opening of the fram strait gateway a review of plate tectonic constraints abstract we have revised the regional crustal structure oceanic age distribution and conjugate margin segmentation in and around the lena trough the oceanic part of the fram strait between the norwegian greenland sea and the eurasia basin arctic ocean the lena trough started to open after eurasia greenland relative plate motions changed from right lateral shear to oblique divergence at chron 13 times 33 3 ma earliest oligocene a new bouguer gravity map supported by existing seismic data and aeromagnetic profiles has been applied to interpret the continent ocean transition and the influence of eocene shear structures on the timing of breakup and initial seafloor spreading assuming that the onset of deep water exchange depended on the formation of a narrow oceanic corridor the gateway formed during early miocene times 20 15 ma however if the initial lena trough was blocked by terrigenous sediments or was insufficiently subsided to allow for deep water circulation the gateway probably formed with the first well developed magnetic seafloor spreading anomaly around chron 5 times 9 8 ma late miocene paleoceanographic changes at odp site 909 northern hovgard ridge are consistent with both hypotheses of gateway formation we cannot rule out that a minor gateway formed across stretched continental crust prior to the onset of seafloor spreading in the lena trough the gravity seismic and magnetic observations question the prevailing hypotheses on the yermak plateau and the morris jesup rise as eocene oceanic plateaus and the hovgard ridge as a microcontinent

the mediterranean sea a miniature ocean for climatic and environmental studies and a key for the climatic functioning of the north atlantic the mediterranean sea provides a case study not only for dense water formation and climatic functioning at a basin scale but also as a body of water evolving in response to the effects of environmental changes through marine circulation marine signatures of changes may be used to provide estimates of the evolution of the external driving forces of climate and environment that is to say to provide a coupling between marine sciences and climatic and socio economic studies different examples may be given i nutrients and trace metal changes in the western mediterranean permit quantification of external changes at a basin scale ii sapropels organic rich layers sedimented in anoxic conditions provide records for the last 2 million years of interactions between marine circulation climate and biology iii temperature and salinity changes that have taken place since the 1960s in response to changes in heat and water budgets across the sea surface sapropel studies and ongoing changes in temperature and salinity also require that the mediterranean functioning be considered in relation to global climate and to the atlantic ocean as well as taking into account the changing role of salty mediterranean waters in the atlantic ocean these factors highlight a dual role for the mediterranean sea which acts as a miniature ocean for physical chemical or climatic and environmental studies and also as a key factor in understanding global ocean circulation in which past changes have taken place

gravitational symmetric and baroclinic instability of the ocean mixed layer abstract a hierarchy of hydrodynamical instabilities controlling the transfer of buoyancy through the oceanic mixed layer is reviewed if a resting ocean of horizontally uniform stratification is subject to spatially uniform buoyancy loss at the sea surface then gravitational instability ensues in which buoyancy is drawn from depth by upright convection but if spatial inhomogeneities in the ambient stratification or the forcing are present as always exist in nature then horizontal density gradients will be induced and within a rotation period horizontal currents in thermal wind balance with those gradients will be set up within the mixed layer there are two important consequences on the convective process upright convection will become modified by the presence of the thermal wind shear fluid parcels are exchanged not along vertical paths but rather along slanting paths in symmetric instability theoretical considerations suggest that this slantwise convection sets the potential vorticity of th

a mechanism governing the estuarine circulation in deep strongly stratified fjords the estuarine circulation in deep strongly stratified fjords is discussed it is argued that a two layer description of the stratification in the fjord is correct in very wide fjords wide compared to the width of the mouth and possibly also in narrow fjords with high runoff and or weak mixing a theory for the thickness and the salinity of the brackish layer in a wide fjord was earlier developed by the present author and published in swedish 1975 and it is presented here among other findings in that theory we may mention that the thickness of the brackish layer is primarily determined by the internal hydraulic control for high specific runoff runoff unit horizontal surface area of the fjord and weak mixing in the other extreme with low specific runoff and strong mixing the thickness of the brackish layer is found to be proportional to the monin obukhov length the circulation in not very wide fjords is also discussed it is found that recirculation in the brackish layer may be expected whereby a two layer description of the flow field breaks down at least locally a critical rayleigh number that seems to control the recirculation of brackish water within the fjord is found a theory for the density difference between the mouth and the head in the brackish layer in the fjord is developed from the critical rayleigh number condition it is found that this density difference normally is proportional to the density difference between the brackish water at the mouth and the underlying sea water provided that the river runoff is not too heavy and or the mixing is not too weak this prediction is confirmed by extensive measurements from the nordfjord

evolution of the academician ridge accommodation zone in the central part of the baikal rift from high resolution reflection seismic profiling and geological field investigations new high resolution seismic reflection data from the central part of lake baikal provide new insight into the structure and stratigraphy of academician ridge a large intra rift accommodation zone separating the central and north baikal basins four seismic packages are distinguished above the basement a thin top of basement unit seismic stratigraphic unit x seismic stratigraphic unit a and seismic stratigraphic unit b units a and b were cored on selected key locations the four packages are correlated with a series of deposits exposed on the nearby western shores the ularyar sequence oligocene the tagay sequence lower to middle miocene the sasa sequence upper miocene to lower pliocene the kharantsy sequence upper pliocene and the nyurga sequence lower pleistocene based on stratal relationships sedimentary geometries distribution patterns and principal morphostructural elements both onshore and offshore we propose a new palaeogeographic evolution model for the area in this model progressive tectonic subsidence of the baikal basins and successive pulses of uplift of various segments of the rift margins lead to a formation of the ridge as a structural and morphological feature separating the central and north baikal basins during the middle to late miocene b gradual flooding of the main parts of the ridge and establishment of a lacustrine connection between the two rift basins during the late miocene and c total submergence of the top parts of the crest of the ridge during the latest pleistocene this new model helps to better constrain numerous phases in the structural evolution of the baikal rift in which the academician ridge as an accommodation zone plays a crucial role

the major and minor element geochemistry of lake baikal funding for u s participation in the fieldwork and sample collection was provided by the u s national science foundation funding for the analytical work was obtained by various means

a model for the exchange of water and salt between the baltic and the skagerrak abstract a model for the exchange of salt and water between the baltic and the sea the skagerrak is presented because of strong inter basin interactions in the baltic entrance area the model must include the kattegat and the belt sea these are modeled by horizontally homogeneous two layer sub models the most prominent dynamical properties of the sub models are wind driven entrainment flows and rotational baroclinic hydraulic controls the model is driven by a meteorologically forced barotropic transport qh calculated from the freshwater supply to the baltic qf and the sea level fluctuations in the kattegat and turbulent entrainment flows coupled to the wind speed w and in the belt sea also to the barotropic transport the most important bathymetric features of the basins are included the model equations are integrated numerically for a test period of 1 years the stratification in the kattegat as well as in the belt sea is quite well predicted it is found that approximately one half of

introduction to special section on cenozoic paleoceanography of the central arctic ocean 1 in late summer 2004 the integrated ocean drilling program iodp conducted one of the most transformational missions in the almost 40 year history of scientific ocean drilling the arctic coring expedition acex backman et al 2006 moran et al 2006a this technically challenging expedition moran et al 2006b to the lomonosov ridge near 88 n recovered the first long term cenozoic sediment record from the arctic ocean extending previous records from 1 5 ma to an unprecedented 56 ma glimpses of the breadth of this transformation were seen during the acex cruise when the massulae from freshwater ferns azolla were found in 49 ma old sediments brinkhuis et al 2006 and the presence of apectodinium augustum confirmed that the paleocene eocene thermal maximum petm 55 ma was unexpectedly recovered sluijs et al 2006 2 soon after the expedition when the cores were opened and analyzed ice rafted debris was found in surprisingly old 46 ma sediments moran et al 2006a these middle eocene sediments are characterized also by their high organic carbon content stein et al 2006 the exciting early results attracted other investigators that expanded the scientific investigating team to more than 40 people analyses were extended to include studies that revealed surprisingly high arctic ocean surface water temperatures sluijs et al 2006 and an amplified hydrological system pagani et al 2006 during the petm initial analyses revealed an extensive hiatus encompassing about 26 million years that occurred below a short interval showing starkly alternating black and white layers that is now dubbed the zebra interval thus the time interval from the late early miocene 18 ma to the middle middle eocene 44 ma is missing although the hiatus is a lost window in time for the arctic paleoclimate record it spawned other studies that integrated the regional tectonic history with acex results revealing a major oceanographic reorganization at 17 5 ma ventilation of the arctic ocean to the north atlantic through the fram strait jakobsson et al 2007 in terms of ventilation and water mass history neogene neodymium isotope data reveal that arctic intermediate waters originate from brine formation on eurasian shelf areas between 15 and 2 ma and during glacial periods throughout pleistocene times haley et al 2008a they conclude that this mode of arctic circulation differs markedly from today s situation showing relatively high contributions of north atlantic intermediate water and minor input from brine formation 3 in this special section the transformation continues results from the large acex scientific family include a robust age model detailed analyses of the middle eocene that document a unique brackish water environment sea ice and iceberg history reconstructions as well as the provenance of ice rafted debris from the eocene to present evolution of depositional environments times of isolation and connection to the global ocean geochemical analyses of the organic carbon rich sediments and unique applications of high resolution proxies and cyclostratigraphy highlights from this special section are presented here

salinity of the eocene arctic ocean from oxygen isotope analysis of fish bone carbonate stable isotope analysis was performed on the structural carbonate of fish bone apatite from early and early middle eocene samples 55 to 45 ma recently recovered from the lomonosov ridge by integrated ocean drilling program expedition 302 the arctic coring expedition the 18o values of the eocene samples ranged from 6 84 to 2 96 vienna peedee belemnite with a mean value of 4 89 compared to 2 77 for a miocene sample in the overlying section an average salinity of 21 to 25 was calculated for the eocene arctic compared to 35 for the miocene with lower salinities during the paleocene eocene thermal maximum the azolla event at 48 7 ma and a third previously unidentified event at 47 6 ma at the azolla event where the organic carbon content of the sediment reaches a maximum a positive 13c excursion was observed indicating unusually high productivity in the surface waters

glacial holocene salinity changes in the mediterranean sea hydrographic and depositional effects oxygen isotope changes as recorded by pleistocene foraminifera from open ocean sediments are primarily a function of changes in the isotopic composition of the global seawater reservoir caused by ice volume changes with a secondary temperature component1 oxygen isotope records from marginal basins such as the gulf of mexico2 the mediterranean sea3 5 and the red sea6 also exhibit the global signal but are far more complicated owing to the strong overprint of local climate conditions in particular glacial interglacial changes in continental aridity and river runoff produce significant salinity changes in these semi enclosed basins using available oxygen isotope records we estimate that glacial 18 000 yr bp salinities in the eastern and western mediterranean sea were 2 7 and 1 2 higher respectively than at present these elevated glacial salinities played an important part in preconditioning the eastern mediterranean for the eventual accumulation of organic carbon rich sediments sapropels at the end of deglaciation

rare earth elements in the sediments of lake baikal lake baikal is the deepest and probably oldest lake on earth its water column is pervasively oxic and sedimentation rates are very low which leads to the formation of a dynamic iron fe and manganese mn enrichment below the mn ii o2 boundary these often massive accumulations can be buried within the reducing part of the sediments and give rise to complex and cryptic redox cycles the mobility of rare earth elements rees is influenced by the dissolution and reduction dynamics of the ferromanganese oxides the present study offers an overview of the ree chemistry in lake baikal and its catchment area and more specifically ree distribution in five 11 to 26 cm long sediment cores situated across the lake at different water depths we analysed and discussed normalised ree patterns and their consequential cerium ce anomalies while particulate ree concentrations are mainly influenced by processes above or near the surface of lake baikal such as the development of a widespread negative ce anomaly processes occurring during early diagenesis in the sediment are most reflected in pore water rees the dissolution of ferromanganese oxides at the mn ii o2 boundary remobilizes significant amounts of ree into the pore water whereby some are likely adsorbed onto colloidal fe oxides however besides the tendency of ce being associated with mn oxides pore water rees fractionate predominantly around the buried fe mn accumulation where light rees preferentially adsorb onto fe oxides

the thermohaline circulation of the arctic ocean and the greenland sea the thermohaline circulation of the arctic ocean and the greenland sea is conditioned by the harsh high latitude climate and by bathymetry warm atlantic water loses its heat and also becomes less saline by added river run off in the arctic ocean this leads to rapid cooling of the surface water and to ice formation brine released by freezing increases the density of the surface layer but the ice cover also insulates the ocean and reduces heat loss this limits density increase and in the central arctic ocean a low salinity surface layer and a permanent ice cover are maintained only over the shallow shelves where the entire water column is cooled to freezing can dense water form and accumulate to eventually sink down the continental slope into the deep ocean the part of the atlantic water which enters the arctic ocean is thus separated into a low density surface layer and a denser deep circulation these two loops exit through fram strait the waters are partly rehomogenized in the greenland sea the main current is confined to the greenland continental slope but polar surface water and ice are injected into the central gyre and create a low density lid allowing for ice formation in winter this leads to a density increase sufficient to trigger convection upwelling and subsequent ice melt the convection maintains the weak stratification of the gyre and also reinforces the deep circulation loop as the transformed waters return to the north atlantic the low salinity upper water of the east greenland current enters the labrador sea and influences the formation of labrador sea deep water the dense loop passes through denmark strait and the faroe shetland channel and sinks to contribute to the north atlantic deep water changes in the forcing conditions might alter the relative strength of the two loops this could affect the oceanic thermohaline circulation on a global scale

on the asymmetry between cyclonic and anticyclonic flow in basins with sloping boundaries the authors present results from laboratory experiments and numerical simulations of the barotropic circulation in a basin with sloping boundaries forced by a surface stress focus is placed on flows with large scale rossby numbers that are significantly smaller than unity the results of the laboratory experiments and simulations show that cyclonic circulation follows the isobaths the flow pattern being independent of the strength of the forcing for anticyclonic circulation the flow pattern changes with forcing strength it is similar to the cyclonic topographically steered pattern for weak forcing and it develops strong cross slope flows for strong forcing linear dynamics are symmetric between cyclonic and anticyclonic circulations and give a good description of the cyclonic and weakly forced anticyclonic circulations the analysis of the nonlinear dynamics shows that topographically steered cyclonic flows are all stable and steady energy minimum solutions to the inviscid nonlinear equations this implies that the nonlinear terms advection of relative vorticity are always small for the topographically steered cyclonic flow for anticyclonic flow the situation is very different it is possible that no anticyclonic topographically steered flow is ever a solution to the steady inviscid equations and if such a steady anticyclonic flow does exist it is likely to be unstable since it must correspond to a saddle point in energy rather than to a minimum or a maximum the nonlinear terms are important when the rossby number is larger than the ekman number which is the case for the anticyclonic experiments with strongest forcing for these experiments the advection of relative vorticity prevents the flow from following topography creating locations with strong relative vorticity and cross slope flow the development of cross slope flow can be understood from the conservation of potential vorticity in basins with irregular topography the separation of anticyclonic flow from steep topography shown in the laboratory experiments and the theoretical analysis herein are in agreement with features like the gulf stream separation from the continental slope at cape hatteras north carolina

early oligocene initiation of north atlantic deep water formation dating the onset of deep water flow between the arctic and north atlantic oceans is critical for modelling climate change in the northern hemisphere1 2 and for explaining changes in global ocean circulation throughout the cenozoic era3 from about 65 million years ago to the present in the early cenozoic era exchange between these two ocean basins was inhibited by the greenland scotland ridge3 4 but a gateway through the faeroe shetland basin has been hypothesized3 5 previous estimates of the date marking the onset of deep water circulation through this basin on the basis of circumstantial evidence from neighbouring basins have been contradictory5 6 7 8 9 ranging from about 35 to 15 million years ago here we describe the newly discovered southeast faeroes drift which extends for 120 km parallel to the basin axis the onset of deposition in this drift has been dated to the early oligocene epoch 35 million years ago from a petroleum exploration borehole we show that the drift was deposited under a southerly flow regime and conclude that the initiation of deep water circulation from the norwegian sea into the north atlantic ocean took place much earlier than is currently assumed in most numerical models of ancient ocean circulation

anoxia and high primary production in the paleogene central arctic ocean first detailed records from lomonosov ridge 1 except for a few discontinuous fragments of the late cretaceous early cenozoic climate history and depositional environment the paleoenvironmental evolution of the pre neogene central arctic ocean was virtually unknown prior to the iodp expedition 302 arctic ocean coring expedition acex drilling campaign on lomonosov ridge in 2004 here we present detailed organic carbon oc records from the entire ca 200 m thick paleogene oc rich section of the acex drill sites these records indicate euxinic black sea type conditions favorable for the preservation of labile aquatic marine algae type oc occur throughout the upper part of the early eocene and the middle eocene explained by salinity stratification due to freshwater discharge the superimposed short term milankovitch type variability in amount and composition of oc is related to changes in primary production and terrigenous input prominent early eocene events of algae type oc preservation coincide with global 13c events such as the petm and elmo events the elmo 13c event has been identified in the arctic ocean for the first time

improved os isotope stratigraphy of the arctic ocean 1 the history of the arctic ocean remained poorly known until the 2004 iodp coring of lomonosov ridge sediments early studies of the recovered sequence demonstrated the existence of an eocene lake stage prior to the transition to marine conditions the marine stage onset was inferred to be 17 5 million years ma ago thus implying a nearly 26 ma gap between the lacustrine and marine episodes and an unusual tectonic history for lomonosov ridge in order to explain this gap more recently rhenium osmium re os isotope measurements of the transition from the lacustrine to marine sediments suggested a much earlier inception of marine conditions and the absence of any significant gap between both episodes here an improved osmium isotope stratigraphy and re os data concur to assign a late eocene age 36 ma to the marine invasion consistent with a relative change in sea level on top of lomonosov ridge either from tectonic origin or from another cause

origin and dynamics of fe and mn sedimentary layers in lake baikal remobilization and accumulation of iron and manganese were measured by porewater and sediment core analyses at six contrasting sedimentary environments of lake baikal with bulk sedimentation rates varying between 0 8 and 0 02 mm year 1 the results allow for the distinction between two types of fe and mn diagenesis in areas of relatively high sedimentation and in regions of low sedimentation rates in the first case only small fe mn enrichments near the sediment water interface were observed in the central and southern basins at the high sediment flux area near the selenga delta and in maloe more strait massive sedimentary layers enriched in fe and mn were found within the upper 15 25 cm of the sediments exclusively in northern baikal and in the underwater academician ridge which are characterized by low sedimentation rates and deep sulfate penetration depths in the porewaters the mn content in the enriched layers ranged from 10 5 mol cm 2 at the sites near the selenga delta up to 10 2 mol cm 2 at academician ridge the accumulation times for the enriched fe mn layers calculated from the size of the fe and mn oxide pools and the diffusive fluxes into the enriched zones also varied by a factor of 1000 they ranged from a few years near the selenga delta to several thousand years for the sites at academician ridge and northern baikal these values were generally congruent with the sediment age of the accumulation zones calculated from sedimentation rates these findings have significant implications for paleolimnological studies iron and manganese dynamics at sites with high sedimentation rates is dominated by allochthonous input which is only partially dissolved close to the sediment surface in contrast the massive fe mn sedimentary layers at sites of slow sedimentation are of autochthonous origin slow dissolution and reprecipitation maintain their constant position with respect to the sediment surface and prevent burial as long as the sedimentation regime remains constant buried fe mn sedimentary layers widespread in lake baikal may therefore serve as general indicators for low sedimentation rates and as specific proxies for sudden changes in the sediment regime d 2004 elsevier b v all rights reserved

depositional and tectonic framework of the rift basins of lake baikal from multichannel seismic data recent multichannel seismic reflection data from lake baikal located in a large active continental rift in central asia image three major stratigraphic units totaling 3 5 to 7 5 km thick in four subbasins a major change in rift deposition and faulting between the oldest and middle rift units probably corresponds to the change from slow to fast rifting in early pliocene time inferred from on land studies a minor modification of fault patterns characterizes the youngest unit a brief comparison of the basins of lake baikal with those of the east african rift system highlights differences in structural style that can be explained by differences in age and evolution of the surrounding basement rocks

an idealized model of the world ocean part i the global scale water masses abstract a primitive equation three dimensional numerical model of the ocean employing idealized versions of the real topography and surface boundary conditions is used to study the water mass structure of the world ocean in particular the response of the model to three fundamental changes in boundary conditions is investigated in an attempt to identify the mechanisms in the model which are responsible for the establishment of the largest scale features of the global water mass structure with the drake passage closed thermohaline driving alone and a fresh north atlantic surface salinity specified only the coarsest aspects of the observed t and s structure are reproduced and the entire world ocean below the thermocline is dominated by water formed at the southern boundary the salinity configuration in particular lacks much of its observed structure in this case when the drake passage is opened the resulting circumpolar flow serves to isolate the extreme southern ocean this allows waters of no

unusual phosphate concretions related to groundwater flow in a continental environment abstract occurrence of phosphate cemented sandstone concretions in alluvial sand containing archaeological layers implies that they have formed during the last 2000 years morphology and petrography of the concretions indicates a relationship with groundwater cementation the phosphate cement of the concretions consists of concentric isopachous aureoles about 10 m thick that wrap the detrital grains aureoles are formed of collophane the cryptocrystalline or amorphous variety of hydroxyapatite geochemical modeling indicates that the apatite cement likely results from the leaching of a preexisting phosphate deposit bones in an acidic soil environment and the precipitation of dissolved phosphate under ph control at the mixing zone of down moving soil water with the calcite saturated groundwater

a rock magnetic record from lake baikal siberia evidence for late quaternary climate change rock magnetic measurements of sediment cores from the academician ridge region of lake baikal siberia show variations related to late quaternary climate change based upon the well dated last glacial interglacial transition variations in magnetic concentration and mineralogy are related to glacial interglacial cycles using a conceptual model interglacial intervals are characterized by low magnetic concentrations and a composition that is dominated by low coercivity minerals glacial intervals are characterized by high magnetic concentrations and increased amounts of high coercivity minerals the variation in magnetic concentration is consistent with dilution by diatom opal during the more productive interglacial periods we also infer an increased contribution of eolian sediment during the colder windier and more arid glacial conditions when extensive loess deposits were formed throughout europe and asia eolian transport is inferred to deliver increased amounts of high coercivity minerals as staining on eolian grains during the glacial intervals variations in magnetic concentration and mineralogy of lake baikal sediment correlate to the specmap marine oxygen isotope record the high degree of correlation between baikal magnetic concentration mineralogy and the specmap oxygen isotope record indicates that lake baikal sediment preserves a history of climate change in central asia for the last 250 ka this correlation provides a method of estimating the age of sediment beyond the range of the radiocarbon method future work must include providing better age control and additional climate proxy data thereby strengthening the correlation of continental and marine climate records

a new age model for the sediment cores from academician ridge lake baikal based on high time resolution ams 14c data sets over the last 30 kyr paleoclimatic and environmental implications abstract we constructed a new age model based on high time resolution 14 c data sets from three sediment cores from academician ridge lake baikal for reconstruction of environmental and biological changes in southern siberia during the last ca 30 kyr we used 14 c ages of total organic carbon toc for the model because terrestrial plant residues and biogenic carbonate were not observed in the sediments for accurate dating and age models based on 14 c ages of toc the freshwater 14 c reservoir effect and the effect of dead carbon from land derived organic materials must be estimated in this study we estimated the correction factor for these effects to be 2100 90 yr on the basis of a key layer the 14 c plateau caused by changes in the atmospheric 14 c concentration during the younger dryas yd cooling event the new age scale along with the toc mass accumulation rate mar toc and stable carbon isotope ratio in the sediment cores clearly indicate a rapid decrease in lake productivity and reduced influx of terrestrial organic materials into the lake during the yd 12 8 11 6 cal ka bp productivity was high mar toc up to 19 7 mg cm 2 kyr in and around lake baikal during 9 3 6 4 cal ka bp holocene climate optimum moreover paleoproductivity changes during the last ca 30 kyr in and around the lake baikal were clearly associated with fluctuations in the east asian monsoon intensity as inferred from the 18 o record from sanbao and hulu caves china during the late quaternary wang et al 2008 nature 451 1090 1093

authigenesis of vivianite as influenced by methane induced sulfidization in cold seep sediments off southwestern taiwan abstract authigenesis of iron rich phosphate nodules occurs in iron rich cold seep sediments md052911 core at yung an ridge offshore southwestern taiwan raman ftir and quantitative x ray energy dispersive spectroscopic analyses indicate that the phosphate mineral is vivianite or baricite and shows fe mg molar ratios spanning from ca 0 6 to 4 0 and a general down core trend of increasing fe mg ratios the formation of vivianite is limited to a depth interval of 13 17 mbsf meters below seafloor and is most prominent at 16 mbsf in association with high dissolved iron concentrations and depleted dissolved sulfide below a peak sulfidization zone enriched in mackinawite and greigite alternate growths of vivianite and iron monosulfides and compositional zoning with mg enriched towards the peripheries of individual nodules occur in the transition from the zone of vivianite mineralization to the sulfidization zone the crystallization of vivianite below the sulfidization front could have been favored by scavenging of downward diffusive dissolved sulfide from pore waters in the sulfidization zone alternate growths and overlapping of the zones of iron monosulfides and vivianite can be attributed to fluctuations of the sulfidization front and methane flux the discovery of vivianite in the yung an ridge sediments implies that authigenic vivianite can be an important sink for phosphorus burial in cold seep sediments that have high reactive iron contents and high sedimentation rates

evolution of atlantic thermohaline circulation early oligocene onset of deep water production in the north atlantic the flow of deep water masses is a key component of heat transport in the modern climate system yet the role of deep ocean heat transport during periods of extreme warmth is poorly understood the present mode of meridional overturning circulation is characterized by deep water formation in both the north atlantic and the southern ocean however a different mode of meridional overturning circulation operated during the extreme greenhouse warmth of the early cenozoic during which time the southern ocean was the dominant region of deep water formation the combination of general global cooling and tectonic evolution of the atlantic basins over the past 55 m y ultimately led to the development of a mode of overturning circulation characterized by both southern ocean and north atlantic deep water sources the change in deep water circulation mode may in turn have affected global climate however unraveling the causes and consequences of this transition requires a better understanding of the timing of the transition new nd isotope data from the southeastern atlantic ocean indicate that the initial transition to a bipolar mode of deep water circulation occurred in the early oligocene ca 33 ma the likely cause of significant deep water production in the north atlantic was tectonic deepening of the sill separating the greenland norwegian sea from the north atlantic

chronology causes and progression of the messinian salinity crisis the messinian salinity crisis is widely regarded as one of the most dramatic episodes of oceanic change of the past 20 or so million years 1 3 earliest explanations were that extremely thick evaporites were deposited in a deep and desiccated mediterranean basin that had been repeatedly isolated from the atlantic ocean1 2 but elucidation of the causes of the isolation whether driven largely by glacio eustatic or tectonic processes have been hampered by the absence of an accurate time frame here we present an astronomically calibrated chronology for the mediterranean messinian age based on an integrated high resolution stratigraphy and tuning of sedimentary cycle patterns to variations in the earth s orbital parameters we show that the onset of the messinian salinity crisis is synchronous over the entire mediterranean basin dated at 5 96 0 02 million years ago isolation from the atlantic ocean was established between 5 59 and 5 33 million years ago causing a large fall in mediterranean water level followed by erosion 5 59 5 50 million years ago and deposition 5 50 5 33 million years ago of non marine sediments in a large lago mare lake sea basin cyclic evaporite deposition is almost entirely related to circum mediterranean climate changes driven by changes in the earth s precession and not to obliquity induced glacio eustatic sea level changes we argue in favour of a dominantly tectonic origin for the messinian salinity crisis although its exact timing may well have been controlled by the 400 kyr component of the earth s eccentricity cycle

liquid freshwater transport and polar surface water characteristics in the east greenland current during the ao 02 oden expedition dynamical features of the east greenland current egc are synthesized from a survey conducted by the swedish icebreaker oden during the international arctic ocean 02 expedition ao 02 in may 2002 with emphasis on the liquid freshwater transport and polar surface water the data include hydrography and lowered acoustic doppler current profiler ladcp velocities in eight transects along the egc from the fram strait in the north to the denmark strait in the south the survey reveals a strong confinement of the low salinity polar water in the egc to the continental slope shelf a feature of relevance for the stability of the thermohaline circulation in the arctic mediterranean the southward transport of liquid freshwater in the egc was found to vary considerably between the sections ranging between 0 01 and 0 1 sverdrup computations based on geostrophic as well as ladcp velocities give a section averaged southward freshwater transport of 0 06 sverdrup in the egc during may 2002 furthermore oden data suggest that the liquid freshwater transport was as large north of the fram strait as it was south of the denmark strait

the age of water and ventilation timescales in a global ocean model abstract the age of water in the world ocean is studied using a passive age tracer introduced into a global ocean model additional information is derived from a transient dye tracer that tracks the time dependent spreading of surface waters into the model ocean interior of particular interest is the nature of ocean ventilation over the 10 100 yr timescale as well as the simulated age of deep and bottom water masses in the upper model levels young water is found to correspond with regions of convergence and downwelling in the surface ekman layer upwelling and convection are both shown to age the upper ocean by entraining older waters into the surface mixed layer in the deep model levels water age varies greatly between oceans with young water found in convectively active regions in the north atlantic and in the ross and weddell seas and old water found in the deep north pacific the oldest water mass mixture located at 2228 m depth in the western pacific ocean is dated at 1494 years made

catastrophic flood of the mediterranean after the messinian salinity crisis around 5 6 million years ago the mediterranean sea became disconnected from the world s oceans and during the period that followed known as the messinian salinity crisis sea levels fell dramatically as the waters evaporated the water returned about 5 3 million years ago but the details about this the largest known flood in earth s history remain sketchy a study making use of boreholes seismic data and numerical modelling suggests that it was a catastrophic event though it started as a trickle that may have lasted several thousand years as much as 90 of the incoming water was transferred in less than two years such an abrupt flood may have involved peak rates of sea level rise of more than 10 metres a day 5 33 million years ago in an event known as the zanclean flood atlantic waters refilled a mostly desiccated mediterranean sea which had become disconnected from the world s oceans however the nature abruptness and evolution of this flood remain poorly constrained using borehole and seismic data and a model study it is now suggested that 90 per cent of the water was transferred in a short period of a few months to two years with peak rates of sea level rise in the mediterranean possibly reaching more than 10 metres per day the mediterranean sea became disconnected from the world s oceans and mostly desiccated by evaporation about 5 6 million years ago during the messinian salinity crisis1 2 3 the atlantic waters found a way through the present gibraltar strait and rapidly refilled the mediterranean 5 33 million years ago in an event known as the zanclean flood4 the nature abruptness and evolution of this flood remain poorly constrained4 5 6 borehole and seismic data show incisions over 250 m deep on both sides of the gibraltar strait that have previously been attributed to fluvial erosion during the desiccation4 7 here we show the continuity of this 200 km long channel across the strait and explain its morphology as the result of erosion by the flooding waters adopting an incision model validated in mountain rivers this model in turn allows us to estimate the duration of the flood although the available data are limited our findings suggest that the feedback between water flow and incision in the early stages of flooding imply discharges of about 108 m3 s 1 three orders of magnitude larger than the present amazon river and incision rates above 0 4 m per day although the flood started at low water discharges that may have lasted for up to several thousand years our results suggest that 90 per cent of the water was transferred in a short period ranging from a few months to two years this extremely abrupt flood may have involved peak rates of sea level rise in the mediterranean of more than ten metres per day

boundary currents and watermass transformation in marginal seas the properties of watermass transformation and the thermohaline circulation in marginal seas with topography and subject to a spatially uniform net surface cooling are discussed the net heat loss within the marginal sea is ultimately balanced by lateral advection from the open ocean in a narrow boundary current that flows cyclonically around the basin heat loss in the interior is offset by lateral eddy fluxes originating in the boundary current the objectives of this study are to understand better what controls the density of waters formed within the marginal sea the temperature of the outflowing waters the amount of downwelling and the mechanisms of heat transport within the marginal sea the approach combines heat budgets with linear stability theory for a baroclinic flow over a sloping bottom to provide simple theoretical estimates of each of these quantities in terms of the basic parameters of the system the theory compares well to a series of eddy resolving primitive equation model calculations the downwelling is concentrated within the boundary current in both a diffusive boundary layer near topography and an eddy driven region on the offshore edge of the boundary current for most high latitude regions the horizontal gyre is expected to transport more heat than does the overturning gyre

the structure and development of the baikal rift depression abstract the baikal rift depression located in southeastern siberia is one of the best investigated intra continental rift structures in the world in addition to being the site of comprehensive studies by russian geo scientists for decades the baikal depression is now the subject of new international investigations using advanced technical means and technologies the present paper summarizes the principal results concerning the morphostructure of the baikal rift the stratigraphy of the cenozoic deposits and the stages of the baikal depression development based on cross sections which exhibit the impact of both tectonic and climatic processes the development of the baikal depression occurred through two stages i the pre crypto rift stage of the late cretaceous eocene and ii active rifting of the oligocene recent the second stage is divided into several steps and substeps separated by tectonic phases formation of the baikal rift zone appears to be related to the indo eurasian plate collision related to a model of passive rifting the uplifted shoulders of the depression have a complex morphostructure overlain by cenozoic deposits which are thin and restricted in area the near marginal zones of the rift are largely defined by the system of longitudinal blocks of different width surfaces of the blocks are inclined either to the uplifted shoulder of the rift bound by listric faults typical for western edges of the depression or to the axis of the depression cenozoic deposits on the blocks consist of accumulative plains composed primarily of thick lacustrine sequences

the zinc stable isotope signature of waste rock drainage in the canadian permafrost region leachate from a well instrumented experimental scale waste rock pile test pile at the diavik diamond mine northwest territories was monitored the well characterized waste rock consists of granite pegmatitic granite and biotite schist with an average total sulfur and carbonate carbon concentration of 0 053 and 0 027 wt respectively the leachate emerging from the southern basal drain of the waste rock pile has been monitored since 2007 the zinc stable isotope footprint was characterized alongside standard monitoring parameters during two field seasons may to november 2011 and 2012 the ph ranged between 4 3 and 6 8 and carbonate alkalinity was low or undetectable 35 mg l 1 caco3 the ph was governed by the oxidation of sulfide minerals and the dissolution of primary carbonate minerals and secondary al and fe oxyhydroxysulfates and hydroxides dissolved al and fe concentrations averaged 6 78 mg l 1 and 175 g l 1 respectively the main processes controlling zn concentrations in the range of 0 4 and 4 7 mg l 1 average 2 2 mg l 1 were the oxidative dissolution of sphalerite zns and the attenuation by secondary fe and al hydroxides zinc isotopes were fractionated mass dependently zinc isotope ratios ranging between 0 16 and 0 18 average 0 05 n 43 were consistent with values reported for sphalerite from other deposits the deviations in isotope ratios 0 36 were significant in comparison to analytical uncertainties 0 06 zinc isotope ratios and concentrations were largely uncorrelated suggesting that the processes affecting zn mobility had little or no impact on the zn isotope signature these data suggest that the zn isotope ratios of the waste rock leachate may be used as a fingerprint to track anthropogenic mine derived zn sources in an environment under fluctuating ph temperature and ionic strength

high time resolution ams 14c data sets for lake baikal and lake hovsgol sediment cores changes in radiocarbon age and sedimentation rates during the transition from the last glacial to the holocene abstract high time resolution 14 c dating of lake baikal sediment cores indicates negative and positive anomalies of calculated linear sedimentation rate lsr 1 1 and 35 6 cm ka respectively during the period of climate transition from the last glacial to holocene the timing of the lake baikal apparent lsr anomalies is consistent with that of the changes in the atmospheric radiocarbon concentration 14 c during younger dryas rapid cooling event 14 c dating of lipids in the lake baikal surface sediments revealed that the sources of sedimentary lipids were different in each basin in the northern basin of lake baikal the 14 c age of total lipids from the surface sediment 4 0 14 c ka was found to be older than that of toc 1 6 14 c ka by contrast the 14 c age of total lipids in the southern basin was younger than that of the toc by ca 0 7 3 0 ka in the lake hovsgol sediment cores ages of the main lithologic boundaries during the last glacial interglacial transition were estimated based on new 14 c data sets toc concentration in the cores started to rapidly increase at 13 8 0 3 14 c ka at the base of the basinwide finely laminated layer deposited during bolling allerod the base of the layer diatomaceous mud corresponds to the end of younger dryas event 10 6 0 1 14 c ka

seismic deformation of varved sediments in southern fennoscandia at 7400 cal bp abstract soft sediment deformation structures are preserved in clastic biogenic varves of the lake nurmijarvi sequence from central southern finland deformation structures include centimeter scale folding and faulting structures and larger convolute bedding which are separated from the overlying undisturbed varved section by a turbidite dated at 7400 cal bp the soft sediment deformation provides evidence for postglacial seismic activity ca 3500 years after the deglaciation of the study area by screening the sizes of potential source faults for the event the maximum earthquake moment magnitudes associated with the deformation structures were constrained to mw 5 1 6 9 with realistic 40 rupture scenarios or up to mw 5 1 7 7 if more conservative scenarios are considered the results of the study thus indicate a relatively high magnitude postglacial seismic event in southern finland which adds to the evidence that the postglacial seismic activity was not just restricted to northern fennoscandia but was a more widespread phenomenon the age of the lake nurmijarvi seismic event further demonstrates that high magnitude seismic activity was not restricted to a relatively short period after deglaciation but the period of high magnitude postglacial seismic activity was much longer than previously thought by assessing the orientations of faults that are presently active and using available focal mechanism data our results suggest that strike slip faulting may be a more important mechanism for the generation of both present day and postglacial earthquakes in southern finland than reverse faulting which should further be accounted for in the assessment of long term seismic hazards

the deacon cell and the other meridional cells of the southern ocean abstract the meridional circulation cells of the southern ocean are investigated using the results from a fine resolution primitive equation model zonal integration along depth levels shows the classical series of meridional cells but integration along density layers shows a number of differences including the virtual disappearance of the deacon cell to investigate the differences the meridional transport is calculated as a function of both density and depth the results show that the deacon cell is associated with systematic changes in the depth of density surfaces between the western boundary current region off south america and the return flow in the interior of the ocean water flowing on each density surface produces a meridional cell with a vertical excursion of a few hundred meters thew cells combine without water crossing density surfaces to produce a single integrated deacon cell extending from the surface to below 2000 m the results also show that at each latitude water on each of the

the early miocene onset of a ventilated circulation regime in the arctic ocean deep water formation in the northern north atlantic ocean and the arctic ocean is a key driver of the global thermohaline circulation and hence also of global climate1 deciphering the history of the circulation regime in the arctic ocean has long been prevented by the lack of data from cores of cenozoic sediments from the arctic s deep sea floor similarly the timing of the opening of a connection between the northern north atlantic and the arctic ocean permitting deep water exchange has been poorly constrained this situation changed when the first drill cores were recovered from the central arctic ocean2 here we use these cores to show that the transition from poorly oxygenated to fully oxygenated ventilated conditions in the arctic ocean occurred during the later part of early miocene times we attribute this pronounced change in ventilation regime to the opening of the fram strait a palaeo geographic and palaeo bathymetric reconstruction of the arctic ocean together with a physical oceanographic analysis of the evolving strait and sill conditions in the fram strait suggests that the arctic ocean went from an oxygen poor lake stage to a transitional estuarine sea phase with variable ventilation and finally to the fully ventilated ocean phase 17 5 myr ago the timing of this palaeo oceanographic change coincides with the onset of the middle miocene climatic optimum3 although it remains unclear if there is a causal relationship between these two events

palynology paleoclimatology and correlation of middle miocene beds from porcupine river locality 90 1 alaska abstract beds in the upper ramparts canyon of the porcupine river alaska 67 20 n 141 20 w yielded a flora rich in pollen of hardwood genera now found in the temperate climates of north america and asia the beds are overlain or enclosed by two basalt flows which were dated to 15 2 0 1 ma by the 40 ar 39 ar method fixing the period of the greatest abundance of warm loving genera to the early part of the middle miocene the assemblage is the most northern middle miocene flora known in alaska organic bed 1 underlies the basalt and is older than 15 2 ma but is of early to middle miocene age the pollen assemblage from organic bed 1 is dominated by conifer pollen from the pine and redwood cypress yew families with rare occurrences of temperate hardwoods organic bed 2 is a forest floor containing redwood trees in life position engulfed by the lowest basalt flow a pine log has growth rings up to 1 cm thick organic beds 3 and 4 comprise lacustrine sediment and peat between the two basalt flows their palynoflora contain conifers and hardwood genera of which about 40 have modern temperate climatic affinities hickory katsura walnut sweet gum wingnut basswood and elm pollen are consistently present and beech and oak alone make up about 20 of the pollen assemblage a warm high latitude climate is indicated for all of the organic beds but organic bed 3 was deposited under a time of peak warmth climate data derived by comparison with modern east asian vegetation suggest that at the time of deposition of organic bed 3 the mean annual temperature mat was ca 9 c the warm month mean temperature wmmt was 20 c and the cold month mean temperature cmmt was ca 2 c in contrast the modern mat for the region is 8 6 c wmmt is 12 6 c and cmmt is 28 c organic beds 3 and 4 correlate to rocks of the middle miocene late seldovian stage of cook inlet and also probably correlate to and more precisely date the lower third of the suntrana formation in the alaska range beds at unalaklect part of the upper mackenzie bay sequence in the beaufort mackenzie basin and the mary sachs gravel of banks island this suggests that forests with significant percentages of temperate deciduous angiosperms existed between latitudes 60 and 72 n during the early middle miocene

authigenic apatite formation and burial in sediments from non upwelling continental margin environments abstract evidence for precipitation of authigenic carbonate fluorapatite cfa in long island sound and mississippi delta sediments suggests that formation of cfa is not restricted to environments of active coastal upwelling we present porewater data suggestive of cfa formation in both these areas application of a sequential leaching procedure designed specifically to separate authigenic carbonate fluorapatite from other phosphorus containing phases including detrital apatite of igneous or metamorphic origin provides strong supporting evidence for authigenic apatite formation in these sediments the size of the authigenic apatite reservoir increases with depth indicating continued formation of cfa during early diagenesis this depth increase is mirrored by a decrease in solid phase organic p at both sites suggesting that cfa is forming at the expense of organic p mass balance considerations application of diagenetic models to interstitial water nutrient data and the saturation state of the interstitial water are consistent with this interpretation diagenetic redistribution of phosphorus among the different solid phase reservoirs is observed at both sites and results in near perfect retention of p by these sediments over the depth intervals sampled formation of cfa in continental margins which do not conform to the classically defined regions of phosphorite formation renders cfa a quantitatively more important sink than has previously been recognized including this reservoir as a newly identified sink for reactive p in the ocean the residence time of p in the modern ocean must be revised downward the implication for ancient oceans of cfa formation in continental margin sediments other than phosphorites is that phosphorite formation may be less a representation of episodicity in removal of reactive p from the oceans than of localized concentration of cfa in phosphatic sediments by secondary physical processes

bound forms compositional features major sources and diagenesis of long chain alkyl mid chain diols in lake baikal sediments over the past 28 000 years abstract to elucidate the possibility of long chain alkyl mid chain diols hereafter mid chain diols in lake baikal sediments over the past 28 ka being paleoproxies we studied their i bound forms and compositional features ii major sources and iii diagenesis during sedimentation of the seven bound forms investigated i e free form free type three base hydrolysable types base 1 base 2 and base 3 and acid hydrolysable type acid 1 type in solvent extractable lipids and base hydrolysable nb and acid hydrolysable na types in non solvent extractable nonex lipids only three viz free nb and base 3 types were found the relative compositions of the three types were 70 100 0 30 and 0 8 respectively the most abundant component of the free type diols was the c 32 1 15 diol whereas that of the base 3 and nb types was the c 30 1 13 diol the average chain length ratio of total amount of even chain lengths to that of odd chain lengths the relative composition of positional isomers for each carbon number and the diol index obtained using the equation c 30 1 15 diol c 30 1 15 diol c 32 1 15 diol 100 hardly responded to reported major paleoenvironmental changes around the lake baikal region over the last 28 ka comparison of mid chain diol compositions and their bound forms with those in possible sources suggested that the major biological source of all mid chain diols in the sediments might be the eustigmatophyceae class of algae in the alga the occurrence of mid chain diols in the five bound forms free base 3 acid 1 nb and na types was suggested while the acid 1 and na types were not found in the sediments under the oxic depositional conditions of lake baikal most of the acid 1 and na type diols and part of the base 3 and nb type diols might be degraded and or released free type diols in the anoxic sediments of the lake the base 3 and nb diols seem to be resistant to diagenesis all investigated parameters for the free base 3 and nb diols in the sediments did not provide any information on paleoenvironments around the lake on the other hand among the fluxes of the three diol types the base 3 type diol flux seems to have responded to the climatic events around the lake especially over the last 15 ka hence this flux might be a potential paleoproxy for the productivity of the biological source s and associated environmental factors

ventilation of the miocene arctic ocean an idealized model study a model study of an idealized early miocene arctic ocean has been undertaken the work is motivated by the first drill core retrieved from the lomonosov ridge in the central arctic ocean which sug

lagrangian decomposition of the deacon cell the meridional overturning cells in the southern ocean are decomposed by lagrangian tracing using velocity and density fields simulated with an ocean general circulation model particular emphasis is given to the deacon cell the flow is divided into four major components 1 water circling around antarctica in the antarctic circumpolar current acc 2 water leaving the acc toward the north into the three world oceans 3 water coming from the north and joining the acc mainly consisting of north atlantic deep water nadw and 4 interocean exchange between the three world oceans without circling around antarctica the deacon cell has an amplitude of 20 sv of which 6 sv can be explained by the the east west tilt of the acc 5 sv by the east west tilt of the subtropical gyre and the remaining 9 sv by the differences of the slope and depth of the southward transport of nadw and its return flow as less dense water the diabatic or cross isopycnal deacon cell is only 2 sv

isopycnal mixing in ocean circulation models abstract a subgrid scale form for mesoscale eddy mixing on isopycnal surfaces is proposed for use in non eddy resolving ocean circulation models the mixing is applied in isopycnal coordinates to isopycnal layer thickness or inverse density gradient as well as to passive scalars temperature and salinity the transformation of these mixing forms to physical coordinates is also presented

formation of ferric iron crusts in quaternary sediments of lake baikal russia and implications for paleoclimate phosphate bearing ferric iron and siliceous crusts ranging in age from recent to approximately 65 000 yr b p are observed in sediments of lake baikal in younger sediments the crusts are at the base of a spectrum of secondary iron and manganese oxides that accumulate near the sediment water interface in the zone of positive oxidation potential beneath an oxygenated water column in areas where the average quaternary sedimentation rates have been slow e g 0 026 mm yr the crusts are more common and span a wider range of ages no crusts have been found where the quaternary sedimentation mode has been deltaic and rapid 0 15 mm yr independent core correlation based on magnetic properties of the sediment suggests that crusts can be correlated over most of academician ridge an area that is particularly sensitive to climatic events affecting the concentration of suspended sediment these crusts may be indicative of periods of low suspended sediment concentration which occur during sustained transitions from glacial periods of high detrital input to interglacial periods of high diatom sedimentation the crusts are dominated by iron rich and siliceous amorphous mineral phases with an feo sio2by weight of 3 1 regardless of age or location in the lake the fe phase always includes ca p and mn extensive microprobe data for these four elements recast as normalized elemental weight percent reveal linear trends of ca p and fe p with increasing p ca also increases such that the two elements maintain a linear relationship passing very close to the origin and with a mean molar ca p 0 3 too low for well characterized apatite conversely with increasing p fe decreases mean molar fe p 3 4 there is no correlation between mn and p molar fe p ratios for vivianite an fe ii phosphate mineral observed in sediments closely below some crusts are clustered around a stoichiometric composition the covariant increase in ca p and the corresponding decrease in fe p may be explained by 1 coupled adsorption of aqueous ca and p by a colloidal ferric hydrous oxide 2 loss of fe from a ca p fe phase or 3 oxidation of vivianite to a metastable mineral phase that gradually loses ca and gains fe the first explanation is favored because there is no petrographic evidence for either the existence of an originating ca p fe phase or for the oxidation of vivianite further it is suggested that by continually equalizing surface charge ca allows more phosphate to be adsorbed leading to thicker crusts and longer preservation after burial

continental climate response to orbital forcing from biogenic silica records in lake baikal changes in insolation caused by periodic changes in the earth s orbital parameters provide the primary forcing for global ice ages1 6 but it is not clear to what extent the climates in continental interiors are controlled directly by regional variations in insolation and to what extent they are driven instead by the highly nonlinear response of the oceans and ice sheets here we investigate this question using the record of biogenic silica in lake baikal as a proxy for climate change in this high latitude mid continental region we find a good correlation between this record and that of marine oxygen isotopes4 over the past 250 kyr the baikal record exhibits both a strongly nonlinear component manifested in a 100 kyr periodicity and weaker direct insolation components manifested in the 41 kyr obliquity and 23 and 19 kyr precession orbital cycles these results show that even though extreme continental climates such as this are influenced directly by insolation variations they are dominated by the nonlinear rhythm of the oceans and ice sheets

choking the mediterranean to dehydration the messinian salinity crisis strait uplift due to isostasy played a pivotal role in the development and maintenance of a desiccated mediterranean basin during the late miocene messinian salinity crisis new three dimensional flexure models for the western mediterranean suggest that most of the giant evaporite body was deposited before sea level lowering any mechanism that subsequently caused a mediterranean sea level lowering by a few hundred meters during several thousand years sufficed to cause isostatic uplift and closure of the gateways thus choking the mediterranean to desiccation due to this isostatic feedback multiple desiccation and reflooding phases driven by milankovitch cycles are unlikely when the atlantic connection had been lost and sea level had dropped a sizeable regional uplift of the strait of gibraltar developed that presented a formidable obstacle to reflooding rollback and steepening of the gibraltar slab may have played a key role at the end of the miocene by dynamically lowering the sill region thus reinstating the oceanic connection

deep ventilation of lake baikal waters due to spring thermal bars increase of density due to mixing cabbeling instability in a spring thermal bar in lake baikal results in the sinking of cold surface water t 3 2 3 4 c w 0 3 cm s 1 below the profile of tmd this density increase generates forced convection and subsequent movement of cold water along the underwater slope to maximum depths cooling of deep and near bottom waters caused by forced convection is compensated during other seasons of the year by eddy heat flux directed toward the bottom on a long term basis vertical temperature profiles in deep waters remain constant

circulation and exchange in choked marginal seas a theory for the exchange between a rotating buoyancy forced marginal sea and an ocean is developed and tested numerically cooling over the marginal sea leads to sinking and sets up a two layer exchange flow with a warm surface layer entering from the ocean and a cool layer exiting at depth the connecting strait is sufficiently narrow and shallow to cause the exchange flow to be hydraulically controlled the incoming surface layer forms a baroclinically unstable boundary current that circles the marginal sea in a cyclonic sense and feeds heat to the interior by way of eddies consistent with the overall heat and volume balances for the marginal sea there is a continuous family of hydraulically controlled states with critical flow at the most constricted section of the strait included in this family is a limiting maximal exchange solution with two sections of hydraulic control in the strait and with fixed layer depths at the most constricted section the state of exchange for a given forcing is predicted using a theory that assumes energy conservation over a certain path connecting the strait to the marginal sea or in some cases the ocean depending on the configuration of the exchange long wave information may be blocked from entering the strait from the marginal sea from the open ocean or both the scenario that holds determines what is predicted and what needs to be input numerical tests of the prediction for the temperature difference and the state of exchange are carried out for straits with a pure contraction in width and for a constant width strait with a topographic sill the comparison is reasonable in most cases though the numerical model is not able to reproduce cases of multiple states predicted by the theory for certain forcing values the analytical model is an alternative to the price and yang and siddall et al models of a marginal sea outflow

new insights into the formation and burial of fe mn accumulations in lake baikal sediments abstract lake baikal is the deepest and oldest lake on earth extraordinary features of the lake are manganese and iron enriched layers and crusts occurring at different depths within the sediment they can be broadly subdivided into an upper accumulation at the o 2 mn ii redox boundary and one or more layers buried within the reducing part of the sediment the processes leading to their formation and peculiar distribution within the sediment have remained subject of debate in particular whether the burial of vast amounts of mn and fe oxides results from a steady state process or if it is the consequence of singular events such as changes in sedimentation rate bottom water oxygen concentrations or the mass accumulation rate mar of organic carbon c org mn or fe we retrieved short cores from the south basin the north basin and academician ridge determined sedimentation rates contents of c org mn and fe and estimated pore water fluxes from concentration profiles of o 2 no 3 mn ii fe ii so 4 2 and ch 4 a consistent picture emerged from the data showing that the upper fe mn layer formed at the lower end of the oxygen penetration depth as a dynamic pattern moving upward with the growing sediment thereby reductive dissolution of mn iv occurred at the lower margin upward diffusing mn ii was oxidized with o 2 forming the upper boundary of the fe mn accumulation the buried fe mn layers were immobilized within the sediment and underwent slow reductive dissolution mainly driven by the anaerobic oxidation of ch 4 the process leading to the detachment of the active fe mn layer from the top redox interface is not unambiguously clear however we suggest a cyclic pattern where the burial of a fe mn layer is accompanied by the generation of a new enrichment at the o 2 mn ii redox boundary which is subsequently nourished by the slowly dissolving old layer

the role of grain dissolution and diagenetic mineral precipitation in the cycling of metals and phosphorus a study of a contaminated urban freshwater sediment this paper describes the detrital mineralogy early diagenetic reactions and authigenic mineral precipitates for freshwater contaminated sediments deposited in an urban water body the salford quays of the manchester ship canal greater manchester uk these sediments contain a mix of natural and anthropogenic detrital grains detrital grains are dominated by quartz and clay grains whilst anthropogenic grains are dominated by metal rich glass grains concentrated at a depth of 12 17 cm in the sediment as a result of historical inputs sediment porewaters contain significant concentrations of fe mn zn and phosphate bacterial fe iii and mn iv reduction are hypothesised to supply fe2 and mn2 to porewaters with phosphate released from fe oxide reduction or organic matter oxidation petrographic observations indicate that the metal rich glass grains are undergoing chemical dissolution during early diagenesis supplying fe and zn to porewaters the most abundant authigenic mineral in the sediments is vivianite fe3 po4 2 8h2o containing a significant level of redlingite with minor framboidal pyrite fes2 electron microprobe analysis shows the vivianite to contain zn cu and pb suggesting that vivianite acts as a long term sink for these metals in this sediment this implies that authigenic vivianite in freshwater sediments may act as a long term sink for metals in a similar manner to sulphides in marine sediments this study highlights that the nature of detrital and diagenetic mineralogy in addition to porewater and sediment chemistry needs to be considered in assessing contaminated sediments

biogeochemical phosphorus mass balance for lake baikal southeastern siberia russia abstract extensive data for lake baikal have been synthesized into a geochemical mass balance for phosphorus p some of the p budget and internal cycling terms for baikal have been compared to similar terms for oligotrophic lake superior mesotrophic lake michigan and the baltic sea and the ocean lake baikal has a large external source of fluvial p compared to the laurentian upper great lakes and the ocean the major tributary to lake baikal has experienced substantial increases in organic p loading during the past 25 years this coupled with potential p inputs from possible phosphorite mining may threaten baikal s oligotrophic status in the future water column remineralization of particulate organic p is substantially greater in lake baikal than in the laurentian great lakes this is probably due to the great water depths of lake baikal there is a gradient in p burial efficiency with very high values 80 for lake baikal and lake superior lower values 50 for lake michigan and the baltic sea and a low value 13 for the ocean the accumulation rate of p in lake baikal sediments is somewhat greater than that in the laurentian upper great lakes and the baltic sea and much greater than in the ocean benthic regeneration rates are surprisingly similar for large lacustrine and marine environments and supply less than 10 of the p utilized for primary production in these aquatic environments

influence of brine formation on arctic ocean circulation over the past 15 million years the early oceanographic history of the arctic ocean is important in regulating and responding to climatic changes however constraints on its oceanographic history preceding the quaternary the past 1 8 myr have become available only recently because of the difficulties associated with obtaining continuous sediment records in such a hostile setting here we use the neodymium isotope compositions of two sediment cores recovered near the north pole to reconstruct over the past approx15 myr the sources contributing to arctic intermediate water a water mass found today at depths of 200 to 1 500 m we interpret high neodymium ratios for the period between 15 and 2 myr ago and for the glacial periods thereafter as indicative of weathering input from the siberian putoranan basalts into the arctic ocean arctic intermediate water was then derived from brine formation in the eurasian shelf regions with only a limited contribution of intermediate water from the north atlantic in contrast the modern circulation pattern with relatively high contributions of north atlantic intermediate water and negligible input from brine formation exhibits low neodymium isotope ratios and is typical for the interglacial periods of the past 2 myr we suggest that changes in climatic conditions and the tectonic setting were responsible for switches between these two modes

the role of eddy transfer in setting the stratification and transport of a circumpolar current abstract high resolution numerical experiments of a circumpolar current are diagnosed to study how lateral and vertical transfer of buoyancy by geostrophic eddies balances advection by a meridional circulation driven by surface wind stresses and buoyancy fluxes a theory is developed in the framework of the residual circulation to relate the vertical and horizontal stratification set up to the transfer properties of eddies and the patterns of imposed wind and buoyancy forcing simple expressions are found for the depth of penetration stratification baroclinic transport and residual circulation of the current finally the ideas are applied to the antarctic circumpolar current acc and yield predictions for how its properties depend on wind and buoyancy forcing