glacial interglacial variablity in the benguela upwelling system spatial distribution and budgets of organic carbon accumulation 1 modern sedimentary total organic carbon toc content as a proxy for surface water export production was mapped on the shelf and on the upper continental slope of the benguela upwelling system using 137 core tops shelf maxima in toc can be correlated with maxima in surface water productivity on the slope high toc contents are observed offshore from sites of strong modern upwelling estimates of modern toc mass accumulation rates mar show that approximately 85 of the total is accumulating on the shelf toc mar were calculated mapped and budgeted for the holocene and for the last glacial maximum lgm using 19 sediment cores from the continental slope during the lgm centers of deposition and production have migrated offshore with respect to their holocene positions toc accumulation on the continental slope was approximately 84 higher during the lgm than during the holocene possibly reflecting enhanced productivity the toc distribution patterns and sediment echo sounding data suggest that undercurrents strongly influence the sedimentation off namibia winnowing and focusing result in great lateral heterogeneity of sedimentation rates and sediment properties individual cores therefore do not necessarily reflect general changes in export production these results highlight the need for detailed regional studies based on a large number of sediment cores for highly heterogeneous high productivity areas in order to derive general statements on total fluxes

a shear instability seeding mechanism for quasiperiodic radar echoes the quasiperiodic echoes with periods in the range of 1 10 minutes originally discovered at the middle and upper atmosphere mu radar in japan in the early 1990s are now known to be a common feature of midlatitude sporadic e a possible role of shear instabilities and the associated kelvin helmholtz structure in seeding the plasma instabilities that produce the radar echoes is suggested in this paper the proposed mechanism has the advantage that the seed structure is generated in situ as part of the same neutral wind structure that serves to initiate the generation of the sporadic e layer in addition the range of observed periods can easily be explained since the kelvin helmholtz structure is embedded in the shear flow and moves with the mean flow in the shear layer the period observed in the ground based frame is simply a product of the horizontal wavelength and the mean flow velocity at the center of the disturbance finally a typical feature of the radar observations has been that the quasiperiodic structure often ebbs and wanes in intensity over a period of 30 to perhaps 60 min recent simulations of unstable neutral shears show that the timescale for the build up and eventual restabilization of the shear flow is 30 40 min comparable to the timescale found in the observations

observations on the characteristics of tides in the bab el mandab strait 1 while well known for its multilayered exchange flow the bab el mandab strait is also of interest as a transitional region between two distinctly different tidal regimes the gulf of aden where tides are mixed and have a range in excess of 2 m and the red sea where tidal fluctuations are principally semidiurnal and their range is generally less than 1 m observations collected in the strait indicate that dominant constituents for both elevations and currents are the k1 and m2 the vertical structure of the tidal currents differs between semidiurnal and diurnal constituents and depends on the location and stratification the major part of the tidal signal is barotropic but energetic baroclinic currents mainly of the diurnal period are observed near perim narrows and the hanish sill during winter months the relationship between the barotropic currents and surface tides near perim is fairly well explained by a simple momentum balance to first order a balance exists between local acceleration and the elevation gradient in the along strait direction while in the cross strait direction a balance between local acceleration coriolis term and elevation gradient is observed at the same location the barotropic transport fluctuations reach amplitudes of 1 6 sv the k1 and m2 barotropic energy fluxes are small and are directed into the strait at perim narrows and the hanish sill for the m2 constituent and into the strait near perim and out of the strait near hanish for the k1 constituent

radar investigations of low altitude quasi periodic echoes in chung li 1 quasi periodic qp radar echoes from the sporadic e layers are also found at altitudes below 100 km which we call low altitude quasi periodic echoes lqp we have used the chung li vhf radar to study correct locations of these echoes creating irregularities which are confined to the height range between 90 km and 100 km have a thickness of 2 4 km and are only slowly descending in altitude they occur with periods of some tens of seconds to maximum three minutes since chung li is close to the equatorial region we can prove that these lqp occur in this temperate region as well the particular progress reported here is that interferometry allows us to determine the position of the scattering irregularities in three dimensions which provides new information about the motion of the scatterers we concur with the assumption that the lqp echoes are created in a strong wind shear below 100 km altitude

boundary scavenging at the east atlantic margin does not negate use of 231pa 230th to trace atlantic overturning abstract the 231 pa 230 th method is a promising tool to reconstruct ocean circulation over the past glacial interglacial cycle however marine particle flux may constrain the applicability of this ratio as a direct quantitative proxy for the strength of atlantic meridional overturning circulation amoc by influencing the fractionation between the in situ produced 231 pa and 230 th in ocean water here we present 231 pa 230 th down core profiles from high particle flux areas off namibia and senegal covering the past 35 ka the 231 pa 230 th profiles at these sites show very different responses to temporal variations of particle fluxes and to changes in water masses our results show that sedimentary 231 pa 230 th in the eastern atlantic margin is linked to particle flux but controlled primarily by the mode of the amoc our data suggest that during the past 30 ka the high productivity eastern margin was not capable of importing and storing significant amounts of 231 pa from the open ocean consequently the applicability of the 231 pa 230 th proxy to reconstruct past ocean circulation is not hampered by this potentially additional 231 pa sink

eddies in the red sea a statistical and dynamical study sea level anomaly sla data spanning 1992 2012 were analyzed to study the statistical properties of eddies in the red sea an algorithm that identifies winding angles was employed to detect 4998 eddies propagating along 938 unique eddy tracks statistics suggest that eddies are generated across the entire red sea but that they are prevalent in certain regions a high number of eddies is found in the central basin between 18 n and 24 n more than 87 of the detected eddies have a radius ranging from 50 to 135 km both the intensity and relative vorticity scale of these eddies decrease as the eddy radii increase the averaged eddy lifespan is approximately 6 weeks aes and cyclonic eddies ces have different deformation features and those with stronger intensities are less deformed and more circular analysis of long lived eddies suggests that they are likely to appear in the central basin with aes tending to move northward in addition their eddy kinetic energy eke increases gradually throughout their lifespans the annual cycles of ces and aes differ although both exhibit significant seasonal cycles of intensity with the winter and summer peaks appearing in february and august respectively the seasonal cycle of eke is negatively correlated with stratification but positively correlated with vertical shear of horizontal velocity and eddy growth rate suggesting that the generation of baroclinic instability is responsible for the activities of eddies in the red sea

direct observations of seasonal exchange through the bab el mandab strait the exchange flow between the red sea and the gulf of aden indian ocean through the bab el mandab strait was measured continuously for 10 months june 1995 march 1996 adcp and temperature salinity chain moorings allow an unprecedented look at the magnitude and seasonal evolution of the inflow layer from the gulf of aden and the high salinity outflow layer from the red sea the timing structure and evolution of the summer season mid depth intrusion of cold low salinity water into the red sea from the gulf of aden is measured for the complete intrusion cycle of 1995 we unexpectedly find the deep outflow still strong in june 1995 with speeds of 0 6 m sec and transport of 0 4 sv 1 sv 106 m sec from july to mid september the deep outflow persists but is attenuated to speeds of 0 2 m sec and transport of 0 05 sv the dominant summer feature the cold low salinity intermediate layer intrusion persists for 3 months occupies 70 of the water column in the strait and carries approximately 1 7 1012 m of cold nutrient rich water into the red sea the winter regime begins in mid september is fully developed by early november and continues to the end of our first observation interval in march 1996 speeds in the lower layer are 0 8 1 0 m sec and 0 4 0 6 m sec in the upper layer at maximum exchange in mid february outflow transport reaches 0 7 sv ubiquitous oscillations in current and salinity at synoptic and intraseasonal periods appear closely related to fluctuations in the along channel wind forcing and perhaps to coastally trapped waves

process modeling studies of physical mechanisms of the formation of an anticyclonic eddy in the central red sea surface drifters released in the central red sea during april 2010 detected a well defined anticyclonic eddy around 23 n this eddy was 45 60 km in radius with a swirl speed up to 0 5 m s the eddy feature was also evident in monthly averaged sea surface height fields and in current profiles measured on a cross isobath shipboard ctd adcp survey around that region the unstructured grid finite volume community ocean model fvcom was configured for the red sea and process studies were conducted to establish the conditions necessary for the eddy to form and to establish its robustness the model was capable of reproducing the observed anticyclonic eddy with the same location and size diagnosis of model results suggests that the eddy can be formed in a red sea that is subject to seasonally varying buoyancy forcing with no wind but that its location and structure are significantly altered by wind forcing initial distribution of water stratification and southward coastal flow from the upstream area momentum analysis indicates that the flow field of the eddy was in geostrophic balance with the baroclinic pressure gradient forcing about the same order of magnitude as the surface pressure gradient forcing

fluxes of 230th and 231pa to the deep sea implications for the interpretation of excess 230th and 231pa 230th profiles in sediments abstract analysis of samples obtained with deep sea moored sediment traps deployed at 15 sites representing a wide range of oceanic conditions confirms that the flux of 230 th scavenged to the seafloor remains close to its production rate from the decay of 234 u in the overlying water column and generally validates the use of 230 th as a normalizing tool for paleoflux reconstruction after correction for trapping efficiency the flux of 230 th measured in the low flux regions amounts to 90 6 of the production rate with the notable exceptions of one site near the arabian sea upwelling and one site in the weddell sea a 230 th flux equivalent to 120 of the production rate was found in panama basin similar or more extensive scavenging of 230 th may be occurring at a pacific margin site off california and south of the polar front but these estimates are obscured by large errors on our trapping efficiency estimates in contrast the flux of 231 pa and the 231 pa 230 th ratio can vary strongly with particle flux following distinct trends in different oceanic basins in the atlantic ocean 231 pa fluxes and 231 pa 230 th are low and not sensitive to particle flux this is because of the short residence time of deep water in this basin resulting from thermohaline circulation which prevents the full development of lateral concentration gradients and full expression of boundary scavenging in the pacific ocean the sensitivity of 231 pa 230 th to particle flux is highest reflecting the longer residence time of deep water in the southern ocean 231 pa 230 th ratios are invariably high even when particle fluxes are low reflecting the predominance of opal which fractionates minimally between the two radionuclides interpretation of 231 pa 230 th recorded in sediments is thus complex in the atlantic this ratio is better suited for recording past changes in the strength of thermohaline circulation in the pacific it has the best potential for providing synoptic maps of past changes in particle flux in the southern ocean retrieval of information from 231 pa 230 th is more difficult and requires a more quantitative understanding of the influence of particle composition

sedimentary patterns in the late quaternary southern ocean the spatial and temporal distribution of biogenic and lithogenic sediments in the late quaternary southern ocean reflects the zonal character of the antarctic circumpolar current and is basically controlled by glacial dynamics in antarctica sea ice distribution temperature gradients wind patterns and thermohaline ocean circulation carbonate patterns in most places reveal a decline in biogenic carbonate preservation during glacial periods mainly attributed to a reduced influx of north atlantic deep water and increased ocean stratification which modified deep water chemistry towards more corrosivity an important lithological feature of the southern ocean is the circumpolar opal belt which today is situated between the polar front and the seasonal sea ice limit to the south during the glacial periods the opal belt shifted to the north in response to a wider sea ice extension that reduced light availability and diatom productivity to the south biosiliceous productivity to the north likely was fueled by detrital iron supplied by aeolian dust input and or hemipelagic processes lithogenic fluxes generally increased during the glacial periods provenance studies on the origin and dispersal of detrital materials suggest combined effects of low sea level stands increased glaciogenic input and enhanced current transport to have caused elevated detrital fluxes the relative and absolute contribution of aeolian dust is difficult to decipher and awaits further clarification by integrated provenance studies of both marine sediments and more reference materials from the potential terrestrial source areas ice rafted debris ird represents a minor fraction of lithogenic sediments but can be used to infer both antarctic ice sheet dynamics and the fate of both sea ice and iceberg survival in the distal southern ocean future work should be concentrated on a better identification of ird origin in terms of volcaniclastic influences the distinction of east and west antarctic sediment sources and sea ice versus iceberg transportation

the influence of particle composition and particle flux on scavenging of th pa and be in the ocean we have examined the relative affinity of th pa and be for sorption from seawater onto particles of variable composition opal carbonate lithogenic particles and organic carbon nuclide concentrations in particles collected from time series sediment traps were normalized by the dissolved nuclide concentration in the overlying water column in order to compute partition coefficients under conditions spanning a wide range of particle flux and particle composition our results suggest that the affinity of particles for pa and be increases with their increasing opal content and decreasing carbonate content while the affinity of particles for th increases with increasing carbonate content and decreases with increasing opal content we find no correlation between the aluminosilicate content of particles and their affinity for scavenging of any of these elements extrapolating to a pure caco3 end member the partition coefficient for th 9 0 106 g g 1 is 40 times greater than for pa and roughly 100 times greater than for be whereas for a pure opal end member the partition coefficient for th 3 9 105 g g 1 is slightly less than that for pa and be partition coefficients decrease with increasing particle flux in open ocean settings but not in an ocean margin region this kinetic effect reflects the increasing contribution of unaltered surface material reaching the sediment traps as particle flux increases the degree of fractionation between pa and th and between be and th depends on the opal carbonate rain ratio these results challenge the use of sedimentary 231pa 230th and 10be 230th ratios as simple proxies of particle flux however the strong dependence of nuclide scavenging on the opal carbonate rain ratio may provide a needed tool for reconstructing past changes in planktonic community composition

a three dimensional model of diurnal and semidiurnal tides on the european shelf a three dimensional hydrodynamic model of the continental shelf is used to examine the sensitivity of computed diurnal k1 and o1 and semidiurnal m2 s2 and n2 tidal elevations and currents to changes in eddy viscosity profile friction coefficient and water depth the influence of the tide generating potential is also considered the model uses a standard finite difference grid in the horizontal with a functional approach in the vertical thereby giving a continuous tidal current profile from sea surface to seabed the magnitude of the vertical eddy viscosity depends upon the flow field comparisons are made between model computed profiles and harmonic analyses of 278 current time series at a range of locations in varying water depths with particular emphasis on locations where there are current measurements at a number of points in the vertical a detailed examination of these comparisons shows that frictional effects in the near bed region are particularly important in determining near bed shear and that an accurate specification of water depth is critical for tidal current magnitude the spatial distribution of computed current ellipses shows that the semidiurnal currents are strongest in shallow water with the diurnal currents exhibiting an intensification in the shelf edge region the inclusion of the equilibrium tide is particularly important for the correct determination of the magnitude of the k1 tidal current as well as k1 elevations in the north sea the detailed comparisons show that the magnitude of the tidal currents is correctly determined to within 5 cm s 1 at 220 locations with the model accurately to within 2 cm s 1 reproducing the vertical variation the most sensitive test of a three dimensional model of the tidal current at most locations

age assignment of a diatomaceous ooze deposited in the western amundsen sea embayment after the last glacial maximum reliable dating of glaciomarine sediments deposited on the antarctic shelf since the last glacial maximum lgm is challenging because of the rarity of calcareous micro fossils and the recycling of fossil organic matter consequently radiocarbon 14 c ages of the acid insoluble organic fraction aio of the sediments bear uncertainties that are difficult to quantify here we present the results of three different methods to date a sedimentary unit consisting of diatomaceous ooze and diatomaceous mud that was deposited following the last deglaciation at five core sites on the inner shelf in the westernamundsen sea west antarctica in three coresconventional 14 c dating of the aio in bulk samples yielded age reversals down core but at all sites the aio 14 c ages obtained from diatomaceous ooze within the diatom rich unit yielded similar uncorrected 14 c ages between 13517 56 and 11543 47 years before present a bp correction of these ages by subtracting the core top ages which probably reflect present day deposition as indicated by 210 pb dating of the sediment surface at one core site yielded ages between ca 10500 and 8400 cal a bp correction of the aio ages of the diatomaceous ooze by only subtracting the marine reservoir effect mre of 1300 a indicated deposition of the diatom rich sediments between 14100 and 11900 cal a bp most of these ages are consistent with age constraints between 13 0 and 8 0ka for the diatom rich unit which we obtained by correlating the relative palaeomagnetic intensity rpi records of three of the sediment cores with global and regional reference curves as a third dating technique we applied conventional radiocarbon dating of the aio included in acid cleaned diatom hard parts extracted from the diatomaceous ooze this method yielded uncorrected 14 c ages of only 5111 38 and 5106 38 a bp respectively we reject these young ages because they are likely to be overprinted by the adsorption of modern atmospheric carbon dioxide onto the surfaces of the diatom hard parts prior to sample graphitisation and combustion for 14 c dating the deposition of the diatom rich unit in the western amundsen sea suggests deglaciation of the inner shelf before ca 13ka bp the deposition of diatomaceous oozes elsewhere on the antarctic shelf around the same time however seems to be coincidental rather than directly related copyright 2009 john wiley sons ltd

an oceanic general circulation model ogcm investigation of the red sea circulation 2 three dimensional circulation in the red sea 1 the three dimensional circulation of the red sea is studied using a set of miami isopycnic coordinate ocean model micom simulations the model performance is tested against the few available observations in the basin and shows generally good agreement with the main observed features of the circulation the main findings of this analysis include an intensification of the along axis flow toward the coasts with a transition from western intensified boundary flow in the south to eastern intensified flow in the north and a series of strong seasonal or permanent eddy like features model experiments conducted with different forcing fields wind stress forcing only surface buoyancy forcing only or both forcings combined showed that the circulation produced by the buoyancy forcing is stronger overall and dominates the wind driven part of the circulation the main circulation pattern is related to the seasonal buoyancy flux mostly due to the evaporation which causes the density to increase northward in the basin and produces a northward surface pressure gradient associated with the downward sloping of the sea surface the response of the eastern boundary to the associated mean crossbasin geostrophic current depends on the stratification and b effect in the northern part of the basin this results in an eastward intensification of the northward surface flow associated with the presence of kelvin waves while in the south the traditional westward intensification due to rossby waves takes place the most prominent gyre circulation pattern occurs in the north where a permanent cyclonic gyre is present that is involved in the formation of red sea outflow water rsow beneath the surface boundary currents are similarly intensified southward undercurrents that carry the rsow to the sill to flow out of the basin into the indian ocean index terms 4243 oceanography general marginal and semienclosed seas 4255 oceanography general numerical modeling 4532 oceanography physical general circulation keywords red sea marginal sea oceanic general circulation model water mass formation

primary productivity and the silica cycle in the southern ocean atlantic sector abstract tentative data for the biogenic silica production in a section along 10 e are calculated from the dissolved silica distribution north of a sharp silica front found south of the antarctic polar front and near the maud rise production was relatively high these areas have also high bottom relief causing redistribution of sediments as is demonstrated from 210pb analyses this overestimates the importance of such areas in budget calculations of the accumulation of biogenic silica dissolved silica concentrations in interstitial waters are highly variable low values are explained by the incorporation of al in diatom frustules dissolution in the surface sediments is 3 times larger than burial this is more than previously assumed calculations of the flux out of the sediments from gradients in interstitial waters and in bottom waters using diffusion coefficients determined from 222rn profiles give reasonable agreement

reappraisal of sea ice distribution in atlantic and pacific sectors of the southern ocean at 18 000 yr bp the question of the distribution of winter and summer sea ice cover during the last glacial maximum 18 000 yr bp is important in climatic modelling of the glacial world we have now compared satellite derived 5 yr monthly averages of per cent summer sea ice cover in the atlantic and pacific sectors of the southern ocean with the distribution of reported sedimentological indicators of sea ice cover at the sediment water interface these data strongly suggest that sediment type cannot be used to identify summer sea ice limits neither in recent sediments nor in sediments of the last glacial maximum rather the data seem to indicate that sediment type can be used to identify spring sea ice limits for these two time intervals

low altitude quasi periodic echoes studied using a large database of gadanki radar observations 1 in this paper we present studies on low altitude quasiperiodic lqp echoes based on a large database of gadanki radar observations lqp echoes have been observed 33 of the time during daytime and 39 during nighttime their occurrence is found to be maximum in the summer daytime 58 nighttime 57 followed by the september equinox daytime 32 nighttime 48 the march equinox daytime 26 nighttime 36 and minimum in the winter daytime 25 nighttime 26 height time occurrence of lqp echoes shows two local time maxima one in the morning 0700 1100 lt and another in the evening 1900 0000 lt the most significant results not reported earlier are the large occurrence rate of lqp echoes and the height time occurrence maps showing a descending pattern with close resemblance to tidal wind behavior the doppler velocities are upward northward downward southward for positive negative sloped lqp echoes also we find the doppler spread as high as 200 m s 1 at times underlining the presence of strong plasma turbulence in the collision dominated lower e region these results are discussed in the light of the current understanding of the lqp echoes

biogeography in 231pa 230th ratios and a balanced 231pa budget for the pacific ocean the ratio of unsupported protactinium 231 to thorium 230 in marine sediments pa th xs is potentially sensitive to several processes of oceanographic and climatological interest deep ocean circulation marine biological productivity as it relates to total particle flux and particle composition specifically biogenic opal and authigenic mn in order to attribute variations in pa th xs observed in sediment records to changes in specific processes through time a better understanding of the chemical cycling of these elements in the modern ocean is necessary to this end a survey was undertaken of pa th xs in surface sediments from the subarctic pacific so202 inopex expedition in combination with a pacific wide compilation of published data throughout the pacific pa th xs is robustly correlated with the opal content of sediments in the north and equatorial pacific simultaneous positive correlations with productivity indicators suggest that boundary scavenging and opal scavenging combine to enhance the removal of pa in the eastern equatorial pacific and subarctic pacific deep ocean water mass ageing 3 5 km 3 5 km associated with the pacific overturning appears to play a secondary role in determining the basin scale distribution of pa th xs a basin wide extrapolation of pa removal is performed which suggests that the pacific pa budget is nearly in balance we hypothesize that through time pa th xs distributions in the pacific could define the evolving boundaries of contrasting biogeographic provinces in the north pacific while the influence of hydrothermal scavenging of pa potentially confounds this approach in the south pacific

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

benthic remineralization and burial of biogenic sio2 caco3 organic carbon and detrital material in the southern ocean along a transect at 170 west abstract we investigated the composition recycling and mass accumulation rates of sediments along a transect in the southern ocean located from 66 s to 57 s at 170 w this transect also corresponds to the location of a sediment trap mooring line the sediments at the seven sites studied range from largely terrigenous material to nearly pure 90 biogenic silica caco3 is a minor but persistent component at most sites mass accumulation rates have been determined on the basis of excess 230th in the sediments i e 230th normalized accumulation rates the influence of redistribution of sediments on the sea floor has been estimated from 14c analyses the recycling of material delivered to the sediments has been characterized on the basis of pore water studies that make extensive use of both in situ sampling and shipboard extractions the influence of the highly variable rates of input of particulate matter that characterize much of the southern ocean upon pore water gradients and fluxes across the sediment water interface has been considered we find only poor correspondence between bsio2 burial fraction burial particulate flux a quantifiable measure of preservation efficiency and bsio2 particulate rain along the transect however preservation does appear to be closely linked to a combination of sedimentation rate and particulate rain the burial fraction of bsio2 is small relative to benthic rain 5 19 despite the small fraction buried burial flux normalized to sedimentation rate 1 2 appears to provide a very consistent means of predicting benthic particulate rain over a large range of rain rates including data from a number of different studies and environments at sites with bsio2 rain 250 mmol m 2 yr 1 the average difference between predicted and observed rain is 25 30 such rain rates occur in many marine areas particularly the southern ocean with the result that this relationship potentially provides a means of estimating bsio2 benthic rain over prolonged periods in the past on the basis of readily measured sediment parameters at the southern most deep ocean station the particulate flux was characterized by an extremely high corg caco3 ratio 10 but this high ratio does not appear to have a substantial influence on caco3 burial caco3 is preserved in the sediments at this site despite a particulate flux with a 10 fold excess of corg above that required for complete dissolution in the sediments the unexpectedly high preservation of caco3 is due largely to the very steep corg oxidation rate profile at this site as a result a large fraction of the organic matter oxidized in the sediments does so in close proximity to the sediment water interface where most of the metabolic co2 is neutralized by co32 from the overlying water rather than by the dissolution of sedimentary caco3 diagenetic modeling indicates that at several of the stations the remineralization fluxes of carbonate species across the sediment water interface may not have been at steady state as a result of the highly pulsed nature of particulate rain in this environment we estimate that at the time of our sampling it is possible that near interface fluxes could have been a factor of 1 6 2 times the annual average at every site on the transect the burial fluxes of detrital material are substantially greater than the detrital particulate rain measured in the sediment traps by as much as a factor of 40 detrital burial is bimodal being greatest at the southern and northern extremes of the transect we postulate that the excess of burial over particulate rain in the south reflects the contribution of ice rafted debris at these high latitudes increases in the supply at the northern stations must have a different source we believe that the excess at these stations is material eroded from the sea floor to the west possibly on the campbell plateau and advected by currents to the northern portion of the transect at depths below the shallow traps

location and dynamics of the antarctic polar front from satellite sea surface temperature data the location of the antarctic polar front pf was mapped over a 7 year period 1987 1993 within images of satellite derived sea surface temperature the mean path of the pf is strongly steered by the topographic features of the southern ocean the topography places vorticity constraints on the dynamics of the pf that strongly affect spatial and temporal variability over the deep ocean basins the surface expression of the pf is weakened and the pf meanders over a wide latitudinal range near large topographic features width and temperature change across the front increase and large scale meandering is inhibited elevated mesoscale variability is seen within and downstream of these areas and may be the result of baroclinic instabilities initiated where the pf encounters large topographic features the strong correlations between topography and pf dynamics can be understood in the context of the planetary potential vorticity ppv or f h field mean ppv at the pf varies by more than a factor of 2 along its circumpolar path however at the mesoscale the pf remains within a relatively narrow range of ppv values around the local mean away from large topographic features the pf returns to a preferred ppv value of 25 10 9 m 1 s 1 despite large latitudinal shifts the mean paths of the surface and subsurface expressions of the pf are closely coupled over much of the southern ocean

230th normalization an essential tool for interpreting sedimentary fluxes during the late quaternary there is increasing evidence indicating that syndepositional redistribution of sediment on the seafloor by bottom currents is common and can significantly affect sediment mass accumulation rates notwithstanding its common incidence this process generally referred to as sediment focusing is often difficult to recognize if redistribution is near synchronous to deposition the stratigraphy of the sediment is not disturbed and sediment focusing can easily be overlooked ignoring it however can lead to serious misinterpretations of sedimentary fluxes particularly when past changes in export flux from the overlying water are inferred in many instances this problem can be resolved at least for sediments deposited during the late quaternary by normalizing to the flux of 230th scavenged from seawater which is nearly constant and equivalent to the known rate of production of 230th from the decay of dissolved 234u we review the principle advantages and limitations of this method notwithstanding its limitations it is clear that 230th normalization does provide a means of achieving more accurate interpretations of sedimentary fluxes and eliminates the risk of serious misinterpretations of sediment mass accumulation rates

the accumulation and cycling of biogenic silica in the southern ocean revisiting the marine silica budget abstract in many of the recent marine silica budgets e g science 268 1995 375 a majority of the world s biogenic silica accumulation is attributed to the siliceous ooze deposits in the antarctic deep sea based on 230 th normalized sediment accumulation rates as well as comparative studies of silica preservation seabed accumulation compared to surface biogenic production the rate of biogenic silica accumulation in antarctic siliceous ooze deposits has been over estimated by as much as 35 the current estimate for silica accumulation in these high latitude deposits is 3 1 10 12 mol yr 1 as compared to previous values of 4 1 4 8 10 12 mol yr 1 to maintain balance between silicate supply and biogenic silica removal in the oceans an additional repository is needed evidence from continental shelf and upper slope sediments suggests that biogenic silica accumulation in continental margin deposits may account for a much larger fraction of the marine silica burial than previously thought compensating for the diminished accumulation in the antarctic deep sea if biogenic silica accumulation in continental margin sediments replaces nearly a third of the silica accumulation in the antarctic deep sea the marine cycles of organic matter and biogenic silica are coupled to a greater extent than reported in previous budgets

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

last glacial maximum sea surface temperature and sea ice extent in the pacific sector of the southern ocean sea surface temperatures and sea ice extent are most critical variables to evaluate the southern ocean paleoceanographic evolution in relation to the development of the global carbon cycle atmospheric co2 and ocean atmosphere circulation here we present diatom transfer function based summer sea surface temperature ssst and winter sea ice wsi estimates from the pacific sector of the southern ocean to bridge a gap in information that has to date hampered a well established reconstruction of the last glacial southern ocean at circum antarctic scale we studied the last glacial maximum lgm at the epilog time slice 19 000e23 000 calendar years before present in 17 cores and consolidated our lgm picture of the pacific sector taking into account published data from its warmer regions our data display a distinct east west differentiation with a rather stable wsi edge north of the pacific antarctic ridge in the ross sea sector and a more variable wsi extent over the amundsen abyssal plain the zone of maximum cooling 4 k during the lgm is in the present subantarctic zone and bounded to its south by the 4 c isotherm the isotherm is in the ssst range prevailing at the modern antarctic polar front representing a circum antarctic feature and marks the northern edge of the glacial antarctic circum polar current acc the northward deflection of colder than modern surface waters along the south american continent led to a significant cooling of the glacial humboldt current surface waters 4e8 k which affected the temperature regimes as far north as tropical latitudes the glacial reduction of acc temperatures may also have resulted in significant cooling in the atlantic and indian southern ocean thus enhancing thermal differentiation of the southern ocean and antarctic continental cooling the comparison with numerical temperature and sea ice simulations yields discrepancies especially con cerning the estimates of the sea ice fields but some simulations reproduce well our proxy based tem perature data

the silica cycle during the last ice age abstract qualitative and quantitative investigations of the silica geochemistry in the ocean and its cycles and changes during the quaternary have been carried out based on more than 4000 sample determinations the present si cycle within the ocean balance and annual silica accumulation were determined the main part of silica has accumulated on the ocean bottom in three silica accumulation belts southern equatorial and northern the changes of the belts were synchronous for the northern and the southern hemispheres and were caused by climatic changes connected with glaciation

50 mhz radar observations of mid latitude e region irregularities at camp santiago puerto rico a 50 mhz radar interferometer was used near salinas puerto rico to probe the meter scale e region plasma density irregularities during two campaigns conducted in 1998 during the february april period e region echoing layers were primarily observed between 90 and 100 km heights the layers were typically thin 1 km and unstructured although in several cases short period 90 s layer oscillations were observed during the june july period e region echoes showed more varied characteristics in addition to low altitude layers quasi periodic structures with descending echoing layers were observed at altitudes above 100 km zonal motions detected during descending layer events were at times variable and oscillated between westward and eastward directions while the layer descent rates remained fixed

three dimensional numerical simulation of m2 internal tides in the east china sea the east china sea and adjacent seas are one of the most significant generation regions of the m 2 internal tide in the world s oceans in the present study we investigate the distribution and energetics of the m 2 internal tide around the continental shelf edge in the east china sea using a three dimensional numerical model the numerical experiment shows that m 2 internal tides are effectively generated over prominent topographic features such as the subsurface ridges in the bashi luzon and tokara straits the ridges along the ryukyu island chain and the continental shelf slope in the east china sea the former particularly so all of these topographic features are characterized by steep slopes at the depth of the thermocline onto which the m 2 barotropic tide is almost normally incident the m 2 internal tides propagating away from these multiple source regions interfere with each other to create a complicated wave pattern it is found that the calculated pattern of the m 2 internal tide agrees well with topex poseidon altimeter observations the conversion rate from m 2 barotropic to baroclinic energy over the whole analyzed model domain is estimated to be 35 gw roughly 10 of the energy in the m 2 surface tide incident on the prominent topographic features is converted to the m 2 internal tide although about half of the m 2 internal tidal energy is subject to local dissipation in close proximity to the generation sites

diatom distribution in southern ocean surface sediments atlantic sector implications for paleoenvironmental reconstructions abstract a study of 230 surface sediment samples collected in the atlantic sector of the southern ocean between the southernmost weddell sea and the subtropical zone documents the modern distribution of diatoms revealing patterns of paleoenvironmental significance estimations of diatom valves per gram dry sediment display numbers of 50 200 106 in the zone of high opal burial located between the mean position of the winter sea ice edge and the polar front and maximum values of greater than 200 106 in the near shore sedimentary basins off the antarctic peninsula lowest diatom concentrations and assemblages strongly affected by dissolution were encountered in the weddell basin despite alteration of the diatom assemblages prior to their incorporation into the sediment record the biogeographic distribution and the abundance pattern of most of the 35 studied diatom species shows a close relationship with the surface hydrography water temperature these relationships can be used to estimate past surface water temperatures based on statistical treatments of the assemblages or on simple relations of species occurrences in the geological record another close link occurs between the distribution of sea ice and sea ice related diatoms

diatom distributions in northern north pacific surface sediments and their relationship to modern environmental variables abstract the quantitative analysis of diatom assemblages preserved in 52 samples from the bellingshausen and the amundsen seas provides the first comprehensive view on the distribution of diatoms in surface sediments of the eastern and central pacific sector of the southern ocean on a latitudinal transect along 120 w diatom valve accumulation rates ar reach maximum values 8 10 108 valves m 2 yr 1 in a zone extending over ca 900 km between the antarctic polar front and the maximum average winter sea ice extent and exceed those ars obtained from an eastern transect along 90 w by one order of magnitude lowest diatom concentrations 1 3 106 valves g 1 were encountered in sediments of the sea ice zone affected by winter and summer sea ice the accumulation rate pattern of the most abundant diatom fragilariopsis kerguelensis 50 abundance in 47 samples mirrors the pattern of the total diatom valve ar and the biogenic silica bsi ar making f kerguelensis the major contributor to the bsi preserved at the sea floor relative abundances of diatom species and species groups were statistically compared with a selection of environmental variables such as the mean summer sea surface temperature and salinity mean annual surface nutrient concentration nitrate phosphate silicon mean annual water column stratification mixed layer depth in summer and mean summer and winter sea ice concentrations polynomial canonical redundancy analysis rda revealed the biogeographic distribution of diatom species had the strongest relationship with summer sea surface temperature ssst out of the nine tested environmental variables this relationship accounted for 69 6 of the total variance of the diatom distribution with 29 7 explained by the first gradient significantly correlated to ssst with r2 0 941 and 15 6 explained by the second gradient correlated to both summer and winter sea ice and silicon concentration azpeitia tabularis hemidiscus cuneiformis and roperia tesselata were associated with warmer water conditions 4 c whereas fragilariopsis curta f separanda f rhombica and thalassiosira gracilis were correlated with cold ssst confirming these environmental relationships is crucial for the development of reference data sets used in quantitative estimations of palaeoclimatic and palaeoceanographic conditions with statistical methods this new data set represents the first modernised treatment of diatom remains from the se pacific ocean and generally supports the use of a circum polar database for the determination of summer sst sea ice and potentially biogenic silica distribution of the southern ocean back into the late quaternary

natural remanent magnetization acquisition in bioturbated sediment general theory and implications for relative paleointensity reconstructions we present a general theory for the acquisition of natural remanent magnetizations nrm in sediment under the influence of a magnetic torques b randomizing torques and c torques resulting from interaction forces dynamic equilibrium between a and b in the water column and at the sediment water interface generates a detrital remanent magnetization drm while much stronger randomizing torques may be provided by bioturbation inside the mixed layer these generate a so called mixed remanent magnetization mrm which is stabilized by mechanical interaction forces during the time required to cross the surface mixed layer drm is lost and mrm is acquired at a rate that depends on bioturbation intensity both processes are governed by a mrm lock in function the final nrm intensity is controlled mainly by a single parameter that is defined as the product of rotational diffusion and mixed layer thickness divided by sedimentation rate this parameter defines three regimes 1 slow mixing 10 with mrm acquisition and full drm randomization and 3 intermediate mixing because the acquisition efficiency of drm is larger than that of mrm nrm intensity is particularly sensitive to in case of mixed regimes generating variable nrm acquisition efficiencies this model explains 1 lock in delays that can be matched with empirical reconstructions from paleomagnetic records 2 the existence of small lock in depths that lead to drm preservation 3 specific nrm acquisition efficiencies of magnetofossil rich sediments and 4 some relative paleointensity artifacts

seasonal overturning circulation in the red sea 1 model validation and summer circulation the overturning circulation in the red sea exhibits a distinct seasonally reversing pattern and is studied using high resolution mit general circulation model simulations in the first part of this study the vertical and horizontal structure of the summer overturning circulation and its dynamical mechanisms are presented from the model results the seasonal water exchange in the strait of bab el mandeb is successfully simulated and the structures of the intruding subsurface gulf of aden intermediate water are in good agreement with summer observations in 2011 the model results suggest that the summer overturning circulation is driven by the combined effect of the shoaling of the thermocline in the gulf of aden resulting from remote winds in the arabian sea and an upward surface slope from the red sea to the gulf of aden set up by local surface winds in the red sea in addition during late summer two processes associated respectively with latitudinally differential heating and increased salinity in the southern red sea act together to cause the reversal of the contrast of the vertical density structure and the cessation of the summer overturning circulation dynamically the subsurface northward pressure gradient force is mainly balanced by vertical viscosity resulting from the vertical shear and boundary friction in the strait of bab el mandeb unlike some previous studies the three layer summer exchange flows in the strait of bab el mandeb do not appear to be hydraulically controlled

carbon and silica megasink in deep sea sediments of the congo terminal lobes carbon and silicon cycles at the earth surface are linked to long term variations of atmospheric co2 and oceanic primary production in these cycles the river sea interface is considered a biogeochemical hotspot and deltas presently receive and preserve a major fraction of riverine particles in shallow water sediments in contrast periods of glacial maximum lowstand were characterized by massive exports of sediments to the deep sea via submarine canyons and accumulation in deep sea fans here we calculate present day mass balances for organic carbon oc and amorphous silica asi in the terminal lobe complex of the congo river deep sea fan as an analogue for glacial periods we show that this lobe complex constitutes a megasink with the current accumulation of 18 and 35 of the oc and asi river input respectively this increases the estimates of organic carbon burial by 19 in the south atlantic ocean in a zone representing less than 0 01 of the basin these megasinks might have played a role in carbon trapping in oceanic sediments during glacial times

polar stratification a critical view from the southern ocean oceanic stratification represents an effective mechanism to reduce vertical mixing of the water column thereby locking up carbon dioxide co2 in the deep sea and preventing air sea exchange of co2 it has been proposed that enhanced stratification of the upper water column in polar oceans during late cenozoic cooling episodes limited the upwelling of co2 rich deep waters and thus co2 release to the atmosphere resulting in a net global drawdown of atmospheric co2 increased stratification in the subarctic northwest pacific during both the onset of northern hemisphere glaciation at 2 73 ma and late quaternary glacial periods has been recently linked to enhanced ocean stratification south of the antarctic polar front apf in the pacific and atlantic sectors of the southern ocean increased stratification of southern ocean surface waters was mainly deduced from a reduction of biological production during these cooling episodes manifested by the decrease of geochemical proxies for productivity such as biogenic opal and barium in the marine sediment records however the records chosen from the southern ocean do not provide evidence for a more stratified upper water column rather the observed decrease in biological productivity is likely to have resulted from an expansion of annual sea ice coverage the sediment records suggest that south of the apf in the pacific and atlantic sectors of the southern ocean extensive sea ice may have contributed to the global co2 drawdown during glacial periods with hypothetical glacial increase of stratification in today s permanent open ocean zone merely being an add on caused by this expansion

southern ocean bioproductivity during the last glacial cycle new detection method and decadal scale insight from the scotia sea we present biogenic opal flux records from two deep sea sites in the scotia sea md07 3133 and md07 3134 at decadal scale resolution covering the last glacial cycle in addition to conventional and time consuming biogenic opal measuring methods we introduce new biogenic opal estimation methods derived from sediment colour b wet bulk density si ti count ratio and fourier transform infrared spectroscopy ftirs all methods capture the biogenic opal amplitude however ftirs a novel method for marine sediment yields the most reliable results 230th normalization data show strong differences in sediment focusing with intensified sediment focusing during glacial times at md07 3134 230th normalized biogenic opal fluxes vary between 0 2 and 2 5 g cm22 kyr21 our biogenic opal flux records indicate bioproductivity changes in the southern ocean strongly influenced by sea ice distribution and also summer sea surface temperature changes south of the antarctic polar front lowest bioproductivity occurred during the last glacial maximum when upwelling of mid depth water was reduced and sea ice cover intensified around 17 ka bioproductivity increased abruptly corresponding to rising atmospheric co2 and decreasing seasonal sea ice coverage

vertical budgets for organic carbon and biogenic silica in the pacific sector of the southern ocean 1996 1998 abstract during the 1996 1998 antarctic environment and southern ocean process study aesops a component of us jgofs we obtained seasonal or longer term data sets on the rates of production vertical transport remineralization and burial of particulate organic carbon poc and biogenic silica bsio2 in the southern ocean at 170 w between 55 s and 68 s the aesops data records enable us to construct vertical c and si budgets for the water column and upper sediments with all estimates derived from direct measurement of the relevant fluxes we constructed annual c and si budgets for each of four ecologically distinct zonal bands within the system for both poc and bsio2 the greatest annual delivery to the sea floor 200 and 1400 mmol m 2 yr 1 respectively and burial 6 and 160 mmol m 2 yr 1 respectively were observed in the southern antarctic circumpolar current acc between 61 5 s and 65 5 s that pattern is consistent with our observation that a diatom bloom propagated southward through the southern acc during the spring and summer of 1997 1998 following the receding ice edge and that this bloom was the main source of both poc and bsio2 in the system on an annual basis in the other zones the annual fluxes of poc and bsio2 to the sea floor ranged from 19 to 67 of those in the zone traversed by the summer diatom bloom the higher benthic fluxes of both poc and bsio2 in the southern acc imply that blooms similar to the one we observed in 1997 1998 occur commonly in the southern acc and that their high productivity signature is transmitted to the sea floor the data show preferential preservation of bsio2 over poc throughout the water column and upper seabed in the four zonal bands we consider bsio2 and poc are produced in mole ratios of 0 1 0 4 exported from the upper 100 m in ratios of 0 2 0 6 arrive at 1000 m in ratios of 1 5 4 5 reach the sea floor in ratios of 2 2 7 6 and are buried in ratios of 11 6 28 despite the preferential preservation of bsio2 accumulation of opal rich sediments beneath the acc does not result from unusually efficient preservation of siliceous material the estimated bsio2 preservation efficiency burial production ranges from 1 2 to 5 5 indistinguishable from the global average of 3 instead opal rich sediment accumulation in this region reflects very high annual rates of bsio2 production in surface waters along with very low accumulation rates of other sedimentary components e g caco3 and detrital material the observed high ratios of bsio2 production to poc production in surface waters are consistent with the known tendency for the si c ratio of diatoms to increase when fe is low if greater fe availability during the last glacial maximum permitted diatoms in the southern ocean to grow with lower more normal si c ratios export of diatom produced poc could have occurred at 2 3 times its present rate a corresponding increase in opal export or opal sediment accumulation is unlikely because silicic acid is almost totally depleted north of 65 s under present conditions thus even large increases in poc production and export during glacial periods would not be reflected in the opal accumulation record

tides and sea level in the gulf of aqaba eilat 1 in this paper we discuss observations of tidal variations in currents and elevation taken in the gulf of aqaba eilat over the fringing coral reef at eilat israel both currents and elevations appear to be strongly affected by conditions in the main body of the red sea tidal currents which vary considerably in strength throughout the year appear to be associated with internal waves generated at the strait of tiran where density driven exchanges between the gulf of aqaba and the red sea take place water level also has significant annual and interannual variations as seen in other studies of the red sea these appear to be associated with corresponding variations in winds acting on the entire red sea

new tools for the reconstruction of pleistocene antarctic sea ice abstract based on the quantitative analysis of diatom assemblages preserved in 274 surface sediment samples recovered in the pacific atlantic and western indian sectors of the southern ocean we have defined a new reference database for quantitative estimation of late middle pleistocene antarctic sea ice fields using the transfer function technique the detrended canonical analysis dca of the diatom data set points to a unimodal distribution of the diatom assemblages canonical correspondence analysis cca indicates that not only winter sea ice wsi but also summer sea surface temperature ssst represent the most prominent environmental variables that control the spatial species distribution to test the applicability of transfer functions for sea ice reconstruction in terms of concentration and occurrence probability we applied four different methods the imbrie and kipp method ikm the modern analog technique mat weighted averaging wa and weighted averaging partial least squares wapls using logarithm transformed diatom data and satellite derived 1981 2010 sea ice data as a reference the best performance for ikm results was obtained using a subset of 172 samples with 28 diatom taxa taxa groups quadratic regression and a three factor model ikm d172 28 3q resulting in root mean square errors of prediction rmsep of 7 27 and 11 4 for wsi and summer sea ice ssi concentration respectively mat estimates were calculated with different numbers of analogs 4 6 using a 274 sample 28 taxa reference data set mat d274 28 4an 6an resulting in rmsep ranging from 5 52 4an to 5 91 6an for wsi as well as 8 93 4an to 9 05 6an for ssi wa and wapls performed less well with the d274 data set compared to mat achieving wsi concentration rmsep of 9 91 with wa and 11 29 with wapls recommending the use of ikm and mat the application of ikm and mat to surface sediment data revealed strong relations to the satellite derived winter and summer sea ice field sea ice reconstructions performed on an atlantic and a pacific southern ocean sediment core both documenting sea ice variability over the past 150 000 yr mis 1 mis 6 resulted in similar glacial interglacial trends of ikm and mat based sea ice estimates on the average however ikm estimates display smaller wsi and slightly higher ssi concentration and probability at lower variability in comparison with mat this pattern is a result of different estimation techniques with integration of wsi and ssi signals in one single factor assemblage by applying ikm and selecting specific single samples thus keeping close to the original diatom database and included variability by mat in contrast to the estimation of wsi reconstructions of past ssi variability remain weaker combined with diatom based estimates the abundance and flux pattern of biogenic opal represents an additional indication for the wsi and ssi extent

late quaternary changes in biogenic opal fluxes in the southern indian ocean abstract late quaternary sedimentary and paleoenvironmental conditions in the southern indian ocean have been reconstructed from radioisotope and proxy element profiles biogenic opal and organic carbon measured on five sediment cores taken along a transect across the indian sector of the antarctic circumpolar current dissolution corrected opal rain rates were used to reconstruct past changes of opal productivity for this region records from these five cores indicate that opal productivity during glacial periods was lower than presently recorded south of the antarctic polar front apf probably due to increased ice cover north of apf opal productivity was slightly greater during glacial periods than during the holocene probably in response to 1 the northward migration of the apf by approximately 5 latitude 2 a northward transport of si from the antarctic zone and 3 an increase of fe necessary for opal producing organisms via upwelling and the erosion of the kerguelen plateau we also invoke a decoupling between opal burial and organic carbon flux to the seabed to explain the variation in buried si c ratio between glacial and interglacial sediment this decoupling is principally explained by better organic carbon preservation in the glacial sediments due to strong sediment focussing an increase in glacial export paleoproductivity is not supported by the data implying that bioproductivity variations in the southern indian ocean are unlikely to have contributed to the glacial drawdown of atmospheric co 2 inferred from ice core data

holocene sediment fluxes in the northeast atlantic from 230thexcess and radiocarbon measurements radiocarbon and 230thexcess data from six ne atlantic box cores are considered the cores form a transect from the porcupine abyssal plain over the east thulean rise to the southern end of feni drift the chronology for the cores is established from bulk sediment carbonate radiocarbon data and reveals that sections exhibiting constant accumulation rates can be identified in all the cores with rates of 3 0 3 5 cm kyr 1 on the plain through the holocene and late holocene rates of 4 3 6 6 cm kyr 1 elsewhere five out of the six cores show accumulations of more 230thexcess than is produced in the overlying water column with the greatest inventories up to 225 of production in the cores from the rise and drift a size fraction comparison between two cores from the plain and rise reveals that the higher overall accumulation rates and 230thexcess inventories in the off plain cores are due to an increased fine 5 m component fraction whereas the flux of coarser material is similar to that received on the plain this suggests that the higher fluxes of materials observed are physically rather than biogeochemically driven and also that drift formation has been continuously active in the late holocene sections of all the cores where regular accumulation is defined by the radiocarbon data are modeled first by a linear radiocarbon age depth model and second by a constant rain 230thexcess 0 model prorated for the observed core inventories these modeling approaches yield historical mass accumulation rate estimates which are generally in reasonable agreement 30 but the differences observed appear to be well organized in time rather than random

growth rate and size effect on carbon isotopic fractionation in diatom bound organic matter in recent southern ocean sediments carbon isotopic fractionation during photosynthesis epep is used to reconstruct past co2 and phytoplankton growth rates typically by measuring the 13c of biomarkers produced by coccolithophorids however organic molecules bound within diatom frustules represent another phase for measurement of 13c and offer the opportunity to obtain epep for specific diatom sizes and geometries here from core top sediments covering a strong productivity gradient in the southern ocean we present determinations of 13c and epep from frustule bound organic matter from a fine opal fraction dominated by pennate diatoms and a coarse opal fraction dominated by larger centric diatoms the 13c of the pennate diatom fraction is typically 2 8 more positive than that of the centric fraction both fractions show a comparable range of 9 10 over the core top transect epep is lowest 6 3 in pennate fraction between the polar front pf and southern antarctic circumpolar current front saccf and increases both to the north and south with maximum values at greatest distance from the pf 18 in the pennate fraction these spatial changes in epep are too large to arise from the rather modest variation in dissolved co2 in surface waters across the core top transect we suggest instead that the maximum epep reflects higher diatom growth rates and in the case of pennate diatom f kerguelensis also an increase in the frustule width and volume to surface area ratio both processes may result from enhanced fe supply due to upwelling of circumpolar deep water between the pf and saccf farther south diatom growth is strongly fe limited and farther north it is fe and si co limited the optima of growth rates between the pf and saccf appears to be a general feature in all sectors of the southern ocean such growth rate induced changes in diatom epep allow us to resolve a 5 northward displacement of the pf during glacial times compared to interglacial times by estimating co2 aq in equilibrium with the holocene ice core atmospheric co2 concentrations we quantify this growth rate effect and document that it is strongly correlated with indicators of trace metal supply such as frustule zn content as well as indicators of diatom productivity such as opal and opal accumulation rates in sediments and sediment traps these relationships may be applied to constrain the effect of growth rate variations on epep and more accurately derive co2 variations from epep during periods prior to ice core co2 proxy records

a biomarker perspective on dust productivity and sea surface temperature in the pacific sector of the southern ocean abstract in this study we present a new multiproxy data set of terrigenous input marine productivity and sea surface temperature sst from 52 surface sediment samples collected along e w transects in the pacific sector of the southern ocean allochthonous terrigenous input was characterized by the distribution of plant wax n alkanes and soil derived branched glycerol dialkyl glycerol tetraethers brgdgts 230th normalized burial of both compound groups were highest close to the potential sources in australia and new zealand and are strongly related to lithogenic contents 232th indicating common sources and transport detection of both long chain n alkanes and brgdgts at the most remote sites in the open ocean strongly suggests a primarily eolian transport mechanism to at least 110 w i e by prevailing westerly winds two independent organic sst proxies were used the u 37 k based on alkenones and the tex86 based on isoprenoid gdgts both u 37 k and tex86 indices show robust relationships with temperature over a temperature range between 0 5 and 20 c likely implying different seasonal and regional imprints on the temperature signal alkenone based temperature estimates best reflect modern summer sst in the study area when using the polar calibration of sikes et al 1997 in contrast tex86 derived temperatures may reflect a subsurface signal rather than surface 230th normalized burial of alkenones is highest close to the subtropical front and is positively related to the deposition of lithogenic material throughout the study area in contrast highest isogdgt burial south of the antarctic polar front may be largely controlled by diatom blooms and thus high opal fluxes during austral summer

scavenging of 230th 231pa and 10be in the southern ocean sw pacific sector the importance of particle flux particle composition and advection abstract the scavenging of 230 th 231 pa and 10 be was studied in the pacific sector of the southern ocean along 170 w using measurements from surface sediments time series sediment traps and the water column all sediment traps collected an annual flux of 231 pa greater than the integrated rate of production by 235 u decay up to 5 5 times greater and a flux of 10 be greater than the global average deposition rate of 10 be up to 3 4 times greater fluxes of 230 th were on average close to the production rate in the overlying water column these large fluxes of 231 pa and 10 be and high unsupported 231 pa 231 th and 10 be 230 th ratios in the sediments are not associated with depletion of nuclides in the water column and therefore are not the result of the classical boundary scavenging mechanism we estimate that of the 231 pa and 230 th advected into the southern ocean as part of the large scale overturning circulation only those nuclides associated with the upper limb of this circulation i e those that pass through the surface as part of the wind driven ekman flow are scavenged efficiently the majority of the nuclides advected into the southern ocean and associated with the bottom water limb are not scavenged to the sediments of the southern ocean but are returned northward throughout the year the unsupported 231 pa 230 th and 10 be 230 th ratios of material reaching sediment traps at 1000 m at a given site increase with increasing particle flux this behavior is explained by a conceptual model in which th pa and be are scavenged reversibly by fine grained suspended particles at all depths while pa and be are in addition scavenged strongly by diatom rich aggregates in surface waters spatial variability in the annually averaged unsupported 231 pa 230 th and 10 be 230 th ratios of sinking particulate matter reflects primarily the variability in particle composition and in the ratio and quantity of nuclides upwelled to the mixed layer rather than variability in particle flux

mesoscale eddies in the gulf of aden and their impact on the spreading of red sea outflow water abstract the gulf of aden goa in the northwestern indian ocean is the receiving basin for red sea outflow water rsow one of the world s few high salinity dense overflows but relatively little is known about spreading pathways and transformation of rsow through the gulf here we combine historical data satellite altimetry new synoptic hydrographic surveys and the first in situ direct observations of subsurface currents in the goa to identify the most important processes in the spreading of rsow the new in situ data sets were collected in 2001 2003 as part of the red sea outflow experiment redsox and consist of two ctd ladcp surveys and 49 one year trajectories from acoustically tracked floats released at the depth of rsow the results indicate that the prominent positive and negative sea level anomalies frequently observed in the goa with satellite altimetry are associated with anticyclonic and cyclonic eddies that often reach to at least 1000 m depth i e through the depth range of equilibrated rsow the eddies dominate rsow spreading pathways and help to rapidly mix the outflow water with the background eddies in the central and eastern gulf are basin scale 250 km diameter and have maximum azimuthal speeds of about 30 cm s at the rsow level in the western gulf smaller eddies not detectable with satellite altimetry appear to form as the larger westward propagating eddies impale themselves on the high ridges flanking the tadjura rift both the hydrographic and lagrangian observations show that eddies originating outside the gulf often transport a core of much cooler fresher water from the arabian sea all the way to the western end of the goa where the highest salinity outflow water is found this generates large vertical and horizontal gradients of temperature and salinity setting up favorable conditions for salt fingering and diffusive convection both of these mixing processes were observed to be active in the gulf two new annually appearing anticyclonic eddies are added to the previously identified gulf of aden eddy gae prasad and ikeda 2001 and somali current ring scr fratantoni et al 2006 these are the summer eddy se and the lee eddy le both of which form at the beginning of the summer monsoon when strong southwest winds blowing through socotra passage effectively split the gae into two smaller eddies the se strengthens as it propagates westward deeper in the goa while the lee eddy remains stationary in the lee of socotra island both eddies are strengthened or sustained by ekman convergence associated with negative wind stress curl patches caused by wind jets through or around high orography the annual cycle in the appearance propagation and demise of these new eddies and those described in earlier work is documented to provide a comprehensive view of the most energetic circulation features in the goa the observations contain little evidence of features that have been shown previously to be important in the spreading of mediterranean outflow water mow in the north atlantic namely a wall bounded subsurface jet the mediterranean undercurrent and submesoscale coherent lenses containing a core of mow meddies this is attributed to the fact that the rsow enters the open ocean on a western boundary high background eddy kinetic energy typical of western boundary regimes will tend to shear apart submesoscale eddies and boundary undercurrents even if a submesoscale lens of rsow did form in the goa westward self propagation would transport the eddy and its cargo of outflow water back toward rather than away from its source

a geochemical approach to reconstruct modern dust fluxes and sources to the south pacific abstract we present the first comprehensive dust provenance and lithogenic flux data set extracted from surface sediments distributed across the polar and subpolar south pacific the dataset comprises 230th normalized lithogenic fluxes combined with rare earth elements strontium neodymium and lead isotope data to determine lithogenic fluxes spatial distribution and sources of dust

vigorous deep sea currents cause global anomaly in sediment accumulation in the southern ocean the vigorous current systems in the southern ocean play a key role in regulating the earth s oceans and climate with the record of long term environmental change mostly contained in deep sea sediments however the well established occurrence of widespread regional disconformities in the abyssal plains of the southern ocean attests to extensive erosion of deep sea sediments during the quaternary we show that a wide belt of rapid sedimentation rates 5 5 cm k y along the southeast indian ridge seir is a global anomaly and occurs in a region of low surface productivity bounded by two major disconformity fields associated with the kerguelen plateau to the east and the macquarie ridge to the west our high resolution numerical ocean circulation model shows that the disconformity fields occur in regions of intense bottom current activity where current speeds reach 0 2 m s and are favorable for generating intense nepheloid layers these layers are transported toward and along the seir to regions where bottom current velocities drop to 0 03 m s and fine particles settle out of suspension consistent with focusing factors significantly greater than 1 we suggest that the anomalous accumulation of sediment along an 8000 km long segment of the seir represents a giant succession of contourite drifts that is a major extension of the much smaller contourite east of kerguelen plateau and has occurred since 3 5 ma based on the age of the oldest crust underlying the deposit these inferred contourite drifts provide exceptionally valuable drilling targets for high resolution climatic investigations of the southern ocean

analysis of a mid latitude e region lqp event observed during the coqui 2 campaign 1 arecibo isr observations and vhf coherent backscatter data collected with a radar situated in southern puerto rico are examined to understand the causes of quasi periodic variations in vhf returns from lower e region heights 93 km it is found that bragg scale density irregularities causing the observed vhf backscatter are formed and propagated horizontally in a density perturbation field localized at the upper boundary of a tidal ion layer the density perturbation has a 7 km horizontal wavelength propagates in southwest direction and it is not aligned with the geomagnetic field thus the production mechanism of the observed density perturbation cannot be the gradient drift instability often invoked to account for the generation of mid latitude sporadic e radar echoes nevertheless secondary gradient drift instability operating on the gradients of the southwest propagating perturbation remains the most likely cause of bragg scale electron density waves responsible for the vhf returns

low altitude quasi periodic radar echoes observed by the gadanki vhf radar 1 we report here on the low altitude quasi periodic lqp radar echoes from low latitude sporadic e layer es observed by the gadanki 13 5 n 79 2 e geomagnetic latitude 6 3 n vhf radar the lqp echoes occurred both during daytime and nighttime and are confined to a slowly descending layer with a thickness of about 2 4 km in the height range of 90 100 km the periods are found to range from tens of seconds to less than about 3 minutes the doppler velocities vary over a range of 20 to 20 m s during daytime and 0 to 10 m s during nighttime and are known to be sensitive to the layer height being dominated by the effect of zonal electric field above and meridional neutral wind below a height of 97 km for the type 2 irregularities krishna murthy et al 1998 the spectral widths are found to be of the order of 50 to 75 m s during daytime and 30 to 60 m s during nighttime the lqp echoes reported here are similar to that observed recently over midlatitudes rao et al 2000 urbina et al 2000 but distinctly different from the widely reported quasi periodic qp echoes occurring at higher altitudes 100 km the observations are discussed briefly in terms of the potential source mechanisms

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

glacial interglacial changes in sediment rain rate in the sw indian sector of subantarctic waters as recorded by 230th 231pa u and δ15n high resolution records of opal carbonate and terrigenous fluxes have been obtained from a high sedimentation rate core md84 527 43 50 s 51 19 e 3269 m by normalization to 230th this method estimates paleofluxes to the seafloor on a point by point basis and distinguishes changes in sediment accumulation due to variations in vertical rain rates from those due to changes in syndepositional sediment redistribution by bottom currents we also measured sediment 15n to evaluate the changes in nitrate utilization in the overlying surface waters associated with paleoflux variations our results show that opal accumulation rates on the seafloor during the holocene and stage 3 based on 14c dating were respectively tenfold and fivefold higher than the vertical rain rates at this particular location changes in opal accumulation on the seafloor appear to be mainly controlled by sediment redistribution by bottom currents rather than variations in opal fluxes from the overlying water column correction for syndepositional sediment redistribution and the improved time resolution that can be achieved by normalization to 230th disclose important variations in opal rain rates we found relatively high but variable opal paleoflux during stage 3 with two maxima centered at 36 and 30 kyr b p low opal paleoflux during stage 2 and deglaciation and a pronounced maximum during the early holocene we interpret this record as reflecting variations in opal production rates associated with climate induced latitudinal migration of the southern ocean frontal system sediments deposited during periods of high opal paleoflux also have high authigenic u concentrations suggesting more reducing conditions in the sediment and high pa 231 th 230 ratios suggesting increased scavenging from the water column sediment 15n is circa 1 5 per mil higher during isotopic stage 2 and deglaciation the low opal rain rates recorded during that period appear to have been associated with increased nitrate depletion this suggests that opal paleofluxes do not simply reflect latitudinal migration of the frontal system but also changes in the structure of the upper water column increased stratification during isotopic stage 2 and deglaciation could have been produced by a meltwater lid leading to lower nitrate supply rates to surface waters

baroclinic tides simulation in the red sea comparison to observations and basic characteristics the author would like to thank james h churchill larry pratt and jim thomas for the discussions and help the topography data are derived from general bathymetric chart of the oceans gebco https www gebco net the initial salinity and temperature is extracted from world ocean atlas 2009 woa09 https www nodc noaa gov oc5 woa09 pr woa09 html the barotropic tidal boundary currents and the spatial distribution of elevation amplitudes and phases are derived from tpxo 7 2 inverse model http volkov oce orst edu tides global html the mitgcm model output data files sea level data from gauges and mooring data can be found at figshare https figshare com projects data for b2018jc013970 bc redsea 57407 the research reported in this manuscript was supported by king abdullah university of science and technology this research made use of the resources from the supercomputing laboratory and or computer clusters at king abdullah university of science and technology

quaternary surface water temperature estimations calibration of a diatom transfer function for the southern ocean the quantitative diatom analysis of 218 surface sediment samples recovered in the atlantic and western indian sector of the southern ocean is used to define a base of reference data for paleotemperature estimations from diatom assemblages using the imbrie and kipp transfer function method the criteria which justify the exclusion of samples and species out of the raw data set in order to define a reference database are outlined and discussed sensitivity tests with eight data sets were achieved evaluating the effects of overall dominance of single species different methods of species abundance ranking and no analog conditions e g eucampia antarctica on the estimated paleotemperatures the defined transfer functions were applied on a sediment core from the northern antarctic zone overall dominance of fragilariopsis kerguelensis in the diatom assemblages resulted in a close affinity between paleotemperature curve and relative abundance pattern of this species downcore logarithmic conversion of counting data applied with other ranking methods in order to compensate the dominance of f kerguelensis revealed the best statistical results a reliable diatom transfer function for future paleotemperature estimations is presented

enhanced scavenging of 231pa relative to 230th in the south atlantic south of the polar front implications for the use of the 231pa 230th ratio as a paleoproductivity proxy abstract the fractionation of 230th and 231pa was investigated throughout the atlantic sector of the southern ocean published scavenging models generally assume that the 231pa 230t ratio of surface sediments is primarily determined by the mass flux of particles this relationship holds north of the polar front where low primary productivity coincides with ratios of unsupported 231pa 230th xs 231pa 230th in surface sediments below the production ratio of both radionuclides in the water column however we observed high xs231pa 230th ratios conventionally interpreted as a high productivity signal in surface sediments south of the polar front especially throughout the weddell sea in contradiction with the low particle flux of this region measurements of both dissolved and particulate fractions of 231pa and 230th in the water column revealed a strong n s decrease in the th pa fractionation factor from typical open ocean values around 10 north of the polar front to values between 1 and 2 south of 60 s this observation clearly indicates that the high xs231pa 230th ratios in surface sediments south of the antarctic circumpolar current are produced by a n s increase in the relative scavenging efficiency of 231pa relative to 230th most probably due to a change in the chemical composition of particulate matter and not by a high mass flux it is speculated that biogenic opal suggested not to significantly fractionate231pa and 230th may explain the enhanced scavenging of 231pa to the south this assumption is further supported by extremely high 231pa 230th ratios up to 0 34 in material collected with sediment traps south of the polar front where fluxes are primarily determined by biogenic opal based on these results we conclude that in regions where the sedimenting flux is dominated by biogenic opal the 231pa 230th ratio is not a reliable indicator for the mass flux of particles thus limiting its use as a paleoproductivity proxy in the southern ocean

seasonal overturning circulation in the red sea 2 winter circulation author posting 0american geophysical union 2014 this article is posted here by permission of american geophysical union for personal use not for redistribution the definitive version was published in journal of geophysical research oceans 119 2014 2263 2289 doi 10 1002 2013jc009331

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

controls on biogenic silica burial in the southern ocean understanding the controls on opal export in the southern ocean can inform both the prediction of how the leakage of silicic acid from the southern ocean responds to climate and the interpretation of paleo proxies we have compiled a database of 185 230thorium normalized opal burial rates and 493 opal concentration measurements in southern ocean sediments and matched these with environmental climatologies by subdividing the southern ocean on the basis of oceanographic regions and interpolating the opal burial rates we estimate a total biogenic si burial south of 40 s of 2 3 1 0 tmol si yr 1 in both the seasonally ice covered and permanently ice free regions we can explain 73 of opal burial variability from surface ocean properties where sea ice is present for at least part of the year the length of the ice free season determines the upper limit of opal burial in the underlying sediments in the ice free regions of the southern ocean the supply of silicic acid through winter mixing is the most important factor our results do not support a strong role of iron in controlling opal burial we do however find that satellite derived net primary production increases with increasing modeled dust delivery these findings support the decoupling between carbon and opal fluxes in the southern ocean when corrected for opal dissolution the observed opal fluxes are in reasonable agreement with fluxes simulated using an ocean biogeochemical model however the results suggest current preservation algorithms for opal could be improved by incorporating the composition of particle flux not only its magnitude

mid latitude e region field aligned irregularities observed with the mu radar fine structures e region field aligned irregularities were observed on june 24 25 1989 with the mu radar at shigaraki japan 34 9 n 136 1 e geomagnetic latitude 25 0 n the 3 2 m scale irregularities were observed with the mu radar in five main beam directions each of which was nearly perpendicular to the geomagnetic field at 100 km altitude doppler spectra were obtained every 20 s with a range resolution of 600 m field perpendicular echoes appeared from 2130 to 2330 lt and from 0400 to 1100 lt times that correspond to postsunset and postsunrise period in the e region a preliminary examination of the doppler spectra indicates spectral widths of 50 120 m s 1 and the mean doppler velocities are well below the ion acoustic speed these spectral characteristics are consistent with those obtained in the equatorial and auroral electrojets and have been attributed to the gradient drift instability the echoes observed during the postsunset and postsunrise periods showed quite different morphologies in the time height distribution for this reason they are classified into two types continuous and quasi periodic the appearance of the continuous echoes was mainly continuous in time and situated between 90 and 100 km altitude during the postsunrise period the appearance of the quasi periodic echoes was intermittent with periods of 5 10 min and situated above 100 km altitude during the postsunset period the quasi periodic echoes showed phase propagation toward the radar while the averaged mean doppler velocity was away from the radar by measuring the time delays in echo regions from five directions an apparent westward motion approximately 120 m s 1 of the irregularity regions was estimated

paleoceanographic changes in the southern ocean off elephant island since the last glacial period links between surface water productivity nutrient utilization bottom water currents and ice rafted debris abstract to understand past changes in ocean cryosphere interactions in the southern ocean off the antarctic peninsula multi proxy analyses of three sediment cores located off elephant island were used to reconstruct changes in paleoproductivity nutrient utilization bottom current intensity and iceberg calving since the last glacial period the glacial period was characterized by low surface water productivity with high nutrient utilization indicating surface water stratification during the deglaciation surface water productivity increased with decreasing nutrient utilization implying that the increase is associated with increased nutrient supply from the subsurface water by enhancing antarctic circumpolar current acc influence as fronts migrate southward with warming abundant occurrence of grains 1 mm during the deglacial period indicates rapid ice sheet retreat with large scale melting and calving during the glacial period however coarse silt fine sand sized fraction represented ice rafted debris ird the different ird grain size characteristics are thought to be related to the ird source material characteristics regardless of ird input the running downcore correlation 5 to 9 point between sortable silt mean grain size and percentage showed that sediments are well sorted by bottom current however the cross plot of them showed different temporal relationships sediments were sorted by the acc and southwestward flowing bottom current along with southward migration of fronts and the acc southwestward flowing bottom current influence diminished whereas the acc influence increased particularly from 7 ka our results indicate that the sedimentary processes in the scotia sea largely depend on the regional interactions between the ocean and the cryosphere

similar glacial and interglacial export bioproductivity in the atlantic sector of the southern ocean multiproxy evidence and implications for glacial atmospheric co2 we present time series of export productivity proxy data including 230thex normalized deposition rates rain rates of 10be dissolution corrected biogenic ba and biogenic opal as well as authigenic u concentrations which are complemented by rain rates of total detrital fe and sea ice indicating diatom abundances from five sediment cores across the atlantic sector of the southern ocean covering the past 150 000 years the results suggest that 10be rain rates and authigenic u concentration cannot serve as quantitative paleoproductivity proxies because they have also been influenced by detrital particle fluxes in the case of 10be and bulk sedimentation rates sediment focussing and deep water oxygenation in the case of u the combined results of the remaining productivity proxies of this study rain rates of biogenic opal and biogenic ba in those sections without authigenic u and other previously published proxy data from the southern ocean 231pa 230th and nitrogen isotopes suggest that a combination of sea ice cover shallow remineralization depth and stratification of the glacial water column south of the present position of the antarctic polar front and possibly fe fertilization north of it have been the main controlling factors of export paleoproductivity in the southern ocean over the last 150 000 years an overall glacial increase of export paleoproductivity is not supported by the data implying that bioproductivity variations in the southern ocean are unlikely to have contributed to the major glacial atmospheric co2 drawdown observed in ice cores

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