stacking paleointensity and oxygen isotope data for the last 1 5 myr piso 1500 coupled relative geomagnetic paleointensity rpi and oxygen isotope records are used to construct rpi and oxygen isotope stacks for the last 1 5 myr the coupled correlations are accomplished using the match algorithm lisiecki l e and lisiecki p a 2002 application of dynamic programming to the correlation of paleoclimate records paleoceanography 17 1049 doi 10 1029 2001pa000733 to simultaneously correlate isotope and rpi records the simultaneous match reduces the degree of freedom associated with correlations using rpi or oxygen isotope records alone the overall compatibility of rpi and oxygen isotopes indicates a dominant global but independent component in both signals the local wavelet power spectrum lwps for the rpi stack indicates little significant orbital power although the accompanying oxygen isotope stack has all the lwps characteristics expected of a high resolution oxygen isotope record containing orbital frequencies the piso 1500 stack represents a new stratigraphic template that can be used to correlate among marine sediment records and link them to polar ice cores via variations in cosmogenic nuclide production scaling the stack to values for virtual axial dipole moment vadm indicate maxima at 15 1022 am2 and minima that imply a threshold of 2 5 1022 am2 below which values are associated with either polarity reversals or magnetic excursions

mg ca ratios in the planktonic foraminifer neogloboquadrina pachyderma sinistral in the northern north atlantic nordic seas in core top samples in the nordic seas mg ca ratios of n pachyderma sin are generally consistent with previous high latitude calibration data but do not reflect the modern calcification temperature gradient from 2 c in the northwest to 8 c in the southeast this is because mg ca ratios in foraminiferal shells from the central nordic seas are 0 4 mmol mol higher than expected from calibrations of nurnberg 1995 and elderfield and ganssen 2000 the enhanced mg ca ratios are observed in an area with low sedimentation rates 5 cm kyr possible factors that may cause this include bioturbation holocene variability in old core tops dissolution pore water chemistry occurrence of volcanic ash and other natural variability the enhanced foraminiferal mg ca ratios in areas of the nordic seas and the northern north atlantic may also be linked with secondary factors related to the presence of fresher and colder water masses possibly combined with pore water chemistry in low sedimentation areas differing from high sedimentation areas

linking the 8 2 ka event and its freshwater forcing in the labrador sea 1 the 8 2 ka event was the last deglacial abrupt climate event a reduction in the atlantic meridional overturning circulation amoc attributed to the drainage of glacial lake agassiz may have caused the event but the freshwater signature of lake agassiz discharge has yet to be identified in 18o of foraminiferal calcite records from the labrador sea calling into question the connection between freshwater discharge to the north atlantic and amoc strength using mg ca paleothermometry we demonstrate that 3 c of near surface ocean cooling masked an 1 0 decrease in western labrador sea 18o of seawater concurrent with lake agassiz drainage comparison with north atlantic 18o of seawater records shows that the freshwater discharge was transported to regions of deep water formation where it could perturb amoc and force the 8 2 ka event

paleointensity assisted chronostratigraphy of detrital layers on the eirik drift north atlantic since marine isotope stage 11 1 four piston cores collected in 1999 and 2002 from the eirik drift southern labrador sea off se greenland provide paleomagnetic environmental magnetic and oxygen isotope records back to marine isotope stage 11 age models for the cores are based on a combination of planktonic oxygen isotope data relative geomagnetic paleointensity proxies and the identification of geomagnetic excursions laschamp and iceland basin environmental magnetic data delineate two distinct detrital signals interpreted to reflect the behavior of the surrounding ice sheets greenland and laurentide to orbital and millennial scale climate forcing broad decimeter scale intervals of increased magnetic concentration and grain size occur during the early part of interglacial marine isotopic stages mis 1 5 7 9 and 11 discrete centimeter scale layers recognized by magnetic concentration and grain size sensitive parameters gamma ray attenuation gra bulk density and carbonate content are observed in glacial and interglacial stages as well as during terminations on the basis of glacial reconstructions on greenland during the last termination the broad decimeter scale coarser grained intervals can be attributed to detrital influx associated with the retreat of the terrestrial based greenland ice sheet in the early holocene a similar magnetic signal observed within interglacial mis 5 7 9 and 11 indicates similar greenland ice sheet behavior during these time intervals two types of centimeter scale detrital layers are also recognized back to mis 11 detrital carbonate dc layers reflect predominately ice rafted debris ird deposition while the low detrital carbonate ldc layers reflect mass movement as evidenced by sharp basal contacts graded bedding and traction structures likely from the greenland slope some detrital layers on eirik drift particularly the dc layers can be tentatively correlated to detrital layers observed in the central north atlantic and to those documented on the southern side of the labrador sea at orphan knoll

multiple stage deglacial retreat of the southern greenland ice sheet linked with irminger current warm water transport 1 there is limited knowledge pertaining to the history of the greenland ice sheet gis during the last glacial interglacial transition as it retreated from the continental margins to an inland position here we use multiproxy data including ice rafted debris ird planktonic isotopes alkenone temperatures and tephra geochemistry from the northern labrador sea off southwest greenland to investigate the deglacial response of the gis and evaluate its implications for the north atlantic deglacial development the results imply that the southern gis retreated in three successive stages 1 early deglaciation of the east greenland margins by tephra rich ird that embrace heinrich event 1 2 progressive retreat during allerod culminating in major meltwater releases 18o depletion of 1 2 at the allerod younger dryas transition 12 8 13 0 kyr b p and 3 a final stage of glacial recession during the early holocene 9 11 kyr b p rather than indicating local temperatures of ambient surface water the alkenones likely were transported to the core site by the irminger current we attribute the timing of gis retreat to the incursion of warm intermediate waters along the base of grounded glaciers and below floating ice shelves on the continental margin the results lend support to the view that gis meltwater presented a forcing factor for the younger dryas cooling

episodic reductions in bottom water currents since the last ice age although north atlantic deep water formation was greatly reduced during the last glacial maximum bottom water currents were as vigorous as at present however they were weakened during periods of north atlantic surface freshening a strong correlation can be seen between bottom water current strength and greenland air temperature records thus confirming a close connection between ocean circulation and abrupt climate change past changes in the freshwater balance of the surface north atlantic ocean are thought to have influenced the rate of deep water formation and consequently climate1 2 although water mass proxies are generally consistent with an impact of freshwater input on meridional overturning circulation3 there has been little dynamic evidence to support this linkage here we present a 25 000 year record of variations in sediment grain size from south of iceland which indicates vigorous bottom water currents during both the last glacial maximum and the holocene period together with reconstructions of north atlantic water mass distribution vigorous bottom currents suggest a shorter residence time of northern source waters during the last glacial maximum relative to the holocene period the most significant reductions in flow strength occur during periods that have been associated with freshening of the surface north atlantic the short term deglacial oscillations in bottom current strength are closely coupled to changes in greenland air temperature with a minimum during the younger dryas cold reversal and a maximum at the time of rapid warming at the onset of the holocene our results support a strong connection between ocean circulation and rapid climate change

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

changes in meridional temperature and salinity gradients in the north atlantic ocean 30 72 n during the last interglacial period eight deep sea sediment cores from the north atlantic ocean ranging from 31 to 72 n are studied to reconstruct the meridional gradients in surface hydrographic conditions during the interval of minimum ice volume within the last interglacial period using benthic foraminiferal 18o measurements and estimates of sea surface temperature sst and sea surface salinity sss we show that summer ssts and ssss decreased gradually during the interval of minimum ice volume at high latitude sites 52 72 n whereas they were stable or increased during the same time period at low latitude sites 31 41 n this increase in meridional gradients of ssts and ssss may have been due to changes in the latitudinal distribution of summer and annual average insolation and associated oceanic and atmospheric feedbacks these trends documented for the eemian ice volume minimum period are similar to corresponding changes observed during the holocene and may have had a similar origin

isotope stratigraphy sedimentation rates deep circulation and carbonate events in the labrador sea during the last 200 ka high resolution stable isotope and accelerator mass spectrometry 14c measurements in 25 box and piston cores from the labrador sea allow the reconstruction of major paleoceanographical changes during the last 200 ka in this basin and also document the links between the interior of the laurentide ice sheet and the north atlantic ocean during this interval two deep circulation regimes are indicated by contrasting sedimentation rates on the slopes i the modern situation is characterized by a gyre of the north atlantic deep water nadw components into the basin which is responsible for the high energy western boundary undercurrent this regime also prevailed during the former true interglacials and possibly during shorter warm intervals e g bolling allerod ii a more frequent nadw free situation during glacial and interstadial intervals is marked by the presence of a vertically homogeneous water mass in the basin sedimentological records also indicate that carbonate events i e pulses of

four climate cycles of recurring deep and surface water destabilizations on the iberian margin centennial climate variability over the last ice age exhibits clear bipolar behavior high resolution analyses of marine sediment cores from the iberian margin trace a number of associated changes simultaneously proxies of sea surface temperature and water mass distribution as well as relative biomarker content demonstrate that this typical north south coupling was pervasive for the cold phases of climate during the past 420 000 years cold episodes after relatively warm and largely ice free periods occurred when the predominance of deep water formation changed from northern to southern sources these results reinforce the connection between rapid climate changes at mediterranean latitudes and century to millennial variability in northern and southern polar regions

timing of meltwater pulse 1a and climate responses to meltwater injections the temporal relationship between meltwater pulse 1a mwp 1a and the climate history of the last deglaciation remains a subject of debate by combining the greenland ice core project d18o ice core record on the new greenland ice core chronology 2005 timescale with the u th dated barbados coral record we conclusively derive that mwp 1a did not coincide with the sharp bolling warming but instead with the abrupt cooling of the older dryas to evaluate whether there is a relationship between meltwater injections north atlantic deep water nadw formation and climate change we present a high resolution record of nadw flow intensity from eirik drift through the last deglaciation it indicates only a relatively minor 200 year weakening of nadw flow coincident with mwp 1a our compilation of records also indicates that during heinrich event 1 and the younger dryas there were no discernible sea level rises and yet these periods were characterized by intense nadw slowdowns shutdowns clearly deepwater formation and climate are not simply controlled by the magnitude or rate of meltwater addition instead our results emphasize that the location of meltwater pulses may be more important with nadw formation being particularly sensitive to surface freshening in the arctic nordic seas

morphologic gradation and ecology in neogloboquadrina pachyderma and n dutertrei planktic foraminifera from core top sediments abstract an analysis of ecologic preferences of n pachyderma n dutertrei and morphologically intermediate forms is used for a test of coincidence of morphologic and ecologic gradation in modern neogloboquadrina relative abundances in 461 indian ocean and north atlantic surface sediment assemblages of planktic foraminifera 150 m climap data are plotted against annual means of physical parameters extracted for each core location sea surface temperature sea surface salinity the temperature at 200 m depth the vertical temperature gradient and the density contrast stratification between the sea surface and 200 m depth the intermediate forms can be considered as n pachyderma living under suboptimum conditions neogloboquadrina dutertrei consists of two populations one in tropical water masses and one in subtropical water masses near ocean margins morphologic gradation in neogloboquadrina does not reflect ecologic gradation two ecological groups exist in neogloboquadrina 1 n dutertrei tropical population and 2 n pachyderma the intermediate forms and n dutertrei subtropical ocean margin population a relative abundance minimum exists between these populations near the limit between tropical and subtropical water masses

adaptation of a flow through leaching procedure for mg ca paleothermometry 1 mg ca ratios in planktonic foraminifera reflect calcification temperatures and are thus useful for sea surface temperature sst reconstructions despite the obvious utility of this paleoceanographic tracer problems of dissolution gametogenic calcification and contaminant phases have thus far limited confidence in mg ca based reconstructions here we show strong evidence of mg heterogeneity in foraminiferal calcite by sequentially measuring the composition of different forms of calcite ontogenetic gametogenic diagenetic in the same shells while monitoring and removing contaminant phases a new flow through method combines chromatographic technology and inductively coupled plasma mass spectrometry icp ms in a series of cleaning and dissolution reactions monitored continuously with time resolved analysis tra this combination of slow controlled dissolution and tra provides a complete elemental description of contaminant phases and sorts the cleaned calcium carbonate based on dissolution sensitivity examination of partially dissolved shells with electron microscopy suggests that the flow through method simulates the natural dissolution sequence and effectively separates the different calcite domains within a single foraminiferal shell heterogeneity of mg ca in foraminiferal calcite is clearly demonstrated in flow through analysis foraminiferal shells have initially high mg levels that decrease steadily throughout dissolution later dissolution yields lower mg ca which is likely due to a combination of subsurface calcification and biomineralization effects mg ca ratios from the most dissolution sensitive high mg portions of surface dwelling species in core tops are used to calculate calcification temperatures a comparison of late holocene core top data with world ocean atlas sst data indicates that the flow through method does yield viable sst estimates furthermore a depth transect in the eastern tropical pacific suggests that this approach provides the opportunity to extract initial calcification temperatures despite partial dissolution of foraminiferal shells

reassessing mg ca temperature calibrations of neogloboquadrina pachyderma sinistral using paired δ44 40ca and mg ca measurements the mg ca temperature calibration of the polar to subpolar planktonic foraminifera neogloboquadrina pachyderma sinistral sinistral indicates left coiling was refined by a multiproxy approach combining hydrographic temperature and salinity data with mg ca delta ca 44 40 and delta o 18 values from holocene nordic seas core top samples reliable mg ca based temperature estimates are limited to foraminiferal tests that calcified in water masses with temperatures above similar to 3 degrees c at habitat depth in these samples mg ca and delta ca 44 40 values are positively correlated mg ca mmol mol 0 77 0 22 x delta ca 44 40 parts per thousand srm 915a 0 52 0 12 n 20 r 2 0 76 both mg ca and delta ca 44 40 derived temperatures projected onto their corresponding depth intervals reveal that the apparent calcification depth of n pachyderma sinistral averaging the specimens whole life cycle is bound to an isopycnal layer defined by water densities sigma t between 27 7 and 27 8 this implies that n pachyderma sinistral prefers gradually deeper habitats with increasing sea surface temperatures thus counterbalancing absolute temperature variations consequently the total temperature range recorded in this foraminiferal species is restricted and only partly reflects environmental changes on the basis of the new mg ca delta ca 44 40 and delta o 18 multiproxy data set we propose a linear mg ca temperature relation for high latitude n pachyderma sinistral mg ca mmol mol 0 13 0 037 t degrees c 0 35 0 17 t 3 degrees c in core top samples from polar waters with peak summer temperatures below similar to 3 degrees c the temperature response in the mg ca and delta ca 44 40 proxy signal is inversed and poorly correlated both mg ca and delta ca 44 40 derived temperature estimates pretend significantly higher calcification temperatures than maximum summer sea surface temperatures of these water masses

holocene paleoclimate data from the arctic testing models of global climate change to evaluate the spatial variability of arctic climate change during the present interglacial cape project members compiled well dated terrestrial marine and ice core paleoenvironmental records spanning the past 10 12 thousand years ka six tundra biomes of increasing summer temperature requirements were defined based on regionally coherent pollen assemblages using a rule based approach pollen spectra were converted to tundra forest tundra or forest biomes ranked by their average growing season requirements marine sea surface reconstructions were based on proxy data following a similar rule based approach from these data based reconstructions departures in summer temperatures from modern normals were calculated in 1 ka time slices through the holocene to test predictive models data based summer temperature reconstructions were compared with general circulation model gcm simulations for 10 ka and 6 ka ago paleodata and model results both show that warming occurred earlier across beringia and asia relative to lands adjacent to the north atlantic and that late holocene cooling was most apparent in the north atlantic region however the gcm over predicts the magnitude of mid holocene warming over northern asia and underestimates the intensification of the north atlantic drift in the early holocene strong spatial variability in environmental response during the holocene despite symmetric insolation forcing suggests that any future changes whether caused by anthropogenic or natural factors are unlikely to result in a uniform change across the arctic adding additional complexity to forecasts of global impacts

stable isotope clue to episodic sea ice formation in the glacial north atlantic sea ice is a determinant parameter of the climate system which acts as amplifier through positive ice albedo feedbacks and induces deep water formation through brine production it is also one of the most elusive parameters in the paleoclimate record most proxies of sea ice provide information on its presence and extent of e g diatoms or dinocysts but do not permit assessment on its rate of formation however seemingly off equilibrium low 18o values in mesopelagic planktic foraminifer species as observed today in the arctic ocean are thought to relate to the production of isotopically light brines during sea ice formation and might thus provide a clue on the rate of sea ice growth with reference to the isotopic properties of modern planktic foraminifers in the arctic ocean and using multi proxy data sets from the last glacial stage in the northwest north atlantic we re examined some of the current interpretations of planktic isotope records in the glacial nw north atlantic the large amplitude light isotopic excursions recorded in neogloboquadrina pachyderma left coiling during heinrich events 1 for example correspond to extensive sea ice cover as reconstructed from dinocysts and do not seem unequivocally linked to low salinity pulses such light isotopic excursion more likely responded to enhanced rates of sea ice formation resulting in the production and sinking of isotopically light brines on the contrary the isotopically heavy planktic foraminifers of the last glacial maximum lgm interval stricto sensu would rather suggest relatively low rates of brine production thus low sea ice growth rates in the area this would imply that the lgm distribution of sea ice in the north atlantic was primarily linked to spreading and drifting from marginal and nordic source areas and not from enhanced in situ production at the scale of glacial interglacial cycles isotopic distillation processes relating to sea ice production at high latitudes could be one of the factors controlling the 18o salinity relationship in deep ocean water masses that might deserve closer examination as it would be independent of continental ice volume changes

oxygen isotope compositions of sinistral neogloboquadrina pachyderma tests in surface sediments north atlantic ocean abstract neogloboquadrina pachyderma left coiled is a planktonic foraminifer indicator species for polar waters it is present in both the glacial and interglacial sediments of the high latitude oceans and therefore is frequently used as a signal carrier for constructing late pleistocene holocene planktonic 18 o records in this study the 18 o compositions of n pachyderma l tests from deep sea surface sediments are compared with surface water 18 o values and summer sea surface temperatures sst in the north atlantic ocean the norwegian greenland sea and the labrador sea we document that for a temperature range of 2 8 c the planktonic 18 o values follow paleotemperature equations with an offset of less than 0 4 and that above 8 c the planktonic 18 o compositions become almost independent of sst and remain nearly constant this pattern suggests that n pachyderma l precipitates its shell nearly at isotopic equilibrium with surface waters colder than 8 c and that in warmer surface waters n pachyderma l changes its habitat depth or its growth season to secrete its shell at an ambient temperature around 7 9 c

magnetic properties of deep sea sediments off southwest greenland evidence for major differences between the last two deglaciations high resolution rock magnetic data atomic mass spectroscopy 14 c dates 18 o and grain size analyses from a piston core hu90 013 013 located off southwest greenland provide a record of the last two deglaciations during termination i a welldefined interval having high volumetric magnetic susceptibility k and a low ratio of anhysteretic susceptibility to volumetric magnetic susceptibility k arm k postdates the younger dryas and the 18 o change marking the stage 2 1 boundary and correlates with sedimentological and geomorphological evidence for greenland ice sheet retreat from the coastline to the continental interior during termination ii a very similar magnetic signal coincides with the 18 o shift marking the stage 6 5 glacial interglacial transition and continues throughout substage 5e we suggest that this magnetic signal during both termination i and termination ii marks continental meltwater carried detritus from greenland if so the synchronous changes in magnetic and oxygen isotopic records at termination ii indicate very early and rapid deglaciation of greenland in contrast to the relatively late deglaciation observed for termination i distinct fluctuations in k and k arm k occur below the onset of the 18 o change at termination i where they occur at 16 900 yr b p and at termination ii these fluctuations are interpreted as due to sudden influxes of detritus into the basin caused by unpinning of ice from the continental shelf at the inception of deglaciation

river mouth bar formation riverbed aggradation and channel migration in the modern huanghe yellow river delta china this paper addresses the recent 1970s 1990s processes of river mouth bar formation riverbed aggradation and distributary migration in the huanghe river mouth area in the light of station based monitoring field measurements and remote sensing interpretation the results show that the morphological changes of the river mouth bar have been closely associated with the largely reduced fluvial discharge and sediment load landforrn development such as bar progradation occurred in two phases i e before and after 1989 which correspond to faster and lower bar growth rates respectively fast riverbed aggradation in the mouth channel was strongly related to river mouth bar progradation during 1976 1996 about 2 8 of the total sediment loads were deposited in the river channel on the upper to middle delta therefore the river water level rose by a few meters from 1984 to 1996 the frequent distributary channel migration which switched the radial channel pattern into the se directed pattern in the mid 1980s was linked with mouth bar formation marine conditions also constrain seaward bar progradation furthermore the history of river mouth bar formation reflects human impacts such as dredging and dyking in order to stabilize the coastal area c 2005 elsevier b v all rights reserved

simulation of abrupt climate change induced by freshwater input to the north atlantic ocean temperature records from greenland ice cores1 2 suggest that large and abrupt changes of north atlantic climate occurred frequently during both glacial and postglacial periods one example is the younger dryas cold event broecker3 speculated that these changes result from rapid changes in the thermohaline circulation of the atlantic ocean which were caused by the release of large amounts of melt water from continental ice sheets here we describe an attempt to explore this intriguing phenomenon using a coupled ocean atmosphere model in response to a massive surface flux of fresh water to the northern north atlantic of the model the thermohaline circulation weakens abruptly intensifies and weakens again followed by a gradual recovery generating episodes that resemble the abrupt changes of the ocean atmosphere system recorded in ice and deep sea cores4 the associated change of surface air temperature is particularly large in the northern north atlantic ocean and its neighbourhood but is relatively small in the rest of the world

transient simulation of last deglaciation with a new mechanism for bolling allerod warming we conducted the first synchronously coupled atmosphere ocean general circulation model simulation from the last glacial maximum to the bolling allerod ba warming our model reproduces several major features of the deglacial climate evolution suggesting a good agreement in climate sensitivity between the model and observations in particular our model simulates the abrupt ba warming as a transient response of the atlantic meridional overturning circulation amoc to a sudden termination of freshwater discharge to the north atlantic before the ba in contrast to previous mechanisms that invoke amoc multiple equilibrium and southern hemisphere climate forcing we propose that the ba transition is caused by the superposition of climatic responses to the transient co 2 forcing the amoc recovery from heinrich event 1 and an amoc overshoot

do river deltas in east india retreat a case of the krishna delta abstract the construction of multiple dams and barrages in many indian river basins over the last few decades significantly reduced river flow to the sea and affected the sediment regime more reservoir construction is planned through the proposed national river linking project nrlp which will transfer massive amounts of water from the north to the south of india the impacts of these developments on fertile and ecologically sensitive deltaic environments are poorly understood and quantified at present in this paper an attempt is made to identify locate and quantify coastal erosion and deposition processes in one of the major river basins in india the krishna using a time series of landsat images for 1977 1990 and 2001 with a spatial resolution ranging from 57 0 m to 28 5 m the dynamics of these processes are analyzed together with the time series of river flow sediment discharge and sediment storage in the basin comparisons are made with similar processes identified and quantified earlier in the delta of a neighboring similarly large river basin the godavari the results suggest that coastal erosion in the krishna delta progressed over the last 25 years at the average rate of 77 6 ha yr 1 dominating the entire delta coastline and exceeding the deposition rate threefold the retreat of the krishna delta may be explained primarily by the reduced river inflow to the delta which is three times less at present than 50 years ago and the associated reduction of sediment load both are invariably related to upstream reservoir storage development

distribution of planktic foraminifera at the ice margin in the arctic fram strait planktic foraminifera were collected in net tows 63 m along two east west transects at 78 and 80 n in the fram strait northern nordic seas at five concurrent depth intervals in the upper 200 m of the water column in the ice free zone absolute abundances in the upper 200 m of the water column up to 500 individuals m3 were obtained along the ice margin the absolute abundances reached up to 1250 ind m3 while in the ice covered areas not more than 50 ind m3 have been found surprisingly these strong variations in abundance are not accompanied by significant changes in faunal assemblages between the ice free and the ice covered regions neogloboquadrina pachyderma is the dominant species in most samples making up to 60 of the total faunal assemblage globigerina quinqueloba contributes 38 and all other species combined make up only 2 of the total fauna both absolute and relative abundances of the collected foraminifera are strongly dependent on the mesh size used using smaller mesh sizes provides a wider species spectrum which is of special interest for paleoceanographic reconstructions in the nordic seas where fossil assemblages 150 m often consist of only one species the specific hydrographic conditions in the fram strait with warm atlantic waters underlying cold polar surface waters result in a rather atypical depth distribution of the planktic foraminifera all species seem to prefer the temperate atlantic waters between 50 m and 200 m thus the species composition as well as geochemical tracers do not reflect the surface ocean conditions which again has potentially interesting implications for paleoceanographic reconstructions

deep sea records from the southeast labrador sea ocean circulation changes and ice rafting events during the last 160 000 years 1 results from two deep sea cores from northeast of newfoundland at 1251 and 2527 m water depth respectively indicate that during the time period from 160 000 to 10 000 years bp ice rafting events in the labrador sea were accompanied by rapid variations in deep and surface water circulation twelve ice rafting events occurred each coinciding with high concentrations of detrital carbonate and oxygen isotopic depletion of both surface and bottom waters eleven of these can be correlated with the north atlantic heinrich events h1 h11 the remaining very conspicuous ice rafting event took place early in mis substage 5e at a time when the planktic faunal assemblage suggests marked warming of the sea surface in the shallower core benthic delta 13 c values rise from a minimum during the deglaciation to peak substage 5e values following the last ice rafting event indicating that the ventilation of intermediate depths was renewed after the deglaciation was complete and continued throughout substage 5e the benthic foraminifera suggest that this well ventilated water mass was comparable to the modern labrador sea water lsw the benthic faunas suggest that a relatively warm intermediate water mass entered the se labrador sea during heinrich events generally low benthic delta 13 c values indicate that this water mass was poorly ventilated and rich in inorganic nutrients isotope data and benthic faunal distributions indicate that north atlantic deep water nadw formed in the norwegian greenland sea reached the se labrador sea between the heinrich events

a new concept for the paleoceanographic evolution of heinrich event 1 in the north atlantic new records of planktonic foraminiferal 18o and lithic and foraminiferal counts from eirik drift are combined with published data from the nordic seas and the ice rafted debris ird belt to portray a sequence of events through heinrich event 1 h1 these events progressed from an onset of meltwater release at not vert similar19 ka bp through the conventional h1 ird deposition phase in the ird belt starting from not vert similar17 5 ka bp to a final phase between 16 5 and not vert similar15 ka bp that was characterised by a pooling of freshwater in the nordic seas which we suggest was hyperpycnally injected into that basin after not vert similar15 ka bp this freshwater was purged from the nordic seas into the north atlantic which preconditioned the nordic seas for convective deep water formation this allowed an abrupt re start of north atlantic deep water nadw formation in the nordic seas at the bolling warming 14 6 ka bp in contrast to previous estimates for the duration of h1 i e 1000 years to only a century or two the total combined composite h1 signal presented here had a duration of over 4000 yrs not vert similar19 14 6 ka bp which spanned the entire period of nadw collapse it appears that deep water formation and climate are not simply controlled by the magnitude or rate of meltwater addition instead the location of meltwater injections may be more important with nadw formation being particularly sensitive to surface freshening in the arctic nordic seas

neogloboquadrina pachyderma dex and sin mg ca and δ18o records from the norwegian sea magnesium calcium mg ca records based on n pachyderma dex and n pachyderma sin from the last 1200 years have been retrieved from high resolution cores in the norwegian sea comparing temperatures inferred from mg ca and the oxygen isotopic composition of calcite 18oc with instrumental temperature records from ocean weather ship mike suggests that n pachyderma calcifies during the summer season with an offset to oxygen isotope equilibrium of 0 6 in this region summer temperatures below the thermocline are related to the winter season ventilation and breakdown of the seasonal thermocline hence the deeper dwelling n pachyderma sin provides a winter season signal down core n pachyderma dex mg ca temperatures display larger variance than observed in 18oc temperatures record derived from the same morphotype the smaller variance in the 18ocn pachyderma dex temperatures is probably linked to salinity changes in the upper 50 m of the water column the mg ca temperature and 18oc records are used to reconstruct changes in the oxygen isotopic composition of water 18ow during the last 1200 years the reconstructed 18ow records show variation within a realistic range allowing the influence of other water masses than those present at the site today and suggest that the mg ca signal in morphotypes of n pachyderma in the norwegian sea responds to changes in climatic parameters

deglacial meltwater discharge north atlantic deep circulation and abrupt climate change high resolution paleogeochemical data from the north atlantic ocean indicate that in the interval 15 000 to 10 000 14c years before present b p north atlantic deep water nadw production was decreased or eliminated four times at about 14 500 and probably older 13 500 12 000 and 10 500 years b p each of these changes occurred at the same time as abrupt events of meltwater discharge to the surface ocean inferred from oxygen isotope studies of planktonic foraminifera and from glacial geological studies on land in addition each of these times may be associated with brief episodes of cooler climate in the north atlantic region the best example of which is the younger dryas cooling of 10 500 years ago these results support models linking meltwater discharge decreased nadw production and decreased north atlantic heat flux

evolution of the northeast labrador sea during the last interglaciation 1 boreal summer insolation during the last interglaciation lig generally warmed the subpolar to polar northern hemisphere more than during the early holocene yet regional climate variations between the two periods remain we investigate northeast labrador sea subsurface temperature and hydrography across terminations t i and ii and during the lig to assess the impact of two different magnitudes of boreal summer insolation increase on the northeast labrador sea we use mg ca ratios in neogloboquadrina pachyderma sinistral as a proxy of calcification temperature to document changes in subsurface temperatures over eirik drift our corresponding record of d 18 o of seawater documents changes in water mass salinity mg ca calcification temperatures peak early in the holocene coincident with peak boreal summer insolation in contrast lig temperatures are relatively constant through the interglaciation and are no warmer than peak holocene temperatures during the first half of the lig d 18 o of seawater remains depleted likely from southern greenland ice sheet retreat and enhanced arctic freshwater and sea ice export to the labrador sea the consequent stratification of the labrador sea and attendant suppressed convection explains delayed deep ocean ventilation and a cooler subsurface in the northeast labrador sea during the lig

sources and distribution of fresh water in the east greenland current abstract fresh water flowing from the arctic ocean via the east greenland current influences deep water formation in the nordic seas as well as the salinity of the surface and deep waters flowing from there this fresh water has three sources pacific water relatively fresh cf atlantic water river runoff and sea ice meltwater to determine the relative amounts of the three sources of fresh water in may 2002 we collected water samples across the east greenland current in sections from 81 5 n to the irminger sea south of denmark strait we used nitrate phosphate relationships to distinguish pacific waters from atlantic waters salinity to obtain the sum of sea ice melt water and river runoff water and total alkalinity to distinguish the latter river runoff contributed the largest part of the total fresh water component in some regions with some inventories exceeding 12 m pacific fresh water pacific source water s 32 cf atlantic source water s 34 9 typically provided about 1 3 of the river runoff contribution sea ice meltwater was very nearly non existent in the surface waters of all sections likely at least in part as a result of the samples being collected before the onset of the melt season the fresh water from the arctic ocean was strongly confined to near the greenland coast we thus conjecture that the main source of fresh water from the arctic ocean most strongly impacting deep convection in the nordic seas would be sea ice as opposed to fresh water in the liquid phase i e river runoff pacific fresh water and sea ice meltwater

last interglacial arctic warmth confirms polar amplification of climate change the warmest millennia of at least the past 250 000 years occurred during the last interglaciation when global ice volumes were similar to or smaller than today and systematic variations in earth s orbital parameters aligned to produce a strong positive summer insolation anomaly throughout the northern hemisphere the average insolation during the key summer months m j j was ca 11 above present across the northern hemisphere between 130 000 and 127 000 years ago with a slightly greater anomaly 13 over the arctic greater summer insolation early penultimate deglaciation and intensification of the north atlantic drift combined to reduce arctic ocean sea ice allow expansion of boreal forest to the arctic ocean shore across vast regions reduce permafrost and melt almost all glaciers in the northern hemisphere insolation amplified by key boundary condition feedbacks collectively produced last interglacial summer temperature anomalies 4 5 c above present over most arctic lands significantly above the average northern hemisphere anomaly the last interglaciation demonstrates the strength of positive feedbacks on arctic warming and provides a potentially conservative analogue for anticipated future greenhouse warming

rapid climate transitions in a coupled ocean atmosphere model recent geochemical data1 2 have challenged the view that rapid climate fluctuations in the north atlantic at the end of the last glacial were caused by the thermohaline circulation of the ocean being switched on or off instead these data suggest that the circulation pattern must have switched between a warm deep mode and a cold shallow mode probably associated with different sites of deep convection3 here i present simulations with a three dimensional ocean model coupled to an idealized atmosphere which show this kind of transition the mechanism for the transition is a rearrangement of convection in the north atlantic triggered by a brief freshwater pulse this results in a drop in sea surface temperature in the north atlantic by up to 5 c within less than 10 years the rate of north atlantic deep water nadw forma tion is the same in the cold climate as in the warm climate but nadw sinks to intermediate depths only while antarctic bottom water pushes north to fill the entire abyssal atlantic

evidence for a steeper eemian than holocene sea surface temperature gradient between arctic and sub arctic regions sediment proxy data from the norwegian greenland and iceland seas nordic seas are presented to evaluate surface water temperature sst differences between holocene and eemian times and to deduce from these data the particular mode of surface water circulation records from planktic foraminiferal assemblages caco3 content oxygen isotopes of foraminifera and iceberg rafted debris form the main basis of interpretation all results indicate for the eemian comparatively cooler northern nordic seas than for the holocene due to a reduction in the northwardly flow of atlantic surface water towards fram strait and the arctic ocean therefore the cold polar water flow from the arctic ocean was less influencial in the southwestern nordic seas during this time as can be further deduced from the eemian data slightly higher eemian ssts are interpreted for the western iceland sea compared to the norwegian sea ca south of 70 n this eemian situation is in contrast to the holocene when the main mass of warmest atlantic surface water flows along the norwegian continental margin northwards and into the arctic ocean thus a moderate northwardly decrease in sst is observed in the eastern nordic seas for this time causing a meridional transfer in ocean heat due to this distribution in ssts the holocene is dominated by a meridional circulation pattern the interpretation of the eemian data imply a dominantly zonal surface water circulation with a steep meridional gradient in ssts

rapid changes in the mechanism of ocean convection during the last glacial period high amplitude rapid climate fluctuations are common features of glacial times the prominent changes in air temperature recorded in the greenland ice cores1 2 are coherent with shifts in the magnitude of the northward heat flux carried by the north atlantic surface ocean3 4 changes in the ocean s thermohaline circulation are a key component in many explanations of this climate flickering5 here we use stable isotope and other sedimentological data to reveal specific oceanic reorganizations during these rapid climate change events deep water was generated more or less continuously in the nordic seas during the latter part of the last glacial period 60 to 10 thousand years ago but by two different mechanisms the deep water formation occurred by convection in the open ocean during warmer periods interstadials but during colder phases stadials a freshening of the surface ocean reduced or stopped open ocean convection and deep water formation was instead driven by brine release during sea ice freezing these shifting magnitudes and modes nested within the overall continuity of deep water formation were probably important for the structuring and rapidity of the prevailing climate changes

increased seasonality in middle east temperatures during the last interglacial period the last interglacial period about 125 000 years ago is thought to have been at least as warm as the present climate owing to changes in the earth s orbit around the sun it is thought that insolation in the northern hemisphere varied more strongly than today on seasonal timescales which would have led to corresponding changes in the seasonal temperature cycle here we present seasonally resolved proxy records using corals from the northernmost red sea which record climate during the last interglacial period the late holocene epoch and the present we find an increased seasonality in the temperature recorded in the last interglacial coral today climate in the northern red sea is sensitive to the north atlantic oscillation a climate oscillation that strongly influences winter temperatures and precipitation in the north atlantic region from our coral records and simulations with a coupled atmosphere ocean circulation model we conclude that a tendency towards the high index state of the north atlantic oscillation during the last interglacial period which is consistent with european proxy records contributed to the larger amplitude of the seasonal cycle in the middle east

contrasting ocean changes between the subpolar and polar north atlantic during the past 135 ka variations in the poleward directed atlantic heat transfer was investigated over the past 135 ka with special emphasis on the last and present interglacial climate development eemian and holocene both interglacials exhibited very similar climatic oscillations during each preceding glacial terminations deglacial ti and tii like ti also tii has pronounced cold warm cold changes akin to events such as h1 bolling allerod and the younger dryas but unlike ti the cold events in tii were associated with intermittent southerly invasions of an atlantic faunal component which underscores quite a different water mass evolution in the nordic seas within the eemian interglaciation proper peak warming intervals were antiphased between the nordic seas and north atlantic moreover inferred temperatures for the nordic seas were generally colder in the eemian than in the holocene and vice versa for the north atlantic a reduced intensity of atlantic ocean heat transfer to the arctic therefore characterized the eemian requiring a reassessment of the actual role of the ocean atmosphere system behind interglacial but also glacial climate changes key points reduced amoc during the eemian ba yd type warming cooling in termination 1 and 2 comparison of glacial inceptions reveals present climate status

heavy metal distribution in sediments of krishna river basin india suspended and bed sediments collected from the entire region of the krishna river and its major tributaries were analyzed for heavy metals v cr mn fe co ni cu zn and pb by the thin film energy dispersive x ray fluorescence technique there is considerable variation in the concentration of elements towards downstream which may be due to the variation in the subbasin geology and various degrees of human impact suspended particles are enriched in heavy metals throughout the basin relative to bed sediments the heavy metals are enriched in coarse size fractions 10 90 m throughout the krishna river except its tributary bhima where finer fractions 2 m dominate transition elements correlate very well with each other there is a striking similarity between the bed sediments of krishna river and the indian average when the annual heavy metal flux carried by the krishna river was estimated and viewed in relation to the other major riverine transport the krishna is seen to be a minor contributor of heavy metals to the bay of bengal

age of the n7 n8 m4 m5 planktonic foraminifera zone boundary constraints from the zircon geochronology and magnetostratigraphy of early miocene sediments in ichishi japan abstract the age assigned to the miocene n7 n8 m4 m5 planktonic foraminifera zone boundary is markedly different from the astronomically tuned neogene time scales published in 2004 atnts2004 and 2012 atnts2012 this difference is primarily because of the lack of reliable assignment of the zone boundary to magnetostratigraphy which needs to be resolved for the better refinement of the geologic time scale our previous biostratigraphic results from an onland sedimentary sequence of the upper ichishi group in central japan allow location of the stratigraphic position of the lowest occurrence datum lod of praeorbulina sicana a key planktonic foraminifera species for defining the n7 n8 m4 m5 zone boundary in this study we performed laser ablation multiple collector inductively coupled plasma mass spectrometry u pb dating on zircons from two felsic tuff beds in the ichishi sequence the age of the zone boundary is approximated by a u pb age of 17 03 0 11 ma for a tuff bed 2 m above the boundary we also conducted a magnetostratigraphic analysis in which site mean characteristic remanent magnetization directions were determined for 19 sites and showed a reverse normal reverse r n r stratigraphic change in polarity the n7 n8 m4 m5 zone boundary is within the upper reverse polarity zone the r n r sequence can be correlated with a stratigraphic portion corresponding to chrons c5dr c5dn c5cr hence the age of the zone boundary is within chron c5cr our results are thus compatible with the age 16 97 ma assigned to the boundary in atnts2004 rather than atnts2012 and should be considered when the neogene time scale is updated a normal polarity subzone found in the upper reverse polarity zone can also be dated at 17 0 ma and is probably correlated with a short normal polarity episode in chron c5cr in terms of tectonic rotation the site mean magnetization directions determined in this study suggest an 35 clockwise rotation in ichishi with respect to the north china block in the asian continent since 17 2 ma the upper boundary age of chron c5dn clockwise rotation of southwest japan which occurred in association with backarc opening of the japan sea was probably in progress during deposition of the upper ichishi group sediments

retroflection of part of the east greenland current at cape farewell the east greenland current egc and the smaller east greenland coastal current egcc provide the major conduit for cold fresh polar water to enter the lower latitudes of the north atlantic they flow equatorward through the western irminger basin and around cape farewell into the labrador sea the surface circulation and transport of the cape farewell boundary current region in summer 2005 is described the egcc merges with arctic waters of the egc to the south of cape farewell forming the west greenland current the egc transport decreases from 15 5 sv south of cape farewell to 11 7 sv in the eastern labrador sea where the water becomes known as irminger sea water the decrease in egc transport is balanced by the retroflection of a substantial proportion of the boundary current 5 1 sv into the central irminger basin a new pathway for fresh water into the interior of the subpolar gyre

impacts of sediment retention by dams on delta shoreline recession evidences from the krishna and godavari deltas india river deltas are the major repositories of terrestrial sediment flux into the world s oceans reduction in riverine inputs into the deltas due to upstream damming might lead to a relative dominance of waves tides and currents that are especially exacerbated by coastal subsidence and sea level rise ultimately affecting the delta environment analysis of multi date satellite imagery and maps covering the krishna and godavari deltas along the east coast of india revealed a net erosion of 76 km2 area along the entire 336 km long twin delta coast during the past 43 years 1965 2008 with a progressively increasing rate from 1 39 km2 yr 1 between 1965 and 1990 to 2 32 km2 yr 1 during 1990 2000 and more or less sustained at 2 25 km2 yr 1 during 2000 2008 at present the krishna has almost become a closed basin with decreased water discharges into the delta from 61 88 km3 during 1951 1959 to 11 82 km3 by 2000 2008 and the suspended sediment loads from 9 million tons during 1966 1969 to as low as 0 4 million tons by 2000 2005 in the case of the godavari delta although the water discharge data do not show any major change there was almost a three fold reduction in its suspended sediment loads from 150 2 million tons during 1970 1979 to 57 2 million tons by 2000 2006 a comparison of data on annual sediment loads recorded along the krishna and godavari rivers showed consistently lower sediment quantities at the locations downstream of dams than at their upstream counterparts reports based on bathymetric surveys revealed considerable reduction in the storage capacities of reservoirs behind such dams apparently sediment retention at the dams is the main reason for the pronounced coastal erosion along the krishna and godavari deltas during the past four decades which is coeval to the hectic dam construction activity in these river basins copyright 2010 john wiley and sons ltd

structure of the upper water column in the northwest north atlantic modern versus last glacial maximum conditions 1 during the last glacial maximum the northwestern north atlantic constituted a major conduit for labrador and greenland ice sheet meltwaters vertical density gradients in its upper water masses have been reconstructed by combining information from transfer functions based on dinocysts and from oxygen isotope measurements 18o in planktonic foraminifera transfer functions yield temperature and salinity and thus potential density for the warmest august and coldest february months in the photic zone the 18o values in different size fractions of epipelagic globigerina bulloides and mesopelagic neogloboquadrina pachyderma left coiled npl foraminifera allow us to assess gradients through the pycnocline between surface and intermediate waters based on the calibration of a versus 18o relationship from transfer function reconstructions the size and density of npl shells provide further constraints on these gradients the results show the development of a very strong pycnocline during the lgm with a difference of about 3 summer to 1 5 winter units between surface and underlying waters they indicate conditions unfavorable for vertical convection and support the hypothesis of the spreading of a shallow low salinity buoyant layer over the northern north atlantic this layer depicted a strong e w gradient with maximum seasonal contrast and minimum absolute values westward

nd and pb isotope signatures of the clay size fraction of labrador sea sediments during the holocene implications for the inception of the modern deep circulation pattern holocene on the basis of sediment supply variations for the last 12 kyr three sources have contributed to the sediment mixture the north american shield the pan african and variscan crusts and the mid atlantic ridge clay isotope signatures indicate two mixtures of sediment sources the first mixture 12 2 6 5 ka is composed of material derived from the north american shield and from a young crustal source from 6 5 ka onward the mixture is characterized by a young crustal component and by a volcanic component characteristic of the midatlantic ridge since the significant decrease in proximal deglacial supplies the evolution of the relative contributions of the sediment sources suggests major changes in the relative contributions of the deep water masses carried by the western boundary undercurrent over the past 8 4 kyr the progressive intensification of the western boundary undercurrent was initially associated mainly with the transport of the northeast atlantic deep water mass until 6 5 ka and with the denmark strait overflow water thereafter the establishment of the modern circulation at 3 ka suggests a reduced influence of the denmark strait overflow water synchronous with the full appearance of the labrador seawater mass our isotopic data set emphasizes several changes in the relative contribution of the two major components of north atlantic deep water throughout the holocene index terms 4267 oceanography general paleoceanography 4558 oceanography physical sediment transport 1040 geochemistry isotopic composition chemistry 9325 information related to geographic region atlantic ocean 9604 information related to geologic time cenozoic keywords clay size fraction sedimentary mixings deep circulation nd and pb isotopes north atlantic labrador sea

ice sheet and ocean interactions margin of the east greenland ice sheet 14 ka to present diatom evidence seven marine sediment cores were collected from the kangerdlugssuaq trough off the southeast coast of greenland the trough cuts across the continental shelf from the fjord mouth to the upper slope in denmark strait and provides a sedimentary environment sheltered from the east greenland current flowing along the shelf the cores have been 14c dated accelerator mass spectroscopy dates and analyzed for diatom accumulation rates and changes in floral composition it was found that the shelf probably was not glaciated by grounded ice but occupied by an ice shelf and or permanent sea ice between 14 000 years b p and the present average retreat rates of glacial permanent sea ice were circa 60 m yr between circa 13 500 and 11 000 years b p the retreat rates increased to about 150 m yr between 11 000 to 10 000 years b p the increase is unexpected because this correlates with fairbanks 1989 projected low glacial meltwater discharge for the same time which is coeval with the younger dryas several events of sea surface warming cooling took place on the outer shelf from 12 000 to 9000 years b p followed by cooling to the present with a possible warming between 3000 4000 years bp on the inner shelf pulses of warm cool surface water occurred from 9000 to 6000 years b p which was succeeded by surface water cooling until present

evolution and demise of the last interglacial warmth in the subpolar north atlantic detailed faunal isotopic and lithic marine records provide new insight into the stability and climate progression of the last interglacial period marine isotope stage mis 5 which peaked approximately 125 000 years ago in the eastern subpolar north atlantic at the latitude of ireland interglacial warmth of the ice volume minimum of substage 5e mis 5e lasted 10 000 years 10 ka and its demise occurred in two cooling steps the first cooling step marked the end of the climatic optimum which was 2 3 ka long minor ice rafting accompanied each cooling step the second larger step encompassing cold events c26 and c25 was previously identified in the northwestern atlantic approximately 41c of cooling occurred between peak interglacial warmth and c25 and the region experienced an additional temporary cooling of at least 1 21c during c24 a cooling event associated with widespread ice rafting in the north atlantic beginning with c24 mis 5 was characterized by oscillations of at least 1 21c superimposed on a generally cool baseline the results of this study imply that the marine climatic optimum of the last interglacial was shorter than previously thought the finding that the eastern subpolar north atlantic cooled significantly before c24 reconciles terrestrial evidence for progressive climate deterioration at similar and lower latitudes with marine conditions our results also demonstrate a close association between modest ice rafting cooling and deep ocean circulation even during the peak of mis 5e and in the earliest stages of ice growth

sr nd pb isotope evidence for ice sheet presence on southern greenland during the last interglacial to ascertain the response of the southern greenland ice sheet gis to a boreal summer climate warmer than at present we explored whether southern greenland was deglaciated during the last interglacial lig using the sr nd pb isotope ratios of silt sized sediment discharged from southern greenland our isotope data indicate that no single southern greenland geologic terrane was completely deglaciated during the lig similar to the holocene differences in sediment sources during the lig relative to the early holocene denote however greater southern gis retreat during the lig these results allow the evaluation of a suite of gis models and are consistent with a gis contribution of 1 6 to 2 2 meters to the 4 meter lig sea level highstand requiring a significant sea level contribution from the antarctic ice sheet