propagation and mechanism of decadal upper ocean variability in the north pacific n n two types of anomaly pathways associated with decadal thermocline variability in the north pacific ocean are identified on constant density surfaces isopycnals one westward and the other southwestward around the subtropical gyre a theory based on two baroclinic planetary wave modes in the thermocline is proposed to account for the observed variability pattern the variability along the westward wave path is ascribed to the non doppler shift ist mode and seems to be forced mainly by wind stress forcing the anomaly along the southwestward subduction path is associated with the advective nature of the 2nd mode and could be excited mainly by surface buoyancy anomalies this study may provide a dynamically unified three dimensional picture of decadal thermocline variability in the north pacific ocean

developments in geothermal resources 1983 1988 hydrothermal resources one of the several types of geothermal resources are being actively developed on a worldwide basis other types of geothermal energy geopressured hot dry rock and magma remain uneconomic but show considerable promise for the future technical problems and low energy prices inhibit the development of each of the 4 geothermal types geothermal energy is used both for generation of electricity and for direct heat applications use of geothermal energy is desirable because it is an environmentally clean utility compatible source of energy that directly displaces the need for more nuclear plants and frees petroleum for other important uses current worldwide hydrothermal generating capacity is about 5 457 electrical megawatts mwe in 18 countries with the united states accounting for 2 609 mwe of the total current worldwide direct uses of hydrothermal energy amount to about 10 000 thermal megawatts mwt geothermal development in the united states currently is depressed due to comparatively low energy costs and a temporary excess in electrical generating capacity because of these factors as well as lack of adequate technology only a small portion of the known hydrothermal resource base can be used economically today

records of the nd isotope composition of seawater from the bay of bengal implications for the impact of northern hemisphere cooling on itcz movement abstract this study presents a record of planktonic foraminiferal neodymium isotopic gradients along a north south transect in the bay of bengal during time slices of late holocene and last glacial maximum lgm age together with a record of planktonic foraminiferal variation in the northern bay of bengal 15 n over the last 195 ky in late holocene core top planktonic foraminifera the north south end gradient rises from nonradiogenic values of 12 at 20 n to 10 at 5 n in parallel with the modern surface salinity gradient controlled by discharge of himalayan rivers in the northern bay during the lgm end increased throughout the bay the contrast between northernmost and southernmost sites decreased and maximum end values of 6 5 occurred between 12 and 15 n a small part of the shift to higher mean end throughout the bay during the glacial may arise from a uniform increase in deposition of far field dust from arabian and persian gulf regions however the spatial pattern of end variation between lgm and late holocene also suggests a shift from modern dominance of nonradiogenic nd sources from the ganges brahmaputra basin to lgm dominance of more radiogenic nd sources from arakan coastal rivers over the last 195 ky at 15 n the most radiogenic end values of 7 occur at glacial maxima and the most nonradiogenic values of 11 occur during interglacials end values are highly correlated with glacial interglacial variations in planktonic foraminiferal 18o in this record shifts in river sources from the more northerly ganges brahmaputra watershed to the more southerly arakan coastal river systems respond dominantly to inter tropical convergence zone itcz movement driven by northern hemisphere cooling during 100 ky glacial interglacial cycles with a small component of variation on precessional timescales the nonlinear correlation of end with ice volume suggests that itcz movement responds to aerial coverage of ice sheets and snow rather than to ice thickness and volume these data add support to recent general circulation models of itcz response to northern hemisphere ice sheets which simulate decreased glacial precipitation in the ganges brahmaputra basin and increased glacial precipitation in the southern arakan coastal basin

midlatitude atmosphere ocean interaction during el nino part i the north pacific ocean abstract atmosphere ocean experiments are experiments are used to investigate the formation of sea surface temperature sst anomalies in the north pacific ocean during fall and winter of the el nino year experiments in which the ncar community climate model ccm surface fields am used to force a mixed layer ocean model in the north pacific no air sea feedback are compared to simulations in which the ccm and north pacific ocean model are coupled anomalies in the atmosphere and the north pacific ocean during el nino are obtained from the difference between simulations with and without prescribed warm sst anomalies in the tropical pacific in both the forced and coupled experiments the anomaly pattern resembles a composite of the actual sst anomaly field during el nino warm ssts develop along the cost of north america and cold ssts form in the central pacific in the coupled simulations air sea interaction results in a 25 to 50 reduction in the magnitude of the sst and mixed layer depth anomalies

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

holocene aridification of india 1 spanning a latitudinal range typical for deserts the indian peninsula is fertile instead and sustains over a billion people through monsoonal rains despite the strong link between climate and society our knowledge of the long term monsoon variability is incomplete over the indian subcontinent here we reconstruct the holocene paleoclimate in the core monsoon zone cmz of the indian peninsula using a sediment core recovered offshore from the mouth of godavari river carbon isotopes of sedimentary leaf waxes provide an integrated and regionally extensive record of the flora in the cmz and document a gradual increase in aridity adapted vegetation from 4 000 until 1 700 years ago followed by the persistence of aridity adapted plants after that the oxygen isotopic composition of planktonic foraminiferglobigerinoides ruberdetects unprecedented high salinity events in the bay of bengal over the last 3 000 years and especially after 1 700 years ago which suggest that the cmz aridification intensified in the late holocene through a series of sub millennial dry episodes cultural changes occurred across the indian subcontinent as the climate became more arid after 4 000 years sedentary agriculture took hold in the drying central and south india while the urban harappan civilization collapsed in the already arid indus basin the establishment of a more variable hydroclimate over the last ca 1 700 years may have led to the rapid proliferation of water conservation technology in south india

characteristic variations of sea surface temperature with multiple time scales in the north pacific abstract temporal evolution and spectral structure of sea surface temperature sst anomalies in the north pacific over the last 37 years are investigated on the three characteristic time scales shorter than 24 months hf 24 60 months es and longer than 60 months dc the leading empirical orthogonal function eof for the dc time scale is characterized by a zonally elongated monopole centered at around 40 n 180 the leading eof for the hf time scale is somewhat similar to that for the dc time scale although there are two centers of action with the same polarity at the mid and western pacific the leading eof for the es time scale however exhibits a different pattern whose center of action at the mid pacific is located farther southeastward in the time evolution of the sst anomalies associated with the leading eof of the dc time scale several anomaly periods can be identified that last five years or longer the transition from a persistent period to another with the opposite polarity is gene

provenance of the late quaternary sediments in the andaman sea implications for monsoon variability and ocean circulation we present a geochemical and sr nd isotopic study on a sediment core collected from the andaman sea in an attempt to reconstruct the late quaternary weathering and erosion patterns in the watersheds of the river systems of myanmar and understand their controlling factors age control is based on nine radiocarbon dates and 18o stratigraphy the rate of sedimentation was strongly controlled by fluctuations of the monsoon we identify three major sediment provenances 1 the irrawaddy catchment 2 the western slopes of the indo burman arakan iba mountain ranges and the andaman islands and 3 the catchments of salween and sittang and the bengal shelf with the first two contributing 30 60 of the material enhanced contributions from juvenile sources and corresponding positive shifts of 18o are observed at seven time periods 11 14 20 23 36 45 53 57 and 62 ka of which five are synchronous with cooling of the northern hemisphere suggesting a link between the changes in sediment provenances and the shifting of the locus of the summer monsoon southward from the himalayas without substantial reduction in intensity our data and that from other cores in the region suggest that an eastward moving surface current disperses sediments derived from the bengal shelf and western margin of myanmar from the eastern bay of bengal into the western andaman sea and that its strength has increased since the lgm the existence of this current during the lgm implies that the andaman sea and the bay of bengal were well connected during the last glacial period

decadal oscillations in a simple coupled model to study the dynamics that may lead to decadal oscillations in the north pacific a simple coupled model is developed the ocean is based on the linear potential vorticity equation for baroclinic planetary waves the atmosphere is reduced to a nonlocal wind response to thermocline depth anomalies the wind stress has a spatially fixed structure and its amplitude depends on the thermocline perturbation at one location or in a predefined index region such a simple coupled model produces decadal oscillations for suitable parameter choices for realistic wind stress patterns the patterns of oceanic variability are similar to those observed it is determined by the speed of long rossby waves at the coupling latitude the period of the oscillation is rather insensitive to the coupling strength and amounts to approximately twice the time the rossby wave needs to travel from the center of the wind stress curl anomaly to the coupling location a stochastic component to the atmospheric forcing is incorporated by white noise added to the feedback with such a forcing typical oceanic spectra become red with a broad peak at decadal timescales superimposed

long timescale variation in bulk and clay mineral composition of indian continental margin sediments in the bay of bengal arabian sea and andaman sea abstract this study documents x ray diffraction results from bulk powders and oriented clay size aggregates using samples from sites drilled and cored during the indian national gas hydrate expedition 01 nghp01 these sites are located in the krishna godavari basin mahanadi basin and andaman accretionary wedge of the bay of bengal and the kerala konkan basin of the arabian sea calcite is more abundant at the pelagic sites of the andaman sea and kerala konkan basin which is consistent with previous studies of biological productivity and dilution by lithogenous influx hemipelagic sediments in the krishna godavari basin and mahanadi basin are comprised primarily of smectite rich and illite rich clay mineral assemblages respectively we attribute those contrasts to differences in detrital sources between the deccan basalts smectite sources and precambrian rocks of the eastern ghats belt those sources remained consistent over the entire history of sedimentation 0 9 ma higher quartz content in the mahanadi basin and higher feldspar content at the krishna godavari basin reinforce these interpretations of detrital provenance smectite is the most abundant clay mineral in the andaman sea sediments likely due to weathering of volcanic sources along the sunda arc strata from the kerala konkan basin show a shift at 23 ma from a smectite kaolinite clay mineral assemblage to an increasingly illite rich assemblage we also see steady decreases in kaolinite and increases in chlorite and quartz over the 30 myr record which indicates increasing influences of material derived from physical weathering the higher abundance of fully hydrated smectite in the krishna godavari basin may play a minor role in gas hydrate formation by sustaining higher permeabilities at any given value of mudstone porosity or void ratio

on thermocline ventilation of active and passive tracers the ventilation propagation of temperature and passive tracer anomalies are compared in a numerical model although both anomalies tend to have pathways close to the mean ventilation flow the temperature anomaly could have a slower propagation speed and a more complex spatial structure the temperature propagation is better understood in terms of baroclinic planetary waves

the ratio in the cenozoic bengal abyssal fan sediments and its use as a paleostream energy indicator abstract the tio 2 al 2 o 3 ratio in the cenozoic bengal abyssal fan sediments displays decisive potential as a paleostream velocity indicator the reason for this is that even in the finest fan suspendates hydrodynamic sorting determines the amounts of heavy tio2 rich minerals relative to lighter al2o3 rich clay minerals in five deep sea drilling project cores 213 217 which have been recovered in and south of the bay of bengal tio 2 al 2 o 3 ratios increase linearly with time from the late miocene to recent the increase reflects fan progradation and intensified bottom current activity on the southern bengal fan these processes are related to the himalayan elevation by factors such as the maturation of northern india river systems evolution of orographic monsoon rains and elevation attributed increases in denudation rates

vertical variation of oxygen isotope in bay of bengal and its relationships with water masses 1 we present here for the first time comprehensive depth specific near surface to 1800 m oxygen isotope 18o data set of 175 water samples collected from 22 different locations in the bay of bengal bob during july august 2009 and december january 2012 2013 the study is aimed to constrain the water mass parameters using oxygen isotope and salinity four water masses are identified on the basis of temperature salinity relationship a bay of bengal water bobw 0 50 m b mixed zone mz 60 120 m c indonesian throughflow itf 200 500 m and d indian ocean deep water idw 600 1800 m our study shows 1 18o salinity correlation slope 0 15 0 01 intercept 4 58 0 24 r2 0 89 n 54 for the bobw is found to be consistent with surface bob water reported earlier 2 relatively lower correlation r2 0 24 n 47 in underlying mixed zone suggesting mixing of various water masses 3 significant linear correlation between 18o and salinity in idw r2 0 70 indicating depleted less saline water from southern hemisphere spread up to 18 n and 4 vertical profiles at various sampling locations showing a continuous enrichment of 18o 0 6 0 8 within top 60 100 m irrespective of their proximity to coastline in conjunction with a sharp decrease in 14c data below the same depth zone 60 100 m as reported earlier we suggest the 18o value reaches to its acme at a zone of mixing between younger bobw and relatively older itf this preliminary study indicates oxygen isotope and salinity together can be used to identify different water masses in the bob

the effects of decadal oscillations of the curl τ 0 line on intergyre water exchange and temperature variability abstract the effect of meridional movement of the curl 0 line on the intergyre transport is investigated by passive tracer experiments in a double gyre circulation furthermore the contribution to temperature distribution is considered the nonlinear quasigeostrophic reduced gravity model is employed to express a fundamental baroclinic ocean response parameter studies show that a decadal wind migration causes the intergyre exchange much more effectively than does an annual wind migration the efficiency of the intergyre exchange is primarily determined by the wind migration period relative to the necessary time in which a tracer crosses the ocean basin from west to east the meridional movement of the curl 0 line can induce temperature change through two processes 1 entrainment of subtropical subpolar water into the subpolar subtropical gyre along the eastern boundary and 2 a vertical movement of the thermocline propagating as a rossby wave the temperature variability is similar to the

preliminary studies on the geochemistry of the mahanadi river basin india water and suspended and bed sediments were collected during 1986 1987 for the two seasons and analysed to study the geochemistry of the mahanadi river basin which is one of the eight major drainage systems in india the water chemistry reflects the control exercised on weathering by the most abundant lithology namely the carbonates in the basin water composition is in equilibrium with dolomite kaolinite and chlorite xrd studies in suspended and bed sediments show the presence of dolomite kaolinite chlorite and minor quantities of montmorillonite the mahanadi annually delivers 15 74 106t of sediments to the bay of bengal which is high compared to its basin size the dissolved load dominates over physical load by a factor of 4 with 95 of the transport taking place in the monsoon season the basin is characterised by an erosion rate of 138 24 t km 2 yr 1 with a lowering rate of 0 31 mm yr 1 textural studies indicate that the bed sediments are relatively coarser grained than the suspended sediments due to reworking the sediments are finer downstream fe mn cu zn and pb concentrations in the sediments are higher compared to the other peninsular indian rivers eventhough mahanadi transports annually to the bay of bengal 10 of the total load by other indian rivers and its weathering in a complex geological terrain with rich mineral deposits controls to a larger extent the chemistry of the sediments in the bay of bengal

a rotated eof analysis of global sea surface temperature variability with interannual and interdecadal scales abstract spatiotemporal variability of preferred global scale sea surface temperature anomaly patterns is documented applying a varimax rotated empirical orthogonal function r eof analysis to monthly mean sst anomalies the present study focuses especially on the interdecadal variability of leading r eof modes it is first found that temporal variability of r eof1 has a quasi periodicity of 2 5 years and coincides quite well with the occurrence of the enso event hence this mode can be identified with the enso mode and distinguished from the other modes dominated by interdecadal variability the authors find that r eof2 typically shows the dominance of interdecadal variability and signals of the enso phenomenon are removed this mode is characterized by increasing indian ocean sst and decreasing central north pacific sst around 40 50 n in the recent ten or more years a further indication is that both r eof3 and r eof4 which show the dominance of interdecadal variability are fundamentally regarded a

variations of current path velocity and volume transport of the kuroshio in relation with the large meander abstract the variations of the kuroshio current path and their relations with current velocity volume transport and upstream position of the kuroshio are examined using sea level data after the long time non large meander nlm path during 1963 75 the kuroshio takes a large meander lm path during most of 1975 91 1975 80 1981 84 1986 88 and 1989 91 the study of these meanders confirms the description of the path of the kuroshio based on the three typical paths and the transitions between them with an exception being the 1981 84 lm path the formation and decay of the large meander are associated with velocity and position of the kuroshio in the tokara strait south of kyushu a small meander precursor of the large meander seems to be formed southeast of kyushu in relation with a temporary increase of kuroshio velocity and a northward shift of the kuroshio in the tokara strait an eastward propagation of the small meander leading to the lm formation is associated with remaining in the northe

effects of chemical weathering and sorting on the petrogenesis of siliciclastic sediments with implications for provenance studies the bulk chemical compositions mineralogy and mineral proportions of sands and muds of the mallacoota basin in southeastern australia reflect the composition of weathering profiles mantling source rocks rather than bedrock muds contain abundant clay minerals that are virtually absent from the source rocks but abundant in the weathering profiles sands are strongly enriched in quartz relative to source rocks even in the headwaters of the fluvial system demonstrating that feldspar destruction occurs by in situ chemical weathering within profiles and before detritus enters the fluvial system k feldspar is proportionally more abundant in fluvial sands than in source rocks because plagioclase is more rapidly destroyed than either quartz or k feldspar in weathering profiles subsequent erosion and sorting produce sands enriched in quartz with high k feldspar plagioclase ratios relative to source rocks the composition of plagioclase incorporated into the fluvial sands is also controlled by chemical weat

interannual variability in the mid and low latitude western north pacific abstract twenty two years 1967 88 of hydrographic data collected by the japan meteorological agency along the 137 e meridian and surface wind data compiled by florida state university fsu were analyzed to study the interannual variability in the western north pacific in the midlatitude region north of 22 n the dominant signal in the dynamic height field was the interannual path variations of the kuroshio whereas the eastward transport of the kuroshio itself had no significant changes between the straight path and meander path years the net transport of the kuroshio system including recirculations showed a 30 increase during the meander path years in the straight path years when the net transport was small the kuroshio tended to take a straight path with a strong recirculation developed to the south the interannual path variations of the kuroshio strongly influenced the water mass movement in the midlatitudes during the kuroshio meander years we found that a significant portion of the north p

prediction of some weathering trends of plutonic and volcanic rocks based on thermodynamic and kinetic considerations abstract the exposed crust consists mainly of plagioclase 35 quartz 20 k feldspar 11 volcanic glass 12 biotite 8 and muscovite 5 quartz is a resistate thus feldspars and glass represent approximately 75 percent of the labile minerals the weathering characteristics of these constituents are summarized in the context of thermodynamic mass balance and kinetic considerations experimentally determined release rate constants were used to predict the proportions of ca na and k released by feldspars of plutonic rocks granites to gabbros to weathering solutions the chemical weathering trends of the weathered residues calculated from the kinetic data conform closely to the initial trends observed in some recent weathering profiles demonstrating the accuracy of the predictions since the weathering of feldspars is controlled by processes that should not change through geological time the relative release rates of ca na and k from the feldspars of granitic rocks can be calculated for future and past episodes of continental weathering experimentally determined release rate constants are not available for a wide range of volcanic glass compositions but the limited data indicate that compositional trends are predictable in weathering profiles developed on volcanic rocks the kinetic data available for rhyolitic glasses accurately predict the initial weathering trends observed in a recent rhyolite weathering profile

geomorphic tectonic control of sediment discharge to the ocean the importance of small mountainous rivers analysis of data from 280 rivers discharging to the ocean indicates that sediment loads yields are a log linear function of basin area and maximum elevation of the river basin other factors controlling sediment discharge e g climate runoff appear to have secondary importance a notable exception is the influence of human activity climate and geology on the rivers draining southern asia and oceania sediment fluxes from small mountainous rivers many of which discharge directly onto active margins e g western south and north america and most high standing oceanic islands have been greatly underestimated in previous global sediment budgets perhaps by as much as a factor of three in contrast sediment fluxes to the ocean from large rivers nearly all of which discharge onto passive margins or marginal seas have been overestimated as some of the sediment load is subaerially sequestered in subsiding deltas before the proliferation of dam construction in the latter half of this century rivers

interdecadal variability over the north pacific in a multi century climate simulation interdecadal variability in the north pacific region is investigated in a 500 y control integration of the hamburg echam lsg coupled ocean atmosphere general circulation model the spectrum is predominantly red but a significant peak with a period of about 18 y is detected in the spectrum of sea surface temperature sst this peak is shown to be associated with an irregular oscillation that involves both the model ocean and atmosphere the sst sea level pressure and geopotential height at 500 hpa all undergo a primarily standing oscillation with an extensive monopole structure centered near the date line the surface anticyclone is situated to the northeast of the warm sst anomaly and there is a small westward tilt with height temporal changes are approximately in phase the anomalous surface heat flux accompanying the warm phase of sst is primarily out of the ocean but is compensated by anomalous warm advection by surface currents allowing the sst anomaly to persist oceanic thermocline anomalies propagate northward in the western pacific and lag the atmosphere indicating a disequilibrium with the atmosphere sub surface thermal advection appears to play an important role a comparison is made between the model s 18 y oscillation and oscillatory components identified in an analysis of the gisst observational sst dataset which have periods of approximately 6 and roughly 30 y

indian monsoonal variations during the past 80 kyr recorded in nghp 02 hole 19b western bay of bengal implications from chemical and mineral properties

monsoon source shifts during the drying mid holocene biomarker isotope based evidence from the core monsoon zone cmz of india abstract a better understanding of past variations of the indian summer monsoon ism that plays a vital role for the still largely agro based economy in india can lead to a better assessment of its potential impact under global climate change scenarios however our knowledge of spatiotemporal patterns of ism strength is limited due to the lack of high resolution continental paleohydrological records here we reconstruct centennial scale hydrological variability during the holocene associated to changes in the intensity of the ism based on a record of lipid biomarker abundances and compound specific stable isotopic composition of a 10 m long sediment core from saline alkaline lonar lake situated in the core monsoon zone of central india we identified three main periods of distinct hydrology during the holocene in central india the period between 10 1 and 6 cal ka bp was likely the wettest during the holocene lower average chain length acl index values 29 4 28 6 and negative 13 c wax values 34 8 to 27 8 of leaf wax n alkanes indicate the dominance of woody c 3 vegetation in the catchment and negative d wax values concentration weighted average 171 to 147 suggest a wet period due to an intensified monsoon after 6 cal ka bp a gradual shift to less negative 13 c wax values particularly for the grass derived n c 31 and appearance of the triterpene lipid tetrahymanol generally considered as a marker for salinity and water column stratification mark the onset of drier conditions at 5 1 cal ka bp an increasing flux of leaf wax n alkanes along with the highest flux of tetrahymanol indicate a major lowering of the lake level between 4 8 and 4 cal ka bp we find evidence for a transition to arid conditions indicated by high and strongly variable tetrahymanol flux in addition a pronounced shift to less negative 13 c wax values in particular for n c 31 25 2 to 22 8 during this period indicates a change of dominant vegetation to c 4 grasses in agreement with other proxy data such as deposition of evaporite minerals we interpret this period to reflect the driest conditions in the region during the last 10 1 ka this transition led to protracted late holocene arid conditions after 4 ka with the presence of a permanent saline lake supported by the sustained presence of tetrahymanol and more positive average d wax values 122 to 141 a late holocene peak of cyanobacterial biomarker input at 1 3 cal ka bp might represent an event of lake eutrophication possibly due to human impact and the onset of cattle livestock farming in the catchment a unique feature of our record is the presence of a distinct transitional period between 4 8 and 4 cal ka bp which was characterized by some of the most negative d wax values during the holocene up to 180 when all other proxy data indicate the driest conditions during the holocene these negative d wax values can as such most reasonably be explained by a shift in moisture source area and or pathways or rainfall seasonality during this transitional period we hypothesize that orbital induced weakening of the summer solar insolation and associated reorganization of the general atmospheric circulation as a possible southward displacement of the tropical rainbelt led to an unstable hydroclimate in central india between 4 8 and 4 ka our findings shed light onto the sequence of changes during mean state changes of the monsoonal system once an insolation driven threshold has been passed and show that small changes in solar insolation can be associated with major hydroclimate changes on the continents a scenario that may be relevant with respect to future changes in the ism system

geochemistry of fine grained clastic sediments in the archean abitibi greenstone belt canada implications for provenance and tectonic setting abstract archean sandstone and shale samples from turbiditic tf and alluvial facies af in the southern volcanic zone of the abitibi greenstone belt canada have been analyzed for major and trace elements the sandstones from tf are mainly greywackes whereas those from af are lithic arenite sio 2 ranges from 51 to 68 geochemically the clastic sediments cluster into mafic element mep and low mafic element lmep populations the mep sediments which include turbiditic facies sediment samples from the larder lake group in the kirkland lake area are characterized by elevated abundances of mgo 5 ni 200 ppm cr 400 ppm sc 22 ppm and feo 7 5 abundances lower contents of incompatible elements such as th u ta hf zr and total rees n ratios are 4 5 with eu eu 1 the lmep sediments which include samples from the beatty dome and three nations lake formations in timmins the kewagama group noranda area and timiskaming group in the kirkland lake area however show reverse abundance distributions the geochemical gaps shown by the major and trace elements define two populations of sediments suggesting contrasting provenances for them the mep sediments require a dominantly mafic and ultramafic 90 source with 10 felsic contribution whereas the lmep sediments require a mixture of felsic 75 and mafic 25 rocks this compositional distribution of the sediments is closely related to their tectonic environments the mep was formed in basins proximal to or within an active oceanic rift consequently having ultramafic and mafic rocks as the major source for the lmep calc alkaline volcanic sequences formed in an island arc like setting were the major source these two contrasting volcanic plutonic terranes were tectonically juxtaposed during late archean collisional tectonics

geochemical record of holocene to recent sedimentation on the western indus continental shelf arabian sea 1 we present a multiproxy geochemical analysis of two cores recovered from the indus shelf spanning the early holocene to recent 14 ka indus 23 is located close to the modern indus river while indus 10 is positioned 100 km further west the holocene transgression at indus 10 was over a surface that was strongly weathered during the last glacial sea level lowstand lower holocene sediments at indus 10 have higherendvalues compared to those at the river mouth indicating some sediment supply from the makran coast either during the deposition or via reworking of older sediments outcropping on the shelf sediment transport from makran occurred during transgressive intervals when sea level crossed the mid shelf the sediment flux from non indus sources to indus 10 peaked between 11 ka and 8 ka a hiatus at indus 23 from 8 ka until 1 3 ka indicates non deposition or erosion of existing indus shelf sequences higherendvalues seen on the shelf compared to the delta imply reworking of older delta sediments in building holocene clinoforms chemical index of alteration cia mg al and sr isotopes are all affected by erosion of detrital carbonate which reduced through the holocene k al data suggest that silicate weathering peaked ca 4 6 ka and was higher at indus 10 compared to indus 23 fine grained sediments that make up the shelf have geochemical signatures that are different from the coarser grained bulk sediments measured in the delta plain the indus shelf data highlight the complexity of reconstructing records of continental erosion and provenance in marine settings

late archaean granites a typology based on the dharwar craton india abstract extensive field work in the eastern dharwar craton associated with petrographic and geochemical major and trace elements investigations allows four main types of late archaean granitoids to be distinguished 1 na rich granitoids of trondhjemitic tonalitic and granodioritic composition ttg that are characterised by strongly fractionated ree patterns and low hree contents and generally interpreted as slab melts generated by partial melting of metamorphosed hydrated basalt most likely in a subduction environment 2 sanukitoids which are k and mg rich monzonites and granodiorites with ttg like ree patterns associated with marked lile enrichment and considered to result from the reaction of slab melts generated in a subduction environment with and assimilation of mantle wedge peridotite 3 uncommon high hfse mg and k granites with strongly ree and lile enrichment that probably formed by partial melting of an enriched mantle source unlike in the genesis of sanukitoids in this case the slab melt is considered to be wholly consumed by reaction with mantle minerals resulting in mantle enrichment subsequent melting of this enriched mantle probably in a post subduction setting gives rise to high hfse mg and k magmas as demonstrated for the closepet granite dharwar craton the hot mantle derived magma can induce melting of continental crust and then mix with the anatectic products 4 k rich mg poor anatectic biotite granites with ree patterns that are less fractionated and show negative eu anomalies these granites result from the remelting of old basement or recently accreted plutons both with ttg compositions such anatexis can occur either in a subduction or in a post subduction environment this typology based on the well exposed dharwar craton can be extended to late archaean granitoids from all over the world about such 500 analysis were compiled and a number of discriminant diagrams based on both major and trace elements are proposed the most likely tectonic setting for the observed rock types is an accretionary orogen with accretion of continental blocks above a subduction system followed by thermal reworking of the newly accreted continental material however it has been found that archaean subduction related granitoids are significantly different from their modern counterparts implying progressive changes in the modes of magma generation at convergent margins from the archaean to the present

multispecies approach to reconstructing eastern equatorial pacific thermocline hydrography during the past 360 kyr 1 stable isotope data from eastern equatorial pacific eep core tr163 19 2 15 n 90 57 w 2348 m are presented for the surface dwelling foraminifers globigerinoides ruber and g sacculifer and thermocline dwelling globorotalia menardii and neogloboquadrina dutertrei using species specific normalization factors derived from experimental and plankton tow data we reconstruct a 360 kyr record of water column hydrography across the past three glacial cycles we demonstrate that g ruber maintains a mixed layer habitat throughout the entire record while g sacculifer records a mixture of thermocline and mixed layer conditions and g menardii and n dutertrei record thermocline properties we conclude that g sacculifer is not appropriate for paleoceanographic applications in regions with steep vertical hydrographic gradients results suggest that this region of the eep had a thicker mixed layer and deeper 13cdic boundary between the surface and equatorial undercurrent during the last two glacial periods a shift in n dutertrei and g sacculifer geochemistry prior to 185 kyr suggests water column structure and chemocline gradients changed possibly due to a shift in the position of the undercurrent relative to this site the timing and magnitude of glacial interglacial 13c variations between species indicates that near surface carbon chemistry is controlled by changes in productivity atmospheric circulation and advected intermediate water sources north of the antarctic polar front these results demonstrate that when properly calibrated for species differences multispecies geochemical data sets can be invaluable for reconstructing water column structure and properties in the past

oxygen isotope evidence for a stronger winter monsoon current during the last glaciation a variety of palaeoclimate data from the northern indian ocean has shown that the asian summer monsoon was weaker during the last glacial maximum 18 000 years ago than it is today1 5 it has also been inferred from these data that the winter monsoon was stronger at that time5 here we present evidence that the transport of low salinity water from the bay of bengal to the arabian sea caused by the winter monsoon6 was higher during the last glacial maximum this inference is based on a negative excursion up to about 1 in magnitude in the oxygen isotope ratios of three planktonic foraminiferal species detected in a sediment core from the arabian sea by high resolution 1 2 cm sampling our results place an upper limit of about 4 000 years on the length of time during which the winter monsoon was stronger than today

on the relationship between tropical and north pacific sea surface temperature variations abstract empirical orthogonal function analysis of winter sea surface temperature sst anomalies over the pacific domain 60 n 20 s reveals an el nino southern oscillation enso mode that is linked to the eastern north pacific and a north pacific mode that is linearly independent of enso the north pacific mode exhibits maximum amplitude and variance explained along 40 n west of 170 w ssts in this region have decreased by 1 5 c from 1950 to 1987 the cooling in winter has been associated with a strengthening of the overlying westerly winds

upper ocean thermal variations in the north pacific during 1970 1991 abstract a newly available extensive compilation of upper ocean temperature profiles was used to study the vertical structure of thermal anomalies between the surface and 400 m depth in the north pacific during 1970 1991 a prominent decade long perturbation in climate occurred during this time period surface waters cooled by 1 c in the central and western north pacific and warmed by about the same amount along the west coast of north america from late 1976 to 1988 comparison with data from coads suggests that the relatively sparse sampling of the subsurface data is adequate for describing the climate anomaly the vertical structure of seasonal thermal anomalies in the central north pacific shows a series of cold pulses beginning in the fall of 1976 and continuing until late 1988 that appear to originate at the surface and descend with time into the main thermocline to at least 400 m depth individual cold events descend rapidly 100 m yr 1 superimposed upon a slower cooling 15 m yr 1 the inter

the ciw index a new chemical index of weathering abstract a new chemical index of weathering that can be applied to modern soils and precambrian paleosis is proposed ciw al2o3 the value of this index increases as the degree of weathering increases and the difference between ciw index values of the silicate parent rock and soil or sediment reflects the amount of weathering experienced by the weathered material

a simple kinematic mechanism for mixing fluid parcels across a meandering jet abstract recent observations of fluid parcel pathways in the gulf stream using isopycnal rafos floats revealed a striking pattern of cross stream and vertical motion associated with meanders bower and rossby 1989 in an attempt to explain the observed pattern a two dimensional kinematic model of a meandering jet has been developed which enables examination of the relationship between streamfunction patterns and fluid parcel trajectories the streamfunction fields are displayed in a reference frame moving with the wave pattern so motions of fluid parcels relative to the jet can be seen more easily the results suggest that the observed pattern of cross stream motion results primarily from the downstream phase propagation of meanders the model successfully reproduces several of the most distinctive features of the float observations 1 entrainment of fluid into the gulf stream occurs at the leading edges of meander extrema while detrainment takes place at the trailing edges 2 exchange between the gu

climate impact of late quaternary equatorial pacific sea surface temperature variations magnesium calcium data from planktonic foraminifera in equatorial pacific sediment cores demonstrate that tropical pacific sea surface temperatures ssts were 2 8 0 7 c colder than the present at the last glacial maximum glacial interglacial temperature differences as great as 5 c are observed over the last 450 thousand years changes in sst coincide with changes in antarctic air temperature and precede changes in continental ice volume by about 3 thousand years suggesting that tropical cooling played a major role in driving ice age climate comparison of sst estimates from eastern and western sites indicates that the equatorial pacific zonal sst gradient was similar or somewhat larger during glacial episodes extraction of a salinity proxy from the magnesium calcium and oxygen isotope data indicates that transport of water vapor into the western pacific was enhanced during glacial episodes

a 900 year 600 to 1500 a d record of the indian summer monsoon precipitation from the core monsoon zone of india 1 we present a near annually resolved record of the indian summer monsoon ism rainfall variations for the core monsoon region of india that spans from 600 to 1500 a d from a 230th dated stalagmite oxygen isotope record from dandak cave our rainfall reconstruction which spans the medieval warm period mwp and the earliest portion of the little ice age lia indicates that the short instrumental record of ism underestimates the magnitude of monsoon rainfall variability periods of severe drought lasting decades occurred during the 14th and mid 15th centuries and coincided with several of india s most devastating famines

on the predictability of decadal changes in the north pacific the predictability of decadal changes in the north pacific is investigated with an ocean general circulation model forced by simplified and realistic atmospheric conditions first the model is forced by a spatially fixed wind stress anomaly pattern characteristic for decadal north pacific climate variations the time evolution of the wind stress anomaly is chosen to be sinusoidal with a period of 20 years in this experiment different physical processes are found to be important for the decadal variations baroclinic rossby waves dominate the response they move westward and lead to an adjustment of the subtropical and subpolar gyre circulations in such a way that anomalous temperatures in the central north pacific develop as a delayed response to the preceding wind stress anomalies this delayed response provides not only a negative feedback but also bears the potential for long term predictions of upper ocean temperature changes in the central north pacific it is shown by additional experiments that once these rossby waves have been excited decadal changes of the upper ocean temperatures in the central north pacific evolve without any further anomalous atmospheric forcing in the second part the model is forced by surface heat flux and wind stress observations for the period 1949 1993 it is shown that the same physical processes which were found to be important in the simplified experiments also govern the evolution of the upper ocean in this more realistic simulation the 1976 77 cooling can be mainly attributed to anomalously strong horizontal advection due to the delayed response to persistent wind stress curl anomalies in the early 1970s rather than local anomalous atmospheric forcing this decadal change could have been predicted some years in advance the subsequent warming in the late 1980s however cannot be mainly explained by advection in this case local anomalous atmospheric forcing needs to be considered

evolution of weathering patterns in the indo burman ranges over the last 280 kyr effects of sediment provenance on 87sr 86sr ratios tracer a high resolution study of mineralogy and major element geochemistry combined with sr and nd isotopes has been conducted on high sedimentation rate cores collected off the irrawaddy river mouth in the andaman sea and the bay of bengal to reconstruct the erosional and weathering history of the irrawaddy river basin in both cores nd 0 values imply that both glacial and interglacial sediments share a common crustal source the irrawaddy river strong glacial interglacial cycles are recorded by 87sr 86sr interglacial periods yield values between 0 713 and 0 717 whereas glacial periods show higher values between 0 717 and 0 719 variations of the pedogenic clays smectite and kaolinite to primary mineral feldspar quartz illite and chlorite ratios show strong precessional cycles suggesting a control by past changes in the summer monsoon intensity each increase in pedogenic clays content is also associated with a net loss of labile elements na k and ca from the detrital minerals under chemical weathering wet periods of summer monsoon reinforcement correspond to an increase in weathering of the irrawaddy plain soils and a decrease of 87sr 86sr ratio plotting 87sr 86sr versus 87rb 86sr gives a pseudo isochrons interpreted as a mixing line representing the strength of chemical weathering during glacial stages enhanced physical erosion induced by glacier scour and frost action in the highland of the irrawaddy river basins produced high volumes of unaltered rb rich minerals the low sea level of glacial times constricted the river to the main channel in the lower reaches and permitted an efficient transport of unaltered rb rich minerals with high radiogenic sr composition from the high relief of the indo burman ranges and the tibetan plateau to the indian ocean

interdecadal variability of the pacific ocean model response to observed heat flux and wind stress anomalies variability of the pacific ocean is examined in numerical simulations with an ocean general circulation model forced by observed anomalies of surface heat flux wind stress and turbulent kinetic energy tke over the period 1970 88 the model captures the 1976 77 winter time climate shift in sea surface temperature as well as its monthly seasonal and longer term variability as evidenced in regional time series and empirical orthogonal function analyses examination of the surface mixed layer heat budget reveals that the 1976 77 shift was caused by a unique concurrance of sustained heat flux input anomalies and very strong horizontal advection anomalies during a multi month period preceding the shift in both the central pacific region where cooling occurred and the california coastal region where warming occurred in the central pacific the warm conditions preceding and the cold conditions following the shift tend to be maintained by anomalous vertical mixing due to increases in the atmospheric momentum flux tke input into the mixed layer which deepens in the model after the shift from the early 1970s to the late 1970s and 1980s since the ocean model does not contain feedback to the atmosphere and it succeeds in capturing the major features of the 1976 77 shift it appears that the midlatitude part of the shift was driven by the atmosphere although effects of midlatitude ocean atmosphere feedback are still possible the surface mixed layer heat budget also reveals that in the central pacific the effects of heat flux input and vertical mixing anomalies are comparable in amplitude while horizontal advection anomalies are roughly half that size in the california coastal region in contrast where wind variability is much weaker than in the central pacific horizontal advection and vertical mixing effects on the mixed layer heat budget are only one quarter the size of typical heat flux input anomalies

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

meanders and detached eddies of a strong eastward flowing jet using a two layer quasi geostrophic model abstract the process of meander growth on and eddy detachment from an eastward flowing oceanic jet which is modeled after the gulf stream east of cape hatteras is studied using numerical solutions of nonlinear equations the equations express potential vorticity conservation in a two layer quasi geostrophic model with a weak planetary effect solutions are restricted to a spatially periodic temporally growing case initially small amplitude meanders are given being superimposed on the jet the solutions describe a process in which the meanders grow increasingly larger the larger meanders are cut off and cyclonic and anticyclonic eddies are detached southward and northward respectively concurrent with the eddy detachment an eastward flow is restored in the upper layer and the lower layer develops an eastward flow under the restored jet and two westward flows north and south of it a baroclinic instability is very effective in meander growth while a weak effect is necessary for eddy detachme

cross gyre ventilation of the subtropical gyre an internal mode in the ventilated thermocline abstract a model of cross gyre geostrophic flow is presented it is a two layer model of the northern hemisphere subtropical thermocline above a resting lower ocean the northern boundary of the gyre is taken to be a latitude circle on which the ekman pumping vanishes in distinction to previous theories the meridional geostrophic velocity at the line of vanishing ekman pumping is not zero instead an internal mode is found which consists of southward potential vorticity conserving flow in the lower layer and northward flow in the upper layer there is net transport across the gyre boundary in agreement with the sverdrup relation the theory describes the longitudinal extent of the internal mode sufficient distortion of the isolines of potential vorticity by the wind stress curl south of the gyre boundary is required in order to allow the flux of fluid in the internal mode to penetrate into the subtropical gyre the model is presented as an additional example of gyre ventilation in this case due t

the composition of suspended matter from ganges brahmaputra sediment dispersal system during low sediment transport season abstract suspended matter supplied from the ganges brahmaputra river system was sampled in waters of the adjacent shelf area in times of low suspended matter load november december 1997 the absolute amount of suspended matter ranges between 500 mg l near the river mouth and chemical and mineralogical analyses of the suspended matter show changes in its composition with distance from the source compositional changes are based on grain size partitioning quartz and heavy minerals are precipitating sooner leaving the suspended matter from the outer shelf depleted in quartz ree zr hf nb ta w u th y and ca the other part of the compositional changes is based on the reaction of suspended matter with seawater manganese hydroxide is producing coatings on suspended matter grains and adsorbing elements out of the seawater as a consequence enrichment of mn zn ni cr co li cs as sb pb tl and cd can be observed in the suspended matter from the outer shelf arsenic is accumulating on the inner shelf by a factor of 2 chemical partitioning in sequential leaching experiments shows that arsenic does not follow the enrichment mechanism of manganese and other transition metals more than 90 of the total arsenic is bound to nearly insoluble phases of the suspended matter e g crystalline iron oxides residual minerals for comparison with suspended matter adjacent surface sediments were sampled and analysed in this sediment the dominating phase is the one which settled down during the times of high suspended load with more quartz and heavy minerals and consequent chemical composition the enrichment of manganese oxide and adsorbed transition metals gets lost because of anaerobic conditions in the bottom near seawater they dissolve from the sediment and get recycled in seawater arsenic is found in nearly insoluble parts of the sediment as it is the case in the suspended matter