the benguela current and associated upwelling on the southwest african margin a synthesis of the neogene quaternary sedimentary record at dsdp sites 362 and 532

seasonal variability in meanders of the california current system off vancouver island satellite infrared images taken over the past few years reveal seasonal variations in the meanders of the california current system ccs off vancouver island the ccs exhibits meanders with wavelength between 120 and 150 km in both winter and spring when the upper ocean current all flows northwestward or southeastward respectively in summer the ccs includes the california undercurrent which flows northwestward beneath the southeastward surface current and has shorter wavelength 75 80 km meanders around the end of august these shorter scale meanders are engulfed by the longer 150 km meanders finally in the fall eddies are detached from the offshore extensions of the longer meanders a linear stability theory using a four layer model of the ccs successfully predicts the wavelengths in the winter and spring but not in the summer and fall the meander evolution observed in summer and fall is instead simulated by using a nonlinear numerical model in a domain with topographic obstacles selected to match the alongshore variations in the continental slope the topographic features with a spatial periodicity of 75 km act as a trigger to initiate the short wavelength 75 km meanders following this these 75 km meanders grow because of baroclinic instability the 75 km meanders which have grown to large amplitudes are replaced by longer 150 km meanders because of nonlinear interactions between these two scales of meanders cyclonic eddies are finally shed from the longer meanders

on the three dimensional numerical modeling of the deep circulation around angel de la guarda island in the gulf of california a three dimensional nonlinear baroclinic model is used to model the circulation in the ballenas channel gulf of california mexico which was inferred from current meter observations over three sills that surround the area the suggested circulation consists of deep inflow that follows two paths the first one is a direct spill of water through san lorenzo sill into ballenas channel the second one a larger route that starts at san esteban sill then flows north of the island passing over tiburon and delfin basins and then turns to the south reaching the north ballenas channel sill and then spills into ballenas channel following the latter result a previous modeling effort to reproduce the circulation was partially obtained the long path was not reproduced and it was believed that finer horizontal resolution was needed in this work the bathymetric resolution was increased by a factor of three and the full path of this deep circulation is now obtained and corroborated

exhumation of an active magmatic hydrothermal system in a resurgent caldera environment the example of ischia italy abstract ischia is a rare case of a well exposed caldera system that has experienced rapid recent resurgence which can be used to dissect the anatomy of an otherwise inaccessible active hydrothermal system developed in a caldera forming environment integrated analyses of melt and fluid inclusions mineralogy and stable isotopic compositions of pumices tuffs and syenitic xenoliths of the ischia volcanic system provide strong physico chemical constraints on the shallow magmatic reservoir and the hydrothermal system the hydrothermal system has been exposed by the rapid uplift of the mt epomeo resurgent block the engine of the hydrothermal system of ischia can be identified in the shallow magmatic system at around 2 km depth that hosts hot c 1000 c trachytic magma the hydrothermal system developed principally within thick intracaldera ignimbrite deposits and extended to a depth of at least 1 km defining a series of facies characterized by associations of alteration mineral assemblages typical of a seawater dominated high temperature geothermal system supplementary material sample descriptions and analytical methods are available at http www geolsoc org uk sup18371

thermohaline circulation in the gulf of california the gulf of california a narrow semienclosed sea is the only evaporative basin of the pacific ocean as a result of evaporative forcing salinities in the gulf are 1 to 2 higher than in the adjacent pacific at the same latitude this paper examines the thermohaline structure of the gulf and the means by which thermohaline exchange between the pacific and the gulf occurs over time scales of months to years in addition to evaporative forcing air sea heat fluxes and momentum fluxes are important to thermohaline circulation in the gulf from observations presented here it appears that the gulf gains heat from the atmosphere on an annual average unlike the mediterranean and red seas which have comparable evaporative forcing as a result outflow from the gulf tends to be less dense than inflow from the pacific winds over the gulf change direction with season blowing northward in summer and southward in winter this same seasonal pattern appears in near surface transports averaged across the gulf the thermohaline circulation then consists of outflow mostly between about 50 m and 250 m inflow mostly between 250 m and 500 m and a surface layer in which the direction of transport changes with seasonal changes in the large scale winds using hydrographic observations from a section across the central gulf total transport in or out of the northern gulf is estimated to be 0 9 sv heat gain from the atmosphere is estimated to be 20 to 50 w m 2 and evaporation is estimated to be 0 95 m yr 1 these estimates are annual averages based on cruises from several years seasonal variations in thermohaline structure in the gulf are also examined and found to dominate the variance in temperature and density in the top 500 m of the water column salinity has little seasonal variability but does exhibit more horizontal variablility than temperature or density major year to year variations in thermohaline structure may be attributable to el nino southern oscillation events

middle to late miocene oxygen isotope stratigraphy of odp site 1085 se atlantic new constrains on miocene climate variability and sea level fluctuations abstract the middle miocene 18o increase represents a fundamental change in earth s climate system due to a major expansion and permanent establishment of the east antarctic ice sheet accompanied by some effect of deepwater cooling the long term cooling trend in the middle to late miocene was superimposed by several punctuated periods of glaciations mi events characterized by oxygen isotopic shifts that have been related to the waxing and waning of the antarctic ice sheet and bottom water cooling here we present a high resolution benthic stable oxygen isotope record from odp site 1085 located at the southwestern african continental margin that provides a detailed chronology for the middle to late miocene 13 9 7 3 ma climate transition in the eastern south atlantic a composite fe intensity record obtained by xrf core scanning odp sites 1085 and 1087 was used to construct an astronomically calibrated chronology based on orbital tuning the oxygen isotope data exhibit four distinct 18o excursions which have astronomical ages of 13 8 13 2 11 7 and 10 4 ma and correspond to the mi3 mi4 mi5 and mi6 events a global climate record was extracted from the oxygen isotopic composition both long and short term variabilities in the climate record are discussed in terms of sea level and deep water temperature changes the oxygen isotope data support a causal link between sequence boundaries traced from the shelf and glacioeustatic changes due to ice sheet growth spectral analysis of the benthic 18o record shows strong power in the 400 kyr and 100 kyr bands documenting a paleoceanographic response to eccentricity modulated variations in precession a spectral peak around 180 kyr might be related to the asymmetry of the obliquity cycle indicating that the response of the dominantly unipolar antarctic ice sheet to obliquity induced variations probably controlled the middle to late miocene climate system maxima in the 18o record interpreted as glacial periods correspond to minima in 100 kyr eccentricity cycle and minima in the 174 kyr obliquity modulation strong middle to late miocene glacial events are associated with 400 kyr eccentricity minima and obliquity modulation minima thus fluctuations in the amplitude of obliquity and eccentricity seem to be the driving force for the middle to late miocene climate variability

a modeling study of coastal trapped wave propagation in the gulf of california part ii response to idealized forcing abstract the evolution of remotely forced coastal trapped waves in the gulf of california is studied using a hydrostatic primitive equation model the sea level time variability at a remote station south of the gulf is assumed to propagate northward into the gulf as a mode 1 coastal trapped wave ctw to validate this assumption observations and model results are compared in general sea level fluctuations are reasonably well represented by the model with model data correlations decreasing from 0 76 at topolobampo close to the entrance of the gulf to 0 52 at santa rosalia in the central gulf model data correlations of velocity are lower 0 6 in the gulf ctws propagate northward along the east side with no significant changes south of the sill which is 600 km north of the entrance when incident waves propagating northward in the gulf along the east side arrive at the sill a small fraction of the wave energy enters the northern gulf and is dissipated most of the wave energy is steered at the

the effect of the seasonal variation of stratification on the circulation of the northern gulf of california abstract direct current measurements reveal that the circulation of the northern gulf of california in the annual timescale consists of a cyclonic basinwide gyre 0 35 m s 1 that lasts from june to september 4 months and an anticyclonic gyre 0 35 m s 1 lasting from november to april 6 months the transitions between regimes take about three weeks each the hypothesis that the difference in duration of the two circulation regimes is due to the seasonal variation of stratification of the water column is explored by simulations with a nonlinear two layer numerical model of circulation and thermodynamics that includes vertical mixing parameterized as an entrainment velocity the model results agree remarkably well with the observations considering its simplified vertical structure in addition the model predicts a net circulation consisting of an anticyclonic gyre of 0 05 m s 1 with a corresponding average concavity of the interface and a two layer exchange through the main channels of the arc

neogene palaeoceanographic and palaeoclimatic events inferred from palynological data cape basin off south africa odp leg 175 abstract sites 1085 1086 and 1087 were drilled off south africa during ocean drilling program odp leg 175 to investigate the benguela current system while previous studies have focused on reconstructing the neogene palaeoceanographic and palaeoclimatic history of these sites palynology has been largely ignored except for the late pliocene and quaternary this study presents palynological data from the upper middle miocene to lower upper pliocene sediments in holes 1085a 1086a and 1087c that provide complementary information about the history of the area abundant and diverse marine palynomorphs mainly dinoflagellate cysts rare spores and pollen and dispersed organic matter have been recovered multivariate statistical analysis of dispersed organic matter identified three palynofacies assemblages a b c in the most continuous hole 1085a and they were defined primarily by amorphous organic matter aom and to a lesser extent black debris structured phytoclasts degraded phytoclasts and marine palynomorphs ecostratigraphic interpretation based on dinoflagellate cyst spore pollen and palynofacies data allowed us to identify several palaeoceanographic and palaeoclimatic signals first the late middle miocene was subtropical and sediments contained the highest percentages of land derived organic matter even though they are rich in aom palynofacies assemblage a second the late miocene was cool temperate and characterized by periods of intensified upwelling increase in productivity abundant and diverse oceanic dinoflagellate cysts and the highest percentages of aom palynofacies assemblage c third the early to early late pliocene was warm temperate with some dry intervals increase in grass pollen and intensified upwelling fourth the neogene carbonate crash identified in other southern oceans was recognized in two palynofacies a samples in hole 1085a that are nearly barren of dinoflagellate cysts one middle miocene sample 590 mbsf 13 62 ma and one upper miocene sample 355 mbsf 6 5 ma finally the extremely low percentages of pollen suggest sparse vegetation on the adjacent landmass and namib desert conditions were already in existence during the late middle miocene

surface circulation in the gulf of california in summer from surface drifters and satellite images 2004 2006 surface drifters released in the gulf of california between june 2004 and august 2006 are used to describe the surface circulation in late spring and summer in the june to september mean there was a poleward coastal current on the shelf and slope of the mainland side of the gulf with mean speed 0 3 m s it reached the northern gulf and joined the cyclonic circulation typical of this zone in summer in the western half of the southern gulf the drifters presented recirculating currents that are due to mesoscale eddies that appear to dominate the surface circulation in summer in june 2004 the coastal current presented an enhancement event with mean speed around 0 60 m s and maximum 0 80 m s it took 20 days for a particular drifter to travel the 1000 km from the gulf entrance to the head this strengthening of the coastal current was apparent in chlorophyll a and sst satellite images the drifters following closely the intrusion of warm chlorophyll poor surface water from outside the gulf the drifters and the satellite images suggest that the current enhancement event lasted less than a month this mesoscale event was linked with a mesoscale remote forcing in the tropical pacific coast and with a mesoscale local forcing of the wind these events seem to occur every year and are probably important in carrying organisms and properties from the entrance to the whole length of the gulf

surface dispersion in the gulf of california abstract surface dispersion is measured in the gulf of california by means of argos drifters released along this semi enclosed elongated basin first basic one particle statistics lagrangian scales absolute dispersion and diffusion coefficients are estimated along and across the gulf absolute dispersion shows a nearly ballistic regime during the lagrangian time scale t 2 where t is time during the subsequent 30 days absolute dispersion enters a random walk regime t along the gulf while being saturated across the basin due to the lateral boundaries secondly the analysis is extended to two particle statistics relative dispersion between pairs of drifters and finite scale lyapunov exponents fsle relative dispersion is nearly exponential in both directions during the first few days though evidence is not conclusive during the subsequent 30 days it grows as t 1 5 along the gulf while being saturated across the basin again it is shown that relative dispersion along the gulf is proportional to t 3 where t represents a shifted time that depends on the initial separation of the particles this form of the richardson regime is consistently measured for particles that are sufficiently separated 30 km or more the richardson regime is verified with the fsle for particle separations ranging from 30 to 140 km approximately the obtained dispersion properties are discussed in terms of the main circulation features within the basin such as mesoscale vortices that occupy the width of the gulf these structures might retain buoys during days or weeks thus preventing or delaying further displacements and therefore affecting the particle dispersion the vortices are also an important mechanism to translate particles across the gulf between the peninsula and the continent thus promoting the saturation of dispersion along this direction

sensitivity of simulated circulation dynamics to the choice of surface wind forcing in the japan east sea abstract the circulation sensitivity to the choice of wind forcing product is investigated with the nrl layered ocean model nlom configured for the japan east sea monthly climatologies from seven different wind stress data sets and wind stress curl are formed from observed and model derived atmospheric data sets the resulting maps of wind stress curl reveal significantly different spatial patterns and magnitudes even two with largely opposite large scale patterns of wind stress curl these wind sets were used in forcing three sets of simulations 1 8 linear and 1 8 and 1 32 nonlinear in addition seasonally varying straits forcing inflow through tsushima balanced by outflow through tsugaru and soya was included in all the simulations and simulations with straits forcing only were performed the 1 5 layer linear reduced gravity simulations include only the lowest order dynamics mainly munk 1 3 western boundary layers due to both wind and straits forcing and a sverdrup interior the nonlinear simulations add bottom topography multiple internal modes diapycnal mixing and ventilation of layer interfaces at 1 8 resolution only weak barotropic baroclinic instabilities occur but at 1 32 resolution these are much stronger allowing vigorous transfer of energy from the upper ocean to the abyssal layer via baroclinic instability this drives much stronger mean abyssal currents that more strongly steer upper ocean current pathways than at 1 8 i e there is much stronger upper ocean topographical coupling the linear model simulates most of the basic features e g the subpolar gyre with all but the straits forcing only the east korean warm current ekwc and its connection to the subpolar front with all but one wind forcing set but the remaining wind set gives a continuous nearshore branch nb of the tsushima warm current along the coast of honshu in all of the linear simulations with an ekwc the separation latitude from the coast of korea is determined by the latitude 41 n of the tsugaru strait outflow too far north except for one which is also too far north all of the nonlinear simulations include the nb which is mainly due to isopycnal outcropping this creates another inflow to outflow pathway diverting some of the flow from the ekwc and allowing the wind stress curl to compete better with straits forcing in determining the ekwc separation latitude using the 1 8 nonlinear model three of the wind forcing sets yield a realistic separation latitude for the ekwc 37 38 n and two more are marginally successful the two remaining and the simulation with straits forcing only yield ekwc overshoot to 40 n at 1 32 resolution one of the simulations one with forcing that gave marginally realistic separation at 1 8 has a realistic ekwc separation latitude the three wind products that yielded realistic ekwc separation at 1 8 continue to give realistic separation at 1 32 via the wind stress curl but the remainder give realistic separation via upper ocean topographical coupling at 1 32 resolution all but one of the simulations showed a strong yamato rise impact on the pathway of the subpolar front due to steering by abyssal currents at 1 8 resolution only two of the eight showed any such impact one due to abyssal currents driven by vertical mixing in the subpolar gyre in all the other 1 8 simulations the mean abyssal currents were weak but in one case weak abyssal currents were aided by a region of strong negative wind stress curl not seen in the other wind products in addition regions of the ventilation of intermediate and deep water in response to each wind set are identified a series of six 1 32 simulations forced interannually with 6 hourly winds 1979 93 are used to separate the model variability due to wind forcing deterministic and flow instabilities nondeterministic this analysis indicates that flow instabilities are the dominant source of ssh variability over a large majority of the basin especially near 37 38 n where the ekwc separates from the coast and along the pathway of the subpolar front following the north rim of the yamato rise towards the tsugaru strait wind forcing dominates the ssh variability in the coastal wave guide and over the deep basins and troughs

miocene evolution of atmospheric carbon dioxide changes in pco2 or ocean circulation are generally invoked to explain warm early miocene climates and a rapid east antarctic ice sheet eais expansion in the middle miocene this study reconstructs late oligocene to late miocene pco2 from ep values based on carbon isotopic analyses of diunsaturated alkenones and planktonic foraminifera from deep sea drilling project sites 588 and 608 and ocean drilling program site 730 our results indicate that highest pco2 occurred during the latest oligocene 350 ppmv but decreased rapidly at 25 ma the early and middle miocene was characterized by low pco2 260 190 ppmv lower intervals of pco2 correspond to inferred organic carbon burial events and glacial episodes with the lowest concentrations occurring during the middle miocene there is no evidence for either high pco2 during the late early miocene climatic optimum or a sharp pco2 decrease associated with eais growth paradoxically pco2 increased following eais growth and obtained preindustrial levels by 10 ma although we emphasize an oceanographic control on miocene climate low pco2 could have primed the climate system to respond sensitively to changes in heat and vapor transport

amplitude variations of 1470 year climate oscillations during the last 100 000 years linked to fluctuations of continental ice mass we describe amplitude variations of a 1470 year y signal in the oxygen isotope record from the gisp2 ice core as a function of continental ice mass as recorded in sea level variations the 1470 y signal is closely tied to dansgaard oeschger interstadial events which perturbed the climate system on a global scale large amplitude 1470 y oscillations occur only if continental ice mass exceeds a threshold level equivalent to sea level at approximately 45 m and are tied to times of change in ice mass minima of the 1470 y signal in the greenland ice are associated with short time intervals of relatively stable phases of sea level and with reduced climate variability in the entire periodicity range between approximately 550 5000 y

palynological evidence for holocene climatic and oceanographic changes off western south africa abstract atmospheric and oceanographic interactions between the atlantic and indian oceans influence upwelling in the southern benguela upwelling system in order to obtain a better knowledge of paleoceanographic and paleoenvironmental changes in the southern benguela region during the holocene 12 marine surface sediment samples and one gravity core geob8331 4 from the namaqualand mudbelt off the west coast of south africa have been studied for organic walled dinoflagellate cysts in high temporal resolution the results are compared with pollen and geochemical records from the same samples our study emphasizes significantly distinct histories in upwelling intensity as well as the influence of fluvial input during the holocene three main phases were identified for the holocene high percentages of cysts produced by autotrophic taxa like operculodinium centrocarpum and spiniferites spp indicate warmer and stratified conditions during the early holocene 9900 8400 cal yr bp suggesting reduced upwelling likely due to a northward shift of the southern westerlies in contrast the middle holocene 8400 3100 cal yr bp is characterized by a strong increase in heterotrophic taxa in particular lejeunecysta paratenella and echinidinium spp at the expense of autotrophic taxa this indicates cool and nutrient rich waters with active upwelling probably caused by a southward shift of the southern westerlies during the late holocene 3100 cal yr bp to modern brigantedinium spp and other abundant taxa interpreted to indicate fluvial nutrient input such as cyst of protoperidinium americanum and lejeunecysta oliva imply strong river discharge with high nutrient supply between 3100 and 640 cal yr bp

changes in miocene through pleistocene dinoflagellates from the eastern equatorial pacific odp site 1039 in relation to primary productivity abstract palynological data from offshore costa rica allow us to investigate the relationship between dinoflagellate cyst assemblages and changes in regional oceanic primary productivity from miocene to pleistocene productivity at odp site 1039 was influenced by tectonic drift as site 1039 approached the continent from the equator to its current position at 10 n in addition dinoflagellate abundance is modulated by regional productivity events which modified primary productivity as also indicated by available data on calcareous nannofossils diatoms toc and caco 3 content five palynomorph intervals are defined the early late miocene one dominated by batiacasphaera represents relatively stable productive oceanic conditions before the closure of the indonesian and panama seaways the late miocene decrease in palynomorph recovery is related to the carbonate crash event the high abundance and diversity of the assemblages at the end of the late miocene to early pliocene indicate increased productivity related to the global biogenic bloom and a change in dominance from batiacasphaera to impagidinium to nematosphaeropsis the low abundance of the late pliocene interval is related to el nino like conditions and there is another change related to the disappearance of batiacasphaera and dominance of impagidinium nematosphaeropsis and operculodinium the abundant pleistocene assemblages represent increased marine productivity and a high influx of continental palynomorphs and bissacate pollen associated with the proximity of the costa rica dome pleistocene dinoflagellates are characterized by spiniferites and selenopemphix together with rare impagidinium and nematosphaeropsis

initial testing of a numerical ocean circulation model using a hybrid quasi isopycnic vertical coordinate abstract an ocean circulation model developed for the study of mesoscale to gyre scale circulation and heat transport is described and tested the model employs density as vertical coordinate except in the immediate vicinity of possible coordinate surface intersections with the ocean surface test simulations are carried out for a double gyre ocean basin of the type used by holland 1978 but with better resolution in the upper 1000 m of the model ocean the final state of a 5 year coarse mesh 50 km resolution on a 2400 km 1200 km domain spin up is used as the initial state for mesoscale experimentation on a 25 km mesh basin energetics as well as mean mass transport streamfunction and mean potential vorticity fields are given for three mesoscale experiments in which the magnitude and formulation of lateral dissipation are varied each of these experiments run for approximately five years exhibits vigorous mesoscale activity associated with western boundary current separation and the free jet

fractionation processes affecting the stable carbon isotope signature of thermal waters from hydrothermal volcanic systems the examples of campi flegrei and vulcano island southern italy abstract the carbon isotopic composition of dissolved c bearing species is a powerful tool to discriminate the origin of carbon in thermal waters from volcanic and hydrothermal systems however the 13 c values of dissolved co 2 and tdic total dissolved inorganic carbon are often different with respect to the isotopic signature that characterizes the potential carbon primary sources i e deep hydrothermal reservoirs magmatic gases and organic activity the most commonly invoked explanation for such isotopic values is related to mixing processes between deep and shallow end members nevertheless experimental and empirical investigations demonstrated that isotopic fractionation due to secondary processes acting on the uprising fluids from the hydrothermal reservoirs is able to reproduce the measured isotopic values in this paper we investigated the chemistry of thermal waters collected at campi flegrei and vulcano island southern italy whose origin is related to interaction processes among magmatic gases meteoric water seawater and hosting rocks a special focus was dedicated to the 13 c values of dissolved co 2 13 c co2 aq and total dissolved inorganic carbon 13 c tdic the 13 c co2 aq and 13 c tdic values in the water samples from both these systems ranged from i those measured in fumarolic gases likely directly related to the deep hydrothermal magmatic reservoir and ii those typically characterizing biogenic co 2 i e produced by microbially driven degradation of organic matter a simple mixing model of the two end members apparently explaining these intermediate carbon isotopic values contrasts with the chemical composition of the dissolved gases on the contrary isotopic fractionation due to secondary processes such as calcite precipitation affecting hydrothermal fluids during their underground circulation seems to exhaustively justify both the chemical and isotopic data if not recognized these processes which frequently occur in volcanic and hydrothermal systems may lead to an erroneous interpretation of the carbon source causing an underestimation of the contribution of the hydrothermal magmatic fluids to the dissolved carbon species these results pose extreme caution in the interpretation of intermediate 13 c co2 aq and 13 c tdic values for the assessment of the carbon budget of hydrothermal volcanic systems

dinoflagellate cyst paleoecology during the pliocene pleistocene climatic transition in the north atlantic dinoflagellate cysts dinocysts are widely used as tracers of sea surface conditions in late quaternary marine records however paleoenvironmental reconstructions across the pliocene pleistocene climatic transition and beyond are limited because the hydrologic conditions influencing assemblage compositions may not have a modern analogue and the ecological optima of extinct dinocyst species are not well known from a study of two cored sites in the central and eastern north atlantic we bypass these issues by statistically analyzing the variations in dinocyst assemblage composition and comparing the results directly to paleoecological parameters 18obulloides 18osalinity and geochemical proxies for sea surface temperature sst derived from the planktonic foraminifer globigerina bulloides recovered from the same samples as the dinocysts through canonical correspondence analysis we demonstrate the co variation of seasonality and dinocyst paleoproductivity we show that pyxidinopsis braboi is a cold tolerant species with an optimum sst between 12 and 14 c we extend the use of nematosphaeropsis labyrinthus as an indicator of transitional climatic conditions to the pliocene we offer evidence for the correlation of bitectatodinium tepikiense and filisphaera microornata to high seasonality and we reiterate an apparent link between spiniferites mirabilis and eastern north atlantic water masses finally we confirm that habibacysta tectata is cold tolerant rather than a strictly cold water indicator that operculodinium eirikianum is a cold intolerant species favoring outer neritic environments and that ataxiodinium confusum and invertocysta lacrymosa are both warm water species

effect of coastal trapped waves and wind on currents and transport in the gulf of california subsurface pressure ssp observations from stations inside and outside of the gulf of california gc are used to analyze the relationship between low frequency currents temperature and transport inside the gc and intraseasonal coastal trapped waves ctws which propagate poleward along the coast toward the gc correlation functions and coherences of ssp stations were consistent with intraseasonal ctws splitting in two at the mouth of the gulf one part enters the gulf propagates around the gulf and eventually toward the mouth and another part that appears to jump the mouth of the gulf and travels poleward along the west coast of the peninsula the correlation and coherence estimates of ssp at manzanillo with currents showed that downwelling ctws generated along gulf current anomalies toward the head of the gulf at the mainland shelf of the mouth whereas at ballenas channel sill san lorenzo sill these waves generated current anomalies toward the mouth near the surface bottom at the san lorenzo sl sill downwelling ctws increased the near bottom 400 m temperature and reduced the bottom transport of deep fresher and colder water that flows toward the head of the gulf cross calibrated multiplatform winds were used to investigate their relationship with currents the first empirical orthogonal function of the along gulf wind stress showed that wind blowing toward the head of the gulf generated a reduction of bottom transport toward the head of the gulf through the sl sill and intensified surface geostrophic current fluctuations toward the head of the gulf there was also significant correlation between inflow bottom transport and outflow surface geostrophic velocities averaged across the gulf consistent with the exchange pattern for the northern gulf

deciphering the palaeoecology of late pliocene and early pleistocene dinoflagellate cysts abstract in an attempt to document the palaeoecological affinities of individual extant and extinct dinoflagellate cysts late pliocene and early pleistocene dinoflagellate cyst assemblages have been compared with geochemical data from the same samples mg ca ratios of globigerina bulloides were measured to estimate the spring summer sea surface temperatures from four north atlantic iodp dsdp sites currently our pliocene pleistocene database contains 204 dinoflagellate cyst samples calibrated to geochemical data this palaeo database is compared with modern north atlantic and global datasets the focus lies in the quantitative relationship between mg ca based i e spring summer sea surface temperatures sstmg ca and dinoflagellate cyst distributions in general extant species are shown to have comparable spring summer sst ranges in the past sstmg ca and today sst from world ocean atlas 2005 locarnini et al 2006 demonstrating that our new approach is valid for inferring spring summer sst ranges for extinct species for example habibacysta tectata represents sstmg ca values between 10 and 15 c when it exceeds 30 of the assemblage and invertocysta lacrymosa exceeds 15 when sstmg ca values are between 18 6 and 23 5 c however comparing pliocene and pleistocene sstmg ca values with present day summer values for the extant impagidinium pallidum suggests a greater tolerance of higher temperatures in the past this species occupies more than 5 of the assemblage at sstmg ca values of 11 6 17 9 c in the pliocene and pleistocene whereas present day summer ssts are around 1 7 to 6 9 c this observation questions the value of impagidinium pallidum as reliable indicator of cold waters in older deposits and may explain its bipolar distribution

chemical and isotopic compositions of minerals and waters from the campi flegrei volcanic system naples italy abstract based on their 34 s signature sulfate minerals and native sulfur around fumaroles and hot water pools from the campi flegrei volcanic area derive from supergenic oxidation of volcanic h 2 s their mean 34 s value 0 2 1 7 matches with that of fumarolic h 2 s at solfatara 0 3 0 3 as well as with the 34 s of 1 4 obtained for total sulfur in fresh trachyte from the area all 34 s values indicate a mostly deep seated origin for sulfur thermal waters were analysed for major and minor chemistry and for oxygen hydrogen and sulfur isotope compositions pools at pisciarelli are filled with evaporated meteoric water heated by rising magmatic gases the water 18 o 3 8 1 3 and 2 h 6 5 2 2 values in these steam heated waters are controlled by mixing and evaporation effects and the 34 s value of dissolved sulfate 1 3 0 3 basically agrees with supergenic oxidation of deep seated h 2 s as the major source of sulfur instead water from thermal springs and wells elsewhere in the campi flegrei appears to be a mixture between dilute meteoric and saline marine components the latter may be local seawater from the bay of pozzuoli the 18 o and 2 h values of waters sampled during 1993 1994 range from 5 6 to 0 3 and from 33 to 3 4 respectively the 34 s values of dissolved sulfate range between 0 1 and 19 5 in general sulfate is probably derived essentially from two sources both within the volcanic cover i e oxidation dissolution of pyrite and anhydrite and marine water an occasional source of water and sulfate is represented by magmatic gases which directly interact with shallow meteoric water as in the case of the hotel tennis well yielding steam heated water with 18 o 1 5 0 2 2 h 17 1 and 34 s 0 1

paleogene early neogene paleoenvironmental reconstruction based on palynological analysis of odp hole 959a west africa abstract five paleoenvironmental intervals interval 1 interval 5 are established in the late paleogene early neogene of the ocean drilling program odp site 959 hole 959a cote d ivoire ghana transform margin in the eastern equatorial atlantic the intervals are based on dinoflagellate cyst and palynofacies analyses of 30 samples covering a 273 3 m interval we observed an abundance of the filisphaera group filisphaera filifera and bitectatodinium tepikiense which is interpreted as an arctic migration to equatorial regions during a narrow interval in the early oligocene early rupelian in addition we document one hiatus within interval 3 in the early miocene aquitanian the dominance of typically restricted marine species of the polysphaeridium group homotryblium plectilum and polysphaeridium zoharyi at several horizons in the open oceanic sediments of odp hole 959a appear to be very distinctive events upon integrating dinoflagellate cyst data with prior lithologic and microfossil data we interpret these dominance events as being due to offshore transportation by turbidity currents intervals 1 and 2 hiatus event interval 3 or hyperstratification conditions intervals 3 and 4 in addition the dominance of cribroperidinium spp c giuseppei and c tenuitabulatum in the upper part of the section within paleoenvironmental interval 5 is suggestive of cold water masses during a strong upwelling period in the latest early miocene burdigalian the general abundance of amorphous organic matter alongside the dinoflagellate cyst assemblage supports an outer neritic oceanic depositional environment for the studied site the consistent occurrence of degraded phytoclasts in the sediments also suggests fluvial outflows to this offshore site

karst pocket valleys and their implications on pliocene quaternary hydrology and climate examples from the nullarbor plain southern australia abstract karst on the nullarbor plain has been studied and described in detail in the past but it lacked the determination of the karst discharge and palaeo watertable levels that would explain the palaeohydrological regime in this area this study explores the existence of previously unrecognised features in this area karst pocket valleys and gives a review on pocket valleys worldwide initial gis analyses were followed up by detailed field work sampling mapping and measuring of morphological geological and hydrological characteristics of representative valleys on the wylie and hampton scarps of the nullarbor plain rock and sand samples were examined for mineralogy texture and grain size and a u pb dating of a speleothem from a cave within a pocket valley enabled the establishment of a time frame of the pocket valleys formation and its palaeoenvironmental implications the pocket valleys document the hydrological evolution of the nullarbor karst system and the neogene pleistocene palaeoclimatic evolution of the southern hemisphere a review of pocket valleys in different climatic and geological settings suggests that their basic characteristics remain the same and their often overlooked utility as environmental indicators can be used for further palaeoenvironmental studies the main period of intensive karstification and widening of hydrologically active underground conduits is placed into the wetter climates of the pliocene epoch subsequent drier climates and lowering of the watertable that followed sea level retreat in the quaternary resulted in formation of the pocket valleys gravitational undermining slumping exudation and collapse which combined with periodic heavy rainfall events and discharge due to impeded drainage caused the retreat of the pocket valleys from the edge of escarpments

orbitally paced climate oscillations across the oligocene miocene boundary the late oligocene and early miocene periods some 21 to 27 million years ago have generally been viewed as times of moderate global warmth and ice free conditions yet several lines of evidence suggest that this interval was punctuated by at least one and possibly several episodes of high latitude cooling and continental glaciation1 2 3 here we present stable isotope and per cent coarse fraction data from an equatorial western atlantic deep sea sediment core that provide high resolution records of the climate variability across the oligocene miocene transition 22 5 25 7 million years ago a strong 40 kyr periodicity in the oxygen isotope record is consistent with a high latitude orbital obliquity control on ice volume and temperature orbital influences are also apparent at precession and eccentricity frequencies including a series of 400 kyr oscillations that culminate in distinct maxima at the oligocene miocene boundary about 23 7 million years ago covariance between the carbon and oxygen isotope records suggests that the oceanic carbon cycle may have contributed to global cooling during the 400 kyr cycles particularly at the oligocene miocene boundary

summer generation of the southern gulf of california eddy train 1 ocean color and sea surface temperature satellite observations show the existence of a series of anticyclonic eddies along the axis of the southern gulf of california sgoc to investigate the summer generation of these eddies a regional version of the hybrid coordinate ocean model hycom has been configured for the goc and has been nested inside the global model a suite of experiments using the nested goc model was developed and used to isolate the effects of the local wind and the effects of the oceanic remote forcing on the generation of the sgoc eddies the results indicate that the local wind is not essential for the generation of these eddies rather it is the oceanic remote forcing in the sgoc the monthly variability of the currents and sea surface height is mainly due to the deterministic near coastal poleward eastern boundary currents pebc the interaction of the pebc with the topographic irregularities the capes at topolobampo and cabo lobos and the ridges extending offshore from the entrance of the san lorenzo and sinaloa rivers generates the sgoc eddies the northward upper ocean transport induced by the pebc includes two maximums one in may june and the other in december during the summers of 1999 and 2004 the pebc were intensified by the arrival of equatorially originated downwelling coastally trapped waves ctws which contributed to the generation of the sgoc eddies the summer 2004 ctw increased the northward upper ocean transport by 2 sv this particular ctw was measured by several tide gauges located along the coast

eddy activity in the four major upwelling systems from satellite altimetry 1992 2007 eddy activity in the four major eastern boundary upwelling systems ebus is investigated using 15 years of satellite altimetry data based on the analysis of more than 4000 long lived eddy trajectories in every ebus we show that mesoscale structures are mainly generated along the continental coasts and south of the main archipelagos and propagate westward with velocities increasing toward the equator these mesoscale eddies having radii of 70 160 km are then frequently observed along the coastal transition zones and frontal regions and some large oceanic areas are preferentially populated by cyclonic or anticyclonic eddies temporal variations of the number of newly formed eddies and the associated eddy activity index defined as the mean eddy energy density are finally examined at seasonal and interannual scales the strongest seasonal interannual respectively variations are observed in the california benguela upwelling systems the proposed indices also exhibit contrasted long term trends in each ebus which suggests that eddy activity might be sensitive to a warming climate

late pliocene vegetation and climate in namibia southern africa derived from palynology of odp site 1082 the present day condition of bipolar glaciation characterized by rapid and large climate fluctuations began at the end of the pliocene with the intensification of the northern hemisphere continental glaciations the global cooling steps of the late pliocene have been documented in numerous studies of ocean drilling program odp sites from the northern hemisphere however the interactions between oceans and between land and ocean during these cooling steps are poorly known in particular data from the southern hemisphere are lacking therefore i investigated the pollen of odp site 1082 in the southeast atlantic ocean in order to obtain a high resolution record of vegetation change in namibia between 3 4 and 1 8 ma four phases of vegetation development are inferred that are connected to global climate change 1 before 3 ma extensive rather open grass rich savannahs with mopane trees existed in namibia but the extension of desert and semidesert vegetation was still restricted 2 increase of winter rainfall dependent renosterveld like vegetation occurred between 3 1 and 2 2 ma connected to strong advection of polar waters along the namibian coast and a northward shift of the polar front zone in the southern ocean 3 climatically induced fluctuations became stronger between 2 7 and 2 2 ma and semiarid areas extended during glacial periods probably as the result of an increased pole equator thermal gradient and consequently globally enhanced atmospheric circulation 4 aridification and climatic variability further increased after 2 2 ma when the polar front zone migrated southward and the influence of atlantic moisture brought by the westerlies to southern africa declined it is concluded that the positions of the frontal systems in the southern ocean which determine the locations of the high pressure cells over the south atlantic and the southern indian ocean have a strong influence on the climate of southern africa in contrast to the climate of northwest and central africa which is dominated by the saharan low pressure cell

source processes of the thermal waters from the phlegraean fields naples italy by means of the study of selected minor and trace elements distribution abstract the geochemical characteristics of hydrothermal waters from the phlegraean fields p f naples italy were analysed for minor and trace elements selectively mobilised in hydrothermal systems such as b f hg as pb and tl the water samples collected from a shallow aquifer likely to be fed by deeper fluids showed various geochemical features resulting from the mixing of three components 1 surface waters of meteoric origin 2 hot deep waters deriving from water rock interaction and including deep waters of marine origin 3 magmatic fluids rising from the local magma chamber lying a few kilometres below the town of pozzuoli this setting although very complex provides a reliable means of studying the distribution of the investigated trace elements in particular within the phlegraean area high contents of b 0 1 48 mg l f 0 5 8 mg l as 16 6050 g l and hg 0 7 232 g l were observed the levels of thallium in the springs close to solfatara about 7 g l were in line with those normally recorded in hydrothermal areas whereas high levels of this element up to 23 3 g l were identified in other wells of the study area lead 1 3 to 29 1 g l appears to be anomalous with respect to its normal content in groundwater about 1 g l owing to the presence of high density brines at depth which enhance the solubility of pb in volcanic rocks under hydrothermal conditions the distribution of the investigated trace elements in the phlegraean fields thermal area is probably related to the different ascent pathways of the fluids clearly apart from the influence exerted by anomalous thermal conditions each element shows a different behaviour depending on its geochemical affinity with mineral phases and as a consequence of the different enthalpy values which determine ion partitioning in gaseous phases based on geochemical evidences and on the distribution of minor and trace elements the source processes of the investigated hydrothermal waters were defined five main groups were identified 1 acid sulphate waters resulting from mixing of meteoric water with magmatic gases mainly h 2 s 2 high sulphate chloride waters from a deep reservoir located in the major upflow zone 3 waters associated with significant degassing of magmatic co 2 4 waters from a deep geothermal neutral chloride reservoir resulting from heating of marine water modified by water rock interaction processes 5 cold waters from the inner area influenced by low temperature water rock interaction processes

native sulfur sulfates and sulfides from the active campi flegrei volcano southern italy genetic environments and degassing dynamics revealed by mineralogy and isotope geochemistry abstract we investigated sulfur bearing minerals from the campi flegrei caldera southern italy in relation to the increase of hydrothermal activity phenomena since 2006 aimed at providing insights into the volcanic system dynamics mineral encrustations and muds were sampled between 2013 and 2015 at the long standing degassing crater of the solfatara tuff cone and its recently restless north eastern pisciarelli slope deep seated sulfides were further separated from two drill cores agip s mofete boreholes 1500 m and 2695 m depth the mineral assemblage and texture of sampled encrustations were determined by x ray diffraction optical and scanning electron microscopy and x ray microanalysis by energy dispersive spectrometry native sulfur and alunite dominate among the newly formed mineral phases other minerals are mostly alunogen and locally pickeringite potassium alum hematite and pyrite mereiterite and amarillite sporadically occur the mud pools are rich in gypsum potassium alum and pyrite quartz and argillic phases locally with analcime are dispersed in the outcropping rocks 34 s values were determined for shallow subsurface native sulfur 5 5 to 0 0 and alunite 1 7 to 0 2 as well as for the deep seated pyrite 3 3 to 7 4 in the depth range 1500 2695 m 18 o values were measured for shallow native alunite 4 2 to 7 0 pisciarelli alunite was finally analyzed for its 87 sr 86 sr ratio and 143 nd 144 nd ratios 0 707517 6 and 0 512459 6 respectively textural and isotopic data constrain the genesis of alunite at the expense of k feldspars through rock alteration by hydrothermal fluids we suggest that the caldera is a low sulfidation system hosting acid sulfate deposits in its active degassing area the acid sulfate environment developed on an argillitic facies that thins outwards and is characteristic for steam heated and magmatic steam environments these environments developed in relation to the fractured settings that facilitates the gas emissions from deeper levels and the meteoric infiltration from surface to depth newly determined 34 s data are lower than previously published values suggesting a progressive decrease in the sulfur isotopic composition through time at least since 1956 the isotopic variation is associated with a lowering of the so 2 h 2 s ratio and the widening of the surface of co 2 degassing in the absence of significant changes in the average co 2 flux values and in the carbon and helium isotope compositions native sulfur and sulfates move from sulfur isotope equilibrium to disequilibrium we ascribe this transition to enhanced so 2 scrubbing due to a high rock permeability that facilitates a faster gas ascent rate in the shallow crust

sequence stratigraphic interpretations from palynofacies dinocyst and lithological data of upper eocene lower oligocene strata in southern mississippi and alabama u s gulf coast abstract this paper presents new information on the sequence stratigraphy of the upper eocene lower oligocene strata in southern mississippi and alabama based on palynological and lithological data from five sections by integrating lithological characteristics with palynofacies assemblages several dinocyst paleoecological groups the deflandrea group and the abundance of reworked dinocysts in samples paleobathymetric curves were reconstructed and used to revise the sequence stratigraphy of the area we identified a maximum flooding surface in the middle of the shubuta clay formation in southern mississippi and dated it as latest eocene in southern alabama the eocene oligocene boundary was placed within a condensed section representing about 0 19 ma and it coincided with the shubuta clay vicksburg group contact this condensed section is equivalent to the accumulation of the upper shubuta and red bluff formations in southern mississippi the forest hill mint spring contact which has been interpreted as a sequence boundary that merged with a transgressive surface does not correlate with the tejas a ta 4 3 4 4 sequence boundary of haq et al 1988 the pachuta marl and lower shubuta clay formations are constituents of a late eocene transgressive systems tract in southern mississippi but this systems tract extended to the shubuta clay vicksburg group contact in southern alabama the overlying early oligocene highstand systems tract consisted of the upper shubuta in mississippi and the red bluff bumpnose forest hill formations a thin sandstone in the mint spring was interpreted as a deposit of a possible lowstand systems tract above the sequence boundary in one southern mississippi section in general the mint spring marl and marianna limestone constituted a transgressive systems tract

the phlegraean fields structural evolution volcanic history and eruptive mechanisms abstract the main event within the volcanic history of the phlegraean fields was the eruption about 35 000 years ago of a huge alkali trachytic ignimbrite 80 km 3 dre followed by caldera collapse the pre caldera activity evidence from geothermal wells and surface outcrops changed from submarine to subaerial shortly before the ignimbrite eruption the caldera was subsequently invaded by the sea and became progressively filled with tuffites and subordinate submarine flows in its northern half the last submarine explosive activity dates back to 12000 10500 yr with the eruption of mostly hydroplinian yellow tuffs recent mostly subaerial activity consists of a series of explosive eruptions whose volume decreases with time until the last eruption of mt nuovo in 1538 a d two peaks in recent activity occur at 10000 8000 and 4700 3000 years ago during post caldera activity eruptive vents migrated from the caldera rim toward the center where there are two distinct zones of recent vents minor collapses occurred within the caldera after the main eruptions often they are eccentric to the vent and displaced toward the caldera center phlegraean explosive activity is characterized by water magma interaction eruptive events without a hydromagmatic component are extremely rare in most cases the evolved trachytic magmas interacted with surface water either the sea or intracaldera lakes however there is evidence of interaction of magma with deep seated aquifers for some plinian events explosivity i e the efficiency of the transformation of thermal into kinetic energy during magma water interaction is largely controlled by the primary fragmentation of the magmatic melt

mineralogical geochemical and isotopic features of tuffs from the cfddp drill hole hydrothermal activity in the eastern side of the campi flegrei volcano southern italy abstract a 506 m drill hole has been recently drilled in the framework of the campi flegrei deep drilling project cfddp and the international continental scientific drilling program icdp with the intention of coring the subsurface in the eastern sector of the campi flegrei caldera the borehole located in the western district of the neapolitan city bagnoli plain 3 km to the east of the most active volcanic area and about 5 m above sea level is now targeted for monitoring purposes this paper reports the results obtained from the analysis of two short cores collected at depths of 443 and 506 m below the ground level the cores sampled two pre caldera tuffs observations performed by optical and scanning electron microscopy energy dispersive spectroscopy and powder x ray diffraction were used to achieve data on the primary lithology both primary and secondary mineralogical assemblages and the relationship between texture and secondary mineralization sr isotope ratios were determined on selected primary feldspars whereas 13c and 18o analyses were performed on carbonates from veins and filled voids in tuffs our results provide information on the hydrothermal system in the eastern sector of the caldera that was not among the goals in the previous drilling programs secondary mineralization suggests a saline hydrothermal environment characterized by fluids that progressively evolved from boiling toward more alkaline and cooler conditions a paleo temperature of ca 160 c has been inferred from authigenic mineral occurrences and calculated on the basis of equilibria between cored calcites and fluids presently emitted at the surface by using carbon and oxygen isotope data the temperature measured at the bottom of the drilling is about 80 c

geographical distributions of organic walled dinoflagellate cysts in surficial sediments of the benguela upwelling region and their relationship to upper ocean conditions the organic walled cyst content of 41 surface sediment samples from the south eastern south atlantic ocean have been studied to create a dataset that can be used for palaeoceanographic reconstructions in order to obtain insight into which environmental factors influence the distribution of individual cyst species the cyst associations have been compared with oceanographic characteristics of the overlying water masses i e temperature salinity density and stratification gradients the associations and relationships have been established by visual examination of the dataset and the multivariate ordination techniques detrended correspondence analysis and canonical correspondence analysis special attention has been given to the factors of transport and preservation of the cysts five associations have been recognised as being characteristic of 1 areas influenced by coastal upwelling and or river outflow 2 open ocean 3 agulhas current and southern benguela current 4 benguela current and 5 walvis bay shelf break area the factors dominant in influencing either directly or indirectly the cyst distributions appear to be the stratification in the upper 50 m of the water column nutrient concentration and seasonality variations in sea surface temperatures and salinities have only minor effect on cyst distribution

dinoflagellate cyst stratigraphy and palaeoecology of the pliocene in northern belgium southern north sea basin dinoflagellate cysts and other palynomorphs from the pliocene kattendijk and lillo formations exposed in two temporary outcrops in northern belgium provide new information on the biostratigraphic position and sequence stratigraphic interpretation of these units dinoflagellate cysts from the kattendijk formation indicate an age between about 5 0 ma and 4 7 4 4 ma early early pliocene in our sections confirming a correlation with standard sequence 3 4 and implying a slightly greater age than the ramsholt member of the coralline crag formation of eastern england the unconformity at the base of the kattendijk formation was not seen but presumably correlates with sequence boundary me2 at 5 73 ma the overlying lillo formation is late early pliocene or early late pliocene c 4 2 2 6 ma in age and the unconformity at its base may be correlated with sequence boundary za2 at 4 04 ma or pia1 at 3 21 ma the oorderen sands and superjacent kruisschans sands members lillo formation are both part of the same depositional cycle they were probably deposited before 2 74 ma and certainly before the onset of northern hemisphere cooling at c 2 6 ma evidence from dinoflagellate cysts indicates that both a shelly unit at the base of the lillo formation and the lower part of the overlying oorderen sands were deposited during a conspicuously cool climatic phase with warmer temperatures returning during later deposition of the oorderen sands and kruisschans sands members many dinoflagellate cyst and acritarch species are reported here for the first time from the southern north sea basin selenopemphix conspicua de verteuil norris 1992 stat nov is proposed

a comparison of long coastal trapped wave theory with remote storm generated wave events in the gulf of california abstract moored pressure temperature and current observations of low frequency coastal trapped wave ctw events in the gulf of california are examined in the context of long wave ctw theory mode 1 ctws that are generated by summer tropical storms are consistent with the occurrences and propagation speeds of the observed wave events in the gulf the mode 1 ctw generation however occurs farther north than observed presumably due to insufficient wind data the mode 1 and observed across shelf wave structure in the gulf are similar in that alongshelf currents are nearly depth independent in 100 m water depth the pressure response is strongest at the coast with decay offshore and with depth and downwelling occurs over the shelf with the amplitude of the mode 1 density response within a factor of two of the observed response the main discrepancies between the mode 1 and observed wave structure are that the speed of the mode 1 alongshelf current increases toward the coast while the weakest observed sp

a brine interface in the salton sea geothermal system california fluid geochemical and isotopic characteristics data from 71 geothermal production intervals in 48 wells from the salton sea geothermal system ssgs indicate that fluids in that system cluster into two distinct populations in terms of their salinity and their stable isotopic compositions the distinctive hot hypersaline brine typically 20 wt total dissolved solids for which the ssgs is known is overlain by a cooler 260 c fluid with distinctly lower salinity typically 10 wt total dissolved solids hypersaline brines have high and rather consistent 18o shifts produced by water rock interaction and have a very narrow range in d values low tds fluids on the other hand show a wide range in both d and 18o production of both types of fluid from closely spaced geothermal wells in many regions of the ssgs indicates that a relatively sharp salinity interface exists over much of the field the fluid interface typically cross cuts sedimentary bedding but is consistently found where reservoir temperatures are approximately 260 c at these temperatures hypersaline brines have densities of approximately 1 0 gm cm3 while the low tds fluids have densities as low as 0 85 gm cm3 this stable density stratified interface acts as a barrier to convective heat and mass transfer in the ssgs isolating the hypersaline reservoir from overlying dilute fluids a lithologic cap implied by previous ssgs models is unnecessary in such a stratified system since heat and mass transfer across the interface must occur by slow conductive diffusional and interface mixing processes regardless of local permeability

the volcanic and geothermally active campi flegrei caldera an integrated multidisciplinary image of its buried structure the campi flegrei caldera in southern italy is one of the greatest geohazard areas on earth evidence of an active magmatic and geothermal system is provided by ongoing ground uplift with volcano tectonic and long period lp seismicity the persistent degassing of 1500 tonnes of co2 per day the presence of hot fumaroles at temperatures of 90 150 c brine rich aquifers with total dissolved solids up to 33 g l 1 and high thermal gradients in the crust with temperatures reaching 420 c at 3 050 m b s l since the 1940s more than 100 exploratory boreholes have been drilled in the area to depths of 80 3 100 m by the azienda geologica italiana petroli agip and the societa anonima forze endogene napoletane safen to date however no systematic reanalysis of the drilling data has been carried out and the buried volcanic structure has not been updated using the most recent scientific results and previous findings by integrating unpublished data from the agip and safen reports with published information from geological volcanological petrological petrophysical and geophysical studies this paper presents an improved picture of the campi flegrei caldera that will be useful for volcanic hazard assessment and mitigation in the naples area and for future research planning the results suggest that intra caldera activity has been influenced by how the magmatic system at depths greater than about 4 km has determined the transfer of magma volatiles and heat to the overlying geothermal system and ultimately to the surface in particular intriguing is that the most volcanically active central eastern sector of the caldera which is subject to intense bradyseismic ground movement and gas emission coincides with a structurally delimited subsurface rock volume characterized by an uprising of the 100 c isotherm a deep water supply to the shallower aquifer the early disappearance of secondary calcite lp seismicity and high seismic s wave attenuation in this area we also document evidence of repeated injection at depths of c 1 5 3 0 km of isolated and small volume batches of magma where occurred their crystallization and degassing shallow intrusions and degassing of magma are thus identified as two of the key processes that drive unrest in campi flegrei

a three dimensional model of the mean and seasonal circulation of the gulf of california 1 the mean and seasonal circulation of the gulf of california is simulated with a three dimensional numerical model forced by the pacific ocean through specifying the sea level the temperature and the salinity fields at its entrance at the sea surface the wind and the heat and freshwater fluxes are specified the model reproduces the observed mean and seasonal variability of sea level of heat and salt balances and the sea surface temperature sst climatology it also reproduces the general surface circulation of the northern gulf which consists of a seasonally reversing basin wide gyre it is found that tides and heat fluxes are both indispensable to reproduce the spatial structure and temporal evolution of the sst tides provide the mixing to upwell the cooler subsurface waters in the large islands area and the heating from the surface raises the sst the general circulation of the southern part of the gulf is due to the wind and the pacific forcing in the ekman layer two periods of anticyclonic circulation and one cyclonic per year occur below this layer two cyclonic periods develop in the northern part the tides play an important role in producing mean residual currents and both tides and winds compete against the pacific forcing to produce a cyclonic and anticyclonic circulation once a year contrary to conclusions of previous studies the thermohaline circulation is found to be unimportant in the gulf

sst thermohaline structure and circulation in the southern gulf of california in june 2004 during the north american monsoon experiment 1 the thermohaline structure circulation and heat fluxes in the gulf of california entrance during june 2004 are described based on conductivity temperature depth and lowering acoustic doppler current profiler data collected in a 14 day survey supported by satellite data the avhrr images show extensive mesoscale structures in the region the most striking being 1 a cool filament extending from the california current domain and 2 a warm intrusion along the mainland shelf on the warm side of the thermal front created by the cool filament there was a strong current flowing into the gulf with speeds up to 0 70 ms 1 in the surface this current which the sst images suggest was associated with a decaying eddy carried 6 sv into the gulf associated with the second structure there was an ingoing coastal current on the mainland shelf with weak surface currents but with speeds 0 25 ms 1 at its core between 70 and 200 m this coastal current transported 2 sv into the gulf the two ingoing currents appear to join inside the gulf forming a very strong speeds 0 40 0 80 ms 1 narrow 30 km coastal current between the surface and 500 m depth changes in the thermohaline structure of the upper layers observed by repeat sampling of three cross sections were dominated by advection however it was found that the advective heat flux is very variable in space and time for the period of observation it was estimated that the lateral heat input was 4 8 3 0 105 wm 2 as estimated with ladcp currents and 5 7 2 20 105 wm 2 with geostrophic velocities

seasonal variation of geostrophic velocity and heat flux at the entrance to the gulf of california mexico 1 the divergence of the surface heat flux in the gulf of california is driven by the exchange of waters with the pacific ocean castro et al 1994 to estimate these exchanges geostrophic velocities and heat fluxes were computed from nine sections of closely spaced conductivity temperature depth stations across the entrance to the gulf of california between 1992 and 1999 the mean geostrophic velocity was composed of two alternating cores of inflow and outflow the two cores that were adjacent to either coast were broader and contained the highest inflow 0 40 m s and outflow 0 25 m s velocities supporting the general idea of inflow along sinaloa and outflow along baja california bc during winter and spring the baroclinic outflow usually occurred near bc and the baroclinic inflow occurred either through the center of the section and or along the sinaloa coast both inflow and outflow cores were 45 km wide and extended deeper than 700 dbar summer and fall showed a more complex pattern with alternating cores of inflow and outflow but with inflow along sinaloa on all cruises during may the inflow was mainly in the center of the section while outflow was concentrated along bc the heat transport associated with the geostrophic flow was calculated and compared with estimates derived from surface heat budgets for the gulf castro et al 1994 both the geostrophic flow and heat transport exhibited for the first empirical orthagonal function mode a strong seasonal signal with the maximum amplitude in may and the minimum amplitude in late october a seasonal fit to the net heat transport had an amplitude of 50 1012 w and phase of 133 days in good agreement with other authors further validating the geostrophic velocity estimates the heat added to subtracted from the pacific ocean accelerates decelerates alongshore currents and appears to propagate 10 westward as a rossby wave

regional weather prediction with a model combining terrain following and isentropic coordinates part i model description abstract a short range numerical prediction model which is part of a real time 3 h data assimilation and forecast system is described the distinguishing feature of the model is the use of terrain following coordinate surfaces in the lower troposphere combined with isentropic surfaces aloft such a hybrid coordinate system allows modeling of processes in a convectively unstable boundary layer while retaining tile advantages of coordinates in representing upper tropospheric frontal and jet stream structures the hybrid approach used in this model represents a in major departure from previous hybrid formulations in atmospheric models oven though it has been used for more than ten years in oceanic modeling part i of this two part paper contains a thorough description of the model and the results of validation experiments results of north american case studies wig be reported in part ii

dinoflagellate cyst assemblages biostratigraphy and paleoenvironment of a paleocene early eocene sedimentary succession in the northern niger delta basin comparison with low mid and high latitude regions abstract this study represents a contribution to the late paleocene early eocene biostratigraphy in a low latitude stratigraphic setting where published studies are few in comparison with mid and high latitude regions we generated data for 62 dinoflagellate cysts from a comprehensive analysis of 33 samples covering a 713 m interval in the alo 1 well in the northern niger delta anambra basin nigeria dinoflagellate cyst recovery in the samples varies from very good to poor and the specimens are commonly well preserved we calibrate the dinoflagellate cyst data with recent biozonation schemes for odp hole 959d cote d ivoire ghana transform margin in the eastern equatorial atlantic which allowed for a valid comparison with published studies in well dated rock sections in northwestern europe the mediterranean region new zealand and tasmania our observations show that there is better correlation between tropical and mid latitude dinoflagellate cyst assemblages compared to those in high latitude regions we use the last occurrence and or last abundance events of dinoflagellate cysts to identify four biostratigraphic zones zone e to zone h in the alo 1 well lithostratigraphic and biostratigraphic analyses suggest a late selandian age for the contact between the imo and nsukka formations abundant thermophilic taxa that include the cordosphaeridium group and apectodinuim dominate the assemblage recovered in the depositional succession the late selandian to early thanetian sediments are dominated by the cordosphaeridium group and are succeeded by abundant to superabundant marker species of apectodinium in the late thanetian to ypresian the superabundance of apectodinium is significant because it is indicative of the global intense climatic warming that characterized the late thanetian to early ypresian the alo 1 well dinoflagellate cyst data also suggest deposition under proximal inner neritic conditions that preserved an assemblage dominated by species of cordosphaeridium damassadinium ifecysta and polysphaeridium

palaeoproductivity and post depositional aerobic organic matter decay reflected by dinoflagellate cyst assemblages of the eastern mediterranean s1 sapropel abstract in the reconstruction of bioproductivity in surface waters the extent to which a proxy has been diagenetically altered is often a matter of debate here we investigate how organic and calcareous walled dinoflagellate cysts can be used for separately estimating bioproductivity and oxygen related diagenesis this is achieved by studying the cyst content of the most recent eastern mediterranean sapropel s1 that is thought to have been deposited under conditions of increased primary production in surface waters and possible anoxia in the bottom waters based on chemical evidence it has been shown that the visible sapropelic layer represents only the residual lower part of what was initially a much thicker sapropel as a result of post depositional decay of organic matter related to oxygen penetration into the sediments the effect of aerobic organic matter decay on the cyst associations is studied through the comparison of the unaffected lower part of the initial sapropel and the oxidised upper part comparing the unaffected sapropelic sediments with pre and post sapropelic material gives insight into the relationship between fossil cysts assemblages and palaeoproductivity impagidinium aculeatum impagidinium patulum operculodinium israelianum polysphaeridium zoharyi and probably impagidinium spp impagidinium paradoxum and nematosphaeropsis labyrinthus are very resistant against aerobic decay and their accumulation rates appear to be primarily related to productivity in surface waters protoperidinium and echinidinium species on the other hand are shown to be very sensitive and can be used to recognise oxygen related decay the calcareous walled dinoflagellate cysts seem to be unaffected by oxic organic matter decay in mediterranean sediments

effects of the 1997 1998 el nino on the exchange of the northern gulf of california 1 we analyze sea level and transports in the gulf of california from two large scale high resolution numerical models the naval research laboratory layered ocean model and the hybrid coordinate ocean model sea level from both models correlates well with sea surface height from a nearby topex track and subsurface pressure measured in the northern gulf during 1997 1998 an 8 year mean 1993 2000 section of the modeled meridional velocity at the mouth of the gulf is in good qualitative agreement with observations showing a localized near surface outflow on the baja california side the 8 year mean laterally integrated modeled near surface transport at the mouth of the gulf shows an opposite direction for both models during the 1997 1998 el nino however both models show a similar structure with increased inflow in the upper 100 m and an increased outflow in the underlying layer to about 500 m depth the modeled surface transport also shows increased inflow in the northern gulf the modeled incoming surface transport from both models during el nino is negatively correlated to near bottom currents measured at a sill in the northern gulf this measured near bottom current has previously been shown to constitute part of the strong localized incoming flow from the pacific ocean the negative correlation strongly suggests that the anomalous incoming surface flow at the mouth of the gulf inhibited the normal near surface outflow of the northern gulf of california water this in turn inhibited the normal deeper inflow entering the northern gulf from the pacific ocean these anomalies apparently increased the residence time of the waters in the northern gulf they are consistent with anomalously high near bottom salinities found during 1997 1998 hydrographic data for july 1997 also show an anomalous low salinity surface water which is most likely associated with advection of tropical waters from the pacific ocean

use of selective degradation to separate preservation from productivity the assessment of diagenetic influences on the sedimentary record is problematic despite its crucial importance for accurate environmental reconstruction and understanding of biochemical cycles we propose a general applicable method that uses differences in degradation rates of organic components to separate degradation and productivity we demonstrate this method on a southeastern atlantic sediment core covering the past 145 k y the new method solves discrepancies between existing organic matter silica and carbonate based productivity reconstructions and emphasizes the importance of bottom and pore water characteristics for transformation of the sedimentary record

first hydroacoustic evidence of marine active fluid vents in the naples bay continental shelf southern italy abstract we present the first results of a multidisciplinary research aimed at the detection and mapping of active fluid vents afvs at the seafloor of the naples bay italy this segment of the campania continental margin is characterised by severe quaternary extension and intense volcanism at ischia and procida islands the campi flegrei and somma vesuvius volcanic complexes high resolution hydroacoustic profilers were used to identify and localize fluid emission from the seafloor rov direct observation showed that each emission centre is generally composed by the coalescence of several emitting points ctd probes showed that there are no significant gradients in temperature profiles the results of this study include the detection and mapping of 54 fluid emission points all located in the 71 158 m depth range and spatially distributed into four main clusters three of the described clusters are located along the margin of a complex toe shaped seafloor morphology southwest of the somma vesuvius representing the shallow expression of partly buried coalesced depositional features namely two flank collapses and one pyroclastic flow associated with the late pleistocene activity of the volcano the fourth afv cluster was detected at the morphological high located about 8 km south of naples banco della montagna represented by a field of volcaniclastic diapirs composed of massive pumiceous deposits originated from the campi flegrei intruding rising through the latest quaternary holocene marine deposits our study suggests that the occurrence of afv in this area could be genetically linked to the interaction between volcanic related seafloor morphologies and the main ne striking faults present in the area i e the magnaghi sebeto line and the vesuvian fault

the late miocene onset of high productivity in the benguela current upwelling system as part of a global pattern abstract we have examined the history of the elevated primary productivity associated with the benguela current upwelling system off southwest africa using sediments from 7 5 to 4 8 ma at ocean drilling program site 1085 in the middle cape basin sedimentation rates are low until 6 9 ma low accumulation rates of benthic foraminifers and organic carbon indicate that biological productivity was also low paleoproductivity dramatically increased at 6 7 6 5 ma and was highly variable until 4 8 ma with productivity maxima during cooler periods the presence of radiolarian opal only between 5 8 and 5 2 ma suggests an interlude of silica rich intermediate water in the cape basin the onset of heightened productivity under the benguela current is mirrored by similar increases reported between 6 9 and 6 7 ma in the tropical eastern pacific the western and northern pacific and the indian ocean the similarity between the patterns at site 1085 and in the pacific and indian oceans suggests that the dramatic productivity increase off southwest africa is part of a global response to paleoceanographic changes

the distribution and relationship between palynomorphs in aerosols and deep sea sediments off the coast of northwest africa abstract palynomorphs in eolian dust and bottom sediments from the northeastern atlantic off the coast of northwest africa were studied primary examination was for terrestrial plant detritus pollen spores opal phytoliths and freshwater diatoms but observations about marine entities were also made three distinct geographic palynofloras were detected a northern palynoflora consisting of pollen derived primarily from the mediterranean basin a central or saharan palynoflora characterized by pollen derived from desert plants and a southern tropical equatorial palynoflora composed of pollen derived from tropical plants but including up to 50 allochthonous pollen from the drier interior of west africa palynomorph distributions are related closely to both source vegetation and to atmospheric and oceanic transport mechanisms and in many cases distribution patterns in bottom sediments and aerosols are complementary the quantity of pollen and spores per gram of bottom sediment ranges from greater than 2000 off the saharan coast in mauritania to less than 50 in deep ocean basins pollen and spores in mediterranean aerosols may exceed 40 per cubic meter of air during the summer and range between 4 to 6 for tropical aerosols during the winter tropical aerosols and bottom sediments contained the greatest abundance of fungal spores the distribution of opal phytoliths and freshwater diatoms in both aerosols and bottom sediments indicates that dust storms are a major transporting agent for these entities from the interior of west africa to the gulf of guinea these storms are also an important agent for the transport of pollen to the tropical atmosphere distances of transport may exceed 5000 km for mediterranean pollen and even greater distances for palynomorphs in eolian dust from interior west africa the abundance of dinoflagellates and microforaminifera in bottom sediments is directly related to the area of upwelling off the west african coast

the generation and propagation of sea level variability along the pacific coast of mexico abstract case history analysis cross spectra and multiple regression analysis have been used in a study of low pass filtered sea level records from the pacific mainland coast of mexico in 1971 and 1973 75 during the summer fall season may october sea level variability is characterized by strong alongshore coherence and nondispersive poleward phase propagation over a wide frequency range 0 02 0 37 cpd the strength and clarity of the propagating signals seem to be related primarily to large amplitude events of elevation 10 30 cm that are generated off the southern coast of mexico by tropical storms these events are typically forced by the alongshore poleward movements of the storms to as far north as 20 n and thereafter continue to propagate freely at least as far as guyamas 28 n large variable phase speeds 250 500 km day 1 are observed in the southern region consistent with the alongshore speeds of the forcing a multiple input statistical forcing model in which adjusted sea level is r

quantitative models of hydrothermal fluid mineral reaction the ischia case abstract the intricate pathways of fluid mineral reactions occurring underneath active hydrothermal systems are explored in this study by applying reaction path modelling to the ischia case study ischia island in southern italy hosts a well developed and structurally complex hydrothermal system which because of its heterogeneity in chemical and physical properties is an ideal test sites for evaluating potentialities limitations of quantitative geochemical models of hydrothermal reactions we used the eq3 6 software package version 7 2b to model reaction of infiltrating waters mixtures of meteoric water and seawater in variable proportions with ischia s reservoir rocks the mount epomeo green tuff units megt the mineral assemblage and composition of such megt units were initially characterised by ad hoc designed optical microscopy and electron microprobe analysis showing that phenocrysts dominantly alkali feldspars and plagioclase are set in a pervasively altered with abundant clay minerals and zeolites groundmass reaction of infiltrating waters with megt minerals was simulated over a range of realistic for ischia temperatures 95 260 c and co 2 fugacities 10 0 2 to 10 0 5 bar during the model runs a set of secondary minerals selected based on independent information from alteration minerals studies was allowed to precipitate from model solutions when saturation was achieved the compositional evolution of model solutions obtained in the 95 260 c runs were finally compared with compositions of ischia s thermal groundwaters demonstrating an overall agreement our simulations in particular well reproduce the mg depleting maturation path of hydrothermal solutions and have end of run model solutions whose na k mg compositions well reflect attainment of full equilibrium conditions at run temperature high temperature 180 260 c model runs are those best matching the na k mg compositions of ischia s most chemically mature water samples supporting quenching of deep reservoir conditions for these surface manifestations whilst fe sio 2 and to a lesser extent so 4 contents of natural samples are better reproduced in low temperature 95 c runs suggesting that these species reflect conditions of water rock interaction in the shallow hydrothermal environment the ability of model runs to reproduce the compositional features of ischia s thermal manifestations demonstrated here adds supplementary confidence on reaction path modelling as a realistic and insightful representation of mineral fluid hydrothermal reactions our results in particular demonstrate the significant impact of host rock minerals assemblage in governing the paths and trends of hydrothermal fluids maturation

dinoflagellate cysts as environmental indicators in surface sediments from the congo deep sea fan and adjacent regions abstract forty nine surface sediment samples from the congo deep sea fan and adjacent hydrographic environments were prepared palynologically and analyzed for fossilizable dinoflagellate cysts the main objective was to investigate the extent to which cysts reflect present day hydrography and therefore may be used downcore as paleoceanographic indicators the region sampled covers a range of marine environments including the congo river plume the area of pronounced upwelling off west central africa and a nearshore offshore gradient from coastal to oceanic waters this is the first study of the effect of a major tropical river plume on associated cyst assemblages cyst counts were low particularly near the river mouth and furthest offshore a combination of statistical treatments was used to analyze the surface cyst assemblages including cluster analysis correspondence analysis and canonical correspondence analysis this helped to identify five distinctive sample groupings representing the main ecological signals in the cyst assemblage data group a dominated by spherical brown protoperidinioid cysts is an upwelling signal group b dominated by the cosmopolitan species o centrocarpum is the main signal for the river plume effect interpreted as reflecting the environmental instability this creates group c dominated by s delicatus with accessory o centrocarpum characterizes the outer plume somehow reflecting the mixing of progressively diluted river plume water and the surrounding oceanic waters group d with high proportions of impagidinium and nematosphaeropsis together with o centrocarpum and s delicatus characterizes the location of the angola benguela front group e with mainly impagidinium species is an oceanic signal the identification of nutrients and water stability as main determining factors influencing cyst signals has implications for cyst based paleoenvironmental interpretations using transfer functions which are developed almost exclusively from comparisons with more easily available data for sea surface temperature salinity and sea ice

determining the origin circulation path and residence time of geothermal groundwater using multiple isotopic techniques in the heyuan fault zone of southern china abstract medium low temperature geothermal resources are abundant in southern china but their heat source and link to fault zones is poorly understood consequently geothermal energy is only used at small scale in order to broaden the footprint of geothermal energy use in southern china it is first necessary to understand and track the geothermal groundwater circulation pattern associated with fault zones the heyuan fault zone serves as a typical medium low temperature geothermal system of south china here we show that the geothermal groundwater circulation pattern can be traced by using stable hydrogen and oxygen isotopes helium and neon isotopes carbon 13 and carbon 14 as well as hydrochemical parameters the results show that in the heyuan fault zone the main hydrochemical type of the hot springs is hco3 na k while the shallow cold groundwater is mainly enriched in hco3 ca the results of the helium isotope and neon isotope indicate that the geothermal groundwater of this area is derived from the crust thus excluding the possibility of extremely deep paths of groundwater tapping into mantle helium sources furthermore the characteristics of the stable hydrogen and oxygen isotopes imply that geothermal groundwater is of local meteoric origin and the recharge area located at the hilly area of the hanging wall of the heyuan main fault with the recharge elevations ranging from about 440 m to 670 m the hot spring geothermometer shows that the highest reservoir temperature is about 157 c and the deepest circulation depth is about 6500 m carbon 14 isotope age dating suggests that the geothermal groundwater ages are mostly from 9 9 kyr bp to 12 3 kyr bp according to the geological structural characteristics of the study area the main upward channel for geothermal groundwater is the heyuan main fault generally the hot springs in this area are mixed with shallow cold groundwater and surface water which raises the ratio of the ca2 in water and dilutes the heavy hydrogen and oxygen isotopes

mercury content and speciation in the phlegrean fields volcanic complex evidence from hydrothermal system and fumaroles abstract mercury is outstanding among the global environmental pollutants of continuing concern although degassing of active volcanic areas represents an important natural source of mercury into the atmosphere still little is known about the amount and behaviour of hg in volcanic aquifers especially regarding its chemical speciation in order to assess the importance of mercury emissions from active volcanoes thermal waters were sampled in the area surrounding la solfatara pozzuoli bay this is the most active zone of the phlegrean fields complex coastal area north west of naples with intense hydrothermal activity at present day studied groundwaters show total hg thg concentrations range from 56 to 171 ng l and are lower than the 1000 ng l threshold value for human health protection fixed by the world health organization who 1993 we also carefully discriminated the different aqueous species of hg in the collected water samples besides original data on hg determination in gaseous manifestations at la solfatara crater are also reported we measured volcanogenic mercury concentration and hg s tot ratio both in the volcanic plume and in fumarolic condensates in order to better constrain hg reactivity once emitted into the atmosphere data on hg s tot reveal that there is no significant difference between hg volcanic composition at the venting source fumaroles and in near vent diluted volcanic plumes 1 6 10 5 and 1 9 10 5 respectively suggesting that there is limited hg chemical processing in volcanic fumarole plumes at least on the timescales of a few seconds investigated here combining the mean fumaroles hg co 2 mass ratio of about 1 3 10 8 molar ratio 2 1 10 9 with the hydrothermal soil diffuse co 2 degassing of the area the annual hg flux from la solfatara is estimated as 7 kg y 1 0 007 t y 1 current mercury emission from la solfatara volcano represents a very small contribution to the estimated global volcanic budget for this element and the estimated hg flux is considerably lower than that estimated from open conduit active basaltic volcanoes

distribution of organic walled dinoflagellate cysts in surface sediments of the southern ocean eastern atlantic sector between the subtropical front and the weddell gyre abstract thirty two surface sediment samples from the southern ocean eastern atlantic sector between the subtropical front and the weddell gyre were investigated to provide information on the distribution of modern organic walled dinoflagellate cysts in relation to the oceanic fronts of the antarctic circumpolar current acc a clearly distinguishable distribution pattern was observed in relation to the water masses and fronts of the acc the dinoflagellate cysts of species characteristic of open oceanic environments such as impagidinium species are highly abundant around the subtropical front whereas south of this front cosmopolitan species such as nematosphaeropsis labyrinthus and the cysts of protoceratium reticulatum characterise the transition from subtropical to subantarctic surface waters the subantarctic surface waters are dominated by the cysts of heterotrophic dinoflagellates such as protoperidinium spp and selenopemphix antarctica the cysts of protoperidinium spp form the dominant part of the assemblages around the antarctic polar front whereas s antarctica concentrations increase further to the south the presence of s antarctica in sediments of the maud rise a region of seasonal sea ice cover reflects its tolerance for low temperatures and sea ice cover a previously undescribed species cryodinium meridianum gen nov sp nov has a restricted distribution pattern between the antarctic polar front and the acc weddell gyre boundary

impact of additional dead carbon on the circulation estimation of thermal springs exposed from deep seated faults in the dongguan basin southern china abstract in hydrothermal systems the dissolved carbon of thermal groundwater may contain components derived from mineral alterations under high temperatures metamorphic source and or from magmatic gases additionally from carbonate dissolution most common these components are known as additional dead carbon which dilutes the modern carbon used for dating leading to the overestimation of 14c ages four typical geothermal springs hosted by deep seated faults and eighteen non thermal springs and wells from the dongguan basin of southern china were investigated to assess the circulation times of the hydrothermal system based on their radiocarbon contents for the thermal springs the circulation depth approximately 3648 m the apparent 14c ages 20 15 to 12 97 ka and the 13c calibrated 14c ages 16 02 to 8 55 ka were estimated the circulation speed of the thermal groundwater was as low as 0 46 m a which was too slow for a fracture hydrothermal system hosted by deep faults the analysis of the helium and carbon isotopes in the thermal groundwater revealed the existence of mantle derived carbon and thermally altered carbon from limestones a 13c 3he 4he illustration was proposed to correct for the additional dead carbon content according to the reassessed 14c ages the groundwater circulation time was overestimated and the circulation speed of the thermal groundwater was underestimated in hydrothermal system the reassessed 14c ages can provide a more reasonable result than the initial slow estimate in the context of a fracture hydrothermal system hosted by deep faults we conclude that measured 14c contents should be reassessed during the use of radiocarbon dating for thermal groundwater if additional dead carbon exists in the water

shelf circulation in the gulf of california a description of the variability the first long term measurements 1983 1984 of winds temperature bottom pressure and currents made in the gulf of california are used to describe the dynamically important spatial and temporal scales and to compare and contrast the shelf circulation on opposite sides of the guaymas basin in addition a qualitative assessment of possible forcing mechanisms of gulf shelf circulation and an account of an energetic coastal trapped wave event are presented winds over the gulf are weak and variable with maximum wind speeds of 10 15 m s and sustained wind events of less than a week low frequency 3 cpd fluctuations in the dominant along gulf component of the wind field which are largely coherent over the study area are directed upgulf during summer and downgulf for the remainder of the year low frequency winds are not significantly correlated 95 confidence level with currents temperature and pressure in part because of weak local winds and nonlocally forced coastal trapped waves on longer time scales seasonal upwelling on both sides of the gulf and guaymas basin mean currents are related to local winds low frequency current fluctuations on the two facing shelf regions guaymas on the mexican mainland and santa rosalia on the baja california peninsula are not significantly correlated along gulf currents in the basin however are negatively correlated with alongshelf currents at guaymas 0 54 due to sporadically occurring eddylike features and santa rosalia 0 61 due to seasonal flow patterns low frequency fluctuations on the mainland shelf are significantly correlated during the summer e g 0 67 in temperature between topolobampo and guaymas separation of 375 km such that topolobampo leads guaymas by approximately 1 5 days this lagged signal is associated with coastal trapped waves that are generated by tropical storms and hurricanes south of the gulf and propagate poleward along the mainland shelf at speeds of 200 250 km day near guaymas current speeds of approximately 50 cm s were measured at the 100 m isobath on the mainland shelf during an event with a 20 cm coastal sea level rise the offshore decay of these waves is of the order of 50 km on the guaymas shelf low frequency temperature or equivalently density and sea level fluctuations are correlated 0 78 such that a 10 cm rise in sea level corresponds to a 20 m drop in isotherm depths over much of the water column this sea surface isotherm relationship is such that the amplitude of pressure fluctuations decays rapidly with depth e folding scale 160 m a similar relationship is only weakly apparent correlation 0 39 on the santa rosalia shelf cross gulf geostrophy is observed with 35 of the along gulf current averaged across the gulf related to dp dx measured between guaymas and santa rosalia on the guaymas and santa rosalia shelves dp dx measured across each shelf explains approximately 20 of the variability in alongshelf currents in the alongshelf momentum balance dp dy accounts for approximately 40 of the low frequency variability in dv dt at the guaymas shelf break consistent with the dynamics of freely propagating coastal trapped waves the same balance is only weakly apparent 10 of variance explained at santa rosalia at higher frequencies temperature fluctuations at guaymas are coherent and in phase to 200 m depth coherent 0 74 with the alongshelf near surface current at the shelf break m8 and exhibit a spring neap modulation consistent with internal tides

modeling the seasonal and interannual variability of the northern gulf of california salinity 1 the 7 years 2003 2009 of output from a regional version of the hybrid coordinate ocean model hycom nested in global hycom are used to study the seasonal and interannual variability of the salinity in the northern gulf of california ngoc previous studies illustrate that the ngoc is characterized by an annual evaporation of 0 9 m yr this evaporation generates high sea surface salinity sss water which reaches a maxima in the ngoc 37 and decreases to 35 toward the entrance of the gulf of california the ngoc surface water is interannually modulated by fluctuations in evaporation and by fluctuations in the low salinity water transported into the region by poleward eastern boundary currents the fluctuations in the transport of low salinity water are linked to the arrival of equatorially originated coastally trapped waves the crucial role of the transport of low salinity water for the interannual variability of sss is illustrated by the 2006 and 2008 fall seasons which include the lowest simulated salinity of the period 2003 2009 the lowest salinity in 2006 and 2008 cannot be explained solely by evaporation because 2006 was characterized by the largest evaporation of the period 2003 2009 however the presence of the lowest salinity environment can be attributed to the evaporation in conjunction with the largest upper ocean transport of low salinity water carried to the ngoc by the 2006 and 2008 coastally trapped waves intensified poleward eastern boundary currents

three dimensional connectivity in the gulf of california based on a numerical model abstract quantifying connectivity is useful for understanding the exchange and trapping of some tracers such as fish larvae and nutrients in the gulf of california connectivity studies have been limited to certain periods and regions the current study investigated the connectivity among 17 areas defined by the presence of eddies and weak or strong flows as obtained from a three dimensional non linear baroclinic model the particles were released into the water column and advected for 28 days using an advection diffusion scheme the results revealed a seasonal connectivity pattern in the northern region particle trapping was greater during the cyclonic circulation period june to september compared with the anticyclonic period november to march this high retention was due to both the presence of a cyclonic eddy in the central portion of the region and the intense northwestward flow off the coast of sonora retentions were low for the large island region due to the intense exchange between the northern and southern regions east of angel de la guarda island the transport occurred predominantly towards the northwest due to the nearly permanent deep flow in that direction and to a branching of the surface flow among the large islands during the anticyclonic period and the northwestward low during the cyclonic period in the peninsular and central areas of the southern region retentions were high due to weak flows and the presence of eddies respectively the greatest retention and low dispersion of particles in practically all of the provinces were recorded during the transition periods of the circulation

mineral control of arsenic content in thermal waters from volcano hosted hydrothermal systems insights from island of ischia and phlegrean fields campanian volcanic province italy this paper documents arsenic concentrations in 157 groundwater samples from the island of ischia and the phlegrean fields two of the most active volcano hosted hydrothermal systems from the campanian volcanic province southern italy in an attempt to identify the environmental conditions and mineral solution reactions governing arsenic aqueous cycling on ischia and in the phlegrean fields groundwaters range in composition from nacl brines which we interpret as the surface discharge of deep reservoir fluids to shallow depth circulating fluids the latter ranging from acid sulphate steam heated to hypothermal cold bicarbonate groundwaters arsenic concentrations range from 1 6 to 6900 g l 1 and from 2 6 to 3800 g l 1 in the phlegrean fields and on ischia respectively they increase with increasing water temperature and chlorine contents and in the sequence bicarbonate groundwatersbsteam heated groundwatersbnacl brines according to thermochemical modeling we propose that high as concentrations in nacl brines form after prolonged water rock interactions at reservoir t fo2 and fh2s conditions and under the buffering action of an arsenopyrite pyrite pyrrhotite rock assemblage on their ascent toward the surface nacl brines become diluted by as depleted meteoric derived bicarbonate groundwaters giving rise to hybrid water types with intermediate to low as contents steam heated groundwaters give their intermediate to high as concentrations to extensive rock leaching promoted by interaction with as bearing hydrothermal steam 2005 elsevier b v all rights reserved

the geological co2 degassing history of a long lived caldera the majority of the 100 holocene calderas on earth host vigorously active hydrothermal systems the heat and volatile budgets of which are sustained by degassing of deeply stored magma calderas may thus contribute a nontrivial although poorly quantified fraction of the global budget of magmatic volatiles such as co2 here we use original isotopic and petrological results from campi flegrei volcano italy to propose that hydrothermal calcites are natural mineral archives for the magmatic co2 that reacted with reservoir rocks during the geological history of a caldera we show that campi flegrei calcites identified in core samples extracted from 3 km deep geothermal wells formed at isotopic equilibrium with magmatic fluids having 18oh2o of 8 7 to 12 7 and 13cco2 of 1 5 this inferred fossil fluid composition is virtually identical to that of present day fumaroles demonstrating a stable carbon source during the caldera s 40 k y history we use the mass of calcites stored in the hydrothermal system to estimate that 12 gt of magmatic co2 reacted with the campi flegrei rocks during the caldera history this corresponds to a time averaged co2 flux of 800 t d 1 this long term co2 flux the first of its kind in the geological literature is similar to the present day soil co2 degassing flux 1100 200 t d 1 we conclude that the actual magmatic co2 degassing flux from calderas may be severely underestimated if subsurface calcite precipitation is not taken into account

seasonal gyres in the northern gulf of california abstract the circulation pattern in the northern gulf of california based on drifting buoys and hydrographic observations can be explained using the results of a linear two layer primitive equations model forced at the annual frequency by the pacific ocean wind stress and heat flux through the surface the modeled surface circulation consists of a cyclonic gyre from june to october and an anticyclonic gyre from december to april both located in the central region of the northern gulf of california which includes angel de la guarda island the maximum intensities of the gyres occur in august and february respectively with values of surface velocities of 65 cm s 1 in agreement with the observations and very low opposite velocities in the bottom layers may and november are transition months in which both gyres can be observed finally in june july or december january the growing gyre is still connected with the rest of the gulf of california through the narrows between tiburon island san este

tidal and atmospheric forcing of the upper ocean in the gulf of california 1 sea surface temperature variability two years of satellite infrared imagery 1984 1986 are used to examine the sea surface temperature sst variability in the northern gulf of california empirical orthogonal functions eofs of the temporal and spatial sst variance for 20 monthly mean images show that the dominant sst patterns are generated by spatially varying tidal mixing in the presence of seasonal heating and cooling these patterns are modified in the fall and winter when shelf temperatures south of tiburon island cool in response to upwelling favorable winds these same winds bring cold dry air from off the continental united states causing local cooling of the shallow northern shelf during the rest of the year the broad shallow shelves are warmer than offshore the seasonally reversing temperature patterns are consistent with recent hydrographic observations which show a cyclonic surface circulation in the summer and a weaker anticyclonic circulation during the rest of the year atmospheric forcing of the northern gulf appears to occur over large spatial scales area averaged ssts for the guaymas basin island region and northern basin show significant fluctuations which are highly correlated these fluctuations in sst correspond to similar fluctuations in the air temperature which are related to synoptic weather events over the gulf during periods of particularly low wind speeds the air temperature over the gulf increases dramatically by afternoon intense heating of the sea surface results in the appearance of warm sst anomalies in the satellite data these ssts are approximately 2 c warmer than surrounding ssts and most likely occur as a result of a spatially varying wind field a regression analysis of the sst relative to the fortnightly tidal range shows that tidal mixing occurs over the sills in the island region as well as on the shallow norther shelf mixing over the sills however occurs as a result of large breaking internal waves or internal hydraulic jumps which mix water over the upper 300 500 m this mixing pumps heat away from the surface deep into the water column there by maintaining the cool ssts since mixing occurs over greater depths in the island region the temperatures there are much colder than those generated by tidal mixing on the shallow shelves resulting in the persistent pool of cool water evident in the satellite data this cooler water is mixed horizontally by the basin scale circulation lowering the ssts over much of the northern gulf these reduced ssts have a large impact on the surface heat flux by lowering the saturation vapor pressure of the air as a result the amount of heat lost to the atmosphere through the latent or evaporative heat flux is reduced this may explain why the gulf of california gains heat on an annual average rather than losing heat as occurs in the mediterranean and red seas where tidal mixing is not significant

a numerical investigation of the annual variability in the gulf of california the observations of sea level at the annual frequency in the gulf of california are reproduced both in amplitude and phase with a horizontal two dimensional linear two layer model the main forcing agents through which variability is explained are wind stress and the action of the pacific ocean which excites an internal wave in the mouth of the gulf the surface heating is shown to play a secondary role the response of the basin is qualitatively similar to that observed that is an energetic circulation in the upper layer cyclonic in summer and anticyclonic in winter compared to a weaker and opposite circulation in the bottom layer as well as a transversely averaged horizontal heat flux equal both in amplitude and phase to that calculated with historical hydrographic data the results of the simulation show that variability across the gulf is as important as the longitudinal variability

isotopic study of the origin of sulfur and carbon in solfatara fumaroles campi flegrei caldera abstract isotopic study of the origin of sulfur and carbon in the hottest solfatara fumaroles of campi flegrei caldera southern italy was carried out on gas samples collected between 1983 and 1988 i e during and after the 1982 1984 seismo volcanic crisis the results for sulfur h2s the first ever reported on these gases indicate a mean 34 s of 0 3 0 3 range 0 7 to 0 1 versus canyon diablo troilite standard consistent with an igneous derivation of this element from either active magma degassing or and leaching of reduced sulfur bearing minerals in the volcanic layers the lack of peculiar 34s variation during and after the crisis suggests that the chemical variation of h2s and s c ratio in the fumaroles increase and then decrease by a factor 3 were not due to a changing origin of sulfur the mean 13c of carbon co2 over the period of survey 1 6 0 2 range 1 9 to 1 3 versus pdb standard is similar to the values obtained before the crisis since 1970 such an isotopic constancy requires a large and stable source of carbon feeding the fumaroles the measured 13c values are much higher than those typical of primary mantle magmatic carbon 6 2 and plot within the 13c range for marine carbonates 0 2 such high values may reflect either a 13c fractionation during degassing of co2 from the underlying 5 km depth magma chamber or b the contribution of heavy co2 of sedimentary origin derived from either thermometamorphism of mesozoic limestone series embedding the magma chamber or possibly past contamination of the local mantle by subducted sediments various arguments among which volcanological evidence of an isolated and cooling magma reservoir which would have been extensively degassed and so depleted in 13c along with time the low 3he 4he ratios and the broad 13c enrichment of volcanic fluids in the region and geochemical evidence of crust magma fluid interactions suggest that a considerable fraction 60 of co2 in solfatara fumaroles derives from carbonate sediments in the basement the contribution of magma derived co2 may be higher within the central part of the caldera including solfatara crater than toward its western margin where fumarolic and geothermal well gases exhibit lower 3he 4he ratios and still higher 13c values such a geochemical pattern is consistent with the central distribution of ground deformation and seismicity during the 1982 1984 crisis and with the idea of a residual magma body confined beneath the central part of the structure alternatively higher 13c and lower 3he 4he ratios toward the western margin may result from dilution of solfatara type gas during progressively deeper water boiling finally accepting that solfatara co2 derives from simple crustal mixing between magmatic and sedimentary carbon its constant isotopic composition together with the constant he isotope ratio would restrict the possibility of magma intrusion and or higher magmatic gas input as mechanisms responsible for the 1982 1984 events however this conclusion would no more hold true if the magma itself or even its mantle source were previously contaminated by crustal carbon

geochemical monitoring of the thermal waters of the phlegraean fields abstract thermal waters from the phlegraean fields pf caldera area have been periodically sampled and analysed during the period 1990 1999 for major chemical constituents and chemico physical parameters to define the most useful variables for geochemical surveillance the variations observed in waters from different locations were compared with ground movements and microseismic events recorded at the time of observation the discontinuous monitoring of the hydrothermal system of the pf has given indications about the geochemical variations brought about by changes in the chemical and physical characteristics of the deep aquifers because of the complexity of the pf geothermal system in each sampling location different variations have been observed and then evaluated on the basis of the different kinds and degrees of deep fluid supply characterising waters sampled in the different zones in some cases a good correspondence between vertical soil movements and chemical changes in the waters has been observed in particular in pools and wells located around the solfatara crater interesting variations in some chemical parameters ph ammonia and or so 4 2 cl ratios have been recorded variations can be observed in all of the sampling locations but pools and wells located near the solfatara crater are the best sites for detecting changes occurring in the deep hydrothermal system and possibly in the activity of the underlying magma chamber

ocean currents across the entrance to the gulf of california observations of transport and currents in april may and december 1992 and january 1993 were made across the entrance to the gulf of california with an acoustically tracked dropsonde flow was into the gulf along sinaloa and out of the gulf along baja california the transports were 5 10 sv and the currents were deep with 10 cm s 1 flow extending to depths greater than 1000 m the currents were intensified in the upper 300 m geostrophic flows compared well with observed currents when smoothed to 2 3 times the rossby radius salinity in the upper 300 m was higher on the baja california side of the gulf indicating modification of subtropical subsurface waters within the gulf as well as the presence of surface and near surface gulf waters the salinity minimum associated with california current waters at 50 m had narrow cores that can be resolved only with closely spaced conductivity temperature depth casts mass and heat fluxes for the upper 300 m were estimated as 280 t s 1 and 0 1 1012 w in may and 170 t s 1 and 2 0 1012 w in december

palynological evidence for sustained deep marine conditions during the eocene miocene in the southern gulf of mexico distal continental margin the present study represents the first attempt to provide palynological data about the southern gulf of mexico distal continental margin during the eocene miocene time interval in addition to documenting the types of fossil palynomorphs preserved in these economically critical rock sequences this study also provides important information about the accumulation and preservation of total sedimentary particulate organic matter along with their paleoenvironmental and paleoceanographic implications this was accomplished through the analysis of cored sediments from the deep sea drilling project site 94 north of the yucatan peninsula and site 540 south of the western florida escarpment the present findings from the deep waters of southern gulf of mexico are expected to greatly assist hydrocarbon geoscientists in their exploration and development efforts reducing investment risk and drilling uncertainty two palynofacies assemblages were recognized based on particulate organic matter analysis marine dominated palynofacies a and terrestrially influenced palynofacies b the organic compositions of these two palynofacies along with the recovered dinoflagellate cyst community suggest that while sustained oceanic depositional conditions were prevalent occasional influxes of terrestrial organic material of variable magnitudes occurred these short term influxes were especially pronounced during the late eocene and earliest oligocene and appear to have happened in response to the cooling and slight global sea level drop that occurred at ca 38 33 5 ma the preserved terrestrial palynomorphs in the samples indicate coastal plain and estuarine vegetation sources in general except during the eocene oligocene transition when anemophilous pollen specimens mostly derived from farther inland and montane sources were recovered

on the evolution of coastally trapped waves generated by hurricane juliette along the mexican west coast 1 an operational real time eddy resolving 1 16 global ocean nowcast forecast system is used to study the evolution of two coastally trapped waves generated by hurricane juliette along the mexican west coast results indicate that the first wave was generated along mainland mexico and it propagated poleward as a free coastally trapped wave it also generated anticyclonic eddies near cabo corrientes and the maria islands upon entering the gulf of california the wave weakened cyclonic eddies and after reaching the shelf break north of guaymas it reversed direction and propagated southward along the east coast of the baja california peninsula bcp next the wave generated an anticyclonic eddy at cabo san lucas finally the wave weakened while exiting the gulf and propagated northward along the bcp west coast the second coastally trapped wave was generated by juliette s poleward winds along the bcp west coast but was subsequently greatly weakened by juliette s equatorward winds

seasonal surface connectivity in the gulf of california abstract a three dimensional numerical model is used to study seasonal connectivity in the gulf of california from the eulerian velocity fields of the model particle trajectories were calculated for the 12 months of the year using an advection diffusion scheme connectivity was quantified for twelve gulf provinces with different dynamic circulation characteristics being defined by the eulerian velocity field strong or weak coastal currents eddies and areas of mixing and exchange retention occurred for 9 12 months of the year in the upper gulf eddy and sonora regions of the northern gulf because of the gulf wide eddy circulation which implies high potential for the auto recruitment of larvae in this province high retention was also found on the peninsula side of the southern gulf in association with weaker residual currents again implying potential for self recruitment in contrast low retention was observed on the mainland side of the central and southern gulf from which particles are exported to many areas by the faster residual currents enhancing the potential for recruitment of distant coastal species empirical orthogonal function analyses revealed a strong annual and semiannual evolution in accordance with the strong seasonality of the gulf dynamics

paleotemperatures and ice volume of the past 27 myr revisited with paired mg ca and 18o 16o measurements on benthic foraminifera 1 we explore the applicability of paired mg ca and 18o 16o measurements on benthic foraminifera from southern ocean site 747 to paleoceanographic reconstructions on pre pleistocene timescales we focus on the late oligocene through pleistocene 27 0 ma history of paleotemperatures and the evolution of the 18o values of seawater 18osw at a temporal resolution of 100 200 kyr absolute paleotemperature estimates depend on assumptions of how mg ca ratios of seawater have changed over the past 27 myr but relative changes that occur on geologically brief timescales are robust results indicate that at the oligocene to miocene boundary 23 8 ma temperatures lag the increase in global ice volume deduced from benthic foraminiferal 18o values but the smaller scale miocene glaciations are accompanied by ocean cooling of 1 c during the mid miocene phase of antarctic ice sheet growth 15 13 ma water temperatures cool by 3 c unlike the benthic foraminiferal 18o values which remain relatively constant thereafter temperatures vary by 3 c and reach maxima at 12 and 8 5 ma the onset of significant northern hemisphere glaciation during the late pliocene is synchronous with an 4 c cooling at site 747 a comparison of our 18osw curve to the haq et al 1987 sea level curve yields excellent agreement between sequence boundaries and times of increasing seawater 18o 16o ratios at 12 11 ma in particular when benthic foraminiferal 18o values do not support a further increase in ice volume the 18osw curve comes to a maximum that corresponds to a major mid miocene sea level regression the agreement between the character of our mg ca based 18osw curve and sequence stratigraphy demonstrates that benthic foramaniferal mg ca ratios can be used to trace the 18osw on pre pleistocene timescales despite a number of uncertainties related to poorly constrained temperature calibrations and paleoseawater mg ca ratios the mg ca record also highlights that deep ocean temperatures can vary independently and unexpectedly from ice volume changes which can lead to misinterpretations of the 18o record

the determination of deep temperatures by means of the co co2 h2 h2o geothermometer an example using fumaroles in the campi flegrei italy chromatographic analyses of fumarolic gases collected in sampling bottles containing an alkaline solution have been carried out using a thermal conductivity detector and a flame ionization detector after catalytic conversion of co and ch4 the latter method enables the concentration of carbon monoxide to be measured with sufficient accuracy for use in a co co2 h2 h2o geothermometer application of this geothermometer to fumaroles in the crater of solfatara in the campi flegrei italy indicates that they are fed from a steam reservoir at 250 15 c and at 10 36 2atm of oxygen on the other hand the ch4 co2 h2 h2o geothermobarometer seems to re equilibrate at superficial temperatures and cannot be used for infering thermodynamic conditions at depth regular sampling of these fumaroles together with a geothermometric interpretation of the gas analyses provides a means of monitoring with comparative accuracy the chemical and thermal evolution of the hydrothermal reservoir below the solfatara crater such monitoring would probably detect an increase in temperature at depth and the injection of magmatic gas into the reservoir

chemical and isotopic signatures of the basement rocks from the campi flegrei geothermal field naples southern italy inferences about the origin and evolution of its hydrothermal fluids abstract the campi flegrei naples campanian plain southern italy geothermal system is hosted by quaternary volcanic rocks erupted before during and after the formation of the caldera that represents one of the major structural features in the neapolitan area the volcanic products rest on a mesozoic carbonate basement cropping out north east and south of the area chemical major minor and trace elements and stable isotope c h o analyses were conducted on drill core samples recovered from geothermal wells mf 1 mf 5 sv 1 and sv 3 at depths of 1100 to 2900 m the study was complemented by petrographic and sem examination of thin sections the water which feeds the system is both marine and meteoric in origin mineral zonation typical of a high temperature geothermal system exists in all the geothermal wells measured temperatures in wells are as high as 400 c the chemical composition of the waters suggests the existence of two reservoirs a shallow reservoir depth 2000 m of hypersaline water the drill cores are mainly hydrothermally altered volcanics of trachy latitic affinity but some altered pelites and limestones are also present published na mg and k concentrations of selected geothermal waters indicate that the hydrothermal fluids are in equilibrium with their host rocks with respect to k feldspar albite sericite and chlorite the measured 18 o smow values of rocks range from 4 3 to 16 5 the measured d smow values range from 79 to 46 the calculated isotopic composition of the fluids at equilibrium with the samples vary from 1 to 8 3 18 o and from 52 to 1 d the estimated isotopic composition of the waters at equilibrium with the studied samples confirmed the existence of two distinct fluid types circulating in the geothermal system the shallower has a marine water signature while the deeper water has a signature consistent both with magmatic and meteoric origins in the latter case the recharge of this aquifer likely occurs at the outcrop of the mesozoic limestones surrounding the campanian plain after infiltration the water percolates through evaporitic layers becoming hypersaline and d depleted

mesoscale variability in the northeastern tropical pacific forcing mechanisms and eddy properties 1 the generation mechanisms and properties of the mesoscale eddies in the northeastern tropical pacific netp are studied using a series of numerical solutions and satellite observations the spatial and temporal resolution of mountain wind jets over the gulfs of tehuantepec and papagayo are essential for an accurate modeling of the regional mesoscale variability three previously proposed eddy generation mechanisms are the local transient wind forcing the combined low frequency wind and boundary forcing and the remote equatorial kelvin wave forcing in our model the transient wind forcing was represented by wind fields with synoptic variability and the remote equatorial kelvin wave forcing by 5 day open boundary conditions with interannual variability solutions with and without high frequency forcings are contrasted to evaluate the contributions of the three mechanisms the combined low frequency wind and boundary forcing is the primary eddy forcing mechanism in the netp in the tehuantepec region the high frequency wind forcing contributes more to the mesoscale variability than the remote equatorial kelvin wave forcing while in the papagayo region their contributions are comparable eddies in the tehuantepec and papagayo regions are larger in both amplitude and size and are more likely to deflect equatorward than eddies in the rest of the netp the maximum temperature anomaly of eddies is at around 50 m depth eddies with lifetimes 6 weeks are more likely anticyclonic while eddies with lifetimes 6 weeks are more likely cyclonic the anticyclone dominance for large amplitude long lived eddies is the combined consequence of wind driven asymmetric dipole spin up and the evolutionary fragility of large amplitude cyclones

steps in the intensification of benguela upwelling over the walvis ridge during miocene and pliocene upwelling is a significant part of the ocean circulation controlling largely the transport of nutrient rich cold waters to the surface and therefore influencing ocean productivity and global climate the benguela upwelling system bus is one of the major upwelling areas in the world previous reconstructions of the bus mainly focused on the onset and intensification in southern and central parts but changes of the northern part have been rarely investigated in detail using the late miocene to pliocene organic walled dinoflagellate cyst record of odp site 1081 we reconstruct and discuss the early upwelling history over the walvis ridge with a special focus on the movement of the angola benguela front abf we suggest that during the late miocene the angola current flowed southwards over the walvis ridge more frequently than today because the abf was probably located further south as a result of a weaker meridional temperature gradient a possible strengthening of the meridional gradient during the latest miocene to early pliocene in combination with uplift of south western africa intensified the upwelling along the coast and increased the upwelling s filaments over the walvis ridge an intermediate period from 6 2 to 5 5 ma is shown by the dominance of habibacysta tectata cysts of a cool tolerant dinoflagellate known from the northern atlantic indicating changing oceanic conditions contemporaneous with the messinian salinity crisis from 4 3 ma on the upwelling signal got stronger again and waters were well mixed and nutrient rich our results indicate a northward migration of the abf as early as 7 ma and the initial stepwise intensification of the bus

mesoscale eddies in the southern gulf of california during summer characteristics and interaction with the wind stress 1 the hydrodynamic characteristics of mesoscale eddies of the southern gulf of california are described from observations made in august 2004 vertical profiles to 1000 m were made with a conductivity temperature depth ctd probe with dissolved oxygen and fluorescence sensors and a lowered acoustic doppler profiler the four sampled eddies were aligned along the gulf axis and had alternating sense of rotation the okubo weiss parameter was used to calculate the eddy core radii and it also revealed that the current field of almost all the sampled area was eddy dominated the mean radii of the eddy cores varied between 32 and 36 km maximum surface velocities were 0 4 0 5 m s the anticyclonic eddies were 500 700 m deep while the cyclones were 450 500 m deep the depression of the isolines associated with the anticyclonic eddies was 100 m at depths between 200 and 400 m however the thermocline pycnocline which spanned from 20 to 75 m was domed by 10 m the cyclonic eddies lifted the isolines by 70 m at depths above 500 m but the isolines were flat above 60 m this suggests that different dynamics operate in the layer above the strong and shallow pycnocline in particular the wind stress curl can affect circulation and pycnocline topography and therefore the patterns that appear in chlorophyll satellite images in our case the eddies were detectable in those images because of the chlorophyll enhanced streamers along their edges and for anticyclones probably because the chlorophyll maximum found at 40 50 m depth was domed following the pycnocline

ocean color observations of eddies during the summer in the gulf of california 1 using seawifs ocean color satellite images collected during 1997 2001 a series of eddies have been observed in the gulf of california these eddies are not clearly seen in the summertime sea surface temperature images the surface circulation between the midriff islands and the mouth of the gulf appears to be dominated by this series of eddies that have an alternating sense of rotation an eddy pair is observed to extend from cabo lobos in each of the three years suggesting that the eddies are topographically locked the formation mechanism of the eddies remains unknown however we suspect the most likely mechanism includes baroclinic instabilities along the coast produced by interactions between coastally trapped waves and local wind driven currents