Anna Cutmore, N. Bale, G. Lange, I. Nijenhuis, Lucas, Joost Lourens
Here, we explore the importance of export productivity versus anoxia in the formation of sedimentary layers with enhanced total organic carbon (TOC) content. We use geochemical, sedimentological and micropaleontological records from two SW Sicily outcropping successions, Lido Rossello (LR) and Punta di Maiata (PM), over three Early Pliocene precession‐forced climate cycles (4.7–4.6 million years ago [Ma]). Gray marls, deposited during precession minima, show enhanced TOC in both records. We suggest that basin‐wide, low‐oxygenated bottom‐waters, resulting from freshwater‐induced stratification during precession minimum, was integral to preserving gray marl TOC. Furthermore, prolonged eastern Mediterranean stratification may have produced a deep chlorophyll maximum (DCM), leading to “shade‐flora” dominated productivity. The LR succession displays two unique laminated layers containing enhanced TOC. These laminations do not occur at specific times in the precession cycle or in time‐equivalent PM samples. They are likely to have been produced by an intermittent dysoxic/anoxic pool at LR, caused by a local depression, which enhanced TOC preservation. Consequently, the laminations provide a rare window into “true” eastern Mediterranean productivity conditions during precession maxima, as organic matter is typically poorly preserved during these period due to enhanced ventilation. The laminated “windows” indicate that eastern Mediterranean export productivity may not have been significantly lower during precession maxima compared to precession minima, as previously thought. During these periods, productivity conditions are likely to have been comparable to the modern eastern Mediterranean, with a spring‐bloom caused by enhanced winter/spring deep‐water mixing preceding a summer “shade‐flora” bloom caused by a summer‐stratification induced DCM.
在这里，我们探讨了出口生产力与缺氧在总有机碳(TOC)含量增加的沉积层形成中的重要性。我们使用了西西里岛西南部Lido Rossello (LR)和Punta di Maiata (PM)两个露头序列的地球化学、沉积学和微古生物学记录，记录了三个上新世早期旋进强迫气候周期(470 - 460万年前)[Ma]。在旋进极小期沉积的灰色泥灰岩，在两个记录中均显示TOC增高。我们认为，在进动极小期，淡水引起的分层导致的盆地范围内的低氧底水是保存灰色泥灰岩TOC的必要条件。此外，长期的东地中海分层可能产生了较深的叶绿素最大值(DCM)，导致“荫区”主导的生产力。LR序列显示出两个独特的层状层，其中TOC含量增加。这些层叠并不发生在岁差周期或时间等效PM样品中的特定时间。它们可能是由LR的间歇性缺氧/缺氧池产生的，这是由局部凹陷引起的，这增强了TOC的保存。因此，叠片提供了一个难得的窗口，了解进动极大期东地中海生产力的“真实”情况，因为在这段时间内，由于通风增强，有机物通常保存得很差。叠层的“窗口”表明，在岁差最大值期间，地中海东部的出口生产率可能并不像之前认为的那样明显低于岁差最小值。在这些时期，生产力条件可能与现代东地中海相当，冬季/春季深水混合增强导致春季开花，而夏季分层引起的DCM导致夏季“荫区”开花。
{"title":"A Window Into Eastern Mediterranean Productivity Conditions Over Three Pliocene Precession‐Forced Climate Cycles","authors":"Anna Cutmore, N. Bale, G. Lange, I. Nijenhuis, Lucas, Joost Lourens","doi":"10.1029/2022PA004550","DOIUrl":"https://doi.org/10.1029/2022PA004550","url":null,"abstract":"Here, we explore the importance of export productivity versus anoxia in the formation of sedimentary layers with enhanced total organic carbon (TOC) content. We use geochemical, sedimentological and micropaleontological records from two SW Sicily outcropping successions, Lido Rossello (LR) and Punta di Maiata (PM), over three Early Pliocene precession‐forced climate cycles (4.7–4.6 million years ago [Ma]). Gray marls, deposited during precession minima, show enhanced TOC in both records. We suggest that basin‐wide, low‐oxygenated bottom‐waters, resulting from freshwater‐induced stratification during precession minimum, was integral to preserving gray marl TOC. Furthermore, prolonged eastern Mediterranean stratification may have produced a deep chlorophyll maximum (DCM), leading to “shade‐flora” dominated productivity. The LR succession displays two unique laminated layers containing enhanced TOC. These laminations do not occur at specific times in the precession cycle or in time‐equivalent PM samples. They are likely to have been produced by an intermittent dysoxic/anoxic pool at LR, caused by a local depression, which enhanced TOC preservation. Consequently, the laminations provide a rare window into “true” eastern Mediterranean productivity conditions during precession maxima, as organic matter is typically poorly preserved during these period due to enhanced ventilation. The laminated “windows” indicate that eastern Mediterranean export productivity may not have been significantly lower during precession maxima compared to precession minima, as previously thought. During these periods, productivity conditions are likely to have been comparable to the modern eastern Mediterranean, with a spring‐bloom caused by enhanced winter/spring deep‐water mixing preceding a summer “shade‐flora” bloom caused by a summer‐stratification induced DCM.","PeriodicalId":54239,"journal":{"name":"Paleoceanography and Paleoclimatology","volume":" ","pages":""},"PeriodicalIF":3.5,"publicationDate":"2023-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47808104","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}
How hot can we expect Greenhouse Earth to have been in the past and the future? This is a question that deep‐time paleoclimatologists have long investigated. In a new paper by Fetrow et al. (2022), https://doi.org/10.1029/2022PA004517, deconvolving the depositional environments and burial history of continental carbonates deposited during known greenhouse climates, such as the Cretaceous, highlight the way Earth scientists can embark on understanding the clumped isotope derived temperatures and properly interpreting such temperatures.
{"title":"Hot Rocks: Interpreting Extremes of Earth Surface Temperatures From the Geologic Record","authors":"M. Suarez","doi":"10.1029/2023PA004641","DOIUrl":"https://doi.org/10.1029/2023PA004641","url":null,"abstract":"How hot can we expect Greenhouse Earth to have been in the past and the future? This is a question that deep‐time paleoclimatologists have long investigated. In a new paper by Fetrow et al. (2022), https://doi.org/10.1029/2022PA004517, deconvolving the depositional environments and burial history of continental carbonates deposited during known greenhouse climates, such as the Cretaceous, highlight the way Earth scientists can embark on understanding the clumped isotope derived temperatures and properly interpreting such temperatures.","PeriodicalId":54239,"journal":{"name":"Paleoceanography and Paleoclimatology","volume":" ","pages":""},"PeriodicalIF":3.5,"publicationDate":"2023-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46036238","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}
Xuewen Zhou, Z. Hui, R. Vachula, Xiao Wei, Peng Chen, Jun Zhang, Xiuxi Wang, T. Peng
Fire plays an important role in the Earth system, and is considered an essential control on global vegetation evolution and climate change. However, few Miocene high–resolution fire records have been obtained with which to assess the controls and possible drivers of fire on multiple timescales. Here, we provide a high–resolution charcoal record of the Nanyu section to reconstruct mid–Miocene fire history in the Wushan Basin. Further, we identify and assess the long–term regional fire regime (frequency and intensity) controls and possible drivers by making comparisons with published paleoclimate and paleoenvironmental records (i.e., palynomorphs, magnetic susceptibility, redness, stable isotope, pCO2 and marine δ18O data etc.). We also performed spectral analysis of the charcoal records to investigate possible controls of fire activity on orbital time scales. The analysis results indicate that (a) the reconstructed fire regime exhibits an increase from ∼16 to 13.86 Ma and a significant decrease after ∼13.86 Ma. (b) The steadily increasing regional fire activity during the period of ∼16–13.86 Ma may be caused by increased fuel ignitability and drying climate, whereas significantly decreased fire activity after ∼13.86 Ma is likely attributed to decreased fuel load due to the Mi–3b global cooling event. (c) On orbital time scales, the finding of the Earth's orbital cycles in fire proxy indicates that mid–Miocene fire activity variability in the study area was likely related to Earth's orbital forcing.
{"title":"Mid–Miocene Palaeofire and Its Complex Relationship With Vegetation Changes in the Wushan Basin, Northeastern Tibetan Plateau, China: Evidence From a High–Resolution Charcoal Record","authors":"Xuewen Zhou, Z. Hui, R. Vachula, Xiao Wei, Peng Chen, Jun Zhang, Xiuxi Wang, T. Peng","doi":"10.1029/2022PA004461","DOIUrl":"https://doi.org/10.1029/2022PA004461","url":null,"abstract":"Fire plays an important role in the Earth system, and is considered an essential control on global vegetation evolution and climate change. However, few Miocene high–resolution fire records have been obtained with which to assess the controls and possible drivers of fire on multiple timescales. Here, we provide a high–resolution charcoal record of the Nanyu section to reconstruct mid–Miocene fire history in the Wushan Basin. Further, we identify and assess the long–term regional fire regime (frequency and intensity) controls and possible drivers by making comparisons with published paleoclimate and paleoenvironmental records (i.e., palynomorphs, magnetic susceptibility, redness, stable isotope, pCO2 and marine δ18O data etc.). We also performed spectral analysis of the charcoal records to investigate possible controls of fire activity on orbital time scales. The analysis results indicate that (a) the reconstructed fire regime exhibits an increase from ∼16 to 13.86 Ma and a significant decrease after ∼13.86 Ma. (b) The steadily increasing regional fire activity during the period of ∼16–13.86 Ma may be caused by increased fuel ignitability and drying climate, whereas significantly decreased fire activity after ∼13.86 Ma is likely attributed to decreased fuel load due to the Mi–3b global cooling event. (c) On orbital time scales, the finding of the Earth's orbital cycles in fire proxy indicates that mid–Miocene fire activity variability in the study area was likely related to Earth's orbital forcing.","PeriodicalId":54239,"journal":{"name":"Paleoceanography and Paleoclimatology","volume":" ","pages":""},"PeriodicalIF":3.5,"publicationDate":"2023-03-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43804406","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}
M. E. Gastaldello, C. Agnini, T. Westerhold, A. Drury, R. Sutherland, M. Drake, A. Lam, G. Dickens, E. Dallanave, S. Burns, L. Alegret
The Late Miocene‐Early Pliocene Biogenic Bloom (∼9–3.5 Ma) was a paleoceanographic phenomenon defined by anomalously high accumulations of biological components at multiple open ocean sites, especially in certain regions of the Indian, and Pacific oceans. Its temporal and spatial extent with available information leaves fundamental questions about driving forces and responses unanswered. In this work, we focus on the middle part of the Biogenic Bloom (7.4–4.5 Ma) at International Ocean Discovery Program Site U1506 in the Tasman Sea, where we provide an integrated age model based on orbital tuning of the Natural Gamma Radiation, benthic foraminiferal oxygen isotopes, and calcareous nannofossil biostratigraphy. Benthic foraminiferal assemblages suggest changes in deep water oxygen concentration and seafloor nutrient supply during generally high export productivity conditions. From 7.4 to 6.7 Ma, seafloor conditions were characterized by episodic nutrient supply, perhaps related to seasonal phytoplankton blooms. From 6.7 to 4.5 Ma, the regime shifted to a more stable interval characterized by eutrophic and dysoxic conditions. Combined with seismic data, a regional change in paleoceanography is inferred at around 6.7 Ma, from stronger and well‐oxygenated bottom currents to weaker, oxygen‐depleted bottom currents. Our results support the hypothesis that the Biogenic Bloom was a complex, multiphase phenomenon driven by changes in ocean currents, rather than a single uniform period of sustained sea surface water productivity. Highly resolved studies are thus fundamental to its understanding and the disentanglement of local, regional, and global imprints.
{"title":"The Late Miocene‐Early Pliocene Biogenic Bloom: An Integrated Study in the Tasman Sea","authors":"M. E. Gastaldello, C. Agnini, T. Westerhold, A. Drury, R. Sutherland, M. Drake, A. Lam, G. Dickens, E. Dallanave, S. Burns, L. Alegret","doi":"10.1029/2022PA004565","DOIUrl":"https://doi.org/10.1029/2022PA004565","url":null,"abstract":"The Late Miocene‐Early Pliocene Biogenic Bloom (∼9–3.5 Ma) was a paleoceanographic phenomenon defined by anomalously high accumulations of biological components at multiple open ocean sites, especially in certain regions of the Indian, and Pacific oceans. Its temporal and spatial extent with available information leaves fundamental questions about driving forces and responses unanswered. In this work, we focus on the middle part of the Biogenic Bloom (7.4–4.5 Ma) at International Ocean Discovery Program Site U1506 in the Tasman Sea, where we provide an integrated age model based on orbital tuning of the Natural Gamma Radiation, benthic foraminiferal oxygen isotopes, and calcareous nannofossil biostratigraphy. Benthic foraminiferal assemblages suggest changes in deep water oxygen concentration and seafloor nutrient supply during generally high export productivity conditions. From 7.4 to 6.7 Ma, seafloor conditions were characterized by episodic nutrient supply, perhaps related to seasonal phytoplankton blooms. From 6.7 to 4.5 Ma, the regime shifted to a more stable interval characterized by eutrophic and dysoxic conditions. Combined with seismic data, a regional change in paleoceanography is inferred at around 6.7 Ma, from stronger and well‐oxygenated bottom currents to weaker, oxygen‐depleted bottom currents. Our results support the hypothesis that the Biogenic Bloom was a complex, multiphase phenomenon driven by changes in ocean currents, rather than a single uniform period of sustained sea surface water productivity. Highly resolved studies are thus fundamental to its understanding and the disentanglement of local, regional, and global imprints.","PeriodicalId":54239,"journal":{"name":"Paleoceanography and Paleoclimatology","volume":" ","pages":""},"PeriodicalIF":3.5,"publicationDate":"2023-03-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41937705","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}
J. R. Hall, Matthew S. Allison, Max T. Papadopoulos, D. Barfod, S. Jones
The Barmur Group (informally Tjörnes beds) sedimentary succession of northern Iceland is key to reconstructing the opening of the Bering Strait oceanic gateway because these rocks record migration of bivalve molluscs from the Pacific to the Atlantic via the Arctic. However, the timing of the migration event is poorly constrained owing to a lack of reliable absolute ages. To address this problem, we present the first Ar‐Ar radiometric dates from four basaltic lavas that underlie, are intercalated with, and overlie the Barmur Group, and integrate them with existing paleomagnetic records. We show that the Barmur Group has a latest Miocene to early Pliocene age range (c. 6.0–4.4 Ma; C3r–C3n.2n), older than all previous age models. Thus, the Barmur Group does not record the mid‐Piacenzian Warm Period, contra some previous suggestions. Abundant Pacific bivalve molluscs appeared in the Barmur Group during subchrons C3n.4n–C3n.3r at 5.235–4.896 Ma, over 1.3 million years earlier than previously suggested. Appearance of Pacific bivalves in the northern Atlantic occurred shortly after the 5.6–5.4 Ma age previously inferred for first appearance of Arctic bivalves in the Pacific. Thus, our data suggest that first opening of the Bering Strait gateway by the latest Miocene (c. 5.5 Ma) was soon followed by bidirectional trans‐Arctic faunal exchange, and argue against a hypothesized two‐stage faunal exchange process spanning c. 2 million years. Our results also confirm that first opening of the Bering Strait gateway was not directly associated with the growth of large northern hemisphere icesheets, which occurred several million years later.
{"title":"Timing and Consequences of Bering Strait Opening: New Insights From 40Ar/39Ar Dating of the Barmur Group (Tjörnes Beds), Northern Iceland","authors":"J. R. Hall, Matthew S. Allison, Max T. Papadopoulos, D. Barfod, S. Jones","doi":"10.1029/2022PA004539","DOIUrl":"https://doi.org/10.1029/2022PA004539","url":null,"abstract":"The Barmur Group (informally Tjörnes beds) sedimentary succession of northern Iceland is key to reconstructing the opening of the Bering Strait oceanic gateway because these rocks record migration of bivalve molluscs from the Pacific to the Atlantic via the Arctic. However, the timing of the migration event is poorly constrained owing to a lack of reliable absolute ages. To address this problem, we present the first Ar‐Ar radiometric dates from four basaltic lavas that underlie, are intercalated with, and overlie the Barmur Group, and integrate them with existing paleomagnetic records. We show that the Barmur Group has a latest Miocene to early Pliocene age range (c. 6.0–4.4 Ma; C3r–C3n.2n), older than all previous age models. Thus, the Barmur Group does not record the mid‐Piacenzian Warm Period, contra some previous suggestions. Abundant Pacific bivalve molluscs appeared in the Barmur Group during subchrons C3n.4n–C3n.3r at 5.235–4.896 Ma, over 1.3 million years earlier than previously suggested. Appearance of Pacific bivalves in the northern Atlantic occurred shortly after the 5.6–5.4 Ma age previously inferred for first appearance of Arctic bivalves in the Pacific. Thus, our data suggest that first opening of the Bering Strait gateway by the latest Miocene (c. 5.5 Ma) was soon followed by bidirectional trans‐Arctic faunal exchange, and argue against a hypothesized two‐stage faunal exchange process spanning c. 2 million years. Our results also confirm that first opening of the Bering Strait gateway was not directly associated with the growth of large northern hemisphere icesheets, which occurred several million years later.","PeriodicalId":54239,"journal":{"name":"Paleoceanography and Paleoclimatology","volume":" ","pages":""},"PeriodicalIF":3.5,"publicationDate":"2023-03-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46991264","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}
{"title":"Issue Information","authors":"","doi":"10.1002/palo.21174","DOIUrl":"https://doi.org/10.1002/palo.21174","url":null,"abstract":"No abstract is available for this article.","PeriodicalId":54239,"journal":{"name":"Paleoceanography and Paleoclimatology","volume":" ","pages":""},"PeriodicalIF":3.5,"publicationDate":"2023-03-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43938899","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}
B. Koffman, S. Goldstein, G. Winckler, M. Kaplan, L. Bolge, P. Biscaye
The Southern Hemisphere westerly winds (SWW) play a critical role in global climate, yet their behavior on decadal to centennial timescales, and the mechanisms driving these changes during the preindustrial era, remain poorly understood. We present a decadally resolved record of dust compositions using strontium and neodymium isotope ratios in mineral dust from the Siple Dome ice core, Antarctica, to explore the potential that abrupt changes in SWW behavior occurred over the past millennium. The record spans portions of the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA) intervals as defined in the Northern Hemisphere. We find evidence of an abrupt strengthening of atmospheric circulation during the MCA at ∼1125 CE (825 BP) that persisted for about 60 yr, indicating increased influence of Patagonia‐sourced dust. This occurs during an extended positive phase of Southern Annular Mode (SAM+)‐like conditions, characterized by high SWW velocities and a southerly shift of the main wind belt toward ∼60°S, suggesting that rapid changes in SWW strength could occur under the present SAM+ pattern. A second 20 yr long shift in dust compositions during the LIA at ∼1748 CE (200 BP) is coincident with higher dust delivery to Siple Dome, and may indicate increased dust emissions related to glacier activity in Patagonia. The new Siple Dome ice core data set demonstrates that Sr‐Nd isotopes can be used to trace shifts in atmospheric circulation on decadal timescales.
{"title":"Abrupt Changes in Atmospheric Circulation During the Medieval Climate Anomaly and Little Ice Age Recorded by Sr‐Nd Isotopes in the Siple Dome Ice Core, Antarctica","authors":"B. Koffman, S. Goldstein, G. Winckler, M. Kaplan, L. Bolge, P. Biscaye","doi":"10.1029/2022PA004543","DOIUrl":"https://doi.org/10.1029/2022PA004543","url":null,"abstract":"The Southern Hemisphere westerly winds (SWW) play a critical role in global climate, yet their behavior on decadal to centennial timescales, and the mechanisms driving these changes during the preindustrial era, remain poorly understood. We present a decadally resolved record of dust compositions using strontium and neodymium isotope ratios in mineral dust from the Siple Dome ice core, Antarctica, to explore the potential that abrupt changes in SWW behavior occurred over the past millennium. The record spans portions of the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA) intervals as defined in the Northern Hemisphere. We find evidence of an abrupt strengthening of atmospheric circulation during the MCA at ∼1125 CE (825 BP) that persisted for about 60 yr, indicating increased influence of Patagonia‐sourced dust. This occurs during an extended positive phase of Southern Annular Mode (SAM+)‐like conditions, characterized by high SWW velocities and a southerly shift of the main wind belt toward ∼60°S, suggesting that rapid changes in SWW strength could occur under the present SAM+ pattern. A second 20 yr long shift in dust compositions during the LIA at ∼1748 CE (200 BP) is coincident with higher dust delivery to Siple Dome, and may indicate increased dust emissions related to glacier activity in Patagonia. The new Siple Dome ice core data set demonstrates that Sr‐Nd isotopes can be used to trace shifts in atmospheric circulation on decadal timescales.","PeriodicalId":54239,"journal":{"name":"Paleoceanography and Paleoclimatology","volume":" ","pages":""},"PeriodicalIF":3.5,"publicationDate":"2023-03-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43658168","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}
L. Kearns, Alex Searle-Barnes, G. Foster, J. A. Milton, C. Standish, T. Ezard
Variation among individuals within species is a biological precondition for co‐existence. Traditional geochemical analysis based on bulk averages facilitates rapid data gathering but necessarily means the loss of large amounts of potentially crucial information into variability within a given sample. As the sensitivity of geochemical analysis improves, it is now feasible to build sufficiently powerful datasets to investigate paleoclimatic variation at the level of individual specimens. Here, we investigate geochemical and morphological variation among the sensu stricto, sensu lato and sensu lato extreme subspecies of the workhorse extant planktic foraminifera Globigerinoides ruber. Our experimental design distinguishes between subspecies and intraspecific variability as well as the repeatability of laser ablation inductively coupled plasma mass spectrometry (LA‐ICP‐MS). We show that geochemical variability in Mg/Ca ratios is driven by differences in subspecies depth habitat and that ontogenetic trends in Mg/Ca ratios are evident in the final whorl, with the final chamber consistently showing depleted Mg/Ca. These ontogenetic trends are not driven by individual chamber or test size. The Mg/Ca value variance among individuals is ∼100 times higher than the variance among repeated laser spot analyses of single chambers, directing laboratory protocols towards the need to sample ecologically and environmentally homogeneous samples. Our results emphasize that we can use LA‐ICP‐MS to quantify how individual variability aggregates to bulk results, and highlights that, with sufficient sample sizes, it is possible to reveal how intraspecific variability alters geochemical inference.
{"title":"The Influence of Geochemical Variation Among Globigerinoides ruber Individuals on Paleoceanographic Reconstructions","authors":"L. Kearns, Alex Searle-Barnes, G. Foster, J. A. Milton, C. Standish, T. Ezard","doi":"10.1029/2022PA004549","DOIUrl":"https://doi.org/10.1029/2022PA004549","url":null,"abstract":"Variation among individuals within species is a biological precondition for co‐existence. Traditional geochemical analysis based on bulk averages facilitates rapid data gathering but necessarily means the loss of large amounts of potentially crucial information into variability within a given sample. As the sensitivity of geochemical analysis improves, it is now feasible to build sufficiently powerful datasets to investigate paleoclimatic variation at the level of individual specimens. Here, we investigate geochemical and morphological variation among the sensu stricto, sensu lato and sensu lato extreme subspecies of the workhorse extant planktic foraminifera Globigerinoides ruber. Our experimental design distinguishes between subspecies and intraspecific variability as well as the repeatability of laser ablation inductively coupled plasma mass spectrometry (LA‐ICP‐MS). We show that geochemical variability in Mg/Ca ratios is driven by differences in subspecies depth habitat and that ontogenetic trends in Mg/Ca ratios are evident in the final whorl, with the final chamber consistently showing depleted Mg/Ca. These ontogenetic trends are not driven by individual chamber or test size. The Mg/Ca value variance among individuals is ∼100 times higher than the variance among repeated laser spot analyses of single chambers, directing laboratory protocols towards the need to sample ecologically and environmentally homogeneous samples. Our results emphasize that we can use LA‐ICP‐MS to quantify how individual variability aggregates to bulk results, and highlights that, with sufficient sample sizes, it is possible to reveal how intraspecific variability alters geochemical inference.","PeriodicalId":54239,"journal":{"name":"Paleoceanography and Paleoclimatology","volume":" ","pages":""},"PeriodicalIF":3.5,"publicationDate":"2023-03-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48373069","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}
Rebekah A. Stein, Andrew C. Turner, R. Amundson, D. Stolper
The genus Celtis includes widespread trees that produce drupes with aragonite endocarps, or “hackberries.” These carbonate endocarps are preserved in the fossil record, often in cave deposits or packrat middens, and thus are targets for paleoclimate reconstructions. Stable oxygen isotopes in Celtis endocarps have been used as proxies for oxygen isotopic composition of past stream water and for paleothermometry. Here, we explore the suitability of hackberry carbonates for paleoclimate reconstructions based on carbonate clumped‐isotope thermometry. We sampled modern hackberries grown at sites across North America (n = 37) for stable and clumped isotope analyses. Measured clumped‐isotope temperatures are found to be within the range of measured local modern growing season surface temperatures and typically in dual clumped‐isotope equilibrium. As such, we propose that hackberry clumped‐isotope measurements can be used to reconstruct past Earth‐surface air temperatures.
{"title":"Clumped Isotope Thermometry in Plant‐Derived Carbonates","authors":"Rebekah A. Stein, Andrew C. Turner, R. Amundson, D. Stolper","doi":"10.1029/2022PA004473","DOIUrl":"https://doi.org/10.1029/2022PA004473","url":null,"abstract":"The genus Celtis includes widespread trees that produce drupes with aragonite endocarps, or “hackberries.” These carbonate endocarps are preserved in the fossil record, often in cave deposits or packrat middens, and thus are targets for paleoclimate reconstructions. Stable oxygen isotopes in Celtis endocarps have been used as proxies for oxygen isotopic composition of past stream water and for paleothermometry. Here, we explore the suitability of hackberry carbonates for paleoclimate reconstructions based on carbonate clumped‐isotope thermometry. We sampled modern hackberries grown at sites across North America (n = 37) for stable and clumped isotope analyses. Measured clumped‐isotope temperatures are found to be within the range of measured local modern growing season surface temperatures and typically in dual clumped‐isotope equilibrium. As such, we propose that hackberry clumped‐isotope measurements can be used to reconstruct past Earth‐surface air temperatures.","PeriodicalId":54239,"journal":{"name":"Paleoceanography and Paleoclimatology","volume":" ","pages":""},"PeriodicalIF":3.5,"publicationDate":"2023-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44372767","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}
E. Arellano‐Torres, Abril Amezcua‐Montiel, Arantza Casas‐Ortiz
The loop current (LC) in the Gulf of Mexico (GoM) is part of the western North Atlantic circulation. Recording its strength and slowdown variations can help us characterize the regional climate over the Late Pleistocene. To reconstruct the sea surface and the LC intensity in the eastern GoM, we study the distribution patterns of planktonic foraminifera in the core EN‐032‐18PC, spanning the end of Marine Isotope Stage (MIS) 9 to early MIS‐4. We reconstructed a sequence of paleoceanographic events based on stable isotopes (δ18O and δ13C) of the surface dweller Globigerinoides ruber and two faunal assemblages. The first assemblage explains most of the glacial and late interglacial periods, suggesting a subtropical environment with a deep thermocline and a reduced LC due to a moderate inflow of warm Caribbean waters. The second assemblage explains the warmest interglacial substages, dominated by tropical species, a shallow thermocline, and an extended LC, driven by summer insolation. Overall, surface ocean conditions led to more ecological successions and instability during the warmest interglacial substages than during glacial periods, as supported by the stable isotope records. Besides the GoM relationship to AMOC, as a regulator of heat transport to higher latitudes, we suggest that fluctuations in the LC rely on the migration of atmospheric circulation patterns and astronomical insolation forcing.
{"title":"The Loop Current Circulation Over the MIS 9 to MIS 5 Based on Planktonic Foraminifera Assemblages From the Gulf of Mexico","authors":"E. Arellano‐Torres, Abril Amezcua‐Montiel, Arantza Casas‐Ortiz","doi":"10.1029/2022PA004568","DOIUrl":"https://doi.org/10.1029/2022PA004568","url":null,"abstract":"The loop current (LC) in the Gulf of Mexico (GoM) is part of the western North Atlantic circulation. Recording its strength and slowdown variations can help us characterize the regional climate over the Late Pleistocene. To reconstruct the sea surface and the LC intensity in the eastern GoM, we study the distribution patterns of planktonic foraminifera in the core EN‐032‐18PC, spanning the end of Marine Isotope Stage (MIS) 9 to early MIS‐4. We reconstructed a sequence of paleoceanographic events based on stable isotopes (δ18O and δ13C) of the surface dweller Globigerinoides ruber and two faunal assemblages. The first assemblage explains most of the glacial and late interglacial periods, suggesting a subtropical environment with a deep thermocline and a reduced LC due to a moderate inflow of warm Caribbean waters. The second assemblage explains the warmest interglacial substages, dominated by tropical species, a shallow thermocline, and an extended LC, driven by summer insolation. Overall, surface ocean conditions led to more ecological successions and instability during the warmest interglacial substages than during glacial periods, as supported by the stable isotope records. Besides the GoM relationship to AMOC, as a regulator of heat transport to higher latitudes, we suggest that fluctuations in the LC rely on the migration of atmospheric circulation patterns and astronomical insolation forcing.","PeriodicalId":54239,"journal":{"name":"Paleoceanography and Paleoclimatology","volume":" ","pages":""},"PeriodicalIF":3.5,"publicationDate":"2023-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48452621","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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