one hundred million years of geomagnetic polarity history since 1968 absolute ages have been assigned to the late cretaceous cenozoic geomagnetic reversal time scale by fixing the ages of two or more calibration points in a composite marine magnetic anomaly profile and interpolating between or extrapolating beyond these points assuming constant spreading rates in each interval previously no more than 4 calibration points were used but it is now possible to specify 11 calibration points in addition to the 0 m y datum this improvement is based on magnetostratigraphic studies in italian pelagic limestones these studies closely tie the geomagnetic reversal sequence to the foraminiferal and coccolith zonations absolute ages of calibration points are provided by the best available dates on stage boundaries which are located from the biostratigraphic zonation the greatest changes from previous scales come in the late paleocene early eocene where the new ages are as much as 3 m y younger than in the 1977 scale of labrecque and others and as much as 1 8 m y younger than in the 1980 scale of ness and others

geomagnetic reversal spurts and episodes of extraterrestrial catastrophism the possibility that the observed 26 32 myr periodicity in the records of extinction events1 and astrobleme ages2 was caused by periodic episodes of physical bombardment of the planetary surface has raised the likelihood that such an astronomical clock also affects geomagnetic reversals3 4 however the detection5 of a comparable 30 myr harmonic in the geomagnetic reversal record has now been found6 to be an accident of data length while the earlier reported7 32 34 myr harmonic of the reversal record may well be an artefact of the data base here we examine the temporal relation between geomagnetic reversals and those catastrophic episodes which occurred during periods of frequent reversals as geomagnetic history comprises long intervals of frequent reversals alternating with intervals of fixed polarity our rationale is that the geomagnetic field should be most susceptible to catastrophism during its relatively unstable periods of frequent reversals we find spurts in the frequency of geomagnetic reversals at approximately 30 myr intervals correlated with catastrophic episodes these spurts can be seen as the geomagnetic signatures of terrestrial catastrophism and we tentatively ascribe them to enhanced core turbulence during episodes of bombardment the absence of reversal spurts during long intervals of fixed polarity is attributed to the failure during these intervals of the geomagnetic dynamo s bi stable oscillations

the mediterranean sea a miniature ocean for climatic and environmental studies and a key for the climatic functioning of the north atlantic the mediterranean sea provides a case study not only for dense water formation and climatic functioning at a basin scale but also as a body of water evolving in response to the effects of environmental changes through marine circulation marine signatures of changes may be used to provide estimates of the evolution of the external driving forces of climate and environment that is to say to provide a coupling between marine sciences and climatic and socio economic studies different examples may be given i nutrients and trace metal changes in the western mediterranean permit quantification of external changes at a basin scale ii sapropels organic rich layers sedimented in anoxic conditions provide records for the last 2 million years of interactions between marine circulation climate and biology iii temperature and salinity changes that have taken place since the 1960s in response to changes in heat and water budgets across the sea surface sapropel studies and ongoing changes in temperature and salinity also require that the mediterranean functioning be considered in relation to global climate and to the atlantic ocean as well as taking into account the changing role of salty mediterranean waters in the atlantic ocean these factors highlight a dual role for the mediterranean sea which acts as a miniature ocean for physical chemical or climatic and environmental studies and also as a key factor in understanding global ocean circulation in which past changes have taken place

multiple impacts across the cretaceous tertiary boundary abstract the stratigraphy and age of altered impact glass microtektites microkrystites ejecta layers from the chicxulub crater are documented in late maastrichtian and early danian sediments in mexico guatemala belize and haiti in northeastern mexico two to four ejecta layers are present in zone cf1 which spans the last 300 ky of the maastrichtian the oldest ejecta layer is dated at 65 27 0 03 ma based on sediment accumulation rates and extrapolated magnetostratigraphy all younger ejecta layers from the maastrichtian and early danian parvularugoglobigerina eugubina zone pla l may represent repeated episodes of reworking of the oldest layer at times of sea level changes and tectonic activity the k t boundary impact event 65 0 ma is not well represented in this area due to widespread erosion an early danian pla l ir anomaly is present in five localities bochil actela coxquihui trinitaria and haiti and is tentatively identified as a third impact event at about 64 9 ma a multiimpact scenario is most consistent with the impact ejecta evidence the first impact is associated with major deccan volcanism and likely contributed to the rapid global warming of 3 4 c in intermediate waters between 65 4 and 65 2 ma decrease in primary productivity and onset of terminal decline in planktic foraminiferal populations the k t boundary impact marks a major drop in primary productivity and the extinction of all tropical and subtropical species the early danian impact may have contributed to the delayed recovery in productivity and evolutionary diversity

a model of correlated episodicity in magnetic field reversals climate and mass extinctions correlated periodicities of mass extinctions climate magnetic field reversals and other geological phenomena may best be explained by cycles of activity within the mantle and core we propose that these cycles are due to variations in the thickness of the thermal boundary layer at the base of the mantle as the layer alternates between two phases of activity in the quiescent phase little flow occurs and the layer thickens with time by thermal diffusion the active phase begins when the thickening layer becomes dynamically unstable hot material erupts from the layer causing it to become thinner as the layer thins the rate of energy supply to the geodynamo and hence its reversal frequency increases the hot material rises to the surface where it causes widespread basaltic volcanic eruptions these eruptions release large amounts of co 2 and sulfates which have a pronounced effect on the climate and biota

ploughing the deep sea floor bottom trawling is a fishing technique whereby heavy nets and gear scrape along the sea bed and is shown here to disturb sediment fluxes and modify the sea floor morphology over large spatial scales the direct impact of bottom trawling on local fish populations has received much attention but trawling also affects other aspects of the ocean environment this paper shows that bottom trawling a commercial practice in which heavy nets and gear are dragged along the ocean floor induces sediment reworking and erosion causing the gradient of the sea floor to become smoother over time this reduces the morphological complexity of deep sea environments the authors draw parallels between the effects of bottom trawling at sea and intensive agriculture on land with the important difference that on land ploughing takes place once or twice a year whereas at sea bottom trawling can be a frequent occurrence bottom trawling is a non selective commercial fishing technique whereby heavy nets and gear are pulled along the sea floor the direct impact of this technique on fish populations1 2 and benthic communities3 4 has received much attention but trawling can also modify the physical properties of seafloor sediments water sediment chemical exchanges and sediment fluxes5 6 most of the studies addressing the physical disturbances of trawl gear on the seabed have been undertaken in coastal and shelf environments7 8 however where the capacity of trawling to modify the seafloor morphology coexists with high energy natural processes driving sediment erosion transport and deposition9 here we show that on upper continental slopes the reworking of the deep sea floor by trawling gradually modifies the shape of the submarine landscape over large spatial scales we found that trawling induced sediment displacement and removal from fishing grounds causes the morphology of the deep sea floor to become smoother over time reducing its original complexity as shown by high resolution seafloor relief maps our results suggest that in recent decades following the industrialization of fishing fleets bottom trawling has become an important driver of deep seascape evolution given the global dimension of this type of fishery we anticipate that the morphology of the upper continental slope in many parts of the world s oceans could be altered by intensive bottom trawling producing comparable effects on the deep sea floor to those generated by agricultural ploughing on land

15 myr periodicity in the frequency of geomagnetic reversals since 100 myr the statistical properties of the magnetic polarity time scale have been examined recently1 2 for several time scales for some of these scales the time evolution of the frequency of reversals as seen through an 8 myr moving rectangular window have been determined in particular over the past 100 myr the mean reversal frequency appears to be dominated by a linearly increasing trend on which is superimposed a rhythmic fluctuation we have attempted to analyse the mathematical structure of the reversal frequency curve in detail and to determine whether the rhythmic fluctuation was indeed periodic by modelling the time evolution of the reversal frequency we find a dominant frequency corresponding to a period of 15 myr this result represents one of the most persistent long term periodicities ever reported for a geophysical phenomenon

inferring optical depth of broken clouds above green vegetation using surface solar radiometric measurements abstract a method for inferring cloud optical depth is introduced and assessed using simulated surface radiometric measurements produced by a monte carlo algorithm acting on fields of broken single layer boundary layer clouds derived from landsat imagery the method utilizes a 1d radiative transfer model and time series of zenith radiances and irradiances measured at two wavelengths 1 and 2 from a single site with surface albedos 1 2 assuming that clouds transport radiation in accordance with 1d theory and have spectrally invariant optical properties inferred optical depths are obtained through cloud base reflectances that are approximated by differencing spectral radiances and estimating upwelling fluxes at cloud base when initialized with suitable values of 1 2 and cloud base altitude h this method performs well at all solar zenith angles relative mean bias errors for are typically less than 5 for these cases relative variances for for given values of inherent are a

a new approach to retrieve cloud base height of marine boundary layer clouds 1 a novel approach for estimating marine boundary layer cloud base height cbh is proposed based on calculated boundary layer lapse rates collocated cloud top height cth cloud top and ocean surface temperatures from the a train satellite constellation the method takes advantage of the assumption that decreases of temperature within and below water clouds may follow the different constant apparent lapse rates in the same region respectively the cbhs derived from the new method compare well with the coincident cbh product from the active sensors of cloud aerosol lidar and infrared pathfinder satellite observation calipso and cloudsat the correlation coefficient the mean difference and the standard deviation are 0 79 0 54 0 02 km 0 03 km and 0 35 km 0 54 km respectively when cth is derived from calipso data or moderate resolution imaging spectroradiometer retrieval besides the relatively small bias the most important advantage of this method compared to previous cbh retrieval techniques is that it is independent of boundary layer cloud types optical thickness and illumination

evidence from crater ages for periodic impacts on the earth recent evidence has indicated that the impact of a comet or asteroid may have been responsible for mass extinction at the ends of both the cretaceous1 and the eocene2 4 quantitative analysis by raup and sepkoski5 showed that mass extinctions occur with a 26 myr period similar to the period seen in qualitative pelagic records by fischer and arthur6 to account for the possibility of periodic comet showers davis et al 7 proposed that such showers could be triggered by an unseen solar companion star as it passes through perihelion on a moderately eccentric orbit to test a prediction implicit in this model we examined records of large impact craters on the earth we report here that most of the craters occur in a 28 4 myr cycle within measurement errors this period and its phase are the same as those found in the fossil mass extinctions the probability that such agreement is accidental is 1 in 103

satellite multiangle cumulus geometry retrieval case study most satellite based analyses have been conducted using near nadir viewing sensors the multi angle imaging spectroradiometer misr recently launched on the national aeronautics and space administration nasa terra platform provides high resolution measurements of reflectance at nine different viewing angles in this study we examine the possible retrieval of detailed cumulus geometry using the new and unique misr datasets we suggested one approach and apply it to an early misr dataset of small marine cumulus clouds this paper also presents validation analysis of this technique with both independent ground based radar measurements and a model output inverse problem collocated and coincident misr data and ground based observations at the atmospheric radiation measurement arm tropical western pacific twp site form the basis of this validation future work will attempt to test the suggested approach with additional misr scenes

how dating uncertainties affect the detection of periodicity in extinctions and craters abstract claims of a highly significant detection of a period of 25 30 myr in the records of major extinction events and large craters have prompted us to examine how dating errors degrade a periodic signal we ran monte carlo simulations in which we placed eight events at equal time intervals and then displaced each event by a random error chosen from a normal distribution if the r m s error is greater than about 13 of the period the periodic data is usually no longer distinguishable from random data at the 90 confidence level at present the r m s dating errors in extinction episodes and craters over the last 250 myr are at least 6 myr or 20 of a 25 to 30 myr period we conclude that even if a periodicity were present it would not normally be detected at a statistically significant level by the tests used in the literature the apparent periodicity is probably due to a statistical fluke or subjective bias

assessing a cloud optical depth retrieval algorithm with model generated data and the frozen turbulence assumption abstract a cloud optical depth retrieval algorithm that utilizes time series of solar irradiance and zenith downwelling radiance data collected at a fixed surface site is assessed using model generated cloud fields and simulated radiation measurements to date the retrieval algorithm has only been assessed using instantaneous cloud fields in which time series were mimicked via the frozen turbulence assumption in this study time series of radiation data are generated for use by the algorithm from a series of snapshots of an evolving and advecting cloud field with values of optical depth retrieved for clouds occurring at the midpoint of the time series this approach resembles conditions encountered in the field much better than those arising from the convenient frozen turbulence assumption values of optical depth are also retrieved for the same cloud field by employing the frozen turbulence approach for the field of broken shallow cumulus considered here differences between the two sets of retrieva

the magnetic reversal record is not periodic statistical analysis of one version of the magnetic reversal record suggests that the frequency of reversals has changed cyclically with a period of 30 myr starting at least 165 myr ago but factors other than periodicity affect the analysis used and here i show that there is no compelling evidence for periodicity in the reversal record the results of essentially identical analyses that have been applied to other geolocial data should also be re evaluated

short polarity intervals within the matuyama transitional field records from hydraulic piston cored sediments from the north atlantic abstract detailed sampling of two short magnetozones within the matuyama chronozone recorded at dsdp site 609 49 86 n 335 77 e confirms that one the cobb mountain subchronozone 1 12 ma is a very short full normal polarity interval and that the other the older interval is a record of a geomagnetic excursion which occurred at approximately 1 55 ma the cobb mountain subchron lasted approximately 25 000 years one third the duration of the jaramillo subchron the normal polarity interval is bounded by two transition zones which document an antisymmetry in the sequence of directions in the reverse to normal and normal to reverse polarity transitions we interpret the antisymmetry as reflecting a dependence upon the sense of the reversal without significant changes in the relative contributions of non dipole terms the polarity interval recorded at 1 55 ma lasted only 8 800 years with what may be regarded as full polarity directions observed across only 3 cm of stratigraphic section this feature is interpreted as an excursion of the geomagnetic field and appears to be correlative with the gilsa subchron similarities between the transition bounding these two magnetozones suggest that these features occur as the result of the same process or triggering mechanisms in the earth s outer core

variability of optical depth and effective radius in marine stratocumulus clouds abstract radiance measurements made by the advanced very high resolution radiometer avhrr at 1 km nadir spatial resolution were used to retrieve cloud optical depth and cloud droplet effective radius reff for 31 marine boundary layer clouds over the eastern pacific ocean and the southern ocean near tasmania in the majority of these scenes each roughly 256 256 km2 in extent and reff are strongly correlated with linear least squares yielding a regression curve of the form reff 1 5 this relationship is consistent with an idealized model of a nonprecipitating layer cloud in which 1 the average cloud liquid water content increases linearly with height at some fraction of the adiabatic lapse rate in a 1 km2 vertical column and 2 the normalized horizontal variability of the cloud liquid water path exceeds the variability of a scaled measure of the cloud droplet number concentration in contrast other scenes of similar horizontal extent show little or no correlation between retrieved val

long range dependence in the cenozoic reversal record the frequency distribution of intervals between cenozoic geomagnetic reversals approximates a power law while their occurrence over time shows temporal clustering of short and long intervals application of the aggregate variance and absolute valuemethods suggest long range dependence in this time series a possible indication that the geodynamo operates as a self organised complex system this hypothesis may allow the cretaceous superchron to be considered as an integral part of the ordinary reversal regime attested in the cenozoic record 2003 elsevier science b v all rights reserved

the periodicity of geomagnetic reversals abstract several periodicities have been claimed in the time series of geomagnetic reversals but none has survived subsequent methodological objections we apply the established tool of periodogram analysis to the most accurate geomagnetic scale available and obtain the following results a trend that is well fitted by an exponential curve is present in the rate of reversals occurrence and there is a 15 ma periodicity that is significant at approximately the 0 05 level no significant period is present in the series of the intervals between reversals these results indicate that geomagnetic reversals since 85 ma bp occur according to a generalized poisson process with a mean which increases exponentially and which may have a superimposed periodic modulation in physical terms this would imply a mechanism of reversal generation which is stochastic and has an energy input increasing in time modulated by a 15 ma periodicity this is consistent with reversals originated by cyclones in the outer core a long term change in the lower mantle temperature distribution and a pulsating 8 10 km thick layer at the base of the mantle

satellite remote sensing of cloud base height for convective cloud fields a case study 1 a method is proposed for estimating base heights of convective clouds from satellite data the approach takes advantage of the fact that convective water clouds appear as geometrically and optically thin clouds near an approximately constant condensation level in their earliest stage of growth and that deriving geometrical thicknesses for such thin clouds is less error prone striking is the fact that the method also provides the base height for clouds with large vertical extensions and high optical thicknesses the method has been applied to noaa avhrr data of 20 selected cloud scenes for an evaluation satellite retrieved cloud base heights have been compared to surface ceilometer measurements at the same time first results are encouraging the standard deviation of the differences between satellite and ceilometer measurements is 369m with no systematic bias

geomagnetic reversal frequency since the late cretaceous models of geomagnetic reversals as a stochastic or gamma renewal process have generally been tested for the heirtzler et al 1 magnetic polarity time scale which has subsequently been superseded examination of newer time scales shows that the mean reversal frequency is dominated in the cenozoic and late cretaceous by a linearly increasing trend on which a rhythmic fluctuation is superposed subdivision into two periods of stationary behavior is no longer warranted the distribution of polarity intervals is visibly not poissonian but lacks short intervals the labrecque et al 2 polarity time scale shows the positions of 57 small wavelength marine magnetic anomalies which may represent short polarity chrons after adding these short events the distribution of all polarity intervals in the age range 0 40 myr is stationary and does not differ significantly from a poisson distribution a strong asymmetry develops in which normal polarity chrons are poisson distributed but reversed polarity chrons are gamma distributed with indexk 2 this asymmetry is of opposite sense to previous suggestions and results from the unequal distribution of the short polarity chrons which are predominantly of positive polarity and concentrated in the late cenozoic if short wavelength anomalies arise from polarity chrons the geomagnetic field may be more stable in one polarity than the other alternative explanations of the origin of short wavelength marine magnetic anomalies cast doubt on the inclusion of them as polarity chrons however the observed behavior of reversal frequency suggests that core processes governing geomagnetic reversals possess a long term memory

the potential for improved boundary layer cloud optical depth retrievals from the multiple directions of misr abstract the multiangle imaging spectroradiometer misr views the earth with nine cameras ranging from a 70 zenith angle viewing forward through nadir to 70 viewing aft misr does not have an operational cloud optical depth retrieval algorithm but previous research has hinted that solar reflection measured in multiple directions might improve cloud optical depth retrievals this study explores the optical depth information content of misr s multiple angles using a retrieval simulation approach hundreds of realistic boundary layer cloud fields are generated with large eddy simulation les models for stratocumulus small trade cumulus and land surface forced fair weather cumulus reflectances in misr directions are computed with three dimensional radiative transfer from the les cloud fields over an ocean surface and averaged to misr resolution and sampled at misr 275 m pixel spacing neural networks are trained to retrieve the mean and standard deviation of optical depth over different size pixel pa

the geochronology of large igneous provinces terrestrial impact craters and their relationship to mass extinctions on earth the relationship between sudden catastrophic events and sudden mass extinctions on earth has attracted a great deal of research effort including measurements of the absolute and relative ages of these events the result has been a rapid improvement in the precision and accuracy of radiometric dates for large igneous provinces lips for which there is now a consensus on the peak eruption times over the last 250 ma in parallel there has been a more gradual improvement in the radiometric dates for craters formed by hypervelocity impacts hvis of asteroids and comets with earth the absolute ages of the largest craters are known to within a few million years but the ages of many smaller craters are poorly constrained in addition whereas relatively few lips have formed in the last 250 ma at least one hvi crater larger than 20 km diameter has formed on earth every million years only 25 such craters have been discovered so coincidence between the ages of hvi crater formation and ages of mass extinctions is related as much to crater preservation as to coincidence of the events the difference in quality of geochronology between hvis and lips is the result of differing availability of samples lips cover large areas and present an array of basalt samples suitable for dating whereas hvi craters are often poorly preserved and present few datable samples the radiometric data for preserved hvis and lips are now sufficiently precise and accurate for us to be confident that there is no one to one correlation between either lips or hvis and global mass extinctions of life on earth however there is a close association between a significant number of lips and sudden environmental change and a very close association between at least one massive hvi crater formation and a mass extinction further there is no apparent correlation between hvis and lips and thus no reason to suggest a causative relationship finally the radiometric dating of hvi craters indicates several clusters in the geological record but the correlation with sudden environmental change is no better than for large craters

the ecology of the deep sea benthic and benthopelagic fish on the slopes of the rockall trough northeastern atlantic abstract a total of over 28 000 benthic and benthopelagic fish belonging to 34 families and comprising at least 85 species were collected from the hebridean terrace in the rockall trough between soundings of 500 and 2000 m commercial type trawls 20 6 m granton or 140 foot german bottom trawls fished on paired warps at 33 stations accounted for 89 of all individual caught the remainder being caught by a 16 4 m prawn trawl fished on a single warp 22 stations and a 3 m agassiz trawl 12 stations the stations sampled with a few exceptions fell into discrete bathymetric zones separated by increments of approximately 250 m and different combinations of nets were used at each of these zones the catch composition of the commercial trawls differed from those of the other nets the most obvious difference was that squalid sharks the alepocephalid alepocephalus bairdii and the black scabbard fish aphanopus carbo were important in the commercial type trawls but were absent or poorly represented in the other nets net size and towing speed were considered to be important factors influencing the catch composition net selectivity was most apparent on the upper and mid slopes but less apparent on the lower slopes relatively few families contribute to the total biomass at a given bathymetric zone and because the families squalidae and alepocephalidae contribute significantly to the biomass on the upper and mid slope it is therefore concluded that small nets must grossly underestimate the biomass at these depths the greatest biomass occurred at mid slope depths 750 1000 m

half a century of progress in research on terrestrial impact structures a review abstract the author who investigated the wolfe creek australia in 1962 and edited two benchmark sets of readings on meteorite craters and possible astroblemes in 1977 and 1979 reviews the state of knowledge at the present time the text is concerned with terrestrial impact structures geological features without any consideration of extraterrestrial analogues a handful of definitive publications are drawn on to present the story of terrestrial impact in a single article the text covers historical aspects briefly the effect of target variations the paucity of human observation of such large scale events distinction from volcanic endogenous structures modification by geological processes the transience of the crater initially formed on the target and its subsequent modifications the global geographic distribution of the 174 structures now listed of which a number are dubious attributions their distribution in geological time many ages being known only known to wide limits maximum or minimum values their size distribution calculations of impact frequencies shock effects processes on impact the stages of formation impact into shallow marine and deep sea targets impacts on ice about which little is known and finally the input of impact into biotic extinctions in this last lengthy section the summaries of the conclusions of scientists researching impact on earth and palaeontologists researching biotic impact are set side by side it is concluded that if the recent foraminiferal evidence obtained by gerta keller and associates is taken at its face value the case of impact as a sole agent in extinction is non existent biotic extinction is clearly a complex process involving a number of causes in some cases it was staggered in time and different sets of organisms responded quite differently and surprisingly even in the same extinction event extraterrestrial impact may have been one of the causes in some cases but it may have been regional rather than global in its effects we may never know how much input it had into the record of biotic extinction on earth an enormous amount of new knowledge has arisen from detailed studies of this new family of remarkable geological structures

inference of cloud optical depth from aircraft based solar radiometric measurements a method is introduced for inferring cloud optical depth t from solar radiometric measurements made on an aircraft at altitude z it is assessed using simulated radiometric measurements produced by a 3d monte carlo algorithm acting on fields of broken boundary layer clouds generated from landsat imagery and a cloud resolving model the method uses upwelling flux and downwelling zenith radiance measured at two solar wavelengths where atmospheric optical properties above z are very similar but optical properties of the surface atmosphere system below z differ this enables estimation of cloud reflectance into nadir for upwelling diffuse flux and finally t above z an approximate one dimensional radiative green s function is used to roughly account for horizontal transport of photons in all even broken clouds this method is compared to its surface based counterpart and shown to be superior most notably the aircraft based approach deals easily with inhomogeneous land surfaces is less susceptible to poor sampling and need not account for aerosol below z the algorithm appears as though it will have little difficulty inferring high resolution time series of t 40 for most single layer clouds for larger values of t biases emerge particularly underestimation for the statistically infrequent interiors of cumuliform clouds as photon leakage through cloud sides is not addressed for the cumuliform and stratiform clouds used here mean bias errors for retrieved t are 1 or 15 and 0 3 or 3 respectively for stratiform clouds with textured bases performance is likely to improve slightly for flights just up from mean cloud base

influence of subpixel scale cloud top structure on reflectances from overcast stratiform cloud layers abstract recent observational studies have shown that satellite retrievals of cloud optical depth based on plane parallel model theory suffer from systematic biases that depend on viewing geometry even when observations are restricted to overcast marine stratus layers arguably the closest to plane parallel in nature at moderate to low sun elevations the plane parallel model significantly overestimates the reflectance dependence on view angle in the forward scattering direction but shows a similar dependence in the backscattering direction theoretical simulations are performed that show that the likely cause for this discrepancy is because the plane parallel model assumption does not account for subpixel scale variations in cloud top height i e cloud bumps monte carlo simulations comparing 1d model radiances to radiances from overcast cloud fields with 1 cloud top height variations but constant cloud volume extinction 2 flat tops but horizontal variations in cloud volume extinction and 3 v

extreme geomagnetic reversal frequency during the middle cambrian as revealed by the magnetostratigraphy of the khorbusuonka section northeastern siberia abstract we present new magnetostratigraphic results obtained for the drumian stage 504 5 500 5 ma epoch 3 middle cambrian from the khorbusuonka sedimentary section in northeastern siberia they complement previous data that did not allow the determination of a reliable estimate of the geomagnetic reversal frequency during this time magnetization of the samples is carried by a mixture of magnetite and hematite in various proportions thermal demagnetization makes it possible to distinguish two magnetization components the low unblocking temperature 20 reversals per myr during the drumian to 1 5 reversals per myr during the furongian upper cambrian such a sharp decrease is consistent with a transition at a 1 myr timescale probably caused by threshold effects in core processes between two geodynamo modes one characterized by reversals occurring at frequencies ranging from 1 to 5 reversals per myr and the other marked by hyperactivity of the reversing process with reversal rates 15 reversals per myr

neural network retrieval of cloud parameters of inhomogeneous clouds from multispectral and multiscale radiance data feasibility study 1 in this paper we investigated the feasibility of retrieving cloud parameters of inhomogeneous and fractional clouds from simulated multispectral and multiscale radiometric data by using mapping neural networks a radiometric database prepared for neural network training consists of area averaged radiance data for two pixel scales i e 1 km 1 km and 0 25 km 0 25 km pixels respectively the cloud parameter retrieval assumes a vertically uniform inhomogeneous and fractional cloud defined with 6 parameters i e the mean and standard deviation of optical thickness the mean and standard deviation of effective radius the fractional cloud cover and the cloud top temperature all defined at a scale of cloud parameter retrieval the retrieval procedure comprises two separate steps the first one is relative to the angular interpolation and correction of radiance data surface reflection and thermal emission contribution the second step concerns the cloud parameter retrieval as such from interpolated and corrected radiance data the input vector to the retrieval mnns consists of 8 radiometric data in addition to a number of necessary ancillary data such as surface temperature and ground albedo the 8 radiometric data are 5 area averaged radiances over 1 km 1 km pixel and 3 standard deviations of radiance over 1 km 1 km pixel estimated from 0 25 km 0 25 km pixel radiances after evaluating the performance of the neural networks trained for each step we tested the whole retrieval procedure for three types of inhomogeneous and fractional clouds flat top bounded cascade clouds and flat top and non flat top gaussian process clouds all the cloud parameters of these clouds can be retrieved with reasonable accuracy in spite of the fact that the mean and standard deviation of optical thickness of non flat top clouds exhibit some dispersion the inclusion of 0 25 km 0 25 km pixel radiance data as input vector components improved significantly the performance of the cloud parameter retrieval finally we analyzed the consequences of some simplifying assumptions on the retrieved cloud parameters and discussed the perspectives of the cloud parameter retrieval based on the neural networks

numerical simulations and a conceptual model of the stratocumulus to trade cumulus transition abstract a two dimensional eddy resolving model is used to study the transition from the stratocumulus topped boundary layer to the trade cumulus boundary layer the 10 day simulations use an idealized lagrangian trajectory representative of summertime climatological conditions in the subtropical northeastern pacific the sea surface temperature is increased steadily at 1 5 k day 1 reflecting the southwestward advection of the subtropical marine boundary layer by the trade winds while the free tropospheric temperature remains unchanged results from simulations with both a fixed diurnally averaged shortwave radiative forcing and a diurnally varying shortwave forcing are presented a two stage model for the boundary layer evolution consistent with these simulations is proposed in the first stage decoupling is induced by increased latent heat fluxes in the deepening boundary layer after decoupling cloud cover remains high but the cloudiness regime changes from a single stratocumulus layer to sporadic

geomagnetic reversal behaviour since 100 ma abstract the new magnetic polarity time scale of cande and kent j geophys res 97 13917 13951 1992a provides an opportunity to analyse further the random character of the geomagnetic polarity sequence since 100 ma large differences in the peak amplitudes of changes in magnetic reversal frequency are observed when the previous harland et al a geological time scale cambridge university press 1990 and new cande and kent sequences are compared these differences illustrate remaining uncertainties in the significance of these changes when the successive lengths of polarity intervals are displayed as a function of their order of occurrence in the sequence a change in behaviour is observed midway through the series flat white noise like behaviour is observed for the last 100 intervals from about 25 ma to the present for older intervals a quasi periodic pattern in interval duration is observed this evolution is more apparent in the cande and kent time scale the quasi periodicity of interval duration as a function of occurrence does not translate into periodicity of reversal frequency as a function of time from 85 ma to about 25 ma our description of the sequence is reminiscent of the findings of dubois and pambrun c r acad sci 311 643 650 1990 who suggested that low dimensional deterministic chaos between 85 and 25 ma preceded a random process occurring since then the details of a long term control or memory of the geomagnetic field remain an open question addition of independent information such as palaeointensity data will probably be necessary to uncover any determinism in reversal chronology

macrofaunal communities within and adjacent to a detritus rich submarine canyon system abstract macrofaunal abundance biomass diversity and species assemblages within scripps and la jolla submarine canyons are compared with those on the nearby continental shelf and slope our primary objective was to examine the effect of detrital aggregates on infaunal communities within canyons two submarines a remotely operated vehicle rov and a soutar box corer were used to collect samples within the canyons organic enrichment by macrophyte detritus was evident from canyon heads down to 550 m and evidence of strong currents coarse sediment was found down to 700 m infaunal density and biomass were higher in the canyons than outside at all depths where comparative data were available 100 500 m infaunal assemblages in canyons were distinct from those at reference stations both the canyon and non canyons samples showed community differentiation with depth species diversity was generally high but decreased with depth outside of canyons and increased with depth within the canyons low diversity at shallow depths within the canyon is attributed to a combination of organic enrichment and physical disturbance submarine canyons are commonly found to contain distinct species assemblages or higher faunal densities and or biomass than nearby non canyon regions at similar depths canyons are regular features along most ocean margins and appear to be important as sites of enhanced secondary production provide diverse habitats and act as conduits of coastal detritus to the deep sea

complex behavior of the geomagnetic field during three successive polarity reversals 11 12 m y b p detailed paleomagnetic records of both the directional and relative field intensity changes occurring during three sequential polarity reversals have been obtained from marine clays of serravallian tortonian boundary age in the island of zackinthos greece the three reversals are characterized by a complicated geometrical and temporal structure periods of rapid changes of the geomagnetic field vector alternate with periods of near stationarity different episodes of collapse and recovery of the field intensity and the presence of rebounds have been documented overall the records obtained here are reminiscent of volcanic records and appear much more complex and quite different from those previously obtained from upper tortonian marine clays in crete in the same geographical area the bearing of these results on some of the published reversal models is discussed and it is also suggested that the greater complexity of the zackinthos records might be related to the fact that they are exactly coeval with the last reversal spurt documented by reversal frequency analyses

deep sea mobile megafauna of mediterranean submarine canyons and open slopes analysis of spatial and bathymetric gradients abstract mediterranean canyons are generally characterized by complex topography and hydrographic conditions and can act as conduits for organic matter and sediments from the shelf to the deep sea which result in enhanced macro and megafaunal abundance and biodiversity here we reviewed the literature of the last 20 years and combined available information with new data from our own datasets including unpublished data on megafaunal species inhabiting submarine canyons and the adjacent slopes we analysed the data acquired using different gears from baited cameras on aluminum frames and landers and baited traps to commercial trawl gears in order to combine and complement the results in megafaunal biodiversity and assemblage structure in mediterranean canyons overall the results of our analysis on megafaunal assemblages allowed identifying 400 species including 28 species of cephalopods 64 of decapod crustaceans 25 of echinoderms 27 of elasmobranches and 127 of actinopterygii we observed significant longitudinal differences in assemblage composition with high species turnover across mediterranean sub basins our analysis also confirmed the importance of depth axis as the main factor influencing the structure of the deep sea demersal assemblages with greater diversity in the upper part of the slopes the multivariate multiple regression analysis showed that geomorphological features of the canyons i e slope dendricity sinuosity and distance from adjacent canyons contribute significantly to explain the observed variability in the taxonomic composition of megafaunal assemblages at sub basin scale the results presented here are important in global biodiversity management perspectives and confirm that canyons represent a seascape unit deserving protection at different levels modulated according to biogeographic and geomorphological features

geomagnetic reversal history the history of geomagnetic polarity reversals in the cenozoic and late mesozoic is well known since the late jurassic oxfordian a continuous record of polarity has been derived for this time interval from the interpretation of oceanic magnetic anomalies most of the polarity chrons in this oceanic record have been verified and dated in coordinated magnetostratigraphic and biostratigraphic studies this has led to the generation of progressively refined and improved geomagnetic reversal time scales that provide a framework for absolute dating of palaeontological zonations by serving as a basis for statistical analysis of reversal frequency they provide information relevant to processes in the earth s core the rate of reversals since the late cretaceous shows a steady increase on which a cyclical variation appears to be superposed a stochastic model for reversals predicts a poisson distribution of polarity interval lengths the polarity time scales contain many fewer short 50 kyr polarity chrons than a poisson distribution and it has been suggested that a gamma renewal process with index greater than unity is a more appropriate statistical model the statistical arguments give no convincing reason for abandoning the model and other physical reasons must be sought to explain the incompleteness of the reversal record the discovery and verification of short chrons in the oceanic record may best be investigated by deep tow magnetometer surveys the reversal history before the late jurassic is not well known magnetostratigraphy in coeval early jurassic sections has not given correlatable records and it has not been possible to compile a definitive polarity sequence evaluation of geomagnetic polarity history for the early mesozoic and the palaeozoic will require unambiguous magnetostratigraphy in well dated sections where verification of the polarity pattern is possible at the fossil zone or stage level

seasonal fluctuations of deep megabenthos finding evidence of standing stock accumulation in a flux rich continental slope abstract throughout the deep oceans diversity in the benthos peaks at intermediate slope depths in the western mediterranean lower slope an accumulation of biomass but not diversity at depths of 1200 1350 m has been observed however the precise causes of this biomass peak are unknown we examined the patterns of megafauna benthic biomass in the catalan sea open slope from 900 to 1750 m depth expanding the results in the context of the whole continental margin sampling was carried out by combining an otter trawl maireta system otms and an agassiz trawl during four different seasons in 2008 2009 at the same time current speed temperature and salinity were obtained year round by means of near bottom deployed sensors current meters and temperature conductivity sensors total biomass followed an inverted u shaped pattern peaking at depths of 1050 1350 m range related ecological forcings between shallower and deeper species may have caused this biomass accumulation at intermediate slope depths we also report on the seasonal variations of biomass in the studied depth range identifying a dynamic zone above 1000 m depth where populations of highly mobile species perform year round migrations throughout the slope and a more static region below 1000 m i e the twilight zone end with substantially less inter annual variations the arrival of new western mediterranean deep water from the deep basin to the lower slope in march may may have driven the accumulation of biomass at 900 and 1050 m depth over the same period in addition an adjacent submarine canyon was sampled with the same procedures to characterize its benthic megafauna community analyses revealed higher diversity but not biomass inside the canyon than in the adjacent open slope and a significantly different assemblage composition between the two habitats these results strengthen the concept of submarine canyons as hotspots of biodiversity and underline the importance of their conservation as diversity repositories

megafauna of vulnerable marine ecosystems in french mediterranean submarine canyons spatial distribution and anthropogenic impacts abstract vulnerable marine ecosystems vme in the deep mediterranean sea have been identified by the general fisheries commission for the mediterranean as consisting of communities of scleractinia lophelia pertusa and madrepora oculata pennatulacea funiculina quadrangularis and alcyonacea isidella elongata this paper deals with video data recorded in the heads of french mediterranean canyons quantitative observations were extracted from 101 video films recorded during the medseacan cruise in 2009 aamp comex qualitative information was extracted from four other cruises two marum comex cruises in 2009 and 2011 and two ifremer cruises in 1995 and 2010 to support the previous observations in the cassidaigne and lacaze duthiers canyons all the species fishing impacts and litter recognized in the video films recorded from 180 to 700 m depth were mapped using gis the abundances and distributions of benthic fishing resources marketable fishes aristeidae octopodidae vulnerable marine species trawling scars and litter of 17 canyons were calculated and compared as was the open slope between the stoechades and toulon canyons funiculina quadrangularis was rarely observed being confined for the most part to the marti canyon and i elongata was abundant in three canyons bourcart marti petit rhone these two cnidarians were encountered in relatively low abundances and it may be that they have been swept away by repeated trawling the lacaze duthiers and cassidaigne canyons comprised the highest densities and largest colony sizes of scleractinian cold water corals whose distribution was mapped in detail these colonies were often seen to be entangled in fishing lines the alcyonacean callogorgia verticillata was observed to be highly abundant in the bourcart canyon and less abundant in several other canyons this alcyonacean was also severely affected by bottom fishing gears and is proposed as a vulnerable marine species our studies on anthropogenic impacts show that seafloor disturbance by benthic fishing is mainly attributable to trawling in the gulf of lion and to long lines where rocky substrates are present the bauxite residue red mud expelled in the cassidaigne canyon was seen to prevent fauna from settling at the bottom of the canyon and it covered much of the flanks litter was present in all of the canyons and especially in considerable quantities in the ligurian sea where the heads of the canyons are closer to the coast three marine protected areas and one fishing area with restricted access have recently been established and should permit the preservation of these deep ecosystems

do superchrons occur without any palaeomagnetic warning abstract the mainly dipolar geomagnetic field generated by the geodynamo within the earth s liquid core has reversed its polarity many times in the past this succession of intervals of alternate polarity defines the geomagnetic polarity time scale gpts usually interpreted as resulting from a gamma renewal process the rate of which would be controlled by the boundary conditions imposed by the mantle on the core in this interpretation boundary conditions would have occasionally evolved towards being unfavourable to reversals leading the reversal rate of the process to progressively decrease and reach zero at least twice causing the onset of the so called kiaman and cretaceous very long polarity intervals superchrons here we reconsider this causal link analysing the latest and best constrained gpts thanks to the continuous record provided by marine magnetic anomalies describing the past 160 myr we found that contrary to earlier claims no long term behaviour over the 40 myr preceding the cretaceous superchron can be seen in the reversal rate that could explain its onset at 120 ma more generally it turns out that hardly any special behaviour can be identified in the gpts which could have announced this superchron only the occurrence of the longest of all pre superchron intervals cm1n 3 myr before the onset of the superchron could be identified as a precursor such a behaviour could possibly be the consequence of medium term on the 10 myr time scale changes in the boundary conditions imposed by the mantle on the core but we note that the sole analysis of the gpts does not allow this to be tested in fact it appears that a single stationary process could also explain the entire pre superchron gpts with the only possible exception of cm1n this suggests that the occurrence of superchrons does not necessarily require changes in boundary conditions and could simply attest for a sudden non linear transition between a reversing and a non reversing state of the geodynamo

accuracy of the independent pixel approximation for satellite estimates of oceanic boundary layer cloud optical depth a theoretical study has been conducted on the effects of cloud horizontal inhomogeneity on the retrieval of optical depth by remote sensing of visible reflectance forty five landsat scenes of oceanic boundary layer clouds provide a sampling of real cloud fields including trade cumulus open and closed cell broken stratocumulus and solid stratocumulus the spherical harmonic discrete ordinate method shdom radiative transfer model is used to calculate two dimensional reflectances from subsampled cloud strips representing the landsat scenes the independent pixel approximation ipa is used to retrieve optical depth for comparison to the original input results for ipa versus ref are presented on scales from the landsat pixel scale 28 5 m to an imager pixel scale 6 km to near mesoscale 60 km the random error decreases as the averaging scale increases but error due to inhomogeneity remains at the 60 km scale the average error is about 6 for high sun 2 for low sun individual scenes however have retrieved optical depth errors as high as 45 due to horizontal radiative transport the ability to retrieve higher statistical moments of the frequency distribution of optical depth is also assessed sigma the standard deviation of is retrieved quite well up to a point then is underestimated due to the smoothing effect of horizontal radiative transport the gamma function parameter another measure of the width of the frequency distribution is retrieved quite well over a wide range but with a systematic bias which varies with solar zenith angle again due to horizontal radiative transport a method is sought to reduce the optical depth retrieval error using a simple correction based on remotely sensed cloud properties of those considered cloud physical aspect ratio computed here from one possible relation which depends on properties obtainable from remote sensing is found to be the most effective correction parameter the aspect ratio correction reduces the retrieved optical depth bias error by 50 to 100 and the rms error by 20 to 50 correction coefficients are presented at three solar zenith angles this work is limited by its consideration of only single level marine boundary layer clouds assumptions of conservative scattering constant cloud droplet size no gas absorption or surface reflectance and restriction to two dimensional radiative transport future work will attempt to remove some of these limitations the landsat data used are also limited due to radiative smoothing

evaluation of radar retrieval algorithms in stratiform clouds using large eddy simulations the performance of algorithms retrieving cloud liquid water content w from radar reflectivity factor z is evaluated using data from a three dimensional large eddy simulation model with detailed size resolving microphysics on the basis of case studies of a marine stratocumulus cloud observed during the atlantic stratocumulus transition experiment in june of 1992 and a continental stratus cloud observed over north central oklahoma on april 30 1994 it is shown that retrieval algorithms based only on z are very sensitive to cloud microphysics and do not reproduce adequately the horizontally averaged vertical profile of w additional independent measurements are needed to constrain the retrieved w profile surprisingly algorithms show little improvement when the exact concentrations of cloud droplets obtained from the model are included in the calculations vertically integrated liquid water path p is found to be a robust constraint that ensures a more accurate retrieval in the two studied cases an algorithm based on the z w relation of the form z a w b gives an optimal performance when a is inversely proportional to p and b 1 32 the horizontal averaging of p over a computational domain of several kilometers does not affect the accuracy of the retrieval of the horizontally averaged profile of cloud liquid water content which adds to the versatility of the algorithm

dynamics of particles along the western margin of the southern adriatic processes involved in transferring particulate matter to the deep basin abstract the southern adriatic is an area of dense shelf water dsw cascading and open ocean convection the impact of dsw cascading events in transferring organic matter to the deep benthic community and in producing a wide range of bedforms along the continental margin has been highlighted in recent years in order to improve our knowledge on the interannual variability of the dsw cascading with the ultimate goal to understand timing of dsw formation and transport as well as the cascading process its variability in intensity and duration and the ultimate impact of the dense water on the deep sea in march 2009 we deployed an instrumented mooring in a field of sediment waves 860 m depth located down current to the bari canyon in march 2010 a second mooring was installed in the northern channel of the canyon winters 2009 2010 and 2011 were mild and particularly wet and the po river discharge remained relatively high throughout the whole winter hence we expected weak dense shelf water formation associated with a shallow shelf water overflowing off the adriatic shelf by contrast in winter 2012 the north adriatic experienced a severe cold wave with ne bora winds and reduced fresh water input these weather conditions allowed the formation of extremely dense shelf water three additional moorings were quickly deployed during this cold event in the southern adriatic sea to investigate the spatial variability of particle and organic matter fluxes exiting from the adriatic continental shelf under the influence of a strong dsw cascading event slow near bottom currents never exceeding 40 cm s 1 were recorded between march 2009 and february 2012 water temperatures depicted minor negative shifts total mass fluxes tmfs were low annual avg 1 7 2 8 g m 2 d 1 and 0 3 0 6 g m 2 d 1 in the canyon and in the sediment wave field respectively and peak values 6 8 g m 2 d 1 but showed significant seasonal and interannual variability fluxes in the canyon were higher than those measured in the sediment wave field at deeper water depth mass flux peaks during the 2112 dsw cascading were up to 5 times higher than the peaks of previous years up to 18 70 g m 2 d 1 with a spatial variability mainly driven by the localized pathways of dsw cascading in the canyon near bottom currents exceeded 70 cm s 1 and temperature dropped to 12 2 c while current speeds were high also at 1200 m depth 60 cm s 1 in the moat surrounding the dauno seamount surprisingly mass flux peaks occurred from the 16th february to the 1st of march 3 4 weeks ahead of the usual dsw occurrence suggesting an early arrival of the dsw the deep dsw cascading was the main process driving the particle transfer across the southern adriatic margin during late winter spring 2012 mooring data showed a nw se gradient of temperature and kinetic energy from upslope to basin floor indicating slope transverse flow modulated by local obstruction caused by the rugged seafloor topography bari canyon is one of the sites of dsw flow and in this area we have the possibility to extend observations back in time using continuous mooring data since 2009 and previous published materials this approach allowed evaluation of additional mechanisms of particle transport e g open ocean convection storm driven downward transport shallow dense water cascading that are particularly relevant in years when the dsw formation is less vigorous and cascading processes are sluggish the small amplitude of total mass flux peaks the weak currents and the relatively high and constant temperatures recorded during 2009 2010 and 2011 springs are consistent with an enhanced vertical particle rain from a mid water nepheloid layer triggered in turn by a shallow cascading of not particularly dense shelf water detaching from the seafloor when reaches its neutral buoyancy thus the intensity of dsw cascading shallow vs deep plays a first order control on the particulate fluxes through the western margin of the southern adriatic while storm induced sediment transport can occasionally be relevant too

the 13 million year cenozoic pulse of the earth abstract the geomagnetic polarity reversal rate changes radically from very low to extremely high such process indicates fundamental changes in the earth s core reorganization and core mantle boundary heat flow fluctuations however we still do not know how critical such changes are to surface geology and climate processes our analysis of the geomagnetic reversal frequency oxygen isotope record and tectonic plate subduction rate which are indicators of the changes in the heat flux at the core mantle boundary climate and plate tectonic activity shows that all these changes indicate similar rhythms on million years timescale in the cenozoic era occurring with the common fundamental periodicity of 13 myr during most of the time the periodicity is disrupted only during the last 20 myr such periodic behavior suggests that large scale climate and tectonic changes at the earth s surface are closely connected with the million year timescale cyclical reorganization of the earth s interior