late quaternary spatial and temporal variability in arctic deep sea bioturbation and its relation to mn cycles changes in intensity and composition of bioturbation and trace fossils in deep sea settings are directly related to changes in environmental parameters such as food availability bottom water oxygenation or substrate consistency because trace fossils are practically always preserved in situ and are often present in environments where other environmental indicators are scarce or may have been compromised or removed by diagenetic processes the trace fossils provide an important source of paleoenvironmental information in regions such as the deep arctic ocean detailed analysis of x ray radiographs from 12 piston and gravity cores from a transect spanning from the makarov basin to the yermak plateau via the lomonosov ridge the morris jesup rise and the gakkel ridge reveal both spatial and temporal variations in an ichnofauna consisting of chondrites nereites phycosiphon planolites scolicia trichichnus zoophycos as well as deformational biogenic structures the spatial variability in abundance and diversity is in close correspondence to observed patterns in the distribution of modern benthos suggesting that food availability and food flux to the sea floor are the most important parameters controlling variations in bioturbation in the arctic ocean the most diverse ichnofaunas were observed at sites on the central lomonosov ridge that today have partially ice free conditions and relatively high summer productivity in contrast the most sparse ichnofauna was observed in the ice infested region on the lomonosov ridge north of greenland since primary productivity and therefore also the food flux at a certain location is ultimately controlled by the geographical position in relation to ice margin and the continental shelves temporal variations in abundance and diversity of trace fossils have the potential to reveal changes in food flux and consequently sea ice conditions on glacial interglacial time scales down core analysis reveal clearly increased abundance and diversity during interglacial interstadial intervals that were identified through strongly enhanced mn levels and the presence of micro and nannofossils warm stages are characterized by larger trace fossils such as scolicia planolites or nereites while cold stages typically display an ichnofauna dominated by small deep penetrating trace fossils such as chondrites or trichichnus the presence of biogenic structures in glacial intervals clearly show that the arctic deep waters must have remained fairly well ventilated also during glacials thereby lending support to the hypothesis that the conspicuous brown layers rich in mn which are found ubiquitously over the arctic basins are related to input from rivers and coastal erosion during sea level high stands rather than redox processes in the water column and on the sea floor however the x ray radiograph study also revealed the presence of apparently post sedimentary diagenetically formed mn layers which are not directly related to mn input from rivers and shelves these observations thus bolster the hypothesis that the bioturbated brownish mn rich layers can be used for stratigraphic correlation over large distances in the arctic ocean but only if post sedimentary diagenetic layers can be identified and accounted for in the mn cycle stratigraphy

distribution of stable isotopes in surface snow along the route of the 1990 international trans antarctica expedition this paper presents the distri bution of average od and 6180 values for the top i m of surface snow for a large area of antarctica the samples were collected on the 1990 internatio nal trans antarctica expedition which crossed the continent from the northern tip of the antarctic penins ula to mirny station the empirical rel ationships between the isotopes temperature and elevation are computed the slopes of od with respect to the surface temperature for the segments west patriot hills v ostok and east ofvostok komso molskaya mirny are not signifi cantly different to that obse rved between dumont d urville and dome c lorius and merlivat 1977 which are often used to inte rpret deep ice core isotopic profiles there is however a noti ceable shift between the two regression lines

diagenetic regimes in arctic ocean sediments implications for sediment geochemistry and core correlation dark brown sediment layers are a potential stratigraphic tool in quaternary arctic ocean sediments they are rich in mn fe and trace metals scavenged from the water column and were most likely deposited during interglacial intervals in this study we combine sediment and pore water data from sediment cores taken in different parts of the arctic ocean to investigate the influence of early diagenetic processes on sediment geochemistry in most studied cores mn co and mo are released into the pore waters from mn oxide dissolution in deeper 1 5 m sediment layers the relationship between sedimentary mn co and mo contents in excess of the lithogenic background elementxs shows thatcoxs moxs values are a diagnostic tool to distinguish between layers with diagenetic metal addition from the pore waters coxs moxs 10 and unaffected layers coxs moxs from 1 to 10 steady state calculations based on current pore water profiles reveal that in the studied cores the diagenetic addition of these metals from the pore water pool alone is not sufficient to produce the sedimentary metal enrichments however it seems evident that dissolution of mn oxides in the mn reduction zone can permanently alter the primary geochemical signature of the dark brown layers therefore pore water data and coxs moxs values should be considered before core correlation when this correlation is solely based on mn contents and dark sediment color in contrast to the mostly nonlithogenic origin of mn in the dark brown layers sedimentary fe consists of a large lithogenic 80 and a small non lithogenic fraction 20 our pore water data show that diagenetic fe remobilization is not currently occurring in the sediment the dominant fe sources are coastal erosion and river input budget calculations show that fe seems to be trapped in the modern arctic ocean and accumulates in shelf and basin sediments the fe isotopic signal 56fe of the solid phase is positive 0 2 to 0 3 in samples defined as the lithogenic background without significant fe enrichments with increasing non lithogenic fe contents in the sediment 56fe becomes more negative which indicates a shelf to basin export of an isotopically lighter fe fraction we assume that the same transport process is true for mn

pelagic carbonate chemostratigraphy sr mg 18o 13c abstract a synthesis of the elementary sr and mg and isotopic 18 o and 13 c geochemistry of mesozoic to recent bulk pelagic carbonates suggests that the influence of late burial diagenesis is considerably less than was previously thought and that bulk carbonate geochemistry could be important for both paleoceanography and stratigraphy numerous chemical fluctuations in sr ca mg ca and 13 c 12 c ratios have occurred in the ocean during the last 140 ma the main factors responsible are 1 variations in submarine hydrothermal activity and 2 sea level fluctuations the validity of the chemostratigraphic methodology can be demonstrated by the synchroneity and the worldwide occurrence of various geochemical shifts

seasonal and spatial variations of 17oexcess and dexcess in antarctic precipitation insights from an intermediate complexity isotope model an intermediate complexity isotope model icm is used to investigate the sensitivity of water isotope ratios in precipitation including 17oexcess to climate variations in the southern hemisphere the icm is forced with boundary conditions from seasonal ncep doe ii reanalysis data perturbations to the surface temperature and humidity fields are used to investigate the isotopic sensitivity the response of 17oexcess to a uniform temperature change is insignificant over the ocean while there is a large magnitude response over the ice sheet particularly in east antarctica a decrease of ocean surface relative humidity produces increased 17oexcess and dexcess with a coherent response over both the ocean and antarctica for interior east antarctica the model simulates a seasonal cycle in 17oexcess that is positively correlated with 18o and of large magnitude 50 per meg consistent with the observations from vostok the seasonal cycle in 17oexcess for interior west antarctica is predicted to be considerably smaller in magnitude 12 per meg and is negatively correlated with 18o consistent with new data from a firn core near the west antarctic ice sheet divide site over the ocean the icm predicts much smaller seasonal cycles in 17oexcess oceanic source changes i e humidity are insufficient to explain the amplitude of the simulated seasonal cycle over the antarctic continent spatial differences in the seasonal response of 17oexcess to local temperature reflect the balance of equilibrium and kinetic fractionation during snow formation

understanding the 17o excess glacial interglacial variations in vostok precipitation combined measurements of delta o 18 delta o 17 and delta d in ice cores leading to d excess and o 17 excess are expected to provide new constraints on the water cycle and past climates we explore different processes both in the source regions and during the poleward transport that could explain the o 17 excess increase by 20 per meg observed from the last glacial maximum lgm to early holocene eh at the vostok station using a single column model over tropical and subtropical oceans we show that the relative humidity at the surface is the main factor controlling o 17 excess in source regions then using a rayleigh type model we show that the o 17 excess signal from the source region is preserved in the polar snowfall contrary to d excess evaporative recharge over mid and high latitudes and delta o 18 seasonality in polar regions can also affect the vostok o 17 excess but cannot account for most of the 20 per meg deglacial increase from lgm to eh on the other hand a decrease of the relative humidity at the surface rh s by 8 to 22 would explain the observed change in o 17 excess such a change would not necessarily be incompatible with a nearly unchanged boundary layer relative humidity if the surface thermodynamic disequilibrium decreased by 4 degrees c such a change in rh s would affect source and polar temperatures reconstructions from delta o 18 and d excess measurements strengthening the interest of o 17 excess measurements to better constrain such changes

triple water isotopologue record from wais divide antarctica controls on glacial interglacial changes in 17oexcess of precipitation measurements of the 17oexcess of h2o were obtained from ice cores in west and east antarctica combined with previously published results from east antarctica the new data provide the most complete spatial and temporal view of antarctic 17oexcess to date there is a steep spatial gradient of 17oexcess in present day precipitation across antarctica with higher values in marine influenced regions and lower values in the east antarctic interior there is also a spatial pattern to the change in 17oexcess between the last glacial maximum lgm and holocene periods at coastal locations there is no significant change in 17oexcess at both the west antarctic ice sheet divide site and at vostok east antarctica the lgm to early holocene change in 17oexcess is about 20 per meg atmospheric general circulation model gcm experiments show that both the observed spatial gradient of 17oexcess in modern precipitation and the spatial pattern of lgm to early holocene change can be explained by kinetic isotope effects during snow formation under supersaturated conditions requiring a high sensitivity of supersaturation to temperature the results suggest that fractionation during snow formation is the primary control on 17oexcess in antarctic precipitation variations in moisture source relative humidity play a negligible role in determining the glacial interglacial 17oexcess changes observed in antarctic ice cores additional gcm experiments show that sea ice expansion increases the area over which supersaturating conditions occur amplifying the effect of colder temperatures temperature and sea ice changes alone are sufficient to explain the observed 17oexcess glacial interglacial changes across antarctica

regional variations in provenance and abundance of ice rafted clasts in arctic ocean sediments implications for the configuration of late quaternary oceanic and atmospheric circulation in the arctic abstract the composition and distribution of ice rafted glacial erratics in late quaternary sediments define the major current systems of the arctic ocean and identify two distinct continental sources for the erratics in the southern amerasia basin up to 70 of the erratics are dolostones and limestones the amerasia suite that originated in the carbonate rich paleozoic terranes of the canadian arctic islands these clasts reached the arctic ocean in glaciers and were ice rafted to the core sites in the clockwise beaufort gyre the concentration of erratics decreases northward by 98 along the trend of the gyre from southeastern canada basin to makarov basin the concentration of erratics then triples across the makarov basin flank of lomonosov ridge and siltstone sandstone and siliceous clasts become dominant in cores from the ridge and the eurasia basin the eurasia suite the bedrock source for the siltstone and sandstone clasts is uncertain but bedrock distribution and the distribution of glaciation in northern eurasia suggest the taymyr peninsula kara sea regions the pattern of clast distribution in the arctic ocean sediments and the sharp northward decrease in concentration of clasts of canadian arctic island provenance in the amerasia basin support the conclusion that the modern circulation pattern of the arctic ocean with the beaufort gyre dominant in the amerasia basin and the transpolar drift dominant in the eurasia basin has controlled both sea ice and glacial iceberg drift in the arctic ocean during interglacial intervals since at least the late pleistocene the abruptness of the change in both clast composition and concentration on the makarov basin flank of lomonosov ridge also suggests that the boundary between the beaufort gyre and the transpolar drift has been relatively stable during interglacials since that time because the beaufort gyre is wind driven our data in conjunction with the westerly directed orientation of sand dunes that formed during the last glacial maximum on the north slope of alaska suggests that atmospheric circulation in the western arctic during late quaternary was similar to that of the present

onset of hudson strait heinrich events in the eastern north atlantic at the end of the middle pleistocene transition 640 ka 1 heinrich events are well documented for the last glaciation but little is known about their occurrence in older glacial periods of the pleistocene here we report scanning xrf and bulk carbonate 18o results from integrated ocean drilling program site u1308 reoccupation of deep sea drilling project site 609 that are used to develop proxy records of ice rafted detritus ird for the last 1 4 ma ca sr is used as an indicator of ird layers that are rich in detrital carbonate i e heinrich layers whereas si sr reflects layers that are poor in biogenic carbonate and relatively rich in detrital silicate minerals a pronounced change occurred in the composition and frequency of ird at 640 ka during marine isotope stage mis 16 coinciding with the end of the middle pleistocene transition at this time hudson strait heinrich layers suddenly appeared in the sedimentary record of site u1308 and the dominant period of the si sr proxy shifted from 41 ka prior to 640 ka to 100 ka afterward the onset of heinrich layers during mis 16 represents either the initiation of surging of the laurentide ice sheet lis off hudson strait or the first time icebergs produced by this process survived the transport to site u1308 we speculate that ice volume i e thickness and duration surpassed a critical threshold during mis 16 and activated the dynamical processes responsible for lis instability in the region of hudson strait we also observe a strong coupling between ird proxies and benthic 13c variation at site u1308 throughout the pleistocene supporting a link between iceberg discharge and weakening of thermohaline circulation in the north atlantic

spatial distribution of 17o excess in surface snow along a traverse from zhongshan station to dome a east antarctica the influence of temperature on the triple isotopic composition of oxygen in water is still an open question and limits the interpretation of water isotopic profiles in antarctic ice cores the main limitation arises from the lack of 17o excess measurements in surface snow and especially for remote regions characterized by low temperature and accumulation rate in this study we present new 17o excess measurements of surface snow along an east antarctic traverse from the coastal zhongshan station to the highest point of the antarctic ice sheet at dome a the 17o excess data significantly decrease inland with a latitudinal gradient of 1 33 0 41 per meg degree an altitudinal gradient of view the mathml source and a temperature gradient of view the mathml source theoretical calculations performed using a rayleigh model attribute this inland decrease to kinetic isotopic fractionation occurring during condensation from vapor to ice under supersaturation conditions at low temperatures however large heterogeneity of 17o excess in antarctic precipitation cannot only be explained by temperature at condensation and or influences of relative humidity in the moisture source region

modern river discharge and pathways of supplied material in the eurasian arctic ocean evidence from mineral assemblages and major and minor element distribution clay mineral heavy mineral and elemental distributions in sediments from the arctic ocean and the adjacent laptev and kara seas can be attributed to the geology of the hinterland and the transport of terrigenous material by rivers onto the shelves kara sea sediments are characterized by increased contents of smectite and elevated ni al ti al and cr al ratios in the western laptev sea sediments are enriched in smectite and clinopyroxene and increased in ti al cr al and ca al ratios the composition of the sediments reflects suspended matter input from the large trap basalt of the putoran mountains the eastern laptev sea sediments display increased illite and amphibole contents as well as a chemical composition similar to average shale this composition is due to the discharge from the lena and yana rivers which drain a large catchment area consisting of sedimentary mesozoic and paleozoic rocks material from the eastern laptev sea is transported by ocean currents and sediment laden sea ice along the transpolar drift into the central arctic ocean this is indicated by similar values of ti al cr al rb al and k al ratios as well as increased concentrations of amphibole and illite determined in sediments from the lomonosov ridge a minor input from the beaufort sea into the central arctic ocean is suggested from increased ca al ratios and increased contents of opaque minerals

synoptic activity in the seas around antarctica abstract the recent ncep department of energy doe reanalysis 2 update of the original ncep ncar dataset provides what is arguably the highest quality analyses spanning two decades available for the high southern latitudes it therefore offers an excellent starting point from which to assemble a modern comprehensive and reliable picture of synoptic activity in the subantarctic region this set covering the modern satellite era from january 1979 to february 2000 is used herein in addition the exploration in this study has been conducted with sophisticated feature tracking and trajectory analysis software it is shown that the high southern latitude cyclone system density is greatest in the indian ocean and to the south of australia near or to the south of 60 s the numbers in winter exceed those in summer except over a few but important regions such as the bellingshausen sea the antarctic coastal region is confirmed as one of high cyclonicity as is that in the northern part of the antarctic

little ice age cold interval in west antarctica evidence from borehole temperature at the west antarctic ice sheet wais divide 1 the largest climate anomaly of the last 1000 years in the northern hemisphere was the little ice age lia from 1400 1850 c e but little is known about the signature of this event in the southern hemisphere especially in antarctica we present temperature data from a 300 m borehole at the west antarctic ice sheet wais divide results show that wais divide was colder than the last 1000 year average from 1300 to 1800 c e the temperature in the time period 1400 1800 c e was on average 0 52 0 28 c colder than the last 100 year average this amplitude is about half of that seen at greenland summit grip this result is consistent with the idea that the lia was a global event probably caused by a change in solar and volcanic forcing and was not simply a seesaw type redistribution of heat between the hemispheres as would be predicted by some ocean circulation hypotheses the difference in the magnitude of the lia between greenland and west antarctica suggests that the feedbacks amplifying the radiative forcing may not operate in the same way in both regions

sources of sediment found in sea ice from the western arctic ocean new insights into processes of entrainment and drift patterns 1 the geochemical fingerprint of entrained fe oxide mineral grains in arctic ocean sea ice is used to determine precise sources of this sediment this approach substantiates the importance of the laptev sea as a source of sea ice and even the presence of russian ice in the beaufort sea off alaska fe oxide grains from the laptev sea were found in floes in the beaufort sea chukchi borderland and central arctic ocean demonstrating the importance of sea ice in distributing itself throughout the arctic ocean and the potential of transporting sediment from russian rivers to north american shelves banks island shelf is the most important source of sediment sampled from ice floes in the beaufort sea northern chukchi sea and chukchi borderland area although most of the entrained sediment fits the criteria for suspension freezing in shallow water the presence of winter polynyas with offshore winds and not the size of shallow areas appears to be the critical factor for sea ice entrainment seven of the 18 ice floes sampled contained fe oxide grains from more than one source area the two most common sources that are found in the same ice floes are banks island and the laptev sea multiple sources in ice floes suggest that either mingling of fragmented ice floes occurs or that a source area containing grains from both these sources has yet to be located the addition of fine sand sized windblown sediment is not thought to be significant

a 420 000 year deuterium excess record from east antarctica information on past changes in the origin of precipitation at vostok here we present and analyze the complete vostok ice cores deuterium excess record which spans the last four climatic cycles back to 420 000 years b p to extract paleoclimate information from this record we use isotopic modeling showing that changes in deuterium excess d d 8 18o of vostok precipitation reflect changes in the average temperature of oceanic moisture sources over the last 250 000 years the deuterium excess is strongly anticorrelated with changes in earth s obliquity this reflects changes in the relative contribution of low and high latitudes to the vostok precipitation resulting from changes in the latitudinal annual mean insolation gradient governed by the obliquity however this modulation by obliquity is not observed prior to 250 000 years b p we attribute this difference to the ice flow the deeper ice under vostok station having accumulated in a location upstream vostok receiving precipitation from different oceanic origins despite this difference between the earlier and the later portions of the record the deuterium excess changes during all the glacial inceptions are similar in amplitude and timing relative to the deuterium decrease the glacial inceptions are characterized by high deuterium excess indicating the significant role of the tropics in supplying moisture to the already cold poles

mid to late pleistocene ice drift in the western arctic ocean evidence for a different circulation in the past the provenance of ice rafted debris ird in four arctic sediment cores implies that icebergs from the northwestern laurentide ice sheets drifted across the western arctic ocean along the 180 0 meridian toward fram strait during mid to late pleistocene deglaciations within the last 700 000 years this iceberg drift was different from the present day beaufort gyre circulation and resembled a dislocated transpolar drift tpd sea ice mainly followed the iceberg trajectories but also frequently drifted from the russian shelves eastward into the amerasian basin

the last deglaciation event in the eastern central arctic ocean oxygen isotope records of cores from the central arctic ocean yield evidence for a major influx of meltwater at the beginning of the last deglaciation 15 7 thousand years ago 16 650 calendar years b c the almost parallel trends of the isotope records from the arctic ocean the fram strait and the east greenland continental margin suggest contemporaneous variations of the eurasian arctic and greenland laurentide ice sheets or increased export of low saline waters from the arctic within the east greenland current during the last deglaciation on the basis of isotope and carbon data the modern surface and deep water characteristics and seasonally open ice conditions with increased surface water productivity were established in the central arctic at the end of termination lb about 7 2 thousand years ago or 6 000 calendar years b c

seasonal variations of 17 o excess and d excess in snow precipitation at vostok station east antarctica the use of water isotopes in polar regions is essential for reconstructing past climate over glacial interglacial cycles in addition to d do rd 18 o linearly related to condensation temperature the second order parameters d excess and 17 o excess provide important information on the climatic conditions of the source of precipitations in order to best interpret the glacial interglacial records of d excess and 17 o excess in polar ice cores it is important to document their present variability especially in remote and cold regions of east antarctica indeed the current climatic conditions encountered in these regions provide a good analogy with glacial climatic conditions in a large part of antarctica here we present the first seasonal variations of 17 o excess and d excess at vostok station on an event basis i e samples were collected immediately after each precipitation event over 1 year these records show strong correlation between 17 o excess and d 18 o over the course of the year with an amplitude 40 per meg 10 3 in the 17 o excess seasonal cycle and strong anticorrelation between d excess and d 18 o with d excess variations up to 20 the d excess and 17 o excess variations can be explained by the influence of kinetic fractionation at very low temperatures the comparison with simple isotopic models confirms this explanation but cannot explain the link between 17 o excess d excess and temperature without 1 a particular relationship between condensation and surface temperature and or 2 seasonal changes in the climatic conditions of the source regions

mg ca and sr ca ratios in planktonic foraminifera proxies for upper water column temperature reconstruction reliable temperature estimates from both surface and subsurface ocean waters are needed to reconstructpast upper water column temperature gradients and past oceanic heat content this work examines therelationships between trace element ratios in fossil shells and seawater temperature for surface dwellingforaminifera species globigerinoides ruber white and globigerina bulloides and deep dwelling species globorotalia inflata globorotalia truncatulinoides dextral and sinistral and pulleniatina obliquiloculata mg ca and sr ca ratios in shells picked in 29 modern core tops from the north atlantic ocean are calibratedusing calculated isotopic temperatures mg ca ratios on g ruber and g bulloides agree with published dataand relationships for deep dwelling species mg ca calibration follows the equation mg ca 0 78 0 04 exp 0 051 0 003 t with a significant correlation coefficient of r

the trace metal content of recent organic carbon rich sediments implications for cretaceous black shale formation organic carbon rich sediments are enriched in several redox sensitive and stable sulfide forming trace metals tm and form an important sink in global tm cycles in today s ocean such sediments are deposited in coastal upwelling areas like those in the gulf of california off peru or off the namibian coast and euxinic basins like the black sea in an attempt to distinguish both environments by their specific tm patterns some important conclusions may be drawn 1 the tm enrichment seen in both environments broadly is rather similar 2 upwelling sediments are often enriched in cd and p and depleted in co and mn 3 sapropels have a tendency towards higher enrichments in ba and mo s re as cu ni sb and fe reflecting the strong sulfidation in an anoxic water column 4 upwelling systems cover a broad range of environmental settings where the steepness of the slope the proximity of h2s to the sediment seawater interface and the intensity of bio accumulation and regeneration play an important role for tm accumulation 5 the tm content of anoxic basins is mainly controlled by tm availability in the water column and sedimentation rate 6 enhanced bio productivity is the main switch turning an oxygenated into an anoxic environment cretaceous black shales oae 2 exhibit tm signatures of both coastal upwelling areas and sapropels the strong enrichments in cd mo tl v cu ni bi and sb demonstrate that bio accumulation and presence of h2s in the water column and associated sulfidation processes persisted during this time interval in large parts of the proto atlantic the usefulness of ba as a paleoproductivity proxy is obscured by diagenesis the extreme accumulation in ag and zn requires either an additional tm source for instance hydrothermal input or a different tm seawater composition during the cretaceous the geochemical data suggest that the major driving force for the widespread occurrence of c t black shales seems to be the increase in volcanic activity and associated co2 input throughout the cretaceous the ocean atmosphere system operated in a mode different from today during this time interval after conversion of the nutrient co2 into organic matter the system switched back into the normal operational mode

moisture sources and synoptic to seasonal variability of north atlantic water vapor isotopic composition the isotopic composition of near surface or planetary boundary layer water vapor on the south coast of iceland 63 83 n 21 47 w has been monitored in situ between november 2011 and april 2013 the calibrated data set documents seasonal variations in the relationship between 18o and local humidity ppmv and between deuterium excess and 18o these seasonal variations are attributed to seasonal changes in atmospheric transport a strong linear relationship is observed between deuterium excess and atmospheric relative humidity calculated at regional sea surface temperature surprisingly we find a similar relationship between deuterium excess and relative humidity as observed in the bermuda islands during days with low amount of isotopic depletion more enriched values our data significantly deviate from the global meteoric water line this feature can be explained by a supply of an evaporative flux into the planetary boundary layer above the ocean which we show using a 1 d box model based on the close relationship identified between moisture origin and deuterium excess we combine deuterium excess measurements performed in iceland and south greenland with moisture source diagnostics based on back trajectory calculations to establish the distribution of d excess moisture uptake values across the north atlantic we map high deuterium excess in the arctic and low deuterium excess for vapor in the subtropics and midlatitudes this confirms the role of north atlantic water vapor isotopes as moisture origin tracers

regional variations in sediment geochemistry on a transect across the mendeleev ridge arctic ocean abstract inorganic geochemical investigations were performed on three arctic surface sediment cores ps72 408 4 ps72 410 2 and ps72 422 4 recovered during rv polarstern expedition ark xxiii 3 on a transect across the mendeleev ridge dark brown layers are geochemically characterized by elevated mn al and fe al ratios and trace metal enrichments trace metals such as as co cu mo and ni seem to be adsorbed onto mn fe oxyhydroxide surfaces due to scavenging from the water column similar enrichment patterns of mn co mo and ni suggest that these trace metals are predominantly bound to mn whereas different patterns for fe as and cu reveal that these trace metals are most probably mainly bound to other sediment phases like fe oxyhydroxides or clay minerals calculating mn and fe excess amounts reveals that the dark brown color of the layers which so far has predominantly been attributed to enhanced mn oxyhydroxide contents alone may as well result from a higher fe oxyhydroxide contribution in the investigated surface sediments mn rich layers seem to originate primarily from particulates formed within the water column this implies that the composition of brown layers may be spatially variable even at short distances a diagenetic overprint is not necessarily required putting constraints on the large scale correlation of brown layers across arctic basins the mn enrichments are presumably related to both siberian river discharge and coastal erosion material input related to ice rafted debris is documented in ca al mg al and tic patterns indicating the occurrence of dolomite from the canadian archipelago this material is transported via the beaufort gyre and shows decreasing abundance towards the west along the transect a more basaltic component presumably originating from the east siberian hinterland is characterized by low si al and k al records cabio and srxs patterns may serve as additional indicators for biogenic carbonate input and glacial interglacial changes

glacial freshwater discharge events recorded by authigenic neodymium isotopes in sediments from the mendeleev ridge western arctic ocean the freshwater budget of the arctic ocean is a key component governing the deep water formation in the north atlantic and the global climate system we analyzed the isotopic composition of neodymium end in authigenic phases of marine sediments on the mendeleev ridge in the western arctic ocean spanning an estimated time interval from present to about 75 ka bp this continuous record was used to reconstruct the end of the polar deep water pdw and changes in freshwater sources to the pdw through time three deviations in end from a long term average of 10 2 were identified at estimated 46 51 35 39 and 13 21 ka bp the estimated 46 51 ka bp event can be traced to bursting of ice dammed lakes accompanying the collapse of the barents kara ice sheet which would have released radiogenic nd to the eastern arctic ocean the cyclonic surface circulation in the eastern arctic ocean must have been stronger than at present for the event to be recorded on the mendeleev ridge for the 35 39 and 13 21 ka bp events it is likely that the laurentide ice sheet lis supplied the unradiogenic freshwater the configuration of the anticyclonic circulation in the western arctic was probably similar to today or expanded eastward our simple mass balance calculations suggest that large amounts of freshwater were released but due to significant deep water formation within the arctic ocean the effect on the formation of nadw was probably minor

manganese rich brown layers in arctic ocean sediments composition formation mechanisms and diagenetic overprint we present inorganic geochemical analyses of pore waters and sediments of two late quaternary sediment cores from the western arctic ocean southern mendeleev ridge rv polarstern expedition ark xxiii 3 focussing on the composition and origin of distinct brown colored mn rich sediment layers carbonate enrichments occur in association with these layers as peaks in ca al mg al sr al and sr mg suggesting enhanced input of both ice rafted and biogenic carbonate for the first time we show that the mn rich layers layers are also consistently enriched in the scavenged trace metals co cu mo and ni distinct bioturbation patterns specifically well defined brown burrows into the underlying sediments suggest these metal enrichments formed close to the sediment water interface the geochemical signature of these metal and carbonate rich layers most probably documents formation under warmer climate conditions with an intensified continental hydrological cycle and only seasonal sea ice cover both rivers and sea ice delivered trace metals to the arctic ocean while enhanced seasonal productivity exported reactive organic matter to the sea floor the coeval deposition of organic matter mn oxyhydr oxides and trace metals triggered intense diagenetic mn cycling at the sediment water interface these processes resulted in the formation of mn and trace metal enrichments and the degradation of labile organic matter with the onset of cooler conditions reduced riverine runoff and or a solid sea ice cover terminated the input of riverine trace metal and fresh organic matter resulting in deposition of grayish yellowish metal poor sediments oxygen depletion of arctic bottom waters under these cooler conditions is not supported by our data and did not cause the sedimentary mn distribution while the original composition and texture of the brown layers resulted from specific climatic conditions and corresponding diagenetic processes pore water data show that diagenetic mn redistribution is still affecting the organic poor deeper sediments given persistent steady state conditions purely authigenic mn rich brown layers may form while others may be partly or completely dissolved the degree of diagenetic mn redistribution largely depends on the depositional environment the mn and organic matter availability and apparently affected the co mo ratios of mn rich layers thus brown arctic layers are not necessarily synchronous features and should not be correlated across the arctic ocean without additional age control

recent change in organic carbon flux to arctic ocean deep basins evidence from acid volatile sulfide manganese and rhenium discord in sediments evidence of recent large scale change in redox conditions in arctic ocean basin sediments is found in profiles of solid phase acid volatile sulfide avs mn and re avs occurs at 2 5 5 5 cm in sediment cores collected from all major arctic basins implying that presently there is a sufficient supply of organic carbon oc to deplete o 2 and form sulfide re which is mobile under oxic conditions but precipitates under suboxic or anoxic conditions is not found enriched in the sediments suggesting that avs is a recent product of enhanced oc fluxes estimated diffusion rates suggest that avs production is recent and that a change from oxic to anoxic diagenesis has taken place within the past 50 y the most likely origin for such widespread change is the ice climate and we infer that reduction in ice cover over the past several decades has led to enhanced oc fluxes to the sea floor

interannual variation of water isotopologues at vostok indicates a contribution from stratospheric water vapor combined measurements of water isotopologues of a snow pit at vostok over the past 60 y reveal a unique signature that cannot be explained only by climatic features as usually done comparisons of the data using a general circulation model and a simpler isotopic distillation model reveal a stratospheric signature in the 17o excess record at vostok our data and theoretical considerations indicate that mass independent fractionation imprints the isotopic signature of stratospheric water vapor which may allow for a distinction between stratospheric and tropospheric influences at remote east antarctic sites

geochemistry of surficial and ice rafted sediments from the laptev sea siberia the laptev sea as a part of the world s widest continental shelves surrounding the arctic ocean is a key area for understanding the land ocean interaction in high latitude regions with a yearly freshwater input of 511 km3 the lena river one of the eight major world rivers has an influencing control over the environment of this arctic marginal sea which is ice covered during most of the year in this paper the first measurements are presented of the major and trace element distribution within the 20 m grain size fraction of surficial sediments and of particulate matter in new and young ice from the laptev sea siberian arctic the concentration and distribution of major and trace elements have been determined in 51 surficial sediment samples covering the whole laptev sea shelf south of the 50 m isobath thirty one samples of particulate matter in newly formed ice were taken during the freeze up period in 1995 median concentration levels of heavy metals in surficial sediments ni 46 g g 1 cu 26 g g 1 zn 111 g g 1 and pb 21 g g 1 are within the concentration range of marine unpolluted sediments also the sediment laden ice showed no indication of anthropogenic perturbation of the trace metal inventory spatial distribution patterns of heavy metals are mainly determined by variation of mineral composition and different fluvial sediment sources in the eastern and western laptev sea the laptev sea shelf is cut by five north south trending submarine valleys enrichment of manganese in the oxic surficial sediment layer within these valleys and the occurrence of small ferromanganese nodules are caused by a high input of dissolved and particulate mn from the lena river and a strong diagenetic cycling of mn on the laptev sea shelf evidence is given that the content of as in surficial sediments is also strongly affected by diagenetic cycling this causes surficial sediment as concentrations of more than 100 g g 1 enrichment of mn and as was mainly observed in the submarine valleys distant from the major river mouth the sediment dilution due to higher sedimentation rates near the river outlets and a strong sediment re working by ice gouging in the shallow areas are the principle causes for the absence of diagenetic accumulation in this region during the formation of new ice scavenging of riverine suspended matter and resuspension of sediments followed by an incorporation of particles into the ice are important processes for the river shelf ocean transport of particulate trace elements it could be shown that particle loaded ice posseses the same geochemical signatures as the suspended matter and surficial seafloor sediments in the area of ice origin this has also strong implications for the contaminant transport on the arctic shelves and allows to use the geochemical signature of sea ice for the reconstruction of ice drift pattern within the arctic ocean

pyritization of trace metals in anoxic marine sediments the pyritization of reactive trace elements in different anoxic marine sediments was investigated to determine the importance of factors such as h2s reactive fe pyrite content and salinity in controlling this process the areas studied included anoxic sulfidic sediments baffin bay a hypersaline coastal lagoon from texas and green canyon a hemipelagic oil seepage area anoxic nonsulfidic sediments with high sedimentation rates atchafalaya bay mississippi delta system hemipelagic anoxic nonsulfidic sediments with low sedimentation rates gulf of mexico shelf and slope and orca basin an euxinic hypersaline basin and organic rich marsh sediments atchafalaya bay results indicate that the degree of trace metal pyritization dtmp of all trace metals except cd increased with increasing degree of pyritization dop irrespective of the type of sedimentary environment involved however for as hg and mo the dtmpdop values were generally above the 1 1 ratio line whereas the transition metals co cu mn and ni displayed a close to linear increase in dtmp with dop and moderate incorporation into pyrite chromium and the class b metals pb and zn were also gradually incorporated into the pyrite phase but without reaching the dtmp levels exhibited by the transition metals cadmium was not incorporated to a significant extent these results are consistent with the chemical attributes of these different classes of trace elements availability of dissolved trace metals and organic matter content are apparently important factors controlling the incorporation of co cr cu and ni into pyrite in anoxicsulfidic fe poor and h2s rich environments

geochemistry of recent toc rich sediments from the gulf of california and the black sea major and minor elements incl ag as ba cd co cr cu mn mo ni pb sr v zn have been determined in recent sediments from the gulf of california upwelling area and black sea sapropels in order to reinterpret their chemical composition in view of reliable seawater and plankton data the chemistry of the gulf of california sediments reflects regeneration processes which occur in the water column i e only a small fraction 10 of elements like cd which in seawater are coupled to the labile nutrients c n p is buried in the sedimentary column in contrast elements like the more resistant nutrients si undergo a deeper regeneration cycle ba several trace metals which are present in comparatively higher concentrations in seawater as mo u v and at the same time are reactive under reducing conditions and or are able to form stable sulfides are fixed in the sediments during early diagenesis the early diagenetic behavior of ba is closely related to bacterial sulfate reduction the formation of barite concretions is discussed anoxic conditions in the water column act as ideal traps for a number of redox sensitive and or stable sulfide forming elements a simple trace metal balance calculation shows that the chemical composition of black sea sapropels is controlled by fluvial and mediterranean seawater element input and the accumulation rate of terrigenous detrital material

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

pitfalls of normalization of marine geochemical data using a common divisor abstract normalization of trace element contents of sediment through division by the content of an immobile element usually aluminum is common practice in marine geochemical studies this might appear to be a simple way of correcting for dilution by sedimentary phases barren of a particular trace element for instance carbonates or silica and for comparison with its content in a standard clay or shale the purpose of this paper is to revive the awareness of the pitfalls of this practice by giving numerical examples of the often unexpected results of normalization taking a statistical perspective it is first shown that uncorrelated variables acquire spurious correlations when normalized but normalization can also increase decrease change sign of or even blur the correlations between unmodified variables next a number of realistic scenarios are worked out to show that the correlations between normalized element contents still suffer from the closure effect only in a few simple cases it is possible to extract from the normalized data realistic estimates of trace element contents in distinct sedimentary phases such as organic matter this is ascertained from data on copper contents in sediment from the black sea and arabian sea when the coefficient of variation i e standard deviation divided by the mean of the aluminum data is relatively low and much lower than for the original values of the trace elements comparisons of correlations can equally well or even better be made on the basis of the unmodified values then the comparison of trace element data with their values for standard shales is discussed the inherent problem is that the composition of the commonly used standard shale and consequently the reference values of normalized elements are not necessarily representative of the local or regional sediments in the study area also this method falls short of identifying the processes responsible for enrichment or diminution in trace element contents finally consideration is given to some aspects of a proper use of al normalization

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

snow precipitation at four ice core sites in east antarctica provenance seasonality and blocking factors snow precipitation is the primary mass input to the antarctic ice sheet and is one of the most direct climatic indicators with important implications for paleo climatic reconstruction from ice cores provenance of precipitation and the dynamic conditions that force these precipitation events at four deep ice core sites dome c law dome talos dome and taylor dome in east ant arctica were analysed with air mass back trajectories cal culated using the lagrangian model and the mean composite data for precipitation geopotential height and wind speed field data from the european centre for med ium range weather forecast from 1980 to 2001 on an annual basis back trajectories showed that the atlantic indian and ross pacific oceans were the main provenances of precipitation in wilkes land 80 and victoria land 40 respectively whereas the greatest influence of the ice sheet was on the interior near the vostok site 80 and in the southwest ross sea 50 an effect that decreased towards the coast and along the antarctic slope victoria land received snowfall atypically with respect to other antarctica areas in terms of pathway eastern instead of western seasonality summer instead of winter and velocity old air age geopotential height patterns at 500 hpa at low 10 days and high 2 6 days frequen cies during snowfall cycles at two core sites showed large positive anomalies at low frequencies developing in the tasman sea eastern indian ocean at higher latitudes 60 70s than normal this could be considered part of an atmospheric blocking event with transient eddies acting to decelerate westerlies in a split region area and accelerate the flow on the flanks of the low frequency positive anomalies

asymmetries in the moisture origin of antarctic precipitation the seasonality of moisture sources for precipitation in antarctica is studied with a lagrangian moisture source diagnostic moisture origin for precipitation in antarctica has strongly asymmetric properties which are related to the antarctic topography seasonal sea ice coverage and the land ocean contrasts in the mid latitudes of the southern hemisphere the highest altitudes of the east antarctic ice shield where major ice cores have been drilled have mean source latitudes of 45 40 s year round this finding contrasts to results from previous lagrangian studies which detected a more southerly moisture origin due to too short trajectories now results from lagrangian moisture source diagnostics are consistent with findings from general circulation models with tagged tracers thus both approaches can serve as a common benchmark for the interpretation of moisture source indicators based on stable isotopes such as deuterium excess in antarctic ice cores

space and time variation of δ18o and δd in antarctic precipitation revisited 1 to better understand the variations over time of precipitation water isotopes measured in polar ice cores we have developed an intermediate complexity model icm of atmospheric water vapor transport and associated isotopic distillation the model builds directly from earlier work by d fisher and m hendricks and is calibrated against the measured modern spatial distribution of d and deuterium excess d model improvements include a correction to the equation governing advective transport which solves a major puzzle arising from the earlier work the new model shows isotopic data to be consistent with dominance of eddy diffusive transport at high latitudes model experiments are used to show that a wide variety of climate changes in subtropical source regions can affect antarctic d and that such d changes are consistently anticorrelated with changes of d magnitudes of d d are 1 to 5 and are much higher at the ice sheet margin than in the interior of the continent changes in the relative dominance of diffusive and advective transport are also shown to cause anticorrelated changes of similar magnitude isotopic sensitivities to temperature change d t are shown to also vary spatially with low values in marginal zones and higher values inland effects of ocean surface relative humidity on antarctic d are shown to be nearly uniform across the continent in contrast to earlier results given by petit et al 1991 but quantitatively small the method used by vimeux et al 2001 for folding humidity effects into source temperature effects is supported we draw attention to a pervasive misapplication of marine composition corrections to antarctic d records arguments are made in support of simple interpretations of calibrated ice core isotopic time series in terms of temperature changes despite the potential complexities in the system

arctic ocean deep sea record of northern eurasian ice sheet history the sediment composition of deep sea cores from the central arctic ocean the fram strait and the yermak plateau was analyzed for several parameters to reconstruct the history of marine paleoenvironment and terrestrial glaciation in the last 200 000 years layers with high amounts of coarse terrigenous ice rafted debris ird and often high contents of smectite were deposited during extensive glaciations in northern eurasia when ice sheets reached the northern continental margins of the barents and kara seas and discharged icebergs into the arctic ocean intercalated layers with relatively low ird and smectite contents but abundant planktic foraminifers in the coarse fraction were deposited during periods of atlantic water inflow to the arctic ocean and seasonally open waters leads in a sea ice cover with only few icebergs in the arctic ocean high ird contents in the sediments reflect the presence of ice sheets on the kara and barents seas shelves and the hinterland during the entire oxygen isotope stage 6 ca 190 130 ka in substage 5b ca 90 80 ka at the stage boundary 5 4 around 75 ka and in late stage 4 early stage 3 ca 65 50 ka these results are in excellent correlation with those from recent field work in northern scandinavia european russia siberia and on the shelves relatively low amounts of ird in central arctic ocean sediments from the late weichselian glacial maximum ca 24 18 ka correlate well with the recent reconstruction of a very limited eastern ice sheet extension during this time oxygen and carbon isotope records of planktic foraminifers from the analyzed sediment cores show a number of prominent excursions which can be interpreted as evidence for freshwater events in the arctic ocean the synchroneity of freshwater events and ird input suggests a common source strongest events were associated with deglaciations of the barents and kara seas after the ice sheets had blocked the outflow of large rivers for several millennia the outflow of freshwater from large ice dammed lakes occurred at ca 130 80 75 and 52 ka freshwater events in the central arctic ocean during the last deglaciation ca 18 ka were relatively small compared to the previous events this indicates that during most of the late weichselian glacial maximum a river outflow from northern siberia to the arctic ocean was possible atlantic water inflow to the arctic ocean and seasonally open waters in the ice leads occurred during the interglacials ofoxygen isotope stage 1 and substage 5e during several interstadials stage 3 substages 5a and 5c and to a lesser degree within stadials and glacials stages 2 4 and 6 with the exception ofthe interglacials these periods were times ofstrong ice growth on the continents as revealed by terrestrial data the coincidence suggests that open waters in the arctic ocean and the nordic seas were an important moisture source in addition to more southerly sources which fostered the growth of ice sheets on northern eurasia

understanding the climatic signal in the water stable isotope records from the neem shallow firn ice cores in northwest greenland 1 samples of precipitation and atmospheric water vapor were collected together with shallow firn ice cores as part of the new deep drilling project in northwest greenland the neem project these samples were analyzed for their isotope composition to understand the processes affecting the climatic signal archived in the water stable isotope records from the neem deep ice core the dominant moisture source for the snow deposited at the neem site may be originating as far south as 35 n from the western part of the atlantic ocean the surface atmospheric water vapor appears in isotopic equilibrium with the snow surface indicating a large water exchange between the atmosphere and snowpack the interannual variability of neem shallow firn ice cores stable isotope data covering the last 40 years shows an unexpectedly weak nao signal regional to global atmospheric models simulate a dominant summer precipitation in the neem area suggesting that the intermittency of modern winter precipitation is responsible for the lack of a strong nao imprint the interannual variability of neem isotope data however shows a strong correlation with interannual variations of baffin bay sea ice cover a relationship consistent with air mass trajectories neem deep ice core isotopic records may therefore provide detailed information on past baffin bay sea ice extent neem stable water isotope content increasing trend points to a local warming trend of 3 0 c over the last 40 years

diagenetic separation of cadmium and manganese in suboxic continental margin sediments abstract the vertical distribution of cd differs from that of mn in sediment cores taken from the continental margins of the arctic and atlantic oceans the oxic surface sediment is depleted in cd and enriched in mn whereas the subsurface sediment is enriched in cd and depleted in mn in some cores the distributions of solid phase and dissolved mn are offset the porewater profiles indicate that mn is being precipitated relatively deep in the sediment whereas the solid phase distributions indicate that mn has been precipitated very close to the sediment surface in the recent past at one deep site located near the base of the continental slope 3000 m the offset may be caused by a relatively recent decrease in ocean productivity a corresponding decrease in the organic carbon flux to the sediment and a subsequent migration of the redox boundary deeper into the sediment however at a site where the upper sediment layers have accumulated during the last few decades this explanation cannot account for the offset distributions we propose that a fluctuating input of organic matter to the sediment on seasonal or decadal timescales causes the position of the redox boundary to fluctuate the fluctuating redox boundary pumps dissolved mn upward and concentrates it as mn oxide in a distinct layer at the upper limit of the redox excursion at the same time it pumps cd downward and concentrates it in a distinct layer at the lower limit of the redox excursion the net result of a fluctuating redox boundary is to increase the spatial separation of cd and mn during the early diagenesis of suboxic sediments

a multiproxy approach to reconstruct the environmental changes along the eurasian continental margin over the last 150 000 years abstract sediment cores located along the eurasian continental margin arctic ocean have been studied to reconstruct the environmental changes in terms of waxing and waning of the barents kara sea ice sheets atlantic water inflow and sea ice distribution over the last 150 kyr the stratigraphy of the cores is based on stable oxygen isotopes ams 14 c and paleomagnetic data we studied variations in marine and terrigenous input by a multiproxy approach involving direct comparison of sedimentological and organo geochemical data extensive episodes of northern barents sea ice sheet growth during marine isotope stages mis 6 and 2 have been supported by at least subsurface atlantic water inflow moisture bearing storms low summer insolation and minimal calving of ice ice advance during mis 4 was probably restricted to the shallow shelf between mis 4 and mis 2 large ice sheet fluctuations correspond to contemporary laurentide surging events and indicate short term climatic changes in the arctic ocean as has been recorded in lower latitudes in contrast in low precipitation areas in eastern eurasia glacial activity was rather limited only distinct ice rafted debris ird input during termination ii and early mis 3 reflects severe glaciations on the northern severnaya semlya margin during mis 6 and mis 4 we conclude that 1 oscillations of ice sheets are less frequent along the eastern eurasian margin than in areas with continuous moisture supply like the western eurasian margins and that 2 major fluctuations of the kara sea ice sheet during the last 150 kyr apparently followed the major interglacial glacial mis 5 4 and mis 7 6 transitions rather than the precession 23 kyr and the tilt 41 kyr cyclicity of the earth s orbit as observed for the scandinavian sis and the svalbard ice sheets respectively mangerud j jansen e landvik j y 1996 late cenozoic history of the scandinavian and barents sea ice sheets in solheim a riis f elverhoi a faleide j j jensen l n cloetingh s eds impact of glaciations on basin evolution data and models from the norwegian margins and adjacent basins global and planetary chance special issue 12 pp 11 26 surface and or subsurface atlantic water masses coupled with seasonally ice free conditions penetrated continuously to at least the franz victoria trough during the last 150 kyr however sustained periods of open water were largely restricted to substages 5 5 5 1 and the holocene as indicated by distinct carbonate dissolution and higher accumulation of marine organic matter mom signals of periodic open water conditions along the northern margin of severnaya semlya are of less importance higher production of foraminifera probably due to atlantic water inflow occurred between 38 and 12 14 c kyr and corresponds to periodic atlantic water advection penetrating into the arctic ocean however marine organic proxies indicate a continuous decrease of surface water productivity from the western to the eastern eurasian continental margin due to a more extensive sea ice cover over the last 150 kyr

arctic ocean evidence for late quaternary initiation of northern eurasian ice sheets a high resolution multiparameter stratigraphy allows the identification of late quaternary glacial and interglacial cycles in a central arctic ocean sediment core distinct sandy layers in the upper part of the otherwise fine grained sediment core from the lomonosov ridge lat 87 5 n correlate to four major glacials since ca 0 7 ma the composition of these ice rafted terrigenous sediments points to a glaciated northern siberia as the main source in contrast lithic carbonates derived from north america are also present in older sediments and indicate a northern north american glaciation since at least 2 8 ma we conclude that large scale northern siberian glaciation began much later than other northern hemisphere ice sheets

record of δ18o and 17o excess in ice from vostok antarctica during the last 150 000 years 1 we measured 17 o and 18 o in recent antarctic snow and down the vostok ice core and calculated the excess of 17 o with respect to vsmow the magnitude of the 17 o excess in the holocene and the last interglacial is 45 per meg and it remains constant in a transect from the coast to the continental interior analysis of the transect data shows that the 17 o excess is not sensitive to temperature variations over the continent there are significant shifts in 70 excess from low values in glacial to high values in interglacial times the observed shifts suggest higher normalized relative humidity and or wind speeds over the source oceanic regions in glacial times

a seasonal deuterium excess signal at law dome coastal eastern antarctica a southern ocean signature the snow isotopic composition 18o and d of two shallow cores from the high accumulation summit region of law dome east antarctica was measured at monthly resolution over the 1980 1992 period while the 18o or d signals clearly reflect the local temperature cycle the deuterium excess d d 8 18o is shifted with respect to 18o cycle by a 4 months lag interpretation of this phase lag is investigated using both an atmospheric general circulation model agcm which includes the water isotopic cycles and a simple isotopic model which better describes the microphysical processes within the cloud using this dual approach we show that the seasonality of 18o and d at law dome summit results from a combination of the southern ocean temperature cycle shifted by 2 3 months with respect to the local insolation and seasonal moisture origin changes due to a strong contribution of the local ocean when ice free both approaches are consistent with a dominant temperate to subtropical moisture origin we thus demonstrate from our present day subseasonal study that the record of d in the dome summit south dss deep ice core represents a potential tool for identifying changes in southern ocean temperatures and or sea ice cover at the scale of the past thousand years

manganese and color cycles in arctic ocean sediments constrain pleistocene chronology sequential variations in manganese mn content and color of deepsea sediments retrieved from the lomonosov ridge 87 n in the central arctic ocean apparently mimic low latitude 18 o glacial interglacial cyclicity thereby providing stratigraphic information that together with biostratigraphic data permit the construction of a detailed chronological model correlation of this mn and color chronology to established apparent brunhes age estimates of geomagnetic excursions reveals a remarkable fit between these two independently derived time scales the mn and color cycles probably provide paleoenvironmental information about material fluxes in the arctic ocean over the past 1 m y we suggest that the primary source for the observed manganese variations in our sediment core is northern siberia which has extensive peat bogs and boreal forests these siberian source areas could operate in an off and on mode tuned to pleistocene glacial and interglacial periods contrasts in ventilation of arctic ocean waters during interglacial glacial cycles probably could also enhance the observed mn and color variability

variations of 17o 16o and 18o 16o in meteoric waters the variations of d 17 o and d 18 o in recent meteoric waters and in ice cores have proven to be an important tool for investigating the present and past hydrologic cycle in order to close significant information gaps in the present distribution ofd 17 o and d 18 o of meteoric water we have run precise measurements with respect to vsmow on samples distributed globally from low to high latitudes based on the new and existing data we present the global meteoric water line gmwl ford 17 o andd 18 o as ln d 17 o 1 0 528 ln d 18 o 1 0 000033 r 2 0 99999 in addition to meteoric water we carried out the first measurements of seawater from the pacific and atlantic oceans with respect to vsmow the obtained results show that the slope of the trend line ln d 17 o 1 vs ln d 18 o 1 of seawater samples is 0 528 the same as for meteoric water but the regression intercept is 5 per meg thus the positive intercept in the gmwl indicates an excess of 17 o in meteoric waters with respect to the ocean an excess or depletion of 17 o in water is defined as 17 o excess ln d 17 o 1 0 528 d 18 o 1 most meteoric water samples have positive 17 o excess of varying magnitudes with an average of 37 per meg with respect to vsmow we explain how these positive values originate from evaporation of sea water into marine air which is undersaturated in water vapor and how subsequent increase of 17 o excess occurs when atmospheric vapor condenses to form liquid and solid precipitation we also clarify the effect of excessive evaporation on 17 o excess finally based on the new results on 17 o excess of seawater we recalculated the relationship of d 17 o vs d 18 o in vapor diffusion in air as 18 adiff 1 0096

contrasting glacial interglacial regimes in the western arctic ocean as exemplified by a sedimentary record from the mendeleev ridge distinct cyclicity in lithology and microfaunal distribution in sediment cores from the mendeleev ridge in the western arctic ocean water depths ca 1 5 km reflects contrasting glacial interglacial sedimentary patterns we conclude that during major glaciations extremely thick pack ice or ice shelves covered the western arctic ocean and its circulation was restricted in comparison with interglacial modern type conditions glacier collapse events are marked in sediment cores by increased contents of ice rafted debris notably by spikes of detrital carbonates and iron oxide grains from the canadian arctic archipelago composition of foraminiferal calcite n 18 o and n 13 c also shows strong cyclicity indicating changes in freshwater balance and or ventilation rates of the arctic ocean light stable isotopic spikes characterize deglacial events such as the last deglaciation at ca 12 14 c kyr bp the prolonged period with low n 18 o and n 13 c values and elevated contents of iron oxide grains from the canadian archipelago in the lower part of the mendeleev ridge record is interpreted to signify the pooling of freshwater in the amerasia basin possibly in relation to an extended glaciation in arctic north america unique benthic foraminiferal events provide a means for an independent stratigraphic correlation of sedimentary records from the mendeleev ridge and other mid depth locations throughout the arctic ocean such as the northwind and lomonosov ridges this correlation demonstrates the disparity of existing age models and underscores the need to establish a definitive chronostratigraphy for arctic ocean sediments 2003 elsevier b v all rights reserved

atmospheric influence on the deuterium excess signal in polar firn implications for ice core interpretation the seasonal deuterium excess signal of fresh snow samples from neumayer station coastal dronning maud land antarctica was studied to investigate the relationship between deuterium excess and precipitation origin an isotope model was combined with a trajectory model to determine the relative influence of different moisture sources on the mean annual course of the deuterium excess focusing on the phase lag between d 18 o and excess d whereas the annual course of d 18 o always shows an austral summer maximum which clearly depends on local temperature and the annual course of moisture source area parameters the deuterium excess of the fresh snow samples shows maximum values already in spring there can be many different reasons for the time lag between d 18 o and deuterium excess in an ice core including post depositional processes and changes in the moisture source of precipitation the use of fresh snow samples enabled us to exclude post depositional processes and study solely the influence of precipitation origin changes in the moisture source connected to systematic changes in the general atmospheric circulation can have a strong influence on the phase lag between deuterium excess and d 18 o which has to be taken into account for climatic interpretation of stable isotope profiles from ice cores

surface sediment geochemistry and hydrothermal activity indicators in the dragon horn area on the southwest indian ridge abstract the fluids found in sulfide producing hydrothermal vents are rich in ore forming elements these elements usually precipitate as solid particles that are dispersed by the plumes and deposited as sediments around the hydrothermal field to assess how the geochemical features of such sediments may be used in seafloor sulfide exploration this study analyzed the surface sediment geochemistry in the dragon horn area on the southwest indian ridge the results indicate that the sediments are mainly composed of pelagic material basalt and ultramafic debris mn fe oxyhydroxides and mn oxides hydrothermal components the debris content in this area is lower than that in sediments found at fast and medium spreading mid ocean ridges with relatively high amounts of ultramafic components indicating that ultramafic rock outcrops are present in the study area precipitated hydrothermal elements in the sediments exhibit zonation in the spatial distributions of zn cu fe and mn the sediments proximal to the hydrothermal field display high cu zn and fe contents and low mn contents hydrothermal cu and zn phases occurred within a limited range of the hydrothermal field and zn was found to precipitate earlier than cu during dispersal from the plume hydrothermal fe distributed similarly with cu spatially but with a larger dispersion distance hydrothermal mn was able to migrate beyond the ridge valley to precipitate in the ridge flank sediments two hydrothermal cu and zn anomalies were identified on the south ridge flanks which suggest the presence of undiscovered hydrothermal field the sediments in the study area are additionally characterized by relatively low mn contents and high fe mn molar ratios the relatively reducing environment of the plume may facilitate the migration of hydrothermal mn over large distances which probably accounts for the lower mn contents in the sediments the cu cu fe molar ratio model was proposed to identify mafic and ultramafic related hydrothermal field the low cu fe molar ratios and ree characteristics of the sediments suggest that ultramafic rocks are likely not the only source of the ore forming element for hydrothermal mineralization low temperature diffuse flow on the ridge flanks of the study area probably results from serpentinization of ultramafic rocks

mineralogical geochemical and magnetic signatures of surface sediments from the canadian beaufort shelf and amundsen gulf canadian arctic mineralogical geochemical magnetic and siliciclastic grain size signatures of 34 surface sediment samples from the mackenzie beaufort sea slope and amundsen gulf were studied in order to better constrain the redox status detrital particle provenance and sediment dynamics in the western canadian arctic redox sensitive elements mn fe v cr zn indicate that modern sedimentary deposition within the mackenzie beaufort sea slope and amundsen gulf took place under oxic bottom water conditions with more turbulent mixing conditions and thus a well oxygenated water column prevailing within the amundsen gulf the analytical data obtained combined with multivariate statistical notably principal component and fuzzy c means clustering analyses and spatial analyses allowed the division of the study area into four provinces with distinct sedimentary compositions 1 the mackenzie trough canadian beaufort shelf with high phyllosilicate fe oxide magnetite and al k ti fe cr v zn p contents 2 southwestern banks island characterized by high dolomite k feldspar and ca mg loi contents 3 the central amundsen gulf a transitional zone typified by intermediate phyllosilicate magnetite k feldspar dolomite and al k ti fe mn v zn sr ca mg loi contents and 4 mud volcanoes on the canadian beaufort shelf distinguished by poorly sorted coarse silt with high quartz plagioclase authigenic carbonate and si zr contents as well as high magnetic susceptibility our results also confirm that the present day sedimentary dynamics on the canadian beaufort shelf is mainly controlled by sediment supply from the mackenzie river overall these insights provide a basis for future studies using mineralogical geochemical and magnetic signatures of canadian arctic sediments in order to reconstruct past variations in sediment inputs and transport pathways related to late quaternary climate and oceanographic changes keywords mineralogy elemental geochemistry magnetic properties surface sediment sediment provenance redox condition canadian beaufort shelf amundsen gulf

seasonal climate information preserved in west antarctic ice core water isotopes relationships to temperature large scale circulation and sea ice as part of the united states contribution to the international trans antarctic scientific expedition itase a network of precisely dated and highly resolved ice cores was retrieved from west antarctica the itase dataset provides a unique record of spatial and temporal variations of stable water isotopes d 18 o and dd across west antarctica we demonstrate that after accounting for water vapor diffusion seasonal information can be suc cessfully extracted from the itase cores we use meteo rological reanalysis weather station and sea ice data to assess the role of temperature sea ice and the state of the large scale atmospheric circulation in controlling seasonal average water isotope variations in west antarctica the strongest relationships for all variables are found in the cores on and west of the west antarctic ice sheet divide and during austral fall during this season positive isotope anomalies in the westernmost itase cores are strongly related to a positive pressure anomaly over west antarctica low sea ice concentrations in the ross and amundsen seas and above normal temperatures analyses suggest that this seasonally distinct climate signal is due to the pronounced meridional oriented circulation and its linkage to enhanced sea ice variations in the adjacent southern ocean during fall both of which also influence local to regional temperatures

synoptic variability in the ross sea region antarctica as seen from back trajectory modeling and ice core analysis 1 synoptic variability in the ross sea region antarctica over the last thirty years is investigated using back trajectory modeling and cluster analysis we identify two dominant air mass trajectory clusters oceanic west antarctic and continental east antarctic our analysis shows that the oceanic west antarctic trajectories have an annual cycle similar to the semiannual oscillation and on average peak in frequency during april while continental east antarctic trajectories reach their annual maximum during december we demonstrate a causal association between the el nino southern oscillation enso and the frequency of oceanic west antarctic trajectories originating from the ross sea and amundsen sea regions in contrast we find that the southern annular mode sam has little influence on the trajectory cluster frequencies we then develop proxy records for synoptic variability using a shallow firn core from gawn ice piedmont in southern victoria land continental east antarctic trajectory frequency correlates with concentrations of nitrate no3 which is sourced from stratospheric air masses descending over the antarctic interior at seasonal to inter annual scales the frequency of oceanic west antarctic trajectory clusters strongly correlate with deuterium excess which is sensitive to changes in relative humidity and sea surface temperature in the ross and amundsen seas inter annual variability in the frequency of oceanic west antarctic trajectories is discussed with respect to enso and changes in sst and sea ice extent

sea ice control of water isotope transport to antarctica and implications for ice core interpretation 1 sea ice in the southern ocean is important for antarctic climate and hydrology the dependence of water isotope abundance 18o and deuterium excess on the winter sea ice state is examined with the isotopic version of the melbourne university general circulation model reductions in the ice concentration provide warmer temperatures in winter and allow higher precipitation totals further south while the reverse occurs with increased ice extent the model shows clear demarcation between the changes in the isotopic conditions over the sea ice pack where local changes in surface exchange dominate and those of the continent interior which depend on the long ranged transport aloft while less sensitive to the forcing the interior response is influenced by changes in turbulent mixing over the ice pack and modification of the vertical transport associated with diabatic heating the interior deuterium excess response is more strongly affected by sea ice as it captures changes in temperature over the ice rather than just the final vapor mass traditional reconstruction of temperature from a single isotopic nuclide would give erroneous interpretation of change in the global mean temperature unless the sea ice changes in parallel instead the spatial structure of the sea ice response gives some hope for extracting past sea ice conditions from multicore analysis this study begins to explore the role of entropy production during transport such that the isotopic interpretation is more closely tied to the dynamics of the atmosphere than is expressed by idealized parcel analysis

radiocarbon chronology of depositional regimes in the western arctic ocean abstract the foraminiferal abundance and percentage of coarse ice rafted detritus ird define glacial deglacial and interglacial depositional regimes in ams radiocarbon dated box cores from the western arctic ocean sediment deposition rates are generally less than 0 5 cm ka for glacial regimes greater than this for deglacial regimes and greater than 1 2 cm ka for interglacial regimes these differences in deposition rates might account for the much lower average sedimentation rates for the last 780 ka of 1 3 mm ka in cores from the central arctic ocean if glacial regimes dominated this interval foraminiferal abundances are less than 500 g during glacial maxima and mostly higher than 2000 g during deglacial and interglacial regimes slightly higher coarse ird percentages occur in deglacial intervals 5 10 up to 30 compared with interglacial intervals mostly 5 which characterize the last 10 12 ka in the western arctic ocean glacial regimes occurred from about 40 to 11 ka except for a brief interglacial or deglacial interval around 24 28 ka in the central arctic ocean the coarsest deglacial events occurred prior to 45 ka the late wisconsin deglaciation sediments approximately 9 16 ka are difficult to detect in the central arctic ocean sediments because they are only slightly coarser than the holocene and in some box cores less coarse than the holocene a previously unrecognized coarse ird event occurred near the core tops 0 3 cm between 1500 and 3500 radiocarbon years ago in the western arctic ocean only sediment older than 40 ka is coarser than this recent ird event which might correspond to a neoglaciation recognized in the north atlantic and elsewhere

paleoenvironmental implications of cenozoic sediments from the central arctic ocean iodp expedition 302 using inorganic geochemistry 1 integrated ocean drilling program iodp expedition 302 arctic coring expedition acex recovered a unique sediment record from the central arctic ocean revealing that this region underwent major environmental fluctuations since the late cretaceous major and trace element composition of 1 300 samples were determined using x ray fluorescence xrf the results show significant compositional variability of the sediments with depth that can be attributed to changes in a provenance and pathways of detrital material b paleoenvironmental conditions and depositional processes and c diagenetic overprint of the primary record in addition to existing lithological units we introduce new geochemical units for a more process related approach interpreting the acex record in detail via the geochemical signature of siberian flood basalts we are able to reconstruct the discontinuous rifting and deepening of the central lomonosov ridge during the paleogene accompanied by changing current regimes and the onset of sea ice eocene biosiliceous sedimentation took place in a relatively shallow setting under predominantly anoxic bottom water conditions causing a positive anoxia productivity feedback although water column stratification was repeatedly interrupted by ventilation events anoxic to sulfidic conditions were even more extreme after biosilica production ceased and significant amounts of pyrite were deposited on the lomonosov ridge especially in organic matter rich paleogene deposits diagenetic processes obscured the paleoenvironmental signals fundamental environmental changes occurred in the middle eocene but geochemical and micropaleontological proxies point not to the identical sediment depth after approximately 26 ma of non deposition or erosion the middle miocene record shows the transition to dominantly oxic bottom water conditions although suboxic diagenesis seemingly affected these deposits