贵州荔波42.0kaB.P.~65.0kaB.P.气候变化的石笋记录

对贵州荔波董哥洞D42石笋进行TIMS-U测年和碳、氧同位素分析,建立末次冰期42．0ka B．P．～65．0ka B．P．的古气候变化时间序列。研究结果表明,荔波地区在65．0ka B．P．～42．0ka B．P．石笋记录的冷暖事件所反映出的季风气候变化,大致可分为3个气候阶段;65．0ka B．P．～60．6ka B．P．相当于海洋氧同位素MIS4晚期,反映本阶段东亚冬季风强盛,气温降低,表现为干旱寒冷的气候环境;60．6ka B．P．～48．4ka B．P．相当于海洋氧同位素MIS3早期,反映东亚夏季风相对增强,气温升高,有效降水相对较少,表现为温暖半干旱的气候环境;48．4ka B．P．～42．0ka B．P．相当于海洋氧同位素MIS3中期,显示东亚夏季风由强变弱,东亚冬季风相对增强,表现为干旱冷凉的气候环境。石笋记录揭示的2次寒冷事件在各类沉积物中均有记录,反映为全球变化的气候事件,相当于北大西洋沉积物中的Heinrich5和Heinrich 6冷事件,可以进行全球对比,显示荔波地区与北极地区存在着古气候的遥相关。     

Deep-sea pollen research in China

This paper briefly presents the progress of deep-sea pollen research in China since the beginning of ninetieths of the last Century. All the deep-sea pollen contri-butions mainly come from the South China Sea (SCS) and the East China Sea (ECS). The German-Chinese joint cruise (Sonne 95) and ODP 184 cruise initiated by Chinese scientists in the SCS provided excellent material for the deep-sea pollen research. So far a number of pollen results of 20-30 ka and million years from the SCS have been published. A couple of deep-sea pollen records from Okinawa Through of the ECS also came out. The high resolution pollen records obtained from the continuous deposits with high sedimentation rates and reliable age control of the deep-sea sediments provided a high time resolution history (hundred to millennial scales) of vegetation, environment and monsoon evolution of the pollen source areas (southern China and Japan). Spectral analysis of deep-sea pollen records from the SCS discovered orbital (100, 41, 23, 10 ka) and suborbital cyclicities(Heinrich and Dansgaard/Oscheger-O/D events) in the vegetation changes. Moreover, cross spectral analysis showed that the trend of vegetation changes in northern SCS was regulated mainly by changes of the ice volume in the Northern Hemisphere. The pollen record of the last 20 ka from the Okinawa Through of the ECS indicates that the marine environmental change lagged that on the terrestrail by about 1000 year. The asynchronous environmental changes between land and sea were probably caused by the time difference in thermohaline circulation. This study underscored the role of the deep-sea plant fossils as a bridge across the land and sea.     

Insolation-driven changes in atmospheric circulation over the past 116,000 years in subtropical Brazil

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.     

Thirty million year deep-sea records in the South China Sea

In the spring of 1999 the Ocean Drilling Program (ODP) Leg 184 Shipboard Party cored 17 holes at 6 deep water sites in the northern and southern parts of the South China Sea (SCS). Chinese scientists actively participated in the entire process of this first deep-sea drilling leg off China, from proposal to post-cruise studies. More than 30 categories of analyses have been conducted post-cruise in various Chinese laboratories on a large number of core samples, and the total number of analyses exceeded 60 thousand.The major scientific achievements of the Leg 184 studies are briefly reported in three successive papers, with the first one presented here dealing with deep-sea stratigraphy and evolution of climate cycles. This ODP leg has established the best deep-sea stratigraphic sequences in the Western Pacific: the 23-Ma isotope sequence from the Dong-Sha area is unique worldwide because of its continuity; the last 5-Ma sequence from the Nansha area represents one of the best 4 ODP sites worldwide with the highest time-resolution for that time interval, and the sequences of physical properties enable a decadal-scale time resolution. All these together have provided for the first time high-quality marine records for paleoenvi-ronmental studies in the Asian-Pacific region. This new set of stratigraphic records has revealed changes in climate cyclicity over the last 20 Ma with the fluctuating power of the 100 ka, 400 ka, 2000 ka eccentricity cycles, indicating the evolving response of the climate system to orbital forcing along with the growth of the Antarctic and Northern Hemisphere ice sheets.     

A palaeotemperature curve for the Precambrian oceans based on silicon isotopes in cherts

The terrestrial sediment record indicates that the Earth's climate varied drastically in the Precambrian era (before 550 million years ago), ranging from surface temperatures similar to or higher than today's to global glaciation events. The most continuous record of sea surface temperatures of that time has been derived from variations in oxygen isotope ratios of cherts (siliceous sediments), but the long-term cooling of the oceans inferred from those data has been questioned because the oxygen isotope signature could have been reset through the exchange with hydrothermal fluids after deposition of the sediments. Here we show that the silicon isotopic composition of cherts more than 550 million years old shows systematic variations with age that support the earlier conclusion of long-term ocean cooling and exclude post-depositional exchange as the main source of the isotopic variations. In agreement with other lines of evidence, a model of the silicon cycle in the Precambrian era shows that the observed silicon isotope variations imply seawater temperature changes from about 70 degrees C 3,500 million years ago to about 20 degrees C 800 million years ago.     

川东北宋家洞石笋氧碳同位素及锶含量突变分析

通过对宋家洞石笋SJ3的氧碳同位素及锶含量进行Mann-Kendall test突变分析,得出以下结论:(1)氧同位素值记录了末次冰盛期向Heinrich Event 1时期的转变;(2)碳同位素值和锶含量记录了由H1冷期向BФlling-AllerФd暖期的转变;(3)碳同位素值和锶含量指示了在19.8～15.3ka时当地的东亚夏季风和冬季风呈正相关关系,在15.3～14.8 ka呈负相关关系,表明石笋SJ3记录了古气候环境的冷干、暖湿变化,且不同气候指标对环境变化的敏感度不同。     

Reconstruction of surface ocean water <Emphasis Type="Italic">p</Emphasis>CO<Subscript>2</Subscript>(aq) in Nansha area,the South China Sea during the last 30 ka

The reconstruction of pCO2 in the tropic ocean is one of the most important issues to understand global climatic changes.In this study,the high-resolution stratigraphic analysis of core 17962 was conducted,which is Iocated in the southern South China Sea(SCS).The contents of sedimentary organic matter,the stable carbon isotopic composition of sedimentary organic matter,and the δ^13C values of black carbon and terrigenons n-alkanes were determined.And the δ^13Cwc value of carbon derived from aquatic was calculated.On the basis of δ^13Corg-pCO2equation proposed by Popp et al.(1989),we estimated the pCO2 in the Nansha area,SCS,since the last glaciation using δ^13Cwc instead of δ^13Corg.The results show that the average pCO2 was estimated at 240 ppm V during the last glaciation,and at 320ppm V in the Holocene.A comparison of surface sea pCO2 with the atmosphere CO2 recorded in the Vostok ice core,indicates that CO2 in surface water of the southern SCS could emit into atmosphere during the last 30ka.     

A high-resolution environmental change record since 19 cal ka BP in Pumoyum Co,southern Tibet

A 380-cm-long sediment core was acquired from the deep water area of Pumoyum Co, southern Tibet. Twenty-five plant residue samples were selected, and organic carbon stable isotopes were obtained using the AMS ¹⁴C chronological method. The ¹⁴C age and carbon reservoir effect were calibrated with surface sedimentation rate measurements using ²¹⁰Pb dating. Results showed that the core sediment deposited over 19 cal ka BP. Based on a multi-proxy analysis of TOC and IC contents, grain size and pollen assemblage data, the palaeoclimatic evolution of Pumoyum Co was reconstructed since the last glacial. Pumoyum Co was a shallow lake prior to 16.2 cal ka BP; although the glacier around the lake began to melt due to increasing temperatures, climate was still cold and dry. In the interval of 16.2–11.8 cal ka BP, the sedimentary environment fluctuated drastically and frequently. Two cold-events occurred at 14.2 and 11.8 cal ka BP, and these may correspond to the Older Dryas and the Younger Dryas events, respectively. After 11.8 cal ka BP, Pumoyun Co developed into the deep lake as it is now. The lake water temperature was relatively lower at that time because of influx of cold water from glacial meltwater entering the lake. As a result, the multi-proxy indicators showed no sign of warm conditions. Comparisons between the sedimentary record of Pumoyum Co with that of other lakes of the same age in southern Tibet indicate a warmer climate following the last deglaciation influenced the southeastern Tibetan Plateau. These results imply that the southwest Asian monsoon gradually became stronger since the deglaciation during its expansion to the inner plateau. The glacial-supplied water of the lake responded sensitively to cold-events. The entire southern Tibet region was dominantly influenced climatically by the southwest Asian monsoon during the Holocene.     

Modelled atmospheric temperatures and global sea levels over the past million years

Marine records of sediment oxygen isotope compositions show that the Earth's climate has gone through a succession of glacial and interglacial periods during the past million years. But the interpretation of the oxygen isotope records is complicated because both isotope storage in ice sheets and deep-water temperature affect the recorded isotopic composition. Separating these two effects would require long records of either sea level or deep-ocean temperature, which are currently not available. Here we use a coupled model of the Northern Hemisphere ice sheets and ocean temperatures, forced to match an oxygen isotope record for the past million years compiled from 57 globally distributed sediment cores, to quantify both contributions simultaneously. We find that the ice-sheet contribution to the variability in oxygen isotope composition varied from ten per cent in the beginning of glacial periods to sixty per cent at glacial maxima, suggesting that strong ocean cooling preceded slow ice-sheet build-up. The model yields mutually consistent time series of continental mean surface temperatures between 40 and 80 degrees N, ice volume and global sea level. We find that during extreme glacial stages, air temperatures were 17 +/- 1.8 degrees C lower than present, with a 120 +/- 10 m sea level equivalent of continental ice present.     

Similar meltwater contributions to glacial sea level changes from Antarctic and northern ice sheets

The period between 75,000 and 20,000 years ago was characterized by high variability in climate and sea level. Southern Ocean records of ice-rafted debris suggest a significant contribution to the sea level changes from melt water of Antarctic origin, in addition to likely contributions from northern ice sheets, but the relative volumes of melt water from northern and southern sources have yet to be established. Here we simulate the first-order impact of a range of relative meltwater releases from the two polar regions on the distribution of marine oxygen isotopes, using an intermediate complexity model. By comparing our simulations with oxygen isotope data from sediment cores, we infer that the contributions from Antarctica and the northern ice sheets to the documented sea level rises between 65,000 and 35,000 years ago were approximately equal, each accounting for a rise of about 15 m. The reductions in Antarctic ice volume implied by our analysis are comparable to that inferred previously for the Antarctic contribution to meltwater pulse 1A (refs 16, 17), which occurred about 14,200 years ago, during the last deglaciation.     

Diatoms from the southwestern continental slope, South China Sea, and their paleoenvironmental significance since the last glacial times

A quantitative study was undertaken on diatoms from cores (SA08-34) obtained from the southwestern continental slope of the South China Sea (SCS). A total of 165 diatom species belonging to 45 genera were identified. We constructed a stratigraphic subdivision and correlation according to the characteristics of diatom assemblages together with ¹⁴C dating and carbonate analysis. We also discuss the sedimentary environment in the sea area since the last glacial times. The research shows that the diatom assemblages coincide with interglacial and glacial times, and changes in diatom abundance reflect the instability of the climate in the southern part of the SCS, such that short-term, temperature descending events correlate with the interglacial interval. The abundance of diatoms is relevant to interglacial and glacial times, since high abundance values were associated with an interglacial interval, and low abundance values with the last glacial maximum. We assume that strong upwelling developed in the interglacial interval, the development of which was influenced by variations of monsoons in the East Asian region.     

Constraints on the duration and freshwater release of Heinrich event 4 through isotope modelling

Heinrich events--abrupt climate cooling events due to ice-sheet instability that occurred during the last glacial period--are recorded in sediment cores throughout the North Atlantic Ocean. Modelling studies have described likely physical mechanisms for these events, but the quantitative characteristics of Heinrich events are less well known. Here we use a climate model of intermediate complexity that explicitly calculates the distribution of oxygen isotopes in the oceans to simulate Heinrich event 4 at about 40,000 yr ago. We compare an ensemble of scenarios for this Heinrich event with oxygen isotope data measured in foraminiferal calcite of a comprehensive set of sediment cores. From this comparison, we obtain a duration of 250 +/- 150 yr and an ice release of 2 +/- 1 m sea-level equivalent for Heinrich event 4, significantly reducing the uncertainties in both values compared to earlier estimates of up to 2,000 yr and 15 m of sea-level equivalent ice release, respectively. Our results indicate that the consequences of Heinrich events may have been less severe than previously assumed, at least with respect to Greenland climate and sea level.     

Sea-level fluctuations during the last glacial cycle

The last glacial cycle was characterized by substantial millennial-scale climate fluctuations, but the extent of any associated changes in global sea level (or, equivalently, ice volume) remains elusive. Highstands of sea level can be reconstructed from dated fossil coral reef terraces, and these data are complemented by a compilation of global sea-level estimates based on deep-sea oxygen isotope ratios at millennial-scale resolution or higher. Records based on oxygen isotopes, however, contain uncertainties in the range of +/-30 m, or +/-1 degrees C in deep sea temperature. Here we analyse oxygen isotope records from Red Sea sediment cores to reconstruct the history of water residence times in the Red Sea. We then use a hydraulic model of the water exchange between the Red Sea and the world ocean to derive the sill depth-and hence global sea level-over the past 470,000 years (470 kyr). Our reconstruction is accurate to within +/-12 m, and gives a centennial-scale resolution from 70 to 25 kyr before present. We find that sea-level changes of up to 35 m, at rates of up to 2 cm yr(-1), occurred, coincident with abrupt changes in climate.     

Precise dating of Dansgaard-Oeschger climate oscillations in western Europe from stalagmite data

The signature of Dansgaard-Oeschger events--millennial-scale abrupt climate oscillations during the last glacial period--is well established in ice cores and marine records. But the effects of such events in continental settings are not as clear, and their absolute chronology is uncertain beyond the limit of (14)C dating and annual layer counting for marine records and ice cores, respectively. Here we present carbon and oxygen isotope records from a stalagmite collected in southwest France which have been precisely dated using 234U/230Th ratios. We find rapid climate oscillations coincident with the established Dansgaard-Oeschger events between 83,000 and 32,000 years ago in both isotope records. The oxygen isotope signature is similar to a record from Soreq cave, Israel, and deep-sea records, indicating the large spatial scale of the climate oscillations. The signal in the carbon isotopes gives evidence of drastic and rapid vegetation changes in western Europe, an important site in human cultural evolution. We also find evidence for a long phase of extremely cold climate in southwest France between 61.2 +/- 0.6 and 67.4 +/- 0.9 kyr ago.     

One-to-one coupling of glacial climate variability in Greenland and Antarctica

Precise knowledge of the phase relationship between climate changes in the two hemispheres is a key for understanding the Earth's climate dynamics. For the last glacial period, ice core studies have revealed strong coupling of the largest millennial-scale warm events in Antarctica with the longest Dansgaard-Oeschger events in Greenland through the Atlantic meridional overturning circulation. It has been unclear, however, whether the shorter Dansgaard-Oeschger events have counterparts in the shorter and less prominent Antarctic temperature variations, and whether these events are linked by the same mechanism. Here we present a glacial climate record derived from an ice core from Dronning Maud Land, Antarctica, which represents South Atlantic climate at a resolution comparable with the Greenland ice core records. After methane synchronization with an ice core from North Greenland, the oxygen isotope record from the Dronning Maud Land ice core shows a one-to-one coupling between all Antarctic warm events and Greenland Dansgaard-Oeschger events by the bipolar seesaw6. The amplitude of the Antarctic warm events is found to be linearly dependent on the duration of the concurrent stadial in the North, suggesting that they all result from a similar reduction in the meridional overturning circulation.     

Deep sea pollen record during 12－1.6 Ma from the southern South China Sea and its response to envi-ronmental change

Based on deep-sea pollen results (512-76 m) from ODP Site 1143 in the southern South China Sea (SCS),the climate and vegetation evolution sequence on the surrounding islands and the exposed continental shelf are discussed. The pollen records show that the pollen influx was quite low before 8.15 Ma and increased dramatically afterwards. The influx changes can be ascribed,on one side,to tectonics deformations around the southern SCS resulting in rapid uplift of islands and subsequent increase of the sediment rates and pollen influx and on the other side to climate cooling and monsoon enhancement. Around 2.63 Ma was another obvious boundary,the increasing of pollen and spores influx since this time was mainly related to global climate cooling. Spectrum analysis of pollen influx values shows that 2 Ma,0.67 Ma,and 0.19-0.17 Ma cycles existed during 12-3.0 Ma,while 0.1 Ma and 46.9 ka cycles existed during 3.0-2.0 Ma.     

Orbital- and millennial-scale variability of the Asian monsoon during MIS8 from Sanbao Cave at Mount Shennongjia,central China

One stalagmite oxygen isotope record from Sanbao Cave, China, established with 7 230Th ages and 355 oxygen isotope data, pro- vides a continuous history of the East Asian Monsoon (EAM) intensity for the period from 284 to 240 thousand years before present (ka BP) with typical errors of 3―4 ka. This new record extends the previously published stalagmite δ18O record back to the marine oxygen isotope stage (MIS) 8. The MIS8 EAM record broadly follows orbitally-induced insolation variations and is punctuated by...     

Vegetation evolution and millennial-scale climatic fluctuations since Last Glacial Maximum in pollen record from northern South China Sea

A large number of paleoclimate records reveal subMilankovitch climatic fluctuations on the millennial-scalesuperimposing on the Earth orbital cycles[1], such as theHeinrich ice draft events in the Atlantic (each intervalabout 7000–10000 a)[2,3], the Dansgaard/Oeschger (D-O)events (millennial-scale) in Greenland Ice Cores and theBond cycle composed of a Heinrcih event after severalD-O events[4]. At present, most recent work on millennial-scale climatic fluctuations focuses on the high lat…     

Magnetostratigraphy of borehole EY02-2 in the southern Yellow Sea and its paleoenvironmental significance

Various media are used for the study of paleoenvi- ronment. Among them, ice-core, loess and marine sediments are the most important for long time re- cording[1]. In all kinds of researches of paleoenviron- ment, age determination of the sediments is the m…