granular disintegration of marble in nature a thermal mechanical origin for a grus and corestone landscape abstract here we document for the first time in detail a natural landscape dominated by granular disintegration of marble and the associated production of marble grus sediment and corestones we provide several lines of evidence for a thermal mechanical origin for the observed granular disintegration and resulting corestones in the san bernardino mountains of southern california calcite marble outcrops whose average grain diameter is greater than approximately 0 5 mm are weathering into grus sediment and exhibit a corestone morphology minimal soil development in thick grus colluvium combined with results from a simple erosion experiment indicates that grus production and erosion is rapid our data indicate that unlike granite marble granular disintegration and corestone development is a uniquely sub aerial process environmental scanning electron microscope esem and micro probe analyses of rock samples collected in recent quarry exposures indicate that detachment of grain boundaries occurs primarily within the upper 2 20 cm of the outcrop surface there is minimal evidence of secondary calcite dissolution or precipitation at grain boundaries below the upper most few centimeters of the rock surface despite widespread intergranular fracturing at depths greater than 20 cm below the natural ground surface granular disintegration and corestone weathering are not evident and dissolution and precipitation of secondary calcite is only observed within a few centimeters of joint planes corestone morphology appears to form through the erosion of loosened grus debris at sharp edges of subaerially exposed joints the resulting form represents a morphologic equifinality to that of granite corestones and results from different processes than those which have been proposed for granite an 8 month once per three minute temperature record from a thermocouple embedded into a marble corestone indicates that the upper 2 5 cm of the corestone regularly achieves temperatures greater than 40 c the temperature which is thought to be sufficient to produce permanent strain in calcite all of these results are consistent with theoretical and experimental studies that indicate that marble is susceptible to mechanical weathering by thermal processes overall this study provides new documentation that solar heating and cooling can be an important driver of physical weathering in natural systems of the earth s surface

stone temperature and moisture variability under temperate environmental conditions implications for sandstone weathering abstract temperature and moisture conditions are key drivers of stone weathering processes in both natural and built environments given their importance in the breakdown of stone a detailed understanding of their temporal and spatial variability is central to understanding present day weathering behaviour and for predicting how climate change may influence the nature and rates of future stone decay subsurface temperature and moisture data are reported from quarry fresh peakmoor sandstone samples exposed during summer june july and late autumn early winter october december in a mid latitude temperate maritime environment these data demonstrate that the subsurface thermal response of sandstone comprises numerous short term minutes low magnitude fluctuations superimposed upon larger scale diurnal heating and cooling cycles with distinct aspect related differences the short term fluctuations create conditions in the outer 5 10 mm of stone that are much more energetic in comparison to the more subdued thermal cycling that occurs deeper within the sandstone samples data show that moisture dynamics are equally complex with a near surface region 5 10 mm in which frequent moisture cycling takes place and this combined with the thermal dynamism exhibited by the same region may have significant implications for the nature and rate of weathering activity data indicate that moisture input from rainfall particularly when it is wind driven can travel deep into the stone where it can prolong the time of wetness this most often occurs during wetter winter months when moisture input is high and evaporative loss is low but can happen at any time during the year when the hydraulic connection between near surface and deeper regions of the stone is disrupted with subsequent loss of moisture from depth slowing as it becomes reliant on vapour diffusion alone these data illustrate the complexity of temperature and moisture conditions in sandstone exposed to the moderate conditions of a temperate maritime environment they highlight differences in thermal and moisture cycling between near surface 5 10 mm and deeper regions within the stone and contribute towards a better understanding of the development of structural and mineralogical heterogeneity between the stone surface and substrate

effect of surface roughness on bidirectional reflectance of antarctic snow the angular pattern of sunlight reflected by snow is altered by surface roughness which in the interior of antarctica is usually in the form of meter scale longitudinal erosional features sastrugi whose axes align with the direction of strong winds the bidirectional reflectance distribution function brdf changes over the course of a day as the solar azimuth changes relative to the sastrugi axis the normalized brdf or anisotropic reflectance factor r was measured at south pole station from a 22 m tower at 600 660 and 900 nm wavelengths the r pattern was similar at the three wavelengths it probably varies little from 300 to 900 nm measurements were made at solar zenith angles 0 from 67 to 90 over the full range of viewing zenith angle r azimuth angle between sun and view and azimuth angle between sun and sastrugi sas variation of r with sas was notable sastrugi oriented perpendicular to the solar beam cause a reduction of the forward peak and sastrugi at an oblique angle cause r to lose its symmetry about the solar azimuth however the effects of sastrugi are mostly restricted to large viewing zenith angles so remote sensing of albedo and atmospheric properties can be carried out accurately without knowledge of sastrugi height and orientation if only near nadir views are used this recommendation is opposite that for observations of broken clouds over dark surfaces for which large r is preferred a parameterization of r is developed valid for viewing angles r 50 sastrugi can cause a reduction of the snow albedo by altering the angle of incidence and by trapping of photons for the small sastrugi of the antarctic plateau the albedo is unaffected at visible wavelengths but can be reduced by a few percent at near infrared wavelengths when the sun is low

on the joint distribution of surface elevation and slopes for a nonlinear random sea with an application to radar altimetry the work of longuet higgins 1963 on the effects of wave nonlinearity on the statistics of the sea surface is extended here to obtain the joint distribution of surface elevation and slopes for a nonlinear random sea the results are used to examine the effect of wave nonlinearity on the form of a radar altimeter pulse which is reflected from the sea surface it is shown how wave information may be derived from the return pulse and how this can be used to correct errors in the altimeter mean sea level estimate a problem known as sea state bias

weathering of granite in antarctica ii thermal stress at the grain scale granular disintegration has long been recognized and referred to in weathering texts from all environments including the antarctic despite this universal identification and referral few to no data exist regarding thermal conditions at this scale and causative mechanisms remain little more than conjecture here as part of a larger weathering study thermal data of individual grains using infrared thermometry and ultra fine thermocouples composing a coarse granite as well as the thermal gradients in the outer 10 cm using thermistors were collected from a north facing exposure measurements were also made regarding the surface roughness of the rock based on recorded temperatures the nature of the rock surface and the properties of the minerals an argument is made for complex stress fields that lead to granular disintegration mineral to mineral temperature differences found to occur were in part due to the changing exposure to solar radiation through the day and through seasons because the thermal conductivity and the coefficient of thermal expansion of quartz are not equal in all directions coupled with the vagaries of heating this leads to inter granular stresses although fracture toughness increases with a decrease in temperature it is suggested that the tensile forces resulting from falling temperatures are able to exceed this and produce granular disassociation the lack of equality with respect to crystal axis of both thermal conductivity and expansion in quartz further exacerbates the propensity to failure grain size and porosity also influence the thermal stresses and may help explain why some grains are held in place despite disassociation near the surface while the data presented here appear to beg more questions than providing answers they do provide a basis for better more detailed studies of this important weathering scale copyright 2007 john wiley sons ltd

sea level anomalies in the tropical atlantic from geosat data assimilated in a linear model 1986 1988 dong track sea level anomalies derived from geosat altimeter data from november 1986 to november 1988 are assimilated by kalman filtering into a wind forced second baroclinic vertical mode linear model of the tropical atlantic ocean to save computer time the filter is degraded mostly by king the error covariance matrix of the estimate once the filter has reached its asymptotic behavior geosat altimeter data have been processed using improved corrections the sea surface height variability signal is extracted using the classical along track technique relative to a complete reference cycle and using only tracks longer than 2200 km this processing has preserved oceanic signals both on large scales above 1000 km and on the mesoscale around 200 km sea level anomalies predicted at principe island are close to in situ tide gage data though some differences can be partly related to tidal or orbit error corrections oceanographic signals are analyzed from two different sets of fields one issued from anisotropic space time objective analysis of geosat data and the other from the model assimilation the latter appears as an interesting method to extract low frequency and propagating signals along the equator eastward propagating features are consistent with kelvin waves correlated with mnal wind stress anomalies upwelling in the gulf of guinea is 1 month earlier in 1987 than in 1988 after elimination of the annual and semiannual signals by harmonic analysis the residual signal over the whole tropical basin decomposed into complex empirical orthogonal functions is found dominated by variations between the 2 years equatorial and tropical signals being anticorrelated

late pleistocene and holocene paleoenvironments of chalco lake central mexico abstract in order to establish paleoenvironmental conditions during the late quaternary four cores from the basin of mexico central mexico were drilled in chalco lake located in the southeastern part of the basin the upper 8 m of two parallel cores were studied using paleomagnetic loss on ignition pollen and diatom analyses based on 11 14c ages the analyzed record spans the last 19 000 14c yr b p volcanic activity has affected microfossil abundances both directly and indirectly resulting in absence or reduction of pollen and diatom assemblages important volcanic activity took place between 19 000 and 15 000 yr b p when the lake was a shallow alkaline marsh and an increase of grassland pollen suggests a dry cold climate during this interval abrupt environmental changes with increasing moisture occurred from 15 000 until 12 500 yr b p the lake level increased and the pollen indicates wetter conditions the highest lake level is registered from 12 500 to ca 9000 yr b p the end of the pleistocene is characterized by an increase in humidity from 9000 until ca 3000 yr b p chalco lake was a saline marsh and the pollen record indicates warmer conditions after 3000 yr b p the lake level increased and human disturbance dominates the lacustrine record

statistical analysis of the spatial evolution of the stationary wind wave field detailed investigation of wind generated water waves in a 5 m long wind wave flume facility is reported careful measurements were carried out at a large number of locations along the test section and at numerous airflow rates the evolution of the wind wave field was investigated using appropriate dimensionless parameters when possible quantitative comparison with the results accumulated in field measurements and in larger laboratory facilities was performed particular attention was given to the evolution of wave frequency spectra along the tank distinguishing between the frequency domain around the spectral peak and the highfrequency tail of the spectrum notable similarity between the parameters of the evolving wind wave field in the present facility and in field measurements was observed

satellite altimeter measurements of surface wind recent analyses of wind speed measurements by the geosat altimeter showed that the radar cross section is affected by oceanographic factors particularly by the degree of sea development which are not directly accounted for in the geophysical model functions gmf in the present work two new gmfs which account for the effects of the actual degree of sea development are proposed along with the radar cross section these models use significant wave height information one particular version is recommended for applications in oceanographic and climate studies where wind speed or wind stress data have to be binned i e averaged over time and or space intervals the accuracy of this gmf overall bias of 0 1 m s and rms error of about 1 6 m s is higher than the accuracy of commonly employed gmfs while the wave age related trend is reduced to a geophysically insignificant level finally the wind speed histograms for the collocated data set are derived and compared with the ground truth data as well as with the histograms yielded by presently known gmfs it is also shown that the accuracy of altimeter measurements could be increased even further if some additional information on the wave field were available from independent sources e g the dominant wavelength from synthetic aperture radar images

boulder weathering in mcmurdo dry valleys antarctica abstract earth s dynamic surface undergoes a continuous cycle of mountain building and denudation one of the important links in this cycle is the break up and comminution of the rocks that allows for effective transportation of debris by surface processes the starting and end points in this transformation are well known bedrock and boulders on one end and silt and clay on the other however the existing knowledge of the rates and processes responsible of the intermediate steps is currently limited to fill this gap in knowledge we studied boulders and their weathering products in the mcmurdo dry valleys antarctica that have been weathering for hundreds of thousands of years sub aerially exposed at the ground surface our study boulders of locally distinct lithology have trails of rock fragments leading downhill revealing the rate of weathering and subsequent transport rate of the fragments the rock fragments emanate from the source boulder and decrease in size as the distance downslope increases we measured the fragment sizes and distances for various lithologies on varying slope angles we found that large fragments up to 0 4 m in diameter can be transported up to 60 m downslope by unknown processes the total length of the fragment trail increases with the slope angle the maximum transport distances of sandstone boulders are approximately 10 times longer than other lithologies which may be explained by the larger observed fragment sizes of the sandstones on the other hand measurements of the smaller generally less than 0 04 m diameter fragments that are transported by wind revealed much shorter transport distances

evidence for freeze thaw events and their implications for rock weathering in northern canada discussions regarding weathering in cold environments generally centre on mechanical processes and on the freeze thaw mechanism in particular despite the almost ubiquitous assumption of freeze thaw weathering unequivocal proof of interstitial rock water actually freezing and thawing is singularly lacking equally many studies have used the crossing of 0 c or values close to that as the basis for determining the number of freeze thaw events in order to assess the weathering regime at a site in northern canada temperatures were collected at the surface 1 cm and 3 cm depth for sets of paving bricks with exposures both vertical and at 45 orientated to the four cardinal directions temperature data were collected at 1 min intervals for 1 year these data provide unequivocal proof for the occurrence of the freezing and thawing of water on and within the rock freeze thaw events the freeze event is evidenced by the exotherm associated with the release of latent heat as the water actually freezes this is thought to be the rst record of such events from a eld situation more signi cantly it was found that the temperature at which freezing occurred varied signi cantly through the year and that on occasion the 1 cm depth froze prior to the rock surface the change in freeze temperature is thought to be due to the chemical weathering of the material coupled with on going salt inputs via the melting of snowfall which it is shown could occur throughout the winter despite air temperatures down to 30 c this nding regarding chemical weathering is also considered to be highly signi cant a number of thermal stress events were also recorded suggesting that rock weathering in cold regions is a synergistic combination of various chemical and mechanical weathering mechanisms copyright 2003 john wiley sons ltd

influence of mineralogy on granite decay induced by temperature increase experimental observations and stress simulation abstract rocks can be subjected to high temperatures in several instances as for example in geothermal processes or if affected by fires temperature variations lead to a complex stress distribution in crystalline rocks due to mineral thermal expansion in polymineralic such as granites these stresses depend on fabric parameters such as mineral proportion grain size and their related thermal properties eight granitic rocks were heated to less than 400 c and their decay patterns were observed and quantified by means of scanning electron microscopy heating was also modeled by finite element simulations oof software with polymineralic microstructures quartz feldspar and biotite contents were used as a variable in the model in order to elucidate the influence of mineralogy on the thermal elastic response of granites real and modeled heating showed similar trends of microcracking in microstructures and of thermal expansion coefficients microscopic observations of real samples revealed mainly intragranular microcracks in quartz opening of cleavage plains and deformation in mica simulations confirmed that in spite of the high thermal and anisotropic expansion of quartz the microstructure of rocks with large amounts of quartz does not necessarily experience large stresses biotite produces a concentration of stresses along their grain boundaries as a result oof models with 10 biotite showed higher stresses than monomineral ones thermal expansion coefficients of real granites fitted within the limits of the simulated ones proving once more the success of using finite element modeling applied to polymineralic rocks

the historical legacy of spatial scales in freeze thaw weathering misrepresentation and resulting misdirection discussion of weathering in cold regions has historically been dominated by widespread acceptance of the significance of the freeze thaw concept among periglacial geomorphologists and an essentially universal acceptance by those geomorphologists not directly involved in researching the topic debris produced by freeze thaw is frequently deemed to be angular in form and the observation of such debris has been used to identify the former or present operation of this weathering mechanism large debris blocks and small debris grains or flakes have been recognised as the outcome of the two scales of freeze thaw weathering macrogelivation and microgelivation respectively however the fusion of climatic geomorphology and process geomorphology in the ongoing development of the freeze thaw concept has resulted in the confusion of product with process whereby microgelivation producing small products and macrogelivation producing large products are seen due to the product dichotomy as distinctly different processes despite the recent highly sophisticated laboratory experimentation on freeze thaw weathering this historical process scale dichotomy still pervades thinking and experimental evaluation here we consider the historical development of microgelivation macrogelivation and outline what are thought to be fundamental flaws with the concepts and their underpinnings built within the two notions are elements of rock properties hard and soft and scale issues regarding rock attributes solid rock and existing weaknesses in rock that serve only to confuse the process and scale issues even more the whole notion of frost weathered debris having a specific form is also highly spurious there being no shape attribute that is uniquely diagnostic of frost action and this in turn leads to the further problem of process synergy or other processes entirely being the cause of rock failure in cold regions ultimately we argue that while there may be a range of product sizes and shapes resulting from frost weathering per se the widely invoked scale concepts are fraught with problems and are best dropped as too are any process shape connotations

high frequency rock temperature data from hyper arid desert environments in the atacama and the antarctic dry valleys and implications for rock weathering in desert environments with low water and salt contents rapid thermal variations may be an important source of rock weathering we have obtained temperature measurements of the surface of rocks in hyper arid hot and cold desert environments at a rate of 1 s over several days the values of temperature change over 1 second intervals were similar in hot and cold deserts despite a 30 c difference in absolute rock surface temperature the average percentage of the time dt dt 2 c min was 8 3 4 c min was 1 0 9 and 8 c min was 0 02 0 03 the maximum change over a 1 second interval was 10 c min when sampled to simulate data taken over intervals longer than 1 s we found a reduction in time spent above the 2 c min temperature gradient threshold for 1 minute samples the time spent above any given threshold was about two orders of magnitude lower than the corresponding value for 1 second sampling we suggest that a rough measure of efficacy of weathering as a function of frequency is the product of the percentage of time spent above a given threshold value multiplied by the damping depth for the corresponding frequency this product has a broad maximum for periods between 3 and 10 s

processes controlling rapid temperature variations on rock surfaces in arid environments thermal oscillations are an important source of rock weathering measurements of temperature have been made on the surface of rocks in a desert environment at a sampling interval of 0 375 s with simultaneous measurements of wind speed air temperature and incoming shortwave radiation over timescales of hours the temperature of the rock surface was determined primarily by shortwave radiation and air temperature while rapid temperature variations high dt dt at intervals of seconds or less were determined by wind speed the maximum values of temperature change and time spent above 2 c min 1 increased at high measurement rates and were much higher than previously reported the maximum recorded value of dt dt was 137 c min 1 and the average percentage time spent above 2 c min 1 was 70 13 maximum values of dt dt did not correlate with the maximum values of time spent above 2 c min 1 simultaneous measurements of two thermocouples 5 5 cm apart on a single rock surface had similar temperature and dt dt values but were not correlated at sampling intervals of less than 10 s it is suggested that this is resulting from rapid fluctuations due to small spatial and timescale wind effects that are averaged out when data is taken at longer sampling intervals 10 s or greater published in 2010 by john wiley sons ltd

thermal weathering of granite spheroidal boulders in a dry temperate climate northern dobrogea romania weathering microforms associated with exfoliation were investigated on 40 granitic spheroidal boulders identified on pricopan ridge m cin mountains in order to establish a spatial distribution pattern continuous thermal monitoring allowed the frequency and intensity distribution assessment of short term temperature changes triggered by summer storms of intense day night amplitudes and frost cycles across a uniform rounded boulder rock strength estimated by schmidt hammer tests differentiates a significantly weaker resistance on the southern face of the boulders rebound values of 27 to 33 in comparison with the northern face 43 50 the lowest resistance of the north south cross boulder profile corresponds to the southern gentle slopes 0 45 thus defining the most susceptible area to exfoliation and other weathering processes it is argued that this low resistant sector fits well with the maximum frequency and intensity of thermal processes recorded on the low and mid slopes 0 45 of the boulders south side with small differences from one process to another whilst the sector of 20 to 30 south corresponds to the peak activity of all in accordance the overlay map of exfoliated surfaces places the high frequency area on a spherical cap developed similarly between 5 north and 45 south the smallest exfoliated surfaces normally appear around 30 south and are inferred to extend in time both to the boulder top and downslope the correlations between the frequency intensity maps of thermal processes and the frequency map of exfoliated surfaces point to a complementary action in the exfoliated surfaces development of the short term temperature changes and diurnal cooling and heating due to the directional insolation effect as similarly inferred in the development of meridional cracks copyright 2016 john wiley sons ltd

a significant wave height dependent function for topex poseidon wind speed retrieval the ocean surface roughness affects the radar cross section measured by altimeters the wind speed is responsible for this roughness and most of present algorithms use the radar cross section rcs to infer it a few authors monaldo and dobson 1989 glazman and greysukh 1993 emphasized the influence of the sea maturity on satellite measurements they found a marginal improvement in wind speed retrieval by including significant wave height in their algorithm in this paper several previously established algorithms relating altimeter radar cross section to ocean surface wind speed are first analyzed the shapes of the rcs versus wind speed curves are shown to depend mainly on the minimization methods used to generate the model functions an empirical wind speed algorithm is then derived from the two altimeters alt and ssalt on board topex poseidon t p satellite using a quality controlled data set in which north atlantic operational surface wind and wave analyses are collocated with altimeter alt measurements unlike usual algorithms this new function depends on both the radar cross section and the significant wave height the improvement in the t p wind speed estimate seems significant at the 99 9 level the accuracy of the derived function is evaluated using an independent collocated ssalt and numerical weather prediction models data set here again the improvement is significant but at the 90 level because of the smaller amount of data available the t p wind speed estimates are furthermore compared to collocated estimates from national oceanic and atmospheric administration data buoys the new algorithm retrieves wind speed from geosat measurements with an accuracy compatible with usual algorithms

lake levels since about 40 000 years ago at lake chalco near mexico city abstract diatoms magnetic susceptibility organic content and14c ages of sediments from a 26 m core suggest that lake chalco in the southern part of the basin of mexico went through a series of major fluctuations during the late pleistocene and the holocene before ca 39 00014c yr b p the lake was very deep about 8 10 m alkaline and saline it then became shallow

late holocene erosion events in the valley of teotihuacan central mexico insights from a soil geomorphic analysis of catenas abstract this paper addresses the timing of accelerated soil erosion and landscape degradation in central mexico it shows data on erosion sequences in the valley of teotihuacan an area where agricultural dates back to at least since 1100 bce and an ideal setting to test ideas on the effect of preconquest versus post conquest anthropogenic impacts on the environment the methods include stratigraphy detailed description of soil profiles and soil micromorphology along with analysis of pottery sherds and radiocarbon dating a chronology of events for two catenas focusing on periods of landscape stability and change establish the sequence of erosion events from pre hispanic to modern times six erosion phases are recognized over the last 2000 years in teotihuacan although results suggest that the most intense erosion occurred after spanish conquest in the 16th century several erosion phases took place during pre hispanic times and also in the postcolonial period including the 20th century probable causes for these impacts are related to settlement dynamics population variability and land use changes thus it provides new information for the discussion on the timing and causes of erosion sedimentation and landscape modification in the central mexican highlands during the late holocene

thermal stress weathering and the spalling of antarctic rocks using in situ field measurements laboratory analyses and numerical modeling we test the potential efficacy of thermal stress weathering in the flaking of millimeter thick alteration rinds observed on cobbles and boulders of ferrar dolerite on mullins glacier mcmurdo dry valleys mdv in particular we examine whether low magnitude stresses arising from temperature variations over time result in thermal fatigue weathering yielding slow crack propagation along existing cracks and ultimate flake detachment our field results show that during summer months clasts of ferrar dolerite experience large temperature gradients across partially detached alteration rinds 4 7 c mm 1 and abrupt fluctuations in surface temperature up to 12 c min 1 the latter are likely due to the combined effects of changing solar irradiation and cooling from episodic winds the results of our thermal stress model coupled with subcritical crack growth theory suggest that thermal stresses induced at the base of thin alteration rinds 2 mm thick common on rocks exposed for 105 years may be sufficient to cause existing cracks to propagate under present day meteorological forcing eventually leading to rind detachment the increase in porosity observed within alteration rinds relative to unaltered rock interiors as well as predicted decreases in rind strength based on allied weathering studies likely facilitates thermal stress crack propagation through a reduction of fracture toughness we conclude that thermal stress weathering may be an active though undervalued weathering process in hyperarid terrestrial polar deserts such as the stable upland region of the mdv

fluvial processes and paleopedogenesis in the teotihuacan valley mexico responses to late quaternary environmental changes a paleosol sequence in the teotihuacan valley was studied in order to reconstruct landscape evolution during the late pleistocene holocene in a cut belonging to a river gully san pablo the sequence is constituted by 4 pedostratigraphic units labeled as sp1 sp4 separated by volcanogenic alluvial colluvial sediments sp4 at the base of the sequence has a prismatic structure clay cutans and vertic features sp3 shows abundant signs of zooturbation krotovinas and clay cutans both paleosols are interpreted to have formed in stable humid forest landscapes during marine isotope stage 3 mis3 however towards the end of mis3 these conditions alternated with the periods of contrasting seasonal climate the overlying sp2 unit is a pedocomplex demonstrating 2 petrocalcic horizons combined with redoximorphic features the pedocomplex merges laterally with gradually stratified gleyic channel deposits gravels in the base to fine sand and silt in the top the age of the lower caliche is 24 000 bp and thus sp2 formed during mis2 including the last glacial maximum lgm the environmental conditions during lgm are mostly dry with stages of high humidity evidenced by gleyic processes and fluvial activity at the end of the pleistocene the landscape becomes highly unstable and pedogenesis is replaced by sedimentation new paleochannels cut through the previously formed paleosols these channels are infilled by poorly sorted sediments with no gradation the configuration of all paleochannels is nne ssw nearly at 90 to the modern san pablo river flow geomorphic stability during the early and middle holocene allowed the development of sp1 in a dry environment the a horizon of this paleosol has been dated at 2900 bp it is well developed with strong vertic features this paleosol is thought to have formed the soil cover when the classic period teotihuacan culture flourished in the valley between the first and third centuries ad soils above sp1 are poorly developed and erosion deposition processes predominate over pedogenesis recent landscape instability is due to human activities that intensified erosion processes during the classic and especially the postclassic and colonial periods

a 2400 yr mesoamerican rainfall reconstruction links climate and cultural change droughts are a recurring feature of mexican climate but few high resolution data are available to test for climate change forcing of mesoamerican civilizations we present a quantitative 2400 yr rainfall reconstruction for the basin of mexico from a precisely dated and highly resolved speleothem that documents highly variable rainfall over the past 2400 yr dry conditions peaked during a 150 yr long late classic ca 600 900 ce common era mega drought that culminated at 770 ce which followed centuries of climatic drying that spanned the fall of the city of teotihuacan ca 550 ce the wettest conditions in the 1450s ce were associated with fl ooding in the basin of mexico our data suggest that rainfall variability was likely forced by the el nino southern oscillation and impacts on spring fed irrigation agriculture may have been a stressor on mesoamerican civilizations

dynamics of the ca 4965 yr 14c bp ochre pumice plinian eruption of popocatepetl volcano mexico abstract the ochre pumice op plinian fallout was produced by popocatepetl volcano in central mexico during a major plinian eruption that occurred 4965 65 14 c yr bp 3700 bc the op is part of the ochre pumice sequence ops that consists of surge fall and pyroclastic flow deposits the op plinian fallout shows a bimodal grain size distribution with poor to moderate sorting that improves progressively towards the upper beds the juvenile component is mainly pumice 83 wt whereas the accidental components consist of igneous sedimentary and metamorphic clasts from the walls of the magma chamber and or conduit the vesicularity of the pumice decreases from bottom to top of the stratigraphic sequence while the crystal and glass contents increase this suggests increasing magma degassing prior and during the eruption the chemical composition of the pumice varies insignificantly at the base it is less evolved sio 2 61 wt and it becomes slightly more silicic towards the top sio 2 63 wt pumice clasts have a crystallinity index that ranges between 10 and 25 vol and display a seriate texture with phenocrysts of euhedral plagioclase pl clinopyroxene cpx orthopyroxene opx olivine ol oxide ox apatite ap the size of the maximum lithic 2 5 cm at a horizontal distance of 19 km indicates an eruption column height of 37 41 km the isopach map allows the recognition of a dispersal axis that points towards the nne where an area of 300 km 2 was covered by 6 cm of pumice and ash a minimum volume for the op plinian fallout deposit was calculated using a minimum thickness of 6 cm found at distal outcrops and was estimated at 4 9 km 3 which corresponds to 2 km 3 of dense rock equivalent dre stratigraphic relations indicate that the entire ops was emplaced during a short time interval of a few days to weeks and consisted of three main different phases phreato magmatic plinian and vulcanian it started violently with the emplacement of surges and then culminated with the eruption of the op fallout deposit as the eruption advanced discharge rates became more intermittent and the height of the column fluctuated and finally collapsed generating pumice and ash flows that were emplaced around the volcano this short but intense activity was followed during subsequent years by the growth of domes in the crater and the emplacement of block and ash flows generated by vulcanian explosions

sea state related altitude errors in the seasat radar altimeter a significant waveheight dependent bias is identified in seasat measured surface heights which cannot be neglected when using seasat data at accuracies within 10 cm ten second averages of the data from 63 waveform sampling rates in the seasat radar altimeter were least squares fitted with a six parameter model the time origin parameter of which provides a measure of the position of the actual mean radar waveform relative to the sampling rate and therefore provides altitude measurement corrections attention is given to actual altimeter point target response function waveform sampler noise baseline waveform sampler gain calibration attitude angle and sea surface skewness as effects not accounted for in seasat altimeter measurements and standard data processing

prehispanic and colonial landscape change and fluvial dynamics in the chalco region mexico abstract the late quaternary deposits of the lakeshore plain and western edge of lake chalco in the southeastern basin of mexico were explored in order to understand the influence of alluvial sedimentation on archeological visibility and preservation as well as to seek out records that would permit direct comparison of erosion and sedimentation with the demographic record derived from the archeological survey the chalco lakeshore plain is traversed by two of the largest rivers in the region and the pattern of human settlement recorded here by archeological survey is partly an artifact of alluvial sedimentation where the most prominent settlements were observed in areas with little or very slow sedimentation detailed radiocarbon dating of the alluvial deposits indicates that prior to the establishment of a sedentary lifestyle alluvial sedimentation was slow catastrophic soil erosion is inferred from a period of widespread rapid alluviation and mass movements during late preceramic early and middle formative periods which were periods of rapid population growth mass movements appear to coincide also with periods of wetter climate no evidence of sedimentation was noted during the population collapse that occurred at the end of the formative the next phase of alluvial sedimentation occurred during the early classic to late toltec periods which were also periods of population expansion during a gradually drying climate the postclassic period which was the largest pre columbian demographic expansion was paradoxically accompanied by minor evidence of alluvial activity the last and most widespread period of alluvial activity occurs in the post conquest period and is difficult to date with precision but appears to occur primarily during the seventeenth and eighteenth centuries

observations on electromagnetic bias in radar altimeter sea surface measurements because the relative radar cross section of the sea surface increases below mean sea level and decreases above it the range measurements of satellite radar altimeters are biased toward the wave troughs published and unpublished direct measurements of this electromagnetic em bias are examined as well as the predictions of theoretical developments the em bias is predominantly a function of the radar frequency used averaging 1 2 percent of the wave height of ka band and 3 3 percent of the wave height at x band the airborne measurements present a consistent picture of the variation of the relative radar cross section as a function of deviation from mean sea level a technique to measure em bias at the ku and c band operating frequencies of the topex satellite altimeter is described

natural building stone composed of light transmissive minerals impacts on thermal gradients weathering and microbial colonization a preliminary study tentative interpretations and future directions a number of modern buildings employing claddings of granites or marbles have experienced bowing of the rock panels together with weathering of the material theoretical and field based data analysis and laboratory experimentation have assumed that heat exchange resulting from incoming solar radiation is at the material surface however a number of recent experiments have clearly shown that some lithologies including both marble and granite comprise a number of light transmissive minerals that significantly change the thermal responses in the outer few millimetres of the rock further this translucence will create mineral to mineral stresses where light transmissive minerals are in contact with opaque ones the whole is further exacerbated by differences in thermal coefficients of expansion and conductivity which themselves may depend on the mineral axis surface modifiers such as paints further complicate the situation the degree of light penetration based on field measurements can be significant and can facilitate rapid changes in temperature t t 2 c min 1 at depth within the rock thereby increasing the sub surface stresses the amount of light penetration for any given mineral will be dependent upon material slope the latitude season and albedo albedo is identified as a complex variable changing as a function of the angle of the sun to the particular surface polished surfaces as often with cladding will further influence this data analysis suggests that in the northern hemisphere south of the polar circle the summer may not be the time of the largest heat loading on the southern aspect and that larger loadings coupled with lower air temperatures occur early and late in the year this seasonal impact has great potential for thermal stresses on the southern aspect the presence of light transmissive minerals also allows sub surface biotic colonization and results in weathering overall where light transmissive minerals lithologies occur the thermal responses are highly complex and in need of more rigorous consideration

global statistical analysis of topex and poseidon data a global statistical analysis of the first 10 months of topex poseidon merged geophysical data records is presented the global crossover analysis using the cartwright and ray 1990 cr tide model and gaspar et al this issue electromagnetic bias parameterization yields a sea level rms crossover difference of 10 05 cm 10 15 cm and 10 15 cm for topex topex poseidon poseidon and topex poseidon crossovers respectively all geophysical corrections give reductions in the crossover differences the most significant being with respect to ocean tides solid earth tide and inverse barometer effect based on topex poseidon crossovers and repeat track differences we estimate the relative bias between topex and poseidon at about 15 5 1 cm this value is dependent however to the electromagnetic bias corrections used an orbit error reduction method based on global minimization of crossover differences over one cycle yields an orbit error of about 3 cm rms this is probably an upper estimate of the orbit error since the estimation absorbs other altimetric signals the rms crossover difference is reduced to 8 8 cm after adjustment a repeat track analysis is then performed using the cr tide model in regions of high mesoscale variability the rms sea level variability agrees well with the geosat results tidal errors are also clearly evidenced a recent tide model ma et al this issue determined from topex poseidon data considerably improves the rms sea level variability the reduction of sea level variance is 4 cm 2 on average but can reach 8 cm 2 in the southeast pacific southeast atlantic and indian oceans the rms sea level variability thus decreases from 6 cm to only 4 cm in quiet ocean regions the large scale sea level variations over these first 10 months most likely show for the first time the global annual cycle of sea level finally we analyze the topex and poseidon sea level anomaly wavenumber spectral characteristics topex and poseidon have identical spectral characteristics at low wavenumbers for wavelengths shorter than 100 km however poseidon spectra are more energetic this is probably related to the topex tracker characteristics and to the way the acceleration correction is made in the geophysical data records poseidon repeat track noise level is estimated at about 3 cm for a 1 s average the topex repeat track noise level is about 1 8 cm rms but this probably corresponds to averages over several seconds

new models for satellite altimeter sea state bias correction developed using global wave model data sea level determination via satellite altimetry is subject to numerous error sources one of these is the sea state bias where changing surface wave conditions alter an altimeter s estimate of mean sea level recent work suggests that present day methods for correcting this bias based solely on wave and wind information from the altimeter may be improved if additional surface gravity wave field measurements become available this paper tests this hypothesis by developing several new sea state bias correction models using a year long combination of jason 1 data with wave field statistics generated from an hindcast of the wavewatch3 ocean wave model each candidate model is produced in the same manner through a nonparametric mapping between jason 1 sea surface height anomaly estimates and two correlatives the first is always the significant wave height from jason 1 and the model differences come through choice of the second variable past studies dictate our selection of these second parameters and they include terms related to the local wind speed swell energy wave age wave period and wave slope evaluation of model skill is conducted in term of explained variance several candidate models do indicate promise for wave model use in future empirical developments results show that in the low latitudes the models developed using the swell height and mean period modestly outperform the operational parameterisation of the bias model thus this study indicates that systematic regional error in the present sea level corrections may be improved by inclusion of wave model information

air circulation in deep fractures and the temperature field of an alpine rock slope the subsurface temperature field of a rock slope is a key variable influencing both bedrock fracturing and slope stability however significant unknowns remain relating to the effect of air and water fracture flow which can rapidly transmit temperature changes to appreciable depths in this work we analyze a unique set of temperature measurements from an alpine rock slope at 2400 m a s l in southern switzerland the monitored area encompasses part of an active slope instability above the village of randa vs and is traversed by a network of open cracks some of which have been traced to 80 m depth we first describe distributed temperature measurements and borehole profiles highlighting deep steady temperatures and different transient effects and then use these data to approximate the conductive temperature field at the site in a second step we analyze the impact of air and water circulation in deep open fractures on the subsurface thermal field on multiple visits to the study site in winter we consistently noted the presence of warm air vents in the snowpack following the trace of deep tension cracks measurements showed that venting air changed temperature gradually from 3 to 2 c between december and may which is similar to the rock temperature at around 50 m depth comparison with ambient air temperature suggests that winter conditions favor buoyancy driven convective air flow in these fractures which acts to cool the deep subsurface as the rock gives up heat to incoming air the potential impact of this process on the local thermal field is revealed by a disturbed temperature profile in one borehole and transient signals observed at depths well below the thermal active layer seasonal water infiltration during snowmelt appears to have little impact on the temperature field in the monitored area copyright 2011 john wiley sons ltd

reply to comment on on the joint distribution of surface elevations and slopes for a nonlinear random sea with an application for radar altimetry by m a srokosz

surface temperature differences between minerals in crystalline rocks implications for granular disaggregation of granites through thermal fatigue thermal expansion differences between minerals within rocks under insolation have previously been assumed to drive breakdown by means of granular disaggregation however there have been no definitive demonstrations of the efficacy of this weathering mechanism different surface temperatures between minerals should magnify thermal expansion differences and thus subject adjacent minerals to repeated stresses that might cause breakdown through fatigue failure this work confirms the existence of surface temperature differences between minerals in granitic rocks under simulated short term temperature fluctuations so as to discriminate their potential for initiating granular disaggregation the influence of colour as a surrogate for albedo and crystal size as a function of thermal mass are specifically identified because of their ease of quantification four rock types with a range of these properties were examined and subjected to repeated short term temperature cycles by radiative heating and cooling under laboratory conditions results show that while albedo is the main control for overall and individual maximum temperatures crystal size is the main factor controlling higher temperature differences between minerals thus stones with large differences of mineral sizes can undergo magnified stresses due to thermal expansion differences

measurements of electromagnetic bias in radar altimetry the accuracy of satellite altimetric measurements of sea level is limited in part by the influence of ocean waves on the altimeter signal reflected from the sea surface the difference between the mean reflecting surface and mean sea level is the electromagnetic bias the bias is poorly known yet for such altimetric satellite missions as the topography experiment topex poseidon it is the largest source of error exclusive of those resulting from calculation of the satellite s ephemeris previous observations of electromagnetic bias have had a large apparently random scatter in the range of 1 5 of significant wave height these observations are inconsistent with theoretical calculations of the bias to obtain a better understanding of the bias we have measured it directly using a 14 ghz scatterometer on the chesapeake bay light tower we find that the bias is a quadratic function of significant wave height h1 3 the normalized bias defined as the bias divided by the significant wave height is strongly correlated with wind speed at 10 m u10 and much less strongly with significant wave height the mean value for is 0 034 and the standard deviation of the variability about the mean is 0 0097 the standard deviation of the variability after removing the influence of wind and waves is 0 0051 0 51 the results are based on data collected over a 24 day period during the synthetic aperture radar and x band ocean nonlinearities saxon experiment from september 19 to october 12 1988 during the experiment hourly averaged values of wind speed ranged from 0 2 to 15 3 m s significant wave height ranged from 0 3 to 2 9 m and air minus sea temperature ranged from 10 2 to 5 4 c because u10 can be calculated from the scattering cross section per unit area 0 of the sea measured by spaceborne altimeters we investigated the usefulness of 0 for calculating bias we find that is strongly correlated with 0 and much less strongly with h1 3 the standard deviation of the variability after removing the influence of the radio cross section and waves is 0 0065 0 65 the results indicate that electromagnetic bias in radar altimetry may be reduced to the level required by the topex poseidon mission using only altimetric data we find furthermore that the relationship between 0 and wind speed agrees with previously published power law relationships within the accuracy of the measurement the mean value of its variability and the sensitivity of to wind speed all agree well with previous measurements made using a 10 ghz radar carried on a low flying aircraft the mean value of its variability and the sensitivity to wind were all significantly larger than previous measurements made using a 39 ghz radar also carried on a low flying aircraft all experiments included a similar range of wind speeds and wave heights the saxon data were however much more extensive and the statistical relationships correspondingly more significant the mean value of is very close to the mean value determined from global measurements of sea level made by geosat

short surface waves in the canadian arctic in 2007 and 2008 1 we have collected time series data of short oceanic waves as a part of the international polar year ipy 2007 2008 using a shipboard laser wave slope lawas system operating at 900 nm we have obtained wave slopes measurements up to 60 rad m 1 wave number we have compared our in situ wave slopes with collocated and concurrent high resolution upwind normalized radar cross sections nrcs collected by quikscat the lawas measured wave slope spectra were consistent with local wind speeds and quikscat measured nrcs our measured short wave mean slopes indicate their enhancement by long waves 0 1 rad m 1 at small values of long wave slope concurrent with wave slope measurements the strength of the reflected lawas light beam was analyzed in terms of the light attenuation coefficient at 900 nm we have observed a correlation between surface elevation and light attenuation the mechanism of wave modulated beam attenuation was found to be related to the instantaneous long wave skewness

oceanographic and geophysical applications of satellite altimetry since the last quadrennial report new satellite altimeter data have not been generally available nevertheless important progress has been made from analyses of geos 3 and seasat data the marine gravity field has been determined to an extraordinary resolution and accuracy and important solid earth geophysical interpretations made in the area of oceanography statistical estimates of the variability of dynamic topography have been published methods for incorporating altimeter data into numerical models have been developed and applied and tentative but interesting determinations of the mean circulation have been made in addition altimeter waveform analysis has made it possible to use altimeter data to determine elevations of major ice fields finally important new insights into the nature of satellite ephemeris error and its influence on altimetrically derived sea surface topography have been achieved

rock surface millimetre scale roughness and weathering of supratidal mallorcan carbonate coasts balearic islands rock surface millimetre scale roughness and weathering of supratidal mallorcan carbonate coasts balearic islands

late quaternary lacustrine paleoenvironments in the cuenca de mexico abstract a late quaternary paleolimnological history from the mexican highlands has been obtained by diatom analysis of short cores and stratigraphic sections of lake and marsh sediments from the cuenca de mexico the large endorheic graben basin that holds mexico city the records dated by radiocarbon and tephrochronologic methods extend back to about 30 ka bp and document the presence of extensive saline lakes in the basin until 25 ka bp thereafter lake levels fell and marginal sites became shallow and fresh under the influence of surficial drainage and especially spring discharge a shallow saline lake existed 18 ka bp in texcoco the central and lowest basin in the system reflecting moderately increased effective moisture at that time by 16 ka bp lake texcoco had become so shallow that diatoms were no longer preserved however marginal sites nourished by spring flow recorded changes in the local hydrologic balance resulting from increased infiltration at higher elevations these changes appear to coincide with glacial advances between about 14 and 10 ka bp on the volcanic mountains surrounding the basin dry climates with reduced infiltration characterized the early holocene but by 5 ka bp a modest increase in precipitation established the modern climatic regime these lacustrine records offer important insights for evaluating the paleoenvironmental history of the cuenca de mexico based on other evidence they confirm glaciological stratigraphic and palynologic data that suggest dry climates and the absence of large pluvial lakes in the cuenca de mexico during and after the full glacial but document climates of significantly increased precipitation at least 10 ka prior to 18 ka bp

the effect of the degree of wave development on the sea state bias in radar altimetry measurement the effect of the degree of wave development on the sea state bias ssb in geosat altimeter height measurement is evaluated theoretical considerations suggest that the altimetric ssb is generally not a linear function of significant wave height but depends also on other factors of wave development of particular interest is its dependence on wave age defined as the ratio of the phase speed of the dominant ocean waves to ocean wind speed we estimate wave age rather crudely on the basis of the significant wave height h and wind speed measured by the altimeter under general conditions when the sea is not in equilibrium with the wind this estimate may not correspond to the wave age in a strict sense and hence is called pseudo wave age in this paper nevertheless the pseudo wave age is a rough indicator for the degree of wave development the general trend in the dependence of the ssb on pseudo wave age as found by analyzing 2 7 years worth of geosat data agrees well with the theoretical prediction for a given h the ssb decreases as the degree of the wave development measured by the pseudo wave age increases this empirical trend is modeled as ssb a m m h where and m are the pseudo wave age and its average value respectively a 0 013 0 005 and m 0 88 0 37 statistically this model performs slightly better than a standard model i e ssb h with being a constant in terms of the global rms error the improvement is by 1 6 cm however because the degree of wave development varies with the season and geographical location this small improvement could become important for more accurate altimetric missions in the future when the centimetric basin scale signals are the focus of the study

observations of the surface properties of the ice sheets by satellite radar altimetry by comparing modelled and averag ed satellite altimeter return it is demonstra ted that time profiles of altimeter return can be used to provide important information on the surface proper ties of the ice sheets alt imeter ice sheet radar echoes from low altit udes and or rela tively low latitudes are in gene ral domin ated by surface scat tering and in greenl and the area of surface d ominated return broadly coi ncides with the zone of summer melting seasonal variations in the echo wave form shapes are negligible in all regions studied with the possib le exception of an area near the margin of the greenland dry snow zone in general the model expla ins well the observed variations in mean wave form shape but small discrepances between the model wave forms and the recorded wave forms indicate that sub sur face layers may be influ encing the shape of the return the poss ibility of deriving quantitative estima tes of surface proper ties is explored by fitting model returns to averaged altimeter wave forms from the wilkes land plateau in anta rctica surface roug hness can be meas ured unambig uously from the wave form data but estim ations of other parameters such as gra in size snow density and snow temperature are found to be ambiguous because different surface para meters have a similar infl uence on the shape of the retur n despite this the derived estimates compare well with ground b ased observations and suggest that the satellite alti meter may have an important role to play in providing info rmation on the surface properties of the ice sheets

comment on on the joint distribution of surface elevations and slopes for a nonlinear random sea with an application for radar altimetry by m a srokosz

thermal fatigue and thermal shock in bedrock an attempt to unravel the geomorphic processes and products widespread acceptance in science at large notwithstanding the ability of thermal stresses to produce thermal fatigue tf and or thermal shock ts in bedrock and coarse debris in the field is often doubted commonly called insolation weathering in geomorphology the results of questionable laboratory experiments have led many geomorphologists to consider terrestrial temperatures to be inadequate to generate thermally induced stresses leading to rock failure the exceptions are the action of fire or lightning we comprehensively survey the general scientific literature on tf and ts while rigorously scrutinizing that relating to geomorphology findings indicate theoretical and experimental information is adequate to establish the feasibility of tf and ts in rock stemming from rock temperatures monitored in the field while ts may exhibit fracture patterns that are uniquely diagnostic those of tf lack any such attributes it would appear unlikely that tf can prepare or weaken rock to increase the likelihood of ts the question of whether widespread polygonal versus rectilinear cracking is diagnostic of ts is presently an open one as possible explanations invoke process es and or host material s and consequently to assign palaeoenvironmental significance to such fracture patterns is premature at this time further geomorphological laboratory research into tf and ts is merited as sufficient theoretical underpinning already exists however laboratory experimentation needs to be much more rigorously defined and executed and is faced with significant hurdles if it is to be effectively linked to field observations

effects of sea maturity on satellite altimeter measurements for equilibrium arid near equilibrium sea states the wave slope variance is a function of wind speed u and of the sea maturity the influence of both factors on the altimeter measurements of wind speed wave height and radar cross section 0 is studied experimentally the necessary theoretical background both on wave statistics and on the near nadir radar backscatter is outlined it is based on a recently proposed view that the effective fractal dimension for a surface patch corresponding to the equilibrium range of wave spectra increases as the wave field matures the experimental part is based on 1 year s worth of geosat altimeter observations colocated with in situ wind and wave measurements by 20 noaa buoys errors and biases in altimeter wind speed and wave height measurements are investigated a geophysically significant error trend correlated with the sea maturity i e with c0 u where c0 is the phase velocity of waves corresponding to the spectral peak and u is the mean wind speed well above the surface is found in wind speed measurements this trend is explained by examining the effect of the generalized wind fetch x gh1 32 u2 on the curves of the observed dependence 0 f u x we conclude in particular that unambiguous measurements of wind speed by altimeter in a wide range of sea states are impossible without accounting for the actual degree of wave development an approach to a more accurate retrieval of wind speeds is suggested as based on accounting for the actual degree of wave development which can be achieved through processing the total radar cross section simultaneously with the significant wave height information contained in altimeter waveforms the potential capability of a satellite altimeter to estimate wave age and similar measures of wind wave coupling is discussed this capability expands the use of satellite altimeters for air sea interaction studies

rock thermal data at the grain scale applicability to granular disintegration in cold environments consideration of the mechanisms associated with the granular disintegration of rock has been limited by available data in most instances both the size of the transducer and the nature of the study have negated any applicability of the resulting data to the understanding of grain to grain separation within rock the application of microthermocouples 0 15 mm diameter and high frequency logging 20 s intervals at a taffoni site on southern alexander island and from a rock outcrop on adelaide island antarctica provide new data pertaining to the thermal conditions at the grain scale of the rock surface the results show that thermal changes t t can be very high with values of 22 c min 1 being recorded although available data indicate that there can be differences in frequency and magnitude of uctuations as a function of aspect all aspects experienced some large magnitude 2 c min 1 uctuations further in many instances large thermal changes in more than one direction could occur within 1 min or in subsequent minutes these data suggest that the surface grains experience rapidly changing stress elds that may with time effect fatigue at the grain boundaries albedo differences between grains and the resulting thermal variations are thought to exacerbate this the available data failed to show any indication of water freezing an exotherm and thus it is suggested that microgelivation may not play as large a role in granular breakdown as is often postulated for cold regions and that in this dry antarctic region thermal stress may play a signi cant role copyright 2003 john wiley sons ltd

on the persistence of weathering abstract the term weathering has been in use for a very long time but it has come to mean different things to different people and hence as scientific short hand it no longer functions here we question the tenets underpinning the most common usage of the term and note that the climate process linkage implicit to the term is often missing and amounts to misdirection rather than climate as the primary driver behind specific weathering processes it is argued that rock properties constitute the dominant control further a case is made for reconsideration of our present bipartite mechanical chemical division of weathering processes and of the weathering processes currently deemed to be those that occur as process studies become evermore reductionist in nature so the functionality of the term comes more and more into question the linkage between process and landform the scaling up attribute is seen as a current weakness and one that will become more confusing as reductionist approaches continue as a way forward it is suggested that weathering stripped of specific preconceived notions of specific processes be envisaged as a function of energy transfer and be investigated in that light identification of new processes as well as restructuring of known processes particularly when considering weathering on other planets is a potential outcome of such an approach with a process foundation rooted in energy transfer rock decay provides a better umbrella term and liberates researchers from the inescapable conceptual baggage implicit to the term weathering

the sea state correction for geos 3 and seasat satellite altimeter data troughs of the ocean surface reflect more electromagnetic radiation to a satellite altimeter than crests causing an apparent lengthening of the altimeter path this effect called the em bias has been estimated to be 2 10 of significant wave height swh by various authors from geos 3 and aircraft experiments or theoretical analyses for the case of the seasat altimeter born et al 1982 at jet propulsion laboratory jpl made an empirical estimate that gave the total correction to the altimeter path length as 7 of the swh a large value was expected for seasat because an instrumental effect in addition to the em bias is known to exist waveform analyses performed at nasa wallops flight center hayne and hancock 1982 give a correction for the instrument effect but according to the authors their results cannot be compared with results obtained elsewhere for several reasons including the large uncertainty 30 of the jpl result in this paper we resolve the situation for both geos and seasat altimeters by reinterpreting the results of hayne and hancock and making empirical studies using very large data sets to estimate the correction required for the effect of sea state empirical estimates of the correction were made by finding a value that minimized in the sense of least squares the differences of many about 300 repeated pairs of altimetric profiles for each satellite the total correction obtained is 1 9 of significant wave height for geos 3 and 6 4 for seasat the latter result consistent with the analysis done at jpl of a smaller data set and our interpretation of the hayne and hancock waveform analysis

evidence for freeze thaw events and their implications for rock weathering in northern canada ii the temperature at which water freezes in rock many undertakings have used either a single value or a narrow window of temperatures as a threshold for the freezing of water within rock these temperatures vary from 0 to 5 c with most windows being in the range 1 to 4 c based on thermal data these thresholds are commonly used to count the number of freeze thaw events as a basis for determining freeze thaw weathering data collected from northern canada indicate that the temperature at which freezing occurs can vary substantially even for the same site using exotherm and zero curtain observations from bricks at angles of 90 and 45 aligned to the four cardinal aspects the various temperatures at which water froze are shown bricks on the north and east commonly did exhibit freezing based on exotherms within the window 1 to 5 c while data for the south and west aspects showed substantial variation with freezes sometimes between 6 4 and 8 9 c the data were evaluated for evidence of zero curtain effects indicative of water freezing but no unequivocal events could be found and it is suggested that at the scale of observation used here they are unlikely it would therefore appear that the use of thermal thresholds may not be meaningful for evaluation of freeze thaw events the available data also indicate many instances when temperatures went substantially sub zero e g 20 c and yet no indication of water freezing occurred most likely because there was no water available to freeze this indicates that any form of freeze thaw event counting in the absence of some indicator of the presence of water and that it actually froze is flawed as thermal conditions alone are not adequate to indicate the occurrence or not of actual freeze thaw weathering events these data suggest that evaluations of freeze thaw occurrence based simply on thermal thresholds may be substantially in error copyright 2006 john wiley sons ltd

radial orbit error reduction and mean sea surface computation from the geosat altimeter data using the altimeter data from the geosat exact repeat mission we have produced yearly averaged mean profiles and a global mean sea surface the radial error of each 6 day orbital arc computed with the gem t2 geopotential was first estimated by calculating the amplitude and phase of the nine dominant frequencies of the difference between the altimetric profiles and the mean sea surface obtained when adding the permanent sea surface topography computed from the levitus climatological atlas to the gem t2 geoid we show that this operation is little affected by the choice of the geoid or by its formal error the resulting correction has been subtracted from each individual arc yearly mean profiles were then obtained by averaging the corrected altimetric data of each repeat cycle on a yearly basis their noise level is 1 to 2 cm and their resolution is 20 km but the differences of the altimetric heights at crossovers of ascending and descending tracks are still 30 cm nns the latter can be reduced to 7 cm rms by a crossover analysis in addition to the mean values standard deviations were computed at each point of the repeat cycle this yearly along track variability is of the order of 10 cm rms and is dominated by the ocean mesoscale variability a global yearly mean sea surface has been derived by bilinear interpolation its resolution ranges approximately from 160 km to 80 km depending on the latitude it is shown to be much less noisy than those deduced from geos 3 and seasat data

satellite altimetry from a short arc orbit technique application to the mediterranean a short arc orbit technique was developed and a very precise and efficient tool for regional orbit determination with a rigorous error budget is proposed for analyzing the topex poseidon t p and ers 1 missions the purpose is to be able to determine very accurately in some conditions the local orbit with a very small error in the radial direction using satellite laser ranging data a precision at the level of 2 cm is obtained with this it was possible to cross validate all the different orbit determination techniques as well as the results of the altimeter calibration showing the great progress made with the topex poseidon mission after that the t p mean sea profiles were computed and improved with high accuracy thanks also to the short arc orbit technique as a result a combined mean sea surface using topex poseidon and ers 1 data has been computed with crossover difference techniques the t p mean sea profiles serving as reference fine structures of the mean sea surface have been evidenced using this combined mean sea surface the ers 1 altimeter calibration was performed over the mediterranean again using the short arc orbit technique the result is in good agreement with the previous ones 41 6 7 cm finally the t p mean sea profiles were computed for different seasons and compared with a yearly averaged mean sea surface variations of about 15 cm are evidenced associated notably with the thermal expansion between fall and winter the short arc orbit technique appears to be well suited for monitoring very accurately the temporal variability of the mediterranean sea at a subcentimetric level

rock surface roughness as an indicator of degree of rock surface weathering rock surface weathering often leads to increased rock surface roughness but roughness has proved difficult to quantify several instruments are available for micro mapping and recording rock surface profiles but the most appropriate for most purposes is the simple profile gauge short profiles can be recorded quickly and accurately a range of roughness indices has been proposed in other areas of geomorphology and their efficacy as measures of roughness at scales of interest in studies of weathering is assessed some are too complex or labour intensive and others are too sensitive to the scale of roughness to provide reliable measures of magnitude the most appropriate indicator of both the scale and magnitude of roughness is the standard deviation of the differences between height values at a range of set horizontal intervals along a profile the deviogram varying the measurement interval records roughness at different scales a regression approach root mean square roughness provides a reliable measure of the magnitude of roughness at the maximum scale present three case studies confirm the efficacy of these approaches to studies of weathering of different rocks in different environments software is supplied which automates the calculation of roughness indices from gauge profiles

small scale open ocean currents have large effects on wind wave heights tidal currents and large scale oceanic currents are known to modify ocean wave properties causing extreme sea states that are a hazard to navigation recent advances in the understanding and modeling capability of open ocean currents have revealed the ubiquitous presence of eddies fronts and filaments at scales 10 100 km based on realistic numerical models we show that these structures can be the main source of variability in significant wave heights at scales less than 200 km including important variations down to 10 km model results are consistent with wave height variations along satellite altimeter tracks resolved at scales larger than 50 km the spectrum of significant wave heights is found to be of the order of 70 hs 2 g2 tm0 1 2 times the current spectrum where hs is the spatially averaged significant wave height tm0 1 is the energy averaged period and g is the gravity acceleration this variability induced by currents has been largely overlooked in spite of its relevance for extreme wave heights and remote sensing

electromagnetic bias estimates based on topex buoy and wave model data 1 for quantitative studies of the ocean using altimetric measurements the sea surface height measurements must be corrected for the electromagnetic em bias effect project provided em bias correction algorithms were derived from the altimeter data as a function of wind speed and wave height through variance minimization techniques gaspar et al 1994 in this paper we characterize the impact of those corrections on the altimeter data and compare it with an empirical algorithm based on tower observations of wave slopes and wave age w k melville et al wave slope and wave age effects in measurements of em bias submitted to journal of geophysical research 2002 and with theoretical predictions of em bias srokosz 1986 we find a significant correlation between high frequency ocean signals with the project provided em bias correction this suggests that an em bias algorithm cannot be estimated from altimeter data alone through variance minimization techniques since the em bias depends on parameters that cannot be measured by an altimeter e g wave slope improved theoretical corrections appear to be preferable to altimetry based empirical estimates using wave buoy and wave model wam data we find good agreement between existing theoretical correction and empirical corrections based on wave slope and wave age information over a significant range of parameters although further work is needed to extend our tests of algorithms to larger wave slopes existing wave slope and wave age based algorithms appear comparable in goodness to project provided empirical algorithms and may be used for routine altimetry processing in combination with wam output on a global basis

an empirical determination of the effects of sea state bias on seasat altimetry a simple linear empirical model has been developed to allow the user of seasat altimetry data to correct the altitude measurements for sea state bias effects this bias is the result of two separate effects one relating to instrumental effects and the other relating to a bias in the electromagnetic mean sea level relative to the geometric mean sea level the electromagnetic bias is caused by the fact that the troughs of the ocean waves reflect the altimeter signal more strongly than the crests thus causing the altimeter determined mean sea level to shift toward the wave troughs an additional but independent instrument related bias is introduced because height corrections applied in the ground processor are not sufficient to compensate for simplifying assumptions made for the processor aboard seasat this altitude bias also is predominately wave height dependent and directed toward the wave trough the sum of these two effects is referred to as sea state bias after applying appropriate corrections to the altimetry data an empirical model for the sea state bias is obtained by differencing significant wave height and height measurements from coincident ground tracks ignoring small temporal variations in surface topography the height differences on a given track should be zero consequently any residual height difference is attributed to sea state bias the height differences are minimized by solving for the coefficient of a linear relationship between height differences and wave height differences that minimize the height differences it is concluded that for the altimeter data released by the jet propulsion laboratory 7 of the value of significant wave height should be subtracted from the seasat height measurements to correct for sea state bias this correction reduced biases in the seasat data by more than 50 in the 36 cases examined here

postprocessing of satellite altimetry return signals for improved sea surface topography accuracy large off nadir attitude deviations and high surface wave heights cause an alteration in the ocean return signal from a satellite radar altimeter this leads to an error in the on board calculation of the height measurement the error can be removed by reprocessing the full radar return signal on the ground in the ground processing the correct tracking point in the return signal is recomputed through a procedure called retracking there has been a controversy over whether or not all altimeter data would be retracked this study analyzes retracked southern ocean data from the first 34 repeat cycles of the geosat exact repeat mission erm covering november 1986 through april 1988 the final data set consists of over 2 5 million smoothed one per second measurements of the ocean surface the significant wave height swh distribution as given on the noaa geophysical data records gdrs for these measurements peaks at around 2 1 m 19 of the measurements and drops down almost linearly to 2 of the measurements at 5 8 m there are over 1100 observations with swh greater than 15 m the difference between the surface heights calculated from the retracked data and the original on board estimates is less than 10 cm for swh less than 10 m but increases to approximately 1 0 m at a swh of 18 m in general the electromagnetic em bias coefficient calculated using the retracked data is slightly less than that using the unretracked data and does not decrease as much with swh as do the em bias coefficients calculated from the unretracked data a map of the sea surface height variability of the southern ocean created using the retracked data shows differences from variability maps created using the unretracked data in regions of high wave heights retracking can be done efficiently on modern unix work stations at 0 064 times real time acquisition this study shows that retracking will improve altimeter precision

advances in permafrost and periglacial research in antarctica a review recently the research on permafrost periglacial morphology and processes had a great stimulus especially from the international polar year permafrost areas of continental antarctica with its extreme dry and cold environment can be considered an analog of extraterrestrial landscapes like those on mars but also preserve much paleoclimatic information of this crucial part of the global climatic system on the other hand maritime antarctica is one of the areas of the world currently affected by the greatest air warming and provides a unique opportunity to understand the impacts of climate change on permafrost and its related ecosystems despite the significant recent progress some gaps on permafrost distribution still remain as the network for permafrost and active layer monitoring needs further enlargement and better standardization ground ice its age and stability over time need further investigation as well as the role of living organisms on the weathering processes within the cryotic rocks the landscape evolution of continental antartica could be improved providing potential implications also for a better understanding and modeling of life and landscape evolution of other planets

characterization of the deep water surface wave variability in the california current region surface waves are crucial for the dynamics of the upper ocean not only because they mediate exchanges of momentum heat energy and gases between the ocean and the atmosphere but also because they determine the sea state the surface wave field in a given region is set by the combination of local and remote forcing the present work characterizes the seasonal variability of the deep water surface wave field in the california current region as retrieved from over two decades of satellite altimetry data combined with wave buoys and wave model hindcast wavewatch iii in particular the extent to which the local wind modulates the variability of the significant wave height peak period and peak direction is assessed during spring summer regional scale wind events of up to 10 m s are the dominant forcing for waves off the california coast leading to relatively short period waves 8 10 s that come predominantly from the north northwest the wave climatology throughout the california current region shows average significant wave heights exceeding 2 m during most of the year which may have implications for the planning and retrieval methods of the surface water and ocean topography swot satellite mission

methods for measuring rock surface weathering and erosion a critical review studies of rates processes and modes of rock surface and near surface deterioration and also hardening are central to rock weathering and building stone research conservation and management there is a need to measure and monitor weathering at the rock atmosphere interface to facilitate understanding of climatic environmental and lithological controls on the evolution and development of surface weathering features this paper reviews long established and recently developed field and laboratory methods used by geomorphologists to monitor and measure the impact of weathering and erosion on physical and mechanical properties of exposed rock surfaces and their immediate subsurface key advances are highlighted their application to multi scalar understanding and modelling of rock surface weathering in different contexts is discussed and potential future advances to provide new insights into rock weathering durability and materials conservation are identified in highlighting key advantages and disadvantages of a wide range of methods to the broader earth science community the paper aims to contribute to further innovative thinking across disciplines to develop new methods for measuring and monitoring rock weathering

observations in the canary basin and the azores frontal region using geosat data this paper discusses observations of the sea level in the azores frontal region and the canary basin as seen by the geosat altimeter frorn 5 to 45 w and 25 to 45 n two years of geosat exact repeat data were processed by colocating the data on a 0 06 grid then removing the mean by the along track difference method and removing the orbit error by a crossover analysis technique the data set was then interpolated by the successive correction method onto 15 day 0 5 maps to produce 47 residual height fields which were analyzed using complex empirical orthogonal functions eof and spectral analysis the results show that there is a region of high variability in the northwest corner reflecting the gulf stream extension and a region of medium variability at approximately 35 n reflecting the azores current the variability changes only slightly throughout the year with the winter season being the highest the data set also shows first mode baroclinic rossby waves between 30 and 35 n there is evidence that these rossby waves have different wavenumbers to the east and west of the mid atlantic ridge it is postulated that these waves have different generation mechanisms the mid atlantic ridge topography in the west and some other generation mechanism in the canary basin rossby waves are not apparent at 40 n

validation of geosat altimeter derived wind speeds and significant wave heights using buoy data this paper presents a comparison of geosat radar altimeter derived wind speeds and significant wave heights with those measured by buoys in the national data buoy center ndbc network measurements from a subset of 43 buoys moored in coastal regions and deep ocean including the north pacific north atlantic and gulf of mexico were examined data from other buoys within the ndbc network were not included because of their proximity to land seven months of altimeter comparisons were obtained during the geosat geodetic mission for the periods may august and october december 1985 only geosat data within 150 km of buoy locations were accessed this resulted in 1166 wind speed and significant wave height pairs an error analysis was performed to better understand the differences between altimeter and buoy derived results and to establish consistency between the two sets of measurements the following error sources were identified and quantified in terms of their impact on wind speed and significant wave height uncertainties 1 inaccuracies due to buoy instrumentation 2 errors resulting from temporal and spatial separations 3 errors arising from averaging of the buoy data in time and averaging of altimeter data over its footprint and 4 altimeter instrumentation errors four algorithms relating altimeter radar cross section to ocean surface wind speed were investigated the brown algorithm brown et al 1981 and the smoothed form of the algorithm of brown et al goldhirsh and dobson 1985 were found to give the smallest rms errors these were 1 7 m s and less for a maximum altimeter track buoy separation of 50 km for most cases considered this uncertainty agreed with the error obtained from the error analysis significant wave heights measured by the altimeter were found to be in agreement with buoy derived values to within 0 5 m rms this value was also found to be in agreement with that derived from the error analysis the measurement goals for geosat were 1 8 m s rms for wind speeds from 1 m s to 18 m s and 0 5 m rms for significant wave height or 10 whichever is greater frain et al 1985 these goals were met for the range of wind speeds compared

measuring ocean wave period with satellite altimeters a simple empirical model a simple empirical model is proposed to retrieve wave period from ku band radar altimeter backscatter and significant wave height the model formulation is heuristic and fitted using a large dataset of collocated topex altimeter and buoys measurements empirical models are proposed for the zero up crossing the mean and the peak wave period and compared with models by davies et al 1997 and hwang et al 1998 their performance is assessed using an independent validation dataset and gives a retrieval error of 0 8s regional analysis indicates that the wave period models perform better in wind seas than in swell dominated conditions