scattering of vhf radio waves from within the top 700 m of the antarctic ice sheet and its relation to the depositional environment a case study along the syowa mizuho dome fuji traverse

re evaluation of paleo accumulation parameterization over northern hemisphere ice sheets during the ice age examined with a high resolution agcm and a 3 d ice sheet model

estimates of atmospheric processed soluble iron from observations and a global mineral aerosol model biogeochemical implications 1 desert dust deposition to the ocean may be a significant source of biogeochemically important elements specifically iron the bioavailability of iron in the oceans requires it to be in a soluble form and because atmospheric iron in desert dust is typically insoluble understanding the atmospheric processes that convert insoluble iron to more soluble forms is essential understanding these relationships is especially important in remote ocean regions where iron may be the limiting nutrient observations of soluble iron from 2001 cruise based aerosol measurements over the atlantic and pacific oceans ranged from 0 to 45 mean of 4 9 in the fine mode 2 5 m in diameter and 0 to 87 mean of 2 10 in the coarse mode we test two simple hypotheses of soluble iron enhancement in the atmosphere using a global model of mineral aerosols the first method assumes that iron solubility increases as iron is exposed to solar radiation approximating photoreduction reactions that are important pathways for enhancement of soluble iron in the presence of acidic solutions the second process imitates cloud processing of iron by increasing the amount of soluble iron when the mineral aerosol comes into contact with a cloud both methods resulted in similar average magnitudes of percent soluble iron compared to observations but did not capture specific events or have sufficient variability perhaps because the model does not include aerosol interactions between species other than mineral dust or other processes that may be important

metal contents of phytoplankton and labile particulate material in the north atlantic ocean abstract phytoplankton contribute significantly to global c cycling and serve as the base of ocean food webs phytoplankton require trace metals for growth and also mediate the vertical distributions of many metals in the ocean we collected bulk particulate material and individual phytoplankton cells from the upper water column

the biogeochemistry of aluminum in the pacific ocean abstract vertical distributions and horizontal surface transects of dissolved and particulate al at several locations in the pacific ocean are presented here concentrations of dissolved al in the pacific range from 0 3 to 5 nmol kg in the surface waters from 0 1 to 1 nmol kg in mid depths and from 0 5 to 2 nmol kg in the deep waters from these data and published data from other regions it is evident that al has a unique oceanic chemistry relative to that of other metals external sources and rapid particle scavenging throughout the water column are the major controls on dissolved al distributions in the oceans vertical profiles generally exhibit a surface maximum a mid depth minimum and increasing concentrations toward the sediment water interface this suggests two sources of dissolved al one to the surface waters and one to the deep waters concentrations of dissolved al in surface waters are lowest within the eutrophic low salinity california current 0 3 1 nmol kg and increase westwardly into the subtropical gyre of the north pacific 5 nmol kg values in the south pacific gyre are fivefold lower these horizontal trends indicate that the primary source of dissolved al to the surface waters of the central pacific is from eolian input dissolved al supplied by rivers to the eastern north pacific appears to be rapidly scavenged in estuaries and or the highly productive coastal region the source of dissolved al to the deep waters is not known but could be due to a flux out of the sediments or a remineralization process suspended particulate al concentrations increase with depth at all stations and decrease with distance from the ocean boundary surface values range from 1 5 nmol kg near shore to 0 3 nmol kg in the central gyres of the pacific deep water concentrations range from 22 nmol kg near shore to 4 nmol kg in the north pacific central gyre and decrease to 1 3 nmol kg in the south pacific central gyre observed distributions indicate that suspended particulate al varies with the intensity of bottom sediment resuspension and the horizontal mixing of the resulting nepheloid layer out from ocean boundary regions particle residence times estimated are consistent with other reported values

hydrothermal contribution to the oceanic dissolved iron inventory mineral dust and marine sediment resuspension are generally considered the primary sources of the nutrient iron to the oceans numerical model results suggest that iron released by hydrothermal activity is also an important source of dissolved iron particularly in the southern ocean iron limits phytoplankton growth and hence the biological carbon pump in the southern ocean1 models assessing the impacts of iron on the global carbon cycle generally rely on dust input and sediment resuspension as the predominant sources2 3 although it was previously thought that most iron from deep ocean hydrothermal activity was inaccessible to phytoplankton because of the formation of particulates4 it has been suggested that iron from hydrothermal activity5 6 7 may be an important source of oceanic dissolved iron8 9 10 11 12 13 here we use a global ocean model to assess the impacts of an annual dissolved iron flux of approximately 9 108 mol as estimated from regional observations of hydrothermal activity11 12 on the dissolved iron inventory of the world s oceans we find the response to the input of hydrothermal dissolved iron is greatest in the southern hemisphere oceans in particular observations of the distribution of dissolved iron in the southern ocean3 chever et al manuscript in preparation bowie et al manuscript in preparation can be replicated in our simulations only when our estimated iron flux from hydrothermal sources is included as the hydrothermal flux of iron is relatively constant over millennial timescales14 we propose that hydrothermal activity can buffer the oceanic dissolved iron inventory against shorter term fluctuations in dust deposition

modeling the evolution of antarctic ice sheet over the last 420 000 years implications for altitude changes in the vostok region a new thermomechanical three dimensional model designed to simulate the evolution of the antarctic ice sheet over long time periods is presented this model incorporates the various types of ice flow found in antarctica relatively slow inland ice flow that is essentially due to ice deformation fast ice flow in the regions with ice streams and ice shelf flow by coupling these three types of flow it is possible to predict grounding line migration simulations covering four glacial interglacial cycles have been conducted by forcing this model with a temperature record from vostok and a sea level record from marine cores our findings indicate that grounding line migration induced by sea level changes is the primary factor governing the evolution of the antarctic ice volume on the other hand the altitude of the ice sheet surface at vostok is driven by accumulation rate variations the amplitude of the altitude change does not exceed 150 m and is very similar for all the sites located on the antarctic plateau

insights into spatial sensitivities of ice mass response to environmental change from the searise ice sheet modeling project ii greenland searise greenland

an overview of dissolved fe and mn distributions during the 2010 2011 u s geotraces north atlantic cruises geotraces ga03 abstract high resolution dissolved fe dfe and dissolved mn dmn distributions were obtained using a trace metal clean rosette during the geotraces ga03 zonal transect cruises usgt10 and usgt11 across the north atlantic ocean this manuscript provides a general overview of the dfe as well as dmn and dissolved al dal distributions that reveal several fe inputs at varying depths across the study region elevated dfe concentrations correlate with elevated dal concentrations in the surface waters of the subtropical gyre indicating a significant atmospheric source of fe in contrast there is no apparent significant dust source for mn in the subsurface waters dfe maxima are a result of the remineralization process as revealed by their correspondence with dissolved oxygen minima within the oxygen minimum the ratio of dfe to apparent oxygen utilization aou is lower than would be expected from the measured fe content of surface water phytoplankton suggesting that a significant amount of dfe that is remineralized at depth 63 90 is subsequently scavenged from the water column the rate of remineralization which is based on the slope of dfe aou plot is similar across a wide area of the north atlantic in addition to the remineralization process sedimentary inputs are apparent from elevated dmn signals in the eastern basin particularly near the african coast in the western basin sedimentary input is also occurring along the advective flow path of the upper labrador sea water ulsw as ulsw transits along the north american continental shelf region the largest dfe anomaly 68 nm which also corresponds to a dmn anomaly up to 33 nm is seen in the neutrally buoyant hydrothermal plume sampled over the mid atlantic ridge and that signal is visible for 500 km to the west of the ridge

a ventilation based framework to explain the regeneration scavenging balance of iron in the ocean our understanding of the processes driving the patterns of dissolved iron dfe in the ocean interior either in observations or models is complicated by the combined influences of subduction from the surface mixed layer notable subsurface sources regeneration and scavenging loss we describe a ventilation based framework to quantify these processes in a global ocean biogeochemical model including diagnostics along potential density surfaces there is a prevailing control of subsurface dfe by the subduction of surface dfe as preformed dfe augmented by benthic sources of dfe from hydrothermal activity and sediments unlike phosphate there is often a first order balance with a near cancelation between regeneration and scavenging with the remaining net regeneration controlled by the ventilation of surface excesses in fe binding ligands this dfe framework provides a more stringent test of how the total dfe distribution is mechanistically controlled within a model and may be subsequently used to interpret observed dfe distributions

influence of anthropogenic combustion emissions on the deposition of soluble aerosol iron to the ocean empirical estimates for island sites in the north atlantic the results of several recent studies challenge the reigning paradigm that continental soil dust provides the only significant atmospheric source of dissolved iron to the surface ocean this evidence includes correlations between the operational solubility of aerosol iron and atmospheric loadings of black carbon and aluminum normalized vanadium and nickel each of which are associated with emissions from the combustion of fossil fuel oil these observations suggest that the relative solubility of aerosol iron hence the eolian flux of soluble iron to the surface ocean may be significantly impacted by anthropogenic oil combustion products using recent field data from the bermuda region we have developed an empirical method to estimate the solubility of aerosol iron using bulk aerosol concentrations of fe v and al we apply this method to a large body of published data from the aeroce program for north atlantic island sites on tenerife barbados bermuda and ireland where the relative proportions of anthropogenic aerosols range from minor to major respectively our aerosol iron solubility estimates suggest that anthropogenic emissions contribute approximately 70 and 85 of the annual dry deposition of soluble iron to the surface ocean near bermuda and ireland respectively implying that human activities have profoundly affected the iron budget of the north atlantic region the annual mean dry deposition of soluble iron at barbados and izana is dominated by soil dust the anthropogenic contribution at these two sites ranges from 12 to 30 and is highly dependent on the soil dust solubility of fe employed in the model the low end 12 estimate appears to be more representative of these high dust sites

a comparison of atmospheric inputs and deep ocean particle fluxes for the sargasso sea trace metal distributions in ocean waters are dominated by internal recycling processes however fluxes out of the water column must balance inputs if steady state is to be maintained we use deep sea particle fluxes at 3200 m in the sargasso sea as measured by sediment traps to define the flux to the sediments beneath the sargasso sea and compare this flux to the atmospheric input for a group of trace metals despite the uncertainties associated with the comparison several important features are revealed for elements predominantly associated with crustal particles al mn fe and v lateral advection provides a significant part of the deep sea particle flux for cd cu ni pb and zn this lateral component is minor and atmospheric inputs to the sargasso sea exceed deep sea particle fluxes these excesses appear to be consistent with calculations of the export of these metals from the sargasso sea arising from ocean boundary scavenging pb and release from decomposing organic matter in the southward flowing north atlantic deep water cd cu ni and zn in the atmospheric deposition itself wet deposition exceeds dry deposition for cd cu mn ni pb and zn while wet and dry deposition are of similar magnitudes for v fe and al

inferring the subduction rate and period over the north atlantic abstract the annual rate at which mixed layer fluid is transferred into the permanent thermocline that is the annual subduction rate sann and the effective subduction period x1d4af eff is inferred from climatological data in the north atlantic from its kinematic definition sann is obtained by summing the vertical velocity at the base of the winter mixed layer with the lateral induction of fluid through the sloping base of the winter mixed layer geostrophic velocity fields computed from the levitus climatology assuming a level of no motion at 2 5 km are used the vertical velocity at the base of the mixed layer is deduced from observed surface ekman pumping velocities and linear vorticity balance a plausible pattern of sann is obtained with subduction rates over the subtropical gyre approaching 100 m yr twice the maximum rate of ekman pumping the subduction period x1d4af eff is found by viewing subduction as a transformation process converting mixed layer fluid into stratified thermocline fluid the effective

fluxes and distribution of dissolved iron in the eastern sub tropical north atlantic ocean aeolian dust transport from the saharan sahel desert regions is considered the dominant external input of iron fe to the surface waters of the eastern sub tropical north atlantic ocean to test this hypothesis we investigated the sources of dissolved fe dfe and quantified dfe fluxes to the surface ocean in this region in winter 2008 surface water dfe concentrations varied between 1 5 nm correlated positively with apparent oxygen utilization aou and showed the importance of organic matter remineralization as an dfe source as a consequence vertical diffusive mixing formed an important fe flux to the surface ocean in this region even surpassing that of a major dust event

parameterization of the annual surface temperature and mass balance of antarctica this study entails the parameterization by means of a linear multiple regression analysis of the annual surface temperature and mass balance of antarctica the analysis was performed for the entire ice cap as well as for three separate regions ice shelves elevation less than 200 m the interior elevation above 1500 m and the escarpment region in between it was found that temperature can be parameterized very well in terms of elevation and latitude the latitudinal gradient on the ice shelves can be explained by the super adiabatic lapse rate along the surface and latitudinal temperature gradient in the interior assuming adiabatic descent of air in the inversion layer from the interior region towards the coast and an axisymmetric spreading over the ice shelves the surface mass balance can be parameterized reliably only in the interior where it has a strong positive correlation with the saturation vapour pressure of the free atmosphere and a significant correlation with the shape of the dome the convex shape of the dome contributes to the mass balance by inducing subsidence of the relatively moist air of the free atmosphere into the inversion layer this results in precipitation as radiative cooling in the inversion exceeds adiabatic warming an estimate is made of the annual horizontal and vertical advective velocities in the free atmosphere above the interior based on regression results and a physical analysis of the precipitation processes in this region a temperature sensitivity analysis was performed for the current mass balance distribution for a 1 k rise in surface temperature the regression estimate of the increase in accumulation on the grounded ice sheet is equivalent to a rate of sea level lowering of 0 2 mm a 1 this is about 30 less than estimates based on the current mass balance perturbated by the increase in saturation vapour pressure of the free atmosphere

impact of atmospheric deposition on the contrasting iron biogeochemistry of the north and south atlantic ocean dissolved iron dfe distributions and atmospheric and vertical subduction fluxes of dfe were determined in the upper water column for two meridional transects of the atlantic ocean the data demonstrate the disparity between the iron biogeochemistry of the north and south atlantic ocean and show well defined gradients of size fractionated iron species in surface waters between geographic provinces the highest dfe and lowest mixed layer residence times 0 4 2 5 years were found in the northern tropical and subtropical regions in contrast the south atlantic gyre had lower dfe concentrations 5 years presumably due to lower atmospheric inputs and more efficient biological recycling of iron in this region vertical input fluxes of dfe to surface waters ranged from 20 to 170 nmol m 2 d 1 in the north atlantic and tropical provinces whereas average fluxes of 6 13 nmol m 2 d 1 were estimated for the south atlantic our estimates showed that the variable dfe distribution over the surface atlantic 50 of total vertical fe flux to surface waters rather than upwelling or vertical mixing this demonstrates the strength of the connection between land derived atmospheric fe fluxes and the biological cycling of carbon and nitrogen in the atlantic ocean

a thermomechanical model of ice flow in west antarctica this study uses a three dimensional thermo mechanical model to investigate the internal flow dynamics of the west antarctic ice sheet wais the model allows ice thickness flow and temperature to interact freely its domain is prescribed as that of the present day grounded wais realistic present day climatic and topographical boundary conditions are employed the analysis of a series of experiments pays particular attention to the location and dynamics of concentrations of ice flow ice streams underlying topographic troughs are crucial in determining the strength and location of these concentrations of flow the flow pattern generated by subglacial troughs is made more distinct by the inclusion of ice flow temperature coupling the inclusion of sliding leads to the generation of limit cycles in the ice flow they are concentrated around the present day ice streams b and c of the siple coast and have a period of 5 to 10 ky there appears to be competition between several preferred ice flow pathways in this area the two end members of the flow regime are a strong ice stream c with a weakened ice stream a b complex and strong ice streams a and b with a dormant ice stream c ice streams appear to require ice discharges above a certain threshold in order to maintain frictional heat generation and fast flow individual ice streams can therefore interact through changes in catchment area size a reduction in catchment area reduces the volume of ice entering a stream and can cause stagnation as the amount of frictional heating falls

high resolution al and fe data from the atlantic ocean clivar co2 repeat hydrography a16n transect extensive linkages between atmospheric dust and upper ocean geochemistry 1 trace element sampling and shipboard flow injection analysis during the june august 2003 climate variability and predictability clivar co2 repeat hydrography a16n transect has produced a high resolution section of dissolved fe and al in the upper 1000 m of the atlantic ocean between 62 n and 5 s using the surface water dissolved al and the model of aluminum for dust calculation in oceanic waters madcow model we have calculated the deposition of mineral dust to the surface ocean along this transect and compare that to dissolved fe concentrations the lowest mean mineral dust depositions of 0 2 g m 2 a 1 are found to the north of 51 n a region which also exhibits characteristics of biological fe limitation through its low dissolved surface water fe 0 1 nm and residual macronutrients e g nitrate 2 m to the south of this region mean dust deposition increases by an order of magnitude reaching 3 g m 2 a 1 at 10 n underneath the saharan dust outflow surface water fe values also increase along this section to 1 nm distinct minima in fe concentrations at the depth of the chlorophyll maximum in the vertical profiles between 18 and 4 n illuminate the role that active biological uptake plays in fe cycling an extensive subsurface zone of enhanced dissolved fe concentrations 1 5 nm underlying this region is a result of the biological vertical transport and remineralization of the surface water fe and is coincident with the intermediate nutrient maximum and oxygen minimum of this region elevated concentrations of dissolved al in subsurface waters seen between 30 and 20 n coincide with the domain of the subtropical mode waters stmw which result from the sinking of surface waters in late winter in regions imprinted by dust deposition the magnitude of the al enrichment observed in this water mass implies that the predominant source to the stmw is from the more dust impacted western atlantic with only limited contributions from the stmw formation region near madeira a deeper subsurface al enrichment 30 45 n is associated with the outflow from the mediterranean another heavily dust impacted basin these two regions of al enrichment show the widespread geochemical connection between atmospheric transport processes and the north atlantic and underscore its susceptibility to imprinting by atmospherically borne materials natural as well as anthropogenic

application of a continuum mechanical model for the flow of anisotropic polar ice to the edml core antarctica we present an application of the newly developed caffe model continuum mechanical anisotropic flow model based on an anisotropic flow enhancement factor to the epica ice core at kohnen station dronning maud land antarctica referred to as the edml core a one dimensional flow model for the site is devised which includes the anisotropic flow law and the fabric evolution equation of the caffe model three different solution methods are employed 1 computing the ice flow based on the flow law of the caffe model and the measured fabrics 2 solving the caffe fabric evolution equation under the simplifying assumption of transverse isotropy and 3 solving the unrestricted caffe fabric evolution equation method 1 demonstrates clearly the importance of the anisotropic fabric in the ice column for the flow velocity the anisotropic enhancement factor produced with method 2 agrees reasonably well with that of method 1 even though the measured fabric shows a girdle structure which breaks the transverse isotropy in large parts of the ice core for method 3 we find that the measured fabric is reproduced well by the model down to 2100 m depth systematic deviations at greater depths are attributed to the disregard of migration recrystallization in the model

atmospheric fe deposition modes at bermuda and the adjacent sargasso sea 1 the atmospheric fluxes of fe and al were determined from bulk wet dry plus wet only deposition and aerosol samples collected at bermuda from 1999 to 2001 during the sampling period dry deposition accounted for majority 70 of total fe deposition estimated by both modeled and measured means this contrasts the north pacific where generally wet dominates dry deposition this may be caused by the size and proximity of continental dust sources and seasonal patterns of precipitation to the north atlantic comparing time series measurement of wet soluble fe deposition indicates that the north atlantic oscillation nao may impact the deposition mode of fe in these areas the dry deposition velocities of fe bearing aerosols ddvfe were estimated from paired averages of measured dry deposition bulk wet fluxes divided by corresponding aerosol concentrations and a seasonal trend was observed during the summer months of 1999 the ddvfe ranged from 0 1 to 0 3 cm s 1 yet during the fall and winter months the ddvfe ranged from 2 0 to 6 0 cm s 1 it is hypothesized that with increased humidity and wind speeds at bermuda during fall and winter mineral aerosol particles could be internally mixed with sea salt and gaseous s and n pollutants to increase effective particle sizes such marine particle aggregation is reported elsewhere and could seasonally increase the apparent dry deposition velocity of mineral aerosols

societal need for improved understanding of climate change anthropogenic impacts and geo hazard warning drive development of ocean observatories in european seas society s needs for a network of in situ ocean observing systems cross many areas of earth and marine science here we review the science themes that benefit from data supplied from ocean observatories understanding from existing studies is fragmented to the extent that it lacks the coherent long term monitoring needed to address questions at the scales essential to understand climate change and improve geo hazard early warning data sets from the deep sea are particularly rare with long term data available from only a few locations worldwide these science areas have impacts on societal health and well being and our awareness of ocean function in a shifting climate substantial efforts are underway to realise a network of open ocean observatories around european seas that will operate over multiple decades some systems are already collecting high resolution data from surface water column seafloor and sub seafloor sensors linked to shore by satellite or cable connection in real or near real time along with samples and other data collected in a delayed mode we expect that such observatories will contribute to answering major ocean science questions including how can monitoring of factors such as seismic activity pore fluid chemistry and pressure and gas hydrate stability improve seismic slope failure and tsunami warning what aspects of physical oceanography biogeochemical cycling and ecosystems will be most sensitive to climatic and anthropogenic change what are natural versus anthropogenic changes most fundamentally how are marine processes that occur at differing scales related the development of ocean observatories provides a substantial opportunity for ocean science to evolve in europe here we also describe some basic attributes of network design observatory networks provide the means to coordinate and integrate the collection of standardised data capable of bridging measurement scales across a dispersed area in european seas adding needed certainty to estimates of future oceanic conditions observatory data can be analysed along with other data such as those from satellites drifting floats autonomous underwater vehicles model analysis and the known distribution and abundances of marine fauna in order to address some of the questions posed above standardised methods for information management are also becoming established to ensure better accessibility and traceability of these data sets and ultimately to increase their use for societal benefit the connection of ocean observatory effort into larger frameworks including the global earth observation system of systems geoss and the global monitoring of environment and security gmes is integral to its success it is in a greater integrated framework that the full potential of the component systems will be realised highlights societies increasingly depend on timely information on ecosystems and natural hazards data is needed to improve climate related uncertainty and geo hazard early warning observatory networks coordinate and integrate the collection of standardised data ocean observatories provide opportunity for ocean science to evolve

dissolved iron in the tropical and subtropical atlantic ocean 1 detailed depth profiles and surface transects of dissolved iron dfe defined by 0 4 m filtration were investigated on three cruises in the subtropical and tropical atlantic ocean where dust deposition varied by 3 orders of magnitude surface dfe and dissolved mn concentrations reflected dust deposition trends but are not proportional to the estimated inputs using estimates of the atmospheric flux of dfe surface dfe residence times were calculated to be on the order of 1 to 5 months deepwater dfe concentrations varied with water masses depending on their source age and transit pathways at a site located on the edge of the equatorial system 10 n 45 w high dfe 1 nmol kg was associated with an oxygen minimum zone at depths of 130 to 1100 m dfe concentrations in north atlantic deep water nadw decreased by 30 from sites in the north atlantic to a site in the south atlantic 24 5 s 37 w and dfe was lower in the antarctic derived water masses 0 4 nmol kg than in nadw at the south atlantic site an estimate of deepwater scavenging residence time for dfe was 270 140 years based on decreasing dfe along the nadw flow path

impact of anthropogenic combustion emissions on the fractional solubility of aerosol iron evidence from the sargasso sea we report empirical estimates of the fractional solubility of aerosol iron over the sargasso sea during periods characterized by high concentrations of saharan dust summer 2003 and by low concentrations of aerosols in north american maritime north atlantic air masses spring 2004 and early summer 2004 we observed a strong inverse relationship between the operational solubility of aerosol iron defined using a flow through deionized water leaching protocol and the total concentration of aerosol iron whereby the operational solubility of aerosol iron was elevated when total aerosol iron loadings were low this relationship is consistent with source dependent differences in the solubility characteristics of our aerosol samples and can be described by a simple mixing model wherein bulk aerosols represent a conservative mixture of two air mass end members that carry different aerosol types saharan air which contains a relatively high loading of aerosol iron 27 8 nmol fe m 3 that has a low fractional solubility 0 44 and north american air which contains a relatively low concentration of aerosol iron 0 5 nmol fe m 3 that has a high fractional solubility 19 historical data for aerosols collected on bermuda indicate that the low iron loadings associated with north american air masses are typically accompanied by elevated v al fe al and v mn mass ratios in the bulk aerosol relative to saharan dust which are indicative of anthropogenic fuel combustion products the identification of similar compositional trends in our sargasso sea aerosol samples leads us to suggest that the elevated solubility of iron in the aerosols associated with north american air masses reflects the presence of anthropogenic combustion products which contain iron that is readily soluble relative to iron in saharan soil dust we thus propose that the source dependent composition of aerosol particles specifically the relative proportion of anthropogenic combustion products is a primary determinant for the fractional solubility of aerosol iron over the sargasso sea this hypothesis implies that anthropogenic combustion emissions could play a significant role in determining the atmospheric input of soluble iron to the surface ocean

an improved numerical scheme to compute horizontal gradients at the ice sheet margin its effect on the simulated ice thickness and temperature in three dimensional numerical ice sheet models that use finite difference schemes the position of ice margins is poorly represented with a regular quadratic grid as a result in a centered difference scheme the surface gradient term and the flux divergence term computed for the gridpoints next to the ice margin may be inaccurate in this paper an improved scheme is presented that computes the horizontal gradients at the ice sheet margin using an asymmetric upstream second order difference scheme in order to avoid using information from the zero thickness gridpoints the model is applied to an idealized synthetic geometry to obtain a steady state ice sheet topography the improved model shows a realistically smooth thickness distribution near the margin thermomechanical coupling is found to enhance the error near the margin the error in simulated thicknesses with the centered difference method was significantly reduced with the new upstream scheme

atmospheric transport of iron and its deposition in the ocean the atmospheric transport of continental weathering products is responsible for much of the mineral material and fe entering the open ocean and is probably the dominant source of nutrient fe in the photic zone in regions where other nutrients are present in high concentrations the flux of fe from the atmosphere may be a limiting factor in primary productivity due to the larger source regions for dust north of the equator 8 times more atmospheric fe is deposited in the northern hemisphere than in the southern hemisphere the mineral aerosol and fe transport and deposition are highly variable due to the episodic nature of dust generation and its transport and deposition processes between 10 and 50 of the total atmospheric fe entering the world ocean appears to dissolve i e it will pass through a 0 4 m pore size filter rapidly when the mineral matter enters the ocean much of the atmospheric fe is present as fe ii apparently produced as a result of photochemical reduction reactions taking place during atmospheric transport this readily soluble fe ii should be available immediately for use as a nutrient by phytoplankton atmospheric transport from the continents is estimated to supply 3 times as much dissolved fe to the oceans as that delivered via rivers

size distributions of coastal ocean suspended particulate inorganic matter amorphous silica and clay minerals and their dynamics particulate inorganic matter pim is a key component in estuarine and coastal systems and plays a critical role in trace metal cycling better understanding of coastal dynamics and biogeochemistry requires improved quantification of pim in terms of its concentration size distribution and mineral species composition the angular pattern of light scattering contains detailed information about the size and composition of particles these volume scattering functions vsfs were measured in mobile bay alabama usa a dynamic pim dominated coastal environment from measured vsfs we determined through inversion the particle size distributions psds of major components of pim amorphous silica and clay minerals an innovation here is the extension of our reported psds significantly into the submicron range the psds of autochthonous amorphous silica exhibit two unique features a peak centered at about 0 8 m between 0 2 and 4 m and a very broad shoulder essentially extending from 4 m to 100 m with an active and steady particle source from blooming diatoms the shapes of amorphous silica psds for sizes 10 m inside the bay likely due to wind induced resuspension of larger frustules that have settled compared to autochthonous amorphous silica the allochthonous clay minerals are denser and exhibit relatively narrower psds with peaks located between 1 and 4 m preferential settling of larger mineral particles as well as the smaller but denser illite component further narrowed the size distributions of clay minerals as they were being transported outside the bay the derived psds also indicated a very dynamic situation in mobile bay relative to the cold weather front that passed through during the experiment with northerly winds of speeds up to 15 m s 1 both amorphous silica and clay minerals showed a dramatic increase in concentration and broadening in size distribution outside the exit of the barrier islands indicative of wind induced resuspension and subsequent advection of particles out of mobile bay while collectively recognized as the pim amorphous silica and clay minerals as shown in this study possess very different size distributions considering how differences in psds and the associated particle areas will effect differences in sorption desorption properties of these components the results also demonstrate the potential of applying vsf inversion in studying biogeochemistry in the estuarine coastal ocean system

thorium isotopes tracing the iron cycle at the hawaii ocean time series station aloha abstract the role of iron as a limiting micronutrient motivates an effort to understand the supply and removal of lithogenic trace metals in the ocean the long lived thorium isotopes 232th and 230th in seawater can be used to quantify the input of lithogenic metals attributable to the partial dissolution of aerosol dust thus th can help in disentangling the fe cycle by providing an estimate of its ultimate supply and turnover rate here we present time series 1994 2014 data on thorium isotopes and iron concentrations in seawater from the hawaii ocean time series station aloha by comparing th based dissolved fe fluxes with measured dissolved fe inventories we derive fe residence times of 6 12 months for the surface ocean therefore fe inventories in the surface ocean are sensitive to seasonal changes in dust input ultrafiltration results further reveal that th has a much lower colloidal content than fe does despite a common source on this basis we suggest fe colloids may be predominantly organic in composition at least at station aloha in the deep ocean 2 km fe approaches a solubility limit while th surprisingly is continually leached from lithogenic particles this distinction has implications for the relevance of fe ligand availability in the deep ocean but also suggests th is not a good tracer for fe in deep waters while uncovering divergent behavior of these elements in the water column this study finds that dissolved th flux is a suitable proxy for the supply of fe from dust in the remote surface ocean

atmospheric deposition of soluble trace elements along the atlantic meridional transect amt abstract we briefly review the role of atmospheric deposition measurements within the atlantic meridional transect amt programme and then go on to present new data on the soluble concentrations of a range of trace metals fe al mn ti zn v ni and cu and major ions in aerosols collected along the amt transect the results allow us to identify emission sources of the trace metals particularly in terms of the relative importance of anthropogenic versus crustal sources we identify strong gradients in concentrations and deposition for both crustal and anthropogenically sourced metals with much higher inputs to the north atlantic compared to the south atlantic reflecting stronger land based emission sources in the northern hemisphere we suggest anthropogenic sources of ni and v may include an important component from shipping we consider the extent to which these gradients are reflected in surface water concentrations of these metals based on the geotraces water column trace metal data we find there is a clear difference in the concentrations of surface water dissolved al and fe between the north and south atlantic gyres reflecting atmospheric inputs however for mn v or ni higher inputs to the north atlantic compared to the south atlantic are not clearly reflected in their water column concentrations

dynamics and mass balance of the ice sheet ice shelf regime at nivlisen antarctica as derived from a coupled three dimensional numerical flow model

north atlantic surface circulation during the 1990 s observed with satellite tracked drifters a new compilation of lagrangian velocity observations describes the state of the north atlantic surface circulation during the 1990s gridded fields of velocity and eddy kinetic energy eke are constructed from trajectories of more than 1500 15 m drogued satellite tracked surface drifters in service between january 1990 and december 1999 this time period overlaps a coordinated field study of circulation and variability in the north atlantic completed between 1996 2000 as part of the world ocean circulation experiment we describe the construction of a self consistent drifter climatology present decadal mean quasi eulerian velocity and eke fields computed on a 1 grid and compare these results with contemporary satellite measurements detailed discussion of the inferred surface circulation is focused on three regions 1 the gulf stream and north atlantic current 2 the labrador sea and subpolar gyre and 3 the caribbean sea the swiftest drifter motions were found in the equatorial region and along the tropical subtropical and subpolar western boundaries the maximum instantaneous speed determined from a single quality controlled and filtered drifter observation was 273 cm s 1 in the gulf stream southeast of cape cod the highest eke value in the north atlantic 2790 cm2 s 2 was found in the gulf stream just downstream of the new england seamounts over most of the atlantic basin drifter derived eke values were found to be o 100 cm2 s 2 higher than corresponding values derived from satellite altimetry in the labrador sea a region of sharply elevated eke appears to be geographically related to the localized ejection of drifters and by extension mass and kinetic energy from the energetic west greenland current between 60 and 62 n when compared to drifter measurements made in the late 1970s our results suggest but do not statistically confirm an enhancement and slight northward shift of the zonal gulf stream extension such a shift is consistent in sign with expectations based on observed interdecadal variations in wind stress and subtropical gyre potential energy associated with the north atlantic oscillation

nature of radio echo layering in the antarctic ice sheet detected by a two frequency experiment a two frequency radio echo sounding experiment was carried out at dome fuji the second highest dome in east antarctica and along a 1150 km long traverse line from the dome to the coast the goal was to determine the dominant causes of the radio echo internal reflections and to investigate their possible changes with depth ranges and regions from the two frequency 60 mhz and 179 mhz radio echo responses at various sites we distinguished four zones each of the zones is characterized by a dominant cause of radio echo internal reflection as follows in the pd zone changes in dielectric permittivity are mainly due to density fluctuations in the pcof zone changes in dielectric permittivity are mainly due to changes in crystal orientation fabrics and in the ca zone changes in electrical conductivity are mainly due to changes in acidity induced by past volcanic eruptions in each of these three zones the changes occur commonly along isochrones in addition a basal echo free zone the fourth zone was found to appear always below the pcof zone these four zones and their distribution suggested variations of the physical conditions within the ice sheet

variability in oceanic dissolved iron is dominated by the colloidal fraction abstract oceanic surface and deep iron distribution and size fractionation were investigated on three cruises in the sub tropical and tropical atlantic ocean detailed profiles and transects were collected and analyzed for dissolved fe dfe 0 4 m filtered and soluble fe sfe 0 02 m filtered the difference between dfe and sfe is inferred to be the colloidal fraction of fe cfe sfe concentration distributions and profiles showed little variability in the atlantic ocean with slightly lower concentrations of sfe in the upper ocean than the relatively uniform concentrations observed in deep water 0 3 to 0 4 nmol kg in contrast variability in the atlantic dfe was dominated by variability in cfe dfe and cfe followed dust deposition trends and observed surface maxima in dfe profiles were always due to maxima in the cfe fraction where dust deposition and surface dfe were low i e the south atlantic the cfe fraction of dfe was low and frequently negligible in surface waters below the surface maxima in cfe and dfe cfe always decreased to negligible levels at 30 80 m remained low or negligible throughout the pycnocline and increased with depth below the pycnocline at a site located on the edge of the equatorial system 10 n high dfe and cfe concentrations were associated with an oxygen minimum zone omz at depths of 130 to 1100 m deep water dfe and cfe concentrations varied between water masses depending on the source age and path of the water masses dfe in nadw decreased by 30 from the north atlantic to the south atlantic site with most of the decrease due to loss of cfe at the south atlantic site nadw had higher dfe and a higher fraction of cfe than the antarctic water masses

polar firn densification and grain growth a 50 m firn core from dome c east antarctica was found to consist of coarse firn which comprised 90 to 95 of the core and fine firn coarse firn was characterized by large crystals with a vertical shape orientation near the surface connected to nearest neighbors by relatively large necks in a structure different from closest packing fine firn was of higher density and consisted of smaller more spherical crystals connected by relatively narrow necks in a more nearly closest packed configuration higher surface free energy in fine firn causes crystals and necks to grow more rapidly than in coarse firn however we find that coarse firn densifies more rapidly with time contrary to the predictions of unconfined sintering models load driven densification due to a power law creep mechanism is found to account for the larger coarse firn densification rate however if the exponent in the power law exceeds one then densification rates are predicted to increase with depth due to increasing load contrary to observed behavior we speculate that different mechanisms may control the densification process in fine and coarse firn

seismic reciprocity field tests from the italian peninsula the conditions for applicability of the reciprocity theorem commonly invoked in seismic data gathering are rarely met in usual practice a field test was conducted in an area characterized by remarkable inhomogeneities of the surface layers to assess quantitatively the discrepancies between direct and reciprocal traces the energy sources used were both of vibratory and impulsive type the results show that the coherence between the two traces is good except for the case of short offsets and early times with explosive sources the vibratory source even if theoretically more reciprocal than the explosive one yields coherencies in the same range and is less uniform along the frequency axis

seasonal variations in the horizontal structure of the amazon plume inferred from historical hydrographic data near surface salinity observations from the national oceanographic data center hydrographic data archive for the region 4 s 10 n 60 40 w show that the amazon river discharge forms a plume of low salinity water that extends northwestward into the western tropical north atlantic the average near surface salinity within the plume increases away from the amazon river mouth consistent with an average entrainment of oceanic water of 2 105 m3 s every 1 of latitude there are two notable seasonal variations in the vicinity of the amazon river mouth 0 2 n the plume extends about 200 300 km eastward from june through december however from march to may the plume was often much wider 400 500 km in the vicinity of the river mouth possibly due to the combination of near maximum river discharge and winds with a southeastward component north of 5 n the amazon plume fans out over a broad region of the western tropical north atlantic during january through june low salinity amazon plume water north of 5 n is primarily found west of 52 w spreading northwestward toward the caribbean beginning typically in may some of the amazon plume water is deflected eastward in the north brazil current nbc retroflection from august through october surface salinities suggest 70 of the amazon plume water is carried eastward in the nbc retroflection while the remaining 30 flows northwestward toward the caribbean

sea level changes at the lgm from ice dynamic reconstructions of the greenland and antarctic ice sheets during the glacial cycles abstract new experiments were performed with three dimensional thermomechanical models of the greenland and antarctic ice sheets to simulate their behaviour during the glacial cycles to reconstruct their thickness and extent at the last glacial maximum lgm and to estimate their glacio eustatic contribution to the global sea level stand the calculations used improved ice dynamic and isostatic treatments updated datasets on higher grid resolutions and refined climatic treatments based on newly calibrated transfer functions between ice core records and climatic perturbations results are discussed from a reference run with standard parameters that is compared with available glacial geological observations and from a series of sensitivity experiments focusing on isostatic adjustment thermomechanical coupling climatic forcing mass balance changes and basal melting rates and viscosity changes of antarctic ice shelves for the antarctic ice sheet we find that volume changes are closely linked with grounding line changes of the west antarctic ice sheet at the lgm the grounding line extended close to the continental shelf break almost everywhere ice over central east antarctica was generally thinner than today and varied mainly in accordance with accumulation fluctuations for the greenland ice sheet melting is important only during interglacial periods and the most sensitive period concerns the size of the ice sheet during the eemian at the lgm the greenland ice sheet extended beyond the present coastline to cover at least the inner continental shelf and thinned by up to several hundred meters in central areas for a plausible range of parameters the experiments indicate that at the time of maximum sea level depression 21 kyr bp the antarctic ice sheet contributed 14 18 m to the sea level lowering and the greenland ice sheet 2 3 m significantly less than the older climap reconstructions whereas both ice sheets were at 21 kyr bp close to their maximum extent the experiments also indicate that their maximum volumes were reached only by 16 5 kyr bp greenland and 10 kyr bp antarctica equal to an additional sea level lowering of respectively 0 4 and 3 7 m holocene retreat was essentially complete by 5 kyr bp in greenland but is found to still continue today in west antarctica before reversing to growth during the next millenium the models were found to reproduce gross features of the ice sheet s history since the lgm in reasonably good agreement with available glacial geological data although observational control on ice thickness changes remains very limited

the dynamic response of the greenland and antarctic ice sheets to multiple century climatic warming new calculations were performed to investigate the combined response of the greenland and antarctic ice sheets to a range of climatic warming scenarios over the next millennium use was made of fully dynamic 3d thermomechanic ice sheet models which were coupled to a two dimensional climate model the experiments were initialized with simulations over the last two glacial cycles to estimate the present evolution and were subsequently forced with temperature scenarios resulting from greenhouse emission scenarios which assume equivalent co2 increases of two four and eight times the present 1990 a d value by the year 2130 a d and a stabilization after that the calculations brought to light that during the next century short term effect the background evolution trend would dominate the response of the antarctic ice sheet but would be negligible for the greenland ice sheet on that timescale the greenland and antarctic ice sheets would roughly balance one another for the middle scenario similar to the ipcc96 is92a scenario with respective contributions to the worldwide sea level stand on the order of about 610 cm on the longer term however both ice sheets would contribute positively to the worldwide sea level stand and the most important effect would come from melting on the greenland ice sheet sensitivity experiments highlighted the role of ice dynamics and the height massbalance feedback on the results it was found that ice dynamics cannot be neglected for the greenland ice sheet not even on a century timescale but becomes only important for antarctica on the longer term the latter is related to an increased outflow of ice into the ice shelves and to the grounding line retreat of the west antarctic ice sheet which are both found to be sensitive to basal melting below ice shelves and the effective viscosity of the ice shelves stretching parameters to their limits yielded a combined maximum rate of sea level rise of 85 cm century21 of which 60 cm would originate from the greenland ice sheet alone

ice sheet model sensitivities to environmental forcing and their use in projecting future sea level the searise project ten ice sheet models are used to study sensitivity of the greenland and antarctic ice sheets to prescribed changes of surface mass balance sub ice shelf melting and basal sliding results exhibit a large range in projected contributions to sea level change in most cases the ice volume above flotation lost is linearly dependent on the strength of the forcing combinations of forcings can be closely approximated by linearly summing the contributions from single forcing experiments suggesting that nonlinear feedbacks are modest our models indicate that greenland is more sensitive than antarctica to likely atmospheric changes in temperature and precipitation while antarctica is more sensitive to increased ice shelf basal melting an experiment approximating the intergovernmental panel on climate change s rcp8 5 scenario produces additional first century contributions to sea level of 22 3 and 8 1 cm from greenland and antarctica respectively with a range among models of 62 and 14 cm respectively by 200 years projections increase to 53 2 and 26 7 cm respectively with ranges of 79 and 43 cm linear interpolation of the sensitivity results closely approximates these projections revealing the relative contributions of the individual forcings on the combined volume change and suggesting that total ice sheet response to complicated forcings over 200 years can be linearized

european ice sheet modelling initiative eismint model intercomparison experiments with first order mechanics 1 the european ice sheet modelling initiative eismint intercomparison experiments with thermomechanical coupling are repeated with an ice sheet model that applies the first order approximation for computing the flow field the experiments impose radially symmetric boundary conditions most of the previous results have shown the loss of implied radial symmetry i e the formation of distinct regularly spaced spokes of cold ice in the simulated basal temperatures a similar result is also observed in the presented first order model results the computed velocity components scatter widely along the marginal grid points this indicates that the spokes may be triggered by the poor representation of the margin with a regular grid where the steep gradients in the surface enhance the numerical errors additionally the generally applied second order discretization scheme tends to decouple even and odd numbered grid points thus leading to wavy solutions with a wavelength of two grid cells these patterns strongly suggest that the loss in radial symmetry is a numerical artifact

steady thermomechanical flow along two dimensional flow lines in large grounded ice sheets a thermomechanical flow model has been developed in order to perform simultaneous calculations of the surface elevation and the distribution of stresses velocities and temperatures along two dimensional flow lines on large grounded ice sheets in order to solve the complex system of full thermomechanical coupled equations the following approximations have been made a coordinate scaling giving a lead order reduced model and an iteration procedure which decouples the energy balance equation from the rest of the equations glen s flow law is used as the constitutive relationship between stresses and deformation in the model and it is found that the longitudinal deviatoric stresses have a significant role in the lead order equations at the ice divide the solution shows that the velocity stress and temperature distributions change rapidly here the basal temperature increases creating a hot spot the surface strain rates increase 50 and the horizontal velocity profile is concave near the base with an inflection point away from the ice divide basal temperature increases and in the example presented here the basal temperature reaches the pressure melting point after 2 3 of the lateral extent and basal sliding begins to influence the flow in the ablation region it is seen that the heat produced by internal deformation is of the same order of magnitude as the geothermal heat flux from the bedrock

dry deposition of trace elements to the western north atlantic 1 data for al fe na sb se v and zn in aerosol particles from bermuda are used in combination with parameterized dry deposition velocities to investigate trace element recycling on atmospheric sea salt during july and august which are in the high dust season 10 of the monthly mean aerosol na can be ascribed to crustal sources rather than sea salt but in general the contribution of mineral dust to na dry deposition is small 1 relative to that from sea salt in fall and winter 10 to 20 of the aerosol al a commonly used indicator of mineral dust is attributable to recycled sea salt but the dust fluxes then are small and longer term averages show a recycling effect of only 1 to 5 on dry deposition the percentage of recycled fe appears to be even less than for al noncrustal non sea salt nc nss sources account for 70 of the aerosol sb se v and zn but differences in the dry deposition velocities for three particle types strongly affect their air sea exchange dust can account for more than half of the new dry deposition inputs of v and zn while the amounts of sb and se recycled on sea spray approach or exceed their new inputs from dust and the nss nc sources

nutrients in atmospheric aerosol particles along the atlantic meridional transect the atmosphere can be an important source of nutrients to remote ocean waters e g in supplying iron to nitrogen fixers in the tropical north atlantic we use results obtained from aerosol collection during four meridional transect cruises of the atlantic ocean in an attempt to identify sources of soluble nutrient species fe n p and si to the atlantic atmosphere the sahara desert was the dominant source of soluble aerosol fe and si and also a significant source of aerosol p biomass burning and another source possibly primary particles derived from vegetation also contribute to the aerosol p loading industrial nox and agricultural ammonium sources contribute to high nitrogen concentrations in the northern hemisphere while biomass burning appears to be a significant seasonal source of n to the southern hemisphere this work is an initial step in our aim to describe the atmospheric nutrient inputs to the atlantic basin using a much larger set of aerosol and rain samples that will be obtained during the atlantic meridional transect amt project and other field campaigns 2006 elsevier ltd all rights reserved

balance velocities and measured properties of the antarctic ice sheet from a new compilation of gridded data for modelling this paper presents a new compilation of gridded data sets for three dimensional modeling of the antarctic ice sheet these are for surface elevation icethickness bedrock elevation and accumulation rate as interpolated on a 281 x 281 mesh with 20 km spacing and encompass all of the ice sheet and thesurrounding continental shelf data sources include the bamber digital elevation model from ers 1 radar altimeter data a redigitization of available ice thicknessdata the giovinetto accumulation data recent ice thickness data from british and german expeditions as well as accumulation data from german and norwegianexpeditions in particular new data were incorporated for the filchner ronne schelfeis and for dronning maud land arising from the epica pre site survey special attention was devoted to carefully match the various data sources both among themselves as across the grounding line and below the ice shelves toenable ice sheet expansion and retreat in dynamic situations as an application the balance flow is calculated over the entire ice sheet using a two dimensionalfinite difference scheme and compared with a previous assessment this brought to light the existence of ice streaming features extending well inland of the icesheet a detailed zoom over dronning maud land exhibits the general flow characteristics of interest for locating a future deep drilling site as a by product anupdated value of 26 4 x 106 km3 was obtained for the total volume of the ice sheet and ice shelves or equivalent to 61 1 m of global sea level rise after removalof the ice sheet and subsequent oceanic invasion and isostatic rebound the total accumulation over the grounded ice sheet including the antarctic peninsula is1924 gta 1 or between 5 and 20 higher than earlier estimates including all of the ice shelves the value is 2344 gta 1

atmospheric depositional fluxes of trace elements 210pb and 7be to the sargasso sea atmospheric wet and bulk depositional fluxes of trace elements fe al mn zn pb cu cd ni and cr 210pb and 7be bulk only to the sargasso sea were measured at bermuda from september 1996 to september 1997 wet deposition was the dominant process of trace element deposition over most of the sampling seasons based on the measured bulk versus wet depositional fluxes although about half of the mn in bermuda precipitation was calculated to originate from noncrustal sources its seasonal trend is similar to the fe and al suggesting primary sources from continental crustal materials on the other hand cd zn pb cu ni and cr in bermuda precipitation originate mainly from noncrustal sources presumably anthropogenic based on enrichment factor analyses the noncrustal sources were highest during the fall winter due to more frequent intrusion of u s continental air as the bermuda high weakens atmospheric depositional fluxes of 210pb showed a good correlation with the 7be fluxes r2 0 84 at bermuda indicating major transport of 210pb via the upper troposphere from continents along with other trace elements annual depositional fluxes of noncrustal elements cd zn pb cu ni and cr at bermuda were a factor of 2 to 3 lower than those at the mid atlantic bight and were about 2 20 fold lower during the sampling year than those during the early 1980s this confirms the rapid evolution of trace element inputs to the upper sargasso sea during the last few decades resulting from industrial emission controls in the surrounding continents

controls on seawater fe iii solubility in the mauritanian upwelling zone iron solubility measurements in the mauritanian upwelling and the adjacent open ocean of the tropical atlantic show for all stations lower values in the surface mixed layer than at depth below the pycnocline we attribute this distribution to a combination of loss terms chiefly photo oxidation of organic ligands in the surface and supply terms predominantly from the release of ligands from the decomposition of organic matter significant correlations with ph oxygen and phosphate for all samples below the surface mixed layer indicate that biogenic remineralisation of organic matter results in the release of iron binding ligands into the dissolved phase the comparison of the cfe s po 4 3 ratio with other published data from intermediate and deep waters in the pacific suggests an enhanced release of iron chelators in the more productive mauritanian upwelling zone citation schlosser c and p l croot 2009 controls on seawater fe iii solubility in the mauritanian upwelling zone

the role of dust deposition in determining surface water distributions of al and fe in the south west atlantic abstract underway dissolved al and fe determinations were made on surface water samples collected between 34 s and 8 n in the southern and tropical atlantic ocean using a towed surface water sampler the general distribution of dissolved al which ranged from 8 nm in the sub tropical gyre to 61 nm under the intertropical convergence zone itcz north of the equator corresponds clearly with atmospheric dust deposition patterns a striking correlation between al and surface water salinities between 28 s and 8 n further indicates that wet deposition is the predominant mechanism of delivery of this atmospheric source iron concentrations in contrast were more uniform varying between 0 6 and 0 8 nm south of the equator highest fe values up to 1 4 nm also were found associated with the maximum dust inputs at the itcz indicating an atmospheric source for this element whose input appears to be limited by the solubility of fe in sea water the lowest fe values 0 4 nm also were observed in the equatorial region and are assumed to result from the biological removal of fe from nutrient rich water masses originating in the nearby equatorial and coastal upwelling regions the high frequency data acquisition of the towed sampler revealed significant variations up to 50 in both al and fe concentrations over short distances most notably along the interface between the south equatorial and canary currents the high variability of a biologically important trace element such as fe in these dynamic regions is indicative of the interplay between chemical and biological patchiness in surface waters

availability of iron and major nutrients for phytoplankton in the northeast atlantic ocean availability of iron and major nutrients for phytoplankton in the northeast atlantic ocean because of recent findings that fe is a limiting factor for phytoplankton activity even at relatively high dissolved iron dfe concentrations the potential importance of fe limitation was revisited in the northeast atlantic ocean 39 45 n 17 21 w we report data gathered during deck incubation experiments performed at three stations in february march 2001 with surface seawater containing dfe concentrations of 0 40 nmol l 1 at all stations fe addition enhanced phytoplankton growth fe limitation was moderate and occurred simultaneously with limitation by major nutrients this was clearly demonstrated for diatoms that were colimited by orthosilicic acid micro nano and picoplankton benefited from fe enrichment experiments performed with the trihydroxamate siderophore desferrioxamine mesylate b dfob indicated that fe reserves exist within the cells especially within the larger cells this reserve could result from luxurious storage of fe by colimited cells during episodic atmospheric deposition of saharan dust simulating concentrations of dust resulting from aerosol deposition in well stratified surface waters we determined that the solubility of saharan dust was very low 0 1 w w but the amount of dfe released in seawater was sufficient to relieve the fe limitation of the ambient phytoplankton community

modelled response of the volume and thickness of the antarctic ice sheet to the advance of the grounded area numerical experiments are performed for the antarctic ice sheet to study the sensitivity of the ice volume to variations in the area of grounded ice and to changes in the climate during the most recent deglaciation the effect of the variations in the grounded area is found to be the major source of changes in the ice volume while the effect of climate change was minor the maximum possible contribution of the ice volume change to sea level rise during the deglaciation is estimated to be 36 m which covers most values estimated in previous studies the effect of the advance of the ice sheet margin over those regions not connected to the major ice shelves contributes one third of the total ice volume change which is comparable to the effect of the grounding of the filchner ronne ice shelf and the contribution of the ross and amery ice shelves together

insights into spatial sensitivities of ice mass response to environmental change from the searise ice sheet modeling project i antarctica atmospheric oceanic and subglacial forcing scenarios from the sea level response to ice sheet evolution searise project are applied to six three dimensional thermomechanical ice sheet models to assess antarctic ice sheet sensitivity over a 500 year timescale and to inform future modeling and field studies results indicate i growth with warming except within low latitude basins where inland thickening is outpaced by marginal thinning ii mass loss with enhanced sliding with basins dominated by high driving stresses affected more than basins with low surface slope streaming ice and iii mass loss with enhanced ice shelf melting with changes in west antarctica dominating the signal due to its marine setting and extensive ice shelves cf minimal impact in the terre adelie george v oates and victoria land region of east antarctica ice loss due to dynamic changes associated with enhanced sliding and or sub shelf melting exceeds the gain due to increased precipitation furthermore differences in results between and within basins as well as the controlling impact of sub shelf melting on ice dynamics highlight the need for improved understanding of basal conditions grounding zone processes ocean ice interactions and the numerical representation of all three key points sensitivity study of antarctica to atmospheric oceanic and subglacial forcings different sectors of antarctica are vulnerable to the forcings atmospheric forcing lead to a growth but dynamic forcing lead to a mass loss 2013 american geophysical union all rights reserved

combining seawater 232th and 230th concentrations to determine dust fluxes to the surface ocean abstract aeolian dust is a significant source of iron and other nutrients to the surface ocean but constraining the size of this flux is difficult chemical tracers such as al are useful but are limited by lack of information about their rate of removal from surface seawater in this study we test the use of th isotopes as an improved tracer of dust input by measuring 232 th and 230 th concentrations of upper ocean seawater at six stations along a meridional atlantic section that spans the saharan dust plume open ocean 232 th like al is dominantly derived from dust dissolution while 230 th is produced in seawater by u decay and provides an assessment of th removal rates the highest 232 th concentrations and 232 th 230 th ratios particularly in the surface waters are observed at stations expected to be influenced by input of saharan dust the pattern of 232 th concentration is in agreement with dissolved al distributions and seawifs aerosol imagery supporting the use of 232 th as a proxy for short term dust addition deeper in the water column 232 th concentration may also reflect longer term dust inputs in addition lateral input of 232 th from mediterranean outflow water is detected at 1000 m in the north atlantic surface water residence times are calculated separately from 230 th and 234 th using a simple scavenging model and values from the two isotopes are generally consistent with one another th 230 residence times appear to reflect the longer term value however rather than exhibiting the strong seasonal influence seen for 234 th these th residence times allow dust flux to the surface ocean to be calculated using the known concentration of th in dust and assumed values for the solubility of dust th in seawater resulting dust fluxes show good agreements with models of dust deposition if th solubility is 1 to 5 in the north atlantic yielding fluxes of 0 4 19 2 g m 2 yr 1 and 5 to 10 in the south atlantic fluxes of 0 2 0 7 g m 2 yr 1 despite the need for better constraints on the fractional solubility of dust th this study demonstrates the power of combining th isotope measurements to constrain dust fluxes to the surface ocean

a northward shift of the north atlantic ocean intertropical convergence zone in response to summertime saharan dust outbreaks 1 the influence on the summertime north atlantic ocean inter tropical convergence zone itcz of saharan dust outbreaks is explored using nine years of continuous satellite observations and atmospheric reanalysis products during dust outbreak events rainfall along the itcz shifts northward by 1 to 4 degrees latitude dust outbreaks coincide with warmer lower tropospheric temperatures compared to low dust conditions which is attributable to advection of the warm saharan air layer enhanced subtropical subsidence and radiative heating of dust the enhanced positive meridional temperature gradient coincident with dust outbreaks is accompanied by an acceleration of the easterly winds on the north side of the african easterly jet aej the center of the positive vorticity region south of the aej moves north drawing the center of low level convergence and itcz rainfall northward with it the enhanced precipitation on the north side of the itcz occurs in spite of widespread sea surface temperature cooling north of the itcz owing to reduced surface solar insolation by dust scattering

simulations of the greenland ice sheet 100 years into the future with the full stokes model elmer ice it is likely that climate change will have a significant impact on the mass balance of the greenland ice sheet contributing to future sea level rise here we present the implementation of the full stokes model elmer ice for the greenland ice sheet which includes a mesh refinement technique in order to resolve fast flowing ice streams and outlet glaciers we discuss simulations 100 years into the future forced by scenarios defined by the searise sea level response to ice sheet evolution community effort for comparison the same experiments are also run with the shallow ice model sicopolis simulation code for polythermal ice sheets we find that elmer ice is 43 more sensitive exhibits a larger loss of ice sheet volume relative to the control run than sicopolis for the ice dynamic scenario doubled basal sliding but 61 less sensitive for the direct global warming scenario based on the a1 b moderate emission scenario for greenhouse gases the scenario with combined a1b global warming and doubled basal sliding forcing produces a greenland contribution to sea level rise of 15cm for elmer ice and 12cm for sicopolis over the next 100 years