P.-N. Lin

Late Glacial Stage and Holocene Tropical Ice Core Records from Huascarán, Peru

Two ice cores from the col of Huascar�n in the north-central Andes of Peru contain a paleoclimatic history extending well into the Wisconsinan (W�rm) Glacial Stage and include evidence of the Younger Dryas cool phase. Glacial stage conditions at high elevations in the tropics appear to have been as much as 8� to 12�C cooler than today, the atmosphere contained about 200 times as much dust, and the Amazon Basin forest cover may have been much less extensive. Differences in both the oxygen isotope ratio ζ18O (8 per mil) and the deuterium excess (4.5 per mil) from the Late Glacial Stage to the Holocene are comparable with polar ice core records. These data imply that the tropical Atlantic was possibly 5� to 6�C cooler during the Late Glacial Stage, that the climate was warmest from 8400 to 5200 years before present, and that it cooled gradually, culminating with the Little Ice Age (200 to 500 years before present). A strong warming has dominated the last two centuries.

Tropical Glacier and Ice Core Evidence of Climate Change on Annual to Millennial Time Scales

This paper examines the potential of the stable isotopic ratios, 18O/16O (δ 18Oice)and 2H/1H (δ Dice), preserved in mid to low latitude glaciers as a toolfor paleoclimate reconstruction. Ice cores are particularly valuable as they contain additional data, such as dust concentrations, aerosol chemistry, and accumulation rates, that can be combined with the isotopic information to assist with inferences about the regional climate conditions prevailing at the time of deposition. We use a collection of multi-proxy ice core histories to explore the δ 18O-climate relationship over the last 25,000 years that includes both Late Glacial Stage (LGS) and Holocene climate conditions. These results suggest that on centennial to millennial time scales atmospheric temperature is the principal control on the δ 18Oice of the snowfall that sustains these high mountainice fields.Decadally averaged δ 18Oice records from threeAndean and three Tibetan ice cores are composited to produce a low latitude δ 18Oice history for the last millennium. Comparison ofthis ice core composite with the Northern Hemisphere proxy record (1000–2000A.D.) reconstructed by Mann et al. (1999) and measured temperatures(1856–2000) reported by Jones et al. (1999) suggests the ice cores have captured the decadal scale variability in the global temperature trends. These ice cores show a 20th century isotopic enrichment that suggests a large scale warming is underway at low latitudes. The rate of this isotopically inferred warming is amplified at higher elevations over the Tibetan Plateau while amplification in the Andes is latitude dependent with enrichment (warming) increasing equatorward. In concert with this apparent warming, in situobservations reveal that tropical glaciers are currently disappearing. A brief overview of the loss of these tropical data archives over the last 30 years is presented along with evaluation of recent changes in mean δ18Oice composition. The isotopic composition of precipitation should be viewed not only as a powerful proxy indicator of climate change, but also as an additional parameter to aid our understanding of the linkages between changes in the hydrologic cycle and global climate.

Climatological significance of δ18O in north Tibetan ice cores

Oxygen isotopic ratios (δ18O) of precipitation samples collected over several years at three meteorological stations on the northern Tibetan Plateau were used to conduct the first investigation of the relationship between δ18O and contemporaneous air temperatures (Ta). Inferring past temperatures from δ18O measured in recently acquired Tibetan ice cores necessitates establishing whether a δ18O-Ta relationship exists. For each station a strong temporal relationship is found between δ18O and Ta, particularly for monthly averages which remove synoptic-scale influences such as changes in condensation level, condensation temperature, and moisture sources. Moisture source is identified as a major factor in the spatial distribution of δ18O, but air temperature determines the temporal fluctuations of δ18O at individual sites on the northern Tibetan Plateau. The 30-year records of annually averaged δ18O from three different ice coring sites are not correlated significantly with contemporaneous air temperature records from their closest meteorological station (150 to 200 km). However, since 1960 the three air temperature records reveal a modest warming trend, while the three contemporaneous δ18O records show a modest 18O enrichment.

Annually Resolved Ice Core Records of Tropical Climate Variability over the Past ~1800 Years

Quelccaya Ice Cap Ice cores drilled in the ice sheets of Greenland and Antarctica are some of the most important sources of information about the paleoclimate of high latitudes. Comparable records from the tropics are rare, however, because there are so few locations at which long-lived, undisturbed ice can be found. Thompson et al. (p. 945, published online 4 April) report results obtained from one of the few such sites, the Quelccaya ice cap in the Peruvian Andes. The annually resolved data, extending back 1800 years, provide a detailed chronicle of changes in the isotopic composition of the oxygen in the ice, which are related to the sea surface temperature of the waters source. Analyses of a collection of major ions such as ammonium and nitrate reveal how atmospheric circulation in the region varied over that period. Finally, the radiocarbon content of ancient plants—recently exposed by the retreat of the ice sheet—reveals that Quelccaya has not been smaller for at least six thousand years. A record from the Quelccaya ice cap in Peru shows the variability of climate in the tropical Andes. Ice cores from low latitudes can provide a wealth of unique information about past climate in the tropics, but they are difficult to recover and few exist. Here, we report annually resolved ice core records from the Quelccaya ice cap (5670 meters above sea level) in Peru that extend back ~1800 years and provide a high-resolution record of climate variability there. Oxygen isotopic ratios (δ18O) are linked to sea surface temperatures in the tropical eastern Pacific, whereas concentrations of ammonium and nitrate document the dominant role played by the migration of the Intertropical Convergence Zone in the region of the tropical Andes. Quelccaya continues to retreat and thin. Radiocarbon dates on wetland plants exposed along its retreating margins indicate that it has not been smaller for at least six millennia.

A 1000 year climate ice-core record from the Guliya ice cap, China: its relationship to global climate variability

In 1992, an American-Chinese expedition successfully recovered three ice cores (308.6, 93.2 and 34.5m) from the Guliya ice cap (summit 6710 m a.s.l) in the far western Kunlun on the Qinghai–Tibetan Plateau, China. Guliya resembles a “polar” icecap with 10 m, 200 m and basal temperatures of –15.6°, –5.9° and –2.1°C, respectively. The 308.6 m core to bedrock is the longest ice core retrieved from an elevation greater than 4000 m a.s.l. and provides the first ice-core history from the western side of the Qinghai Plateau. The Plateau experiences a pronounced annual precipitation cycle during which 70–80% of annual total precipitation falls in the summer monsoon season. This leads to a marked visible stratigraphy in the glaciers which allows accurate dating of the ice cores and reconstruction of the net mass accumulation. This paper presents (1) the results of the geophysical program to determine ice thickness, ice flow and surface topography, (2) an assessment of net accumulation from stake measurements, snow pits and shallow core samples, and (3) the analyses of the upper 100 m of the 308.6 m core which provide a 1000 year history, including the ‘“Little Ice Age”, which is compared with Chinese historical records. Extended periods of positive accumulation on Guliya are closely contemporaneous with dry periods in eastern China. A trans-Pacific teleconnection is suggested by the strong temporal coherence between extended wet and dry phases on Guliya and on the Quelccaya ice cap, Peru.

Holocene climate variability archived in the Puruogangri ice cap on the central Tibetan Plateau

Abstract Two ice cores (118.4 and 214.7 m in length) were collected in 2000 from the Puruogangri ice cap in the center of the Tibetan Plateau (TP) in a joint US-Chinese collaborative project. These cores yield paleoclimatic and environmental records extending through the Middle Holocene, and complement previous ice-core histories from the Dunde and Guliya ice caps in northeast and northwest Tibet, respectively, and Dasuopu glacier in the Himalaya. The high-resolution Puruogangri climate record since AD 1600 details regional temperature and moisture variability. The post-1920 period is characterized by above-average annual net balance, contemporaneous with the greatest 18O enrichment of the last 400 years, consistent with the isotopically inferred warming observed in other TP ice-core records. On longer timescales the aerosol history reveals large and abrupt events, one of which is dated ∼4.7 kyr BP and occurs close to the time of a drought that extended throughout the tropics and may have been associated with centuries-long weakening of the Asian/Indian/African monsoon system. The Puruogangri climate history, combined with the other TP ice-core records, has the potential to provide valuable information on variations in the strength of the monsoon across the TP during the Holocene.

Climate of the last 500 years: High resolution ice core records

Precipitation accumulating on the Earths ice sheets and ice caps records a variety of physical and chemical information about the atmosphere and, in some cases, provides unique insight to both the history and the mechanics of the Earths environmental system. High resolution (well-dated) dust records from both polar ice sheets suggest a linkage between increased atmospheric dust and cooler temperatures over Antarctica, but a similar relationship is not observed in ice cores from either Greenland or China. Net accumulation histories for the last 490 years reveal no discemible global pattern although interesting regional differences and similarities exist. Excess (non-sea salt) sulfate profiles provide

Recording of El Niño in ice core δ18O records from Nevado Huascarán, Peru

The 68-year monthly resolved time series of δ 18 O from ice cores retrieved from the glaciated col of Nevado Huascaran, Peru (9°S, 77°W, 6050 m) reflects climate variability over Amazonia and the western tropical Atlantic. Over the 25-year period (1968-1993) of midtroposphere observations, the interannual variations in Huascaran δ 18 O relate closely with the zonal wind variations over tropical South America at the 500 hPa level. Additionally, there is some evidence that the spatial distribution of temperature anomalies in the western tropical Atlantic has influence on the 500 hPa circulation and hence the isotopic fractionation of moisture advected across Amazonia. During El Nino warming, the moisture convergence axis over the Atlantic Ocean is commonly diverted northward, leading to unusual warm and dry conditions over northeast Brazil, and 18 O-enriched snowfall at Huascaran. This enrichment phase is enhanced when the peak Pacific warming occurs during the first half of the calendar year, coincident with the wet season over Amazonia. Approximately 12 months later, the El Nino demise is affiliated with a reprisal of strong trade wind circulation, and the resultant cool, pluvial environment over Amazonia triggers a reversal to strongly depleted isotope anomalies.

Recent ice-core climate records from the Cordillera Blanca, Peru

Ice cores recently drilled to bedrock on the col of Huascaran (9°06′ S, 77°36′ W, 6047 m a.s.l.) offer the potential for a long, annually resolved climate record from tropical South America. This paper presents the record from 1950 to 1993 preserved in microparticle and nitrate concentrations and oxygen-isotopic ratios. Average monthly temperatures from a satellite-linked automatic weather station installed on nearby Hualcan in 1991 are presented. Annual temperatures from local high-altitude meteorological stations, along with the annual Huascaran isotopic record, show a warming trend over the last two decades. The marked preservation of the climate record in oxygen-isotopic ratios on Huascaran is absent at lower-elevation sites, which have been affected by the recent warming. This paper demonstrates the establishment of a time-scale for the Huascaran core, the preservation of the climatic signal with depth and the linkage of the ice-core “proxy-climate” parameters with measured climatic variations.

A multi-century ice-core perspective on 20th-century climate change with new contributions from high-Arctic and Greenland (PARCA) cores

Abstract A global collection of high temporally resolved ice-core-derived δ18O records is examined to assess whether the proxy records are consistent with contemporaneous observed temperature variations in their respective regions. This is prerequisite to using the older parts of the proxy (δ18O) records to assess whether 20th-century temperatures remain within the range of longer-term natural variability. Excluding the high plateaus in East and West Antarctica where 20th-century temperatures show modest cooling, the ice-core records from other regions suggest modest to strong 20th-century warming. The recent warming over Greenland has been modest and spatially variable. The 20th-century warming over both the Barents Sea region and the Tibetan Plateau now falls well outside the range of prior longer-term temperature variability. Similarly, over the South American Andes and the Antarctic Peninsula the recent warming exceeds the long-term mean for the last 1000 and 500 years, respectively. The ice fields in these regions are in danger of being compromised or lost if the present warming trend in these regions persists.