将其从非海盐硫酸盐背景中分离出来，以揭示扩散的影响：随着深度和年龄的增加，峰值在时域中的振幅阻尼和拓宽。硫酸盐峰形还会因冰流导致冰层随深度变薄而改变。必须对这两个过程进行模拟，才能得出有效的扩散率。为此，我们运行了一个前向模型，以不同的速率扩散理想化的硫酸盐峰，同时还考虑了冰层变薄的因素。我们的模拟结果表明，全新世冰层中硫酸根离子的有效扩散速率中值为 2.4±1.7×10-7 m2 yr-1，略快于之前的研究结果。在更深的冰层中观测到的有效扩散速率要低得多，全新世冰层的有效扩散速率是过去 450 千年中最高的。在全新世之后，尽管可溶性离子浓度、尘埃负荷和冰粒半径存在差异，但冰川期和间冰期的有效扩散速率没有系统性差异。40 ka 到 200 ka 期间的有效扩散率相对恒定，约为 1×10-8 m2 yr-1。我们的研究结果表明，硫酸根离子在火山峰内部的扩散速度最初相对较快，可能是通过相互连接的矿脉网络进行的，但在 40 kyr 之后明显减慢。由于没有明确的证据表明温度对硫酸盐扩散率随深度和年龄的变化有控制性影响，我们假设从沉积到 50 ka 年龄的冰的有效扩散率的快速下降可能是由于硫酸根离子在冰微观结构中的位置变化和/或矿脉与晶界的相互连接所导致的扩散机制的转换。
{"title":"New estimates of sulfate diffusion rates in the EPICA Dome C ice core","authors":"Rachael H. Rhodes, Yvan Bollet-Quivogne, Piers Barnes, Mirko Severi, Eric W. Wolff","doi":"10.5194/cp-20-2031-2024","DOIUrl":"https://doi.org/10.5194/cp-20-2031-2024","url":null,"abstract":"Abstract. To extract climatically relevant chemical signals from the deepest, oldest Antarctic ice, we must first investigate the degree to which chemical ions diffuse within solid ice. Volcanic sulfate peaks are an ideal target for such an investigation because they are high-amplitude, short-duration (∼3 years) events with a quasi-uniform structure. Here we present an analysis of the EPICA Dome C sulfate record over the last 450 kyr. We identify volcanic peaks and isolate them from the non-sea-salt sulfate background to reveal the effects of diffusion: amplitude damping and broadening of peaks in the time domain with increasing depth and age. Sulfate peak shape is also altered by the thinning of ice layers with depth that results from ice flow. Both processes must be simulated to derive effective diffusion rates. This is achieved by running a forward model to diffuse idealised sulfate peaks at different rates while also accounting for ice thinning. Our simulations suggest a median effective diffusion rate of sulfate ions of 2.4±1.7×10-7 m2 yr−1 in Holocene ice, slightly faster than suggested by previous work. The effective diffusion rate observed in deeper ice is significantly lower, and Holocene ice shows the highest rate of the last 450 kyr. Beyond the Holocene, there is no systematic difference between the effective diffusion rates of glacial and interglacial periods despite variations in soluble ion concentrations, dust loading, and ice grain radii. Effective diffusion rates for 40 to 200 ka are relatively constant and of the order 1×10-8 m2 yr−1. Our results suggest that the diffusion of sulfate ions within volcanic peaks is relatively fast initially, perhaps through an interconnected vein network, but slows significantly after 40 kyr. In the absence of clear evidence for a controlling influence of temperature on sulfate diffusivity with depth and age, we hypothesise that the rapid decrease in effective diffusion rate from the time of deposition to ice of 50 ka age may be due to a switch in the mechanism of diffusion resulting from the changing location of sulfate ions within the ice microstructure and/or interconnectedness of veins and grain boundaries.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"16 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-09-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142253691","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract. During the Last Glacial Maximum (LGM), tidal dissipation was about 3-fold higher than today, which could have led to a considerable increase in vertical mixing. This increase might have enhanced the glacial Atlantic Meridional Overturning Circulation (AMOC), contradicting the shoaled AMOC indicated by paleoproxies. Here, we conduct ocean model simulations to investigate the impact of background climate conditions and tidal mixing on the AMOC during the LGM. We successfully reproduce the stratified ocean characteristics of the LGM by accurately simulating the elevated salinity of the deep sea and the rapid temperature decrease in the ocean's upper layers. Our findings indicate that the shoaled glacial AMOC is mainly due to strong glacial-ocean stratification, regardless of enhanced tidal dissipation. However, glacial tidal dissipation plays a critical role in the intensification of Antarctic Bottom Water (AABW) during the LGM. Given the critical role of the AMOC in (de-)glacial climate evolution, our results highlight the complex interactions of ocean stratification and tidal dissipation that have been neglected so far.
{"title":"Glacial AMOC shoaling despite vigorous tidal dissipation: vertical stratification matters","authors":"Yugeng Chen, Pengyang Song, Xianyao Chen, Gerrit Lohmann","doi":"10.5194/cp-20-2001-2024","DOIUrl":"https://doi.org/10.5194/cp-20-2001-2024","url":null,"abstract":"Abstract. During the Last Glacial Maximum (LGM), tidal dissipation was about 3-fold higher than today, which could have led to a considerable increase in vertical mixing. This increase might have enhanced the glacial Atlantic Meridional Overturning Circulation (AMOC), contradicting the shoaled AMOC indicated by paleoproxies. Here, we conduct ocean model simulations to investigate the impact of background climate conditions and tidal mixing on the AMOC during the LGM. We successfully reproduce the stratified ocean characteristics of the LGM by accurately simulating the elevated salinity of the deep sea and the rapid temperature decrease in the ocean's upper layers. Our findings indicate that the shoaled glacial AMOC is mainly due to strong glacial-ocean stratification, regardless of enhanced tidal dissipation. However, glacial tidal dissipation plays a critical role in the intensification of Antarctic Bottom Water (AABW) during the LGM. Given the critical role of the AMOC in (de-)glacial climate evolution, our results highlight the complex interactions of ocean stratification and tidal dissipation that have been neglected so far.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"14 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142190493","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}
James D. Annan, Julia C. Hargreaves, Thorsten Mauritsen, Erin McClymont, Sze Ling Ho
Abstract. We present a reconstruction of the surface climate of the mid-Pliocene Warm Period (mPWP), specifically Marine Isotope Stage (MIS) KM5c or 3.205 Ma. We combine the ensemble of climate model simulations, which contributed to the Pliocene Model Intercomparison Project (PlioMIP), with compilations of proxy data analyses of sea surface temperature (SST). The different data sets we considered are all sparse with high uncertainty, and the best estimate of annual global mean surface air temperature (SAT) anomaly varies from 2.1 up to 4.8 °C depending on the data source. We argue that the latest PlioVAR analysis of alkenone data is likely more reliable than other data sets we consider, and using this data set yields an SAT anomaly of 3.9±1.1 °C, with a value of 2.8±0.9 °C for SST (all uncertainties are quoted at 1 standard deviation). However, depending on the application, it may be advisable to consider the broader range arising from the various data sets to account for structural uncertainty. The regional-scale information in the reconstruction may not be reliable as it is largely based on the patterns simulated by the models.
{"title":"Can we reliably reconstruct the mid-Pliocene Warm Period with sparse data and uncertain models?","authors":"James D. Annan, Julia C. Hargreaves, Thorsten Mauritsen, Erin McClymont, Sze Ling Ho","doi":"10.5194/cp-20-1989-2024","DOIUrl":"https://doi.org/10.5194/cp-20-1989-2024","url":null,"abstract":"Abstract. We present a reconstruction of the surface climate of the mid-Pliocene Warm Period (mPWP), specifically Marine Isotope Stage (MIS) KM5c or 3.205 Ma. We combine the ensemble of climate model simulations, which contributed to the Pliocene Model Intercomparison Project (PlioMIP), with compilations of proxy data analyses of sea surface temperature (SST). The different data sets we considered are all sparse with high uncertainty, and the best estimate of annual global mean surface air temperature (SAT) anomaly varies from 2.1 up to 4.8 °C depending on the data source. We argue that the latest PlioVAR analysis of alkenone data is likely more reliable than other data sets we consider, and using this data set yields an SAT anomaly of 3.9±1.1 °C, with a value of 2.8±0.9 °C for SST (all uncertainties are quoted at 1 standard deviation). However, depending on the application, it may be advisable to consider the broader range arising from the various data sets to account for structural uncertainty. The regional-scale information in the reconstruction may not be reliable as it is largely based on the patterns simulated by the models.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"51 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142190491","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}
Basil A. S. Davis, Marc Fasel, Jed O. Kaplan, Emmanuele Russo, Ariane Burke
Abstract. Pollen data represent one of the most widely available and spatially resolved sources of information about the past land cover and climate of the Last Glacial Maximum (LGM; 21 000 yr BP). Previous pollen data compilations for Europe, the Mediterranean, and the Middle East, however, have been limited by small numbers of sites and poor dating control. Here we present a new compilation of pollen data from the region that improves on both the number of sites (63) and the quality of the chronological control. Data were sourced from both public data archives and published (digitized) diagrams. The analysis is presented based on a standardized pollen taxonomy and sum, with maps shown for the major pollen taxa and biomes and the total arboreal pollen (AP), and on quantitative reconstructions of forest cover and of winter, summer, and annual temperatures and precipitation. The reconstructions are based on the modern analogue technique (MAT) adapted using plant functional type (PFT) scores and with a modern pollen dataset taken from the latest Eurasian Modern Pollen Database (EMPD) (∼8000 samples). A site-by-site comparison of the MAT and the inverse modelling method shows little or no significant difference between the methods for the LGM, indicating that the presence of low-CO2 conditions and no modern analogue during the LGM does not appear to have had a major effect on MAT transfer function performance. Previous pollen-based climate reconstructions using modern pollen datasets show a much colder and drier climate for the LGM than both inverse modelling and climate model simulations do, but our new results suggest much greater agreement. Differences between our latest MAT reconstruction and those in earlier studies can largely be attributed to bias in the small modern dataset previously used and to differences in the method itself (Brewer et al., 2008; Salonen et al., 2019). We also find that quantitative forest cover reconstructions show more forest than previously suggested by biome reconstructions but less forest than suggested by simply the percentage of arboreal pollen, although uncertainties remain large. Overall, we find that LGM climatic cooling and drying were significantly greater in winter than in summer but with large site-to-site variance that emphasizes the importance of topography and other local factors in controlling the climate and vegetation of the LGM.
摘要花粉数据是有关末次冰川极盛时期（LGM；公元前 21000 年）过去的土地覆盖和气候的最广泛、空间分辨率最高的信息来源之一。然而，以前对欧洲、地中海和中东地区的花粉数据进行汇编时，受到了地点数量少和年代控制差的限制。在此，我们对该地区的花粉数据进行了新的汇编，在遗址数量（63 个）和年代控制质量方面都有所改进。数据来源于公共数据档案和出版的（数字化）图表。分析基于标准化的花粉分类和总和，并显示了主要花粉类群和生物群落以及树栖花粉总量（AP）的分布图，以及森林覆盖率和冬季、夏季及全年气温和降水量的定量重建。这些重建是基于现代模拟技术（MAT），利用植物功能类型（PFT）评分和最新欧亚现代花粉数据库（EMPD）中的现代花粉数据集（8000 个样本）进行的。对 MAT 和反建模方法进行的逐点比较显示，这两种方法在远古时期几乎没有显著差异，这表明远古时期低二氧化碳条件的存在和没有现代类似物似乎并没有对 MAT 转移函数的性能产生重大影响。以前使用现代花粉数据集进行的基于花粉的气候重建显示，远古至近代的气候比反演模拟和气候模式模拟都要寒冷干燥得多，但我们的新结果表明两者的一致性要大得多。我们最新的 MAT 重建结果与之前研究结果之间的差异主要归因于之前使用的小型现代数据集的偏差以及方法本身的差异（Brewer 等人，2008 年；Salonen 等人，2019 年）。我们还发现，定量森林覆盖率重建结果显示，森林覆盖率高于之前生物群落重建所显示的森林覆盖率，但低于简单的树栖花粉百分比所显示的森林覆盖率，尽管不确定性仍然很大。总之，我们发现 LGM 气候变冷和变干在冬季明显大于夏季，但地点与地点之间的差异很大，这强调了地形和其他地方因素在控制 LGM 气候和植被方面的重要性。
{"title":"The climate and vegetation of Europe, northern Africa, and the Middle East during the Last Glacial Maximum (21 000 yr BP) based on pollen data","authors":"Basil A. S. Davis, Marc Fasel, Jed O. Kaplan, Emmanuele Russo, Ariane Burke","doi":"10.5194/cp-20-1939-2024","DOIUrl":"https://doi.org/10.5194/cp-20-1939-2024","url":null,"abstract":"Abstract. Pollen data represent one of the most widely available and spatially resolved sources of information about the past land cover and climate of the Last Glacial Maximum (LGM; 21 000 yr BP). Previous pollen data compilations for Europe, the Mediterranean, and the Middle East, however, have been limited by small numbers of sites and poor dating control. Here we present a new compilation of pollen data from the region that improves on both the number of sites (63) and the quality of the chronological control. Data were sourced from both public data archives and published (digitized) diagrams. The analysis is presented based on a standardized pollen taxonomy and sum, with maps shown for the major pollen taxa and biomes and the total arboreal pollen (AP), and on quantitative reconstructions of forest cover and of winter, summer, and annual temperatures and precipitation. The reconstructions are based on the modern analogue technique (MAT) adapted using plant functional type (PFT) scores and with a modern pollen dataset taken from the latest Eurasian Modern Pollen Database (EMPD) (∼8000 samples). A site-by-site comparison of the MAT and the inverse modelling method shows little or no significant difference between the methods for the LGM, indicating that the presence of low-CO2 conditions and no modern analogue during the LGM does not appear to have had a major effect on MAT transfer function performance. Previous pollen-based climate reconstructions using modern pollen datasets show a much colder and drier climate for the LGM than both inverse modelling and climate model simulations do, but our new results suggest much greater agreement. Differences between our latest MAT reconstruction and those in earlier studies can largely be attributed to bias in the small modern dataset previously used and to differences in the method itself (Brewer et al., 2008; Salonen et al., 2019). We also find that quantitative forest cover reconstructions show more forest than previously suggested by biome reconstructions but less forest than suggested by simply the percentage of arboreal pollen, although uncertainties remain large. Overall, we find that LGM climatic cooling and drying were significantly greater in winter than in summer but with large site-to-site variance that emphasizes the importance of topography and other local factors in controlling the climate and vegetation of the LGM.","PeriodicalId":10332,"journal":{"name":"Climate of The Past","volume":"9 1","pages":""},"PeriodicalIF":4.3,"publicationDate":"2024-09-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142190524","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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