a model based interpretation of low frequency changes in the carbon cycle during the last 120 000 years and its implications for the reconstruction of atmospheric δ14c a main caveat in the interpretation of observed changes in atmospheric d14c during the last 50 000 years is the unknown variability of the carbon cycle which together with changes in the 14c production rates determines the 14c dynamics a plausible scenario explaining glacial interglacial dynamics seen in atmospheric co2 and d13c was proposed recent ly kohler et al 2005 a similar approach and expanding its interpretation to the 14c cycle is an important step towards a deeper understanding of d14c variability this approach is based on an ocean atmosphere biosphere box model of the global carbon cycle bicycle to reproduce low freque ncy changes in atmospheric co2 as seen in antarctic ice cores the model is forced forward in time by various paleo climatic records derived from ice and sediment cores the simulation results of our proposed scenario match a compiled co2 record from various ice cores during the last 120 000 years with high accuracy r2 0 89 we analyze scenarios with different 14c production rates which are either constant based on 10be measured in greenland ice cores or the recent high resolution geomagnetic field reconstruction glopis 75 and compare them with the available d14c data covering the last 50 000 years our results suggest that during the last glacial cycle in general less than 110 o oo of the increased atmospheric d14c are based on variations in the carbon cycle while the largest part 5 6 of the variations has to be explained by other factors glacial atmospheric d14c larger than 700 o oo cannot not be explained within our framework neither through carbon cycle based changes nor through variable 14c production superimposed on these general trends might lie positive anomalies in atmospheric d14c of 50 o oo caused by millennial scale variability of the northern deep water production during heinrich events and dansgaard oeschger climate fluctuations according to our model the dominant processes that increase glacial d14c are a reduced glacial ocean circulation 40 o oo a restricted glacial gas exchange between the atmosphere and the surface ocean through sea ice coverage 20 o oo and the enrichment of dic with 14c in the surface waters through isotopic fractionation during higher glacial marine export production caused by iron fertilization 10 o oo

younger dryas a data to model comparison to constrain the strength of the overturning circulation 1 the university of victoria earth system climate model uvic escm is used to compare simulated time series of radiocarbon during the younger dryas yd with paleoceanographic records i find that only a complete shut down and recovery of the atlantic meridional overturning circulation amoc can simulate both the rise in atmospheric co2 concentrations seen in ice core records and the peak and subsequent decrease in atmospheric 14c comparable to the peak recorded in the varved sediments of the cariaco basin simulated radiocarbon profiles in the western north atlantic match well with data from deep sea corals at the beginning of the yd whereas planktonic benthic foraminifera records match best with a transient state during the rapid recovery of the amoc the steepness of the increase in atmospheric 14c at 12 9 ka cal could not be simulated with oceanic circulation changes only because the response time of the climate system is too slow

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

the deglacial evolution of north atlantic deep convection deepwater formation in the north atlantic by open ocean convection is an essential component of the overturning circulation of the atlantic ocean which helps regulate global climate we use water column radiocarbon reconstructions to examine changes in northeast atlantic convection since the last glacial maximum during cold intervals we infer a reduction in open ocean convection and an associated incursion of an extremely radiocarbon 14c depleted water mass interpreted to be antarctic intermediate water comparing the timing of deep convection changes in the northeast and northwest atlantic we suggest that despite a strong control on greenland temperature by northeast atlantic convection reduced open ocean convection in both the northwest and northeast atlantic is necessary to account for contemporaneous perturbations in atmospheric circulation

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

numerical simulations of large water waves due to landslides a mathematical model based on the hydrodynamic shallow water equations is developed for numerical simulation of slide generated waves in fjords the equations are solved numerically by a finite difference technique to examine the performance of the numerical model we have simulated the slide catastrophe in tafjord western norway 1934 the predicted runup heights are in good agreement with measured runup heights the effects of wave amplification are estimated in runup zones with gentle beach slopes the model results reveal wave energy trapping due to the fjord geometry this causes standing wave oscillations in accordance with the observations

ventilation of the north atlantic ocean during the last glacial maximum a comparison between simulated and observed radiocarbon ages the distribution of radiocarbon during simulations of the last glacial maximum with a coupled ocean atmosphere sea ice model is compared with sediment core measurements from the equatorial atlantic ceara rise blake ridge caribbean sea and south china sea during these simulations we introduce a perturbation of north atlantic freshwater fluxes leading to varying strengths of the atlantic meridional overturning the best fit with the observations is obtained for an overturning weakened by 40 compared with today further we simulate the phenomenon of an age reversal found in deep sea corals but we suggest that this indicates rather a sudden interruption of deep water formation instead of an increase in ventilation which was suggested earlier

the assessment of rockfall hazard at the base of talus slopes fragmental rockfall is characterized by the independent movement of individual rock fragments after detachment from a rock face the continued operation of the process leads to the accumulation of talus slopes on talus slopes the rockfall shadow extends beyond the base of the talus and consists of scattered boulders that have run out beyond the base of the slope the landing probability of boulders in the shadow is examined return periods of the order of 1000 years relative to a house site are typical rockfall behaviour particularly with respect to run out into the shadow can be assessed using geological evidence empirical methods physical modelling and computer based analytical models an empirical minimum shadow angle of 27 5 i e the angle between the distal limit of the shadow and the top of the talus slope is suggested and would be useful in rockfall vulnerability studies at the base of talus slopes as a first approximation to shadow limits it is preferable to the use of the rockfall fahrb

the stromboli 2002 tsunamigenic submarine slide characteristics and possible failure mechanisms 1 on 30 december 2002 a major instability event deeply involving the submarine slope occurred on the sciara del fuoco on the western flank of stromboli volcano in the aeolian islands tsunami waves with a maximum runup of over 10 m in stromboli were generated having a measurable impact as far as the sicily coast just 10 months before the event a multibeam bathymetry had been collected in the area down to 1000 m of depth a repetition of the survey after the slide allowed the unique opportunity to verify the occurrence of a large submarine slide and to define volumes involved and morphology generated by the event through the comparison of the preevent and postevent bathymetric grids a morphological characterization of the slope before and after the submarine landslide is presented showing how the preexisting features interacted with the slide event in controlling the instability mechanisms of the submarine failure are discussed on the basis of the geometrical characters of the landslide event structural and stratigraphic setting of the submerged slope and geotechnical considerations on the behavior of slope material

the record of continental dust from australia in tasman sea sediments abstract the flux of aeolian dust from australia to sediments of the tasman sea has increased during glacial stages of the last four glacial cycles low fluxes of dust from australia before 350 ka were followed by an increase in stage 10 and high fluxes in peak glacial periods thereafter the initiation of higher dust fluxes in stage 10 is consisten with previous estimates of the age of onset of aridity in the source area dust flux to the tasman sea is thought to record the intensity of deflation from the source area in interior southeastern australia which was marked by arid conditions and possibly greater windiness during the last glacial a transect of five cores from the central tasman sea revealed consistently low dust fluxes north of 33 s increasing southward to approximately 40 s glacial to interglacial movement of the northern boundary of the dust plume governed by the position of the subtropical ridge was less than 6 latitude probably closer to 3 350 km the position of the dust plume determined in this study and its response to climate change are significantly different from a previous reconstruction based on the measurement of quartz content of the non biogenic sediment fraction

the last glacial termination a major puzzle of paleoclimatology is why after a long interval of cooling climate each late quaternary ice age ended with a relatively short warming leg called a termination we here offer a comprehensive hypothesis of how earth emerged from the last global ice age a prerequisite was the growth of very large northern hemisphere ice sheets whose subsequent collapse created stadial conditions that disrupted global patterns of ocean and atmospheric circulation the southern hemisphere westerlies shifted poleward during each northern stadial producing pulses of ocean upwelling and warming that together accounted for much of the termination in the southern ocean and antarctica rising atmospheric co2 during southern upwelling pulses augmented warming during the last termination in both polar hemispheres

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

a minimum thermodynamic model for the bipolar seesaw 1 the simplest possible model is proposed to explain a large fraction of the millennial climate variability measured in the isotopic composition of antarctic ice cores the model results from the classic bipolar seesaw by coupling it to a heat reservoir in this thermal bipolar seesaw the heat reservoir convolves northern time signals with a characteristic timescale applying the model to the data of grip and byrd we demonstrate that maximum correlation can be obtained using a timescale of about 1000 1500 years higher correlations are obtained by first filtering out the long term variability which is due to astronomical and greenhouse gas forcing and not part of the thermal bipolar seesaw the model resolves the apparent confusion whether northern and southern climate records are in or out of phase synchronous or time lagged

subaerial and subaqueous dynamics of coastal rockfalls in spite of the hazard represented by rockfalls in coastal areas few investigators have studied the movement of rocks falling in water this work describes a model for the propagations of coastal rockfalls i e blocks detaching from a subaerial cliff propagating initially in air impacting against the water surface and finally coming to rest in the water basin application of the model to two real cases in italy shows a satisfactory agreement between the predicted rockfall run out and the field data some scattering observed in the data is explained as the consequence of different heights of the source area it is shown that largest boulders usually reach a longer distance however the schematic shape for blocks adopted in the model likely results in a much more regular behaviour compared to reality

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

relative timing of deglacial climate events in antarctica and greenland the last deglaciation was marked by large hemispheric millennial scale climate variations the bolling allerod and younger dryas periods in the north and the antarctic cold reversal in the south a chronology from the high accumulation law dome east antarctic ice core constrains the relative timing of these two events and provides strong evidence that the cooling at the start of the antarctic cold reversal did not follow the abrupt warming during the northern bolling transition around 14 500 years ago this result suggests that southern changes are not a direct response to abrupt changes in north atlantic thermohaline circulation as is assumed in the conventional picture of a hemispheric temperature seesaw

uncorking the southern ocean s vintage co2 antarctic ice cores provide a well documented link between earth s climate and the co2 content of the atmosphere over the past 800 000 years 1 many hypotheses to explain this relationship envision releases of co2 to the atmosphere from the deep waters of the southern ocean around antarctica 2 but there has been limited evidence on page 1147 of this issue skinner et al 3 use the radiocarbon 14c content in the shells of surface and bottom dwelling organisms foraminifera recovered from the southern ocean to track how co2 moved from the deep sea to the atmosphere during the warming transition out of the last ice age deglaciation first bottom dwelling foraminifera record the buildup of 14c depleted co2 in the deep ocean during the last glacial period more than 21 000 years ago second the shells of surface dwellers record the transfer of 14c depleted co2 to the surface between 17 000 and 21 000 years ago

oceanic carbon and water masses during the mystery interval a model data comparison study 1 the mystery interval 17 5 14 5 ka bp is characterized by a large decline in atmospheric 14c synchronous with an increase in atmospheric co2 the most widely accepted hypothesis to explain these observed shifts involves the existence of an isolated old ocean carbon reservoir that was subsequently ventilated here we use the uvic earth system climate model to locate a potential carbon rich and 14c depleted water mass under 17 5 ka bp boundary conditions we then investigate two mechanisms for the potential ventilation of such a reservoir namely the weakening of the north atlantic meridional overturning due to iceberg calving and latitudinal shifts in southern hemisphere westerlies shw due to southern hemispheric warming we find that simulations derived from an equilibrium state forced with present day shw and moderate north atlantic deep water nadw formation are in better agreement with atmospheric and ocean 14c reconstructions than simulations derived from an equilibrium state forced with a northward shifted shw belt resulting in a shut down of the atlantic meridional overturning and formation of north pacific deep water for simulations with present day shw the oldest water masses are found in the north pacific although the southern ocean cannot be ruled out as a potential mystery reservoir according to our simulations the strength of atlantic overturning is the dominant mechanism in increasing the ocean atmosphere carbon flux while shifting shw results in a rearrangement of deep ocean carbon largely between the atlantic and pacific basins in our best case scenario the model can account for 58 of the atmospheric co2 increase and 48 of the atmospheric 14c decline while the rate of ventilation and the age of ventilated water masses are comparable with observations the ventilation in the model could not be sustained long enough to account for the full excursion seen in paleodata

hydrological impact of heinrich events in the subtropical northeast atlantic reconstructing the impact of heinrich events outside the main belt of ice rafting is crucial to understanding the underlying causes of these abrupt climatic events a high resolution study of a marine sediment core from the iberian margin demonstrates that this midlatitude area was strongly affected both by cooling and advection of low salinity arctic water masses during the last three heinrich events these paleoclimatic time series reveal the internal complexity of each of the last three heinrich events and illustrate the value of parallel studies of the organic and inorganic fractions of the sediments