productivity collapses in the arabian sea during glacial cold phases 1 productivity in the arabian sea is one of the highest in the world it is controlled by seasonally reversing monsoonal wind driven upwelling of nutrient rich deeper waters which fuel phytoplankton growth the detailed history of upwelling induced productivity in the eastern arabian sea is unknown here we present paleoproductivity records from a composite sediment core at the millennial scale during the last 80 kyr b p these records are based on relative abundance counts of planktonic foraminifera and organic carbon contents which are shown to mainly vary in concert the eastern arabian sea upwelling induced productivity was higher in the glacial period than in the holocene but it fell repeatedly on millennial timescales these productivity declines occurred during cold events in the north atlantic region with the most pronounced changes prevailing during the heinrich events hence seasonal monsoon winds that drive upwelling induced productivity in the east were weak when the north atlantic was cold these weak winds resulted in stratification of the water column comparable to today s arabian sea stratification in the intermonsoonal period combining the new eastern with published western arabian sea results shows that the entire biological factory was severely diminished during the north atlantic heinrich events and the seasonal productivity change in the arabian sea monsoon system was reduced with year round low productivity

late quaternary halimeda bioherms and aragonitic faecal pellet dominated sediments on the carbonate platform of the western continental shelf of india abstract the fifty fathom flat is a drowned carbonate platform located on the outer continental shelf of western india it is unique because the carbonate depositional environment prevailed until early holocene in spite of its proximity to a major siliciclastic tidal embayment study of the bathymetry seismic and sonograph data together with the petrology mineralogy and geochemistry of the carbonate sediments and limestones recovered from the platform resulted in a the discovery of late quaternary halimeda bioherms and b aragonitic faecal pellet dominated sediments echograms reveal buried pinnacles between 62 and 38 m and exposed 2 to 14 m high pinnacles between 65 and 85 m on the platform these pinnacles occur as narrow to broad mounds bioherms in seismic profiles and as linear ridges and massive structures in sonographs seismic profiles also show a prominent reflector about 25 m below the sea bed identified by boreholes as a late pleistocene erosion surface the platform consists of relict carbonate sands and limestones rounded and ovoid to ellipsoidal aragonite grains are predominant in the sediments sem studies indicate elongated parallel canals and crescent to hook shaped canals corresponding to faecal pellets occur in some grains algal grains and pellets enclosing algal fragments are also present the grains in the limestones are similar to those in the sediments halimeda and crustacean faecal pellets are abundant components with minor echinoid mollusc and benthic foraminifera the limestones are characterised by abundant pores dissolution cavities relic aragonite needles meniscus cements and drusy calcite fill the pores produced by dissolution of aragonite needles these features indicate vadose diagenesis the stable isotopes of the carbonate sands and limestones are almost identical and similar to isotope values of beachrocks of the red sea the limestones ages 8400 9200 yr b p lie within the same age limits 10 400 8300 yr b p as the surficial sediments it appears that fluvial sediments largely accumulate in the inner shelf and did not hinder carbonate growth on the platform lying on the outer shelf we presume that arid climate and nutrients brought by river runoff and shelf edge currents favoured the growth of algal bioherms dominated by halimeda between 13 700 and 8300 yr b p the absence of late holocene and modern carbonates on the platform may be due to the combined influence of climatic change upwelling and neo tectonic activity at about 9000 yr b p the bioherms dominated by halimeda produced abundant aragonite muds deposit feeding crustaceans and other invertebrates subsequently excreted these muds as faecal pellets the platform thus contains faecal pellet dominated sediments

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

ocean chemistry during glacial time abstract measurements of co2 to air ratios in the gas trapped in bubbles in ice of glacial age suggest that the co2 content of the atmosphere was considerably lower during peak glacial time than during holocene time the purpose of this paper is to show that such a change must in all likelihood be the result of alterations in the nutrient element chemistry of sea water two possible scenarios are presented one involves alternate storage and erosion of phosphorous leaving residues from shelf sediments the other involves changes in the c p ratio in the organic debris falling to the deep sea means of verifying the nutrient cycle hypothesis are also given it is shown that the 13c record as we know it in planktonic and benthic foraminifera the oxygen record as inferred from benthic foraminifera species distributions and the early post glacial caco3 preservation event as recorded by aragonitic pteropods are consistent with both of the hypotheses presented only if an early post glacial spike in the 13c record for planktonic shells could be found would it be possible to eliminate one of these hypotheses i e that involving shelf storage the implications of these nutrient hypotheses to climate theory are as follows if shelf storage is responsible for the glacial to interglacial co2 increase then the co2 change must be considered an amplifier of some primary cause the reason is that sea level changes are needed to drive deposition on and erosion from the shelves on the other hand if changes in the c p ratio for falling debris are responsible then the co2 change could either be an amplifier or a primary cause for the major glacial to interglacial climatic cycle the latter is possible as self sustained oscillations in ocean chemistry might be driven by interactions between ocean ecology and ocean nutrient chemistry

variability of southwest indian summer monsoon precipitation during the bolling allerod we have generated a high resolution 20 yr 2 3 0 th dated stalagmite oxygen isotope record from timta cave in the western himalaya in india that documents southwest indian summer monsoon ism precipitation variations during the bolling allerod interstadial from 15 2 to 11 7 ka compared with the glacial and younger dryas ism precipitation was enhanced during the bolling allerod ism precipitation was apparently coupled to variations in the east asian monsoon and north atlantic climate on millennial and multicentennial time scales during the deglaciation analyses of a high growth rate interval 2 5 yr resolution encompassing the late bolling early alterod suggest that multidecadal monsoon variability was an important aspect of ism behavior at that time the frequency spectrum of ism precipitation during this time interval is similar to that of the 1 4 c record and other ism precipitation records during the latest holocene this raises the hypothesis that multidecadal climate dynamics during the late boiling early allerod may have been similar to those that operated during the last several millennia even though the boundary conditions of these two time intervals were very different

the early holocene sea level rise the causes anatomy and consequences of the early holocene sea level rise ehslr are reviewed the rise of ca 60m took place over most of the earth as the volume of the oceans increased during deglaciation and is dated at 11 650 7000 cal bp the ehslr was largely driven by meltwater release from decaying ice masses and the break up of coastal ice streams the patterns of ice sheet decay and the evidence for meltwater pulses are reviewed and it is argued that the ehslr was a factor in the ca 8470 bp flood from lake agassiz ojibway patterns of relative sea level changes are examined and it is argued that in addition to regional variations temporal changes are indicated the impact of the ehslr on climate is reviewed and it is maintained that the event was a factor in the 8200 bp cooling event as well as in changes in ocean current patterns and their resultant effects the ehslr may also have enhanced volcanic activity but no clear evidence of a causal link with submarine sliding on continental slopes and shelves can yet be demonstrated the rise probably influenced rates and patterns of human migrations and cultural changes it is concluded that the ehslr was a major event of global significance knowledge of which is relevant to an understanding of the impacts of global climate change in the future

multi centennial scale sst and indian summer monsoon precipitation variability since the mid holocene and its nonlinear response to solar activity indian summer monsoon ism shows a weak correlation with solar variability in the 20th century however such climatological observations on solar activity monsoon relationship are very short and

holocene paleoclimates of india we present a comprehensive summary of the available palaeoclimate records from india and compare the results from different proxies the results indicate i fluctuating lake levels during the early holocene the period of relatively higher lake levels from increased precipitation efficiency was reached only 7 2 6 0 cal kyr bp possibly due to increased contribution from winter rainfall ii the onset of aridity in nw india could have begun as early as 5 3 cal kyr bp subsequently there were multiple wet events but of shorter duration and smaller magnitude than during the mid holocene iii there is evidence of several short term climate events in the proxy record however in the absence of a rigorous chronological framework a detailed regional correlation is not possible at this stage finally a comparison between marine and terrestrial records indicates that episodes of strongest and weakest monsoon winds were not always associated with wettest and driest episodes respectively in the nw indian lakes

karakorum hindukush western himalaya assessing high altitude water resources the high mountains of central and south asia provide irrigation water for their adjacent lowlands the indus irrigation scheme depends on approximately 50 of its runoff originating from snowmelt and glacier melt from the eastern hindukush karakorum and western himalaya the atlas of pakistan indicates that these mountains gain a total annual rainfall of between 200 and 500 mm amounts that are generally derived from valley based stations and not representative for elevated zones high altitude snowfall seems to be neglected and is obviously still rather unknown estimates derived from accumulation pits runoff above 4000 m range from 1000 mm to more than 3000 mm depending on the site and time of investigation as well as on the method applied to assess the vertical spatio temporal distribution of total annual precipitation a combined approach is presented this approach links in situ measurements of snow depth and water equivalent 10 year time series derived from automatic weather stations at elevations between 1500 and 4700 m a s l the spatial distribution and period of snow coverage remotely sensed data and digital elevation models and the runoff characteristics of streams originating from snow or snow ice covered watersheds modified snowmelt runoff model including intermediate snowfall and glacier runoff based on conservative assumptions the vertically changing seasonal ratio between liquid and solid precipitation is calculated using a combined snow cover and ablation model total annual amounts of precipitation are derived for different altitudinal zones amounts of modelled and measured runoff complement the investigation horizontal gradients along the indus gilgit hunza transect indicate the varying dominance of seasonal precipitation regimes monsoonal mediterranean and continental disturbances south of nanga parbat between nanga parbat and batura wall west karakorum rainfall regime 1500 1800 mm year 1 at 5000 m and areas north of batura central asian rainfall regime 600 mm year 1 at 5000 m copyright 2005 john wiley sons ltd

late holocene primary productivity and sea surface temperature variations in the northeastern arabian sea implications for winter monsoon variability variability in the oceanic environment of the arabian sea region is strongly 34 influenced by the seasonal monsoon cycle of alternating wind directions prominent and well studied is the summer monsoon but much less is known about late holocene changes in winter monsoon strength with winds from the northeast that drive convective mixing and highsurface ocean productivity in the northeastern arabian sea to establish the first high resolution record of winter monsoon variability for the late holocene we analyzed alkenone derived sea surface temperature sst variations and proxies of primary productivity organic carbon and 15n in a well laminated sediment core from the pakistan continental margin increased summer monsoon and weak winter monsoon intensities off pakistan are indicated from 400 b c to 700 a d by reduced productivity and relatively high sst at about 700 a d the intensity of the winter monsoon increased off pakistan as indicated by a trend to lower sst we infer that winter monsoon was still weak from 700 to 1400 a d because primary production did not increase despite decreasing sst declining sst and elevated biological production from 1400 to 1900 a d suggest invigorated convective winter mixing by strengthening winter monsoon circulation most likely a regional expression of colder climate conditions during the little ice age on the northern hemisphere the comparison of winter monsoon intensity with records of summer monsoon intensity suggests that an inverse relationship between summer and winter monsoon strength exists in the asian monsoon system during the late holocene effected by shifts in the intertropical convergence zone

planktonic percentage of foraminiferal fauna in surface sediments of the arabian sea indian ocean and a regional model for paleodepth determination abstract the percentage of planktonic specimens in foraminiferal assemblages were determined in 126 surface sediment samples depth range 13 to 1050 m from the arabian sea along the western continental margin of india the results obtained are in agreement with previous studies in other areas that planktonic percentage increases with depth the resultant pattern is compared with results from the atlantic margin of the northeastern united states gulf of mexico timor sea and red sea comparisons reveal that in spite of diversity between various areas the over all pattern indicate a positive correlation between planktonic percentage and depth based on the above relationship a regional model has been constructed for the western continental margin of india in the arabian sea region to determine paleodepth from the planktonic percentage of fossil foraminiferal fauna regional differences in salinity patterns could be one of the main reasons for deviation of the regional model for the arabian sea with other regional models from pacific and atlantic regions and also with the global model

early to late holocene contrast in productivity omz intensity and calcite dissolution in the eastern arabian sea the oxygen minimum zone omz is a potential source of co2 to the atmosphere and the extensive omz spread to 1 37 106 km2 in the northern arabian sea would be an important contributor to the co2 budget in this perspective we report here that the eastern arabian sea experienced coeval increase in productivity and denitrification from 7 to 0 kyr which coincides with minimum dissolved oxygen levels in bottom waters in addition during the same period an increased calcium carbonate dissolution occurred as evidenced by low caco3 content decreasing shell weights of planktonic foraminifer species globigerinoides ruber with well marked dissolution features on their shells therefore this study has implications on the role of omz in governing caco3 dissolution and contributing to an increase in atmospheric co2

planktic foraminifera particle flux and oceanic productivity off pakistan ne arabian sea modern analogues and application to the palaeoclimatic record

punctuated eustatic sea level rise in the early mid holocene whether eustatic sea level rise through the holocene has been punctuated or continuous has remained controversial for almost two decades resolving this debate has implications for predicting future responses of remaining ice sheets to climate change and also for understanding the drivers of human settlement and dispersal patterns through prehistory here we present a sea level curve for the past 8900 yr from singapore a tectonically stable location remote from ice loading effects we also present critical and unique sedimentation rate organic 13c and foraminiferal 13c proxy records of sea level change derived from a shallow marine sediment core from the same area over the same time interval the sea level curve corroborated by the independent proxy records suggests rapid rise at a rate of 1 8 m 100 yr until 8100 cal calibrated yr b p a near cessation in the rate of sea level rise between 7800 and 7400 cal yr b p followed by a renewed rise of 4 5 m that was complete by 6500 cal yr b p we suggest that this period of relatively stable sea level during the early to mid holocene enabled modern deltas to advance providing a highly productive environment for the establishment of coastal sedentary agriculture periods of rapid sea level rise before and after may have catalyzed significant postglacial episodes of human dispersal in coastal regions

high resolution temperature and evaporation changes during the late holocene in the northeastern arabian sea in order to reconstruct the monsoonal variability during the late holocene we investigated a complete annually laminated sediment record from the oxygen minimum zone omz off pakistan for oxygen isotopes of planktic foraminifera and alkenone derived sea surface temperatures sst significant sst changes of up to 3 c which cannot be explained by changes in the alkenone producing coccolithophorid species inferred from the gephyrocapsa oceanica emiliania huxleyi ratio suggest that sst changes are driven by changes in the monsoon strength our high decadal resolution data indicate that the late holocene in the northeastern arabian sea was not characterized by a stable uniform climate as inferred from the greenland ice cores but by variations in the dominance of the sw monsoon conditions with significant effects on temperatures highest sst fluctuations of up to 3 0 c and 2 5 c were observed for the time interval from 4600 to 3300 years b p and during the past 500 years the significant short term sst changes during the past 500 years might be related to climatic instabilities known from the northern latitudes little ice age and confirm global effects surface salinity values reconstructed from 18o records after correction for temperature related oxygen isotope fractionation suggest that in general the past 5000 years were characterized by higher than recent evaporation and more intense sw monsoon conditions however between 4600 and 3700 years b p evaporation dropped sw monsoon weakened and ne monsoon conditions were comparatively enhanced for the past 1500 years we infer strongly fluctuating monsoon conditions comparisons of reconstructed salinity records with ice accumulation data from published tibetan ice core and tibetan tree ring width data reveal that during the past 2000 years enhanced evaporation in the northeastern arabian sea correlates with periods of increased ice accumulation in tibet and vice versa this suggests a strong climatic relationship between both monsoon controlled areas

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

oxygen and carbon isotopic composition and biogeographic distribution of planktonic foraminifera in the indian ocean five planktonic foraminiferal assemblages were encountered along a north south transect in the indian ocean with the following dominant species globorotalia truncatulinoides in the southern subtropical assemblage globigerinoides ruber globigerinella aequilateralis and globorotalia menardii in the northern subtropical assemblage globigerinoides sacculifer and pulleniatina obliquiloculata in the tropical assemblage neogloboquadrina dutertrei and globigerina bulloides in the tropical upwelling assemblage and globigernoides conglobatus in the tropical arabian sea assemblage oxygen and carbon isotopic analyses were performed on three surface dwelling species of planktonic foraminifera in tropical and subtropical waters 22 30 c the 18o of globigerinoides ruber and g sacculifer varies with surface water temperature and the slope of the isotope temperature regression line is similar to that of epstein et al 1953 for marine molluscs however foraminiferal 18o values are significantly lighter than those of molluscs indicating isotopic disequilibrium comparison between plankton tows taken within and below the mixed layer at the same stations shows that g ruber has similar low 18o values in both sets suggesting that it secretes its shell within the mixed layer by contrast g sacculifer has slightly higher 18o values below than within the mixed layer because it continues to secrete calcite below the thermocline no significant 18o variations with shell size were found on the other hand 13c values were strongly size dependent i e the smaller the size the lighter the 13c comparison of living g ruber and g sacculifer with recent specimens from the surface sediment shows that the living foraminifera are generally lighter in 18o than the fossils supporting independent observations that the latter have secreted additional calcite during gametogenesis when the organisms settle freely from the euphotic zone for about 12 h and pass through waters lower in temperature than the epipelagic waters where the foraminifera form the bulk of their shells

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

organic carbon preservation in southeastern arabian sea sediments since mid holocene implications to south asian summer monsoon variability the earlier studies show a contrasting long term trend of the south asian summer monsoon sasm after attaining the precessional forcing induced mid holocene maximum the increasing total organic carbon toc concentration of marine sediments in the southeastern arabian sea seas has been interpreted to imply strengthening sasm since mid holocene by a few studies however toc concentration is also influenced by redox conditions sedimentation rate and an influx of terrigenous matter depending on the regional settings so it needs to be ascertained whether the toc concentration of the sediments in the seas is a signal of productivity related to the sasm strength or preservation therefore we studied multiple proxies toc total nitrogen atomic c n 13corg caco3 and major and trace elements concentration for determining the productivity redox conditions detrital supply and provenance in a sediment core from the upper continental slope of the seas spanning the past 4700 years at centennial scale resolution the present study shows that the observed toc increase is not a result of enhanced productivity but is because of better preservation due to the increased sedimentation rate along with increasingly reducing conditions since mid holocene we further show that the sasm has been declining since mid holocene after attaining a precession forced maximum which corroborates the earlier model ensemble studies

lipid biomarker fluxes in the arabian sea with a comparison to the equatorial pacific ocean abstract fluxes and distributions of organic carbon oc and lipid biomarkers were measured in the western arabian sea as a function of season depth and distance from the coast of oman during the us jgofs arabian sea process study in 1994 1995 a strong seasonal pattern in oc and lipid flux is related to the annual monsoon cycle in the western arabian sea with the highest fluxes measured during the southwest monsoon fluxes were greatly attenuated with depth in the water column and in surface sediments as remineralization effectively consumed particulate organic matter a comparison of water column fluxes with oc and lipid accumulation rates in sediments confirms that the water sediment interface is a hot spot for organic matter degradation biomarker compositions also varied seasonally and with distance offshore reflecting seasonal and spatial succession of their biological sources and their subsequent export through the water column degradation of oc and biomarkers was extremely efficient with only a tiny fraction

revisiting reconstructed indian monsoon rainfall variations during the last 25 ka from planktonic foraminiferal δ18o from the eastern arabian sea abstract a careful reanalysis of recently published large body of surface seawater salinity and 18 o data indicates that the variations in the surface seawater 18 o of the eastern arabian sea appear to be governed mainly by the influx of low salinity water through the winter monsoon current from the relatively fresher bay of bengal and transported northwards by the west india coastal current armed with this calibration for the present day we revisit the south asian summer monsoon variability during the past 25 ka by compiling high resolution fossil planktonic foraminiferal 18 o data from a large number of well dated sediment cores from the eastern arabian sea we clearly demonstrate that there is no evidence to believe that the south asian summer monsoon steadily declined during the holocene as reported in a few earlier papers from the western arabian sea and speleothems from oman on the contrary a majority of sediment core data corroborate the inference of a much earlier paper sarkar et al 2000 of a steadily increasing monsoon rain during the holocene that the south asian monsoons were driven solely by past insolation change appears invalid

the distribution of nutrients in the southeastern beaufort sea implications for water circulation and primary production hydrographic data collected above the shelf and slope in the southeastern beaufort sea show marked contrast in surface properties of nutrients temperature salinity and oxygen between august 1974 a year when ice remained close to shore and august 1975 a year with much open water the near surface properties are dominated by river inputs biological activity and the ice regime below the winter mixed zone 40 50 m properties are similar to those observed elsewhere in the arctic ocean bering sea water is detected at 50 60 m as a very weak signal in temperature nutrients and oxygen upwelling in both years was observed at the eastern side of mackenzie canyon this upwelling likely results from the interaction of coastal circulation with topography estimates of new productivity based on nutrient budgets are low 20 g c m 2 yr 1 compared to temperate coastal waters but fall in the range expected for the arctic in 1974 the heavy ice year turbid water and ice cover appear to have reduced new production by about 30 calculations show that this production over the shelf could potentially supply a significant portion of the nutrients found in the upper halocline over a wide region of the arctic ocean by regeneration at the shelf bottom and transport off the shelf in brine drainage

variation in the indian summer monsoon intensity during the bolling allerod and holocene variations in the indian summer monsoon ism intensity during the last 16 7 ka have been studied using organic carbon corg 15 n of sedimentary organic matter caco3 sediment texture 18 oc and mg ca derived sea surface temperature 18 o of sea water and sea surface salinity in a 14 c dated sediment core from the eastern arabian sea the 18 o in water and planktonic foraminifera shells off the central west coast of india may be controlled by the ism intensity as this area receives high precipitation and land runoff also the corg and caco3 contents of sediments and 15 n of sedimentary organic matter may be linked to ism induced productivity and denitrification the results of the present study reveal that between 16 and 15 2 ka bp the ism was weak with minor fluctuations and started intensifying around 15 2 ka bp at the onset of the bolling allerod b a event the b a event is characterized by higher water column denitrification rates comparable to the present day the ism signatures observed in the 18 oc record of b a event compare well with those from timta cave of the western himalayas and also the asian summer monsoon signatures from the hulu caves in china and warming signatures in greenland ice sheet project 2 gisp2 suggesting atmospheric tele connections through intertropical convergence zone itcz the boundary between the younger dryas and the holocene is discernible with small episodes of abrupt events of increased ism intensity this decrease in 18 oc values at 11 8 ka bp is contemporary with june solar insolation maximum at 30 north and the increase in methane in the gisp2 ice core supporting episodes of warmer climate and increase in ism intensity the ism seems to have been most stable between 7 and 5 6 ka bp the core exhibits periodicity of 500 that is comparable to the atlantic water formation and the chinese monsoon

mid holocene climate and land sea interaction along the southern coast of saurashtra western india abstract the relict mudflat from the southern saurashtra coast of gujarat was investigated using geochemical and palynological analyses supported by radiocarbon dating to understand whether climate fluctuations and sea level operated in tandem during mid holocene the study revealed that the saurashtra coast experienced relatively wet climatic conditions with simultaneous occurrence of marginally high sea level between 4710 and 2825 cal yr bp subsequently a gradual onset of aridity and lowering of the sea level was observed between 2825 and 1835 cal yr bp and further a slight decrease in aridity is observed after 1835 cal yr bp the present day coastal configuration was probably achieved after around 1500 cal yr bp considering the tectonic instability of saurashtra coast land level changes the effective mid holocene sea level was estimated to be 1 m higher than the present the study demonstrates that sea level changes climate variability and land level changes were coupled during the mid holocene

distribution of organic carbon in surface sediments along the eastern arabian sea a revisit abstract one hundred twelve surface sediment samples along the western continental margin of india were analyzed for organic carbon oc elevated oc concentrations are associated with sediments deposited in areas where productivity is moderate to high very high oc concentrations as reported in earlier studies even for regions where productivity is comparatively low could not be confirmed the re analysis of selected samples by coulometry shows that oc concentrations determined previously by the wet oxidation method may be too high by up to more than a factor of two a broad similarity in the distribution of oc and bioproductivity is observed which is in accordance with other productivity proxies such as the abundance of planktonic foraminiferal species g bulloides and hydrogen indices hi our results indicate the importance of bioproductivity for oc accumulation along the western continental margin of india even though low dissolved oxygen concentrations in the water column sedimentation rate sediment texture clay mineral content dilution by quartz and carbonate as well as topography are considered responsible for the general oc distribution in this area

indian summer monsoon variability and vegetation changes in the core monsoon zone india during the holocene a multiproxy study we present the results of sediment texture 13c values toc tn toc tn and magnetic susceptibility lf of a 1 54 m deep sediment trench recovered from the core monsoon zone cmz of central in

east west similarities and differences in the surface and deep northern arabian sea records during the past 21kyr abstract this study analyses monsoon proxy globigerina bulloides from ocean drilling program odp hole 723a western arabian sea and hole abp 25 02 northeastern arabian sea as well as dominant benthic foraminifera pteropods total organic carbon toc inorganic carbon ic and stable isotope values of benthic foraminifera from hole abp 25 02 to understand summer monsoon driven changes in the western and eastern arabian sea and their impacts on deep sea ventilation during the past 21 kyr we have also combined published toc data from odp hole 724b to understand if deep sea conditions in the arabian sea were same throughout the region during the studied interval the summer monsoon was generally weaker during cold intervals including the last glacial maximum the younger dryas and the bond events of the holocene from 20 to 10 kyr the deep northeastern arabian sea was better oxygenated with less organic carbon supply except during 14 12 5 kyr when toc values increased indicating a weaker summer monsoon and a weak oxygen minimum zone omz the toc values and the abundance of the eutrophic benthic foraminiferal species bulimina aculeata melonis barleeanum and uvigerina peregrina increased during the late holocene whereas well oxygenated low organic carbon benthic species sphaeroidina bulloides as well as pteropods decreased indicating an intense omz and an increased supply of refractory organic material to the arabian sea it is important to note that although the surface response to monsoon variability was more or less similar in the western and northeastern arabian sea the deep sea conditions show a marked contrast in the two regions during the past 21 kyr

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

impacts on phytoplankton dynamics by free drifting icebergs in the nw weddell sea abstract glacier ice released to the oceans through iceberg formation has a complex effect on the surrounding ocean waters we hypothesized that phytoplankton communities would differ in abundance composition and production around or close to an iceberg this paper tests the influence of individual icebergs on scales of meters to kilometers observed through shipboard oceanographic sampling on march april 2009 surface waters integrated 0 100 m depth within the euphotic zone sampled close to the iceberg c 18a 10 m and the salps on smaller cells 3 10 m the iceberg s main influence in the austral fall is measured not so much by phytoplankton accumulation but by reactivation of the classic antarctic food chain facilitating diatom growth and sustaining high antarctic krill populations

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

paleoproductivity from benthic foraminifera abundance glacial to postglacial change in the west equatorial pacific surface productivity is correlated with the rate of accumulation of benthic foraminifera on the deep sea floor as a rule of thumb for each 1 mg of organic carbon arriving at the sea floor one benthic foram shell 150 m is deposited the correlation can be used to reconstruct organic flux to the sea floor in the past and hence the productivity of past oceans applying the appropriate equations to box core data from the ontong java plateau in the western equatorial pacific we found that productivity during the last glacial maximum exceeded present productivity by a factor of between 1 5 and 2 0 with intermediate values for the mid transition period accumulation of benthic foraminifera was depressed on top of the plateau during the glacial and transitional period presumably because increased winnowing removed part of the food supply

holocene submarine terraces on the western continental shelf of india implications for sea level changes abstract detailed echosounding side scan sonar and high resolution seismic reflection profiling on the western continental shelf of india have revealed a series of submarine terraces at different depths between the outer fringe of the inner shelf and the shelf break being more common between 11 and 20 n the terraces are prominent between water depths of 50 and 115 m and occur at six distinct levels 1 55 60 m 2 65 70 m 3 75 80 m 4 85 90 m 5 95 100 m and 6 110 115 m they are categorized into 1 wave cut terraces 2 coral algal reef induced terraces and 3 palaeo beach barrier terraces the reef induced terraces occur predominantly in the carbonate rich province 20 13 n while both the wave cut and palaeo beach barrier terraces are discernible in the terrigenous regime which is located north and south of these latitudes despite their genetic differences their evolution is ascribed to reef growth progradation and wave activity during the lowstands of sea level and reflect different phases of stillstands of the late pleistocene to mid holocene age

a radiometric calibration of the specmap timescale the astronomical theory of climate change asserts that earth s climate is affected by changes in its orbit which vary the seasonal and latitudinal distribution of solar radiation this theory is the basis of the orbitally tuned specmap timescale a key constraint for this important chronology was the mid point of the penultimate deglaciation initially dated to 127 000 years ago recent work suggests this event may be considerably older casting doubt on the astronomical theory the specmap timescale and the accuracy of orbitally tuned chronologies difficulties with u th coral dating of sea level events have impeded progress on this problem because most corals are not closed systems here we use a new approach to u th dating that corrects for open system behavior and produces a sea level curve of sufficient resolution to confidently correlate with specmap over the last 240 000 years permitting a reassessment of both this critical chronology and a central tenet of climate change theory high precision ages for 24 oxygen isotope events provide a 240 000 year chronology for marine 18o records that is independent of orbital tuning assumptions although there appear to be significant differences between the radiometric and orbitally tuned timescales near the lastglacial maximum and at the marine isotope stage 7 6 boundary a comparison of radiometric and specmap ages for identical isotope events suggest that the specmap timescale is quite accurate and that its errors were in general overestimated despite suborbital complexity orbital cyclicity is clearly evident in our record high amplitude sea level oscillations at periods greater than 20 000 years are very close in phase to summer insolation in the northern hemisphere although sea level changes cannot be uniquely tied to a specific season or latitude of insolation forcing the simplest explanation is that long period high amplitude sea level change is linked to northern hemisphere insolation forcing these results validate the principles of orbital tuning and suggest such timescales are generally robust

holocene climate variability although the dramatic climate disruptions of the last glacial period have received considerable attention relatively little has been directed toward climate variability in the holocene 11 500 cal yr b p to the present examination of similar to50 globally distributed paleoclimate records reveals as many as six periods of significant rapid climate change during the time periods 9000 8000 6000 5000 4200 3800 3500 2500 1200 1000 and 600 150 cal yr b p most of the climate change events in these globally distributed records are characterized by polar cooling tropical aridity and major atmospheric circulation changes although in the most recent interval 600 150 cal yr b p polar cooling was accompanied by increased moisture in some parts of the tropics several intervals coincide with major disruptions of civilization illustrating the human significance of holocene climate variability c 2004 university of washington all rights reserved

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

coccolithophore fluxes from sediment traps in the northeastern arabian sea off pakistan abstract we investigated coccolithophore fluxes from four sediment traps located in the northeastern arabian sea at the continental slope of pakistan two moorings wpt and ept western isastern pakomin trap consisting of one and two sediment traps were deployed at water depths of about 500 m and 1500 m they collected settling particles from october 1993 to february 1994 and from may 1995 to february 1996 at intervals of 22 and 24 days respectively a longer sampling was prevented probably due to high sedimentation events which occluded the trap cones both areas were characterised by a strong seasonality in coccolith fluxes high fluxes were recorded with up to 2000 10 6 coccoliths m 2 d 1 in the early sw summer monsoon and up to 5400 10 6 coccoliths m 2 d 1 in the early ne winter monsoon generally coccosphere fluxes exhibited a similar trend but were some orders of magnitude lower than coccolith fluxes twenty seven taxa were identified in this study all well to moderately well preserved and with a small range of diversity the species composition was dominated by gephyrocapsa oceanica florisphaera profunda and emiliania huxleyi making up about 70 of the assemblages during the sw summer monsoon high productivity in the surface waters of the eastern arabian sea may be linked to the upwelling system off oman apparently nutrient rich surface water derived from the southwestern upwelling areas off oman with high standing stocks were carried into this area by northeast flowing currents in contrast during the ne winter monsoon the locally observed high coccolithophore production is hypothesised to respond to local injections of nutrient rich deep water into the surface water due to sea surface cooling leading to convection consequently fluxes during the winter monsoon were in the same range as during the summer monsoon

paleoproductivity the benthic planktonic ratio in foraminifera as a productivity index abstract when the effects of differential dissolution are excluded the benthic to planktonic ratio in deep sea foraminifera can be read as a productivity index for pelagic conditions we use the bz index which is the product of the benthic planktonic ratio in percent and the depth of deposition which controls supply of organic matter for hemipelagic conditions we use bz d which is the product of the bz value and a factor for proximity to the shore square root of distance from land which controls coastal productivity anomalous values readily stand out from the normal populations which cluster around typical values of bz or bz d off northwest africa wherever calcite dissolution can be excluded as a factor because of presence of aragonite these anomalies are due to lateral supply of redeposited organic matter

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

sea surface temperatures during the sw and ne monsoon seasons in the western arabian sea over the past 20 000 years abstract the western arabian sea is influenced by the seasonal southwest and northeast monsoon wind systems in the modern day sw monsoon induced upwelling of cold water leads to lowest ssts in summer while in glacial periods weakened upwelling and increased cooling by ne monsoon winds may have resulted in lowest sst in winter in order to reconstruct the western arabian sea seasonal sea surface temperature sst evolution during the monsoons over the past 20 000 years a novel proxy is used that captures the contrast in seasonal ssts the presented proxy concerns the difference in 18o between two shallow dwelling species of planktonic foraminifera globigerinoides ruber which calcifies throughout the year and globigerina bulloides which mainly calcifies during sw monsoon driven upwelling we convert this 18o difference to the difference in calcification temperature tcrub bul and use it in combination with mg ca derived temperatures to reconstruct seasonal ssts we present the monsoon evolution record of core niop929 located nw of the island of socotra based on our results we distinguish three distinct modes i a glacial monsoon mode 20 13 ka bp characterised by weakly negative tcrub bul values and sw monsoon ssts tsw that are 2 c higher than ne monsoon ssts tne this pattern is indicative for a weak sw monsoon and stronger cooling by glacial ne monsoon winds compared to the modern situation ii a transitional mode 13 8 ka bp characterised by tcrub bul values around 0 and thus a reduced difference between tsw and tne iii the modern monsoon mode which started at 8 ka bp with the main shift toward low summer ssts and high winter ssts the modern mode is characterised by tcrub bul values around 4 c indicative of a strong sw monsoon associated with strong upwelling and weak influence of the ne monsoon on sst we propose that measuring mg ca on both species will improve the accuracy of the sst estimates

modulation and amplification of climatic changes in the northern hemisphere by the indian summer monsoon during the past 80 k y high frequency suborbital variations dansgaard oeschger cycles characterize the climatic history of the northern hemisphere as observed in greenland ice cores deep sea sediments of the north atlantic the californian borderland the arabian sea the south china sea and the chinese loess area paleoceanographic data from core kl126 from the bay of bengal in combination with data from the other asian monsoonal areas indicate that the feedback processes involving snow and dust of the tibetan plateau vary the summer monsoon capacity to transport moisture into central south asia and into the atmosphere we postulate that the summer monsoon initiates amplifies and terminates these cycles in the northern hemisphere

the depth dependency of planktonic benthic foraminiferal ratios constraints and applications abstract study of the ratio between planktonic and benthic foraminifera in a great number of areas shows that variation of this ratio with depth can be described using organic matter flux equations essentially the share of benthic foraminifera in the total association is inversely proportional to depth as is the amount of organic matter resulting from primary productivity reaching the sea bottom variation in the p b ratio from area to area appears to be strongly dependent on the amount of inbenthic living foraminifera if the ratios are corrected for this the regressions between the proportion of planktonic foraminifera p and depth appear to be near identical in the gulf of mexico the gulf of california the west coast of the usa and the adriatic sea this regression can be described by depth e 3 58718 0 03534 p a study of the behaviour of this function in nine cores from the adriatic upper quaternary reveals that the palaeodepth reconstructions are not influenced by fluctuations in productivity and temperature but that they are significantly influenced by redeposition of fine grained deposits

sharp decrease in summer monsoon strength 4000 3500 cal yr b p in the central higher himalaya of india based on pollen evidence from alpine peat age constrained pollen data and magnetic susceptibility of an alpine peat profile from the garhwal higher himalaya display a continuous record of climate and monsoon trends for the past 7800 yr about 7800 cal yr b p dominance of evergreen oak quercus semecarpifolia alder alnus and grasses in the pollen record reflect a cold wet climate with moderate monsoon precipitation from 7800 to 5000 cal yr b p vegetation was progressively dominated by conifers indicating ameliorated climate with a stronger monsoon a warm humid climate with highest monsoon intensity from 6000 4500 cal yr b p represents the mid holocene climatic optimum between 4000 and 3500 cal yr b p the abundance of conifers sharply decreased with the greatest increase in evergreen oak this trend suggests progressive cooling with a decrease in the monsoon to its minimum about 3500 cal yr b p two relatively minor cold dry events at ca 3000 and 2000 cal yr b p marked step wise strengthening of the monsoon until ca 1000 cal yr b p after a cold dry episode that culminated ca 800 cal yr b p the monsoon again strengthened and continued until today a sharp decrease in temperature and rainfall at 4000 3500 cal yr b p represents the weakest monsoon event of the holocene record this cold dry event correlates with proxy data from other localities of the indian subcontinent arabian sea and western tibet

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

processes driving estuary infilling by marine sands on an embayed coast abstract detailed measurements of waves currents and sediment transport from an intertidal sandflat at the mouth of a partially filled new zealand estuary in an embayment with low littoral drift are presented with a view to establishing how marine sands are transported into the estuary waves mobilised sediments during episodic events early in events when waves were energetic sediments were in motion throughout the tidal cycle under abating waves sediment motion became intermittent finally becoming restricted to periods around low tide when wave orbital motions were able to penetrate to the bed three components of the total sediment flux were estimated from the data and analysed 1 a wind driven current which presumably has a complicated spatial expression in the vicinity of the estuary mouth controlled the net i e integrated over event direction of flux of suspended sediment entrained by waves and advected by currents there was no evidence of non symmetry over the tidal cycle in the suspension process that might drive a net sediment flux however there is some suggestion that lag in growth and decay of the estuary wave field over the tidal cycle systematically enhances offshore transport 2 net bedload transport by waves and currents was directed onshore which was guaranteed by two mechanisms firstly increasing wave orbital current skewness as the tide ebbed turned bedload transport onshore late in the ebb tide against the current and secondly bedload peaked early in the flood tide when skewed waves were reinforced by the flooding current 3 correlation between seaward directed forced mean flow and enhanced suspension under groups of high waves resulted in persistent offshore flux of suspended sediment at infragravity frequencies suspended sediment flux carried by gravity waves was directed seawards on flood tides and counter to the waves and onshore on ebb tides and with the waves which was explained in terms of a simple vortex ejection model we conclude that sediment transport on the sandflat at the mouth of this partially filled estuary is governed by subtle interactions between waves and currents that vary over the tidal cycle some interactions such as those that drive bedload transport promote estuary infilling by marine sands and others such as those that drive suspended sediment flux at infragravity frequencies do the opposite

timing and structure of the 8 2 kyr b p event inferred from δ18o records of stalagmites from china oman and brazil oxygen isotope records of stalagmites from china and oman reveal a weak summer monsoon event with a double plunging structure that started 8 21 0 02 kyr b p an identical but antiphased pattern is also evident in two stalagmite records from eastern brazil indicating that the south american summer monsoon was intensifi ed during the 8 2 kyr b p event these records demonstrate that the event was of global extent and synchronous within dating errors of 50 years in comparison with recent model simulations it is plausible that the 8 2 kyr b p event can be tied in changes of the atlantic meridional overturning circulation triggered by a glacial lake draining event this in turn affected north atlantic climate and latitudinal position of the intertropical convergence zone resulting in the observed low latitude monsoonal precipitation patterns

monsoon influenced variations in productivity and lithogenic flux along offshore saurashtra ne arabian sea during the holocene and younger dryas a multi proxy approach abstract a sediment core from ne arabian sea was studied to reveal the variations in shelf environment of western continental margin of india a multi proxy analysis based on planktonic foraminifera abundance pfa benthic foraminifera abundance bfa planktonic benthic foraminiferal ratio p b caco 3 percentage wt oxygen 18 o g ruber and carbon 18 o g ruber isotopes of foraminifera as well as sediment x ray studies were carried out on 3 4 m long core sk 240 485 recovered from offshore saurashtra ne arabian sea the study aims to understand the monsoon variability in the ne arabian sea offshore saurashtra since the late pleistocene holocene transition and how monsoon climate coupled with sea level change influenced paleo productivity pattern six ams radiocarbon dates place the core in the time interval 12 1 ka our study reveals that there have been three periods of major changes in the monsoonal climate productivity and sea level viz 12 8 ka younger dryas and early holocene 8 4 ka middle holocene and 4 1 ka late holocene the studied time period was also marked by weakened south west monsoon swm during the cold events such as younger dryas yd abrupt event ae centring around 9 8 ka as well as 8 2 and 4 ka cold events the younger dryas and early holocene shows the low sea level stand and less indus river discharge thereafter during middle and late holocene the monsoon strengthened which resulted in raised sea level and increased indus river discharge the proxy records broadly suggest relatively low foraminiferal productivity at the core location during the younger dryas and early holocene we record a moderate foraminiferal productivity during the middle holocene between 8 and 4 ka which suggest the mesotrophic condition the foraminiferal productivity however was relatively high since 4 ka suggesting the eutrophic conditions at the core site

gas hydrate dissociation prolongs acidification of the anthropocene oceans anthropogenic warming of the oceans can release methane ch4 currently stored in sediments as gas hydrates this ch4 will be oxidized to co2 thus increasing the acidification of the oceans we employ a biogeochemical model of the multimillennial carbon cycle to determine the evolution of the oceanic dissolved carbonate system over the next 13 kyr in response to co2 from gas hydrates combined with a reasonable scenario for long term anthropogenic co2 emissions hydrate derived co2 will appreciably delay the neutralization of ocean acidity and the return to preindustrial like conditions this finding is the same with ch4 release and oxidation in either the deep ocean or the atmosphere a change in caco3 export coupled to ch4 release would intensify the transient rise of the carbonate compensation depth without producing any changes to the long term evolution of the carbonate system overall gas hydrate destabilization implies a moderate additional perturbation to the carbonate system of the anthropocene oceans

evaporation precipitation changes in the eastern arabian sea for the last 68 ka implications on monsoon variability 1 variations in sea surface temperature sst 18o of sea water 18ow and salinity were reconstructed for the past 68 ka using a sediment core aas9 21 from the eastern arabian sea eas in order to understand the changes in evaporation and precipitation associated with the monsoon system the mg ca derived sst record varies by 4 c it shows that marine isotope stage mis 4 was warmer than mis 3 that the last glacial maximum was 4 c cooler than the present and that there was a 2 c increase within the holocene mis 4 records higher 18ow and salinity values than mis 2 suggesting variable flow of low salinity bay of bengal flow into the eas during glacial periods the transition from mis 4 to mis 3 was marked with a conspicuous shift from higher to lower 18ow values which reflects a decrease in the evaporation precipitation budget in the eas perhaps due to the strengthening of southwest monsoon monsoon reconstructions based on 18ow reveal that monsoon driven precipitation was higher during mis 3 and mis 1 and was lower during mis 2 and mis 4 this is consistent with earlier monsoon reconstructions based on upwelling indices from the western arabian sea however the amplitude of monsoon fluctuations derived through upwelling indices and 18ow varies significantly which may indicate spatial variability of monsoon rainfall

timing of millennial scale climate change in antarctica and greenland during the last glacial period a precise relative chronology for greenland and west antarctic paleotemperature is extended to 90 000 years ago based on correlation of atmospheric methane records from the greenland ice sheet project 2 and byrd ice cores over this period the onset of seven major millennial scale warmings in antarctica preceded the onset of greenland warmings by 1500 to 3000 years in general antarctic temperatures increased gradually while greenland temperatures were decreasing or constant and the termination of antarctic warming was apparently coincident with the onset of rapid warming in greenland this pattern provides further evidence for the operation of a bipolar see saw in air temperatures and an oceanic teleconnection between the hemispheres on millennial time scales

deglaciation in the tropical indian ocean driven by interplay between the regional monsoon and global teleconnections abstract high resolution climate records of the ice age terminations from monsoon dominated regions reveal the interplay of regional and global driving forces speleothem records from chinese caves indicate that glacial terminations were interrupted by prominent weak monsoon intervals wmi lasting a few thousand years deglacial wmis are interpreted as the result of cold temperature anomalies generated by sea ice feedbacks in the north atlantic most prominently during heinrich events recent modeling results suggest however that wmis reflect changes in the intensity of the indian rather than the east asian monsoon here we use foraminiferal trace element mg ca and ba ca and stable isotope records from a sediment core off the malabar coast in the southeastern arabian sea with centennial scale resolution to test this hypothesis and to constrain the nature and timing of deglacial climate change in the tropical indian ocean the malabar deglacial sst record is unique in character and different from other tropical climate records sst at the last glacial maximum was 2 7 0 5 c colder than pre industrial sst deglacial warming started at 18 6 95 ci range 18 8 18 1 kyr bp within error of the onset of warming at other tropical sites as well as in antarctica and the southern ocean and either coeval with or up to 1 kyr before the atmospheric co 2 rise warming took place in two steps separated by an interval of stable sst between 15 7 16 2 14 9 and 13 2 13 9 12 0 kyr bp the 18 o water record and the ba ca record which is a measure of indian sub continent riverine runoff indicate that the last ice age termination was marked by a prominent weak indian monsoon interval interrupted by an intense monsoon phase as seen in speleothem records and predicted by modeling a strong correspondence between the timing of the malabar 18 o sw record and the hulu cave monsoon record suggests that deglacial 18 o changes in both localities dominantly reflect compositional changes in precipitation likely driven by changes in the north atlantic

abrupt weakening of the indian summer monsoon at 8 2 kyr b p article history an oxygen isotope record of biogenic carbonate from paleolake riwasa in northwestern nw india provides a history of the indian summer monsoon ism from 11 to 6k yr b p the lake was dry throughout the late glacial period when aeolian sands were deposited lacustrine sedimentation commenced in the early holocene and the lake deepened significantly at 9 4 kyr b p indicating a strengthening of the ism in response to summer insolation forcing this high lake stand was interrupted by an abrupt desiccation which is marked by a 12 cm limestone hardground that formed during a period of sub aerial exposure after 8 3 kyr b p the base of the hardground surface coincides with the beginning of the 8 2 kyr b p cooling event in the north atlantic that has been associated with a glacial outburst flood and slowdown of atlantic meridional overturning circulation the hardground provides robust evidence of a weakening of the ism on the indian subcontinent at 8 2 kyr b p and supports previous results of a strong teleconnection between monsoon asia and north atlantic climate lacustrine sedimentation resumed at 7 9 kyr b p suggesting the 8 2 kyr desiccation of paleolake riwasa represented an abrupt response of the ism to forcing from the north atlantic