response of planktonic foraminifera to glacial cycles mid pleistocene change in the southern south china sea a high resolution study 2 ka of planktonic foraminifers in 997 samples from odp site 1143 9821 72vn 113817 11ve water depth 2772 m in the southern south china sea scs reveals faunal response to glacial cycles in the last 2 1 ma most distinctive is the contrasting variations in the abundance of two tropical subtropical species that exhibit similar resistance to dissolution in modern oceans the relative and absolute abundances of globorotalia menardii are high in interglacials and low in glacials and covary with d 18 o fluctuations over the studied interval pulleniatina obliquiloculata however follow oxygen isotopes only before the mid pleistocene revolution mpr showing high abundances during glacials and low during interglacials after 850 ka three abundance maxima of p obliquiloculata are observed corresponding to three major glacial episodes marine isotope stages mis 2 12 and 16 respectively this change in abundance patterns of p obliquiloculata appears to be unique to the southern scs as in late pleistocene records from other western pacific regions including the okinawa trough and the northern scs all show co varying patterns with d 18 oa sg menardii does cross spectral analyses performed between percentages of globorotalia menardii and d 18 o records show high coherency at 41 ka obliquity and then at 100 ka eccentricity bands we suggest that the high abundances of g menardii during interglacials in the past 2 1 ma reflect warmer temperatures percentages of pulleniatina obliquiloculata vs oxygen isotope records show quite large phase difference at 41 ka obliquity band before the mpr as a contrast there are negligible phase differences in the vicinity of 100 and 41 ka after the mpr which means reverse trend between percentages of p obliquiloculata and d 18 o fluctuations the differences of p obliquiloculata from g menardii in abundance and orbital forcings are interpreted as resulting from a profound change in the regional upper ocean structure during the mpr time probably relating to a final glacial cut off of the southern scs from the indian water at 850 ka and to higher salinity during glacial times after 850 ka we speculate that this change is related to the decreased connection between the pacific and indian ocean d 2004 elsevier b v all rights reserved

benthic foraminiferal δ18o in the ocean s temperature salinity density field constraints on ice age thermohaline circulation benthic 18o data from 95 core sites are used to infer possible temperature salinity t s fields of the atlantic and pacific oceans at the last glacial maximum lgm a constraint of stable density stratification yields logically consistent scenarios for both t and s the solutions are not unique but are useful as a thinking tool using geosecs data we solve for the modem relationship between 18owater w and salinity in the deep sea w smow 1 529 s 53 18 as a starting point we assume that the slope of this equation applies to lgm conditions and predict 18ocalcite c gradients in equilibrium with probable t s fields of lgm deep and bottom waters benthic foraminiferal 18o data from the deep pacific 2 4 km depth and the bottom atlantic 4 km depth are 0 1 0 2 lower than from the deep atlantic 2 4 km depth at the lgm if the modern w s slope applies atlantic deep and bottom waters were more dense than pacific deep waters this assumption would imply bottom waters both fresher s 0 5 and colder t 3 c than overlying deep waters in conflict with other data suggesting ice age deep water much colder than at present it is also possible that the observed c gradients are an artifact of laboratory intercalibration if atlantic deep and bottom water c values were similar to deep pacific values this would be consistent with the hypothesis of a stronger southern ocean versus north atlantic source for deep ocean ventilation at the lgm taking the observed gradients at face value however a solution could be that the lgm w s slope in deep and bottom waters was higher than at present conceivably because of a stronger contribution of salt to the deep ocean via more intense sea ice freezing this would allow pacific deep waters and atlantic bottom waters to have a common source again in the antarctic both would be more dense than atlantic deep waters even though the deep waters were much colder than at present to better constrain these inferences drawn from the spatial distribution of benthic 18o we must reduce scatter in the 18o data with more high quality measurements in high sedimentation rate cores this is especially true at bottom water sites also we must intercalibrate mass spectrometers at different isotope laboratories more accurately to insure our isotope data are compatible

subsidence of the northern south china sea and formation of the bashi strait in the latest miocene paleoceanographic evidences from 9 myr high resolution benthic foraminiferal δ 18 o and δ 13 c records abstract we present astronomically tuned high time resolution 3 4 kyr benthic foraminiferal 18o and 13c records between 9 ma and 5 ma from ocean drilling program odp site 1143 in the southern south china sea scs we found that the late miocene ocean carbon shift lmocs which was linked with the late miocene early pliocene biogenic bloom also occurred in the northern and southern scs a marked deep water 13c gradient as much as 1 0 of the northern and southern scs was observed between 6 5 ma and 5 9 ma which was probably caused by the significant difference in paleoproductivity between the northern and southern scs the deep 13c gradient was likely produced by rapid tectonic subsidence in the northern scs at 6 0 ma and the final formation of the bashi strait at 6 5 ma a reversed benthic 13c gradient of the northern and southern scs was also observed between 1 2 ma and 0 35 ma which was probably caused by the consecutive closures of the interarc water gates within the bashi strait at 3 0 ma and 1 2 ma closures of the interarc water gates within the bashi strait at 3 0 ma and 1 2 ma further semi enclosed the scs basin and made the paleoproductivity the major factor influencing the deep water 13c leading to the reversed deep water 13c gradient of the northern and southern scs between 1 2 ma and 0 35 ma

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

an updated astronomical timescale for the plio pleistocene deposits from south china sea and new insights into asian monsoon evolution abstract here we present an improved astronomical timescale since 5 ma as recorded in the odp site 1143 in the southern south china sea using a recently published asian summer monsoon record hematite to goethite content ratio hm gt and a parallel benthic 18o record correlation of the benthic 18o record to the stack of 57 globally distributed benthic 18o records lr04 stack and the hm gt curve to the 65 n summer insolation curve is a particularly useful approach to obtain refined timescales hence it constitutes the basis for our effort our proposed modifications result in a more accurate and robust chronology than the existing astronomical timescale for the odp site 1143 this updated timescale further enables a detailed study of the orbital variability of low latitude asian summer monsoon throughout the plio pleistocene comparison of the hm gt record with the 18o record from the same core reveals that the oscillations of low latitude asian summer monsoon over orbital scales differed considerably from the glacial interglacial climate cycles the popular view that summer monsoon intensifies during interglacial stages and weakens during glacial stages appears to be too simplistic for low latitude asia in low latitude asia some strong summer monsoon intervals appear to have also occurred during glacial stages in addition to their increased occurrence during interglacial stages vice versa some notably weak summer monsoon intervals have also occurred during interglacial stages next to their anticipated occurrence during glacial stages the well known mid pleistocene transition mpt is only identified in the benthic 18o record but not in the hm gt record from the same core this suggests that the mpt may be a feature of high and middle latitude climates possibly determined by high latitude ice sheet dynamics for low latitude monsoonal climate its orbital scale variations respond more directly to insolation and are little influenced by high latitude processes thus the mpt is likely not recorded in addition the hm gt record suggests that low latitude asian summer monsoon intensity has a long term decreasing trend since 2 8 ma with increased oscillation amplitude this long term variability is presumably linked to the northern hemisphere glaciation since then

obscuring of long eccentricity cyclicity in pleistocene oceanic carbon isotope records abstract long eccentricity 400 kyr cycles in carbon isotope records from the pacific and atlantic oceans and the mediterranean sea of the past 5 0 ma are compared all records show maximum 13c values 13cmax at eccentricity minima during the pliocene but this relationship obscured in the pleistocene after 1 6 ma in particular for the open ocean deep water 13c records since a clear anti phase relationship was set up between oceanic 18o and 13c in the 100 kyr band from this time we attribute the obscured 400 kyr signal to a major change in the oceanic carbon reservoir probably associated with restructure of the southern ocean a similar change occurred in the miocene at 13 9 ma when the 400 kyr cyclicity in 13c records flattened out together with a drastic cooling and antarctic ice sheet expansion a remarkable exception is the mediterranean surface water 13c record which remained paced by the long term eccentricity cycle throughout the pliocene and pleistocene suggesting a low latitude climatic origin of the 400 kyr signal that is independent of glacial interglacial forcing since the earth is currently passing through an eccentricity minimum it is crucial to understand the nature of the 13cmax events

an automatic orbital tuning method for paleoclimate records the recognized linkage of climatic events to the earth s orbital variations has provided the basis for establishing time scales of pleistocene climatic records most of the classic orbital tuning methods developed so far however need visual judgements to add new time control points into the climatic records thus being time consuming and hindering the construction of high resolution climatic time series in this study we propose to use the dynamic optimization method to overcome the shortcomings with this technique the additional time control points can be automatically added into the climatic records and a best age for each of the climatic data can be calculated results of a case study conducted on the baoji loess section show that the automatic orbital tuning method can lead to a much better agreement of climatic time series with theoretical changes in the orbital elements relative to the classic ones

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

x ray fluorescence core scanning records of chemical weathering and monsoon evolution over the past 5 myr in the southern south china sea with benthic foraminiferal d 18 o reveal that phases of the east asian summer monsoon abruptly changed by more than 90 at 4 0 ma 2 75 ma 1 0 ma and 0 6 ma relative to global ice volume at the obliquity and the precession bands over the past 5 myr strong 400 kyr and 100 kyr cycles in the k al and ti al records consistently exist over the past 5 myr particularly these cycles are highly coherent with the long and short eccentricity cycles in the truncated insolation at 65 n indicating an eccentricity forcing of the east asian summer monsoon the chemical weathering recorded in the elemental records of odp site 1143 also shows highly coherent relationship with the ocean carbon reservoir at the eccentricity the obliquity and the precession bands over the late pliocene and pleistocene

late quaternary east asian monsoon variability in the south china sea evidence from planktonic foraminifera faunal and hydrographic gradient records the surface hydrographic conditions of the south china sea scs are influenced strongly by fluctuations of the east asian monsoon eam long term fluctuations of the eam have been previously investigated through analysis of several proxy records obtained from scs sediment cores however in this marginal sea interpretation of these records is complicated by ice volume sea level effects here we have extracted east west hydrographic gradients from two images core records in the scs which are proposed to indicate monsoon variability this strategy minimizes the effect of ice volume sea level on the monsoon signal highresolution records of planktonic foraminifer faunal assemblages and sea surface temperature sst of the last 135 kyr have been generated for two cores taken off the vietnam margin md012394 in the western scs and near palawan island md972142 in the southeastern scs these core sites represent contrasting hydrographic conditions in modern monsoon climates where the winter eam drives cold and strong mixing conditions in the western scs but maintains warm and deep thermocline conditions in the southeastern scs a planktonic foraminifera hydrographic index pfhi is established based on the abundance ratios of warm thermocline and cold mixing species assemblages and sst estimates from a modern analogue technique mat the records of the east west gradients for pfhi pfhi and for sst sst between the two cores md012394 and md972142 show a dominance of 23 kyr precession cycles in the precession cycles the pfhi and sst increased at the december 21 perihelion which is associated with seasons of minimum northern hemisphere winter and maximum southern hemisphere summer insolation cross spectral analysis between pfhi sst and the precession cycles indicates coherent and in phase relationships considering that the december 21 perihelion of the cycle of precession accorded with the time of maximum summer insolation in the southern hemisphere we suggest that the scs variability of hydrographic gradients for the last 135 kyr has been dominated by winter monsoon dynamics in response to geographic forcing controlled by the strength of the australian summer monsoon

tectonic and climatic controls on long term silicate weathering in asia since 5 ma determining the interplay between tectonic deformation climate atmospheric co2 concentrations and continental weathering and erosion is key to understanding the mechanisms that forced cenozoic global cooling in contrast with studies of paleo climate and pco 2 the history of long term silicate weathering in the himalaya and tibetan plateau htp during the late cenozoic remains unclear we reconstruct 5 m y of silicate sedimentary records at ocean drilling program odp site 1143 in the south china sea to explore the weathering history of the mekong river basin that supplied the sediment coherent variation of weathering proxies from the south china sea bay of bengal loess plateau as well as the yangtze and yellow rivers indicates weakening chemical weathering intensity since the late pliocene as the climate cooled this cooling coupled with tectonic activity shifted the dominant weathering regime from more transport limited to more weathering limited causing less chemical depletion of silicate minerals while silicate weathering rates became strongly correlated to erosion rates they were decoupled from chemical weathering intensity physical denudation and associated silicate weathering rates in the htp area increased in the pliocene driven by both rock uplift and stronger monsoon precipitation decreasing atmospheric co2 concentrations and so contributing to northern hemisphere glaciation nhg citation wan s p d clift a li z yu t li and d hu 2012 tectonic and climatic controls on long term silicate weathering in asia since 5 ma geophys res lett 39 l15611 doi 10 1029 2012gl052377

potential origins of 400 500 kyr periodicities in the ocean carbon cycle a box model approach 1 cenozoic proxy records of both the isotopic composition of dissolved inorganic carbon in the oceans 13cdic and deep ocean carbonate preservation show significant periodicities in the range 400 500 kyr sensitivity analysis of the ocean carbon cycle to potential variability on this timescale in patterns of global oceanic primary productivity and or continental weathering fluxes is performed using a 7 box ocean atmosphere model the data constraints imposed by plio pleistocene proxy records of 13cdic carbonate preservation and atmospheric pco2 variability allow different scenarios to be evaluated forcing with the global oceanic primary production ratio of inorganic and organic carbon leads to the relative phases of response most consistent with the proxy data however only when changes also occur in total marine primary production can the observed relative amplitudes of 13cdic and pco2 variability also be reproduced this scenario is consistent with oscillations between a highly productive coccolithophore rich global ocean and a less productive diatom rich one such oscillations have been proposed to originate from the orbital eccentricity cycle leading to changes in seasonality and thus silica utilization in the southern ocean however the period of response in model 13cdic is always close to that of the forcing function used and thus a significant discrepancy remains between the orbital eccentricity cycle period of 413 kyr and the observed 500 kyr 13cdic periodicity seen in the pleistocene

investigating the history of east asian monsoon and climate during the last glacial interglacial period 0 140 000 years mineralogy and geochemistry of odp sites 1143 and 1144 south china sea abstract monsoon climate is an important component of the global climatic system a comprehensive understanding of its variability over glacial interglacial time scales as well as of its effects on the continent and in the ocean is required to decipher links between climate continental weathering and productivity a detailed multiproxy study including bulk and clay mineralogy grain size analysis phosphorus geochemistry sedex extraction organic matter characterization and nitrogen stable isotopes was carried out on samples from odp sites 1143 and 1144 leg 184 south china sea covering the past 140 000 years we tentatively reconstruct the complex sedimentation and climatic history of the region during the last glacial interglacial cycle when sea level variations linked to the growth and melting of ice caps interact with monsoon variability during interglacial periods of high sea level summer monsoon was strong and humid and warm climate characterized the adjacent continent and islands clay minerals bear signals of chemical weathering during these intervals high calcite and reactive phosphorus mass accumulation rates mars indicate high productivity especially in the southern region of the basin during glacial intervals strong winter monsoon provided enhanced detrital input from the continent as indicated by high detrital mar glacial low sea level resulted in erosion of sediments from the exposed sunda shelf to the south and clay mineral variations indicate that warm and humid conditions still prevailed in the southern tropical areas enhanced supply of nutrients from the continent both by river and eolian input maintained high primary productivity reduced circulation during these periods possibly induced active remobilization of nutrients such as phosphorus from the sediments intense and short cold periods recorded during glacial and interglacial stages correlate with loess records in china and marine climatic records in the north atlantic confirming a teleconnection between low and high latitude climate variability

modeling oxygen isotopes in the pliocene large scale features over the land and ocean the first isotope enabled general circulation model gcm simulations of the pliocene are used to discuss the interpretation of 18o measurements for a warm climate the model suggests that spatial patterns of pliocene ocean surface 18o 18osw were similar to those of the preindustrial period however arctic and coastal regions were relatively depleted while south atlantic and mediterranean regions were relatively enriched modeled 18osw anomalies are closely related to modeled salinity anomalies which supports using 18osw as a paleosalinity proxy modeled pliocene precipitation 18o 18op was enriched relative to the preindustrial values but with depletion of 2 over some tropical regions while usually modest 4 the enrichment can reach 25 over ice sheet regions in the tropics 18op anomalies are related to precipitation amount anomalies although there is usually a spatial offset between the two this offset suggests that the location of precipitation change is more uncertain than the amplitude when interpreting 18op at high latitudes 18op anomalies relate to temperature anomalies however the relationship is neither linear nor spatially coincident a large 18op signal does not always translate to a large temperature signal these results suggest that isotope modeling can lead to enhanced synergy between climate models and climate proxy data the model can relate proxy data to climate in a physically based way even when the relationship is complex and nonlocal the 18o climate relationships identified here from a gcm could not be determined from transfer functions or simple models

glacial deep water properties in the west equatorial pacific bathyal thermocline near a depth of 2000 m abstract the stable isotope stratigraphy of planulina wullerstorfi in three box cores from ontong java plateau in the western equatorial pacific shows that there existed a bathyal thermocline near the depth of 2000 m during glacial time waters below the boundary were colder by about 1 c those above were about the same as now the deep waters were slightly enriched and the upper waters depleted in nutrients compared with present values the differences in 13 c to the present after correcting for the global change are of the order of 0 1 more positive above 2000 m and 0 1 more negative below corresponding to changes in phosphate of the order of 0 1 mol kg less phosphate above and more below the boundary

astronomically modulated neogene sediment records from the south china sea 1 general global cooling over the neogene has been modulated by changes in earth s orbital parameters investigations of deep sea sediment sequences show that various orbital cycles can dominate climate records for different latitudes or for different time intervals however a comprehensive understanding of astronomical imprints over the entire neogene has been elusive because of the general absence of long continuous records extending beyond the pliocene we present benthic foraminiferal 18o and 13c records over the past 23 ma at ocean drilling program site 1148 in the northern south china sea and construct an astronomically tuned timescale tj08 for these records based on natural gamma radiation and color reflectance data at this site our results show that a 41 ka cycle has dominated sediment records at this location over the neogene displaying a linear response to orbital forcing a 100 ka cycle has also been significant however it is correlated nonlinearly with earth s orbital variations at the 100 ka band the sediment records also display a prominent 405 ka cycle although this cycle was coherent with orbital forcing during the oligocene and the early miocene it was not coherent with earth s orbital variations at the 405 ka band over the whole neogene amplification of northern hemisphere and southern hemisphere glaciation since the middle miocene may be responsible for this change in sedimentary response our benthic foraminifera 18o and 13c records further exhibit amplitude variations with longer periods of 600 1000 1200 and 2400 ka apparently these cycles are nonlinear responses to insolation forcing

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

changes in deep ocean water δ18o and temperature from the last glacial maximum to the present estimates are made of changes of the oxygen isotope anomaly of deep ocean water and of deep ocean temperature for the atlantic indian and pacific oceans from the time of the last glacial maximum to the present several independent sources of data including oxygen isotope records of planktic and benthic foraminifera at selected core sites primarily in the equatorial oceans climate long range investigation mapping and prediction sea surface temperatures estimates and geosecs 18o data for the present ocean water are utilized together with the paleotemperature equation of epstein et al 1953 glacial to interglacial change in oxygen isotope composition of the global deep ocean water is found to be 1 41 per mil compared with a global average change of 1 75 per mil for benthic foraminifera the former value implies a sea level change between 128 and 141 m depending on the choice of the isotope sea level conversion constant a global deep ocean warming of 1 4 c from glacial maximum to the present is found from the above isotopic difference of 0 34 per mil the consistency of the results in this paper with those of chappell and shackleton 1986 suggest that there is no significant contribution from isotopically light floating ice shelves surrounding antarctica as proposed by johnson and andrews 1986 at least for the change from glacial maximum to the present the ocean transition from glacial to interglacial episodes was accompanied by an estimated warming of 2 0 c in the atlantic 1 4 c in the indian and 1 1 c in the pacific oceans the glacial pacific was colder than the atlantic ocean but the difference between the two oceans was smaller than today

two issues concerning surface frontogenesis abstractwith the weather research and forecasting wrf model specifically configured to simulate the intensification and evolution of an extratropical baroclinic wave this study first investigates why cold fronts are characteristically longer narrower and more intense than warm fronts in the extratropical atmosphere it is found that the differential thermal advection by the geostrophic and ageostrophic wind components in the two frontal regions results in a greater thermal contrast across the cold front the length of the cold front is essentially the length scale of the intensifying baroclinic wave i e on the order of radius of deformation the frontal system as a whole moves eastward under the influence of a steering flow in addition the cold front outpaces the warm front eastward making the western portion of the warm front progressively occluded and the eastern portion of the warm front shorter the dynamical processes tend to move the cold front eastward whereas the diabatic heating proc

reorganization of pacific deep waters linked to middle miocene antarctic cryosphere expansion a perspective from the south china sea article i nfo article history changes in intermediate and deep ocean circulation likely played a significant role in global carbon cycling and meridional heat moisture transport during the middle miocene climate transition 14 ma high resolution middle miocene 16 13 ma benthic foraminifer stable isotope records from the south china sea reveal a reorganization of regional bottom waters which preceded the globally recognized middle miocene 1 18 o increase 13 8 ma by 100 000 years an observed reversal of the benthic foraminifera 13 c gradient between odp sites 1146 2092 m and 1148 3294 m 13 9 13 5 ma is interpreted to reflect an

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

modeling the middle pliocene climate with a global atmospheric general circulation model 1 a new climate simulation for the middle pliocene ca 3 ma bp is performed by a global grid point atmospheric general circulation model developed at the institute of atmospheric physics iap agcm with boundary conditions provided by the u s geological survey s pliocene research interpretations and synoptic mapping prism group it follows that warmer and slightly wetter conditions dominated at the middle pliocene with a globally annual mean surface temperature increase of 2 60 c and an increase in precipitation of 4 0 relative to today at the middle pliocene globally annual terrestrial warming was 1 86 c with stronger warming toward high latitudes annual precipitation enhanced notably at high latitudes with the augment reaching 33 5 32 5 of the present value at 60 90 n 60 90 s on the contrary drier conditions were registered over most parts at 0 30 n especially in much of east asia and the northern tropical pacific in addition both boreal summer and winter monsoon significantly decreased in east asia at the middle pliocene it is indicated that the iap agcm simulation is generally consistent with the results from other atmospheric models and agrees well with available paleoclimatic reconstructions in east asia additionally it is further revealed that the prism warmer sea surface temperature and reduced sea ice extent are main factors determining the middle pliocene climate the simulated climatic responses arising from the prism reconstructed vegetation and continental ice sheet cannot be neglected on a regional scale at mid to high latitudes like over greenland and the qinghai tibetan plateau and around the circum antarctic but have little influence on global climate

late quaternary linkage of sedimentary records to three astronomical rhythms and the asian monsoon inferred from a coastal borehole in the south bohai sea china abstract the bohai sea was formed by subsidence during the cenozoic some 2000 3000 m of fluvial lacustrine and marine sediments has been deposited in this basin previous studies focused mainly on the transgression history with little examination of orbital variation in relation to other areas within the asian monsoon domain here we present the late quaternary results of a new borehole in the south bohai sea optically stimulated luminescence and radiocarbon dating which provide concordant age estimates were employed to generate an initial chronology for the borehole after refining the chronology through astronomical tuning the results showed that 1 the grain size variation represents asian monsoon intensity which was dominated by both solar insolation major and global ice volume minor forcing 2 the magnetic susceptibility indicates river incision processes which were sensitive to orbital tilt with influence from solar insolation 3 the vegetation coverage responded to global ice volume coupled obliquity changes and that 4 neither external nor internal factors could dominate the paleoenvironmental evolution on orbital timescales in an independent way and they are both integrated in a complex pattern we conclude that three different astronomical rhythms have affected coastal evolution and that the sedimentary records in the south bohai sea china result from the nonlinear interaction and the complex response to driving processes

astronomic timescale for the pliocene atlantic δ18o and dust flux records of ocean drilling program site 659 high resolution benthic oxygen isotope and dust flux records from ocean drilling program site 659 have been analyzed to extend the astronomically calibrated isotope timescale for the atlantic from 2 85 ma back to 5 ma spectral analysis of the 18o record indicates that the 41 kyr period of earth s orbital obliquity dominates the pliocene record this is shown to be true regardless of fundamental changes in the earth s climate during the pliocene however the cycles of sahelian aridity fluctuations indicate a shift in spectral character near 3 ma from the early pliocene to 3 ma the periodicities were dominantly precessional 19 and 23 kyr and remained strong until 1 5 ma subsequent to 3 ma the variance at the obliquity period 41 kyr increased the timescale tuned to precession suggests that the pliocene was longer than previously estimated by more than 0 5 m y

neogene and quaternary paleoceanographic changes in the southern south china sea site 1143 the benthic foraminiferal record deep sea benthic foraminiferal assemblages from ocean drilling program odp site 1143 located in the southern south china sea scs were investigated to evaluate the relationship between faunal composition patterns and paleoceatiographic changes during the last 6 million years late miocene to holocene we used multivariate statistics correspondence analysis to analyze carbon flux related changes in assemblage composition of benthic foraminifers additional proxies for carbon flux and deep water ventilation include delta 13 c records of epifaunal cibicidoides wuellerstoifi and infaunal uvgefina peregrina var dirupta and melonis pompilioides benthic foraminiferal accumulation rates bfarss diversity indices and relative abundances of indicator species we observe three significant benthic faunal changes in the southern south china sea during the last 6 million years strong fluctuations in bfar and relative abundance of productivity indicator species between glacial and inter glacial stages after the mid pleistocene revolution mpr at approximately 0 9 ma indicating stronger seasonal carbon flux fluctuations are accompanied by the extinction of such species as stilostomella spp increases in carbon flux indicator species are coupled with an overall deer ease in benthic foraminifer diversity around 3 0 ma in the late pliocene this may indicate increasing carbon flux in a period of productivity maximum caused by enhanced offshore upwelling from intensified winter monsoon wind strength c 2004 elsevier b v all rights reserved

delta o 18 sr ca and mg ca records of porites lutea corals from leizhou peninsula northern south china sea and their applicability as paleoclimatic indicators combined seasonal to monthly resolution coral skeletal delta 18 o sr ca and mg ca records are reported for one modem and two late holocene porites lutea corals from a fringing reef at leizhou peninsula the northern coast of the south china sea scs all the profiles for the period 1989 2000 reveal annual cycles well correlated with instrumental sea surface temperatures sst and display broad peaks in summer and narrow troughs in winter reflecting seasonal growth rate variations calibration against instrumental sst yields the following equations delta 18 o 0 174 0 010 xsst degrees c 1 02 0 27 mswd 5 8 sr ca mmol mol 0 0424 0 0031 xsst degrees c 9 836 0 082 mswd 8 6 and mg ca mmol mol 0 110 0 009 xsst degrees c 1 32 0 23 mswd 55 the scatter in the mg ca sst relationship is much larger than analytical uncertainties can account for suggesting the presence of sst unrelated components in the mg ca variation calculated sr ca sst values for two later holocene porites lutea samples u series ages similar to 541 bc and similar to 487 ad respectively from the same reef suggest that sst in the scs at similar to 541 bc was nearly as warm as in the 1990s the warmest decade of the last century but at similar to 487 ad it was significantly cooler this observation is consistent with climatic data reported in chinese historic documents confirming that the sr ca sst relationship is a reliable thermometer removing the sst component in the delta 18 o variation based on calculated sr ca sst values the residual delta 18 o reflects the deviation of the holocene seawater delta 18 o from the modem value which is also a measure of the holocene sea surface salinity sss or the summer monsoon moisture level in mainland china such residual delta 18 o was close to zero at similar to 541 bc and 0 3 parts per thousand at similar to 487 ad suggesting that it was as wet as in the 1990s at similar to 541 bc but significantly drier at similar to 487 ad in mainland china which are also consistent with independent historic records calculated mg ca sst values for the two late holocene corals are significantly lower than the sr ca sst values and are also in conflict with chinese historic records suggesting that coral mg ca is not reliable proxy for sst at comparable sr ca ranges fossil corals always display negative mg ca offsets if compared with the modem coral of the same site we interpret this observation as due to preferential loss of mg during meteoric dissolution of cryptic mg calcite bearing microbialites in the exposed fossil corals microbialites mgo up to 17 sr only 100 300 ppm are ubiquitous during reef building processes and their presence in only a trace amount will have a significant impact on coral mg ca ratios without detectable influence on coral sr ca ratios c 2004 elsevier b v all rights reserved

4 ma coarsening of sediments from baikal chinese loess plateau and south china sea and implications for the onset of nh glaciation abstract intense tectonic movement occurred along the northeastern margin of the tibetan plateau 3 4 ma during the same time period global climate changed from a period of stability to a period of frequent and abrupt changes which prevented fluvial and glacial systems from establishing a state of equilibrium thus it is difficult to directly attribute the 3 4 ma coarse grained sediment accumulation in east asia to climate change or tectonic activity this study compares late cenozoic multi proxy records from the chinese loess plateau clp to the low latitude grain size sea level and benthic 18 o records from the south china sea scs and the high latitude grain size record from lake baikal all records suggest a steady and persistent cooling since 4 ma which correlates well with those cooling records from other regions around the world this coincided in timing with the modeling results that the closure of the central american seaway cas initiated strengthening of atlantic meridional overturning circulation between 4 8 and 4 0 ma which led to both warming of the northern hemisphere nh and cooling of the southern hemisphere sh cooling of the sh would induce a marked development of the antarctic ice sheets at 4 ma pushing the intertropical convergence zone itcz northward this was superimposed on warming of the nh and brought more precipitation to the middle latitudes of the nh resulting in increases in coarse grained sediments in the sikouzi section from the western clp since 4 2 ma notably the absence of coarse grained sedimentation in the sikouzi section during 3 0 2 1 ma and the gradual decrease in coarse grained peaks since 2 1 ma reflected by the sikouzi grain size record probably resulted from stepwise increase in the nh ice volume pushing the itcz southward on the other hand development of the antarctic ice sheets would induce global cooling and enhancement of physical weathering initiating increases in sedimentation rates as well as increases in grain size from lake baikal to the clp to the scs therefore the closure of the cas during 4 8 4 0 ma and its influence on ocean heat transport was possibly the major forcing factor for global cooling since 4 ma a persistent and steady cooling during 4 3 ma probably made a significant contribution to the establishment of the nh ice sheets at 2 75 ma ago

towards an orbital time scale for chinese loess deposits abstract in this study we analyzed the grain size of the baoji loess soil sequence at 10 cm intervals results show that grain size variations are very sensitive to loess soil alternations with loess units being much coarser than soils such a change in loess soil grains is interpreted as the result of the glacial interglacial cyclic variations in the intensity of the winter monsoon winds out of siberia the grain size record is thus employed as a proxy indicator of the winter monsoon circulation and tuned to the orbital records calculated recently by berger and loutre 1991 under the control of major magnetic reversals the tuning is independent of any correlation with 18o signals in the deep sea sediments the resulting grain size time scale is tightly constrained as suggested by the following facts 1 the filtered obliquity and precession components from the grain size data on the orbital time scale closely match the theoretical orbital records 2 ages of the major magnetic reversals estimated from the grain size time scale are in good agreement with the k ar dated ages 3 there is close coherence between the baoji grain size time series and the orbital variations at the orbital frequency bands over the entire 0 2 5 ma period and 4 the grain size record on the orbital time scale shows a close similarity to the orbitally tuned dsdp site 607 and odp site 677 18o records examination of time dependent characteristics of the grain size record suggests that there are two major shifts of dominant periodicities in the long term monsoonal cycles one occurring at about 0 8 ma bp and the other around 1 7 ma bp

doppler radar study of the trailing anvil region associated with a squall line abstract the kinematic structure and reflectivity distribution within a region of widespread precipitation associated with a summertime midlatitude illinois squall line as revealed by an analysis of doppler radar data are presented and discussed the squall line moved in a southeasterly direction while active convection forming on its leading edge moved in a northeasterly direction decaying thunderstorms and their anvils merged to form the extensive region of stratiform precipitation which trailed the squall line an extension of the vad velocity azimuth display method or the evad extended vad method has been developed for the analysis of single doppler radar data in contrast to the vad method which requires knowledge of the particle fall velocities or assumptions regarding it to calculate the divergence of the horizontal wind the evad method yields the vertical distributions of both the particle fall speed and the divergence also presented are results from a multiple doppler mdop analy

gradual and abrupt changes during the mid pleistocene transition abstract during the mid pleistocene transition mpt the dominant glacial interglacial cyclicity as inferred from the marine 18 o records of benthic foraminifera 18 o benthic changed from 41 kyr to 100 kyr years in the absence of a comparable change in orbital forcing currently only two mg ca derived high resolution bottom water temperature bwt records exist that can be used with 18 o benthic records to separate temperature and ice volume signals over the pleistocene however these two bwt records suggest a different pattern of climate change occurred over the mpt a record from north atlantic dsdp site 607 suggests bwt decreased with no long term trend in ice volume over the mpt while south pacific odp site 1123 suggests that bwt has been relatively stable over the last 1 5 myr but that there was an abrupt increase in ice volume at 900 kyr in this paper we attempt to reconcile these two views of climate change across the mpt specifically we investigated the suggestion that the secular bwt trend obtained from mg ca measurements on cibicidoides wuellerstorfi and oridorsalis umbonatus species from n atlantic site 607 is biased by the possible influence of co 3 2 on mg ca values in these species by generating a low resolution bwt record using uvigerina spp a genus whose mg ca values are not thought to be influenced by co 3 2 we find a long term bwt cooling of 2 3 c occurred from 1500 to 500 kyr in the n atlantic consistent with the previously generated c wuellerstorfi and o umbonatus bwt record we also find that changes in ocean circulation likely influenced 18 o benthic bwt and 18 o seawater records across the mpt n atlantic bwt cooling starting at 1 2 ma presumably driven by high latitude cooling may have been a necessary precursor to a threshold response in climate ice sheet behavior at 900 ka at that point a modest increase in ice volume and thermohaline reorganization may have caused enhanced sensitivity to the 100 kyr orbital cycle

high precision tims u series and ams c 14 dating of a coral reef lagoon sediment core from southern south china sea accurate dating of lagoon sediments has been a difficult problem although lagoon profiles usually with high deposition rates have a great potential for high resolution climate reconstruction we report 26 high precision tims u series dates on 25 coral branches and five ams c 14 dates on foraminifera for a 15 4 m long lagoon core from yongshu reef nansha area southern south china sea all the dates are in the correct stratigraphical sequence providing the best chronology so far reported for lagoon deposits the results reveal a similar to 4000 a continuous depositional history with sedimentation rates varying from 0 8 to 24 6 mm a 1 with an average of 3 85 mm a 1 which corresponds to an average net carbonate accumulation rate of similar to 2700 g caco3 m 2 a 1 significantly higher than the mean value 800 400 g caco3 m 2 a 1 used for lagoons in general in previous studies of global carbonate budget episodes of accelerated depositions within the last 1000 years correlate well with strong storm events identified by u series dates of storm transported coral blocks in the area however in the longer term the sedimentation rates during the past 1000 years were much higher than earlier on probably due to more vigorous wave reef interaction as a result of relative sea level fall since 500 ad and expansion of reef flat area supplying more sediments the coral tims u series ages and foraminifera ams 14c dates reveal intriguing apparent radiocarbon reservoir ages r from 572 to 1052 years which are much higher than global mean values of similar to 400 years c 2006 elsevier ltd all rights reserved

spatial distribution and controlling factors of planktonic foraminifera in the modern western pacific abstract studies of the spatial distribution of living planktonic foraminifera in modern water columns are still lacking in the western pacific in this study 40 plankton tows at 8 stations were conducted focusing on the terminus of the north equatorial current nec and its two bifurcated branches in the western pacific the results show that planktonic foraminifera were in high abundance around the kuroshio current kc source region and the mindanao current mc system but in low abundance in the nec the planktonic foraminiferal assemblage was dominated by g sacculifer and g ruber with relative abundances of 44 0 and 27 3 respectively according to a cluster analysis of the results of seven stations the stations can be divided into three groups namely group nec group kc and group mc which displayed different features of planktonic foraminiferal assemblages the low abundance of planktonic foraminifera that characterized the nec stations may be induced by the thick mixed layer and deep thermocline nutricline in this region however stations in the kc region which also had thick mixed layers and deep thermoclines showed higher abundances of planktonic foraminifera than the nec stations this result was probably caused by the higher terrigenous input the planktonic foraminifera show the highest abundance at the mc stations which may be the result of existing upwelling conditions

the mid pleistocene climate transition a deep sea carbon isotopic perspective five 13c records from the deep ocean extending back to 1 3 ma were examined in order to constrain changes in mean ocean carbon isotope composition and thermohaline circulation over the 41 to 100 ka climate transition these data show that significant perturbations in mean ocean carbon chemistry were associated with the mid pleistocene climate transition notable features of the last 1 3 myr are 1 a pronounced 0 3 decrease in mean ocean 13c between 0 9 and 1 0 myr followed by a return to pre 1 0 ma values by 400 ka b p which we propose was due to the onetime addition of isotopically depleted terrestrial carbon to the ocean possibly associated with an increase in global aridity and decrease in the size of the biosphere across the 41 to 100 ka transition 2 no change in the atlantic pacific a p 13c gradient over the last 1 3 myr suggesting no change in mean ocean nutrient content accompanied the addition of light carbon and 3 stronger vertical nutrient fractionation in the north atlantic in the middle pleistocene between sites 607 and 552 suggesting weaker north atlantic deep water formation at this time relative to the early and late pleistocene we also find evidence for a more pronounced deep recirculation gyre in the western north atlantic basin in the early brunhes as evidenced by aging of deep northern basin water site 607 relative to deep water in the equatorial atlantic site 664

magnetostratigraphic age of the xiantai paleolithic site in the nihewan basin and implications for early human colonization of northeast asia timing of the early habitation and stone technologies in the nihewan basin north china has provided insights into our understanding of early human adaptability to high northern latitudes in east asia here we contribute to this topic with detailed magnetostratigraphic investigation coupled with mineral magnetic measurements and palynological analyses on a lacustrine sequence in this basin which contains the xiantai paleolithic site magnetite and hematite were identified as the main carriers for the characteristic remanent magnetizations magnetostratigraphic results show that the xiantai lacustrine sequence recorded the brunhes chron the jaramillo and the olduvai subchrons and successive reverse polarity portions of the intervening matuyama chron stratigraphic correlation in terms of lithology magnetic susceptibility and magnetic polarity sequences between the xiantai and xiaochangliang sections indicates that the xiantai artefact layer is readily contemporary with the xiaochangliang artefact layer which has been previously estimated to be about 1 36 ma r x zhu k a hoffman r potts c l deng y x pan b guo c d shi z t guo b y yuan y m hou w w huang earliest presence of humans in northeast asia nature 413 2001 413 417 early humans of the xiantai paleolithic site lived in a steppe paleoenvironment indicated from fossil pollens furthermore the combined evidence of our magnetostratigraphy and previously published magnetochronology and paleoclimate data documents that early humans of north china were able to adjust to an increasing variability of paleoclimates and paleoenvironments over the early pleistocene

planktonic foraminiferal records of east asia monsoon changes in the southern south china sea during the last 40 000 years planktonic foraminiferal assemblages and benthic foraminiferal oxygen isotopes were obtained in a gravity core n507 25 6 degrees 39 945 n 113 degrees 32 9361 e water depth 2006 m collected from the southern south china sea scs to investigate east asia monsoon changes during the last 40 000 years four cold events identified from four peaks of the relative abundance of neogloboquadrina pachyderma dex and globigerina quinqueloba correlate well with those in the hulu monsoon record within age uncertainty and can be linked to heinrich events in the northern atlantic high latitudes we suggest that the relative abundance of n pachyderma dex and g quinqueloba in the southern scs can be used as a direct proxy for east asia winter monsoon eawm changes during glacial periods in contrast to its low abundance in the northern scs and okinawa trough the relative abundance of pulleniatina obliquiloculata shows high values during the last glacial in the southern scs caused likely by the combined impact of optimum winter sea surface temperature sst and stronger mixing enhanced upwelling at that time a p obliquiloculata minimum event pme found in the okinawa trough and the northern and southern scs during the h1 period was possibly related to a large drop in winter sst due to the intensified eawm we propose that this pme can be also used as a reliable regional stratigraphic marker as the holocene one a 9 cm sandy silt layer deposit in core ns07 25 during the hi period probably related to the enhanced current that was caused by the especially strengthened eawm at that time the last deglacial warming recorded in the relative abundance of warm and cold species of planktonic foraminifer reveals that changes between the easm and eawm were not in phase but alternating between a winter monsoon dominated northern hemisphere influence and a summer monsoon dominated influence of the tropical dynamics and or southern hemisphere climate changes c 2009 elsevier b v all rights reserved

a 4 ma record of thermal evolution in the tropical western pacific and its implications on climate change article i nfo orbital resolution thermal histories over the last 4 ma at odp site 1143 in the tropical western pacific are reconstructed using alkenone paleothermometry the temperature profile is characterized by a steady state of 29 c with fluctuations b1 c before 2 7 ma and by a strong oscillating state from 2 7 ma largely due to cooling by up to 4 c from 29 c in interglacial to 26 c in glacial intervals this implies a relative warm and stable surface hydrography during the early and mid pliocene in this region influenced by the warm pool before temperature decreases in responding to global cooling and the formation of the distinct glacial stages since the late pliocene therefore the smaller sst gradient between tropical eastern and western pacific and between southern and northern south china sea before the late pliocene indicates a super sized pliocene pacific warm pool while the larger sst gradient since then marks progressively intensification of the zonal walker circulation and meridional hadley circulation representing the monsoon circulations in the region the intensification of the walker and hadley circulations over the tropical pacific may also have helped on the onset of glaciations and subsequent deglaciations during the late pliocene and pleistocene 2011 published by elsevier b v

response of western pacific marginal seas to glacial cycles paleoceanographic and sedimentological features abstract this paper reviews the recent progress in late quaternary studies in five northwestern pacific marginal seas especially the south china sea as an example a series of marginal seas separate asia from the pacific ocean and significantly modify the material and energy flux linkage between land and sea during glacial cycles the sea level induced environmental signal was amplified in the marginal seas giving rise to drastic changes in areas and configurations of these seas and to reorganization of sea water circulation in basins since most of the western pacific marginal seas are influenced by monsoon circulation and some of these are located within the western pacific warm pool the glacial geographic changes have produced a profound impact on regional and global climate for example the decrease of sea area and sea surface temperature sst in the marginal seas was one of the factors responsible for the enhanced aridity of inland china during the glaciation glacial intensification of the winter monsoon and increased seasonality of sst in marginal seas might explain at least partly the apparent discrepancy between the tropical paleotemperature estimations based on terrestrial and open ocean records in this region as the western pacific marginal seas trap terrigenous material supplied by east asia the deep water sedimentation rates there can be one to two orders of magnitude higher than in the open ocean down slope sediment transport is more active when the sea level changes particularly during the deglaciation at least four types of carbonate cycles have been recognized in the western pacific marginal seas and each of those contains environmental signals from the surface and deep sea water as well as from the drainage basin

magnetostratigraphy of odp site 1143 in the south china sea since the early pliocene abstract ocean drilling program site 1143 of leg 184 in the southern south china sea scs recovered a continuous sedimentary sequence since the late miocene 10 ma which provides a unique record for better understanding the tectonic environmental and climatic evolution in the southern part of the scs in this study we conducted a detailed rock magnetism and paleomagnetism study on 637 discrete samples taken from 512 1 m cores of hole 1143c rock magnetic measurements indicate that the main magnetic mineral is single domain magnetite for samples from the upper 200 mcd meter composite depth all samples were subjected to stepwise alternating field demagnetization the demagnetization behaviors of the samples below 200 mcd were erratic and unstable owing to very weak remanent magnetization a total of 15 reliable magnetic reversal events were identified in the upper 190 mcd cores of hole 1143c based on the declination variations of the characteristic remanent magnetization which can be correlated very well with the geomagnetic polarity time scale 2012 in combination with biostratigraphic data and astronomical time scales our new magnetostratigraphic results provide a more confident age framework for the southern scs since the early pliocene

past environmental and circulation changes in the south china sea input from the magnetic properties of deep sea sediments abstract the south china sea located at the transition between the pacific and the indian ocean receives every year mainly during the rain season enormous amounts of river sediments originating from the erosion weathering of rocks in the catchment basins at sea these sediments are carried by different water masses to their deposition site and they constitute a unique archive for past environmental studies in this region the magnetic fraction of deep sea sediments though forming a minority in volume provides incredibly valuable information for paleoceanographic reconstructions as long as its provenance and source to sink processes are well constrained after a brief description of the climatic sedimentological and oceanographic context of the south china sea scs a review of the information available so far in the literature about the magnetic properties of scs sediments is presented it shows a large variety of interpretations conclusions that finally results in a rather unclear picture because in such a context the characterization of the sediment at the source is critical the magnetic properties recently obtained from a set of samples from rivers and marine surface sediments are summarized to describe the present day situation they are then used to interpret paleorecords from a set of seven marine cores distributed from the southern to the northern basins at different water depths and all covering at least the last climatic cycle the results reported here for the first time suggest that the magnetic mineralogy remains rather stable in time on land and that its time and spatial distribution at sea is an interplay of changes in sea level and deep sea circulation during low sea level periods bottom deep sea circulation is weak and the deposited sediment originates from the proximal rivers on the contrary during high sea level the circulation is enhanced transporting more sediment most likely from taiwan and luzon to the northwestern part of the scs and also in smaller proportion to the southern basin where it mixes with the local river borne sediment by comparing the two longest records we observe that this pattern is repeated over the last 900 ka superimposed to the 100 kyr cyclicity we also observe a longer term evolution with a maximum in the bottom current strength around 500 ka coinciding with global changes in the deep ocean circulation and carbon cycle these new results based on a wide spectrum of magnetic properties of numerous marine sedimentary cores from the scs show that the magnetic fraction yields important insights into past changes of the sedimentary pathways in particular the dynamic of the deep sea circulation depending on the global climatic context

long eccentricity cycle in pliocene oceanic carbon reservoir a comparison between the mediterranean and the south china sea abstract as quantitative paleoclimate time series extend deeper into the geological past growing evidence indicates the extensive occurrence of the 400 kyr long eccentricity cycle in geological records the long cycles are best manifested in the marine carbon isotope as a series of 13 cmax which correspond to the long eccentricity s minima however it remains unclear how eccentricity affects the oceanic carbon reservoir to determine what processes are involved in generating the 400 kyr cycles one long eccentricity cycle in the late pliocene from 3 2 myr to 2 8 myr was examined in two sections respectively from the mediterranean and the south china sea the results indicate that the mediterranean section displays distinct precession cycles in all of the studied proxy time series and their amplitudes are modulated by eccentricity whereas the precession cycles and the eccentricity modulation are much weaker in the proxy sequences from the south china sea the difference is attributed to the fact that african monsoon was overwhelmingly dominated by precessional forcing and the mediterranean basin was isolated from glacial induced reorganizations of the global ocean whereas totally different conditions existed in the south china sea it may be inferred from the comparison that the 13 cmax originated largely from the global ocean and was unlikely caused by local basin factors at the long eccentricity maximum summer insolation reached a maximum at low latitudes and the intensified global monsoon changed the ocean carbon reservoir and the 13 c value because of the long residence time of carbon in the ocean 13 c changes in the global oceanic reservoir primarily occur on a 10 5 yr time scale with a smoothing effect in the lower frequencies the 400 kyr long eccentricity was pervasive at least in the cenozoic ocean but its expression was subject to spatio temporal variations particularly under the influence of the ice sheet development

east asian winter monsoon variability over the last glacial cycle insights from a latitudinal sea surface temperature gradient across the south china sea article i nfo high resolution planktonic foraminifer mg ca sea surface temperature sst and 18 o records of images core md052896 from the southern south china sea scs provide a history of east asian winter monsoon variability over the past 23 kyr specifically we find that the latitudinal sst gradient of the north south scs shows promise as a useful proxy of east asian winter monsoon changes the sst record of core md052896 from the southern scs and odp site 1145 from the northern scs documents several positive anomalies indicating east asia winter monsoon maxima during cold periods of the past 23 kyr including the h1 and younger dryas events the sst record also indicates that after 8 5 ka the east asian winter monsoon strengthened relative to the deglaciation reaching levels of the last glacial period comparison of the scs sst record with stalagmite 18 o records suggests that both the east asian summer and winter monsoons strengthened from the last glacial to the holocene and that summer and winter monsoon strength probably are not anti correlated at least over the last glacial interglacial cycle

development of the east asian summer monsoon evidence from the sediment record in the south china sea since 8 5 ma 128 samples from ocean drilling program odp site 1143 in the southern south china sea were analyzed for grain size clay minerals biogenic opal content and quartz in order to reconstruct changes in east asian monsoon climate since 8 5 ma an abrupt change of terrigenous mass accumulation rate mar clay mineral assemblage median grain size and biogenic opal mar about 5 2 ma suggests that between 8 5 5 2 ma the source of terrigenous sediment was mainly in the region of surface uplift and basaltic volcanism in southern vietnam a simple model of east asian summer monsoon evolution was based on the clay feldspar ratio kaolinite chlorite ratio and biogenic opal mar the summer monsoon has two periods of maximum strength at 8 5 7 6 ma and 7 1 6 2 ma subsequently there was a relatively stable period at 6 2 3 5 ma continued intensification about 3 5 2 5 ma and gradually weakening after 2 5 ma since i ma the monsoon has intensified with remarkable high frequency and amplitude variability simultaneous increase in sedimentation rates at odp sites 1143 1146 and 1148 as well as in mar of terrigenous materials quartz feldspar and clay minerals at odp site 1143 at 3 5 2 5 ma may be the erosional response to both global climatic deterioration and the strengthening of the east asian summer monsoon after about 3 4 ma c 2006 elsevier b v all rights reserved

regional and global benthic δ18o stacks for the last glacial cycle although detailed age models exist for some marine sediment records of the last glacial cycle 0 150 ka age models for many cores rely on the stratigraphic correlation of benthic 18o which measures ice volume and deep ocean temperature change the large amount of data available for the last glacial cycle offers the opportunity to improve upon previous benthic 18o compilations such as the lr04 global stack not only are the age constraints for the lr04 stack now outdated but a single global alignment target neglects regional differences of several thousand years in the timing of benthic 18o change during glacial terminations here we present regional stacks that characterize mean benthic 18o change for 8 ocean regions and a volume weighted global stack of data from 263 cores age models for these stacks are based on radiocarbon data from 0 to 40 ka correlation to a layer counted greenland ice core from 40 to 56 ka and correlation to radiometrically dated speleothems from 56 to 150 ka the regional 18o stacks offer better stratigraphic alignment targets than the lr04 global stack and furthermore suggest that the lr04 stack is biased 1 2 kyr too young throughout the pleistocene finally we compare global and regional benthic 18o responses with sea level estimates for the last glacial cycle

an improved comparison of chinese loess with deep sea δ18o record over the interval 1 6 2 6 ma 1 based on a refined orbital timescale for the lower portion of pleistocene loess paleosol sequence at lingtai section we present an improved comparison of chinese loess with deep sea 18o record over the interval 1 6 2 6 ma unlike previous land ocean comparison our result suggests that each paleosol unit from s25 to s32 is approximately including two interglacial oxygen isotope stages the rationality of our revised comparison is supported by the well constrained ages of geomagnetic reversal boundaries in chinese loess and the almost cycle to cycle correlation between the grain size and deep sea 18o record spectral analyses demonstrate that variations of the magnetic susceptibility and grain size in the interval 1 6 2 6 ma were dominated by a prominent 410 ka periodicity implying a possible response of the east asian monsoon evolution to orbital eccentricity forcing

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

low latitude hydro climatic changes during the plio pleistocene evidence from high resolution alkane records in the southern south china sea abstract high resolution records of long chain n alkane biomarkers from the southern south china sea reveal tightly response of n alkane distribution to hydro climate changes over the past 5 ma with increasing longer chain n c31 alkanes indicating a correlation with drier conditions and increasing shorter chain n c27 alkanes with wetter conditions the variations of the c31 c27 ratio or the alkane chain length index imply humid conditions before 2 9 ma progressively reduced moisture since then and to bigger fluctuations between wet and dry conditions since 1 2 ma this long term hydro climate trend is superimposed by glacial dry and interglacial wet patterns over the plio pleistocene glacial cycles combined with other proxy records our results indicate that precipitation over the tropical asia pacific strengthened before the onset of the northern hemisphere glaciation and the mid pleistocene climate transition at about 1 2 ma these dramatic humidity changes over major climate transitions imply a crucial role of tropical hydrology dynamics on global climate change in the late cenozoic

integrated stratigraphy of odp site 1115 solomon sea southwestern equatorial pacific over the past 3 2 ma abstract we provide an integrated stratigraphy for the southern margin of the indo pacific warm pool back to 3 2 million years ago ma from odp site 1115 hole b 9o11 s 151o34 e water depth 1149 m 0 217 m below sea floor the only hole with core recovery beyond 4 4 m an initial age model based on 14 calcareous nannofossil datums 5 planktonic foraminiferal biostratigraphic events and 12 magnetic polarity reversals is refined by planktonic foraminiferal globigerinoides sacculifer 300 355 m 18o stratigraphy the planktonic 18o record with an average 3 4 kyr resolution matches the global stack lr04 lisiecki and raymo 2005 the 41 kyr obliquity and 100 kyr eccentricity patterns show good correlation between the lr04 and the dataset presented herein the precession amplitude matches eccentricity supporting the established stratigraphy sedimentation rates at hole 1115b have decreased from 9 3 to 4 5 cm kyr during the past 3 2 ma toward present mainly due to the gradual deepening of the woodlark basin the planktonic 18o record from site 1115 matches the global climate evolution well

first toba supereruption revival little has been known about the earliest toba eruptive episodes that created the largest known caldera complex of quaternary age here we report evidence for the eastward dispersal of the oldest toba tuff in south china sea sediments to 2500 km away from the source the tephra deposits occur below the brunhes matuyama geomagnetic boundary 778 ka and slightly above the australasian microtektite layer 793 ka calibrated by astronomically tuned oxygen isotope stratigraphy the middle pleistocene toba eruption occurred during the deglaciation at 788 2 2 ka according to the tephra occurrence between marine isotope stages 20 and 19 this refined age is in good agreement with the 4 0 ar 3 9 ar date of 800 20 ka for the toba tephra layer d from ocean drilling program odp site 758 but significantly younger than the commonly cited ar ar age of 840 30 ka the eruption expelled at least 800 1000 km 3 dense rock equivalent of rhyolitic magma on the basis of the widespread tephra fall deposit in the basins of the indian ocean and the south china sea in spite of its exceptional magnitude the timing of this major eruption does not indicate a causal linkage between this event and a long term global climatic deterioration

nonstationary phase of the plio pleistocene asian monsoon paleoclimate records indicate that the strength of the asian summer monsoon is sensitive to orbital forcing at the obliquity and precession periods 41 000 and 23 000 years respectively and the extent of northern hemisphere glaciation over the past 2 6 million years the timing phase of strong monsoons has changed by 83 degrees in the precession and 124 degrees in the obliquity bands relative to the phase of maximum global ice volume inferred from the marine oxygen isotope record these results suggest that one or both of these systems is nonstationary relative to orbital forcing

stable isotopes in modern planktonic foraminifera sediment trap and plankton tow results from the south china sea abstract this study reports on the stable isotopic composition of modern planktonic foraminifera tests collected from plankton tows and sediment trap moorings in the northern south china sea plankton tow samplings were conducted at water depths of 50 100 and 200 m during various seasons between december 2002 and august 2008 the sediment trap array was deployed between august 2004 and february 2005 at water depths of 121 m 619 m and 3451 m four common and widely distributed tropical subtropical planktonic foraminifer species including globigerinoides ruber white variety globigerinoides sacculifer without sac neogloboquadrina dutertrei and pulleniatina obliquiloculata were analyzed for 18o and 13c within narrow shell size ranges and compared with the concurrent sea surface temperature sst and wind stress our results show that foraminiferal 18o is primarily influenced by seawater temperature while 13c is affected by surface water nutrients which in this region can be discerned from wind stress data the 18o and 13c values from foraminifers recovered in plankton tows generally show greater variability and more depleted 18o than values of tests collected by sediment traps for foraminifer tests collected by sediment trap the 18o of the shallow dwelling g ruber shows the largest amplitude variation ca 1 6 among the four species in contrast the 13c of p obliquiloculata shows relatively constant values throughout the study period a pattern of enriched 18o values associated with marked 13c depletion is common to three species collected between late october and late december 2004 this distinct isotopic signal corresponds to a decrease in sst and increase in wind stress indicating the onset of prevailing northeast winds during the winter season

magnetostratigraphic and archaeological records at the early pleistocene site complex of madigou nihewan basin implications for human adaptations in north china abstract the nihewan basin in north china contains the densest concentration of early pleistocene paleolithic sites outside africa this paper introduces a new archaeological site complex at madigou mdg that was systematically excavated from 2011 to 2014 in the northeastern part of the nihewan basin the site contains fossils and well preserved stone artefacts in fluvio lacustrine sediments our magnetostratigraphic results situate the mdg sedimentary sequence in the early brunhes normal chron and the late matuyama reverse chron including the jaramillo normal subchron the mdg artifact layers are positioned within the pre jaramillo matuyama chron with an estimated age of ca 1 2 ma close to the onset of mid pleistocene climate transition the mdg core and flake technology includes bipolar flaking of siliceous dolomite cobbles and freehand flaking of chert and brecciated chert block fragments mammalian fauna and pollen compositions indicate that the mdg hominins lived in an open habitat varying from lightly wooded grassland to an ecosystem dominated by sparse steppe near the shore of the nihewan paleolake our combined results in the fields of archaeology paleontology palynology and magnetochronology suggest that innovations in technological behavior may correlate with adaptations to high environmental variability during the start of mid pleistocene climate transition

oxygen and carbon isotope record of east pacific core v19 30 implications for the formation of deep water in the late pleistocene north atlantic abstract a detailed oxygen and carbon isotope record has been obtained from benthic foraminifera in core v19 30 from the carnegie ridge on the south side of the panama basin expressing these records and the oxygen and carbon isotope records previously published for atlantic core m 12392 on a common timescale it is apparent that the oxygen isotope records are very similar but that the carbon isotope records are quite different by obtaining the carbon isotope gradient between the two sites as a function of time we show that the production of north atlantic deep water has varied over a wide range during the late pleistocene and that the pattern of variation is not simply related to the well known oxygen isotope record although the two oxygen isotope records are very similar changes in the interoceanic gradient are detectable and support the hypothesis that in the glacial mode the north atlantic was colder and less oxygenated than it is today shackleton s 1 1977 interpretation whereby the carbon isotope record from the atlantic core reflects changes in the terrestrial biomass is an over simplification however the record from the pacific core v19 30 probably can be explained in these terms since it probably approximates the carbon isotope record of global mean oceanic dissolved co 2

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

local and regional trends in plio pleistocene δ18o records from benthic foraminifera we present new orbital resolution pliocene pleistocene benthic stable oxygen isotope 18ob records from ocean drilling program sites 1264 and 1267 from walvis ridge in the southeast atlantic we compare long term 250 kyr interbasin 18ob gradients between pacific and north atlantic regional stacks as well as intra and interbasin gradients from the perspective of walvis ridge the 18ob values from sites 1264 and 1267 are almost always higher than deep north atlantic and pacific sites with large gradients 0 5 emerging abruptly at 2 4 ma and persisting until 1 3 ma from this we infer the presence of a new water mass which resulted from the influence of dense 18o enriched nordic sea overflow waters via the abyssal east atlantic meanwhile long term average 18ob values in the north atlantic appear to have remained within 0 0 25 lower than in the pacific however the magnitude of this difference is sensitive to the inclusion of records from the equatorial west atlantic these results together with constraints based on temperature salinity and density suggest an influence of the seawater 18o 18osw versus salinity relationship of source waters on 18ob values within the atlantic in particular the abrupt emergence at 2 4 ma of higher 18ob values at sites 1264 and 1267 relative to north atlantic records appears to require a low latitude surface water 18osw signal this implies a connection between northward heat transport and deep water export into the abyssal east atlantic hence our results have implications for the interpretation of 18ob records and highlight the potential for 18ob to constrain deep atlantic water mass sources and pathways during the plio pleistocene

quaternary upper ocean thermal gradient variations in the south china sea implications for east asian monsoon climate 1 the east asian monsoon climate has an overwhelming influence on local climatic conditions of the south china sea scs here we present results from a 3 year study of modern sediment traps from the central scs in which the percentage of opal the fluxes of pulleniatina obliquiloculata and globigerinoides ruber the organic carbon flux and primary productivity all show highest values during winter when the mixed layer depth is deepest the 18o difference 18o p g between the subsurface dwelling p obliquiloculata and the mixed layer dwelling g ruber in core top samples from 12 piston cores and one ocean drilling program odp site in the scs is large 0 6 in a cold eddy area with a shallow mixed layer off vietnam but is reduced in deep mixed layer settings lacking cold eddies we also present 1 56 myr long isotope records of g ruber and p obliquiloculata from odp site 1143 in the southern scs that reveal upper ocean thermal gradient variations during the quaternary lower 18o p g values indicate increased mixed layer depths over most glacial episodes likely due to stronger winter monsoon winds in contrast higher 18o p g values during interglacial intervals suggest decreased mixed layer depths and thus weaker winter monsoon winds comparisons of 18o p g with the percentage of p obliquiloculata at site 1143 and the percentage of herbs and opal flux at site 1144 demonstrate that glacial interglacial variations were strongly influenced by stronger and weaker east asian winter monsoons during glacials and interglacials respectively therefore the upper ocean thermal gradient variations in the scs have been consistently affected by the east asian winter monsoon since at least the beginning of the pleistocene

paleoceanography of the mid pleistocene south china sea high frequency fluctuations in paleoenvironmental proxies from the south china sea including stable isotopes and abundance of planktonic foraminifers nannofossils radiolarians and palynomorphs reveal a dynamic local response to the stepwise development of the mid pleistocene climate transition mpt these proxies indicate a dramatic drop in sea surface temperature sst at about 900 ka the first largest sst decrease in the region during the quaternary estimated winter sst declined from 24 25 degrees c to 17 18 degrees c in the northern and from 26 27 degrees c to 23 24 degrees c in the southern south china sea subsequent changes in the thermocline depth and faunal floral turnovers imply a period of about 300 ka in the final stage of the mpt winter monsoons increased at similar to 900 ka and reached a maximum strength toward the end of the mpt when summer monsoons also strengthened in interglacials as a result thermal gradient between the northern and southern south china sea increased substantially with stronger winter monsoon influence in the north and warm and saline conditions in the south especially during glacial periods these n s paleoceanographic contrasts indicate an initial establishment of the modern styled semi enclosed south china sea about 900ka ago when passages in the south started to become completely exposed during glacial lowstands coupled with deep water cooling and ventilation uplift of the sill depth in the bashi strait to near the present 2400 m during this period caused sudden decline and extinction of pacific deep water benthic foraminifers in the isolated deep sea basin together with data from the oceanic western pacific these results further imply a considerable weakening of the western pacific warm pool during mis 23 22 and in subsequent glacial periods while the mpt may have invoked high latitude processes especially an increased ice volume tropical processes more likely have facilitated the restoration of heat and energy to the western pacific in each interglacial rebound planktonic delta c 13 maxima on eccentricity periocities leading major cooling events during the quaternary indicate the important role of global carbon reservoir changes due to low as well as high latitude processes in past climate change c 2008 elsevier ltd all rights reserved

late pliocene monsoon linkage in the tropical south china sea the onset of northern hemisphere glaciation nhg 2 7 ma ago coincided with prominent climate changes in the tropical regions such as the african and the asian monsoons however the relationship between tropical and sub tropical monsoonal variations and high northern latitude ice sheet expansion as well as processes such as late pliocene tropical sea surface temperature sst change is not clear our late pliocene 2 5 3 3 ma monsoon proxy records and mg ca derived sst records at ocean drilling program odp site 1143 from the southern south china sea scs reveal that while tropical sst shows a stepwise decrease of 2 3 c during this period the east asian monsoon gradually strengthens in response to the onset of the nhg at the 41 kyr and 23 kyr bands ice volume change lags tropical sst by 4 kyr but leads the east asian monsoon by 12 17 kyr our finding highlights the significant role of the tropical pacific region in driving global climate change in the late pliocene which has invariable leading phase relative to the ice volume change as in the late pleistocene however the east asian monsoon shows a linear response to the onset of the nhg in the late pliocene with much bigger phase lagged at the 41 kyr and 23 kyr bands than in the pleistocene which suggests that at the obliquity and precession bands the phases of the plio pleistocene east asian monsoon variations relative to the global ice volume changes are not constant but variable therefore the east asian monsoons are not only simply driven by northern summer insolation at the precession period but also modulated by global ice volume change in high latitudes

links between the onset of modern walker circulation and the mid pleistocene climate transition sea surface temperatures ssts reconstructed from ocean drilling program sites 806 and 849 in the western and eastern equatorial pacific provide a history of the strength of the walker circulation between 1 5 and 0 5 ma a progressive cooling in the eastern equatorial pacific is paralleled by intensification of the equatorial zonal sst gradient that began 1 17 ma prior to the expansion of global ice volume associated with the mid pleistocene climate transition the ssts in the eastern equatorial pacific and the zonal gradient reached modern values by 0 9 ma we propose that this onset and intensification of the modern walker circulation reduced heat flux but increased moisture transport to high latitudes leading to the development of more extensive ice sheets and the shift toward the 100 ka world

monospecific pliocene oyster buildups murray basin south australia brackish water end member of the reef spectrum abstract paleoestuarine monospecific oyster bioherms and biostromes formed by the extant soft bottom oyster ostrea angasi are prolific in the pliocene norwest bend formation murray basin south australia these buildups are pioneer communities that record arrested ecological succession comprising only the stabilization and colonization stages of reef development each of these stages is directly linked to a different phase of marine inundation stabilization is restricted to the early transgressive systems tract when pre existing topographic highs were flooded and populated by dense aggregations of oyster clusters colonization is manifest throughout the transgressive and highstand systems tracts when increased accommodation allowed the vertical and lateral accretion of juvenile oyster communities into large buildups bioherms formed in areas of low terrigenous clastic sedimentation and seafloor disturbance both of which encouraged rapid community growth biostromes in contrast record buildup development on an unstable seafloor where episodic catastrophic community burial by storm sedimentation created repeated conditions of seafloor stabilization and colonization subaqueous dunes formed as part of the falling stage systems tract when river and tidal currents reworked shell material from bioherms and biostromes into large scale subaqueous bedforms brackish water conditions in the palaeoestuary a turbid water column mesotrophic nutrient levels and high spatial homogeneity of oyster buildups are interpreted to have prevented recruitment of specialized stenohaline organisms that typify the diversification stage of other metazoan reefs comparison with modern low diversity oyster communities imply that high fecundity and growth rates as well as exogenic nutrient cycling also made oysters in the norwest bend formation highly adapted competitors capable of thriving in this nutrient rich setting

millennial scale climate variability during the mid pleistocene transition period in the northern south china sea abstract stable isotopes of foraminiferal multispecies surface dwelling globigerinoides ruber thermocline dwelling pulleniatina obliquiloculata and benthic uvigerina peregrina and mg ca ratios of g ruber shells were analyzed with an average time resolution of 370 yr for reconstructing the orbital and millennial scale changes in the east asian monsoon and associated upper water structure during the mid pleistocene period of 800 1060 ka at odp site 1144 in the northern south china sea scs it has been found that generally the sea surface temperature sst were lower and the depth of thermocline dot was deeper during glacial stages and vice versa during interglacial stages indicating a strengthened winter monsoon and weakened summer monsoon during glacial stages the sea surface salinity sss was relatively lower during glacials induced by the greatly reduced distance of this site to the shore during times of low sea level further spectral analyses have revealed significant semi precessional and or precessional cycles in the planktic 18 o sst and the proxies of sss and dot showing the typical characteristics of tropical climate change this means that during the mid pleistocene climate transition mpt period the east asian monsoon evolution and associated changes of upper water column structure in the northern scs were probably driven partly by tropical forcing like in the southern scs and should not be related only to the high latitude ice sheet changes particularly millennial scale climate fluctuations mainly 1 4 kyr cycle were found to exist throughout the glacial and interglacial stages during the mpt period in the northern scs but slightly different from the sawtooth like d o events recorded in late quaternary greenland ice cores during the mid pleistocene terminations the sst warming was synchronous with the northern ice sheet retreat indicated by benthic 18 o in the northern scs which is consistent to the previous findings in the late quaternary scs and apparently different from that in the western equatorial pacific ocean providing new insights into the studies of east asian monsoon evolution and rapid climate change

pliocene pleistocene magneto cyclostratigraphy of iodp site u1499 and implications for climate driven sedimentation in the northern south china sea abstract a high resolution astronomical tuned magnetostratigraphy was obtained from a continuous 333 m succession recovered at international ocean discovery program iodp hole u1499a in the north margin of the south china sea scs during joint legs 367 368 a total of 12 magnetic reversals are identified through the pliocene and pleistocene the cycle analysis of natural gamma ray ngr data shows an average suite of ca 33 m and 8 m wavelengths with lesser 1 5 m cycles which are consistent with the ratios of milankovitch orbital climate oscillations caused by long eccentricity 405 kyr short eccentricity 100 kyr and precession 20 kyr the astronomical tuned magnetostratigraphy correlates with nearly all features of the pliocene pleistocene geomagnetic polarity time scale there was a significant shift to 100 kyr dominated cyclicity at ca 1 3 ma which marks the onset of the mid pleistocene transition during which the influx of the clay component decreased a general enrichment in silt sand influx during the past 0 4 myr was punctuated by surges in coarser grained components lowest ngr during or at the end of each major global glacial event comparison to a high resolution sediment record spanning the pliocene pleistocene on the southern margin of the scs odp site 1143 indicates common intervals of changing rates of sediment accumulation in both regions there are relatively lower rates of sediment accumulation during the late zanclean mid pliocene ca 4 1 to 3 6 ma early gelasian ca 2 5 to 2 0 ma early calabrian ca 1 6 to 1 4 ma and the earliest middle pleistocene ca 0 6 ma the merger of magnetostratigraphy cyclostratigraphy and the ngr record to produce a high resolution profile of bulk sediment accumulation rates and relative clay to sand silt components is a powerful tool and climate proxy to reconstruct the general history of sediment input into the scs and its relationships to east asia monsoon and tectonic evolution

mid pliocene asian monsoon intensification and the onset of northern hemisphere glaciation the late pliocene onset of major northern hemisphere glaciation nhg is one of the most important steps in the cenozoic global cooling although most attempts have been focused on high latitude climate feedbacks no consensus has been reached in explaining the forcing mechanism of this dramatic climate change here we present a key low latitude climate record the high resolution asian monsoon precipitation variability for the past fi ve million years reconstructed from south china sea sediments our results with supporting evidence from other records indicate signifi cant mid pliocene asian monsoon intensifi cation preceding the initiation of nhg at ca 2 7 ma ago this 1 4 million year long monsoon intensifi cation probably enhanced monsoon induced asian continental erosion and chemical weathering and in the process left fi ngerprints in marine calcium isotopes furthermore increased rock weathering and or organic carbon burial probably lowered the contemporary atmospheric co 2 and may have triggered the nhg onset

surface hydrographic and water mass variability in the eastern equatorial pacific during interglacial like marine isotope stage 14 surface temperature and water masses variability in the eastern equatorial pacific eep is sensitive to global climate changes in response to either northern southern hemisphere forcing or low latitude atmosphere ocean feedback high latitude processes can influence tropical oceans via atmospheric bridges and oceanic tunnels whereas perturbations in the low latitude atmosphere ocean modulate the behavior of low latitude oceans for climate paradoxes of prolonged warmth mis marine isotope stage 15 13 little has known about any causes or any possible tele connections between the eep and high low latitudes because lack of observations to address this issue multiple sea surface temperature sst records i e faunal transfer function based mg ca ratio on mono species and uk 37 derived temperature estimates and faunal derived water masses are generated from the eep core odp 1240 our results reveal a glacial eep mis 14 cooling 1 2 c with higher eastern boundary current faunal abundances as compared to adjacent interglacial stages in a glacial mis 14 scenario we suggest that the eep areas would receive more nutrient rich cold waters from high latitudes via the peru chile current the atmospheric bridge of a northwardly intertropical convergence zone itcz shift and the resulting heat moisture transport across the eastern equatorial atlantic eea would weaken the magnitude of the eep cold tongue in mis 14 we also think of another scenario in that the orbital variations in glacial mis 14 was characterized by higher obliquity fluctuations lower eccentricity precession the orbital variations shape an inter hemispheric asymmetry with higher seasonality this scenario could result in a stagnant an inactive atlantic meridional ocean circulation and northward shifts in the itcz southward displacement of westerlies in the southeastern pacific during mis 14 the retreat of the west antarctic sea ice and enhancement of the antarctic circumpolar current would also bring less high latitude cold upwelled water the subantarctic mode water antarctic intermediate water into the eastern tropical pacific atlantic oceans we suggest that a diminished la nina like condition and a relatively weakened eep eea cold tongue developed in glacial mis 14 compared to other glacial mis in the late quaternary the interglacial like mis 14 is therefore characterized by a small magnitude of eastern tropical upwelling areas and greater extension of western pacific atlantic warm surface waters such amplifications in glacial mis 14 could lead to less fluctuation of termination vi and persistent warmth in mis 15 13

early onset and tropical forcing of 100 000 year pleistocene glacial cycles between 1 5 and 0 6 myr ago the period of the earth s glacial cycles changed from 41 kyr the period of the earth s obliquity cycles to 100 kyr the period of the earth s orbital eccentricity1 2 which has a much smaller effect on global insolation the timing of this transition and its causes pose one of the most perplexing problems in palaeoclimate research3 here we use complex demodulation to examine the phase evolution of precession and semiprecession cycles the latter of which are phase coupled to both precession and eccentricity in the tropical and extra tropical atlantic ocean we find that about 1 5 myr ago tropical semiprecession cycles with periods of about 11 5 kyr started to propagate to higher latitudes coincident with a growing amplitude envelope of the 100 kyr cycles evidence from numerical models suggests that cycles of about 10 kyr in length may be required to explain the high amplitude of the 100 kyr cycles4 combining our results with consideration of a modern analogue we conclude that increased heat flow across the equator or from the tropics to higher latitudes around 1 5 myr ago strengthened the semiprecession cycle in the northern hemisphere and triggered the transition to sustained 100 kyr glacial cycles

extinction of deep sea foraminifera as a result of pliocene pleistocene deep sea circulation changes in the south china sea odp sites 1143 and 1146 during the late pliocene middle pleistocene 56 species and 15 genera of elongate cylindrical benthic foraminifera disappeared from the deep sea in the south china sea odp sites 1143 and 1146 as part of the last global extinction in the deep sea this extinction group ext gp exhibited a pulsed decline in abundance and species richness mostly during glacials and often associated with periods of expansion of polar ice that resulted front increased cooling of the earth s climate since similar to 2 5 ma particularly during the mid pleistocene climate transition mpt 1 2 0 6 ma we infer that the ext gp decline in abundance and disappearance was a result of the increased glacial cooling and consequent increased ventilation of the deep sea water masses the detailed record of withdrawal of the ext gp differs between the two sites with far more disappearances occurring prior to the mpt in the deeper site 1143 2772m than in the shallower site 1146 2092 in the late pliocene and early pleistocene declines in deeper parts of the south china sea site 1143 may have resulted from enhanced glacial production of deep southern sourced water passing over the sill into the basin from the north west pacific during the mpt however the ext gp declines and disappearances were of similar timing and magnitude in both sites implying that both were influenced by the same deep water mass during glacials at this time this could have been north pacific deep water which many workers infer was formed in the northern pacific during the last glacial and may have begun forming during mpt glacials in association with the progressively enhanced cooling of the northern hemisphere c 2006 elsevier ltd all rights reserved

a geomagnetic paleointensity stack between 0 8 and 3 0 ma from equatorial pacific sediment cores 1 we have conducted a paleomagnetic study of six sediment cores taken from the equatorial pacific three from the west caroline basin and three from the manihiki plateau in order to make a relative paleointensity stack during the matuyama and late gauss chrons the age of the bottom of the cores ranges from 1 2 to 3 0 ma the sediments show little downcore changes in the proxies of magnetic grain size and mineralogy and are hence suitable for estimating relative paleointensity the age of the cores is controlled by correlating variations in magnetic concentration magnetic susceptibility and or anhysteretic remanent magnetization arm to target oxygen isotope 18o curves all cores from the manihiki plateau show an upward decrease of the natural remanent magnetization nrm intensity normalized by arm and isothermal remanent magnetization irm with a decrease in sedimentation rate such a trend was removed before being converted to relative paleointensity this observation implies that a sedimentation rate change can affect relative paleointensity estimation relative paleointensity records from the six cores coincide well with each other within uncertainty of age we constructed a stacked curve between 0 8 and 3 0 ma the equatorial pacific paleointensity stack epapis 3ma after adjusting age the number of cores stacked is three to four throughout the record quasiperiodic paleointensity lows occur in the epapis 3ma and corresponding paleointensity lows can be found in previously published records with some shifts in age at least parts of the paleointensity minima seem to be accompanied by geomagnetic excursions the asymmetric sawtooth pattern of paleointensity variations is not observed at the matuyama gauss boundary and thereafter in our record a spectral analysis shows that 100 kyr orbital eccentricity frequency may exist in paleointensity variations during the matuyama and late gauss chrons

enhanced silicate weathering of tropical shelf sediments exposed during glacial lowstands a sink for atmospheric co2 atmospheric co2 and global climate are closely coupled since 800 ka co2 concentrations have been up to 50 higher during interglacial compared to glacial periods because of its dependence on temperature humidity and erosion rates chemical weathering of exposed silicate minerals was suggested to have dampened these cyclic variations of atmospheric composition cooler and drier conditions and lower non glacial erosion rates suppressed in situ chemical weathering rates during glacial periods however using systematic variations in major element geochemistry sr nd isotopes and clay mineral records from ocean drilling program sites 1143 and 1144 in the south china sea spanning the last 1 1 ma we show that sediment deposited during glacial periods was more weathered than sediment delivered during interglacials we attribute this to subaerial exposure and weathering of unconsolidated shelf sediments during glacial sealevel lowstands our estimates suggest that enhanced silicate weathering of tropical shelf sediments exposed during glacial lowstands can account for 9 of the carbon dioxide removed from the atmosphere during the glacial and thus represent a significant part of the observed glacial interglacial variation of 80 ppmv as a result if similar magnitudes can be identified in other tropical shelf slope systems the effects of increased sediment exposure and subsequent silicate weathering during lowstands could have potentially enhanced the drawdown of atmospheric co2 during cold stages of the quaternary this in turn would have caused an intensification of glacial cycles

last global extinction in the deep sea during the mid pleistocene climate transition 1 twenty percent 19 genera 95 species of cosmopolitan deep sea 500 4000 m benthic foraminiferal species became extinct during the late pliocene middle pleistocene 3 0 12 ma with the peak of extinctions 76 species occurring during the mid pleistocene climate transition mpt 1 2 0 55 ma one whole family stilostomellidae 30 species was wiped out and a second pleurostomellidae 29 species was decimated with just one species possibly surviving through to the present our studies at 21 deep sea core sites show widespread pulsed declines in abundance and diversity of the extinction group species during more extreme glacials with partial interglacial recoveries these declines started in the late pliocene in southern sourced deep water masses antarctic bottom water circumpolar deep water and extending into intermediate waters antarctic intermediate water north atlantic deep water in the mpt with the youngest declines in sites farthest downstream from high latitude source areas for intermediate waters we infer that the unusual apertural types that were targeted by this extinction period were adaptations for a specific kind of food source and that it was probably the demise of this microbial food that resulted in the foraminiferal extinctions we hypothesize that it may have been increased cold and oxygenation of the southern sourced deep water masses that impacted on this deep water microbial food source during major late pliocene and early pleistocene glacials when antarctic ice was substantially expanded the food source in intermediate water was not impacted until major glacials in the mpt when there were significant expansion of polar sea ice in both hemispheres and major changes in the source areas temperature and oxygenation of global intermediate waters

last glacial pollen record from lanzhou northwestern china and possible forcing mechanisms for the mis 3 climate change in middle to east asia abstract the vegetation on the northeastern margin of the tibetan plateau is highly sensitive to climatic changes and thus represents a potentially interesting environmental archive pollen samples from the fanjiaping loess section in lanzhou on the western chinese loess plateau clp were analyzed in conjunction with osl dating the results indicate that pollen zone b 60 6 46 0 ka correlative to the early mis 3 had the greatest abundances of cupressaceae tsuga gramineae and cyperaceae of the entire section suggesting a warm phase during the last glacial period these pollen taxa decreased significantly in abundance in the zones c 46 0 39 0 ka and d 39 0 27 0 ka reflecting a substantial climate cooling from the middle mis 3 to mis 2 these results correlate with climate records from the south china sea the clp baikal lake north america north atlantic ocean and other regions and probably correspond with the decline of northern high latitude insolation and the increase of global ice volume from 50 to 20 ka in particular arboreal pollen fern spore and algae abundances declined sharply since 40 ka while shrub and herb pollen reached the highest abundances conifer pollen picea and abies abundance also rose markedly and increased up the section this implies significant climate deterioration and likely corresponded with substantial growth of the polar ice sheets since 40 ka the decreasing temperature caused by an insolation decline during the last glacial period probably reinforced the cooling effect in a snow ice albedo feedback which would result in less climate sensitivity to radiative forcing meanwhile vegetation decline in the northern hemisphere during the last glacial period and tundra development at high latitudes possibly caused additional cooling enhancing the growth of polar ice sheets since 40 ka the development of polar ice sheets increased the polar to equator temperature and pressure gradients strengthening the westerlies and supplying plenty of moisture to northwest china during 40 30 ka lake sediments developed widely on the tibetan plateau during 40 30 ka probably related to an increase in the seasonality of middle to low latitude insolation which caused an enhancement of glacier melting on the plateau

dynamics of the australian indonesian monsoon across termination ii implications of molecular biomarker reconstructions from the timor sea abstract molecular biomarker derived proxies in a marine sediment core from the eastern timor sea have been employed to track changes in the australian indonesian monsoon system over the time period from the penultimate glacial to the last interglacial the average chain length of n alkanes originating from terrestrial higher plants reveals an expansion of woody plants during both termination ii and the last interglacial with respect to the penultimate glacial this is consistent with previous reconstructions for the last glacial interglacial cycle indicating that water stress conditions during dry seasons of southern indonesia should have been relieved during interglacials and deglacials relative to glacials however in contrast to an only muted response during heinrich stadial 1 the vegetation composition showed a dramatic and prominent change during heinrich stadial 11 this was probably caused by a much more significant and longer duration iceberg discharge event to the northern north atlantic during heinrich stadial 11 relative to heinrich stadial 1 which exerted a significant influence on the tropical hydrological cycle and monsoon rainfall seasonality in addition marine algae derived biomarkers are used to reconstruct primary productivity variations which are in agreement with previous studies from the same area the precessional cyclicity of paleo productivity variations is possibly induced by changes in the australian indonesian winter monsoon intensity showing a correlation with boreal winter insolation however this phase relationship is in contrast to the inference based on other lines of evidence which suggests strong winter monsoon strength during boreal summer insolation maxima new winter monsoon proxies are therefore required to clarify this discrepancy

pliocene sedimentation in a shallow cool water estuarine gulf murray basin south australia the pliocene norwest bend formation is a well preserved succession of terrestrial and shallow marine deposits in the murray basin south australia sediments in this unit consist of two discrete terrigenous clastic rich decametre scale sequences or informal members which record episodes of marine incursion during the early and late pliocene respectively the base of each sequence is a transgressive lag and or strandline deposit that is transitional upwards into a highstand subtidal terrigenous clastic and cool water carbonate sediment accumulation the top of each sequence is incised by fluvial channels that are filled by river deposits which formed as relative sea level fell and terrestrial environments prograded basinward sedimentological data suggest that gross stratigraphic architecture was primarily determined by glacioeustasy differences in sedimentary style between these two sequences however reflect a major climatic change that took place in southern australia during the mid pliocene the lower quartzose sand member is formed of siliciclastic sediment derived from prolonged deep subaerial weathering and contains a bivalve dominated cool temperate open marine mollusc assemblage these sediments accumulated under an equitable relatively warm humid climate the murray basin during this time because of high fluvial discharge was a salt wedge estuary with typical estuarine circulation in contrast the upper oyster rich member is typified by large monospecific oyster buildups that grew in restricted coastal environments strandline deposits contain a warm temperate skeletal assemblage contemporaneous aeolian sediments accumulated under warm semi arid climatic conditions well developed ferricrete silcrete and calcrete horizons reflect cyclic conditions of rainwater infiltration and evaporation in the seasonally dry climate that typifies southern australia today highly seasonal rainfall produced an estuary that fluctuated annually from being well to partially mixed these pliocene sediments support the notion that mollusc rich facies are the signature of cool water carbonate accumulations in inboard neritic environments unlike bryozoans that dominate the outer parts of cenozoic cool water carbonate shelves molluscs evolved to exploit an array of coastal ecosystems with wide salinity variations and variable sedimentation rates

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

an astronomically tuned 8 1 ma eolian record from the chinese loess plateau and its implication on the evolution of asian monsoon the chinese loess paleosol sequences have led to a great understanding of the evolution of the east asian monsoon eam in the quaternary however evolution of the eam in the late miocene and pliocene is quite blurry hindering our understanding of the mechanisms driving the eam thus we obtained high resolution grain size records of 8 1 ma from the thickest eolian red clay sequence at chaona on the chinese central loess plateau and astronomically tuned the grain size records to the orbital variation with a time resolution of 1 5 ka to 5 8 ka the variability of coarse size fraction a recognized proxy for the east asian winter monsoon eawm indicates a persistent but stepwise intensification of the eawm at ca 5 5 ma 3 6 ma 2 6 ma and 1 ma filtering of this proxy record at 100 41 and 21 ka bands was conducted to trace the evolution of the eawm in a frequency domain over 8 1 ma temporal variations of these three cycles show a remarkable simultaneous enhancement at ca 5 5 ma indicating a synchronous intensification of high and low latitude signals in the eawm record we suggest that the closure of panama seaway to form the north atlantic thermohaline circulation and the high latitude cooling during this time might collectively trigger such a response copyright 2011 by the american geophysical union

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

productivity and continental denudation history from the south china sea since the late miocene late miocene recent micropaleontological and geochemical records from ocean drilling program odp site 1143 in the southern south china sea scs indicate that increase and decrease in abundance of siliceous plankton may be controlled mainly by the input of nutrients derived from land and provided by upwelling a high export production event a biogenic bloom event occurred in the southern scs between 12 and 6 ma during this period high ratios of smectite illite chlorite smectite quartz and al k indicate a high weathering intensity of the asian continent possibly due to the intensification of the east asian summer monsoon easm which may have increased the net flux of nutrients to the ocean both directly through terrestrial input and indirectly through upwelling activity a drop in ba ti al ti and ca ti values around 6 ma may indicate a lowering of productivity possibly due to the large consumption of sea surface nutrients by the biogenic bloom alternatively it may indicate a shift in terrigenous input source area at about 5 4 ma a decrease in weathering intensity as indicated by a sudden decrease in the values of smectite illite chlorite smectite quartz and al k might have led to a sudden decrease of terrestrial nutrient input to the scs we suggest that the biogenic bloom ended when nutrients in surface waters were exhausted because of a decrease in supply as well as a decrease in upwelling intensity due to weakening of the easm as a result radiolarians were absent in the studied area between similar to 6 and 3 2 ma at similar to 3 2 ma radiolarians began to recover possibly because the start of northern hemispheric glaciation and the rapid uplift of the tibet plateau led to intensification of the east asian monsoon after the mid pleistocene climate transition at 0 9 ma the abundance and mass accumulation rates of radiolarians increased probably as a result of increased upwelling activity driven by the increasing intensity of the summer monsoon crown copyright c 2009 published by elsevier b v all rights reserved

major pleistocene stages in a carbon perspective the south china sea record and its global comparison 1 carbon isotope sequences at ocean drilling program site 1143 south china sea reveal a long term cyclicity of 500 kyr that is superimposed on the glacial cycles and is present in long 13c sequences from all oceans the quaternary 13c record is punctuated by four 13c maximum events 13cmax i which began in marine isotope stage mis 3 around 50 60 kyr ago 13cmax ii mis 13 0 47 0 53 ma 13cmax iii mis 27 29 0 97 1 04 ma and 13cmax vi mis 53 57 1 55 1 65 ma as the same cyclicity is also found in carbonate curves the 13cmax events must denote major reorganization in the carbon reservoir of the global ocean they also are associated with major changes in glacial cyclicity such as the mid brunhes event following 13cmax ii and the mid pleistocene revolution following 13cmax iii which in turn were associated with expansion of the ice sheets from a carbon perspective therefore the quaternary period has passed through three major stages and each appears to represent a further step in ice cap development

carbon reservoir changes preceded major ice sheet expansion at the mid brunhes event the beginning of the mid brunhes event ca 430 ka coincided with the largest amplitude change in d 18 o in the global ocean over the past 6 m y this large d 18 o change recorded a major ice sheet expansion that cannot be explained by small changes in orbital forcing our recent studies at ocean drilling program site 1143 from the south china sea show that this large d 18 o change was preceded by a significant negative d 13 c shift a global survey of long deep sea records has revealed periodic d 13 cmax episodes i e maximum positive values of d 13 c and both major ice sheet expansion events in the pleistocene the mid brunhes event and the middle pleistocene revolution were preceded by d 13 cmax ep isodes followed by negative d 13 c shifts this new finding suggests that disturbance in carbon reservoirs leads to major growth of ice sheet size and challenges the prevalent concept of arctic control of glacial cycles because earth is now passing again through a d 13 cmax episode it is crucial to understand the causal relationship between the successive d 13 c changes and ice sheet growth events

a detailed paleomagnetic record between 2 1 and 2 75 ma at iodp site u1314 in the north atlantic geomagnetic excursions and the gauss matuyama transition 1 this study investigated the detailed geomagnetic field variation between 2 1 and 2 75 ma from a sediment core iodp site u1314 with high sedimentation rate 10 cm kyr and good age control characteristic remanent magnetization directions were well resolved by stepwise alternating field demagnetization as a proxy of relative paleointensity natural remanent magnetization nrm normalized by anhysteretic remanent magnetization arm was used after testing that the influence of magnetic interaction in arm is negligible as a result the following features of the geomagnetic field in the studied period have been revealed during the transition of the gauss matuyama g m reversal and the reunion subchron the paleointensity decreased to the value lower than 20 of the average intensity in the whole studied interval in addition to these lows eight paleointensity lows were found associated with large directional changes that satisfy the definition of a geomagnetic excursion four of these have ages close to ages reported for geomagnetic excursions in prior studies whereas the other four excursions have not previously been observed in our results we confirm that the g m transition occurred in marine isotope stage 103 even if we consider the shift in depth due to the lock in process of magnetic particles the temporal variation in paleointensity showed asymmetric behavior associated with the g m transition with a gradual decrease prior to the transition and a rapid recovery after the transition