diatom inferred salinity in palaeolakes an indirect tracer of climate change lakes in arid and semi arid regions respond to climatic change through shifts in lake water volume and ionic concentration because diatom distribution is highly correlated with lake hydrochemistry diatoms can be used to infer changes in salinity and brine composition and thus to infer past climates here we critically examine the use of diatom inferred salinity as a climate proxy with examples taken from both modern waterbodies and sedimentary profiles sediment records may contain assemblages mixed from periods or sites of differing hydrochemistries because of the high degree of spatial and temporal heterogeneity in saline systems dissolution and diagenesis in saline brines may further complicate interpretation of sedimentary assemblages furthermore threshold effects salinity regulation via groundwater seepage antecedent conditions and other aspects of local hydrology may modify the relationship between salinity change and climatic forcing these complexities necessitate critical examination of the ecology and taphonomy of sedimentary assemblages as well as evaluation of potential non linearities in the salinity climate relationship through comparison of diatom inferred salinity with other proxy records of hydrochemical change historical documents where they exist and with other regional lake systems

air pollutant contamination and acidification of surface waters in the north york moors uk multi proxy evidence from the sediments of a moorland pool despite the extensive geographical range of palaeolimnological studies designed to assess the extent of surface water acidification in the united kingdom during the 1980s little attention was paid to the status of surface waters in the north york moors nym in this paper we present sediment core data from a moorland pool in the nym that provide a record of air pollution contamination and surface water acidification the 41 cm long core was divided into three lithostratigraphic units the lower two comprise peaty soils and peats respectively that date to between approximately 8080 and 6740 cal bp the uppermost unit comprises peaty lake muds dating from between approximately ad 1790 and the present day ad 2006 the lower two units contain pollen dominated by forest taxa whereas the uppermost unit contains pollen indicative of open landscape conditions similar to those of the present heavy metal spheroidal carbonaceous particle mineral magnetics and stable isotope analysis of the upper sediments show clear evidence of contamination by air pollutants derived from fossil fuel combustion over the last c 150 years and diatom analysis indicates that the naturally acidic pool became more acidic during the 20th century we conclude that the exceptionally acidic surface waters of the pool at present ph c 4 1 are the result of a long history of air pollution and not because of naturally acidic local conditions we argue that the highly acidic surface waters elsewhere in the nym are similarly acidified and that the lack of evidence of significant recovery from acidification despite major reductions in the emissions of acidic gases that have taken place over the last c 30 years indicates the continuing influence of pollutant sulphur stored in catchment peats a legacy of over 150 years of acid deposition

assessing the potential for developing internal diatom based transfer functions for lake baikal we explore possible quantitative relationships between diatom species and environmental data for lake baikal using multivariate techniques our approach differs from published studies in other regions on training sets and transfer functions because 1 although only one lake is examined we use the internal lake gradients rather than gradients among lakes and 2 the majority of the dominant diatom taxa are endemic canonical correspondence analysis on 93 surface sediment diatom assemblages reveals that major taxa show distinct relationships with measured environmental variables five significant variables were identified snow thickness on ice which accumulates on the frozen lake surface between january and april may water depth suspended matter annual solar radiation and mean july temperature of surface waters the strongest relationship is with snow thickness which influences light levels in the water below the ice a diatom based inference model has been developed to predict snow thickness on the ice using weighted averaging wa and wa with tolerance down weighting wa tol models results suggest that lake baikal diatom assemblages in surface sediments can be used to develop a robust model for estimating snow thickness across frozen lake baikal r 2 jack 0 607 rmsep 0 138 log cm this model has potential applications for recent paleoclimate studies in this region of continental eurasia

melting runoff and the formation of frozen lakes in a mixed snow and blue ice field in dronning maud land antarctica large scale melting phenomena such as meltwater drainage channels and meltwater accumulation basins of frozen lakes were surveyed on the land ice mass in jutulgryta dronning maud land antarctica during the norwegian antarctic research expedition in 1989 90 nare 1989 90 the largest frozen lake that was observed was close to 1 km in width these melting features were also detected in a landsat thematic mapper image recorded on 12 february 1990 then during nare 1993 94 a 5year glaciological programme was started in this area in spite of negative air temperatures and the presence of a frozen ice surface sub surface melting and runoff were found within the uppermost metre in blue ice fields the sub surface melting is a consequence of solar radiative penetration and absorption within the ice i e the solid state greenhouse effect temperatures in blue ice were about 6 c higher than for snow internal melt and meltwater transport were observed throughout the 1 month of measurements the conditions for active melting in jutulgryta are probably marginal a slight increase of air temperatures can result in more classical surface melting whereas a cooling may disable sub surface melting studies of how the extent and characteristics of the melting features change with time can be particularly valuable as indicators of climate change this ongoing programme clearly identifies the importance of analyzing how these melting features originate of mapping their present areal distribution of determining how sensitive they are to climate change and of studying changes in the past and possible changes in the future

a record of pleistocene diatom preservation from the amundsen sea west antarctica with possible implications on silica leakage article i nfo accumulation of fossil diatoms in marine sediments is variably affected by the production and dissolution of diatom frustules across space and time no quantitative proxy exists for estimating the amount of silica lost to dissolution in southern ocean sediment cores to address this gap cultured valves of fragilariopsis kerguelensis the dominant planktonic diatom in the pleistocene to recent southern ocean were dissolved progressively under controlled laboratory conditions expansion and eventual conjoining of the areolae of f kerguelensis advances through several phases which are presented herein as a measure of diatom dissolution in order to evaluate the validity of laboratory methods this proxy is applied to sediments from piston core ps58 254 from the amundsen sea dissolution induced degradation morphologies from laboratory experiments are seen to be identical to those preserved naturally in sediments thus suggesting the laboratory conditions accurately reflect the natural process of dissolution these resultsrepresentthe firstapplication of afullyquantitativeproxyfordiatomdissolution tosouthernocean sediments revealing that meaningful paleoceanographic data can be generated via taphonomic analysis of diatom valves intensity of diatom dissolution in core ps58 254 does not correspond to the relative abundance of any diatom species clay mineralogy or linear sedimentation rates however a correlation does exist between glacial cyclicity and diatom dissolution indicating that variation in average wall thickness and susceptibility to dissolution reflects primary conditions during formation of the silica wall transit through the water column and eventual deposition higher overall silica dissolution is observed during each glacial period and enhanced silica preservation during interglacials this result is consistent with the predictions of the silicic acid leakage hypothesis salh whereby reduced rates of si usage in the southern ocean lead to shifts in marine primary productivity in the tropics from coccolithophoriddominance duringinterglacialstodiatomdominanceduringglacials thiswouldfuela decrease in atmospheric pco2duringglacials silica acidleakage isdrivenbya decreaseinthe si nratioofdiatoms caused by increased iron input to glacial aged southern ocean waters this resulted in more lightly silicified diatom valves in the southern ocean which dissolved more quickly in the upper water column thereby maintaining the high silica content of glacial aged so waters and allowing for export of si to upwelling zones in the lower latitudes

reconstructing hydrological variability in lake baikal during mis 11 an application of oxygen isotope analysis of diatom silica in this paper we reconstruct hydrological variability in lake baikal during marine isotope stage 11 mis 11 427 362 ka bp from oxygen isotope analysis of diatom silica highest d 18 odiatom values are found during mis 11 3 highlighting the dominance of hydrological input from rivers flowing into the south and central basins of lake baikal especially the selenga river hydrological input from south basin rivers dominated for over 30 ka however there is evidence from both biogenic silica and d 18 odiatom records for an abrupt cooling event at ca 390 ka bp stadial conditions at this time are coincident with an iceberg discharge event into the north atlantic the decline in d 18 odiatom values suggests increasing proportion of hydrological input from rivers to the north of lake baikal due to greater influence of winter precipitation and snow melt after a period of interstadial conditions during the early stages of mis 11 1 biogenic silica and d 18 odiatom values decline mirroring the slow growth in northern hemisphere ice sheets despite rigorous cleaning procedures palaeoclimatic inferences need to be treated with caution due to contamination of the d 18 odiatom record during stadial and glacial periods contamination of the d 18 odiatom record is even more significant natural environment research council nerc copyright 2008 reproduced with the permission of nerc published by john wiley sons ltd

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

the paleoclimatology of lake baikal a diatom synthesis and prospectus abstract the paleoclimatic archive held in lake baikal sediments is of significant importance given the lake s position in one of the world s most continental regions where there are few continuous high quality records spanning the quaternary here i review diatom and associated biogenic silica records from lake baikal sediments and provide a paleoclimatic synthesis of changes at various timescales over the quaternary i initially highlight major climatic and hydrological aspects of lake baikal as understanding the contemporary system both regionally and within the lake are fundamental to understanding past change interpreted from the sedimentary archive in this respect special attention is given to factors that can affect the integrity of the diatom record most notably dissolution processes these mechanisms are likely to have had a relatively greater impact on the preservation of diatom valves during glacial periods because of overall lower diatom productivity lower diatom numbers and relative increased dissolution during cold periods explains the lack of diatoms and low biogenic silica concentrations found in the lake sediments during glacial periods the biogenic record highlights the nature of the 100 ka cycle especially during the last 800 ka although there is also a strong precessional component further work is needed to reassess biological responses in lake baikal with respect to different orbital forcing mechanisms together with their impacts on evolution and speciation of diatoms the biological record from lake baikal confirms that the last interglacial in central asia lasted approximately 10 5 ka productivity in the lake as inferred from diatom biovolume accumulation rates exhibits millennial scale variability with the occurrence of centennial scale reductions in diatom biomass throughout the last interglacial period the most severe reduction in diatom biomass at c 120 ka bp is concurrent with millennial scale cooling in the north atlantic region links to changes in north atlantic ocean thermohaline circulation via teleconnections are also evident in the nature of the abrupt ecological changes in the lake throughout the last 60 ka linked to ice rafting into the north atlantic otherwise known as heinrich events new robust radiocarbon chronologies for sediments deposited during the late glacial and holocene in lake baikal allow detailed multi decadal records to be constructed for the last 14 000 years cooling events associated with millennial scale cycles are also apparent in the lake baikal record and both the diatom record and oxygen isotope record of the diatom silica highlight that biological responses to these abrupt events are almost simultaneous comparisons made between lake baikal records with others worldwide highlights that many of the holocene cooling events are associated with melt water outburst from the laurentide ice sheet and changes in solar insolation during the last 1000 years snow cover on lake baikal has been inferred from past diatom assemblages and is closely linked to weakening of the north atlantic oscillation allowing increasing intensity of the siberian high to develop and during the 17th and 18th centuries in the last 150 years diatom species have been shown to be sensitive indicators of recent warming however impacts from future global warming will be complex and are likely to impact not only on the balance between endemic and cosmopolitan diatoms throughout the lake but on the balance between siliceous and non siliceous algae and sources of primary productivity

palaeolimnological approaches to climate change with special regard to the biological record abstract lakes systems respond physically chemically and biologically to changes in climate and these responses are registered in many various ways in lake sediment records this paper focuses principally on the biological record and describes recent research that aims to reconstruct i past variability in effective moisture and ii past variability in temperature changes in effective moisture are manifested especially by changes in lake water level in closed lake basins water level change can cause significant changes in water salinity that is registered in sediments by changes in the composition of fossil assemblages especially diatoms in open freshwater lake basins changes in water level are best reconstructed from the aquatic macrofossil record and potentially from the ratio of open water to littoral species of cladocera ostracods and diatoms the most promising biological method for reconstructing past temperature is chironomid analysis and a range of new chironomid temperature transfer functions are being developed however biological responses to changing temperature are usually indirect as a result of temperature effects on water column stratification nutrient cycling and alkalinity generation and in most cases a correct interpretation of the climatic significance of changes in the fossil record requires an understanding of the processes that are operating in the water column a multi proxy whole lake approach is advocated as the best way forward not only as a means of reconstructing past climate but also as a means of assessing the impact of climate change on lake systems

quantitative and qualitative relationships between planktonic diatom communities and diatom assemblages in sedimenting material and surface sediments in lake baikal siberia endemic planktonic diatoms are a major component of lake baikal sediments during interglacial periods to investigate how these diatom assemblages are altered during sediment formation quantitative plankton monitoring 1995 1998 was integrated with sediment trapping over 2 yr 1996 1997 in baikal s southern basin depth 1 400 m the traps consisted of both open 6 monthly and sequential 2 weekly collectors deployed throughout the water column sedimentation was seasonal with diatom species composition valve abundance and total dry mass reflecting changes in the planktonic communities sedimented assemblages were transmitted largely intact to the deepest traps 1 300 1 390 m some compositional blurring occurred from differential sinking rates and dissolution of diatom valves a rapid mass flux event of aulacoseira skvortzowii and a baicalensis was recorded in summer 1997 with particle sinking rates between 60 and 100 m d 21 and dry mass fluxes 5gm 22 d 21 although dissolution was evident for all species more delicate taxa were preferentially affected e g a skvortzowii vegetative cells and finesynedra species whereas nitzschia acicularis valves were almost entirely dissolved within the water column comparing trap and plankton diatom assemblages with those in nearby core tops demonstrated that a fundamental taphonomic change occurs in the surface sediment with sedimentary diatom accumulation rates being only about 1 of trap deposition and plankton production rates dissolution was significant in explaining 5 30 of species variance between all taphonomic levels plankton trap samples and surface sediments results indicate that diatom based paleoclimatic records in lake baikal sediments could be improved and refined by taking taphonomic considerations into account

origin and pathways of winter intermediate water in the northwestern mediterranean sea using observations and numerical simulation received 25 june 2013 revised 31 october 2013 accepted 6 november 2013 published 6 december 2013 1 the study of water masses worldwide their formation spreading mixing and impact on general circulation is essential for a better understanding of the ocean circulation and variability in this paper the formation and main pathways of winter intermediate water wiw in the northwestern mediterranean sea nwmed are investigated during the winter spring 2011 using observations and numerical simulation the main results show that the wiw formed along the continental shelves of the gulf of lion and balearic sea circulates southward following five preferential pathways depending on the wiw formation site location and the oceanic conditions wiw joins the northeastern part of the balearic sea or flows along the continental shelves until joining the balearic current maximum of 0 33 sv in early april or further south until the ibiza channel entrance two additional trajectories contributing to water mass exchanges with the southern part of the western mediterranean sea bring the wiw through the ibiza and mallorca channels maxima of 0 26 sv in late march and 0 1 sv in early april respectively the circulation of wiw over the nwmed at 50 200 m depth its mixing and spreading over the western mediterranean sea reaching the south of the balearic islands the algero provencal basin the ligurian and the alboran seas suggest that the wiw may have an impact on the ocean circulation by eddy blocking effect exchange of water masses between north and south subbasins of western mediterranean sea through the ibiza channel or modification of the ocean stratification

particle fluxes induced by benthic storms during the 2012 dense shelf water cascading and open sea convection period in the northwestern mediterranean basin abstract the effects of deep dense shelf water cascading and open sea convection on the sediment dynamics of the northwestern mediterranean basin were studied by near bottom moored instruments recording trapped particle fluxes suspended particle fluxes water properties and hydrodynamics from november 2011 to july 2012 during this period near bottom currents induced by winter dense water formation generated benthic storms that caused resuspension at 2450 m water depth increasing by more than one order of magnitude the ambient suspended sediment concentrations the trapped particle fluxes and the suspended sediment fluxes during the preconditioning phase of the open sea convection from december 2011 to mid february 2012 currents 1 10 cm s 1 suspended sediment concentrations

quantification of the biogenic silica dissolution in southern ocean sediments abstract a transfer function has been established to quantify the dissolution of diatom silica in southern ocean sediments the relationship between the amount of silica dissolution and changes in diatom species distribution is built by controlled progressive dissolution of biogenic silica in five recent sediment samples from box core tops each representative of a modern diatom species sediment assemblage the amount of dissolved silica was measured for each experiment the resulting data set of species abundances 42 samples containing 32 diatom species and 2 silicoflagellate genera was added to the modern data base of diatom species distributed over the southern ocean 124 core tops q mode factor analysis individualizes four factors explaining 83 of the variance the first three factors are controlled by surface water properties mostly temperature the fourth factor is the only one correlated with loss of silica in the reference samples r 0 900 we quantified the dissolution factor using this correlation superficial sediments of the southeast indian ocean are characterized from low to high latitudes by a decrease in silica loss by dissolution from 50 to 10 from the subantarctic zone 40 s to around 55 s followed by an increase of silica loss to values larger than 60 between 63 and 68 s application of the dissolution factor in two cores from the southern ocean 44 and 55 s shows enhanced opal dissolution during the last glaciation particularly during emiliani s stage 3 from 40 000 to 30 000 yr b p

mid to late holocene geomorphological and hydrological changes in the south taihu area of the yangtze delta plain china abstract the taihu plain of the lower yangtze valley china was a centre of rice agriculture during the neolithic period reasons for the rapid development of rice cultivation during this period however have not been fully understood for this coastal lowland which is highly sensitive to sea level change to improve understanding of the geomorphological and hydrological context for evolution of prehistoric rice agriculture two sediment cores dtx4 and dtx10 in the east tiaoxi river plain south taihu plain were collected and analysed for radiocarbon dating diatoms organic carbon and nitrogen stable isotopes 13c and 15n grain size and lithology these multiproxy analyses revealed that prior to ca 7500 cal yr bp the east tiaoxi river plain was a rapidly aggrading high salinity estuary the palaeo taihu estuary after ca 7500 cal yr bp low salinity conditions prevailed as a result of strong yangtze freshwater discharge subsequently seawater penetration occurred and saltmarsh developed between ca 7000 and 6500 cal yr bp due to accelerated relative sea level rise this transgression event influenced a large area of the taihu plain during the holocene as shown by multiple sediment records from previous studies persistent freshwater marsh or subaerial land formed due to dramatic shrinkage closure of the palaeo taihu estuary after ca 5600 cal yr bp when sea level was relatively stable we speculate that geomorphological and hydrological changes of the east tiaoxi river plain played an important role in agricultural development across the taihu plain during the neolithic period the closure of the palaeo taihu estuary and the formation of stable freshwater marsh or subaerial land after ca 5600 cal yr bp were critical preconditions encouraging the rapid rise of rice productivity in the liangzhu period 5500 4500 cal yr bp this development changed the landscape and river systems and thus provided adequate freshwater supply to the taihu plain

below surface ice melt on the coastal antarctic ice sheet in the jutulgryta area of dronning maud land antarctica subsurface melting of the ice sheet has been observed the melting takes place during the summer months in blue ice areas under conditions of below freezing air and surface temperatures adjacent snow covered regions having the same meteorological and climatic conditions experience little or no subsurface melting to help explain and understand the observed melt rate differences in the blue ice and snow covered areas a physically based numerical model of the coupled atmosphere radiation snow and blue ice system has been developed the model comprises a heat transfer equation which includes a spectrally dependent solar radiation source term the penetration of radiation into the snow and blue ice depends on the solar radiation spectrum the surface albedo and the snow and blue ice grain sizes and densities in addition the model uses a complete surface energy balance to define the surface boundary conditions it is run over the full annual cycle simulating temperature profiles and melting and freezing quantities throughout the summer and winter seasons the model is driven and validated using field observations collected during the norwegian antarctic research expedition nare 1996 97 the simulations suggest that the observed differences between subsurface snow and blue ice melting can be explained largely by radiative and heat transfer interactions resulting from differences in albedo grain size and density between the two mediums

tectonostratigraphic evolution of the eastern algerian margin and basin from seismic data and onshore offshore correlation abstract the eastern algerian basin part of the western mediterranean domain is a back arc basin resulting from the se drift of the lesser kabylia block gave rise to continental extension and birth of a new oceanic domain we aim here to define the structure and tectonostratigraphic evolution of this basin and the adjoining continental margin indeed the absence of wells and the lack of published mcs data kept this area mostly unknown the crustal architecture down to the moho and seismo stratigraphy of the sedimentary infill are detailed emphasizing particularly the pre messinian series by combining a new set of offshore deep penetrating seismic conventional mcs sections and wide angle seismic data because no well exist offshore we realized new field descriptions of the late oligocene and miocene deposits on land and propose onshore offshore extrapolation and age correlations the pre messinian series display four main units pmsu1 to 4 above which messinian units are consistent with stratigraphic models already proposed for the mediterranean basin the deep basin displays units as old as the omk oligo miocene kabyle series on land the basement is shaped by conjugate transcurrent faults striking n120 n40 forming a series of rhombic troughs resulting from transtensional tectonics the coeval e w extension and nw se stretching of the continental crust suggest a radial opening of the algerian basin during late oligocene lower miocene followed by a progressive uplift of the upper margin after the collision of lesser kabylia with africa besides steep slope of the eastern algerian margin downward flexure of the oceanic basin near the margin toe and growth of s dipping thrusts within the margin evidence a significant quaternary stress inversion overall this study highlights the complex stress evolution of the east algerian margin since oligocene times as evidenced by significant upward downward vertical motions and crustal extensional compressional successions we summarize this evolution into three main stages 1 rifting including sea floor spreading at late oligocene burdigalian in the context of back arc 2 collision between alkapeca blocks and africa at 17 ma and post rift sag basin infill till late tortonian to messinian and 3 inversion of the margin and development of flexural basins at quaternary times

three dimensional modeling of lacustrine diatom habitat areas improving paleolimnological interpretation of planktic benthic ratios three dimensional modeling of lake morphometry enables the calculation of lake volume planar surface area and basin surface area which are critical components of a conceptual model of how planktic and benthic habitat areas change with changing lake level we have applied three dimensional modeling to foy lake montana and compared model results of changing ratios of planktic and benthic habitat areas at all possible lake levels to sediment cores recovered from the lake the model allows us to produce semiquantitative depth reconstructions and greatly improves lake level reconstruction of this morphometrically complex basin the conceptual model also was modified to examine the influence of resuspension versus gravity redistribution of diatomaceous material on the sedimentary record comparison of the model results with both long and short sedimentary records from foy lake montana suggests that planktic benthic ratios may be a better predictor of mean lake depth than maximum lake depth the model developed here is simple enough to be easily implemented has few requirements can be adapted to suit any lake basin and can be augmented to examine a variety of different lake processes that affect habitat availability

the dilemma of disappearing diatoms incorporating diatom dissolution data into palaeoenvironmental modelling and reconstruction abstract taphonomic issues pose fundamental challenges for quaternary scientists to recover environmental signals from biological proxies and make accurate inferences of past environments the problem of microfossil preservation specifically diatom dissolution remains an important but often overlooked source of error in both qualitative and quantitative reconstructions of key variables from fossil samples especially those using relative abundance data a first step to tackling this complex issue is establishing an objective method of assessing preservation here diatom dissolution that can be applied by different analysts and incorporated into routine counting strategies here we establish a methodology for assessment of diatom dissolution under standard light microscopy lm illustrated with morphological criteria for a range of major diatom valve shapes dissolution data can be applied to numerical models transfer functions from contemporary samples and to fossil material to aid interpretation of stratigraphic profiles and taphonomic pathways of individual taxa using a surface sediment diatom salinity training set from the northern great plains ngp as an example we explore a variety of approaches to include dissolution data in salinity inference models indirectly and directly results show that dissolution data can improve models with apparent dissolution adjusted error rmse up to 15 lower than their unadjusted counterparts internal validation suggests improvements are more modest with bootstrapped prediction errors rmsep up to 10 lower when tested on a short core from devils lake north dakota which has a historical record of salinity dissolution adjusted models infer higher values compared to unadjusted models during peak salinity of the 1930s 1940s dust bowl but nonetheless significantly underestimate peak values site specific factors at devils lake associated with effects of lake level change on taphonomy preservation and re working implied by dissolution data may override model improvements incorporating dissolution dissolution adjusted salinity models are also applied to a 150 year sediment record from spiritwood lake north dakota which suggests that this lake has a damped and lagged response to major regional climate forcing of salinity during the dust bowl at this site dissolution data also suggest different taphonomic behaviour of taxa related to their seasonal patterns of growth and sedimentation thus dissolution data can improve models and aid interpretation of sedimentary profiles as records of limnological ecological and environmental change filtered by taphonomy

modelling of superimposed ice formation during the spring snowmelt period in the baltic sea development of landfast sea ice and its snow cover was monitored in the gulf of bothnia baltic sea for a period of 4 weeks during the early melt season of 2004 during this period approximately 90 of the snow layer was transformed into superimposed ice while the rest sublimated a one dimensional thermodynamic snow ice model was used to simulate this process the modelled snowmelt and superimposed ice growth were consistent with the observations but the net accumulation of superimposed ice was slightly overestimated the errors in calculation of temporal variations of the refreezing were probably due to the uncertainties in the external forcing and simplification of snow processes in the model the modelled snow thickness was sensitive to the atmospheric forcing and the influence was amplified when the albedo was parameterized as a function of surface temperature in the sensitivity tests without this feedback the direct effect of the inaccuracy in the albedo parameterization was minor errors in the parameterized longwave radiation were critical for the modelled snow surface temperature during night time but did not have a large effect on the mass balance during this spring melt period

sediment dynamics during wet and dry storm events on the tet inner shelf sw gulf of lions abstract the importance of short term processes such as floods and storms on sediment delivery and reworking on the tet inner shelf was investigated the tet inner shelf is a small event dominated system located in the south western part of the gulf of lions the expected sedimentary scenario in this environment is that fluvial sediment should be deposited on the prodelta and later dispersed around the shelf and slope by wave and current reworking during storms this paper investigates differences in inner shelf sediment dynamics between storm events occurring during usual river discharges and those occurring during river floods waves current velocities near bottom water turbidity bottom sediment grain size and sea floor erosion accretion were concurrently measured at 28 m water depth on the tet inner shelf from november 2003 to march 2004 two major storms took place on 4 december 2003 and 21 february 2004 and two moderate storms occurred on 8 december 2003 and 14 march 2004 the two major storms displayed similar wave characteristics maximum significant wave height h s 7 m peak period t p 12 s and wave direction around 90 the main environmental differences during the two major storm events correspond to the amount of sediment discharged from the tet river about 2 10 4 t of sediment was delivered by the river during the 4 december flood wet storm and less than 5 10 2 t during the 21 february storm dry storm sediment dynamics were quite similar during the storm events resuspension caused by waves and sediment advection towards the southeast due to near bottom shelf currents were the dominant sedimentary processes the result was a bottom sediment erosion of several centimetres at the study site during both the wet and dry events the main differences between the wet and dry events arose after the storm immediately after the peak of the wet storm sediment supplied by the tet river and probably from other rivers was deposited around the river mouth a few days later during a moderate storm this unconsolidated sediment was resuspended transported offshore and deposited on the inner shelf in contrast a moderate storm which occurred some days after the dry february storm caused bottom erosion on the inner shelf because no fresh sediment was available on the shallower area the results from this study indicate that the tet inner shelf at 28 m water depth is mainly a bypass zone for sediment that is transported s se towards the middle outer shelf and slope although ephemeral sediment deposits may be favoured by the sediment supplied from flood events sediment transport across the shelf from the river to the slope follows a complex multi step pattern that needs to be addressed using a multi event approach

origin and dynamics of mesoscale eddies in the catalan sea nw mediterranean insight from a numerical model study past observations and satellite sea surface temperature imagery indicate the presence of mesoscale anticyclonic eddies drifting along the catalan coast in september 2001 one of these anticyclonic eddies was surveyed over the shelf break during an oceanographic cruise which permitted the 3 d description of its structure in this work we investigate the origin and dynamics of such catalan eddies using a numerical circulation model of the northwest mediterranean at 3 km resolution driven by high resolution atmospheric analyses and compare model eddies with the observations in the catalan sea we identify two zones of eddy formation in the gulf of lions in front of the city of marseille and at the southeast of coast of roussillon from which anticyclonic eddies are observed to drift toward the catalan sea the hydrology and dynamics of the structures observed in the simulations are characterized sensitivity experiments and energy analysis are performed which allow us to identify the mechanisms associated with their generation properties of the eddy observed during the 2001 cruise at the catalan shelf break are found to compare well with model eddies generated at the southeast of the roussillon coast the model relates the origin of these eddies to the separation of the coastal current downstream from creus cape flow separation is linked to intense downwelling taking place in front of the roussillon coast when strong northwesterly winds events occur

physical and chemical predictors of diatom dissolution in freshwater and saline lake sediments in north america and west greenland diatom dissolution in surface sediment samples from two regional lake datasets in the northern great plains ngp n 5 64 and west greenland n 5 40 is assessed using a morphological approach categorizing valves during routine diatom analysis two dissolution indices are derived to parameterize diatom dissolution and when compared between two analysts in a blind test show good correspondence and are closely correlated to diatom fragmentation we explore the relationships between hydrochemical and physical lake parameters including meromixis on dissolution within both lake regions using multivariate methods and modeled with logistic regression salinity is the sole significant predictor of dissolution in west greenland but salinity carbonate concentration co3 22 and meromixis are significant predictors in the ngp limnological parameters explain 40 59 of variation in dissolution in both regions for both dissolution indices the dissolution index methodology is applied to a short sediment sequence from devils lake north dakota where diatom inferred salinity inferences can be compared with a historical record of salinity fluctuations over the 20th century absolute errors in paleosalinity estimates are strongly correlated with diatom dissolution with salinity overestimated in 8 out of 11 poorly preserved samples preservation does appear to constrain the reliability of the inferred paleosalinity at this site and may also affect the quality of diatom based paleoenvironmental inferences elsewhere including estimates of biogenic silica where preservation state is often not explicitly considered

lake sediments record large scale shifts in moisture regimes across the northern prairies of north america during the past two millennia six high resolution climatic reconstructions based on diatom analyses from lake sediment cores from the northern prairies of north america show that shifts in drought conditions on decadal through multicentennial scales have prevailed in this region for at least the last two millennia the predominant broad scale pattern seen at all sites is a major shift in moisture regimes from wet to dry or vice versa depending on location that occurred after a period of relative stability these large scale shifts at the different sites exhibit spatial coherence at regional scales the three canadian sites record this abrupt shift between anno domini 500 and 800 and subsequently conditions become increasingly variable all three u s sites underwent a pronounced change but the timing of this change is between anno domini 1000 and 1300 thus later than in all of the canadian sites the mechanisms behind these patterns are poorly understood but they are likely related to changes in the shape and location of the jet stream and associated storm tracks if the patterns seen at these sites are representative of the region this observed pattern can have huge implications for future water availability in this region

characterization of the ebre and rhone estuaries a basis for defining and classifying salt wedge estuaries river discharge is the main factor controlling the hydrologic dynamics of the ebre and rhone estuaries the topography of the estuary bed also influences the extent advance and retreat of the salt wedge tides have little influence because of the low tidal range mean annual river discharge is close to the critical value determining the formation and breakup of the salt wedge this is related to the fact that river flow controls the sedimentary dynamics of the estuary including the sandbar at the mouth when discharge is lower than the mean annual river flow the salt wedge is established and the estuary becomes a depositional environment with higher flows the salt wedge is washed away and erosive conditions prevail on the basis of the conditions in which the salt wedge is formed two types of highly stratified estuaries can be identified in the first one a salt wedge regime is established during low river flows whereas during high flows the wedge is washed away and the estuary becomes a river this circulation pattern corresponds to the salt wedge estuary or type 4 of the hansen rattray classification typical of riverdominated estuaries in microtidal seas in the second one a salt wedge is established during high river flows whereas a partially mixed estuary occurs during low flows this pattern corresponds to types 3b and 2b of the hansen rakray classification

impact of an intrusion by the northern current on the biogeochemistry in the eastern gulf of lion nw mediterranean abstract we present the results from the rhoma2011 leg2 campaign that took place in the eastern gulf of lion from 7 to 17 oct 2011 and combine them with remote sensing observations and results from a 3d coupled hydrodynamic biogeochemical model to study an intrusion event of the northern current nc onto the continental shelf in the gulf of lion nw mediterranean our analysis shows that during the intrusion the previously upwelled nutrient rich water present on the shelf is replaced by warmer and mostly oligotrophic nc water within a matter of 2 3 days this has a marked impact on the local biogeochemistry in the gulf with pre intrusion chl a concentrations in the surface layer of over 0 5 mg m 3 dropping to near the detection limit within less than 72 h the intrusion event leads to a dramatic albeit short lived regime shift in the limiting nutrient for primary production prior to the intrusion most of production on the shelf is nitrogen limited while the intrusion induces a shift to phosphorous limitation the relatively high frequency of occurrence of these intrusions in combination with their impact on the local ecosystem make them primary targets for future study

a quantitative assessment of diatom dissolution and late quaternary primary productivity in the eastern equatorial pacific the eastern equatorial pacific eep is an important area for ocean atmosphere carbon exchange and yields different opal accumulation records for sites influenced by equatorial divergence and peru upwelling the divergence zone is characterized by a lower opal accumulation rate during the last glacial compared with the holocene but the reverse is true for the peru upwelling zone as a gauge of opal production versus preservation in the eep differential diatom preservation was investigated via a quantitative four stage preservation index using the vellum of the ubiquitous tropical centric diatom azpeitia nodulifer we find similar dissolution records at both sites from the last glacial maximum lgm through the holocene despite differing accumulation rates implying that production not preservation controlled the accumulation rates thus the increased silica accumulation in the peru upwelling region is related to increased production suggesting higher availability of silica in the photic zone in accord with the silica leakage hypothesis described by matsumoto et al 2002 silicic acid leakage from the southern ocean a possible explanation for glacial atmospheric co global biogeochemical cycles 5 doi 10 1029 2001gb001442 and discussed by richaud et al 2007 furthermore we suggest an ecological control on opal preservation due to silica recycling by diatoms in the water column most likely in the photic zone increased production causes rapid silica recycling and thinner walled frustules resulting in enhanced water column dissolution in this setting diatom dissolution is independent of the rate of accumulation of silica or sediment high opal productivity does not necessarily lead to high preservation as proposed for southern ocean sediments sayles f martin w chase z anderson r 2001 benthic remineralization and burial of biogenic sio2 caco3 organic carbon and detrital material in the southern ocean along a transect at 170 west deep sea research ii 48 4323 4383 our observations are compatible with a production increase in the late deglacial and early holocene as reported by loubere 2001 nutrient and oceanographic changes in the eastern equatorial pacific from the last full glacial to the present global and planetary change 29 77 98 and inferred by spero h and lea d 2002 the cause of carbon isotope maximum events on glacial terminations science 296 522 525 and rickaby r and osborne a 2006 oceanic redistribution of phosphate during the last deglaciation in preparation

on the numerical resolution in a thermodynamic sea ice model the numerical integration of the heat conduction equation is one of the main components in a thermodynamic sea ice model the spatial resolution in the ice normally varies from a minimum of three layers up to a few tens of layers the temporal resolution varies from a few minutes up to hours in this paper the impact of numerical resolution on the prediction of a one dimensional thermodynamic ice model is studied analytical solutions for idealized cases were derived and compared with the numerical results for the full ice model groups of simulations were made applying average climatic weather forcing data corresponding to the ice freezing ice thermal equilibrium and ice warm up seasons special attention was paid to the effect of model spatial resolution early in the freezing season the influence of resolution on model predictions is not significant when the shortwave radiation becomes large its absorption within the ice or snow cover was found to modulate the effect of numerical resolution on predictions of ice temperature and surface heat fluxes e g the model run with a coarse spatial resolution yielded large daily variations in surface temperature resolution also affects the in ice temperature profile for process studies a two layer scheme for the solar radiation penetrating into the ice is suitable for a fine spatial resolution ice model

solar heating rates and temperature profiles in antarctic snow and ice observations of temperature maxima at about 10 cm depth in cold antarctic snow during summer have previously been explained by proposing that solar heating is distributed with depth whereas thermal infrared cooling is localized at the surface the solid state greenhouse an increase in temperature from the surface to 10 cm depth t 4 k found by rusin 1961 on the antarctic plateau was successfully reproduced by schlatter 1972 in a combined radiative transfer and heat transfer model

palaeovegetation changes recorded in palaeolake olduvai ogcp core 2a 2 09 2 12 ma naibor soit formation olduvai gorge tanzania abstract for five decades olduvai gorge has been a key site to reconstruct and understand the relationship between environmental and landscape conditions and use of affordances by early african hominin populations following the first olduvai gorge coring project ogcp during 2014 a multiproxy microbiological analysis which includes phytoliths pollen diatoms sponge spicules and chrysophyte cysts was undertaken on samples collected from various borehole cores the aim of the study is to better understand palaeoenvironmental and palaeovegetation conditions and changes through time and their relationship to hominin presence and evolution this study details the first palaeobotanical and palaeoenvironmental study of borehole 2a at olduvai gorge it represents the as yet oldest known sedimentary sequence in the olduvai basin for a portion of the pre bed i naibor soit formation this is a unit that is not accessible in any natural exposures in olduvai gorge and has only recently been encountered by drilling here we present the results from a particularly phytolith prone portion between 2 09 ma and 2 12 ma phytolith results indicate a savannah environment dominated by grasses where poaceae were a key component and where the c3 pooideae grasses were mostly dominant alternating with c4 grasses oscillations between grass subfamilies c3 pooideae c4 chloridoideae and c4 panicoideae to lesser degrees indicate five substantial climatic shifts varying between more humid and arid conditions associated with phytoliths freshwater indicators such as diatoms sponge spicules and chrysophyte cysts were also identified suggesting the presence of wetlands in the lake catchment area pollen is extremely rare in the sediments but when present comprises fungal spores and poaceae pollen thus supporting the wetland and grassland reconstructions respectively these results offer for the first time a whole picture of the palaeovegetation and associated palaeoenvironments for this pre bed i period together with previous results from other areas and chronological periods they improve our understanding of the evolution and adaptation of early hominins and their close relationship to the surrounding landscape

diatom oxygen isotopes evidence of a species effect in the sediment record diatom oxygen isotope measurements are commonly made on bulk mixed species assemblages due to the difficulty in purifying and separating individual taxa as such it is essential to understand processes in diatoms which may lead to isotope offsets both between and within individual species existing studies have suggested that mechanisms which may lead to isotopes offset in diatoms such as vital effects are either nonexistent or negligible here we present a suite of diatom oxygen isotope data from the onset of major northern hemisphere glaciation at odp site 882 in the northwest pacific ocean which display large offsets mean 1 23 max 3 51 error 0 84 between two different size fractions 75 150 um and 150 um that are dominated by only two species coscinodiscus marginatus and coscinodiscus radiatus these offsets are most likely size related although additional interspecies and intraspecies effects may also be important in determining the exact magnitude of the offsets consequently considerable care is needed when interpreting bulk diatom oxygen isotope data in relation to paleoenvironmental change especially when the amount of stratigraphical change within the isotopes is small

experimental diatom dissolution and the quantification of microfossil preservation in sediments abstract four laboratory experiments on fresh modern diatoms collected from lakes in the northern great plains of north america were carried out to assess the effects of dissolution on diatom abundance and composition marked differences in mean dissolution susceptibility exist between species despite sometimes significant intra specific variation between heterovalves twenty four taxa were ranked according to susceptibility to dissolution using an exponential decay model of valve abundance this dissolution ranking was used to derive two weighted indices of sample preservation a third index f was based on a simple binary classification of valve morphology into dissolved and pristine categories as distinguished by light microscopy lm when compared against rank indices and a measure of species diversity this diatom dissolution index was found to be the best predictor of the progress of dissolution as estimated by total valve abundance or biogenic silica bisi loss strong empirical relationships between f index values and diatom abundance r2 0 84 n 32 and bisi r2 0 89 n 32 were developed and applied to a diatom sequence from a short core from devils lake north dakota and compared to diatom inferred and observed salinity at this site the f index is a simple effective diagnostic tool to assess important aspects of diatom preservation the index can provide insight into si cycling and record changes in conditions pertinent to diatom dissolution and has a role in validation of transfer functions or other inferences derived from compositional data

a review of the oxygen isotope composition of lacustrine diatom silica for palaeoclimate reconstruction diatom silica frustules are a form of biogenic opal and contain oxygen isotopes that are being increasingly used in palaeoclimate studies frustules are comprised of an inner tetrahedrally bonded silica skeleton si o si with an outer hydrous layer the hydrous layer is freely exchangeable and must be removed prior to oxygen isotope measurement using oxidising reagents and or high temperatures analysis of the oxygen isotope composition of diatom silica requires samples that are almost pure diatomite since extraction techniques will liberate oxygen from all the components in the sediment there is a generally acceptable protocol involving chemistry sieving and settling techniques and more recently laminar flow separation recent studies of lacustrine diatoms have shown that even a small proportion of contaminant can have a significant influence on the oxygen isotope value all lake sediments require their own specific procedure and every sample must be scrutinised by microscopy to check for the level of contamination prior to analysis where sediment cannot be purified sufficiently a semi quantitative assessment of the diatom content can facilitate mass balance techniques when robust preparation methods are used diatom silica offers an important palaeoclimate proxy providing an additional complementary rather than an alternative host of oxygen isotopes in carbonates in lacustrine isotope studies it is often assumed but rarely proven that diatom silica form in isotope equilibrium and hence empirically derived palaeotemperature equations usually made in vitro can be used most studies lack the detailed investigation of contemporaneous materials from natural waters of the region under study to test these equations further investigations need to be conducted in order to understand the systematic relationship between temperature water isotope composition and diatom isotope composition to enable quantitative interpretation of the sediment record experiments to test for vital effects and inter specific differences have so far revealed little variation it is useful to know when and where the diatom silica is formed in the modern environment so details of diatom ecology are important in the interpretation of isotope data here we show that valuable palaeoclimate data can be gained from the oxygen isotope composition of diatom silica 18odiatom especially since diatoms are abundant in many lakes sensitive to climate variation where other hosts e g carbonates are absent to date the most successful studies have been conducted in areas where the 18odiatom registers changes in the oxygen isotope composition of the lake water rather than temperature which is then related to other aspects of climate in these studies the range of values obtained is often greater than the error introduced by contaminating materials

environmental history of a closed basin lake in the us great plains diatom response to variations in groundwater flow regimes over the last 8500 cal yr bp sediment records from closed basin lakes in the northern great plains ngp of north america have contributed significantly to our understanding of regional paleoclimatology a high resolution near decadal fossil diatom record from kettle lake nd usa that spans the last 8500 cal yr bp is interpreted in concert with percent abundance of aragonite in the sediment as an independent proxy of groundwater flow to the lake and thus lake water level kettle lake has been relatively fresh for the majority of the holocene likely because of the coarse substrata and a strong connection to the underlying aquifer interpretation of diatom assemblages in four groups indicative of low to high groundwater flow based on the percent of aragonite in sediments allow interpretations of arid periods and probable meromictic lake conditions that could not be detected based on diatom based salinity reconstructions alone at the centennial millennial scale the diatom record suggests humid wet periods from 8351 to 8088 4364 to 1406 and 872 to 620 cal yr bp with more arid periods intervening during the last 4500 years decadal centennial scale periods of drought have taken place despite the generally wetter climate these droughts appear to have had similar impacts on the kettle lake hydrology as the dust bowl era droughts but were longer in duration

a sensitivity study of the general circulation of the western mediterranean sea part ii the response to atmospheric forcing abstract this paper investigates the influence of sea surface thermohaline fluxes and wind stress on the circulation of the western mediterranean sea using a high resolution 3d primitive equation model an 18 year experiment was forced with the daily output of a fine grid mesh numerical weather prediction model the major characteristics of the circulation are well reproduced the basin surface circulation is cyclonic over all of the basin the two anticyclonic alboran gyres are present the instabilities of the algerian current generate large anticyclonic eddies that invade the whole algerian basin the liguro provencal catalan current is well marked deep water convection down to the bottom only occurs during the first 3 years then winter intermediate water is produced the north south gradient of the atmospheric thermohaline fluxes induces a northward surface transport of water from the algerian basin into the liguro provencal basin this pattern can be associated with the balearic front sensitivity

modeling the deep convection in the northwestern mediterranean sea using an eddy permitting and an eddy resolving model case study of winter 1986 1987 1 in the northwestern mediterranean sea winter 1986 1987 was particularly cold inducing a strong open ocean convection event in order to investigate the impact of numerical models spatial resolution on the convection representation and the effects of deep convection on the northwestern mediterranean circulation we perform two numerical three dimensional simulations eddy permitting versus eddy resolving models are forced at the surface by the era40 atmospheric fluxes with a simple heat flux correction to better mimic the observed value we examine the characteristics of the deep convection mixed layer water masses characteristics convection zone and mesoscale structures and perform temporal analysis of this event in terms of kinetic energy buoyancy equilibrium and deep water dw evolution the convection characteristics are similarly represented on a global scale by both models and are in good agreement with observations except for the size of the convection region however the eddy resolving model better reproduces the mesoscale structures whose role in the dw formation mixing and transport is shown to be essential the boundary circulation and the overturning are enhanced during the convection event sixty six percent of the dw spreading is due to the bleeding effect into the catalan sea during the convection event whereas 33 is due to the mesoscale structures southwestward advection after the event sixty percent of the restratification with respect of the water column initial structure occurs before july 1987 and is due to light water advection afterward restratification is due to the mixing and is not complete before next year convection

on the nature of near inertial oscillations in the uppermost part of the ocean and a possible route toward hf radar probing of stratification abstractinertial band response of the upper ocean to changing wind is studied both theoretically and by analysis of observations in the northwestern mediterranean on the nontraditional f plane because of the horizontal component of the earth s rotation for waves of inertial band with frequencies slightly below the local inertial frequency f there is a waveguide in the mixed layer confined from below by the pycnocline it is argued that when the stratification is shallow these waves are most easily and strongly excited by varying winds as near inertial oscillations nios these motions have been overlooked in previous studies because they are absent under the traditional approximation the observations that employed buoys with thermistors adcps and two 16 3 mhz wellen radar wera hf radars were carried out in the gulf of lion in april june 2006 the observations support the theoretical picture a pronounced inertial band response occurs only in the presence of shallow stratification and is confined

the fetch experiment an overview the flux etat de la mer et teledetection en conditions de fetch variable fetch was aimed at studying the physical processes associated with air sea exchanges and mesoscale oceanic circulation in a coastal region dominated by frequent strong offshore winds the experiment took place in march april 1998 in the northwestern mediterranean sea gulf of lion observations were collected with the r v l atalante with an air sea interaction spar asis buoy with waverider buoys and with research aircraft equipped for in situ and remote sensing measurements the present paper is an introduction to the following special section which groups 12 papers including this one presenting results on turbulent flux measurements at the ocean surface on the behavior of the marine atmospheric boundary layer on the ocean waves characteristics on the ocean circulation and on remote sensing of surface parameters this overview presents the background and objectives of fetch the experimental setup and operations and the dominant atmospheric and oceanic conditions and introduces the different papers of the special section

last millennia sedimentary record on a micro tidal low accumulation prodelta tet nw mediterranean statistical sequential analysis was performed on a series of sediment cores collected from the tet prodelta in the gulf of lions northwestern mediterranean sea between october 2003 and october 2004 seabed changes during that period were correlated to hydrodynamic conditions waves and currents and river discharge low sediment supply prevents full preservation of new sediment strata on this low accumulation prodelta located on a microtidal storm dominated inner shelf severe meteorological events caused a rapid succession of erosion and deposition phases for example the december 2003 flood and storm produced a flood layer deposit that persisted for 2 months with only slight transformations due to early diagenesis and or bioturbation until a new storm event eroded this layer a typical sedimentary sequence was observed for the secular deposits composed of a 10 cm thick sandy layer overlaying siltyclayey layers these characteristic features were used to analyse the last millennia sedimentary record of the tet prodelta the low preservation of freshly deposited sediments and variable sedimentation rates during the last millennia period yield a sedimentary sequence formed by the outcropping of muddy prodeltaic units intersected by heterogeneous siltysandy units similar to those formed under present day hydrodynamic conditions no flood layer was found related to catastrophic flooding of the last century in the sedimentary record the little ice age 1550 1850 ad probably favoured the formation of a well developed muddy prodelta in the mouth of the tet river later on the decrease of sediment supply by rivers due to climate change and or human activities damming irrigation and the increase of the number of high energy storms reaching the coast induced a coarsening of the top sediment layer on this prodelta this modern change of the substrate is also observed in the composition of benthic biota found in the substrate

the rhone river plume in unsteady conditions numerical and experimental results surface current maps obtained in the plume of the rhome river by two vhf radars gave rise to comparisons with simulations produced by a primitive equation model two situations were investigated one in steady conditions the other with a variable wind the model gives a good estimation of current direction and velocity not only in the plume itself but also in the surrounding water the model reveals the mechanisms involved in the plume dilution and more generally in the renewal of surface water near the coast when the wind changes direction the sensitivity of the model results to the upper boundary condition for turbulent kinetic energy is also shown

nutrients and plankton spatial distributions induced by a coastal eddy in the gulf of lion insights from a numerical model a plankton functional types model forced by a hydrodynamic model is used in the present work to study the impacts of a coastal eddy on the distribution of nutrients and plankton in the western part of gulf of lion nw mediterranean sea this study based on a realistic simulation of the year 2001 focuses on a long life anticyclonic eddy detected during summer the studied anticyclonic eddy has some biogeochemical characteristics of those observed in the open ocean as for example the low productivity at their core and rising up of nutricline on their edges however the functioning and consequences of such coastal eddy on nutrients and plankton distributions are complicated by potential interactions with topography wind induced upwelling along the languedoc coast and nearby northern current nc especially the proximity of the southern edge of the eddy with the nc makes possible the exchanges of organic matter plankton at times during the eddy s life the coastal eddy thus transports organic matter from the coastal zone to the offshore domain the coupled model also suggests the importance of offshore to coastal transport by nc through a seeding process of the eddy in plankton at the beginning of its life a detailed biogeochemical functioning of the studied eddy all along its lifetime is proposed from the model results at the beginning the eddy mainly acts as a transporter of the plankton wind induced bloom occurring along the languedoc coast several days before the eddy set up at the same time the eddy shows upwards vertical velocities on its edges creating upwelling of nutrient enriched waters the process of eddy induced upwelling is notably enhanced on the eddy western side along the roussillon coast due to the shelf topography the around eddy advection and relative lower temperatures prevent the large development of phytoplankton along the roussillon coast and the eddy induced bloom is predicted to occur near the northwestern side of the eddy the eddy induced and wind induced blooms of phytoplankton then merge on the eastern side by advection and this process of aggregation may explain the persistent occurrence of a filament of high chlorophyll observed on the offshore edge of the eddy throughout the study period the changes in plankton composition due to a combination of top down and bottom up processes during the coast to offshore transport may explain the disappearance of the filament south of 43 n at the surface

modeling the thermodynamics of a sea ice thickness distribution 1 sensitivity to ice thickness resolution a one dimensional ice thickness distribution model is presented to determine the minimum number of ice thicknesses necessary to resolve the area averaged annual cycles of ice thickness and turbulent fluxes the baseline case includes 40 ice thickness categories ice thickness and area meltwater ponds ice salinity and age snow cover and surface albedo evolve independently for each ice category a ridging and ice export parameterization and a coupled one dimensional ocean mixed layer model are also included sensitivity studies indicate that 16 ice thickness categories can accurately resolve the baseline annual cycles of area averaged ice thickness and the summertime turbulent fluxes in this model provided that one third of the thickness categories represent ice thinner than 0 8 m resolving the distribution of ice in this thickness range is important in simulating the area averaged ice characteristics wintertime values of the turbulent fluxes differ from the baseline by up to 1 w m 2 for fewer than 40 ice thickness categories the large difference in turbulent fluxes between open water and ice thicker than 1 6 m makes the area averaged value sensitive to the number of ice thickness categories since this number can affect the categories that are merged the categories that melt completely ice that is ridged and the resolution of the ice thickness distribution this makes an accurate simulation of the baseline wintertime turbulent fluxes difficult model simulations with fewer than 40 categories provide a reasonable estimate of the baseline response to a surface longwave heat flux perturbation of greater than 5 w m 2 the annually area averaged ice thickness is within 10 cm the model response to a heat flux perturbation of less than 5 w m 2 is similar for a wide range of ice thickness categories since the thickness distribution of ice thinner than 1 m is not affected

silica diagenesis porosity evolution and mechanical behavior in siliceous mudstones mowry shale cretaceous rocky mountains u s a quartz in mudstones of the mowry shale cretaceous rocky mountain region takes several forms extrabasinal detrital silt some with transported overgrowths replacement of skeletal debris minor overgrowth on detrital quartz and replaced radiolaria pore filling in the intragranular pores of allochems and authigenic microquartz that is dispersed through the clay size matrix the matrix dispersed microquartz has cl character similar to the overgrowths with which it is intergrown supporting the interpretation that it is authigenic and pore filling radiolaria are widely observed in these mudrocks but are poorly preserved by partial mineral replacement quartz dolomite calcite pyrite we interpret dissolved radiolaria and possibly now cryptic diatoms as the likely source of silica for the overgrowths and microquartz through a reaction pathway that entailed the formation of opal ct lepispheres that subsequently recrystallized to microquartz a newly devised variation of the igv intergranular volume concept a parameter igvm is applied for partitioning the causes of porosity decline in mudstones all of the samples examined contain authigenic microquartz which averages around 40 of the rock volume the large volume of microquartz together with the volumes of surviving intergranular pores and pore filling solid hydrocarbon constrain the porosity to around 50 at the time of initial lepisphere formation despite the exceptional abundance of cement overall porosity decline is compaction dominated the presence of significant volumes of cement has implications for mechanical rock properties in the mowry shale which is expected to manifest brittle behavior where cements are most prominently developed

century scale paleoclimatic reconstruction from moon lake a closed basin lake in the northern great plains estimates of past lake water salinity from fossil diatom assemblages were used to infer past climatic conditions at moon lake a climatically sensitive site in the northern great plains a good correspondence between diatom inferred salinity and historical records of mean annual precipitation minus evapotranspiration p et strongly suggests that the sedimentary record from moon lake can be used to reconstruct past climatic conditions century scale analysis of the holocene diatom record indicates four major hydrological periods an early holocene transition from an open freshwater system to a closed saline system by 7300 b p which corresponds with a transition from spruce forest to deciduous parkland to prairie and indicates a major shift from wet to dry climate a mid holocene period of high salinity from 7300 to 4700 b p indicating low effective moisture p et a transitional period of high salinity from 4700 to 2200 b p characterized by poor diatom preservation and a late holocene period of variable lower salinity during the past 2 200 yr indicating fluctuations in effective moisture

diatom based transfer functions for inferring past hydrochemical characteristics of african lakes abstract a new dataset of 282 modern diatom samples and associated environmental information has been created by merging existing regional datasets from north and east africa and niger the relationships between diatom species distributions and hydrochemistry are examined using canonical correspondence analysis cca and partial cca variables reflecting water conductivity ph and cation and anion composition account for significant and independent components of the total variation in the diatom data predictive models transfer functions are developed using the method of weighted averaging for conductivity r 2 0 87 ph r 2 0 77 and ratios between alkali and alkaline earth metals r 2 0 81 and carbonate bicarbonate and sulphate chloride ions r 2 0 82 prediction errors are estimated using the computer intensive method of jackknifing these transfer functions enlarge the potential domain for reconstruction of past hydrochemistry from fossil diatoms preserved in lake sediments

interaction of a coastal current with a gulf application to the shelf circulation of the gulf of lions in the mediterranean sea abstract the interaction of a coastal current with a shallow shelf is studied using analytical model and numerical simulations first the wave propagations along a steplike bottom topography in a two layer fluid are investigated the authors focus on the case in which the interface between the two layers is deeper than the shelf depth and show analytically that two waves propagate along the shelf break one is represented by a barotropic baroclinic double kelvin wave the other by a baroclinic wave trapped at the shelf break the velocity of the latter is proportional to the difference between the depth of the shelf and the depth of the upper layer off the shelf a primitive equation model was also used to study more realistic configurations 1 with an idealized shallow gulf and 2 with a realistic topography like that of the gulf of lions it is shown that the steady component of the coastal current follows the shelf break a transient cross shelf transport can be induced by a gulf scale gyre associated

geophysics of sea ice in the baltic sea a review abstract with improved observation methods increased winter navigation and increased awareness of the climate and environmental changes research on the baltic sea ice conditions has become increasingly active sea ice has been recognized as a sensitive indicator for changes in climate although the inter annual variability in the ice conditions is large a change towards milder ice winters has been detected from the time series of the maximum annual extent of sea ice and the length of the ice season on the basis of the ice extent the shift towards a warmer climate took place in the latter half of the 19th century on the other hand data on the ice thickness which are mostly limited to the land fast ice zone basically do not show clear trends during the 20th century except that during the last 20 years the thickness of land fast ice has decreased due to difficulties in measuring the pack ice thickness the total mass of sea ice in the baltic sea is however still poorly known the ice extent and length of the ice season depend on the indices of the arctic oscillation and north atlantic oscillation sea ice dynamics thermodynamics structure and properties strongly interact with each other as well as with the atmosphere and the sea the surface conditions over the ice covered baltic sea show high spatial variability which cannot be described by two surface types such as ice and open water only the variability is strongly reflected to the radiative and turbulent surface fluxes the baltic sea has served as a testbed for several developments in the theory of sea ice dynamics experiences with advanced models have increased our understanding on sea ice dynamics which depends on the ice thickness distribution and in turn redistributes the ice thickness during the latest decade advance has been made in studies on sea ice structure surface albedo penetration of solar radiation sub surface melting and formation of superimposed ice and snow ice a high vertical resolution has been found as a prerequisite to successfully model thermodynamic processes during the spring melt period a few observations have demonstrated how the river discharge and ice melt affect the stratification of the oceanic boundary layer below the ice and the oceanic heat flux to the ice bottom in general process studies on ice ocean interaction have been rare in the future increasingly multidisciplinary studies are needed with close links between sea ice physics geochemistry and biology

interpretations of the jebar term abstract in diagnostic calculations of the ocean s circulation the so called jebar joint effect of baroclinicity and relief term may induce a significant depth average current field as has been noted in the oceanographic literature here we present two consistent interpretations of this term in the equation governing the vorticity of the depth averaged current a topographic vortex stretching term proportional to the dot product of depth averaged velocity and the depth gradient arises we show that jebar corrects this term by removing the contribution of the geostrophic flow referenced to the bottom which cannot generate topographic vortex stretching in the evolution equation for the vorticity of the depth integrated flow a bottom torque term is present we show that the jfbar term discussed above enters here as a contribution to the bottom torque emphasizing the role of jebar as a forcing term we also show that when a diagnostic calculation is formulated completely in terms of the transport str

hydrologic variation in the northern great plains during the last two millennia abstract reconstructions of lake water salinity at decadal resolution for the last 2000 yr are compared among three lakes in north dakota to infer regional patterns of drought the intersite comparisons are used to distinguish local variation in climate or hydrology from regional patterns of change at one lake diatom inferred salinity and lake water mg ca inferred from ostracode shell chemistry are coherent both in terms of direction and magnitude of change indicating that each is a robust technique for reconstructing lake water chemistry the data show that the last 2000 yr have been characterized by frequent shifts between high and low salinity suggesting shifts between dry and moist periods long intervals of high salinity suggest periods of multiple decades when droughts were intense and frequent thus indicating times when drought was more persistent than in the 20th century both the medieval period and little ice age were hydrologically complex and there is no clear evidence to suggest that either interval was coherent or unusual in effective moisture relative to long term patterns differences among the three sites may be attributed to variation in local hydrology and these differences emphasize the need for multiple sites in deriving regional climate interpretations from paleoecological data

impact of water particle interactions on molybdenum budget in humid tropical rivers and estuaries insights from nethravati gurupur and mandovi river systems abstract the study presents the seasonal and inter annual monitoring of molybdenum mo distribution and variability in humid tropical riverine and estuarine systems nethravati gurupur and mandovi estuaries of west coast of india the study investigates the geochemical behaviour of mo in the river and estuaries and their ultimate fluxes into the ocean the riverine flux of dissolved mo dmo to the nethravati gurupur and mandovi estuaries are 1800 mol yr 1 4 88 mol day 1 195 mol yr 1 0 53 mol day 1 and 10 5 103 mol yr 1 28 mol day 1 respectively and the riverine particulate mo pmo flux to nethravati estuary is 10 8 103 mol yr 1 the dmo in river 30 to 40 is scavenged onto particles under oxidized acidic river water conditions and subsequently released in the estuary impacting the solute budget of mo to the sea in the estuaries under low salinity conditions dmo is sequestered onto particles during pre monsoonal season the dmo sequestration in the estuary is estimated to be 2 mol day 1 in the nethravati estuary and 1 9 mol day 1 in the mandovi estuary during this season sequestration in the estuary is higher than the riverine supply indicating the sequestration of both marine and river borne dmo however the mechanisms involved in the removal process are different in these estuaries viz oxidative adsorption process in the nethravati gurupur estuary and microbial utilization in the mandovi estuary the lower salinity region during monsoon and post monsoon season shows slight excess of dmo river borne particulate mo could release up to 3 to 4 nmol l 1 by desorption under alkaline higher ionic strength conditions at higher salinity 20 psu in both the estuaries and in all the seasons dmo gain is systematic 1 to 37 nmol l 1 mo release from river borne particles could contribute only up to 3 to 4 nmol l 1 which is not sufficient to balance the observed mo excess on the other hand the reductive mo remobilization from bottom sediments mo 4 mg kg 1 during sediment diagenesis and subsequent tidal activity release up to 28 nmol l 1 of dmo to the estuarine water mo release to water column is supported by the gradual enrichment of dmo with depth in the estuary therefore diagenetic release of dmo forms the potential source of dmo excess in the estuary

isotope offsets in marine diatom δ18o over the last 200 ka previous work has suggested that a species effect may be present in diatom oxygen isotope ratios 18odiatom while predominantly attributed to be a size related species effect currently the precise mechanism remains unknown here two size fractions of diatoms 38 75 m and 100 m covering the last 200 ka are analysed for 18o from odp site 882 in the north west pacific ocean synchronous variations of up to 13 occur in both size fractions however large isotope offsets mean 2 02 exist between the two fractions with no relationship between their magnitude and the overlying palaeoenvironmental conditions in contrast to earlier work from the same site no one size fraction is constantly higher or lower in 18o relative to the other as such the dominant mechanism is most likely separate to the size effect previously detected in addition no relationship exists between the magnitude of the offsets and the species composition of the two size fractions the presence of these isotope offsets imposes significant constraints upon the future use of 18odiatom in palaeoceanographic reconstructions and reiterates the need to extract and analyse only species and size specific diatom samples

changes in lake stratification and oxygen distribution inferred from two contrasting records of magnetotactic bacteria and diatoms 1 magnetotactic bacteria mtb and diatoms produce hard parts on seasonal timescales that continuously becomes embedded in various soft sediment archives consequently they can and are frequently used to reconstruct past environmental conditions in oceans fjords and freshwater basins in this study we observe how these two cosmopolitan creatures can be used to track vertical shifts in the distribution of oxygen in a small mountain lake situated in western norway several short and long sediment cores have been retrieved from the lake allowing for a detailed reconstruction that spans the last 2500 years during periods of enhanced runoff from the catchment the oxic anoxic transition zone oatz is lowered down to the lake sediment interface due to increased convection we posit that this condition reduces the concentration of microaerophilic magnetite producing mtb an interpretation partly supported by rock magnetic analyzes preservation of diatom frustules is however improved whenever this oxygen rich scenario prevails similarly when runoff is low and the oatz is lifted above the lake sediment interface mtb concentration seems to increase whereas dissolution of diatoms is more common this consistent antiphase relationship between mtb concentration and diatom preservation occurring on a multidecadal timescale during lowest reconstructed lake water ph in the lake s history suggest a coupled response to subtle changes in external environmental variables that affect catchment and lake hydrology

transfer and early diagenesis of biogenic silica oxygen isotope signals during settling and sedimentation of diatoms in a temperate freshwater lake lake holzmaar germany abstract we have investigated the transfer of oxygen isotope signals of diatomaceous silica 18odiatom from the epilimnion 0 7 m through the hypolimnion to the lake bottom 20 m in freshwater lake holzmaar germany sediment traps were deployed in 2001 at depths of 7 and 16 m to harvest fresh diatoms every 28 days the 7 m trap collected diatoms from the epilimnion being the main zone of primary production while the 16 m trap collected material already settled through the hypolimnion also a bottom sediment sample was taken containing diatom frustules from approximately the last 25 years the 18odiatom values of the 7 m trap varied from 29 4 in spring autumn to 26 2 in summer according to the temperature dependence of oxygen isotope fractionation and represent the initial isotope signal in this study remarkably despite the short settling distance 18odiatom values of the 7 and the 16 m trap were identical only during spring and autumn seasons while from april to september 18odiatom values of the 16 m trap were roughly 1 5 enriched in 18o compared to those of the 7 m trap isotopic exchange with the isotopically lighter water of the hypolimnion would shift the 18odiatom value to lower values during settling from 7 to 16 m excluding this process as a cause for the deviation dissolution of opal during settling with intact organic coatings of the diatom cells and near neutral ph of the water should only cause a minor enrichment of the 16 m values nevertheless opal from the bottom sediment was found to be 2 5 enriched in 18o compared to the weighted average of the opal from the 7 m trap thus resuspension of bottom material must have contributed to the intermediate 18odiatom signal of the 16 m trap during summer dissolution experiments allowed further investigation of the cause for the remarkably enriched 18odiatom value of the bottom sediment experiments with different fresh diatomaceous materials show an increase of opaline 18o at high ph values which is remarkably reduced when organic coatings of the cells still exist or at near neutral ph in contrast high ph conditions do not affect the 18odiatom values of sub fossil and even fossil opal ir analyses show that the 18o enrichment of the sedimentary silica is associated with a decrease in si oh groups and the formation of si o si linkages this indicates a silica dehydroxylation process as cause for the isotopic enrichment of the bottom sediment silica dissolution and dehydroxylation clearly induce a maturation process of the diatom oxygen isotope signal presumably following an exponential behaviour with a rapid initial phase of signal alteration the dynamics of this process is of particular importance for the quantitative interpretation of sedimentary 18odiatom values in terms of palaeothermometry

lake baikal record of continental climate response to orbital insolation during the past 5 million years the sedimentary record of biogenic silica from lake baikal in south central siberia suggests that this region of central asia was impacted by two major cooling episodes at 2 8 to 2 6 and 1 8 to 1 6 million years ago the spectral evolution of this continental interior site parallels the evolutionary frequency spectra for various marine oxygen isotope records in the baikal record the 41 000 year obliquity cycle is particularly strong from 1 8 to 0 8 million years ago variance in the 100 000 year eccentricity band increases during the past 0 8 million years the expected precession frequency of 23 000 years is highest during the past 400 000 years the modulation of the predicted 23 000 and 41 000 year insolation forcing by the 100 000 and 400 000 year eccentricity bands indicates that the transfer of variance from the precession and obliquity frequencies to the eccentricity part of the spectrum occurred in the eurasian continental interior as well as in tropical and high latitude ocean sites

oxygen isotope ratios of sedimentary biogenic silica reflect the european transcontinental climate gradient oxygen isotope ratios of biogenic silica offer considerable potential in tracing past climate change using both marine and lacustrine sediment records despite recent improvements and standardisation in preparatory and analytical methods evidence for a systematic relationship between climate parameters and the oxygen isotope composition of sedimentary diatom silica 18osilica is contradictory in particular observed differences between the 18osilica of living and sedimentary diatom silica in both lake and marine environments question the validity of applying isotope fractionation models derived from living diatoms to reconstructing climate from sediment records in order to address this issue oxygen isotope ratios of biogenic silica 18osilica are examined from a suite of lake surface sediment samples which span a large climatic gradient across western europe 18osilica values are strongly correlated with air temperature and the isotope composition of precipitation 18op when evaporation of lake waters is accounted for the time averaged surface sediment data suggest a fractionation of 35 between water and biogenic silica however the effect of temperature appears less marked than that observed between contemporary diatoms and lake water over short timescales suggesting that diagenetic processes may lead to a reduction in the temperature sensitivity of sediment 18osilica records comparison of 18osilica data with d analysed from n alkanes of aquatic origin n c17 n c21 and n c23 demonstrates that the slope of the regional 18o d water line is preserved within the sediment record offering exciting potential for palaeoclimate research

sea surface transport in the western mediterranean sea a lagrangian perspective 2 we study the sea surface transport in the western mediterranean sea from a lagrangian point of view in particular the alboran and the north western subbasins the study is carried out through the analysis of 3 years of surface velocity model data through finite size lyapunov exponents residence time and virtual particle trajectories complementing the classical eulerian approach the spatiotemporal variability of the main transport processes is inferred from the empirical orthogonal function modes of the lyapunov exponents being the most relevant modes discussed and physically interpreted results indicate that some of the variability in the surface transport patterns in the western mediterranean can be explained by specific modes which provide an indication of connectivity among subbasins like the inflow of atlantic waters through the ibiza channel

spatial and temporal variability of downward particle fluxes on a continental slope lessons from an 8 yr experiment in the gulf of lions nw mediterranean abstract a long term experiment of downward particle fluxes and currents has been initiated in 1993 on the continental slope of the gulf of lions nw mediterranean and pursued within the frame of several french and european projects pnec euromarge nb mtp ii mater eurostrataform sediment traps and current meters were deployed at several locations on this slope deeply incised by numerous canyons with an extensive spatial coverage for the first 2 years canyons at the entrance middle and exit of the gulf with respect to the general along slope circulation head and mid canyon depths adjacent open slope from late 1995 onwards this design was reduced to the two mid canyon moorings at the entrance and exit of the gulf monthly fluxes and hourly temperatures and currents were recorded at 500 m 30 m above bottom mab in the canyon heads at 500 and 1000 m respectively 530 and 30 mab nominal depths at the mid canyon sites and at 750 m 30 mab open slope this study aims at describing the spatial seasonal and interannual variability of flux intensity and composition of settling particles and at analyzing the role of diverse forcings in the control of particle exchange across the margin results from the first 8 years 1993 2001 show that total mass fluxes in the 101 104 mg m 2 d 1 range increase along slope particularly for the near bottom traps between the ne planier canyon and the sw lacaze duthiers canyon limits of the gulf of lions indicating an increased shelf export of particulate matter in the western part of the system bulk chemical composition organic matter carbonate opal and lithogenic fraction remained rather stable during the course of the experiment tending towards values typical of superficial shelf sediments at higher mass fluxes first order calculations using a simple two component mixing model suggest a decreasing contribution of primary particles settling out of the overlying waters to the total flux from the entrance towards the exit of the system particulate material transferred to the deeper slope in the southwestern part of the gulf of lions appears therefore to predominantly originate in resuspended shelf and or upper slope sediment downward particle fluxes and potential forcing parameters exhibit a high seasonal variability with higher values from late autumn to early spring furthermore unprecedented winter flux peaks observed in 1999 dominated the interannual differences which otherwise were quite limited correlations between sources of particulate material on the shelf i e river and atmospheric inputs phytoplankton biomass and sediment resuspension cross slope exchange mechanisms derived from in situ temperature and current records and flux data indicate a predominant effect of dense cold water cascading on the exchange of particulate matter between the shelf and the slope

intrusion of rhone river diluted water into the bay of marseille generation processes and impacts on ecosystem functioning the rhone river provides the largest inputs of terrestrial freshwater and nutrients into the mediterranean sea the rhone river diluted water intrusions into the bay of marseille were investigated examining their physical generation processes and associated biogeochemical impact by using in situ observations remote sensing data and a three dimensional physical biogeochemical coupled model during our study period from 2007 to 2011 rhone river intrusions occurred on average 7 6 times per year and affected more frequently the northern part of the bay a classification of intrusion events in three categories is proposed short lived big and small as a function of their duration and spatial extent the intrusions appeared to be driven by i wind forcing ii the presence of a mesoscale eddy iii the rhone river discharge volume and iv the variation in thermocline depth typically a combination of these favorable factors was necessary to induce an intrusion an intrusion strongly impacts the biogeochemical functioning of the bay of marseille by bringing large quantities of nutrients into the bay mass balances were computed allowing us to quantify this impact on the bay of marseille the results show that the ecological impact depends very much on the type of intrusion with big intrusions having the highest impact

observation and modeling of the winter coastal oceanic circulation in the gulf of lion under wind conditions influenced by the continental orography fetch experiment 1 hydrological and currentmeter observations were collected on the continental shelf and slope of the gulf of lion during the fetch experiment 13 march to 15 april 1998 results from the first part of the cruise characterized by strong northern winds are presented the hydrological structures evidence well mixed water masses on the eastern and western ends of the shelf in the central part the situation is more complex with the influence of the rhone river s freshwater plume in the first 40 m of the water column and closer from the bottom with the confrontation of downwelled coastal cold water and upwelled warmer and saltier slope water current measurements show the path of the cyclonic circulation along the slope which is part of the general circulation of the western mediterranean and suggest the presence of large and temporary eddies on the shelf this oceanic circulation is simulated with a free surface three dimensional model using realistic forcing the model outputs are in agreement with the main hydrological and circulation patterns the results further indicate that coastal eddies are generated by the mesoscale structure of the wind field

oxygen isotopes of marine diatoms and relations to opal a maturation in order to develop the potential tool of diatom oxygen isotopes for paleoenvironmental studies we compared oxygen isotopes of natural marine diatoms sampled from ocean surface water sediment traps and surface sediments with oxygen isotopic fractionations determined for laboratory diatom cultures freshly grown natural diatoms phytoplankton samples and sediment trap material and cultured diatoms reveal similar oxygen isotope fractionation factors the fresh diatoms have 3 to 10 parts per thousand lower isotope fractionation factors than fossil sedimentary diatoms a temperature related oxygen isotope fractionation could not be established for the laboratory cultures and the natural phytoplankton samples and there is evidence that diatom growth rate until reaching the stationary growth state also controls the measured silica water oxygen isotope fractionation factor it is possible however that slow diatom growth in sea surface water may well lead to a temperature dependent silica water oxygen isotope fractionation which is the prerequisite for a use of diatom oxygen isotopes in palco surface water studies ftir spectroscopic analyses of various diatomaceous materials revealed that the ratio of integrated peak intensities for si o si si oh correlates with the 3 to 10 parts per thousand delta o 18 silica increase from fresh to fossil diatoms open system flow through silica dissolution experiments suggest that the diatom frustules are isotopically homogenous and that the increase in o 18 is therefore not due to dissolution of isotopically light surficial si oh groups it is concluded that slow internal condensation reactions during silica maturation in surface sediments cause both an increase in the intensity ratio of si o si si oh and the o 18 content of framework oxygen these findings also indicate that the oxygen isotope compositions of marine sediment diatoms do not indicate sea surface water temperature but rather reflect variable o 18 contents of surface sediments copyright c 2001 elsevier science ltd

a numerical study of the effects of coastline geometry on wind induced upwelling in the gulf of lions an attempt is made to explain the fixed locations of coastal upwelling centers in the gulf of lions as a function of the coastline geometry alone the semi implicit numerical model based on two layer shallow water equations uses a spatial discretization with triangular finite elements vertical mixing is shown to play an important role in determining the final shape of the upwelling centers it is conjectured that an observed upwelling filament results from the straining and stretching of a coastal upwelling center by the observed anticyclonic circulation farther offshore

dissolution and preservation of antarctic diatoms and the effect on sediment thanatocoenoses abstract comparison of southern ocean diatom populations from i surface ocean production ii underlying antarctic sediments and iii laboratory dissolution experiments demonstrates that dissolution can account for the temporal and spatial variations in sedimentary diatom assemblages observed in southern ocean sediments increasing dissolution causes relative depletions in n kerguelensis k enrichments in t lentiginosa l and slight enrichments in e antarctica a this reflects the relative susceptibility to dissolution of the three species that dominate antarctic sediments we have devised a preservation index for the southern ocean based on the ratio k k l to estimate relative extents of dissolution and applied it to natural assemblages holocene southern ocean sediments display increasing opal preservation toward higher latitudes but south of the antarctic polar front preservation decreases in the order well preserved se indian s atlantic sw indian se pacific poorly preserved dissolution also accounts for the pattern of diatom assemblages in the last glacial maximum lgm sediments of the indian and pacific sectors but in the atlantic increased e antarctica abundances at lgm must have resulted from an increase in surface ocean production of this species holocene and lgm diatoms in atlantic and pacific sector sediments are equally well preserved but in the indian sectors holocene sediments are better preserved than those of lgm age paleoceanographic and paleoclimatic transfer functions derived from factor analyses of variations in the sedimentary abundances of these three diatoms have ignored the effects of differential dissolution on thanatocoenosis and thus should be interpreted with caution

a multi proxy palaeolimnological study to reconstruct the evolution of a coastal brackish lake lough furnace ireland during the late holocene abstract this study examines the evolution of lough furnace a coastal brackish lake in the west of ireland using high resolution sensors in the water column and palaeolimnological examination of the sediment archive palaeoenvironmental reconstructions suggest that meromixis formed as a result of sea level rise prior to ca 4000 cal yr bp increased seawater inflow has progressively led to permanent water stratification which caused the onset of anoxia making the monimolimnion a harsh environment for biological life diatom floristic interpretations suggest a progressive upcore increase in salinity which is paralleled by a reduction in cladocera remains diagenetic processes have not altered the sediment organic matter signature organic matter mainly derives from freshwater doc and appears to be linked to the presence of peat bogs in the catchment as confirmed by the c n ratio upcore variations in the c n ratio with a ca 800 year periodicity have been interpreted as the result of alternating dry and wet climatic phases during the late holocene which appear synchronous with the nao and long term solar cycles the current hydrology is largely controlled by freshwater inflow which determines permanent meromictic conditions overturns are rare requiring a specific combination of factors such as exceptionally dry and warm summers followed by cool autumns according to the climate projections for the next century in ireland permanent meromictic conditions will probably continue

biogenic silica dissolution in the oceans reconciling experimental and field based dissolution rates 1 on average 50 60 of diatomaceous opal produced in the euphotic zone redissolves within the upper 100 m of the water column high specific silica dissolution rates in the surface ocean contrast with order of magnitude lower values in deep sea sediments the lack of a mechanistic understanding of these large variations in dissolution kinetics is a major source of uncertainty in models of nutrient silicon cycling in the oceans here we show that the observed variability in biogenic silica reactivity is consistent with results of experimental dissolution studies differences in aluminum content and specific surface area of the diatom skeletons plus differences in temperature and degree of undersaturation all contribute to lowering silica dissolution rates in deep sea sediments relative to the euphotic zone when variations in these material and environmental properties are accounted for the predicted specific opal dissolution rate in average surface ocean water is over 2 orders of magnitude faster than the rate measured in recently deposited biosiliceous oozes of the southern ocean the predicted specific dissolution rate however is approximately 5 times higher than the value obtained from global estimates of the depth integrated dissolution rate and biogenic silica concentration in the upper water column this discrepancy likely reflects the inhibitory effect of protective organic coatings on fresh diatom shells in surface waters the experimental data further imply that aluminum incorporation in the silica matrix during biomineralization or after death of the organisms enhances the preservation efficiency of biogenic opal in marine sediments

occurrence of microplastics in surface waters of the gulf of lion nw mediterranean sea abstract between 2014 and 2016 a total of 43 microplastic samples were collected at six sampling stations in the eastern section of the gulf of lion located in the northwestern mediterranean sea as well as upstream of the rhone river microplastics were found in every sample with highly variable concentrations and masses concentrations ranged from 6 103 items km 2 to 1 106 items km 2 with an average of 112 103 items km 2 and mass ranged from 0 30 g km 2 to 1018 g km 2 dw mean 61 92 178 03 g km 2 the samples with the highest and lowest microplastic count originate both from the bay of marseille for the bay of marseille it is estimated that the total microplastic load consist of 519 103 101 106 items weighing 0 07 118 kg estimations for daily microplastic transport by the northern current and the rhone river two important hydrologic features of the northwestern mediterranean sea range from 0 18 to 86 46 t and from 0 20 to 21 32 kg respectively particles

a high resolution diatom inferred palaeoconductivity and lake level record of the aral sea for the last 1600 yr formerly the world s fourth largest lake by area the aral sea is presently undergoing extreme desiccation due to large scale irrigation strategies implemented in the soviet era as part of the intas funded climan project into holocene climatic variability and the evolution of human settlement in the aral sea basin fossil diatom assemblages contained within a sediment core obtained from the aral sea have been applied to a diatom based inference model of conductivity r2 0 767 rmsep 0 469 log10 s cm 1 this has provided a high resolution record of conductivity and lake level change over the last ca 1600 yr three severe episodes of lake level regression are indicated at ca ad 400 ad 1195 1355 and ca ad 1780 to the present day the first two regressions may be linked to the natural diversion of the amu darya away from the aral sea and the failure of cyclones formed in the mediterranean to penetrate more continental regions human activity however and in particular the destruction of irrigation facilities are synchronous with these early regressions and contributed to the severity of the observed low stands