organic walled microfossils and geochemical tracers sedimentary indicators of productivity changes in the north water and northern baffin bay during the last centuries analyses performed on 26 surface sediment samples collected with a box corer at 17 stations throughout the north water and northern baffin bay 75 791n 68 801w revealed abundantorganic walled microfossils most ly dinoflagellate cysts 10 3 10 4 cysts g 1 and organic linings of benthic foraminifers 10 2 10 3 ol g 1 as well as high organic carbon concentrations 0 87 2 81 dry weight these data indicate high productivity in both the pelagic and benthic environments of the north water and slightly lower productivity in northern baffin bay the data also showed calcium carbonate and biogenic silica dissolution throughout the study area the dinocyst assemblages were relatively uniform in the north water and dominated by heterotrophic taxa algidasphaeridium minutum and brigantedinium spp whereas northern baffin bay assemblages were dominated by autotrophic taxa notably operculodinium centrocarpum and spiniferites elongatus the difference between these two assemblages may be related to higher diatomaceous primary production in the north water than in northern baffin bay since diatoms constitute the principal food source of heterotrophic dinoflagellates the biogeographical boundary between the north water and northern baffin bay has been maintained for at least the last few centuries as shown by analyses of microfossils and geochemical tracers in two sediment cores one taken in the southeastern part of the north water 76117 0 n 72102 0 w and the other in northeastern baffin bay 75135 0 n 70148 0 w the analyses of the north water core revealed relatively uniform microfossil assemblages and organic carbon fluxes ranging from 1 1 to 1 5 mg corg cm 2 yr 1 for the last few centuries which corresponded to 4 6 of the present annual primary production in the euphotic zone these data suggest high productivity and relatively stable conditions in the polynya on a decadal time scale in the northeastern baffin bay core the analyses indicated generally lower organic carbon fluxes ranging from 0 3 to 0 6 mg corg cm 2 yr 1 and from the microfossil data significant variations in sea surface conditions at this lower latitude over the last centuries r 2002 elsevier science ltd all rights reserved

the formation of helgafell southwest iceland a monogenetic subglacial hyaloclastite ridge sedimentology hydrology and volcano ice interaction abstract helgafell a little eroded basaltic hyaloclastite ridge in southwest iceland formed in a single eruption under a pleistocene ice sheet the ice thickness at the eruption site was at least 500 m and it was probably located some 15 km from the glacier s snout the eruption created a 2 km long 0 8 km wide and initially 300 m high ridge gravity modelling indicates that helgafell has a bulk density of 1800 kg m 3 and that holocene lavas around it are 40 80 m thick this confirms that helgafell is predominantly made of hyaloclastite with pillow lavas and intrusions only making up a few percent of the total volume the southeast side is made of unsorted eruption fed hyaloclastites considered to have been piled up against an ice wall while moderately to well sorted water transported material is found on the northwest side glacier flow and meltwater drainage was towards the northwest the absence of basal pillow lavas suggests that magma fragmentation occurred from the onset of the eruption until its end the lithofacies preserved indicate a fully subglacial eruption although a final subaerial eruptive phase may have taken place through an ice chimney the volatile contents h 2 o 0 26 0 37 wt of several glass samples from the southeast side of the mountain indicate water pressures of 1 mpa throughout the eruption efficient syn eruptive drainage of meltwater coupled with rapid ice subsidence probably led to partial dynamic support of the ice causing water pressure in the vault to be much lower than the static load of the overlying ice observed lack of correlation between elevation and volatile content may be a consequence of gradual reduction in dynamic support as the eruption rate declined and the edifice grew higher helgafell demonstrates that explosive activity may occur under 500 m thick ice and it may be an analogue to the ridge formed in the gjalp eruption in 1996

synchronizing ice cores from the renland and agassiz ice caps to the greenland ice core chronology 1 four ice cores from the agassiz ice cap in the canadian high arctic and one ice core from the renland ice cap in eastern greenland have been synchronized to the greenland ice core chronology 2005 gicc05 which is based on annual layer counts in the dye 3 grip and ngrip ice cores volcanic reference horizons seen in electrical conductivity measurements ecm have been used to carry out the synchronization throughout the holocene the agassiz ice cores have been matched to the ngrip ice core ecm signal while the renland core has been matched to the grip ice core ecm signal thus tying the cores to gicc05 furthermore it has been possible to synchronize the renland ice core to ngrip gicc05 in the glacial period back to 60 000 years b2k years before a d 2000 on the basis of a matching of transitions between stadials and interstadials this work brings the total number of ice core records that have been rigorously tied to the gicc05 timescale up to nine renland annual layer thicknesses are increasing with depth during the period from 7 to 8 5 ka b2k a highly unusual observation only matched by a similar thickness increase in the glacial section of the renland core some 60 ka ago annual layer thicknesses in the agassiz ice cores point to a well developed raymond bump in the agassiz ice cap

sea surface conditions in northernmost baffin bay during the holocene palynological evidence the analysis of cores collected in northernmost baffin bay from within the area of the north water polynya permits definition of a composite sedimentary sequence ca 12 m thick spanning the last 10 000 14 c yr with only a few discontinuities palynological analyses were performed in order to reconstruct changes in surface water conditions and biogenic production transfer functions using dinocyst assemblages were applied to estimate sea surface temperature sst and salinity as well as the seasonal duration of sea ice cover at the base of the record prior to 9300 14 c yr bp dinocysts and organic linings of benthic foraminifers are sparse indicating harsh conditions and low productivity after ca 9300 14 c yr bp the increased concentration of benthic foraminifers up to 10 3 linings cm 3 and dinocyst fluxes 10 2 10 3 cysts cm 2 yr 1 reveals high biological productivity related to open water conditions the early to middle holocene from ca 9000 to ca 3600 14 c yr bp is marked by relatively high species diversity in dinocyst assemblages and the significant occurrence of autotrophic taxa such as spiniferites elongatus pentapharsodinium dalei and impagidinium pallidum this assemblage suggests conditions at least as warm as at present from ca 6400 to ca 3600 14 c yr bp transfer functions indicate warmer conditions than at present with sst in august fluctuating up to 5 5 c after 3600 14 c yr bp the dinocyst record suggests a trend of decreasing temperature toward modern values marked by recurrent cooling events copyright 2001 john wiley sons ltd

fossil andisols identified with mass balance geochemistry oligocene john day formation oregon u s a mass balance geochemistry of thick sequences of fossil soils oligocene john day formation central oregon show trends similar to those produced by modern andisol soil forming processes these andic trends include phosphorus accumulation potassium retention and alumina and iron depletion identification of these trends benefited from the geochemical comparison of numerous fossil soil horizons from two paleosol sequences one andic and one non andic the comparison of two paleosol sequences is justified because both sequences developed from the same type of parent material in nearly identical tectonic depositional settings the two sequences are 1 the early oligocene big basin member dominated by clayey alfisol like paleosols and 2 the mid oligocene turtle cove member dominated by ash rich andisol like paleosols with calcareous horizons the change in paleosol type occurred circa 30 ma throughout the john day basin and is most likely due to global cooling which changed climatic conditions in central oregon from humid to subhumid drier climate is interpreted to have caused a decrease in weathering intensity so that amorphous weathering products of volcanic glass accumulated in soils to form andisols prior to this circa 30 ma transition weathering produced crystalline clays from volcaniclastic detritus to form alfisols rather than amorphous weathering products

chemical processes affecting the mobility of major minor and trace elements during weathering of granitic rocks abstract the behaviour of 38 major and trace elements as well as changes in the mineralogy have been examined in 10 weathering profiles developing on some portuguese granitic rocks element mobilities are calculated from geochemical data normalized with respect to ti in the fresh parent rock chemical elements are divided into two groups immobile and mobile on the basis of their geochemical distribution during weathering elements that are immobile during weathering are zr hf fe al th nb sc and the ree very mobile are ca na p k sr ba rb mg and si mobile elements are derived mainly from leachable minerals such as feldspars micas and apatites whereas immobile elements are either concentrated in resistate phases or strongly adsorbed by secondary minerals the geochemical behaviour of mn cr v fe and ce is very dependent on redox conditions redox transformations of these elements can be used to set limits on the oxidation state of a weathering suite the ree are mobilized or fractionated during late stages of weathering but not during moderate stages of weathering this fractionation is caused by selective leaching of rocks composed of both stable and unstable minerals containing ree

chemical weathering of basalts southwest iceland effect of rock crystallinity and secondary minerals on chemical fluxes to the ocean river ground and peat water from a basaltic catchment area laxa in kjos southwest iceland were sampled and analyzed for major element concentrations to define the effect of glassy versus crystalline basalt the formation of secondary minerals and runoff on fluxes of dissolved elements to the ocean the proportions of the dissolved solids in the water samples derived from precipitation air and rock weathering were estimated the amounts of na mg ca k and s originating from precipitation were calculated from the respective solute cl marine ratios and the estimated aqueous cl originated from precipitation which was calculated using measured b content of the waters and b cl molal marine and rock ratios the rock contribution from weathering ranged from 22 to 46 percent of the total dissolved solids of the waters iron and al showed low mobility compared to na this was primarily due to consumption of these elements by ferrihydroxides allophane imogolite and clay minerals also si and to a lesser degree ca show apparent slightly lower mobility than na these results are in good agreement with these phases being dominant in the soils of the study area wada and others 1992 and the main secondary minerals of basaltic glass in iceland crovisier and others 1992 reaction progress calculations support these findings according to a model interaction of basaltic glass and meteoric water al fe and si are consumed by amorphous fe and al hydroxides and imogolite and allophane at low reaction progress with increasing reaction progress ca fe mg smectite became the primary secondary minerals limiting the mobility of ca fe mg si and al these findings suggest that the weathering in the laxa in the kjos catchment area has evolved into the beginning of the smectite weathering stage and that it is dominated by a relatively low reaction progress and a high water to rock ratio in the present study the effect of runoff and rock crystallinity was quantified for dissolved elemental fluxes temperature lithology other than rock crystallinity and rock age were similar in all of the catchment areas in this study silica ca f s al k mg and b had a very similar dependence on runoff on the other hand na fluxes were found to be less dependent on runoff and fe fluxes were found to be independent of runoff basaltic glass dissolves faster than fully crystallized basaltic rocks gislason and eugster 1987a therefore increased glass content of the primary rocks is thought to increase the leaching and elemental fluxes at constant runoff however because some of the solutes particularly al and fe were highly influenced or even controlled by the formation of secondary minerals this increasing dissolution with increasing glass content was hidden on the other hand basaltic glass was observed to enhance the fluxes of more mobile elements like na si ca f and s by a factor of 2 to 5 at a constant runoff of 200 cm yr constant vegetative cover and 0 to 100 percent glass content of the rocks the k and mg fluxes were found to be independent of rock crystallinity however runoff alone cannot explain the fluxes of these elements and it seems that vegetative cover and seasonal variations in biomass activities influence the k and mg fluxes

chemical weathering of volcanic rocks at the island of pantelleria italy information from soil profile and soil solution investigations abstract concentrations of major minor and trace elements were determined in soil profiles and soil solutions from the island of pantelleria sicily channel to evaluate the weathering extent of soils evolved on trachytic and pantelleritic rocks and the aqueous transport of elements by their soil solutions the chemical index of alteration cia indicates a low to moderate degree of weathering consistently the mineralogical and geochemical imprints of the parent rocks are generally preserved the chemical weathering appears to be incongruent owing to primary minerals and glass dissolving to a variable degree while secondary minerals have formed based on the calculated saturation state of primary and secondary minerals with respect to the soil solutions and on mineralogical observations olivine and pyroxene are unstable and dissolving whereas magnetite and hematite are stable the main weathering products are amorphous phases such as ferrihydrite amorphous aluminium hydroxide and silica clay mineral formation appears to be incipient and mainly limited to kaolinite and smectite although for some soil profiles a hydrothermal origin is suggested for these minerals chemical characteristics of soil solutions and elemental mobility are controlled by the element source and water rock interaction

paleoproterozoic ca 1 9 ga megascopic life on land in western australia abstract controversial hairpin shaped trace fossils myxomitodes stirlingensis and discoid fossils cyclomedusa davidi are here reinterpreted in a reassessment of sedimentology and paleosols of the 1 9 0 1 ga stirling range formation of western australia paleosols in the stirling range formation were recognized from complex cracking patterns peds and cutans chemical and mineralogical zonation soil horizons and poikiloblastic crystals desert roses redox profiles of the paleosols are evidence of well drained profiles of a coastal plain under a low oxygen 433 116 ppmv and carbon dioxide 564 64 ppmv atmosphere gypsum pseudomorphs in paleosols that are deeply weathered chemically represent a persistence of acid sulfate weathering better known in archean paleosols before the great oxidation event at 2 45 ga chemical composition of the paleosols is evidence of a humid 1478 182 mm mean annual precipitation temperate 11 3 0 5 c mean annual temperature paleoclimate their paleoenvironmental setting was a coastal plain on a passive tectonic margin megafossils were found on paleosols of western red sandstones of the stirling range formation not in gray shales and sandstones of marine facies to the east trace fossils myxomitodes stirlingensis and discoid fossils are both found at the surface of well drained paleosols and so were not metazoan trails nor sea jellies myxomitodes was more likely a grex slug trail of soil slime molds and the cyclomedusa discoids were probably microbial colonies pervasive microfilamentous structures in the paleosol surface are additional evidence of paleoproterozoic microbial earth ecosystems

do red beds indicate paleoclimatic conditions a permian case study abstract terrestrial red beds have long been interpreted as desert deposits by comparison with modern red deserts more recently red beds have been interpreted as evidence of seasonally dry conditions and a permo triassic pangean monsoon red beds of cala viola sardinia are identified as paleosols and used to reconstruct late permian paleoclimatic conditions reconstruction of paleoenvironmental conditions based on the paleosols of the cala viola indicates warm humid conditions with no evidence of dry conditions as in a desert or of extreme seasonality as in a monsoon instead it is suggested that the red color of the paleosols is a result of former good drainage and that red color in general does not indicate specific paleoclimatic conditions

comparative characterization of volcanic ash soils exposed to decade long elevated carbon dioxide concentrations at mammoth mountain california elevated concentrations of soil co 2 ranging from 20 to 90 from a magmatic source have been killing coniferous trees in the last decade in several distinct areas on the flanks of mammoth mountain california these areas of elevated soil co 2 provide a natural laboratory to examine how chemical weathering in soils responds to extremely high co 2 concentrations in conjunction with possible changes in organic acids resulting from vegetation mortality these volcanic ash soils have a particularly low resistance to chemical weathering due to the predominance of volcanic glass and other noncrystalline phases thus decade long exposure to anomalous conditions may result in differences in soil characteristics soil samples from within the high co 2 region have been analyzed and compared to samples from outside the anomalous area in the adjacent healthy forest areas where background co 2 concentrations are less than 1 compared to the control soil the high co 2 soil has lower ph values 5 0 compared to 5 6 higher soil moisture content and higher surface area dithionite citrate and acid oxalate extractants were less effective in leaching al and si from the high co 2 than from the control soil indicating a distinct difference in the mineralogy of these soils the observed differences between the high co 2 and control soils are consistent with an enhancement of weathering intensity in the soil exposed to elevated co 2 concentrations

geochemical behaviour of ni cr cu zn and pb in an andosol cambisol climosequence on basaltic rocks in the french massif central abstract the objective of this study is to identify parameters influencing trace elements te vertical distributions in an andosol andic cambisol climosequence in order to understand processes involved in the current distribution of trace elements from basaltic rocks to associated soils six pedons developed on tertiary massive basaltic formations located at similar position in the hill slopes submitted to the same wet mountainous climate but under various microclimatic conditions altitude and annual rainfall were considered the six studied soils are andic and rich in organo metallic complexes two different and quantitative methods were used to compare the geochemical distributions of major and trace elements both being calculated with ti as invariant element isovolumetric mass balance and enrichment factors anthropogenic pedogenetic microclimatic inherited factors were discriminated anthropogenic influences are pointed out for k in two pedons and for pb in all studied sites distributions of other te are affected by discontinuities between underlying rocks and soil horizons zinc and cu distributions are controlled by organic matter whereas cr and ni distributions are influenced by pedogenetic processes results emphasize the relative trace element immobilization in andic soils under temperate climate

mobilization and redistribution of rees and thorium in a syenitic lateritic profile a mass balance study abstract ree th geochemistry and mineralogy have been studied in a lateritic profile derived from a syenite at akongo in sw cameroon ree and th mass balance calculations for the host rock minerals show that at least 70 of the lree s and 50 of the hrees are contained in allanite apatite titanite and epidote and at least 50 of the th is controlled by the same accessory minerals which represent about 2 wt of the unaltered syenite these accessory phases are destroyed during the first stages of weathering causing most of the rees and th to be rapidly released into the soil comparison of the variation in the zr ti and th content as a function of the apparent density of the different zones of the saprolite shows that th is the least mobile element the presence of secondary thorianite tho2 the etched surface on zircon grains and the presence of ti in secondary cerianite support this geochemical interpretation the concentration of thorium was therefore chosen as invariant relative to the concentration of the other elements especially the rees in mass balance calculations most of the rees are leached in the iron rich upper horizons loose nodular horizon iron crust and top of mottled clay horizon where the groundwater table moves saprolite and bottom of the mottled clay horizon the rees are fractionated and redistributed there is a juxtaposition of leached and accumulation zones with precipitation of lree aluminous hydrated phosphates this study supports the existence of two different cycles for the redistribution of elements in the soil 1 1 as dissolved ions in the saprolite horizon and 2 2 as individual particles in the upper part of the profile

pedogenesis and geochemical alteration of the picture gorge subgroup columbia river basalt oregon reddened clay rich horizons between basalt flows have historically been identified as baked zones or as zones of lateral groundwater movement the reddening has been attributed to thermal or chemical alteration of the permeable portion of the basalt flow many of these red horizons are instead paleosols that record significant hiatuses in basalt flow emplacement paleosols were identified in the field on the basis of features such as horizonation ped morphology and root traces terrestrial gastropods fossil plants and peats also occur locally plots of weathering indices such as base loss are consistent with a pedogenic origin for these horizons ca na mg fe 21 and p have been extensively lost from the a and bt horizons of the paleosols consistent with modern weathering patterns k and rb have been added to the upper portions of the profiles and lost in the lower portions of the profiles relative to the parent material with rb added disproportionately historically this pattern of enrichment has been cited as evidence of k metasomatism the apparent metasomatism can be explained using a new model in which there was extensive felsic volcanism contemporaneous with pedogenesis and k and rb were likely added by windborne ash the apparent discordance between k and rb contents of the paleosols can be explained by the presence of land plants because k is an important electrolyte and rb does not serve any major biological role this model could account for apparent k metasomatism in other paleosols following the advent of land plants and may be applicable to older paleosols as well

stratification of parent material in european volcanic and related soils studied by laser diffraction grain sizing and chemical analysis abstract sedimentary stratification identified by field descriptions of 12 soils derived wholly or partly from volcanic materials was compared with results obtained by chemical analyses contents and ratios of lithogenic elements contents of heavy metals and detailed grain size data after removal of organic matter and amorphous fractions the finest sedimentary stratification was indicated by cluster analysis of ratios of lithogenic elements and by the grain size analyses sedimentary stratification in the field is difficult to determine or describe when 1 the deposits are strongly weathered 2 soil horizon boundaries coincide with stratification boundaries or 3 stratification is very fine nevertheless field descriptions are a reasonably good way of differentiating parent materials though they often underestimate the number of sedimentary layers

glacier fluctuation and inferred climatology of langjokull ice cap through the little ice age abstract emerging paleoclimate records from proglacial lake hvitarvatn central iceland suggest that langjokull ice cap attained its maximum holocene extent within the last 400 years with the aim of constructing glaciological models and appropriate model inputs for holocene simulations of langjokull we begin by simulating the evolution of langjokull through the little ice age to present a period for which we have some constraint on ice cap geometry using modern measured mass balance distributions 1997 2003 and meteorological data from nearby hveravellir we derive a reference precipitation field for the period 1961 1990 over the ice cap our simulations suggest langjokull attained its maximum little ice age volume around 1840 with a second local maximum around 1890 the two outlet glaciers terminating in hvitarvatn nor urjokull and su urjokull advance slowly into the lake occupying their maximum lake area in the late 19th century and retreat comparatively rapidly in the mid to late 20th century simulations of nor urjokull are much more faithful to the geomorphic evidence than are simulations of su urjokull potentially suggesting a difference in dynamics between these two glaciers while only 35 of the hvitarvatn catchment area is ice covered meltwater from langjokull comprises 70 of the water input to the lake two thirds of this input from the ice cap is transported as groundwater simulated glacier derived discharge to the lake through the little ice age suggests that a sediment concentration of 1 5 kg m 3 would have resulted in the transport of 1 5 10 11 kg of material to the lake over the last 300 years comparable to the estimated mass of sediment in the most recently deposited sedimentary unit in the lake

determining weathering rates of soils in china abstract as an important parameter for critical load calculation and soil acidification simulation weathering rates of soils in china were studied using different methods of calculation the approaches used were the mass balance approach the soil mineralogical classification the total analysis correlation the profile model the magic model and a simulated leaching experiment since chemical weathering of secondary minerals usually plays a much more important role in neutralizing the long term acidification of soils in china than that of parent material soil mineralogy rather than parent rock material type which is regarded as the most suitable factor representing weathering rates in europe should be adopted as the basis for soil classification the weathering rate assigned to each soil should also be corrected when the effect of temperature is considered due to the variation in experimental conditions the weathering rates of soils from laboratory experiment may be difficult to compare with field determined rates and should be adjusted by ph and percolation rate the comparison of various methods in this study shows that the weathering rates of soils estimated by the profile model coincide well with those from other independent methods such as the dynamic modeling by magic and the modified leaching experiment the weathering rates were very low usually lower than 1 0 keq ha 1 year 1 for allites including latosol lateritic red earth red earth yellow earth and yellow brown earth in south china and silalsols consisting of dark brown forest soil black soil and podzolic soil in northeast china and very high for alpine soils desert soils and pedocals in west china the content of weatherable minerals in soil is the most important factor in determining the spatial distribution of weathering rate in china while the difference in temperature may be the reason why the weathering rate of soil in northeast china was lower than that in southeast china

water column structure and circulation under the north water during spring transition april july 1998 abstract the north water is a large recurring polynya in northern baffin bay over 400 hydrographic ctd profiles taken over a grid of stations between april and july 1998 were analysed to understand the water column structures underlying the polynya during spring transition in the north water imported and dissimilar water masses converge over a complex bathymetry northern assembly na waters are derived from inflows through nares strait and jones sound southern assembly sa waters are derived from a northern moving branch of the west greenland current wgc na and sa waters mix primarily over the north south smith sound canyon between 76 5 n and 77 n latitude to form a distinct relatively thick halocline layer termed north water assembly nwa characterised by density compensating thermohaline intrusions in the southern portion of the north water a sharp front between nwa waters and sa waters roughly aligns with the 500 m isobath flow patterns deduced from potential temperature vs salinity s diagrams and from minima in stability frequency n profiles indicate that this front results from the convergence of nwa waters and a branch of the wgc that is cyclonically re directed as it approaches smith sound canyon not all sa waters are immediately re directed south towards the front as a second branch follows the greenland coast toward smith sound while s signatures show some evidence of upwelling along the greenland coast e g outcropping of isopycnal surfaces no surfacing of warm atlantic derived water was observed during the sampling period 1998 suggesting that mechanical removal of ice by winds and currents is the primary mechanism by which the north water forms some sensible heat exchange associated with brine rejection and penetrative convection may occur but only during periods of active ice formation

volcanic sands of iceland diverse origins of aeolian sand deposits revealed at dyngjusandur and lambahraun the origin formation and evolution of volcanic sands are less well known than the formation of the much more common quartz rich sand sheets combining active volcanism and a cold climate iceland is covered for about 21 of its surface by sandy areas the sands were analyzed in detail at two sites and results reveal their diverse origins the first site is dyngjusandur located north of vatnajokull and the second site is the lambahraun area located south of langjokull at both sites the sand origin is determined from field observations wind directions from ventifacts chemical and mineralogical analyses of rocks and sands at dyngjusandur the sand is dominated by glass grains a situation typical of sand plains in iceland hyaloclastite ridges presently buried beneath vatnajokull are the dominant source of the sand and only large size plagioclase crystals 0 5 cm in sands seem to be derived from the lava flows hyaloclastite ridges were crushed by glaciers and mechanically eroded sediments were washed out by melt water onto flood plains the sand chemical composition is spatially homogeneous and similar to the average composition of neighboring sub aerial lava flows reflecting efficient mixing of distinct sources below the glacier the presence of sand north of dyngjujokull can be taken as a way to explore the average chemical composition of non exposed volcanic material beneath the glacier in the case of lambahraun prevailing winds indicate several potential sources of sand at the north of the sand sheet comparison of chemical and mineralogical analyses of sands and rock samples helped to refine the exact origin in contrast with the first site the sand is dominated by crystals and is chemically consistent with a mixture of material derived from the lava flows of eldborgir and skersli shield volcanoes analysis of the contact between the lava flows and the glacier reveals that basaltic sand grains formed as the result of recent advances of the glacier abrading the rocks the direct interaction of glacial and fluvio glacial activity with basaltic plains appears to be necessary to produce a large amount of sands in a relatively short period of time 4000years this site appears to be an excellent natural laboratory for further studies concerning the sand evolution and physical sorting processes in basaltic material which have important implications for understanding aeolian processes on mars copyright c 2011 john wiley sons ltd

ice volcano interaction of the 1996 gjalp subglacial eruption vatnajokull iceland volcanic eruptions under glaciers can cause dangerous floods and lahars1 2 3 and create hyaloclastite fragmented glassy rock mountains4 5 6 7 8 but processes such as the rate of heat transfer between ice and magma edifice formation and the response of the surrounding glacier are poorly understood because of the lack of data here we present observations from the fissure eruption at vatnajokull ice cap iceland in october 1996 in the 13 days of the eruption 3 km3 of ice were melted and the erupted magma fragmented into glass forming a hyaloclastite ridge 6 7 km long and 200 300 m high under 500 750 m of ice meltwater of temperatures of 15 20 c flowed along a narrow channel at the glacier bed into the grimsvotn subglacial lake for five weeks before draining in a sudden flood or jokulhlaup subsidence and crevassing of the ice cap occurred over the eruptive fissure and the meltwater path whereas elsewhere the glacier surface remained intact suggesting that subglacial eruptions do not trigger widespread basal sliding in warm based glaciers

geochemistry and palaeoclimatic reconstruction of a palaeosol sequence at langebaanweg south africa abstract neogene langebaanweg lbw palaeosol sediment sequences at the west coast of south africa are well known for their well preserved rich palaeontological heritage the palaeosols developed on estuarine marine coastal alluvial deposits stacked on each other ranging in age from the mid miocene to quaternary elemental mobility and redistribution based on major and minor element geochemistry of 11 horizons of the 18 m sequences were studied to evaluate the degree of chemical weathering a major process of soil formation and to reveal important palaeoenvironments in which the palaeosols developed elemental geochemistry was carried out on 2 50 mean wt two wi 1 and wi 2 of the four weathering indices applied to evaluate weathering intensity proved unsuitable for use in an alluvial palaeosol sediment sequences such as lbw chemical index of alteration cia and chemical index of weathering ciw values were relatively more consistent in distribution pattern across the pedocomplex but caution should be applied when using them in similar cases the pedogenic carbonate horizons on average had the lowest values for both cia and ciw 1 12 2 60 suggesting more advanced weathering plots of geochemical ratios quantifying pedogenic processes against depth show striking variations among and within the palaeosol and sediment sections soil formation was more advanced in the mid miocene and pliocene than in the quaternary suggesting a more humid and warmer climate than present we evaluated selected geochemical climofunctions and conclude that more data are obviously needed for a more robust calibration of the models in langebaanweg palaeosols

geochemistry of historical age silicic tephras in iceland the major element chemistry of nine silicic tephras of historical age from iceland is assessed as a key step in the development of the recent tephrochronology of the north atlantic region the tephras include the largest such layers produced by each of the five central volcanoes hekla o raefajokull eyjafjallajokull torfajokull and askja since the ninth century ad h 1104 o1362 e 1821 landnam tephra c 870 a 1875 and four other tephras h 1158 h 1510 h 1947 o1727 the determination of grain discrete major element chemistry of the glass fraction is a fundamental stage in the identification and correlation of tephra and allows links to be made between icelandic source areas with precise dating evidence and distal deposits elsewhere in the north atlantic region although major element data can be used to discriminate between tephra layers produced by the different central volcanoes on its own it cannot be used to identify all the holocene layers produc

pedogenesis and weathering rates of a histic andosol in iceland field and experimental soil solution study abstract it is important to study the rate determining processes of chemical weathering and soil formation in volcanic islands since a significant part of the carbon fixed by chemical weathering of silicates on earth is fixed at the surface of volcanic islands these soils are fertile and much of the river suspended matter delivered to the ocean stems from these islands this study determines the factors that drive the pedogenesis of a histic andosol in western iceland soil solutions were extracted from the profile in the field from undisturbed ex situ mesocosms and from repacked laboratory microcosms concentrations of measured and calculated inorganic species in the field and experimental soil solutions were used for thermodynamic and kinetic interpretation and to calculate the weathering rates the main primary rock constituent of the 205 cm thick soil profile was basaltic glass allophane content ranged from 2 to 22 and the soil carbon content ranged from 11 to 42 mean soil solution ph value ranged from 4 to 6 with the lowest value at 80 cm depth and highest between 150 to 205 cm the high solute concentrations in soil solutions in the beginning of the microcosm weathering experiment declined faster for anions than cations under field conditions inorganic anions were supplied by marine and anthropogenic rather than pedogenic sources and hence these anions were subsequently leached out during the experimental duration when there was a limited input of anions through experimental precipitation the factor which defined the rate at which each ion was depleted from the exchange complex of the soil decreased down the soil profile the release sequence at 50 cm depth was cl na so 4 f si the si and base cations experimental weathering rate when normalized to geographical surface area are similar to or lower than those measured from river catchments in southwestern iceland the dissolved al flux was much higher from the soil when compared to the river catchments field and experimental soil solutions were all highly undersaturated with respect to basaltic glass field and mesocosm samples were supersaturated with respect to secondary allophane and imogolite while samples from the microcosms were often undersaturated with respect to allophane and imogolite predicted dissolution rate was dictated by the soil solution a h 3 a al 3 activity ratio but slowed down by up to 20 and 30 by decreasing undersaturation in field and mesocosms respectively predicted dissolution rates according to the a h 3 a al 3 activity ratio increased up to factor of 7 30 and 37 by speciating al 3 with oxalate in field mesocosms and microcosms respectively speciation with oxalate which represents the maximum effect of the dissolved organic carbon doc on dissolution rates generally had more effect near the surface than at deep levels in the soil profile this study shows that at fixed temperature reactive surface area and composition of the volcanic glass in the soil the chemical weathering rates of andosols are dictated by 1 aeolian deposition rates and drainage which affect the saturation state and the a h 3 a al 3 activity ratio 2 the production of organic anions within the soil and 3 external supply of anions capable of complexing al 3

constitutive mass balance relations between chemical composition volume density porosity and strain in metasomatic hydrochemical systems results on weathering and pedogenesis relations characterizing the chemical physical and mechanical changes resulting from metasomatic hydrochemical processes are developed using mass balance models which formally link chemical composition to bulk density mineral density volumetric properties porosity and amount of deformation strain rigorous analysis of aqueous solute transport effects is then made possible in a variety of porous media flow environments including chemical weathering pedogenesis soil formation diagenesis ore deposition and enrichment and metamorphism application of these linear constitutive relations to chemical weathering profiles shows that immobile and locally mobile chemical elements with masses conserved on the scale of soil profiles can be accurately identified from analysis of appropriate data arrays and then used as natural geochemical tracers to infer the nature and extent of hydrochemical weathering processes and volume changes during pedogenesis assumptions commonly made in the past about the supposed immobility of certain elements e g ti and zr become unnecessary quantitative differentiation between the effects of residual and supergene fractionation is then easily made these methods are applied to ni rich laterites developed by weathering of ultramafic rocks showing that during ordinary residual enrichment ni is concentrated by as much as 4 protolith peridotite concentrations this occurs simply by silicate mineral dissolution and removal of chemical elements other than ni e g mg with a corresponding reduction in saprolite density and increase in bulk porosity without significant deformation in contrast laterites with mineable concentrations of ni which are similarly undeformed such as the nickel mountain mine in riddle oregon have experienced in addition to residual enrichment strong supergene enrichment by fractionation of ore elements between a leached zone from which ni is extracted and a complementary enriched zone positioned farther along the direction of ground water flow soil forming processes in podzol chronosequences developed on sandy beach terraces of the mendocino coast of california involved soil column collapse of 60 percent by dissolution of silicate minerals in the albic horizon of al and fe leaching and 70 percent dilation expansion in the overlying organic rich layer by root growth the amount of erosion based upon paleosurface reconstructions using the excess mass of fe al pb ga and cu in the zone of supergene enrichment spodic horizon below the ground water table indicates that subsurface erosion by dissolutional collapse is three times that of surficial erosion finally using published chemical data for ti zr and cr on major bauxite deposits in australia where erosion rates are thought to be low we infer that there may have been major amounts of dissolutional collapse to explain the upwards increase of detrital zircon and rutile in weathering profiles

the behaviour of so called immobile elements in hydrothermally altered rocks associated with volcanogenic submarine exhalative ore deposits evidence is available that some elements notably zr tio2 y sc ce and nb are largely immobile during the alteration of volcanic rocks owing to metamorphism hydrothermal events and weathering e g floyd and winchester 1978 however it is shown by reference to analyses of rocks from the environment of five volcanogenic massive sulphide bodies that while zr tio2 and ce are mostly immobile even during intense hydrothermal alteration y and particularly sc and nb may be extremely mobile when elements are removed by solution in a hydrothermal fluid it seems that reaction rates are such that these elements are almost totally removed from the rock therefore of the so called immobile trace elements only zr and tio2 may be used with any reliability to identify the degree of magmatic differentiation in an hydrothermally altered rock however if an element has been mobile it is usually readily identified as having moved

dynamics of volcanic systems in iceland example of tectonism and volcanism at juxtaposed hot spot and mid ocean ridge systems volcanic systems are swarms of tectonic fractures and basalt volcanoes formed as a result of plate pull as the plates are pulled apart associated with the mid ocean ridges and the magma dynamics of the iceland mantle plume most systems are 40 150 km long 5 20 km wide and develop a central volcano they supply magma to all eruptions in iceland data obtained in the last few years have greatly improved our knowledge of their volcanotectonic environment as a result the geometry of the plume is better constrained and the crust previously considered thin 10 km is now modeled as thick 20 40 km depending on the location of the volcanic systems their activity either decreases or increases faulting in the two main seismic zones from this we can infer that emplacement of the feeder dike to the largest historical eruption in iceland that of laki in 1783 increased shear stress in the south iceland seismic zone and almost certainly triggered the largest m 7 1 in 1784 historical earthquake in ic

concentrations of major and trace elements in soil and grass at shimba hills national reserve kenya concentrations of major and trace elements in soils and grass are determined at shimba hills national reserve in kenya using geochemical mapping techniques the study investigates the influence of soil and vegetation type on the concentrations of na k mg ca mn p co cu zn mo ni and se in soils and grass the implications are assessed for the nutrition of the sable antelope of which the reserve supports the last remaining viable population in kenya low concentrations in surface soils of a number of major and minor elements are attributed to the geochemical nature of the underlying parent materials of sands sandstone and grits within the reserve variations in the element status of surface soils are related to the vegetation and soil types elevated element concentrations in surface soils in natural forest areas are attributed to the influence of litterfall whilst in grassland areas soil element status is controlled by soil type and decreases in the order ferralsols acrisols arenosols the general depletion of major and minor elements in soils at shimba hills is not reflected as fully in grasses in which nutrient concentrations were of similar magnitude to those reported from other kenyan conservation areas burning of grassland areas leads to elevated concentrations of k p co cu and mo in grasses elevated soil plant uptake ratios for p and k and elevated soil ph it is suggested that increased availability of p in soils at elevated soil ph levels contributes to its enhanced uptake into grass a tentative assessment of the mineral status of grass at the reserve using guidelines developed for domestic ruminants indicates deficiencies of na k p and zn and that the ca p ratio exceeds the tolerable range for animals in addition the low concentrations of cu co and zn in surface soils in the reserve indicate that the potential supply of these elements to plants is limited

climate dependent chemical weathering of volcanic soils in iceland abstract the major element mobility within soil profiles of brown to gleyic andosols that developed under diverse climatic conditions in iceland is assessed the volcanic soils were selected from areas with good monitoring of annual temperature and precipitation and the degree of weathering and elemental behavior is compared icelandic soils are subject to high fluxes of aeolian dust and at times to tephra ejecta from volcanic eruptions the source of dust input is assessed for each profile based on comparison of the chemical signatures found in the less weathered upper horizons with those of volcanic systems supplying material to source areas results show that tio 2 al 2 o 3 and fe 2 o 3 t and mno are the least mobile species and generally found enriched within more mature horizons the mobile base cations mgo cao and na 2 o are depleted in these horizons as a result of chemical weathering during pedogenesis soils developed in colder climatic conditions with mean annual temperature mat 1 c give values for the chemical index of weathering ciw of 37 45 that reflect only weak chemical weathering soils developed in milder climates mat 2 4 c are more strongly affected by weathering ciw 50 77 the parent material has ciw values of 37 temperature is demonstrated as the dominant variable exerting control on the extent of weathering with only minor mobilization following the incipient near surface weathering stage a robust linear relationship is found between ciw and model mat mat 0 21ciw 8 93 r 2 0 81 this climofunction can deliver proxy climate estimations from volcanic soils and paleosols of basaltic origin in cool to subarctic conditions 2 to 6 c

long term mobilisation of chemical elements in tephra rich peat ne iceland this paper presents geochemical profiles of a tephra bearing minerotrophic peat column from ne iceland obtained using various elemental analyses of the solid phase and the pore water the influence of tephra grain size thickness and composition of each tephra on the peat geochemistry was investigated interpretations are supported by a statistical approach in particular by autocorrelation and by microscopy observations minerotrophic peat geochemistry may be strongly dependent upon post depositional mobilization and possible leaching of elements as demonstrated by fe and trace metal concentration profiles chemical elements and more specifically potentially harmful metals can be slowly leached out of volcanic falls during their weathering and re accumulate downwards it is emphasised that a tephra deposit can act as an active geochemical barrier blocking downward elemental movements and leading to the formation of enriched layers in this study the formation of poorly amorphous fe phases above the hekla 3 tephra is shown these poorly crystalline fe phases scavenged ni

inter basaltic clay bole bed horizons from deccan traps of india implications for palaeo weathering and palaeo climate during deccan volcanism abstract reddened clay rich horizons between basalt flows have historically been identified as baked zones or as zones of lateral groundwater movement the reddening was interpreted as a form of alteration due to thermal or chemical processes many of these zones are referred to as bole beds in deccan traps and occur as prominent horizons showing red to brown green purple or grey colors and are composed of fine grained clayey material the red and green colors are caused by the presence of variable amounts of fe 2 o 3 and mgo in the bole samples the geochemistry of bole beds suggests that they were derived from basalts due to weathering processes these boles record significant hiatuses in basalt flow emplacement and in some cases resemble incipient palaeosol deposits samples have been collected in profiles from the overlying basalt flow through the bole down to the underlying flow geochemical analyses suggest loss of ca na mg fe 2 fe and p in the boles compared to neighboring basalts consistent with the weathering patterns observed in present day volcanic islands the observed high concentration of k and rb in the green bole samples compared to the adjoining basalts have been argued as features suggesting eolian transportation of volcanic ashes and deposition rather than evidence of metasomatism the mean d and 18 o values of clays from red and green bole outcrops were 83 05 and 15 8 respectively clays analyzed from green boles were marginally more depleted probably indicating a process of high temperature fractionation during deposition transformation of ash into green bole our estimate of the average meteoric water 18 op 8 1 value calculated from measured isotopic data with the assumption of environmental temperature is similar to or higher than previous estimate from palaeosol carbonates from cretaceous central india the depleted meteoric water composition observed in this study provides independent evidence of intensive precipitation during deccan trap eruption

periglacial paleosols and cryogenian paleoclimate near adelaide south australia abstract late cryogenian deformation of the reynella siltstone near hallett cove south australia has been interpreted as shallow marine methane seeps which were furthermore proposed to have played a role in deglaciation from snowball earth re examination and new analyses of these same outcrops confirms an earlier interpretation of this intrastratal deformation as periglacial paleosols which are evidence that even at maximum extent late cryogenian glaciers did not cover all continental lowlands let alone the world ocean known miocene and pliocene methane seeps of california examined for this study are very different in their gray color rounded nodules and clayey host rock compared with red highly deformed and silty to pebbly reynella siltstone of hallett cove stable isotopic composition of nodular carbonate in the reynella siltstone fails to show extreme carbon isotopic depletion or the meteoric oxygen lines characteristic of known methane seeps and sphaerosideritic waterlogged paleosols but instead shows covariance of carbon and oxygen isotopic composition comparable with that in pedogenic and subaerial carbonate of well drained soils mass balance geochemical analyses show modest weathering compatible with sand wedge structures and evaporitic pseudomorphs indicative of arid and frigid paleoclimate outcrops of reynella siltstone near hallett cove represent frigid low latitude floodplains not submarine methane seeps nor global glaciation

the ciw index a new chemical index of weathering abstract a new chemical index of weathering that can be applied to modern soils and precambrian paleosis is proposed ciw al2o3 the value of this index increases as the degree of weathering increases and the difference between ciw index values of the silicate parent rock and soil or sediment reflects the amount of weathering experienced by the weathered material

refractory element mobility in volcanic soils refractory trace element concentrations in strongly weathered hawaiian soils ranging in age from 20 to 4100 ka are highly elevated over parent rock values due to extensive mass loss of more soluble major elements during pedogenesis nb and ta exhibit virtually no mobility soil nb ta ratios are within the range of fresh bedrock even when soil nb concentrations are residually enriched by a factor of 10 in contrast al zr and hf are depleted relative to nb in surface soil horizons but are enriched at depth clearly indicating mobility of these elements variations in th nb ratios in soil profiles indicate significant th mobility within the soil column however mass balance calculations require that accretion of th enriched asian dust has resulted in a net increase in th in some soils soils developed on a 150 ka rainfall gradient show that the mobility and loss of zr increase with mean annual precipitation

clay minerals of four soils formed in eolian and tephra materials in iceland abstract clay minerals in a vitricryand and three haplocryands derived from eolian and tephra materials in different parts of iceland and in glacial till samples representative of underlying strata were studied by a combination of methods the soils are primarily used as rangelands and are highly susceptible to wind erosion allophanes imogolite and poorly crystalline ferrihydrite are abundant 700 g kg of the clay throughout the soils including a horizons this clay mineralogy would give rise to stable low density aggregates that influence the susceptibility of the soils to wind erosion it also affects chemical properties such as high phosphate retention of the soils even of the cryands with relatively low clay contents 160 275 g kg imogolite was found in some but not all horizons of all soils no particular relationship of imogolite to measured si al molar ratios of the oxalate oxalic acid soluble fractions of the clays 0 51 to 1 13 was evident layer silicate minerals and laminar opaline silicas are either not present or occur in small quantities plagioclase augite and or their weathering residues were found in the clay and silt separates dark colored glass is predominant in the fine sand throughout the soils and the tills one till sample had a clay mineral composition similar to the eolian andic soils while the other contained smectite and possibly a spherical halloysite smectite intermediate but not allophane and imogolite as major weathering products the clay mineral composition of these soils and tills was compared with those derived from basic tephras in other regions

volcanic soils of iceland abstract the parent materials of all icelandic soils are volcanic in origin and most of the soils are classified as andosols iceland has the largest area of andosols in europe and may have 5 of all andosols in the world a new classification scheme based on the world reference base world reference base for soil resources world soil resources reports 84 fao rome is used to provide an overview of icelandic volcanic soils the data were acquired as part of a recently initiated effort to build a database for icelandic soils but are also partly based on data from the eu cost 622 action a literature review and unpublished icelandic research the main soil types in iceland are histosols histic andosols gleyic andosols brown andosols vitrisols and leptosols in the icelandic language a single term is used to refer to each soil type this system reflects the dominant influence of eolian deposition and drainage conditions on the formation of histosols and andosols the parent materials of icelandic soils are mixtures of tephra layers and eolian sediments consisting mostly of volcanic glass the steady flux of eolian sediments from unstable sandy deserts constantly recharges the surface with basaltic tephra materials the histosols 20 c have appreciable amounts of andic materials because of the eolian deposition the andosols histic gleyic and brown andosols show characteristic properties of soils dominated by andic materials with allophane contents of up to 30 ferrihydrite commonly accounts for 5 15 of the soil the contents of both allophane and ferrihydrite generally decrease with increasing organic c content of soil horizons as organic matter inhibits allophane formation and iron tends to become reduced and lost in poorly drained locations the vitrisols are soils of desert surfaces with low organic content but they usually meet criteria for andic materials with 30 glass and al 1 2fe o 0 4 cryoturbation is intense in iceland resulting in a range of geomorphic surface features the cryoturbation is related to both climatic factors and the andic soil properties including high water retention and rapid hydraulic conductivity

quantitative geochemical approach to pedogenesis importance of parent material reduction volumetric expansion and eolian influx in lateritization abstract using mass balance techniques we test the prevalent view that laterite genesis is dominated by in situ residual enrichment during chemical weathering of bedrock through calculation of net mass fluxes through the laterite soils in mali west africa we show that residual enrichment by removal of mobile elements with a corresponding increase in bulk porosity and decrease in bulk density contributes only a very minor fraction of the enrichment of al fe si and au instead we demonstrate that the abundance of these elements is due to the influx and accumulation by selective retention of chemically mature detritus of local and foreign origin clearly evident in micromorphological infilling features at the same sample depths that accumulation reaches extreme values we show that volumetric expansion in excess of 200 has occurred locally we infer that these spatially coincidental zones of mass influx of rock forming metals fe al si and also au with dilational hyperstrains result from a mutually reinforcing mechanical interaction between material influx and the effects of subsurface deformational processes such as shrink swell cycles and root growth and decay we propose that with progressive infilling of available connected voids by illuvial microsedimentary deposits of insoluble resistate and neoformed minerals the capacity for the combined skeleton and plasma to remain isovulumetric is exceeded we speculate that the resultant space problem is relieved by upwards expansion towards the overlying free surface continued translocation and void infilling occur and are limited to the depth where the size of translocational particles is smaller than that of the connected voids consequently progressive hyperstrains accumulate above this critical depth by the long term influence of a proposed translocational wedge of chemically resistant minerals against which numerous generations of plant roots have exerted stresses eclectic surficial contaminants involved are continuously derived from above leaving no indication of a relict source region within the present soil profile from which they might have been extracted instead the source region is largely the existing regolith column itself which releases local material and in addition is supplemented by deposition of colluvial detritus shed nearby by escarpment retreat

mobilization and re distribution of major and trace elements during extreme weathering of basalt in hainan island south china major trace and organic elements of a laterite profile developed on neogene basalts in northern hainan island south china were reported in this paper the aim of which was to investigate element mobilization and re distribution during extreme weathering the results indicate that most of the elements have been mobilized and transferred downwards along the profile by aqueous solution organic matter om can significantly improve the transport of insoluble elements among all the elements th is the least mobile as for the general conservative elements during incipient chemical weathering such as fe ti zr hf nb and ta the removals are up to 20 40 in the upper profile however these elements behave as conservatively as th in the lower profile in the middle profile oxic environment occurs accompanied with significant om decomposition the mn and ce transferred downward are readily oxidized into insoluble mn iv and ce iv and precipitate in the oxic front important om decomposition decreases the capacity of transfer of insoluble elements in aqueous solution consequently al significantly precipitates in the oxic front and rees with the exception of ce precipitate largely in the omdepleted layers co and u are also concentrated in the oxic front in association with mn and ce respectively however cr shows a negative correlation with mn because its response to redox condition changes is reversed from that of mn mn oxides hydroxides fe oxides hydroxides and secondary phosphate minerals other than clay minerals are potential hosts for rees except for ce in the profile rees with high concentrations in the profile seem closely associated with mn oxides hydroxides remarkable highly correlated ce and gd anomalies are observed in the profile ce anomalies are caused by ce precipitation in the oxic environment and successive decomposition of organic matter gd anomalies are likely to have resulted from lower stability constants of gd om complexes compared to those of neighboring rees the overall elemental behaviors in this profile suggest that organic matter plays a very important role in the mobilization and re distribution of the elements during extreme weathering

revised wonoka isotopic anomaly in south australia and late ediacaran mass extinction the global late ediacaran shuram wonoka carbon isotope anomaly has been regarded as the largest and longest known isotopic anomaly in the ocean assuming that all ediacaran carbonate is marine disregarding carbonate in south australia shown here to be palaeosol or palaeokarst the synchronous marine organic carbonate excursion is only 8 for 13 c organic and 6 for 13 c carbonate and lasted less than a million years this revised magnitude and duration is comparable with perturbations across the permian triassic boundary and correlative with a global late ediacaran acritarch mass extinction like permian triassic isotopic excursions the revised organic carbonate wonoka excursion may also have been a greenhouse palaeoclimatic warm spike which terminated valley incision and glacioeustatic drawdown during the mid ediacaran fauquier glaciation and preceded chill of the late ediacaran billy springs glaciation supplementary material measured sections and tables of mineral and grain size proportions major element and stable isotope analyses are available at www geolsoc org uk sup18756

an overview of physical processes in the north water the presence of a polynya strongly affects biological processes by influencing underwater light levels water column stratification the upwelling of nutrients and the timing of production cycles an overview of the existing literature on the oceanography meteorology and sea ice conditions of the north water a large recurring polynya in northern baffin bay is presented the north water is influenced by a cold inflow of arctic ocean water from the north and in some areas a warmer inflow of atlantic water from the south earlier observations and modeling studies suggested that both wind and ocean advection of sea ice as well as heat input to the surface waters by either upwelling or mixing were responsible for the formation and maintenance of the polynya recent data indicate the north water to be primarily generated by the southward drift of ice by winds and currents as opposed to melting ice by sensible heat input over large areas localized sensible heat effects occur in fall winter and spring along the greenland side of the polynya

yttrium the immobility mobility transition during basaltic weathering trace elements have been used as provenance indicators of igneous rocks for many years even though the conditions under which they remain immobile during subaerial weathering have not been thoroughly defined we have used a novel geochemical and quantitative mineralogical data set of variably weathered basaltic rocks from northeast ireland to investigate the immobility of various elements titanium and niobium seem to be the most immobile of all elements relative to these elements zirconium is predominantly depleted but is also locally enriched yttrium displays a marked depletion from the early stages of weathering during the growth of clay minerals yttrium zirconium and their ratios with other elements should thus be used with caution as provenance indicators unless the rocks show no detectable signs of weathering

composition and origin of the clay cover on north brazilian laterites the belterra clay in northern brazil is a uniform yellowish unstratified kaolinitic clay with variable contents of gibbsite it is generally 5 10 m thick and covers a lateritic weathering crust on remnants of a dissected table land complete profiles with belterra clay the underlying bauxite laterite and saprolite bed rock were sampled in three areas of the amazon region the chemical and mineralogical data show a distinct affinity between the belterra clay and the underlying layers above all with the saprolite variations in the composition of the underlaying layers are reflected by the belterra clay among the structural and textural features important for the discussion of the origin of the belterra clay are the sharp contact between the clay cover and the underlying laterite as well as conglomeritic brecciate textures and occasional bedding structure in the upper part of the lateritic crust

a hot spot model for early tertiary volcanism in the n atlantic s u m m a r y the initial stages of rifting of the n atlantic were accompanied by massive extrusion of volcanic rocks and the accretion to the lower crust of even greater volumes of igneous rock emplacement of the bulk of the igneous rocks along the 2000 km long continental rift occurred in as little as 2 3 my the pattern and timing of magmatic activity can be explained by partial melting of anomalously hot asthenosphere as it welled up to fill the space left by the stretched and thinned continental lithosphere asthenosphere temperatures were elevated regionally by 100 150 over a 2000 km diameter region by the mushroom shaped head of hot material fed by a mantle plume which at present is centred beneath iceland

holocene climate conditions and glacier variation in central iceland from physical modelling and empirical evidence abstract lacustrine sediment cores from proglacial lake hvitarvatn central iceland reveal a detailed chronology of holocene sedimentation from which environmental conditions and the attendant fluctuations of langjokull ice cap have been interpreted we apply a numerical ice sheet model to determine the climatic conditions under which the empirical reconstruction is glaciologically plausible modelling constraints are derived from core records of diatom concentration benthic diatom fraction and ice rafted debris occurrence as well as lake bottom morphology and the present day ice cap geometry holocene simulations driven by the ngrip 18 o record that are consistent with the empirical constraints show the most extensive advance of langjokull ice cap to be its most recent beginning somewhere between 5 and 3 ka bp ice advance in response to the 8 2 ka bp cold event is followed by several thousand years of nearly ice free conditions in the mid holocene all simulations suggest that the maximum holocene stand of the ice cap occurred during the little ice age lia those consistent with the constraints show little to no ice advance into hvitarvatn before 1 ka bp and indicate the lake area occupied by ice was much greater during the lia than at any previous time the most plausible simulation results were obtained for a maximum holocene warming of 3 4 c relative to the 1961 1990 reference twice the arctic average and for holocene thermal maximum htm precipitation amounts comparable to or slightly greater than the modern reconciling the simulated subglacial discharge record to the empirically derived sediment volumes and emplacement times requires mean holocene sediment concentrations of 0 8 1 6 kg m 3 these estimates increase to 1 4 2 0 kg m 3 when sedimentation rates are highest

holocene and latest pleistocene climate and glacier fluctuations in iceland abstract multiproxy climate records from iceland document complex changes in terrestrial climate and glacier fluctuations through the holocene revealing some coherent patterns of change as well as significant spatial variability most studies on the last glacial maximum and subsequent deglaciation reveal a dynamic iceland ice sheet iis that responded abruptly to changes in ocean currents and sea level the iis broke up catastrophically around 15 ka as the polar front migrated northward and sea level rose indications of regional advance or halt of the glaciers are seen in late allerod early younger dryas time and again in preboreal time due to the apparent rise of relative sea level in iceland during this time most sites contain evidence for fluctuating tidewater glacier termini occupying paleo fjords and bays the time between the end of the younger dryas and the preboreal was characterized by repeated jokulhlaups that eroded glacial deposits by 10 3 ka the main ice sheet was in rapid retreat across the highlands of iceland the holocene thermal maximum htm was reached after 8 ka with land temperatures estimated to be 3 c higher than the 1961 1990 reference and net precipitation similar to modern such temperatures imply largely ice free conditions across iceland in the early to mid holocene several marine and lacustrine sediment climate proxies record substantial summer temperature depression between 8 5 and 8 ka but no moraines have been detected from that time termination of the htm and onset of neoglacial cooling took place sometime after 6 ka with increased glacier activity between 4 5 and 4 0 ka intensifying between 3 0 and 2 5 ka although a distinct warming during the medieval warm period is not dramatically apparent in icelandic records the interval from ca ad 0 to 1200 is commonly characterized by relative stability with slow rates of change the literature most commonly describes little ice age moraines ca ad 1250 1900 as representing the most extensive ice margins since early holocene deglaciation with temperature depressions of 1 2 c compared to the ad 1961 1990 average steep north south and west east temperature gradients are reconstructed in the holocene records of iceland suggesting a strong maritime influence on the terrestrial climate of iceland

are there ancient soils in the 3 7 ga isua greenstone belt greenland abstract a lens of black schist within 3 7 ga quartzites of greenland may be earth s oldest known alluvial paleosol the suspect metamorphic rock is a lens in orthoquartzite of berthierine schist with crystals of ripidolite but it has a truncated top above dark gray grading down to gray color ptygmatically folded surface cracks filled with silt grains and large sand crystals unusual for sedimentary or metamorphic rocks the paleosol hypothesis was tested with thin sections showing plausible mineral weathering trends and by chemical analysis showing molar weathering ratios and ree distribution like those of soils the schist is deeply weathered and at the culmination of weathering trends from analysis of other metasediments of the isukasia area the protolith can be reconstructed as a saponite clay with a salt rich horizon of kieserite like other acid sulfate paleosols of the early earth models for proton and electron consumption of paleosols applied to the profile reveal an atmosphere with only 36 510 ppm o2 and 820 201 ppm co2 and humid cool temperate paleoclimate the profile has organic 13cpdb consistently of 24 2 to 27 4 and modest raleigh distillation near the top similar consistent values and trends are produced by decay of organic matter in living soils but biotic carbon isotopic composition of sediments is erratic from bed to bed and abiotic carbon compounds of meteorites differ dramatically for each kerogen particle thus life in this very ancient soil is not precluded by our analyses but ultrastructural and geochemical testing of carbon particles would further test this hypothesis

decoding potential effects of climate and vegetation change on mineral weathering in alpine soils an experimental study in the wind river range wyoming usa abstract climate change and a related increase in temperature particularly in alpine areas force both flora and fauna to adapt to the new conditions these changes should in turn affect soil formation processes the aim of this study was to identify possible consequences for soils in a dry alpine region with respect to weathering of primary minerals and leaching of elements under expected vegetation and climate changes to achieve this a field empirical approach investigating an altitudinal sequence was used in combination with laboratory weathering experiments simulating several scenarios the study sites are located in sinks canyon and stough basin of the wind river range wyoming usa the following sites from moist to dry with increasing temperature along the sequence were investigated 10 soil profiles typic haplocryoll in a tundra ecotone 10 soil profiles ustic haplocryoll in a pine fir forest and 20 soil profiles ustic argicryoll in sagebrush all soils developed on granitoid moraines soil mineralogy was analysed using cathodoluminescence and x ray diffraction this revealed that biotite and plagioclase were both weathered to smectite while plagioclase also weathered to kaolinite cooler wetter altitude dependent conditions promoted weathering of primary minerals furthermore the soils of the tundra and forest zone exhibited a higher acidity and more organic carbon in a series of wet laboratory batch experiments materials from topsoils a horizons and subsoils b horizons in each ecotone were examined alone or in combination with other samples in a first step aqueous extracts of the topsoil samples were generated in batch reactors and analysed for the main ions in a second and a third step the topsoil extracts were reacted with the subsoil samples of the same ecotone and with the subsoil samples of the ecotones at higher altitude the total duration of these batch experiments was 1800 h and the solutes were measured using icp oes and ion chromatography dissolved ca mg and k were mainly controlled by the chemical weathering of oligoclase k feldspar and biotite with increasing altitude the total concentrations of ca mg and k in the aqueous extracts decreased the relative ionic contribution from k decreased while the ionic contribution from ca increased climate change warming changed precipitation potentially will reduce weathering intensity soil acidity and the content of organic carbon an altitudinal shift in vegetation due to climate change seems to affect the ionic composition of the soil solution in the case of a shift from forest to sagebrush and tundra to forest or sagebrush the relative contribution from k would increase at the expense of ca we hypothesise that k will play an important role in future biogeochemical cycles under the assumptions of climate warming and subsequent vegetation shifts to higher altitudes

field weathering rates of mt st helens tephra the initial stages of chemical weathering in tephra were examined under field conditions in a cool and humid forest ecosystem in the cascade mountains of washington unleached tephra from the 1980 eruption of mt st helens was applied in 5 cm and 15 cm depths to simulate natural tephra deposition leachate solutions from the tephra were then collected and analyzed over a 4 year period concentrations of dissolved elements were combined with the water fluxes to determine elemental fluxes from tephra and to estimate chemical weathering rates solutions leached from the tephra layer indicate incongruent dissolution resulting in formation of a cation depleted silica rich leached layer on glass and mineral surfaces measured weathering rates were 1 3 orders of magnitude less than comparable rates reported in the literature for laboratory dissolution studies but considerably greater than those measured for entire watersheds in field studies dissociation of carbonic acid originating primarily from upward transport of carbon dioxide from the buried soil was the dominant source of protons for weathering reactions weathering rates in the 5 cm treatment were approximately twice those of the 15 cm treatment a greater flux of co2 per unit volume of tephra in the 5 cm treatment is believed to be responsible for the differential weathering rates

variations in weathering processes and rates with time in a chronosequence of soils from glen feshie scotland chemical and mineralogical characteristics have been determined for a chronosequence of six soil profiles ranging in age from 80 13 000 years bp developed on river terraces in the western cairngorms of scotland the c horizons are similar chemically and mineralogically and the soils have similar pedogenetic histories exchangeable ca and mg decrease with time and base saturation decreases exponentially from 24 6 in the ah horizon of the youngest profile to 2 8 in the comparable horizon of the 10 000 year old profile according to the chronofunction y 3 372 22 612 exp 0 0007365t long term weathering rates of base cations calculated from the loss of these cations relative to zr appear to decrease exponentially with time but this may be due to the method of calculation the magnitude of loss of base cations decreases in the sequence na k mg ca but when the relative mobilities of these elements are considered the loss is in the order mg na ca k this reflects the dissolution of chlorite and loss of mg and the more rapid weathering of plagioclase feldspar and loss of na and ca particularly in the coarse sand fraction than k feldspar the clay fractions although 2 of all horizons also show distinct patterns with age in that chlorite and mica are less abundant in older soils and vermiculite is more abundant the latter phase often having hydroxyaluminium polymers in the interlayer region the chemical and mineralogical trends in the soil sequence are closely associated and are induced by pedogenic weathering

a new paleothermometer for forest paleosols and its implications for cenozoic climate climate is a primary control on the chemical composition of paleosols making them a potentially extensive archive applicable to problems ranging from paleoclimate reconstruction to paleoaltimetry however the development of an effective widely applicable paleosol temperature proxy has remained elusive this is attributable to the fact that various soil orders behave differently due to their respective physical and chemical properties therefore by focusing on an individual order or a subset of the 12 soil orders whose members exhibit similar process behavior a better constrained paleothermometer can be constructed soil chemistry data were compiled for 158 modern soils in order to derive a new paleosol paleothermometry relationship between mean annual temperature and a paleosol weathering index pwi that is based on the relative loss of major cations na mg k ca from soil b horizons the new paleothermometer can be applied to clay rich paleosols that originally formed under forest vegetation including inceptisols alfisols and ultisols and halves the uncertainty relative to previous approaches a case study using cenozoic paleosols from oregon united states shows that paleotemperatures produced with this new proxy compare favorably with paleobotanical temperature estimates global climatic events are also evident in the oregon paleosol record including a 2 8 c drop across the eocene oligocene transition comparable to marine records and a neogene peak temperature during the mid miocene climatic optimum

the circulation water masses and sea ice of baffin bay abstract the oceanographic meteorological and sea ice conditions in baffin bay are studied using historical hydrographic satellite and meteorological data and a set of current meter data from a mooring program of the bedford institute of oceanography baffin bay is partially covered by sea ice all year except august and september the interannual variation of the ice extent is shown to be correlated with winter air temperature available hydrographic data were used to study the water masses and the horizontal and vertical distribution of temperature salinity three water masses can be identified arctic water in the upper 100 300 m of all regions except the southeast west greenland intermediate water at 300 800 m in most of the interior of baffin bay and deep baffin bay water in all regions below 1200 m the temperature and salinity in baffin bay have limited seasonal variability except in the upper 300 m of eastern davis strait northern baffin bay and the mouth of lancaster sound summer data have a temperature minimum at 100 m which suggests winter convection does not penetrate deeper than this depth current meter data and results of a circulation model indicate that the mean circulation is cyclonic the seasonal variation of the currents is complex overall summer and fall tend to have stronger currents than winter and spring at all depths among the different regions the largest seasonal variation occurs at the mouth of lancaster sound and the baffin island slope model generated velocity fields show a basic agreement with the observed currents and indicate strong topographic control in the vicinity of davis strait and on the greenland shelves the model also produces a southward counter current on the greenland slope which may explain the observed high horizontal shears over the greenland slope estimates of the volume and fresh water transports through lancaster jones and smith sounds are reviewed transports through davis strait are computed from the current meter data the balance of freshwater budget and sensitivity of the thermohaline circulation to freshwater transport are discussed

mineralogy and weathering processes in recent and holocene tephra deposits of the pacific northwest usa abstract weathering and evolution of minerals in tephra deposits in the cascade range of washington state usa are influenced by climate vegetation time microtopography and in the vicinity of mt st helens naturally acidic precipitation we have observed the interaction of these factors in spodosols developed on holocene tephra in the central cascades and in entisols formed on the 1980 pyroclastic flow of mt st helens weathering regimens in these tephritic soils can be qualitatively characterized by the soil solution composition weathering reactions in the spodosol are driven by organic acids in the upper soil horizons and by carbonic acid in the lower b and c horizons the mineral assemblage in the spodosol reflects in part the chemical regimen dictated by each proton donor the presence of smectite in the highly acidic e horizon ph

significance of indigenous eocene larger foraminifera discocyclina dispansa in western foothills central taiwan a paleogene marine rift basin in chinese continental margin the western foothills of taiwan was known to be composed of late oligocene to pleistocene shallow marine strata continuously deposited on the stable passive chinese continental margin without significant stratigraphic break here we present multiple micropaleontological evidences including occurrence of larger foraminifera discocyclina dispansa ex interc sella dispansa and calcareous nannoplanktons to show that there are middle eocene marine strata first named as the chungliao formation exposed in the tsukeng anticline of the western foothills central taiwan occurrences of intact tests with thin delicate outer rims and well preserved embryonic chambers suggest that the discocyclina dispansa ex interc sella dispansa lutetian to bartonian in the tethys region are buried indigenously on shallow inner shelf during an episodic transgression in the early middle eocene the conclusion is consistent with a biostratigraphy study of calcareous nannoplanktons zones np14 15 in the shale sandstone alternations overlying the discocyclina bearing bed of the chungliao formation and calcareous nannofossils of zone np16 integrated with an age dating of 38 8 1 ma late middle eocene on zircon grains of the overlying pinglin tuff the middle eocene syn rift sequences chungliao formation and pinglin tuff exposed along the tsukeng anticline are unconformably covered by the latest oligocene miocene post rift sequence a scenario similar to what have been drilled in the east china sea taiwan strait south china sea this rift basin named as the nantou basin is sitting on the peikang basement high margin which further extends southwestward to the central uplift of the pearl river mouth basin in the northern slope of the south china sea the present work documents a hitherto unknown occurrence of the exposed early tertiary marine rift basin sequence in the western foothills of taiwan the study extends our knowledge of the western foothills geohistory from the late oligocene downward to the early middle eocene the occurrence of the paleogene nantou rift basin in the western foothills may also suggest that there could have similar paleogene rift sequences exposed in other parts of the taiwan mountain belt like the hsuehshan range and the central range east of the western foothills