tracking the arctic s shrinking ice cover another extreme september minimum in 2004 1 satellite passive microwave observations document an overall downward trend in arctic sea ice extent and area since 1978 while the record minimum observed in september 2002 strongly reinforced this downward trend extreme ice minima were again observed in 2003 and 2004 although having three extreme minimum years in a row is unprecedented in the satellite record attributing these recent trends and extremes to greenhouse gas loading must be tempered by recognition that the sea ice cover is variable from year to year in response to wind temperature and oceanic forcings

provenancing and archaeology of roman millstones from the mediterranean area abstract roman rotary grain mills in the mediterranean area are mainly of two styles hourglass shaped pompeian style mills and flatter cylindrical millstones many of these millstones are made of igneous rocks imported to the sites where the mills are found and they may therefore be important indicators of resource procurement and trade if the source of the rock of manufacture can be traced three types of igneous rock were used to make millstones 1 reddish rhyolitic ignimbrite 2 leucite phyric lavas and 3 generally fresh grey vesicular lavas of basic intermediate composition potential source rocks and millstones of all three types of rock were characterized using petrographic examination in thin section and chemical analysis for major and 15 trace elements determined by low dilution fusion wavelength dispersive x ray fluorescence analysis one hundred and forty six millstones and lavas from archaeological contexts were studied and 113 of these were successfully assigned to geological sources sixteen areas of igneous rocks were used by the romans for millstone production these include the basic and intermediate composition grey vesicular lavas of olot northeast spain agde southern france volvic and possibly the le puy area central and southeast france respectively vulture italy etna and monti iblei in sicily pantelleria sardinia ustica the aeolian islands nisyros aegean libya and the middle atlas and rif areas of morocco the red rhyolite was quarried at the village of mulargia in sardinia and the leucite phyric rocks originated on the italian mainland including the quarry of orvieto in umbria there is a wide variation in size and style of millstones from individual production centres and some were exported in unfinished form grey vesicular millstones were traded up to at least 820 km from their sources and fall into four mainly separate distributions in the mediterranean the mulargia rhyolite and the leucitites were moved mainly from north to south were traded further than the grey vesicular rocks and were probably the most desirable types they are found 1350 and 1500 km distant from their sources respectively the millstones were moved mainly by sea perhaps on grain collecting ships on outward voyages from italy to the south and west of the mediterranean

a 21 year record of arctic sea ice extents and their regional seasonal and monthly variability and trends satellite passive microwave data have been used to calculate sea ice extents over the period 1979 1999 for the north polar sea ice cover as a whole and for each of nine regions over this 21 year time period the trend in yearly average ice extents for the ice cover as a whole is 32 900 6 100 sq km yr 2 7 0 5 decade indicating a reduction in sea ice coverage that has decelerated from the earlier reported value of 34 000 8 300 sq km yr 2 8 0 7 decade for the period 1979 1996 regionally the reductions are greatest in the arctic ocean the kara and barents seas and the seas of okhotsk and japan whereas seasonally the reductions are greatest in summer for which season the 1979 1999 trend in ice extents is 41 600 12 900 sq km yr 4 9 1 5 decade on a monthly basis the reductions are greatest in july and september for the north polar ice cover as a whole in september for the arctic ocean in june and july for the kara and barents seas and in april for the seas of okhotsk and japan only two of the nine regions show overall ice extent increases those being the bering sea and the gulf of st lawrence for neither of these two regions is the increase statistically significant whereas the 1079 1999 ice extent decreases are statistically significant at the 99 confidence level for the north polar region as a whole the arctic ocean the seas of okhotsk and japan and hudson bay

sea ice melt onset associated with lead opening during the spring summer transition near the north pole in the central arctic ocean autonomous observations of the ocean mixed layer and ice documented the transition from cold spring to early summer in 2011 ice motion measurements using gps drifters captured three events of lead opening and ice ridge formation in may and june satellite sea ice concentration observations suggest that locally observed lead openings were part of a larger scale pattern we clarify how these ice deformation events are linked with the onset of basal sea ice melt which preceded surface melt by 20 days observed basal melt and ocean warming are consistent with the available input of solar radiation into leads once the advent of mild atmospheric conditions prevents lead refreezing we use a one dimensional numerical simulation incorporating a local turbulence closure scheme to investigate the mechanisms controlling basal melt and upper ocean warming according to the simulation a combination of rapid ice motion and increased solar energy input at leads promotes basal ice melt through enhanced mixing in the upper mixed layer while slow ice motion during a large lead opening in mid june produced a thin low density surface layer this enhanced stratification near the surface facilitates storage of solar radiation within the thin layer instead of exchange with deeper layers leading to further basal ice melt preceding the upper surface melt

influence of granite mineralogy rainfall vegetation and relief on stream water chemistry vosges mountains north eastern france abstract the influence of rock mineralogy climate vegetation and relief on stream water composition and export as a result of weathering is a major scientific concern both at the local scale because of the link between stream chemistry and biodiversity and at the global scale in relation to global climate changes environmental factors influencing stream chemistry at baseflow were studied for 95 forested catchments located in the granite part of the vosges mountains ne france mean annual rainfall slope altitude catchment area forest cover and granite composition were attributed to each catchment using a geographic information system gis and spatially distributed databases these variables were then used to model stream water concentrations in so4 ca mg k na si anc acid neutralizing capacity and ph via linear regression analyses sulfate concentration is mainly negatively correlated to the mean altitude of the catchment silica and na concentrations are strongly correlated and negatively related to the mean annual rainfall and not to altitude ph is positively related to the sum of ca mg and k but not to so4 for any type of granite ca mg and ph are generally negatively related to the mean annual rainfall and positively related to the catchment area calcium is best explained by the rock content in hornblende mg by the rock contents of biotite and hornblende k by the content in k feldspar nevertheless models differ for each granite type in relation to the availability of weatherable minerals and probably to water pathways this study shows the interest of spatial analysis methods for understanding stream water concentrations at the mountain range scale in combination with local process studies and modelling at the catchment scale

platelet ice the southern ocean s hidden ice a review basal melt of ice shelves is not only an important part of antarctica s ice sheet mass budget but it is also the origin of one of the most peculiar types of sea ice found in the polar oceans platelet ice in many regions around coastal antarctica tiny ice crystals form and grow in supercooled plumes of ice shelf water releasing heat into the surrounding ocean they usually rise towards the surface eventually becoming trapped under an ice shelf as marine ice frequently masses of those crystals are advected out of the ice shelf cavity and accumulate below a solid sea ice cover to form a semiconsolidated layer when the overlying sea ice grows into this so called sub ice platelet layer the loose crystals are consolidated adding additional thickness to the sea ice these phenomena are generally referred to as platelet ice although confusion about the terminology is widespread in the literature the presence of platelet ice has a profound impact on sea ice properties and processes in several regions of antarctica with numerous implications for the local polar marine biosphere most notably sub ice platelet layers provide a stable sheltered nutrient and food rich habitat which usually results in a highly productive and uniquely adapted ecosystem it has also been hypothesised that platelet ice may be an indicator of the state of an ice shelf although comprehensive time series are limited to the ross sea this paper clears up the terminology by providing exact definitions of the relevant terms we review platelet ice formation observational methods as well as geographical and seasonal occurrence the physical properties and ecological implications are merged in a way understandable for physicists and biologists alike to lay the foundation for the interdisciplinary research that is necessary to tackle the current knowledge gaps

the strontium isotopic budget of himalayan rivers in nepal and bangladesh abstract himalayan rivers have very unusual sr characteristics and their budget cannot be achieved by simple mixing between silicate and carbonate even if carbonates are radiogenic we present sr o and c isotopic data from river and rain water bedload and bedrock samples for the western and central nepal himalaya and bangladesh including the monsoon season central himalayan rivers receive sr from several sources carbonate and clastic tethyan sediments high himalayan crystalline hhc gneisses and granitoids with minor marbles carbonates and metasediments of the lesser himalaya lh and miocene recent foreland basin sediment from the siwaliks group and the modern flood plain in the tethyan himalaya rivers have dissolved sr 6 mol l and 87sr 86sr 0 717 with a large contribution from moderately radiogenic carbonate rivers draining hhc gneisses are very dilute with sr 0 2 mol l and 87sr 86sr 0 74 lesser himalayan streams also have low sr 0 4 mol l and are highly radiogenic 87sr 86sr 0 78 highly radiogenic carbonates of the lh do not contribute significantly to the sr budget because they are sparse and have very low sr in large rivers exiting the himalaya sr systematics can be modeled as a mixture between tethyan rivers where slightly radiogenic carbonates mean 87sr 86sr 0 715 are the main source of sr and lesser himalaya waters where extremely radiogenic silicates 0 8 are the main source of sr hhc waters are less important because of their low sr rivers draining the siwaliks foreland basin sediments have sr 4 mol l and 87sr 86sr 0 725 weathering of silicates in the siwaliks and the flood plain results in a probably significant radiogenic 0 72 0 74 input to the ganges and brahmaputra g b but quantification of this flux is limited by uncertainties in the hydrologic budget the g b in bangladesh show strong seasonal variability with low sr and high 87sr 86sr during the monsoon sr in the brahmaputra ranges from 0 9 mol l and 0 722 in march to 0 3 mol l and 0 741 in august we estimate the seasonally weighted flux from the g b to be 6 5 108 mol yr with 87sr 86sr 0 7295

delineation of intrabasin structure in a dilational jog of the san jacinto fault zone southern california three high resolution seismic reflection lines were acquired in the northern part of the san jacinto graben the graben a pull apart basin formed by a dilational right step of the san jacinto fault zone has been previously interpreted as a simple rhombochasm the reflection survey located at least one significant and previously unidentified intrabasin fault referred to here as the farm road strand this fault lies approximately halfway between the claremont and casa loma strands of the san jacinto fault zone at the north end of the basin the southwestern boundary of the graben is interpreted to be the newly identified farm road strand and not the casa loma strand as was previously thought the identification of this intrabasin fault allows us to infer that the san jacinto basin comprises coalescing subbasins and is not a simple pull apart basin with an unusually large length width ratio the distances between the en echelon casa loma farm road and claremont strands are between 1 and 2 km this close spacing would likely permit an earthquake rupture to jump between strands and thus propagate through the san jacinto basin

sea ice mass balance observations from the north pole environmental observatory in recent years the periphery of the arctic sea ice cover has undergone significant changes with a reduction in summer ice extent a thinning of the ice and a shift from multiyear to first year ice here we examine sea ice conditions during nine summers between 2000 and 2013 in the interior of the ice pack using autonomous measurements of sea ice mass balance deployed near the north pole results exhibit no definitive trends there is large interannual variability with surface melt ranging from 0 02 m to 0 50 m and bottom melt from 0 10 m to 0 57 m the largest amounts of bottom melt have occurred in the past few years for all 9 years the ice at the end of the melt season was at least 1 2 m thick

northern latitude chemical weathering rates clues from the mackenzie river basin canada abstract the main scope of this study is to investigate parameters controlling chemical weathering rates for a large river system submitted to subarctic climate more than 110 river water samples from the mackenzie river system northern canada have been sampled and analyzed for major and trace elements and sr isotopic ratios in the dissolved phase the three main morphological units are reflected in water chemistry rivers from the canadian shield are very dilute dominated by silicate weathering millot et al 2002 whereas the rivers of the rocky and mackenzie mountains as well as the rivers of the sedimentary interior platform are dominated by carbonate weathering and are so 4 rich compared to the rivers of the mackenzie and rocky mountains the rivers of the interior plains are organic silica and na rich and constitute the dominant input term to the mackenzie river mainstream rivers of the canadian shield area do not significantly contribute to the mackenzie river system using elemental ratios and sr isotopic ratios a mathematical inversion procedure is presented that distinguishes between solutes derived from silicate weathering and solutes derived from carbonate weathering carbonate weathering rates are mostly controlled by runoff which is higher in the mountainous part of the mackenzie basin these rates are comparable to the carbonate weathering rates of warmer areas of the world it is possible that part of the carbonate weathering is controlled by sulfide oxidative weathering but its extent remains difficult to assess conversely to what was stated by edmond and huh 1997 overall silicate weathering rates in the mackenzie basin are low ranging from 0 13 to 4 3 tons km 2 yr na k ca mg and confirm the negative action of temperature on silicate weathering rates for river basins in cold climates in contrast to what has been observed in other large river systems such as the amazon and ganges rivers silicate weathering rates appear 3 to 4 times more elevated in the plains than in the mountainous headwaters this contradicts the raymo hypothesis raymo and ruddiman 1992 isotopic characterization of suspended material clearly shows that the higher weathering rates reported for the plains are not due to the weathering of fine sediments produced in the mountains e g by glaciers and deposited in the plains rather the relatively high chemical denudation rates in the plains are attributed to lithology uncompacted shales high mechanical denudation and the abundance of soil organic matter derived from incomplete degradation and promoting crystal lattice degradation by element complexation the three to fourfold factor of chemical weathering enhancement between the plains and mountains is similar to the fourfold factor of enhancement found by moulton et al 2000 between unvegetated and vegetated watershed this study confirms the negative action of temperature on silicate weathering for cold climate but shows that additional factors such as organic matter associated with northern watersheds are able to counteract the effect of temperature this acceleration by a factor of 4 in the plains is equivalent to a 6 c increase in temperature

the mechanical properties of macrolithic artifacts a methodological background for functional analysis natural technical and social factors led to the use of a wide range of rocks for the production of macrolithic artifacts during the later prehistory in the case of some artifact types such as the grinding stones rocks with very different petrographic qualities appear analysis of the material behavior as developed by material sciences provides a tool which allows the translation of these petrographic characteristics into mechanical properties experiments with a group of rocks subjected to different forms of abrasion in industrial machines allow an evaluation of the adjustment between the mechanical properties of the rock and the functions for which they were chosen by prehistoric societies finally the understanding of the mechanical properties of the raw materials together with their forms of exploitation distribution and use allows the designation of social and economic meaning to the production systems linked to the macrolithic tools

natural variations of δ30si ratios during progressive basalt weathering hawaiian islands abstract silicon stable isotopes can be used to trace the biogeochemical pathways of si as it moves from its continental sources to its sink in ocean sediments along the way si is incorporated into clay minerals taken up by plants where it forms plant opal and leached into rivers the major land to ocean conduit compared to igneous rocks the waters that drain continents are enriched in heavy si isotopes but the mechanisms that control fractionation have not been elucidated we studied si isotope fractionation along a 4 million yr basaltic soil chronosequence on the hawaiian islands using the natural context of these samples in combination with laboratory experiments we demonstrate that the isotopic composition of dissolved si in weathering systems is determined by the combined effects of rock disintegration clay mineral neosynthesis and si biocycling weathering preferentially releases 28si into solution whereas secondary mineral formation preferentially removes 28si from solution in humid environments leached soils have lost large amounts of this soluble si thus creating a net loss of 30si from the entire soil system as soils develop and greater fractions of si reside in neoformed clay minerals 30sibulk soil values change progressively toward more negative values basalt 30si values are about 0 5 but older soils have 30si values up to 2 5 the difference between the solid and solution 30si values remains more or less constant with progressive weathering and therefore soil water from older soils has a more negative 30si composition in the upper horizons of the hawaiian soils this weathering driven 30si shift is modified by the addition of unweathered primary minerals via dust carrying 30si values of about 0 5 and by biocycling of si via plants producing negative 30si values in phytoliths and positive 30si values in soil solutions derived from upper horizons due to the high concentrations of dissolved si in these near surface layers rivers have more positive 30si values than predicted based on the weathering status of the lower horizons when combined with published 30si values from large rivers worldwide we find that the results from hawaii point to weathering control of si isotopes delivered to the oceans and thus to an important continent ocean linkage that warrants further investigation

seasonal ice mass balance buoys adapting tools to the changing arctic monitoring the local mass balance of arctic sea ice provides opportunities to attribute the observed changes in a particular floe s mass balance to specific forcing phenomena a shift from multi year to seasonal ice in large portions of the arctic presents a challenge for the existing lagrangian array of autonomous ice mass balance buoys which were designed with a perennial ice cover in mind this work identifies the anticipated challenges of operation in seasonal ice and presents a new autonomous buoy designed to monitor ice mass balance in the seasonal ice zone the new design presented incorporates features which allow the buoy to operate in thin ice and open water and reduce its vulnerability to ice dynamics and wildlife damage while enhancing ease of deployment a test deployment undertaken from april to june 2009 is discussed and results are presented with analysis to illustrate both the features and limitations of the buoy s abilities

validating icesat over thick sea ice in the northern canada basin only in the past eight years has the feasibility of using satellite borne altimeters to estimate sea ice freeboard and thickness been demonstrated and these estimates still have uncertainties primarily associated with limited knowledge of snow loading on sea ice because accurate estimates of arctic wide sea ice thickness and volume are fundamental inputs to global climate models validation of satellite derived thickness estimates using independent data is required a detailed assessment of freeboard retrieved by the geoscience laser altimeter system glas aboard the ice cloud and land elevation satellite has been carried out using high resolution laser altimetry from the national aeronautics and space administration s airborne topographic mapper atm the delay doppler radar altimeter and digital photography collected along a 300 km segment of sea ice in the canada basin exploiting the repeat coverage of the aircraft flight line a correction was applied to glas footprint geolocations to adjust for sea ice drift that occurred during the time between satellite and aircraft acquisitions comparisons of glas and atm measurements over sea ice show excellent agreement about a 0 00 m mean with no apparent bias between data sets freeboard estimates were examined using data from glas and atm independently employing measurements over refrozen leads to estimate local sea surface heights sshs the results demonstrate the sensitivity of freeboard and thickness calculations to an accurate estimation of local ssh snow depth derived by differencing laser and radar data was combined with the freeboard estimates to yield a mean sea ice thickness of 5 5 m over a 250 km subsection of the flight track

the composition of the continental river weathering flux deduced from seawater mg isotopes this study establishes the magnesium isotopic composition of seawater and evaluates its constancy as a function of depth and geographic location it also provides results on the magnesium isotopic composition of river water samples draining specific lithologies in combination the results are used to obtain an average magnesium isotopic composition of 1 54 for the global continental weathering flux compared to the 2 value of the global ocean both relative to nist srm 980 analyses of modern and fossil carbonate secreting echinoderms suggest that these can serve as archives of seawater 26mg values it is demonstrated that these records of the magnesium isotopic composition of ancient oceans can be used to make important inferences about the relative contribution of different lithologies to the global continental weathering flux particularly carbonate versus silicate weathering preliminary results suggest that the composition of the continental weathering flux has not undergone dramatic changes during the phanerozoic

from points to poles extrapolating point measurements of sea ice mass balance the amount of ice growth and ablation are key measures of the thermodynamic state of the ice cover while ice extent and even ice thickness can be determined using remote sensing techniques this is not the case for the mass balance mass balance measurements require an ability to attribute the change establishing whether a change in the thickness of the ice cover occurs at the top or bottom surface and whether it is a result of growth or ablation we have developed and implemented a tool that can be used to measure thermodynamic changes in sea ice mass balance at individual locations the ice mass balance buoy imb the primary limitation of the imb is that it provides a point measurement of the ice mass balance defined by a particular combination of snow and ice conditions determining if and how such point measurements can be extrapolated is critical to understanding the large scale mass balance of the sea ice cover we explore the potential for extrapolation using mass balance observations from the surface heat budget of the arctic sheba field experiment during sheba mass balance measurements were made at over 100 sites covering a 100 km 2 area results indicate that individual point measurements can provide reasonable estimates for undeformed and unponded multi year ice which represented more than two thirds of the ice cover at sheba and is the dominant ice type in the perennial pack a key is carefully selecting a representative location for the instrument package the contribution of these point measurements can be amplified by integrating them with other tools designed to measure ice thickness and assimilating these combined data into sea ice models

arctic wide sea ice thickness estimates from combining satellite remote sensing data and a dynamic ice ocean model with data assimilation during the cryosat 2 period exploiting the complementary character of cryosat 2 and soil moisture and ocean salinity satellite sea ice thickness products daily arctic sea ice thickness estimates from october 2010 to december 2016 are generated by an arctic regional ice ocean model with satellite thickness assimilated the assimilation is performed by a local error subspace transform kalman filter coded in the parallel data assimilation framework the new estimates can be generally thought of as combined model and satellite thickness cmst it combines the skill of satellite thickness assimilation in the freezing season with the model skill in the melting season when neither cryosat 2 nor soil moisture and ocean salinity sea ice thickness is available comparisons with in situ observations from the beaufort gyre exploration project ice mass balance buoys and the nasa operation icebridge demonstrate that cmst reproduces most of the observed temporal and spatial variations results also show that cmst compares favorably to the pan arctic ice ocean modeling and assimilation system product and even appears to correct known thickness biases in the pan arctic ice ocean modeling and assimilation system due to imperfect parameterizations in the sea ice model and satellite thickness retrievals cmst does not reproduce the heavily deformed and ridged sea ice along the northern coast of the canadian arctic archipelago and greenland with the new arctic sea ice thickness estimates sea ice volume changes in recent years can be further assessed

surface freshening in the arctic ocean s eurasian basin an apparent consequence of recent change in the wind driven circulation 1 data collected by an autonomous ice based observatory that drifted into the eurasian basin between april and november 2010 indicate that the upper ocean was appreciably fresher than in 2007 and 2008 sea ice and snowmelt over the course of the 2010 drift amounted to an input of less than 0 5 m of liquid freshwater to the ocean comparable to the freshening by melting estimated for those previous years while the observed change in upper ocean salinity over the melt period implies a freshwater gain of about 0 7 m results of a wind driven ocean model corroborate the observations of freshening and suggest that unusually fresh surface waters observed in parts of the eurasian basin in 2010 may have been due to the spreading of anomalously fresh water previously residing in the beaufort gyre this flux is likely associated with a 2009 shift in the large scale atmospheric circulation to a significant reduction in strength of the anticyclonic beaufort gyre and the transpolar drift stream

geochemistry and water dynamics ii trace metals and pb sr isotopes as tracers of water movements and erosion processes abstract a dynamic scheme for water movements over a flood in a small watershed was proposed in a previous paper ben othman d luck j m tournoud m g 1997 geochemistry and water dynamics application to short time scale flood phenomena in a small mediterranean catchment i alkalis alkali earths and sr isotopes chem geol 140 9 28 based on major alkali alkali earth trace elements and sr isotopes in the present paper metal contents and pb isotope data are reported for the same samples and compared to natural and anthropogenic local sources analysed for this purpose water treatment plants have stable 206 pb 204 pb but show relatively large 207 pb 204 pb variations presumably related to yet unidentified industrial pb sources some cu zn rich chemicals used extensively on vineyards have unradiogenic 206 pb 204 pb around 17 7 local rains sampled over two years show roughly similar low values pb from rocks is variable and more radiogenic 206 pb 204 pb 18 8 22 8 except for the first hours trace element concentrations in the dissolved load are similar to or slightly higher than those observed over the year and similar to other moderately anthropogenic areas shiller a m boyle e a 1987 variability of dissolved trace metals in the mississippi river geochim cosmochim acta 51 3273 3277 for pb 0 05 0 45 nm zn 10 75 nm and cd 0 03 0 18 nm dissolved u and co show simple variations correlated to carbonate related to local natural sources most trace elements in the particulate load are strongly correlated lead isotopes in the dissolved and particulate loads show ranges over the flood again similar to those observed over the year 206 pb 204 pb 17 9 18 3 implying the same sources the very good alignments observed in 207 pb 204 pb and 208 pb 204 pb vs 206 pb 204 pb diagrams especially for the particulate are interpreted as mixing phenomena generally pb isotopic signature of the dissolved load is less radiogenic than the particulate indicating differences in sources or proportions and absence of isotopic equilibration with respect to the time of transfer pb isotopes shift regularly with time away from the road runoff endmember towards more radiogenic values the strong negative correlation between pb isotopes in the particulate load and sr isotopes in the dissolved load observed for the first time in a small watershed probably reflects the local coupling between mechanical and chemical erosion respectively

a record minimum arctic sea ice extent and area in 2002 1 arctic sea ice extent and area in september 2002 reached their lowest levels recorded since 1978 these conditions likely resulted from 1 anomalous warm southerly winds in spring advecting ice poleward from the siberian coast 2 persistent low pressure and high temperatures over the arctic ocean in summer promoting ice divergence and rapid melt

calcite supersaturation and precipitation kinetics in the lower colorado river all american canal and east highline canal in situ ph determinations and analysis of major ions in solution indicated that the lower colorado river is supersaturated with respect to calcite throughout the entire daily cycle in both winter and summer although the ion activity product was 4 to 6 times greater than the calcite solubility product there was no detectable precipitation chemical analyses of water samples taken along 350 km of the river and canals from parker dam to the salton sea also revealed no evidence of calcium carbonate precipitation despite the inflow of saline and highly supersaturated irrigation return flows laboratory kinetic studies indicated that calcite crystal growth rates with colorado river water are about 30 of the rate for pure ca hco3 waters and about 70 of that for synthetic colorado river water calcite precipitation by crystal growth in the river is limited by the combination of short residence times and unavailability of reactive calcite critical supersaturation levels necessary for heterogeneous nucleation do not occur a high suspended load limits algal photosynthesis and thus prevents large decreases in daytime h2co3 levels

multiyear sea ice thermal regimes and oceanic heat flux derived from an ice mass balance buoy in the arctic ocean the conductive and oceanic heat fluxes and the mass balance of sea ice were investigated utilizing an ice mass balance buoy imb deployed in the arctic ocean after imb deployment the ice thinned from 1 95 m in late august to 1 46 m by mid october 2008 from then on ice growth until mid june 2009 increased the ice thickness to 3 12 m the ice temperature and consequently the conductive heat flux at the ice surface exhibited persistent high frequency variations due to diurnal and synoptic scale atmospheric forcing these signals propagated downward with damped magnitude and temporal lag the competition of oceanic and conductive heat flux dominated the low frequency variations of ice growth however high frequency variations in ice growth were controlled largely by the oceanic heat flux from mid november 2008 to mid june 2009 the average oceanic heat flux along a track from 86 2 n 115 2 w to 84 6 n 33 9 w was 7 1 w m2 this was in agreement with that derived from an imb deployed in 2005 about 1 5 to the north of our buoy we attributed the relatively high oceanic heat flux 10 15 w m2 observed during autumn and early winter to summer warming of the surface ocean upward mixing of warm deep water as observed when our buoy drifted over the shallow region of the lomonosov ridge 85 4 85 9 n 52 2 66 4 w demonstrated the impact of bathymetry on the oceanic heat flux under ice cover and consequently on the basal ice mass balance 2013 american geophysical union all rights reserved

geochemistry of dissolved and suspended loads of the seine river france anthropogenic impact carbonate and silicate weathering this study focuses on the chemistry of the seine river system one of the major rivers in europe and constitutes the first geochemical investigation of both suspended and dissolved loads of this river the seine river drains a typical mesozoic cenozoic sedimentary basin the paris basin constituted of limestones mixed or interbedded with terrigenous sediments derived from the paleoreliefs bordering the mesozoic and cenozoic seas in the context of quantifying the global influence of carbonate and silicate weathering on atmospheric co2 consumption the seine river offers the possibility of examining weathering rates in a flat sedimentary environment under temperate climatic conditions one of the major problems associated with the seine river as with many temperate rivers is pollution we propose in this paper 2 approaches in order to correct the dissolved load of the seine river for anthropogenic inputs and to calculate weathering rates of carbonates and silicates the first uses the dissolved load of rivers and tries to allocate the different solutes to different sources a mixing model based on elemental ratios is established and solved by an inversion technique the second approach consists in using the suspended load geochemistry under steady state conditions we show that the geochemistry of suspended sediments makes it possible to estimate the amount of solutes released during the chemical weathering of silicates and thus to calculate weathering rates of silicates the total dissolved load of the seine river at paris can be decomposed into 2 of solutes derived from natural atmospheric sources 7 derived from anthropogenic atmospheric sources 6 derived from agriculture 3 derived from communal inputs and 82 of solutes derived from rock weathering during high floods the contribution of atmospheric and agriculture inputs predominates the weathering rate of carbonates is estimated to be 48 t km2 yr 25 mm 1000 yr only 10 of carbonates are transported in a solid form the rest being transported in solution co2 consumption by carbonate weathering approaches 400 103 mol km2 yr in the seine river at paris about 2 3 mg l of dissolved cations are found to originate from the chemical weathering of silicates by taking dissolved silica into accounts the total dissolved load derived from silicate weathering is about 6 7 mg l this value is minimal because biological uptake of silica probably occur in the seine river the chemical weathering rate of aluminosilicates is estimated to be 2 t km2 yr the ratio of physical over chemical weathering of silicates range between 1 and 3 and the total chemical and physical erosion rates of sedimentary silicates are about 2 3 mm kyr the co2 consumption by silicate weathering 15 24 103 mol km2 yr and is independent of dissolved silica concentration silicate consumption is thus 20 times less than carbonate consumption in the paris basin compared to the neighboring granitic areas the sedimentary region drained by the seine river has 2 to 3 times lower co2 consumption rates we attribute this difference to the cation depleted nature of the seine basin aluminosilicates which are of sedimentary origin at a world scale the chemical denudation rates found for the seine basin are very low and comparable to those given for tropical lowland rivers draining silicates such as the rivers of the congo and amazon basins in spite of huge climatic differences we attribute this similarity to the low mechanical denudation that characterizes these two types of regions

ice ridging and ice drift in southern gulf of st lawrence canada during winter storms during february and march 2004 satellite tracked ice beacons and helicopter borne sensors collected ice drift and ice thickness data from the southern gulf of st lawrence canada to study the region s ice thickness evolution and ice drift behavior in response to winter storms three northeasterly storms passed through the area during the observation period pushing the pack ice against the north shore of prince edward island the resulting severe ice deformation caused major changes in the ice thickness distribution of two pack ice areas tracked by ice beacons that survived the storms the ice drift ranged from 1 4 to 2 9 of the wind speed during free ice drift conditions decreasing to 0 when the pack ice compacted against the shoreline most of the thinner ice deformed first increasing the mean ice thickness over 6 8 km line sections around the beacons from 0 6 and 0 3 m before the storms to 1 9 and 2 0 m after the storms the ice thickness increases can be accounted for by the reduced pack ice area due to ice ridging over the next 4 weeks deformation continued and the mean ice thickness around the beacons increased to 2 8 m well in excess of the maximum undeformed possible ice growth of 65 cm ice charts captured the ice thickness of undeformed and composite ice floes but did not capture the ice volume in ice rubble fields

thin and thinner sea ice mass balance measurements during sheba 1 as part of a large interdisciplinary study of the surface heat budget of the arctic ocean sheba we installed more than 135 ice thickness gauges to determine the sea ice mass balance while installing these gauges during the fall of 1997 we found that much of the multiyear ice cover was only 1 m thick considerably thinner than expected over the course of the yearlong field experiment we monitored the mass balance for a wide variety of ice types including first year ice ponded ice unponded ice multiyear ice hummocks new ridges and old ridges initial ice thicknesses for these sites ranged from 0 3 to 8 m and snow depths varied from a few centimeters to more than a meter however for all of their differences and variety these thickness gauges sites shared a common trait at every site there was a net thinning of the ice during the sheba year the thin ice found in october 1997 was even thinner in october 1998 the annual cycle of ice thickness was also similar at all sites there was a steady increase in thickness through the winter that gradually tapered off in the spring this was followed by a steep drop off in thickness during summer melt and another tapering in late summer and early fall as freeze up began maximum surface melting was in july while bottom ablation peaked in august combining results from the sites we found an average winter growth of 0 51 m and a summer melt of 1 26 m which consisted of 0 64 m of surface melt and 0 62 m of bottom melt there was a weak trend for thicker ice to have less winter growth and greater net loss for the year however ice growth was also impacted by the snow depth considerable variability was observed between sites in both accretion and ablation the total accretion during the 9 month growth season ranged from zero for thick ridged ice to more than a meter for young ice ponds tended to have a large amount of surface melting while ridges had considerable bottom ablation

assimilation of ice motion observations and comparisons with submarine ice thickness data 1 aided by submarine observations of ice thickness for model evaluation we investigate the effects of assimilating buoy motion data and satellite ssm i 85 ghz ice motion data on simulation of arctic sea ice the sea ice model is a thickness and enthalpy distribution model and is coupled to an ocean model ice motion data are assimilated by means of optimal interpolation assimilating motion data particularly from drifting buoys significantly improves the modeled ice motion reducing the error to 0 04 m s 1 from 0 07 m s 1 and increasing the correlation with observations to 0 90 from 0 66 without data assimilation the modeled ice moves too slowly with excessive stoppage assimilation leads to more robust ice motion with substantially reduced stoppage which in turn leads to strengthened ice outflow at fram strait and enhanced ice deformation everywhere enhanced deformation doubles the production of ridged ice to an arctic ocean average of 0 77 m yr 1 and raises the amount of ridged ice to half the total ice volume per unit area of 2 58 m assimilation also significantly alters the spatial distribution of ice mass and brings the modeled ice thickness into better agreement with the thickness observed in four recent submarine cruises reducing the error to 0 66 m from 0 76 m and increasing the correlation with observations to 0 65 from 0 45 buoy data are most effective in reducing model errors because of their small measurement error ssm i data because of their more complete spatial coverage are helpful in regions with few buoys particularly in coastal areas assimilating both ssm i and buoy data combines their individual advantages and brings about the best overall model performance in simulating both ice motion and ice thickness

weathering processes in the ganges brahmaputra basin and the riverine alkalinity budget abstract we present river chemistry data for a network of rivers draining the western and central nepal himalaya our sampling locations cover the system from the sources of rivers in tibet to the gangetic plain water samples were collected throughout the year including the monsoon season for rivers in nepal and for the ganges and brahmaputra in bangladesh rivers draining the north himalaya are characterized by low discharge under a cold and arid climate main stream waters have 13 c dic near 0 and high so42 so42 hco3 ratios xso4 with values around 40 eq and high cl ca is the dominant cation ca2 cations 55 to 75 eq after correction of sodium by chloride dissolved sulfate is produced in waters from the tethian sedimentary series whereas chlorine is related to thermal waters dissolved sulfate is primarily derived from sulfide oxidation rather than evaporite dissolution 13 c dic values of up to 3 9 show that metamorphic co2 is an important weathering agent rivers of the north himalayan basins have about 50 of their alkalinity derived from carbonate dissolution 20 from biogenic activity and 30 from metamorphic co2 on the south flank of the himalaya rivers are more depleted in 13 c and have on average lower xso4 most rivers have 13 c dic and xso4 values compatible with a simple mixing between soil co2 and sulfate derived from sulfide oxidation during the monsoon discharge increases by a factor 20 but the total dissolved concentration is only slightly reduced xso4 and 13 c decrease while ca cations increases implying enhanced dissolution of pedogenic calcite as a whole the g b riverine flux of alkalinity derived from silicate weathering is around 2 7 1011 mol year modest at the global scale sulphuric acid controls 20 30 of the weathering reaction in the brahmaputra and 6 to 9 in the ganges na and k balance 60 to 65 of the silicate derived alkalinity flux and the long term co2 consumption by ganges and brahmaputra is near 6 4 1010 mol year the flux of metamorphic co2 converted to alkalinity via weathering reactions is ca 1 1010 mol year

microwear features on vein quartz rock crystal and quartzite a study combining optical light and scanning electron microscopy abstract in general quartz and most of non flint rocks have not been extensively studied from a functional point of view very frequently the definitions of micro features connected with flint surfaces have been used to describe those encountered on non flint tools this circumstance has repeatedly posed serious methodological problems for evaluating the accuracy of functional results when analysing use wear on quartz and quartzite implements this is due to the intrinsic divergences in morphology and distribution of use wear with regard to the different lithic raw materials even though important efforts to systematise use wear features on quartz have been done almost since the beginning of the discipline there continues to be confusion and lack of standardisation regarding terminology in this aspect in this paper we try to contribute to new insights in this research by means of selecting examples from an extensive experimental programme involving different raw materials from rock crystal the purest form of quartz found in nature to vein quartz and quartzite with the latter two materials extensively used for knapping throughout prehistory and still poorly understood in terms of microwear for data recording we preferentially used sequential experiments and resorted to both optical light and scanning electron microscopy we focused our interest on describing the main groups of wear features the results obtained allowed us to assess the different mechanical behaviours under the stressors induced by tool use from a group of raw materials with the same chemical composition but very different in structure furthermore we propose the revision of some terms commonly employed when documenting micro wear on quartz and similar rocks as well as recurring concepts coming from materials and geological sciences e g tribology quartz exoscopy

ice mass balance buoys a tool for measuring and attributing changes in the thickness of the arctic sea ice cover recent observational and modeling studies indicate that the arctic sea ice cover is undergoing significant climate induced changes affecting both its extent and thickness the thickness or more precisely the mass balance of the ice cover is a key climate change indicator since it is an integrator of both the surface heat budget and the ocean heat flux accordingly efforts are underway to develop and deploy in situ observing systems which when combined with satellite remote sensing information and numerical models can effectively monitor and attribute changes in the mass balance of the arctic sea ice cover as part of this effort we have developed an autonomous ice mass balance buoy imb which is equipped with sensors to measure snow accumulation and ablation ice growth and melt and internal ice temperature plus a satellite transmitter the imb is unique in its ability to determine whether changes in the thickness of the ice cover occur at the top or bottom of the ice cover and hence provide insight into the driving forces behind the change since 2000 imbs have been deployed each spring from the north pole environmental observatory and in several other areas including a few in the beaufort sea and central basin at this point the collective time series is too short to draw significant and specific conclusions regarding interannual and regional variability in ice mass balance comparisons of available data indicate that ice surface ablation is greater in the beaufort region 67 80 cm relative to the north pole 0 30 cm consistent with a longer period of melt in the more southerly location ablation at the bottom of the ice 22 cm maximum ice thickness 235 cm and maximum snow depth 28 cm were comparable in the two regions

processes controlling surface bottom and lateral melt of arctic sea ice in a state of the art sea ice model we present a modelling study of processes controlling the summer melt of the arctic sea ice cover we perform a sensitivity study and focus our interest on the thermodynamics at the ice atmosphere and ice ocean interfaces we use the los alamos community sea ice model cice and additionally implement and test three new parametrization schemes i a prognostic mixed layer ii a three equation boundary condition for the salt and heat flux at the ice ocean interface and iii a new lateral melt parametrization recent additions to the cice model are also tested including explicit melt ponds a form drag parametrization and a halodynamic brine drainage scheme the various sea ice parametrizations tested in this sensitivity study introduce a wide spread in the simulated sea ice characteristics for each simulation the total melt is decomposed into its surface bottom and lateral melt components to assess the processes driving melt and how this varies regionally and temporally because this study quantifies the relative importance of several processes in driving the summer melt of sea ice this work can serve as a guide for future research priorities

geologic control of sr and major element chemistry in himalayan rivers nepal our study of the seti river in far western nepal shows that the solute chemistry of the river and its tributaries is strongly controlled by geology the seti flows through four distinct terranes starting with the tethyan sedimentary series tss and greater himalayan series ghs tss ghs waters display 87 sr 86 sr ratios of 0 73 and high sr and ca consistent with the composition of limestone and marble common in these terranes the 87 sr 86 sr ratio and mg increase markedly as the river passes into the lesser himalayan series lhs where tributaries have 87 sr 86 sr ratios from 0 75 to 1 02 and high sr ca and mg the high mg in lhs waters correlate with high 87 sr 86 sr ratios which we attribute to weathering of highly radiogenic 0 71 0 82 dolostones tributaries to the seti river draining the largely carbonate free dadeldhura thrust sheet dts have ratios near 0 74 but low sr ca and mg and therefore have little impact on seti mainstem chemistry mass balance calculations and camg weathering indices show that carbonate weathering accounts for 70 of total dissolved solids to the seti river sr ca ratios of river waters provide a minimum estimate of the carbonate weathering contribution to sr due to partitioning of sr and ca during incongruent dissolution and reprecipitation of calcite overall we attribute high 87 sr 86 sr ratios in the seti river and its tributaries to the weathering of metacarbonates especially dolostones in the upper nawakhot group which have exchanged sr with silicates during metamorphism our modeling of sr fluxes in the seti river indicates that the tss ghs accounts for 36 39 of the sr the lhs for 40 53 and 8 23 for the dts prior to exposure of lhs rocks at 12 ma tss and ghs carbonates with low 87 sr 86 sr ratios dominated himalayan rivers we attribute the elevated 87 sr 86 sr ratios of himalayan paleorivers during the late miocene and pliocene to exposure and weathering of lhs metacarbonates copyright 2000 elsevier science ltd

evidence for rapid thinning of sea ice in the western arctic ocean at the end of the 1980s examination of springtime ice drafts obtained from submarine profiles in a narrow band of the western arctic ocean from offshore alaska to 89 n indicates that the mean ice draft decreased 1 5 m between the mid 1980s and early 1990s no similar trend was evident in ice drafts near the north pole the 1980s drafts were composed largely of ice exceeding 3 5 m while the early 1990s drafts contained more ice in thinner categories the differences in drafts between the two periods appear to be related largely to ice dynamics effects associated with the presence and strength of the beaufort gyre which weakened considerably in the early 1990s

seasonal evolution of an ice shelf influenced fast ice regime derived from an autonomous thermistor chain ice shelves strongly interact with coastal antarctic sea ice and the associated ecosystem by creating conditions favorable to the formation of a sub ice platelet layer the close investigation of this phenomenon and its seasonal evolution remains a challenge due to logistical constraints and a lack of suitable methodology in this study we characterize the seasonal cycle of antarctic fast ice adjacent to the ekstrom ice shelf in the eastern weddell sea we used a thermistor chain with the additional ability to record the temperature response induced by cyclic heating of resistors embedded in the chain vertical sea ice temperature and heating profiles obtained daily between november 2012 and february 2014 were analyzed to determine sea ice and snow evolution and to calculate the basal energy budget the residual heat flux translated into an ice volume fraction in the platelet layer of 0 18 0 09 which we reproduced by a independent model simulation and agrees with earlier results manual drillings revealed an average annual platelet layer thickness increase of at least 4 m and an annual maximum thickness of 10 m beneath second year sea ice the oceanic contribution dominated the total sea ice production during the study effectively accounting for up to 70 of second year sea ice growth in summer an oceanic heat flux of 21 w m 2 led to a partial thinning of the platelet layer our results further show that the active heating method in contrast to the acoustic sounding approach is well suited to derive the fast ice mass balance in regions influenced by ocean ice shelf interaction as it allows subdiurnal monitoring of the platelet layer thickness

thinning of the arctic sea ice cover comparison of sea ice draft data acquired on submarine cruises between 1993 and 1997 with similar data acquired between 1958 and 1976 indicates that the mean ice draft at the end of the melt season has decreased by about 1 3 m in most of the deep water portion of the arctic ocean from 3 1 m in 1958 1976 to 1 8 m in the 1990s the decrease is greater in the central and eastern arctic than in the beaufort and chukchi seas preliminary evidence is that the ice cover has continued to become thinner in some regions during the 1990s

arctic sea ice melt in 2008 and the role of solar heating there has been a marked decline in the summer extent of arctic sea ice over the past few decades data from autonomous ice mass balance buoys can enhance our understanding of this decline these buoys monitor changes in snow deposition and ablation ice growth and ice surface and bottom melt results from the summer of 2008 showed considerable large scale spatial variability in the amount of surface and bottom melt small amounts of melting were observed north of greenland while melting in the southern beaufort sea was quite large comparison of net solar heat input to the ice and heat required for surface ablation showed only modest correlation however there was a strong correlation between solar heat input to the ocean and bottom melting as the ice concentration in the beaufort sea region decreased there was an increase in solar heat to the ocean and an increase in bottom melting

indirect measurements of the mass balance of summer arctic sea ice with an electromagnetic induction technique abstract in the framework of the surface heat budget of the arctic ocean sheba study indirect non invasive icemass balance measurements were carried out at a drifting station in the northern chukchi sea between mayand august of 1998 ice thickness was derived from electromagnetic induction em measurements ofapparent conductivity along 13 profiles 60 to 900 m long as shown through sensitivity studies with a 1 d model the apparent conductivity data from individual points can be inverted to yield estimates of icethickness and ablation with an accuracy of approximately 0 05 m for 2 m thick level ice ablation ratesranged between 8 and 18 mm d 1 with total ablation amounting to roughly 0 9 to 1 2 m measurements ofthickness and melt rates along different profiles in undeformed multi year ice corresponded closely indicating that the sampling statistics are adequate the roughness of undeformed ice has been found toincrease during the summer due to deepening of melt ponds and enhanced bottom melt ice under melt pondswas disproportionately thinner most likely a result of thicker snow cover reducing winter accretion

geochemistry and trade of eastern mediterranean millstones from the neolithic to roman periods millstones and grindstones of the prehistoric to roman periods include saddle querns rectangular hopper rubber mills rotary querns and pompeian style donkey mills many of these were manufactured from igneous rocks which can be provenanced to their geological sources using chemical analysis giving information about trade contacts of sites sixty nine samples of 10 20 g each were removed from broken parts of lava millstones of prehistoric and early historic date from sites in israel syria egypt greece and turkey these were analysed for major and trace elements using x ray fluorescence and petrological features were examined in thin section the millstones were all young generally fresh lavas ranging from vesicular basalt to porphyritic andesite potential sources occur in younger volcanics of mainland greece the aegean turkey and the levant israel syria and jordan and in egypt thirty four geological samples from israel syria and turkey were collected and analysed in the same way as the archaeological samples and an intensive literature survey carried out to supplement these by published analyses comparison of archaeological samples with source data is done by using a series of discrimination graphs following a simple flow diagram the archaeological samples were of two types within plate lavas and island arc or other subduction related lavas all samples were successfully assigned to sources and results show use of the source areas as follows during the prehistoric period neolithic bronze age pre 6th century bc iron age samples saddle querns in mainland greece were made of aegina andesire while sites in north syria used local syrian lavas and in israel basalts from near lake tiberias and from the dead sea area were used earlier work by the authors and others has shown import of levant millstones to cyprus in the late bronze age hopper rubbers of the 5th century bc onwards were made at specialized quarries in aegean islands on nisyros kimolos and santorini and exported to mainland greece western turkey egypt and cyprus less well finished hopper rubbers were made and used in western turkey and in israel roman pompeian style mills were made of levant lavas from several sources particularly around lake tiberias and were transported within israel as well as to cyprus as shown by earlier studies rotary querns were made of lavas from santorini and probably nisyros and of locally used west anatolian rocks rotary querns of roman and later 10th 12th century ad dates were also produced at several sources in the levant again around lake tiberias and probably in north syria and within the dead sea volcanics for use within israel olive crushing trapeta used in turkey and greece were manufactured from andesites from anatolia and aegina respectively west anatolian lavas mill types unknown have also been identified at roman sites in the eastern desert of egypt millstone distributions increased in complexity and extent over time with hopper rubbers being traded up to 820 km from sources and roman rotary millstones up to 1300 km the three major source areas aegean anatolia and the levant were in apparent competition by the roman period when there is extensive overlap of distributions from different sources with aegean and anatolian products traded the furthest the millstone trade in the eastern mediterranean is separate from that of the west mediterranean west of greece except for one hopper rubber of nisyros lava identified in a shipwreck off mallorca this dichotomy is in marked contrast to the distribution of amphorae within which west mediterranean italian products were widely used in the east from at least the 2nd century bc stylistically east mediterranean millstones also show differences from those in the west in the prevalence of hopper rubbers and later in decorative features common on pompeian style mills

comparison of seasonal sea ice thickness change in the transpolar drift observed by local ice mass balance observations and floe scale em surveys local and transect ice thickness measurements were performed between may and november 2007 on an ice floe in the transpolar drift of the arctic ocean using an ice mass balance buoy and electromagnetic induction em sounding repeated em surveys along an originally 2160 m long profile including level and deformed ice showed that between june and september modal and mean thicknesses decreased by 0 6 and 0 86 m respectively the modal thickness decrease is in good agreement with the thinning of 0 6 m observed by the ice mass balance buoy at one location on unponded ice during the same period although the local observations do not capture the different melt rates on level and rough ice the paper discusses methodological and operational challenges in sustaining both measurements over periods of several months and concludes that more work needs to be done to better understand their representativeness

magnesium isotope systematics of the lithologically varied moselle river basin france abstract magnesium and strontium isotope signatures were determined during different seasons for the main rivers of the moselle basin northeastern france this small basin is remarkable for its well constrained and varied lithology on a small distance scale and this is reflected in river water sr isotope compositions upstream where the moselle river drains silicate rocks of the vosges mountains waters are characterized by relatively high 87sr 86sr ratios 0 7128 0 7174 in contrast downstream of the city of epinal where the moselle river flows through carbonates and evaporites of the lorraine plateau 87sr 86sr ratios are lower down to 0 70824 magnesium in river waters draining silicates is systematically depleted in heavy isotopes 26mg values range from 1 2 to 0 7 relative to the value presently estimated for the continental crust and a local diorite 0 5 in comparison 26mg values measured in soil samples are higher 0 0 this suggests that mg isotope fractionation occurs during mineral leaching and or formation of secondary clay minerals on the lorraine plateau tributaries draining marls carbonates and evaporites are characterized by low ca mg 1 5 3 2 and low ca sr 80 400 when compared to local carbonate rocks ca mg 29 59 ca sr 370 2200 similar to other rivers draining carbonates the most likely cause of the mg and sr excesses in these rivers is early thermodynamic saturation of groundwater with calcite relative to magnesite and strontianite as groundwater chemistry progressively evolves in the aquifer 26mg of the dissolved phases of tributaries draining mainly carbonates and evaporites are relatively low and constant throughout the year from 1 4 to 1 6 and from 1 2 to 1 4 respectively within the range defined for the underlying rocks downstream of epinal the compositions of the moselle river samples in a 26mg vs 87sr 86sr diagram can be explained by mixing curves between silicate carbonate and evaporite waters with a significant contribution from the vosgian silicate lithologies 70 temporal co variation between 26mg and 87sr 86sr for the moselle river throughout year is also observed and is consistent with a higher contribution from the vosges mountains in winter in terms of runoff and dissolved element flux overall this study shows that mg isotopes measured in waters rocks and soils coupled with other tracers such as sr isotopes could be used to better constrain riverine mg sources particularly if analytical uncertainties in mg isotope measurements can be improved in order to perform more precise quantifications

further evidence of ice thinning in the arctic ocean a sea ice thickness profile obtained in september 1996 from the eurasian basin of the arctic ocean between fram strait and the north pole was compared with a profile obtained in the same region in september october 1976 a decline in mean ice draft of 43 was observed over the 20 year interval in agreement with changes observed in other parts of the arctic ocean by rothrock et al 1999

assimilating summer sea ice concentration into a coupled ice ocean model using a lseik filter the decrease in summer sea ice extent in the arctic ocean opens shipping routes and creates potential for many marine operations for these activities accurate predictions of sea ice conditions are required to maintain marine safety in an attempt at arctic sea ice prediction the summer of 2010 is selected to implement an arctic sea ice data assimilation da study the da system is based on a regional arctic configuration of the massachusetts institute of technology general circulation model mitgcm and a local singular evolutive interpolated kalman lseik filter to assimilate special sensor microwave imager sounder ssmis sea ice concentration operational products from the us national snow and ice data center nsidc based on comparisons with both the assimilated nsidc ssmis concentration and concentration data from the ocean and sea ice satellite application facility the forecasted sea ice edge and concentration improve upon simulations without data assimilation by the nature of the assimilation algorithm with multivariate covariance between ice concentration and thickness sea ice thickness fields are also updated and the evaluation with in situ observation shows some improvement compared to the forecast without data assimilation

changes in the thickness and circulation of multiyear ice in the beaufort gyre determined from pseudo lagrangian methods from 2003 2015 we combine eulerian ice draft observations from moored ice profiling sonars with buoy and satellite derived ice drift data to obtain lagrangian observations of changes in the thickness distribution of sea ice circulating the beaufort sea we examine repeat measurements of ice draft by identifying events where buoys or pseudobuoys made repeat overpasses within 30 km of ice profiling sonar equipped beaufort gyre exploration project moorings comparison of ice draft distributions from each overpass indicates that summertime melt rates are related to drift track with more melt occurring in the southern beaufort sea than to the north additionally we find that ice surviving summer in the beaufort sea since 2007 is similar in thickness to surrounding first year sea ice by the end of the following winter these findings are supported by continuous ice thickness data from ice mass balance buoys by examining plumes of pseudobuoys originating at each mooring location we identify anomalous northward transport of ice in the southern beaufort sea in 2007 that likely contributed to the record breaking reduction in sea ice extent that year we also find that repeat overpasses have been much rarer since 2007 due to reduced summertime sea ice extent in the beaufort gyre and possible changes in ice drift patterns these changes contribute to diminished replenishment of multiyear sea ice volume in the arctic

regional variability in sea ice melt in a changing arctic in recent years the arctic sea ice cover has undergone a precipitous decline in summer extent the sea ice mass balance integrates heat and provides insight on atmospheric and oceanic forcing the amount of surface melt and bottom melt that occurs during the summer melt season was measured at 41 sites over the time period 1957 to 2014 there are large regional and temporal variations in both surface and bottom melting combined surface and bottom melt ranged from 16 to 294 cm with a mean of 101 cm the mean ice equivalent surface melt was 48 cm and the mean bottom melt was 53 cm on average surface melting decreases moving northward from the beaufort sea towards the north pole however interannual differences in atmospheric forcing can overwhelm the influence of latitude substantial increases in bottom melting are a major contributor to ice losses in the beaufort sea due to decreases in ice concentration in the central arctic surface and bottom melting demonstrate interannual variability but show no strong temporal trends from 2000 to 2014 this suggests that under current conditions summer melting in the central arctic is not large enough to completely remove the sea ice cover

geochemistry of the amazon 1 precipitation chemistry and the marine contribution to the dissolved load at the time of peak discharge analyses of precipitation and surface water are used to estimate the fluxes of marine cyclic salts through that part of the amazon river system draining past obidos 80 of the basin at the time of peak discharge in june amazon precipitation chemistry can be devided into two principal components marine and terrestrial the marine component determined from analyses of marine rain consists of na k mg ca and cl in approximately sea salt proportions with s doubly enriched the excess sulfur is probably derived from gas phase inputs the terrestrial component makes an important contribution of k ca s and n much of which can be related to biological emissions the emission of reduced sulfur in the marine and terrestrial environment and nitrogen in the terrestrial environment is responsible for a natural acid rain in the amazon region with a ph from 4 7 to 5 7 this is about one tenth the acidity of polluted urban rain the chloride content of lowland rivers which drain regions lacking significant geologic sources of chloride shows a systematic decrease in chloride with increasing distance from the ocean this trend is used to define the cyclic salt background for amazonian surface waters cyclic salts in general make only a minor contribution relative to terrestrial inputs to the chemistry of amazon basin rivers even those draining intensely weathered terrains an estimated 17 6 cl 6 9 na 1 3 mg 3 6 s 0 4 k and 0 1 ca of the dissolved load at obidos during peak discharge is cyclic

influences of the ocean surface mixed layer and thermohaline stratification on arctic sea ice in the central canada basin 1 variations in the arctic central canada basin mixed layer properties are documented based on a subset of nearly 6500 temperature and salinity profiles acquired by ice tethered profilers during the period summer 2004 to summer 2009 and analyzed in conjunction with sea ice observations from ice mass balance buoys and atmosphere ocean heat flux estimates the july august mean mixed layer depth based on the ice tethered profiler data averaged 16 m an overestimate due to the ice tethered profiler sampling characteristics and present analysis procedures while the average winter mixed layer depth was only 24 m with individual observations rarely exceeding 40 m guidance interpreting the observations is provided by a 1 d ocean mixed layer model the analysis focuses attention on the very strong density stratification at the base of the mixed layer in the canada basin that greatly impedes surface layer deepening and thus limits the flux of deep ocean heat to the surface that could influence sea ice growth decay the observations additionally suggest that efficient lateral mixed layer restratification processes are active in the arctic also impeding mixed layer deepening

structural study of two quartzite varieties from the utrillas facies formation olmos de atapuerca burgos spain from a petrographic characterisation to a functional analysis design abstract this overall research initiative was undertaken to evaluate the role of lithic raw material variability in use wear formation processes focusing specifically on two lithological varieties of quartzite present in the lower and middle pleistocene lithic assemblages of the gran dolina galeria and sima del elefante sites sierra de atapuerca burgos two arenas de utrillas facies varieties from a sand quarry located in olmos de atapuerca were studied using petrographic and sem analyses they were both identified as metaquartzites revealing differences in their granular structure and metamorphic grade sequential experiments employing the same quartzite varieties were then conducted involving different activities and several worked materials which made it possible to determine use wear formation on these two quartzite varieties the results helped to clarify the role of intra raw material variability in the process of use wear formation on quartzite and contributed to ongoing studies of the lithic materials from these archaeological sites

arctic ocean ice thickness modes of variability and the best locations from which to monitor them abstract model simulations of arctic sea ice and ocean systems are used to determine the major spatial and temporal modes of variability in the ice thickness a coupled ice ocean model is forced with daily ncep ncar reanalysis surface air pressure and surface air temperature fields for the period 1951 2003 with the analysis of the results performed for the 51 yr period 1953 2003 ice concentration data and ice velocity data beginning in 1979 are assimilated to further constrain the simulations to match the observed conditions the simulated ice thins over the study period with the area of greatest thinning in a band from the laptev sea across the pole to fram strait the thinning rate is greatest since 1988 the major spatial modes of variability were determined with empirical orthogonal functions eofs for the ice thickness within the arctic ocean the first three eofs account for 30 18 and 15 respectively of the annual mean ice thickness variance the first eof is a nearly basinwide pattern a

mg isotopic composition of carbonate insight from speleothem formation simultaneous high precision measurement of 24 mg 25 mg and 26 mg isotopic compositions were made by multiple collector inductively coupled mass spectrometry mc icp ms relative to the international standard srm980 data are presented on low mg calcite speleothems and their associated host rocks and waters from four caves one in the french alps and three in israel covering various climate conditions in addition data are presented on three dolostones and three limestones from the himalaya the overall variation is 4 13x and 2 14x in n 26 mg and n 25 mg respectively this is 35 times the uncertainty of the measurements and clearly demonstrates that the terrestrial isotopic composition of mg is not unique each speleothem shows a characteristic range of n 26 mg values that are attributed to the isotopic composition of the local water differences between the isotopic composition of mg in the water dripping from stalactites and that of the modern speleothem are interpreted as being due to mg isotopic fractionation during carbonate precipitation in the temperature range of 4 18 c the low mg calcite is enriched in light isotopes by 1 35x amu and the dependence on temperature has been found to be less than 0 02x amu c despite various geological settings the n 26 mg of the studied dolostones is 2 0 1 2x higher than the n 26 mg of the limestones all together these results suggest a strong mineralogical control and a weak temperature effect on the mg isotopic composition of carbonate a 2002 elsevier science b v all rights reserved

icesat observations of arctic sea ice a first look 1 analysis of near coincident icesat and radarsat imagery shows that the retrieved elevations from the laser altimeter are sensitive to new openings containing thin ice or open water in the sea ice cover as well as to surface relief of old and first year ice the precision of the elevation estimates measured over relatively flat sea ice is 2 cm using the thickness of thin ice in recent openings to estimate sea level references we obtain the sea ice freeboard along the altimeter tracks this step is necessitated by the large uncertainties in the sea surface topography compared to that required for accurate determination of freeboard unknown snow depth introduces the largest uncertainty in the conversion of freeboard to ice thickness surface roughness is also derived for the first time from the variability of successive elevation estimates along the altimeter track overall these icesat measurements provide an unprecedented view of the arctic ocean ice cover at length scales at and above the spatial dimension of the altimeter footprint of 70 m

sea ice and snow cover characteristics during the winter spring transition in the bellingshausen sea an overview of simba 2007 abstract the sea ice mass balance in the antarctic simba experiment was conducted from the rvib n b palmer in september and october 2007 in the bellingshausen sea in an area recently experiencing considerable changes in both climate and sea ice cover snow and ice properties were observed at 3 short term stations and a 27 day drift station ice station belgica isb during the winter spring transition repeat measurements were performed on sea ice and snow cover at 5 isb sites each having different physical characteristics with mean ice snow thicknesses varying from 0 6 m 0 1 m to 2 3 m 0 7 m ice cores retrieved every five days from 2 sites and measured for physical biological and chemical properties three ice mass balance buoys imbs provided continuous records of snow and ice thickness and temperature meteorological conditions changed from warm fronts with high winds and precipitation followed by cold and calm periods through four cycles during isb the snow cover regulated temperature flux and controlled the physical regime in which sea ice morphology changed level thin ice areas had little snow accumulation and experienced greater thermal fluctuations resulting in brine salinity and volume changes and winter maximum thermodynamic growth of 0 6 m in this region flooding and snow ice formation occurred during cold spells in ice and snow of intermediate thickness in contrast little snow ice formed in flooded areas with thicker ice and snow cover instead nearly isothermal highly permeable ice persisted in spring short lived cold air episodes did not effectively penetrate the sea ice nor overcome the effect of ocean heat flux thus favoring net ice thinning from bottom melt over ice thickening from snow ice growth in all cases these warm ice conditions were consistent with regional remote sensing observations of earlier ice breakup and a shorter sea ice season more recently observed in the bellingshausen sea

the arctic ice thickness anomaly of the 1990s a consistent view from observations and models 1 observations of sea ice draft from submarine cruises in much of the arctic ocean show that the ice cover was unusually thin in the mid 1990s here we limit our examination to digitally recorded draft data from eight cruises spanning the years 1987 to 1997 and find a decrease of about 1 m over the 11 year span comparisons of our modeled draft with observed draft show good agreement in the temporal change comparing average draft over entire cruises the rms discrepancy between modeled and observed draft is 0 3 m and the correlation is 0 98 agreement in the spatial patterns of draft is somewhat lower the rms discrepancy of 50 km averages of draft is 0 7 m and the correlation is 0 73 we review reports of interannual variations of ice thickness or volume from other model studies all models agree that thickness decreased by between 0 6 and 0 9 m from 1987 to 1996 our model shows a modest recovery in thickness from 1996 to 1999 for the 1950s 1960s and 1970s models tend to disagree on the size and to a lesser extent the timing or phase of interannual variations

beaufort gyre freshwater reservoir state and variability from observations 1 we investigate basin scale mechanisms regulating anomalies in freshwater content fwc in the beaufort gyre bg of the arctic ocean using historical observations and data collected in 2003 2007 specifically the mean annual cycle and interannual and decadal fwc variability are explored the major cause of the large fwc in the bg is the process of ekman pumping ep due to the arctic high anticyclonic circulation centered in the bg the mean seasonal cycle of liquid fwc is a result of interplay between the mechanical ep and thermal ice transformations factors and has two peaks one peak occurs around june july when the sea ice thickness reaches its minimum maximum ice melt the second maximum is observed in november january when wind curl is strongest maximum ep and the salt input from the growing ice has not yet reached its maximum interannual changes in fwc during 2003 2007 are characterized by a strong positive trend in the region varying by location with a maximum of approximately 170 cm a 1 in the center of ep influenced region decadal fwc variability in the period 1950 2000 is dominated by a significant change in the 1990s forced by an atmospheric circulation regime change the center of maximum fwc shifted to the southeast and appeared to contract in area relative to the pre 1990s climatology in spite of the areal reduction the spatially integrated fwc increased by over 1000 km 3 relative to climatology

transpolar observations of the morphological properties of arctic sea ice save for an area between 8830 0 n and 8930 0 n where polynyas and thin ice were observed surveys of snow depth ice thickness and ice properties were conducted at ice stations thickness observations suggest a general latitudinal trend of increasing ice thickness moving northward with considerable variability from floe to floe and within a single floe average floe thicknesses varied from 1 0 to 2 8 m and the standard deviation of thickness on an individual floe was as large as 1 m ice crystallography showed a large amount of granular ice the average optical equivalent soot content was 4n g cg 1 for new snow 8 ng c g 1 for the surface granular layer of multiyear ice and 18 ng c g 1 for the interior of multiyear ice indicating a tendency of the particulates to concentrate at the surface with melting

reconciling the elemental and sr isotope composition of himalayan weathering fluxes insights from the carbonate geochemistry of stream waters determining the relative proportions of silicate vs carbonate weathering in the himalaya is important for understanding atmospheric co2 consumption rates and the temporal evolution of seawater sr however recent studies have shown that major element mass balance equations attribute less co2 consumption to silicate weathering than methods utilizing ca sr and 87sr 86sr mixing equations to investigate this problem we compiled literature data providing elemental and 87sr 86sr analyses for stream waters and bedrock from tributary watersheds throughout the himalaya mountains in addition carbonate system parameters pco2 mineral saturation states were evaluated for a selected suite of stream waters the apparent discrepancy between the dominant weathering source of dissolved major elements vs sr can be reconciled in terms of carbonate mineral equilibria himalayan streams are predominantly ca2 mg2 hco3 waters derived from calcite and dolomite dissolution and mass balance calculations demonstrate that carbonate weathering contributes 87 and 76 of the dissolved ca2 and sr2 respectively however calculated ca sr ratios for the carbonate weathering flux are much lower than values observed in carbonate bedrock suggesting that these divalent cations do not behave conservatively during stream mixing over large temperature and pco2 gradients in the himalaya the state of calcite and dolomite saturation was evaluated across these gradients and the data show that upon descending through the himalaya 50 of the streams evaluated become highly supersaturated with respect to calcite as waters warm and degas co2 stream water ca mg and ca sr ratios decrease as the degree of supersaturation with respect to calcite increases and mg2 ca2 and hco3 mass balances support interpretations of preferential ca2 removal by calcite precipitation on the basis of patterns of saturation state and pco2 changes calcite precipitation was estimated to remove up to 70 of the ca2 originally derived from carbonate weathering accounting for the nonconservative behavior of ca2 during riverine transport brings the ca sr and 87sr 86sr composition of the carbonate weathering flux into agreement with the composition of carbonate bedrock thereby permitting consistency between elemental and sr isotope approaches to partitioning stream water solute sources these results resolve the dissolved sr2 budget and suggest that the conventional application of two component ca sr and 87sr 86sr mixing equations has overestimated silicate derived sr2 and hco3 fluxes from the himalaya in addition these findings demonstrate that integrating stream water carbonate mineral equilibria divalent cation compositional trends and sr isotope inventories provides a powerful approach for examining weathering fluxes