cenozoic ice rafting history of the central arctic ocean terrigenous sands on the lomonosov ridge the cenozoic ice rafted debris ird history of the central arctic is reconstructed utilizing the terrigenous coarse sand fraction in iodp 302 cores from 0 to 273 meters composite depth this holocene middle eocene quantitative record of terrigenous sand accumulation on the lomonosov ridge along with qualitative information on grain texture and composition confirms the interpretation that ice initiation sea ice and glacial ice occurred 46 ma in the arctic and provides a long term pattern of arctic ice expansion and decay since the middle eocene ird mass accumulation rates range from 0 to 0 13 g cm2 ka in the middle eocene and from 0 to 0 36 g cm2 ka in the neogene ird mass accumulation rate mar maxima in the miocene and pliocene cooccur with either glacial initiation or intensification in the sub arctic the 46 25 ma ird onset in the central arctic slightly precedes the earliest evidence of ice in the antarctic and compares in timing with a 1000 ppm decrease in atmospheric concentrations of co2 the decline of pco2 in the middle eocene may have driven both poles across the temperature threshold that enabled the nucleation of glaciers on land and partial freezing of the surface arctic ocean especially during times of low insolation

variable eocene miocene sedimentation processes and bottom water redox conditions in the central arctic ocean iodp expedition 302 abstract in 2004 integrated ocean drilling program expedition 302 arctic coring expedition acex to the lomonosov ridge drilled the first central arctic ocean sediment record reaching the uppermost cretaceous 430 m composite depth while the neogene part of the record is characterized by grayish yellowish siliciclastic material the paleogene part is dominated by biosiliceous black shale type sediments the lithological transition between paleogene and neogene deposits was initially interpreted as a single sedimentological unconformity hiatus of 26 ma duration separating eocene from miocene strata more recently however continuous sedimentation on lomonosov ridge throughout the cenozoic was proclaimed questioning the existence of a hiatus in this context we studied the elemental and mineralogical sediment composition around the paleogene neogene transition at high resolution to reconstruct variations in the depositional regime e g wave current activity detrital provenance and bottom water redox conditions already below the hiatus mineralogical and geochemical proxies imply drastic changes in sediment provenance and or weathering intensity in the hinterland and point to the existence of another earlier gap in the sediment record the sediments directly overlying the hiatus the zebra interval are characterized by pronounced and abrupt compositional changes that suggest repeated erosion and re deposition of material regarding redox conditions euxinic bottom waters prevailed at the eocene lomonosov ridge and became even more severe directly before the hiatus with detrital sedimentation rates decreasing authigenic trace metals were highly enriched in the sediment this continuous authigenic trace metal enrichment under persistent euxinia implies that the arctic trace metal pool was renewed continuously by water mass exchange with the world ocean so the eocene arctic ocean was not fully restricted above the hiatus extreme positive ce anomalies are clear signs of a periodically well oxygenated water column but redox conditions were highly variable during deposition of the zebra interval significant mn enrichments only occur above the zebra interval documenting the miocene establishment of stable oxic conditions in the arctic ocean in summary extreme and abrupt changes in geochemistry and mineralogy across the studied sediment section do not suggest continuous sedimentation at the lomonosov ridge around the eocene miocene transition but imply repeated periods of very low sedimentation rates and or erosion

coeval eocene blooms of the freshwater fern azolla in and around arctic and nordic seas abstract for a short time interval c 1 2 myr during the early middle eocene 49 myr the central arctic ocean was episodically densely covered by the freshwater fern azolla implying sustained freshening of surface waters coeval azolla fossils in neighboring nordic seas were thought to have been sourced from the arctic the recognition of a different azolla species in the north sea raised doubts about this hypothesis here we show that no less than five azolla species had coeval blooms and spread in the arctic and nw european regions a likely trigger for these unexpected azolla blooms is high precipitation prevailing by the end of the warmest climates of the early eocene climatic optimum eeco

paleogene paleoceanography of the arctic ocean is constrained by the middle or late eocene age of usgs core fl 422 evidence from silicoflagellates arctic ocean core fl 422 has been of central importance in arctic tectonics and paleoceanography because it provides the sole evidence for early cenozoic marine conditions in the arctic the presence of several eocene and eocene or oligocene guide species of silicoflagellates in samples from this core shows that it is no older than middle eocene and is not paleocene as previously reported there is no evidence of any paleocene 54 to 65 ma siliceous microfossils from core fl 422 paleoceanographic inferences conerning the cretaceous tertiary boundary and the timing of silica deposition in the arctic have been erroneous because of unsupported biostratigraphic correlations

silica burp in the eocene ocean the eocene was a time of greatly increased silica accumulation in the ocean and the peak was in the early middle eocene at about 50 ma the responsible geohistorical configuration included the following elements extensive volcanism about 4 m y earlier as part of the chron 24 plate reorganization early eocene warming with deep weathering to high latitudes and accumulation of the released silica in a sluggish ocean and sharp cooling in the earliest middle eocene stimulating oceanic upwelling and biosilicification it is possible on the evidence of carbon and oxygen isotopic patterns that the trigger for the exhalation of silica was a reverse greenhouse effect

significance of euxinic condition in the middle eocene paleo arctic basin a geochemical study on the iodp arctic coring expedition 302 sediments article 34 s on the early to middle eocene section of the acex cores the ts were high in all the examined intervals and the sedimentary sulfur occurred mainly as framboidal pyrite indicating that sufficient sulfate indicative of seawater was present in the deep layer of the paleo arctic basin and that the pyrite was formed in the sediments under sufficient iron input the high ts values with low 34 s values also indicate the continuous existence and supply of seawater the high accumulation of sulfide in unit 1 6 was due to a significant increase of toc supply which increased sulfate reduction rates by bacteria the toc ts diagram shows excess sulfur content relative to the toc suggesting euxinic condition of the bottom water during the studied period such an oxygen depleted environment was brought about by salinity stratification and restricted water circulation the patterns observed in the acex data can be comparable with the mediterranean sapropels the global 34

variability in the length of the sea ice season in the middle eocene arctic finely laminated middle eocene sediments from the central arctic contain high abundances of the delicate sea ice dwelling fossil diatoms synedropsis spp and sea ice rafted debris sea ice ird establishing an offshore seasonal sea ice regime ca 47 ma synedropsis spp co occur with other diatom taxa and microfossils requiring open water this strongly indicates seasonality nonetheless seasonal reconstruction of the flux cycle cannot be resolved by standard bulk sediment analysis which destroys sedimentary fabrics and averages data within samples here we resolve and reconstruct seasonal scale flux events from these sediments using backscattered electron imagery bsei of resin embedded sediment a nondestructive technique that preserves the integrity of sedimentary microfabrics thus revealing discrete productivity flux events at ultrahigh e g 30 m resolution seasonality is expressed at the submillimeter scale by successions of discrete mono specific laminae and micro lenses of synedropsis spp terrigenous material sea ice ird and open water taxa indicating that first year ice existed in the central arctic further bsei reveals millimeter scale alternation of bundles of laminae and microlenses of two distinct types one characterized by synedropsis spp and terrigenous material the other by mainly open water taxa and little terrigenous material the sedimentation rate and preliminary assessment of annual cycles indicate suborbital variability on the order of multi decadal to centennial duration we argue that this reflects variations in the sea ice season length

paleogene record of elemental concentrations in sediments from the arctic ocean obtained by xrf analyses we present a high resolution x ray fluorescence xrf core scanner record for the expanded middle eocene section from integrated ocean drilling program iodp expedition 302 acex drilled on the lomonosov ridge central arctic ocean the division of the middle eocene into two units subunit 1 6 and unit 2 is seen in the cyclical behavior of the elements as well as the changing interelemental correlations and their relationship to physical property measurements of bulk sediment al ti and k strongly correlate throughout the record while the behavior of fe mn and si is more complex utilizing sediment geochemistry calibration to ground truth the xrf data we suggest the middle eocene arctic ocean was predominately euxinic although periodic oxygenation of bottom waters must have occurred during unit 2 49 7 45 4 ma initially the sediments are rich in biogenic silica unit 2 but there is a pronounced shift to terrigenous dominated sediment accumulation in subunit 1 6 we report changes in the elemental concentrations of these elements and investigate the relationship between fe content and pyrite additionally we explore the potential change in paleoenvironmental conditions across the unit boundary

the fall dump a new perspective on the role of a shade flora in the annual cycle of diatom production and export flux investigations of diatom fluxes recorded in laminated sediments using scanning electron microscope techniques together with evidence from sediment trap studies have contributed to a reappraisal of the annual cycle of diatom production and export flux we propose that where there is a strong seasonal thermocline and nutricline a number of diatoms hitherto regarded as typical sparse summer flora characteristic of oligotrophic waters are able to generate substantial production at depth these species including rhizosolenia spp stephanopyxis palmeriana thalassiothrix spp and some coscinodiscus spp may represent a shade flora that have adapted to grow in low light conditions and or to regulate their buoyancy to move between a deep nutrient source and the euphotic zone although rates of growth and primary production are substantially lower than species characteristic of spring bloom or upwelling conditions the total primary production integrated over the several month period of summer stratification may be as significant as the spring bloom or greater the term fall or autumn bloom as a counterpart of the spring bloom is therefore a misnomer whereas the spring bloom involves a rapid burst of reproduction and sedimentation the fall dump is the sedimentation of a long lived episode of production lasting the duration of the seasonal thermocline and triggered by the fall winter mixing that breaks down stratification the fall dump may produce as much or in some cases more export production than the spring bloom the results of this study suggest that a reorientation of thinking on diatom ecology and palaeoecology may be required

salinity of the eocene arctic ocean from oxygen isotope analysis of fish bone carbonate stable isotope analysis was performed on the structural carbonate of fish bone apatite from early and early middle eocene samples 55 to 45 ma recently recovered from the lomonosov ridge by integrated ocean drilling program expedition 302 the arctic coring expedition the 18o values of the eocene samples ranged from 6 84 to 2 96 vienna peedee belemnite with a mean value of 4 89 compared to 2 77 for a miocene sample in the overlying section an average salinity of 21 to 25 was calculated for the eocene arctic compared to 35 for the miocene with lower salinities during the paleocene eocene thermal maximum the azolla event at 48 7 ma and a third previously unidentified event at 47 6 ma at the azolla event where the organic carbon content of the sediment reaches a maximum a positive 13c excursion was observed indicating unusually high productivity in the surface waters

introduction to special section on cenozoic paleoceanography of the central arctic ocean 1 in late summer 2004 the integrated ocean drilling program iodp conducted one of the most transformational missions in the almost 40 year history of scientific ocean drilling the arctic coring expedition acex backman et al 2006 moran et al 2006a this technically challenging expedition moran et al 2006b to the lomonosov ridge near 88 n recovered the first long term cenozoic sediment record from the arctic ocean extending previous records from 1 5 ma to an unprecedented 56 ma glimpses of the breadth of this transformation were seen during the acex cruise when the massulae from freshwater ferns azolla were found in 49 ma old sediments brinkhuis et al 2006 and the presence of apectodinium augustum confirmed that the paleocene eocene thermal maximum petm 55 ma was unexpectedly recovered sluijs et al 2006 2 soon after the expedition when the cores were opened and analyzed ice rafted debris was found in surprisingly old 46 ma sediments moran et al 2006a these middle eocene sediments are characterized also by their high organic carbon content stein et al 2006 the exciting early results attracted other investigators that expanded the scientific investigating team to more than 40 people analyses were extended to include studies that revealed surprisingly high arctic ocean surface water temperatures sluijs et al 2006 and an amplified hydrological system pagani et al 2006 during the petm initial analyses revealed an extensive hiatus encompassing about 26 million years that occurred below a short interval showing starkly alternating black and white layers that is now dubbed the zebra interval thus the time interval from the late early miocene 18 ma to the middle middle eocene 44 ma is missing although the hiatus is a lost window in time for the arctic paleoclimate record it spawned other studies that integrated the regional tectonic history with acex results revealing a major oceanographic reorganization at 17 5 ma ventilation of the arctic ocean to the north atlantic through the fram strait jakobsson et al 2007 in terms of ventilation and water mass history neogene neodymium isotope data reveal that arctic intermediate waters originate from brine formation on eurasian shelf areas between 15 and 2 ma and during glacial periods throughout pleistocene times haley et al 2008a they conclude that this mode of arctic circulation differs markedly from today s situation showing relatively high contributions of north atlantic intermediate water and minor input from brine formation 3 in this special section the transformation continues results from the large acex scientific family include a robust age model detailed analyses of the middle eocene that document a unique brackish water environment sea ice and iceberg history reconstructions as well as the provenance of ice rafted debris from the eocene to present evolution of depositional environments times of isolation and connection to the global ocean geochemical analyses of the organic carbon rich sediments and unique applications of high resolution proxies and cyclostratigraphy highlights from this special section are presented here

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

humidity estimate for the middle eocene arctic rain forest the exquisite preservation of fossilized metasequoia trees that grew near 808n latitude during the middle eocene ca 45 ma in nunavut canada allowed for dd and d 18 o analyses of cellulose techniques previously restricted to wood 30 000 yr old from the isotopic results we determined that the middle eocene arctic atmosphere contained 23 the water found in the region s atmosphere today this water vapor contributed to a middle eocene greenhouse effect that insulated the polar region during dark polar winters

rapid fluctuations in mid latitude siliceous plankton production during the middle eocene climatic optimum odp site 1051 western north atlantic abstract the middle eocene climatic optimum meco 40 million years ago ma is one of the most prominent transient global warming events in the paleogene although the event is well documented in geochemical and isotopic proxy records at many locations the marine biotic response to the meco remains poorly constrained we present new high resolution quantitative records of siliceous microplankton assemblages from the meco interval of ocean drilling program odp site 1051 in the subtropical western north atlantic ocean which are interpreted in the context of published foraminiferal and bulk carbonate stable isotope 18o and 13c records high diatom radiolarian and silicoflagellate accumulation rates between 40 5 and 40 0 ma are interpreted to reflect an 500 thousand year kyr interval of increased nutrient supply and resultant surface water eutrophication that was associated with elevated sea surface temperatures during the prolonged onset of the meco relatively low pelagic siliceous phytoplankton sedimentation accompanied the peak meco warming interval and the termination of the meco during an 70 kyr interval centered at 40 0 ma following the termination of the meco an 200 kyr episode of increased siliceous plankton abundance indicates enhanced nutrient levels between 39 9 and 39 7 ma throughout the site 1051 record abundance and accumulation rate fluctuations in neritic diatom taxa are similar to the trends observed in pelagic taxa implying either similar controls on diatom production in the neritic and pelagic zones of the western north atlantic or fluctuations in sea level and or shelf accommodation on the north american continental margin to the west of site 1051 these results combined with published records based on multiple proxies indicate a geographically diverse pattern of surface ocean primary production changes across the meco notably however increased biosiliceous accumulation is recorded at both odp sites 1051 and 748 southern ocean in response to meco warming this may suggest that increased biosiliceous sediment accumulation if indeed a widespread phenomenon resulted from higher continental silicate weathering rates and an increase in silicic acid supply to the oceans over several 100 kyr during the meco

a siliceous microfossil view of middle eocene arctic paleoenvironments a window of biosilica production and preservation integrated ocean drilling program iodp expedition 302 the arctic coring expedition acex unearthed the most significant find of paleogene siliceous microfossils in nearly 2 decades 100 m of early middle eocene organic rich finely laminated sediments contain abundant marine and freshwater siliceous microfossils allowing intriguing insights into central arctic paleoenvironments during the start of cenozoic cooling largely endemic assemblages of marine diatoms and ebridians are preserved along with very high abundances of chrysophyte cysts the endogenously formed resting stage of freshwater algae an overall brackish environment is invoked but variations in group dominance suggest episodic changes in salinity stratification and trophic status with the backing of inorganic geochemistry we synthesize the sediment characteristics by hypothesizing an environmental model for the cooccurrence of these diverse siliceous microfossil groups we also report on initial insights into the composition of some of the laminations which may help explain the formation of this rich sediment archive

magnetostratigraphic calibration of eocene oligocene dinoflagellate cyst biostratigraphy from the norwegian greenland sea the presence of abundant age diagnostic dinoflagellate cysts in ocean drilling program odp hole 913b leg 151 deep sea drilling project hole 338 leg 38 and odp hole 643a leg 104 has enabled the development of a new biostratigraphy for the eocene oligocene interval in the norwegian greenland sea this development is important because the calcareous microfossils usually used for biostratigraphy in this age interval are generally absent in high latitude sediments as a result of dissolution in parallel with this biostratigraphic analysis we developed a magnetic reversal stratigraphy for these norwegian greenland sea sequences this has allowed independent age determination and has enabled the dinocyst biostratigraphy to be firmly tied into the global geomagnetic polarity timescale gpts the relatively high resolution of this study has enabled identification of dinoflagellate cyst assemblages that have affinities with those from the north sea and the north atlantic which allows regional correlation correlation of each site with the gpts has also allowed comparison of the stratigraphic record preserved in each drill hole hole 913b is the most complete and is the best preserved record of the eocene and oligocene in the northern hemisphere high latitudes and can serve as a reference section for palaeoenvironmental reconstructions of this age interval

a 200 000 year high resolution record of diatom productivity and community makeup from lake baikal shows high correspondence to the marine oxygen isotope record of climate change siliceous microfossil succession was analyzed in a 200 000 yr sediment sequence recovered from the buguldeika saddle in lake baikal russia siliceous microfossil abundance varied among core depths from no preserved microfossils during inferred colder climate conditions to recent interglacial sediments containing over 300 3 10 6 microfossils per g dry sediment depth age microfossil assemblage zones ca i to ca iv identified using correspondence analysis had high correspondence to stages in the marine d 18 o isotope record and could be partially aligned with late pleistocene glacial interglacial cycling models from the mid siberian highland these observations suggest that lake baikal phytoplankton communities have responded to climatic changes driven by insolation parameters and global ice volumes on temporal scales similar to tropical and polar oceans microfossil zone ca i 0 11 4 kyr b p corresponded to the holocene interglacial or d 18 o stage 1 0 11 4 kyr b p a period of higher production in lake baikal during a climatic optimum microfossil zone ca ii 12 3 18 7 kyr b p corresponded to the sartan glaciation and d 18 o stage 2 12 24 kyr b p zone ca iii 21 3 73 2 kyr b p comprised d 18 o stages 3 and 4 however within zone ca iii subzones ca iiia and iiib 21 3 56 8 kyr b p grouped were well aligned with d 18 o stage 3 and contained sediments deposited during the inferred karginskiy interstade microfossil zone ca iva 77 4 129 2 kyr b p and ca ivb 130 3 172 5 kyr b p included d 18 o stages 5 and 6 respectively with sediments that were most likely deposited during the taz glaciation and the kazantsevo interstade climate induced changes are reflected in production differences and in community composition specificity within microfossil zones or climate stages this suggests that climate change drives major historical successional patterns in lake baikal s primary producer community changes in primary producers must have further impacted the system s entire biota

anoxia and high primary production in the paleogene central arctic ocean first detailed records from lomonosov ridge 1 except for a few discontinuous fragments of the late cretaceous early cenozoic climate history and depositional environment the paleoenvironmental evolution of the pre neogene central arctic ocean was virtually unknown prior to the iodp expedition 302 arctic ocean coring expedition acex drilling campaign on lomonosov ridge in 2004 here we present detailed organic carbon oc records from the entire ca 200 m thick paleogene oc rich section of the acex drill sites these records indicate euxinic black sea type conditions favorable for the preservation of labile aquatic marine algae type oc occur throughout the upper part of the early eocene and the middle eocene explained by salinity stratification due to freshwater discharge the superimposed short term milankovitch type variability in amount and composition of oc is related to changes in primary production and terrigenous input prominent early eocene events of algae type oc preservation coincide with global 13c events such as the petm and elmo events the elmo 13c event has been identified in the arctic ocean for the first time

improved os isotope stratigraphy of the arctic ocean 1 the history of the arctic ocean remained poorly known until the 2004 iodp coring of lomonosov ridge sediments early studies of the recovered sequence demonstrated the existence of an eocene lake stage prior to the transition to marine conditions the marine stage onset was inferred to be 17 5 million years ma ago thus implying a nearly 26 ma gap between the lacustrine and marine episodes and an unusual tectonic history for lomonosov ridge in order to explain this gap more recently rhenium osmium re os isotope measurements of the transition from the lacustrine to marine sediments suggested a much earlier inception of marine conditions and the absence of any significant gap between both episodes here an improved osmium isotope stratigraphy and re os data concur to assign a late eocene age 36 ma to the marine invasion consistent with a relative change in sea level on top of lomonosov ridge either from tectonic origin or from another cause

climate sensitivity to arctic seaway restriction during the early paleogene abstract the opening and closing of ocean gateways affects the global distribution of heat salt and moisture potentially driving climatic change on regional to global scales between 65 and 45 million years ago ma during the early paleogene exchange between the arctic and global oceans occurred through two narrow and shallow seaways the greenland norway seaway and the turgai strait sediments from the arctic ocean suggest that during this interval the surface ocean was warm brackish and episodically enabled the freshwater fern azolla to bloom the precise mechanisms responsible for the development of these conditions in the paleogene arctic remain uncertain here we show results from an isotope enabled atmosphere ocean general circulation model which indicate that northern hemisphere climate would have been very sensitive to the degree of oceanic exchange through the arctic seaways we also present modelled estimates of seawater and calcite 18o for the paleogene by restricting these seaways we simulate freshening of the surface arctic ocean to 6 psu and warming of sea surface temperatures by 2 c in the north atlantic and 5 10 c in the labrador sea our results may help explain the occurrence of low salinity tolerant taxa in the arctic ocean during the eocene and provide a mechanism for enhanced warmth in the north western atlantic we propose that the formation of a volcanic land bridge between greenland and europe could have caused increased ocean convection and warming of intermediate waters in the atlantic if true this result is consistent with the theory that bathymetry changes may have caused thermal destabilisation of methane clathrates and supports a tectonic trigger hypothesis for the paleocene eocene thermal maximum petm

orbitally forced azolla blooms and middle eocene arctic hydrology clues from palynology the high abundances and cyclic distribution of remains of the freshwater fern azolla in early middle eocene sediments from the arctic ocean have previously been related to episodic surface water freshening which was speculated to be orbitally modulated our integrated palynological and cyclostratigraphical analysis of the recovered azolla interval in integrated ocean drilling program iodp core 302 m0004a 11x resulted in the recognition of two clear periodicities a dominant 1 2 m cyclicity which we relate to changes in obliquity 40 k y and a weaker 0 7 m cyclicity which we link to precession 21 k y cycles in the abundances of azolla cysts of freshwater tolerant dinoflagellates and swamp vegetation pollen show covariability in the obliquity domain this strong correlation suggests periods of enhanced rainfall and runoff during azolla blooms presumably linked to increased local summer temperatures during obliquity maxima larix and bisaccate conifer pollen covary at the precession frequency with peak occurrences corresponding to precession minima possibly as a result of enhanced continental runoff from a more remote source area and a stronger seasonal contrast following the sudden demise of azolla ca 48 1 ma runoff cycles continued to influence the central arctic at decreased intensity this and a concomitant decline in swamp vegetation pollen suggest edaphically drier conditions on land and decreased runoff into the arctic ocean causing salinity changes which might have been fatal for azolla moreover a sea level rise inferred from overall decreasing total terrestrial palynomorph concentrations possibly facilitated oceanic connections 2011 geological society of america

chrysophyte cysts as potential environmental indicators many chrysophyte algae produce morphologically distinctive siliceous microscopic cysts during a resting stage of their life cycles these cysts are often preserved in sediments scanning electron microscopy and nomarski optics permit much more detailed observation of these cysts than was heretofore possible we have used an ecologic and biogeographic approach to study the distribution of cyst forms in sediments and have established that many cyst types are found only in specific habitats such as montane lakes wet meadows ephemeral ponds and sphagnum bogs in the samples we have studied cysts seem to be most common in fluctuating fresh water habitats of low to moderate ph and some winter freezing numerous taxonomic problems have yet to be resolved we believe that chrysophyte cysts have the potential to become a useful tool for both modern environmental assessments and paleoecological studies of cenozoic fresh water lacustrine deposits

high temperatures in the late cretaceous arctic ocean to understand the climate dynamics of the warm equable greenhouse world of the late cretaceous period it is important to determine polar palaeotemperatures the early palaeoceanographic history of the arctic ocean has however remained largely unknown because the sea floor and underlying deposits are usually inaccessible beneath a cover of floating ice a shallow piston core taken from a drifting ice island in 1970 fortuitously retrieved unconsolidated upper cretaceous organic rich sediment from alpha ridge a submarine elevated feature of probable oceanic origin a lack of carbonate in the sediments from this core has prevented the use of traditional oxygen isotope palaeothermometry here we determine arctic palaeotemperatures from these upper cretaceous deposits using tex86 a new palaeothermometer that is based on the composition of membrane lipids derived from a ubiquitous component of marine plankton crenarchaeota from these analyses we infer an average sea surface temperature of approximately 15 degrees c for the arctic ocean about 70 million years ago this calibration point implies an equator to pole gradient in sea surface temperatures of approximately 15 degrees c during this interval and by extrapolation we suggest that polar waters were generally warmer than 20 degrees c during the middle cretaceous approximately 90 million years ago

eocene silicoflagellate and ebridian paleoceanography in the central arctic ocean the silicoflagellate and ebridian assemblages in early middle eocene arctic cores obtained by iodp expedition 302 acex were studied in order to decipher the paleoceanography of the upper water column the assemblages in lithologic unit 2 49 7 45 1 ma one of the biosiliceous intervals were usually endemic as compared to the assemblages that occurred outside of the arctic ocean the presence of these endemic assemblages is probably due to a unique environmental setting controlled by the degree of mixing between the low salinity arctic waters and relatively high salinity waters supplied from outside the arctic ocean such as the atlantic and possibly the western siberian sea using the basin to basin fractionation model the early middle eocene arctic ocean corresponds to an estuarine circulation type which includes the modern day black sea the abundant down core occurrence of ebridians strongly suggests the past presence of low salinity waters and may indicate that low oxygen concentrations prevailed in the euphotic layer on the basis of the ecology of the modern ebridian hermesinum adriaticum

cyclicity in the middle eocene central arctic ocean sediment record orbital forcing and environmental response 1 continuous x ray fluorescence scanning of middle eocene 46 ma core m0002a 55x 236 241 m composite depth recovered during integrated ocean drilling program expedition 302 revealed a strong cyclical signal in some major and trace geochemical elements we performed a multiproxy study of the same core which included organic geochemical sedimentological and biological parameters and integrated our results with available geochemical and physical properties data the target was to look for cyclicity in the several proxies investigate their frequency and understand the environmental response to the potential forcing results indicate that a higher terrigenous component corresponds to lower organic carbon concentration smaller contributions by angiosperm pollen and spores organic walled dinoflagellate cysts and chrysophyte cysts lower productivity shorter growing season for flowering plants and lower stratification but higher contributions by bisaccate pollen and diatoms drier conditions on land more marine conditions and higher terrigenous sand ice rafted debris ird our investigation shows that physical proxy parameters hold cyclicity with periods of about 50 and 100 cm and that these frequency components are compatible with a milankovitchtype orbital forcing representing precession and obliquity respectively the longer 100 cm cyclicity is also present in the biological pollen dinoflagellate cysts and siliceous microfossils and in the sedimentological ird proxies the environmental signal derived from the integrated multiproxy analysis suggests that in an enclosed arctic ocean at time of ice sea ice and glacial ice initiation the biological proxies responded more strongly to growing season length darkness whereas the terrigenous components directly driven by sea ice and or glacial ice formation and extent responded more directly to seasonal insolation

a critical look at iron paleoredox proxies new insights from modern euxinic marine basins enrichments in reactive iron occur under euxinic marine conditions that is where dissolved sulfide is present in the water column these enrichments result primarily from the export of remobilized iron from the oxic shelf which is scavenged from the euxinic water column during syngenetic pyrite formation and deposited in the underlying sediments strongly elevated ratios of highly reactive iron to total iron fehr fet and total iron to aluminum fet al and high degrees of pyritization dop are each products of this enrichment process these paleoredox proxies are among the most faithful recorders of ancient euxinia contrary to previous arguments iron enrichment is decoupled from biogenic sediment inputs but it does appear to be a uniquely euxinic phenomenon in other words we can rule out a major contribution from preferential physical transport of fehr rich detrital sediment to the deep basin which could also operate under oxic conditions furthermore enrichment via the shuttling of iron remobilized from oxic shelves appears to be limited by inefficient transport and trapping processes in deep oxic basins elevated fet al ratios in the euxinic sediments also cannot be a product of internal enhancement of the reactivity of the detrital iron pool without net fehr addition these conclusions are supported by observations in the modern black sea orca basin and effingham inlet fet al ratios are unambiguous recorders of paleoredox even in sediments that have experienced high degrees of metamorphic alteration however this study suggests that high siliciclastic accumulation rates can swamp the enrichment mechanism resulting in only intermediate dop values for euxinic sediments and fet al ratios that mimic the oxic shelf such dilution effects are well expressed in black sea basinal turbidites and rapidly accumulating muds on euxinic basin margins under conditions of persistent euxinia varying extents of fehr enrichment can illuminate spatial and temporal gradients in siliciclastic sedimentation the magnitude of enrichment is a function of the source shelf to sink ocean basin areal ratio suggesting that iron proxies can also record ocean scale paleoenvironmental properties through muted enrichments at times of very widespread euxinia for the first time manganese data are interpreted in light of the redox shuttle model as for the iron data the black sea orca basin and effingham inlet show enrichments in total manganese in the deep euxinic basin suggesting export from the suboxic porewaters of the oxic shelf and scavenging and burial in the basin the black sea data reveal iron and manganese enrichment across the broad deep euxinic basin suggesting efficient lateral transport and deep water mixing tied to the physical properties of the water column

recent anthropogenic and climatic history of nunatsiavut fjords labrador canada this study aimed at reconstructing past climatic and environmental conditions of a poorly known and documented subarctic region the nunatsiavut northern labrador a multiproxy approach was chosen using fossil dinoflagellate cysts diatoms and pollen from sediment cores taken into three fjords nachvak 59 n saglek 58 5 n and anaktalak 56 5 n it allowed estimating terrestrial and marine influences in each fjord and documenting the recent history of human activities of the southern fjords saglek and anaktalak fossil pollen and dinoflagellate cyst assemblages allowed depicting the climate history of the region over the last 200 300 years in contrast to the general warming trend observed in the arctic and subarctic canada since the beginning of the industrial era the nunatsiavut has experienced relative climate stability over this period fossil pollen data show a shift of the tree limit to the south illustrating the cooling of terrestrial conditions our reconstructions suggest that the labrador region has remained climatically stable over the last 150 300 years with just a slight cooling trend of the reconstructed sea surface temperatures only perceptible in saglek and anaktalak fjords

visions of ice sheets in a greenhouse world abstract backstripped eustatic estimates from new jersey and the russian platform show large 25 m and rapid 18 o record highlights the enigma this was the warmest interval of the past 200 my yet it was bracketed by two inferred eustatic falls of 25 m that were associated with two large 0 75 deep sea 18 o increases 92 93 ma mid turonian and 96 ma mid cenomanian we reconcile records of warm high latitudes with glacioeustasy by proposing that late cretaceous early eocene ice sheets generally reached maximum volumes of 8 12 10 6 km 3 20 30 m glacioeustatic equivalent but did not reach the antarctic coast hence coastal antarctica hence deep water remained relatively warm even though there were significant changes in sea level as the result of glaciation unlike the oligocene and younger icehouse world these ice sheets only existed during short intervals of peak milankovitch insolation leaving antarctica ice free during much of the greenhouse late cretaceous to middle eocene these results highlight the need to re evaluate the paradigm that polar ice sheets did not exist during times of warm high latitude climates

enhanced siliceous plankton productivity in response to middle eocene warming at southern ocean odp sites 748 and 749 the middle eocene climatic optimum meco is a major transient warming event that occurred at 40 ma and reversed a long term cooling trend through the early and middle eocene we report the results of a high resolution quantitative study of siliceous microfossils at ocean drilling program sites 748 and 749 southern kerguelen plateau southern ocean 58 s across a 1 4 myr interval spanning the meco event at both sites a significant increase in biosiliceous sedimentation is associated with the meco event rich siliceous planktonic microfossil assemblages in this interval are unusual in that they are dominated by ebridians with radiolarians as a secondary major component silicoflagellates and diatoms comprise only a minor fraction of the assemblage in contrast to siliceous microfossil assemblages that characterize modern southern ocean sediments based on our new siliceous microfossil records we interpret two 300 kyr periods of elevated nutrient availability in southern ocean surface waters which span the peak warming interval of the meco and the post meco cooling interval a diverse assemblage of large silicoflagellates belonging to the dictyocha grandis plexus is linked to the rapid rise in sea surface temperatures immediately prior to peak warmth and a pronounced turnover is observed in both ebridian and silicoflagellate assemblages at the onset of peak warming the interval of peak warmth is also characterized by high abundance of cosmopolitan ebridians e g ammodochium spp and silicoflagellates e g naviculopsis spp and increased abundance of tropical and subtropical diatom genera e g asterolampra and azpeitia these observations confirm the relative pattern of temperature change interpreted from geochemical proxy data at multiple southern ocean sites furthermore rapid assemblage changes in both autotrophic and heterotrophic siliceous microfossil groups indicate a reorganization of southern ocean plankton communities in response to greenhouse warming during the meco event

mid cenozoic tectonic and paleoenvironmental setting of the central arctic ocean drilling results from the integrated ocean drilling program s arctic coring expedition acex to the lomonosov ridge lr document a 26 million year hiatus that separates freshwater influenced biosilica rich deposits of the middle eocene from fossil poor glaciomarine silty clays of the early miocene detailed micropaleontological and sedimentological data from sediments surrounding this mid cenozoic hiatus describe a shallow water setting for the lr a finding that conflicts with predrilling seismic predictions and an initial postcruise assessment of its subsidence history that assumed smooth thermally controlled subsidence following rifting a review of cenozoic tectonic processes affecting the geodynamic evolution of the central arctic ocean highlights a prolonged phase of basin wide compression that ended in the early miocene the coincidence in timing between the end of compression and the start of rapid early miocene subsidence provides a compelling link between these observations and similarly accounts for the shallow water setting that persisted more than 30 million years after rifting ended however for much of the late paleogene and early neogene tectonic reconstructions of the arctic ocean describe a landlocked basin adding additional uncertainty to reconstructions of paleodepth estimates as the magnitude of regional sea level variations remains unknown

os isotope insights into major environmental changes of the arctic ocean during the cenozoic 1 recent studies of lomonosov ridge sediments provided evidence for an eocene lacustrine stage in the arctic basin and concluded at its merging into global oceanic circulation some 17 5 ma ago with a 26 ma gap in between here re os data are used to document these events high os concentrations in the lacustrine unit and overlying transitional layer point to low sedimentary o2 conditions highly radiogenic os isotope values mark this layer suggesting massive input of old continental material above os concentrations decrease to typical oxic sediment values whereas 187os 188os ratios follow the trend observed in other oceans however re os isochrons from layers assigned to the upper and lower limit of the 26 ma gap yield identical ages suggesting a short transitional event marking the opening of fram strait and a ca 38 ma for the inception of marine conditions if confirmed this new chronology would modify views about the tectonic evolution of lomonosov ridge

the early miocene onset of a ventilated circulation regime in the arctic ocean deep water formation in the northern north atlantic ocean and the arctic ocean is a key driver of the global thermohaline circulation and hence also of global climate1 deciphering the history of the circulation regime in the arctic ocean has long been prevented by the lack of data from cores of cenozoic sediments from the arctic s deep sea floor similarly the timing of the opening of a connection between the northern north atlantic and the arctic ocean permitting deep water exchange has been poorly constrained this situation changed when the first drill cores were recovered from the central arctic ocean2 here we use these cores to show that the transition from poorly oxygenated to fully oxygenated ventilated conditions in the arctic ocean occurred during the later part of early miocene times we attribute this pronounced change in ventilation regime to the opening of the fram strait a palaeo geographic and palaeo bathymetric reconstruction of the arctic ocean together with a physical oceanographic analysis of the evolving strait and sill conditions in the fram strait suggests that the arctic ocean went from an oxygen poor lake stage to a transitional estuarine sea phase with variable ventilation and finally to the fully ventilated ocean phase 17 5 myr ago the timing of this palaeo oceanographic change coincides with the onset of the middle miocene climatic optimum3 although it remains unclear if there is a causal relationship between these two events

surface water productivity and paleoceanographic implications in the cenozoic arctic ocean study of bulk nitrogen contents and isotopic composition in arctic ocean sequences integrated oceandrilling program expedition 302 over the past 60 ma revealed changes in the export flux and sources ofsedimentary nitrogen the paleoproductivity calculated from the fraction of organic nitrogen to total nitrogen isdistinctly lower 20 g c m

implications for the history of cenozoic opal deposition from a quantitative model in addition to being a time of enhanced crustal activity and a warmer climate the eocene also saw prolonged periods of silica accumulation on the ocean floor the peak of this accumulation occurred at approximately 50 ma creating horizon ac a layer of silica rich sediments spanning approximately 4 my horizon ac is comparatively isolated in time from known silicic acid addition processes leading mcgowran 1989 mcgowran b 1989 silica burp in the eocene ocean geology 17 pp 857 860 to suggest a novel mechanism the silica burp hypothesis that centres on the temporal decoupling of silicic acid supply and burial by climatic variation here we examine this hypothesis using a quantitative biogeochemical model of the silicon cycle our results unequivocally show that mcgowran s hypothesis is unable to account for horizon ac the model s residence time and ocean capacity for silicic acid are insufficient to permit the degree of temporal decoupling proposed by mcgowran inverting the model s results suggests that instead the sediment record may be a useful proxy for silicic acid additions to the ocean

early to middle eocene history of the arctic ocean from nd sr isotopes in fossil fish debris lomonosov ridge strontium and neodymium radiogenic isotope ratios in early to middle eocene fossil fish debris ichthyoliths from lomonosov ridge integrated ocean drilling program expedition 302 help constrain water mass compositions in the eocene arctic ocean between 55 and 45 ma the inferred paleodepositional setting was a shallow offshore marine to marginal marine environment with limited connections to surrounding ocean basins the new data demonstrate that sources of nd and sr in fish debris were distinct from each other consistent with a salinity stratified water column above lomonosov ridge in the eocene the 87sr 86sr values of ichthyoliths 0 7079 0 7087 are more radiogenic than eocene seawater requiring brackish to fresh water conditions in the environment where fish metabolized sr the 87sr 86sr variations probably record changes in the overall balance of river sr flux to the eocene arctic ocean between 55 and 45 ma and are used here to reconstruct surface water salinity values the nd values of ichthyoliths vary between 5 7 and 7 8 compatible with periodic or intermittent supply of nd to eocene arctic intermediate water aiw from adjacent seas although the norwegian greenland sea and north atlantic ocean were the most likely sources of eocene aiw nd input from the tethys sea via the turgay strait in early eocene time and the north pacific ocean via a proto bering strait also contributed

chrysophycean microfossils in paleolimnological studies abstract the chrysophyceae represent a diverse group of algae with approximately 1000 described species most of which are planktonic and found in oligotrophic lakes a characteristic feature of this class is the endogenous formation of a siliceous resting stage known as a statospore vegetative cells in the family mallomonadaceae are covered by overlapping siliceous scales that are often sculptured and ornamented both the statospores and scales are species specific and because they are siliceous they are usually well preserved in lake sediments this paper reviews the applicability of these microfossils in the interpretation of past lake conditions

origin and environment of manganese rich sediments within black shale basins abstract sediments with unusually high manganese contents occur in anoxic basins of the central baltic sea we present a new model for the enrichment of manganese which is based on sedimentological and geochemical analyses of holocene sediments from the gotland deep and on published hydrographic data due to salinity stratification and high primary production bottom waters of the central baltic sea are anoxic and rich in dissolved mn 2 episodically bottom waters become oxygenated by inflows of denser water from the north sea mixing results in oxidation of mn 2 to fine grained particulate oxides which accumulate in the deepest parts of the basins where currents are mostly absent here anoxic conditions are re established within a few months or years and manganese oxides are again dissolved causing high concentrations of mn 2 in the near bottom layer alkalinity is high as a consequence of bacterial reduction of manganese oxides and sulphate under these conditions manganese is reprecipitated and forms a layer of ca rich rhodochrosite on the top of laminated sapropels occasionally periods of such extremely and rapidly changing redox conditions are followed by long term oxygenation of bottom waters in that case a layer rich in manganese oxides forms on the top of a bioturbated layer due to dissolution of rhodochrosite and oxidation of manganese in the near surface sediment return of anoxic conditions results again in the transformation of manganese oxides into rhodochrosite varying rhodochrosite contents in the basinal sediments therefore record a detailed history of redox conditions in bottom waters the manganese rich sediments of the baltic sea share many features with some occurrences of lower jurassic and lower carboniferous manganese ores in western and central europe we therefore suggest that these manganese enrichments were formed by similar processes

seismo electric exploration expected signal amplitudes1 for more than 20 years soviet scientists have published papers and registered patents describing the conversion of seismic to electromagnetic energy in geological environments and the detection of the electric or magnetic signals as a method of geophysical exploration because of the potential importance of a reliable geophysical technique for locating quartz veins the authors have been conducting extensive laboratory and field tests of the phenomena for the purposes of designing appropriate field tests the approximate signal magnitudes must be known but little has been published on them the paper describes a simplified model from which order of magnitude estimates of expected electric and magnetic signal strengths can be made with sufficient accuracy for such purposes for mathematical convenience the target is modeled as a homogeneous sphere in which the seismic input induces uniform time varying electric polarization more realistic configurations can be described by linear superposition of the potentials of appropriate sub elements

paleoceanographic and paleoclimatic constraints on the global eocene diatom and silicoflagellate record abstract eocene diatom and silicoflagellate biostratigraphy are summarized and correlated with the most recent geologic time scale as well as with the global oxygen isotope and eustatic sea level curves the global distribution of eocene diatom silicoflagellate bearing sediments varies considerably reflecting changing oceanic gateways and paleoceanography with changing patterns that are punctuated by four major depositional events event 1 49 million years ago ma at the end of the early eocene climatic optimum eeco saw the cessation of diatom silicoflagellate deposition in epicontinental regions of the north sea region and in the northern russia and the onset of biosilica deposition in the arctic event 2 46 ma which coincided with intensification of the middle eocene cooling trend marked the widespread expansion of diatom silicoflagellate deposition in both the north and south atlantic a shift of diatom silicoflagellate deposition from the atlantic to the pacific began at event 3 at the end of the middle eocene climatic optimum meco 40 ma that was likely tied to the initial opening of the drake passage between antarctica and south america event 4 39 ma coincided with a major sea level fall and a widespread deep sea hiatus in the latest middle eocene late eocene diatom silicoflagellate deposition became more concentrated in middle to high latitude regions and coastal upwelling regions particularly in the pacific ocean tabulation of the first and last occurrences of 132 biostratigraphically important diatoms suggests increased species turnover during the latest paleocene to earliest eocene that may be in part due to a monographic effect an increasing rate of evolution of new diatom species between 46 and 43 ma and after 40 ma coincides respectively with the widespread expansion of diatom deposition in the atlantic and with an increased pole to equator thermal gradient that witnessed the expansion of diatoms in high latitude oceans and coastal upwelling settings

episodic fresh surface waters in the eocene arctic ocean it has been suggested on the basis of modern hydrology and fully coupled palaeoclimate simulations that the warm greenhouse conditions that characterized the early palaeogene period 55 45 myr ago probably induced an intensified hydrological cycle with precipitation exceeding evaporation at high latitudes little field evidence however has been available to constrain oceanic conditions in the arctic during this period here we analyse palaeogene sediments obtained during the arctic coring expedition showing that large quantities of the free floating fern azolla grew and reproduced in the arctic ocean by the onset of the middle eocene epoch approximately 50 myr ago the azolla and accompanying abundant freshwater organic and siliceous microfossils indicate an episodic freshening of arctic surface waters during an approximately 800 000 year interval the abundant remains of azolla that characterize basal middle eocene marine deposits of all nordic seas probably represent transported assemblages resulting from freshwater spills from the arctic ocean that reached as far south as the north sea the termination of the azolla phase in the arctic coincides with a local sea surface temperature rise from approximately 10 degrees c to 13 degrees c pointing to simultaneous increases in salt and heat supply owing to the influx of waters from adjacent oceans we suggest that onset and termination of the azolla phase depended on the degree of oceanic exchange between arctic ocean and adjacent seas

cenozoic microfossils in northern finland local reworking or distant wind transport abstract allochthonous cenozoic microfossils have been reported from late pleistocene lake and mire host sediments across an area of 30 000 km2 in northern finland two main groups of microfossils are recognised palaeogene marine diatoms silicoflagellates and ebridians that include taxa from around the time of the palaeocene eocene thermal maximum and pliocene to early pleistocene freshwater diatoms the presence of these microfossils has been regarded as evidence that eocene marine and late neogene freshwater sediments formerly existed on the shield surface both groups have been referred to frequently in reconstructions of the sea level tectonic and erosion history of the northern fennoscandian shield the questions raised by the presence of allochthonous cenozoic microfossils in northern finland are however strongly resonant of the debate over the biota origin and age of the pliocene sirius group in antarctica where competing hypotheses have been put forward of local deposition and reworking versus distant wind transport of marine diatoms from the continental shelf this review explores alternative origins for the allochthonous cenozoic microfossils in northern finland local reworking of palaeogene marine sediments during pleistocene glaciation is unlikely as no source rocks of palaeogene age are known from the shield surface or from surrounding sedimentary basins in the baltic and white sea moreover at all sites except akanvaara the marine diatom taxa cover wide age ranges and occur only as minor components in diatom assemblages that are dominated by quaternary freshwater taxa local reworking of pliocene pleistocene freshwater diatoms is however compatible with the widespread survival of pre pleistocene deep weathering although no in situ or unmixed ice rafted pliocene pleistocene lacustrine sediment has yet been found an alternative origin for the marine palaeogene microfossils by distant wind transport is proposed in this hypothesis palaeogene diatomites on the barents sea shelf were exposed to deep glacial and fluvioglacial erosion during the pliocene and early pleistocene and in low sea level stages of the middle and late pleistocene intense wind action acting on comminuted mudstones on outwash plains carried dust including microfossils into northern fennoscandia to be deposited by rain out in lakes and wetlands this material may have been later further recycled by glacial and meltwater transport and more localised wind action processes that also may help to account for the distribution of eemian marine diatoms well beyond eemian shorelines the distant wind transport hypothesis implies that the presence of marine palaeogene diatoms on the shield surface in northern finland cannot be regarded as vestiges of former marine sediments and so do not constrain the tectonic and geomorphic history of the northern fennoscandian shield in the cenozoic

phosphorus burial and diagenesis in the central bering sea bowers ridge iodp site u1341 perspectives on the marine p cycle abstract to reconstruct the cycling of reactive phosphorus p in the bering sea a p speciation record covering the last 4 ma was generated from sediments recovered during integrated ocean drilling program iodp expedition 323 at site u1341 bowers ridge a chemical extraction procedure distinguishing between different operationally defined p fractions provides new insight into reactive p input burial and diagenetic transformations reactive p mass accumulation rates mars are 20 110 mol cm2 ka which is comparable to other open ocean locations but orders of magnitude lower than most upwelling settings we find that authigenic carbonate fluorapatite cfa and opal bound p are the dominant p fractions at site u1341 an overall increasing contribution of cfa to total p with sediment depth is consistent with a gradual sink switching from more labile p fractions fish remains fe oxides organic matter to stable authigenic cfa however the positive correlation of cfa with al content implies that a significant portion of the supposedly reactive cfa is non reactive detrital contamination by eolian and or riverine cfa in contrast to cfa opal bound p has rarely been studied in marine sediments we find for the first time that opal bound p directly correlates with excess silica contents this p fraction was apparently available to biosiliceous phytoplankton at the time of sediment deposition and is a long term sink for reactive p in the ocean despite the likelihood for diagenetic re mobilisation of this p at depth indicated by increasing ratios of excess silica to opal bound p average reactive p mars at site u1341 increase by 25 if opal bound p is accounted for but decrease by 25 if 50 of the extracted cfa fraction based on the lowest cfa value at site u1341 is assumed to be detrital combining our results with literature data we present a qualitative perspective of terrestrial cfa and opal bound p deposition in the modern ocean riverine cfa input has mostly been reported from continental shelves and margins draining p rich lithologies while eolian cfa input is found across wide ocean regions underlying the northern hemispheric dust belt opal bound p burial is important in the southern ocean north pacific and likely in upwelling areas shifts in detrital cfa and opal bound p deposition across ocean basins likely occurred over time responding to changing weathering patterns sea level and biogenic opal deposition

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

sources and cycling of mercury in the paleo arctic ocean from hg stable isotope variations in eocene and quaternary sediments abstract mercury stable isotopic compositions were determined for marine sediments from eight locations in the arctic ocean basin mass dependent fractionation mdf and mass independent fractionation mif of hg stable isotopes were recorded across a variety of depositional environments water depths and stratigraphic ages 202hg mdf ranges from 2 34 to 0 78 199hg mif from 0 18 to 0 12 and 201hg mif from 0 29 to 0 05 for the complete data set n 33 holocene sediments from the chukchi sea and morris jesup rise record the most negative 199hg values while pleistocene sediments from the central arctic ocean record the most positive 199hg values the most negative 202hg values are recorded in pleistocene sediments eocene sediments lomonosov ridge show some overlap in their hg isotopic compositions with quaternary sediments with a sample of the arctic ocean petm 56 ma most closely matching the average hg isotopic composition of holocene arctic marine sediments collectively these data support a terrestrially dominated hg source input for arctic ocean sediment through time although other sources as well as influences of sea ice atmospheric mercury depletion events amdes and anthropogenic hg in core top samples on hg isotopic signatures must also be considered

taxonomy phylogeny and paleoecology of eoseira wilsonii gen et sp nov a middle eocene diatom bacillariophyceae aulacoseiraceae from lake sediments at horsefly british columbia canada a new centric diatom genus is described from laminated freshwater sediments of middle eocene age near horsefly british columbia canada this diatom eoseira wilsonii gen et sp nov grew in filaments that constitute dense monospecific sub horizons within the white couplets that represent summer deposition in the varved sequence although eoseira clearly belongs within the family aulacoseiraceae several features distinguish its valve structure from aulacoseira gigantism of spines and the lack of geometric relationships between spine position and mantle areolae are the most conspicuous features of the genus eoseira is among the oldest freshwater diatoms known and one of relatively few extinct freshwater genera in addition to serving as a potential biostratigraphic marker eoseira is a cornerstone to undertanding the evolutionary trajectory of the aulacoseiraceae likely the oldest family of freshwater diatoms as such it refines our understanding of early radiations from the marine realm in western