el nino evolution during the holocene revealed by a biomarker rain gauge in the galapagos islands abstract the el nino southern oscillation enso represents the largest perturbation to the climate system on an inter annual time scale but its evolution since the end of the last ice age remains debated due to the lack of unambiguous enso records lasting longer than a few centuries changes in the concentration and hydrogen isotope ratio of lipids produced by the green alga botryococcus braunii which blooms during el nino rains in the galapagos islands indicate that the early holocene 9200 5600 yr bp was characterized by alternating extremes in the intensity and or frequency of el nino events that lasted a century or more our data from the core of the enso region thus calls into question earlier studies that reported a lack of el nino activity in the early holocene in agreement with other proxy evidence from the tropical pacific the mid holocene 5600 3500 yr bp was a time of consistently weak el nino activity as were the early middle ages 1000 1500 yr bp el nino activity was moderate to high during the remainder of the last 3500 years periods of strong or frequent el nino tended to occur during peaks in solar activity and during extended droughts in the united states great plains linked to la nina these changing modes of enso activity at millennial and multi centennial timescales may have been caused by variations in the seasonal receipts of solar radiation associated with the precession of the equinoxes and or changes in solar activity respectively

the hafnium and neodymium isotope composition of seawater in the atlantic sector of the southern ocean we present the first combined dissolved hafnium hf and neodymium nd concentrations and isotope compositions of deep water masses from the atlantic sector of the southern ocean eight full depth profiles were analyzed for hf and twelve for nd hafnium concentrations are generally depleted in the upper few hundred meters ranging between 0 2 pmol kg and 0 4 pmol kg and increase to relatively constant values of around 0 6 pmol kg in the deeper water column at the stations north of the polar front pf nd concentrations increase linearly from about 10 pmol kg at depths of 200 m to up to 31 pmol kg close to the bottom indicating particle scavenging and release within the weddell gyre wg however nd concentrations are essentially constant at 25 pmol kg at depths greater than 1000 m the distributions of both elements show a positive correlation with dissolved silicon implying a close linkage to diatom biogeochemistry hafnium essentially shows invariant isotope compositions with values averaging at ehf 4 6 whereas nd isotopes mark distinct differences between water masses such as modified north atlantic deep water nadw end 11 to 10 and antarctic bottom water aabw end 8 6 to 9 6 but also waters locally advected via the agulhas current can be identified by their unradiogenic nd isotope compositions mixing calculations suggest that a small fraction of nd is removed by particle scavenging during mixing of water masses north of the pf nevertheless the nd isotope composition has apparently not been significantly affected by uptake and release of nd from particles as indicated by mixing calculations a mixing envelope of an approximated north pacific and a north atlantic end member shows that nd isotope and concentration patterns in the lower circumpolar deep water lcdw can be fully explained by 30 70 percentage contributions of these respective end members

quasi conservative behaviour of 10be in deep waters of the weddell sea and the atlantic sector of the antarctic circumpolar current we present the first transect of dissolved 10be depth profiles across the antarctic circumpolar current acc in the atlantic sector north of the polar front the 10be concentrations increase continuously from very low values at the surface to values of up to 1600 atoms g at depth deep water 10be concentrations of particular water masses are consistent with earlier results obtained further north south of the polar front and in the weddell sea the distribution of 10be is also characterised by low surface concentrations but below 1000 m depth the concentrations are relatively constant and significantly higher up to 2000 atoms g than further north probably as a result of mixing and advection of water masses of pacific origin overall the deep water 10be distribution is obviously not significantly affected by scavenging processes or ice melt and comparison with the density distribution suggests that 10be can be viewed as a quasi conservative tracer this provides a tool for an improved understanding of the behaviour of other more particle reactive trace metals in the southern ocean such as 230th in deep waters north of the acc weddell gyre boundary awb 10be 230th has a relatively constant value 1 7 0 3 109 atoms dpm over a wide density range whereas south of the awb the ratio is significantly lower 1 1 0 2 109 atoms dpm this normalisation to 10be corroborates that 230th is enriched by 50 due to accumulation south of the awb as a consequence of minimal particulate fluxes the quasi conservative behaviour deduced from our results also implies that 10be can only be used as a tracer for southern ocean particle fluxes in the past if ocean circulation patterns and water mass residence times did not change significantly

high productivity in an ice melting hot spot at the eastern boundary of the weddell gyre 1 the southern ocean so plays a key role in modulating atmospheric co2 via physical and biological processes however over much of the so biological activity is iron limited new in situ data from the antarctic zone south of africa in a region centered at 20 e 25 e reveal a previously overlooked region of high primary production comparable in size to the northwest african upwelling region here sea ice together with enclosed icebergs is channeled by prevailing winds to the eastern boundary of the weddell gyre where a sharp transition to warmer waters causes melting this cumulative melting provides a steady source of iron fuelling an intense phytoplankton bloom that is not fully captured by monthly satellite production estimates these findings imply that future changes in sea ice cover and dynamics could have a significant effect on carbon sequestration in the so

molecular transformation and degradation of refractory dissolved organic matter in the atlantic and southern ocean more than 90 of the global ocean dissolved organic carbon doc is refractory has an average age of 4000 6000 years and a lifespan from months to millennia the fraction of dissolved organic matter dom that is resistant to degradation is a long term buffer in the global carbon cycle but its chemical composition structure and biochemical formation and degradation mechanisms are still unresolved we have compiled the most comprehensive molecular dataset of 197 fourier transform ion cyclotron resonance mass spectrometry ft icr ms analyses from solid phase extracted marine dom covering two major oceans the atlantic sector of the southern ocean and the east atlantic ocean ranging from 50 n to 70 s molecular trends and radiocarbon dating of 34 dom samples comprising 14c values from 229 to 495 were combined to model an integrated degradation rate for bulk doc resulting in a predicted age of 24 ka for the most persistent dom fraction first order kinetic degradation rates for 1557 mass peaks indicate that numerous dom molecules cycle on timescales much longer than the turnover of the bulk doc pool estimated residence times of up to 100 ka and the range of validity of radiocarbon dating changes in elemental composition were determined by assigning molecular formulae to the detected mass peaks the combination of residence times with molecular information enabled modelling of the average elemental composition of the slowest degrading fraction of the dom pool in our dataset a group of 361 molecular formulae represented the most stable composition in the oceanic environment island of stability these most persistent compounds encompass only a narrow range of the molecular elemental ratios h c average of 1 17 0 13 and o c average of 0 52 0 10 and molecular masses 360 28 and 497 51 da in the weddell sea doc concentrations in the surface waters were low 46 3 3 3 m while the organic radiocarbon was significantly more depleted than that of the east atlantic representing average surface water dom ages of 4920 180 a these results are in accordance with a highly degraded dom in the weddell sea surface water as also shown by the molecular degradation index ideg obtained from ft icr ms data further we identified 339 molecular formulae which probably contribute to an increased doc concentration in the southern ocean and potentially reflect an accumulation or enhanced sequestration of refractory doc in the weddell sea these results will contribute to a better understanding of the persistent nature of marine dom and its role as an oceanic carbon buffer in a changing climate

on the structure and the transport of the eastern weddell gyre abstract the circulation pattern and volume transports in the eastern weddell gyre are estimated on the basis of hydrographic data collected by r v polarstern between 1989 and 1996 in the northeastern edge of the weddell gyre eastward flowing water masses from the antarctic circumpolar current and the weddell sea converge due to the strong effect of topographic constraints on ocean currents in the weakly stratified waters of high latitudes the wedge like structure of the southwest indian ridge can cause the convergence the increased shear leads to instabilities of the current at the eastern end of the ridge which produce an intense mesoscale eddy field between 15 and 30 e in the eddies water from the weddell cold regime and the antarctic circumpolar current waters mix and form the water masses of the weddell warm regime these waters are advected southward and flow towards the westward southern rim current which is driven by the antarctic eastwind band hence there is not a continous flow from the northern to the southern rim but a decay of the mean flow in the northeast and a reformation in the south volume transports across the greenwich meridian estimated on the basis of a combined ctd adcp data set result in an eastward flow of 61 sv in the northern rim current and a westward return flow of 66 sv in the southern part of the gyre the transport is about twice as high as previous estimates between kapp norvegia and the northern tip of the antarctic pensinsula indicating a significant gyre circulation north of 70 s

channel changes in badlands stripping of the vegetation and soil from a 13 hectare site in virginia underlain by coastal plain sediments created a rapidly evolving badland topography two types of channels developed 1 sand bed alluvial channels were graded to transport the bed material load supplied from slope erosion with available runoff but they also generally eroded their beds slowly and 2 steeper bedrock floored channels incised rapidly in bedrock channels the erosion rate was proportional to the 4 9ths power of drainage area and the 2 3rds power of gradient these exponents are consistent with a model in which the erosion rate is proportional to the bed shear during high flows due to rapid mass wasting and reduced runoff the alluvial channels became as much as 50 steeper during the winter than the summer with an attendant yearly cycle of winter aggradation and summer entrenchment the gradients their seasonal variability and their downstream hydraulic geometry were consistent with the predictions of total load transport formulas for sand beds and high loads the hydraulic geometry of alluvial channels in the virginia badlands were similar to that on the morrison formation in the western united states

a bimillennial length tree ring reconstruction of precipitation for the tavaputs plateau northeastern utah abstract despite the extensive network of moisture sensitive tree ring chronologies in western north america relatively few are long enough to document climatic variability before and during the medieval climate anomaly mca ca ad 800 1300 we developed a 2300 yr tree ring chronology extending to 323 bc utilizing live and remnant douglas fir pseudotsuga menziesii from the tavaputs plateau in northeastern utah a resulting regression model accounts for 70 of the variance of precipitation for the ad 1918 2005 calibration period extreme wet and dry periods without modern analogues were identified in the reconstruction the mca is marked by several prolonged droughts especially prominent in the mid ad 1100s and late 1200s and a lack of wet or dry single year extremes the frequency of extended droughts is not markedly different however than before or after the mca a drought in the early ad 500s surpasses in magnitude any other drought during the last 1800 yr a set of four long high resolution records suggests this drought decreased in severity toward the south in the western united states the spatial pattern is consistent with the western dipole of moisture anomaly driven by el nino and is also similar to the spatial footprint of the ad 1930s dust bowl drought

the supply and accumulation of silica in the marine environment rivers and submarine hydrothermal emanations supply 6 1 1014g sio2 yr to the marine environment approximately two thirds of the silica supplied to the marine environment can be accounted for in continental margin and deep sea deposits siliceous deep sea sediments located beneath the antarctic polar front convergence account for over a fourth 1 6 1014g sio2 yr of the silica supplied to the oceans deep sea sediment accumulation rates beneath the polar front are highest in the south atlantic with values as large as 53cm kyr during the last 18 000 yr siliceous sediments in the bering sea sea of okhotsk and subarctic north pacific accumulate 0 6 1014g sio2 yr or 10 of the dissolved silica input to the oceans the accumulation of biogenic silica in estuarine deposits removes a maximum of 0 8 1014g sio2 yr although estuarine silica versus salinity plots indicate extensive removal of riverine silica from surface waters the removal rates must be considered as maximum values because of dissolution of siliceous material in estuarine sediments and bottom waters siliceous sediments from continental margin upwelling areas e g gulf of california walvis bay or peru chile coast have the highest biogenic silica accumulation rates in the marine environment 69 g sio2 cm2 kyr despite the rapid accumulation of biogenic silica upwelling areas account for less than 5 of the silica supplied to the marine environment because they are confined laterally to such small areas

the influence of bedrock geology on knickpoint development and channel bed degradation along downcutting streams in south central indiana geologic controls on knickpoint development and the mechanics of channel bed degradation were eluci dated by comparison of downcutting streams in south central indiana developed in lithologically homoge neous carbonate units and layered siliciclastic strata knickpoints formed in a single lithologic unit are stepped each step consists of a knickpoint face and tread the height of each step is equal to and controlled by bed thickness spatially knickpoints in homogeneous terrain are limited to jointed strata that dip 1 upstream or 2 downstream at angles less than the channel gradient knickpoints observed in lithologically layered strata are characterized by a single step in which resistant jointed rocks overlie and protect weaker units total knickpoint relief is influenced by thickness of the weaker strata knickpoints in layered siliciclastic strata are spatially limited to bedrock reaches produced by differential rates of channel incision knickpoint distribution is also influenced by joint

the global ocean flux of particulate organic carbon areal distribution and magnitude the magnitude and distribution of the particulate organic carbon poc rain rate to the seafloor in the atlantic pacific and indian ocean basins between 61 n and 61 s has been estimated from benthic oxygen flux estimates for water depths 1000 m only the calculation utilizes the extensive data sets of sedimentary organic carbon caco3 and accumulation rate to extrapolate between individual benthic flux measurement sites using an empirically derived correlation between the seafloor oxygen flux and these parameters the poc flux through the 1000 m depth horizon was then estimated from published correlations between sediment trap determined fluxes and water depth total oxygen utilization in the deep ocean is estimated to be 1 2 1014 mol o2 yr 1 a value that agrees well with previous estimates which were based on surface water primary productivity sediment trap and depth relationships and with deep water respiration rates estimated from apparant oxygen utilization aou 14c relationships on the basis of the derived global ocean flux distribution it is concluded that 1 dissolved organic carbon doc inputs are not required to account for estimated deep water respiration rates 2 the majority of the poc input to the deep ocean occurs within 30 of the equator 3 the proportion of primary production that reaches the deep sea does not vary greatly with latitude 4 gyre and continental margin regions contribute roughly equally to the deep poc flux with a relatively minor contribution from the equatorial divergence region 5 of the estimated 7 2 1013 mol c yr 1 of poc that sinks below the 1000 m depth horizon 45 3 3 1013 mol c yr 1 reaches the seafloor where it is oxidized 6 when normalized to basin area average deep flux rates in the atlantic and pacific are similar while highest rates are observed in the indian ocean and 7 the results can be fully reconciled only if the benthic flux of doc is significantly less than the benthic o2 flux

morphometric variability in the diatom fragilariopsis kerguelensis implications for southern ocean paleoceanography abstract diatoms play a central role in the ecosystem of the southern ocean where they represent the main producers and carriers of organic carbon and dissolved silicon towards the deep ocean variability in space and time of the size of the most abundant species fragilariopsis kerguelensis may directly impact the way this ecosystem functions and also affect the nutrient balance of the global ocean as important water masses e g the antarctic intermediate water get their nutrient signature in this area we used a biometric approach and analyzed the size variability of f kerguelensis valves in sixty four surface sediment samples from the southern ocean in sediment trap samples from a mooring site pf3 at the antarctic polar front apf and along a nearby piston core ps1654 2 the average length and valve area of f kerguelensis displayed a distinct increase in the proximity of the apf and lower values to the north and south of it and also changed markedly over seasonal cycles as diatom blooms and nutrient availability waxe and wane the last glacial to interglacial transition also witnesses important changes in the general shape and valve size of f kerguelensis with specimens from glacial intervals being ca 30 larger than their interglacial counterparts 195 versus 150 m 2 valve area a sharp peak in average area and a very specific valve morphology correspond to the first signs of deglaciation and concurring sst sea surface temperature increase and sea ice retreat the latter together with melting icebergs may have contributed dissolved iron to surface waters the highest average sizes during glacial intervals are higher than what found anywhere in the southern ocean today the newly proposed proxy valve area and shape of f kerguelensis may thus prove useful for the reconstruction of the past position and nutrient characteristics of the apf and opal belt a region characterized by high production and export of biogenic silica in a particularly sensitive and dynamic area such as the southern ocean

234th based carbon export during an ice edge bloom sea ice algae as a likely bias in data interpretation abstract total 234th and 238u vertical profiles in the water column were determined along a three station transect perpendicular to the eastern weddell sea ice shelf the transect was sampled during pre bloom 6 7 december 2003 and bloom 19 20 december 2003 conditions to follow changes occurring in the particulate organic carbon poc flux during an antarctic phytoplankton ice edge bloom during the pre bloom period 234th 238u ratios 1 up to 1 3 were measured just above the thermocline at all stations and throughout the entire mixed layer at the ice edge these water column data appear to be the first which support the hypothesis that sea ice algae could represent an input of 234th rich material in polar waters due to cellular uptake of the radionuclide and or its adsorption onto the extracellular polymeric substances eps produced by these organisms a simple conceptual model is proposed to link observed 234th 238u ratios to the input of 234th enriched sea ice algae caused by ice melting the extensive deep water 234th deficit observed during the second transect likely results from the combination of vertical particle export and water seafloor exchange processes poc steady state ss fluxes out of the photic layer were negative or nil 11 to 2 mmol m 2 d 1 under pre bloom conditions probably due to ice algae input at the ice edge and remineralization elsewhere whereas poc non steady state nss fluxes were generally higher 7 to 33 mmol m 2 d 1 when the bloom was developing we have estimated that these flux values could change by as much as 75 if a sea ice algae 234th input term were included in the simple one box model used this suggests that failure to consider the sea ice algae compartment when using 234th as a proxy to assess carbon export in seasonally ice covered regions could at times lead to significant biases in the interpretation of 234th based particle flux estimates

winter and summer distributions of copper zinc and nickel along the international geotraces section gipy05 insights into deep winter mixing abstract first measurements of labile dissolved copper ldcu and dissolved zinc dzn and nickel dni in the atlantic sector of the southern ocean in winter are compared with summer data at reoccupied stations in order to better understand the winter reset state and supply of these trace metals to support productivity in summer vertical profiles of zinc behaved similarly to silicate si and increased from sub nanomolar surface concentrations to 8 nmol kg 1 in bottom waters copper profiles also resembled si and were typically 1 nmol kg 1 in surface waters and increased to 3 nmol kg 1 at depth first summer nickel data reported from this transect displayed comparatively higher surface concentrations of 4 6 nmol kg 1 increasing more rapidly to local intermediate depth maximums between 6 5 and 7 0 nmol kg 1 similar to phosphate po4 trace metal seasonality was most apparent in the mixed layer where the average of winter concentrations within the mixed layer exceeded summer values by approximately 0 2 nmol kg 1 for ldcu 1 2 nmol kg 1 for dzn and 0 3 nmol kg 1 for dni owing to low utilization under unfavourable growth conditions for phytoplankton in an effort to estimate the winter reserve two scenarios were considered scenario 1 accounted for in situ mixed layer depths mld where the winter reserve inventory was calculated by subtracting the summer depth integrated metal inventory surface to summer mld from the winter equivalent surface to winter mld scenario 2 assumed a constant mixed layer taken as the depth of the maximum winter mixed layer where summer depth integrated metal inventories surface to maximum winter mld were subtracted from the winter equivalents surface to maximum winter mld results for scenario 1 were predominantly dependent on the mixed layer depth which varied spatially and seasonally scenario 2 showed a southwards increase in the winter reserve inventory suggesting a greater role for entrainment at higher latitudes in this region this is however heavily dependent on other physical processes controlling vertical trace metal supply e g diapycnal diffusion ekman upwelling downwelling zinc r2 0 75 and copper r2 0 73 were strongly correlated with si throughout the study implicating diatoms as strong controllers of their biogeochemical cycling nickel was more strongly correlated with po4 in the upper water column r2 0 75 as compared to the whole water column r2 0 52 while in the deep ocean nickel appears to correlate with si although more deep ocean data is needed to confirm this trace metal to major nutrient ratios were higher in winter suggesting reduced micronutrient requirement relative to macronutrients under stressed but low productivity conditions this article is part of a special issue entitled cycles of trace elements and isotopes in the ocean geotraces and beyond edited by tim m conway tristan horner yves plancherel and aridane g gonzalez

a numerical model of the weddell sea large scale circulation and water mass distribution a circumpolar model for regional studies of the wind driven and thermohaline circulation of the southern ocean including the major sub ice shelf areas is described a first series of numerical experiments focusing on the weddell sea reveals a pronounced and persistent double cell structure of the weddell gyre with a maximum transport of 60 sv in agreement with observations experiments with artificial passive tracers point to the shallow shelf areas off the filchner ronne ice shelf as main locations for bottom water production the trajectories of lagrangian floats are used to determine the pathways and timescales of water mass spreading in the model in addition the effect of sub ice shelf forcing on the water mass characteristics is evaluated it is shown that water modified in the sub ice cavities contributes significantly to the deep and bottom water formation along the continental slope and affects the water mass characteristics throughout the weddell sea by increasing the stability of the near surface stratification and preventing deep convection

234th in surface waters distribution of particle export flux across the antarctic circumpolar current and in the weddell sea during the geotraces expedition zero and drake abstract as part of the geotraces polarstern expedition antxxiv 3 zero and drake we have measured the vertical distribution of 234th on sections through the antarctic circumpolar current along the zero meridian and in drake passage and on an ew section through the weddell sea steady state export fluxes of 234th from the upper 100 m derived from the depletion of 234th with respect to its parent 238u ranged from 621 105 to 1773 90 dpm m 2 d 1 this 234th flux was converted into an export flux of organic carbon ranging from 3 1 to 13 2 mmol c m 2 d 1 2 1 9 0 mmol c m 2 d 1 using poc 234th ratio of bulk respectively 50 m suspended particles at the export depth 100 m non steady state fluxes assuming zero flux under ice cover were up to 23 higher in addition particulate and dissolved 234th were measured underway in high resolution in the surface water with a semi automated procedure particulate 234th in surface waters is inversely correlated with light transmission and pco2 and positively with fluorescence and optical backscatter and is interpreted as a proxy for algal biomass high resolution underway mapping of particulate and dissolved 234th in surface water shows clearly where trace elements are absorbed by plankton and where they are exported to depth quantitative determination of the export flux requires the full 234th profile since surface depletion and export flux become decoupled through changes in wind mixed layer depth and in contribution to export from subsurface layers in a zone of very low algal abundance 54 58 s at the zero meridian confirmed by satellite chl a data the lowest carbon export of the acc was observed allowing fe and mn to maintain their highest surface concentrations an ice edge bloom that had developed in december january in the zone 60 65 s as studied during the previous leg had caused a high export flux at 64 5 s when we visited the area 2 months later february march the ice edge bloom had then shifted south to 65 69 s evident from uptake of co2 and dissolved fe mn and 234th without causing export yet in this way the parallel analysis of 234th can help to explain the scavenging behavior of other trace elements

longitudinal profiles in simple alluvial systems theoretical considerations suggest that exponential or quadratic functions are apt for describing the longitudinal profiles of aggrading alluvial systems that are unaffected by significant lateral inputs of water or sediment a new set of field data confirms this for individual sedimentary links along a wandering gravel bed river in british columbia canada each link is viewed as a simple alluvial system without major water or sediment inputs within which grain size typically fines downstream in a relatively systematic manner such homogeneous reaches are suitable for the investigation of simple profile form it is found that quadratic approximations are the most flexible descriptor for link longitudinal profiles overall the river forms an irregularly cuspate long profile structured by these fundamental length scale units both link gradients and link fining rate reflect size selective aggradation associated with the bounding lateral inputs

the distribution of dissolved zinc in the atlantic sector of the southern ocean the distribution of dissolved zinc zn was investigated in the atlantic sector of the southern ocean in the austral autumn of 2008 as part of the ipy geotraces expedition zero drake research focused on transects across the major frontal systems along the zero meridian and across the drake passage there was a strong gradient in surface zinc concentrations observed across the antarctic polar front along both transects and high zinc levels were found in surface waters throughout the southern ocean vertical profiles for dissolved zinc showed the presence of local minima and maxima in the upper 200 m consistent with significant uptake by phytoplankton and release by zooplankton grazing respectively highest deep water zinc concentrations were found in the centre of the weddell gyre associated with central intermediate water ciw a water mass which is depleted in o2 elevated in co2 and is regionally a cfc minimum our data suggests that the remineralization of sinking particles is a key control on the distribution of zn in the southern ocean disappearance ratios of zinc to phosphate zn p in the upper water column increased southwards along both transects and based on laboratory studies they suggest slower growth rates of phytoplankton due to iron or light limitation zinc and silicate were strongly correlated throughout the study region but the disappearance ratio zn si was relatively uniform overall except for the region close to the ice edge on the zero meridian

234th deficit and excess in the southern ocean during spring 2001 particle export and remineralization 1 234th deficit and excess were examined in the upper 500 m of the southern ocean from sub antarctic to seasonal ice zones australian sector during austral spring 2001 234th fluxes at 100 m indicate that particle export was low in the north 46 9 51 0 s minimal in the polar and inter polar frontal zones and high in the south 61 s these results are in tight agreement with new production estimates from the same cruise our data indicate that polar and inter polar frontal zones were not zones of intense export in the australian sector at this time of year in contrast with other sectors of the southern ocean also we highlight the usefulness of 234th excess below the mixed layer as a tool to study mesopelagic remineralization

carbon dynamics of the weddell gyre southern ocean the accumulation of carbon within the weddell gyre and its exchanges across the gyre boundaries are investigated with three recent full depth oceanographic sections enclosing this climatically important region the combination of carbon measurements with ocean circulation transport estimates from a box inverse analysis reveal that deep water transports associated with warm deep water wdw and weddell sea deep water dominate the gyre s carbon budget while a dual cell vertical overturning circulation leads to both upwelling and the delivery of large quantities of carbon to the deep ocean historical sea surface pco2 observations interpolated using a neural network technique confirm the net summertime sink of 0 044 to 0 058 0 010 pg c yr 1 derived from the inversion however a wintertime outgassing signal similar in size results in a statistically insignificant annual air to sea co2 flux of 0 002 0 007 pg c yr 1 mean 1998 2011 to 0 012 0 024 pg c yr 1 mean 2008 2010 to be diagnosed for the weddell gyre a surface layer carbon balance independently derived from in situ biogeochemical measurements reveals that freshwater inputs and biological drawdown decrease surface ocean inorganic carbon levels more than they are increased by wdw entrainment resulting in an estimated annual carbon sink of 0 033 0 021 pg c yr 1 although relatively less efficient for carbon uptake than the global oceans the summertime weddell gyre suppresses the winter outgassing signal while its biological pump and deep water formation act as key conduits for transporting natural and anthropogenic carbon to the deep ocean where they can reside for long timescales

shallow remineralization in the weddell gyre 1 the region influenced by the polar front in the southern ocean is characterized by relatively high productivity which is mirrored in strong depletions of 234th in the surface water a good tracer of export production and by high accumulation rates on the underlying seabed farther south the weddell sea is generally considered a low productivity region with very low export fluxes this finding is based on satellite observations sediment accumulation rates trap deployments and phytoplankton distribution if this would be true 234th should be close to equilibrium with its parent however in a series of high resolution transects of 234th 238u across the antarctic circumpolar current acc 234th was found to be depleted by 10 15 throughout the clear weddell gyre only to reach equilibrium in sea ice covered regions of the coastal zone vertical profiles showed that the depletion was limited to the upper mixed layer and was balanced by an enrichment of similar magnitude at 100 250m depth this implies that the export of particles below 250 m is negligible such shallow remineralization is in line with the discrepancies between biogenic silica production rates and sediment trap data observed in the weddell and ross seas these observations in the weddell sea are fully consistent with our inverse modeling results for both organic carbon and opal and they are not inconsistent with tco2 and oxygen sections that show a tco2 enriched oxygen reduced shallow subsurface layer this blue ocean characterized by upwelling of co2 enriched deep waters supports sufficient productivity to be a net sink for co2 to abyssal depths hoppema et al 1999 no record of this productivity and export is stored in the underlying sediment which has important palaeoceanographic consequences

oceanic stratified euphotic zone as elucidated by 234th 238u disequilibria1 profiles of dissolved and particulate 234th were determined at the vertex 2 and 3 stations off manzanillo mexico and at the vertex 4 station about 900 km north of hawaii by modeling the disequilibria between 234th and 238u in the dissolved and particulate form estimates of scavenging rates for th from the dissolved to particulate phases particle residence times and the flux of th via particle removal can be obtained 234th 238u activity ratio profiles indicate that the euphotic zone can be separated into two layers an upper oligotrophic layer characterized by low new production values low net scavenging and long dissolved 234th residence times and a subsurface eutrophic layer with higher new production values more intense scavenging and shorter dissolved 234th residence times new production rather than total primary production may determine net scavenging rates of reactive elements from oceanic surface waters these results contribute to the emerging descriptions of the layered structure of oligotrophic euphotic zones and support the notion that this may be a general and ubiquitous feature of global stratified oligotrophic regimes these layered systems can be structured not only in biological and nutrient parameters but also in terms of the rates of chemical scavenging and elemental transport the layered structure of biological processes within stratified oceanic euphotic zones has been recognized for quite some time since steele and yentsch s 1960 paper on the vertical distribution of chlorophyll the subsurface chlorophyll maximum has received a great deal of attention and is now a well known oceanographic feature dugdale 1967 proposed a two layer model for oceanic euphotic zones in which nutrient limited phytoplankton populations overlie light limited populations venrick 1982 reported two distinct floral assemblages associated with each of these layers which also seem to be differentiated ecologically in terms of competition and predation herbland et al 1985 showed a strong stratification in size classes of photosynthetic organisms especially 1 pm of the equatorial atlantic with the major shift in size spectra occurring at or near the base of the mixed layer recently the presence of stratified systems in meso and oligotrophic regimes has been further interpreted in terms of the concepts of dugdale and goering 1967 and eppley and peterson 1979 regarding new and regenerated pro

holocene flood histories in south western usa harden t macklin m g baker v r 2010 holocene flood histories in south western usa earth surface processes and landforms 35 6 707 716 sponsorship aberystwyth university university of arizona

evidence for elevated alkalinity in the glacial southern ocean an increase in whole ocean alkalinity during glacial periods could account in part for the drawdown of atmospheric co2 into the ocean such an increase was inevitable due to the near elimination of shelf area for the burial of coral reef alkalinity we present evidence based on downcore measurements of benthic foraminiferal b ca and mg ca from a core in the weddell sea that the deep ocean carbonate ion concentration co32 was elevated by similar to 25 mu mol kg during each glacial period of the last 800 kyr the heterogeneity of the preservation histories in the different ocean basins reflects control of the carbonate chemistry of the deep glacial ocean in the atlantic and pacific by the changing ventilation and chemistry of weddell sea waters these waters are more corrosive than interglacial northern sourced waters but not as undersaturated as interglacial southern sourced waters our inferred increase in whole ocean alkalinity can be reconciled with reconstructions of glacial saturation horizon depth and the carbonate budget if carbonate burial rates also increased above the saturation horizon as a result of enhanced pelagic calcification the weddell records display low co32 during deglaciations and peak interglacial warmth coincident with maxima in percent caco3 in the atlantic and pacific oceans should the burial rate of alkalinity in the more alkaline glacial deep waters outstrip the rate of alkalinity supply then pelagic carbonate production by the coccolithophores at the end of the glacial maximum could drive a decrease in ocean co32 and act to trigger the deglacial rise in pco 2

determining the mean large scale circulation of the atlantic with the adjoint method abstract a new model approach based on the adjoint formalism and aimed at assimilating large sets of hydrographic data is presented the goal of the model calculations is to obtain the mean large scale ocean circulation together with coefficients of iso and diapycnal mixing and air sea heat and freshwater fluxes the final optimal solution is required to be consistent with the principle of geostrophy and must predict realistic distributions of temperature and salinity the model covers the entire atlantic and has realistic topography model resolution is nonuniform and ranges from 2 5 to 10 horizontally and from 60 m to 500 m in the vertical model velocities are initialized with geostrophic flows calculated from original hydrographic station data initial air sea heat fluxes and mixing coefficients are taken from the literature mass heat and salt budgets are satisfied exactly and for given boundary conditions and model flows the model temperature and salinity distributions are calculated then h

quantifying the opal belt in the atlantic and southeast pacific sector of the southern ocean by means of 230th normalization 1 a set of 114 samples from the sediment surface of the atlantic eastern pacific and western indian sectors of the southern ocean has been analyzed for 230th and biogenic silica maps of opal content th normalized mass flux and th normalized biogenic opal flux into the sediment have been derived significant differences in sedimentation patterns between the regions can be detected the mean bulk vertical fluxes integrated into the sediment in the open southern ocean are found in a narrow range from 2 9 g m 2 yr 1 eastern weddell gyre to 15 8 g m 2 yr 1 indian sector setting upper and lower limits to the vertically received fraction of open ocean sediments the silica flux to sediments of the atlantic sector of the southern ocean is found to be 4 2 1 4 1011 mol yr 1 just one half of the last estimate this adjustment represents 6 of the output term in the global marine silica budget

southern ocean winter mixed layer austral winter 1986 observations from the polarstern along the greenwich meridian from the ice edge to the antarctic margin show the mixed layer beneath the winter sea ice cover to be significantly depressed in oxygen saturation incorporation of weddell deep water wdw into the winter mixed layer responsible for this undersaturation also introduces heat and salinity into the surface layer which strongly influences the mixed layer sea air exchanges and sea ice formation processes the total wdw transfer into the mixed layer averages 45 myr 1 implying a residence time for the surface water of 2 5 years the associated winter heat flux is 41 w m 2 which limits ice thickness to about 0 55 m agreeing quite well with observations the air temperatures during the cruise are just sufficient to remove the wdw heat input in the presence of observed ice thickness and concentration this suggests that the sea ice cover and wdw heat input into the mixed layer are in approximate balance by midwinter the annual heat flux from wdw to the surface layer and hence into the atmosphere is estimated as 16 w m 2 extrapolation of the greenwich meridian wdw entrainment value to the full circumpolar 60 70 s belt yields total up welling of 24 106 m3 s 1 similar extrapolation of the heat flux value gives a circumpolar total of 2 8 1014 w as a consequence of circulation topography interaction the maud rise water column stands out as an anomaly relative to the surrounding region with a significantly more saline and dense mixed layer below the mixed layer the water column over the crest of the rise is identical to that over the flanks if the latter water column is upwelled by 400 m this uplifting is believed to be a response of the upstream flow encountering the rise increased upstream flow would be expected to increase maud rise upwelling and the dependent salinity density of the mixed layer slight increases in the mixed layer density could trigger a convective mode and generation of a polynya it is hypothesized that spin up of the weddell gyre s barotropic circulation induced by an increase of the regional wind stress curl would enhance the probability of polynya development over maud rise

annual export production in the interior weddell gyre estimated from a chemical mass balance of nutrients nitrate phosphate and silicate data are presented from 1992 austral winter and 1998 austral autumn cruises with fs polarstern in the weddell gyre because in the weddell gyre away from the boundary current the surface layer is eventually formed from upwelled deep water the difference in nutrient concentrations between these layers can be used to compute net nutrient consumptions identical with the export production this method renders a value for the export production that is based on observed annual changes the results are consistent for two years and two regions within the central gyre the calculated net nitrate and phosphate consumptions were scaled to net carbon consumptions using canonical redfield ratios yielding 16 17 mol c kg 1 yr 1 this equals 21 4 g c m 2 yr 1 as a robust estimate for the marginal ice zone the net annual silicate consumption in the surface layer which equals the export of biogenic silica amounts to 15 18 mol kg 1 yr 1 there is a tendency for higher values in the eastern weddell gyre the estimated silicate consumption of about 1 8 mol si m 2 yr 1 is relatively high compared to earlier estimations of biogenic silica export the silicate to carbon consumption ratio of about 1 is very high and documents the dominance of diatoms in the export of organic material

application of a new in situ 3d laser scanner to study the scale effect on the rock joint surface roughness application of a new in situ 3d laser scanner to study the scale effect on the rock joint surface roughness

the pulse of calm fan deltas abstract at the heart of interpreting the history of earth surface evolution preserved in the rock record is distinguishing environmental allogenic forcing from internally generated autogenic noise allogenic deposits classically have been recognized by their cyclic nature which apparently results from periodic changes in base level sediment supply or tectonics autogenic deposits which are quite variable in their origin and scale are caused by the nonlinearity of sediment transport and might be expected to have a random or scale free fractal signature here we describe a robust mechanism that generates cyclic deposits by an autogenic process in experimental fan deltas sheet flow over the fan surface induces deposition and an increase in fluvial slope and curvature to a point where the surface geometry is susceptible to a channelization instability similar to channel initiation on hillslopes channelized flow results in incision and degrading of the fan surface to a lower slope releasing a

headwater channel dynamics in semiarid rangelands colorado high plains usa incised ephemeral channels provide a window into the fluvial processes that help sculpt rangeland landscapes this paper presents observations of ephemeral channels and valley networks in the high plains of colorado usa with an eye toward painting a picture of the ingredients that must be included in mathematical models of landscape evolution in such environments channel incision in the study area is driven by summer thunderstorms which can with reasonable frequency 3 5 yr generate boundary shear stresses high enough to penetrate the highly resistant vegetation armor but only within erosional hot spots where hydraulic forces are amplified by channel constriction and locally steep gradients focusing of erosion at these hot spots which correspond to knickpoints and channel heads is amplified by the small areal footprint and short erosional reach of most convective storms upstream migration of knickpoints creates a pattern of short active channel reaches separated by unchanneled or weakly channeled fully vegetated stable reaches based on our observations we interpret the necessary and sufficient conditions leading to the observed channel forms and dynamics as 1 a resistant vegetation layer overlying an erodible substrate which sets up a conditional instability through which erosional perturbations can grow by positive feedback 2 high flow variability 3 moderate to high substrate cohesion and 4 a high volume fraction of fine grained erodible material concave upward valley long profiles are interpreted as a trade off between downstream increasing flood frequency and downstream decreasing flood effectiveness the observed process dynamics imply that long term rates of valley incision should be especially sensitive to climatic oscillations between episodes of drought and warm season convective rainfall

meridional circulation across the antarctic circumpolar current serves as a double 231pa and 230th trap abstract upwelling of circumpolar deep water in the weddell gyre and low scavenging rates south of the antarctic circumpolar current acc cause an accumulation of particle reactive nuclides in the weddell gyre a ventilation reversible scavenging model that successfully described the accumulation of 230th in this area was tested with other particle reactive nuclides and failed to adequately describe the depth distributions of 231pa and 210pb we present here a modified model that includes a nutrient like accumulation south of the antarctic polar front in an upper meridional circulation cell as well as transport to a deep circulation cell in the weddell gyre by scavenging and subsequent release at depth the model also explains depletion of 231pa and 230th in weddell sea bottom water wsbw by ventilation of newly formed deep water on a timescale of 10 years but this water mass is too dense to leave the weddell gyre in order to quantify the processes responsible for the 231pa and 230th composition of newly formed antarctic bottom water aabw we present a mass balance of 231pa and 230th in the atlantic sector of the southern ocean based on new data from the geotraces program the acc receives 6 0 1 5 10 6 dpm s 1 of 230th from the weddell sea similar in magnitude to the net input of 4 2 3 0 10 6 dpm s 1 from the north for 231pa the relative contribution from the weddell sea is much smaller only 0 3 0 1 10 6 compared to 2 7 1 4 10 6 dpm s 1 from the north weddell sea deep water wsdw leaving the weddell gyre northward to form aabw is exposed in the acc to resuspended opal rich sediments that act as efficient scavengers with a th pa fractionation factor f 1 hydrothermal inputs may provide additional removal with low f scavenging in the full meridional circulation across the opal rich acc thus acts as a double 231pa and 230th trap that preconditions newly formed aabw