iron control of past productivity in the coastal upwelling system off the atacama desert chile 1 biogenic opal and organic carbon vertical rain rates in sediment cores reveal a strong cyclicity in the productivity of the upwelling system off presently arid northern chile during the last 100 000 years changes in productivity are found to be in phase with the precessional cycle 20 000 years and with inputs of iron from the continent during austral summer insolation maxima increased precipitation and river runoff in the region appear to have brought high inputs of iron mainly from the andes to the coastal ocean enhancing primary productivity there we interpret our results as providing evidence for iron control of past productivity in this upwelling system and for a tight link between productivity and orbital forcing at midlatitudes

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

particulate organic carbon fluxes to the ocean interior and factors controlling the biological pump a synthesis of global sediment trap programs since 1983 particulate organic carbon poc is vertically transported to the oceanic interior by aggregates and their ballasts mainly caco3 and biogenic opal with a smaller role for lithogenic aerosols through the mesopelagic zone diel migrating zooplankton communities effect vertical transport and remineralization of poc in the upper layers of the ocean below 1 5 km the presence of zooplankton is reduced and thus the aggregates travel mainly by gravitational transport we normalized the fluxes of poc caco3 and biogenic opal from data published on samples collected at 134 globally distributed bottom tethered time series sediment trap ts trap stations to annual mole fluxes at the mesopelagic bathypelagic boundary m b at 2 km and defined them as fm bcorg fm bcinorg and fm bsibio using this global data set we investigated 1 the geographic contrasts of poc export at m b and 2 the supply rate of co2 to the world mesopelagic water column fm bcorg varies from 25 pacific warm pool to 605 divergent arabian sea mmolc m 2 yr 1 fm bcinorg varies from 8 high latitude polar oceans or 15 pacific warm pool to 459 divergent arabian sea mmolc m 2 yr 1 and fm bsibio the most spatially temporally variable flux ranges from 6 north atlantic drift to 1118 pacific subarctic gyre mmolsi m 2 yr 1 the oceanic region exhibiting the highest poc flux over a significantly large region is the area of the north pacific boreal gyres where the average fm bcorg 213 fm bcinorg 126 and fm bsibio 578 mmol m 2 yr 1 fm bcorg and fm bcinorg are particularly high in large upwelling margins including the divergent arabian sea and off cape verde one of the data sets showing the lowest flux over a significant region basin is fm bcorg 39 fm bcinorg 69 and fm bsibio 22 mmol m 2 yr 1 in the north pacific subtropical tropical gyres pan atlantic average fluxes are similar except fm bsibio fluxes are even lower where corg cinorg and sibio cinorg are 1 defines the carbonate ocean and where these ratios are 1 defines the silica ocean the carbonate ocean occupies about 80 of the present world pelagic ocean between the two major oceanographic fronts the north pacific polar front and the antarctic polar front and the silica ocean is found on the polar sides of these fronts the total global annual fluxes of fm bcorg fm bcinorg and fm bsibio at m b calculated by parameterizations of the export flux data from 134 stations are surprisingly similar 36 2 33 8 and 34 6 teramol yr 1 120 112 and 114 mmol m 2 yr 1 respectively resulting in a near uniform binary ratio between the above three elements of about one the global ternary ratios estimated from 152 ts trap samples of the three elements are 35 32 33 from our global fm bcorg and a published model estimate of the global export production we estimate the regeneration rate of co2 through the mesopelagic zone by the biological pump is 441 teramolc yr 1 based on our global fm bcinorg and recently estimated global primary production of pic 36 86 teramolc yr 1 of pic is assumed to be dissolved within the upper 2 km of the water column

the dangeard and explorer canyons south western approaches uk geology sedimentology and newly discovered cold water coral mini mounds the celtic margin is a complex area in terms of sedimentary dynamics and evolution with a number of submarine canyons dissecting the continental slope and outer continental shelf the complex terrain and diverse range of sea bed sediments play a part in submarine canyons being described as areas of high habitat heterogeneity this study has concentrated on the heads of two canyons dangeard also known as dangaard and explorer first named here located in uk territorial waters in water depths between 138 and 1165 m multibeam echosounder 2d reflection seismic and photographic ground truthing data have been combined to map the sea bed geomorphology sedimentary features and canyon megafauna of these canyons in addition two previously unknown provinces of cold water coral cwc mini mounds were discovered on the interfluves of the dangeard and explorer canyons the study area comprises a dendritic network of gullies feeding into the canyon thalwegs amphitheatre rims where slope angles are commonly in excess of 20 occur along the margins and heads of both canyons and are interpreted as drainage basins indicative of retrogressive mass wasting in a shelfward direction the cwc mini mounds occur in water depths between 250 m and 410 m with more than 400 mounds identified they are up to 3 m in height and 50 150 m in diameter with no sub surface expression suggesting these mounds are in geological terms relatively young and possibly holocene in age biological analyses revealed that the mounds form a habitat for ophiuroids and munida associated with lophelia pertusa coral rubble suggesting these mini mounds are not present day living features

sources and exchanges of mercury in the waters of the northwestern mediterranean margin abstract ocean margins are focal regions in terms of mercury hg exchanges between the continent and the open sea the aim of this paper is to describe the distribution and partition of hg between the gaseous dissolved and particulate phases in the waters of the northwestern mediterranean nwm margin in order to assess the hg sources and exchanges within the continuum between the continental shelf gulf of lions and the open sea northern gyre mean standard deviation of total hg species hgt concentrations in unfiltered water samples were 1 52 1 00 pmol l 1 n 36 in the inner shelf 1 09 0 15 pmol l 1 n 30 along the slope and 1 10 0 13 pmol l 1 n 99 in the northern gyre the dissolved phase the hg from the open sea water is the largest hg input to the gulf of lions 5 7 kmol yr 1 whereas inputs from the riverine source account for 3 4 kmol yr 1 and atmospheric deposition for less than 0 5 kmol yr 1 the hg accumulated in the sediments of the shelf is 4 5 kmol yr 1 including 0 6 1 7 kmol yr 1 in the rhone prodelta sediments the evasion to the atmosphere represents a hg flux of 2 6 kmol yr 1

changes in biological productivity and ocean climatic fluctuations during the last 1 5 kyr in the humboldt ecosystem off northern chile 27 s a multiproxy approach abstract a sedimentary box core biac072014 collected in a coastal environment in the humboldt current ecosystem hce inglesa bay 27 s northern chile was used to reconstruct the changes in biological productivity and ocean climate fluctuations during the last 1 5 kyr via geochemical mineralogical and micropaleontological analyses from 510 ce to 930 ce el nino like conditions prevailed while during the medieval climate anomaly mca 950 ce to 1450 ce la nina like conditions predominated this pattern might have resulted from weakening strengthening of the walker cell contraction expansion of the south pacific sub tropical high spsh and a predominance of warm cold phases of the pacific decadal oscillation pdo between 1820 ce and the present inglesa bay experienced a reduction in the oxygen minimum zone omz intensity and biological productivity an increase in the detritic input and a decrease in sea surface temperature sst despite the regional intensification and secular cooling 14 s and 27 s of coastal upwelling the similarity between the reduction in biological productivity and omz intensity in this region and that in the central zone of chile 36 s suggests that inglesa bay acts a transition zone in relation to the oceanographic behaviour of the hce the reduction in the omz intensity and biological productivity during the last 200 years could be explained by greater subsurface ventilation in intermediate depths due to more northward displacement of the subduction region of the eastern south pacific intermediate water espiw near 30 s in response to the strengthening of the circulation of the subtropical gyre the coastal cooling observed in the northern section of hce during the current warm period suggests that it is not possible to demonstrate that el nino like conditions promoted the reduction in biological productivity and omz intensity in inglesa bay

detecting subtle seasonal transitions of upwelling in north central chile abstractbiological productivity in the ocean along the chilean coast is tied to upwelling that is primarily forced by equatorward wind stress and wind stress curl on the ocean surface southerly alongshore flow is driven by the southeast pacific sep anticyclone and its intensity and position vary on a range of time scales variability of the sep anticyclone has been linked to large scale circulations such as el nino southern oscillation and the madden julian oscillation the actual timing duration and nature of the seasonal meridional drift of the sep anticyclone are associated with the onset demise and strength of the local upwelling season seasonal variation is especially marked at the punta lavapie 37 s upwelling focus where there is a clear upwelling season associated with a change of the cumulative upwelling index cui slope between positive and negative the punta lengua de vaca 30 s focus typically exhibits upwelling year round and has less distinct transitions making it more difficu

northeastern pacific oxygen minimum zone variability over the past 70 kyr impact of biological production and oceanic ventilation 1 during the last glacial period the oxygen minimum zone omz within the northeastern pacific ocean strengthened and weakened on a millennial time scale demonstrating a tight linkage with northern high latitude climate although the precise mechanisms responsible remain unknown core md02 2508 retrieved off baja california was analyzed for major and trace elements br ca ti fe mn and sr using a xrf scanner and redox sensitive trace elements cu ni cd as v cr mo and u using the icp ms the trace element content the fe ti ratio and br based organic carbon exhibit higher values during the holocene and during warm dansgaard oeschger events than during the last glacial maximum lgm stadials and heinrich h events a principal component analysis of the element al ratio indicated that the following two main factors controlled the chemical composition of the sediments 1 export production as represented by organic carbon that was lower during cold periods and 2 regional intermediate water oxygenation as represented by u and mo variability that was not supported by a change in export production the latter suggests that intermediate water oxygenation improved during h events but slightly deteriorated during late marine isotope stage mis 3 and mis 2 a local biogeochemical effect forced by atmospheric processes impacted the lgm and h events in the same manner whereas regional intermediate oceanic circulation varied in an opposite manner during the lgm and h events possibly as a result of the global reorganization of intermediate water circulation during the lgm

a review of nitrogen isotopic alteration in marine sediments key points use of sedimentary nitrogen isotopes is examined on average sediment 15n 14n increases approx 2 per mil during early burial isotopic alteration scales with water depth abstract nitrogen isotopes are an important tool for evaluating past biogeochemical cycling from the paleoceanographic record however bulk sedimentary nitrogen isotope ratios which can be determined routinely and at minimal cost may be altered during burial and early sedimentary diagenesis particularly outside of continental margin settings the causes and detailed mechanisms of isotopic alteration are still under investigation case studies of the mediterranean and south china seas underscore the complexities of investigating isotopic alteration in an effort to evaluate the evidence for alteration of the sedimentary n isotopic signal and try to quantify the net effect we have compiled and compared data demonstrating alteration from the published literature a 100 point comparison of sediment trap and surface sedimentary nitrogen isotope values demonstrates that at sites located off of the continental margins an increase in sediment 15n 14n occurs during early burial likely at the seafloor the extent of isotopic alteration appears to be a function of water depth depth related differences in oxygen exposure time at the seafloor are likely the dominant control on the extent of n isotopic alteration moreover the compiled data suggest that the degree of alteration is likely to be uniform through time at most sites so that bulk sedimentary isotope records likely provide a good means for evaluating relative changes in the global n cycle

sources and modes of terrigenous sediment input to the chilean continental slope abstract physical chemical and mineralogical properties of a set of surface sediment samples collected along the chilean continental slope 21 44 s are used to characterise present day sedimentation patterns and sediment provenance on the chilean margin despite the presence of several exceptional latitudinal gradients in relief oceanography tectonic evolution volcanic activity and onshore geology the present day input of terrigenous sediments to the chilean continental margin appears to be mainly controlled by precipitation gradients and source rock composition in the hinterland general trends in grain size denote a southward decrease in median grain size of the terrigenous corganic caco3 and opal free fraction which is interpreted as a shift from aeolian to fluvial sedimentation this interpretation is supported by previous observations of southward increasing bulk sedimentation rates north south trends in sediment bulk chemistry are best recognised in the iron fe and titanium ti vs potassium k and aluminium al ratios of the sediments that most likely reflect the contribution of source rocks from the andean volcanic arc these ratios are high in the northernmost part abruptly decrease at 25 s and then more or less constantly increase southwards to a maximum at 40 s

contrasting evolution of sea surface temperature in the benguela upwelling system under natural and anthropogenic climate forcings we present alkenone derived sea surface temperature sst records from three marine cores collected within the southern benguela upwelling system bus spanning the last 3 ka the sst evolution over the last 3 millennia is marked by aperiodic millennial scale oscillations that broadly correspond to climatic anomalies identified over the north atlantic region the bus sst data further suggest cooling and warming trends opposite to the temperature evolution in the moroccan upwelling region and in antarctica in contrast the last decades are marked by a cooling of unprecedented magnitude in both the benguela and moroccan upwelling systems which is not observed in the antarctic record these contrasted responses in atlantic upwelling systems triggered by natural and anthropogenic forcings shed light on how different climatic mechanisms are mediated by ocean atmosphere interactions and transmitted to the geological records of past and present climate changes citation leduc g c t herbert t blanz p martinez and r schneider 2010 contrasting evolution of sea surface temperature in the benguela upwelling system under natural and anthropogenic climate forcings geophys res lett 37 l20705 doi 10 1029 2010gl044353

enso tropical extratropical climate teleconnections and mechanisms for holocene debris flows along the hyperarid coast of western south america 17 24 s abstract el nino the warm phase of the enso cycle involves ocean climate anomalies in the tropical pacific ocean and in the extratropics which frequently result in heavy rainfall episodes along the equatorial and subtropical regions of western south america here we investigate meteorological mechanisms producing heavy rains floods and debris flows along the less known hyperarid coasts of southern peru and northern chile to evaluate the paleoclimate significance of holocene debris flow deposits our results reveal that heavy rainfall over the coast of southernmost peru occurs either during austral summer at the mature stage of el nino in connection with warmer sea surface temperatures and anomalous jet streams off northern chile or during the previous austral winter spring associated with equatorward shifted pacific south america psa atmospheric teleconnection patterns at antofagasta in northern chile such events occur almost exclusively in the latter season when deeper psa related anomaly poles extend their influence equatorwards beyond central chile during non el nino conditions short lived heavy rainfall episodes in southernmost peru can be associated with similar albeit weaker or less persistent circulation anomalies in addition to that a seasonally enhanced low level southerly flow provides orographic uplift rainfall favourable conditions by the andes at the 18 s coastal bend ultimately the trigger for rainfall events in all seasons and phases of the enso cycle was invariably connected with mid troposphere wave disturbances from mid latitudes the chronostratigraphy of debris flow deposits from both areas and its comparison with other paleoclimate records at the western side of the andes suggests that the enso related teleconnection patterns operated only during the second half of the holocene supporting an onset of modern el nino manifestations at 5300 5500 cal bp and increased frequency of major events during recent times we suggest that several debris flows dated between 12 900 and 8400 cal bp in southernmost peru previously interpreted as an indication of strong el nino events were associated with short and intense heavy rainfall episodes similar to those described here during the late winter spring season in non el nino conditions concomitant with stronger low level southerlies strengthened south eastern pacific subtropical anticyclone and intensified coastal upwelling

late quaternary changes in intermediate water oxygenation and oxygen minimum zone northern japan a benthic foraminiferal perspective 1 a strong oxygen minimum zone omz currently exists at upper intermediate water depths on the northern japanese margin nw pacific the omz results largely from a combination of high surface water productivity and poor ventilation of upper intermediate waters we investigated late quaternary history last 34 kyr of ocean floor oxygenation and the omz using quantitative changes in benthic foraminiferal assemblages in three sediment cores taken from the continental slope off shimokita peninsula and tokachi northern japan at water depths between 975 and 1363 m these cores are well located within the present day omz a region of high surface water productivity and in close proximity to the source region of north pacific intermediate water late quaternary benthic foraminiferal assemblages experienced major changes in response to changes in dissolved oxygen concentration in ocean floor sediments foraminiferal assemblages are interpreted to represent three main groups representing oxic suboxic and dysoxic conditions assemblage changes in all three cores and hence in bottom water oxygenation coincided with late quaternary climatic episodes similar to that known for the southern california margin these episodes in turn are correlated with orbital and millennial climate episodes in the greenland ice core including the last glacial episode bolling allerod b a younger dryas preboreal earliest holocene early holocene and late holocene the lowest oxygen conditions marked by dysoxic taxa and laminated sediments in one core occurred during the b a and the preboreal intervals suboxic taxa dominated mainly during the last glacial the younger dryas and most of the holocene dysoxic conditions during the b a and preboreal intervals in this region were possibly caused by high surface water productivity at times of reduced intermediate ventilation in the northwestern pacific remarkable similarities are evident in the late quaternary sequence of benthic foraminiferal assemblage change between the two very distant continental margins of northern japan and southern california the oscillations in omz strength reflected by these faunal changes were widespread and apparently synchronous over wide areas of the north pacific reflecting broad changes in intermediate water ventilation and surface ocean productivity closely linked with late quaternary climate change on millennial and orbital timescales

benthic foraminifera of a miocene canyon and fan abstract we present benthic foraminiferal assemblage data from an exhumed miocene canyon and fan system from the tabernas basin se spain the presence of good indicator taxa and unique assemblages occupying specific environments allows the distinction of slope canyon and fan environments within the tabernas basin by foraminiferal assemblages alone five assemblages are defined on the basis of the occurrence of the indicator taxa primary control on the distribution of these assemblages is consistent with trends of physical disturbance and consequent defaunation barren samples which are predominantly found in high energy parts of the proximal canyon are recognized as representing recently defaunated substrates i e early successional assemblages high diversity assemblages containing a high abundance of agglutinated taxa are recognised in the undisturbed slope sequences as being the regional equilibrium climax fauna intermediate between these end members are assemblages with low diversity dominated by calcareous taxa typically found in the relatively low energy canyon and fan environments which are recognized as representing the middle phases of the ecological succession two further assemblages a low diversity assemblage typified by cassidulina laevigata and bulimina costata and a very low diversity assemblage dominated 10 of all benthic tests by globobulimina spp are restricted to low energy parts of the canyon and fan and are absent from the proximal canyon and slope the composition of these assemblages indicate that nutrient supply oxygenation is a secondary control on the palaeoecology of the canyon system a conceptual model for the recolonisation of defaunated substrates in el buho canyon is proposed in which either an oligotrophic climax assemblage or a eutrophic climax assemblage can be achieved at the completion of recolonisation of defaunated substrates depending on environmental conditions

changes in the advection of antarctic intermediate water to the northern chilean coast during the last 970 kyr 1 the antarctic intermediate water aaiw is a key player in global scale oceanic overturning processes and an important conduit for heat fresh water and carbon transport the aaiw past variability is poorly understood mainly due to the lack of sedimentary archives at intermediate water depths we present records of benthic stable isotopes from sediments retrieved with the seafloor drill rig marum mebo at 956 m water depth off northern chile geob15016 27 29 48 s 71 07 58 w that extend back to 970 ka the sediments at this site are presently deposited at the boundary between aaiw and pacific deep water pdw for previous peak interglacials our results reveal similar benthic 13c values at site geob15016 and of a newly generated stack of benthic 13c from various deep pacific cores representing the average pdw this suggests unlike today the absence of aaiw at the site and the presence of nearly pure pdw in contrast more positive 13c values at site geob15016 compared to the stack imply a considerable aaiw contribution during cold phases of interglacials and especially during glacials besides we used three short sediment cores to reconstruct benthic 13c values from the aaiw core during the last glacial and found a 13c signature similar to today s assuming that this was the case also for the past 970 kyr we demonstrate that sea level changes and latitudinal migrations of the aaiw formation site can only account for about 50 of the full range of past 13c increases at site geob15016 during cold periods other processes that could explain the remaining of the positive 13c anomalies are increases in glacial aaiw production and or deeper convection of the aaiw with respect to preceding interglacials

reply to comment on crustal contributions to arc magmatism in the andes of central chile by w hildreth and s moorbath

seasonality of u k 37 temperature estimates as inferred from sediment trap data abstract the seasonality of sea surface temperatures sst estimated from the alkenone u k 37 index has been a debated issue since the development of the proxy using a compilation of sediment trap time series data from 34 sampling locations we show that the seasonality of maximum alkenone flux in sediment traps varies markedly across the oceans depending not only on latitude and light availability but also on local oceanographic conditions the seasonality of the alkenone flux to sediments may also be shaped by the complexity of sedimentation processes and a consistent globally applicable seasonal pattern is not apparent nevertheless u k 37 values display a world ocean scale correlation with mean annual ssts 0 m that closely resembles the standard calibration equation now established for modern surface sediment records thus with a few notable exceptions at oceanographic locations proximate to major hydrographic fronts it can be concluded that the integrated sedimentation patterns for u k 37 measured in sediment trap time series provide a measure of annual mean sst

anchovy population and ocean climatic fluctuations in the humboldt current system during the last 700 years and their implications a marine sedimentary record collected from 87 m water depth in a coastal environment of the humboldt current system mejillones bay 23 s northern chile was used to reconstruct the past 700 years of ocean climatic conditions and to study the influence of any changes on anchovy population dynamics we analyzed quartz organic carbon total nitrogen alkenones and fish scales four stratigraphic units in the sediment column correspond with fluctuations in these and other proxies low scale deposition rate sdr values from 1330 to 1420 suggest a low abundance of anchovy in this coastal environment three subsequent cycles of ca 170 years each showed an increase and decrease of anchovy populations which is in agreement with changes in the wind regime sea surface temperature and primary productivity since ca 1840 marked fluctuations of sdr have been observed probably as a consequence of the onset of a different oceanographic regime characterized by intensified southern winds and upwelling colder surface waters higher primary productivity and enhanced la nina like interdecadal variability an increase of the anchovy population was observed until halfway through the 20th century followed by a decrease even though water temperature decreased and primary productivity increased this situation is likely the consequence of the increased fishery activity that developed in this zone during the last 60 years after analyzing the results obtained for anchovy sdr we can determine that there is a relation between the abundance of this species and phases of the pacific decadal oscillation pdo in which an increase in the sdr coincides with a pdo cold phase while a decline coincides with a warm phase fast fourier transformation analysis applied to the time series obtained from the mejillones sediment core and to the north atlantic oscillation nao the pdo and the solar irradiance index time series shows three different decadal cycles 80 100 years 61 75 years and 45 48 years approximately furthermore the results of this study suggest that both the pdo and the nao and the biogeochemical markers of mejillones exhibit periodicities that fall within the 80 to 100 year gleissberg solar cycle indicating that global solar radiation plays a key role in the local ocean climatic processes and confirming teleconnection linkages between widely separated regions

organic matter budget in the southeast atlantic continental margin close to the congo canyon in situ measurements of sediment oxygen consumption abstract a study of organic carbon mineralization from the congo continental shelf to the abyssal plain through the congo submarine channel and angola margin was undertaken using in situ measurements of sediment oxygen demand as a tracer of benthic carbon recycling two measurement techniques were coupled on a single autonomous platform in situ benthic chambers and microelectrodes which provided total and diffusive oxygen uptake as well as oxygen microdistributions in porewaters in addition sediment trap fluxes sediment composition org c tot n caco3 porosity and radionuclide profiles provided measurements of respectively input fluxes and burial rate of organic and inorganic compounds the in situ results show that the oxygen consumption on this margin close to the congo river is high with values of total oxygen uptake tou of 4 0 6 3 6 0 5 mmol m 2 d 1 at 1300 and 3100 m depth respectively and between 1 9 0 3 and 2 4 0 2 mmol m 2 d 1 at 4000 m depth diffusive oxygen uptakes dou were 2 8 1 1 2 3 0 8 0 8 0 3 and 1 2 0 1 mmol m 2 d 1 respectively at the same depths the magnitude of the oxygen demands on the slope is correlated with water depth but is not correlated with the proximity of the submarine channel levee system which indicates that cross slope transport processes are active over the entire margin comparison of the vertical flux of organic carbon with its mineralization and burial reveal that this lateral input is very important since the sum of recycling and burial in the sediments is 5 8 times larger than the vertical flux recorded in traps transfer of material from the congo river occurs through turbidity currents channelled in the congo valley which are subsequently deposited in the lobe zone in the congo fan below 4800 m ship board measurements of oxygen profiles indicate large mineralization rates of organic carbon in this zone which agrees with the high organic carbon content 3 and the large sedimentation rate 19 mm y 1 found on this site the lobe region could receive as high as 19 mol c m 2 y 1 1 3 being mineralized and 2 3 being buried and could constitute the largest depocenter of organic carbon in the south atlantic

biogeochemical study of a coccolithophore bloom in the northern bay of biscay ne atlantic ocean in june 2004 abstract the present paper synthesizes data obtained during a multidisciplinary cruise carried out in june 2004 at the continental margin of the northern bay of biscay the data set allows to describe the different stages of a coccolithophore bloom dominated by emiliania huxleyi the cruise was carried out after the main spring phytoplankton bloom that started in mid april and peaked in mid may consequently low phosphate po4

late quaternary variability of sedimentary nitrogen isotopes in the eastern south pacific ocean 1 we present high resolution bulk sedimentary 15n data from the southern edge of the present day oxygen minimum zone of the eastern south pacific the record is interpreted as representing changes in water column nitrogen removal during the last 70 000 years we found significant fluctuations in the isotopic signal that suggest major reorganizations of the oxygen minimum zone at millennial timescales these fluctuations were not related to other millennial scale changes like the northern hemisphere s dansgaard oeschger climate swings or local changes in primary productivity so appear to be dictated by the southern hemisphere s climate rhythm this is preliminarily corroborated by an overall agreement between our 15n data and the sedimentary proxy of ice sheet dynamics in patagonia which is in turn correlated with surface water properties at the midlatitude subduction region of the eastern south pacific intermediate waters finally potential implications on late quaternary changes in atmospheric co2 concentrations are discussed

suspended sediment fluxes and transport processes in the gulf of lions submarine canyons the role of storms and dense water cascading contemporary suspended sediment transport was studied in seven submarine canyons of the gulf of lions gol current meters equipped with turbidity sensors were moored 4 m above bottom at 300 m depth in the canyon axis from november 2003 to may 2004 sediment transport events were monitored and studied in relation to forcing conditions there was a large flood in early december during which discharges from all of the coastal rivers increased by more than one order of magnitude a smaller flood of the rhone river occurred later in mid january followed by a persistent high river discharge that lasted until mid february there were also several e se storm events during the measurement period two of them causing large swell one in early december max hs 8 4 m coinciding with the major river flood andoneinlatefebruary maxhs 7m duringaperiodoflowerriverdischarge mostofthevariabilityindown canyoncurrentspeeds waslinkedtostrongdownwellinginducedbye sestormsandtocascadingofdenseshelfwaterinducedbynandnwwinds theintensity and timing of these processes strongly varied spatially eastern storms generated higher waves and induced stronger downwelling in the western than in the eastern sector of the gol shelf dense water cascading events were enhanced during eastern storms and they were also more intense in the western sector of the gol these events occurred frequently from january to may along the western canyons and from february to april along the eastern canyons from february to april they occurred simultaneously in all the canyons sediment transport was mainly down canyon and mostly concentrated during storm induced downwelling and dense water cascading events during the high river discharge season most of the newly supplied and resuspended sediment remained stored on theshelf however duringthelatefebruarystormandcascadingevent thestoredsedimentwasquicklyresuspendedandtransported mainly through the westernmost submarine canyon cap de creus following a flushing pattern later although minor storms and shelfdensewatercascadinghardlyincreasedsuspendedsedimentconcentrationswithinthecanyons theyinducedstrongnear bottom current velocities increasing down canyon sediment fluxes and generating small but significant sediment transport events most of the shelf canyon transfer took place during the late february storm and cascading event through the cap de creus canyon where the net suspended sediment flux was between one and two orders of magnitude higher than in the other canyons

210pb sediment radiochronology an integrated formulation and classification of dating models abstract environmental archives such as sediments banded corals and tree rings are widely used to reconstruct past environmental conditions of ecosystems in particular 210 pb has been used during more than 4 decades through dating of undisturbed sediment cores to study ecosystem changes during the last 100 yr since its inception diverse dating models have been proposed developed used and validated in numerous environments but their nomenclature and formulation is not homogenous in this work we emphasize that conceptual models used to date undisturbed sediment cores can be deduced from a single fundamental equation which relates excess 210 pb concentration in sediment its flux to the sediment surface and mass accumulation rate from this equation models were consistently named based on the main hypothesis used and using a unified and logical nomenclature dating equations were derived in detail we applied in detail most of the described models to a sediment core from mexico and uncertainty expressions were also included finally some recommendations to use the models are proposed we believe that this work can facilitate the use of 210 pb as a tool to date sediment cores in a more homogeneous way

benthic foraminifera as proxies of organic matter flux and bottom water oxygenation a case history from the northern arabian sea abstract benthic foraminifera have been quantified in two sediment cores from a topographic high murray ridge in the northern arabian sea one core is from a station within the present day oxygen minimum zone omz the other from a station below the omz changes in the intensity of the omz linked to monsoonal climate variability had a strong impact on benthic foraminiferal composition and accumulation rates at the shallower omz station 920 m an intensification of the omz resulted in lower diversities and high dominances of low oxygen tolerant species the deeper station 1470 m was far less affected though at least once during the last 225 000 years the benthic faunal composition and accumulation rates show evidence for a deepening of the base of the omz to a level close to or even below 1470 m we suggest that percentages of miliolids can be used for rapid reconstruction of periods of increased ventilation in the northern arabian sea and are a promising proxy for tracing changes in bottom and pore water oxygenation in general omz conditions are characterised by high abundances of deep infaunal species and increased burial efficiency of organic matter the proportion of deep infaunal species appears to be a measure for the anoxic burial efficiency of organic matter and not a direct measure for the arriving flux at the seabed results furthermore show that benthic foraminiferal accumulation rates cannot be used as a proxy for surface water productivity under the prevalence of severe dysoxia

marine radiocarbon reservoir effect along the northern chile southern peru coast 14 24 s throughout the holocene abstract through an extensive sampling and dating of pairs of associated shells and charcoal fragments combined with reanalysis of all the available previous data we reconstruct the evolution throughout the holocene of the regional marine radiocarbon reservoir effect r values along the northern chile southern peru area 14 24 s after elimination of the cases in which the terrestrial component yielded older ages than the marine shells to which they were associated the study is based upon data from 47 pairs of associated marine and terrestrial material our results suggest major changes in both the magnitude and variability range of r during the whole holocene period 1 between 10 400 and 6840 cal yr bp high values 511 278 yr probably result from a strengthened se pacific subtropical anticyclone and shoaling of equatorial subsurface waters during intensified upwelling events 2 between 5180 and 1160 cal yr bp lower values 226 98 yr may reflect a major influence of subtropical water and diminished coastal upwelling processes 3 during the last thousand years high values between 355 105 and 253 207 yr indicate an increased influence of 14 c depleted water masses and of enso for the early twentieth century a r value of 253 207 yr was calculated