enhanced diapycnal mixing in the south china sea profiles of current velocity temperature and salinity were obtained in the internal wave and mixing experiment in the south china sea scs the luzon strait and the north pacific the observations are examinedforevidenceofenhanceddiapycnalmixinginthescs whichreacheso 10 23 m 2 s 21 inmagnitude resultsfrom independent casts reveal that diapycnal diffusivity in the scs andthe luzon strait is elevatedby two orders of magnitude over that of the smooth bathymetry in the north pacific which are typical of background values in an open ocean the vertical distribution of diapycnal diffusivity is nonuniform in the scs exhibiting higher values at depths greater than about 1000 m this result compares favorably with the direct microstructure measurements at four stations in the scs velocity and density profiles are combined to estimatetheinternaltideenergyfluxgeneratedintheluzonstraitanddirectedintothescs theenergyamounts to 10 gw most of which is rationalized to be the potential energy source for enhanced mixing in the scs

evidence from u th dating against northern hemisphere forcing of the penultimate deglaciation milankovitch proposed that summer insolation at mid latitudes in the northern hemisphere directly causes the ice age climate cycles1 this would imply that times of ice sheet collapse should correspond to peaks in northern hemisphere june insolation but the penultimate deglaciation has proved controversial because june insolation peaks 127 kyr ago whereas several records of past climate suggest that change may have occurred up to 15 kyr earlier2 3 4 5 6 7 8 there is a clear signature of the penultimate deglaciation in marine oxygen isotope records but dating this event which is significantly before the 14c age range has not been possible here we date the penultimate deglaciation in a record from the bahamas using a new u th isochron technique after the necessary corrections for recoil mobility of 234u and 230th and a small age correction for sediment mixing the midpoint age for the penultimate deglaciation is determined to be 135 2 5 kyr ago this age is consistent with some coral based sea level estimates but it is difficult to reconcile with june northern hemisphere insolation as the trigger for the ice age cycles potential alternative driving mechanisms for the ice age cycles that are consistent with such an early date for the penultimate deglaciation are either the variability of the tropical ocean atmosphere system or changes in atmospheric co2 concentration controlled by a process in the southern hemisphere

recent environmental changes in laguna mar chiquita central argentina a sedimentary model for a highly variable saline lake laguna mar chiquita a highly variable closed saline lake located in the pampean plains of central argentina is presently the largest saline lake in south america 6000 km 2 recent variations in its hydrological budget have produced dry and wet intervals that resulted in distinctive lake level fluctuations results of a multiproxy study of a set of sedimentary cores indicate that the system has clearly recorded these hydrological variations from the end of the little ice age ad 1770 to the present sedimentological and geochemical data combined with a robust chronology based on 2 1 0 pb profiles and historical data provide the framework for a sedimentary model of a lacustrine basin with highly variable water depth and salinity lake level drops and concurrent increases in salinity promoted the development of gypsum calcite halite layers and a marked decrease in primary productivity the deposits of these dry stages are evaporite bearing sediments with a low organic matter content conversely highstands are recorded as diatomaceous organic matter rich muds average bulk sediment accumulation rose from 0 22 g cm 2 year 1 in lowstands to 0 32 g cm 2 year 1 during highstands these results show that laguna mar chiquita is a good sensor of high and low frequency changes in the recent hydrological budget and therefore document climatic changes at middle latitudes in south eastern south america dry conditions were mostly dominant until the last quarter of the twentieth century when a humid interval without precedent during the last 240 years of the lake s recorded history started thus it is an ideal system to model sedimentary and geochemical response to environmental changes in a saline lacustrine basin

evidence from earthquake data for a partially molten crustal layer in southern tibet earthquake data collected by the indepth ii passive source experiment show that there is a substantial south to north variation in the velocity structure of the crust beneath southern tibet north of the zangbo suture beneath the southern lhasa block a midcrustal low velocity zone is revealed by inversion of receiver functions rayleigh wave phase velocities and modeling of the radial component of teleseismic p waveforms conversely to the south beneath the tethyan himalaya no low velocity zone was observed the presence of the midcrustal low velocity zone in the north implies that a partially molten layer is in the middle crust beneath the northern yadong gulu rift and possibly much of southern tibet

tracking slabs beneath northwestern pacific subduction zones article i nfo article history this study uses the amplitudes of bottom side reflected shear waves to constrain the morphology and dynam ics of subducted oceanic lithosphere beneath northwestern pacific subduction zones across honshu arc the 410 and 660 km seismic discontinuities are detected at the respective depths of 395 5 and 685 5 km within the wadati benioff zone their topographies are negatively correlated along slab dip showing the dominant effect of temperature on the olivine phase changes within the upper mantle transition zone the base of the upper mantle shows broad depressions as well as localized zones of shallow average depths be neath korea and northeast china the 15 km peak to peak topography west of the wadati benioff zones suggests that the stagnant part of the subducted pacific plate is not as flat as previously suggested eastward slab pile up is also possible at the base of the upper mantle across southern kuril arc the shear wave reflec tion coefficients of major olivine phase boundaries fall below 5 within the wadati benioff zone the appar ent reflection gaps and the spatial connection between a strong reflector at 900 km depth may imply 1 possible compositional variations at the top and bottom of the transition zone and 2 substantial mass heat flux across the 660 km seismic discontinuity we also identify strong reflectors within the subducted oceanic lithosphere at mid transition zone depths the depths and strengths of these reflectors are highly variable be tween honshu and southern kuril islands

holocene landscape evolution along the andean piedmont bolivian chaco abstract as part of the gran chaco the andean piedmont in eastern bolivia is characterized by a highly seasonal climate and large rainfall variability it receives sediments from small drainage basins in the subandean ranges therefore it should constitute a suitable sedimentary and geomorphic archive for the detection of past environmental changes this study reconstructs holocene landscape evolution along the andean piedmont in the bolivian chaco by combining large scale geomorphological analysis and the investigation of sedimentary sequences fluvial aggradation and channel avulsions are the dominant processes of piedmont construction and were particularly pronounced during the mid holocene this is interpreted to reflect a generally active landscape characterized by reduced forest cover as result of increased aridity widespread soil formation and landscape stability in all investigated catchments start after 4 cal ka bp indicating the onset of wetter conditions and successively denser forest cover in the bolivian chaco renewed sedimentation during the last millennium could imply a shift to more arid environmental conditions probably in relation to larger scale climatic phenomena such as the little ice age lia particularly during the last centuries the fluvial system of the study area has undergone the most profound changes of the entire holocene with sedimentation of very coarse sediments and subsequent incision this reflects important changes both in discharge and sediment supply and might be the result of either shorter term climate changes or increasing human impact

esr dating of pleistocene mammals and marine shells from the coastal plain of rio grande do sul state southern brazil abstract the coastal plain of rio grande do sul state cprs in southern brazil encompasses four barrier lagoon depositional systems formed by marine highstands during the quaternary but the ages of the pleistocene systems older than 125 ka are not precisely known due to the lack of numerical dates in order to refine the chronology of these deposits several fossils of terrestrial mammals collected in the fluvial facies of the lagoon system iii and fossil shells from the marine facies of the barrier system ii exposed in the southern sector of the cprs were subject to dating by electron spin resonance esr the ages of the mammalian remains range from 90 10 to 43 3 ka thus representing the last glacial cycle mis 4 and 3 the mean eu age of the shells is 224 24 6 ka but this value is considered younger than the real age because of excessive uranium uptake observed among the younger shells an estimated mean age of some 235 238 ka would agree with other esr and tl ages obtained for fossils and sediments collected from beds overlying the shells and would be consistent with the sea level highstand at the early mis 7 substage 7e the presence of bivalves and foraminifers that indicate ocean temperatures higher than at present seems to corroborate this estimate given that mis 7e was characterized by hypsithermal conditions

late quaternary paleosols stratigraphy and landscape evolution in the northern pampa argentina the field properties micromorphology grain size geochemistry and optically stimulated luminescence osl ages of two late quaternary sections have been used to reconstruct the sequence of pedosedimentary processes and to provide insights into landscape evolution in part of the northern pampa of argentina paleosols developed in paludal sediments adjacent to the parana river at baradero and in loess at lozada can both be correlated and linked to other sites thus enabling for the first time the tentative recognition and tracing of a diachronous soil stratigraphic unit that probably spans the equivalent of at least part of marine oxygen isotope stage ois 5 the paleosol at lozada was truncated and buried beneath fluvial sediments during the time span of ois 4 and 3 eolian gradually replaced paludal inputs at baradero over this period and there were also two clearly defined breaks in sedimentation and development of paleosols the period corresponding to ois 2 was marked by significant loess accumulation at both sites with accretion continuing into the mid holocene only at lozada the more developed nature of the surface soil at baradero probably reflects a combination of a moister climate and a longer soil forming interval

sharp mantle transition from cratons to cordillera in southwestern canada the western canada sedimentary basin marks the transition from the old north american continental lithosphere to young accreted terranes earlier studies in this region have suggested a large number of intricate basement domains as well as major seismic velocity gradients in the mantle to investigate the effect of the accretion and subduction on the mantle structure beneath the western margin of the north american craton we analyze p to s converted waves from upper mantle discontinuities from the canadian rockies and alberta network a regional broadband seismic array based in alberta canada the depths of the 410 and 660 km seismic discontinuities are correlated and on average are 9 km and 7 km greater than their respective global estimates the largest depression is observed beneath the rocky mountain foreland belt in southern alberta which highlights a steep southward westward structural gradient from the cratons to cordillera at lithospheric mantle depths the severity of the depressions especially in the southernmost alberta may be triggered by diffuse partial melt or increased water content above the 410 km discontinuity this result is corroborated by locally increased impedance contrast across the 410 km discontinuity and a strongly depressed 660 km discontinuity a relic mesozoic slab fragment may be partially responsible for the deep olivine phase boundary at the base of the upper mantle

deep convection and brine rejection in the japan sea received 15 october 2002 accepted 13 january 2003 published 19 february 2003 1 direct water mass renewal through convection deeper than 1000 m and the independent process of dense water production through brine rejection during sea ice formation occur at only a limited number of sites globally our late winter observations in 2000 and 2001 show that the japan east sea is a part of both exclusive groups japan sea deep convection apparently occurs every winter but massive renewal of bottom waters through brine rejection had not occurred for many decades prior to the extremely cold winter of 2001 the sites for both renewal mechanisms are south of vladivostok in the path of cold continental air outbreaks index terms 4283 oceanography general water masses 4243 marginal and semienclosed seas 4223 4215 climate and interannual variability 3309 citation talley l d v lobanov v ponomarev a salyuk p tishchenko i zhabin and s riser deep convection and brine rejection in the japan sea geophys res lett 30 4 1159 doi 10 1029 2002gl016451 2003

laser raman detection of authigenic carbonates from cold seeps at the formosa ridge and east of the pear river mouth basin in the south china sea abstract laser raman spectroscopy has been successfully applied for the in situ detection of gases and liquids but has not yet been extensively applied to rocks in the deep sea authigenic carbonate rocks are widely distributed at the formosa ridge site f and the eastern region of the pear river mouth basin site p in the south china sea scs considerable raman spectral information on authigenic carbonates was obtained from laboratory measurements of slices of authigenic carbonate direct measurements in a simulation environment and in situ measurements in the deep sea the dominant band of authigenic carbonate from site f ranges from 1084 to 1087 cm 1 while the dominant band from site p ranges from 1088 to 1091 cm 1 suggesting that compositional differences exist between the samples from the two cold seep areas the results of the point counting method indicates that the aragonite content in site f is higher than that at site p the wider peak width of the aragonites at site p shows the aragonites at site p have lower degree of crystallinity which suggests that aragonite is likely to be destroyed when the cold seep weakens or dies the above information obtained via the raman spectroscopy can guide sample collection in the deep sea and can be used in conjunction with other analysis methods to better understand environmental changes or the geological processes

a low velocity zone atop the transition zone in northwestern canada 1 seismic studies over the past decade have identified an s wave low velocity zone lvz above the transition zone at various locations around the globe this layer is hypothesized to be a lens of dense hydrous silicate melt ponding atop the 410 km discontinuity beneath the silicate melt density crossover predicted to exist within the upper mantle we have assembled a p and s receiver function data set to quantify the physical properties and geographical extent of the layer in northwestern canada geographic profiles formed from 1 d migration of receiver functions computed for the canadian northwest experiment canoe and portable observatories for lithospheric analysis and research investigating seismicity polaris slave arrays reveal an lvz beneath many stations at a nominal depth of 340 km to constrain layer thickness and poisson s ratio we performed a grid search over a suite of 1 d velocity profiles to model the relative delay times of direct conversions and reverberations from the top of the lvz and 410 km discontinuity as recorded at the yellowknife array in addition we performed linearized inversion of transmission coefficient amplitudes to estimate s velocity contrasts at the bounding interfaces the lvz is characterized by a thickness of 36 km with an s velocity contrast of 7 8 and poisson s ratio of 0 42 taken at face value the two latter results require an increase in p velocity into the lvz the poisson s ratio lies well above the iasp91 average of 0 29 0 3 for this depth range and favors the presence of high melt or fluid fractions

global mapping of topography on the 660 km discontinuity long period precursors to the ss seismic phase are used to produce global maps of topography for the discontinuity at 660 km depth in the upper mantle these maps indicate discontinuity depth variations of up to 30 km and suggest a correlation between regional depressions in the 660 km discontinuity and subduction zones a result more consistent with models in which the subducting slabs are deflected horizontally at the discontinuity than with models of unhindered slab penetration into the lower mantle

chronology of late pleistocene pampa loess from the cordoba area in argentina in argentina loess palaeosol sequences were studied from the two sections at monte ralo and corralito located near to the city of cordoba in the east of the pampean ranges infrared optically stimulated luminescence irsl and thermoluminescence tl dating techniques were applied to set up a more reliable chronological framework for the upper pleistocene loess record irsl ages increase with depth and are stratigraphically consistent the oldest loess exposed correlates at least to the penultimate glaciation the luminescence dating study gives evidence for humid climate conditions with soil formation during the last interglacial period and the middle pleniglacial correlating to marine isotope stage mis 5 and 3 respectively three extended periods of soil formation are recorded in the loess palaeosol sequences at the corralito section these buried soils most likely correlate with the last interglacial and early last glacial period during the middle pleniglacial two palaeosols are intercalated in the loess successions in the cordoba area the periods of increased loess accumulation and deposition of loessic sediments correlate with more arid and glacial periods during the early pleniglacial the middle pleniglacial and the late glacial copyright 2009 john wiley sons ltd

paleoenvironmental reconstruction of quaternary valley fill successions in summit paleosurfaces of southern sierras pampeanas cordoba province argentina abstract climatic and environmental changes were inferred from the study of late quaternary sequences that represent paleo valleys filling in the summit pampas at the center south of the sierra de comechingones cordoba province argentina a representative sedimentological section p1 was described and sampled and sediments age 14 c granulometric characteristics and organic matter content were determined in the analyzed succession four main stratigraphic units were recognized and interpreted the stratigraphic and pedological characteristics diatom levels presence geomorphological features and altitude conditions of the study area allow us to conclude that 1 valley fill deposits are holocene from 8310 110 yr bp to present days and composed exclusively of loessic loessoid material from surrounding areas 2 the dominant transport mechanism could have been laminar and or hyperconcentrated flows mainly associated with slope evolution processes sheet flow and high density flows 3 isolated swamps with important biological activity were the dominated environments in to the valleys these environments suggest an alternating pedogenic cycles were the most important was the middle late holocene indicating a landscape stabilization tendency 4330 130 yr bp 4 temperate wet climatic conditions and high seasonality characterized middle early holocene hypsithermal period more arid conditions dominated late holocene from 1500 to 1000 bp to the present temperate wet climatic conditions occurred and this period was interrupted by the little ice age 5 in the mountains both in wet and dry periods the rainfalls were probably higher as well as the temperature must be lower than the surrounding plain especially in winters perhaps reaching periglacial conditions during more arid periods

pleistocene lake outburst floods and fan formation along the eastern sierra nevada california implications for the interpretation of intermontane lacustrine records berin d i owen l a finkel r c clemmens s 2006 pleistocene lake outburst floods and fan formation along the eastern sierra nevada california implications for the interpretation of intermontane lacustrine records quaternary science reviews 25 2729 2748 sponsorship national science foundation grant ear 0207245

luminescence chronology of late pleistocene loess paleosol and tephra sequences near fairbanks alaska abstract thermoluminescence tl and infrared stimulated luminescence irsl sediment dating methods have been applied to paleosol and tephra bearing loess sequences younger than marine oxygen isotope stage mis 7 at three important sites tl ages indicate the development of significant paleosols 75 000 and 30 000 yr ago in the loess sequence at the gold hill site relatively minor soil development occurred 70 000 and 48 000 yr ago like the 75 000 yr old soil the 30 000 yr old soil is apparently of global extent and consistent in timing with inferred warm intervals elsewhere e g greenland europe western and central china at birch hill replicate tl dating of primary loess combined with two earlier tl results from the same site and with an earlier mean fission track glass shard age of 140 000 10 000 yr for the associated old crow tephra yield a more precise numeric age of 142 300 6600 yr for this alaska yukon chronostratigraphic marker ash bed three of the tl ages at the halfway house site are difficult to interpret but combined with other evidence they indicate 1 the upper 5 6 m of loess from halfway house is not part of the gold hill loess equivalent to pre mis 5 age as long thought by t l pewe but rather is much younger 2 the regionally significant variegated tephra found in the fairbanks and klondike areas and previously thought to be older than mis 5 has an age of 77 800 4100 yr late mis 5

geomorphology and chronology of late quaternary dune fields of western argentina abstract stabilized dune fields are common in western argentina and potentially reflect drought variability in the late quaternary this study focussed on deciphering geomorphic and stratigraphic record of three vegetated dune fields from east to west san luis medanos negros and medanos grandes with a mean annual precipitation from 700 to 91 mm optically stimulated luminescence single aliquot regeneration protocols yield ages on eolian quartz grains constraining depositional events the san luis dune field the wettest area exhibits evidence for repeated activation during the last glaciation ca 33 20 ka generally coincident with regional loess deposition these dunes were locally reformed in the past 100 years which is apparently coincident with intensified agrarian use and drying in the late 19th and early 20th century the two driest and western most dune fields medanos negros and medanos grandes show reactivation at ca 2 5 ka 0 9 and 0 5 ka and ca 4 3 4 2 1 and 0 6 0 4 ka respectively eolian depositional events at ca 2 5 2 1 ka and 0 6 0 4 ka may be coeval for medanos grandes and negros dune fields sustained drought conditions conducive for eolian activity is associated with warmer sea surface temperatures in the south atlantic a weakened south american convergent zone and a dispersed and southeasterly flow of tropical moisture from the low level chaco jet this nascent analysis indicates drought variability beyond historic observations with potentially at least four dune reactivation events in the past ca 4 5 ka

deep south china sea circulation 1 the analysis of an updated monthly climatology of observed temperature and salinity from the u s navy generalized digital environment model reveals a basin scale cyclonic circulation over the deep south china sea scs the cyclonic circulation lies from about 2400 m to the bottom the boundary current transport of the cyclonic circulation is around 3 0 sv our results suggest that the cyclonic circulation is mainly forced by the luzon overflow with bottom topography playing an important role the structures of potential temperature salinity and potential density in the deep scs are consistent with the existence of the cyclonic circulation specifically low salinity water is found in the interior region west of luzon island and surrounded by saline pacific water in boundary current regions to the north west and southwest our results show the potential density distribution and the corresponding cyclonic circulation in deep scs are primarily controlled by salinity variations in the deep basin

a detailed map of the 660 kilometer discontinuity beneath the izu bonin subduction zone dynamical processes in the earth s mantle such as cold downwelling at subduction zones cause deformations of the solid state phase change that produces a seismic discontinuity near a depth of 660 kilometers observations of short period shear to compressional wave conversions produced at the discontinuity yield a detailed map of deformation beneath the izu bonin subduction zone the discontinuity is depressed by about 60 kilometers beneath the coldest part of the subducted slab with a deformation profile consistent with the expected thermal signature of the slab the experimentally determined clapeyron slope of the phase transition and the regional tectonic history

crustal imprints of precambrian orogenesis in western laurentia crustal low velocity zones lvzs have been reported in active orogens such as the himalayas and the andes but rarely in stable cratonic regions in this study we provide compelling evidence for a significant midcrustal lvz beneath eastern central alberta an integral part of the precambrian canadian shield covered by thick phanerozoic sedimentary deposits this 200 km wide over 10 km thick midcrustal lvz is well resolved by shear velocity inversions using p to s receiver functions from more than 4600 earthquakes it is generally overlain by a high velocity upper crust in the depth range of 8 15 km especially in western central alberta which coincides with the previously documented winagami reflection sequence we interpret the lvz to be of granitic composition potentially in connection with the crystallization of partially molten crust during the paleoproterozoic eon in addition to the precambrian tectonic history of western laurentia which featured plate convergence conducive to crustal melting our crustal model is further supported by 1 a moderate spatial correlation between the lvz and heat flow and 2 shear velocities consistent with that of granite the well preserved winagami reflection sequence and the lvz are potential evidence of distinct episodes of magmatism and crust modification in the precambrian basement of the western canada sedimentary basin the existence of a broad crustal lvz suggests extensive subduction orogenesis and crustal melting during the precambrian assembly of the north american craton

determination and analysis of long wavelength transition zone structure using ss precursors summary global mapping of 410 and 660 km discontinuity topography and transition zone thickness has proven to be a powerful tool for constraining mantle chemistry dynamics and mineralogy numerous seismic and mineral physics studies suggest that the 410 km discontinuity results from the phase change of olivine to wadsleyite and the 660 km discontinuity results from the phase change of ringwoodite to perovskite and magnesiowustite underside reflections of the 410 and 660 km discontinuities arrive as precursors to ss with the recent development of a semi automated method of determining ss arrivals we have more than tripled the flanagan and shearer 1998a data set of handpicked ss waveforms we are able to increase resolution by stacking waveforms in 5 rather than 10 radius bins as well as increasing data coverage significantly in the southern hemisphere the resulting ss s410s and ss s660s times are heavily influenced by upper mantle velocity structure we perform a joint inversion for discontinuity topography and velocity heterogeneity as well as performing a simple velocity correction to the precursor differential times and find little difference between the two methods the 660 km discontinuity topography and transition zone thickness are correlated with velocities in the transition zone whereas the 410 km discontinuity topography is not in addition the 410 km discontinuity topography is not correlated with the 660 km discontinuity topography rather anticorrelated as expected due to the opposite signs of the clapeyron slopes of their respective phase changes these results suggest that whereas the topography of 660 km discontinuity could be dominated by thermal effects the topography of the 410 km discontinuity is likely dominated by compositional effects in addition unlike previous studies which find less topography on the 410 km discontinuity than on the 660 km discontinuity our 410 and 660 km topography have similar amplitudes

climatological distribution of aragonite saturation state in the global oceans aragonite saturation state arag in surface and subsurface waters of the global oceans was calculated from up to date through the year of 2012 ocean station dissolved inorganic carbon dic and total alkalinity ta data surface arag in the open ocean was always supersaturated 1 ranging between 1 1 and 4 2 it was above 2 0 2 0 4 2 between 40 n and 40 s but decreased toward higher latitude to below 1 5 in polar areas the influences of water temperature on the ta dic ratio combined with the temperature effects on inorganic carbon equilibrium and apparent solubility product k sp explain the latitudinal differences in surface arag vertically arag was highest in the surface mixed layer higher hydrostatic pressure lower water temperature and more co2 buildup from biological activity in the absence of air sea gas exchange helped maintain lower arag in the deep ocean below the thermocline aerobic decomposition of organic matter along the pathway of global thermohaline circulation played an important role in controlling arag distributions seasonally surface arag above 30 latitudes was about 0 06 to 0 55 higher during warmer months than during colder months in the open ocean waters of both hemispheres decadal changes of arag in the atlantic and pacific oceans showed that arag in waters shallower than 100 m depth decreased by 0 10 0 09 0 40 0 37 yr 1 on average from the decade spanning 1989 1998 to the decade spanning 1998 2010

future acidification of marginal seas a comparative study of the japan east sea and the south china sea the response of marginal peripheral seas to ocean acidification on short and long time scales is not well established through modeling we examine the future acidification of two adjacent marginal seas the south china sea scs and the japan east sea j es our results illustrate the importance of unique features in determining their acidification the j es basin will become completely undersaturated with regard to calcite rapidly in the next few decades while the scs basin will experience relatively slower acidification during its acidification the j es will continually act as a sink for atmospheric co2 whereas the scs will temporarily switch from a source to a sink during the peak pco2 interval only to return slowly to being a source again marginal sea acidification will be determined by multiple factors including their connections with the open ocean and their unique physical and biogeochemical dynamics in addition to the level of atmospheric co2

a detailed receiver function image of the upper mantle discontinuities in the japan subduction zone abstract we have imaged the upper mantle discontinuities in a 30 20 large region at the active continental margin of the japan subduction zone and neighboring areas using p to s converted phases from teleseismic records of permanent broadband stations the 410 km discontinuity is detected within 10 km of its global average position an interesting exception in its observation is a gap near 135 e very close to the slab penetration of the 410 km discontinuity and in an area where we have rather high data density the 660 km discontinuity reaches 700 km depth at two places where it is hit directly by the slab these data generally show good agreement with tomographic results both the 660 km discontinuity depression and the p velocity anomalies suggest about 400 500 k temperature deficit within the slab however no downward bending of the 660 km discontinuity is observed in eastern china where the flat lying slab is imaged by tomography this suggests that the slab does not cool the 660 km discontinuity in this region therefore the positive buoyancy required to keep the slab lying flat cannot have been provided by the negative clapeyron slope of the spinel perovskite phase transition another mechanism is needed which could possibly be metastable olivine in the cold core of the slab we have also imaged the shallower portion of the slab down to about 150 km underneath some seismic stations likely because metastable gabbro is still existing to this depth providing a sufficient velocity contrast a strong negative converted phase is observed at 150 200 km depth underneath a volcanic region in japan if real observed at one station only the zone which produces this conversion and which may begin exactly above the slab would require fluid fed melting

large accumulation of anthropogenic co2 in the east japan sea and its significant impact on carbonate chemistry received 19 december 2005 revised 10 july 2006 accepted 26 july 2006 published 22 november 2006 1 this paper reports on a basin wide inventory of anthropogenic co2 in the east japan sea determined from high quality alkalinity chlorofluorocarbon and nutrient data collected during a summertime survey in 1999 and total dissolved inorganic carbon data calculated from ph and alkalinity measurements the data set comprises measurements from 203 hydrographic stations and covers most of the east sea with the exception of the northwestern boundary region anthropogenic co2 concentrations are estimated by separating this value from total dissolved inorganic carbon using a tracerbased chlorofluorocarbon separation technique wintertime surface cfc 12 data collected in regions of deep water formation off vladivostok russia improve the accuracy of estimates of anthropogenic co2 concentrations by providing improved airsea co2 disequilibrium values for intermediate and deep waters our calculation yields a total anthropogenic co2 inventory in the east sea of 0 40 0 06 petagrams of carbon as of 1999 anthropogenic co2 has already reached the bottom of the east sea largely owing to the effective transport of anthropogenic co2 from the surface to the ocean interior via deep water formation in the waters off vladivostok the highest specific column inventory vertically integrated inventory per square meter of anthropogenic co2 of 80 mol c m 2 is found in the japan basin 40n 44n comparison of this inventory with those for other major basins of the same latitude band reveal that the east sea values are much higher than the inventory for the pacific ocean 20 30 mol c m 2 and are similar to the inventory for the north atlantic 66 72 mol c m 2 the substantial accumulation of anthropogenic co2 in the east sea during the industrial era has caused the aragonite and calcite saturation horizons to move upward by 80 220 m and 500 700 m respectively these upward movements are approximately 5 times greater than those found in the north pacific both the large accumulation of anthropogenic co2 and its significant impact on carbonate chemistry in the east sea suggest that this sea is an important site for monitoring the future impact of the oceanic invasion of anthropogenic co2

invariance of the carbonate chemistry of the south china sea from the glacial period to the holocene and its implications to the pacific ocean carbonate system abstract substantial and correlated changes in marine carbonate caco3 content of oceanic sediments commonly accompany the transitions from cold glacial periods to warm interglacial periods the south china sea scs is said to be ocean dominated at depth and its caco3 records should reflect and preserve the effects of changes in the carbonate chemistry of the western pacific ocean using published and newly acquired caco3 data and a model for carbonate compensation dynamics we show that a significant change with respect to carbonate saturation is unlikely to have occurred in the scs during the last glacial interglacial transition instead the results from a carbonate deposition model argue that the saturation state of the scs was largely invariant a separate diagenetic model argues that changes in sediment caco3 content can be explained by alterations in lithogenic input in turn this could indicate that the carbonate ion concentration of the western pacific at depths shallower than the sill to the scs ca 2 400 m has not changed appreciably between the last glacial period and the present interglacial

late pleistocene to recent climate change in cordoba province argentina geomorphological evidence abstract repeated episodes of climate change affected the cordoba plains during the late pleistocene and holocene many of the geomorphologic features of cordoba province were developed in response to climatic oscillations and their development can be correlated to changes in precipitation and hydrologic regimes alternating periods marked by dry climate and high evapotranspiration rates were interspersed with more humid intervals and can be correlated using stratigraphic and geomorphic evidence at the regional level the initial phase of the late pleistocene was characterized by significant loess deposition and the formation of large alluvial fans these sediments and landforms are representative of a dry climate the transition to the late pleistocene was marked by the initiation of a humid climate regime giving rise to enhanced fluvial activity and sedimentation expansion and integration of drainage networks and development of paludal areas and successions pedogenesis occurred in the interbasin areas involving precipitation of silica and sesquioxides during latest pleistocene early holocene time coinciding in part with the last glacial maximum a dry and cool climate resulted in widespread aeolian sand and loess deposition the early to mid holocene was characterized by humid subtropical conditions which became established throughout the region accompanied by pedogenic development of profiles with prominent bt horizons and further modification of drainage networks during the mid to late holocene these warm and humid conditions were replaced by a semiarid climate resulting in widespread aeolian deposition wind action formed deflation hollows and dune fields in several areas the climate reverted to subhumid and temperate conditions during the latter part of the late holocene and small areas of wetlands developed the little ice age was marked by climatic deterioration and the deposition of a thin layer of aeolian sediment the current climate of cordoba is subhumid and temperate

a comparison of the receiver structure beneath stations of the canadian national seismograph network three component broadband data from the recently deployed canadian national seismograph network provide a new opportunity to examine the structure of the crust and upper mantle beneath the canadian landmass receiver function analysis is an ideal method to use with this data set as it can provide constraints on the s velocity structure beneath each station of this seismograph network this analysis method is particularly useful in that it provides site specific information i e within 5 15 km of the station low velocity layers can be identified and it is possible to examine structure to upper mantle depths in this study receiver functions were computed for each of the 19 stations that made up the seismograph network in june 1994 five stations sampling a variety of tectonic environments including the appalachian orogen the canadian shield the western canadian sedimentary basin and the cascadia subduction zone were chosen for detailed modelling the results presented here are the first estimates of the s velocity structure beneath these five stations for those stations where comparisons can be made with seismic reflection and refraction results there is excellent agreement in eastern canada simple receiver functions and clear moho ps conversions at most stations indicate a relatively transparent crust and a moho depth of 40 45 km in northwestern canada moho ps phases indicate a crustal thickness of 33 38 km beneath inuvik northwest territories the moho is interpreted as two velocity steps separated in depth by 5 km and an upper mantle low velocity zone is near 47 km depth in western canada the data indicate a mid crustal low velocity zone beneath edmonton the moho of the subducting juan de fuca plate is interpreted at 52 krn depth beneath southern vancouver island several stations exhibiting complex receiver functions warrant further study they include stations at scheffewille quebec in the canadian shield deer lake newfoundland on the boundary of the grenville province and the appalachian orogen and yellowknife northwest territories at the intersection of the churchill and slave provinces and the western plains

global de correlation of the topography of transition zone discontinuities analysis of long period shear wave underside reflections from upper mantle discontinuities shows the shape of the 410 km discontinuity to be neither globally nor locally correlated with that of the 660 km discontinuity the long wavelength pattern of 410 topography is dominated by degree 1 spherical harmonics and has a reasonable correlation with the seismic velocity perturbations in the mantle above it the global topography of 660 dominated by degree 2 spherical harmonics is strongly correlated with shear wave velocity variations in the transition zone the poor correlation between the observed topography of the 410 and 660 km discontinuities is inconsistent with a simple model of large scale whole mantle flow thus implying a more complex pattern which includes at least temporary accumulation of subducted material in the transition zone ringwood and irifune nature 331 1988 131 136 tackley et al nature 361 1993 699 704 the modest seismic discontinuity at 520 km is well observed when the reflections are under mid age oceans but is not observed when they are under continental shields interpretation of this observation in terms of olivine depletion in the deep continental mantle indicates the possible existence of continent ocean chemical heterogeneity at depths exceeding 500 km

geochemistry of surface waters and weathering effects in the upper catchment of the ctalamochita river cordoba s sierras pampeanas central argentina the chemical compositions of waters from the upper basin of the ctalamochita river draining the cordoba pampean ranges were analyzed to determine the chemical signature related to different forcings geochemical processes and solutes sources the catchment has four sub basins santa rosa river grande river quillinzo river and de los sauces river most of the riverine chemical compositions are dominated by the hco3 ca2 type to ca2 na mg2 the specific conductivity is higher in the santa rosa and de los sauces rivers 347 59 and 409 00 s cm respectively than in the grande and quillinzo rivers 125 56 and 87 54 s cm respectively mineral hydrolysis of andesine and oligoclase and the dissolution of calco magnesian limestone are the main dissolved solids contributors to the river waters higher contribution of bicarbonate ions is associated to those sub basin having quarry mining activity saturation indexes show that the santa rosa and de los sauces rivers are saturated with calcite dolomite and talc

carbonate mineral saturation states along the u s east coast to assess the impact of ocean acidification on the carbonate chemistry of the shelf waters off the southeastern united states south atlantic bight sab we measured carbonate mineral saturation states from january 2005 to may 2006 the findings reveal that aragonite varag 2 6 4 0 and calcite vcal 4 1 6 0 saturation states were considerably higher than those recently reported along the west coast of north america different water mass age between the atlantic and pacific oceans during global ocean circulation is the primary reason for the higher carbonate mineral saturation states in the sab than along the west coast the contrasting water temperatures in the two coasts contribute to such differences both upwelling and freshwater discharge also play important roles in controlling saturation state carbonate mineral saturation in the surface water of the west coast is strongly controlled by the upwelling of high salinity low temperature low oxygen and low ph deep water in comparison saturation states in the surface water of the sab coast are rarely affected by upwelling instead they are strongly influenced by the input of low saturation state water from rivers continued increases of atmospheric co2 under the intergovernmental panel on climate change b1 emission scenario will decrease the carbonate mineral saturation states by up to 40 by the end of this century and aragonite will approach undersaturation near the coast

low velocity zone atop the 410 km seismic discontinuity in the northwestern united states the seismic discontinuity at 410 km depth in the earth s mantle is generally attributed to the phase transition of mg fe 2sio 4 from the olivine to wadsleyite structure variation in the depth of this discontinuity is often taken as a proxy for mantle temperature owing to its response to thermal perturbations for example a cold anomaly would elevate the 410 km discontinuity because of its positive clapeyron slope whereas a warm anomaly would depress the discontinuity but trade offs between seismic wave speed heterogeneity and discontinuity topography often inhibit detailed analysis of these discontinuities and structure often appears very complicated here we simultaneously model seismic refracted waves and scattered waves from the 410 km discontinuity in the western united states to constrain structure in the region we find a low velocity zone with a shear wave velocity drop of 5 on top of the 410 km discontinuity beneath the northwestern united states extending from southwestern oregon to the northern basin and range province this low velocity zone has a thickness that varies from 20 to 90 km with rapid lateral variations its spatial extent coincides with both an anomalous composition of overlying volcanism and seismic receiver function observations observed above the region we interpret the low velocity zone as a compositional anomaly possibly due to a dense partial melt layer which may be linked to prior subduction of the farallon plate and back arc extension the existence of such a layer could be indicative of high water content in the earth s transition zone

loess of southern south america abstract loess and loessoid loess like reworked loess sediments extend across the chaco pampean plains and the nw mountain environments of argentina and in neighbouring countries paraguay brazil uruguay bolivia loessoid sediments are much more abundant than primary loess the beginning of the loessoid sedimentation cycle was related to a phase of late miocene orogeny in the andes the plio pleistocene record is mostly composed of loessoid sediments modified by pedogenesis which produced welded palaeosols the late pleistocene holocene loess record reveals a heterogeneous composition across the region coarse textures and an andean derived volcanic composition prevail in the southern pampas finer textures and material coming from the andes and the other two sources sierras pampeanas and the parana basin characterize the loess deposits of the northern pampas and the eastern chaco a southern patagonian source is also suggested for the mountain valley loess of tucuman although a western andean provenance has been proposed it is believed that the material in the western chaco was derived from the bolivian andes loess deposition was related to a multistage transport mechanism involving fluvial and aeolian processes inferred westerly and southwesterly wind directions as dominant carriers of the aeolian deposits are in agreement with westerly palaeowind simulations using climate models however the role played by westerly tropospheric winds and northerly winds remains to be established

deepwater overflow through luzon strait 1 this study examines water property distributions in the deep south china sea and adjoining pacific ocean using all available hydrographic data our analysis reveals that below about 1500 m there is a persistent baroclinic pressure gradient driving flow from the pacific into the south china sea through luzon strait applying hydraulic theory with assumptions of zero potential vorticity and flat bottom to the luzon strait yields a transport estimate of 2 5 sv 1 sv 106 m3 s 1 some implications of this result include 1 a residence time of less than 30 years in the deep south china sea 2 a mean diapycnal diffusivity as large as 10 3 m2 s 1 and 3 an abyssal upwelling rate of about 3 10 6 m s 1 these quantities are consistent with residence times based on oxygen consumption rates the fact that all of the inflowing water must warm up before leaving the basin implies that this marginal sea contributes to the water mass transformations that drive the meridional overturning circulation in the north pacific density distributions within the south china sea basin suggest a cyclonic deep boundary current system as might be expected for an overflow driven abyssal circulation

rock varnish microlamination dating of late quaternary geomorphic features in the drylands of western usa abstract varnish microlamination vml dating is a correlative age determination technique that can be used to date and correlate various geomorphic features in deserts in this study we establish a generalized late quaternary i e 0 300 ka varnish layering sequence for the drylands of western usa and tentatively correlate it with the specmap oxygen isotope record we then use this climatically correlated varnish layering sequence as a correlative dating tool to determine surface exposure ages for late quaternary geomorphic features in the study region vml dating of alluvial fan deposits in death valley of eastern california indicates that during the mid to late pleistocene 5 15 ky long aggradation events occurred during either wet or dry climatic periods and that major climate shifts between glacial and interglacial conditions may be the pacemaker for alteration of major episodes of fan aggradation during the holocene interglacial time however 0 5 1 ky long brief episodes of fan deposition may be linked to short periods of relatively wet climate vml dating of alluvial desert pavements in death valley and the mojave desert reveals that pavements can be developed rapidly

carbonate compensation dynamics 1 carbonate saturation zsat and compensation zcc depths change with deep ocean acidification and basification we present simple explicit mechanistic formulas for the positions of these two critical depths in particular zcc is expressed as a function of the mean dissolved carbonate ion concentration of the deep ocean co3 d the supply of dissolvable caco3 fc and the dissolution rate constant at the sediment water interface kc which we show to be essentially mass transfer controlled calculations reveal that zsat and zcc are today some 0 9 km apart and will rise and separate by as much as 1 7 km with acidification conversely if co3 d increases zsat and zcc will deepen but their separation will asymptote to 0 7 km

synchrony of southern hemisphere late pleistocene arid episodes a review of luminescence chronologies from arid aeolian landscapes south of the equator abstract luminescence dating chronologies that have been reported in various studies of late pleistocene arid land aeolian sequences from australia southern africa and south america are reviewed with the objective of determining whether any pan hemispheric synchroneity existed in the timing of landscape responses to late quaternary climate changes south of the equator the results broadly show that contemporaneous regional arid land aeolian activity occurred in australia and southern africa during the periods ca 65 41 and 36 9 ka the relatively limited luminescence data from the south american subcontinent also point to recurrent arid land aeolian deposition between 63 and 8 ka with increasing frequency in the period ca 32 8 ka records from all three continents suggest a period of reduced aeolian activity between 41 and 36 ka overall the data are indicative of extensive landscape instability of the low to mid latitudes in the southern hemisphere during the last glacial period particularly at the last glacial maximum which accords with mainstream opinions aeolian activity during the holocene has generally been localised the rigour with which comparisons can be made between the different studies however is constrained by variations in practices between laboratories and changes that have occurred to luminescence dating procedures over the years

neogene and quaternary tectonics of the eastern sierras pampeanas argentina active intraplate deformation inboard of flat slab subduction 1 the ranges of the eastern sierras pampeanas are located 600 km east of the andean cordillera in central argentina and have been interpreted to be a response to shortening related to flat slab subduction of the nazca plate uplift of the ranges has been broadly documented to occur during neogene time but many questions remain regarding the timing and style of deformation and the subsurface structural configuration in this study we address these unknowns with observations at multiple scales integrate our results into a tectonic model for the area and discuss how our structural interpretation fits with more regional tectonic models our major findings are 1 the range bounding faults thrust late proterozoic to cambrian schist and gneiss over poorly dated pliocene to pleistocene alluvial strata the timing of fault displacement and age of footwall strata suggest that deformation may have been active at least by pliocene time 2 apatite and zircon u th he thermochronometry exhibits cooling ages that range from permian to early jurassic time and suggests that rock exhumation in the area is less than 2 3 km since that time 3 deploying a local seismic array allowed for locating seismicity and calculating receiver functions these observations indicate that the moho lies at a depth of 37 km and that a midcrustal discontinuity appears to correspond to a detachment zone between 15 and 20 km depth and aligns with a plane of seismicity in our tectonic model the craton appears to act as a rigid backstop to the eastward propagation of stresses from the shallowly subducting slab deformation then propagates back to the west via westward verging faults along a midcrustal detachment

waveform inversion of ss precursors an investigation of the northwestern pacific subduction zones and intraplate volcanoes in china abstract the arrival time and amplitude of underside reflections from mantle seismic discontinuities ss precursors have made major contributions to the understanding of mantle composition and dynamics in this study we introduce a nonlinear waveform inversion technique to simultaneously constrain shear velocities and discontinuity depths beneath the northwestern pacific subduction system based exclusively on a large ss precursor waveform dataset we are able to clearly delineate the morphology of the descending pacific plate which flattens at the base of the upper mantle and extends westward by 1500 km toward northern central china our grid search yields the maximum correlation between shear velocity and transition zone thickness at an angle of 30 consistent with the reported average slab dip beneath the study region the strongly positive correlation suggests predominantly thermal rather than compositional variations along the descending pacific plate the joint depth velocity solution also shows a 5 10 km depression of the 410 km discontinuity and an average decrease of 1 2 in upper mantle shear velocity beneath the intraplate volcanic fields in northeastern china this anomaly which reaches the middle of the upper mantle transition zone beneath the changbai hotspot initiates at a significantly shallower 320 km depth beneath the wudalianchi region high amplitude reflections at depths greater than 410 km suggest a water poor melt layer in possible association with 1 decompression melting from passive upwelling and or 2 active upwelling through a slab window

historical climatic extremes as indicators for typical scenarios of holocene climatic periods in the pampean plain abstract the holocene has been marked by two different climatic periods in the pampas one 8 5 3 5 kyr b p characterized by temperatures and precipitation higher than today and the other 3 5 1 4 kyr b p semiarid generating parabolic dunes the humid period produced intense pedogenesis down to 40 lat s and a mobilization of iron oxides to 30 lat s which means tropical climate with temperatures above 20 c and precipitation higher than 2000 mm yr sand deflation and development of parabolic dunes occur under climates with 300 400 mm yr this contribution is based on geological and physical proxies typical weather scenarios of those climates are sporadically reproduced today during extremely humid or dry periods on that basis meteorological parameters of years beyond the thresholds of 2000 and 400 mm yr were processed dry periods were characterized by a large thermal amplitude frosts and stronger winds reproducing the continental anticyclonic circulation of the late holocene humid extremes were warmer than normal lower thermal amplitude with rains produced by local convection processes typical scenarios with precipitation above 2000 mm yr are 21 c mean temperature ca 1 c higher than the present record 27 c maximal annual temperatures 16 c minimal annual temperatures more than 1 c higher than the present as a consequence thermal amplitude was smaller than today virtually without frosts characteristic parameters of the late holocene were mean annual precipitation ca 350 mm yr 15 c mean temperature 22 c maximal annual temperatures 8 c minimal annual temperatures showing significative shifts in the dry season lower than normal monthly maximal and mean temperatures higher than today the result is a thermal amplitude larger than today probably higher quantity of frosts per year stronger winds and lower relative air humidity in comparison with the humid climate extreme complete the scenario

geomorphological study of the cafayate dune field northwest argentina during the last millennium abstract the cafayate depression is a dry valley located in the pre andean region of northwest argentina the area shows the development of a large dune field its significance has been established from geomorphological and mineralogical evidence grain shape characteristics and chronological data osl dating archaeological remains and historical data the dating results were between 1000 1100 ad to1740 1830 ad showing that the aeolian dynamics remained active during the last millennium it was not possible to identify stabilised phases marked by ruptures or paleosol development nevertheless other regional and local proxies from northwest argentina archaeological documentary etc were used to complete the interpretative framework to propose the paleoenvironmental evolution of the area in addition human activity and land use must be considered as a complementary factor affecting aeolian dynamics during the most recent stage

holocene 4 5 1 7 cal kyr bp paleoenvironmental conditions in central argentina inferred from entire shell and intra shell stable isotope composition of terrestrial gastropods the isotopic fingerprint of terrestrial gastropods has been increasingly used as a credible natural paleoenvironmental archive most published work has used this proxy at tropical and temperate latitudes of the northern hemisphere and focused on entire shell analysis the present study provides entire shell and intra shell isotopic profiles to infer average and seasonal late holocene environmental conditions in central argentina 30 s shells of plagiodontes daedaleus gastropoda odontostomidae were retrieved from the alero deodoro roca sector b site one of the few archaeological sites in central argentina rich in shells collected by pre hispanic hunter gatherer groups ancient entire shells exhibited values that were 2 5 higher in 13c and 1 8 higher in 18o than modern individuals pointing to higher abundance of c4 plants and overall drier conditions lower relative humidity and or higher rain 18o during 4 5 1 7 cal kyr bp than today in agreement with published regional proxies intra shel

global variability of transition zone thickness 1 we analyze recordings from more than 3000 shallow earthquakes and measure s410s s660s differential travel times on a global scale these differential times are obtained using a novel cross correlation technique that eliminates effects associated with a priori assumptions of crustal thickness and velocity variations above the upper mantle transition zone our measurements show absolute perturbations up to 8 s from the global average 242 km which imply transition zone thickness variations of 20 km on a length scale of 2000 km the transition zone under major subduction zones e g the western pacific and south america is significantly thicker than the global average this could be associated with large scale depressions of the 660 km discontinuity due to the accumulation of cold oceanic lithosphere at the base of the upper mantle a narrow transition zone is observed under the central pacific and northern atlantic oceans we also observe a modest anticorrelation between s410s s660s times and the delay times of shear waves predicted using s12 wm13 su et al 1994 in the transition zone which suggests considerable thermal influence on the large scale topography of the 410 and 660 km discontinuities the lack of a stronger anticorrelation suggests that 1 compositional heterogeneities may be present and 2 a significant fraction of thermal anomalies near the transition zone do not extend through the transition zone and influence both the 410 and the 660 km discontinuities a regional analysis shows that the transition zone is on average 6 8 km thicker under continents than under oceans this implies a temperature difference of 50 70 c however we do not observe a clear correlation between thickness and the age of the crust

the tsushima warm current through tsushima straits estimated from ferryboat adcp data abstract current structures across the tsushima straits are studied using results from long term acoustic doppler current profiler adcp observations by a ferryboat between hakata and pusan conducted since february 1997 two maxima of the northeastward current are observed in the central parts of the eastern and western channels and the maximum velocity in the western channel is stronger than that of the eastern channel downstream of the tsushima islands a southwestward countercurrent is observed associated with a pair of cyclonic and anticyclonic eddies in the western channel the deep countercurrent is observed pronouncedly on the bottom slope of the korean side from summer to winter the volume transport of the tsushima warm current through the straits has strong seasonal variation with a minimum in january and two maxima from spring to autumn double peaks the spring peak of the volume transport through the eastern channel is more pronounced than the autumn peak and the autumn peak of the west

gas hydrate dissociation prolongs acidification of the anthropocene oceans anthropogenic warming of the oceans can release methane ch4 currently stored in sediments as gas hydrates this ch4 will be oxidized to co2 thus increasing the acidification of the oceans we employ a biogeochemical model of the multimillennial carbon cycle to determine the evolution of the oceanic dissolved carbonate system over the next 13 kyr in response to co2 from gas hydrates combined with a reasonable scenario for long term anthropogenic co2 emissions hydrate derived co2 will appreciably delay the neutralization of ocean acidity and the return to preindustrial like conditions this finding is the same with ch4 release and oxidation in either the deep ocean or the atmosphere a change in caco3 export coupled to ch4 release would intensify the transient rise of the carbonate compensation depth without producing any changes to the long term evolution of the carbonate system overall gas hydrate destabilization implies a moderate additional perturbation to the carbonate system of the anthropocene oceans

dating fluvial terraces with and profiles application to the wind river wyoming abstract fluvial strath terraces provide a record of river incision and the timing of climatic perturbations to the fluvial system dating depositional surfaces like terraces that are older than the range of 14 c however is difficult we employ a cosmogenic radionuclide crn profile technique that addresses a major problem of crn dating on such surfaces nuclide inheritance by measuring 10 be and 26 al profiles we constrain the exposure age and the mean crn inheritance for the deposit the crn profile also yields a self check on the assumptions underlying the method we report our attempts to date terraces along the wind river wy like many sequences of western north american fluvial terraces these are inferred to reflect oscillation between glacial and interglacial conditions in the headwaters previous dating of some of these terraces and the associated terraces and glacial deposits makes this a unique location to compare dating methods dates from five sites along the bull lake glacial correlative terrace wr 3 are 118 125 ka which agrees with dates on bull lake age moraines and independent age estimates on the terrace and is consistent with the model of terrace glacial relationship crn inheritance is significant and highly variable requiring it be considered despite the additional sampling complexity assuming all inheritance in wr 3 deposits arises during exhumation in the headwaters we obtain minimum mean rates of exhumation of 13 130 m my for the source rocks alternatively assuming the crns are inherited during clast transport the time of fluvial transport from source to terrace is 10 ka it increases downstream and is lower for sand than cobbles the crn ages for older terraces wr 7 300 ka and wr 15 510 ka are lower by 50 than previous estimates based on tephrochronology the most plausible explanation is eolian deflation of a once thicker loess cover on the terrace surfaces mean thicknesses of loess of 0 5 1 5 m are required to reconcile these concentrations of crn with the previous estimates of age difficulty in dating the older terraces emphasizes that geologic caution independent estimates of age and multiple sample sites should still be part of dating depositional surfaces with crns even when employing the inheritance correction technique

carbonate chemistry of the sea of japan the alkalinity and total co2 data were collected during the kuroshio edge exchange processes marginal sea studies expedition july 28 to august 5 1992 in the sea of japan the concentrations of normalized alkalinity nta ta 35 s s represents salinity and normalized total co2 ntco2 tco2 35 s in the deep water are fairly low relative to that of the northwest pacific ocean indicating relatively little caco3 dissolution and organic carbon decomposition in the subsurface waters of the sea of japan a benthic front between the deep water and the bottom water can be characterized by discontinuities of dissolved oxygen and ntco2 at about 2000 m the bottom water is quite homogeneous with 0 1 0 05 c s 34 07 0 005 dissolved oxygen 215 5 mol kg nta 2373 5 mol kg and ntco2 2297 5 mol kg the inorganic carbon organic carbon ratio shows that about a 15 increase in ntco2 of the deep water is contributed by the inorganic caco3 dissolution this is rather low compared to the open pacific ocean values of 30 40 the degrees of saturation with respect to calcite and aragonite show that the deep water is undersaturated with respect to calcite below 1300 m the water below 300 m is undersaturated with respect to aragonite excess co2 is present from surface to bottom confirming rapid turnover of the sea of japan deep water 100 years turnover time reported previously based on tritium freons 11 12 and 226ra data previous age estimation of 300 years for deep waters based on 14c data was inconsistent with the above results recalculation based on proper prebomb 14c value gives an age of about 120 years for deep sea of japan water overall the sea of japan contains 3 1 0 5 1014 g excess carbon

japan sea thermohaline structure and circulation part ii a variational p vector method abstract the second part of this work investigates the seasonal variabilities of the japan east sea jes circulation using the u s navy generalized digital environmental model gdem climatological temperature and salinity dataset public domain on a 0 5 0 5 grid a variational p vector method was developed to invert the velocity field the gdem for the jes was built up on historical 1930 97 136 509 temperature and 52 572 salinity profiles the climatological mean and seasonal variability of the current systems are well inverted especially the tsushima warm current and its bifurcation the east korean warm current ekwc the japan nearshore branch the confluence of the ekwc and the north korean cold current near the korean coast and flows northeastward along the subpolar front and a mesoscale anticyclonic eddy in the ulleng tsushima basin furthermore this method has the capability to invert flow reasonably well across the shallow straits such as the tsushima korea tsugaru and soya strait

thermohaline circulation in the deep south china sea basin inferred from oxygen distributions 1 on the basis of the historical oxygen data available distributions of dissolved oxygen were analyzed in detail to investigate the thermohaline circulation in the south china sea scs the analyses confirmed the existence of a layer of minimal oxygen content at intermediate depths of the basin which shows a low oxygen 1 6 ml l 1 core in the southern basin with water ages shorter than 100 years after entering the scs and which appears isolated from its counterpart of the western philippine sea north to the core along the northern slope there is a band of oxygen rich water in both upper and intermediate layers above 700 m the band can be attributed to the intrusion of high oxygen water through the luzon strait while vertical flux appears to be responsible between 700 and 1500 m the oxygen distribution provides additional evidence for a sandwiched vertical structure in transports through the luzon strait with outflows in the intermediate layer and inflows above and below while the abyssal water of the scs is being replenished by the deep inflows an abrupt change of water properties was observed in both upper and intermediate layers across the luzon strait suggesting possible domination of local vertical mixing over horizontal spreading of inflows in the northern scs a four cell conceptual model was proposed for the thermohaline circulation which consists of a three layer cross basin exchange cell in the luzon strait an active ventilation cell in the upper and intermediate layers along the northern slope an abyssal replenishment cell in the deep and a cyclonic recirculation cell in the interior basin

holocene changes in trophic states of shallow lakes from the pampa plain of argentina changes in trophic status of shallow lakes from the southeastern pampa plain of argentina are evaluated based on the relative presence of submerged macrophytes and phytoplankton the evolution of lake lonkoy is reconstructed for the last 5000 years using pollen non pollen palynomorphs npps and macrofossil remain analyses revealing three main lake stages a macrophyte dominated clear lake prevailed until 670 cal yr bp afterwards the lake changed to a turbid phytoplankton dominated state recently the lake has turned to a turbid phase caused by resuspended sediment these results are compared with two other paleolimnological records from the region lakes hinojales and nahuel ruca revealing a similar late holocene evolution with a shift from a macrophyte to phytoplankton dominated lake occurring at broadly the same time the shift of states may be attributed to a shift in climate after 1000 cal yr bp towards wetter conditions during the medieval climate anomaly

millennial scale varnish microlamination dating of late pleistocene geomorphic features in the drylands of western usa abstract varnish microlamination vml dating is a climate based correlative age determination technique used to correlate and date various geomorphic features in deserts in this study we establish a generalized late pleistocene 18 74 ka millennial scale microlamination sequence in fine grained fast accumulating rock varnish for the drylands of western usa radiometrically calibrate the sequence and correlate it with the 18 o record in the gisp2 greenland ice core we then use this climate correlated varnish microstratigraphy to estimate surface exposure ages for radiometrically dated late pleistocene geomorphic features in the study region the vml dating of debris flow deposits on the sehoo recessional shorelines of lake lahontan at the jessup embayment of central nevada yields a minimum limiting age of 14 95 15 95 ka in good agreement with a calibrated 14 c age of 15 22 0 12 ka for the timing of the lake recession the vml dating of a giant ejecta block on the rim of meteor crater in northern arizona yields a minimum limiting age of 49 15 ka closely matching a thermoluminescence tl age of 49 3 ka and slightly younger than a recently updated cosmogenic 36 cl age of 56 0 2 4 ka for the meteor impact event the vml dating of distal q2c fan surfaces on hanaupah canyon alluvial fan in death valley california yields a minimum limiting age of 73 55 ka in accord with cosmogenic 36 cl depth profile ages of 66 22 14 ka and 72 24 20 ka for the same fan deposits the close agreement between the vml age estimates and the independently derived radiometric ages for these geomorphic features attests to the validity and reliability of millennial scale vml dating to further assess its potential in desert geomorphological research we use the vml method to study alluvial fan responses to millennial scale climatic changes the vml dating of a small tributary fan in death valley reveals two episodes of fan aggradation one ceasing at 73 55 86 75 ka during the dry period of the last interglacial mis 5a and the other finishing at 66 15 ka during the wet period of the last glacial mis 4 the vml and 36 cl dating of the distal q2c fan surfaces on hanaupah canyon fan reveal two episodes of large scale fan aggradation ended at 72 24 20 ka and 73 55 ka during the wet period of mis 4 fanhead incision and associated within channel or fantoe aggradation are found to take place during the relatively dry period of the glacial to interglacial climatic transition 12 24 ka and the holocene interglacial dry period 0 12 ka these data indicate that on the millennial to sub milankovitch timescale 10 3 10 4 years fan aggradation is a discrete sedimentational process under various climatic conditions because fan aggradation is ultimately controlled by the intensity and frequency of precipitation events which in turn are modulated by major climatic oscillations such as heinrich events dansgaard oeschger do events and glacial interglacial shifts these major climatic changes could be the pacemaker of regionally contemporaneous large area fan segmentation