intertropical latitudes and precessional and half precessional cycles a mcintyre and b molfino in their report about the forcing of atlantic equatorial and subpolar millennial cycles by precession suggest that climatic changes in high polar latitudes which are related to heinrich iceberg surges may be caused by events that occur in low latitudes 1 1 this

wetland expansion on the continental shelf of the northern south china sea during deglacial sea level rise abstract to identify environmental causes for past changes in vegetation in subtropical east asia we present carbon isotope compositions of plant wax n alkanes and provide estimates of the c4 plant contribution across the past four glacial terminations and interglacials based on cores recovered from the northern south china sea our results show a comparable c4 plant contribution between the last glacial maximum lgm and the holocene an increase of the c4 plant contribution by 15 20 is found for terminations iv ii and i relative to subsequent interglacial peaks coeval with an expansion of cyperaceae and poaceae in contrast termination v reveals a lower c4 plant contribution than marine isotope stage mis 11c the data exhibit a long term trend with a stepwise increase of the c4 plant contribution across interglacials mis 11c 9e 7e and 1 we suggest that no substantial changes in humidity levels over glacial interglacial cycles occurred facilitating a similar c3 c4 plant ratio for the lgm and the holocene instead deglacial sea level rises caused an extensive development of floodplains and wetlands on the exposed continental shelf providing habitats for the spread of c4 sedges and grasses the progressive subsidence of chinese coastal areas and the broadening of the continental shelf over the late quaternary explains the nearly absence of c4 plant occurrence during termination v and a gradual increase of the c4 plant contribution across interglacial peaks taken together changes in coastal environments should be considered when interpreting marine based vegetation reconstructions from subtropical asia

living coccolithophore communities in the norwegian greenland sea and their record in sediments abstract investigation of epipelagic coccolithophore communities along a transect from the voring plateau off norway to scoresbysund east greenland and comparison with coccolith assemblages in underlying surface sediments reveal that sedimentation of coccoliths is dependent on the following factors 1 composition of the coccolithophore communities and their bloom phases 2 grazing and selective destruction by zooplanktonic organisms 3 type of vertical flux in fecal pellets and 4 varying carbonate dissolution in different water masses dissolution increases towards the boundaries of carbonate sedimentation as a result the original composition of the living communities becomes increasingly obscured in the impoverished taphocoenoses however differential resistance to dissolution of the two primary calcareous nannoplankton species emiliana huxleyi and coccolithus pelagicus is such that occurrence and ratio of the two species in surface sediments reflect the various water masses in the norwegian greenland sea

climate instability during the penultimate glaciation evidence from two high resolution loess records china the xinzhuangyuan and lijiayuan loess sections in the northwestern part of the chinese loess plateau were studied down to paleosol unit s2 which probably formed during marine oxygen isotopic stage 7 200 000 years b p the thickness of the loess soil sequence above s2 is 63 m at xinzhuangyuan and 43 m at lijiayuan a 2 cm sample spacing yields a mean depositional resolution of 50 80 years for the last and penultimate glacial loess units l1 and l2 and 200 years for the last interglacial soil unit sl thus enabling us to reconstruct high resolution climatic changes during the last two glacial interglacial cycles the grain size records of the two sections are regarded as a proxy for changes in the monsoon desert system over northern china results show that frequent large amplitude climatic oscillations on millennial timescales occurred during the penultimate glaciation in a manner similar to that during the last glaciation suggesting that suborbital scale climatic variations may be a common feature of the climate system during glacial periods of the pleistocene the last interglacial soil s1 is composed of three individual soils and two thin intervening loess horizons in both of the sections short term variations in grain size are not prominent within the soil complex implying the absence of strong millennial scale climatic oscillations during the last interglaciation in northern china

faroe marine ash zone iv a new mis 3 ash zone on the faroe islands margin a basaltic tephra layer from mis 3 has been discovered by analysis of cores from the faroe islands margin the tephra layer appears up to 20 cm thick in some records after the first main fall out event the tephra is believed to be mainly deposited and redistributed by bottom currents geochemical analyses suggest that the tephra is relatively undisturbed by allochtonous tephra grains and unmixed the peak occurrences are in the lower part of gis greenland interstadial 12 and we suggest naming this new tephra faroe marine ash zone iv fmaz iv following the nomenclature adopted for previous ash zones found on the faroe islands margin geochemical analyses of the tephra show affinities with the grimsvotn volcanic system in the eastern volcanic zone in south iceland the average age of fmaz iv from four independent age models is 46 800 1000 years bp we suggest that the v5 ash zone found on the reykjanes ridge is a correlative to the fmaz iv

effects of ice coverage and ice rafted material on sedimentation in the fram strait as little is known about pelagic sedimentation processes in arctic environments1 the interpretation of biological and chemical processes as well as the reconstruction of ancient conditions including those in the glacial north atlantic is difficult here we provide sediment trap results which show that the position of the sea ice boundary significantly influences the particle flux the seasonal variability of the particle flux differed markedly in the various sediment trap sites in fram strait depending on the behaviour of the sea ice under complete ice cover sedimentation is very low whereas maximum sedimentation is found at the ice margin the highest particle flux observed showing a large lithogenic component was observed at the ice edge where the water was warmer 2 c we find that high biogenic opal fluxes are characteristic of the summer ice margin indicating that the sedimentary record of opal fluxes may allow the position of ice margins in the past to be reconstructed

composition and origin of sediments on the mid oceanic kolbeinsey ridge north of iceland in order to characterize the sediments of the south kolbeinsey ridge and to determine the influence of morpho and hydrodynamic conditions in this area a comprehensive sedimentological investigation was combined with detailed geochemical analyses lithological composition and grain size are mainly controlled by the input from two different sources the submarine active mid ocean ridge and iceland coarse grained volcanic material dominates in the ridge area whereas fine grained detritus from iceland characterizes the adjacent basin further the distribution of these sediments is largely influenced by hydrodynamic conditions and redeposition processes strong bottom water currents indicated by the benthic foraminifer species cibicides lobatulus prevent extensive deposition of fine grained material on the top of the ridge the ridge slope is characterized by redeposited sediments of various grain sizes bulk sediment chemical analyses show element distribution patterns that are strongly correlated with the ratio of volcanic vs detritic particle composition this ratio reflects particle input and distribution processes two element associations are notable elements coupled with 1 ridge derived volcanic particles and 2 the detrital 2 m fraction which reflects weathered material from iceland

the late holocene gargano subaqueous delta adriatic shelf sediment pathways and supply fluctuations the gargano subaqueous delta formed on the eastern and southeastern sides of the gargano promontory in the western adriatic this subaqueous deposit represents the southernmost portion of the late holocene highstand systems tract hst growing along the western side of the adriatic as an extensive wedge of deltaic and shallow marine mud the late holocene hst rests above a regional downlap surface that marks the time of maximum landward shift of the shoreline attained around 5 5 cal kyr bp at the end of the late pleistocene holocene sea level rise high resolution seismic stratigraphic and tephra correlation indicate the presence of a thin basal unit recording condensed deposition between 5 5 and 3 7 cal kyr bp over much of the basin above this unit sediment accumulation rates increased to high values as much as 1 5 cm yr 1 reflecting the stabilisation of relative sea level and the forcing from high frequency climatic or anthropogenic changes affecting river dynamics the late holocene mud wedge of which the gargano subaqueous delta is a significant component reaches up to 35 m in thickness and has a volume of ca 180 km3 the shore parallel thickness distribution of the mud wedge reflects the dominant oceanographic regime of the basin and the asymmetric location of the mostly western sediment sources with a combined modern delivery of 51 7 106 t yr 1 of mean suspended load in sections perpendicular to the coast the late holocene mud wedge appears composed of forestepping clinoforms with gently dipping foresets typically 0 5 the gargano subaqueous delta is characterised by a submarine topset in water depths shallower than 25 28 m and accounts for about 1 7th of the total volume of the late holocene mud wedge despite the absence of direct river supply to the gargano area in the area of maximum interaction between shore parallel currents and basin morphology progradation occurs onto a flat and barren bedrock outcrop in about 50 80 m water depth the rapid transition from a thickness of 30 m of late holocene mud to nil is a good indication of the role of southward flowing bottom hugging shelf currents in causing the redistribution of sediment along the adriatic inner shelf additional evidence of this regime comes from 1 the most recent sigmoid defined at seismic stratigraphic scale deposited since the onset of the little ice age showing a shore parallel thickness distribution and a main depocentre to the southeast of the gargano promontory 2 the maximum values of sediment accumulation rates over the last century documented by 210pb measurements defining a narrow shore parallel belt immediately seaward of the depocentre of the most recent sigmoid the gargano subaqueous delta grows from the outbuilding of progressively younger progradational sigmoids that tend to parallel the previous ones the gargano subaqueous delta differs from other documented late holocene subaqueous deltas because its growth reflects 1 sediment transport dominated by bottom currents sub parallel to the strike of the composing clinoforms 2 a complex supply regime including the po delta 350 km to the north and several coalescing apennine rivers acting as line source 3 several alternating intervals of enhanced outbuilding and condensed deposition and 4 an in phase growth of the most recent sigmoid with the major progradation of the po delta during the little ice age

ash layers from iceland in the greenland grip ice core correlated with oceanic and land sediments four previously known ash layers ash zones i and ii saksunarvatn and the settlement layer all originating in iceland have been identified in the central greenland ice core grip this correlation of the ash between the different environments is achieved by comparison of the chemical composition of glass shards from the ash this establishes and confirms detailed correlations between the different types of depositional records and the absolute dating of the younger part of the ice core by counting annual layers dates the eruptions accurately a precise connection with dates obtained by14c beyond the range of dendrochronology is established which provides an excellent confirmation of230th 234u dates from corals four additional icelandic ash layers have also been identified in the core but not yet correlated with known ash deposits

last interglacial climates the last interglacial commonly understood as an interval with climate as warm or warmer than today is represented by marine isotope stage mis 5e which is a proxy record of low global ice volume and high sea level it is arbitrarily dated to begin at approximately 130 000 yr b p and end at 116 000 yr b p with the onset of the early glacial unit mis 5d the age of the stage is determined by correlation to uranium thorium dates of raised coral reefs the most detailed proxy record of interglacial climate is found in the vostok ice core where the temperature reached current levels 132 000 yr ago and continued rising for another two millennia approximately 127 000 yr ago the eemian mixed forests were established in europe they developed through a characteristic succession of tree species probably surviving well into the early glacial stage in southern parts of europe after ca 115 000 yr ago open vegetation replaced forests in northwestern europe and the proportion of conifers increased significantly farther south air temperature at vostok dropped sharply pulses of cold water affected the northern north atlantic already in late mis 5e but the central north atlantic remained warm throughout most of mis 5d model results show that the sea surface in the eastern tropical pacific warmed when the ice grew and sea level dropped the essentially interglacial conditions in southwestern europe remained unaffected by ice buildup until late mis 5d when the forests disappeared abruptly and cold water invaded the central north atlantic ca 107 000 yr ago

evaluation of trace element concentration acid leachable in sediments from river panuco and its adjacent lagoon areas ne mexico a set of forty one surface sediment samples were collected in river panuco and its adjoining lagoon areas in ne mexico to identify the enrichment pattern of trace elements the samples were analyzed for sediment texture carbonates organic carbon and acid leachable trace elements altes using autoclave method fe mn cr cu ni co pb zn cd v be ba sr as geochemical results of fe cr ni co v and sr in zone 1 indicate that erosion in the upland region sierra madre oriental mountains is very high the above feature is supported by the supremacy of finer sediments 82 12 carbonates 44 67 and organic carbon 10 74 which are brought down from the drainage basin the overall average concentration of altes mn 607 g g 1 cu 28 29 g g 1 ni 16 56 g g 1 pb 46 11 g g 1 cd 1 81 g g 1 and zn 92 18 g g 1 indicates higher values than the lowest effect level lel and effects range low erl of environmental indicators the results suggest that they are due to the increase in oil refineries metal based industries shipping activities and the effluent input which could enter the biological cycle and might create human health problems

intra interglacial cold events an eemian holocene comparison this paper is included in the special publication entitled geological evolution of ocean basins results from the ocean drilling program edited by a cramp c j macleod s v lee and e j w jones rapid oscillations between warm and cold climates have been found in the oxygen isotope record of the greenland ice core project grip ice core during the eemian marine oxygen isotope stage mis 5e in contrast the variability in greenland ice sheet project 2 gisp2 ice core is significantly different and some atlantic deep sea records suggest no such climate variations we present here a high resolution 50 300 years set of marine proxies from the low latitude east atlantic margin odp site 658 which suggest that in general the eemian was climatically very similar to the holocene we however observe that the upwelling intensity off the west african coast was greatly reduced during the early eemian corresponding to the very mild climate observed in the european lake records we observe that mis 5e contains one significant short cold spell 400 years which is marked by a reduction of upper north atlantic deep water ventilation we suggest this cold event may correlate with the cold interval found in the european terrestrial records the cause of the intra eemian event was likely to be the freshening and cooling observed in the norwegian sea this brief cold spell however did not affect the overall stability of mis 5e and moreover it has an analogue event in the holocene sub boreal period marine and terrestrial records thus seem to be incompatible with those of the grip ice core record supporting the suggestion that the grip record has been altered by ice tectonics

iceberg discharges into the north atlantic on millennial time scales during the last glaciation high resolution studies of north atlantic deep sea cores demonstrate that prominent increases in iceberg calving recurred at intervals of 2000 to 3000 years much more frequently than the 7000 to 10 000 year pacing of massive ice discharges associated with heinrich events the calving cycles correlate with warm cold oscillations called dansgaard oeschger events in greenland ice cores each cycle records synchronous discharges of ice from different sources and the cycles are decoupled from sea surface temperatures these findings point to a mechanism operating within the atmosphere that caused rapid oscillations in air temperatures above greenland and in calving from more than one ice sheet

forcing of atlantic equatorial and subpolar millennial cycles by precession abundance cycles of the marine alga florisphaera profunda centered on a period of 7600 carbon 14 years 8400 calendar years are present in high resolution records from the equatorial atlantic spanning 0 to 45 000 years ago these cycles correlate with heinrich events 1 through 5 which document rapid changes in continental ice melting around the subpolar north atlantic these variations in f profunda are a direct response to modulation in zonal wind driven divergence produced by a precessional component of orbital variation during a time of reduced eccentricity modulation

source of ash zone 1 in the north atlantic geochemical evidence shows that the silicic component of the widespread ash zone 1 in the north atlantic is derived from a major ignimbrite forming eruption which occurred at the katla caldera in southern iceland during the transition from glacial to interglacial conditions in younger dryas time both trace and major element evidence of the rhyolitic products excludes the oraefajokull volcano as a source the high ti basaltic component in the marine ash zone can also be attributed to contemporaneous eruption in the katla volcanic complex dispersal of tephra from this event is primarily attributed to the generation of co ignimbrite ash columns in the atmosphere with ash fallout on both sea ice and on the ocean floor north and east of iceland owing to the changing ocean circulation characteristics of the glacial regime including suppression of the irminger current and a stronger north atlantic current tephra was rafted on sea ice south into the central north atlantic and deposited as dispersed ash zone 1 sediments south of iceland also show evidence of the formation of ash turbidites generated either by the entrance of pyroclastic flows into the sea or during discharge of jokulhlaups or glacier bursts from this subglacial eruption

world wide delivery of river sediment to the oceans new data and new estimates from old data show that rivers with large sediment loads annual discharges greater than about 15 times 10 6 tons contribute about 7 times 10 9 tons of suspended sediment to the ocean yearly extrapolating available data for all drainage basins the total suspended sediment delivered by all rivers to the oceans is about 13 5 times 10 9 tons annually bedload and flood discharges may account for an additional 1 2 times 10 9 tons about 70 of this total is derived from southern asia and the larger islands in the pacific and indian oceans where sediment yields are much greater than for other drainage basins

the environmental effects of the uplift of the qinghai xizang plateau the intense upheaval of the qinghai xizang plateau took place 2 ma bp the terraces of the yellow river in the lanzhou region and its upper sections provide a record of the uplift of the plateau the interaction of glaciation cycles resulting from climatic changes and pulsating tectonic upheavals are both involved in the record of environmental change across the plateau three tectonic climatic events which are termed respectively the qinghai xizang movement the huanghe yellow river movement and the gonghe movement occurred 2 1 5 1 0 and 0 15 ma bp the upheaval of the qinghai xizang plateau was the trigger mechanism of the asian monsoon the loess plateau was formed in the monsoon triangle of east asia human origins and human evolution may have been stimulated by the uplift of the qinghai xizang plateau

a pollen record of the last 37 ka in deep sea core 17940 from the northern slope of the south china sea this paper presents the palynological record of deep sea core 17940 from the south china sea 20 07 n 117 23 e water depth 1727 m this core is about 13 30 m long and covers the last 37 ka a total of 103 samples were counted at 10 cm intervals with a time resolution of ca 360 yr three pollen zones are recognized zone p1 14c age ca 37 0 15 0 ka b p 13 06 8 70 m is characterized by the expansion of montane conifers tsuga picea and abies and colonization by temperate grassland mainly artemisia on the exposed northern continental shelf as well as by frequent natural fires indicated by high values of charcoal concentrations this implies that the climate of this period was cool and dry frequent alternations of montane conifers and grassland dominated by artemisia indicate that oscillations of comparatively cool and humid conditions with temperate and dry conditions occurred according to the oxygen isotope data the period corresponds to stage 3 and the last glacial maximum climatic warming p2 a 8 70 7 23 m 15 0 11 3 ka b p associated with a rapid rise in sea level from ca 14 ka b p is inferred by expansion of tropical subtropical broad leaved forest with a replacement of grassland by mangroves mainly rhizophora and sonneratia this time interval may be assigned to the bolling allerod warming stage subsequently climatic cooling reflected by expansion of both montane conifers and upper montane rain forests mainly podocarpus and dacrydium during the period of ca 11 3 10 0 ka b p p2 b 7 23 6 6 m may be correlated with the younger dryas cold spell the similarity of pollen assemblages during the holocene and in the surface sediment from the northern south china sea implies that the vegetation and climate during the last 10 000 years was close to those of the present during the last 1400 years human activities are reflected in the sharp increase of dicranopteris fern spores

climate variations in europe over the past 140 kyr deduced from rock magnetism rapid shifts in climate during the last glacial are now well documented particularly from the oxygen isotope records of the two greenland ice cores grip1 2 and gisp23 in the grip record1 2 these climate events are also seen during the preceding eemian interglacial which may be an analogue for the future climate warmed by the greenhouse effect but these shifts are not found in the eemian section of the gisp2 core3 casting doubt on whether the rapid shifts in the grip oxygen isotope record really do represent a climate signal here we present magnetic susceptibility pollen and organic carbon records from maar lake deposits in the massif central france these data provide an independent record of past climate and we find that they correlate well with the ice core records during the last glacial during the eemian two rapid cooling events seen in our record also correlate with those seen in the grip ice core supporting the idea that rapid climate change did occur in the eemian interglacial and demonstrating that it extended to continental europe

orbital and millennial scale vegetation and climate changes of the past 225 ka from bear lake utah idaho usa continuous high resolution pollen data for the past 225 ka from sediments in bear lake utah idaho reflect changes in vegetation and climate that correlate well with variations in summer insolation and global ice volume during mis 1 through 7 spectral analysis of the pollen data identified peaks at 21 22 and 100 ka corresponding to periodicities in earth s precession and eccentricity orbital cycles suborbital climatic fluctuations recorded in the pollen data denoted by 6 and 5 ka cyclicities are similar to greenland atmospheric temperatures and north atlantic ice rafting heinrich events our results show that millennial scale climate variability is also evident during mis 5 6 and 7 including the occurrence of heinrich like events in mis 6 showing the long term feature of such climate variability this study provides clear evidence of a highly interconnected ocean atmosphere system during the last two glacial interglacial cycles that extended its influence as far as continental western north america our study also contributes to a greater understanding of the impact of long term climate change on vegetation of western north america such high resolution studies are particularly important in efforts of the scientific community to predict the consequences of future climate change r 2007 elsevier ltd all rights reserved

quaternary tephrachronology on the iceland plateau north of iceland four major ash zones recorded in piston cores raised from the iceland plateau north of iceland are shown to be coincident with the last four interglacial isotopic stages their geochemical composition links the ashes to volcanic events on iceland the occurrence of these ash layers which record events orders of magnitude larger than the normal holocene volcanic eruptions can not be explained by changes in sea ice cover and atmospheric circulation alone it is suggested that these events are related to pressure releases in the magma chambers resulting from major deglaciations of the icelandic ice cap

palynology of eastern indonesian marine piston cores a late quaternary vegetational and climatic record for australasia abstract pollen analyses of late quaternary sediments from nine marine piston cores reveal a continuous vegetation and environmental record for eastern indonesia and northern australia on the island of halmahera a montane oak forest largely replaced the tropical lowland vegetation during the last glacial period while fern cover was strongly reduced during its maximum 18 000 yr b p climate was cooler and slightly drier than today around 10 000 yr b p mangrove vegetation expanded following the rising sea level in our western new guinea record at 14 000 yr b p climate grew warmer and slightly wetter until it stabilised around 10 000 yr b p at that time the mid to upper montane forests expanded to their full altitudinal range and fern cover increased while montane oak forest grassland and woodland areas had contracted in our marine pollen records during the last glacial the climate of northern australia was distinctly drier than today grassland vegetation with sedges increased considerably at 38 000 and 24 000 yr b p replacing eucalypt forest and culminating in a maximum grassland cover at the height of the last glaciation 18 000 yr b p the rapid sea level rise allowed the expansion of mangrove forests and salt bush marshes which had become established on the large tidal flats of the drowning sahul shelf around 12 000 yr b p one piston core g6 4 extends to 300 000 yr b p and shows that glacial periods are characterized by high pollen concentrations in marine sediments recording expanding grassland vegetation during interglacial woodland and fern cover increased while pollen concentrations in the sediments were low after 190 000 yr b p a more open vegetation suggests that conditions were in general much more arid than before repeated mangrove vegetation expansions suggest major rises in sea level at around 244 000 220 000 and 130 000 yr b p

oxygen isotope record of sea level and climate variations in the sulu sea over the past 150 000 years the sulu sea is located in the warm pool of the western pacific ocean where mean annual temperatures are the highest of anywhere on earth because this large heat source supplies the atmosphere with a significant portion of its water vapour and latent heat understanding the climate history of the region is important for reconstructing global palaeoclimate and for predicting future climate change changes in the oxygen isotope composition of planktonic foraminifera from sulu sea sediments have previously been shown to reflect changes in the planetary ice volume at glacial interglacial and millenial timeseales and such records have been obtained for the late pleistocene epoch and the last deglaciation1 3 here i present results that extend the millenial time resolution record back to 150 000 years before present on timescales of around 10 000 years the sulu sea oxygen isotope record matches changes in sea level deduced from coral terraces on the huon peninsula4 this is particularly the case during isotope stage 3 an interglacial period 23 000 to 58 000 years ago where the sulu sea oxygen isotope record deviates from the specmap deep ocean oxygen isotope record5 thus these results support the idea4 6 that there were higher sea levels and less continental ice during stage 3 than the specmap record implies and that sea level during this interglacial was just 40 50 metres below present levels the subsequent rate of increase in continental ice volume during the return to full glacial conditions was correspondingly faster than previously thought

a 9000 year old ash bed on the faroe islands abstract radiocarbon datings of the saksunarvatn ash bed on the faroe islands indicate an age of 9000 9100 yr b p the saksunarvatn ash bed differs geochemically from both ash zone 1 in the north atlantic and the vedde ash bed of norway and the norwegian sea all mentioned ashes are assumed to originate from iceland the vedde ash has been dated at 10 600 60 yr b p consequently the saksunarvatn and vedde ash beds provide an opportunity for precise dating of events around the pleistocene holocene boundary in marine cores especially from the region where the two plumes overlap

suborbital timescale variability of north atlantic deep water during the past 200 000 years we generated 200 kyr long proxy records of surface and deepwater variability from a subpolar north atlantic core v29 202 enabling us to assess the linkage between surface and deepwater changes on suborbital timescales in particular we used a benthic 13c record to evaluate the deep water response to dansgaard oeschger temperature oscillations and to heinrich events times of massive iceberg delivery to the north atlantic we found that the reduction of north atlantic deep water nadw production was generally associated with cold or dropping sea surface temperatures ssts as indicated by planktonic foraminiferal assemblages the nadw contribution to the site did not drop appreciably during heinrich events h4 through h2 probably because these events followed intervals of prolonged surface cooling already characterized by low rates of nadw production by contrast nadw reduction appears to have been synchronous with h5 sst rise associated with both dansgaard oeschger oscillations and heinrich events was usually accompanied by increasing nadw strength in a few cases the nadw recovery appeared to lag the sst rise however the apparent delay is most likely an artefact of the sedimentary record low concentrations of benthic foraminifera as a result of low benthic foraminiferal abundances during stage 6 the stage 6 benthic foraminiferal 13c record is of lower resolution than the younger part of the record the stage 6 proxy records for surface hydrography nevertheless reveal millennial scale oscillations similar to those seen in stage 3 the available 13c data suggest that nadw weakened in association with the cold portions of stage 6 sst oscillations we also sought to confirm a recent study which concluded that there was little nadw variability during the peak of the last interglaciation marine oxygen isotope substage 5e eemian isotope stage 5 was marked by a trend of increasing benthic 13c in v29 202 rising 13c through isotope stage 5 is also seen in tropical surface water records and at some deep atlantic sites and may reflect the common derivation of these water masses variations of 0 5 superimposed on this rising 13c trend within substage 5e in v29 202 are so far not evident in tropical feed waters and may therefore indicate that nadw production was weaker during the late than mid eemian an electronic supplement of this material may be obtained on a diskette or anonymous ftp from kosmos agu org login to agu s ftp account using anonymous as the username and guest as the password go to the right directory by typing cd apend type ls to see what files are available type get and the name of the file to get it finally type quit to leave the system paper 95pa02089 suborbital timescale variability of north atlantic deep water during the past 200 000 years by d w oppo and s j lehman diskette may be ordered from american geophysical union 2000 florida avenue n w washington dc 20009 15 00 payment must accompany order

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

the sequence of events surrounding termination ii and their implications for the cause of glacial interglacial co2 changes events surrounding termination ii as preserved in the vostok ice core provide a number of clues about the mechanisms controlling glacial to interglacial climate change antarctic temperature and the atmosphere s co2 content increased together over a period of 8000 years this increase is bounded by a drop in dust flux at its onset and by a drop in the 18o of trapped air at its finish a similar lag between dust flux and foraminiferal 18o is seen in a southern ocean marine record suggesting that the 18o in air trapped in vostok ice is a valid proxy for ice volume the synchronous change of atmospheric co2 and southern hemisphere temperature thus preceded the melting of the northern hemisphere ice sheets this observation coupled with the fact that nutrient reorganization in the north atlantic occurs with or after the sea level rise eliminates many scenarios proposed to explain the co2 rise including those which rely on sea level change conveyor related nutrient redistribution or north atlantic cooling southern ocean scenarios become the front runners but the most popular mechanism iron fertilization has two problems in explaining the co2 rise before termination ii first much of the dust demise occurs prior to the change in co2 so if iron is the villain a threshold value of its supply must be called upon above which productivity does not continue to increase second the co2 rise continues for some 4 5 kyr after the dust flux has fallen to close to zero these problems may be solved if the increased iron supply in dust caused higher rates of nitrogen fixation during the glacial periods in this case the residence time of oceanic nitrate of a few thousand years would enable decreasing productivity to be a global rather than a local phenomenon and would explain the slow rampup of atmospheric co2

orbital controls on the el nino southern oscillation and the tropical climate the global synchroneity of glacial interglacial events is one of the major problems in understanding the link between milankovitch forcing and the climate of the late quaternary in this study we isolate a part of the climate system the tropical pacific and test its sensitivity to changes in solar forcing associated with changes in the earth s orbital parameters we use a simplified coupled ocean atmosphere model that is run for the past 150 000 years and forced with milankovitch changes in the solar insolation this system responds primarily to the precessional cycle in solar forcing and is capable of generating a mean response to the changes in the seasonal distribution of solar radiation even while the annual mean insolation is roughly constant the mean response to the precessional forcing is due to an interaction between an altered seasonal cycle and the el nifio southern oscillation enso changes in the enso behavior result in a mean tropical climate change the hypothesis is advanced that such a change in the tropical climate can generate a globally synchronous climate response to milankovitch forcing

the pacemaker always rings twice we generated new long high resolution climate proxy records from deep sea drilling project dsdp sites 607 and 609 in the subpolar north atlantic over the interval 225 970 ka which have pronounced variability at periods f 1 7 kyr variance in our north atlantic climate proxy records is shown using bispectral and cross bispectral methods to be explainable as harmonics and or combination tones of orbital scale climatic variability of the north atlantic region itself thus the timing and amplitude of high frequency climate change in the north atlantic region appears to be a nonlinear function of variations in high latitude climate at milankovitch frequencies

distribution and dispersal of clay minerals on the western continental shelf of india abstract sediment samples distributed over a distance of 1700 km from the inner continental shelf of western india were analysed for their clay mineral content by x ray diffraction the clay minerals present in the sediments in order of abundance are montmorillonite kaolinite illite chlorite and gibbsite based on the abundance of montmorillonite and kaolinite four clay mineral provinces on the continental shelf have been demarcated these are 1 the montmorillonite kaolinite illite chlorite province off the gulf of kutch 2 the montmorillonite rich zone off the gulf of cambay 3 a transition zone on the central parts of the shelf and 4 a relatively montmorillonite poor gibbsite province on the southwestern part of the shelf source rock influence on clay mineral composition appears to be more important than physical transport the southwest monsoon drift in the present case in the northwestern part of the study area the high velocity tidal streams of the macrotidal gulf of kutch act as dynamic barriers to longshore sediment dispersal leading to distinct clay mineral assemblages on the shelf north and south of the gulf mouth

composition and origin of volcanic ash zones in late quaternary sediments from the reykjanes ridge evidence for ash fallout and ice rafting abstract seven quaternary volcanic ash zones including the well known ash zones az i and az ii have been investigated in five well dated sediment cores from the reykjanes ridge between 59 and 60 n the zones were defined on their geochemical composition morphological variation of the particles and stratigraphic position the ash zones az i and az ii show a mixture of colorless bubble wall shards and brown blocky glasses whereas ash zones vz 1 to 5 are composed of dark to light brown volcanic glasses ranging in shape and texture from blocky nonvesicular shards to highly vesicular pumiceous types the dark brown glass shards of ash zones vz 1 to 5 represent subalkalic and low k subalkalic basaltic series geochemical correlation of the ash zones with possible source areas indicates that they all derived from iceland the colorless shards in az i and az ii are of rhyolitic composition the eastern volcanic zone on iceland is the most important source with abundant volcaniclastics being produced by subaerial subglacial eruptions and secondary erosion of volcanic rocks explosive volcanism on iceland is manifested by marine ash layers az i and az ii most of the volcaniclastic zones vz 1 to 5 coincide chronologically with peak abundances of coarse ice rafted material ird indicating that most of this volcanic glass was incorporated into the icelandic ice sheet and released to the ocean by iceberg calving and subsequent melting however two layers in vz 1 and vz 5 have no correlatives in the ird record suggesting that they were probably transported by local sediment gravity flows from this we must infer that most of the ice rafting episodes bearing volcanic particles as observed in sediments from reykjanes ridge monitor glacier fluctuations on iceland

coral record of equatorial sea surface temperatures during the penultimate deglaciation at huon peninsula uplifted coral terraces at huon peninsula papua new guinea preserve a record of sea level sea surface temperature and salinity from the penultimate deglaciation remnants have been found of a shallow water reef that formed during a pause similar to the younger dryas in the penultimate deglaciation at 130 000 2000 years ago when sea level was 60 to 80 meters lower than it is today porites coral which grew during this period has oxygen isotopic values and strontium calcium ratios that indicate that sea surface temperatures were much cooler 22 2 c than either last interglacial or present day tropical temperatures 29 1 c these observations provide further evidence for a major cooling of the equatorial western pacific followed by an extremely rapid rise in sea level during the latter stages of termination ii

north atlantic deep sea sedimentation of late quaternary tephra from the iceland hotspot piston cores recovered from the north atlantic were used to study the sedimentation of holocene and pleistocene volcanic ash in the irminger and iceland basins ash zones 1 11 100 yr b p 2 55 000 yr b p and 3 305 000 yr b p were identified from their major element glass composition the silicic and alkalic ash zones 1 and 2 originate from the southeastern volcanic zone of iceland where they correlate with the solheimar ignimbrite from katla volcano and the thorsmork ignimbrite from tindfjallajokull volcano respectively the low alkali composition of silicic ash zone 3 indicates a source from one of the silicic centers in the active rift system ash zones 2 and 3 occur in the irminger basin as dispersed glass shards over a depth interval of several tens of centimeters their compositional and granulometric characteristics reflect an initial fallout on pack ice north of iceland followed by ice rafting sedimentation in the denmark strait prior to bioturbation 18o stratigraphy of foraminifera in the cores indicates that the ash zones were deposited during a cold interval at the time when seas north of iceland were ice covered sedimentary features indicate that turbidity currents were also involved in the dispersal of ash zones 1 and 2 south of iceland the initiation of these gravity currents from the shelf can be attributed to either glacier bursts jokulhlaups carrying tephra or the entrance of pyroclastic flows into the ocean

the classic marine isotope substage 5e since its identi cation nearly fty years ago marine iso tope stage 5 mis 5 has been placed onto absolute time scaleson the basis of three independent approaches cesare emiliani who set up the isotope stages emiliani 1955 depended onuranium series dating of the sediments a method that today isregarded as not generally capable of yielding useful precisionor accuracy broecker and van donk 1970 pioneered the ap proach of correlating to radiometrically dated marine coral ter races thishasbeenmuchaidedinrecentyearsbyimprovementsin the precision and accuracy of these age determinations thathave owed from the development of thermal ionization massspectrometry tims for uranium series dating edwards

a high resolution study of ne atlantic sediments at station bengal geochemistry and early diagenesis of heinrich layers abstract high resolution geochemical analysis of a piston core from the deep ne atlantic revealed large differences in the major and trace element signature within the sedimentary record at station bengal 48 58 n 16 28 w water depth 4804 m a prominent heinrich layer h4 containing large amounts of ice rafted detritus ird and two less pronounced layers h1 and h2 were identified from mg al si al zr al and porosity profiles h3 and h5 were much less developed therefore not all identification criteria are applicable elevated si al and zr al ratios were probably caused by enhanced eolian loess input element al ratios of other elements cr rb fe v and zn not shown point to a change in the provenance of the terrigenous material of upper continental crust material delivered during the most intense heinrich event h4 the use of ba al toc al and carbonate content as paleoproductivity tracers revealed enhanced carbon input to the seafloor before and during he as well as for the period between h2 and h4 this results in redox boundary compressions in the sediments which has likely resulted in fe cycling at the sediment seawater interface as revealed by fe al and p al ratios a loss of mn by diffusion out of the sediments is probably also caused by this migration of the redox boundary to the sediment seawater interface a combination of low detrital al ratios in the upper part of h4 and redox enrichments at the base of this hl produced ambiguous signals of the redox metals fe ni and v

reflection of scandinavian ice sheet fluctuations in norwegian sea sediments during the past 150 000 years the record of glacier fluctuations in western scandinavia as reconstructed from continental data has been correlated with records of ice rafted detritus ird from well dated sediment cores from the norwegian sea covering the past 150 000 yr b p the input of ird into the ocean is used as a proxy for ice sheet advances onto the shelf and thus for the calibration of a glaciation curve the marine results generally support land based reconstructions of glacier fluctuations and improve the time control on glacial advances the saalian ice sheet decayed very rapidly approximately 125 000 yr b p in the early weichselian a minor but significant ird maximum indicates the presence of icebergs in isotope substage 5b especially between 95 000 and 83 000 yr b p reduced amounts of calcareous nannofossils indicate that surface waters were influenced by meltwater discharges during isotope substages 5d and 5b an extensive build up of inland ice began again during isotope stage 4 but maximum glaciation was reached only in early stage 3 58 000 53 000 yr b p marine sediments have minimum carbonate content indicating strong dilution by lithogenic ice rafted material generally the ird accumulation rate was considerably higher in stages 4 2 than in stage 5 a marked peak in ird accumulation rates from 47 000 to 43 000 yr b p correlates well with a second middle weichselian ice sheet advance dated by the laschamp olby paleomagnetic event minimum ice extent during the alesund interstade 38 500 32 500 yr b p and several glacial oscillations during the late weichselian are also seen in the ird record of several late weichselian glacial oscillations on the shelf at least four correspond to the north atlantic heinrich events ice sheet behavior was either coupled or linked by external forcing during these events whereas internal ice sheet mechanisms may account for the noncoherent fluctuations

diffuse spectral reflectance as a proxy for percent carbonate content in north atlantic sediments diffuse reflectance records from fern drift in the north atlantic faithfully record sediment percent carbonate a high resolu tion reflectance based age model for these sediments derived from an orbitally tuned age model for western equatorial atlantic ceara rise sediments was generated by spectral frequency mapping power spectra of the fern drift record indicate statistically significant sub milankovitch cyclicity at 7 6 8 4 and 4 8 6 1 kyr we infer that these 8 and 5 kyr cycles document a linkage between north and equa torial atlantic climate given our ability to correlate these records these climate cycles influence atlantic basin carbonate prior to the intensification of northern hemisphere glaciation and thus must arise from some portion of the climate system other than the dynamics of large ice sheets the presence of these peaks which could be related to equatorial clipped precession implies a possible non linear response to milankovitch forcing abstract diffuse reflectance records from feni drift in the north atlantic faithfully record sediment percent carbonate a high resolu tion reflectance based age model for these sediments derived from an orbitally tuned age model for western equatorial atlantic ceara rise sediments was generated by spectral frequency mapping power spectra of the feni drift record indicate statistically significant sub milankovitch cyclicity at 7 6 8 4 and 4 8 6 1 kyr we infer that these 8 and 5 kyr cycles document a linkage between north and equa torial atlantic climate given our ability to correlate these records these climate cycles influence atlantic basin carbonate prior to the intensification of northern hemisphere glaciation and thus must arise from some portion of the climate system other than the dynamics of large ice sheets the presence of these peaks which could be related to equatorial clipped precession implies a possible non linear response to milankovitch forcing

environmental change during the penultimate glacial cycle a high resolution pollen record from odp site 1144 south china sea abstract in order to study environmental change within the penultimate glacial cycle mis 6 5 a total of 385 pollen samples with an average time resolution of 530 years were analyzed from odp site 1144 20 3 18 n 1170 25 14 e northeastern south china sea a characteristic feature of pollen diagram is the alternating peaks of pine and herbs generally corresponding to the glacial cycle pine dominates in the interglacial herb pollen dominates in the glacial a detailed comparison shows that the pollen assemblages changed earlier at the glacial interglacial transition between mis 6 and 5 termination ii than the ice volume indicated by the oxygen isotope record implying that mid low latitude climate warming preceded high latitude ice sheet retreat responses of pollen assemblages to orbital and suborbital cyclicities and to monsoon variations are also discussed

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

deep sea pollen from the south china sea pleistocene indicators of east asian monsoon abstract a high resolution pollen record sampling interval averages 820 years has been obtained from odp site 1144 water depth 2037 m northern south china sea the 504 m sequence in composition length covers the last 1 03 million years according to micropaleontological and isotopic stratigraphy the pollen assemblages are characterized by high proportions of pinus and herb pollen and by their frequent alternations based on these alternations 29 pollen zones have been recognized that are closely correlated to the marine oxygen isotope stages mis 1 29 pinus dominant pollen zones correspond to interglacial periods with lighter 18o values while herb marked ones relate to the heavier 18o stages assigned to glacials judging from the pollen data the exposed northern continental shelf of the south china sea during the glacials was covered by grassland and the extensive northern shelf has formed only since mis 6 ca 150 ka probably as a result of tectonic subsidence tree pollen influx values are indicative of winter monsoon which began to intensify 600 ka ago the summer monsoon variations can be approximated by the fern percentage within the total pollen and spore abundance and the result shows high values in general occurring at interglacials with the maxima at mis 15 5e and 1 the relatively high fern percentage with smaller amplitude in variations before 600 ka might suggest more stable humid conditions before the intensification of winter monsoon

marine core evidence for reduced deep water production during termination ii followed by a relatively stable substage 5e eemian we present oxygen and carbon isotope records of benthic foraminifera from the glacial stage 6 through interglacial substage 5e eemian sections of several cores from the subpolar north atlantic the cores range in water depth from 1451 to 2658 m in one core we generated estimates of sea surface temperature sst and of ice rafted detritus ird delivery for all of stage 5 we reconstruct bathymeric profiles of 13c for stage 6 termination ii and three time slices of substage 5e the 13c profiles indicate that local deep water geometry during stage 6 was similar to that of the last glaciation with glacial north atlantic intermediate water gnaiw overlying deeper waters partially of southern origin an anomalously large peak in ird coupled with planktonic 18o evidence for iceberg melting immediately precedes termination ii and is otherwise similar to stage 2 and 3 heinrich events during the termination low 13c values are observed in cores near and above 2 km providing evidence of reduced gnaiw production in association with deglacial melting in the shallowest cores low 13c values persist into early substage 5e indicating that the southward retreat of southern source waters was not completed until well after the beginning of the substage in contrast to termination i ssts remained cold until the end of the deglaciation this may be why there is little evidence from marine and terrestrial sequences for a pronounced climate reversal on termination ii despite what is now clear evidence of a significant reduction in ocean ventilation the faunal data suggest that ssts during early 5e were about 7 c warmer than during the glaciation sst rose several degrees from early to middle substage 5e peaked in middle substage 5e at about 10 c above glacial values and then gradually declined by about 5 c these changes were linked to variations in water mass configuration as interpreted from benthic 13c evidence most of the evidence suggests that oscillations superimposed on the gradual sst trend were 1 2 c in contrast to the larger sst changes 3 4 c documented for substage 5d

filtering of milankovitch cycles by earth s geography abstract earth s land sea distribution modifies the temperature response to orbitally induced perturbations of the seasonal insolation we examine this modification in the frequency domain by generating 800 000 yr time series of maximum summer temperature in selected regions with a linear two dimensional seasonal energy balance climate model previous studies have demonstrated that this model has a sensitivity comparable to general circulation models for the seasonal temperature response to orbital forcing on land although the observed response in the geologic record is sometimes significantly different than modeled here differences attributable to model limitations and feedbacks involving the ocean atmosphere cryosphere system there are several results of significance 1 in mid latitude land areas the orbital signal is translated linearly into a large 10 c seasonal temperature response 2 although the modeled seasonal response to orbital forcing on antarctica is 6 c the annual mean temperature effect

quaternary volcanic ash zones on the iceland plateau southern norwegian sea four quaternary volcanic ash zones in the southern norwegian sea have been investigated in core p57 7 from the iceland plateau both the geochemical composition and morphological variation of each ash layer have been studied the four volcanic ash zones appear in the light oxygen isotope stages 1 5 7 and 11 the ash zones are composed of transparent platy grains light brown transparent grains brown blocky and black blocky grains and white transparent pumice and each zone shows a distinct stratigraphic evolution the geochemical results show a mixture of basaltic and silicic grains in each ash zone and that each zone contains grains from more than one eruption the geochemical investigations strongly suggest that all the ashes are derived from iceland the youngest ash zone includes two layers which based on their geochemical composition and stratigraphic position are correlated with the 14c dated vedde ash 10 600 yr bp and saksunarvatn ash 9 100 yr bp possible sources on iceland for these layers are discussed

high resolution benthic foraminifer δ13c records in the south china sea during the last 150 ka abstract high resolution 13c ratios of benthic foraminifer cibicidoides wuellerstorfi in core md97 2151 from the southern south china sea scs and core so50 31kl from the northern scs indicate deep water variations in the scs during the last 150 ka the 13c records of both show a general variation pattern with higher 13c during interglacial periods than glacial periods and rapid increases during terminations this variation pattern resembles those of the west pacific intermediate deep water the sources of the scs deep water and the general variation of global deep water indicating that the variation of the scs deep water is largely controlled by global factors such as carbon cycles and global deep water circulation spectra analysis exhibits robust milankovitch cycles in the scs deep water 13c again supporting global controls significant semi precession cycles can also be seen in the spectra implying that changes of local surface productivity also influence the scs deep water 13c

a younger dryas ash bed in western norway and its possible correlations with tephra in cores from the norwegian sea and the north atlantic abstract a bed of volcanic ash up to 23 cm thick is found in lacustrine and marine sediments in western norway it is formally mamed the vedde ash bed and its age is approximately 10 600 yr b p i e mid younger dryas the bed consits of pure glass having a bimodal basaltic and rhyolitic somposition the geochemistry of the glass shards suggests an icelandic source by means of stratigraphic position and geochemistry the ash is correlated with ash zones found in cores from the continental shelf the norwegian sea and the north atlatic

reconstruction of the variability of the southwest monsoon during the past 3 ka from the continental margin of the southeastern arabian sea from temporal variation in 18o in globigerinoidesruber and g sacculifer and geochemical indices of weathering erosion chemical index of alteration al and ti we infer rapid southwest monsoon swm deterioration with dwindling fluvial and detrital fluxes at ca 450 650 1000 and 1800 2200 cal a bp during the late holocene we have evaluated the role of solar influx reconstructed and high latitude climate variability archived in grip and gisp 2 cores on swm precipitation broadly our 18o climate reconstruction is concordant with grip and gisp 2 and supports a teleconnection through atmospheric connection between the swm and the north atlantic climate albeit temporal extents of the little ice age and medieval warm period from high latitude are not entirely coeval moreover there is a humid climate and enhanced precipitation during the terminal stages of the little ice age the medieval warming ca ad 800 1300 is not synchronous either and is punctuated by an arid event centred at 1000 a bp although the delineation of the specific influence of solar influx on swm precipitation is elusive we surmise that swm precipitation is a complex phenomenon and local orography along southwestern india may have a role on the entrapment of moisture from the southwest trade winds when these hit land copyright 2009 john wiley sons ltd

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

vostok ice core provides 160 000 year record of atmospheric co2 direct evidence of past atmospheric co2 changes has been extended to the past 160 000 years from the vostok ice core these changes are most notably an inherent phenomenon of change between glacial and interglacial periods besides this major 100 000 year cycle the co2 record seems to exhibit a cyclic change with a period of some 21 000 years

a multi proxy reconstruction of monsoon variability in the late holocene south india abstract pookode lake kerala south india a fresh water lake situated at an altitude of 770 m a s l receives predominantly rains from the south west monsoon a sediment core 125 cm long was investigated for sediment texture dating and geochemical composition radiocarbon dates obtained on the organic carbon rich sediments of the pookode lake range in age from the mid holocene to more recent 6240 565 14 c bp bc 4786 to ad 1434 cal geochemical data of the sediment cores were corroborated with phytolith and pollen studies although phytoliths occur in the entire sediment core pollen assemblages start occurring only since 1500 14 c bp ad 650 cal the sediments older than 1500 14 c bp were not suitable for the preservation of the pollen assemblages there is a major change in the lake hydrology indicating lacustrine conditions subsequent to 1500 bp occurrence of diatoms in the upper sediment layers of the sediment core indicates shallowing of the lake both the medieval warm period mwp and the little ice age lia are represented in the pookode lake sediment core sediment texture chemical weathering intensity cwi values supported by phytolith and pollen assemblages indicate that overall warm and dry conditions prevailed during 6200 420 14 c bp bc 4786 ad 1434 cal but this was interrupted by short intense wet phases between 3900 and 1900 bc 4000 ad 300 cal 1400 760 ad 800 ad 1200 cal and 420 140 14 c bp ad 1570 ad 1860 cal the wet events resulted from the strengthening of south west monsoon swm causing rising water levels and brief expansion of the pookode lake margin

holocene monsoon and sea level related changes of sedimentation in the northeastern arabian sea abstract the indian monsoon and the westerlies strongly influence the sedimentation in the northeastern arabian sea by impacting rainfall and erosion on land and on biogeochemical processes in the ocean to disentangle the terrestrial and oceanic processes we analysed mineralogical and bulk geochemical components of a holocene sediment core offshore pakistan endmember modelling of grain sizes and principal component analyses pca of major and trace elements identify the origin of sediments and their dominant mode of transport sedimentation processes during the early holocene 10 8 8 2 ka bp were influenced by the post glacial sea level rise and orbitally forced strengthening of the indian summer monsoon ism and westerlies this led to a shift from rather terrestrial dominated towards a marine dominated sedimentation whereas the fluvial source shifted from the makran rivers to the hab river near karachi during the mid holocene 8 2 4 2 ka bp a combination of weakening ism and southward displacement of the itcz enhanced the influence of the westerlies together decreasing river discharges and enhancing aeolian input probably from the sistan basin region this trend continued during the last ca 4 ka when the increasing aridification of the hab river catchment further increased the aeolian inputs solar and lunar driven short term variations as well as bond events known from the north atlantic ocean superpose these trends they lead to a pronounced increase of fluvial inputs between 8 6 8 4 ka bp and at ca 3 ka bp as well as to dry events around 4 2 ka and 1 2 1 ka bp our study highlights the increasing influence of the westerlies on the sedimentation processes in the northeastern arabian sea towards the late holocene

molecular record of secular sea surface temperature changes on 100 year timescales for glacial terminations i ii and iv high resolution palaeoclimate records based on oxygen isotope data have provided important insights into climate variability and rates of natural climate change on about a thousand year timescale1 3 little is known4 however about the variation of climate and of palaeoceanographic conditions throughout the quaternary on timescales of less than 1 000 years at frequencies far greater than those of the milankovitch orbital cycles here we show that such high time resolution is possible from molecular stratigraphic studies based on biomarker organic molecules alkenones we have sampled alkenone stratigraphic records at 70 to 200 yr intervals across glacial terminations i ii and iv in sediment cores from oop site 658 off northwest africa5 sea surface temperatures ssts derived from the alkenone uk37 index6 8vary rapidly beyond the range of analytical noise by up to 2 5 c in 300 yr showing hitherto unknown cycles with about 600 yr periodicities some of the changes parallel similar events in the oxygen isotope stratigraphy sst oscillations may be linked in part to abrupt breakdowns in atlantic deep water ventilation resulting from meltwater events of quaternary glacial terminations3 9 10

evaluation of the influence of monsoon climatology on dispersal and sequestration of continental flux over the southeastern arabian sea abstract associated with the coupled land ocean heating cooling seasonal reversal of monsoon winds regulates hydrography precipitation upwelling fluvial influx and a host of biogeochemical processes we evaluate the role of the monsoon winds fluvial discharge and currents on continental flux dynamics from advection magnitude of clays over an anomalous high precipitation regime of the southeastern arabian sea coupled with the intense rains and a high fluvial discharge we archived an elevated content of detrital clays 41 mg l 1 during the southwest monsoon over the 40 m however had much reduced detrital clays

pollen distribution in hemipelagic surface sediments of the south china sea and its relation to modern vegetation distribution abstract this paper analyses the distribution of pollen in the surface sediments of the south china sea as recorded in 28 samples from the area 6 09 20 07 n and 112 05 119 45 e at water depths of 329 4307 m pollen concentrations range from 444 kgrains g dry wt on the lower part of the continental slope in the northeast to zero in the central basin below 4000 m water depth pollen distribution patterns in the concentration and percentage isopolls incorporating data from the literature reflect the routes and mechanisms of pollen transport pollen source areas and considerable systematic differences between north and south the northern scs is distinguished by very high concentrations due to the high production and effective long distance transport of pine pollen and fern spores the maximum of their concentration occurs in the north adjacent to the convergence of the bashi and taiwan straits rather than near the estuaries of big rivers and stretches as a saddle from ne to sw consistent with the direction of the ne winter monsoon and sea current this pattern implies that pine pollen and fern spores adapted to wind transport and water flotation come from the northeast through the straits borne on the winter monsoon and sea current forced by it their source areas should cover large regions probably including south and southeast china most pollen of tropical and subtropical broad leaved trees found in the northern part of the scs occur in low concentrations however these concentrations decrease uniformly offshore implying a fluvial discharge from nearby lowlands in south china in the southern part of the scs pollen of tropical and subtropical broad leaved trees predominate total pollen concentrations however are much lower only 1 10 of those of the northern part the greatest concentrations occur offshore north borneo and decrease toward deep water suggesting fluvial input from relatively local sources on the adjacent islands e g borneo

paleoprecipitation record from coral sr ca and δ18o during the mid holocene in the northern south china sea coupled high resolution sr ca and delta o 18 records of a modern and a mid holocene coral from sanya in the southern hainan island northern south china sea scs were reported and the residual delta o 18 delta delta o 18 were calculated to indicate precipitation change in this region unlike other paleoclimate studies this study focused on changes of precipitation time rather than precipitation amount as negative delta delta o 18 peaks in coral generally correspond to peak precipitations or rainy seasons in the surrounding region the time offsets between negative delta delta o 18 peaks and other seasonal indicators such as sea surface temperature sst can well indicate the time of rainy seasons and the precise time offsets can be estimated by the method of cross spectral analysis the results of the modern coral indicate that the variation of the coral delta delta o 18 lags that of the instrumental measured precipitation by about 2 months and about 3 months to the sst derived from coral sr ca ratios this agrees well with the modern observation that the salinity change in the southern coastal regions generally lags that of the precipitation in hianan island by about 2 months and the precipitation change lags about 1 month behind the sst in this region thus coral delta delta o 18 records can be a reliable proxy for the change of rainy seasons in this region the results of the mid holocene coral show about 2 5 months leading of the delta delta o 18 variation ahead of the sst by compensating the approximate 3 months lag of the delta delta o 18 variation behind the sst in modern time the occurrence of rainy seasons during the mid holocene may have advanced about 5 6 months in detail it may start around december and end around april to may with maximum occurring around february therefore rainy seasons mainly occur in winter through early spring during the mid holocene compared with that from may through october in modern times such precipitation patterns appear to agree with the mid holocene pollen records in this region variations of large scale circulation may possibly result in such a different precipitation pattern further studies in particular climate model studies collaborated with meteorologists are required for a better understanding of the mechanism

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

anomalous inland influx of the river indus gulf of kachchh india the gulf of kachchh is a funnel shaped macrotidal water body located in the arid region of northwestern india with 50 cm annual rainfall and insignificant fluvial input the gulf waters however have high suspended matter time series measurements of total suspended matter tsm and synchronous validated hydrodynamic modeling have been used to decipher the dispersal pathways and the sources of the high turbidity contrary to the prevalent offshore reducing trend for most of the indian coast the gulf is anomalous for having an enhanced turbidity at the mouth with lower concentrations in the inland areas the hydrography of the gulf is dominated by strong alongshore currents at the mouth which move in out during flood ebb and undergo cyclic dynamic changes with tidal phases the flood tidal currents amplify inland with propagating tides pulling in the offshore waters and acting as a feeder of high saline turbid offshore waters into the gulf most of which are trapped inland due to time lag of ebb and flood between the outer and the inner gulf based upon the distribution maps of tsm and clays in the water column it is deduced that a large segment of the gulf is nourished by contributions from the indus river

major and trace element variations of the sediments at odp site 1144 south china sea during the last 230 ka and their paleoclimate implications abstract we present here the major and trace element data of the sediments at odp site 1144 of the last 230 ka with time resolution about 1 5 kyr to investigate their relations to the climate changes estimated from tio2 and cao contents over 70 in weight of the sediments are terrestrial materials and caco3 abundance ranges between 7 and 19 the variation patterns of some of the major elements such as al fe k mg and mn and some of the trace elements such as the alkali elements such as rb and cs the alkali earth elements such as ba and most transition metals such as sc v co cr zn well match that of the oxygen isotopes of the planktonic foraminifer after normalized with ti with higher values during interglacial periods and lower values during glacial periods whilst the na abundance exhibits inverse variation patterns with lower values during interglacial periods and higher values during glacial periods however most refractory elements such as y zr nb hf ta rees th and u do not show such patterns these agree well with the behaviors of these elements during chemical weathering therefore the changes of chemical weathering intensity in south china the source area of these sediments may account for such variation patterns during interglacials wet and warm climate might occur at south china which resulted in stronger chemical weathering and dry climate might occur during glacials which resulted in weaker chemical weathering such paleoclimate interpretation agrees with those from other paleoclimate proxies such as pollen records indicating that change of the east asian monsoon especially change of the winter monsoon is the key for such paleoclimate variation patterns

a finite element simulation of tidal circulation in the gulf of kutch india abstract a finite element fe model using the software package adcirc was developed to simulate the tides and currents in the gulf of kutch located on the northwest coast of india the surface elevations from the model were analysed for the amplitudes and phases of four major tidal constituents m 2 s 2 k 1 and o 1 and the principal overtide m 4 and compared with observed values model currents were compared with observations at three locations along with the corresponding results from a finite difference model for the same region the results were found to be consistent with the fe model providing improved resolution in key areas residual circulation evaluated by forcing the fe model with m 2 tide and winds those typical of the southwest monsoon show currents which are directed upstream in the shallow region of the gulf a better simulation of lateral variations in currents in the fe model helps in identifying relative differences in tidal circulation and residual circulation between the deep and shallow regions of the gulf

evidence for massive discharges of icebergs into the north atlantic ocean during the last glacial period sediments in the north atlantic ocean contain a series of layers that are rich in ice rafted debris and unusually poor in foraminifera1 here we present evidence that the most recent six of these heinrich layers deposited between 14 000 and 70 000 years ago record marked decreases in sea surface temperature and salinity decreases in the flux of planktonic foraminifera to the sediments and short lived massive discharges of icebergs originating in eastern canada the path of the icebergs clearly marked by the presence of ice rafted detrital carbonate can be traced for more than 3 000 km a remarkable distance attesting to extreme cooling of surface waters and enormous amounts of drifting ice the cause of these extreme events is puzzling they may reflect repeated rapid advances of the laurentide ice sheet perhaps associated with reductions in air temperatures yet temperature records from greenland ice cores appear to exhibit only a weak corresponding signal moreover the 5 10 000 yr intervals between the events are inconsistent with milankovitch orbital periodicities raising the question of what the ultimate cause of the postulated cooling may have been

fine grained sediment transport and sorting by tidal exchange in xiangshan bay zhejiang china abstract during the winter of 1983 25 h measurements of current speed flow direction water depth and suspended sediment concentration were carried out at six stations located in the inlet section of xiangshan bay during spring and neap tides an analysis of the data obtained shows that tidal exchange in the form of either vertical residual circulation or bay mouth water mixing is responsible for the observed net landward movement of suspended sediment though the ebb currents are stronger than the flood currents in the inlet the analysis suggests also that the tidal exchange processes in combination with the settling behaviour of the suspended sediments and the morphological features of the inlet section lead to marked sorting of the fine grained sediments with the clayey material predominating in the inner part of the bay and the silty material in the outer part

the tephrochronology of iceland and the north atlantic region during the middle and late quaternary a review the tephrochronology of iceland and the north atlantic region is reviewed in order to construct a unified framework for the last 400 kyr bp nearly all of the tephra layers described are also characterised geochemically a number of new tephra layers are analysed for the first time for their geochemical signature and a number of pre holocene tephra layers have been given an informal denotation the tephrostratigraphy of ash zone ii is highlighted where possible the rhyolitic tephra layers found outside iceland have been correlated to known icelandic tephra layers or to the volcanic source area the application of tephra fallout in various depositional environments is described and discussed copyright 2000 john wiley sons ltd

integrating the intimate records using tephrochronology rising to the challenge little has challenged our understanding of climate change more so than the abruptness with which large scale shifts in temperature occurred during the late quaternary the causal mechanisms driving

late pleistocene holocene climate and sea level changes inferred based on the tidal terrace sequence kachchh western india abstract an estuarine tidal terrace sequence at the mouth of the kharod river kachchh western india is investigated for pleistocene to holocene climate and sea level changes based on sedimentology major element geochemistry mineralogy supported by optical dating the study reports a lowered sea level during 13 8 ka followed by gradual rise in the sea level until around 6 ka this is ascribed to a combination of enhanced melt water discharge and strengthened indian summer monsoon ism the temporal changes in major elements detrital proxies suggest a fluctuating to an overall arid monsoon conditions during 5 7 to 3 1 ka with a rapidly rising sea level this is further supported by the dominance of fine textured sediment along with the occurrences of shell rich horizon in the absence of any evidence of land level changes the study suggests that at around 6 ka to 3 ka the sea was approximately 2 m higher then present the decline in the concentration of geochemical proxies and occurrence of aeolian sand after 3 ka is interpreted as the onset of aridity and present day like conditions the three levels of sea stands during early middle and late holocene are synchronous with various archeological harappan settlements in the region

the vegetation and climate at the last glaciation on the emerged continental shelf of the south china sea studies on the dispersal mechanism and source areas of pollen from hemipelagic sediments recovered from the continental slopes of the south china sea scs reveal that vegetation existed on the exposed shelves at the last glacial maximum lgm and the latter part of the marine isotope stage 3 at the low sea level stand artemisiadominated grassland covered the northern continental shelf and tropical lowland rainforest and mangroves grew on the southern shelf sunda land consequently the climate in the northern scs must have been much colder and drier during the last glacial period compared to the present sunda land experienced only a marginally lower temperature but was not drier than today the enhanced contrast between the northern and southern parts of the scs in vegetation and climate during the lgm may be ascribed at least partly to the strengthening of winter monsoon during the last glacial period 2000 elsevier science b v all rights reserved

volcaniclastic sediments from mid oceanic kolbeinsey ridge north of iceland evidence for submarine volcanic fragmentation processes volcaniclastic sediments of the active kolbeinsey ridge north of iceland reflect changing fragmentation mechanisms due to increasing sea level during the last deglaciation glass shards deposited on the western flank of the mid oceanic ridge before 13 4 ka are vesicular 20 60 whereas shards deposited since 13 4 ka are mostly vesicle free and of hyaloclastic origin the vesicle rich shards display morphology thought to be atypical for submarine eruptions at this depth 400 500 m the environmental conditions during the deposition of these layers regional ice cover more than 200 km from the nearest subaerial source preclude a subaerial origin for these shards we propose an eruption mechanism in which hot vesiculating bombs from a low energy eruption are transported upward through the water column by convection these particles reach their volcanic fragmentation depth vfd and undergo secondary fragmentation creating the vesicle rich shards recovered near the ridge rising sea level since the end of the last glaciation was sufficient to prevent the erupted particles from reaching the vfd thus ending the formation of vesicle rich shards this model explains the presence of vesicular shards in sediments of mid oceanic ridges where no subaerial source can be inferred

indian summer monsoon and winter hydrographic variations over past millennia resolved by clay sedimentation 1 reconstruction of century scale indian monsoon and winter hydrography is made from an ams dated core located in the unique region of the southeast arabian sea which lies in the pathways of the low salinity bay of bengal waters advecting during winter northeast monsoon nem based upon clay mineral analyses in seawaters we identify chlorite and kaolinite as specific clays supplied by the bay of bengal waters and local fluvial flux by the southwest monsoon swm precipitation from the peninsular india respectively along the southwest continental margin of india an evaluation of clay flux and 18o in g ruber portrays century scale weaker swm precipitation events during 450 650 yr 1000 yr and 1800 2200 cal yr bp kaolinite wt and flux were found to be low during all these events though chlorite had a persistent or enhanced flux from the enhanced flux of chlorite and reduced kaolinite chlorite ratio during weaker phases of swm we deduce a stronger nem winter hydrography implying an inverse coupling between the summer and the winter monsoon

millennial and centennial scale vegetation and climate changes during the late pleistocene and holocene from northern new mexico usa abstract high resolution pollen and magnetic susceptibility ms data from a sediment core from an alpine bog 3100 m in the sangre de cristo mountains new mexico record variations in treeline elevation and in sedimentation for the last 14 ka cal yr bp strong correspondence between the paleovegetation and the ms profile suggests that both records can be used to reconstruct past climatic conditions the coldest conditions in this area occurred at the end of the late pleistocene during the pinedale glaciation and the younger dryas chron a general warming trend took place during the early holocene lasting until 5 6 ka when the warmest conditions occurred a progressive climate cooling is then observed until today millennial and centennial scale changes are also observed throughout the vegetation and ms records the higher amplitude millennial scale cold events appear to correlate with the timing and duration of episodes of enhanced sea ice drift in the north atlantic and the lower amplitude centennial scale cold events may correlate with periods of lower solar activity a solar climate connection is suggested from these records by a prominent ca 200 yr cycle in tree pollen abundance which may correlate with the 208 yr suess solar cycle this study shows an immediate response of the vegetation treeline to climate change at millennial and centennial scales probably related to variations in summer insolation and solar activity during the late pleistocene and holocene such high resolution studies are very important in order to predict future climate change and particularly in very arid areas where human activity and economies are strongly influenced by climate

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr