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

dynamic phase boundary topography by latent heat effects abstract when radial flow passes through a mantle phase boundary the interplay of advection and diffusion of latent heat creates dynamic topography of this boundary which means a deflection that is related to the sense and magnitude of radial velocity even though the flow does not advect temperature differences towards the phase boundary a one dimensional stationary model is used to quantify the effect which does not dependent on the sign of the clapeyron slope significant deflection requires slow radial flow and a narrow phase loop these conditions are most probably met for the phase transition from spinel to perovskite and magnesiowustite at 660 km depth up to 4 km of topography peak to peak are created with a mass anomaly that is equivalent to 440 m of dynamic topography at the earth s surface other phase transitions of the olivine component also contribute to a degree that is less certain the time scale of adjustment of phase boundary topography is studied in a two dimensional model where a deep mass anomaly in an isentropic mantle drives flow through the 660 km phase boundary the adjustment time depends on the inverse square of the vertical velocity and is on the order of 10 ma in the earth which is shorter than the convective time scale for a high viscosity lower mantle dynamic phase boundary topography created by this mechanism can replace a significant part of the surface topography required in dynamic geoid models and can help to reduce the misfit between predicted dynamic surface topography and the upper limit that observations pose on its amplitude

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

identification of paleo arctic winter sea ice limits and the marginal ice zone optimised biomarker based reconstructions of late quaternary arctic sea ice abstract analysis of 100 surface sediments from across the barents sea has shown that the relative abundances of the mono unsaturated sea ice diatom derived biomarker ip 25 and a tri unsaturated highly branched isoprenoid hbi lipid hbi iii are characteristic of the overlying surface oceanographic conditions most notably the location of the seasonal sea ice edge thus while ip 25 is generally limited to locations experiencing seasonal sea ice with higher abundances found for locations with longer periods of ice cover hbi iii is found in sediments from all sampling locations but is significantly enhanced in sediments within the vicinity of the retreating sea ice edge or marginal ice zone miz the response of hbi iii to this well defined sea ice scenario also appears to be more selective than that of the more generic phytoplankton biomarker brassicasterol the potential for the combined analysis of ip 25 and hbi iii to provide more detailed assessments of past sea ice conditions than ip 25 alone has been investigated by quantifying both biomarkers in three marine downcore records from locations with contrasting modern sea ice settings for sediment cores from the western barents sea intermittent seasonal sea ice and the northern norwegian sea ice free high ip 25 and low hbi iii during the younger dryas ca 12 9 11 9 cal kyr bp is consistent with extensive sea cover with relatively short periods of ice free conditions resulting from late summer retreat towards the end of the yd ca 11 9 11 5 cal kyr bp a general amelioration of conditions resulted in a near winter maximum ice edge scenario for both locations although this was somewhat variable and the eventual transition to predominantly ice free conditions was later for the western barents sea site ca 9 9 cal kyr bp compared to nw norway ca 11 5 cal kyr bp for both locations coeval elevated hbi iii but absent ip 25 potentially provides further evidence for increased atlantic water inflow during the early holocene but this interpretation requires further investigation in contrast ip 25 and hbi iii data obtained from a core from the northern barents sea demonstrate that seasonal sea ice prevailed throughout the holocene but with a gradual shift from winter ice edge conditions during the early holocene to more sustained ice cover in the neoglacial a directional shift that has undergone a reverse in the last ca 150 yr according to observational records our combined surface and downcore datasets suggest that combined analysis of ip 25 and hbi iii can provide information on temporal variations in the position of the maximum winter arctic sea ice extent together with insights into sea ice seasonality by characterisation of the miz combining ip 25 with hbi iii in the form of the previously proposed pip 25 index yields similar outcomes to those obtained using brassicasterol as the phytoplankton marker importantly however some problems associated with use of a variable balance factor employed in the pip 25 calculation are potentially alleviated using hbi iii

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

magnetostratigraphy of marine sediment core md01 2414 from okhotsk sea and its paleoenvironmental implications abstract this study used a paleomagnetic method to analyze the marine sediment core called md01 2414 taken from the okhotsk sea during the images vii cruise in 2001 the results indicate that the brunhes matuyama boundary appeared at the depth of 27 76 m with the age of 0 78 ma the lower and upper bounds of the jaramillo event are located at 36 96 and 34 74 m depth respectively cobb mountain event is found at a depth between 40 67 m and 41 06 m close to the bottom of the core normal polarity is observed it is proposed to be the termination of the olduvai normal event this event implies that this core signifies an age interval of about 1 8 ma excursions could be identified from the paleomagnetic directional record such as kamikatsula santa rosa the relative paleo intensity secular variation pattern also helped to delimit magnetic excursions in the brunhes normal epoch e g iceland basin event big lost event etc thus the age model of this core can be well established based on the age model the variations of magnetic susceptibility and arm of this core indicated that highly abundant but relatively coarse grain of magnetic minerals appeared in the even stages of oxygen isotope chronology while low abundance with finer grain appeared in the interglacial periods this suggests that there are different sources and transportation pathways of the sediments deposited in the area studied during glacial and interglacial periods during the glacial time terrigenous sediments containing abundant magnetic minerals eroded by the ice river from the kamchatka peninsula were brought into the central okhotsk sea by the west kamchatkan current wkc while the central and western parts of the okhotsk sea were completely covered by sea ice during the interglacial time the wkc and the east sakhalin current esc brought lots of terrigenous sediments from the north and west the siberia continent which contain less abundant magnetic minerals and dilute the signal of magnetic susceptibility

variability of sea ice conditions in the fram strait over the past 30 000 years sea ice is a critical component of the climate and oceanographic system in the north atlantic ocean a biomarker record reveals millennial scale and glacial interglacial fluctuations in sea ice coverage in the northernmost atlantic ocean over the past 30 000 years

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

modeling obliquity and co2effects on southern hemisphere climate during the past 408 ka abstractthe effect of obliquity and co2 changes on southern hemispheric climate is studied with a series of numerical modeling experiments using the earth system model of intermediate complexity loch vecode ecbilt clio agism model loveclim and a coupled general circulation model model for interdisciplinary research on climate miroc it is shown in time slice simulations that phases of low obliquity enhance the meridional extratropical temperature gradient increase the atmospheric baroclinicity and intensify the lower and middle troposphere southern hemisphere westerlies and storm tracks furthermore a transient model simulation is conducted with loveclim that covers the greenhouse gas ice sheet and orbital forcing history of the past 408 ka this simulation reproduces reconstructed glacial interglacial variations in temperature and sea ice qualitatively well and shows that the meridional heat transport associated with the orbitally paced modulation of middle troposphere westerlies and storm tr

ice rafted debris ird based sea ice expansion events during the past 100 kyrs in the okhotsk sea abstract ice rafted debris ird from sediment traps surficial sediments and sediment cores were investigated in order to reconstruct the extent history of sea ice cover during the last 100 kyrs in the okhotsk sea the seasonal ird buried into the sediments during and just after sea ice melting in spring consists of silt and sand size terrigenous particles the spatial distribution of ird within surficial sediments clearly corresponds to the extent of sea ice coverage sea ice expanded to a maximum extent during the glacial periods although sea ice cover was not perennial the okhotsk sea sea ice expansion osie events which are recognized by millennial scale abrupt peaks of ird content have occurred 13 times during the past 100 kyrs these events were amplified during the glacial periods a significant modification of the polar atmospheric circulation in the northern hemisphere is a key process in explaining these osie events

rapid shifts in subarctic pacific climate between 138 and 70 ka during the past decades remarkable changes in sea surface temperature sst and sea ice extent have been observed in the marginal seas of the subarctic pacific however little is known about natural climate variability at millennial time scales far beyond instrumental observations geological proxy records such as those derived from marine sediments offer a unique opportunity to investigate millennial scale natural climate variability of the artic and subarctic environments during past glacial interglacial cycles here we provide reconstructions of sea ice variability inferred from ip25 ice proxy with 25 carbon atoms sea ice biomarker and sst fluctuations based on alkenone unsaturation index graphic of the subarctic pacific realm between 138 and 70 ka warmest sea surface conditions were found during the early eemian interglacial 128 to 126 ka exceeding modern ssts by 2 c the further north pacific climate evolution is marked by pronounced oscillations in sst and sea ice extent on millennial time scales which correspond remarkably well to short term temperature oscillations known from greenland and the north atlantic these results imply a common forcing which seems to be closely coupled to dynamics of the atlantic meridional overturning circulation however immediate propagation of such climate fluctuations far beyond the north atlantic basin suggests a rapid circumpolar coupling mechanism probably acting through the atmosphere a prerequisite to explain the apparent synchronicity of remote climatic reorganizations in the subarctic pacific

a novel chemical fossil of palaeo sea ice ip25 a unique and novel organic compound has been detected in sea ice samples from three locations in the canadian arctic thousands of kilometers apart it is likely that this biomarker is produced by diatoms living in the sea ice and we provide evidence which suggests that the compound a c25 monounsaturated hydrocarbon ip25 may be a specific sensitive and stable proxy for sea ice in sediments over at least the holocene since it has not been reported before we confirmed its identity by synthesis and used the synthesized compound as a reference for quantifying ip25 in a range of sediments from an east west transect in the canadian arctic the recent sediments are either seasonally covered with ice or have permanent ice cover older sediments containing ip25 have been dated using radiocarbon methods to at least 9000 yr if the concept proves generally applicable monitoring ip25 in further sediment cores along with other accepted proxies should allow movements in the position of the ice edge throughout the holocene at least to be better determined which is essential for accurate calibration of climate prediction models a similar approach for antarctic samples of ice and sediments would also seem worthwhile

the arctic sea ice biomarker ip25 a review of current understanding recommendations for future research and applications in palaeo sea ice reconstructions in recent years a novel proxy for the past occurrence of arctic sea ice has been proposed that is based on the variable marine sedimentary abundance of an organic geochemical lipid derived from sea ice diatoms in the spring this lipid termed ip25 ice proxy with 25 carbon atoms is a highly branched isoprenoid mono unsaturated alkene that appears to be sufficiently stable in sediments to permit meaningful palaeo sea ice reconstructions to be carried out over short to long term timescales since the first proposed use of ip25 as a proxy for palaeo sea ice by belt et al 2007 a number of laboratories have measured this biomarker in arctic sediments and it is anticipated that research activity in this area will increase further in the future the content of this review is divided into a number of sections firstly we describe the scientific basis for the ip25 proxy and its initial discovery in arctic sea ice sedimenting particles and sediments secondly we summarise the relatively few studies that have to date concentrated on examining the factors that influence the production and fate of ip25 and we identify some areas of future research that need to be addressed in order to improve our understanding of ip25 data obtained from sedimentary analyses what is clear at this stage however it that the presence of ip25 in arctic marine sediments appears to represent a proxy measure of past seasonal sea ice rather than permanent or multi year ice conditions thirdly we highlight the importance of rigorous analytical identification and quantification of ip25 especially if measurements of this biomarker are going to be used for quantitative sea ice reconstructions rather than qualitative analyses alone presence absence fourthly we review some recent attempts to make the interpretations of ip25 biomarker data more detailed and quantitative by combining sedimentary abundances with those of phytoplankton and other sea ice derived biomarkers thus the bases for the so called pip25 and dip25 indices are described together with an overview of potential limitations concluding that investigations into the use of these indices needs further research before their full potential can be realised in the final section we provide a summary of ip25 based palaeo sea ice reconstruction case studies performed to date these case studies cover different arctic regions and timescales spanning decades to tens of thousands of years

increase and decrease of sea ice area in the sea of okhotsk ice production in coastal polynyas and dynamic thickening in convergence zones 1 this paper examines the production and reduction of sea ice area in the sea of okhotsk analyses were carried out for 10 winters december april from 1991 1992 to 2000 2001 using daily data of sea ice velocity and concentration derived from images of the defense meteorological satellite program dmsp special sensor microwave imager ssm i first we mapped sea ice divergence which was calculated from the daily ice velocity field in the case of offshore winds high divergence was observed along the coastline while there existed a broad convergence area with inshore winds next we examined local changes in an area of sea ice as in the case of ice divergence ice production and reduction are strongly controlled by wind direction we found that a large amount of sea ice was produced in coastal areas under offshore wind conditions the geographical distribution of the ice production area agrees well with that of the well known coastal polynya areas our estimation shows that 8 7 105 km2 yr 1 of sea ice is produced in the northern coastal area and 3 7 105 km2 yr 1 in the sakhalin coastal area in contrast 7 4 105 km2 yr 1 of the ice area disappeared in shantarskiy bay this reduction of ice area is mainly caused by dynamic deformation of existing ice forming rafted ice or pressure ridges this dynamic deformation plays an important role not only in the reduction of okhotsk sea ice area but also in the thickening of ice

precession and atmospheric co2 modulated variability of sea ice in the central okhotsk sea since 130 000 years ago abstract recent reduction in high latitude sea ice extent demonstrates that sea ice is highly sensitive to external and internal radiative forcings in order to better understand sea ice system responses to external orbital forcing and internal oscillations on orbital timescales here we reconstruct changes in sea ice extent and summer sea surface temperature ssst over the past 130 000 yrs in the central okhotsk sea we applied novel organic geochemical proxies of sea ice ip25 ssst tex l 86 and open water marine productivity a tri unsaturated highly branched isoprenoid and biogenic opal to marine sediment core md01 2414 53 11 77 n 149 34 80 e water depth 1123 m to complement the proxy data we also carried out transient earth system model simulations and sensitivity tests to identify contributions of different climatic forcing factors our results show that the central okhotsk sea was ice free during marine isotope stage mis 5e and the early mid holocene but experienced variable sea ice cover during mis 2 4 consistent with intervals of relatively high and low ssst respectively our data also show that the sea ice extent was governed by precession dominated insolation changes during intervals of atmospheric co2 concentrations ranging from 190 to 260 ppm however the proxy record and the model simulation data show that the central okhotsk sea was near ice free regardless of insolation forcing throughout the penultimate interglacial and during the holocene when atmospheric co2 was above 260 ppm past sea ice conditions in the central okhotsk sea were therefore strongly modulated by both orbital driven insolation and co2 induced radiative forcing during the past glacial interglacial cycle

assessment and calibration of tex86 paleothermometry in the sea of okhotsk and sub polar north pacific region implications for paleoceanography abstract we measured tex86 indices in surface sediments and sediment cores from marginal seas and open ocean sites in the north pacific to test the accuracy of tex86 paleothermometry in the region application of the global core top tex 86 l and tex 86 h calibrations in the sea of okhotsk and northern north pacific sub polar region results in over and under estimations of tex86 derived ssts in surface sediments in deep ocean and coastal areas respectively further challenges apparent in applying tex 86 l and tex 86 h in late quaternary sediment cores from the okhotsk sea mr06 04 pc7 and northwestern pacific mr00 k03 pc1 are unrealistically warm holocene mean annual reconstructed temperatures tex 86 l and excessively cold glacial temperatures tex 86 h compared with other high latitude records and climate models application of a calibration based on a sub set of deep tex 86 h in the glacial period in the okhotsk sea core mr06 04 pc7 however a regional comparison of okhotsk sea and sub polar surface sediment tex 86 l values with observational sea water temperatures at different seasons and water depths reveals that an optimized positive correlation is obtained with summer sub surface temperatures august 20 m depth the unique hydrographic setting of the okhotsk sea region likely exerts a strong control on the ecology of gdgt producers assumed to be primarily be marine thaumarchaeota resulting in highly season and depth specific export production and a distinct regional gradient in surface sediment tex86 values when our new regional tex 86 l calibration is applied to the sediment cores tex 86 l and alkenone u 37 k temperature estimates overlap in the holocene and tex 86 l produces plausible lgm to holocene temperature reconstructions our study provides a region specific calibration and confirms the importance of acquiring local calibration equations to optimize tex86 paleothermometry for specific regions and ocean basins

variability in modern sea surface temperature sea ice and terrigenous input in the sub polar north pacific and bering sea reconstruction from biomarker data in order to study the modern sea surface characteristics of the sub polar north pacific and the bering sea i e sea surface temperature sst and sea ice cover surface sediments recovered during the rv sonne expedition 202 in 2009 were analysed to distinguish between marine and terrestrial organic carbon hydrogen index values long chain n alkanes and specific sterols have been determined the results show that in the bering sea especially on the sea slope the organic carbon source is mainly caused by high primary production in the north pacific on the other hand the organic material originates predominantly from terrestrial higher plants probably related to dust input from asia sst has been reconstructed using the modified alkenone unsaturation index calibration from muller et al 1998 offers the most reliable estimate of mean annual temperature in the central north pacific but does not correlate with mean annual temperature throughout the study area in the eastern north pacific and the bering sea the sikes et al 1997 calibration seems to be more accurate and matches summer sst the distribution of the novel sea ice proxy ip25 highly branched c25 isoprenoid alkene in surface sediments is in accord with the modern spring sea ice edge and shows the potential of this proxy to track past variation in sea ice cover in the study area

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