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Articles 1 - 30 of 67
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Locating Cryptotephra In Sediments Using Fluid Imaging Technology, Robert D'Anjou, Nicholas L. Balascio, Raymond S. Bradley
Locating Cryptotephra In Sediments Using Fluid Imaging Technology, Robert D'Anjou, Nicholas L. Balascio, Raymond S. Bradley
Raymond S Bradley
We report a new approach to locate and quantify cryptotephra in sedimentary archives using a continuously-imaging Flow Cytometer and Microscope (FlowCAM_). The FlowCAM rapidly photographs particles flowing in suspension past a microscope lens and performs semi-automated analysis of particle images. It has had primarily biological applications, although the potential sedimentological applications are numerous. Here we test the ability of this instrument to image irregularly shaped, vesicular glass shards and to screen sediment samples for the presence of cryptotephra. First, reference samples of basalt and rhyolite tephra (sieved <63>microns) were analyzed with the FlowCAM, demonstrating the ability of the instrument to …
Biogeochemical Evidence For Hydrologic Change During The Holocene In A Lake Sediment Record From Southeast Greenland, Nicholas L. Balascio, William J. D'Andrea, Raymond S. Bradley, Bianca B. Perren
Biogeochemical Evidence For Hydrologic Change During The Holocene In A Lake Sediment Record From Southeast Greenland, Nicholas L. Balascio, William J. D'Andrea, Raymond S. Bradley, Bianca B. Perren
Raymond S Bradley
Holocene paleoclimate records from Greenland help us understand the response of the Greenland Ice Sheet and regional oceanic and atmospheric circulation systems to natural climate variability in order to place recent changes in a longer-term perspective. Here biogeochemical analysis of a lake sediment core from southeast Greenland is used to define changes in moisture balance and runoff during the Holocene in a catchment near the margin of the Greenland Ice Sheet. A 1.6 m sediment core that spans the last 8.8 ka was recovered from Flower Valley Lake on Ammassalik Island. Magnetic susceptibility, diatoms, bulk biogeochemical properties (TOC, C/N, δ13Corg), …
Assessment Of Regional Climate Model Simulation Estimates Over The Northeast United States, M. A. Rawlins, Raymond S. Bradley, H. F. Diaz
Assessment Of Regional Climate Model Simulation Estimates Over The Northeast United States, M. A. Rawlins, Raymond S. Bradley, H. F. Diaz
Raymond S Bradley
Given the coarse scales of coupled atmosphere-ocean global climate models, regional climate models (RCMs) are increasingly relied upon for studies at scales appropriate for many impacts studies. We use outputs from an ensemble of RCMs participating in the North American Regional Climate Change Assessment Program (NARCCAP) to investigate potential changes in seasonal air temperature and precipitation between present (1971–2000) and future (2041–2070) time periods across the northeast United States. The models show a consistent modest cold bias each season and are wetter than observations in winter, spring, and summer. Agreement in spatial variability and pattern correlation is good for air …
Proxy-To-Proxy Calibration: Increasing The Temporal Resolution Of Quantitative Climate Reconstructions, Lucien Von Gunten, William J. D'Andrea, Raymond S. Bradley, Yongsong Huang
Proxy-To-Proxy Calibration: Increasing The Temporal Resolution Of Quantitative Climate Reconstructions, Lucien Von Gunten, William J. D'Andrea, Raymond S. Bradley, Yongsong Huang
Raymond S Bradley
No abstract provided.
Evaluating Holocene Climate Change In Northern Norway Using Sediment Records From Two Contrasting Lake Systems., Nicholas L. Balascio, Raymond S. Bradley
Evaluating Holocene Climate Change In Northern Norway Using Sediment Records From Two Contrasting Lake Systems., Nicholas L. Balascio, Raymond S. Bradley
Raymond S Bradley
We analyzed Holocene sedimentary records from two lakes in the Lofoten Islands, northern Norway to evaluate environmental changes during the Holocene related to northern North Atlantic climate dynamics. The lakes are located in different geomorphological settings, and thus provide a contrast in their response to regional climate change. Environmental changes at both lakes were interpreted based on magnetic susceptibility, organic-matter flux, C/N, d13 Corg , Ti concentrations, and mass accumulation rates. Chronologies were established using 16 AMS radiocarbon dates, and average deposition rates in both environments are higher than 0.2 mm/year throughout the Holocene. At Vikjordvatnet, sedimentary geochemical properties define …
Biogeochemical Evidence For Prehistoric Human Impacts On The Environment In Northwestern Norway, Raymond S. Bradley, Robert D'Anjou, Nicholas L. Balascio, David B. Finkelstein
Biogeochemical Evidence For Prehistoric Human Impacts On The Environment In Northwestern Norway, Raymond S. Bradley, Robert D'Anjou, Nicholas L. Balascio, David B. Finkelstein
Raymond S Bradley
Disentangling the effects of climate change and anthropogenic activities on the environment is a major challenge in paleoenvironmental research. Here, we used fecal sterols and other biogeochemical compounds in lake sediments from northern Norway to identify both natural and anthropogenic signals of environmental change during the late Holocene. The area was first occupied by humans and their grazing animals at ∼2,250 ± 75 calendar years before 1950 AD (calendar years before present). The arrival of humans is indicated by an abrupt increase in coprostanol (and its epimer epicoprostanol) in the sediments and an associated increase in 5β-stigmastanol (and 5β-epistigmastanol), which …
A Mild Little Ice Age And Unprecedented Warmth In An 1800 Year Record From Svalbard, William J. D'Andrea, Raymond S. Bradley, David Vaillencourt, Nicholas L. Balascio, Al Werner, Steve Roof, Michael J. Retelle
A Mild Little Ice Age And Unprecedented Warmth In An 1800 Year Record From Svalbard, William J. D'Andrea, Raymond S. Bradley, David Vaillencourt, Nicholas L. Balascio, Al Werner, Steve Roof, Michael J. Retelle
Raymond S Bradley
The Arctic region is subject to a great amplitude of climate variability and is currently undergoing large-scale changes due in part to anthropogenic global warming. Accurate projections of future change depend on anticipating the response of the Arctic climate system to forcing, and understanding how the response to human forcing will interact with natural climate variations. The Svalbard Archipelago occupies an important location for studying patterns and causes of Arctic climate variability; however, available paleoclimate records from Svalbard are of restricted use due to limitations of existing climate proxies. Here we present a sub-decadal- to multidecadal-scale record of summer temperature …
Natural Archives, Changing Climates, Raymond S. Bradley
Natural Archives, Changing Climates, Raymond S. Bradley
Raymond S Bradley
Climatic changes have occurred throughout human history, but instrumental measurements do not provide us with a very long perspective on climate variations. In many regions, instrumental records only extend back a century or two. To understand the longer-term variability of the climate system, we rely on natural archives— sediments, ice caps, peat bogs, cave deposits, banded corals and tree rings—in which a record of past changes in climate has been preserved. They are a treasure trove of the climatic and environmental history of the planet and provide information about factors that may have caused the climate to change, such as …
Distal Tephra Found In A Viking Boathouse: The Potential For Tephrochronology In Reconstructing The Iron Age In Norway, Nicholas L. Balascio, Stephen Wickler, L E. Narmo, Raymond S. Bradley
Distal Tephra Found In A Viking Boathouse: The Potential For Tephrochronology In Reconstructing The Iron Age In Norway, Nicholas L. Balascio, Stephen Wickler, L E. Narmo, Raymond S. Bradley
Raymond S Bradley
Distal tephra deposits from Icelandic volcanic eruptions have been found in Norway and can be used to precisely date a variety of sedimentary environments. Tephrochronology has not yet been applied to archaeological investigations in Norway because tephra are generally not found as visible layers, but are present as very low concentrations of glass shards (i.e. cryptotephra). In this study, we present results from the analysis of cryptotephras found in an Iron Age boathouse in northern Norway. The boathouse was associated with the chieftain center at Borg on Vestvågøy in the Lofoten Islands. In 2003, a trench was excavated and the …
A Multi-Proxy Approach To Assessing Isolation Basin Stratigraphy From The Lofoten Islands, Norway, Nicholas L. Balascio, Zhaohui Zhang, Raymond S. Bradley, Bianca B. Perren, Svein-Olaf Dahl, Jostein Bakke
A Multi-Proxy Approach To Assessing Isolation Basin Stratigraphy From The Lofoten Islands, Norway, Nicholas L. Balascio, Zhaohui Zhang, Raymond S. Bradley, Bianca B. Perren, Svein-Olaf Dahl, Jostein Bakke
Raymond S Bradley
This study takes a comprehensive approach to characterizing the isolation sequence of Heimerdalsvatnet, a coastal lake in the Lofoten Islands, northern Norway. We use established methods and explore new techniques to assess changes in marine influence. Bathymetric and sub-bottom profiles were acquired to examine basin-wide sedimentation and a 5.8 m sediment core spanning the last 7800 cal yr BP was analyzed. We measured magnetic susceptibility, bulk organic matter properties, molecular biomarkers, diatom assemblages, and elemental profiles acquired by scanning X-ray fluorescence. These characteristics of the sediment reflect detailed changes in salinity and water column conditions as the lake was progressively …
An Analysis Of Past And Future Changes In The Ice Cover Of Two High-Arctic Lakes Based On Synthetic Aperture Radar (Sar) And Landsat Imagery, Timothy L. Cook, Raymond S. Bradley
An Analysis Of Past And Future Changes In The Ice Cover Of Two High-Arctic Lakes Based On Synthetic Aperture Radar (Sar) And Landsat Imagery, Timothy L. Cook, Raymond S. Bradley
Raymond S Bradley
Space-borne remotely sensed data can provide valuable insight into cryospheric processes in remote high-latitude regions for which direct observations are limited. In this study we use synthetic aperture radar (SAR) and Landsat imagery to evaluate recent changes in the ice cover of Upper and Lower Murray Lakes (81°20′N, 69°30′W) on Ellesmere Island, Nunavut, Canada. These data highlight changes in ice conditions that have occurred over the past decade and provide a means for assessing the likely impacts of rising temperatures on future lake-ice conditions. Under current (1997–2007) climatic conditions the Murray Lakes average several weeks of ice-free conditions in August …
Recent Changes In Freezing Level Heights In The Tropics With Implications For The Deglacierization Of High Mountain Regions, Raymond S. Bradley, F. Keimig, H. F. Diaz, D. R. Hardy
Recent Changes In Freezing Level Heights In The Tropics With Implications For The Deglacierization Of High Mountain Regions, Raymond S. Bradley, F. Keimig, H. F. Diaz, D. R. Hardy
Raymond S Bradley
The height of the freezing level in the tropical atmosphere (the free air 0°C isotherm) has increased across most of the region, particularly in the outer Tropics. In the tropical Andes, south of the Equator, high elevation surface temperatures and upper air data show a similar trend in temperature, of ∼0.1°C/decade over the last 50 years. Meteorological observations at 5680 m on the summit of the Quelccaya Ice Cap, the largest ice mass in the Tropics, indicate that daily maximum temperatures often exceed 0°C from October–May, and rise well above freezing for much of the year around the ice cap …
Evidence For A Widespread Climatic Anomaly At Around 9.2 Ka Before Present, Dominik Fleitmann, Manfred Mudelsee, Stephen J. Burns, Raymond S. Bradley, Jan Kramers, Albert Matter
Evidence For A Widespread Climatic Anomaly At Around 9.2 Ka Before Present, Dominik Fleitmann, Manfred Mudelsee, Stephen J. Burns, Raymond S. Bradley, Jan Kramers, Albert Matter
Raymond S Bradley
No abstract provided.
Proxy-Based Reconstructions Of Hemispheric And Global Surface Temperature Variations Over The Past Two Millennia, M. E. Mann, Z. Zhang, M. K. Hughes, Raymond S. Bradley, S. K. Miller, S. Rutherford, F. Ni
Proxy-Based Reconstructions Of Hemispheric And Global Surface Temperature Variations Over The Past Two Millennia, M. E. Mann, Z. Zhang, M. K. Hughes, Raymond S. Bradley, S. K. Miller, S. Rutherford, F. Ni
Raymond S Bradley
Following the suggestions of a recent National Research Council report [NRC (National Research Council) (2006) Surface Temperature Reconstructions for the Last 2,000 Years (Natl Acad Press, Washington, DC).], we reconstruct surface temperature at hemispheric and global scale for much of the last 2,000 years using a greatly expanded set of proxy data for decadal-to-centennial climate changes, recently updated instrumental data, and complementary methods that have been thoroughly tested and validated with model simulation experiments. Our results extend previous conclusions that recent Northern Hemisphere surface temperature increases are likely anomalous in a long-term context. Recent warmth appears anomalous for at least …
Climate Change Scenario For Costa Rican Montane Forests, A. V. Karmalkar, Raymond S. Bradley, H. F. Diaz
Climate Change Scenario For Costa Rican Montane Forests, A. V. Karmalkar, Raymond S. Bradley, H. F. Diaz
Raymond S Bradley
Tropical montane cloud forests are characterized by persistent immersion in clouds, an important source of moisture during the dry season. Future changes in temperature and precipitation could alter cloud cover at the vegetation level and seriously affect mountain ecosystems. A regional climate modeling study that focuses on changes in the distributions of temperature and precipitation in Costa Rica shows, in general, an increase in temperature and a decrease in precipitation under the A2 scenario. At high elevations, warming is amplified and future temperature distribution lies outside the range of present-day distribution. Compared to the Caribbean side, temperature changes are greater …
Variations Of Twentieth-Century Temperature And Precipitation Extreme Indicators In The Northeast United States, Michael L. Griffiths, Raymond S. Bradley
Variations Of Twentieth-Century Temperature And Precipitation Extreme Indicators In The Northeast United States, Michael L. Griffiths, Raymond S. Bradley
Raymond S Bradley
An examination of five temperature and five precipitation extreme indicators reveals an increase in both temperature and precipitation extremes over the 1926–2000 period in the northeast United States, with most of this increase occurring over the past four decades. Empirical orthogonal function (EOF) analysis of winter frost days (FD) and warm nights (TN90) and also winter consecutive dry days (CDD) and very wet days (R95T) over the 1950–2000 period reveals that some of the variability associated with changes in these extremes may be explained by variations in the Arctic Oscillation (AO), El Niño–Southern Oscillation (ENSO), and Pacific–North American (PNA) pattern. …
Solar Modulation Of Little Ice Age Climate In The Tropical Andes, P. J. Polissar, M. B. Abbott, A. P. Wolfe, M. Bezada, V. Rull, Raymond S. Bradley
Solar Modulation Of Little Ice Age Climate In The Tropical Andes, P. J. Polissar, M. B. Abbott, A. P. Wolfe, M. Bezada, V. Rull, Raymond S. Bradley
Raymond S Bradley
The underlying causes of late-Holocene climate variability in the tropics are incompletely understood. Here we report a 1,500-year reconstruction of climate history and glaciation in the Venezuelan Andes using lake sediments. Four glacial advances occurred between anno Domini (A.D.) 1250 and 1810, coincident with solar-activity minima. Temperature declines of −3.2 ± 1.4°C and precipitation increases of ≈20% are required to produce the observed glacial responses. These results highlight the sensitivity of high-altitude tropical regions to relatively small changes in radiative forcing, implying even greater probable responses to future anthropogenic forcing.
Proxy-Based Northern Hemisphere Surface Temperature Reconstructions: Sensitivity To Method, Predictor Network, Target Season, And Target Domain, S. Rutherford, M. E. Mann, T. J. Osborne, Raymond S. Bradley, K. R. Briffa, M. K. Hughes, P. D. Jones
Proxy-Based Northern Hemisphere Surface Temperature Reconstructions: Sensitivity To Method, Predictor Network, Target Season, And Target Domain, S. Rutherford, M. E. Mann, T. J. Osborne, Raymond S. Bradley, K. R. Briffa, M. K. Hughes, P. D. Jones
Raymond S Bradley
Results are presented from a set of experiments designed to investigate factors that may influence proxy-based reconstructions of large-scale temperature patterns in past centuries. The factors investigated include 1) the method used to assimilate proxy data into a climate reconstruction, 2) the proxy data network used, 3) the target season, and 4) the spatial domain of the reconstruction. Estimates of hemispheric-mean temperature are formed through spatial averaging of reconstructed temperature patterns that are based on either the local calibration of proxy and instrumental data or a more elaborate multivariate climate field reconstruction approach. The experiments compare results based on the …
Stable Isotopes In East African Precipitation Record Indian Ocean Zonal Mode, M. Vuille, M. Werner, Raymond S. Bradley, R. Y. Chan, F. Keimig
Stable Isotopes In East African Precipitation Record Indian Ocean Zonal Mode, M. Vuille, M. Werner, Raymond S. Bradley, R. Y. Chan, F. Keimig
Raymond S Bradley
Observational stable isotope data and model simulations show that the δ18O composition of precipitation in East Africa is closely related to the coupled ocean-atmosphere system over the Indian Ocean. During the rainy seasons δ18O is a very sensitive recorder of the Indian Ocean Zonal Mode (IOZM). The link between δ18O and the IOZM is established through adjustments in the large-scale overturning circulation over the Indian Ocean and associated changes in convective activity and precipitation over East Africa. The IOZM is recorded as significant departures in δ18O not only over East Africa but as a dipole mode with opposite sign to …
Multidecadal North Atlantic Climate Variability And Its Effect On North American Salmon Abundance, A. Condron, R. Deconto, Raymond S. Bradley, F. Juanes
Multidecadal North Atlantic Climate Variability And Its Effect On North American Salmon Abundance, A. Condron, R. Deconto, Raymond S. Bradley, F. Juanes
Raymond S Bradley
Climate variability is now known to play a key role in the abundance of marine fisheries, and must be accounted for to implement sustainable management strategies. We show that North American Atlantic salmon abundance has fluctuated in parallel with the Atlantic Multidecadal Oscillation (AMO); a basin-wide, low frequency climate mode producing cold-warm-cold sea surface temperatures over the last century. During the AMO warm (cool) phase salmon abundance is lower (higher). Changes in sea surface temperature associated with the AMO are most pronounced in the winter season near the Grand Banks of Newfoundland, a known overwintering area for salmon and an …
Surface Mass Balance Of The Ward Hunt Ice Rise And Ward Hunt Ice Shelf, Ellesmere Island, Nunavut, Canada, C. Braun, D. R. Hardy, Raymond S. Bradley, V. Sahanatien
Surface Mass Balance Of The Ward Hunt Ice Rise And Ward Hunt Ice Shelf, Ellesmere Island, Nunavut, Canada, C. Braun, D. R. Hardy, Raymond S. Bradley, V. Sahanatien
Raymond S Bradley
The Ward Hunt Ice Rise and Ward Hunt Ice Shelf, located on Ellesmere Island, Canada, are two of the northernmost land ice masses on the North American continent. Surface mass balance measurements (excluding calving and subice processes) began in 1959 on the ice rise and in 1966 on the ice shelf but were frequently interrupted, most recently between 1986 and 2002. The surface balance of the ice rise and ice shelf follows the temporal pattern seen on other measured High Arctic glaciers. The overall surface mass losses over the last 45 years have been comparatively low (1.68 m water equivalent …
Modern Glacier Retreat On Kilimanjaro As Evidence Of Climate Change: Observations And Facts, Georg Kaser, Douglas R. Hardy, Thomas Molg, Raymond S. Bradley, Tharsis M. Hyera
Modern Glacier Retreat On Kilimanjaro As Evidence Of Climate Change: Observations And Facts, Georg Kaser, Douglas R. Hardy, Thomas Molg, Raymond S. Bradley, Tharsis M. Hyera
Raymond S Bradley
In recent years, Kilimanjaro and its vanishing glaciers have become an ‘icon’ of global warming, attracting broad interest. In this paper, a synopsis of (a) field observations made by the authors and (b) climatic data as reported in the literature (proxy and long-term instrumental data) is presented to develop a new concept for investigating the retreat of Kilimanjaro’s glaciers, based on the physical understanding of glacier–climate interactions. The concept considers the peculiarities of the mountain and implies that climatological processes other than air temperature control the ice recession in a direct manner. A drastic drop in atmospheric moisture at the …
Projected Temperature Changes Along The American Cordillera And The Planned Gcos Network, Raymond S. Bradley, F. T. Keimig, H. F. Diaz
Projected Temperature Changes Along The American Cordillera And The Planned Gcos Network, Raymond S. Bradley, F. T. Keimig, H. F. Diaz
Raymond S Bradley
Analysis of 7 GCM simulations with 2x CO2 levels shows large and statistically significant free air temperature changes (compared to controls) along the axis of the American Cordillera (from Alaska to southern Chile). At all latitudes, the modeled change in temperature increases with elevation. Temperature increases are especially large in boreal summer months from ∼35–50°N, and year-round in the high mountains of Peru, Bolivia and northern Chile. If these models are correct, mountain ranges that extend high into the lower troposphere are likely to experience significant warming, with implications for glacier mass balance and water resources, montane ecosystems and high …
Optimal Surface Temperature Reconstructions Using Terrestrial Borehole Data, M. E. Mann, S. Rutherford, Raymond S. Bradley, M. K. Hughes, F. T. Keimig
Optimal Surface Temperature Reconstructions Using Terrestrial Borehole Data, M. E. Mann, S. Rutherford, Raymond S. Bradley, M. K. Hughes, F. T. Keimig
Raymond S Bradley
We derive an optimal Northern Hemisphere mean surface temperature reconstruction from terrestrial borehole temperature profiles spanning the past five centuries. The pattern of borehole ground surface temperature (GST) reconstructions displays prominent discrepancies with instrumental surface air temperature (SAT) estimates during the 20th century, suggesting the presence of a considerable amount of noise and/or bias in any underlying spatial SAT signal. The vast majority of variance in the borehole dataset is efficiently retained by its two leading eigenvectors. A sizable share of the variance in the first eigenvector appears to be associated with non-SAT related bias in the borehole data. A …
Variability Of Snow Accumulation And Isotopic Composition On Nevado Sajama, Bolivia, D. R. Hardy, M. Vuille, Raymond S. Bradley
Variability Of Snow Accumulation And Isotopic Composition On Nevado Sajama, Bolivia, D. R. Hardy, M. Vuille, Raymond S. Bradley
Raymond S Bradley
High-elevation ice caps develop an archive of atmospheric constituents and properties through the accumulation of snowfall. The timing of precipitation events, therefore, fundamentally governs the environmental information that ice core records can provide. These events are often highly seasonal, as are various postdepositional processes influencing the snow's physical and chemical properties. Knowledge of climatic conditions at an ice core site is essential to a full understanding of the ice core record. This work reports on 4 years of meteorological measurements near the summit of Nevado Sajama, an ice-capped peak rising ∼2500 m above the South American Altiplano (elevation 6542 m), …
Rapid Lacustrine Response To Recent High Arctic Warming: A Diatom Record From Sawtooth Lake, Ellesmere Island, Nunavut, Bianca B. Perren, Raymond S. Bradley, Pierre Francus
Rapid Lacustrine Response To Recent High Arctic Warming: A Diatom Record From Sawtooth Lake, Ellesmere Island, Nunavut, Bianca B. Perren, Raymond S. Bradley, Pierre Francus
Raymond S Bradley
Diatoms from Sawtooth Lake (79 20'N, 81 51'W) on the Fosheim Peninsula in Central Ellesmere Island, Canada were analyzed to assess the temporal extent and magnitude of climatic change in the High Arctic during the late Holocene. Diatom results from the sediment cores show an absence of diatoms throughout the last ;2.5 ka (4.6 m) until the 1920s. However, ca. 1926 (5.3-cm depth), a rapid colonization of diatoms in the lake occurred. Within the uppermost section of the core (;1920 to ;1997), the diatom flora shift from a small Fragilaria-dominated assemblage to a more diverse assemblage that is dominated by …
Reply To Comment By N. D. Marsh And H. Svensmark On “Solar Influences On Cosmic Rays And Cloud Formation: A Reassessment”, B. Sun, Raymond S. Bradley
Reply To Comment By N. D. Marsh And H. Svensmark On “Solar Influences On Cosmic Rays And Cloud Formation: A Reassessment”, B. Sun, Raymond S. Bradley
Raymond S Bradley
No abstract provided.
Modeling Δ18o In Precipitation Over The Tropical Americas: 1. Interannual Variability And Climatic Controls, M. Vuille, Raymond S. Bradley, M. Werner, R. Healy, F. Keimig
Modeling Δ18o In Precipitation Over The Tropical Americas: 1. Interannual Variability And Climatic Controls, M. Vuille, Raymond S. Bradley, M. Werner, R. Healy, F. Keimig
Raymond S Bradley
We use two atmospheric general circulation models (AGCMs), the ECHAM-4 and the GISS II models, to analyze the interannual variability of δ18O in precipitation over the tropical Americas. Several different simulations with isotopic tracers forced with observed global sea surface temperatures (SST) between 1950 and 1998 reveal the influence of varying temperature, precipitation amount, and moisture source contributions on the predicted δ18O distribution. Observational evidence from climatic (NCEP-NCAR) and sparse stable isotope (IAEA-GNIP) data is used to evaluate model performance. The models capture the essential features of surface climate over the tropical Americas in terms of both their spatial and …
Modeling Δ18o In Precipitation Over The Tropical Americas: 2. Simulation Of The Stable Isotope Signal In Andean Ice Cores, M. Vuille, Raymond S. Bradley, R. Healy, M. Werner, D. R. Hardy, L. G. Thompson, F. Keimig
Modeling Δ18o In Precipitation Over The Tropical Americas: 2. Simulation Of The Stable Isotope Signal In Andean Ice Cores, M. Vuille, Raymond S. Bradley, R. Healy, M. Werner, D. R. Hardy, L. G. Thompson, F. Keimig
Raymond S Bradley
We use the ECHAM-4 and the GISS II atmospheric general circulation models (AGCM) with incorporated stable isotopic tracers and forced with observed global sea surface temperatures (SST) between 1979 and 1998, to simulate the δ18O signal in three tropical Andean ice cores, from Huascarán (Peru), Quelccaya (Peru), and Sajama (Bolivia). In both models, the simulated stable isotopic records compare favorably with the observational data, when the seasonality of precipitation and dry season loss due to sublimation and wind scour are taken into account. Our simulations indicate a significant influence of the local climatic conditions (temperature and precipitation amount) on the …
Low Latitude Ice Cores Record Pacific Sea Surface Temperatures, Raymond S. Bradley, M. Vuille, D. R. Hardy, L. G. Thompson
Low Latitude Ice Cores Record Pacific Sea Surface Temperatures, Raymond S. Bradley, M. Vuille, D. R. Hardy, L. G. Thompson
Raymond S Bradley
Oxygen isotope variations in ice cores from Bolivia and Peru are highly correlated with sea surface temperatures (SSTs) across the equatorial Pacific Ocean, which are closely linked to ENSO variability. Circulation anomalies associated with this variability control moisture flux from the equatorial and tropical Atlantic Ocean and Amazon Basin to the ice core sites. Below average SSTs lead to higher accumulation rates and isotopically lighter snow; such conditions are also associated with lower atmospheric freezing levels. During warm events, opposite conditions prevail. Oxygen isotope variations in an ice core from the Himalayas also reflect SST variations in the equatorial Pacific …