the micrometeorite flux to earth during the frasnian famennian transition reconstructed in the coumiac gssp section france abstract we have reconstructed the distribution of extraterrestrial chrome spinels in a marine limestone section across the frasnian famennian stratotype section at coumiac in southern france providing the first insights on the types of micrometeorites and meteorites that fell on earth at this time the data can test whether the small cluster of roughly coeval large impact structures is related to an asteroid breakup and shower with possible bearings also on the late devonian biodiversity crisis a total of 180 extraterrestrial spinel grains 32 m were recovered from 957 kg of rock noble gas measurements of individual grains show high solar wind content implying an origin from decomposed micrometeorites element analyses indicate a marked dominance of ordinary chondritic over achondritic grains similar to the recent flux the relation between h l and ll meteorites is 29 58 13 similar to the late silurian flux 31 63 6 but different from the distribution 45 45 10 in the recent and the cretaceous flux our data show no indication of a generally enhanced late devonian micrometeorite flux that would accompany an asteroid shower however in a single limestone bed that formed immediately before the upper kellwasser horizon that represents the main end frasnian species turnover event we found an enrichment of 10 ordinary chondritic grains 63 m per 100 kg of rock compared to the 1 3 grains per 100 kg that characterise background the anomalously abundant grains are of mixed h l and ll types and may be related to an enhanced flux of extraterrestrial dust during postulated minima in both the 405 ka and 2 4 ma earth orbit eccentricity cycles at the onset of the upper kellwasser event in the present solar system the dust accretion at earth is the highest at eccentricity minima because of the spatial distribution of dust bands of the zodiacal cloud besides this small grain anomaly the data here and in previous studies support a stable meteorite flux through the late silurian and devonian in contrast to the mid ordovician when achondritic meteorites that are rare on earth today were common followed by the influx of a flood of debris related to the breakup of the l chondrite parent body our accumulated data for six time windows through the phanerozoic indicate that the ordinary chondrites make up a major fraction in the meteorite flux since at least the mid ordovician we note that the sources in the asteroid belt of the h and l meteorites the two most common types of meteorites today and through much of the phanerozoic remain elusive

the bering and okhotsk seas modern and past paleoceanographic changes and gateway impact abstract the high biological productivity and an efficient biological pumping in the subarctic pacific and adjacent seas make this region important to the modern carbon cycle and both modern and the past climate of the earth knowledge of the northern marginal seas of the pacific however is unsubstantial the bering sea is located between the pacific ocean and the arctic sea and plays an important role in ocean circulation involving balances of heat salt and various chemical properties thus it is necessary to unravel the geologic history of the bering sea as a gateway to the pacific and the arctic atlantic during the last 5 million years and beyond the okhotsk sea is considered a locus of north pacific intermediate water formation today the intermediate water formation is linked with seasonal sea ice cover diatom records from the okhotsk sea demonstrate that sea ice cover was distributed on the western side of the sea and the eastern part was open water during the last glacial maximum this configuration permitted a better ventilation of the glacial okhotsk sea through increased quantity of intermediate water presumably formed there at that time

last glacial holocene water structure in the southwestern okhotsk sea inferred from radiolarian assemblages abstract in order to reconstruct paleoceanographic conditions in the southwestern sw okhotsk sea radiolarian assemblages were analyzed from 10 surface sediments and 5 sediment cores obtained from various water depths ranging between 461 and 1348 m we also measured geochemical components such as biogenic opal calcium carbonate total organic carbon total sulfur and total nitrogen for one sediment core these data imply that the complicated water structure in the sw okhotsk sea changed with time from the last glacial to holocene the glacial surface water was characterized by low primary production in the summer and expanded sea ice coverage in the winter during this time the ventilation might have reached deeper than during the holocene during the major deglacial period including the melt water pulses 1a and 1b the deep sea oxygen content had declined with less ventilation and or more oxygen consumption with organic matter supply into the deeper depths the intermediate layer has been well ventilated and has supplied large amount of organic matter during the last 20 kyrs especially in the early mid holocene however such condition ceased during 3 to 2 ka the warm pacific deep water has been present since 9 ka the influence of warmer surface water such as the soya warm current swc increased in the coastal area during 7 to 4 ka and since 2 ka till present neritic derived productivity might be extended at 2 2 1 8 ka and since 1 2 ka till present

origin and evolution of cycladophora davisiana ehrenberg radiolaria in dsdp site 192 northwest pacific this paper documents the evolutionary history of cycladophora davisiana ehrenberg from an uppermost miocene to pleistocene sedimentary record in the high latitude northwest pacific it apparently evolved from c sakaii motoyama through a series of intermediates c sakaii has a relatively large shell with an external spongy layer the evolutionary transition is characterized by a relatively rapid decrease in thorax size with a reduction of the spongy appendage this change occurred during about 0 4 m y from 2 8 to 2 4 ma without cladogenesis following this interval a decrease in thorax size continued gradually up to the recent resulting in a very small morphology although the population of c davisiana first appeared at about 2 5 ma some morphotypic specimens may occur in earlier periods as indistinguishable very small endmembers in the c sakaii populations timing of the first appearance events both of morphotypic specimens and of a population of c davisiana in site 192 and previously reported cores does not disprove the idea that c davisiana evolved first in the northwest pacific region and later migrated into other regions of the world ocean biometrics clearly indicate no direct phylogenetic relationships between c davisiana and c cornutoides kling in the studied core thus the latter species which was originally described as a variation and later elevated to a subspecies of the former species is separated from the former species and raised to the species rank

the progressive intensification of northern hemisphere glaciation as seen from the north pacific ocean drilling project odp site 882 50 22 n 167 36 e provides the first high resolution grape density magnetic susceptibility carbonate opal and foraminifera planktonic and benthic stable isotopes records between 3 2 and 2 4 ma in the northwest pacific we observed a dramatic increase in ice rafting debris at site 882 at 2 75 ma which is coeval with that found in the norwegian sea suggesting that the eurasian arctic and northeast asia were significantly glaciated from 2 75 ma onwards prior to 2 75 ma planktonic foraminifera 18o records indicate a warming or freshening trend of 4 c or 2 over 80 ka if this is interpreted as a warm pre glacial pliocene north pacific it may have provided the additional moisture required to initially build up the northern hemisphere continental ice sheet the dramatic drop in sea surface temperatures sst 7 5 c at 2 75 ma ended this suggested period of enhanced sst and thus the proposed moisture pump moreover at 2 79 and 2 73 ma opal mass accumulation rates mar decrease in two steps by five fold and is accompanied by a more gradual long term decrease in caco3 mars evidence from the southern ocean odp site 704 indicates that just prior to 2 6 ma there is a massive increase in opal mars the opposite to what is found in the north pacific this indicates that the intensification of northern hemisphere glaciation was accompanied by a major reorganisation of global oceanic chemical budget possibly caused by changes in deep ocean circulation the initiation of northern hemisphere glaciation occurred in the late miocene with a significant build up of ice on southern greenland however the progressive intensification did not occur until 3 5 3 ma when the greenland ice sheet expanded to include northern greenland following this stage we suggest that the eurasian arctic and northeast asia glaciated at 2 75 ma approximately 100 ka before the glaciation of alaska 2 65 ma and 200 ka before the glaciation of the north east american continent 2 54 ma

noble gas isotopes and mineral assemblages of antarctic micrometeorites collected at the meteorite ice field around the yamato mountains from november 1998 to january 1999 the 39th japanese antarctic research expedition jare conducted a large scale micrometeorite collection at 3 areas in the meteorite ice field around the yamato mountains antarctica the antarctic micrometeorites amms collected were ancient cosmic dust particles this is in contrast with the dome fuji amms which were collected previously from fresh snows in 1996 and 1997 and which represent modern micrometeorites to determine the noble gas concentrations and isotopic compositions of individual amms noble gas analyses were carried out using laser gas extraction for 35 unmelted yamato mountains amms and 3 cosmic spherules x ray diffraction analyses were performed on 13 amms before the noble gas measurement and mineral compositions were determined amms are classified into 4 main mineralogical groups defined from the heating they suffered during atmospheric entry heating temperatures of amms inferred from their mineral compositions are correlated with 4he concentrations and reflect the effect of degassing during atmospheric entry jarosite an aqueous alteration product is detected for 4 amms indicating the aqueous alteration during long time storage in antarctic ice jarosite bearing amms have relatively low concentrations of 4he which is suggestive of loss during the alteration high 3he 4he ratios are detected for amms with high 20ne 4he ratios showing both cosmogenic 3he and preferential he loss sep solar energetic particles he and ne rather than the solar wind sw were dominant in amms presumably showing a preferential removal of the more shallowly implanted sw by atmospheric entry heating the mean 20ne 22ne ratio is 11 27 0 35 which is close to the sep value of 11 2 cosmogenic 21ne is not detected in any of the particles which is probably due to the short cosmic ray exposure ages ar isotopic compositions are explained by 3 component mixing of air q and sep ar ar isotopic compositions can not be explained without significant contributions of q ar sep ne contributed more than 99 of the total ne as for 36ar and 38ar the abundance of the q component is comparable to that of the sep component 84kr and 132xe are dominated by the primordial component and solar derived xe is almost negligible

the production scheme of cycladophora davisiana radiolaria in the okhotsk sea and the northwestern north pacific implication for the paleoceanographic conditions during the glacials in the high latitude oceans 1 the sediment trap study clearly unraveled that the distinct peaks of c davisiana fluxes occurred during summer to autumn in both the okhotsk sea and the northwestern north pacific the production of c davisiana is closely related to the microbial production in the intermediate water in the okhotsk sea the distinct microbial biomass in the intermediate water which is associated with the seasonal sea ice rejected brine water during winter may support the high c davisiana abundance therefore the significantly high c davisiana abundance during the last glacial maximum lgm in the high latitude open oceans implies the distinct microbial biomass in the intermediate water caused by the seasonal sea ice coverage analogous to the present okhotsk sea

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

diatom evidence on wisconsin and holocene events in the bering sea abstract previous work on surface modern sediments has defined diatom species which appear to be good indicators of various oceanographic ecologic conditions in the north pacific ocean and marginal seas three long cores from the eastern and northern sides of the aleutian basin show changes in species assemblage which can be interpreted in terms of changes in the ocean environment during the last glaciation wisconsin and the holocene the early and late wisconsin maxima were times of prolonged annual sea ice cover and a short cool period of phytoplankton productivity during the ice free season the middle wisconsin interstade at least in the southern bering sea had greater seasonal contrast than today with some winter sea ice cover an intensified temperature minimum and high spring productivity variations in clastic and reworked fossil material imply varying degrees of transport to the basin by alaskan rivers the results of jouse from the central bering sea generally correspond with those presented here although there are problems with direct comparison

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

polycystine radiolarians in surface sediments from the bering sea green belt area and their ecological implication for paleoenvironmental reconstructions radiolarians in surface sediments along transects from the shelf edge along the slope into the deep basin of the northern bering sea are dominated by stylochlamydium venustum antarctissa sp 1 the spongodiscidae juvenile pseudodictyophimus gracilipes ceratospyris borealis the plagoniidae phormacantha group and plectacantha group siphocampe arachnea cycladophora davisiana and spongotrochus glacialis this dominance is most extreme on the shelf edge and slope where s venustum antarctissa sp 1 the spongodiscidae juvenile the plagoniidae and s glacialis have their highest relative abundance there is thus a close relation between radiolarian distribution and the high productivity of the bering sea green belt bsgb due to periodic sea ice melt the radiolarian depth distribution patterns indicate that some radiolarian species have specific ecological preferences s venustum the spongodiscidae juvenile and s glacialis live close to the surface water under relatively low temperature and low salinity conditions due to sea ice melting or melt water influx antarctissa sp 1 appears to dwell mainly in surface to subsurface waters but has not been recorded in trap samples of the bering sea the plagoniidae probably live in subsurface and intermediate waters s arachnea and c davisiana are intermediate to deep dwellers the close association of these radiolarians with the bsgb and specific water depths provides a valuable reference for paleoenvironmental reconstruction in the region

dating the earliest lowland glaciation of eastern england a pre mis 12 early middle pleistocene happisburgh glaciation this paper outlines the evidence for the happisburgh glaciation the first middle pleistocene glaciation of lowland eastern england and the adjacent margins of the north sea basin we propose that this glaciation occurred during a pre elsterian anglian mis 12 cold stage based on evidence of clasts of till erratics and heavy minerals from the third youngest terrace of the pre glacial bytham river in southern norfolk the heavy minerals show a progressive increase in glacially sourced materials from the bottom to the top of the bytham river third terrace sediments the till clasts are correlated with the extensive deposits of the happisburgh formation on the basis of their colour heavy minerals and particle size properties thus the happisburgh glaciation occurred during the accumulation of the bytham river terrace deposits and prior to mis 12 when the bytham river system was destroyed by the anglian glaciation in the absence of any geochronology or robust biostratigraphy the age of the happisburgh glaciation is estimated by the synchronisation of the pattern of large scale river activity with patterns of milankovitch forced global climate change on this basis and assuming the british ice sheet acted in phase with global patterns of ice volume the happisburgh glaciation is considered to have occurred during mis 16 and be equivalent of the don glaciation of eastern europe

radiolarian faunal provinces in surface sediments of the greenland iceland and norwegian gin seas the overall abundance and species composition of the polycystine and phaeodarian radiolaria have been determined in 63 surface sediment samples from the gin seas these results are compared to chemical and physical properties of the overlying water masses there are three abundance maxima in the distribution of radiolarian skeletal debris preserved in these surface sediments centered on the iceland plateau southern norwegian basin and northern norwegian basin the most commonly encountered species were a spumellarida actinomma boreale a leptoderma larcospira minor and phorticium clevei b nassellarida amphimelissa setosa artobotrys boreale lithomelissa setosa lithocampe platycephala pseudodictyophimus gracilipes cycladophora davisiana a ndlithomitra lineata based on factor analysis of the core top assemblages the radiolarian species were grouped into three associations factor 1 a polar and arctic water association dominated by amphimelissa setosa varimax factor score 5 269 high factor component values are found in the iceland plateau area and in a wedge just north of the iceland faeroe ridge factor 2 an atlantic water association dominated by pseudodictyophimus gracilipes 3 247 lithomelissa setosa 2 731 and actinomma boreale 1 851 high factor component values are found in the eastern part of the norwegian sea particularly in the area under the influence of the norwegian current and factor 3 an atlantic and arctic water mixed association dominated by lithocampe platycephala 3 251 lithomelissa setosa 2 176 actinomma leptoderma 1 994 and artobotrys boreale 1 504 high factor component values are found immediately to the east of the iceland plateau in correspondence to the deepest part of the norwegian basin the correlation coefficients obtained between seasonal sea surface temperature and factors 1 r 2 d 0 835 a nd 2 r 2 d 0 891 show a good fit whilst for factor 3 there was a less marked r 2 d 0 497 but still significant at the 5 confidence level correlation for fifth degree polynomial regression functions the factors correlated better with the summer than the winter sea surface temperatures however at 20 50 100 and 200 m depth the correlation became increasingly better particularly so for the winter situation the highest species richness for polycystine radiolarians 28 species was found in the warm atlantic domain the lowest 24 species was found in the colder arctic and polar domains whilst an area approximating the position of the arctic front had between 24 and 28 species 1998 elsevier science b v all rights reserved

late pleistocene stratigraphy and palaeoceanographic implications in northern bering sea slope sediments evidence from the radiolarian speciescycladophora davisiana a high resolution abundance curve of the radiolarian species cycladophora davisiana was obtained from a late pleistocene sediment core pc 23a which was obtained from the northern slope of the bering sea the abundance pattern of this species was high during the glacial period and low during the holocene this general stratigraphic pattern was correlated with a previously reported pattern for the subarctic pacific ocean however planktonic foraminifera based accelerator mass spectrometry 14c dating revealed that a significant peak in the c davisiana curve during the glacial period correlates to 15 5 ka which is younger than that previously estimated as being the last glacial maximum the higher abundance of this species implies that there was well ventilated water with a large amount of organic matter in the intermediate water layer an unusually high propagation of c davisiana during the earliest holocene period bolling allerod b a and dansgaad oescheger interstadial event 12 was most likely related to a significant increase in the amount of organic matter released into the intermediate water depths by a brine pump system via ventilation in addition centennial scale variations in the abundance of c davisiana during the b a period suggest that the intermediate water ventilation was sensitively affected by brine rejection during sea ice formation as well as large scale atmospheric circulations such as the arctic oscillation copyright 2009 john wiley sons ltd

numbers types and compositions of an unbiased collection of cosmic spherules abstract abstract micrometeorites collected from the bottom of the south pole water well spww may represent a complete well preserved sample of the cosmic dust that accreted on earth from 1100 1500 a d we classified 1588 cosmic spherules in the size range 50 800 pm the collection has 41 barred olivine spherules 17 glass spheres 12 cryptocrystalline spherules 11 porphyritic olivine spherules 12 relic grain bearing spherules 3 scoriaceous spherules 2 i type spherules 1 ca al ti rich cat spherules and 1 g type spherules we also found bubbly glass spherules spherules with glass caps and ones with sulfide coatings particles that are absent from other collections a classification sequence of the stony spherules scoriaceous relic grain bearing porphyritic barred olivine cryptocrystalline glass and cat is consistent with progressive heating and evaporation of fe from chondritic materials the modem day accretion rate and size distribution measured at the spww can account for the stony spherules present in deep sea collection through preferential dissolution of glass and small stony spherules however weathering alone cannot account for the high accretion rate of i type spherules determined for two deep sea collections the spww collection provides data to constrain models of atmospheric entry heating and to assess the effects of terrestrial weathering

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

the evolution of pleistocene climate a time series approach abstract in the later part of the pleistocene variations in global ice volume have been dominated by an approximate 100 000 year cycle analysis of 2 myr long oxygen isotope record from an equatorial pacific core indicates that this is true only for the last 900 000 years prior to this time the amplitude of the 100 000 year cycle is much reduced as is the variance of all oscillations with periods greater than 60 000 years based on results of time series analysis of this 2 myr long record the pleistocene glacial cycles can be divided into three sections 1 the late pleistocene 0 900 kyr b p where the variations in the isotope record are dominated by the 100 000 year cycle 2 the middle pleistocene 900 1450 kyr b p in which low frequency components are not as important as in the later period of the pleistocene and 3 the early pleistocene late pliocene 1450 2000 kyr b p where general reductions of importance at all frequencies is seen as compared to the later intervals recent modeling efforts which describe variations in global ice volume show that the dominant low frequency component observed in the late pleistocene can result from different time constants for the rate of glacial growth and decay in response to variations in the earth s orbital parameters it is hypothesized that during the early pleistocene the rate of growth and decay of glaciers were more similar and that continental erosion by successive glacial advances lowered the land surface in areas of ice cap formation to below sea level when the ice caps became marine based more rapid decay of the ice became possible

measurement of53mn in deep sea iron and stony spherules abstract cosmic ray produced 53 mn t 1 2 3 7 10 6 years was measured in individual and groups of deep sea iron and stony spherules by highly sensitive neutron activation analysis the activities found were less than 20 dpm 53 mn kg fe 10 5 10 6 dpm 53 mn sample in iron spherules except one iron spherule whose activity was 241 73 dpm 53 mn kg fe these low activities may indicate evaporative loss of 53 mn due to heating in the earth s atmosphere on the other hand all stony spherules contained 200 260 dpm 53 mn kg fe which is similar to chondritic values these spherules may be ablation debris from large objects

orbital and suborbital environmental changes in the southern bering sea during the last 50 kyr abstract high resolution geochemical paleontological and lithological records of two sediment cores in the southern bering sea manifest regional environmental changes over the last 50 kyr on orbital and millennial time scales high ice rafted debris ird content and percentages of radiolarian species cycladophora davisiana ehrenberg during marine isotope stages miss 3 and 2 indicate active intermediate water ventilation driven by intensive winter sea ice formation in the southern bering sea although the total abundance of siliceous microfossils in glacial sediments is relatively low glacial productivity is higher than in the late holocene on the millennial time scale decreases in the abundance of calcareous and siliceous microfossils and in c davisiana at studied core may imply enhancement of sea ice influence synchronous with heinrich events h 5 to 2 changes in the 18o of fossil benthic and planktonic foraminifera during h 5 3 are inferred to be related to variability in ice sheet volume similar to the pattern from antarctica accompanied by glacioeustatic sea level fluctuations up to 20 30 m in amplitude the maximum benthic and planktonic 18o values in the studied cores occur during the lgm when sea level was at the lowest stand and sea bottom water temperature was around 0 4 c strong environmental changes during the heinrich event 1 and b a warming in the southern bering sea provide evidence of deglacial injection of very old water and the subsequent increase in productivity due to surface and intermediate water mixing from the lgm to the mid holocene the 18obenth foram changes corresponded to changes in the global deep water 18o and a rise in the deep water temperature to 1 0 c at 8 5 6 5 kyr bp the subsequent environmental changes in late holocene helped establishment of near modern day hydrological and environmental conditions featuring strong surface water stratification and weakened deep water ventilation

orbital and millennium scale environmental changes in the southern bering sea during the last glacial holocene geochemical and paleontological evidence the d 18 o benthic foraminiferal curve and ams 14 c radiocarbon data provide a representative age model for a southern bering sea sediment core gc 11 downcore profiles of d 18 oo fn pachyderma s and u auberiana carbonate and organic carbon contents species changes in the planktonic foraminifera assemblages and some diatom species show orbital mis 1 2 and 3 and millennium scale variability influenced by the alaska current flowing into the studied region three warmer episodes in the southern bering sea environment were assumed to be synchronous with do interstadials 8 12 and 14 in gisp 2 chronology during mis 3 more severe climate and environmental conditions in the southern bering sea during mis 2 occurred synchronously with the lgm within a 17 19 ka time span two well pronounced environmental warming events productivity spikes and changes in the pore water geochemistry separated by younger dryas cooling were observed at the base of mis 1 coeval with mwp 1a and 1b regional glacial primary productivity based on the calculation of the organic carbon mar similar to that found in the far northwestern pacific exceeded the late holocene values under conditions close to the present day r 2005 elsevier ltd all rights reserved

middle pliocene sea surface temperatures a global reconstruction identification and analyses of pliocene marine microfossils from 64 globally distributed stratigraphic sequences have been used to produce a middle pliocene sea surface temperature reconstruction of the earth this reconstruction shows little or no change from current conditions in low latitude regions and significant warming of the ocean surface at mid and higher latitudes of both hemispheres this pattern of warming is consistent with terrestrial records and suggests a combination of enhanced meridional ocean heat transport and enhanced greenhouse effect were responsible for the middle pliocene warmth

middle to late holocene changes of the okhotsk sea intermediate water and their relation to atmospheric circulation 1 high abundance of the radiolarian cycladophora davisiana in the sea of okhotsk has been observed at the okhotsk sea intermediate water osiw this water is formed by brine rejection in the polynya and is characterized by cold oxygenated conditions with high a microbial content the c davisiana abundance recorded in three sediment cores from the southwestern part of the sea implies ventilation changes of the osiw during the last 7 5 kyrs the ventilation had significantly increased during the interval from 7 5 to 3 5 ka corresponding to a warm period but declined during 3 to 2 ka and at 0 3 0 4 ka coincident with cold periods such as the neoglaciation and little ice age respectively the declined ventilation might be caused by reduction of the polynyas with the wind vector change from a northerly to an easterly direction relating to the southward shift of the aleutian low during the strong winter

effects of late neogene climatic cooling on north pacific radiolarian assemblages and oceanographic conditions abstract radiolarian census and abundance data were collected from three deep sea cores drilled by the ocean drilling program sites 884 887 and 1151 to investigate patterns of ecologic changes in space and time during the last 16 million years for the mid latitude to subarctic north pacific high concentrations of radiolarians occurred between 9 0 and 2 7 ma radiolarian species richness was highest in the early middle miocene at each site and gradually decreased up to about 7 ma coinciding with a well established global cooling trend a degree of overlap index calculated for radiolarian assemblages revealed 11 faunal change events of which 8 corresponded to global cooling events and expansions of polar ice sheets three of the faunal change events were observed within the peak of radiolarian accumulation rate and were ascribed to changes in primary productivity in the north pacific rather than global climatic changes our assemblage analyses revealed that north south differentiation in radiolarian assemblages in the northwestern pacific has existed since 16 ma and became more distinct via major steps at 6 8 ma and 2 7 ma coinciding with major glaciation events and that east west faunal contrasts in the subarctic region became obvious beginning at 11 7 ma and changed to a different mode around 6 8 ma the observed east west faunal differences possibly reflect east to west climate differences that were characterized by cooler temperatures in the east than the west during the late miocene 11 7 6 8 ma and then by the opposite temperature trend 6 8 ma recent a severe glaciation at 2 7 ma played a large role particularly in temporal changes in radiolarian accumulation rate and assemblage composition

late pliocene monsoon linkage in the tropical south china sea the onset of northern hemisphere glaciation nhg 2 7 ma ago coincided with prominent climate changes in the tropical regions such as the african and the asian monsoons however the relationship between tropical and sub tropical monsoonal variations and high northern latitude ice sheet expansion as well as processes such as late pliocene tropical sea surface temperature sst change is not clear our late pliocene 2 5 3 3 ma monsoon proxy records and mg ca derived sst records at ocean drilling program odp site 1143 from the southern south china sea scs reveal that while tropical sst shows a stepwise decrease of 2 3 c during this period the east asian monsoon gradually strengthens in response to the onset of the nhg at the 41 kyr and 23 kyr bands ice volume change lags tropical sst by 4 kyr but leads the east asian monsoon by 12 17 kyr our finding highlights the significant role of the tropical pacific region in driving global climate change in the late pliocene which has invariable leading phase relative to the ice volume change as in the late pleistocene however the east asian monsoon shows a linear response to the onset of the nhg in the late pliocene with much bigger phase lagged at the 41 kyr and 23 kyr bands than in the pleistocene which suggests that at the obliquity and precession bands the phases of the plio pleistocene east asian monsoon variations relative to the global ice volume changes are not constant but variable therefore the east asian monsoons are not only simply driven by northern summer insolation at the precession period but also modulated by global ice volume change in high latitudes

last glacial holocene change in intermediate water ventilation in the northwestern pacific abstract the modern north pacific is the terminus for deep water circulation while no deep water mass is formed today the region is the source of north pacific intermediate water 300 800 m formed primarily in the sea of okhotsk however the source and strength of intermediate water in the glacial north pacific was likely different from the present intermediate water here we present microfossil evidence of late quaternary ventilation changes associated with changes in intermediate water intermediate water ventilation decreased drastically at the glacial termination when it switched to the modern circulation system the ventilation change appears to have been widespread and synchronous in the north pacific glacial microfossil assemblages indicate that there was relatively strong ventilation of intermediate water which seems to have been cold and well oxygenated as if produced by brine rejection during the formation of sea ice on the basis of the glacial distribution of microfossils in the north pacific we suggest that intermediate water was derived from the bering sea during the glacials rather than the sea of okhotsk

the mid pleistocene climate transition onset of 100 ka cycle lags ice volume build up by 280 ka the mid pleistocene climate transition mpt is the complex climatic change which brought the late pleistocene ice ages we explore the mpt in the time and frequency domains by new methods of time series analysis high resolution oxygen isotope records reveal that the ice volume related increase in 18o mean amplitude 0 29 0 05 1 transition midpoint 922 12 ka duration 40 9 ka significantly preceded the abrupt increase in the amplitude of the 100 ka cycle at 641 9 ka this finding can be quantitatively simulated using a simple ice bedrock model in which due to the additional ice the calving threshold is exceeded the simulated calving events prior to 650 ka are separated by 77 ka whereas after 650 ka they occur pseudo periodically with a mean period of nearly 100 ka the cause for the delay of the 100 ka calving cycle was not a slow bedrock relaxation rather the coincidental combination of insolation existing ice mass and bedrock depression

neon measurements of individual greenland sediment particles proof of an extraterrestrial origin and comparison with edx and morphological analyses abstract the work reported here confirms the existence of largely unmelted micrometeorites in sediments from seasonal lakes on the greenland ice sheet approximately1 3 of the dark and irregularly shaped particles selected from disaggregated sediments had sufficient contents of ne to permit measurement of isotopic compositions the sediments consisted of a mixture of biologically derived contaminants and minor amounts of terrestrial minerals and extraterrestrial fragments although terrestrial mineral contamination varied by a factor of 20 for the two different sediments a yield of 1000 cosmic particles kg of wet cryoconite was found for both samples the isotopic compositions of the ne in both rounded and irregular 25 of total particles that contained enough gas to measure were non terrestrial plotting in a field defined by solar wind sw solar energetic particle sep and spallation exposure ages ranged from

interior textures chemical compositions and noble gas signatures of antarctic cosmic spherules possible sources of spherules with long exposure ages abstract the interior texture and chemical and noble gas composition of 99 cosmic spherules collected from the meteorite ice field around the yamato mountains in antarctica were investigated their textures were used to classify the spherules into six different types reflecting the degree of heating 13 were cryptocrystalline 40 were barred olivine 3 were porphyritic a 24 were porphyritic b 9 were porphyritic c and 10 were partially melted spherules while a correlation exists between the type of spherule and its noble gas content there is no significant correlation between its chemical composition and noble gas content fifteen of the spherules still had detectable amounts of extraterrestrial he and the majority of them had 3he 4he ratios that were close to that of solar wind sw the ne isotopic composition of 28 of the spherules clustered between implantation fractionated sw and air extraterrestrial ar confirmed to be present because it had a 40ar 36ar ratio lower than that of terrestrial atmosphere was found in 35 of the spherules an enigmatic spherule labeled m240410 had an extremely high concentration of cosmogenic nuclides assuming 4 exposure to galactic and solar cosmic rays as a micrometeoroid and no exposure on the parent body the cosmic ray exposure cre age of 393 myr could be computed using cosmogenic 21ne under these model assumptions the inferred age suggests that the particle might have been an edgeworth kuiper belt object alternatively if exposure near the surface of its parent body was dominant the cre age of 382 myr can be estimated from the cosmogenic 38ar using the production rate of the 2 exposure geometry and implies that the particle may have originated in the mature regolith of an asteroid

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

glacial age hydrography of the far northwest pacific ocean stable isotope data on benthic foraminifera from more than 30 cores on the northern emperor seamounts and in the okhotsk sea are synthesized in paleohydrographic profiles spanning the depth range 1000 4000 m holocene core top benthic foraminiferal 18o and 13c data are calibrated to modern hydrographic properties through measurements of 13c of co2 and 18o of seawater cibicidoides stable isotope ratios are close to the 13c and equilibrium 18o of seawater whereas uvigerina 18o and 13c are variably offset from cibicidoides glacial maximum 13c of cibicidoides displays a different vertical profile than that of the holocene when results are adjusted by 0 32 to account for the secular change in 13c during the last glacial maximum the data coincide with the modern seawater and foraminiferal curves deeper than 2 km however at shallower depths 13c gradually increases by as much as 1 above the modern value furthermore above 2 km the benthic 18o decreases by 0 5 these results are consistent with a benthic front at 2 km in the north pacific see herguera et al 1992 but they differ from interpretations based on trace metal data which indicate a source of nutrient depleted deep water during glaciation the isotopic data suggest that during glaciation there was a better ventilated watermass at intermediate depths in the far northwestern pacific it was relatively fresher than deep waters there and deep waters were as nutrient rich as today

early to middle pleistocene paleoceanographic history of southern japan based on radiolarian data from iodp exp 314 315 sites c0001 and c0002 abstract during the mid pleistocene transition mpt spanning from 0 8 to 1 2 ma the prevailing 41 kyr glacial cycles were replaced by longer cycles with a period of ca 100 kyr this event was also accompanied by important climate changes such as the expansion of the northern hemisphere ice sheet the impact of the mpt on the kuroshio current off southern japan remains unknown however in the absence of a long core covering the period of the mpt in this area preservation of calcareous microfossils is poor but polycystine radiolarians are abundant and well preserved therefore they are an excellent alternative proxy for reconstructing past climate change indeed because numerous studies have examined the geographic distribution of modern radiolarian species the relationships between several radiolarian assemblage groups e g equatorial to sub arctic assemblage groups and climatic conditions are well understood we examined the impact of the mpt on the kuroshio current off the kii peninsula southern japan by investigating radiolarian assemblages in deep sea cores collected during integrated ocean drilling program expedition 314 315 we studied the radiolarian assemblages in 293 samples from cores obtained at site c0001 holes e and f and site c0002 hole d the age models for these cores which are based on biostratigraphy and chemostratigraphy showed that sediments from the period between marine isotope stage mis 15 and mis 8 which includes the mid brunhes event are missing from these cores however continuous data are available between mis 63 1 82 ma and mis 15 0 5 ma therefore using the ecological properties of 11 key radiolarian species we reconstructed regional paleoceanographic changes between 1 82 and 0 5 ma radiolarian fauna revealed that the relative abundance of kuroshio and the central pacific water taxa e g didymocyrtis tetrathalamus and the polysolenia spinosa lappacea group respectively increased drastically during the mpt possibly indicating a northward shift of the kuroshio at that time the relative abundance of rhizosphaera mediana an oyashio kuroshio mixed water species also increased during this interval thus a southward shift of the oyashio current may have occurred synchronously with a northward shift of the kuroshio during the mpt

a mechanism for giant raindrop formation in warm shallow convective clouds abstract giant raindrops 4 8 mm diameter have been observed recently within warm convective rainbands with depths 2 km off the coast of the big island of hawaii the presence of giant raindrops in these clouds was initially surprising since model and laboratory results support the view that collisional breakup should rapidly destroy such drops in natural clouds a mechanism proposed by beard et al and others to explain the giant raindrops is that exceptionally large aerosol particles act as nuclei for very large cloud droplets near cloud base such rare large cloud drops then grow rapidly into giant raindrops by accretion of smaller cloud droplets in the updraft we show here that an additional set of circumstances is required to explain the existence of giant raindrops in hawaiian rainband clouds one which prolongs their growth and separates them from smaller raindrops we present data from the 1985 joint hawaiian warm rain project that suggest that giant raindrops result when selected small raindro

pliocene variations in the position of the antarctic convergence in the southwest atlantic middle to late pliocene 4 1 1 9 ma variations in the positions of surface water masses and migrations of the polar front in the southwest atlantic are inferred from a factor analysis of radiolarian assemblages from dsdp site 514 faunal results suggest that surface water masses underwent progressive cooling as the polar front zone pfz advanced northward during the latest gilbert to late gauss chron the late gilbert chron 4 12 3 86 ma was the waning phase of a mid gilbert warm interval northern subantarctic surface water prevailed between 4 12 and 3 97 ma indicative of surface water temperatures warmer than those during the succeeding pliocene a long term sea surface cooling trend began between 3 97 and 3 86 ma which moved the pfz northward and closer to site 514 bringing cooler southern subantarctic surface waters to the site this movement northward of cooler surface waters is inferred to be related to the initial growth of sea ice and ice shelves throughout regions of west antarctica which were deglaciated or unglaciated during the prior warming interval of the gilbert chron a major late gilbert early gauss chron increase in the production of antarctic bottom water aabw resulted in an erosional or nondepositional hiatus at site 514 spanning 3 86 to 3 18 ma increased aabw activity at this time is linked to continued growth of expansive ice shelves and sea ice in the west antarctic region in the east antarctic margin and possibly in the marine embayments of east antarctica decreased aabw production led to a 3 2 ma resumption of sedimentation at site 514 and elsewhere in the southern ocean antarctic surface water assemblages above the hiatus 3 18 3 16 ma suggest that the pfz first passed over site 514 during the 3 86 3 18 ma interval of the hiatus following this initial invasion of antarctic surface waters between 3 16 and 2 94 ma the pfz retreated to a position near or south of the site this slight retreat of the pfz with a corresponding decrease in aabw activity is possibly related to a significant reduction in the area of shelf and sea ice as grounded ice expanded in the west antarctic region we interpret the widespread global enrichment of 18o at approximately 3 2 ma to be partially related to a cooling of surface waters the production of cooler bottom waters and an expansion of west antarctic ice volume associated with its grounding phase between 3 5 and 2 7 ma based on surface water mass migrations at site 514 the west antarctic ice volume increased significantly slightly prior to or at approximately 3 2 ma decreased between 3 14 and 2 7 ma and then increased by 2 67 ma to a more stable configuration with a volume at least as great as that at 3 2 ma during the late gauss 2 94 2 47 ma four northward advances of the pfz led to the migration of antarctic surface waters over the site by 2 67 ma and continued dominance of antarctic surface water through the remainder of the pliocene we suggest that this permanent change from subantarctic to antarctic surface water mass dominance was linked indirectly to the initial growth of northern hemisphere ice and a reduction of sea level we propose a model of simultaneous northern and southern hemisphere ice volume growth induced by interhemisphere positive feedback which is responsible for the major late gauss advance of antarctic surface waters and the global enrichment of 18o at 2 5 ma

spatial distribution pattern of living polycystine radiolarian taxa baseline study for paleoenvironmental reconstructions in the southern ocean atlantic sector the horizontal and vertical distribution of living polycystine radiolarian taxa was investigated at seven locations on a n s transect between the antarctic zone 54 s in the southern ocean and the subtropical zone 30 s in the southeastern south atlantic during austral autumn four to five depth intervals from 0 to 1000 m depth were sampled with 55 m mesh opening closing nets in combination with a hydrographic ctd survey a factor analysis for the delineation of specific assemblages and the relation between different taxa and taxa groups resulted in eight factors of which five represent surface and subsurface factors and three deep water factors the spatial distribution pattern of the factors shows that distinct radiolarian assemblages are closely related to water depth distribution of water masses hydrographic boundaries such as frontal systems and nutrients this documents that the distribution of individual radiolarian assemblages is controlled by specific hydrographic conditions and water depth and allows the definition and consolidation of the autecological demands these data are crucial for the paleoenvironmental interpretation of fossil polycystine radiolarian assemblages the comparison of living polycystine radiolarian taxa with those preserved in surface sediments shows general similarities this study includes the first documentation on the distribution of living cycladophora davisiana in circumpolar deep water and supports previous studies stating that c davisiana also lives in deep water masses

raindrop sorting induced by vertical drafts in convective clouds evidence of raindrop sorting induced by a convective updraft is presented using a vertically pointing 94 ghz doppler radar 3 2 mm and capitalizing on the resonant nature of the backscattering cross section as a function of the raindrop size mie scattering the vertical air motions to an accuracy of 0 1 ms 1 and the shape of the raindrop size distribution are retrieved from the doppler spectra the interaction of vertical drafts and raindrops is documented for the first time by high resolution radar data the updraft structure clearly causes horizontal and vertical sorting of the raindrops in the updraft core small raindrops d 1 7 mm that have terminal velocities less than the updraft velocities 6 7 ms 1 and a clear absence of drops 3 mm are observed towards the updraft periphery a gradual increase in the raindrop sizes is documented where large raindrops d 3 mm are observed the observations demonstrate the importance of updrafts in distributing the raindrops in space

laser extraction of helium isotopes from antarctic micrometeorites source of he and implications for the flux of extraterrestrial 3he to earth helium isotopes have been measured in 45 putative micrometeorites in the size range 50 to 400 m that were extracted from antarctic ice forty of the antarctic micrometeorites amms are irregular in shape and display varying degrees of partial melting whereas five are spherical and thought to represent completely melted particles of the 30 50 to 100 m suspected micrometeorites only 8 released neither 3he or 4he sixteen released 3he and 4he 0 004 3 5 10 3 cm3 stp g having 3he 4he in the range 1 5 10 4 to 4 1 10 4 six particles released only 3he yielding minimum 3he 4he of 1 6 to 10 6 10 4 5 of which fall in the range of values for amms that had measurable 3he and 4he only 2 of the 15 100 to 400 m amms released measurable 4he 4 44 10 7 cc g 1 these have 3he 4he of 6 10 4 and 20 10 4 respectively significantly higher than the majority of the ratios of 50 to 100 m amms implanted solar energetic particles are the dominant source of he in the 50 to 100 m amms with small contributions of solar wind and or spallogenic he present in 10 particles the absence of sw he is likely due to the loss of the outermost layers of the micrometeorites by ablation during atmospheric entry and abrasion during residence in ice and sampling spallation he is most important in the 100 to 400 m amms consistent with their smaller surface area to volume ratio maximum spallation 3he exposure ages of six particles are close to that predicted from poynting robertson spiral in times of asteroidal micrometeorites the two terrestrial particles identified by chemical composition and mineralogy released only 4he yielding radiogenic he isotope compositions an inverse relationship between particle sizes and solar he abundance is explained by he loss during entry helium loss is likely controlled by phyllosilicate breakdown where present and diffusion controlled bubble growth and rupture rather than melting the 50 to 100 m micrometeorites deliver 8 10 8 cm3 stp 3he g to earth this is more than 100 times less than transported by 20 m particles 2 10 5 cm3 stp 3he g but because 50 to 100 m micrometeorites deliver approximately 20 times more extraterrestrial matter to earth than 20 m particles the larger particles may contribute 5 of the total flux of extraterrestrial 3he to terrestrial sediments the mean he concentrations of the 50 to 100 m amms antarctic micrometeorites and the five spherules 2 1 10 9 cm3 stp 3he g 1 overlap those of the magnetic fraction of deep sea sediments 0 8 68 10 9 cm3 stp g a combination of this material could provide the extraterrestrial 3he measured in ancient deep sea sediments without calling upon the survival of friable 20 m chondritic interplanetary dust particles for tens of millions of years

millennial scale variations of late pleistocene radiolarian assemblages in the bering sea related to environments in shallow and deep waters abstract a high resolution record of the radiolarian assemblage from 60 to 10 ka was investigated using a piston core pc 23a obtained from the northern slope of the bering sea faunal changes based on the 29 major radiolarian taxa demonstrated that the surface and deep water conditions in the bering sea were related to the orbital and millennial scale climatic variations known as glacial interglacial and dansgaard oeschger d o cycles respectively during interstadial periods of the d o cycles the assemblage was characterized by increases in the high latitude coastal species rhizoplegma boreale and the upper intermediate water species cycladophora davisiana while the sea ice related species actinomma boreale and a leptodermum and many deep water species such as dictyophimus crisiae and d hirundo tended to be reduced this trend was more apparent in two laminated intervals at 15 13 5 and 11 5 11 ka which were correlated with well known ice sheet collapse events that occurred during the last deglaciation melt water pulse mwp 1a and mwp 1b respectively the radiolarian faunal composition in these periods suggests that oceanic conditions were different from today 1 surface water was affected by increased melt water discharge from continental ice sheet occurring at the same time as an abrupt increase in atmospheric temperature 2 upper intermediate water ca 200 500 m was well ventilated and organic rich and 3 lower intermediate water ca 500 1000 m was oxygen poor conversely the sea ice season might have been longer during stadial periods of the d o cycles and the last glacial maximum lgm compared to the interstadial periods and the earliest holocene in these colder periods deep water species were very abundant and this corresponded to increases in the oxygen isotope value of benthic foraminifera our findings suggest that the oxygen rich water was present in the lower intermediate layer resulting from intensified ventilation

comparison of radiolarian vertical distributions in the okhotsk sea near the kuril islands and in the northwestern north pacific off hokkaido island abstract the vertical distribution of radiolarians was investigated by using a closing type net with 63 m mesh in the okhotsk sea station nu 2 near bussol strait down to 1000 m depth and in the northwestern north pacific oyashio region station x down to 500 m depth both stations were sampled in september 1995 radiolarian standing stocks were high between 50 and 200 m at both stations and generally decreased with depth the depth integrated living total radiolarian standing stock from 0 to 500 m at station nu 2 was more than three times higher than that at station x the maximum standing stocks of polycystine radiolarians occurred in the 50 100 m depth interval but there were also significant abundance peaks of phaeodarian radiolarians in the 100 200 m interval at both stations the radiolarian production is likely to be associated with not only phytoplankton production in upper waters but also with microbial production in intermediate waters a total of 79 taxa were encountered 25 spumellaria 41 nassellaria and 13 phaeodaria five radiolarian groups were obtained based on r mode cluster analysis group a lower intermediate water dwellers 300 1000 m group b taxa with different distributions in the okhotsk sea 300 1000 m and in the oyashio region 0 100 m group c upper intermediate water dwellers 200 500 m group d surface subsurface water dwellers 0 200 m and group e taxa with pronounced 200 m

radiolarians in the sea of okhotsk and their ecological implication for paleoenvironmental reconstructions to assess the relationship of radiolarian production species distribution in water and surface sediment to water mass characteristics biological productivity and export regimes in the sea of okhotsk sok we accomplished a quantitative analysis of radiolarian assemblages obtained from 35 surface sediment samples and 115 plankton samples recording the radiolarian depth distribution in the upper 1000 m of the water column at 23 locations this study augments the knowledge on the autecological demands of radiolarians dwelling in a specific hydrographic and biological environment and extracts new information on the significance of radiolarians for the assessment of past oceanographic and climatic development in high latitudes highest radiolarian accumulation rates and seasonal radiolarian standing stocks are encountered in the western part of the sok close to sakhalin marking the environmental conditions in this area as most favorable for radiolarian production maximum standing stocks occur during summer indicating that the radiolarian signal preserved in the sediment record is mainly produced during this season when the mesopelagic biomass is at highest activity we identified seven radiolarian species and groups related to specific water mass characteristics depth habitats and productivity regimes of those dictyophimus hirundo and cycladophora davisiana are most prominent in the sea of okhotsk intermediate water 200 1000 m the latter representing an indicator of the occurrence of cold and well ventilated intermediate deep water and enhanced export of organic matter from a highly productive ocean surface while antarctissa sp 1 is typically related to the cold water sea of okhotsk dicothermal layer sodl ranging between 50 and 150 m water depth the surface waters above the sodl affected by strong seasonal variability are inhabited predominantly by taxa belonging to the spongodiscidae having a broad environmental tolerance taxa only found in the sediment record show that the plankton study did not cover all assemblages occurring in the modern sok this accounts for an assemblage restricted to the western kurile basin and apparently related to environmental conditions influenced by north pacific and japan sea waters other important taxa include species of the plagoniidae group representing the most prominent contributors to the sok plankton and surface sediments these radiolarians show a more opportunistic occurrence and are indicative of high nutrient supply in a hydrographic environment characterized by pronounced stratification enhancing heterotrophic activity and phytodetritus export r 2005 elsevier ltd all rights reserved

micropaleontological evidence for increased meridional heat transport in the north atlantic ocean during the pliocene the middle pliocene approximately 3 million years ago has been identified as the last time the earth was significantly warmer than it was during the last interglacial and holocene a quantitative micropaleontological paleotemperature transect from equator to high latitudes in the north atlantic indicates that middle pliocene warmth involved increased meridional oceanic heat transport

late miocene early pliocene stratigraphy and paleoceanography of the south atlantic and southwest pacific oceans a synthesis the stratigraphy and paleoceanography of the late miocene and early pliocene have been examined at six sites in the south atlantic and southwest pacific oceans deep sea drilling project dsdp sites 284 516a 519 588 and 590 and two piston cores from chain cruise 115 a consistent stratigraphy was developed among sites using graphic correlation which resulted in age models for all sites that are tied to the revised paleomagnetic time scale of berggren et al 1985 applying these chronologies we assessed latitudinal and interocean contrasts in the stratigraphic ranges of late miocene early pliocene planktonic foraminiferal and nanno fossil datums salient stratigraphic results include 1 the last appearance datum lad of globoquadrina dehiscens is a late miocene 6 4 ma event in the subtropics and is not useful for the placement of the miocene pliocene m p boundary in this biogeographic province 2 the first appearance datum fad of globorotalia crassaformis occurred at 5 1 ma in the south atlantic near the m p boundary suggesting that gr crassaformis may have first evolved in the south atlantic and later migrated to other regions 3 in the southwest pacific the fads of gr margaritae 5 97 ma gr puncticulata 5 09 ma and gr crassaformis 4 87 ma are significantly time transgressive between temperate and warm subtropical regions time lags of 1 0 m y were required for these species to adapt to physical and or biotic conditions peripheral to their endemic biogeographic provinces 4 between the subtropics of the south atlantic and southwest pacific many planktonic foraminiferal datums fad of dentogloboquadrina altispira gr cibaoensis gr conomiozea gr margaritae and gq dehiscens and lad of gr cibaoensis markedly depart from the correlation suggested by magnetostratigraphy indicating that these datum levels are unreliable for correlation between these ocean basins 5 in contrast available calcareous nannofossil datum levels fall on or near the paleomagnetic correlation line indicating synchroneity of events within the subtropics 6 biostratigraphic magnetic and 87sr 86sr correlation between sites 588 and 519 and the m p neostratotype at capo rossello sicily suggests that the base of the zanclean stratotype occurs at 5 1 5 0 ma in the lower reversed subchron of the gilbert about 2 3 105 years above the gilbert chron 5 boundary oxygen isotopic results from dsdp sites 284 519 and ch115 piston cores confirm a prolonged benthic 18o increase in the latest miocene between 5 6 and 5 0 ma as originally proposed by shackleton and kennett 1975 at dsdp site 588 the benthic 18o record in the latest miocene is marked by high frequency fluctuations with amplitude variations of 0 5 and a long period wavelength component of 400 000 years maximum 18o values however occurred during the late miocene kapitean stage between 5 5 and 5 1 ma the late miocene 18o changes resulted from mid and high latitude cooling and pulses of ice sheet expansion and contraction glacial events were most intense during the latest miocene kapitean stage and occurred at 5 50 5 35 ma and at 5 10 ma glacial events are estimated to have lowered sea level by 40 to 60 m and contributed to the isolation and desiccation of the mediterranean basin during the late messinian interglacial conditions prevailed at 5 2 ma and between 5 0 and 4 1 ma ihe early pliocene the beginning of the pliocene was marked by changes in many proxy climatic indicators at all sites suggesting a prolonged interval of warm interglacial conditions between 5 0 and 4 1 ma during the earliest pliocene supplementary tables are available with entire article onmicrofiche order from american geophysical union 2000florida avenue n w washington dc 20009 documentp86 001 2 50 payment must accompany order

the initiation of northern hemisphere glaciation for well over a century scientists have speculated that variations in the atmospheric concentration of radiatively important trace gases such as carbon dioxide could control the earth s climate e g arrhenius 1 896 recent observations of significant glacial interglacial variation in atmo spheric co2 in ice cores put this idea on a firm observational as well as theoretical footing e g barnola et ai1 987 in this century as atmospheric co2 levels creep steadily upwards in response to the burning of fossil fuels and forests the specter of manmade global climate change looms before us ipcc 1990 a possibility that has heightened interest in the natural variability of climate in the past in particular the 3 c warming pre dicted for the next century has stimulated interest in past warm climates such as the middle pliocene around 3 0 million years ma ago an interval that has often been invoked as a greenhouse world budyko et al 1985 in this paper the climate transition from the warm mid pliocene around 3 2 ma to the onset of northern hemisphere ice ages around 2 4 ma is examined evidence for the initiation of significant northern hemisphere glaciation is examined as well as how this event affected climate around the globe while the cause of individual glacial interglacial oscillations is tied to milankovitch variations in the earth s orbit around the sun e g imbrie et ai 1 992 these insolation changes cannot account for the long term cooling trend which culminated in northern hemisphere glaciation in the final section of this paper mechanisms of long term climate change

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

depth related radiolarian assemblage in the water column and surface sediments of the japan sea plankton tows and surface sediments from the japan sea a marginal sea of the northwestern pacific were examined to study the depth distribution of modern radiolarians the depth distribution patterns between the living assemblage in the water column and the thanatocoenose in surface sediments are similar to each other indicating that the depth related assemblage in sediments is closely related to the living depths of major species four clear restrictions of many species to discrete depth zones are recognized in the water column from the surface down to 2000 m 1 upper subsurface water species which are abundant from 40 to 120 m larcopyle butschlii juvenile form spirocyrtis subscalaris spongodiscus resurgens and lipmanella virchowii 2 lower subsurface water species which are abundant from 40 to 300 m larcopyle butschlii adult form ceratocyrtis histricosa and spongotrochus glacialis 3 intermediate water species which have population maxima from 160 to 300 m ceratospyris borealis and 4 deep water species which have maxima between 1000 and 2000 m cycladophora davisiana and actinomma boreale only a few specimens of a boreale were found in the water column ranging from 1000 to 2000 m depth although this is a dominant species in surface sediments from depths below 2000 m of which the dominance increases with water depth a boreale may live mainly in the bottom water cycladophora davisiana and a boreale which characterize the japan sea deep assemblage are naturally shallow or intermediate dwellers in other oceans on the other hand the typical deep dwellers e g cornutella profunda cyrtopera languncula and peripyramis circumtexta of other oceans have not been found in the japan sea such a peculiar deep assemblage is a result of the deep circulation system in the japan sea and the shallow depths of the sills around it

formation conditions of pyroxene olivine and magnesian olivine chondrules abstract dynamic crystallization experiments performed on a type i and an intermediate type ii iii composition demonstrate chondrule texture is controlled by the abundance of heterogeneous nuclei this factor is controlled by the maximum initial temperature relative to the olivine disappearance temperature for the given heating time glassy and excentroradial textures form from superheated melts with no nuclei and barred textures form with initial temperatures near the olivine disappearance temperature porphyritic and granular textures form with initial temperatures below the liquidus with abundant nuclei comparison of zoning characteristics of experimental olivines with those in natural porphyritic olivine chondrules indicates cooling rates of 100 to 1000 c h whereas olivine morphology indicates barred olivines cooled at rates of 250 to 1000 c h texture composition relationships suggest chondrules experienced initial temperatures below 1750 c these observations are consistent with the idea that chondrules formed by transient heating in dust rich regions i e in the midplane of the solar nebula

placers of cosmic dust in the blue ice lakes of greenland a concentration process occurring in the melt zone of the greenland ice cap has produced the richest known deposit of cosmic dust on the surface of the earth extraterrestrial particles collected from this region are well preserved and are collectable in large quantities the collected particles are generally identical to cosmic spheres found on the ocean floor but a pure glass type was discovered that has not been seen in deep sea samples iron rich spheres are conspicuously rare in the collected material

orbital and millennial scale changes of radiolarian assemblages during the last 220 kyrs in the japan sea abstract significant abundance changes of seven radiolarian species during the last 220 kyrs in the japan sea are reported herein based on three sediment cores during the interglacial periods warm water species the tetrapyle octacantha group and warmer high nutrient water species lithomelissa setosa occurred commonly which may indicate inflows of the tsushima warm current on the other hand cold water species such as ceratospyris borealis and stylochlamydium venustum dominated the assemblage during the glacial periods when the japan sea was mostly isolated from the adjacent seas due to lower eustatic sea level however at glacial maxima the habitat of s venustum was strongly limited due to low salinity surface waters the abundance of the deep water species cycladophora davisiana seems to have changed significantly possibly related to the intrusion of oxygen and organic materials into deeper waters higher abundances of this species in mis marine isotope stage 1 mis 3 and mis 5c resulted from well ventilated deep water and high organic flux while its low abundance during the glacial maxima and mis 5e was probably caused by oxygen poor deep water millennial scale variations of c davisiana abundance show high abundance at the transition intervals from interstadial to stadial periods of the dansgaard oeschger cycles the disappearance events of lychnocanoma nipponica sakaii and amphimelissa setosa were recognized at 54 ka and 85 ka respectively both of these events in the japan sea can be correlated with those in the north pacific bering sea and sea of okhotsk

oceanographic conditions associated with high abundances of the radiolarian cycladophora davisiana abstract the cosmopolitan radiolarian cycladophora davisiana usually comprises less than 5 of the radiolarian fauna in holocene sediments in recent sediments from the sea of okhotsk however this species frequently represents more than 20 of the radiolarian assemblage at times during the late pleistocene abundances of this species in excess of 40 are recorded in marine sediments from high latitude oceans 40 of both hemispheres the sea of okhotsk apparently represents a modern analogue of climatic and oceanographic conditions that existed throughout large portions of high latitude oceans at times during the late pleistocene the near surface water structure of the sea of okhotsk is characterized by a low salinity surface layer with a strong temperature minimum near its base the low surface salinities are responsible for maintaining near freezing subsurface temperatures as well as establishing relatively stable temperatures and salinities at depths below the temperature minimum this water structure is produced at least in part by intense freezing of sea ice in winter with subsequent summer melting the physical characteristics of the upper water column affect the abundance and activity of shallow dwelling flora and fauna while providing a stable subsurface environment for deeper dwelling fauna

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

radiolarians under the seasonally sea ice covered conditions in the okhotsk sea flux and their implications for paleoceanography abstract four time series sediment traps at two stations and three piston cores from the okhotsk sea were quantitatively examined for coarse sized radiolarian shells 63 m traps were deployed at 300 m and 1550 m at station m4 53 01 n 145 30 e and at 300 m and 700 m at station m6 49 30 n 146 28 e during august 1998 through may 2000 the chronologies of the piston cores were established applying 18 o and paleomagnetic intensity variations they provide records extending back to marine isotope stage mis 5 51 the modern and past changes in radiolarian assemblages are associated with environmental and productivity changes radiolarian fluxes in the sediment traps exhibited significant summer to autumn flux peaks with suppressed values during the winter when sea ice covered the sea surface at the trap sites total radiolarian accumulation rate rar variations in each core tended to correspond to glacial interglacial cycles and increased during the last deglaciation in particular the temporal rar variation in core xp98 pc1 off kamchatka showed a similar trend with the climatic changes expressed by 18 o values during the glacial interglacial cycles for the last 125 kyr regional differences were also apparent rars showed extremely low values during 12 40 kyr and 63 70 kyr in core xp98 pc2 central okhotsk sea indicating the enhanced sea ice impact the sea ice coverage might have continued for a significant part of the year during the intervals since radiolarians did not appear to increase even during the summer to autumn rar variations in core xp98 pc4 off sakhalin showed higher values than xp98 pc2 during mis 2 and 4 thus in eastern sakhalin around site xp98 pc4 sea ice coverage might have been seasonal but not perennial even during mis 2 and 4 among the radiolarian taxa cycladophora davisiana was the most abundant species at the lower traps and in all cores the fluxes of c davisiana at lower traps showed much higher values than those of upper traps and also showed similar temporal patterns with the fluxes of aluminum and terrigenous materials therefore c davisiana fluxes may be associated with terrigenous organic materials increased nutrient supply from the continental shelves presumably transported by seasonal sea ice and released by sea ice melting might be mainly responsible for the high production of c davisiana in the okhotsk sea especially during the last deglaciation

noble gas compositions of antarctic micrometeorites collected at the dome fuji station in 1996 and 1997 the noble gases he ne ar kr and xe were measured in 27 individual antarctic micrometeorites amms in the size range 60 to 250 m that were collected at the dome fuji station eleven of the amms were collected in 1996 f96 series and 16 were collected in 1997 f97 series one of the f97 amms is a totally melted spherule whereas all other particles are irregular in shape noble gases were extracted using a nd yag continuous wave laser with an output power of 2 5 3 5 w for 5 min most particles released measurable amounts of noble gases 3he 4he ratios are determined for 26 amms 0 85 9 65 10 4 solar energetic particles sep are the dominant source of helium in most amms rather than solar wind sw and cosmogenic he three samples had higher 3he 4he ratios compared to that of sw showing the presence of spallogenic 3he the ne isotopic composition of most amms resembled that of sep as in the case of helium spallogenic 21ne was detected in three samples two of which had extremely long cosmic ray exposure ages 100 ma calculated by assuming solar cosmic ray scr galactic cosmic ray gcr production these two particles may have come to earth directly from the kuiper belt most amms had negligible amounts of cosmogenic 21 ne and exposure ages of 1 ma 40ar 36ar ratios for all particles 3 9 289 were lower than that of the terrestrial atmosphere 296 indicating an extraterrestrial origin of part of the ar with a very low 40ar 36ar ratio plus some atmospheric contamination indeed 40ar 36ar ratios for the amms are higher than sw sep and q ar values which is explained by the presence of atmospheric 40ar the average 38ar 36ar ratio of 24 amms 0 194 is slightly higher than the value of atmospheric or q ar suggesting the presence of sep ar which has a relatively high 38ar 36ar ratio according to the elemental compositions of the heavy noble gases dome fuji amms can be classified into three groups chondritic eight particles air affected nine particles and solar affected eight particles the eight amms classified as chondritic preserve the heavy noble gas composition of primordial trapped component due to lack of atmospheric adsorption and solar implantation the average of 129xe 132xe ratio for the 16 amms not affected by atmospheric contamination 1 05 corresponds to the values in matrices of carbonaceous chondrites 1 04 one amm f96dk038 has high 129xe 132xe in excess of this ratio our results imply that most dome fuji amms originally had chondritic heavy noble gas compositions and carbonaceous chondrite like objects are appropriate candidate sources for most amms

variations in the radiolarian assemblages in the bering sea since pliocene and their implications for paleoceanography radiolarian assemblages were analyzed using samples from the iodp site u1340 to reconstruct the paleoceanographic conditions in the bering sea based on the characteristic faunal changes the radiolarian evolution at site u1340 was divided into four major intervals from stages i to iv with stage iv divided into substages iva and ivb the radiolarians in each stage recorded significant paleoenvironmental conditions in general the bering sea was governed by an ocean ecological environment with stable warm and saline surface water during stage i 4 15 myr to 3 91 myr the environment in the bering sea fluctuated strongly during stage 11 3 91 myr to 2 75 myr and was controlled by the cold water masses and sea ices during stage iii 2 75 myr to 1 07 myr with the gradual development of cold and well ventilated intermediate water stage iva 1 07 myr to 0 47 myr was a transitional period characterized by the enhanced formation of cold subsurface and intermediate water as well as of the oxygen rich deep water during stage ivb after 0 47 myr the bering sea was mainly characterized by enhanced warmth during interglacial episodes and well developed water layers that were generally comparable to those of the modern bering sea these conditions indicated that the vertical water mass structure of the modern bering sea began to form since 0 47 ma every stage boundary in the studied core was marked by notable changes in the radiolarian assemblages these changes corresponded to the climatic cooling event at similar to 3 91 ma the intensification of northern hemisphere glaciation at similar to 2 75 ma the beginning of the middle pleistocene transition at similar to 1 07 ma and the low latitude radiolarian ecology event at similar to 0 47 ma in addition the relative abundance pattern of cycladophora davisiana indicates that the bering sea was the main source of the past north pacific intermediate water at ca 0 85 ma mis22 ca 0 63 ma mis16 and ca 0 18 ma mis6 just as it was during the last glacial maximum c 2014 elsevier b v all rights reserved

upwelling intensification as part of the pliocene pleistocene climate transition a deep sea sediment core underlying the benguela upwelling system off southwest africa provides a continuous time series of sea surface temperature sst for the past 4 5 million years our results indicate that temperatures in the region have declined by about 10 c since 3 2 million years ago records of paleoproductivity suggest that this cooling was associated with an increase in wind driven upwelling tied to a shift from relatively stable global warmth during the mid pliocene to the high amplitude glacial interglacial cycles of the late quaternary these observations imply that atlantic ocean surface water circulation was radically different during the mid pliocene

polycystine radiolarians in surface sediments in the arctic ocean basins and marginal seas abstract the polycystine radiolarian faunas in the arctic ocean including the adjacent arctic seas have been studied in more than 377 surface samples the deep basins in the arctic ocean have revealed 31 polycystine radiolarian species 11 spumellarians and 20 nassellarians the polycystine radiolarian fauna in the southern norwegian sea was introduced from the north atlantic ocean ca 13 400 yr bp the shallow low arctic marginal sea sediments iceland barents and chukchi seas have a strong dominance of cannobotryidae 79 77 and 74 respectively while the deep arctic ocean basins nansen amundsen and makarov basins have a dominance of actinommidae 90 70 and 75 respectively the arctic polycystine radiolarian faunas have a strong affinity with the norwegian sea fauna which supplies the arctic ocean with faunal elements that can live thrive and reproduce there in the chukchi sea the pacific faunal influence is obvious 41 species but none of the pacific species are found in any abundance in the amerasian basin no radiolarian species was found to be endemic to the arctic ocean except for a morphotype of actinomma l leptoderma with a round inner sphere this species is a possible endemic candidate for the arctic ocean eight species are to be found in all of the central arctic basins and can therefore be referred to as circumpolar species actinomma leptoderma leptoderma a l leptoderma with round middle sphere a l longispina a boreale spongotrochus glacialis pseudodictyophimus platycephalus cycladophora davisiana and tholospyris gephyristes while amphimelissa setosa probably is the only true arctic radiolarian species

pronounced warmth during early middle pleistocene interglacials investigating the mid brunhes event in the british terrestrial sequence the mid brunhes event mbe is a climatic transition occurring between mis 13 and 11 that separates two climatic modes 1 early middle pleistocene interglacials 780 450 ka that are characterised by only moderate warmth and 2 middle and late pleistocene interglacials occurring after 450 ka that are characterised by greater warmth consistent with or warmer than the holocene this event is observable within a variety of long climate records such as specmap and epica but its effect on terrestrial systems is poorly understood the impact of this event is examined in the british terrestrial sequence by comparing the occurrence of a range of thermophilous plant and animal species and climate reconstructions derived from assemblages containing them from interglacials of the early middle pleistocene with those from the late middle and late pleistocene this comparison reveals that interglacial climates during the early middle pleistocene in britain were as warm as and in some cases warmer than those that occurred during the late middle and late pleistocene this interpretation is supported by sea surface temperature records in the north atlantic which show that temperatures during early middle pleistocene interglacials were at least as warm as those experienced during the holocene there is therefore no evidence in climate records of britain and the north atlantic for a mid brunhes event this suggests that the mbe is not a global climatic transition but is restricted to specific regions in particular the higher latitudes of the southern hemisphere further work is needed to understand the regional variability and cause of the mbe

biogeochemical cycling in the bering sea over the onset of major northern hemisphere glaciation the bering sea is one of the most biologically productive regions in the marine system and plays a key role in regulating the flow of waters to the arctic ocean and into the subarctic north pacific ocean cores from iodp expedition 323 to the bering sea provide the first opportunity to obtain reconstructions from the region that extend back to the pliocene previous research at bowers ridge south bering sea has revealed stable levels of siliceous productivity over the onset of major northern hemisphere glaciation nhg c 2 85 2 73 ma however diatom silica isotope records of oxygen 18odiatom and silicon 30sidiatom presented here demonstrate that this interval was associated with a progressive increase in the supply of silicic acid to the region superimposed on shift to a more dynamic environment characterized by colder temperatures and increased sea ice this concluded at 2 58 ma with a sharp increase in diatom productivity further increases in photic zone nutrient availability and a permanent shift to colder sea surface conditions these transitions are suggested to reflect a gradually more intense nutrient leakage from the subarctic northwest pacific ocean with increases in productivity further aided by increased sea ice and wind driven mixing in the bering sea in suggesting a linkage in biogeochemical cycling between the south bering sea and subarctic northwest pacific ocean mainly via the kamchatka strait this work highlights the need to consider the inter connectivity of these two systems when future reconstructions are carried out in the region

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

carbon reservoir changes preceded major ice sheet expansion at the mid brunhes event the beginning of the mid brunhes event ca 430 ka coincided with the largest amplitude change in d 18 o in the global ocean over the past 6 m y this large d 18 o change recorded a major ice sheet expansion that cannot be explained by small changes in orbital forcing our recent studies at ocean drilling program site 1143 from the south china sea show that this large d 18 o change was preceded by a significant negative d 13 c shift a global survey of long deep sea records has revealed periodic d 13 cmax episodes i e maximum positive values of d 13 c and both major ice sheet expansion events in the pleistocene the mid brunhes event and the middle pleistocene revolution were preceded by d 13 cmax ep isodes followed by negative d 13 c shifts this new finding suggests that disturbance in carbon reservoirs leads to major growth of ice sheet size and challenges the prevalent concept of arctic control of glacial cycles because earth is now passing again through a d 13 cmax episode it is crucial to understand the causal relationship between the successive d 13 c changes and ice sheet growth events

reconciliation of late quaternary sea levels derived from coral terraces at huon peninsula with deep sea oxygen isotope records a major discrepancy between the late quaternary sea level changes derived from raised coral reef terraces at the huon peninsula in papua new guinea and from oxygen isotopes in deep sea cores is resolved the two methods agree closely from 120 ka to 80 ka and from 20 ka to 0 ka ka 1000 yr before present but between 70 and 30 ka the isotopic sea levels are 20 40 m lower than the huon peninsula sea levels derived in earlier studies new high precision u series age measurements and revised stratigraphic data for huon peninsula terraces aged between 30 and 70 ka now give similar sea levels to those based on deep sea oxygen isotope data planktonic and benthic 18o data using the sea level and deep sea isotopic data oxygen isotope ratios are calculated for the northern continental ice sheets through the last glacial cycle and are consistent with results from greenland ice cores the record of ice volume changes through the last glacial cycle now appears to be reasonably complete