A record of Miocene carbon excursions in the South China Sea

High-resolution δ¹³C records are presented for the Miocene benthic foraminifersCibicidoides wuellerstorfi andC. kullenbergi (24-5 Ma) and the planktonic foraminiferGlobigerinoides sacculifer (18-5 Ma) from ODP Site 1148A (18° 50.17’N, 116° 33.93’E, water depth 3308.3 m), northern South China Sea. The general pattern of parallel benthic and planktonic δ¹³C shows a decrease trend of δ¹³C values from the early-middle Miocene to the middle-late Miocene. Two distinct δ¹³C positive excursions at 23.1-22.2 and 17.3-13.6 Ma, and two negative excursions at 10.2-9.4 and 6.9-6.2 Ma have been recognized. All these events are cosmopolitan, providing the good data for the stratigraphic correlation of the South China Sea with the global oceans as well as for studying the changes of the global carbon reservoir and its corresponding climate.     

Climatic variations in the past 140 ka recorded in core RM, east Qinghai-Xizang Plateau

The sequences of climatic evolution are reconstructed by the analyses of δ¹³C and δ¹⁸O of carbonate from core RM in the Zoige Basin since 140 kaB. P. During the Last Glaciation there existed at least seven warm climatic fluctuations and five cold events correlated with the records of ice core and deep sea, and during the preceding last interglacial period there were two cold climatic variations coinciding with the record of ice core GRIP. These results de-pict climatic instability in east Qinghai-Xizang Plateau over the last interglacial period. In addition, the environmental proxies of the carbonate content and pigments indicate the similar results to the stable isotope record from core RM. Project supported by the Chinese Climbing Project (85-029-02-01).     

Neogene oxygen isotopic stratigraphy, ODP Site 1148, northern South China Sea

A detailed stable isotopic study based on benthic foraminifera from 1165 samples of ODP Site 1148 (18° 50.17.3’N, 116° 33.93’E, water depth 3308.3 m), northern South China Sea, provides an excellent oxygen isotopic record with an average resolution of 30 ka. It contains the most continuous δ¹⁸O data with highest resolution for the whole Neogene sequence in the world. The δ¹⁸O curve shows a step-like increasing upwards and records 5 increases, 3 decreases and 2 stable stages during the Neogene, reflecting the general trend of global cooling. Among these events the δ¹⁸O decrease at 17.2–14.5 Ma, and two δ¹⁸O increases at 14.5-13.6 and 3.0-2.4 Ma are most marked and globally comparable. The intervals at 13.6-10.2 and 6.0-3.0 Ma with the lowest-amplitude and least fluctuation in δ¹⁸O represent the most stable bottom water periods for the South China Sea.     

Relationships between δ18O in summer precipitation and temperature and moisture trajectories at Muztagata, western China

Based on summer observations of stable isotope of precipitation at Muztagata, western China, during 2002-2003, this paper presents the relationship between δ ¹⁸O in precipitation and air temperature, and discusses the effect of moisture transport on δ ¹⁸O in precipitation. Results show that air temperature correlates positively with δ ¹⁸O in precipitation, and the temperature effect controls the δ ¹⁸O of precipitation in this area. The Muztagata region exhibits high δ ¹⁸O values in summer precipitation, similar to those shown at stations in adjacent regions. According to the results of our model set up to trace the moisture trajectories, the westerlies and local moisture circulation contribute to variations of oxygen isotopes in precipitation. In addition, the impacts of the moisture transport distance, the moisture transport level, and the incursion of the polar air mass also influence the variations of δ ¹⁸O in precipitation. The moisture origins and transport mechanisms also contribute to the variation of δ ¹⁸O in precipitation at Muztagata.     

High-resolution climate variability of southwest China during 57-70 ka reflected in a stalagmite δ18O record from Xinya Cave

A 26-cm-long stalagmite (XY2) from Xinya Cave in northeastern Chongqing of China has been ICP-MS ²³⁰Th/U dated, showing a depositional hiatus at 2.3 cm depth from the top. The growth of the 2.3–26 cm interval determined by four dates was between 57 ka and 70 ka, with a linear growth rate of 0.023 mm/a. We have analyzed 190 samples for δ ¹⁸O and δ ¹³C, mostly in the 2.3–26 cm part. The δ ¹⁸O and δ ¹³C values between 57 ka and 70 ka reveal decadal-to-centennial climatic variability during the glacial interval of Marine Isotope Stage 4 (MIS4), exhibiting much higher resolution than that of the published Hulu and Dongge records during this interval. Speleothem δ ¹⁸O in eastern China, including our study area can be used as a proxy of summer monsoon strength, with lighter values pointing to stronger summer monsoon and higher precipitation, and vice versa. Two decreases in the δ ¹⁸O signature of XY2 record around 59.5 and 64.5 Ka are argued to correspond to the Dansgaard-Oeschger (D-O) events 17 and 18 respectively. The Heinrich event 6 (H6) can be identified in the record as a heavy δ ¹⁸O peak around 60 ka, indicating significant weakening of the monsoon in Chongqing during the cold period. The XY2 δ ¹⁸O record shows very rapid change toward to the interstadial condition of the D-O event, but more gradual change toward to the cold stadial condition. This phenomenon found in the Greenland ice core records is rarely observed so clearly in previously published speleothem records. According to SPECMAP δ ¹⁸O record, the glacial maximum of MIS 4 was around 64.5 ka with the boundary of MIS 3/4 around 60 ka. Unlike the marine record, the speleothem record of XY2, China, exhibits much high frequency variations without an apparent glacial maximum during MIS 4. However, the timing of MIS 3/4 boundary seems to be around 60 ka when the H6 terminated, in agreement with the marine chronology. The growth period of sample XY2 during glacial times probably reflects a local karstic routing of water, rather than having climatic significance. Supported by the National Natural Science Foundation of China (Grant Nos. 40672165, 90511004, 40672202) and the Academician Special Project of Chongqing Science Committee (Grant No. 2003-7835)     

Variations of <Emphasis Type="Italic">δ</Emphasis><Superscript>18</Superscript>O in precipitation from the Muztagata Glacier,East Pamirs

Expeditions to Muztagata (in the eastern Pamirs) during the summer seasons of 2002 and 2003 collected precipitation samples and measured their oxygen isotopes. The δ ¹⁸O in precipitation displays a wide range, varying from −17.40‰ to +1.33‰ in June-September 2002 and from −22.31‰ to +4.59‰ in May-August 2003. The δ ¹⁸O in precipitation correlates with the initial temperature of precipitation during the observing periods. The positive correlation between δ ¹⁸O and temperature suggests that δ ¹⁸O can be used as an indicator of temperature in this region. The δ ¹⁸O values in fresh-snow samples collected from two snow events at different elevations on the Muztagata Glacier show a strong “altitude effect”, with a ratio of nearly −0.40% per 100 m from 5500 m to 7450 m.     

Temporal and spatial variations of <Emphasis Type="Italic">δ</Emphasis><Superscript>15</Superscript>N and <Emphasis Type="Italic">δ</Emphasis><Superscript>18</Superscript>O for atmospheric N<Subscript>2</Subscript>O above the oceanic surface from Shanghai to Antarctica

During the 22nd Chinese Antarctic Research Expedition (CHINARE-22), the atmospheric gas samples above the oceanic surface and near the surface were collected on the track for the scientific ship “Xuelong” and on Millor Peninsula of eastern Antarctica, respectively, using the Tedlar gas bags. Every day the sampling times were 10:00 and 22:00 (local time), respectively. In the laboratory, high-precision measurement of the isotopic compositions for N₂O in these gas samples was conducted using Thermo Finnigan MAT-253 Isotopic Mass Spectrometer with a fully automated interface for the pre-GC concentration (PreCon) of trace gases. The temporal and spatial variations of δ ¹⁵N and δ ¹⁸O in atmospheric N₂O were analyzed. The mean δ ¹⁵N and δ ¹⁸O-N₂O values above the oceanic surface were (7.21±0.50)‰ and (44.52±0.52)‰, respectively. From 30°N to Antarctica, the δ ¹⁵N (6.05‰–7.88‰) linearly increased with the rate of about 0.01‰ with the latitude while the δ ¹⁸O (43.05‰–48.78‰) showed a large fluctuation. The δ ¹⁵N negatively correlated with air temperature and N₂O concentration, and slightly positively correlated with δ ¹⁸O. The summertime variations of δ ¹⁵N and δ ¹⁸O-N₂O appeared the same trend on Millor Peninsula of eastern Antarctica. They significantly positively correlated with each other and negatively with N₂O concentration. The δ ¹⁵N and δ ¹⁸O-N₂O at different sites averaged (7.42±0.35)‰ and (44.69±0.49)‰, respectively, slightly higher than those above the oceanic surface, significantly higher than those of atmospheric N₂O in the low-latitude regions of Northern Hemisphere. The predominant factors affecting the spatial variations of δ ¹⁵N and δ ¹⁸O values were also discussed. The isotopic data given in this study can help to investigate the global and regional N₂O budgets. Supported by the National Natural Science Foundation of China (Grant Nos. 40676005 and 40406001)     

Stable isotopic records of the glacial deep-water properties in the South China Sea

Based on the oxygen and carbon stable isotopic records of benthic foraminifera in nine deep-sea cores of the South China Sea (SCS), the bathymetric profiles of δ¹⁸O and δ¹³C since the last glacial maximum (LGM) are preliminarily established. The bathymetric gradients of deep-water δ¹⁸O and δ¹³C in the SCS are obviously greater during the LGM than during the Holocene, showing the existence of the deep thermocline and nutricline at water depth of about 2 000 m. Particularly, the differences in δ¹⁸O and δ¹³C between the LGM and Holocene, from which the ice-volume effect and the global mean shift have been subtracted respectively, are positive values at water depths of 1 000–2 500 m in the SCS. This indicates the existence of deep-water mass with relatively cool temperature or higher salinity, better ventilation and more δ¹³C within the water depth range of the SCS during the LGM, which is distinctly different from that at present. These changes further confirm the existence of the glacial “North Pacific Deep Water” which, however, is possibly confined to the water depth range of 1 000–2 500 m. Project supported by the National Natural Science Foundation of China (Grant Nos. 49576286 and 49732060).     

Temporal variations of <Emphasis Type="Italic">δ</Emphasis><Superscript>18</Superscript>O of atmospheric water vapor at Delingha

Oxygen stable isotope of atmospheric water vapor is widely used to study the modern process of climate. Atmospheric water vapor samples were collected at Dlingha, northeast of Tibetan Plateau during the period from July 2005 to February 2006. The variation of δ ¹⁸O and the relationships between δ ¹⁸O and both the temperature and specific humidity are analyzed in this paper. Results show that the seasonal variation of δ ¹⁸O of atmospheric water vapor at Delingha is remarkable with higher δ ¹⁸O in summer and lower δ ¹⁸O in winter. The temporal variation of vapor δ ¹⁸O shows obvious fluctuations, with magnitude of over 37‰ The daily variation of the δ ¹⁸O is highly correlated with air temperature. The relationship between δ ¹⁸O and atmospheric water vapor content is complex. Study shows that δ ¹⁸O of atmospheric water vapor is positively correlated with specific humidity in winter in seasonal scale and inversely correlated with specific humidity in summer rainy period. The δ ¹⁸O values of atmospheric water vapor are lower than those of precipitation at Delingha, and the average difference is 10.7‰ Variations of δ ¹⁸O of atmospheric water vapor is also found to be affected by precipitation events, The model results show that the precipitation effect could have caused the vapor δ ¹⁸O in the raining season to lower by 7% in average in July and August. Supported by the National Natural Science Foundation of China (Grant Nos. 40671043, 40571039 and 40771048) and National Basic Research Program of China (Grant No. 2005CB422002)     

Environmental records of carbon in recent lake sediments

Based on careful sampling and accurate analysis of recent sediments in Lake Chenghai, this paper discusses the staggered positive/negative correlation between organic carbon (OC) concentration and inorganic carbon (IC) concentration. The result indicates that temperature change, and its induced relative changes are the main factors affecting the relationship between IC concentration, δ¹³C of carbonate and OC concentration. When temperature and its induced photosynthesis strength change control autochthonous calcite precipitation, OC concentration is positively correlated with IC concentration and δ¹³C of carbonate. When temperature and its induced physical/chemical changes dominate, OC concentration displays negative correlation with IC concentration and δ¹³C of carbonate. IC concentration and δ¹³C of carbonate in sediments of Lake Chenghai are good proxies for climatic warm/cold changes.     

Climatic significance of δ <Superscript>18</Superscript>O records from an 80.36 m ice core in the East Rongbuk Glacier,Mount Qomolangma (Everest)

The δ ¹⁸O variations in an 80.36 m ice core retrieved in the accumulation zone of the East Rongbuk Glacier, Mount Qomolangma (Everest), is not consistent with changes of air temperature from both southern and northern slopes of Himalayas, as well as these of the temperature anomalies over the Northern Hemisphere. The negative relationship between the δ ¹⁸O and the net accumulation records of the ice core suggests the “amount effect” of summer precipitation on the δ ¹⁸O values in the region. Therefore, the δ ¹⁸O records of the East Rongbuk ice core should be a proxy of Indian Summer Monsoon intensity, which shows lower δ ¹⁸O values during strong monsoon phases and higher values during weak phases.     

The paleoclimate change of Qaidam Basin during the last 2.85 Ma recorded by Gamma-ray logging

The geographical location of Qaidam Basin corresponds to N36°05’-38°10’ and E90°10’-98°05’. The thickness of the Quaternary deposits in the basin reaches 2000-3000 m. This paper deals mainly with the aspect of paleoclimate change of the basin. The approach used for the study consisted of (1) establishing the paleoclimate curve of the basin according to the climate indices, including the spore-pollen statistics, carbonate content and δ¹⁸O, obtained from the samples of the 760 m continuously-cored exploration holes sited in the basin, (2) comparing the paleoclimate curve with the natural gamma-logs of the same exploration holes, and (3) determining the paleoclimatic changes in the last 2.85 Ma on the basis of detailed geochronological calculations. These results are extremely important for comparison with the δ¹⁸O-based climate curve derived from the ODP659 in the Atlantic Ocean and with the cycles of paleosol in the Chinese loess.     

Carbon isotopic variations of Proterozoic carbonates in Jixian,Tianjin, China

Along the Proterozoic stratigraphic sections of Jixian, Tianjin, the δ13C values of carbonates are mostly negative in the Changchengian (Changcheng System), varying approximately within a range of (0±1 )‰in the Jixianian (Jixian System), and have commonly positive values of (2±2)‰ in the Qingbaikouan (Qingbaikou System). From Chuanlinggou Formation to Dahongyu Formation, i.e. from ca. 1700 Ma to 1600 Ma, the δ13C values of carbonates increase from about -3‰ to 0‰, but oscillate with large excursion in Dahongyu Formation. Two large excursions occur in the Jixianian, one in Yangzhuang Formation and the other in the third sub-member of Wumishan Formation overlaying. These integrated and continuous records of carbon isotope reflect secular variations of δ13C value in ancient seawater from ca. 1700 Ma to ca. 800 Ma. The increase and subsequent oscillation of seawater δ13C value occurring from the ages of ca. 1700 to ca. 1600 Ma and <1300 Ma may signify two correlative global tectonic events.     

A possible Younger Dryas-type event during Asian monsoonal Termination 3

1 Introduction The Younger Dryas (YD) cold spell is one of the most prominent abrupt climate change events in the past and a key feature of the last glacial termination. A great agreement has been attained in terms of the tim- ing and geographic extent of…     

Applications of interannual-resolution stable isotope records of speleothem: Climatic changes in Beijing and Tianjin, China during the past 500 years—the δ 18O record

δ¹⁸O of a stalagmite collected from Shihua Cave, 50 km southwest of Beijing is analyzed. The uppermost 2 cm was sampled at about 3-year intervals by a computer-controlled microsampling device. A total of 133 samples were analyzed, covering the last 480 years. A comparison of the δ¹⁸O record with the instrumentally recorded precipitation in Beijing and Tianjin back to 1840 AD shows that high precipitation correlates with negative δ¹⁸O peaks. The long-term δ¹⁸O trend records temperature changes. Between 1620 and 1900 AD, the temperature was cooler than the average value for the 480-year record, corresponding to the Little Ice Age. Temperatures warmer than the average prevailed during 1520–1620 and 1900—present. Superimposed on the long-term trend are about 14 δ¹⁸O cycles of 30–40-year periodicity, with wet periods centered around 1985, 1955, 1910, 1880, 1840, 1800, 1760, 1730, 1690, 1660, 1630, 1600, 1560 and 1530 AD. Project supported by the National Natural Science Foundation of China (Grant No. 9615875).     

Chemocline instability and isotope variations of the Ediacaran Doushantuo basin in South China

Stable isotope analyses in sections across a shelf to basinal transect of the Ediacaran Doushantuo basin show substantial isotope variabilities. In Songlin section where sediments were deposited in an intrashelf basin, δ 13C values are persistently negative (_3‰ to _5‰, VPDB) through the entire Doushantuo Formation, similar to those obtained from the slope section in Wuhe (_5‰ to _10‰, VPDB). Shallow water sections in Weng'an and Duoding show two broad δ 13C anomalies overprinted with significant meter-scale variations, but none of the curves has similar absolute δ 13C values compared to the Yangtze Gorges areas in South China and other sections globally. Such isotope variations, if partially recording ancient seawater signature, imply spatial and temporal chemocline instability in the Doushantuo basin. In combination with available δ 13C records from other Ediacaran successions globally, the data from the Doushantuo basin are consistent, in first order, with the existence and oxidation of a large dissolved organic carbon (DOC) reservoir in Ediacaran oceans, but imply local environmental controls on Neoproterozoic isotope values and call attentions for using δ 13C anomalies as time lines in stratigraphic correlation.     

Contrasting hydrothermal activity at Sierra Negra and Alcedo volcanoes, Galapagos Archipelago, Ecuador

2 and approximately 85% SO₂ of the total sulfur gas. Relative amounts of He, Ar, and N₂ show a distinct hot-spot signature ( ). The δ¹³C–CO₂ is approximately −3.6‰ and δ³⁴S_T is approximately +3.3‰. The δD/δ¹⁸O of fumarole H₂O indicates steam separation from local meteoric waters whose estimated minimum mean residence time from ³H analyses is ≤40 years. Fumarolic activity at Alcedo is controlled by a caldera-margin fault containing at least seven hydrothermal explosion craters, and by an intracaldera rhyolite vent. Two explosion craters which formed in 1993–1994 produce approximately 15 m³/s of steam, yet discharge temperatures are ≤97°C. Water content of the total gas is 95–97 mol.%, noncondensible gas is 92–98 mol.% CO₂, and sulfur gas is dominated by H₂S. Relative amounts of He, Ar, and N₂ show extensive mixing between hot spot and air or air-saturated meteoric water components but the average . The δ¹³C–CO₂ is approximately −3.5‰ and δ³⁴S_T is approximately −0.8‰. The δD/δ¹⁸O of fumarole steam indicates separation from a homogeneous reservoir that is enriched 3–5‰ in ¹⁸O compared with local meteoric water. ³H indicates that this reservoir water has a maximum mean residence time of approximately 400 years and empirical gas geothermometry indicates a reservoir temperature of 260–320°C. The intracaldera hydrothermal reservoir in Alcedo is probably capable of producing up to 150 MW; however, environmental concerns as well as lack of infrastructure and power users will limit the development of this resource. Received: 19 April 1999 / Accepted: 23 October 1999     

Climatic and environmental changes over the last millennium recorded in the Malan ice core from the northern Tibetan Plateau

In this paper, climatic and environmental changes were reconstructed since 1129A.D. based on the Malan ice core from Hol Xil, the northern Tibetan Plateau. The record of δ 18O in the Malan ice core indicated that the warm-season air temperature variations displayed a general increase trend, the 20th-century warming was within the range of natural climate variability, and the warmest century was the 17th century while the warmest decade was the 1610s, over the entire study period. The “Medieval Warm Epoch” and “Little Ice Age” were also reflected by the ice core record. The dust ratio in the Malan ice core is a good proxy for dust event frequency. The 870-year record of the dust ratio showed that dust events occurred much frequently in the 19th century. Comparing the variations of δ 18O and the dust ratio, it is found that there was a strong negative correlation between them on the time scales of 101―102 years. By analyses of all the climatic records of ice cores and tree rings from the northern Tibetan Plateau, it was revealed that dust events were more frequent in the cold and dry periods than in the warm and wet periods.     

Seasonal variations of stable isotope in precipitation and moisture transport at Yushu,eastern Tibetan Plateau

Precipitation δ 18O at Yushu, eastern Tibetan Plateau, shows strong fluctuation and lack of clear seasonality. The seasonal pattern of precipitation stable isotope at Yushu is apparently different from either that of the southwest monsoon region to the south or that of the inland region to the north. This different seasonal pattern probably reflects the shift of different moisture sources. In this paper, we present the spatial comparison of the seasonal patterns of precipitation δ 18O, and calculate the moisture transport flux by using the NCAR/NCEP reanalysis data. This allows us to discuss the relation between moisture transport flux and precipitation δ 18O. This study shows that both the southwest monsoon from south and inland air mass transport from north affected the seasonal precipitation δ 18O at Yushu, eastern Tibetan Plateau. Southwest monsoon brings the main part of the moisture, but southwest transport flux is weaker than in the southern part of the Tibetan Plateau. However, contribution of the inland moisture from north or local evaporation moisture is enhanced. The combined effect is the strong fluctuation of summer precipitation δ 18O at Yushu and comparatively poor seasonality.     

Temperature variations recovered from tree-rings in the middle Qilian Mountain over the last millennium

During the past 1000 years, there had been sev-eral widespread climate events on the earth, such asthe ‘Medieval Warm Period’, the ‘Little Ice Age’ andthe recent warming from the later part of the nine-teenth century onward[1,2]. To better understand thedetails of climatic history on a regional scale, morehigh-resolution, millennia-length climate reconstruc-tions are needed by intensive, multiproxy investigationof ice cores, sediments of loess and lakes, corals andtree-rings. Since …