bay of bengal exhibits warming trend during the younger dryas implications of amoc a sharp decline in temperature during the younger dryas yd preceding the current warmer holocene is well documented in climate archives from the northern hemisphere high latitudes although the magnitude of yd cooling varied spatially the response of yd cooling was well documented in the atlantic and pacific oceans but not in the indian ocean here we investigate whether the modern remote forcing of tropical indian ocean sea surface temperature sst by northern hemisphere climate changes holds true for events such as the yd our sst reconstruction from the western bay of bengal exhibits an overall warming of 1 8 c during the yd we further compared our data with other existing mg ca based sst records from the northern indian ocean and found no significant negative sst anomalies in both the arabian sea and the bay of bengal compared to pre and post yd suggesting that no apparent cooling occurred during the yd in the northern indian ocean in contrast most part of the yd exhibits positive sst anomalies in the northern indian ocean that coincide with the slowdown of the atlantic meridional overturning circulation during this period

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

proposing a formula for evaporation measurement from salt water resources evaporation involves the change in state of a liquid to a vapour the evaporation rate from salt water resources depends mostly on saturated vapour pressure above its surface on the other hand the saturated vapour pressure is affected by the ion activity coefficient which stems from the chemical salt concentration of water thus an increase in concentration of water results in a reduction of saturated vapour pressure in order to acquire the actual rate of evaporation from salt water resources a uniform set of evaporation pans with different but specified salt concentrations were used in a meteorological station under the same conditions the difference in evaporation rate of each pan can only stem from the difference in chemical salt concentration and indeed the molar fraction of water in each saline solution therefore by applying the water molar fraction in the pressure term of fresh water evaporation measurement formulas these equations were developed further for determination of evaporation rate from salt water resources the proposed formulas using very simple terms seem to be suitable for determination of evaporation rate from any water typically saline semi saline and fresh water with a satisfactory precision copyright 2007 john wiley sons ltd

a 25 ka indian ocean monsoon variability record from the andaman sea recent paleoclimatic work on terrestrial and marine deposits from asia and the indian ocean has indicated abrupt changes in the strength of the asian monsoon during the last deglaciation comparison of marine paleoclimate records that track salinity changes from asian rivers can help evaluate the coherence of the indian ocean monsoon iom with the larger asian monsoon here we present paired mg ca and d 18 o data on the planktic foraminifer globigerinoides ruber white from andaman sea core rc12 344 that provide records of sea surface temperature sst and d 18 o of seawater d 18 osw over the past 25 000 years ka before present bp age control is based on nine accelerator mass spectrometry ams dates on mixed planktic foraminifera mg ca sst data indicate that sst was 31c cooler during the last glacial maximum lgm than the late holocene andaman sea d 18 osw exhibited higher than present values during the lateglacial interval ca 19 15 ka bp and briefly during the younger dryas ca 12 ka bp lower than present d 18 osw values during the bolling allerod ca 14 5 12 6 ka bp and during the early holocene ca 10 8 5 5 ka bp are interpreted to indicate lower salinity reflect some combination of decreased evaporation precipitation e p over the andaman sea and increased irrawaddy river outflow our results are consistent with the suggestion that iom intensity was stronger than present during the bolling allerod and early holocene and weaker during the late glaciation younger dryas and the late holocene these findings support the hypothesis that rapid climate change during the last deglaciation and holocene included substantial hydrologic changes in the iom system that were coherent with the larger asian monsoon r 2007 elsevier ltd all rights reserved

explosive eruptions of the ayarza calderas southeastern guatemala abstract the ayarza calderas southeastern guatemala form a figure 8 shaped depression that is now occupied by laguna de ayarza the smaller eastern caldera is also the older it formed upon eruption of a mixed plinian air fall that is locally overlain by a comagmatic ash flow deposit called the mixta unit the air fall portion contains rhyolitic 75 2 wt sio 2 pumice basaltic 52 wt sio 2 blobs and compositional hybrids that are either spectacularly banded or homogeneous in color although of limited aerial extent and volume 0 1 km 3 dense rock equivalent the unit is of considerable petrologic interest because the basalt contains pristine phenocrysts and quench crystallites of calcic hornblende virtually identical 87 sr 86 sr ratios 0 70373 of both rhyolite and basalt end members suggest a common magmatic source a log from the mixta ash flow deposit has been c 14 dated at 27 000 1 600 y b p eruption of the younger pyroclastic sequence at ayarza culminated in formation of the western caldera this rhyolitic sequence also consists of a plinian air fall overlain by a comagmatic ash flow deposit the ash flow unit is quite fine grained and probably phreatomagmatic in origin a thin horizon of air fall material is locally interbedded within the ash unit volume dre of the younger sequence has been estimated at a minimum 2 km 3 a log from the younger ash flow unit has been c 14 dated at 23 100 500 y b p the age of formation of the western caldera and the last recognized activity at ayarza although major element geochemistry of the ayarzan rhyolites is very similar to that of other silicic units of northern central america minor and trace element contents permit all the rhyolites to be distinguished from each other sr isotopic ratios of the mixta rhyolite reaffirm that older radiogenic crustal rocks are not involved in the petrogenesis of rhyolites in northern central america

late pleistocene holocene radiolarian paleotemperatures in the norwegian sea based on artificial neural networks artificial neural networks ann were trained by using an extensive radiolarian census dataset from the nordic greenland norwegian and iceland seas the regressions between observed and predicted summer sea temperature sst indicate that lower error margins and better correlation coefficients are obtained for 100 m sst100 compared to 10 m sst10 water depth and by using a subset of species instead of all species the trained anns were subsequently applied to radiolarian data from two norwegian sea cores hm 79 4 and md95 2011 for reconstructions of ssts through the last 15 000 years the reconstructed sst is quite high during the bolling allerod when it reaches values only found later during the warmest phase of the holocene the climatic transitions in and out of the younger dryas are very rapid and involve a change in sst100 of 6 2 and 6 8 8c taking place over 440 and 140 years respectively sst100 remains at a maximum during the early holocene and this radiolarian holocene optimum temperature interval rhoti predates the commonly recognized middle holocene climatic optimum hco during the 8 2 ka event sst100 decreases by ca 3 8c and this episode marks the establishment of a cooling trend roughly spanning the middle holocene until ca 4 2 ka successively since then and through the late holocene sst100 follows instead a statistically significant warming trend the general patterns of the reconstructed ssts agree quite well with previously obtained results based on application of imbrie and kipp transfer functions iktf to the same two cores for sst0 a statistically significant cyclic component of our sst record period of 278 years has been recognized this is close to the de vries or suess cycle linked to solar variability and documented in a variety of other high resolution holocene records d 2005 elsevier b v all rights reserved

tropical sea surface temperatures during the last glacial period a view based on alkenones in indian ocean sediments abstract the quantification of tropical temperatures during the last glacial cycle 0 150 kyr bp is a controversial issue since different proxies seem to provide conflicting informations to obtain a complementary point of view we use the alkenone method to estimate sea surface temperatures and focus our work on deep sea sediments recovered from the tropical indian ocean we present alkenone data obtained in two cores which cover in detail the last deglaciation and in about twenty cores distributed between 20 s and 20 n that were chosen to evaluate the temperature contrast of the last glacial interglacial transition our results indicate that indian ocean tropical temperatures remained an average within 1 5 2 5 c of their present values during the last glaciation at 10 n the last deglaciation is characterized by two warming steps which is similar to the classical deglacial chronology observed in the north atlantic area at 20 s the deglacial warming occurred at ca 15 cal kyr bp lagging significantly 5 4 kyr behind the antarctic warming but in phase with northern hemisphere time series

vegetation and climate history inferred from a qinghai crater lake pollen record from tengchong southwestern china abstract a palynological investigation of a 514 cm long continuous core section from qinghai crater lake western yunnan province southwestern china was performed in order to reconstruct regional vegetation and climate from 15 8 cal kyr bp to the present the results show that the area was covered with deciduous broadleaved forest dominated by deciduous quercus between 15 8 and 12 8 cal kyr bp suggesting slightly cold and dry conditions from 12 8 to 8 3 cal kyr bp the vegetation continued to be dominated by deciduous broadleaved forest but there was also a sudden increase in castanopsis lithocarpus and a slight drop in deciduous quercus and alnus reflecting a gradual increase in both temperature and humidity during the period 8 3 4 6 cal kyr bp the mixed deciduous forests became more diverse and dense with thermophilous and hygrophilous species expanding to their maximum extents implying a warm and rather humid climate from 4 6 to 0 5 cal kyr bp the vegetation was succeeded by open mixed deciduous forest dominated by alnus with a retreating evergreen broadleaved forest indicating a cool and slightly dry climate after 0 5 cal kyr bp the vegetation became less diverse and more open but evergreen broadleaved trees increased their spread markedly suggesting that the climate had become warmer and drier in recent decades human activity resulted in a large increase in alnus and pinus around this lake basin specifically we concluded that the warm and moist climate detected between 8 3 and 4 6 cal kyr bp may have occurred in response to the high sea surface temperatures and high sea levels in the bay of bengal existent at that time

holocene mean annual air temperature maat reconstruction based on branched glycerol dialkyl glycerol tetraethers from lake ximenglongtan southwestern china abstract here we investigate the sources of branched glycerol dialkyl glycerol tetraethers brgdgts in lake ximenglongtan from southwestern china and present a brgdgts based holocene 9 4 cal kyr bp temperature reconstruction the similarities in the distributions of brgdgts between surface sediments and catchment soils indicate that soil is the dominant source of brgdgts this contrasts with the recent emphasis on lacustrine gdgts in other regional studies holocene temperature evolution is characterized by an early cool phase with a mean annual air temperature maat of 12 5 c prior to 7 6 cal kyr bp followed by a rapid warming towards the local thermal maximum maat 13 8 c from 7 6 to 5 5 cal kyr bp and a subsequent long term cooling that ended at 1 5 cal kyr bp temperature changes after 1 5 cal kyr bp show high variability and low correspondence to global climate events such as the medieval warm period overall holocene temperature variation has been primarily controlled by boreal summer insolation changes the larger amplitude 1 5 4 0 c in annual cooling during the early holocene in maat contrasts with summer temperature records from this region range of cooling 0 3 1 0 c and indicates the likely influence of lower winter temperature on maat variation we suggest that substantial remnants of the northern hemisphere ice sheets during the early holocene enhanced the winter westerlies and east asian winter monsoon eawm and decreased the winter temperature in southwestern china leading to a cold early holocene climate

reconstructing sea surface temperature and salinity using δ 18 o and alkenone records the oxygen isotope 18o composition of foraminiferal tests from deep sea sediments is widely used as a palaeoclimate proxy but it includes contributions from sea surface temperature global ice volume and local salinity which are difficult to separate recently a new technique for deriving palaeotemperatures has been developed which is based on the abundance ratios of unsaturated alkenones in phytoplankton algae1 2 here we use a combination of oxygen isotope and alkenone records in a deep sea core from the juncture of the arabian sea and the bay of bengal to extract the salinity signal from the former record variations in salinity are related to the balance between evaporation and precipitation3 and are thus a sensitive indicator of climate change our 170 kyr salinity record enables us to reconstruct changes in the indian monsoon over this period considerably extending earlier studies which reached back to 18 kyr ago 4 8 like these previous studies we find that large variations in the monsoon occurred during the transition from the last glacial period to the present interglacial but our results also provide a view of the monsoon throughout the last glacial and demonstrate the potential of this approach for reconstructing palaeosalinity

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

seasonal sea surface temperature contrast between the holocene and last glacial period in the western arabian sea ocean drilling project site 723a modulated by monsoon upwelling 1 annual summer and winter sea surface temperatures ssts in the western arabian sea were reconstructed through the last 22 kyr using artificial neural networks anns based on quantitative analyses of planktic foraminifera down core sst estimates reveal that annual summer and winter ssts were 2 1 2 and 2 6 c cooler respectively during the last glacial period than in the holocene a 2 5 c sst increase during termination 1a hereinafter referred as glacial to holocene transition in the western arabian sea the study reveals a strong seasonal sst contrast between winter and summer from 18 to 14 calendar kyr owing to the combined effect of weak upwelling and strong cold northeasterly winds minor or no seasonal sst changes were noticed within the holocene period which is attributed to the intense upwelling during the summer monsoon this causes a lowering of sst to values similar to those of the winter season in analogy with the present day a 3 c rise in winter ssts during the glacial to holocene transition coincides with a strengthening of the monsoon suggesting a link between winter sst and monsoon initiation from the beginning of the holocene strikingly annual summer and winter ssts show a cooling trend from 8 ka to the present day implying tropical cooling in the late holocene

sea surface temperature pattern reconstructions in the arabian sea from throughout the arabian sea for four distinct time intervals 0 ka 8 ka 15 ka and 20 ka with the aim of understanding the history of the indian monsoon and the climate of the arabian sea region this was accomplished through the use of paired mg ca and d 18 o measurements of the planktonic foraminifer globigerinoides ruber by analyzing basin wide changes and changes in cross basinal gradients we assess both monsoonal and regional scale climate changes sst was colder than present for the majority of sites within all three paleotime slices furthermore both the indian monsoon and the regional arabian sea mean climate have varied substantially over the past 20 kyr the 20 ka and 15 ka time slices exhibit average negative temperature anomalies of 2 5 3 5 c attributable in part to the influences of glacial atmospheric co2 concentrations and large continental ice sheets the elimination of the cross basinal sst gradient during these two time slices likely reflects a decrease in summer monsoon and an increase in winter monsoon strength changes in d 18 ow that are smaller than the d 18 o signal due to global ice volume reflect decreased evaporation and increased winter monsoon mixing ssts throughout the arabian sea were still cooler than present by an average of 1 4 ci n the 8 ka time slice these cool ssts along with lower d 18 ow throughout the basin are attributed to stronger than modern summer and winter monsoons and increased runoff and precipitation the results of this study underscore the importance of taking a spatial approach to the reconstruction of processes such as monsoon upwelling

holocene climatic change in morocco a quantitative reconstruction from pollen data annual precipitation july and january temperatures were reconstructed from a continuous holocene pollen sequence from the middle atlas morocco using the best modern analogues method the reconstructions show a clear difference between the early and late holocene from 10 ka to 6 5 ka the climate was drier and warmer than during the period since 6 5 ka the average value of annual precipitation was 870 mm until 6 5 ka then rose to 940 mm between 10 ka and 6 5 ka january and july temperatures were about 4 c higher than the present both temperatures show a marked decrease between 7 ka and 6 ka after 6 5 ka july and january temperatures fluctuated between 21 and 23 c and 2 5 and 5 c respectively january temperatures show a period of intermediate values 3 5 c between 4 ka and 5 5 ka the reconstructed climate values generally match palaeolimnological data from the same core which show five intervals of low lake level during the holocene they are also consistent with regional scale cohmap simulated palaeoclimate that shows contrasting patterns of rainfall variation between the northwesternmost part of africa and the intertropical band

millennial scale hydroclimate variations in southwest china linked to tropical indian ocean since the last glacial maximum indian summer monsoon ism variations have been linked to the orbital scale boreal summer insolation and millennial scale north atlantic climates recent studies show the critical role of indian ocean sea surface temperatures ssts in affecting deglacial millennial scale monsoon oscillations however it is unclear whether ssts can affect monsoon rainfall and terrestrial hydroclimate during the holocene here we report multiproxy evidence of hydroclimate changes in southwest china since the last glacial maximum similar to the often documented gradual decrease in holocene monsoon rainfall with superimposed millennial scale variations our records particularly show pronounced hydroclimate fluctuations including wet conditions at 5000 4000 yr ago and perhaps over the past 1000 yr we also find coherent variations between our records and sea surface salinities in the eastern indian ocean suggesting that terrestrial hydroclimate and resultant continental drainage have affected surface ocean conditions these fluctuations are likely linked to changes in ssts downstream of the monsoon source in the tropical western indian ocean i e a warmer ocean and more monsoon rainfall we conclude that the influence of both insolation and tropical ssts on the ism has persisted from the last deglaciation into holocene

orbital scale anti phase variation of sea surface temperature in mid latitude north pacific margins during the last 145 000 years 1 the late quaternary records of alkenone sea surface temperature sst in the japan and california margins showed orbital scale anti phase sst variations between the two margins this east west seesaw like change agreed well with the long term el nino southern oscillation enso behavior predicted by the zebiak cane enso model clement et al 1999 as regards both the timing and frequency during 0 60 ka and 120 145 ka and is attributed to the precession controlled change in tropical enso behavior this anti phase sst change was not clearly demonstrated during 60 120 ka this finding suggests that the influence of tropical climatic dynamics on the mid latitude north pacific varied in response to glacial interglacial cycles

planktonic foraminiferal and alkenone records of the last deglaciation from the eastern arabian sea the oxygen isotope record of planktonic foraminifera from tropical core md77194 eastern arabian sea exhibits a clear two step deglaciation with a brief 18o transient event in the tropics this 18o maximum could correspond to a cooling or to a change in the 18o content of sea water in this study past sea surface temperature sst and primary production pp are reconstructed from foraminiferal transfer functions and compared to values estimated from alkenone measurements sst and pp records from both proxies indicate a 1 5 2 5 c deglacial warming coupled with a pp decrease and a 0 5 1 c cooling during the younger dryas yd a detailed comparison between independent micropaleontological and geochemical proxies helps us identify potential biases and thus strengthen the paleo reconstructions

variations of indian monsoon precipitation during the last 32 kyr reflected in the surface hydrography of the western bay of bengal hydrography of the bay of bengal is highly influenced by the river runoff and rainfall during the southwest monsoon we have reconstructed 18 osw sea surface salinity and sea surface temperature sst changes in the bay of bengal by using paired measurements of 18 o and mg ca in a planktonic foraminifera species globigerinoides ruber from core sk218 1 in the western bay of bengal in order to understand the rainfall variability associated with southwest monsoon over the past 32 kyr our sst reconstructions reveal that bay of bengal was 3 2 c cooler during the lgm as compared to present day temperature and a 3 5 c rise in sst is documented from 17 to 10 ka both sst and 18 osw exhibit greater amplitude fluctuations during mis 2 which is attributable to the variability of ne monsoon rainfall and associated river discharge into the bay of bengal in association with strong seasonal temperature contrast on set of strengthening phase of sw monsoon was started during bolling allerod as evidenced by the low 18 osw values 14 7 ka 18 osw show consistently lower values during holocene with an exception around 5 ka which suggests that the freshening of bay of bengal due to heavy precipitation and river discharge caused by strong sw monsoon results of this study signify that the maximum fluctuations of the ne monsoon rainfall during mis 2 appear to be controlled by the

northeast african temperature variability since the late pleistocene abstract the development and application of lacustrine paleotemperature proxies based on microbial membrane lipid structures including the tex86 and branched glycerol dialkyl glycerol tetraether brgdgt paleothermometers have greatly advanced our understanding of the late glacial and postglacial temperature history of africa however the currently available records are from equatorial and southern hemisphere sites limiting our understanding of the spatial patterns of temperature change here we use the brgdgt paleotemperature proxy to reconstruct late pleistocene and holocene temperatures from lake tana ethiopia 12 n 37 e following the termination of heinrich stadial 1 at 15 ka lake tana experienced a 3 7 c oscillation over 1 2 ky temperatures then increased abruptly by nearly 7 c between 13 8 and 13 0 ka followed by a slow warming trend that peaked during the mid holocene temperatures subsequently cooled from 6 ka to 0 4 ka these data indicate that temperature at lake tana was sensitive to climate changes caused by variations in the atlantic meridional overturning circulation during the late pleistocene as well as to regional hydroclimatic changes and reorganizations of the monsoons our record suggests that late glacial temperature changes in northeast africa were linked to high latitude northern hemispheric climate processes but that subsequent post glacial temperature variations were strongly influenced by tropical hydrology

glacial to interglacial contrasts in the northern indian ocean differences between the 18o 16o ratios of planktonic foraminifera deposited during the last glacial maximum about 18 000 yr ago and those deposited during the holocene show that in the indian ocean the south west monsoon was weaker than today but that the north east monsoon was stronger the upwelling observed in modern conditions along the southern coast of arabia had disappeared because of the low speed of the southwestern winds during glacial summers the reduction in rainfall and runoff over the continent caused a reduction of the salinity gradient in the bay of bengal and along the western coast of india increased precipitation fell on the sea south of 10 n while strong evaporation over the northernmost arabian sea produced an enhanced salinity gradient in that area

spatial patterns of vegetation and climate on the chinese loess plateau since the last glacial maximum abstract in order to identify the spatial patterns of vegetation and climate on the chinese loess plateau since the last glacial maximum lgm pollen analysis was conducted for loess deposits from seven sites which constitute two north south and west east transects across the plateau results show that steppe prevailed both in the lgm and the holocene optimum during the lgm vegetation in the northwest mainly consisted of artemisia echinops type taraxacum type and chenopodiaceae and vegetation in the southeast was characterized by the same types but with a slight increase in poaceae during the holocene optimum vegetation was more diverse with poaceae artemisia echinops type and chenopodiaceae dominant in the northwest and pinus corylus poaceae artemisia and selaginella sinensis dominant in the southeast our records also show that from the lgm to the holocene optimum the presence of echinops type and taraxacum type pollen decreased while poaceae pollen became more prevalent as it has been found that most species of poaceae prefer relatively humid conditions and abundances of echinops type and taraxacum type increase in desert vegetation a new proxy poaceae echinops type taraxacum type ratio p e t was thus developed to compare the spatial differences in climate between the lgm and the holocene optimum with high p e t values indicating relatively warm and wet conditions the p e t ratio shows an overall southward and eastward increase for both the lgm and the holocene optimum furthermore it exhibits a prominent north south and west east gradient during the holocene optimum but displays a flat one during the lgm indicating more pronounced spatial contrasts in climate during the holocene than in the lgm this phenomenon may be attributed to the unique geographic location of the loess plateau which was located in the marginal zone of the east asian summer monsoon during interglacials but was dominated by the winter monsoon during glacials due to a southward displacement of climate zones

apparent long term cooling of the sea surface in the northeast atlantic and mediterranean during the holocene reconstructions of upper ocean temperature t during the holocene 10 0 ka b p were established using the alkenone method from seven high accumulation sediment cores raised from the northeast atlantic and the mediterranean sea 361n 751n all these paleo t records document an apparent long term cooling during the last 10 kyr in records with indication of a constant trend the apparent cooling ranges from 0 27 to 0 151c kyr 1 records with indication of time variable trend show peak to peak amplitudes in apparent temperatures of 1 2 2 91c a principal component analysis shows that there is one factor which accounts for a very large fraction 67 of the total variance in the biomarker paleo t records and which dominates these records over other potential secondary influences two possible contributions are 1 a widespread surface cooling which may be associated with the transition fromthe hypsithermal interval b9 5 7 ka b p to the neoglaciation b5 7 0 ka b p and 2 a change in the seasonal timing and or duration of the growth period of alkenone producers prymnesiophyte algae the first contribution is consistent with many climate proxy records from the northeast atlantic area and with climate model simulations including milankovitch forcing the second contribution is consistent with the divergence between biomarker and summer faunal paleo t fromearly to late holocene observed in two cores further work is necessary and in particular the apparent discordance between biomarker and faunal t records for the relative stable holocene period must be understood to better constrain the climatic and ecological contributions to the apparent cooling observed in the former records r 2002 elsevier science ltd all rights reserved

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

the oxygen isotope composition of tropical ocean surface water during the last deglaciation evidence of abrupt climate change in each of the tropical oceans can be found in high deposition rate sediments from the continental margins new ams 14 c dated sediments from the arabian sea reveal a two step depletion of surface ocean 18 o 16 o during the last deglaciation with a return to more enriched values approximately 10 5 ka bp the two step depletion can be correlated among isotope records derived from foraminifer calcite in the arabian sea the gulf of mexico the sulu sea and gulf of california confirming the existence of the two step depletion and 18 o enriched event at 10 5 ka bp in at least three tropical sites outside the north atlantic to determine whether the isotopic enrichment at 10 5 ka bp was caused by local cooling of the surface ocean we estimated sea surface temperatures over this interval using quantitative paleo ecological techniques there is no evidence for cooling in the arabian sea sulu sea or gulf of mexico consistent with the hypothesis that the enrichment at 10 5 ka bp is related to a change in the isotopic composition of the tropical surface ocean and not change in the temperature of calcification we conclude that the cooling at higher latitudes that occurred at 10 5 ka bp did not extend southward to the tropical ocean more cores from high sedimentation rate sites in the tropics are needed to identify the cause and extent of the 18 o signal however these preliminary results are consistent with two meltwater pulses during the deglaciation that distributed isotopically depleted water into each of the tropical oceans with a slow down in meltwater flux at 10 5 ka bp the most likely transport route for the isotopically depleted water from the melting northern hemisphere ice sheets to these isolated tropical ocean basins is via the relatively fast circulation of the atmosphere although other pathways are possible

moored observations of upper ocean response to the monsoons in the arabian sea during 1994 1995 the role of surface forcing in the semiannual evolution of the upper ocean temperature salinity and velocity fields in the arabian sea is examined to do so variability in the upper ocean in the central arabian sea was observed from an array of moorings deployed from october 1994 to october 1995 the northeast ne monsoon was characterized by moderate winds clear skies and dry air sea surface temperature sst dropped by 31c the ocean lost an average of 19 7 w m 2 and the mixed layer deepened by 100 m in response the southwest sw monsoon was accompanied by strong winds cloudy skies and moist air the ocean gained an average of 89 5 w m 2 but sst dropped by 5 51c and the mixed layer deepened to almost 80 m the response to the ne monsoon included daily cycling in the depth of the mixed layer in response to the diurnal cycle in the buoyancy forcing and a weak local wind driven response stronger windforcing during the sw monsoon dramatically reduced diurnal restratification and a clearer signal of local wind driven flow in the upper ocean was found the strongest velocity signal in the upper ocean however was the flow associated with mesoscale geostrophic features that passed slowly through the moored array dominating the current meter records in the first part of the ne monsoon and again in the latter part of the sw monsoon one dimensional heat and freshwater balances which held at other times through the year broke down during the passage of these features r 2002 published by elsevier science ltd

application of artificial neural networks to paleoceanographic data abstract artificial neural networks are computer systems that have the ability to learn a set of output or target vectors from a set of input vectors learning is achieved by self adjustment of a set of parameters to minimize the error between a desired output and the actual network output we have explored the potential of this approach in paleoceanography by application of a neural network algorithm to a problem involving prediction of sea surface water temperatures from relative abundances of planktonic foraminifer species in the southern indian ocean we employed a backpropagation bp network to assess how well it was able to predict the actual summer and winter surface water temperatures we compared the results with those obtained from statistical methods previously used for temperature predictions imbrie kipp transfer functions the modern analog technique and soft independent modelling of class analogy the efficiency of predictions was tested using the leaving one out technique in which each of the observations in the data set is left out one at a time while the remaining observations are used to generate a predictor the accuracy of the predictor is then tested on the observation left out by comparison with its actual value a set of tests using 1 2 3 4 5 and 10 neurons processing elements in a 3 layer bp network showed that a network with 3 neurons gave the smallest errors of prediction for both summer and winter temperatures 0 71 and 0 76 respectively corresponding errors for the statistical pattern recognition techniques ranged between 1 01 and 1 26 for summer temperatures and 1 05 1 13 for winter temperatures hence predictions of paleotemperatures from new data on planktonic foraminifer relative abundances in the southern indian ocean may be made with a precision of 0 7 0 8 c using the bp network and 1 0 1 3 c using the statistical pattern recognition procedures the bp network was thus the most successful among the methods employed here for temperature predictions artificial neural networks may therefore be seen as a viable alternative to more conventional approaches to data analysis in paleoceanography

application of artificial neural networks to chemostratigraphy artificial neural networks a branch of artificial intelligence are computer systems formed by a number of simple highly interconnected processing units that have the ability to learn a set of target vectors from a set of associated input signals neural networks learn by self adjusting a set of parameters using some pertinent algorithm to minimize the error between the desired output and network output we explore the potential of this approach in solving a problem involving classification of geochemical data the data taken from the literature are derived from four late quaternary zones of volcanic ash of basaltic and rhyolithic origin from the norwegian sea these ash layers span the oxygen isotope zones 1 5 7 and 11 respectively last 420 000 years the data consist of nine geochemical variables oxides determined in each of 183 samples we employed a three layer back propagation neural network to assess its efficiency to optimally differentiate samples from the four ash zones on the basis of their geochemical composition for comparison three statistical pattern recognition techniques linear discriminant analysis the k nearest neighbor k nn technique and simca soft independent modeling of class analogy were applied to the same data all of these showed considerably higher error rates than the artificial neural network indicating that the back propagation network was indeed more powerful in correctly classifying the ash particles to the appropriate zone on the basis of their geochemical composition

variations in denitrification and ventilation within the arabian sea oxygen minimum zone during the holocene the continental slope of india is exposed to an intense perennial oxygen minimum zone omz supporting pelagic denitrification sediments that are presently in contact with the lower boundary of the denitrification zone indicate marked changes in the intermediate and bottom waters ventilation of omz during the past 9 500 years the 15n of sediment suggests that the omz waters were less ventilated during the early holocene between 9 5 and 8 5 ka bp resulting in intensified denitrifying conditions with an average 15n value of 7 8 while at the same time stable mo isotope composition average 98mo of 0 02 indicates that the bottom waters that were in contact with the sediments were better oxygenated by the mid holocene omz became more oxygenated suppressing denitrification average 15n of 6 2 while bottom waters gradually became less oxygenated average 98mo of 1 7 the mid holocene reduction in denitrification coincided with a global decrease in atmospheric n2o as inferred from ice core records which is consistent with a decreased contribution from the arabian sea since 5 5 ka bp omz waters have again been undergoing progressive deoxygenation accompanied by increasing denitrification

coupled sea surface temperature seawater δ18o reconstructions in the arabian sea at the millennial scale for the last 35 ka two sediment cores from the western 905 10 46 9 n 51 56 4 e water depth 1586 m and eastern sk17 15 15 n 72 58 e water depth 840 m arabian sea were used to study past sea surface temperatures sst and seawater 18o 18ow variations for the past 35 ka we used coupled mg ca 18o calcite variability in two planktonic foraminiferal species globigerinoides ruber which thrives throughout the year and globigerina bulloides which occurs mainly when surface waters contain high nutrients during upwelling or convective mixing ssts in both areas based on mg ca in g ruber were 3 to 4 c lower during the last glacial maximum lgm 21 ka than today and the holocene period the sst records based on g bulloides also indicate general cooling down to 18 c in both areas ssts in the western arabian sea based on g bulloides were always lower than those based on g ruber indicating the presence of strong seasonal temperature contrast during the holocene and lgm we interpret the consistent presence of this seasonal temperature contrast to reflect a combination of seasonal summer upwelling sw monsoon and winter convective mixing ne monsoon in the western arabian sea in the eastern arabian sea g bulloides based ssts were slightly lower about 1 c than g ruber based ssts during the holocene indicating the almost absence of a seasonal temperature gradient similar to today however a large seasonal temperature contrast occurred during the lgm which favors the assumption that strong ne monsoon winds forced winter upwelling or convective mixing offshore goa sst and 18ow reconstructions reveal evidence of millennial scale cycles particularly in the eastern arabian sea here the stadial periods northern hemisphere cold periods such as younger dryas and heinrich events are marked by increasing ssts and salty sea surface conditions relative to those during the interstadial periods indeed the 18ow record shows evidence of low saline surface waters during interstadial periods indicating increased freshwater runoff from the western ghats as a consequence of enhanced sw monsoon intensity

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

new evidence on the sequence of deglacial warming in the tropical indian ocean transition from the last glacial maximum to holocene has undergone a sequence of fluctuations which exhibit large spatial and temporal variations in different regions of the world here we show that deglaciation warming in the northen indian ocean was initiated 19 ka which is contemporary to the deglaciation warming in the antarctica and southern ocean a gradual warming occurred during the glacial to holocene transition in the northern indian ocean unlike two step warming noticed in the greenland and north atlantic synchronous deglacial warming 19ka in the antarctica and northern indian ocean suggest a strong connection in propagating climate signals between antarctica and the indian ocean probably through the indonesian through flow and or sub antarctica mode water

holocene glacier and climate fluctuations on franz josef land arctic russia 80 n fluctuations in glacier extent provide the first comprehensive record of holocene paleoclimate for franz josef land glacier fluctuations were constrained using 45 14c ages from 16 glacier margins many glaciers were behind present margins before 9 4 kyr possibly as early as 10 3 kyr and probably remained so until at least 4 4 kyr where kyr 14c yr b p 1000 subsequently glaciers expanded probably reaching present margins before 3 2 kyr but certainly by 2 kyr a prominent neoglacial advance occurred ca 1 kyr and was followed by little ice age advances including one in the middle 1600s a d glaciers were larger than present at the turn of the century followed by widespread retreat soon after the holocene glacier record closely mimics that of svalbard 500 to 1000 km to the west suggesting similar glacier mass balance changes over a broad region of the eurasian arctia independent paleoclimate evidence from svalbard indicates higher than present summer air temperatures during the early to middle holocene when glaciers were behind present margins followed by generally cooler summer conditions and intermittent glacier advances and retreats holocene glacier variations were probably more influenced by summer temperature than winter precipitation

mesoscale eddies coastal upwelling and the upper ocean heat budget in the arabian sea estimation of the terms in the upper ocean heat budget from a moored array in the central arabian sea shows periods when a rough balance between the temperature trend and the horizontal advection of heat exists altimetry and sea surface temperature imagery are used to demonstrate that these episodes of strong horizontal advection are associated with mesoscale features during the wintertime northeast ne monsoon these are capped off mesoscale eddy features generated during the previous summertime southwest sw monsoon and have little horizontal transport of heat within the mixed layer during the sw monsoon the major contribution is strong offshore export of coastally upwelled water in a filament with a strong surface presence temperature and salinity properties from the moored array and a seasoar survey during the formation of the coastal filament confirm the offshore transport of the upwelled water mass to the site of the moored array more than 600 km offshore estimates of the filament section heat flux are several percent of the total estimated heat flux due to upwelling along the arabian peninsula and remote sensing data show that similar mesoscale variability along the coast is enhanced during the sw monsoon this points to the importance of mesoscale modulated transports in not only the observed heat budget at the moored array but in the overall upper ocean heat budget in the arabian sea

boron calcium ratios in globigerinoides ruber from the arabian sea implications for controls on boron incorporation abstract culture and downcore studies have been used to argue that b ca ratios in planktic foraminifera are correlated with seawater ph and may record seawater borate bicarbonate ratios although other factors may also control b ca specimens of globigerinoides ruber from the ocean drilling program odp site 723a western arabian sea and core aas9 21 eastern arabian sea from the last 22 kyr were analysed for b ca 18 o and mg ca b ca was compared to reconstructed salinity and sea surface temperature sst records to gain insight into the processes controlling the incorporation of boron in both cores b ca and mg ca are positively correlated which suggests that temperature governs the incorporation of boron in g ruber to some extent higher b ca ratios at the site affected by upwelling odp 723a than in the non upwelling region core aas9 21 and a positive correlation between b ca and shell size in g ruber are observed we observe no significant correlation between b ca in g ruber and salinity ph or dissolved inorganic carbon dic in either the western or eastern arabian sea which throws considerable doubt on the utility of b ca ratios as a ph or pco 2 proxy

holocene high resolution quantitative summer temperature reconstruction based on subfossil chironomids from the southeast margin of the qinghai tibetan plateau this paper reports the first quantitative summer mean july temperature reconstruction based on subfossil chironomids from the southeast margin of the qinghai tibetan plateau qtp covering the end of the last deglaciation and the entire holocene spanning 11 800 cal yr bp to the present the record is based on 223 chironomid samples throughout a 927 cm sediment core providing a temporal resolution of 50 years per sample we validate the record by applying several statistical reconstruction diagnostics and comparing with pollen and diatom records from the same sediment core the record suggests the summer temperature varies by 2 5 c across the entire period a generally warmer period occurred between c 8500 and c 6000 cal yr bp and a cooling trend was initiated from c 5500 cal yr bp the overall pattern broadly matches the summer insolation at 30 n and the asian summer monsoon records from the surrounding regions suggesting that summer temperatures from the southeast margin of the qtp respond to insolation forcing and monsoon driven variability on a multi millennial time scale modifications of this overall trend are observed on the finer temporal resolution and we suggest that solar activity could be an important mechanism driving the centennial scale variability it may have a strengthened effect in the late holocene when the monsoon influence weakened further detailed investigation is needed to disentangle these effects on the climate change over the highlands of southwestern china

arctic north atlantic oscillation signature in holocene sea surface temperature trends as obtained from alkenone data 1 the variability in alkenone derived sea surface temperatures ssts in the north atlantic realm shows that a continuous sst decrease in the northeast atlantic from the early to the late holocene was accompanied by a persistent warming over the western subtropical atlantic the eastern mediterranean sea and the northern red sea based on the analysis of the instrumental data and of atmospheric general circulation model experiments we show that this variation in ssts during the holocene can be attributed to a continuous weakening of a northern hemisphere atmospheric circulation pattern similar to that of the arctic north atlantic oscillation

a 2 200 years periodicity in the asian monsoon system we have carried out a high resolution study of fluctuations in upwelling intensity along the oman margin western arabian sea through the last 19 130 years based on several marine microfossil indices of upwelling we document a periodicity of 2 200 years in the upwelling indices which would be governed by the south west sw monsoon with such a periodicity our data further demonstrate greater amplitude in the variability of the sw monsoon during the holocene than during the last glacial period our reported 2 200 years periodicity has two implications 1 oceanic circulation changes partly influence monsoon strength at sub milankovitch cycles 2 previously documented 2 300 years periodicity in atmospheric 14c might be induced by oceanic circulation changes

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

a high resolution absolute dated deglacial speleothem record of indian ocean climate from socotra island yemen abstract stalagmite m1 5 from socotra island yemen in the northwest indian ocean provides a robust high resolution paleoclimate record from 27 4 11 1 ka based on 717 stable isotope and 28 230 th measurements variations in m1 5 oxygen isotope ratios 18 o are interpreted to be primarily driven by an amount effect related to changes in the mean position and or intensity of convection of the intertropical convergence zone the island s only source of precipitation the m1 5 18 o time series is strongly correlated to the greenland ice cores similar to an older socotra speleothem deposited from 53 40 ka s j burns d fleitmann a matter j kramers a al subbary indian ocean climate and an absolute chronology over dansgaard oeschger events 9 to 13 science 301 2003 1365 1367 indicating that a north atlantic indian ocean cold dry warm wet teleconnection persisted through the end of the last glacial period peak aridification occurred at 23 ka and a gradual increase in moisture thereafter was interrupted by an abrupt drying event at 16 4 ka perhaps related to heinrich event 1 indian ocean rainfall increased dramatically during the bolling period and then decreased continuously and gradually through the allerod and younger dryas the holocene began abruptly with increased precipitation at 11 4 ka and was followed by a major but short lived drying during the preboreal oscillation at 11 2 ka m1 5 is highly correlated to the dongge cave record from 15 5 11 ka suggesting much of the indian ocean monsoon region responded similarly to the major climate changes of the last deglaciation the transitions into the younger dryas and to a lesser extent the bolling are remarkably gradual in m1 5 as they are in all other asian speleothem records occurring over several centuries these gradual transitions are in striking contrast to high resolution records from around the north atlantic basin where the transitions are extremely abrupt and generally occur in under a century this spatially variable pattern of climate change is consistent with an atlantic origin for these deglacial climate events

a 28 ka history of sea surface temperature primary productivity and planktonic community variability in the western arabian sea 1 uranium series radionuclides and organic biomarkers which represent major groups of planktonic organisms were measured in western arabian sea sediments that span the past 28 ka variability in the past strength of the southwest and northeast monsoons and its influence on primary productivity sea surface temperature sst and planktonic community structure were investigated the average alkenone derived sst for the last glacial period was 3 c lower than that measured for the holocene prior to the deglacial the lowest ssts coincide with the highest measured fluxes of organic biomarkers which represent primarily a planktonic suite of diatoms coccolithophorids dinoflagellates and zooplankton we propose that intensification of winter northeast monsoon winds during the last glacial period resulted in deep convective mixing cold ssts and enhanced primary productivity in contrast postdeglacial 17 ka ssts are warmer during times in which biomarker fluxes are high associated with this transition is a planktonic community structure change in which the ratio of the average cumulative flux of diatom biomarkers to the cumulative flux of coccolithophorid biomarkers is twice as high during the deglacial and holocene than the average ratio during the last glacial period we suggest that this temporal transition represents a shift from a winter northeast monsoon dominated pre 17 ka to a summer southwest monsoon dominated post 17 ka wind system

red sea during the last glacial maximum implications for sea level reconstruction the red sea is connected to the indian ocean via a narrow and shallow strait and exhibits a high sensitivity to atmospheric changes and a reduced sea level we used an ocean general circulation model to investigate the hydrography and circulation in the red sea in response to reduced sea level and modified atmospheric conditions occurring during the last glacial maximum lgm the model salinity shows high sensitivity to sea level reduction together with a mild atmospheric impact sea level reduction affects the stratification and alters the circulation pattern at the strait of bab el mandab which experiences a transition from a submaximal flow to a maximal flow the best correlation to reconstructed conditions during lgm exists when the water depth of the hanish sill the shallowest part in the strait of bab el mandab is 33 10 75 m which would be affected by a sea level lowering of approximately 105 m our results support the reconstructed maximum salinity of around 57 practical salinity units because of a simple model that takes into account mixing processes along the strait and comparison of the surface salinity gradient to reconstructions based on isotopic records from sedimentary cores the salinity and 18o are sensitive to the mixing process at the strait and the sensitivity increases as the sea level is further reduced a local relative sea level reduction of approximately 105 m is also in close agreement with the inference of the lgm low stand of the sea at the location of the sill based on the ice 5g vm2 model

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

contrasting sea surface temperature of summer and winter monsoon variability in the northern arabian sea over the last 25 ka abstract the seasonal monsoon cycle with winds from the southwest sw in summer and from the northeast ne in winter strongly impacts on modern regional sea surface temperature sst patterns in the arabian sea northern indian ocean to reconstruct the temporal and spatial variation in the dynamically coupled winter and summer monsoon strength over the last 25 ka we analyzed alkenone derived sst variations in one sediment core from the northwestern arabian sea that is influenced by the summer monsoon sst affected by upwelling processes and in one core from the northeastern arabian sea where sst is mainly governed by the winter monsoon no upwelling comparison of the sst records reveals an antagonistic relationship of summer and winter monsoon strength throughout the late deglaciation and the holocene upwelling along the arabian peninsula associated with peak sw monsoonal wind strength was strongest during the early holocene climate optimum between 11 and 8 ka and coincided with the northernmost position of the intertropical convergence zone itcz marked by maximum precipitation over northern oman the sw monsoon weakened over the middle to late holocene while the ne monsoon gained strength this different evolution was caused by the southward displacement of the itcz throughout the holocene superimposed over the long term trend are variations in northeast monsoon wind strength at time scales of centuries that were synchronous with late holocene climate variations recorded on the asian continent and in the high latitude northern hemisphere their likely driving forces are insolation changes associated with sunspot cycles enhanced by feedback mechanisms e g land sea thermal contrast they enforced centennial scale fluctuations in wind strength and temperature in the northern arabian sea monsoon system

latest pleistocene and holocene vegetation and climate history inferred from an alpine lacustrine record northwestern yunnan province southwestern china abstract reconstructing past changes of the summer monsoon in southwestern china is key to understanding the paleoclimatic dynamics of the indian summer monsoon southwest monsoon a major tropical system with impacts beyond the region high resolution pollen and conifer stoma data are presented from a sediment core tiancai lake located just below treeline in the hengduan mountains northwestern yunnan province of china these data record changes in vegetation and climate for the latest pleistocene and holocene c the last 12 230 cal yr bp and by comparing these results with the pollen records from the nearby erhai lake and lugu lake a regional climate history in yunnan province can be inferred during the period of 12 230 11 510 cal yr bp open alpine meadow around tiancai lake indicates a relatively cold and dry climate corresponding to the younger dryas cold event yd between 11 510 and 10 000 cal yr bp the vegetation types around tiancai lake changed into picea and abies forest and alpine rhododendron shrubland reflecting increases in the temperature and humidity from 10 000 to 6100 cal yr bp tsuga forest expanded persistently toward tiancai lake indicating further climate changed towards warmer and wetter conditions between 6100 and 3410 cal yr bp tsuga forest was the dominant vegetation type nearest to tiancai lake denoting warm and humid climatic conditions corresponding to the holocene climatic optimum in the northwestern yunnan province tsuga forest in mountains around lugu lake shrank quickly at 3410 cal yr bp reflecting significant decline of humidity since 2930 cal yr bp tsuga forest around tiancai lake shrank gradually indicating a fluctuating decrease of temperature these climatic changes reflect changes of the southwest monsoon namely warm and humid climate indicating strong southwest monsoon cold and dry climate denoting weak southwest monsoon