A broad deglacial δ13C minimum event in planktonic foraminiferal records in the Okinawa Trough

The equatorial Pacific upwelling zone has been suspected of playing an important role in the global atmospheric CO2 changes associated with glacial-interglacial cycles.In order to assess the influencing scope of the surface water deglacial δ13C minimum in the tropical Iow-latitude Pacific,the core DGKS9603, collected from the middle Okinawa Trough, was examined for δ13C records of planktonic foraminifera N. dutertrei and G. ruber. The planktonic foraminiferal δ13C records show a clear decreasing event from 20 to 6 cal. kaBP., which is characterized by long duration of about 14 ka and amplitude shift of 0.4 × 10-3. Its minimum value occurred at 15.7 cai kaBP. The event shows fairly synchrony with the surface water deglacial δ13C minimum identiffed in the tropical Pacific and its marginal seas. Because there is no evidence in planktonic foraminiferal fauna and δ18O records for upwelling and river runoff enhancement,the broad deglacial δ13C minimum event in planktonic foraminiferal records revealed in core DGKS9603 might have been the direct influencing result of the deglacial surface water of the tropical Pacific. The identification for the event in the Okinawa Trough provides new evidence that the water evolution in the tropical low-latitude Pacific plays a key role in large regional, even global carbon cycle.     

Warming magnitude of Indonesian Throughflow during the penultimate deglaciation (Termination II) and its relationship with climate change in high-latitude regions

The tropical oceans are important source areas for global heat and water vapor transport, and changes in tropical sea surface tem-perature (SST) will have important impacts on high-latitude and global climate change. It is crucial to establish the precise phase relationship between tropical and high-latitude climate variability to gain insight into the mechanisms of global climate change. Here, we present multi-proxy records across the penultimate deglaciation (Termination II) from sediment Core SO18459, which is located in the outflow area of the Indonesian Throughflow (ITF) of the Timor Sea. These proxy records include planktonic and benthic foraminifera δ¹⁸O, planktonic foraminifera G. ruber Mg/Ca-derived SST, and δ¹⁸O_w of sea surface water. The Mg/Ca-SST records indicate a warming of 4.1°C in the Timor Sea over Termination II, which is in phase with decrease in planktonic and benthic δ¹⁸O. Our results suggest that at millennial timescales, climate change of the tropical oceans is synchronous with high-latitude ice volume changes. Furthermore, warming of the Timor Sea is almost simultaneous with warming of the Antarctic, suggesting a rapid heat transfer from the tropics to the Antarctic via the atmosphere and/or ocean circulations. The G. ruber δ¹⁸O and SST records of Core SO18459 show a marked YD-like event during Termination II, which is probably caused by decrease in Australian rainfall or strengthening of the Western Pacific Warm Pool. However, a similar YD-like event is not observed in East Asian rainfall records. This discrepancy indicates that different tropical climate systems may have different responses to the same forcing, such as El Niño Southern Oscillation. A similar YD-like event is observed in the global benthic foraminiferal δ¹⁸O records during Termination II, implying teleconnection of millennial scale climate change between the tropical regions and high latitudes.     

Past temperature and delta18O of surface ocean waters inferred from foraminiferal Mg/Ca ratios

Determining the past record of temperature and salinity of ocean surface waters is essential for understanding past changes in climate, such as those which occur across glacial-interglacial transitions. As a useful proxy, the oxygen isotope composition (delta18O) of calcite from planktonic foraminifera has been shown to reflect both surface temperature and seawater delta18O, itself an indicator of global ice volume and salinity. In addition, magnesium/calcium (Mg/Ca) ratios in foraminiferal calcite show a temperature dependence due to the partitioning of Mg during calcification. Here we demonstrate, in a field-based calibration experiment, that the variation of Mg/Ca ratios with temperature is similar for eight species of planktonic foraminifera (when accounting for Mg dissolution effects). Using a multi-species record from the Last Glacial Maximum in the North Atlantic Ocean we found that past temperatures reconstructed from Mg/Ca ratios followed the two other palaeotemperature proxies: faunal abundance and alkenone saturation. Moreover, combining Mg/Ca and delta18O data from the same faunal assemblage, we show that reconstructed surface water delta18O from all foraminiferal species record the same glacial-interglacial change--representing changing hydrography and global ice volume. This reinforces the potential of this combined technique in probing past ocean-climate interactions.     

Variations in upper water structure during MIS 3 from the western South China Sea

Core 17954 is located in the modern summer upwelling area in western South China Sea, its sediments recorded the variations of upwelling generated by East Asia Summer Monsoon (EASM) during MIS 3. Based on the strict age model of AMS 14C dating, the paleo-Sea Surface Temperature (SST) and Salinity (SSS) are reconstructed by pairing Mg/Ca-Paleothermometer and δ 18o of planktonic foraminifera Globigerinoides ruber (white s.s.). Results show that in Core 17954, the δ 18O record of G.ruber has sig- nificant mill...     

Molecular evidence for genetic mixing of Arctic and Antarctic subpolar populations of planktonic foraminifers

Bipolarity, the presence of a species in the high latitudes separated by a gap in distribution across the tropics, is a well-known pattern of global species distribution. But the question of whether bipolar species have evolved independently at the poles since the establishment of the cold-water provinces 16-8 million years ago, or if genes have been transferred across the tropics since that time, has not been addressed. Here we examine genetic variation in the small subunit ribosomal RNA gene of three bipolar planktonic foraminiferal morphospecies. We identify at least one identical genotype in all three morphospecies in both the Arctic and Antarctic subpolar provinces, indicating that trans-tropical gene flow must have occurred. Our genetic analysis also reveals that foraminiferal morphospecies can consist of a complex of genetic types. Such occurrences of genetically distinct populations within one morphospecies may affect the use of planktonic foraminifers as a palaeoceanographic proxy for climate change and necessitate a reassessment of the species concept for the group.     

Low-latitude seasonality of Cretaceous temperatures in warm and cold episodes

The Cretaceous period is generally considered to have been a time of warm climate. Evidence for cooler episodes exists, particularly in the early Cretaceous period, but the timing and significance of these cool episodes are not well constrained. The seasonality of temperatures is important for constraining equator-to-pole temperature gradients and may indicate the presence of polar ice sheets; however, reconstructions of Cretaceous sea surface temperatures are predominantly based on the oxygen isotopic composition of planktonic foraminifera that do not provide information about such intra-annual variations. Here we present intra-shell variations in delta18O values of rudist bivalves (Hippuritoidea) from palaeolatitudes between 8 degrees and 31 degrees N, which record the evolution of the seasonality of Cretaceous sea surface temperatures in detail. We find high maximum temperatures (approximately 35 to 37 degrees C) and relatively low seasonal variability (< 12 degrees C) between 20 degrees and 30 degrees N during the warmer Cretaceous episodes. In contrast, during the cooler episodes our data show seasonal sea surface temperature variability of up to 18 degrees C near 25 degrees N, comparable to the range found today. Such a large seasonal variability is compatible with the existence of polar ice sheets.     

High-resolution multi-proxy records of Asian monsoon activities from terrestrial sediments over the last 75,000 years

Our research group have investigated chronology and sedimentology of terrestrial sediments including loess-paleosols sediments over the last 75 ka at Lanzhou, northwestern China, and over the last 45ka at Tokyo, central Japan. Based on chronology of high resolution dating of ESR, TL, and IRSL and tephrochronology in these sediments, we investigated to reconstruct activities of Asian summer and winter paleomonsoons by using magnetic susceptibility, color reflectance and eolian dust concentrations over the last 75ka. Relations between standard curves of delta ~(18)O in GISP2 and color reflectance in loess-paleosol sediments of Linxia over last 140 ka shows that color reflectances are good proxy records indicating Asian summer paleomonsoon activity in time and are closely related to standard curve of delta ~(18)O in GRIP since the last interglacial. Also, relations between standard curve of delta ~(18)O in GISP2 and eolian dust concentrations over the last 75 ka at Lanzhou shows the Asian winter paleomonsoon activities have coincided with climatic changes in North Atlantic by GISP2 ice cores, and suggests that response of winter monsoon was rapid in global cooling stages, but slow in warming stage. Other results of our research in terrestrial sediments show as follows; 1) Horizons of Heinrich events from H1 to H4 in loess-paleosol sequences at Lanzhou. 2) Magnetic susceptibility and MS frequency dependent are possible to be available as proxy records for pedogenesis of tile Kanto Loam in Japan. 3) 8.2ka cooling event was recognized in Holocene loess-paleosol sequences at Lanzhou.     

Strong coherence between solar variability and the monsoon in Oman between 9 and 6 kyr ago

Variations in the amount of solar radiation reaching the Earth are thought to influence climate, but the extent of this influence on timescales of millennia to decades is unclear. A number of climate records show correlations between solar cycles and climate, but the absolute changes in solar intensity over the range of decades to millennia are small and the influence of solar flux on climate is not well established. The formation of stalagmites in northern Oman has recorded past northward shifts of the intertropical convergence zone, whose northward migration stops near the southern shoreline of Arabia in the present climate. Here we present a high-resolution record of oxygen isotope variations, for the period from 9.6 to 6.1 kyr before present, in a Th-U-dated stalagmite from Oman. The delta18O record from the stalagmite, which serves as a proxy for variations in the tropical circulation and monsoon rainfall, allows us to make a direct comparison of the delta18O record with the Delta14C record from tree rings, which largely reflects changes in solar activity. The excellent correlation between the two records suggests that one of the primary controls on centennial- to decadal-scale changes in tropical rainfall and monsoon intensity during this time are variations in solar radiation.     

Distribution,ecology, and oxygen and carbon isotope characteristics of modern planktonic foraminifers in the Makarov Basin of the Arctic Ocean

The Arctic region, with magnificent ice cover on the surface of the Arctic Ocean and adjacent seas, is not only extremely sensitive to but also has strong amplification effects on climate change. Observations during the past decades have documented substantial retreat and thinning of the Arctic sea-ice cover, a process that is accelerating. Its feedback and impact on the global climate has become an important subject of current climate change research. Calcite tests of planktonic foraminifers are major constituents in pelagic sediments, and they provide valuable materials for the reconstruction of past oceanographic conditions. However, research is still sparse in the Arctic sea area because of limited availability of the materials for investigation. Here, we present a study of modern foraminifers from the plankton tow samples taken in the Makarov Basin of the Arctic Ocean during the fourth Arctic expedition of China. We have analyzed ecological information stored in the modern planktonic foraminifers and in their stable isotope signals, and established a relationship between the distribution of the main taxa and the environment. Our main observations are as follows:(1) in the Makarov Basin, the polar species Neogloboquadrina pachyderma(sinistral coiling) dominates the [150 lm planktonic foraminiferal assemblages.(2) The planktonic foraminifers live mainly in the upper halocline at a water depth of 50–100 m and less in the depth interval of 100–200 m.(3) Temperature change in the halocline can affect the absolute abundance of planktonic foraminifers and their distribution in the water column. The warmer halocline is more favorable to the development of planktonic foraminifers.(4) A lighter d18O value(2.11 %) of N. pachyderma(sin.) is recorded in the depth interval of 100–200 m, which is likely related to the isotopically light brines separated out during sea ice freezing. The relatively heavy d18O value(1.68 %–2.68 %, average 2.27 %) in the depth interval of 50–100 m may be influenced by the low salinity water with the relatively heavy d18O value formed during the sea-ice melting in the surface layer.     

Oxygen and carbon isotope records of calcareous nannofossils for the past 1 Ma in the southern South China Sea

Oxygen and carbon isotopic analyses have been carried out on calcareous nannofossils from ODP Site 1143 in the southern South China Sea. The results demonstrate that the δ18O values of calcareous nannofossils for the past 1 Ma vary systematically with those of planktonic and benthic foraminifera from the same site. But the average δ18O value of nannofossils is 1.869‰ higher than that of planktonic foraminifera, and is 3.855‰ lower than that of benthic foarminifera. There are systematic differences between the δ13C values of nannofossils, planktonic foarminifera and benthic foraminifera. The average δ13C of nannofossils is 0.756‰ higher than that of benthic foraminifera, and is 0.460‰ lower than that of planktonic foraminifera. The δ13C values of nannofossils exhibit a significant positive shift beginning near isotope stage 14 and lasting until stage 8. This study also finds that there is a close ralationship between the δ13C of nannofossils and the percentage of Florisphaera profunda. This implies that the δ13C of nannofossils can be used as an indicator of sea water surface paleoproductivity.     

Changes in sea surface temperature in western South China Sea over the past 450 ka

Sea surface temperature over the past 450 ka was obtained by the unsaturation of molecular fossil-long chain alkenone with a resolution of about 1 ka from the western South China Sea. This is the longest temperature profile in the South China Sea at such high resolution. The U37^κ-SST results revealed similar glacial-interglacial cycles as the δ^18O profile of planktonic foraminifera, with SST variability of 23-25.5℃ for glacial and 25-28℃ for interglacial periods. The highest SST （28.4℃） was recorded at MIS5.5 and lowest SST （22.6℃） during MIS2. The SST record preceded the planktonic foraminiferal δ^18O on five glacial-interglacial transitions. Comparison of temperature records from the Southern and Northern Hemispheres indicated a more Southern Hemisphere-like pattern for the temperature variation in the SCS. Strong precession and semiprecession signals in the spectra of our SST record manifest the tropical phenomena.     

Indicators of δ13C and δ18O of gas hydrate-associated sediments

The analyses of δ13C and δ18O of gas hydrate-associated sediments from two cores on Hydrate Ridge in Cascadia convergent margin offshore Oregon, eastern North Pacific show the values of d 13C from -29.81‰ to -48.28‰ (PDB) and d 18O from 2.56‰ to 4.28‰ (PDB), which could be plotted into a group called typical carbonate minerals influenced by the methane in cold venting. Moreover, the values of d 13C and d 18O show a consistent trend in both cores from top to bottom with increasing of d 13C and decreasing of d 18O. This trend could be explained as an effect caused by the anaerobic oxidation of methane (AOM) in depth and the oxygen fraction during the formation of gas hydrate in depth together. These characteristics of d 13C and d 18O indicate that the gas hydrate-associated sediments are significantly different from the normal marine carbonates, and they are deeply influenced by the formation and evolution of gas hydrate. So, the distinct characteristics of d 13C and d 18O of gas hydrate-associated sediments could be undoubtedly believed as one of parameters to determine the presence of gas hydrates in other unknown marine sediment cores.     

Anomalous 17O compositions in massive sulphate deposits on the Earth

The variation of delta 18O that results from nearly all physical, biological and chemical processes on the Earth is approximately twice as large as the variation of delta 17O. This so-called 'mass-dependent' fractionation is well documented in terrestrial minerals. Evidence for 'mass-independent' fractionation (delta 17O = delta 17O-0.52 delta 18O), where deviation from this tight relationship occurs, has so far been found only in meteoritic material and a few terrestrial atmospheric substances. In the rock record it is thought that oxygen isotopes have followed a mass-dependent relationship for at least the past 3.7 billion years, and no exception to this has been encountered for terrestrial solids. Here, however, we report oxygen-isotope values of two massive sulphate mineral deposits, which formed in surface environments on the Earth but show large isotopic anomalies (delta 17O up to 4.6%). These massive sulphate deposits are gypcretes from the central Namib Desert and the sulphate-bearing Miocene volcanic ash-beds in North America. The source of this isotope anomaly might be related to sulphur oxidation reactions in the atmosphere and therefore enable tracing of such oxidation. These findings also support the possibility of a chemical origin of variable isotope anomalies on other planets, such as Mars.     

Oxygen isotope evidence for two-stage water-rock interactions of the Nianzishan A-type granite in NE China

The oxygen isotope ratios of whole-rock, common rock-forming minerals and zircon from Mesozoic A-type granitic pluton at Nianzishan in northeastern China were analyzed by the conventional BrF5 method and the laser-probe technique, respectively. Both whole-rock and rock-forming minerals show large δ18O variations up to 5.5%. with significant oxygen isotope disequilibrium between zircon and the other minerals, whereas the δ18O values of zircon are tightly clustered between 3.12%. and 4.19%. and thus lower than the normal-mantle δ18O values. These results indicate that the Nianzishan A-type granite experienced two-stage water-rock interactions subsequentially. The remarkably low zircon δ18O values are genetically due to sea-water exchange with granite protolith in the first stage, and the oxygen isotope disequilibrium fractionations between zircon and rock-forming minerals are caused by meteoric-hydro thermal alteration in the second stage. It is inferred that the 18O-depleted A-type granitic magma was derived from partial melting of subducted lower oceanic crust which was isotopically exchanged with seawater at high temperatures. In the process of granite emplacement into the upper crust, meteoric-hydrothermal circulation was triggered to overprint crystallizing granite under subsolidus conditions.     

Evidence from detrital zircons for the existence of continental crust and oceans on the Earth 4.4 Gyr ago

No crustal rocks are known to have survived since the time of the intense meteor bombardment that affected Earth between its formation about 4,550 Myr ago and 4,030 Myr, the age of the oldest known components in the Acasta Gneiss of northwestern Canada. But evidence of an even older crust is provided by detrital zircons in metamorphosed sediments at Mt Narryer and Jack Hills in the Narryer Gneiss Terrane, Yilgarn Craton, Western Australia, where grains as old as approximately 4,276 Myr have been found. Here we report, based on a detailed micro-analytical study of Jack Hills zircons, the discovery of a detrital zircon with an age as old as 4,404+/-8 Myr--about 130 million years older than any previously identified on Earth. We found that the zircon is zoned with respect to rare earth elements and oxygen isotope ratios (delta18O values from 7.4 to 5.0%), indicating that it formed from an evolving magmatic source. The evolved chemistry, high delta18O value and micro-inclusions of SiO2 are consistent with growth from a granitic melt with a delta18O value from 8.5 to 9.5%. Magmatic oxygen isotope ratios in this range point toward the involvement of supracrustal material that has undergone low-temperature interaction with a liquid hydrosphere. This zircon thus represents the earliest evidence for continental crust and oceans on the Earth.     

Subtropical to boreal convergence of tree-leaf temperatures

The oxygen isotope ratio (delta(18)O) of cellulose is thought to provide a record of ambient temperature and relative humidity during periods of carbon assimilation. Here we introduce a method to resolve tree-canopy leaf temperature with the use of delta(18)O of cellulose in 39 tree species. We show a remarkably constant leaf temperature of 21.4 +/- 2.2 degrees C across 50 degrees of latitude, from subtropical to boreal biomes. This means that when carbon assimilation is maximal, the physiological and morphological properties of tree branches serve to raise leaf temperature above air temperature to a much greater extent in more northern latitudes. A main assumption underlying the use of delta(18)O to reconstruct climate history is that the temperature and relative humidity of an actively photosynthesizing leaf are the same as those of the surrounding air. Our data are contrary to that assumption and show that plant physiological ecology must be considered when reconstructing climate through isotope analysis. Furthermore, our results may explain why climate has only a modest effect on leaf economic traits in general.     

Distribution of <Emphasis Type="Italic">δ</Emphasis><Superscript>18</Superscript>O in surface snow along a transect from Zhongshan Station to Dome A,East Antarctica

Surface snow samples were collected during the 14th (1997/1998) and 24th (2007/2008) Chinese National Antarctica Research Expeditions along a transect from Zhongshan Station to Dome A. The stable oxygen isotope ratios of these samples were measured to investigate their relationships with temperature and geographical parameters (latitude, longitude, altitude and distance to the coast). The results reveal a strong positive correlation (R=0.945) between δ¹⁸O and mean annual temperature, with a gradient of 0.84‰°C ^–1, which is a little higher than that in Terre Adelie Land. Regression analyses also show that the δ¹⁸O of surface snow is strongly correlated with distance to the coast (R=0.942), latitude (R=0.942), and altitude (R=0.941). But no significant correlation was found between δ¹⁸O and longitude in study area. Altitude should be the most important factor influencing the δ¹⁸O distribution because of distinctive topography. The δ¹⁸O-altitude and T-altitude gradients along this transect are determined to be –1.1‰/100 m and 1.31°C/100 m, respectively.     

Oxygen isotope variation in the water cycle of the Yamzho lake Basin in southern Tibetan Plateau

Given the potential use of stable isotope in the paleoclimate reconstruction from lacustrine records as well as in the local hydrology cycle, it is crucial to understand the processes of stable isotope evolution in catchment in the Tibetan Plateau region. Here we present a detailed study on the water oxygen isotope based on 2 years observation including precipitation, river water and lake water in the Yamzho Lake, south of the Tibetan Plateau. Temporal variation of local precipitation 5180 shows an apparent ＂monsoon cycle＂. In monsoon season, 5180 in waters is lower. In non-monsoon season, δ^18O in precipitation and lake water is higher and higher river δ^18O exists in spring, probably reflecting the effect of land surface evaporation, together with the higher δ^18O values in spring precipitation. It is also found that the surface lake water δ^18O varies seasonally and annually. The lower lake water δ^18O in the late summer is apparently related to the summer monsoon precipitation. The mean δ^18O value of lake water in 2007 is 1.2‰ higher than that in 2004, probably due to the less monsoon precipitation in summer of 2007, as can be confirmed from the precipitation data at the Langkazi meteorological data. It is also found that an obvious shift of vertical lake water δ^18O reflects the fast mixture of lake water. δ^18O values of lake water are over 10‰ higher than those of precipitation and river water in this region due to the evaporation fractionation. The modeled results show that the evaporation process of the lake water is sensitive to relative humidity, and the present lake water δ^18O reflects a relative humidity of 51% in the Yamzho Lake. It shows that the lake will take 30.5 years to reach present lake water δ^18O given a large shift in the input water δ^18O. The modeled results also reveal that surface lake water temperature and inflow δ^18O have slight effect on the isotopic balance process of lake water in the Yamzho Lake.     

Southwest monsoon changes indicated by oxygen isotope of ostracode shells from sediments in Qinghai Lake since the late Glacial

The δ 18O records of ostracode shells in sediments of core QH-2000 from Qinghai Lake can be used as a better proxy to reflect monsoon changes. Low monsoon precipitation between 17.5 and 11 cal. ka BP is indicated by positive δ 18O values averaging 2.37‰. A fast shift in δ 18O from positive at 11 cal. ka BP to negative at 10 cal. ka BP indicates sharp increase of monsoon precipitation. An interval of generally high monsoon precipitation is observed between 10 and 6 cal. ka BP with δ 18O values averaging -2.15‰. Decrease of monsoon precipitation between 6 and 2.5 cal. ka BP is indicated by positive δ 18O values. δ 18O keeps positive values averaging 3.0‰ between 2.5 and 0 cal. ka BP suggesting low high monsoon precipitation. The climatic changes indicated by δ 18O records of ostracode shells in sedi- ments of core QH-2000 from Qinghai Lake and our broader regional comparison show that the climate in Qinghai Lake since the late Glacial is probably controlled by southwest monsoon other than southeast monsoon.     

Δ-Σ频率合成器带外量化噪声抑制技术

基于对电荷泵电流不匹配引起的高阶Δ-Σ调制器（DSM）量化噪声建模,提出一种改进型小数分频频率合成器（Frac-N）模型,即：在传统小数分频频率合成器的反馈支路上嵌入一个不含分频器的宽频带锁相环（PLL）构成的噪声滤除器（NF）。另外,为了减小鉴频鉴相器（PFD）输入端相位误差,设计了一个线性度能达到89%的电荷泵。该频率合成器采用0.18μm CMOS电路实现,仿真结果表明采用该噪声滤除技术可以对高阶DSM产生的带外量化噪声进行有效抑制。