glaciers and rock glaciers distribution at 28 sl dry andes of argentina and some considerations about their hydrological significance the area studied includes a little known portion on the dry andes of the san juan frontal cordillera argentina where the hydrological significance of glaciers and rock glaciers was earlier never studied the surveyed sector includes cerro el potro 5 870 m asl and nearby mountain chains 28 s the predominant landforms in these areas were shaped in a periglacial environment superimposed on an earlier glacial landscape these regions comprise abundant rock glaciers a noteworthy rock glacier zone in the world of which little is known in south america this work employs geomorphological mapping to analyze the distribution of active rock glaciers in relation to altitude aspect and slope using optical remote sensing techniques with gis statistical estimation techniques were used based on a digital elevation model dem and aerial photos and spot images interpretation the specific density of rock glaciers estimation in the surveyed area argentine border is 1 56 with corresponds to 38 rock glaciers with an area of 5 86 km2 and 0 12 km3 of water equivalent furthermore the analytical results show that elevations 4 270 m asl a southeast facing aspect and slope between 2 and 40 favor the existence of rock glaciers finally a comparison with glacier water equivalent which covers an area of 16 km2 and 0 9 km3 of water equivalent shows that glaciers are the main stores of water at 28 s cerro el potro glacier however the importance of rock glaciers as water reserves in this portion of argentina should not be underestimated

statistical estimation and generalized additive modeling of rock glacier distribution in the san juan mountains colorado united states 1 our goal is to quantify rock glacier abundance and analyze the topographic controls of rock glacier distribution patterns for this purpose we use statistical estimation techniques and generalized additive models relating rock glacier occurrences to terrain attributes significant applied results include the ability to determine water equivalence and denudation rates the statistical estimation of regional rock glacier abundance based on local interpretation of air photos is an efficient alternative to costly rock glacier inventories these presence absence data n 2933 also allow us to analyze the partly nonlinear topographic controls on rock glacier distribution with generalized additive models we apply these techniques in the san juan mountains 2874 km2 above 3400 m colorado where we obtained a total rock glacier surface area of 70 km2 corresponding to a water equivalence in the order of 0 50 0 76 km3 estimated rock glacier debris volumes imply postglacial denudation rates on the order of 0 5 1 1 mm yr 1 within the talus sheds of rock glaciers the distribution model shows the nonlinear factors of local slope slope of the contributing area local curvature and size of the contributing area controlling the probability of rock glacier occurrence the model yields an area under the receiver operating characteristics curve of 0 91 which indicates an excellent fit on the basis of the present results the integration of terrain attributes with remote sensing data will be the next step toward automatic mapping of rock glaciers in vast mountain areas

permafrost activity and atmospheric warming in the argentinian andes abstract rock glaciers are permafrost or glacial landforms of debris and ice that deform under the influence of gravity recent estimates hold that in the semiarid chilean andes for example active rock glaciers store more water than glaciers however little is known about how many rock glaciers might decay because of global warming and how much this decay might contribute to water and sediment release we investigated an inventory of 6500 rock glaciers in the argentinian andes spanning the climatic gradient from the desert andes to cold temperate tierra del fuego we used active rock glaciers as a diagnostic of permafrost assuming that the toes mark the 0 c isotherm in climate scenarios for the twenty first century and their impact on freezing conditions near the rock glacier toes we find that under future worst case warming up to 95 of rock glaciers in the southern desert andes and in the central andes will rest in areas above 0 c and that this freezing level might move up more than twice as much 500 m as during the entire holocene 200 m many active rock glaciers are already well below the current freezing level and exemplify how local controls may confound regional prognoses a bayesian multifactor analysis of variance further shows that only in the central andes are the toes of active rock glaciers credibly higher than those of inactive ones elsewhere in the andes active and inactive rock glaciers occupy indistinguishable elevation bands regardless of aspect the formation mechanism or shape of rock glaciers the state of rock glacier activity predicts differences in elevations of toes to 140 m at best so that regional inference of the distribution of discontinuous permafrost from rock glacier toes cannot be more accurate than this in the argentinian andes we conclude that the central andes where rock glaciers are largest cover the most area and have a greater density than glaciers is likely to experience the most widespread disturbance to the thermal regime of the twenty first century

iron and manganese diagenesis in deep sea volcanogenic sediments and the origins of pore water colloids abstract volcanogenic sediments are typically rich in fe and mn bearing minerals that undergo substantial alteration during early marine diagenesis however their impact on the global biogeochemical cycling of fe and mn has not been widely addressed this study compares the near surface 0 20 cm below sea floor cmbsf aqueous no 3 and solid phase reactive fe distributions between two volcanogenic sediment settings 1 a deep sea tephra rich deposit neighbouring the volcanically active island of montserrat and 2 mixed biosiliceous volcanogenic sediments from abyssal depths near the volcanically inactive crozet islands archipelago shallow penetration of o2 aq into montserrat sediments was observed 5 cmbsf and largely controlled by the oxidation of organic matter dissolved fe and mn distributions in montserrat pore waters were lowest in the surface oxic layer 0 3 m fe 32 m mn with maxima 20 m fe 200 m mn in the upper 1 15 cmbsf unlike montserrat fe and mn in crozet pore waters were ubiquitously partitioned between 0 2 m and 0 02 m filtrations indicating that the pore water distributions of fe and mn in the traditionally termed dissolved size fraction are dominated by colloids with respective mean abundances of 80 and 61 plausible mechanisms for the origin and composition of pore water colloids are discussed and include prolonged exposure of crozet surface sediments to early diagenesis compared to montserrat favouring nano particulate goethite formation and the elevated dissolved si concentrations which are shown to encourage fine grained smectite formation in addition organic matter may stabilise authigenic fe and mn in the crozet pore waters we conclude that volcanogenic sediment diagenesis leads to a flux of colloidal material to the overlying bottom water which may impact significantly on deep ocean biogeochemistry diffusive flux estimates from montserrat suggest that diagenesis within tephra deposits of active island volcanism may also be an important source of dissolved mn to the bottom waters and therefore a source for the widespread hydrogenous mnox deposits found in the caribbean region

factors regulating the great calcite belt in the southern ocean and its biogeochemical significance the great calcite belt gcb is a region of elevated surface reflectance in the southern ocean so covering 16 of the global ocean and is thought to result from elevated seasonal concentrations of coccolithophores here we describe field observations and experiments from two cruises that crossed the gcb in the atlantic and indian sectors of the so we confirm the presence of coccolithophores their coccoliths and associated optical scattering located primarily in the region of the subtropical agulhas and subantarctic frontal regions coccolithophore rich regions were typically associated with high velocity frontal regions with higher seawater partial pressures of co2 pco2 than the atmosphere sufficient to reverse the direction of gas exchange to a co2 source there was no calcium carbonate caco3 enhancement of particulate organic carbon poc export but there were increased poc transfer efficiencies in high flux particulate inorganic carbon regions contemporaneous observations are synthesized with results of trace metal incubation experiments 234th based flux estimates and remotely sensed observations to generate a mandala that summarizes our understanding about the factors that regulate the location of the gcb

controls on the silicon isotope distribution in the ocean new diagnostics from a data constrained model the global distributions of the silicon isotopes within silicic acid are estimated by adding isotope fractionation to an optimized data constrained model of the oceanic silicon cycle that is embedded in a data assimilated steady circulation including fractionation during opal dissolution improves the model s ability to capture the approximately linear relation between isotope ratio 30si and inverse silicic acid concentration observed in the deep atlantic to quantify the importance of hydrographic control on the isotope distribution 30si is partitioned into contributions from preformed and regenerated silicic acid further partitioned according to euphotic zone origin we find that the large scale features of the isotope distribution in the atlantic basin are dominated by preformed silicic acid with regenerated silicic acid being important for setting vertical gradients in the pacific and indian oceans preformed and regenerated silicic acid make roughly equally important contributions to the pattern of the isotope ratio with gradients of the preformed and regenerated contributions tending to cancel each other in the deep pacific the southern ocean euphotic zone is the primary origin of both the preformed and regenerated contributions to 30si nearly the entire preformed part of 30si is of southern ocean and north atlantic origin the regenerated part of 30si in the atlantic basin also has a contribution of central atlantic 40 s 40 n origin that is comparable in magnitude to the north atlantic contribution in other basins the central pacific and indian ocean are the second largest contributors to the regenerated part of 30si

microfabric analysis of mn carbonate laminae deposition and mn sulfide formation in the gotland deep baltic sea the manganese carbonate deposits of the anoxic littorina sediments of the gotland deep have been commonly related to the periodic renewal of deep water by inflowing saline water from the north sea the use of scanning electron microscopy based techniques allows identification of small scale sedimentary and geochemical features associated with mn carbonate laminae which has significant implications for models of mn carbonate formation varves occurring in the littorina sequence contain up to four laminae that may be placed in a seasonal cycle and kutnahorite laminae occur within varves only as a winter early spring deposit this kutnahorite laminae seasonality is in agreement with the seasonal distribution of major baltic inflow events recorded in historical records and a direct causal link between inflows and kutnahorite deposition is implied benthic foraminifera tests are found to be heavily encrusted in kutnahorite implying that benthic recolonization during oxidation events occurs concurrently with kutnahorite formation the relatively common occurrence of small 50 to 100 m hexagonal mn sulfide pseudomorphs associated with 13 of kutnahorite laminae studied is reported in gotland deep sediments for the first time although mn sulfide crystals are not usually preserved in the sediment the discovery of mn sulfide pseudomorphs suggests that initial formation of mn sulfide in the gotland deep may occur much more commonly during the process of kutnahorite formation than previous reports of mn sulfide occurrence have implied

assimilation of radiocarbon and chlorofluorocarbon data to constrain deep and bottom water transports in the world ocean a coarse resolution global model with time invariant circulation is fitted to hydrographic and tracer data by means of the adjoint method radiocarbon and chlorofluorocarbon cfc 11 and cfc 12 data are included to constrain deep and bottom water transport rates and spreading pathways as well as the strength of the global overturning circulation it is shown that realistic global ocean distributions of hydrographic parameters and tracers can be obtained simultaneously the model correctly reproduces the deep ocean radiocarbon field and the concentrations gradients between different basins the spreading of cfc plumes in the deep and bottom waters is simulated in a realistic way and the spatial extent as well as the temporal evolution of these plumes agrees well with observations radiocarbon and cfc observations place upper bounds on the northward transports of antarctic bottom water aabw into the pacific atlantic and indian oceans long term mean aabw transports larger than 5 sv sv 10 6 m 3 s 1 through the vema and hunter channels in the south atlantic and net aabw transports across 30 s into the indian ocean larger than 10 sv are found to be incompatible with cfc data the rates of equatorward deep and bottom water transports from the north atlantic and southern ocean are of similar magnitude 15 7 sv at 50 n and 17 9 sv at 50 s deep and bottom water formation in the southern ocean occurs at multiple sites around the antarctic continent and is not confined to the weddell sea a cfc forecast based on the assumption of unchanged abyssal transports shows that by 2030 the entire deep west atlantic exhibits cfc 11 concentrations larger than 0 1 pmol kg 1 while most of the deep indian and pacific oceans remain cfc free by 2020 the predicted cfc concentrations in the deep western boundary current dwbc in the north atlantic exceed surface water concentrations and the vertical cfc gradients start to reverse

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

spatial prediction of permafrost occurrence in sikkim himalayas using logistic regression random forests support vector machines and neural networks abstract we have generated permafrost probability distribution maps 10 m resolution for the north eastern himalayan region in sikkim using remote sensing measurements and machine learning algorithms four machine learning algorithms logistic regression random forests support vector machines and neural networks and two different sets of input data set were used to generate a total of 8 machine learning models and hence 8 permafrost probability distribution maps the first set of input data set included surface reflectance from atmospherically corrected sentinel 2a spectral bands elevation and slope parameters while the second set of input data set included mean annul air temperature maat and potential incoming solar radiation pisr permafrost probability distribution maps obtained from the 8 models show reasonable agreement in the total spatial extent of permafrost occurrence but dissimilarities in the pattern of probability distribution accuracy assessment results are more optimistic towards models developed using spectral reflectance elevation and slope parameters as input data set nevertheless 5 out of 8 models agree that around 60 of total area under observation is highly likely to contain permafrost this congruence in outputs despite the use of different machine learning algorithms and separate sets of input data set establishes reliability in the application of machine learning models for the preliminary estimation of permafrost distribution for remote and data scarce himalayan region

230th and 231pa on geotraces ga03 the u s geotraces north atlantic transect and implications for modern and paleoceanographic chemical fluxes abstract the long lived uranium decay products 230th and 231pa are widely used as quantitative tracers of adsorption to sinking particles scavenging in the ocean by exploiting the principles of radioactive disequilibria because of their preservation in the pleistocene sediment record and through largely untested assumptions about their chemical behavior in the water column the two radionuclides have also been used as proxies for a variety of chemical fluxes in the past ocean this includes the vertical flux of particulate matter to the seafloor the lateral flux of insoluble elements to continental margins boundary scavenging and the southward flux of water out of the deep north atlantic in a section of unprecedented vertical and zonal resolution the distributions of 230th and 231pa across the north atlantic shed light on the marine cycling of these radionuclides and further inform their use as tracers of chemical flux enhanced scavenging intensities are observed in benthic layers of resuspended sediments on the eastern and western margins and in a hydrothermal plume emanating from the mid atlantic ridge boundary scavenging is clearly expressed in the water column along a transect between mauritania and cape verde which is used to quantify a bias in sediment fluxes calculated using 230th normalization and to demonstrate enhanced 231pa removal from the deep north atlantic by this mechanism the influence of deep ocean ventilation that leads to the southward export of 231pa is apparent the 231pa 230th ratio however predominantly reflects spatial variability in scavenging intensity complicating its applicability as a proxy for the atlantic meridional overturning circulation

southern ocean control of silicon stable isotope distribution in the deep atlantic ocean the fractionation of silicon si stable isotopes by biological activity in the surface ocean makes the stable isotope composition of silicon delta si 30 dissolved in seawater a sensitive tracer of the oceanic biogeochemical si cycle we present a high precision dataset that characterizes the delta si 30 distribution in the deep atlantic ocean from denmark strait to drake passage documenting strong meridional and smaller but resolvable vertical delta si 30 gradients we show that these gradients are related to the two sources of deep and bottom waters in the atlantic ocean waters of north atlantic and nordic origin carry a high delta 30 sisignature of 1 7 parts per thousand into the deep atlantic while antarctic bottom water transports si with a low delta si 30 value of around 1 2 parts per thousand the deep atlantic delta si 30 distribution is thus governed by the quasi conservative mixing of si from these two isotopically distinct sources this disparity in si isotope composition between the north atlantic and southern ocean is in marked contrast to the homogeneity of the stable nitrogen isotope composition of deep ocean nitrate delta n 15 no3 we infer that the meridional delta si 30 gradient derives from the transport of the high delta si 30 signature of southern ocean intermediate mode waters into the north atlantic by the upper return path of the meridional overturning circulation moc the basin scale deep atlantic delta si 30 gradient thus owes its existence to the interaction of the physical circulation with biological nutrient uptake at high southern latitudes which fractionates si isotopes between the abyssal and intermediate mode waters formed in the southern ocean

a role for scavenging in the marine biogeochemical cycling of zinc and zinc isotopes zinc zn and cadmium cd are important biologically active trace metals in the ocean to date the marine distributions of these elements have been understood primarily in terms of biological assimilation by growing phytoplankton and regeneration of sinking biological material initial studies of zn and cd concentrations and stable isotope ratios 66zn and 114cd have therefore focused on their use as simple tracers of assimilation and regeneration in the oceans however these two processes are insufficient to explain new data on the marine distribution of zn and 66zn here using the first high resolution paired marine depth profiles of zn cd 66zn and 114cd we suggest that scavenging of zn onto organic matter plays a major yet largely unconsidered role in the marine cycling of zn this hypothesis is supported by culture experiments which show that zn released from degrading phytoplankton is rapidly scavenged back onto organic matter and that adsorbed zn is isotopically heavier than the dissolved phase by 0 58 in contrast very little cd or phosphate was scavenged and cd isotopes were not significantly fractionated during degradation our hypothesis is further supported by one dimensional modeling which reproduces observed marine 66zn profiles with 1 of zn adsorbed to particles understanding how zn cycling in the oceans is a balance between assimilation scavenging and regeneration is necessary in order to investigate 66zn as a tracer of marine productivity we anticipate that paired analyses of 66zn and 114cd will prove to be valuable new tools in constraining patterns of global primary productivity providing key information for the marine carbon cycle during periods of past and present global climate change

south pacific dissolved nd isotope compositions and rare earth element distributions water mass mixing versus biogeochemical cycling despite its enormous extent and importance for global climate the south pacific has been poorly investigated in comparison to other regions with respect to chemical oceanography here we present the first detailed analysis of dissolved radiogenic nd isotopes end and rare earth elements rees in intermediate and deep waters of the mid latitude 40 s south pacific along a meridional transect between south america and new zealand the goal of our study is to gain better insight into the distribution and mixing of water masses in the south pacific and to evaluate the validity of nd isotopes as a water mass tracer in this remote region of the ocean the results demonstrate that biogeochemical cycling scavenging processes in the eastern equatorial pacific and release of lrees from the sediment clearly influence the distribution of the dissolved ree concentrations at certain locations nevertheless the nd isotope signatures clearly trace water masses including aaiw antarctic intermediate water average end 8 2 0 3 lcdw lower circumpolar deep water average end 8 3 0 3 npdw north pacific deep water average end 5 9 0 3 and the remnants of nadw north atlantic deep water average end 9 7 0 3 filtered water samples taken from the sediment water interface under the deep western boundary current off new zealand suggest that boundary exchange processes are limited at this location and highlight the spatial and temporal variability of this process these data will serve as a basis for the paleoceanographic application of nd isotopes in the south pacific

evaluation of palaeoenvironmental changes during the last 18 000 years in the myrtoon basin sw aegean sea abstract high resolution last glacial maximum to holocene palaeoenvironmental changes corresponding to a time interval between 200 and 500 years are examined in the myrtoon basin in the sw aegean sea using the abundance variation in foraminifera and pollen in relation to accelerator mass spectrometry 14 c dating and limited oxygen isotope data foram abundance variation shows that from 18 ka to the late glacial holocene boundary at around 10 5 to 9 5 ka the sea surface was cold during this period two intervals of relatively high and low sea surface temperature sst were observed the first high sst occurred at around 14 2 ka whereas the second high sst was centred at around 12 8 ka and appears to correspond to the termination 1a event the first low sst was centred at around 13 7 ka and the second low sst occurred between 11 8 and 10 8 ka the former event may correspond to the heinrich 1 event and the latter to the younger dryas chronozone the holocene started with a sharp warming of sea surface water reaching present day levels and probably associated with a reduction in salinity the formation of the sapropel sequence in the myrtoon basin started at about 10 ka about the same time as the sapropel formation in the other aegean basins which means that the environmental conditions became suitable for the formation of sapropels in the aegean about 800 years earlier than in the adriatic ionian and levantine basins within the sapropel sequence there are two high organic carbon corg content sublayers s 1 a 9 7 9 ka and s 1 b 7 3 6 9 ka separated by a lower corg content sublayer indicating variation in the oceanographic and climatic conditions prevailing in the area during the sapropel sequence formation the depositions of s 1 a and s 1 b coincide with an increase in sst increased temperature and enhanced fresh water inputs from the outflowing rivers in to the aegean sea which later was supplemented by the overflowing of the black sea lowered the sea surface density and reduced the vertical water masses circulation resulting in reduced bottom water ventilation the reduction of o 2 supply to the seabed in combination with increased fluxes of terrigenous and or marine organic matter were responsible for the creation of dysoxic to anoxic conditions in the seabed which led to the formation of sapropel s 1 the sapropel formation ended at 5 2 ka and about the same time the sst attained present day levels during the last glacial maximum and late glacial periods the pollen source area was providing a suitable environment for the growth and survival of arboreal taxa the source area was apparently ice free and was characterized by sufficient humidity and non lethal low temperatures probably only a few degrees colder than present day

logistic regression modeling of rock glacier and glacier distribution topographic and climatic controls in the semi arid andes abstract logistic regression is applied to a random sample of surface points in the semi arid andes of santiago and mendoza chile argentina 32 45 34 30 s 12 000 km 2 above 3000 m a s l to identify local and regional controls on rock glacier and glacier distribution the study area is among the areas with the greatest abundance of rock glaciers worldwide the explanatory variables used for model selection are related to local and regional morphometric and climatic characteristics the models achieve a very good fit area under the roc curve 0 84 for rock glaciers and 0 95 for glaciers and are able to reproduce the regional distribution pattern model results are used to determine the optimal morphographic and climatic niche of rock glaciers and glaciers in the study area and help explain the presence of low elevation rock glaciers under favorable topoclimatic conditions

a pervasive link between antarctic ice core and subarctic pacific sediment records over the past 800 kyrs recently developed xrf core scanning methods permit paleoceanographic reconstructions on timescales similar to those of ice core records we have investigated the distribution of biogenic barium ba al opal and carbonate ca al in a sediment core retrieved from the abyssal subarctic pacific odp 882 50 n 167 e 3244 m over an interval that spans the full length of the epica dome c edc ice core record ba al and biogenic opal show a strong resemblance to the edc dd and co2 with generally high concentrations during interglacials and lower values during ice ages of the past 800 kyrs the sedimentary ba al and biogenic opal are most easily interpreted as indicating a reduced sinking flux of organic matter from the surface ocean during cold periods the ba al maxima during peak interglacials are accompanied by transient ca al peaks in these otherwise carbonate devoid sediments which are best explained by a deepening of the calcite lysocline presumably due to reduced storage of respired co2 in the deep north pacific for most of the luke warm interglacials noted between 420 and 750 ka in edc the ba al peaks in odp 882 are also lower further strengthening the evidence for a simple physical link between global climate and the biogeochemistry of the subarctic pacific

an inventory and estimate of water stored in firn fields glaciers debris covered glaciers and rock glaciers in the aconcagua river basin chile abstract an inventory of firn fields glaciers debris covered glaciers and rock glaciers was conducted in the aconcagua river basin of the semiarid andes of central chile a total of 916 landforms were identified of which rock glaciers were the most abundant 669 and occupied the most total area glaciers and debris covered glaciers were less numerous but were about five times larger in comparison the total area occupied by glaciers and debris covered glaciers was roughly equivalent to the total area of rock glaciers debris covered glaciers and rock glaciers were subcategorized into six ice content classes based on interpretation of surface morphology with high resolution satellite imagery over 50 of rock glaciers fell within a transitional stage 85 of debris covered glaciers were either fully covered or buried most landforms occupied elevations between 3500 and 4500 m glaciers and firn occurred at higher elevations compared to rock glaciers and debris covered glaciers rock glaciers had a greater frequency in the northern part of the study area where arid climate conditions exist firn and glaciers were oriented south debris covered glaciers west and rock glaciers southwest an analysis of water contribution of each landform in the upper andes of the aconcagua river basin was conducted using formulas that associate the size of the landforms to estimates of water stored minimum and maximum water storage was calculated based on a range of debris to ice content ratios for debris covered glaciers and rock glaciers in the aconcagua river basin rock glaciers accounted for 48 to 64 of the water stored within the landforms analyzed glaciers accounted for 15 to 25 debris covered glaciers were estimated at 15 to 19 firn fields contained only about 5 to 8 of the water stored expansion of agriculture prolonged drought and removal of ice rich landforms for mining have put additional pressure on already scarce water resources to develop long term sustainable solutions the importance of the water stored in rock glaciers or other alpine permafrost landforms such as talus slopes must be weighed against the economic value of mineral resources

recent sedimentation and sedimentary budgets on the western iberian shelf abstract thus study is based on 31 box core samples collected mainly from the mud patches of the galician and north portuguese shelf each of these cores some decimetres in length have been described radiographied and sampled each centimetre for grain size analysis and measurement of the particulate organic carbon corg content 210pb excess profiles have been measured using gamma spectrometry which combined with the analysis of the vertical variations of the sedimentary facies have allowed estimates of sedimentation rates these rates were found to vary between 0 05 and 0 40 cm yr 1 considering the latitudinal variation of sedimentation rates around the 100m contour we note that the maximum rates occurred off the douro estuary in the southern sector and also near the galician rias to the north the organic content corg of sediments varied between 0 4 and 2 latitudinally corg showed a decrease from the south to the north these results coupled with the sedimentary map see dias gonzalez garcia diaz del rio 2001 have permitted us to establish the detrital mass budget and an inventory of corg burial

winter dynamics on the northern portuguese shelf part 1 physical processes results of a program of observations carried out on the northern portuguese shelf and slope between july 1996 and june 1999 are used to characterise the main physical processes of the winter regime the data set includes time series of waves and currents at mid shelf 86 m depth and of winds atmospheric pressure and sea level at the coast as well as hydrographic and suspended particle matter spm observations carried during three multidisciplinary surveys the wave regime was found to be characterised by highly energetic conditions during the winter with storm events leading to waves of significant heights exceeding 5 m with mean periods of over 10 s prevailing southerly winds force a downwelling regime over the shelf with poleward flow at mid shelf 10 20 cm s and offshore transport in the bottom ekman layer episodic strong upwelling events can occur during this period leading to important changes in the near bottom stratification at mid shelf tidal currents at mid shelf are dominated by the contribution of the m2 tide 3 cm s and are polarised in the cross shelf direction reflecting the guiding effect of the porto canyon

silicon and zinc biogeochemical cycles coupled through the southern ocean zinc is vital for the physiology of oceanic phytoplankton the striking similarity of the depth profiles of zinc to those of silicate suggests that the uptake of both elements into the opaline frustules of diatoms and their regeneration from these frustules should be coupled however the zinc content of diatom opal is negligible and zinc is taken up into and regenerated from the organic parts of diatom cells thus since opaline frustules dissolve deep in the water column while organic material is regenerated in the shallow subsurface ocean there is little reason to expect the observed close similarity between zinc and silicate and the dissimilarity between zinc and phosphate here we combine observations with simulations using a three dimensional model of ocean circulation and biogeochemistry to show that the coupled distribution of zinc and silicate as well as the decoupling of zinc and phosphate can arise in the absence of mechanistic links between the uptake of zinc and silicate and despite contrasting regeneration length scales our simulations indicate that the oceanic zinc distribution is in fact a natural result of the interaction between ocean biogeochemistry and the physical circulation through the southern ocean hub our analysis demonstrates the importance of uptake stoichiometry in controlling ocean biogeochemistry and the utility of global scale elemental covariation in the ocean in understanding these controls zinc and silicon distributions co vary in much of the global oceans observations and numerical modelling suggest that this co variation can arise in the absence of mechanistic links between the uptake of zinc and silicate

deglacial si remobilisation from the deep ocean reveals biogeochemical and physical controls on glacial atmospheric co2 levels abstract during the last glacial period the sluggish deep ocean circulation sequestered carbon into the abyss leading to the lowering of atmospheric co2 the impact of this redistribution on biologically essential nutrients remains poorly constrained using sedimentary 30 si of diatoms and biogenic accumulation rates in the eastern equatorial pacific eep we present evidences for the remobilisation of dissolved silica dsi along with carbon from the deep ocean during the last deglaciation because dsi is essential for diatoms growing in the surface ocean its concentration in the abyss during the glacial periods amounts to a negative feedback on the oceanic co2 uptake however this effect can be muted by the increased fe inputs during glacial periods which reduces diatom si requirements in fe limited regions such as the eep our results from the eep suggest that the efficiency of the biological co2 pump and the size of the local co2 source is tightly controlled by changes in dsi utilisation driven by fe availability across the last glacial interglacial transition we use a modified pandora box model to illustrate that the inventory of dsi in the global ocean surface is controlled by fe availability in hnlc areas rather than by straightforward si supply though upwelling the holocene is characterised by a fast mode of si cycling driven by high biological requirement for si under conditions of iron limitation and efficient overturning promoting co2 outgassing and an inefficient biological c pump via the rapid exhaustion of dsi in the surface the last glacial period saw slower marine si cycling as a result of decreased dsi biological requirement under fe replete conditions in the sea surface and increased si and co2 sequestration in the abyssal ocean the switch between the two modes of si cycling happened at 15 ka bp i e mid deglaciation and resulted in contrasting biological carbon drawdown responses in the eep and globally between both phases of the deglacial co2 rise this illustrates that in addition to deep sea co2 storage and overturning the efficiency of the biological pump also plays a crucial role in determining ocean atmosphere co2 exchange and shows the dual controls of ocean circulation and fe si availability in this process

silica cycling and isotopic composition in northern marguerite bay on the rapidly warming western antarctic peninsula the southern ocean is a key region for silica si cycling and the isotopic signatures established here influence the rest of the world s oceans the climate and ecosystem of the southern ocean are changing rapidly with the potential to impact si cycling and isotope dynamics this study examines high resolution time series dataset of dissolved si concentrations and isotopic signatures particulate si concentrations and diatom speciation at a coastal site on the western antarctic peninsula wap in order to characterise changes in si cycling with respect to changes occurring in productivity and diatom assemblages dissolved and particulate si phases reflect the dominant control of biological uptake and combined with isotopic fractionation were consistent with a season of low intermediate productivity biogenic si is tightly coupled to both chlorophyll and particulate organic carbon at the sampling site consistent with diatom dominated phytoplankton assemblages along the wap variability in diatom speciation has a negligible impact on the isotopic signature of dissolved si in surface waters although this is unlikely to hold for sediments due to differential dissolution of diatom species a continued decline in diatom productivity along the wap would likely result in an increasing unused si inventory which can potentially feed back into si limited areas promoting diatom growth and carbon drawdown further afield

the effect of topography latitude and lithology on rock glacier distribution in the lemhi range central idaho usa abstract statistical analysis of rock glaciers in the lemhi range demonstrates that their development and preservation is controlled primarily by annual insolation and lithology we inspected 171 alpine valleys in the lemhi range using optical remote sensing techniques digital topographic analysis and field examination in those valleys we identified 48 rock glaciers and examined them for lichen cover evidence of ice presence specific evidence of movement and distinctive morphological features in addition to recording the presence or absence of a rock glacier in each alpine valley existing rock glaciers were classified according to their morphology factors such as topographic shading lithology relief aspect and elevation determine the development and preservation of rock glaciers analysis of these factors in the lemhi range shows that elevation 2600 m a north facing aspect 300 60 and multivariate statistical analysis of controlling parameters demonstrates that annual insolation and latitude influence rock glacier occurrence most strongly whereas duration of insolation is a logical controlling factor latitude is more enigmatic additional statistical analysis indicates that the latitude factor is likely a reflection of lithologic changes with latitude along the range lithology may affect rock glacier distribution through its effects on hydrology or air ventilation moreover statistical analysis shows that rock glacier occurrence correlates with protalus lobe occurrence suggesting that protalus lobes play a role in the genesis of rock glaciers in the lemhi range separate analysis of the classification systems shows that each morphologic class inferred to correlate with rock glacier activity is statistically significant and distinguishable from other classes in addition to the effect of insolation statistical analysis of the classification system also shows that latitude influences distribution of existing rock glacier classes independent of lithology

barium isotopic fractionation in seawater mediated by barite cycling and oceanic circulation the marine biogeochemical cycle of ba is thought to be controlled by particulate baso4 barite precipitation associated with the microbial oxidation of organic carbon and its subsequent dissolution in the baso4 undersaturated water column despite many of these processes being largely unique to ba cycling concentrations of ba and si in seawater exhibit a strong linear correlation the reasons for this correlation are ambiguous as are the depth ranges corresponding to the most active baso4 cycling and the intermediate sources of ba to particulate baso4 stable isotopic analyses of dissolved ba in seawater should help address these issues as ba isotopic compositions are predicted to be sensitive to the physical and biogeochemical process that cycle ba we report a new methodology for the determination of dissolved ba isotopic compositions in seawater and results from a 4500 m depth profile in the south atlantic at 39 99 s 0 92 e that exhibit oceanographically consistent variation with depth these data reveal that water masses obtain their ba and ba isotopic signatures when at or near the surface which relates to the cycling of marine baso4 the shallow origin of these signatures requires that the substantial ba isotopic variations in the bathypelagic zone were inherited from when those deep waters were last ventilated indeed the water column below 600 m is well explained by conservative mixing of water masses with distinct ba and ba isotopic compositions this leads us to conclude that large scale oceanic circulation is important for sustaining the similar oceanographic distributions of ba and si in the south atlantic and possibly elsewhere these data demonstrate that the processes of organic carbon oxidation baso4 cycling and ba isotopic fractionation in seawater are closely coupled such that ba isotopic analyses harbor great potential as a tracer of the carbon cycle in the modern and paleo oceans

a multiproxy approach of the holocene evolution of shelf slope circulation on the nw iberian continental shelf abstract textural mineralogical geochemical and microfaunal data benthic foraminifera were studied along the omex core ksgx 40 recovered in the galicia mud deposit of the nw iberian outer continental shelf off the ria de vigo north of spain this core included the records of the last ca 4 8 ka cal bp and consists from the base to the top of a sedimentary sequence exhibiting gradual upward decrease in grain size sediments of this core are mainly siliciclastic largely composed of quartz k feldspars plagioclases and phyllosilicates mica illite kaolinite and chlorite showing a great continental influence in this zone two periods of deposition of finer sediments are registered between 2 2 1 2 ka cal bp and 0 5 0 ka cal bp since the last 2 2 ka bp but mainly during both muddy intervals the galicia mud deposit was nourished with a lower and finer supply of detrital minerals compensated by higher amounts of organic matter as it is suggested by a benthic foraminifera high productivity bfhp proxy processes involved in organic matter degradation by aerobic organisms led to depressed levels of oxygen in the sediments as shown by a benthic foraminiferal oxygen index bfoi peaks of redox sensitive elements like mn fe cu ni cr co zn ni and pb as well as the presence of diagenetic minerals such as pyrite suggest the development of anoxic conditions beneath the sedimentary surface and early diagenetic changes due to high organic matter flux in both muddy intervals two different hydrodynamic regimes were inferred through the analysis of the different proxies textural mineralogical geochemical and benthic foraminifera 1 a strong hydrodynamic regime between 4 8 and 2 2 ka cal bp characterized by the prevalence of winter storms which gave rise to a deep mixed layer on the shelf 2 weak hydrodynamic regime between 2 2 1 2 ka cal bp and 0 5 0 ka cal bp with a high predominance of upwelling and an increase in oceanic stratification

the southern ocean silicon trap data constrained estimates of regenerated silicic acid trapping efficiencies and global transport paths received 16 august 2013 revised 10 november 2013 accepted 7 december 2013 published 16 january 2014 1 we analyze an optimized model of the global silicon cycle embedded in a dataassimilated steady ocean circulation biological uptake is modeled by conditionally restoring silicic acid in the euphotic zone to observed concentrations where the modeled concentrations exceed the observational climatology an equivalent linear model is formulated to which green function based transport diagnostics are applied we find that the models opal export through 133 m depth is 166 6 24 tmol si yr with the southern ocean so providing 70 of this export 50 of which dissolves above 2000 m depth the global scale gradients of the opal dissolution rate are primarily meridional while the global scale gradients of phosphate remineralization are primarily vertical the mean depth of the temperature dependent silicic acid regeneration reaches 2300 m in the so compared to 600 m for phosphate remineralization silicic acid is stripped out of the euphotic zone far more efficiently than phosphate with only 34 6 5 of the global silicic acid inventory being preformed compared to 61 6 7 for phosphate subantarctic and tropical waters contribute most of the ocean s regenerated silicic acid while antarctic waters provide most of the preformed silicic acid about half of the global silicic acid inventory is trapped in transport paths connecting successive so utilizations with silicic acid last utilized in the so having only a 5 6 2 chance of being next utilized outside the so this trapping depletes subantarctic mode waters of silicic acid relative to phosphate which has a 44 6 2 probability of escaping successive so utilization

application of logistic regression and frequency ratio in the spatial distribution of debris rockslides precordillera of san juan argentina abstract this study employs statistical modeling techniques and geomorphological mapping to analyze the distribution of debris rockslides in relation to altitude aspect slope angle lithology and distance to lineaments using optical remote sensing techniques with gis the study area includes a portion of the central precordillera of san juan around 32 s 69 w where few geomorphological studies have been conducted a debris rockslides inventory map was prepared using debris rockslides locations identified from satellite imageries a total of 35 debris rockslides were identified in an area of 288 13 km 2 with a total slide area of 6 36 km 2 all of the debris rockslides were rotational slides affecting upper ordovician and upper devonian deposits the volumes of debris rockslides were estimated using the sloping local base level technique that allows computing the possible pre rockslide topography and the bedrock deposits interface the relationship between the variables and the slide distribution was analyzed using the frequency ratio method and logistic regression models the analytical results show that lithology and slope exert major influences lithology is found to be the most important aspect in the study area

rare earth elements rees in the tropical south atlantic and quantitative deconvolution of their non conservative behavior this study presents new concentration measurements of dissolved rare earth elements drees along a full depth east west section across the tropical south atlantic 12 s and uses these data to investigate the oceanic cycling of the rees enrichment of drees associated with the redox cycling of fe mn oxides is observed in the oxygen minimum zone omz off the african shelf for deeper waters a multi parameter mixing model was developed to deconvolve the relative importance of physical transport i e water mass mixing from biogeochemical controls on the dree distribution in the deep atlantic this approach enables chemical processes involved in ree cycling not apparent from the measurements alone to be distinguished and quantified results show that the measured dree concentrations below 1000 m are dominantly controlled 75 by preformed ree concentrations resulting from water mass mixing this result indicates that the linear correlation between drees and dissolved si observed in atlantic deep waters results from the dominantly conservative behavior of these tracers rather than from similar chemical processes influencing both drees and si minor addition of drees 10 of dnd and 5 of dyb is observed in the deep 4000 m brazil basin resulting from either remineralization of particles in situ or along the flow path greater addition of drees up to 25 for dnd and 20 for dyb is found at 1500 m and below 4000 m in the angola basin near the african continental margin cerium anomalies suggest that different sources are responsible for these dree addition plumes the 1500 m excess is most likely attributed to dree release from fe oxides whereas the 4000 m excess may be due to remineralization of calcite higher particulate fluxes and a more sluggish ocean circulation in the angola basin may explain why the dree excesses in this basin are significantly higher than that observed in the brazil basin hydrothermal venting over the mid atlantic ridge acts as a regional net sink for light rees but has little influence on the net budget of heavy rees the combination of dense ree measurements with water mass deconvolution is shown to provide quantitative assessment of the relative roles of physical and biogeochemical processes in the oceanic cycling of rees

recent benthic foraminiferal assemblages in deep high energy environments from the gulf of cadiz spain the benthic environment in the gulf of cadiz north eastern atlantic is strongly affected by the mediterranean outflow water undercurrent mow which flows northwards along the western iberian margin at 500 1500 m water depth foraminiferal census counts of living and dead assemblages from 27 surface samples ranging from 103 to 1917 m water depth and the examination of hard substrates reveal a close correlation of the fauna with the local hydrography and sediment facies four different faunal groups are separated by factor analysis of the living fauna assemblage 1 contains typical lower slope species and dominates samples from the lower mow core layer and in the north atlantic deep water below shelf edge foraminifera are common in assemblage 2a which shows the highest proportions in samples from 103 to 272 m assemblage 2b is dominated by upper slope species and suspension feeders that are frequent in the upper mow core layer and in distal settings between 396 and 901 m species from assemblage 3 prefer epibenthic habitats and are recorded with high proportions exclusively in the immediate flow paths of the upper mow between 496 and 881 m colonisation structures and species composition of epibenthic assemblages from the proximal facies largely differ from those in distal settings in general epibenthic foraminifers only use elevated substrates under the influence of near bottom flow under high current velocities epibenthic foraminifers prefer large and heavy objects they colonise high attachment levels where a maximum yield of advected food particles can be achieved in distal settings at lower flow velocities the elevation height does not exceed 20 mm above the surrounding sediment surface this level is related to a hydrologic transition layer with high concentrations of suspended particles the comparison of microhabitat preferences and faunal structure under high and low current velocities reveal that substrate stability may be a confining environmental variable for endobenthic and shallow epibenthic foraminifers the observations also indicate that the preferential settling height of epibenthic foraminifera is related to the highest lateral flux rates of food particles within reach from the sea floor a dynamic selection of elevated microhabitats is only used by 7 8 of all species recognised in the gulf of cadiz area

sediment distribution patterns on the galicia minho continental shelf abstract a sedimentological and bathymetric study of the minho galicia shelf shows a strong contrast between a southern shelf region with a thin partially relict cover of sands and gravel and a northern region where fine grained sediments predominate this contrast is explained through differences in the sediment supply the oceanographic environment storms and ocean currents and the morphology of the shelf which results from its underlying tectonic framework most sediment is supplied to the galicia minho shelf by river discharges onto the minho shelf particularly that from the douro river in the northern part of the shelf the galician rias act as sediment traps rather than sediment suppliers the bulk of the sediment washes out of the rivers during episodic storm events while most of the coarse sediments remain deposited close to the coast the fine grained material is exported to the outer areas of the shelf subsequently coarse sediments close to the coast are transported southwards by the littoral drift whereas the fine grained material is frequently resuspended through the action of the large swells who influence reaches deep into the water this frequent resuspension has a long term sorting effect on the sediments furthermore resuspended sediments on the middle and outer regions of the shelf are transported northwards by a poleward flowing bottom current as a consequence of the differential transport of coarse sediments to the south and of the fine grained sediments to the north the outer reaches of the minho shelf are relatively poor in recent sediments in many areas relict sediments as well as features associated with ancient coastlines and river mouths still appear as seabed features in contrast the northern regions of the shelf are covered by a thin veneer of fine grained material that smooth other most of these fossil features the fine grained sediment fractions mostly very fine sands to coarse silts are deposited in two large mud patches the douro and the galicia mud patches which are situated at water depths of around 100 120 m these two mud patches are both controlled by the local hydrodynamics and morphology the beiral de viana to the west of the douro mud patch is a plateau up to 20 m high lying parallel to the shelf break and is a morphological expression of an underlying horst system this plateau acts as a barrier that prevents the drift of some of the fine grained material to the west out over the shelf break and the continental slope the galicia mud patch is situated on the eastern part of the galician shelf to the north of the douro mud patch it is situated near the extension of the porto tomar fault which results in the shelf being usually steep in this region down to a depth of about 100 m west of this area the slope is much more gentle northward transport of the sediment is strongly reduced by the e w trending outcrops of plutonic and metamorphic rocks

the relationship between zinc its isotopes and the major nutrients in the north east pacific abstract trace metal micronutrients play key roles in photosynthesis by oceanic phytoplankton though they are required in much smaller amounts than the major nutrients p n si their bioavailable forms are also present in the seawater solution at much lower levels relationships between the dissolved chemistry of the nutrient type trace metals their stable isotope variations as well those of the major nutrients have highlighted the importance of biological and physical processes in the southern ocean in controlling their oceanic biogeochemistry however the first order southern ocean processes are overprinted by vertical cycling in other parts of the ocean particularly upwelling regions remote from the southern ocean with the north pacific standing out in particular here we present new zinc zn concentration and isotope as well as major nutrient data for the ne pacific and couple these new data with a compilation of published data from across the region with the objective of better understanding the impact of this important region on oceanic biogeochemical cycles the new zn isotope data for two stations along line p p04 and p26 show a large range in 66 zn in the upper ocean 0 4 up to 1 associated with a very small isotope fractionation but extreme depletion of the dissolved pool during photic zone biological uptake and the regeneration of this cellular zn at very shallow depths 50 m beneath this the two profiles approach the 66 zn value of 0 5 seen throughout the deep ocean by about 500 m the minimum 66 zn resulting from regeneration is associated with very high zn concentrations particularly at the marginal p04 station where diatoms dominate the phytoplankton ecology combining the new data with published zn and major nutrient concentrations from across the north pacific emphasises the role of vertical biological cycling in controlling regional biogeochemistry in the north pacific resulting in the partial overprinting of biogeochemical signatures transported out of the southern ocean by the ocean circulation zinc isotope data document the uptake of this metal into diatoms and the co regeneration of zn with phosphate in the upper water column silica in contrast is regenerated at greater depth resulting in a decoupling of the zn si correlation that is set in the southern ocean and that dominates the atlantic previous work has suggested that the decoupling of zn and si in the subarctic north pacific results from removal of zn and other metals to water column particulate sulphide in our dataset and in the compilation of data documenting relationships between zn and the major nutrients across the north pacific this decoupling is clearly due to the different lengthscales of regeneration for organic matter zn and p and diatom opal si

a new estimate of the caco3 to organic carbon export ratio 1 we use an ocean biogeochemical transport box model of the top 100 m of the water column to estimate the caco3 to organic carbon export ratio from observations of the vertical gradients of potential alkalinity and nitrate we find a global average molar export ratio of 0 06 0 03 this is substantially smaller than earlier estimates of 0 25 on which a majority of ocean biogeochemical models had based their parameterization of caco3 production contrary to the pattern of coccolithophore blooms determined from satellite observations which show high latitude predominance we find maximum export ratios in the equatorial region and generally smaller ratios in the subtropical and subpolar gyres our results suggest a dominant contribution to global calcification by low latitude nonbloom forming coccolithophores or other organisms such as foraminifera and pteropods

abyssal ocean overturning shaped by seafloor distribution the abyssal ocean is broadly characterized by northward flow of the densest waters and southward flow of less dense waters above them understanding what controls the strength and structure of these interhemispheric flows referred to as the abyssal overturning circulation is key to quantifying the ocean s ability to store carbon and heat on timescales exceeding a century here we show that north of 32 s the depth distribution of the seafloor compels dense southern origin waters to flow northward below a depth of about 4 kilometres and to return southward predominantly at depths greater than 2 5 kilometres unless ventilated from the north the overlying mid depths 1 to 2 5 kilometres deep host comparatively weak mean meridional flow backed by analysis of historical radiocarbon measurements the findings imply that the geometry of the pacific indian and atlantic basins places a major external constraint on the overturning structure

high resolution cd isotope systematics in multiple zones of the southern ocean from the antarctic circumnavigation expedition abstract the southern ocean plays a major role in determining the global distribution of trace metals such as cadmium cd here we present 17 high depth resolution profiles of dissolved cd and its stable isotope composition 114 cd over the top 1000 m of the pacific and atlantic sectors of the southern ocean collected during the antarctic circumnavigation expedition our dataset reinforces the view that cd and its isotopes are dominated by shallow biological cycling in this region a close examination of variations in cd cycling across the different zones of the southern ocean reveals how the interplay between uptake and regeneration seasonal mixing and upwelling controls both cd and 114 cd in this region the only deviations from these systematics are due to the influence of local processes such as continental influence or fe fertilization close to the mertz glacier and the balleny islands respectively deep convection during winter incorporates the southern ocean cd isotope signatures into subantarctic mode water and antarctic intermediate water during water mass formation incorporating published data we present the first complete picture of how cd is cycled through the entire pacific ocean revealing the manner in which the southern ocean controls the global cycling of cd and 114 cd analogous to si or zn we propose that southern ocean processes in combination with global ocean circulation cause a division into two separate cd regimes a cd depleted surface ocean above a cd rich deep ocean loop therefore the relationship between cd and po4 on a global scale is largely a result of these processes in the southern ocean rather than a local correlation between the two elements

deconvolving the controls on the deep ocean s silicon stable isotope distribution abstract we trace the marine biogeochemical silicon si cycle using the stable isotope composition of si dissolved in seawater expressed as 30 si open ocean 30 si observations indicate a surprisingly strong influence of the physical circulation on the large scale marine si distribution here we present an ocean general circulation model simulation that deconvolves the physical and biogeochemical controls on the 30 si distribution in the deep oceanic interior by parsing dissolved si into its preformed and regenerated components we separate the influence of deep water formation and circulation from the effects of biogeochemical cycling related to opal dissolution at depth we show that the systematic meridional 30 si gradient observed in the deep atlantic ocean is primarily determined by the preformed component of si whose distribution in the interior is controlled solely by the circulation we also demonstrate that the 30 si value of the regenerated component of si in the global deep ocean is dominantly set by oceanic regions where opal export fluxes to the deep ocean are large i e primarily in the southern ocean s opal belt the global importance of this regionally dynamic si cycling helps explain the observed strong physical control on the oceanic 30 si distribution since most of the regenerated si present within the deep atlantic and indo pacific oceans is in fact transported into these basins by deep waters flowing northward from the southern ocean our results thus provide a mechanistic explanation for the observed 30 si distribution that emphasizes the dominant importance of the southern ocean in the marine si cycle

the last 3000 years in the ria de vigo nw iberian margin climatic and hydrographic signals the hydrographic evolution of the r o a de vigo nw spain during the last 3000 years has been reconstructed using benthic foraminiferal assemblages stable oxygen isotopes molecular biomarkers and sea surface temperatures sst reconstructed from the u k9 37 index benthic oxygen isotopes and sst records provide evidence of episodic salinity contrasts between surface and bottom waters the comparison of ssts with other climate records for the northern hemisphere has allowed the inference of oceanographic and climatic signals which describe the changes in hydrographic conditions of the r oa in general two different periods can be recognized from 975 cal bc to cal ad 1000 the organic carbon is mainly of continental origin benthic foraminiferal assemblages are typical of environments that are poorly oxygenated rich in organic matter and dominated by eurihaline taxa percentages of planktonic foraminifera are low and ssts are warmer than today these data suggest a restricted environment where the exchange with open ocean waters was diminished at cal ad 1000 an important hydrographic change in the r oa circulation involved an intensie cation of coastal upwelling processes as ree ected in colder ssts and increases in the contribution of marine organic carbon and planktonic and opportunistic benthic foraminifera in these conditions the sediments of the r oa recorded not only local factors but also several well known northern hemisphere climate signals

silicic acid biogeochemistry in the gulf of california insights from sedimentary si isotopes reflects transient iron limitation our new d 30 si record from the guaymas basin shows dramatic variations at millennial timescales low d 30 si values synchronous with heinrich events are interpreted as resulting from the decline in si oh 4 utilization at times of decreased upwelling strength while nearly complete si oh 4 utilization was observed at times of invigorated upwelling and increased opal burial during the holocene the bolling allerod and the last glacial period we attribute the complete utilization of si oh 4 to the occurrence of transient fe limitation at these times our study highlights the importance of fe limitation on si and c cycling in coastal upwelling regions and suggests that upwelling dynamics in combination with fe availability have the potential to modulate marine si distribution and opal burial even at short timescales citation pichevin l r s ganeshram b c reynolds f prahl t f pedersen r thunell and e l mcclymont 2012 silicic acid biogeochemistry in the gulf of california insights from sedimentary si isotopes paleoceanography 27 pa2201

geochemical tracers of northern portuguese estuarine sediments on the shelf the northern portuguese coastal zone is drained by large iberian rivers along which there is intensive industrial agricultural and urban activity offshore of the two main river basins of the douro and minho two fine grained sedimentary formations can be characterised a geochemical study of this sediment cover has been performed focussing in particular on the fine deposits and the adjacent estuaries the chemical composition of superficial sediments collected from the northern portuguese shelf and from the river basins of the minho and douro rivers was determined for major minor and trace elements the rare earth elements ree composition was also determined in selected samples statistical analyses of these data for the shelf sediments allow us to identify elements with similar behaviours and the different sediment types along the shelf and to evaluate of their origins downcore profiles of the chemical composition of the fine sediments reveal no evidence for changes induced by recent human activities to assess the influence of the rivers on the fine sedimentary formations the elemental distribution patterns of selected sediments have been compared with the estuarine sediments lithogenic elements composition normalised to al and the shale normalised ree distributions showed there are similarities between the douro river sediments and the sediment composition of the douro and galicia mud patches however the galicia mud field showed no relationship in its chemical composition to sediments derived from the minho river nor was any evidence for heavy metal contamination originating from the douro estuary detected in anthropogenic element al ratios in the shelf sediments this may be because of processes associated with resuspension complexation and bioturbation that occur during sediment transport and deposition nevertheless the douro river seems to be the main continental source of fine sediments being deposited on the northern portuguese shelf

the application of gis based logistic regression for landslide susceptibility mapping in the kakuda yahiko mountains central japan as a first step forward in regional hazard management multivariate statistical analysis in the form of logistic regression was used to produce a landslide susceptibility map in the kakuda yahiko mountains of central japan there are different methods to prepare landslide susceptibility maps the use of logistic regression in this study stemmed not only from the fact that this approach relaxes the strict assumptions required by other multivariate statistical methods but also to demonstrate that it can be combined with bivariate statistical analyses bsa to simplify the interpretation of the model obtained at the end in susceptibility mapping the use of logistic regression is to find the best fitting function to describe the relationship between the presence or absence of landslides dependent variable and a set of independent parameters such as slope angle and lithology here an inventory map of 87 landslides was used to produce a dependent variable which takes a value of 0 for the absence and 1 for the presence of slope failures lithology bed rock slope relationship lineaments slope gradient aspect elevation and road network were taken as independent parameters the effect of each parameter on landslide occurrence was assessed from the corresponding coefficient that appears in the logistic regression function the interpretations of the coefficients showed that road network plays a major role in determining landslide occurrence and distribution among the geomorphological parameters aspect and slope gradient have a more significant contribution than elevation although field observations showed that the latter is a good estimator of the approximate location of slope cuts using a predicted map of probability the study area was classified into five categories of landslide susceptibility extremely low very low low medium and high the medium and high susceptibility zones make up 8 87 of the total study area and involve mid altitude slopes in the eastern part of kakuda mountain and the central and southern parts of yahiko mountain

the silicon isotope composition of ethmodiscus rex laminated diatom mats from the tropical west pacific implications for silicate cycling during the last glacial maximum the cause of massive blooms of ethmodiscus rex laminated diatom mats ldms in the eastern philippine sea eps during the last glacial maximum lgm remains uncertain in order to better understand the mechanism of formation of e rex ldms from the perspective of dissolved silicon dsi utilization we determined the silicon isotopic composition of single e rex diatom frustules 30sie rex from two sediment cores in the parece vela basin of the eps in the study cores 30sie rex varies from 1 23 to 0 83 average 1 04 a range that is atypical of marine diatom 30si and that corresponds to the lower limit of reported diatom 30si values of any age a binary mixing model upwelled silicon versus eolian silicon accounting for silicon isotopic fractionation during dsi uptake by diatoms was constructed the binary mixing model demonstrates that e rex dominantly utilized dsi from eolian sources i e asian dust with only minor contributions from upwelled seawater sources i e advected from subantarctic mode water antarctic intermediate water or north pacific intermediate water e rex utilized only 24 of available dsi indicating that surface waters of the eps were eutrophic with respect to silicon during the lgm our results suggest that giant diatoms did not always use a buoyancy strategy to obtain nutrients from the deep nutrient pool thus revising previously proposed models for the formation of e rex ldms

variability of neodymium isotopes associated with planktonic foraminifera in the pacific ocean during the holocene and last glacial maximum abstract the deep pacific ocean holds the largest oceanic reservoir of carbon which may interchange with the atmosphere on climatologically important timescales the circulation of the deep pacific during the last glacial maximum lgm however is not well understood neodymium nd isotopes of ferromanganese oxide coatings precipitated on planktonic foraminifera are a valuable proxy for deep ocean water mass reconstruction in paleoceanography in this study we present nd isotope compositions e nd of planktonic foraminifera for the holocene and the lgm obtained from 55 new sites widely distributed in the pacific ocean the holocene planktonic foraminiferal e nd results agree with the proximal seawater data indicating that they provide a reliable record of modern bottom water nd isotopes in the deep pacific there is a good correlation between foraminiferal e nd and seawater phosphate concentrations r 2 0 80 but poorer correlation with silicate r 2 0 37 our interpretation is that the radiogenic nd isotope is added to the deep open pacific through particle release from the upper ocean during deep water mass advection and aging the data thus also imply the nd isotopes in the pacific are not likely to be controlled by silicate cycling in the north pacific the glacial nd isotopic compositions are similar to the holocene values indicating that the nd isotope composition of north pacific deep water npdw remained constant 3 5 to 4 during the lgm the southwest pacific cores throughout the water column show higher e nd corroborating previous studies which suggested a reduced inflow of north atlantic deep water to the pacific however the western equatorial pacific deep water does not record a corresponding radiogenic excursion implying reduced radiogenic boundary inputs during the lgm probably due to a shorter duration of seawater particle interaction in a stronger glacial deep boundary current a significant negative glacial e nd excursion is evident in mid depth 1 2 km cores of the eastern equatorial pacific eep which may suggest a stronger influence of npdw return flow to the core sites and decreased local input in the eep taken together our nd records do not support a dynamically slower glacial pacific overturning circulation and imply that the increased carbon inventory of pacific deep water might be due to poor high latitude air sea exchange and increased biological pump efficiency in glacial times

quantifying antarctic bottom water and north atlantic deep water volumes 1 a near global census of antarctic bottom water aabw and north atlantic deep water nadw is essayed through a nonnegative least squares analysis of conservative and quasi conservative seawater properties aabw thickness generally decreases from south to north modulated by ocean bathymetry likewise nadw thickness generally decreases from north to south in the atlantic ocean nadw dominates below the thermocline of the atlantic ocean at least as far south as the subtropical gyre of the south atlantic with a lesser but still significant influence around the entire antarctic circumpolar current in the indian ocean and in the pacific ocean however in the pacific and indian oceans aabw dominates below the thermocline in addition measurable quantities of aabw reach into the abyssal north atlantic on both sides of the mid atlantic ridge the census results suggest that aabw occupies roughly twice the volume of nadw in the three main oceans and that aabw is in contact with roughly twice the area of the deep main ocean floor compared with nadw however these results are somewhat sensitive to choices of water masses their values of seawater properties and the weightings of the seawater properties used in the analysis

iron and silicic acid concentrations regulate si uptake north and south of the polar frontal zone in the pacific sector of the southern ocean abstract we investigated the relative roles of fe and silicic acid availabilities in regulating si uptake rates across the polar frontal zone in the pacific sector of the southern ocean 59 68 s 170 w during the us jgofs antarctic environment southern ocean process study aesops meridional gradients in silicic acid concentration si oh 4 of about 0 25 0 56 m km 1 were observed in this area during austral spring and summer 1997 1998 with si oh 4 ranging from 32 si oh 4 and 15 no 3 uptake rates biogenic silica concentrations and si oh 4 no3 uptake ratios fe addition had little or no effect on si uptake rates in enrichments conducted in the low si waters north of the si gradient however fe addition increased si uptake rates 3 5 times over controls in enrichments conducted in the high si waters south of the gradient in both spring and summer fe addition decreased si oh 4 no3 uptake ratios by 2 5 times largely due to stimulation of no3 uptake rates zn addition had no effect on si oh 4 and no3 uptake rates short term 24 h si additions had varying effects on si uptake rates depending on season and location in spring additions of 40 m si to water from bottle enrichments conducted north of the si gradient in situ si oh 4 15 m did not increase si uptake rates initially but did increase uptake rates after 8 days in the summer enrichment north of the si gradient in situ si oh 4 5 m 50 m si additions doubled in situ si uptake rates in the initial water collected for the enrichment and increased si uptake rates as much as 16 fold during the experiment south of the si gradient where in situ si oh 4 was 40 m in both spring and summer si addition had no effect on in situ si uptake rates in the initial enrichment water nor on any si uptake rates measured during the experiment our results indicate that both fe and si availabilities regulate si uptake rates and silica production in the southern ocean along 170 w fe limitation appears to restrict si uptake rates south of the si gradient and plays a role in preventing si depletion south of the acc where ambient si oh 4 never fell below 40 m during 1997 1998 our experiments in the seasonal ice zone at 62 suggest that si uptake in this area switched from being fe limited in the spring when in situ si oh 4 was 40 m to si limited in the summer when si oh 4 was

a preliminary inventory of rock glaciers at 30 s latitude cordillera frontal of san juan argentina abstract the dry andes of the cordillera frontal of san juan 30 s latitude is characterized by high relief with peaks up to 5000 m a s l this geological province is mainly made up of a suite of triassic to miocene volcanic rocks modern ice glaciers are small and few in number and persistent snow fields are similarly small and scattered the predominant landforms in these areas have been shaped in a periglacial environment superimposed on an earlier glacial landscape a preliminary inventory map of rock glaciers was constructed using optical remote sensing techniques digital topographic analysis and aerial photograph data organized in a geographic information system gis over 140 rock glaciers have been identified 90 are active or inactive and the rest are fossil a total of 88 rock glaciers are considered active the most common periglacial features recognized in the area are talus glaciers and only 23 are tongue shaped glaciers

benthic foraminiferal assemblages from the eastern weddell sea between 68 and 73 s distribution ecology and fossilization potential surface sediment samples taken with a vented box corer from the eastern weddell sea on four profiles perpendicular to the continental margin have been investigated for their benthic foraminiferal content the live fauna was differentiated from empty tests comprising the foraminiferal death assemblage based on the dead assemblages potential fossil assemblages were calculated to facilitate the analogy with late neogene core material five distinct live assemblages inhabit the continental margin today six dead assemblages and five potential fossil assemblages respectively correspond to these biocoenoses a predominantly calcareous live fauna dominated by trifarina angulosa is correlated with strong bottom currents and sandy sediments at the shelf break and on the uppermost continental slope below this on the upper slope down to 2000 m water depth the predominantly calcareous bulimina aculeata assemblage coincides with the core of warm 0 c weddell deep water and with fine and more organic rich sediments these calcareous live assemblages completely change composition during early diagenesis because of calcite dissolution within the uppermost sediment which depends largely on the grain size distribution of the sediment and the fluxes of organic matter therefore a still calcareous t angulosa dominated fossil assemblage indicates the sandy substrates on the shelf break and the upper slope whereas the deeper slope with hemipelagic calm sedimentation and with high fluxes of organic matter is indicated by martinottiella nodulosa the characteristic arenaceous fossil remnant of the former predominantly calcareous live b aculeata fauna on a continental terrace between 2500 and 3500 m water depth cribrostomoides subglobosus dominates the live fauna but because of rapid disintegration of the empty tests of this agglutinated species a predominantly calcareous fauna characterized by oridorsalis umbonatus and epistominella exigua comprises the dead assemblage and the potential fossil assemblage respectively on the lower continental slope between the carbonate lysocline 3500 m and the carbonate compensation depth 4000 m tests of nuttallides umbonifer are the characteristic dead and potential fossil remnants of a former predominantly arenaceous live fauna which is associated with the lower part of the antarctic bottom water aabw this corroborates earlier investigations suggesting a relationship between the carbonate corrosiveness of water masses and the distribution of n umbonifer this is important for inferring paleo routes and estimates of paleo production rates of aabw during the neogene

rock glacier nomenclature a re assessment several contentious issues have arisen from rock glacier nomenclature for example whether the term rock glacier implies genesis from glacial ice or genesis from permafrost the situation is compounded since rock glacier classification may be based on several different parameters some of which are measured and quantified others inferred these include gross morphology dynamics processes of formation location internal characteristics thermal regime and age uncertainties in specifying the genesis in the light of the potential complexity means that definitions should be related to recognisable topographic forms which allow mapping of such features the distinction is made between rock glaciers sensu stricto which follows the original descriptions and typology of the early years of the 20th century and protalus lobes the forms can usually be differentiated in terms of length breadth ratios as well as by their relative locations some of the most common issues of contention within rock glacier research can be solved by this approach

radiocarbon decay and oxygen utilization in the deep atlantic ocean a parameter based on the sum of the concentrations of po4 and o2 divided by the redfield coefficient o2 po4 is used to separate the contributions of the northern and southern components to deep waters in the atlantic this separation allows the amount of radiocarbon lost by radiodecay and the amount of oxygen lost to respiration during residence in the deep atlantic to be calculated maps of these quantities reveal strong west to east gradients and weak north to south gradients consistent with ventilation along the western boundary from both ends of the ocean coupled with mixing outward from the boundary the o2 and 14c deficiences are highly correlated suggesting an o2 utilization rate of 12 m kg per century the apparent mean isolation time of water in the deep atlantic is about 200 years

clay minerals from the sedimentary cover from the northwest iberian shelf abstract the northern iberian margin is a typical example of a continental margin subjected to seasonal highly energetic regime waves and tides and receiving inputs of continental sediments via riverine discharges the principal goal of this study has been to use clay minerals as indicators of sedimentary dynamics in the open shelf system the distributions of clay mineral in the top layer of the sedimentary cover are shown to be related to their continental sources but also reflect the influences of winter storms and longshore currents in determining the pathways of sediment transport the mineralogical composition of the material issuing from the rivers is very similar to the general mineralogical composition of the fine fractions of the seabed sediments those deposits that are directly influenced by riverine discharges have higher contents of kaolinite 20 whereas those that are not have higher contents of illite 80 the available data indicate no significant quantities of terrigenous particles are being discharged from the spanish rias therefore we conclude that physical processes are controlling the clay mineral distributions and that despite contributions from the minho river the main source of fine detrital particles to the shelf region is the douro river discharge these particles settle on the middle shelf below the 60 m isobath during storm events these particles are re suspended and advected northwards to the galician shelf or into deeper domains thus the distributions of the clays indicate there is a net transport of fine sediments both northwards and off shelf

reactive iron in marine sediments abstract a combined field laboratory study has been undertaken to explore the mineralogy concentrations and reactivity towards sulfide of iron in marine sediments also considered is the importance of bacterial fe liberation in regulating pore water chemistry two contrasting marine environments are included one is the relatively fe poor foam site and the other is the fe rich sediment of the subaqueous mississippi delta results show that oxide minerals are the most important fe phases in early diagenetic pyrite formation however viewed separately lepidocrocite and ferrihydrite are more reactive towards sulfide than goethite and hematite when fe oxides are present in relatively high concentrations dissolved sulfide is nearly absent from sediment pore waters with concomitant high concentrations of dissolved fe even in the presence of active sulfide production by sulfate reduction a combination of experimental results and diagenetic modelling shows that in some sediments pore water fe finds it origin in the bacterial reduction of iron oxides this seems the case even though greater amounts of fe are reduced by reaction of sulfide with iron oxides it appears that distinct microenvironments may exist in marine sediments where in one microenvironment sulfide reacts with fe oxides locally precipitating fe sulfide minerals in another fe reduced and solubilized by microorganisms migrates freely into solution

the influence of water mass mixing on the dissolved si isotope composition in the eastern equatorial pacific silicon isotopes are a powerful tool to investigate the cycling of dissolved silicon si in this study the distribution of the si isotope composition of dissolved silicic acid 30si oh 4 was analyzed in the water column of the eastern equatorial pacific eep where one of the globally largest oxygen minimum zones omzs is located samples were collected at 7 stations along two meridional transects from the equator to 14 s at 85 50 w and 82 00 w off the ecuadorian and peruvian coast surface waters show a large range in isotope compositions 30si oh 4 2 2 to 4 4 with the highest values found at the southernmost station at 14 s this station also revealed the most depleted silicic acid concentrations 0 2 mol kg which is a function of the high degree of si utilization by diatoms and admixture with waters from highly productive areas samples within the upper water column and the omz at oxygen concentrations below 10 mol kg are characterized by a large range in 30si oh 4 which mainly reflects advection and mixing of different water masses even though the highly dynamic hydrographic system of the upwelling area off peru does not allow the identification of clear si isotope signals for distinct water masses therefore we cannot rule out that also dissolution processes have an influence on the 30si oh 4 signature in the subsurface water column deep water masses 2000 m in the study area show a mean 30si oh 4 of 1 2 0 2 which is in agreement with previous studies from the eastern and central pacific comparison of the new deep water data of this study and previously published data from the central pacific and southern ocean reveal substantially higher 30si oh 4 values than deep water signatures from the north pacific as there is no clear correlation between 30si oh 4 and silicic acid concentrations in the entire data set the distribution of 30si oh 4 signatures in deep waters of the pacific is considered to be mainly a consequence of the mixing of several end member water masses with distinct si isotope signatures including lower circumpolar deep water lcdw and north pacific deep water npdw

the oceanic biogeochemistry of nickel and its isotopes new data from the south atlantic and the southern ocean biogeochemical divide abstract nickel ni is important for a number of enzymes in oceanic phytoplankton it has received less attention than some other bioactive metals because it is not reduced to extremely low dissolved concentrations in the photic zone however there are strong indications in previous studies that this residual pool is not bio available oceanic ni isotope data are still scarce but have great potential for understanding this issue as well as for understanding the ni mass balance of the oceans now and in the past here we present new concentration and isotope data for the uk geotraces section at 40 s in the atlantic ga10 nickel concentration data show typical nutrient like profiles slightly modified by variable pre formed concentrations in sub surface water masses e g north atlantic deep water nickel isotopes in common with findings in previous studies are homogeneous beneath 500 m at about 1 3 in 60 ni in samples with ni concentrations above 3 3 5 nm the surface south atlantic however has concentrations below 3 nm and shows significantly higher 60 ni up to 1 74 that are closely anti correlated with ni concentrations the data for the deep south atlantic dissolved pool with a 60 ni 1 31 0 12 average and 2sd confirm the homogeneity of the global deep ocean which previous data demonstrate extends all the way to the surface in the upwelling zone of the southern ocean south of the polar front this ni isotope composition is significantly heavier than known inputs to the oceanic dissolved pool this mass balance requires an isotopically light sink that may be represented by sedimentary mn oxide associated ni the magnitude of the isotope fractionation implied by the upper ocean data is not consistent with plausible potential abiotic removal processes rather these data are best explained by biological uptake however consideration of the detailed relationships between ni concentrations and isotope compositions requires that a substantial portion of the oceanic dissolved ni pool is not bio available the data are consistent either with a small preference for the light isotope during uptake about 0 1 or two distinct pools of dissolved ni one bio available and one strongly bound in organic complexes with limited isotopic exchange between them patterns of co variation in ni concentrations and isotopes with the major nutrients point to strong contrasts across the polar front of the southern ocean contrasts that exhibit both similarities and differences with those for the major nutrients and other trace metal micronutrients south of the polar front ni is taken up in modest amounts by diatoms without isotope fractionation north of the polar front the data are most consistent with cyanobacteria as the dominant control on ni uptake leading to significant coupled abundance and isotope variation

on the origin of the marine zinc silicon correlation abstract the close linear correlation between the distributions of dissolved zinc zn and silicon si in seawater has puzzled chemical oceanographers since its discovery almost forty years ago due to the apparent lack of a mechanism for coupling these two nutrient elements recent research has shown that such a correlation can be produced in an ocean model without any explicit coupling between zn and si via the export of zn rich biogenic particles in the southern ocean consistent with the observation of elevated zn quotas in southern ocean diatoms here we investigate the physical and biological mechanisms by which southern ocean uptake and export control the large scale marine zn distribution using suites of sensitivity simulations in an ocean general circulation model ogcm and a box model ensemble these simulations focus on the sensitivity of the zn distribution to the stoichiometry of zn uptake relative to phosphate po4 drawing directly on observations in culture our analysis reveals that ogcm model variants that produce a well defined step between relatively constant high zn po4 uptake ratios in the southern ocean and low zn po4 ratios at lower latitudes fare best in reproducing the marine zn si correlation at both the global and the regional southern ocean scale suggesting the presence of distinct zn biogeochemical regimes in the high and low latitude oceans that may relate to differences in physiology ecology or micro nutrient status furthermore a study of the systematics of both the box model and the ogcm reveals that regional southern ocean zn uptake exerts control over the global zn distribution via its modulation of the biogeochemical characteristics of the surface southern ocean specifically model variants with elevated southern ocean zn po4 uptake ratios produce near complete zn depletion in the si poor surface subantarctic zone where upper ocean water masses with key roles in the global oceanic circulation are formed by setting the main preformed covariation trend within the ocean interior the subduction of these zn and si poor water masses produces a close correlation between the zn and si distributions that is barely altered by their differential remineralisation during low latitude cycling we speculate that analogous processes in the high latitude oceans may operate for other trace metal micronutrients as well splitting the ocean into two fundamentally different biogeochemical and thus biogeographic regimes

deep ocean biogeochemistry of silicic acid and nitrate 1 observations of silicic acid and nitrate along the lower branch of the global conveyor belt circulation show that silicic acid accumulation by diatom opal dissolution occurs at 6 4 times the rate of nitrate addition by organic matter remineralization the export of opal and organic matter from the surface ocean occurs at a si n mole ratio that is much smaller than this almost everywhere cf sarmiento et al 2004 the preferential increase of silicic acid over nitrate as the deep circulation progresses from the north atlantic to the north pacific is generally interpreted as requiring deep dissolution of opal together with shallow remineralization of organic matter broecker 1991 however sarmiento et al 2004 showed that the primary reason for the low silicic acid concentration of the upper ocean is that the waters feeding the main thermocline from the surface southern ocean are depleted in silicic acid relative to nitrate by implication the same southern ocean processes that deplete the silicic acid in the surface southern ocean must also be responsible for the enhanced silicic acid concentration of the deep ocean we use observations and results from an updated version of the adjoint model of schlitzer 2000 to confirm that this indeed the case

on the origins of deep and bottom waters of the indian ocean the characteristics of the deep and bottom waters of the indian ocean when illustrated on potential density anomaly surfaces indicate that the waters enter from both the atlantic and pacific oceans the paths of spreading are constrained by the complex topography and characteristics are seen to be altered by exchange with the overlying and underlying water and with the sediments especially in the northern indian ocean the weddell sea contributes to the densest waters found in the western basins and the ross sea and adelie coast to the densest waters found in the eastern basins both dense water varieties are altered by and incorporated in the less dense water above initially water carried by the circumpolar current then water from the north atlantic and finally by deep water whose characteristics are derived in the northern indian ocean contact with the sediments increases the silica content of the bottom water in the southern ocean in the northern indian ocean the sediments alter the silica of the water at the bottom and together with enhanced salinity from diffusion of saline overflows from the marginal seas above imprint unique markers to the deep water that flows back to the south at middepths the series of ridges between madagascar and australia confine the flow to a series of gyres that carry characteristics from the circumpolar current equatorward and the northern indian ocean characteristics southward within the circumpolar current low oxygen deep water from the pacific is carried across the atlantic and into the indian ocean south of africa part flows around the cyclonic weddell sea gyre and part extends across the southern ocean water from another pacific source can be seen near 2000 m extending westward from the tasman sea south of aus tralia and across the indian ocean and perhaps to the aghulas current region southeast of africa in this study we show some maps of deep and bottom water characteristics of the indian ocean which may be used in a qualitative sense to infer pathways of spreading of water below a depth of about 2000 m the indian ocean has numerous ridges and basins figure 1 that severely restrict possible pathways of deep and bottom wa ter flow in the following we will begin by looking at char acteristics at the bottom of the ocean to reveal the path ways of spreading of the densest bottom waters from basin to basin then a series of six potential density anomaly surfaces at progressively shallower depths from about 4000 m up to about 2000 m will be shown to see what character istics influence the deep waters and how pathways of flow are constrained by the bathymetry of the indian ocean the choice of the specific density levels table 1 was based primarily on various property extrema shown by the 18os atlantis ii cruise 93 colored sections that accompany warren s 1981 detailed discussion of the major features of the central indian ocean between madagascar and aus tralia the sections approximately midway between antarctica and the northern indian ocean boundaries are well positioned to show features originating from both the north and the south as well as some brought into the indi an ocean by the antarctic circumpolar current the full ocean area isopycnal maps provide essential evidence on the origins and fates of features seen in the sections and

silicic acid enrichment of subantarctic surface water from continental inputs along the patagonian archipelago interior sea 41 56 s abstract we estimated si the surplus or deficit of orthosilicic acid dsi relative to nitrate available for diatom growth in the chilean patagonian archipelago interior sea pais si and salinity were negatively correlated in the pais because of the mixing of high nitrate low dsi subantarctic surface water and high dsi low nitrate continental freshwater runoff both the slope and the intercept of this relationship decreased from northern to southern patagonia which was likely a consequence of reduced dsi inputs from several overlapping hydrological biological and geological drivers along this gradient in general lower freshwater dsi concentrations were expected below 46 s and a lower total dsi load was expected from reduced runoff below 51 s the north south decreasing dsi concentration trend may be linked to dilutions from a higher proportion of runoff in latitudes with higher precipitation rates 45 53 s the transition to more resistant granitic rocks and glacial melt water from the northern and southern patagonia ice fields 46 51 s and a reduced density of volcanoes active during the holocene 48 56 s the intensification of a southward dsi deficit may be a forcing factor involved in the reported southward reductions in plankton biomass and a more frequent occurrence of non diatom blooms in southern pais

modeling the modern marine δ30si distribution 1 the silicon isotopic composition of opal sediments can be used as a proxy for past si utilization and hence paleoproductivity for a fixed ocean circulation interpretation of this si utilization proxy is limited by our understanding of the present marine si isotope distribution observations show significant isotopic variations is silicic acid between deep water masses that are not captured by a previous global climate model gcm here simple box models of the global oceans for the si cycle are presented which can account for the observed 0 3 o difference between atlantic and pacific deep water 30 si values using typical opal export fluxes the 30 si gradient results from both a high 30 si of dissolved si overturning in the north atlantic and the dissolution of low 30 si of opal in the deep waters around the southern ocean that feed into the pacific

present day sedimentary processes on the northern iberian shelf abstract the galicia minho shelf features two large mud patches the douro and the galicia mud patches these are recent sediment bodies that have accumulated under a combination of conditions including 1 abundant supplies of sediment 2 morphological barriers that act as sediment traps and 3 hydrographic conditions that favour the accumulation of fine sediment in these sinks this paper describes the mechanisms controlling the deposition of the fine grained sediment depositions and the processes that result in resuspension processes on the galicia minho shelf fine grained sediments are provided from discharges from the river basins on the southern sector of the shelf mainly the douro and minho rivers sediments are exported from river estuaries onto the shelf during episodic flood events in contrast most of the sediments originating from the galician hinterland fail to contribute significantly to sedimentation on the shelf because they are retained in the galician rias which function as sediment traps sediments deposited on the shelf are frequently remobilized particularly during southwesterly storms that coincide with downwelling conditions once in suspension the fine grained sediments are transported northwards by the poleward flowing bottom currents and are eventually deposited on the douro and galicia mud patches after a series of resuspension events the locations of the two mud patches are strongly influenced by the shelf morphology fines already deposited on the mud patches are occasionally reintroduced into the system by large storm events some material from the douro mud patch and adjacent areas is re deposited in the galicia mud patch it is probable that sediments re suspended from the galicia mud patch are carried off the shelf when storm events coincide with downwelling conditions

application of frequency ratio and logistic regression to active rock glacier occurrence in the andes of san juan argentina this study employs statistical modeling techniques and geomorphological mapping to analyze the distribution of active rock glaciers in relation to altitude aspect slope lithology and solar radiation using optical remote sensing techniques with gis the study area includes a portion of the dry andes of the cordillera frontal of san juan around 30 s latitude where few geomorphological studies have been conducted over 155 rock glaciers have been identified and 85 are considered active the relationship between the variables and the rock glaciers distribution was analyzed using the frequency ratio method and logistic regression models the analytical results show that elevations 3824 m a s l a south facing or east facing aspect areas with relatively low solar radiation and slope between 2 and 20 favor the existence of the rock glaciers and demonstrate that lithology and slope exert major influences

biogenic silica dissolution in the oceans reconciling experimental and field based dissolution rates 1 on average 50 60 of diatomaceous opal produced in the euphotic zone redissolves within the upper 100 m of the water column high specific silica dissolution rates in the surface ocean contrast with order of magnitude lower values in deep sea sediments the lack of a mechanistic understanding of these large variations in dissolution kinetics is a major source of uncertainty in models of nutrient silicon cycling in the oceans here we show that the observed variability in biogenic silica reactivity is consistent with results of experimental dissolution studies differences in aluminum content and specific surface area of the diatom skeletons plus differences in temperature and degree of undersaturation all contribute to lowering silica dissolution rates in deep sea sediments relative to the euphotic zone when variations in these material and environmental properties are accounted for the predicted specific opal dissolution rate in average surface ocean water is over 2 orders of magnitude faster than the rate measured in recently deposited biosiliceous oozes of the southern ocean the predicted specific dissolution rate however is approximately 5 times higher than the value obtained from global estimates of the depth integrated dissolution rate and biogenic silica concentration in the upper water column this discrepancy likely reflects the inhibitory effect of protective organic coatings on fresh diatom shells in surface waters the experimental data further imply that aluminum incorporation in the silica matrix during biomineralization or after death of the organisms enhances the preservation efficiency of biogenic opal in marine sediments

landslide susceptibility mapping in the damrei romel area cambodia using frequency ratio and logistic regression models this study applied tested and compared a probability model a frequency ratio and statistical model a logistic regression to damre romel area cambodia using a geographic information system for landslide susceptibility mapping landslide locations were identified in the study area from interpretation of aerial photographs and field surveys and a spatial database was constructed from topographic maps geology and land cover the factors that influence landslide occurrence such as slope aspect curvature and distance from drainage were calculated from the topographic database lithology and distance from lineament were extracted and calculated from the geology database land cover was classified from landsat tm satellite imagery the relationship between the factors and the landslides was calculated using frequency ratio and logistic regression models the relationships frequency ratio and logistic regression coefficient were overlaid to make landslide susceptibility map then the landslide susceptibility map was compared with known landslide locations and tested as the result the frequency ratio model 86 97 and the logistic regression 86 37 had high and similar prediction accuracy the landslide susceptibility map can be used to reduce hazards associated with landslides and to land cover planning

microhabitat preferences and stable carbon isotopes of endobenthic foraminifera clue to quantitative reconstruction of oceanic new production seventeen surface sediment samples from the north atlantic ocean off ne greenland between 76 and 81 n and nine samples from the south atlantic ocean close to bouvet island between 48 and 55 s were taken with the aid of a multiple corer and investigated for their live rose bengal stained benthic foraminiferal content within the upper 15 cm of sediment preferentially endobenthic melonis barleeanum m zaandami and bulimina aculeata as well as preferentially epibenthic lobatula lobatula were counted from 1 cm thick sediment slices each and analyzed for stable carbon and oxygen isotopic compositions of their calcareous tests live and dead specimens were counted and measured separately the carbon isotopic composition of the foraminifera was compared to that of the dissolved inorganic carbon dic of simultaneously sampled bottom water during a period of one month one station off ne greenland was replicately sampled once every week and samples were processed as above live specimens of lobatula lobatula are confined to the uppermost two centimeters of sediment live specimens of melonis spp are found down to eight centimeters within the sediment but with a distinct sub surface maximum between two and five centimeters the down core distribution of live bulimina aculeata shows a distinct surface maximum in the top centimeter and constant but low numbers down to 11 cm subbottom depth the average stable carbon isotopic composition d13c per mil vpdb of live l lobatula off ne greenland is by 0 4 0 1 per mil higher than the d13cdic of the ambient bottom water at the time of sampling there is evidence that this species calcify before the ice free season when bottom water d13cdic is supposed to be higher this would reconfirm the one to one relationship between d13c of ambient water dic and cibicids widely used by paleoceanographers live m barleeanum show a negative offset from bottom water dic of 1 7 0 6 per mil in the uppermost sediment and of 2 2 0 5 per mil in three to four centimeters subbottom depth all d13c values of live melonis spp decrease within the upper four centimeters regardless of the time of sampling and site investigated the offset of live b aculeata from bottom water d13cdic values of eight stations rather constantly amounts 0 6 0 1 per mil no matter what subbottom depth the specimens are from at one station however where is strong indication of elevated organic carbon flux the negative offset averaged over all sub bottom depths increases to 1 5 0 2 per mil buliminids actively move within the sediment and by this either record an average isotope signal of the pore water or the signal of one specific calcification depth the recorded signal however depends on the organic carbon flux and reflects general but site specific pore water d13cdic values if compared with epibenthic d13c values from the same site not influenced by pore water and related phytodetritus layer effects bulimina d13c values bear some potential as a paleoproductivity proxy specimens of melonis spp seem to prefer a more static way of life and calcify at different but individually fix depths within the sediment although live specimens thus record a stratified pore water d13c signal there is no means yet to correct for bioturbational and early diagenetic effects in fossil faunas