time variations of δ15n of organic nitrogen in deep western subarctic pacific sediment over the last 145 ka we present 15n data of organic nitrogen 15non from a deep western subarctic pacific wsap sediment core over the last 145 ka to remove the effect of inorganic nitrogen in on bulk nitrogen bn we used the contents of in and bn and the isotopic ratios of in 15nin and bn 15nbn the contribution of in to bn was largest 59 and 15nin had lower values than 15nbn however the large contributions of in to bn and the distinct isotopic values did not largely change any variability associated with 15non in the 15nbn thus it is possible to use 15nbn in carrying out paleoceanographic research with 15n at least in the open wsap the 15non values have been affected by long term diagenesis making the values lower with depth in the sediment but the values during less productive colder periods were generally lower compared to those during neighboring productive warmer periods the results might indicate that 15non during the less productive colder periods i e glacial periods were lower than that during the productive warmer periods i e interglacial periods previous studies have reported that the biological production in wsap where it is limited by iron at present during glacial periods was at more reduced level than during interglacials despite there being more eolian dust supply during glacial periods this indicates that the increase of biological production with enhanced iron supply derived from eolian dust during the glacial periods did not occur if this is the case and alternatively the iron input from the subsurface layer to the surface mixed layer by ventilation process is more important as suggested by recent works the variations in 15non would be explained by the variations in the fe no3 ratio in the upwelled water although 15non has been affected by long term diagenesis in the sediment the usage of this isotopic ratio provides new implication regarding the past ocean circulation in the open wsap

impact processes permafrost dynamics and climate and environmental variability in the terrestrial arctic as inferred from the unique 3 6 myr record of lake el gygytgyn far east russia a review lake el gygytgyn in far east russia is a 3 6 myr old impact crater lake located in an area that has never been affected by cenozoic glaciations nor desiccation the unique sediment record of the l

patterns of deglacial warming in the pacific ocean a review with emphasis on the time interval of heinrich event 1 abstract based on a compilation of currently available records of past sea surface temperature sst variability estimated from a variety of different proxies the regional scale deglacial sst development in the pacific ocean is tentatively classified into four endmember types the subtropical and tropical pacific is characterized by a continuous deglacial warming without marked interruption during the time interval of heinrich event 1 h1 whereas the subarctic north pacific exhibits centennial scale warm cold oscillations during this time interval sst records from marginal seas of the pacific show a deglacial warming interrupted by a cooling event coeval with h1 followed by a marked bolling sst increase a single sst record from the southwestern subantarctic pacific displays a continuous deglacial warming across h1 followed by an antarctic cold reversal type cooling during the allerod thus in contrast to the deglacial sst development in the atlantic which has been inferred to be overwhelmingly driven by the redistribution of heat through changes in the meridional overturning circulation moc none of the open oceanic pacific sst records reviewed here displays any obvious and or dominant response to the reduction of the moc and or the reorganization of atmospheric circulation during h1 within the limits of absolute chronologies all tropical and subtropical pacific sst records show an onset of deglacial warming at 19 1 ka coeval with the onset of the deglacial rise in sea level

evidence from diatom bound nitrogen isotopes for subarctic pacific stratification during the last ice age and a link to north pacific denitrification changes higher diatom bound d 15 n 70 wt lower opal content and 1200 ppm lower biogenic barium taken together and with constraints on sediment accumulation rate these results suggest a reduced supply of nitrate to the surface due to stronger stratification of the upper water column of the bering sea during glacial times with more complete nitrate consumption resulting from continued iron supply through atmospheric deposition this finding extends the body of evidence for a pervasive link between cold climates and polar ocean stratification in addition we hypothesize that more complete nutrient consumption in the glacial age subarctic pacific contributed to the previously observed ice age reduction in suboxia and denitrification in the eastern tropical north pacific by lowering the nutrient content of the intermediate depth water formed in the subpolar north pacific in the deglacial interval of the bering sea record two apparent peaks in export productivity are associated with maxima in diatom bound and bulk sediment d 15 n the high d 15 n in these intervals may have resulted from greater surface nutrient consumption during this period however the synchroneity of the deglacial peaks in the bering sea with similar bulk sediment d 15 n changes in the eastern pacific margin and the presence of sediment lamination within the bering sea during the deposition of the productivity peaks raise the possibility that both regional and local denitrification worked to raise the d 15 n of the nitrate feeding bering sea surface waters at these times

rapid and quantitative major element analysis method for wet fine grained sediments using an xrf microscanner several types of x ray fluorescence xrf core scanners have been developed to fulfill the demands for high resolution rapid chemical analysis of wet sediment cores however their application to quantitative analysis has been hampered by the difficulty of evaluating the xrf absorption effect of water in a water film on the sediment surface and interstitial water within the sediments especially for lighter elements in this study we established a non destructive rapid high resolution and quantitative chemical analysis method for wet fine grained sediment samples using an xrf microscanner results of our experiments suggest that the degree of xrf absorption by the water film which develops on the wet sample surface covered with mylar film shows a clear positive correlation with the water content of the sediments under the measurement area a clear positive correlation also exists between the degree of xrf absorption by the interstitial water and the water content of the sediments under the measurement area we evaluated the xrf absorption by the thin water film using the relationship between the water content and thickness of the thin water film and the xrf absorption by the interstitial water using its relation with the water content the water content under the measurement area is estimated from the average transmitted x ray intensity that is measured on the same measurement area simultaneously with the measurement of xrf intensities the dry sample equivalent xrf intensities of major elements al si k ca ti and fe which are the xrf intensities of wet samples corrected for the xrf absorption by the thin water film and the interstitial water show better correlation with the major element concentrations determined by conventional xrf methods using this new method it is possible to measure the average water content and average concentrations of the 6 major elements simultaneously for a square area as small as 0 5 0 5 mm on the wet fine grained sediment within 6 min which is nearly ten times faster than the conventional xrf method

glacial interglacial changes in subarctic north pacific stratification since the first evidence of low algal productivity during ice ages in the antarctic zone of the southern ocean was discovered there has been debate as to whether it was associated with increased polar ocean stratification or with sea ice cover shortening the productive season the sediment concentration of biogenic barium at ocean drilling program site 882 indicates low algal productivity during ice ages in the subarctic north pacific as well site 882 is located southeast of the summer sea ice extent even during glacial maxima ruling out sea ice driven light limitation and supporting stratification as the explanation with implications for the glacial cycles of atmospheric carbon dioxide concentration

refining the alkenone pco2 method i lessons from the quaternary glacial cycles abstract the alkenone pco2 method is one of the most widely used approaches to reconstruct atmospheric co2 in the cenozoic the method depends upon fractionation of stable carbon isotopes during algal photosynthesis expressed as ep37 2 and a physiological scaling parameter b that accounts for biological factors such as growth rate cell size and membrane permeability alkenone derived co2 records for the late pleistocene however are poorly correlated with ice core co2 challenging the classic model that considers most of the co2 used for coccolithophore photosynthesis to be acquired through simple diffusion in this study we investigate the nature of the b term and the underlying patterns of the sensitivity of ep37 2 to pco2 changes we generated two new ep37 2 records from the south china sea md01 2392 and tropical atlantic ocean odp 668b and compiled other published ep37 2 records over glacial interglacial cycles using the ep37 2 data ocean temperature estimates and ice core co2 we were able to back calculate the corresponding values of b at all locations b varies over glacial cycles the highest values of b correspond to peak interglacial stages indicating that the phytoplankton growth rate is faster or cell size is smaller during interglacials than during glacial periods we further show that the range of ep37 2 between glacial and interglacial conditions ep37 2 scales with growth conditions consistent with the predictions of the carbon isotope fractionation model based on co2 diffusion in other words the sensitivity of ep37 2 to pco2 changes increases where the modern b values are large contradicting the recommendations that oligotrophic sites are the best for alkenone co2 applications because of the presumed stability of b using the average back calculated b value for each site the composite pco2 estimates from md01 2392 and odp 668b the two sites with adequate ep37 2 sensitivity show broad agreement with the ice core co2 record

size specific opal bound nitrogen isotope measurements in north pacific sediments abstract the nitrogen isotope composition of diatom opal 15 n db is a valuable recorder of nitrate utilization in the polar surface oceans and a measure of the efficiency of the biological pump past down core records of 15 n db involved the measurement of the biogenic opal fraction up to 150 m in size which should represent the bulk of the preserved diatoms but may also include non diatom opal such as radiolaria and sponge spicules in this study the opal from subarctic pacific and bering sea sediments from the holocene back to the last glacial was separated into different size fractions to measure their individual 15 n we found a general trend of decreasing 15 n with increasing size at all sites and through time microscopic investigation of smear slides and image area analysis of microphotographs of the analyzed opal revealed that the larger size fractions contained greater proportions of sponge spicules and radiolaria manual isolation and measurement of the sponge spicules showed that they have a very low 15 n 11 ultrasonication during sample preparation caused greater spicule and radiolaria contamination due to fragmentation of these relatively large fossils leading to a dramatic 15 n db decrease with increasing size and lower 15 n db across all size fractions in sonicated versus non sonicated samples nevertheless these contaminants were also present albeit less abundant in the various size fractions of samples separated without sonication and these samples also showed a 15 n db decrease with increasing size simple isotope mass balance calculations of holocene bering sea sediments indicate that most of the 15 n db variations among the larger size fractions can be explained by the relative abundance of low 15 n sponge spicules in each fraction however some of the size fraction 15 n differences in the downcore records require a different explanation both diatom inter or intra species effects are evident and indicate lower 15 n db among the larger centric versus smaller pennate diatom species and a 15 n db decrease with increasing size of centric diatom frustules contamination of n by non diatomaceous opal should not normally compromise total diatom bound 15 n 0 150 m because the non diatom opal typically contributes less than 5 to the total opal however the early deglacial heinrich stadial 1 correlative period in the subarctic north pacific is an important possible exception a substantial fraction of its low concentration of opal appears to be sponge spicules and radiolaria such that the reconstructed total diatom 15 n db decrease at this time may be an artifact while the glacial age sediments are also vulnerable to non diatom contamination this should work to lower 15 n db such that the observed high glacial 15 n db in north pacific sediments cannot be explained by contamination thus the previous interpretation of enhanced nutrient consumption in the north pacific regions during the last ice age remains valid

a pervasive link between antarctic ice core and subarctic pacific sediment records over the past 800 kyrs recently developed xrf core scanning methods permit paleoceanographic reconstructions on timescales similar to those of ice core records we have investigated the distribution of biogenic barium ba al opal and carbonate ca al in a sediment core retrieved from the abyssal subarctic pacific odp 882 50 n 167 e 3244 m over an interval that spans the full length of the epica dome c edc ice core record ba al and biogenic opal show a strong resemblance to the edc dd and co2 with generally high concentrations during interglacials and lower values during ice ages of the past 800 kyrs the sedimentary ba al and biogenic opal are most easily interpreted as indicating a reduced sinking flux of organic matter from the surface ocean during cold periods the ba al maxima during peak interglacials are accompanied by transient ca al peaks in these otherwise carbonate devoid sediments which are best explained by a deepening of the calcite lysocline presumably due to reduced storage of respired co2 in the deep north pacific for most of the luke warm interglacials noted between 420 and 750 ka in edc the ba al peaks in odp 882 are also lower further strengthening the evidence for a simple physical link between global climate and the biogeochemistry of the subarctic pacific

late quaternary lake level changes of lake el gygytgyn ne siberia abstract lake el gygytgyn is situated in a 3 6 ma old impact crater in northeastern siberia presented here is a reconstruction of the quaternary lake level history as derived from sediment cores from the southern lake shelf there a cliff like bench 10 m below the modern water level has been investigated deep water sediments on the shelf indicate high lake levels during a warm mid pleistocene period one period with low lake level prior to marine oxygen isotope stage mis 3 has been identified followed by a period of high lake level 10 m above present in the course of mis 2 the lake level dropped to 10 m at the end of mis 2 the bench was formed and coarse beach sedimentation occurred subsequently the lake level rose rapidly to the holocene level changes in water level are likely linked to climate variability during relatively temperate periods the lake becomes free of ice in summer strong wave actions transport sediment parallel to the coast and towards the outlet where the material tends to accumulate resulting in lake level rise during cold periods the perennial lake ice cover hampers any wave activity and pebble transport keeping the outlet open and causing the lake level to drop

paleoproductivity and paleoceanography of the last 4 3 myrs at iodp expedition 323 site u1341 in the bering sea based on biogenic opal content abstract site u1341 in the southern bering sea was drilled and cored down to 600 meters below sea floor mbsf during integrated ocean drilling program iodp expedition 323 covering a nearly complete record of the last 4 3 million years myrs analyses of the biogenic opal content of sediments at the site provide detailed and useful information on past biological productivity and paleoceanographic changes that occurred in the region including shifts in the oceanographic condition during the intensification of the northern hemisphere glaciation nhg and the mid pleistocene transition mpt an overall decreasing trend in the biogenic opal record combined with evidence from microfossil assemblages indicates a gradual shift in environmental conditions during the last 4 3 myrs from warm and nutrient rich conditions to cool conditions with sea ice on the other hand biogenic opal mass accumulation rates mar were high during 2 6 2 1 ma after the intensification of the nhg unlike in the western north pacific high biological productivity during this specific interval is consistent with the results of previous studies in the other marginal seas possibly suggesting that iron leakage from the bering continental shelf occurred after the mpt the data suggest that there was sea ice expansion and discharge of lithogenic matter during glacial periods and high productivity during interglacial periods

paleoenvironmental changes in the east japan sea during the last 48 ka indications from high resolution x ray fluorescence core scanning paleoceanographic changes in the east japan sea during the late quaternary based on high resolution elemental variations particularly correlations between dark light laminations and millennial scale climatic changes have remained poorly understood because of the lack of the high resolution proxies the recent application of micro x ray fluorescence xrf core scanning provides the potential for high resolution study on the laminations deposited in the east japan sea in this study we present a geochemical study by using micro xrf core scanning on a 730 cm core recovered from the east japan sea elemental variations and factor analysis indicate that the sedimentary environment changed from anoxic to suboxic conditions from marine isotope stage mis 2 3 to mis 1 which is induced by increased contribution of high salinity sea water from the open ocean due to the rising sea level the dark and light laminations during mis 2 3 were correlated with dansgaard oeschger cycles and summer monsoon proxy with dark colored sediments related to higher terrigenous concentration corresponding to warm moist and enhanced summer monsoon period during the interstadial period more terrigenous sediments were transported to the east japan sea via the strengthened fluvial discharge from the surrounding continents caused by enhanced monsoon rainfall thus the development of the east asian summer monsoon and consequent variations in fluvial discharge would have significantly affected the paleoceanographic conditions in the east japan sea during the mis 2 3 sea level lowstand copyright 2012 john wiley sons ltd

palaeoceanography polar twins ice ages in the north pacific ocean and the southern ocean were marked by low productivity accumulating evidence indicates that strong stratification restricted the supply of nutrients from the deep ocean to the algae of the sunlit surface in these regions

expansion of subarctic water masses in the north atlantic and pacific oceans and implications for mid pleistocene ice sheet growth 1 past surface ocean circulation changes associated with the mid pleistocene transition 0 9 0 6 ma were reconstructed in the northern north atlantic odp 983 and the northwest pacific odp 882 using proxies for subarctic subpolar water mass distributions c37 4 alkenone and sea surface temperature u37 both sites experienced a secular expansion of subarctic waters from 1 15 ma spanning both glacial and interglacial intervals after 0 9 ma low c37 4 at site 983 records a northward retreat of subarctic waters during interglacials in the atlantic while continued high glacial c37 4 indicate extensive subarctic waters during glacial maxima associated with the development of the larger late pleistocene ice sheets in contrast a secular decline in c37 4 occurred at site 882 from 0 9 to 0 5 ma marking a more gradual retreat of subarctic conditions in the pacific it is proposed that the expansion of subarctic waters between 1 15 and 0 9 ma exerted negative feedbacks to the moisture supply to the ice sheet source regions and may account for the apparent delayed ice sheet response to atmosphere ocean circulation changes associated with the mid pleistocene transition that began as early as 1 2 ma

combined oxygen and silicon isotope analysis of diatom silica from a deglacial subarctic pacific record we present an sif4 separation line coupled to a laser fluorination system which allows for an efficient combined silica d18o and d30si analysis 50 min per sample the required sample weight of 1 5 2 0mg allows for high resolution isotope studies on biogenic opal besides analytical tests the new instrumentation set up was used to analyse two marine diatom fractions 63 mm 10 20mm with different diatom species compositions extracted from a bolling allerod holocene core section md01 2416 north west nw pacific to evaluate the palaeoceanographic significance of the diatom isotopic signals and to address isotopic effects related to contamination and species related isotope effects vital and environmental effects while d30si offsets between the two fractions were not discernible supporting the absence of species related silicon isotope effects systematic offsets occur between the d18o records although small these offsets point to species related isotope effects as bias by contamination can be discarded the new records strengthen the palaeoceanographic history during the last deglaciation in the nw pacific characterized by a sequence of events with varying surface water structure and biological productivity with such palaeoceanographic evolution it becomes unlikely that the observed systematic d18o offsets signal seasonal temperature variability this calls for reconsideration of vital effects generally excluded to affect d18o measurements

dynamics of the last four glacial terminations recorded in lake van turkey abstract a well dated suite of lake van climate proxy data covering the last 360 ka documents environmental changes over 4 glacial interglacial cycles in eastern anatolia turkey the picture of cold and dry glacials and warm and wet interglacials emerging from pollen organic carbon authigenic carbonate content elemental profiling by xrf and lithological analyses is inconsistent with classical interpretation of oxygen isotopic composition of carbonates pointing to a more complex pattern in lake van region detailed analysis of glacial terminations allows for the constraining of a depositional model explaining different patterns observed in all the proxies we hypothesize that variations in relative contribution of rainfall snowmelt and glacier meltwater recharging the basin have a very important role for all sedimentary processes in lake van lake level of glacial lake van predominantly fed by snowmelt was low the water column was oxic and carbonates precipitating in the epilimnion recorded the light isotopic signature of inflow during terminations increasing rainfall and significant supply of mountain glaciers meltwater contributed to lake level rise increased rainfall enhanced density gradients in the water column and hindered mixing leading to development of bottom water anoxia carbonates precipitating during terminations show large fluctuations in their isotopic composition full interglacial conditions in lake van are characterized by high or slowly falling lake level rainfall and snowmelt feed the lake but due to re established mixing the isotopic composition of authigenic carbonates is heavier and closer to that of evaporation influenced lake water than that of runoff representing snowmelt and atmospheric precipitation

changes and influencing factors in biogenic opal export productivity in the bering sea over the last 4 3 ma evidence from the records at iodp site u1340 we reconstructed changes in biogenic opal export productivity boep in the southern bering sea bs over the last similar to 4 3 ma based on mass accumulation rate mar of biogenic opal from integrated ocean drilling program iodp site u1340 the results show that the boep in the bs was high and variable between similar to 4 3 and similar to 1 9 ma extremely low and relatively stable from similar to 1 9 to similar to 1 1 ma and then fluctuated frequently generally high during interglacials and low during glacials during the last similar to 1 1 ma one interval of enhanced boep from similar to 4 3 to similar to 3 2 ma is a response to the late miocene early pliocene biogenic bloom event another interval from similar to 2 8 to similar to 1 9 ma correlates with global opal burial shifting from high latitude oceans to upwelling influenced regions following the intensification of the northern hemisphere glaciation nhg whereas the increase in bs opal export productivity during the last similar to 1 1 ma tends to be a local phenomenon overall the boep shows a similar trend and good correspondence to the input of the alaskan stream as which can be traced using the na2o k2o ratio we thus conclude that the as may be the direct and primary factor on boep variability in the bs during the last similar to 4 3 ma in addition although the poor correlation between opal mar and volcanic glass suggests that boep variability was not controlled by longterm variations in the volcanism or ash abundance increased ash abundance indicated by high contents of volcanic glasses was also a possible reason for enhanced boep during the period from similar to 4 3 to similar to 3 2 ma and the last similar to 0 5 ma

palaeoproductivity at the antarctic continental margin opal and barium records for the last 400 ka abstract records of biogenic opal and barium were measured in sediment cores at the antarctic continental margin in the area of the weddell lazarev and cosmonaut seas these records provide a qualitative and quantitative tool to estimate changes in palaeoproductivity over the last 400 ka the stratigraphy of the investigated cores is calibrated to a lithostratigraphy adjusted to a stable isotope record from the eastern weddell sea which is supported by a th dating method we present evidence that interglacial productivity along the antarctic continental margin is twice as high compared to subantarctic sites near south orkney a glacial interglacial pattern with high productivity during peak warm stages can be observed back to 400 ka high interglacial productivity is linked to a reduced sea ice coverage which is regulated by the heat flux introduced by north atlantic deep water nadw to the antarctic ocean generally good correlations between the barium and opal records of the sediment cores indicate that dissolution of opal in the water column and the sediment does not obscure the surface productivity signal therefore in this area biogenic opal in combination with other proxies can be used for palaeoproductivity estimates palaeoproductivity is also assessed quantitatively from the barium record using the approaches of dymond et al dymond j suess e lyle m 1992 barium in deep sea sediments a geochemical proxy for paleoproductivity paleoceanography 7 163 181 and francois et al francois r honjo s manganini s j ravizza g e 1995 biogenic barium fluxes to the deep sea implications for paleoproductivity reconstructions glob biochem cycles 9 2 289 303 palaeoproductivity rates obtained by both methods show a good temporal correspondence in peak warm stages higher values are computed with the approach of dymond et al 1992 though some barium may be provided by lateral advection of material as indicated by th data near south orkney both methods provide values which are representative of a high productivity area they are drastically reduced during glacial times the extent and duration of sea ice coverage and the persistence of coastal polynyas is considered to be of primary importance in controlling the flux of biogenic material to sediments of the antarctic continental margin

pore fluid constraints on the temperature and oxygen isotopic composition of the glacial ocean pore fluids from the upper 60 meters of sediment 3000 meters below the surface of the tropical atlantic indicate that the oxygen isotopic composition 18 o of seawater at this site during the last glacial maximum was 0 8 0 1 per mil higher than it is today combined with the 18 o change in benthic foraminifera from this region the elevated ratio indicates that the temperature of deep water in the tropical atlantic ocean was 4 c colder during the last glacial maximum extrapolation from this site to a global average suggests that the ice volume contribution to the change in 18 o of foraminifera is 1 0 per mil which partially reconciles the foraminiferal oxygen isotope record of tropical sea surface temperatures with estimates from barbados corals and terrestrial climate proxies

polar stratification a critical view from the southern ocean oceanic stratification represents an effective mechanism to reduce vertical mixing of the water column thereby locking up carbon dioxide co2 in the deep sea and preventing air sea exchange of co2 it has been proposed that enhanced stratification of the upper water column in polar oceans during late cenozoic cooling episodes limited the upwelling of co2 rich deep waters and thus co2 release to the atmosphere resulting in a net global drawdown of atmospheric co2 increased stratification in the subarctic northwest pacific during both the onset of northern hemisphere glaciation at 2 73 ma and late quaternary glacial periods has been recently linked to enhanced ocean stratification south of the antarctic polar front apf in the pacific and atlantic sectors of the southern ocean increased stratification of southern ocean surface waters was mainly deduced from a reduction of biological production during these cooling episodes manifested by the decrease of geochemical proxies for productivity such as biogenic opal and barium in the marine sediment records however the records chosen from the southern ocean do not provide evidence for a more stratified upper water column rather the observed decrease in biological productivity is likely to have resulted from an expansion of annual sea ice coverage the sediment records suggest that south of the apf in the pacific and atlantic sectors of the southern ocean extensive sea ice may have contributed to the global co2 drawdown during glacial periods with hypothetical glacial increase of stratification in today s permanent open ocean zone merely being an add on caused by this expansion

influence of the water content on x ray fluorescence core scanning measurements in soft marine sediments the x ray fluorescence xrf core scanner provides bulk sediment chemistry data measured nondestructively at the split core sediment surface although this method is widely accepted there is little known about the effects of physical properties such as density and water content on xrf core scanner data comparison of xrf scanner measurements from the sediment surface and dry powder samples of sediment core geob7920 indicates strongly reduced element intensities for the lighter elements al and si we relate the lower element intensities of the measurements taken at the sediment surface to the amount of water in the sample volume analyzed by the xrf core scanner the heavier elements k ca ti and fe remain relatively unaffected by the variation of any physical property within sediment core geob7920 additionally we successfully use the elemental intensity of cl as a proxy for the seawater content in the sample volume analyzed by the xrf core scanner this enables the establishment of a correction function for the elements al and si that corrects for the radiation absorption of the water content in sediment core geob7920 off cape blanc nw africa

calibration of xrf core scanners for quantitative geochemical logging of sediment cores theory and application abstract on line analysis of split sediment cores by xrf core scanners has become increasingly popular in the past decade because it allows nondestructive extraction of near continuous records of element intensities from sediment cores with a minimum of analytical effort a disadvantage of xrf core scanning relative to conventional geochemical analysis is the problematic conversion of core scanner output to element concentrations the main reason for this long standing problem is the poorly constrained measurement geometry attributable to inhomogeneity of the specimens e g variable water content and grain size distribution irregularities of the split core surface and in some setups spatial variations in thickness of an adhesive pore water film which forms directly below a protective foil covering the core surface we propose a log ratio calibration model for xrf core scanners derived from a combination of xrf spectrometry theory principles of compositional data analysis and empirical evidence the log ratio calibration model provides accurate and precise predictions of sediment composition element concentrations from xrf core scanner output with a limited number of parameters namely 2 d 1 where d equals the number of chemical elements whose concentrations are to be estimated the model can accommodate the inherent non linearity of the relation between relative intensities and concentrations which is apparent from the fact that it provides unbiased estimates an immediate corollary of our results is that log ratios of element intensities which are related to log ratios of element abundances by a simple linear transformation provide the most easily interpretable signals of relative changes in chemical composition consistent use of log ratios of element intensities or concentrations should minimise the risk of drawing erroneous conclusions from geochemical proxies the relative standard deviation precision of predicted element concentrations in core geob7920 is less than 2 stochastic simulations indicate that this level of precision can be attained with 40 randomly selected calibration specimens improved control over input errors and development of robust goodness of fit statistics allows xrf core scanning to be developed into a rigorous quantitative measurement technology the log ratio calibration equation derived in this study may be adapted to inter laboratory and inter instrument calibration as well

early diagenetic greigite as an indicator of paleosalinity changes in the middle miocene paratethys sea of central europe the miocene epicontinental paratethys sea of central eurasia has experienced multiple restriction and reconnection events to the open ocean magnetostratigraphy is an important dating tool to better understand the temporal and spatial paleoenvironmental variations associated with these changes magnetostratigraphy in the paratethys domain however is complicated by the presence of greigite fe3s4 here we report rock magnetic and x ray fluorescence data of the tisa section romania which was previously magnetostratigraphically dated at the middle miocene base at 12 8 ma and top at 12 2 ma this section comprises the badenian sarmatian extinction event bsee which is marked by a major salinity change from marine to brackish environments related to the opening of the connection between the central and the eastern paratethys basins in the marine badenian sediments below the bsee the pyritization process is shown to be complete because of abundant sulfate supply in the brackish sarmatian deposits four intervals with early diagenetic greigite are observed and linked to insufficient sulfate in the water column these four greigite intervals appear to correspond to maxima in the 100 kyr eccentricity cycle we propose that increased fresh water from the eastern paratethys basin during eccentricity maxima restricted the sulfate availability in the tisa area leading to a reduced hs production and enhanced greigite preservation the early diagenetic formation of greigite enables a quasi syn depositional recording of the paleomagnetic field which allows reliable paleomagnetic dating in this section our results further suggest greigite as a potential indicator for salinity changes during marine brackish transitions

the magmatic record in the arghash region northeast iran and tectonic implications the area of arghash in northeast iran promi nent for its gold mineralization was newly mapped on a scale of 1 20 000 with particular attention to the occurring generations of igneous rocks in addition geochronological and geochemical investigations were carried out the oldest geological unit is a late precambrian hornblende bearing diorite pluton with low k composition and primi tive isotope signatures this diorite u pb zircon age 554 6 ma is most likely a remnant from a peri gondwana island arc or back arc basin about one third of the map area is interpreted as an upper cretaceous mag matic arc consisting of a volcanic and a plutonic part the plutonic part is represented by a suite of hornblende bearing medium k i type granitoids minor diorite mainly quartz monzodiorite and granodiorite dated at 92 8 1 3 ma u pb zircon age the volcanic part comprises medium k andesite dacite and tuffitic rocks and must be at least slightly older because it is locally affected by contact metamorphism through the hornblende grani toids the upper cretaceous arc magmatism in the arg hash massif is probably related to the northward subduction of the sabzevar oceanic basin which holds a back arc position behind the main neotethys subduction front small occurrences of pillow basalts and sediments sandstone conglomerate limestone tectonically interca lated in the older volcanic series may be relics of earlier cretaceous or even pre cretaceous rocks in the early cenozoic the cretaceous magmatic arc was intruded by bodies of felsic weakly peraluminous granite u pb zircon age 55 4 2 3 ma another strong pulse of magmatism followed slightly later in the eocene producing large masses of andesitic to dacitic volcanic rocks the geo chemistry of this prominent eocene volcanism is very distinct with a high k signature and trace element contents similar to shoshonitic series high p zr cr sr and ba high sr y ratios feature affinities to adakite magmas the eocene magmatism in the arghash massif is interpreted as related to thermal anomalies in crust and mantle that developed when the sabzevar subduction system collapsed the youngest magmatic activities in the arghash massif are lamprophyres and small intrusions of quartz monzo diorite porphyries which cut through all other rocks including an oligocene miocene conglomerate cover series

marine radiocarbon evidence for the mechanism of deglacial atmospheric co2 rise we reconstructed the radiocarbon activity of intermediate waters in the eastern north pacific over the past 38 000 years radiocarbon activity paralleled that of the atmosphere except during deglaciation when intermediate water values fell by more than 300 per mil such a large decrease requires a deglacial injection of very old waters from a deep ocean carbon reservoir that was previously well isolated from the atmosphere the timing of intermediate water radiocarbon depletion closely matches that of atmospheric carbon dioxide rise and effectively traces the redistribution of carbon from the deep ocean to the atmosphere during deglaciation

paleonutrient and productivity records from the subarctic north pacific for pleistocene glacial terminations i to v our study addresses fundamental questions of the mode and timing of orbital and millennial scale changes in the meridional overturning circulation moc of the subarctic north pacific particular concerns are the vertical mixing the present and past abundance of nutrients in surface waters despite strong stratification and the north pacific north atlantic seesaw of oscillations in sea surface temperature sst we do this by generating and interpreting multiple records for glacial terminations i v down two long piston cores one each from the western and eastern subarctic pacific chlorins and biogenic opal are proxies for surface water productivity delta 13 c of epibenthic foraminifera is a record of deepwater ventilation and the delta 13 c of n pachyderma sin is a tracer of nutrients in subsurface waters that extend up to the sea surface during times of vertical mixing the degree of mixing is traced by pairing sst and delta 18 o records of planktic surface and subsurface pycnocline dwellers tight age control is deduced from a suite of age calibrated 14 c plateau boundaries for termination i and benthic delta 18 o and geomagnetic events for the last 800 ka carbon 14 paleoreservoir ages record the ages of surface and deep waters to uncover short term changes in moc over termination i we have defined a standard sequence of short term productivity events for termination i also evident during terminations ii to v and subsequent interglacials over the last 450 ka the peak glacial regime of stable stratification and low productivity terminated together with the end of ice rafting and melting near 17 ka similar to 2000 years after the onset of termination i pulses of vertical mixing and incursion of warm surface waters from the subtropics followed convected young water masses finally penetrated down to 3600 m water depth at 17 0 to less than 14 5 ka significantly improving bottom water ventilation through the late deglacial and earliest interglacial mixing with upwelled nutrients from the pycnocline induced short term maxima in algal production of chlorins and biogenic opal near 17 15 and 15 12 ka respectively deglacial meltwater incursions in the aleutian current and silica input from north american rivers also promoted east pacific productivity after 15 5 ka productivity decreased during the late deglacial and early interglacial coeval with an exceptional peak in caco 3 preservation caused by both low organic flux and well ventilated deepwater subsequently low salinity and cool surface waters and in turn stratification were gradually restored a second opal dominated productivity maximum marked the ends of interglacials the deglacial pulses of vertical mixing around 17 11 ka imply an important contribution of the north pacific to the coeval release of oceanic co 2 into the atmosphere and support the east west seesaw model of climate change

glacial interglacial variations in marine phosphorus cycling implications for ocean productivity 1 using a box model of organic carbon c and phosphorus p cycling in the global ocean we assess the effects of changes in the continental supply of reactive p oceanic mixing and sea level on the marine p cycle on glacial interglacial timescales our model results suggest that mixing is a dominant forcing during early glaciation causing retention of p in the deep ocean thereby lowering primary production and associated organic c and p burial sea level fall is the dominant forcing during late glaciation when reduced coastal trapping of reactive p enhances its transfer to the open ocean restoring primary production and p burial during postglacial periods changes in circulation and weathering dominate open ocean processes and oceanic primary production peaks as primary production is reduced upon glaciation changes in the marine p cycle are unlikely to drive enhanced primary production and co2 drawdown during glaciation

southern ocean control on the extent of denitrification in the southeast pacific over the last 70 ka abstract temporal changes in oceanic denitrification the bacterial reduction of nitrate under suboxic conditions highlight the potential importance of n inventory changes and the production of n 2 o on the climate system at the same time the cause of the globally observed variation in denitrification remains unclear high resolution benthic foraminiferal oxygen isotope and bulk sediment nitrogen isotope records from odp site 1234 on the chile margin record integrated denitrification changes within the peru chile upwelling system over the last 70 ka denitrification changes in the southeast pacific are coherent with antarctic climate changes recorded by the byrd ice core 18 o record and lead northern hemisphere climate events the southern hemisphere character of the chile margin 15 n record suggests that episodes of reduced denitrification in the se pacific represent times when more oxygen was supplied as the result of changes in the ventilation and preformed nutrient content of subantarctic mode water samw which forms in the subantarctic zone of the southern ocean and feeds into the low latitude thermocline

glacial to interglacial surface nutrient variations of bering deep basins recorded by δ13c and δ15n of sedimentary organic matter stable carbon and nitrogen isotopic ratios 13c and 15n of organic matter were measured in three sediment cores from deep basins of the bering sea to investigate past changes in surface nutrient conditions for surface water reconstructions hemipelagic layers in the cores were distinguished from turbidite layers on the basis of their sedimentary structures and 14c ages and analyzed for isotopic studies although 13c profiles may have been affected by diagenesis both 15n and 13c values showed common positive anomalies during the last deglaciation we explain these anomalies as reflecting suppressed vertical mixing and low nutrient concentrations in surface waters caused by injection of meltwater from alpine glaciers around the bering sea appendix tables are available with entire article on microfiche order from american geophysical union 2000 florida avenue n w washington dc 20009 document p95 003 2 50 payment must accompany order

glacial interglacial changes in nutrient supply and stratification in the western subarctic north pacific since the penultimate glacial maximum abstract in piston cores from the open subarctic pacific and the okhotsk sea diatom bound 15n 15ndb biogenic opal calcium carbonate and barium were measured from coretop to the previous glacial maximum mis 6 glacial intervals are generally characterized by high 15ndb 8 and low productivity whereas interglacial intervals have a lower 15ndb 5 7 6 3 and indicate high biogenic productivity these data extend the regional swath of evidence for nearly complete surface nutrient utilization during glacial maxima consistent with stronger upper water column stratification throughout the subarctic region during colder intervals an early deglacial decline in 15ndb of 2 at 17 5 ka previously observed in the bering sea is found here in the open subarctic pacific record and arguably also in the okhotsk and a case can be made that a similar decrease in 15ndb occurred in both regions at the previous deglaciation as well the early deglacial 15ndb decrease best explained by a decrease in surface nutrient utilization appears synchronous with southern hemisphere associated deglacial changes and with the heinrich 1 event in the north atlantic this 15ndb decrease may signal the initial deglacial weakening in subarctic north pacific stratification and or a deglacial increase in shallow subsurface nitrate concentration if the former it would be the north pacific analogue to the increase in vertical exchange inferred for the southern ocean at the time of heinrich event 1 in either case the lack of any clear change in paleoproductivity proxies during this interval would seem to require an early deglacial decrease in the iron to nitrate ratio of subsurface nutrient supply or the predominance of light limitation of phytoplankton growth during the deglaciation prior to bolling allerod warming

mid holocene origin of the sea surface salinity low in the subarctic north pacific images core md01 2416 511n 1681e provides the first centennial scale multiproxy record of holocene variation in north pacific sea surface temperature sst salinity and biogenic productivity our results reveal a gradual decrease in subarctic sst by 3 51c from 11 1 to 4 2 ka and a stepwise long term decrease in sea surface salinity sss by 2 3 p s u early holocene sss were as high as in the modern subtropical pacific the steep halocline and stratification that is characteristic of the present day subarctic northpacific surface ocean is a fairly recent feature developed as a product of mid holocene environmental ch ange highsss matched a salient productivity maximum of biogenic opal during bolling to early holocene times reaching levels similar to those observed during preglacial times in the warm mid pliocene prior to 2 73 ma similar productivity spikes marked every preceding glacial termination of the last 800 ka indicating recurrent short term events of mid pliocene style intense upwelling of nutrient rich pacific deepwater in the pleistocene such events led to a repeated exposure of co2 richdeepwater at the ocean surface facilitating a transient co2 release to the atmosphere but the timing and duration of these events repudiate a long term influence of the subarctic northpacific on global atmosph eric co 2 concentration r 2004 elsevier ltd all rights reserved

hydrological changes and paleoproductivity in the gulf of california during middle and late holocene and their relationship with itcz and north american monsoon variability abstract this study investigates changes in precipitation patterns and variations in paleoproductivity in the tropical pacific region associated with the north american monsoon intertropical convergence zone itcz latitudinal migration and changes in insolation during the middle and late holocene major and trace element records al ba c k si and ti and zr al and ba al ratios in a core from alfonso basin southern gulf of california are used as proxies of terrigenous input and bio productivity records reveal an increase in precipitation and low bio productivity ca 6200 to 2400 cal yr bp associated with the strengthening of monsoonal precipitation and northward shift of the itcz mean position in the eastern tropical pacific a multi centennial drought from ca 2400 to 1900 cal yr bp and a dry and cold interval ca 700 and 500 cal yr bp are characterized by strong aeolian input and enhanced productivity associated with diminution of the summer monsoonal precipitation and reduced insolation in the northern hemisphere and more southerly itcz position correlation of alfonso basin records with other records in the gulf of california and the pigmy and cariaco basins in the gulf of mexico and central atlantic provides constraints on nam itcz migration and insolation driven changes

nutrient leakage from the north pacific to the bering sea iodp site u1341 following the onset of northern hemispheric glaciation 1 intergrated ocean drilling program expedition 323 recovered a sediment record covering the last 4 3 ma from the bering sea integrated ocean drilling program site u1341 bowers ridge 2177 m water depth to resolve pliocene pleistocene paleoenvironmental changes in this marginal basin 190 sediment samples were analyzed for their bulk element composition aluminium contents in bowers ridge sediments are variable but overall higher toward younger sediments probably related to the intensification of the northern hemispheric glaciation and increasing sea ice transport in the bering sea the gradual increase of terrigenous input is mirrored by decreasing sio2 and excess si sixs contents but the overall si enrichment of the deposits reflects continuous opal deposition since the pliocene at bowers ridge unlike in the north pacific the sixs record at site u1341 does not support a dramatic decrease in opal export following the onset of the northern hemispheric glaciation around 2 7 ma but sio2xs have higher accumulation rates up to 8 g cm2 ka between 2 6 and 1 8 ma bp during this period the major oceanic opal deposition centers shifted globally from open marine high latitude regions to upwelling areas we here discuss how the onset of north pacific stratification at 2 7 ma bp may have caused leakage of nutrient rich deep intermediate north pacific water into the bering sea via the deep kamtchatka strait leading to increased opal deposition and likely reactive organic matter export at bowers ridge as a result magnetic and geochemical records were overprinted by intensified diagenesis significantly affecting their applications as paleoceanographic proxies

push from the pacific enhanced upwelling and co2 degassing from the subpolar north pacific during a warm event 14 000 years ago may have helped keep atmospheric co2 levels high enough to propel the earth out of the last ice age

paleomagnetism of the late neoproterozoic blueflower and risky formations of the northern cordillera canada paleomagnetic analysis of the risky and underlying blueflower formations at the top of the neoproterozoic windermere supergroup in the northern cordillera of canada revealed several magnetic components of geological significance rock strata of the blueflower locality in the mackenzie mountains yielded no primary remanence due to extensive pyritization and weathering however dolomitic rocks of the risky locality in the eastern wernecke mountains 250 km to the north yielded a probable primary remanence the remanence has a direction at d i 055 64 n 11 samples from 4 sites k 18 95 11 and pole at 007 e 29 s p m 14 18 and indicates a paleolatitude of 46 14 s comparison between poles from the risky and the overlying backbone ranges and ingta formations suggests a profound post risky unconformity three secondary components are also present component b in both the blueflower and risky units appears to be a thermal overprint possibly related to vendian rifting its respective direction in each unit is d i 062 77 n 4 sites k 143 95 8 and d i 064 56 n 6 sites k 21 95 15 yielding poles of 110 e 64 s p m 13 14 and 142 e 44 s p m 15 21 component c only found in the risky is attributed to late cambrian to middle ordovician extension and magmatism component d which predominates in both formations relates to late mesozoic compression and to weathering

barium accumulation in the atlantic sector of the southern ocean results from 190 000 year records extensive investigations of sedimentary barium were performed in the southern south atlantic in order to assess the reliability of the barium signal in antarctic sediments as a proxy for paleoproductivity maximum accumulation rates of excess barium were calculated for the antarctic zone south of the polar front where silica accumulates at high rates the correspondence between barium and opal supports the applicability of barium as a proxy for productivity within the antarctic zone north of today s average sea ice maximum interglacial vertical rain rates of excess barium are high with a maximum occurring during the last deglaciation and early holocene and during oxygen isotope chronozone 5 5 during these periods the maximum silica accumulation was supposedly located south of the polar front glacial paleoproductivity instead was low within the antarctic zone north of the polar front significantly higher barium accumulation occurs during glacial times the vertical rain rates however are as high as in the glacial antarctic zone therefore there was no evidence for an increased productivity in the glacial southern ocean

the evolution of hypoxia off the changjiang estuary in the last 3000 years evidence from benthic foraminifera and elemental geochemistry abstract estuarine hypoxia has exerted great influence on the ecological system and fishery production in the past decades consequently attracting intensive concern in this study the upper 18 0 m of core yd0902 retrieved from the hypoxic area off the changjiang estuary was dated by ams 14c method and analyzed with lithology grain size benthic foraminifera and geochemical elements to decipher the paleoenvironmental change and hypoxic history in the last 3000 years the core location was in the neritic to prodelta transitional environment during 3000 2160 cal yr bp and the delta front environment after 2160 cal yr bp no hypoxia occurred during 3000 2600 cal yr bp potentially related to the contemporary occurrence of a rapid cold climate event in the northern hemisphere hypoxia has likely existed persistently since 2600 cal yr bp the period 2600 600 cal yr bp characterizes persistently severe hypoxia mainly linked with the warm climate strong east asian summer monsoon easm and rainfall intensified taiwan warm current intrusion and upwelling and high primary production lessened hypoxia followed in the period 600 260 cal yr bp because of the cold climate weak easm and minor precipitation the recent period post 260 cal yr bp was not disclosed by the core due to lost sediments in the top 4 5 m and could only be surmised to have severe hypoxia because of climate factors similar to the period 2600 600 cal yr bp our findings shed new light on long term hypoxic evolution and controlling factors in mega river estuaries

foraminiferal oxygen and carbon isotopes during the last 34 kyr off northern japan northwestern pacific abstract oxygen and carbon isotopes of foraminifera were analyzed in core pc4 water depth 1366 m off northern japan near the east side of the tsugaru strait 130 m depth between the open northwestern pacific ocean and the japan sea at present the site is at the confluence of the tsugaru warm current which flows eastwards out of the sea of japan through the tsugaru strait the subarctic oyashio current and the subtropic kuroshio current during the last glacial maximum lgm the oyashio current penetrated further to the south and outflow from the japan sea was restricted by glacio eustatic sea level lowering the isotopic values of the planktic foraminifer neogloboquadrina pachyderma sinistral and the benthic foraminifer uvigerina akitaensis reflect rapid millennial scale paleoceanographic changes between 34 and 6 ka hydrographic changes during deglaciation were related to events at high northern latitudes but holocene hydrographic changes were dominated by local effects such as the development of the outflow of the tsugaru warm current high values of planktic 18 o during the lgm reflect the southward advance of the oyashio current these values decreased by 0 3 from 19 4 to 18 9 ka then increased by 0 5 at 18 ka with highest values between 17 5 and 15 ka the 18 o oscillations between 19 4 and 15 ka may reflect millennial scale warm cold oscillations during heinrich event 1 planktic microfossil data indicate that cold oyashio waters flowed from the northwestern pacific into the japan sea via the tsugaru strait between 17 and 16 ka consistent with the occurrence of the highest planktic 18 o values in core pc4 planktic 18 o values rapidly decreased by 0 9 at 15 ka possibly reflecting the effects of both a rapid increase in fresh water flux and rising temperatures in the subarctic north pacific during the younger dryas cold event planktic 18 o values increased by 0 5 followed by a gradual decrease by 1 from the early to middle holocene reflecting a gradual increase in eastward outflow via the tsugaru strait with sea level rise both planktic and benthic foraminiferal 13 c values oscillated between 34 and 10 ka at relatively large amplitudes about 0 5 then remained relatively stable during the last 10 kyr several negative planktic and benthic 0 7 13 c excursions were present in sediment dated between the precipitation of secondary carbonates during episodic methane release possibly associated with methane release from continental margin sediments

global deep sea burial rate of calcium carbonate during the last glacial maximum global databases concentrations rates in holocene and last glacial of calcium carbonate and mass accumulation maximum sediments were used to estimate the deep sea sedimentary calcium carbonate burial rate during these two time intervals sparse calcite mass accumulation rate data were extrapolated across regions of varying calcium carbonate concentration using a gridded map of calcium carbonate concentrations and the assumption that accumulation of noncarbonate material is uncorrelated with calcite concentration within some geographical region mean noncarbonate accumulation rates were estimated within each of nine regions determined by the distribution and nature of the accumulation rate data for core top sediments data coverage 67 of the high calcite the regions of reasonable encompass 75 sediments globally and within these regions we estimate an accumulation rate of 55 9 3 6x1011 mol yr 1 the same regions cover 48 of glacial high caco3 sediments the smaller fraction is due to a shift of calcite deposition to the poorly sampled south pacific and total 44 1 6 0x1011 mol yr 1 projecting to 100 coverage south and total 44 1 6 0x1011 both estimates yields accumulation estimates of 8 3x1012 mol yr 1 today and 9 2x1012 mol yr 1 during glacial time this is little better than a guess given the incomplete data coverage but it suggests that glacial deep sea calcite burial rate was probably not considerably faster than today in spite of a presumed decreasein shallow water burial during glacial time

similar glacial and interglacial export bioproductivity in the atlantic sector of the southern ocean multiproxy evidence and implications for glacial atmospheric co2 we present time series of export productivity proxy data including 230thex normalized deposition rates rain rates of 10be dissolution corrected biogenic ba and biogenic opal as well as authigenic u concentrations which are complemented by rain rates of total detrital fe and sea ice indicating diatom abundances from five sediment cores across the atlantic sector of the southern ocean covering the past 150 000 years the results suggest that 10be rain rates and authigenic u concentration cannot serve as quantitative paleoproductivity proxies because they have also been influenced by detrital particle fluxes in the case of 10be and bulk sedimentation rates sediment focussing and deep water oxygenation in the case of u the combined results of the remaining productivity proxies of this study rain rates of biogenic opal and biogenic ba in those sections without authigenic u and other previously published proxy data from the southern ocean 231pa 230th and nitrogen isotopes suggest that a combination of sea ice cover shallow remineralization depth and stratification of the glacial water column south of the present position of the antarctic polar front and possibly fe fertilization north of it have been the main controlling factors of export paleoproductivity in the southern ocean over the last 150 000 years an overall glacial increase of export paleoproductivity is not supported by the data implying that bioproductivity variations in the southern ocean are unlikely to have contributed to the major glacial atmospheric co2 drawdown observed in ice cores

transient stratification as the cause of the north pacific productivity spike during deglaciation during the last deglaciation the north pacific ocean was characterized by a spike in primary productivity which has been attributed to iron input marine sediment analyses suggest that instead the productivity may have been fuelled by deep convection and subsequent stratification