boron isotopes and b ca in benthic foraminifera proxies for the deep ocean carbonate system abstract accurate records of the state of the ocean carbonate system are critical for understanding past changes in pco 2 ocean acidification and climate the chemical principles underlying the proxy of oceanic ph provided by the boron isotope ratio of foraminiferal carbonate are relatively well understood but the proxy s reliability has been questioned we present 76 new multi collector inductively coupled plasma mass spectrometry mc icpms 11 b measurements on a range of benthic foraminifera from 23 late holocene samples from the atlantic that reaffirm the utility of the 11 b ph proxy our boron isotope measurements on 10 benthic foraminifera tests typically yield a precision of 0 25 at 2 s d equivalent to 0 03 ph units 11 b values of epifaunal species are within analytical uncertainty of those predicted from a simple model assuming sole incorporation of b oh 4 from seawater and no vital effects using the independently determined fractionation factor of 1 0272 between 11 b 10 b of aqueous boron species infaunal foraminifera are consistent with this model but record the combined effects of lower pore water 11 b and ph no influence of partial dissolution or shell size on 11 b is observed we have also measured the b ca ratios of the same samples for individual cibicidoides species b ca shows a good correlation with co 3 2 but the b ca of different co occurring species morphotypes varies considerably these effects are not seen in 11 b which may therefore provide a more robust proxy of the ocean carbonate system whilst in theory 11 b and b ca can be combined to provide a quantitative reconstruction of alkalinity and dissolved inorganic carbonate dic in practice this is precluded by propagated uncertainties 11 b data give significant constraints on foraminifera calcification mechanisms and seem most simply explained by incorporation of b oh 4 into a hco 3 pool which is then completely incorporated in foraminiferal caco 3 our demonstration of the predictable variation of 11 b with ph across a wide range of species and locations provides confidence in the application of mc icpms measurements of foraminiferal 11 b to reconstruct past changes in the ocean carbonate system

lithological evidence for the evolution of weathered mantles in uganda by tectonically controlled cycles of deep weathering and stripping abstract landscape evolution in terrains that have been unaffected by glacial or aeolian erosion occurs by cycles of deep weathering and stripping several factors have been proposed to control these cycles including sea level climate and tectonics in this study a tectonic model of landscape evolution recently developed for uganda was tested by detailed study of the weathered mantle the study involved an analysis of weathered mantle stratigraphy texture mineralogy and elemental geochemistry and was conducted in two catchments of central and southwestern uganda which feature contrasting geomorphic processes deep weathering and stripping and different post mid miocene evolutionary histories application of graphical sedimentological logs to weathered mantle stratigraphy is introduced in this work and represents an improvement upon more subjective classification schemes employed previously the stratigraphy texture mineralogy and elemental geochemistry of the weathered mantle support cycles of deep weathering and stripping predicted by the tectonic model of landscape evolution in central uganda deep weathering of the landsurface as a result of tectonic quiescence since the mid miocene is indicated by thick 30 m weathered profiles that result from prolonged chemical denudation this is evident from the progressive alteration of crystalline rock from relatively unweathered bedrock fragments at the base of the profile to a ferricrete crust at the top lithological evidence indicates that the weathered mantle has developed in situ and that the water table separates environments of different weathering intensity in southwestern uganda stripping of the landsurface following mid pleistocene uplift is reflected by thinner truncated weathered profiles that are not capped by ferricrete and are composed primarily of coarser less weathered material

radon 222 as a tracer for mixing in the water column and benthic exchange in the southern california borderland the concentrations of222rn and226ra in the water column and in the sediments of santa barbara and san nicolas basins have been measured semi annually over the last four years approximately one third of excess radon profiles obtained in the water column in these basins can be adequately fit with a one dimensional eddy diffusion decay model exponential profiles in the center of san nicolas basin yield a vertical eddy diffusivity of 26 16 cm2 s and 3 4 1 0 cm2 s for santa barbara basin the application of a two dimensional eddy diffusion decay model to profiles obtained in the center and on the margins of san nicolas basin produces a better fit than is found using a one dimensional vertical eddy diffusivity the two dimensional model for san nicolas basin predicts a vertical eddy diffusivity of 17 cm2 s and a horizontal eddy diffusivity of 105 cm2 s these values are in reasonable agreement with those predicted from the vertical buoyancy gradient and the horizontal length scale the vertically integrated radon excess standing crop in the water column of santa barbara basin averages 53 23 atoms m2 s this is in good agreement with the flux across the sediment water interface of 60 15 atoms m2 s calculated by measuring radon emanation in the sediments as a function of depth and applying a molecular diffusion reaction model hence one dimensional molecular diffusion accurately predicts the flux of radon from the laminated santa barbara basin sediments in san nicolas basin the integrated radon excess in the water column is 376 143 atoms m2 s but the diffusive randon flux from san nicolas basin sediments averages only 190 53 atoms m2 s this descrepancy indicates that a non diffusive process probably macrofaunal irrigation supplies much of the flux of radon from san nicolas basin sediments

seawater ph pco2 and co2 3 variations in the caribbean sea over the last 130 kyr a boron isotope and b ca study of planktic foraminifera abstract here a new analytical methodology is described for measuring the isotopic composition of boron in foraminifera using multicollector inductively coupled plasma mass spectrometry mc icpms this new approach is fast 10 samples analysed in duplicate per analytical session and accurate to better than 0 25 at 95 confidence with acceptable sample size requirements 1 3 mg of carbonate a core top calibration of several common planktic and two benthic species from geographically widespread localities shows a very close agreement between the isotopic composition measured by mc icpms and the isotopic composition of b oh 4 in seawater as predicted using the recently measured isotopic equilibrium factor of 1 0272 at the depth of habitat a down core and core top investigation of boron concentration b ca ratio shows that the partition coefficient is influenced by co2 3 complicating the application of this proxy nevertheless it is demonstrated that these two proxies can be used to fully constrain the carbonate system of surface water in the caribbean sea odp site 999a over the last 130 kyr this reconstruction shows that during much of the holocene and the last interglacial period surface water at site 999a was in equilibrium with the atmosphere with respect to co2 during the intervening colder periods although the surface water pco2 was lower than the holocene it was a minor to significant source of co2 to the atmosphere possibly due to either an expansion of the eastern equatorial atlantic upwelling zone or a more local expansion of coastal upwelling in the southern caribbean such reorganisation of the oceanic carbonate system in favour of a larger source of co2 to the atmosphere from the equatorial ocean may require mechanisms responsible for lowering atmospheric co2 during glacial periods to be more efficient than previously supposed

boron carbon and oxygen isotopic composition of brachiopod shells intra shell variability controls and potential as a paleo ph recorder abstract the boron isotopic composition of biogenic carbonates has been used to reconstruct seawater ph and atmospheric pco 2 on pleistocene and cenozoic timescales because of their excellent preservation and extensive fossil record throughout the phanerozoic brachiopods are a promising candidate for extending the boron isotope record as far back as the cambrian here we present stable carbon oxygen and boron isotopic measurements of modern terebratulid brachiopod calcite in comparison with environmental ph estimates calculated from oceanographic data geochemical transects along the length and depth of single shells confirm previously published trends in carbon and oxygen isotopic composition in the outer surface primary and outermost secondary layers 11 b covaries with 13 c and 18 o with more negative values in the outer and more positive values in the middle of the shell however 11 b deviates from 13 c and 18 o in the inner part of the secondary layer where the 13 c and 18 o values are more positive and near equilibrium whereas 11 b returns to more negative values a comparison of different specimens of the species terebratalia transversa sowerby 1846 and laqueus californianus kuster 1844 microsampled from the middle part of the fibrous secondary layer demonstrates a clear correlation to ambient ph with a sensitivity similar to other empirical calibration curves for cultured planktic foraminifers corals and inorganic calcite the relationship in other species is less clear and significantly offset necessitating the use of a single species or a cross calibration method with other species in paleo ph reconstructions

modelling the geochemical cycle of boron implications for the long term δ11b evolution of seawater and oceanic crust the boron geochemical cycle has been simulated using a time dependent geochemical box model that was coupled to a onedimension model of seawater oceanic crust interactions boron elemental and isotopic compositions of oceanic rocks as a function of depth were calculated by mass balance using the temperature and porosity profiles of the crust as well as the available experimental and empirical distribution coefficients and fractionation factors between mineral and water ranges of boron elemental and isotopic variations of seawater were calculated for crust seawater interactions that take place from the ridge axis to the off axis closure of the hydrothermal system the present day d11b of seawater 40 could represent a steady state value however depending on crustal permeability lifetime of water rock interactions and expansion rate of the oceanic ridge the d11b of seawater may vary from 30 to 50 at the 10 million year scale some boron isotope compositions of cretaceous biogenic carbonates and ophiolitic serpentinites from oman are comparable to modern rock samples suggesting that the d11b of cretaceous seawater was close to the present day value low d11b values of some biogenic carbonates cannot be attributed to low ph values of past seawater but more probably to d11b variations of seawate or diagenetic alteration by crustal aqueous fluids boron isotope composition of hydrothermally altered serpentines could be considered as a promising proxy of the seawater composition

modern and pleistocene boron isotope composition of the benthic foraminifer cibicidoides wuellerstorfi abstract here we present the first species specific study of boron isotopes in the epibenthic foraminifer species cibicidoides wuellerstorfi coretop samples from a water depth profile from 1000 to 4500 m on the northern flank of the walvis ridge are 4 4 lower than the values expected based on calculations of the 11bborate of ambient seawater similar values for this foraminifer species are presented from odp site 668b at the sierra leone rise in the equatorial atlantic the consistency between data of the same species suggests the offsets are primary rather than diagenetic glacial c wuellerstorfi from odp 668b and walvis ridge have boron isotope compositions only slightly different to interglacial samples that is no larger than 0 10 ph units or 23 mol kg 1 in co32 above the reconstructed glacial lysocline and 0 07 ph units or 14 mol kg 1 in co32 below we use these results to suggest that glacial deep water ph in the atlantic was similar to interglacial ph the new data resolve the inconsistency between the previously reported high bottom water ph and the lack of significant carbonate preservation of the glacial deep ocean

empirical relationship between ph and the boron isotopic composition of globigerinoides sacculifer implications for the boron isotope paleo ph proxy culture experiments were carried out with the planktonic foraminifera globigerinoides sacculifer at three different ph values 7 6 0 05 8 20 0 05 8 60 0 05 in order to establish the ph dependence of the boron isotopic fractionation between the calcitic tests of g sacculifer and seawater additional objectives were to compare the ph dependences of boron isotopic composition of g sacculifer with that of orbulina universa and inorganic calcite in order to evaluate the robustness of the boron isotope paleo ph proxy the relationship between the boron isotopic composition of g sacculifer and the culture water ph shows heavier boron isotopic values at higher ph this empirical relationship is similar but slightly offset by 3 per mil from that of o universa indicating the presence of biogenic influence vital effect on the boron isotopic composition of foraminifera however comparison of the boron isotopic composition of o universa and g sacculifer with that of inorganic calcite grown over a common ph range shows that inorganic processes are the dominant control on the boron isotopic composition of foraminifera and the vital effects play a small but not insignificant role the results imply that in spite of a small biogenic influence the variation in boron isotopic composition of foraminiferal shells with ph at least for o universa and g sacculifer is consistent with that for inorganic calcite demonstrating the potential of this isotopic signature in foraminifera as a reliable paleo ph proxy

light element distributions n b li in baltic basin bentonites record organic sources abstract distributions of nitrogen boron and lithium were studied in illite smectite from ordovician silurian k bentonites in the baltic basin these trace elements are linked to thermal maturation of organic matter creating fluid signatures that are distinct from those in regionally buried sediments the fluid chemistry is ideally recorded in authigenic illite within the k bentonite because b substitutes in tetrahedral sites of illite li in octahedral sites and n is fixed in the interlayers as nh 4 three nanometric size fractions of illite 10 among these size fractions relate mainly to changes in fluid composition during illite growth bentonite volcanic ash layers mark stratigraphic timelines while illitization of the bentonite k bentonite varies as a function of burial and tectonic temperature gradients in the central baltic basin bentonites were deposited across a carbonate platform near estonia grading to deep basin shales near denmark and poland compositional variations in illite reflect fluids from different sources high n illite 2000 ppm in the southwest basin transitions to high b 250 ppm and high li 100 ppm illite to the northeast these trends follow a thermal gradient decreasing from southwest 200 c to northeast 90 c isotope ratios of b and li show opposing trends in samples across this thermal gradient the bisotopes decrease from southwest to northeast 18 to 4 while li isotopes increase from 5 to 32 the cambrian alum shale a regional hydrocarbon source rock was studied as a potential source of b and li as more than 50 of its b and li was associated with organic matter with increasing thermal maturity illite 11b decreased from 0 to 13 while 7li increased from 20 to 5 these opposing trends are similar to those observed in the k bentonites this suggests that organic sources of n b and li dominate fluids in bentonites from the southwestern baltic basin whereas basement derived fluids dominate in the northeastern baltic basin these trace elements record paleofluid changes during illite crystal growth and can identify pathways of chemically distinct oil and gas related fluids

reevaluation of the oxygen isotopic composition of planktonic foraminifera experimental results and revised paleotemperature equations cultured planktonic foraminifera orbulina universa symbiotic and globigerina bulloides nonsymbiotic are used to reexamine temperature 18o relationships at 15 25 c relationships for both species can be described by linear equations equations for o universa grown under low light ll and high light hl share a slope of 4 80 0 21 c 1 with a hl ll offset of 0 33 due to symbiont photosynthetic activity the effect of co32 on o universa is 0 002 mol 1 kg 1 and is insensitive to temperature for g bulloides ontogenetic effects produce size related trends in temperature 18o whereby larger shells are enriched in 18o relative to smaller specimens the o universa temperature 18o relationships are more accurate than previously published equations for describing plankton tow data our equations do not explain planktonic core top data with the same precision but provide a good fit to benthic cibicidoides data below 10 c temperature 18o relationships for g bulloides provide good agreement with field data for this species from the northeast pacific

rainfall and recharge to a dolomite aquifer in a semi arid climate at kabwe zambia abstract rainfall at kabwe is stable over long periods of time but varies considerably in the short term over periods of approximately 8 and 4 years corresponding variations are present in the recharge to a dolomite aquifer using a slightly modified version of the penman grindley recharge model it is possible to make estimates of recharge from rainfall and evaporation data the validity of the model is verified by comparison with borehole hydrographs estimates of specific yield from the hydrographs agree closely with those determined by conventional pumping tests

glaciation aridification and carbon sequestration in the permo carboniferous the isotopic record from low latitudes to evaluate the isotopic record of climate change and carbon sequestration in the late paleozoic we have compiled new and published oxygen and carbon isotopic measurements of more than 2000 brachiopod shells from carboniferous through middle permian 359 260 ma strata we focus on the isotopic records from the u s midcontinent and the russian platform because these two regions provide well preserved marine fossils spanning a broad time interval both regions show a 18o increase at the mid carboniferous boundary ca 318 ma that roughly correlates with geologic evidence for an expansion of gondwanan glaciers only the russian platform record shows a 18o maximum during the glacial maximum in the asselian in contrast to a previous study korte c jasper t kozur h w and veizer j 2005 18o and 13c of permian brachiopods a record of seawater evolution and continental glaciation palaeogeogr palaeoclimatol palaeoecol 224 333 351 our data show no oxygen isotope evidence for glacial retreat in the early permian but instead show increasing 18o values related to aridification dissimilarity in the 18o trends for the epicontinental seas of north american and the russian platform suggests that at least one region experienced periodic restriction that altered regional salinities and seawater 18o values these results highlight the need for complementary proxies to identify restricted circulation in epicontinental seas carbon isotopic compositions of carbonates exhibit substantial regional variation with low values in western north america intermediate values in the midcontinent and high values in the sverdrup basin russian platform and northern spain nevertheless both u s midcontinent and russian platform records show a late serpukhovian minimum a sharp increase across the mid carboniferous boundary and a minimum centered on the kasimovian the correlative increase in brachiopod 13c and 18o values at the mid carboniferous boundary is our best isotopic evidence for a link between the carbon burial and glaciation in the permo carboniferous

heterogeneity cyclicity and diagenesis in a mississippian brachiopod shell of palaeoequatorial britain a shell of gigantoproductus okensis shows twenty growth lines with marked changes of fabric indicating periodical reduction of growth rates caused by environmental perturbations the number of growth lines suggests a lifespan of 20 years in agreement with the survival rates of extant brachiopods and with spiral deviation analysis geochemical analyses across the growth profile show a heterogeneous distribution of stable isotopes and trace elements it is possible to distinguish primary from altered carbonate and to interpret the isotopic data the oxygen isotope signal in the unaltered parts is periodical and annual with oscillation of 1 1 the higher values are at the growth lines winter and therefore most likely related to monsoon circulation during the visean the annual periodicity seems also present in the altered part of the shell suggesting that diagenesis could have reset the primary values but preserved their cyclicity

oceanic ph control on the boron isotopic composition of foraminifera evidence from culture experiments culture experiments were carried out with the species orbulina universa at four different ph values 7 70 0 05 8 15 0 05 8 60 0 05 and 9 00 0 10 in order to establish the ph dependence of boron isotope fractionation between seawater and foraminifera a clear relationship between the boron isotopic composition of the foraminifera and the ph of the seawater culture solutions was found showing heavier boron isotopic composition at higher ph this finding supports the viability of boron isotopes as a paleo ph tool it is important to note that orbulina universa cultured in natural seawater as well as those obtained from coretop samples have a significantly lighter boron isotopic ratio than globigerinoides sacculifer from coretop samples suggesting that at least for this species a vital effect is active

geochemistry of modern brachiopods applications and implications for oceanography and paleoceanography abstract modern rhynchonellida terebratulida thecideida and a few inarticulated brachiopods were collected live or soon after death at 30 locations from depths of 2 3940 m from the equator to high latitudes covering the atlantic pacific indian caribbean and mediterranean oceans seas well preserved fibers of the secondary layer combined with sr 450 1928 mg kg mn 1 199 mg kg and fe 1 610 mg kg contents confirm with few exceptions the excellent preservation of the modern brachiopod material evaluation of the stable isotope compositions was conducted on 276 specimens and on 374 published samples for a total database of 650 samples from 80 locations it revealed that oxygen isotope incorporation into shell calcite secondary layer of modern articulated brachiopods in most cases occurs in equilibrium with the ambient water and as such reflects surrounding environmental conditions thecideida as a group shallow water and low latitude incorporate oxygen isotopes 3 04 to 0 35 into shell calcite in equilibrium with their ambient water a large majority of genera and species of the terebratulida shallow water and low mid latitude also incorporate oxygen 2 30 to 3 48 into shell calcite in isotopic equilibrium with their surrounding water in contrast equilibrium incorporation of oxygen isotopes into shell calcite by the rhynchonellida is uncertain but a vital effect probably applies to the craniida the question of equilibrium disequilibrium incorporation of carbon isotopes into shell calcite of modern brachiopods remains unresolved at this time isotope compositions range up to 4 5 5 6 and 1 5 for 13 c and up to 5 5 5 9 and 0 3 for 18 o for shallow water low mid and high latitude brachiopods respectively strontium isotopes of modern brachiopods as expected show no significant variation with location latitude water depth temperature salinity and general water conditions once local habitat and ecological influences of fossil brachiopods from similar latitudes are considered their isotopic elemental values should be valuable diagenetic indicators and important oceanographic chemostratigraphic proxies

boron and magnesium isotopic composition of seawater the isotopic systems of boron and magnesium are increasingly being used as proxies for a number of environmental variables and processes the isotopic composition of seawater for both systems plays a central role in these studies and is an important interlaboratory standard given the long residence times of both elements 10 7 years it is commonly assumed that seawater is isotopically homogenous for these systems yet no systematic studies currently exist here we present the b and mg isotopic composition of 26 28 seawater samples from a number of ocean basins that encompass a significant range in salinity 32 to 38 psu temperature 0 3 to 25 9c and water depth 0 to 1240 m we find no significant or systematic variation for either system in accordance with their long residence times we recommend that the mean values we report 11 b 39 61 0 04 2 s e n 28 25 mg 0 43 0 01 2 s e n 26 26 mg 0 82 0 01 2 s e n 26 be used in future studies involving mg and b isotopes copyright 2010 by the american geophysical union

effects of seawater carbonate ion concentration and temperature on shell u mg and sr in cultured planktonic foraminifera we investigate the sensitivity of u ca mg ca and sr ca to changes in seawater co3 and temperature in calcite produced by the two planktonic foraminifera species orbulina universa and globige rina bulloides in laboratory culture experiments our results demonstrate that at constant temperature u ca in o universa decreases by 25 7 per 100 mol co3 k g 1 as seawater co3 increases from 110 to 470 mol kg 1 results from g bulloides suggest a similar relationship but u ca is consistently offset by 40 at the same environmental co3 in o universa u ca is insensitive to temperature between 15 c and 25 c applying the o universa relationship to three u ca records from a related species globigerinoides sacculifer we estimate that caribbean and tropical atlantic co3 was 110 70 mol kg 1 and 80 40 mol kg 1 higher respectively during the last glacial period relative to the holocene this result is consistent with estimates of the glacial interglacial change in surface water co3 based on both modeling and on boron isotope ph estimates in settings where the addition of u by diagenetic processes is not a factor down core records of foraminiferal u ca have potential to provide information about changes in the ocean s carbonate concentration below ambient ph ph 8 2 mg ca decreased by 7 5 o universa t o 16 6 g bulloides per 0 1 unit increase in ph above ambient ph the change in mg ca was not significant for either species this result suggests that mg ca based paleotemperature estimates for the quaternary during which surface ocean ph has been at or above modern levels have not been biased by variations in surface water ph sr ca increased linearly by 1 6 0 4 per 0 1 unit increase in ph shell mg ca increased exponentially with temperature in o universa where mg ca 0 85 exp 0 096 t whereas the change in sr ca with temperature was within the reproducibility of replicate measurements copyright 2004 elsevier ltd

seawater ph control on the boron isotopic composition of calcite evidence from inorganic calcite precipitation experiments experiments involving boron co precipitation with calcite have been carried out inorganically under controlled ph conditions 7 9 0 05 8 3 0 05 and 8 6 0 05 to determine the dependence of the boron isotopic composition 11b of calcite on the ph of seawater another purpose of these experiments was to estimate the magnitude of the biogenic influence on the 11b value of foraminifera by comparing their boron isotopic composition with that of the inorganic calcite over a common ph range the results show a clear relationship between 11b of inorganic calcite and the ph of artificial seawater the variation of boron isotopic fractionation between seawater and calcite with ph estimated from these experiments is similar to that estimated for cultured o universa and the theoretically predicted trend the results also support the hypothesis that b oh 4 is the dominant species incorporated into the calcite structure however the boron isotopic fractionation between seawater and inorganic calcite is lower than that estimated for o universa indicating the presence of a biogenic effect on the boron isotopic composition at least of this species of foraminifera most importantly the results imply that in spite of a small biogenic influence on the boron isotopic composition of foraminifera the variation in 11b of foraminiferal shells with ph at least for o universa is comparable to that for inorganic calcite supporting the potential of this isotopic signature in foraminifera as a reliable paleo ph proxy

sand supply to the lake albert basin uganda during the miocene pliocene a multiproxy provenance approach a multi proxy provenance approach heavy mineral analysis u pb zircon geochronology and pb isotopic analysis of k feldspar has constrained sediment supply within the upper nile drainage system in the miocene pliocene provenance data from sandstones were obtained from three exploration wells two situated on the north eastern margin and one on the eastern flank of the lake albert basin nw uganda data suggest that high to low grade metamorphic rocks and granitoids have variably supplied the heavy mineral assemblages around the lake albert basin during the miocene pliocene with contributions from the isotopically heterogeneous archean cratons including the local ugandan craton tanzanian and congo cratons and the pan african rocks the mozambique belt with possible contributions from the neoproterozoic and paleoproterozoic rocks these data also highlight clear differences between supply to the eastern basin margin compared with the northeast which is reconcilable with current models for miocene pliocene drainage in the region supply to northeastern lake albert during the miocene pliocene appears to have been through a proto albert nile draining from ne to sw and from a proto victoria nile or similarly oriented palaeo river systems draining from the east in contrast the eastern flanks of the basin were likely supplied via the palaeo nkusi river tapping local hinterland sources and more distal basement to the far east mozambique belt this study highlights the importance of utilizing a multi proxy approach in provenance analysis as no one signal is capable of distinguishing the different source lands and constraining the evolving drainage patterns

ground truthing the boron isotope paleo ph proxy in planktonic foraminifera shells partial dissolution and shell size effects 1 sediment samples from the ontong java plateau in the pacific and the 90 east ridge in the indian ocean were used to investigate whether shell size and early diagenesis affect 11b of the symbiont bearing planktonic foraminifer globigerinoides sacculifer in pristine shells from both study locations we found a systematic increase of 11b and mg ca with shell size shells in the sieve size class 515 865 m revealed 11b values 2 1 to 2 3 higher than shells in the 250 380 m class this pattern is most likely due to differences in symbiont photosynthetic activity and its integrated effect on the ph of the foraminiferal microenvironment we therefore suggest smaller individuals must live at approximately 50 100 m water depth where ambient light levels are lower using the empirical calibration curve for 11b in g sacculifer only shells larger than 425 m reflect surface seawater ph partial dissolution of shells derived from deeper sediment cores was determined by shell weight analyses and investigation of the shell surface microstructure by scanning electron microscopy the 11b in partially dissolved shells is up to 2 lower relative to pristine shells of the same size class in agreement with a relatively higher weight loss in smaller shells samples from the ontong java plateau show a more pronounced dissolution effect than larger shells on the basis of the primary size effect and potential postdepositional dissolution effects we recommend the use of shells that are visually pristine and in the case of g sacculifer larger than 500 m for paleoreconstructions

post palaeozoic evolution of weathered landsurfaces in uganda by tectonically controlled deep weathering and stripping a model for the evolution of weathered landsurfaces in uganda is developed using available geotectonic climatic sedimentological and chronological data the model demonstrates the pivotal role of tectonic uplift in inducing cycles of stripping and tectonic quiescence for cycles of deep weathering it is able to account for the development of key landforms such as inselbergs and duricrust capped plateaux which previous hypotheses of landscape evolution that are based on climatic or eustatic controls are unable to explain development of the ugandan landscape is traced back to the permian following late palaeozoic glaciation a trend towards warmer and more humid climates through the mesozoic enabled deep weathering of the jurassic mid cretaceous surface in uganda during a period of prolonged tectonic quiescence uplift associated with the opening south atlantic ocean terminated this cycle and instigated a cycle of stripping between the mid cretaceous and early miocene deep weathering on the succeeding miocene to recent african surface has occurred from miocene to present but has been interrupted in the areas adjacent to the western rift where development of a new drainage base level has prompted cycles of stripping in the miocene and pleistocene

effects of seawater ph and biomineralization on the boron isotopic composition of deep sea bamboo corals abstract the ocean is currently absorbing excess carbon from anthropogenic emissions leading to reduced seawater ph termed ocean acidification instrumental records of ocean acidification are unavailable from well ventilated areas of the deep ocean necessitating proxy records to improve spatio temporal understanding on the rate and magnitude of deep ocean acidification here we investigate boron carbon and oxygen isotopes on live collected deep sea bamboo corals genus keratoisis from a phtot range of 7 5 8 1 these analyses are used to explore the potential for using bamboo coral skeletons as archives of past deep sea ph and to trace anthropogenic acidification in the subsurface north atlantic ocean 850 2000 m water depth boron isotope ratios of the most recently secreted calcite of bamboo coral skeletons are close to the calculated isotopic composition of borate anion in seawater 11bborate for north atlantic corals and 1 2 higher than 11bborate for pacific corals within individual coral skeletons carbon and oxygen isotopes correlate positively and linearly a feature associated with vital effects during coral calcification 11b variability of 0 5 2 is observed within single specimens which exceeds the expected anthropogenic trend in modern north atlantic corals 11b values are generally elevated in pacific corals relative to 11bborate which may reflect ph driven physiological processes aiding coral calcification in environments unfavorable for calcite precipitation elevated 11b values are also observed proximal to the central axis in multiple atlantic and pacific specimens relative to 11bborate which might reflect ontogenetic variability in calcification rates although the observed boron isotope variability is too large to resolve the present anthropogenic ocean acidification signal at the studied depths in the north atlantic 0 03 0 07 ph units ph changes 0 1 units might still be reconstructed using 11b measurements in bamboo corals

use of stable oxygen isotope determinations from brachiopod shells in palaeoenvironmental reconstruction abstract stable oxygen isotope analyses were obtained from fossil brachiopod shells from a shallow marine deposit of upper pleistocene age approximately 80 ka in new zealand as part of a palaeoenvironmental investigation bulk analyses of entire shells of calloria inconspicua yielded highly variable results a range of 2 30 rendering these data of limited use as palaeoenvironmental proxies attempts to obtain consistent oxygen isotope values by removing areas of the brachiopod shell thought to be prone to oxygen isotope disequilibrium effects vital effects revealed that the matching anterior portions of ventral and dorsal valves from the same individual which were secreted at the same time also yielded different oxygen isotope ratios the dorsal valve 18o values were higher and less variable than those obtained from the ventral valve of the same individual the investigation was then extended to living representatives of the same species from a similar shallow water habitat from the south island of new zealand the pattern of dorsal valves yielding higher and less variable oxygen isotope values than matching areas of the ventral valves was repeated in seven out of eight individuals investigated although there was considerable variation in the absolute values from specimen to specimen contrary to common practice therefore it seems that in this species it is the much thinner and lighter dorsal valve that provides a more consistent isotopic measurement if converted into absolute temperature estimates the dorsal valve measurements correspond to a temperature midway between the mean and maximum annual temperature experienced by this species in its present day habitat which may make it acceptable as a palaeoenvironmental indicator the high level of variation between individuals including an inferred temperature from one ventral valve above the mean maximum temperature experienced indicates that a range of individuals needs to be investigated in any palaeoenvironmental investigation to avoid misleading interpretations however intra and inter specimen variation in isotopic composition may provide valuable palaeobiological information on growth rates metabolism and possibly also pathological conditions in the past

groundwater recharge in the victoria nile basin of east africa support for the soil moisture balance approach using stable isotope tracers and flow modelling across equatorial africa increasing demand for groundwater has raised concerns about resource sustainability and has highlighted the need for reliable estimates of groundwater recharge recharge investigations in this environment are typically inhibited by a shortage of good quality meteorological and hydrogeological records moreover when recharge studies are attempted they tend to rely on a single technique and frequently lack corroborating evidence to substantiate recharge predictions in recent studies undertaken in the aroca catchment of the victoria nile basin in central uganda the timing and magnitude of recharge determined by a soil moisture balance approach are supported by stable isotope data and groundwater flow modelling the soil moisture balance study reveals that recharge averages in the order of 200 mm year 1 and is more dependent on the number of heavy more than 10 turn day 1 rainfall events than the total annual volume of rainfall stable isotope data suggest independently that recharge occurs during the heaviest rains of the monsoons and further establish that recharge stems entirely from the direct infiltration of rainfall an assumption implicit in the soil moisture balance approach deforestation over the last 30 years is shown to have more than doubled the recharge estimate aquifer flow modelling supports the recharge estimates but demonstrates that the vast majority over 99 of recharging waters must be transmitted by the aquifer in the regolith rather the underlying bedrock fractures which have traditionally been developed for rural water supplies

assessing the biomineralization processes in the shell layers of modern brachiopods from oxygen isotopic composition and elemental ratios implications for their use as paleoenvironmental proxies abstract fossil brachiopod shells are often used as valuable archives to reconstruct paleoenvironmental conditions in deep time however biomineralization processes can impact their fidelity as geochemical proxies brachiopod shells comprise an outer primary layer a secondary fibrous layer and sometimes a tertiary columnar layer therefore it is essential to assess the potential effects of the biomineralization processes in each of the different shell microstructures of modern brachiopods this study analyses the oxygen isotopic composition together with li ca na ca mg ca and sr ca data at high spatial 20 50 m resolution in seven modern brachiopod species focusing on differences between the primary secondary and tertiary layers in all studied species 18o values of the outer primary layer are consistently out of equilibrium with seawater also this shell layer is enriched in li na mg and sr contrary to the primary layer the innermost secondary layer is near or at oxygen isotopic and elemental equilibrium with ambient seawater the columnar tertiary shell layer if present has the least variable and the heaviest oxygen isotopic composition within the range of equilibrium values with seawater this tertiary layer however is depleted in minor and trace elements relative to the other shell layers thus the tertiary layer is more suitable for oxygen isotopic studies whereas the innermost secondary layer of the most mature parts of the shell is the best target in two layered shells while we do not observe any clear interspecific relationships between mg ca and sr ca ratios on one hand and environmental parameters such as temperature salinity and ph on the other hand there is a positive interspecific relationship between na ca and salinity and a negative interspecific relationship between li ca and temperature suggesting their potential use as proxies of physicochemical parameters of seawater

permian triassic mass extinction pulses driven by major marine carbon cycle perturbations the permian triassic boundary approximately 251 9 million years ago marked the most severe environmental crisis identified in the geological record which dictated the onwards course for the evolution of life magmatism from siberian traps is thought to have played an important role but the causational trigger and its feedbacks are yet to be fully understood here we present a new boron isotope derived seawater ph record from fossil brachiopod shells deposited on the tethys shelf that demonstrates a substantial decline in seawater ph coeval with the onset of the mass extinction in the latest permian combined with carbon isotope data our results are integrated in a geochemical model that resolves the carbon cycle dynamics as well as the ocean redox conditions and nitrogen isotope turnover we find that the initial ocean acidification was intimately linked to a large pulse of carbon degassing from the siberian sill intrusions we unravel the consequences of the greenhouse effect on the marine environment and show how elevated sea surface temperatures export production and nutrient input driven by increased rates of chemical weathering gave rise to widespread deoxygenation and sporadic sulfide poisoning of the oceans in the earliest triassic our findings enable us to assemble a consistent biogeochemical reconstruction of the mechanisms that resulted in the largest phanerozoic mass extinction the end permian mass extinction was linked with ocean acidification due to carbon degassing associated with siberian trap emplacement according to boron isotopes from fossil shells and reconstruction of the carbon cycle

δ18o and δ13c of permian brachiopods a record of seawater evolution and continental glaciation abstract two hundred sixty four 18 o and 13 c values of permian articulate brachiopod shells were analyzed and 81 of these values were characterized as well preserved and biostratigraphically well defined these were then utilized for construction of baseline oxygen and carbon isotope curves for the permian interval in addition 21 13 c whole rock values are reported for the wordian and capitanian the early permian asselian to artinskian times are characterized by 2 5 decrease in oxygen isotope values from 0 7 to 3 3 v pdb this is attributed to a 4 7 c increase in temperature in the southern urals concomitant with the retreat of the permo carboniferous ice sheets and return of the 18 o depleted melt water into the oceans the late permian samples from iran jolfa at kuh e ali bashi and china meishan yield 18 o values and presumably temperatures similar to those that followed the termination of the large scale glaciation in the lower permian in between the upper kungurian to capitanian samples from the delaware basin guadalupe mountains are enriched in 18 o at 1 5 to 3 we have no definitive explanation for these data but tentatively suggest that the anomaly can potentially be a result of evaporative enrichment of seawater in 18 o due to intracratonic arid setting of the basin the 18 o enriched nature of the zechstein samples 1 2 to 2 5 on the other hand is in all probability a reflection of the high evaporation rates in the zechstein sea the permian interval is characterized by a relatively constant 13 c at about 4 the exceptions are again the brachiopods from the delaware basin guadalupe mountains which show 1 6 increase in the guadalupian to values of up to 5 9 in the wordian a tentative explanation as in the case of oxygen is based on the proposition that the semi enclosed delaware basin was likely stratified with sequestration of the 13 c depleted carbon to the deeper water layers and a complementary 13 c enrichment in the upper oxygenated layer the coeval open ocean water dic may have been similar to that of the remainder of the permian interval at 4 as indicated by whole rock carbonate samples from oman sicily and iran in the latest permian the trend mimics the well known 13 c drop at the permian triassic boundary

constraints on the exploitation of basement aquifers in east africa water balance implications and the role of the regolith abstract recent hydrogeological studies in southwestern uganda have focused on the resource potential of crystalline basement rocks of pre cambrian age these rocks are a major source of potable water for many communities throughout equatorial africa but are rarely evaluated hydrogeologically prior to development consequently the risk of resource over exploitation is not known and few reliable data are available for formulating effective groundwater management policies the studies show that the basement rocks of the region form a very weak aquifer which is highly susceptible to over production and water level decline soil zone recharge is normally very low with a median value of just 17 mm year 1 aquifer throughflow calculations indicate that less than 1 of this amount is transmitted via the bedrock aquifer as a consequence future problems may include the lowering of water levels in production wells and the drying up of natural springs the risk of such problems imposes serious constraints on the bedrock aquifer s future use and development on a positive note it is believed that the aquifer within the overlying may be transmitting the considerable majority of the soil zone recharge and therefore may provide the key to future resource development in the region development of this aquifer may be achieved either through wells constructed and screened in the regolith s water bearing zone or where conditions permit through deeper bedrock wells inducing vertical leakage by pumping

quantifying the ph vital effect in the temperate zooxanthellate coral cladocora caespitosa validation of the boron seawater ph proxy boron isotopic and elemental systematics are used to define the vital effects for the temperate shallow water mediterranean coral cladocora caespitosa the corals are from a range of seawater ph conditions pht 7 6 to 8 1 and environmental settings 1 naturally living colonies harvested from normal ph waters offshore levanto 2 colonies transplanted nearby a subsea volcanic vent system and 3 corals cultured in aquaria exposed to high 700 atm and near present day 400 atm pco2 levels b ca compositions measured using laser ablation inductively coupled mass spectrometry la icpms show that boron uptake by c caespitosa cultured at different pco2 levels is independent of ambient seawater ph being mainly controlled by temperature dependent calcification in contrast the boron isotope compositions 11bcarb of the full suite of corals determined by positive thermal ionisation mass spectrometry ptims shows a clear trend of decreasing 11bcarb from 26 7 to 22 2 with decreasing seawater ph reflecting the strong ph dependence of the boron isotope system the 11bcarb compositions together with measurements of ambient seawater parameters enable calibration of the boron ph proxy for c caespitosa by using a new approach that defines the relationship between ambient seawater ph phsw and the internally controlled ph at the site of calcification phbiol c caespitosa exhibits a linear relationship between phsw and the shift in ph due to physiological processes ph phbiol phsw giving the regression phclad 4 80 0 52 phsw for this species we further apply this method ph phsw to calibrate tropical species of porites acropora and stylophora reported in the literature the temperate and tropical species calibrations are all linearly correlated r2 0 9 and the biological fractionation component ph between species varies within 0 2 ph units our ph phsw approach provides a robust and accurate tool to reconstruct palaeoseawater phsw for both temperate and tropical corals further validating the boron fractionation factor b3 b4 1 0272 determined experimentally by klochko et al 2006 and the boron isotope ph proxy both of which have been the foci of considerable debate

atmospheric carbon dioxide concentration across the mid pleistocene transition the dominant period of pleistocene glacial cycles changed during the mid pleistocene from 40 000 years to 100 000 years for as yet unknown reasons here we present a 2 1 million year record of sea surface partial pressure of co2 pco2 based on boron isotopes in planktic foraminifer shells which suggests that the atmospheric partial pressure of co2 pco2 was relatively stable before the mid pleistocene climate transition glacial pco2 was approximately 31 microatmospheres higher before the transition more than 1 million years ago but interglacial pco2 was similar to that of late pleistocene interglacial cycles 450 000 years ago these estimates are consistent with a close linkage between atmospheric co2 concentration and global climate but the lack of a gradual decrease in interglacial pco2 does not support the suggestion that a long term drawdown of atmospheric co2 was the main cause of the climate transition

deciphering kinetic metabolic and environmental controls on stable isotope fractionations between seawater and the shell of terebratalia transversa brachiopoda this study presents carbon and oxygen stable isotope data obtained from high resolution sampling 500 m of the brachiopod terebratalia transversa from the san juan islands washington state usa the aim of this study is to unravel the respective effects of physiological and environmental controls on the stable isotopic composition of brachiopod shell calcite based on an sem study of the shell a three dimensional sampling was performed in order to investigate carbon and oxygen isotope variations along isochrons and ontogenetic transects the primary as well as the outer part of the secondary shell layer display large and variable isotopic offsets as high as 7 for 13c and 6 for 18o relative to expected equilibrium values the significant positive correlations between 18o and 13c values indicate that the isotopic compositions of these shell domains are mainly controlled by kinetic isotope fractionation effects the ontogenetic 13c and 18o variations can be used to establish a growth curve of the studied specimen whose age is estimated close to 8 years the extent of apparent o 18 disequilibrium observed in this study is about as large as any yet measured in any organism which makes this brachiopod an interesting and important case the carbon and oxygen isotope compositions increase from the outer towards the inner part of the secondary layer where they reach values of 0 0 8 and 0 8 to 0 2 respectively corresponding calculated temperatures are between 12 and 13 8 c and fall in the range of seawater temperatures recorded off the san juan islands 7 13 c these results suggest that the calcite fibres were secreted more and more slowly during the thickening of the shell throughout the animal s life finally approximating isotopic equilibrium this study illustrates that the stable isotopic composition of the modern brachiopod t transversa is predominantly influenced by kinetic fractionation and to a minor degree by metabolic effects except for the innermost part of the shell the measured isotope ratios do not reflect environmental conditions during shell precipitation it remains to be tested by comparable studies whether other modern brachiopod species or even fossil brachiopods reflect comparable fractionation effects these results point out the need for re examination of paleozoic oceanographic conditions

stable isotope variations in modern articulate brachiopods abstract carbon and oxygen isotopic analyses were performed on several species of holocene articulate brachiopods from various locations in the caribbean sea and in the atlantic and pacific oceans from salinities ranging between 30 and 38 pmil and over a temperature range from 4 to 28 c 39 to 82 f the dgr18o of articulate brachiopods are systematically related to the dgr18o and temperatures of the ambient waters lowenstam in 1961 concluded that articulate brachiopods secrete calcium carbonate low magnesium calcite in isotopic equilibrium with the surrounding waters the data compiled in this study along with that of lowenstam closely approximate the equilibrium calcite water end page 500 line deviation from apparent equilibrium was most evident for samples from a few cold water sites intraspecific isotopic variations in several warmer water assemblages were up to 2 pmil and isotopic variation within individual specimens as high as 1 5 pmil were noted articulate brachiopods were not separable at any taxonomic level on the basis of ranges in isotopic values the two extant orders of brachiopods the terebratulida and the rhynchonellida as well as the suborder thecideidina had essentially equivalent isotopic ranges at any given locality thus there is no evidence for significant taxonomic control of oxygen isotope fractionation among articulate brachiopods no correlation appears to exist between dgr18o and dgr13c values our results suggest strongly that isotopic data from small populations or communities of well preserved articulate brachiopods can be used in paleogeographic and paleo oceanographic reconstructions end of article last page 501

experimental measurement of boron isotope fractionation in seawater abstract the boron isotopic composition of marine carbonates is considered to be a tracer of seawater ph use of this proxy benefits from an intimate understanding of chemical kinetics and thermodynamic isotope exchange reactions between the two dominant boron bearing species in seawater boric acid b oh 3 and borate ion b oh 4 however because of our inability to quantitatively separate these species in solution the degree of boron isotope exchange has only been known through theoretical estimates in this study we present results of a spectrophotometric procedure wherein the boron isotope equilibrium constant 11 10 k b is determined empirically from the difference in the dissociation constants of 11 b oh 3 and 10 b oh 3 in pure water 0 6 mol kg 1 h 2 o kcl and artificial seawater within experimental uncertainty our results show no dependence of 11 10 k b on temperature but 11 10 k b at 25 c in pure water was statistically different than results obtained in solutions at high ionic strength 11 10 k b of the seawater s 35 b t 0 01 mol kg 1 h 2 o at 25 c is 1 0272 0 0006 this result is significantly larger than the theoretical value used in numerous paleo ph studies 11 10 k b 1 0194

unprecedented pressure increase in deep magma reservoir triggered by lava dome collapse 1 the collapse of the soufriere hills volcano lava dome on montserrat in july 2003 is the largest such event worldwide in the historical record here we report on borehole dilatometer data recording a remarkable and unprecedented rapid 600s pressurisation of a magma chamber triggered by this surface collapse the chamber expansion is indicated by an expansive offset at the near dilatometer sites coupled with contraction at the far site by analyzing the strain data and using added constraints from experimental petrology and long term edifice deformation from gps geodesy we prefer a source centered at approximately 6 km depth below the crater for an oblate spheroid with overpressure increase of order 1 mpa and average radius 1 km pressurisation is attributed to growth of 1 3 of gas bubbles in supersaturated magma triggered by the dynamics of surface unloading recent simulations demonstrate that pressure recovery from bubble growth can exceed initial pressure drop by nearly an order of magnitude

using species specific paleotemperature equations with foraminifera a case study in the southern california bight abstract species specific paleotemperature equations were used to reconstruct a record of temperature from foraminiferal 18 o values over the last 25 kyr in the southern california bight the equations yield similar temperatures for the 18 o values of globigerina bulloides and neogloboquadrina pachyderma in contrast applying a single paleotemperature equation to g bulloides and n pachyderma 18 o yields different temperatures which has been used to suggest that these species record the surface to thermocline temperature gradient in santa barbara basin an isotopically distinct morphotype of g bulloides dominates during glacial intervals and yields temperatures that appear too cold when using a paleotemperature equation calibrated for the morphotype common today when a more appropriate paleotemperature equation is used for glacial g bulloides we obtain more realistic glacial temperatures glacial interglacial temperature differences g i t calculated in the present study indicate significant cooling 8 10 c throughout the southern california bight during the last glacial maximum lgm the magnitude of glacial cooling varies from 8 c near the middle of the southern california bight tanner basin and san nicolas basin to 9 c in the north santa barbara basin and 9 5 10 c in the south velero basin and no name basin our temperature calculations agree well with previous estimates based on the modern analog technique in contrast studies using n pachyderma coiling ratios u k 37 indices and transfer functions estimate considerably warmer lgm temperatures and smaller g i t

boron isotope systematics in large rivers implications for the marine boron budget and paleo ph reconstruction over the cenozoic abstract the chemical composition of the oceans and long term climate changes are believed to be linked reconstruction of seawater ph evolution is desirable as ph may be related to atmospheric pco2 and hence to climate evolution boron isotopes in oceanic carbonates have been suggested to be a proxy for oceanic paleo ph reconstruction nevertheless the calculation of paleo ph values over geological periods requires a precise knowledge of the boron isotopic composition of the oceans when calcite precipitated we present the systematics of boron isotopic composition of the world s main rivers we deduce a continental boron flux to the oceans of 38 1010 gb year with a mean isotopic composition of 10 these results lead to a balanced boron budget in the oceans and allow the development of a model for the marine boron secular evolution over the past 100 myr it is shown that the oceanic boron cycle is mainly controlled by the boron continental discharge and the boron uptake from the oceans during low temperature alteration of oceanic crust however the recent important increase of the clastic sediment supply linked to the himalayan erosion impacts the oceanic boron budget by enhancing significantly the boron uptake by adsorption on sediments we predict a boron isotopic composition in the oceans lower during the cenozoic and slightly higher during the cretaceous than today the modelled values for the marine boron isotopes follow the variations of boron isotopes in carbonates over the cenozoic era provided by previous studies suggesting that the variations of the seawater ph may not have been important on this time scale if this is the case it involves that buffering mechanisms occur in the oceans to maintain seawater ph at a roughly constant value against past atmospheric pco2 variations

the influence of tectonic setting on the hydrological characteristics of deeply weathered terrains evidence from uganda abstract deeply weathered landscapes occur throughout equatorial regions and are transformed by cycles of deep weathering and stripping these processes are driven by rainfall that infiltrates the subsurface as groundwater recharge or runs across the landsurface recent work in uganda demonstrates that long term 10 5 10 6 a cycles of deep weathering and stripping are tectonically controlled the influence of tectonics on the present day hydrological regime and hence contemporary geomorphic process is examined in this study the hydrological characteristics of two humid basins in uganda were determined using soil moisture balance techniques hydrograph separation methods borehole hydrographs and stable isotope 2 h 18 o tracers these were in turn related to the dominant geomorphic process deep weathering or stripping suggested by the local tectonic history in central uganda where deep weathering of the landsurface has occurred since the miocene soil moisture balance calculations monitoring well records and stable isotope data show that groundwater recharge is derived from monsoon rainfall is in the order of 120 mm a 1 and greatly exceeds surface runoff of 3 4 mm a 1 basin output occurs as evapotranspiration from a wetland that runs centrally through the catchment consistency in this discharge despite highly seasonal rainfall reflects a large basin storage that is permitted by a thick weathered mantle in south western uganda where stripping of the landsurface has occurred since the mid pleistocene soil moisture balance calculations and hydrograph separation techniques indicate groundwater recharge is restricted to years of exceptionally high rainfall annual surface runoff 34 mm a 1 generated primarily from monsoon rainfall events exceeds the recharge flux 8 15 mm a 1 streamflow discharge varies considerably from 0 2 to 14 m 3 s 1 and occurs along well incised drainage channels the comparatively smaller basin storage results from a thinner partially stripped weathered mantle the influence of tectonics is indicated by the conclusion that deep weathering associated with prolonged tectonic stability in central uganda is facilitated by a recharge dominated hydrological regime whereas stripping prompted by mid pleistocene tectonic uplift in south western uganda continues to occur under a runoff dominated regime

brachiopods as indicators of original isotopic compositions in some paleozoic limestones the original stable isotopic composition of paleozoic marine carbonate rocks is important to establish a baseline for evaluating diagenetic alteration and providing a reliable data base for modeling exogenic geochemical cycles of the elements we have compared the 18 o and 13 c values in the nonluminescent portions of brachiopods with similar published data of whole brachiopods other whole fossils and estimates of original isotopic composition of marine cements the oxygen and carbon isotopic records for each of these paleozoic components show generally good internal consistency significant discrepancies however were noted between results on the different components isotopic and trace element data presented in this study suggest that permo carboniferous whole brachiopods are little altered chemically nonetheless a more reliable but not fool proof approach for obtaining pristine isotopic values is microsampling of least altered regions based on cathodoluminescence in conjunction with staining techniques and elemental analyses the carbon and oxygen isotopic compositions of all components decrease in 18 o and 13 c in geologically older material neither temporal trend is monotonic however oxygen isotopic results suggest an important positive shift in 18 o of about 2 during the early carboniferous whereas the carbon isotope trend shows a major positive shift 2 3 during the mid carboniferous

chemical variation in pennsylvanian brachiopod shells diagenetic taxonomic microstructural and seasonal effects abstract to improve our ability to use minor and trace element mte variation in biotic carbonates as diagenetic and paleoenvironmental indicators we performed electron probe microanalysis on more than 100 late pennsylvanian brachiopod shells from texas kansas missouri and new mexico texturally preserved specimens of the genera crurithyris composita and neospirifer from all three regions were analyzed as were eridmatus specimens from texas twenty measurements were made in two transects across each shell shell microstructure and cathodoluminescence were described for each spot analyzed three modern shells were analyzed for comparison diagenesis as indicated by cathodoluminescence and or absence of microstructure tends to enrich shells in fe and mn x ca 0 7 mmol mol and deplete shells in na and s mg content shows no consistent trend with diagenesis in fabric retentive nonluminescent shell areas mg na and s contents vary twofold to sevenfold depending on taxonomy microstructure and season overall taxonomy is the dominant factor controlling mte composition na and s concentrations are consistently highest in crurithyris and eridmatus intermediate in neospirifer and lowest in composita in taxa with mixed microstructure composita neospirifer secondary fibrous layer calcite contains 1 5 to 2 times more na than does interlayer prismatic calcite thus whole shell na contents of these taxa depend on the proportion of fibrous and prismatic shell seasonal cycles are revealed in mte transects across growth lines mg na and s contents commonly vary by more than a factor of two between maxima presumably summer and minima winter within the same shell retention of taxonomic microstructural and seasonal effects in shell chemistry argues for preservation of original chemistry in fabric retentive nonluminescent paleozoic brachiopod shells

quantification of the specific yield in a two layer hard rock aquifer model abstract hard rock aquifers hra have long been considered to be two layer systems with a mostly capacitive layer just below the surface the saprolite layer and a mainly transmissive layer underneath the fractured layer although this hydrogeological conceptual model is widely accepted today within the scientific community it is difficult to quantify the respective storage properties of each layer with an equivalent porous medium model based on an hra field site this paper attempts to quantify in a distinct manner the respective values of the specific yield sy in the saprolite and the fractured layer with the help of a deterministic hydrogeological model the study site is the plancoet migmatitic aquifer located in north western brittany france with piezometric data from 36 observation wells surveyed every two weeks for eight years whereas most of the piezometers 26 are located where the water table lies within the saprolite thus representing the specific yield of the unconfined layer sy1 10 of them are representative of the unconfined fractured layer sy2 due to their position where the saprolite is eroded or unsaturated the two layer model based on field observations of the layer geometry runs with the modflow code 81 values of the sy1 sy2 parameter sets were tested manually as an inverse calibration was not able to calibrate these parameters in order to calibrate the storage properties a new quality of fit criterion called advar was also developed equal to the mean squared deviation of the seasonal piezometric amplitude variation contrary to the variance advar is able to select the best values for the specific yield in each layer it is demonstrated that the saprolite layer is about 2 5 times more capacitive than the fractured layer with sy1 10 7

oxygen isotope values from high latitudes clues for permian sea surface temperature gradients and late palaeozoic deglaciation abstract the permian was a period of waning large scale continental glaciations in the southern hemisphere the waning of these ice sheets during the early permian led to discharge of 18o depleted ice melt water into the oceans this coupled with rising seawater temperatures resulted in a concomitant decline of about 2 5 in the 18o of seawater as recorded by brachiopod shells from low latitude

ocean acidification during the early toarcian extinction event evidence from boron isotopes in brachiopods this project was funded by the european union s horizon 2020 research and innovation program under the marie sklodowska curie grant agreement and project base line earth 643084 and by the slovak research and development agency apvv17 0555 and the slovak scientific grant agency vega 0169 19

shell structure patterns and trends of oxygen and carbon stable isotopes in modern brachiopod shells this study investigates 13c and 18o variations in the shells of modern brachiopods representing all extant groups of calcite precipitating brachiopods collected live from 8 locations sem examinations determined the ultrastructural characteristics of each species prior to isotope analyses 13c and 18o analyses of shell carbonate were carried out with samples representing disparate morphological features and ultrastructural shell layers of both ventral and dorsal valves generally 18o values from the fibrous secondary or prismatic tertiary shell layers of the articulated terebratulida and rhynchonellida species were in oxygen isotopic equilibrium with ambient seawater isotopic temperatures extrapolated from these values are close to measured annual mean seawater temperatures 18o values were relatively unaffected by shell specialisation the only exception was antarctic species liothyrella uva which did not have a complete tertiary shell layer typical of this genus and had 18o values of the innermost layer strongly correlated with 13c and mostly not in oxygen isotopic equilibrium with ambient seawater with the exception of the rhynchonellid notosaria nigricans the outer primary layer material was depleted in 13c and 18o and highly variable inclusion of this material even as part of a whole shell sample could lead to misinterpretation of seawater temperature therefore only fossil secondary layer material should be used the anomalous articulated thecideidine brachiopod thecidellina barretti is composed of mainly primary shell material and was not in oxygen isotope equilibrium 18o values from the laminar secondary layer material of the inarticulated craniida are highly variable therefore these species are not recommended for use as palaeoenvironmental proxies this study suggests caution when employing fossil brachiopod shells with similar ultrastructures to modern craniid and thecideidine brachiopods the carbon isotope composition is highly variable in all of the brachiopods studied analysis of samples from specialised regions of the secondary shell layer show a pattern of depletion in 13c relative to non specialised secondary material the carbon isotope variability is independent of 18o and is repeated in most of the articulated species regardless of geographical location this is possibly a vital effect produced by metabolic prioritisation

amphibole reaction rims as a record of pre eruptive magmatic heating an experimental approach abstract magmatic minerals record the pre eruptive timescales of magma ascent and mixing in crustal reservoirs and conduits investigations of the mineral records of magmatic processes are fundamental to our understanding of what controls eruption style as ascent rates and magma mixing processes are well known to control and or trigger potentially hazardous explosive eruptions thus amphibole reaction rims are often used to infer pre eruptive magma dynamics and in particular to estimate magma ascent rates however while several experimental studies have investigated amphibole destabilization during decompression only two investigated thermal destabilization relevant to magma mixing processes this study examines amphibole decomposition experimentally through isobaric heating of magnesio hornblende phenocrysts within a natural high silica andesite glass the experiments first equilibrated for 24 h at 870 c and 140 mpa at h2o saturated conditions and o2 re reo prior to rapid heating to 880 900 or 920 c and hold times of 3 48 h at 920 c rim thicknesses increased from 17 m after 3 h to 55 m after 12 h and became pseudomorphs after longer durations at 900 c rim thicknesses increased from 7 m after 3 h to 80 m after 24 h to pseudomorphs after longer durations at 880 c rim thicknesses increased from 7 m after 3 h to 18 m after 36 h to pseudomorphs after 48 h reaction rim microlites vary from 5 16 m in size with no systematic relationship between crystal size and the duration or magnitude of heating time averaged rim microlite growth rates decrease steadily with increasing experimental duration from 3 97 10 7 mm s 1 to 3 1 to 3 5 10 8 mm s 1 time averaged microlite nucleation rates also decrease with increasing experimental duration from 1 2 10 3 mm 3 s 1 to 5 3 mm 3 s 1 there is no systematic relationship between time averaged growth or nucleation rates and the magnitude of the heating step ortho and clinopyroxene together constitute 57 90 modal mineralogy in each reaction rim at constant temperature clinopyroxene abundances decrease with increasing experimental duration from 72 modal 3 h at 900 c to 0 48 h at 880 c and 36 h at 900 and 920 c fe ti oxides increase from 6 12 modal after 3 6 h to 26 34 modal after 36 48 h plagioclase occurs in relatively minor amounts 500 m from reacted amphibole are consistent with inter microlite rim glasses 71 3 77 7 wt sio2 within a given experiment and there is a weakly positive correlation between increasing run duration and inter microlite melt sio2 68 9 78 5 wt our results indicate that experimental heating induced amphibole reaction rims have thicknesses textures and mineralogies consistent with many of the natural reaction rims seen at arc andesite volcanoes they are also texturally consistent with experimental decompression reaction rims on this basis it may be challenging to distinguish between decompression and heating mechanisms in nature

carbon and oxygen isotopic compositions of modern brachiopod shells from a warm temperate shelf environment sagami bay central japan this study presents carbon 13c and oxygen 18o isotopic compositions of shells of an articulated brachiopod laqueus rubellus living in a warm temperate shelf environment in japan high resolution three dimensional samplings were conducted 1 to clarify variations in the isotopic compositions within a single shell 2 to evaluate offset of the compositions from those of the calcite precipitated in isotopic equilibrium with ambient seawater equilibrium calcite and 3 to specify shell portions that reflect the isotopic compositions of ambient seawater the 13c and 18o values of samples from the secondary shell layer which constitutes the main body of the brachiopod shell are in and or out of those of the equilibrium calcite the isotopic compositions of samples from the outermost part of the secondary shell layer outer surface of the secondary shell layer correlated well with growth rates positive correlations are recognized between the 13c and 18o values of these samples which can be ascribed to a kinetic fractionation effect although limited data on 13c of total dissolved inorganic carbon dic and 18o of seawater at the brachiopod sample site enable only approximate estimates of the 13c and 18o of the equilibrium calcite they are comparable with those of the brachiopod shell the 18o values of samples from the outermost part of the secondary layer along a growth axis of laqueus rubellus are a reliable environmental proxy because they mostly fall in the 18o range for the equilibrium calcite although samples from the inner series of l rubellus are depleted partially enriched in 13c 18o by 0 8 0 3 relative to the equilibrium calcite both isotopic variations are quite small therefore the isotopic compositions in this series would also be useful if the offsets are corrected this study clearly illustrates that although the 13c and 18o of modern brachiopod shells are influenced by the kinetic fractionation effect appropriate selection of species and shell portions reflecting the isotopic compositions of ambient seawater enables the reconstruction of secular variations in 13c or 18o in the oceans throughout geologic time

strontium isotope evolution of late permian and triassic seawater the 87sr 86sr values based on brachiopods and conodonts define a nearly continuous record for the late permian and triassic intervals minor gaps in measurements exist only for the uppermost brahmanian lower part of the upper olenekian and middle norian and only sparse data are available for the late permian these 219 measurements include 67 brachiopods and 114 conodont samples from the tethyan realm as well as 37 brachiopods and one conodont sample from the mid european middle triassic muschelkalk sea the late permian lower triassic interval is characterized by a steep 1 3 10 3 rise from 0 7070 at the base of the dzhulfian to 0 7082 in the late olenekian a rate of change comparable to that in the cenozoic in the mid triassic anisian and ladinian the isotope values fall to 0 7075 followed again by a rise to 0 7081 in the middle late norian the 87sr 86sr values decline again in the late norian sevatian and rhaetian to 0 7076 the sharp rise in the 87sr 86sr values during the late permian early triassic was coincident with widespread clastic sedimentation because of the paucity of tectonic uplifts the enhanced erosion may have been due to intermittent humid phases during mainly an arid interval coupled with the absence of a dense protective land plant cover following the mass extinction during the latest permian the apex of the 87sr 86sr curve at the olenekian anisian boundary coincides with cessation of the large scale clastic sedimentation and also marks the final recovery of land vegetation as indicated by the renewed onset of coal formation in the middle triassic the rising 87sr 86sr values from the middle carnian to the late norian coincide with the uplift and erosion of the cimmeride indosinian orogens marking the closure of the palaeotethys the subsequent rhaetian decline that continues into jurassic pliensbachian toarcian boundary on the other hand coincides with the opening of the vardar ocean and its eastern continuation in the izmir ankara ophiolitic belt samples from the upper muschelkalk are more radiogenic than the global trend this may reflect separation of the basin from the open ocean due to strong meteoric influx from a large land mass in the north the germanic basin became increasing brackish up section in the north and east but because of the high evaporation rates the salt content was not much reduced in the southern and central basin where a rich but increasingly endemic marine fauna survived

boron isotope geochemistry of paleozoic brachiopod calcite implications for a secular change in the boron isotope geochemistry of seawater over the phanerozoic abstract boron isotope composition of marine carbonates has been proposed as a paleo ph proxy and potential tool to reconstruct atmospheric pco2 the precise knowledge of the boron isotopic composition of ancient seawater represents the fundamental prerequisite for any paleo ph reconstruction this contribution presents boron isotope values for silurian to permian brachiopod calcite that might be used to reconstruct ph or boron isotope composition of past oceans all brachiopod shells were screened for diagenetic recrystallization by means of cathodoluminescence microscopy trace element geochemistry b fe mn sr as well as sem only nonluminescent shells revealing well preserved microstructures high strontium and boron concentrations as well as low iron and manganese contents were accepted for boron isotope analysis the boron isotope ratios of silurian devonian pennsylvanian and permian brachiopod calcite range from 6 8 to 11 0 7 3 to 14 9 12 4 to 15 8 and 10 1 to 11 7 respectively these 11b values are significantly lower in comparison to 11b values of modern biogenic carbonates and indicate that the paleozoic oceans were depleted in 11b by up to 10 box modeling of the boron geochemical cycle suggests that the significant depletion of 11b in the oceanic reservoir may have been initiated by an enhanced continental boron discharge our data support the earlier made conclusion that boron isotopes may not be used in the geological past as reliable paleo ph proxy unless the boron isotopic composition of ancient oceans can be constrained by further studies

δ18o and δ13c values of modern brachiopod shells abstract researchers have not rigorously tested the hypothesis that calcite from modern brachiopod shells is precipitated in oxygen isotope equilibrium with ambient seawater isotopic variability at the intraspecimen and intertaxon levels has not been examined without such data for modern brachiopods similar data from ancient brachiopods cannot be accurately interpreted in this study a survey is made of 18 o and 13 c values of terebratulid rhynchonellid thecideidine and craniacean brachiopods from antarctica the bay of fundy curacao japan new zealand norway puget sound palau sicily and south africa this suite of samples provides a wide range of taxonomic levels temperatures salinities and depositional environments for evaluating the degree of isotopic equilibrium attained during precipitation of brachiopod calcite new data indicate that modem brachiopod calcite is not always precipitated in oxygen and carbon isotope equilibrium with ambient seawater calcite from the primary layer and specialized shell structures hinge brachidium foramen interarea muscle scars are depleted in both 18 o and 13 c a characteristic of biological fractionation or vital effects often found in other calcerous marine organisms our findings suggest that these portions of the brachiopod shell should be avoided during sampling of ancient brachiopods secondary layer calcite the material most often analyzed in ancient brachiopods has higher 18 o and 13 c values which approach and sometimes correspond with predicted equilibrium values therefore secondary layer calcite is the most suitable portion of the brachiopod shell for use as an ancient seawater proxy although near equilibrium precipitation in secondary layer calcite is encouraging to those studying the isotopic composition of ancient oceans these data come with caveats large intraspecimen variability in the 18 o values of secondary layer calcite 1 in some samples limits the use of brachiopods as precise indicators of the 18 o value or temperature of ancient seawater the 18 o and 13 c values of secondary layer calcite deviate from predicted equilibrium values toward the lower values of the primary layer and specialized shell structures indicating a measurable vital effect in most cases measured 18 o values are lower than the calculated equilibrium values dictated by seasonal variations in the 18 o value and temperature of seawater ontogenetic variations in the 13 c values of secondary layer calcite have also been measured and must be assessed when interpreting ancient data modern brachiopods occur in a wide range of seawater salinities and temperatures therefore the relation between salinity and the 18 o value of seawater must be known to correctly calculate the temperature of calcite precipitation from secondary layer 18 o values errors of up to 15 c are found if ambient seawater is assumed to have a constant 18 o value e g 0 smow and the 18 o values of secondary layer calcite are used to calculate temperature coupled with vital effects and intraspecimen variability these errors can obscure the resolution of secular variations in the rock record

surface ocean ph response to variations in pco2 through two full glacial cycles abstract knowledge of past atmospheric pco 2 is important for evaluating the role of greenhouse gases in climate forcing ice core records show the tight correlation between climate change and pco 2 but records are limited to the past 900 kyr we present surface ocean ph and pco 2 data reconstructed from boron isotopes in planktonic foraminifera over two full glacial cycles 0 140 and 300 420 kyr the data co vary strongly with the vostok pco 2 record and demonstrate that the coupling between surface ocean chemistry and the atmosphere is recorded in marine archives allowing for quantitative estimation of atmospheric pco 2 beyond the reach of ice cores

constraining the evolution of neogene ocean carbonate chemistry using the boron isotope ph proxy abstract over the course of the neogene the earth underwent profound climatic shifts from the sustained warmth of the middle miocene to the development of plio pleistocene glacial interglacial cycles major perturbations in the global carbon cycle have occurred alongside these shifts however the lack of long term carbonate system reconstructions currently limits our understanding of the link between changes in co2 carbon cycling and climate over this time interval here we reconstruct continuous surface ocean ph co2 and surface ocean aragonite saturation state using boron isotopes from the planktonic foraminifer trilobatus trilobus and we perform a sensitivity analysis of the key variables in our calculations e g 11 bsw ca sw ccd we show that the choice of 11 b sw influences both seawater ph and co2 while ca sw reconstructed dissolved inorganic carbon exerts a significant influence only on co2 over the last 22 myr the lowest ph levels occurred in the middle miocene climate optimum mmco 17 14 myr ago reaching 7 6 0 1 units in all our scenarios the extended warmth of the mmco corresponds to mean co2 and aragonite saturation state levels of 470 630 ppm and 2 7 3 5 respectively despite a general correspondence between our co2 record and climate all co2 scenarios show a peak at 9 ma not matched by corresponding changes in climate reconstructions this may suggest decoupling i e significant co2 change without a discernible climate response for a limited interval in the late miocene 11 6 8 5 ma although further refinement of our understanding of the temporal evolution of the boron isotopic composition of seawater is necessary to fully evaluate the nature of the relationship between co2 and climate nonetheless from our long term view it is clear that low latitude open ocean marine ecosystems are unlikely to have experienced sustained surface ph and saturation levels below 7 7 and 1 7 respectively during the past 14 million years 66 ci