comparison of some gridding methods gridding of irregularly spaced data is extremely common in geology and geophysics consider scattered well data depth picks on radiating or irregularly spaced seismic lines and of course land gravity surveys gridding is necessary and prevalent because contouring processing and even forward modeling and inversion require that data be regularly sampled this paper compares the accuracy and efficiency of three gridding methods minimum curvature natural neighbor and equivalent source as applied to potential fields data

did a katian large igneous province trigger the late ordovician glaciation a hypothesis tested with a carbon cycle model abstract the ordovician is known as a period with high temperatures and high sea levels and a cooling event at the end of the period leading to the hirnantian glaciation and the first of the big five mass extinctions of marine life the cause of this cooling event remains unclear several authors correlate it with a drop in atmospheric p co 2 to a threshold permitting the ice accumulation on the gondwana supercontinent however what are the reasons of the atmospheric p co 2 decrease here we follow the hypothesis initiated by barnes 2004 that an ordovician superplume event occurred during the middle to late ordovician such an event would not only have a large impact on the ordovician biodiversification barnes 2004 but it would also be responsible for the climatic upheaval during the late ordovician by the emplacement of a low latitudinal continental basaltic province that had an impact on the atmospheric p co 2 there is no direct evidence of a superplume event or of basaltic traps and the present study is therefore a hypothetical modelling approach where we demonstrate with a numerical box model including carbon alkalinity and phosphorus cycles coupled with a 1d climate model energy balance model ebm francois and walker 1992 that such a scenario allows to explain both the mid ashgill katian global warming event known as the boda event fortey and cocks 2005 and the subsequent late ordovician hirnantian glaciation because silicate weathering is enhanced upon warm and wet climate we try to constrain the size and the latitudinal emplacement of the basaltic province leading to a sufficient consumption of atmospheric p co 2 to the threshold proposed by herrmann et al 2004 a b to initiate a glaciation on gondwana

early palaeozoic cooling events peri gondwana and beyond the short lived end ordovician hirnantian glaciation allied to marine mass extinction is variously considered as a short lived event or as the peak of long drawn out climatic cooling through at least late ordovician early silurian times evidence from early palaeozoic facies faunas and stable isotope excursions used to interpret climatic cooling events ranges farther from late mid cambrian to late silurian times glacigenic sediments structures and geomorphology provide direct evidence of glacial episodes cool water carbonate deposition which is particularly widespread during the late ordovician boda event in high latitude peri gondwana gondwana and beyond into mid low palaeolatitudes is interpreted as indicating global cooling not warming as has been proposed such carbonates also characterize mid latitude continents widely at horizons earlier in the ordovician and more locally in the mid silurian in high latitude gondwana cool water carbonate mounds have distinctive facies controlled mound faunas across palaeocontinents other facies evidence for palaeoclimates includes black shale deposition including deglacial organic rich hot shales which indicate transgression in epeiric seas and sea level curves interpreted from facies and faunal successions correlation is shown between facies evidence and positive c isotope excursions from which cyclicities are apparent the possible interface of orbitally controlled rhythms is considered against evolving palaeobiogeography and changes in global sea level and in pco2 facies and faunal evidence from peri gondwanan terranes armorica central europe alborz is assessed with that from gondwana mostly north africa south america and correlatives in avalonia baltica and laurentia to establish a wider picture of early palaeozoic cooling events

metalliferous mining geophysics state of the art after a decade in the new millennium mining exploration was very active during the first decade of the twenty first century because there were numerous advances in the science and technology that geophysicists were using for mineral exploration development came from different sources instrumentation improvements new numerical algorithms and cross fertilization with the seismic industry in gravity gradiometry kept its promise and is on the cusp of becoming a key technology for mining exploration in potential field methods in general numerous techniques have been developed for automatic interpretation and 3d inversion schemes came into frequent use these inversions will have even greater use when geologic constraints can be applied easily in airborne electromagnetic em methods the development of time domain helicopter em systems changed the industry in parallel improvements in em modeling and interpretation occurred in particular the strengths and weaknesses of the various algorithms became better understood simpler imaging schemes came into standard use whereas layered inversion seldom is used in the mining industry today improvements in ground em methods were associated with the development of squid technology and distributed acquisition systems the latter also impacted ground induced polarization ip methods developments in borehole geophysics for mining and exploration were numerous borehole logging to measure physical properties received significant interest perhaps one reason for that interest was the desire to develop links between geophysical and geologic results which also is a topic of great importance to mining geologists and geophysicists

calibrating the late ordovician glaciation and mass extinction by the eccentricity cycles of earth s orbit a process based sedimentological analysis of upper ordovician glacial marine rocks in africa suggests that full glaciation of the continental shelf started in the late extraordinarius zone of the hirnantian two cycles of ice sheet growth are represented during full glaciation initial terrestrial ice sheet growth in the early extraordinarius zone influenced the first event of the late ordovician mass extinction retreat of the ice sheet from the shelf ended by the persculptus zone when the second event of the late ordovician mass extinction began eccentricity controlled ice sheet growth is assumed periodicity 0 1 m y hence two cycles of full glaciation lasted 0 2 m y the duration of the extraordinarius zone is estimated as 0 5 m y therefore the minimum duration of the first extinction event was 0 3 m y

a mid caradocian 453 ma drawdown in atmospheric pco2 without ice sheet development abstract previous workers have recognized a positive 13 c excursion during the mid caradocian in laurentian and baltic platform carbonates this study documents the mid caradocian guttenberg excursion gice in the kullsberg limestone in central sweden significantly we observed increases in both 13 c and 18 o unlike most previous studies of gice which only observed increased 13 c marine values brachiopods from the lower kullsberg limestone reflect pre excursion conditions having more negative 13 c 0 1 and 18 o 4 to 6 values compared with least altered marine cement from the upper kullsberg limestone which have more positive 13 c 2 1 3 6 and 18 o 1 8 to 3 6 values least altered marine cements from the kullsberg limestone include columnar calcite first generation equant calcite and translucent fibrous calcite from earliest to latest in timing of formation kullsberg seawater during the 13 c excursion event likely decreased in temperature by up to 15 c with an approximate 1 increase in 18 o h 2 o attributable to increased salinity during the mid caradocian the results of this study are consistent with multiple independent approaches to characterize the composition of the ordovician atmosphere hydrosphere systems specifically results of this study are consistent with formation of abiotic calcite at moderately low paleotemperatures during the gice excursion of 10 17 c and ordovician atmospheric pco 2 values of

trace interpolation by slant stack migration the slant stack migration formula based on the radon transform is studied with respect to the depth step z of wavefield extrapolation it can be viewed as a generalized trace interpolation procedure including wave extrapolation with an arbitrary step z for z 0 the formula yields the familiar plane wave decomposition while for z 0 it provides a robust tool for migration transformation of spatially undersampled wavefields using the stationary phase method it is shown that the slant stack migration formula degenerates into the rayleigh sommerfeld integral in the far field approximation consequently even a narrow slant stack gather applied before the diffraction stack can significantly improve the representation of noisy data in the wavefield extrapolation process the theory is applied to synthetic and field data to perform trace interpolation and dip reject filtration the data examples presented prove that the radon interpolator works well in the dip range including waves with mutual stepouts smaller than half the dominant period

radon transform application to the improved gridding of airborne geophysical survey data1 the radon transform is applied to airborne geophysical data which consist of parallel profiles analogous to a seismic record the plane wave decomposition pwd thus becomes the strike direction decomposition sdd since the observed spatially distributed information is represented by its strike directions in a domain achieved by the transformation it is important that after the sdd we can identify anomalies and work on them according to their strikes in particular for gridding purposes we may guide the second interpolation of the bi directional gridding approach along the strike directions in principle the proposed radon transform gridding method rtgm transforms the observed parallel profiles into a domain where information is mapped as its strike direction traces against its wavelengths the number of strike directions into which the data are decomposed is equal to the number of lines to be interpolated the fourier spectrum of the grid is reconstructed from the strike wavenumber domain by using the projection slice theorem and the final square grid is obtained by performing an inverse fourier transformation on the spectrum the sdd is restricted to the nyquist wavenumber bandwidth imposed by the survey line spacing so that there is no addition of ambiguous short wavelengths in the gridded data a tapering window is employed to prevent any gibb s oscillation in the final grid because of the sharp nyquist cut off in the reconstructed spectrum due to the survey line spacing the rtgm is first tested on a set of synthetic line based data it is also applied to aeromagnetic profile data from northern botswana as a practical example

numerical studies of submerged moored box type floating breakwaters with different shapes of cross sections using sph abstract the wave attenuation performances and hydrodynamics of moored box type floating breakwaters with the same weight same wall thickness and six different cross sections i e circular triangle down triangle up rectangular trapezoid down and trapezoid up are investigated numerically using the smoothed particle hydrodynamics sph method coupling between dualsphysics and moordyn is implemented in the coupled sph mooring model the effects of the key parameters such as the breakwater density immersion depth ballast water gravity and wave condition on wave attenuation performance are examined systematically the results reveal that the performances of floating breakwaters are significantly affected by the immersion depth and wave condition however they are hardly affected by density and ballast water gravity furthermore the top deck is found to be an extremely effective part of a well designed breakwater and asymmetrical designs such as longer top faces and shorter bottom faces should be adopted for achieving reasonable material utilizations irrespective of the shapes of the cross sections the best performances of the different breakwaters are almost at the same level after careful designs are implemented importantly a strong relationship is identified between the motions mooring tensions and wave attenuation performances which implies that the motions are directly proportional to the wave attenuation performances and the mooring tensions

numerical simulation of interactions between water waves and inclined moored submerged floating breakwaters abstract this paper studies the interactions of water waves with submerged floating breakwaters moored by inclined tension legs using a numerical wave tank model proposed by lee and mizutani 2009 and based on the navier stokes solver this model combines a direct forcing immersed boundary ib method volume of fluid vof method and the mechanics model of the floating breakwater the floating breakwaters are free on three degrees of freedoms namely surge heave and pitch two floating breakwater shapes rectangular and circular are used in the experimental and numerical investigations to validate that the model is capable of treating solid boundaries with complex shapes the non breaking and breaking waves are carefully chosen to study the nonlinear interactions between water waves and the submerged floating breakwaters comparisons of the computed and measured results reveal a favorable agreement in terms of the free water surface tension force acting on the mooring line and dynamics of the floating body a slight phase discrepancy is found between the offshore and onshore mooring forces in the case of a circular floating breakwater whereas this phenomenon is not observed in the rectangular case in addition fully nonlinear phenomena and viscous process in the flow field such as wave breaking the boundary layer separation on the interface vortex formation and motion can be reproduced and captured accurately using the numerical model

trace interpolation in seismic data processing trace interpolation of spatially aliased seismic data is used to improve the quality of multi trace processing especially that of migration we consider non rectangular sampling lattices after stating the real sampling requirements for two dimensional or 3 d digitized signals the paper explains geometrically the effect of migration and of the 2 d dip filtering upon the aliased events as well as our ability to interpolate traces from undersampled seismic data

interpretive gridding by anisotropic kriging most interpolation algorithms perform poorly on data sampled along profiles crossing features whose length scales are small along the profiles but large transverse to them such as lineaments rather than reproducing the linear features these algorithms create a series of closures around the profiles by introducing additional information into the algorithm in particular by using an anisotropic covariance model for kriging that contains a priori information about the lineations more realistic results can be obtained an algorithm of this type produces a much more reasonable map of aeromagnetic data from the cobb offset zone of the juan de fuca ridge than either minimum curvature gridding or isotropic kriging

the fractal dimension of gravity data sets and its implication for gridding gravity survey station locations are in general inhomogeneously distributed this inevitably results in interpolation errors in the computation of a regular grid from the gravity data the fractal dimension of the station distribution can be used to determine if an interpolated map is aliased at a specific wave length and moreover it is often possible to determine an optimum gridding interval synthetic distributions of gravity station locations have been used for theoretical studies and it is found that for randomly distributed data there is a range of sizes for which the spatial data distribution has a fractal dimension of 2 that is euclidean the minimum length scale at which the distribution ceases to be euclidean is the optimum interpolation interval obeying shannon s sampling theorem for dimensions less than 2 the optimum interpolation interval is the shortest length at which the scaling regime is constant in this case the gravity field cannot be interpolated without introducing some aliasing as the fractal dimension characterizes the data distribution globally over the whole study area the actual gridding interval in some cases will be smaller in order to represent short wavelength features properly in the more densely sampled sub areas but this may generate spurious anomalies elsewhere the proposed technique is applied to the station distribution of the canadian national gravity data base and a series of sub areas a fractal dimension of 1 87 is maintained over a range of sizes from 15 km to over 1600 km although aliasing occurs since the gravity field certainly contains much shorter wavelength anomalies aliasing errors may be minimized by selecting the proper interpolation interval from the fractal analysis

automated trend reinforcement of aeromagnetic data aeromagnetic maps poorly represent lineaments that are at acute angles to the flight line direction commonly used gridding algorithms cannot cope with local trends magnetic anomalies at an angle with the main trend of the map and tend to generate closed contours around the flight lines by introducing some a priori information it is possible to add extra data between the flight lines i e trend lines to reinforce local trends the proposed automated technique is based on a nearest neighbour search of the maxima and minima in the aeromagnetic map the resulting map is more realistic and derived maps such as vertical gradients and analytical signal maps are greatly improved moreover this automated procedure is user independent and easy to implement the technique is demonstrated on aeromagnetic data from the kirkland lake region in north eastern ontario canada

simulating the wave induced response of a submerged wave energy converter using a non hydrostatic wave flow model abstract with the increasing interest in wave energy and when moving towards commercial scale wave energy projects a detailed understanding of the interactions between single and arrays of wave energy converters wecs with the ambient wave and flow field becomes imperative for both design and operational purposes as well as assessment of their environmental impacts this work presents a new numerical approach to simulate the nonlinear evolution of the waves and their interactions with a submerged wave energy converter at the scale of a realistic coastal region the numerical approach is based on the non hydrostatic framework and implemented in the open source swash model which provides an efficient tool to simulate the nonlinear evolution of waves over realistic coastal bathymetries here we present a numerical extension to the non hydrostatic approach to account for interactions between waves and a submerged point absorber and to capture the response of such a wave energy device model results are compared with an analytical solution based on potential flow theory a cfd simulation and experimental data to validate its capabilities in simulating the wave wec interactions for both linear and nonlinear wave conditions overall the results of this validation demonstrate that the model captures the wave structure interactions and the body response with satisfactory accuracy notably the results also indicate that a coarse vertical resolution was sufficient to capture these dynamics making the model sufficiently computationally efficient to simulate the interaction of waves and wecs over large scales as a consequence this new modelling approach should provide a promising new alternative to simulate the interactions between nonlinear wave fields and submerged point absorbers at the scale of a realistic coastal region

the late ordovician mass extinction abstract near the end of the late ordovician in the first of five mass extinctions in the phanerozoic about 85 of marine species died the cause was a brief glacial interval that produced two pulses of extinction the first pulse was at the beginning of the glaciation when sea level decline drained epicontinental seaways produced a harsh climate in low and mid latitudes and initiated active deep oceanic currents that aerated the deep oceans and brought nutrients and possibly toxic material up from oceanic depths following that initial pulse of extinction surviving faunas adapted to the new ecologic setting the glaciation ended suddenly and as sea level rose the climate moderated and oceanic circulation stagnated another pulse of extinction occurred the second extinction marked the end of a long interval of ecologic stasis an ecologic evolutionary unit recovery from the event took several million years but the resulting fauna had ecologic patterns similar to the fauna that had become e

a pre hirnantian late ordovician interval of global cooling the boda event re assessed facies analysis suggests that the early mid ashgill late ordovician boda event of fortey and cocks fortey r a cocks l r m 2005 late ordovician global warming the boda event geology 33 5 405 408 was an episode of global cooling not of warming as they proposed limestones are widely developed at this level from mid latitude to high latitude commonly interrupting thick ordovician successions of fine clastic sediments bryozoan carbonate mud mounds in a laterally extensive cool water carbonate belt along the high palaeolatitude margin of w gondwana are associated with glacial diamictites and grew during glacial lowstand with sea ice prior to the hirnantian glaciation from high to mid palaeolatitudes contemporaneous cool water carbonates with mud mounds including stromatactis both in gondwana and in baltica developed in mid outer ramp settings during regression in the dominantly clastic welsh basin of avalonia phosphatic facies on an iapetus facing carbonate ramp indicate upwelling cold waters down ramp yet up ramp coralliferous algal limestones suggest warm surface waters we propose that the late ordovician cool water carbonates developed in response to global cooling and expansion of gondwanan terrestrial and sea ice that lowered eustatic sea level and on the w gondwanan shelf reduced or shut down fluvial clastic input previously poorly circulated salinity stratified oceans that had restricted benthic dispersal in mid low latitudes were replaced by thermohaline ocean circulation that oxygenated bottom waters and dispersed benthic faunas an earlier caradoc carbonate interval in low mid palaeolatitudes that shares many facies characteristics with the ashgill cool water limestones and correlates with a widely recognised isotope excursion is interpreted as indicating an earlier global cooling episode

high resolution carbon isotopic records from the ordovician of south china links to climatic cooling and the great ordovician biodiversification event gobe abstract the great ordovician biodiversification event gobe represented the largest increase in diversity in the marine biosphere during the phanerozoic eon yet its causes and consequences remain poorly understood patterns of isotopic variation in high resolution 13ccarb and 13corg records from a well exposed section at honghuayuan in south china may provide important insights regarding the gobe the honghuayuan isotopic profiles which can be correlated with c isotopic records from contemporaneous sections globally reveal large perturbations to the global carbon cycle during the ordovician a 8 increase in 13corg values in the floian implies a large albeit transient increase in the burial rate of organic matter during the mid early ordovician that may have contributed to climatic cooling and played an important role in triggering the gobe a 4 increase in 13ccarb and high frequency variation in 13corg in the darriwilian to sandbian suggest a second episode of elevated organic carbon burial rates accompanied by substantial instability in the global carbon cycle during the late middle and early late ordovician this pattern may mark the onset of climate changes culminating in the end ordovician hirnantian glaciation and mass extinction event that terminated the gobe

trend enhancement in aeromagnetic maps using constrained coherence enhancing diffusion filtering abstractgeophysical data have to be modeled on a regular grid for various numerical procedures however airborne data tend to be collected with fine spacing along traverses but with much coarser spacing between traverses gridding only honors flight line data when the mesh size is close to the sample spacing otherwise high frequency information is always lost which creates aliasing artifacts for example linear trends at an acute angle with respect to flight lines are imaged as bull s eyes which resemble a boudinage at line intersections the presence of boudinage artifacts can significantly distort anomalies of interest and thus lead to incorrect interpretation of shapes or sizes of causative bodies we evaluated a method called constrained coherence enhancing diffusion filtering that only diffuses the image in specific areas where strong anisotropy is detected this method was tested on synthetic and field data set results indicated that the method can be efficiently used to enhance linear stru

numerical modeling of dynamic responses and mooring forces of submerged floating breakwater using the volume of fluid vof method a numerical model is developed to estimate the nonlinear dynamics of a pontoon type moored submerged breakwater under wave action and the forces acting on the mooring lines for both the vertical and inclined mooring alignments the model is developed for a two dimensional wave field in a vertical plane the finite displacements of the breakwater such as sway heave and roll in a very small time step are considered and the numerical grid cells intersected by the breakwater surfaces for changing its position due to wave action are treated using the concept of porous body model also two dimensional experimental studies are carried out to investigate the performance of the proposed model the comparison of the computed and measured results reveals that the developed numerical model can reproduce well the dynamics of the floating body and the mooring line forces

stratigraphic variation in marine carbonate carbon isotope ratios stratigraphic variation in the carbon isotopic 13c value of marine carbonate and organic matter preserved within it has become a popular tool for supporting paleoclimatic hypotheses and refining stratigraphic correlation virtually every important biostratigraphic and sequence stratigraphic event of the last 800 million years has had a 13c dataset collected to aid in interpreting the causal environmental factors that contributed to the event the stratigraphic resolution obtainable using 13c has yielded critical temporal constraints on the interplay between carbon cycle variation and environmental events such as mass extinction and eustasy although the non uniqueness of the carbon isotopic response to different environmental stimuli has frustrated the identification of a unified mechanism linking marine 13c variation with distinct environmental forcing functions the interpretation of 13c variation can nonetheless provide important insights into processes that influence major global climatic and surficial systems early studies of marine carbonate minerals suggested that the 13c value of ancient oceans was essentially 0 versus the peedee belemnite standard pdb clayton and degens 1959 schidlowski et al 1975 see also keith and weber 1964 it was later recognized however that departures from the pdb standard represented secular variation in the 13c values of the marine environment rather than analytical noise that the record was potentially rich with stratigraphic and paleoenvironmental information scholle and arthur 1980 veizer et al 1980 wadleigh and veizer 1982 arthur et al 1985 holser et al 1986 zachos and arthur 1986 and that variation was intimately linked to the global carbon oxygen and sulfur cycles kump and garrels 1986 holser et al 1988 it is now well established that carbonate 13c values vary within 3 from the pdb standard for

first plants cooled the ordovician the late ordovician period ending 444 million years ago was marked by the onset of glaciations the expansion of non vascular land plants accelerated chemical weathering and may have drawn down enough atmospheric carbon dioxide to trigger the growth of ice sheets

interpolation and gridding of aliased geophysical data using constrained anisotropic diffusion to enhance trends geophysical data are frequently collected with a fine sample interval along traverse lines but with a coarser sampling in the direction perpendicular to the traverses this disparity in sampling intervals is particularly evident when magnetic data are collected simultaneously with airborne electromagnetic data interpolating this traverse data onto an evenly spaced 2d grid can result in aliasing artifacts for example narrow linear structures that trend at acute angles to the traverse lines are imaged as a thick thin thick feature looking like a boudinage or string of beads applying the anisotropic diffusion process to the resulting grids of data removes the artifacts but the grid values close to the traverses are altered significantly from their initial values the altered values are therefore not faithful to the original traverse data the anisotropic diffusion algorithm can be modified to constrain values close to the original traverses this modification removes the aliasing artifacts and produces a data grid faithful to the original traverse data some small artifacts along the traverse lines in the final data grid become more evident when grids containing derivative data such as the analytic signal are generated from the new data grid however these small traverse line artifacts can be removed with standard microleveling procedures the constrained anisotropic diffusion process is iterative and some experimentation is required to determine the appropriate number of iterations

three dimensional structure and temporal evolution of submesoscale thermohaline intrusions in the north pacific subtropical frontal zone abstract four instances of persistent intrusive deformation of the north pacific subtropical front were tagged individually by a lagrangian float and tracked for several days each feature was mapped in three dimensions using repeat towed observations referenced to the float isohaline surface deformations in the frontal zone included sheetlike folds elongated in the alongfront direction and narrow tongues extending across the front all deformations appeared as protrusions of relatively cold and fresh water across the front no corresponding features of the opposite sign or isolated lenslike structures were observed the sheets were o 10 m thick protruded about 10 km into the warm saline side of the front and were coherent for 10 30 km along the front having about the same thickness and cross frontal extent as the sheets tongues extended less than 5 km along the front all of the intrusions persisted as long as they were followed several days to one week their structures evolved on both inertial

polar front shift and atmospheric co2 during the glacial maximum of the early paleozoic icehouse our new data address the paradox of late ordovician glaciation under supposedly high pco2 8 to 22 pal preindustrial atmospheric level the paleobiogeographical distribution of chitinozoan mixed layer marine zooplankton biotopes for the hirnantian glacial maximum 440 ma are reconstructed and compared to those from the sandbian 460 ma they demonstrate a steeper latitudinal temperature gradient and an equatorwards shift of the polar front through time from 55 70 s to 40 s these changes are comparable to those during pleistocene interglacial glacial cycles in comparison with the pleistocene we hypothesize a significant decline in mean global temperature from the sandbian to hirnantian proportional with a fall in pco2 from a modeled sandbian level of 8 pal to 5 pal during the hirnantian our data suggest that a compression of midlatitudinal biotopes and ecospace in response to the developing glaciation was a likely cause of the end ordovician mass extinction

a new method for interpolating linear features in aeromagnetic data this paper is 2019 society of exploration geophysicists the posting is available free of charge and its use is subject to the seg terms and conditions https seg org terms of use

an atmospheric pco2 threshold for glaciation in the late ordovician the late ordovician glaciation differs from other major phanerozoic glaciations because of its short duration 1 m y a satisfactory explanation for this glaciation must be able to account for its sudden initiation short duration and rapid termination mechanisms operating on tectonic time scales appear to be precluded given recent studies of a major perturbation in the carbon cycle during the glaciation a climate model investigation of the sensitivity of the late ordovician climate to changes in atmospheric p co2 was undertaken under the condition of a 4 5 reduction in solar luminosity permanent snow cover taken as a key indicator of potential for glaciation is dramatically different between five experiments the range of 18x present atmospheric level co2 ice free to 8x runaway icehouse lies within the uncertainty of previous geochemical estimates of late ordovician atmospheric p co2 the strong sensitivity to the modest direct forcing from p co2 changes is due to the ice albedo feedback a plausible increase in organic carbon burial could have drawn down enough atmospheric co2 to have briefly lowered the climate system below a critical glacial inception threshold at the end of the ordovician conversely a high p co2 is required for the rest of the early paleozoic which was essentially ice free

modeling the early paleozoic long term climatic trend the early paleozoic climate has been described as warm and equable however recent data based on conodont oxygen isotopic composition reveal a large long cooling trend through the ordovician followed by an abrupt cooling during the late ordovician glaciation this long term climate change is associated with a major radiation in the earth life history nonetheless the driving mechanisms for this cooling trend remain unknown carbon dioxide consumption by the weathering of fresh rocks from volcanic arcs has recently been suggested as a possible driver for this climate change however the impact of the plate motion context has not been explored yet although it might have a major impact on atmospheric co 2 levels simulations with a climate model coupled to a biogeochemical model geoclim show that the atmospheric co 2 decreased from more than 20 pal 5600 ppmv in the furongian down to approximately 10 pal 2800 ppmv in the llandovery before rising again in the early devonian we suggest that changes in geography and exposure of fresh volcanic rocks on continents are required to explain the large co 2 drawdown that led to the onset of cooler to glacial conditions from the middle ordovician to the llandovery the weathering of fresh volcanic rocks is itself responsible for 33 of the late ordovician atmospheric co 2 decrease the rest being related to the continent motion through the intertropical convergence zone itcz mean annual continental temperature falls by 3 c in the early ordovician reaching 13 5 c during the glacial interval and rises to 16 c in the early devonian