World Data Center for Paleoclimatology, NCDC Paleoclimatology Branch

What's New on the Paleo Web Pages for 2005

	Atmospheric methane and nitrous oxide of the late Pleistocene from Antarctic ice cores Spahni et al. Science Vol. 310, Issue 5752, pp. 1317-1321, 25 November 2005. The European Project for Ice Coring in Antarctica Dome C ice core enables us to extend existing records of atmospheric methane (CH₄) and nitrous oxide (N₂O) back to 650,000 years before the present. A combined record of CH₄ measured along the Dome C and the Vostok ice cores demonstrates, within the resolution of our measurements, that preindustrial concentrations over Antarctica have not exceeded 773 +/- 15 ppbv (parts per billion by volume) during the past 650,000 years. Before 420,000 years ago, when interglacials were cooler, maximum CH₄ concentrations were only about 600 ppbv, similar to lower Holocene values. In contrast, the N₂O record shows maximum concentrations of 278 +/- 7 ppbv, slightly higher than early Holocene values.
	Stable Carbon Cycle-Climate Relationship During the Late Pleistocene Siegenthaler et al. Science Vol. 310, Issue 5752, pp. 1313-1317, 25 November 2005. A record of atmospheric carbon dioxide (CO2) concentrations measured on the EPICA (European Project for Ice Coring in Antarctica) Dome Concordia ice core extends the Vostok CO2 record back to 650,000 years before the present (yr B.P.). Before 430,000 yr B.P., partial pressure of atmospheric CO2 lies within the range of 260 and 180 parts per million by volume. This range is almost 30% smaller than that of the last four glacial cycles; however, the apparent sensitivity between deuterium and CO2 remains stable throughout the six glacial cycles, suggesting that the relationship between CO2 and Antarctic climate remained rather constant over this interval.
	A 70-kyr sea surface temperature record off southern Chile (Ocean Drilling Program Site 1233) Kaiser et al. Paleoceanography Vol. 20, PA4009, October 2005 We present the first high-resolution alkenone-derived sea surface temperature (SST) reconstruction in the southeast Pacific (Ocean Drilling Program Site 1233) covering the major part of the last glacial period and the Holocene. The record shows a clear millennial-scale pattern that is very similar to climate fluctuations observed in Antarctic ice cores, suggesting that the Southern Hemisphere high-latitude climate changes extended into the midlatitudes, involving simultaneous changes in air temperatures over Antarctica, sea ice extent, extension of the Antarctic Circumpolar Current, and westerly atmospheric circulation. A comparison to other midlatitude surface ocean records suggests that this "Antarctic" millennial-scale pattern was probably a hemisphere-wide phenomenon. In addition, we performed SST gradient reconstructions over the complete latitudinal range of the Pacific Eastern Boundary Current System for different time intervals during the last 70 kyr. The main results suggest an equatorward displaced subtropical gyre circulation during marine isotope stages 2 and 4.
	Temperature and Precipitation Variability in the European Alps Since 1500. Casty et al. International Journal of Climatology Volume 25, Issue 14, pp. 1855-1880, 30 November 2005 High-resolution temperature and precipitation variations and their seasonal extremes since 1500 are presented for the European Alps (43.25-48.25 °N and 4.25-16.25 °E). The spatial resolution of the gridded reconstruction is given by 0.5° x 0.5° and monthly (seasonal) grids are reconstructed back to 1659 (1500-1658). The reconstructions are based on a combination of long instrumental station data and documentary proxy evidence applying principal component regression analysis.
	Preindustrial to modern interdecadal variability in coral reef pH Pelejero et al. Science Volume 309, No. 5744, pp. 2204-2207, 30 September 2005 The oceans are becoming more acidic due to absorption of anthropogenic carbon dioxide from the atmosphere. The impact of ocean acidification on marine ecosystems is unclear, but it will likely depend on species adaptability and the rate of change of seawater pH relative to its natural variability. To constrain the natural variability in reef-water pH, we measured boron isotopic compositions in a ~300-year-old massive Porites coral from the southwestern Pacific. Large variations in pH are found over ~50-year cycles that covary with the Interdecadal Pacific Oscillation of ocean-atmosphere anomalies, suggesting that natural pH cycles can modulate the impact of ocean acidification on coral reef
	Reconstructed Temperature and Precipitation on a Millennial Timescale from Tree-Rings in the Southern Colorado Plateau, U.S.A. Salzer and Kipfmueller Climatic Change Volume 70, Number 3, pp. 465 - 487, June 2005 Two independent calibrated and verified climate reconstructions from ecologically contrasting tree-ring sites in the southern Colorado Plateau, U.S.A. reveal decadal-scale climatic trends during the past two millennia. Combining precisely dated annual mean-maximum temperature and October through July precipitation reconstructions yields an unparalleled record of climatic variability. The approach allows for the identification of thirty extreme wet periods and thirty-five extreme dry periods in the 1,425-year precipitation reconstruction and 30 extreme cool periods and 26 extreme warm periods in 2,262-year temperature reconstruction.
	Extracting a Climate Signal from 169 Glacier Records Oerlemans Science Vol. 308, No. 5722, pp. 675-677, 29 April 2005. I constructed a temperature history for different parts of the world from 169 glacier length records. Using a first-order theory of glacier dynamics, I related changes in glacier length to changes in temperature. The derived temperature histories are fully independent of proxy and instrumental data used in earlier reconstructions. Moderate global warming started in the middle of the 19th century. The reconstructed warming in the first half of the 20th century is 0.5 kelvin. This warming was notably coherent over the globe. The warming signals from glaciers at low and high elevations appear to be very similar.
	Eocene bipolar glaciation associated with global carbon cycle changes Tripati et al. Nature Vol. 436, Number 7049, pp.341-346, 21 July 2005 doi: 10.1038/nature03874. The transition from the extreme global warmth of the early Eocene 'greenhouse' climate, ~55 million years ago to the present glaciated state is one of the most prominent changes in Earth's climatic evolution. It is widely accepted that large ice sheets first appeared on Antarctica ~34 million years ago, coincident with decreasing atmospheric carbon dioxide concentrations and a deepening of the calcite compensation depth in the world's oceans. Here we present records of sediment and foraminiferal geochemistry covering the greenhouse-icehouse climate transition. We suggest that the greenhouse-icehouse transition was closely coupled to the evolution of atmospheric carbon dioxide, and that negative carbon cycle feedbacks may have prevented the permanent establishment of large ice sheets earlier than 34 million years ago.
	Reconstruction of temperature in the Central Alps during the past 2000 yr from a d18O stalagmite record. Mangini et al. Earth and Planetary Science Letters Vol. 235, Issues 3-4, Pages 741-751, 15 July 2005. doi:10.1016/j.epsl.2005.05.010 The precisely dated isotopic composition of a stalagmite from Spannagel Cave in the Central Alps is translated into a highly resolved record of temperature at high elevation during the past 2000 yr. Temperature maxima during the Medieval Warm Period between 800 and 1300 AD are in average about 1.7°C higher than the minima in the Little Ice Age and similar to present-day values. The high correlation of this record to Δ14C suggests that solar variability was a major driver of climate in Central Europe during the past 2 millennia.
	Insolation-driven changes in atmospheric circulation over the past 116,000 years in subtropical Brazil Cruz et al. Nature Vol. 434, No. 7029, pp. 63 - 66, 3 March 2005. During the last glacial period, large millennial-scale temperature oscillations-the 'Dansgaard/Oeschger' cycles-were the primary climate signal in Northern Hemisphere climate archives from the high latitudes to the tropics. But whether the influence of these abrupt climate changes extended to the tropical and subtropical Southern Hemisphere, where changes in insolation are thought to be the main direct forcing of climate, has remained unclear. Here we present a high-resolution oxygen isotope record of a U/Th-dated stalagmite from subtropical southern Brazil, covering the past 116,200 years. The oxygen isotope signature varies with shifts in the source region and amount of rainfall in the area, and hence records changes in atmospheric circulation and convective intensity over South America. We find that these variations in rainfall source and amount are primarily driven by summer solar radiation, which is controlled by the Earth's precessional cycle. The Dansgaard/ Oeschger cycles can be detected in our record and therefore we confirm that they also affect the tropical hydrological cycle, but that in southern subtropical Brazil, millennial-scale climate changes are not as dominant as they are in the Northern Hemisphere.
	Highly variable Northern Hemisphere temperatures reconstructed from low- and high-resolution proxy data Moberg et al. Nature Vol. 433, No. 7026, pp. 613 - 617, 10 February 2005. A number of reconstructions of millennial-scale climate variability have been carried out in order to understand patterns of natural climate variability, on decade to century timescales, and the role of anthropogenic forcing. These reconstructions have mainly used tree-ring data and other data sets of annual to decadal resolution. Lake and ocean sediments have a lower time resolution, but provide climate information at multicentennial timescales that may not be captured by tree-ring data. Here we reconstruct Northern Hemisphere temperatures for the past 2,000 years by combining low-resolution proxies with tree-ring data, using a wavelet transform technique to achieve timescale-dependent processing of the data. Our reconstruction shows larger multicentennial variability than most previous multi-proxy reconstructions, but agrees well with temperatures reconstructed from borehole measurements and with temperatures obtained with a general circulation model. According to our reconstruction, high temperatures - similar to those observed in the twentieth century before 1990- occurred around AD 1000 to 1100, and minimum temperatures that are about 0.7K below the average of 1961-90 occurred around AD 1600. This large natural variability in the past suggests an important role of natural multicentennial variability that is likely to continue.
	High-latitude influence on the eastern equatorial Pacific climate in the early Pleistocene epoch Liu and Herbert Nature Vol. 427, No. 6976, pp. 720 - 723, 19 February 2004. Many records of tropical sea surface temperature and marine productivity exhibit cycles of 23 kyr (orbital precession) and 100 kyr during the past 0.5Myr, whereas high-latitude sea surface temperature records display much more pronounced obliquity cycles at a period of about 41 kyr. Little is known, however, about tropical climate variability before the mid-Pleistocene transition about 900 kyr ago, which marks the change from a climate dominated by 41-kyr cycles (when ice-age cycles and high-latitude sea surface temperature variations were dictated by changes in the Earth�s obliquity) to the more recent 100-kyr cycles of ice ages. Here we analyse alkenones from marine sediments in the eastern equatorial Pacific Ocean to reconstruct sea surface temperatures and marine productivity over the past 1.8Myr. We find that both records are dominated by the 41-kyr obliquity cycles between 1.8 and 1.2Myr ago, with a relatively small contribution from orbital precession, and that early Pleistocene sea surface temperatures varied in the opposite sense to local annual insolation in the eastern equatorial Pacific Ocean. We conclude that during the early Pleistocene epoch, climate variability at our study site must have been determined by high-latitude processes that were driven by orbital obliquity forcing.
	An unusually active Sun during recent decades compared to the previous 11,000 years. Solanki et al. Nature Vol. 431, No.7012, pp.1084-1087, 28 October 2004. Direct observations of sunspot numbers are available for the past four centuries, but longer time series are required, for example, for the identification of a possible solar influence on climate and for testing models of the solar dynamo. Here we report a reconstruction of the sunspot number covering the past 11,400 years, based on dendrochronologically dated radiocarbon concentrations. We combine physics-based models for each of the processes connecting the radiocarbon concentration with sunspot number. According to our reconstruction, the level of solar activity during the past 70 years is exceptional, and the previous period of equally high activity occurred more than 8,000 years ago. We find that during the past 11,400 years the Sun spent only of the order of 10% of the time at a similarly high level of magnetic activity and almost all of the earlier high-activity periods were shorter than the present episode. Although the rarity of the current episode of high average sunspot numbers may indicate that the Sun has contributed to the unusual climate change during the twentieth century, we point out that solar variability is unlikely to have been the dominant cause of the strong warming during the past three decades.
	Stable sea surface temperatures in the western Pacific warm pool over the past 1.75 million years de Garidel-Thoron et al. Nature Vol. 433, No.7023, 20 January 2005. About 850,000 years ago, the period of the glacial cycles changed from 41,000 to 100,000 years. This mid-Pleistocene climate transition has been attributed to global cooling, possibly caused by a decrease in atmospheric carbon dioxide concentrations. However, evidence for such cooling is currently restricted to the cool upwelling regions in the eastern equatorial oceans, although the tropical warm pools on the western side of the ocean basins are particularly sensitive to changes in radiative forcing. Here we present high-resolution records of sea surface temperatures spanning the past 1.75 million years, obtained from oxygen isotopes and Mg/Ca ratios in planktonic foraminifera from the western Pacific warm pool. In contrast with the eastern equatorial regions, sea surface temperatures in the western Pacific warm pool are relatively stable throughout the Pleistocene epoch, implying little long-term change in the tropical net radiation budget. Our results challenge the hypothesis of a gradual decrease in atmospheric carbon dioxide concentrations as a dominant trigger of the longer glacial cycles since 850,000 years ago. Instead, we infer that the temperature contrast across the equatorial Pacific Ocean increased, which might have had a significant influence on the mid-Pleistocene climate transition.
	Grape ripening as a past climate indicator Chuine et al. Nature Vol. 432, No.7015, 18 November 2004. French records of grape-harvest dates in Burgundy were used to reconstruct spring-summer temperatures from 1370 to 2003 using a process-based phenology model developed for the Pinot Noir grape. Our results reveal that temperatures as high as those reached in the 1990s have occurred several times in Burgundy since 1370. However, the summer of 2003 appears to have been extraordinary, with temperatures that were probably higher than in any other year since 1370.
	Antarctic Timing of Surface Water Changes off Chile and Patagonian Ice Sheet Response. Lamy et al. Science Vol. 304, No. 5679, pp.1959-1962, 25 June 2004. Marine sediments from the Chilean continental margin are used to infer millennial-scale changes in southeast Pacific surface ocean water properties and Patagonian ice sheet extent since the last glacial period. Our data show a clear "Antarctic" timing of sea surface temperature changes, which appear systematically linked to meridional displacements in sea ice, westerly winds, and the circumpolar current system. Proxy data for ice sheet changes show a similar pattern as oceanographic variations offshore, but reveal a variable glacier-response time of up to ~1000 years, which may explain some of the current discrepancies among terrestrial records in southern South America.


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