We introduce a new hypothesis concerning the role of internal climate dynamics in the non‐linear transitions from interglacial to glacial (IG‐G) state since the Mid Pleistocene Transition (MPT). These transitions encompass large and abrupt changes in atmospheric CO2, ice volume, and temperature that we suggest involve critical interactions between insolation and high amplitude oscillations in ocean/atmosphere circulation patterns. Specifically, we highlight the large amplitude of millennial‐scale climate oscillations across the transition from Marine Isotope Stage (MIS) 5 to 4, which we argue led to amplified cooling of the deep ocean and we demonstrate that analogous episodes of extreme cooling systematically preceded glacial periods of the last 800 kyr. We suggest that such cooling necessitates a reconfiguration of the deep ocean to avoid a density paradox between northern and southern‐sourced deep waters (SSW), which could be accomplished by increasing the relative volume and or salinity of SSW, thus providing the necessary storage capacity for the subsequent (delayed) and relatively abrupt drawdown of CO2. We therefore explain the transient decoupling of Antarctic temperature from CO2 across MIS 5/4 as a direct consequence of millennial activity at that time. We further show that similar climatic decoupling typically occurred during times of low obliquity and was a ubiquitous feature of IG‐G transitions over the past 800 kyr, producing the appearance of bimodality in records of CO2, benthic δ18O and others. Finally we argue that the apparent lack of bimodality in the pre‐MPT record of benthic δ18O implies that the dynamics associated with IG‐G transitions changed across the MPT.
我们提出了一个新的假设，即自中更新世过渡（MPT）以来，内部气候动力学在从间冰期向冰川期（IG-G）的非线性过渡中的作用。这些转变包括大气中二氧化碳、冰量和温度的巨大突变，我们认为这涉及日照和海洋/大气环流模式中高振幅振荡之间的关键相互作用。具体而言，我们强调了从海洋同位素阶段（MIS）5 到 4 的过渡期间千年尺度气候振荡的大振幅，我们认为这导致了深海的放大冷却，我们还证明了在过去 800 千年的冰川期之前系统性地出现了类似的极端冷却现象。我们认为，这种冷却需要对深海进行重新配置，以避免北源深水和南源深水（SSW）之间的密度悖论，这可以通过增加 SSW 的相对体积和盐度来实现，从而为随后（延迟）和相对突然的二氧化碳减少提供必要的储存能力。因此，我们将整个 MIS 5/4 中南极温度与 CO2 的瞬时脱钩解释为当时千年活动的直接结果。我们进一步证明，类似的气候脱钩通常发生在低纬度时期，是过去 800 千年 IG-G 转换的一个普遍特征，导致二氧化碳、底栖生物 δ18O 等记录出现双峰现象。最后，我们认为，MPT前的底栖生物δ18O记录明显缺乏双峰性，这意味着与IG-G转换相关的动力学在整个MPT期间发生了变化。
{"title":"A Systematic Role for Extreme Ocean‐Atmosphere Oscillations in the Development of Glacial Conditions Since the Mid Pleistocene Transition","authors":"Stephen Barker, G. Knorr","doi":"10.1029/2023pa004690","DOIUrl":"https://doi.org/10.1029/2023pa004690","url":null,"abstract":"We introduce a new hypothesis concerning the role of internal climate dynamics in the non‐linear transitions from interglacial to glacial (IG‐G) state since the Mid Pleistocene Transition (MPT). These transitions encompass large and abrupt changes in atmospheric CO2, ice volume, and temperature that we suggest involve critical interactions between insolation and high amplitude oscillations in ocean/atmosphere circulation patterns. Specifically, we highlight the large amplitude of millennial‐scale climate oscillations across the transition from Marine Isotope Stage (MIS) 5 to 4, which we argue led to amplified cooling of the deep ocean and we demonstrate that analogous episodes of extreme cooling systematically preceded glacial periods of the last 800 kyr. We suggest that such cooling necessitates a reconfiguration of the deep ocean to avoid a density paradox between northern and southern‐sourced deep waters (SSW), which could be accomplished by increasing the relative volume and or salinity of SSW, thus providing the necessary storage capacity for the subsequent (delayed) and relatively abrupt drawdown of CO2. We therefore explain the transient decoupling of Antarctic temperature from CO2 across MIS 5/4 as a direct consequence of millennial activity at that time. We further show that similar climatic decoupling typically occurred during times of low obliquity and was a ubiquitous feature of IG‐G transitions over the past 800 kyr, producing the appearance of bimodality in records of CO2, benthic δ18O and others. Finally we argue that the apparent lack of bimodality in the pre‐MPT record of benthic δ18O implies that the dynamics associated with IG‐G transitions changed across the MPT.","PeriodicalId":54239,"journal":{"name":"Paleoceanography and Paleoclimatology","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2023-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139019903","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}
Jing Lyu, G. Auer, O. Bialik, Beth A Christensen, Ryo Yamaoka, David, De Vleeschouwer
A significant shift in Earth's climate characterizes the Neogene, transitioning from a single‐ice‐sheet planet to the current bipolar configuration. This climate evolution is closely linked to changing ocean currents, but globally‐distributed continuous high‐resolution sedimentary records are needed to fully capture this interaction. The Ocean Drilling Program (ODP) Site 752, located on Broken Ridge in the Indian Ocean, provides such a Miocene‐to‐recent archive. We use X‐ray fluorescence (XRF) core scanning to build an eccentricity‐tuned age‐depth model and reconstruct paleoceanographic changes since 23 Ma. We find two intervals of enhanced productivity, during the early and middle Miocene (18.5–13.7 Ma) and late Pliocene/early Pleistocene (3–1 Ma). We also report a mixed eccentricity‐obliquity imprint in the XRF‐derived paleoproductivity proxy. In terms of grain size, three coarsening steps occur between 19.2–16 Ma, 10.8–8 Ma, and since 2.6 Ma. The steps respectively indicate stronger current winnowing in response to vigorous Antarctic Intermediate Water flow over Broken Ridge in the early Miocene, the first transient onset of Tasman Leakage in the Late Miocene, and the intensification of global oceanic circulation at the Plio‐Pleistocene transition. High‐resolution iron and manganese series provide a detailed Neogene dust record. This study utilized a single hole from an ODP legacy‐site. Nevertheless, we managed to provide novel perspectives on past Indian Ocean responses to astronomical forcing. We conclude that Neogene sediments from Broken Ridge harbor the potential for even more comprehensive reconstructions. Realizing this potential necessitates re‐drilling of these sedimentary archives utilizing modern drilling strategies.
新近纪地球气候发生了重大变化，从单一冰盖行星过渡到目前的双极构造。这种气候演变与不断变化的洋流密切相关，但需要全球分布的连续高分辨率沉积记录来充分捕捉这种相互作用。位于印度洋布罗肯海脊的大洋钻探计划（ODP）752站点提供了这样一个中新世到新近的档案。我们利用 X 射线荧光（XRF）岩心扫描建立了一个偏心调谐年龄-深度模型，并重建了自 23 Ma 以来的古海洋学变化。我们发现在中新世早期和中期（18.5-13.7 Ma）以及上新世晚期/更新世早期（3-1 Ma）有两个生产力增强的时期。我们还报告了 XRF 衍生的古生产率代理中的偏心-偏斜混合印记。就粒度而言，在 19.2-16 Ma、10.8-8 Ma 和自 2.6 Ma 之间出现了三个粗化阶段。这三个阶段分别表明，在中新世早期，南极中层水流过断裂海脊时产生了更强的海流绞杀作用；在中新世晚期，塔斯曼漏流首次瞬时出现；在上新世-早更新世过渡时期，全球大洋环流加强。高分辨率的铁和锰系列提供了详细的新近纪尘埃记录。这项研究只利用了 ODP 遗址中的一个钻孔。尽管如此，我们还是成功地为过去印度洋对天文作用力的响应提供了新的视角。我们的结论是，布罗肯岭的新近纪沉积物具有进行更全面重建的潜力。要实现这一潜力，就必须利用现代钻探策略对这些沉积档案进行重新钻探。
{"title":"Astronomically‐Paced Changes in Paleoproductivity, Winnowing, and Mineral Flux Over Broken Ridge (Indian Ocean) Since the Early Miocene","authors":"Jing Lyu, G. Auer, O. Bialik, Beth A Christensen, Ryo Yamaoka, David, De Vleeschouwer","doi":"10.1029/2023pa004761","DOIUrl":"https://doi.org/10.1029/2023pa004761","url":null,"abstract":"A significant shift in Earth's climate characterizes the Neogene, transitioning from a single‐ice‐sheet planet to the current bipolar configuration. This climate evolution is closely linked to changing ocean currents, but globally‐distributed continuous high‐resolution sedimentary records are needed to fully capture this interaction. The Ocean Drilling Program (ODP) Site 752, located on Broken Ridge in the Indian Ocean, provides such a Miocene‐to‐recent archive. We use X‐ray fluorescence (XRF) core scanning to build an eccentricity‐tuned age‐depth model and reconstruct paleoceanographic changes since 23 Ma. We find two intervals of enhanced productivity, during the early and middle Miocene (18.5–13.7 Ma) and late Pliocene/early Pleistocene (3–1 Ma). We also report a mixed eccentricity‐obliquity imprint in the XRF‐derived paleoproductivity proxy. In terms of grain size, three coarsening steps occur between 19.2–16 Ma, 10.8–8 Ma, and since 2.6 Ma. The steps respectively indicate stronger current winnowing in response to vigorous Antarctic Intermediate Water flow over Broken Ridge in the early Miocene, the first transient onset of Tasman Leakage in the Late Miocene, and the intensification of global oceanic circulation at the Plio‐Pleistocene transition. High‐resolution iron and manganese series provide a detailed Neogene dust record. This study utilized a single hole from an ODP legacy‐site. Nevertheless, we managed to provide novel perspectives on past Indian Ocean responses to astronomical forcing. We conclude that Neogene sediments from Broken Ridge harbor the potential for even more comprehensive reconstructions. Realizing this potential necessitates re‐drilling of these sedimentary archives utilizing modern drilling strategies.","PeriodicalId":54239,"journal":{"name":"Paleoceanography and Paleoclimatology","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2023-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139018247","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}
C. Wood, Kathleen R. Johnson, Lindsey. E. Lewis, K. Wright, Jessica K. Wang, A. Borsato, Michael L. Griffiths, Andrew Mason, Gideon M. Henderson, Jacob B. Setera, S. Frisia, Sengphone Keophanhya, Joyce C. White
The 8.2 ka event is the most significant global climate anomaly of the Holocene epoch, but a lack of records from Mainland Southeast Asia (MSEA) currently limits our understanding of the spatial and temporal extent of the climate response. A newly developed speleothem record from Tham Doun Mai Cave, Northern Laos provides the first high‐resolution record of this event in MSEA. Our multiproxy record (δ18O, δ13C, Mg/Ca, Sr/Ca, and petrographic data), anchored in time by 9 U‐Th ages, reveals a significant reduction in local rainfall amount and weakening of the monsoon at the event onset at ∼8.29 ± 0.03 ka BP. This response lasts for a minimum of ∼170 years, similar to event length estimates from other speleothem δ18O monsoon records. Interestingly, however, our δ13C and Mg/Ca data, proxies for local hydrology, show that abrupt changes to local rainfall amounts began decades earlier (∼70 years) than registered in the δ18O. Moreover, the δ13C and Mg/Ca also show that reductions in rainfall continued for at least ∼200 years longer than the weakening of the monsoon inferred from the δ18O. Our interpretations suggest that drier conditions brought on by the 8.2 ka event in MSEA were felt beyond the temporal boundaries defined by δ18O‐inferred monsoon intensity, and an initial wet period (or precursor event) may have preceded the local drying. Most existing Asian Monsoon proxy records of the 8.2 ka event may lack the resolution and/or multiproxy information necessary to establish local and regional hydrological sensitivity to abrupt climate change.
8.2 ka事件是全新世时期最重要的全球气候异常现象，但目前东南亚大陆（MSEA）记录的缺乏限制了我们对气候响应的时空范围的了解。老挝北部 Tham Doun Mai 洞穴新发现的岩浆记录首次提供了东南亚大陆这一事件的高分辨率记录。我们的多代理记录（δ18O、δ13C、Mg/Ca、Sr/Ca 和岩石学数据）以 9 个铀-钍年龄为时间锚定，揭示了在事件开始（8.29 ± 0.03 ka BP）时当地降雨量的显著减少和季风的减弱。这种反应至少持续了 170 年，与其他岩浆δ18O 季风记录估计的事件持续时间相似。然而，有趣的是，我们的δ13C 和 Mg/Ca 数据（当地水文的代用指标）显示，当地降雨量的突然变化比δ18O 记录的时间早几十年（∼70 年）。此外，δ13C 和 Mg/Ca 还表明，降雨量的减少至少持续了 200 年，比根据δ18O 推断的季风减弱的时间要长。我们的解释表明，MSEA 8.2 ka事件带来的较干旱条件超出了δ18O推断的季风强度所定义的时间界限，在局部干燥之前可能有一个初始的湿润期（或前兆事件）。大多数关于 8.2 ka 事件的现有亚洲季风代用记录可能缺乏必要的分辨率和/或多代用信息，无法确定当地和区域水文对突变气候变化的敏感性。
{"title":"High‐Resolution, Multiproxy Speleothem Record of the 8.2 ka Event From Mainland Southeast Asia","authors":"C. Wood, Kathleen R. Johnson, Lindsey. E. Lewis, K. Wright, Jessica K. Wang, A. Borsato, Michael L. Griffiths, Andrew Mason, Gideon M. Henderson, Jacob B. Setera, S. Frisia, Sengphone Keophanhya, Joyce C. White","doi":"10.1029/2023pa004675","DOIUrl":"https://doi.org/10.1029/2023pa004675","url":null,"abstract":"The 8.2 ka event is the most significant global climate anomaly of the Holocene epoch, but a lack of records from Mainland Southeast Asia (MSEA) currently limits our understanding of the spatial and temporal extent of the climate response. A newly developed speleothem record from Tham Doun Mai Cave, Northern Laos provides the first high‐resolution record of this event in MSEA. Our multiproxy record (δ18O, δ13C, Mg/Ca, Sr/Ca, and petrographic data), anchored in time by 9 U‐Th ages, reveals a significant reduction in local rainfall amount and weakening of the monsoon at the event onset at ∼8.29 ± 0.03 ka BP. This response lasts for a minimum of ∼170 years, similar to event length estimates from other speleothem δ18O monsoon records. Interestingly, however, our δ13C and Mg/Ca data, proxies for local hydrology, show that abrupt changes to local rainfall amounts began decades earlier (∼70 years) than registered in the δ18O. Moreover, the δ13C and Mg/Ca also show that reductions in rainfall continued for at least ∼200 years longer than the weakening of the monsoon inferred from the δ18O. Our interpretations suggest that drier conditions brought on by the 8.2 ka event in MSEA were felt beyond the temporal boundaries defined by δ18O‐inferred monsoon intensity, and an initial wet period (or precursor event) may have preceded the local drying. Most existing Asian Monsoon proxy records of the 8.2 ka event may lack the resolution and/or multiproxy information necessary to establish local and regional hydrological sensitivity to abrupt climate change.","PeriodicalId":54239,"journal":{"name":"Paleoceanography and Paleoclimatology","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2023-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139026502","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}
To better understand the effect of the Paleocene‐Eocene Thermal Maximum (PETM) on continental ecosystems, we studied 40 new palynological samples from the Bighorn Basin (BHB), northwestern Wyoming, USA. We see palm and fern abundances increase in the last 20–40 ka of the Paleocene, then dramatically with the onset of the carbon isotope excursion (CIE) defining the base of the PETM. Palynomorphs of plant groups with modern temperate climate distributions are absent from the CIE body, and this is when tropical plants are most diverse and abundant. During the CIE recovery, pollen of mesophytic/wetland plants become more common while tropical taxa persist. In the post‐CIE early Eocene tropical taxa are rare and temperate forms abundant, similar to the late but not latest Paleocene. Changes in the palynoflora are more easily detected if reworked palynomorphs are removed from analyses. We interpret palynofloral changes to indicate warming in the latest Paleocene, rapid warming and drying with the CIE onset, dry tropical climates through the CIE body, a return to wetter floodplains during a very warm CIE recovery, and cooler wet conditions in the post‐PETM early Eocene. These inferences are consistent with geochemical and paleobotanical proxies. Strikingly similar patterns in the palynoflora and megaflora suggest changes in vegetation were a basin‐wide phenomenon. These rapid, climatically forced changes in floral composition occurred without major extinction, perhaps indicating nearby refugia in which plants adapted to cooler and wetter climates persisted through the PETM.
{"title":"Palynofloral Change Through the Paleocene‐Eocene Thermal Maximum in the Bighorn Basin, Wyoming","authors":"Vera A. Korasidis, S. Wing","doi":"10.1029/2023pa004741","DOIUrl":"https://doi.org/10.1029/2023pa004741","url":null,"abstract":"To better understand the effect of the Paleocene‐Eocene Thermal Maximum (PETM) on continental ecosystems, we studied 40 new palynological samples from the Bighorn Basin (BHB), northwestern Wyoming, USA. We see palm and fern abundances increase in the last 20–40 ka of the Paleocene, then dramatically with the onset of the carbon isotope excursion (CIE) defining the base of the PETM. Palynomorphs of plant groups with modern temperate climate distributions are absent from the CIE body, and this is when tropical plants are most diverse and abundant. During the CIE recovery, pollen of mesophytic/wetland plants become more common while tropical taxa persist. In the post‐CIE early Eocene tropical taxa are rare and temperate forms abundant, similar to the late but not latest Paleocene. Changes in the palynoflora are more easily detected if reworked palynomorphs are removed from analyses. We interpret palynofloral changes to indicate warming in the latest Paleocene, rapid warming and drying with the CIE onset, dry tropical climates through the CIE body, a return to wetter floodplains during a very warm CIE recovery, and cooler wet conditions in the post‐PETM early Eocene. These inferences are consistent with geochemical and paleobotanical proxies. Strikingly similar patterns in the palynoflora and megaflora suggest changes in vegetation were a basin‐wide phenomenon. These rapid, climatically forced changes in floral composition occurred without major extinction, perhaps indicating nearby refugia in which plants adapted to cooler and wetter climates persisted through the PETM.","PeriodicalId":54239,"journal":{"name":"Paleoceanography and Paleoclimatology","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2023-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138609884","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}
T. C. Brachert, C. Agnini, C. Gagnaison, J.‐P. Gély, M. J. Henehan, T. Westerhold
Abstract Astrochronologically calibrated deep‐sea records document the Cenozoic (66–0 Ma) global climatic cooling in great detail, but the magnitude of sea‐level fluctuations of the middle Eocene Warmhouse state (47.8–37.7 Ma) and the ∼40.3 Ma warming event of the Middle Eocene Climatic Optimum (MECO) is not well constrained. Here, we present a sequence stratigraphic classification of a shallow marine mixed carbonate—clastic ramp system for this time interval in Paris basin, France. Based on sedimentologic, paleogeographic and biostratigraphic data, we hypothesize that the 22 elementary sequences recognized each correspond to the long cycle of orbital eccentricity (0.405 Myr). With the exception of the MECO, the shoreline trajectory of superimposed, third‐order depositional sequences evolved in phase with the very long cycles of orbital eccentricity (2.4 Myr), suggesting significant polar ice build‐up leading to sea level lowstands during nodes of the very long eccentricity cycle. Inferred from Fischer Plot methodology, Lutetian third‐order eustasy was in the order of 5–10 m and during the MECO 30 m or more. Furthermore, the shallow‐water record implies that third order sea‐level changes were astronomically paced in the middle Eocene Warmhouse climate state, but a decoupling occurred during the transient MECO warming.
天文年代学校准的深海记录非常详细地记录了新生代(66-0 Ma)全球气候变冷，但中始新世暖室状态(47.8-37.7 Ma)和中始新世气候优化(MECO)的~ 40.3 Ma变暖事件的海平面波动幅度没有得到很好的约束。本文对法国巴黎盆地这一时期的浅海混合碳酸盐-碎屑斜坡体系进行了层序地层分类。根据沉积学、古地理和生物地层学资料，我们假设22个已识别的基本层序对应于轨道偏心长旋回(0.405 Myr)。除MECO外，叠加的海岸线轨迹，三级沉积序列与轨道偏心旋回(2.4 Myr)相演化，表明在极长偏心旋回的节点期间，显著的极地冰积聚导致海平面低水位。根据Fischer样地方法推断，Lutetian三阶海平面上升幅度为5-10 m, MECO期间为30 m或更大。此外，浅水记录表明，在始新世中期的暖化气候状态中，三级海平面的变化是以天文速度进行的，但在短暂的MECO变暖期间发生了解耦。
{"title":"Astronomical Pacing of Middle Eocene Sea‐Level Fluctuations: Inferences From Shallow‐Water Carbonate Ramp Deposits","authors":"T. C. Brachert, C. Agnini, C. Gagnaison, J.‐P. Gély, M. J. Henehan, T. Westerhold","doi":"10.1029/2023pa004633","DOIUrl":"https://doi.org/10.1029/2023pa004633","url":null,"abstract":"Abstract Astrochronologically calibrated deep‐sea records document the Cenozoic (66–0 Ma) global climatic cooling in great detail, but the magnitude of sea‐level fluctuations of the middle Eocene Warmhouse state (47.8–37.7 Ma) and the ∼40.3 Ma warming event of the Middle Eocene Climatic Optimum (MECO) is not well constrained. Here, we present a sequence stratigraphic classification of a shallow marine mixed carbonate—clastic ramp system for this time interval in Paris basin, France. Based on sedimentologic, paleogeographic and biostratigraphic data, we hypothesize that the 22 elementary sequences recognized each correspond to the long cycle of orbital eccentricity (0.405 Myr). With the exception of the MECO, the shoreline trajectory of superimposed, third‐order depositional sequences evolved in phase with the very long cycles of orbital eccentricity (2.4 Myr), suggesting significant polar ice build‐up leading to sea level lowstands during nodes of the very long eccentricity cycle. Inferred from Fischer Plot methodology, Lutetian third‐order eustasy was in the order of 5–10 m and during the MECO 30 m or more. Furthermore, the shallow‐water record implies that third order sea‐level changes were astronomically paced in the middle Eocene Warmhouse climate state, but a decoupling occurred during the transient MECO warming.","PeriodicalId":54239,"journal":{"name":"Paleoceanography and Paleoclimatology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135516240","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 H. Tiger, Stephen Burns, Robin R. Dawson, Nick Scroxton, Laurie R. Godfrey, Lovasoa Ranivoharimanana, Peterson Faina, David McGee
Abstract The low latitude Indian Ocean is warming faster than other tropical basins, and its interannual climate variability is projected to become more extreme under future emissions scenarios with substantial impacts on developing Indian Ocean rim countries. Therefore, it has become increasingly important to understand the drivers of regional precipitation in a changing climate. Here we present a new speleothem record from Anjohibe, a cave in northwest (NW) Madagascar well situated to record past changes in the Intertropical Convergence Zone (ITCZ). U‐Th ages date speleothem growth from 27 to 14 ka. δ 18 O, δ 13 C, and trace metal proxies reconstruct drier conditions during Heinrich Stadials 1 and 2, and wetter conditions during the Last Glacial Maximum and Bølling–Allerød. This is surprising considering hypotheses arguing for southward (northward) ITCZ shifts during North Atlantic cooling (warming) events, which would be expected to result in wetter (drier) conditions at Anjohibe in the Southern Hemisphere tropics. The reconstructed Indian Ocean zonal (west‐east) sea surface temperature (SST) gradient is in close agreement with hydroclimate proxies in NW Madagascar, with periods of increased precipitation correlating with relatively warmer conditions in the western Indian Ocean and cooler conditions in the eastern Indian Ocean. Such gradients could drive long‐term shifts in the strength of the Walker circulation with widespread effects on hydroclimate across East Africa. These results suggest that during abrupt millennial‐scale climate changes, it is not meridional ITCZ shifts, but the tropical Indian Ocean SST gradient and Walker circulation driving East African hydroclimate variability.
{"title":"Zonal Indian Ocean Variability Drives Millennial‐Scale Precipitation Changes in Northern Madagascar","authors":"Benjamin H. Tiger, Stephen Burns, Robin R. Dawson, Nick Scroxton, Laurie R. Godfrey, Lovasoa Ranivoharimanana, Peterson Faina, David McGee","doi":"10.1029/2023pa004626","DOIUrl":"https://doi.org/10.1029/2023pa004626","url":null,"abstract":"Abstract The low latitude Indian Ocean is warming faster than other tropical basins, and its interannual climate variability is projected to become more extreme under future emissions scenarios with substantial impacts on developing Indian Ocean rim countries. Therefore, it has become increasingly important to understand the drivers of regional precipitation in a changing climate. Here we present a new speleothem record from Anjohibe, a cave in northwest (NW) Madagascar well situated to record past changes in the Intertropical Convergence Zone (ITCZ). U‐Th ages date speleothem growth from 27 to 14 ka. δ 18 O, δ 13 C, and trace metal proxies reconstruct drier conditions during Heinrich Stadials 1 and 2, and wetter conditions during the Last Glacial Maximum and Bølling–Allerød. This is surprising considering hypotheses arguing for southward (northward) ITCZ shifts during North Atlantic cooling (warming) events, which would be expected to result in wetter (drier) conditions at Anjohibe in the Southern Hemisphere tropics. The reconstructed Indian Ocean zonal (west‐east) sea surface temperature (SST) gradient is in close agreement with hydroclimate proxies in NW Madagascar, with periods of increased precipitation correlating with relatively warmer conditions in the western Indian Ocean and cooler conditions in the eastern Indian Ocean. Such gradients could drive long‐term shifts in the strength of the Walker circulation with widespread effects on hydroclimate across East Africa. These results suggest that during abrupt millennial‐scale climate changes, it is not meridional ITCZ shifts, but the tropical Indian Ocean SST gradient and Walker circulation driving East African hydroclimate variability.","PeriodicalId":54239,"journal":{"name":"Paleoceanography and Paleoclimatology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135564900","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}
S.‐B. Wilmes, V. K. Pedersen, M. Schindelegger, J. A. M. Green
Abstract Studies of the Last Glacial Maximum (LGM; 26.5–19 ka) tides showed strong enhancements in open ocean tidal amplitudes and dissipation rates; however, changes prior to the LGM remain largely unexplored. Using two different ice sheet and sea level reconstructions, we explicitly simulate the evolution of the leading semi‐diurnal and diurnal tidal constituents (M 2 , S 2 , K 1 , and O 1 ) over the last glacial cycle with a global tide model. Both sets of simulations show that global changes, dominated by the Atlantic, take place for the semi‐diurnal constituents, while changes for the diurnal constituents are mainly regional. Irrespective of the reconstruction, open ocean dissipation peaks during the sea level lowstands of MIS 2 (∼20 ka) and MIS 4 (∼60 ka), although dissipation values prior to MIS 2 are sensitive to differences in reconstructed ice sheet extent. Using the statistically significant relationship between global mean sea level and dissipation, we apply regression analysis to infer open ocean and shelf dissipation, respectively, over the last four glacial cycles back to 430 ka. Our analysis shows that open ocean tidal energy was probably increased for most of this period, peaking during glacial maxima, and returning to near‐present‐day values during interglacials. Due to tidal resonance during glacial phases, small changes in bathymetry could have caused large changes in tidal amplitudes and dissipation, emphasizing the need for accurate ice margin reconstructions. During glacial phases, once global mean sea level decreased by more than ∼100 m, the amount of open ocean tidal energy available for ocean mixing approximately doubled.
{"title":"Late Pleistocene Evolution of Tides and Tidal Dissipation","authors":"S.‐B. Wilmes, V. K. Pedersen, M. Schindelegger, J. A. M. Green","doi":"10.1029/2023pa004727","DOIUrl":"https://doi.org/10.1029/2023pa004727","url":null,"abstract":"Abstract Studies of the Last Glacial Maximum (LGM; 26.5–19 ka) tides showed strong enhancements in open ocean tidal amplitudes and dissipation rates; however, changes prior to the LGM remain largely unexplored. Using two different ice sheet and sea level reconstructions, we explicitly simulate the evolution of the leading semi‐diurnal and diurnal tidal constituents (M 2 , S 2 , K 1 , and O 1 ) over the last glacial cycle with a global tide model. Both sets of simulations show that global changes, dominated by the Atlantic, take place for the semi‐diurnal constituents, while changes for the diurnal constituents are mainly regional. Irrespective of the reconstruction, open ocean dissipation peaks during the sea level lowstands of MIS 2 (∼20 ka) and MIS 4 (∼60 ka), although dissipation values prior to MIS 2 are sensitive to differences in reconstructed ice sheet extent. Using the statistically significant relationship between global mean sea level and dissipation, we apply regression analysis to infer open ocean and shelf dissipation, respectively, over the last four glacial cycles back to 430 ka. Our analysis shows that open ocean tidal energy was probably increased for most of this period, peaking during glacial maxima, and returning to near‐present‐day values during interglacials. Due to tidal resonance during glacial phases, small changes in bathymetry could have caused large changes in tidal amplitudes and dissipation, emphasizing the need for accurate ice margin reconstructions. During glacial phases, once global mean sea level decreased by more than ∼100 m, the amount of open ocean tidal energy available for ocean mixing approximately doubled.","PeriodicalId":54239,"journal":{"name":"Paleoceanography and Paleoclimatology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135566538","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 Sapropels are dark, organic‐rich layers found in Mediterranean sediments that formed during periods of bottom water anoxia. While various mechanisms have been proposed to have caused anoxic conditions, a primary factor is considered to be water column stratification induced by freshwater runoff related to intensified North African monsoon precipitation during precession minima. Monsoon intensification also induced Green Sahara Periods that may have impacted North African hominin dispersal. In this study, we present a novel regression‐based deconvolution of a high‐resolution planktonic foraminiferal oxygen isotope record to estimate the combination of freshwater runoff reaching the eastern Mediterranean and associated surface warming of the water column over the past 5 million years. Sapropels are known to occur in clusters associated with periods of high orbital eccentricity. Our analysis reveals a consistent influence of orbital eccentricity in modulating the North African monsoon, and a possible shift in runoff source area induced by the initiation of Northern Hemisphere ice sheets. Our findings provide important insights into the role of the North African monsoon in shaping Mediterranean environmental changes over the past 5 million years.
{"title":"Estimating Plio‐Pleistocene North African Monsoon Runoff Into the Mediterranean Sea and Temperature Impacts","authors":"D. Heslop, U. Amarathunga, E. J. Rohling","doi":"10.1029/2023pa004677","DOIUrl":"https://doi.org/10.1029/2023pa004677","url":null,"abstract":"Abstract Sapropels are dark, organic‐rich layers found in Mediterranean sediments that formed during periods of bottom water anoxia. While various mechanisms have been proposed to have caused anoxic conditions, a primary factor is considered to be water column stratification induced by freshwater runoff related to intensified North African monsoon precipitation during precession minima. Monsoon intensification also induced Green Sahara Periods that may have impacted North African hominin dispersal. In this study, we present a novel regression‐based deconvolution of a high‐resolution planktonic foraminiferal oxygen isotope record to estimate the combination of freshwater runoff reaching the eastern Mediterranean and associated surface warming of the water column over the past 5 million years. Sapropels are known to occur in clusters associated with periods of high orbital eccentricity. Our analysis reveals a consistent influence of orbital eccentricity in modulating the North African monsoon, and a possible shift in runoff source area induced by the initiation of Northern Hemisphere ice sheets. Our findings provide important insights into the role of the North African monsoon in shaping Mediterranean environmental changes over the past 5 million years.","PeriodicalId":54239,"journal":{"name":"Paleoceanography and Paleoclimatology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135455169","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 Three recently published papers including Napier et al. (2022, https://doi.org/10.1029/2021PA004355 ) utilize novel microanalytical approaches with varved marine sediments to demonstrate the potential to reconstruct seasonal and inter‐annual climate variability. Obtaining paleoclimate data at a resolution akin to the observational record is vitally important for improving our understanding of climate phenomena such as monsoons and modes of variability such as the El Niño Southern Oscillation, for which appraisals of past inter‐annual variability is critical. The ability to generate seasonal and inter annual resolution sea surface temperature proxy time series spanning a thousand years or more is revolutionary and has the potential to fill gaps in our knowledge of climate variability. Although generally limited to sediments from regions with oxygen depleted bottom waters, there is great potential to integrate shorter seasonal resolution climate “snap shots” from other archives such as annually banded corals into composite time series. But as paleoceanographic data are used more by the observational and modeling fields, we make the case for conducting a thorough case‐by‐case assessment of the processes that influence the climate signal recovered from proxies, using careful replication to validate new approaches. Understanding or exploring the potential influence of processes which effectively filter the climate signal will lead to more quantitative paleoceanographic data that will better serve the broader climate science community.
{"title":"Assessing seasonal and inter‐annual marine sediment climate proxy data","authors":"Ed Hathorne, Andrew M. Dolman, Thomas Laepple","doi":"10.1029/2023pa004649","DOIUrl":"https://doi.org/10.1029/2023pa004649","url":null,"abstract":"Abstract Three recently published papers including Napier et al. (2022, https://doi.org/10.1029/2021PA004355 ) utilize novel microanalytical approaches with varved marine sediments to demonstrate the potential to reconstruct seasonal and inter‐annual climate variability. Obtaining paleoclimate data at a resolution akin to the observational record is vitally important for improving our understanding of climate phenomena such as monsoons and modes of variability such as the El Niño Southern Oscillation, for which appraisals of past inter‐annual variability is critical. The ability to generate seasonal and inter annual resolution sea surface temperature proxy time series spanning a thousand years or more is revolutionary and has the potential to fill gaps in our knowledge of climate variability. Although generally limited to sediments from regions with oxygen depleted bottom waters, there is great potential to integrate shorter seasonal resolution climate “snap shots” from other archives such as annually banded corals into composite time series. But as paleoceanographic data are used more by the observational and modeling fields, we make the case for conducting a thorough case‐by‐case assessment of the processes that influence the climate signal recovered from proxies, using careful replication to validate new approaches. Understanding or exploring the potential influence of processes which effectively filter the climate signal will lead to more quantitative paleoceanographic data that will better serve the broader climate science community.","PeriodicalId":54239,"journal":{"name":"Paleoceanography and Paleoclimatology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135324769","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 Foraminiferal isotopes are widely used to study past oceans, with different species recording conditions at different depths. Their δ 18 O values record both seawater oxygen‐18 and temperature according to species‐specific fractionation factors, while their Δ 47 signatures likely depend only on temperature. We describe an open‐source framework to collect/combine data relevant to foraminiferal isotopes, by constraining species‐specific oxygen‐18 fractionation factors ( 18 α ) based on culture experiments, stratified plankton tows or core‐top sediments; compiling stratified plankton tow constraints on living depths for planktic species; extracting seawater temperature, δ 18 O, and chemistry from existing databases for any latitude, longitude, and depth‐range; inferring calcification temperatures based on the above data. We find that although 18 α differs between species, its temperature sensitivity remains indistinguishable from inorganic calcite. Based on > 2,600 observations we show that, although most planktic δ 18 O values are consistent with seawater temperature and δ 18 O over their expected living depths, a sizable minority (12%–24%) have heavier‐than‐predicted δ 18 O, best explained by calcification in deeper waters. We use this framework to revisit three recent Δ 47 calibration studies of planktic/benthic foraminifera, confirming that planktic Δ 47 varies systematically with oxygen‐18‐derived temperature estimates, even for samples whose δ 18 O disagrees with assumed climatological conditions, and demonstrating excellent agreement between planktic foraminifera and modern, largely inorganic Δ 47 calibrations. Benthic foraminifera remain ambiguous: modern benthic Δ 47 values appear offset from planktic ones, yet applying equilibrium Δ 47 calibration to the Cenozoic benthic foraminifer record of Meckler et al. (2022, https://doi.org/10.1126/science.abk0604 ) largely reconciles it with δ 18 O‐derived temperatures, with discrete Δ 47 /δ 18 O discrepancies persisting in the Late Paleocene/Eocene/Plio‐Pleistocene.
{"title":"Revisiting oxygen‐18 and clumped isotopes in planktic and benthic foraminifera","authors":"M. Daëron, W. R. Gray","doi":"10.1029/2023pa004660","DOIUrl":"https://doi.org/10.1029/2023pa004660","url":null,"abstract":"Abstract Foraminiferal isotopes are widely used to study past oceans, with different species recording conditions at different depths. Their δ 18 O values record both seawater oxygen‐18 and temperature according to species‐specific fractionation factors, while their Δ 47 signatures likely depend only on temperature. We describe an open‐source framework to collect/combine data relevant to foraminiferal isotopes, by constraining species‐specific oxygen‐18 fractionation factors ( 18 α ) based on culture experiments, stratified plankton tows or core‐top sediments; compiling stratified plankton tow constraints on living depths for planktic species; extracting seawater temperature, δ 18 O, and chemistry from existing databases for any latitude, longitude, and depth‐range; inferring calcification temperatures based on the above data. We find that although 18 α differs between species, its temperature sensitivity remains indistinguishable from inorganic calcite. Based on > 2,600 observations we show that, although most planktic δ 18 O values are consistent with seawater temperature and δ 18 O over their expected living depths, a sizable minority (12%–24%) have heavier‐than‐predicted δ 18 O, best explained by calcification in deeper waters. We use this framework to revisit three recent Δ 47 calibration studies of planktic/benthic foraminifera, confirming that planktic Δ 47 varies systematically with oxygen‐18‐derived temperature estimates, even for samples whose δ 18 O disagrees with assumed climatological conditions, and demonstrating excellent agreement between planktic foraminifera and modern, largely inorganic Δ 47 calibrations. Benthic foraminifera remain ambiguous: modern benthic Δ 47 values appear offset from planktic ones, yet applying equilibrium Δ 47 calibration to the Cenozoic benthic foraminifer record of Meckler et al. (2022, https://doi.org/10.1126/science.abk0604 ) largely reconciles it with δ 18 O‐derived temperatures, with discrete Δ 47 /δ 18 O discrepancies persisting in the Late Paleocene/Eocene/Plio‐Pleistocene.","PeriodicalId":54239,"journal":{"name":"Paleoceanography and Paleoclimatology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136079720","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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