the role of caco3 compensation in the glacial to interglacial atmospheric co2 change the only viable explanations put forth to date for the glacial to interglacial change in atmospheric co2 content suggested from measurements of the co2 content of gas extracted from ice cores involve changes in the ocean s nutrient cycles any nutrient change capable of creating the 80 atm changes in atmosphere co2 pressure suggested by the ice core results also creates significant change in the deep ocean s co3 content evidence from deep sea sediments suggests that these co3 changes are compensated on the time scale of a few thousand years by reductions or increases in amount of caco3 accumulating in deep sea sediments this compensation process has two important consequences first it significantly increases the magnitude of the co2 change per unit of nutrient forcing second it causes a delay in the response of the atmospheric co2 change while the first of these consequences is a boon to those seeking to explain the co2 change the second may prove to be a curse the ice core co2 record shows no evidence of a significant lag between the co2 response and the polar warming in any case it is important that we improve our knowledge of the magnitude and timing of the caco3 preservation events which mark the close of episodes of glaciation and of the dissolution events which mark the onset of these episodes

diatom stable isotopes sea ice presence and sea surface temperature records of the past 640 ka in the atlantic sector of the southern ocean 1 high resolution 13c and 15n records of diatom bound organic matter 13cd 15nd from odp site 1094 south of the polar front are combined with reconstructions of summer sea surface temperature and winter sea ice to establish changes in surface water characteristics associated with the main climatic events of the past 640 ka the six glacial interglacial 13cd cycles show excellent agreement with specmap 18o and vostok co2 content suggesting that global physical processes rather than local biological factors were the main influences on 13cd by contrast there is weak correspondence between the vostok dust record and the 13cd and 15nd records the data do not support the hypothesis that glacial iron fertilization of the southern ocean was the main factor lowering atmospheric co2 if dust accumulation represents iron input the records indicate that sea ice cover water column stratification and iron addition from deep water mixing are more likely to explain our observations

deep pacific caco 3 compensation and glacial interglacial atmospheric co 2 abstract benthic foraminiferal 13c suggests that there was a net shift of isotopically light metabolic co2 from the upper ocean into the deep ocean during the last glacial period according to the caco3 compensation hypothesis this should have caused a transient drop in deep ocean co32 that was eventually reversed by seafloor dissolution of caco3 the resulting increase in whole ocean ph may have had a significant impact on atmospheric co2 compounding any decrease that was due to the initial vertical co2 shift the opposite hypothetically occurred during deglaciation when co2 was returned to the upper ocean and atmosphere and deep ocean co32 temporarily increased followed by excess burial of caco3 and a drop in whole ocean ph the deep sea record of caco3 preservation appears to reflect these processes with the largest excursion during deglaciation as expected but various factors make quantification of deep sea paleo co32 difficult here we reconstruct deep equatorial pacific co32 over the last glacial interglacial cycle using benthic foraminiferal zn ca which is strongly affected by saturation state during calcite precipitation our data are in agreement with the caco3 compensation theory including glacial co32 concentrations similar to or slightly lower than today and a termination i co32 peak of 25 30 mol kg 1 the deglacial co32 rise precedes ice sheet melting consistent with the timing of the atmospheric co2 rise a later portion of the peak could reflect removal of co2 from the atmosphere ocean system due to boreal forest regrowth caco3 compensation alone may explain more than one third of the atmospheric co2 lowering during glacial times

patterns of deglacial warming in the pacific ocean a review with emphasis on the time interval of heinrich event 1 abstract based on a compilation of currently available records of past sea surface temperature sst variability estimated from a variety of different proxies the regional scale deglacial sst development in the pacific ocean is tentatively classified into four endmember types the subtropical and tropical pacific is characterized by a continuous deglacial warming without marked interruption during the time interval of heinrich event 1 h1 whereas the subarctic north pacific exhibits centennial scale warm cold oscillations during this time interval sst records from marginal seas of the pacific show a deglacial warming interrupted by a cooling event coeval with h1 followed by a marked bolling sst increase a single sst record from the southwestern subantarctic pacific displays a continuous deglacial warming across h1 followed by an antarctic cold reversal type cooling during the allerod thus in contrast to the deglacial sst development in the atlantic which has been inferred to be overwhelmingly driven by the redistribution of heat through changes in the meridional overturning circulation moc none of the open oceanic pacific sst records reviewed here displays any obvious and or dominant response to the reduction of the moc and or the reorganization of atmospheric circulation during h1 within the limits of absolute chronologies all tropical and subtropical pacific sst records show an onset of deglacial warming at 19 1 ka coeval with the onset of the deglacial rise in sea level

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

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

glacial interglacial changes in subarctic north pacific stratification since the first evidence of low algal productivity during ice ages in the antarctic zone of the southern ocean was discovered there has been debate as to whether it was associated with increased polar ocean stratification or with sea ice cover shortening the productive season the sediment concentration of biogenic barium at ocean drilling program site 882 indicates low algal productivity during ice ages in the subarctic north pacific as well site 882 is located southeast of the summer sea ice extent even during glacial maxima ruling out sea ice driven light limitation and supporting stratification as the explanation with implications for the glacial cycles of atmospheric carbon dioxide concentration

the southern ocean s biological pump during the last glacial maximum ice core records from antarctica show large 80 ppm and regular climate related changes in atmospheric co2 with minimum values during glacial periods and maximum values during peak interglacials the suggested role of the southern ocean in driving these changes is based on either the potential for increased utilization of surface nutrients or the potential for decreased ventilation of deep waters during glacial times several recent studies have invoked increased stratification of the southern ocean to explain lower glacial atmospheric co2 levels in terms of reduced exchange of co2 between the deep sea and the atmosphere a northward displacement and or substantial weakening of the westerly winds during glacial periods are implicit in the scenarios that invoke enhanced stratification however both circulation models and proxy results argue against a weakening of the westerlies in fact the mean flow of the antarctic circumpolar current and wind driven upwelling during the last glacial maximum lgm are thought to be at least as vigorous as those which exist today given these boundary conditions we offer two competing scenarios for ecosystem structure and export production of the glacial southern ocean the first scenario satisfies all proxy records for nutrient utilization and phytoplankton growth rate and requires increased relative to today nitrate utilization south of the antarctic polar front apf by phytoplankton other than diatoms together with a shift in the zone of maximum diatom growth from south interglacials to north glacials of the apf the second scenario has reduced growth of all phytoplankton species south of the apf during glacials and a shift in the zone of maximum export production to the north of the polar front the principal weakness of the first scenario is that there is little sedimentary evidence to support the increased export of particulate organic carbon required by the inferred increase in nitrate utilization south of the apf the principal weakness of the second scenario is that it requires a change in the isotopic fractionation of nitrogen by phytoplankton growing south of the polar front for reasons presently unknown the southern ocean s biological pump at the lgm has yet to be characterized unequivocally

warmings in the far northwestern pacific promoted pre clovis immigration to america during heinrich event 1 well dated multidecadal to centennial scale sediment records from the subarctic northwest pacific show that the early deglacial 18 5 15 0 ka was marked by 3 pronounced short term warmings of 5 c they lasted 500 1500 yr each and were coeval with early to late stages of cold heinrich event 1 in the north atlantic these regional climate windows may have promoted a pre clovis emigration of people from the cold arid monsoon climate in east asia to the climatically more favorable then emerged beringian and aleutian shelf regions and the americas as suggested by archeological findings

sedimentary nitrogen isotopic ratio as a recorder for surface ocean nitrate utilization in two contrasting regions of the ocean the equatorial pacific and the southern ocean the 15n of core top sediments were strongly related to no3 in surface waters with distance from the equator in the equatorial pacific 15n increased from 7 to 16 as no3 decreased from 8 m to 0 1 m going from 60 to 30 s in the se indian ocean core top 15n increased from 5 to 11 as surface no3 decreased from 25 m to 0 1 m these results are strong evidence that sedimentary 15n in these regions is recording the increasing isotopic enrichment of near surface no3 with its depletion by phytoplankton in the case of the equatorial pacific 15n values for sinking particles collected at 150 m matched well the core top sediment values demonstrating little diagenetic alteration of the near surface generated isotopic signal these equatorial pacific data sets have variations with near surface no3 consistent with rayleigh fractionation kinetics for a fractionation factor u of 2 5 this value is substantially lower than previously found for temperate or polar regions perhaps as a result of differences in phytoplankton species assemblage or growth condition in the southern ocean south of the polar front comparison of 15n values for opal rich sediments south and sinking particles indicates an apparent 5 diagenetic enrichment relative to the surface generated signal that requires further investigation this exception aside our observations show that the surface water relationship of increasing 15n with increasing no3 depletion is generally transmitted to and preserved in the sediments an important requirement for further development and application of this important paleoceanographic tool

the effect of cold climate upon north atlantic deep water formation in a simple ocean atmosphere model the sensitivity of north atlantic deep water formation to variations in mean surface temperature is explored with a meridional vertical plane ocean model coupled to an energy balance atmosphere it is found that north atlantic deep water formation is favored by a warm climate while cold climates are more likely to produce southern ocean deep water or deep decoupling oscillations when the southern sinking region is halocline covered this behavior is traced to a cooling induced convective instability near the north atlantic sinking region that is to unstable horizontal spreading of a halocline that stratifies part of the region under the convective instability it is found that climate cooling is generally equivalent to increased freshwater forcing this is because in a cold climate high latitude water masses approach the temperature of maximum density and the convectiondriving upward thermal buoyancy flux induced by surface cooling becomes insufficient to overcome the stratifying effect of surface freshening a downward buoyancy flux an extensive halocline is then formed and this halocline interferes with the heat loss necessary for the steady production of north atlantic deep water

carboniferous and permian granites of the northern tasman orogenic belt queensland australia insights into petrogenesis and crustal evolution from an in situ zircon study in situ u pb dating and lu hf systematics of zircon in granites of the hodgkinson province in the northern tasman orogenic belt queensland australia reveal input of isotopically more evolved crustal magmas and larger ranges in 176hf 177hf in the carboniferous i type granites 0 28219 0 28269 weighted average 0 28245 than in the permian s type granites 0 28249 0 28280 weighted average 0 28262 and permian i type granites 0 28253 0 28274 weighted average 0 28260 the wide range in the hf isotope compositions of zircons in the carboniferous and permian granites can be explained by remelting of a heterogeneous mesoproterozoic crustal source whereas a narrow range reflects the subsequent dissolution of inherited grains cores and magma homogenisation before zircon crystallisation alternatively mixing between the most radiogenic and unradiogenic magmas can produce the isotopic variation seen in other carboniferous granites remelting of neoproterozoic average crust or mafic younger crust can produce the more radiogenic hf isotope compositions of zircons in the permian s type granites an overlap between the hf isotope signatures of the carboniferous i type granites in the southwestern hodgkinson province and the northeastern australian craton 0 28211 0 28254 and evidence for major magmatic events at 1 585 1 545 and 345 300 ma imply that the southwestern province is underlain by cratonic crust which wedges out towards the northeast the more radiogenic hf isotope signature of the permian granites and a lack of evidence for these major magmatic events in the southeastern and central hodgkinson province imply that these parts are characterised by different crustal sources and crustal evolution histories

pliocene pleistocene evolution of the north pacific ocean atmosphere system interpreted from fossil diatoms the relative abundance of diatom taxa in 216 core tops has been quantified and compared using cluster analysis with assemblages in six cores located beneath different water masses of the north pacific ocean all but one sequence span at least 1 5 m y early pleistocene to holocene and one extends to 2 6 ma the quantitative abundance of each taxon and the space time occurrence of each cluster are interpreted as tracers of oceanographic conditions in addition to high frequency glacial interglacial oscillations the records display rapid steplike changes at 2 4 ma 1 6 1 5 ma 1 0 ma 0 8 0 7 ma and 0 35 ma two secondary transitions recorded only in the northwestern cores occur at 2 0 ma and 1 1 ma we conclude that both the high frequency oscillations and the stepwise transitions reflect variations in extent of subarctic water masses under the influence of the siberian high pressure and aleutian low pressure atmospheric cells we further conclude that 1 the subarctic water mass has developed progressively and attained its modern structure only in the late pleistocene 2 some stages of this evolution may have occurred earlier in the eastern subarctic 3 the holocene is an atypical warm extreme so that the present is not a very good key to the past 4 there were several glaciations between 2 4 and 2 0 ma and 5 the subtropical gyre is more conservative than the subarctic gyre and major changes in the region have been due to forcing from the north we propose a conceptual model of oscillating metastable climatic modes maintained by internal feedback and suggest that steplike changes may occur when one set of boundary conditions is temporarily exceeded

a pervasive link between antarctic ice core and subarctic pacific sediment records over the past 800 kyrs recently developed xrf core scanning methods permit paleoceanographic reconstructions on timescales similar to those of ice core records we have investigated the distribution of biogenic barium ba al opal and carbonate ca al in a sediment core retrieved from the abyssal subarctic pacific odp 882 50 n 167 e 3244 m over an interval that spans the full length of the epica dome c edc ice core record ba al and biogenic opal show a strong resemblance to the edc dd and co2 with generally high concentrations during interglacials and lower values during ice ages of the past 800 kyrs the sedimentary ba al and biogenic opal are most easily interpreted as indicating a reduced sinking flux of organic matter from the surface ocean during cold periods the ba al maxima during peak interglacials are accompanied by transient ca al peaks in these otherwise carbonate devoid sediments which are best explained by a deepening of the calcite lysocline presumably due to reduced storage of respired co2 in the deep north pacific for most of the luke warm interglacials noted between 420 and 750 ka in edc the ba al peaks in odp 882 are also lower further strengthening the evidence for a simple physical link between global climate and the biogeochemistry of the subarctic pacific

sedimentary organic matter preservation a test for selective degradation under oxic conditions the authors report here a test of the hypothesis that the extent of organic matter preservation in continental margin sediments is controlled by the average period accumulating particles reside in oxic porewater immediately beneath the water sediment interface oxygen penetration depths organic element compositions and mineral surface areas were determined for 16 sediment cores collected along an offshore transect across the washington continental shelf slope and adjacent cascadia basin individual amino acid sugar and pollen distributions were analyzed for a 11 to 12 cm horizon from each core and sup 14 c based sediment accumulation rates and stable carbon isotope compositions were determined from depth profiles within a subset of six cores from representative sites sediment accumulation rates decreased and dissolved o sub 2 penetration depths increased offshore along the sampling transect as a result oxygen exposure times oet increased seaward from decades mid shelf and upper slope to more than a thousand years outer cascadia basin organic contents and compositions were essentially constant within individual sediment cores but varied consistently with location in particular organic carbon surface area ratios decreased progressively offshore and with increasing oet three independent compositional parameters demonstrated that the remnant organic matter in farther offshore sediments is more degraded both concentrationmore and compositional patterns indicated that sedimentary organic matter exhibits a distinct and reproducible oxic effect oet helps integrate and explain organic matter preservation in accumulating continental margin sediments and hence provides a useful tool for assessing transfer of organic matter from the biosphere to the geosphere less

orbital and millennial antarctic climate variability over the past 800 000 years a high resolution deuterium profile is now available along the entire european project for ice coring in antarctica dome c ice core extending this climate record back to marine isotope stage 20 2 800 000 years ago experiments performed with an atmospheric general circulation model including water isotopes support its temperature interpretation we assessed the general correspondence between dansgaard oeschger events and their smoothed antarctic counterparts for this dome c record which reveals the presence of such features with similar amplitudes during previous glacial periods we suggest that the interplay between obliquity and precession accounts for the variable intensity of interglacial periods in ice core records

biogenic opal indicating less productive northwestern north pacific during the glacial ages 1 biogenic opal and ice rafted detritus ird data from sediments in the okhotsk sea and the neighboring north pacific revealed the remarkable reduction in opal production and southward advancement of sea ice covered area during the last glacial maximum resulting also southward shift of high biological productive area in the northwestern north pacific it implies that the substantial reduction in outflux of co2 to the atmosphere in northwestern north pacific and the pronounced increase in co2 sequestering in temperate north pacific this could be an additional co2 reduction mechanism of atmospheric co2 in the last glacial period

effect of global ocean temperature change on deep ocean ventilation 1 a growing number of paleoceanographic observations suggest that the ocean s deep ventilation is stronger in warm climates than in cold climates here we use a general ocean circulation model to test the hypothesis that this relation is due to the reduced sensitivity of seawater density to temperature at low mean temperature that is at lower temperatures the surface cooling is not as effective at densifying fresh polar waters and initiating convection in order to isolate this factor from other climate related feedbacks we change the model ocean temperature only where it is used to calculate the density to which we refer below as dynamic temperature change we find that a dynamically cold ocean is globally less ventilated than a dynamically warm ocean with dynamic cooling convection decreases markedly in regions that have strong haloclines i e the southern ocean and the north pacific while overturning increases in the north atlantic where the positive salinity buoyancy is smallest among the polar regions we propose that this opposite behavior of the north atlantic to the southern ocean and north pacific is the result of an energy constrained overturning

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

a comparison between excess barium and barite as indicators of carbon export 1 since dymond et al 1992 proposed the paleoproductivity algorithm based on bio ba which relies on a strong correlation between ba and organic carbon fluxes in sediment traps this proxy has been applied in many paleoproductivity studies barite the main carrier of particulate barium in the water column and the phase associated with carbon export has also been suggested as a reliable paleoproductivity proxy in some locations we demonstrate that baexcess total barium minus the fraction associated with terrigenous material frequently overestimates babarite barium associated with the mineral barite most likely due to the inclusion of barium from phases other than barite and terrigenous silicates e g carbonate organic matter opal fe mn oxides and hydroxides a comparison between overlying oceanic carbon export and carbon export derived from baexcess shows that the dymond et al 1992 algorithm frequently underestimates carbon export but is still a useful carbon export indicator if all caveats are considered before the algorithm is applied babarite accumulation rates from a wide range of core top sediments from different oceanic settings are highly correlated to surface ocean 14 c and chlorophyll a measurements of primary production this relationship varies by ocean basin but with the application of the appropriate f ratio to 14 c and chlorophyll a primary production estimates the plot of babarite accumulation and carbon export for the equatorial pacific atlantic and southern ocean converges to a global relationship that can be used to reconstruct paleo carbon export index terms 3022 marine geology and geophysics marine sediments processes and transport 4267 oceanography general paleoceanography 4825 oceanography biological and chemical geochemistry keywords paleoproductivity barite export production excess barium marine sediments citation eagle m a paytan k r arrigo g van dijken and r w murray a comparison between excess barium and barite as indicators of carbon export paleoceanography 18 1 1021 doi 10 1029 2002pa000793 2003

nitrogen isotopic evidence for a poleward decrease in surface nitrate within the ice age antarctic abstract surface sediment diatom bound 15 n along a latitudinal transect of 170 w shows a previously unobserved increase to the south of the antarctic polar front the southward 15 n increase is best explained by the combination of two changes toward the south a decrease in the isotope effect of nitrate assimilation e and an increase in the degree of nitrate consumption both associated with shoaling of the mixed layer into the seasonal ice zone siz new downcore records show high amplitude changes in diatom bound 15 n during the last ice age with intervals of higher 15 n including the last glacial maximum the transition between marine isotope stages 5 and 4 and marine isotope stage 6 while other intervals are similar in 15 n to interglacial sediments variation in the range of 0 3 as seen in previously published records may be entirely due to changes in e however the observed magnitude of the change of 4 10 in the three new records and the locations of these records relative to the modern meridional gradient in mixed layer depth appear to require increased nitrate consumption to explain the high 15 n intervals the new sites are near the modern southern antarctic circumpolar current front saccf and one of the sites has been shown to be associated with sporadic summer sea ice during the lgm as with other antarctic sites the available proxy data suggest that they were characterized by lower export production based on these and other observations we propose that the weak southward nitrate decrease in the modern antarctic surface was a fully developed nutrient front in the glacial antarctic associated with the saccf both modern ocean and paleoceanographic work is needed to test this hypothesis which would have major implications for atmospheric co 2

stable carbon cycle climate relationship during the late pleistocene a record of atmospheric carbon dioxide co2 concentrations measured on the epica european project for ice coring in antarctica dome concordia ice core extends the vostok co2 record back to 650 000 years before the present yr b p before 430 000 yr b p partial pressure of atmospheric co2 lies within the range of 260 and 180 parts per million by volume this range is almost 30 smaller than that of the last four glacial cycles however the apparent sensitivity between deuterium and co2 remains stable throughout the six glacial cycles suggesting that the relationship between co2 and antarctic climate remained rather constant over this interval

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

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

revisiting nutrient utilization in the glacial antarctic evidence from a new method for diatom bound n isotopic analysis holocene in the indian sector is smaller than in previous measurements these data suggest no change in the degree of nitrate utilization in the atlantic sector and at most a 20 increase from 25 to 45 in the indian sector the new measurements suggest that during the last ice age in the atlantic sector of the antarctic the atmospheric source of biologically available iron was not so great as to become significant relative to the iron supply from below given the apparent spatial variability in the degree of nitrate drawdown more work is required to develop an adequate picture of the glacial antarctic nutrient field index terms 4806 oceanography biological and chemical carbon cycling 4845 oceanography biological and chemical nutrients and nutrient cycling 4894 oceanography biological and chemical instruments and techniques 9310 information related to geographic region antarctica

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

deep ocean biogeochemistry of silicic acid and nitrate 1 observations of silicic acid and nitrate along the lower branch of the global conveyor belt circulation show that silicic acid accumulation by diatom opal dissolution occurs at 6 4 times the rate of nitrate addition by organic matter remineralization the export of opal and organic matter from the surface ocean occurs at a si n mole ratio that is much smaller than this almost everywhere cf sarmiento et al 2004 the preferential increase of silicic acid over nitrate as the deep circulation progresses from the north atlantic to the north pacific is generally interpreted as requiring deep dissolution of opal together with shallow remineralization of organic matter broecker 1991 however sarmiento et al 2004 showed that the primary reason for the low silicic acid concentration of the upper ocean is that the waters feeding the main thermocline from the surface southern ocean are depleted in silicic acid relative to nitrate by implication the same southern ocean processes that deplete the silicic acid in the surface southern ocean must also be responsible for the enhanced silicic acid concentration of the deep ocean we use observations and results from an updated version of the adjoint model of schlitzer 2000 to confirm that this indeed the case

impact of climate change on the magnetic mineral assemblage in marine sediments from izu rear arc nw pacific ocean over the last 1 myr abstract a rock magnetic study was conducted on upper pleistocene marine sediments from international ocean discovery program expedition 350 site u1437 in order to highlight the paleoenvironmental changes in the nw pacific ocean influenced by the east asian monsoon regime remanent magnetization analyses hysteresis properties first order reversal curves and low temperature magnetic measurements were carried out along with electron microscope observations the results indicate that coarse grained titano magnetite is the dominant magnetic phase in the magnetic mineral assemblage time series analysis supports that this assemblage is modulated by global climate changes over the last 1 myr during the interglacial stages magnetic minerals are more abundant and are dominated by coarse grained titano magnetite of both terrigenous likely from mainland china and volcanic izu arc front japan origin during the glacial stages the magnetic mineral content is lower probably reflecting partial dissolution of ti magnetite and the magnetic assemblage is composed of terrigenous coarse grained titano magnetite and of higher coercivity presumably finer eolian particles likely hematite as a result of the enhancement of the winter monsoon in continental asia the magnetic mineral assemblage reflects a superimposition of volcanic and global climate signals bulk organic geochemical analyses for total and organic carbon as well as nitrogen and sulfur contents confirm a climatic signature in the composition of the sediments with more oxygenated water masses being present during glacial periods additional x ray fluorescence measurements on bulk samples indicate various origins of the sediment particles with both proximal and distal sources

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

structural evolution of gavilgarh tan shear zone central india a possible case of partitioned transpression during mesoproterozoic oblique collision within central indian tectonic zone abstract gavilgarh tan shear zone gtsz a map scale ductile shear zone occurring in the southern part of the central indian tectonic zone citz contains many important clues to the tectonics of this important proterozoic mobile belt of central india which is yet controversial and hotly debated data from structural mapping microstructural study and kinematic analyses of the gtsz have been presented in this paper which clearly implies that gtsz is mainly represented by a wrench dominated transpressional shear zone with sinistral shear sense analysis of lineation patterns shows that while horizontal stretching dominated within the ductile shear zone rocks on either side north and south of it stretched vertically with a transition zone of simultaneous horizontal and vertical stretching in between these two domains a general transpressional strain has thus been partitioned into wrench and pure shear dominated domains at large scale further strain partitioning also took place at the outcrop scale geochemistry of the granitoids occupying the shear zone and its surrounding area indicates continental collision set up which supports the structural model on the basis of earlier proposed tectonic models and limited geochronological data available of the southern part of citz it is suggested here that an oblique collision and final suturing between the northern bundelkhand craton and southern bastar craton terrains within the citz around 1100 ma have been partly accommodated by partitioned transpression along gtsz and its surrounding gneiss granitoid terrain more intensive geochronological constraint of the collision event from both northern and southern side are however lacking at present