oxygenation episodes on the continental shelf of central peru remote forcing and benthic ecosystem response abstract the interplay between the oxygen minimum zone and remotely forced oxygenation episodes determines the fate of the benthic subsystem off the central peruvian coast we analyzed a 12 year monthly time series of oceanographic and benthic parameters at 94 m depth off callao central peru 12 s to analyze i near bottom oxygen level on the continental shelf in relation to dynamic height on the equator 095 w and ii benthic ecosystem responses to oxygen change macrobiotic infauna meiofauna and sulphide oxidizing bacteria thioploca spp shelf oxygenation episodes occurred after equatorial dynamic height increases one month before consistent with the propagation of coastal trapped waves several but not all of these episodes occurred during el ninos the benthic biota responded to oxygenation episodes by undergoing succession through three major ecological states under strong oxygen deficiency or anoxia the sediments were nearly defaunated of macro invertebrates and thioploca was scarce such that nematode biomass dominated the macro and meiobiotas when frequency of oxygenation events reduced the periods of anoxia but the prevailing oxygen range was 10 20 mol l 1 mats of thioploca formed and dominated the biomass finally with frequent and intense 40 mol l 1 oxygenation the sediments were colonized by macrofauna which then dominated biomass the thioploca state evolved during the 2002 2003 weak en while the macrofauna state was developed during the onset of the strong1997 1998 en repeated episodes of strong oxygen deficiency during the summer of 2004 in parallel with the occurrence of red tides in surface waters resulted in the collapse of thioploca mats and development of the nematode state ecological interactions may affect persistence or the transition between benthic ecosystem states

variability of the north atlantic thermohaline circulation during the last interglacial period studies of natural climate variability are essential for evaluating its future evolution greenland ice cores suggest that the modern warm period the holocene has been relatively stable for the past 9 000 years much less is known about other warm interglacial periods which comprise less than 10 of the climate record during the past 2 5 million years here we present high resolution ocean sediment records of surface and deep water variables from the bermuda rise spanning the last interglacial period about 118 000 127 000 years ago in general deep water chemical changes are coincident with transitions in surface climate at this site the records do not show any substantial fluctuations relative to the much higher variability observed during the preceding and subsequent cool climates the relatively stable interglacial period begins and ends with abrupt changes in deep water flow we estimate using 230 th measurements to constrain the chronology that transitions occur in less than 400 years

organic matter oxidation and aragonite diagenesis in a coral reef abstract a combination of field and theoretical work is used to study controls on the saturation state of aragonite inside a coral reef framework a closed system ion speciation model is used to evaluate the effect of organic matter oxidation on the saturation state of aragonite the aragonite saturation state initially drops below 1 but becomes oversaturated during sulfate reduction the c n ratio of the organic matter affects the degree of oversaturation with n poor organic material resulting in a system more corrosive to aragonite precipitation of sulfide as fes strongly affects the aragonite saturation state and systems with much fes formation will have a stronger tendency to become oversaturated with respect to aragonite both precipitation and dissolution of aragonite are predicted at different stages of the organic reaction pathway if the model system is maintained at aragonite saturation field data from a coral reef framework indicate that the system maintains itself at aragonite saturation and model predicted changes in dissolved calcium follow those observed in the interstitial waters of the reef aragonite probably acts as a solid phase buffer in regulating the ph of interstitial waters because interstitial water in the reef has a short residence time the observed equilibration suggests rapid kinetics

origin of fine scale wind stress curl structures in the benguela and canary upwelling systems numerous studies have shown the primary importance of wind stress curl in coastal upwelling dynamics the main goal of this new analysis is to describe the quikscat surface wind stress curl at various scales in the benguela and canary upwelling systems the dominant spatial pattern is characterized by cyclonic curl near continental boundaries and anticyclonic curl offshore in association with equatorward alongshore upwelling favorable wind stress at a smaller scale we demonstrate the sensitivity of the quikscat wind stress curl to coastal processes related to sea surface temperature sst mesoscale fluctuations by presenting a linear relationship between the curl and crosswind sst gradients despite the spatial and temporal sensitivity of the underlying thermal coupling coefficient a local analysis of the fraction of the curl ascribed to sst variability shows that sst is a main driver of the wind stress curl variability and magnitude over the upwelling extension zone 100 300 km from the coast in both the canary and benguela systems closer to the shore the curl patterns derived from quikscat observations are only loosely related to sst wind interactions as a working hypothesis they can also be associated with the coastline geometry and orographic effects that are likely to play an important role in local cooling processes

low phosphorus sediments in a hypersaline marine bay abstract shark bay western australia is a large shallow hypersaline coastal lagoon with low nutrient input dissolved inorganic p in the water column decreased from 0 2 m in the oceanic region of the bay to undetectable limits in the hypersaline areas of the bay organic c total n and total p were measured in the sediments along the salinity gradient the sediment organic c was 1 3 mmol c g 1 and increased into the bay total n was positively correlated with c but p decreased from 15 mol p g 1 in the outer bay to less than 1 mol p g 1 in the hypersaline region sediment inorganic p comprised 80 90 of the total sediment p the molar c p ratio of the sediment organic phase increased from 1700 in the outer bay to 12 000 in the hypersaline region organic c and total p were also measured in the benthic plants p content of the plants also decreased as salinity increased resulting in an increase in the plant c p ratio which was similar to the increase in the c p ratio of the sediment organic phase p composition of the coastal sediments can change dramatically in a relatively short distance as a result of net uptake and sedimentation by benthic communities

dynamics of seasonal and interannual variability of the peru chile undercurrent 1 coastal sea level current satellite altimeter data and an equatorial kelvin wave model are used to study the dynamics of seasonal and interannual fluctuations of the peru chile undercurrent satellite altimetry shows that low frequency sea level anomalies near 30 s propagate offshore as expected from rossby wave theory those anomalies are related to disturbances of equatorial origin observed near the coast of south america with a wind forced equatorial kelvin wave model and simple rossby wave dynamics we show that much of the sea level anomalies and more than 50 of the observed undercurrent variability near 30 s at seasonal and interannual periods can be explained by long rossby waves forced by the equatorial kelvin waves the amplitude of the equatorial kelvin wave can be used to estimate the amplitude of the rossby wave near the south american coast and thus to monitor low frequency changes in the peru chile undercurrent

evidence of 550 year and 1000 year cyclicities in north atlantic circulation patterns during the holocene sedimentological colour data obtained from north atlantic deep sea sediment core neap15k pro vide a continuous climate record for the last 11500 yr with a mean sampling interval of 15 yr variations in sediment lightness a proxy for changes in north atlantic deep water nadw circulation are characterized by high frequency fluctuations with periodicities equivalent to 550 and 1000 yr as well as a 1600 yr cyclicity comparable to that reported in other studies of holocene climate cross spectral analysis suggests that the 550 yr and 1000 yr cyclical variations in nadw circulation were coherent with fluctuations in atmospheric con ditions over greenland where both these periodicities have been identified previously in the holocene gisp2 d18o record stuiver et al 1995 a similar statistical comparison provides evidence that high frequency 550 yr variability in nadw circulation patterns may have been linked to short term variations in atmospheric 14c values during the holocene in general nadw pro

vertical structure variability in a seasonal simulation of a medium resolution regional model of the eastern south pacific a seasonal simulation from a medium resolution ocean general circulation mode ogcm is used to investigate the vertical structure variability of the southeast pacific sep the focus is on the extra tropical rossby wave etrw variability and associated forcing mechanism some aspects of the model mean state are validated from available observations which justifies a vertical mode decomposition of the model variability the analysis of the baroclinic mode contributions to sea level indicates that the gravest mode is dominant over most of the domain at all frequencies annual variability is on average twice as large as the semi annual variability which is confined near the coast for all the modes the first baroclinic mode contribution to the annual cycle exhibits a clear westward propagation north of the critical latitude the higher order modes only contribute near the coast where they are associated with vertically propagating energy the residual variability which is the energy at all timescales other than annual and semi annual periods peaks offshore between similar to 20 degrees s and similar to 30 degrees s for all baroclinic modes the third baroclinic mode also exhibits a relative maximum variability off the coast of peru south of the critical latitude of the annual cycle similar to 13 degrees s where the peru chile undercurrent is the most intense sensitivity experiments to the atmospheric and boundary forcing suggest that the residual variability results from the non linear interaction between annual rossby waves and the mean flow while the annual etrws in the model result from the summed contribution from both the local wind stress and remote equatorial forcing overall the study extends the classical analysis of sea level variability in the sep based on linear theory and suggests that the peculiarities of the baroclinic modes need to be taken into account for interpreting the sea level variability and understanding its connection with the equatorial variability c 2008 published by elsevier ltd

circulation and low frequency variability near the chilean coast remotely forced fluctuations during the 1991 92 el nino results are reported from the first long recording current meter observations over the slope off chile these observations at 308s during the 1991 92 el nino event are analyzed together with observations of currents at a local deep sea site local wind and sea level sea level from the peru and chile coasts and wind temperature and currents from the equatorial pacific mean poleward flow of 12 cm s21 was observed within the peru chile undercurrent over the slope mean flow in the depth range of antarctic intermediate water was not distinguishable from zero in the presence of strong low frequency lf variability which dominated slope currents at all depths the strongest lf fluctuations had periods of about 50 days but periods of 10 and about 5 days were also observed significant local wind forcing of slope currents was only found in the period band 6 10 days and may be related to coastal trapped waves in the atmosphere our analysis shows that free coastal trapped waves in the ocean arriving from the north dominated the lf variability over the shelf and slope off northern and central chile during the 1991 92 el nino event strong 50 day period fluctuations there started their journey about two months earlier and 15 000 km farther up the coastal equatorial waveguide near the date line in the equatorial pacific as equatorial kelvin waves forced by westerly wind events of similar period upon reaching the south american coast these waves forced coastal trapped waves which propagated along the peru coast into the study region likewise a scenario of equatorial trapped waves forcing coastal trapped waves may explain 10 day as well as 6 day and 4 5 day period coastal trapped waves off chile stemming from mixed rossby gravity and inertia gravity waves trapped at the equator since the large 50 day period coastal trapped waves may strongly modify coastal upwelling source water such remotely forced waves may have a significant influence on the pelagic ecosystem off chile at least during el nino events

observations of coupling between surface wind stress and sea surface temperature in the eastern tropical pacific satellite measurements of surface wind stress from the quikscat scatterometer and sea surface temperature sst from the tropical rainfall measuring mission microwave imager are analyzed for the three month period 21 july 20 october 1999 to investigate ocean atmosphere coupling in the eastern tropical pacific oceanic tropical instability waves tiws with periods of 20 40 days and wavelengths of 1000 2000 km perturb the sst fronts that bracket both sides of the equatorial cold tongue which is centered near 1 8s to the east of 1308w these perturbations are characterized by cusp shaped features that propagate systematically westward on both sides of the equator the space time structures of these sst perturbations are reproduced with remarkable detail in the surface wind stress field the wind stress divergence is shown to be linearly related to the downwind component of the sst gradient with a response on the south side of the cold tongue that is about twice that on the north side the wind stress curl is linearly related to the crosswind component of the sst gradient with a response that is approximately half that of the wind stress divergence response to the downwind sst gradient the perturbed sst and wind stress fields propagate synchronously westward with the tiws this close coupling between sst and wind stress supports the wallace et al hypothesis that surface winds vary in response to sst modification of atmospheric boundary layer stability

the role of ocean atmosphere reorganizations in glacial cycles abstract a case is made that glacial to interglacial transitions involve major reorganizations of the ocean atmosphere system such reorganizations constitute jumps between stable modes of operation which cause changes in the greenhouse gas content and albedo of the atmosphere only in this way can the rapidity of glacial terminations the hemispheric synchroneity and symmetry of mountain glaciation and the large polar air temperature and dustiness variations be accounted for if these reorganizations are driven in some fashion by orbitally induced seasonal insolation changes then the connection between insolation and climate is most likely through impacts of fresh water transport on the ocean s salinity distribution

benthic nutrient recycling in port phillip bay australia benthic chamber measurements of the reactants and products involved with biogenic matter remineralization oxygen ammonium nitrate nitrite phosphate silicate tco2and alkalinity were used to define solute exchange rates between the sediment and overlying water column of port phillip bay australia measurements at various sites throughout the bay conducted during the summers of 1994 and 1995 indicate that the variability in flux values within a site is comparable to year to year variability 50 four regions of the bay were distinguished by sediment properties and the northern region was identified as having 3 30 times greater nutrient regeneration rates than the other regions benthic recycling accounted for 63 and 72 of the annualized n and p input respectively to the entire bay as determined by summing benthic dissolved riverine atmospheric and dissolved effluent sources however bay wide sedimentary denitrification accounted for a loss of 63 of the potentially recyclable n this fraction is higher than many other coastal regions with comparable carbon loading denitrification efficiency is apparently not enhanced by benthic productivity nor by bio irrigation the rate of bio irrigation is negatively correlated with denitrification efficiency bio irrigation was studied using radon 222 and cscl spike injection chamber measurements radon fluxes from sediments in port phillip bay were enhanced over the diffusive flux by 3 16 times the modelled rate of loss of cs from chamber water was positively correlated with radon flux enhancement results both methods identify regions within port phillip bay that have particularly high rates of non diffusive pore water overlying water solute exchange

carbonate dissolution and temporal abundances of foraminifera in long island sound sediments the dynamics of benthic foraminifera assemblages can be used to examine carbonate dissolution processes in nearshore sediments and as a general assay of physical chemical factors affecting survival of juvenile benthos abundances of total foraminifera live and dead fluctuate regularly throughout the year in long island sound lis mud deposits with highest numbers in spring summer and lowest in winter essentially all forams disappear each year pore water undersaturation with respect to carbonate minerals coincides with periods of rapid disappearance of forams and suggests that these fluctuations reflect a balance between the rate of production recruitment and the rates of death and dissolution of the calcareous tests of the animals reworking by macrofauna in lis central basin sediments inhibits accumulation or depletion of pore water solutes and is responsible for minimizing pore water carbonate saturation states quantitative estimates of seasonal patterns of foram dissolution with a simple mass balance model give a minimum average annual flux of caz in lis sediments of 6 mmol ca2 m 2 d 1 due solely to foraminifera dissolution abandoned tests have a maximum mean residence time of 86 13 d dissolution precipitation of forams may significantly affect benthic zco fluxes and likely accounts for a large proportion 30 during some seasons or at some locales other organisms with carbonate tests of similar size particularly juvenile bivalves may also be affected by periods of undersaturated pore waters conditions promotinn dissolution of tests may represent an important source of mortality for calcareous meiofauna

a numerical study of the upwelling circulation off central chile effects of remote oceanic forcing 1 a numerical ocean model is used to study the upwelling circulation off central chile in response to local winds and remote forcing in an idealized study of equatorial forced intraseasonal variability period of 50 days a first mode coastal trapped wave ctw paddle is applied to the northern boundary with coastal sea level amplitude of 12 cm without this ctw forcing the steady seasonal winds upwell undercurrent water from depths of 250 320 m to depths of 180 250 m the subsequent formation of mesoscale and headland eddies drive this water into the gulf of arauco and to depths of 50 120 m with the ctw paddle the circulation is strongly modified the mesoscale and headland eddies reform during the ctw upwelling phase during the ctw upwelling phase the upwelling over winds and eddies is enhanced by up to 40 m on the shelf model simulations are undertaken using realistic winds and a ctw paddle modulated by observed sea level without ctw forcing included in the model the agreement with data is poor in the gulf of arauco area the variability of alongshore currents below 130 m is dominated by ctw activity above 130 m wind driven current variability dominates in agreement with the idealized ctw analysis water is found to be upwelled from depths of 320 m to 100 m or less and 10 c undercurrent water is found at the surface and within the gulf

upwelling response to atmospheric coastal jets off central chile a modeling study of the october 2000 event the spatial and temporal variability of nearshore winds in eastern boundary current systems affect the oceanic heat balance that drives sea surface temperature changes in this study regional atmospheric and oceanic simulations are used to document such processes during an atmospheric coastal jet event off central chile the event is well reproduced by the atmospheric model and is associated with the migration of an anomalous anticyclone in the southeastern pacific region during october 2000 a robust feature of the simulation is a sharp coastal wind dropoff which is insensitive to model resolution as expected the simulated oceanic response is a significant sea surface cooling a surface heat budget analysis shows that vertical mixing is a major contributor to the cooling tendency both in the jet core area and in the nearshore zone where the magnitude of this term is comparable to the magnitude of vertical advection sensitivity experiments show that the oceanic response in the coastal area is sensitive to wind dropoff representation this is because total upwelling i e the sum of coastal upwelling and ekman pumping depends on the scale of wind dropoff because the latter is much larger than the upwelling scale coastal wind dropoff has only a weak positive effect on vertical velocities driven by ekman pumping but has a strong negative effect on coastal upwelling interestingly though the weakening of coastal winds in the dropoff zone has a larger effect on vertical mixing than on vertical advection with both effects contributing to a reduction of cooling

sediment nutrient dynamics on the south atlantic bight continental shelf continental shelf sediments on the south atlantic bight sab consist of relict sands that at depths ranging from 14 45 m fall within the photic zone and are sites in which significant rates of benthic primary production are observed thus sab seafloor sediments are a source of organic matter to the shelf system and are possibly a sink for nutrients regenerated within the sediments we have investigated the nutrient dynamics in sab shelf sediments along two transects off the coasts of georgia and florida as part of a study that addresses the significance of benthic primary production in terms of overall shelf biogeochemistry sandy sediments were sampled with a newly designed corer that permits retention of pore water in highly permeable sands and thus avoids commonly encountered washout problems nutrient ammonium silicate nitrate nitrite and phosphate distributions from sediments along both transects show substantial variation in concentration magnitudes and profile shapes over short horizontal spatial scales meters laboratory experiments and numerical models of diagenetic processes in these sediments suggest that 1 pore water advection driven by current flows over wave ripples and bioturbational features is likely an important transport process in promoting nutrient exchange in these porous sands more so than irrigation and 2 reaction rates in sab sediments are rapid and are comparable to those in nearshore muddy habitats in spite of this variation and the apparently high rates of advective transport time series measurements show a gradual increase in depth integrated nutrient concentrations at one station along the georgia transect from the spring through the fall this increase is probably related to elevations in temperature and metabolic rates in sediments during the warmer summer months measured oxygen and nutrient fluxes across the sediment water interface in paired transparent light chambers and opaque dark chambers did not conform to trends observed in shallow water systems where oxygen is typically evolved and nutrients are consumed in the light versus oxygen that is consumed and nutrients that are evolved in the dark the absence of measurable or consistent fluxes on the sab shelf is likely the result of low concentrations of nutrients in both the water column and the upper sediment layers however rapid regeneration rates in sediments and generally higher nutrient concentrations in deeper sediment layers suggest that sediments are an important source of the nutrients that fuel benthic primary production although ammonium is rapidly produced in these oxic sands nitrate concentrations are uniformly low and measurable nitrate generally appears in the oxic sedimentary layers the absence of high nitrate concentrations in the suboxic or anoxic zone suggests that denitrification may not be an important process in sab shelf sediments

coastal lows along the subtropical west coast of south america mean structure and evolution the typical conditions of the eastern boundary of the subtropical anticyclone e g well defined marine boundary layer mbl equatorward low level flow that prevail along the mountainous west coast of subtropical south america are frequently disrupted by shallow warm core low pressure cells with alongshore and crossshore scales of 1000 and 500 km respectively these so called coastal lows cls occur up to five times per month in all seasons although they are better defined from fall to spring marked weather changes along the coast and farther inland are associated with the transition from pressure drop to pressure rise the mean structure and evolution of cls is documented in this work using a compositing analysis of 57 episodes selected from hourly pressure observations at a coastal station at 30 8s during the austral winters of 1991 1993 and 1994 and concurrent measurements from a regional research network of nine automatic weather stations ncep ncar reanalysis fields and high resolution visible satellite imagery coastal lows tend to develop as a migratory surface anticyclone approaches southern chile at about 408s producing a poleward oriented pressure gradient and geostrophically balanced offshore component in the low level wind at subtropical latitudes the transition from negative to positive geopotential anomalies occurs around 850 hpa enhanced mid and lowlevel subsidence near the coast and downslope flow over the coastal range and andes mountains leads to the replacement of the cool marine air by adiabatically warmed air lowering the surface pressure at the coast and offshore as the midlatitude ridge moves to the east of the andes the alongshore pressure gradient reverts back and the easterly wind ceases to act the recovery of the surface pressure toward mean values occurs as the cool cloud topped mbl returns to the subtropical coast although the pressure rise can be attenuated by midlatitude troughing the return of the mbl resembles a kelvin wave propagating along the coast from northern chile where the mbl eventually thickened into subtropical latitudes in about a day

the low level jet off the west coast of subtropical south america structure and variability abstract the subtropical anticyclone over the southeast pacific drives low level southerly flow along the west coast of south america in turn the alongshore flow induces coastal upwelling that supports a wealth of fishery resources within this region satellite data marine reports and coastal observations indicate the existence of a southerly coastal jet i e a maximum of wind speed off central chile 26 36 s the mean features and variability of this southerly jet is documented in this work using 4 yr of satellite derived sea surface winds complemented by satellite derived cloud amount fields and atmospheric reanalysis furthermore analysis of in situ data and model results of a well defined jet event during october 2000 allows a preliminary description of the jet s three dimensional structure and a comparison with the northerly jet off the coast of california southerly jet events off central chile occur year round but they are more frequent during spring summer over 60 of the time the

modification of sea surface temperature by chlorophyll concentration in the atlantic upwelling systems the influence of the chlorophyll on the upper tropical atlantic ocean is investigated with long term 1979 2012 regional oceanic simulations with 1 4 horizontal resolution based on the nemo3 6 model the model solar radiation penetration scheme depends on the chlorophyll concentration simulations with time and spatially varying concentrations obtained from satellite ocean color observations are compared with a simulation forced with constant chlorophyll concentration of 0 05 mg m 3 representative of chlorophyll depleted waters results indicate that regions of the tropical atlantic with chlorophyll concentrations larger than in the reference simulation i e chl 0 05 mg m 3 get warmer at the surface with the exception of the main upwelling regions where high chlorophyll concentrations are associated with a significant cooling of the sea surface 1 c in the benguela upwelling the analysis of the model heat balance shows that the biological differential heating causes negative temperature anomalies in subsurface source waters prior to their upwelling at the coast the shallow mixed layer in the eastern equatorial and tropical atlantic favors the persistence of these subsurface anomalies and may explain why the benguela is particularly sensitive to the biological differential heating in spite of the presence of high chlorophyll concentrations in the upwelling regions both the larger amount of shortwave radiation captured in the surface layers and the modifications of the horizontal and vertical advection at the coast are found to play a secondary role in the sst change in the upwelling region

low frequency modulation of intraseasonal equatorial kelvin wave activity in the pacific from soda 1958 2001 intraseasonal equatorial kelvin wave activity iekw at a low frequency in the pacific is investigated using the simple ocean data assimilation soda oceanic reanalyses a vertical and horizontal mode decomposition of soda variability allows estimation of the kelvin wave amplitude according to the most energetic baroclinic modes a wavenumber frequency analysis is then performed on the time series to derive indices of modulation of the iekw at various frequency bands the results indicate that the iekw activity undergoes a significant modulation that projects onto baroclinic modes and is not related in a straightforward manner to the low frequency climate variability in the pacific linear model experiments corroborate that part of the modulation of the iekw is tightly linked to change in oceanic mean state rather than to the low frequency change of atmospheric equatorial variability

biogeochemical impact of submarine ground water discharge on coastal surface sands of the southern baltic sea this study evaluates the effect of submarine ground water discharge sgd on biogeochemical processes of sandy sediments of hel bight poland in the shallow southern baltic sea using stirred benthic chambers combined to seepage meters deep pore water profiles and a reactive transport model the main impacts of fresh anoxic groundwater seepage are due to 1 the efflux of methane 2 the efflux of phosphate and silicate 3 the efflux of dissolved organic carbon doc of aquifer origin methane from sgd is assumed to be only slightly oxidized within the sediments and potentially reach the atmosphere at a maximum rate of 30 mmol ch4 m 2 d 1 silicate and phosphate supplied by sgd promote a seep site net community production rate that is more than twice as compared to adjacent non seeping sites 70 and 30 mmol c m 2 d 1 respectively however oxygen uptake rates at the seep site during the night 30 mmol o2 m 2 d 1 are lower than those observed at the reference sites 50 mmol o2 m 2 d 1 we hypothesize that autogenic relatively labile doc is available at the reference site leading to higher oxygen uptake rates as compared to the seep sites where it is being replaced by less reactive doc originating from the ground water

processes on the continental slope off north carolina with special reference to the cape hatteras region historical data from the slope off cape hatteras show this environment to be atypical of the rest of the atlantic slope in terms of high rates of sedimentation and high benthic demersal standing stocks this paper focuses on identifying potential sources for sediments and nutrients on the hatteras slope and on likely transport mechanisms sediments consist mainly of subequal mixtures of sand silt and clay and contain an average of 1 carbon this pool of carbon represents weathered organic matter containing polyunsaturated fatty acids pufa and sterols typical of relatively refractory shelf estuarine sediments the labile organic fraction is derived from phytoplankton and zooplankton as reflected in short chain fatty acids c22 planktic sterols and chlorophylla that are found in higher concentrations than observed elsewhere on the eastern u s continental slope the inventory of organic nitrogen is much higher on the mid slope 800 1 000 m than shallower or deeper bottom areas as predicted from plots of organic nitrogen versus grain size for the u s atlantic continental margin the midslope region is the major focusing area for sedimentation bioturbation is an important diagenetic process that has profound influence on sediment profiles of sulphate methane fatty acids sterols chlorophylla viable diatoms and metals the low inventory of relatively refractory carbon 1 stands in contrast to high measured rates of organic carbon sedimentation 28 121 g organic c m 2 year 1 this paradox is probably related to high remineralization rates in the water column and on the bottom the refractory nature of the small residual pool of deposited organic matter may define the trophic niche filled by those benthos found on this slope that are more typically encountered on the shelf e g oligochaetes and opportunistic polychaetes a likely mechanism for high input rates of both organic and inorganic particulates to the hatteras slope may be attributed to the position of cape hatteras relative to the adjacent narrow shelf the cape extends outward almost to the shelf edge topographically diverting sediment and primary production seaward that is moving southward along the outer shelf the funnel hypothesis transport of outer shelf sands to the slope may take place by the impingement of gulf stream eddies on the outer shelf and upper slope as well as by storm generated waves once shelf sediment is deposited on the upper slope it is apparently redistributed as no strong on shore to off shore or depth related gradients are observed in any of the measured sedimentary parameters the hatteras slope apparently represents an estuarine type of sedimentary nutrient regime that is displaced to an otherwise oceanic deep sea environment by outwelling and funnelling of nutrients and sediments from the shelf to the slope

holocene climatic instability a prominent widespread event 8200 yr ago the most prominent holocene climatic event in greenland ice core proxies with approximately half the amplitude of the younger dryas occurred 8000 to 8400 yr ago this holocene event affected regions well beyond the north atlantic basin as shown by synchronous increases in windblown chemical indicators together with a significant decrease in methane widespread proxy records from the tropics to the north polar regions show a short lived cool dry or windy event of similar age the spatial pattern of terrestrial and marine changes is similar to that of the younger dryas event suggesting a role for north atlantic thermohaline circulation possible forcings identified thus far for this holocene event are small consistent with recent model results indicating high sensitivity and strong linkages in the climatic system

geographical variability of the first baroclinic rossby radius of deformation global 1 83 18 climatologies of the first baroclinic gravity wave phase speed c1 and the rossby radius of deformation l1 are computed from climatological average temperature and salinity profiles these new atlases are compared with previously published 5 83 58 coarse resolution maps of l1 for the northern hemisphere and the south atlantic and with a 1 83 18 fine resolution map of c1 for the tropical pacific it is concluded that the methods used in these earlier estimates yield values that are biased systematically low by 5 15 owing to seemingly minor computational errors geographical variations in the new high resolution maps of c1 and l1 are discussed in terms of a wkb approximation that elucidates the effects of earth rotation stratification and water depth on these quantities it is shown that the effects of temporal variations of the stratification can be neglected in the estimation of c1 and l1 at any particular location in the world ocean this is rationalized from consideration of the wkb approximation

rapid changes in ocean circulation and atmospheric radiocarbon a latitude depth coupled global ocean ice atmosphere model is extended to include a simple biosphere component a physically reasonable adjustment of runoff into the north atlantic is invoked to achieve a transient response to glacial meltwater perturbations which closely resembles the younger dryas climate event we then investigate the evolution of the isotopic ratio of atmospheric radiocarbon 14c due to the rapid changes of deep ocean circulation when the north atlantic branch of the conveyor belt circulation is interrupted the oceanic uptake of radiocarbon is reduced resulting in an increase of atmospheric 14c by about 35 the reduction of ventilation in the north atlantic is partly compensated by an increase of the 14c ratios of the biosphere the southern ocean and the upper ocean above 1000 m depth a plateau of the 14c year calendar year relation can be generated at the time of the rapid reinitiation of deep ocean ventilation which begins coincident with the major temperature increase and lasts for about 60 years it is hence significantly shorter than that found by analyzing tree rings during the termination of younger dryas longer than 400 years a sensitivity study reveals that the duration of the plateau depends strongly on the transient evolution of the gas exchange rate and can increase to 150 300 years if changes of pco2 or sea ice coverage are taken into account

rapid interglacial climate fluctuations driven by north atlantic ocean circulation recent data from the grip ice core1 3 in greenland suggest that the climate of the last eemian interglacial period was much less stable than that of the present interglacial rapid transitions between warm and cold periods were found to occur on timescales of just a few decades the north atlantic climate during the eemian period was also shown to be characterized by three states respectively warmer than similar to and colder than today1 2 recent data from the nearby gisp2 ice core have revealed some discrepancies with these findings which remain to be resolved4 5 here we present simulations using an idealized global ocean model which suggest that the north atlantic ocean has three distinct circulation modes each of which corresponds to a distinct climate state we find that adding a simple random component to the mean freshwater flux which forces circulation can induce rapid transitions between these three modes we suggest that increased variability in the hydrological cycle associated with the warmer eemian climate could have caused transition between these distinct modes in the north atlantic circulation which may in turn account for the apparent rapid variability of the eemian climate

western north atlantic evidence for millennial scale changes in ocean circulation and climate two late quaternary series of high resolution percent carbonate data from western north atlantic sediment drifts bermuda rise and bahama outer ridge show millennial scale oscillations superimposed on the familiar longer period oscillations of orbital origin the dominant high frequency oscillation in these records has a quasi period of about 4000 years these percent caco3 changes most likely result from the influence of climate change on the flux of terrigenous material from eastern canada the resuspension of continental margin sediment by deep eddy kinetic energy and carbonate dissolution sediment is transported to the bermuda rise by deep recirculating gyres and to the bahama outer ridge by the deep western boundary current system stable isotope results on foraminifera across several of these oscillations from interstadial climate conditions and from a glacial inception display variability similar to that of percent caco3 oxygen isotope ratios of planktonic foraminifera suggest large variations in near surface temperature and or salinity and carbon isotope ratios of benthic foraminifera indicate that there were significant oscillations in the flux of north atlantic deep water nadw these data support models which couple surface ocean conditions in the north atlantic production of nadw north atlantic heat flux and evidence for temperature oscillations in ice cores

modes of covariability between sea surface temperature and wind stress intraseasonal anomalies along the coast of peru from satellite observations 2000 2008 1 the tropical rainfall measuring mission microwave imager sea surface temperature sst and quikscat wind stress satellite data are used to investigate the intraseasonal upwelling variability along the coat of peru over the period 2000 2008 two regions of peak variance correspond to the central peru region pisco region 15 s and the northern peru region piura region 5 s a covariance analysis reveals a significant coherency between winds and sst anomalies off pisco consistent with ekman pumping and transport dynamics the upwelling cell consists in a meridionally extended fringe of colder warmer water extending as far as 250 km from the coast at 15 s in the piura region the intraseasonal covariability pattern is represented by two modes one relevant to the direct ekman dynamics and the other one associated with the remote forcing of intraseasonal oceanic kelvin wave two regimes of variability are evidenced a low period regime 10 25 days is the signature of ekman transport pumping dynamics and is remotely forced by the migratory atmospheric disturbances across the southeastern pacific anticyclone a high period regime 35 60 day band is associated with the combined forcing of oceanic equatorial kelvin waves and migratory atmospheric disturbances in the midlatitudes in particular the modes of covariability exhibit a prominent 50 day period energy peak it is shown that this period arises from the impact of the first two baroclinic modes kelvin wave with the second baroclinic mode kelvin wave being more influential on the piura region

influence of sediment permeability and mineral composition on organic matter degradation in three sediments from the gulf of aqaba red sea abstract in order to investigate the influence of sediment physical and chemical characteristics on the degradation of deposited organic matter decomposition in three sediments from the gulf of aqaba red sea that differ in permeability and mineral composition were compared freeze dried spirulina was added to coarse carbonate and silicate sands from a shallow nearshore region and silt clay sediment from the deeper center region of the gulf incubated in laboratory chambers the stirring in the chambers caused higher solute exchange in the coarse permeable sands relative to the fine less permeable silt due to the generation of advective fluid exchange between the sediment and overlying water this enhanced exchange increased the decomposition rates of organic matter in the incubated sands the decomposition rates of total organic carbon in the permeable carbonate 3 0 mg c m 2 d 1 and silicate sands 2 0 mg c m 2 d 1 exceeded that in the fine grained sediment 1 4 mg c m 2 d 1 oxygen consumption in the coarse sands was 3 fold higher than in the silt clay sediment with highest rates in the carbonate sand in carbonate and silicate sands of the same grain size the carbonate sediment was more permeable than the silicate resulting in 1 4 fold higher fluid exchange rates and 1 4 fold larger sedimentary organic matter mineralization rates an in situ experiment comparing trapping efficiencies in carbonate and silicate sands showed that the higher fluid exchange rate in the carbonate sand results in larger filtration rates and a faster accumulation of particulate organic matter from the boundary layer these experiments demonstrate that with respect to sedimentary mineralization rates higher transport rates in permeable coarse sediments can outweigh the effect of a higher specific surface area in fine grained silt sediments in permeable sands however the higher specific surface area and fluid exchange in biogenic carbonate sands result in higher mineralization rates than in silicate sands of the same grain size

deglacial changes in ocean circulation from an extended radiocarbon calibration temporal variations in the atmospheric concentration of radiocarbon sometimes result in radiocarbon based age estimates of biogenic material that do not agree with true calendar age this problem is particularly severe beyond the limit of the high resolution radiocarbon calibration based on tree ring data which stretches back only to1 2 about 11 8 kyr before present bp near the termination of the younger dryas cold period if a wide range of palaeoclimate records are to be exploited for better understanding the rates and patterns of environmental change during the last deglaciation extending the well calibrated radiocarbon timescale back further in time is crucial several studies attempting such an extension using uranium thorium dated corals3 4 5 and laminae counts in varved sediments6 7 8 9 show conflicting results here we use radiocarbon data from varved sediments in the cariaco basin in the southern caribbean sea to construct an accurate and continuous radiocarbon calibration for the period 9 to 14 5 kyr bp nearly 3 000 years beyond the tree ring based calibration a simple model compared to the calculated atmospheric radiocarbon concentration and palaeoclimate data from the same sediment core suggests that north atlantic deep water formation shut down during the younger dryas period but was gradually replaced by an alternative mode of convection possibly via the formation of north atlantic intermediate water

advective transport affecting metal and nutrient distributions and interfacial fluxes in permeable sediments abstract our laboratory flume experiments demonstrate that advective porewater flows produce biogeochemical reaction zones in permeable sediments leading to specific and reproducible complex patterns of fe mn and nutrients oxygenated water forced into the sediment when boundary flows were deflected by protruding sediment structures generated distinct zones of nitrification and ferric iron precipitation this inflow was balanced by ammonium rich porewater ascending from deeper sediment layers thereby creating an anoxic channel where dissolved fe2 and mn2 could reach the surface between the zones of ferric iron precipitation and fe2 upwelling a layer with increased manganese oxide and solid phase fe ii concentrations formed indicating redox reaction between these components the establishment of topography on the previously smooth sediment surface reversed the net interfacial flux of solutes while the smooth control core was found to be a sink for metals and nutrients the sediment with mounds acted as a source for these substances our experiments show that in sandy sediment with an oxidised surface layer reduced metal species can be released to the water column by flow topography interactions we conclude that advective transport processes constitute an important process controlling biogeochemical zonations and fluxes in permeable sea beds

the gisp2 δ18o climate record of the past 16 500 years and the role of the sun ocean and volcanoes measured 18o 16o ratios from the greenland ice sheet project 2 gisp2 ice core extending back to 16 500 cal yr b p provide a continuous record of climate change since the last glaciation high resolution annual 18o 16o results were obtained for most of the current millennium a d 818 1985 and record the medieval warm period the little ice age and a distinct 11 yr 18o 16o cycle volcanic aerosols depress central greenland annual temperature 1 5 c maximally and annual 18o 16o for about 4 yr after each major eruptive event on a bidecadal to millennial time scale the contribution of solar variability to holocene greenlandic temperature change is 0 4 c the role of thermohaline circulation change on climate problematic during the holocene is more distinct for the 16 500 10 000 cal yr b p interval analogous to 14c age calibration terminology we express time in calibrated cal yr b p a d 1950 0 cal yr b p the oldest dryas bolling older dryas allerod younger dryas sequence appears in great detail bidecadal variance in 18o 16o but not necessarily in temperature is enhanced during the last phase of lateglacial time and the younger dryas interval suggesting switches of air mass transport between jet stream branches the branched system is nearly instantaneously replaced at the beginning of the bolling and holocene at 14 670 and 11 650 cal yr b p respectively by an atmospheric circulation system in which 18o 16o and annual accumulation initially track each other closely thermodynamic considerations of the accumulation rate temperature relationship can be used to evaluate the 18 o 16o temperature relationship the gisp2 ice layer count years of major gisp2 climate transitions also support the use of coral 14c ages for age calibration

comparison of oxygen isotope records from the gisp2 and grip greenland ice cores recent results1 2 from the greenland ice core project grip summit ice core suggest that the climate in greenland has been remarkably stable during the holocene but was extremely unstable for the time period represented by the rest of the core spanning the last two glaciations and the intervening eemian inter glacial here we present the complete oxygen isotope record for the greenland ice sheet project 2 gisp2 core drilled 28 km west of the grip core we observe large rapid climate fluctuations throughout the last glacial period which closely match those reported for the grip core however in the bottom 10 of the cores spanning the eemian interglacial and the previous glacia tion there are significant differences between the two records it is possible that ice flow may have altered the chronological sequences of the stratigraphy for the bottom part of one or both of the cores considerable further work will be necessary to evaluate the likelihood of this and the extent to which it will still be possible to extract meaningful climate information from the lowest sections of the cores

el nino sea level and currents along the south american coast comparison of observations with theory abstract interannual sea level fluctuations along the south american coast and 7 3 year long current records at 30 s off central chile were examined with a low frequency linear numerical model the model includes stratification and shelf and slope bottom topography which varies alongshore the coastal flow is driven by interannual alongshore wind stress and an interannual alongshore pressure gradient resulting from el nino la nina pressure fluctuations at the equator calculations suggest that along the south american coast the coastal interannual variability is primarily due to the remote equatorial forcing rather than interannual coastal alongshore wind stress past work using this model has shown that due to the scattering of lower vertical modes to higher ones by bottom friction the model predicts a low frequency jet trapped near the bottom along the continental slope until now adequate interannual current time series were unavailable to check this prediction analysis of the observations shows th

adjustment of the marine atmospheric boundary layer to a coastal cape abstract during summer significant changes in marine atmospheric boundary layer mabl speed and depth occur over small spatial scales 100 km downstream from topographic features along the california coast in june and july 1996 the coastal waves 96 project collected observations of such changes at capes with an instrumented aircraft this paper presents observations from the 7 june flight when the layer averaged speed increased 9 m s 1 and depth decreased by 500 m over a 75 km downwind from cape mendocino accompanied by enhanced surface fluxes and local cloud clearing the acceleration and thinning are reproduced when the flow is modeled as a shallow transcritical layer of fluid impinging the bends of a coastal wall leading to the interpretation that they are produced by an expansion fan model runs were produced with different coastlines and imposed pressure gradients with the best match provided by a coastline in which the cape protruded into the flow and forced a response in the subcritical r

carbon cycling hysteresis in permeable carbonate sands over a diel cycle implications for ocean acidification dissolved inorganic carbon dissolved oxygen h and alkalinity fluxes from permeable carbonate sediments at heron island great barrier reef were measured over one diel cycle using benthic chambers designed to induce advective pore water exchange a complex hysteretic pattern between carbonate precipitation and dissolution in sands and the aragonite saturation state var of the overlying chamber water was observed throughout the incubations during the day precipitation followed a hysteretic pattern based on the incidence of photosynthetically active radiation with lower precipitation rates in the morning than in the afternoon the observed diel hysteresis seems to reflect a complex interaction between photosynthesis and respiration rather than var of the overlying water as the main driver of carbonate precipitation and dissolution within these permeable sediments changes in flux rates over a diel cycle demonstrate the importance of taking into account the shortterm variability of benthic metabolism when calculating net daily flux rates based on one diel cycle the sediments were a net daily source of alkalinity to the water column 5 13 to 8 84 mmol m22 d21 depending on advection rates and advection had a net stimulatory effect on carbonate dissolution the enhanced alkalinity release associated with benthic metabolism and pore water advection may partially buffer shallow coral reef ecosystems against ocean acidification on a local scale

pathways of organic carbon oxidation in three continental margin sediments we have combined several different methodologies to quantify rates of organic carbon mineralization by the various electron acceptors in sediments from the coast of denmark and norway rates of nh4 and sigma co2 liberation sediment incubations were used with o2 penetration depths to conclude that o2 respiration accounted for only between 3 6 17 4 of the total organic carbon oxidation dentrification was limited to a narrow zone just below the depth of o2 penetration and was not a major carbon oxidation pathway the processes of fe reduction mn reduction and sulfate reduction dominated organic carbon mineralization but their relative significance varied depending on the sediment where high concentrations of mn oxide were found 3 4 wt mn only mn reduction occurred with lower mn oxide concentrations more typical of coastal sediments fe reduction and sulfate reduction were most important and of a similar magnitude overall most of the measured o2 flux into the sediment was used to oxidized reduced inorganic species and not organic carbon we suspect that the importance of o2 respiration in many coastal sediments has been overestimated whereas metal oxide reduction both fe and mn reduction has probably been well underestimated

benthic photosynthesis and oxygen consumption in permeable carbonate sediments at heron island great barrier reef australia abstract in order to investigate benthic photosynthesis and oxygen demand in permeable carbonate sands and the impact of benthic boundary layer flow on sedimentary oxygen consumption in situ and laboratory chamber experiments were carried out at heron island great barrier reef australia total photosynthesis net primary production and respiration were estimated to be 162 9 43 4 98 0 40 7 and 64 9 15 0 mmol c m 2 d 1 respectively din and dip fluxes for these sands reached 0 34 and 0 06 mmol m 2 d 1 respectively advective pore water exchange had a strong impact on oxygen consumption in the permeable sands consumption rates in the chamber with larger pressure gradient 20 rpm 1 2 pa between centre and rim simulating a friction velocity of 0 6 cm s 1 were approximately two fold higher than in the chambers with slow stirring 10 rpm 0 2 pa between centre and rim friction velocity of 0 3 cm s 1 in the laboratory chamber experiments with stagnant water column oxygen consumption was eight times lower than in the chamber with fast stirring laboratory chamber experiments with br tracer revealed solute exchange rates of 2 6 2 2 0 7 ml cm 2 d 1 at stirring rates of 20 10 and 0 rpm respectively in a laboratory experiment investigating the effect of sediment permeability on oxygen and dic fluxes a three fold higher permeability resulted in two to three fold higher oxygen consumption and dic release rates these experiments demonstrate the importance of boundary flow induced flushing of the upper layer of permeable carbonate sediment on oxygen uptake in the coral sands the high filtration and oxidation rates in the sub tropical permeable carbonate sediments and the subsequent release of nutrients and dic reveal the importance of these sands for the recycling of matter in this oligotrophic environment

sites of river derived sedimentation in the ocean most of the world9s rivers have discharged sediment on wide continental shelves and in estuaries since the last rise in sea level in most cases sediments are thus trapped on these areas and are not deposited on the now relict submarine fans oceanward of these rivers the conclusions are based on remote sensing on data in the literature on present sedimentation rates on the shelves and the submarine fans and on river sediment discharges for the 22 rivers studied these submarine fans will remain cut off from their fluvial sources until the shelves and estuaries are filled and sediments can bypass these areas the time required to fill these shelves and estuaries ranges from 2 600 to 3 400 yr for the ganges brahmaputra to 1 to 1 2 m y for the yenisei ob for most river systems sea level will change before shelves and estuaries are filled with sediments

offshore ekman transport and ekman pumping off peru during the 1997 1998 el nino 1 satellite ocean vector wind measurements are used to describe onshore offshore ekman transport and ekman pumping suction i e downward upward velocity in the coastal ocean at 15 s off peru where upwelling is the dominant physical process normal and el nino conditions are defined for may 1992 april 1997 and may 1997 may 1998 respectively during normal conditions both ekman suction and offshore ekman transport produced upwelling during the el nino the may august speed of ekman pumping 9 10 6 m s 1 was nearly 4 times larger than the normal speed of ekman suction and offshore ekman transport nearly doubled the strong ekman pumping may be the source for the deepened coastal thermocline during el nino although the evidence is not conclusive because of the absence of in situ observations

flow induced uptake of particulate matter in permeable sediments we demonstrate the fast transfer of suspended particles from the boundary layer into the upper strata z 2 x 10 l l m2 incubated in a laboratory flume increased pressure up and downstream of small mounds z 2 5 cm drove water 5 5 cm into the core carrying suspended particles 1 pm to 2 2 cm sediment depth within 10 h simultaneously decreased pressure at the downstream slope of the protrusions drew pore fluid from deeper layers z 5 10 cm to the surface in the sediment friction reduced the velocity of the particulate tracers resulting in size fractionation and layers of increased particle concentration ripple topography 0 8 2 8 cm high enhanced interfacial particle 1 pm flux by a factor 2 3 when compared to a level control core the pathways of the particle and solute tracers below a sediment ripple are explained with a source sink model that describes the pore flow velocity field our results suggest that bedform induced interfacial flows are important for the uptake of particulate organic matter into permeable shelf sediments

impulse framework for unsteady flows reveals superdiffusive bed load transport 1 sediment transport is an intrinsically stochastic process and measurement of bed load in the environment is further complicated by the unsteady nature of river flooding here we present a methodology for analyzing sediment tracer data with unsteady forcing we define a dimensionless impulse by integrating the cumulative excess shear velocity for the duration of measurement normalized by grain size we analyze the dispersion of a plume of cobble tracers in a very flashy stream over two years the mean and variance of transport distance collapse onto well defined linear and power law relations respectively when plotted against cumulative dimensionless impulse data suggest that the asymptotic limit of bed load tracer dispersion is superdiffusive in line with a broad class of geophysical flows exhibiting strong directional asymmetry advection thin tailed step lengths and heavy tailed waiting times the impulse framework justifies the use of quasi steady flow approximations for long term river evolution modeling

equatorially forced intraseasonal propagations along the peru chile coast and their relation with the nearshore eddy activity in 1992 2000 a modeling study 1 a regional eddy resolving oceanic model spanning the 1992 2000 period is used to study the influence of 50 to 80 day intraseasonal equatorial kelvin waves iekw on mesoscale eddy activity off the west coast of peru and northern and central chile the model is shown to realistically simulate nearshore intraseasonal sea level variability poleward propagation of equatorially forced coastal trapped waves along the coastal waveguide and offshore variability related to mesoscale eddies and rossby waves rw in agreement with linear theory rw are confined equatorward of 12 s in the 50 80 days period range south of that critical latitude westward propagation is dominated by energetic mesoscale signals resulting mainly from coastal flow instability sensitivity experiments to the open boundary conditions are then used to estimate to what extent eddy activity is impacted by the remote equatorial forcing a coastal increase in eddy kinetic energy related to the energetic 60 day iekw activity present in the open boundary forcing is evidenced and is largest off northern peru whereas no major changes are observed offshore additional regional simulations with different open boundary conditions corroborate our findings and suggest that this limited effect of iekw on the offshore eddy kinetic energy may be a robust feature citation belmadani a v echevin b dewitte and f colas 2012 equatorially forced intraseasonal propagations along the peru chile coast and their relation with the nearshore eddy activity in 1992 2000 a modeling study j geophys res 117 c04025 doi 10 1029 2011jc007848

distribution and bioturbation effects of the tropical alpheid shrimp alpheus macellarius in sediments impacted by milkfish farming the impact of milkfish fish pens on the distribution of the alpheid shrimp alpheus macellarius was studied in the bolinao area philippines in addition the impact of the alpheid shrimp on sediment biogeochemistry including organic matter mineralization nutrient and sulfur cycling was compared in sediments affected and unaffected by fish farming the fish farming activity had negative impact on the distribution of shrimps by reducing the abundance up to 60 in the vicinity of the net pens and to almost absence inside the net pens at a farm site abandoned seven month prior to sampling the abundance of shrimps was still low and sediment pools of reduced sulfur high indicating a slow benthic recovery the shrimp had large physical impact on the sediments and the mineralization rates were stimulated by the presence of the shrimp in pristine sediments whereas the fish farm impacted sites showed high mineralization rates both in sediments with and without the presence of the shrimp suggesting that the organic matter enrichment stimulated the mineralization in these low organic sediments whereas the shrimp had less impact sulfate reduction rates and in particular pools of sulfides increased in the farm impacted sediments and sulfate reduction was an important process for organic matter mineralization 67 in all sediments although the shrimp had minor effect on the organic matter mineralization and nutrient fluxes in the farm impacted sediments they appeared to increase the oxidation of sulfides by increasing the zone of oxidized surface sediment and thereby improving the sediment conditions for recolonization after fish farming has ceased

holocene periodicity in north atlantic climate and deep ocean flow south of iceland climate fluctuations during the past millennium are relatively well documented1 on a longer timescale there is growing evidence of millennial scale variability of holocene climate at periodicities of 2 500 and 950 years possibly caused by changes in solar flux 2 3 and 1 500 years maybe related to an internal oscillation of the climate system 4 5 6 but the involvement of deep water masses in these holocene climate changes has yet to be established here we use sediment grain size data from the iceland basin to reconstruct past changes in the speed of deep water flow the study site is under the influence of iceland scotland overflow water isow the flow of which is an important component of the thermohaline circulation that modulates european climate flow changes coincide with some known climate events the little ice age and the mediaeval warm period and extend over the entire holocene epoch with aquasi periodicity of 1 500 years the grain size data indicate afaster isow flow when the climate of northern europe is warmer however a second mode of operation is observed in the early holocene when warm climate intervals are associated with slower isow flow at that time the melting remnant of land based glacial age ice may have provided a sufficient source of fresh water to the ocean to reduce isow flow south of iceland

dynamics of the low level jet off the west coast of subtropical south america the subtropical west coast of south america is under the influence of the southeast pacific anticyclone year round which induces persistent southerly winds along the coast of north central chile these winds often take the form of a low level coastal jet in many aspects similar to the coastal jet existing off the california coast extensive diagnostics of mesoscale model results for a case in october 2000 are used here to describe the mean momentum budget supporting the coastal jet the jet appears to occur when midlatitude synoptic conditions induce a northerly directed pressure gradient force along the coast of northcentral chile the very steep coastal terrain precludes the development of a significant easterly low level wind that would geostrophically balance the pressure gradient instead the meridional flow accelerates until turbulent friction in the marine boundary layer balances the meridional pressure gradient the resulting force balance is semigeostrophic with geostrophy valid only in the zonal cross shore direction at higher levels the topographic inhibition of the easterlies relaxes and a small easterly flow ensues which turns out to be very important in the temperature and stability budgets of the layer capping the marine boundary layer

equilibrium structure and dynamics of the california current system this paper addresses the structure and dynamical mechanisms of regional and mesoscale physical variability in the subtropical northeast pacific ocean using the regional oceanic modeling system roms the model is configured with a u s west coast domain that spans the california current system ccs with a mesoscale horizontal resolution up to as fine as 3 5 km its mean seasonal forcing is by momentum heat and water fluxes at the surface and adaptive nudging to gyre scale fields at the open water boundaries its equilibrium solutions show realistic mean and seasonal states and vigorous mesoscale eddies fronts and filaments the level of eddy kinetic energy eke in the model is comparable to drifter and altimeter estimates in the solutions with sufficiently fine resolution because the model lacks nonseasonal transient forcing the authors conclude that the dominant mesoscale variability in the ccs is intrinsic rather than transiently forced the primary eddy generation mechanism is the baroclinic instability of upwelling alongshore currents there is progressive movement of meanseasonal currents and eddy energy offshore and downward into the oceanic interior in an annually recurrent cycle the associated offshore eddy heat fluxes provide the principal balance against nearshore cooling by mean ekman transport and upwelling the currents are highly nonuniform along the coast with important influences by capes and ridges in both maintaining mean standing eddies and launching transient filaments and fronts

the isotopic signature of planktonic foraminifera from ne atlantic surface sediments implications for the reconstruction of past oceanic conditions the stable isotope compositions of the planktonic foraminifera globigerina bulloides globigerinoides ruber white and pink varieties globigerinoides trilobus globorotalia inflata and globorotalia truncatulinoides right and left coiling types were examined as recorders of north atlantic surface water properties based on 40 box core surface sediments between 60 and 30 n while g ruber white and pink varieties and g trilobus mainly reflect summer surface water conditions in their oxygen isotope composition g bulloides reflects temperatures of the northward migrating spring bloom february march in the south to may june in the north our data show that g bulloides cannot be regarded as an indicator for summer temperatures as deduced from duplessy et al s data gt inflata and gt truncatulinoides right and left coiling build their shells in the coldest waters compared with the other species and reflect temperatures between 100 and 400 m water depth the difference in oxygen isotope composition between g bulloides and g inflata serves as a proxy for water mass stratification g bulloides is the only species that gives a distinct pattern in its carbon isotopic composition showing a high correlation with the surface water phosphate values along the transect and may serve as a proxy for palaeonutrients and or productivity

synchronized terrestrial atmospheric deglacial records around the north atlantic on the basis of synchronization of three carbon 14 c 14 dated lacustrine sequences from sweden with tree ring and ice core records the absolute age of the younger dryas preboreal climatic shift was determined to be 11 450 to 11 390 80 years before the present a 150 year long cooling in the early preboreal associated with rising delta 14 c values is evident in all records and indicates an ocean ventilation change this cooling is similar to earlier deglacial coolings and box model calculations suggest that they all may have been the result of increased freshwater forcing that inhibited the strength of the north atlantic heat conveyor although the younger dryas may have begun as an anomalous meltwater event

ranking of dissolution susceptibility of planktonic foraminifera at high latitudes of the south atlantic ocean surface sediment samples from the maurice ewing bank eastern falkland plateau south atlantic ocean have been analyzed to rank dissolution susceptibility of cool water planktonic foraminiferal species a dissolution index is formulated from quantitative analyses of sedimentological properties caco3 content frequency of planktonic foraminiferal fragments radiolarians mineral grains and ratio of a dissolution tolerant to a dissolution susceptible planktonic foraminiferal species this index is used to assess degrees of dissolution in the samples quantified differences in relative abundance of species between the two dissolution regimes less prominent and stronger dissolution formed the basis for differentiation the species were ranked in the following order from most resistant to least resistant sinistrally coiled variety ofneogloboquadrina pachyderma antarctic variety of this species globorotalia inflata g truncatulinoides globigerina bulloides andglobigerinita glutinata a tie dextraln pachyderma subantarctic variety globigerinita uvula andglobigerina quinqueloba fragmentation frequency of damaged tests increases with increasing dissolution in tolerant species but not in susceptible species this may be because susceptible species are completely dissolved under intense dissolution whereas tolerant species although damaged remain and increase in abundance

transport and degradation of phytoplankton in permeable sediment in flume and field experiments we demonstrate that interfacial water flows generated when bottom currents interact with sea bed topography provide a fast and efficient pathway for the transport of suspended phytoplankton into subsurface layers of permeable sandy sediments the advective transport associated with small mounds and ripples as commonly found on shelf sediments increased penetration depth of unicellular algae dunaliella spec into sandy sediment permeability k 5 4 3 10 211 m 2 up to a factor of 7 and flux up to a factor of 9 relative to a smooth control sediment the pore water flow field produced a distinct distribution pattern of particulate organic matter in the sediment with subsurface concentration maxima and zones depleted of algae flux chamber simulations of advective transport of algae into sands of different grain sizes revealed increasing fluxes algal penetration depths and degradation rates with increasing permeability of the sediment two experiments conducted in intertidal sand flats confirmed the importance of the advective interfacial transport of phytoplankton for natural settings showing permeability dependent penetration of planktonic algae into embedded sand cores of different grain sizes the significance of our results is discussed with respect to particulate organic matter flux and mineralization in shelf sands and we suggest the concept of a decomposition layer in contrast to muddy sea beds with low permeabilities where transport of solutes is mainly driven by diffusion water can flow through marine sands providing a fast carrier for the exchange of substances between the water column and the upper sediment layers surface gravity waves cause pressure oscillations that increase fluid exchange at the sediment water interface and dispersion of solutes within the

enhancement of denitrification in permeable carbonate sediment due to intra granular porosity a multi scale modelling analysis abstract it has recently been hypothesized that bulk denitrification rates in carbonate sands may be enhanced by reactions occurring in the intra granular pores cracks and crevices we tested this hypothesis using a series of flow and reactive transport models spanning from the pore scale mm to the continuum scales 10 cm bedforms pore scale simulations solved the coupled navier stokes and brinkman equations and represented flow through reactor experiments previously performed on coral reef sands the results revealed that intra granular transport and reactions can explain over all denitrification enhancement a sensitivity study with a single grain diffusive transport model showed that in the majority of cases the resultant increase in denitrification was not coupled to nitrification within a single grain only for large grain diameters of 2 and 4 mm was coupled nitrification denitrification important in most cases coupled nitrification denitrification instead arose as conditions became more reducing along a flow path as is the case in quartz sands without intragranular pores an intra granular reaction rate based on a single grain model was incorporated into a continuum scale darcy flow and reactive transport model for a rippled sand bed where porewater flow is driven by the turbulent current over the ripple the results of the darcy scale model suggest that intra granular pores increase the amount of slow flowing areas within which coupled nitrification denitrification can occur we conclude that the complex advective flow field does not strongly inhibit denitrification enhancement by carbonate sand grains as it does in silica sands thus intra granular reactions may enhance bulk denitrification in carbonate sediment with porous grains under natural advective conditions

oxygen minimum zones omzs in the modern ocean in the modern ocean oxygen minimum zones omzs are potential traces of a primitive ocean in which archean bacteria lived and reduced chemical anomalies occurred but omzs are also keys to understanding the present unbalanced nitrogen cycle and the oceans role on atmospheric greenhouse control omzs are the main areas of nitrogen loss as n2 n2o to the atmosphere through denitrification and anammox and could even indirectly mitigate the oceanic biological sequestration of co2 it was recently hypothesized that omzs are going to spread in the coming decades as a consequence of global climate change despite an important omz role for the origin of marine life and for the biogeochemical cycles of carbon and nitrogen there are some key questions on the structure of omzs at a global scale there is no agreement concerning the threshold in oxygen that defines an omz and the extent of an omz is often evaluated by denitrification criteria which at the same time are o2 dependent our work deals with the identification of each omz the evaluation of its extent volume and vertical structure the determination of its seasonality or permanence and the comparison between omzs and denitrification zones at a global scale the co existence in the omz of oxic in its boundaries and suboxic even anoxic in its core conditions involves rather complex biogeochemical processes such as strong remineralization of the organic matter removal of nitrate and release of nitrite the quantitative omz analysis is focused on taking into account the whole water volume under the influence of an omz and adapted to the study of the specific low oxygen biogeochemical processes a characterization of the entire structure for the main and most intense omzs o2 10 mu m maximum zone the larger omz relative to the extent of denitrification zone suggests that the unbalanced nitrogen cycle on the global scale could be more intense than previously recognized and that evaluation of the omz from denitrification could underestimate their extent

short term upwelling events at the western african coast related to synoptic atmospheric structures as derived from satellite observations satellite scatterometers provide continuously valuable surface wind speed and direction estimates over the global ocean on a regular grid both in space and time the level 3 data derived from the advanced scatterometer ascat available at 1 4 spatial resolution hereafter as25 and quick scatterometer quikscat available on 1 2 and 1 4 horizontal grids qs50 and qs25 respectively are studied at regional scales in both the benguela and canary upwelling systems they are compared to the european center for medium range weather forecast surface wind analysis with insight into their intrinsic and actual spatial resolutions in the coastal band the finest spatial patterns are found in the qs25 winds and are o 75 km this demonstrates the sensitivity of the high resolution satellite derived winds to coastal processes related to sea surface temperature sst perturbations and land sea transition next short lived upwelling episodes sues calculated from sst anomalies are defined consistently with the qs25 actual resolution these cold events refer to local short lived perturbations that add to seasonal upwelling variability we characterize concomitant atmospheric synoptic conditions for sues identified at chosen latitudes and highlight two subregions in both upwelling systems with contrasted patterns for the alongshore wind stress component and curl the complexity of the latter patterns is closely linked to local short term sst variability closer to the shore numerical sensitivity experiments show that the imbalance between ekman transport and ekman pumping has an impact on ocean dynamics wind reduction in the coastal qs25 forcing partially induced by orography tends to reduce coastal sst cooling

impact of nearshore wind stress curl on coastal circulation and primary productivity in the peru upwelling system 1 coastal upwelling dynamics are strongly affected by alongshore wind stress and nearshore wind stress curl a coupled physical biogeochemical regional model and lagrangian diagnostics are used in the peru current system to determine how the upwelling of nutrients and the primary productivity are impacted by the spatial structure of the nearshore wind stress three wind stress products derived from the ers and quikscat scatterometers and a smoothed quikscat field mainly differing in nearshore wind stress curl patterns were used simulations are found to produce significantly different mean surface chlorophyll distributions and show that strong upwelling favorable nearshore wind stress curl may locally induce a wide coastal productive zone through upwelling of nutrient replete waters brought by a shoaling coastal undercurrent using wind stress products with realistic nearshore patterns is therefore crucial for the modeling of coupled physical biogeochemical coastal processes

the benguela upwelling system quantifying the sensitivity to resolution and coastal wind representation in a global climate model abstractof all the major coastal upwelling systems in the world s oceans the benguela located off southwest africa is the one that climate models find hardest to simulate well this paper investigates the sensitivity of upwelling processes and of sea surface temperature sst in this region to resolution of the climate model and to the offshore wind structure the community climate system model version 4 is used here together with the regional ocean modeling system the main result is that a realistic wind stress curl at the eastern boundary and a high resolution ocean model are required to well simulate the benguela upwelling system when the wind stress curl is too broad as with a 1 atmosphere model or coarser a sverdrup balance prevails at the eastern boundary implying southward ocean transport extending as far as 30 s and warm advection higher atmosphere resolution up to 0 5 does bring the atmospheric jet closer to the coast but there can be too strong a wind stress curl the most

preservation efficiencies and accumulation rates for biogenic silica and organic c n and p in high latitude sediments the ross sea rates of biogenic sediment accumulation biogenic silica and organic c n and p and pore water flux have been established for a variety of depositional environments in the ross sea on the basis of 14c measurements in kasten cores sediment accumulation rates ranged from 250 cm kyr 1 in the coastal basin of granite harbor to 1 2 cm kyr 1 in the shelf and slope environments of the northern and eastern ross sea burial of biogenic material was most rapid in the southwestern ross sea where biogenic silica accumulation rates ranged from 2 to 31 g cm 2 kyr 1 and organic carbon accumulation rates ranged from 0 05 to 1 4 g cm 2 kyr 1 in the northern and eastern ross sea biogenic silica and organic carbon accumulation rates typically equaled 0 02 0 03 g sio2 cm 2 kyr 1 and 0 002 0 004 g c cm 2 kyr 1 flux core measurements were used to estimate seabed regeneration rates for biogenic silica organic carbon and phosphorus pore water fluxes in general showed much less variability across the ross sea than did the biogenic accumulation rates pore water silicate fluxes in the study area ranged from 0 6 to 5 3 g sio2 cm 2 kyr 1 whereas carbon fluxes ranged from 0 1 to 1 2 g c cm 2 kyr 1 and phosphate fluxes varied from 0 006 to 0 012 g p cm 2 kyr 1 seabed preservation efficiencies were calculated for biogenic silica organic carbon and phosphorus by combining the solid phase and pore water data the seabed preservation efficiencies for biogenic silica 1 86 were greater than for organic carbon 1 71 at all nine stations examined the preferential preservation of biogenic silica relative to organic carbon also was apparent in ross sea sediments because the biogenic silica organic carbon ratio in the material buried in the seabed generally was 2 times greater than the ratio in sediment particles arriving at the sediment water interface sediment accumulation rate correlated strongly with both the biogenic silica and the organic carbon preservation efficiency data p preservation efficiencies remained relatively high 24 65 even when the accumulation rates were low 1 2 cm kyr 1 because of the near zero phosphate fluxes out of the seabed of the total p in the seabed 0 04 0 09 wt approximately 25 existed in the form of organic p the total amount of biogenic silica accumulating on the ross sea shelf is 2 3 1012 g sio2 yr 1 which is approximately an order of magnitude less than the ledford hoffman et al 1986 estimate that was based on 210pb chronologies biogenic silica accumulation rates in the southern central and western ross sea increased during the mid and late holocene reaching their maximum values during the past 500 to 1000 years

palaeoenvironmental history of the last six centuries in the nettilling lake area baffin island canada a multi proxy analysis the baffin island region in the eastern canadian arctic has recently experienced a rapid warming possibly unprecedented in millennia to investigate theresponse of freshwater environments to this warming and place it in a secular perspective we analyzed a 90 cm long sediment core from nettilling lake the largest lake of the canadian arctic archipelago the core was taken from a part of the lake basin that receives meltwater and sediment inputs from thenearby penny ice cap the core time scale established using 137cs and palaeomagnetic techniques spans an estimated 600 years a multi proxy approachwas used to document changes in the physical chemical and biological properties of the sediments we found evidence for a relatively warm period mid late 15th century to mid late 16th century during the early part of the little ice age lia characterized by high sedimentation rates and laminations this was followed by colder drier and windier conditions corresponding to the coldest phase of lia and coinciding with the latest and most extensiveperiod of regional ice cap expansion early 16th to late 19th centuries a rapid warming occurred at the beginning of the 20th century variations intitanium ti content in the core a proxy for detrital sediment inputs showed good agreement with reconstructed secular variations in summer meltrates on penny ice cap between the mid 14th century and the present day providing supporting evidence for a climatic hydrological connection betweenthe ice cap and nettilling lake

radiometrically determined sedimentary fluxes in the sub polar north atlantic during the last 140 000 years abstract we have examined the record of sediment input during the last 140 000 years in a deep sea core from 49 27 n 22 16 w in the eastern north atlantic using uranium series disequilibria to constrain time we have calculated mass fluxes of total sediment as well as mass and particle fluxes of major sedimentary components sediment accumulation rates were generally lower and relatively constant during broadly defined interglacial intervals driven primarily by the burial of biogenic material accumulation rates were higher and more variable during glacial intervals and were influenced primarily by terrigenous material peaks in bulk mass fluxes were associated with particular episodes heinrich events within the last glacial and during each of the last two deglaciations the flux of ice rafted debris as uniquely identified by coarse detrital fragments was higher during layers representing each of the glacial heinrich events with modest increases during events h3 and h6 and dramatic increases during the others confirming the widespread interpretation of these layers as episodes of enhanced iceberg delivery the burial flux of foraminifera was markedly lower during each of the glacial heinrich events also confirming the original identification of these layers as barren intervals ice rafting events within marine isotope stage 5 left neither a large detrital nor biogenic flux imprint at our study site variations in the burial rates of non carbonate sediments were largely responsible for overall changes in sediment accumulation throughout the last climate cycle ice rafting was apparently an important delivery mechanism for this terrigenous material the instantaneous chronometer established here for the last 140 000 years in the subpolar north atlantic allows the transformation of existing and subsequent data from relative values to absolute burial fluxes

grain size and depositional environment as predictors of permeability in coastal marine sands more than half of the surface sediments covering the continental shelves are sandy which may permit substantial sub seafloor pore water advection knowledge of sediment permeability is required for quantifying advection and associated solute transport but studies of marine sediments typically report grain size analyses rather than permeability here data from 23 studies were examined to determine the range in permeabilities reported for sublittoral marine sands and to assess the utility of permeability grain size relationships in this setting in the resulting database the permeability of small w30 cm undisturbed cores collected from the sea floor all fell between 2 10 12 and 4 10 10 m 2 a range where advective transport induced by wave and current action should be pervasive the range in grain size was very similar for near shore 10 m water depth but the permeability of the continental shelf samples was consistently lower for the same median grain size empirical permeability grain size relationships generated a poor fit r 2 0 35 for the aggregate data but separate relationships for near shore and continental shelf samples were significantly better r 2 0 66 and 0 77 respectively permeability grain size relationships thus may be useful for sublittoral sands but a larger database needs to be accumulated before reliable fit parameters and variability can be predicted thus it is recommended that permeability be routinely determined when characterizing sedimentological properties of marine sand deposits concurrent determinations of sediment bulk density and porosity may further improve estimates of permeability 2008 published by elsevier ltd

an analysis of sst gradients off the peruvian coast the impact of going to higher resolution abstract the peruvian coastal upwelling system pcus is one of the most productive fisheries in the world upwelling events are associated with changes in the magnitude and location of frontal structures sst gradients from four different data sets ncdc remss ostia and mur are compared in two test areas off the pcus paita 5 s and pisco 14 s in both areas gradients derived from the mur data set show greater magnitudes as well as larger seasonal cycles off pisco the magnitude of the seasonal cycle of 2 2 c 100 km in mur is larger than the one derived from the lower resolution data sets all data sets at pisco exhibit a seasonal cycle that peaks in late austral summer and early fall hovmoller diagrams calculated at 5 5 s 10 5 s and 14 5 s show clearly defined offshore maxima in the cross shore gradients for all the data sets upwelling scales determined by the distance to the first maxima vary depending on the data set used at 5 5 s upwelling scales vary from 10 km for mur to 50 km for ncdc at 14 5 s the scales vary from 20 km for mur to 40 km for ostia all four data sets show similar large scale structures associated with the peruvian upwelling however mur shows finer scale structures that are most likely due to submesoscale to mesoscale eddies sub sampled mur 1 km data at the 25 km 9 km and 4 km resolutions compare well in magnitude and phase with the lower resolution products agreement in gradient magnitude between the lower resolution data sets and the mur sub sampled at their respective resolutions implies that the pixel to pixel analysis noise in mur is at a similar level as the other data sets

the north atlantic atmosphere sea surface 14c gradient during the younger dryas climatic event abstract we attempt to quantify the 14c difference between the atmosphere and the north atlantic surface during a prominent climatic period of the last deglaciation the younger dryas event yd our working hypothesis is that the north atlantic may have experienced a measurable change in 14c reservoir age due to large changes of the polar front position and variations in the mode and rate of north atlantic deep water nadw production we dated contemporaneous samples of terrestrial plant remains and sea surface carbonates in order to evaluate the past atmosphere sea surface 14c gradient we selected terrestrial vegetal macrofossils and planktonic foraminifera neogloboquadrina pachyderma left coiling mixed with the same volcanic tephra the vedde ash bed which occurred during the yd and which can be recognized in north european lake sediments and north atlantic deep sea sediments based on ams ages from two norwegian sites we obtained about 10 300 yr bp for the atmospheric 14c age of the volcanic eruption foraminifera from four north atlantic deep sea cores selected for their high sedimentation rates 10 cm kyr 1 were dated by ams 21 samples for each core the raw 14c ages assigned to the ash layer peak is significantly older than the 14c age obtained on land part of this discrepancy is due to bioturbation which is shown by numerical modelling nevertheless after correction of a bioturbation bias the mean 14c age obtained on the planktonic foraminifera is still about 11 000 11 100 yr bp the atmosphere sea surface 14c difference was roughly 700 800 yr during the yd whereas today it is 400 500 yr a reduced advection of surface waters to the north atlantic and the presence of sea ice are identified as potential causes of the high 14c reservoir age during the yd

seasonal and interannual variability of currents and temperature off central chile results are reported for continuous 6 year records of current and temperature from a continental slope station at 308s off chile these observations for november 1991 to november 1997 span the moderate weak and strong el nino events of 1991 1992 1994 and 1997 and the la nina event of 1995 1996 results for current and temperature are analyzed together with observations of wind along the south american coast from the ers 1 and 2 satellite scatterometers wind from a local coastal site sea level from northern and central chile sea surface temperature anomalies from the south pacific region and traditional el nino indices mean poleward flow of 12 8 cm s 21 was observed for the 6 year period in the core of the peru chile undercurrent 220 m mean flow in the depth range of antarctic intermediate water 750 m was equatorward at 1 1 cm s 21 intraseasonal scale variability associated with coastal trapped waves was weaker during the austral winter greatest during el nino events and weakest during the la nina event winds adjacent to the coast showed a strong annual cycle with a southward progression of maximum equatorward upwelling favorable winds alongshore flow over the slope exhibited strong semiannual and weaker annual variations poleward flow in the undercurrent was strongest in the austral spring and fall and weakest in the winter near the bottom 750 m seasonal scale variability was less intense but led that higher up in the water column 220 m by 1 month strong interannual variability of alongshore current and temperature was found at all depths over the slope whereby changes at depth led changes higher up a rapid warming event was observed at the end of 1996 beginning of 1997 over the slope this event also seen in sea level and sea surface temperature off chile led el nino indices by several months and may be best explained by local wind anomalies coupled to atmospheric teleconnections from the western tropical pacific at the onset of el nino some aspects of our current and temperature observations are consistent with results from eastern boundary current models our results indicate that both ocean and atmosphere pathways from the equatorial pacific contribute significantly to interannual scale variability of alongshore flow and thermocline depth off chile

what level of resolution is attainable in a deep sea core results of a spectrophotometer study a minolta cm 2022 spectrophotometer has been used to characterize downcore fluctuations in sediment lightness and color in core neap15k a 7 m core collected from the northeast atlantic ocean high resolution data series measured using a 4 mm diameter measurement spot and a 1 cm sampling interval were generated along two independent tracks down the core to investigate the statistical significance of fluctuations across the 2 20 cm depth range this small scale variability is characterized by abrupt changes in the lightness and color of the sediment that are several orders of magnitude greater than the instrumental precision our results establish that significant information is preserved at the 1 cm scale in spite of bioturbation effects these findings demonstrate that high resolution studies using conventional paleoclimatic proxies have the potential to recover meaningful century scale climate records in regions of the ocean where sedimentation rates exceed 10 cm per thousand years the coherency of these downcore records also implies that the spectrophotometer is a powerful instrument for establishing precise centimeter scale stratigraphic correlations between cores

sst wind interaction in coastal upwelling oceanic simulation with empirical coupling observations primarilyfromsatellites haveshownastatisticalrelationshipbetweenthesurfacewindstress and underlying sea surface temperature sst on intermediate space and time scales in many regions inclusive of eastern boundary upwelling current systems in this paper this empirical sst wind stress relationship is utilized to provide a simple representation of mesoscale air sea coupling for an oceanic model forced by surface winds namely the regional oceanic modeling system roms this model formulation is applied to an idealized upwelling problem with prevailing equatorward winds to determine the coupling consequencesonflow sst stratification andwindevolutions theinitiallyuniformwindfieldadjuststhrough coupling to a cross shore profile with weaker nearshore winds similar to realistic ones the modified wind stress weakens the nearshore upwelling circulation and increases sst in the coastal zone the sst induced wind stress curl strengthens offshore upwelling through ekman suction the total curl driven upwelling exceeds the coastal upwelling the sst induced changes in the nearshore wind stress field also strengthen and broaden the poleward undercurrent the coupling also shows significant impact on the developing mesoscale eddies by damaging cyclonic eddies more than anticyclonic eddies which leads to dominance by the latter dynamically this is a consequence of cyclones with stronger sst gradients that induce stronger wind perturbations inthis particularupwellingproblemandthatarethereforegenerally moresusceptibletodisruption than anticyclones at finite rossby number the net effect is a weakening of eddy kinetic energy

characterizing low temperature aqueous alteration of mars analog basalts from mauna kea at multiple scales we performed a multi scale characterization of aqueous alteration of mars analog basaltic rock from a mauna kea drill core using high resolution visible and short wave infrared vis swir spectral imaging scanning electron microscopy x ray diffraction and point vis swir spectra several types of smectites zeolites and primary minerals were identified mineral classes were mapped in cut sections extracted from the drill core and used to represent the range of alteration products seen in field data collected over 1000 m depth calvin et al 2020 ten distinct spectral end members identified in the cut sections were used to map the field point spectra trioctahedral fe and mg rich smectites were present toward the top of the zone of analysis 972 m below the surface and increased in abundance toward the bottom of the drill core 1763 m depth the mineralogy demonstrates a general trend of discontinuous alteration that increases in intensity with depth with less pervasive phyllosilicate alteration at the top several zones of different mixtures of zeolites toward the center followed by more abundant phyllosilicates in the lowest sections distinctly absent are fe mg phyllosilicates other than smectites as well as carbonates sulfates and al phyllosilicates such as kaolinite or illite furthermore hematite was only detected in two of 24 samples the suite of assemblages points to aqueous alteration at low to moderate temperatures at neutral to basic ph in low oxygen conditions with little evidence of extensive surface interaction presenting a possible analog for an early mars subsurface environment we also present a library of vis swir spectra of the analyzed cut sections including both spatial averages i e unweighted linear mixtures of spectral images of each cut section and single point spectra of the cut sections this will allow for consideration of nonlinear mixing effects in point spectra of these assemblages from natural surfaces in future terrestrial or planetary work

the role of the deep ocean in north atlantic climate change between 70 and 130 kyr ago the suggestion1 that changes in north atlantic deep water nadw production are linked through surface heat flux to the atmospheric temperature over greenland is supported by earlier indications2 3 that nadw production decreased during glacial times and by the subsequent finding4 6 that it declined during the younger dryas cool period at the end of the last glaciation changes in north atlantic surface temperatures have been found7 to mirror high frequency temperature changes recorded in greenland ice cores over the past 80 kyr but the connection to abyssal circulation has yet to be established except for one or two isolated oscillations8 9 here we present carbon and oxygen isotope analyses of benthic foraminifera in a high resolution north atlantic deep sea sediment core for the period 70 130 kyr ago these data allow us to reconstruct the history of nadw production which shows a close correlation with greenland climate variability for much of this time interval suggesting that the climate influence of nadw variability was widespread we see no evidence however for changes in nadw production during substage 5e the eemian interglacial period in contrast with recent ice core data10 which suggest severe climate instability in greenland during this time period our results may support suggestions based on data from a second ice core that this apparent instability is an artefact caused by ice flow11 alternatively the eemian climate instability may have had a different origin from the subsequent climate events

what shapes mesoscale wind anomalies in coastal upwelling zones observational studies have shown that mesoscale variations in sea surface temperature may induce mesoscale variations in wind in eastern subtropical upwelling regions such as the california coast this mechanism could be of great importance for the mean state and variability of the climate system in coastal regions orography also creates mesoscale variations in wind and the orographic effect may extend more than 100 km offshore the respective roles of sst wind links and coastal orography in shaping mesoscale wind variations in nearshore regions is not clear we address this question in the context of the california upwelling system using a high resolution regional numerical modeling system coupling the wrf atmospheric model to the roms oceanic model as well as additional uncoupled experiments to quantify and separate the effects of sst wind links and coastal orography on mesoscale wind variations after taking into account potential biases in the representation of the strength of sst wind links by the model our results suggest that the magnitude of mesoscale wind variations arising from the orographic effects is roughly twice that of wind variations associated with mesoscale sst anomalies this indicates that even in this region where coastal orography is complex and leaves a strong imprint on coastal winds the role of sst winds links in shaping coastal circulation and climate cannot be neglected

numerical study of convection observed during the winter monsoon experiment using a mesoscale two dimensional model abstract a two dimensional version of the pennsylvania state university mesoscale model has been applied to winter monsoon experiment data in order to simulate the diurnally occurring convection observed over the south china sea the domain includes a representation of part of borneo as well as the sea so that the model can simulate the initiation of convection also included in the model are parameterizations of mesoscale ice phase and moisture processes and longwave and shortwave radiation with a diurnal cycle this allows use of the model to test the relative importance of various heating mechanisms to the stratiform cloud deck which typically occupies several hundred kilometers of the domain frank and cohen s cumulus parameterization scheme is employed to represent vital unresolved vertical transports in the convective area the major conclusions are ice phase processes are important in determining the level of maximum large scale heating and vertical motion because there is a strong anvil componen

orographic shaping of us west coast wind profiles during the upwelling season spatial and temporal variability of nearshore winds in eastern boundary current systems is affected by orography coastline shape and air sea interaction these lead to a weakening of the wind close to the coast the so called wind drop off in this study regional atmospheric simulations over the us west coast are used to demonstrate monthly characteristics of the wind drop off and assess the mechanisms controlling it using a long term simulation we show the wind drop off has spatial and seasonal variability in both its offshore extent and intensity the offshore extent varies from around 10 to 80 km from the coast and the wind reduction from 10 to 80 we show that when the mountain orography is combined with the coastline shape of a cape it has the biggest influence on wind drop off the primary associated processes are the orographically induced vortex stretching and the surface drag related to turbulent momentum flux divergence that has an enhanced drag coefficient over land orographically induced tilting twisting can also be locally significant in the vicinity of capes the land sea drag difference acts as a barrier to encroachment of the wind onto the land through turbulent momentum flux divergence it turns the wind parallel to the shore and slightly reduces it close to the coast another minor factor is the sharp coastal sea surface temperature front associated with upwelling this can weaken the surface wind in the coastal strip by shallowing the marine boundary layer and decoupling it from the overlying troposphere

stoichiometric modeling of carbon diagenesis within a coral reef framework abstract water sampled from the interior framework of checker reef oahu hawaii indicates that the aerobic and anaerobic oxidation of organic matter dominates diagenesis within the reef framework reef interstitial water chemistry shows clear deviations from surface seawater oxygen is depleted while dissolved inorganic carbon h inorganic nutrients sulfide and methane concentrations are elevated dissolved calcium is also elevated in most interstitial waters indicating net dissolution of calcium carbonates a mass balance model used to determine the extent to which major biogeochemical reactions occur reveals that sulfate reduction is the predominant anaerobic process

evidence for enhanced phosphorus regeneration from marine sediments overlain by oxygen depleted waters phosphorus regeneration and burial fluxes determined from in situ benthic flux chamber and solid phase measurements at sites on the californian continental margin peruvian continental slope north carolina continental slope and from the santa monica basin california are reported comparison of these sites indicates that o2 depleted bottomwaters enhance p regeneration from sediments diminishing overall phosphorus burial efficiency based on these observations a positive feedback linking ocean anoxia enhanced benthic phosphorus regeneration and marine productivity is proposed on shorter timescales these results also suggest that o2 depletion in coastal regions caused by eutrophication may enhance p regeneration from sediments thereby providing additional p necessary for increased biological productivity