Pub Date : 2024-01-25DOI: 10.1146/annurev-earth-031621-114105
J. Tyler Faith, John Rowan, Andrew Du
Africa's fossil record of late Cenozoic mammals documents considerable ecological and evolutionary changes through time. Here, we synthesize those changes in the context of the mechanisms proposed to account for them, including bottom-up (e.g., climate change) and top-down (e.g., hominin impacts) processes. In doing so, we ( a) examine how the incompleteness of the fossil record and the varied spatiotemporal scales of the evidence complicate efforts to establish cause-effect relationships; ( b) evaluate hypothesized drivers of long-term ecological and evolutionary change, highlighting key unknowns; and ( c) synthesize major taxonomic and functional trends through time (e.g., downsizing of faunal communities) considering the proposed drivers. Throughout our review, we point to unresolved questions and highlight research avenues that have potential to inform on the processes that have shaped the history of what are today the most diverse remaining large mammal communities on Earth.▪ The study of late Cenozoic African mammal communities is intertwined with questions about the context, causes, and consequences of hominin evolution. ▪ The fossil record documents major functional (e.g., loss of megaherbivores) and taxonomic (e.g., rise of the Bovidae) changes over the past ∼7 Myr. ▪ Complexities inherent to the fossil record have made it difficult to identify the processes that drove ecological and evolutionary changes. ▪ Unanswered questions about the drivers of faunal change and the functioning of past ecosystems represent promising future research directions.Expected final online publication date for the Annual Review of Earth and Planetary Sciences, Volume 52 is May 2024. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
{"title":"Late Cenozoic Faunal and Ecological Change in Africa","authors":"J. Tyler Faith, John Rowan, Andrew Du","doi":"10.1146/annurev-earth-031621-114105","DOIUrl":"https://doi.org/10.1146/annurev-earth-031621-114105","url":null,"abstract":"Africa's fossil record of late Cenozoic mammals documents considerable ecological and evolutionary changes through time. Here, we synthesize those changes in the context of the mechanisms proposed to account for them, including bottom-up (e.g., climate change) and top-down (e.g., hominin impacts) processes. In doing so, we ( a) examine how the incompleteness of the fossil record and the varied spatiotemporal scales of the evidence complicate efforts to establish cause-effect relationships; ( b) evaluate hypothesized drivers of long-term ecological and evolutionary change, highlighting key unknowns; and ( c) synthesize major taxonomic and functional trends through time (e.g., downsizing of faunal communities) considering the proposed drivers. Throughout our review, we point to unresolved questions and highlight research avenues that have potential to inform on the processes that have shaped the history of what are today the most diverse remaining large mammal communities on Earth.▪ The study of late Cenozoic African mammal communities is intertwined with questions about the context, causes, and consequences of hominin evolution. ▪ The fossil record documents major functional (e.g., loss of megaherbivores) and taxonomic (e.g., rise of the Bovidae) changes over the past ∼7 Myr. ▪ Complexities inherent to the fossil record have made it difficult to identify the processes that drove ecological and evolutionary changes. ▪ Unanswered questions about the drivers of faunal change and the functioning of past ecosystems represent promising future research directions.Expected final online publication date for the Annual Review of Earth and Planetary Sciences, Volume 52 is May 2024. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.","PeriodicalId":8034,"journal":{"name":"Annual Review of Earth and Planetary Sciences","volume":null,"pages":null},"PeriodicalIF":14.9,"publicationDate":"2024-01-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139565604","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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 : 2024-01-18DOI: 10.1146/annurev-earth-031621-063108
Philippe Carrez, Alexandre Mussi, Patrick Cordier
▪ An understanding of the rheological behavior of the solid Earth is fundamental to provide a quantitative description of most geological and geophysical phenomena. The continuum mechanics approach to describing large-scale phenomena needs to be informed by a description of the mechanisms operating at the atomic scale. These involve crystal defects, mainly vacancies and dislocations. This often leads to a binary view of creep reduced to diffusion creep or dislocation creep. However, the interaction between these two types of defects leading to dislocation climb plays an important role, and may even be the main one, in the high-temperature, low strain rate creep mechanisms of interest to the Earth sciences. Here we review the fundamentals of dislocation climb, highlighting the specific problems of minerals. We discuss the importance of computer simulations, informed by experiments, for accurately modeling climb. We show how dislocation climb increasingly appears as a deformation mechanism in its own right. We review the contribution of this mechanism to mineral deformation, particularly in Earth's mantle. Finally, we discuss progress and challenges, and we outline future work directions. Dislocations can be sources or sinks of vacancies, resulting in a displacement out of the glide plane: climb. ▪ Dislocation climb can be a recovery mechanism during dislocation creep but also a strain-producing mechanism. ▪ The slow natural strain rates promote the contribution of climb, which is controlled by diffusion. ▪ In planetary interiors where dislocation glide can be inhibited by pressure, dislocation climb may be the only active mechanism.Expected final online publication date for the Annual Review of Earth and Planetary Sciences, Volume 52 is May 2024. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
{"title":"On Dislocation Climb as an Important Deformation Mechanism for Planetary Interiors","authors":"Philippe Carrez, Alexandre Mussi, Patrick Cordier","doi":"10.1146/annurev-earth-031621-063108","DOIUrl":"https://doi.org/10.1146/annurev-earth-031621-063108","url":null,"abstract":"▪ An understanding of the rheological behavior of the solid Earth is fundamental to provide a quantitative description of most geological and geophysical phenomena. The continuum mechanics approach to describing large-scale phenomena needs to be informed by a description of the mechanisms operating at the atomic scale. These involve crystal defects, mainly vacancies and dislocations. This often leads to a binary view of creep reduced to diffusion creep or dislocation creep. However, the interaction between these two types of defects leading to dislocation climb plays an important role, and may even be the main one, in the high-temperature, low strain rate creep mechanisms of interest to the Earth sciences. Here we review the fundamentals of dislocation climb, highlighting the specific problems of minerals. We discuss the importance of computer simulations, informed by experiments, for accurately modeling climb. We show how dislocation climb increasingly appears as a deformation mechanism in its own right. We review the contribution of this mechanism to mineral deformation, particularly in Earth's mantle. Finally, we discuss progress and challenges, and we outline future work directions. Dislocations can be sources or sinks of vacancies, resulting in a displacement out of the glide plane: climb. ▪ Dislocation climb can be a recovery mechanism during dislocation creep but also a strain-producing mechanism. ▪ The slow natural strain rates promote the contribution of climb, which is controlled by diffusion. ▪ In planetary interiors where dislocation glide can be inhibited by pressure, dislocation climb may be the only active mechanism.Expected final online publication date for the Annual Review of Earth and Planetary Sciences, Volume 52 is May 2024. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.","PeriodicalId":8034,"journal":{"name":"Annual Review of Earth and Planetary Sciences","volume":null,"pages":null},"PeriodicalIF":14.9,"publicationDate":"2024-01-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139494788","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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 : 2024-01-18DOI: 10.1146/annurev-earth-031621-081700
David S. Schimel, Dustin Carroll
The Paris Agreement calls for emissions reductions to limit climate change, but how will the carbon cycle change if it is successful? The land and oceans currently absorb roughly half of anthropogenic emissions, but this fraction will decline in the future. The amount of carbon that can be released before climate is mitigated depends on the amount of carbon the ocean and terrestrial ecosystems can absorb. Policy is based on model projections, but observations and theory suggest that climate effects emerging in today's climate will increase and carbon cycle tipping points may be crossed. Warming temperatures, drought, and a slowing growth rate of CO2 itself will reduce land and ocean sinks and create new sources, making carbon sequestration in forests, soils, and other land and aquatic vegetation more difficult. Observations, data-assimilative models, and prediction systems are needed for managing ongoing long-term changes to land and ocean systems after achieving net-zero emissions. ▪ International agreements call for stabilizing climate at 1.5° above preindustrial, while the world is already seeing damaging extremes below that. ▪ If climate is stabilized near the 1.5° target, the driving force for most sinks will slow, while feedbacks from the warmer climate will continue to cause sources. ▪ Once emissions are reduced to net zero, carbon cycle-climate feedbacks will require observations to support ongoing active management to maintain storage.Expected final online publication date for the Annual Review of Earth and Planetary Sciences, Volume 52 is May 2024. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
{"title":"Carbon Cycle–Climate Feedbacks in the Post-Paris World","authors":"David S. Schimel, Dustin Carroll","doi":"10.1146/annurev-earth-031621-081700","DOIUrl":"https://doi.org/10.1146/annurev-earth-031621-081700","url":null,"abstract":"The Paris Agreement calls for emissions reductions to limit climate change, but how will the carbon cycle change if it is successful? The land and oceans currently absorb roughly half of anthropogenic emissions, but this fraction will decline in the future. The amount of carbon that can be released before climate is mitigated depends on the amount of carbon the ocean and terrestrial ecosystems can absorb. Policy is based on model projections, but observations and theory suggest that climate effects emerging in today's climate will increase and carbon cycle tipping points may be crossed. Warming temperatures, drought, and a slowing growth rate of CO<jats:sub>2</jats:sub> itself will reduce land and ocean sinks and create new sources, making carbon sequestration in forests, soils, and other land and aquatic vegetation more difficult. Observations, data-assimilative models, and prediction systems are needed for managing ongoing long-term changes to land and ocean systems after achieving net-zero emissions. ▪ International agreements call for stabilizing climate at 1.5° above preindustrial, while the world is already seeing damaging extremes below that. ▪ If climate is stabilized near the 1.5° target, the driving force for most sinks will slow, while feedbacks from the warmer climate will continue to cause sources. ▪ Once emissions are reduced to net zero, carbon cycle-climate feedbacks will require observations to support ongoing active management to maintain storage.Expected final online publication date for the Annual Review of Earth and Planetary Sciences, Volume 52 is May 2024. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.","PeriodicalId":8034,"journal":{"name":"Annual Review of Earth and Planetary Sciences","volume":null,"pages":null},"PeriodicalIF":14.9,"publicationDate":"2024-01-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139494769","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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 : 2024-01-18DOI: 10.1146/annurev-earth-032320-100333
Jiang Zhu, Christopher J. Poulsen, Bette L. Otto-Bliesner
Simulating the warmth and equability of past hothouse climates has been a challenge since the inception of paleoclimate modeling. The newest generation of Earth system models (ESMs) has shown substantial improvements in the ability to simulate the early Eocene global mean surface temperature (GMST) and equator-to-pole gradient. Results using the Community Earth System Model suggest that parameterizations of atmospheric radiation, convection, and clouds largely determine the Eocene GMST and are responsible for improvements in the new ESMs, but they have less direct influence on the equator-to-pole temperature gradient. ESMs still have difficulty simulating some regional and seasonal temperatures, although improved data reconstructions of chronology, spatial coverage, and seasonal resolution are needed for more robust model assessment. Looking forward, key processes including radiation and clouds need to be benchmarked and improved using more accurate models of limited domain/physics. Earth system processes need to be better explored, leveraging the increasing ESM resolution and complexity. ▪ Earth system models (ESMs) are now able to simulate the large-scale features of the early Eocene. ▪ Remaining model-data discrepancies exist at regional and seasonal scales and require improvements in both proxy data and ESMs. ▪ A hierarchical modeling approach is needed to ensure relevant physical processes are parameterized reasonably well in ESMs. ▪ Future work is needed to leverage the continuously increasing resolution and complexity of ESMs.Expected final online publication date for the Annual Review of Earth and Planetary Sciences, Volume 52 is May 2024. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
{"title":"Modeling Past Hothouse Climates as a Means for Assessing Earth System Models and Improving the Understanding of Warm Climates","authors":"Jiang Zhu, Christopher J. Poulsen, Bette L. Otto-Bliesner","doi":"10.1146/annurev-earth-032320-100333","DOIUrl":"https://doi.org/10.1146/annurev-earth-032320-100333","url":null,"abstract":"Simulating the warmth and equability of past hothouse climates has been a challenge since the inception of paleoclimate modeling. The newest generation of Earth system models (ESMs) has shown substantial improvements in the ability to simulate the early Eocene global mean surface temperature (GMST) and equator-to-pole gradient. Results using the Community Earth System Model suggest that parameterizations of atmospheric radiation, convection, and clouds largely determine the Eocene GMST and are responsible for improvements in the new ESMs, but they have less direct influence on the equator-to-pole temperature gradient. ESMs still have difficulty simulating some regional and seasonal temperatures, although improved data reconstructions of chronology, spatial coverage, and seasonal resolution are needed for more robust model assessment. Looking forward, key processes including radiation and clouds need to be benchmarked and improved using more accurate models of limited domain/physics. Earth system processes need to be better explored, leveraging the increasing ESM resolution and complexity. ▪ Earth system models (ESMs) are now able to simulate the large-scale features of the early Eocene. ▪ Remaining model-data discrepancies exist at regional and seasonal scales and require improvements in both proxy data and ESMs. ▪ A hierarchical modeling approach is needed to ensure relevant physical processes are parameterized reasonably well in ESMs. ▪ Future work is needed to leverage the continuously increasing resolution and complexity of ESMs.Expected final online publication date for the Annual Review of Earth and Planetary Sciences, Volume 52 is May 2024. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.","PeriodicalId":8034,"journal":{"name":"Annual Review of Earth and Planetary Sciences","volume":null,"pages":null},"PeriodicalIF":14.9,"publicationDate":"2024-01-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139494784","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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 : 2024-01-18DOI: 10.1146/annurev-earth-032320-105438
Steven B. Shirey, D. Graham Pearson, Thomas Stachel, Michael J. Walter
Sublithospheric diamonds and the inclusions they may carry crystallize in the asthenosphere, transition zone, or uppermost lower mantle (from 300 to ∼800 km), and are the deepest minerals so far recognized to form by plate tectonics. These diamonds are distinctive in their deformation features, low nitrogen content, and inclusions of these major mantle minerals: majoritic garnet, clinopyroxene, ringwoodite, CaSi perovskite, ferropericlase, and bridgmanite or their retrograde equivalents. The stable isotopic compositions of elements within these diamonds (δ11B, δ13C, δ15N) and their inclusions (δ18O, δ56Fe) are typically well outside normal mantle ranges, showing that these elements were either organic (C) or modified by seawater alteration (B, O, Fe) at relatively low temperatures. Metamorphic minerals in cold slabs are effective hosts that transport C as CO3 and H as H2O, OH, or CH4 below the island arc and mantle wedge. Warming of the slab generates carbonatitic melts, supercritical aqueous fluids, or metallic liquids, forming three types of sublithospheric diamonds. Diamond crystallization occurs by movement and reduction of mobile fluids as they pass through host mantle via fractures—a process that creates chemical heterogeneity and may promote deep focus earthquakes. Geobarometry of majoritic garnet inclusions and diamond ages suggest upward transport, perhaps to the base of mantle lithosphere. From there, diamonds are carried to Earth's surface by eruptions of kimberlite magma. Mineral assemblages in sublithospheric diamonds directly trace Earth's deep volatile cycle, demonstrating how the hydrosphere of a rocky planet can connect to its solid interior. ▪ Sublithospheric diamonds from the deep upper mantle, transition zone, and lower mantle host Earth's deepest obtainable mineral samples. ▪ Low-temperature seawater alteration of the ocean floor captures organic and inorganic carbon at the surface eventually to become some of the most precious gem diamonds. ▪ Subduction transports fluids in metamorphic minerals to great depth. Fluids released by slab heating migrate, react with host mantle to induce diamond crystallization, and may trigger earthquakes. ▪ Sublithospheric diamonds are powerful tracers of subduction—a plate tectonic process that deeply recycles part of Earth's planetary volatile budget.Expected final online publication date for the Annual Review of Earth and Planetary Sciences, Volume 52 is May 2024. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
岩石圈下金刚石及其可能携带的包裹体在星体层、过渡带或最上层下地幔（300 至 800 千米）中结晶，是迄今公认的由板块构造形成的最深层矿物。这些金刚石的独特之处在于它们的变形特征、低含氮量以及这些主要地幔矿物的包裹体：主石榴石、倩辉石、环钨矿、CaSi透辉石、铁闪长岩、桥粒岩或它们的逆行等价物。这些金刚石中的元素（δ11B、δ13C、δ15N）及其包裹体（δ18O、δ56Fe）的稳定同位素组成通常远远超出正常地幔范围，表明这些元素要么是有机元素（C），要么是在相对较低的温度下被海水蚀变（B、O、Fe）而改变的。冷板块中的变质矿物是有效的宿主，它们以 CO3 的形式将 C 和以 H2O、OH 或 CH4 的形式将 H 运送到岛弧和地幔楔以下。板块升温产生碳酸盐熔体、超临界水液或金属液，形成三种岩石圈下金刚石。金刚石的结晶是由流动流体在通过裂缝穿过主地幔时的移动和还原而产生的--这一过程会产生化学异质性，并可能促进深部聚焦地震。橄榄榴石包裹体的测地线和钻石的年龄表明，钻石是向上迁移的，可能迁移到地幔岩石圈的底部。从那里，金伯利岩浆的喷发将钻石带到地球表面。岩石圈下钻石中的矿物组合直接追溯了地球的深层挥发循环，展示了岩石行星的水圈是如何与其固体内部相联系的。来自深层上地幔、过渡带和下地幔的岩石圈下金刚石拥有地球上可获得的最深矿物样本。洋底的低温海水蜕变在表层捕获有机碳和无机碳，最终成为一些最珍贵的宝石钻石。俯冲作用将变质矿物中的流体带到很深的地方。板块加热释放的流体迁移，与主地幔发生反应，诱发钻石结晶，并可能引发地震。岩石圈下的钻石是俯冲--板块构造过程--的强大示踪剂，它深度回收了地球行星挥发性预算的一部分。《地球与行星科学年刊》第52卷的最终在线出版日期预计为2024年5月。修订后的预计日期请参见 http://www.annualreviews.org/page/journal/pubdates。
{"title":"Sublithospheric Diamonds: Plate Tectonics from Earth's Deepest Mantle Samples","authors":"Steven B. Shirey, D. Graham Pearson, Thomas Stachel, Michael J. Walter","doi":"10.1146/annurev-earth-032320-105438","DOIUrl":"https://doi.org/10.1146/annurev-earth-032320-105438","url":null,"abstract":"Sublithospheric diamonds and the inclusions they may carry crystallize in the asthenosphere, transition zone, or uppermost lower mantle (from 300 to ∼800 km), and are the deepest minerals so far recognized to form by plate tectonics. These diamonds are distinctive in their deformation features, low nitrogen content, and inclusions of these major mantle minerals: majoritic garnet, clinopyroxene, ringwoodite, CaSi perovskite, ferropericlase, and bridgmanite or their retrograde equivalents. The stable isotopic compositions of elements within these diamonds (δ<jats:sup>11</jats:sup>B, δ<jats:sup>13</jats:sup>C, δ<jats:sup>15</jats:sup>N) and their inclusions (δ<jats:sup>18</jats:sup>O, δ<jats:sup>56</jats:sup>Fe) are typically well outside normal mantle ranges, showing that these elements were either organic (C) or modified by seawater alteration (B, O, Fe) at relatively low temperatures. Metamorphic minerals in cold slabs are effective hosts that transport C as CO<jats:sub>3</jats:sub> and H as H<jats:sub>2</jats:sub>O, OH, or CH<jats:sub>4</jats:sub> below the island arc and mantle wedge. Warming of the slab generates carbonatitic melts, supercritical aqueous fluids, or metallic liquids, forming three types of sublithospheric diamonds. Diamond crystallization occurs by movement and reduction of mobile fluids as they pass through host mantle via fractures—a process that creates chemical heterogeneity and may promote deep focus earthquakes. Geobarometry of majoritic garnet inclusions and diamond ages suggest upward transport, perhaps to the base of mantle lithosphere. From there, diamonds are carried to Earth's surface by eruptions of kimberlite magma. Mineral assemblages in sublithospheric diamonds directly trace Earth's deep volatile cycle, demonstrating how the hydrosphere of a rocky planet can connect to its solid interior. ▪ Sublithospheric diamonds from the deep upper mantle, transition zone, and lower mantle host Earth's deepest obtainable mineral samples. ▪ Low-temperature seawater alteration of the ocean floor captures organic and inorganic carbon at the surface eventually to become some of the most precious gem diamonds. ▪ Subduction transports fluids in metamorphic minerals to great depth. Fluids released by slab heating migrate, react with host mantle to induce diamond crystallization, and may trigger earthquakes. ▪ Sublithospheric diamonds are powerful tracers of subduction—a plate tectonic process that deeply recycles part of Earth's planetary volatile budget.Expected final online publication date for the Annual Review of Earth and Planetary Sciences, Volume 52 is May 2024. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.","PeriodicalId":8034,"journal":{"name":"Annual Review of Earth and Planetary Sciences","volume":null,"pages":null},"PeriodicalIF":14.9,"publicationDate":"2024-01-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139494756","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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 : 2024-01-12DOI: 10.1146/annurev-earth-040522-122817
Jeremy N. Bassis, Anna Crawford, Samuel B. Kachuck, Douglas I. Benn, Catherine Walker, Joanna Millstein, Ravindra Duddu, Jan Åström, Helen Fricker, Adrian Luckman
The largest uncertainty in future sea-level rise is loss of ice from the Greenland and Antarctic Ice Sheets. Ice shelves, freely floating platforms of ice that fringe the ice sheets, play a crucial role in restraining discharge of grounded ice into the ocean through buttressing. However, since the 1990s, several ice shelves have thinned, retreated, and collapsed. If this pattern continues, it could expose thick cliffs that become structurally unstable and collapse in a process called marine ice cliff instability (MICI). However, the feedbacks between calving, retreat, and other forcings are not well understood. Here we review observed modes of calving from ice shelves and marine-terminating glaciers, and their relation to environmental forces. We show that the primary driver of calving is long-term internal glaciological stress, but as ice shelves thin they may become more vulnerable to environmental forcing. This vulnerability—and the potential for MICI—comes from a combination of the distribution of preexisting flaws within the ice and regions where the stress is large enough to initiate fracture. Although significant progress has been made modeling these processes, theories must now be tested against a wide range of environmental and glaciological conditions in both modern and paleo conditions. ▪ Ice shelves, floating platforms of ice fed by ice sheets, shed mass in a near-instantaneous fashion through iceberg calving. ▪ Most ice shelves exhibit a stable cycle of calving front advance and retreat that is insensitive to small changes in environmental conditions. ▪ Some ice shelves have retreated or collapsed completely, and in the future this could expose thick cliffs that could become structurally unstable called ice cliff instability. ▪ The potential for ice shelf and ice cliff instability is controlled by the presence and evolution of flaws or fractures within the ice.Expected final online publication date for the Annual Review of Earth and Planetary Sciences, Volume 52 is May 2024. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
{"title":"Stability of Ice Shelves and Ice Cliffs in a Changing Climate","authors":"Jeremy N. Bassis, Anna Crawford, Samuel B. Kachuck, Douglas I. Benn, Catherine Walker, Joanna Millstein, Ravindra Duddu, Jan Åström, Helen Fricker, Adrian Luckman","doi":"10.1146/annurev-earth-040522-122817","DOIUrl":"https://doi.org/10.1146/annurev-earth-040522-122817","url":null,"abstract":"The largest uncertainty in future sea-level rise is loss of ice from the Greenland and Antarctic Ice Sheets. Ice shelves, freely floating platforms of ice that fringe the ice sheets, play a crucial role in restraining discharge of grounded ice into the ocean through buttressing. However, since the 1990s, several ice shelves have thinned, retreated, and collapsed. If this pattern continues, it could expose thick cliffs that become structurally unstable and collapse in a process called marine ice cliff instability (MICI). However, the feedbacks between calving, retreat, and other forcings are not well understood. Here we review observed modes of calving from ice shelves and marine-terminating glaciers, and their relation to environmental forces. We show that the primary driver of calving is long-term internal glaciological stress, but as ice shelves thin they may become more vulnerable to environmental forcing. This vulnerability—and the potential for MICI—comes from a combination of the distribution of preexisting flaws within the ice and regions where the stress is large enough to initiate fracture. Although significant progress has been made modeling these processes, theories must now be tested against a wide range of environmental and glaciological conditions in both modern and paleo conditions. ▪ Ice shelves, floating platforms of ice fed by ice sheets, shed mass in a near-instantaneous fashion through iceberg calving. ▪ Most ice shelves exhibit a stable cycle of calving front advance and retreat that is insensitive to small changes in environmental conditions. ▪ Some ice shelves have retreated or collapsed completely, and in the future this could expose thick cliffs that could become structurally unstable called ice cliff instability. ▪ The potential for ice shelf and ice cliff instability is controlled by the presence and evolution of flaws or fractures within the ice.Expected final online publication date for the Annual Review of Earth and Planetary Sciences, Volume 52 is May 2024. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.","PeriodicalId":8034,"journal":{"name":"Annual Review of Earth and Planetary Sciences","volume":null,"pages":null},"PeriodicalIF":14.9,"publicationDate":"2024-01-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139431171","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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 : 2024-01-12DOI: 10.1146/annurev-earth-031621-111700
Mark A. Kendrick
Each of the halogens constrains a different aspect of volatile cycling in the solid Earth. F is moderately incompatible in the mantle and has a low mobility at Earth's surface, meaning that it is preferentially retained in the mantle and continental crust. In contrast, Cl, Br, and I are strongly incompatible and highly soluble. Chloride is the dominant anion in seawater and many geofluids and a major component of evaporite minerals. Br and I are essential for life and significantly incorporated into organic matter that accumulates in marine sediments. Surficial fluids circulated into continental and oceanic crust incorporate surface-derived halogens into alteration minerals. As a result, subducting slabs and arc lavas are weakly enriched in F and strongly enriched in Cl, Br, and I. Subduction has maintained mantle Cl and Br concentrations at relatively constant levels since Earth's early differentiation, but mantle I/Cl has decreased over time. ▪ Halogen abundances on the early Earth were affected by I partitioning into Earth's core and possible loss of hydrophilic Cl, Br, and I in an early formed ocean. ▪ Halogens are powerful tracers of subduction zone processes on the modern Earth, with Cl, Br, and I having a dominantly subducted origin in Earth's mantle. ▪ The deep subduction cycles of Cl, Br, and I are more similar to that of H2O than they are to F, but the geochemical cycle of each halogen differs in detail. ▪ Halogen abundance ratios and stable isotope ratios vary systematically in Earth's surface reservoirs, meaning that halogens are powerful tracers of geological fluids and melts.Expected final online publication date for the Annual Review of Earth and Planetary Sciences, Volume 52 is May 2024. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
每种卤素都对固体地球中的挥发循环有不同方面的影响。F 在地幔中具有中度不相容性，在地球表面的流动性较低，这意味着它优先保留在地幔和大陆地壳中。相比之下，Cl、Br 和 I 具有强烈的不相容性和高溶解性。氯化物是海水和许多地球流体中的主要阴离子，也是蒸发岩矿物的主要成分。溴和碘是生命所必需的，并大量融入海洋沉积物中积累的有机物中。循环到大陆和大洋地壳中的地表流体将地表衍生的卤素纳入蚀变矿物中。因此，俯冲板块和弧状熔岩中 F 的富集程度较低，而 Cl、Br 和 I 的富集程度较高。自地球早期分异以来，俯冲作用使地幔中 Cl 和 Br 的富集程度保持在相对稳定的水平，但地幔中 I/Cl 的富集程度则随着时间的推移而降低。早期地球上的卤素丰度受到 I 分入地核以及早期形成的海洋中亲水性 Cl、Br 和 I 可能流失的影响。卤素是现代地球俯冲带过程的强大示踪剂，Cl、Br 和 I 主要来源于地球地幔的俯冲。与 F 相比，Cl、Br 和 I 的深俯冲周期与 H2O 更为相似，但每种卤素的地球化学周期在细节上都有所不同。卤素丰度比和稳定同位素比在地球表面储层中有系统地变化，这意味着卤素是地质流体和熔体的强大示踪剂。《地球与行星科学年刊》第 52 卷的最终在线出版日期预计为 2024 年 5 月。修订后的预计日期请参见 http://www.annualreviews.org/page/journal/pubdates。
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Pub Date : 2024-01-12DOI: 10.1146/annurev-earth-032320-090307
Arlene M. Fiore, Loretta J. Mickley, Qindan Zhu, Colleen B. Baublitz
The hydroxyl radical (OH) largely controls the tropospheric self-cleansing capacity by reacting with gases harmful to the environment and human health. OH concentrations are determined locally by competing production and loss processes. Lacking strong observational constraints, models differ in how they balance these processes, such that the sign of past and future OH changes is uncertain. In a warmer climate, OH production will increase due to its water vapor dependence, partially offset by faster OH-methane loss. Weather-sensitive emissions will also likely increase, although their net impact on global mean OH depends on the balance between source (nitrogen oxides) and sink (reactive carbon) gases. Lightning activity increases OH, but its response to climate warming is of uncertain sign. To enable confident projections of OH, we recommend efforts to reduce uncertainties in kinetic reactions, in measured and modeled OH, in proxies for past OH concentrations, and in source and sink gas emissions. ▪ OH is strongly modulated by internal climate variability despite its lifetime of a few seconds at most, with implications for interpreting trends in methane. ▪ Improved kinetic constraints on key reactions would strengthen confidence in regional and global OH budgets, and in the response of OH to climate change. ▪ Future OH changes will depend on uncertain and compensating processes involving weather-sensitive chemistry and emissions, plus human choices. ▪ Technological solutions to climate change will likely impact tropospheric oxidizing capacity and merit further study prior to implementation.Expected final online publication date for the Annual Review of Earth and Planetary Sciences, Volume 52 is May 2024. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
{"title":"Climate and Tropospheric Oxidizing Capacity","authors":"Arlene M. Fiore, Loretta J. Mickley, Qindan Zhu, Colleen B. Baublitz","doi":"10.1146/annurev-earth-032320-090307","DOIUrl":"https://doi.org/10.1146/annurev-earth-032320-090307","url":null,"abstract":"The hydroxyl radical (OH) largely controls the tropospheric self-cleansing capacity by reacting with gases harmful to the environment and human health. OH concentrations are determined locally by competing production and loss processes. Lacking strong observational constraints, models differ in how they balance these processes, such that the sign of past and future OH changes is uncertain. In a warmer climate, OH production will increase due to its water vapor dependence, partially offset by faster OH-methane loss. Weather-sensitive emissions will also likely increase, although their net impact on global mean OH depends on the balance between source (nitrogen oxides) and sink (reactive carbon) gases. Lightning activity increases OH, but its response to climate warming is of uncertain sign. To enable confident projections of OH, we recommend efforts to reduce uncertainties in kinetic reactions, in measured and modeled OH, in proxies for past OH concentrations, and in source and sink gas emissions. ▪ OH is strongly modulated by internal climate variability despite its lifetime of a few seconds at most, with implications for interpreting trends in methane. ▪ Improved kinetic constraints on key reactions would strengthen confidence in regional and global OH budgets, and in the response of OH to climate change. ▪ Future OH changes will depend on uncertain and compensating processes involving weather-sensitive chemistry and emissions, plus human choices. ▪ Technological solutions to climate change will likely impact tropospheric oxidizing capacity and merit further study prior to implementation.Expected final online publication date for the Annual Review of Earth and Planetary Sciences, Volume 52 is May 2024. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.","PeriodicalId":8034,"journal":{"name":"Annual Review of Earth and Planetary Sciences","volume":null,"pages":null},"PeriodicalIF":14.9,"publicationDate":"2024-01-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139431179","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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 : 2024-01-02DOI: 10.1146/annurev-earth-040722-100453
Fu-Yuan Wu, Qiu-Li Li, Yi Chen, Sen Hu, Zong-Yu Yue, Qin Zhou, Hao Wang, Wei Yang, Heng-Ci Tian, Chi Zhang, Jin-Hua Li, Lin-Xi Li, He-Jiu Hui, Chun-Lai Li, Yang-Tin Lin, Xian-Hua Li, John W. Delano
The Chinese spacecraft Chang'e-5 (CE-5) landed on the northern Ocean Procellarum and returned 1,731 grams of regolith. The CE-5 regolith is composed mostly of fragments of basalt, impact glass, agglutinates, and mineral fragments. The basalts could be classified as of a low-Ti and highly fractionated type based on their TiO2 content of ∼5.3 wt% and Mg# of ∼28. Independent of petrographic texture, the CE-5 basalts have a uniform eruption age of 2,030 ± 4 Ma, demonstrating that the Moon remained volcanically active until at least ∼2.0 Ga. Although the CE-5 landing site lies within the so-called Procellarum KREEP [potassium (K), rare earth elements (REE), and phosphorus (P)] Terrane, neither the CE-5 basalts nor the mantle source regions of those basalts were enriched in KREEP components, such as incompatible elements, water, sulfur, or chlorine. Therefore, it would be a new and stimulating task in the future to look for the triggering mechanism of the young volcanism on the Moon. ▪ The CE-5 spacecraft returned 1,731 grams of lunar regolith in December 2020. It was the first new lunar sample since the last collection in August 1976. ▪ CE-5 regolith is basaltic in chemical composition, with only ∼1% highland materials of anorthosite, Mg suite, alkali suite, and KREEP. ▪ The CE-5 basalt is low Ti and highly differentiated. It was extruded at ∼2.0 Ga, being the youngest lunar basalt identified so far from the Moon. ▪ The triggering mechanism of the ∼2.0 Ga lunar volcanism is not clearly understood because its mantle source was dry and contained low abundances of KREEP elements.Expected final online publication date for the Annual Review of Earth and Planetary Sciences, Volume 52 is May 2024. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
{"title":"Lunar Evolution in Light of the Chang'e-5 Returned Samples","authors":"Fu-Yuan Wu, Qiu-Li Li, Yi Chen, Sen Hu, Zong-Yu Yue, Qin Zhou, Hao Wang, Wei Yang, Heng-Ci Tian, Chi Zhang, Jin-Hua Li, Lin-Xi Li, He-Jiu Hui, Chun-Lai Li, Yang-Tin Lin, Xian-Hua Li, John W. Delano","doi":"10.1146/annurev-earth-040722-100453","DOIUrl":"https://doi.org/10.1146/annurev-earth-040722-100453","url":null,"abstract":"The Chinese spacecraft Chang'e-5 (CE-5) landed on the northern Ocean Procellarum and returned 1,731 grams of regolith. The CE-5 regolith is composed mostly of fragments of basalt, impact glass, agglutinates, and mineral fragments. The basalts could be classified as of a low-Ti and highly fractionated type based on their TiO<jats:sub>2</jats:sub> content of ∼5.3 wt% and Mg# of ∼28. Independent of petrographic texture, the CE-5 basalts have a uniform eruption age of 2,030 ± 4 Ma, demonstrating that the Moon remained volcanically active until at least ∼2.0 Ga. Although the CE-5 landing site lies within the so-called Procellarum KREEP [potassium (K), rare earth elements (REE), and phosphorus (P)] Terrane, neither the CE-5 basalts nor the mantle source regions of those basalts were enriched in KREEP components, such as incompatible elements, water, sulfur, or chlorine. Therefore, it would be a new and stimulating task in the future to look for the triggering mechanism of the young volcanism on the Moon. ▪ The CE-5 spacecraft returned 1,731 grams of lunar regolith in December 2020. It was the first new lunar sample since the last collection in August 1976. ▪ CE-5 regolith is basaltic in chemical composition, with only ∼1% highland materials of anorthosite, Mg suite, alkali suite, and KREEP. ▪ The CE-5 basalt is low Ti and highly differentiated. It was extruded at ∼2.0 Ga, being the youngest lunar basalt identified so far from the Moon. ▪ The triggering mechanism of the ∼2.0 Ga lunar volcanism is not clearly understood because its mantle source was dry and contained low abundances of KREEP elements.Expected final online publication date for the Annual Review of Earth and Planetary Sciences, Volume 52 is May 2024. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.","PeriodicalId":8034,"journal":{"name":"Annual Review of Earth and Planetary Sciences","volume":null,"pages":null},"PeriodicalIF":14.9,"publicationDate":"2024-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139081550","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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 : 2024-01-02DOI: 10.1146/annurev-earth-031621-113343
Imran A. Rahman, Samuel Zamora
Echinoderms are a major group (phylum) of invertebrate animals with a rich fossil record stretching back to the Cambrian period, approximately 518 million years ago. While all modern species are characterized by pentaradial (i.e., fivefold) symmetry, Cambrian echinoderms also include taxa with different types of symmetry (e.g., bilateral symmetry). These distinct forms were present from very early in the phylum's history, demonstrating that the initial diversification of echinoderm body plans was extremely rapid. The phylogenetic relationships of Cambrian echinoderms have long been debated, hindering efforts to reconstruct the evolution of the phylum, but recent analyses have consistently recovered bilaterally symmetrical forms as the earliest-diverging echinoderms. This reveals the sequence of character acquisition in echinoderm evolution, indicating that radial symmetry is a derived character of the group, which evolved after the acquisition of a mineralized skeleton. Cambrian echinoderms were adapted to diverse modes of life, with ecology an important factor shaping their early evolution. However, the reasons why echinoderms evolved their unique pentaradial body plan remain unclear. ▪ The Cambrian fossil record provides valuable insights into the origin and early evolution of echinoderms over half a billion years ago. ▪ Cambrian echinoderms were morphologically diverse, with several extinct groups exhibiting character combinations that distinguish them from living species. ▪ Phylogenetic analyses of bilateral, asymmetrical, triradial, and pentaradial fossils have allowed us to decipher the assembly of the modern echinoderm body plan. ▪ Echinoderms became ecologically diverse early in their history, with varied modes of feeding, locomotion, and attachment.Expected final online publication date for the Annual Review of Earth and Planetary Sciences, Volume 52 is May 2024. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
{"title":"Origin and Early Evolution of Echinoderms","authors":"Imran A. Rahman, Samuel Zamora","doi":"10.1146/annurev-earth-031621-113343","DOIUrl":"https://doi.org/10.1146/annurev-earth-031621-113343","url":null,"abstract":"Echinoderms are a major group (phylum) of invertebrate animals with a rich fossil record stretching back to the Cambrian period, approximately 518 million years ago. While all modern species are characterized by pentaradial (i.e., fivefold) symmetry, Cambrian echinoderms also include taxa with different types of symmetry (e.g., bilateral symmetry). These distinct forms were present from very early in the phylum's history, demonstrating that the initial diversification of echinoderm body plans was extremely rapid. The phylogenetic relationships of Cambrian echinoderms have long been debated, hindering efforts to reconstruct the evolution of the phylum, but recent analyses have consistently recovered bilaterally symmetrical forms as the earliest-diverging echinoderms. This reveals the sequence of character acquisition in echinoderm evolution, indicating that radial symmetry is a derived character of the group, which evolved after the acquisition of a mineralized skeleton. Cambrian echinoderms were adapted to diverse modes of life, with ecology an important factor shaping their early evolution. However, the reasons why echinoderms evolved their unique pentaradial body plan remain unclear. ▪ The Cambrian fossil record provides valuable insights into the origin and early evolution of echinoderms over half a billion years ago. ▪ Cambrian echinoderms were morphologically diverse, with several extinct groups exhibiting character combinations that distinguish them from living species. ▪ Phylogenetic analyses of bilateral, asymmetrical, triradial, and pentaradial fossils have allowed us to decipher the assembly of the modern echinoderm body plan. ▪ Echinoderms became ecologically diverse early in their history, with varied modes of feeding, locomotion, and attachment.Expected final online publication date for the Annual Review of Earth and Planetary Sciences, Volume 52 is May 2024. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.","PeriodicalId":8034,"journal":{"name":"Annual Review of Earth and Planetary Sciences","volume":null,"pages":null},"PeriodicalIF":14.9,"publicationDate":"2024-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139081760","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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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