increased productivity in the eastern equatorial pacific during the last glacial maximum 19 000 to 14 000 yr b p a widespread pronounced enrichment in the organic carbon content occurs at shallow depths in eastern equatorial pacific sediments the c org peak is shown by radiocarbon dating to be temporally coincident with the last stage 2 or wisconsin glacial maximum in contrast caco 3 profiles show less overall variation which appears to be partly a function of the location of the sediments relative to the lysocline consideration of the iodine c org ratio in the sediments rules out enhanced preservation as a cause of the stage 2 organic carbon enrichment the peak instead must have resulted from a significant increase in productivity during the glacial maximum

circulation patterns in the late pennsylvanian north american midcontinent sea inferred from spatial gradients in sediment chemistry and mineralogy abstract the north american midcontinent sea nams reached its maximum extent during glacio eustatic highstands of the late paleozoic ice age during which organic rich core shales accumulated under a stratified water column with anoxic deep waters the core shales of cyclothems are composed of a lower organic rich laminated black shale and an upper bioturbated gray shale the present study investigates circulation patterns within the nams by examining secular variations and spatial gradients in the concentrations and ratios of major elements trace elements and organic carbon as well as carbon and nitrogen isotopes within one cyclothemic core shale the heebner shale the heebner shale represents the core shale member of the upper pennsylvanian lowermost gzhelian virgilian oread limestone formation in kansas and iowa and it is correlative with the teutopolis shale of the mattoon formation in illinois the heebner was sampled at high stratigraphic resolution at five sites on the northern midcontinent shelf and two sites in the illinois basin clay and silt fraction proxies show influences from multiple distinct terrestrial sources the paleosalinity proxy sr ba in combination with spatial patterns of clay and silt proxies implies large scale counterclockwise cyclonic rotation of the nams watermass which was possibly driven by the hydrodynamics of upwelling on the southern midcontinent shelf margin and or riverine discharge into the eastern nams spatial patterns of 13c and 15n are consistent with regionally variable productivity and redox conditions differences in the magnitude of a positive 15n excursion among the study sites record spatially variable water column denitrification rates enrichment of trace metals on the northern midcontinent shelf was a product of intensified water column recycling within an estuarine saltwater wedge trace metal enrichments and fe al ratios are consistent with moderate watermass restriction throughout the nams the results of the present study permit major refinement of the existing superestuarine circulation model for the nams algeo t j et al 2008 modern and ancient epeiric seas and the super estuarine circulation model of marine anoxia in b pratt and c holmden eds dynamics of epeiric seas geol assoc canada spec publ 48 pp 7 38

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

climate records covering the last deglaciation the oxygen 18 oxygen 16 ratio of molecular oxygen trapped in ice cores provides a time stratigraphic marker for transferring the absolute chronology for the greenland ice sheet project gisp ii ice core to the vostok and byrd ice cores in antarctica comparison of the climate records from these cores suggests that near the beginning of the last deglaciation warming in antarctica began approximately 3000 years before the onset of the warm bolling period in greenland atmospheric carbon dioxide and methane concentrations began to rise 2000 to 3000 years before the warming began in greenland and must have contributed to deglaciation and warming of temperate and boreal regions in the northern hemisphere

synchronous high frequency oscillations in tropical sea surface temperatures and north atlantic deep water production during the last glacial cycle stable isotopic measurements of g sacculifer and c wuellerstorfi in a core from the western equatorial atlantic imply that there are parallel suborbital oscillations in surface water hydrography and deep water circulation occurring during oxygen isotope stages 2 and 3 low values of g sacculifer 18o accompany high values of c wuellerstorfi 13c linking warmer sea surface temperatures ssts in the tropics with increased production of lower north atlantic deep water nadw the amplitude of the 18o oscillations is 0 6 or 2 3 c which is superimposed on a glacial interglacial amplitude of about 2 1 using the g sacculifer 18o data we calculate that surface waters were colder during stage 2 than calculated by climap 1976 1981 the longer period 2 kyr oscillations in air temperature recorded in the greenland and antarctic ice cores appear to correlate with oscillations in sea surface temperature in the equatorial atlantic the magnitude of these oscillations in tropical sst is too large to have resulted from changes in meridional heat transport caused by the global conveyor alone the apparent synchroneity of equatorial sst and polar air temperature changes as well as the amplitude of the sst changes at the equator are consistent with the climate effects expected from changes in the atmosphere s greenhouse gas content h2ovapor co2 and ch4

glacial holocene biogenic sedimentation patterns in the south china sea productivity variations and surface water pco2 a bathymetric transect of cores in the south china sea extending from 4200 m to less than 1000 m water depth has been examined for glacial interglacial changes in carbonate and organic carbon sedimentation typical pacific carbonate cycles high carbonate content during glacials and low carbonate content during interglacials characterize cores from water depths deeper than 3500 m in contrast atlantic carbonate cycles low carbonate during glacials and high carbonate during interglacials are observed in cores from depths shallower than 3000 m as a result of increased dilution of carbonate by terrigenous material during glacial low stands of sea level glacial interglacial changes in the carbonate chemistry of south china sea intermediate and deep waters resulted in significant changes in the positions of the carbonate compensation depth ccd and the aragonite compensation depth acd during the last glacial the ccd and acd were at least 400 and 1200 m deeper respectively than at present organic carbon accumulation rates in the south china sea were approximately 2 times higher during the last glacial than the holocene carbon isotopic analyses and c n ratios of the organic matter indicate that only a small fraction of the increase in glacial organic carbon accumulation can be attributed to input of terrestrial carbon on the basis of this we conclude that surface water productivity in the south china sea was approximately 2 times higher during the last glacial maximum this is consistent with previous studies which have demonstrated that glacial productivity was higher in low to mid latitude regions of the atlantic and eastern pacific the deglacial decrease in organic carbon accumulation is accompanied by a decrease in 13corg using the relationship between 13corg and co2 aq developed by popp et al 1989 we estimate that surface water pco2 values in the south china sea during the last 25 000 years were very similar to atmospheric co2 concentrations

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

enhanced marine productivity off western north america during warm climate intervals of the past 52 k y studies of the santa barbara basin off the coast of california have linked changes in its bottom water oxygen content to millennial scale climate changes as recorded by the oxygen isotope composition of greenland ice through the use of detailed records from a sediment core collected off the magdalena margin of baja california mexico we demonstrate that this teleconnection predominantly arose from changes in marine productivity rather than changes in ventilation of the north pacific as was originally proposed

millennial scale oscillation of denitrification intensity in the arabian sea during the late quaternary and its potential influence on atmospheric n2o and global climate the intensity of denitrification in the arabian sea during the last 65 kyr is reconstructed using high resolution 15 n records of three sediment cores in conjunction with other geochemical tracers for water column oxygenation and productivity the results reveal a close link to the greenland ice core record with low or absent water column denitrification during the last glacial maximum the stadials and at the time of the heinrich events including the younger dryas in contrast denitrification was high during the holocene and the interstadials the intensification of denitrification is related to stronger sw monsoonal upwelling which enhances organic matter flux and degradation resulting in a strengthening of the midwater oxygen deficiency such a combination of enhanced upwelling and denitrification has also been implied for the eastern tropical north pacific etnp where these events occur during the holocene and to some extent during the interstadials too today the arabian sea and the etnp together contribute substantially to the global marine water column denitrification and a significant fraction of the ocean atmosphere n 2 o flux originates from these areas changes in n 2 o emissions from these areas could thus have effected the recently described stadial interstadial variations in the atmospheric concentration of this greenhouse gas as deduced from ice cores moreover denitrification is the major sink for oceanic nitrate and provides a primary control for the oceanic nutrient inventory which in turn influences global primary productivity and co 2 sequestration by the biological pump short term switches between a nondenitrification mode and a denitrification mode in these marine regions therefore have an impact on global climate

deglacial climatic oscillations in the gulf of california a high resolution accelerator radiocarbon dated climate record of the interval 8 000 18 000 years b p from deep sea drilling project site 480 guaymas basin gulf of california shows geochemical and lithological oscillations of oceanographic and climatic significance during deglaciation nonlaminated sediments are associated with cooler climatic conditions during the late glacial up to 13 000 years b p and from 10 300 to 10 800 years b p equivalent to the younger dryas event of the north atlantic region we propose that the changes from laminated varved to nonlaminated sediments resulted from increased oxygen content in pacific intermediate waters during the glacial and the younger dryas episodes and that the forcing for the latter event was global in scope prominent events of low 18o are recorded in benthic foraminifera from 8 000 to 10 000 and at 12 000 years b p evidence for an earlier event between 13 500 and 15 000 years b p is weaker maximum 18o is found to have occurred 10 500 13 500 and 15 000 years ago and beyond oxygen isotopic variability most likely reflects changing temperature and salinity characteristics of pacific waters of intermediate depth during deglaciation or environmental changes within the gulf of california region several lines of evidence suggest that during deglaciation the climate of the american southwest was marked by increased precipitation that could have lowered salinity in the gulf of california recent modelling studies show that cooling of the gulf of mexico due to glacial meltwater injection which is believed to have occurred at least twice during deglaciation would have resulted in increased precipitation with respect to evaporation in the american southwest during summertime the timing of deglacial events in the gulf of mexico and the gulf of california supports such an atmospheric teleconnection

oxygen minimum zone expansion in the eastern tropical north pacific during deglaciation concentrations lamination preservation and d 15 n values from cores located between 540 750 m water depth in the gulf of tehuantepec southern mexico these results differ from similar proxies found even 5 n of the site where there is evidence for omz changes related to rapid climate change in the northern hemisphere instead omz expansion in the gulf was contemporaneous with changes in sea ice extent and zonal wind shifts around antarctica pointing to subantarctic mode water and antarctic intermediate water as likely sources of oxygen depleted water these observations reinforce the importance of the southern ocean as a primary modulator of northern hemisphere ocean climate as far as 15 n in the etnp citation hendy i l and t f pedersen 2006 oxygen minimum zone expansion in the eastern tropical north pacific during deglaciation geophys res lett 33 l20602 doi 10 1029 2006gl025975

latest quaternary north pacific surface water responses imply atmosphere driven climate instability a full sequence of brief interstadials dansgaard oeschger d o cycles are recorded from 60 to 25 ka in santa barbara basin california ocean drilling program hole 893a by planktonic foraminiferal isotopic and assemblage changes at unparalleled high resolution for the oceans synchronous climatic response between north pacific surface waters and the greenland ice sheet during d o cycling is strongly indicated by remarkable similarities in speed magnitude and character of rapid oceanic and atmospheric reorganizations inferred sea surface temperature warmings of as much as 5 c within a few decades and brief warming overshoots of as much as 3 c suggest involvement of an atmospheric amplification top down in situ atmospheric warming of the ocean is implied by differential responses partial decoupling in the changes recorded in surface and thermoclinal waters

direct evidence for nitrogen isotope discrimination during sedimentation and early diagenesis in lake kasumigaura japan abstract sediment core samples from the center of lake kasumigaura japan were collected from 1979 to 2007 at intervals of 1 month to 5 yr we evaluated the degree of modification in n isotope composition during sedimentation and diagenesis we estimated the degree of isotope discrimination during diagenesis by comparing historical changes in n isotope composition of the surface sediment top 2 cm against the vertical profile of the isotope composition of sediment core samples 15 cm depth the degree of 15 n enrichment during sedimentation appeared to be significant under the preferential n decomposition that occurred in the periods with low c n ratio values of suspended particulate organic matter we documented 15 n depletion in sediment deeper than approximately 3 cm during diagenesis the contrasting directions of n isotope discrimination during sedimentation and diagenesis suggest changing mechanisms of isotopic shift across an oxidation reduction boundary

millennial scale variations in hydrography and biogeochemistry in the eastern equatorial pacific over the last 100 kyr abstract in this study we use records of nitrogen isotope ratios 15n uk 37 temperature estimates organic carbon and opal percentages from high resolution sediment cores located in the eastern equatorial pacific eep to explore the mechanisms linking millennial scale changes in low latitude sea surface temperature water column denitrification and surface productivity to the timing of northern or southern polar climate during the last 100 000 yr our results support a hypothesis that the southern hemisphere and its connection to the low latitudes via shallow subsurface ocean circulation has a primary influence on the biogeochemistry of the eep in addition our results suggest that during the last glacial stage denitrification rates fluctuated on millennial timescales in response to water column ventilation rather than upstream oxidant demand in intermediate depth waters however due to the poor age constraints available for marine isotopic stage mis 3 the eep sedimentary data presented here could support two conflicting mechanisms one driven by enhanced intermediate overturning circulation in the southern ocean during heinrich events antarctic warm events implying that subsurface flow rates control thermocline ventilation and a second one consistent with more sluggish intermediate circulation during antarctic warm events and giving a central role to the temperature control on oxygen solubility in southern ocean surface waters

nitrogen isotopic evidence for deglacial changes in nutrient supply in the eastern equatorial pacific 1 the eastern equatorial pacific eep is a high nutrient low chlorophyll region of the ocean downcore nitrogen isotope records from the eep have been previously interpreted as a direct reflection of changes in nutrient consumption however the observed changes in sedimentary 15n since the last glacial maximum have no coherent relationship with export productivity or an inferred variation in the iron to nitrate ratio of the surface waters rather downcore n isotope records in the eep strongly resemble changes in the extent of water column denitrification as recorded in nearby sedimentary 15n records along the western margin of the americas this similarity is attributed to the overprinting of the n isotopic composition of nitrate in the eep through the advection of nitrate westward from the margins in the subsurface a local nitrogen isotope record of changes in the degree of nutrient consumption is extracted from the bulk sedimentary record by subtracting two different sedimentary 15n records of denitrification changes from two new eep 15n records tr163 22 and odp site 1240 the denitrification records used are from 1 the central american margin odp site 1242 and 2 the south american margin geob7139 2 the degree of consumption in the surface waters declines rapidly from elevated values during the last glacial maximum to a pair of minima around 15 and 11 13 ka and finally it increases into the holocene the derived eep nitrogen isotope record indicates that the regional peak in export productivity occurred when the supply of nutrients exceeded the apparently high demand the influx of nutrients during the deglaciation is attributed to the resumption of intense overturning in the southern ocean and the release of sequestered co2 and nutrient rich o2 poor waters from the deep ocean this has important implications for understanding the glacial interglacial scale variation in intermediate water suboxia and water column denitrification

the linkage of nitrogen isotopic composition and depositional environment of black mudstones in the upper triassic yanchang formation ordos basin northern china abstract in this study we report new analyses of stable nitrogen isotopic compositions 15n of the black mudstones from the chang 7 member of the upper triassic yanchang formation in the ordos basin china to examine the possible linkage of such isotopic compositions with the depositional environment these mudstones were deposited mainly under suboxic bottom water column conditions the core descriptions and trace element concentrations differ between samples obtained from the chang 73 and chang 71 2 members situated at the bottom and top of the chang 7 member respectively such that the depositional condition of the former implies a more reduced water regime the bulk rock nitrogen isotope 15nbulk values of the samples obtained from the chang 73 member are higher than those of the chang 71 2 member no significant differences were identified in the organic carbon isotopes 13corg total organic carbon toc or total nitrogen tn values between the two units the results of 15nbulk cross plotting with the toc tn and carbon to nitrogen atomic ratio c n show an absence of significant modification of the primary nitrogen isotopic compositions from post depositional processes given the depositional history of these units we suggest that the sedimentary redox environment can have a significant influence on 15nbulk denitrification which occurs mainly in suboxic conditions plays an important role in such an environment resulting in 15n enrichment during the original deposition thus owing to its sensitivity to sedimentary redox environments the 15nbulk index can be an effective tool for evaluating depositional redox conditions particularly for further subdivision of suboxic environments

n2o and ch4 variations during the last glacial epoch insight into global processes 1 greenhouse gas measurements along polar ice cores provide important insight into the former composition of the atmosphere its natural variations and the responses to fast climatic changes in the past we present high resolution nitrous oxide n2o and methane ch4 records measured along two ice cores from central greenland covering part of marine isotope stages 3 and 4 in the last glacial epoch the n2o data confirm the hypothesis that n2o shows variations in phase to fast climatic changes observed in the northern hemisphere the so called dansgaard oeschger d o events variations exist not only for events with a long duration 1500 years and more but also for the shorter ones the comparison with ch4 unveils interesting differences between the response of ch4 and n2o to d o events while the average amplitudes of ch4 oscillations associated with d o events are similar to those of the northern hemisphere summer insolation the magnitude of the n2o concentration change instead correlates with the duration of the d o events the records give further insight into the timing of concentration changes at the beginning of d o events they show that for long lasting events the n2o concentration starts to increase before both the sharp increase in the ch4 concentration and the temperature reconstructed for greenland

global variations of surface ocean productivity in low and mid latitudes influence on co2 reservoirs of the deep ocean and atmosphere during the last 21 000 years based on detailed reconstructions of global distribution patterns both paleoproductivity and the benthic 13c record of co2 which is dissolved in the deep ocean strongly differed between the last glacial maximum and the holocene with the onset of termination i about 15 000 years ago the new export production of low and mid latitude upwelling cells started to decline by more than 2 4 gt carbon year this reduction is regarded as a main factor leading to both the simultaneous rise in atmospheric co2 as recorded in ice cores and with a slight delay of more than 1000 years to a large scale gradual co2 depletion of the deep ocean by about 650 gt c this estimate is based on an average increase in benthic 13c by 0 4 0 5 the decrease in new production also matches a clear 13c depletion of organic matter possibly recording an end of extreme nutrient utilization in upwelling cells as shown by sarnthein et al 1987 the productivity reversal appears to be triggered by a rapid reduction in the strength of meridional trades which in turn was linked via a shrinking extent of sea ice to a massive increase in high latitude insolation i e to orbital forcing as primary cause

climatically forced organic carbon burial in equatorial atlantic and pacific oceans over the past ten years sedimentary geochemists have noted that climate changes associated with pleistocene glaciations have had a pronounced effect on the rate of organic carbon burial found in the tropical oceans1 4 in particular two to five times higher organic carbon accumulation rates have been observed for the 18 kyr bp glacial maximum than for the holocene in several short sediment cores from both oceans see fig 1 here i present 300 kyr time series for organic carbon mass accumulation rate from four sediment cores two each from the equatorial pacific and atlantic and show that orbital forcing of global climate has strongly affected the rate of organic carbon burial in the equatorial oceans

western north atlantic evidence for millennial scale changes in ocean circulation and climate two late quaternary series of high resolution percent carbonate data from western north atlantic sediment drifts bermuda rise and bahama outer ridge show millennial scale oscillations superimposed on the familiar longer period oscillations of orbital origin the dominant high frequency oscillation in these records has a quasi period of about 4000 years these percent caco3 changes most likely result from the influence of climate change on the flux of terrigenous material from eastern canada the resuspension of continental margin sediment by deep eddy kinetic energy and carbonate dissolution sediment is transported to the bermuda rise by deep recirculating gyres and to the bahama outer ridge by the deep western boundary current system stable isotope results on foraminifera across several of these oscillations from interstadial climate conditions and from a glacial inception display variability similar to that of percent caco3 oxygen isotope ratios of planktonic foraminifera suggest large variations in near surface temperature and or salinity and carbon isotope ratios of benthic foraminifera indicate that there were significant oscillations in the flux of north atlantic deep water nadw these data support models which couple surface ocean conditions in the north atlantic production of nadw north atlantic heat flux and evidence for temperature oscillations in ice cores

atypical δ 15 n variations at the southern boundary of the east pacific oxygen minimum zone over the last 50 ka abstract we report a nitrogen isotope record odp site 1233 from the southern chile margin at 41 s the site is located slightly south of the southern boundary of the peru chile upwelling system and the associated oxygen minimum zone off peru and northern chile we show that our nitrogen isotope record from the time interval 0 50 calendar kiloyears before present ka b p bears an atypical pattern both in shape and timing when compared with records obtained from either the continental margin of the eastern pacific or the subantarctic zone saz of the southern ocean the 15 n values at site 1233 are relatively high throughout the record varying between 9 and 13 the major features are a pronounced 15 n increase at the beginning of the deglaciation a maximum from 19 to 10 ka b p thereafter a large decrease during the early holocene and millenial scale oscillations showing an antarctic timing we propose that the record results from an amalgam of low latitude and high latitude processes low latitude processes including a stronger advection signal of heavy nitrates from the denitrifying zones off peru and northern chile would explain the timing of the deglaciation rise and the heaviest values found over this interval excluding the antarctic cold reversal period the overall differences between site 1233 and records from peru and northwest american margins suggest however that the origin of the 15 n signal off chile is largely controlled by hydrologic and climatic changes in the southern ocean we propose that the interplay between nutrient demand in the saz and latitudinal shifts of hydrologic fronts controlled both the concentrations and the isotopic signature of the remaining nitrate delivered to the chile margin then the glacial surface waters of the southern chile margin were likely lower in nitrate concentration and bear a higher 15 n than during interglacial periods

comparison of oxygen isotope records from the gisp2 and grip greenland ice cores recent results1 2 from the greenland ice core project grip summit ice core suggest that the climate in greenland has been remarkably stable during the holocene but was extremely unstable for the time period represented by the rest of the core spanning the last two glaciations and the intervening eemian inter glacial here we present the complete oxygen isotope record for the greenland ice sheet project 2 gisp2 core drilled 28 km west of the grip core we observe large rapid climate fluctuations throughout the last glacial period which closely match those reported for the grip core however in the bottom 10 of the cores spanning the eemian interglacial and the previous glacia tion there are significant differences between the two records it is possible that ice flow may have altered the chronological sequences of the stratigraphy for the bottom part of one or both of the cores considerable further work will be necessary to evaluate the likelihood of this and the extent to which it will still be possible to extract meaningful climate information from the lowest sections of the cores

brief interstadial events in the santa barbara basin ne pacific during the past 60 kyr the instability of the northern hemisphere glacial climate over the past 100 kyr has been revealed by at least 20 brief warm interstadial episodes called dansgaard oeschger events recorded in greenland ice cores1 3 and in north atlantic sedimentary records4 5 a few of these events have been recognized elsewhere6 8 here we describe a record of ocean oxygenation and circulation from the santa barbara basin in the northeast pacific ocean which correlates well with the greenland ice core records we see 19 of the 20 dansgaard oeschger events in the form of laminated sediments deposited under anoxic conditions and we can correlate at least 16 of these with the 17 ice core interstadials of the past 60 kyr thus these short term events were not restricted to the north atlantic region the events had substantial ecological and oceanographic effects in the santa barbara basin including changes in benthic faunal populations and in the age and composition of bottom waters similar ventilation changes have been seen in the gulf of california9 10 suggesting that these changes may have been widespread and synchronous along the northeast pacific margin these results suggest sensitivity of broad areas of the ocean atmosphere cryosphere system to short term climate change

suborbital timescale variability of north atlantic deep water during the past 200 000 years we generated 200 kyr long proxy records of surface and deepwater variability from a subpolar north atlantic core v29 202 enabling us to assess the linkage between surface and deepwater changes on suborbital timescales in particular we used a benthic 13c record to evaluate the deep water response to dansgaard oeschger temperature oscillations and to heinrich events times of massive iceberg delivery to the north atlantic we found that the reduction of north atlantic deep water nadw production was generally associated with cold or dropping sea surface temperatures ssts as indicated by planktonic foraminiferal assemblages the nadw contribution to the site did not drop appreciably during heinrich events h4 through h2 probably because these events followed intervals of prolonged surface cooling already characterized by low rates of nadw production by contrast nadw reduction appears to have been synchronous with h5 sst rise associated with both dansgaard oeschger oscillations and heinrich events was usually accompanied by increasing nadw strength in a few cases the nadw recovery appeared to lag the sst rise however the apparent delay is most likely an artefact of the sedimentary record low concentrations of benthic foraminifera as a result of low benthic foraminiferal abundances during stage 6 the stage 6 benthic foraminiferal 13c record is of lower resolution than the younger part of the record the stage 6 proxy records for surface hydrography nevertheless reveal millennial scale oscillations similar to those seen in stage 3 the available 13c data suggest that nadw weakened in association with the cold portions of stage 6 sst oscillations we also sought to confirm a recent study which concluded that there was little nadw variability during the peak of the last interglaciation marine oxygen isotope substage 5e eemian isotope stage 5 was marked by a trend of increasing benthic 13c in v29 202 rising 13c through isotope stage 5 is also seen in tropical surface water records and at some deep atlantic sites and may reflect the common derivation of these water masses variations of 0 5 superimposed on this rising 13c trend within substage 5e in v29 202 are so far not evident in tropical feed waters and may therefore indicate that nadw production was weaker during the late than mid eemian an electronic supplement of this material may be obtained on a diskette or anonymous ftp from kosmos agu org login to agu s ftp account using anonymous as the username and guest as the password go to the right directory by typing cd apend type ls to see what files are available type get and the name of the file to get it finally type quit to leave the system paper 95pa02089 suborbital timescale variability of north atlantic deep water during the past 200 000 years by d w oppo and s j lehman diskette may be ordered from american geophysical union 2000 florida avenue n w washington dc 20009 15 00 payment must accompany order

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

the sequence of events surrounding termination ii and their implications for the cause of glacial interglacial co2 changes events surrounding termination ii as preserved in the vostok ice core provide a number of clues about the mechanisms controlling glacial to interglacial climate change antarctic temperature and the atmosphere s co2 content increased together over a period of 8000 years this increase is bounded by a drop in dust flux at its onset and by a drop in the 18o of trapped air at its finish a similar lag between dust flux and foraminiferal 18o is seen in a southern ocean marine record suggesting that the 18o in air trapped in vostok ice is a valid proxy for ice volume the synchronous change of atmospheric co2 and southern hemisphere temperature thus preceded the melting of the northern hemisphere ice sheets this observation coupled with the fact that nutrient reorganization in the north atlantic occurs with or after the sea level rise eliminates many scenarios proposed to explain the co2 rise including those which rely on sea level change conveyor related nutrient redistribution or north atlantic cooling southern ocean scenarios become the front runners but the most popular mechanism iron fertilization has two problems in explaining the co2 rise before termination ii first much of the dust demise occurs prior to the change in co2 so if iron is the villain a threshold value of its supply must be called upon above which productivity does not continue to increase second the co2 rise continues for some 4 5 kyr after the dust flux has fallen to close to zero these problems may be solved if the increased iron supply in dust caused higher rates of nitrogen fixation during the glacial periods in this case the residence time of oceanic nitrate of a few thousand years would enable decreasing productivity to be a global rather than a local phenomenon and would explain the slow rampup of atmospheric co2

glacial to interglacial fluctuations in productivity in the equatorial pacific as indicated by marine barite an empirical correlation between marine barite baso4 accumulation rate in core top sediment samples from two equatorial pacific transects at 140 w and 110 w and the estimated primary productivity of the overlying water column were used to evaluate glacial to interglacial changes in productivity fluctuations in barite accumulation rates down core indicate that during glacial periods of the past 450 000 years the productivity in the central and eastern equatorial pacific was about two times that during intervening interglacial periods this result is consistent with other evidence that productivity was high in the eastern and central equatorial pacific during the last glacial

the response of benthic foraminifera to productivity cycles in the eastern equatorial pacific faunal and geochemical constraints on glacial bottom water oxygen levels the stage 2 glacial maximum in eastern equatorial pacific ocean sediments is characterized by a pronounced increase in the organic carbon content which has been attributed either to increased upwelling and higher production along the equatorial divergence during the last glacial period or to enhanced preservation as a consequence of a lower concentration of dissolved o2 in glacial bottom water several lines of evidence are presented based on data from two gravity cores collected from the central panama basin which support the former interpretation first both the abundance and the size of benthic foraminifera of the genus uvigerina increase in stage 2 coincident with the increase in organic carbon concentration most probably because of the greater availability of organic detritus during the glacial period the increase in foraminiferal size and associated greater requirement of oxygen for respiration argues against the probability that oxygen was substantially depleted in the upper centimeter where uvigerina spp are thought to live second the number of meiofaunal faecal pellets increases markedly during the stage 2 maximum indicating a more populous and active infauna which again argues against oxygen depletion third there is no significant decrease in the iodine organic carbon i corg ratio in the stage 2 sediments because iodine is depleted relative to carbon in anoxic basins but enriched in association with organic matter in oxic environments the absence of a depletion in the i corg ratio in stage 2 is evidence that bottom water remained oxygen replete during the last glacial fourth molybdenum is not enriched in sediments deposited in stage 2 the presence of anoxic or dysaerobic bottom water or shallow pore waters during that time would have been recorded by the addition of mo to the sediments via coprecipitation with authigenic iron sulphides the combined faunal and geochemical data are consistent with the notion that panama basin deep waters remained oxygen replete during the last glacial maximum it is concluded that the late stage 2 carbon enrichment in the eastern equatorial pacific more probably reflects higher productivity rather than enhanced preservation

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

deconstructing the last glacial termination the role of millennial and orbital scale forcings using an earth system model of intermediate complexity forced by continuously varying boundary conditions and a hypothetical profile of freshwater forcing the model simulates heinrich event 1 h1 the bolling warm period the older dryas the antarctic cold reversal acr and the younger dryas in close agreement with paleo proxy data from different regions worldwide the acr can be simulated as the bipolar seesaw response to the amoc recovery during the termination of h1 however this study also demonstrates that the amplitude of the acr can be further amplified by a rapid deglacial retreat of the antarctic ice sheets we suggest that melting from both the laurentide and the antarctic ice sheets contributed to the sea level rise associated with meltwater pulse 1 a mwp 1a it is hypothesized that the northern hemispheric source of mwp 1a caused the older dryas cooling in the northern hemisphere whereas the southern hemispheric source contributed to the acr the study also documents that for the majority of paleo climate proxies considered here the relative timing can be qualitatively reproduced by the transient modeling experiments the climate model solution presented here may provide a means to further constrain dating uncertainties of some of paleo climate proxies during the last glacial termination

silica depletion of the thermocline in the eastern north pacific during glacial conditions clues from ocean drilling program site 893 santa barbara basin california sedimentation of opaline skeletons diatoms radiolarians is greatly reduced during the last glacial period in the santa barbara basin compared with the holocene the overall pattern is similar to that of the accumulation of organic matter but differs in detail apparently both silicate and phosphate supply are reduced during glacial time within the basin which derives its surface waters and thermocline waters from the california current the pattern of reduced glacial diatom productivity suggests a decrease in the estuarine aspects of the subarctic north pacific as a result of decrease in excess precipitation which dominates the present situation variability is greater in silicate accumulation than in organic matter accumulation we hypothesize that this difference is due to greater sensitivity of silicate to changes in nutrient enrichment and depletion in subsurface waters as compared with phosphate

evidence from chlorin nitrogen isotopes for alternating nutrient regimes in the eastern mediterranean sea abstract nitrogen isotopes of chlorins degradation products of chlorophyll reflect the isotopic composition of nutrient n utilized by marine phytoplankton communities here we show that in sediments of the eastern mediterranean pleistocene and holocene values of 15n for chlorins and total nitrogen vary in concert with a consistent offset of 5 reflecting the fractionation imparted during chlorophyll biosynthesis samples from the integrated ocean drilling program sites 964 and 969 were analyzed at a sampling resolution of 4 10 cm clustered around sapropel events 2 3 4 and 5 100 170 ka in low organic content sediments chlorin values of 0 coincident with total nitrogen values of 5 indicate that the latter reflects the original biomass and is not a consequence of diagenetic isotope enrichment in sapropel horizons the chlorin and total nitrogen values are 5 more negative 5 and 0 respectively resembling previously reported modern day water column particulates 0 we suggest that nutrient conditions in the eastern mediterranean correspond to three scenarios and that the similarity between sapropel and modern day bulk 15n is coincidental organic poor marl sediments formed under oligotrophic conditions where surface productivity resulted from upwelling of atlantic sourced nitrate sapropels were characterized by enhanced diazotrophy that was likely fueled by increased riverine p fluxes to surface waters present day conditions are dominated by anthropogenic n sources these scenarios agree with a model of sapropel formation in which stratification caused by increased fresh water inputs led to n fixation due to p n nutrient imbalance enhanced production combined with stratification promoted and maintained anoxic deep waters consequently increasing organic matter preservation such a model may be relevant to interpreting other episodes of intense organic matter deposition in past oceans

interpretation of the nitrogen isotopic composition of precambrian sedimentary rocks assumptions and perspectives nitrogen isotope compositions in sedimentary rocks d 15 n sed are routinely used for reconstructing cenozoic n biogeochemical cycling and are also being increasingly applied to understanding the evolution of ancient environments here we review the existing knowledge and rationale behind the use of d 15 n sed as a proxy for the precambrian n biogeochemical cycle with the aims of i identifying the major uncertainties that affect analyses and interpretation of nitrogen isotopes in ancient sedimentary rocks ii developing a framework for interpreting the precambrian d 15 n sed record iii testing this framework against a database of precambrian d 15 n sed values compiled from the literature and iv identifying avenues of focused research that should increase confidence in interpreting precambrian d 15 n sed data this review highlights the intrinsic complexity of the d 15 n sed proxy and the significant effort that remains to realize its potential specifically it is crucial to gain a better understanding of how and when diagenesis and metamorphism affect the d 15 n of bulk and kerogen bound nitrogen ultimately more data are required to apply statistics to interpreting d 15 n sed variability within given geological time intervals finally numerical modeling of the d 15 n sed variability expected in different environments under varying redox scenarios is necessary to establish a predictive template for interpreting the ancient nitrogen isotope record in spite of the challenges facing the application of this proxy to the precambrian the existing d 15 n sed record shows several features possibly related to the stepwise oxygenation of the surface environment underlining the potential for nitrogen isotopes to reveal clues about the evolution of early earth

timing of late quaternary productivity pulses in the panama basin and implications for atmospheric co2 high resolution percent corg and 18oforam records obtained from panama basin core atlantis ii 54 25pc and additional data from nearby core p7 show that enhanced burial of organic carbon has characterized every major glacial period for the last 500 kyr in that area both corg concentration and mass accumulation rate profiles exhibit a sawtooth pattern with maxima occurring typically in the later stages of glacial periods comparison with dust records suggests that the carbon accumulation rate profile reflects both the upwelling history and a variable rate of iron input during the late quaternary the sawtooth character may derive from increased wind velocities and rates of upwelling during glacials which are indirectly related to ice volume sarnthein et al 1988 the rapid decline in export production at the end of glacials in the equatorial pacific may be attributed to the retreat of ice sheets thus reduced wind velocities and upwelling coupled with a coincident decline in atmospheric dust load and or delivery rate the corg accumulation rate profiles do not correlate well with atmospheric co2 records for example atmospheric co2 was already at a minimum 40 kyr ago when production in the panama basin began increasing dramatically commensurate with an increase in global dust levels using the relationship between the degree of photosynthetic fractionation and the concentration of free co2 in the surface ocean postulated by popp et al 1989 13corg measurements made on core p7 show that panama basin surface waters have been supplying co2 to the atmosphere continually for at least the last 50 kyr there is no evidence for a flux of co2 into the surface ocean in this area at any time during this period despite the higher production if the panama basin cores are representative of the eastern and central equatorial pacific then these observations weaken the influence on co2 drawdown postulated for increased glacial productivity at low latitudes

nitrate reduction sulfate reduction and sedimentary iron isotope evolution during the cenomanian turonian oceanic anoxic event onset of the oae in italy have unusually low bulk d 57 fe values unlike those found in the black shale livello bonarelli deposited during the oceanic anoxic event itself these latter conform to the phanerozoic norm for organic rich sediments pyrite formation in the pre oae black shales has apparently taken place via dissimilatory iron reduction dir within the sediment a suboxic process that causes an approximately 2 fractionation between a lithogenic fe iii oxide source and fe ii aq in contrast bacterial sulfate reduction bsr at least partly in the water column characterized the oae itself and was accompanied by only minor iron isotope fractionation this change in the manner of pyrite formation is reflected in a decrease in the average pyrite framboid diameter from 10 to 7 mm the gradual albeit irregular increase in fe isotope values during the oae as recorded in the italian section is taken to demonstrate limited isotopic evolution of the dissolved iron pool consequent upon ongoing water column precipitation of pyrite under euxinic conditions given that evidence exists for both nitrate and sulfate reduction during the oae it is evident that redox conditions in the water column were highly variable in both time and space

ventilation changes in the northeast pacific during the last deglaciation under present climate conditions convection at high latitudes of the north pacific is restricted to shallower depths than in the north atlantic to what extent this asymmetry between the two ocean basins was maintained over the past 20 kyr is poorly known because there are few unambiguous proxy records of ventilation from the north pacific we present new data for two sediment cores from the california margin at 800 and 1600 m depth to argue that the depth of ventilation shifted repeatedly in the northeast pacific over the course of deglaciation the evidence includes benthic foraminiferal cd ca 18o 16o and 13c 12c data as well as radiocarbon age differences between benthic and planktonic foraminifera a number of features in the shallower of the two cores including an interval of laminated sediments are consistent with changes in ventilation over the past 20 kyr suggested by alternations between laminated and bioturbated sediments in the santa barbara basin and the gulf of california keigwin and jones 1990 kennett and ingram 1995 behl and kennett 1996 data from the deeper of the two california margin cores suggest that during times of reduced ventilation at 800 m ventilation was enhanced at 1600 m depth and vice versa this pronounced depth dependence of ventilation needs to be taken into account when exploring potential teleconnections between the north pacific and the north atlantic

oxygen minimum zone biotic baseline transects for paleoceanographic reconstructions in santa barbara basin ca abstract we describe modern ocean floor biological trends employing exploratory remotely operated vehicle rov hercules dives in the santa barbara basin california usa through the nautilus exploration program using rov videos in situ measurements and sediment cores we described oxygenation temperature biological zonation and bulk sediment 15n across three 120 meter vertical transects from 380 to 500 m m that cross the depth of the ventilating sill 475 m and upper omz boundary these observations revealed major changes in the distribution of biota tied largely to changes in dissolved oxygen concentration upward increases in oxygen and temperature were coincident with successive disappearance and appearance of megafauna and foraminifera species and overall increases in community diversity the most significant and abrupt change in seawater measurements biological communities sediment textures and nitrogen isotopes were observed near the depth of the ventilating sill from 480 to 450 m microbial mats were observed up to the depth of 475 m dense populations of alia permodesta were identified at depths where dissolved oxygen o2 was

cu isotope systematics of conduit type cu pge mineralization in the eastern gabbro coldwell complex canada chalcopyrite from the cu pge sulfide deposits in the eastern gabbro coldwell complex canada exhibit a 2 variation in 65cu in the marathon deposit the 65cu of chalcopyrite increases from the lower footwall zone 1 49 to 0 75 to the main zone 1 04 to 0 08 to the upper w horizon 0 35 to 1 07 in the northern deposits chalcopyrite at four dams and sally have 65cu that range from 0 08 to 0 47 and 0 59 to 0 05 respectively notably samples from the marathon deposit with lower chalcopyrite 65cu values tend to have higher s se and cu pd ratios integrated geological and geochemical evidence suggests that secondary hydrothermal alteration and redox processes are unlikely to have been the primary causes of the observed cu isotope variation numerical modeling of 65cu cu pd s se of mineralization in the eastern gabbro illustrates three key aspects of cu isotope behavior in magmatic ni cu pge systems first r factors less than 10 000 can exhibit significant control on the 65cu of sulfides second sulfide liquid silicate melt fractionation factors for cu 65cusul sil greater than 0 5 are applicable to ni cu pge systems third sulfide segregation exhibits no measurable control on the 65cu of sulfides at degrees of fractionation typical of ni cu pge systems 0 3 in the marathon deposit the range of 65cu s se cu pd is attributed to the addition of archean sedimentary cu to a pool of sulfide liquid located at depth followed by progressive dilution of the contaminated 65cu s se signature and decrease in cu pd ratio by influxes of uncontaminated pulses of magma i e increasing r factor some of which had cu isotope compositions heavier than the mantle variably contaminated and enriched with respect to pd sulfides from this pool were entrained by magma pulses and emplaced to form the marathon deposit this contribution demonstrates that cu isotopes can fractionate at high temperatures and when combined with other geochemical proxies can be valuable in characterizing magmatic post magmatic processes in ni cu pge sulfide deposits and for identifying pge rich sulfide deposits

nitrogen isotope variations in santa barbara basin sediments implications for denitrification in the eastern tropical north pacific during the last 50 000 years nitrogen isotope variations preserved in santa barbara basin sediments are used to evaluate changes in denitrification in the eastern tropical north pacific etnp during the last 50 000 years a significant component of the subsurface waters 100 400 m that presently fill the santa barbara basin is derived from the low oxygen denitrifying zone in the etnp and the nitrate in these waters has a 15n value of 8 9 during the last glacial the 15n values of santa barbara basin sediments were typically 6 7 indicating decreased denitrification in the etnp and a better oxygenated intermediate water mass in the santa barbara basin at this time this reduced denitrification during the last glacial would have increased the pool of fixed nitrogen and may have contributed to the higher productivity previously reported for various regions of the global ocean during this period at the onset of deglaciation sediment 15n values increase by more than 2 indicating increased denitrification in the etnp during younger dryas time 15n values decreased by 3 and record a brief return to better ventilated conditions in the subsurface waters of the etnp this is followed by an increase in 15n to over 9 at 10 000 years ago indicating intense denitrification at the beginning of the holocene

sources of fine sized organic matter in north atlantic heinrich layers δ13c and δ15n tracers organic carbon oc and total nitrogen tn concentrations and stable isotope ratios d13c d15n of fine 50 m size fractions of deep sea sediments from the central north atlantic were employed to identify changes in sources of organic matter over the past 50 ka bp ambient glacial sediments are characterised by values that reflect mixtures of marine and terrestrial inputs averages 1s oc tn 7 6 0 8 d13c 22 8 1 0 d15n 5 5 0 6 d13c oc and tn concentrations shift to higher values during the holocene indicating a gradual decrease of fine terrigenous supply to the north atlantic the unchanged d15n record between last glacial and holocene stages indicates that the central north atlantic region remained oligotrophic at least during the past 50 ka bp but additional studies are required to support this result in terms of nitrogen oceanic budget during the phases of enhanced ice rafted detrital supply corresponding to prominent heinrich events hl1 hl2 hl4 and hl5 fine sized sedimentary organic matter has lower oc and tn concentrations contrasting sharply with those of ambient glacial sediments lower d13c down to 28 and d15n down to 1 6 values and high oc tn ratios up to 14 7 1 1 are found for hl1 hl2 and with lesser extent for hl4 these values reflect enhanced detrital supply originating from poorly differentiated soil horizons that characterise periglacial climate conditions and from organic matter bearing rock sources of the underlying geological basement during hl5 only the d13c offset records the input of fine size ice rafted organic matter gradually changing soil development conditions during the time interval covering hl5 to hl1 marine isotope stages 5 to 2 as well as varying erosion levels have been hypothesized on the basis of constant d13c increasing oc tn and decreasing d15n values

plio pleistocene denitrification in the eastern tropical north pacific intensification at 2 1 ma 1 global climate has changed substantially over the past 4 million years ma toward on average colder conditions and higher amplitude oscillation between glacial and interglacial periods corresponding changes in marine biogeochemistry could have linked oceanic circulation changes to the global carbon cycle but remain poorly understood we report a high resolution 4 ma long 15n record from ocean drilling program site 1012 on the california margin which monitors denitrification intensity in one of the principal oxygen minimum zones omzs of the open ocean the 15n record demonstrates that eastern tropical north pacific etnp denitrification was weak for much of the late pliocene though there was no apparent change associated with northern hemisphere glaciation nhg at 2 7 ma denitrification strengthened substantially by 2 in 15n at 2 1 ma since 2 1 ma intense denitrification in the etnp occurred during interglacial periods and was generally very climate sensitive we infer that two oceanic changes the shoaling of the thermocline in the eastern pacific and thus the strengthened walker circulation and the development of a modern like frontal system in high latitude southern ocean around 2 1 ma provided favorable conditions for intensification of etnp denitrification that was also likely mirrored south of the equator intermediate water circulation changes likely created the poorly ventilated zones susceptible to the suboxic condition required by denitrification 2 1 ma thus marks a critical point for the reorganization of the ocean s nitrogen cycle in which open ocean denitrification became a significant loss term during interglacial phases of climate given linkage between the ocean s n and c cycle etnp denitrification changes probably contributed to plio pleistocene climatic changes

nitrogen isotope and chlorin paleoproductivity records from the northern south china sea remote vs local forcing of millennial and orbital scale variability abstract variations in nitrogen isotopic composition 15n and total chlorin accumulation rate ar are employed as proxies to reconstruct oceanic nitrate inventory the balance between denitrification and n fixation and paleoproductivity in a rapidly accumulating sediment drift deposit beneath the western pacific warm pool for the last 145 kyr subsurface and deep waters of the northern south china sea scs are sourced from the shallow kuroshio current kc and pacific intermediate water respectively their relative importance in determining sedimentary 15n and paleoproductivity have been altered by changes in equatorial circulation summer and winter monsoon intensity and relative sea level the location and basin configuration of the marginal scs renders it especially sensitive to such changes assuming complete annual nitrate utilization low 15n values during glacial stages are interpreted as a reflection of reduced remote denitrification in the eastern tropical north pacific etnp source waters while much of marine isotope stage mis 3 and the last interglacial were characterized by high denitrification however intervals of anomalously low 15n values are interpreted as reflecting the contribution from regional n fixation in west pacific surface waters transmitted to the site by the shallow kc unusually the holocene is characterized by declining 15n values and an inverse correlation with organic matter content since ca 8 2 ka millennial scale variations during mis 3 indicate higher frequency variations in both etnp denitrification and local n fixation which may be coherent with a hemispheric response to dansgaard oeschger events recorded at high latitudes for much of the last 145 kyr paleoproductivity was decoupled from 15n and instead seems to reflect the extent of the global nitrate inventory stimulated by elevated dust fertilization and regional mixed layer deepening associated with the relative intensity of the se asian winter monsoon despite evaluation of possible conflicting influences on the record of each proxy we interpret our data as clear evidence of glacial interglacial changes in marine nutrient inventory across the whole of the north pacific with a corresponding biogeochemical response and important implications for global co2 drawdown via an invigorated biological pump the relative importance of local regional and global contributions to our records appears to be strongly modulated by relative sea level controlling trans and extra basinal circulation in the scs

expansion of the southern california oxygen minimum zone during the early to mid holocene due to reduced ventilation of the northeast pacific abstract oceanic deoxygenation observed since the 1950s has drawn increasing concern as dissolved oxygen do regulates marine biodiversity and biogeochemical cycles yet the do time series from direct instrumental measurements is insufficiently long several decades to constrain the centennial to millennial variability here we present redox sensitive metal re u and mo records from santa barbara basin sbb california to reconstruct subsurface do through the holocene significantly higher authigenic metal fluxes and coherent benthic foraminifera faunal responses along a published depth transect reveal vertical expansion and intensification of the southern california oxygen minimum zone omz prior to 6 ka comparison with post industrial trace metal records suggests low oxygen conditions were more extreme during early to mid holocene mh highlighting the magnitude of omz variability in the absence of anthropogenic influences inconsistencies between authigenic metal fluxes and local oxygen control indicate a remote weakening of the north pacific intermediate water npiw formation prior to the mh reduced ventilation of the mid depth north pacific is supported by state of the art earth system model simulations with realistic mh 6 ka forcing highlighting the importance of brine rejection during sea ice formation in changing the buoyancy of npiw and its basin wide influences on north pacific omz evidence from holocene marine lake records and model simulations further suggests a southward intertropical convergence zone itcz migration and a consequent deepening of the aleutian low al towards late holocene which favors more sea ice brine rejection thus mid depth ventilation in the north pacific was closely associated with atmospheric circulation during the holocene

biotic response to late quaternary rapid climate switches in santa barbara basin ecological and evolutionary implications benthic foraminiferal assemblages from santa barbara basin exhibit major faunal and ecological switches associated with late quaternary millennial to decadal scale global climate oscillations repeated turnovers of entire faunas occurred rapidly 40 400 yr without extinction or speciation in conjunction with dansgaard oeschger shifts in thermohaline circulation ventilation and climate confirming evolutionary model predictions of roy et al consistent faunal successions of dysoxic taxa during successive interstadials reflect the extreme sensitivity and adaptation of the benthic ecosystem to the rapid environmental changes that marked the late quaternary and possibly other transitional intervals in the history of the earth s ocean atmosphere cryosphere system these data support the hypothesis that broad segments of the biosphere are well adapted to rapid climate change

glacial interglacial modulation of eastern tropical north pacific denitrification over the last 1 8 myr 1 a 1 8 myr long 15n record from the california margin provides the first continuous record of denitrification in the eastern tropical north pacific etnp over the entire pleistocene epoch comparison of the nitrogen isotopic time series with proxies for ice volume sea surface temperature sst and biological productivity place variations in the intensity of the denitrification zone in the context of global and regional climatic changes throughout the pleistocene etnp denitrification remained linked to glacial interglacial climate cycles the pacing of denitrification cycles switched from 41 kyr in the mid to early pleistocene to 100 kyr in the late pleistocene in tandem with the well known frequency shift identified from ice volume records it therefore appears that denitrification remained an integral component of the marine feedbacks to orbital forcing and through its effect on the nitrate inventory of the ocean might have played a role in driving atmospheric co2 cycles throughout the pleistocene

co variation of nitrogen isotopes and redox states through glacial interglacial cycles in the black sea abstract in all aquatic environments nitrogen cycling within the water column is strongly influenced by oxygen we hypothesize that the nitrogen isotopic composition 15 n of organic matter deposited in the sediments is a proxy for the redox state of the water column at the time of deposition we tested the hypothesis by measuring the bulk sedimentary 15 n values in a drill core from the black sea a basin that alternates between oxic less saline conditions and anoxic marine conditions on glacial interglacial time scales we reconstructed these changes in black sea redox conditions using sedimentary 15 n total organic carbon toc total nitrogen tn redox sensitive metals and micropaleontological data from a deep sea core dsdp site 380 the sedimentary data reveal that during the transitions between oxic and anoxic conditions 15 n values increased relative to the preceding and succeeding quasi steady state oxic and anoxic periods the results indicate that the reciprocal transitional states from anoxic to oxic conditions were accompanied by intense denitrification during the quasi stable oxic and anoxic states characterized by glacial fresh water and interglacial marine conditions nitrification and complete nitrate utilization respectively dominate the nitrogen cycle while other factors may influence the 15 n record our results support the hypothesis that the variations in nitrogen isotopic composition of organic matter are strongly influenced by changes in redox state in the black sea subphotic zone on glacial interglacial time scales and can be explained by a relatively simple model describing the effects of oxygen on the microbial processes that drive the nitrogen cycle in marine ecosystems our model suggests that the nitrogen isotopic composition of marine sediments on geological time scales can be used to reconstruct the redox state of the overlying water column

calibration of the c 14 timescale over the past 30 000 years using mass spectrometric u th ages from barbados corals uranium thorium ages obtained by mass spectrometry from corals raised off the island of barbados confirm the high precision of this technique over at least the past 30 000 years comparison of the u th ages with 14c ages obtained on the holocene samples shows that the u th ages are accurate because they accord with the dendrochronological calibration before 9 000 yr bp the 14c ages are systematically younger than the u th ages with a maximum difference of 3 500 yr at 20 000 yrbp the u th technique thus provides a way of calibrating the radiocarbon timescale beyond the range of dendrochronological calibration

the tice event perturbation of carbon nitrogen cycles during the mid tournaisian early carboniferous greenhouse icehouse transition abstract carbonate carbon 13ccarb and bulk nitrogen 15n isotopic variation during the mid tournaisian was analyzed in the malanbian and long an sections of south china their c isotope profiles document a large positive excursion herein termed the mid tournaisian carbon isotope excursion tice during the siphonodella isosticha conodont zone although its magnitude differed between the two sections 6 at malanbian versus 3 at long an the tice event coincided with sedimentologic and oxygen isotopic evidence of climatic cooling and glaciation during the mid tournaisian it was probably triggered by an increase in organic carbon burial rates linked to changes in global ocean circulation the study sections also document a large positive shift in 15n from 1 7 to 4 2 at malanbian and from 1 5 to 3 8 at long an the n isotope shift shows no termination within the study sections and is likely to mark the onset of an extended interval of 15n enriched marine nitrate that lasted for the duration of the late paleozoic ice age its initiation coincided with tice and thus may have been linked to ocean circulation changes that resulted in intensified upwelling and an increase in water column denitrification the continuation of the n isotope shift over millions of years may have been linked to glacio eustatic fall and a long term shift in the locus of denitrification from continental shelf sediments to continent margin oxygen minimum zones the tice event thus marks the onset of sustained continental glaciation during the late paleozoic ice age

interhemispheric leakage of isotopically heavy nitrate in the eastern tropical pacific during the last glacial period denitrification zone while the nicaragua site is at the southern boundary the d 15 n record from nicaragua shows an antarctic timing similar to denitrification changes observed off peru chile but is radically different from the northern records we attribute this to the leakage of isotopically heavy nitrate from the south pacific oxygen minimum zone omz into the nicaragua basin the nicaragua record leads the other eastern tropical north pacific etnp records by about 1000 years because denitrification peaks in the eastern tropical south pacific etsp before denitrification starts to increase in the northern hemisphere omz i e during warming episodes in antarctica we find that the influence of the heavy nitrate leakage from the etsp is still noticeable although attenuated in the gulf of tehuantepec record particularly at the end of the heinrich events and tends to alter the recording of millennial timescale denitrification changes in the etnp this implies 1 that sedimentary d 15 n records from the southern parts of the etnp cannot be used straightforwardly as a proxy for local denitrification and 2 that denitrification history in the etnp like in the arabian sea is synchronous with greenland temperature changes these observations reinforce the conclusion that on millennial timescales during the last ice age denitrification in the etnp is strongly influenced by climatic variations that originated in the highlatitude north atlantic region while commensurate changes in southern ocean hydrography more directly and slightly earlier affected oxygen concentrations in the etsp furthermore the d 15 n records imply ongoing physical communication across the equator in the shallow subsurface continuously over the last 50 70 ka citation pichevin l e r s ganeshram s francavilla e arellano torres t f pedersen and l beaufort 2010 interhemispheric leakage of isotopically heavy nitrate in the eastern tropical pacific during the last glacial period paleoceanography 25 pa1204 doi 10 1029 2009pa001754

glacial holocene δ15n record from the gulf of tehuantepec mexico implications for denitrification in the eastern equatorial pacific and changes in atmospheric n2o 1 the intensity of denitrification in the gulf of tehuantepec along the mexican margin of the eastern tropical north pacific etnp was reconstructed for the last 23 000 years using the nitrogen isotopic composition of sediment organic matter 15norg in conjunction with other geochemical tracers of water column productivity during the last glacial period 15norg values ranged from 6 5 to 8 6 with values increasing between 23 and 17 ka deglaciation was marked by an abrupt increase in 15norg with maximum values 9 9 occurring during the bolling allerod period and the earliest holocene a decline in 15norg values occurred over the last 10 000 years with late holocene values being similar to those of the glacial period our data suggest that denitrification in this region was minimal during the last glacial and is consistent with the deposition of bioturbated sediments at the study site the intensity of denitrification increased dramatically during deglaciation and the early holocene signaling the presence of a strong oxygen minimum zone this period is also marked by the deposition of laminated sediments in the region the 15norg records display similar temporal trends to those seen in the greenland ice core record of atmospheric n2o concentrations at present denitrification within the eastern tropical pacific and arabian sea accounts for a major portion of the global marine loss of fixed nitrogen and a significant fraction of the ocean atmosphere n2o flux originates from these areas large changes in n2o emissions from these regions in the past would have directly impacted global greenhouse gas concentrations

reply to the comment on monsoon related changes in sea surface productivity and water column denitrification in the eastern arabian sea during the last glacial cycle by v k banakar t oba a r chodankar t kuramoto m yamamoto m minagawa

the acceleration of oceanic denitrification during deglacial warming the marine nitrogen cycle was altered during the transition from glacial to interglacial conditions an analysis of 15n records throughout the world s oceans suggests that rates of denitrification in the water column accelerated during the last deglaciation

evaluation of redox versus thermal maturity controls on δ15n in organic rich shales a case study of the woodford shale anadarko basin oklahoma usa abstract bulk sedimentary nitrogen isotopes 15nbulk have been primarily used to identify bottom water redox states during deposition in sedimentary environments that have not undergone significant diagenetic or catagenetic alteration recently the utility of sedimentary 15nbulk as a paleoredox proxy in hydrocarbon bearing shale intervals was demonstrated by qualitatively correlating the 15nbulk profiles from shale units to their depositional redox conditions however the effect of thermal maturity on the 15nbulk signal remains unknown we analyzed samples from three cores from the devonian mississippian age woodford shale in the anadarko basin with vitrinite reflectance values ranging from the oil window to the gas window in order to investigate how depositional redox conditions and thermal maturation affect the bulk sedimentary 15n signals our results indicate that the 15nbulk values for the woodford do not correlate with thermal maturity instead the 15nbulk values primarily reflect the depositional redox conditions which are supported by trace metal concentrations and depositional features such as burrow abundance and lamination the expected relationship between 15nbulk and paleoredox conditions was observed both within each core and between cores on a basin wide scale with samples deposited under suboxic bottom water conditions having higher 15nbulk values than those deposited under anoxic bottom water conditions our data also indicate that redox bottom water column conditions in the anadarko basin varied spatially and temporally during the deposition of the woodford shale

deglacial nitrogen isotope changes in the gulf of mexico evidence from bulk sedimentary and foraminifera bound nitrogen in orca basin sediments 1 constraining variations in marine n2 fixation over glacial interglacial timescales is crucial for determining the role of the marine nitrogen cycle in modifying ocean productivity and climate yet paleo records from n2 fixation regions are sparse here we present new nitrogen isotope 15n records of bulk sediment and foraminifera test bound fb nitrogen extending back to the last ice age from the oligotrophic gulf of mexico gom previous studies indicate a substantial terrestrial input during the last ice age and early deglacial for which we attempt to correct the bulk sediment 15n using its observed relationship with the c n ratio both corrected bulk and fb 15n reveal a substantial glacial to holocene decrease of 15n toward holocene values of around 2 5 similar to observations from the caribbean this 15n change is most likely due to a glacial to holocene increase in regional n2 fixation a deglacial peak in the fb 15n of thermocline dwelling foraminifera orbulina universa probably reflects a whole ocean increase in the 15n of nitrate during deglaciation the 15n of the surface dwelling foraminifera globigerinoides ruber and the corrected bulk 15n show little sign of this deglacial peak both decreasing from last glacial values much earlier than does the 15n of o universa this may indicate that g ruber and bulk n reflect the euphotic zone signal of an early local increase in n2 fixation our results add to the evidence that during the last ice age the larger iron input from dust did not lead to enhanced n2 fixation in this region rather the glacial to holocene decrease in 15n is best explained by a response of n2 fixation within the atlantic to the deglacial increase in global ocean denitrification

glacial interglacial variability in upwelling and bioproductivity off nw mexico implications for quaternary paleoclimate sedimentary accumulation of biogenic components organic carbon opal and biogenic barium on the northwestern mexican margin declined during every glacial interval of the past 140 kyr indicating decreases in upwelling induced productivity during cold periods the glacial interglacial contrasts in upwelling on this margin are attributed to reversals in land ocean thermal contrast the waxing and waning of the laurentide ice sheet and consequent responses of the western hemisphere wind fields this scenario is consistent with three independent lines of evidence terrestrial paleoclimatic data general circulation model results and our marine records this pattern of glacial interglacial variability in upwelling off nw mexico is opposite to that observed in other low latitude and midlatitude upwelling areas such as the eastern equatorial pacific these results add to a growing pool of observations that the response of oceanic upwelling to glacial climatic forcing has been regionally variable

vostok ice core provides 160 000 year record of atmospheric co2 direct evidence of past atmospheric co2 changes has been extended to the past 160 000 years from the vostok ice core these changes are most notably an inherent phenomenon of change between glacial and interglacial periods besides this major 100 000 year cycle the co2 record seems to exhibit a cyclic change with a period of some 21 000 years

elevated foraminifera bound nitrogen isotopic composition during the last ice age in the south china sea and its global and regional implications 1 we report a new foraminifera bound d 15 n fb d 15 n record from the south china sea scs extending back to 42 ka this record shows a 1 2 glacial to interglacial d 15 n decrease with a deglacial d 15 n maximum similar to that observed in many bulk sedimentary d 15 n records and in a caribbean fb d 15 n record the glacial to interglacial d 15 n decrease is smaller than in the caribbean record indicating that at least half of the caribbean d 15 n decrease into the holocene was regional not global supporting the interpretation of a holocene increase in atlantic nitrogen fixation at the same time the glacial to interglacial d 15 n decrease observed in the scs may also be explained as a regional signal of increasing nitrogen fixation into the holocene other aspects of the scs record suggest an effect of physical circulation on fb d 15 n fb d 15 n starts to increase toward its deglacial maximum before the last ice age ends and it continues to decrease through the later holocene in contrast to the more pure glacial deglacial interglacial steps in the caribbean record these changes have parallels in other pacific d 15 n records precessionally driven east asian monsoon records and the slow holocene warming of scs surface waters in addition the scs record exhibits two one point high d 15 n spikes in multiple foraminiferal species that coincide with apparent hydrographic events thinning or weakening of the thermocline in the late glacial and early holocene as well as during the noted events may have yielded a higher d 15 n for thermocline nitrate and thus a higher fb d 15 n

southern ocean control on the extent of denitrification in the southeast pacific over the last 70 ka abstract temporal changes in oceanic denitrification the bacterial reduction of nitrate under suboxic conditions highlight the potential importance of n inventory changes and the production of n 2 o on the climate system at the same time the cause of the globally observed variation in denitrification remains unclear high resolution benthic foraminiferal oxygen isotope and bulk sediment nitrogen isotope records from odp site 1234 on the chile margin record integrated denitrification changes within the peru chile upwelling system over the last 70 ka denitrification changes in the southeast pacific are coherent with antarctic climate changes recorded by the byrd ice core 18 o record and lead northern hemisphere climate events the southern hemisphere character of the chile margin 15 n record suggests that episodes of reduced denitrification in the se pacific represent times when more oxygen was supplied as the result of changes in the ventilation and preformed nutrient content of subantarctic mode water samw which forms in the subantarctic zone of the southern ocean and feeds into the low latitude thermocline

on the sedimentological origin of down core variations of bulk sedimentary nitrogen isotope ratios 1 the bulk sedimentary nitrogen isotopic composition of two cores from nearby sites on the northern slope of the south china sea site 17940 and ocean drilling program odp site 1144 differs by up to 2 during the last glacial period given their close proximity both core sites are located in the same biogeographic zone and nutrient regime and it is thus unlikely that this offset is due to a true gradient in surface ocean conditions in an attempt to resolve this offset we have investigated the possible effects of two sedimentological parameters that can affect bulk sedimentary 15n namely the variable contribution of inorganic n to bulk n in the sediment and the grain size dependence of bulk 15n we find that neither effect singly or in combination is sufficient to explain the significant 15n offset between the two down core records by elimination the most likely explanation for the observed discrepancy is a different origin of both the organic and inorganic nitrogen at each site this study adds to the growing body of evidence highlighting the complex nature and origin of the sedimentary components in sediment drifts such as odp site 1144

atmospheric nitrous oxide during the last 140 000 years article i nfo reconstructions of past atmospheric concentrations of greenhouse gases provide unique insight into the biogeochemical cycles and the past radiative forcing in the earth s climate system we present new measurements of atmospheric nitrous oxide along the ice cores of the north greenland ice core project and talos dome sites using records of several other ice cores we are now able to establish the first complete composite nitrous oxide record reaching back to the beginning of the previous interglacial about 140 000 yr ago on the basis of such composite ice core records we further calculate the radiative forcing of the three most important greenhouse gases carbon dioxide methane and nitrous oxide during more than a full glacial interglacial cycle nitrous oxide varies in line with climate reaching very low concentrations of about 200 parts per billion by volume during marine isotope stages 4 and 2 and showing substantial responses to millennial time scale climate variations during the last glacial a large part of these millennial time scale variations can be explained by parallel changes in the sources of methane and nitrous oxide however as revealed by high resolution measurements covering the dansgaard oeschger events 17 to 15 the evolution of these two greenhouse gases may be decoupled on the centennial time scale carbon dioxide and methane concentrations do not reach interglacial levels in the course of millennial time scale climate variations during the last glacial in contrast nitrous oxide often reaches interglacial concentrations in response to both glacial terminations and dansgaard oeschger events this indicates from a biogeochemical point of view similar drivers in both temporal cases while carbon dioxide and methane concentrations are more strongly controlled by climate changes in high latitudes nitrous oxide emissions changes may mainly stem from the ocean and or from soils located at low latitudes accordingly we speculate that high latitudes could play the leading role to trigger glacial terminations

tracing river chemistry in space and time dissolved inorganic constituents of the fraser river canada abstract the fraser river basin in southwestern canada bears unique geologic and climatic features which make it an ideal setting for investigating the origins transformations and delivery to the coast of dissolved riverine loads under relatively pristine conditions we present results from sampling campaigns over three years which demonstrate the lithologic and hydrologic controls on fluxes and isotope compositions of major dissolved inorganic runoff constituents dissolved nutrients major and trace elements 87 sr 86 sr d a time series record near the fraser mouth allows us to generate new estimates of discharge weighted concentrations and fluxes and an overall chemical weathering rate of 32 t km 2 y 1 the seasonal variations in dissolved inorganic species are driven by changes in hydrology which vary in timing across the basin the time series record of dissolved 87 sr 86 sr is of particular interest as a consistent shift between higher more radiogenic values during spring and summer and less radiogenic values in fall and winter demonstrates the seasonal variability in source contributions throughout the basin this seasonal shift is also quite large 0 709 0 714 with a discharge weighted annual average of 0 7120 2 s d 0 0003 we present a mixing model which predicts the seasonal evolution of dissolved 87 sr 86 sr based on tributary compositions and water discharge this model highlights the importance of chemical weathering fluxes from the old sedimentary bedrock of headwater drainage regions despite their relatively small contribution to the total water flux

millennial scale climate change and intermediate water circulation in the bering sea from 90 ka a high resolution record from iodp site u1340 1 millennial scale climate events in the north pacific are thought to be related to changes in the circulation of north pacific intermediate water which may have formed in the bering sea in the past to advance our understanding of the mechanisms that underlie millennial scale events bering sea sediment cores from the integrated ocean drilling program site u1340 were used to construct high resolution multiproxy climate records of the last 90 000 years sediment density records show millennial scale events resembling dansgaard oeschger events several of which are laminated interstadials were characterized by 3 5 c warming increased productivity driven by upwelling and reduced benthic oxygenation bering sea intermediate water also changed over longer timescales our records show the presence of intermediate water with lower salinity and higher oxygen content than modern beginning around 60 ka and persisting until the beginning of the deglaciation the bolling allerod was characterized by high productivity laminated sediments and strong denitrification signature our data support the idea that productivity derived changes in oxygenation at intermediate water source regions may have contributed to the intensification of the north pacific wide oxygen minima during the bolling allerod

co 2 record in the byrd ice core 50 000 5 000 years bp the analysis of air in polar ice cores revealed 30 lower co2 values during glacial periods than during interglacial periods at present this is confirmed by results from six different ice cores two from greenland and four from antarctica1 5 in all cores the co2 change coincides with the change in the isotopic composition of the ice expressed as either the 18o or d ratio both are indicators for the mean annual surface temperature6 to investigate the relationship between atmospheric co2 concentration changes with changes in climate the atmospheric co2 concentration during and at the end of the last glaciation has to be known in detail to achieve this we have studied a great number of samples from the deep ice core from byrd station westantarctica drilled in 1968 these measurements allow us to reconstruct the atmospheric co02 concentration in the time period 50 000 15 000 yr bp in great detail

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

surface nitrate utilization in the bering sea since 180 ka bp insight from sedimentary nitrogen isotopes we present high resolution records of sedimentary nitrogen 15nbulk and carbon isotope ratios 13cbulk from piston core so201 2 85kl located in the western bering sea the records reflect changes in surface nitrate utilization and terrestrial organic matter contribution in submillennial resolution that span the last 180 kyr the 15nbulk record is characterized by a minimum during the penultimate interglacial indicating low nitrate utilization 62 80 despite the relatively high export production inferred from opal concentrations along with a significant reduction in the terrestrial organic matter fraction mterr this suggests that the consumption of the nitrate pool at our site was incomplete and even more reduced than today 84 15nbulk increases from marine isotope stage mis 5 4 and culminates during the last glacial maximum which indicates that nitrate utilization in the bering sea was raised during cold intervals mis 5 4 5 2 4 and almost complete during mis 3 and 2 93 100 this is in agreement with previous hypotheses suggesting that stronger glacial stratification reduced the nutrient supply from the subeuphotic zone thereby increasing the iron to nutrient ratio and therefore the nitrate utilization in the mixed surface layer large variations in 15nbulk were also recorded from 180 to 130 ka bp mis 6 indicating a potential link to insolation and sea level forcing and its related feedbacks millennial scale oscillations were observed in 15nbulk and 13cbulk that might be related to greenland interstadials

quaternary shelf sea palaeoceanography recent developments in europe abstract high quality palaeoceanographic reconstructions based on sequences preserved in shallow marine environments demonstrate that these constitute significant archives of climatic and oceanographic change such sequences are important first because their often very high resolution sometimes laminated nature enables high frequency cycles to be resolved and provides the basis for establishing spatial and temporal variability in the marine radiocarbon reservoir effect second sea level index points from shelves are important for the validation of glacio hydro isostatic geophysical models and for understanding sea level change during early deglaciation third shallow marine sequences contain excellent records of land ocean interaction often preserving paired terrestrial marine proxies in the same stratigraphic sequence a new development in shelf sea palaeoceanography is documenting the long term dynamics of shelf sea stratification this is the dominant hydrodynamic phenomenon of tide dominated shelf seas in the middle and high latitudes and has a profound influence on productivity and therefore global change through the carbon cycle detailing the evolution of seasonal stratification during eustatic highstands is therefore of relevance to the climate system

sediment fluxes and varve formation in santa barbara basin offshore california results from a year long sediment trap study provide the first direct observations of seasonal variability in sediment fluxes to the sea floor in santa barbara basin offshore california and are used to evaluate varve formation in this basin sediment fluxes throughout the year are dominated by lithogenic material biogenic sediments primarily silica are of secondary importance we conclude that the combination of high lithogenic fluxes and low biogenic fluxes during the fall winter period results in the deposition of dark laminae the onset of upwelling and high surface productivity in the spring results in high biogenic silica fluxes that last into the summer the relative contribution of silica to the total sediment flux is highest during this spring summer period and we suggest that light laminae are formed at that time this is consistent with previous suggestions that sediment input is the primary factor controlling varve formation in this basin

preservation of organic matter and alteration of its carbon and nitrogen isotope composition during simulated and in situ early sedimentary diagenesis abstract the carbon and nitrogen isotope composition of organic matter has been widely used to trace biogeochemical processes in marine and lacustrine environments in order to reconstruct past environmental changes from sedimentary organic matter it is crucial to consider potential alteration of the primary isotopic signal by bacterial degradation in the water column and during early diagenesis in the sediments in a series of oxic and anoxic incubation experiments we examined the fate of organic matter and the alteration of its carbon and nitrogen isotopic composition during microbial degradation the decomposition rates determined with a double exponential decay model show that the more reactive fraction of organic matter degrades at similar rates under oxic and anoxic conditions however under oxic conditions the proportion of organic matter resistent to degradation is much lower than under anoxic conditions within three months of incubation the 13c of bulk organic matter decreased by 1 6 with respect to the initial value the depletion can be attributed to the selective preservation of 13c depleted organic compounds during anoxic decay the 15n values continuously decreased to about 3 below the initial value the decrease probably results from bacterial growth adding 15n depleted biomass to the residual material in the oxic experiment 15n values increased by more then 3 before decreasing to a value indistinguishable from the initial isotopic composition the dissimilarity between oxic and anoxic conditions may be attributed to differences in the type timing and degree of microbial activity and preferential degradation in agreement with the anoxic incubation experiments sediments from eutrophic lake lugano are on average depleted in 13c 1 5 and 15n 1 2 with respect to sinking particulate organic matter collected during a long term sediment trap study

nitrogen cycling in the sediments of santa barbara basin and eastern subtropical north pacific nitrogen isotopes diagenesis and possible chemosymbiosis between two lithotrophs thioploca and anammox riding on a glider abstract this article presents data on the isotopic composition of pore water ammonium and n org in the anoxic sediments of the santa barbara basin and the eastern subtropical north pacific esnp region ammonium 15 n behaves differently in the two regions reflecting variability in bacterial processes of sedimentary nitrogen cycling in santa barbara basin stoichiometry of tco 2 and nh 4 production defined by pore water chemistry indicates that the only reaction influencing pore water ammonium concentration in these sediments appears to be organic matter decomposition pore water ammonium was found to be 1 3 heavier than decomposing organic matter in contrast the upper 15 30 cm of esnp pore waters have ammonium with 15 n that is more than 10 heavier than decomposing organic matter at greater depth the 15 n of deeper pore waters approaches that of decomposing organic matter mass balance calculations indicate that the observed isotopic enrichment is not due to the preferential loss of isotopically enriched organic matter pore water profiles show that the zone with heavy isotopes is characterized by a tco 2 nh 4 inputs ratio of 4 or less we attribute this to the presence of thioploca bacteria who transport no 3 to depth and reduce it to nh 4 while oxidizing sulfide based on pore water stoichiometry and reaction diffusion modeling of pore water isotopic composition we propose that the 15 n enriched ammonium is produced as the result of chemosymbiosis between thioploca and anammox like bacteria in these sediments our work provides the new insights into benthic microbial ecology and the role of coupled individual metabolic pathways in sedimentary nitrogen cycling in santa barbara basin factors which contribute to the isotopic fractionation of 1 3 between pore water ammonium and solid n org were also considered in this sediments 23 of the rain of organic nitrogen is lost to diagenesis therefore the isotopic effect of degradation on the residual n org is estimated to be small 0 7 the most likely cause of fractionation is preferential degradation of an isotopically heavier more labile marine fraction relative to an isotopically lighter more refractory terrestrial component of the organic matter but other possibilities cannot be ruled out when corrected for the observed fractionation it appears that the 15 n of these sediments may represent non steady state conditions

determining the influences of late quaternary ventilation and productivity variations on santa barbara basin sedimentary oxygenation a multi proxy approach abstract a correlation between warm interstadials implied by 18oice in the gisp greenland ice core and anoxic events recorded by the sediments drilled at odp site 893 in santa barbara basin sbb has been used previously to relate variations in bottom water oxygenation to high frequency changes in the ventilation of the sbb nature 379 1996 243 however an additional control on the oxygen content at depth is the local settling flux of metabolizable organic matter to assess the impact of oxygen consumption related to this source mo cd re and u concentration data are used here in conjunction with corg and 15n to deduce past redox conditions variations in the sedimentary redox boundary depth and the impact of local organic flux on the oxygenation of sbb deep waters comparisons between odp sites 893 1017 and 1019 allow the differentiation of regional signals dominated by ventilation changes from local signals dominated by vertical organic flux it is concluded that prior to the holocene local productivity changes in the santa barbara basin are not solely the cause of sedimentary anoxia episodic injections of low oxygen intermediate water identified on the regional scale strongly influenced the oxygen content of the sbb during this time however over the last 10 000 years the influence of local productivity has increased and the regional similarity among the three sites is complicated by local signals

nitrogen isotopic variations in the gulf of california since the last deglaciation response to global climate change high resolution records of the nitrogen isotopic composition of organic matter 15norg opal content and opal accumulation rates from the central gulf of california reveal large and abrupt variations during deglaciation and gradual holocene changes coincident with climatic changes recorded in the north atlantic homogenous sediments with relatively low 15norg values and low opal content were deposited at the end of the last glacial period during the younger dryas event and during the middle to late holocene in contrast laminated sediments deposited in the two deglacial stages are characterized by very high 15norg values 14 and opal accumulation rates 29 41 mg cm 2 yr 1 abrupt shifts in 15norg were driven by widespread changes in the extent of suboxic subsurface waters supporting denitrification and were amplified in the central gulf record due to variations in upwelling vertical mixing and or the latitudinal position of the intertropical convergence zone

a global marine fixed nitrogen isotopic budget implications for holocene nitrogen cycling 1 a nitrogen stable isotopic model was constructed in order to constrain the holocene marine fixed nitrogen budget the primary sources and sinks considered were riverine and atmospheric sources nitrogen fixation sedimentary and water column denitrification and sediment burial the source budget was found to be insensitive to changes in nitrogen fixation rates and thus could not be used to constrain this term however the isotopic value of fixed nitrogen losses was very sensitive to the amount of sedimentary denitrification if the isotopic value of marine fixed nitrogen has not changed during the holocene as supported by sedimentary records then in order to balance the isotopic value of sinks and sources approximately 280 tg n yr 1 of sedimentary denitrification is required if such a high rate of denitrification has been sustained throughout the holocene it implies that present day estimates of marine nitrogen fixation are grossly underestimated it also implies that the marine nitrogen budget has a residence time of less than 2000 years

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