Papers by Brendan M Buckley
Modern Asian Studies, 2012
Radiocarbon, 2010
... High-precision radiocarbon measurements of contemporaneous tree-ring dated wood from the Brit... more ... High-precision radiocarbon measurements of contemporaneous tree-ring dated wood from the British Isles and New Zealand: AD1850-950. Radiocarbon 44, 633-640. McCormac, FG, Hogg, AG, Higham, TFG, Lynch-Stieglitz, J., Broecker, WS, Baillie, MGL, Palmer, J., Xiong, L ...
ABSTRACT We present a 1248-year reconstruction of May precipitation (AD 750-1998) for the Mid-Atl... more ABSTRACT We present a 1248-year reconstruction of May precipitation (AD 750-1998) for the Mid-Atlantic Region of the United States. The reconstruction is based on the first principal component (PC1) of two millennial-length eastern redcedar (Juniperus virginiana) tree-ring chronologies collected from rocky, limestone sites in the Ridge and Valley province of West Virginia. A split-calibration linear regression model accounted for 32% of the variance in the instrumental record and was stable through time. The model was well verified by the reduction of error (RE = 0.33) and coefficient of efficiency (CE = 0.30) statistics. Centennial-length changes in precipitation were rare but wetter than median conditions and drier than median conditions occurred during the Medieval Warm Epoch (AD 1000-1300) and the Little Ice Age (AD 1450-1850), respectively. The full reconstruction contained substantial inter-annual and decadal variability, however, the 19th and 20th centuries recorded the greatest number of annual and decadal extreme wet and dry periods. A comparison of the May precipitation reconstruction to other regional reconstructions of July Palmer Hydrologic Drought Index and Chesapeake Bay salinity showed that not only did drought and pluvial events extend into the Ridge and Valley province but they also began early in the growing season. A positive correlation between PC1 and the winter North Atlantic Oscillation Index indicates that eastern redcedar's response to May precipitation is mediated by winter temperature. Full May precipitation reconstruction from AD 750-1998. The gray line represents the annual predicted values. A 10-year 4th order smoothing spline is used to highlight decadal trends (thick black line).
Agu Fall Meeting Abstracts, Dec 1, 2008
We present the first spatial reconstructions of Asian monsoon climate variability over the past m... more We present the first spatial reconstructions of Asian monsoon climate variability over the past millennium from long tree-ring records. The reconstructions, for both the monsoon (JJA) and pre-monsoon (MAM) seasons, are based on a 534-point grid of instrumental Palmer Drought Severity Indices (PDSI) covering all of monsoon Asia and an irregular network of 312 annual tree-ring chronologies over most of the same domain. The seasonal reconstructions were initially estimated at each grid point using a local "point-by-point regression" (PPR) method that has been used successfully in reconstructing drought over North America. Different levels of predictor variable screening applied in PPR produced a 5-member ensemble of reconstructions for each season. The estimated noise level in these reconstructions was relatively high (average cross-validation R2 over the 534 grid point domain typically <0.30). In addition, the lengths of the grid point reconstructions varied over space due to the variable length tree-ring series available for use in PPR. For these reasons, each ensemble member was iteratively refined using a local variant of PPR to improve its reconstructions, with missing values imputed as necessary, to produce complete fields extending back to AD 1000 over all 534 grid point locations. An ensemble average for each season, with estimated uncertainties, was then calculated and used for analysis. The reconstructions reveal the occurrence of some persistent "megadroughts" in the past that appear to be unprecedented in the instrumental records. These megadroughts are not restricted to any particular part of "Monsoon Asia", but the ones in Southeast Asia stand out particularly strong. Comparisons made between these drought reconstructions and a companion field of SST reconstructions for the tropical Pacific back to AD 1400, based on independent tree-ring data from the American Southwest and Mexico, suggest that unusual ENSO variability is a contributor to the development of past severe droughts in monsoon Asia. An association between monsoon drought variability and explosive volcanism is also indicated. Implications for future work, especially related to expanding and improving the tree-ring network for reconstruction in certain regions, are also discussed.
Agu Fall Meeting Abstracts, Dec 1, 2007
The need for understanding the natural range of climate variability in the monsoon regions of Asi... more The need for understanding the natural range of climate variability in the monsoon regions of Asia - among the worldês most heavily populated and most dependent on agriculture - is critical for making sound planning decisions in the face of expected hydrological changes associated with global climate change. As part of a US National Science Foundation-funded project (Tree Ring Reconstructions of Asian Monsoon Climate Variability) we have produced climate-responsive tree-ring records from tropical Asia that span the past five centuries. We find compelling evidence for 18th century decadal-scale summer monsoon droughts that span from India to Vietnam. Historical records corroborate that periods of severe drought occurred across much of the region during this time, while speleothem and coral records suggest multiple decadal-scale droughts for much of the Little Ice Age period in India, and elevated Sea Surface Temperature (SST) during the 18th century for much of the tropical Pacific, respectively. Tropical Pacific SST anomalies are seen as one key component to monsoon variability over the study region, with El Ni?o and La Ni?a like conditions resulting in rainfall reductions and increases, respectively, with corresponding opposite-sign anomalies across much of western North America. Persistent anomaly trends in the SST fields can result in the kinds of decadal-scale variability our studies suggest, although this is not the entire story. We explore the role of the Interdecadal Pacific Oscillation (IPO), first defined in 1999 as a Pacific-wide measure of variability that is physically distinct from both the Pacific Decadal Oscillation (PDO) and the El Ni?o Southern Oscillation (ENSO), in contributing to protracted -mega-droughts" in the region related to weakening monsoon strength, as suggested by recent research. Interestingly, near-millennium-aged conifers from Vietnam and Laos have been located and much longer records are now being constructed. Of great interest is the period of the late 14th and early 15th centuries when a very week monsoon is thought to have occurred, possibly contributing to the demise of the Angkor Wat civilization in Cambodia.
Increment cores and stems were obtained from trees grown in arsenic (As) contaminated soil at the... more Increment cores and stems were obtained from trees grown in arsenic (As) contaminated soil at the US EPA Vineland Superfund Site in New Jersey. The tree-ring widths were measured and crossdated to produce chronologies that were then compared with control chronologies created from trees sampled in nearby uncontaminated areas. Dendrochemical analysis by wet digestion and High Resolution Inductively Coupled Plasma
Clim Dynam, 2003
The climate of Labrador is uniquely influenced by Labrador Sea atmosphere-ocean dynamics and rela... more The climate of Labrador is uniquely influenced by Labrador Sea atmosphere-ocean dynamics and related sea surface temperature, sea ice and atmospheric fluctuations in the northwest Atlantic. Here we describe composite ring width and maximum latewood density white spruce records averaged over five (four for density) treeline sites in northern Labrador, spanning the past four centuries. These records correlate significantly with surface air and sea surface temperature records for the northwest Atlantic as well as with the North Atlantic Oscillation (NAO). Temperatures over Labrador appear to have been influenced by climate processes operating on interannual to multidecadal time scales over the length of the tree-ring record. The ring width composite reveals a significant (>99% level) mode of variation centered at around 40-60 years which appears to be robust over the full length of record and may correspond to multidecadal modes identified in model and instrumental studies of North Atlantic climate. The density composite indicates significant peaks at about 21-24, 9 and 2-3 years, which generally correspond to spectral modes identified for the NAO. This density series also shows a significant (>99% level) mode of variation at 3.6 years, which is statistically coherent with the winter (DJF) Southern Oscillation Index. This mode decreases in amplitude in the 1800s period of the Little Ice Age, one of the lowest growth periods in the Labrador tree-ring series as well as other northern temperature proxies. This period was also a time of diminished solar activity and several major volcanic events, including the eruption of Tambora in 1815. The ensuing summer of 1816 was the coldest over the past four centuries as inferred from the Labrador density composite. Hardships suffered by Labrador Inuit resulting from the extreme cold period of 1816-17 are mentioned in Moravian mission records. Archaeological and ethnohistorical data also document shifts in the subsistence practices and settlement patterns of Labrador Inuit throughout the 1800s. Many of the cultural changes have been attributed to the effects of European settlement of the region, but may also be a response to the severe climatic conditions during this time.
Clim Dynam, 2000
We describe an improved tree-ring reconstruction of mean warm-season (November-April) temperature... more We describe an improved tree-ring reconstruction of mean warm-season (November-April) temperatures for Tasmania from Huon pine. This record extends back to 1600 BC and is based on a tree-ring chronology that was processed to retain as much low-frequency variance as possible. The resulting reconstruction explains 46.6% of the variance and verifies significantly when compared to withheld instrumental data. Cross-spectral analysis of actual and estimated temperatures over the 1886-1991 common period indicates that most of the unexplained variance is at periods < 12 years in length. At periods > 12 years, the squared coherency ranges between 0.6-0.8, and the cross-spectral gain indicates that the amplitude of the reconstruction is a nearly unbiased estimate of the true temperature amplitude. Therefore, this reconstruction should be especially useful for studying multi-decadal temperature variability in the Tasmanian sector of the Southern Hemisphere over the past 3592 years. To this end, we examined the time evolution of low-frequency temperature amplitude fluctuations and found evidence for a 35% amplitude reduction after AD 100 that persisted until about AD 1900. Since that time, the low-frequency temperature amplitude has systematically increased. We also show how this reconstruction is related to large-scale sea surface temperatures (SST) in the Indian Ocean and eastward to the dateline. Pointwise correlations between the Tasmanian record and SSTs reveal a relationship that extends across the southern Indian Ocean and towards the Arabian Sea. This pattern is largely determined by inter-decadal temperature variability, with correlations in this > 10-year bandwidth commonly exceeding 0.6 over most of the southern Indian and southwestern Pacific sectors. A rotated empirical orthogonal function analysis reveals that the pattern of pointwise correlations found between the temperature reconstruction and SSTs is largely explained by the linear combination of three orthogonal modes of SST variability.
Recently, a network of gridded PDSI reconstructions for the contiguous United States was produced... more Recently, a network of gridded PDSI reconstructions for the contiguous United States was produced, based on the available network of drought-sensitive tree-ring chronologies (Cook et al. 1999). Analyses were constrained to the common period of 1700 - 1979 due to the limitations of the available tree-ring data. While several chronologies from the western U.S. span 1,000 years or more, very few chronologies from the eastern U.S. covered even the past 500 years. The objective of this project, funded by the National Science Foundation's ESH program, is to extend the tree-ring chronology network from the eastern U.S. with chronologies spanning the past 500-1,000 years. This aim is being achieved by sampling in areas that have escaped the effects of development, logging and major disturbance such as fire. The two main target species are Thuja occidentalis (eastern white cedar) and Juniperus virginiana (eastern red cedar). The primary terrain types are on cliffs, rocky outcrops, and other areas that have been difficult to access. We have already developed chronologies from Wisconsin, New Hampshire, Pennsylvania, West Virginia, and Virginia that span from 500 to 1500 years. The temporal depth of these chronologies is being extended through the exploitation of "sub-fossil" wood found at these sites, in the form of standing-dead stems and downed and buried logs. We are also currently pursuing leads in Maine, Vermont, Massachusetts, Connecticut, New York, New Jersey Pennsylvania, Kentucky and North Carolina where old cedar trees have either been reported or where terrain types match criteria developed for this project. In this paper we discuss the current status of the network, and explore the spatio-temporal characteristics of climate and drought across the eastern US for the past 500 years and more. We use our preliminary network to explore the regional expression of climate anomalies such as drought. Our analyses so far demonstrates multicentennial variability suggestive of Medieval Warm Period (MWP) and Little Ice Age (LIA) type signatures from an eastern red cedar chronology from West Virginia that spans the past 1,500 years. This is the oldest chronology so far developed from this project, though we anticipate the development of several more millennial length time-series within the next year. References Cook, E.R., Meko, D.M., Stahle, D.W., and Cleaveland, M.K. 1999. Drought reconstructions for the continental United States. Journal of Climate 12:1145-1162.
Http Dx Doi Org 10 1175 2011jcli3911 1, Jul 1, 2011
Agu Fall Meeting Abstracts, Dec 1, 2007
We use coral and tree-ring proxies to reconstruct spatiotemporal patterns of Indian Ocean sea sur... more We use coral and tree-ring proxies to reconstruct spatiotemporal patterns of Indian Ocean sea surface temperature (SST) anomalies over the last several centuries. Tropical proxies including Indonesian tree-ring chronologies and coral oxygen isotope series from sites within the region permit skillful estimates of the leading mode of Indian Ocean variability since 1750. Extratropical tree-ring chronologies from continental Asia extend the reconstruction back to the period of the Medieval Climate Anomaly. We examine the sensitivity of our climate field reconstructions to season, proxy selection, and methodology, and assumptions of stationarity. Patterns of low frequency variability in the Indian Ocean and Arabian Sea are compared to marine and terrestrial instrumental fields and paleoclimate reconstructions in order to identify relationships between SST anomalies and changes in the characteristics of the Asian monsoon.
Agu Fall Meeting Abstracts, Dec 1, 2006
No current tree-ring (TR) based reconstruction of Northern Hemisphere (NH) temperatures, that ext... more No current tree-ring (TR) based reconstruction of Northern Hemisphere (NH) temperatures, that extends into the 1990s, captures the full range of late 20th century warming observed in the instrumental record. Over recent decades, a clear divergence between large-scale reconstructed (colder) and instrumental temperatures (warmer) is observed. We hypothesize that this problem is partly related to the fact that some of the constituent chronologies used for previous reconstructions show divergence against local temperatures in the recent period. In this study, we compiled TR data and published local-regional reconstructions that show no divergence against local temperatures. These data have not been included in other large scale temperature reconstructions. Utilizing this data-set, we developed a new completely independent reconstruction of NH temperatures (1750-2000). Although the mean over the 1976-2000 period is still lower in the reconstruction compared to the instrumental data, the new series tracks the increase in NH temperatures over the last few decades reasonably well (within the error range of the calibration). This record is not meant to replace existing reconstructions, but rather to demonstrate that TR data can successfully model recent warming at large- scales when careful selection of constituent chronologies is made. We finally discuss possible reasons why it is so difficult to model recent post-1976 warming and describe several criteria that should be followed in future NH reconstruction attempts that should result in more robust large scale temperature reconstructions.
We present the first spatial reconstructions of Asian monsoon climate variability over the past m... more We present the first spatial reconstructions of Asian monsoon climate variability over the past millennium from long tree-ring records. The reconstructions, for both the monsoon (JJA) and pre-monsoon (MAM) seasons, are based on a 534-point grid of instrumental Palmer Drought Severity Indices (PDSI) covering all of monsoon Asia and an irregular network of 312 annual tree-ring chronologies over most of
Climatic Variations and Forcing Mechanisms of the Last 2000 Years, 1996
Palaeogeography, Palaeoclimatology, Palaeoecology, 1996
Long instrumental or proxy climatic records are scarce for the Southern Hemisphere relative to ma... more Long instrumental or proxy climatic records are scarce for the Southern Hemisphere relative to many northern regions, but are essential for a global perspective of past climate variability. In this paper we describe two tree-ring width chronologies of pink pine which are the first published for Stewart Island, New Zealand (47°S, 168°E), one of the southernmost forested land masses on the globe. A chronology for western-central Stewart Island (Doughboy-Rakeahua) extends from 1682 to 1990; the other, for southern Stewart Island (Pegasus) from 1690 to 1991. Both series are positively correlated with warm-season surface air temperatures for southern New Zealand and vicinity. Although there are shorter intervals of comparable warmth, the highest 20-year periods of growth during the past 300 years occurred during the middle 1950s-1970s, coinciding with record warming since around 1950 in New Zealand. Chronologies developed from two related species: silver pine (Lagarostrobus colensoi) from Ahaura, western South Island, New Zealand, and huon pine (Lagarostrobus franklinii) from Tasmania also indicate recent warming which is unusual, although not statistically unprecedented, within the contexts of the past 642 and 2290 years of record, respectively.
Journal of Geophysical Research: Atmospheres, 2013
1] We analyze multiple global reanalysis and precipitation datasets in order to explain the dynam... more 1] We analyze multiple global reanalysis and precipitation datasets in order to explain the dynamic mechanisms that lead to an observed intensification of the monsoon trough and associated tropical cyclone (TC) activity over the Bay of Bengal (BOB) during the premonsoon month of May. We find that post-1979 increases in both premonsoon precipitation and TC intensity are a result of enhanced large-scale monsoon circulation, characterized by lower-level cyclonic and upper-level anticyclonic anomalies. Such circulation anomalies are manifest of the tropospheric expansion that is caused by regional warming. The deepened monsoon trough in the BOB not only affects TC frequency and timing, but also acts to direct more cyclones towards Myanmar. We propose that increasing sea surface temperature in the BOB has contributed to an increase in cyclone intensity. Our analyses of the Community Earth System Model single-forcing experiments suggest that tropospheric warming and a deepening of the monsoon trough can be explained by two discreet anthropogenic causes-an increase in absorption due to aerosol loading and an increase in the land-ocean thermal contrast that results from increased greenhouse gases. The ensuing circulation changes provide favorable conditions for TCs to grow and to track eastward towards Myanmar.
The Asian monsoon system can be studied using a complementary proxy/simulation approach which eva... more The Asian monsoon system can be studied using a complementary proxy/simulation approach which evaluates climate models using estimates of past precipitation and temperature, and which subsequently applies the best understanding of the physics of the climate system as captured in general circulation models to evaluate the broad-scale dynamics behind regional paleoclimate reconstructions. Here, we use a millennial-length climate field reconstruction
ABSTRACT Increment cores and stems were obtained from trees grown in arsenic (As) contaminated so... more ABSTRACT Increment cores and stems were obtained from trees grown in arsenic (As) contaminated soil at the US EPA Vineland Superfund Site in New Jersey. The tree-ring widths were measured and crossdated to produce chronologies that were then compared with control chronologies created from trees sampled in nearby uncontaminated areas. Dendrochemical analysis by wet digestion and High Resolution Inductively Coupled Plasma Mass Spectrometry (HR ICP-MS) confirmed little As incorporation (0.05-1.0 ppm) in the xylem rings, and showed species-specific patterns in annual rings. Trees grown in As-contaminated soils had much higher xylem As than those from uncontaminated areas. Within individual trees, As levels were highest in the leaves, followed by the pith and bark, and are lowest in the xylem rings. These levels are several orders of magnitude lower than reported levels in roots and soils. Low growth periods in one pine sample, most notably in 1960&#39;s, appear to follow regional growth trends and correspond with higher As levels. One oak sample showed a unique fast growth period with normal As levels from 1955 to 1970, but a higher As period in the 1980&#39;s and early 1990&#39;s with no apparent growth anomaly. These periods may be related to either regional climatic, or local hydrologic and environmental changes induced by the operation of the Vineland Chemical Company and As disposal. The nutrient levels in xylem rings show little correlation with As. Our tree ring As results support the possibility of using As levels and profiles as a biomarker for local environmental contamination.
SUMMARY New data added to the exi sting tree-ring width chronologie s of moun tain pine (Pinus k... more SUMMARY New data added to the exi sting tree-ring width chronologie s of moun tain pine (Pinus kesiya and Pinus merkusiii result in a total of se ven chronologies for these speci es for Thailand. The olde st (1647-1993) is from a P merkusii site at Phu Kradung. north central Thailand. An anal ysis of the three longest P. kesiya
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Papers by Brendan M Buckley