benthic metazoan biomass community structure and bioturbation at three contrasting deep water sites on the northwest european continental margin size structure taxonomic composition and bioturbation potential of benthic metazoan communities were examined at three contrasting sites on the northwest european continental margin as part of a wider study of biogeochemical cycling in the deep sea benthic boundary layer sampling was conducted in the hatton rockall basin 1100 m depth on the north feni ridge 1920 m and in the south rockall trough 3580 m on two cruises bracketing the expected 1998 spring phytodetrital flux density and biomass of epibenthic megafauna declined with depth and were consistent with previous data from the deep northeast atlantic aggregations of the hexactinellid sponge pheronema carpenteri occurred at 1100 m the percentage contribution of suspension feeders to megafaunal biomass at the lower slope sites was much higher than expected for these depths macrofauna sensu stricto were consistently undersampled by a box corer relative to an hydraulically damped multiple corer estimated macrofaunal densities declined with depth polychaete trophic group structure was very different at the three sites with more small carnivores at 1100 m surface deposit and interface feeders at 1920 m and a higher representation of subsurface deposit feeders at 3580 m meiofaunal densities were low in comparison with published data from comparable depths in the northeast atlantic meiofaunal numbers increased at all three sites from may to july 1998 the increase at 1920 m was statistically significant and was associated with the greatest phytodetrital accumulation observed during the study period the relative contribution of the mega macro and meiofauna to benthic metazoan biomass did not vary consistently with depth and no trend was apparent in a review of data from other studies in the north atlantic depth related patterns in community size structure recorded from previous north atlantic studies were not all replicated suggesting the importance of local hydrodynamics and other environmental factors there was no obvious link between faunal parameters and biodiffusion coefficients or mixing modes estimated from radiotracer profiles diffusion analogue 210pbexcess profiles recorded at 3580 and 1100 m resulted from a combination of macrofaunal and megafaunal sediment mixing some of it advective at 1920 m a combination of deep megafaunal subduction and near surface concentration of macrofaunal feeding activity produced subsurface radiotracer peaks the poorly known burrowing megafauna probably play a significant role in bioturbation at all three sites

arctic sea ice variability in the context of recent atmospheric circulation trends abstract forty years 1958 97 of reanalysis products and corresponding sea ice concentration data are used to document arctic sea ice variability and its association with surface air temperature sat and sea level pressure slp throughout the northern hemisphere extratropics the dominant mode of winter january march sea ice variability exhibits out of phase fluctuations between the western and eastern north atlantic together with a weaker dipole in the north pacific the time series of this mode has a high winter to winter autocorrelation 0 69 and is dominated by decadal scale variations and a longer term trend of diminishing ice cover east of greenland and increasing ice cover west of greenland associated with the dominant pattern of winter sea ice variability are large scale changes in sat and slp that closely resemble the north atlantic oscillation the associated sat and surface sensible and latent heat flux anomalies are largest over the portions of the marginal sea ice zone in which the tr

physical controls on biogeochemical zonation in the southern ocean the primary control on the n s zonation of the southern ocean is the wind induced transport of the antarctic circumpolar current acc the acc divides the southern ocean into three major zones the subantarctic zone saz north of the acc the acc transport zone and the zone south of the acc saccz the zone of acc transport is most often subdivided into two zones the polar frontal zone pfz and the antarctic zone aaz but it may be appropriate to define more subzones or indeed only one at some longitudes to maintain geostrophic balance isopycnals must slope upwards to the south across the acc thus raising nutrient rich deep water closer to the surface as one goes polewards in addition silicate concentrations increase polewards along isopycnals because of diapycnic mixing with silicate rich bottom water surface silicate concentrations therefore decrease northwards from high levels in the saccz to low levels in the saz within the saz and pfz and even in the northern part of the aaz silicate levels may drop to limiting levels for siliceous phytoplankton production during summer nitrate concentrations also decrease northwards but only become limiting in the subtropical zone north of the saz the second circumpolar control is the changing balance of stratification with temperature dominating near surface stratification in the saz and salinity dominating further south because of fresh water input to the surface from melting ice this results in circumpolar features such as the subsurface 2 c temperature minimum and the subduction of the salinity minimum of antarctic intermediate water which are often but not always associated with frontal jets and large transports the transport of the acc is dynamically constrained into narrow bands the number and latitudinal location of which are controlled by the bathymetry and so vary with longitude thus it is not the fronts that are circumpolar but the total acc transport and scalar properties of the salinity and temperature fields evidence of summer silicate and nitrate uptake in all zones saz pfz and aaz shows that there is productivity despite their high nutrient low chlorophyll status blooms covering large areas say 400 km across in the pfz and aaz are found in the vicinity of submarine plateaux which suggest benthic iron fertilizatio

wind driven atlantic water flow as a direct mode for reduced barents sea ice cover abstractvariability in the barents sea ice cover on interannual and longer time scales has previously been shown to be governed by oceanic heat transport based on analysis of observations and results from an ocean circulation model during an event of reduced sea ice cover in the northeastern barents sea in winter 1993 it is shown that the ocean also plays a direct role within seasons positive wind stress curl and associated ekman divergence causes a coherent increase in the atlantic water transport along the negative thermal gradient through the barents sea the immediate response connected to the associated local winds in the northeastern barents sea is a decrease in the sea ice cover due to advection despite a subsequent anomalous ocean to air heat loss on the order of 100 w m 2 due to the open water the increase in the ocean heat content caused by the circulation anomaly reduced refreezing on a time scale of order one month furthermore it is found that coherent ocean heat transport anomalies occ

hydrolysable amino acids in sediments from the porcupine abyssal plain northeast atlantic ocean abstract the distributions of hydrolysable amino acids have been examined in replicate sediment cores from the porcupine abyssal plain in the northeastern atlantic ocean the amino acid concentrations in surficial sediments ranged from 11 4 to 12 6 mol g 1 dry sediment with a mean of 11 8 mol g 1 dry sediment and decreased with increasing sediment depth but showed a marked maximum between 20 and 40 mm albeit with significant variability in their abundance at that depth normalisation of the concentrations of hydrolysable amino acids to total organic carbon showed that the organic matter at the surface and in the sub surface maximum was relatively fresh the vertical concentration profiles of hydrolysable amino acids were also reflected by organic carbon and total nitrogen and are attributed to the transfer of relatively fresh organic matter from the sediment surface by bioturbation probably by large detritovores the depth of the zone of bioturbation i e 40 mm is consistent with the zone of maximum biological activity in the porcupine abyssal plain sediments

the transient atmospheric circulation response to north atlantic sst and sea ice anomalies abstract the objective of this study is to investigate the transient evolution of the wintertime atmospheric circulation response to imposed patterns of sst and sea ice extent anomalies in the north atlantic sector using a large ensemble of experiments with the ncar community climate model version 3 ccm3 the initial adjustment of the atmospheric circulation is characterized by an out of phase relationship between geopotential height anomalies in the lower and upper troposphere localized to the vicinity of the forcing this initial baroclinic response reaches a maximum amplitude in 5 10 days and persists for 2 3 weeks diagnostic results with a linear primitive equation model indicate that this initial response is forced by diabatic heating anomalies in the lower troposphere associated with surface heat flux anomalies generated by the imposed thermal forcing following the initial baroclinic stage of adjustment the response becomes progressively more barotropic and increases in both spatial extent an

arctic sea ice variability on a timescale of weeks and its relation to atmospheric forcing abstract northern hemisphere sea ice concentration 500 hpa height sea level pressure and 1000 500 hpa thickness at 7 day intervals are examined for the period 1972 1989 with emphasis on the winter season the temporal variability of sea ice concentration is largest along the climatological mean ice edge where its frequency distribution is strongly bimodal with ice free and ice covered conditions being observed much more frequently than partial ice cover these results confirm impressions based on visual inspection of satellite imagery that most of the variability in these regions is associated with the advance and retreat of the ice edge relationships between large scale patterns of atmospheric variability and sea ice variability are investigated making use of singular value decomposition of the temporal covariance matrix the analysis is conducted separately for the atlantic and pacific sectors in agreement with earlier studies based upon monthly mean data on sea ice concentration the strongest

live stained deep sea benthic foraminiferans in the western weddell sea trends in abundance diversity and taxonomic composition along a depth transect entire live foraminiferal assemblages i e including soft walled species were analysed using replicate subcores 3 45 cm2 surface area 0 1 cm layer 63 m fraction from multiple corer samples collected along a transect 1100 5000 m water depth of the continental slope and rise and adjacent abyssal plain to the east of the antarctic peninsula foraminiferans usually accounted for 61 83 of all meiofaunal organisms mean densities were highest 576 individuals indiv 10 cm 2 at 2100 m water depth and declined to 240 indiv 10 cm 2 at 5000 m although there was considerable variability between replicates at some stations e g 304 333 1090 indiv 10 cm 2 at 2100 m foraminiferan and metazoan meiofaunal densities were broadly coherent across the depth range sampled a total of 158 live foraminiferal species was recognized assemblages were most diverse on the lower slope with species numbers peaking at 3100 m and the fisher diversity index at 3100 4100 m monothalamous taxa increased in relative abundance from 8 at 1100 m to 33 at 4975 m and there was a corresponding decrease in the proportion of calcareous taxa from 65 to 16 on the continental slope 1100 3100 m the most abundant hard walled species were epistominella exigua adercotryma glomeratum alabaminella weddellensis and stetsonia hovarthi in the deeper samples 4100 5000 m a glomeratum became the dominant hard walled species important soft walled species included tinogullmia riemanni and bathyallogromia weddellensis in some samples from 1100 and 2100 m more than a third of the live assemblage was hidden within phytodetrital aggregates species such as e exigua a weddellensis and t riemanni were concentrated within these microhabitats many of the weddell sea species are typical bathyal and abyssal forms well known from the north atlantic and elsewhere the phytodetrital assemblages are strikingly similar to those reported from abyssal sites in the north atlantic our observations suggest that there are close faunal links between the deep water faunas of the weddell sea and those of other oceanic regions perhaps mediated by thermohaline circulation

dynamic and thermodynamic characteristics of atmospheric response to anomalous sea ice extent in the sea of okhotsk abstract influence of sea ice extent anomalies within the sea of okhotsk on the large scale atmospheric circulation is investigated through an analysis of the dynamic and thermodynamic characteristics of the response in an atmospheric general circulation model to specified anomalous sea ice cover significant response appears not only around the sea of okhotsk but also downstream over the bering sea alaska and north america in the form of a stationary wave train in the troposphere this remote response associated with wave activity flux emanating from the okhotsk area to the downstream is regarded as a stationary rossby wave generated thermally by the anomalous turbulent heat fluxes from the ocean surface as a result of the anomalous sea ice cover the pacific storm track in the model that extends zonally at 35 n is located too far south of the sea of okhotsk to exert substantial feedback forcing on the local and remote response since a similar stationary wave train is identified in the composite di

the effects of north atlantic sst and sea ice anomalies on the winter circulation in ccm3 part i main features and storm track characteristics of the response observed multidecadal trends in extratropical atmospheric flow such as the positive trend in the north atlantic oscillation nao index may be attributable to a number of causes this study addresses the question of whether the atmospheric trends may be caused by observed trends in oceanic boundary forcing experiments were carried out using the ncar atmospheric general circulation model with specified sea surface temperature sst and sea ice anomalies confined to the north atlantic sector the spatial pattern of the anomalous forcing was chosen to be realistic in that it corresponds to the recent 40 yr trend in sst and sea ice but the anomaly amplitude was exaggerated in order to make the response statistically more robust the wintertime response to both types of forcing resembles the nao to first order even for an exaggerated amplitude the atmospheric response to the sst anomaly is quite weak compared to the observed positive trend in the nao but has the same sign indicative of a weak positive feedback the anomalies in sea ice extent are more efficient than sst anomalies at exciting an atmospheric response comparable in amplitude to the observed nao trend however this atmospheric response has the opposite sign to the observed trend indicative of a significant negative feedback associated with the sea ice forcing additional experiments using sst anomalies with opposite sign to the observed trend indicate that there are significant nonlinearities associated with the atmospheric response the transient eddy response to the observed sst trend is consistent with the positive nao response with the north atlantic storm track amplifying downstream and developing a more pronounced meridional tilt in contrast the storm track response to the observed sea ice trend corresponds to a weaker southward shifted more zonal storm track which is consistent with the negative nao response

variability of north pacific sea ice and east asia north pacific winter climate abstract sea ice variability in the north pacific and its associations with the east asia north pacific winter climate were investigated using observational data two dominant modes of sea ice variability in the north pacific were identified the first mode features a dipole pattern between the sea of okhotsk and the bering sea the second mode is characterized by more uniform ice changes throughout the north pacific using the principal components of the two dominant modes as the indices pc1 and pc2 analyses show that the positive phases of pc1 feature a local warming cooling in the sea of okhotsk the bering sea which is associated with the formation of the anomalous anticyclone extending from the northern pacific to siberia accompanied by a weakening of the east asian jet stream and trough the associated anomalous southeasterlies easterlies reduce the climatological northwesterlies westerlies leading to warm and wet conditions in northeast china and central siberia the positive phases of pc2

observed interaction between pacific sea ice and the western pacific pattern on intraseasonal time scales the relationship between north pacific sea ice and the western pacific wp pattern is examined using wintertime observational data between 1978 and 2008 weekly averaged data are chosen to capture the characteristically short time scale of the wp a clear relationship is found between the wp and sea ice concentrations in the bering sea where the positive polarity of the wp is accompanied by increasing sea ice concentrations and the negative wp by decreasing sea ice concentrations sea ice concentrations in the sea of okhotsk however are shown to be largely insensitive to the strength of the wp feedback of bering sea sea ice concentrations onto the wp is tested by fitting weekly averaged observations to a vector autoregressive var model results from the var model indicate that feedback of bering sea sea ice onto the wp plays a significant role in the dynamics of the wp and that this feedback is positive that is wp induced changes in bering sea sea ice concentrations help sustain existing wp conditions thereby lengthening the time scale of variability of the wp

the application of cosi corr to determine dune system dynamics in the southern namib desert using aster data the coregistration of optically sensed images and correlation cosi corr algorithm was used to estimate dune migration and sand flux rates from a series of remotely sensed optical image pairs several areas of barchan and transverse dunes transport sand along definite pathways feeding the southern part of the namib sand sea from beaches and deflationary basins in the sperrgebiet we give a detailed description of the pre and post processing routines used for our cosi corr analysis and we evaluate the sub pixel dune migration results at the dune and dune field scales the best set of parameters for the application of the algorithm was systematically derived resulting in methodological refinements of the cross correlation windows the advanced spaceborne thermal emission and reflection radiometer aster sensor aboard the terra satellite provided the remote sensing imagery few comparisons have been made between dune migration measurements using cosi corr and other types of change detection analysis and few dune fields have served as test cases for cosi corr we suggest that analysis and interpretation of cosi corr output from aster data is more valuable if combined with other image analysis techniques such as manual digitization of dunes in a geographic information system gis processing of write memory function insertion wmfi imagery and multispectral image msi analysis of composition the dune migrations estimated from cosi corr results were validated using gis and wmfi and later msi analysis added an important regional contextual framework of sand transport pathways the synthesis of these works lends more confidence to understanding the namib dune system s dynamics and provides a basis for future comparisons to other dune fields copyright 2013 john wiley sons ltd

intra seasonal relationship between the northern hemisphere sea ice variability and the north atlantic oscillation 1 an intra seasonal relationship including a possible feedback is investigated between the north atlantic oscillation nao and a hemispheric scale seesaw like pattern dominant in sea ice variability over the wintertime northern hemisphere with one polarity in the bering and labrador seas and the other in the okhotsk and greenland barents seas statistical analysis using observational data suggests that a particular phase of nao and anomalous atmospheric circulation in the pacific during early winter contribute toward the development of the midwinter hemispheric sea ice seesaw in contrast the ice seesaw tends to damp the preexisting nao signal during late winter indicating a reversal of the phase relation between them this nao damping may be triggered by the pacific sea ice anomalies results from numerical experiments generally support this notion and further suggests a stationary rossby wave train emanated from the north pacific as a dynamical mechanism for damping the nao signal

distribution biomass and diversity of benthic foraminifera in relation to sediment geochemistry in the arabian sea the distribution biomass and diversity of living rose bengal stained deep sea benthic foraminifera 30 mu m were investigated with multicorer samples from seven stations in the arabian sea during the intermonsoonal periods in march and in september october 1995 water depths of the stations ranged between 1916 and 4425 m the distribution of benthic foraminifera was compared with dissolved oxygen organic carbon calcium carbonate ammonium silica chloroplastic pigment equivalents sand content pore water content of the sediment and organic carbon flux to explain the foraminiferal patterns and depositional environments a total of six species communities comprising 178 living species were identified by principal component analysis the seasonal comparison shows that at the western stations foraminiferal abundance and biomass were higher during the spring intermonsoon than during the fall intermonsoon the regional comparison indicates a distinct gradient in abundance biomass and diversity from west to east and for biomass from north to south highest values are recorded in the western part of the arabian sea where the influence of coastal and offshore upwelling are responsible for high carbon fluxes estimated total biomass of living benthic foraminifera integrated for the upper 5 cm of the sediment ranged between 11 mg corg m 2 at the southern station and 420 mg corg m 2 at the western station foraminifera in the size range from 30 to 125 mu m the so called microforaminifera contributed between 20 and 65 to the abundance but only 3 to 28 to the biomass of the fauna highest values were found in the central and southern arabian sea indicating their importance in oligotrophic deep sea areas the overall abundance of benthic foraminifera is positively correlated with oxygen content and pore volume and partly with carbon content and chloroplastic pigment equivalents of the sediment the distributional patterns of the communities seem to be controlled by sand fraction dissolved oxygen calcium carbonate and organic carbon content of the sediment but the critical variables are of different significance for each community

observed atmospheric response to cold season sea ice variability in the arctic abstractthe relation between weekly arctic sea ice concentrations sics from december to april and sea level pressure slp during 1979 2007 is investigated using maximum covariance analysis mca in the north atlantic sector the interaction between the north atlantic oscillation nao and a sic seesaw between the labrador sea and the greenland barents sea dominates the nao drives the seesaw and in return the seesaw precedes a midwinter spring nao like signal of the opposite polarity but with a strengthened northern lobe thus acting as a negative feedback with maximum squared covariance at a lag of 6 weeks statistical significance decreases when slp is considered in the whole northern hemisphere but it increases when north pacific sic is included in the analysis the maximum squared covariance then occurs after 8 weeks resembling a combination of the nao response to the atlantic sic seesaw and the aleutian icelandic low seesaw like response to in phase sic changes in the bering and okhotsk seas w

recent benthic foraminifera from the eastern south atlantic ocean dependence on food supply and water masses abstract sixty surface sediment samples from the eastern south atlantic ocean including the walvis ridge the angola and cape basins and the southwest african continental margin were analysed for their benthic foraminiferal content to unravel faunal distribution patterns and ecological preferences live stained with rose bengal and dead faunas were counted separately and then each grouped by q mode principal component analysis into seven principal faunal end members then multiple regression technique was used to correlate recent assemblages with available environmental variables and to finally differentiate between four principal groups of environmental agents acting upon the generation of benthic foraminiferal assemblages 1 seasonality of food supply and organic carbon flux rates together with oxygen content in the pore and bottom waters 2 lateral advection of deep water masses 3 bottom water carbonate corrosiveness and 4 energetic state at the benthic boundary layer and grain size composition of the substrate food supply and corresponding dissolved oxygen contents in the pore and bottom waters turned out to be the most important factors which control the distribution pattern of the recent benthic foraminifera at the continental margin in the zone of coastal upwelling and its mixing area benthic foraminiferal assemblages are dominated by stenobathic high productivity faunas characterized by elevated standing stocks low diversities and a large number of endobenthic living species at the continental shelf and upper continental slope the live assemblages are characterized by rectuvigerina cylindrica uvigerina peregrina s 1 uvigerina auberiana and rhizammina spp while the dead assemblages are characterized by cassidulina laevigata bolivina dilatata bulimina costata and b mexicana at the lower continental slope strong influence of high organic matter fluxes on the species composition is restricted to the area off the cunene river mouth where the live assemblage is dominated by uvigerina peregrina s 1 the corresponding dead assemblage by melonis barleeanum and m zaandamae in the adjacent areas of the lower continental slope the biocoenosis is characterized by reophax bilocularis and epistominella exigua which becomes dominant in the corresponding dead assemblage at the walvis ridge and in the abyssal angola and cape basins where organic matter fluxes are low and highly seasonal benthic foraminiferal assemblages reflect both the oligotrophic situation and the deep and bottom water mass configuration the top and flanks of the walvis ridge are inhabited by the rhizammina psammosphaera and r bilocularis live assemblages the corresponding dead assemblages are dominated by g subglobosa on the ridge top and e exigua on the flanks within the highly diverse e exigua dead assemblage several associated epibenthic species coincide with the core of nadw between about 1600 and 3700 m water depth these species include osangularia culter cibicidoides kullenbergi melonis pompilioides bolivinita pseudothalmanni and bulimina alazanensis the assemblages of the abyssal cape and angola basins are characterized by nuttallides umbonifer and a high proportion of agglutinated species these species are adapted to very low organic matter fluxes and a carbonate corrosive environment

impacts of the aleutian icelandic low seesaw on surface climate during the twentieth century abstract an interannual seesaw between the intensities of the icelandic and aleutian lows and its impact on surface climate observed during the twentieth century are investigated in a recent period from the late 1960s to the early 1990s their seesaw relationship was particularly apparent in late winter the associated anomalies in surface air temperature were significant in many regions over the extratropical northern hemisphere except in central portions of the continents the seesaw also modified the ocean atmosphere exchange of heat and moisture extensively over the north atlantic and north pacific by changing evaporation and precipitation since the seesaw formation was triggered by eastward propagation of stationary rossby wave trains from the north pacific into the north atlantic anomalous circulation over the north pacific in january was identified as a good precursor for february surface air temperatures in the euro atlantic sector during that period the seesaw relationship between the two low

propagation of the arctic oscillation from the stratosphere to the troposphere geopotential anomalies ranging from the earth s surface to the middle stratosphere in the northern hemisphere are dominated by a mode of variability known as the arctic oscillation ao the ao is represented herein by the leading mode the first empirical orthogonal function of low frequency variability of wintertime geopotential between 1000 and 10 hpa in the middle stratosphere the signature of the ao is a nearly zonally symmetric pattern representing a strong or weak polar vortex at 1000 hpa the ao is similar to the north atlantic oscillation but with more zonal symmetry especially at high latitudes in zonal mean zonal wind the ao is seen as a north south dipole centered on 40 45 n in zonal mean temperature it is seen as a deep warm or cold polar anomaly from the upper troposphere to 10 hpa the association of the ao pattern in the troposphere with modulation of the strength of the stratospheric polar vortex provides perhaps the best measure of coupling between the stratosphere and the troposphere by examining separately time series of ao signatures at tropospheric and stratospheric levels it is shown that ao anomalies typically appear first in the stratosphere and propagate downward the midwinter correlation between the 90 day low pass filtered 10 hpa anomaly and the 1000 hpa anomaly exceeds 0 65 when the surface anomaly time series is lagged by about three weeks the tropospheric signature of the ao anomaly is characterized by substantial changes to the storm tracks and strength of the midtropospheric flow especially over the north atlantic and europe the implications of large stratospheric anomalies as precursors to changes in tropospheric weather patterns are discussed

influence of low arctic sea ice minima on anomalously cold eurasian winters 1 influence of low arctic sea ice minima in early autumn on the wintertime climate over eurasia is investigated observational evidence shows that significant cold anomalies over the far east in early winter and zonally elongated cold anomalies from europe to far east in late winter are associated with the decrease of the arctic sea ice cover in the preceding summer to autumn seasons results from numerical experiments using an atmospheric general circulation model support these notions the remote response in early winter is regarded as a stationary rossby wave generated thermally through an anomalous turbulent heat fluxes as a result of anomalous ice cover over the barents kara seas in late autumn which tends to induce an amplification of the siberian high causing colder conditions over the far east the late winter cold anomalies over eurasia are also reproduced in our experiment which is associated with the negative phase of the north atlantic oscillation

temporal variability in living deep sea benthic foraminifera a review the deep ocean environment is disturbed by various processes many of which involve episodic inputs of organic matter some inputs e g phytodetritus at mid high latitudes in the north atlantic and northeast pacific are seasonally pulsed others e g falls of whale carcasses are irregular and unpredictable but together they evoke a variety of responses from the benthic biota in the case of deep sea foraminifera only those responses arising from seasonal food pulses have been fairly well documented the population dynamics of deep sea benthic foraminifera total live populations and individual species appear to be controlled largely by two inversely related parameters the flux of organic matter to the seafloor and concentrations of oxygen in the sediment porewater organic matter food inputs are most intense along bathyal continental margins and their oxidation often leads to the depletion of oxygen in surface sediments under these conditions foraminiferal faunas are dominated by low oxygen tolerant infaunal species the abundance of which fluctuate in response to seasonally varying amounts of food and oxygen at some sites e g sagami bay off japan species migrate up and down in the sediments tracking critical oxygen concentrations where oxygen concentrations are consistently low less than about 0 5 ml l 1 as in parts of the california borderland foraminifera may undergo population increases solely in response to food pulses in the abyssal north atlantic and in some continental margin areas of this ocean organic matter inputs are weaker and do not lead to oxygen depletion within surface sediments these systems are food limited and seasonal population fluctuations reflect the availability of food phytodetritus rather than oxygen here the species which respond to phytodetritus are mainly epifaunal or shallow infaunal opportunists which represent a small proportion of highly diverse communities 2 or 3 out of 120 species per core of 25 5 cm2 surface area seasonal phytodetrital pulses to the deep seafloor and hence foraminiferal population dynamics are not entirely predictable being dependent on climatic and upper ocean processes they vary in intensity from year to year and occasionally e g at the porcupine abyssal plain pap in 1997 fail to materialise foraminiferal responses to irregular non seasonal organic matter inputs are poorly known however there is some evidence that whale falls turbidite deposits hydrothermal vents and seeps are exploited by species typical of organically enriched low oxygen environments rather than by a specialised fauna fossil foraminiferal assemblages from bathyal and abyssal environments may provide evidence for an increase or decrease in the seasonality of surface production as well as for longer term changes in palaeoproductivity however the accurate interpretation of this record depends on filling the many gaps which remain in our understanding of relations between benthic foraminiferal ecology and seasonal phenomena in the deep ocean

sub mesoscale structure and the development of an eddy in the subantarctic front north of the crozet islands two stations only 20 km apart were observed to have quite different biological and biogeochemical characteristics the first site had low concentrations of chlorophyll and sufficient nutrients to support phytoplankton growth the second site had high concentrations of chlorophyll depleted nutrient concentrations and significant export of phytodetrital material had taken place the two sites were located in the polar frontal zone of the southern ocean to the northwest of the crozet islands the main physical difference between the two sites was in the depth of the mixed layer at the first site the mixed layer was deep and well mixed whereas the second site had a shallow stratified layer otherwise the horizontal gradients of physical properties were weak survey data from the surrounding area showed that the productive site was located on the edge of a filament of water drawn into a developing meander of the subantarctic front remotely sensed data provided a history of the growth of the meander in the subantarctic front and its development into an eddy in the polar frontal zone the dynamics associated with the filament in the meander were clearly important in driving the primary productivity as an intrusion of saline water into adjacent fresher water generated a shallow mixed layer and conditions suitable for phytoplankton growth the dynamics promoting conditions favourable to phytoplankton growth continued to operate as chlorophyll was enhanced in the eddy after the main bloom had died away later measurements suggested that the surface layer had changed from diatom dominated to a coccolithophore or calcite rich community

observed impact of atlantic sst anomalies on the north atlantic oscillation the large scale patterns of covariability between monthly sea surface temperature sst and 500 mb height anomalies z500 in the atlantic sector are investigated as a function of time lag in the ncep ncar reanalysis 1958 97 in agreement with previous studies the dominant signal is the atmospheric forcing of sst anomalies but statistically significant covariances are also found when sst leads z500 by several months in winter a panatlantic sst pattern precedes the north atlantic oscillation nao by up to 6 months such long lead time covariance is interpreted in the framework of the stochastic climate model reflecting the forcing of the nao by persistent atlantic sst anomalies a separate analysis of midlatitudes 208 708n and tropical 208s 208n sst anomalies reveals that the bulk of the nao signal comes from the midlatitudes a dipolar anomaly with warm sst southeast of newfoundland and cold sst to the northeast and southeast precedes a positive phase of the nao and it should provide a prediction of up to 15 of its monthly variance several months in advance since the forcing sst pattern projects significantly onto the tripole pattern generated by the nao these results indicate a positive feedback between the sst tripole and the nao with a strength of up to 25 mk 21 at 500 mb or 2 3 mb k21 at sea level additionally a warming of the tropical atlantic 208s 208n roughly symmetric about the equator induces a negative nao phase in early winter this tropical forcing of the nao is nearly uncorrelated with and weaker than that resulting from the midlatitudes and is associated with shorter lead times and reduced predictive skill

phytodetritus at the abyssal seafloor across 10 of latitude in the central equatorial pacific fresh phytoplankton detritus or phytodetritus has been reported from numerous deep seafloor sites in the temperate north atlantic and pacific oceans following seasonal phytoplankton blooms here we report the first strong evidence for abyssal accumulations of phytodetritus in the tropics in the central equatorial pacific in november december 1992 we obtained photographs and or sediment core samples from 61 abyssal stations water depths of 4280 5012 m between 12 s and 9 n along 140 w greenish flocculent material was recovered from the top of multiple core samples from 5 s to 5 n this material was most abundant from 2 s to 2 n in some areas forming continuous layers at least 5 mm thick and individual aggregates 1 cm in diameter the greenish material was clearly visible in bottom photographs as a green veneer that covered 95 of the seafloor near the equator and as individual cm scale aggregates covering 1 of the seafloor occasionally thick accumulations of cm scale aggregates occurred in biogenic pits cleared trails and feeding traces suggest that surface deposit feeding holothurians and echiurans grazed the greenish material microscopic examination of greenish material recovered from core tops and a burrow lumen revealed relatively intact diatoms including rhizosolenia sp and other microalgae with chloroplasts containing chlorophyll the greenish material was 1 12 5 organic carbon by weight i e 5 39 times richer than associated seafloor sediments it also contained high excess activities of 234th suggesting arrival from the water column in the previous 100 days samples of the greenish flocculent material from 0 and 5 n incubated at simulated environmental pressure and temperature with 14c labeled glutamate exhibited 5 fold higher rates of microbial activity than underlying sediments or brown floc from 9 n surface sediment samples which included the greenish flocculent material from 5 s to 5 n also contained significant concentrations of chlorophyll a and other chloropigments the chloropigment concentrations were roughly comparable to deep sea phytodetritus collected in the north atlantic we conclude that fresh organic rich phytodetritus was present on the seafloor from 5 s to 5 n along 140 w in november december 1992 with highest concentrations within 2 3 of the equator this material is likely to be a concentrated high quality food resource for deep sea microbes and metazoans we estimate an upper limit for the standing stock of this phytodetritus to be 2 6 mmol corg m2 this corresponds to 3 of the annual flux of organic carbon to the seafloor at these latitudes in 1992 because the degradation rate of this material appears to be very high its presence at the seafloor for several months per year could yield significant phytodetrital contributions to the annual seafloor organic carbon budget we also suggest that the phytodetrital aggregates are formed at intense convergence zones resulting from seasonal passage of tropical instability waves within 5 of the equator if so phytodetrital accumulations are likely to recur seasonally over broad areas of the abyssal equatorial pacific

northeastern atlantic benthic foraminifera during the last 45 000 years changes in productivity seen from the bottom up we studied benthic foraminifera from the last 45 kyr in the 63 mu m size fraction in biogeochemical ocean flux studies bofs cores 5k 50 degrees 41 3 n 21 degrees 51 9 w depth 3547 m and 14k 58 degrees 37 2 n 19 degrees 26 2 w depth 1756 m at a time resolution of several hundreds to a thousand years the deepest site showed the largest fluctuations in faunal composition species richness and benthic foraminiferal accumulation rates the fluctuations resulted from changes in abundance of epistominella exigua and alabaminella weddellensis in the present oceans these species bloom opportunistically when a spring plankton bloom results in seasonal deposition of phytodetritus on the seafloor the phytodetritus species had very low relative abundances and accumulation rates during the last glacial maximum a strong increase in absolute and relative abundance of e exigua and a weddellensis during deglaciation paralleled the decrease in abundance of the polar planktonic foraminifer neogloboquadrina pachyderma s and the increase in abundance of warmer water planktonic species such as globigerina bulloides this strong increase in relative abundance of the phytodetritus species and the coeval increase in benthic foraminiferal accumulation rate were thus probably caused by an increase in the deposition of phytodetritus to the seafloor and thus probably of surface productivity when the polar front retreated to higher latitudes the abundance of phytodetritus species decreased during the younger dryas but not to the low levels of fully glacial conditions during heinrich events periods of excessive melt water formation and ice rafting benthic accumulation rates were very low as were the absolute and relative abundances of the phytodetritus species supporting suggestions that surface productivity was very low during these events in both cores pullenia and cassidulina species were common during isotope stages 2 3 and 4 as were bolivinid buliminid and uvigerinid species high relative abundances of these species have been interpreted as indicative either of sluggish deep water circulation or of high organic carbon fluxes to the seafloor in our cores relative abundances of these species are negatively correlated with benthic foraminiferal accumulation rates and we can thus not interpret them as indicative of increased productivity during glacials the percentage of these low oxygen species calculated on a phytodetritus species free basis decreased slightly at deglaciation at 5k but not at 14k this suggests that decreased production of north atlantic deep water during the last glacial might have slightly affected benthic foraminiferal faunas in the eastern north atlantic at 3547 m depth but not at 1756 m in conclusion major changes in deep sea benthic foraminiferal faunas over the last 45 000 years in our cores from the northeastern atlantic were the result of changes in surface water productivity not of changes in deep water circulation productivity was lower during the glacial probably because of extensive ice cover

observed feedback between winter sea ice and the north atlantic oscillation abstract feedback between the north atlantic oscillation nao and winter sea ice variability is detected and quantified using approximately 30 years of observations a vector autoregressive model var and testable definitions of granger causality and feedback sea ice variability is quantified based on the leading empirical orthogonal function of sea ice concentration over the north atlantic the greenland sea ice dipole gsd which in its positive polarity has anomalously high sea ice concentrations in the labrador sea region to the southwest of greenland and low sea ice concentrations in the barents sea region to the northeast of greenland in weekly data for december through april the var indicates that nao index n anomalies cause like signed anomalies of the standardized gsd index g and that g anomalies in turn cause oppositely signed anomalies of n this negative feedback process operates explicitly on lags of up to four weeks in the var but can generate more persistent effects because o

controls on sediment geochemistry in the crozet region sediment composition to the north m10 east m5 and south m6 of the crozet plateau in the southern ocean polar frontal zone pfz reflects the dual control on input from the locally elevated upper water column export production and the proximity to the volcanic islands the magnitude of the major sedimentary components biogenic and lithogenic has been constrained down core the major lithogenic input to the three sites is identified as crozet island basalts based on linear extrapolation of sedimentary major element data to known island basalt domains high resolution x ray scanning of cores identified significant heterogeneity in the distribution of biogenic and lithogenic phases all sites are characterised by a significant heavy mineral fraction that has been identified by sem as biogenic barite and a mixed titanium iron oxide of volcanic origin there are multiple mass flow or turbidite events in the sediment records at each site that are inferred to be generally associated with sea level rise during deglaciation 230thexcess corrected holocene mass accumulation rates have been estimated for the sedimentary constituents calcium carbonate biogenic silica lithogenic material organic carbon authigenic u and baexcess the core top proxy records indicate that there is a significant enhancement of biogenic silica export both north and south of the plateau and lower values east of the plateau organic carbon export is highest to the north of the plateau lower within the high nutrient low chlorophyll hnlc waters to the south of the plateau and indistinguishable from the background pfz values to the east of the island the presence of the crozet plateau has a significant impact on organic carbon production and export throughout the holocene corroborating shipboard and remote observations of enhanced productivity in this region

factors influencing the distribution of subantarctic deep sea benthic foraminifera campbell and bounty plateaux new zealand abstract we investigate the combination of environmental factors that influence the distribution patterns of benthic foraminiferal tests 63 m in a topographically varied region crossed by both the subtropical and subantarctic fronts south east of new zealand seafloor sample sites extending from outer shelf 50 m to abyssal 5000 m depths are bathed by five different water masses and receive phytodetritus from subtropical subantarctic and circumpolar surface water masses eight mappable associations are recognised by q mode cluster analysis of the benthic foraminiferal census data similar associations are identified using cluster analysis based solely on the presence or absence of species canonical correspondence analysis and a correlation coefficient matrix were used to relate the faunal data to a set of environmental proxies these show that factors related to water depth especially decreasing food supply with increasing depth are the most significant in determining the overall foraminiferal distribution other contributing factors include surface water productivity and its seasonality bottom water ventilation energetic state of the benthic boundary layer and resulting substrate texture and bottom water carbonate corrosiveness three shallow water associations 50 700 m dominated by cassidulina carinata trifarina angulosa globocassidulina canalisuturata gavelinopsis praegeri and bolivina robusta occur in coarse substrates on the continental shelf and on the crests and upper slopes of four seamounts under well oxygenated high energy regimes and high food input three mid bathyal to upper abyssal associations 500 3300 m dominated by alabaminella weddellensis c carinata and epistominella exigua occur in biopelagic sandy mud beneath a region of strongly seasonal food supply with their composition influenced by total food flux ventilation oxygen minimum zone and bottom current strength an unusual lower bathyal association 1200 2100 m dominated by t angulosa and ehrenbergina glabra occurs in a belt of coarser sandy substrate that runs along the crest of the submarine plateaux slopes beneath the strongly flowing subantarctic front related currents a deep abyssal association 3500 5000 m dominated by nuttallides umbonifer and globocassidulina subglobosa occurs on the abyssal plain beneath oligotrophic lower circumpolar water south east of the subantarctic front and is strongly influenced by the cold carbonate corrosive conditions the faunal composition of this subantarctic region is most similar to adjacent southern new zealand but with the addition of a few significant antarctic elements e g e glabra globocassidulina crassa

recent benthic foraminiferal associations and ecology of the scotia sea and argentine basin abstract we investigated 88 surface sediment samples taken with a multiple corer from the southwestern south atlantic ocean for their live rose bengal stained and dead benthic foraminiferal content using q mode principal component analysis six live and six dead associations are differentiated live and dead association distributions correspond fairly well differences are mainly caused by downslope transport and selective test destruction in addition four potential fossil associations are calculated from the dead data set after removal of non fossilizable species these potential fossil associations are expected to be useful for paleoceanographic reconstructions environments are described in detail for the live and potential fossil associations and for selected species along the upper argentine continental slope strong bottom currents control the occurrence of live dead and potential fossil angulogerina angulosa associations here particles of a high organic carbon flux rate remain suspended below this high energy environment live dead and potential fossil uvigerina peregrina dominated associations correlate with enhanced sediment organic carbon content and still high organic carbon flux rates the live a angulosa and u peregrina associations correlate with high standing crops furthermore live and dead epistominella exigua nuttallides umbonifer associations were separated dominance of a nuttallides umbonifer potential fossil association relates to coverage by antarctic bottom water aabw and lower circumpolar deep water lcdw above the calcite compensation depth ccd three associations of mainly agglutinated foraminifera occur in sediments bathed mainly by aabw or cdw a reophax difflugiformis association was found in mud rich and diatomaceous sediments below the ccd a psammosphaera fusca association occurs in coarse sediments poor in organic carbon while a cribrostomoides subglobosus ammobaculites agglutinans association covers a more variable environmental range with mud contents exceeding 30 one single eggerella bradyi martinottiella communis association poor in both species and individuals remains from the agglutinated associations below the ccd if only preservable species are considered for calculation

cenozoic deep sea benthic foraminifers tracers for changes in oceanic productivity from late middle eocene through earliest oligocene high latitude regions cooled and by the end of the period continental ice sheets existed in antarctica diversity of planktonic microorganisms declined and modern groups of terrestrial vertebrates originated coeval faunal changes in deep sea benthic foraminifers have been related to cooling of deep waters and increased oxygenation cooling however occurred globally whereas species richness declined at high latitudes and not in the tropics the late eocene and younger lower diversity high latitude faunas typically contain common epistominella exigua and alabaminella weddellensis opportunistic phytodetritus exploiting species that indicate a seasonally fluctuating input of organic matter to the sea floor we speculate that the species richness gradient and increase in abundance of phytodetritus exploiting species resulted largely from the onset of a more unpredictable and seasonally fluctuating food supply especially at high latitudes

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

two abyssal sites in the southern ocean influenced by different organic matter inputs environmental characterization and preliminary observations on the benthic foraminifera abstract the abundance and diversity of the deep sea benthos are intimately linked to inputs of organic matter from the euphotic zone however it is often difficult to isolate the influence of surface productivity on benthic ecosystems from other environmental factors to this end two abyssal sites 4200 m water depth located under contrasting productivity regimes around the crozet plateau in the indian ocean sector of the southern ocean were sampled during the austral summer of 2004 2005 one site m5 east of the crozet isles was located beneath an area where there was an enduring seasonal phytoplankton bloom the second site m6 was located in an oligotrophic high nutrient low chlorophyll hnlc region to the south of the islands organic fluxes to the seafloor at these sites are thought to reflect the overlying productivities so that the benthic environment to the east of the islands was more eutrophic than at the southerly station all other environmental variables were similar at the two sites which are located just 460 km apart the concentrations of chlorophyll a and total organic carbon in the surficial sediments were significantly greater at the relatively eutrophic site east of the islands m5 than at the southerly site m6 total nitrogen however was similar at both sites significantly higher phytopigment concentrations were observed in the surficial sediments at the eutrophic site in particular the concentration of chlorophyll a was 3 times greater than at the southern site although the freshness of the labile component as measured by chlorophyll a to pheophorbide ratio was not different between sites these results confirm that fluxes of organic matter to the seafloor were higher at the site located beneath the bloom region this was reflected in the abundance and diversity of live stained and dead benthic foraminifera 125 m which were greater at the eutrophic site the species composition of the dead foraminiferal assemblages were similar at both sites however and were dominated by nuttallides umbonifera pullenia bulloides and melonis pompiloides an exception was the phytodetritus species epistominella exigua which was more abundant at the eutrophic site indicating a larger seasonal component to the export under the bloom region differences in the organic matter input regimes at the two sites appear to influence the abundance and diversity but not the overall species composition of the foraminiferal assemblages

atmospheric response to the north atlantic ocean variability on seasonal to decadal time scales the ncep twentieth century reanalyis and a 500 year control simulation with the ipsl cm5 climate model are used to assess the influence of ocean atmosphere coupling in the north atlantic region at seasonal to decadal time scales at the seasonal scale the air sea interaction patterns are similar in the model and observations in both a statistically significant summer sea surface temperature sst anomaly with a horseshoe shape leads an atmospheric signal that resembles the north atlantic oscillation nao during the winter the air sea interactions in the model thus seem realistic although the amplitude of the atmospheric signal is half that observed and it is detected throughout the cold season while it is significant only in late fall and early winter in the observations in both model and observations the north atlantic horseshoe sst anomaly pattern is in part generated by the spring and summer internal atmospheric variability in the model the influence of the ocean dynamics can be assessed and is found to contribute to the sst anomaly in particular at the decadal scale indeed the north atlantic sst anomalies that follow an intensification of the atlantic meridional overturning circulation amoc by about 9 years or an intensification of a clockwise intergyre gyre in the atlantic ocean by 6 years resemble the horseshoe pattern and are also similar to the model atlantic multidecadal oscillation amo as the amoc is shown to have a significant impact on the winter nao most strongly when it leads by 9 years the decadal interactions in the model are consistent with the seasonal analysis in the observations there is also a strong correlation between the amo and the sst horseshoe pattern that influences the nao the analogy with the coupled model suggests that the natural variability of the amoc and the gyre circulation might influence the climate of the north atlantic region at the decadal scale

the north pacific oscillation west pacific teleconnection pattern mature phase structure and winter impacts abstract the north pacific oscillation npo in sea level pressure and its upper air geopotential height signature the west pacific wp teleconnection pattern constitute a prominent mode of winter midlatitude variability the npo wp its mature phase expression is identified from principal component analysis of monthly sea level pressure variability as the second leading mode just behind the pacific north american variability pattern npo wp variability primarily on subseasonal time scales is characterized by a large scale meridional dipole in slp and geopotential height over the pacific and is linked to meridional movements of the asian pacific jet and pacific storm track modulation the hemispheric height anomalies at upper levels resemble the climatological stationary wave pattern attributed to transient eddy forcing the npo wp divergent circulation is thermal wind restoring pointing to independent forcing of jet fluctuations intercomparison of sea level pressure geopotential height and zonal

dissolved iron in the vicinity of the crozet islands southern ocean the annual phytoplankton bloom occurring north of the crozet plateau provides a rare opportunity to examine the hypothesis that natural iron fertilization can alleviate high nutrient low chlorophyll hnlc conditions normally associated with the southern ocean therefore during crozet natural iron bloom and export experiment crozex a large multidisciplinary study performed between november 2004 and january 2005 measurements of total dissolved iron dfe0 2 m were made on seawater from around the islands and atmospheric iron deposition estimated from rain and aerosol samples dfe concentrations were determined by flow injection analysis with n n dimethyl p phenylenediamine dihydrochloride dpd catalytic spectrophotometric detection dfe concentrations varied between 0 086 and 2 48 nm with low values in surface waters enrichment of dissolved iron 1 nm at close proximity to the islands suggests that the plateau and the associated sediments are a source of iron waters farther north also appear to be affected by this input of coastal and shelf origin although dissolved iron concentrations decrease as a function of distance to the north of the plateau with a gradient of 0 07 nm km 1 at the time of sampling using lateral and vertical diffusion coefficients derived from ra isotope profiles and also estimates of atmospheric inputs it was then possible to estimate a dfe concentration of 0 55 nm to the north of the islands prior to the bloom event which is sufficient to initiate the bloom the lateral island source being the largest component a similar situation is observed for other sub antarctic islands such as kerguelen south georgia that supply dissolved iron to their surrounding waters thus enhancing chlorophyll concentrations

the atmospheric response to realistic arctic sea ice anomalies in an agcm during winter abstract the influence of realistic arctic sea ice anomalies on the atmosphere during winter is investigated with version 3 6 of the community climate model ccm3 6 model experiments are performed for the winters with the most 1982 83 and least 1995 96 arctic ice coverage during 1979 99 when ice concentration estimates were available from satellites the experiments consist of 50 member ensembles using large ensembles proved critical to distinguish the signal from noise the local response to ice anomalies over the subpolar seas of both the atlantic and pacific is robust and generally shallow with large upward surface heat fluxes 100 w m 2 near surface warming enhanced precipitation and below normal sea level pressure where sea ice receded and the reverse where the ice expanded the large scale response to reduced enhanced ice extent to the east west of greenland during 1982 83 resembles the negative phase of the arctic oscillation north atlantic oscillation ao nao with a ridge over t

on the feedback of the winter nao driven sea ice anomalies satellite derived sea ice concentration sic and re analysed atmospheric data are used to analyse the potential feedback of the north atlantic oscillation nao driven sea ice anomalies in winter onto the atmosphere during 1979 2013 a maximum covariance analysis shows that this feedback can be detected with monthly data when sic leads the covariability between atlantic sic and the euro atlantic atmospheric circulation in february is statistically significant but shows intra seasonal differences the december sic influence is dominated by anomalies east of greenland with maximum amplitude in the greenland sea gs while the january sic influence is dominated by anomalies west of greenland in the davis strait labrador sea dl region the lagged atmospheric anomalies are likewise different a reduction of sic over gs in december is followed in february by a negative nao like pattern near the surface and a hemispheric signature in the upper troposphere thus acting as a negative feedback on the other hand a reduction of sic over dl in january is followed by an atmospheric anomaly over the north atlantic that projects on the positive phase of the east atlantic pattern the dynamics associated with these atmospheric anomalies is described indicating that transient eddy activity is likely at work in settling the large scale patterns the role of concomitant north atlantic sea surface temperature anomalies is discussed

deep sea benthic foraminiferal assemblage response to a surface ocean productivity gradient a test a transect of samples from the eastern equatorial pacific where surface ocean productivity is the only changing environmental variable was used to test the response of benthic foraminiferal assemblages to an open ocean productivity gradient the transect runs along the east pacific rise from the highly productive waters near the equator to the oligotrophic south pacific subtropical gyre surface sediment benthic assemblages show progressive change along the transect with strong compositional shifts corresponding to the rapid productivity gradient near the equator and to the position of the southern convergence near 18 19 s the relationship of the assemblages to surface ocean productivity was tested by statistical regression of quantitative estimates of productivity on the assemblage principal component scores calculated for each sampling location the regression yielded an r squared of 0 87 demonstrating a clear relationship between surface ocean productivity and deep sea benthic foraminiferal assemblage composition the species most important to this relationship display a consistent response to oceanic productivity for long stretches of geologic time this conservative behavior and the results of the regression analysis indicate that benthic foraminiferal assemblages can be used to estimate surface ocean productivity for the geologic past

bioturbation geochemistry and geotechnics of sediments affected by the oxygen minimum zone on the oman continental slope and abyssal plain arabian sea abstract we investigate the way the oxygen minimum zone omz alters interactions between bioturbation and sediment geochemistry and geotechnical properties sediments are compared within and below the omz on the oman continental slope and adjacent abyssal plain during the post monsoonal autumn season quantitative measurements were made of eh and ph of total organic matter tom and carbonate of water content and shear strength and of bioturbation structures in vertical profiles of subcores taken from spade box core samples the omz stations had distinctively low redox conditions and high carbonate content and different geotechnical properties and different bioturbation structures than stations below the omz on the abyssal plain these differences are related to the degree of anoxia and to water depth within the omz eh ph and carbonate increased with water depth and tom and water content decreased we also noted the presence of subsurface sediment heterogeneity on the continental slope within the omz in the omz eh water content and bioturbation decreased with increasing sediment depth there was a slight decrease in ph in the top 5 cm at all stations shear strength nearly always increased with increasing sediment depth at each water depth correlations show down core trends in these parameters while across all water depths correlations were significant at deeper sediment depths 20 30 cm an eh ph diagram identified two water depth groupings 391 1008 and 1265 3396 m cluster analysis showed the upper and lower sediment depths form separate clusters the break occurring at 4 7 5 cm while there are also distinct clusters related to water depth we relate our results to bottom water oxygen concentrations reported by other investigators and to regional scale geochemical processes

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

microbial respiration and diffusive oxygen uptake of deep sea sediments in the southern ocean antares i cruise abstract benthic microbial respiration and diffusive oxygen uptake were measured and used to calculate rates of aerobic mineralisation of organic matter and concomitant co2 production at the sediment water interface in the abyssal region of the crozet basin this study was part of the antares i cruise on the r v marion dufresne in the permanent open ocean zone of the southern ocean on a south to north transect from 52 to 42 s in the indian ocean at all stations oxygen penetrated much deeper than 10 cm aerobic respiration was maximal in the top 1 cm 10 96 nmol cm 3 day 1 was always detectable down to 5 cm depth and at some stations even to 10 cm depth total depth integrated oxygen consumption corresponded to within 25 of the diffusive oxygen uptake across the sediment water interface the shape of the profile indicated that a diffusive downward flow of oxygen occurred below 10 cm depth thymidine incorporation experiments suggested that bacteria present at depths of between 15 cm and 1 m in the sediment were in a dormant state or growing extremely slowly however rapid dna synthesis started within 4 h after thymidine was added indicating a deep bacterial biosphere in southern ocean sediments it is proposed that the diffusive downward flux of oxygen below 10 cm depth sustains aerobic bacterial metabolism and survival at greater depths along the transect the total depth integrated oxygen uptake peaked at 48 s close to the polar front and at the subantarctic and subtropical convergence frontal zone nevertheless in general the differences were not very pronounced the average value of depth integrated microbial o2 consumption was 0 61 mmol m 2 day 1 which is equivalent to a carbon mineralisation rate of 2 3 g c m 2 year 1 these observations together with relatively high electron transport system ets values 6 6 l o2 g 1 h 1 and bacterial numbers 4 109 g 1 dry weight in the top centimeter imply that this region is less oligotrophic than previously assumed

benthic foraminiferal assemblages from the eastern south atlantic polar front region between 35 and 57 s distribution ecology and fossilization potential abstract surface sediment samples taken with a multiple corer from the polar front region along two profiles in the eastern south atlantic sector between 35 and 57 s have been investigated for their benthic foraminiferal content live fauna was differentiated from the death assemblage based on the dead assemblages potential fossil assemblages dead fauna reduced by non resistant agglutinants were calculated for comparison with upper neogene core material the distribution of the potential fossil assemblages defined byq mode principal component analysis mirrors the recent hydrographic as well as the trophic situation in the eastern south atlantic ocean circulation and productivity two southern component bottom water faunas reflect the northward flow of antarctic bottom water aabw and lower circum polar deep water lcdw an assemblage dominated by the arenaceousmultifidella nodulosa below the calcite compensation depth ccd and anuttallides umbonifer dominated assemblage above the ccd in the region of highest bio silicious primary productivity south of the polar front and north of the winter sea ice limit these faunas are overprinted by a southern high productivity fauna dominated by infaunal species such aspullenia bulloides melonis pompilioides andm zaandamae north atlantic deep water nadw meets the circum polar deep water cdw at intermediate depth as reflected in the distribution of the northern component deep water fauna dominated byepistominella exigua the high productivity assemblage overprinting this fauna the northern high productivity fauna is dominated by the shallow endobenthicbulimina aculeata a strong bottom current fauna dominated byangulogerina angulosa characterizes areas between 400 and 900 m water depth with sandy sediment independent from water mass characteristics and food supply

antares i a biogeochemical study of the indian sector of the southern ocean abstract the first expedition of the antares program the french contribution to southern jgofs investigated the biology and the chemistry of the benthic environment and the water column in a region located between 60 s 72 e and 39 s 55 e in this special issue we present a detailed description of the transports of water masses across the polar front zone which are corroborated by chemical and microbial tracer studies a description of the sediment water interface bridging biological chemical and microbial studies and new insights into the diagenesis of biogenic silica

large scale circulation around the crozet plateau controls an annual phytoplankton bloom in the crozet basin the circulation in the vicinity of the crozet plateau in the southwest indian ocean sector of the southern ocean is examined using hydrographic sections argo floats surface drifters and satellite altimetry all four techniques confirm that a major branch of the antarctic circumpolar current the subantarctic front saf flows anticyclonically round the del cano rise west of the crozet plateau i e eastward to the south of the del cano rise then northward and sometimes northwestward into the crozet basin before turning back eastward in a combined front with the agulhas return current and the subtropical front this s bend in the saf is a permanent feature controlled by the bathymetry as has been inferred previously by pollard and read pollard r t read j f 2001 circulation pathways and transports of the southern ocean in the vicinity of the southwest indian ridge journal of geophysical research 106 c2 2881 2898 similar but much weaker anticyclonic flow is found round the crozet plateau itself with no more than 5 10 106 m3 s 1 turning north to the east of the crozet islands circulation north of the crozet plateau between the plateau and the s bend of the saf is extremely weak fed only by anticyclonic meanders breaking off the saf into the area from the west or north and occasional input from the northward partially wind driven i e ekman flow south and east of the islands in consequence of the weak circulation dissolved iron from the land or sediments of the crozet plateau and islands can build up during the winter in the polar frontal zone between crozet and the saf which gives rise to an annual bloom in this area biological evidence from satellite images and from phytoplankton and zooplankton distributions supports the circulation pattern we develop this pattern confirms that patchiness of productivity in the bloom area results from close juxtaposition of water that has entered the area from the west from the saf and from the south and east after flowing past the islands flow from the south and east has had a chance to entrain iron from the islands and sediments whereas flow from the west has not

microphyte pigments and resting spores at the water sediment interface in the subantarctic deep sea indian sector of the southern ocean during the antares i cruise april may 1993 in the indian sector of the southern ocean deep sea sediments were collected using a multiple gravity corer in the polar frontal zone pfz and frontal zone between crozet and kerguelen islands and in the permanently open ocean zone pooz south west of kerguelen and heard islands microphyte biomass indicators chl a b c and related phaeopigments measured by spectrofluorometry tests on natural fluorescence and detection of encysted diatoms observed by scanning electron microscopy sem were carried out on both sediment and overlying fluff whenever present evaluation of the phytoplankton biomass in the overlying surface water masses also was performed at each sampling station the phytoplankton biomass was on the whole very low and decreased from north to south 0 25 0 10 g 1 1 chl a with a maximum on the frontal zone whereas the sediment water interface of the southern sampling stations pooz was pigment enriched a consistent bioclastic fluffy layer was only present in the pooz stations up to 13 g 1 1 chl a 157 g 1 1 phaeo a biodeposition of this type was very thin or absent north of the pf polar front illustrating stronger advection in the northern part of the study area hydrodynamic studies of the crozet basin and the presence of benthic pennate coastal diatoms at the sediment interface of these northern stations further suggest increased advective activity in the north surficial sediments first 5 mm also were enriched with pigments in the pooz up to 0 15 g g 1 dw chl a 3 5 g g 1 dw phaeo a whereas in the pfz the chl a concentrations were insignificant pigment gradients in the sediments particularly well marked in the pooz indicate the absence of a secondary intense reworking such as bioturbation or resuspension nevertheless also in the pooz an unusual and well preserved megafaunal faecal cast was sampled and analysed sediments at southern stations 50 55 s 56 75 e 3600 4700 m depth were the most enriched with encysted microphytic cells mainly diatoms belonging to the genus chaetoceros this was related primarily to the presence of a fluffy layer composed mainly of well preserved detritic frustules of various diatom genera including robust nitzschia and thalassiosira as well as chains of delicate chaetoceros corethron and rhizosolenia well preserved coccoliths and silicoflagellates also were noticeable in the fluffs revival tests cultures on f2 medium initiated with samples from the water sediment interface were positive for the southern stations leading to low diversity diatom assemblages dominated by the genera chaetoceros and nitzschia

the role of rossby wave breaking in shaping the equilibrium atmospheric circulation response to north atlantic boundary forcing abstract the role of rossby wave breaking rwb is explored in the transient response of an atmospheric general circulation model to boundary forcing by sea ice anomalies related to the north atlantic oscillation nao when the ncar community climate model version 3 was forced by an exaggerated sea ice extent anomaly corresponding to one arising from a positive nao a localized baroclinic response developed and evolved into a larger scale equivalent barotropic pattern resembling the negative polarity of the nao the initial baroclinic response shifted the phase speeds of the dominant eddies away from a critical value equal to the background zonal flow speed resulting in significant changes in the spatial distribution of rwb the forcing of the background zonal flow by the changes in rwb accounts for 88 of the temporal pattern of the response and 80 of the spatial pattern of the zonally averaged response although results here focus on one experiment this rwb critical line mechanism appears to be