modelling glacial climatic millennial scale variability related to changes in the atlantic meridional overturning circulation a review abstract since the discovery of glacial abrupt variability in greenland and the north atlantic about two decades ago its modelling remains a conceptual and technical challenge while the global climatic signature of heinrich events can reasonably be ascribed to the fresh water discharge related to the massive iceberg armadas released by the laurentide ice sheet in the north atlantic the existence of such a triggering mechanism is elusive as far as dansgaard oeschger type variability is concerned even if other mechanisms have been proposed the majority of modelling attempts to better understand glacial climate variability has assumed it to be linked to abrupt variations in the atlantic meridional overturning circulation amoc in this review we introduce the rationale behind this approach i e the possible existence of several deep ocean circulation equilibria associated with distinct climate signatures we then review the published fresh water hosing experiments and the mechanisms at work to explain the climate differences related to the different amoc states most of these works have been performed under pre industrial boundary conditions the few hosing experiments run under glacial conditions show that the sensitivity of the climate system to fresh water hosing is very dependent on the background climate state in order to rigourously compare several types of experiments equilibrium runs vs transient runs with pre industrial vs glacial boundary conditions we present experiments especially run for this review with two climate models of intermediate complexity uvic and loveclim although there are similarities between the responses simulated by these models there are also many differences which would benefit being compared to reconstructions such as those presented in this special issue however a strict comparison will require to consider boundary conditions as realistic as possible for marine isotopic stage 3 modelling glacial variability to compare model results with paleoclimatic data remains a big challenge

mercury emissions and stable isotopic compositions at vulcano island italy abstract sampling and analyses methods for determining the stable isotopic compositions of hg in an active volcanic system were tested and optimized at the volcanic complex of vulcano aeolian islands italy condensed gaseous fumarole hg fum t plume gaseous elemental hg g 0 and plume particulate hg p ii were obtained at fumaroles f0 f5 f11 and fa the average total hg emissions based on hgt so2 in condensed fumarolic gases and plumes range from 2 5 to 10 1 kg y 1 in agreement with published values ferrara r mazzolai b lanzillotta e nucaro e pirrone n 2000 volcanoes as emission sources of atmospheric mercury in the mediterranean basin sci total environ 259 1 3 115 121 aiuppa a bagnato e witt m l i mather t a parello f pyle d m martin r s 2007 real time simultaneous detection of volcanic hg and so2 at la fossa crater vulcano aeolian islands sicily geophys res lett 34 l21307 plume hg p ii increases with distance from the fumarole vent at the expense of hg g 0 and indicates significant in plume oxidation and condensation of fumarole hg fum t relative to the nist srm 3133 hg standard the stable isotopic compositions of hg are 202hg fum t 0 74 0 18 2sd n 4 for condensed gaseous fumarole hg fum t 202hg g 0 1 74 0 36 2sd n 1 for plume gaseous elemental hg g 0 at the f0 fumarole and 202hg p ii 0 11 0 18 2sd n 4 for plume particulate hg p ii the enrichment of hg p ii in the heavy isotopes and hg g 0 in the light isotopes relative to the total condensed fumarolic hg fum t gas complements the speciation data and demonstrates a gas particle fractionation occurring after the gas expulsion in ambient t atmosphere a first order rayleigh equilibrium condensation isotope fractionation model yields a fractionation factor cond gas of 1 00135 0 00058

mercury as a proxy for volcanic emissions in the geologic record abstract large igneous province lip eruptions are increasingly considered to have driven mass extinction events throughout the phanerozoic however uncertainties in radiometric age dating of lip materials along with difficulty in accurate age dating of sedimentary rocks that record the environmental and biological history of our planet create inherent uncertainties in any linkage as such there is interest in using geochemical proxies to fingerprint periods of major volcanism in the sedimentary record termed here lip marks the use of sedimentary mercury hg contents has been suggested to be the best tool to accomplish this goal and recent work is reviewed here studies to date show that most extinction events ocean anoxic events and other environmental crises through the phanerozoic have an associated sedimentary hg anomaly it remains unclear though if each hg anomaly is truly a signature of massive volcanism or if it is controlled by local or regional processes as hg has a strong affinity to organic matter om normalisation with total organic carbon toc has been used to assess anomalies the measurement of toc has been fraught with error throughout many studies leaving some claimed hg toc anomalies questionable normalisation by other elements that can affect hg sequestration such as al and s are less common but warrant further investigation stable isotope systematics of hg have helped to further clarify the origin of hg spikes and clearly show that not all hg anomalies are directly related to volcanism although a promising tool the hg proxy requires more refinement to accurately understand the nuances of an hg anomaly in the rock record

variability of an under ice river plume in hudson bay observations of the great whale river plume in the coastal waters of hudson bay canada during late winter and early spring during four different years showed its area to vary as a power of the discharge the under ice plume area was much larger than plume area in open water for comparable discharges differences in plume geometry were related to elapsed time since ice formation and low frequency variability of the coastal circulation the strength and orientation of the coastal motion was weakly correlated with the cross hudson bay atmospheric pressure gradient the passage of low pressure systems over hudson bay is thought to generate a progressive edge wave in the absence of direct wind forcing the amplitude of the low frequency variations in coastal circulation decreased with the increasing spatial extent of the landfast ice in the study area

geochemical modeling of mixing between magmatic and hydrothermal gases the case of vulcano island italy abstract in this study we present a geochemical approach to model the mixing of magmatic and hydrothermal gases our model is based on a rigorous formulation of a perfectly dimensioned system of mass and energy balance equations inputs of the equation set are the h2o and co2 content and gas emission temperature at the surface together with some constraints gained from the chemical physical features of the hydrothermal system the output data give the composition of magmatic gas mixing fractions and temperatures of gas mixtures in the mixing zone the comparison of the emission temperature of fumarolic gases with their calculated mixing temperatures provides valuable indications on the expansion process that gases undergo during their ascent towards the surface our mixing model is exemplified by the fumarolic system of vulcano island italy we calculate the thermodynamic parameters of the hydrothermal system by means of an h2o co2 nacl equation of state while the thermo baric conditions of the magma have been assessed by previous geophysical and petrologic investigations the obtained results show that during volcanic crises at vulcano island and in agreement with magma degassing processes both the co2 and the he contents of magmatic gas display peaks with a progressively declining amplitude suggesting a progressive magmatic impoverishment of volatiles strongly partitioned in the gas phase mixing fractions of various fumaroles are normally variable while they display almost homogeneous values during periods of increased volcanic activity on the basis of results gained some implications regarding the hazard of phreato magmatic explosions are also discussed the high temperature reached by fumarolic gases strongly constrains their probable expansion process during the ascent towards the surface a comparison between the temperature of the fumarolic gas and the calculated mixing temperature at depth indicates that the expansion process can be reasonably described as almost iso enthalpic although field evidences suggest that the fumarolic emission temperature could be affected by the sharp permeability changes in the last few hundred meters therefore our results and field evidences clearly indicate that variations in gas emission temperature cannot be considered a good indicator of volcanic activity as it is strongly dependent on expansion process and ultimately on rock permeability changes the model greatly improves the knowledge of the volcanic system of vulcano island and provides an important tool for the interpretation and evaluation of volcanic activity moreover a similar approach can be considered for other volcanic systems having analogous characteristics

evidence for zn isotopic fractionation at merapi volcano abstract fumarolic gases rocks and condensate samples from merapi volcano indonesia have been analyzed by multiple collector inductively coupled plasma mass spectrometry mc icp ms for their zn isotopic compositions the variation observed expressed as 66 zn 66 zn 66 zn 64 zn sample 66 zn 64 zn jmc 3 049l 1 10 3 ranges from 0 05 to 1 68 the overall reproducibility was found to be better than 0 10 2sd the 66 zn of andesitic rock samples are homogeneous with a mean value of 0 24 which is comparable to previously reported basalt data 66 zn in the woro fumerolic field are ranging from 0 05 to 0 85 and 1 48 to 1 68 in fumarolic gases and condensates respectively upon cooling from 590 to 297 c gaseous zn concentrations decrease and become increasingly enriched in the lighter zn isotopes while the condensates become increasingly enriched in the heavier isotopes gas and condensate isotopic compositions can be explained with a rayleigh condensation model with temperature dependent isotope fractionation factor solid vapor over the 574 c to 297 c range of observations 1000 ln solid vapour c 1 c 2 t c 3 t 2 with c 1 0 c 2 0 88 10 3 c 3 1 00 10 6 and t in degrees kelvin which corresponds to solid vapor of 1 00033 to 1 00153 respectively at the indicated temperatures

north atlantic climate response to lake agassiz drainage at coarse and ocean eddy permitting resolutions abstractthe north atlantic climate response to the catastrophic drainage of proglacial lake agassiz into the labrador sea is analyzed with coarse and ocean eddy permitting versions of a global coupled climate model the north atlantic climate response is qualitatively consistent in that a large scale cooling is simulated regardless of the model resolution or region of freshwater discharge however the magnitude and duration of the north atlantic climate response is found to be sensitive to model resolution and the location of freshwater forcing in particular the long term entrainment of freshwater along the boundary at higher resolution and its gradual partially eddy driven escape into the interior leads to low salinity anomalies persisting in the subpolar atlantic for decades longer as a result the maximum decline of the atlantic meridional overturning circulation amoc and the ocean meridional heat transport mht is amplified by about a factor of 2 at ocean eddy permitting resolution and the re

impact of climate variability on the tidal oceanic magnetic signal a model based sensitivity study esa s satellite magnetometer mission swarm is supposed to lower the limit of observability for oceanic processes while periodic magnetic signals from ocean tides are already detectable in satellite magnetometer observations changes in the general ocean circulation are yet too small or irregular for a successful separation an approach is presented that utilizes the good detectability of tidal magnetic signals to detect changes in the oceanic electric conductivity distribution ocean circulation tides and the resultant magnetic fields are calculated with a global general ocean circulation model coupled to a 3 d electromagnetic induction model for the decay of the meridional overturning circulation as an example the impact of climate variability on tidal oceanic magnetic signals is demonstrated total overturning decay results in anomalies of up to 0 7 nt in the radial magnetic m2 signal at sea level the anomalies are spatially heterogeneous and reach in extended areas 30 or more of the unperturbed tidal magnetic signal the anomalies should be detectable in long time series from magnetometers on land or at the ocean bottom the anomalies at satellite height 430 km reach 0 1 nt and pose a challenge for the precision of the swarm mission climate variability induced deviations in the tide system e g tidal velocities and phases are negligible changes in tidal magnetic fields are dominated by changes in seawater salinity and temperature therefore it is concluded that observations of tidal magnetic signals could be used as a tool to detect respective state changes in the ocean

isotope geochemistry of mercury and its relation to earthquake in the wenchuan earthquake fault scientific drilling project hole 1 wfsd 1 abstract based on the wenchuan earthquake fault scientific drilling project wfsd we first investigated the distribution of the total mercury thg from 600 m to 1035 m of wfsd hole 1 core wfsd 1 the concentrations of thg in the fault gouge are significantly higher than in the sandstone shale siltstone and cataclasite in wfsd 1 the thg concentrations in the main seismic fault zone range from 9 9 to 73 5 ng g while those under the main fault range from 20 5 to 36 ng g to determine the source of hg typical rocks from different depths were chosen for hg isotope analysis the results show that 202hg in the main seismic fault zone range from 0 11 to 2 68 and below the seismic fault zone 202hg are from 0 64 to 1 33 the seismic fault rocks are more enriched in thg and have a larger variation of 202hg compared to the other rocks mercury has different isotopic compositions and fractionation mechanisms in the fault zone which are mainly affected by the earthquake and the fluid the mercury isotope compositions reflect the fluid activities at the main fault zone we demonstrate that mercury stable isotope ratios could serve as an effective tool for tracing mercury sources and monitoring and predicting earthquakes

mercury distributions and mercury isotope signatures in sediments of dongjiang the pearl river delta china abstract the pearl river delta prd is one of the most industrialized and urbanized regions in china in order to assess the pollution status of mercury hg in prd river system the distribution of total mercury hgt and methylmercury me hg in sediment from a large river named dongjiang dj was for the first time investigated hgt concentrations in sediment increased from the upstream to downstream of dongjiang area and at most sites of dj were significantly higher than the background values which suggested that the dj was contaminated with hg especially in the downstream of dj me hg concentrations in sediment of dj ranged from 0 56 to10 62 ng g and were significantly correlated with hgt and organic matter in order to determine the potential hg contamination sources typical sediments from different parts of dj were chosen for hg isotope analysis the results showed that the mass dependent fraction mdf in the sediments varied significantly 202hg 2 35 to 0 60 and the mass independent fraction mif in the sediments also varied considerably 199hg 0 02 to 0 27 the samples with the highest hgt located in the industrial area had the highest 202hg 1 14 to 0 60 measured values and insignificant mif 199hg 0 04 to 0 01 meanwhile the samples with the lowest hgt located in the background area had the lowest 202hg 2 16 to 1 55 and 199hg 0 20 to 0 27 measured values unlike the above two cases are the samples located in the urban area which have relative lower mdf 202hg 2 35 to 1 96 and small but significant mif 199hg 0 10 to 0 08 with relative higher hgt we demonstrated that the dominant hg sources in dj sediments could be categorized as the regional background urban and industrial sources in our study we demonstrated that hg stable isotope method could serve as an effective tool for tracing mercury contamination sources in the environment

historical variations of mercury stable isotope ratios in arctic glacier firn and ice cores the concentration and isotopic composition of mercury hg were determined in glacier core samples from canadian arctic ice caps dating from pre industrial to recent time early 21st century mean hg levels increased from 0 2 ng l 1 in pre industrial time to 0 8 1 2 ng l 1 in the modern industrial era last 200 years hg accumulated on arctic ice caps has 199hg and 201hg that are higher 1 to 2 9 than previously reported for arctic snow mostly 1 impacted by atmospheric hg depletion events suggesting that these events contribute little to hg accumulation on ice caps the range of 202hg 199hg and 201hg in glacier cores overlaps with that of arctic hg0 g and of seawater in baffin bay but also with that of mid latitude precipitation and industrial hg sources including coal and hg ores a core from agassiz ice cap 80 7 n shows a 1 shift in 202hg over the 19th 20th centuries that could reflect changes in the isotopic composition of the atmospheric hg pool in the high arctic in response to growing industrial emissions at lower latitudes this study is the first ever to report on historical variations of hg stable isotope ratios in arctic ice cores results could help constrain future modeling efforts of the global hg biogeochemical cycle and the atmosphere s response to changing hg emissions past and future

a new method for sampling fumarolic gases analysis of major minor and metallic trace elements with ammonia solutions abstract a new method using ammonia solutions in pre evacuated quartz bottles has been experimented for volcanic gas sampling and analysing various tests reproducibility variability and comparison with known methods such as naoh pre evacuated bottles and acid condensates have been performed to check for their efficiency by using ammonia solutions acid gases st hcl hf carbon dioxide noncondensible gases n 2 ar and metallic trace elements mte can be measured with standard methods hplc gc titrimetry icp ms results show that acid gases co 2 and noncondensible gases are sampled and analysed with similar efficiency in nh 4 oh bottles than by using the known and accurate naoh method moreover a key point is that nh 4 oh solutions after undergoing adequate processing oxidation and acidification allow also precise mte measurements by using standard icp ms methods such mte measurements appear much more reliable than those performed on acid condensates pre evacuated ammonia bottles appear therefore as an optimum tool to collect volcanic gases and to obtain their complete chemical composition

mercury isotope fractionation in waters and sediments of the murray brook mine watershed new brunswick canada tracing mercury contamination and transformation abstract mercury isotope fractionation was investigated in different environmental compartments of a mining impacted ecosystem the watershed of the murray brook deposit in northern new brunswick canada mercury contaminated ground water surface water as well as sediment and samples of suspended particulate matter were collected alongside gossan creek downstream of mine tailings and analyzed for mercury isotopic composition while leachates from the tailings and ground water samples showed a uniform and similar mercury isotopic signature confirming the predominant role of the mining residues in the contamination of the surrounding environment samples collected from the surface flow system provided evidence of significant mass dependent fractionation of mercury with distance from the source as dissolved mercury contents steadily decreased from 31 1 to 1 4 g hg l 1 with distance from the headwaters of the stream 202hg in the creek water progressively increased resulting in a fractionation of 0 9 over 1 6 km as a result mercury isotopic ratios in the creek appeared to closely follow a rayleigh model assuming a constant fractionation factor reactant product of 1 00038 stream bed sediments also demonstrated an enrichment of heavy isotopes along the creek with an isotopic shift of 1 over the distance of gossan creek 3100 m although mercury losses from the water column result partly from partitioning to the sediments measured mercury isotopic ratios differences between dissolved and solid phases were likely small and this study did not observe significant fractionation due to partitioning processes results rather suggested that fractionation observed in the surface water system of gossan creek is most likely the result of a combined effect of reduction and volatilisation processes the lighter isotopes being preferentially reduced and evaporated from the water column additional sediment samples collected along reaches of eighteen mile brook and the upsalquitch river that receive water from gossan creek and from tributaries unaffected by the mine contamination were analyzed for mercury isotopic composition data obtained from those sediments clearly demonstrated that mercury derived from mining activities is isotopically different from mercury naturally present in the area measured isotopic differences can ultimately be employed to trace sources of mercury notwithstanding potential fractionation caused by natural transformation processes

meltwater routing and the younger dryas the younger dryas the last major cold episode on earth is generally considered to have been triggered by a meltwater flood into the north atlantic the prevailing hypothesis proposed by broecker et al 1989 nature 341 318 321 more than two decades ago suggests that an abrupt rerouting of lake agassiz overflow through the great lakes and st lawrence valley inhibited deep water formation in the subpolar north atlantic and weakened the strength of the atlantic meridional overturning circulation amoc more recently tarasov and peltier 2005 nature 435 662 665 showed that meltwater could have discharged into the arctic ocean via the mackenzie valley 4 000 km northwest of the st lawrence outlet here we use a sophisticated high resolution ocean sea ice model to study the delivery of meltwater from the two drainage outlets to the deep water formation regions in the north atlantic unlike the hypothesis of broecker et al freshwater from the st lawrence valley advects into the subtropical gyre 3 000 km south of the north atlantic deep water formation regions and weakens the amoc by 30 we conclude that meltwater discharge from the arctic rather than the st lawrence valley was more likely to have triggered the younger dryas cooling

a new collector for sampling volcanic aerosols abstract a new apparatus venturi effect system ves designed for sampling volcanic plumes is described and tested at vulcano italy this device together with purified basic nh 4 oh solutions supplies optimal conditions to obtain reliable s total cl f ratios and enrichment factors for metallic trace elements mte good concordance for acid gas ratios and metal enrichment factors in both the gas phase and the related plume allows the procedure to be validated the ves appears in vulcano conditions as a simple robust and easily portable apparatus that allows reliable collection of both acid gases and mte within a single sample and the analysis with current chemical methods high pressure liquid chromatography inductively coupled plasma mass spectrometry this apparatus may be suitable for more difficult volcanoes where only the plume can be sampled

the effect of arctic freshwater pathways on north atlantic convection and the atlantic meridional overturning circulation abstractthis study examines the relative roles of the arctic freshwater exported via different pathways on deep convection in the north atlantic and the atlantic meridional overturning circulation amoc deep water feeding the lower branch of the amoc is formed in several north atlantic marginal seas including the labrador sea irminger sea and the nordic seas where deep convection can potentially be inhibited by surface freshwater exported from the arctic the sensitivity of the amoc and north atlantic to two major freshwater pathways on either side of greenland is studied using numerical experiments freshwater export is rerouted in global coupled climate models by blocking and expanding the channels along the two routes the sensitivity experiments are performed in two sets of models cm2g and cm2m with different control simulation climatology for comparison freshwater via the route east of greenland is found to have a larger direct impact on labrador sea convection in response to the changes of

real time simultaneous detection of volcanic hg and so2 at la fossa crater vulcano aeolian islands sicily 1 measuring hg so2 ratios in volcanic emissions is essential for better apportioning the volcanic contribution to the global hg atmospheric cycle here we report the first real time simultaneous measurement of hg and so2 in a volcanic plume based on lumex and multigas techniques respectively we demonstrate that the use of these novel techniques allows the measurements of hg so2 ratios with a far better time resolution than possible with more conventional methods the hg so2 ratio in the plume of f0 fumarole on la fossa crater vulcano island spanned an order of magnitude over a 30 minute monitoring period but was on average in qualitative agreement with the hg so2 ratio directly measured in the fumarole mean plume and fumarole ratios being 1 09 10 6 and 2 9 10 6 respectively the factor 2 difference between plume and fumarole compositions provides evidence for fast hg chemical processing the plume

mercury stable isotope compositions in magmatic affected coal deposits new insights to mercury sources migration and enrichment abstract mercury hg is commonly present at trace levels in coal deposits geological processes particularly magmatic intrusion and hydrothermal cycling in coal bearing strata can significantly increase hg levels in coals however the effects of thermal stress magmatic components magmatic hydrothermal fluids low temperature hydrothermal fluids on hg enrichment are confounded in a magmatic affected coal basin here we demonstrate the use of stable hg isotopes to understand the controlling factors on hg enrichment in two well known chinese coal deposits affected by magmatic activities wulantuga low temperature hydrothermal altered coal deposit and wolonghu magmatic intruded coal deposit the wulantuga no 6 coal seam is extremely enriched in hg varying from 0 37 g g in middle coal benches to 40 90 g g in the upper most and lowest coal benches approximately 2 5 variation in mass dependent fractionation mdf 3 07 to 0 58 in 202hg is observed 202hg vs 1 hg diagram suggests a mixture of three hg end members original hydrothermal fluids fractionated hydrothermal fluids and native coal forming materials in addition wulantuga coals all show positive mass independent fractionation mif of odd isotopes up to 0 87 in 199hg and 0 66 in 201hg the 199hg 201hg ratios range from 1 3 to 3 3 suggesting that a large fraction of photodegraded methylmercury was likely incorporated into the coal deposit the magmatic intruded wolonghu no 8 coal seam is only slightly to intermediately enriched in hg varying from 0 10 g g to 0 40 g g the coals near the contact sill 5 cm 1 81 to 1 52 have similar 202hg as the magmatic sill rocks 2 05 to 1 80 both with insignificant mif values coals far from the contact sill 15 cm have 202hg values varying from 3 40 to 1 61 and 199hg varying from 0 26 to 0 58 which are significantly enriched in light and odd hg isotopes compared to coals near the contact sill 199hg and 201hg in wolonghu coals far from the contact sill resemble those of meteoritic waters and seawater in both magnitude and 199hg 201hg ratio our two case studies show significant mdf and mif of hg isotopes which inform on hg migration and sequestration in the magmatic rocks and coal deposits and on the roles of meteoric water and hydrothermal fluid circulation

mercury isotopic composition of hydrothermal systems in the yellowstone plateau volcanic field and guaymas basin sea floor rift abstract to characterize mercury hg isotopes and isotopic fractionation in hydrothermal systems we analyzed fluid and precipitate samples from hot springs in the yellowstone plateau volcanic field and vent chimney samples from the guaymas basin sea floor rift these samples provide an initial indication of the variability in hg isotopic composition among marine and continental hydrothermal systems that are controlled predominantly by mantle derived magmas fluid samples from ojo caliente hot spring in yellowstone range in 202hg from 1 02 to 0 58 0 11 2sd and solid precipitate samples from guaymas basin range in 202hg from 0 37 to 0 01 0 14 2sd fluid samples from ojo caliente display mass dependent fractionation mdf of hg from the vent 202hg 0 10 0 11 2sd to the end of the outflow channel 202hg 0 58 0 11 2sd in conjunction with a decrease in hg concentration from 46 6 pg g to 20 0 pg g although a small amount of hg is lost from the fluids due to co precipitation with siliceous sinter we infer that the majority of the observed mdf and hg loss from waters in ojo caliente is due to volatilization of hg0 aq to hg0 g and the preferential loss of hg with a lower 202hg value to the atmosphere a small amount of mass independent fractionation mif was observed in all samples from ojo caliente 199hg 0 13 1 0 06 2sd but no significant mif was measured in the sea floor rift samples from guaymas basin this study demonstrates that several different hydrothermal processes fractionate hg isotopes and that hg isotopes may be used to better understand these processes

local and remote impacts of a tropical atlantic salinity anomaly the climatic impacts of an enhanced evaporation prescribed during 50 years in the tropical atlantic are investigated in a coupled ocean atmosphere general circulation model locally the salinity increase leads to a rapid deepening and cooling of the surface mixed layer this induces a deepening of the equatorial undercurrent and an intensification of the south equatorial current a remote atmospheric response to the tropical atlantic perturbation is detected in the north atlantic sector after ten years it has the form of a robust wave like tropospheric perturbation seemingly excited by the weakening of atmospheric deep convection over the amazonian basin meanwhile the salt anomaly is carried northward by the mean oceanic circulation it is traced up to the convection sites and then on its return path at depth towards lower latitudes consistent with the density increase deep convection is enhanced after the arrival of the salt anomaly and the atlantic meridional overturning circulation amoc intensifies about 20 years after the beginning of the perturbation the adjustment of the tropical atlantic to the amoc intensification then modifies its initial response to the freshwater forcing leading to a weaker cooling in the northern tropical atlantic than in the southern tropical atlantic a slight northward shift of the tropical atlantic precipitation pattern and an intensification of the north brazil current on the other hand no significant anomalous precipitations are found in the pacific the initial remote atmospheric response is also modulated by an nao like response to the amoc intensification

the sensitivity of the atlantic meridional overturning circulation to freshwater forcing at eddy permitting resolutions the effect of increasing horizontal resolution is examined to assess the response of the atlantic meridional overturning circulation amoc to freshwater perturbations versions of a global climate model with horizontal resolutions ranging from 1 8 latitude 3 6 longitude to 0 2 0 4 are used to determine if the amoc response to freshwater forcing is robust to increasing resolution in the preindustrial equilibrium climate the representation of western boundary currents and meridional heat transport are improved with resolution freshwater forcings similar to the final drainage of proglacial lakes agassiz and ojibway are applied evenly over the labrador sea and exclusively along the western boundary the duration and maximum amplitude of model responses to freshwater forcing showed little sensitivity to increasing resolution an evaluation with tracers of the forcing impact on different regions of north atlantic deep water formation revealed the possibility that increases in labrador sea deep convection at higher resolution mitigate the effect of stronger boundary currents and enhanced mixing with increasing resolution there is less cooling in the subpolar west atlantic more cooling in the subpolar east atlantic and greater variability in the deep ocean response to the boundary forcing while differences exist the coarseresolution model response remains robust at finer horizontal resolutions

impact of freshwater release in the north atlantic under different climate conditions in an oagcm abstract the response of climate to freshwater input in the north atlantic na has raised a lot of concern about the issue of climate stability since the discovery of abrupt coolings during the last glacial period such coolings have usually been related to a weakening of the atlantic meridional overturning circulation amoc probably associated with massive iceberg surges or meltwater pulses additionally the recent increase in greenhouse gases in the atmosphere has also raised the possibility of a melting of the greenland ice sheet which may impact the future amoc and thereby the climate in this study the extent to which the mean climate influences the freshwater release linked to ice sheet melting in the na and the associated climatic response is explored for this purpose the simulations of several climatic states last interglacial last glacial maximum mid holocene preindustrial and future 2 co2 are considered and the climatic response to a freshwater input computed interactively acc

north pacific climate response to freshwater forcing in the subarctic north atlantic oceanic and atmospheric pathways abstract sudden changes of the atlantic meridional overturning circulation amoc are believed to have caused large abrupt climate changes over many parts of the globe during the last glacial and deglacial period this study investigates the mechanisms by which a large freshwater input to the subarctic north atlantic and an attendant rapid weakening of the amoc influence north pacific climate by analyzing four different ocean atmosphere coupled general circulation models gcms under present day or preindustrial boundary conditions when the coupled gcms are forced with a 1 sv sv 106 m3 s 1 freshwater flux anomaly in the subarctic north atlantic the amoc nearly shuts down and the north atlantic cools significantly the south atlantic warms slightly shifting the atlantic intertropical convergence zone southward in addition to this atlantic ocean atmosphere response all of the models exhibit cooling of the north pacific especially along the oceanic frontal zone consistent with paleoclimate recons

a box model test of the freshwater forcing hypothesis of abrupt climate change and the physics governing ocean stability 1 observations and an ocean box model are combined in order to test the adequacy of the freshwater forcing hypothesis to explain abrupt climate change given the uncertainties in the parameterization of vertical buoyancy transport in the ocean the combination is carried out using bayesian stochastic inversion which allows us to infer changes in the mass balance of northern hemisphere nh ice sheets and in the meridional transports of mass and heat in the atlantic ocean that would be required to explain dansgaard oeschger interstadials dois from 30 to 39 kyr b p the mean sea level changes implied by changes in nh ice sheet mass balance agree in amplitude and timing with reconstructions from the geologic record which gives some support to the freshwater forcing hypothesis the inversion suggests that the duration of the dois should be directly related to the growth of land ice our results are unaffected by uncertainties in the representation of vertical buoyancy transport in the ocean however the solutions are sensitive to assumptions about physical processes at polar latitudes

variations in the stable isotope composition of mercury in coal bearing sequences indications for its provenance and geochemical processes abstract mercury hg stable isotope variations provide a potential tool to better understand the provenance and geochemical processes that control hg occurrences in coal deposits in this study we explore the variations in hg isotope compositions in coal benches of a single coal seam no 3 1 coal seam daizhuang coal mine jining coalfield shandong province and in successive coals seams of a coal bearing sequence no 1 to no 11 2 coal seams zhuji coal mine huainan coalfield anhui province to assess hg isotopes as a hg biogeochemical tracer in coal deposits large variations in mass dependent hg isotope fractionation mdf were observed in both daizhuang and zhuji coal deposits with 202hg values ranging from 2 34 to 0 25 0 12 2 sd n 8 and from 1 62 to 0 44 0 12 2 sd n 18 respectively daizhuang coals showed insignificant mass independent hg isotope fractionation mif in most samples 0 04 to 0 12 0 08 for 199hg 2 sd n 8 whereas mif in the younger nos 7 11 coal seams of zhuji coals 0 06 to 0 22 0 08 for 199hg 2 sd n 7 were positive and significant increased trends in both hg concentrations and 202hg values going from older to younger zhuji coal seams were observed and were possibly related to variations in coal forming environment of different coal seams the significant negative correlations of 202hg vs 1 hg in the zhuji coals and of 202hg vs 199hg in the daizhuang coals suggest that hg isotopes can potentially be used to trace organic and inorganic hg end members in coal deposits natural coke a metamorphosed form of coal is on average two fold enriched in hg compared to coal indicating that hydrothermal fluids derived from magmatic intrusions bring hg into coal deposits in addition coke has either distinctly higher 0 70 to 0 91 0 12 2 sd n 2 or lower 202hg 4 00 to 3 47 0 12 2 sd n 3 than corresponding coals demonstrating that significant hg mdf occurred when coals were thermally contacted by intruded magmas

temporal geographical meltwater influences on the north atlantic conveyor implications for the younger dryas the temporal and geographical roles of meltwater discharge from the laurentide ice sheet on north atlantic deep water nadw production are investigated utilizing a global realistic geometry coupled climate model which does not require the use of flux adjustments model results suggest that preconditioning by meltwater discharge to the mississippi prior to the younger dryas yd is capable of pushing nadw beyond the limit of its sustainability the diversion of meltwater to the st lawrence then merely serves to completely inhibit nadw production the modeled change in surface air temperature generally agrees with the global pattern and magnitude of temperature change seen in paleoclimatic reconstructions of the yd and is intimately linked to changes in nadw formation the global thermohaline circulation provides an interhemispheric teleconnection with the southern oceans while changes in the atmospheric heat transport reacting to a global redistribution of oceanic heat transport provide a mechanism for interbasin teleconnection although the primary thermodynamic and hydrological cycle feedback processes are included within the atmospheric model in the absence of additional feedbacks an equilibrium without the presence of nadw is possible the inclusion of the wind stress speed feedback is found to significantly contribute to the resumption of nadw production as suggested by previous studies contrary to these same studies however the coupled model indicates an advective spin up timescale is required for resumption of nadw production and hence the termination of the modeled yd like climate event as opposed to a decadal century timescale the reason for the discrepancy is unclear but may be associated with the use of fixed salt flux fields applied in previous studies or the duration strength and geographical location of the imposed meltwater applied

h2s fluxes from mt etna stromboli and vulcano italy and implications for the sulfur budget at volcanoes abstract we present here new measurements of sulfur dioxide and hydrogen sulfide emissions from vulcano etna and stromboli italy made by direct sampling at vents and by filter pack and ultraviolet spectroscopy in downwind plumes measurements at the f0 and fa fumaroles on vulcano yielded so 2 h 2 s molar ratios of 0 38 and 1 4 respectively from which we estimate an h 2 s flux of 6 to 9 t d 1 for the summit crater for mt etna and stromboli we found so 2 h 2 s molar ratios of 20 and 15 respectively which combined with so 2 flux measurements suggest h 2 s emission rates of 50 to 113 t d 1 and 4 to 8 t d 1 respectively we observe that source and plume so 2 h 2 s ratios at vulcano are similar suggesting that hydrogen sulfide is essentially inert on timescales of seconds to minutes this finding has important implications for estimates of volcanic total sulfur budget at volcanoes since most existing measurements do not account for h 2 s emission

structure and variability of the west greenland current in summer derived from 6 repeat standard sections abstract six historical sections across the west greenland current are examined three sections have been regularly occupied since the late 1950s while the three southern ones have been taken since 1984 significant variability is observed for the freshwater core of the coastal current on the shelf with salinity varying by over 3 units between years there is also significant variability in the shape and offshore position of the main shelf break front leading to large variability in eulerian velocities significant presence of irminger water is seen during the 1960s and the 2000s being found right across the sections in recent years maximum mean transport relative to the 34 8 isohaline of 5 5 3 9 sv relative to 700 db for 1984 2005 is observed at the cape desolation section transports decrease to the north with the majority of the exchange with the interior of the labrador sea occurring between cape desolation and fylla bank inter decadal transport variability is observed at fylla bank while a decline in transports since peaks in the early 1990s is seen at cape farewell and cape desolation freshwater transport is largest at cape desolation with a mean summer transport of 60 2 20 5 msv freshwater transport increases slightly between cape farewell and cape desolation and we suggest it is related to local discharge by glaciers into juliannehaab bight as well as the melting of sea ice we also find that years of high greenland ice cap melt are consistently associated with years of high freshwater transport at cape desolation suggesting a portion of the freshwater transport of the west greenland current may be associated with melt from the greenland ice sheet finally significantly enhanced freshwater transports 33 msv at cape desolation compared to the long term mean are seen in 2008 probably a signature of the record arctic ocean ice melt and export in 2007

estimations of mercury fluxes emitted by mount etna volcano a sampling and measuring device which enables the assessment of atmospheric particulate and gaseous mercury concentrations has been tested on mount etna volcano particulate matter is collected on a whatman gf c of 1 0 m pore size gaseous mercury species on a au column the analysis is carried out in two steps 1 the mercury species collected on the filter or the au column are transferred to a fixed analytical au column 2 mercury liberated from this column during the second step is detected with a mercury vapour monitor average concentrations of gaseous and particulate mercury in ambient sampling sites on mount etna are 3 8 ng m 3 and 0 49 ng m 3 respectively average concentrations of gaseous and particulate mercury in the plume of bocca nuova on mount etna are 15 ng m 3 and 24 ng m 3 respectively an estimation of the total mercury discharge from mount etna amounts to 2 5 10 2 tons day 1

global mercury cycle during the end permian mass extinction and subsequent early triassic recovery abstract the end permian mass extinction epme at 252 ma was the most severe extinction in the phanerozoic marine ecosystems devastated by the epme had a highly prolonged recovery and did not substantially recover until after the smithian spathian substage boundary ssb of the lower triassic 5 to 9 ma after the epme while the siberian traps large igneous province stlip has been invoked as the driver of the mass extinction there remains controversy as to the cause of the protracted early triassic recovery although renewed stlip volcanism has been suggested these previous studies though have drawn conclusions based on geochemical records of sediments deposited in northern latitude settings to investigate the relationship between stlip and extinction recovery processes on a global base we examined mercury chemostratigraphy including mercury concentrations and isotopes from high southern latitude and equatorial sections that span the late permian changhsingian to early triassic spathian substage successions the guryul ravine section kashmir in northern india and the chaohu section in southern china organic and inorganic carbon isotope data define the epme horizon in the chaohu section and the ssb in the guryul ravine section respectively hg toc values are dramatically elevated approaching the epme horizon and maintain high values until the lower isarcicella isarcica conodont zone the base of which is believed to be the end of the mass extinction in the stratigraphically overlying beds hg toc generally displays lower values with slight fluctuations through the two sections these fluctuations are likely related to the increased terrestrial hg influx associated with strong chemical weathering in the early triassic as shown by a positive correlation between the contents of hg and al and by less positive 199 hg values in early triassic samples our data presenting the first southern hemisphere hg record from guryul ravine in combination with previous results indicates that anomalous high mercury deposition at the epme occurred globally the generally positive 199 hg values at this time reflects atmospheric derived hg consistent with a volcanic hg source which we suggest indicates global impact of stlip eruption in contrast there is no evidence for a global hg toc anomaly during the protracted early triassic biotic recovery suggesting that potentially renewed stlip volcanism had only a northern hemisphere influence on the global hg cycle this more limited impact may still have played a role in the delayed early triassic recovery

mercury isotope fractionation in fossil hydrothermal systems the hg isotopic compositions of samples throughout the vertical extent of two fossil hydrothermal systems were analyzed by multicollector inductively coupled plasma mass spectrometry results show 5 2 0 2 hg 1 9 8 hg relative to nist 3133 fractionation more than 50 times greater than the 0 1 2 external reproducibility of the analyses the hg isotope compositions from both hydrothermal systems can be grouped by dominant mineralogy and position 2 0 2 hg 1 9 8 hg values at the tops of the systems are 3 5 to 0 4 in cinnabar dominant sinter and 0 2 to 2 1 in metacinnabar dominant sinter and the underlying veins have 2 0 2 hg 1 9 8 hg values of 1 4 to 1 3 these differences probably resulted from the combination of boiling of the hydrothermal fluid oxidation near the surface and kinetic effects associated with mineral precipitation the natural variation in hg isotopic compositions observed in this study is higher than that expected from the trend of decreasing mass dependent fractionation with increasing mass extrapolated from stable isotope systems up to z 26 fe confirming that even the heaviest elements undergo significant stable isotope fractionation in hydrothermal systems

collateral variations between the concentrations of mercury and other water soluble ions in volcanic ash samples and volcanic activity during the 2014 2016 eruptive episodes at aso volcano japan abstract during 2014 2016 the aso volcano located in the center of the kyushu islands japan erupted and emitted large amounts of volcanic gases and ash two episodes of the eruption were observed firstly strombolian magmatic eruptive episodes from 25 november 2014 to the middle of may 2015 and secondly phreatomagmatic and phreatic eruptive episodes from september 2015 to february 2016 bulk chemical analyses on total mercury hg and major ions in water soluble fraction in volcanic ash fall samples were conducted during the strombolian magmatic eruptive episodes total hg concentrations averaged 1 69 0 87 ng g 1 n 33 with a range from 0 47 to 3 8 ng g 1 in addition the temporal variation of total hg concentrations in volcanic ash varied with the amplitude change of seismic signals in the aso volcano the volcanic tremors are always observed during eruptive stages and quiet interludes and the amplitudes of tremors increase at eruptive stages so the temporal variation of total hg concentrations could provide an indication of the level of volcanic activity during the phreatomagmatic and phreatic eruptive episodes on the other hand total hg concentrations in the volcanic ash fall samples averaged 220 88 ng g 1 n 5 corresponding to 100 times higher than those during the strombolian eruptive episode therefore it is possible that total hg concentrations in volcanic ash samples are largely varied depending on the eruptive type in addition the ash fall amounts were also largely different among the two eruptive episodes this can be also one of the factors controlling hg concentrations in volcanic ash

isotopic signatures of mercury contamination in latest permian oceans sedimentary records from the northwest margin of pangea and the tethys show anomalously high hg levels at the latest permian extinction boundary background 202 hg values are consistent with normal marine conditions but exhibit negative shifts coincident with increased hg concentrations hg isotope mass independent fractionation 199 hg trends are consistent with volcanic input in deep water marine environments in contrast nearshore environments have 199 hg signatures consistent with enhanced soil and or biomass input we hypothesize that the deep water signature represents an overall global increase in volcanic hg input and that this isotope signature is overwhelmed in nearshore locations due to hg from terrestrial sources high productivity nearshore regions may have experienced stressed marine ecosystems due to enhanced hg loading

mercury enrichments provide evidence of early triassic volcanism following the end permian mass extinction abstract oceanic environments and biotas were in a state of near continuous perturbation during the early triassic the 5 million year interval following the latest permian mass extinction lpme but the underlying cause s remain uncertain the role of episodic volcanic or intrusive magmatic activity in triggering global scale perturbations during this interval is suspected but has not been strongly evidenced to date here we investigate the record of volcanism through the early triassic with a focus on the smithian spathian boundary or ssb using mercury hg concentrations in marine sediments as a proxy this study examines five marine sections from three paleo oceans paleo tethys neo tethys and panthalassa representing a range of depositional settings from shallow platform to deep slope our results suggest that volcanic and magmatic activity of the siberian traps large igneous province stlip was most intense during the first 1 3 million years following the lpme and that termination of its most active stage was responsible for a sharp cooling event at the ssb variations in the intensity of stlip activity are thus likely to account for the large 8 fluctuations of 13ccarb and related changes in oceanic redox and environmental conditions that characterized the griesbachian to smithian substages of the early triassic in marine sections globally we hypothesize that a strong reduction or cessation of stlip activity at the ssb set the stage for the recovery of marine biodiversity and ecosystems in the spathian and later

mercury content and speciation in the phlegrean fields volcanic complex evidence from hydrothermal system and fumaroles abstract mercury is outstanding among the global environmental pollutants of continuing concern although degassing of active volcanic areas represents an important natural source of mercury into the atmosphere still little is known about the amount and behaviour of hg in volcanic aquifers especially regarding its chemical speciation in order to assess the importance of mercury emissions from active volcanoes thermal waters were sampled in the area surrounding la solfatara pozzuoli bay this is the most active zone of the phlegrean fields complex coastal area north west of naples with intense hydrothermal activity at present day studied groundwaters show total hg thg concentrations range from 56 to 171 ng l and are lower than the 1000 ng l threshold value for human health protection fixed by the world health organization who 1993 we also carefully discriminated the different aqueous species of hg in the collected water samples besides original data on hg determination in gaseous manifestations at la solfatara crater are also reported we measured volcanogenic mercury concentration and hg s tot ratio both in the volcanic plume and in fumarolic condensates in order to better constrain hg reactivity once emitted into the atmosphere data on hg s tot reveal that there is no significant difference between hg volcanic composition at the venting source fumaroles and in near vent diluted volcanic plumes 1 6 10 5 and 1 9 10 5 respectively suggesting that there is limited hg chemical processing in volcanic fumarole plumes at least on the timescales of a few seconds investigated here combining the mean fumaroles hg co 2 mass ratio of about 1 3 10 8 molar ratio 2 1 10 9 with the hydrothermal soil diffuse co 2 degassing of the area the annual hg flux from la solfatara is estimated as 7 kg y 1 0 007 t y 1 current mercury emission from la solfatara volcano represents a very small contribution to the estimated global volcanic budget for this element and the estimated hg flux is considerably lower than that estimated from open conduit active basaltic volcanoes

isopycnal mixing in ocean circulation models abstract a subgrid scale form for mesoscale eddy mixing on isopycnal surfaces is proposed for use in non eddy resolving ocean circulation models the mixing is applied in isopycnal coordinates to isopycnal layer thickness or inverse density gradient as well as to passive scalars temperature and salinity the transformation of these mixing forms to physical coordinates is also presented

global mercury flux from volcanic and geothermal sources abstract the global hg flux from natural sources is poorly known we present data on hg levels in volcanic fumaroles that in combination with sulfur analyses and published so 2 flux data lead to new global hg flux estimates the volcanogenic hg flux from passively degassing volcanoes is small 30 mg hg yr the flux from erupting volcanoes is much larger but less well constrained we estimate it at about 800 mg yr these data are interpreted as evidence for early hg degassing from magmas geothermal sources contribute roughly 60 mg yr hg to the atmosphere an estimate based on average hg contents of hot springs and global convective heat transport total natural hg emissions from land amount to 1290 mg yr including a revised soil vapor flux of 400 mg yr estimates of anthropogenic contributions to the atmospheric hg budget vary between 3000 and 11 500 mg yr and are substantial compared to our natural hg flux estimate

the sensitivity of the atlantic meridional overturning circulation to enhanced freshwater discharge along the entire eastern and western coast of greenland the possible responses of the atlantic meridional overturning circulation amoc to increased freshwater discharge along the greenland coast has become an issue of growing concern given the increasing rate of the greenland ice sheet gris melting a recent model study suggested a weakened amoc of about 13 30 when a freshwater anomaly of 0 1 sv 1 sv 106 m3 s 1 was released along the entire greenland coast during the late twentieth century 1965 2000 in this study we use a fully coupled climate model to examine the sensitivity of amoc to a similar amount of freshwater forcing but released separately along the eastern the western and the entire greenland coast our results show that in all three cases there is a general weakening of the amoc mainly due to a reduced formation of labrador sea water moreover when additional freshwater is released along the eastern coast of greenland the amoc weakens more compared to the other two cases the different degree of convective mixing reduction in the irminger sea is the main reason for the spread in amoc responses in the three freshwater hosing experiments compared to the other two experiments the eastern coast experiment shows a relative warming in the labrador sea and the generation of a negative greenland tip jet like wind pattern anomaly these anomalies lead to a weaker convective mixing in the southern irminger sea and result subsequently in less formation of the simulated upper labrador sea water ulsw in the eastern coast experiment this study therefore highlights a potential important role for ulsw formation in determining the sensitivity of the amoc in response to large gris melting

acid gas and metal emission rates during long lived basalt degassing at stromboli volcano the discharge of acid gases and metals from stromboli is determined from airborne and ground based filter sampling of particulate matter in the volcanic plume combined with cospec measurements of so2 fluxes smaller particle sizes and high enrichment factors distinguish the most volatile elements by order s se br cl cd bi in as sb sn f au pb cr cu from those strictly fe mn ree sc sr th ti v or mainly al ba ca co k na u derived from volcanic ash time averaged volatile fluxes show that stromboli is a representative arc emittor producing 1 2 of the global volcanic budget of sulfur halogens and several trace metals while 15 25 of volcanic emissions of bi cd cs pb and sn in southern italy subaerial degassing of its s cl rich shoshonitic magma over the last 2 ky of similar activity may have released as much copper and gold as is encountered in magma derived high sulfidation ore deposits

warming of the subpolar atlantic triggered by freshwater discharge at the continental boundary 1 the traditional view is that widespread discharge of freshwater into the north atlantic leads to a reduction of the atlantic meridional overturning circulation amoc a concomitant reduction of poleward heat transport and a cooling of the climate of the north atlantic here we report upon coupled atmosphere ocean general circulation model experiments that suggest a more non uniform response of the north atlantic climate to large freshwater perturbations we show that in a cold climate with extensive sea ice coverage in the labrador sea a massive discharge of freshwater along coastal boundaries leads to an anomalous warming in the western north atlantic the warming persist despite a significant weakening of the amoc and its associated heat transport it is maintained by major reorganizations of the large scale wind field oceanic circulation and convection in the subpolar atlantic

sources of mercury to san francisco bay surface sediment as revealed by mercury stable isotopes abstract mercury hg concentrations and isotopic compositions were examined in shallow water surface sediment 0 2 cm from san francisco sf bay to determine the extent to which historic hg mining contributes to current hg contamination in sf bay and to assess the use of hg isotopes to trace sources of contamination in estuaries inter tidal and wetland sediment had total hg hgt concentrations ranging from 161 to 1529 ng g with no simple gradients of spatial variation in contrast inter tidal and wetland sediment displayed a geographic gradient of 202hg values ranging from 0 30 in the southern most part of sf bay draining the new almaden hg district to 0 99 in the northern most part of sf bay near the sacramento san joaquin river delta similar to sf bay inter tidal sediment surface sediment from the alviso slough channel draining into south sf bay had a 202hg value of 0 29 while surface sediment from the cosumnes river and sacramento san joaquin river delta draining into north sf bay had lower average 202hg values of 0 90 and 0 75 respectively this isotopic trend suggests that hg contaminated sediment from the new almaden hg district mixes with hg contaminated sediment from a low 202hg source north of sf bay tailings and thermally decomposed ore calcine from the new idria hg mine in the california coast range had average 202hg values of 0 37 and 0 03 respectively showing that hg calcination fractionates hg isotopes resulting in hg contamination from hg ii mine waste products with higher 202hg values than metallic hg 0 produced from hg mines thus there is evidence for at least two distinct isotopic signals for hg contamination in sf bay hg associated with calcine waste materials at hg mines in the coast range such as new almaden and new idria and hg 0 produced from these mines and used in placer gold mines and or in other industrial processes in the sierra nevada region and sf bay area

isotope geochemistry of mercury in source rocks mineral deposits and spring deposits of the california coast ranges usa abstract we present here the first study of the isotopic composition of mercury in rocks ore deposits and active spring deposits from the california coast ranges a part of earth s crust with unusually extensive evidence of mercury mobility and enrichment the franciscan complex and great valley sequence which form the bedrock in the california coast ranges are intruded and overlain by tertiary volcanic rocks including the clear lake volcanic sequence these rocks contain two types of mercury deposits hot spring deposits that form at shallow depths the franciscan complex and great valley sequence contain clastic sedimentary rocks with higher concentrations of mercury than volcanic rocks of the clear lake volcanic field mean mercury isotopic compositions 202hg for all three rock units are similar although the range of values in franciscan complex rocks is greater than in either great valley or clear lake rocks hot spring and silica carbonate mercury deposits have similar average mercury isotopic compositions that are indistinguishable from averages for the three rock units although 202hg values for the mercury deposits have a greater variance than the country rocks precipitates from spring and geothermal waters in the area have similarly large variance and a mean 202hg value that is significantly lower than the ore deposits and rocks these observations indicate that there is little or no isotopic fractionation