precisely dated ams 14c marine cores reveal the complexity of millennial scale asian monsoon variability in the northern south china sea md972146 md972148 abstract high sedimentation rate sr cores retrieved from the south china sea scs form the basis for studying the marine components of millennial scale asian monsoon am variability and for comparison with the am reconstructions from cave records on land e g dongge and hulu however carefully correlating the scs sedimentary records to the cave records that are precisely dated by u th methods with resolution of decadal scale has not been completed such a correlation is essential when comparing am influences expressed over land and sea but requires a construction of marine ams 14c age models that are precise enough to be compared to the cave u th age models for the purpose of establishing such a correlation this study presents new data from intensive ams 14c dated marine cores retrieved from the northern scs md972146 md972148 the discrepancy of marine and cave 18o record for the interval of 18 30 ka might be due to the change of marine 14c reservoir age in scs surface water during the glacial period and to the change in interhemispheric dominance of the am systems with the new ams 14c dating on md972146 and md972148 we examined the millennial scale records of planktonic foraminifer 18o and carbonate contents of md972146 md97248 and sonne 17940 2 and compared those records with dongge hulu 18o record of the past 30 ka our results show that in the intervals corresponding to the high latitude northern hemisphere nh younger dryas yd and heinrich i event h1 the ams 14c dated millennial scale oscillations show relatively heavy 18o and low carbonate contents but h2 and h3 are in the opposite direction our results indicate the complexity for the marine cores which were used in interpreting the millennial scale am variability

glacial holocene biogenic sedimentation patterns in the south china sea productivity variations and surface water pco2 a bathymetric transect of cores in the south china sea extending from 4200 m to less than 1000 m water depth has been examined for glacial interglacial changes in carbonate and organic carbon sedimentation typical pacific carbonate cycles high carbonate content during glacials and low carbonate content during interglacials characterize cores from water depths deeper than 3500 m in contrast atlantic carbonate cycles low carbonate during glacials and high carbonate during interglacials are observed in cores from depths shallower than 3000 m as a result of increased dilution of carbonate by terrigenous material during glacial low stands of sea level glacial interglacial changes in the carbonate chemistry of south china sea intermediate and deep waters resulted in significant changes in the positions of the carbonate compensation depth ccd and the aragonite compensation depth acd during the last glacial the ccd and acd were at least 400 and 1200 m deeper respectively than at present organic carbon accumulation rates in the south china sea were approximately 2 times higher during the last glacial than the holocene carbon isotopic analyses and c n ratios of the organic matter indicate that only a small fraction of the increase in glacial organic carbon accumulation can be attributed to input of terrestrial carbon on the basis of this we conclude that surface water productivity in the south china sea was approximately 2 times higher during the last glacial maximum this is consistent with previous studies which have demonstrated that glacial productivity was higher in low to mid latitude regions of the atlantic and eastern pacific the deglacial decrease in organic carbon accumulation is accompanied by a decrease in 13corg using the relationship between 13corg and co2 aq developed by popp et al 1989 we estimate that surface water pco2 values in the south china sea during the last 25 000 years were very similar to atmospheric co2 concentrations

astronomically tuned plio pleistocene benthic δ 18 o record from south china sea and atlantic pacific comparison based on benthic foraminiferal n 18 o from odp site 1143 a 5 myr astronomical timescale for the west pacific plio pleistocene was established using an automatic orbital tuning method the tuned brunhes matuyama paleomagnetic polarity reversal age agrees well with the previously published age of 0 78 ma the tuned ages for several planktonic foraminifer bio events also agree well with published dates and new ages for some other bio events in the south china sea were also estimated the benthic n 18 o from site 1143 is highly coherent with the earth s orbit etp both at the obliquity and precession bands for the last 5 myr and at the eccentricity band for the last 2 myr in general the 41 kyr cycle was dominant through the plio pleistocene although the 23 kyr cycle was also very strong the 100 kyr cycle became dominant only during the last 1 myr a comparison of the benthic n 18 o between the atlantic odp 659 and the east and west pacific 846 and 1143 reveals that the atlantic pacific benthic oxygen isotope difference ratio vn 18 oatlpac displays an increasing trend in three time intervals 3 6 2 7 ma 2 7 2 1 ma and 1 5 0 25 ma each of the intervals begins with a rapid negative shift in vn 18 oatlpac followed by a long period with an increasing trend corresponding to the growth of the northern hemisphere ice sheet this means that all three intervals of ice sheet growth in the northern hemisphere were accompanied at the beginning by a rapid relative warming of deep water in the atlantic as compared to that of the pacific followed by its gradual relative cooling this general trend superimposed on the frequent fluctuations with glacial cycles should yield insights into the processes leading to the boreal glaciation cross spectral analyses of the vn 18 oatlpac with the earth s orbit suggests that after the initiation of northern hemisphere glaciation at about 2 5 ma obliquity rather than precession had become the dominant force controlling the vertical structure or thermohaline circulation in the paleo ocean a 2002 elsevier science b v all rights reserved

carbonate dissolution fluctuations in the western equatorial pacific during the late quaternary planktonic foraminiferal test fragmentation in three cores along a depth transect from the western equatorial pacific erdc 93p 1619 m rc17 177 2600 m v28 238 3120 m thompson 1976 were examined for the last 500 kyr at sample intervals from 2 5 to 5 kyr to study the fluctuations of dissolution in the western equatorial pacific the age models were constructed by correlating the 18o records with the specmap stack imbrie et al 1984 results showed that intermediate and deep waters experienced the same patterns of dissolution through climatic cycles fragmentation varied with a greater amplitude and the carbonate ion concentration changed less in the deep than in the intermediate water dissolution has significant variance distributions and coherencies with 18o over the 100 41 and 23 kyr periods of orbital variations dissolution maxima lag ice volume minima by 6 to 20 kyr the dissolution variability was consistent with recent geochemical models which seek to explain the reduction of atmospheric co2 concentration at the last glacial maximum broecker 1982 boyle 1988

climatic change and caco3 preservation an 800 000 year bathymetric reconstruction from the central equatorial pacific ocean sixteen deep sea cores from the central equatorial pacific are used to reconstruct a continuous 800 000 year 800 kyr record of bathymetric variations in carbonate preservation as measured by calcium carbonate caco3 content the depth of the sedimentary lysocline has fluctuated markedly in conjunction with late pleistocene climate cycles while the carbonate critical depth ccrd which is the water depth where the sediments contain 10 caco3 has remained relatively constant as a result the depth of the lysocline controls the bathymetric position and thickness of the caco3 transition zone defined as the depth from the lysocline to the ccrd modern and interglacial aged sediments show poor caco3 preservation and thick caco3 transition zones glacial aged sediments show good preservation and deep thin zones due to the deepening of the lysocline detailed comparison of the caco3 preservation and oxygen isotope records from the central equatorial pacific confirms the observation that preservation maxima and minima tend to occur during the latter half of glacial and interglacial stages and on climate transitions rather than during the middle of climatic stages during the nine major glacial stages of the last 800 kyr the lysocline deepened by at least 400 to 800 m this deepening indicates an increase in the abyssal carbonate ion concentration co3 and a depression of the calcite saturation horizon best explained by the deeper presence of a more carbonate saturated water mass the bottom of the transition zone has remained at a relatively constant depth during the brunhes chron indicating a balance between caco3 sedimentation and dissolution in the deepest waters of the central equatorial pacific

geomagnetic paleointensity dating of south china sea sediments for the last 130 kyr relative paleointensity records from the northern south china sea northwest pacific ocean were studied in two gravity piston cores continuous mineral magnetic and paleomagnetic measurements were made using discrete sediment samples detailed rock magnetic parameters such as thermomagnetic and high field hysteresis data indicate that pseudo single domain magnetite in a narrow range of grain size and concentration is the main contributor to the remanent magnetization the uniform magnetic mineralogy meets the commonly accepted criteria for establishing relative paleointensity records the relative paleointensity rpi curves were constructed by normalizing the natural remanent magnetization nrm with isothermal remanent magnetization irm both in the 20 60 mt demagnetization state dating constraints have been provided by radiocarbon ages in the upper 400 cm of both cores furthermore we have correlated our paleointensity records with napis 75 s atlantic 1089 sint 200 and nopapis 250 to determine the chronological rpi framework for the south china sea scs pis although some temporal offsets of paleointensity features between the different records have been recognized their similar shape suggests that relative paleointensity on the 10 3 10 4 year scale is globally coherent and can provide an age framework for sediments independent of delta 18 o ages c 2009 elsevier b v all rights reserved

paleoenvironmental changes in the northern south china sea over the past 28 000years a study of tex86 derived sea surface temperatures and terrestrial biomarkers abstract we have generated a record of tex86 tex 86 h derived sea surface temperatures ssts over the last 28 ka for core md97 2146 from the northern south china sea scs the tex 86 h derived temperature of a core top sample corresponds to the ssts in warmer seasons the sst record shows a drop during the oldest dryas period an abrupt rise at the onset of the bolling allerod period a plateau across the younger dryas period and an abrupt rise at the beginning of the holocene the glacial interglacial contrast in tex 86 h derived temperature is almost the same as that in foraminiferal mg ca ratio derived temperature but it is larger than those in u 37 k and transfer function derived temperatures possible interpretations are 1 the seasonal shift of glycerol dialkyl glycerol tetraether gdgt production 2 the overestimation of temperature change by tex 86 h and 3 the underestimation of temperature change by u 37 k and transfer function approaches the similar variation in tex 86 h derived temperature at the study site and chinese stalagmite 18o during the last deglaciation suggests that changes in tex 86 h derived temperature in this period reflected atmospheric and oceanic reorganization on a millennial timescale the long chain n alkanes are mainly of higher plant origin before 14 ka and a mixture of higher plant and lithic origins after 14 ka the abundance ratio of long chain to short chain n fatty acids decreases at 15 ka suggesting a drastic change in sediment sources at 14 15 ka we attribute the higher content of fresh higher plant n alkanes and long chain n fatty acids before 14 15 ka to enhanced aeolian transportation and or arid environments increased precipitation likely due to intensified summer monsoon after 14 15 ka enhanced the erosion of sedimentary rocks and increased the contribution of lithic n alkanes

astronomical forcing of the east asian monsoon mirrored by the composition of pliocene south china sea sediments abstract high precision major and minor element records of pliocene core intervals from ocean drilling program odp site 1145 located in the northern part of the south china sea were generated at a 5 cm approximately 2 kyr resolution from the geochemical data distinct proxies those indicating changes in detrital matter provenance as well as those indicating productivity variations could be derived both the terrigenous input to the northern south china sea k si and variations in productivity ba al show a response to insolation forced monsoon variability while the fluvial input k si responds to changes in the summer monsoon productivity increases as documented by ba enrichments seem to reflect variations in winter monsoon intensity a stronger winter monsoon may have increased nutrient availability via dust input and or upwelling phenomena according to our geochemical proxy records summer and winter monsoons are approximately 180 out of phase this may imply forcing of the winter monsoon through southern hemisphere summer insolation maxima the k si ratio shows a linear correlation with the la90 1 0 5 northern hemisphere summer insolation record and has therefore been used to create an astronomical timescale for the investigated sediments of odp site 1145 carbonate contents and corresponding color reflectances display 41 and 100 kyr cycles we propose that these do not reflect glacial cycles but are rather the result of an interference signal of dilution by fluvial and eolian terrigenous material and carbonate production burial flux a sudden onset of gradual changes in sediment composition occurs after 3 0 ma this is also documented by an increase in sedimentation rates and may be caused by enhanced fluvial input from the pearl river due to intensified weathering rates on the asian continent this may be linked to tectonic processes around the himalayan tibetan complex and its consequences regarding land sea heating and atmospheric circulation

clay minerals sr nd isotopes and provenance of sediments in the northwestern south china sea abstract the clay mineralogy and sr nd isotopic composition of sediments collected in the northwestern south china sea scs were investigated to understand sediment provenance and changes in the scs since the late pleistocene our results show that the clay mineral assemblages of the surface sediments are characterized by high amounts of illite and smectite and low amounts of kaolinite and chlorite the 87sr 86sr ratios of the surface sediments vary from 0 709617 to 0 734416 and end values range from 11 6 to 8 3 the clay minerals and sr nd isotope records suggest that sediments in the northwestern scs are derived from multiple sources the sediments deposited in the eastern shelf offshore of hainan originate predominantly from hainan island and south china whereas sediments in the western shelf offshore of hainan are derived mainly from indochina and hainan island however sediment source and transport mechanisms in the northwestern slope of the scs are more complicated our results suggest that input from the west may be the major sediment source but regions in the east taiwan and luzon also contribute part of the terrigenous materials downcore variations of sr nd isotopic composition in core sediments show clear glacial interglacial fluctuations higher 87sr 86sr ratios occur during glacial period indicating that the input of terrigenous materials from old continental rocks becomes one of the important sediment sources during these periods the exposure of continental shelf and southward migration of the coastline during the glacial sea level lowstand led to an increase of terrigenous supply to the northwestern slope of the scs the paleo red river and indochina are also potentially important contributors

planktonic foraminifera in the western north pacific during the past 150 000 years comparison of modern and fossil assemblages abstract planktonic foraminiferal abundance variations in 186 deep sea piston core tops from the western north pacific were used to create a calibration set to characterize the present day kuroshio gyre system q mode factor analysis helped identify six faunal assemblages 93 variance related to modern water masses two tropical assemblages differing in relative dissolution three assemblages representing subtropical subpolar and transitional conditions and a gyre margin assemblage lying between the kuroshio current and the mainland of asia multivariate regression produced transfer functions relating observed summer august and winter february sea surface temperatures sst to the assemblages with standard errors of estimate of 1 5 c and 2 5 c respectively data from 24 piston cores was used to interpret variations of the kuroshio gyre system during the past 150 000 yr stratigraphic control is based on oxygen isotopic measurements the extinction of pink pigmented globigerinoides ruber at 120 000 b p coiling direction changes in neogloboquadrina pachyderma north of 30 n and dissolution variations between resistant and fragile taxa major dynamic changes in the circulation of the kuroshio gyre occurred during the last two glacial maxima at 15 20 000 b p isotopic stage 2 and at 140 150 000 b p isotopic stage 6 these intervals are characterized by 1 lowered sea levels which reduced flow into the sea of japan and sea of okh okhotsk 2 advance of the polar front from its modern position at about 42 n to 35 38 n 3 southward penetration of the oyashio current along the pacific coast of japan to tokyo 4 2 3 c lowered sst in tropical areas little or no change in subtropical areas and a 4 6 c decrease in transitional areas and 5 an overall decrease in carbonate dissolution relative to interglacial stages the maximum interglacial at 120 000 b p isotopic substage 5e shows a retreat of the polar front north of its modern position and an overall relative increase in interglacial carbonate dissolution that does not become severe until substage 5d

comparison between radiocarbon ages obtained on coexisting planktonic foraminifera as a test of the reliability of paleocean ventilation rates reconstructed from radiocarbon age differences between planktonic and benthic foraminifera measurements have been made on coexisting species of planktonic foraminifera while ideally no differences should exist we do find them in this paper we discuss the possible causes for these differences and attempt to evaluate their impact on the interpretation of benthic planktonic age differences

ocean ventilation during the last 12 000 years hypothesis of counterpoint deep water production abstract available radiocarbon data on selected planktonic foraminifera species suggest that differential dissolution reduces the 14 c c ratio in planktonic tests removing 14c rich specimens from assemblages of surface dwelling species the effect is analogous to that observed for stable isotope composition in planktonic foraminifera other disturbing factors apparently affect benthic radiocarbon data as well thus radiocarbon stratigraphies are difficult to interpret in terms of history of deep water ages that is deep ocean mixing the best data at hand south china sea after corrections for differential dissolution and benthic vital deviations suggest a high variability of deep water mass ages in the late glacial period which is explained in terms of vertical motion of deep water mass boundaries across the recording sites the fluctuations are ascribed to sporadic increases in deep water production in the north pacific during cold periods and to the presence of a glacial bottom water mass which resisted mixing during deglaciation

a millennial scale u37k sea surface temperature record from the south china sea 8 n over the last 150 kyr monsoon and sea level influence we report 150 kyr records of u37 sea surface temperature sst and carbonate content with 150 200 year sampling resolution from the southern south china sea scs in the northern margin of the western pacific warm pool wpwp using images core md972151 the glacial interglacial sst change is about 5 c for termination ii 23 5 to 28 5 c and 4 c for termination i 24 to 28 c the simultaneous rise of sea level and u37 sst during termination i suggests that sea level change has played an important role in the scs sst variability by influencing the exchange of tropical ocean warm surface water with the scs through the sunda shelf region sill depth 30 50 m when sea level drop was less than 30 m relative to today s md972151 sst was constantly above 27 c a situation which occurred during mis 5e part of mis5c and 5a and over the last 11 kyr sea level change was also the main control on carbonate content in the scs this was lower during low sea level stands due to the dilution effect of enhanced terrigenous inputs within the limitations of our age model millennial scale sst oscillations 1 5 c over a few hundred years occurred frequently during the entire glacial period correlating reasonably well with the hulu monsoon record from eastern china and the dansgaard oeschger d o cycles recorded for high latitude regions in the northern hemisphere such correlations suggest a possible teleconnection between higher latitude atmospheric forcing and low latitude climate oscillations in the western pacific tropical region via the asian monsoon system carbonate content also reveals millennial scale oscillations during the glacial period with higher content correlated with higher sst millennial scale fluctuations of sst and carbonate contents at this low latitude scs provide additional evidence that high frequency climate changes are global phenomena

development of east asian summer monsoon environments in the late miocene radiolarian evidence from site 1143 of odp leg 184 abundant radiolarians are preserved in the relatively complete upper miocene section of odp site 1143 three radiolarian zones rn6 rn7 and rn8 are recognized on the basis of diartus petterssoni total range in rn6 6 7 ma variations in the abundance of radiolarians especially pyloniid forms radiolarian flux and species diversity are good proxies of upwelling which similar to today s was likely driven by summer monsoons these radiolarian paleomonsoon proxies indicate that the east asian summer monsoon first initiated close to the middle late miocene boundary at similar to 12 11 ma and reached a maximum strength at similar to 8 24 ma therefore the initiation of the east asian summer monsoon was likely earlier than the first indian monsoon which appeared similar to 8 myr ago c 2003 elsevier b v all rights reserved

new evidence from the south china sea for an abrupt termination of the last glacial period abrupt changes in climatic conditions have been seen at high latitudes in the north atlantic1 and the antarctic2 3 at 13 kyr bp it is important to determine whether this abrupt change was confined to high latitude regions or whether it was global here we present results demonstrating an abrupt change in the rate and character of sedimentation in the south china sea at the close of the last glacial period radiocarbon dating and its position in the oxygen isotope shift suggest that this change may be coincident with the changes found at high latitudes

paleoceanography of the south china sea since the middle miocene evidence from planktonic foraminifera late middle miocene to pleistocene planktonic foraminifera pf in fairly continuous hemipelagic sediments recovered at ocean drilling program odp site 1143 from the southern south china sea scs were studied with sampling intervals of 10 to 150 cm a total of 16 pf events are revised for the 516 m long section providing an age model for the last 12 ma at this site on the basis of benthic foraminiferal d 18 o stratigraphy and the smoothed planktonic age model new ages are assigned to three pf events last occurrence lo globorotalia multicamerata sensu lato s l at 2 18 ma first occurrence fo sphaeroidinella dehiscens sensu stricto s s at 3 6 ma and fo globigerinoides conglobatus at 6 6 ma in the south china sea distinct pf faunal transition from globorotalia siakensis g mayeri group to mixed layer species occurred during the early late miocene 9 6 ma the transition reflects a deepened upper water thermocline possibly corresponding to the closure of the indonesian seaway and intensification of equatorial pacific warm currents abundance variations of neogloboquadrina spp indicate a marked shoaling of the thermocline in the northern south china sea after 3 2 5 ma affected possibly by a strengthened asian winter monsoon while a deeper thermocline existed in the southern south china sea since the late miocene characterizing the west pacific bwarm poolq wpwp a deepening thermocline influenced by consistently warm surface water since the late miocene in the southern south china sea is also evidenced by a two stepwise increase of pulleniatina group by a gradually decreasing sphaeroidinella sphaeroidinellopsis spp and abundant globorotalia menardii and related species the fo globigerinoides ruber pink at approximately 1 ma and an abrupt increase in the pink to all ratio of g ruber at 0 4 ma at site 1143 provide two additional pf events for deciphering pleistocene biostratigraphy and paleoceanography d 2004 elsevier b v all rights reserved

millennial scale dynamics of the winter cold tongue in the southern south china sea over the past 26 ka and the east asian winter monsoon millennial scale variations of the east asian winter monsoon eawm remain elusive due to sparse and controversial reconstructions by compiling a variety of alkenone based sea surface temperature sst estimates we find that the west east sst gradient in the southern south china sea scs well documents the temporal dynamics of the winter cold tongue off the southern vietnam and by inference variations in the eawm intensity over the past 26 ka our results reveal that the winter cold tongue ssts were significantly colder during heinrich event 1 and the younger dryas event resulting in an increased west east sst gradient in the southern scs due to a strengthened eawm within dating uncertainties an intensified eawm during cold stadials was coeval with the shutdown or a reduction in strength of the atlantic meridional overturning circulation amoc exhibiting a strong linkage between the amoc and the eawm system the west east sst gradient also indicates an enhanced eawm during the early holocene which may be induced by postglacial ice sheet dynamics and a strong seasonal contrast in solar insolation our findings suggest that the eawm was probably modulated by a complex interplay between the amoc solar insolation and ice sheet dynamics on sub orbital time scales

pleistocene paleoceanography of the south china sea progress over the past 20 years article i nfo the south china sea scs has become one of the foci in paleoceanographic research and hydrocarbon explora tions over the last 20 years over the period at least 16 international cruises including odp ocean drilling pro gram leg 184 have investigated the scs and more than 2000 exploratory wells have been drilled the present paper attempts to synthesize progress in pleistocene paleoceanography because of the high depositional rates and favorable carbonate preservation the scs keeps valuable paleoceanographic archives for the low latitude pacific region which have helped to uncover potential ties between the low latitude oceanic biogeochemical evolution and step wise development of the boreal ice sheet it has been found that the 1 6 ma event marked a reorganization of the oceanic carbon reservoir associated with the restructuring of the southern and the tropical pacific ocean the mpt mid pleistocene transition and mbe mid brunhes event centered at 0 9 ma and 0 4 ma respectively were preluded by carbon isotope maxima 13 cmax iii and 13 cmax ii suggesting that major steps in the ice sheet development were preceded by significant changes in oceanic biogeochemistry the late pleistocene records have demonstrated the amplifying role of the scs in responding to glacial cycles as the amplitudes of sst and 18 ov ariations have been significantly amplified in the scs as compared with the open ocean at the same latitudes the amplification is ascribed to its semi enclosed morphology and the prevail ing monsoon climate the closure of the southern margin during glacial times led to stratification of the upper waters and specific faunal changes in the southern scs the seasonally reversing monsoon winds not only drive the surface circulation but also the biological production the n s gradient in oceanography and the sed iment transportdynamics such asthe asymmetric growth of the mekong river delta becauseof its distinguished position in the low latitudes between the largest continent and the largest ocean the scs provides important insight into the mechanism of environmental evolution with regards to ocean continent or high low latitude interactions

analysis of vegetation and climate change during late pleistocene from ziro valley arunachal pradesh eastern himalaya region abstract vegetation and climate during later part of late pleistocene have been reconstructed from ziro valley arunachal pradesh eastern himalaya based on pollen data along with carbon isotope and magnetic susceptibility data the study reveals that the area and the vicinity is occupied by mixed broad leaved conifer forest and pine grass savanah at variable densities at least since 66 000yr bp the phases of expansions and declines of oaks with decline and increase of pines and grasses probably occurred under increase warm moist and decrease cool dry of s w monsoon precipitation respectively the increasing trend of s w monsoon and temperature is recorded during 44 000 to 34 000 cal yr bp synchronizing with the peat development and which peaked at around 35 000 cal yr bp this may link to the interstadial phase during the last major glacial cycle in the himalayan region it is also reflected in the decline of 13c value indicating dominance of c 3 type of vegetation the increased values of fd and lower values lf magnetic susceptibility recorded during the phase of the peat deposit further advocate s higher monsoon intensity impact of expansion of glacier felt with peak lgm around 20 000 cal yr bp is perceived tree line had moved to lower altitudes due to increased aridity and low temperature during this time existence of savannah type of vegetation is also evident by the increase of c4 taxa decreased fd and increased lf susceptibility also indicate reduced s w monsoon intensity

seasonal variations of modern planktonic foraminifera in the south china sea although foraminiferal census and isotope analyses from sediment cores have been widely applied to paleoceanographic reconstructions in the south china sea scs their modern counterparts i e foraminiferal shells from sediment traps and plankton tows have been the subjects of few studies in this region in this investigation relative abundances of the most popular species used to reconstruct late quaternary tropical sea surface conditions have been studied in plankton tows from the scs in order to offer better constraints on the interpretation of downcore records in addition to the seasonal differences the spatial variations in the faunal assemblage are evident from south to north in the scs basin based on contemporary tows for example the species globigerinella aequilateralis is found to be relatively dominant in the southern lower latitude basin but its relative abundance is significantly higher in planktonic tows than in sediments indicating its proneness to burial dissolution pulleniatina obliquiloculata an index taxon for the kuroshio current is only abundant in the northern part of the scs basin the measured oxygen isotope compositions 18o of globigerinoides ruber globigerinoides sacculifer neogloboquadrina dutertrei and p obliquiloculata all show a good relationship with temperature in the mixed layer tmix the carbon isotope compositions 13c also display a positive distribution pattern relative to tmix but with a less significant correlation in winter months than 18o differences of 18o between shallower g sacculifer and g ruber and deep dwellers n dutertrei and p obliquiloculata accurately record the temperature gradient between the surface mixed layer and 100 m water depth supporting application of this proxy to the reconstruction of upper water column stratification

last glacial maximum in china comparison between land and sea abstract as a result of the sea level drop at the last glacial maximum about 100 120 m in the south china sea and 130 150 m in the east china sea the size and configurations of the china seas changed greatly the east china sea with the yellow sea and bohai gulf was reduced into an elongated trough while the south china sea became a semi enclosed gulf due to the southern shift of the polar front in the north pacific and the reorganization of the surface current system the winter temperature in the south china sea was 6 10 c colder and the seasonality was much stronger than it is now the reduced sea area and thus the increased distance to the coast together with the declined sea surface temperature led to intensified aridity on the land the enhanced eolian processes related to the intensification of the winter monsoon caused an expansion of the loess deposition area reaching the southeastern part of china to the south of the yangtze river and off the modern sea coast vegetation zones greatly shifted to the southeast in north china deserts and steppes were much more extensive than they are now and the modern areas of warm temperate broad leaved forests were occupied by steppes or woodland in south china the deciduous broadleaved forests were developed in areas now covered by evergreen forests and the monsoon rain forest completely disappeared the changes in the climate on land and the configurations of seas altered the sediment supply and sedimentation rate in the china seas giving rise to the atlantic type late quaternary caco3 curve there

optical dating in archaeology thirty years in retrospect and grand challenges for the future in 1982 when richard klein first became one of the editors of this journal the luminescence dating community was embarking on a new phase of exploratory research attention was turning from the use of thermoluminescence tl dating to estimate the time of last heating of archaeological objects such as pottery and burnt flint to the tl dating of unheated sediments that had been transported by wind and then deposited on the landscape this revolutionary development enabled the extension of tl dating to sedimentary deposits in a variety of environmental settings and to the multitude of archaeological sites that lack suitably heated artefacts in sediment dating the age of most interest is usually the time elapsed since grains of quartz or feldspar were last exposed to sunlight as the energy of the sun s rays is sufficient to evict electrons from their light sensitive traps these traps are steadily refilled after sediment deposition and the longer the grains remain buried the more tl they will emit when measured in 1985 huntley and colleagues proposed optical dating as a simpler and superior means of stimulating the light sensitive traps in quaternary sediments and this is now the principal luminescence based method of dating geological and archaeological deposits optical dating is an umbrella term for an armada of acronyms the most common in archaeological contexts being osl optically stimulated luminescence tt osl thermally transferred osl irsl infrared stimulated luminescence and pirir post infrared irsl all of these variants are founded on the same basic tenet measurement of a light sensitive signal to determine typically the last time that sediment grains were sun bleached but each approach has its virtues and vices in this paper we review this family of luminescence dating techniques and look back on 30 years of optical dating in archaeology some of the more interesting and important achievements are highlighted including the critical insights gained in the last two decades from osl measurements of individual grains of quartz we also look to the future of optical dating in archaeological contexts efforts to extend the age limits of optical dating to older hominin and archaeological sites will remain a key goal and understanding how archaeological sites of all ages form and evolve over time could be improved greatly by combining micromorphology analysis with optical dating of undisturbed intact sediments the latter poses a series of particularly formidable technical challenges but if the past is any guide to the future then we can expect optical dating to illuminate much more of human history before celebrating its golden jubilee

early interglacial carbonate dilution events in the south china sea implications for strengthened typhoon activities over subtropical east asia abstract a compilation of many late quaternary marine sediment records from the northern south china sea scs continental slope confirms 15 50 reductions in sedimentary calcium carbonate concentrations between 11 0 and 8 5 ka bp in the early holocene this low carbonate event occurred at a time when the regional sea level rose from 50 m to 10 m which drowned large areas of continental shelves especially those near and within the taiwan strait this event is associated with a significant increase in bulk sedimentation rates on the upper continental slope and the relative abundance of fine grained detritus sediment provenance analyses suggest a dominant terrigenous input from taiwan and a minor contribution from luzon during the low carbonate event similar to the background terrigenous deposition in other periods of the holocene two comparable low carbonate events respectively from the beginning of marine isotope stages 5 5 and 7 3 have also been recognized pointing to similar causal factors while carbonate dissolution and carbonate accumulation rate should not have been responsible increased terrigenous input and dilution is considered as the main cause for the recurrent low carbonate events in early interglacials we further hypothesize that during early interglacials fluvial sediment discharge from taiwan and luzon intensified due to stronger typhoon activities and massive fine grained sediments from these two end members may have been transported to the northern scs continental slope via surface and deep ocean currents the conjecture of strengthened typhoon activities over east asia during the early holocene is supported by high ocean heat contents in the west pacific warm pool area with the prevailing la nina like conditions

late quaternary paleoceanography of the south china sea glacial interglacial contrasts in an enclosed basin the sea surface paleotemperature of the south china sea scs is estimated quantitatively based on the quantitative analysis of planktonic foraminiferal faunas recovered from piston cores v36 06 3 v36 06 5 and so49 kl8 on the northern continental slope the results lead to a reconstruction of the history of paleocirculation patterns during the last 200 000 years the postglacial and interglacial transbasinal circulation pattern was replaced by a semienclosed basin flow pattern during glacial episodes lowered sea level transformed the scs into a semienclosed basin with the only passageway to the open ocean in its northeastern corner the east asian monsoon which governs circulation patterns in the scs both today and during the late quaternary created both clockwise summer and counterclockwise winter surface gyres during glacials the inflow of tropical surface water masses from both the pacific and indian oceans decreased or was completely cut off from this marginal sea causing a greater decrease in glacial sea surface temperature than in the open ocean of the same latitude inferred increased influence of pacific temperate waters and decreased influence of tropical subtropical waters are confirmed by changes in the planktonic foraminiferal assemblages glacial interglacial fluctuation in sea surface temperature sst 6 8 9 3 c for winter and 2 3 c for summer as well as the seasonality 4 6 c for postglacial and interglacials and 9 10 c for glacials are much greater than the adjacent open western pacific reflecting the amplification of the climatic signal in the marginal sea

variable remanence acquisition efficiency in sediments containing biogenic and detrital magnetites implications for relative paleointensity signal recording widespread geological preservation of biogenic magnetite makes it important to assess how such particles contribute to sedimentary paleomagnetic signals we studied a sediment core from the south china sea that passes the strict empirical criteria for magnetic uniformity used in relative paleointensity studies such assessments are based routinely on bulk magnetic parameters that often fail to enable identification of mixed magnetic mineral assemblages using techniques that enable component specific magnetic mineral identification we find that biogenic and detrital magnetites occur in approximately equal concentrations within the studied sediments we analyzed normalized remanence signals associated with the two magnetite components to assess whether co occurring biogenic and detrital magnetites record geomagnetic information in the same way and with the same efficiency paleomagnetic directions for the two components have no phase lag which suggests that the biogenic and detrital magnetites acquired their magnetizations at equivalent times however we find that the biogenic magnetite is generally 2 4 times more efficient as the detrital magnetite in contributing to the natural remanent magnetization nrm despite their approximately equal magnetic contributions variations in the concentration and efficiency of remanence acquisition of the two components suggest that a significant part of the nrm is controlled by nongeomagnetic factors that will affect relative paleointensity recording we recommend that methods suited to the detection of variable recording efficiency associated with biogenic and detrital magnetites should be used on a routine basis in relative paleointensity studies

hydrographic variability in the northern south china sea over the past 45 000 years new insights based on temperature reconstructions by uk 37 and texh86 proxies from a marine sediment core md972146 abstract millennial scale climate variability was persistent feature for greenland ice core and north atlantic marine records during the marine isotope stage mis 3 studying high quality climatic archives outside of the greenland and north atlantic with precise constraint of absolute dating and high resolution sampling is a prerequisite to understand how the millennial scale changes well expressed in north hemisphere nh high latitudes had been propagated out to the other regions here we generated the surface and subsurface hydrography u k 37 and tex h 86 temperatures and terrestrial material input n alkanes records with precise ams 14 c dated control for the 45 ka from a core md972146 retrieved from the northern south china sea scs then we compared our records to the oxygen isotope record from a greenland ngrip ice core and the mean grain size record from a loess sequence at gulang china we found that the millennial scale oscillations of hydrolography and terrestrial material inputs records during the time since the last deglaciation and of 33 45 ka share similar patterns in timing and amplitude of the nh high latitude climate however we found that a non nh pattern of millennial scale oscillations for the late mis 3 20 33 ka of our hydrography and terrestrial material inputs records our studies imply that the changes of obliquity also may be important in determining the timing and amplitude of millennial scale east asian monsoon eam variability expressed in the northern scs hydrography and terrestrial material inputs

in situ calibration of mg ca ratio in planktonic foraminiferal shell using time series sediment trap a case study of intense dissolution artifact in the south china sea this study examines mg ca temperature equations through the use of planktonic foraminifers collected from continuous time series sediment traps at four water depths in the south china sea this deployment provides an opportunity to refine partial dissolution artifacts and to identify responses of shell chemistry to changes in ambient seawater conditions paired mg ca and 18o measurements on shells are strongly correlated with seasonal variability in terms of temperature at specific habitat depths however partial dissolution can significantly alter mg ca ratios even at depths well above the calcite lysocline or carbonate compensation depth of the three species studied neogloboquadrina dutertrei is the most sensitive species to dissolution relative to the other surface dwelling species globigerinoides ruber and globigerinoides sacculifer differences between the mg derived temperature equation here and those from previously established core top or sediment trap calibrations can be attributed to various degrees of dissolution and lateral advection thus highlighting the need for in situ empirical calibration for different ocean basins

clay mineral assemblages in the northern south china sea implications for east asian monsoon evolution over the past 2 million years abstract clay mineral assemblages at odp site 1146 in the northern south china sea are used to investigate sediment source and transport processes and to evaluate the evolution of the east asian monsoon over the past 2 myr clay minerals consist mainly of illite 22 43 and smectite 12 48 with associated chlorite 10 30 kaolinite 2 18 and random mixed layer clays 5 22 hydrodynamic and mineralogical studies indicate that illite and chlorite sources include taiwan and the yangtze river that smectite and mixed layer clays originate predominantly from luzon and indonesia and that kaolinite is primarily derived from the pearl river mineral assemblages indicate strong glacial interglacial cyclicity with high illite chlorite and kaolinite content during glacials and high smectite and mixed layer clay content during interglacials during interglacials summer enhanced monsoon southwesterly currents transport more smectite and mixed layer clays to site 1146 whereas during glacials enhanced winter monsoon northerly currents transport more illite and chlorite from taiwan and the yangtze river the ratio smectite mixed layers illite chlorite was adopted as a proxy for east asian monsoon variability higher ratios indicate strengthened summer monsoon winds and weakened winter monsoon winds during interglacials in contrast lower ratios indicate a strongly intensified winter monsoon and weakened summer monsoon during glacials spectral analysis indicates the mineral ratio was dominantly forced by monsoon variability prior to the development of large scale glaciation at 1 2 myr and by both monsoon variability and the effects of changing sea level in the interval 1 2 myr to present

comparison and implication of tex86 and u37k temperature records over the last 356kyr of odp site 1147 from the northern south china sea abstract proxy records from the south china sea scs have played an important role in understanding late quaternary scs environmental changes and the east asian monsoon eam variations but few long sea surface temperature sst records have been generated from the scs the recently established tex86 index provides an opportunity to generate long sst records especially for tropical oceans but the applicability and climatic interpretation of the tex86 index for the scs need further study we report and compare orbital scale resolution ca 5 3 kyr tex86 and u37k temperature records of the past 356 kyr for odp site 1147 from the northern scs both records display clear and similar glacial interglacial patterns the u37k sst fluctuated between 22 3 c and 28 3 c with a glacial interglacial difference of 4 5 c while the tex86 temperature fluctuated between 20 3 c and 25 4 c with a slightly smaller glacial interglacial difference of ca 4 c the tex86 temperature has been consistently lower than the u37k temperature over the past 356 kyr consistent with previous studies suggesting that the u37k index is a proxy for sst but the tex86 index is a proxy for subsurface temperature thus it is proposed that the temperature difference t between the u37k and tex86 records reflects mixed layer depth mld changes in the northern scs which fluctuated between 0 3 and 4 0 c with high values mostly during interglacials and lower values mostly during glacial stages mld changes in the northern scs are interpreted to be driven by eam changes with stronger winter monsoon resulting in a deeper mld and a smaller t thus the combination of u37k and tex86 records and their t can be used to reconstruct east asian winter monsoon variations as well as their influences on the hydrographic structure of the scs

summer monsoon induced upwelling dominated coastal sea surface temperature variations in the northern south china sea over the last two millennia the south china sea scs situated to the north of the indo pacific warm pool ipwp is under the strong influence of the asian monsoon system however coastal sea surface temperature sst reco

palaeoceanographic change in the northeastern south china sea during the last 15000 years the sedimentary succession of piston core rc26 16 dated by 14 c accelerator mass spectrometry provides a nearly continuous palaeoceanographic record of the northeastern south china sea for the last 15 000 yr planktic foraminiferal assemblages indicate that winter sea surface temperatures ssts rose from 18 c to about 24 c from the last glacial to the holocene a short lived cooling of 1 c in winter temperature centred at about 11 000 14 cy r ago may reflect the younger dryas cooling event in this area summer ssts have remained between 27 c and 29 c throughout the record the temperature difference between summer and winter was about ca 9 c during the last glacial much higher than the holocene value of ca 5 c during the late holocene a short lived cooling event occurred at about 4000 14 cy r ago oxygen and carbon isotopic gradients between surface 0 50 m and subsurface 50 100 m waters were smaller during the last glacial than those in the holocene the fluctuation in the isotopic gradients are caused most likely by changes in upwelling intensity smaller gradients indicate stronger upwelling during the glacial winter monsoon the fauna derived estimates of nutrient content of the surface waters indicate that the upwelling induced higher fertility and biological productivity during the glacial the winter monsoon became weaker during the holocene the carbonate compensation depth and foraminiferal lysocline were shallower during the holocene except for a short lived deepening at about 5000 14 c yr ago a preservation peak of planktic foraminifera and calcium carbonate occurred between 13400 and 12 000 14 c

a pleistocene paleoceanographic record from the north slope of the spratly islands southern south china sea abstract a 1 4 my paleoceanographic history for offshore north central spratly islands southern south china sea is reconstructed using stable isotope carbonate content coarse fraction and planktonic foraminifera census data from gravity core so95 17957 2 the chronological framework for so95 17957 2 is based on stable oxygen isotope correlation with open ocean records and constrained with ams 14c dates floral and faunal bioevents and a pleistocene microtektite event stable oxygen isotope composition of surface water reflects mainly changes in high latitude ice volume but also riverine water influx from surrounding land stable carbon isotope record suggests that surface water 13c in the southern south china sea has been modulated primarily by global changes in atmospheric co2 since the early pleistocene dissimilarities between 18o patterns in so95 17957 2 and those in various cores from the rest of the south china sea indicate that between 60 and 120 ka surface water chemistry at offshore north central spratly islands may be affected by different mechanisms those differences likely reflect unknown hydrological conditions during stages 4 and 5 carbonate content is lower during the interglacial periods than during the glacial deglacial periods which are opposite to the general trend in the shallow south china sea areas during the same period faunal composition rsp and various dissolution indices suggest that productivity is the most important factor controlling carbonate preservation dissolution above the lysocline may modify the productivity signal but cannot reverse the entire pattern faunal composition and carbonate flux suggests productivity is higher during glacial deglacial than during interglacial stronger glacial winter monsoon induces stronger upwelling and deep mixing and enhances nutrient cycling in the surface ocean which in turn increases productivity estimated summer sea surface temperature sst based on transfer function fp 12e agrees with 18o and is consistently between 28 and 29 c during most of the last 1 4 my winter sst reflects geographic location and changes in surface hydrology and fluctuates between 25 and 28 c during the last glacial period disconnection of the south china sea from the indian ocean and the influx of temperate water through the bashi channel allowed winter ssts to vary by as much as 3 5 c comparison of modern and estimated sst and sst estimates based on different methods suggest that g bulloides and g menardii are probably overweighed in transfer function fp 12e which cause discrepancies in sst estimation

global nature of the younger dryas cooling event inferred from oxygen isotope data from sulu sea cores the younger dryas an approximately 1 000 year long return to near glacial conditions interrupted the glacial holocene climate transition during which most of the northern hemisphere ice sheets melted evidence for the younger dryas event has been found mainly in sediments from the north atlantic ocean and northwest europe and this has led to the idea that the event was caused by an injection of meltwater into the north atlantic ocean1 3 this model however has been recently questioned in the light of coral reef data on the rate of sea level changes during this transition4 here we present high resolution oxygen isotope records from benthic and planktonic foraminifera from two radiocarbon dated cores in the sulu sea showing that the younger dry as occurred synchronously in the surface and deep waters of the sulu sea and the northern atlantic ocean by combining our results with other palaeoclimate data we suggest that the younger dry as event was a global phenomenon and we believe it to have been caused by low atmospheric co2concentrations

carbonate deposition and benthicδ13c in the subarctic pacific implications for changes of the oceanic carbonate system during the past 750 000 years abstract carbonate deposition at two core sites in the subarctic pacific 48 n 133 w 2 9 km and 3 7 km water depth follows the standard pacific carbonate cycles with glacial values being increased over interglacial values benthic 13c follows the global trend that is glacial values are more negative than interglacial values comparison with the benthic 13c record of north atlantic dsdp site 552 56 n 23 w 2 3 km water depth shows the north pacific records to be nearly in phase with and continuously more negative relative to the north atlantic record this suggests that concentrations of co2 org were permanently higher in the north pacific than in the north atlantic during the past 750 000 years conceivably supporting the hypothesis that there was no deep water forming in the late pleistocene north pacific whereas one would expect that the north pacific deep waters were continuously more corrosive to carbonates than deep waters in the north atlantic carbonate deposition at the deep north pacific core sites is enhanced during glacial periods and occasionally higher than at shallow north atlantic site 552 even though site 552 was probably above lysocline depth during most of the late pleistocene this apparent paradox can be resolved only by invoking an increase in alkalinity in the glacial north pacific which would have increased the degree of carbonate ion saturation and thereby improved the state of carbonate preservation

a test of different factors influencing the isotopic signal of planktonic foraminifera in surface sediments from the northern south china sea abstract the stable isotope composition of planktonic foraminifera is one of the most important proxies in paleoenvironmental research in this study three parameters affecting the stable isotope values of globigerinoides ruber from surface sediment from the northern south china sea were tested different cleaning methods different morphotypes and different size fractions our results show that in the small size fraction there is a small but significant effect on 13c by oxidizing the tests prior to measurement our data also confirm a small but significant difference between different morphotypes of g ruber however the variability caused by the seasonal effect stable isotope value is larger than the effect caused by different cleaning protocols or different morphotypes the large spread of the isotope values up to 2 have some implications to paleoceanographic reconstructions when measurements are performed on a small number of foraminiferal tests the isotope value does not necessarily reflect yearly average or a certain season but is a random value of the seasonal variability in that region

rate of production dissolution and accumulation of biogenic solids in the ocean the equatorial current system by its response to global circulation changes provides a unique recording mechanism for long range climatic oscillations a permanent record of the changes in rate of upwelling and organic production is generated in the equatorial deep sea sediments particularly by such biogenic components which are unaffected by secondary dissolution in order to determine the rates of accumulation of various sedimentary components a reliable differential measurement of age of the strata must be obtained various approaches to this problem are reviewed and sources of error discussed secondary dissolution of calcium carbonate introduces a substantial and variable difference between the dissolution modified and hence a priori unknown rate of deposition on one hand and the rate of accumulation derivable from the observed concentration on the other the cause and magnitude of these variations are of importance particularly since some current dating schemes are based on assumed constancy in the rate of accumulation of this and in some cases also all other sedimentary components the concepts used in rate evaluation are discussed with emphasis on the difference between the state of dissolution an observable property of the sediment and the rate of dissolution a parameter that requires deduction of the carbonate fraction dissolved and of the time differential as a most likely cause of the enhanced state of dissolution of the interglacial carbonate sediments is proposed the lowered rates of biogenic production and deposition which cause longer exposure of the carbonate microfossils to corrosion in the bioturbated surface layer of the sediment historical perspective is included in the discussion in view of the dedication of the symposium to hans pettersson the leader of the swedish deep sea expedition 1947 1948 an undertaking that opened a new era in deep sea research and planetary dynamics

late quaternary paleoceanography of the south china sea surface circulation and carbonate cycles paleoceanographic information from 34 sediment cores is summarized to investigate the glacial interglacial variations in sea surface circulation and late quaternary carbonate cycles in the south china sea judging from the distribution pattern of deposition rates the enormous terrigenous supply by rivers is responsible for the high rate of hemipelagic sedimentation which was even higher during glacial periods paleotemperature maps based on transfer function temperature estimates have revealed a e w gradient of sst for glacial summer and a s n gradient for glacial winter and this agrees well with the clockwise surface circulation in summer and counterclockwise in winter during glacials as shown by a preliminary computer modelling the high resolution paleotemperature curves of core v36 3 from the northern slope show an abrupt cooling event which may belong to the younger dryas carbonate percentage in sediments and preservation of foraminifers and pteropods are used to study the carbonate cycles in the marginal sea it turns out that two mechanisms are functioning there being a basin with large drainage areas vast amount of river borne terrigenous input dilutes carbonate and its intensification during glacial decreases the glacial cac03 being a basin connected with the pacific the fluctuations of lysocline ccd and acd in the scs are related to those in the pacific ocean and dissolution is strengthened at interglacial thus above the present ccd the dilution factor predominates and the atlantic cycles are produced below the present ccd the dissolution factor prevails resulting in the pacific pattern of carbonate cycles

using textural analysis for regional landform and landscape mapping eastern guiana shield availability of digital elevation models dem of increased spatial resolution has triggered interest in texture based methods for automated geomorphometry this prospect is all the more appealing concerning tropical countries for which mapping of geomorphic entities has remained limited despite its relevance for natural resource assessment and land planning in this paper we applied to the shuttle radar topography mission srtm dem a multiscale texture analysis based on fourier 2d periodogram foto method to reach a spatially coherent mapping that would agree with current knowledge over the conterminous territories of french guiana and amapa brazil through a principal component analysis foto extracted textural features were found complementary and combined with six common physiographic criteria convexity wetness index dissection elevation and percent of steep and low slopes calculated from the dem this provided a primary semiautomated mapping of 16 classes of landform types to increase legibility we aggregated into eight landscape unit classes that were the most similar in terms of texture and relief criteria while being frequently contiguous the resulting map was compared with existing maps that were however more local or of lesser resolution and informative content over the region of interest multiscale fourier spectra proved useful to depict land surface texture and in synergy with relief variables allowed identifying a large variety of landforms for broad scale geomorphic mapping in the humid tropics

development of the east asian monsoon and northern hemisphere glaciation oxygen isotope records from the south china sea abstract oxygen isotope records of the surface dwelling foraminifer globigerinoides ruber from odp site 1143 in the southern south china sea scs are presented for the last 5 ma the g ruber 18o of site 1143 for the past 500 ka is lighter by 0 5 1 0 in interglacial and by 0 1 0 5 in glacial periods than the site 806b record from the ontong java plateau we infer the light glacial interglacial g ruber 18o at site 1143 compared with the open western pacific to have been caused by stronger monsoon induced precipitation over the scs while glacial interglacial planktonic 18o values remained stable over the 3 3 2 5 ma period the benthic cibicidoides wuellerstorfi 18o gradually became positive leading to an obvious slope in their 18o difference 18ob p the stable glacial interglacial g ruber 18o over this period is probably caused by the decrease of sea surface salinity which counteracted the effects of global ice volume and sea surface temperature on the g ruber 18o we interpret that the intensification of the east asian monsoon winds coupled with the northern hemisphere glaciation 3 3 2 5 ma ago likely brought frequent and strong precipitation over the scs and or caused large scale intrusions of borneo alongshore low salinity waters to the southern scs which greatly freshened the scs and decreased its salinity after 2 5 ma especially in the quaternary period the planktonic and benthic 18o show similar variations over glacial interglacial cycles in responding to the waxing and waning of the northern hemisphere continental ice sheet and their relatively stable 18o difference 18ob p indicates a period of steady fluctuations of the east asian monsoon winds the more positive values of 18ob p probably suggest stronger east asian winter monsoon during quaternary glacials whereas the more negative values of 18ob p may imply stronger east asian summer monsoon during quaternary interglacials

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr