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What's New on the Paleo Web Pages - 2002

What's New in 2002:
Grazing Bison.  Yellowstone National Park photo Drought in the Western Great Plains, 1845-56: Impacts and Implications
Woodhouse et al., Bulletin of the American Meteorological Society
83, 1485-1493, October 2002.

A sustained mid-19th century drought in the western Great Plains has been indicated by analyses of trees flanking the western Great Plains. The development of new tree-ring chronologies for the western Great Plains, now enables a more detailed assessment of the spatial and temporal characteristics of this drought. The analysis indicates a core area of drought from south-central Wyoming to northeastern New Mexico for the years 1845-56. Drought was particularly severe in the years 1845-48, 1851, and 1854-56, contracting and affecting smaller regions in intervening years. The impact of this drought on natural ecosystems and human activities is difficult to gauge. However, it is probable that this drought played a role in the decimation of bison herds in the second half of the 19th century. Were it to occur today, this relatively small but persistent drought would have significant impacts on the Colorado Front Range metropolitan area and the agricultural regions of eastern Colorado.

New Mexico Neural Network Precipitation Reconstructions Cool-season precipitation in the southwestern USA since AD 1000: comparison of linear and nonlinear techniques for reconstruction
Ni et al., International Journal of Climatology
Volume 22, Issue 13, pp. 1645 - 1662, doi:10.1002/joc.804.

A 1000 year reconstruction of cool-season (November-April) precipitation was developed for each climate division in Arizona and New Mexico from a network of 19 tree-ring chronologies in the southwestern USA. Linear regression (LR) and artificial neural network (NN) models were used to identify the cool-season precipitation signal in tree rings. In most of the climate divisions, both techniques can successfully reconstruct dry and normal years, and the NN seems to capture large precipitation events and more variability better than the LR. In the 1000 year reconstructions the NN also produces more distinctive wet events and more variability, whereas the LR produces more distinctive dry events. The 1000 year reconstructed precipitation from the two models shows several sustained dry and wet periods comparable to the 1950s drought (e.g. 16th century mega drought) and to the post-1976 wet period (e.g. 1330s, 1610s).

Snow accumulation, Mt. Logan, Yukon Climate change in the North Pacific region over the past three centuries
Moore et al., Nature, 420, 6914, 401-403; doi:10.1038/nature01229, 28 November 2002.

We present a 301-year snow accumulation record from an ice core at a height of 5,340 m above sea level - from Mount Logan, in northwestern North America. This record shows features that are closely linked with the Pacific North America pattern for the period of instrumental data availability. Our record extends back in time to cover the period from the closing stages of the Little Ice Age to the warmest decade in the past millennium. We find a positive, accelerating trend in snow accumulation after the middle of the nineteenth century. This trend is paralleled by a warming over northwestern North America which has been associated with secular changes in both the Pacific North America pattern and the Pacific Decadal Oscillation.

Extracting a sediment core from Echo Lake, Plymouth, Vermont. Millennial-scale Storminess Variability in the Northeastern United States during the Holocene Epoch
Noren et al., Nature, 419, 821 - 824; doi:10.1038/nature01132, 24 October 2002.

The study of natural change in past climate has proved particularly difficult with regard to the variability in the occurrence of extreme climate events, such as storms with exceptional rainfall. Previous investigations have established storm chronologies using sediment cores from single lakes, but such studies can be susceptible to local environmental bias. Here we date terrigenous inwash layers in cores from 13 lakes, which show that the frequency of storm-related floods in the northeastern United States has varied in regular cycles during the past 13,000 years (13 kyr), with a characteristic period of about 3 kyr. Our data show four peaks in storminess during the past 14 kyr, approximately 2.6, 5.8, 9.1 and 11.9 kyr ago. This pattern is consistent with long-term changes in the average sign of the Arctic Oscillation, suggesting that modulation of this dominant atmospheric mode may account for a significant fraction of Holocene climate variability in North America and Europe.

Laguna Pallcacocha, Ecuador Variability of El Niņo/Southern Oscillation activity at millennial timescales during the Holocene epoch
Moy et al., Nature, 420, 162 - 165; doi:10.1038/nature01194, 14 November 2002.

The variability of El Niņo/Southern Oscillation (ENSO) during the Holocene epoch, in particular on millennial timescales, is poorly understood. Palaeoclimate studies have documented ENSO variability for selected intervals in the Holocene, but most records are either too short or insufficiently resolved to investigate variability on millennial scales. Here we present a record of sedimentation in Laguna Pallcacocha, southern Ecuador, which is strongly influenced by ENSO variability, and covers the past 12,000 years continuously. We find that changes on a timescale of 2-8 years, which we attribute to warm ENSO events, become more frequent over the Holocene until about 1,200 years ago, and then decline towards the present. Periods of relatively high and low ENSO activity, alternating at a timescale of about 2,000 years, are superimposed on this long-term trend. We attribute the long-term trend to orbitally induced changes in insolation, and suggest internal ENSO dynamics as a possible cause of the millennial variability.

Kilimanjaro Kilimanjaro Ice Core Records: Evidence of Holocene Climate Change in Tropical Africa
Thompson et al., Science, Volume 298, 5593, 18 October 2002.

Six ice cores from Kilimanjaro provide an ~11.7-thousand-year record of Holocene climate and environmental variability for eastern equatorial Africa, including three periods of abrupt climate change: ~8.3, ~5.2, and ~4 thousand years ago (ka). The latter is coincident with the "First Dark Age," the period of the greatest historically recorded drought in tropical Africa. Variable deposition of F- and Na+ during the African Humid Period suggests rapidly fluctuating lake levels between ~11.7 and 4 ka. Over the 20th century, the areal extent of Kilimanjaro's ice fields has decreased ~80%, and if current climatological conditions persist, the remaining ice fields are likely to disappear between 2015 and 2020.

China Temperature reconstructions General characteristics of temperature variation in China during the last two millennia.
Yang et al., Geophysical Research Letters, 10.1029/2001GL014485, 11 May 2002

Three alternate China-wide temperature composites covering the last 2000 years were established by combining multiple paleoclimate proxy records obtained from ice cores, tree rings, lake sediments and historical documents. Five periods of temperature variation can be identified: a warm stage in AD 0-240, a cold interval between AD 240 and 800, a return to warm conditions from AD 800-1400, including the Medieval Warm Period between AD 800-1100, the cool Little Ice Age period between 1400-1920, and the present warm stage since 1920. The temperature reconstructions for China and the Northern Hemisphere show good agreement over the past millennium.

WDC for Paleoclimatology Mirror Sites Two New WDC-Paleo Mirror Sites in Asia

The World Data Center for Paleoclimatology is pleased to welcome two new Asian mirror sites to the family. These new mirrors are located in Lanzhou, China at the Cold and Arid Regions Environmental and Engineering Research Institute, and in Pune, India at the Indian Institute of Tropical Meteorology.

Red River Valley, Manitoba, Canada Hydroclimatic change in southern Manitoba since A.D. 1409 inferred from tree rings.
Scott St. George and Erik Nielsen Quaternary Research, Volume 58, pp. 103-111, September 2002.

A record of estimated annual (prior August to current July) precipitation derived from a regional bur oak (Quercus macrocarpa Michx.) tree-ring chronology indicates that southern Manitoba's hydroclimate has been relatively stable over the last 200 years. The reconstruction indicates that the Red River basin experienced extremely dry conditions between A.D. 1670 and 1775, with below-normal precipitation occurring approximately 2 years out of 3. Annual precipitation was estimated at more than two standard deviations below the mean during A.D. 1477, 1485, 1556, 1595, 1612, 1644, 1661, 1743, 1900, and 1980. Comparisons with limnological records from North Dakota and Minnesota suggest that multidecadal fluctuations in regional hydroclimate have been remarkably coherent across the northeastern Great Plains during the last 600 yr.

North Atlantic Oscillation Reconstruction A Well-Verified, Multiproxy Reconstruction of the Winter North Atlantic Oscillation Index since A.D. 1400
Cook et al., Journal of Climate, Volume 15, pp. 1754-1764, 2002.

A new, well-verified, multiproxy reconstruction of the winter North Atlantic Oscillation (NAO) index is described that can be used to examine the variability of the NAO prior to twentieth century greenhouse forcing. It covers the period A.D. 1400-1979 and successfully verifies against independent estimates of the winter NAO index from European instrumental and noninstrumental data as far back as 1500. This result is a significant improvement over previous proxy-based estimates, which often failed to verify prior to 1850, and is related to the use of an extended reconstruction model calibration period that reduced an apparent bias in selected proxies associated with the impact of anomalous twentieth century winter NAO variability on climate teleconnections over North Atlantic sector land areas.

Pyramid Island and Pyramid Lake, Nevada Holocene multidecadal and multicentennial droughts affecting Northern California and Nevada
Benson et al., Quaternary Science Reviews Volume 21, No. 4-6, February 2002.

Continuous, high-resolution d18O records from cored sediments of Pyramid Lake, Nevada, indicate that oscillations in the hydrologic balance occurred, on average, about every 150 years (yr) during the past 7630 calendar years (calyr). The records are not stationary; during the past 2740yr, drought durations ranged from 20 to 100yr and intervals between droughts ranged from 80 to 230yr. Comparison of tree-ring-based reconstructions of climate change for the past 1200yr from the Sierra Nevada and the El Malpais region of northwest New Mexico indicates that severe droughts associated with Anasazi withdrawal from Chaco Canyon at 820calyrBP (calendar years before present) and final abandonment of Chaco Canyon, Mesa Verde, and the Kayenta area at 650calyrBP may have impacted much of the western United States.

Indian Monsoon Diagram, NASA GSFC Increase in the Asian SW Monsoon During the Past Four Centuries
Anderson et al., Science Volume 297, Number 5581, 26 July 2002.

Climate reconstructions reveal unprecedented warming in the last century, however little is known about trends in aspects such as the monsoon. We reconstructed the monsoon winds for the last 1,000 years using fossil Globigerina bulloides abundance in box cores from the Arabian Sea, and found that monsoon wind strength increased during the past 4 centuries, as the northern hemisphere warmed. We infer that the observed link between Eurasian warmth/ snow cover and the SW monsoon persists on the centennial scale. Alternately, the forcing implicated in the warming trend (volcanic aerosols, solar output, greenhouse gases) may directly affect the monsoon. Either interpretation is consistent with the hypothesis that the SW monsoon strength will increase during the coming century as greenhouse gas concentrations continue to rise and northern latitudes continue to warm.

Twelvemile Summit, Alaska Spatial and temporal variability in the growth and climate response of treeline trees in Alaska
Lloyd and Fastie, Climatic Change Volume 58, 481-509, 2002.

We investigated the response of trees growing at the cold margins of the boreal forest to climate variation in the 20th century. We found that there was substantial regional variability in response to climate variation. Contrary to our expectations, we found that after 1950 warmer temperatures were associated with decreased tree growth in all but the wettest region, the Alaska Range. Although tree growth increased from 1900-1950 at almost all sites, significant declines in tree growth were common after 1950 in all but the Alaska Range sites. Growth declines were most common in the warmer and drier sites, and thus support the hypothesis that drought-stress may accompany increased warming in the boreal forest.

Pacific Ocean SST High- and low-latitude climate control on the position of the southern Peru-Chile Current during the Holocene.
Lamy et al., Paleoceanography v.17-3

Reconstructed changes of paleotemperature, paleosalinity, and paleoproductivity within the southern Peru-Chile Current during the last 8,000 years using alkenones, isotope ratios of planktic foraminifera, biogenic opal, and organic carbon. Paleotemperatures and paleosalinities reached maximum values at ~5500 years and thereafter declined to modern values, whereas paleoproductivity continuously increased throughout the last 8,000 years. We ascribe these long-term Holocene trends primarily to latitudinal shifts of the Antarctic Circumpolar Current (ACC).

Gridded Lake Level Status, 12,000 Years BP Holocene variations in the global hydrological cycle quantified by objective gridding of lake level databases
Viau and Gajewski, Journal of Geophysical Research-Atmosphere
106(D23): 31703-31716.

Lake level fluctuations provide evidence about past variations in the global hydrological balance. The geostatistical approach is here used to more objectively identify global patterns using an ensemble of lake level databases by examining spatial autocorrelation between sites. The spatial structures of the lake level data are then modeled and grids produced for the last 12,000 years at 3,000 year intervals using ordinary and indicator kriging techniques. The resulting lake-status grids are in general agreement with the previous paleoclimatic reconstructions using only site-by-site lake status point maps. The 6 ka lake-status grids were compared to simulations of four atmospheric general circulation models to illustrate their usefulness in validating broad-scale climate model outputs.

Drilling rig on Fremont Glacier, Wyoming Atmospheric Mercury Deposition during the Last 270 Years: A Glacial Ice Core Record of Natural and Anthropogenic Sources
Schuster et al., Environmental Science and Technology
Volume 36, No. 11, pp.2303-2310.

Mercury (Hg) contamination of aquatic ecosystems and subsequent methylmercury bioaccumulation are significant environmental problems of global extent. At regional to global scales, the primary mechanism of Hg contamination is atmospheric Hg transport. Ice cores collected from the Upper Fremont Glacier, Wyoming, contain a high-resolution record of total atmospheric Hg deposition (ca. 1720-1993). The record indicates major atmospheric releases of both natural and anthropogenic Hg from regional and global sources. Integrated over the past 270-year ice-core history, anthropogenic inputs contributed 52%, volcanic events 6%, and background sources 42%.

New Additions to the Software Library
The NOAA Paleoclimatology Program/World Data Center for Paleoclimatology has a Free Software page from which in-house and contributed software may be downloaded free of charge. The most recent additions include PALYHELP, a set of statistical programs used in pollen analysis, and Arand, a Macintosh time series and spectral analysis package. We encourage authors of software applicable to paleoclimate and paleoecological problems to contribute their work. All software is distributed on an As-Is basis, we cannot provide technical support nor guarantee the software's performance.
Fig. 2 Dome C long term trends of CO2, CH4, and N2O High-resolution Holocene N2O ice core record and its relationship with CH4 and CO2
Flückiger et al., Global Biogeochemical Cycles
Volume 16, No. 1, March 2002.

Nitrous oxide (N2O ) concentration records exist for the last 1000 years and for time periods of rapid climatic changes like the transition from the last glacial to today's interglacial and for one of the fast climate variations during the last ice age. Little is known, however, about possible N2O variations during the more stable climate of the present interglacial (Holocene) spanning the last 11 thousand years. Here we fill this gap with a high resolution N2O record measured along the EPICA Dome C Antarctic ice core. On the same ice we obtained high resolution methane and carbon dioxide records. This provides the unique opportunity to compare variations of the three most important greenhouse gases (after water vapour) without any uncertainty in their relative timing.

Fig. 3 Southern Hemisphere surface temperature anomalies The Evolution of Climate Over the Last Millennium
Jones et al., Science
Volume 292, No. 5517, pp.662, April 27, 2001.

This article reviews present knowledge of changes in temperatures and two major circulation features--El Niņo-Southern Oscillation (ENSO) and the North Atlantic Oscillation (NAO)--over much of the last 1000 years, mainly on the basis of high-resolution paleoclimate records. Average temperatures during the last three decades were likely the warmest of the last millennium, about 0.2°C warmer than during warm periods in the 11th and 12th centuries. The 20th century experienced the strongest warming trend of the millennium (about 0.6°C per century). Some recent changes in ENSO may have been unique since 1800, whereas the recent trend to more positive NAO values may have occurred several times since 1500.

Fig. 3, Winter NAO graph Extending North Atlantic Oscillation reconstructions back to 1500
Luterbacher et al., Atmospheric Science Letters
2002, pp. 1-11 (doi:10.1006/asle.2001.0044)

Monthly (1659-2001) and seasonal (1500-1658) North Atlantic Oscillation (NAO) indices were estimated using instrumental and documentary proxy predictors from Eurasia. Uncertainty estimates were calculated for the reconstructions, and the variability of the 500-year winter NAO has been assessed. The late twentieth century NAO extremes are within the range of variability during earlier centuries.

Fig. 1 Proxy data locations and region boundaries Low-frequency Temperature Variations from a Northern Tree Ring Density Network
Briffa et al., Journal of Geophysical Research,
106 D3 (16-Feb-2001) pp. 2929-2941

We describe new reconstructions of northern extratropical summer temperatures for nine subcontinental-scale regions and a composite series representing quasi "Northern Hemisphere" temperature change over the last 600 years. These series are based on tree ring density data that have been processed using a novel statistical technique (age band decomposition) designed to preserve greater long-timescale variability than in previous analyses. The new regional estimates are generally cooler in almost all precalibration periods, compared to estimates obtained using earlier processing methods, particularly during the 17th century. We compare our new hemisphere series to other published large-regional temperature histories, most of which lie within the 1 sigma confidence band of our estimates over most of the last 600 years. The 20th century is clearly shown by all of the palaeoseries composites to be the warmest during this period.

Otolith Photomicrograph Otolith d18O Record of Mid-Holocene Sea Surface Temperatures in Peru
Andrus et al., Science
Volume 295, No. 5559, pp.1508, February 22, 2002.

Peruvian sea catfish (Galeichthys peruvianus) sagittal otoliths preserve a record of modern and mid-Holocene sea surface temperatures (SSTs). Oxygen isotope profiles in otoliths excavated from Peruvian archaeological sites record mean annual temperatures ~3° to 4°C warmer than were measured under modern conditions. Trophic level and population diversity and equitability data support the isotope interpretations and suggest that upwelling of the Peru-Chile current intensified after ~5000 yr B.P.

AIMS Coral Drilling Rig Abrupt Decrease in Tropical Pacific Sea Surface Salinity at End of Little Ice Age
Hendy et al., Science
Volume 295, No. 5559, pp.1511, February 22, 2002.

A 420-year history of strontium/calcium, uranium/calcium, and oxygen isotope ratios in eight coral cores indicates that sea surface temperature and salinity were higher in the 18th century than the 20th century. An abrupt freshening after 1870 occurred simultaneously throughout the southwestern Pacific, coinciding with cooling tropical temperatures. Higher salinities between 1565 and 1870 are best explained by a combination of advection and wind-induced evaporation resulting from a strong latitudinal temperature gradient and intensified circulation. The global Little Ice Age glacial expansion may have been driven, in part, by greater poleward transport of water vapor from the tropical Pacific.

Historical Phillipines Map Atmospheric Circulation Changes in the Tropical Pacific Inferred from the Voyages of the Manila Galleons in the Sixteenth-Eighteenth Centuries,
Garcia et al., Bulletin of the American Meteorological Society
Volume 82, Number 11, pp. 2435, November 2001.

Historical accounts of the voyages of the Manila galleons derived from the Archivo General de Indias (General Archive of the Indies, Seville, Spain) are used to infer past changes in the atmospheric circulation of the tropical Pacific Ocean. It is shown that the length of the voyage between Acapulco, Mexico, and the Philippine Islands during the period 1590-1750 exhibits large secular trends, such that voyages in the middle of the seventeenth century are some 40% longer than those at the beginning or at the end of the century, and that these trends are unlikely to have been caused by societal or technological factors. These results suggest that the atmospheric circulation of the western Pacific underwent large, multidecadal fluctuations during the seventeenth century.

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2 January 2003