1) A speleothem record from central-eastern Brazil spanning 1.3-10.2 kyr BP reveals abrupt variations in South American monsoon rainfall that match Bond events and show a ~800 yr pacing.
2) The precipitation variations over central-eastern Brazil are broadly anti-phased with Asian and Indian Monsoons during Bond events and show differences between early and late Holocene.
3) The results suggest these abrupt multicentennial precipitation events are primarily linked to changes in the North Atlantic meridional overturning circulation, which may have modulated the South American monsoon and El Niño-like conditions in the tropical Pacific during the Holocene.
A high resolution-history_of_the_south_aGeorgeaMelo1
This document summarizes a new high-resolution paleoclimate record from Brazil spanning the last glacial maximum to the Holocene. Stalagmites from Jaraguá cave in central Brazil provide the best-resolved geochronology yet of changes in the South American monsoon. Isotopic analysis of the stalagmites indicates that variations in the monsoon closely tracked abrupt climate changes in the northern hemisphere during this period. However, the influence of southern hemisphere climate changes on the monsoon remains unclear. This new record will improve understanding of how tropical South American climate varied during the last deglaciation.
Noah, Joseph, And High-Resolution PaleoclimatologyScott St. George
In 1968, Benoit Mandelbrot and James Wallis published an article titled ‘Noah, Joseph, and operational Hydrology’ in the journal Water Resources Research. In it, they argued that hydrological models of the day were not able to estimate the true risk of extreme floods or prolonged drought, and that rare hydrological events were much more common than usually assumed.
In this lecture, I’ll review how high-resolution paleoenvironmental archives can help us judge more accurately the risks posed by the ‘Noah’- and ‘Joseph’-style events described by Mandelbrot and Wallis. I’ll give particular emphasis to the environmental information recovered from the rings of ancient trees, and explain how dendrochronology (tree-ring research) has been used to redefine the ‘flood of record’, test potential avenues for long-lead climate predictions, and gage the performance of state-of-the-art climate models.
The decadal character of northern California's winter precipitationScott St. George
Starting in the 1930s, northern California has experienced major decade-to-decade swings in the amount of precipitation that falls during winter. Is this behavior
This document summarizes a study that assessed the sensitivity of a data-driven soil water balance model to estimate summer evapotranspiration along a forest chronosequence using three sites with Eddy Covariance measurements. The study explored the model's sensitivity to forest succession state, computational time step, rooting depth, and canopy interception capacity. It found that the model generally agreed with observations and was not dependent on stand age, but an optimal combination of parameters was needed to avoid underestimation of actual evapotranspiration.
Many of the decisions we make about environmental issues are based on experience. Whether we're setting limits for the use of scarce resources, estimating the risks posed by natural hazards, or deciding how to manage protected areas, our plans for the future often reflect our understanding of the past. The problem is that, when it comes to the environment, our society has a fairly short memory. In this presentation, Dr. St. George will discuss how the study of ancient trees is expanding our perspective on the natural history of the northern Plains and helping to answer questions about what the future may hold for Minnesota's environment.
The document discusses the Little Ice Age (LIA), a period of cooling between the 14th-19th centuries. It examines potential causes like changes in solar activity, volcanic eruptions, and variations in ocean/atmospheric circulation patterns. Evidence from regions outside Europe is also presented, showing glacial advances in the Andes and Tibetan Plateau during the proposed LIA timeframe, though dates varied. While no single cause can explain the heterogeneous global cooling, orbital forcing, solar variability, volcanism, and internal climate variations likely all contributed to climate conditions during this period.
The "Year Without A Summer" was not a year without a ringScott St. George
The Tambora eruption of 1815 cooled the planet and caused the "Year Without A Summer" in western Europe and eastern North America. But was it cold enough to cause trees across the Northern Hemisphere to skip a ring?
These visuals were prepared to support a string quartet performance and panel on climate change at Northwestern University in February 2106.
A well-designed graphic can help audiences to quickly understand the main message embedded within a complex set of climate data and to retain those ideas longer than they would have if they were conveyed by words alone. But the visual aids used regularly by climate scientists also have their limitations: they are most easily understood by people who are already fluent in technical illustrations; they're usually static and sometimes do not tell an obvious story; and for many, they don't elicit a strong emotional response.
Music, by contrast, is inherently narrative and is known to exert a powerful influence on human emotions. Because of this, sonification — the transformation of data into acoustic signals — may have considerable promise as a tool to enhance the communication of climate science.
Daniel Crawford and Scott St. George report on a collaboration between scientists and artists that uses music to transmit the evidence of climate change in an engaging and visceral way.
A high resolution-history_of_the_south_aGeorgeaMelo1
This document summarizes a new high-resolution paleoclimate record from Brazil spanning the last glacial maximum to the Holocene. Stalagmites from Jaraguá cave in central Brazil provide the best-resolved geochronology yet of changes in the South American monsoon. Isotopic analysis of the stalagmites indicates that variations in the monsoon closely tracked abrupt climate changes in the northern hemisphere during this period. However, the influence of southern hemisphere climate changes on the monsoon remains unclear. This new record will improve understanding of how tropical South American climate varied during the last deglaciation.
Noah, Joseph, And High-Resolution PaleoclimatologyScott St. George
In 1968, Benoit Mandelbrot and James Wallis published an article titled ‘Noah, Joseph, and operational Hydrology’ in the journal Water Resources Research. In it, they argued that hydrological models of the day were not able to estimate the true risk of extreme floods or prolonged drought, and that rare hydrological events were much more common than usually assumed.
In this lecture, I’ll review how high-resolution paleoenvironmental archives can help us judge more accurately the risks posed by the ‘Noah’- and ‘Joseph’-style events described by Mandelbrot and Wallis. I’ll give particular emphasis to the environmental information recovered from the rings of ancient trees, and explain how dendrochronology (tree-ring research) has been used to redefine the ‘flood of record’, test potential avenues for long-lead climate predictions, and gage the performance of state-of-the-art climate models.
The decadal character of northern California's winter precipitationScott St. George
Starting in the 1930s, northern California has experienced major decade-to-decade swings in the amount of precipitation that falls during winter. Is this behavior
This document summarizes a study that assessed the sensitivity of a data-driven soil water balance model to estimate summer evapotranspiration along a forest chronosequence using three sites with Eddy Covariance measurements. The study explored the model's sensitivity to forest succession state, computational time step, rooting depth, and canopy interception capacity. It found that the model generally agreed with observations and was not dependent on stand age, but an optimal combination of parameters was needed to avoid underestimation of actual evapotranspiration.
Many of the decisions we make about environmental issues are based on experience. Whether we're setting limits for the use of scarce resources, estimating the risks posed by natural hazards, or deciding how to manage protected areas, our plans for the future often reflect our understanding of the past. The problem is that, when it comes to the environment, our society has a fairly short memory. In this presentation, Dr. St. George will discuss how the study of ancient trees is expanding our perspective on the natural history of the northern Plains and helping to answer questions about what the future may hold for Minnesota's environment.
The document discusses the Little Ice Age (LIA), a period of cooling between the 14th-19th centuries. It examines potential causes like changes in solar activity, volcanic eruptions, and variations in ocean/atmospheric circulation patterns. Evidence from regions outside Europe is also presented, showing glacial advances in the Andes and Tibetan Plateau during the proposed LIA timeframe, though dates varied. While no single cause can explain the heterogeneous global cooling, orbital forcing, solar variability, volcanism, and internal climate variations likely all contributed to climate conditions during this period.
The "Year Without A Summer" was not a year without a ringScott St. George
The Tambora eruption of 1815 cooled the planet and caused the "Year Without A Summer" in western Europe and eastern North America. But was it cold enough to cause trees across the Northern Hemisphere to skip a ring?
These visuals were prepared to support a string quartet performance and panel on climate change at Northwestern University in February 2106.
A well-designed graphic can help audiences to quickly understand the main message embedded within a complex set of climate data and to retain those ideas longer than they would have if they were conveyed by words alone. But the visual aids used regularly by climate scientists also have their limitations: they are most easily understood by people who are already fluent in technical illustrations; they're usually static and sometimes do not tell an obvious story; and for many, they don't elicit a strong emotional response.
Music, by contrast, is inherently narrative and is known to exert a powerful influence on human emotions. Because of this, sonification — the transformation of data into acoustic signals — may have considerable promise as a tool to enhance the communication of climate science.
Daniel Crawford and Scott St. George report on a collaboration between scientists and artists that uses music to transmit the evidence of climate change in an engaging and visceral way.
This document analyzes the teleconnections between climate indices, sea surface temperature (SST), and vegetation productivity in the Sahel as measured by NDVI from 1982-2007. It finds significant correlations between climate indices like ENSO, NAO, PDO, and IOD and NDVI across the Sahel, though the strength of correlations varies between western, central, and eastern regions. Pixel-level correlations between global SST anomalies and NDVI also show an east-west gradient, with stronger associations in western Sahel. Warmer Mediterranean SSTs correlate with higher NDVI in central Sahel, while cooler eastern Pacific and warmer eastern Atlantic SSTs correlate with higher NDVI in western Sahel.
The document discusses satellite radar altimeter measurements of elevation changes in the Larsen Ice Shelf between 1992 and 2001. It finds that the ice shelf lowered by up to 0.27 meters per year on average. This thinning is explained by increased summer meltwater and loss of basal ice through melting. Enhanced ocean-driven melting may provide a link between regional climate warming and the successive breakup of sections of the Larsen Ice Shelf. Testing rules out other potential causes of thinning like changes in sea level, ocean density, or surface accumulation. The long-term thinning observed suggests meltwater production alone does not account for the lowering, indicating additional thinning mechanisms are also involved.
This document discusses several principles of dendrochronology:
- The principle of ecological amplitude describes the range of habitats a tree species can grow in, and trees at the limits may be more sensitive to environmental changes.
- The principle of site selection states that dendrochronologists should consider limiting factors and ecological amplitude to identify trees most likely to provide information about a specific environmental signal.
- The principles of cross-dating, aggregate tree growth, and replication are important for dendrochronology research to build robust tree-ring chronologies.
1. Tree ring records from across the Northern Hemisphere provide a powerful tool to study past climate, though the information that can be recovered varies regionally depending on climate influences on individual tree species.
2. The large global tree ring network allows understanding of tree-climate relationships without being influenced by decisions to include or exclude certain records, improving the accuracy of paleoclimate reconstructions.
3. Tree ring records have been used to generate reconstructions of large-scale climate drivers like the El Nino-Southern Oscillation and Pacific Decadal Oscillation, though conclusions depend on the choice of reconstruction method and data.
This document discusses tree ring dendroclimatology and how tree ring records can be used to understand past climates. Tree ring growth is influenced by climate factors like temperature and precipitation. Multiple tree ring records from a region can be combined and correlated with observed climate data to develop climate reconstructions spanning centuries. However, tree ring growth can be affected by non-climatic factors as well, and some recent studies have found a divergence or weakening correlation between tree growth and temperatures in some northern sites. Overall, tree ring records are a valuable but imperfect proxy for understanding past climate variability over centuries to millennia when used carefully.
Impact of Climate Modes such as El Nino on Australian RainfallAlexander Pui
This document analyzes the impact of large-scale climate modes like ENSO, IOD, and SAM on daily and subdaily rainfall characteristics in east Australia. It finds that the occurrence of rainfall events, rather than average rainfall intensity, is most influenced by these climate modes. This is shown to be associated with changes in the time between wet spells. Furthermore, ENSO remains the leading driver of rainfall variability in east Australia, especially further inland during winter and spring. The results have implications for water resource management and how climate models capture rainfall variability.
This research proposal examines the link between climate change and drought in the Southwestern United States. The researcher will use quantitative data on precipitation, temperature, and drought conditions to analyze how climate change has affected and may further impact drought severity and duration in Texas, Oklahoma, New Mexico, and Arizona. Understanding future drought risks can help mitigate their effects on communities. The proposal reviews literature indicating the Southwest will likely experience more severe and prolonged droughts due to rising temperatures and decreasing rainfall from climate change.
BC3 has in place a program called BC3 Visiting Programme under the attainment of its strategic objectives, Talent Attraction.
The aim of this programme is to promote research and dialogue between BC3 and other institutions by supporting and hosting local and international professors wishing to undertake research at BC3.
This is a presentation that Prof Maria Fernanda Sanchez Goñi (University of Bourdeauxl) gave withing the BC3 Seminars Programme.
The document provides an overview of the Yamal LCLUC Project and the objectives of a meeting. It summarizes that the project examines linkages between greening trends in the Arctic, impacts on reindeer herding Nenets people, and regional sea ice conditions. Field research and modeling is conducted along a bioclimate transect on the Yamal Peninsula, Russia to understand how changing patterns of sea ice may affect terrestrial ecosystems and indigenous populations with increasing oil/gas development and climate change. The agenda outlines presentations on natural systems, remote sensing results, field expedition reports, and modeling over three days.
Margeaux Carter will present on using satellite remote sensing to extend records of hidden meltwater in Greenland's ice sheet. The discovery of large subsurface pools of meltwater, called Perennial Firn Aquifers, has changed understanding of meltwater retention, but they are currently only observed intermittently by aircraft. Ms. Carter proposes analyzing microwave reflectance signals from satellites, which have regularly observed Greenland since 1979, to identify subsurface meltwater throughout the year and establish longer records of aquifer formation and hydrology. Comparing results to meteorological data will evaluate the method's accuracy in extending observations of these important features.
This document discusses remote sensing of phenology, which is the study of periodic biological events and their relationship to climate and environment. Satellite imagery can be used to observe seasonal landscape dynamics over large areas by analyzing time-series vegetation index data. Key phenological metrics like start of season, end of season, and duration of growing season can be derived from this data. This provides insights into how plant life cycles respond to climate change at regional scales.
Greening of the Arctic: An IPY initiative
1-Rationale and overview of the GOA initiative.
2-North American Arctic Transect.
3-Yamal Russia Transect.
4-Circumpolar analysis of 28-year trends of sea-ice concentration, land-surface temperatures and greening patterns
This document summarizes the Greening of the Arctic Project led by Dr. Skip Walker at the University of Alaska Fairbanks. It provides an overview of the project, lists the principal collaborators from various institutions, and outlines the funding sources. It then previews the topics that will be covered in Dr. Walker's presentation, including hierarchical spatial and temporal analysis of Arctic greening using NDVI data, regional observations along transects, and case studies using high-resolution satellite imagery. A key focus is examining linkages between changes in climate (sea ice, temperatures), and vegetation greening patterns across the Arctic. Landscape disturbances are hypothesized to be a main driver of NDVI change locally. Recent diverging greening trends
The North America and Eurasia Arctic transects: Edie Barbour
Walker, D.A., Kuss, H.P., Kopecky, M., Frost, G.V., Kade, A., Vonlanthen, C., Raynolds, M.K., and Epstein, H., 2011, The North America and Eurasia Artctic transects: Using phytosociology and remote sensing to detect vegetation pattern and change: Proceedings Euiropean Vegetation Survey, 20th Workshop, Rome, 6-9 April 2011,
Pecological implications of summer fog decline in the coast redwood6D45520z848622K444
This document summarizes a study on summer fog decline along the Pacific coast of California and its implications for coast redwood and other ecosystems. The key points are:
1) The study presents a novel 58-year record (1951-2008) of summer fog frequency in northern California based on hourly cloud ceiling height measurements, showing a 33% reduction in fog since the early 20th century.
2) Summer fog frequency is found to correlate strongly with the wind-driven upwelling system of the California Current and the Pacific Decadal Oscillation ocean temperature pattern.
3) Tree physiological data suggests that reduced summer fog frequency and increased evaporative demand may stress coast redwoods and other west coast ecosystems.
Guarding against false discovery in large-scale dendroclimatologyScott St. George
Measurements of tree-ring widths are the most widely-distributed and best replicated source of surrogate environmental information on the planet, and are one of the main archives used to estimate changes in regional and global climate during the past several centuries or millennia. Because the Northern Hemisphere ring-width network is now so large, it is more crucial than ever to ensure our understanding of tree-environment relations is not influenced by decisions to include or exclude certain records. It may be the case that a particular set of ring-width records are, for whatever reason, more tightly coupled to a particular climate factor than other records from the same region or species and, as a result, may be superior estimators of that factor’s past behavior. At the same time, it is known that selecting a small number of predictors from a large pool of potential candidates increases the likelihood of a Type I error. That effect may be particularly relevant to dendroclimatology because the total number of available ring-width records is often much larger than the number of records used to produce reconstructions of large-scale climate features. As an initial step, it would be helpful if paleoclimate reconstructions derived from tree rings described more explicitly the criteria used to select ring-width records as potential predictors and specified those records excluded by that screening. By comparing ring-width chronologies and their relations with climate against the standard set by thousands of records across the hemisphere, we should be better able to distinguish climate signals from proxy noise and produce more accurate reconstructions of climate during the late Holocene.
Behavior of ocean eddies in the Southern OceanKaiheYAMAZAKI
The document summarizes research on ocean eddies and circulation in the Southern Ocean. It discusses:
1) How baroclinic eddies drive residual meridional overturning circulation in the Southern Ocean through "thickness diffusion", counteracting wind-driven circulation.
2) Evidence that the transport of the Antarctic Circumpolar Current is "saturated" and insensitive to changes in wind forcing, due to prevailing baroclinic instability.
3) Observations of multidecadal warming and poleward shift of boundaries in the Southern Ocean, attributed mainly to shifts in Antarctic Circumpolar Current fronts rather than along-frontal warming.
Presented by Keyla Soto:
Penetration of Human-InducedWarming into the World’s Oceans
Tim P. Barnett, David W. Pierce, Krishna M. AchutaRao,Peter J. Gleckler, Benjamin D. Santer, Jonathan M. Gregory,Warren M. Washington
The document summarizes Martin P. Hoerling's response to criticisms of claims made in a New York Times Op-Ed by James E. Hansen regarding the impacts of climate change. Hoerling takes issue with several specific assertions made by Hansen, arguing they are contrary to peer-reviewed literature and climate change assessments. He provides analysis and references to studies to support his counterarguments. The overall summary is that the certainty expressed in Hansen's claims is not supported by the current scientific understanding of regional climate change projections and uncertainties.
This document investigates the correlation between rainfall in equatorial Africa and tropical cyclone activity in the North Atlantic. It discusses how rainfall anomalies in Africa can impact the formation of African waves that seed tropical cyclones. Two studies are compared - one analyzing paleo-pollen data from Africa and the other a statistical model of tropical cyclone activity. There are some correlations found, particularly between low rainfall periods in Africa and fewer tropical cyclones. However, correlations are not as clear during high rainfall periods, suggesting other factors also influence tropical cyclone formation.
This document analyzes the teleconnections between climate indices, sea surface temperature (SST), and vegetation productivity in the Sahel as measured by NDVI from 1982-2007. It finds significant correlations between climate indices like ENSO, NAO, PDO, and IOD and NDVI across the Sahel, though the strength of correlations varies between western, central, and eastern regions. Pixel-level correlations between global SST anomalies and NDVI also show an east-west gradient, with stronger associations in western Sahel. Warmer Mediterranean SSTs correlate with higher NDVI in central Sahel, while cooler eastern Pacific and warmer eastern Atlantic SSTs correlate with higher NDVI in western Sahel.
The document discusses satellite radar altimeter measurements of elevation changes in the Larsen Ice Shelf between 1992 and 2001. It finds that the ice shelf lowered by up to 0.27 meters per year on average. This thinning is explained by increased summer meltwater and loss of basal ice through melting. Enhanced ocean-driven melting may provide a link between regional climate warming and the successive breakup of sections of the Larsen Ice Shelf. Testing rules out other potential causes of thinning like changes in sea level, ocean density, or surface accumulation. The long-term thinning observed suggests meltwater production alone does not account for the lowering, indicating additional thinning mechanisms are also involved.
This document discusses several principles of dendrochronology:
- The principle of ecological amplitude describes the range of habitats a tree species can grow in, and trees at the limits may be more sensitive to environmental changes.
- The principle of site selection states that dendrochronologists should consider limiting factors and ecological amplitude to identify trees most likely to provide information about a specific environmental signal.
- The principles of cross-dating, aggregate tree growth, and replication are important for dendrochronology research to build robust tree-ring chronologies.
1. Tree ring records from across the Northern Hemisphere provide a powerful tool to study past climate, though the information that can be recovered varies regionally depending on climate influences on individual tree species.
2. The large global tree ring network allows understanding of tree-climate relationships without being influenced by decisions to include or exclude certain records, improving the accuracy of paleoclimate reconstructions.
3. Tree ring records have been used to generate reconstructions of large-scale climate drivers like the El Nino-Southern Oscillation and Pacific Decadal Oscillation, though conclusions depend on the choice of reconstruction method and data.
This document discusses tree ring dendroclimatology and how tree ring records can be used to understand past climates. Tree ring growth is influenced by climate factors like temperature and precipitation. Multiple tree ring records from a region can be combined and correlated with observed climate data to develop climate reconstructions spanning centuries. However, tree ring growth can be affected by non-climatic factors as well, and some recent studies have found a divergence or weakening correlation between tree growth and temperatures in some northern sites. Overall, tree ring records are a valuable but imperfect proxy for understanding past climate variability over centuries to millennia when used carefully.
Impact of Climate Modes such as El Nino on Australian RainfallAlexander Pui
This document analyzes the impact of large-scale climate modes like ENSO, IOD, and SAM on daily and subdaily rainfall characteristics in east Australia. It finds that the occurrence of rainfall events, rather than average rainfall intensity, is most influenced by these climate modes. This is shown to be associated with changes in the time between wet spells. Furthermore, ENSO remains the leading driver of rainfall variability in east Australia, especially further inland during winter and spring. The results have implications for water resource management and how climate models capture rainfall variability.
This research proposal examines the link between climate change and drought in the Southwestern United States. The researcher will use quantitative data on precipitation, temperature, and drought conditions to analyze how climate change has affected and may further impact drought severity and duration in Texas, Oklahoma, New Mexico, and Arizona. Understanding future drought risks can help mitigate their effects on communities. The proposal reviews literature indicating the Southwest will likely experience more severe and prolonged droughts due to rising temperatures and decreasing rainfall from climate change.
BC3 has in place a program called BC3 Visiting Programme under the attainment of its strategic objectives, Talent Attraction.
The aim of this programme is to promote research and dialogue between BC3 and other institutions by supporting and hosting local and international professors wishing to undertake research at BC3.
This is a presentation that Prof Maria Fernanda Sanchez Goñi (University of Bourdeauxl) gave withing the BC3 Seminars Programme.
The document provides an overview of the Yamal LCLUC Project and the objectives of a meeting. It summarizes that the project examines linkages between greening trends in the Arctic, impacts on reindeer herding Nenets people, and regional sea ice conditions. Field research and modeling is conducted along a bioclimate transect on the Yamal Peninsula, Russia to understand how changing patterns of sea ice may affect terrestrial ecosystems and indigenous populations with increasing oil/gas development and climate change. The agenda outlines presentations on natural systems, remote sensing results, field expedition reports, and modeling over three days.
Margeaux Carter will present on using satellite remote sensing to extend records of hidden meltwater in Greenland's ice sheet. The discovery of large subsurface pools of meltwater, called Perennial Firn Aquifers, has changed understanding of meltwater retention, but they are currently only observed intermittently by aircraft. Ms. Carter proposes analyzing microwave reflectance signals from satellites, which have regularly observed Greenland since 1979, to identify subsurface meltwater throughout the year and establish longer records of aquifer formation and hydrology. Comparing results to meteorological data will evaluate the method's accuracy in extending observations of these important features.
This document discusses remote sensing of phenology, which is the study of periodic biological events and their relationship to climate and environment. Satellite imagery can be used to observe seasonal landscape dynamics over large areas by analyzing time-series vegetation index data. Key phenological metrics like start of season, end of season, and duration of growing season can be derived from this data. This provides insights into how plant life cycles respond to climate change at regional scales.
Greening of the Arctic: An IPY initiative
1-Rationale and overview of the GOA initiative.
2-North American Arctic Transect.
3-Yamal Russia Transect.
4-Circumpolar analysis of 28-year trends of sea-ice concentration, land-surface temperatures and greening patterns
This document summarizes the Greening of the Arctic Project led by Dr. Skip Walker at the University of Alaska Fairbanks. It provides an overview of the project, lists the principal collaborators from various institutions, and outlines the funding sources. It then previews the topics that will be covered in Dr. Walker's presentation, including hierarchical spatial and temporal analysis of Arctic greening using NDVI data, regional observations along transects, and case studies using high-resolution satellite imagery. A key focus is examining linkages between changes in climate (sea ice, temperatures), and vegetation greening patterns across the Arctic. Landscape disturbances are hypothesized to be a main driver of NDVI change locally. Recent diverging greening trends
The North America and Eurasia Arctic transects: Edie Barbour
Walker, D.A., Kuss, H.P., Kopecky, M., Frost, G.V., Kade, A., Vonlanthen, C., Raynolds, M.K., and Epstein, H., 2011, The North America and Eurasia Artctic transects: Using phytosociology and remote sensing to detect vegetation pattern and change: Proceedings Euiropean Vegetation Survey, 20th Workshop, Rome, 6-9 April 2011,
Pecological implications of summer fog decline in the coast redwood6D45520z848622K444
This document summarizes a study on summer fog decline along the Pacific coast of California and its implications for coast redwood and other ecosystems. The key points are:
1) The study presents a novel 58-year record (1951-2008) of summer fog frequency in northern California based on hourly cloud ceiling height measurements, showing a 33% reduction in fog since the early 20th century.
2) Summer fog frequency is found to correlate strongly with the wind-driven upwelling system of the California Current and the Pacific Decadal Oscillation ocean temperature pattern.
3) Tree physiological data suggests that reduced summer fog frequency and increased evaporative demand may stress coast redwoods and other west coast ecosystems.
Guarding against false discovery in large-scale dendroclimatologyScott St. George
Measurements of tree-ring widths are the most widely-distributed and best replicated source of surrogate environmental information on the planet, and are one of the main archives used to estimate changes in regional and global climate during the past several centuries or millennia. Because the Northern Hemisphere ring-width network is now so large, it is more crucial than ever to ensure our understanding of tree-environment relations is not influenced by decisions to include or exclude certain records. It may be the case that a particular set of ring-width records are, for whatever reason, more tightly coupled to a particular climate factor than other records from the same region or species and, as a result, may be superior estimators of that factor’s past behavior. At the same time, it is known that selecting a small number of predictors from a large pool of potential candidates increases the likelihood of a Type I error. That effect may be particularly relevant to dendroclimatology because the total number of available ring-width records is often much larger than the number of records used to produce reconstructions of large-scale climate features. As an initial step, it would be helpful if paleoclimate reconstructions derived from tree rings described more explicitly the criteria used to select ring-width records as potential predictors and specified those records excluded by that screening. By comparing ring-width chronologies and their relations with climate against the standard set by thousands of records across the hemisphere, we should be better able to distinguish climate signals from proxy noise and produce more accurate reconstructions of climate during the late Holocene.
Behavior of ocean eddies in the Southern OceanKaiheYAMAZAKI
The document summarizes research on ocean eddies and circulation in the Southern Ocean. It discusses:
1) How baroclinic eddies drive residual meridional overturning circulation in the Southern Ocean through "thickness diffusion", counteracting wind-driven circulation.
2) Evidence that the transport of the Antarctic Circumpolar Current is "saturated" and insensitive to changes in wind forcing, due to prevailing baroclinic instability.
3) Observations of multidecadal warming and poleward shift of boundaries in the Southern Ocean, attributed mainly to shifts in Antarctic Circumpolar Current fronts rather than along-frontal warming.
Presented by Keyla Soto:
Penetration of Human-InducedWarming into the World’s Oceans
Tim P. Barnett, David W. Pierce, Krishna M. AchutaRao,Peter J. Gleckler, Benjamin D. Santer, Jonathan M. Gregory,Warren M. Washington
The document summarizes Martin P. Hoerling's response to criticisms of claims made in a New York Times Op-Ed by James E. Hansen regarding the impacts of climate change. Hoerling takes issue with several specific assertions made by Hansen, arguing they are contrary to peer-reviewed literature and climate change assessments. He provides analysis and references to studies to support his counterarguments. The overall summary is that the certainty expressed in Hansen's claims is not supported by the current scientific understanding of regional climate change projections and uncertainties.
This document investigates the correlation between rainfall in equatorial Africa and tropical cyclone activity in the North Atlantic. It discusses how rainfall anomalies in Africa can impact the formation of African waves that seed tropical cyclones. Two studies are compared - one analyzing paleo-pollen data from Africa and the other a statistical model of tropical cyclone activity. There are some correlations found, particularly between low rainfall periods in Africa and fewer tropical cyclones. However, correlations are not as clear during high rainfall periods, suggesting other factors also influence tropical cyclone formation.
This review analyzes 214 published phylogeography studies of South American organisms to identify emerging patterns. The studies find striking genetic divergence among lineages, suggesting high undocumented diversity. Pleistocene climate oscillations and Pliocene/Miocene geological events shaped modern distributions in tropical and temperate regions. Herpetofauna diverged earlier than other groups. Forest species' ranges contracted more in glacial periods, while open habitat species responded variably to climate change. The results reveal a complex mosaic of phylogeography patterns across South America.
La foresta amazónica y el cambio climático - Philip FearnsideInstituto Humboldt
The document discusses the role of the Amazon forest and climate change. It provides statistics on water flows in the Amazon, including precipitation in the basin, evapotranspiration, water transported by winds to other regions, and the average flow of the Amazon River. It also notes that deforestation and climate change, such as more frequent droughts, threaten the Amazon and could feed into a cycle of forest dieback.
Large-scale dendrochronology and low-frequency climate variabilityScott St. George
Large-scale low-frequency variability has emerged as a priority for climate research, but instrumental observations are not long enough to characterize this behavior or gage its impacts on dependent geophysical or ecological systems. As the leading source of high-resolution paleoclimate information in the middle- and high-latitudes, tree rings are essential to understand low-frequency variability prior to the instrumental period. But even though tree rings possess several advantages as climate proxies, like other natural archives they also have their own particular impediments. In this lecture, Dr. St. George will describe the structure and characteristics of the Northern Hemisphere tree-ring width network, and outline how the fingerprint of decadal and multidecadal climate variability encoded within ancient trees varies across the hemisphere.
Global temperatures have increased over the past century, with the 15 hottest years occurring since 1990. Warming is projected to continue over the coming decades and centuries according to climate models. Projections show continents warming around 50% more than oceans, with the largest temperature increases at high northern latitudes. Precipitation patterns are also changing, with some areas receiving more rain and others less. The frequency and intensity of extreme weather events like heat waves, droughts, and heavy rain are also increasing. These changes are projected to impact human and natural systems.
Analysis of Downburst Occurrences in BrazilElias Galvan
This document summarizes a presentation given at the 4th American Association for Wind Engineering Workshop in Miami, Florida in August 2016. The presentation analyzed downburst occurrences in Brazil. Downbursts are strong downdrafts of air that induce powerful diverging winds at the surface. The document provides background on Brazil's climate and weather systems and discusses several downburst events that have occurred in Brazil, with damages. It also presents meteorological parameters that can help identify downbursts and suggests regions of Brazil that are most at risk for downburst occurrences, including the southern region, São Paulo state, western Amazon Basin, and northeast coast.
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diurnal temperature range trend over North Carolina and the associated mechan...Sayem Zaman, Ph.D, PE.
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correlation analysis. The DTRs were found to be negatively correlated with the precipitation, TCC, and soil moisture across the state for all the seasons and annual basis. It appears that the moisture components related better to the DTR than to the atmospheric circulation modes.
Disentangling the decadal ‘knot’ in high-resolution paleoclimatologyScott St. George
Even after more than a century of coordinated monitoring, instrumental weather observations are still too short to adequately constrain decadal or multidecadal behavior in the Earth’s climate system. Leading climatologists and climate modelers have called for the wider application of high-resolution proxy records to decadal variability and prediction studies, and our community has responded by producing new paleoclimate products that specifically target this type of ‘intermediate-term’ behavior. But we now also know our medium changes that message: the biological and geological systems that encode climate information into natural archives often also alter the original ‘input’, usually due to either seasonal filtering or non-climatic persistence. In this talk, we’ll discuss some of the challenges inherent to the use of high-resolution proxies to study decadal or multi-decadal climate variability, and suggest strategies that might clarify how climate acts on those timescales. And we’ll also present a new theoretical framework that could help paleo-scientists evaluate competing ideas about the causes of decadal- or multi-decadal events known to have occurred during the past one or two millennia.
This paper provides a 2000-year climate and environmental history for the Sierra Nevada mountains in California based on paleoclimate data from the region. It finds that abrupt climate changes, including severe droughts and temperature increases, have occurred in the Sierra Nevada over this period, often coinciding with abrupt changes seen in Greenland ice core records. These abrupt climate shifts were associated with severe wildfires and accelerated erosion in the Coburn Lake watershed, suggesting vegetation and landscapes were vulnerable to rapid climate fluctuations. The timing of drought conditions shifting between the Sierra Nevada and Greenland provides evidence these regions' climates were teleconnected and affected by changes in global precipitation patterns during periods of abrupt climate change.
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Physical Forcing Mechanisms Controlling the Variability of Chlorophyll-a over...Meyre Da Silva
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The largest association of meteorologists and climate scientists issued a fresh statement on the scientific evidence for human-driven climate change and possible impacts. This is an update from the 2007 statement that can be found here: http://www.ametsoc.org/policy/2007climatechange.html
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This document summarizes an experiment that analyzed the relationship between annual increases in carbon dioxide levels in Mauna Loa, Hawaii from 1959-2011 and the frequency of major hurricanes in the Pacific Ocean from 1992-2009. The experiment found a negative correlation between the two variables, which did not support the hypothesis that higher carbon dioxide levels would increase hurricane frequency. Methodology included formatting data sets into a spreadsheet, graphing the variables, and determining the correlation coefficient and coefficient of determination to analyze the strength of the relationship between carbon dioxide increases and hurricane frequency.
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LAND USE LAND COVER AND NDVI OF MIRZAPUR DISTRICT, UPRAHUL
This Dissertation explores the particular circumstances of Mirzapur, a region located in the
core of India. Mirzapur, with its varied terrains and abundant biodiversity, offers an optimal
environment for investigating the changes in vegetation cover dynamics. Our study utilizes
advanced technologies such as GIS (Geographic Information Systems) and Remote sensing to
analyze the transformations that have taken place over the course of a decade.
The complex relationship between human activities and the environment has been the focus
of extensive research and worry. As the global community grapples with swift urbanization,
population expansion, and economic progress, the effects on natural ecosystems are becoming
more evident. A crucial element of this impact is the alteration of vegetation cover, which plays a
significant role in maintaining the ecological equilibrium of our planet.Land serves as the foundation for all human activities and provides the necessary materials for
these activities. As the most crucial natural resource, its utilization by humans results in different
'Land uses,' which are determined by both human activities and the physical characteristics of the
land.
The utilization of land is impacted by human needs and environmental factors. In countries
like India, rapid population growth and the emphasis on extensive resource exploitation can lead
to significant land degradation, adversely affecting the region's land cover.
Therefore, human intervention has significantly influenced land use patterns over many
centuries, evolving its structure over time and space. In the present era, these changes have
accelerated due to factors such as agriculture and urbanization. Information regarding land use and
cover is essential for various planning and management tasks related to the Earth's surface,
providing crucial environmental data for scientific, resource management, policy purposes, and
diverse human activities.
Accurate understanding of land use and cover is imperative for the development planning
of any area. Consequently, a wide range of professionals, including earth system scientists, land
and water managers, and urban planners, are interested in obtaining data on land use and cover
changes, conversion trends, and other related patterns. The spatial dimensions of land use and
cover support policymakers and scientists in making well-informed decisions, as alterations in
these patterns indicate shifts in economic and social conditions. Monitoring such changes with the
help of Advanced technologies like Remote Sensing and Geographic Information Systems is
crucial for coordinated efforts across different administrative levels. Advanced technologies like
Remote Sensing and Geographic Information Systems
9
Changes in vegetation cover refer to variations in the distribution, composition, and overall
structure of plant communities across different temporal and spatial scales. These changes can
occur natural.
3. 1076 GEOLOGY, November 2011
The speleothems were dated by the U-Th method using inductively
coupled plasma−mass spectrometry (ICP-MS) techniques at the Uni-
versity of Minnesota following the procedures described by Shen et al.
(2002). Most dates, 24 in total, yield errors (2σ) <1% (Table DR1 in the
GSA Data Repository1
). Oxygen isotope ratios are reported as δ18
O rela-
tive to the Vienna Peedee belemnite standard (for methods and analytical
procedures, see the Data Repository). The Lapa Grande record spans from
1.3 to 10.2 kyr B.P., with a hiatus from 6.3 to 5.9 kyr B.P.. The early and
middle Holocene is represented by stalagmite LG11, while the middle
to late Holocene is represented by stalagmite LG3. The isotope profile is
composed of 600 δ18
O samples, yielding a temporal resolution between
1 and 40 yr (10 yr on average) and exhibiting a large range of ~4.5‰
throughout the Holocene. The wide range of temporal resolution is due
to large differences in growth rates observed along the speleothem long
axis, which varies from 0.01 to 0.35 mm/yr. Hence some of the events
that appear to be very brief might in fact result from the coarse temporal
sampling during some time intervals.
RESULTS AND DISCUSSION
Model experiments suggest that the δ18
O in precipitation is primarily
controlled by the “amount effect” over areas such as northern Minas Gerais,
where precipitation is fundamentally the result of SAMS activity (Vuille et
al., 2003). This interpretation is confirmed by the strong negative correla-
tion between monthly rainfall amount with monthly weighted mean δ18
O
at the InternationalAtomic EnergyAgency−Global Network of Isotopes in
Precipitation station in Brasília between 1963 and 1987 (R2
= 0.64), where
precipitation is climatologically identical to the study region (Fig. DR1A
in the Data Repository). Relatively low correlation coefficients between
δ18
O and δ13
C along the speleothem growth axes suggest that stalagmites
LG3 (r2
= 0.13) and LG11 (r2
= 0.24) were deposited in approximate isoto-
pic equilibrium according to the Hendy test (Fig. DR1B).
The novel characteristics of this new record are abrupt fluctuations
in δ18
O punctuating the entire Holocene, with some differences in the
structure and duration of events between the early and middle Holocene
(considered here to extend from 10 to 7 kyr B.P. and from 7 to 4 kyr B.P.,
respectively) and the late Holocene (after 4 kyr B.P.). The Lapa Grande
δ18
O record shows strong events of increased precipitation centered at
9.2, 8.2, 7.4, 7.0, 6.6, 5.2, 4.0, 3.2, 2.7, 2.3, 2.2, and 1.9 kyr B.P. During
the early and middle Holocene the duration of these events was ~300 yr
with amplitudes varying from 0.9‰ to 1.5‰. The strongest wet events,
in terms of duration and more negative values of δ18
O, correspond to
Bond event 4 and the 8.2 kyr B.P. event, respectively (Fig. 2). Soon
after the 8.2 kyr B.P. event, a dry event with similar amplitude (~1.5‰)
and duration (~0.3 k.y.) occurred at 7.8 kyr B.P., an event without any
equivalent in the paleoclimate records from South America. These
abrupt events recorded in Brazil present isotopic amplitudes that are 2 to
3 times larger than documented in the Dongge Cave speleothem records
(eastern China), where the largest event took place at 8.2 kyr B.P. with
only a ~0.5‰ shift (Wang et al., 2005).
Late Holocene abrupt events are equivalent to those observed in
the early and middle Holocene in terms of their amplitude; however,
they are much more short-lived, not lasting longer than 100 yr. The
longest event occurred at 2.7 kyr B.P. and lasted ~100 yr, followed by
other abrupt shorter fluctuations of <~50 yr (3.2, 2.3, 2.2, and 1.9 kyr
B.P.), which are constrained by 2–8 data points (see Fig. DR2). These
results suggest significant differences in the mechanism controlling mul-
tidecadal to centennial SAMS variability between the early to middle
Holocene and late Holocene.
Figure 2 presents a comparison of the Lapa Grande isotope record
with IRD pulses in the North Atlantic expressed in terms of percentage
of hematite-stained grain variations and with other paleomonsoon records
from South America and eastern China. Abrupt negative shifts of δ18
O in
the Lapa Grande record show a striking match with Bond events during
the early and middle Holocene, consistent with the notion of a SAMS
intensification during cold events in the Northern Hemisphere (Baker et
al., 2001, 2005; Ekdahl et al., 2008; Cheng et al., 2009). These abrupt
decreases in δ18
O values, associated with increased precipitation in cen-
tral-eastern Brazil, closely correspond with an anomalously cold North
Atlantic during Bond events 6, 5, and 4, and during the 8.2 kyr B.P. event
(Fig. 2). However, it is important to note that other significant wet events,
albeit with shorter duration, occurred at 7.1 and 6.6 kyr B.P. at times of
low IRD input to the North Atlantic, apparently unrelated to Bond events.
Conversely, the impact of these events seems to produce a differ-
ent rainfall response over tropical South America during the late Holo-
cene. Even though negative excursions of δ18
O in our speleothems are still
1
GSA Data Repository item 2011314, analytical methods, Figures DR1−
DR4, and Table DR1, is available online at www.geosociety.org/pubs/ft2011.htm,
or on request from editing@geosociety.org or Documents Secretary, GSA, P.O.
Box 9140, Boulder, CO 80301, USA.
90°W 70 50 30
20°N
0
20°S
40
60
0 200 400 600 800 1000
Precipitation (mm)
ITCZ
SACZ
1
Minas GeraisMinas Gerais
statestate
3
2
Minas Gerais
state
Figure 1. Long-term mean (A.D. 1979–2000) precipitation (in mm)
for December–February (DJF) from the Climate Prediction Center
Merged Analysis of Precipitation. Numbers on map indicate study
site and other paleoclimate records: 1—Lapa Grande Cave in Minas
Gerais State, central-eastern Brazil; 2—Lake Titicaca, Bolivia and
Peru (Baker et al., 2001); 3—Cariaco Basin, Venezuela (Haug et
al., 2001). White square indicates location of Brasília International
Atomic Energy Agency−Global Network of Isotopes in Precipitation
station. ITCZ—Intertropical Convergence Zone; SACZ—South Atlan-
tic Convergence Zone.
on November 28, 2011geology.gsapubs.orgDownloaded from
4. GEOLOGY, November 2011 1077
coherent with Bond events 2 and 4, a change in the temporal structure of
the events is apparent. For example, the Lapa Grande record shows no
response to Bond events 1 and 3.
Anomalously cold conditions in the NorthAtlantic region apparently
affected SAMS precipitation over part of the continent, as indicated by
the large coherence in both amplitude and duration of wet events in Brazil
with periods of high lake levels of Titicaca inferred from δ13
C of organic
matter in sediments (Fig. 2C) (Baker et al., 2005). The relationship also
appears to have been valid during periods of strong reductions in SAMS
paleoprecipitation that occurred synchronously in Bolivia and central-
eastern Brazil within age errors.
The Lapa Grande paleoprecipitation record shows a prominent anti-
phased relationship with Asian Monsoon precipitation as recorded in the
Dongge speleothem record (Wang et al., 2005) (Fig. 2). Low Asian Mon-
soon activity over eastern China during Bond events 6, 5, and 2 (9.2, 7.4,
and 3.1–2.7 kyr B.P.) and the 8.2 kyr B.P. event coincided with an intensi-
fication of the SAMS over central-eastern Brazil (Fig. 2.).
Differences in the climate response to typical Northern Hemisphere
cold events throughout the Holocene might be the result of glacial bound-
ary conditions that persisted until ca. 7 kyr B.P. (Carlson et al., 2008). The
longer duration of abrupt wet events recorded in central-eastern Brazil
during the early Holocene is probably related to the rapid meltdown of
the remaining Laurentide ice caps, potentially reducing the strength of the
AMOC (Carlson et al., 2008; Fleitmann et al., 2008; Bernal et al., 2011).
This mechanism may have exerted a strong influence on meridional SST
gradients in the tropical Atlantic, thereby increasing monsoonal rainfall
in southern tropical South America. However, after ca. 7 kyr B.P., the
absence of significant ice would have reduced the potential effectiveness
of such a meltwater-driven mechanism.
Our record of variations in SAMS precipitation shows some con-
sistencies with the Ti record from the Cariaco Basin, an extensively used
proxy record for rainfall distribution within the area influenced by the
Intertropical Convergence Zone (ITCZ) (Fig. DR2). Despite the ampli-
tude of climate oscillations in northern Minas being much larger than
those recorded in the Cariaco Basin, abrupt events recorded during the
early and middle Holocene are generally synchronous within age errors
(e.g., Bond events 6 and 4, and the 8.2 kyr B.P. event), as are some of the
shorter events that occurred during the late Holocene. In addition, the gen-
erally antiphased pattern of tropical precipitation between hemispheres
is evident when comparing speleothem records from Brazil and China,
for example ca. 2.7 and 2.3 kyr B.P., during Bond event 2, suggesting an
intrinsic control on SAMS precipitation activity through the mean latitudi-
nal position of the ITCZ. Some incongruities between South America and
CentralAmerica are in part due to a stronger influence of El Niño/La Niña
Southern Oscillation (ENSO) in certain regions such as Central America
and the Caribbean during the late Holocene (Haug et al., 2001; Lachniet et
al., 2004). In contrast, central-eastern Brazil is not significantly influenced
by ENSO (Garreaud et al., 2009).
A spectral analysis of the composite stalagmites LG3 and LG11
shows that the most prominent periodicity observed in the Lapa Grande
paleoprecipitation record during the early and middle Holocene is at
~820 yr (Figs. DR2 and DR4). The same periodicity is described in the
Cueva del Diablo record, southwestern Mexico (Bernal et al., 2011), and
for SST variations in the eastern equatorial Pacific (Marchitto et al., 2010),
where warmer SST are observed during Bond events. In order to highlight
the importance of this cycle during the early and middle Holocene, a sine
function with a wavelength of 820 yr is compared with the δ18
O time series
in Figure DR3. Multidecadal periodicities peaking at 60 and 110 yr are
identified in our records from both the spectral analysis and the wavelet
spectrum, suggesting an influence of theAtlantic Multidecadal Oscillation
(Timmermann et al., 2007; Chiessi et al., 2009) on monsoon precipitation
in central-eastern Brazil (Fig. DR3).
Bond et al. (2001) argued that most of the North Atlantic SST oscil-
lations are likely tied to solar activity; hence, at least part of the Bond
events could be driven by variations in solar activity. Indeed, the events at
9.2, 8.2, 7.5, 5.2, 2.7, and 2.3 kyr B.P. coincide with periods of low solar
activity (high 14
C based on atmospheric Δ14
C and cosmogenic 10
Be deposi-
tion on the Greenland ice sheet) centered on 9.4, 8.2, 7.4, 5.4, 2.7, and 2.3
kyr B.P. (Bond et al., 2001). However, variations in solar irradiance alone
cannot explain all these interhemispheric changes in monsoon rainfall. For
example, none of the speleothem records from Brazil and China shows a
significant covariance with solar activity during the events at 4.0 and 3.2
kyr B.P. (Fig. DR4).
Abrupt increases (decreases) in South American monsoon (Asian
and Indian monsoon) rainfall have been related to lower SST in the North
Atlantic, an intensification of the northeast trade winds, and a southward
displacement of the ITCZ, invoking an intensification of cross-equatorial
flow. At the same time of increased SAMS, warm SST is observed in the
eastern equatorial Pacific (Marchitto et al., 2010). These results may have
-3
-2
-1
0
1
2
3
Chinaδ18
O(detrended)
LapaGrandeδ18
O(‰,VPDB)
Titicacaδ13
C(normalized)
2 3 4 5 6 7 8 9 10
30
25
20
15
10
5
0
Age (kyr B.P.)
1 3
%HSG
2 4 5 6
Age (kyr B.P.)
dry
wet
wet
dry
warm
cold
2 3 4 5 6 7 8 9 10
0.50
0.25
0.00
-0.25
-0.50
-9
-8
-7
-6
-5
-4
0
100
200
300
LG3
Depth(mm)
LG11
8.2
kyr B.P.
D
E
C
B
A
Figure 2. A: Hematite-stained quartz grain (HSG) record from
North Atlantic marine core VM 29-191 (Bond et al., 2001). B: Com-
posite δ18
O record from stalagmites LG3 and LG11, Lapa Grande
Cave, central-eastern Brazil. Vertical dashed line marks area that
is not represented by either LG3 or LG11 isotope profiles. VPDB—
Vienna Peedee belemnite. C: Age-depth (in mm, relative to top) rela-
tions. Horizontal error bars indicate typical U/Th dating errors for
speleothems. D: Detrended δ13
C record from Lake Titicaca (Bolivia
and Peru; Baker et al., 2005). E: Detrended DA (light gray) and D4
(dark gray) stalagmite δ18
O record from Dongge Cave, eastern China
(Wang et al., 2005; Yuan et al., 2004). A 20 yr running mean of DA δ18
O
time series is in black. Bond events 1–6 and 8.2 kyr B.P. event are
indicated by gray bars.
on November 28, 2011geology.gsapubs.orgDownloaded from
5. 1078 GEOLOGY, November 2011
important implications for the notion of the establishment of El Niño–like
conditions in the eastern tropical Pacific because atmospheric circulation
changes forced by negative anomalies of SST in the Atlantic Ocean are
partly controlled by the strength of theAMOC (Timmermann et al., 2007).
In this context, our results demonstrate that the slowdown of the
AMOC associated with freshwater pulses in the North Atlantic can pro-
mote abrupt changes in monsoonal precipitation in South America, poten-
tially influenced by feedback processes.
ACKNOWLEDGMENTS
We thank M.H. Hollanda, L. Mancine, and O. Antunes for their support dur-
ing the stable isotope data acquisition at the University of São Paulo. We are grate-
ful to the Brazilian Institute of Environment and Renewable Natural Resources
and C. Mendes for permission to collect stalagmite samples. We thank Cristiano
Chiessi for insightful scientific discussions. This paper was significantly improved
after incorporating the suggestions of one anonymous reviewer. This work was sup-
ported by the Fundação de Amparo a Pesquisa do Estado de São Paulo (FAPESP),
Brazil (grant to Cruz and Karmann), U.S. National Science Foundation grants
0502535 and 1103403 to Edwards and Cheng, and fellowship from Brazil CAPES
(Coordenação de Aperfeiçoamento de Pessoal de Nível Superior) to Stríkis.
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Manuscript received 21 January 2011
Revised manuscript received 21 June 2011
Manuscript accepted 22 June 2011
Printed in USA
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