Late Holocene glacier variations indicated by theδ18O of ice core enclosed gaseous oxygen in the central Tibetan Plateau

Theδ18O of ice core enclosed gaseous oxygen(δ18Obub)has been widely used for climate reconstruction in polar regions.Yet,less is known about its climatic implication in the mountainous glaciers as the lack of continuous record.Here,we present a long-term,continuousδ18Obub record from the Tanggula glacier in the central Tibetan Plateau(TP).Based on comparisons of its variation with regional climate and glacier changes,we found that there was a good correlation between the variation of theδ18Obub in this alpine ice core and the accumulation and melting of this glacier.The more developed the firn layer on glacier surface,the more positive theδ18Obub.Conversely,the more intense the glacier melting,the more negative theδ18Obub.Combined with the chronology of ice core enclosed gases,the glacier variations since the late Holocene in the central TP were reconstructed.The result showed that there were four accumulation and three deficit periods of glaciers in this region.The strongest glacier accumulation period was 1610-300 B.C.,which corresponds to the Neoglaciation.The most significant melting period was the last 100 years,which corresponds to the recent global warming.The Medieval Warm Period was relatively significant in the central TP.However,during the Little Ice Age,there was no significant glacier accumulation in the central TP,and even short deficit events occurred.Comparisons of the late Holocene glacier variation in the central TP with glacier and climate variations in the TP and the Northern Hemisphere showed that it was closely related to the North Atlantic Oscillation.

A concise overview on historical black carbon in ice cores and remote lake sediments in the northern hemisphere

Black Carbon(BC),as a driver of environmental change,could significantly impact the snow by accelerating melting and decreasing albedo.Systematic documentation of BC studies is crucial for a better understanding of its spatial and temporal trends.This study reviewed the BC studies in the ice core and remote lake sediments and their sources in the northern hemisphere.The literature surveyed points to around 2.9 to 3.7 times increase of BC in the European Alps and up to a three-fold increase of BC in the Himalayan-Tibetan Plateau(HTP)after the onset of industrialization in Europe and Asia,respectively.BC concentration from Greenland ice core showed seven times increase with an interrupted trend after 1950's.South Asian emissions were dominant in the HTP along with a contribution from the Middle East,whereas Western European and local emissions were responsible for the change in BC concentration in the European Alps.In the Arctic,contributions from North America,Europe and Asia persisted.Similarly,a historical reconstruction of lake sediments records demonstrates the effects of emissions from long-range transport,sediment focusing,local anthropogenic activities,precipitation and total input of flux on the BC concentration.

Source of major ions from an ice core of the No.12 Glacier in Laohugou Valley,Qilian Mountain

In June 2006,a 20.12 m shallow ice core was recovered from an elevation of 5,040 m in the northern branch firn basin of No.12 Glacier,Great Snow Mountain,in the western part of Qilian Mountain,China.Isotopes(δ 18 O),major soluble ions,and radionuclide(β-activity) measurements from the ice core revealed a 46-year record(1960-2006).In this paper,the method of sea-salt ion tracer,correlation analysis and trend analysis were used in this research to confirm the source of the chemical composition.The correlation analysis and HYSPLIT backward trajectory analysis suggests that atmospheric soluble dust species dominate the chemical signature.

Ice core extraction at Naimona’nyi Glacier

Headed by YAO Tandong,director of the CAS Institute of Tibetan Plateau Research, and Prof. Lonnie Thomp-

THE LABORATORY OF ICE CORE AND COLD REGIONS ENVIRONMENT

Affiliation unit: Lanzhou Institute of Glaciology and Cold Regions Environment, CAS Brief history: The Laboratory of Ice Core and Cold Regions Environment (LICCRE) was formally approved to open domestically and internationally by Chinese Academy of Sciences in April 1997. It is attached to the Lanzhou Institute of Glaciology and Geocryology, CAS.

ICE CORE RESEARCH & GLOBAL CHANGE

The article gives a simplified narration on the ice core research throughout the world today. A important tool for detecting the global change in the past times, the research reveals many clues of vital significance in climatic and environmental evolution on the Earth. In addition, the article envisages the future trend in this special aspect of hydrological research.

Human activity over natural inputs determines the bacterial community in an ice core from the Muztag ata glacier

Ice core provides a valuable vertical timeline of past climates and anthropogenic activities.Environmental proxies have been widely used in these studies,but there are few biological indicators available.To address this gap,we investigated the bacterial community from a 74 m ice core of Muztag ata glacier on the Tibetan Plateau to link biological indicators with past climate and anthropogenic activities.By analyzing the portion of the ice core with environmental proxies available(corresponding to 1907 to 1991),we observed an increase in bacterial richness throughout the ice core,which was associated with higher NH_(4)^(+),an indicator of agricultural development.The bacterial community was jointly determined by human activity,natural input,and air temperature,with a strong human influence after the 1950s.Furthermore,the relative abundance of animal gut-associated bacteria,including Aerococcaceae,Nocardiaceae,Muribaculaceae,and Lachnospiraceae,was associated with livestock number changes in the Central Asian region.Together with other bacterial lineages,they jointly explained 59.8%of the livestock number changes.This study provides quantitative evidence of the associations between bacterial indicators and past climate and human activities,highlighting the potential of using bacterial proxies for ice core studies.

Variation of CH_4 concentrations recorded in Dunde ice core bubbles

GREENHOUSE gases such as CH4 in the ancient atmospheric concentration can be reconstructed by extracting and analyzing the gases trapped in polar ice core bubbles. It is a new attempt to extract and analyze the CH4 concentration in Dunde ice core for the study of mountain glacier. Samples were taken from the about 140-m ice core drilled in 1987 in Dunde ice cap in Qilian Mountain. The ice core has been well preserved in cold room. 12 samples were taken from the upper 95 m, and cut to 15 cm in length and 5cm in diameter. CH4 concentrations were measured in CNRS Laboratory of Glaciology, Grenoble, France.

A shallow ice core from East Greenland showing a reduction in black carbon during 1990-2016

This study reports on the measurements of ion and refractory black carbon(rBC)concentrations in a shallow(10.96 m)ice core sample which was drilled from the field site of the East Greenland Ice Core Project(EGRIP)in July,2016.The results provide a recent record of rBC deposition in the East Greenland ice sheet from 1990 to 2016.The annual variability in oxygen(δ^(18)O)and hydrogen(δD)isotopic compositions indicated that notably warm events occurred since 2008.Peaks in rBC occurred during summer seasons,which may be attributed to the burning of biomass in boreal summer.The rBC record and analysis of historical air trajectories using the HYSPLIT model indicated that anthropogenic BC emissions from Russia,North America and Europe contributed to the majority of rBC deposition in the Greenland region,and a reduction in anthropogenic BC consumption in these areas played a dominant role in the decrease in BC concentrations since 2000.This record also suggests that the emissions from the East Asian region(China)contributed very little to the recorded BC concentrations in East Greenland ice core.The model results indicated that radiative forcing due to BC had decreased significantly since 1990,and had remained below 0.02W m^(-2) since 2000.

Radar isochronic layer dating for a deep ice core at Kunlun Station, Antarctica

The ages and accumulation rates of ice are important boundary conditions for paleoclimatic ice models. Radardetected isochronic layers can be used to date the ice column beneath the ice surface and infer past accumulation rates. A Deep Ice-Core Drilling Project has been carried out at Kunlun station in the Dome A region, East Antarctica. Radio echo sounding data are collected during the 2004/2005 Chinese National Research Expedition and the 2007/2008 Dome Connection East Antarctica project of the Alfred Wegener Institute(Germany). Radar isochronic layers from the dataset were linked to compare a new deep ice core site from Kunlun station and the Vostok ice core site. Ten visible layers, accounting for ~50% ice thickness at the Kunlun station ice core site, were dated based on the Vostok ice core chronology. At 1,640 m depth below surface, an age of ~160,400 yr was determined, corresponding to a bright layer at Kunlun station. These layers provided geometric information on the past surface of the ice sheet around the ice core site through the Wisconsin glacial stage, Eemian interglacial and Marine Isotope Stage6. Based on a simple ice flow model and the age-depth relationship, we concluded that the region around the Kunlun ice core site had lower past accumulation rates, consistent with the present pattern. The age-depth relationship would thus be expected to correlate and constrain the chronology of the deep ice core at Kunlun station in the future.

Influence of meteorological elements on chemical evolution of snow and ice of Urumqi Glacier No.1,eastern Tianshan Mountains

For most mountain glaciers,chemical components in snowfall are subject to the elution process under the influences of meltwater before they are preserved in ice,creating difficulties for interpreting ice core records.To understand the formation process of ice core records and analyze the influences of meteorological factors on the ice core resolution,we measured ion concentrations of snowpacks from 2003 to 2006 in the PGPI(Program for Glacier Processes Investigation)site of Urumqi Glacier No.1.The ion concentration variation in snowpack exhibits apparent seasonality.In summer,the higher snowmelt rates due to air temperature rise intensify dilution and lead to an exponential decrease in ion concentrations as the accumulated positive temperature increases.In winter,the snow ion concentrations are stable and low as a result of reduced temperature and rare precipitation.Many ions from summer precipitation are leached out by meltwater,and only the precipitation that occurs at the end of the wet season can be preserved.Through tracking the evolution of magnesium ion peaks in the snowpack,it is concluded that the ice core resolution is one year on Urumqi Glacier No.1,albeit 70%of the concentration information is lost.

The older ice,the better science

Ice cores have revolutionized our views of the Earth system.They record past climatic and environmental parameters that range on time scales from synoptic events to hundreds of thousands of years.For instance,the Vostok ice core reached an age of 420 ka(thousand years)(Figure 1),revealing a close linkage between climate and greenhouse gas concentrations over the last four glacial-interglacial cycles(Petit et al.,1999).

Holocene precipitationδ^18O as an indicator of temperature history in arid central Asia:an overview of recent advances

Holoceneδ^18O records from various archives(ice cores,cave stalagmites,and peat sediments)from the Xinjiang region of northwestern China,in arid central Asia(ACA),are all derived ultimately from local precipitationδ^18O(δ^18Op).Nevertheless,they have been proposed as indicators of different climatic parameters,such as wetness and temperature changes.This article summarizes previously reported records of moisture sources for the Xinjiang region and the results of modern observations conducted at an ice core site and a peat site in the Altai Mountains.The findings are used to propose that the overall positive trends in Holoceneδ^18O records from the various archives from the Xinjiang region primarily reflect the Holocene's long-term warming trend.It is concluded that more site-specific modern observations are needed to further elucidate the environmental significance of Holoceneδ^18O records from this region,especially for the separation of different seasonal temperature signals present withinδ^18O records.

青藏高原冰芯记录揭示早-中全新世发生多次融水事件

Understanding the impact of meltwater discharge during the final stage of the Laurentide Ice Sheet(LIS)has important implications for predicting sea level rise and climate change.Here we present a highresolution ice-core isotopic record from the central Tibetan Plateau(TP),where the climate is sensitive to the meltwater forcing,and explore possible signals of the climate response to potential LIS meltwater discharges in the early to mid-Holocene.The record shows four abrupt large fluctuations during the 7–9 ka BP(kiloannum before present),reflecting large shifts of the mid-latitude westerlies and the Indian summer monsoon(ISM)over this period,and they corresponded to possible LIS freshwater events documented in other paleoclimate records.Our study suggests that multiple rapid meltwater discharge events might have occurred during the final stage of LIS.The finding implies the possibility of rapid sea level rise and unstable climate in the transition zone between the mid-latitude westerlies and the ISM due to fast polar ice retreat under the anthropogenic global warming.

Precise dating of East-Asian-Monsoon D/O events during 95―56 ka BP:Based on stalagmite data from Shanbao Cave at Shennongjia,China

Based on 23 U/Th analyses and 532 oxygen isotopic data, an averaged 80-a stalagmite oxygen isotopic composition series was established through 95 to 56 thousand years before present (ka BP) from two speleothems in Shanbao Cave, Shennongjia, central China. Shanbao Cave record (referred to as SB record) replicates well with Hulu Cave record, extending the characteristics of millennial oscillations in East-Asian-Summer-Monsoon (EASM) to the past 95 ka. The trend of the SB record generally follows mid-July solar insolation at 65°N, suggesting that mid-high northern latitude insolation, in the first or- der, controls changes of EASM intensity. Millennial oscillations of EASM recorded in the stalagmites are well related to the Greenland interstadials referred to as Dansgaard/Oeschger (D/O) events from 1 to 22, indicating that rapid ocean-atmosphere reorganization in North Atlantic has a remote effect in EASM. The well-dated D/O events by stalagmites probably provide an absolute calibration for chro- nologies of Greenland ice cores. The timings of D/O events in the SB record are different variously from those in Greenland ice cores. For D/O 19 and 20, the age offsets between the stalagmites' and the Greenland ice cores' record are significant, larger than the uncertainties of uranium-series dating. The two events in the SB record are younger than those in North GRIP time scale by 1―2 ka, and older than the counterparts in GISP2 by approximately 3―4 ka. A comparison between the SB and Brazil stalag- mite record shows an anti-phase relation in millennial-scale monsoon precipitation between the two localities. This supports a mode for the coupled ocean-atmosphere "See-saw".

Fifty years of Quaternary palynology in the Tibetan Plateau

Quaternary palynology in the Tibetan Plateau(TP)was initiated in the 1960s to meet the needs of economic development in western China.Pollen analysis was conducted for the first time on a 200-m long core of Quaternary lacustrine sediments taken from the main body of the TP in order to study pollen assemblages as well as vegetation and climate changes of glacial(cold)/interglacial(warm)periods.Pollen analysis of alpine snow and ice began at the first scientific expedition to the TP in the 1970s.After the 1980s,a series of international collaborative programs were carried out under Sino-French,Sino-German,Sino-Australian,and Sino-American cooperation,marking the integration of Chinese Quaternary palynology society with the international community.New methods for Quaternary palynology were gradually promoted and applied,changing the vegetational and climatic interpretation of Quaternary palynology from qualitative to quantitative.Since the 1990s,many palynologists have carried out extensive Quaternary palynological studies on fossil pollen sites of more than 60 lakes/sections and alpine glaciers in the TP to discuss the spatiotemporal vegetation changes and climatic and environmental evolution of the TP since the Pleistocene.Over the past half-century,Quaternary palynology in the TP has contributed to the establishment of the Chinese Quaternary pollen database and the study of vegetation and climate evolution since the Last Glacial Maximum(LGM)in the TP.Currently available pollen records revealed the spatial and temporal distribution of vegetation in the TP since the LGM,exhibiting expansions and shrinkages of forest,meadow,grassland and desert in different periods such as the LGM,the last deglaciation,and Holocene optimum period.The paleomonsoon reflected by paleovegetation since the LGM has undergone the changes of weak-strengthening-strong-weakening but still active-shrinking,which is mainly affected by solar insolation.