lack of enhanced preservation of organic matter in sediments under the oxygen minimum on the oman margin the impingement of oxygen minima on continental margins is widely thought to promote the accumulation of sedimentary facies enriched in well preserved organic matter it is shown here however that such a relationship does not clearly apply to the productive oman margin in the arabian sea which hosts one of the most severe oxygen minima in the oceans measurements made on the 0 1 cm depth interval from fourteen box cores collected from the outer shelf upper continental slope area off oman show that 1 1 deposited organic matter is overwhelmingly of marine origin 2 2 there is no significant correlation between the abundance of sedimentary organic carbon corg and the bottom water o2 concentration 3 3 there is no relation between the sedimentary corg n ratio and bottom water o2 4 4 there is no correlation between the hydrogen index hi of the organic matter and bottom water oxygen there are however significant correlations between the corg n ratio and the i corg cr al and zr al ratios as well as between the corg n ratio and the hydrogen index these relationships are interpreted as being the result of winnowing and attendant reworking which produce a progressive increase in the corg n ratio and a decrease in the hi and the i corg ratio as organic matter becomes progressively degraded commensurate rises in the cr al and zr al ratios result from the increased proportion of heavy minerals associated with winnowed lag deposits overall these data suggest that the bottom water oxygen concentration has little effect in governing either the distribution or the degree of preservation of organic matter on this margin thus the generally high but spatially variable corg content of the sediments on the oman margin may not reflect the occurrence of an oxygen minimum but instead be the result of a high settling flux of organic matter supported by monsoon driven upwelling and post depositional redistribution of the organic material by hydrodynamic influences

quantification of holocene asian monsoon rainfall from spatially separated cave records abstract a reconstruction of holocene rainfall is presented for southwest china an area prone to drought and flooding due to variability in the east asian monsoon the reconstruction is derived by comparing a new high resolution stalagmite 18 o record with an existing record from the same moisture transport pathway the new record is from heshang cave 30 27 n 110 25 e 294 m and shows no sign of kinetic or evaporative effects so can be reliably interpreted as a record of local rainfall composition and temperature heshang lies 600 km downwind from dongge cave which has a published high resolution 18 o record wang y j cheng h edwards r l he y q kong x g an z s wu j y kelly m j dykoski c a li x d 2005 the holocene asian monsoon links to solar changes and north atlantic climate science 308 854 857 by differencing co eval 18 o values for the two caves secondary controls on 18 o e g moisture source moisture transport non local rainfall temperature are circumvented and the resulting 18 o signal is controlled directly by the amount of rain falling between the two sites this is confirmed by comparison with rainfall data from the instrumental record which also allows a calibration of the 18 o proxy the calibrated 18 o record provides a quantitative history of rainfall in southwest china which demonstrates that rainfall was 8 higher than today during the holocene climatic optimum 6 ka but only 3 higher during the early holocene significant multi centennial variability also occurred with notable dry periods at 8 2 ka 4 8 4 1 ka 3 7 3 1 ka 1 4 1 0 ka and during the little ice age this holocene rainfall record provides a good target with which to test climate models the approach used here of combining stalagmite records from more than one location will also allow quantification of rainfall patterns for past times in other regions

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

sea surface temperatures of the western arabian sea during the last deglaciation 1 in this study we present a sea surface temperature sst record from the western arabian sea for the last 20 000 years we produced centennial scale d 18 o and mg ca sst time series of core niop929 with focus on the glacial interglacial transition the western arabian sea is influenced by the seasonal ne and sw monsoon wind systems lowest ssts occur during the sw monsoon season because of upwelling of cold water and highest ssts can be found in the low productivity intermonsoon season the mg ca based temperature record reflects the integrated sst of the sw and ne monsoon seasons the results show a glacial interglacial sst difference of 2c which is corroborated by findings from other arabian sea cores at 19 ka b p a yet undescribed warm event of several hundred years duration is found which is also reflected in the d 18 o record a second centennial scale high sst low d 18 o event is observed at 17 ka b p this event forms the onset of the stepwise yet persistent trend toward holocene temperatures highest mg ca derived ssts in the niop929 record occurred between 13 and 10 ka b p interglacial sst is 24c indicating influence of upwelling the onset of arabian sea warming occurs when the north atlantic is experiencing minimum temperatures the rapid temperature variations at 19 17 and 13 ka b p are difficult to explain with monsoon changes alone and are most likely also linked to regional hydrographic changes such as trade wind induced variations in warm water advection

high resolution holocene environmental changes in the thar desert northwestern india sediments from lunkaransar dry lake in northwestern india reveal regional water table and lake level fluctuations over decades to centuries during the holocene that are attributed to changes in the southwestern indian monsoon rains the lake levels were very shallow and fluctuated often in the early holocene and then rose abruptly around 6300 carbon 14 years before the present 14c yr b p the lake completely desiccated around 4800 14c yr b p the end of this 1500 year wet period coincided with a period of intense dune destabilization the major harrapan indus civilization began and flourished in this region 1000 years after desiccation of the lake during arid climate and was not synchronous with the lacustral phase

the phytoplankton bloom in the northwestern arabian sea during the southwest monsoon of 1979 the biological variability of the northwestern arabian sea during the 1979 southwest monsoon has been investigated by the synthesis of satellite ocean color remote sensing with analysis of in situ hydrographic and meteorological data sets and the results of wind driven modeling of upper ocean circulation the phytoplankton bloom in the northwestern arabian sea peaked during august september extended from the oman coast to about 65 e and lagged the development of open sea upwelling by at least 1 month in total the pigment distributions hydrographic data and model results all suggest that the bloom was driven by spatially distinct upward nutrient fluxes to the euphotic zone forced by the physical processes of coastal upwelling and offshore ekman pumping coastal upwelling was evident from may through september yielded the most extreme concentrations of phytoplankton biomass and along the arabian coast was limited to the continental shelf in the promotion of high concentrations of phytoplankton upward ekman pumping to the northwest of the somali jet axis stimulated the development of a broad open sea phytoplankton bloom oceanward of the oman shelf vertical mixing during the 1979 southwest monsoon was apparently not a primary cause of the regional scale phytoplankton bloom

seasonal variation of hydrographic and nutrient fields during the us jgofs arabian sea process study abstract between september 1994 and december 1995 the us jgofs arabian sea process experiment collected extensive high quality hydrographic data temperature salinity dissolved oxygen and nutrients during all seasons in the northern arabian sea an analysis of this unique data suite suggests the presence of many features that are described in the canonical literature but these new data provided the following insights 1 although the seasonal evolution of mixed layer depths was in general agreement with previous descriptions the deepest mixed layer depths in our data occurred during the late ne monsoon instead of the sw monsoon 2 the region exhibits considerable mesoscale variability resulting in extremely variable temperature salinity ts distributions in the upper 1000 db this mesoscale variability is readily observed in satellite imaging in the high resolution data taken by a companion onr funded project and in underway adcp data 3 the densest water reaching the sea surface during coastal upwelling appeared to have maximum offshore depths of 150 m and s close to the core value 25 for the saline arabian sea water asw but salinities in these upwelling waters were relatively low the densest water found at the sea surface during late ne monsoon conditions has s 24 8 and relatively high salinities suggesting that they are a source for the asw salinity maximum 4 persian gulf water pgw with a core of 26 6 forms a widespread salinity maximum despite the considerable extent of this feature persian gulf outflow water with a salinity 4 of 39 at its source can only be a minor contributor within the standard us jgofs sampling grid maximum salinities on this surface are 36 8 at stations near the gulf falling to values as low as 35 3 at the stations farthest removed from its influence even at our standard stations closest to the gulf n 1 and n 2 the high salinity low nutrient persian gulf water has only a modest direct effect on nutrient concentrations this pgw salinity maximum is associated with the suboxic portions of the arabian sea s oxygen minimum zone 5 the salinity maximum associated with red sea water rsw core 27 2 in the jgofs study region is clearly evident at the southermost sampling site at 10 n s 15 elsewhere this signal is weak or absent and salinity on the 27 2 surface tends to increase towards the persian gulf suggesting that the disappearance of this salinity maximum is due at least in part to the influence of the persian gulf outflow 6 inorganic nitrogen to phosphate ratios were lower frequently much lower than the standard redfield ratio of 15 1 16 1 by atoms at all times and all depths suggesting that inorganic nitrogen was more important than phosphate as a limiting nutrient for phytoplankton growth and that the effects of denitrification dominated the effects of nitrogen fixation 7 the water upwelling off the omani coast during the sw monsoon has inorganic nitrogen to silicate ratios that were higher 2 1 than the 1 1 ratio often assumed as the ratio of uptake during diatom growth 8 the temporal evolution of inorganic nitrogen to silicate ratios suggests major alteration by diatom uptake only during the late sw monsoon cruise tn050 in august september 1995 9 widespread moderate surface layer nutrient concentrations occurred during the late ne monsoon 10 a zone of high offshore nutrient concentrations was encountered during the sw monsoon but instead of being associated with offshore upwelling it may represent offshore advection from the coastal upwelling zone the influence of an eddy or both 11 although our data do not contradict previous suggestions that the volume of subtoxic water may be reduced the sw monsoon they suggest a weaker re oxygenation than indicated by some previous work similarly they do not confirm results suggesting that secondary nitrite maxima may be common in waters with oxygen concentrations 5 m

glacial to holocene fluctuations in hydrography and productivity along the southwestern continental margin of india oxygen isotope and sedimentological records of a sediment core from the southwestern continental margin of india are used to reconstruct the fluctuations in sea surface hydrography and productivity during the last deglaciation the delta o 18 records of globigerinoides ruber and globigerinoides sacculifer exhibit high amplitude oscillations during the early deglaciation and holocene significant variations in delta o 18 during the holocene and a high glacial interglacial amplitude in delta o 18 values delta delta o 18 similar to 2 1 o suggest large fluctuations in sea surface hydrography related to monsoonal precipitation on land our results suggest that although the last deglacial events are coherent in time with the regional and global climatic events fluctuations in sea surface salinity during holocene are unique to this region maximum monsoonal precipitation appears to have occurred after similar to9 8 ka bp unlike the records from the western arabian sea biological productivity was maximum between similar to 18 and 15 ka bp and substantially diminished between similar to 13 and 6 ka bp the increased strength in the winter monsoon during the glacial period could have enhanced convective mixing and nutrient injection leading to high primary production reduced surface productivity during the early holocene may be attributed to the complex dynamics of the circulation system and hydrological cycle along the southwest coast of india c 2001 elsevier science b v all rights reserved

carbonate dissolution in recent sediments of the eastern equatorial indian ocean preservation patterns and carbonate loss above the lysocline abstract multiple dissolution indices from 45 sediment samples show that the foraminiferal lysocline is near 3800 m in the eastern equatorial indian ocean close to the saturation horizon with respect to calcite in the water column below the lysocline the increase in foraminiferal fragmentation decrease in absolute abundance and progressive modification of planktic foraminiferal assemblages with depth is accompanied by an increasing rate of loss of carbonate from the sediments above the lysocline some dissolution must occur in order to produce the dramatic reduction in foraminiferal numbers up to 60 and the pattern of increased fragmentation with depth however the amount of carbonate actually lost from supralysoclinal sediments reaches at most 20 30 of the total at the depth of the lysocline the principal driving force behind supralysoclinal dissolution is most likely the oxidation of organic matter incorporated into the sediments dissolution above the lysocline has a greater apparent impact on relative preservation in the coarse 150 m fraction than it does on total carbonate loss because of redistribution of carbonate to the finer size fractions as fragments though the effects of dissolution on foraminiferal preservation are clearly visible at all depths the lysocline itself does appear to mark the local onset of large scale loss of dissolved carbonate from the sediments such an interpretation is broadly consistent with models regarding the saturation state of the overlying waters as the principal driving force behind the preservation or dissolution of recent carbonate sediments on the sea floor

strong coherence between solar variability and the monsoon in oman between 9 and 6 kyr ago variations in the amount of solar radiation reaching the earth are thought to influence climate but the extent of this influence on timescales of millennia to decades is unclear a number of climate records show correlations between solar cycles and climate1 but the absolute changes in solar intensity over the range of decades to millennia are small2 and the influence of solar flux on climate is not well established the formation of stalagmites in northern oman has recorded past northward shifts of the intertropical convergence zone3 whose northward migration stops near the southern shoreline of arabia in the present climate4 here we present a high resolution record of oxygen isotope variations for the period from 9 6 to 6 1 kyr before present in a th u dated stalagmite from oman the 18o record from the stalagmite which serves as a proxy for variations in the tropical circulation and monsoon rainfall allows us to make a direct comparison of the 18o record with the 14c record from tree rings5 which largely reflects changes in solar activity6 7 the excellent correlation between the two records suggests that one of the primary controls on centennial to decadal scale changes in tropical rainfall and monsoon intensity during this time are variations in solar radiation

sea surface temperature and productivity records for the past 240 kyr in the arabian sea abstract deep sea sediments of two cores from the western ty93 929 p and the southeastern md900963 arabian sea were used to study the variations of the indian monsoon during previous climatic cycles core ty93 929 p was located between the sw monsoon driven upwelling centres off somalia and oman which are characterized by large seasonal sea surface temperature sst and particle flux changes by contrast core md900963 was situated near the maldives platform an equatorial ocean site with a rather small sst seasonality less than 2 c for both cores we have reconstructed sst variations by means of the unsaturation ratio of c37 alkenones which is compared with the 18o records established on planktonic foraminifera in general the sst records follow the 18o variations with an sst maximum during oxygen isotope stage 5 5 the last interglacial at about 120 130 kyr and a broad sst minimum during isotope stage 4 and 3 3 approximately 40 50 kyr the sst difference between the holocene and the last glacial maximum lgm is of the order of 2 c in both cores the ssts during isotope stage 6 are distinctly higher by 1 2 c than the cold sst minima during the last glacial cycle lgm and stage 3 to reconstruct qualitatively the past productivity variations for the two cores we used the concentrations and fluxes of alkenones and organic carbon together with a productivity index based on coccolith species florisphaera profunda relative abundance within each core there is a general agreement between the different palaeoproductivity proxies in the southeastern arabian sea core md900963 glacial stages correspond to relatively high productivity whereas warm interstadials coincide with low productivity all time series of productivity proxies are dominated by a cyclicity of about 21 23 kyr which corresponds to the insolation precessional cycle a hypothesis could be that the ne monsoon winds were stronger during the glacial stages which induced deepening of the surface mixed layer and injection of nutrients to the euphotic zone by contrast the records are more complicated in the upwelling region of the western arabian sea core ty93 929 p this is partly due to large changes in the sedimentation rates which were higher during specific periods isotope stages 6 5 4 5 2 3 and 2 unlike core md900963 no simple relationship emerges from the comparison between the 18o stratigraphy and productivity records the greater complexity observed for core ty93 929 p could be the result of the superimposition of different patterns of productivity fluctuations for the two monsoon seasons the sw monsoon being enhanced during interglacial periods whereas the ne monsoon was increased during glacial intervals a similar line of reasoning also could help explain the sst records by the superimposition of variations of three components global atmospheric temperature and sw and ne monsoon dynamics

temporal variability in the northern arabian sea oxygen minimum zone omz during the last 225 000 years the northern arabian sea is one of the few regions in the open ocean where thermocline water is severely depleted in oxygen the intensity of this oxygen minimum zone omz has been reconstructed over the past 225 000 years using proxies for surface water productivity water column denitrification winter mixing and the aragonite compensation depth acd changes in omz intensity occurred on orbital and suborbital timescales lowest o2 levels correlate with productivity maxima and shallow winter mixing precession related productivity maxima lag early summer insolation maxima by 6 kyr which we attribute to a prolonged summer monsoon season related to higher insolation at the end of the summer periods with a weakened or even non existent omz are characterized by low productivity conditions and deep winter mixing attributed to strong and cold winter monsoonal winds the timing of deep winter mixing events corresponds with that of periods of climatic cooling in the north atlantic region

quaternary history of calcium carbonate fluctuations in the western equatorial indian ocean somali basin abstract a study of the quaternary history of calcium carbonate fluctuations in the equatorial indian ocean based on the swedish deep sea expedition core 154 demonstrates that the calcite compensation depth ccd was shallower during interglacial periods than during glacials higher percentages of calcium carbonate lower percentages of dissolution resistant planktonic foraminifera and lower values of the berger dissolution index suggesting better calcium carbonate preservation are recorded during glacial periods and or at glacial interglacial transitions in contrast interglacial periods are marked by stronger calcium carbonate dissolution the data indicate that dissolution is the main controlling factor of calcium carbonate in the western equatorial indian ocean higher dissolution during interglacial periods and enriched 13 c are due to higher noncarbonate productivity and enhanced antarctic bottom water aabw ventilation in the equatorial indian ocean

concentrations and burial fluxes of organic and inorganic carbon on the eastern margins of the arabian sea abstract eleven sediment cores were analysed from the continental margins of the eastern arabian sea 22 n to 10 n for organic carbon c org nitrogen n and caco 3 contents similar variations are observed in both lateral and the vertical org n and caco 3 ranging from 1 6 0 10 0 82 and 10 81 respectively the c n ratios varying from 6 15 averaging 9 3 indicate that c org is mostly of marine origin the burial fluxes bf of c org and caco 3 are in the range of 0 8 21 and 39 194 g m 2 a 1 respectively the upper limits of burial efficiency be for caco 3 compared to its rain rate of 25 g m 2 a 1 in sediment trap at a depth of 2500 m from a nearby region ranges from 39 to 780 be values greater than 100 in the northern 15 n could be most likely due to redeposition of material from shelf and slope regions as well as influx of detrital carbonates from coastal areas the inverse correlation observed in c org and caco 3 distribution is indicative of post depositional effects due to sulphate reduction associated processes this can lead to dissolution of caco 3 and a better preservation of c org due to faster deposition rate and higher detrital clay content the bf and paleoproductivity calculated using the transfer function of sarnthein et al miner soc spec publ 64 1992 411 show increasing trend between 10 and 2 ka with a significant periodicity of 3000 a corresponding to that observed for monsoon induced productivity

the oman upwelling zone during 1993 1994 and 1995 abstract satellite derived sea surface temperature topex poseidon t p sea level anomalies slas model wind data and hydrographic data are used to characterize the upwelling along the oman coast during the us joint global ocean flux study us jgofs arabian sea process study asps in 1995 as well as to look at interannual variability in the upwelling over the period 1993 1995 empirical orthogonal function eof analysis of the satellite derived sea surface temperature sst at the locations of the us jgofs standard stations shows the first mode which represents a biannual variability contributes 67 of the total variance in addition the sst shows the upwelling front moving offshore with the development of southwest sw monsoon in early june 1995 reaching a maximum distance of approximately 120 km by late august 1995 finally sst shows the persistence of cold upwelling waters for nearly a month after the end of the sw monsoon within the bays along the oman coast topex poseidon slas indicate that with the onset of the sw monsoon a 30 cm drop in steric height is observed along the oman coast associated the presence of the cool upwelled waters this drop in steric height sets up a horizontal pressure gradient and results in a compensating along shore northeastward flowing geostrophic current east arabian current eac during the sw monsoon similarly the altimeter data slow an offshore decrease in steric height during the northeast ne monsoon indicating a seasonal reversal in direction of the eac with flow to the southwest subsurface temperature data indicate that the actual uplifting of isotherms associated with the upwelling can be found to a distance of approximately 260 km from the shore and to a depth of 150 200 m using along track altimetry data we estimate that for a region 260 km in offshore distance and 600 km alongshore 2 2 10 6 1 4 10 6 and 0 55 10 6 m 3 s 1 were upwelled through the 100 m level with upwelling velocities o 2 0 10 5 m s 1 during the sw monsoons of 1993 1994 and 1995 respectively the reduced upwelling in the summer of 1995 is attributed to a reduction in wind stress curl along the arabian coast when compared to 1993 and 1994

global monsoons in the mid holocene and oceanic feedback the response of the six major summer monsoon systems the north american monsoon the northern africa monsoon the asia monsoon the northern australasian monsoon the south america monsoon and the southern africa monsoon to mid holocene orbital forcing has been investigated using a coupled ocean atmosphere general circulation model foam with the focus on the distinct roles of the direct insolation forcing and oceanic feedback the simulation result is also found to compare well with the ncar csm the direct effects of the change in insolation produce an enhancement of the northern hemisphere monsoons and a reduction of the southern hemisphere monsoons ocean feedbacks produce a further enhancement of the northern africa monsoon and the north american monsoon however ocean feedbacks appear to weaken the asia monsoon although the overall effect direct insolation forcing plus ocean feedback remains a strengthened monsoon the impact of ocean feedbacks on the south american and southern african monsoons is relatively small and therefore these regions especially the south america experienced a reduced monsoon regime compared to present however there is a strong ocean feedback on the northern australian monsoon that negates the direct effects of orbital changes and results in a strengthening of austral summer monsoon precipitation in this region a new synthesis is made for mid holocene paleoenvironmental records and is compared with the model simulations overall model simulations produce changes in regional climates that are generally consistent with paleoenvironmental observations

coupling between sw monsoon related surface and deep ocean processes as discerned from continuous particle flux measurements and correlated satellite data particle flux data obtained by time series sediment traps deployed at water depths of approximately 3000 m in the western central and eastern arabian sea since 1986 were compared with wind speeds derived from measurements made by microwave radiometer flying on polar orbiting satellites and sea surface temperatures ssts provided by the physical oceanography distributed active archive center at jet propulsion laboratory this comparison has allowed us to trace the link between the oceanographic and biological processes related to the development of the sw monsoon with the pattern and interannual variability of particle fluxes to the interior of the arabian sea we could recognize the well known upwelling systems along the coasts of somalia and oman as well as open ocean upwelling at the beginning of the sw monsoon both open ocean upwelling and coastal upwelling off oman cause a cooling of surface waters at our western and central arabian sea stations when ssts fall below their long term average an increase in fluxes which are dominated by coccolithophorid derived carbonates occurs the timing of this increase is determined by the rate of surface water cooling further intensification of upwelling as the sw monsoon progresses causes additional increases in biogenic opal fluxes denoting diatom blooms in the overlying waters the total fluxes during this period are the highest measured in the open arabian sea at the central arabian sea location the fluxes are only randomly affected by these blooms the particle flux in the eastern arabian sea is as high as in the central arabian sea but is influenced by a weaker upwelling system along the indian coast the observed interannual variability in the pattern of particle fluxes during the sw monsoons is most pronounced in the western arabian sea this is controlled by the intensity of the upwelling systems on the one hand and the transport of cold nutrient poor south equatorial water into the oman region on the other the latter effect which is strongest during the sw monsoon with highest recorded wind speeds reduces the influence of upwelling and the related particle fluxes at the western arabian sea station where highest fluxes occur during sw monsoons with moderate wind speeds thus coastal and open ocean upwelling are most effective in transferring biogenic matter to the deep sea during the sw monsoons of intermediate strength

the influence of the sw monsoon on the deep sea organic carbon cycle in the holocene abstract results from long term sediment trap experiments carried out since 1986 in the western central and eastern arabian sea are combined with satellite derived wind fields and paleoceanographic information to link the intensity of the sw monsoon to organic carbon fluxes and its preservation in sediments the sw monsoon is characterized by the low level jet findlater jet that crosses the arabian sea almost parallel to the arabian coast the intensity of the findlater jet mainly controls the velocities of upwelling that occurs to the northeast of the jet since up welling in turn mainly governs the organic carbon fluxes in the western arabian sea variation in the strength of the findlater jet is the dominant factor determining the organic carbon fluxes on seasonal time scales changes in the subsurface nutrient concentrations due to variations in the surface ocean current systems seem to be another factor influencing the organic carbon fluxes mostly on interannual time scales the translation of sedimentary organic carbon burial rates into organic carbon fluxes according to jahnke 1996 global biogeochemical cycles 10 71 88 allows us to extend our reflections also to a millennium time scale this indicates that changes in the sw monsoon intensity as observed during the last decade could almost account for the range of organic carbon fluxes deciphered from the holocene record

a first look at past sea surface temperatures in the equatorial indian ocean from mg ca in foraminifera 1 sea surface temperature sst for the central equatorial indian ocean has been reconstructed over the last 137 kyr from mg ca of the planktonic foraminiferal species globigerinoides ruber according to our record the equatorial indian ocean sst was 2 1 c colder during the last glacial maximum as compared to present times the data further shows that the surface equatorial indian ocean was comparatively warmer during isotopic stage 5e than at present 29 9 vs 28 5 c comparison of the equatorial indian ocean sst with the antarctic d and greenland 18o records shows that the major high latitude cooling warming events are also present in the equatorial indian ocean sst variation record similarity between the equatorial indian ocean sst and the equatorial pacific sst suggests the possibility of a common mechanism controlling the ssts in both the equatorial indian ocean and the pacific ocean

preservation of elemental and isotopic source identification of sedimentary organic matter the amount and type of organic matter in the sediments of lakes and oceans contribute to their paleoenvironmental and paleoclimatological records only a small fraction of the initial aquatic organic matter survives destruction and alteration during sinking and sedimentation selective degradation modifies the character of the surviving small fraction of organic matter which becomes incorporated in bottom sediments organic matter alterations can continue to sub bottom depths of hundreds of meters corresponding to millions of years source and paleoenvironmental information nonetheless remains preserved in the molecular elemental and isotopic compositions of organic matter c n and 13c values of total organic matter in particular appear to retain paleoenvironmental information for multi myr time periods

biogenic structures in modern slope to deep sea sediments in the sulu sea basin philippines abstract slowly accumulated slope and rise sediments 5 20 cm 1000 yr are totally bioturbated as compared to only 10 30 in rapidly deposited abyssal plain sediments 100 200 cm 1000 yr in contrast to a decrease in degree of bioturbation biogenic trace diversity increases with water depth all ichnocoenoses are clearly influenced by the low oxygen content of the bottom water caused by minimal circulation and restricted water exchange oxygen deficiency and relatively high sedimentation rates have created nutrient rich sediments thus there is no need for optimal fractionation into individual ecological niches and behavioral programs are not highly developed 1 in slope and rise sediments animal traces are associated with biodeformational structures 2 in slope to abyssal plain sediments trace assemblages are dominated by burrows with open tubes for circulation of respiration water 3 in abyssal plain sediments small diameter biogenic traces common in turbidite sequences graphoglyptids e g paleodictyon are absent this may be due to rapid sedimentation leading to inefficiency of graphoglyptid behavior where graphoglyptids are lacking ichnocoenoses are dominated by forms like phycosiphon in slope and rise sediments graphoglyptids may have been destroyed by deeper burrowing organisms

a high resolution record of holocene rainfall variations from the western chinese loess plateau antiphase behaviour of the african indian and east asian summer monsoons tropical monsoons are key mechanisms for transfer of heat and moisture to higher latitudes here we present a high resolution terrestrial proxy summer monsoon record for the southeast asian monsoon from a rapidly accumulating holocene loess soil sequence in the western chinese loess plateau we use magnetic and clastic grain size proxies to make quantitative estimates of holocene rainfall and identify variations in winter monsoon intensity our record reveals cyclical millennial and multimillennial rainfall changes as with the northwest african southwest asian monsoon records a short arid interval at 12 5 to 11 5 ka bp the younger dryas and subsequent summer monsoon intensification are recorded however at 6 ka bp the southeast asian summer monsoon weakened when the northwest african southwest asian monsoons strengthened and then from 5 ka bp intensified when northwest africa southwest asia became dry these antiphase monsoonal relationships may reflect competition between sea surface temperature changes and solar forcing the intensity of the southeast asian winter monsoon intensified from 9 ka bp onwards varying in its phase relationships with summer monsoon intensity after 2 25 ka bp extreme climatic instability is indicated by both climate proxies

variations in tropical convection as an amplifier of global climate change at the millennial scale the global expression of millennial scale climatic change during the glacial period and the persistence of this signal in holocene records point to atmospheric teleconnections as the mechanism propagating rapid climate variations we suggest rearrangements in the tropical convection system globally affected the concentration and location of atmospheric water vapour and modulated terrestrial and marine emissions of ch4 and n2o providing a tropical mechanism of amplifying and perpetuating millennial scale climate changes a multi proxy reconstruction reflecting various aspects of the intensity of the arabian sea summer monsoon shows strong millennial scale variability over the past 90 kyr in which low intensity is associated with a southern shift of the intertropical convergence zone itcz and an eastward shift in the equatorial convergence zone the monsoon reconstruction which is based on new data from a somali margin sediment core is supported by previously reported tropical paleoclimatic records and suggests that global scale millennial climatic variability is in part driven by modulations in the tropical hydrological cycle and tropical emissions of the greenhouse gases ch4 and n2o

high resolution characterization of the asian monsoon between 146 000 and 99 000 years b p from dongge cave china and global correlation of events surrounding termination ii abstract speleothem samples from hulu eastern china 32 30 n 119 10 e and dongge southern china 25 17 n 108 5 e caves provide a nearly continuous record of the asian monsoon over the last 160 ka wang y j cheng h edwards r l an z s wu j y shen c c dorale j a 2001 a high resolution absolute dated late pleistocene monsoon record from hulu cave china science 294 2345 2348 yuan d cheng h edwards r l dykoski c a kelly m j zhang m qing j lin y wang y wu j dorale j a an z cai y 2004 timing duration and transitions of the last interglacial asian monsoon science 304 575 578 we have obtained higher resolution data in the interval between 99 and 146 ka b p providing a detailed account of 18o variations over most of mis 5 and the latter portion of mis 6 precise 230th dating has replicated the chronology of the samples within error the higher resolution data set confirms the timing of asian monsoon termination ii the midpoint of the negative shift in 18o marking the onset of the last interglacial asian monsoon placing it at 129 0 0 9 ka b p the bulk of this transition 1 7 took place within approximately 70 years with the total range of the transition being 3 the most abrupt portion of the shift in 18o values 1 1 marking the end of the last interglacial asian monsoon occurred in 120 years the midpoint of which is 120 7 1 0 ka b p the dongge cave monsoon 18o record over late mis 6 exhibits a series of sub orbital millennial scale climate shifts that average 1 3 in magnitude and occur on average every 1 8 ky abrupt shifts in 18o of up to 1 also occurred throughout the last interglacial asian monsoon with periods at multi decadal to centennial timescales similar to the amplitude and periodicities of events found by dykoski et al dykoski c a edwards r l cheng h yuan d cai y zhang m lin y an z revenaugh j 2005 a high resolution absolute dated holocene and deglacial asian monsoon record from dongge cave china earth and planetary science letters 233 71 86 during the holocene in the dongge record these shifts cover more than 1 2 of the amplitude of millennial scale and multi centennial scale interstadial events during the last glacial period wang y j cheng h edwards r l an z s wu j y shen c c dorale j a 2001 a high resolution absolute dated late pleistocene monsoon record from hulu cave china science 294 2345 2348 and millennial scale and multi centennial scale interstadial events during the penultimate glacial period in china this study abrupt decadal to millennial scale climate events therefore appear to be a general feature of both glacial and interglacial climate we demonstrate that monsoon intensity correlates well with atmospheric ch4 concentrations over the transition into the bolling allerod the bolling allerod and the younger dryas in addition we correlate an abrupt jump in ch4 concentration with asian monsoon termination ii on the basis of this correlation we conclude that the rise in atmospheric co2 antarctic warming and the gradual portion of the rise in ch4 around termination ii occur within our weak monsoon interval wmi an extended interval of heavy 18o between 135 5 1 0 and 129 0 1 0 ka b p prior to asian monsoon termination ii and northern hemisphere warming antarctic warming over the millennia immediately preceding abrupt northern warming may result from the bipolar seesaw mechanism as such warming albeit to a smaller extent also preceded asian monsoon termination i the bipolar seesaw mechanism may play a critical role in glacial terminations

interannual variability in phytoplankton blooms observed in the northwestern arabian sea during the southwest monsoon interannual changes in the strength and seasonal evolution of the 1979 through 1982 surface level southwest monsoon winds have been related to variations in the summer phytoplankton bloom of the northwestern arabian sea by synthesis of satellite ocean color remote sensing with analysis of in situ hydrographic and meteorological data sets the 1979 1981 southwest monsoon phytoplankton blooms in the northwest arabian sea peaked during august september extended from the omani coast to about 65 e and appeared to lag the development of open sea upwelling by at least 1 month in all 3 years the bloom was driven by spatially distinct upward nutrient fluxes to the euphotic zone forced by the physical processes of coastal upwelling and offshore ekman pumping coastal upwelling was evident from may through september yielded the most extreme concentrations of phytoplankton biomass and along the omani coast was limited in its impact on upper ocean biological variability to the continental shelf ekman pumping stimulated the development of a broad open ocean component of the southwest monsoon phytoplankton bloom oceanward of the omani shelf phytoplankton biomass on the omani continental shelf was increased during both the early and late phases of the 1980 southwest monsoon due to stronger coastal upwelling under the most intense southwesterly winds of the four summers investigated diminished coastal upwelling during the early phase of the weak 1982 southwest monsoon resulted in a coastal bloom that reached a mean phytoplankton pigment concentration that was 28 of that seen in 1980 the lack of a strong regional northwestern arabian sea bloom in late summer 1982 is attributed to the development of persistent shallow temperature stratification that rendered ekman pumping less effective in driving upward nutrient fluxes

a synthesis of abrupt changes in the asian summer monsoon since the last deglaciation we have compiled 36 previously published palaeoclimate records to determine the timing and spatial pattern of century scale abrupt changes in asian monsoon precipitation since the last deglaciation we identify abrupt events from 1 the interpretations of the authors of these records and 2 the more objective moving t test calculation our results indicate that abrupt climatic changes occurred at 11 5 cal ka 4 5 5 0 cal ka and ad 1300 at the start of the holocene 11 5 cal ka asian monsoon precipitation increased dramatically this climatic change is synchronous with an abrupt warming in the north atlantic during the middle holocene there was a time of preferred and widespread weakening in monsoon strength 4 5 5 0 cal ka this result contradicts previous notions of either a gradual trend towards drier conditions or a series of abrupt events that occurred in an unorganized fashion across space and time the middle holocene abrupt event could have been synchronous with an abrupt cooling event in the north atlantic as well as a warming and intensie cation of internannual variability in the tropical pacie c in contrast to previous periods precipitation changes at ad 1300 have a heterogeneous spatial pattern we e nd no conclusive evidence for a change in the asian monsoon at 8 2 cal ka as suggested by several previous studies more high resolution data may be needed to observe this short lived event overall our results attest to the potential for rapid and major shifts in asian monsoon precipitation that may be triggered by variations in other components of the climatic system

abrupt changes in the asian southwest monsoon during the holocene and their links to the north atlantic ocean during the last ice age the indian ocean southwest monsoon exhibited abrupt changes that were closely correlated with millennial scale climate events in the north atlantic region1 2 3 suggesting a mechanistic link in the holocene epoch which had a more stable climate the amplitude of abrupt changes in north atlantic climate was much smaller and it has been unclear whether these changes are related to monsoon variability here we present a continuous record of centennial scale monsoon variability throughout the holocene from rapidly accumulating and minimally bioturbated sediments in the anoxic arabian sea our monsoon proxy record reveals several intervals of weak summer monsoon that coincide with cold periods documented in the north atlantic region4 including the most recent climate changes from the medieval warm period to the little ice age and then to the present we therefore suggest that the link between north atlantic climate and the asian monsoon is a persistent aspect of global climate

changes in surface productivity and subsurface denitrification during the holocene a multiproxy study from the eastern arabian sea spatial and temporal variations in the intensity of subsurface denitrification in the water column of the eastem arabian sea have been investigated using chemical and isotopic proxies the data show a steady increase in the denitrification intensity from 10 ka to 2 ka bp probably caused by changes in surface productivity fuelled by strengthening of upwelling monsoonal intensity in addition changes in redox conditions and detrital material input are assessed using abundances of a suite of major and trace elements the temporal variations in some of the monsoonal proxies are characterized by periodicities of 1400 and 700 years similar to those reported in the south asian chinese monsoon and high latitude climate north atlantic region

variations of oxygen minimum and primary productivity recorded in sediments of the arabian sea abstract two deep sea sediment cores from the northeastern and the southeastern arabian sea were studied in order to reconstruct the palaeoenvironments of the past glacial cycles core 136kl was recovered from the high productivity area off pakistan within the modern oxygen minimum zone omz by contrast modern primary productivity at the site of md900963 close to maldives is moderate and bottom waters are today well oxygenated for both cores we reconstructed the changes in palaeoproductivity using a set of biomarkers alkenones dinosterol and brassicasterol the main result is that primary productivity is enhanced during glacial stages and lowered during interstadials the proxies associated with productivity show a 23 kyr cyclicity corresponding to the precession related insolation cycle palaeoredox conditions were studied in both cores using a new organic geochemical parameter c35 c31 n alkane ratio developed by analysing surface sediments from a transect across the omz off pakistan the value of this ratio in core 136kl shows many variations during the last 65 kyr indicating that the omz was not stable during this time it disappeared completely during heinrich and the younger dryas events pointing to a connection between global oceanic circulation and the stability of the omz the c35 c31 ratio determined in sediments of core md900963 shows that bottom waters remained rather well oxygenated over the last 330 kyr which is confirmed by comparison with authigenic metal concentrations in the same sediments a zonally averaged circulation biogeochemical ocean model was used to explore how the intermediate indian ocean responds to a freshwater flux anomaly at the surface of the north atlantic as suggested by the geochemical time series both the abundance of southern ocean water and the oxygen concentration are significantly increased in response to this freshwater perturbation

did the indo asian summer monsoon decrease during the holocene following insolation a few studies from the western arabian sea indicate that the indian summer or southwest monsoon ism after attaining its maximum intensity at ca 9 ka declined during the holocene as did insolation in contrast earlier and later observations from both the eastern and the western arabian sea do not support this inference analysis of multiple proxies of productivity in a new sediment core from the western arabian sea fails to confirm the earlier single proxy e g abundance of globigerina bulloides based inference of the holocene weakening of ism following insolation the reason for the observed decreasing trend in foraminiferal abundance the basis for the earlier inference could be the favouring of silicate rather than carbonate productivity by the increased ism wind strength although ism exhibits several multi millennial scale fluctuations there is no evidence from several multi proxy data to conclude that it declined during the holocene this is consistent with the phase lag analysis of longer time series of monsoon proxies thus on sub milankovitch timescales ism did not follow insolation highlighting the importance of internal feedbacks a comparison with east asian summer monsoon easm records suggests that both ism and easm varied in unison implying common forcing factors on such longer timescales copyright 2010 john wiley sons ltd

a 350 000 year summer monsoon multi proxy stack from the owen ridge northern arabian sea five summer monsoon proxies from the northern arabian sea are combined using stacking and principal components analysis pca to create two very similar multi proxy records of summer monsoon variability the five individual proxies all respond to monsoon variability but are largely independent in terms of the processes that complicate their interpretation as summer monsoon indicators e g preservation dissolution diagenesis sediment reworking as such stacking and pca average out non monsoon variance yielding a more pure monsoon signal these stacked and pca records hereafter summer monsoon stack and summer monsoon factor allow evaluation of relative monsoon strength through time as well as the relative concentration of variance within orbital bands these two parameters are less reliable when estimated from individual proxy records in fact the summer monsoon factor smf accounts for only 33 of the total variance in the five records suggesting that relative amplitude variations in each individual proxy time series are influenced by non monsoon processes the summer monsoon stack sms and smf are spectrally very similar dominated by variance in the 41 k y obliquity and 23 k y precession bands there is very little variance at the 100 k y eccentricity band associated with large scale changes in global ice volume indeed equally strong monsoons occur in both glacial and interglacial intervals within the 23 k y precession cycle monsoon maxima fall at 121 relative to precession minima june 21 perihelion maximum northern hemisphere nh summer insolation this phase falls midway between 18o minima 78 and december 21 perihelion 180 indicating that two mechanisms exert equal influence in determining the timing of strong summer monsoons within the precession band 1 sensible heating of the asian plateau which is maximized at times of ice volume minima 78 and 2 latent heat export from the southern subtropical indian ocean which is maximized at times of december 21 perihelion 180 the seasonal cycle at december 21 perihelion is characterized by warm southern hemisphere sh summers followed by cold sh winters a combination that preconditions the ocean to export latent heat during the boreal summer monsoon season summer monsoon winds transport this latent heat into asia where it is released during precipitation enhancing the asian monsoon low within the 41 k y obliquity cycle monsoon maxima are in phase with obliquity maxima this indicates that two mechanisms quite similar to those in the precession band influence the timing of strong summer monsoons in the obliquity band 1 sensible heating of the asian plateau but with no ice volume delay and 2 latent heat export from the southern subtropical indian ocean which is maximized at times of obliquity maxima again the seasonal cycle at obliquity maximum is characterized by warm sh summers followed by cold sh winters ideal for maximizing latent heat export during the boreal summer monsoon

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

retrospective dry bulk density estimates from southeast indian ocean sediments comparison of water loss and chloride ion methods abstract knowledge of absolute accumulation rates permits quantitative comparison between and within sediment components from cores of differing age and lithologic character dry bulk density is an essential parameter in the calculation of absolute accumulation rates dry bulk density measurements require a wet volume term and are best made when a core is first recovered such measurements were not routinely made on eltanin cores from the southeast indian ocean in an effort to recover this information we have estimated the dry bulk density of sixty samples from five eltanin cores using a water loss method and a chloride ion method which is independent of the state of desiccation of the cores based on the consistency of the results using these two independent methods we feel confident in our estimation of dry bulk density comparison of dry bulk density and caco 3 allowed us to develop the following non linear regression equation for estimating the dry bulk density based on caco 3 a more easily and accurately measured property 3 104x10 3 caco 3 2 2 176x10 3 caco 3 0 430 this equation can be used to estimate dry bulk density to within 0 097 g cm 3 thus providing the information needed to reliably calculate absolute accumulation rates our indian ocean dry bulk density equations are different from those developed by similar techniques for the pacific and atlantic oceans indicating that different lithologies necessitate the development of regional equations

a 5000 yr record of climate change in varved sediments from the oxygen minimum zone off pakistan northeastern arabian sea the upper holocene marine section from a kasten core taken from the oxygen minimum zone off karachi pakistan at water depth 700 m contains continuously laminated sediments with a sedimentation rate of 1 2 mm yr and a unique record of monsoonal climatic variability covering the past 5000 years our chronostratigraphy is based on varve counts verified by conventional and ams 14 c dating individual hemipelagic varve couplets are about 0 8 1 5 mm thick with light colored terrigenous laminae a deposited mainly during the winter monsoon alternating with dark colored laminae b rich in marine organic matter coccoliths and fish debris that reflect deposition during the high productivity season of the late summer monsoon august october precipitation and river runoff appear to control varve thickness and turbidite frequency we infer that precipitation decreased in the river watershed indicated by thinning varves after 3500 4000 yr b p this is about the time of increasing aridification in the near east and middle east as documented by decreasing nile river runoff data and lake level lowstands between turkey and northwestern india this precipitation pattern continued until today with precipitation minima about 2200 1900 yr b p 1000 yr b p and in the late middle ages 700 400 yr b p and precipitation maxima in the intervening periods as documented by spectral analysis the thickness of varve couplets responds to the average length of a 250 yr cycle a 125 yr cycle the gleissberg cycle of solar activity 95 yr and a 56 yr cycle of unknown origin higher frequency cycles are also present at 45 39 29 31 and 14 yr the sedimentary gray value also shows strong variability in the 55 yr band plus a 31 yr cycle because high frequency cyclicity in the enso band ca 3 5 and 5 yr is only weakly expressed our data do not support a straightforward interaction of the pacific enso with the monsoon driven climate system of the arabian sea

the southwest indian monsoon over the last 18 000 years previously published results suggest that the strength of the sw indian monsoon can vary significantly on century to millenium time scales an observation that has important implications for assessments of future climate and hydrologic change over densely populated portions of asia we present new well dated multi proxy records of past monsoon variation from three separate arabian sea sediment cores that span the last glacial maximum to late holocene to a large extent these records confirm earlier published suggestions that the monsoon strengthened in a series of abrupt events over the last deglaciation however our data provide a somewhat refined picture of when these events took place and suggest the primacy of two abrupt increases in monsoon intensity one between 13 and 12 5 ka and the other between 10 and 9 5 ka this conclusion is supported by the comparisons between our new marine data and published paleoclimatic records throughout the african asian monsoon region the comparison of data sets further supports the assertion that maximum monsoon intensity lagged peak insolation forcing by about 3000 years and extended from about 9 5 to 5 5 ka the episodes of rapid monsoon intensification coincided with major shifts in north atlantic european surface temperatures and ice sheet extent this coincidence coupled with new climate model experiments suggests that the large land sea thermal gradient needed to drive strong monsoons developed only after glacial conditions upstream of and on the tibetan plateau receded cold north atlantic sea surface temperatures european ice sheets and extensive asian snow cover it is likely that abrupt changes in seasonal soil hydrology were as important to past monsoon forcing as were abrupt snow related changes in regional albedo our analysis suggests that the monsoon responded more linearly to insolation forcing after the disappearance of glacial boundary conditions decreasing gradually after about 6 ka our data also support the possibility that significant century scale decreases in monsoon intensity took place during the early to mid holocene period of enhanced monsoon strength further highlighting the need to understand paleomonsoon dynamics before accurate assessments of future monsoon strength can be made

a high resolution record of late quaternary upwelling along the oman margin arabian sea based on planktonic foraminifera planktonic foraminiferal abundances fluxes test sizes and coiling properties are influenced in various ways by the southwest monsoon winds and associated upwelling in the western arabian sea to determine the short term changes in the southwest monsoon we have carried out a high resolution time series analysis of three upwelling indices total flux of planktonic foraminiferal tests and flux and relative abundance of the planktonic foraminiferal species globigerina bulloides from ocean drilling program odp site 723a oman margin western arabian sea spanning the last 19 kyr in addition we have determined the relationships between upwelling intensity and the relative abundance fluxes and shell concentrations of various planktonic foraminiferal species upwelling indices suggest that from 19 to 16 ka 22 to 18 2 cal kyr b p the sw monsoon was relatively strong compared to the period 15 8 to 12 5 ka 17 8 to 13 8 cal kyr b p the intensification of the sw monsoon took place at 12 ka 13 1 cal kyr b p and reached a peak between 10 and 5 ka 10 6 and 4 8 cal kyr b p the high resolution data further demonstrate that the sw monsoon has started weakening from 5 ka 4 8 cal kyr b p and the weakest phase was in place at 3 5 ka 3 cal kyr b p which coincides with evidence of an arid climate in western tibet fluxes and shell concentrations of many of the planktonic foraminiferal species increased between 12 and 5 ka in response to the intensification of the sw monsoon winds after the last glacial period globigerina bulloides shows a fivefold to tenfold increase in flux during this period of intense upwelling the other species whose fluxes are influenced by this upwelling change are in order from strongest to weakest response globigerinita glutinata globigerinoides ruber neogloboquadrina dutertrei globigerinella aequilateralis globigerina falconensis and globigerinoides sacculifer the relative abundances of g bulloides and g ruber increased during intense upwelling whereas the relative abundances of g glutinata n dutertrei g falconensis and g sacculifer did not increase during this period which might be due to differences in the productivity of various species in relation to upwelling change therefore the fluxes and shell concentrations provide better and more reliable information about the changes in the monsoon system in the arabian sea than relative abundance data

holocene moisture evolution in arid central asia and its out of phase relationship with asian monsoon history we synthesize palaeoclimate records from the mid latitude arid asian region dominated today by the westerlies arid central asia aca to evaluate spatial and temporal patterns of moisture changes during the holocene sediment records from i i takes with reliable chronologies and robust proxies were selected to reconstruct moisture histories based on a five class ordinal wetness index with assigned scores from the driest to wettest periods at individual sites for 200 year time slices the proxies used in these records include pollen and diatom assemblages sediment lithology lake levels and geochemistry mainly isotope data the results of our synthesis show that aca as a whole experienced synchronous and coherent moisture changes during the holocene namely a dry early holocene a wetter less dry early to mid holocene and a moderately wet late holocene during the early holocene most of the lakes experienced very low water levels and even dried out before ca 8 ka 1 ka 1000cal a bp hence the effective moisture history in aca is out of phase with that in monsoonal asia as documented by numerous palaeoclimate records in monsoonal asia a strong summer monsoon and humid climate characterized the early holocene and a weakened summer monsoon and drier climate prevailed during the late holocene which were mainly controlled by changes in low latitude summer insolation in contrast we propose that the pattern of holocene effective moisture evolution in the westerly dominated aca was mainly determined by north atlantic sea surface temperatures ssts and high latitude air temperatures that affect the availability amount and transport of water vapor also topography of the tibetan plateau and adjacent asian highlands could have contributed to the intensification of dry climate in aca during the early holocene as a result of strengthening the subsidence of dry air masses associated with stronger uplift motion on the plateau by intense heating under a stronger summer insolation summer insolation might have played a key role in directly controlling moisture conditions in aca but only after the northern hemisphere ice sheets had disappeared in the mid and late holocene c 2007 elsevier ltd all rights reserved

palaeo climate reconstruction from stable isotope variations in speleothems a review abstract speleothems are now regarded as valuable archives of climatic conditions on the continents offering a number of advantages relative to other continental climate proxy recorders such as lake sediments and peat cores they are ideal materials for precise u series dating yielding ages in calendar years thereby circumventing the radiocarbon calibration problems associated with most other continental records stable isotope studies in speleothems have shifted away from attempting to provide palaeo temperature reconstructions to the attainable goal of providing precise estimates for the timing and duration of major o isotope defined climatic events characterised by high signal to noise ratios e g glacial interglacial transitions dansgaard oeschger oscillations the 8200 year event unlike the marine records speleothem data sets are not tuned and their independent chronology offers opportunities to critically assess leads and lags in the climate system that in turn can provide important insights into forcing and feedback mechanisms improved procedures for the extraction and measurement of stable isotope ratios in fluid inclusions trapped in speleothems are likely to provide in the near future a much enhanced basis for the quantitative interpretation of o isotope ratios in speleothem calcite the latter developments open up once again the tantalising prospect of palaeo temperature estimates but more importantly perhaps provide a direct test for a new generation of general circulation models whose hydrological cycles will incorporate the water isotopes the literature is reviewed briefly to provide for the reader a sense of the current state of the art and to provide some pointers for future research directions

high resolution holocene monsoon record from the eastern arabian sea through stable oxygen and carbon analyses of rapidly accumulating sediment cores from the eastern arabian sea we show that the excess of evaporation over precipitation e p steadily appears to have decreased during the last 10 000 to 2000 years most probably due to an increasing trend in the summer monsoon rainfall contrary to the land based paleoclimatic data from this region which indicate onset of aridity around 4000 years ago our results are consistent with the hypothesis that significant spatial variability in the monsoon rainfall observed today was persistent during most of the holocene alternatively the trend can be seen as an adjustment between two phases one between 10 000 and 6000 years ago of increasing precipitation and another between 3500 and 2000 years ago after the arid episode we also report a significant 700 year periodicity similar to that reported recently from the south china sea indicating that the centennial millennial scale response of the indian and chinese monsoons to high latitude forcing may be alike

permian carbonaceous rocks from the bonito coalfield santa catarina brazil organic facies approaches abstract permian sedimentary rocks of the rio bonito formation parana basin in the santa catarina state brazil contain three important coal seams in a descending order barro branco bonito superior and pre bonito superior artinskian carbonaceous shale samples corresponding to the so called bonito coal were sampled at the mine face of the coal bed of the bonito i underground mine these samples were analyzed in order to discuss their petrographical geochemical palynological and paleobotanical characteristics palynological analyses demonstrated abundant and well preserved palynomorphs showing a dominance of bisaccate pollen grains related to gymnospermic plants wood fragments preserved as coalified compression show the presence of lycophyta palynofacies on samples demonstrated good results for the recognition of preserved organic matter and changes in paleoenvironmental conditions along the sedimentary sequence palynofacies and palynological analyses indicate changes in paleoecological conditions that have favored the development of different plant communities during the depositional time span from a forested gymnosperm at the base to a lycophyte arborescent plant dominated scenario at the top suggesting a shift to coastal environment the microscopic maceral group analyses reveal a predominance of liptinite and vitrinite over inertinite while among microlithotypes carbargilite is abundant the joint occurrence of inertinite as a maceral in the carbonaceous rock and charcoal in associated shales suggests that the mire and near surroundings were regularly subject to wildfires mean random vitrinite reflectance rr varies from 0 88 to 1 04 the liptinite spectral fluorescence parameters obtained for samples show the max values varying from 610 to 650 indicating equivalent vitrinite reflectance rreq values from 0 83 to 1 10 these results show that the equivalent vitrinite reflectance rreq correlates well with the measured vitrinite reflectance rr the bonito coal is a high volatile bituminous coal according to the iso 11760 2005 standard total organic carbon varies from 2 4 to 44 0 wt and sulfur is present in moderate to high contents gc ms analyses evidenced a predominance of even saturated hydrocarbons and the presence of hopanes and steranes

a 225 kyr record of dust supply paleoproductivity and the oxygen minimum zone from the murray ridge northern arabian sea abstract analysis of a 15 m long sediment core recovered from the murray ridge northern arabian sea reveals a 225 000 year record of climate induced variations in surface water productivity mid water ventilation and dust input in the northern arabian sea productivity and dust input records closely resemble those from the owen ridge and oman margin also the phase lag of 10 kyr between maximum productivity and precession minimum is in phase with the summer monsoon upwelling record from the owen ridge and the oman margin this implies that the productivity variations in the northern arabian sea during the last 225 kyr are primarily controlled by changes in the indian ocean summer monsoon the winter monsoon obviously played a minor role in the productivity history of the northern arabian sea another result from this study is that the mg al record from the murray ridge nicely documents the post glacial flooding of the persian gulf which is the main glacial source for dolomite dust in this region finally it is concluded that the intensity of the omz co varies with surface water productivity being weak during periods of reduced summer monsoon especially during glacial periods

controls on the east asian monsoon during the last glacial cycle based on comparison between hulu cave and polar ice core records previous studies have suggested a sound chronological correlation between the hulu cave record east asian monsoon and greenland ice core records which implies a dominant control of northern hemisphere climate processes on monsoon intensity we present an objective straightforward statistical evaluation that challenges this generally accepted paradigm for sub orbital variability we propose a more flexible global interpretation which takes into account a broad range of variability in the signal structures in the hulu cave and polar ice core records rather than a limited number of major transitions our analysis employs the layer counted greenland ice core chronology 2005 gicc05 which was developed for greenland records and has since been applied via methane synchronisation to the high resolution 18oice series from epica dronning maud land edml the gicc05 chronology allows these ice core records to be compared to the u th dated hulu cave record within relatively narrow 3 bounds of age uncertainty following previous suggestions our proposed interpretation suggests that the east asian monsoon is influenced by a combination of northern hemisphere pull which is more intense during boreal warm periods and southern hemisphere push which is more intense monsoon during austral cold periods our analysis strongly suggests a dominant control on millennial scale monsoon variability by southern hemisphere climate changes during glacial times when the monsoon is weak overall and control by northern hemisphere climate changes during deglacial and interglacial times when the monsoon is strong the deduced temporally variable relationship with southern hemisphere climate records offers a statistically more plausible reason for the apparent coincidence of major east asian monsoon transitions with northern hemisphere dansgaard oeschger do climate events during glacial times than the traditional a priori interpretation of strict northern hemisphere control

climate change at the 4 2 ka bp termination of the indus valley civilization and holocene south asian monsoon variability 1 planktonic oxygen isotope ratios off the indus delta reveal climate changes with a multi centennial pacing during the last 6 ka with the most prominent change recorded at 4 2 ka bp opposing isotopic trends across the northern arabian sea surface at that time indicate a reduction in indus river discharge and suggest that later cycles also reflect variations in total annual rainfall over south asia the 4 2 ka event is coherent with the termination of urban harappan civilization in the indus valley thus drought may have initiated southeastward habitat tracking within the harappan cultural domain the late holocene drought cycles following the 4 2 ka bp event vary between 200 and 800 years and are coherent with the evolution of cosmogenic 14c production rates this suggests that solar variability is one fundamental cause behind holocene rainfall changes over south asia

a high resolution absolute dated late pleistocene monsoon record from hulu cave china oxygen isotope records of five stalagmites from hulu cave near nanjing bear a remarkable resemblance to oxygen isotope records from greenland ice cores suggesting that east asian monsoon intensity changed in concert with greenland temperature between 11 000 and 75 000 years before the present yr b p between 11 000 and 30 000 yr b p the timing of changes in the monsoon as established with 230th dates generally agrees with the timing of temperature changes from the greenland ice sheet project two gisp2 core which supports gisp2 s chronology in this interval our record links north atlantic climate with the meridional transport of heat and moisture from the warmest part of the ocean where the summer east asian monsoon originates

sedimentation in the western arabian sea the role of coastal and open ocean upwelling monsoon induced coastal and open ocean upwelling explain 84 of the variations of the organic carbon fluxes measured in the deep western arabian sea in this paper sea level measurements satellite derived wind speeds sea surface temperatures and nutrient profiles are used to discern the relative importance of these factors on fluxes measured during nine years of continuous sediment trap deployments this exercise shows i the increase in fluxes observed during the initial stages of the sw monsoons are caused by open ocean upwelling which develops faster than the coastal upwelling ii coastal upwelling triggers diatom blooms from nutrients from subsurface water and sediment resuspension and more importantly by injecting resting stages of diatoms back into the euphotic zone iii silica depletion resulting from diatom blooms in laterally advecting water masses leads to a replacement of diatoms by other nitrate limited organisms iv organic carbon fluxes to the deep arabian sea increase in response to an intensification of both coastal and open ocean upwelling weak coastal upwelling and strong open ocean upwelling also increase organic carbon fluxes the varying dominance of their influence is reflected in the timing and the composition of the peak fluxes v the link between organic carbon flux and monsoon strength is non linear probably due to changes in the surface currents and to vigorous turbulence in the surface water during strong sw monsoons these processes could reduce the organic carbon flux in the western arabian sea by about 65

inverse phase oscillations between the east asian and indian ocean summer monsoons during the last 12 000 years and paleo el nino abstract the inverse phase variations between the east asian and indian ocean summer monsoons on the interannual timescale result from the el nino southern oscillation activity in the tropical pacific which potentially provides a new way for studying paleo enso here we reconstruct a 12 000 yr proxy record for the east asian summer monsoon from 13 c time series of the plant cellulose of the hani peat bog in the northeastern china the comparison of it with the peat proxy record of the indian ocean summer monsoon suggests that the el nino conditions are coincident with strong east asian summer monsoons weak indian summer monsoons and drift ice events in the north atlantic at both orbital and millennial time scales the orbital scale inverse phase relationships between the monsoons indicate the occurrence of a long term enso like pattern confirming the sensitivity of the monsoon systems associated with enso to insolation forcing the nine inverse phase variations on the millennial time scales may suggest the nine el nino like patterns superimposing the long term enso like pattern the inverse phase variations between the monsoons also show close correspondence to the drift ice events at high northern latitudes in every case when the abrupt ice rafted debris events occurred in the north atlantic the inverse phase relationship established and the el nino like pattern occurred in the tropical pacific correspondingly the discussions on the influence of ocean thermohaline circulation on these global linkages have been made

asian monsoon oscillations in the northeastern qinghai tibet plateau since the late glacial as interpreted from visible reflectance of qinghai lake sediments abstract qinghai lake is a large saline lake on the qinghai tibetan plateau of central asia that is effected by both the indian and asian monsoons we used reflectance spectroscopy to characterize the sediments in a 795 cm long core taken from the southeastern part of the lake sediment redness which is related to iron oxide content seems to monitor paleoclimatic changes in the core iron oxides appear to be eroded from nearby red beds or loess deposits and are transported by fluvial means into the lake thus redness increases at times of increased precipitation that is as monsoon strength increases our redness monsoon proxy shows climate changes on several times scales on a millennial scale it records humid conditions during the early and mid holocene from about 4200 to 2300 yr bp low redness values suggest a two millennial long dry period which in the late holocene is followed by a more humid period on a centennial scale the redness proxy records not only the little ice age but also the medieval warm period the dark ages cool period and the roman warm period time series analysis of the redness record indicates a 200 yr frequency which corresponds to the de vries solar cycle suggesting that in addition to insolation changes resulting from orbital variations solar forcing also results from cyclic changes in the sun s luminosity

holocene forcing of the indian monsoon recorded in a stalagmite from southern oman a high resolution oxygen isotope record from a thorium uranium dated stalagmite from southern oman reflects variations in the amount of monsoon precipitation for the periods from 10 3 to 2 7 and 1 4 to 0 4 thousand years before the present ky b p between 10 3 and 8 ky b p decadal to centennial variations in monsoon precipitation are in phase with temperature fluctuations recorded in greenland ice cores indicating that early holocene monsoon intensity is largely controlled by glacial boundary conditions after approximately 8 ky b p monsoon precipitation decreases gradually in response to changing northern hemisphere summer solar insolation with decadal to multidecadal variations in monsoon precipitation being linked to solar activity

speleothem u series dating of semi synchronous climate oscillations during the last deglaciation evidence for nearly synchronous climate oscillations during the last deglaciation has been found throughout the northern hemisphere but few records are based on independent time scales of calendar years we present a rare uranium series dated oxygen carbon isotope record for a speleothem from tangshan cave china which demonstrates that abrupt deglacial climatic oscillations from 16 800 to 10 500 yr bp are semi synchronous with those found in greenland ice core records relatively rapid shifts in speleothem oxygen isotope ratios demonstrate that the intensity of the east asian monsoon switched in parallel with the abrupt transitions separating the bolling allerod younger dryas and pre boreal climatic reversals however the dated isotopic transitions appear to have lasted longer our results demonstrate the dominant role of atmospheric teleconnections in the rapid propagation of deglacial climatic signals on a hemispheric scale and highlight the importance of u series dated speleothems in the timing and characterization of abrupt climate change c 2003 elsevier b v all rights reserved

sea surface temperatures and the history of monsoon upwelling in the northwest arabian sea during the last 500 000 years abstract arabian sea sediments record changes in the upwelling system off arabia which is driven by the monsoon circulation system over the nw indian ocean in accordance with climate models and differing from other large upwelling areas of the tropical ocean a 500 000 yr record of productivity at odp site 723 shows consistently stronger upwelling during interglaciations than during glaciations sea surface temperatures ssts reconstructed from the alkenone unsaturation index uk 37 are high up to 27 c during interglaciations and low 22 24 c during glaciations indicating a glacial interglacial temperature change of 3 c in spite of the dampening effect of enhanced or weakened upwelling the increased productivity is attributed to stronger monsoon winds during interglacial times relative to glacial times whereas the difference in ssts must be unrelated to upwelling and to the summer monsoon intensity the winter ne monsoon was more effective in cooling the arabian sea during glaciations then it is now

synchroneity of oxygen minimum zone intensity on the oman and pakistan margins at sub milankovitch time scales abstract in this paper we present evidence for sub milankovitch variability in monsoon intensity from the oman and pakistan margins northern arabian sea a new high resolution geochemical record from the oman margin combined with microfossil data shows high frequency variations in sea surface productivity caused by changes in the intensity of summer monsoon induced upwelling the local oxygen minimum zone omz which presently impinges on the oman margin was reconstructed using laminations redox sensitive elements and aragonite preservation comparison with a pakistan margin record shows that omz intensity varied synchronously across the basin omz intensity varies together with summer monsoon strength being weakest during periods of minimum summer monsoon intensity correlating the pattern of summer monsoon variability with that of the winter monsoon inferred from proxy records in the northeastern arabian sea suggests a reversed relationship between summer and winter monsoon strength furthermore the oman and pakistan margin records confirm earlier results suggesting a link between high northern latitude climate as reconstructed from greenland ice cores and monsoonal climate

spatial and temporal variability in the stable isotope systematics of modern precipitation in china implications for paleoclimate reconstructions the stable isotopic composition of materials such as glacial ice tree rings lake sediments and speleothems from low to mid latitudes contains information about past changes in temperature t and precipitation amount p however the transfer functions which link 18op to changes in t or p d 18op dt and d 18op dp can exhibit significant temporal and spatial variability in these regions in areas affected by the southeast asian monsoon past variations in 18o and d of precipitation have been attributed to variations in monsoon intensity storm tracks and or variations in temperature proper interpretation of past 18op variations here requires an understanding of these complicated stable isotope systematics since temperature and precipitation are positively correlated in china and have opposite effects on 18op it is necessary to determine which of these effects is dominant for a specific region in order to perform even qualitative paleoclimate reconstructions here we evaluate the value of the transfer functions in modern precipitation to more accurately interpret the paleorecord the strength of these transfer functions in china is investigated using multiple regression analysis of data from 10 sites within the global network for isotopes in precipitation gnip 18op is modeled as a function of both temperature and precipitation the magnitude and signs of the transfer functions at any given site are closely related to the degree of summer monsoon influence 18op values at sites with intense summer monsoon precipitation are more dependent on the amount of precipitation than on temperature and therefore exhibit more negative values in the summer in contrast 18op values at sites that are unaffected by summer monsoon precipitation exhibit strong relationships between 18op and temperature the sites that are near the northern limit of the summer monsoon exhibit dependence on both temperature and amount of precipitation comparison with simple linear models 18op as a function of t or p and a geographic model 18op as a function of latitude and altitude shows that the multiple regression model is more successful at reproducing 18op values at sites that are strongly influenced by the summer monsoon the fact that the transfer function values are highly spatially variable and closely related to the degree of summer monsoon influence suggests that these values may also vary temporally since the southeast asian monsoon intensity is known to exhibit large variations on a number of timescales annual to glacial interglacial and the magnitude and sign of the transfer functions is related to monsoon intensity we suggest that as monsoon intensity changes the magnitude and possibly even the sign of the transfer functions may vary therefore quantitative paleoclimate reconstructions based on 18op variations may not be valid

orbital insolation forcing of the indian monsoon a motor for global climate changes abstract both modern and ancient indian summer monsoons are driven by transequatorial pressure differences directly coupled with the insolation difference between the northern and southern subtropical hemispheres a high resolution record of upwelling and dust flux from the western arabian sea resembles an insolation based indian summer monsoon index this index and the observed monsoonal climate variations share major elements on the orbital obliquity and precessional band with the specmap marine oxygen isotope record representing global ice volume the long term evolution of the index mirrors almost exactly the insolation changes at 65 n showing that the forcing of low latitude climate variability has a structure similar to that of the insolation forcing in the high northern latitudes moreover insolation forcing in the low latitudes directly controls atmospheric processes in the african indian and asian monsoon being responsible for a huge amount of transequatorial water vapour and therefore latent heat transport millennial scale variability of the monsoonal climate is concentrated at periodicities near 1100 1450 1750 and 2300 years these cycles are not strictly periodic but occur in bands with specific activity phases and amplitude increases during warm stages and interstadials for the 1100 and 1750 yr cycles whereas the 1450 yr cycle dominates the cold intervals