geology of the d entrecasteaux new hebrides arc collision zone results from a deep submersible survey abstract during the subpso1 cruise seven submersible dives were conducted between water depths of 5350 and 900 m over the collision zone between the new hebrides island arc and the d entrecasteaux zone dez the dez a topographic high on the australian plate encompasses the north d entrecasteaux ridge ndr and the bougainville guyot both of which collide with the island are slope in this report we use diving observations and samples as well as dredging results to analyse the geology of the bougainville guyot and the outer arc slope in the dez arc collision zone and to decipher the mechanisms of scamount subduction these data indicate that the bougainville guyot is a middle eocene island arc volcano capped with reef limestones that appear to have been deposited during the late oligocene to early miocene and in miocene pliocene times this guyot possibly emerged during the middle and late miocene and started to sink in the new hebrides trench after the pliocene the rocks of the new hebrides arc slope in the collision zone consist primarily of pliocene recent volcaniclastic rocks derived from the arc and underlying fractured island arc volcanic basement possibly of late miocene age however highly sheared upper oligocene to lower miocene nannofossil ooze and chalk are exposed at the toe of the arc slope against the northern flank of the ndr based on a comparison with cores collected at dsdp site 286 the ooze and chalk can be interpreted as sediments accreted from the downgoing plate east of the bougainville guyot an antiform that developed in the arc slope as a consequence of the collision reveals a 500 m thick wedge of strongly tectonized rocks possibly accreted from the guyot or an already subducted seamount the wedge that is overlain by less deformed volcaniclastic island arc rocks and sediments includes imbricated layers of late oligocene to early miocene reef and micritic limestones this wedge which develops against the leading flank of the guyot tends to smooth its high drag shape a comparison between the 500 m thick wedge of limestones that outcrops southeast of the guyot and the absence of such a wedge over the flat top of the guyot although the top is overthrust by island arc rocks and sediments can be interpreted to suggest that the wedge moves in the subduction zone with the guyot and facilitates its subduction by streamlining

latest quaternary oceanographic changes in the okhotsk sea based on diatom records abstract the okhotsk sea is a locus of the north pacific intermediate water formation today the formation of the okhotsk intermediate water is linked with seasonal sea ice cover diatom records from the okhotsk sea show the following 1 during the last glacial maximum between 21 000 yr b p and 18 000 yr b p sea ice covered the western side of the sea throughout the whole year but the eastern part was open this permitted more efficient heat exchange with the atmosphere than waters and hence ventilation of the glacial okhotsk sea waters which in turn caused a greater extent of intermediate water formation through the bussol strait 2 the perennial sea ice cover extended northward and sea ice was present throughout the whole year over a great part of the sea except for the eastern part between 18 000 yr b p and 17 000 yr b p 3 the ice free area extended greatly to the south during the interval between 17 000 yr b p and 11 000 yr b p 4 there was no perennial ice cover over the whole sea and the ice free area that appeared as the seasonal ice area began to extend to the western part between 11 000 yr b p and 8 000 yr b p 5 after 8000 yr b p the ice free waters contracted to the present extent

holocene sea surface temperature and sea ice extent in the okhotsk and bering seas accurate prediction of future climate requires an understanding of the mechanisms of the holocene climate however the driving forces mechanisms and processes of climate change in the holocene associated with different time scales remain unclear we investigated the drivers of holocene sea surface temperature sst and sea ice extent in the north pacific ocean and the okhotsk and bering seas as inferred from sediment core records by using the alkenone unsaturation index as a biomarker of sst and abundances of sea ice related diatoms f cylindrus and f oceanica as an indicator of sea ice extent to explore controlling mechanisms in the high latitude pacific temporal changes in alkenone content suggest that alkenone production was relatively high during the middle holocene in the okhotsk sea and the western north pacific but highest in the late holocene in the eastern bering sea and the eastern north pacific the holocene variations of alkenone ssts at sites near kamchatka in the northwest pacific as well as in the western and eastern regions of the bering sea and in the eastern north pacific track the changes of holocene summer insolation at 50 n but at other sites in the western north pacific in the southern okhotsk sea and the eastern bering sea they do not in addition to insolation other atmosphere and ocean climate drivers such as sea ice distribution and changes in the position and activity of the aleutian low may have systematically influenced the timing and magnitude of warming and cooling during the holocene within the subarctic north pacific periods of high sea ice extent in both the okhotsk and bering seas may correspond to some periods of frequent or strong winter spring dust storms in the mongolian gobi desert particularly one centered at 4 3 thousand years before present kyr bp variation in storm activity in the mongolian gobi desert region may reflect changes in the strength and positions of the aleutian low and siberian high we suggest that periods of eastward displacement or increased intensity of the aleutian low correspond with times of increased extent of sea ice in the western okhotsk sea and eastern bering sea

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

the depth of trenches as a function of the subduction rate and age of the lithosphere abstract the trench is one of the most characteristic features of the subduction zones for a given arc or for all the subduction zones put together relationships between their depth variations the variations of the subduction rate and the age of the sinking lithosphere can be established certain other parameters have been examined with those mentioned above but without success it will be demonstrated that the observed relationships can be interpreted in terms of an elastic model and of a viscous model

regionalized primary paleoproduction variability in the sea of okhotsk during late pleistocene and holocene abstract in order to reconstruct the history of primary paleoproductivity changes during the last 160 kyr in the okhotsk sea os the high resolution down core analyses of chlorin content were performed on 11 sediment cores obtained from various part of the studied area with wide ranged depths spatial and temporal distributions of the marine phytoplankton paleoproductivity depend on sea ice condition and nutrient supply the observed discrepancies among the reconstructed records allow us to separate out three main regions with specific environmental conditions during glacial stages the paleoproductivity was depressed and vice versa productivity in the central region is low comparing to other regions due to nutrient limitation increased paleoproductivity in the southeastern area was affected by influence of nutrient rich pacific waters

evidence of sea ice driven terrigenous detritus accumulation and deep ventilation changes in the southern okhotsk sea during the last 180 ka abstract sediment core os03 1 retrieved from the akademia nauk rise in southern okhotsk sea was analyzed for the contents of rare earth elements rees and combined with carbon isotope 13c time series of benthic foraminifera to infer changes in terrigenous accumulation and bottom water ventilation on glacial interglacial timescales in the study area the age model of os03 1 was constructed by a combination of foraminifer 18o stratigraphy and 14c ams dating revealing that the 380 cm long core provides a window on climate change in the southern okhotsk sea since 180 ka a grain size controlled ree content shows strong glacial interglacial changes the cerium and europium anomalies vary from 0 89 to 1 32 and from 1 14 to 1 37 respectively the la yb n values range between 0 55 to 0 92 both results suggest a significant contribution of volcanic debris in the core sediments in addition the relationships between sm vs nd suggest main contribution origin from the amur river and sea ice during warm intervals and from the sea ice during cold intervals indicating that the sea ice played an important role in transporting terrigenous materials to the study site in the southern okhotsk sea during the last 180 ka the mass accumulation rates mar of rees are relatively higher during glacials and lower during interglacials with a peak accumulation during the early deglacial period we infer that an intensified mongolia high is responsible for the first order accumulation pattern of rees in the southern okhotsk sea by mediating the dynamic changes in sea ice extent furthermore six 13c minima are associated with intensified asian monsoon am precipitation and maximum mars of rees indicating that the dominance of barrier layer effects by high fresh water input through sea ice melting the maximum mar of rees during the marine isotope stage mis 5c coincides with the minimum of benthic foraminiferal 13c indicating a major interruption of ventilation in the bottom water in the okhotsk sea the major low ventilation event in the deep water of the okhotsk sea appears to be dampened by a cooling condition and a major blooming of surface productivity preceded the event

orbital scale changes of sea ice conditions of sea of okhotsk during the last glaciation and the holocene mis 4 mis 1 abstract in this paper 5 schemes for reconstructing the sea ice conditions in the sea of okhotsk the so during the last 74 kyr are presented these schemes were constructed based on calculations of the ice rafted debris ird fluxes in 16 sediment cores and the available published mineralogical data derkachev et al 2004 we obtained new data on the orbital scale changes of the ird fluxes in the studied area for the last four marine isotopic stages mis as a result the key areas of sea ice formation and general direction of sea ice drift and in turn dominate direction of geostrophic wind in the so were established for each of the investigated miss it allows us to suppose the positions of siberian high and aleutian low during the individual miss at that the sea ice was of predominantly seasonal for studied period except for the northwestern and western parts of sea where perennial sea ice fields were preserved over a period of several years during mis 2 the variations of sea ice conditions attest to a particular type of atmospheric pressure field prevailing over the so during individual miss the secondary sea ice drift directions points out that the predominant atmospheric pressure field during individual miss were inconstant except the mis 2

evidence for late paleocene to late eocene seafloor in the southern new hebrides basin abstract we interpret marine magnetic anomaly data from the southern part of the new hebrides basin as showing that a fragment of late paleocene late eocene oceanic crust is preserved between the new caledonia loyalty islands platform and the new hebrides island arc trench system the magnetic lineations which trend about ne sw are interpreted as anomalies 18 through 23 42 55 m y b p with the inferred crustal ages increasing to the north drilling at dsdp site 286 which is located on oceanic crust slightly older than 55 m y according to our magnetic anomaly identifications revealed mid eocene sediments overlying igneous basement

lake sediment evidence for the last deglaciation of eastern greenland in this review we compile the evidence of lake and isolation basin sediments for the chronology of the last deglaciation along the coastal parts of eastern greenland between 70 n and 83 n radiocarbon dates of remains of freshwater plants and bulk organic carbon extracted from lacustrine sediments suggest that the present day ice free parts of eastern greenland were not deglaciated prior to the early holocene older dates do exist but must be used with caution due to possible contamination with old carbon however many inland locations in eastern north and central east greenland became ice free distinctly later between 10 000 and 7500 cal yr bp depending on their relative position to the ice margin this compilation confirms former suggestions that hitherto no secure late glacial lacustrine sediments have been found in the ice free parts of eastern greenland late glacial sediments are only known from lakes in southern greenland and from few marine locations off eastern greenland the here summarized lake sediment evidence for the last deglaciation supports the results of an earlier compilation of dates from marine shells 2007 elsevier ltd all rights reserved

tectonic stresses seaward of an aseismic ridge trench collision zone a remote sensing approach on the loyalty islands sw pacific abstract the loyalty islands are a series of limestone karstified islands on the australian plate that are presently approaching the vanuatu subduction zone sw pacific they are deformed due to the combined effects of the bulging of the subducting lithosphere and the beginning collision between the loyalty ridge and the vanuatu subduction zone therefore they constitute a series of markers for early phases of ridge arc collision lineaments deduced from remote sensing images aerial photos spot3 spot4 and envisat data termed here as fractures are analyzed by comparison with planar structures measured during field studies and termed as geological data fracture data indicate a stable main n110 direction with a large variance of nearly 15 in rms and two minor directions 45 apart which may constitute shear directions associated to the major one a scale dependent analysis shows that fractures longer than 2000 m are close to the n110 direction and that their orientation shifts progressively to reach the n125 direction for l

responses of the okhotsk sea environment and sedimentology to global climate changes at the orbital and millennial scale during the last 350 kyr abstract we measured productivity proxies chlorin carbonate and organic carbon opal and biogenic ba content and lithophysical proxies magnetic susceptibility water content density and coarse sediment fraction in sediment of central okhotsk sea core pc 7r the age model covering the last 350 kyr of this core was constructed by correlating the dated series of relative paleointensity lows recognized in geomagnetic intensity records marine isotope stage mis boundaries determined in broad variations of the lithophysical and productivity proxies and tephrochronology the orbital changes of the lithophysical and productivity proxy stacks lag behind northern hemisphere summer radiation by approximately 6 3 and 5 9 kyr respectively this lag is consistent with a milankovich model of climate control by solar radiation through the northern ice sheet volume and sea surface and surrounding land responses which are fast compared with sedimentological evidence productivity proxies of the okhotsk sea also demonstrate 52 abrupt pronounced productivity minima associated with regional climate coolings during the last 350 kyr which present useful indicators of millennial scale climate changes in this marginal sea based on the postulated synchronicity of dansgaard oeschger cycles in the northern hemisphere and the established simultaneity of 11 okhotsk sea coolings in the last 77 kyr with abrupt severe cold events in the greenland ice core and north atlantic heinrich events all of these may be regarded as heinrich equivalent event anomalies the okhotsk sea events have their counterparts in the records of north atlantic sediments the greenland ice sheet east asia summer monsoon and the antarctic ice sheet probably the arctic oscillation was the main factor determining orbital and millennial climate oscillations in the high latitude northern hemisphere including the okhotsk sea region

the production of ice and dense shelf water in the okhotsk sea polynyas this paper examines the ice and dense water production in the okhotsk sea coastal polynyas for the 1990 1995 winters the dominant polynyas occur on the northwest and northern shelves and in shelikhov bay we use an algorithm developed for the special sensor microwave imager ssm i to derive for each polynya the area and composition of thin ice and open water and a heat flux algorithm to derive the ice and brine production historic oceanographic observations show that the northwest shelf is the only north pacific region where the 26 8 potential density surface outcrops to the surface and is also that part of the okhotsk shelf where the densest water is observed to occur in support of these observations we find that the northwest shelf polynya is the dominant ice and brine producer contributing on average about 55 of the total production shelikhov bay is the second largest producer with about 25 of the total this region has been previously neglected by both oceanographic and remote sensing studies using a combination of two dense water production models we find that the 6 year average dense water production lies between 0 2 0 4 sv the ice and brine production for the dominant northwest shelf vary interannually by a factor of 3 while the production from all the northern polynyas varies by factor of 2 the source of the variability for the northwest shelf comes from the fact that the southwest to northeast trend of the coastline and the mean winter geostrophic wind velocities are roughly parallel which means that small variations in the wind direction yield large changes in the ice production

changes in detrital input ventilation and productivity in the central okhotsk sea during the marine isotope stage 5e penultimate interglacial period abstract by presenting benthic foraminifera isotope profiles and bulk geochemical composition of core sediments we offer a mutiproxy reconstruction of the central okhotsk sea oceanography between 130 to and 115 kyr related to the marine isotopic stage 5e mis 5e sediments from the site mr0604 pc7a have been compared with paleo sea surface temperatures and other records this multiparameter approach allowed to recognize three periods for mis 5e evolution characterized by variations in marine productivity and bottom oxygenation these variations have been ultimately associated with the production of okhotsk sea intermediate water and the presence or absence of nutrient contribution from the pacific deep water into central okhotsk sea aeolian input reconstructed by th sc ratio indicates higher values during the mis 6 and mis 5d compared with the mis 5e eu values indicate an input of detrital material from kurile islands and east kamchatka during the late mis 5e absent during the early mis 5e and glacial periods

dense water production on the northern okhotsk shelves comparison of ship based spring summer observations for 1996 and 1997 with satellite observations for the northern okhotsk sea polynyas five russian ctd surveys taken during 1995 to 1997 are used to examine the evolution of the polynya dense water the surveys show that consistent with other investigations the largest potential densities are 26 99 and the densest water occurs in sakhalin and shelikhov bays the surveys also suggest that the shelikhov water drains directly into the deep okhotsk while on the northern shelves gravity currents transport the dense water west to sakhalin bay for comparison determination of the polynya sizes and ice production from satellite passive microwave and meteorological observations shows that polynyas occur on the northwest shelf nws between ayan and okhotsk city on the northern shelf between okhotsk city and magadan and in shelikhov bay in contrast the observations show that sakhalin bay is a region of land fast ice with no polynyas so that the dense water observed here cannot form locally for all polynyas the satellite observations show that the nws contributes 60 to 70 of the total ice production and due to the warmer 1997 air temperatures the 1996 production is about 1 5 times the 1997 value an estimate of the ice production from the surveys shows a similar regional distribution and enhancement of the 1996 production with the satellite and ship estimates in agreement within their error bars finally analysis of the dense water outflow shows that the upper okhotsk sea mode water has a renewal time of about 4 years the lower part about 14 years

processes controlling the advance and retreat of sea ice in the sea of okhotsk using defense meteorological satellite program dmsp special sensor microwave imager ssm i sea ice data and meteorological data we investigate processes controlling the advance and retreat of sea ice in the sea of okhotsk for this investigation we apply a new algorithm to the ssm i data which is capable of calculating ice concentration and distinguishing sea ice types this algorithm is confirmed by comparison with national oceanic and atmospheric administration noaa advanced very high resolution radiometer avhrr imagery our investigations show that there exists a locality for the areas of new ice formation and the ice formation near the ice edge always occurs as a recovery after sea ice has retreated suddenly we also reveal that the speed of ice edge advance fairly coincides with that predicted by 2 of the geostrophic wind furthermore there exists a good correspondence between the times when the overall advance and retreat of ice cover begin and the decrease and increase of air temperature begin we conclude that the advance of the ice cover in the sea of okhotsk occurs primarily through ice advection by wind and that the interannual variation in the maximum sea ice extent can be interpreted by that in wind and air temperature conditions

new sw pacific tectonic model cyclical intraoceanic magmatic arc construction and near coeval emplacement along the australia pacific margin in the cenozoic various reconstructions of the sw pacific for the late cretaceous and cenozoic suggest that northeast dipping subduction began in the south loyalty basin slb at 55 50 ma and that subsequent closure of the slb resulted in the diachronous emplacement of cretaceous paleocene ophiolitic nappes onto the norfolk ridge in new caledonia at 40 34 ma and in northland new zealand around 24 21 ma a fundamental problem with these models is that they do not account for the fact that ne dipping subduction had already been established offshore papua new guinea by at least 65 60 ma which resulted in the emplacement of the papuan ultramafic belt pub ophiolite at 59 58 ma a second issue is that the reconstructions are based largely upon unfounded assumptions as to the age and nature of the basement beneath the loyalty arc and three kings ridge finally reconstructions of the northland region are based upon the erroneous assumption that the age of the majority of the igneous component comprising the northland allochthon is late cretaceous paleocene when in fact it is oligocene a new model is presented whereby the pub new caledonia and northland ophiolites formed and were emplaced in a cyclical fashion above an extensive ne dipping cenozoic intraoceanic arc system which diachronously propagated n s along the entire eastern margin of the australian plate these infant arc ophiolites represent fragments of suprasubduction zone lithosphere sszl generated in the earliest stages of magmatic arc formation that were emplaced shortly after 20 m y as a result of forearc australian plate collision subduction inception was the result of subsidence of older morb like lithosphere generated within an extensive back arc basin to the east of the norfolk ridge during the earliest stages of slb formation above a southwest dipping pacific plate during emplacement of each ophiolite a crustal fragment of the older lithosphere was scraped off the ne dipping slab and subsequently back thrust beneath each ophiolite during its emplacement

recent tectonics associated with the subduction collision of the d entrecasteaux zone in the central new hebrides abstract recent data from the new hebrides vanuatu subduction zone have enabled a morphological description and tectonic interpretation to be made of the complex plate contact between the d entrecasteaux zone and the west torres massif on the one hand and the old santo malekula block on the other between latitudes 14 30 and 17 s no trench occurs owing to the presence of the old rigid santo malekula block at the edge of the overriding plate the outer limit of plate contact describes a tortuous line westward of the projected line of the adjacent trenches this may be explained by local collision of the north d entrecasteaux ridge and the south d entrecasteaux chain with the west flank of santo this collision is compensated for by lateral plastic flow of the inner wall downward into the small basins which separate the d entrecasteaux zone ridges a process which may be explained by plastic plane strain theory the westward jump of the plate contact zone here may result from pieces of the north d entrecasteaux ridge being cut off and incorporated in the frontal arc a review of the geological evidence and the shallow seismicity of the central new hebrides shows that radiant horizontal stresses resulting from this collision have generated a specific compressive stress regime which influences the whole width of the arc the resultant deformation shows a close resemblance to a theoretical strain field produced by the indentation of a long narrow plastic body cf the arc by a rigid flat die cf the d entrecasteaux zone thus the central new hebrides block is both elastically bent under vertical stresses and plastically deformed and pushed eastwards by horizontal stresses recent uplift of the eastern chain can be explained by this model in contrast at the rear of both the northern and southern sections of the arc the tectonics are mainly controlled by a tensional stress regime the strong plate interaction due to the subduction of the d entrecasteaux zone is thought to be responsible for the compressive stress regime across the central new hebrides the same cause can be invoked to account for the tensional stress regime observed in north and south new hebrides rear arc regions

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

behaviour of the oceanic lithosphere at subduction zones plastic yield strength from a finite element method abstract using the finite element method to study the deflection of the oceanic lithosphere at subduction zones shows that deflection of an elastic plastic model agrees with observed bathymetry data except for 2 examples kermadec and mariana where the lithospheric behaviour remains elastic seaward of the trench seven of the cases we studied could be easily fitted and enabled us to compute an effective yield strength the average value of which is about 3 8 to 4 8 kbar and seems to be the same in every case

on the relationship between atmospheric circulation and the fluctuations in the sea ice extents of the bering and okhotsk seas monthly and 3 day averaged nimbus 5 electrically scanning microwave radiometer sea ice data have been analyzed to document the fluctuations of the bering sea and sea of okhotsk ice covers for the four winters 1972 1973 through 1975 1976 on the short term seasonal and interannual time scales and to define those periods for which there is an out of phase relationship between the fluctuations of the two sea ice covers the sea ice fluctuations are shown to be related to changes in the position and intensity of quasi stationary high and low pressure systems associated with large scale standing wave patterns in the atmosphere through a comparison of the areal changes in ice cover with changes in the amplitude and phase of zonal harmonics 1 2 and 3 of the sea level pressure field on the seasonal time scale the sea level pressure for december the month of most rapid seasonal sea ice growth for both the bering and okhotsk seas is dominated by harmonic 2 which explains almost 60 of the total sea level pressure variance on average over the four winters the phase of harmonic 2 which is associated with the position of the aleutian low shifts from 156 e in 1972 1973 to 190 e in 1975 1976 thus providing a connection between the increasingly heavy bering sea ice cover over these four winters and the general circulation of the atmosphere on the short term episodes of midwinter bering sea ice retreat are generally preceded by or coincident with the breakdown of harmonic 1 and the intensification of harmonics 2 and 3 these episodes are also related to the coincidence of the phases of harmonics 2 and 3 with a mean position of 165 e this result is in excellent agreement with a study of the north pacific oscillation showing that the two modes of the oscillation are associated with the longitudinal position of the aleutian low it is suggested here that these two modes result from changes in the amplitudes and phases of atmospheric long waves 1 2 and 3 evidence is also presented indicating that the interaction of standing and transient components of wave 1 may play an important role in these fluctuations finally these results establish an observational connection relating climate dynamics to changes in ice covers in seasonal sea ice zones

magnetostratigraphic dating of the uplifted atoll of mare geodynamics of the loyalty ridge sw pacific the loyalty islands sw pacific are uplifted as they are progressively affected by the lithospheric flexure of the australian plate before its subduction under the new hebrides arc these geodynamic changes are constrained by magnetostratigraphically dating two sections from mare island where mineral extractions coupled with rock magnetic experiments suggest that the magnetic remanence is mostly carried by a mixture of single domain to multidomain magnetite maghemite with the help of faunal determinations and radiometric dating the sequences of polarity reversals correlated to the geomagnetic polarity timescale range from the top of chron c4n late miocene to the top of the gauss chron late pliocene this new chronostratigraphy refines the timing of two distinctive carbonate units rhodolith platform coral reefs separated by a hardground whose transition is known to coincide approximately with a regional event around the miocene pliocene boundary the magnetostratigraphic dating indicates that the hardground represents about a 1 9 m y hiatus and suggests variable sedimentation rates ranging from 4 7 to 65 4 m m y during the atoll construction the lithospheric bulge seems to have influenced the evolution of mare island some 3 1 m y ago leading to a diachronous emersion of the northeast and southwest rim of the atoll with a mean uplift rate of the order of 4 cm kyr

structure of the collision zone between bougainville guyot and the accretionary wedge of the new hebrides island arc southwest pacific multichannel seismic reflection data show the structure that develops within an island arc guyot collision zone the bougainville guyot fills the new hebrides trench stands about 3 km above the abyssal ocean plain and is capped by a broad platform that is underlain by a parallel bedded sequence probably lagoon and reef rocks a thick debris apron made up of unconsolidated sediment underlies the unsubducted part of the lower guyot flank and possibly the subducted flank as well the contact zone between the arc and the north and east sides of the guyot is marked by discontinuous antiforms that include reflective thrust faulted rocks that may have been derived from the guyot the extent of collision deformation to the arc and guyot depends in part on the contrast in compressibility and viscosity between these features we propose that the high drag subcircular guyot evolves during collision into a more streamlined shape streamlining may be achieved by processes like 1 bulk deformation of the guyot by thrust faulting and sediment compaction 2 ripping away of projecting parts of the guyot and blunting sharp edges tectonic erosion like that formed by the limestone cap and 3 formation of a boundary layer between the guyot and the arc that is made up of water rich mobilized units of soft sediment we draw an analogy between some features of glacial origin and the subducted part of a guyot if the bulk of the guyot is low strength especially in view of the thick debris apron then the guyot may behave like till that was overridden by a glacier and forms a drumlin an elongated blunt faced streamlined feature thrust faults evident in the guyot may indicate deformation that leads toward a streamlined shape and not necessarily to accretion of guyot rocks

subduction of the bougainville seamount vanuatu mechanical and geodynamic implications new bathymetric data gathered during a seabeam survey seapso cruise leg 1 enable us to re examine the flexural response of the oceanic lithosphere subducting under the new hebrides vanuatu island arc the bougainville seamount and sabine bank are interpreted as immerged fossil atolls the recent subsidence of which is related to the subduction of the oceanic lithosphere the position and altitude of the different fossil atolls which belong to the d entrecasteaux or loyalty ridges are in good agreement with predictions of elastic flexure of the lithosphere we deduce an average effective elastic thickness of the lithosphere of about 22 km for the area under study this value is slightly smaller than the one corresponding to the lithospheric age as given by the magnetic anomalies but is in good agreement with the age after a correction for thermal rejuvenation this assumption of a thermal rejuvenation of the north loyalty basin is also supported by previously reported high heat flow values and attenuation of sn seismic waves however the location and depth of the trench in front of the north loyalty basin do not agree with the model which fits the other data this discrepancy is interpreted as the result of variations of the value of pb vertical force per unit length of trench applied at the edge of the plate along the subduction zone such variations may be related to the length of the subducted slab which is shorter in front of the d entrecasteaux and loyalty ridges than in front of the north loyalty basin according to the hypocentral distribution of earthquakes and a tomographic image of the slab

mineralogical petrological characterization of near earth asteroids studies of near earth asteroids are aimed at determining their dynamical and structural history the mineralogy and petrology of 17 near earth asteroids are characterized using reflectance spectroscopy with ground based telescopes as one method to address their major issues implications for the origin and evolution are discussed in a separate paper assuming the surfaces are composed of cosmically abundant materials the presence of certain mineralogical species can be determined from diagnostic absorption features and spectral characteristics which have been studied under known laboratory conditions and understood in terms of crystal field theory with one possible exception the surface composition of near earth asteroids consists of common rock forming minerals such as olivine pyroxene and phyllosilicates opaque components are present but cannot be mineralogically identified with existing experimental data the spectrum of 2201 oljato cannot be interpreted in terms of common rock forming minerals this spectrum was examined for cometary features because its high orbital eccentricity suggests a possible relation to comets no common cometary features are identified in its spectrum the predominance of mafic silicate absorption features in spectra of near earth asteroids compared to the majority of main belt asteroids may be a primary compositional feature or may be the signature of relatively fresher asteroid material

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

mechanisms for the variation of sea ice extent in the northern hemisphere using daily sea ice data derived from satellite borne sensors and atmospheric data we examined processes controlling the variation of sea ice extent in the northern hemisphere the daily ice motion field was computed from imagery of the defense meteorological satellite program dmsp special sensor microwave imager ssm i for seven winters december to april from 1991 1992 to 1997 1998 by employing the maximum cross correlation method in order to examine mechanisms of the temporal variation of the ice extent we analyzed 50 specified lines across the daily ice edge although a high correlation between the ice motion and the geostrophic wind speed was observed in all the ice edge areas the degree for correlation between the speed of the ice edge displacement and the wind speed varied with region the degree for response of the ice edge speed to the wind speed largely depended upon that of the ice edge speed to the ice motion the following mechanisms controlling the variation of ice extent for regions in the northern hemisphere were anticipated in the barents sea bering sea and the sea of okhotsk the ice extent advances by wind driven ice advection and the daily scale variation of the ice extent were also controlled by the variation in wind speed in contrast the ice extent in the labrador sea and the greenland sea seemed to be considerably affected by oceanographic factors such as the location of the thermal front and was not related to the variation in wind speed the regional difference of the variation mechanism was also reflected in the interannual variation in maximum ice extent

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

characteristics and ages of tephra layers in the central okhotsk sea over the last 350 kyr abstract a sequence of 9 ash layers tephra found in the middle late pleistocene and holocene sediments of the central okhotsk sea was established on the basis of glass chemical composition and refractive indices grain size distributions and heavy mineral assemblages five tephras were also characterized by rare earth element distributions volcanic sources and ages of the identified tephra were estimated based on pre existing marine sediment core chronostratigraphy and correlation between these marine tephra deposits with geochemically similar terrestrial deposits on the kamchatka peninsula and adjacent kurile islands areal distributions and approximate eruptive volumes of pyroclastic material were also estimated for some of these tephras

satellite passive microwave studies of the sea of okhotsk ice cover and its relation to oceanic processes 1978 1982 this paper describes the use of the nimbus 7 scanning multichannel microwave radiometer smmr satellite data to study the ice cover in the sea of okhotsk during the four winters of 1978 1982 the ice concentration estimates obtained from smmr are used to study two different polynyas one over the kashevarova bank and the other over the northwest continental shelf for the kashevarova polynya this study shows that the polynya which may be related to the upwelling observed in historic summer cruises occurs directly over the bank for the continental shelf which because of strong offshore winds and cold temperatures is a region of high ice production the polynya areas are combined with heat flux estimates from weather station data to yield the production rates of ice salt and dense shelf water as a previous study by kitani 1973 shows the mixing of this dense shelf water with pacific water yields a water mass unique to the okhotsk which is the layer of cold low salinity intermediate water between depths of 150 and 800 m from our calculations we estimate that the dense shelf water is produced at an annual rate of about 0 5 sv and that the intermediate water is produced at a rate of 1 2 sv which yields a renewal time for this layer of 10 40 years

relationship between sea ice motion and geostrophic wind in the northern hemisphere this paper presents maps showing the relationship between sea ice motion derived from defense meteorological satellite program dmsp special sensor microwave imager ssm i imagery and the geostrophic wind in the northern hemisphere for seven winters 1991 92 1997 98 the sea ice motion is highly correlated with the geostrophic wind except for some coastal regions overall the direction of the ice motion is nearly parallel to the wind an obvious contrast between seasonal ice zones and the interior of the arctic is observed in the speed reduction factor ratio of ice speed to wind speed which is probably caused by the spatial variation of internal ice stress surface ocean currents are also derived by subtracting the wind effect from the ice motion

control of paleoshorelines by trench forebulge uplift loyalty islands abstract unlike most tropical pacific islands which lie along island arcs or hotspot chains the loyalty islands between new caledonia and vanuatu owe their existence and morphology to the uplift of pre existing atolls on the flexural forebulge of the new hebrides trench the configuration and topography of each island is a function of distance from the crest of the uplifted forebulge both mare and lifou are fully emergent paleoatolls upon which ancient barrier reefs form highstanding annular ridges that enclose interior plateaus representing paleolagoon floors whereas the partially emergent ouvea paleoatoll rim flanks a drowned remnant lagoon emergent paleoshoreline features exposed by island uplift include paleoreef flats constructed as ancient fringing reefs built to past low tide levels and emergent tidal notches incised at past high tide levels present paleoshoreline elevations record uplift rates of the islands since last interglacial and mid holocene highstands in global and regional sea levels respectively and paleoreef stratigraphy reflects net quaternary island emergence the empirical uplift rates vary in harmony with theoretical uplift rates inferred from the different positions of the islands in transit across the trench forebulge at the trench subduction rate the loyalty islands provide a case study of island environments controlled primarily by neotectonics

late pleistocene holocene oceanographic variability in the okhotsk sea geochemical lithological and paleontological evidence sedimentary geochemical and paleontological data extracted from a sediment core taken from the central okhotsk sea record climatic and sedimentary changes over the past 100 ky benthic foraminiferal oxygen isotope record and accelerator mass spectrometry ams 14c data provide the basis for the core age chronology planktonic and benthic foraminiferal 18o and 13c measurements magnetic susceptibility ice rafted debris and coarse fraction content carbonate and organic carbon content and diatom and pollen spectra show major changes in regional climate sea surface conditions ice extent and sedimentary regime which are correlated with the global glacial interglacial changes of marine isotope stages mis 1 through 5 3 regional cooling and intensification of winter sea ice formation during the last glaciation increased the northern shelf surface water density and sea of okhotsk intermediate water soiw formation in addition to major milankovitch scale changes lithological geochemical and paleontological indices also show suborbital oscillations in okhotsk sea hydrology sedimentation and regional climate these shorter term oscillations are characterized by coupled maxima in ice rafted debris and sediment coarse fraction lithodynamic indices ldi values and most are associated with cold events involving enhanced winter ice formation and intensification of soiw and north pacific intermediate water npiw formation the terminations of ldi maxima were induced by climate warming and reductions in ice formation and were accompanied by sharp decreases in planktonic foraminiferal 18o during the glacial terminations of mis 2 and 4 however the onset of suborbital scale ldi maxima occurs close to sharp negative 18o shifts in planktonic foraminifera 18opf associated with climate warming in these special cases the ldi maxima occurred under warm climate and rising sea levels and did not lead to increases in soiw or npiw ventilation

quaternary uplift of the torres islands northern new hebrides frontal arc comparison with santo and malekula islands central new hebrides frontal arc coral reef terraces on the torres islands have recorded the quaternary uplift of part of the northern new indian plate underthrusts the arc from the west 14c and 230thp34u ages for torres fossil corals indicate that for approximately the past 100 000 years the islands uplifted at a constant rate ranging geographically from 0 7 to 0 9 yr the occurrence of similar uplift rates and eastward tilting directions and the absence of major crosscutting structures or rupture zone boundaries suggest that the islands may be part of a single tectonic block or arc segment the frontal arc morphology in the torres area is typical of frontal arcs farther south the central new hebrides frontal arc has no physiographic trench at the plate boundary west of santo and malekula islands and the axes of the maximum uplift rate are at the seaward edge of the plate the d entrecasteaux ridge dr a massive e w trending bathymetric feature on the indian plate is underthrusting santo and malekula the eastern parts of santo and malekula are physiographically equivalent to the torres islands and seem to have been on a former axis of maximum uplift rate however in response to subduction of the dr the uplift axes of santo and malekula may have shifted westward in a few hundred thousand years the new uplift axes caused the western parts of these islands to achieve their present topographic dominance over the earlier uplift axes holocene uplift rates on southern santo and northern malekula are about twice the average rates of the previous 100 000 years the accelerated holocene uplift could be explained if a particularly prominent part of the dr has recently underthrust santo and malekula d hebrides frontal arc these isles lie about midway between the volcanic chain and trench axis where the

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

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

sea ice conditions in the okhotsk sea during the last 550 kyr deduced from environmental magnetism 1 reconstructing past sea ice conditions in the okhotsk sea is important because sea ice conditions vary in response to global climate changes which in turn may affect global ocean circulation through intermediate water mass formation we conducted an environmental magnetic study of six cores from three stations in the central okhotsk sea to better understand temporal and spatial sea ice variations intercore correlations and age estimations are based mainly on geomagnetic paleointensity an oxygen isotope stratigraphy is available for one station magnetic susceptibility ms minima are accompanied by maxima in color b the ratio of the anhysteretic remanent magnetization susceptibility to saturation isothermal remanent magnetization karm sirm and the s ratio which indicates a higher proportion of biogenic to terrigenous magnetic components this reflects enhanced ocean productivity first order reversal curve diagrams and irm component analyses support the dominance of biogenic magnetite at ms minima in contrast color b karm sirm and s ratio values are low when ms is high which indicates an increased proportion of the terrigenous component that was probably transported as ice rafted debris ird for the southern two stations ird accumulation increased in glacial and deglacial periods which implies mobile sea ice conditions even in full glacials this was succeeded by extremely enhanced ocean productivity in early interglacials which suggests nearly ice free conditions for the northernmost station on the other hand ird accumulation was low in glacials and increased in early interglacials which indicates perennial sea ice coverage with little mobility in glacials succeeding ocean productivity enhancement was delayed compared to the southern stations

tectonic accretion and underplating of mafic terranes in the late eocene intraoceanic fore arc of new caledonia southwest pacific geodynamic implications this paper deals with the tectonic events that result in the accretion of mafic terranes in the fore arc region and a close juxtaposition of ultramafic rocks low grade and high grade mafic terranes in many collisional orogens the example is taken from new caledonia where tectonic accretion subduction underplating and obduction of mafic terranes took place during the late eocene in an intra oceanic forearc setting the late eocene tectonic complex comprised three major terranes an overlying ultramafic mainly harzburgitic allochthon named the ophiolitic nappe an intermediate mafic mainly basaltic off scraped melange composed of kilometre scale slices of oceanic upper crust called the poya terrane parts of which have been metamorphosed into an eclogite blueschist facies complex the pouebo terrane and a lower continental basement formed by the norkolk ridge terranes based upon exhaustive sampling of the mafic terranes and field surveys our tectonic micropaleontologic and geochemical data reveal that poya and pouebo terranes rocks originally formed within one single campanian to late paleocene oceanic basin floored by tholeiitic basalt associated with some minor seamount related intraplate alkali basalt the tholeiitic basalt displays a continuous range of compositions spanning between undepleted and depleted end members the former being volumetrically predominant the overall geochemical and isotopic features indicate an origin from a prominently heterogeneous mantle source during the opening of a marginal basin the south loyalty basin which almost completely disappeared during eocene convergence the opening of this basin originally located to the east of the norfolk ridge was synchronous with that of tasman sea basin as a consequence of oceanward migration of the west dipping pacific subduction zone establishing the origin of the ultramafic ophiolitic nappe is beyond the scope of this paper however it appears to be genetically unrelated to the mafic poya and pouebo terranes although it was located in the late eocene fore arc the ophiolitic nappe and the corresponding oceanic lithosphere originated before the late cretaceous to the east of the south loyalty basin in a back arc setting or alternatively in a much older trapped basin for reasons that remain unclear a new east dipping subduction started in the eocene and consumed most of the south loyalty basin forming the intra oceanic loyalty arc due to a changing subduction regime underplating of the diahot terrane the mafic slices that now form the poya terrane were tectonically accreted in the loyalty fore arc region and remained under low pressure low temperature conditions possibly at the subsurface until the norfolk ridge reached the subduction zone diachronously this resulted in the final obduction of the fore arc area the two step obduction involved first the mafic complex forming the poya terrane and thereafter the lithospheric mantle that now forms the ophiolitic nappe in contrast pieces of the accretionnary complex were dragged down into the subduction zone underplated at depth ca 70 km and metamorphosed into high temperature eclogite to form the pouebo terrane metamorphics that display the same geochemical features as the poya terrane basalt a mid to late eocene syntectonic piggy back sedimentary basin the nepoui flysch basin mainly filled with mafic clastic material and shallow water carbonates that record the progressive uplift of the fore arc region due to the accretion and underplating of mafic ocean related and other material in contrast a slightly younger foreland basin located upon the norfolk ridge the priabonian bourail flysch basin received a massive input of detrital material derived from the norfolk ridge itself and a time increasing amount of mafic poya derived material that recorded the first step of obduction thereafter the bourail flysch was overthrust by the poya terrane and finally by the ophiolitic nappe at the same time buoyancy driven uplift and exhumation of the high pressure metamorphic complex occurred as a consequence of the diachronous blocking of the subduction zone finally for a short time a new subduction started along the west coast of new caledonia and generated small amounts of active margin related magmas these events have resulted in the close juxtaposition of unmetamorphosed and highly metamorphosed mafic and ultramafic terranes that may represent a good pre collision analogue of mafic ultramafic belts found in many collisional mountain ranges

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

millennial mode of variability of sea ice conditions in the okhotsk sea during the last glaciation mis 4 mis 2 abstract coarse fraction cf content grain size distribution roundness of cf gravels and pebbles and examination of surface of pebbles were studied in core lv28 44 4 recovered from the eastern okhotsk sea os the age model of the studied core was based on the ams 14c data tephrochronology 18o benthic foraminifera record and correlation of peaks of productivity proxies with long lasted dansgaard oeschger do interstadials the results show that sea ice was the main transport agent for cf ice rafted debris ird in the eastern os published mineralogical studies of clastic material of the os indicated that the coast of western kamchatka was the main source of ird in the eastern os we found 19 peaks of ird which mostly coincided with do stadials the distribution of cf indicates a different pattern of ird supply during mis 4 3 and 2 comparison of ird records in the eastern and central parts of the os allow us to reconstruct millennial changes in ice and wind modes for mis 4 mis 2 significant strengthening of northeastern and eastern winds during doss of mis 3 and of northern and north western winds during mis 2 were observed

continental margin tectonics forearc processes recent studies of convergent plate margins and the structural development of forearc terranes are summarized in a critical review of u s research from the period 1987 1990 topics addressed include the geometry of accretionary prisms coulomb wedge taper and vertical motion in response to tectonic processes offscraping vs underplating or subduction the response to oblique convergence fluids in forearc settings the thermal framework and the effects of fluid advection and serpentinite seamounts also included is a comprehensive bibliography for the period

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

magnetostratigraphy and tephrochronology of the upper quaternary sediments in the okhotsk sea implication of terrigenous volcanogenic and biogenic matter supply seven lithological units alternating between horizons enriched in biogenic opal diatoms and carbonate foraminifera and units composed largely of terrigenous sediment with very low biogenic admixture were distinguished in a series of late quaternary sediment cores from the sea of okhotsk sediments were characterised using on board visual description smear slides analyses grain size composition and magnetic susceptibility ms records five tephra marker layers identified as ko tr k2 k3 and k4 were distinguished using petrological mineralogical and geochemical analyses age models were developed by comparing lithological units tephra stratigraphy and ms records with oxygen isotope curves and with records of biogenic caco3 opal content and sediment grain size composition in three ams radiocarbon dated okhotsk cores this chronological framework allowed us to investigate climate control over the sedimentation regime and productivity and to clarify the formation times of the lithological and tephra units the data show that sediment ms variations in the south eastern area of the glacial okhotsk sea arose primarily from volcanic material input the sedimentation in all other parts of the sea was mainly controlled by the supply of terrigenous material the cores show a tight correlation between ms sediment grain size and climate change in the okhotsk sea coarse sediments with a high ms were accumulated during the cold period oxygen isotope stages mis 2 4 6 fine sediments with a low ice rafted debris ird content and ms were formed in the warm isotope stages according to the oxygen isotope stratigraphy and radiocarbon data the ko tr k2 k3 and k4 tephra were deposited at 7 7 8 0 26 0 kyr bp in mis 4 about 60 70 kyr ago and near mis 5 4 respectively comparison of tephra mineralogy petrology spatial distributions and ages with the history of kurile kamchatka volcanism allows us to identify likely candidates for the tephra source eruptions the combined use of ms records tephrochronology and lithological unit sequences provides a detailed basis for okhotsk sea sediment stratigraphy

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

climatic and oceanological changes in the southwestern part of the sea of okhotsk during the last 94 kyr abstract this paper presents the results of a study on a sediment core obtained from the southwestern part of the sea of okhotsk by analyzing the diatoms in the sediment along with the productivity proxy and ice rafted debris data we reconstructed the regional environmental and climatic changes occurring over last 94 kyr sea ice expansion periods of active ice melting and variations in marine plankton productivity local warming and cooling events occurring in the late pleistocene and holocene periods as well as transgressive regressive fluctuations in the sea level were documented the shift in the relatively warm interglacial conditions to severe glaciation over 34 kyr ago that occurred in the studied area of the sea of okhotsk was reported for the first time the time at which the la perouse strait opened the soya current input began and the establishment of modern hydrological conditions was approximately 5 6 kyr

seafloor structural geomorphic evolution of the accretionary frontal wedge in response to seamount subduction poverty indentation new zealand abstract high quality swath bathymetry and seismic reflection data reveal that the steep forearc slope along the northern sector of the obliquely convergent hikurangi subduction zone is characteristic of non accretionary and tectonically eroding continental margins with reduced sediment supply in the trench relative to further south and the presence of subducting seamount relief on the hikurangi plateau these seamounts influence the subduction process and the structurally driven geomorphic development of the over riding margin of the australian plate frontal wedge the origin of the poverty indentation on the inboard trench slope is attributed to multiple seamount impacts over the last c 1 myr period accompanied by canyon incision thrust fault propagation into the trench fill and numerous large scale gravitational collapse structures with multiple debris flow and avalanche deposits ranging in downslope length from a few hundred metres to more than 40 km the indentation is directly offshore of the waipaoa river which is currently estimated to have a high sediment yield into the marine system the poverty canyon stretches 70 km from the continental shelf edge directly offshore from the waipaoa to the trench floor incising into the axis of the indentation the sediment delivered to the margin from the waipaoa catchment and elsewhere during sea level high stands including the holocene has remained largely trapped in a large depocentre on the poverty shelf while during low stand cycles sediment bypassed the shelf to develop a prograding clinoform sequence out onto the upper slope the formation of the indentation and the development of the upper branches of the poverty canyon system has led to the progressive removal of a substantial part of this prograding wedge by mass movements and gully incision sediment has also accumulated in the head of the poverty canyon and episodic mass flows contribute significantly to continued modification of the indentation by driving canyon incision and triggering instability in the adjacent slopes prograding clinoforms lying seaward of active faults beneath the shelf and overlying a buried inactive thrust system beneath the upper slope reveal a history of deformation accompanied by the creation of accommodation space the middle to lower poverty canyon represents a structural transition zone within the indentation coincident with the indentation axis the lower to mid slope south of the canyon conforms more closely to a classic accretionary slope deformation style with a series of east facing thrust propagated asymmetric anticlines separated by early stage slope basins north of the canyon system seamount impact has resulted in frontal tectonic erosion associated with the development of an over steepened lower to mid slope margin fault reactivation and structural inversion and over printing

lithospheric flexure and thermal anomalies plots of effective elastic thickness te of the oceanic lithosphere as a function of age when elastically deformed show a general increase in te with the square root of age although there is much scatter some of the scatter can be eliminated by correcting for the effect of finite yield strength in rocks which makes te for more sharply bent plates underestimate the true depth tm to the rheological boundary at the base of the high strength mechanical lithosphere after converting effective values te to true thicknesses tm it appears that the mechanical lithosphere is always thinner beneath islands and seamounts compared to lithosphere of similar age flexed at subduction zones from several other lines of evidence such as depth anomalies seamount subsidence and heat flow data it has been suggested that the thermal structure in plates subjected to hot spot type volcanism is reset to values appropriate for much younger lithosphere the reduction in mechanical plate thickness beneath hot spot volcanoes is also consistent with this concept of thermal rejuvenation since the strength of rocks decreases exponentially with rising temperature this dependence implies that variations in mechanical plate thickness can be used to map temperature anomalies in the lithosphere since the mechanical plate thickness depends principally upon the temperature at one depth specifically the depth at which the temperature reaches 550 600 c depending on strain rate flexural data are particularly sensitive indicators of the vertical structure of lithospheric reheating compared to quantities dependent on depth integrals of temperature such as swell height and subsidence the thermal rejuvenation hypothesis predicts that the flexural profile should mimic viscoelastic relaxation in the first 10 ma after loading if initially reheating is confined to depths close to and below the 550 c isotherm the flexural data combined with depth anomaly information for hawaii point to extremely rapid reheating localized in the lower lithosphere rejuvenation in the society islands on the other hand is compatible with slower methods of heat injection involving the entire lithospheric column

dominant northern hemisphere climate control over millennial scale glacial sea level variability abstract based on a radiocarbon and paleomagnetically dated sediment record from the northern red sea and the exceptional sensitivity of the regional changes in the oxygen isotope composition of sea water to the sea level dependent water exchange with the indian ocean we provide a new global sea level reconstruction spanning the last glacial period the sea level record has been extracted from the temperature corrected benthic stable oxygen isotopes using coral based sea level data as constraints for the sea level oxygen isotope relationship although the general features of this millennial scale sea level records have strong similarities to the rather symmetric and gradual southern hemisphere climate patterns we observe in constrast to previous findings pronounced sea level rises of up to 25 m to generally correspond with northern hemisphere warmings as recorded in greenland ice core interstadial intervals whereas sea level lowstands mostly occur during cold phases corroborated by climber 2 model results the close connection of millennial scale sea level changes to northern hemisphere temperature variations indicates a primary climatic control on the mass balance of the major northern hemisphere ice sheets and does not require a considerable antarctic contribution

distribution formation and seasonal variability of okhotsk sea mode water 1 russian historical data and recently completed conductivity temperature depth surveys are used to examine the formation and spread in the deep ohkotsk sea of dense shelf water dsw produced in the okhotsk sea polynyas isopycnal analysis indicates that all of the main polynyas contribute to the ventilation at 27 1 vigorous tidal mixing leads to outflow of water with a density of only about 26 7 in the western okhotsk sea the east sakhalin current rapidly transports modified dense shelf water along the eastern sakhalin slope to the kuril basin where it is subject to further mixing because of the large anticyclonic eddies and tides most of the dense water flows off the shelves in spring their average flux does not exceed 0 2 sv in summer and fall the shelf water transport and water exchange with the north pacific cause large seasonal variations of temperature at densities of 26 7 27 0 depths of 150 500 m in the kuril basin where the average temperature minimum occurs in april may and the average temperature maximum occurs in september with a range of 0 2 0 7 c the average seasonal variations of salinity are quite small and do not exceed 0 05 psu the soya water mixed by winter convection penetrating to depths greater than 200 m in the southern kuril basin also produces freezing water with density greater than 26 7 using a simple isopycnal box model and seasonal observations the osmw production rate is seen to increase in summer up to 2 2 1 7 sv mainly because of increased north pacific inflow and drops in winter to 0 2 0 1 sv a compensating decrease in temperature in the kuril basin implies a dsw volume transport of 1 4 1 1 sv from february through may the residence time of the osmw in the kuril basin is 2 1 7 years

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

orbital and millennial scale environmental and hydrological changes of the central okhotsk sea over the last 136 kyr inferred from micropaleontological radiolarian and benthic foraminifera geochemical and lithological proxies and the mechanisms responsible for them abstract the response of benthic foraminifera bf and radiolarian production in the central okhotsk sea os to orbital and millennial changes of climate and environment over the last 136 kyr have been studied on the basis of the sediment core pc 7r with available productivity geochemical and lithological records and a modified age model we used the calculated accumulation rate of microfossils ar fluxes of the main ecological groups and species indicative of radiolarians and of bf as quantity responses in their production which is related to environmental and hydrological changes of the water column and surface sediment in the central os and to global and regional climate changes the responses of the opportunistic bf alabaminella weddellensis and the suboxic group during the last 136 kyr were mostly related to changes in organic fluxes from the surface sea ice cover and surface sediment oxygenation at both orbital and millennial time scales the ar of radiolarians from the surface dichothermal and mesopelagic groups significantly differed from the ar of bf the ar has a maximum during the middle and late marine isotope stage 5e and lower values during the earlier holocene while the minimum happened during cold marine isotope stages 6 4 and 2 with maximal ventilation of os intermediate water production of the mesopelagic radiolarian cycladophora davisiana in the os was mostly related to the lateral delivery of terrigenous material and om into the water column from the northwestern shelf and or from the western subarctic pacific due to the sensitivity of marine organisms to environmental conditions the production of radiolarians and bf sharply changed with the extinction of amphimelissa setosa since heinrich stadial 8 is related to the termination of global environment cooling and the hydrology changes of the early last glacial

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr