hydrological changes in the mediterranean sea over the last 30 000 years sea surface temperatures were reconstructed over the last 30 000 years from alkenone paleothermometry sst alk and planktonic foraminifera assemblages using the modern analog technique mat sst foram along two cores of the mediterranean sea md84 632 levantine basin and md04 2797 siculo tunisian strait oxygen isotope of planktonic foraminifera g bulloides for core md04 2797 and g ruber for core md84 632 were also determined sst alk in the levantine basin indicate colder values at the last glacial maximum lgm 14 c than earlier established from mat and a cooling amplitude of 6 7 c comparable to the central mediterranean sea climatic events such as the younger dryas yd and heinrich events 1 and 2 h1 and h2 were times of significant cooling in the two cores in the eastern basin values of local seawater oxygen isotope w indicate relatively saltier waters during the lgm and deglaciation than today with increasing w values higher salinity in the eastern basin and decreasing ones lower salinity in the central mediterranean sea during cold stadials the observed alterations of surface water properties t and w in the central and eastern mediterranean at the lgm are consistent with model experiments showing slightly lower evaporation in the mediterranean than today except for the eastern basin

mapping of sea ice production in the arctic coastal polynyas 1 high ice production in coastal polynyas over the continental shelves in the arctic ocean is responsible for the formation of cold saline water which contributes to the maintenance of the arctic ocean halocline the accurate detection of coastal polynyas including an estimate of thin ice thickness is essential for the estimation of sea ice production this paper presents an algorithm that estimates thin ice thickness using special sensor microwave imager ssm i data in the arctic ocean detection and estimation of sea ice thicknesses of 0 15 m are based on the ssm i 85 and 37 ghz polarization ratios pr85 and pr37 through a comparison with sea ice thicknesses estimated from the advanced very high resolution radiometer avhrr data in the three different arctic coastal polynyas thus for the entire arctic ocean the algorithm can be used for the detection of coastal polynyas and for the estimation of sea ice production through combination with heat flux calculation this study provides the first circumpolar mapping of sea ice production in coastal polynyas over the entire arctic ocean high ice production is confined to the major arctic coastal polynyas with the highest ice production rate being in the north water polynya this study also presents the interannual variability of sea ice production in the 10 major coastal polynyas from 1992 to 2007 in general interannual variability in sea ice production has good correlation with polynya extent rather than surface air temperature the mapping also provides surface heat and salt flux conditions in the ice covered region which have not been well understood to date

helicopter borne observations with portable microwave radiometer in the southern ocean and the sea of okhotsk accurately measuring and monitoring the thickness distribution of thin ice is crucial for accurate estimation of ocean atmosphere heat fluxes and rates of ice production and salt flux in ice affected oceans here we present results from helicopter borne brightness temperature tb measurements in the southern ocean in october 2012 and in the sea of okhotsk in february 2009 carried out with a portable passive microwave pmw radiometer operating at a frequency of 36 ghz the goal of these measurements is to aid evaluation of a satellite thin ice thickness algorithm which uses data from the spaceborne advanced microwave scanning radiometer earth observing system amsr e or the advanced microwave scanning radiometer ii amsr ii amsr e and amsr ii tb agree with the spatially collocated mean tb from the helicopter borne measurements within the radiometers precision in the sea of okhotsk in february 2009 the amsr e 36ghz tb values are closer to the mean than the modal tb values measured by the helicopter borne radiometer in an antarctic coastal polynya in october 2012 the polarization ratio of 36ghz vertical and horizontal tb is estimated to be 0 137 on average our measurements of the tb at 36ghz over an iceberg tongue suggest a way to discriminate it from sea ice by its unique pmw signature

polynya dynamics a review of observations and modeling 1 polynyas are nonlinear shaped openings within the ice cover ranging in size from 10 to 105 km2 polynyas play an important climatic role first winter polynyas tend to warm the atmosphere thus affecting atmospheric mesoscale motions second ocean surface cooling and brine rejection during sea ice growth in polynyas lead to vertical mixing and convection contributing to the transformation of intermediate and deep waters in the global ocean and the maintenance of the oceanic overturning circulation since 1990 there has been an upsurge in polynya observations and theoretical models for polynya formation and their impact on the biogeochemistry of the polar seas this article reviews polynya research carried out in the last 2 decades focusing on presenting a state of the art picture of the physical interactions between polynyas and the atmosphere sea ice ocean system observational and modeling studies the surface heat budget and water mass transformation within these features are addressed

thickness distribution texture and stratigraphy and a simple probabilistic model for dynamical thickening of sea ice in the southern sea of okhotsk 1 sea ice thickness data and sea ice samples were analyzed to examine the characteristics of the ice thickness distribution and ice texture and to understand ice growth processes in the southern sea of okhotsk ice thickness data and samples were obtained aboard the icebreaker soya in early february the ice growth season ice thickness data which were obtained with a video monitoring system installed on the side deck of the ship each winter from 1991 to 2000 except 1995 show that the average thickness ranges from 19 7 to 55 23 cm and that it matches the characteristics of a poisson distribution ice structure analysis reveals that granular texture occupies about three quarters of the total ice thickness and that the ice exhibits a layered structure with unit thickness averaging 5 to 10 cm stratigraphy and stable isotopic composition of the ice indicate that snow ice accounts for 10 and frazil ice accounts for 64 of the total ice thickness this suggests that dynamic ice thickening processes such as frazil ice growth and piling up are more significant than congelation growth on the basis of these characteristics which resemble more those of antarctic than arctic sea ice we propose a conceptual model for the ice thickening process in this region it is shown that this model can explain the shape of the ice thickness distribution well and is analogous with the concept of the pancake cycle and multiple rafting of antarctic sea ice growth and thickening

seasonal variability of water transport through the straits of gibraltar sicily and corsica derived from a high resolution model of the mediterranean circulation abstract the variability of the water transport through three major straits of the mediterranean sea gibraltar sicily and corsica was investigated using a high resolution model this model of the mediterranean circulation was developed in the context of the mercator project the region of interest is the western mediterranean between the strait of gibraltar and the strait of sicily the major water masses and the winter convection in the gulf of lions were simulated the model reproduced the meso scale and large scale patterns of the circulation in very good agreement with recent observations the western and the eastern gyres of the alboran sea were observed but high interannual variability was noticed the algerian current splits into several branches at the longitude of the strait of sicily level forming the tyrrhenian branch and the atlantic ionian stream and the atlantic tunisian current in the eastern mediterranean the north current retroflexed north of the balearic islands and a dome structure was observed in the gulf of lions the cyclonic barotropic algerian gyre which was recently observed during the mater and elisa experiment was evidenced in the simulation from time series of 10 day mean transport the three straits presented a high variability at short time scales the transport was generally maximum in april for the strait of gibraltar in november for the strait of sicily and in january for the strait of corsica the amplitudes of the transport through the straits of gibraltar 0 11 sv and sicily 0 30 sv presented a weaker seasonal variability than that of the strait of corsica 0 70 sv the study of the relation between transport and wind forcing showed that the transport through the strait of gibraltar is dependent on local zonal wind over short time scales 70 which was not the case for the other straits less than 30 the maximum minimum of the transport occurred for an eastward westward wind stress in the strait an interannual event was noticed in november december 2001 which corresponded to a very low transport 0 3 sv which was characterised by a cyclonic circulation in the western alboran sea that circulation was also reproduced by the model for other periods than winter during the interannual simulation the transport through the strait of sicily is not influenced by local wind the wind stress curl of the northwestern mediterranean influenced the transport through the strait of corsica

the precession phase of the boreal summer monsoon as viewed from the eastern mediterranean odp site 968 the astronomical timescale of the eastern mediterranean plio pleistocene builds on tuning of sapropel layers to northern hemisphere summer insolation maxima a 3000 year precession lag has become instrumental in the tuning procedure as radiocarbon dating revealed that the midpoint of the youngest sapropel s1 in the early holocene occurred approximately 3000 years after the insolation maximum the origin of the time lag remains elusive however because sapropels are generally linked to maximum african monsoon intensities and transient climate modeling results indicate an in phase behavior of the african monsoon relative to precession forcing here we present new high resolution records of bulk sediment geochemistry and benthic foraminiferal oxygen isotopes from odp site 968 in the eastern mediterranean we show that the 3000 year precession time lag of the sapropel midpoints is consistent with 1 the global marine isotope chronology 2 maximum monsoonal precipitation conditions in the mediterranean region and china derived from radiometrically dated speleothem records and 3 maximum atmospheric methane concentrations in antarctica ice cores we show that the time lag relates to the occurrence of precession paced north atlantic cold events which systematically delayed the onset of strong boreal summer monsoon intensity our findings may also explain a non stationary behavior of the african monsoon over the past 3 million years due to more frequent and intensive cold events in the late pleistocene

neodymium associated with foraminiferal carbonate as a recorder of seawater isotopic signatures neodymium isotopic ratios in marine environments have been used as a tracer of water masses and exchange processes between dissolved and particulate phases the interest in this tracer has been growing with improvement of our knowledge on its chemical behaviour in the modern ocean and the identification of sedimentary phases that preserve past seawater epsilon nd values in the last few decades the nd isotopic composition measured on fe mn crusts sediment leachates bulk carbonate fraction corals and fish teeth have been increasingly interpreted in the context of understanding the role of the ocean in paleoclimate changes in particular calcareous foraminiferal tests shells have acquired increasing attention as an archive of seawater nd isotopic signatures because it allows continuous high resolution records to be measured and directly compared to other proxies including stable isotopes and trace metals the main challenge of interpreting the nd isotopic composition of foraminifera is determining the origin of the nd preserved within them in this review we present an overview of methodological progress including that of bulk foraminifera and microanalyses within foraminiferal tests as well as geochemical meaning of extracted nd concentrations and isotopic compositions the growing body of evidence suggests that nd isotopic signatures of sedimentary planktonic foraminifera correspond to bottom water values rather than surface water ones the nd rich phases associated with sedimentary foraminifera are adhesive nano scale particles of mn and fe oxides and hydroxides and mn rich carbonates formed within layers of foraminiferal calcite mechanical cleaning to remove clay minerals is likely to be sufficient in most cases to reconstruct past bottom water circulations unresolved issues include the potential influence of pore water nd on epsilon nd values extracted from sedimentary foraminiferal tests under different sedimentalogical and oceanographic conditions c 2013 elsevier ltd all rights reserved

the african humid period and the record of marine upwelling from excess 230th in ocean drilling program hole 658c using a high resolution 230 th normalized record of sediment flux we document the deglacial and holocene history of north african aridity and coastal upwelling at ocean drilling program hole 658c at both the end of the younger dryas and after the 8 2 ka event there are significant drops in terrigenous accumulation at our site indicating an increase in the monsoon moisture flux over africa at this time at 5 5 ka there is an abrupt end to the african humid period and a return to stronger upwelling conditions for carbonate and opal fluxes the 230 th normalization completely changes the shape of each record based on percentage variations alone this site is a clear example of how variations in one sediment component can obscure changes in the others and it demonstrates the need for radionuclide measurements more generally in paleoceanography by taking our new records and a large amount of previous data from this site we conclude that increases in african moisture are tightly coupled to decreases in coastal upwelling intensity

mediterranean climate and oceanography and the periodic development of anoxic events sapropels mediterranean sapropels are layers with elevated organic carbon concentrations that contrast with surrounding sediments which are organic poor sapropels occur quasi periodically in sedimentary sequences of the last 13 5 million years and exist both in the eastern and western mediterranean sub basins they have been the subject of extensive study based on records from both short conventional and long ocean drilling program sediment cores and from a wide variety of uplifted marine sediment sequences on the basin margins and islands previous syntheses in the 1990s and 2000s have discussed how the formation of sapropels is commonly ascribed to deep sea anoxia enhanced export productivity or a combination of these effects however a wealth of new evidence and insights has emerged during the past 1 2 decades based on traditional and novel proxy data as well as modelling which has revealed intriguing new aspects and nuances to the reconstructed conditions hence it is timely to present a new synthesis of current understanding of the processes behind the formation of sapropels which have over the past decade also become a matter of commercial interest in sub salt hydrocarbon exploration in this review we present a context of modern mediterranean climate and oceanography followed by an integrated assessment of the growing understanding of climatological and ocean circulation changes that were associated with sapropel deposition we find that sapropels predominantly formed during astronomically timed episodes when climatic and oceanographic conditions and ecological responses broadly preconditioned the basin for sapropel deposition there is strong correspondence with times of monsoon intensification fuelling runoff from north africa into the mediterranean sea while preconditioning due to sea level rise and regional precipitation and runoff may have contributed as well within these broad episodes of surface buoyancy gain and resultant decline in deep water ventilation specific deposition under dysoxic anoxic or even euxinic conditions occurred within a clearly dynamic system that was characterised by complex spatial and depth dependent patterns gradients with distinct temporal variability on at least decadal to centennial millennial timescales in the final section we evaluate the implications of different modes of deep water removal from silled basins to investigate why sapropels are more frequently and often more intensely developed in the eastern mediterranean than in the western mediterranean

estimation of thin sea ice thickness from noaa avhrr data in a polynya off the wilkes land coast east antarctica antarctic coastal polynyas are major areas of intense ocean atmosphere heat and moisture flux and associated high sea ice production and dense water formation their accurate detection including an estimate of thin ice thickness is therefore very important in this paper we apply a technique originally developed in the arctic to an estimation of sea ice thickness using us national oceanic and atmospheric administration noaa advanced very high resolution radiometer avhrr data and meteorological data in the vincennes bay polynya off wilkes land east antarctica the method is based upon the heat flux calculation using sea ice surface temperature estimates from the satellite thermal infrared data combined with global objective analysis european centre for medium range weather forecasts ecmwf data the validity of this method is assessed by comparing results with independent ice surface temperature and ice thickness data obtained during an australian led research cruise to the region in 2003 in thin ice polynya regions ice thicknesses estimated by the heat flux calculation using avhrr and ecmwf data show reasonable agreement with those estimated by a applying the heat flux calculation to in situ radiation thermometer and meteorological data and b in situ observations the standard deviation of the difference between the avhrr derived and in situ data is 0 02 m comparison of the avhrr ice thickness retrievals with coincident satellite passive microwave polarization ratio data confirms the potential of the latter as a means of deriving maps of thin sea ice thickness on the wider scale uninterrupted by darkness and cloud cover

testing the extraction of past seawater nd isotopic composition from north atlantic deep sea sediments and foraminifera neodymium isotopes provide a paleoceanographic proxy for past deep water circulation and local weathering changes and have been measured on various authigenic marine sediment components including fish teeth ferromanganese oxides extracted by acid reductive leaching cleaned foraminifera and foraminifera with fe mn oxide coatings here we compare nd isotopic measurements obtained from ferromanganese oxides leached from bulk sediments and planktonic foraminifera as well as from oxidatively reductively cleaned foraminiferal shells from sediment cores in the north atlantic sedimentary volcanic ash contributes a significant fraction of the nd when the ferro manganese fe mn oxide coatings are leached from bulk sediments reductive leachates of marine sediments from north atlantic core tops near iceland or directly downstream from iceland scotland overflow waters record nd values that are significantly higher than seawater indicating that volcanic material is easily leached by acid reductive methods the nd values from sites more distal to iceland are similar to modern seawater values showing little contamination from iceland derived volcanogenic material in all comparisons core top planktonic foraminifera nd values more closely approximate modern deep seawater than the bulk sediment reductive leached value suggesting that the foraminifera provide a route toward quantifying the nd isotopic signature of deep north atlantic water masses

estimation of the thin ice thickness and heat flux for the chukchi sea alaskan coast polynya from special sensor microwave imager data 1990 2001 1 one of the largest arctic polynyas occurs along the alaskan coast of the chukchi sea between cape lisburne and point barrow for this polynya a new thin ice thickness algorithm is described that uses the ratio of the vertically and horizontally polarized special sensor microwave imager ssm i 37 ghz channels to retrieve the distribution of thicknesses and heat fluxes at a 25 km resolution comparison with clear sky advanced very high resolution radiometer data shows that the ssm i thicknesses and heat fluxes are valid for ice thicknesses less than 10 20 cm and comparison with several synthetic aperture radar sar images shows that the 10 cm ice ssm i ice thickness contour approximately follows the sar polynya edge for the twelve winters of 1990 2001 the ice thicknesses and heat fluxes within the polynya are estimated from daily ssm i data then compared with field data and with estimates from other investigations the results show the following first our calculated heat losses are consistent with 2 years of over winter salinity and temperature field data second comparison with other numerical and satellite estimates of the ice production shows that although our ice production per unit area is smaller our polynya areas are larger so that our ice production estimates are of the same order because our salinity forcing occurs over a larger area than in the other models the oceanic response associated with our forcing will be modified index terms 4540 oceanography physical ice mechanics and air sea ice exchange processes 3360 meteorology and atmospheric dynamics remote sensing 4504 oceanography physical air sea interactions 0312 4572 oceanography physical upper ocean processes 4207 oceanography general arctic and antarctic oceanography keywords chukchi sea coastal polynya remote sensing

circulation changes in the eastern mediterranean sea over the past 23 000 years inferred from authigenic nd isotopic ratios the eastern mediterranean sea ems is a key region to study circulation change because of its own thermohaline circulation in this study we focused on intermediate deep water circulation since the last glacial maximum lgm including the sapropel s1 period two cores from the levantine sea and the strait of sicily respectively collected at 1 780 m and 771 m water depth were studied using 143nd 144nd end of foraminiferal tests and leachates as well as benthic foraminiferal stable isotopes 13c 18o this approach allowed the determination of variations in 1 the north atlantic water contribution to the mediterranean basin 2 water exchanges at the strait of sicily and 3 the influence of the nile river over the last 23 000 years during the lgm high benthic foraminiferal 13c values indicate well ventilated intermediate and deep waters in the ems the end values were more radiogenic than at present reflecting a smaller contribution of unradiogenic north atlantic waters to the ems due to reduced exchange at the strait of sicily the sluggish circulation in the ems initiated during deglaciation was further enhanced by increased nile river freshwater inputs between 15 ka bp and the s1 period partial dissolution of nile river particles contributed to an increase in ems end the large end gradient between the ems and the western mediterranean sea observed during lgm and s1 suggests that each basin had a distinct circulation mode decreasing end values at the strait of sicily after s1 reflected improved water exchange between both basins leading to the modern circulation pattern

nd isotopic compositions of eastern mediterranean sediments tracers of the nile influence during sapropel s1 formation abstract nd isotopic composition of eastern mediterranean sediments are used to investigate the influence of nile flux variations during the formation of the youngest sapropel s1 four box cores located on an east west transect around 35 n at increasing distance from the nile source were studied nd 0 signatures were measured in the lithogenic alumino silicate residue fraction and the authigenic biogenic carbonates organic matter and fe mn oxyhydroxides fraction of the sediment after 1 m hcl leaching the nd 0 profiles of the residual fraction show more radiogenic values in the sapropel layers than in the adjacent sediments these profiles follow the gaussian shaped ba al profile shape which defines s1 the nd 0 variations can be related to changes in the proportions of two continental sources of particulate material nile particles and saharan aerosols a simple mixing model reveals that the contribution of nile particulates to the sediments increases relative to saharan aerosols during sapropel formation indicating a higher nile discharge and a decrease in eolian input at that time for the cores located closest to the nile fan the nd 0 signatures of the leachable fraction are always higher in the sapropel layer 5 to 4 than in the adjacent sediments 6 the sapropel layer nd 0 values increase with decreasing distance to the nile towards values close to the nile particulates all the results obtained on the leachable fraction point towards a massive input of nile freshwater during s1 deposition

glacial water mass geometry and the distribution of δ13c of σco2 in the western atlantic ocean 1 oxygen and carbon isotopic data were produced on the benthic foraminiferal taxa cibicidoides and planulina from 25 new piston cores gravity cores and multicores from the brazil margin the cores span water depths from about 400 to 3000 m and intersect the major water masses in this region these new data fill a critical gap in the south atlantic ocean and provide the motivation for updating the classic glacial western atlantic 13c transect of duplessy et al 1988 the distribution of 13c of co2 requires the presence of three distinct water masses in the glacial atlantic ocean a shallow 1000 m southern source water mass with an end member 13c value of about 0 3 0 5 vpdb a middepth 1500 m northern source water mass with an end member value of about 1 5 and a deep 2000 m southern source water with an end member value of less than 0 2 and perhaps as low as the 0 9 values observed in the south atlantic sector of the southern ocean ninnemann and charles 2002 the origins of the water masses are supported by the meridional gradients in benthic foraminiferal 18o a revised glacial section of deep water 13c documents the positions and gradients among these end member intermediate and deep water masses the large property gradients in the presence of strong vertical mixing can only be maintained by a vigorous overturning circulation

investigations of newly formed sea ice in the cape bathurst polynya 2 microwave emission 1 this study examines the role of newly formed sea ice geophysical state on microwave emission coincident with sea ice geophysical sampling ship based passive microwave emission data dual polarized at 19 37 and 85 ghz were collected in the cape bathurst polynya during 18 october and 13 november 2003 using polarization ratios prs we found that bare thin ice was separable from snow covered ice thin snow equal to 0 02 0 13 m thickness is significantly correlated with the spectral gradient ratios grv 85 19 r2 0 55 p value 0 2 the relationship between atmospherically corrected r37 and bare ice thickness showed an exponential relationship very comparable to that reported by martin et al 2004 which is ascribed to the reduction of bare ice surface salinity based on both observational and modeling studies however the relationship quickly becomes invalid for even thin snow covered ice due to significant impact of thin wet liquid water fraction 0 02 0 04 snow on microwave emission our results suggest that the sea ice algorithms nasa team and nasa team 2 could underestimate total ice concentration over thin bare ice by 35 on average while both algorithms underestimate the total ice concentration by 20 over snow covered ice using pr 85 sea ice could be delineated from open water using a properly adjusted threshold value accounting for cloud or fog effects possibly with the exception of dark nilas and or bare consolidated pancakes

proliferation and demise of deep sea corals in the mediterranean during the younger dryas abstract uranium series and radiocarbon ages are reported for deep sea corals madrepora oculata desmophyllum dianthus lophelia pertusa and caryophyllia smithii from the mediterranean sea u series dating indicates that deep sea corals have persisted in the mediterranean for over 480 000 years especially during cool interstadial periods the most prolific period of growth however appears to have occurred within the younger dryas yd period from 12 900 to 11 700 years bp followed by a short 330 years phase of post yd coral growth from 11 230 to 10 900 years bp this indicates that deep sea corals were prolific in the mediterranean not only during the return to the more glacial like conditions of the yd but also following the rapid deglaciation and transition to warmer conditions that followed the end of the yd surprisingly there is a paucity last glacial maximum lgm coral ages implying they were largely absent during this period when cold water conditions were more prevalent radiocarbon ages show that the intermediate depth waters of the mediterranean generally had 14 c compositions similar to surface waters indicating that these waters were extremely well ventilated the only exception is a narrow period in the yd 12 500 100 years bp when several samples of lophelia pertusa from the ionian sea had 14 c values falling significantly below the marine curve using a refined approach isolation ages isol of 300 years to 500 years are estimated for these intermediate 800 1000 m depth waters relative to surface marine waters indicating a reduction or absence of deep water formation in the ionian and adjacent adriatic seas during the yd contrary to previous findings we find no evidence for widespread intrusion of low 14 c atlantic waters into the mediterranean prolific growth of deep sea corals in the mediterranean ended abruptly at 10 900 years bp with many of the coral bearing mounds on the continental slopes being draped in a thin veneer of mud their demise is attributed to a number of factors including the direct loss of habitat due to high sedimentation that accompanied glacial meltwater pulses together with rising temperatures that would have finally pervaded the deeper water of the mediterranean following the onset of holocene warming

thickness and production of sea ice in the okhotsk sea coastal polynyas from amsr e 1 from comparisons with thickness of sea ice from advanced very high resolution radiometer avhrr and ice profiling sonar data we have developed an advanced microwave scanning radiometer eos amsr e thin ice thickness algorithm for the sea of okhotsk this algorithm can estimate ice thickness of 0 2 m without snow using the polarization ratio of amsr e brightness temperature at a 36 5 ghz channel from a linear relationship with avhrr ice thickness when a snow cover exists on the thin ice surface as occurred a few times in each winter it is shown that the algorithm cannot detect the thin ice sea ice and dense shelf water dsw production in coastal polynya are estimated on the basis of heat flux calculation with the daily amsr e ice thickness for three winters december march of 2002 2003 to 2004 2005 the ice production is largest in the northwest shelf nws polynya which accounts for 45 of the sum of ice production in major coastal polynyas the ice production in major coastal polynyas would cover the maximum ice area of the okhotsk sea if the average ice thickness is assumed to be 1 m variability of the ice production is mainly modulated by air temperature in the nws polynya which is the main dsw production area the annual dsw formation rate is estimated to be 0 36 sv

variability of the large scale general circulation of the mediterranean sea from observations and modelling a review abstract in this paper we present an overview of the most recent findings about the mediterranean sea present day circulation structure both historical observations and numerical model simulations are presented outlining the differences and agreement the model simulations are presented for both an eddy resolving and a coarse resolution numerical model and the results are intercompared the importance of the mesoscales in modifying the large scale flow field is elucidated the critical point is the discovery of the large amplitude interannual variability of the circulation and water mass structure associated with the anomalies of atmospheric forcing over the basin the seasonal variability can be strictly related to changes in heat and momentum fluxes while the interannual variability has a component which is related to the mesoscale field the latter is very intense in the algerian current region and levantine basin but different in structure in the two regions results are shown which confirm the importance of wind driving in establishing the kinetic energy of the flow field by comparing the current transport at the strait of corsica with observations in conclusion the essential characteristics of the present day circulation are associated with the atmospheric forcing and the basin topographic structure results from palaeoceanographic simulations for the last 20 000 years show that changing the atmospheric forcing can cause large changes in the circulation structure which may have affected sapropel formation

new neodymium isotope data quantify nile involvement in mediterranean anoxic episodes the development of widespread anoxic conditions in the deep oceans is evidenced by the accumulation and preservation of organic carbon rich sediments but its precise cause remains controversial the two most popular hypotheses involve 1 circulation induced increased stratification resulting in reduced oxygenation of deep waters or 2 enhanced productivity in the surface ocean increasing the raining down of organic matter and overwhelming the oxic remineralization potential of the deep ocean in the periodic development of deep water anoxia in the pliocene pleistocene mediterranean sea increased riverine runoff has been implicated both as a source for nutrients that fuel enhanced photic zone productivity and a source of a less dense freshwater cap leading to reduced circulation basin wide stagnation and deep water oxygen starvation monsoon driven increases in nile river discharge and increased regional precipitation due to enhanced westerly activity two mechanisms that represent fundamentally different climatic driving forces have both been suggested as causes of the altered freshwater balance here we present data that confirm a distinctive neodymium nd isotope signature for the nile river relative to the eastern mediterranean providing a new tracer of enhanced nile outflow into the mediterranean in the past we further present nd isotope data for planktonic foraminifera that suggest a clear increase in nile discharge during the central intense period of two recent anoxic events our data also suggest however that other regional freshwater sources were more important at the beginning and end of the anoxic events taken at face value the data appear to imply a temporal link between peaks in nile discharge and enhanced westerly activity

stable isotopes in benthic foraminiferal calcite from a river influenced arctic marine environment kara and pechora seas oxygen and carbon stable isotope compositions of modern benthic foraminifera in the kara and pechora estuarine regions of the arctic continental shelf were compared with water 1 8 o 1 3 c d i c temperature and salinity the foraminiferal 1 8 o distribution is mostly similar to that of equilibrium calcite primarily controlled by mixing of runoff and seawater in near estuarine areas depth 15 20 m with additional temperature control seaward the 1 3 c composition is controlled by remineralization of organic matter mostly imported by rivers and by water mixing most analyses used the common arctic foraminifer elphidium excavatum forma clavata which yields depleted 1 3 c as expected for an infaunal species isotope records for sediment cores off the pechora and yenisey rivers show a decelerating rise in isotope values of up to 10 in 1 8 o over the last 10 kyr in a pattern similar to that of rising sea level and concomitant retreat of river mouths with local complexities probably resulting from glacio isostatic rebound and changes in sedimentation

rapid coupling between ice volume and polar temperature over the past 150 000 years a new approach to dating a continuous sea level record using speleothem u th ages shows that past variations in global ice volume occurred within centuries of polar climate change with rates of sea level rise reaching at least 1 metre per century

sea ice production and export from coastal polynyas in the weddell and ross seas 1 for 1992 2008 we use data from the special sensor microwave imager ssm i and the advanced microwave scanning radiometer eos amsr e to examine differences in ice production and export in the weddell and ross seas we find that the ross production is three times that in the weddell the ross export twice that in the weddell in the ross the ice production has a statistically significant positive trend of about 21 km3 y 1 and approximately equals the export while in the weddell the production trend is statistically flat and provides only about 60 of the export for each sea comparison of the ice production with the total winter sea ice volume shows that the weddell polynyas produce 5 10 of the total the ross polynyas 20 50 the explanation for these differences is that in the ross the low pressure system is better situated for generation of large polynyas than in the weddell

validation of avhrr and modis ice surface temperature products using in situ radiometers ship borne and airborne infrared radiometric measurements during the arise cruise of september october 2003 permitted in situ validation studies of two satellite based ice surface skin temperature algorithms the avhrr polar pathfinder ice surface temperature and the modis sea ice surface temperature observations of sea ice from the aurora australis ship s rail using a kt 19 82 radiometer were conducted between 25 september and 21 october during clear sky overflights by avhrr 41 passes and modis 17 passes on their respective satellite platforms data from both sensors show highly linear fits to 1 min integrated radiometer spot measurements spanning the range 245 270 k with a 1 48c 1 avhrr and 1 08c modis variation relative to a 1 1 relationship there was no significant offset helicopter observations made with a kt 19 85 radiometer on three dates 8 19 and 20 october provided more data 236 gridcell sites total but over a more limited sea ice skin tem perature range 252 268 k with higher variation 1 78c 1 due to mixed pixel issues comparison of modis and avhrr algorithms directly with both images acquired during a helicopter flight indicates very high correlation and near unity slope for the two satellite based algorithms ship air temperature data during the validation indicated moderate to strong inversions over sea ice under clear skies these formed and decayed rapidly tens of minutes as clouds moved out of and into the zenith area

the use of foraminifera as a record of the past neodymium isotope composition of seawater 1 we present new isotopic data for sedimentary planktonic foraminifera as well as for potential water column and sedimentary sources of neodymium nd which confirm that the isotopic composition of the foraminifera is the same as surface seawater and very different from deep water and sedimentary nd the faithfulness with which sedimentary foraminifera record the isotopic signature of surface seawater nd is difficult to explain given their variable and high nd ca ratios ratios that are often sedimentary foraminifera ratios that are often much higher than is plausible for direct incorporation within the calcite structure we present further data that demonstrate a similarly large range in nd ca ratios in plankton tow foraminifera a range that may be controlled by redox conditions in the water column cleaning experiments reveal in common with earlier work that large amounts of nd are released by cleaning with both hydrazine and diethylene triamine penta acetic acid but that the nd released at each step is of surface origin while further detailed studies are required to verify the exact location of the surface isotopic signature and the key controls on foraminiferal nd isotope systematics these new data place the use of planktonic foraminifera as recorders of surface water nd isotope ratios and thus of variations in the past supply of nd to the oceans from the continents via weathering and erosion on a reasonably sure footing

dense water dynamics along the strait of sicily mediterranean sea abstract hydrographic and current meter data gathered in different periods in the strait of sicily and in the southern tyrrhenian sea allow the outflow characteristics from the eastern toward the western mediterranean basin to be analyzed the evolution through the strait of a deep vein of dense water coming from the eastern mediterranean is described together with the dynamic interaction with overlying layers these data are related to a slightly generalized version of recent density current models such as those of emms and those of baringer and price taking into account the dynamic influence of the overlying currents and in particular their friction and mixing this model explains the path of this deep flow and enables estimates of entrainment and bottom friction to be made with these new data a phenomenon of considerable interest namely the dynamics of density currents crossing and outflowing from a strait is examined and discussed

thin ice thickness from satellite thermal imagery sea ice thickness is an important parameter in the surface energy exchange and mass balance of the polar oceans remote sensing offers the opportunity to monitor thin ice routinely we combine measurements of surface temperature from an advanced very high resolution radiometer avhrr with a thermodynamic ice growth model to estimate thin ice and its thickness distribution during the cold season in a beaufort sea area of perennial ice we find that thin ice up to a meter thick had a concentration of 18 in december 1990 and 3 in april 1991 thin ice concentrations near the ice edge in the greenland sea range from 20 to 50 these avhrr derived estimates generally compare well with thickness observations from upward looking sonar given the uncertainties in all the model inputs estimated from avhrr such as radiative and turbulent heat flux components and surface albedo we find that ice thickness is estimated with an uncertainty of roughly 50 the uncertainty in the cumulative thickness distribution is about 3 for ice less than 20 cm thick and about 9 for ice around 1 m thick these magnitudes are significantly smaller than the variations in thin ice observed by satellite in different months and regions we conclude that avhrr is capable of resolving the regional and seasonal variations in thin ice to a level of accuracy useful both for establishing a climatology and for testing ice models

mapping of sea ice production for antarctic coastal polynyas 1 active sea ice production in antarctic coastal polynyas causes dense water formation finally leading to antarctic bottom water aabw formation this study gives the first mapping of sea ice production in the antarctic ocean based on heat flux calculation with ice thickness data derived from satellite data the highest ice production occurs in the ross ice shelf polynya region the ice production there decreased by 30 from the 1990s to the 2000s which can be one candidate for causing the recent freshening of aabw the cape darnley polynya in east antarctica is found to be the second highest production area suggesting a possible aabw formation area according to our estimation around 10 of southern ocean sea ice is produced in the major antarctic coastal polynyas the mapping provides surface heat and salt flux conditions in the ice covered region which have not been well understood

acoustic doppler current profiler surveys along the yangtze river an acoustic doppler current profiler is used to characterize the river velocity against the morphology of the yangtze river from chonqing to the sea high flow velocities occur in the three gorges section and lower velocities in the middle and lower reaches of the river this is largely due to the change in river pattern from a high gradient deeply cut valley to a flat fluvial plain flow velocities fluctuate in the middle yangtze due to the presence of meander bends of different length there are numerous smaller velocity fluctuations in the lower yangtze channel that reflect multichannel pattern with numerous sand bars and a river morphology affected by bedrock outcrops water depths of 40 100 m occur in the three gorges valley but decrease to 15 40 m in the middle and lower yangtze at the gezhou reservoir 30 km downstream of the three gorges damsite velocity drops to low 1 0 m s 1 20 km reach a second low velocity 0 5 m s 1 zone about 20 km in length is located in the lower yangtze near the coast probably due to the tidal influence the results from this research will serve as a datum for evaluating changes to the river once the three gorges dam is completed in 2009

late quaternary sedimentation history of the lena delta abstract core and outcrop analysis from lena mouth deposits have been used to reconstruct the late quaternary sedimentation history of the lena delta sediment properties heavy mineral composition grain size characteristics organic carbon content and age determinations 14c ams and ir osl are applied to discriminate the main sedimentary units of the three major geomorphic terraces which form the delta the development of the terraces is controlled by complex interactions among the following four factors 1 channel migration according to the distribution of 14c and ir osl age determinations of lena mouth sediments the major river runoff direction shifted from the west during marine isotope stages 5 3 third terrace deposits towards the northwest during marine isotope stage 2 and transition to stage 1 second terrace to the northeast and east during the holocene first terrace deposits 2 eustasy sea level rise from last glacial lowstand to the modern sea level position reached at 6 5 ka bp resulted in back filling and flooding of the palaeovalleys 3 neotectonics the extension of the arctic mid ocean ridge into the laptev sea shelf acted as a halfgraben showing dilatation movements with different subsidence rates from the continent side differential neotectonics with uplift and transpression in the siberian coast ridges are active both likely have influenced river behavior by providing sites for preservation with uplift in particular allowing accumulation of deposits in the second terrace in the western sector the actual delta setting comprises only the eastern sector of the lena delta 4 peat formation polygenetic formation of ice rich peaty sand ice complex was most extensive 7 11 m in thickness in the southern part of the delta area between 43 and 14 ka bp third terrace deposits in recent times alluvial peat 5 6 m in thickness is accumulated on top of the deltaic sequences in the eastern sector first terrace

improved mapping of sea ice production in the arctic ocean using amsr e thin ice thickness algorithm new and improved estimates of sea ice production in the arctic ocean are derived from amsr e satellite and atmospheric reanalysis data for the period 2002 2011 at a spatial resolution of 6 25 km and using a newly developed fast ice mask high ice production in the major coastal polynyas is well demonstrated the total annual cumulative ice production in the major 10 polynya regions is about 1180 70km 3 the interannual variability of the ice production for each polynya is presented during 2002 2011 no obvious relationship is noted between the ice production and the recent drastic reduction in the preceding summer arctic sea ice extent most polynya regions exhibit maximum ice production in autumn october november before areas offshore have been covered with consolidated pack ice sea ice production from october to november in the marginal ice zone of the pacific ocean sector is negatively correlated with summer ice extent there the ice production from october to november of 2007 a record minimum summer ice extent was about twice as large as that in other years the high ice production area shifted to higher latitudes i e toward the deep canada basin due to the retreat of the summer ice edge we speculate that the resultant increase in brine input could change the oceanic structure in the basin specifically deepening the winter mixed layer 2014 american geophysical union all rights reserved

channel morphology and river flow in the northern russian plain in the late glacial and holocene the relicts of large meandering palaeochannels are found throughout the territory of the periglacial zone of the last valdai weichselian glaciation on the russian plain channel widths of macromeanders can be 15 times larger than the recent meanders of the same rivers palaeolandscape and palaeohydrological reconstructions show that these periglacial river channels were formed under conditions of high spring water flow up to eight times greater than the modern discharges when the flow coefficient was close to 0 9 1 0 due to presence of permafrost summers were dry and streams lacked ground water supply permafrost degradation increased soil permeability in spring and increased ground water flow in summer causing a decrease of annual flow due mainly to the flood flow decrease in spring as a result large periglacial channels were abandoned and transformed into lakes and bogs late holocene channels have much smaller channel widths and meander lengths these were formed under conditions of lower annual flows and much steadier flow regime

hydrological impact of heinrich events in the subtropical northeast atlantic reconstructing the impact of heinrich events outside the main belt of ice rafting is crucial to understanding the underlying causes of these abrupt climatic events a high resolution study of a marine sediment core from the iberian margin demonstrates that this midlatitude area was strongly affected both by cooling and advection of low salinity arctic water masses during the last three heinrich events these paleoclimatic time series reveal the internal complexity of each of the last three heinrich events and illustrate the value of parallel studies of the organic and inorganic fractions of the sediments

neodymium isotopic composition of the mediterranean outflow and the eastern north atlantic the neodymium concentration and isotopic composition of the mediterranean outflow in the strait of gibraltar has been directly determined the outflow has a dissolved nd concentration of 23 pmoles kg with nd 0 9 4 these results are in clear disagreement with previous values inferred for the mediterranean this concentration and nd 0 do not sharply contrast with north atlantic deep water nadw values and can produce isotopic anomalies no larger than 1 unit in the north atlantic a new profile in the eastern north atlantic does not exhibit an nd 0 anomaly at the depth of the mediterranean water core in accordance with the above inferences while concentrations and nd 0 at this site indicate that nd is conservative in the deep eastern north atlantic a previously reported nd 0 anomaly in the eastern north atlantic originally associated with the mediterranean outflow has a different source the direct contribution of the mediterranean outflow to the nadw nd budget is small 10 of the high latitude sources however the outflow plus entrained water supply 30 of the total nd associated with northern latitude deep water sources concentrations of dissolved nd in the outflow are enriched compared to the atlantic inflow which has 16 pmoles kg with nd 0 11 8 the principal source of the excess dissolved nd is inferred to be partial dissolution of detrital particles simple mass balance calculations suggest that 0 6 of the nd associated with detrital river transported sediments and or 3 5 of the nd associated with eolian particles delivered to the mediterranean is mobilized during passage into the marine environment if general these mobilization efficiencies imply that the dissolution of detrital particles is a significant source of dissolved nd and other rare earth elements in seawater

mass balance for nd in the mediterranean sea abstract the mass balance for nd in the mediterranean sea has been assessed through the measurement of nd isotope ratios in particulates from rivers entering the mediterranean sea floor clays and ferromanganese crusts and samples of atmospheric dusts nd values for the po and rhone rivers respectively are 10 8 and 9 7 whereas the nile seyhan and tarsus have 3 3 6 2 and 6 3 sea floor clays and ferromanganese crusts range from 2 0 to 10 1 and dust samples vary from 8 2 to 11 0 the relatively radiogenic nd isotope composition of the mediterranean seawater ed 6 to 7 compared to the atlantic nd 12 reflects partial equilibration of the particulate input into the basin rather than merely the dissolved input

observations of ice thickness and frazil ice in the st lawrence island polynya from satellite imagery upward looking sonar and salinity temperature moorings 1 for the 1999 winter this paper examines the behavior of the bering sea st lawrence island polynya using a combination of advanced very high resolution radiometer avhrr radarsat synthetic aperture radar sar meteorological data over winter moored upward looking sonars uls and seabird salinity temperature sensors we define a thermal ice thickness from the avhrr retrieval of ice surface temperature combined with meteorological observations and a heat flux model south of the island we compare the uls and thermal thicknesses for congelation and frazil ice when the satellites observe congelation ice over the ulss the uls and thermal ice thicknesses generally agree when sar observes langmuir plumes over the ulss which indicate frazil ice formation the ulss show scatterers at 5 20 m depths in the water column and the seawater temperatures are either within 0 01 c of freezing or are slightly supercooled this suggests that during frazil events crystals either nucleate at depth or are transported to depth by the langmuir circulation the combination of the sar imagery and uls observations also allow measurement of the pack ice advection velocity the polynya width and the downwind frazil accumulation thickness giving widths of 10 to 30 km and thicknesses of 0 1 0 2 m substitution of these observed values with the heat flux into the pease polynya model yields polynya widths that approximately agree with the observed