the impact of oxic alteration on plume derived transition metals in ridge flank sediments from the east pacific rise we describe transition metal behaviour during early diagenesis in sediments collected along a transect across the eastern flank of the east pacific rise epr at 14 s overlying crust with magnetic ages of 0 36 ma to 4 6 ma the sediments are lithologically simple and consist of biogenic carbonate hydrothermal plume precipitates and minor basaltic debris sedimentation rates range from 1 cm ka in the near axis region 0 36 ma to 0 1 0 2 cm ka across the young ridge flank by 1 9 ma or within 142 km from axis redox indicators porewater mn ii aq and solid phase mo mn ratios indicate fully oxic conditions in near axis sediments changing to mildly suboxic conditions across the ridge flank sequential extraction analysis of sediments from the 0 36 ma site indicates that oxic alteration of fe oxyhydroxides is dominated by transformation of ferrihydrite to goethite implying that alteration occurs via dissolution followed by nucleation and precipitation the extent of alteration amorphous fe total plume derived fe ranges from 0 3 to 0 8 and the time to half conversion is on the order of 100 ka v associated with plume derived ferrihydrite is strongly discriminated against during alteration to goethite and the distribution coefficient dv v fe goethite v fe dissolved is in the range 0 45 0 59 cu zn and ni are delivered to the sediment in association with both fe oxyhydroxides and mn oxides where 70 of cu and zn and 10 of ni are associated with fe oxyhydroxides the fe adsorbed cu and zn are incorporated quantitatively into the lattice structure of goethite during alteration the fe associated ni most likely represents ni co precipitated as ni fe ferrihydrite and incorporated into goethite during alteration co is associated only with mn oxides the oxic alteration of hydrothermal fe oxyhydroxides therefore represents a relatively permanent sink where goethite dissolution is a prerequisite for metal release for a maximum of 70 of plume derived cu and zn 50 of v 10 of ni and 0 of co in oxic sediments the remaining plume derived metals are retained in association with amorphous fe oxyhydroxides and mn oxides although this fraction is highly susceptible to diagenetic remobilization under suboxic conditions

potential vorticity of flow along the alps abstract observations from the german front experiment are presented here that show the existence in conditions with a dominant flow component parallel to the main alpine chain of a mesoscale region to the north of the alps where the absolute and potential vorticity pv are substantially negative these structures exist before the front arrives to the alps and appear to be affected little by the passage of the front a dynamical explanation for these and other mesoscale structures is sought by considering a simple unsheared airflow impinging on the alps from the west a linear frictionless model for the steady state response is used as well as a full nonlinear numerical model with and without friction a vastly simplified alpine orography is considered as well as one that adequately describes its mesoscale detail the results show that the frictionless linear dynamics lead to a zone north of the alps with anticyclonic vorticity but with uniform positive potential vorticity with boundary layer processe

progressive dissolution of fine carbonate particles in pelagic sediments abstract large systematic variations occur in the proportion of coccolith sized carbonate particles relative to other types of carbonate particles within the

quantification of foraminifer and coccolith carbonate in south atlantic surface sediments by means of carbonate grain size distributions this study presents a differentiated carbonate budget for marine surface sediments from the mid atlantic ridge of the south atlantic with results based on carbonate grain size composition upon separation into sand silt and clay sub fractions the silt grain size dis tribution was measured using a sedigraph 5100 we found regionally characteristic grain size distributions with an overall minimum at 8 mm equivalent spherical diameter esd sem observations reveal that the coarse particles 8 mm esd are attributed to planktic for aminifers and their fragments and the fine particles 8 mm esd to coccoliths on the basis of this division the regional variation of the contribution of foraminifers and coccoliths to the carbonate budget of the sediments are calculated foraminifer carbonate dominates the sed iments in mesotropic regions whereas coccoliths contribute most car bonate in oligotrophic regions the grain size of the coccolith share is constant over water depth indicating a lower susceptibility for car bonate dissolution compared to foraminifers finally the characteristic grain size distribution in fine silt 8 mm esd is set into context with the coccolith assemblage counted and biometrically measured using a sem the coccoliths present in the silt fraction are predominantly large species length 4 mm smaller species length 4 mm belong to the clay fraction 2 mm esd the average length of most frequent coccolith species is connected to prominent peaks in grain size distri butions esd with a shape factor the area below gaussian distri butions fitted to these peaks is suggested as a way to quantitatively estimate the carbonate contribution of single coccolith species more precisely compared to conventional volume estimates the quantitative division of carbonate into the fraction produced by coccoliths and that secreted by foraminifers enables a more precise estimate for source sink relations of consumed and released co 2 in the carbon cycle the allocation of coccolith length and grain size esd suggests size windows for the separation or accumulation of distinct coccolith species in investigations that depend on non to slightly mixed signals e g isotopic studies

eocene carbonate accumulation in the north central pacific ocean new insights from ocean drilling program site 1209 shatsky rise abstract major climate transitions and perturbations in global carbon cycle are known to have occurred during the eocene between 56 and 34 million years ago ma a series of carbon isotope excursions cies mark variations in the global carbon cycle and changes in climate through early eocene paleocene eocene thermal maximum petm ca 56 ma is the most pronounced and well documented of these events expressed as a clay rich layer in many deep sea sections resulting from widespread carbonate dissolution on the seafloor which is in turn related to shoaling of the carbonate compensation depth ccd and lysocline other cies of early eocene had similar response however response of these geologically instantaneous hyperthermals differ from long term warmth multi million year time scale of the early eocene climate optimum eeco in terms of sea floor carbonate accumulation following the termination of eeco earth s climate transitioned into long term cooling pronounced fluctuations in ccd of equatorial pacific are known to have occurred during middle late eocene as well whose global extent and origin are still unresolved most proxy records either span the interval of early eocene or document particular climatic events in eocene which significantly limits visualizing the long term eocene climate change and response of open marine carbonate preservation the present study documents change in carbonate dissolution and carbonate mass accumulation rate through the entire eocene 56 34 ma at odp site 1209 on shatsky rise north central pacific and ties it to a stable carbon and oxygen isotope record our study determines the correlation between deep sea carbonate dissolution and carbon cycling process during the dynamic climate regime of eocene a strong correlation between magnitude of cies and intensity of dissolution for early eocene hyperthermal events appears to significantly weaken for multiple dissolution events in middle late eocene thereby indicating fundamental difference in their causal mechanism

inferring maximum geostrophic current velocities in the norwegian greenland sea from settling velocity measurements of sediment surface samples methods application and results abstract critical shear velocities and geostrophic current velocities were calculated from measured grain sizes and settling velocities using a shields type threshold curve of particle movement and assuming bedload transport for particles that were found to be transported by currents because this reconstruction of the current velocities is based on the coarsest transported component that could be recognized in the sediment the resulting current velocities represent a maximum flow speed that was effective during deposition of sediment the shape of the settling velocity distributions identifies the dominant type of deposition that controlled the accumulation of sediment residual well sorted or low energy depositional the resulting pattern of reconstructed maximum geostrophic current velocities in the norwegian greenland sea reflects the known features of present day thermohaline circulation which is influenced by the bathymetry at many places reconstructed current velocities are higher in areas where the cross section of meridional flows is restricted by topographic barriers the distribution of the depositional characters shows that residual and well sorted sediment types are generally associated with higher current velocities in areas of strong geostrophic currents e g fram strait and east greenland continental slope the low energy depositional sediment type is widespread in the basins of the eastern norwegian greenland sea where lower reconstructed maximum current velocities occur the high reconstructed velocities on the spitsbergen bank can be attributed to the disturbance from storm waves in shallower water depths

fluxes of planktic foraminifera in response to monsoonal upwelling on the somalia basin margin abstract sediment trap samples collected off somalia bi weekly from early june 1992 through mid february 1993 show large seasonal variations in the shell flux and species composition of planktic foraminifera these variations mirror the monsoon driven circulation which resulted in massive upwelling and offshore eddy transport in summer during the sw monsoon june september and accounted for nearly 90 of the estimated annual shell flux of planktic foraminifera g bulloides dominated the sw monsoon along with g glutinata t quinqueloba n dutertrei and t iota in a fauna rich species but with a low diversity and equitability during the autumn intermonsoon november december the ocean became stratified and the nutrient exhausted whereas during the ne monsoon january march a warm surface mixed layer developed with the nutrients entrained by deep wind mixing it was dominated by g ruber in association with g tenella g aequilateralis g trilobus g sacculifer and g menardii in a fauna poorer in species but with a higher diversity and equitability consequently the ratio in the abundance of g bulloides and g ruber follows the monsoonal cycle closely as both species persist throughout the year only the rare g theyeri seems to be restricted to the sw monsoon in october at the end of the sw monsoon the trap at 265 m above the bottom intercepted massive amounts of fine grained carbonate m resuspended from the shelf and upper slope it contained extreme fluxes of bioclastic fragments benthic foraminifera and benthic ostracods as well as enhanced fluxes of small sized planktic foraminifera m notably g rubescens integrated over the year the species composition intercepted by the trap shows a very good match with the shell fauna in a core top sediment from the same site apparently the year estimated monsoonal record of planktic foraminifera which is strongly dominated by the sw monsoon production survives burial intact consequently the species composition of planktic foraminifera and measures such as the bulloides ruber ratio can be applied as a proxy for past changes in the intensity of the sw monsoon off somalia compared to the modern condition

grain size variations in pelagic carbonate oozes from the walvis ridge se atlantic ocean odp site 1265 a low resolution miocene record of carbonate sedimentation and preservation abstract a record of variations in winnowing and dissolution was established for miocene 19 7 ma deep sea sediments at site 1265 from the walvis ridge south atlantic in this study we apply a new preservation index based on the abundance of coarse calcareous silt fraction 10 63 m the miocene record of this silt preservation index corresponds well with the conventional foraminiferal preservation index and variations in sand content preservation ranging from good to moderate during the miocene indicates that site 1265 is located above and close to the foraminiferal lysocline grain size mass accumulation rates of carbonate and organic carbon records indicate that changes in productivity and carbonate production play a minor role in variations of calcium carbonate concentration the miocene variation in carbonate content is caused mostly by a combination of winnowing and dissolution significant decreases of preservation at 17 3 16 3 13 8 13 0 11 6 and 10 4 ma coincide with miocene glacial events mi events suggesting that dissolution was caused by an increase of southern component water scw influence which occurred as a response to the intensification of antarctic ice sheet development the scw acts as the major deep water source during the global miocene cooling at 10 4 ma a change to overall better preservation points to a weakening of scw that occurred as a response to the initiation or strengthening of north atlantic deep water nadw

late quaternary variations in calcium carbonate preservation of deep sea sediments in the northern cape basin results from a multiproxy approach in this study we test various parameters in deep sea sediments bulk sediment parameters and changes in microfossil abundances and preservation character which are generally accepted as indicators of calcium carbonate dissolution we investigate sediment material from station geob 1710 3 in the northern cape basin eastern south atlantic 280 km away from the namibian coast well outside today s coastal upwelling as northern benguela upwelling cells were displaced westward and periodically preceded the core location during the past 245 kyr volbers et al submitted geob 1710 3 sediments reflect these changes in upwelling productivity results of the most commonly used calcium carbonate dissolution proxies do not only monitor dissolution within these calcareous sediments but also reflect changes in upwelling intensity accordingly these conventional proxy parameters misrepresent to some extent the extent of calcium carbonate dissolution these results were verified by an independent dissolution proxy the globigerina bulloides dissolution index bdxp volbers and henrich submitted the bdxp is based on scanning electronic microscope ultrastructural investigation of planktonic foraminiferal tests and indicates persistent good carbonate preservation throughout the past 245 kyr with the exception of one pronounced dissolution event at early oxygen isotopic stage ois 6 the early ois 6 is characterized by calcium carbonate contents sand contents and planktonic foraminiferal concentrations all at their lowest levels for the last 245 kyr at the same time the ratio of radiolarian to planktonic foraminiferal abundances and the ratio of benthic to planktonic foraminiferal tests are strongly increased as are the rain ratio the fragmentation index and the bdxp the sedimentary calcite lysocline rose above the core position and geob 1710 3 sediments were heavily altered as attested to by the unusual accumulation of pellets aggregates sponge spicules radiolaria benthic foraminifera and planktonic foraminiferal assemblages solely the early ois 6 dissolution event altered the coarse fraction intensely and is therefore reflected by all conventional calcium carbonate preservation proxies and the bdxp we attribute the more than 1000 m rise of the sedimentary calcite lysocline to the combination of two processes a a prominent change in the deep water mass distribution within the south atlantic and b intense degradation of organic material within the sediment preserved as maximum total organic carbon content creating microenvironments favorable for calcium carbonate

size sorting in marine muds processes pitfalls and prospects for paleoflow speed proxies the basis for and use of fine grain size parameters for inference of paleoflow speeds is reviewed here the basis resides in data on deposited sediment taken in conjunction with flow speed measurements in the field experimental data on suspended sediment transport and deposition and theoretical treatments of the generation of size distributions of deposits from suspension controlled by particle settling velocity and flow speed in the deep sea sorting events occur under resuspension deposition events in benthic storms at flow speeds below 10 15 cm s 1 size in the noncohesive sortable silt 10 63 m range is controlled by selective deposition whereas above that range removal of finer material by winnowing also plays a role the best particle size instruments to measure a flow speed related grain size employ the settling velocity method while laser diffraction sizers can yield misleading results because of particle shape effects potential problems including source effects downslope supply on continental margins spatial variability of flow over bedforms and influence of ice rafted detritus are examined a number of studies using the sortable silt flow speed proxy are reviewed and inverse modeling of grain size distributions is examined outstanding problems are that corroboration is sparse because almost no studies have yet used the full range of proxies for flow rate and water mass identification and that the sortable silt mean size is not yet properly calibrated in terms of flow speed

another look at downslope windstorms part i the development of analogs to supercritical flow in an infinitely deep continuously stratified fluid abstract numerical simulations are conducted to examine the role played by different amplification mechanisms in the development of large amplitude mountain waves it is shown that when the static stability has a two layer structure the nonlinear response can differ significantly from the solution to the equivalent linear problem when the parameter nh u is as small as 0 3 in the cases where the nonlinear waves are much larger than their linear counterparts the highest stability is found in the lower layer and the flow resembles a hydraulic jump simulations of the 11 january 1972 boulder windstorm are presented which suggest that the transition to supercritical flow forced by the presence of a low level inversion plays an essential role in triggering the windstorm the similarities between breaking waves and nonbreaking waves which undergo a transition to supercritical flow are discussed

late quaternary sedimentation within a submarine channel levee system offshore cap timiris mauritania aeolian and fluvial sediment transport to the atlantic ocean offshore mauritania were reconstructed based on grain size distributions of the carbonate free silt fraction of three marine sediment records of cap timiris canyon to monitor the climatic evolution of present day arid north western africa during the late pleistocene predominantly coarse grained particles which are interpreted as windborne dust characterise glacial dry climate conditions with a low sea level and extended sand seas that reach onto the exposed continental shelf off mauritania subsequent particle fining and the abrupt decrease in terrigenous supply are attributed to humid climate conditions and dune stabilisation on the adjacent african continent with the onset of the holocene humid period indications for an ancient drainage system which was discharging fluvial mud offshore via cap timiris canyon are provided by the finest end member for early to mid holocene times however in comparison to the senegal and niger river further south the river system connecting cap timiris canyon with the mauritanian hinterland was starved during the late holocene and is non discharging under present day arid climate conditions

on the clague mathews relation for jokulhlaups in the empirical study of jokulhlaups the peak discharge q max and water volume drained by the ice dammed lake during the floods v t appear to follow a power law relation q max kv t b where k are b are constants determined from field data first identified by clague and mathews 1973 this relation is a useful reference for predicting flood magnitude but its physical origin remains unclear here we develop the theory that connects it to contemporary models for simulating the flood hydrograph we explain how the function q max f v t arises from nye s 1976 theory of time dependent water flow in a subglacial channel coupled to a lake and we describe how discharger volume data record the monotonically increasing form of this function so long as the lake is not emptied in the floods the grimsvotn jokulhlaups present an example where because of partial draining of the lake agreement between the model derived f and data is excellent it is documented that other lake systems drain completely but we explain how the exponent b 2 3 observed for them collectively is due primarily to a scaling effect related to their size modified by other factors such as the flood initiation process

dynamics of atlantic water advection to the norwegian greenland sea a time slice record of carbonate distribution in the last 300 ky abstract short term variability in volume and configuration of atlantic water advection to the norwegian greenland sea ngs has recently been identified as a new and significant element for northern hemisphere glacial interglacial climatic fluctuations the amount of salt heat and moisture transferred by atlantic waters to the high arctic effectively influences northern hemisphere climates and is critical for the overall oceanic turnover rate in particular determining the extent and duration of atlantic water intrusions in the ngs is essential because of 1 its effect on the climate of the nordic continents and 2 its trigger function on the stability of the ice sheets with a weak inflows of atlantic water during glacials promoting an increase in ice volume by moisture supply to polar areas and b positive feed back mechanisms of atlantic water intrusions during ice sheet decay in this study the dynamics of surface water mass regimes in the ngs have been reconstructed for the past 300 ky by means of time slice compilations of calcium carbonate distribution and micropaleontologic proxies in addition carbonate preservation records are used to quantify deep water ventilation and production rates in contrast to the climap scenario but in accordance with many recent publications results of this study indicate that atlantic water advection was also a common feature during most glacial periods but varied strongly in volume and configuration significant modes recognized are 1 the full interglacial mode with a wide inflow of warm atlantic waters covering a broad area in the eastern sector of the ngs and extending far north combined with excellent carbonate preservation and very efficient deep water formation stages 1 and 5 5 1 2 the moderate interglacial mode with a rather small extension of atlantic waters along a narrow corridor in the southeastern sector of the ngs but still very efficient deep water exchange stages 9 isotopic events 7 5 7 3 7 1 5 3 and 5 1 3 pronounced cool phases during interglacials with only a very narrow inflow of atlantic waters into the southeastern ngs while the coastal areas off norway were still affected by iceberg drift substages 7 4 and 5 2 carbonate preservation records indicate ongoing deep water formation in the ngs 4 the normal glacial mode characterized by a variable but persistent inflow of cool temperate atlantic water lower stage 8 repetitively during stages 6 4 3 1 and 2 carbonate preservation records indicate ongoing deep water formation in the ngs 5 short glacial and deglacial periods characterized by episodic high inputs of ird evidenced by a wide coverage of diamicton deposition and strong carbonate dissolution e g episodically within stages 10 6 and 2 the 6 5 4 3 and 2 1 transitions some of these ngs diamicton layers correlate with heinrich layers in the north atlantic but generally ngs diamicton layers occur more frequently than heinrich layers the role of atlantic water influence during these events remains enigmatic but atlantic water influence is frequently found just above and below these sections a scenario with rapid ice sheet disintegration induced by atlantic water advection via increase of the thermal regime along the ice margin possibly triggered by small scale sea level rise might be envisaged more obviously the short term cessation of deep water formation in the ngs as evidenced by the dissolution spikes may be correlated with contemporaneous ventilation minima in the north atlantic

ratio of coccolith caco3 to foraminifera caco3 in late holocene deep sea sediments 1 on the basis of measurements of the relative amounts of caco3 in the less than 20 m and the greater than 20 m size fractions in open ocean core tops we find that the coccoliths contribute about half the calcite present in late holocene deep sea sediments which have experienced little or no dissolution although this ratio is of importance to the understanding of the ocean s caco3 cycle we can find only a few quantitative estimates of their relative contribution to currently forming marine sediments as dissolution of foraminifera calcite takes place more rapidly than that of coccolith calcite coccoliths dominate the caco3 in sediments which have experienced sizable dissolution although coccoliths contribute 40 60 of the caco3 in tropical sediments higher latitude sediments and those adjacent to continental margins often have larger proportions of coccolith caco3

calculation of coccolith volume and its use in calibration of carbonate flux estimates abstract estimates of coccolith volume help in determining total coccolith carbonate fluxes and the relative contributions of various coccolith species it is argued here that the best approach to deriving such coccolith volumes is to calculate shape factors k s for each species separately based on reconstruction of cross profiles and to determine mean sizes from measurement of size variation in the sample of interest then volume k s l 3 values of k s are given for the most important extant coccolith species based on reconstruction of cross sections followed by calculation of a volume of rotation using an iterative routine implemented in an image analysis package substantial errors ca 50 are inevitable in such calculations but the resultant data are nonetheless of value coccolith assemblages from north atlantic 47 n 20 w jgofs 1989 sediment trap samples are analysed as a test case calculated coccolith pic fluxes constitute 30 80 of the chemically determined total pic fluxes

quaternary carbonate record from the equatorial indian ocean and its relationship with productivity changes abstract the caco3 content in quaternary deep sea sediments from pacific and atlantic oceans have been suggested to respond differently to glacial interglacial cycles caco3 contents are highest during glacials in the pacific but highest during interglacials in the atlantic ocean it is not yet clear as to whether a pacific or an atlantic pattern of caco3 fluctuations dominates the indian ocean we have analyzed the ocean drilling program odp site 709a from the western equatorial indian ocean for the last 1370 ka to determine the relationships between percentages and fluxes of caco3 and quaternary paleoclimatic changes we also analyzed the coarse 25 m and fine 18 o of the planktonic foraminifera globigerinoides ruber this indicates that caco3 fluctuations at this site do not show either a pacific or an atlantic pattern of caco3 fluctuations fluxes of caco3 0 38 to 2 46 g cm 2 ka 1 in total sediment and ba al ratios 0 58 to 3 93 g cm 2 ka 1 show six fold variability through the last 1370 ka which points out that productivity changes are significant at this site fluxes of the fine caco3 component demonstrate a 26 fold change 0 02 to 0 52 g cm 2 ka 1 whereas the coarse caco3 component exhibit eight fold change 0 13 to 1 07 g cm 2 ka 1 this suggests that productivity variations of calcareous nannofossils are greater in comparison with the foraminifera on the other hand mean values of coarse caco3 fluxes are higher compared to those of fine caco3 which reveals that the foraminifera contribute more to the bulk caco3 flux than the calcareous nannofossils in the equatorial indian ocean

fast reconnaissance of carbonate dissolution based on the size distribution of calcareous ooze on walvis ridge se atlantic ocean we present a new index of carbonate fragmentation based on the size distribution of bulk sediments in core md962094 from walvis ridge se atlantic ocean the carbonate fragmentation index is constructed by taking a ratio of the two coarsest fractions in the grain size distributions of the bulk calcareous ooze the coarsest two fractions 25 90 small mu greekm and 90 small mu greekm of the bulk sediments consist primarily of complete shells and fragments of adult foraminifera shells and juvenile foraminifera shells and fragments respectively the ratio of the proportions of the two fractions is interpreted as a measure of fragmentation of the foraminifera shells caused by carbonate dissolution downcore changes in our carbonate fragmentation index compare very well with those in the coarse carbonate fragmentation index in sediments from a nearby core on walvis ridge the latter commonly used fragmentation index is defined as a ratio of foraminifera fragments over whole foraminifera in the 150 small mu greekm fraction as seen with a light microscope fragmentation is relatively high during glacial stages and relatively low during interglacial stages during the last 300 kyr caused by the combined effect of wind driven upwelling of corrosive water and increased production of organic matter decreasing the preservation potential of carbonates both during and after deposition the carbonate fragmentation index we present here provides a precise and fast method to establish a downcore fragmentation record it can be applied to bulk sediments that are carbonate rich caco3 68 and to all other deep marine sediments of which the grain size distribution of the carbonate free fraction is available

biogenic carbonate and ice rafted debris heinrich layer accumulation in deep sea sediments from a northeast atlantic piston core abstract biogenic carbonate mass accumulation rates show distinct quaternary glacial interglacial changes in a mid latitude northeast atlantic deep sea core during the last 208 kyr these were generally higher during interglacials averaging 2 2 g cm 2 kyr than during glacial periods with a maximum average of 1 2 g cm 2 kyr intervals containing high ice rafted debris have very low biogenic carbonate accumulation rates paleo primary productivity estimates based on biogenic carbonate accumulation rates are generally higher during interglacials averaging 80 gc m 2 yr than during glacials which average 49 gc m 2 yr maximum estimate short intervals with possibly reduced primary productivity correspond to heinrich layers which are the result of pulses of massive iceberg production and rapid melting in the north atlantic we identified thirteen heinrich layers in isotopic stages 7 to 2 they have calendar ages of about 201 189 182 183 164 167 146 149 142 128 131 64 67 52 54 40 43 29 31 21 and 15 kyr these heinrich layers contain large amounts of ice rafted debris including detrital carbonate low amounts of coccoliths and planktic foraminifera mainly neogloboquadrina pachyderma sinistral the upper five heinrich layers are almost barren of coccoliths and the fourth layer is also free of foraminifera the virtual absence of coccoliths is interpreted to reflect reduced coccolithophorid productivity in the photic zone due to low salinity of surface waters and to blockage of light by ice and suspended materials shed off by melting icebergs considering the limited use of other proxies such as organic carbon diatom and benthic foraminifera due to their very low content abundance in the sediments biogenic carbonate mass accumulation rates offer a workable paleo primary productivity proxy in open ocean sediments of the carbonate dominated northeast atlantic

flow over mountains coriolis force transient troughs and three dimensionality some issues concerning uniform stratified flow over a three dimensional mountain that have not been fully explored are studied using primitive equation models when the froude number fr is small e g fr 0 5 we find that the coriolis force cannot be neglected for flow over small scale mountains characteristic length l 50 km even though the rossby number ro is large when the coriolis force is neglected a pair of symmetric vortices is induced on the lee side irrespective of the scale of the mountain as long as fr lies roughly between 0 1 and 0 5 the major effect of the coriolis force is to modify or diminish the lee vortices due to the leftward deflection on the upstream side of the mountain the coriolis deflection also reduces the upstream propagation when fr is 1 most of the flow goes over the mountain and the coriolis effect is small for the same ro therefore the importance of the coriolis effect is determined by both ro and fr as the scale of the mountain increases from small scale to mesoscale 100 km l 300 km the upstream flow is deflected more to the left by the coriolis effect and a trough develops on the lee side the length scale of the trough depends on the scale of the mountain in the along flow direction for smaller scale mountains small vortices can be generated within the lee side trough when fr is small when the mountain scale is increased the lee side vortices disappear and only a lee side trough remains depending on the mean wind speed and the mountain scale the lee side trough can be advected by the anticyclonic flow over the mountain to the south and remain attached to the mountain for a long time a train of troughs is generated on the lee side of an elliptic mountain associated with the lee side gravity waves simulations of flows over mountains in two dimensional and three dimensional models with the same cross sectional profile are compared for small scale mountains l 100km the two dimensional model overestimates the amount of airflow over the mountain and also the lee side downslope wind

simmax a modern analog technique to deduce atlantic sea surface temperatures from planktonic foraminifera in deep sea sediments we present a data set of 738 planktonic foraminiferal species counts from sediment surface samples of the eastern north atlantic and the south atlantic between 87 n and 40 s 35 e and 60 w including published climate long range investigation mapping and prediction climap data these species counts are linked to levitus s 1982 modern water temperature data for the four caloric seasons four depth ranges 0 30 50 and 75 m and the combined means of those depth ranges the relation between planktonic foraminiferal assemblages and sea surface temperature sst data is estimated using the newly developed simmax technique which is an acronym for a modern analog technique mat with a similarity index based on 1 the scalar product of the normalized faunal percentages and 2 a weighting procedure of the modern analog s ssts according to the inverse geographical distances of the most similar samples compared to the classical climap transfer technique and conventional mat techniques simmax provides a more confident reconstruction of paleo ssts correlation coefficient is 0 994 for the caloric winter and 0 993 for caloric summer the standard deviation of the residuals is 0 90 c for caloric winter and 0 96 c for caloric summer at 0 m water depth the sst estimates reach optimum stability standard deviation of the residuals is 0 88 c at the average 0 to 75 m water depth our extensive database provides sst estimates over a range of 1 4 to 27 2 c for caloric winter and 0 4 to 28 6 c for caloric summer allowing sst estimates which are especially valuable for the high latitude atlantic during glacial times an electronic supplement of this material may be obtained on adiskette or anonymous ftp from kosmos agu org login toagu s ftp account using anonymous as the username and guestas the password go to the right directory by typing cd append typels to see what files are available type get and the name of the file toget it finally type exit to leave the system paper 95pa01743 simmax a modern analog technique to deduce atlantic sea surfacetemperatures from planktonic foraminifera in deep sea sediments uwepflaumann josette duprat claude pujol and laurent d labeyrie diskette may be ordered from american geophysical union 2000florida avenue n w washington dc 20009 payment mustaccompany order

low level potential vorticity and cyclogenesis to the lee of the alps abstract high resolution numerical model simulations over the alpine region are presented that reveal the presence of low level elongated bands of potential vorticity pv downstream of high topography these pv streamers or pv banners occur when the synoptic scale wind turns into a direction across the alps individual pairs of banners with anomalously positive and negative values of pv can be attributed to flow splitting either on the scale of the whole of the alps primary banners or on that of individual massifs and peaks of the model topography secondary banners the pv bands have amplitudes of up to 2 5 and 5 pvu a width of 50 150 km can attain a length of up to 1500 km and extend in the vertical from the surface up to the 500 hpa level on occasions the pv banners are associated with zones of enhanced horizontal wind shear the analysis of daily output from the operational nwp model run of the swiss meteorological institute also demonstrates that such pv streamers are a frequent feature

the final miocene carbonate crash in the atlantic assessing carbonate accumulation preservation and production abstract in many palaeoceanographic studies low carbonate contents in neogene deep sea sediments are interpreted as dissolution events related to prominent shifts in intermediate and deep water circulation in the middle to late miocene such carbonate crash events were a widespread phenomenon throughout the world s ocean basins however low carbonate contents may also derive from terrigenous dilution and carbonate production changes in surface waters as shown for late miocene records of the south atlantic diester haass et al 2004 westerhold et al 2005 in order to contribute to solve this question we investigated the youngest of the miocene crash events 10 5 ma to 9 0 ma at a prominent key location of global deep water circulation i e the equatorial atlantic ceara rise depth transect odp sites 926 927 and 928 by analysing different carbonate preservation proxies like carbonate content silt grain size parameters sand content fragmentation index and mass accumulation rates we were able to quantify dissolution dilution and production and to assess previous conflicting interpretations critical evaluation of the different dissolution proxies and comparison to former studies revealed that silt preservation proxies do not entirely reproduce the depth dependant dissolution in the miocene sediments as indicated by foraminifer fragmentation in the investigated late miocene time slice three minima of carbonate accumulation were detected the predominant control on these events changed from dissolution of carbonate to lowered production the last event at 9 6 ma is accompanied by an increased preservation but reduced carbonate accumulation during this time the first prominent pulses of northern component water ncw occurred sourced most probably from the labrador sea this may be understood as a first short term precursor of long time persistent and much stronger ncw production that is characteristic for younger periods and marks the turnover to the modern type of basin to basin fractionation between the atlantic and pacific furthermore preservation trends of caribbean and ceara rise records were in phase in contrast to former hypotheses that suggested antithetical preservation during carbonate crash events the similarity of the preservation records in the studied ocean basins in conjunction with the inconsistency in timing of the cc events and proposed ncw estimates indicates that changes in the carbon cycle other than dissolution controlled the cc events prior to 9 9 ma

an intercomparison of model predicted wave breaking for the 11 january 1972 boulder windstorm abstract two dimensional simulations of the 11 january 1972 boulder colorado windstorm obtained from 11 diverse nonhydrostatic models are intercompared with special emphasis on the turbulent breakdown of topographically forced gravity waves as part of the preparation for the mesoscale alpine programme field phase the sounding used to initialize the models is more representative of the actual lower stratosphere than those applied in previous simulations upper level breaking is predicted by all models in comparable horizontal locations and vertical layers which suggests that gravity wave breaking may be quite predictable in some circumstances characteristics of the breaking include the following pronounced turbulence in the 13 16 km and 18 20 km layers positioned beneath a critical level near 21 km a well defined upstream tilt with height and enhancement of upper level breaking superpositioned above the low level hydraulic jump sensitivity experiments indicate that the structure of the wave bre

depositional mechanisms for upper miocene sediments in the south china sea central basin evidence from calcareous nannofossils abstract in 2014 the international ocean discovery program iodp expedition exp 349 discovered carbonate layers at sites located in the south china sea scs central basin preliminary results from shipboard investigation showed that most of these carbonate layers are calcareous nannofossil ooze and interpreted them as turbidites however more detailed studies are required to determine their depositional mechanisms and paleoenvironmental implications in this study we have analyzed caco3 content calcareous nannofossil abundance assemblage composition and preservation in carbonate and clay samples from the upper miocene sections of site u1433 in the scs central basin we confirm that these carbonate layers are of turbidity current genesis but are not typical nannofossil ooze while the clays represent regular in situ deep sea sediments the study interval spanned approximately from 10 to 5 million years before present ma calcareous nannofossil abundance and assemblage are used to reconstruct the evolution of the upper seawater structure in the scs central basin our results indicate that the seawater shifted from strongly stratified to well mixed due to enhanced monsoon this shift was accompanied by an increase in pelagic productivity at 8 ma this environmental change is critical for component variations of the carbonate turbidites since we suggest that these turbidites mainly sourced from periplatform ooze in the southern scs composed by of mixed neritic and pelagic particles the neritic and pelagic caco3 production have inversed responses to the change of seawater environment in the scs and thus cause the component variations in the carbonate turbidites of site u1433

abyssal hills hidden source of increased habitat heterogeneity benthic megafaunal biomass and diversity in the deep sea abyssal hills are the most abundant landform on earth yet the ecological impact of the resulting habitat heterogeneity on the wider abyss is largely unexplored topographic features are known to influence food availability and the sedimentary environment in other deep sea habitats in turn affecting the species assemblage and biomass to assess this spatial variation benthic assemblages and environmental conditions were compared at four hill and four plain sites at the porcupine abyssal plain here we show that differences in megabenthic communities on abyssal hills and the adjacent plain are related to environmental conditions which may be caused by local topography and hydrodynamics although these hills may receive similar particulate organic carbon flux food supply from the surface ocean to the adjacent plain they differ significantly in depth slope and sediment particle size distribution we found that megafaunal biomass was significantly greater on the hills mean 13 45 g m 2 95 confidence interval 9 25 19 36 g m 2 than the plain 4 34 g m 2 95 ci 2 08 8 27 g m 2 anova f 1 6 23 8 p 0 01 assemblage and trophic compositions by both density and biomass measures were significantly different between the hill and plain and correlated with sediment particle size distributions hydrodynamic conditions responsible for the local sedimentary environment may be the mechanism driving these assemblage differences since the ecological heterogeneity provided by hills in the abyss has been underappreciated regional assessments of abyssal biological heterogeneity and diversity may be considerably higher than previously thought

stable isotopic fractionation among particles in quaternary coccolith sized deep sea sediments oxygen and carbon isotopic ratios of individual grain size splits of the 38 m fraction of deep sea carbonate particles vary systematically with size over a range of 1 25 4 0 most splits are dominated by just a few coccolith taxa and other types of particles the 18o and 13c values of individual splits are linearly related to each other with a slope of 1 5 13c 18o in all holocene and glacial samples analyzed although the observed variability is less than predicted from culture experiments of individual components compositional variations can significantly influence the stable isotopic stratigraphies measured on the nannofossil fraction

comparison between the orographic response of the ecmwf model and the pyrex 1990 data recent observations and analyses of the atmospheric flow in the vicinity of the pyrenees made during pyrex are compared with numerical experiments carried out with the t213l31 european centre for medium range weather forecasts ecmwf global model this study shows that the model simulates a certain proportion of the measured pressure drag but always underestimates it in the current model this deficit is not adequately made up by any of the parametrized subgrid scale processes when the flow is along the range the pressure drag value depends on the synoptic background flow structure it is close to zero when the flow impinging on the range is baroclinic it is not zero when the atmosphere is more barotropic e g in the absence of any fronts and the model misses important lift processes when the flow is normal to the ridge the model response to the mountain forcing is essentially ageostrophic in this case comparison between the vertical profiles of the model stresses and the measured profile suggests that further drag should be applied in the model at low level this is supported by comparisons of isentropic diagnostics from the ecmwf model and the french mesoscale model peridot these diagnostics show that the ecmwf model underestimates irreversible low level processes such as the flow separation on the mountain flanks and the associated downstream wake which can be related to the drag they also show that low level parametrized drags have a realistic impact on the model simulation of the mountain wake this analysis supports the current developments at the ecmwf of a new subgrid scale orographic drag scheme which parametrizes the low level impact of mesoscale mountains

carbonate preservation patterns at the ceara rise evidence for the pliocene super conveyor enhanced atlantic overturning during the pliocene was first proposed almost 10 yrs ago evidence for this pliocene super conveyor scenario has been collected using a number of proxies e g benthic 13c nd isotopic composition of manganese crusts the present study contributes to the existing evidences by using carbonate dissolution and current vigour history of early pliocene sediments from the ceara rise odp sites 927 and 929 in order to reveal carbonate dissolution history a number of commonly used and newly established proxies were applied i e sand and carbonate contents foraminifer fragmentation index bulloides dissolution index and carbonate silt grain size distributions terrigenous silt grain size distributions were used to unravel variations in relative current strength and sediment input to the two sites overall good carbonate preservation at the shallow site 927 3314 m water depth shows that this level was bathed in north atlantic deep water throughout the early pliocene the contrastingly poor carbonate preservation record of the deeper site 929 4358 m water depth at present exposed to antarctic bottom water is frequently interrupted by phases of good carbonate preservation these results indicate that the depth of the calcite lysocline was mainly tied to present level 4200 m water depth and sometimes even dropped to water depths greater than 4360 m due to even more enhanced circulation surprisingly the expansion of nadw is not clearly reflected by an increase in current speed as shown by continuously fine terrigenous grain size

production and accumulation of calcium carbonate in the ocean budget of a nonsteady state present day production of caco3 in tne world ocean is calculated to be about 5 billion tons bt per year of which about 3 bt accumulate in sediments the other 40 is dissolved nearly half of the carbonate sediment accumulates on reefs banks and tropical shelves and consists largely of metastable aragonite and magnesian calcite deep sea carbonates predominantly calcitic coccoliths and planktonic foraminifera have orders of magnitude lower productivity and accumulation rates than shallow water carbonates but they cover orders of magnitude larger basin area twice as much calcium is removed from the oceans by present day carbonate accumulation as is estimated to be brought in by rivers and hydrothermal activity 1 6 bt suggesting that outputs have been overestimated or inputs underestimated that one or more other inputs have not been identified and or that the oceans are not presently in steady state one missing calcium source might be groundwater although its present day input is probably much smaller than that of rivers if as seems likely caco3 accumulation presently exceeds terrestial and hydrothermal input this imbalance presumably is offset by decreased accumulation and increased input during lowered sea level shallow water accumulation decreases by an order of magnitude with a 100 m drop in sea level while groundwater influx increases because of heightened piezometric head and the diagenesis of metastable aragonite and magnesian calcite from subaerially exposed shallow water carbonates

present water mass calcium carbonate corrosiveness in the eastern south atlantic inferred from ultrastructural breakdown of globigerina bulloides in surface sediments abstract the atlantic is regarded as a huge carbonate depocenter due to an on average deep calcite lysocline however calculations and models that attribute the calcite lysocline to the critical undersaturation depth hydrographic or chemical lysocline and not to the depth at which significant calcium carbonate dissolution is observed sedimentary calcite lysocline strongly overestimate the preservation potential of calcareous deep sea sediments significant calcium carbonate dissolution is expected to begin firstly below 5000 m in the deep guinea and angola basin and below 4400 m in the cape basin our study that is based on different calcium carbonate dissolution stages of the planktic foraminifera globigerina bulloides clearly shows that it starts between 400 and 1600 m shallower depending on the different hydrographic settings of the south atlantic ocean in particular coastal areas are severely affected by increased supply of organic matter and the resultant production of metabolic co2 which seems to create microenvironments favorable for dissolution of calcite well above the hydrographic lysocline

the middle to late miocene climatic development of southwest africa derived from the sedimentological record of odp site 1085a sediments from the odp site 1085a were studied to investigate the impacts of global cooling in the middle and late miocene on the climate in southwestern africa the size composition of the sediment was analysed emphasising the silt fraction a comparison with the modern grain size distribution and suitable transport processes made it possible to assign specific transport processes to the grain size composition three processes are considered for transport of terrigeneous silt while there was no evidence found for 1 transport by ocean currents the analyses showed signals of 2 wind transport indicating dry conditions associated with a cool climate and 3 fluvial transport that points to humid and warm conditions three climatic phases were defined the first phase from 13 8 to 11 8 myr reveals a stable humid climate in southwest africa independent of the antarctic glaciations during the second phase from 11 8 to 10 4 myr the regional climate cooled considerably but was not drier additionally the climate during this phase reacted to the antarctic glaciations this cooling trend continued during phase 3 from 10 4 to 9 0 myr with a significant increase in dust input pointing to overall drier conditions however fluvial transport still remained as the main source

depositional regimes in the norwegian greenland sea the last two glacial to interglacial transitions various models of surface and deep water circulation in the norwegian greenland sea ngs have been proposed for the last two glacial to interglacial transitions although much progress has been made in understanding the sedimentary response to climatic and oceanographic changes conflicting interpretations have been developed to clarify some of these discrepancies and to test or modify the existing circulation concepts a multiparameter approach is applied combining sedimentological micropaleontological organic geochemical and isotopic methods on the basis of indicative properties a combined litho and organofacies concept is developed and calibrated with modern depositional settings beneath different surface water masses sedimentary regimes are then derived for glacial and deglacial settings

quantifying carbonate dissolution and calibration of foraminiferal dissolution indices in the somali basin two sediment traps moored off somalia in 1992 1993 collected similar settling fluxes of carbonate and siliceous shells formed by various plankton groups planktic foraminifera showed large seasonal variations with more than 74 of the total planktic foraminifera flux collected during the sw monsoon summer upwelling when globigerina bulloides was dominating along with globigerinita glutinata and neogloboquadrina dutertrei the intermonsoon and ne monsoon assemblages were dominated by globigerinoides ruber we used the trap records as our no dissolution reference for comparison with three boxcore recorders in order to quantify the carbonate dissolution along a depth transect dissolution increases downslope from station 905 to 907 and 915 at depths of 1567 m 2807 m and 4035 m respectively the carbonate fraction of the sediment at station 915 which is located near the ccd is the most affected by dissolution with more than 97 of the planktic foraminifera dissolved here the planktic foraminifera assemblage is strongly modified with thick walled species such as n dutertrei globorotalia tumida and pulleniatina obliquiloculata as the most resistant it is not representative of the settling assemblage the planktic foraminiferal assemblages of the sediment surface at stations 905 and 907 remain similar to the trap assemblages and the foraminifera are well preserved although only 25 of foraminifera are apparently preserved at station 905 and 8 at station 907 those numbers are surprisingly low and infer that only a small fraction of the foraminiferal carbonate production is buried and removed from the carbon cycle this discrepancy between the export and buried flux is partly be due to bio mechanical destruction by benthic processes and to supralysoclinal dissolution due to metabolic co2 generated by the benthic organisms another important factor is the interannual variability of the productivity well known in the arabian sea the calibration of commonly used foraminiferal dissolution indices percentage of foraminiferal fragments percentage of resistant species foraminiferal dissolution index fdx to our data only shows reliable results for high dissolution levels 97 off somalia the most accurate of the proxies is the percentage of foraminiferal fragments compared to the other methods tested i e fdx planktic foraminiferal loss l percentage of radiolarians and diatoms percentage of benthic foraminifera the species assemblage appears to be not significantly modified by dissolution unless the estimated shell loss is high 92 of the arriving shells in our samples this level is expressed in the percentage of fragmentation the percentage of radiolarians and diatoms the percentage of resistant foraminifera species and fdx as 80 35 25 and 1 8 respectively the relative abundance of globigerina bulloides is a valid sw monsoon upwelling proxy only when dissolution is moderate 92 globigerina bulloides and globigerinoides ruber have similar burial efficiencies and susceptibilities to dissolution thus the ratio g bulloides g ruber is a valid proxy for past changes in the intensity of the sw monsoon even in the strongly dissolved samples in our sediment record the ratio g bulloides g ruber indicates that the sw monsoon was stronger in the recent past than in 1992 93

coccolithophore caco3 flux in the sea of okhotsk seasonality settling and alteration processes abstract coccolithophore fluxes were determined in the sea of okhotsk using samples from a 1 year experiment 12 august 1990 to 12 august 1991 with sediment traps at 258 and 1061 m depth a special study was made on coccolithus pelagicus using fragmentation and the degree of etching as indicators of transport mechanisms a corrosion index for c pelagicus is developed the coccolithophore flux pattern at 258 m depth was characterised by a strong seasonality with flux peaks during autumn 1990 late november to early december and spring 1991 march the assemblage consisted almost entirely of the two species c pelagicus and emiliania huxleyi during autumn coccolithophore transportation to 258 m depth mainly occurred within cylindrical fecal pellets and marine snow aggregates of silicoflagellates and through agglutination on tintinnids grazing caused severe fragmentation of coccoliths and disintegration of coccospheres marine snow aggregates contained many intact coccospheres of c pelagicus during spring coccolithophores were probably removed from the euphotic zone by the ballast effect of sinking diatoms the coccolithophore flux peak in spring occurred immediately after the ice had retreated from the trap station and the trapped assemblage included coccoliths of subtropical species these features indicate drifting from an ice free location to the south or east the coccolith and coccosphere flux at 1061 m was respectively 7 and 12 times lower than at 258 m depth and maximum fluxes were recorded 2 months later increasing carbonate dissolution from 258 to 1061 m depth is expressed in the coccolithophore caco 3 flux reduction of 82 and in the increasing percentage of etched coccoliths of coccolithus pelagicus from 32 to 90

alleviation of a systematic westerly bias in general circulation and numerical weather prediction models through an orographic gravity wave drag parametrization systematic westerly biases in the northern hemisphere wintertime flow of the meteorological office 15 layer operational model and 11 layer general circulation model are described evidence that the failure to parametrize subgrid scale orographic gravity wave drag may account for such biases is presented this evidence is taken from aircraft studies surface pressure drag measurements and studies of the zonally averaged momentum budget a parametrization scheme is described in which the surface stress is proportional to the near surface wind speed and static stability and to the variance of subgrid scale orography the stress is absorbed in the vertical by considering the influence of such gravity wave activity on static stability and vertical wind shear a richardson number dependent wave breaking formulation is devised and the vertical stress profile determined by a saturation hypothesis whereby the breaking waves are maintained at marginal stability it is shown that wave breaking preferentially occurs in the boundary layer and in the lower stratosphere results from a simple zonally symmetric model show how the adjustment to thermal wind balance with a wave drag in the stratosphere warms polar regions by adiabatic descent and decelerates the mean westerlies in the troposphere the influence of the parametrization scheme on integrations of the 11 layer model is described and found to be generally beneficial in a discussion of the reasons why this problem has only recently emerged it is suggested that the satisfactory northern hemisphere winter circulations of previous coarser general circulation models were due to a compensation implied by underestimating both the surface drag and the horizontal flux of momentum by explicitly resolved large scale eddies

sources of mesoscale variability of gravity waves part i topographic excitation abstract aircraft measurements of winds and temperatures collected during the gasp program are used to study the effects of topography as a source of mesoscale variability variances of fluctuations at the mesoscale over rough terrain are enhanced up to nearly two orders of magnitude compared to nonsource regions in some cases and are frequently enhanced by an order of magnitude the implications of these episodic enhancements of variances for the vertical transports of energy and momentum are considered in the framework of gravity wave theory the observed flight data are used to estimate the momentum flux u w on several flight segments results show that the flux is generally negative with mean value 0 26 m2 s 2 and with magnitudes ranging up to 1 5 m2 s 2 spectral analysis shows that the largest contributions to the net flux come from horizontal scales of 25 x 60 km finally the observed momentum fluxes are used to infer the anisotropy factor of gravity waves over rough terrain which is foun

what is the source of the stratospheric gravity wave belt in austral winter abstractduring austral winter and away from orographic maxima or hot spots stratospheric gravity waves in both satellite observations and interim european centre for medium range weather forecasts ecmwf re analysis era interim data reveal enhanced amplitudes in a broad midlatitude belt extending across the southern ocean from east of the andes to south of new zealand the peak latitude of this feature slowly migrates poleward from 50 to 60 s wave amplitudes are much weaker across the midlatitude pacific ocean these features of the wave field are in striking agreement with diagnostics of baroclinic growth rates in the troposphere associated with midlatitude winter storm tracks and the climatology of the midlatitude jet this correlation suggests that these features of the stratospheric gravity wave field are controlled by geographical variations of tropospheric nonorographic gravity wave sources in winter storm tracks spontaneous adjustment emission from the midlatitude winter jet frontogenesi

orbital forcing of bottom current enhanced sedimentation on feni drift ne atlantic during the mid pleistocene feni ridge is a plastered sediment drift deposited along the northwestern flank of rockall trough ne atlantic under the influence of deep geostrophic currents formed by intermittent overflows of arctic intermediate water from the norwegian sea across the iceland scotland ridge nsow lower deep water ldw a derivative of antarctic bottom water from the south atlantic mixed with old north atlantic deep water nadw also bathes the lower flanks of the drift below 2500 m deep sea drilling project site 610 was drilled in a sediment wave field on the surface of feni drift 2417 m though the sediments recovered proved to be typically pelagic preserving a high resolution 5 cm kyr 1 quaternary record of orbitally modulated ice rafting and biogenic productivity cycles but showing little evidence of current affected deposition from particle size and compositional analyses of the biogenic and lithogenic 10 m silt which we then compared with records of the percentage and flux of ice rafted detrital ird sand foraminifera and coccoliths for the same interval cross spectral comparisons were then made between these records and variations in a model of northern hemisphere ice volume ice sheet growth and decay in response to orbitally forced insolation changes at 65 n variations in the relative proportions and fluxes of ird sand foraminifera and coccoliths all covary closely with orbitally forced ice volume fluctuations but with differing amplitude coherency and phase relationships at each milankovitch frequency however there is a significant component of variance in pelagic and ice rafted sedimentation which is controlled by bottom currents and this shows excellent phase and coherency agreement with the ice volume model at all orbital frequencies the relative enrichment coarseness and flux of the contourite silt fraction of feni drift sediments all increase during glacial or cold stages of the mid pleistocene relative to warm stages suggesting that currents were stronger during these periods possible explanations for such changes in current activity include 1 an increased flux of nsow via the wyville thompson ridge into the rockall trough during glacials but not due to increased production of nsow 2 ldw presently lying below 2500 m rises during glacials by at least 50 60 m thereby flooding over the surface of feni ridge at site 610 3 the path of a major recirculation gyre in the lower nadw ldw system presently situated marginally south of site 610 encroaches upon the southern tip of feni ridge during glacials and 4 the rockall trough itself is a site of deep water formation during glacials analogous to labrador sea deep water formation today

carbonate dissolution revealed by silt grain size distribution comparison of holocene and last glacial maximum sediments from the pelagic south atlantic the current issue of global warming and the role of the ocean in global exchange of co2 increases the interest in solid budgets of marine carbonate production and dissolution the present study utilizes grain size composition of pelagic sediments in order to trace spatial and temporal variability of carbonate sedimentation in the south atlantic for the holocene and last glacial maximum lgm 19 23 cal kyr bp a decrease in grain size e g sand content mean grain size of coarse carbonate silt indicates increased carbonate dissolution as a result of increased fragmentation of calcareous microfossils the spatial grain size pattern suggests a threshold water depth below which a gradual grain size decrease becomes increasingly rapid this water depth is considered as the sedimentary lysocline for the holocene time slice a constant gradual decrease of foraminifer carbonate of about 5 10 per 1000 m water depth above the lysocline gives evidence for supra lysoclinal dissolution the water depth of the lysocline for the holocene is tied to the interface of north atlantic deep water and antarctic bottom water aabw ca 4100 m submarine ridges which restrict intrusion of aabw into the angola basin cause an asymmetry in carbonate preservation across the mid atlantic ridge the lysocline was reconstructed at ca 3100 m for the lgm these data suggest that the ca 1000 m rise of the lysocline eradicated the holocene east west asymmetry

glacier change in norway since the 1960s an overview of mass balance area length and surface elevation changes in this paper we give an overview of changes in area length surface elevation and mass balance of glaciers in mainland norway since the 1960s frontal advances have been recorded in all regions except the northernmost glaciers in troms and finnmark storsteinsfjellbreen lyngen and langfjordjokelen more than half of the observed glaciers 27 of 49 had marked advances in the 1990s the glaciological mass balance values for the period 1962 2018 where 43 glaciers have been measured show great inter annual variability the results reveal accelerated deficit since 2000 the most negative decade being 2001 2010 some years with a positive mass balance or less negative after 2010s can be attributed to variations in large scale atmospheric circulation a surface elevation change and geodetic mass balance were calculated for a sample of 131 glaciers covering 817 km 2 in the 1960s and 734 km 2 in the 2010s giving an area reduction of 84 km 2 or 10 the sample covers many of the largest glaciers in norway and they had an overall change in surface elevation of 15 5 m for the 50 year period converted to a geodetic mass balance this gives a mean mass balance of 0 27 0 05 m w e a 1

frequency and characteristics of glacier floods in the swiss alps damage due to glacier floods in the swiss alps occurs about once every two years at present despite the pronounced retreat of glaciers during the twentieth century and the installation of many water reservoirs which act as flood retention basins over half 60 to 70 of the observed floods are caused by outbursts of marginal glacier lakes or sudden breaks of ice dams and 30 to 40 by ruptures of water pockets in a glacierized mountain region as densely populated as the swiss alps even debris flows triggered by outbursts of very small water masses may be dangerous historical information about glacier floods in the swiss alps although incomplete and heterogeneous is used as an empirical basis for an attempt to recognize potential hazards at an early stage by considering outburst processes volumes of water involved potential peak discharge values lithology and inclination within the reach of glacier streams

factors controlling the flux of organic carbon to the bathypelagic zone of the ocean 1 particle fluxes measured with time series sediment traps deployed below 2000 m at 68 sites in the world ocean are combined with satellite derived estimates of export production from the overlying water to assess the factors affecting the transfer of particulate organic matter from surface to deep water multiple linear regression is used to derive an algorithm suggesting that the transfer efficiency of organic carbon defined as the settling flux of organic carbon normalized to export production increases with the flux of carbonate and decreases with water depth and seasonality the algorithm predicts 80 of the organic carbon transfer efficiency variability in diverse oceanic regions the influence of the carbonate flux suggests that the ballasting effect of this biogenic mineral may be an important factor promoting export of organic carbon to the deep sea by increasing the density of settling particles however the lack of a similar effect for biogenic opal suggests that factors other than particle density also play a role the adverse effect of increasing seasonality on the transfer efficiency of carbon to the deep sea is tentatively attributed to greater biodegradability of organic matter exported during bloom events in high latitude opal dominated regions with high f ratios and seasonality while a higher fraction of net production is exported a higher fraction of the exported organic matter is remineralized before reaching bathypelagic depths on the other hand in warm low latitude carbonate dominated regions with low f ratios and seasonality a higher fraction of the exported organic matter sinks to the deep sea

fine fraction carbonate stable isotopes as indicators of seasonal shallow mixed layer paleohydrography we have measured stable isotopic compositions of miocene pelagic fine fraction 6 63 wm carbonates from oligotrophic deep sea sites in the pacific and atlantic oceans and compared them with those of coexisting foraminifers to test their utility as near sea surface indicators fine fraction carbonates primarily polyspecific nannofossils and surface dwelling planktic foraminiferal globigerinoides stable isotopes both have been considered to reflect surfacewater hydrographic conditions however our results indicate that fine fraction stable isotopes are offset from and do not correlate well with those of globigerinoides in contrast stable isotopic records of the deep dwelling planktic foraminifer globoquadrina are in good correspondence with the fine fraction records in terms of long term ca s 1 m y trends and temporal variability on the basis of a time series hydrography and flux study site in the oligotrophic subtropical north atlantic we interpret the isotopic discrepancies between fine fraction and globigerinoides as resulting primarily from season of calcification as well as possible vital effects we suggest that fine fraction stable isotope values from oligotrophic waters reflect late winter early spring relatively cool nutrient rich shallow mixedlayer conditions during the time of deep mixing i e spring bloom whereas globigerinoides stable isotope values record conditions that prevailed in the stratified surface waters in the warmer late spring fall this implies that paired analyses of fine fraction and surface dwelling planktic foraminiferal n 18 o could be applied to reconstruct paleoseasonality of the open oceans however because the fine fraction n 13 c values are not representative of the annual mean surface water n 13 c we recommend use of near surface dwelling planktic foraminiferal n 13 c as a proxy for n 13 c of stratified surface waters that are more or less in equilibrium with the atmosphere with respect to pco2

clay mineral distribution in surface sediments of the south atlantic sources transport and relation to oceanography abstract surface samples mostly from abyssal sediments of the south atlantic from parts of the equatorial atlantic and of the antarctic ocean were investigated for clay content and clay mineral composition maps of relative clay mineral content were compiled which improve previous maps by showing more details especially at high latitudes large scale relations regarding the origin and transport paths of detrital clay are revealed high smectite concentrations are observed in abyssal regions primarily derived from southernmost south america and from minor sources in southwest africa near submarine volcanoes of the antarctic ocean south sandwich bouvet island smectite contents exhibit distinct maxima which is ascribed to the weathering of altered basalts and volcanic glasses the illite distribution can be subdivided into five major zones including two maxima revealing both south african and antarctic sources a particularly high amount of mg and fe rich illites are observed close to east antarctica they are derived from biotite bearing crystalline rocks and transported to the west by the east antarctic coastal current chiorite and well crystallized dioctaedral illite are typical minerals enriched within the subantarctic and polarfrontal zone but of minor importance off east antarctica kaolinite dominates the clay mineral assemblage at low latitudes where the continental source rocks west africa brazil are mainly affected by intensive chemical weathering surprisingly a slight increase of kaolinite is observed in the enderby basin and near the filchner ronne ice shelf the investigated area can be subdivided into ten large scale clay facies zones with characteristic possible source regions and transport paths clay mineral assemblages of the largest part of the south atlantic especially of the western basins are dominated by chlorite and illite derived from the antarctic peninsula and southernmost south america and supported by advection within the circumantarctic deep water flow in contrast the east antarctic provinces are relatively small assemblages of the eastern basins north of 30 s are strongly influenced by african sources controlled by weathering regimes on land and by a complex interaction of wind river and deep ocean transport the strong gradient in clay mineral composition at the brazilian slope indicate a relatively low contribution of tropically derived assemblages to the western basins

a forward in time anelastic nonhydrostatic model in a terrain following coordinate a three dimensional 3d forward in time anelastic nonhydrostatic model in a terrain following coordinate is developed to investigate mesoscale circulations over topography the anelastic nonhydrostatic model utilizes the deep continuity equation rather than the vertical momentum equation commonly adopted to compute vertical velocity hence the anelastic nonhydrostatic model is identical to the hydrostatic model except that the former perturbation pressure must be solved from an elliptic equation to coincide with nondivergent wind to enhance the efficiency of iterations for convergence the elliptic pressure equation is transformed to an artificial parabolic form that allows semi implicit time integration as adopted in most elastic nonhydrostatic models numerical experiments using the anelastic model the same anelastic model but employing the vertical momentum equation and the compressible model were conducted for comparisons the presented anelastic model is reasonably accurate as compared to linear analytical solution and the three nonhydrostatic models show similar performances for 2d less hydrostatic flow over a bell shaped mountain the anelastic approach was found to be reasonably efficient for nonlinear flow over terrain slopes somewhat less than 1 above which ill convergence for the pressure equation was observed simulations of 3d mountain induced wake circulation with without the boundary layer effects indicate that there is little difference between the downstream wake forms for the hydrostatic model and the anelastic nonhydrostatic model a substantiation of the feasibility of the presented anelastic formulation

the fate of coccoliths at 48 n 21 w northeastern atlantic abstract as part of the joint global ocean flux study program jgofs north atlantic bloom experiment nabe coccolithophore fluxes were recorded over one year period from april 1989 to april 1990 three vertically moored sediment traps synchronized on a 14 day interval were deployed at 48 n 21 w at three water depths at 1 2 and 3 7 km sea floor at 4 4 km we present the results on the vertical variability of coccolith and coccosphere fluxes through the water column calcium carbonate was the largest component of the total mass flux followed by particulate organic matter and opal coccolith and coccosphere seasonal fluxes followed the seasonality of the biogeochemical particle fluxes at all three depths with maxima occurring during the spring particle bloom the decrease in correlation between coccosphere and coccolith fluxes with depth from r 0 98 at 1 km depth to 0 60 at 3 7 km depth documents that disaggregation of the coccospheres occurs during settling in the deeper part of the water column between 1 and 3 7 km water depth annual coccosphere and coccolith fluxes were 1 5 108 and 0 9 10 11 m 2 year 1 respectively at 1 km depth or 3 1 108 and 1 4 10 11 m 2 year 1 including the spring 1990 episode for the 3 7 km trap the corresponding values were 0 5 108 and 1 1 1011 0 6 108 and 1 1 1011 including the partially recorded spring 1990 episode the slight increase in coccolith numbers with water depth can be explained by coccosphere disintegration and lateral influx nevertheless selective dissolution of delicate coccolith species from 1 to 3 7 km water depth occurs e g relative abundances of oolithothus fragilis coccoliths decrease from 3 at 1 km to less than 0 5 at 3 7 km water depth emiliania huxleyi gephyrocapsa muellerae calcidiscus leptoporus and coccolithus pelagicus constitute from 65 at 1 km depth to 95 at 3 7 km depth of the total coccolith assemblages the same four coccolith taxa dominate the fossil assemblages in the underlying surface sediments selective dissolution continues in the sediments most notably the abundance of the solution resistant species c leptoporus increases from 10 to 15 in the trap samples to 15 40 in the sediments annual flux of calcium carbonate in sediment trap samples accounts for about 60 of the total annual mass flux with the coccolith fraction m being about 45 of the annual carbonate flux mean value of 41 at 1 km and 50 at 3 7 km water depth the correlation between the m caco 3 and the calculated coccolithophore and calcisphere caco3 fluxes decreases with depth r 0 92 at 1 km and r 0 86 at 3 7 km indicating that partial dissolution and fragmentation of the delicate less calcified coccolithophore and planktic foraminifera species occurs during settling this fine fragmentation of biogenic caco3 can contribute to the m fraction causing the decrease of correlation with the calculated caco3 fluxes being based only on the flux of intact coccoliths and calcispheres

outburst floods from glacier dammed lakes the effect of mode of lake drainage on flood magnitude published accounts of outburst floods from glacier dammed lakes show that a significant number of such floods are associated not with drainage through a tunnel incised into the basal ice the process generally assumed but rather with ice marginal drainage mechanical failure of part of the ice dam or both non tunnel floods are strongly correlated with formation of an ice dam by a glacier advancing from a tributary drainage into either a main river valley or a pre existing body of water lake or fiord for a given lake volume non tunnel floods tend to have significantly higher peak discharges than tunnel drainage floods statistical analysis of data for floods associated with subglacial tunnels yields the following empirical relation between lake volume v and peak discharge qp qp 46v0 66 r2 0 70 when qp is expressed in metres per second and v in millions of cubic metres this updates the so called clague mathews relation for non tunnel floods the analogous relation is qp 1100v0 44 r2 0 58 the latter relation is close to one found by costa 1988 for failure of constructed earthen dams this closeness is probably not coincidental but rather reflects similarities in modes of dam failure and lake drainage we develop a simple physical model of the breach widening process for non tunnel floods assuming that 1 the rate of breach widening is controlled by melting of the ice 2 outflow from the lake is regulated by the hydraulic condition of critical flow where water enters the breach and 3 the effect of lake temperature may be dealt with as done by clarke 1982 calculations based on the model simulate quite well outbursts from lake george alaska dimensional analysis leads to two approximations of the form qp vqf hi 0 where q 0 5 to 0 6 hi is initial lake depth 0 is lake temperature and the form of f hi 0 depends on the relative importance of viscous dissipation and the lake s thermal energy in determining the rate of breach opening these expressions along with the regression relations should prove useful for assessing the probable magnitude of breach type outburst floods

calcareous phytoplankton standing stocks fluxes and accumulation in holocene sediments off bermuda n atlantic abstract standing stocks and taxonomic composition of dominant coccolithophore taxa in the photic zone at bermuda hydrostation s are compared to their fluxes measured in a sediment trap at 3200 m water depth located 1200 m above the sea floor and to their accumulation in holocene sediments on the sea floor a pronounced monthly variability of coccolithophore cell densities in the photic zone over the three year plankton sampling interval 1991 1994 was observed in the sediment trap only an integrated seasonal signal is reflected in the fluxes of coccoliths and the fine fraction m carbonate which were determined for 12 biweekly sampling intervals during 1992 the average daily flux of all coccoliths during 1992 was 1 4 109 coccoliths m 2 d 1 but it varied by at least a factor of five with highest fluxes in late winter and late spring and low fluxes in late fall the fluxes of individual coccoliths of the two dominant species e huxleyi and f profunda accounted for 85 of the total coccolith fluxes the contribution of the other biogenic carbonate mostly calcispheres of thoracosphaerids to the fine fraction carbonate fluxes was minor compared to that of coccoliths fluxes of the fine fraction carbonate to the deep sargasso sea determined over 2 week intervals in 1992 were high in early spring up to 23 mg caco 3 m 2 d 1 and low in late fall minimum of 5 mg caco 3 m 2 d 1 with an annual mean of 12 mg caco 3 m 2 d 1 the surface sediments accumulating se of bermuda at 4300 m water depth consist of 11 by weight planktic foraminifera 56 fine fraction m carbonate and 33 inorganic clay the 14c age difference between the planktic foraminifera carbonate 1 5 ka and the fine fraction carbonate 6 7 ka at 13 cm core depth together with the fact that the accumulation rate of fine fraction carbonate in the sediment is about an order of magnitude higher than the corresponding fluxes to the trap confirms the previous reports of large scale resuspension of fine grained sediments in this area the taxonomic composition of the coccolith assemblages accumulating in holocene sediments near bermuda is very similar to the composition of coccoliths sampled in the trap and to that of the average living assemblage suggesting that transport and dissolution processes in this area affect all taxa in a similar way

lidar observations of a breaking mountain wave associated with extreme turbulence observations from a doppler lidar which are enhanced by stratospheric aerosols from mount pinatubo s eruption provide unique measurements of mountain waves over the rocky mountains including nearly instantaneous observations of wave breaking in the lower stratosphere the wave breaking is revealed by a flow reversal aloft that marks a localized critical layer created when the wave amplitude was great enough to cause overturning the altitude spatial scale and duration of this wave induced critical layer are documented the mountain waves led to turbulence affecting commercial aircraft including one accident in which a cargo jet lost an engine and part of a wing in extreme turbulence at the same time the lidar was making observations nearby although earlier observations of mountain wave drag assumed wave stationarity over 3 5 h significant changes over less than 2 h are documented here such nonstationarity could contribute to discrepancies remaining between observations and simulations of mountain wave drag

high resolution stratigraphy and the response of biota to late cenozoic environmental changes in the central equatorial pacific ocean manihiki plateau an undisturbed 16 m late pliocene pleistocene sediment core spanning 2 6 myr of deposition was recovered from the manihiki plateau by the german research vessel sonne in 1990 this core 34kl complements the heavily disturbed late pliocene pleistocene core sections of dsdp site 317 and is well suited for stratigraphic correlation the sediments consist of calcareous microfossils 93 97 caco3 minor portions of siliceous microfossils and detrital minerals all important calcareous microfossil zones could be identified and correlated with the magnetostratigraphic and isotope stratigraphic events stages and periods due to the high degree of silica dissolution the late quaternary radiolarian buccinosphaera invaginata zone is the only siliceous fossil zone which could be identified an interval with globigerinoides gomitulus pink was found within the middle pleistocene which is clearly distinguished from the globigerinoides ruber pink interval of the late pleistocene the magnetostratigraphic gauss matuyama and matuyama brunhes boundaries as well as the olduvai and jaramillo events were clearly identified the 180 curve displays the 100 kyr milankovitch and the 41 kyr laplace cyclicity periods the beginning of the laplace period and the last occurrence of the calcareous nannofossil discoaster brouweri which marks the end of the pliocene fall within the base of the olduvai event there is also a marked drop in sedimentation rates around this time which seems to be a regional phenomenon prominent 3 5 khz subbottom reflectors at 8 ms and 15 ms reflection time are related to lithologic changes near the mid pleistocene revolution mpr and the beginning of the laplace period or the pleistocene respectively it is possible to trace these reflectors laterally to the eroded eastern edge of the manihiki plateau where they can be tied to older strata

coccolithophore variability across marine isotope stage 11 in the pacific sector of the southern ocean and its potential impact on the carbon cycle proxy based reconstructions of past changes in the marine biological carbon pumps are limited especially in the southern ocean this work provides new insights into the productivity variations in the pacific sector of the southern ocean we present new data derived from three sediment cores that show glacial interglacial coccolithophore variability across marine isotope stage 11 mis 11 the cores were retrieved during r v polarstern cruise ps75 from the subantarctic zone and polar front zone at the western flank of the east pacific rise and in the vicinity of the antarctic pacific ridge coccolithophore assemblages were overwhelmingly dominated by the species gephyrocapsa caribbeanica and small gephyrocapsa total numbers of coccoliths coccolith accumulation rates coccolith fraction cf 20 m fraction sr ca data and temperature corrected cf sr ca records consistently showed an increase in coccolithophore productivity during termination v mis 12 11 boundary highest productivity throughout mis 11 424 374 kyr and a decrease during late mis 11 in all the cores we end with a discussion of back calculated coccolith calcification rate in the surface ocean and its potential contribution to changes in the concentration of atmospheric co2

coccolithophore export production species composition and coccolith caco3 fluxes in the ne atlantic and abstract coccolithophores were examined in two sediment traps deployed for one year april 1989 to april 1990 at approximately 1 km water depth in the subtropical ne atlantic at 34 n 21 w station nabe 34 and in the temperate ne atlantic 48 n 21 w station nabe 48 as part of the jgofs north atlantic bloom experiment nabe at both stations maximum coccolith and coccosphere fluxes were recorded during local spring bloom periods the average coccolith and coccosphere fluxes at nabe 34 were 1 12 10 9 m 2 d 1 and 4 90 10 6 m 2 d 1 respectively at this station coccoliths from 51 taxa were identified a marked seasonal change was noticed in relative abundances of emiliania huxleyi and deep photic zone species e huxleyi dominated during spring while in late autumn the coccolith assemblage was dominated by florisphaera profunda and the coccosphere assemblage by g flabellatus and algirosphaera spp emiliania huxleyi was the most abundant species in the overall coccolith and coccosphere assemblages with 69 and 64 respectively at nabe 48 the average daily fluxes were significantly lower with 3 88 10 8 coccoliths m 2 d 1 and 8 45 10 5 coccospheres m 2 d 1 and only 36 taxa were recorded in the trap samples emiliania huxleyi was the dominant species in the coccolith assemblage throughout the year with 72 and showed maximum fluxes during spring 1990 coccolithus pelagicus exhibited a distinct seasonal pattern with maximum fluxes in early june 1989 probably related to the development of a mesoscale cyclonic eddy in the vicinity of the trap site holococcolithophore fluxes were highest during maximum sea surface temperatures in summer the coccosphere assemblage was dominated by gephyrocapsa spp syracosphaera spp and e huxleyi estimated caco3 fluxes of coccoliths coccospheres and calcareous dinophytes were compared with the caco3 content in the fine m fraction the annual mass estimated caco3 flux of coccoliths and coccospheres was 5 1 g m 2 yr at nabe 34 and 2 7 g m 2 yr at nabe 48 and that of calcareous dinophytes 0 9 and 0 1 g m 2 yr respectively these summed mass estimated values contributed on average only 55 at nabe 34 and 60 at nabe 48 to the fine fraction caco3

severe downslope windstorm calculations in two and three spatial dimensions using anelastic interactive grid nesting a possible mechanism for gustiness abstract the clark nonhydrostatic anelastic code is extended to allow for interactive grid nesting in both two and three spatial dimensions tests are presented which investigate the accuracy of three different quadratic interpolation formulae which are used to derive boundary conditions for the fine mesh model application of the conservation condition of kurihara and others is shown to result in significant improvements in the treatment of interactive nesting a significant improvement in the solutions for interactive versus parasitic nesting is also shown in the context of forced gravity wave flow this result for the anelastic system is in agreement with the earlier results of phillips and shukla who considered the hydrostatic shallow water system of equations the interactive nesting model is applied to the simulation of the severe downslope windstorm of 11 january 1972 in boulder using both two and three spatial dimensions the three dimensional simulation results in a gustiness signature in the

mountain wave turbulence in the presence of directional wind shear over the rocky mountains abstractmountain wave turbulence in the presence of directional wind shear over the rocky mountains in colorado is investigated pilot reports pireps are used to select cases in which moderate or severe turbulence encounters were reported in combination with significant directional wind shear in the upstream sounding from grand junction colorado gjt for a selected case semi idealized numerical simulations are carried out using the wrf arw atmospheric model initialized with the gjt atmospheric sounding and a realistic but truncated orography profile to isolate the role of directional wind shear in causing wave breaking sensitivity tests are performed to exclude the variation of the atmospheric stability with height the speed shear and the mountain amplitude as dominant wave breaking mechanisms significant downwind transport of instabilities is detected in horizontal flow cross sections resulting in mountain wave induced turbulence occurring at large horizontal distances from the first wave br

toward better paleocarbonate ion reconstructions new insights regarding the caco3 size index 1 the reconstruction of paleocarbonate ion concentrations provides an important constraint on the contribution of the caco3 cycle to the decrease in atmospheric co2 content during glacial time such reconstructions have been challenging because each of the existing paleo co32 indices has serious limitations in this study we reexamine the broecker clark caco3 size index by analyzing the 20 m 20 to 38 m and 38 to 63 m fractions in sediments from the ontong java plateau and the ceara rise scanning electron microscope analyses demonstrate that the less than 20 m caco3 is dominated by coccoliths and the greater than 20 m caco3 is dominated by foraminifera our results clearly indicate that the coccoliths are far more resistant to dissolution than the foraminifera referenced to a core top sample from 2 31 km depth in a core top sample from 4 04 km depth on the ontong java plateau 70 of the foraminifera caco3 was dissolved as opposed to only 7 of the coccolith caco3 we found that the dissolution of foraminifera shells did not produce a significant amount of fragments smaller than 63 m in size and thus the broecker clark size index is not a measure of the extent of fragmentation rather it is a measure of the extent of differential dissolution of foraminifera relative to coccoliths on the basis of these results we propose a new dissolution index which involves the ratio of dissolution susceptible foraminifera caco3 to total caco3

sedimentary facies of glacial interglacial cycles in the norwegian sea during the last 350 ka sediment fluxes were highest in the norwegian sea during late glacial early deglacial periods i e at oxygen isotope transition 43 below transition 65 at various levels within stage 6 and below stage 9 dark diamictons deposited at these times reflect intense iceberg rafting in surface waters fed by surges along the front of the marine based parts of the continental ice sheets in the southeastern sector of the norwegian sea the high organic carbon content 0 5 1 3 in these layers reflects input from erosion of terrigenious matter rich sediments outcropping on the shelves partial oxidation of organic matter and decreased deep water renewal may explain the strong carbonate dissolution observed during these periods interglacial environments were strongly variable throughout the last 350 ka circulation patterns of stage 5e best resemble modern conditions while stage 7 and 9 sediments record a much weaker norwegian current

glacial interglacial variability of particle accumulation in the canary basin a time slice approach abstract particle supply and sediment accumulation in the canary basin are strongly modified by seasonal coastal upwelling and dust input from the sahara along an e w depth profile and fertility gradient north of the canary islands we demonstrate an increase in total mass accumulation rates from a low of 1 2 g cm 2 ka 1 in the outer oceanic domain to 6 12 g cm 2 ka 1 closer to the moroccan shelf in holocene sediments during the last glacial maximum lgm oxygen isotopic event 2 2 a steeper gradient was found with two to four times higher mass accumulation rates at the near shore sites total mass accumulation rates during the last interglacial climax lic isotopic event 5 5 and end of the penultimate glaciation epg isotopic event 6 2 resemble holocene values with lowered near shore maxima of 3 and 4 g cm 2 ka 1 respectively analyses of separate sediment components show that total organic carbon total carbonate lithogenic and diatom accumulation rates were generally enhanced during glacial times especially during the lgm in contrast glacial accumulation rates of biogenic carbonate particles coccoliths and planktic foraminifera shells remained constant or were lowered with respect to interglacial time periods at the site closest to the moroccan shelf despite a doubling of bulk carbonate accumulation this could indicate lowered supply from the productive euphotic zone or a latitudinal offshore shift of the main sedimentary depocentre however enhanced carbonate dissolution could by itself account for this decrease in biogenic carbonate accumulation increased glacial input of detrital carbonate derived from the exposed moroccan shelf appears to be responsible for the overall enhanced carbonate accumulation at the same sites east of lanzarote

sortable silt and fine sediment size composition slicing parameters for palaeocurrent speed and palaeoceanography fine sediment size 63 ixm is best measured by a sedimentation technique which records the whole size distribution repeated size measurement with intermediate steps of removal of components by dissolution allows inference of the size distribution of the removed component as well as the residue in this way the size of the biogenic and lithogenic noncarbonate fractions can be determined observations of many size distributions suggest a minimum in grain size frequency curves at 8 to 10 ixm the dynamics of sediment erosion deposition and aggregate breakup suggest that fine sediment behavior is dominantly cohesive below 10 1xm grain size and noncohesive above that size thus silt coarser than 10 ixm displays size sorting in response to hydrodynamlc processes and its properties may be used to infer current speed silt that is f mer than 10 ixm behaves in the same way as clay 2 xm useful parameters of the distribution are the 10 63 ixm mean size and the percentage 10 63 ixm in the fine fraction we cannot use size distributions to distinguish the nature of the currents therefore to infer water mass advection speeds i e the mean kinetic energy of the flow ku regions of high eddy kinetic energy ke must be avoided at the present such abyssal regions lie under the high surface k e of major current systems gulf stream kuroshio agulhas antarctic circmpolar current and brazil falldand currents in the argenthe basin this is probably a satisfactory guide for the pleistocene with regard to the carbonate subfraction of the size spectrum size modes due to both cocco iths and foramlnlferal fragments can be recognized and analyzed with the boundary between them again at about 10 lm the flux of less than 10 lm carbonate at pelagic sites above the lysocline is another candidate for a productivity indicator

controls on carbonate and terrigenous deposition in the incipient benguela upwelling system during the middle to the late miocene odp sites 1085 and 1087 this study deals with the variability of biogenic carbonate and terrigenous depositional patterns in the cape basin area of the south atlantic during the middle to the late miocene focusing on odp sites 1085 and 1087 sediments at the benguela upwelling area southwest africa the investigations are based on grain size analysis and clay mineralogy the sedimentary records at both sites provide information about climate and environmental changes the direct input of terrigenous material from southwestern africa is driven by a complex interaction of river and wind transport and ocean currents the considerable amount of dust input derived from the namib desert started to become important after 11 2 ma pointing to an increased supply of cool intermediate waters to mid latitude surface waters in the upwelling regions which coincided with the establishment of the winddriven benguela upwelling system a major drop in caco3 concentration between 10 4 and 10 1 ma is caused mainly by changes in calcareous nannoplankton production while another drop between 9 6 and 9 ma is triggered by a combination of production changes of calcareous nannoplankton and dilution in response to high shelf supply during global lowering of the sea level

pro glacial lake sedimentation from jokulhlaups glof blamannsisen northern norway outburst floods from glacier dammed lakes are major events associated with glacier thinning and volume reduction this paper investigates jokulhlaups emanating from the glacier dammed lake ovre messingmalmvatn at rundvassbreen an outlet glacier of the blamannsisen ice cap in northern norway since 2001 the lake has several times been observed to drain suddenly causing jokulhlaup outbursts into the pro glacial lake rundvatnet varve analysis and lead 210 210pb dating were used to date sediment cores taken from rundvatnet it was found that sedimentation from jokulhlaups is recognizable in the lake as distinct sand layers embedded in the varved silt clay sequence which represents the normal lake sedimentation sand fractions were carried in suspension because of the extreme hydraulic conditions of jokulhlaups the thickest sand layer was deposited during the 2001 jokulhlaup which lasted three days and had a total volume of 40 106 m3 jokulhlaups were also recorded in 2005 2007 2009 and 2010 they each resulted in a sand layer annual sediment accumulation in rundvatnet increased up to 10 fold during the years with jokulhlaup outburst floods from a normal value of 1 2 mm yr 1 to 8 10 mm yr 1 five other jokulhlaups were identified from the 1910 1930 sedimentation interval in addition to those observed in 2001 2010 there appear to have been none for 70 years during 1931 2000 each jokulhlaup was preceded by a period when the glacier thinned to a critical volume and could no longer withstand the hydrostatic pressure of ovre messingmalmvatn consequently a tunnel developed beneath the glacier leading to a jokulhlaup statistical analyses of the correlations between the pro glacial sedimentation rate and temperature and precipitation suggested that although climate conditions are expected to influence sedimentation in the pro glacial catchment a host of other interacting factors moderate the availability and delivery of sediment to the pro glacial system making the processes responsible for changes in pro glacial sedimentation to remain uncertain copyright 2014 john wiley sons ltd

carbonate dissolution and abyssal hydrography in the atlantic ocean abstract surface sediment samples from two regions in the eastern atlantic angola basin and cape verde basin and two regions in the western atlantic brazil basin and vema channel were examined to evaluate the relationship among carbonate dissolution abyssal hydrography and carbonate chemistry of the water column at each of these locations the position of the lysocline was determined carbonate saturation 1 was calculated and major deep water mass boundaries were identified as previously observed the correlation among these variables is strikingly different between the eastern and western atlantic in the vema channel and the brazil basin there is a first order correlation among the position of the lysocline the benthic thermocline aabw nadw boundary and the transition from saturation to undersaturation with respect to carbonate this relationship breaks down in the eastern atlantic where there is no noticeable benthic thermocline and the lysocline occurs significantly deeper than the saturation undersaturation transition

an 1899 glacier inventory for nordland northern norway produced from historical maps glaciers depicted on old maps reveal their historical extents before the advent of aerial and satellite remote sensing digital glacier inventories produced from these maps can be employed in assessments of centennial scale glacier change this study reconstructs the 1899 covering the period 1882 1916 glacier extent in nordland northern norway from historical gradteigskart maps with an emphasis on examining the accuracy of the mapped glaciers glacier outlines were digitised from georectified scans of the analogue maps in a raster graphics editor and were subsequently inventoried in a gis the accuracy of the historical glacier extent was established from written descriptions and landscape photographs created during the original field surveys and further validated against independent glacier outlines of 1 the maximum little ice age extent derived from geomorphological evidence and 2 the 1945 extent derived from vertical aerial photographs an overall uncertainty of 17 is associated with our inventory nordland s glaciers covered an area of 1712 291 km2 in 1899 by 2000 total ice cover had decreased by 47 807 137 km2 at a rate of 6 10 a 1 80 14 km2 10 a 1 the approach presented here may serve as a blueprint for future studies intending to derive glacier inventories from historical maps

carbon and oxygen isotopes of bulk carbonate in sediment deposited beneath the eastern equatorial pacific over the last 8 million years to improve the understanding and utility of bulk carbonate stable carbon and oxygen isotope measurements we examine sediment from cores in the eastern equatorial pacific that span the last 8ma we measured c 13 and o 18 in 791 samples from integrated ocean drilling program site u1338 and deep sea drilling project site 573 both located close to the pacific equator in 100 samples we measured c 13 and o 18 on isolated 63 mu m and 38 mu m fractions which concentrates calcareous nannofossil carbonate and progressively excludes foraminiferal carbonate bulk carbonate c 13 and o 18 records are similar to published records from other sites drilled near the equator and seem to reflect mixed layer conditions albeit with some important caveats involving the precipitation of calcite by coccolithophores the comparatively lower c 13 and o 18 of the 63 mu m and 38 mu m fractions in sediments younger than 4 4ma is attributed to an increase in deep dwelling planktic foraminifera material in bulk carbonate shifting the bulk isotopic signals toward higher values bulk carbonate c 13 is similar over 2500km along the pacific equator suggesting covarying concentrations and c 13 of dissolved inorganic carbon within surface waters since 8ma greater bulk sediment c 13 and o 18 higher sedimentation rates and low content of coarse material suggest intensified wind driven upwelling and enhanced primary productivity along the pacific equator between 8 0 and 4 4ma although a full understanding of bulk carbonate records will require extensive future work