High resolution oxygen isotope and grayscale records of a medieval fossil giant clam(Tridacna gigas) in the South China Sea: physiological and paleoclimatic implications

Mollusks are well known for their detailed recording of paleoenvironmental and paleoclimatic changes in their carbonate shells. In this study, we constructed 18-year blue color intensity and oxygen isotope profiles of a14C dated （AD 990±40） fossil giant clam,Tridacna gigas, from Shidao Island, South China Sea. Theδ18O profile of theT. gigas specimen displayed regular annual cycles and was probably controlled by seasonal variations of the climatic parameters. The blue color intensity profile showed good agreement with theδ18O series, and both had 18 clear annual cycles in accordance with the 18 visually identified annual growth bands. The annual shell growth rate determined from the blue color intensity and oxygen isotope profiles indicated that the annual shell increment of theTridacna specimen was stable after the onset of sexual ma-turity. Spectral analysis of theδ18O and blue color intensity time series suggested that the El Ni？o-Southern Oscillation （ENSO） period observed in the instrumental temperature and precipitation records of the South China Sea during the past 50 years also existed in medieval times. Our results showed that fossil giant clams could provide a good archive of historical intra-seasonal to decadal climate variations.

Heat budget analysis in three typical warm periods simulated by FGOALS-s2

This study compared basic warming patterns among three typical warm periods — the midHolocene（MH）, Medieval Warm Period（MWP）, and the twentieth century warming（20CW） — and carried out a comprehensive heat budget analysis using four experiments simulated by the Flexible Global Ocean–Atmosphere–Land System model, Spectral Version 2（FGOALS-s2）. The model simulates similar spatial warming patterns in all three warm periods, e.g. stronger warming appears in the high latitudes. However, changes in surface air temperature（SAT） over the tropical regions are different： a significant warming occurs in the 20 CW and MWP but a significant cooling in the MH. The heat budget analysis suggested that SAT changes are mainly induced by the heat flux. In the MH, the insolation and positive snow and ice feedback are responsible for the warming in the Southern Ocean but the wind anomalies and decreased downward longwave radiation（DLR） induce the cooling in the tropics. In the 20 CW, the decreased shortwave radiation and increased sea surface temperature dependency of evaporation dampen the warming in the tropics. In the MWP, the shortwave radiation induces the Southern Ocean warming, but the DLR and wind anomalies warm the SAT in the tropics. The simulated ocean temperature and ocean heat content anomalies are different in the upper ocean（above 1500 m）, which are mainly induced by the wind stress changes, but similar in the deep ocean in all three warm periods.

Shakespeare:Related History and Creation Themes

As a world-level author,Shakespeare is more and more popular to Chinese readers.However,Shakespeare is hard to un⁃derstand for students who are not familiar to British history.To facilitate the understanding of Shakespeare’s plays,this paper intro⁃duces the historical background and historical events depicted in the works of Shakespeare and lists several themes discussed in Shakespeare’s history plays and tragedies.

Coastal environment of the past millennium recorded by a coastal dune in Fujian,China

Coastal dune is a common aeolian geomorphology in a sandy coast,which records the evolution process of the aeolian landscape system and reflects the complex interaction among land surface,atmosphere and ocean.Coast is a sensitive area to global climate change.Restricted by chronology,most previous researches in China focused only on the cause of formation of coastal dunes.In recent years,the development of optically stimulated luminescence （OSL） dating provides a good method and acts as a carrier for coastal dunes to paleoclimate and paleoenvironmental studies.In this study,we selected an aeolian dune at the Anshan archaeological site,Fujian,China as the research object based on field observations.For determining their sedimentary stages and the primary influencing factors,we used the OSL dating method to construct a chronological framework for the aeolian dune.In addition,the sizes of grains were analyzed for identifying factors influencing the winter monsoon during the Medieval Warm Period （MWP） and the Little Ice Age （LIA） in this area.The results showed that the deposition of the aeolian dune was closely related to variations in the winter monsoon intensity.The changes of the winter monsoon were similar to the tendency of the East Asian winter monsoon,although there were several sub-fluctuations.From an overall perspective,the winter monsoon was strengthened during the MWP （1050–1300） .The results of a power spectrum analysis showed that the intensity of the East Asian winter monsoon is correlated with sunspot activity.

Multi-scale analysis on last millennium climate variations in Greenland by its ice core oxygen isotope

The empirical mode decomposition method is used for analyzing the paleoclimate proxy δ18O from Greenland GISP2 ice core.The results show that millennium climate change trends in Greenland record the Medieval Warm Period (MWP) from 860AD-1350AD lasting for about 490 years,and the Little Ice Age (LIA) from 1350AD-1920AD lasting about 570 years.During these events,sub cooling-warming variations occurred.Its multi-scale oscillations changed with quasi-period of 3-year,6.5-year,12-year,24-year,49-year,96-year,213-year and 468-year,and are not only affected by ENSO but also by solar activity.The oscillation of intrinsic mode function IMF7,IMF8 and their tendency obviously appear in 1350AD which is considered as the key stage of transformation between MWP and LIA.The results give more detailed changes and their stages of millennium climate change in high latitude areas of the Northern Hemisphere.

Temperature variations along the Silk Road over the past 2000 years:Integration and perspectives

Reconstructing temperature changes along the Silk Road(SR)over the last two millennia can provide insights into past global changes and their impact on the rise and fall of ancient civilizations in this region.Numerous high-quality single-site paleotemperature records have been produced for the eastern part of the SR(mainly for the Xinjiang region and its surrounding areas),which provide the data basis for a comprehensive synthesis.In this study,we used objective criteria to select 10 highquality ones from 30 temperature reconstructions derived from various geological archives including lacustrine sediments,ice cores,and tree rings in this region.Our aims are to summarize the pattern of temperature change over the past 2000 years,to provide a long-term viewpoint on the present warming,and to evaluate the impact of climate change on civilizations along the SR.The principal results are as follows:(1)The temperature variations over the last millennium are mutually consistent within these records.The study area experienced typical climate anomalies during the Medieval Warm Period(MWP,AD 1000-1250),the Little Ice Age(LIA,AD 1450-1850),and the Current Warm Period(CWP,AD 1850 to present);however,contrary to previous knowledge,the amplitude of climatic warming during the CWP did not exceed that during the MWP.(2)Fewer temperature records were available for the interval AD 1–1000,and there were large differences between them.For example,the reconstructed climate during both the Han Dynasty and the Sui-Tang Dynasties was either warm or cold,without prevailing consensus.(3)The warming during the MWP favored the rapid development of the SR route along the northern slopes of the Tianshan Mountains,and the cooling during the LIA contributed to the decline of the SR marked by the closure of the Jiayuguan Pass.Notably,the scarcity of temperature records and the discrepancies between them during AD 1-1000 in the eastern part of the SR have hindered our understanding of the hydroclimatic changes and their influence on the development of civilizations along the SR.Thus,it is important to obtain an increased number of high-quality reliable records spanning the past 2000 year,and to examine the occurrence of local signals of temperature changes during the period of AD 1-1000.On the other hand,the paleotemperature investigation on the western part of the SR over the last two millennia is wholly insufficient,and thus more high-quality single-site and integrated studies are needed,to facilitate more comprehensive insights into the coupled relationship between climate change and the rise and fall of civilizations along the entire length of the Silk Road.

Palaeo-sea-ice changes on the North Icelandic shelf during the last millennium:Evidence from diatom records

A high resolution record of sea-ice concentration on the North Icelandic shelf during the last millennium has been reconstructed using a diatom-based sea-ice transfer function. The reconstructed sea-ice record for the top of sediment core MD99–2275 exhibits a slightly increasing trend over the last 1000 years. Prior to AD 1300 sea-ice abundance was generally below the mean value, suggesting the strong influence of warm waters from the Irminger Current during the Medieval Warm Period. A marked increase of sea-ice concentration indicates an abrupt change to colder conditions after AD 1300, corresponding to the onset of the Little Ice Age. The agreement between the reconstructed sea-ice concentration and IP25 data obtained from the same core, as well as with historical records of Icelandic sea ice, suggests that diatoms may provide a valuable tool for future quantitative reconstructions of past sea-ice variability. In addition, agreement between changes in the reconstructed sea-ice record and variations in the abundance of the major diatom components indicates that sea-ice conditions on the North Icelandic shelf are generally strongly influenced by changes in the strength of two different water masses, the cold Polar water periodically derived from the East Greenland Current and the warm Irminger Current derived from the North Atlantic Current. Our proxy evidence also indicates that variations in solar activity have a considerable impact on ocean dynamics, which in turn affects sea-ice abundance.

Human activity and climate change triggered the expansion of rocky desertification in the karst areas of Southwestern China

It is conducive to the sustainable development of human beings in karst regions to research the mechanism of karst rocky desertification(KRD)expansion.Whether the large-scale KRD in southwestern China is caused by climate change or human activities is still controversial.In this study,the evolution of the KRD in southwestern China over the past 2000 years was reconstructed through the high-precisionδ^(13)C record of stalagmites from Shijiangjun(SJJ)Cave,Guizhou Province,China.Theδ^(13)C of the stalagmites from SJJ Cave exhibited heavy values from the Medieval Warm Period(MWP)to the Little Ice Age(LIA).Furthermore,theδ^(13)C records of other stalagmites and tufa from southwestern China also showed the same significant heavy trend.Because the stalagmiteδ^(13)C could record the change of ecological environment,it indicated that the consistent change of the stalagmitesδ^(13)C may record the process of KRD expansion in the karst regions of southwestern China.During the MWP,the stronger Asian summer monsoon and the northward movement of the rain belt led to a dry period in southwestern China and a wet period in northern China.In contrast,it was wet in southwestern China and dry in northern China during the LIA.In addition,after the Jing-Kang event(JK event,AD1127)occurred at the end of the Northern Song dynasty,the political and economic center of China migrated to southern China for the first time,which changed the population distribution pattern of larger population in the north and smaller population in the south.Therefore,the expansion of KRD in southwestern China was exacerbated in the MWP due to the change of climate in southwestern China,the migration of a large number of people,wars,the large-scale reclamation of arable land,and the cultivation of large areas of crops.