planktonic foraminiferal biostratigraphy and assemblages in the bering sea during the pliocene and pleistocene iodp sites u1340 and u1343 abstract iodp site u1340 and site u1343 in the bering sea have been investigated with regard to planktonic foraminifers and fragmentation the base of site u1340 dates back to the early pliocene and the base of site u1343 to the early pleistocene site u1340 is situated at bowers ridge the southern bering sea site u1343 is situated near the gateway to the arctic ocean in the northern bering sea at both sites there are none or very few planktonic foraminifers during the pliocene and early pleistocene after 1 3 1 4 ma the planktonic foraminifers are continuously present for most of the samples examined three stratigraphic events have been identified in this study the first occurrence fo of neogloboquadrina inglei is observed at 1 4 1 5 ma although this event may be affected by poor preservation of foraminifers in older sediments the observed age of the change in the coiling ratio of neogloboquadrina pachyderma from right to left at 1 2 ma agrees with the dating of the same event at the californian margin the age of the last occurrence lo of n inglei also seems to match the same event from the californian margin at 0 7 ma this implies that these events are robust regional events for the entire northern pacific multivariate analyses of the quantitative planktonic foraminifer data show three main faunal assemblages the oldest assemblage from 1 3 1 4 ma to 1 2 ma is dominated by n pachyderma s l dex together with globigerina bulloides other species in this fauna are n inglei n pachyderma s l sin globigerina umbilicata and turborotalita quinqueloba after 1 2 ma the faunal assemblage is dominated by n pachyderma s l sin but the remaining species are the same as before at 0 7 ma n inglei disappears whilst the remaining fauna assemblage stays the same with n pachyderma s l sin still dominating reflecting subpolar polar conditions prior to 1 4 1 3 ma there are very few or no planktonic foraminifers low shell fragmentation and lower toc suggest that the lack of planktonic foraminifers in these sediments cannot be explained either by a shoaling of the carbonate compensation depth or by enhanced supralysoclinal dissolution instead we argue that the appearance of abundant foraminifers in the sediment reflects the same evolutionary adaption of n pachyderma sin to cold conditions to have occurred after 1 1 1 0 ma as in the north atlantic

the bering sea and paleoceanography abstract this paper serves as an introduction to the bering sea preceding the 14 contributed papers contained in this volume several parts of the paper are allocated for current reviews of the bering sea included in the review topics are geomorphology surface water circulation and the importance of the formation of intermediate waters representative results of previous paleoceanographic studies are also presented in particular focusing on spatial and temporal distributions of biosiliceous microfossils as well as isotopic analyses of carbon and nitrogen concerning changes in productivity and nutrients motivations behind the scientific expeditions conducted which resulted in the many papers included here are briefly discussed in order to illustrate the recent trend in paleoceanography in the bering sea and the adjacent regions brief summaries or highlights of each of the contributed papers are given in order to provide an overview of the volume

greatly expanded tropical warm pool and weakened hadley circulation in the early pliocene the pliocene warm interval has been difficult to explain we reconstructed the latitudinal distribution of sea surface temperature around 4 million years ago during the early pliocene our reconstruction shows that the meridional temperature gradient between the equator and subtropics was greatly reduced implying a vast poleward expansion of the ocean tropical warm pool corroborating evidence indicates that the pacific temperature contrast between the equator and 32 n has evolved from 2 c 4 million years ago to 8 c today the meridional warm pool expansion evidently had enormous impacts on the pliocene climate including a slowdown of the atmospheric hadley circulation and el nino like conditions in the equatorial region ultimately sustaining a climate state with weak tropical sea surface temperature gradients may require additional mechanisms of ocean heat uptake such as enhanced ocean vertical mixing

productivity changes in the bering sea during the late quaternary changes in biological productivity of the bering sea have been evaluated for the late quaternary based on biogenic opal calcium carbonate and microfossils in two piston cores biological productivity increased during marine isotope stage mis 1 after the last glaciation during the last deglaciation two pronounced peaks of calcium carbonate content were observed at ca 2400 m water depth which can be explained by the caco3 compensation hypothesis and coccolithophore blooms simultaneous with the caco3 peaks oxygen poor deep water was apparently distributed in the aleutian basin based on benthic foraminiferal assemblages the low o2 events seem to be related to deep water circulation and or elevated productivity in the northwest pacific after the caco3 peak events biogenic opal contents and diatoms increased gradually associated with enhanced vertical mixing with an inflow of the alaskan stream through the eastern aleutian arc passes r 2005 elsevier ltd all rights reserved

diatoms silicoflagellates and ebridians at site u1341 on the western slope of bowers ridge iodp expedition 323 abstract the biostratigraphy and datum levels of diatoms silicoflagellates and ebridians are presented at site u1341 drilled by the iodp expedition 323 on the western slope of bowers ridge in the bering sea identified biostratigraphic diatom zones were from the neodenticula seminae zone to the thalassiosira oestrupii subzone silicoflagellate and ebridian zones were from the distephanus octangulatus zone to the distephanus jimlingii zone the bottom age in the deepest hole u1341b is estimated between 4 1 ma and 5 0 ma based on the succession of microfossil assemblages throughout the studied holes the changes in paleoceanographic conditions are outlined

mineralogical geochemical and isotopic characterization of authigenic carbonates from the methane bearing sediments of the bering sea continental margin iodp expedition 323 sites u1343 u1345 abstract during expedition 323 of the integrated ocean drilling program to the bering sea july 5 september 4 2009 three sites were drilled along the bering sea northeastern continental margin u1343 down to 745 meters below sea floor mbsf u1344 745 mbsf u1345 150 mbsf diagenetic carbonates are present at all sites within the clayey diatom rich oozes of the bering sea where pore waters are also characterized by extremely high methane concentrations we here present mineralogical elemental and isotopic data obtained from the authigenic carbonate rich intercalations within the clay rich pleistocene sediments deposited along the bering sea continental margin the mineralogy of the authigenic carbonates is generally represented by composite mixtures of very small crystals of magnesian calcite dolomite and iron rich carbonates with the latter phases occurring below 260 mbsf at site u1343 below 200 mbsf at site u1344 and below 130 mbsf at site u1345 element geochemistry shows that ca mg fe ba mn sr and u are enriched in the carbonate rich intercalations relative to the background sediments due to their incorporation into the carbonates and into other authigenic phases e g barite and pyrite the oxygen and carbon isotopic compositions of the authigenic carbonate minerals show that they were sequentially precipitated from pore waters at different temperatures i e different burial depths and with different isotopic compositions of dissolved inorganic carbon dic the authigenic mg calcite precipitated early during diagenesis and shallow burial from a 13 c depleted dic pool whereas dolomite and fe rich carbonates formed during later diagenesis and deeper burial from a 13 c enriched dic pool these authigenic carbonate occurrences are interpreted as resulting from microbial sulfate reduction combined with anaerobic oxidation of methane and methanogenesis that was intimately linked to the alteration of silicates especially iron rich clay minerals

orbital scale benthic foraminiferal oxygen isotope stratigraphy at the northern bering sea slope site u1343 iodp expedition 323 and its pleistocene paleoceanographic significance abstract a continuous composite oxygen isotope 18o stratigraphy from benthic foraminifera in the bering sea was reconstructed in order to provide insight into understanding sea ice evolution in response to northern hemisphere glaciation oxygen isotope records from multiple species of benthic foraminifera at integrated ocean drilling program iodp expedition 323 site u1343 54 33 4 n 176 49 0 e water depth 1950 m yield a highly refined orbital scale age model spanning the last 1 2 ma and a refined age model between 1 2 and 2 4 ma an inter species calibration was used to define species offsets and to successfully obtain a continuous composite benthic 18o record correlated with the global composite benthic 18o stack curve lr04 to construct an orbital scale age model the consistency of the benthic 18o stratigraphy with biostratigraphy and magnetostratigraphy confirms the reliability of both methods for constraining age the time difference between cyclic changes in sedimentary physical properties and glacial interglacial cycles since 0 8 ma is notable and suggests that physical properties alone cannot be used to construct an orbital scale age model amplitude changes in physical properties and a significant drop in the linear sedimentation rate during glacials after 0 9 ma indicate that the glacial sea ice edge extended beyond the bering sea slope site u1343 at this time

the middle pleistocene transition characteristics mechanisms and implications for long term changes in atmospheric pco2 abstract the emergence of low frequency high amplitude quasi periodic 100 kyr glacial variability during the middle pleistocene in the absence of any significant change in orbital forcing indicates a fundamental change internal to the climate system this middle pleistocene transition mpt began 1250 ka and was complete by 700 ka its onset was accompanied by decreases in sea surface temperatures ssts in the north atlantic and tropical ocean upwelling regions and by an increase in african and asian aridity and monsoonal intensity during the mpt long term average ice volume gradually increased by 50 m sea level equivalent whereas low frequency ice volume variability experienced a 100 kyr lull centered on 1000 ka followed by its reappearance 900 ka although as a broad band of power rather than a narrow persistent 100 kyr cycle additional changes at 900 ka indicate this to be an important time during the mpt beginning with an 80 kyr event of extreme sst cooling followed by the partial recovery and subsequent stabilization of long term north atlantic and tropical ocean ssts increasing southern ocean sst variability primarily associated with warmer interglacials the loss of permanent subpolar sea ice cover and the emergence of low frequency variability in pacific ssts and global deep ocean circulation since 900 ka ice sheets have been the only component of the climate system to exhibit consistent low frequency variability with the exception of a near universal organization of low frequency power associated with marine isotope stages 11 and 12 all other components show an inconsistent distribution of power in frequency time space suggesting a highly nonlinear system response to orbital and ice sheet forcing most hypotheses for the origin of the mpt invoke a response to a long term cooling possibly induced by decreasing atmospheric pco2 none of these hypotheses however accounts for the geological constraint that the earliest northern hemisphere ice sheets covered a similar or larger area than those that followed the mpt given that the mpt was associated with an increase in ice volume this constraint requires that post mpt ice sheets were substantially thicker than pre mpt ice sheets indicating a change in subglacial conditions that influence ice dynamics we review evidence in support of the hypothesis that such an increase in ice thickness occurred as crystalline precambrian shield bedrock became exposed by glacial erosion of a thick mantle of regolith this exposure of a high friction substrate caused thicker ice sheets with an attendant change in their response to the orbital forcing marine carbon isotope data indicate a rapid transfer of organic carbon to inorganic carbon in the ocean system during the mpt if this carbon came from terrigenous sources an increase in atmospheric pco2 would be likely which is inconsistent with evidence for widespread cooling apparently rapid carbon transfer from terrestrial sources is difficult to reconcile with gradual erosion of regolith a more likely source of organic carbon and nutrients which would mitigate pco2 rise is from shelf and upper slope marine sediments which were fully exposed for the first time in millions of years in response to thickening ice sheets and falling sealevels during the mpt modeling indicates that regolith erosion and resulting exposure of crystalline bedrock would cause an increase in long term silicate weathering rates in good agreement with marine sr and os isotopic records we use a carbon cycle model to show that a post mpt increase in silicate weathering rates would lower atmospheric pco2 by 7 12 ppm suggesting that the attendant cooling may have been an important feedback in causing the mpt

introduction to pliocene pleistocene paleoceanography of the bering sea abstract high resolution paleoceanography of the pliocene pleistocene is important in understanding climate forcing mechanisms and associated environmental changes during this major transition from global warmth to the ice ages this is particularly true in high latitude marginal seas such as the bering sea the bering sea has been very sensitive to changes in global climate during interglacial and glacial or milankovitch time scales this is due to significant changes in water circulation land ocean interaction and sea ice formation with the aim to reveal the climate and oceanographic history of the bering sea over the past 5 my iodp expedition 323 cored a total of 5741 m of sediment 97 4 recovery at seven sites in 2009 on d v joides resolution covering three regions the umnak plateau the bowers ridge and the bering slope the water depths of the drill sites range from 818 m to 3174 m allowing for the characterization of past vertical water mass distribution including changes in the oxygen minimum zone the four deepest holes range from 600 m to 745 m below the seafloor and resulted in the recovery of long sediment sequences ranging from 1 9 my to 5 my in age following the expedition two sampling parties at kochi core center for acquisition of ca 58 000 subsamples and two scientific meetings were conducted in order to proceed with the analyses of sediment core samples and discussions here pertinent results primarily from iodp expedition 323 are consolidated as a single special volume of deep sea research part ii topical studies in oceanography

modelling pliocene warmth contribution of atmosphere oceans and cryosphere the relative role of the atmosphere oceans and cryosphere in contributing towards middle pliocene warmth ca 3 ma bp is investigated using the hadcm3 coupled ocean atmosphere general circulation model the model was initialised with boundary conditions from the usgs prism2 data set and a pliocene atmospheric co2 level of 400 ppmv and run for 300 simulated years the simulation resulted in a global surface temperature warming of 3degreesc compared to present day in contrast to earlier modelling experiments for the pliocene surface temperatures warmed in most areas including the tropics 1 5degreesc compared with present day the model predicts a general pattern of ocean warming 1 5degreesc in both hemispheres to a depth of 2000 m below which no significant differences are noted sea ice coverage is massively reduced up to 90 the flow of the gulf stream north atlantic drift is up to 100 mm s 1 greater in the pliocene case analysis of the model predicted meridional streamfunction suggests a global pattern of reduced outflow of antarctic bottom water aabw up to 5 sv a shallower depth for north atlantic deep water formation and weaker thermohaline circulation 3 sv the decrease in aabw occurs mainly in the pacific rather than atlantic ocean model diagnostics for heat transports indicate that neither the oceans nor the atmosphere are transporting significantly more heat in the pliocene scenario rather these results indicate that the major contributing mechanism to global pliocene warmth was the reduced extent of high latitude terrestrial ice sheets 50 reduction on greenland 33 reduction on antarctica and sea ice cover resulting in a strong ice albedo feedback these results highlight the need for further studies designed to improve our knowledge regarding pliocene terrestrial ice configurations

permanent el nino like conditions during the pliocene warm period during the warm early pliocene 4 5 to 3 0 million years ago the most recent interval with a climate warmer than today the eastern pacific thermocline was deep and the average west to east sea surface temperature difference across the equatorial pacific was only 1 5 0 9 c much like it is during a modern el nino event thus the modern strong sea surface temperature gradient across the equatorial pacific is not a stable and permanent feature sustained el nino like conditions including relatively weak zonal atmospheric walker circulation could be a consequence of and play an important role in determining global warmth

conditions of mytilus edulis extracellular body fluids and shell composition in a ph treatment experiment acid base status trace elements and δ11b mytilus edulis were cultured for 3 months under six different seawater pco 2 levels ranging from 380 to 4000 mu atm specimen were taken from kiel fjord western baltic sea germany which is a habitat with high and variable seawater pco 2 and related shifts in carbonate system speciation e g low ph and low caco3 saturation state hemolymph hl and extrapallial fluid epf samples were analyzed for ph and total dissolved inorganic carbon c t to calculate pco 2 and hco3 a second experiment was conducted for 2 months with three different pco 2 levels 380 1400 and 4000 mu atm boron isotopes delta b 11 were investigated by la mc icp ms laser ablation multicollector inductively coupled plasma mass spectrometry in shell portions precipitated during experimental treatment time additionally elemental ratios b ca mg ca and sr ca in the epf of specimen from the second experiment were measured via icp oes inductively coupled plasma optical emission spectrometry extracellular ph was not significantly different in hl and epf but systematically lower than ambient water ph this is due to high extracellular pco 2 values a prerequisite for metabolic co2 excretion no accumulation of extracellular hco3 was measured elemental ratios b ca mg ca and sr ca in the epf increased slightly with ph which is in accordance with increasing growth and calcification rates at higher seawater ph values boron isotope ratios were highly variable between different individuals but also within single shells this corresponds to a high individual variability in fluid b ca ratios and may be due to high boron concentrations in the organic parts of the shell the mean delta b 11 value shows no trend with ph but appears to represent internal ph epf rather than ambient water ph

40 ar 39 ar dating and tectonic implications of volcanic rocks recovered at iodp hole u1342a and d on bowers ridge bering sea abstract during the integrated ocean drilling program iodp a total of 41 54 m of basement rock consolidated volcaniclastic sediment was recovered beneath a thin sediment cover the drilled site is at the eastern end of the crestal area of bowers ridge a north and westward sweeping offshoot of the aleutian arc into the bering sea the volcanic sequence recovered from holes u1342a and u1342d was divided into six major lithologic units we used the single grain 40 ar 39 ar dating method performed by step wise heated laser fusion technique to date andesites of unit 1 thereby two ages of oligocene volcanism 34 32 ma 28 26 ma were distinguished each other according to our 40 ar 39 ar data these ages refute a hypothesized cretaceous origin in the north pacific as an exotic arc massif or sector of the hawaiian emperor chain and indicate that the bowers ridge is a bering sea formed arc or remnant arc that ceased forming in the latest oligocene to the earliest miocene time

reconstruction of submesoscale velocity field from surface drifters abstractthe extensive drifter deployment during the lagrangian submesoscale experiment laser provided observations of the surface velocity field in the northern gulf of mexico with high resolutio

late quaternary changes of the oxygen conditions in the bottom and intermediate waters on the western kamchatka continental slope the sea of okhotsk microfossil data on the foraminifers and radiolarians in the sediment core komex lv28 44 3 the kamchatka slope in the eastern sea of okhotsk exhibit the changes in the water oxygen conditions during the last 146 ky the paleoenvironmental proxies are the radiolarian species cycladophora davisiana as indicator of the upper intermediate water ventilation and the benthic planktonic foraminifers as indicators of the bioproductivity and bottom water oxygenation in case of sediment core lv28 44 3 the bottom water represents the lower intermediate one so that conclusions on paleoenvironments are applicable for the most range of the local intermediate water the well oxygenated intermediate and near bottom waters existed in the area of study during the penultimate glaciation of mis 6 early weichselian initiation of the last glaciation within mis 5b d and last glacial stages of mis 3 2 the intervals of the short low o2 bottom events with suboxic conditions dissolved o2 in water 0 3 1 2 ml l occur during the last interglacial mis 5e eemian stage 125 to 113 ka and during the last deglaciation 17 5 to 6 5 ka eemian low o2 bottom events are associated with the high bioproductivity of the subsurface water but poor ventilation on the upper intermediate depths the low o2 bottom events during the last deglaciation occurred at the high bioproductivity of the subsurface water and active ventilation on the upper intermediate depths

warm upwelling regions in the pliocene warm period 1 given the importance of upwelling processes to coastal productivity and regional climate it is critical to study the role of upwelling regions within the context of global climate change we generated sea surface temperature sst records for the last 5 million years in three important upwelling regions the eastern equatorial pacific the california margin and the peru margin prior to 3 0 ma ssts at all sites were significantly warmer than today by 3 9 c indicating that cold upwelling regions that characterize the modern pacific ocean did not exist in the early pliocene warm period 4 6 to 3 1 ma earth s most recent period of sustained global warmth alkenone phosphorus and organic carbon mass accumulation rate records indicate that changes in productivity and sst were decoupled and that upwelling of nutrient enriched water occurred even when ssts were warm during the early pliocene thus the long term trends in sst are likely explained by changes in the temperature of upwelled water rather than in the strength of upwelling favorable winds alone the fact that gradual cooling of upwelling regions began before the onset of significant northern hemisphere glaciation provides further evidence that the growth of ice sheets and their influence on atmospheric winds alone can not explain the cooling of upwelling regions our results suggest that the long term average ssts of upwelling regions are influenced by global changes in the depth and or temperature of the ventilated thermocline

pliocene and pleistocene paleoceanography in the western subarctic pacific based on diatom analyses of odp leg 145 hole 884b and iodp expedition 323 holes u1341b and u1343e abstract late pliocene pleistocene fossil diatom assemblages from ocean drilling program odp leg 145 hole 884b in the western subarctic pacific were investigated to improve the diatom biostratigraphy moreover the paleoceanographic records at hole 884b were compared with those in integrated ocean drilling program iodp expedition 323 holes u1341b and u1343e in the bering sea for the time interval of 2 5 0 ma in order to clarify the differences in the diatom assemblage fluctuations and the history of past ocean circulations around the subarctic pacific in hole 884b five diatom zones from the neodenticula koizumii neodenticula kamtschatica zone to the neodenticula seminae zone were identified the decreases in the relative abundance of temperate water species were recognized at ca 1 9 ma in hole u1343e ca 2 1 ma in holes 884b and u1341b the decreases of the temperate water species at these sites indicate that a widespread cooling event must have occurred over the subarctic pacific at 2 ma in addition the continuous low occurrences of the sea ice related species from around 2 ma onward which indicate the presence of sea ice were observed at sites 884 and u1341 we also point out that the age differences in decrease of temperate water species at the three sites i e delay in response of the temperate water species at site u1343 may be related to changes of seawater inflow from the north pacific to sites u1341 and u1343 and of the east kamchatka current from the bering sea to site 884

diatoms as paleoenvironmental proxies for seasonal productivity sea ice and surface circulation in the bering sea during the late quaternary abstract diatom assemblages in suspended particulate matter spm surface sediments and piston core samples in the southern bering sea and the western subarctic pacific were examined the distribution of diatom assemblages in the southern bering sea shows not only differences in species composition between the spm and surface sediment samples but also preferential dissolution of different species in the upper water column or surface sediments furthermore we present the downcore profiles of selected diatom taxa for four piston cores to indicate changes in paleoceanographic conditions e g seasonal productivity sea ice and surface water circulation of the glacial and deglaciation periods during the late quaternary in particular we propose five models for the annual cycling of the water masses in the western subarctic pacific and the southern bering sea during the late quaternary significant regional differences in diatom accumulation rates and taxonomic composition between the southern bering sea and the western subarctic pacific reflect spatial shifts in water masses caused by the variable extent of sea ice cover and cold low salinity surface waters in these regions

late quaternary paleoceanographic changes in the bering sea and the western subarctic pacific based on radiolarian assemblages seven piston cores were obtained from the bering sea and the western subarctic pacific during cruise kh99 3 of r v hakuho maru in august 1999 cores bow 8a bow 9a bow 12a ab umk 3a gat 3a in the bering sea and core es in the western subarctic pacific the quantitative high resolution analyses of radiolarians in the cores revealed significant variations in both their faunal assemblages and accumulation rates ar a trend of conspicuous turn over of the surface dwellers and intermediate dwellers increase of one at expense of the other after the last glacial maximum lgm is clearly visible in the bering sea data set however this turn over is not present at site es in the western subarctic pacific core these changes in radiolarian assemblages around the lgm suggest that the surface waters had extremely low temperature and low salinity and that the subsurface dichothermal layer temperature minimum layer was thickened all the way across the entire east west span of the bering sea furthermore sea ice coverage extended to the central aleutian basin around the lgm this suggests that the water mass structure in the western subarctic pacific around the lgm was basically the same as that of the eastern bering sea based on the species composition of the surface dwellers however the detailed development of intermediate water masses differed from that of the eastern bering sea during marine isotope stage mis 5 to 3 such species turn over events did not occur and species abundance stayed relatively uniform in the studied cores therefore the present water mass structure is interpreted to have been formed after the lgm based on the relative abundances of cycladophora davisiana the most dominant species dwelling in the intermediate water and a useful tracer of cold and well oxygenated intermediate water in the north pacific the past north pacific intermediate water npiw had the following source regions during the last 100 kyr 1 both the okhotsk sea and the bering sea during mis 5 to 3 2 the bering sea around the lgm and 3 shifting from the bering sea to the okhotsk sea after the lgm relatively low radiolarian ar at site bow 8a which is the shallowest site studied here present water depth 884 m were observed during the glacial periods this is due to decrease of radiolarian production in the thinned upper water layer above the dicothermal layer caused by sea level drop cycladophora davisiana probably lived deeper during the glacials than today as it was absent in the shallow piston core r 2005 elsevier ltd all rights reserved

interior hydrography and circulation of the glacial pacific ocean abstract the deep water of the pacific ocean is a key component of the global climate system on the time scale of late pleistocene glaciation and deglaciation despite its importance the deep pacific during the last glacial maximum has received relatively little attention compared to the deep atlantic in part because the pacific poorly preserves carbonate sediments on the sea floor here we review the current state of knowledge of the deep hydrography and circulation of the glacial pacific by examining available nutrient proxy data including some new 13 c and 18 o data measured on benthic foraminifera planulina wuellerstorfi from the vicinity of japan available benthic 13 c and 18 o and radiocarbon data from the pacific support the presence of a deep hydrographic boundary at around 2000 m during the last glacial maximum paleoceanography 3 1988 343 paleoceanography 7 1992 273 paleoceanography 13 4 1998 323 the deep hydrographic divide in the glacial pacific is similar to what is inferred in the atlantic quaternary research 18 1982 218 paleoceanography 3 1988 317 paleoceanography 3 1988 343 annual reviews of earth planetary sciences 20 1992 245 science 259 1993 1148 the indian nature 333 1988 651 paleoceanography 13 1998 20 and the southern ocean paleoceanography 11 1996 191 suggesting that this is a global phenomenon during the glacial time the upper water mass has a distinctly enriched 13 c compared to the deeper water mass whose possible origins are discussed

paleomagnetic field variability and chronostratigraphy of brunhes chron deep sea sediments from the bering sea iodp expedition 323 abstract iodp expedition 323 recovered six complete and replicate records of brunhes chron paleomagnetic field variability 0 780 000 years bp in 2820 m core depth below sea floor csf of deep sea sediments on shipboard we made more than 220 000 paleomagnetic measurements on the recovered sediments since then we have u channel sampled more than 300 m of brunhes chron sediments to corroborate our shipboard measurements and improve our paleomagnetic and rock magnetic understanding of these sediments several intervals of distinctive paleomagnetic secular variation psv have been identified that appear to be correlatable among sites 1343 1344 and 1345 one magnetic field excursion is recorded in sediments of sites 1339 1343 1344 and 1345 we identify this to be excursion 7 iceland basin event 192 000 years bp which is also seen in the high latitude north atlantic ocean channell et al 1997 we have verified in u channels the placement of the brunhes matuyama boundary 780 000 years bp at sites 1341 and 1343 finally we have developed a medium quality relative paleointensity record for these sediments that is correlatable among the sites even though it is still biased by large amplitude environmental variability on the basis of these observations we have built a magnetic chronostratigraphy of expedition 323 sediments suitable for regional correlation and dating over the last 1 million years and compared this with oxygen isotope chronostratigraphy from sites u1339 and u1345

diatom silicoflagellate and ebridian biostratigraphy and paleoceanography in iodp 323 hole u1343e at the bering slope site abstract integrated ocean drilling program iodp expedition 323 was dedicated to reconstruct the details of the pliocene pleistocene paleoenvironmental conditions of the bering sea in this study fossil diatom assemblages from hole u1343e were investigated to define diatom biostratigraphy and reveal paleoceanography of the bering slope region throughout pleistocene as the results four diatom zones with neogene north pacific diatom zone codes npd were determined from the neodenticula seminae zone npd 12 to the n koizumii zone npd 9 diatom biohorizons defined in this study closely correspond with onboard data but the distinct difference is recognized at the top of the n koizumii additional four biostratigraphic zones estimated by three silicoflagellate and one ebridian datums suggest the core sediment age younger than 2 5 ma the fluctuations of several paleoenvironmental diatom indicators show that cold conditions with sea ice existed throughout the duration of the interval studied as well as sea ice expansion occurred at ca 1 9 ma and ca 0 9 ma moreover increases of neritic diatom species reveal a drop in sea level neodenticula seminae is the diatom tracer of the aleutian current and hence the decrease of this taxon suggests decrease in inflow of the north pacific water mass although the sea levels must have been dropped during the cold time interval the consistent occurrences of n seminae indicate that the surface water circulation in the bering sea was significantly influenced by the alaskan stream at ca 1 9 ma on the other hand during the other cooling event at ca 0 9 ma which corresponds to the mid pleistocene transition mpt event an increase of neritic diatom species and decrease of n seminae were observed this suggests that coastal environmental conditions accompanied the sea level drop and that the inflow from the north pacific was weakened the increases of sea ice and neritic diatom species suggest that the sea ice and coastal conditions were developed after the cooling at 0 9 ma the ages at remarkable changes of silicoflagellate assemblages correspond to the ages of global climate shifts at ca 1 4 ma 1 25 ma and 0 8 0 9 ma the unusual alternate dominances of distephanus medianoctisol in glacial and dictyocha species in interglacial periods during the 1 25 0 8 ma interval suggest the north south migration of water masses between the bering sea and the subarctic north pacific

the dansgaard oeschger cycles discovered in the up stream source region of the north pacific intermediate water formation 1 millennial scale oceanographic oscillations were identified in the southern okhotsk sea based on high resolution measurements of total organic carbon toc c n ratios and biogenic opal employing core md01 2412 53 m with the bottom age of 115 ka the oscillations are linked with the dansgaard oeschger d o climatic cycles inadequate data existed in the source regions of the north pacific intermediate water npiw formation thus far we report the first decisive documentation of the d o cycles in the up stream source region of the npiw illustrating that the d o cycles observed in the down stream regions e g santa barbara basin due to expansion of the npiw were in part governed by the climatic variations occurred in the okhotsk sea increases in toc and c n ratios reflect abrupt sea level rises associated with 14 interstadial events over the past 115 kyrs attributing to the downward transport of eroded continental shelf sediments

sediment classification using neural networks an example from the site u1344a of iodp expedition 323 in the bering sea abstract a novel approach based on the concept of bayesian neural network bnn has been implemented for classifying sediment boundaries using downhole log data obtained during integrated ocean drilling program iodp expedition 323 in the bering sea slope region the bayesian framework in conjunction with markov chain monte carlo mcmc hybrid monte carlo hmc learning paradigm has been applied to constrain the lithology boundaries using density density porosity gamma ray sonic p wave velocity and electrical resistivity at the hole u1344a we have demonstrated the effectiveness of our supervised classification methodology by comparing our findings with a conventional neural network and a bayesian neural network optimized by scaled conjugate gradient method scg and tested the robustness of the algorithm in the presence of red noise in the data the bayesian results based on the hmc algorithm bnn hmc resolve detailed finer structures at certain depths in addition to main lithology such as silty clay diatom clayey silt and sandy silt our method also recovers the lithology information from a depth ranging between 615 and 655 m wireline log matched depth below sea floor of no core recovery zone our analyses demonstrate that the bnn based approach renders robust means for the classification of complex lithology successions at the hole u1344a which could be very useful for other studies and understanding the oceanic crustal inhomogeneity and structural discontinuities

bering sea radiolarian biostratigraphy and paleoceanography at iodp site u1341 during the last four million years abstract radiolarian assemblages in sediment cores were investigated at the integrated ocean drilling program site u1341 on bowers ridge in the southern bering sea radiolarian biozones at site u1341 spanned the last 4 my from the youngest amphimelissa setosa zone late quaternary via the stylatractus universes zone the eucyrtidium matuyamai zone and a part of the cycladophora sakaii zone middle to late pliocene the a setosa zone newly proposed in this paper is well correlated with the botryostrobus aquilonaris zone in the north pacific ocean the bottom of the s universus and top of the e matuyamai zones are emended in this paper by using the first common occurrence of a setosa seventeen radiolarian datum points were identified at site u1341 and tied to the geomagnetic and oxygen isotope stratigraphy radiolarian assemblages during the last 4 my showed a turnover from subarctic transitional species spongopyle osculosa and larcopyle buetschlii to subarctic species ceratospyris borealis between 3 6 and 2 4 ma corresponding to the intensification of the northern hemisphere glaciation nhg recent polar species a setosa and actinomma boreale appeared abundantly after the mid pleistocene transition mpt 1 2 0 8 ma repeated numbers of individual peaks of the abundances of cycladophora davisiana dwelling in cold and well ventilated intermediate water suggest intermediate to deep water formation in the bering sea during the last 1 my

repeated occurrences of methanogenic zones diagenetic dolomite formation and linked silicate alteration in southern bering sea sediments bowers ridge iodp exp 323 site u1341 abstract diagenetic precipitates such as dolomite and the chemistry of residual deeply buried porewater often represent the only traces of past biogeochemical activity in marine sediments a 600 m thick sedimentary section recently drilled at integrated ocean drilling program iodp site u1341 on bowers ridge southern bering sea provides insight into such a 4 3 ma old paleo diagenetic archive hard lithified calcite dolomite layers and laminae of disseminated carbonate were recovered in diatom rich sediments over a depth range of 400 m carbon isotope values of the diagenetic carbonates between 16 6 and 14 4 vpdb and strontium isotope ratios of dolomites close to past seawater values suggest carbonate precipitation induced by the production of dissolved inorganic carbon dic during elevated rates of organic carbon mineralization primarily via sulfate reduction at shallow sediment depth below the paleo seafloor diagenetic carbonates at 280 440 m below seafloor were likely also produced by the intermittent onset of sulfate reduction coupled to the anaerobic oxidation of methane aom at sulfate methane transition zones smtz these microbially mediated processes do not occur in the sediment at this site at present but were likely connected to the presence of a methanogenic zone at 2 58 2 51 ma a minimum in sulfate concentrations in modern porewaters and low sedimentary ba al ratios resulting from former sulfate depletion are reminiscent of the presence of this large methanogenic zone the minimum in sulfate concentrations is reflected in a minimum in magnesium concentrations less radiogenic strontium and isotopically light calcium in the porewater it is proposed that magnesium was removed from the porewater during carbonate precipitation and volcanic ash alteration which occurred in the former methanogenic zone and also released strontium with a less radiogenic isotope ratio and isotopically light calcium into the porewater the isotopic composition of porewater calcium was also influenced by ammonium calcium exchange on clay minerals and carbonate recrystallization our study elucidates the response of porewater element concentrations and isotopic profiles interlinked with the formation of diagenetic carbonates to changes in the deposition of organic carbon in sediments of deeper water sites 2000 m water depth over prolonged timescales it shows that variations in biogeochemical processes in response to changes in oceanographic conditions and a dynamic subseafloor biogeochemical zonation have to also be taken into account at these deep water sites for a global assessment of organic carbon burial fluxes and remineralization

tropical forcing of north pacific intermediate water distribution during late quaternary rapid climate change abstract evidence is presented demonstrating intermediate water 500 m temperature variability at odp hole 893a in santa barbara basin during submillennial climate change 11 60 ka benthic 18 o oscillations are considered to result primarily from shifts in intermediate water temperature at the site detailed comparison of both benthic and planktonic records from the basin provide crucial evidence for differing surface and intermediate water mass temporal responses to rapid climate change gradual warming of intermediate water compared to abrupt cooling suggests mechanistic differences between processes controlling north pacific intermediate water expansion and contraction relative to southern component intermediate waters comparisons suggest intermediate water warming preceded by 60 200 years the most rapid interval of surface warming inferred to be associated with north pacific atmospheric reorganization tropical forcing of sea level anomalies in the eastern pacific via trade wind strength may control california undercurrent flow 300 500 m and be the cause of early intermediate water warming in santa barbara basin

pleistocene deep sea ostracods from the bering sea iodp expedition 323 abstract the study presents the first pleistocene 0 1 9 ma record of deep sea ostracods from the bering sea derived primarily from integrated ocean drilling program expedition 323 site u1344 59 3 0 n 179 12 2 w 3171 m of water depth deep sea ostracod abundances in the bering sea sediments are some of the lowest that have been recorded in bathyal and abyssal marine environments

surface nitrate utilization in the bering sea since 180 ka bp insight from sedimentary nitrogen isotopes we present high resolution records of sedimentary nitrogen 15nbulk and carbon isotope ratios 13cbulk from piston core so201 2 85kl located in the western bering sea the records reflect changes in surface nitrate utilization and terrestrial organic matter contribution in submillennial resolution that span the last 180 kyr the 15nbulk record is characterized by a minimum during the penultimate interglacial indicating low nitrate utilization 62 80 despite the relatively high export production inferred from opal concentrations along with a significant reduction in the terrestrial organic matter fraction mterr this suggests that the consumption of the nitrate pool at our site was incomplete and even more reduced than today 84 15nbulk increases from marine isotope stage mis 5 4 and culminates during the last glacial maximum which indicates that nitrate utilization in the bering sea was raised during cold intervals mis 5 4 5 2 4 and almost complete during mis 3 and 2 93 100 this is in agreement with previous hypotheses suggesting that stronger glacial stratification reduced the nutrient supply from the subeuphotic zone thereby increasing the iron to nutrient ratio and therefore the nitrate utilization in the mixed surface layer large variations in 15nbulk were also recorded from 180 to 130 ka bp mis 6 indicating a potential link to insolation and sea level forcing and its related feedbacks millennial scale oscillations were observed in 15nbulk and 13cbulk that might be related to greenland interstadials

surface ocean cooling in the subarctic north pacific during the late pliocene suggests an atmospheric reorganization prior to extensive northern hemisphere glaciation abstract this paper presents records of tex 86 l and u 37 k derived sea surface temperatures ssts from ocean drilling program site 882 in the subarctic north pacific over the last 5 8 million years the tex 86 l derived sst record shows a cooling trend from 17 c at 3 6 ma to 8 c at 2 3 ma this cooling preceded the onset of extensive northern hemisphere glaciation nhg at 2 7 ma coinciding with the intensification of the east asian winter monsoon surface cooling in the north atlantic and the gradual development of nhg the results of this study suggest that the reorganization of atmospheric circulations in the northern high latitudes from 3 6 to 2 3 ma was associated with the early stage development of the ice sheets and sea ice in the arctic and subarctic regions inducing the cooling of the north atlantic and the subarctic north pacific and the intensification of the east asian winter monsoon

stable isotope and lithologic evidence of late glacial and holocene oceanography of the northwestern pacific and its marginal seas abstract stable isotopes geochemical lithological and micropaleontological results from cores from the far northwest fnw pacific and the okhotsk and bering seas are used to reconstruct the regional environment for the last glaciation the deglacial transition and the holocene 18 o records of planktonic foraminifera of the region show two light shifts during deglacial time provoked by the freshening of the surface water and climate warming these north pacific terminal events t1anp and t1bnp with ages of 12 500 and 9300 yr b p respectively occur almost simultaneously with two episodes of accelerated glacier melting around the north atlantic along with the isotopic shifts the caco 3 content in regional sediments increased abruptly 1a and 1b carbonate peaks probably due to changes of productivity and pore water chemistry of surface sediments organic matter and opal concentration increased during the transition between t1anp and t1bnp events in the sediments of the fnw pacific and the southern part of the bering sea and opal content increased in the holocene in the bering and okhotsk seas 13 c records of cores from the okhotsk and bering seas and the fnw pacific do not contradict the hypothesis of increased intermediate water formation in the region during glaciation during deglaciation accumulation of the coarse terrigenous component decreased in sediments of the bering sea and the fnw pacific before the t1anp event probably as a result of rising sea level and opening of the bering strait

the deglacial history of surface and intermediate water of the bering sea the lithology of deglacial sediments from the bering sea includes intervals of laminated or dysaerobic sediments these intervals are contemporaneous with the occurrence of laminated sediments from the california margin and gulf of california which suggests widespread low oxygen conditions at intermediate depths in the north pacific ocean the cause could be reduced intermediate water ventilation increased organic carbon flux or a combination of the two we infer abrupt decreases of planktonic foraminifer d 18 o at 14 400 and 11 650 yr bp which may be a combination of both freshening and warming on the shirshov ridge the abundance of sea ice diatoms of the genus nitzschia reach local maxima twice during the deglaciation the latter of which may be an expression of the younger dryas these findings expand the extent of the expression of deglacial millennial scale climate events to include the northernmost pacific r 2005 elsevier ltd all rights reserved