arctic ocean circulation patterns revealed by grace abstractmeasurements of ocean bottom pressure obp anomalies from the satellite mission gravity recovery and climate experiment grace complemented by information from two ocean models are used to investigate the variations and distribution of the arctic ocean mass from 2002 through 2011 the forcing and dynamics associated with the observed obp changes are explored major findings are the identification of three primary temporal spatial modes of obp variability at monthly to interannual time scales with the following characteristics mode 1 50 of the variance is a wintertime basin coherent arctic mass change forced by southerly winds through fram strait and to a lesser extent through bering strait these winds generate northward geostrophic current anomalies that increase the mass in the arctic ocean mode 2 20 reveals a mass change along the siberian shelves driven by surface ekman transport and associated with the arctic oscillation mode 3 10 reveals a mass dipole with mass decreasing

cosmogenic 3he production rates from 39 n to 46 n latitude western usa and france the in situ production rate of cosmogenic 3he was determined in seven different olivine or pyroxene bearing rocks between the latitudes 39 n and 46 n the integrated production rate over the last 17 500 years is about 115 4 atoms gram yr for high latitude at sea level the variation in the integrated production rate between 2000 and 18 000 years is less than 30 and is probably on the order of 20 or less

cosmic ray labeling of erosion surfaces in situ nuclide production rates and erosion models a number of in situ cosmogenic radionuclides and stable nuclides have been measured in natural exposed rock surfaces with a view to study their in situ production and rock erosion rates 1 the in situ radionuclides can be used for a high resolution tomography of the erosional history of an exposed surface two stable nuclides 3he 21ne and five radionuclides 10be 26al 36cl 14c 39ar having half lives in the range of 300 1 5 106 yr half life are measurable in many rock types a prerequisite for the application of the in situ nuclides for the study of erosional histories of surfaces is a knowledge of their production rates under different irradiation conditions altitude latitude irradiation geometry and shielding relative nuclide production rates can be determined fairly accurately using the extensive available data on cosmic ray neutrons 2 absolute nuclide production rates cannot generally be predicted with any accuracy because of lack of data on excitation functions of nuclides unless some normalization is possible as was done in the case of several cosmic ray produced isotopes in the atmosphere 3 based on a recent natural calibration experiment in which erosion free surfaces exposed to cosmic radiation for 11 000 yrs were sampled the absolute production rates of 10be and 26al in quartz have been accurately estimated for mountain altitudes in sierra nevada 4 the absolute production rates of 10be and 26al in quartz can therefore be estimated fairly accurately for any given latitude and altitude some measurements of 14c in rocks of low erosion rate 5 similarly allow an estimate of its production rate attempts made to measure the in situ production rates of 3he in rocks have not yet led to a convergent production rate in view of the importance of knowing the production rates of isotopes of he ne and ar i present here theoretical estimates of their production rates based on available cross section data i discuss the information that can be extracted from the study of the in situ nuclides in rocks useful parameters characterizing the exposure history of a rock surface are 1 the effective surface exposure age and 2 the time averaged erosion rate the implications of these parameters for single and multiple nuclide studies are discussed in terms of the erosion models considered

origin of freshwater and polynya water in the arctic ocean halocline in summer 2007 extremely low summer sea ice coverage in the arctic ocean in 2007 allowed extensive sampling and a wide quasi synoptic hydrographic and 18o dataset could be collected in the eurasian basin and the makarov basin up to the alpha ridge and the east siberian continental margin with the aim of determining the origin of freshwater in the halocline fractions of river water and sea ice meltwater in the upper 150 m were quantified by a combination of salinity and 18o in the eurasian basin two methods applying the preformed phosphate concentration po and the nitrate to phosphate ratio n p were compared to further differentiate the marine fraction into atlantic and pacific derived contributions while po based assessments systematically underestimate the contribution of pacific derived waters n p based calculations overestimate pacific derived waters within the transpolar drift due to denitrification in bottom sediments at the laptev sea continental margin within the eurasian basin a west to east oriented front between net melting and production of sea ice is observed outside the atlantic regime dominated by net sea ice melting a pronounced layer influenced by brines released during sea ice formation is present at about 30 to 50 m water depth with a maximum over the lomonosov ridge the geographically distinct definition of this maximum demonstrates the rapid release and transport of signals from the shelf regions in discrete pulses within the transpolar drift the ratio of sea ice derived brine influence and river water is roughly constant within each layer of the arctic ocean halocline the correlation between brine influence and river water reveals two clusters that can be assigned to the two main mechanisms of sea ice formation within the arctic ocean over the open ocean or in polynyas at the continental slope where relatively small amounts of river water are found sea ice formation results in a linear correlation between brine influence and river water at salinities of about 32 to 34 in coastal polynyas in the shallow regions of the laptev sea and southern kara sea sea ice formation transports river water into the shelf s bottom layer due to the close proximity to the river mouths this process therefore results in waters that form a second linear correlation between brine influence and river water at salinities of about 30 to 32 our study indicates which layers of the arctic ocean halocline are primarily influenced by sea ice formation in coastal polynyas and which layers are primarily influenced by sea ice formation over the open ocean accordingly we use the ratio of sea ice derived brine influence and river water to link the maximum in brine influence within the transpolar drift with a pulse of shelf waters from the laptev sea that was likely released in summer 2005

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

records of cosmogenic radionuclides 10be 26al and 36cl in corals first studies on coral erosion rates and potential of dating very old corals we present results of measurements of cosmogenic 10 be 26 al and 36 cl and the indigenous intrinsic concentrations of the stable elements be al and cl in 120 200 kyr old corals from barbados and puerto rico the concentration levels of these radionuclides in the corals lie in the range 10 4 to 10 8 atoms g a comparison of the measured nuclide concentrations with those expected to be produced in the corals by nuclear interactions of energetic cosmic radiation shows that i the radionuclides 26 al and 36 cl are derived from in situ cosmic ray interactions in the corals after their formation but that ii the radionuclide 10 be owes its provenance in the coralline lattice primarily due to incorporation of dissolved beryllium in seawater in the lattice structure of the corals copyright 2005 elsevier ltd we discuss production rates and potential uses of cosmogenic radionuclides in corals and the implications of the measure ments reported here on the concentration of the cosmogenic radionuclides 10 be 26 al and 36 cl we show that the latter two radionuclides serve as gauges of coral terrace erosion rates whereas the cosmogenic 10 be is suitable for determining the ages of old corals of ages exceeding a few million years up to 10 myr the erosion rates of the corals range from 0 7 to 5 10 3 cm yr corresponding to an appreciable surface loss after aerial exposure 1 3 m since the last interglacial and 8m since the penultimate interglacial

quaternary palaeolakes in the evolution of semidesert basins with special emphasis on lake bonneville and the great basin u s a abstract this paper reviews attributes of quaternary lakes and lake basins which are often important in the environmental prehistory of semideserts basin floor and basin closure morphometry have set limits on palaeolake sizes lake morphometry and basin drainage patterns have influenced lacustrine processes and water and sediment loads have influenced basin neotectonics information regarding inundated runoff producing and extra basin spatial domains is acquired directly from the palaeolake record including the littoral morphostratigraphic record and indirectly by reconstruction increasingly detailed hypotheses regarding lake bonneville the largest late pleistocene palaeolake in the great basin are subjects for further testing and refinement oscillating transgression of lake bonneville began about 28 ka the highest stage occurred about 15 ka and termination occurred abruptly about 13 ka a final resurgence of perennial lakes probably occurred in many subbasins of the great basin between 11 and 10 ka when the highest stage of great salt lake successor to lake bonneville developed the gilbert shoreline and when the russell shoreline formed 500 600 km away in the carson desert of the lake lahontan basin the highest post gilbert stage of great salt lake which has been one of the few permanent lakes in the great basin during holocene time probably occurred between 3 and 2 ka a set of eighteen general observations regarding geologic aspects of the palaeolake record in semidesert basins is helping to guide quaternary studies in the great basin

a new extraction technique and production rate estimate for in situ cosmogenic 14c in quartz the potential of in situ cosmogenic 14c in situ 14c for surficial process studies is widely recognized yet a reliable means of isolating it has proved difficult to develop we present here a new method for extracting in situ 14c from quartz that overcomes difficulties encountered with earlier techniques yielding more reliable production rate estimates comparison of 14c thermal release patterns from surficial and deeply shielded quartz samples lifton 1997 demonstrated that contaminant 14c is released at or below 500 c and that 14c released between 500 and 1500 c is essentially all in situ produced the new technique builds on this key result using resistance heating of samples in the presence of a lithium metaborate libo2 flux and collection of all evolved carbon as co2 between 500 c and 1100 to 1200 c our improved method has four distinct advantages over other extraction methods 1 we can identify and quantitatively eliminate atmospheric organic 14c contamination 2 we can identify the in situ 14c component unambiguously without assumptions of 14co 14co2 production proportions within the rock or equilibria on extraction 3 in situ 14c is reliably extracted from quartz at lower temperatures and in less time than earlier methods and 4 blank 14c levels are consistently low 2 3 0 1 105 14c atoms 1 our new extraction procedures should thus enable researchers to use in situ 14c in diverse applications without reservation we developed our new procedures using samples of wave cut quartzite benches from the well dated bonneville 17 4 0 3 cal ky and provo 16 8 0 3 cal ky shorelines of pleistocene lake bonneville utah and from underlying deeply shielded locations in situ 14c was extracted from quartz separated from 2 bonneville shoreline samples 6 aliquots and 1 provo shoreline sample 2 aliquots results demonstrate that our new procedures can effectively isolate the in situ 14c fraction with replicate analytical precision better than 2 1 n 5 while remaining consistent with earlier results this level of precision and accuracy is comparable to or exceeds those currently obtainable with in situ cosmogenic 10be 26al 3he 21ne and 36cl resulting weighted mean in situ 14c site production rates for the bonneville and provo shorelines are 52 9 1 7 14c atoms g sio2 y and 48 7 2 8 14c atoms g sio2 y 1 respectively consistent with earlier production rate estimates current and previously published in situ 14c site production rate estimates were then scaled to sea level and high geomagnetic latitude using the latitude altitude scaling models of lal 1991 and dunai 2000 results indicate that both models yield sea level high latitude production rates consistent with independent estimates our new in situ 14c data yield integrated late quaternary production rate estimates at sea level and high latitude of 15 1 0 5 14c atoms g sio2 y using the lal 1991 model and 15 8 0 5 14c atoms g sio2 y with that of dunai 2000 until significant uncertainties in these models are addressed however we prefer the value from the widely used lal 1991 model as our best estimate of the integrated late quaternary production rate for in situ 14c

export of nutrients from the arctic ocean 1 this study provides the first physically based mass balanced transport estimates of dissolved inorganic nutrients nitrate phosphate and silicate for the arctic ocean using an inverse model generated velocity field in combination with a quasi synoptic assemblage of hydrographic and hydrochemical data we quantify nutrient transports across the main arctic ocean gateways davis strait fram strait the barents sea opening bso and bering strait we found that the major exports of all three nutrients occur via davis strait transports associated with the east greenland current are almost balanced by transports associated with the west spitsbergen current the most important imports of nitrate and phosphate to the arctic occur via the bso and the most important import of silicate occurs via bering strait oceanic budgets show that statistically robust net silicate and phosphate exports exist while the net nitrate flux is zero within the uncertainty limits the arctic ocean is a net exporter of silicate 15 7 3 2 kmol s 1 and phosphate 1 0 0 3 kmol s 1 net 1 standard error to the north atlantic the export of excess phosphate relative to nitrate from the arctic calculated at 1 1 0 3 kmol s 1 is almost twice as large as previously estimated net transports of silicate and phosphate from the arctic ocean provide 12 and 90 respectively of the net southward fluxes estimated at 47 n in the north atlantic additional sources of nutrients that may offset nutrient imbalances are explored and the relevance and the pathway of nutrient transports to the north atlantic are discussed

correlation of river water and local sea ice melting on the laptev sea shelf siberian arctic hydrographic and stable isotope 18o data from 4 summer surveys in the laptev sea are used to derive fractions of sea ice meltwater and river water sea ice meltwater fractions are found to be correlated to river water fractions while initial heat of river discharge is too small to melt the observed 0 158 km3 of sea ice meltwater arctic rivers contain suspended particles spm and colored dissolved organic material cdom that preferentially absorb solar radiation accordingly heat content in surface waters is correlated to river water fractions but in years when river water is largely absent within the surface layer absolute heat content values increase to considerably higher values with extended exposure time to solar radiation and sensible heat nevertheless no net sea ice melting is observed on the shelf in years when river water is largely absent within the surface layer the total freshwater volume of the central eastern laptev sea 72 76 n 122 140 e varies between 1000 1500 km3 34 92 reference salinity it is dominated by varying river water volumes 1300 1800 km3 reduced by an about constant freshwater deficit 350 400 km3 related to sea ice formation net sea ice melt 109 158 km3 is only present in years with high river water budgets intermediate to bottom layer 25 salinities contain 60 and 30 of the river budget in years with low and high river budgets respectively the average mean residence time of shelf waters was 2 3 years during 2007 2009

dynamic topography of the ice covered arctic ocean from icesat 1 we construct the dynamic ocean topography dot of the arctic ocean for five icesat campaigns winter of 2004 2008 using sea surface height estimates in open leads results show that the mean winter dot over the arctic ocean varies by 1 m and features a distinct dome of 40 cm over the beaufort sea standard deviation of the mean field is 20 cm spatial coherence between the five winter dots is consistently high 0 9 whereas the coherence between the dots and the winter djfm sea level pressure fields over the arctic basin is variable this suggests persistence of the underlying hydrodynamic processes at interannual time scales compared to seasonal atmospheric forcing comparison of dynamic heights dh from hydrographic surveys and the dot in 2008 shows a remarkable correlation of 0 92 the geostrophic velocity fields computed from the dot and interpolated dh fields highlight the smaller scale oceanographic features in the satellite estimates

a cosmic trip 25 years of cosmogenic nuclides in geology terrestrial cosmogenic nuclides produced by secondary cosmic ray interactions in the atmosphere and in situ within minerals in the shallow lithosphere are widely used to date surface exposure of rocks and sediments to estimate erosion and weathering rates and to date sediment deposition or burial their use has transformed geomorphology and quaternary geology for the first time allowing landforms to be dated and denudation rates to be measured over soil forming time scales the application of cosmogenic nuclides to geology began soon after the invention of accelerator mass spectrometry ams in 1977 and increased dramatically with the measurement of in situ produced nuclides in mineral grains near earth s surface in the 1980s the past 25 yr have witnessed the development of cosmogenic nuclides from their initial detection to their prevalence today as a standard geochronological and geochemical tool this review covers the major developments of the past 25 yr by comparing the state of the field in 1988 with that of today and by identifying key advances in that period that moved the field forward we emphasize the most commonly used in situ produced nuclides measured by ams for geological applications but we also discuss other nuclides where their applications overlap our review covers ams instrumentation cosmogenic nuclide production rates the methods of surface exposure dating measurement of erosion and weathering and burial dating and meteoric 10 be in memoriam devendra lal 1929 2012 whose vision inspired the field

reinterpretation of the exposed record of the last two cycles of lake bonneville western united states a substantially modified history of the last two cycles of lake bonneville is proposed the bonneville lake cycle began prior to 26 000 yr b p the lake reached the bonneville shoreline about 16 000 yr b p poor dating control limits our knowledge of the timing of subsequent events lake level was maintained at the bonneville shoreline until about 15 000 yr b p or somewhat later when catastrophic downcutting of the outlet caused a rapid drop of 100 m the provo shoreline was formed as rates of isostatic uplift due to this unloading slowed by 13 000 yr b p the lake had fallen below the provo level and reached one close to that of great salt lake by 11 000 yr b p deposits of the little valley lake cycle are identified by their position below a marked unconformity and by amino acid ratios of their fossil gastropods the maximum level of the little valley lake was well below the bonneville shoreline based on degree of soil development and other evidence the little valley lake cycle may be equivalent in age to marine oxygenisotope stage 6 the proposed lake history has climatic implications for the region first because the fluctuations of lake bonneville and lake lahontan during the last cycle of each were apparently out of phase there may have been significant local differences in the timing and character of late pleistocene climate changes in the great basin second although the bonneville and little valley lake cycles were broadly synchronous with maximum episodes of glaciation environmental conditions necessary to generate large lakes did not exist during early wisconsin time

variations in the proportions of melted sea ice and runoff in surface waters of the chukchi sea a retrospective analysis 1990 2012 and analysis of the implications of melted sea ice in an under ice bloom abstract retrospective analysis of apparent freshwater isotopic end members through use of salinity 18 o mixing lines for 15 research cruises from 1990 to 2012 indicates that the freshwater contributed by melted seasonal sea ice does not directly reflect the large change in seasonal sea ice extent in the chukchi sea observed over the past several decades instead the freshwater that appears to be contributed by melting sea ice relative to runoff is highly dependent upon cruise track e g proximity to runoff and sampling capabilities in sea ice icebreakers sample waters with less melted sea ice although under certain circumstances including later seasonal sampling and recurrent cruise tracks between years increased melted sea ice in surface waters can be readily detected this suggests a more ephemeral influence of melted sea ice on ecosystem properties despite the significant decadal changes in sea ice extent as a recent case study the freshwater component present in waters within an under ice bloom in the chukchi sea reported by arrigo et al 2012 included a significant fraction 10 or more of freshwater primarily from melted sea ice these results suggest that this under ice bloom which extended more than 60 km under solid ice still might be reasonably interpreted as being part of a continuum with other ice melt associated blooms and not independent of sea ice retreat and dissolution

comparison of geodetic and geologic data from the wasatch region utah and implications for the spectral character of earth deformation at periods of 10 to 10 million years the wasatch fault and adjacent fault zones provide an opportunity to compare present day deformation rate estimates obtained from space geodesy with geologic displacement rates over at least four temporal windows ranging from the last millennium up to 10 myr the three easternmost gps sites of the basin and range geodetic network bargen at this latitude define a 130 km wide region spanning three major normal faults extending east west at a total rate of 2 7 0 4 mm yr with an average regional strain rate estimated to be 21 4 nstrain yr about twice the basin and range average on the wasatch fault the vertical component of the geologic displacement rate is 1 7 0 5 mm yr since 6 ka 0 6 mm yr since 130 ka and 0 5 0 7 mm yr since 10 ma however it appears likely that at the longest timescale rates slowed over time from 1 0 to 1 4 mm yr between 10 and 6 ma to 0 2 to 0 3 mm yr since 6 ma the cumulative vertical displacement record across all three faults also shows time variable strain release ranging from 2 to 4 mm yr since 10 ka to 1 mm yr averaged over the past 130 kyr conventional earthquake recurrence models reid type behavior would require an accordingly large variation in strain accumulation or loading rate on a 10 kyr timescale for which there appears to be no obvious geophysical explanation alternatively seismic strain release given a wide range of plausible constitutive behaviors for frictional sliding may be clustered on the 10 kyr timescale resulting in the high holocene rates with comparatively low uniform strain accumulation rates on the 100 kyr timescale wallace type behavior the latter alternative combined with observations at the million year timescale and the likelihood of a significant contribution of postseismic transients implies maxima of spectral amplitude in the velocity field at periods of 10 myr variations in tectonic loading 10 kyr clustered strain release and of 100 years postseismic transients if so measurements of strain accumulation and strain release may be strongly timescale dependent for any given fault system

cosmogenic neon in recent lavas from the western united states the absolute cosmogenic production of 21ne 21nec and 3he 3hec in olivine fo81 is measured for the well dated tabernacle hill flow values scaled to sea level and high latitude 60 are 45 atoms g yr for 21nec and 109 atoms g yr for 3hec for the past 17 800 years production rates for 21nec are about 50 higher than the theoretical values given by lal 1991 a ratio of 21nec 3hec of 0 41 0 05 is measured in olivines that have a range of 25 in cosmogenic exposure there is no evidence of 3hec loss in samples older than 100 000 years volcanic plagioclase is shown to be a suitable mineral for cosmogenic 21nec dating of surfaces 21nec in co existing plagioclase and olivine phenocrysts have a constant ratio of 0 42 04 in samples with more than 106 atoms of 21nec using all of the 21nec data and the 3hec as a cosmic ray flux monitor production of 21nec in ab36 plagioclase is calculated at 16 8 1 7 atoms g yr for the past 17 800 years the production of 21nec from 23na is estimated at 160 50 atoms g yr at 60 and sea level or equivalent to that on 24mg

kara sea freshwater dispersion and export in the late 1990s 1 a regional coupled ice ocean model for the kara sea forced with boundary conditions from a large scale north atlantic arctic ocean model is used to study dispersion and export of freshwater from ob and yenisei rivers toward the arctic ocean and the laptev sea for the period 1996 2001 the years 1998 and 1999 were characterized by a strong positive sea level pressure slp anomaly in the siberian part of the arctic ocean owing to prevailing northeasterly winds the slp anomaly caused a blocking situation which suppressed the otherwise eastward freshwater export to the arctic ocean and laptev sea this reversal of the prevailing circulation scheme led to a dramatic freshening of the kara sea through accumulation of low saline river water in the central and western parts additionally the kara strait inflow from the barents sea which presents the main source for saline atlantic derived water was reduced and partly even reversed the suppressed freshwater export during winter 1998 1999 recovered in the following winter 1999 2000 when a significant pulse of low saline surface water left toward the laptev sea the variability of the river discharge plays a minor role for the investigated period because the interannual variability of runoff rates is generally too low to explain the observed hydrographic changes the results underline the importance of local shelf sea processes for the variability of the freshwater export from the arctic shelves to the central arctic ocean

high precision 14c measurements demonstrate production of in situ cosmogenic 14ch4 and rapid loss of in situ cosmogenic 14co in shallow greenland firn abstract measurements of radiocarbon 14 c in carbon dioxide co 2 methane ch 4 and carbon monoxide co from glacial ice are potentially useful for absolute dating of ice cores studies of the past atmospheric ch 4 budget and for reconstructing the past cosmic ray flux and solar activity interpretation of 14 c signals in ice is complicated by the fact that the two major 14 c components trapped atmospheric and in situ cosmogenic are present in a combined form as well as by a very limited understanding of the in situ component this study measured 14 ch 4 and 14 co content in glacial firn with unprecedented precision to advance understanding of the in situ 14 c component 14 ch 4 and 14 co were melt extracted on site at summit greenland from three very large 1000 kg each replicate samples of firn that spanned a depth range of 3 6 5 6 m non cosmogenic 14 c contributions were carefully characterized through simulated extractions and a suite of supporting measurements in situ cosmogenic 14 co was quantified to better than 0 6 molecules g 1 ice improving on the precision of the best prior ice 14 co measurements by an order of magnitude the 14 co measurements indicate that most 99 of the in situ cosmogenic 14 c is rapidly lost from shallow summit firn to the atmosphere despite this rapid 14 c loss our measurements successfully quantified 14 ch 4 in the retained fraction of cosmogenic 14 c to 0 01 molecules g 1 ice or better and demonstrate for the first time that a significant amount of 14 ch 4 is produced by cosmic rays in natural ice this conclusion increases the confidence in the results of an earlier study that used measurements of 14 ch 4 in glacial ice to show that wetlands were the likely main driver of the large and rapid atmospheric ch 4 increase approximately 11 6 kyr ago

accelerator mass spectrometry in geologic research the ability of accelerator mass spectrometry ams to measure very small concentrations of the nuclides 10 be 14 c 26 al 36 cl and 129 i has led to many innovative applications in geologic research to take advantage of this opportunity in the geosciences it is important to understand how ams works how these nuclides are produced and how they can be applied to geologic problems we first discuss the basics of ams explaining what gives the method its ability to count small numbers of these nuclides we review how these nuclides are produced and transported in the atmosphere hydrosphere and lithosphere we then explain the ways that ams is being used to solve a wide range of problems in geologic research by discussing specific applications in areas such as geomorphology tectonics climatology hydrology and geochronology

some controls on flow and salinity in bering strait 1 during 1993 1994 steric forcing of flow through bering strait represented a northward sea level drop of 0 7 m from the bering sea basin to the adjacent deep arctic ocean of which 2 3 was due to the salinity difference between the basins seasonal variability of steric forcing appears small 0 05 m in contrast to large seasonal wind effects interannual changes in steric forcing may exceed 20 however and warm inflow from the north atlantic accumulation of freshwater in the southwest canada basin and temperature and salinity changes in the upper bering sea have all contributed to recent changes the mean salinity balance in bering strait is primarily maintained by large runoff to the bering shelf dilute coastal inflow from the gulf of alaska and on shelf movement of saline and nutrient rich oceanic waters from the bering sea basin in bering strait therefore both the throughflow and its salinity are affected by remote events

image processing and roughness analysis of exposed bedrock fault planes as a tool for paleoseismological analysis results from the campo felice fault central apennines italy abstract morphologic investigations along the campo felice cf fault central apennines italy have been made in order to develop a procedure for the paleoseismological analysis of bedrock fault scarps the cf fault has been responsible for the formation of an impressive limestone fault scarp geomorphologic work on the cf basin and related fault indicated that the scarp originated from tectonic fault displacements three morphologic units have been distinguished along the fault scarp and defined as morphosome m1 lowest part of the scarp m2 and m3 the uppermost part these units display different karstic features which are the result of their different duration of exposure to weathering micromorphologic analyses focused on the morphosome m1 along which the cf fault plane is exposed for a height ranging between 4 and 7 m these analyses were aimed at defining differently weathered bands located at various heights and parallel to the fault scarp top and base the presence of these bands suggests repeated fault movements the exposed fault surface displays a low grade biokarstic weathering due to the action of epilithic and endolithic organisms the biokarst distribution is however inhomogeneous and conditioned by the presence of nourishing elements moisture and by light intensity an area preferentially affected by the biokarstic processes develops as a band at the bedrock soil contact at the base of the scarp roughness and colour analyses were made to identify uplifted bands which previously formed at the bedrock soil contact the roughness analysis was made using a microroughness meter along 20 cm long horizontal transects repeated each 20 cm of fault height for the entire morphosome m1 at various sites along the scarp the roughness variance data plotted vs the fault height failed to identify differently weathered bands of paleoseismological interest this result is probably due to the complex distribution of biokarst along the investigated fault plane more reliable results have been obtained by areal analysis of the variation of the colour rendering of the rocks exposed along the fault plane at different sites photographic images of large portions of fault surfaces have been processed with standard graphic computer programs the variations of colour indicated the presence of bands at various heights along the fault plane two uplifted bands have been recognised at all the investigated sites suggesting two displacement events e1 and e2 a preliminary chronological framework for these two events the youngest of which affected the cf fault can be derived from the paleoseismological data available for the southernmost branch of the regional fault system that includes the cf fault according to these data e1 may have occurred between 860 and 1300 ad while e2 may have occurred at about 1900 bc work is in progress to define surface exposure ages of different parts of the fault plane by means of in situ produced cosmogenic 36 cl this procedure will give further chronological constraints for the age of e1 and e2 and will also permit to test the validity of the micromorphologic analysis of bedrock fault scarps for paleoseismological aims

importance of slope gradient and contributing area for optimal prediction of the initiation and trajectory of ephemeral gullies abstract ephemeral gully erosion rates are controlled by various factors out of which topography plays an important role this study investigates the possibility to predict the location of ephemeral gullies using two topographic attributes only i e local slope gradient s and upslope contributing area per unit length of contour a s an inverse relationship between s and a s in which the relative importance of the area exponent was varied was evaluated as to its performance in predicting the location of ephemeral gullies for three intensively cultivated catchments in the belgian loess belt this model is easily applicable as it only uses information on topography which can be derived from a digital elevation model and land use predicted locations of ephemeral gullies were confronted with the locations recorded over 5 years of field observations for all catchments a high relative area exponent relative to the slope exponent was required to yield good results the optimal relative area exponent ranged from 0 7 to 1 5 however the quality of the prediction did not vary significantly when changing the exponent within this range an average relative area exponent of ca 1 is appropriate for all three study areas and may therefore be proposed for similar areas under similar conditions a striking discrepancy was found between the high relative area exponent required to predict optimally the trajectory of the gullies and the low relative area exponent 0 2 required to identify the spots in the landscape where ephemeral gullies begin this indicates that spots in the landscape where gullies start are more controlled by slope gradient while the presence of concavities control the trajectory of the gullies until the slope gradient is too low and sediment deposition starts no relationship was found between the frequency of the occurrence of ephemeral gullies and the percentage of predicted gully pixels for each frequency class this indicates that frequently occurring gullies at the same location are not easier to predict than accidental gullies

cosmogenic 14c in carbonate rocks abstract the rate of in situ production of cosmogenic 14 co in limestone is 18 3 atom g caco3 year corrected to high latitude and sea level based on measurements of 14 co in limestone associated with the bonneville provo shoreline complex in utah in situ cosmogenic 14 co was separated cryogenically from co2 using 14 c dead co as a carrier for in situ cosmogenic 14 co this rate of production was used to estimate an age of 4360 1220 cal year b p for the last movement on the south oquirrh mountain fault zone in northern utah and an age of at least 10 600 900 years for the penultimate event of the pleasant valley fault in northern nevada

effective attenuation lengths of cosmic rays producing 10be and 26al in quartz implications for exposure age dating we have measured cosmic ray produced 10be t 1 5 my and 26al t 0 72 my as functions of depth in a core of quartz sandstone bedrock collected in south victoria land antarctica these data were used to place limits on the exposure age and erosion rate of the exposed surface and to calculate the effective attenuation lengths of cosmic rays producing these nuclides these latter results indicate that the production attenuation length for 26al is comparable to that for 10be this suggests that the production ratio 26al 10be does not vary substantially with depth in a rock and that its value at the surface of exposed rock is not strongly affected by erosional losses allowing wider use of the ratio in determining exposure ages

large mid holocene and late pleistocene earthquakes on the oquirrh fault zone utah abstract the oquirrh fault zone is a range front normal fault that bounds the east side of tooele valley and it has long been recognized as a potential source for large earthquakes that pose a significant hazard to population centers along the wasatch front in central utah scarps of the oquirrh fault zone offset the provo shoreline of lake bonneville and previous studies of scarp morphology suggested that the most recent surface faulting earthquake occurred between 9000 and 13 500 years ago based on a potential rupture length of 12 to 21 km from previous mapping moment magnitude mw estimates for this event range from 6 3 to 6 6 in contrast our results from detailed mapping and trench excavations at two sites indicate that the most recent event actually occurred between 4300 and 6900 yr b p 4800 and 7900 cal b p and net vertical displacements were 2 2 to 2 7 m much larger than expected considering estimated rupture lengths for this event empirical relations between magnitude and displacement yield mw 7 0 to 7 2 a few short discontinuous fault scarps as far south as stockton utah have been identified in a recent mapping investigation and our results suggest that they may be part of the oquirrh fault zone increasing the total fault length to 32 km these results emphasize the importance of integrating stratigraphic and geomorphic information in fault investigations for earthquake hazard evaluations at both the big canyon and pole canyon sites trenches exposed faulted lake bonneville sediments and thick wedges of fault scarp derived colluvium associated with the most recent event bulk sediment samples from a faulted debris flow deposit at the big canyon site yield radiocarbon ages of 7650 90 yr b p and 6840 100 yr b p all lab errors are 1 a bulk sediment sample from unfaulted fluvial deposits that bury the fault scarp yield a radiocarbon age estimate of 4340 60 yr b p stratigraphic evidence for a pre bonneville lake cycle penultimate earthquake was exposed at the pole canyon site and although displacement is not well constrained the penultimate event colluvial wedge is comparable in size to the most recent event wedges charcoal from a marsh deposit which overlies the penultimate event colluvium and was deposited during the bonneville lake cycle transgression yields an ams radiocarbon age of 20 370 120 yr b p multiple charcoal fragments from fluvial deposits faulted during the penultimate event yield an ams radiocarbon age of 26 200 200 yr b p indirect stratigraphic evidence for an antepenultimate event was also exposed at pole canyon charcoal from fluvial sediments overlying the eroded free face for this event yields an ams age of 33 950 1160 yr b p providing a minimum limiting age on the antepenultimate event ages for the past two events on the oquirrh fault zone yield a recurrence interval of 13 300 to 22 100 radiocarbon years and estimated slip rates of 0 1 to 0 2 mm yr temporal clustering of earthquakes on the nearby wasatch fault zone in the late holocene does not appear to have influenced activity on the oquirrh fault zone however consistent with findings on the wasatch fault zone and with some other quaternary faults within the bonneville basin we found evidence for higher rates of activity during interpluvial periods than during the bonneville lake cycle if a causal relation between rates of strain release along faults and changes in loads imposed by the lake does exist it may have implications for fault dips and mechanics however our data are only complete for one deep lake cycle the past 32 000 radiocarbon years and whether this pattern persisted during the previous cutler dam and little valley deep lake cycles is unknown

cosmogenic chlorine 36 production rates in terrestrial rocks abstract chlorine 36 is produced in rocks exposed to cosmic rays at the earth surface through thermal neutron activation of 35cl spallation of 39k and 40ca and slow negative moun capture by 40ca we have measured the 36cl content of 14c dated glacial boulders from the white mountains in eastern california and in a 14c dated basalt flow from utah effective time intergrated production parameters were calculated by simultaneous solution of the 36cl production equations the production rates due to spallation are 4160 310 and 3050 210 atoms 36cl yr 1 mol 139k and 40ca respectively the thermal neutron capture rate was calculated to be 3 07 0 24 105 neutrons kg of rock 1 yr 1 the reported values are normalized to sea level and high geomagnetic latitudes production of 36cl at different altitudes and latitudes can be estimated by appropriate scaling of the sea level rates chlorine 36 dating was performed on carbonate ejecta from meteor crater arizona and late pleistocene morainal boulders from the sierra nevada california calculated 36cl ages are in good agreement with previously reported ages obtained using independent methods

observed increases in bering strait oceanic fluxes from the pacific to the arctic from 2001 to 2011 and their impacts on the arctic ocean water column 1 mooring data indicate the bering strait throughflow increases 50 from 2001 0 7 sv to 2011 1 1 sv driving heat and freshwater flux increases increase in the pacific arctic pressure head explains two thirds of the change the rest being attributable to weaker local winds the 2011 heat flux 5 1020j approaches the previous record high 2007 due to transport increases and warmer lower layer ll temperatures despite surface temperature sst cooling in the last decade warmer ll waters arrive earlier 1 6 1 1 days yr though winds and sst are typical for recent decades maximum summer salinities likely set in the bering sea remain remarkably constant 33 1 psu over the decade elucidating the stable salinity of the western arctic cold halocline despite this freshwater flux variability strongly driven by transport exceeds variability in other arctic freshwater sources remote data winds sst prove insufficient for quantifying variability indicating interannual change can still only be assessed by in situ year round measurements

distribution of atlantic and pacific waters in the upper arctic ocean implications for circulation the atlantic and pacific oceans provide source waters for the arctic ocean that can be distinguished by their differing nitrate and phosphate concentration relationships using these relationships we estimate the amount of atlantic and pacific waters in the surface layer top 30 m of the arctic ocean atlantic source water is dominant in most of the eurasian basin and is present in significant amounts in the makarov basin north of the east siberian sea pacific source water is dominant in most of the canadian basin and is present in significant amounts in the amundsen basin north of greenland we deduce circulation patterns from the distributions of atlantic and pacific source waters in the surface layer of the arctic ocean and conclude that the flow within the surface layer differs from ice drift along the north american and european boundaries of the polar basin

predicting the topographic limits to a gully network using a digital terrain model and process thresholds a digital terrain model is used with process thresholds to predict the extent of a stable gully network in a 5 km2 catchment of the southeastern highlands of australia the model developed by dietnch et al 1992 1993 predicts the topographic controls on channel networks and interprets these in terms of a critical shear stress for channel incision c applied by saturation overland flow we adapt the model slightly to compare the shear stress applied by hortonian overland flow to that applied by saturation overland flow the limits to gully erosion in the catchment are controlled strongly by a topographic threshold that has an inverse relationship between upslope catchment area and local gradient the topographic threshold for channel incision is reproduced using a simple model of hortonian overland flow and a c appropriate for incision into a degraded grass surface c 245 dyn cm2 this is consistent with historical evidence for the timing of gully erosion the study confirms a strong topographic control on the extent of the channel network in a catchment significantly different from the western north america catchments where the topographic threshold was first demonstrated despite its simplicity the model for incision by overland flow appears capable of distinguishing the hydrological processes responsible for channel incision when these are reflected in the relationship between channel network and landscape morphology the model requires relatively simple inputs suggesting it may be useful for mapping gully erosion hazard in actively eroding catchments

river runoff sea ice meltwater and pacific water distribution and mean residence times in the arctic ocean hydrographic and tracer data collected during ark iv 3 fs polarstern in 1987 arctic91 ib oden and aos94 ccgs louis s st laurent expeditions reveal the evolution of the near surface waters in the arctic ocean during the late 1980s and early 1990s salinity nutrients dissolved oxygen and 18 o data are used to quantify the components of arctic freshwater river runoff sea ice meltwater and pacific water the calculated river runoff fractions suggest that in 1994 a large portion of water from the pechora ob yenisey kotuy and lena rivers did not flow off the shelf closest to their river deltas but remained on the shelf and traveled via cyclonic circulation into the laptev and east siberian seas river runoff flowed off the shelf at the lomonosov ridge and most left the shelf at the mendeleyev ridge arctic91 and aos94 pacific water fraction estimates of upper halocline water the traditionally defined core of the pacific water mass document a decrease in extent compared to historical data the front between atlantic water and pacific water shifted from the lomonosov ridge location in 1991 to the mendeleyev ridge in 1994 the relative age structure of the upper waters is described by using the 3 h 3 he age the mean 3 h 3 he age measured in the halocline within the salinity surface of 33 1 0 3 is 4 3 1 7 years and that for the 34 2 0 2 salinity surface is 9 6 4 6 years lateral variations in the relative age structure within the halocline and atlantic water support the well known cyclonic boundary current circulation

deterioration of perennial sea ice in the beaufort gyre from 2003 to 2012 and its impact on the oceanic freshwater cycle time series of ice draft from 2003 to 2012 from moored sonar data are used to investigate variability and describe the reduction of the perennial sea ice cover in the beaufort gyre bg culminating in the extreme minimum in 2012 negative trends in median ice drafts and most ice fractions are observed while open water and thinnest ice fractions 0 3 m have increased attesting to the ablation or removal of the older sea ice from the bg over the 9 year period monthly anomalies indicate a shift occurred toward thinner ice after 2007 in which the thicker ice evident at the northern stations was reduced differences in the ice characteristics between all of the stations also diminished so that the ice cover throughout the region became statistically homogenous the moored data are used in a relationship with satellite radiometer data to estimate ice volume changes throughout the bg summer solid fresh water content decreased drastically in consecutive years from 730 km3 in 2006 to 570 km3 in 2007 and to 240 km3 in 2008 after a short rebound solid fresh water fell below 220 km3 in 2012 meanwhile hydrographic data indicate that liquid fresh water in the bg in summer increased 5410 km3 from 2003 to 2010 and decreased at least 210 km3 by 2012 the reduction of both solid and liquid fresh water components indicates a net export of approximately 320 km3 of fresh water from the region occurred between 2010 and 2012 suggesting that the anticyclonic atmosphere ocean circulation has weakened

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

a meteoric water budget for the arctic ocean a budget of meteoric water mw river runoff net precipitation minus evaporation and glacial meltwater over four regions of the arctic ocean is constructed using a simple box model regional precipitation evaporation estimates from reanalysis data sets and estimates of import and export fluxes derived from the literature with a focus on the 2003 2008 period the budget indicates an approximate slightly positive balance between mw imports and exports i e no change in storage thus the observed total freshwater increase observed during this time period likely resulted primarily from changes in non mw freshwater components i e increases in sea ice melt or pacific water and or a decrease in ice export further our analysis indicates that the mw increase observed in the canada basin resulted from a spatial redistribution of mw over the arctic ocean mean residence times for mw were estimated for the western arctic 5 7 years eastern arctic 3 4 years and lincoln sea 1 2 years the mw content over the siberian shelves was estimated 14 000 km3 based on a residence time of 3 5 years the mw content over the entire arctic ocean was estimated to be 44 000 km3 the mw export through fram strait consisted mostly of water from the eastern arctic 3 237 1 370 km3 yr 1 whereas the export through the canadian archipelago was nearly equally derived from both the western arctic 1 182 534 km3 yr 1 and lincoln sea 972 391 km3 yr 1

differentiating fluvial components of upper canada basin waters on the basis of measurements of dissolved barium combined with other physical and chemical tracers 1 the utility of dissolved barium ba as a quasi conservative tracer of arctic water masses has been demonstrated previously here we report distributions of salinity temperature and ba in the upper 200 m of the canada basin and adjacent areas observed during cruises conducted in 2003 2004 as part of the joint western arctic climate study and beaufort gyre exploration project a salinity oxygen isotope mass balance is used to calculate the relative contributions from sea ice melt meteoric and saline end members and ba measurements are incorporated to resolve the meteoric fraction into separate contributions from north american and eurasian sources of runoff large fractions of eurasian runoff as high as 15 5 were observed in the surface layer throughout the canada basin but significant amounts of north american runoff in the surface layer were only observed at the southernmost station occupied in the canada basin in 2004 nearest to the mouth of the mackenzie river smaller contributions from both eurasian and north american runoff were evident in the summer and winter pacific derived water masses that comprise the underlying upper halocline layer in the canada basin significant amounts of eurasian and north american runoff were observed throughout the water column at a station occupied in amundsen gulf in 2004 this suggests the export of runoff from both sources through the passages of the canadian arctic archipelago

on the geochemical heterogeneity of rivers draining into the straits and channels of the canadian arctic archipelago ten rivers across northern canada and the canadian arctic archipelago caa were sampled during spring 2014 and summer 2015 to investigate their geochemical heterogeneity for comparison against larger north american i e mackenzie and yukon rivers and siberian rivers in general rivers draining the western and or northern regions of the study area have higher solute concentrations and lower 87sr 86sr ratios compared to rivers draining the eastern and or southern regions the inorganic geochemical signatures largely reflect the bedrock geology which is predominately carbonate in the western and or northern regions and silicate in the eastern and or southern regions riverine 18o values primarily correlate with latitude with only a few exceptions measurements of total alkalinity ta were combined with a regional analysis of bedrock geology and extrapolated to produce a range for the mean characteristic ta of rivers draining into the straits and channels of the caa 628 819 eq kg 1 combining this estimate with contributions from the mackenzie river yields a revised north american river runoff ta of 935 1182 eq kg 1 which is much lower than that of the mackenzie river 1540 eq kg 1 this lower concentration suggests that ta may not be used to distinguish between north american and siberian river contributions in regions such as davis strait

retreat of the cold halocline layer in the arctic ocean we present a comparison of arctic ocean hydrographic data sets from the 1990s with a focus on changes in the upper few hundred meters of the eurasian basin the most recent observations discussed here were collected during the spring 1995 scientific ice expedition scicex 95 the second in a series of scientific cruises to the arctic ocean aboard u s navy nuclear submarines although the 1990s have seen an abundance of synoptic cruises to the arctic this was the only one to take place in winter spring conditions other data considered here were collected during the first scicex cruise in summer 1993 scicex 93 and during an icebreaker cruise to the eurasian basin in summer 1991 oden 91 a new russian american winter climatology is also used as a reference these comparisons reveal that the eurasian basin cold halocline layer has retreated during the 1990s to cover significantly less area than in previous years specifically we find a retreat from the amundsen basin back into the makarov basin the latter is the only region with a true cold halocline layer during scicex 95 changes are also seen in other halocline types and in the atlantic water layer heat content and depth since the cold halocline layer insulates the surface layer and thus the overlying sea ice from the heat contained in the atlantic water layer this should have profound effects on the surface energy and mass balance of sea ice in this region using a simple mixing model we calculate maximum ice ocean heat fluxes of 1 3 w m 2 in the eurasian basin where during scicex 95 the surface layer lay in direct contact with the underlying atlantic water layer the overall cause of water mass changes in the 1990s might have been a shift in the atmospheric wind forcing and resulting sea ice motion during the late 1980s which we speculate influenced the location where fresh shelf waters flow into the deeper basins of the arctic ocean finally we discuss two different mechanisms that have been proposed for cold halocline water formation and we propose a compromise that best fits these data

calibration of the c 14 timescale over the past 30 000 years using mass spectrometric u th ages from barbados corals uranium thorium ages obtained by mass spectrometry from corals raised off the island of barbados confirm the high precision of this technique over at least the past 30 000 years comparison of the u th ages with 14c ages obtained on the holocene samples shows that the u th ages are accurate because they accord with the dendrochronological calibration before 9 000 yr bp the 14c ages are systematically younger than the u th ages with a maximum difference of 3 500 yr at 20 000 yrbp the u th technique thus provides a way of calibrating the radiocarbon timescale beyond the range of dendrochronological calibration

geometry and kinematics of active normal faults south oquirrh mountains utah implication for fault growth the nnw striking south oquirrh mountains normal fault zone consists of four individual faults the individual faults are arranged in a right stepping pattern in the north and a left stepping pattern in the south forming a convex shaped fault zone in map view with the apex towards the hanging wall late quaternary fault activity is characterized by 2 0 4 5 m high discontinuous fault scarps developed in both late quaternary alluvium and bedrock the fault scarps in bedrock contain evidence of two large rupture events the last large earthquake occurred prior to the highstand of the bonneville lake cycle 15 ka based on cross cutting relationship between the bonneville shoreline and the fault scarp and on comparisons of fault scarp morphology cumulative displacement patterns inferred from range crest elevations bouguer gravity data in the adjacent basin and rotation of the subsidiary faults adjacent to the west mercur fault are similar to the pattern of displacements measured across late quaternary fault scarps that is the maximum displacement is near the apex of the convex shaped fault zone where the west mercur fault is located and then tapers off towards both ends of the fault zone fault traces that range from a few meters to tens of kilometers long are characterized by two dominant orientations strike n11 w and n43 w the two orientations are separated from each other by a statistically constant angle of 33 3 slip directions concentrate on a trend of s70 w for both groups of faults perpendicular to the average strike of the fault zone these data indicate that the geometry of the fault surfaces is non cylindrical and may be composed of self similar structural ridges and troughs of variable wavelength and amplitude that are elongated parallel to slip direction the relationships between fault geometry displacement and geomorphology in the south oquirrh mountains fault zone suggests a growth model of normal faults in which apex points on the convex shaped fault sections mark the nucleation points of primary faults secondary faults developed at the ends of the primary fault step into the footwall block as the fault zone grows laterally intersecting regions between two laterally growing fault zones are concave shaped in map view

freshwater budget of the canada basin arctic ocean from salinity δ18o and nutrients 1 the contribution of freshwater components e g meteoric sea ice and pacific water in the canada basin is quantified using salinity 18o and nutrient data collected in 2003 and 2004 the penetration depth of sea ice meltwater is limited to the upper 30 m and brine rejected during sea ice formation is observed from 30 to 250 m depth the fraction of meteoric water is high in the upper 50 m and decreases with depth pacific water entering via bering strait is the main source of freshwater below 50 m depth bering strait throughflow which transports pacific water with salinity 32 5 together with meteoric water supplied upstream of the bering strait contributes up to 75 of freshwater input 3200 km3 a 1 to the canada basin the mean residence time of pacific water in the canada basin is estimated to be 11 years precipitation and river runoff from both north american and eurasian continents add 800 km3 a 1 and sea ice formation removes 900 km3 a 1 0 6 m a 1 of fresh water the export of ice and liquid fresh water from the canada basin contributes 40 of the freshwater flux from the arctic ocean to the north atlantic ocean

the freshwater composition of the fram strait outflow derived from a decade of tracer measurements the composition of the fram strait freshwater outflow is investigated by comparing 10 sections of concurrent salinity 18o nitrate and phosphate measurements collected between 1997 and 2011 the largest inventories of net sea ice meltwater are found in 2009 2010 and 2011 the 2009 2011 sections are also the first to show positive fractions of sea ice meltwater at the surface near the core of the egc sections from september 2009 2011 show an increased input of sea ice meltwater at the surface relative to older september sections this suggests that more sea ice now melts back into the surface in late summer than previously comparison of april july and september sections reveals seasonal variations in the inventory of positive sea ice meltwater with maximum inventories in september sections the time series of sections reveals a strong anti correlation between meteoric water and net sea ice meltwater inventories suggesting that meteoric water and brine may be delivered to fram strait together from a common source we find that the freshwater outflow at fram strait exhibits a similar meteoric water to net sea ice meltwater ratio as the central arctic ocean and siberian shelves suggesting that much of the sea ice meltwater and meteoric water at fram strait may originate from these regions however we also find that the ratio of meteoric water to sea ice meltwater inventories at fram strait is decreasing with time due to an increased surface input of sea ice meltwater in recent sections

displacement history of a limestone normal fault scarp northern israel from cosmogenic 36cl the abundance of cosmogenic 36 cl measured in 41 limestone samples from a 9 m high bedrock fault scarp allows us to construct the 14 kyr fault displacement history of the nahef east normal fault northern israel 300 m above sea level n33 latitude the nahef east fault is one of a series of fault scarps located along the 700 m high zurim escarpment a major geomorphic feature samples at the top of the scarp have the highest nuclide concentrations 79 x 10 4 atoms g rock 1 samples at the base have the lowest 11 x 10 4 atoms g rock 1 using chemical data from the samples nahef east fault scarp geometry and surface and subsurface production rates for the 36 cl producing reactions we have constructed a numerical model that calculates 36 cl accumulation on a scarp through time given a series of unique displacement scenarios the resulting model 36 cl concentrations are compared to those measured in the scarp samples faulting histories that result in a good match between measured and modeled 36 cl abundances show three distinct periods of fault activity during the past 14 kyr with over 6 vertical meters of motion occurring during a 3 kyr time period in the middle holocene smaller amounts of displacement occurred before and after the period of most rapid motion the episodic behavior of the nahef east fault indicates that the average displacement rate of this fault system has varied through time

exchange of laptev sea and arctic ocean halocline waters in response to atmospheric forcing combined delta o18 salinity data reveal a distinctive water mass generated during winter sea ice formation which is found predominantly in the coastal polynya region of the southern laptev sea export of the brine enriched bottom water shows interannual variability in correlation with atmospheric conditions summer anticyclonic circulation is favoring an offshore transport of river water at the surface as well as a pronounced signal of brine enriched waters at about 50 m water depth at the shelf break summer cyclonic atmospheric circulation favors onshore or an eastward alongshore water transport and at the shelf break the river water fraction is reduced and the pronounced brine signal is missing while on the middle laptev sea shelf brine enriched waters are found in high proportions residence times of bottom and subsurface waters on the shelf may thereby vary considerably an export of shelf waters to the arctic ocean halocline might be shut down or strongly reduced during onshore cyclonic atmospheric circulation while with offshore anticyclonic atmospheric circulation brine waters are exported and residence times may be as short as 1 year only

an observational estimate of volume and freshwater flux leaving the arctic ocean through nares strait abstract the arctic ocean is an important link in the global hydrological cycle storing freshwater and releasing it to the north atlantic ocean in a variable fashion as pack ice and freshened seawater an unknown fraction of this return flow passes through nares strait between northern canada and greenland surveys of ocean current and salinity in nares strait were completed in the summer of 2003 high resolution data acquired by ship based acoustic doppler current profiler and via hydrographic casts revealed subtidal volume and freshwater fluxes of 0 8 0 3 sv and 25 12 msv sv 103 msv 106 m3 s 1 respectively the observations resolved the dominant spatial scale of variability the internal rossby radius of deformation ld 9 km and revealed a complex yet coherent along channel flow with a rossby number of about 0 13 close to geostrophic balance approximately one third of the total volume flux was associated with across channel slope of the sea surface and two thirds 68 with across cha

chronology of expansion and contraction of four great basin lake systems during the past 35 000 years abstract during the past 35 000 years lake bonneville lake russell and lake searles underwent a major period of lake level change the lakes were at moderate levels or dry at the beginning of the period and seem to have achieved highstands between about 15 000 and 13 500 yr b p the rise of lake lahontan was gradual but not continuous in part because of topographic constraints intrabasin spill lake lahontan also had an oscillation in lake level at 15 500 yr b p radiocarbon age estimations for materials that were deposited in the lake basins indicate that lake bonneville rose more or less gradually from 32 000 yr b p and had major oscillations in level between 23 000 and 21 000 yr b p and between 15 250 and 14 500 yr b p lake russell and lake searles had several major oscillations in lake level between 35 000 and 14 000 yr b p the timing and exact magnitude of the oscillations are difficult to decipher but both lakes may have achieved multiple highstand states all four lakes may have had nearly synchronous recessions between about 14 000 and 13 500 yr b p after the recessions the lakes seem to have temporarily stabilized or experienced a minor increase in size between about 11 500 and 10 000 yr b p these data provide circumstantial evidence that the younger dryas event affected climate on at least a hemispheric scale during the holocene the four lakes remained at low levels and small oscillations in lake level occurred an important aspect of the lake level data is the accompanying expansion of lake surface area at the time of the last highstand lake bonneville and lake lahontan had surface areas about 10 times larger than their mean historical reconstructed areas whereas lake russell and lake searles had surface areas about 5 times larger than their mean historical reconstructed areas differences in the records of effective wetness may have been due to the locations of the basins relative to the position of the jetstream or they may have resulted from lake atmosphere feedback processes

wind driven transport pathways for eurasian arctic river discharge distributions of temperature salinity and barium in near surface waters depth 50 m of the laptev sea and adjacent areas of the arctic ocean are presented for the summers of 1993 1995 and 1996 the tracer data indicate that while fluvial discharge was largely confined to the shelf region of the laptev sea in the summer of 1993 surface waters containing a significant fluvial component extended beyond the shelf break and over the slope and basin areas north of the laptev sea in the summers of 1995 and 1996 these distributions of fluvial discharge are consistent with local winds and suggest two principal pathways by which river waters can enter the central arctic basins from the laptev sea when southerly to southeasterly wind conditions prevail river waters are transported northward beyond the shelf break and over the slope and adjacent basin areas these waters can then enter the interior arctic ocean via upper layer flow in the vicinity of the lomonosov ridge under other wind conditions river waters are steered primarily along the inner laptev shelf and into the east siberian sea as part of the predominantly eastward coastal current system these waters then appear to cross the shelf and enter the interior arctic ocean via upper layer flow aligned roughly along the mendeleyev ridge the extent to which either pathway is favored in a given year is largely determined by local wind patterns during the summer months when fluvial discharge is greatest and shelf waters are at the lowest salinity of their annual cycle

ages and composition of gas trapped in allan hills and byrd core ice gas is extracted from large 6 31 kg antarctic ice samples to obtain sufficient co2 for14c measurements with small low level proportional counters the14c ages of byrd core ice are in accord with glaciological estimates ranging from 2 2 1 1 1 4 103 yr at 271 m depth to more than 8 103 yr at 1071 m depth the co2 abundances in gas extracted from byrd core ice range from 0 0216 to 0 051 with below present day atmosphere co2 abundances for ice from 1068 and 1469 m depths the co2 abundance in gas from allan hills surface ice samples ranges between four and six times the atmospheric value and the co2 had a specific activity three times that of contemporary carbon a possible explanation for the anomalously high specific activity is surface melting with the incorporation into co2 of14c produced by cosmic ray spallation of oxygen in ice the co2 abundance in gas extracted from subsurface allan hills ice ranged from 0 030 to 0 065 and the specific activities are below contemporary carbon indicating ages greater than 5 103 yr the18o 16o ratio of oxygen in the trapped gas is the same as that of atmospheric oxygen and differs markedly from the18o 16o ratio in the ice the o2 n2 and ar abundances and isotopic compositions are similar to those in contemporary air except for positive15n 14n ratios in a few samples

on the feedback of ice ocean stress coupling from geostrophic currents in an anticyclonic wind regime over the beaufort gyre abstractbased on analysis of observational data it has been suggested that a negative feedback of ice ocean stress coupling may limit freshwater accumulation in the beaufort gyre bg in this pape

cosmogenic 3he and 21ne age of the big lost river flood snake river plain idaho the big lost river flood in southeastern idaho occurred 20 500 calibrated yr b p on the basis of dates derived from cosmogenic 3 he and 21 ne measurements of samples from flood deposited boulders and from scour features this date corresponds to a date of 16 900 14 c yr b p and is close in age to several other cataclysmic flood events in western north america it may mark evidence for widespread warming at the end of the pleistocene in western north america the big lost river flood was smaller than some other late pleistocene floods such as the bonnevi1le flood and the missoula floods thus some samples exposed after the flood had significant amounts of cosmogenic 3 he and 21 ne that was acquired before the flood occurred

accuracy of topographic index models at identifying ephemeral gully trajectories on agricultural fields abstract topographic index ti models have been widely used to predict trajectories and initiation points of ephemeral gullies egs in agricultural landscapes prediction of egs strongly relies on the selected value of critical ti threshold and the accuracy depends on topographic features agricultural management and datasets of observed egs this study statistically evaluated the predictions by ti models in two paired watersheds in central kansas that had different levels of structural disturbances due to implemented conservation practices four ti models with sole dependency on topographic factors of slope contributing area and planform curvature were used in this study the observed egs were obtained by field reconnaissance and through the process of hydrological reconditioning of digital elevation models dems the kernel density estimation analysis was used to evaluate ti distribution within a 10 m buffer of the observed eg trajectories the eg occurrence within catchments was analyzed using kappa statistics of the error matrix approach while the lengths of predicted egs were compared with the observed dataset using the nash sutcliffe efficiency nse statistics the ti frequency analysis produced bi modal distribution of topographic indexes with the pixels within the eg trajectory having a higher peak the graphs of kappa and nse versus critical ti threshold showed similar profile for all four ti models and both watersheds with the maximum value representing the best comparison with the observed data the compound topographic index cti model presented the overall best accuracy with nse of 0 55 and kappa of 0 32 the statistics for the disturbed watershed showed higher best critical ti threshold values than for the undisturbed watershed structural conservation practices implemented in the disturbed watershed reduced ephemeral channels in headwater catchments thus producing less variability in catchments with egs the variation in critical thresholds for all ti models suggested that ti models tend to predict eg occurrence and length over a range of thresholds rather than find a single best value

hydrographic changes in the lincoln sea in the arctic ocean with focus on an upper ocean freshwater anomaly between 2007 and 2010 hydrographic data from the arctic ocean show that freshwater content in the lincoln sea north of greenland increased significantly from 2007 to 2010 slightly lagging changes in the eastern and central arctic the anomaly was primarily caused by a decrease in the upper ocean salinity in 2011 upper ocean salinities in the lincoln sea returned to values similar to those prior to 2007 throughout 2008 2010 the freshest surface waters in the western lincoln sea show water mass properties similar to fresh canada basin waters north of the canadian arctic archipelago in the northeastern lincoln sea fresh surface waters showed a strong link with those observed in the makarov basin near the north pole the freshening in the lincoln sea was associated with a return of a subsurface pacific water temperature signal although this was not as strong as observed in the early 1990s comparison of repeat stations from the 2000s with the data from the 1990s at inline image showed an increase of the atlantic temperature maximum which was associated with the arrival of warmer atlantic water from the eurasian basin satellite derived dynamic ocean topography of winter 2009 showed a ridge extending parallel to the canadian archipelago shelf as far as the lincoln sea causing a strong flow toward nares strait and likely fram strait the total volume of anomalous freshwater observed in the lincoln sea and exported by 2011 was close to inline image approximately 13 of the total estimated fw increase in the arctic in 2008

composition and fluxes of freshwater through davis strait using multiple chemical tracers 1 freshwater transport through davis strait can supply additional buoyancy to the deep convection region of the labrador sea which influences the strength of the meridional overturning circulation and consequently the global climate the freshwater contribution from local sea ice meltwater meteoric water fluvial glaciofluvial and precipitation and the arctic outflow were quantified using oxygen isotope composition 18o salinity and nutrient relationships in september october 2004 freshwater transported by the arctic outflow was isolated using a modified nutrient relationship method and further deconvoluted into sea ice meltwater meteoric water and pacific water for the first time fluxes of individual freshwater components were estimated using observations of the velocity field derived from mooring arrays and geostrophic currents from hydrography the arctic outflow dominated in western davis strait 60 and its influence extended eastward close to the greenland slope the sea ice meltwater fraction was small 6 and attributed to glacial meltwater the freshwater inventory of the 0 100 m layer was equivalent to 7 4 m in western davis strait 8 m from the arctic outflow and 0 6 m from brine rejection in eastern davis strait the freshwater inventory was 4 m 3 m from meteoric water and 1 m from sea ice meltwater the arctic outflow contributed 82 99 msv to the southward freshwater transport about 67 81 of the total glacial meltwater contributed the largest northward transport of 10 30 msv

modelling the occurrence of gullies in rangelands of southwest spain gully erosion has been recognized as an important soil degradation process in rangelands of southwest spain in this paper a relatively new data mining technique called multivariate adaptive regression splines mars was applied to construct a model capable of predicting the location of gullies a large database was used to support the model composed of a target variable presence or absence of gullies and 36 independent variables related to topography lithology soils rainfall land use and vegetation cover the performance of the model was evaluated using the receiver operating characteristic roc curve for five external datasets the model had high predictive power with values for the area under the roc curve of the external validation datasets varying from 0 75 to 0 98 1 0 being perfect prediction the most important variables explaining the spatial distribution of gullies were lithology and soil type finally the model was compiled and implemented into a geographical information system to obtain maps of susceptible areas for gully erosion these maps show that approximately 7 of the study area presents favourable conditions for the development of gullies the results demonstrate that mars constitutes a valuable model in geomorphic research and could also be a useful tool for assessing the impacts of changing climate and land use on gully erosion copyright 2009 john wiley sons ltd

circulation of summer pacific halocline water in the arctic ocean 1 we present an analysis of arctic ocean hydrographic and sea ice observations from the 1990s with a focus on the circulation of water that originates in the north pacific ocean previous studies have shown the presence of two varieties of relatively warm summer halocline water in the vicinity of the chukchi sea i e the relatively fresh alaskan coastal water acw and the relatively saltier summer bering sea water sbsw here we extend these studies by tracing the circulation of these waters downstream into the arctic ocean we find that acw is generally most evident in the southern beaufort gyre while sbsw is strongest in the northern portion of the beaufort gyre and along the transpolar drift stream we find that this separation is most extreme during the early mid 1990s when the arctic oscillation was at historically high index values this leads us to speculate that the outflow to the north atlantic ocean through the canadian archipelago and fram strait may be similarly separated as arctic oscillation index values fell during the later 1990s acw and sbsw began to overlap in their regions of influence these changes are evident in the area north of ellesmere island where the influence of sbsw is highly correlated with a 3 year lag with the arctic oscillation index we also note the presence of winter bering sea water wbsw which underlies the summer varieties all together this brings the number of distinct pacific water types in our arctic ocean inventory to three acw sbsw and wbsw

late pleistocene basaltic ash and volcanic eruptions in the bonneville basin utah microprobe analyses of glass and radiocarbon dating of samples associated with three basaltic volcanic ashes in the deposits of lake bonneville make the ashes useful stratigraphic markers for correlation within the bonneville basin two of the ashes were derived from tuff cones pavant butte and tabernacle hill that erupted into lake bonneville in what is now the black rock desert of south central utah near kanosh utah the pavant butte ash is interbedded with barrier beach lagoon marl that is slightly less than 16 000 yr old five radiocarbon dates on carbonate materials stratigraphically associated with the ash elsewhere in the sevier desert average 15 300 yr b p lake bonneville was in its transgressive phase about 15 m below the bonneville shoreline when the pavant butte eruption began at the tabernacle hill tuff cone a basalt flow that has pillows wave rounded cobbles and tufa on its outer margins was erupted into lake bonneville shortly after the tuff cone at or near the provo shoreline the tabernacle hill tuff cone and basalt flow are older than a radio carbon date of about 14 300 yr b p on tufa collected from the outer margin of the basalt flow but younger than the bonneville flood at about 14 500 yr b p the third ash informally termed the thiokol ash has been found interbedded with lake bonneville deposits in two exposures in northern utah and in sediment cores from the great salt lake it is about 25 000 yr old and may have been erupted from a volcanic field on the northwest shore of great salt lake or from the snake river plain microprobe analyses of glass from samples of the black rock desert ashes show them to have similar chemical compositions but glass from tabernacle hill can be distinguished from pavant butte glass by its higher concentrations of cao and p 2 o 5 systematic differences in chemical composition between samples of pavant butte glass can be explained by comagmatic processes thiokol glass has less sio 2 ai 2 o 3 mgo and na 2 o but greater total iron and p 2 o 5 than do the black rock desert glasses

chronology of taylor glacier advances in arena valley antarctica using in situ cosmogenic 3he and 10be abstract in situ produced cosmogenic nuclides provide a new technique for constraining exposure ages of glacial deposits in situ3he and 10be in quartz sandstone boulders from arena valley southern victoria land antarctica provide chronological constraints for a sequence of moraines taylor ii ivb moraines related to expansions of taylor glacier and the east antarctic ice sheet mean 3he ages are 113 000 45 000 yr 208 000 67 000 yr 335 000 187 000 yr and 1 2 0 2 myr for taylor ii iii iva and ivb moraines respectively mean 1 corresponding mean 10be ages for taylor ii and ivb moraines are 117 000 51 000 yr and 2 1 0 1 myr for the older deposits the 3he ages are probably lower limits due to diffusive loss although the exposure ages appear consistent with the few previous age estimates particularly with an isotope stage 5 age for taylor ii each moraine exhibits a broad age distribution the distribution probably results from a variety of factors which may include prior exposure to cosmic rays 3he loss erosion postdepositional boulder movement and radiogenic production of 3he nonetheless the exposure ages provide direct chronological constraints for the moraine sequence and suggest a maximum thickening of taylor glacier relative to the present ice surface of 500 m since the late pliocene early pleistocene

recent trends in arctic ocean mass distribution revealed by grace 1 measurements of ocean bottom pressure by the gravity recovery and climate experiment grace and new in situ bottom pressure measurements confirm the accuracy and utility of grace measurements in the arctic ocean they reveal a declining trend in bottom pressure that corresponds to mass changes due to decreasing upper ocean salinities near the north pole and in the makarov basin the spatial distribution and magnitude of these trends suggest the arctic ocean is reverting from the cyclonic state characterizing the 1990s to the anticyclonic state that was prevalent prior to the 1990s

freshwater fluxes in the east greenland current a decade of observations 1 over a decade of mooring measurements in the western fram strait at 78 50 n shows that the annual mean liquid freshwater flux fwf in the east greenland current is relatively constant at 1274 453 km3 yr 1 40 4 14 4 msv despite the fact that the annual mean total volume transport of the egc has more than doubled since 2001 this is shown to be due to an increase of the transport in the deeper ocean and the fact that the largest fw content is present on the east greenland shelf and not in the core of the egc in order to capture the fwf on the shelf modeling results of naosim are included showing that a mean contribution of fwf on the shelf of at least 807 357 km3 yr 1 25 6 11 3 msv should be added to the fwf obtained for the egc when compared to the extra input of freshwater required to account for the 1960 1990 freshening of the northern north atlantic the observed variations in the 1998 2008 egc liquid freshwater fluxes are small

radiocarbon chronology of lake bonneville eastern great basin usa abstract lake bonneville occupied a series of connected topographically closed structural basins in the eastern great basin from about 30 ka to 12 ka the following synthesis of lake bonneville history is based on a critical evaluation of the stratigraphic and geomorphic contexts of 83 radiocarbon ages of a variety of samples including wood charcoal dispersed organic matter mollusk shells and tufa the lake began to rise from levels close to average holocene levels after about 28 ka by 22 ka it had transgressed approximately 100 m between 22 and 20 ka it regressed about 45 m in the stansbury oscillation and the stansbury shoreline was formed transgression after 20 ka proceeded in two phases a rapid phase from 20 to 18 ka and a slower phase from 18 to 15 ka the lake overflowed intermittently at its highest level the bonneville shoreline from about 15 to 14 5 ka then catastrophically dropped 100 m during the bonneville flood to the level of the provo shoreline which it occupied until about 14 ka subsequent closed basin regression was rapid and complete by 12 ka and was followed by a modest transgression to form the gilbert shoreline between 10 9 and 10 3 ka the lake bonneville record is an accurate proxy of the changing water balance in the bonneville basin during the late pleistocene although the nature of the climatic changes during this period are still uncertain

fault slip rates and initiation age based on diffusion equation modeling wasatch fault zone and eastern great basin models of the evolution of fault scarp morphology provide time elapsed since slip initiated on a faulted surface and may therefore provide more accurate estimates of slip rate than the rate calculated by dividing scarp offset by the age of the ruptured surface to accomplish this task linear and nonlinear models of sediment transport are calibrated from the morphology of lake bonneville shoreline scarps and fault scarps formed by multiple surface rupturing earthquakes along the wasatch fault zone wfz profile modeling of scarps formed by several events distributed through time is done using a constant slip rate csr solution and yields a value of a 1 2 slip rate diffusivity time elapsed since slip initiated on a fault is determined by establishing a value for and measuring total scarp offset csr nonlinear modeling 0 2 8 1 1 m2 kyr wfz of faults along the west slope of the oquirrh mountains indicates a slip rate of 0 1 mm yr since 50 to 65 ka which is corroborated by cosmogenic dating 10be 26al age 75 ka the slip rate along the west flank of the stansbury mountains varies from 0 04 to 0 2 mm yr for time frames of 10 to 100 ka with the most recent rupture on the northern portion of the fault zone 10 ka scarp analysis of the southern end of the nephi segment wfz suggests either temporal clustering or variable slip rate as indicated by differences in the short term 1 3 mm yr for 4 3 ka versus long term 0 4 mm yr for 70 ka slip rates

variability in the meteoric water sea ice melt and pacific water contributions to the central arctic ocean 2000 2014 fourteen years 2000 2014 of bottle chemistry data collected during the north pole environmental observatory were compiled to examine variations in the composition of freshwater meteoric water net sea ice meltwater and pacific water over mixed layer of the central arctic ocean in addition to significant spatial and interannual variability there was a general decrease in meteoric water mw fractions at the majority of stations reoccupied over the duration of the program that was approximately balanced by a concomitant increase in freshwater from sea ice melt sim fw between 2000 and 2012 inventories 0 120 m of mw and sim fw computed using available data between 2005 and 2012 exhibited similar variations over the study area allowing for first order estimates of the mean annual changes in mw 389 194 km3 yr 1 and sim fw 292 97 km3 yr 1 for the central arctic region these mean annual changes were attributed to the diversion of siberian river runoff to the beaufort gyre and the overall reduction of sea ice volume across the arctic respectively in addition to this lower frequency variability spatial gradients and interannual variations in mw sim fw and pacific water contributions to specific locations were attributed to shifts in the transpolar drift that advects waters of eastern and western arctic origin through the study area

wind driven summer surface hydrography of the eastern siberian shelf 1 high interannual variability of summer surface salinity over the laptev and east siberian sea shelves derived from historical records of the 1950s 2000s is attributed to atmospheric vorticity variations in the cyclonic regime positive vorticity the eastward diversion of the laptev sea riverine water results in a negative salinity anomaly to the east of the lena delta and farther to the east siberian sea and a positive anomaly to the north of the lena delta anticyclonic negative vorticity results in negative salinity anomalies northward from the lena delta due to freshwater advection toward the north and a corresponding salinity increase eastward

gully erosion impacts factors and control gully erosion attracts increasing attention from scientists as reflected by two recent international meetings poesen and valentin eds catena 50 2 4 87 564 li et al 2004 gully erosion under global change sichuan science technology press chengu china 354 pp this growing interest is associated with the increasing concern over off site impacts caused by soil erosion at larger spatial scales than the cultivated plots the objective of this paper is to review recent studies on impacts factors and control of gully erosion and update the review on dgully erosion and environmental change importance and research needst poesen et al 2003 catena 50 2 4 91 134 for the farmers the development of gullies leads to a loss of crop yields and available land as well as an increase of workload i e labour necessary to cultivate the land gullies can also change the mosaic patterns between fallow and cultivated fields enhancing hillslope erosion in a feedback loop in addition gullies tend to enhance drainage and accelerate aridification processes in the semi arid zones fingerprinting the origin of sediments within catchments to determine the relative contributions of potential sediment sources has become essential to identify sources of potential pollution and to develop management strategies to combat soil erosion in this respect tracers such as carbon nitrogen the nuclear bomb derived radionuclide 137 cs magnetics and the strontium isotopic ratio are increasingly used to fingerprint sediment recent studies conducted in australia china ethiopia and usa showed that the major part of the sediment in reservoirs might have come from gully erosion gullies not only occur in marly badlands and mountainous or hilly regions but also more globally in soils subjected to soil crusting such as loess european belt chinese loess plateau north america and sandy soils sahelian zone north east thailand or in soils prone to piping and tunnelling such as dispersive soils most of the time the gullying processes are triggered by

uncertainty in modeled arctic sea ice volume 1 uncertainty in the pan arctic ice ocean modeling and assimilation system piomas arctic sea ice volume record is characterized a range of observations and approaches including in situ ice thickness measurements icesat retrieved ice thickness and model sensitivity studies yields a conservative estimate for october arctic ice volume uncertainty of 1 35 103 km3 and an uncertainty of the ice volume trend over the 1979 2010 period of 1 0 103 km3 decade 1 a conservative estimate of the trend over this period is 2 8 103 km3 decade 1 piomas ice thickness estimates agree well with icesat ice thickness retrievals 0 1 m mean difference for the area for which submarine data are available while difference outside this area are larger piomas spatial thickness patterns agree well with icesat thickness estimates with pattern correlations of above 0 8 piomas appears to overestimate thin ice thickness and underestimate thick ice yielding a smaller downward trend than apparent in reconstructions from observations piomas ice volume uncertainties and trends are examined in the context of climate change attribution and the declaration of record minima the distribution of 32 year trends in a preindustrial coupled model simulation shows no trends comparable to those seen in the piomas retrospective even when the trend uncertainty is accounted for attempts to label september minima as new record lows are sensitive to modeling error however the september 2010 ice volume anomaly did in fact exceed the previous 2007 minimum by a large enough margin to establish a statistically significant new record

quantitative considerations of dissolved barium as a tracer in the arctic ocean 1 dissolved barium ba was measured along transects across fram and denmark straits as part of the 1998 ark xiv 2 polarstern expedition results are combined with other available tracer observations to analyze water mass composition at fram strait a combination of pacific water and eurasian river runoff dominated 80 and 10 of the total mass respectively the upper east greenland current egc while the remainder of the section was dominated by north atlantic water a much smaller contribution of pacific water to the egc 50 at fram strait in 1987 suggests that this component can be quite variable in time north american river water was not detectable at fram strait in 1998 presumably the eurasian river water we observed at fram strait transited eastward along shelf within the arctic mixed with pacific water in the vicinity of the east siberian sea and was borne by the transpolar drift across the arctic ocean in the absence of significant net ice formation along the way such a pathway can be expected to produce more pronounced freshening of the egc than when eurasian river water mixes more directly off shelf into salty atlantic waters and pacific water is diverted largely through the canadian archipelago existing measurements at the main arctic gateways were used to construct a ba budget for the arctic ocean under conditions of simultaneous mass heat and salt conservation this preliminary budget is statistically consistent with the steady state hypothesis on the arctic basin scale ba appears to be conservative

cosmic ray production rates of 10be and 26al in quartz from glacially polished rocks we have studied the concentrations of 10be and 26al in quartz crystals extracted from glacially polished granitic surfaces from the sierra nevada range these surfaces were identified with the glacial advance during the tioga period 11 000 years ago our measurements yield the most accurate estimates to date for the absolute production rates of these nuclides in sio2 due to cosmic ray nucleons and muons for geomagnetic latitudes 43 8 44 6 n and altitudes 2 1 3 6 km the estimates are relatively free from uncertainties in snow cover since we studied a suite of rock surfaces inclined 0 75 with respect to the horizontal the principal uncertainty arises due to the lack of a precise date for the glacial retreat event about 10 the 26al 10be ratio at production 6 0 is determined more accurately since the exposure age of the samples is 2 orders of magnitude smaller than the mean lives of the two nuclides production rates of 10be and 26al in quartz at other latitudes and altitudes in the troposphere can be determined from the present measurements by scaling using the known altitude and latitude dependence of cosmic ray fluxes of nucleons and negative muons knowledge of the production rates of these nuclides is a prerequisite for their application in erosion and geomorphological studies

formation and evolution of the surface mixed layer and halocline of the arctic ocean fresh water from summer ice melt and the total freshwater content of the arctic ocean water column above the thermocline are estimated from vertical profiles of temperature and salinity observed on the i b oden 1991 cruise the seasonal ice melt ranges from 0 5 m to slightly above 1 m and is moderately uniform over the observation area regions of lower melting are seen over the morris jesup plateau the freshwater content is calculated relative to the salinity just above the thermocline north of the barents sea the freshwater content increases toward the interior of the arctic ocean showing that fresh water is advected from other regions into the observation area regions of different freshwater content are separated by fronts over the nansen gakkel ridge over the lomonosov ridge and in the western eurasian basin between waters derived from the eurasian and canadian basins denser water homogenized north of the barents sea is recognized by a temperature minimum layer the absence of the temperature minimum near the nansen gakkel ridge indicates that heat is transferred from the atlantic layer over a longer time than the shortest route would allow this observation can be explained if the layer circulates together with the atlantic layer i e toward the east and returns above the nansen gakkel ridge and along the amundsen basin north of the laptev sea this water formed north of the barents sea becomes covered by low salinity shelf water the increased freshwater content limits the winter convection so it no longer reaches the thermocline and an intermediate halocline is formed the halocline in the eurasian basin consists of water originating from winter convection in the arctic ocean north of the barents sea which then circulates around the basin such a formation mechanism also explains the observed distribution of low no water the strong density increase limits vertical exchange and the vertical diffusion coefficient in the halocline is small 1 10 6 m2 s 1 the increased temperature of the halocline shows that the heat lost upward by the atlantic layer mainly by double diffusive convection is trapped below the mixed layer

constraining processes of landscape change with combined in situ cosmogenic 14c 10be analysis abstract reconstructing quaternary landscape evolution today frequently builds upon cosmogenic nuclide surface exposure dating however the study of complex surface exposure chronologies on the 102 104 years timescale remains challenging with the commonly used long lived radionuclides 10be 26al 36cl in glacial settings key points are the inheritance of nuclides accumulated in a rock surface during a previous exposure episode and partial shielding of a rock surface after the main deglaciation event e g during phases of glacier readvance combining the short lived in situ cosmogenic 14c isotope with 10be dating provides a valuable approach to resolve and quantify complex exposure histories and burial episodes within lateglacial and holocene timescales the first studies applying the in situ 14c 10be pair have demonstrated the great benefit from in situ 14c analysis for unravelling complex glacier chronologies in various glacial environments worldwide moreover emerging research on in situ 14c in sedimentary systems highlights the capacity of combined in situ 14c 10be analysis to quantify sediment transfer times in fluvial catchments or to constrain changes in surface erosion rates nevertheless further methodological advances are needed to obtain truly routine and widely available in situ 14c analysis future development in analytical techniques has to focus on improving the analytical reproducibility reducing the background level and determining more accurate muonic production rates these improvements should allow extending the field of applications for combined in situ 14c 10be analysis in earth surface sciences and open up a number of promising applications for dating young sedimentary deposits and the quantification of recent changes in surface erosion dynamics

2 d seismic trenching of colluvial wedges and faults abstract images of the depth and shape of colluvial wedges by 3 d travel time tomography can be valuable in estimating the past history of ancient earthquakes and assessing the earthquake hazard of a fault unfortunately 3 d seismic surveys can be both costly and time consuming in this paper we report our first successful results of detecting the shapes and depths of colluvial wedges with 2 d travel time tomography the locations of the colluvial wedges are along the oquirrh fault and the salt lake city segment of the wasatch fault we also report that the tomogram from one of our 2 d surveys suggests the possibility of detecting multiple colluvial wedges at depth using both reflection and tomographic images at another site clearly reveals the presence of a known shallow fault and the contact between native soil and recent fill our results suggest the synergistic use of both seismic tomography and reflection imaging we denote as seismic trenching as a means of detecting shallow colluvial wedges and faults seismic trenching has the potential to significantly expand the lateral extent and depth of investigation of paleoseismology

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

in situ10be 26al exposure ages at meteor crater arizona a new method of dating the surface exposure of rocks from in situ production of 10be and 26al has been applied to determine the age of meteor crater arizona a lower bound on the crater age of 49 200 1 700 years has been obtained by this method

cosmogenic chlorine 36 chronology for glacial deposits at bloody canyon eastern sierra nevada deposits from mountain glaciers provide an important record of quaternary climatic fluctuations but have proved difficult to date directly a chronology has been obtained for glacial deposits at bloody canyon california by measurement ofthe accumulation of chlorine 36 produced by cosmic rays in boulders exposed on moraine crests the accumulation ofchlorine 36 indicates that episodes of glaciation occurred at about 21 24 65 115 145 and 200 ka thousand years ago although the timing of the glaciations correlates well with peaks of global ice volume inferred from the marine oxygen isotope record the relative magnitudes differ markedly the lengths of the moraines dating from 115 ka and 65 ka show that the early glacial episodes were more extensive than those during the later wisconsin and indicate that the transition from interglacial to full glacial conditions was rapid

age and geomorphic history of meteor crater arizona from cosmogenic 36cl and 14c in rock varnish abstract using cosmogenic 36 cl buildup and rock varnish radiocarbon we have measured the exposure age of rock surfaces at meteor crater arizona our 36 cl measurements on four dolomite boulders ejected from the crater by the impact yield a mean age of 49 7 0 85 ka which is in excellent agreement with an average age of 49 3 ka obtained from thermoluminescence studies on shock metamorphosed dolomite and quartz these ages are supported by undetectably low 14 c in the oldest rock varnish sample

drifting arctic sea ice archives changes in ocean surface conditions 18o profiles in drifting arctic sea ice are coupled with back trajectories of ice drift and an ice growth model to reconstruct the surface hydrography of the arctic ocean interior the results compare well with 18o values obtained by traditional oceanographic methods and known water mass distributions analysis of the stable isotopic composition of sea ice floes sampled at strategic and relatively accessible locations e g fram strait could aid in mapping spatial and temporal variations in arctic ocean surface waters