deep water formation in the north pacific and deglacial co2 rise deep water formation in the north atlantic and southern ocean is widely thought to influence deglacial co 2 rise and climate change here we suggest that deep water formation in the north pacific may also play an important role we present paired radiocarbon and boron isotope data from foraminifera from sediment core md02 2489 at 3640 m in the north east pacific these show a pronounced excursion during heinrich stadial 1 with benthic planktic radiocarbon offsets dropping to 350 years accompanied by a decrease in benthic 11 b we suggest that this is driven by the onset of deep convection in the north pacific which mixes young shallow waters to depth old deep waters to the surface and low ph water from intermediate depths into the deep ocean this deep water formation event was likely driven by an increase in surface salinity due to subdued atmospheric monsoonal freshwater flux during heinrich stadial 1 the ability of north pacific deep water npdw formation to explain the excursions seen in our data is demonstrated in a series of experiments with an intermediate complexity earth system model these experiments also show that breakdown of stratification in the north pacific leads to a rapid 30 ppm increase in atmospheric co 2 along with decreases in atmospheric 13 c and 14 c consistent with observations of the early deglaciation our inference of deep water formation is based mainly on results from a single sediment core and our boron isotope data are unavoidably sparse in the key hs1 interval so this hypothesis merits further testing however we note that there is independent support for breakdown of stratification in shallower waters during this period including a minimum in 15 n younging in intermediate water 14 c and regional warming we also re evaluate deglacial changes in north pacific productivity and carbonate preservation in light of our new data and suggest that the regional pulse of export production observed during the bolling allerod is promoted by relatively stratified conditions with increased light availability and a shallow potent nutricline overall our work highlights the potential of npdw formation to play a significant and hitherto unrealized role in deglacial climate change and co 2 rise

old radiocarbon ages in the southwest pacific ocean during the last glacial period and deglaciation marine radiocarbon 14c dates are widely used for dating oceanic events and as tracers of ocean circulation essential components for understanding ocean climate interactions past ocean ventilation rates have been determined by the difference between radiocarbon ages of deep water and surface water reservoirs but the apparent age of surface waters currently approximately 400 years in the tropics and approximately 1 200 years in antarctic waters might not be constant through time as has been assumed in radiocarbon chronologies and palaeoclimate studies here we present independent estimates of surface water and deep water reservoir ages in the new zealand region since the last glacial period using volcanic ejecta tephras deposited in both marine and terrestrial sediments as stratigraphic markers compared to present day values surface reservoir ages from 11 900 14c years ago were twice as large 800 years and during glacial times were five times as large 2 000 years contradicting the assumption of constant surface age furthermore the ages of glacial deep water reservoirs were much older 3 000 5 000 years the increase in surface to deep water age differences in the glacial southern ocean suggests that there was decreased ocean ventilation during this period

climate and upper ocean variability off baja california mexico 1997 2008 abstract temperature and salinity anomalies derived from observations obtained in the period 1997 2008 are used to study the changes in physical properties off the baja california west coast 24 31 n near surface anomalies were used to characterize four periods of distinctive variability 1 a warm and saline phase of el nino 1997 1998 2 a saline period from 1999 to 2002 3 fresh subarctic water in 2002 2006 and 4 a saline fresh el nino la nina phase in late 2006 to early 2008 subsurface 200 m salinity anomalies depicted a trend towards saltier conditions s 0 1 from 2001 onwards and did not show the four periods discernible near surface eof analysis of sea surface wind stress and wind stress curl suggested that after the intense westerly winds in late 2001 freshening during late 2002 2006 was due to the weakening strengthening of the north pacific current aleutian low and to a decrease of wind stress curl produced upwelling data also showed differences in the timing and magnitude of anomalies observed between the north poleward of 28 n and the south equatorward of 28 n subsurface geostrophic currents demonstrated the existence of two large scale cyclonic gyres one associated with a subarctic domain in the northern region and another having tropical characteristics the likely role of subsurface cyclonic pairs in the definition of a provincial boundary and the importance in influencing the ccs ecosystem are discussed

mid depth circulation in the northwest pacific during the last deglaciation evidence from foraminiferal radiocarbon ages 1 sediment cores mr01 k03 pc4 pc5 1366 m water depth collected from off northern japan were studied using coexisting planktonic and benthic foraminiferal radiocarbon measurements to reconstruct the history of mid depth circulation in the northwest pacific reconstructed ventilation ages indicate that consistent with data from a previous radiocarbon study at a shallower site there was significant variation in mid depth circulation during the last deglaciation especially in the bolling allerod 13 15 ka and younger dryas 11 5 13 ka intervals our record indicates that the ventilation changes in the north pacific were antiphase to those of the north atlantic suggesting that atmospheric moisture transport associated with the asian monsoon might have played a great role in millennium scale ventilation changes in the north pacific during the last deglaciation

no signature of abyssal carbon in intermediate waters off chile during deglaciation the rise in atmospheric carbon dioxide at the end of the last glacial maximum has been attributed to the release of carbon dioxide from the deep southern ocean however reconstructions of the radiocarbon signature of chilean margin intermediate waters during the glacial termination do not reflect the influence of such a release

reconstruction of the last deglaciation deconvolved records of δ18o profiles micropaleontological variations and accelerator mass spectrometric14c dating bioturbation acts as a low pass filter in displacing and reducing the amplitudes of stratigraphic signals this often leads to a loss of high frequency events in the stratigraphic record in addition when considering an isotopic signal 18o 14c measured in stratigraphic carriers such as foraminifera bioturbation and carrier abundance changes can create artifacts which may be falsely interpreted as leads or lags in the paleoclimatic record

deepwater formation in the north pacific during the last glacial termination between approximately 17 500 and 15 000 years ago the atlantic meridional overturning circulation weakened substantially in response to meltwater discharges from disintegrating northern hemispheric glacial ice sheets the global effects of this reorganization of poleward heat flow in the north atlantic extended to antarctica and the north pacific here we present evidence from north pacific paleo surface proxy data a compilation of marine radiocarbon age ventilation records and global climate model simulations to suggest that during the early stages of the last glacial termination deep water extending to a depth of approximately 2500 to 3000 meters was formed in the north pacific a switch of deepwater formation between the north atlantic and the north pacific played a key role in regulating poleward oceanic heat transport during the last glacial termination

radiocarbon age of late glacial deep water from the equatorial pacific radiocarbon age differences for pairs of coexisting late glacial age benthic and planktic foraminifera shells handpicked from 10 sediment samples from a core from a depth of 2 8 km in the western equatorial pacific are not significantly different from that of 1600 years calculated from measurements on prenuclear seawater this places a lower limit on the depth of the interface for the hypothetical radiocarbon depleted glacial age seawater reservoir required to explain the 190 drop in the 14c c for atmospheric co2 which occurred during the mystery interval 17 5 to 14 5 calendar years ago these measurements restrict the volume of this reservoir to be no more than 35 that of the ocean further 14c measurements on a single last glacial maximum age sample from a central equatorial pacific core from a depth of 4 4 km water fail to reveal evidence for the required 5 to 7 kyr age difference between benthic and planktic foraminifera shells if the isolated reservoir occupied only one third of the ocean nor does the 13c record for benthic forams from this abyssal core yield any evidence for the excess respiration co2 expected to be produced during thousands of years of isolation nor as indicated by the presence of benthic foraminifera was the dissolved oxygen used up in this abyssal water

seasonal associations of phytoplankton and planktic foraminifera in an upwelling region and their contribution to the seafloor abstract seasonal occurrences of both phytoplankton and zooplankton are closely associated with upwelling and stabilization in waters overlying the san pedro basin this region is situated within the southern california bight and is affected by variations in the general southward flowing california current and variable intrusion of oceanic waters increased northerly wind stress in spring and early summer results in upwelling of deeper nutrient rich waters into the photic zone a seven month time series sediment trap experiment revealed clear patterns in seasonal succession of both phytoplankton and planktic foraminifera several distinct high and low flux periods occurred over the study period some of which can be related to rapid changes in the hydrographic environment caused by upwelling and subsequent surface water stratification factor analysis of relative abundances of combined phytoplankton and foraminiferal taxa defines seven assemblages reflecting seven stages of production which range in duration from two to five weeks factor scores describe phytoplankton and foraminiferal taxa indicative of specific production stages periods of high flux of the more abundant diatoms and planktic foraminifera also illustrate preferred production stages and compare well with percentage based results a comparison of the sediment trap assemblage with local sediment from an oxygenated portion of the basin suggests that long term phytoplankton accumulation in this region is dominated by taxa associated with winter bloom and post upwelling bloom production implying that brief but massive episodic events overwhelm and dominate the annually averaged diatom species assemblage found in the sediments foraminifera however are modified by dissolution to the extent that the high production periods of late spring and during upwelling are poorly represented rather species indicative of early spring and post upwelling conditions dominate the planktic foraminiferal sedimentary assemblage

14c activity and global carbon cycle changes over the past 50 000 years a series of 14c measurements in ocean drilling program cores from the tropical cariaco basin which have been correlated to the annual layer counted chronology for the greenland ice sheet project 2 gisp2 ice core provides a high resolution calibration of the radiocarbon time scale back to 50 000 years before the present independent radiometric dating of events correlated to gisp2 suggests that the calibration is accurate reconstructed 14c activities varied substantially during the last glacial period including sharp peaks synchronous with the laschamp and mono lake geomagnetic field intensity minimal and cosmogenic nuclide peaks in ice cores and marine sediments simulations with a geochemical box model suggest that much of the variability can be explained by geomagnetically modulated changes in 14c production rate together with plausible changes in deep ocean ventilation and the global carbon cycle during glaciation

ventilation of the deep southern ocean and deglacial co2 rise past glacial interglacial increases in the concentration of atmospheric carbon dioxide co2 are thought to arise from the rapid release of co2 sequestered in the deep sea primarily via the southern ocean here we present radiocarbon evidence from the atlantic sector of the southern ocean that strongly supports this hypothesis we show that during the last glacial period deep water circulating around antarctica was more than two times older than today relative to the atmosphere during deglaciation the dissipation of this old and presumably co2 enriched deep water played an important role in the pulsed rise of atmospheric co2 through its variable influence on the upwelling branch of the antarctic overturning circulation

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

a new survey of multiring impact basins on mars multiring impact basins have profoundly influenced the geologic evolution of mars we compile and summarize the evidence for martian impact basins and suggest eight new examples multiring basins on mars define three morphologic subclasses with increasing basin size basins having diameters 300 3600 km have extremely shallow topographic profiles and numerous concentric structures expressed as scarps massifs and channels radial and concentric structures analogous to those associated with orientale are not apparent for basins of argyre size or larger these variations in basin morphology and structure may be associated with mechanical interactions between basin forming impacts relatively thin weak lithosphere and for the largest impacts spherical target geometry multiring basins are recognized on all parts of mars including tharsis elysium and the northern lowlands much of the subsequent resurfacing of cratered terrain such as lunae planum ridged plains is associated spatially with multiring basins nucleation of long lived volcanic complexes in tharsis and elysium was probably aided by early impact basins the planetary terrain dichotomy was probably established during the period of heavy meteoritic bombardment and subsequent processes in the northern plains region were not sufficiently vigorous to destroy or completely obscure the underlying multiring basin fabric the revised population of multiring basins is consistent with the size frequency distribution of craters 500 km in diameter on mars basins having diameters 500 d 1850 km are characterized by a cumulative frequency slope of 0 75 0 16 whereas the larger basins define a slope of 1 7 0 45 this change in slope occurs over the same diameter range as the significant change from orientale type basin morphology at smaller diameters to argyre and chryse type basin morphology the population of craters and basins on mars confirms that the relative crater densities on the terrestrial planets due to heavy bombardment are comparable perhaps suggesting a common source for the impacting objects

north atlantic circulation and reservoir age changes over the past 41 000 years 1 constraints on the timing of atlantic meridional overturning circulation amoc changes during the last deglaciation are fundamental to understanding the climate s rapid response to insolation forcing however uncertainty about high latitude north atlantic hlna radiocarbon reservoir ages has previously precluded robust age model development for this critical region hlna reservoir ages also serve as a proxy for amoc strength we present regionally averaged hlna reservoir ages for 0 to 41 thousand years before the present kyr bp based on over 500 radiocarbon dates from 33 north atlantic cores an early deglacial increase to 1000 14c yr reservoir ages between 18 5 and 16 5 kyr bp suggests reduced amoc before peak heinrich stadial 1 hs1 ice rafted debris ird a rapid decrease in reservoir ages coincident with the ird maximum at 16 kyr bp indicates strong stratification of the upper water column caused by massive freshwater release

multispecies approach to reconstructing eastern equatorial pacific thermocline hydrography during the past 360 kyr 1 stable isotope data from eastern equatorial pacific eep core tr163 19 2 15 n 90 57 w 2348 m are presented for the surface dwelling foraminifers globigerinoides ruber and g sacculifer and thermocline dwelling globorotalia menardii and neogloboquadrina dutertrei using species specific normalization factors derived from experimental and plankton tow data we reconstruct a 360 kyr record of water column hydrography across the past three glacial cycles we demonstrate that g ruber maintains a mixed layer habitat throughout the entire record while g sacculifer records a mixture of thermocline and mixed layer conditions and g menardii and n dutertrei record thermocline properties we conclude that g sacculifer is not appropriate for paleoceanographic applications in regions with steep vertical hydrographic gradients results suggest that this region of the eep had a thicker mixed layer and deeper 13cdic boundary between the surface and equatorial undercurrent during the last two glacial periods a shift in n dutertrei and g sacculifer geochemistry prior to 185 kyr suggests water column structure and chemocline gradients changed possibly due to a shift in the position of the undercurrent relative to this site the timing and magnitude of glacial interglacial 13c variations between species indicates that near surface carbon chemistry is controlled by changes in productivity atmospheric circulation and advected intermediate water sources north of the antarctic polar front these results demonstrate that when properly calibrated for species differences multispecies geochemical data sets can be invaluable for reconstructing water column structure and properties in the past

radiocarbon age anomaly at intermediate water depth in the pacific ocean during the last deglaciation 1 benthic and planktonic 14c ages are presented for the last glacial termination from marine sediment core vm21 30 from 617 m in the eastern equatorial pacific the benthic planktonic 14c age differences in the core increased to more than 6000 years between heinrich 1 time and the end of the younger dryas period several replicated 14c ages on different benthic and planktonic species from the same samples within the deglacial section of the core indicate a minimal amount of bioturbation scanning electron microscopy reveals no evidence of calcite alteration or contamination the oxygen isotope stratigraphy of planktonic and benthic foraminifera does not indicate anomalously old glacial age values and there is no evidence of a large negative stable carbon isotope excursion in benthic foraminifera that would indicate input of old carbon from dissociated methane it appears therefore that the benthic 14c excursion in this core is not an artifact of diagenesis bioturbation or a pulse of methane a benthic 14c stratigraphy reconstructed from the 14c ages from the deglacial section of vm21 30 appears to match that of baja margin core mv99 mc19 gc31 pc08 705 m but the magnitude of the low 14c excursion is much larger in the vm21 30 record this would seem to imply that the vm21 30 core was closer to the source of 14c depleted waters during the deglaciation but the source of this co2 remains elusive

shortcomings of the isolated abyssal reservoir model for deglacial radiocarbon changes in the mid depth indo pacific ocean severely negative 14c anomalies from the mid depth pacific and the arabian sea have been taken as support for the hypothesized deglacial release of a previously isolated extremely 14c deplete deep ocean carbon reservoir we report box model simulations that cast doubt on both the existence of the hypothesized deep reservoir and its ability to explain the mid depth 14c anomalies first the degree of ice age isolation needed to substantially reduce the deep 14c of the deep reservoir causes anoxia and the trapping of alkalinity from caco3 dissolution the latter increasing atmospheric co2 second even with a completely 14c free deep reservoir achieving the mid depth 14c anomalies of observed duration requires ad hoc stifling of aspects of deep circulation to prevent rapid dissipation of the anomalous 14c free carbon to the rest of the ocean and the atmosphere we suggest that the mid depth anomalies do not record basin scale 14c changes but are instead local phenomena

the surface expression of radiocarbon anomalies near baja california during deglaciation abstract periods of declining atmospheric radiocarbon activity 14 c during the heinrich 1 17 8 14 6 ka and younger dryas 12 8 11 5 ka stadials of the last deglaciation coincide with intervals of rising atmospheric co2 as well as evidence of 14c depleted carbon at intermediate ocean depths near baja california mexico and in the arabian sea the latter has been interpreted as the signature of aged carbon emerging through the intermediate ocean to the atmosphere from a previously isolated deep ocean reservoir here we report measurements from near baja california that enable us to reconstruct the 14 c of surface waters as recorded by three different species of planktonic foraminifera we find that surface ocean 14 c recorded by planktonic foraminifera was anomalously low relative to the coeval atmosphere during previously documented periods of low benthic 14 c consistent with upwelling and subsequent mixing and or partial atmospheric equilibration of the intermediate depth benthic signal we also propose an oceanographic explanation for observed 14 c differences between individual planktonic species during deglaciation at this location based on seasonal growth habitats and a seasonal change in the source of coastal upwelling waters from northern in the spring to southern in late summer as the shelf trapped poleward california undercurrent strengthens an analysis of the contemporary hydrography and planktic habitat preferences suggests that g bulloides and g sacculifer record primarily springtime conditions off baja california when the local influence of waters sourced from the surface of the north pacific is greatest this is supported by the strong resemblance of the 14 c of those species and a recent record of planktic 14 c from the northeast pacific during deglaciation lower 14 c recorded by the late summer species g ruber suggests that locally upwelling waters carried 14c depleted carbon that was proximately sourced from equatorial subsurface waters entrained by the california undercurrent together with the benthic record these observations are consistent with transport of an anomalous 14c depletion signal carried primarily by antarctic intermediate water from an ultimate source in the southern ocean

separating natural and bomb produced radiocarbon in the ocean the potential alkalinity method alkalinity method provides an estimate of surface ocean prebomb d 14 c concentrations predictions with the technique appear to be unbiased and have uncertainties which are less than previous techniques index terms 4860 oceanography biological and chemical radioactivity and radioisotopes 4894 oceanography biological and chemical instruments and techniques

radiocarbon age offsets of foraminifera resulting from differential dissolution and fragmentation within the sedimentary bioturbated zone 1 shells of coexisting species of planktonic foraminifera from the ontong java plateau reveal radiocarbon age offsets of up to 2200 years similar offsets are found between fragments and whole shells of single species steady state modelling of dissolution and bioturbation within the sedimentary mixed layer predicts age differences of up to several kiloyears due to the interplay between differential dissolution and fragmentation of foraminifer shells and bioturbation the observation that fragile foraminiferal shells are systematically older than those of more robust species is more difficult to explain mechanisms of chemical erosion interface dissolution and sediment redistribution are all apparently unable to explain this phenomenon a possible solution is presented in which a particular species may be represented by two distinct classes of shells which are more or less robust in this case differential dissolution and fragmentation causes an increase in the mean age as the fragile class contributes less to the remaining intact shells this study highlights the vulnerability of low sedimentation rate cores to the effects of dissolution and bioturbation

coastal trapped waves alongshore pressure gradients and the california undercurrent abstractthe california undercurrent cuc a poleward flowing feature over the continental slope is a key transport pathway along the west coast of north america and an important component of regional upwelling dynamics this study examines the poleward undercurrent and alongshore pressure gradients in the northern california current system ccs where local wind stress forcing is relatively weak the dynamics of the undercurrent are compared in the primitive equation navy coastal ocean model and a linear coastal trapped wave model both models are validated using hydrographic data and current meter observations in the core of the undercurrent in the northern ccs in the linear model variability in the predominantly equatorward wind stress along the u s west coast produces episodic reversals to poleward flow over the northern ccs slope during summer however reproducing the persistence of the undercurrent during late summer requires additional incoming energy from sea level variability applied south

no evidence for a deglacial intermediate water δ14c anomaly in the sw atlantic abstract the last deglaciation was characterized by an increase in atmospheric pco 2 and decrease in atmospheric radiocarbon activity one hypothesis is that these changes were due to out gassing of 14 c depleted carbon from the abyssal ocean reconstructions of foraminiferal 14 c from the eastern tropical pacific arabian sea and high latitude north atlantic show that severe depletions in 14 c occurred at intermediate water depths during the last deglaciation it has been suggested that 14 c depleted water from the abyss upwelled in the southern ocean and was then carried by antarctic intermediate water aaiw to these sites however locations in the south pacific in the direct path of modern day aaiw do not exhibit the 14 c excursion and therefore cast doubt upon the aaiw mechanism de pol holz et al 2010 rose et al 2010 here we evaluate whether or not a deglacial 14 c anomaly occurred at intermediate depths in the southwest atlantic we find that the deglacial benthic 14 c trend at our site is similar to the atmospheric 14 c trend our results are also largely consistent with results from u th dated corals at shallower water depths on the brazil margin mangini et al 2010 we find no evidence in the southwestern atlantic of a 300 decrease in intermediate water 14 c from 18 to 14 kyr bp like that observed in the eastern tropical pacific marchitto et al 2007 when our results are paired with those from the south pacific it appears aaiw did not carry a highly 14 c depleted signal during the deglaciation another source of carbon is apparently required to explain the intermediate depth 14 c anomalies in the north atlantic indian and pacific oceans

the southern ocean s role in carbon exchange during the last deglaciation changes in the upwelling and degassing of carbon from the southern ocean form one of the leading hypotheses for the cause of glacial interglacial changes in atmospheric carbon dioxide we present a 25 000 year long southern ocean radiocarbon record reconstructed from deep sea corals which shows radiocarbon depleted waters during the glacial period and through the early deglaciation this depletion and associated deep stratification disappeared by 14 6 ka thousand years ago consistent with the transfer of carbon from the deep ocean to the surface ocean and atmosphere via a southern ocean ventilation event given this evidence for carbon exchange in the southern ocean we show that existing deep ocean radiocarbon records from the glacial period are sufficiently depleted to explain the 190 per mil drop in atmospheric radiocarbon between 17 and 14 5 ka

marine isotope stage mis 8 millennial variability stratigraphically identical to mis 3 the marine isotope stage mis 3 stratigraphy is highly robust and was reproduced during another period mis 8 6 global ice volume was similar during mis 8 6 to mis 3 60 to 90 m sea level equivalent but the milankovitch insolation forcing was different implying that earth s predisposition to millennial internal variability is controlled by the configuration of the major ice sheets the involvement of additional factors cannot be ruled out but by identifying several such periods using new deep ice cores from dome concordia and dome fuji antarctica as well as the marine record we may isolate the factors predisposing earth to these highly significant modes of climate variability