evidence of cfc degradation in groundwater under pyrite oxidizing conditions summary a detailed local scale monitoring network was used to assess cfc distribution in an unconfined sand aquifer in southwestern ontario where the zone of 1 5 year old groundwater was known with certainty because of prior use of a bromide tracer groundwater 5 years old was confined to an aerobic zone at 5 m depth and had cfc concentrations consistent with modern atmospheric mixing ratios at recharge temperatures of 7 11 c as was observed in the 3 m thick vadose zone at the site at depths below 6 m the groundwater became progressively more reducing however with a denitrifying horizon at 6 7 m depth and a mn and fe reducing zone below 7 m depth in the anaerobic zone 3 h 3 he ratios indicated that groundwater age continued to increase uniformly with depth to a maximum value of 27 years at 13 m depth cfc concentrations however decreased abruptly within the denitrifying zone leading to substantial age overestimation compared to the 3 h 3 he ages noble gas data indicated that the apparent cfc mass loss was not likely the result of gas stripping from possible bubble formation thus cfc degradation was indicated in the anoxic zone the field data are consistent with first order degradation rates of 0 3 yr 1 for cfc 12 0 7 yr 1 for cfc 11 and 1 6 yr 1 for cfc 113 cfc attenuation at this site coincides with a zone where reduced s pyrite is actively oxidized by no 3 and dissolved oxygen do similar behavior has been observed at other sites tesoriero a j liebscher h cox s e 2000 mechanism and rate of denitrification in an agricultural watershed electron and mass balance along groundwater flow path water resour res 36 6 1545 1559 hinsby k hojberg a l engesgaard p jensen k h larsen f plummer l n busenberg e accepted for publication transport and degradation of chlorofluorocarbons cfcs in a pyritic aquifer rabis creek denmark water resour res further demonstrating that the use of cfcs for age dating anaerobic groundwater should be approached with caution particularly if the sediment contains pyrite

thinning and volume loss of the arctic ocean sea ice cover 2003 2008 1 we present our best estimate of the thickness and volume of the arctic ocean ice cover from 10 ice cloud and land elevation satellite icesat campaigns that span a 5 year period between 2003 and 2008 derived ice drafts are consistently within 0 5 m of those from a submarine cruise in mid november of 2005 and 4 years of ice draft profiles from moorings in the chukchi and beaufort seas along with a more than 42 decrease in multiyear my ice coverage since 2005 there was a remarkable thinning of 0 6 m in my ice thickness over 4 years in contrast the average thickness of the seasonal ice in midwinter 2 m which covered more than two thirds of the arctic ocean in 2007 exhibited a negligible trend average winter sea ice volume over the period weighted by a loss of 3000 km3 between 2007 and 2008 was 14 000 km3 the total my ice volume in the winter has experienced a net loss of 6300 km3 40 in the 4 years since 2005 while the first year ice cover gained volume owing to increased overall area coverage the overall decline in volume and thickness are explained almost entirely by changes in the my ice cover combined with a large decline in my ice coverage over this short record there is a reversal in the volumetric and areal contributions of the two ice types to the total volume and area of the arctic ocean ice cover seasonal ice having surpassed that of my ice in winter area coverage and volume became the dominant ice type it seems that the near zero replenishment of the my ice cover after the summers of 2005 and 2007 an imbalance in the cycle of replenishment and ice export has played a significant role in the loss of arctic sea ice volume over the icesat record

poleward deflection of storm tracks an analysis of 11 years of european centre for medium range weather forecasts data focuses primarily on the vertically averaged high frequency transients the conclusions are discussed in the context of a the winter storm track b monthly variability and c interannual variability a winter storm track results show that the pattern of the forcing by the high frequency eddies along the storm track is highly correlated with the stationary circulation and the forcing itself is primarily responsible for the location of the trough ridge system associated with the stationary flow the results also clarify the role of wind component covariance terms u9y9 and y9 2 2 u9 2 in the column averaged vorticity forcing the simpler term u9y9 has the well known effect of intensifying the anticyclonic cyclonic tendencies on the southern northern side of the jet thereby producing an increase in the barotropic component of the zonal jet the y9 2 2 u9 2 term displays a quadrupole pattern which is also approximately in phase with the trough ridge system associated with the stationary flow b monthly variability eddy activity has been shown to possess a seasonal life cycle increasing during the early fall and reaching a maximum around the month of november then decaying for most of the winter months month to month variations in eddy activity over the pacific ocean show that energy levels increase up through november decreasing thereafter at the same time the trough ridge circulation pattern is intensifying by december baroclinicity in the western pacific has increased substantially and low level eddies are found to break by the middle of the ocean upper level eddies start to break well before reaching the west coast of north america resulting in a displacement of the maximum in y9 2 2 u9 2 westward from its november position and increasing the trough ridge forcing by the high frequency eddies c interannual variability wintertime eddy kinetic energy is seen to extend further eastward through the pacific ocean during the warm phase but displays an abrupt termination during the cold phase anomalies in the eddy transient forcing tend to be quite similar to that of the pacific north american pattern itself the extension of the storm track during the warm phase resembles that of fall conditions and is present in the winter season because the source of low level baroclinicity

on the origin of the chemical properties of the arctic ocean halocline profiles of chemical constituents in seawater above the alpha ridge in the central arctic ocean obtained during the canadian expedition to study the alpha ridge cesar support a model in which the halocline is maintained by dense saline water produced on the continental shelves within the arctic ocean by the formation of sea ice it is argued that nutrient regeneration on the continental shelves largely accounts for the nutrient maximum that has been observed in the upper halocline over a wide region of the arctic ocean and that while the bering sea and north altantic can be recognized as origins of halocline water water masses from these regions undergo sufficient changes in their chemical properties within the arctic ocean significant that they no longer retain their identity in the halocline

hydrographic conditions during the 2002 sbi process experiments abstract a review of the hydrographic data from the 2002 western arctic shelf basin interactions sbi process cruises permits the following conclusions 1 temperature salinity relationships were similar to canonical descriptions but at five stations in the outer shelf slope region warm high salinity atlantic layer water appeared to have risen displaced the lower halocline and mixed with shelf upper halocline water 2 primary production in the sbi study region was strongly influenced by the advection of dissolved inorganic nitrogen din entering via bering strait this import of din ammonium nitrate nitrite is modified by local processes but without the bering strait inflow biological productivity in the sbi region would be much lower 3 in comparison to the inflowing atlantic waters din urea phosphate and din urea silicate ratios in the pacific waters that dominated the upper 150 m of the water column were low they were also low relative to redfield uptake ratios for phytoplankton 4 microbial processes continue to destroy din in significant quantities as the pacific waters transit the sbi region 5 nitrate and ammonium were the principal contributors to din nitrite concentrations were always

fixed point observation of mixed layer evolution in the seasonally ice free chukchi sea turbulent mixing due to gale winds and internal gravity waves abstracta fixed point observation using the r v mirai was conducted in the ice free northern chukchi sea of the arctic ocean during september of 2013 during the program the authors performed repeated microstructure measurements to reveal the temporal evolution of the surface mixed layer and mixing processes in the upper water column the shelf region was initially characterized by a distinct two layer system comprising a warmer fresher top layer and a colder saltier bottom layer during the two week observation period the top layer water showed two types of mixing processes near surface turbulence due to strong wind forcing and subsurface mixing due to internal gravity waves in the first week when the top layer was stratified with fresh sea ice meltwater turbulent energy related to internal waves propagated through the subsurface stratification resulting in a mechanical overturning near the pycnocline followed by enhanced mixing there in the second week gale winds directly stirred up the upper w

testing model parameters for wave induced dune erosion using observations from hurricane sandy models of dune erosion depend on a set of assumptions that dictate the predicted evolution of dunes throughout the duration of a storm lidar observations made before and after hurricane sandy at over 800 profiles with diverse dune elevations widths and volumes are used to quantify specific dune erosion model parameters including the dune face slope which controls dune avalanching and the trajectory of the dune toe which controls dune migration wave impact models of dune erosion assume a vertical dune face and erosion of the dune toe along the foreshore beach slope observations presented here show that these assumptions are not always valid and require additional testing if these models are to be used to predict coastal vulnerability for decision making purposes observed dune face slopes steepened by 43 yet did not become vertical faces and only 50 of the dunes evolved along a trajectory similar to the foreshore beach slope observations also indicate that dune crests were lowered during dune erosion moreover analysis showed a correspondence between dune lowering and narrower beaches smaller dune volumes and or longer wave impact

east west differences in water mass nutrient and chlorophyll a distributions in the sea ice reduction region of the western arctic ocean 1 the r v mirai conducted hydrographic surveys in the western arctic ocean during summer 2004 across a front between cold arctic water and warm water from the pacific ocean where sea ice cover has been largely reduced in recent summers the hydrographic data indicate a new type of vertical temperature minimum water west of the front along isohaline surfaces with approximate salinity s of 32 which is fresher than the typical temperature minimum s 33 caused by spreading of pacific winter water pww mainly to the east of the front both of the temperature minimum waters are characterized by low potential vorticity with near freezing temperature suggesting that they are formed by winter convection with sea ice formation a difference between the waters results from a large contribution of sea ice meltwater to the fresh temperature minimum frtmin water of s 32 the distributions of the sea ice meltwater contribution and nitrogen deficit suggest that summer shelf water largely influenced by the sea ice melt in the chukchi sea is modified by winter convection on its way to the chukchi abyssal plain to form the frtmin water this water supplies nutrients through the water distribution to the west of the front at depths shallower than the nutrient maximum layer caused by the pww spreading the shallower nutrient supply by the frtmin water combined with light penetration without sea ice cover could produce a prominent chlorophyll a maximum layer west of the front

circulation on the north central chukchi sea shelf abstract mooring and shipboard data collected between 1992 and 1995 delineate the circulation over the north central chukchi shelf previous studies indicated that pacific waters crossed the chukchi shelf through herald valley in the west and barrow canyon in the east we find a third branch through the central channel onto the outer shelf the central channel transport varies seasonally in phase with bering strait transport and is 0 2 sv on average although some of this might include water entrained from the outflow through herald valley a portion of the central channel outflow moves eastward and converges with the alaskan coastal current at the head of barrow canyon the remainder appears to continue northeastward over the central outer shelf toward the shelfbreak joined by outflow from herald valley the mean flow opposes the prevailing winds and is primarily forced by the sea level slope between the pacific and arctic oceans current variations are mainly wind forced but baroclinic forcing associated with upstream dense water formation in coastal polynyas might occasionally be important winter water mass modification depends crucially on the fall and winter winds which control seasonal ice development an extensive fall ice cover delays cooling limits new ice formation and results in little salinization in such years bering shelf waters cross the chukchi shelf with little modification in contrast extensive open water in fall leads to early and rapid cooling and if accompanied by vigorous ice production within coastal polynyas results in the production of high salinity 33 shelf waters such interannual variability likely affects slope processes and the transport of pacific waters into the arctic ocean interior

understanding the hydrochemical evolution of a coastal dune system in sw england using a multiple tracer technique an improved knowledge of the hydrology of coastal dune systems is desirable for successful management of their diverse ecology under a changing climate as a near pristine coastal dune spit system braunton burrows sw england is an ideal location for the study of the natural processes governing recharge to the dune groundwater system and the evolution of its water quality whereas previous investigations have tended to focus on inter dune slacks this study has also given attention to infiltration through the high dunes cores were taken through dunes and the resulting sand samples processed to provide information on grain size distribution and porewater chemistry groundwater samples were obtained from beneath dunes and slacks a variety of geochemical techniques were applied including hydrochemistry stable isotopes and residence time indicators the unsaturated zone profiles indicate the existence of piston flow recharge with an infiltration rate of 0 75 1 m yr although faster rates probably also occur locally groundwater beneath the high dunes gave ages in the range 13 16 yr compared to the dune slack groundwater ages of 5 7 yr and an age of 22 yr for groundwater from the underlying mudstone aquifer the chemistry of waters in both unsaturated and saturated zones is dominated by ca and hco3 supplemented by variable amounts of other ions derived from marine aerosols and limited reaction with sand grains and their coatings the main chemical evolution of the porewaters occurs rapidly through the mobilisation of surface salt crusts and dissolution of shell carbonate this situation changes little in the underlying groundwater though an evolution towards reducing conditions increases the concentrations of redox sensitive species such as fe and mn the rapid chemical evolution of the infiltrating water means that its composition will respond quickly to changes in the supply of shell material and or marine salts which are possible consequences of climate change however the residence time measurements suggest the dune aquifer has a relatively long turnover time which will to some extent buffer such changes the results of the present study should be transferable to natural dune systems in similar coastal situations

nutrient supply and biological response to wind induced mixing inertial motion internal waves and currents in the northern chukchi sea a fixed point observation station was set up in the northern chukchi sea during autumn 2013 and for about 2 weeks conductivity temperature depth ctd water samplings 6 h and microstructure turbulence measurements 2 to 3 times a day were performed this enabled us to estimate vertical nutrient fluxes and the impact of different types of turbulent mixing on biological activity there have been no such fixed point observations in this region where incoming low salinity water from the pacific ocean river water and sea ice meltwater promote a strong pycnocline halocline that stabilizes the water column previous studies have suggested that because of the strong pycnocline wind induced ocean mixing could not change the stratification to impact biological activity however the present study indicates that a combined effect of an uplifted pycnocline accompanied by wind induced inertial motion and turbulent mixing caused by intense gale force winds 10 m s 1 did result in increases in upward nutrient fluxes primary productivity and phytoplankton biomass particularly large phytoplankton such as diatoms convective mixing associated with internal waves around the pycnocline also increased the upward nutrient fluxes and might have an impact on biological activity there for diatom production at the fixed point observation station it was essential that silicate was supplied from a subsurface silicate maximum a new feature that we identified during autumn in the northern chukchi sea water mass distributions obtained from wide area observations suggest that the subsurface silicate maximum water was possibly derived from the ventilated halocline in the canada basin

experiments and modeling of flow processes in freshwater lenses in layered island aquifers analysis of age stratification travel times and interface propagation summary the management of fresh groundwater resources and the delineation of protection zones on islands require a thorough understanding of flow processes within freshwater lenses previous studies of freshwater lenses have mainly focused on interface geometries disregarding flow patterns within the lens in this study we use physical analytical and numerical modeling to investigate the influence of vertically and horizontally layered aquifers and variations in recharge on the age stratification travel times and transient development of freshwater lenses four generalized settings were examined in detail on a laboratory scale the experiments show significant deviations from homogeneous models the case of a high permeability layer underlying a layer of lower permeability shows the strongest deviations in the processes investigated here water in the more permeable lower layer overtakes water flowing only through the upper layer causing a bimodal distribution of travel times and a vertical repeating of the age stratification near the coast the effects of heterogeneities revealed by the physical model experiments are expected to also occur on real islands and have thus to be considered when developing conceptual models for the management of such freshwater lenses

the role of sea ice and other fresh water in the arctic circulation salinity stratification is critical to the vertical circulation of the high latitude ocean we here examine the control of the vertical circulation in the northern seas and the potential for altering it by considering the budgets and storage of fresh water in the arctic ocean and in the convective regions to the south we find that the present day greenland and iceland seas and probably also the labrador sea are rather delicately poised with respect to their ability to sustain convection small variations in the fresh water supplied to the convective gyres from the arctic ocean via the east greenland current can alter or stop the convection in what may be a modern analog to the halocline catastrophes proposed for the distant past the north atlantic salinity anomaly of the 1960s and 1970s is a recent example it must have had its origin in an increased fresh water discharge from the arctic ocean similarly the freshening and cooling of the deep north atlantic in recent years is a likely manifestation of the increased transfer of fresh water from the arctic ocean into the convective gyres finally we note that because of the temperature dependence of compressibility a slight salinity stratification in the convective gyres is required to efficiently ventilate the deep ocean

wind driven shelf basin exchange on an arctic shelf the joint roles of ice cover extent and shelf break bathymetry 1 the efficiency of shelf basin exchange sbe in polar regions during summer is strongly moderated by the location of the ice edge relative to underlying topography numerical model calculations suggest that upwelling favorable winds generate very little sbe so long as the ice edge remains shoreward of the shelf break but an abrupt onset of shelf break upwelling takes place when the ice edge retreats beyond the shelf break a climatology 1968 2000 of ice conditions from the canadian shelf of the beaufort sea shows large interannual variability in ice edge extent and duration of ice free conditions in summer similarly available hydrographic data reflect a corresponding variability in water mass properties under scenarios of climate warming associated with greenhouse gas build up both the extent and duration of summer melt back are predicted to increase and this may have dramatic impacts on sbe and biological productivity

barrow canyon volume heat and freshwater fluxes revealed by long term mooring observations between 2000 and 2008 1 barrow canyon in the northeast chukchi sea is a major conduit for pacific water to enter the interior arctic basins assemblies of annual september 2000 to august 2008 temperature salinity and velocity data acquired from a mooring array in the mouth of barrow canyon and high resolution hydrographic and velocity transects along the mooring array in 2002 2010 and 2011 have enabled a direct computation of volume heat and freshwater fluxes annual mean volume transport through barrow canyon was 0 45 sv which consisted of 0 44 sv of pacific water and 0 01 sv of atlantic water annual mean pacific water transport through barrow canyon represents 55 of the long term mean pacific water inflow through the bering strait during summer more of the pacific inflow was advected to an eastern path as the alaskan coastal current that flows along the alaskan coast to barrow canyon the freshwater flux through barrow canyon was 904 km3 yr which is equivalent to 5 of the freshwater content of the canada basin the annual averaged heat flux displayed substantial interannual variability ranging from 0 93 to 3 02 tw which could melt 88 000 290 000 km2 of 1 m thick ice a relationship exists between the measured barrow canyon transport and local winds such that under southerly winds the northward flow of water through the canyon increases such wind conditions are induced by the weaker sea level pressure contrast between the arctic and north pacific caused by a decrease in the pressure over the arctic and an increase over the north pacific

spatial patterns of primary production on the shelf slope and basin of the western arctic in 2002 in the spring and summer of 2002 primary production in the chukchi sea was measured using 14 c uptake experiments our cruise track encompassed the shelf and continental slope area of the chukchi and beaufort seas progressing into deep water over the canada basin the study area experienced upwards of 90 ice cover during the spring with ice retreating into the basin during the summer production in the spring was light limited due to ice cover with average euphotic zone production rates of o0 3 g c m 2 d 1 values of 8 g c m 2 d 1 were observed in association with surface bloom conditions during the initial ice breakup considerable nutrient reduction in the surface waters took place between the spring and summer cruise and although not observed this was attributed to a spring bloom decreased ice cover and increased clarity of surface waters in the summer allowed greater light penetration the highest rates of production during the second cruise were found at 25 30 m coincident with the top of the nutricline daily euphotic zone productivity in the summer averaged 0 78 g c m 2 d 1 on the shelf and 0 32 g c m 2 d 1 on the edge of the canada basin these data provide an estimated annual production of 90 g c m 2 yr 1 in the study area

use of ammonium and other nitrogen tracers to investigate the spreading of shelf waters in the western arctic halocline 1 the contribution of nutrient regeneration in summer to the nutrient maximum associated with bering sea winter water bsww is estimated from the ammonium data which was obtained in the outer shelf region of the chukchi sea for the first time by the r v mirai in 2002 the contribution rate reaches 20 30 which is larger than the rate studied earlier inside the chukchi shelf such bsww influenced by the regeneration spreads to the chukchi shelf slope up to the isobath of 3000 m however was not found in the canada basin the ammonium and a nitrogen deficit are also useful tracers to study the spreading of shelf waters that are less saline than bsww in the canada basin a small amount of ammonium 2 m was observed east of the northwind ridge this small amount of ammonium would be associated with the spreading of eastern chukchi summer water via the barrow canyon around the chukchi borderland a prominent nitrogen deficit layer was found it would be accompanied by western chukchi summer water via the hope valley herald valley channel the water flows into the chukchi abyssal plain and then spreads eastward to the west of the northwind ridge with the decrease of nitrogen deficit signal

shoaling of the nutricline with an increase in near freezing temperature water in the makarov basin 1 the water mass changes in the makarov basin and adjacent areas associated with the recent loss of arctic sea ice had not been studied in detail we combined data obtained from multiple cruises in these regions and used chemical tracers to investigate the spatial and temporal changes in water masses our data show that a previously present temperature maximum water has disappeared from the makarov basin and chukchi abyssal plain due to enhanced cooling and convection in the east siberian sea in addition a large volume of water has formed by cooling and convection and is flowing into the makarov basin producing a temperature minimum with relatively high nutrients and resulting in a shoaling of the nutricline this temperature minimum water likely originated from the eastern part of the east siberian sea where significant open water areas appeared after 2005 in the freeze up season the water mass boundary between this temperature minimum water and the pacific origin temperature minimum water shifted westward from the chukchi plateau in the early 2000s to the mendeleyev ridge in the late 2000s probably owing to a westward flow of the enhanced beaufort gyre associated with recent sea ice loss in the canada basin although the shoaling of the nutricline in the makarov basin could increase phytoplankton production such production could decrease in the southern makarov basin because a large amount of sea ice meltwater covers that region and might decrease the nutrient supply from the subsurface layer

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

soil moisture and dry bulk density patterns in bare dune sands abstract recent research has shown that irregular wetting and preferential flow may occur in heterogeneous field soils bare dune sands which at first sight show the greatest homogeneity were sampled volumetrically at nine locations in temperate and arid areas to determine the spatial distribution of soil moisture content and dry bulk density soil moisture patterns were irregular even in extremely dry situations as functions for dune sands are very steep in the dry range small differences in water content result in huge differences in hydraulic conductivity these differences induced by soil moisture variability may result in anisotropy of the system and hysteresis tends to magnify this phenomenon so if soil moisture differences exist they will be consolidated and even amplified during new rain events at one site on a recently deposited dune sand infiltrating water was able to transform a one layer soil system into a two layer soil system inducing preferential flow at the layer interface at another site preferential flow paths appeared at the soil surface as sand columns as a result of the displacement of the dry sand between the flow paths caused by wind erosion in all the dunes studied dry bulk density patterns were irregular and tended to be slightly vertically orientated spatial distributions of volumetric and gravimetric soil water content showed great similarity