the shape of mars and the topographic signature of the hemispheric dichotomy reanalysis of occultation data from the mariner 9 and viking orbiter spacecraft to determine the shape of mars indicated that the hemispheric dichotomy is not a fundamental feature of the shape of the planet it is a consequence of an approximately 3 kilometer offset between mars9s center of mass and center of figure and the boundary along most of its length consists of broad gradual surface slopes over distances of thousands of kilometers this result was supported by analysis of high spatial resolution earth based radar topographic profiles any successful model for the origin of the dichotomy must explain a planet with an ellipsoidal shape and a long wavelength gradual topographic transition between the northern and southern hemispheres

biogenic silica fluxes and accumulation rates in the gulf of california the gulf of california though small in size plays an important role in the global silica cycle the seasonal pattern of biogenic silica flux in the gulf is closely related to that of phytoplankton biomass levels and is controlled by changes in weather and hydrographic conditions the highest opal fluxes approximately 0 35 g center dot m sup minus 2 center dot d sup minus 1 occur during winter and spring and they are comparable to those measured in some of the most productive ecosystems of the world approximately 15 25 of the biogenic silica produced in surface waters is preserved in gulf sediments a figure significantly higher than the average global ocean preservation rate however the flux of opal at 500 m water depth is less than 25 of that being produced at the surface suggesting that most of the recycling of biogenic silica in the gulf of california occurs in the upper water column 28 refs 3 figs

mars interior structure and excitation of free oscillations based on available chemical models of the planet philos trans r soc london 349 1994 285 supply and loss of volatile constituents during the accretion of terrestrial planets in s k attreya j b pollack m s matthews eds origin and evolution of planetary and satellite atmospheres univ arizona press pp 268 288 icarus 126 1997 373 phys earth planet inter 112 1999 43 space sci rev 92 2000 34 a new set of global models of the martian interior has been constructed a model comprises four submodels a model of the outer porous layer a model of the crust a model of the mantle and a model of the core the first 10 11 km layer is considered as an averaged transition from regolith to consolidated rock the mineral composition of the crustal basaltic rock varies with depth because of the gabbro eclogite phase transition as a starting point for mantle modeling the experimental data obtained by bertka and fei j geophys res 102 1997 525 earth planet sci lett 157 1998 79 along the areotherm have been used iron content of the mantle being varied the measured or estimated up to now elastic properties for a set of mantle minerals are used seismic velocities determined from new high p t data on elastic properties are 2 3 lower than the velocities calculated earlier new high p t measurements of the density of fe fe fes and feh enable us to refine the core model taking into account available chemical models and the fact that noticeable amount of hydrogen could enter the martian core during its formation solar syst res 30 1996 456 such parameters as a ferric number of the mantle fe sulfur and hydrogen content in the core are varied the following tendency is seen the presence of hydrogen leads to the increase of the fe si ratio and decreases fe in the mantle due to the increase of the core radius the higher sulfur and hydrogen content in the core and the smaller mantle fe the less likely a perovskite layer exists the modeling shows that to obtain the fe si ratio up to the chondrite ratio of 1 71 more than 50 mol of hydrogen should be incorporated into the core in the second part of the paper based on the available estimates of the martian seismic activity and the sensitivity of current instruments the amplitudes for different types of free oscillations have been estimated it is found down to what depth the normal modes can sound the planetary interiors a marsquake with a seismic moment of 10 25 dyn cm is required for spheroidal oscillations with 17 to be detected these spheroidal modes are capable sounding the outer layers of mars down to a depth of 700 800 km

composition of mars constrained using geophysical observations and mineral physics modeling abstract we use the total mass possible core radius and the observed mean moment of inertia factor of mars to constrain mineralogical and compositional structures of mars we adopt a liquid fe s system for the martian core and construct density models of the interior of mars for a series of mantle compositions core compositions and temperature profiles the moment of inertia factor of the planet is then calculated and compared to the observation to place constraints on mars composition based on the independent constraints of total mass possible core radius of 1630 1830 km and the mean moment of inertia factor 0 3645 0 0005 of mars we find that fe content in the martian mantle is between 9 9 and 11 9 mol al content in the martian mantle smaller than 1 5 mol s content in the martian core between 10 6 and 14 9 wt the inferred fe content in the bulk mars lies between 27 3 and 32 0 wt and the inferred fe si ratio in mars between 1 55 and 1 95 within a range too broad to make a conclusion whether mars has the same nonvolatile bulk composition as that of ci chondrite we also conclude that no perovskite layer exists in the bottom of the martian mantle based on the inferred density models we estimate the flattening factor and j 2 gravitational potential related to the hydrostatic figure of the rotating mars to be 5 0304 0 0098 10 3 and 1 8151 0 0065 10 3 respectively we also discuss implications of these compositional models to the understanding of formation and evolution of the planet

rhenium and molybdenum enrichments in sediments as indicators of oxic suboxic and sulfidic conditions of deposition abstract the trace elements re and mo both behave conservatively in seawater yet are strongly enriched in reducing sediments their potential for authigenic enrichment above crustal concentrations is greater than for many other elements due to the high ratio of metal sw metal crust we present sedimentary re and mo data from box and multi cores spanning a range of redox conditions from well oxygenated sites to locations with substantial sulfide concentrations at the oxic sites re and mo as expected accumulate at concentrations close to their crustal abundances re shows substantial enrichment in suboxic absence of o 2 and h 2 s sediments of the sea of japan in sediments within the oxygen minimum of the pakistan margin as well as in sediments underlying the sulfide bearing waters of the black sea and saanich inlet re enrichment occurs in these cores just below the depths of fe and u reduction only in the sediments underlying the sulfidic waters of the black sea and saanich inlet is there substantial authigenic mo accumulation absence of re and mo enrichments in sediment trap samples from the sulfide bearing basins suggests that the addition of both metals occurs at or below the sediment water interface the re and mo concentration profiles are modeled to hindcast the removal depth of re and mo in the sediments which along with the re mo ratio determine whether oxic suboxic or sulfidic conditions were present in the water column or in the sediments in the past using this approach historical redox conditions can be inferred even in environments such as continental margins where a substantial lithogenic component can obscure authigenic enrichments of other metals

geochemical cycles in sediments deposited on the slopes of the guaymas and carmen basins of the gulf of california over the last 180 years sediments deposited on the slopes of the guaymas and carmen basins in the central gulf of california were recovered in two box cores q mode factor analyses identified detrital clastic carbonate and redox associations in the elemental composition of these sediments the detrital clastic fraction appears to contain two source components a more mafic component presumably derived from the sierra madre occidental along the west coast of mexico and a more felsic component most likely derived from sedimentary rocks mostly sandstones of the colorado plateau and delivered by the colorado river the sediments also contain significant siliceous biogenic components and minor calcareous biogenic components but those components were not quantified in this study redox associations were identified in both cores based on relatively high concentrations of molybdenum which is indicative of deposition under conditions of sulfate reduction decreases in concentrations of molybdenum in younger sediments suggest that the bottom waters of the gulf have became more oxygenated over the last 100 years many geochemical components in both box cores exhibit distinct cyclicity with periodicities of 10 20 years the most striking are 20 year cycles in the more mafic components e g titanium particularly in sediments deposited during the 19th century in that century the titanium cycles are in very good agreement with warm phases of the pacific decadal oscillation implying that at times of greater influx of titanium rich

evidence for decreasing south asian summer monsoon in the past 160 years from varved sediment in lake xinluhai tibetan plateau 1 we report glacial varves in the sediment of lake xinluhai tibetan plateau independent data of 137cs and 210pb indicate that these are annually deposited varves varves appear as rhythmic units of light colored silt layer capped by a dark clay layer under microscope varve thickness in lake xinluhai is sensitive to precipitation because sediment accumulation is strongly affected by monsoon rainfall in the area a general decreasing trend can be observed in the varve thickness over the past 160 years spectral analyses of the varve record are dominated by cycles which are similar to enso periodicities it implies that the decreasing trend of the south asia monsoon may be linking with enso spatially the decreasing trend can be observed across different proxy records in the south of the tibetan plateau although arguments still remain for the dynamic mechanisms and spatial rainfall difference the south asian summer monsoon could be weakened due to rising temperatures

water column anomalies associated with hydrothermal activity in the guaymas basin gulf of california abstract sea floor hydrothermal activity in the guaymas basin gulf of california is quite different from that associated with ridge crest spreading centers injection of hydrothermal fluids occurs in the bottom of a semi enclosed basin and water column anomalies produced by this activity increase to much higher values than in the open ocean in the guaymas basin the hydrothermal venting generates large clouds of fine suspended particulate matter spm 100 300 m above active mounds and chimneys these hydrothermal clouds have potential temperature anomalies of about 0 010 0 020 c are enriched in dissolved silica particulate manganese and depleted in dissolved oxygen relative to areas away from the vents the particulate manganese values increase from about 3 nmol kg at 1000 m well above the enclosing topography of the subsill basin to 100 150 nmol kg in the clouds of spm and in the bottom nepheloid layer the particulate mn in the hydrothermal clouds appears to originate from both direct precipitation of dissolved mn2 injected by the vents and entrainment of mn rich spm in the rising hydrothermal plumes injection of silica rich vent fluids into the basin bottom waters produces a silica anomaly of 10 15 mol relative to the other deep basins of the gulf of california spillover of guaymas basin deep water produces a silica plume just above the basin sill depth which is detectable to the mouth of the gulf a simple two endmember mixing model indicates that the deep waters of the guaymas basin contain approximately 0 1 hydrothermal fluid oxygen anomalies associated with the hydrothermal clouds are on the order of 5 mol relative to regions away from active vents the basin as a whole shows a depletion in oxygen of about 13 mol relative to the other deep basins of the gulf the mixing model shows that this oxygen consumption can be explained by the oxidation of dissolved sulfide and methane injected by the hydrothermal vents box models of the deep basins of the southern gulf of california indicate that the guaymas basin has a significantly higher source term for dissolved silica and sink term for dissolved oxygen than the other basins the calculated flux of hydrothermal fluids into the guaymas basin is 10 12 m3 s

an improved gravity model for mars goddard mars model 1 doppler tracking data of three orbiting spacecraft have been reanalyzed to develop a new gravitational field model for the planet mars goddard mars model 1 gmm 1 this model employs nearly all available data consisting of approximately 1100 days of s band tracking data collected by nasa s deep space network from the mariner 9 and viking 1 and viking 2 spacecraft in seven different orbits between 1971 and 1979 gmm 1 is complete to spherical harmonic degree and order 50 which corresponds to a half wavelength spatial resolution of 200 300 km where the data permit gmm 1 represents satellite orbits with considerably better accuracy than previous mars gravity models and shows greater resolution of identifiable geological structures the notable improvement in gmm 1 over previous models is a consequence of several factors improved computational capabilities the use of optimum weighting and least squares collocation solution techniques which stabilized the behavior of the solution at high degree and order and the use of longer satellite arcs than employed in previous solutions that were made possible by improved force and measurement models the inclusion of x band tracking data from the 379 km altitude near polar orbiting mars observer spacecraft should provide a significant improvement over gmm 1 particularly at high latitudes where current data poorly resolve the gravitational signature of the planet

sensitivity of the free core nutation and the chandler wobble to changes in the interior structure of mars abstract in view of the forthcoming mars missions with seismological and geodetic experiments on board the sensitivity of mars normal modes to interior structure changes is examined the emphasis is put on the chandler wobble cw and the free core nutation fcn as both can play an important role in the nutations and tides of mars the fcn especially is found to have a large potential for inferring properties of the interior structure of mars if observed it will prove that mars contains a liquid core and information about the core radius and density jump at the core mantle boundary cmb can be obtained spheroidal oscillation modes of mars are also shown to provide a powerful and additional constraint on the martian interior

evidence in support of first order dissolution kinetics of calcite in seawater abstract re examination of an experimental determination of the dissolution rate of reagent grade calcite in seawater shows that the original conclusion of rate law with 4 5 order dependence on undersaturation was very sensitive to uncertainties in the saturation state of the seawater with respect to calcite c in particular use of an erroneously high value of the calcite stoichiometric solubility product generated correspondingly low values of the saturation state extrapolation of the experimental measurements to a rate of zero dissolution indicates that the calcite solubility was about 20 lower than that used in the original study similar to more recent estimates if the lower solubity is used for recalulation of the experimental saturation states the dissolution rate rd c day 1 is adequately described by the rate experssion rd c 38 1 omega c 1 in situ measurements of ph in the pore waters of calcite rich sea floor sediments are more consistent with first order kinetics than with 4 5 order kinetics interpretation of pore water ph data using the 4 5 order rate expression requires dissolution rate constants that are different by at least two orders of magnitude and stoichiometric calcite solubility products that are different by several percent between two otherwise similar sites application of the first order dissolution reduces the variability in the rate constant to less than one order of magnitude and all in situ observations are consistent with a single estimate of calcite solubility first order kinetics do not reduce the discrepancy between the laboratory determined rate constants and those based on pore water measurements dissolution rate constants constrained by the in situ ph measurements are at least two orders of magnitude less than the laboratory results

the contrasting biogeochemistry of iron and manganese in the pacific ocean abstract vertical and horizontal distributions of dissolved and suspended particulate fe and mn and vertical fluxes of these metals obtained with sediment traps were determined throughout the pacific ocean in general dissolved fe is low in surface and deep waters 0 1 to 0 7 nmol kg with maxima associated with the intermediate depth oxygen minimum zone 2 0 to 6 6 nmol kg vertical distributions of dissolved mn are similar to previous reports exhibiting a surface maximum a subsurface minimum a mn maximum layer coincident with the oxygen minimum zone and lowest values in deep waters near shore removal processes are more intense for dissolved fe than for dissolved mn dissolved mn in the surface mixed layer remains elevated much farther offshore than dissolved fe elevated near surface dissolved mn concentrations occur in the north pacific equatorial current suggesting transport from the eastern boundary near surface mixed layer dissolved mn concentrations are higher in the north pacific gyre reflecting enhanced northern hemisphere aeolian sources residence time estimates for the settling of refractory paniculate fe and mn from the upper water column are 62 220 days fe and 105 235 days mn in contrast residence times for the scavenging of dissolved fe and mn are 2 13 years fe and 3 74 years mn scavenging residence times for dissolved mn based on horizontal mixing in the surface mixed layer of the northeast pacific are 0 4 years nearshore to 19 years 1000 km offshore there is no evidence for in situ fe redox dissolution within sub oxic waters in the eastern tropical north pacific dissolved fe appeared to be controlled by dissolution from sub oxic sediments with oxidative scavenging in the water column or upper sediment layers however in situ mn dissolution within the oxygen minimum zone was evident

assessment of mars pathfinder landing site predictions remote sensing data at scales of kilometers and an earth analog were used to accurately predict the characteristics of the mars pathfinder landing site at a scale of meters the surface surrounding the mars pathfinder lander in ares vallis appears consistent with orbital interpretations namely that it would be a rocky plain composed of materials deposited by catastrophic floods the surface and observed maximum clast size appears similar to predictions based on an analogous surface of the ephrata fan in the channeled scabland of washington state the elevation of the site measured by relatively small footprint delay doppler radar is within 100 m of that determined by two way ranging and doppler tracking of the spacecraft the nearly equal elevations of the mars pathfinder and viking lander 1 sites allowed a prediction of the atmospheric conditions with altitude pressure temperature and winds that were well within the entry descent and landing design margins high resolution 38 m pixel viking orbiter 1 images showed a sparsely cratered surface with small knobs with relatively low slopes consistent with observations of these features from the lander measured rock abundance is within 10 of that expected from viking orbiter thermal observations and models the fractional area covered by large potentially hazardous rocks observed is similar to that estimated from model rock distributions based on data from the viking landing sites earth analog sites and total rock abundance the bulk and fine component thermal inertias measured from orbit are similar to those calculated from the observed rock size frequency distribution a simple radar echo model based on the reflectivity of the soil estimated from its bulk density and the measured fraction of area covered by rocks was used to approximate the quasi specular and diffuse components of the earth based radar echos color and albedo orbiter data were used to predict the relatively dust free or unweathered surface around the pathfinder lander compared to the viking landing sites comparisons with the experiences of selecting the viking landing sites demonstrate the enormous benefit the viking data and its analyses and models had on the successful predictions of the pathfinder site the pathfinder experience demonstrates that in certain locations geologic processes observed in orbiter data can be used to infer surface characteristics where those processes dominate over other processes affecting the martian surface layer

calcite dissolution driven by benthic mineralization in the deep sea in situ measurements of ca 2 ph pco 2 and o 2 abstract in situ measured microprofiles of ca 2 pco 2 ph and o 2 were performed to quantify the caco 3 dissolution and organic matter mineralization in marine sediments in the eastern south atlantic a numerical model simulating the organic matter decay with oxygen was used to estimate the calcite dissolution rate from the oxygen microprofiles measured at four stations along a 1300 m isobath of the eastern african margin and one in front of the river niger at a water depth of 2200 m the diffusive oxygen uptake dou and oxygen penetration depth opd was calculated dou rates were in the range of 0 3 to 3 mmol m 2 d 1 and showed a decrease with increasing water depth corresponding to an increase in opd the calculated amount of degradated organic matter is in the range of 1 to 8 5 gc m 2 a 1 the metabolic co 2 released from mineralization of the organic matter drives calcite dissolution in these sediments overlain by calcite supersaturated water fluxes across the sediment water interface calculated from the in situ ca 2 microprofiles were 0 6 mmol m 2 d 1 for two stations at a water depth of 1300 m the ratio of calcite dissolution flux and organic c degradation is 0 53 and 0 97 respectively the microprofiles indicate that co 2 produced within the upper oxic sediment layer dissolves up to 85 of the calcite rain to the seafloor modeling our o 2 ph and ca 2 profiles from one station predicted a calcite dissolution rate constant for this calcite poor site of 1000 mol kgw 1 a 1 mol per kg water and year which equals 95 d 1 this rate constant is at the upper end of reported in situ values

biogenic sedimentation beneath the california current system for the past 30 kyr and its paleoceanographic significance a north south transect of 17 cores was constructed along the eastern boundary of the california current system from 33 to 42 n to investigate the changes in biogenic sedimentation over the past 30 kyr percentages and mass accumulation rates of caco3 corg and biogenic opal were assembled at 500 to 1000 years sample to provide relatively high resolution time space maps reveal a complex pattern of changes that do not follow a simple glacial interglacial two mode model biogenic sedimentation shows responses that are sometimes time transgressive and sometimes coeval and most of the responses show more consistency within a limited geographic area than any temporal consistency reconstructed conditions during late oxygen isotope stage 3 were more like early holocene conditions than any other time during the last 30 kyr coastal upwelling and productivity during oxygen isotope stage 3 were relatively strong along the central california margin but were weak along the northern california margin precipitation increased during the last glacial interval in the central california region and the waters of the southern california margin had relatively low productivity productivity on the southern oregon margin was relatively low at the beginning of the last glacial interval but by about 20 ka productivity in this area significantly increased this change suggests that the center of the divergence of the west wind drift shifted south at this time the end of the last glacial interval was characterized by increased productivity in the southern california margin and increased upwelling along the central california margin but upwelling remained weak along the northern california margin a sudden 300 years decrease in caco3 corg and biogenic opal occurred at 13 ka the changes suggest a major reorientation of the atmospheric circulation in the north pacific and western north america and the establishment of a strong seasonality in the central california region a carbonate preservation event occurred at 10 ka that appears to reflect the uptake of co2 by the terrestrial biosphere as the northern latitudes were reforested following retreat of the glaciers the holocene has been a period of relatively high productivity in the southern california margin relatively strong coastal upwelling along the central california margin relatively weak upwelling along the northern california margin and the northward migration of the divergence zone of the west wind drift

an improved solution of the gravity field of mars gmm 2b from mars global surveyor a spherical harmonic solution of the mars gravity field to degree and order 80 goddard mars model 2b gmm 2b has been developed using x band tracking data of mars global surveyor mgs from october 1997 to february 2000 and altimeter crossovers formed from the mars orbiter laser altimeter mola data between march and december 1999 during the mapping mission mgs was located in a near polar 92 9 inclination and near circular orbit at a mean altitude of 400 km the tracking data from this orbit provide a detailed global and high resolution view of the gravity field of mars mars gravity solutions are stable to 60 60 even without application of a kaula power law constraint the valles marineris is resolved distinctly with lows reaching 450 mgals olympus mons and its aureole are both separately resolved and the volcano has a peak anomaly of 2950 mgals the global correlation of the gmm 2b gravity coefficients with mola derived topography is 0 78 through degree 60 and the correlation remains above 0 6 through degree 62 the global gravity anomaly error predicted from the gmm 2b error covariance through 60 60 is 11 mgal the global geoid error from gmm 2b through 60 60 is 1 8 m mgs orbit quality using gmm 2b as measured by overlapping orbital arcs is 1 m in the radial direction and 10 m in total position

joint estimation of martian 20 and rotation variations from simultaneous geodetic measurements numerical simulations of a network science experiment 1 the martian global scale co2 seasonal cycle implies temporal variations in both the zonal gravity coefficients such as 20 and in the rotation rate to estimate the ability to detect simultaneously these two main geodetic signatures a new approach based on a network science experiment is investigated we have numerically simulated the two types of doppler signals involved accurate orbiter tracking from the earth and martian lander tracking from the orbiter by using a model of both the rotation variations and the seasonal variations of 20 then through a least square process we have jointly adjusted the rotation and 20 parameters from an a priori knowledge our results show that it is possible to decorrelate 20 from all rotation parameters we obtain an accurate adjustment of the 20 variations and a precision at the level of a few milliarcseconds for the estimation of the rotation rate variations

manganese geochemistry in the guaymas basin gulf of california manganese geochemistry in the guaymas basin gulf of california is dominated by hydrothermal processes the concentration of particulate mn in the subsill basin is about four times higher than in the non hydrothermally active basins of the southern gulf this excess mn closely matches the predicted anomaly from a model of hydrothermal fluxes based on dissolved silica and sup 3 he the hot spring flux of mn is about 4 times greater than the benthic flux from the sediments on the slopes of the basin dissolved hydrothermal mn has a residence time of about one week in the water column the particulate mn phase consist of 2 5 mu m size particles that are distinct from all other suspended particulate matter these mn rich particles are responsible for the observed turbidity in the water column hydrothermal clouds above vents and chimneys in the guaymas basin and bear a striking resemblance to the mn oxidizing bacterium metallogenium the rapid conversion of mn to a particulate phase in these clouds is consistent with bacterial catalysis this contrasts with the particles at 21 sup 0 n east pacific rise where mn is more slowly co precipitated with or adsorbed onto an iron oxyhydroxide phase

interior structure models fe si ratio and parameters of figure for mars abstract a set of global interior structure models for mars which agree with the mars pathfinder mpf value of the mean moment of inertia factor is constructed the models are obtained by combining the crust models of babeiko and zharkov babeiko a yu zharkov v n 1997 mineralogical composition and seismic model of the martian crust sol syst res 31 361 368 babeiko a yu zharkov v n 1998 density and seismic profiles of the martian crust in the event of an extra low temperature gradient sol syst res 32 14 16 with the model martian mantle of bertka and fei bertka c m fei y 1996 a profile of martian mantle mineralogy and density up to core mantle boundary pressures lunar planet sci xxvii 107 108 bertka c m fei y 1997 mineralogy of the martian interior up to core mantle boundary pressures j geophys res 102 5251 5264 and the core model of zharkov zharkov v n 1996 the internal structure of mars a key to understanding the origin of terrestrial planets sol syst res 30 456 465 the models of the crust are constructed by numerical thermodynamic simulation by using the compositions of basaltic snc meteorites the model martian mantle is based on mineral physics data obtained by recent high pressure experiments these laboratory measurements were carried out by bertka and fei 1997 along a model marstherm up to core pressures of mars using mineral mixtures with the cosmochemical composition proposed by dreibus and wanke dreibus g wanke h 1989 supply and loss of volatile constituents during the accretion of terrestrial planets in atreya s k pollack j b matthews m s eds origin and evolution of planetary and satellite atmospheres univ arizona press pp 268 288 and wanke and dreibus wanke h dreibus g 1994 chemistry and accretion history of mars philos trans r soc london 349 285 293 dw composition the model of the core is also constructed for this composition but the fact that the martian core may contain a significant amount of hydrogen is taken into account based on an analogy with earth where the iron content in crust basalts is noticeably higher than in mantle silicates we have calculated a set of models with a molecular concentration of iron in the martian mantle equal to 20 mol rather than 25 mol dw composition for models with this modified iron content of the mantle and the values of hydrogen content in the core between 0 and 50 mol the fe si weight ratio is found to vary from 1 525 to 1 695 this is in good accord with the chondritic value of 1 71 predicted by dreibus and wanke s chemical model of mars only a determination of the planetary core radius with sufficiently high accuracy can substantially improve our understanding of the martian interior the parameters of the equilibrium figure of mars are calculated for the constructed models

interior structure and seasonal mass redistribution of mars from radio tracking of mars pathfinder doppler and range measurements to the mars pathfinder lander made using its radio communications system have been combined with similar measurements from the viking landers to estimate improved values of the precession of mars pole of rotation and the variation in mars rotation rate the observed precession of 7576 35 milliarc seconds of angle per year implies a dense core and constrains possible models of interior composition the estimated annual variation in rotation is in good agreement with a model of seasonal mass exchange of carbon dioxide between the atmosphere and ice caps

influence of the pacific decadal oscillation el nino southern oscillation and solar forcing on climate and primary productivity changes in the northeast pacific evidence of 11 year schwabe solar sunspot cycles el nino southern oscillation enso and the pacific decadal oscillation pdo were detected in an annual record of diatomaceous laminated sediments from anoxic effingham inlet vancouver island british columbia radiometric dating and counting of annual varves dates the sediments from ad 1947e1993 intact sediment slabs were x rayed for sediment structure lamina thickness and composition based on gray scale and subsamples were examined for diatom abundances and for grain size wavelet analysis reveals the presence of w2e3 w4 5 w 7a ndw9e12 year cycles in the diatom record and an w11e13 year record in the sedimentary varve thickness record these cycle lengths suggest that both enso and the sunspot cycle had an influence on primary productivity and sedimentation patterns sediment grain size could not be correlated to the sunspot cycle although a peak in the grain size data centered around the mid1970s may be related to the 1976e1977 pacific climate shift which occurred when the pdo index shifted from negative cool conditions to positive warm conditions additional evidence of the pdo regime shift is found in wavelet and cross wavelet results for skeletonema costatum a weakly silicified variant of s costatum annual precipitation and april to june precipitation higher spring april may values of the north pacific high pressure index during sunspot minima suggest that during this time increased cloud cover and concomitant suppression of the aleutian low al pressure system led to strengthened coastal upwelling and enhanced diatom production earlier in the year these results suggest that the 11 year solar cycle amplified by cloud cover and upwelling changes as well as enso exert significant influence on marine primary productivity in the northeast pacific the expression of these cyclic phenomena in the sedimentary record were in turn modulated by the phase of pdo as indicated by the change in period of enso and suppression of the solar signal in the record after the 1976e1977 regime shift

the mars pathfinder mission mars pathfinder one of the first discovery class missions quick low cost projects with focused science objectives will land a single spacecraft with a microrover and several instruments on the surface of mars in 1997 pathfinder will be the first mission to use a rover carrying a chemical analysis instrument to characterize the rocks and soils in a landing area over hundreds of square meters on mars which will provide a calibration point or ground truth for orbital remote sensing observations in addition to the rover which also performs a number of technology experiments pathfinder carries three science instruments a stereoscopic imager with spectral filters on an extendable mast an alpha proton x ray spectrometer and an atmospheric structure instrument meteorology package the instruments the rover technology experiments and the telemetry system will allow investigations of the surface morphology and geology at submeter to a hundred meters scale the petrology and geochemistry of rocks and soils the magnetic properties of dust soil mechanics and properties a variety of atmospheric investigations and the rotational and orbital dynamics of mars landing downstream from the mouth of a giant catastrophic outflow channel ares vallis at 19 5 n 32 8 w offers the potential of identifying and analyzing a wide variety of crustal materials from the ancient heavily cratered terrain intermediate aged ridged plains and reworked channel deposits thus allowing first order scientific investigations of the early differentiation and evolution of the crust the development of weathering products and the early environments and conditions on mars

tidally induced surface displacements external potential variations and gravity variations on mars abstract we have used and extended roosbeek s tidal potential for mars to calculate tidal displacements gravity variations and external gravitational potential variations the tides on mars are caused by the sun and to a lesser degree by the natural satellites phobos 8 relative to the sun and deimos 0 08 relative to the sun to determine the reaction of mars to the tidal forcing the love numbers h l and k and the gravimetric factor were calculated for interior models of mars with different state density and radius of the core and for models which include mantle anelasticity the latitude dependence and frequency dependence of the love numbers have been taken explicitly into account the love numbers are about three times smaller than those for the earth and are very sensitive to core changes e g a difference of about 30 is found between a model with a liquid core and an otherwise similar model with a solid core tidal displacements on mars are much smaller than on earth due to the smaller tidal potential but also due to the smaller reaction of mars smaller love numbers for both the tidal diplacement and the tidal external potential perturbations the tidal signal is at the limit of detection and is too small to permit properties of mars s interior to be inferred on the other hand the phobos tidally induced gravity changes which are subdiurnal with typical periods shorter than 12 h can be measured very precisely by the very broad band seismometer with thermal control of the seismological experiment seis of the upcoming netlander mission it is shown that the phobos induced gravity tides could be used to study the martian core

mars time variable gravity and its determination simulated geodesy experiments 1 the seasonal carbon dioxide co2 cycle on mars results in a time variable global redistribution of mass these large scale variations are associated with changes in the gravity field mainly in the two zonal gravity coefficients and which have been recently evaluated from doppler tracking data of the mars global surveyor mgs spacecraft in the present study we calculated these variations from the mass redistribution obtained from outputs of two general circulation models gcm as well as from co2 thickness measurements by the high energy neutron detector hend instrument on board the mars odyssey spacecraft and compared them to the observations tracking observations provide one of the most direct measures of the global scale atmospheric mass cycle however the associated uncertainties are relatively large partly because the low degree zonals obtained from a single orbiter tracking analysis are contaminated by higher degree harmonics which are shown to have nonnegligible seasonal variations thus we investigated possibilities to improve the determination of the time variable gravity field by means of simulated geodesy experiments additional radio tracking of a second spacecraft with suitable orbital characteristics was shown to be able to separate the higher degree geodetic signatures radio links between landers on the martian surface and a near polar orbiter can further better estimate especially the even zonals

holocene laminated sediments from the southern gulf of california geochemical mineral magnetic and microfossil study geochemical magnetic mineral analyses and microfossils radiolarians are used to characterise a holocene laminated sequence from the alfonso basin northern bay of la paz southern gulf of california in most cases dark and light laminae show similar bulk chemical compositions and magnetic mineral properties however dark laminae contain relatively more terrigenous elements al si fe k and mg supporting a pluvial origin related to the volcanic siliceous tuffs around the bay of la paz in light laminae calcium content is higher representing biogenic input the magnetic signal is dominated by low coercivity fine grained low titanium titanomagnetites and magnetite hysteresis ratio parameters in domain state plots show that samples fall in the pseudo single domain field indicating mixtures of single and multi domain particles variations in hysteresis saturation magne tisation parameters for dark and light laminae reflect changes in relative mineral concentration results indicate a dominant volcanic source for magnetic minerals into the basin associated with variable pluvial and or aeolian transport low radiolarian abundance in dark laminae seems to be associated with larger penetration and longer residence time of oligotrophic subtropical waters into the bay that occurred during el nino southern oscillation enso events light laminae are the result of episodic pulses of high productivity we suggest that dark light laminae result from oceanographic and climatic cyclic processes with main terrigenous input variation possibly associated with enso forcing of pluvial influx and or latitudinal migration of the intertropical convergence zone the laminated sequence of the alfonso basin formed a non annual depositional system in contrast to the varved sediments characteristic of the central gulf of california basins copyright 2010 john wiley sons ltd

on models of mars interior and amplitudes of forced nutations 1 the effects of deviation of mars from its equilibrium state on the flattening of the core mantle boundary abstract in a static approach the effects of deviation of mars from its equilibrium state on the flattening of the core mantle boundary cmb are studied the calculations are performed for a set of interior structure models with 50 and 100 km thick crust and averaged crustal density varying in the range of 2700 3200 kg m 3 which are based on new values for the moment of inertia and the elastic tidal love number k 2 s defined by konopliv et al konopliv a s yoder c f standish e m yuan d n sjorgen w l 2006 a global solution for the mars static and seasonal gravity mars orientation phobos and deimos masses and mars ephemeris icarus 182 23 50 the models differ in density contrast at the crust mantle boundary and the core radius the observational data constrain the radius of a liquid core to be within 1700 1800 km for joint interpretation of gravity and topography data an outer surface of a hydrostatical model is chosen as a reference surface the green s functions or loading factors technique for the case of a single anomalous density wave located at two depth level is used to compute the second degree cmb deformation and then the cmb flattening two types of models have been calculated an elastic model and a model with an elastic lithosphere and weakened layers below it relaxed values of shear modulus the effective shear modulus of the mantle is reduced in comparison with an elastic one and in extreme case it is approaching zero everywhere except the elastic lithosphere non equilibrium state of mars results in three axiality of the core mantle boundary for an elastic case the deformation of cmb leads to the large decrease of the semiaxis b going through the central region of tharsis rise by 660 780 m and the increase of the equatorial semiaxis a by 240 300 m and the polar axis c by 400 490 m tharsis rise plays a constitutive role for the cmb deformation the second degree harmonics in the expansion of non equilibrium part of gravity field and topography are sensitive first of all to the properties of the crust in the tharsis region non hydrostatic contributions decrease the flattening of the cmb by about 5 6 the effect of loading increases when the value of shear modulus decreases by a factor of 10 but as the shear modulus is decreasing up to zero the flattening is approaching its hydrostatic value

mars dynamics from earth based tracking of the mars pathfinder lander measurements of mars rotational variations can be conducted via earth based radio tracking observations of the mars pathfinder lander during an extended mission two way range measurements between an earth tracking station and the lander will enable precise monitoring of the planet s orientation allowing details of mars internal structure and global surface atmosphere interactions to be determined an analysis has been performed to investigate the accuracy with which key physical parameters of mars can be determined using the earth based radio tracking measurements acquisition of such measurements over one martian year should enable determination of mars polar moment of inertia to 1 or better providing a strong constraint on radial density profiles and hence on the iron content of the core and mantle and on long term variations of the obliquity which influences the climate variations in mars length of day and polar motion should also be detectable and will yield information on the seasonal cycling of carbon dioxide between the atmosphere and the surface

variations of upwelling intensity recorded in varved sediment from the gulf of california during the past 3 000 years circulation in the pacific ocean is periodically affected by el nino events which are a direct response to intensity changes in trade winds1 2 the appearance of anomalously warm surface water in the eastern equatorial pacific ocean is one of the most spectacular manifestations of this event warm surface water anomalies are also observed in the northern hemisphere along the californian coast and in the gulf of california in the gulf strengthened trade winds induce upwelling during the winter whereas in the summer prevailing southerly winds provoke an input of warm water from the south3 we have sampled laminated sediments from the slopes of guaymas basin to reconstruct with high resolution variations of the hydrology of surface waters in the central part of the gulf of california sedimentation rate is of the order of 4 mm yr 1 at the top and 1 2 mm yr 1 down core by analysing the oxygen isotope ratio of biogenic silica of diatoms4 we have recorded the surface water temperature variations in the guaymas basin the comparison of these fluctuations and variations of silicoflagellate abundance has allowed us to reconstruct changes in upwelling intensity during the past three thousand years the present conditions of low upwelling activity are seen to be abnormal in comparison with those prevailing in the past

mars without tharsis the significant power in the martian gravitational field due to the tharsis rise may mask or modify gravitational signatures that contain important information on martian geophysical processes in order to isolate gravity signals in regions where the field is significantly affected by tharsis as well to investigate characteristics of the global field we present a numerical technique to remove tharsis from the martian gravitational field our analysis will show that to first order tharsis can be represented as a sixth degree spherical harmonic zonal gravitational feature in a reference frame in which the axis of symmetry runs through the center of the province we produced the mars without tharsis mwt field by subtracting the gravitational signature of tharsis from the full field and rotating the spherical harmonics back to the original coordinate system in which the z axis is coincident with the planetary rotation axis our study yields limits on the moment of inertia factor of 0 361 c mr2 0 366 for the range of allowable non hydrostatic contributions to the flattening the analysis indicates that the formation of tharsis may have resulted in re orientation of the spin axis though if the planet retained rotational fossil bulge due to a thick elastic lithosphere then changes in the global figure could have been inhibited the zonal and tesseral components of the degree 2 field in the gmm i and rotated configurations indicates that tharsis is 5 times more axisymmetric about its pole than mars as a whole is about the rotation axis with the removal of tharsis long wavelength gravitational power regional structures become better defined in a spatial sense while maintaining their local dynamic range the olympus mons volcanic shield displays clear evidence of a gravitational flexural moat our method for removing tharsis may also be applied to analyze other global scale geophysical features that may be considered axisymmetric to first order such as mantle plumes major volcanic constructs or large impact basins

mars atmospheric dynamics as simulated by the nasa ames general circulation model 2 transient baroclinic eddies a large set of experiments performed with the nasa ames mars general circulation model gcm have been analyzed to determine the properties structure and dynamics of the simulated transient baroclinic eddies the mars gcm simulations span a wide range of seasonal dates and dust loadings and include a number of special sensitivity experiments e g with flat topography there is strong transient baroclinic eddy activity in the extratropics of the northern hemisphere during the northern autumn winter and spring seasons the eddy activity remains strong for very large dust loadings though it shifts northward the eastward propagating eddies are characterized by zonal wavenumbers of 1 4 and periods of 2 10 days in several simulations the eddy variance is dominated by a single zonal wavenumber and a narrow range of periods the longer wavenumbers 1 and 2 transient eddies have a very deep vertical structure exhibiting a maximum kinetic energy density at the model top 45 50 km in many of the simulations in a simulation for early northern spring the eddies are quite shallow however the transient eddies generate the bulk of their energy baroclincally via large meridional and vertical heat fluxes at both lower and upper levels this is despite the fact that their vertical structure is typically close to equivalent barotropic above the lowest 10 km the eddies also appear to generate a substantial amount of energy barotropically via large meridional momentum fluxes at both lower and upper levels in the tropics and northern subtropics at upper levels 25 50 km there are strong transient eddy motions with structures resembling those characteristic of inertially unstable modes this eddy activity appears to be a response to the forcing of a region of marginal inertial stability by the extratropical transient baroclinic eddies as the wavenumbers and periods are the same as those in the extratropics a major surprise is the presence of very weak transient eddy activity in a number of the southern winter simulations it appears that this is partly a consequence of the stabilizing effects of the zonally symmetric topography in the gcm but it also must be associated with certain aspects of the zonal mean circulation in southern winter this is indicated by the presence of relatively large amplitude eddies in simulations for early southern autumn and spring and in a southern winter solstice simulation incorporating a different topography derived from the mars digital terrain model this topography differs from that used in most of the gcm simulations in not being characterized by steep symmetric slopes which are stabilizing to baroclinic instability in southern high latitudes it is hypothesized that the very large extent of the southern seasonal polar cap and high elevations in the south both might contribute to weakening the transient eddy activity large zonally symmetric topography in the northern hemisphere of the mars gcm also appears to have a strong impact on the transient eddies acting to increase the dominant zonal wavenumbers and phase speeds the properties of the gcm baroclinic eddies in the northern extratropics are compared in detail with analogous properties inferred from viking lander meteorology observations the gcm eddies are found to be very similar to those observed in most respects a notable exception is that the eddy amplitudes in the highly dusty gcm simulations are much larger than those observed by viking during the 1977 winter solstice dust storm this is almost certainly at least partly due to the relatively small latitudinal expansion of the hadley circulation in the highly dusty gcm experiments

polar wander of mars evidence from giant impact basins abstract we investigate the polar wander of mars in the last 4 2 ga we identify two sets of basins from the 20 giant impact basins reported by frey frey h 2008 geophys res lett 35 l13203 which trace great circles on mars and propose that the great circles were the prevailing equators of mars at the impact times monte carlo tests are conducted to demonstrate that the two sets of basins are most likely not created by random impacts also fitting 63 771 planes to randomly selected sets of 5 6 or 7 basins indicated that the identified two sets are unique we propose three different positions for the rotation pole of mars besides the present one accordingly tharsis bulge was initially formed at 50 n and moved toward the equator while rotating counterclockwise due to the influence of the two newly forming volcanic constructs alba patera and elysium rise the formation of the giant impact basins subsequent mass concentrations mascons in argyre isidis and utopia basins and surface masses of volcanic mountains such as ascraeus pavonis arsia and olympus caused further polar wander which rotated tharsis bulge clockwise to arrive at its present location the extensive polar motion of mars during 4 2 3 9 ga implies a weak lithosphere on a global scale deduced from a total of 72 000 polar wander models driven by tharsis bulge alba patera and elysium rise as the major mass perturbations different compensation states 0 100 are examined for each of the surface loads and nine different thicknesses are considered for an elastic lithosphere the lithosphere must have been very weak with an elastic thickness of less than 5 km if the polar wander was driven by these mass perturbations

new constraints on mars rotation determined from radiometric tracking of the opportunity mars exploration rover abstract the opportunity mars exploration rover remained stationary between january and may 2012 in order to conserve solar energy for running its survival heaters during martian winter while stationary extra doppler tracking was performed in order to allow an improved estimate of the martian precession rate in this study we determine mars rotation by combining the new opportunity tracking data with historic tracking data from the viking and pathfinder landers and tracking data from mars orbiters mars global surveyor mars odyssey and mars reconnaissance orbiter the estimated rotation parameters are stable in cross validation tests and compare well with previously published values in particular the mars precession rate is estimated to be 7606 1 3 5 mas yr a representation of mars rotation as a series expansion based on the determined rotation parameters is provided

geodetic constraints on the composition of mars the mean density and mean moment of inertia are remotely accessible geodetic parameters which provide two integral constraints on the radial density profile of mars the mean density is presently well known but until the axial precession rate is better determined the amount of inertia will remain uncertain values anywhere in the interval from 0 345 mr sup 2 to 0 365 mr sup 2 can be obtained from the observed gravitational field depending on how that field is partitioned into hydrostatic and nonhydrostatic components even if the moment were accurately known a considerable degree of nonuniqueness would still remain concerning the density and composition this nonuniqueness is illustrated by construction of a family of orthogonal polynomials in the normalized radius which make no contribution to either the mean density or the mean inertial moment if the mean moment is near to the lower end of its plausible range the nonuniqueness in density and composition is considerably diminished in order to avoid unrealistically high densities in the deep interior the martian mantle must have a density appreciably lower than the terrestrial mantle and must consequently be significantly depleted in iron on the other hand if the mean moment is near the upper end ofmore its plausible range a much broader range of density profiles can be accommodated including but not restricted to iron enriched mantles less

a harmonic analysis of martian topography the topography of mars is represented by a spherical harmonic model complete to degree and order 50 the data source is a recently revised u s geological survey compilation which encompasses a diverse array of spacecraft measurements and earth based radar ranges because of the disparate nature of the original data sources it is difficult to obtain reliable estimates of the likely errors in martian topography however the variance spectrum has a shape similar to that found for other terrestrial planets and the topography correlates well with recent estimates of the gravitational field of mars both of these considerations suggest that the existing data provide a reasonable approximation to the true topography of mars nevertheless a detailed topographic mapping of the planet such as will be provided by the mars global surveyor will be required before significant advances are made in understanding the relationship between topography and gravity on mars

accurate analytic representations of solar time and seasons on mars with applications to the pathfinder surveyor missions efficient analytic recipes are presented for a moderately accurate closed form calculation of the areocentric longitude ls analemmic equation of time and solar hour angles on mars along with an approximate recovery of the viking local lander time the adopted fit to the fictitious mean sun implies a mars tropical orbit period of 686 9725d

the geochemical model of mars an estimation from the high pressure experiments recent high pressure experiments on the model martian mantle provide firm constraints on the internal structure and chemistry of mars we examined the martian models proposed by morgan and anders 1979 and dreibus and wanke 1985 based on the mineral physics data obtained by the recent high pressure experiments original models proposed by these authors must be modified to reduce the mass fraction of the core and thus the bulk iron content of mars in order to satisfy the geophysical constraints we present a new model of the martian interior which satisfies the geophysical and cosmochemical constraints our model mars is composed of a mixture of three components 15 7 metal m component 39 3 refractory silicate r component and 45 volatile rich v component the mass fraction of the core is 18 2 wt and the bulk iron content is about 23 wt in this model the present analysis implies that the bulk iron content of mars is significantly smaller than the iron contents of the other terrestrial planets and chondrite this suggests existence of some processes to fractionate iron and silicate in formation of the planets

early agriculture and palaeoenvironmental history in the north of the iberian peninsula a multi proxy analysis of the monte areo mire asturias spain a multi proxy study pollen and npps geochemical composition and radiocarbon dating combined with principal components analysis was applied to a core sampled in the monte areo mire asturias n spain which covers the last 11 600 years cal bp both signals of holocene climate change and transformations by human activities were recorded the cooler stage of the early holocene the hypsithermal and the neoglaciation periods were indentified but later holocene abrupt climate changes seem not to have been recorded due to the particular evolution of the fen mire system and the impact of human activities on the local hydrology evidence for human activity included a first phase of pastoralism by 7300 cal bp and an extraordinary record of adoption and establishment of agriculture the first evidence of cereal pollen dated to approximately 6700 cal bp represents one of the earliest records of agriculture in northern spain contrary to previous studies which based on assumed biogeographical limitations proposed a late adoption of agriculture in the area our results indicate a rapid expansion of agriculture in northern spain from the eastern to the westernmost areas more in agreement with recent archaeobotanical investigations zapata et al 2004 zapata et al 2005 the research also indicates that climate and human activities interplayed to determine the evolution of the studied area and that a multi proxy approach applied to natural archives appropriately located in areas with evidence of past human occupation is a productive way to obtain circumstantial evidence of early human activity

interior structure of terrestrial planets modeling mars mantle and its electromagnetic geodetic and seismic properties 1 we present a new procedure to describe the one dimensional thermodynamical state and mineralogy of any earth like planetary mantle with mars as an example the model parameters are directly related to expected results from a geophysical network mission in this case electromagnetic geodetic and seismological processed observations supplemented with laboratory measurements we describe the internal structure of the planet in terms of a one dimensional model depending on a set of eight parameters for the crust the thickness and the mean density for the mantle the bulk volume fraction of iron the olivine volume fraction the pressure gradient and the temperature profile and for the core its mass and radius currently available geophysical and geochemical knowledge constrains the range of the parameter values in the present paper we develop the forward problem and present the governing equations from which synthetic data are computed using a set of parameter values among all martian models fitting the currently available knowledge we select eight candidate models for which we compute synthetic network science data sets the synergy between the three geophysical experiments of electromagnetic sounding geodesy and seismology is emphasized the stochastic inversion of the synthetic data sets will be presented in a companion paper

pleistocene to holocene contrasts in organic matter production and preservation on the california continental margin organic matter in sediments from cores collected from the upper continental slope 200 2700 m off california and southern oregon shows marked differences in concentration and marine character between the last glacial interval ca 24 10 ka and either holocene time or last interstadial oxygen isotope stage 3 ca 60 24 ka in general sediments deposited during holocene time and stage 3 contain higher amounts of marine organic matter than those deposited during the last glacial interval and this contrast is greatest in cores collected off southern california the most profound differences in stage 3 sediments are between predominantly bioturbated sediments and occasional interbeds of laminated sediments the sediments are from cores collected within the present oxygen minimum zone on the upper continental slope from as far north as the oregon california border to as far south as point conception these upper pleistocene laminated sediments contain more abundant hydrogen rich type ii marine algal organic matter than even surface sediments that have large amounts of nonrefractory organic matter the stable carbon isotopic composition of the organic matter does not change with time between bioturbated and laminated sediments indicating that the greater abundance of type ii organic matter in the laminated sediments is not due to a change in source but rather represents a greater degree of production and preservation of marine organic matter the presence of abundant well preserved organic matter supports the theory that the oxygen minimum zone in the northeastern pacific ocean was more intense and possibly anoxic during late pleistocene time as a result of increased coastal upwelling that enhanced algal productivity

on models of mars interior and amplitudes of forced nutations 2 the effects of liquid core and mantle elasticity abstract the numerical modeling of mars forced nutation of the real mars model with a radially heterogeneous compressible self gravitating liquid core and elastic mantle is performed effects of three axiality of mars figure are taken into account to compute values for the periods of free core nutation fcn and the amplitudes of forced nutations the effects of the liquid core for different models are of the order of few percents for the prograde semi annual component and of the order of 10 15 for the semi annual retrograde component the absolute values of these effects are of the order of 5 20 ms of arc mas and 1 3 mas respectively taking into account that the modern accuracy of vlbi measurements for the case of the earth is of the order of 0 02 mas we see that important results about mars internal structure may be obtained even if the accuracy of mars nutational measurements 1 2 order of magnitude less than accuracy for the earth the effects of the shear stress relaxation during long time intervals are studied the corrections to the nutational amplitudes for prograde semi annual component are between 8 93 and 9 8 for retrograde semi annual component are between 4 81 and 8 2 ms of arc and the period of free core nutation is varied in the limits between 257 2 and 295 8 earth s solar days the differences exceed significantly the errors of mars nutational components measurements and consequently these measurements can give new important information about martian mantle rheology the possibilities of inferring properties of the interior structure of mars based on the measurements of its rotation are discussed

suboxic trace metal geochemistry in the eastern tropical north pacific abstract we analyzed al ti fe mn cu ba cd u mo v and re in water column settling particulate and sediment 0 to 22 cm samples from the intense oxygen minimum zone omz of the eastern tropical north pacific near mazatlan mexico the goal was to determine how the geochemistry of these elements was influenced by suboxic water column conditions and whether the sediments have a unique suboxic geochemical signature the water column was characterized by a mn maximum reaching 8 nmol kg 1 at 400 m concentrations of cu ba cd mo re u and v were unaffected by the low o2 conditions and were comparable to those of the open ocean sinking particles were composed of lithogenic particles of detrital origin and nonlithogenic particles of biogenic origin al ti and fe were mostly at least 79 lithogenic about 75 of the mn was nonlithogenic significant amounts at least 58 of cu ba cd and mo were nonlithogenic sediment geochemistry varied across the continental shelf and slope cadmium u and re have prominent maxima centered at 310 m with 12 3 ppm 10 9 ppm and 68 3 ppb respectively at the core top high values of mo averaging 6 8 ppm and v averaging 90 ppm are seen in omz surface sediment additional down core enrichment occurs for all redox sensitive elements in the top 10 cm for u mo v and re surface sediments are a poor indicator of metal enrichment comparison of the nonlithogenic composition of sediments with sinking particles suggests that direct input of plankton material enriched in metals makes a significant contribution to the total composition especially for cd u and mo we evaluated re mo and cd u ratios as tracers for redox environments rhenium and mo concentrations and re mo ratios do not lead to consistent conclusions concurrent enrichments of re and mo are an indicator of an anoxic depositional environment in contrast high re mo ratios are an indicator of suboxic conditions cadmium is enriched in surface sediments while u has considerable down core enrichment the concentrations of cd and u and the cd u ratio do not follow patterns predicted from thermodynamics though the water column is suboxic these four redox sensitive elements indicate that the sediments are anoxic the implication for paleostudies is that a trace metal sediment signature that indicates anoxic conditions is not necessarily attributable to an anoxic water column

early holocene decadal scale ocean variability recorded in gulf of california laminated sediments scanning electron microscope examination of holocene laminated sediment from guaymas basin gulf of california resolves up to five depositional events per year each lamina sublamina of an early holocene section of continuously laminated sediment was recorded from backscattered electron imagery photomosaic analysis diatom mat laminae composed predominantly of thalassiothrix longissima are associated with early winter mixed diatom flora laminae mats are probably brought into the gulf with pacific water during the summer concentrated at the surface or at the pycnocline and then rapidly deposited in the early winter as water column stratification breaks down time series analysis of one 300 year section from piston core jpc56 revealed significant periodicities in the deposition of mat laminae at 50 years 11 years and 22 24 years an 50 year cycle in fish populations has been related to changing north pacific ocean atmosphere circulation these pacific wide changes in circulation affect the currents dominant at the mouth of the gulf when the california current is dominant fewer diatom mats are imported into the gulf and when the north equatorial pacific gyre is dominant more are imported the 11 year 22 to 24 year and 50 year cycles are all suggested to be influenced by solar cycles

dinoflagellate cysts and enso pdo climate forcing in the southern gulf of california abstract this paper presents a high resolution analysis of dinoflagellate cyst groups 1959 to 2009 in the southern gulf of california goc we analyzed 100 samples of laminated sediments with an effective sampling resolution of 7 months our primary goal is to clarify the relation between changes in these groups and the climate forcing defined by the el nino southern oscillation enso and pacific decadal oscillation pdo indices principal component analysis indicates three groups a1 a2 and a3 a1 and a3 are mostly constituted by dinoflagellate cysts of heterotrophic taxa while a2 is composed mainly of autotrophic taxa strong el nino events decrease the contribution of all dinoflagellate cyst groups while extreme la nina events increase the contribution of the a2 and a3 groups also the pdo modulates the marine productivity in the southern goc with cold phases increasing productivity while the warm stages decrease productivity as with climatic events in the southern goc autotrophic and heterotrophic taxa of dinoflagellate cysts respond clearly when pdo and enso are in phase finally dinoflagellate cyst concentrations in laminated sediments can be used regionally as a chronostratigraphic tool in the last 50 years

contrasting sulfur geochemistry and fe al and mo al ratios across the last oxic to anoxic transition in the cariaco basin venezuela an abrupt transition from oxic to anoxic sulfidic euxinic marine bottom waters occurred in the cariaco basin in response to increasing productivity resulting from the late pleistocene post glacial rise in sea level and corresponding increase in surface water nutrient availability the microlaminated sediments of the euxinic interval which span the last f14 5 ky suggest a predominance of water column syngenetic pyrite formation based on 1 high pyrite sulfur spy concentrations in the surficial sediment layers 2 values for degree of pyritization dop that generally do not increase appreciably with increasing burial 3 ratios of total iron fet to al that are elevated above the continental baseline recorded in the underlying oxic sediments and 4 spy isotope trends that largely mimic the d 34 shsof the modern water column intermediate dop values in the microlaminated deposits and fet al ratios that are slightly above continental levels indicate an iron reservoir controlled by scavenging during syngenetic pyrite formation in combination with intermediate rates of fe bearing siliciclastic accumulation as predicted from the relative rates of siliciclastic delivery fet al and dop data lie between end member values observed in the modern black sea as viewed broadly fet al and dop relationships in euxinic sediments reflect the balance between syngenetic fe scavenging and temporal and spatial gradients in siliciclastic input pyrite concentrations are generally low in the underlying oxic marine deposits because of limitations in the supply of organic carbon corg however the upper 80 cm of the fe rich corg poor bioturbated sediment show evidence for a strong diffusional hsoverprint from the overlying fe limited euxinic marine environment this post glacial transition manifests in pyrite overprints that are strongly 34 s depleted relative to those in restricted presently euxinic marine settings elsewhere in the world such as the black sea where the sedimentary sequence spanning the last glacial interglacial transition begins with a shift from freshwater to corg poor oxic marine deposition and thus dominantly sulfate diffusion trends for mo al ratios in the microlaminated sediments suggest that mo is enriched by roughly two orders of magnitude above the continental levels recorded in the oxic deposits organic matter plays a role by enhancing hsproduction and or by providing a substrate for mo scavenging significant mo enrichment via diffusion into the upper portion of the bioturbated zone was not observed despite hs rich pore waters as recorded in the heavy iron sulfide overprint we have

water mass formation in the gulf of california the gulf of california is a long narrow marginal sea lying between the baja california peninsula and the mainland of mexico air sea fluxes of heat and moisture in the gulf are enhanced because of geographical isolation from the pacific provided by the mountainous baja california peninsula in the northern gulf annual evaporation rates are about 1 m y 1 unlike most evaporative basins however the gulf gains heat from the atmosphere at an annual average rate of 20 to 80 w m 2 bray 1988 given the unusual air sea forcing of the gulf what form or forms should water mass formation take the annual moisture loss and heat gain require that high salinity surface water be transported downward to an intermediate depth and that cold fresh inflow be transported upward to an intermediate depth this is accomplished through several mechanisms 1 winter convection this occurs only in a limited geographical region the wagner basin of the far northern gulf except in el nino southern oscillation years when convection appears to be more widespread 2 dispersion of convected water in small eddylike features this occurs within a large scale southward transport possibly driven by the large scale density gradient associated with atmospheric fluxes 3 an anticyclonic circulation in the northern gulf this is found south of the convection region and transports high salinity water off the shallow shelves and to substantial depths where it may mix with water of central gulf origin 4 tidal mixing most of the energy available for mixing in the northern gulf derives from the tides in particular tidal mixing over the sill in the island region is responsible for the substantial reduction in salinity of northern gulf waters as they enter the central gulf

sediment mixing and accumulation rates in the sulu and south china seas implications for organic carbon preservation in deep sea environments abstract recent rates of carbon burial in two deep sea basins the sulu and south china seas are contrasted to determine factors influencing organic carbon preservation in deep sea sediments the sulu sea is an oxygen deficient warm water basin whereas the adjacent south china sea is more typical of open ocean conditions high resolution sea bed profiles of 14c reveal that accumulation rates for the sulu sea are 2 3 times higher than the south china sea at any given water depth e g 1 3 g cm 2 kyr 1 versus 4 3 g cm 1 kyr 1 respectively at 3000 m higher accumulation rates for the sulu sea are attributed to higher terrigenous input and better carbonate preservation in the warmer bottom waters benthic mixing rates determined using 210pb geochronology generally are lower in the sulu sea 0 004 0 254 cm2 yr 1 as compared with the south china sea 0 17 1 57 cm2 yr 1 especially at the 3000 m and 4000 m sites in the sulu sea where benthic mixing is negligible despite the higher bottom water oxygen levels in the south china sea organic carbon concentration profiles are strikingly similar for the two basins at any given water depth with similar concentration profiles higher accumulation rates in the sulu sea result in equivalently higher carbon preservation rates as primary production is thought to be similar for both basins if anything slightly higher for the south china sea the production rate can not explain the observed differences in carbon preservation in addition benthic mixing rates apparently do not play a major role in carbon preservation as extremely low rates at the deeper sulu sea would predict relatively low carbon preservation contrary to our observations we conclude that sediment accumulation rate is the dominant control on carbon preservation in this area of the western equatorial pacific

martian precession and rotation from viking lander range data the spatial orientation of the martian pole of rotation and axial rotation parameters have been determined at a midpoint in the viking epoch january 1 1980 the mean obliquity e and node angles are e 25 1894 0 0001 35 4796 0 0002 2 the mean precession rate is o 7 83 0 30 arc sec yr 1 the corresponding moment estimate is c mre2 0 355 0 015 and covers two extreme theoretical estimates seasonal annual and semiannual variations in mars rotation angle have also been observed and are 279 100 and 311 100 milliarc second of angle mas respectively after correcting for a general relativity effect a simple model has been constructed for the main contribution involving seasonal mass exchange between the ice caps and atmosphere where the air pressure at the viking 1 lander site is a proxy for the global ice cap air pressure histories the annual term is about 190 mas smaller and differs in phase by 30 compared to the model prediction the semiannual term is 100 mas larger and also differs in phase by 30 compared to the model a combination of tidally driven rotation changes zonal winds polar motion and ice cap model deficiencies may account for any discrepancy the upcoming pathfinder lander and mars global surveyor missions carry ranging transponders which can dramatically improve our knowledge of mars interior through precise determination of the precession rate and detection of core and tidal effects we advocate that plans be developed for a coordinated campaign of simultaneous ranging and doppler tracking to each transponder

tidal variations of earth rotation we have rederived the periodic variations of the earth s rotation due to the tidal deformation of the earth by the sun and moon and included all terms with amplitudes 0 002 milliseconds 1 mm this series applies to the mantle plus crust and oceans which rotate together for characteristic tidal periods the parameter which scales the rotational series is k c where k is that fraction of the love number which causes the tidal variation in the moment of inertia of the coupled mantle and oceans while c is the dimensionless polar moment of inertia of the coupled units if the whole earth minus oceans were coupled rotationally then k 0 30 and c 0 33 ocean tides increase k by 0 04 decoupling of the fluid core from the mantle decreases k by 0 06 while c cmantle 0 29 since neither pressure viscous nor hydromagnetic coupling locks the fluid to the mantle for periods less than 5 to 25 years from the analysis of lunar laser ranging data we find that k c at monthly and fortnightly frequencies equals 0 99 0 15 and 0 99 0 20 as compared with a theoretical value of 0 94 0 04 in addition we have estimated theoretically the effects of ocean tides on earth rotation nutation and polar motion using models based on the laplace tidal equations

computation of mars transfer functions for nutations tides and surface loading abstract mars transfer functions for nutations tides and surface loading are computed for different models in order to study the influence of the physics of the interior on the planet s response to external forcing if the core is liquid there is a resonance at the free core nutation fcn period which must be taken into account the fcn period depends on the density of the core and consequently on the density jump at the core mantle boundary cmb and on the dimensions of the core the responses of mars forced by the solar gravitational attraction involve frequencies which could be very close to the fcn the observation of their amplitudes can in that case give us information about whether the core is liquid or not about its dimensions as well as about the density jump at the cmb we therefore consider several models for the interior structure of mars involving different normal mode frequencies and compute the transfer functions for nutations tides and loading as a function of the forcing frequency we show that the amplitudes of the semi annual tri annual and quadri annual nutations could be amplified by several ten percent or even several hundred percent by the fcn resonance depending on the fcn eigenfrequency value here annual means one martian year the same holds for the second degree diurnal tides and loading effects the impact of the core radius density and state on the body and load love numbers is analysed body and low degree load love numbers h and k can change by up to 25 for variations in the core radius of 200 km or for a change in the core state liquid solid the corresponding variations in the tidal gravimetric factor and the loading green s function are about 10 times smaller high degree load love numbers are more sensitive to the upper mantle rheology

changes in wind driven upwelling during the last three centuries interocean teleconnections based u37 0 paleothermometer yielded high resolution records of sea surface temperatures sst from 1700 to 2000 ad the trends in the u37 0 index reveal steady sst increases of 1 to 2c at both sites since the end of the little ice age higher frequency changes in sst indicate a decoupling in the relative intensity of wind driven upwelling at the two sites periods of enhanced upwelling in guaymas correspond to periods of decreased upwelling in cariaco and vice versa we propose that these contrasts reflect regional differences in the upwelling response of upwelling to changes in the positioning of the inter tropical convergence zone itcz and the subtropical high sh under current climate conditions citation goni m a r c

phosphorus composition of sinking particles in the guaymas basin gulf of california phosphorus p composition and fluxes were measured in samples collected using a moored sediment trap located at 500 m in depth in the center of guaymas basin gulf of california from february 1991 through september 1997 p composition was measured using a sequential extraction technique that chemically separates the particulate inorganic p pip pool into exchangeable oxide bound authigenic and detrital phases pip comprised 69 6 15 of the total particulate p pool with significantly higher concentrations during the rainy summer strong relationships between authigenic and detrital p fluxes with lithogenic material r2 0 85 indicate that a significant component of pip is terrestrially derived and varies with large scale changes in regional climate particulate organic p pop fluxes were significantly higher during the winter as a result of stimulation of biological production during upwelling average particulate organic carbon poc pop ratios also varied seasonally with higher ratios in the summer 221 vs the winter 158 the fact that poc fluxes remained relatively constant throughout the year indicates that in winter fresher less degraded organic material was more effectively transported to depth strong correlations between pop and opal fluxes r2 5 0 63 further support a ballast mechanism whereby enhanced sinking rates reduce the time during which organic matter is subjected to water column degradation compared to trap concentrations pop is preferentially remineralized over pip in concert with an increase in the authigenic p pool this signifies rapid diagenetic transformations of sedimentary p between the sediment trap and underlying sediments

what can olympus mons tell us about the martian lithosphere abstract under gravitational loading a volcanic edifice deforms and the underlying lithosphere downflexes this has been observed on earth but is equally true on other planets we use finite element models to simulate this gravity driven deformation at olympus mons on mars eleven model parameters including the geometry and material properties of the edifice lithosphere and underlying asthenosphere are varied to establish which parameters have the greatest effect on deformation values for parameters that affect deformation at olympus mons mars are constrained by minimising misfit between modelled and observed measurements of edifice height edifice radius and flexural moat width our inferred value for the young s modulus of the martian lithosphere 17 8 gpa is significantly lower than values used previously suggesting that the martian lithosphere is more porous than generally assumed the best fitting values for other parameters edifice density 2111 2389 kg m 3 and lithosphere thickness 83 3 km are within ranges proposed hitherto the best fitting values of model parameters are interdependent a decrease in lithosphere young s modulus must be accompanied by a decrease in edifice density and or an increase in lithosphere thickness our results identify the parameters that should be considered within all models of gravity driven volcano deformation highlight the importance of the often overlooked young s modulus and provide further constraints on the properties of the martian lithosphere namely its porosity which have implications for the transport and storage of fluid throughout mars history

high resolution migration history of the subtropical high trade wind system of the northeastern pacific during the last 55 years implications for glacial atmospheric reorganization 1 guaymas basin gulf of california is a restricted basin located under the present day wet dry subtropical divide 27 n and is ideally circumstanced for detecting variations in the north pacific subtropical high npsh trade wind system controlled by climate cell boundary displacement npsh midwinter location was the primary influence on timing and intensity of upwelling seasons in guaymas basin analysis of high resolution x ray fluoresence data and sediment fabric log from 75 laminated core md02 2517 2515 western guaymas basin reveals systematic changes in npsh behavior over the last 55 kyr bp southward displacement of the wet dry subtropical divide controlled upwelling related diatom productivity while sea level and regional rainfall controlled terrigenous supply the basin was oxic during the glacial and preservation was ensured by high burial rate due to the increased deposition of terrigenous sediment sediment fabric style number and or thickness of laminae plus color banding and homogeneous intervals changes systematically through the core and gives insights into the number of seasons occurring in guaymas basin and the occurrence and intensity of the upwelling season five millennial scale low flux events with close timing to heinrich events and ten decadal centennial scale low biogenic silica events occurring in the interval 33 16 5000 years before present kyr bp are interpreted as times of extreme aridity at 16 5 kyr bp a regime shift from terrigenous dominated oxic to evenly balanced biogenic terrigenous dysoxic conditions occurred although there was a further extreme arid event at 11 5 kyr bp 16 5 kyr bp was essentially the beginning of the interglacial

solar forcing of gulf of california climate during the past 2000 yr suggested by diatoms and silicoflagellates abstract high resolution records of the past 2000 yr are compared in a north south transect 28 n to 24 n of three cores from the eastern slopes of the guaymas carmen and pescadero basins of the gulf of california hereafter referred to as the gulf evenly spaced samples from the varved sediments in each core allow sample resolution ranging from 16 to 37 yr diatoms and silicoflagellates capture the seasonal variation between a late fall to early spring period of high biosiliceous productivity that is driven by northwest winds and a summer period of warmer more stratified waters during which these winds slacken and or reverse direction monsoonal flow as these winds decrease tropical waters enter the gulf and spread northward individual samples represent a composite of 7 to 23 yr of deposition and are assumed to record the relative dominance of the winter vs summer floral components intervals of enhanced summer incursion of tropical waters alternating with periods of increased late fall to early spring biosiliceous productivity are recorded in all three cores regularly spaced cycles 100 yr duration of octactis pulchra a silicoflagellate proxy for lower sst and high productivity and azpeitia nodulifera a tropical diatom occur between a d 400 and 1700 in the more nearshore carmen basin core nh01 21 26 3 n suggesting a possible solar influence on coastal upwelling cores bam80 e 17 27 9 n and nh01 26 24 3 n contain longer duration cycles of diatoms and silicoflagellates the early part of medieval climate anomaly a d 900 to 1200 is characterized by two periods of reduced productivity warmer sst with an intervening high productivity cool interval centered at a d 1050 reduced productivity and higher sst also characterize the record of the last 100 to 200 yr in these cores solar variability appears to be driving productivity cycles as intervals of increased radiocarbon production sunspot minima correlate with intervals of enhanced productivity it is proposed that increased winter cooling of the atmosphere above southwest u s during sunspot minima causes intensification of the northwest winds that blow down the gulf during the late fall to early spring leading to intensified overturn of surface waters and enhanced productivity a new silicoflagellate species dictyocha franshepardii bukry is described and illustrated

new insights into productivity and redox controlled trace element ag cd re and mo accumulation in a 55 kyr long sediment record from guaymas basin gulf of california a high resolution 55 kyr long record of chalcophile and redox sensitive trace element accumulation ag cd re and mo from md02 2515 western guaymas basin is investigated in conjunction with patterns in stratigraphy and productivity high opal concentrations 59 wt representing increased diatom production coincide with laminated sediments and dilute the concentrations of organic carbon corg and metals a similarity between opal and normalized corg ag and cd concentrations suggests delivery to the sediments by diatom export production while patterns in normalized re and mo accumulation suggest a different emplacement mechanism although mo enrichment in organic rich laminated sediments typically represents anoxic conditions at other locations mo and re in guaymas basin is enriched in nonlaminated and bioturbated sediments that are representative of oxygenated conditions adsorption onto fe and or mn oxyhydroxide surfaces during oxygenation inadequately explains both the re and mo enrichments thus recently published mechanisms invoking direct re and mo removal from the water column and bioturbation assisted irrigation of re into the sediments are used to explain the counterintuitive observations in guaymas basin the md02 2515 stratigraphic and proxy records are also different from other records in the northeast pacific in that there is little correspondence with greenland dansgaard oeschger interstadials there is some correlation with heinrich events suggesting that ventilation of intermediate waters and or reduced productivity may be important in controlling stratigraphy and trace element accumulation the results question whether md02 2515 records can be compared to northeast pacific open margin records especially before 17 kyr b p

diatoms in the gulf of california seasonal flux patterns and the sediment record for the last 15 000 years flux and taxonomic composition of the diatom assemblage was determined for biweekly sediment traps in the central gulf of california over a 2 year period fluxes and relative abundance of taxa are not significantly different in traps from the eastern side of the guaymas basin and the western side of the carmen basin indicating that patterns of diatom production are uniform across the central gulf at all seasons of the year the annual maximum in diatom flux occurred during the winter season of both years either as a sustained event over many weeks 1990 or as a series of short blooms 1991 1992 of the most abundant taxa only hyalochaete chaetoceros species showed a clear seasonal cycle with a flux maximum in the spring of both years factor analysis defines five assemblages representing 1 summer and fall conditions of surface stratification and nutrient limitation 2 winter bloom triggered by onset of strong northwesterly winds 3 late spring to summer production probably related to sporadic events during periods of weak southeasterly winds 4 spring 1991 inferred to reflect the distal edge of a coastal upwelling phase 5 lateral advection of resuspended sediments from the continental shelf possibly resulting from trapped coastal waves during summer hurricanes and from storms during the 1991 1992 el nino southern oscillation enso the diatom data support the inference that subtropical pacific water penetrates deeper into the gulf during enso events in order to compare the sediment trap record to a sediment core a second factor analysis was done using only the taxa which are preserved in the sediment and omitting the most abundant taxa which showed little downcore variation this produces five factors representing 1 summer fall low production 2 early winter bloom 3 late winter spring upwelling 4 enso conditions and 5 a late spring summer assemblage of uncertain significance variation of species characterisic of each factor was examined in piston core atlantis ii 125 8 56jpc taken from the oxygen minimum zone in guaymas basin correlation to nearby deep sea drilling project hole 480 indicates that the core penetrates to about 15 ka with laminated sediments in the holocene 0 10 ka and late deglacial 11 13 ka and massive nonlaminated sediments around younger dryas time 10 11 ka and before 13 ka downcore variations in the diatom assemblage do not correspond directly to presence of laminations implying that the processes controlling bottom water oxygen content are not determined by conditions of surface water production presence of calcareous nannofossils downcore correlates inversely with two diatom assemblages enso and winter bloom indicators and not with occurrence of laminations suggesting that occurrence of calcareous nannofossils in the sediment is at least partly a function of surface water production prior to 12 ka production was lower than at present during all seasons implying weaker winds throughout the year subtropical waters extended to the midgulf as they do today during enso events between 11 and 12 ka conditions were similar to those of the present with relatively high winter and spring production resulting from northwesterly winds enso events were still common although less so than during the preceding period younger dryas time was one of transition with intermediate conditions a slackening of winter spring northwesterly winds and reduction of total annual production and increased occurrence of enso conditions in the early to middle holocene winter northwesterlies increased to a maximum resulting in very high production but apparently did not persist into spring subtropical waters mostly disappeared from the gulf in the late holocene northwesterly winds have supported high production during both winter and spring seasons

mars high resolution gravity fields from mro mars seasonal gravity and other dynamical parameters abstract with 2 years of tracking data collection from the mro spacecraft there is noticeable improvement in the high frequency portion of the spherical harmonic mars gravity field the new jpl mars gravity fields mro110b and mro110b2 show resolution near degree 90 additional years of mgs and mars odyssey tracking data result in improvement for the seasonal j 3 gravity changes which compares well to global circulation models and odyssey neutron data and mars rotation and precession 7594 10 mas year once atmospheric dust is accounted for in the spacecraft solar pressure model solutions for mars solar tide are consistent between data sets and show slightly larger values k2 0 164 0 009 after correction for atmospheric tide compared to previous results further constraining core models an additional 4 years of mars range data improves the mars ephemeris determines 21 asteroid masses and bounds solar mass loss dgmsun dt

the radiocarbon record in varved sediments of carmen basin gulf of california a measure of upwelling intensity variation during the past several hundred years the decrease in 14c 12c with depth in a varved sediment core raised from the eastern flank of carmen basin gulf of california is greater than expected from varve and 210pb chronology the discrepancy is ascribed to a virtually monotonic decrease in upwelling intensity from several hundred years ago to the present this radiochemical study presents an approach independent of previously used biostratigraphic techniques for evaluating temporal variations in upwelling intensity in the gulf of california

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