a 2100 year trace element and stable isotope record at decadal resolution from rice lake in the northern great plains usa a 2100 year multiple proxy record at decadal resolution from a topographically closed but hydrolog ically open lake basin was used to reconstruct changes in lake salinity and evaporative intensity and to evaluate the reliability of different proxies for inferring climatic change in the glaciated northern great plains ngp at rice lake north dakota the ostracode mg ca ratios show good correlation with other ostracode diatom and aeolian proxy records from other sites in the ngp all of these records show significant century scale periodicities which have been related to solar variability as inferred from atmospheric radiocarbon records this coherent and consistent pattern suggests that these sites record climatic variability at regional scales the interval of the mediaeval climatic anomaly from 900 to 550 cal yr bp contains two pronounced dry periods during the following little ice age a single period of frequent drought that peaked at 300 cal yr bp was bracketed by wet periods before and af

sea surface circulation variability in the ionian adriatic seas abstract the surface circulation of the ionian and adriatic seas is explored by the re analysis of available datasets that estimate the mean monthly ocean state for the 60 years long time period 1955 2015 emphasis is given to the major recurrent and transitional events in the area two circulation indices are utilized for the quantification of the cyclonic or anticyclonic circulation modes and intensity one based on the vorticity flux of the reconstructed mean monthly surface velocity field and another based on an appropriately modified version of the velocity field such quantification consequently allows for a detailed analysis of the surface circulation variability for the entire ionian and adriatic basins as well as for sub regions of particular interest discontinuities associated with possible regime shifts of the examined flow field were identified by time series analysis of the circulation indices and compared to well documented events in the hydrography of the studied area subsequently the statistically significant components of the surface circulation variability were resolved out of a red noise background in the time frequency domain and their evolution was studied the results highlight the presence of various circulation modes and reversals in different temporal scales mainly seasonal and decadal to inter decadal which are discussed in reference to the dynamics of both the sub regional western northern eastern and southern ionian as well as northern and southern adriatic and of the basin wide ionian or adriatic spatial scales the relationships of the surface circulation variability between the ionian and the adriatic basins are also assessed through wavelet coherence

proxy records of holocene storm events in coastal barrier systems storm wave induced markers abstract extreme storm events in the coastal zone are one of the main forcing agents of short term coastal system behavior as such storms represent a major threat to human activities concentrated along the coasts worldwide in order to better understand the frequency of extreme events like storms climate science must rely on longer time records than the century scale records of instrumental weather data proxy records of storm wave or storm wind induced activity in coastal barrier systems deposits have been widely used worldwide in recent years to document past storm events during the last millennia this review provides a detailed state of the art compilation of the proxies available from coastal barrier systems to reconstruct holocene storm chronologies paleotempestology the present paper aims i to describe the erosional and depositional processes caused by storm wave action in barrier and back barrier systems i e beach ridges storm scarps and washover deposits ii to understand how storm records can be extracted from barrier and back barrier sedimentary bodies using stratigraphical sedimentological micro paleontological and geochemical proxies and iii to show how to obtain chronological control on past storm events recorded in the sedimentary successions the challenges that paleotempestology studies still face in the reconstruction of representative and reliable storm chronologies using these various proxies are discussed and future research prospects are outlined

influences of forested and grassland vegetation on late quaternary ecosystem development as recorded in lacustrine sediments geosphere biosphere interactions are ubiquitous features of the earth surface yet the development of interactions between newly exposed lithologic surfaces and colonizing plants during primary succession after glaciation are lacking temporal detail to assess the nature rate and magnitude of vegetation influence on parent material and sediment delivery we analyzed ecosystem and geochemical proxies from lacustrine sediment cores at a grassland site and a forested site in the northern united states over time terrigenous inputs declined at both sites with increasing amounts of organic inputs toward present the similarities between sites were striking given that the grassland sequence began in the early holocene and the forested sequence began after the last glacial maximum multiple mechanisms of chemical weathering hydrologic transport and changes in source material potentially contribute to this pattern although there were strong links between vegetation composition and nitrogen cycling at each site it appears that changes in forest type or from oak woodland to grassland did not exert a large influence on elemental k ti si ca fe mn and s abundance in the sedimentary sequences rather other factors in the catchment lake system determined the temporal sequence of elemental abundance

the holocene history of lop nur and its palaeoclimate implications abstract the holocene hydrological history of lop nur in northwestern china s tarim basin and its response to climate conditions are inferred from a relatively well dated multi proxy record including grain size pollen and spores and soluble salt data a dated pit section ykd0301 with a depth of 570 cm in the center of the dry lop nur basin was investigated the sediments contain a total of twenty fining upward cycles as a result of strong discharge from the catchment to the lake during relatively wet conditions the fluvial sediments were probably widely dispersed by wind driven waves and currents in the large and shallow basin of lop nur higher runoff and dilution of lake waters are also indicated by lower contents of soluble salt in the sediments and recorded ostracod shells of brackish and oligohaline to freshwater species in contrast sediment sections with smaller mean grain size and fewer flood layers are dominated by aeolian sediments which were accumulated during drier periods ostracod shells are mostly lacking from these sections suggesting a higher salinity in the lake lop nur experienced six stages during the last 9 ka relatively wet conditions existed between 9 0 8 9 8 7 5 1 and 2 4 1 8 ka with periods of increased aridity in between and after 1 8 ka the lowest salinity was recorded between 8 7 and 5 1 ka which represents the wettest phase during the last 9 ka and probably the regional holocene optimum relatively wet climate conditions between 2 4 and 1 8 ka and dry conditions afterwards possibly first fostered and later on caused the devastation of the ancient loulan kingdom in the region the uppermost sediments of the section represent a massive salt crust formed during the final desiccation of the lake in the last century the effective moisture change pattern of the lop nur region is roughly consistent with synthesized holocene moisture records for western china dominated by the westerlies

early holocene aeolian dust accumulation in northeast china recorded in varved sediments from lake sihailongwan abstract annually laminated sediments of lake sihailongwan shl in northeast china preserve a high resolution record of past climatic and environmental changes thin sections of varved early holocene sediments were analyzed using light optical and scanning electron microscopic methods sediment micro facies and geochemical analyses reveal two different seasonal clastic layer types spring snow melt and dust layers dust layers distinctly differ from snow melt layers through their finer grain size better sorting higher al and lower mg and ca contents in contrast to recent lake shl sediments during the early holocene silt sized dust has been deposited after spring snow melt and after pronounced spring diatom blooms for the time interval between 11 580 and 7060 varve years bp dust layers were quantified at annual resolution highest intensities and frequencies of dust accumulation are observed in the period from 11 100 to 8200 varve years bp in good agreement with dry conditions in this time interval documented by palaeoclimatic records derived from lake sediments and loess in central asia and northern china based on modern meteorological observation of dust storms in china the dust accumulation record mirrors mainly the variation in climatic conditions governing generation of cyclone and cold air surges in the arid and semi arid mid latitude regions of china and mongolia on multidecadal and centennial time scales solar activity might have been an additional forcing factor for dust accumulation frequency in the early holocene spectral analyses reveal 205 years and 88 years periodicities in variations of dust accumulation frequency that likely reflect the de vries suess and the gleissberg solar cycles

variable ecosystem response to climate change during the holocene in northern minnesota usa both terrestrial and aquatic ecosystems should respond to abrupt climate changes such as those that affected the midcontinent of north america during the holocene a variety of paleorecords indicate that the onset of prolonged dry conditions in this region occurred as rapidly as 300 yr during the early holocene with a subsequent increase in moisture occurring rapidly in the late holocene here we report a 9500 yr multiproxy sediment record from deming lake minnesota usa that demonstrates only subtle dynamics during rapid climate changes that caused vegetation in the catchment to shift among pine forest open grassland and deciduous forest the most substantial changes in ecosystem properties immediately followed deglaciation of the landscape formation of the lake and initial development of pine forests in contrast there were only muted responses to pronounced mid holocene climate changes that caused vegetation in the catchment to switch from pine forest to open grassland ca 8000 yr b p and then deciduous forest ca 5400 yr b p the flux of organic and inorganic terrigenous material the processing of carbon and catchment erosion changed rapidly during the most recent shift at 3300 yr b p to the modern pine forest these changes coincided with the onset of meromictic conditions that influenced internal lake dynamics however the terrestrial influence on the lake sedimentary record gradually diminished over time indicating a trajectory of increasing catchment stabilization that was relatively impervious to dramatic regional climate changes the relative complacency of the deming lake record during the late holocene indicates relative resistance to abrupt climate change at later stages of ecosystem development

rates timing and cyclicity of holocene eolian activity in north central united states evidence from varved lake sediments most of the sediment components that accumulated in elk lake northwestern minnesota during the holocene are autochthonous or biogenic delivered to the sediment water interface on a seasonal schedule preserved in distinct annual laminae varves the main allochthonous component is detrital clastic material as measured by bulk sediment concentrations of aluminum sodium potassium titanium and quartz that enters the lake mostly as eolian dust the eolian clastic influx to elk lake was considerably greater during the mid holocene 8 4 ka than it has been for the past 4000 yr when periods of increased eolian activity correspond to the time of the little ice age and the dust bowl geochemical records of eolian activity exhibit distinct cyclicities with dominant periodicities of 400 and 84 yr

portable dense geophone array for shallow and very shallow 3d seismic reflection surveying part 2 3d imaging tests in part i of this paper we demonstrate how the use of a portable dense geophone array increases s n ratio and the ability to record faint near surface reflections the dense array can also be used as an approximate acoustical lens with appropriate prestack imaging techniques similar to those used in medical imaging and nondestructive testing such use of the array provides flexibility when imaging with sparse shot distributions and improves the overall resolution of the array we show how with prestack focusing one can extend the subsurface coverage beyond conventional common midpoint cmp coverage we study optimal imaging configurations and show that although the effective aperture of the array is reduced when focusing off center targets we can still image small targets adequately maximum aperture and therefore best target definition occur when the source and geophone arrays are on top of the target both synthetic and field results show that the limited aperture array can image very small targets

little ice age aridity in the north american great plains a high resolution reconstruction of salinity fluctuations from devils lake north dakota usa the little ice age was an interval between about ad 1500 and 1850 characterized by advancing glaciers in mountainous regions of europe and western north america however it is unclear whether this cool moist period was truly global in extent or how it was manifested in other regions with different climatic controls a high resolution reconstruction of salinity fluctuations in devils lake north dakota based on fossil diatoms ostracode shell geochemistry and bulk carbonate geochemistry indicates that saline conditions prevailed throughout much of the recent past these results suggest an arid climate in the northern great plains throughout the little ice age and that during this interval climatic gradients between the great plains and regions to both the east and west may have been quite steep

seasonal variability of the mixed layer depth in the mediterranean sea as derived from in situ profiles a new 0 5 resolution mediterranean climatology of the mixed layer depth based on individual profiles of temperature and salinity has been constructed the criterion selected is a threshold value of temperature from a near surface value at 10 m depth mainly derived by a method applied on the global de boyer montegut et al 2004 dbm04 with respect to dbm04 the main differences reside in the absence of spatial interpolation of the final fields and in the improved spatial resolution these changes to the method are necessary to reproduce the mediterranean mixed layer s behavior in the derived climatological maps the most relevant features of the basin surface circulation are reproduced as well as the areas prone of the deep water formation are clearly identified finally the role of density in the definition of the mixed layer s differing behaviors between the oriental and the occidental regions of the basin is presented

a mixed layer study of the formation of levantine intermediate water a mixed layer model is used to investigate the formation of levantine intermediate water liw over the eastern mediterranean the one dimensional model is initialized with climatological hydrography and integrated over the levantine basin with forcing by climatological surface fluxes realistic and repeated seasonal mixed layer cycles are obtained if the annual surface heat input and water loss are offset by a parameterized horizontal advection the model integrations show that liw is formed during winter in the mixed layer of the northwestern levantine the preferred formation region for liw is found through idealized experiments to be controlled by the preconditioning of the hydrography especially that of the cold cyclonic rhodes gyre rather than by the pattern of the climatological fluxes the annual mean formation rate of liw is estimated to be 1 0 sv using the climatological surface fluxes the magnitude of the annual surface fluxes alters the formation rate and modifies the formation region an additional annual heat flux reduces the formation rate of liw whereas an extra cooling enhances it as well as forming waters denser than liw in the center of the rhodes gyre

hydroclimatic change in southern manitoba since a d 1409 inferred from tree rings abstract a record of estimated annual prior august to current july precipitation derived from a regional bur oak quercus macrocarpa michx tree ring chronology indicates that southern manitoba s hydroclimate has been relatively stable over the last 200 yr although this stability was interrupted briefly by pronounced wet intervals in the late a d 1820s and 1850s hydroclimatic conditions since permanent euro canadian settlement were much less variable and persistent than those prior to a d 1790 the reconstruction indicates that the red river basin experienced extremely dry conditions between a d 1670 and 1775 with below normal precipitation occurring approximately 2 years out of 3 annual precipitation was estimated at more than two standard deviations below the mean during a d 1477 1485 1556 1595 1612 1644 1661 1743 1900 and 1980 comparisons with limnological records from north dakota and minnesota suggest that multidecadal fluctuations in regional hydroclimate have been remarkably coherent across the northeastern great plains during the last 600 yr however individual dry years in the red river basin were usually associated with larger scale drought across much of the north american interior

predicting gully occurrence at watershed scale comparing topographic indices and multivariate statistical models abstract in this study the ability of five topographic indices to predict the gully trajectories observed in two adjacent watersheds located in sicily italy was evaluated two of these indices named mspi and mtwi as far as we know have never been employed to this aim they were obtained by multiplying the stream power index spi and the topographic wetness index twi respectively by the convergence index ci the predictive ability of the topographic indices was measured by using both cut off independent auc area under the receiver operating characteristic curve and dependent statistics cohen s kappa index sensitivity specificity these statistics were calculated also for 100 mars multivariate adaptive regression splines and 100 lr logistic regression model runs which used as predictors the topographic variables i e contributing area slope steepness plan curvature and convergence index combined into the five indices performance statistics of both topographic indices and statistical models were calculated using 100 random samples of 2 m grid cells which were extracted only from flow concentration lines this was done in order to focus the validation process on where gully erosion is more likely to occur mspi achieved the best predictive skill auc 0 93 0 71 among the topographic indices and exhibited similar and better accuracy than local i e trained and validated in the same watershed and transferred i e trained in one watershed and tested in the other one lr models respectively on the other hand mspi performed similarly to transferred mars runs auc 0 92 0 71 but slightly worse than local mars runs auc 0 95 0 77 based on the results of this experiment it can be inferred that i including ci helps in detecting hollow areas where gullies are more likely to occur and ii mpsi can be a valid alternative to a data driven approach for mapping gully erosion susceptibility in areas where a gully inventory is not available which is necessary to calibrate statistical models

diffraction problems of 3d seismic imaging migration is essential to seismic imaging it is carried out by backward extrapolation of the wavefield registered on the observation surface the quality of images depends on the accuracy of the wavefield reconstruction at interior subsurface points from the theory based on the exact solution of the scalar wave equation it is known that for accurate wave extrapolation data must be obtained from an infinite observation surface limiting of migration apertures which is inevitable in practice leads to artefacts in extrapolated fields the distortion they cause in 2d and 3d imaging is different in 2d migration the artefacts known as truncation effects are much weaker than the signals being extrapolated and for this reason attract no special attention in 3d migration diffractions caused by an aperture edge are stronger and may create serious problems for a circular aperture their amplitudes are comparable to the amplitudes of the signals themselves the study of aperture diffractions is intended to help in the search for ways of either suppressing them efficiently or deliberately utilizing them in order to improve imaging in optics diffractions by an aperture play a constructive role in image making this research shows that the same may take place in seismic imaging

climate change and decadal to centennial scale periodicities recorded in a late holocene ne pacific marine record examining the role of solar forcing abstract we present a decadal scale late holocene climate record based on diatoms biogenic silica and grain size from a 12 m sediment core vec02a04 obtained from frederick sound in the seymour belize inlet complex of british columbia canada sediments are characterized by graded massive and laminated intervals laminated intervals are most common between c 2948 2708 cal yr bp and c 1992 1727 cal yr bp increased preservation of laminated sediments and diatom assemblage changes at this time suggest that climate became moderately drier and cooler relative to the preceding and succeeding intervals spectral and wavelet analyses are used to test for statistically significant periodicities in time series of proxies of primary production total diatom abundance biogenic silica and hydrology grain size preserved in the frederick sound record periodicities of c 42 53 60 70 82 89 241 243 and 380 yrs are present results are compared to reconstructed sunspot number data of solanki et al 2004 using cross wavelet transform to evaluate the role of solar forcing on ne pacific climate significant common power of periodicities between c 42 60 70 89 241 243 and of 380 yrs occur suggesting that celestial forcing impacted late holocene climate at frederick sound replication of the c 241 243 yr periodicity in sunspot time series is most pronounced between c 2900 cal yr bp and c 2000 cal yr bp broadly correlative to the timing of maximum preservation of laminated sedimentary successions and diatom assemblage changes high solar activity at the suess de vries band may have been manifested as a prolonged westward shift and or weakening of the aleutian low in the mid late holocene which would have diverted fewer north pacific storms and resulted in the relatively dry conditions reconstructed for the seymour belize inlet complex

the holocene paleosecular variation record from elk lake minnesota the paleosecular variation record of the geomagnetic field from elk lake minnesota is presented and its implications are discussed the elk lake record is compiled from measurements of four parallel cores with a 2 cm sampling interval 15 years time control is provided by radiocarbon dates and by annual laminations varves in the sediment stratigraphic control is provided by the annual laminations and by fine scale 2 5 cm variations in magnetic susceptibility the varve chronology provides improved time control for the central north american paleosecular variation record back to about 4000 years the results of this study largely confirm the results of lund and banerjee from lake st croix and kylen lake and demonstrate the general utility of holocene sediment paleomagnetic records differences between the records appear to be due to experimental procedure so minimal procedures are recommended for future work comparison of north american and european records suggests that two drifting non dipole sources one having its advent during the last 5000 years can account for much of the secular variation

diatom inferred changes in effective moisture during the late holocene from nearshore cores in the southeastern region of the winnipeg river drainage basin canada the winnipeg river drainage basin wrdb within the boreal forest region of northwest ontario is a region that is expected to be negatively affected by climate warming inferences of droughts over the past two millennia from little raleigh lake were based on two nearshore sediment cores the core locations were from depths of 12 and 15 m and were based on sufficient nearshore sediment accumulation and distance from the modern benthic to planktonic diatom boundary where a distinct shift from dominance of benthic taxa changed to dominance of planktonic taxa in surficial sediments at 11 8 m diatom inferred depth was based on a model developed from 60 surficial sediments within the study lake depth inferences indicate that prolonged periods of aridity occurred from ad 950 to 1300 corresponds to medieval climate anomaly and from ad 1625 to 1750 aridity during little ice age we found that the core collected from a depth closer to the benthic to planktonic diatom boundary was more sensitive to changes in lake level than the deeper core where planktonic diatoms dominated the assemblage the inferred low water stands of the past two millennia are well outside of the range of the past 100 years suggesting that recent drought history may not be a good estimate of future extremes

lake qinghai sediment geochemistry linked to hydroclimate variability since the last glacial abstract geochemistry of basin sediments from semi arid regions is valuable to understand past hydroclimatic changes here we investigate the links of sedimentary geochemistry rb sr ca zr toc and caco 3 carbonate mineralogy and ostracod shell 18 o of lake qinghai a basin proximal to major dust production centers at mid latitudes of the northern hemisphere to changes in depositional conditions and hydroclimate during the past 32 ka surface lacustrine sediments are characterized by low rb high sr low rb sr high caco 3 and high ca zr values in contrast to the chemical compositions of eolian loess high rb low sr high rb sr low caco 3 and low ca zr a direct comparison of soluble ca and sr in two short cores with instrumental water discharge data suggests that lacustrine precipitates in lake qinghai are dominated by authigenic aragonite formed under ca 2 limited water conditions and that the accumulation rate of aragonite dominantly depends on solute fluxes into the lake during the rainy seasons late may to september our high resolution down core records show that sediments during the last glacial 32 19 8 ka had high rb low sr low caco 3 and low ca zr indicating eolian dust loess accumulation in a desiccated basin under dry glacial conditions further supported by grain size and pollen results this type of sedimentation was maintained during the last deglacial 19 8 11 5 ka but interrupted by episodic lacustrine precipitates with high sr high caco 3 high ca zr and low rb at 11 5 ka sedimentary rb sr ca zr caco 3 and toc show dramatic and permanent changes implying an abrupt shift in the atmospheric circulation at the onset of the holocene in the lake qinghai region lacustrine precipitates have persisted throughout the holocene with a maximum during the early to mid holocene 10 5 8 0 ka since 8 0 ka the gradual and significant decreases in aragonite and sr accumulations in tandem with increasing dust deposit and more positive ostracod 18 o may be linked to a weakening of asian summer monsoons during the mid to late holocene overall our records appear to show a high sensitivity of sediment development and geochemistry in lake qinghai to the regional hydroclimate changes since the last glacial

loess record of dry climate and aeolian activity in the early to mid holocene central great plains north america thick holocene bignell loess sections provide new evidence for the timing of early to middle holocene aridity in the central great plains the immediate source of loess in these sections was dune fields just upwind based on thickness trends and grain size data thus periods of rapid loess accumulation indicate episodes of extensive dune activity under drier than present climate in typical bignell loess sections a thick zone of coarse textured loess with minimal pedogenic alteration is interpreted as a record of the most rapid sustained holocene loess accumulation optical ages indicate that loess in this zone was deposited beginning about 9000 10000 years ago at five study sites accumulation ended shortly after 6500 years ago at three sites but possibly earlier at the other two in two well dated sections the average rate of loess accumulation between 9000 10000 and 6500 years ago was about 1 6 3 5 times greater than in the late holocene thus we infer that the most extensive sustained holocene

regional aridity in north america during the middle holocene increased aridity throughout the great plains and rocky mountain region during the middle holo cene has been documented from pollen records aeolian proxy variables in lake cores and active sand dune migration varve calibration provided by a continuously varved record of the holocene from a core from elk lake northwestern minnesota shows that the influx of aeolian clastic material increased beginning about 8 ka and ended about 3 8 ka with peak aeolian activity at about 6 ka if aeolian influx to elk lake corresponds in time to aeolian influx in other lakes and to maximum dune activity in minnesota dune fields then the varve calibration in elk lake provides precise time calibration of periods of peak aeolian activity in minnesota palaeowind studies from the minnesota dune fields show that the dominant wind direction when the dunes were active was from the northwest the same as the dominant wind direction in dune fields throughout the great plains and rocky mountains if the mid holocene aeolian act

late holocene flood probabilities in the black hills south dakota with emphasis on the medieval climate anomaly abstract a stratigraphic record of 35 large paleofloods and four large historical floods during the last 2000 years for four basins in the black hills of south dakota reveals three long term flooding episodes identified using probability distributions at a d 120 395 900 1290 and 1410 to present during the medieval climate anomaly a d 900 1300 the four basins collectively experienced 13 large floods compared to nine large floods in the previous 800 years including the largest floods of the last 2000 years for two of the four basins this high concentration of extreme floods is likely caused by one or more of the following 1 instability of air masses caused by stronger than normal westerlies 2 larger or more frequent hurricanes in the gulf of mexico and atlantic ocean and or 3 reduced land covering vegetation or increased forest fires caused by persistent regional drought

the response of the aegean sea eastern mediterranean to the extreme 2016 2017 winter the exceptionally cold december 2016 over the aegean sea one of the most important dense water formation areas of the eastern mediterranean sea resulted in winter heat loss comparable to the peak eastern mediterranean transient winters 1992 1993 hydrological data sampled in march april 2017 showed that newly produced dense waters ventilated the north aegean deep basins up to density horizons of 29 35 kg m3 the water column ventilation was unable to reach the bottom as the present upper thermohaline circulation of the eastern mediterranean does not favor the salinity preconditioning of the aegean sea in the southwest aegean the myrtoan basin was ventilated by dense waters traceable further south to the west cretan straits export of these masses from the aegean sea can potentially have a broader impact on the thermohaline circulation of the eastern mediterranean

recent changes in deep water formation and spreading in the eastern mediterranean sea a review abstract observations of the last decade testify that the characteristics of the deep thermohaline circulation in the eastern mediterranean sea have changed thoroughly the source of the most dense waters of the basin has moved from the adriatic to the aegean sea this new source has proved to be very efficient since the estimated formation rate for the period 1989 95 was more than 1 sv about three times more than the dense water formation rate of the adriatic sea these new waters with hydrological characteristics that are warmer and more saline have replaced almost 20 of the older deep waters of the basin and have uplifted the deep isopycnals by about 500 m this major event can be attributed to important meteorological anomalies in the eastern mediterranean and to changes of circulation patterns the extended dry period of 1988 93 and the exceptionally cold winters of 1987 and 1992 93 created favorable conditions for increased formation of dense water in the aegean furthermore changes in the circulation patterns in the intermediate water range levantine intermediate water liw and cretan intermediate water themselves possibly linked to meteorological anomalies appear to have played an important role in the redistribution of salt as a result of an interruption to exchanges between the ionian and levantine basin the salinities in the latter started to rise high salinity waters were diverted into the aegean malanotte rizzoli p manca b b ribera dacala m theocharis a 1998 the eastern mediterranean in the 80s and in the 90s the big transition emerged from the poem bc observational evidence rapport du commission international de la mer medittanee 35 174 175 and the westward transport of liw was reduced an additional effect of the deep water discharge from the aegean and the resulting uplifting of mid depth waters was to lower salinities in the liw layer this effect is most strongly felt in the ionian sea a 3 d primitive equation numerical model for the eastern mediterranean with a 20 km grid size is used to simulate the observed changes and understand the basic mechanisms which caused them under appropriate atmospheric forcing the model successfully reproduces the main characteristics of the transient these results indicate that the observed changes can be at least partially explained as a response of the eastern mediterranean and more specifically of the aegean to atmospheric forcing variability

detailed images of the shallow alpine fault zone new zealand determined from narrow azimuth 3d seismic reflection data previous high resolution seismic reflection investigations of active faults have been based on 2d profiles unfortunately 2d data may be contaminated by out of the plane reflections and diffractions that may be difficult to identify and eliminate although full 3d seismic reflection methods allow out of the plane events to be recognized and provide superior resolution to 2d methods they are only rarely applied in environmental and engineering studies because of high costs a narrow azimuth 3d acquisition and processing strategy is introduced to produce a high resolution seismic reflection volume centered on the alpine fault zone new zealand the shallow 3d images reveal late quaternary deformation structures associated with this major transpressional plate boundary fault the relatively inexpensive narrow azimuth 3d acquisition pattern consisting of inline source and receiver lines was easily implemented in the field to provide 2 by 4 m cmp coverage over an approximately 500 by 200 m area the narrow

geochemical and sedimentological responses of arctic glacial lake ilirney chukotka far east russia to palaeoenvironmental change since 51 8 ka bp abstract palaeoenvironmental reconstructions with temporal coverages extending beyond marine isotope stage mis three are scarce within the data sparse region of chukotka far east russia the objective of this paper is to infer palaeoenvironmental variability from a 10 76 m long osl and 14c dated sediment core from lake ilirney chukotka 67 21 n 168 19 e we analysed high resolution sediment geochemistry xrf sedimentology tc tn toc grain size mineralogy xrd and preliminary micropalaeontological data diatoms and pollen from the core as well as acoustic sub bottom profiling data from the lake basin our results affirm the application of xrf based sediment geochemical proxies as effective tracers of palaeoenvironmental variability within arctic lake systems our study reveals that a lake formed during mis3 from 51 8 4 1 ka bp following extensive mis4 glaciation catchment palaeoenvironmental conditions during this time remained harsh associated with the continued presence of a catchment glacier until 36 2 2 6 ka bp partial amelioration reflected by increased diatom catchment vegetation and lake organic productivity and clastic sediment input from mixed sources from 36 2 2 6 ka bp resulted in a lake high stand 15 m above present and is interpreted as evidence of a more productive palaeoenvironment coincident with the mis3 interstadial optimum a transitional period of deteriorating palaeoenvironmental conditions occurred 30 27 9 ka bp and was superseded by periglacial glacial conditions from 27 9 0 8 ka bp during the last glacial maximum deglaciation as marked by sediment geochemical proxies commenced at 20 2 0 8 ka bp our findings are compared with lacustrine yedoma and river bluff records from across beringia and potentially yield limited support for a marked younger dryas cooling in the study area

circulation and hydrography of the levantine basin results of poem coordinated experiments 1985 1986 abstract a brief review of the meteorological setting hydrography and the circulation in the levantine basin of the eastern mediterranean is given the recent high resolution data obtained in poem coordinated experiments of 1985 1986 are then used to optimally estimate the circulation in the basin in two different seasons and to describe the water mass distributions some of the features observed during the experiments support the historical knowledge on the locations of sub basin scale gyres and the general circulation in addition to which some new features are established details of the circulation such as the intensity the multiple scales and the three dimensional structure of the various vortices and the central levantine basin current are displayed extensively a variety of sub basin meso and sub mesoscale vortices occur with highly assymmetric baroclinic vertical structures some eddies split into multiple centres with depth interpreted as indicating possible coalescences a number of long lived eddies were persistent in both surveys the sub surface atlantic water aw is advected by and entrapped within the eddy field the levantine intermediate water liw at intermediate depths is shown to be maintained throughout the year in the northeastern sector of the levantine basin and along the periphery of the rhodes gyre the levantine intermediate water also has a patchy distribution owing to the advection and trapping by the eddy field which it helps to generate through adjustment processes

dust records from varved lacustrine sediments of two neighboring lakes in northeastern china over the last 1400 years dust storms are natural phenomena described in chinese historical documents as early as 1150 bc these documents provide a way to evaluate proxy data from different natural records the minerogenic clastic content and grain size from two closed maar lakes located a short distance apart in northeastern china were analyzed the area is located in the path of dust storms the minerogenic clastics in the studied maar lakes originate mainly from dust deposition general variations of the minerogenic clastic content in these two neighboring lakes show a good coincidence with dust concentration in a tibet ice core and dust events as recorded in historical documents the minerogenic clastic content in the lake sediments is linked with the climate conditions in the dust source regions and wind strength three periods of intensive dust events ad 1050 1330 ad 1590 1690 and the last 200 years have been identified during the past 1500 years the recent increasing pattern of clastic content could be linked to human activity in the dust source regions significantly most of the medieval warm period mwp was marked by a high frequency of dust storms

reconstruction of past storminess evaluation of an indicator approach using aeolian mineral grains buried in peat deposits estonia abstract this study aims to evaluate a reconstruction method of past storminess using aeolian sand influx asi in peat deposits we use high resolution records of asi from four peat bogs along the estonian coast and compare those with local instrumentally recorded storminess data since 1920 ad and with historical climatic records around the baltic sea over the last two centuries potential effects of local changes in forest cover and anthropogenic disturbances on the asi signals are also evaluated with historical maps available for the study sites diameter of all sand grains 65 m is measured with an image analysis system to detect temporal changes in the grain size distribution our results demonstrate two major periods of high asi over the last centuries in the region during the 19th century and since the 1950s with highest values in 1980 2000 ad cross correlations between the changes in asi and the instrumentally recorded storm days during the last century are positive and significant high asi values recorded during the 19th century correspond to the positive nao indices and high cyclonic activity reconstructed in southern sweden we find that sand grains

high resolution paleomagnetic record of geomagnetic field fluctuations from the varved sediments of elk lake minnesota measurements of samples taken from three parallel cores from elk lake in northern minnesota have been combined to produce a high quality record of recent variations in the local magnetic field annual laminations in the sediment provide excellent time control for the record and evidence for a consistent depositional environment the elk lake paleomagnetic record contributes significantly to our understanding of the recent history of the magnetic field in central north america modifying several previous conclusions

the holocene history of oro lake one of the western canada s longest continuous lacustrine records over the past decade there have been significant advances in our understanding of the holocene history of the great plains region of western canada however despite this increased interest paleolimnological research is limited by a paucity of study sites with relatively long uninterrupted stratigraphic sequences to date only three canadian great plains lakes have provided complete uninterrupted sequences spanning the past 10 000 years oro lake is one of these oro lake is small perennial and saline it occupies a topographically closed basin on the missouri coteau in southern saskatchewan canada its 10 000 year stratigraphic sequence consists mainly of well bedded calcareous and gypsiferous clayey silts a short lived early holocene freshwater siliciclastic dominated lake occupied the newly formed basin immediately after deglaciation at 9300 bp limnological conditions changed dramatically and abruptly since then alkaline high salinity brines with high mg ca ratios have prevailed stable meromictic conditions existed from about 9300 to 7400 bp with maximum salinities 75 ppt occurring at 8300 bp about 7400 years ago gradually increasing aridity during the mid holocene resulted in increased eolian sedimentation reorganization of the groundwater influx and occasional breakdown of meromixis about 4000 bp the lake returned to a mainly stratified water column with subaqueous soluble salts being precipitated from the monimolimnion and aragonite and mg carbonates being generated from the mixolimnion during the most recent 1000 years periodic hypersaline conditions became more common coincident with decreased concentrations of ca 2 and complimentary increased proportions of mg 2 and na ions d 2002 elsevier science b v all rights reserved

early holocene change in atmospheric circulation in the northern great plains an upstream view of the 8 2 ka cold event elk lake in northwestern minnesota contains numerous proxy records of climatic and environmental change contained in varved sediments with annual resolution for the last 10 000 years these proxies show that about 8200 calendar years ago 8 2 cal ka 7300 radiocarbon years elk lake went froma well stratified lake that was wind protected in a boreal forest to a wellmixed lake in open prairie savanna receiving northwesterly wind blown dust probably from the dry floor of lake agassiz this change in climate marks the initiation of the widely recognized mid holocene altithermal in central north america the coincidence of this change with the so called 8 2 cal ka cold event recognized in ice core and other records fromthe circum north atlantic and thought by some to be caused by catastrophic discharge of freshwater from proglacial lakes agassiz and ojibway suggests that the two events might be related our interpretation of the elk lake proxy records and of other records from less accurately dated sites suggests that change in climate over north america was the result of a fundamental change in atmospheric circulation in response to marked changes in the relative proportions of land water and especially glacial ice in north america during the early holocene this change in circulation probably post dates the final drainage of proglacial lakes along the southern margin of the laurentide ice sheet and may have produced a minor perturbation in climate over greenland that resulted in a brief cold pulse detected in ice cores r 2002 elsevier science ltd all rights reserved

possible solar forcing of century scale drought frequency in the northern great plains a 2100 yr decadal resolution salinity and aridity proxy record of lacustrine ostracode shell mg ca ratios from a closed basin lake in the northern great plains shows statistically significant periodicities of 400 200 130 and 100 yr these periodicities are similar to the three principal solar oscillation periods 420 218 143 yr as inferred from the atmospheric radiocarbon record suggesting strong solar forcing of century scale drought frequency with a fundamental 400 yr period and its 2nd 3rd and 4th harmonics our proxy record correlates visually and statistically cross spectral analysis with the atmospheric 14 c record solar proxy and the gisp2 greenland ice sheet project two 18 o record climate proxy showing that solar minima are in phase with drought periods in the northern great plains and cold periods in greenland this spectral similarity together with phase correlation indicates a possible teleconnection of century scale global climate fluctuations through common solar forcing

a late quaternary record of eolian silt deposition in a maar lake st michael island western alaska abstract recent stratigraphic studies in central alaska have yielded the unexpected finding that there is little evidence for full glacial late wisconsin loess deposition because the loess record of western alaska is poorly exposed and not well known we analyzed a core from zagoskin lake a maar lake on st michael island to determine if a full glacial eolian record could be found in that region particle size and geochemical data indicate that the mineral fraction of the lake sediments is not derived from the local basalt and is probably eolian silt deposition took place from at least the latter part of the mid wisconsin interstadial period through the holocene based on radiocarbon dating based on the locations of likely loess sources eolian silt in western alaska was probably deflated by northeasterly winds from glaciofluvial sediments if last glacial winds that deposited loess were indeed from the northeast this reconstruction is in conflict with a model derived reconstruction of paleowinds in alaska mass accumulation rates in zagoskin lake were higher during the pleistocene than during the holocene in addition more eolian sediment is recorded in the lake sediments than as loess on the adjacent landscape the thinner loess record on land may be due to the sparse herb tundra vegetation that dominated the landscape in full glacial time herb tundra would have been an inefficient loess trap compared to forest or even shrub tundra due to its low roughness height the lack of abundant full glacial eolian silt deposition in the loess stratigraphic record of central alaska may be due therefore to a mimimal ability of the landscape to trap loess rather than a lack of available eolian sediment

abnormal rb sr ratio in lacustrine sediments of qaidam basin ne qinghai tibetan plateau a significant role of aeolian dust input abstract the rb sr ratio is an important indicator of weathering intensity in both lacustrine and loess sediments because of the inertness of the rb element and the activity of the sr element during the weathering process generally the environmental interpretation of rb sr ratio proxy in lacustrine sediments is contrary to that in the loess paleosol sequence it shows a negative correlation between the rb sr ratio and chemical weathering intensity in lacustrine sediments but shows a positive pattern in the loess paleosol sequence however in this study we investigated the rb sr ratio of a lacustrine core isl1a from qarhan salt lake qsl in eastern qaidam basin qb and found the rb sr ratio indicated a positive correlation with regional precipitation this pattern is similar to that of the loess paleosol sequence rather than the lacustrine sediments according to grain size statistics and the comparison of rb sr ratio with other proxies halite and calcite contents grain size and f values of grain size discriminant function we preliminarily proposed that the abundant input of aeolian materials transported by the strong northwest wind cause these unexpected rb sr ratio fluctuations in the isl1a core the comparison between background rb and sr elemental data of relevant regions and these of the core indicated the aeolian origin of rb sr ratio in the lacustrine sediments and the rb and sr elemental composition probably represents the geochemical characteristics of the dust source area the sr nd isotopic composition indicates that the erosive paleo lake strata in western qb could be the origin of aeolian materials in lacustrine sediments in the qsl as well as the loess deposits in dulan county qinghai lake basin and xining basin the regional correlation between proxies of the isl1a core and other aeolian records also supports the aeolian origin of detrital input in the core finally we propose that the origin of the detrital input must be distinguished before the rb sr ratio is applied as a weathering intensity proxy in lacustrine sediments especially in arid basins

effects of holocene climate change on mercury deposition in elk lake minnesota the importance of eolian transport in the mercury cycle sediments in elk lake minnesota consist of 10 400 varve layers that provide a precise chronology for holocene fluctuations in climate and biota recorded in the strata progressively greater concentrations and accumulation rates of mercury since ca a d 1875 reflect deposition of anthropogenic mercury additions to the atmosphere within the holocene record are numerous short intervals in which mercury concentrations and accumulation rates exceed the modern values the highest mercury concentrations formed ca 8 ka coincident with a rapid change from cool moist conditions to warm dry conditions a related change in flora from pine forest to prairie caused destruction of organic forest soils and the release of mercury that had been sequestered in them resulting in a short lived pulse of mercury to the lake accumulation rates of mercury were highest during the 4 k y mid holocene dry interval and show a correlation with periods of rapid deposition of eolian dust the mercury was probably bound to wind borne mineral particles which were derived from an unidentified mercury rich source region west of elk lake

a 1000 year record of dry conditions in the eastern canadian prairies reconstructed from oxygen and carbon isotope measurements on lake winnipeg sediment organics a short sediment core 162cm covering the period ad 920 1999 was sampled from the south basin of lake winnipeg for a suite of multi proxy analyses leading towards a detailed characterisation of the recent millennial lake environment and hydroclimate of southern manitoba canada information on the frequency and duration of major dry periods in southern manitoba in light of the changes that are likely to occur as a result of an increasingly warming atmosphere is of specific interest in this study intervals of relatively enriched lake sediment cellulose oxygen isotope values d 18 ocellulose were found to occur from ad 1180 to 1230 error range ad 1104 1231 to 1160 1280 1610 1640 error range ad 1571 1634 to 1603 1662 1670 1720 error range ad 1643 1697 to 1692 1738 and 1750 1780 error range ad 1724 1766 to 1756 1794 regional water balance inferred from calculated lake winnipeg water oxygen isotope values d 18 oinf lw suggest that the ratio of lake evaporation to catchment input may have been 25 40 higher during these isotopically distinct periods associated with the enriched d 18 ocellulose intervals are some depleted carbon isotope values associated with more abundantly preserved sediment organic matter d 13 com these suggest reduced microbial oxidation of terrestrially derived organic matter and or subdued lake productivity during periods of minimised input of nutrients from the catchment area with reference to other corroborating evidence it is suggested that the ad 1180 1230 1610 1640 1670 1720 and 1750 1780 intervals represent four distinctly drier periods droughts in southern manitoba canada additionally lower magnitude and duration dry periods may have also occurred from 1320 to 1340 error range ad 1257 1363 1530 1540 error range ad 1490 1565 to 1498 1572 and 1570 1580 error range ad 1531 1599 to 1539 1606 copyright 2009 john wiley sons ltd

prestack and poststack migration of crooked line seismic reflection data a case study from the south portuguese zone fold belt southwestern iberia crooked line 2d seismic reflection survey geometries violate underlying assumptions of 2d imaging routines affecting our ability to resolve the subsurface reliably we compare three crooked line

ca isotope cycling in a forested ecosystem reports of large ca isotope fractionations between trees and soils prompted this study of a boreal forest ecosystem near la ronge saskatchewan to improve understanding of this phenomenon the results on five tree species black spruce trembling aspen white spruce jack pine balsam poplar confirm that nutrient ca uptake by plants favors the light isotopes thus driving residual ca in plant available soil pools towards enrichment in the heavy isotopes substantial within tree fraction occurs in tissues formed along the transpiration stream with low 44ca values in fine roots 2 mm intermediate values in stemwood and high values in foliage separation factors between different plant tissues are similar between species but the initial fractionation step in the tips of the fine roots is species specific and or sensitive to the local soil environment soil water 44ca values appear to increase with depth to at least 35 cm below the top of the forest floor which is close to the deepest level of fine roots the heavy plant fractionated signature of ca in the finely rooted upper soils filters downward where it is retained on ion exchange sites leached into groundwater and discharged into surface waters the relationship between ca uptake by tree fine roots and the pattern of 44ca enrichment with soil depth was modeled for two ca pools the forest floor litter and the underlying upper b mineral soil six study plots were investigated along two hillside toposequences trending upwards from a first order stream we used allometric equations describing the ca distribution in boreal tree species to calculate weighted average 44ca values for the stands in each plot and estimate ca uptake rates the 44ca value of precipitation was measured and soil weathering signatures deduced by acid leaching of lower b mineral soils steady state equations were used to derive a set of model ca fluxes and fractionation factors for each plot the model reproduces the increase in 44ca with depth found in forest floor and upper b soil waters transient model runs show that the forest ca cycle is sensitive to changes in plant ca uptake rate such as would occur during ontogeny or disturbance accordingly secular records of 44ca in tree ring cellulose have the potential to monitor changes in the forest ca cycle through time thus providing a new tool for evaluating natural and anthropogenic impacts on forest health another model run shows that by changing the size of the isotope fractionation factor and adjusting for differences in forest productivity that the range in ca isotope fractionation in forested ecosystems reported in the literature thus far is reproduced as a quantitative tool the ca cycling model produces a reasonable set of relative ca fluxes for the la ronge site consistent with environment canada s measurements for wet deposition in the region and simulated ca release from soil mineral weathering using the profile model but the sensitivity of the model is limited by the small range of fractionation observed in this boreal shield setting of 1 which limits accuracy if the model were applied to a site with a greater range in 44ca values among the principal ca fluxes it is capable of producing robust and reliable estimations of ca fluxes that are otherwise difficult to measure in forested ecosystems

open ocean convection observations theory and models we review what is known about the convective process in the open ocean in which the properties of large volumes of water are changed by intermittent deep reaching convection triggered by winter storms observational laboratory and modeling studies reveal a fascinating and complex interplay of convective and geostrophic scales the large scale circulation of the ocean and the prevailing meteorology two aspects make ocean convection interesting from a theoretical point of view first the timescales of the convective process in the ocean are sufficiently long that it may be modified by the earth s rotation second the convective process is localized in space so that vertical buoyancy transfer by upright convection can give way to slantwise transfer by baroclinic instability moreover the convective and geostrophic scales are not very disparate from one another detailed observations of the process in the labrador greenland and mediterranean seas are described which were made possible by new observing technology when interpreted in terms of underlying dynamics and theory and the context provided by laboratory and numerical experiments of rotating convection great progress in our description and understanding of the processes at work is being made

impact of a base metal smelter on the geochemistry of soils of the flin flon region manitoba and saskatchewan the regional dispersal patterns of six trace metals as cd cu hg pb zn emitted from the base metal smelter at flin flon were examined in surface soils and at depth using an extensive regiona

a general reconstruction scheme for dominant azimuth 3d seismic data seismic data are usually irregularly and sparsely sampled along the spatial coordinates which yields suboptimal imaging results for time lapse data differences in the spatial sampling of base and monitor surveys lead to undesired differences between the images of the surveys that are not due to differences in the subsurface in this paper an efficient two step reconstruction method is proposed for irregularly and sparsely sampled 3d seismic data recorded with a dominant azimuth for large offsets the first step is reconstruction along the receiver lines such that the midpoints are exactly on crosslines the second step is a 2d reconstruction in the crossline midpoint offset domain using a least squares estimation of fourier components sparse sampling can be handled by optimizing the parameterization of the least squares estimation of the fourier coefficients and consequently it is possible to reconstruct data that would be aliased when considering single common midpoint gathers the method can be used

transient eastern mediterranean deep waters in response to the massive dense water output of the aegean sea in the 1990s abstract we present a detailed account of the changing hydrography and the large scale circulation of the deep waters of the eastern mediterranean emed that resulted from the unique high volume influx of dense waters from the aegean sea during the 1990s and of the changes within the aegean that initiated the event the so called eastern mediterranean transient emt the analysis uses repeated hydrographic and transient tracer surveys of the emed in 1987 1991 1995 1999 and 2001 2002 hydrographic time series in the southern aegean and southern adriatic seas and further scattered data aegean outflow averaged nearly 3 10 6 m 3 s 1 between mid 1992 and late 1994 and was largest during 1993 when south and west of crete aegean influenced deep waters extended upwards to 400 m depth emt related aegean outflow prior to 1992 confined to the region around crete and to 1800 m depth wise amounted to about 3 of the total outflow outflow after 1994 up to 2001 2002 derived from the increasing inventory of the tracer cfc 12 contributed 20 to the total of 2 8 10 14 m 3 densities in the southern aegean sea deep waters rose by 0 2 kg m 3 between 1987 and 1993 and decreased more slowly thereafter the aegean waters delivered via the principal exit pathway in kasos strait east of crete propagated westward along the cretan slope such that in 1995 the highest densities were observed in the hellenic trench west of crete aegean influenced waters also crossed the east mediterranean ridge south of crete and from there expanded eastward into the southeastern levantine sea transfer into the ionian mostly followed the hellenic trench largely up to the trench s northern end at about 37 n from there the waters spread further west while mixing with the resident waters additional transfer occurred through the herodotus trough in the south levantine waters after 1994 consistently showed temperature salinity t s inversions in roughly 1000 1700 m depth with amplitudes decreasing in time the t s distributions in the ionian sea were more diverse one cause being added aegean outflow of relatively lower density through the antikithira strait west of crete spreading of the aegean influenced waters was quite swift such that by early 1995 the entire emed was affected and strong mixing is indicated by near linear t s relationships observed in various places referenced to 2000 and 3000 dbar the highest aegean generated densities observed during the event equaled those generated by adriatic sea outflow in the northern ionian sea prior to the emt a precarious balance between the two dense water source areas is thus indicated a feedback is proposed which helped triggering the change from a dominating adriatic source to the aegean source but at the same time supported the previous long year dominance of the adriatic the emed deep waters will remain transient for decades to come

formal subdivision of the holocene series epoch a discussion paper by a working group of intimate integration of ice core marine and terrestrial records and the subcommission on quaternary stratigraphy international commission on stratigraphy this discussion paper by a working group of intimate integration of ice core marine and terrestrial records and the subcommision on quaternary stratigraphy sqs of the international commission on stratigraphy ics considers the prospects for a formal subdivision of the holocene series epoch although previous attempts to subdivide the holocene have proved inconclusive recent developments in quaternary stratigraphy notably the definition of the pleistocene holocene boundary and the emergence of formal subdivisions of the pleistocene series epoch mean that it may be timely to revisit this matter the quaternary literature reveals a widespread but variable informal usage of a tripartite division of the holocene early middle or mid and late and we argue that this de facto subdivision should now be formalized to ensure consistency in stratigraphic terminology we propose an early middle holocene boundary at 8200 a bp and a middle late holocene boundary at 4200 a bp each of which is linked to a global stratotype section and point gssp should the proposal find a broad measure of support from the quaternary community a submission will be made to the international union of geological sciences iugs via the sqs and the ics for formal ratification of this subdivision of the holocene series epoch copyright 2012 john wiley sons ltd

another look at the question of azimuth the question of azimuth seems to be an emotional issue in 3 d seismic exploration some people believe that 3 d surveys should contain a wide range of source receiver azimuths so that the subsurface is sampled from all directions and the acquisition is closer to a true 3 d survey others on the other hand argue the case for narrow azimuth acquisition a few years ago malcolm lansley then with halliburton geophysical gave an excellent presentation regarding the question of azimuth at an seg summer workshop in this talk which was recently presented to the houston geophysical society lansley provided an extensive summary of the advantages and disadvantages of wide azimuth surveying and listed many aspects that one should consider when deciding between narrow and wide azimuth acquisition

natural and anthropogenic variations in atmospheric mercury deposition during the holocene near quelccaya ice cap peru mercury hg is a toxic metal that is transported globally through the atmosphere the emission of hg from mineral reservoirs and subsequent recycling in surface reservoirs i e soil biomass ocean and atmosphere are fundamental to the modern global hg cycle yet past emissions from anthropogenic and natural sources are not fully constrained we use a sediment core from yanacocha a headwater lake in southeastern peru to study the anthropogenic and natural controls on atmospheric hg deposition during the holocene from 12 3 to 3 5 ka hg fluxes in the record are relatively constant mean 1 1 4 0 6 g m 2 a 1 n 189 past hg deposition does not correlate with changes in regional temperature and precipitation inferred from nearby paleoclimate records or with most large volcanic events that occurred regionally in the andean central volcanic zone 300 400 km from yanacocha and globally in b c 1450 3 4 ka hg fluxes abruptly increased and reached the holocene maximum flux 6 7 g m 2 a 1 in b c 1200 concurrent with a 100 year peak in fe and chalcophile metals as ag tl and the presence of framboidal pyrite continuously elevated hg fluxes from b c 1200 500 suggest a protracted mining dust source near yanacocha that is identical in timing to documented pre incan cinnabar mining in central peru during incan and colonial time a d 1450 1650 hg deposition remains elevated relative to background levels but lower relative to other hg records from sediment cores in central peru indicating a limited spatial extent of preindustrial hg emissions hg fluxes from a d 1980 to 2011 4 0 1 0 g m 2 a 1 n 5 are 3 0 1 5 times greater than pre anthropogenic fluxes and are similar to modern fluxes documented in remote lakes around the world

climatic changes in the aegean sea influence the eastern mediterranean thermohaline circulation 1986 1997 recent changes of water mass characteristics in the south aegean sea have considerably influenced the eastern mediterranean thermohaline circulation a combination of salinity increase 1987 92 and temperature drop 1992 94 caused massive dense water formation and strong outflow towards the deep and bottom parts of the eastern mediterranean this climatic shift the most important since the existence of observations in the basin is a combined effect of extreme meteorological events superimposed on large scale trends it has initiated a series of modifications in the hydrology and dynamics of the entire eastern mediterranean with possible influence on the mediterranean outflow in the north atlantic ocean

recurrent intrusions of transitional waters of eastern mediterranean origin in the cretan sea as a tracer of aegean sea dense water formation events abstract available temperature and salinity data in the cretan sea from 1955 up to 2014 as well as literature sources were revisited in order to trace the appearance of low salinity temperature oxygen and nutrient rich waters inside the basin at depths below the intermediate layer first appearing as far back as 1961 in literature these waters were found originating in the layers that separate intermediate and deep waters of the eastern mediterranean sea emed and were named transitional mediterranean water tmw in the 1990s data analysis showed that the appearance of tmw in the cretan sea is a recurrent phenomenon connected to water mass exchanges between the aegean sea and the emed in particular the inflow of tmw in the cretan basin acts as compensation for the outflow of equally dense or denser masses from the aegean this export is a result of dense water formation dwf events taking place inside the aegean sea triggering tmw compensatory inflow into the cretan sea through the cretan straits in this context tmw intrusions in the cretan basin can be used as a tracer of dwf in the aegean sea while the depth of the intrusion can provide valuable information about the intensity of the dwf event the importance of tmw intrusions is not solely restricted to the tracing and evaluation of dwf events but could additionally expand to the impact on local ecological processes as tmw is a nutrient carrier for the oligotrophic cretan sea

hanging wall vectoring for buried volcanogenic massive sulfide deposits paleoproterozoic flin flon mining camp manitoba canada the paleoproterozoic flin flon mining district is one of the world s most prolific volcanogenic massive sulfide vms camps and includes a single stratigraphic interval that hosts the 85 5 million tonne mt flin flon 777 and callinan zn cu au deposits rapid seafloor burial of the vms hydrothermal system by a thick succession of pillowed basalt resulted in the hanging wall strata being affected to varying degrees by the still upward migrating fluids this hanging wall alteration hydrothermal fingerprint allows delineation of the regionally metamorphosed paleohydrothermal system and its characterization has the potential to lead to discovery of buried stacked or structurally displaced mineralization evidence for the presence of continued seafloor hydrothermal activity above the flin flon callinan vms horizon is observed in the pillowed flows interlayered hyaloclastite rich flow tops and also within finely bedded interflow volcaniclastic sediment a 30 to 60 metalliferous exhalative component was detected through geochemical and mineral analysis in interpillow volcaniclastic rocks chert and epidosite in the hanging wall sequence the regional distribution of fe and mg rich chlorite epidote clinozoisite biotite annite actinolite hornblende ferrotschermakite and stilpnomelane and albite oligoclase modifies metamorphic isograds and defines discrete vertical fluid pathways controlled by synvolcanic growth faults and associated sill dike swarms silica enriched hanging wall alteration zones are proximal to fe ti basalt sills and occur as discrete hanging wall zones parallel to the plunge of the 62 mt flin flon deposit anomalous concentrations of hg sb ag pb te as au and bi form within these hanging wall halo alteration zones indicating migration of the more volatile metals present in the underlying vms deposits synvolcanic depressions dike swarms and hydrothermal metamorphic fluid corridors are detectable through trace element anomalies trace mineral chemistry and 18o isotope geochemistry oxygen isotope analysis of the flin flon 777 callinan vms hanging wall strata defines a number of high o18 anomalies extending 1 200 m above that indicate that 300 c subseafloor hydrothermal activity continued after burial of the massive sulfide deposits coupled with the geochemical and mineral chemical anomalies this is indicative of the presence of continued relatively low temperature hydrothermal fluid leakage from a robust seafloor hydrothermal event that generated the vms deposits a combination of techniques including mineral chemistry isotope and trace element data is demonstrated to be successful in identifying and delineating zones of hanging wall hydrothermal alteration in greenschist to amphibolite grade metamorphic rocks of the flin flon mining camp use of these coupled with mapping to define periods of quiescence as marked by horizons of sedimentary rocks in the hanging wall basalts of the hidden formation has the potential to lead to discovery of deeply buried deposits on the flin flon horizon or deposits at higher stratigraphic levels our findings indicate that the basaltic hanging wall on the flin flon 777 callinan hydrothermal system was an efficient cap on the system with vestiges of continued hydrothermal fluid flow detected in the interpillow and interflow components these volumetrically minor components are critical sampling media and are pertinent to global exploration for detection of vms mineralization buried beneath thick mafic volcanic sequences

grain size in sediments from lake sugan a possible linkage to dust storm events at the northern margin of the qinghai tibetan plateau samples of surface deposits in the lake sugan catchment as well as surface lake sediments eolian materials occulted in the lake ice cover and airborne dust were collected for grain size analysis the results show that the coarse fraction of the lake sediments could be transported by ambient winds and to a lesser extent by river flow in the study area sediment cores were retrieved from lake sugan in december 2000 and 210pb and 137cs dating and grain size analyses were performed on these samples 210pb ages and the volume percentage of the fraction of lake sediments 63 m were used to reconstruct the dust storm history from 1957 to 2000 observational data for dust storm events collected at a local meteorological station largely agrees with the reconstructed trend for the past 44 years suggesting that lake sediments can be employed to trace the dust storm history of the northern qinghai tibetan plateau

can internal processes sustain reversals of the ocean upper circulation the ionian sea example 1 in 1997 an inversion in the ionian upper layer circulation was documented and ascribed to a massive inflow of aegean dense waters associated with the eastern mediterranean transient emt and not to the wind stress borzelli et al 2009 here we generalize the concept hypothesizing that such inversions are possible even in the absence of the aegean influence indeed salinity and density data collected in the southern adriatic the main source of the eastern mediterranean deep water show decadal variations coherent with changes in the sea level height in the northern ionian scaling considerations suggest that the redistribution of ionian water masses resulting from changes in the thermohaline properties of waters entering the basin can sustain inversions of the upper layer circulation therefore we propose a feedback mechanism named the adriatic ionian bimodal oscillating system bios between variations in the thermohaline properties of waters formed in the southern adriatic and the ionian circulation

a record of late holocene environmental change from southern new england usa article i nfo article history received 28 march 2011 available online 31 august 2011 analyses of a sediment core from little pond located in the town of bolton massachusetts provide new insights into the history of environmental and ecological changes in southern new england during the late holocene declines in organic content and peaks in the abundance of isoetes spores indicate reduced water depth at 2900 2600 2200 1800 and 1200 800 calibrated years before present cal yr bp generally consistent with the timing of dry conditions in records from elsewhere in the northeastern united states the little pond pollen record features little change over the last 3000 yr indicating that the surrounding vegetation was relatively insensitive to these periods of drought the 1200 800 cal yr bp dry interval however coincides with increased abundance of castanea pollen suggesting that the expansion of castanea in southern new england may have been influenced by late holocene climatic variability

late holocene climate and ecosystem history from chesapeake bay sediment cores usa palaeoclimate records from late holocene sediments in chesapeake bay the largest estuary in the usa provide evidence that both decadal to centennial climate variability and european colonization

new perspectives on the flin flon belt trans hudson orogen manitoba and saskatchewan an introduction to the special issue on the natmap shield margin project part 1 a new tectonic framework for the flin flon belt in southeastern reindeer zone of the trans hudson orogen has emerged in recent years through four dimensional studies bedrock and subsurface mapping

holocene environmental and climatic change in the northern great plains as recorded in the geochemistry of sediments in pickerel lake south dakota the sediments in pickerel lake northeastern south dakota provide a continuous record of climatic and environmental change for the last 12000 yr sediments deposited between 12 and 6 ka radiocarbon show extreme variations in composition oxygen and carbon isotopic composition of bulk carbonate carbon isotopic composition of organic matter and magnetic susceptibility these variations re ect changes in sources of moisture regional vegetation types precipitation evaporation balance ground and surface water in ux water residence time erosion lake productivity water level and water temperature the total carbonate content of late pleistocene sediments steadily increased from 20 at the base of the core to as much as 80 in sediments deposited between 11 and 9 ka by about 8 ka the total carbonate content of the sediments had declined to about 40 where it remained with little variation for the past 8 kyr suggesting relatively stable conditions there are marked increases in values of d13c and d18 oi n bulk carbonate and d13c of organic matter in sediments deposited between 10 and 6 ka as evaporation increased and the vegetation in the watershed changed from forest to prairie this shift toward more 18o enriched carbonate may also re ect a change in source or seasonality of precipitation during this early holocene interval the organic carbon oc content of the sediments remained relatively low 2 3 but then increased rapidly to 4 5 between 7 and 6 ka re ecting the rapid transition to a prairie lake the oc content uctuates slightly between 4 and 6 in sediments deposited over the past 6 kyr like oc and total carbonate most variables measured show little variation in the 13 m of sediment deposited over the past 6 kyr particularly when compared with early holocene variations although the magnetic susceptibility of this upper 13 m of sediment is generally low 10 si units the upper six meters of the section is marked by striking 1 m cycles ca 400 500 yr periodicity in susceptibility these cycles are interpreted as being due to variations in the in ux of eolian detrital clastic material century scale cyclic variations in di erent proxy variables for aridity and eolian activity from sediments deposited over the past 2000 yr in other lakes in the northern great plains as well as in sand dune activity suggest that aridity cycles were the dominant feature of late holocene climate of the northern great plains 2000 elsevier

landscape evolution valley excavation and terrace development following abrupt postglacial base level fall many high latitude fluvial systems are adjusting to base level changes since the last glaciation channels that experienced base level fall may still be incising often through glacial diamictons tills these tills can be quite competent behaving more like weak bedrock than unconsolidated sediment and erode at a fast pace thus providing a unique opportunity to test models of channel incision and knickpoint migration in transient systems here we integrate light detection and ranging lidar topography strath terrace chronology and numerical modeling to determine knickpoint migration and incision history of the le sueur river in central minnesota usa results indicate that the le sueur river is best modeled as a detachment limited channel with downstream coarsening related to lag clasts from tills playing a critical factor in longitudinal profile development the le sueur river meanders as it incises so we coupled the best fit incision model to a meander model to determine valley excavation history the excavation history was used to determine a natural background erosion rate prior to land use changes associated with settlement and agricultural expansion in the mid 1800s we compared background fine sediment silt and clay erosion rates with historic decadal average annual suspended loads results show that modern fine sediment contributions from sources associated with valley excavation are three times higher than modeled presettlement loads recent changes in hydrology associated with land use and climate change have increased flows in rivers leading to higher sediment loads not just from field erosion but from increased bank and bluff erosion in the deeply incised valleys

changes in the volume and salinity of lake khubsugul mongolia in response to global climate changes in the upper pleistocene and the holocene two gravity cores 1 1 and 2 2 m long of deep water bottom sediments from lake khubsugul mongolia were studied the holocene biogenic silica and organic matter rich part of the first core was subjected to ams radiocarbon dating which placed the date of dramatic increase of pelagic diatoms 40 cm below sediment surface at a calendar age of 11 5 cal ky bp icp ms analysis of weak nitric acid extracts revealed that the upper pleistocene compared to the holocene samples were enriched in ca cinorg sr mg and depleted of u w sb v and some other elements transition to the holocene resulted in an increase of total diatoms from 0 to 108 g 1 of bisi from 1 to 20 of organic matter from 6 the bolling allerod younger dryas holocene abrupt climate oscillations manifested themselves in oscillations of geochemical proxies a remarkable oscillation also occurred at 22 cm ca 5 5 ky bp the pleistocene section of the second longer core was enriched in carbonate co2 up to 10 and water extractable so42 up to 300 times greater than that in holocene pore waters all this evidence is in an accord with the earlier finding of drowned paleo deltas at ca 170 m below the modern lake surface of the lake dokl akad nauk 382 2002 261 and suggests that due to low ca 110 mm regional precipitation at the end of the pleistocene lake khubsugul was only 100 m deep and that its volume was ca 10 times less than today

possible connection between surface winds solar activity and the earth s magnetic field records of 14c in tree rings provide a proxy for changes in solar activity on timescales of decades to centuries1 2 here i report an association between maunder type solar cycles recorded in tree rings and fluctuations in surface wind intensity on a roughly 200 year timescale over a period of about 2 000 years in the mid holocene the wind record is preserved as changes in the thickness of varved sediments in elk lake minnesota which contain a large aeolian component changes in cyclonic activity and tropospheric winds have been reported1 5 to occur in this region a few days after strong coronal mass ejections cmes increases of up to 7 in zonal flow have been reported5 at an altitude of 300 m after strong cmes in winter the implication of this association is that century scale changes in surface winds over minnesota were the long term maunder scale counterpart of short term daily changes in winds after cmes the weak magnetic field strength of the earth at this time6 7 might be relevant to a possible mechanism for the association

shallow 3d seismic reflection imaging of fracture zones in crystalline rock a limited 3d seismic reflection data set was used to map fracture zones in crystalline rock for a nuclear waste disposal site study seismic reflection data simultaneously recorded along two roughly perpendicular profiles 1850 and 1060 m long and with a 400 x 400 m receiver array centered at the intersection of the lines sampled a 680 x 960 m 2 area in three dimensions high levels of source generated noise required a processing sequence involving surface consistent deconvolution which effectively increased the strength of reflected signals and a linear tau p filtering scheme to suppress any remaining direct sv wave energy a flexible binning scheme significantly balanced and increased the cmp fold but the offset and azimuth distributions remain irregular a wide azimuth range and offsets 800 m are only found at the edges of the site three dimensional dip moveout and 3d poststack migration were necessary to image events with conflicting dips up to about 40 degrees despite the irregular acquisition geometry and the high level of source generated noise we obtained images rich in structural detail seven continuous to semicontinuous reflection events were traced through the final data volume to a maximum depth of around 750 m previous 2d seismic reflection studies and borehole data indicate that fracture zones are the most likely cause of the reflections

widespread drought episodes in the western great lakes region during the past 2000 years geographic extent and potential mechanisms we compared high resolution reconstructions of peatland water table depth at two raised bogs in the western great lakes region separated by 1000 km the sites included minden bog in southeastern michigan and hole in the bog in north central minnesota our objectives were to 1 determine whether large decadal to multidecadal droughts of the past 2000 yrs were spatially and temporally coherent across the region and 2 assess the underlying mechanisms of widespread droughts in the region we found a strong correlation between bog inferred records of moisture variability in the two regions r 0 53 between 2100 and 600 bp extreme drought events centered on 1850 1800 1650 1000 800 and 700 bp are recorded in both regions many of these drought events were contemporaneous with large droughts already documented at sites far to the west in the great plains and rocky mountains to identify potential modern climate analogues we used empirical orthogonal function eof analysis to reveal spatial modes of variability in drought and precipitation records of north america for the past century the first eofs of annual precipitation and palmer drought severity index pdsi were similar to each other and consistent with a pattern of widespread continental drought correlations between these eofs and annual sea surface temperatures ssts indicate strong relationships to ssts in both the atlantic and pacific basins we hypothesize that widespread droughts between 1000 and 700 bp were related to amplification of a spatial mode of moisture variability associated with an anomalously warm north atlantic a warm mid latitude north pacific and an anomalously cold tropical pacific a more extensive network of hydroclimate records developed using a consistent set of methods and proxies could be used in conjunction with high resolution records of past ssts to test this hypothesis

the structure of holocene climate change in mid latitude north america abstract a sequence of long term and rapid changes during the holocene appears in a network of 40 well resolved paleoclimate datasets from mid latitude north america including records of pollen inferred temperatures alkenone derived sea surface temperatures ssts lake level changes dust accumulation and lake isotopes from idaho to maine statistical analyses reveal that changes in insolation and the laurentide ice sheet explain 51 7 of the variance in the records especially multi millennial trends but peak rates of change indicate additional rapid changes at ca 10 8 9 4 8 3 7 0 5 5 5 2 4 7 2 1 and 0 9 ka step changes between 9 4 and 8 3 ka relate to ice sheet dynamics that warmed much of the region and changes at 5 5 ka were the largest since the demise of the ice sheet the shift at 5 5 ka initiated widespread cooling and increases in effective moisture which culminated in the coolest wettest millennia in most areas after 2 1 ka replicated evidence from multiple records also shows a spatially varied set of multi century fluctuations including 1 low temperatures and high effective moisture at 5 5 4 8 ka in the mid continent and 2 repeated phases of low ssts cool summers and drought superimposed upon long cooling moistening trends in eastern north american since 5 5 ka

gully erosion susceptibility assessment by means of gis based logistic regression a case of sicily italy article i nfo article history this research aims at characterizing susceptibility conditions to gully erosion by means of gis and multivariate statistical analysis the study area is a 9 5 km 2 river catchment in central northern sicily where agriculture ac tivities are limited by intense erosion by means of field surveys and interpretation of aerial images we prepared a digitalmap of thespatial distribution of 260 gulliesinthestudy area inaddition fromavailable thematicmaps a 5 m cell size digital elevation model and field checks we derived 27 environmental attributes that describe the variability of lithology land use topography and road position these attributes were selected for their potential influence on erosion processes while the dependent variable was given by presence or absence of gullies within two different types of mapping units 5 m grid cells and slope units average size 2 66 ha the functional re lationships between gully occurrence and the controlling factors were obtained from forward stepwise logistic regression to calculate the probability to host a gully for each mapping unit in order to train and test the predictive models three calibration and three validation subsets of both grid cells and slope units were randomly selected results of validation based on roc receiving operating characteristic curves attest for acceptable to excellent accuracies of the models showing better predictive skill and more stable performance of the susceptibility model based on grid cells

middle holocene mobilization of aeolian sand in western upper michigan and the potential relationship with climate and fire a forested dunefield covers the baraga plains in western upper michigan the ages of five dunes from across the dunefield were determined by optically stimulated luminescence osl employing the single aliquot regenerative dose sar method on quartz grains the results indicate that sand mobilization was restricted to the middle holocene at around 7 ka four environmental variables rapid climatic oscillations fire strong winds and a dry climate are invoked as a combined cause of dune formation this study provides further evidence for the wide extent of aeolian activity in the upper midwest of north america during the middle holocene

water masses and circulation in the central region of the eastern mediterranean eastern ionian south aegean and northwest levantine 1986 1987 in the framework of the major multinational coordinated poem ii 86 march april 1986 and poem v 87 september october 1987 cruises in the eastern mediterranean high resolution hydrographic ctd data were collected by r v aegaio in the eastern ionian sea south aegean sea and northwest levantine basin the intercalibrated data sets were analyzed objectively for an optimal estimation of the basin s circulation in two different seasons the analysis reveals a rather complex general circulation pattern consisting of basin sub basin and mesoscale features during both study periods the major results concern the advection of the modified atlantic water maw along its eastward route the spreading of the levantine intermediate water liw and its trapping by the eddy fields the interaction between the south aegean sea and the eastern mediterranean and the reverse circulation in the cretan sea during winter and summer from the hydrography and the dynamic height maps synthetic schemes show the main circulation features in the two seasons

eastern mediterranean transient and reversal of the ionian sea circulation 1 maps of the remotely sensed absolute dynamic topography adt and sea surface temperature sst over the eastern mediterranean in the period june 1993 to june 2001 show a dramatic and sudden change in the sea surface structure this change which is presumably associated with the relaxation of the eastern mediterranean transient emt had taken place by the middle of 1997 and consisted of a complete reversal of the ionian upper layer circulation from anticyclonic to cyclonic in the emt phase sst and adt maps suggest enhanced communication between the ionian and the aegean basins as well as aegean waters spreading northward along the eastern ionian flank negative wind vorticity in the ionian suggests that the switch of the upper layer circulation from anticyclonic to cyclonic cannot be explained in terms of the wind forcing therefore we suggest the predominance of the baroclinic vorticity production term in determining the upper layer circulation inversion

hydrography of the eastern mediterranean basin derived from argo floats profile data abstract as the eastern mediterranean integrates different sub basins with important hydrological features during recent decades it has often become a target of study by the oceanographic community the recent expansion of observational tools and methods in the marginal seas has allowed more enhanced studies of the oceanographic processes that dominate such areas in this work temperature and salinity profile data collected by argo floats in the eastern mediterranean are analysed for the period 2004 2017 the spatio temporal variability of the basin s physical properties together with the depicted changes in the different sub basins is investigated in an attempt to construct the latest hydrographic picture of the region the findings describe the dominant water masses and reveal a general positive trend in the basin s thermohaline properties the inter annual variability of the stored heat and salt and their distribution in the water column reveals strong climatic signals that are dominated by previously reported alternations of the general circulation and convection events in the area the latter are correlated with the surface temperature and salinity fields and are traced within the area s different sub basins in the early period 2004 2010 data from levantine and ionian depict inter annual variability of the upper layers salinity field that is correlated with previously reported alternations of the levantine s circulation and intermediate water production in the ionian during the latest period 2012 2017 when the data coverage is denser and more representative for the wider area of the eastern mediterranean the adriatic sub basin presents intense dense water production activity while the aegean sea undergoes a relaxation period with significant variability at intermediate layers due to water mass exchanges

late holocene dune activity linked to hydrological drought nebraska sand hills usa dunee elds of the great plains contain stratigraphic records of episodic holocene aeolian activity potentially providing a valuable record of climatic change it has been dife cult to establish unambiguous links between activity at specie c sites and regional palaeoclimate however here we demonstrate that widespread late holocene aeolian activity in the nebraska sand hills the largest dunee eld on the great plains of north america occurred during a period of hydrological drought aeolian sand sheets are interbedded with peat that accumulated in interdunes throughout much of the holocene the youngest of these sand sheets was deposited between 950 and 650 cal bp about the same time as the most recent major episode of aeolian activity at upland sites up to 120 km apart sand sheets could only have advanced across the interdunes if the local groundwater e ow systems that maintain interdune wetlands were temporarily reduced or eliminated by a reduction in recharge both reduced recharge and upland aeolian activity are best explained by regional megadrought

modeling the dispersal of levantine intermediate water and its role in mediterranean deep water formation this paper demonstrates the importance of levantine intermediate water liw in the deep water formation process in the mediterranean using the modular ocean general circulation model at 0 25 resolution 19 vertical levels over the entire mediterranean with an open gibraltar strait liw formation is strongly prescribed in the rhodes gyre region by haney 1971 relaxation while in other regions surface salinity relaxation is much reduced by applying the mixed thermohaline surface boundary conditions isopycnal diagnostics are used to trace water mass movements and volume fluxes are monitored at straits low viscosity and diffusion are used to permit baroclinic eddies to play a role in water mass dispersal the overall water budget is measured by an average flux at gibraltar of 0 8 sv of which 0 7 sv is exchanged with the eastern basin at sicily liw density around 28 95 spreads rapidly after formation throughout the entire levantine due to baroclinic eddies toward the west liw accumulates in the northern and central ionian with some entering the adriatic through otranto and some mixing southward in eddies and exiting to the western mediterranean through sicily liw is converted to deep water in the south adriatic at an average rate of 0 4 sv water exchange through the otranto strait appears to be buoyancy driven with a strong bias to the end of winter march april while at sicily the exchange has a strong symmetric seasonal cycle with maximum transport of 1 1 sv in december indicating the effects of wind driving liw pathways in the west are complex and variable in the tyrrhenian intermediate water becomes uniform on isopycnal surfaces due to eddy stirring west of sardinia two liw boundary currents are formed in the balearic basin one flows northward up the west coast of sardinia and corsica and one westward along the northern african coast the northward current is consistent with observations while the westward current is intermittent for the first 10 years often breaking up into eddies which enter the basin interior some observations of high salinity waters near the african coast may support this interpretation liw retains a subsurface salinity maximum of 38 4 38 5 practical salinity units psu when reaching the northwestern mediterranean contrasting with surface waters fresher than 38 0 psu west mediterranean deep water is formed below 1500 m depth with climatological characteristics when it is mixed and cooled during winter convection in lions gyre

dense intermediate water outflow from the cretan sea a salinity driven recurrent phenomenon connected to thermohaline circulation changes data collected from different platforms in the cretan sea during the 2000s decade present evidence of gradually increasing salinity in the intermediate and deep intermediate layers after the middle of the decade the observed gradual salt transport toward the deeper layers indicates contributions of dense water masses formed in various aegean sea subbasins the accumulation of these saline and dense water masses in the cretan sea finally led to outflow from both cretan straits with density greater than typical levantine cretan intermediate water but not dense enough to penetrate into the deep layers of the eastern mediterranean we name this outflowing water mass as dense cretan intermediate water dciw a retrospective analysis of in situ data and literature references during the last four decades shows that similar events have occurred in the past in two occasions a in the 1970s and b during the eastern mediterranean transient emt onset 1987 1991 we argue that these salinity driven aegean outflows are mostly attributed to recurrent changes of the eastern mediterranean upper thermohaline circulation that create favorable dense water formation conditions in the aegean sea through salinity preconditioning we identify these phenomena as emt like events and argue that in these cases internal thermohaline mechanisms dominate over atmospheric forcing in dense water production however intense atmospheric forcing over an already salinity preconditioned basin is indispensable for creating massive deep water outflow from the cretan sea such as the emt event

high frequency paleoclimate signals from foulden maar waipiata volcanic field southern new zealand an early miocene varved lacustrine diatomite deposit abstract a freshwater diatomite deposit near dunedin south island new zealand provides an exceptional archive of mid latitude seasonal climate variation during latest oligocene early early miocene time the diatomite accumulated in a small 1 5 km diameter maar floored lake that formed during basaltic volcanism except for exposures of basanite dated at 23 2 ma by 40 ar 39 ar and remnants of a paleogene sandstone and conglomerate cover the diatomite body is surrounded by otago schist geophysical profiles indicate that the total diatomaceous sediment thickness may exceed 100 m two depositional facies are described from 15 5 m of weakly consolidated fresh diatomite accessible in two pits a thinly laminated facies comprising 60 of the section consists of dark brown and white couplets of average thickness 0 5 mm both brown and white laminae are composed essentially of frustules of a single pennate diatom along with 1 2 of siliceous sponge spicules dark laminae also contain abundant 5 7 5 m diameter siliceous chrysophycean stomatocysts and organic matter decalcified complete skeletons of galaxias a southern hemisphere group of freshwater or diadromous fish are found throughout diverse well preserved leaves some with attached scale insects are dominated by lauraceae rare flowers are also present trace fossils preserved in the laminated comprise 1 1 5 mm wide pale diatomaceous strings of probable faecal origin and isolated 20 40 mm diameter sand lenses interpreted as faecal remains of swimming waterfowl the second diatomite facies group comprises dark brown speckled beds interpreted as sediment gravity flows up to 14 cm thick and interspersed throughout the study section they incorporate abundant laminated diatomite flecks and leaves and minor woody plant matter and terrigenous silt almost all are capped by 1 8 mm of white diatomite that is interpreted as post flow fall out of resuspended diatom frustules associated breccia and swirly beds up to 8 cm thick are composed of variably contorted clasts of laminated diatomite in a speckled matrix nodules spheroids and films of authigenic framboidal pyrite are commonly associated with plant and fish remains as in modern lakes white laminae likely formed from diatom blooms when light flux temperature or nutrients were optimal during spring early summer dark laminae accumulating during autumn winter months laterally continuous pinstripe lamination absence of bioturbation and excellent fish and plant preservation indicate that the profundal lake and floor were anoxic periodic variations in couplet thickness of 3 10 years compare with quaternary records of el nino southern oscillation variability and indicate that the early early miocene low altitude new zealand climate was seasonal and strongly ocean influenced as it is today