sea ice motion in response to geostrophic winds it is an old rule of thumb that sea ice moves with a speed of about 2 of the surface wind and about 45 to the right of the wind a similar relationship between the ice velocity and the geostrophic wind is examined here it is found that only about half of the long term several month average ice motion is directly related to the geostrophic wind the other half being due to the mean ocean circulation on shorter time scales and in all seasons more than 70 of the variance of the ice velocity in the central arctic ocean is explained by the geostrophic wind within about 400 km of the coasts the geostrophic wind is less successful in explaining the ice motion the spatial variations in ice velocity are also partly explained by the geostrophic wind about half of the variance in the large scale ice vorticity and shear are accounted for on the other hand none of the large scale ice divergence can be explained by the wind the long term average ocean current is estimated by subtracting the share of the ice motion caused by the wind from the total ice motion

observations of a deep mixing event in crater lake oregon we present observations of the evolution of a deep mixing event in a deep temperate lake the observations were obtained from thermistors mounted on a long term mooring in the lake the event seems to have originated near 150 m depth and resulted in a plume or layer of cold water from the upper half of the lake that descended to the lake bottom 590 m over a 3 d period net mixing associated with this event resulted in an overall vertical heat exchange of nearly loi j and a volume exchange of 0 7 3 2 km 4 18 of the lake volume between the upper and lower portions of the lake the deep water displaced during the event is estimated to have carried 0 32 5 x lo6 mol of nitrate to the upper lake which accounts for a significant portion of the average annual nitrate flux 2 4 x 10 mol yr thought to be upwelled in this highly oligotrophic system

hydrothermal germanium over the southern east pacific rise germanium enrichment in the oceanic water column above the southern axis of the east pacific rise results from hydrothermal solutions emanating from hot springs along the rise crest this plume signature provides a new oceanic tracer of reactions between seawater and sea floor basalts during hydrothermal alteration in contrast to the sharp plumes of 3he and manganese the germanium plume is broad and diffuse suggesting the existence of pervasive venting of low temperature solutions off the ridge axis

modeling deep convection in the greenland sea the development of deep convective events in the high latitude ocean is studied using a three dimensional coupled ice ocean model oceanic mixing is described according to the level 2 5 turbulence closure scheme in which convection occurs in a continuous way i e convective adjustment is not invoked the model is forced by strong winds and surface cooling strong upwelling at the multiyear ice edge and consequent entrainment of warm atlantic waters into the mixed layer is produced by winds parallel to the ice edge concomitant cooling drives deep convection and produces chimneylike structures inclusion of a barotropic mean flow over topography to the model provides important preconditioning and selects the location of deep convection the most efficient preconditioning occurs at locations where the flow ascends a slope in a stratified environment similar to the greenland sea with a 12 m s 1 wind the model simulations show that localized deep convection takes place after about 10 days to depths of 1000 m

lithium in waters of a polar desert abstract lithium li concentrations were measured in a series of stream and lake samples from a cold dry desert the mcmurdo dry valleys mdv in southern victoria land antarctica li geochemistry has been of great interest and utility in part because of its solubility and mobility during rockwater interactions in general the values determined for the streams and the dilute lake waters in this polar desert environment are similar to those found in temperate streams and lakes the source of li to these waters is a combination of marine aerosol and crustal weathering within the stream channels the hypersaline hypolimnion of lake bonney has extremely high concentrations of li which has been concentrated via a previous drawdown of the lake and its subsequent evapoconcentration the different distributions of li within the lakes is also due to past climatic changes and their effects on the chemical evolution of the lakes the high relative mobility of li controls its distribution within the aquatic systems of this cold desert environment

variation of antarctic sea ice an update abstract analysis of antarctic sea ice area for the period 1973 to the 30th week of 1982 showed that after a decrease from 1973 to 1980 the total sea ice area had increased sea ice area in the atlantic sector decreased from 1973 to 1977 but increased afterward sea ice area in the pacific and indian ocean sectors decreased from 1973 to 1980 by 1980 sea ice area anomalies in these ocean sectors have rebounded and increased to above average values by the end of 1981

biological and environmental changes in lake baikal during the late quaternary inferred from carbon nitrogen and sulfur isotopes abstract an 8 m continuous sediment core approximately 250 ky old at the bottom from academician ridge in lake baikal has been analyzed for the stable isotopes of carbon nitrogen and sulfur in order to study the paleoclimatic and paleobiological changes that occurred in the eurasian continental interior these isotopic changes are closely related to changes in vertical lake water circulation between glacial and interglacial periods sedimentary organic carbon in cool periods is more enriched in 13 c 23 8 on average than that in warm periods 27 0 on average the 13 c enrichment of organic carbon suggests a decrease of land derived organic matter influx to the lake less precipitation and loss of terrestrial vegetation around lake baikal in cool periods pyrite in high total sulfur total organic carbon ts toc layers shows strong depletion in 34 s 20 8 to 32 4 during climate transitions from glacial to interglacial periods at the beginning of oxygen isotope stages ois 1 5 and 7 the 34 s depleted pyrite indicates augmentation of dissimilatory sulfate reduction by sulfate reducing bacteria srb at the sediment water interface enhancement of aqueous sulfate concentrations and limitation of oxygen circulation to the surface sediments might also occur in the climate transition periods the 15 n values of total nitrogen increase abruptly by 2 just after the 34 s negative peaks which may result from low nutrient concentrations in the euphotic zone associated with water circulation changes in lake baikal

absence of a regional surface thermal high in the baikal rift new insights from detailed contouring of heat flow anomalies heat flow in active tectonic zones as the baikal rift is a crucial parameter for evaluating deep anomalous structures and lithosphere evolution based on the interpretation of the existing datasets the baikal rift has been characterized in the past by either high heat flow or moderately elevated heat flow or even lacking a surface heat flow anomaly we made an attempt to better constrain the geothermal picture by a detailed offshore contouring survey of known anomalies and to estimate the importance of observed heat flow anomalies within the regional surface heat output a total of about 200 new and close spaced heat flow measurements were obtained in several selected study areas in the north baikal basin with an outrigged and a violin bow designed thermoprobe of 2 3 m length both the sediment temperature and thermal conductivity were measured the new data show at all investigated sites that the large heat flow highs are limited to local heat flow anomalies the maximum measured heat flow reaches values of 300 35000 mw m2 but the extent of the anomalies is not larger than 2 to 4 km in diameter aside of these local anomalies heat flow variations are restricted to near background values of 50 70 mw m2 except in the uplifted academician zone the extent of the local anomalies excludes a conductive source and therefore heat transport by fluids must be considered in a conceptual model where all bottom floor heat flow anomalies are the result of upflowing fluids along a conduit an extra heat output of 20 mw including advection is estimated for all known anomalies in the north baikal basin relative to a basal heat flow of 55 65 mw m2 these estimations suggest an extra heat output in the northern lake baikal of only 5 corresponding to a regional heat flow increase of 3 mw m2 the source of this heat can be fully attributed to a regional heat redistribution by topographically driven ground water flow thus the surface heat flow is not expected to bear a signal of deeper lithospheric thermal anomalies that can be separated from heat flow typical for orogenically altered crust 40 70 mw m2 the new insights on the geothermal signature in the baikal rift once more show that continental rifting is not by default characterized by high heat flow

a heton model of the spreading phase of open ocean deep convection abstract a point vortex heton model of the lateral dispersion of cold water formed in open ocean deep convection is developed and studied as an idealized representation of the sinking and spreading phase of open ocean deep convection the overturning and geostrophic adjustment of dense fluid on and below the radius of deformation scale formed by cooling on the large scale are parameterized in the model by introducing paired discrete point vortices hetons of cyclonic sense in the surface layer anticyclonic below driving a cold baroclinic vortex the convection site is imagined to be made up of many such baroclinic vortices each with a vertically homogeneous core carrying cold convectively tainted waters the point vortices are introduced at a rate that depends on the large scale cooling and the intensity assumed for each vortex the interaction of many cold baroclinic vortices making up a cloud is studied using point vortex green s function techniques the current solenoids of the individual ele

modeling deep water renewal in lake baikal temperature dissolved oxygen nutrients and chlorofluorocarbon 12 data obtained from lake baikal are used to describe deep water renewal in a deep temperate latitude lake observations are used to propose the physical mechanism governing convection and to formulate a model of deep ventilation the key physical mechanism governing deep water renewal is the so called thermobaric instability because the temperature of maximum density decreases with depth a lake can become conditionally unstable if the base of the cold mixed layer is displaced to a depth at which its temperature matches the local temperature of maximum density thereby resulting in sinking plumes an important consequence of this phenomenon is that deep temperate lakes such as baikal do not completely mix twice yearly instead deep ventilation is episodic a two dimensional model of a wind and buoyancy driven lake shows many strong mixing events and a fairly realistic seasonal cycle indicating that the hypothesis is physically realizable a filling box model is used to deduce the annually averaged fluxes necessary to produce a steady vertical distribution of tracers as observed good fits are obtained to oxygen and chlorofluorocarbon distributions by this model about 50 of the world s liquid freshwater is contained in the large deep lakes located in the temperate latitudes between 45 and 65 n see hutchinson 1957 of fundamental importance to such lakes is their ventilation time the time scale associated with renewal of deep water for it is the deep convection process that most strongly controls the internal redistribution of scalar properties such as dissolved oxygen nutrients and anthropogenic pollutants see wiiest et al 1988 however surprisingly few attempts to study and quantify ventilation in deep

diagenetic barium cycling in black sea sediments a case study for anoxic marine environments high resolution sedimentary records of major and minor elements al ba ca sr ti total organic carbon toc and profiles of pore water constituents view the mathml sourceso42 ch4 ca2 ba2 mg2 alkalinity were obtained for two gravity cores core 755 501 m water depth and core 214 1686 m water depth from the northwestern black sea the records were examined in order to gain insight into the cycling of ba in anoxic marine sediments characterized by a shallow sulfate methane transition smt as well as the applicability of barite as a primary productivity proxy in such a setting the ba records are strongly overprinted by diagenetic barite baso4 precipitation and remobilization authigenic ba enrichments were found at both sites at and slightly above the current smt transport reaction modeling was applied to simulate the migration of the smt during the changing geochemical conditions after the holocene seawater intrusion into the black sea based on this sediment intervals affected by diagenetic ba redistribution were identified results reveal that the intense overprint of ba and baxs ba excess above detrital average strongly limits its correlation to primary productivity these findings have implications for other modern and ancient anoxic basins such as sections covering the oceanic anoxic events which ba is frequently used as a primary productivity indicator our study also demonstrates the limitations concerning the use of baxs as a tracer for downward migrations of the smt due to high sedimentation rates at the investigated sites diagenetic barite fronts are buried below the smt within a relatively short period thus relict barite fronts would only be preserved for a few thousands of years if at all

sources and sinks of methane in lake baikal a synthesis of measurements and modeling we studied the methane ch4 budget of lake baikal the most voluminous lake in the world and the only freshwater body with known occurrences of methane hydrates in the sediments ch4 concentrations were measured in water samples taken during six expeditions between october 2002 and june 2004 these expeditions covered the entire lake volume a one dimensional model was applied to 1 estimate the large scale vertical ch4 fluxes within the south basin of lake baikal 2 determine the exchange with the atmosphere and 3 constrain the ch4 inputs from seeps and mud volcanoes to the deep water fluxes were generally several orders of magnitude below previous estimates the annual internal source of ch4 to the pelagic surface mixed layer was roughly estimated to be 40 mg ch4 a large part of this input diffuses downwards and is consumed in the water column with a ch4 residence time of about 4 yr the input of ch4 from deep gas seeps and mud volcanoes is less than a few 10 mg ch4 yr21 most of which is oxidized before reaching the surface the net ch4 flux between the atmosphere and the main waterbody distant from shallow areas is negligible and not significantly different from zero however occasional high ch4 concentrations both in the surface water and in the atmosphere indicate that the region near the selenga delta is a local ch4 source to the atmosphere ch4 fluxes in the central basin are very similar to those in the south basin whereas in the north basin the shallow ch4 sources are weaker

oxygen and hydrogen isotope systematics of lake baikal siberia implications for paleoclimate studies we interpret oxygen and hydrogen isotope data for water samples from lake baikal siberia its tributaries and other local rivers and local precipitation in terms of the known water budget for the modern lake in order to gain insight into past limnological and climatic processes that influenced the lake lake baikal is remarkably uniform in its isotopic composition i80 15 8 0 2 0 6d 123 f 2 0 and lies slightly to the right of the global meteoric water line which suggests significant evaporation water is supplied to the lake by over 300 rivers and streams the oxygen isotope values 8180 of the rivers in the baikal catchment range from 13 4 to 21 2 0 the hydrogen isotope values sd for the same area range from 103 to 156 0 both these ranges generally conform to the global meteoric water line the weighted average isotopic composition of input to the lake rivers plus precipitation is 15 2 0 for 6 0 and 116 0 for 6d values higher than those of the modern lake therefore the isotopic composition of the modem lake cannot be related to the modern input through simple evaporation instead modeling of the isotopic mass balance of the lake suggests that inputs precipitation and influx from rivers and outputs evaporation and outflow are not at a steady state equilibrium under current climate conditions we found previous input to the lake had lower zy o and 6d values than modern input which reflects cooler climates in the past compared with modern conditions under constant climate conditions steady state conditions are not expected to be reached by the lake for at least 700 yr because of its large size and the long residence time of water in the lake

multifrequency turam measurements over a sulfide deposit a six frequency electromagnetic em system has been developed and used for a turam type survey over the sulfide deposit of mailaram copper belt in andhra pradesh india turam field strength ratio fsr and phase difference pd are measured in the range 84 to 2688 hz sulfides in this belt occur as thin concentrated lodes which grade into disseminations soil covers a major part of the area interpretation of the results is carried out using a thin sheet model in free space however an attempt has been made to account for finite resistivity of the normal ground by computing turam response of a conducting half space appropriate for the area and subtracting the same from the observed response the results of the survey confirm the known advantage of the turam method viz its greater depth of investigation compared to a method like slingram the normal ground at mailaram is only mildly conducting so that the free air approximation is valid at low frequencies a correction for the finite resistivity of t

a rectangular loop source of current on a two layered earth using the concept of reciprocity and the known solution for the electric field of a vertical oscillating magnetic dipole source placed over a two layered halfspace an integral expression for the vertical magnetic field produced by a horizontal rectangular loop carrying an oscillating current and placed on the surface of the same halfspace is deduced this expression is such that it can be evaluated by a combination of straightforward numerical integration and digital linear filter techniques displacement currents everywhere in space are neglected fields both inside and outside the loop are presented as sounding curves a little over a decade of frequencies 100 3000 hz appears to be the minimum requirement and two decades 100 10000 hz are sufficient for most situations parametric and geometric sounding curves both show good resolution of subsurface layering phase shows better resolution than amplitude similarly resolution is higher when conductivity increases with depth than when it decreases besides being useful for the electromagnetic depth sounding for layered earth structures such computations can be applied to determine normal corrections to turam observations whenever a rectangular loop of finite size is used as a transmitter

drivers of deep water renewal events observed over 13 years in the south basin of lake baikal lake baikal with a depth of 1637 m is characterized by deep water intrusions that bridge the near surface layer to the hypolimnion these episodic events transfer heat and oxygen over large vertical scales and maintain the permanent temperature stratified deep water status of the lake here we evaluate a series of intrusion events that reached the bottom of the lake in terms of the stratification and the wind conditions under which they occurred and provide a new insight into the triggering mechanisms we make use of long term temperature and current meter data 2000 2013 recorded in the south basin of the lake combined with wind data produced with a regional downscaling of the global ncep ra1 reanalysis product a total of 13 events were observed during which near surface cold water reached the bottom of the south basin at 1350 m depth we found that the triggering mechanism of the events is related to the time of the year that they take place we categorized the events in three groups 1 winter events observed shortly before the complete ice cover of the lake that are triggered by ekman coastal downwelling 2 under ice events and 3 spring events that show no correlation to the wind conditions and are possibly connected to the increased spring outflow of the selenga river

processes of deep water renewal in lake baikal deep water renewal in lake baikal siberia the world s deepest lake and largest lake by volume is relatively fast water age calculated from tritium and helium as well as from chlorofluorocarbons does not exceed 19 yr relative saturation of dissolved oxygen typically exceeds 80 the equation of state of baikal water was determined including the effect of dissolved ions and silicic acid based on nearly 600 ctd profiles taken between 1993 and 1995 two mechanisms of deep water mixing were identified 1 in spring cold and relatively saline water from the selenga the major inflow to the lake forms a density plume that reaches the bottom of the central basin during april and early may due to entrainment of lake water the plume transports about 125 km of water per year to the deepest part of the basin later in spring the river water forms the thermal bar observed along the eastern shore there are indications that parts of the selenga are also plunging to the deep part of the southern basin 2 at academician ridge separating the cold and saline water of the central basin from the warmer and slightly less saline water of the northern basin horizontal mixing results in a water mass that can sink on either side of the sill whereas in the central basin the water mass stays at intcrmediatc depth in the northern basin it sinks to the decpcst part more detailed data are needed to quantify this density flux no indication of a wind induced thermobaric instability was found

bottomwater formation due to hydrothermal activity in frolikha bay lake baikal eastern siberia hydrothermal water enters frolikha bay a well known site of high geothermal heat flux in the northern part of lake baikal at 400 m depth on the basis of ctd profiles the hydrothermal water is identified as forming an anomalous bottom layer with a higher temperature 0 15 c and salinity 2 5 mg kg 1 than the overlying water due to the entrainment of lake water a distinct dense water layer up to 40 m thick stabilised by its slightly higher salinity becomes established close to the bottom of the bay the density current thus generated flows out of the bay towards the deeper parts of the basin since helium isotope analysis shows that the geochemical characteristics of the hydrothermal water are similar to those of water from nearby hot springs on land the bottomwater of frolikha bay is easily interpreted in terms of the mixing of ordinary fresh water from the lake and hydrothermal water carrying isotopically heavy he from the continental crust because of its high crustal he content a similar hydrothermal component may even be identified in the open water of the northern basin

biological nitrate utilization in south siberian lakes baikal and hovsgol during the last glacial period the influence of climate change on primary productivity abstract stable nitrogen isotope ratios 15 n in sediment cores recovered from two siberian lakes baikal and hovsgol are determined in order to evaluate the biologically mediated nitrogen cycle from the last glacial period to the postglacial period the ranges of 15 n values from the two lakes are similar varying from 2 8 to 6 7 the high values of 15 n around 6 during the last glacial maximum lgm 26 5 19 cal ka bp indicate that a larger fraction of the available nitrate in both lakes was utilised by phytoplankton a cool and dry climate during the lgm may have limited the input of terrestrial nitrate resulting in the use of a large fraction of the nitrate and low productivity in both lakes the use of a smaller fraction of the nitrate by phytoplankton in both lakes after the lgm 19 12 cal ka bp is reflected in the lower 15 n values down to 3 0 the increase in summer insolation after the lgm caused increased vertical mixing of the lake water column which transported nitrate upwards from the deeper waters and into the photic zone the reduced rate of nitrogen consumption after the lgm indicates that nitrate was more readily available to phytoplankton at this time and did not limit their activities this change suggests that other factors limited phytoplankton activity during this period at the climatic transition between oxygen isotope stages 2 and 1 around 11 5 cal ka bp the rapid increase in 15 n from 3 0 to 6 0 reflected a rapid increase in nitrate utilization at this transition increases in precipitation and lake levels which were associated with the increased intensity of the east asian monsoon may have brought a large influx of nutrients required by the phytoplankton into the lakes from the watershed this hydrological change led to increased phytoplankton activity in both lakes resulting in increased nitrate consumption the 15 n data obtained here from the sediments of lakes baikal and hovsgol suggest that the nitrogen cycle in the siberian region is strongly linked to hydrological changes across the asian continent which are related to global climate change

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

deep water renewal in lake issyk kul driven by differential cooling during two field campaigns on lake issyk kul in march and august 2001 179 high resolution conductivitytemperature depth profiles were measured along with profiles of dissolved oxygen and light transmission on the basis of this extensive data set we investigated the large scale vertical advective processes responsible for deepwater renewal in lake issyk kul at some locations sampled in march variable peak structures in the tracer profiles were observed that indicate horizontally localized intrusions these intrusions have their origin in density plumes that propagate along the bottom of the channels in the eastern shelf region the cold dense water at the bottom of the channels is most likely generated by differential cooling of the water in the shallow shelf regions during winter during summer vertical advective processes appear to be limited to the upper 200 m where upwelling in the open water leads to a doming structure the august data support the results of earlier investigations that suggested that dynamic forcing by a basinwide gyre is responsible for the upwelling in the open water

large scale short period sea ice atmosphere interaction changes in the microwave brightness temperature measured by the electrically scanning microwave radiometer esmr flown on board the nimbus v satellite reveal large scale sea ice fluctuations in the antarctic marginal ice zone these ice margin fluctuations arre predominantly wave numbers 1 4 with phase speeds of about 3 m s independent of wave number the spatial pattern and eastward advection of the sea ice anomalies match those of the atmospheric sea level pressure and are consistent with sea ice displacement due to surface wind stress examination of the outgoing longwave radiation indicates that suppression of high clouds in regions of increased sea ice inc reases the radiative cooling which contributes to maintaining the ice data from three winter seasons indicate about a one third probability of occurence of this large scale high frequency sea ice atmosphere interaction during any given 2 week period in winter

vertical turbulent diffusion and upwelling in lake baikal estimated by inverse modeling of transient tracers vertical turbulent diffusion coefficients upwelling velocities and oxygen depletion rates are estimated by inverse modeling of the concentrations of cfc 11 ccl3f cfc 12 ccl2f2 3h 3he and dissolved oxygen for the southern central and northern basin of lake baikal a model is developed that considers two regions in each basin of lake baikal 1 a surface mixed layer sml 400 m thick and 2 a deepwater column dwc below 400 m the smls are assumed to be well mixed in each of the dwcs passive tracers are transported by vertical turbulent diffusion and upwelling upwelling is generated by a depth dependent source of water because of density plumes propagating from the sml downward to larger depths this water is considered to contain the same tracer concentrations as the sml the tracer concentrations in the smls of the three basins are coupled to the atmosphere by gas exchange including water vapor transport and precipitation to the catchment by river inflow and outflow and to the neighboring basins via diffusive exchange and advection smls and dwcs of the same basin are connected by vertical turbulent diffusion density driven water transport and upwelling beginning at the turn of this century the tracers cfc 11 cfc 12 3h and 3he are modeled simultaneously to predict modern concentrations on the basis of the tracer data the vertical diffusion coefficient k is determined to be 4 6 10 4 m2 s 1 10 for the southern 6 3 10 4 m2 s 4 10 for the central and 1 7 10 4 m2 s 4 25 for the northern basin the vertical advective flux of water at 400 m water depth is calculated as 110 km3 yr 1 in the southern 70 km3 yr 1 in the central and 290 km3 yr 1 in the northern basin concentration of dissolved molecular oxygen is modeled by using the estimated transport parameters and by fitting for the unknown consumption rate inverse modeling of oxygen suggests that o2 depletion in the dwc can be described by a volume sink of 44 3 mgo2 m 3 yr 1 combined with an areal sink at the sediment water interface of 17000 3000 mgo2 m 2 yr 1

small scale turbulence and vertical mixing in lake baikal the water column of lake baikal is extremely weakly but permanently stratified below 250 m despite the thickness of this relatively stagnant water mass of more than 1000 m the water age time since last contact with the atmosphere is only slightly more than a decade indicating large scale advective exchange in the stratified deep water the fate of water constituents is determined by the combined action of advective processes deep water intrusions and small scale turbulent vertical diffusion here vertical diffusivity is addressed through the analysis of 25 temperature microstructure profiles collected in the three major basins of lake baikal to a depth of 600 m in addition in the 1 432 m deep south basin monthly ctd profiles and a two year record of near bottom currents were analyzed balancing turbulent kinetic energy and small scale temperature variance leads to the conclusions that 1 vertical diffusivity in the stratified deep water ranges from 10 90 3 10 24 m 2 s 21 between 600 and 250 m which is three orders of magnitude more than estimated by killworth et al 1996 2 the mixing efficiency is 0 16 comparable to that found in stronger stratification e g the ocean interior 3 turbulence under ice decays with a time scale of 40 6 2 d and 4 the interior of the permanently stratified deep water below 250 m and the bottom boundary layer contribute roughly equally to the tke production the latter implies that mixing in the deep water of lake baikal s three sub basins is dominated by bottom boundary mixing as found in smaller lakes and ocean basins

observations with moored acoustic doppler current profilers in the convection regime in the golfe du lion abstract in the golfe du lion south of france favorable conditions for deep winter convection exist and were documented by the medoc experiments during 1969 75 a renewed investigation of that regime with upward looking moored acoustic doppler current profilers adcps was carried out during 24 january 5 march 1987 to record the three dimensional currents associated with the deep mixing while in the earlier studies initial deep convection did not begin until fairly late in the winter season a very strong mistral around 10 january 1987 had already generated a 1arge deep mixed patch homogeneous down to around 2000 m at deployment time three adcps two working at 150 khz and one at 75 khz were moored in a triangle of 15 km sidelength at 550 780 m depth full records at 1 hour ensemble time intervals 400 pings per ensemble 8 m bin lengths were obtained by the 75 khz and one of the 150 khz adcps in mid february a second mistral hit the region with the onset of strong winds and surface cooling the

a three dimensional numerical model of deep ventilation in temperate lakes because of the variation in the temperature of maximum density with depth it is known that the upper above 250 m and lower water columns circulate separately in deep temperate lakes while near surface water overturns twice per year the deep waters often mix only partially during a complete annual cycle it is believed that deep convection is triggered by storm surge forcing of some of the relatively cold upper water column downward through its compensation depth so that it becomes unstable and sinks the scale and intensity of the resulting deep water forming plumes are studied numerically a high resolution model based on the nonhydrostatic boussinesq equations is used deep water formation is initiated by applying a statically unstable initial temperature profile over various regions of the domain at depths below 300 m the grid spacing is small enough to resolve individual plumes which carry surface water to the lake bottom the domain of study is also large enough that the geostrophic eady 1949 wave breakup of newly formed deep water can be observed it is found that when the initial instability is applied in midbasin remote from the solid sidewalls relatively little fresh deep water is formed and the fluid quickly reaches a geostrophic and hydrostatic balance vigorous vertical mixing ceases after 4 days and the resulting baroclinic fluid has a well defined and predictable scale in contrast when the initial instability is applied immediately adjacent to a solid boundary vigorous plume motion continues for the duration of the numerical simulations 12 days producing a much greater volume of fresh deep water a parametric study investigates the scale and intensity of this boundary mixing it is found that reduced surface water temperature coriolis acceleration or higher horizontal diffusion coefficients increase the rate of deep water renewal

quaternary sedimentation and subsidence history of lake baikal siberia based on seismic stratigraphy and coring the long continuous high latitude stratigraphic record of lake baikal was deposited in three broad sedimentary environ ments defined by high resolution seismic reflection and coring meth ods 1 turbidite depositional systems by far the most widespread characterizing most of the margins and floors of the main basins of the lake 2 large deltas of major drainages and 3 tectonically or topographically isolated ridges and banks holocene sedimentation rates based on radiocarbon ages vary by more than an order of mag nitude among these environments from less than about 0 03 mm yr on ridges and banks to more than about 0 3 mm yr on basin floors ex trapolating these rates with a correction for compaction yields ten tative estimates of about 25 and 11 ma for the inception of rifting in the central and north basins respectively and less than 6 ma for the 200 m sediment depth on academician ridge the selenga delta has the distinctive form of a classic prograding gilbert type delta but its history appears to represent a complex com bination of tectonism and sedimentation the central part of the delta is underlain by prograding shallow water sequences now several hun dred meters below the lake surface these deposits and much of the delta slope are mantled by fine grained deep water hemipelagic de posits whose base is estimated to be about 650 000 years old modern coarse grained sediment bypasses the delta slope through fault con trolled canyons that feed large subaqueous fans at the ends of the south and central basins these relations along with abundant other evidence of recent faulting and the great depths of the central and south basins suggest that these two rift basins have experienced a period of unusually rapid subsidence over the last 650 000 years dur ing at least part of which sedimentation has failed to keep pace

sea ice motion as a drunkard s walk observations of sea ice displacement over short periods of time are used to deduce some statistics of the ice motion over long periods of time the objective is to follow the trajectory of a piece of ice starting at a randomly selected time and location and ending when the ice either melts or leaves the arctic basin trajectories are also followed backward in time to the time and location where the piece of ice was formed statistical properties considered are the age and remaining lifetime of ice in various locations and the probability that ice presently occupying a particular location was originally created or will ultimately melt in certain regions possible applications are to the distribution of pollutants by sea ice and to the design of experiments involving drifting measurement platforms

environmental response to volcanic activity and its effect on organic matter enrichment in the permian lucaogou formation of the malang sag santanghu basin northwest china abstract lacustrine organic rich fine grained rocks are widespread in the second member of the permian lucaogou formation p2l2 in the malang sag santanghu basin with complex lithology and significant changes of lithofacies due to frequent volcanic activity in this study the mineralogical and petrological characteristics types of organic matter om and effect of volcanism on the sedimentary environment and om accumulation were analyzed using organic carbon and oxygen isotopes as well as major and trace element data the results revealed that the p2l2 was characterized by mixed deposition of volcanic ash and carbonate minerals with four main rock types tuff dolomitic tuff tuffaceous dolomite and dolomite the fine grained rocks dominantly contain type i and ii1 kerogens which were in a low mature stage and exhibited excellent original hydrocarbon generative potential when volcanic activity was strong large amounts of nutrients were released by the volcanic ash which then entered the lake in turn promoting the blooming of phytoplankton and causing the 13c values in the tuff to decrease in addition the paleotemperature decreased for a short time and the suboxic euxinic environment was conducive to the preservation of om resulting in high total organic carbon toc content in the tuff in contrast during intermittent or weak periods of volcanic activity the climate was hotter and drier and evaporation resulted in a sustained increase of salinity consequently the growth of algae was restricted which brought about an increase in the 13c values and relatively low toc content in the dolomite the relationships among primary productivity redox conditions clastic influx proxies and toc content illustrate that primary productivity was the most vital control on the accumulation of om high primary productivity was mainly driven by volcanic ash falls meanwhile high salinity and suboxic euxinic conditions were beneficial to the preservation of om giving rise to a high degree of om enrichment

ams radiocarbon analyses from lake baikal siberia challanges of dating sediments from a large oligotrophic lake abstract a suite of 146 new accelerator mass spectrometer ams radiocarbon ages provides the first reliable chronology for late quaternary sediments in lake baikal in this large highly oligotrophic lake biogenic and authigenic carbonate are absent and plant macrofossils are extremely rare total organic carbon is therefore the primary material available for dating several problems are associated with the toc ages one is the mixture of carbon sources in toc not all of which are syndepositional in age this problem manifests itself in apparent ages for the sediment surface that are greater than zero however because most of the organic carbon in lake baikal sediments is algal autochthonous in origin this effect is limited to about 1000 500 years which can be corrected at least for young deposits the other major problem with dating lake baikal sediments is the very low carbon contents of glacial age deposits which makes them extremely susceptible to contamination with modern carbon this problem can be minimized by careful sampling and handling procedures the ages show almost an order of magnitude difference in sediment accumulation rates among different sedimentary environments in lake baikal from about 0 04 mm year on isolated banks such as academician ridge to nearly 0 3 mm year in the turbidite depositional areas beneath the deep basin floors such as the central basin the new ams ages clearly indicate that the dramatic increase in diatom productivity in the lake as evidenced by increases in biogenic silica and organic carbon began about 13 ka in contrast to previous estimates of 7 ka for the age of this transition holocene net sedimentation rates may be less than equal to or greater than those in the late pleistocene depending on the site this variability reflects the balance between variable terrigenous sedimentation and increased biogenic sedimentation during interglaciations the ages reported here and the temporal and spatial variation in sedimentation rates that they imply provide opportunities for paleoenvironmental reconstructions at different time scales and resolutions

clay minerals in the sediments of lake baikal a useful climate proxy lake baikal in south central siberia has been the focus of an international effort the baikal drilling project bdp to obtain continuous long cores upwards of 100 m from this unique rift valley lake and to interpret the paleoclimatic history from various proxy data as part of this effort the clay minerals were examined by two research teams a consistent clay mineral assemblage containing illite inter stratified illite smectite chlorite and kaolinite as the major minerals characterizes much of the modern sediments the relative abundance of these minerals changes with depth in both short piston cores from various parts of the lake and in 100 m long cores taken from the distal toe of the selenga delta bdp 93 independent analyses of the abun dance changes and correlation with other data from the cores show that the clays are responding to two influences 1 climatic fluctua tions particularly in the upper 40 m of the sedimentary record which show the relative amount of illite smectite and sometimes kaolinite increasing during warmer climate episodes and 2 source area chang es which are most evident below 40 m in the bdp 93 cores and mark a shift from an eastern buguldeika river to a western selenga river source the clay mineral based climate fluctuations are correlative with the marine oxygen isotope record through stage 7 and provide a relatively simple and cost effective tool for gaining insight into the pa leoclimate of this interior continental site

the geochemistry of inorganic germanium in natural waters we present the initial results from a survey of the distribution of dissolved inorganic germanium in rivers in the oceans and in hydrothermal vents and plumes in the ocean germanium cycling mimics that of silica since siliceous organisms incorporate ge as a trace constituent in biogenic opal the vertical and horizontal distributions of ge concentrations in seawater are thus identical to those of silica ge si 0 7 10 6 and reflect uptake into and dissolution from the frustules of siliceous organisms germanium enters the ocean via dissolution of continental and seafloor silicates the naturally weathered flux from continents to oceans carries a dissolved ge si atom ratio in rivers of about 0 7 10 6 which reflects the ratio in average continental granites rivers draining industrial regions with significant coal combustion are contaminated with ge leached from fly ash particles resulting in ge si ratios up to tenfold above the naturally weathered background the flux to the oceans via high temperature alteration of seafloor basalts hot springs produces a ge anomaly in hydrothermal plumes over the east pacific rise crest 20 s combining the observed ge and 3he anomalies in plumes with 3he si observations in hot springs suggests that the ge si hydrothermal flux to the oceans is about 4 10 6 near the ratio for average oceanic basalts 2 6 10 6 vent effluents from the galapagos hot springs measured directly display ge si ratios of 16 10 6 suggesting that the ratio is variable between vent fields metalliferous sediments accumulating on the epr crest 17 s are enriched in germanium suggesting that a fraction of the hydrothermal germanium source on the rise crest is scavenged into these rapidly accumulating iron and manganese hydroxyoxide phases

distribution of aluminium in waters of the north east atlantic 25 n to 35 n abstract dissolved al concentrations from the ne atlantic between 25 n and 35 n off the coast of nw africa range from 16 nm to 32 nm in a well mixed surface layer extending to 150 m depth increasing towards the maximum of the saharan dust plume mediterranean outflow water is detected as a high al anomaly corresponding to the salinity signal of the mediterranean water other than in surface and mediterranean waters al concentrations are invariant with depth but increase from 6 nm to 11 nm towards the continental margin the magnitude of the dissolved al signal in the surface layer is compatible with dissolution of al from the highest of present estimates of dust input to this area comparison with data from other areas indicates that al cannot be cycled through the oceans in parallel to silica as has been previously suggested

electromagnetic sounding of the kapurdi lignite deposit in western rajasthan india in the kapurdi block of the barmer lignite field in western rajasthan india lignite occurs as a number of discontinuous seams of varying thickness up to a few m the country rock is a succession of clay sand and various members of the clay sand family the overburden comprising sand fuller s earth bentonitic clay clayey sand sandy clay and clay is thick and electrically highly conductive both its thickness 40 90 m and conductivity 0 5 1 0 s m are highly variable the lignite seams may occur anywhere in the clay sand sequence below this overburden a ten layered electrical model of the kapurdi area was parameterized on the basis of galvanic resistivity sounding and core drilling results this model was then validated by electromagnetic sounding measurements made with a 200 200 m square loop transmitter and energizing current of variable frequency 80 hz to 11 khz using central induction sounding techniques with a loop of this size only formations in the overburden could be mapped subsequent computer modeling has shown that a larger loop of size say 800 m and a frequency band of 30 500 hz are required to map formations below as well as those within the overburden even then only various clay sand interfaces can be mapped i e only over burden thickness and the likely depth range of lignite seams if they occur can be estimated direct mapping of lignite seams is not feasible in practice this is true of loop dipole as well as central induction sounding it is interesting that skin depth need not always be a factor limiting depth of exploration in electromagnetic prospecting

lake baikal deepwater renewal mystery solved deepwater renewal by intrusions and turbulent diffusion in lake baikal is very effective despite the enormous depth of up to 1642 m and the permanently stable stratification below similar to 300 m depth temperature time series recorded at the bottom of a mooring installed since march 2000 in the south basin of the lake indicate recurrent freshwater intrusions with volumes of 50 to 100 km 3 about one order of magnitude larger than previously observed intrusions numerous mechanisms have been proposed to explain the advective deep water renewal here we present for the first time direct observations which prove that they are caused by coastal downwelling and subsequent thermobaric instability along the steep lake shores understanding these mechanisms is an important prerequisite for studying biogeochemical cycles for predicting the effects of climate change on this unique ecosystem and for evaluating the local climate history from the extraordinary sedimentary record of lake baikal

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

aluminium in the northwest atlantic abstract a series of profiles between woods hole and bermuda has been measured on board ship for al the extrema in the upper waters can be explained by the accumulation of aeolian inputs in the thin summer mixed layer the depletion of the underlying winter water by scavenging during the spring bloom and the enrichment of the subtropical mode 18 c water by aeolian accumulation during winter and local convection before the spring bloom the pronounced minimum at mid depth is associated with the antarctic intermediate water and the underlying labrador sea med water complex presumably the aaiw and the med water are depleted by the ageing effect on this short residence time element during their transit to the area the lsw is formed from surface waters containing a large component of arctic waters extremely depleted in al advected south in the east greenland current the linear increase to the bottom is caused by mixing of enriched lower north atlantic deep water with the depleted bottom water and lsw cores the enrichment in the deep water appears to be produced by the entrainment of high al waters from the north european shelf by the gyre in the norwegian greenland sea and its injection into the denmark straits overflow waters in a manner recently described for the radiocaesium releases from the windscale reprocessing plant on the irish sea an additional contribution probably comes from the shelf north of iceland

quantification of bioturbation in hemipelagic sediments via thin section image analysis traditional ichnofabric descriptive semiquantitative l schemes rely upon subjective estimates of the degree to which original sedimentary fabrics have been disrupted this paper presents an objective method of quantifying bioturbation in hemipelagic sediments based on a thin section image analysis technique in order to perform these analyses optical or backscattered electron micrographs are processed in order to obtain black and white images in these images black pixels are silt size larger grains and the clay size sedimentary matrix are white pixels once the initial processing has been accomplished an index h is defined to quantify the horizontal orientation of the larger grain size fraction of the sediment h is low for bioturbated fabric and high for laminated sediments in hemipelagic suspension deposits h can he used to quantify bioturbation assuming that no other sedimentary processes have disrupted the original depositional fabric the quantitive bioturbation scheme described here is consistent with existing semiquantitative bioturbation schemes in addition it is objective and provides higher resolution descriptions of biological processes that disrupted the sediment after deposition applying this quantitative scheme should refine future paleoecological reconstruction derived from lacustrine and marine successions

calcium magnesium and strontium cycling in stratified hardwater lakes lake kinneret sea of galilee israel abstract in stratified hardwater lakes calcite crystallization in the epilimnion and partial dissolution in the hypolimnion play important roles in the cycling of ca2 in the water column mg2 and sr2 coprecipitate with this mineral to be released together with ca2 upon its dissolution here we focus on lake kinneret sea of galilee israel a stratified warm hardwater lake searching for an interpretable high resolution picture of the processes that drive ca2 mg2 and sr2 cycling in this and similar lakes elsewhere in total 1428 water samples were collected from the lake and another 81 samples were collected from the jordan river and two small streams discharging into it covering a full monomictic cycle from december 2001 through march 2003 particulate material was retrieved from sediment traps in the hypolimnion the water samples were analyzed for na k mg2 ca2 sr2 cl so42 hco3 and br and the trapped particulates were examined under sem and analyzed for their ca mg and sr content individual calcite crystals within the particulate material underwent la icp ms analysis for ca mg and sr downward transport of ca2 involves crystallization of calcite in the epilimnion followed by its settling through the water column followed by its partial dissolution in the hypolimnion magnesium and sr2 follow ca2 by coprecipitation in calcite and are released upon its dissolution in the hypolimnion upward cycling of the three solutes occurs through an admixture of the hypolimnetic water into the epilimnion during thermocline deepening terminated by overturn of the lake removal rates of mg2 and sr2 from the lake relative to that of ca2 and the water calcite distribution coefficients dmg and dsr were calculated from the analyses using 1 epilimnion water and bulk particulates 2 epilimnion water only and 3 epilimnion water and calcite crystals in the particulates the dsr values obtained were internally consistent 0 194 5 9 0 22 0 28 and 0 204 0 232 respectively however the dmg value for the bulk particulates 0 0477 was 6 times higher than that corresponding to calcite crystals included therein 0 00841 this difference is attributed to phytoplankton debris in the bulk particulates and should be of concern to geochemists using mg ca ratios in limestone to reconstruct ancient aquatic environments the cycling of ca2 mg2 and sr2 in the stratified lake is monitored by mg ca vs sr ca regression diagrams where each line represents the water column composition on a specific date the distance of the data points from the initial mixed lake coordinates reflects the fractionation of ca2 mg2 and sr2 after the onset of stratification the regression lines rotate in an orderly anticlockwise direction in response to the high calcite flux from the epilimnion in spring and the higher rate of mg2 replenishment than that of sr2 compensating for their loss in calcite the release of mg2 and sr2 from dissolving calcite in the hypolimnion at an mg sr ratio 7 5 eq eq much lower than that in the surrounding water 160 eq eq lends additional support to the anticlockwise rotation reversal of rotation occurs in summer when calcite crystallization and the freshwater supply slow down and brackish and saline water sources take control over the mg sr ratio in the lake subsequent turnover and mixing of the lake in winter reset the mg ca and sr ca ratios to their original values before the next stratification

a three dimensional numerical study of deep water formation in the northwestern mediterranean sea abstract deep water formation dwf in the northwestern mediterranean sea and the subsequent horizontal circulation are investigated in a rectangular basin with a three dimensional primitive equation model the basin is forced by constant climatological heat and salt fluxes convective motion is parameterized by a simple nonpenetrative convective adjustment process plus richardson number dependent vertical eddy viscosity and diffusivity a homogeneous column of dense water is progressively formed in the forcing area meanders of 40 km wavelength develop at the periphery of the column these features agree with observations energy studies show that the meanders are generated mainly through a baroclinic instability process these meanders and the associated cells of vertical motion contribute to the process of dwf they generate vertical advection while the associated horizontal advection tends to restratify the surface water of the column and thus to inhibit very deep convection just before the end o

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

constraining modern day silicon cycling in lake baikal constraining the continental silicon cycle is a key requirement in attempts to understand both nutrient fluxes to the ocean and linkages between silicon and carbon cycling over different time scales silicon isotope data of dissolved silica 30sidsi are presented here from lake baikal and its catchment in central siberia as well as being the world s oldest and voluminous lake lake baikal lies within the seventh largest drainage basin in the world and exports significant amounts of freshwater into the arctic ocean data from river waters accounting for 92 of annual river inflow to the lake suggest no seasonal alteration or anthropogenic impact on river 30sidsi composition the absence of a change in 30sidsi within the selenga delta through which 62 of riverine flow passes suggests a net balance between biogenic uptake and dissolution in this system a key feature of this study is the use of 30sidsi to examine seasonal and spatial variations in dsi utilization and export across the lake using an open system model against deepwater 30sidsi values from the lake we estimate that 20 24 of dsi entering lake baikal is exported into the sediment record while highlighting the impact that lakes may have upon the sequestration of continental dsi mixed layer 30sidsi values from 2003 and 2013 show significant spatial variability in the magnitude of spring bloom nutrient utilization with lower rates in the north relative to south basin

the relative roles of diapycnal and isopycnal mixing on subsurface water mass conversion abstract fluid motion in the sea is known to occur predominantly along quasi horizontal neutral surfaces but the very small diapycnal i e across isopycnal velocities often make a significant contribution to the conversation equations of heat salt and tracer by eliminating the diapycnal advection term between the conservation equations for i heat and ii salt an equation is derived for the rate of change lagrangian derivative of potential temperature on a neutral surface which has terms caused by a turbulent mixing along isopycnal surfaces i e isopycnal mixing b diapycnal turbulent mixing and c double diffusive convection bemuse of the nature of the isopycnal reference frame the diapycnal mixing terms do not take their expected forms for example the diapycnal turbulent mixing term is proportional to the diapycnal eddy diffusivity d multiplied by the curvature of the s curve d2s d 2 rather than the usual form d x x if the s curve is locally straight small scale turbulen

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

convection with rotation in a neutral ocean a study of open ocean deep convection abstract the intensity and scale of the geostrophically adjusted end state of the convective overturning of a homogeneous rotating ocean of depth h at a latitude where the coriolis parameter is f induced by surface buoyancy loss of magnitude b0 are studied by numerical experiment the experiments are related to observations and laboratory studies of open ocean deep convection a numerical model based on the nonhydrostatic boussinesq equations is used the grid spacing of the model is small enough that gross aspects of convective plumes themselves can be resolved yet the domain of integration is sufficiently large to permit study of the influence of plumes on the large scale and geostrophic adjustment of the convected water numerical simulations suggest that cooling at the sea surface is offset by buoyancy drawn from depth through the agency of convective plumes these plumes efficiently mix the water column to generate a dense chimney of fluid which subsequently breaks up through the mechanism of bar

ventilation and dissolved oxygen cycle in lake superior insights from a numerical model ventilation and dissolved oxygen in lake superior are key factors that determine the fate of various natural and anthropogenic inputs to the lake we employ an idealized age tracer and biogeochemical tracers in a realistically configured numerical model of lake superior to characterize its ventilation and dissolved o2 cycle our results indicate that lake superior is preferentially ventilated over rough bathymetry and that spring overturning following a very cold winter does not completely ventilate the lake interior while this is unexpected for a dimictic lake no part of the lake remains isolated from the atmosphere for more than 300 days our results also show that lake superior s oxygen cycle is dominated by solubility changes as a result the expected relationship between biological consumption of dissolved o2 and ventilation age does not manifest

mixing and its effects on biogeochemistry in the persistently stratified deep tropical lake matano indonesia in the 590 m deep tropical lake matano indonesia stratification is characterized by weak thermal gradients 2uc per 500 m and weak salinity gradients 0 14 per 500 m these gradients persist over seasons decades and possibly centuries under these nearly steady state conditions vertical eddy diffusion coefficients k z cannot be estimated by conventional methods that rely on time derivatives of temperature distributions we use and compare several alternative methods one dimensionalk emodeling three dimensional hydrodynamic modeling correlation with the size of thorpe instabilities and correlation with the stability frequency in the thermocline region at 100 m depth thek z is 5310 26 m 2 s 21 but below 300 m the small density gradient results in large 20 m vertical eddies and high mixing rates k z 10 22 m 2 s 21 the estimated timescale of water renewal in the monimolimnion is several hundred years intense evaporation depletes the surface mixed layer of 16 o and 1 h isotopes making it isotopically heavier the lake waters become progressively isotopically lighter with depth and the isotopic composition in the deep waters is close to those of the ground and tributary waters the vertical distribution ofk z is used in a biogeochemical reaction transport model we show that outside of a narrow thermocline region the vertical distributions of dissolved oxygen iron methane and phosphorus are shaped by vertical variations in transport rates rather than by sources or sinks

mixing processes in crater lake oregon subsurface hydrothermal activity dominates the heat and salt budgets of the deep water column in crater lake oregon from a time series of conductivity temperature depth data and data from a thermistor chain mooring we estimate that the net hydrothermal heat flow is 1 w m 2 and the corresponding salt flux is 5 gg 2 s f s a r ds u m thi p pe c sses the observation of these fluxes and the mechanisms and time scales of mixing re spo nsible for the redistribution of these properties through the water column free convection and wind mixing homogenize the upper 200 m of the lake twice annually deep lake ventilation occurs during early winter and to some extent during late spring however since the deep lake does not reach atmospheric saturation with reseect to dissolved oxygen at any time during the year ventilation of the deep water appears to be incomplete t uring periods of seasonal stratification the active input of hydrothermally enriched fluids produces heterogeneities and instabilities in the density structure of the deep lake that may drive deep lake mixing as a result of these and other mixing processes crater lake remains relatively well mixed despite its great depth

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

sublacustrine mud volcanoes and methane seeps caused by dissociation of gas hydrates in lake baikal four lake floor seeps have been studied in the gas hydrate area in lake baikal s south basin by using side scan sonar detailed bathymetry measurements of near bottom water properties heat flow measurements and selected seismic profiles in relation to results from geochemical pore water analysis the seeps at the lake floor are identified as methane seeps and occur in an area of high heat flow where the base of the gas hydrate layer shallows rapidly toward the vent sites from 400 m to 150 m below the lake floor at the site of the seep a vertical fluid conduit disrupts the sedimentary stratification from the base of the hydrate layer to the lake floor the seeps are interpreted to result from local destabilization of gas hydrate caused by a pulse of hydrothermal fluid flow along an active fault segment this is the first time that methane seeps and or mud volcanoes as sociated with gas hydrate destabilization have been observed in a sublacustrine setting the finding demonstrates the potential of tectonically controlled gas hydrate destabiliza tion to cause extreme pore fluid overpressure and short lived mud volcanism

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

distribution of helium and tritium in lake baikal the 3 h 3 he age of a water mass is a measure of the time that has passed since the water mass was last in contact with the atmosphere between 1992 and 1995 a detailed study of 3 h 3 he ages was conducted in lake baikal the deepest and largest lake by volume on earth to investigate deep water renewal in its three major basins maximum 3 h 3 he ages are 14 17 years in the southern basin 16 18 years in the central basin and 10 11 years in the northern basin rates of renewal of deep water with surface water deduced from volume weighted mean 3 h 3 he ages below 250 m depth are about 10 yr 1 in the southern and central basins and 15 yr 1 in the northern basin in the southern basin the mean 3 h 3 he age below 250 m depth increased steadily from 9 6 years in 1992 to 11 years in 1995 indicating a slight diminution in deep water renewal during this time bottom water renewal by large scale advection was estimated from the mass balance of 3 he in the 200 m thick bottom layer of each basin bottom water renewal rates in the northern basin were found to be between 80 and 150 km 3 yr 1 and in the central basin between 10 and 20 km 3 yr 1 whereas in the southern basin they were practically zero correlating oxygen and dissolved helium 4 concentrations with 3 h 3 he age allowed us to determine the mean hypolimnetic oxygen depletion rate in the water column 4 5 mol l 1 yr 1 as well as mean helium fluxes from the lake bottom 2 8 x 10 11 atoms m 2 s 1 in the northern basin and 1 3 x 10 11 atoms m 2 s 1 in the central and southern basins the helium isotope ratio of the terrigenic helium component injected from the lake bottom determined from measurements of water from hydrothermal springs in the vicinity of the lake was found to be 2 2 x 10 7

concentration gradients and growth decay characteristics of the seasonal sea ice cover the growth and decay characteristics of sea ice in the northern and southern hemispheres are presented quantitatively by using brightness temperature data from the nimbus 5 electrically scanning microwave radiometer the areal extent of 15 ice cover follows a basically symmetrical seasonal cycle in the northern hemisphere ranging from 8 106 km2 in summer to 16 106 km2 in winter in contrast the seasonal cycle in the southern hemisphere is asymmetrical with longer periods of growth than decay and areal extent ranging from 4 106 km2 in summer to 20 106 km2 in winter at different longitudes the occurrences of the maximum rates of advance of the ice edge differ by up to 2 months and similarly for retreat the distribution of the rate of change in the latitudinal position of the ice edge using as a reference point the 50 ice concentration line near the ice ocean boundary follows a quasi gaussian function with peak at about 60 km month and with a standard deviation of about 120 km month however for some months rates as large as a 940 km month change in the latitudinal position are observed when the movement of the ice edge tends to be in the eastward or westward direction as for example in the weddell sea the gradient of ice concentration near the ice edge has considerable variability following a poisson distribution with peaks at about 0 89 ice concentration per kilometer as derived from the 3 day averages and 0 62 ice concentration per kilometer from the monthly averages during the growth cycle the dominant change in ice cover is the advance of consolidated ice behind the advancing ice edge while during decay the retreat of the ice edge is accompanied by massive reduction of ice concentration within the ice pack the monthly changes in ice edge position in the southern hemisphere are also shown to have good correlation with the rates of advance and retreat of the 271 k surface temperature isotherms inferred from climatological temperature data

space time spectral structure of a glas general circulation model and a comparison with observations abstract the wavenumber frequency spectra of geopotential height have been computed from a winter simulation of a glas general circulation model and are compared to the spectra obtained from 15 winters of observed analyses the variances in several broadly defined space time categories are presented and their distribution with latitude and height discussed the low frequency planetary waves wavenumbers 1 4 in the model have substantially less variance than is observed and their latitudinal structure also differs from observations the same is true for the medium frequency planetary waves the synoptic scale waves wavenumbers 5 10 with both low and medium frequencies are quite well reproduced by the model with the total variances and their latitude height structure comparing well to the observations the net propagation tendency is examined for low frequency planetary waves and the medium frequency synoptic scale waves the model results show too much tendency for eastward propagation the discrepan

cold intrusions in lake baikal direct observational evidence for deep water renewal we studied cold deep water intrusions in the south basin of lake baikal on the basis of 2 yr of data december 1995 november 1997 from near bottom and near surface thermistor strings monthly conductivity temperature depth ctd profiles and a near bottom current meter all collected near the south basin maximum depth of 1 461 in the data show intrusions into the greatest depths with temperatures of 0 08 0 20degreesc below ambient similar to3 33 to similar to3 38degreesc at maximum depth the intrusions were observed three times per year between january and june when surface water is always cooler than deep water with durations of a few at least 1 3 days the estimated water input ranged from 1 to 10 km 3 per event and the annually accumulated volume was estimated to be 10 30 km 3 which is significantly less than the steady state indirect estimates of 30 70 km 3 yr 1 to the permanently stratified deep water depth 300 in this indicates that not all of the cold intrusions reach the deepest area because the cooling of the near bottom waters was not accompanied by a significant increase in ion or particle content and because deep sediment traps did not contain significant enrichments of minerogenic particles we concluded that selenga river inflow is not a possible source of the cold intrusions two ctd profiles in june 1996 and 1997 showed lower temperature throughout the deep water as expected from thermobaric instabilities the required downwelling is definitely not occurring in the pelagic interior but most probably by near coast counterclockwise currents the source of the regularly occurring deep intrusions is clearly cold surface water but the actual mechanism is uncertain

numerical simulation of the weddell sea pack ice to investigate the role of ice dynamics on the seasonal cycle of antarctic sea ice a series of 2 year simulations of the weddell sea pack ice are carried out the simulations employ the dynamic thermodynamic model developed by hibler 1979 and use a 1 day time step on an 18 15 grid with a resolution of 222 km daily atmospheric data from 1979 are used to drive the simulations with atmospheric temperature fields modified to reflect buoy observations the simulations yield a seasonal cycle of ice with maximum and minimum extents close to that observed except for portions of the western weddell the advance of the ice is found to be primarily thermodynamic in nature while the rapid decay depends critically on the presence of both leads and lateral ice advection the average fraction of open water is substantial even in winter and varies from a minimum of 10 in september to a maximum of 35 in march these values are in general agreement with estimates from satellite microwave data in early summer the ice motion causes a residual tongue of ice to extend eastward from the antarctic peninsula in agreement with observations mean ice thicknesses are consistent with observations and vary from about 3 m in the perennial ice in the western weddell to 1 m in first year ice in the eastern weddell possible feedback between the ice extent and atmosphere are investigated by simulations with the surface air temperatures constrained to below freezing values in the presence of ice these coupled simulations yield a more realistic rapid decay in summer with dynamics included but an unrealistically small decay without dynamics simulated ice drift results yield mean drift rates of about 5 km day in good agreement with buoy drift observations but with slightly inadequate northward transport in the western weddell near the ice edge the drift rates are relatively insensitive to the ice strength near the coast however lower strengths are found to yield a decrease in northward drift rates

impact of lake level change on deep water renewal and oxic conditions in deep saline lake van turkey 1 changes in the hydrological regime of the saline closed basin lake van a large deep lake in eastern turkey resulted in a lake level increase by about 2 m between 1988 and 1995 followed by a 1 5 m decrease until 2003 and a relatively constant lake level thereafter based on measurements of transient tracers sulfur hexafluoride cfc 12 3h 3he 4he ne dissolved oxygen light transmission conductivity temperature depth profiles and thermistor data we investigate the implications associated with lake level fluctuations for deep water renewal and oxygenation our data suggest that deep water renewal was significantly reduced in lake van between 1990 and 2005 this change in mixing conditions resulted in the formation of a more than 100 m thick anoxic deep water body below 325 m depth apparently the freshwater inflows responsible for the lake level rise between 1988 and 1995 decreased the salinity of the surface water sufficiently that the generation of density plumes during winter cooling was substantially reduced compared to that in the years before the lake level rise significant renewal and oxygenation of the deep water did not occur until at least 2005 although by 2003 the lake level was back to almost the same level as in 1988 this study suggests that short term changes in the hydrological regime resulting in lake level changes of a couple of meters can lead to significant and long lasting changes in deep water renewal and oxic conditions in deep saline lakes

physical and chemical properties of the waters of saline lakes and their importance for deep water renewal lake issyk kul kyrgyzstan the relationships between electrical conductivity temperature salinity and density are studied for brackish lake issyk kul these studies are based on a newly determined major ion composition which for the open lake shows a mean absolute salinity of 6 06 g kg 1 the conductivity temperature relationship of the lake water was determined experimentally showing that the lake water is about 1 25 times less conductive than seawater diluted to the same absolute salinity as that of the lake water based on these results an algorithm is presented to calculate salinity from in situ conductivity measurements applied to the field data this shows small but important vertical salinity variations in the lake with a salinity maximum at 200 m and a freshening of the surface water with increasing proximity to the shores the algorithm we adopt to calculate density agrees well with earlier measurements and shows that at 20 c and 1 atm lake issyk kul water is about 530 g m 3 denser than seawater at the same salinity the temperature of maximum density at 1 atm is about 0 15 c lower than that for seawater diluted to the same salinity despite its small variations salinity plays an important role together with temperature changes in the static stability and in the production of deep water in this lake changes in salinity may have had important consequences on the mixing regime and the fate of inflowing river water over geological time uncharged silicic acid is negligible for the stability of the water column except near an 15 m thick nepheloid layer observed at the bottom of the deep basin copyright 2002 elsevier science ltd

transient electromagnetic modeling of shallow a type sections with 3 d inhomogeneities a hard rock area underlain by granitic gneissic or basaltic rocks often has an a type three layer geoelectric section in which resistivity increases with depth the middle layer of moderate resistivity caused by fracturing fissuring that lies between the surface weathered layer and the substratum of unfractured rock is not a good target for a direct current dc resistivity sounding since it is generally suppressed in the observations moreover its definition requires expanding the electrode spacing to a length several times the depth of the target layer and this may be a drawback if the target layer is either laterally variable or limited in its horizontal extent we first studied the transient electric field of a horizontal electric dipole hed source excited by a step turn off current for a 1 d model of an a type geoelectric section the results of this theoretical study are presented as graphs of normalized apparent resistivity versus a time related dimensionless parameter irrespective of the sepa

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

density driven exchange between the basins of lake lucerne switzerland traced with the 3h 3he method lake lucerne is divided by sills into four major and two minor basins during winter differential vertical mixing due to non uniform wind exposure and different total dissolved solid concentrations in the main tributaries of the lake cause considerable interbasin density gradients these gradients induce density driven currents across the sills that contribute significantly to the deep water exchange in the basins and gradually reduce the density gradients during summer over a period of 2 yr 1990 1992 the spatial and temporal evolution of water density and water age measured by the 3 h 3 he method was investigated variation in water age between the different basins and the occasional occurrence of age inversions older water overlying younger one can be explained in terms of the observed density distribution and the exchange flows the density gradients cause water age provides an integral measure of the magnitude of deep water renewal which in some basins can be roughly separated into contributions from density driven currents and wind induced vertical mixing by correlating water age with dissolved helium and oxygen concentrations radiogenic helium fluxes and average oxygen depletion rates were determined for the main basins of the lake the helium flux was between 1 and 2x10 10 atoms m 2 s 1 indicating dynamic equilibrium with helium production in the underlying crust oxygen depletion rates per unit sediment area were roughly equal in all basins between 220 and 290 g m 2 yr 1 whereas volumetric depletion rates varied from 1 8 g m 3 yr 1 in the deepest basin to 10 g m 3 yr 1 in the shallowest