structure and breakup history of the rifted margin of west antarctica in relation to cretaceous separation from zealandia and bellingshausen plate motion 1 geophysical data acquired using r v polarstern constrain the structure and age of the rifted oceanic margin of west antarctica west of the antipodes fracture zone the 145 km wide continent ocean transition zone cotz of the marie byrd land sector resembles a typical magma poor margin new gravity and seismic reflection data indicates initial continental crust of thickness 24 km that was stretched 90 km farther east the bellingshausen sector is broad and complex with abundant evidence for volcanism the cotz is 670 km wide and the nature of crust within the cotz is uncertain margin extension is estimated to be 106 304 km in this sector seafloor magnetic anomalies adjacent to marie byrd land near the pahemo fracture zone indicate full spreading rate during c33 c31 80 68 myr of 60 mm yr 1 increasing to 74 mm yr 1 at c27 62 myr and then dropping to 22 mm yr 1 by c22 50 myr spreading rates were lower to the west extrapolation towards the continental margin indicates initial oceanic crust formation at around c34y 84 myr subsequent motion of the bellingshausen plate relative to antarctica 84 62 myr took place east of the antipodes fracture zone at rates 40 mm yr 1 typically 5 20 mm yr 1 the high extension rate of 30 60 mm yr 1 during initial margin formation is consistent with steep and symmetrical margin morphology but subsequent motion of the bellingshausen plate was slow and complex and modified rift morphology through migrating deformation and volcanic centers to create a broad and complex cotz

passive acoustic localization of the atlantic bottlenose dolphin using whistles and echolocation clicks a method for localization and tracking of calling marine mammals was tested under realistic field conditions that include noise multipath and arbitrarily located sensors experiments were performed in two locations using four and six hydrophones with captive atlantic bottlenose dolphins tursiops truncatus acoustic signals from the animals were collected in the field using a digital acoustic data acquisition system the data were then processed off line to determine relative hydrophone positions and the animal locations accurate hydrophone position estimates are achieved by pinging sequentially from each hydrophone to all the others a two step least squares algorithm is then used to determine sensor locations from the calibration data animal locations are determined by estimating the time differences of arrival of the dolphin signals at the different sensors the peak of a matched filter output or the first cycle of the observed waveform is used to determine arrival time of an echolocation click cross correlation between hydrophones is used to determine inter sensor time delays of whistles calculation of source location using the time difference of arrival measurements is done using a least squares solution to minimize error these preliminary experimental results based on a small set of data show that realistic trajectories for moving animals may be generated from consecutive location estimates

a model of gas buildup and release in crater lakes the sudden release of carbon dioxide gas which may accumulate gradually within the stratified water bodies of a crater lake caused two fatal disasters in cameroon during the past decade we model the various processes that may have led to the release by considering 1 gas injection 2 an internal triggering mechanism 3 propagation of a disturbance after triggering and 4 the forces that end the outburst we suggest that the 1986 lake nyos outburst was triggered at the lake bottom the final explosive stage of the release ended quickly when a sufficiently large volume of gas bubbles prevented circulation of water eddies within the lake a cellular automaton model is used to estimate the amount of carbon dioxide gas released and the characteristic time interval between successive outbursts if both the gas accumulation rate and the diffusion rate of carbon dioxide through water are constant then rapid gas release will occur at fairly regular intervals in which case the amount of gas released from lake nyos is 0 17 0 05 km3 at standard temperature and pressure each 37 10 years it is possible however that an external event could trigger a sudden release or that the diffusion rate of carbon dioxide may change as more gas accumulates which could shorten the release time

seismic stratigraphic record of the amundsen sea embayment shelf from pre glacial to recent times evidence for a dynamic west antarctic ice sheet studies of the sedimentary architecture and characteristics of the antarctic continental margin provide clues about past ice sheet advance retreat cycles and help improve constraints for paleo ice dynamic models since early glacial periods a first seismostratigraphic analysis of the amundsen sea embayment shelf and slope of west antarctica reveals insights into the structural architecture of the continental margin and shows stages of sediment deposition erosion and transport reflecting the history from pre glacial times to early glaciation and to the late pleistocene glacial interglacial cycles the shelf geometry consists of a large pre and syn rift basin in the middle shelf region between basement cropping out on the inner shelf and buried basement ridge and highs on the outer shelf a subordinate basin within the large basin on the mid shelf may be associated with motion along an early west antarctic rift system branch at least 4 km of pre glacial strata have been eroded from the present inner shelf and coastal hinterland by glacial processes six major sedimentary units ass 1 to ass 6 separated by five major erosional unconformities ass u1 to ass u5 are distinguished from bottom to top unconformity ass u4 results from a major truncational event by glacial advance to the middle and outer shelf which was followed by several episodes of glacial advance and retreat as observed from smaller scale truncational unconformities within the units above ass u4 some of the eroded sediments were deposited as a progradional wedge that extends the outer shelf by 25 to 65 km oceanward of the pre glacial shelf break we compare the observed seismic characteristics with those of other antarctic shelf sequences and assign an early cretaceous age to bottom sedimentary unit ass 1 a late cretaceous to oligocene age to unit ass 2 an early to mid miocene age to unit ass 3 a mid miocene age to unit ass 4 a late miocene to early pliocene age to unit ass 5 and a pliocene to pleistocene age to the top unit ass 6 buried grounding zone wedges in the upper part of unit ass 5 on the outer shelf suggest pronounced warming phases and ice sheet retreats during the early pliocene as observed for the ross sea shelf and predicted by paleo ice sheet models our data also reveal that on the middle and outer shelf the flow path of the pine island thwaites paleo ice stream system has remained stationary in the central pine island trough since the earliest glacial advances which is different from the ross sea shelf where glacial troughs shifted more dynamically this study and its stratigraphic constraints will serve as a basis for future drilling operations required for an improved understanding of processes and mechanisms leading to change in the west antarctic ice sheet such as the contemporary thinning and grounding line retreat in the amundsen sea drainage sector

long term sea level fluctuations driven by ocean basin dynamics earth9s long term sea level history is characterized by widespread continental flooding in the cretaceous period 145 to 65 million years ago followed by gradual regression of inland seas however published estimates of the late cretaceous sea level high differ by half an order of magnitude from 40 to 250 meters above the present level the low estimate is based on the stratigraphy of the new jersey margin by assimilating marine geophysical data into reconstructions of ancient ocean basins we model a late cretaceous sea level that is 170 85 to 270 meters higher than it is today we use a mantle convection model to suggest that new jersey subsided by 105 to 180 meters in the past 70 million years because of north america9s westward passage over the subducted farallon plate this mechanism reconciles new jersey margin based sea level estimates with ocean basin reconstructions

a numerical simulation of the evolution of temperature and co2 stratification in lake nyos since the 1986 disaster a one dimensional numerical model has been applied to simulate the evolution of the temperature and co2 stratification in lake nyos since the 1986 disaster it incorporates a second moment turbulence closure scheme for mixing and heating and cooling in the upper layers of the lake the effects of inflowing stream water and input of the co2 heat and dissolved solids at the bottom of the lake are taken into account the model is initialized by conditions observed immediately after the disastrous outgassing event in 1986 and integrated forward for 10 years forced by seasonally modulated diurnal heating and nocturnal cooling and heavy summer time precipitation at the surface four possible conditions are investigated the first simulation considers the normal seasonal heating cooling cycle and steady input of heat dissolved solids and co2 at the bottom it shows that the upper layers of the lake are quite stable under normal seasonal forcing but the bottom layers reach high co2 concentrations in less than a decade the second simulation considers a brief introduction at the bottom of the lake of cooler waters that contain less co2 and temporarily destabilize the bottom layers the third and fourth simulations consider anomalous surface forcing conditions that can produce anomalous mixed layer deepening during the cooling seasons capable of releasing the co2 stored immediately below the normal mixed layer these results suggest that a destabilization of the bottom layers is more likely to lead to massive and catastrophic degassing the results also demonstrate the utility of a numerical model in investigations of caldera crater lakes such as lake nyos

one hydrophone method of estimating distance and depth of phonating dolphins in shallow water previous attempts at localizing cetaceans have generally used multiple hydrophone arrays and multichannel recording systems in this paper a low budget localization technique using only one hydrophone is described the time delays of the signals traveling via the surface and bottom reflection paths to the hydrophone relative to the direct signal are used to calculate the distance and the depth of a phonating animal only two additional measures the depth of the bottom and hydrophone have to be taken the method requires relatively shallow waters and a flat bottom surface echolocating and burst pulsing hawaiian spinner dolphins stenella longirostris at the waianae coast of oahu hawaii were localized over different bottom substrates a tracking range of up to 100 m was achieved the accuracy of the method is estimated by the total error differential technique the relative distance estimation error is below 35 and the absolute depth error below 0 7 m so that the location method is sufficiently precise for examining source levels in our study area because of its simplicity the method ideally complements sound recordings and visual sightings of marine mammals and could lead to a better understanding of the nature and use of click trains by dolphins

turbulent bubble plumes and co2 driven lake eruptions abstract we examine the motion of turbulent bubble plumes within lakes containing large quantities of dissolved co2 such as lake nyos cameroon first we describe some new laboratory experiments in which we examine the dynamics of turbulent bubbles plumes produced by electrolysis in an aqueous solution these experiments were analysed to determine the entrainment rate into the plume using the experimental results we then develop a model of the motion of a bubble plume through a co2 rich lake the model identifies that for a sufficient amount of dissolved co2 in the lake or a sufficient flux of co2 at the base of the lake a turbulent bubble plume can rise through the lake and erupt at the surface the model predicts that owing to the rapid entrainment of ambient fluid the surface flux of co2 may be 104 105 times greater than that at the base of the lake we also show that the return flow in the lake acts to decrease the co2 content at all depths as the co2 is erupted at the surface and that this eventually leads to termination of the activity the model provides the first quantitative analysis that co2 saturated lakes can overturn convectively and lead to rapid degassing events such as occurred at lake nyos in cameroon in 1986

long range acoustic detection and localization of blue whale calls in the northeast pacific ocean analysis of acoustic signals recorded from the u s navy s sound surveillance system sosus was used to detect and locate blue whale balaenoptera musculus calls offshore in the northeast pacific the long low frequency components of these calls are characteristic of calls recorded in the presence of blue whales elsewhere in the world mean values for frequency and time characteristics from field recorded blue whale calls were used to develop a simple matched filter for detecting such calls in noisy time series the matched filter was applied to signals from three different sosus arrays off the coast of the pacific northwest to detect and associate individual calls from the same animal on the different arrays a u s navy maritime patrol aircraft was directed to an area where blue whale calls had been detected on sosus using these methods and the presence of a vocalizing blue whale was confirmed at the site with field recordings from sonobuoys

temperate rainforests near the south pole during peak cretaceous warmth the mid cretaceous period was one of the warmest intervals of the past 140 million years1 5 driven by atmospheric carbon dioxide levels of around 1 000 parts per million by volume6 in the near absence of proximal geological records from south of the antarctic circle it is disputed whether polar ice could exist under such environmental conditions here we use a sedimentary sequence recovered from the west antarctic shelf the southernmost cretaceous record reported so far and show that a temperate lowland rainforest environment existed at a palaeolatitude of about 82 s during the turonian santonian age 92 to 83 million years ago this record contains an intact 3 metre long network of in situ fossil roots embedded in a mudstone matrix containing diverse pollen and spores a climate model simulation shows that the reconstructed temperate climate at this high latitude requires a combination of both atmospheric carbon dioxide concentrations of 1 120 1 680 parts per million by volume and a vegetated land surface without major antarctic glaciation highlighting the important cooling effect exerted by ice albedo under high levels of atmospheric carbon dioxide multi proxy core data and model simulations support the presence of temperate rainforests near the south pole during mid cretaceous warmth indicating very high co2 levels and the absence of antarctic ice

simulated atlantic multidecadal oscillation during the holocene abstractthe atlantic multidecadal oscillation amo and its possible change during the holocene are examined in this study using long term simulations of the earth system model community earth system models cosmos a quasi persistent 55 80 yr cycle characterizing in the north atlantic sea surface temperature is highly associated with the multidecadal variability of the atlantic meridional overturning circulation amoc during the holocene this mode can be found throughout the holocene indicating that the amo is dominated by internal climate variability stronger than normal amoc results in warmer than normal surface temperature spreading over almost the whole north hemisphere in particular the north atlantic ocean during the warm phase of the amo more precipitation is detected in the north atlantic low and high latitudes it also generates a dipolar seesaw pattern in the sea ice anomaly the results reveal that the influence of the amo can be amplified by a more vigorous amoc variability during t

climate warming during antarctic ice sheet expansion at the middle miocene transition during the expansion of the antarctic ice sheet about 14 million years ago sea surface temperatures in the southern ocean rose climate model simulations suggest that this short lived warming was related to changes in ocean atmosphere circulation induced by the growth of the ice sheet

abrupt glacial climate shifts controlled by ice sheet changes the volume of the northern hemisphere ice sheet controlled abrupt millennial scale climate changes during the last glacial dansgaard oeschger events are millennial scale warm periods interrupting cold glacial climates although they are perhaps the most prominent example of abrupt change observed in the ice core record of the past 800 000 years their underlying physical controls remain debated xu zhang and colleagues now use a fully coupled climate model to show that dansgaard oeschger events tend to occur when ice sheets are at an intermediate height a condition in which small perturbations to the coupled atmosphere ocean sea ice system can lead to rapid nonlinear feedbacks and abrupt changes in climate during glacial periods of the late pleistocene an abundance of proxy data demonstrates the existence of large and repeated millennial scale warming episodes known as dansgaard oeschger do events1 this ubiquitous feature of rapid glacial climate change can be extended back as far as 800 000 years before present bp in the ice core record2 and has drawn broad attention within the science and policy making communities alike3 many studies have been dedicated to investigating the underlying causes of these changes but no coherent mechanism has yet been identified3 4 5 6 7 8 9 10 11 12 13 14 15 here we show by using a comprehensive fully coupled model16 that gradual changes in the height of the northern hemisphere ice sheets nhiss can alter the coupled atmosphere ocean system and cause rapid glacial climate shifts closely resembling do events the simulated global climate responses including abrupt warming in the north atlantic a northward shift of the tropical rainbelts and southern hemisphere cooling related to the bipolar seesaw are generally consistent with empirical evidence1 3 17 as a result of the coexistence of two glacial ocean circulation states at intermediate heights of the ice sheets minor changes in the height of the nhiss and the amount of atmospheric co2 can trigger the rapid climate transitions via a local positive atmosphere ocean sea ice feedback in the north atlantic our results although based on a single model thus provide a coherent concept for understanding the recorded millennial scale variability and abrupt climate changes in the coupled atmosphere ocean system as well as their linkages to the volume of the intermediate ice sheets during glacials

water and gas chemistry of lake nyos and its bearing on the eruptive process abstract the isotopic and chemical composition of water samples collected from lake nyos some two and eight weeks after the eruption of august 21 1986 point to the existence of three distinct mixing regimes involving three water components an essentially homogeneous unmixed body of water at depths 100 m overlain by water increasingly affected by surface evaporation and a 5 10 m layer containing recent but pre eruption rain water the cationic constituents na k mg ca mn fe of the lake water correspond to the dissolution of around 0 1 g of local rock the waters are close to saturation with respect to siderite the composition of the gas dissolved in the deep lake waters 0 65 b w of co2 pco2 4 4b corresponds in mmol mol 1 to 996 co2 2 0 ch4 2 0 n2 0 05 ar 0 004 he 0 0002 h2 0 0001 ne co 2 13 c 3 4 and of he rair 5 5 suggest deep magmatic origins the 13c and 2h content of ch4 organic sedimentary origin the presence of aromatic hydrocarbons indicates very high temperatures of hydrocarbon formation exsolution of gas will first lead to the precipitation of siderite then iron hydroxide the chemistry of the lake waters points to a loss of some 240 000 t of co2 from the upper 100 m of the lake their isotopic composition is consistent with the assumption that the eruption was triggered by the accumulation of cold rain waters at the lake surface prior to the eruption inducing partial convective overturn there is no need to invoke addition of chemical or isotopic constituents from deeper levels during the eruption

mid cretaceous albian santonian sea surface temperature record of the tropical atlantic ocean paleoclimate records of geologic time periods characterized by extreme global warmth such as the mid cretaceous are important for a better understanding of the earth9s climate system operating in an exceptionally warm mode here we applied an organic geochemical proxy tex 86 on organic matter rich albian santonian sediments recovered from ocean drilling program leg 207 sites 1258 and 1259 on demerara rise to reconstruct sea surface temperatures ssts in the western equatorial atlantic preceded by a stepwise cenomanian warming trend 31 35 c the onset of the cretaceous thermal maximum coincided here with the cenomanian turonian boundary event once established this extreme warm climate regime characterized by averaged tropical ssts close to 35 c lasted up to the turonian coniacian transition two pronounced cooler intervals 2 3 c interrupt this otherwise remarkably stable record providing the first 18 o independent evidence for middle turonian cooling that previously has been attributed to glacioeustatic sea level lowering coniacian ssts decline stepwise reaching a minimum in the santonian 32 33 c where cooling is most pronounced presumably concomitant with the first progressive opening of a deep water passage through the equatorial atlantic gateway

an inference on the process of gas outburst from lake nyos cameroon abstract a large volume of lethal gas was released from lake nyos in the northwest province of cameroon on august 21 1986 some 50 days after the event a hydro physical and chemical survey of lake nyos was carried out by four japanese scientists including the author vertical density distributions of lake water showed remarkably stable stratification through the whole water column chemical analyses showed high concentrations of dissolved co2 and fe which contribute to stable stratification assuming an initial saturation of dissolved co2 in lake water released gas volume was estimated to be 0 68 km3 as a difference between saturated and remaining gas contents in the present lake temperature drops due to quasiadiabatic expansion of co2 gas exsolved from various water layers were estimated for every 10 m layer thickness assuming a constant temperature distribution and a complete thermal exchange between expanding gas and lake water the calculated temperature profile agreed well with the profile measured by ctd conductivity temperature depth profiler the height of the gas cloud over the lake and the flow velocity of draining gas from the outlet of the rim were evaluated using a simple geometrical flux model assuming a sinusoidal variation of ejection with equal volume mixing with air and head loss coefficient of cd 0 3 the calculated maximum gas height of 110 m and the corresponding drain velocity of 19 m s 1 were obtained

high temperatures in the late cretaceous arctic ocean to understand the climate dynamics of the warm equable greenhouse world of the late cretaceous period it is important to determine polar palaeotemperatures the early palaeoceanographic history of the arctic ocean has however remained largely unknown because the sea floor and underlying deposits are usually inaccessible beneath a cover of floating ice a shallow piston core taken from a drifting ice island in 1970 fortuitously retrieved unconsolidated upper cretaceous organic rich sediment from alpha ridge a submarine elevated feature of probable oceanic origin a lack of carbonate in the sediments from this core has prevented the use of traditional oxygen isotope palaeothermometry here we determine arctic palaeotemperatures from these upper cretaceous deposits using tex86 a new palaeothermometer that is based on the composition of membrane lipids derived from a ubiquitous component of marine plankton crenarchaeota from these analyses we infer an average sea surface temperature of approximately 15 degrees c for the arctic ocean about 70 million years ago this calibration point implies an equator to pole gradient in sea surface temperatures of approximately 15 degrees c during this interval and by extrapolation we suggest that polar waters were generally warmer than 20 degrees c during the middle cretaceous approximately 90 million years ago

tropical warming and intermittent cooling during the cenomanian turonian oceanic anoxic event 2 sea surface temperature records from the equatorial atlantic oceanic anoxic event 2 oae 2 occurring during the cenomanian turonian c t transition is evident from a globally recognized positive stable carbon isotopic excursion and is thought to represent one of the most extreme carbon cycle perturbations of the last 100 myr however the impact of this major perturbation on and interaction with global climate remains unclear here we report new high resolution records of sea surface temperature sst based on tex86 and 18o of excellently preserved planktic foraminifera and stable organic carbon isotopes across the c t transition from black shales located offshore suriname french guiana demerara rise ocean drilling program leg 207 site 1260 and offshore senegal cape verde basin deep sea drilling project leg 41 site 367 at site 1260 where both sst proxy records can be determined a good match between conservative sst estimates from tex86 and 18o is observed we find that late cenomanian ssts in the equatorial atlantic ocean 33 c were substantially warmer than today 27 29 c and that the onset of oae 2 coincided with a rapid shift to an even warmer 35 36 c regime within the early stages of the oae a marked 4 c cooling to temperatures lower than pre oae conditions is observed however well before the termination of oae 2 the warm regime was reestablished and persisted into the turonian our findings corroborate the view that the c t transition represents the onset of the interval of peak cretaceous warmth more importantly they are consistent with the hypotheses that mid cretaceous warmth can be attributed to high levels of atmospheric carbon dioxide co2 and that major oaes were capable of triggering global cooling through the negative feedback effect of organic carbon burial led co2 sequestration evidently however the factors that gave rise to the observed shift to a warmer climate regime at the onset of oae 2 were sufficiently powerful that they were only briefly counterbalanced by the high rates of carbon burial attained during even the most extreme interval of organic carbon burial in the last 100 myr

gas buildup in lake nyos cameroon the recharge process and its consequences the gases dissolved in lake nyos cameroon were quantified recently december 1989 and september 1990 by two independent techniques in situ measurements using a newly designed probe and laboratory analyses of samples collected in pre evacuated stainless steel cylinders the highest concentrations of co2 and ch4 were 0 30 mol kg and 1 7 mmol kg respectively measured in cylinders collected 1 m above lake bottom probe measurements of in situ gas pressure at three different stations showed that horizontal variations in total dissolved gas were negligible total dissolved gas pressure near the lake bottom is 1 06 mpa 10 5 atm 50 as high as the hydrostatic pressure of 2 1 mpa 21 atm comparing the co2 profile constructed from the 1990 data to one obtained in may 1987 shows that co2 concentrations have increased at depths to below 150 m based on these profiles the average rate of co2 input to bottom waters was 2 6 108 mol a increased deep water temperatures require an average heat flow of 0 32 mw into the hypolimnion over the same time period the transport rates of co2 heat and major ions into the hypolimnion suggest that a low temperature reservoir of free co2 exists a short distance below lake bottom and that convective cycling of lake water through the sediments is involved in transporting the co2 into the lake from the underlying diatreme increased ch4 concentrations at all depths below the oxycline and a high14c content 41 modern in the ch4 4 m above lake bottom show that much of the ch4 is biologically produced within the lake the ch4 production rate may vary with time but if the co2 recharge rate remains constant co2 saturation of the entire hypolimnion below 50 m depth would require 140a given present day concentrations

rollover in volcanic crater lakes a possible cause for lake nyos type disasters abstract seemingly stably stratified fluids that is a heavier layer of fluid underlying an upper layer of lighter fluid can overturn if there is a heat flux through the system such events are termed rollover in the engineering literature occurring for instance in liquid natural gas tanks they take place as well in lakes and ponds in all such cases the stratification starts off with the heavier more dense fluid underlying lighter convection driven mixing at the stratification interface due to the heat flux as well as other processes serves to minimize with time the stabilizing density differences which may eventually cause the stratification to invert if gas has been contained under pressure in the lower layer this gas may explosively vent from the fluid as it suddenly rises to the top such as occurs in liquid natural gas tanks where rollover is a hazard these processes are quantifiable and are applied here to various scenarios that might refer to volcanic crater lakes whose lower layers are charged with volatiles provided herein are some examples of calculated conditions and calculated time of evolution leading to rollover with attendant release of gases from supersaturated ascending fluids these calculations suggest rollover could occur in volcanic lakes the august 1986 gas release at lake nyos is employed as an example these estimates were made taking note that water is commonly supersaturated in co2

clay mineral distribution in surface sediments of the south atlantic sources transport and relation to oceanography abstract surface samples mostly from abyssal sediments of the south atlantic from parts of the equatorial atlantic and of the antarctic ocean were investigated for clay content and clay mineral composition maps of relative clay mineral content were compiled which improve previous maps by showing more details especially at high latitudes large scale relations regarding the origin and transport paths of detrital clay are revealed high smectite concentrations are observed in abyssal regions primarily derived from southernmost south america and from minor sources in southwest africa near submarine volcanoes of the antarctic ocean south sandwich bouvet island smectite contents exhibit distinct maxima which is ascribed to the weathering of altered basalts and volcanic glasses the illite distribution can be subdivided into five major zones including two maxima revealing both south african and antarctic sources a particularly high amount of mg and fe rich illites are observed close to east antarctica they are derived from biotite bearing crystalline rocks and transported to the west by the east antarctic coastal current chiorite and well crystallized dioctaedral illite are typical minerals enriched within the subantarctic and polarfrontal zone but of minor importance off east antarctica kaolinite dominates the clay mineral assemblage at low latitudes where the continental source rocks west africa brazil are mainly affected by intensive chemical weathering surprisingly a slight increase of kaolinite is observed in the enderby basin and near the filchner ronne ice shelf the investigated area can be subdivided into ten large scale clay facies zones with characteristic possible source regions and transport paths clay mineral assemblages of the largest part of the south atlantic especially of the western basins are dominated by chlorite and illite derived from the antarctic peninsula and southernmost south america and supported by advection within the circumantarctic deep water flow in contrast the east antarctic provinces are relatively small assemblages of the eastern basins north of 30 s are strongly influenced by african sources controlled by weathering regimes on land and by a complex interaction of wind river and deep ocean transport the strong gradient in clay mineral composition at the brazilian slope indicate a relatively low contribution of tropically derived assemblages to the western basins

the international bathymetric chart of the southern ocean ibcso version 1 0 a new bathymetric compilation covering circum antarctic waters the international bathymetric chart of the southern ocean ibcso version 1 0 is a new digital bathymetric model dbm portraying the seafloor of the circum antarctic waters south of 60 degrees s

the lake nyos gas disaster chemical and isotopic evidence in waters and dissolved gases from three cameroonian crater lakes nyos monoun and wum abstract to better understand the cause of the nyos gas disaster of august 21 1986 we conducted geochemical and limnological surveys in october 1986 of three lakes nyos monoun and wum which are located in the cameroon volcanic zone that is characterized by a prevalence of young alkaline basalts and basanitoids lake wum was studied as a non active control co2 is dissolved in significant concentrations about 1 5 of saturation in gas active lakes nyos and monoun but is virtually absent in lake wum stable isotopic ratios of total dissolved carbon 13c 3 for nyos and 5 5 for monoun and of helium 5 7 ratm for nyos and 3 6 ratm for monoun indicate a mantle origin of these gases however so42 and cl concentrations are found to be very low concentrations of dissolved chemical species like fe2 mg2 ca2 and hco3 are high in the two gas active lakes whereas they are very low in the gas inactive lake high salinities in the gas active lakes are probably due to dissolution of indigenous mafic rocks and transported lateritic soil in acidic co2 rich warm water the gas active lakes are characterized by increasing temperature and salinity with increasing depth indicating an active influx of heat and dissolved materials at the bottom density estimates show that the lake water is stably stratified in spite of the inverse temperature profile of the lakes on account of dissolved chemical species the concentrations of dissolved carbonate species co2 aq and hco3 are positively correlated with those of ionic dissolved species indicating their common occurrence in the bottom water the august 1986 gas bursts from lake nyos were most likely caused by rapid exsolution of dissolved co2 within the lake an explosive process such as a phreatic eruption or a co2 gas jetting from beneath the bottom is unlikely because of low concentrations of cl and so42 no oxygen isotopic shift low turbidity and no reported perturbation of the bottom sediments exsolution of co2 bubbles could occur if co2 saturated bottom water was displaced upwards by an increased influx of high salinity water from the bottom during the rainy season exsolution of co2 at the upper layers was possibly accelerated by upwelling of a two phase fluid co2 bubbles and solution a mechanism known as a pneumatic lift pump resulting in discharge of a large amount of co2 gas the h2s concentration in the gas cloud must have been kept far below the lethal level because of a high fe2 concentration of the lake water

comparison between visual and passive acoustic detection of finless porpoises in the yangtze river china recently sonar signals and other sounds produced by cetaceans have been used for acoustic detection of individuals and groups in the wild however the detection probability ascertained by concomitant visual survey has not been demonstrated extensively the finless porpoises neophocaena phocaenoides have narrow band and high frequency sonar signals which are distinctive from background noises underwater sound monitoring with hydrophones b k8103 placed along the sides of a research vessel concurrent with visual observations was conducted in the yangtze river from wuhan to poyang lake in 1998 in china the peak to peak detection threshold was set at 133 db re 1 mu pa with this threshold level porpoises could be detected reliably within 300 m of the hydrophone in a total of 774 km cruise 588 finless porpoises were sighted by visual observation and 44 864 ultrasonic pulses were recorded by the acoustical observation system the acoustic monitoring system could detect the presence of the finless porpoises 82 of the time a false alarm in the system occurred with a frequency of 0 9 the high frequency acoustical observation is suggested as an effective method for field surveys of small cetaceans which produce high frequency sonar signals c 2001 acoustical society of america

reconstruction of the west antarctic ice sheet in pine island bay during the last glacial maximum and its subsequent retreat history abstract marine geological and geophysical studies were conducted to determine the late quaternary glacial history of the west antarctic ice sheet in pine island bay antarctica the data set includes sea floor imagery in the form of multibeam swath bathymetry and deep tow side scan sonar surveys distribution of sedimentary deposits and basal surface conditions are revealed through intermediate resolution seismic data and chirp 3 5 khz sub bottom profiles sedimentary deposits were sampled with piston cores and calcareous material was dated using ams radiocarbon techniques results from the study indicate the ice sheet was grounded on the outer shelf during its maximum extent sometime in the past thick ice flowing slowly and resting on crystalline bedrock was influenced by significant amounts of subglacial meltwater on the inner shelf thinner but more rapidly flowing ice characterized the seaward extent of the ice sheet which was grounded on a sedimentary substrate deglaciation occurred in two phases beginning soon after the last glacial maximum the outer most extension of the ice sheet retreated gradually pausing on a bathymetric high on the middle shelf by 16 000 14c years ago between 16 000 and 12 000 14c years ago ice sheet retreat resumed and may have proceeded rapidly to reach a present day position by 10 000 14c years ago

recent ph and co2 profiles at lakes nyos and monoun cameroon implications for the degassing strategy and its numerical simulation abstract in situ ph profiles are reported for the first time for lakes nyos and monoun the ph profiles were converted to co2 profiles using hco3 profiles calculated from conductivity data recent observations 1993 1996 at lake nyos indicates that co2 still accumulates below 180 m depth at a rate of 125 mmol year 1 at lake monoun the majority of co2 is present below a depth of 60 m only 25 m below the saturation depth consequently a potential danger of gas explosion is high at both lakes and artificial degassing of the lakes should be performed as soon as possible a system for industrial degassing of the lakes is proposed the system based on the self sustained gas lift principle consists of multiple pipes 14 cm in diameter with different intake depths 12 pipes for lake nyos four each at 185 195 and 205 m and three pipes for lake monoun at 70 80 and 90 m the stepped degassing at different depths is intended to keep the maximum stability of the lakes the proposed degassing operation was simulated using the dyresm code for both lakes in 5 years approximately 50 of currently dissolved co2 in lake nyos and 90 in lake monoun will be removed the expected changes in the thermal and chemical structures of the lakes as degassing proceeds will be most easily monitored with a carefully calibrated ctd equipped with a ph sensor the simulation indicates that the discharged degassed water will sink to a level of neutral buoyancy i e to a maximum of 70 m at lake nyos and 35 m at lake monoun there would be no possibility of triggering a gas explosion by this plunge of discharged water because the water present there would have already been replaced by water at lower co2 concentration during the degassing from shallower pipes

dynamics of co2 driven lake eruptions on 21 august 1986 a massive release of carbon dioxide from lake nyos in cameroon killed about 1 700 people a similar event occurred on 15 august 1984 at lake monoun also in cameroon it was suggested1 5 that the co2 released was initially dissolved in the hypolimnion dense lower layer of the lake and was released by eruptive outgassing because of its violence the nyos outburst was at first thought6 to have been volcanic but undisturbed sediments and other evidence indicate that no large volcanic eruption occurred7 9 recent experiments10 11 have shown that decompression of co2 saturated water is able to power explosive eruptions here i analyse the dynamics of co2 driven lake water eruptions by deriving an equation of state for gas liquid mixtures and using it to integrate the bernoulli equation which describes the dynamics of the bubbly flow i find that under certain conditions these eruptions can be violent the lake surface exit velocity of an initially gas saturated water parcel may reach 89m s 1 for lake nyos and 51m s 1 for lake monoun the dynamics are similar to those of water driven volcanic eruptions which are also powered by gas exsolution from a liquid

carbon dioxide bursts of lake nyos cameroon modelled as periodic supersaturation in a countercurrent reactor abstract large scale degassing of carbon dioxide from lake nyos cameroon on august 21 1986 was caused by local gas supersaturation within the lake water carbon dioxide of volcanic origin accumulates in the lake but the dissolved solids originate from leaching of the bedrock atmospheric and organic nitrogen diffuses into the lake from its surface the lake is modelled as a countercurrent chemical reactor carbon dioxide bubbles rising from the bottom sediment dissolve as aqueous co2 which control the ph of the water at about 3 8 siderite formed within the lake settles and counteracts the upwards transport of co2 rising co2 bubbles also account for upwards transport of dissolved nitrogen local gass supersaturation causes a spontaneous large scale degassing event giving rise to catastrophic bursts of co2 chemical hazard evaluation at lake nyos can only be based on monitoring of total dissolved gases since variables such as conductivity and ph are insensitive to changes in aqueous co2 hazard prevention at lake nyos can be accomplished due to the great volume of annual precipitation relative to the volume of the lake by damming of the natural outlet of the lake and draining of the co2 rich bottom layer through a pipeline resulting in the gradual replacement of the gas rich bottom layer