reconstruction of surface water conditions in the central region of the okhotsk sea during the last 180 kyrs abstract core gc9a a 6 7 m long gravity core collected from the central region of the okhotsk sea during cruise yk0712 on r v yokosuka jamstec was used to reconstruct the changes in surface water conditions by measuring biogenic components biogenic opal caco3 total organic carbon and 15n of sediment organic matter of sediment samples the age of core gc9a was determined indirectly by graphic correlation comparing the b psychometric yellow blue chromaticness values with those of well dated core md01 2415 with complement to the tephra layer k3 50 ka the bottom age of core gc9a was estimated to be about 180 kyr therefore it provides the history of surface water conditions from mis 1 to mis 6 the biogenic opal caco3 and toc contents were high during the interglacial periods as expected indicating enhanced surface water production under warm climatic conditions this condition resulted from sufficient nutrient supply to the surface waters by active vertical mixing which was validated by low 15n values of the sediment organic matter in contrast surface water productivity was depressed during the colder glacial periods probably due to the expanded sea ice distribution and limited nutrient supply however the glacial sediments had moderately high 15n values indicating enhanced nitrate utilization resulting from the limited nutrient supply caused by strong stratification of the surface water high 15n values were also observed during the deglaciation which was attributed to the increased nitrate utilization during enhanced surface water productivity however the low 15n values during the glacial and deglacial periods may be attributed to the increased supply of terrestrial organic matter diatom production was primarily responsible for surface water paleoproductivity during the interglacial periods rather than coccolithophores however the succession of glacial to early deglacial coccolithophore production and late deglacial to interglacial diatom production was remarkable corresponding to the present day seasonal phytoplankton succession such an advanced coccolithophore production relative to diatom production might be attributed to the degree of nutrient availability associated with surface water conditions on the basis of variations in the 15n value finally the opal and toc contents decreased abruptly in conjunction with a gradual decrease in caco3 content from about 2 ka which seems to implicate a late holocene sudden decrease in paleoproductivity in the central region of the okhotsk sea according to the increase in 15n values during this interval nutrient availability appears to be poor which is likely attributed to the resumed strong stratification that occurred due to the southward shift of the aleutian low atmospheric pressure system

assessment for paleoclimatic utility of terrestrial biomarker records in the okhotsk sea sediments we measured terrestrial plant biomarker long chain n alkanes in the sediment cores taken from the sea of okhotsk to examine paleoclimatic utility of long chain n alkanes in marine sediments this study demonstrates that sedimentary record of n alkane in the sea has a high potential to provide important complementary paleo climate paleo environmental information molecular distributions of long chain n alkanes in marine sediments show a typical signature of terrestrial plant wax derived n alkanes with strong odd carbon number predominance from the last glacial to the present suggesting a source of long chain n alkanes in the okhotsk sea sediments has been terrestrial higher plants throughout the time the down core profiles of concentrations of c25 c35 n alkanes in xp07 c9 collected from the northwestern site revealed three events of enhanced terrestrial organic matter input during the last deglaciation the two pronounced events correspond to melt water pulse mwp events 1a 14 5 12 5 ka and 1b 11 6 5 ka these events possibly linked to increases in river discharge and erosion of submerged continental shelf due to drastic rise in sea level down core profiles of molecular distributions of n alkanes in the okhotsk sea sediments significantly vary over the last 25 kyr and are similar to that of a peat core sequence in the east russia and essentially consistent with pollen data from marine and peat core sequences

sediment cd and mo accumulation in the oxygen minimum zone off western baja california linked to global climate over the past 52 kyr 1 concentrations of organic carbon orgc cadmium cd and molybdenum mo were measured in two sediment cores raised from depths of 430 and 700 m within the oxygen minimum zone omz off southern baja california at a temporal resolution of 0 5 kyr over the past 52 kyr these records are supplemented with diffuse spectral reflectance dsr measurements obtained on board ship soon after collection at a resolution of 0 05 kyr in the core from 700 m depth a component extracted from the dsr data and the three geochemical proxies generally vary in concert with each other and over a wide range 4 22 orgc 1 40 mg kg cd 5 120 mg kg mo intervals of increased orgc cd and mo accumulation generally correspond to warm periods recorded in the oxygen isotopic composition of greenland ice with the exception of the bolling allerod which is only weakly expressed off baja california concentrations of the biogenic proxies are higher in the core from 430 m depth but erratic sediment accumulation before 15 ka precludes dating of the older intervals that are laminated and contain elevated orgc cd and mo concentrations the new data provide further evidence of an intimate teleconnection between global climate and the intensity of the omz and or productivity along the western margin of north america on the basis of a comparison with cd and mo records collected elsewhere in the region we conclude that productivity may actually have varied off southern baja california by no more than a factor of 2 over the past 52 kyr

consistent relationship between global climate and surface nitrate utilization in the western subarctic pacific throughout the last 500 ka 1 the open subarctic pacific is at present a high nitrate low chlorophyll hnlc region where nitrate is perennially abundant at the surface theoretically the hnlc status of this region is subject to modification by ocean circulation and or micronutrient supply with implications for the effectiveness of the biological pump and hence carbon sequestration in the ocean interior records of biogenic detritus in sediments from throughout the subarctic pacific indicate that export production was generally lower during glacial maxima while nitrogen isotope measurements from the bering sea have shown that nitrate consumption there was more complete during the last glacial period than it is today here nitrogen isotopic analyses of bulk sediments 15nbulk from three deep water sites in the open subarctic pacific are evaluated in terms of regional nitrate isotopic composition and local relative nitrate utilization the eastern subarctic pacific 15nbulk record bears great similarity to 15nbulk records from the western margin of north america over the last glacial cycle suggesting that variability in the isotopic composition of subeuphotic zone nitrate the growth substrate is reasonably coherent throughout the northeast pacific and dominates at these sites however the two western subarctic pacific records which lie at the heart of the hnlc region display a different pattern implying that significant changes in local relative nitrate utilization overlie the regional background variability after a novel correction intended to remove the background signal associated with denitrification in the eastern tropical north pacific these nitrate utilization records are correlated with a benthic oxygen isotope stack reflecting global deep ocean temperature and ice volume r2 0 65 the correlation implies a strong link between global climate and subarctic pacific nitrate utilization with nearly complete nitrate consumption during glacial periods when export production was low

freshwater impacts recorded in tetraunsaturated alkenones and alkenone sea surface temperatures from the okhotsk sea across millennial scale cycles 1 we present records of phytoplankton produced alkenones down a long piston core which reveal changes of sea surface temperature sst and sea surface salinity sss in the southwestern okhotsk sea over the past 120 ka between 20 and 60 ka b p alkenone derived temperatures typically increased by 6 c 8 c from periods corresponding within a few hundred years to stadials to those corresponding to interstadials recorded in greenland ice cores the abundance of c37 4 alkenone relative to total c37 alkenones percent c37 4 a possible proxy for salinity indicated that during most low sss was associated with high sst the warm freshwater events might be related to 1 a decline in the supply of saline water entering the okhotsk sea through the soya strait 2 strengthening of the freshwater supply from the amur river and precipitation over the okhotsk sea associated mainly with increased asian summer monsoon activity and 3 the effect of melting sea ice these findings increase our understanding of the close linkage between high and low latitudes in relation to climate change and the synchronicity of climate changes within a few centuries between the pacific and the atlantic sides of the northern hemisphere

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

comparing dust flux records from the subarctic north pacific and greenland implications for atmospheric transport to greenland and for the application of dust as a chronostratigraphic tool we present a new record of eolian dust flux to the western subarctic north pacific snp covering the past 27 000 years based on a core from the detroit seamount comparing the snp dust record to the north greenland ice core project ngrip ice core record shows significant differences in the amplitude of dust changes to the two regions during the last deglaciation while the timing of abrupt changes is synchronous if dust deposition in the snp faithfully records its mobilization in east asian source regions then the difference in the relative amplitude must reflect climate related changes in atmospheric dust transport to greenland based on the synchronicity in the timing of dust changes in the snp and greenland we tie abrupt deglacial transitions in the 230th normalized 4he flux record to corresponding transitions in the well dated ngrip dust flux record to provide a new chronostratigraphic technique for marine sediments from the snp results from this technique are complemented by radiocarbon dating which allows us to independently constrain radiocarbon paleoreservoir ages we find paleoreservoir ages of 745 140 years at 11 653 year b p 680 228 years at 14 630 year b p and 790 498 years at 23 290 year b p our reconstructed paleoreservoir ages are consistent with modern surface water reservoir ages in the western snp good temporal synchronicity between eolian dust records from the subantarctic atlantic and equatorial pacific and the ice core record from antarctica supports the reliability of the proposed dust tuning method to be used more widely in other global ocean regions

a 15 000 year paleoenvironmental record from meiji seamount far northwestern pacific late glacial and holocene hemipelagic sediments from meiji seamount in the far northwest pacific contain common to abundant planktonic and benthic foraminifera for ams 14c dating for stable isotope analysis and for interpreting paleoclimate change we present here chronostratigraphic faunal and geochemical results from a piston core which indicate that during glacial times as young as 14 000 yrs bp the northwest pacific sea surface salinity was at least as low as today effectively inhibiting convective overturn between 12 000 and 13 000 yrs ago after a major flux of ice rafting there is faunal and 18o evidence of an abrupt decrease in surface ocean salinity coincident with this event was an increase in biological productivity shown by higher fluxes of calcium carbonate organic carbon opal and greater abundances and lower 13o of the benthic foraminifera uvigerina oxygen isotope ratios in uvigerina and cibicidoides show step like decreases at about 13 000 14 000 11 000 10 000 and 6000 8000 yrs bp these events may be analogous to steps in the north atlantic 18o record during meltwater events if this interpretation is correct then the temperature and salinity history of the deep pacific lags that of the north atlantic by about 1000 yrs consistent with the transport time of deep water from the north atlantic to the north pacific

mechanisms controlling dissolved iron distribution in the north pacific a model study mechanisms controlling the dissolved iron distribution in the north pacific are investigated using the biogeochemical elemental cycling bec model with a resolution of approximately 1 in latitude and longitude and 60 vertical levels the model is able to reproduce the general distribution of iron as revealed in available field data surface concentrations are generally below 0 2 nm concentrations increase with depth and values in the lower pycnocline are especially high in the northwestern pacific and off the coast of california sensitivity experiments changing scavenging regimes and external iron sources indicate that lateral transport of sedimentary iron from continental margins into the open ocean causes the high concentrations in these regions this offshore penetration only appears under a scavenging regime where iron has a relatively long residence time at high concentrations namely the order of years sedimentary iron is intensively supplied around continental margins resulting in locally high concentrations the residence time with respect to scavenging determines the horizontal scale of elevated iron concentrations budget analysis for iron reveals the processes by which sedimentary iron is transported to the open ocean horizontal mixing transports sedimentary iron from the boundary into alongshore currents which then carry high iron concentrations into the open ocean in regions where the alongshore currents separate from the coast most prominently in the northwestern pacific and off of california

depth profiles of δ13c in bottom water and core top c wuellerstorfi on the ontong java plateau and emperor seamounts we have measured the carbon isotopic composition of dissolved inorganic carbon in bottom waters of the ontong java plateau western equatorial pacific and on the northern emperor seamounts northwest pacific each of these locations is several hundred miles from the nearest geochemical ocean sections study geosecs stations and the observed 13c values at each site differ substantially from regionally averaged geosecs 13c profiles we discuss the possible causes of these differences including horizontal variability near bottom effects and problems with the pacific geosecs 13c data we also measured the isotopic composition c and o of core top c wuellerstorfi from a depth transect of cores at each location the 18o data are used to verify that our samples are holocene comparison of foraminiferal and bottom water 13c values shows that this species faithfully records bottom water 13c at both sites and demonstrates that there is no depth related artifact in the dissolved inorganic carbon c wuellerstorfi 13c relationship at these sites

last glacial maximum to holocene sea surface conditions at umnak plateau bering sea as inferred from diatom alkenone and stable isotope records 1 the bering sea gateway between the pacific and arctic oceans impacts global climate when glacial interglacial shifts in shore line position and ice coverage change regional albedo previous work has shown that during the last glacial termination and into the holocene sea level rises and sea ice coverage diminishes from perennial to absent yet existing work has not quantified sea ice duration or sea surface temperatures sst during this transition here we combine diatom assemblages with the first alkenone record from the bering sea to provide a semiquantitative record of sea ice duration sst and productivity change since the last glacial maximum lgm during the lgm diatom assemblages indicate that sea ice covered the southeastern bering sea perennially at 15 1 cal ka b p the diatom assemblage shifts to one more characteristic of seasonal sea ice and alkenones occur in the sediments in low concentrations deglaciation is characterized by laminated intervals with highly productive and diverse diatom assemblages and inferred high coccolithophorid production at 11 3 cal ka b p the diatom assemblage shifts from one dominated by sea ice species to one dominated by a warmer water north pacific species simultaneously the sst increases by 3 c and the southeastern bering sea becomes ice free year round productivity and temperature proxies are positively correlated with independently dated records from elsewhere in the bering sea the sea of okhotsk and the north pacific indicating that productivity and sst changes are coeval across the region

provenance of intermediate waters in the western north pacific deduced from thermodynamic imprint on δ13c of dic 1 stable carbon isotopes of dissolved inorganic carbon 13cdic together with phosphate concentrations po43 of the western north pacific marginal area are presented although 13cdic controlled not only air sea exchange but also biological activities by subtracting po43 as a biological factor from the 13cdic the thermodynamic imprint on the carbon isotopic composition 13cas is used as a conservative tracer the linear relationship between 13cas and temperature with the 13cas temperature slope of 0 104 c is observed in the north pacific subtropical region this relationship can be extended to the weddell sea deep waters therefore oceanic dic is apparently in temperature dependent isotopic equilibrium with atmospheric co2 to characterize each water mass the isotopically labeled temperature tiso which is derived from 13cas temperature relationship obtained for the subtropical gyre water and weddell sea water is introduced in contrast the 13cas temperature relationship is not necessarily linear for the northern japan sea water the kuroshio oyashio mixed water and the okhotsk sea water this nonlinearity implies apparent air sea carbon isotopic disequilibria resulting from water cooling without accompanying air sea carbon isotope equilibrium by using the potential temperature tpot and the tiso the source waters constituting intermediate waters 26 8 have been estimated the results clearly indicate that 1 the intermediate water in the southern okhotsk sea contains up to 20 japan sea water and that 2 new north pacific intermediate water npiw consists of okhotsk sea water subarctic gyre water and old subtropical npiw

glacial holocene environment of the southeastern okhotsk sea evidence from geochemical and palaeontological data abstract environmental conditions and productivity changes in the southeastern okhotsk sea have been reconstructed for the last 20 ka using planktonic and benthic foraminiferal oxygen isotope records and calcium carbonate organic carbon and opal content data from two sediment cores species variability in benthic foraminiferal and diatom assemblages provides additional palaeoceanographic evidence ams radiocarbon dating of the sediments and oxygen isotope stratigraphy serve as the basis for the age models of the cores for the last 20 14 c kyr and for correlation between environmental variations in the okhotsk sea and regional and global climate changes benthic foraminiferal assemblages in the two cores depth 1590 and 1175 m varied with time so that we could recognise seven zones with different species composition changes in the benthic foraminiferal assemblages parallel major environmental and productivity variations during the last glaciation fluxes of organic matter to the sea floor showed strong seasonal variations indicated by the presence of abundant a weddellensis and infaunal uvigerina spp benthic foraminiferal assemblages changed with warming at 12 5 11 and 10 8 14 c kyr bp when productivity blooms and high organic fluxes were coeval with global meltwater pulses 1a and 1b younger dryas cooling caused a decline in productivity 11 10 kyr bp affecting the benthic faunal community subsequent warming triggered intensive diatom production opal accumulation and a strong oxygen deficiency causing significant changes in benthic fauna assemblages from 5 26 4 4 kyr bp to present time

size fractionated iron distributions and iron limitation processes in the subarctic nw pacific 1 comparison of vertical profiles of size fractionated iron between the western and eastern subarctic north pacific clearly showed higher labile particulate iron concentrations towards the west and this result strongly supports the higher iron supply in the western region additionally the results of the seeds experiment the first meso scale iron enrichment experiment in the subarctic north pacific clearly showed that artificially enriched iron in the dissolved fraction mainly in colloidal fraction was rapidly transformed to suspended labile particulate iron during phytoplankton growth and was retained in the surface mixed layer probably this same rapid transformation process occurs naturally after sporadic atmospheric iron supply and the labile particulate iron is retained in the western region furthermore this transformation process reduces dissolved concentration of iron and its bioavailability therefore the transformation process is important for understanding how phytoplankton became iron limited and the biogeochemical iron cycle in the western subarctic north pacific

intermediate water ventilation change in the subarctic northwest pacific during the last deglaciation 1 the laminated sediments suggest significant depletion in dissolved oxygen of intermediate water in the north pacific during the last deglaciation however the cause of depleted oxygen during deglaciation is still a matter of debate here we present foraminiferal mg ca based intermediate and surface temperatures and 18o of seawater 18ow a proxy of salinity in the oyashio region in order to investigate intermediate water circulation through the last deglaciation results indicate that the intermediate water temperature and 18ow increased in association with ventilation age at the bolling allerod period suggesting that the poor ventilation at that time the surface record shows that the decrease of salinity preceded the slowdown of intermediate ventilation the coupled variation of intermediate and surface water suggests that the supply of cold fresh intermediate water diminished because of poor ventilation at the high latitude due to surface freshening

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

geochemical multielement signatures of glacial and interglacial facies of the okhotsk sea deepwater sediments during the past 350 kyr a response to global climate changes at the orbital and millennial scales the previously dated deepwater sediment core mr06 04 pc 7r length 1723 cm 350 kyr recovered from the central okhotsk sea os was analyzed for biogenic compounds and for 63 chemical elements using the inductively coupled plasma mass spectrometry method with a high resolution 1 cm 200 years a one box model with two main members and mathematical methods based on multielemental composition of sediments for the calculation of weight fractions at each time slice of two main types of geochemical facies that dominate during considerably diverse climatic periods glacial maxima and interglacial optima were proposed and tested this model can be applied to other analogous natural systems whose sedimentation is driven by two main types of geochemical facies the application of the developed model to the studied core revealed that variations of weight fractions of the typical interglacial and glacial geochemical facies in the sediments along the core depth named as warm and cold covariators respectively change synchronously with global and regional climate variability profiles of warm and inversed cold covariators coincide tightly and their values increase during warm marine isotope stages and substages and decrease during cold ones over the last 350 kyr millennial scale changes in covariators had occurred simultaneously with abrupt variability in the os productivity and sediment lithology and with millennial global climate variability some discrepancies in the warm and inversed cold covariators calculated using specific mathematical treatments revealed the episodic influence of volcanogenic matter presented in the core by visible tephra layers and cryptotephras

deglacial development of sub sea surface temperature and salinity in the subarctic northwest pacific implications for upper ocean stratification based on models and proxy data it has been proposed that salinity driven stratification weakened in the subarctic north pacific during the last deglaciation which potentially contributed to the deglacial rise in atmospheric carbon dioxide we present high resolution subsurface temperature tmg ca and subsurface salinity approximating 18oivc sw records across the last 20 000 years from the subarctic north pacific and its marginal seas derived from combined stable oxygen isotopes and mg ca ratios of the planktonic foraminiferal species neogloboquadrina pachyderma sin our results indicate regionally differing changes of subsurface conditions during the heinrich stadial 1 and the younger dryas cold phases our sites were subject to reduced thermal stratification brine rejection due to sea ice formation and increased advection of low salinity water from the alaskan stream in contrast the bolling allerod warm phase was characterized by strengthened thermal stratification stronger sea ice melting and influence of surface waters that were less diluted by the alaskan stream from direct comparison with alkenone based sea surface temperature estimates sstuk 37 we suggest deglacial thermocline changes that were closely related to changes in seasonal contrasts and stratification of the mixed layer the modern upper ocean conditions seem to have developed only since the early holocene

on the preservation of laminated sediments along the western margin of north america 1 piston gravity and multicores as well as hydrographic data were collected along the pacific margin of baja california to reconstruct past variations in the intensity of the oxygen minimum zone omz gravity cores collected from within the omz north of 24 n did not contain laminated surface sediments even though bottom water oxygen bwo concentrations were close to 5 mol kg however many of the cores collected south of 24 n did contain millimeter to centimeter scale brown to black laminations in holocene and older sediments but not in sediments deposited during the last glacial maximum in addition to the dark laminations holocene sediments in soledad basin silled at 290 m also contain white coccolith laminae that probably represent individual blooms two open margin cores from 430 and 700 m depth that were selected for detailed radiocarbon dating show distinct transitions from bioturbated glacial sediment to laminated holocene sediment occurring at 12 9 and 11 5 ka respectively the transition is delayed and more gradual 11 3 10 0 ka in another dated core from soledad basin the observations indicate that bottom water oxygen concentrations dropped below a threshold for the preservation of laminations at different times or that a synchronous hydrographic change left an asynchronous sedimentary imprint due to local factors with the caveat that laminated sections should therefore not be correlated without independent age control the pattern of older sequences of laminations along the north american western margin reported by this and previous studies suggests that multiple patterns of regional productivity and ventilation prevailed over the past 60 kyr

freshwater chlorophycean algae in recent marine sediments of the beaufort laptev and kara seas arctic ocean as indicators of river runoff freshwater chlorophycean algae are characteristic organic walled microfossils in recent coastal and shelf sediments from the beaufort laptev and kara seas arctic ocean the persistent occurrence of the chlorophycean algae pediastrum spp and botryococcus cf braunii in marine palynomorph assemblages is related to the discharge of freshwater and suspended matter from the large siberian and north american rivers into the arctic shelf seas the distribution patterns of these algae in the marine environments reflect the predominant deposition of riverine sediments and organic matter along the salinity gradient from the outer estuaries and prodeltas to the shelf break sedimentary processes overprint the primary distribution of these algae resuspension of sediments by waves and bottom currents may transport sediments in the bottom nepheloid layer along the submarine channels to the shelf break bottom sediments and microfossils may be incorporated into sea ice during freeze up in autumn and winter leading to an export from the shelves into the deep sea the presence of these freshwater algae in sea ice and bottom sediments in the central arctic ocean confirm that transport in sea ice is an important process which leads to a redistribution of shallow water microfossils

characteristics of gas hydrate occurrences associated with mud diapirism and gas escape structures in the northwestern sea of okhotsk abstract an interpretation of 8450 line km of seismic reflection data acquired during four cruises in the northwestern sea of okhotsk shows widespread occurrence of free gas or gas hydrates in the sediment this occurrence is documented seismically by gas escape structures acoustic blanking and by a bottom simulating reflector bsr gas escape structures and vents are concentrated on the northern sakhalin continental margin here they are associated with local tectonic movements along a n s trending dextral shear system the inessa shear zone mud diapirism is common in the derugin basin where compression dominates this diapirism is probably closely related to the gas accumulations in the sediment below the base of the gas hydrate stability zone bghsz conductive heat flow derived from the bsr depth distribution averages about 30 8 mw m 2 only adjacent to basement highs and around the inessa shear zone do values higher than 80 22 mw m 2 occur these high values are attributed to an elevated geothermal gradient in the tectonically active zone where fluid venting takes place areas of drift sedimentation and mass wasting where sedimentation rates are high are characterised by computed heat flow values below 30 8 mw m 2 however these values must be corrected upwards by 3 20 depending on the sedimentation rate applicable 3 8 100 cm kyr the total amount of methane preserved in the hydrate stability zone hsz and trapped as free gas beneath the bsr is estimated at 17 14 10 12 m 3 for the northwestern sea of okhotsk and 15 12 10 13 m 3 for the entire sea of okhotsk the latter figure represents about 0 8 of the global reservoir of methane gas from hydrates our study documents that the semi enclosed sea of okhotsk offers favourable conditions for the accumulation of gas in its sediments on account of its subarctic climate and the prevailing hydrologic regime these conditions include high primary productivity low bottom water temperatures and high sedimentation rates

productivity and sedimentary δ15n variability for the last 17 000 years along the northern gulf of alaska continental slope 1 biogenic opal organic carbon organic matter stable isotope and trace metal data from a well dated high resolution jumbo piston core ew0408 85jc 59 33 3 n 144 9 21 w 682 m water depth recovered from the northern gulf of alaska continental slope reveal changes in productivity and nutrient utilization over the last 17 000 years maximum values of opal concentration 10 occur during the deglacial bolling allerod b a interval and earliest holocene 11 2 to 10 8 cal ka bp moderate values 6 occur during the younger dryas 13 0 to 11 2 cal ka bp and holocene and minimum values 3 5 occur during the late glacial interval lgi when converted to opal mass accumulation rates the highest values 5000 g cm 2 kyr 1 occur during the lgi prior to 16 7 cal ka bp which points to a strong influence by lgi glacimarine sedimentation regimes similar patterns are also observed in total organic carbon and cadmium paleoproductivity proxies mid holocene peaks in the terrestrial organic matter fraction at 5 5 4 7 3 5 and 1 2 cal ka bp indicate periods of enhanced delivery of glaciomarine sediments by the alaska coastal current the b a and earliest holocene intervals are laminated and enrichments of redox sensitive elements suggest dysoxic to anoxic conditions in the water column the laminations are also associated with mildly enriched sedimentary 15n ratios indicating a link between productivity nitrogen cycle dynamics and sedimentary anoxia after applying a correction for terrestrial 15n contributions based on end member mixing models of terrestrial and marine organic matter the resulting b a marine 15n 6 3 0 4 ratios are consistent with either mild denitrification or increased nitrate utilization these findings can be explained by increased micronutrient fe availability during episodes of rapid rising sea level that released iron from the previously subaerial coastal plain iron input from enhanced terrestrial runoff and or the intermittent presence of seasonal sea ice resulting from altered ocean atmospheric circulation during the b a in the gulf of alaska

carbon isotopes and habitat of polar planktic foraminifera in the okhotsk sea the carbonate ion effect under natural conditions the upper 500 or 1000 m of the water column in the okhotsk sea was sampled for living planktic foraminifera the polar species neogloboquadrina pachyderma sinistral strongly dominates the foraminiferal assemblage the subpolar to temperate species globigerina bulloides accounts for 10 25 other species account for up to 3 only the shell 18o and 13c values of the species n pachyderma sin are compared to water 18o values and 13c values of dissolved inorganic carbon dic the strong gradient in 18o composition and temperature in the upper water column is reflected in the 18o of n pachyderma sin relative to the values expected for inorganic calcite precipitated under equilibrium conditions n pachyderma sin displays a vital effect of about 1 in 18o the 13c composition of n pachyderma sin is about constant with water depth and the reflection of 13cdic in the foraminiferal shell seems to be masked by other effects most foraminifera are found above or slightly below the thermocline and can be assumed to calcify in the upper 200 m of the water column the gradient of 13cdic extends well below this depth therefore the lack of correlation can partly be attributed to this fact the remaining discrepancy between 13c of n pachyderma sin and 13cdic correlates with the carbonate ion concentration in the water column this leads to the conclusion that the carbonate ion effect cie which has been derived from culturing experiments for other species spero et al 1997 nature 390 497 500 is found here under natural conditions when the magnitude of the cie derived for g bulloides is applied to n pachyderma sin cie corrected 13c of n pachyderma sin is a direct reflection of 13cdic in the water column with a constant offset of 1 2

building and testing age models for radiocarbon dates in lateglacial and early holocene sediments the growing importance of understanding past abrupt climate variability at a regional and global scale has led to the realisation that independent chronologies of past environmental change need to be compared between various archives this has in turn led to attempts at significant improvements in the required precision at which records can be dated radiocarbon dating is still the most prominent method for dating organic material from terrestrial and marine archives and as such many of the recent developments in improving precision have been aimed at this technique these include 1 selection of the most suitable datable fractions within a record 2 the development of better calibration curves and 3 more precise age modelling techniques while much attention has been focussed on the first two items testing the possibilities of the relatively new age modelling approaches has not received much attention here we test the potential for methods designed to significantly improve precision in radiocarbon based age models wiggle match dating and various forms of bayesian analyses we demonstrate that while all of the methods can perform very well in some scenarios caution must be taken when applying them it appears that an integrated approach is required in real life dating situations where more than one model is applied with strict error calculation and with the integration of radiocarbon data with sedimentological analyses of site formation processes

atmospheric transport of iron and its deposition in the ocean the atmospheric transport of continental weathering products is responsible for much of the mineral material and fe entering the open ocean and is probably the dominant source of nutrient fe in the photic zone in regions where other nutrients are present in high concentrations the flux of fe from the atmosphere may be a limiting factor in primary productivity due to the larger source regions for dust north of the equator 8 times more atmospheric fe is deposited in the northern hemisphere than in the southern hemisphere the mineral aerosol and fe transport and deposition are highly variable due to the episodic nature of dust generation and its transport and deposition processes between 10 and 50 of the total atmospheric fe entering the world ocean appears to dissolve i e it will pass through a 0 4 m pore size filter rapidly when the mineral matter enters the ocean much of the atmospheric fe is present as fe ii apparently produced as a result of photochemical reduction reactions taking place during atmospheric transport this readily soluble fe ii should be available immediately for use as a nutrient by phytoplankton atmospheric transport from the continents is estimated to supply 3 times as much dissolved fe to the oceans as that delivered via rivers

large changes in seasonal sea ice distribution and productivity in the sea of okhotsk during the deglaciations changes in the surface environment of the central sea of okhotsk were reconstructed using tex86 paleothermometry facilitated by the bit index in order to investigate paleoenvironmental changes during the glacial interglacial cycles the core top tex86 derived temperature is the same as the present day summer sea surface temperature sst suggesting that tex86 records seasonal rather than annually averaged ssts in this region the tex86 record reveals 3 c lower summer sst during glacial maxima than during interglacial periods and significant warming during the deglaciations 15 10 ka and 136 130 ka this is consistent with previous inferences of more expanded and persistent seasonal sea ice during the glacial periods than the present day and its substantial retreat during the deglaciation timing of the deglacial warming also coincided with a distinct increase in coccolithophorid productivity suggesting a causal relationship between sea surface warming and coccolithophorid blooms during the deglaciations the relationship could reflect an increase in the supply of fresh and warm water from the amur river during deglaciation which significantly impacted hydrology by facilitating sea surface stratification which in turn promoted production of coccolithophids

environmental change in the sea of okhotsk during the last 1 1 million years on the basis of two sedimentary records from the central sea of okhotsk we reconstruct the closely coupled glacial interglacial changes in terrigenous flux marine productivity and sea ice coverage over the past 1 1 myr the correspondance of our sedimentary records to the china loess grain size record china loess particle timescale chiloparts suggests that environmental changes in both the sea of okhotsk area and in se asia were closely related via the siberian atmospheric high pressure cell during full glacial times our records point to a strong siberian high causing northerly wind directions the extension of the sea ice cover and a reduced amur river discharge deglacial maxima of terrigenous flux were succeeded by or synchronous to high productivity events marine productivity was strengthened during glacial terminations because of an effective nutrient utilization at times of enhanced water column stratification and high nutrient supply from fluvial runoff and sea ice thawing during interglacials se monsoonal winds prevailed analogous to today s summer situation of a pronounced mongolian heat low and a strong hawaiian high strong freshwater discharge induced by high precipitation rates in the amur drainage area and a seasonally reduced and mobile sea ice cover favored marine productivity although being considerably lower than during the terminations and a lowered flux of ice rafted detritus

iron and macro nutrient concentrations in sea ice and their impact on the nutritional status of surface waters in the southern okhotsk sea abstract to elucidate the roles of sea ice in biogeochemical cycles in the sea of okhotsk the concentrations of macro nutrients no3 no2 po4 sio2 and nh4 and trace elements fe al were measured in samples of sea ice overlying snow and seawater the oxygen isotope ratio 18o in the sea ice was used to distinguish between snow ice and seawater origin ice except for nh4 the macro nutrient concentrations were lower in sea ice than in surface water in the ice covered area a linear relationship between salinity and concentrations of no3 no2 po4 and sio2 in the sea ice indicated that these macro nutrients originated mainly from seawater the fe concentrations in sea ice were variable and several orders of magnitude higher than those in surface water in the ice covered area the fe concentrations in the sea ice were positively correlated with al concentrations the suggestion being that the fe contained in the sea ice originated mainly from lithogenic mineral particles the annual fe flux into the surface water from sea ice melting in the southern sea of okhotsk was estimated to be 740 mol fe m 2 yr 1 this flux is comparable to the reported annual atmospheric fe flux 267 929 mol fe m 2 yr 1 in the western north pacific in spring sea ice melting may slightly dilute macro nutrient concentrations but increase fe concentrations in surface water these results suggest that sea ice may contribute to phytoplankton growth by release of fe into the water column and have a large impact on biogeochemical cycles in the sea of okhotsk

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

the deglacial transition on the southeastern alaska margin meltwater input sea level rise marine productivity and sedimentary anoxia 1 oxygen isotope data from planktonic and benthic foraminifera on a high resolution age model 44 14c dates spanning 17 400 years document deglacial environmental change on the southeast alaska margin 59 33 32 n 144 9 21 w 682 m water depth surface freshening i e 18o reduction of 0 8 began at 16 650 170 cal years b p during an interval of ice proximal sedimentation likely due to freshwater input from melting glaciers a sharp transition to laminated hemipelagic sediments constrains retreat of regional outlet glaciers onto land circa 14 790 380 cal years b p abrupt warming and or freshening of the surface ocean i e additional 18o reduction of 0 9 coincides with the bolling interstade of northern europe and greenland cooling and or higher salinities returned during the allerod interval coincident with the antarctic cold reversal and continue until 11 740 200 cal years b p when onset of warming coincides with the end of the younger dryas an abrupt 1 reduction in benthic 18o at 14 250 290 cal years b p likely reflects a decrease in bottom water salinity driven by deep mixing of glacial meltwater a regional megaflood event or brine formation associated with sea ice two laminated opal rich intervals record discrete episodes of high productivity during the last deglaciation these events precisely dated here at 14 790 380 to 12 990 190 cal years b p and 11 160 130 to 10 750 220 cal years b p likely correlate to similar features observed elsewhere on the margins of the north pacific and are coeval with episodes of rapid sea level rise remobilization of iron from newly inundated continental shelves may have helped to fuel these episodes of elevated primary productivity and sedimentary anoxia

deglacial variability in okhotsk sea intermediate water ventilation and biogeochemistry implications for north pacific nutrient supply and productivity highlights multi proxy multi site reconstruction of okhotsk sea palaeo productivity and mid depth ventilation changes from 8 to 18 ka link between hinterland river discharge and downstream okhotsk sea intermediate water osiw ventilation nutrient signatures surplus fe si oh 4 export in osiw during bolling allerod to pelagic pacific supported transient nutrient replete conditions subarctic and subtropical pacific gyres disconnected during bolling allerod with restricted osiw flow to lower latitudes deglacial osiw export and mid depth pacific biogeochemistry modulate millennial scale regional co2 source sink conditions the modern north pacific plays a critical role in marine biogeochemical cycles as an oceanic sink of co2 and by bearing some of the most productive and least oxygenated waters of the world ocean the capacity to sequester co2 is limited by efficient nutrient supply to the mixed layer particularly from deeper water masses in the pacific s subarctic and marginal seas the region is in addition only weakly ventilated by north pacific intermediate water npiw which receives its characteristics from okhotsk sea intermediate water osiw here we present reconstructions of intermediate water ventilation and productivity variations in the okhotsk sea that cover the last glacial termination between eight and 18 ka based on a set of high resolution sediment cores from sites directly downstream of osiw formation in a multi proxy approach we use total organic carbon toc chlorin biogenic opal and caco3 concentrations as indicators for biological productivity c n ratios and xrf scanning derived elemental ratios si k and fe k as well as chlorophycean algae counts document changes in amur freshwater and sediment discharge that condition the osiw stable carbon isotopes of epi and shallow endobenthic foraminifera in combination with 14c analyses of benthic and planktic foraminifera imply decreases in osiw oxygenation during deglacial warm phases from c 14 7 to 13 ka bolling allerod and c 11 4 to 9 ka preboreal no concomitant decreases in okhotsk sea benthic planktic ventilation ages are observed in contrast to nearby but southerly locations on the japan continental margin we attribute okhotsk sea mid depth oxygenation decreases in times of enhanced organic matter supply to maxima in remineralization within osiw in line with multi proxy evidence for maxima in primary productivity and supply of organic matter sedimentary c n and fe k ratios indicate more effective entrainment of nutrients into osiw and thus an increased nutrient load of osiw during deglacial warm periods correlation of palynological and sedimentological evidence from our sites with hinterland reference records suggests that millennial scale changes in osiw oxygen and nutrient concentrations were largely influenced by fluvial freshwater runoff maxima from the amur caused by a deglacial northeastward propagation of the east asian summer monsoon that increased precipitation and temperatures in conjunction with melting of permafrost in the amur catchment area we suggest that osiw ventilation minima and the high lateral supply of nutrients and organic matter during the allerod and preboreal are mechanistically linked to concurrent maxima in nutrient utilization and biological productivity in the subpolar northwest pacific in this scenario increased export of nutrients from the okhotsk sea during deglacial warm phases supported subarctic pacific shifts from generally fe limiting conditions to transient nutrient replete regimes through enhanced advection of mid depth nutrient and fe rich osiw into the upper ocean this mechanism may have moderated the role of the subarctic pacific in the deglacial co2 rise on millennial timescales by combining the upwelling of old carbon rich waters with a transient delivery of mid depth derived bio available fe and silicate

simulation of high concentration of iron in dense shelf water in the okhotsk sea abstract an ocean general circulation model coupled with a simple biogeochemical model was developed to simulate iron circulation in and around the sea of okhotsk the model has two external sources of iron dust iron at the sea surface and sedimentary iron at the seabed shallower than 300 m the model represented characteristic features reasonably well such as high iron concentration in the dense shelf water dsw and its mixing which extends southward in the intermediate layer from the northwestern shelf along sakhalin island and finally flows into the pacific sensitivity experiments for the solubility of dust iron in seawater suggest that a solubility of 1 is appropriate in our simulation higher solubilities 5 and 10 result in too low phosphate in the northwestern north pacific in summer as well as too high iron concentrations at the sea surface compared with observations besides these experiments show that dust iron hardly contributes to the high iron concentration in the intermediate layer to investigate locations from which the iron in the intermediate layer originates the fate of sedimentary iron input from four regions in the okhotsk sea was examined results suggest that the western and central parts of the northern shelf are important

the continental margin is a key source of iron to the hnlc north pacific ocean here we show that labile particulate iron and manganese concentrations in the upper 500m of the western subarctic pacific an iron limited high nutrient low chlorophyll hnlc region have prominent subsurface maxima between 100 200 m reaching 3 nm and 600 pm respectively the subsurface concentration maxima in particulate fe are characterized by a more reduced oxidation state suggesting a source from primary volcagenic minerals such as from the kuril kamchatka margin the systematics of these profiles suggest a consistently strong lateral advection of labile mn and fe from redox mobilized labile sources at the continental shelf supplemented by a more variable source of fe from the upper continental slope this subsurface supply of iron from the continental margin is shallow enough to be accessible to the surface through winter upwelling and vertical mixing and is likely a key source of bioavailable fe to the hnlc north pacific

the mangaroon orogeny synchronous c 1 7 ga magmatism and low p high t metamorphism in the west australian craton abstract the capricorn orogen records nearly one billion years of intraplate orogenesis within the west australian craton although the processes responsible for this protracted punctuated reworking remain unclear of the major tectonic events that affected the region the 1680 1620 ma mangaroon orogeny is one of the least well understood mainly due to a lack of direct ages for metamorphism an absence of pressure p temperature t constraints and uncertainty regarding the duration of granitic magmatism that is spatially and possibly temporally associated with deformation in this study we define the p t time t conditions associated with the mangaroon orogeny based on in situ shrimp u pb monazite and xenotime geochronology and calculated p t pseudosections data from a pelitic migmatite constrain the timing of low p high t metamorphism to 1691 7 ma at conditions of 665 755 c and 2 7 4 3 kbar 175 240 c kbar data from a garnet bearing sillimanite biotite pelitic gneiss suggests higher pressure during the clockwise prograde history at one locality furthermore the onset of the metamorphism coincides with the oldest granites in the region 1695 9 ma which constrain the onset of the mangaroon orogeny our results also show that deposition and burial of the precursor sediments occurred at most c 70 million years before the onset of partial melting at c 1695 ma therefore there was no long incubation period before the onset of orogenesis we conclude that unlike many of the proterozoic orogenic events in australia the c 1 7 ga low p high t metamorphism recorded in the upper crust in the capricorn orogen cannot be explained by a thermal lid model but rather was synchronous with granitic magmatism

subarctic pacific evidence for a glacial deepening of the oceanic respired carbon pool abstract measurements of benthic foraminiferal cadmium calcium cd ca have indicated that the glacial interglacial change in deep north pacific phosphate po4 concentration was minimal which has been taken by some workers as a sign that the biological pump did not store more carbon in the deep glacial ocean here we present sedimentary redox sensitive trace metal records from ocean drilling program odp site 882 nw subarctic pacific water depth 3244 m to make inferences about changes in deep north pacific oxygenation and thus respired carbon storage over the past 150 000 yr these observations are complemented with biogenic barium and opal measurements as indicators for past organic carbon export to separate the influences of deep water oxygen concentration and sedimentary organic carbon respiration on the redox state of the sediment our results suggest that the deep subarctic pacific water mass was depleted in oxygen during glacial maxima though it was not anoxic we reconcile our results with the existing benthic foraminiferal cd ca by invoking a decrease in the fraction of the deep ocean nutrient inventory that was preformed rather than remineralized this change would have corresponded to an increase in the deep pacific storage of respired carbon which would have lowered atmospheric carbon dioxide co2 by sequestering co2 away from the atmosphere and by increasing ocean alkalinity through a transient dissolution event in the deep sea the magnitude of change in preformed nutrients suggested by the north pacific data would have accounted for a majority of the observed decrease in glacial atmospheric pco2

the siberian loess record and its significance for reconstruction of pleistocene climate change in north central asia abstract the siberian loess represents the most significant terrestrial proxy record of quaternary climatic history in northern asia loess is extensive in southern siberia between the irtysh basin in the west and the angara basin in the east palaeoenvironmental multi proxy data magnetic susceptibility ms grain size caco 3 toc pollen etc from high resolution loess palaeosol sections provide evidence for a strongly fluctuating climatic sequence in north central asia during the late quaternary displaying the globally diagnostic sequences found in the deep sea oxygen isotope records ms provides the most continuous and detailed record encompassing the last two interglacial glacial cycles in loess sections in the minusinsk basin yenisei area and on the northern altai plains evidence for periodic atmospheric shifts is provided by gradual changes in the main vegetation zones with parkland steppe and mixed taiga during warm interglacial interstadial stages being replaced by boreal tundra forest and arid periglacial tundra steppe during stadials climatic pulses from warm intervals to cold are recorded by incipient forest steppe tundra gleysols the occurrence of the highest sediment accumulation rates in glacial stages ois 4 and ois 2 in the southern plains and depressions indicates that the most intensive aeolian dust deposition followed the glacial maxima with the most recent interval dated to ca 19 15 ka bp because of its zonal distribution and pronounced climatic continentality the siberian loess region represents an important data source for reconstructing past climates in the northern hemisphere it provides a key to the correlation of other loess regions within the west east eurasian continental zone

a biomarker approach for assessing marine and terrigenous inputs to the sediments of sea of okhotsk for the last 27 000 years abstract a sediment core taken from the sea of okhotsk which is located in the western north pacific rim with an extensive seasonal sea ice cover was investigated for lipid class compounds total organic carbon total nitrogen and 13 c of bulk organic matter to reconstruct changes in sedimentary regimes of marine and terrestrial organic matter over the last 27 kyrs higher molecular weight n alkanes fatty acids and fatty alcohols showed an increase in terrigenous inputs in glacial and to a greater extent in early deglacial periods the enhanced terrestrial input in the deglaciation stages has for the first time been found and never been reported in the open ocean biomarker profiles together with the coarse grain size distribution in nearby sediment cores suggested that sea ice rafting was the main transport mechanism of continental material to the okhotsk sea sediments however the ice rafting inputs have been weakened from 14 kyrs bp to the holocene probably due to a rapid reduction of the sea ice cover and continental shelf erosion profiles of c 37 alkenones phytol and brassicasterol as well as temporal variation in calcium carbonate and organic carbon contents indicated that the marine inputs were enhanced during the deglaciation the enhanced marine inputs were likely caused by an intensification of the primary production induced by a possibly increased nutrient supply from the continental shelves in early deglaciation and by the deglacial retreat of the sea ice cover at 14 kyrs bp this study demonstrates that biomarkers in the marginal marine sediments had recorded changes in the biogeochemical processes in the sea of okhotsk over the last 27 kyrs which may be significantly affected by changes in the okhotsk water exchange processes such as sea ice activity and sea ice transport of terrigenous materials

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

okhotsk sea ice coverage and kamchatka glaciation over the last 350ka evidence from ice rafted debris and planktonic δ18o high resolution records of ice rafted debris ird and oxygen isotope records spanning an e w trending transect across the okhotsk sea unravel the marine and terrestrial cryogenic history of ne siberia over the last 350 kyr ird predominantly dispersed basin wide by sea ice shows lowest fluxes during interglacial periods implying a reduced and seasonal sea ice coverage highest ird accumulation rates are observed during glacial and deglacial periods with a more extended but highly dynamic ice cover although being rather synchronous ird fluxes are on average higher in the western okhotsk sea than in the eastern part pointing to a persistent but mobile particle supplying sea ice cover even during full glacial conditions presumably less dense in the eastern parts mis 6 is exceptional in this respect asynchronous fluxes of ird which vary spatially reflect rapid paleoclimatic and paleo glaciomarine changes ird accumulation rates were by factor 2 3 higher during mis 6 as compared to the last glacial maximum and the ird depositional center shifted from the western okhotsk sea early mis 6 toward kamchatka late mis 6 synchronous to a distinct change in the ird mineral composition both the characteristic composition of late mis 6 ird originating from the sredinny mountain range of kamchatka and their significantly enhanced accumulation rates refer to intensified iceberg dispersal across the eastern part of the okhotsk sea at 138 ka 135 ka 129 ka and 128 ka bp this scenario affords the presence of extended mountain glaciers protruding down to sea level on the western side of kamchatka anomalously light planktonic stable oxygen isotopes during mis 6 3 termination ii and mis 5 5 5 4 suggest significant freshwater supply related to the westward drainage of kamchatka glaciers the intensified kamchatka glaciation observed during late mis 6 was repeated during mis 3 iceberg discharges into the eastern okhotsk sea are observed at 60 ka 51 ka 42 ka 38 ka 36 ka and 31 ka and may partly correspond to n atlantic heinrich events

oceanic iron supply mechanisms which support the spring diatom bloom in the oyashio region western subarctic pacific 1 multiyear 2003 2008 time series observations along the a line provided information on the temporal variability of the dissolved iron diss fe concentration in the oyashio region of the western subarctic pacific and the data indicated that there was an annual cycle in the concentration of surface diss fe occurring every year diss fe was supplied into the surface water in this region every winter and supports the spring phytoplankton bloom after development of the thermocline the diss fe concentration was drawn down during the phytoplankton bloom period and was depleted in summer in some water masses then diss fe increased from autumn to winter with the increasing depth of the surface mixed layer the high diss fe concentrations in the surface layer in winter were controlled by mesoscale oceanic intrinsic processes such as vertical winter mixing and horizontal fe rich intermediate water transport difference in magnitude of the winter mixing processes among different water masses caused the heterogeneous distribution of diss fe concentration in the surface layer moreover the vertical section profiles along a cross oyashio transect showed the occurrence of fe rich intermediate water and upward transport of materials from the intermediate water to the surface layer via tidal and winter mixing processes are important mechanisms to explain the high winter surface diss fe concentrations additionally the substantially higher diss fe no3 ratio in the winter surface layer in this studied area other than the high nutrient low chlorophyll region indicates that the winter surface water in the oyashio and the oyashio kuroshio transition zone has a high potential to stimulate phytoplankton growth

new pollen records of late pleistocene and holocene changes of environment and climate in the lower amur river basin ne eurasia abstract the late pleistocene holocene paleoclimate and paleoenvironmental changes of the lower amur basin are presented based on pollen records from radiocarbon dated peat sections the gur section represents the most complete terrestrial record of the russian far east and probably for all of northeast asia landscape changes are reconstructed for warm events corresponding to the bolling and allerod and cold episodes as middle dryas and younger dryas in europe there were three warm periods in the lower amur basin 8900 8300 5000 5700 and 3200 4200 bp a major expansion of diverse species in the forest formations in the entire lower amur river basin occurred at 5000 5700 bp changes and developments of paleoclimate events and paleoenvironmental changes of late pleistocene and holocene in lower amur basin were correlative with european climate events

amundsen sea bathymetry the benefits of using gravity data for bathymetric prediction bathymetric charts are essential for modeling oceanic processes yet in remote areas direct measurements of seafloor depth are often scarce it is possible to augment sparse depth soundings with dense satellite derived gravity data to provide additional bathymetric detail in regions devoid of sounding data we demonstrate this method by using marine gravity derived from the european remote sensing ers 1 satellite altimeter combined with depth soundings to form a bathymetric prediction of the amundsen sea west antarctica we estimate the root mean square error of depth estimates at unsurveyed locations in our solution to be 120 m we use a monte carlo method to assess the value of gravity as a bathymetric predictor in sparsely surveyed regions by comparing our solution to predictions formed from depth soundings alone when less than 11 of 10 km grid cells contain depth soundings inclusion of gravity data improves the depth accuracy of the solution by up to 17 as compared to a minimum curvature surface interpolation of the depth soundings alone when depth data are sparse our gravity derived prediction reveals additional short wavelength bathymetric features such as troughs on the continental shelf which are not resolved by interpolations of the depth soundings alone

a high resolution absolute dated holocene and deglacial asian monsoon record from dongge cave china abstract we present a continuous record of the asian monsoon over the last 16 ka from 18o measurements of stalagmite calcite over 900 oxygen isotopic measurements providing information on shifts in monsoon precipitation are combined with a chronology from 45 precise 230th dates 18o and therefore asian monsoon intensity generally follows changes in insolation although changes in 18o are generally accommodated in abrupt shifts in contrast to smoothly varying insolation indicating that threshold effects may be important 18o decreased dramatically 3 at the start of the holocene 11 5 ka and remained low for 6 ka four positive 18o events centered at 11225 97 yr bp 1 05 10880 117 yr bp 1 15 9165 75 yr bp 1 4 and a double event centered at 8260 64 yr bp 1 1 and 8080 74 yr bp 1 0 punctuated this period of high monsoon intensity all four events correlate within error with climate changes in greenland ice cores thus the relationship between the asian monsoon and the north atlantic observed during the glacial period appears to continue into the early holocene in addition three of the four events correlate within error with outburst events from lake agassiz the decline of monsoon intensity in the mid late holocene is characterized by an abrupt positive shift in 18o which occurs at 3550 59 yr bp 1 1 in 100 yr in addition the holocene is punctuated by numerous centennial and multi decadal scale events amplitudes 0 5 to 1 up to half the amplitude of the glacial interstadial events seen in the last glacial period thus holocene centennial and multi decadal scale monsoon variability is significant although not as large as glacial millennial scale variability the monsoon shows a strong connection with northern south american hydrological changes related by changes in itcz position spectral analysis of the 18o record shows significant peaks at solar periodicities of 208 yr and 86 yr suggesting variation is influenced by solar forcing however there are numerous other significant peaks including peaks at el nino frequencies observed for high resolution portions of the record between 8110 and 8250 yr which suggest that changes in oceanic and atmospheric circulation patterns in addition to those forced by solar changes are important in controlling holocene monsoon climate in addition for this high resolution portion we observe a distinctive biennial oscillation of the asian monsoon which has been associated with the tropospheric biennial oscillation tbo

radiocarbon profiles of the nw pacific from the lgm and deglaciation evaluating ventilation metrics and the effect of uncertain surface reservoir ages during the last deglaciation the ventilation of the subarctic pacific is hypothesized to have changed dramatically including the rejuvenation of a poorly ventilated abyssal water mass that filled the deep ocean and fluctuations in the strength of north pacific intermediate and deep water formation at millennial timescales foraminiferal radiocarbon reconstructions of past ventilation changes in the pacific are valuable but are hampered by poor carbonate preservation low sediment accumulation rates bias from bioturbation and poorly constrained past surface reservoir age in this study we present paired benthic planktonic radiocarbon measurements from the okhotsk sea and emperor seamounts we take advantage of large contemporaneous peaks in benthic abundances from the last glacial maximum bolling allerod ba and early holocene to produce time slices of radiocarbon from 1 to 4 km water depth we explore the impact of uncertain surface reservoir age and evaluate several approaches to quantifying past ocean radiocarbon distribution using our nw pacific data and a compilation of published data from the north pacific both the calendar age and the absolute value of an ocean radiocarbon estimate depend on the assumed surface reservoir age but for a time slice from a small geographical area with radiocarbon independent stratigraphic correlation between cores the shape of a water column profile is independent of surface reservoir age the nw pacific profiles are similar in shape to the compilation profiles for the entire north pacific which suggests that deglacial surface reservoir age changes across the n pacific did not diverge dramatically across the areas sampled the last glacial maximum lgm profile 2 km spans a wide range of values ranging from values similar to today to lower than today however by the ba the profile has a similar shape to today ultimately local surface reservoir ages end member water mass composition and mixing ratios must each be constrained before a radiocarbon activity reconstruction can be used to confidently infer ventilation changes

direct ventilation of the north pacific did not reach the deep ocean during the last deglaciation 1 despite its tremendous size the deep north pacific has received relatively little attention by paleoceanographers it was recently suggested that the deep north pacific was directly ventilated by dense waters formed in the subarctic pacific during heinrich stadial 1 hs1 of the early deglaciation here we present new redox sensitive trace metal data from a sediment core at 2393 m in the subarctic pacific in comparison with previously published data from elsewhere in the region the combined picture shows no sign of ventilation during the early deglaciation in any available core from water depths of 2393 m and deeper while the deepest core to display clear signs of enhanced ventilation during hs1 was raised from 1366 m water depth thus it appears likely that although the north pacific was well ventilated to intermediate depths during hs1 the deep ocean did not receive a significant input of dense waters from a local source but remained isolated from the surface waters above

glacial to deglacial ventilation and productivity changes in the southern okhotsk sea abstract as a source region of north pacific intermediate water the okhotsk sea plays an important role in the ventilation of the north pacific to understand the detailed oceanographic changes in this marginal sea since the last glaciation we studied decadal to centennial scale proxy records from new sediment cores from the southwestern okhotsk sea glacial to holocene 14 c records of benthic foraminiferal shells suggested enhanced ventilation in the okhotsk sea during the early deglacial period between 18 and 15 ka corresponding to heinrich event 1 although the 14 c reconstruction has considerable uncertainties the okhotsk sea may have acted as a source for vigorous ventilation of the subarctic pacific during this period caco 3 preservation events appear to be better explained by the ventilation history of the okhotsk sea than by coccolithophores and foraminifera production caco 3 preservation started to improve during 18 to 15 ka and pronounced peaks in the caco 3 content corresponded to the bolling allerod 15 to 13 ka and preboreal 11 5 to 10 ka warm periods diatom and coccolithophore productivity remained low in the okhotsk sea throughout the glacial to deglacial periods different from the situation in the open subarctic pacific where high productivity was observed during the bolling allerod period after the preboreal period biogenic opal gradually increased and 15 n decreased in the southern okhotsk sea suggesting that productivity was enhanced by a relaxation of the nitrate limitation

sea surface temperature variability and sea ice extent in the subarctic northwest pacific during the past 15 000 years past changes in north pacific sea surface temperatures and sea ice conditions are proposed to play a crucial role in deglacial climate development and ocean circulation but are less well known than from the north atlantic here we present new alkenone based sea surface temperature records from the subarctic northwest pacific and its marginal seas bering sea and sea of okhotsk for the time interval of the last 15 kyr indicating millennial scale sea surface temperature fluctuations similar to short term deglacial climate oscillations known from greenland ice core records past changes in sea ice distribution are derived from relative percentage of specific diatom groups and qualitative assessment of the ip25 biomarker related to sea ice diatoms the deglacial variability in sea ice extent matches the sea surface temperature fluctuations these fluctuations suggest a linkage to deglacial variations in atlantic meridional overturning circulation and a close atmospheric coupling between the north pacific and north atlantic during the holocene the subarctic north pacific is marked by complex sea surface temperature trends which do not support the hypothesis of a holocene seesaw in temperature development between the north atlantic and the north pacific key points millennial scale changes in sst in the north pacific during the last 15 kyr changes in sea ice extent suggest a close coupling to sst fluctuations middle to late holocene ssts show no clear sst trend in the north pacific

increased dissolved terrestrial input to the coastal ocean during the last deglaciation 1 here we present the first downcore results for a new paleoproxy the mn ca ratio of foraminiferal calcite applied to sediment accumulated in the extreme eastern tropical north pacific etnp over the last 30 000 years the mn ca results are compared to oxygen isotopes and sea surface temperature calculated from mg ca we determined metal ratios using flow through time resolved analysis to minimize the effects of secondary mineralization the foraminiferal species used for this study calcify at different depths core top ratios of these variant species change in proportion to the concentration of dissolved manganese in the water column at the depth of calcification since terrestrial input and oxidation reduction reactions control the levels of dissolved mn in the oceans today it therefore should be possible to use the mn ca ratios of foraminifera as a proxy for these processes in the past mn ca of a mixed layer species g ruber suggest that dissolved terrestrial input to the surface waters of the etnp during the last glacial maximum was lower than today but began to increase with initial sea level rise and reached a maximum at 15 ka b p before coming down to present day levels at the end of sea level rise in the mid holocene 7 5 ka ratios of a deeper calcifying species n dutertrei mimic those of g ruber over this same time period consistent with shoaling of the 18 c thermocline mn ca of a benthic species u peregrina does not show a maximum at 15 ka suggesting that mn was efficiently remineralized in the water column during deglaciation assuming that the period from the last glacial until the mid holocene was a time of increased productivity as elevated mn might imply the oxygen minimum zone omz was at least as well developed during deglaciation as it is today expansion of the omz may have contributed to the mn ca trends we observe through time