metallogenesis at paleo spreading centers lead isotopes in sulfides rocks and sediments from the troodos ophiolite cyprus abstract new pb isotopic data for metalliferous deposits and pelagic sediments from the troodos ophiolite complex cyprus are presented we use these data to re evaluate the genetic models for these deposits in the light of recent results obtained for different types of hydrothermal sites presently active on spreading ridges in contrast to previous conclusions of earlier studies we find that the troodos hydrothermal deposits sulfides as well as umbers and mn crusts have isotopic compositions very similar to that of most of the rocks from this ophiolite complex they display a 207 pb 204 pb ratio higher than present day typical ridges this result has been interpreted as evidence for a subduction related origin of the troodos ophiolite this different geodynamic setting of the ophiolite is also the reason for the isotopic difference between troodos and semail oman sulfides the latter being typical of a normal oceanic crust when examined in more detail the troodos sulfide results are very homogeneous within one site but show significant differences from one site to another at least three different isotopic end members are required to interpret these variations one of these end members is found in the pelagic sediments data analyzed here which have a 207 pb 204 pb typical of continental crust signature higher than that of the rocks and sulfides on present ridges the involvement of such a component has been similarly described for the guaymas basin and for the gorda rise deposits however some of the isotopic variations observed between sulfides cannot be interpreted only by this end member one possibility is that a second sedimentary component as yet unidentified has been involved in the hydrothermal circulation as recently demonstrated for red sea brines finally the determination of the exact proportion of pb leached out of the ophiolite basaltic crust itself would require a more complete knowledge of the initial isotopic heterogeneities within the massif indeed several rock results are significantly less radiogenic than those of the sulfides which however show themselves initial compositions this could result either from a sediment contribution to the sulfide pb or from a biased sampling of the massif heterogeneities this question remains open in the present state of the data

formation of large sulfide mineral deposits along fast spreading ridges example from off axial deposits at 12 43 n on the east pacific rise abstract submersible investigations with nautile near the 13 n hydrothermal field on the epr were made in 1992 we selected diving areas based on deep towed side scan sonar imaging close to a pit crater at the top of a young seamount 2 km east of the axial ridge we discovered one of the largest 70 m high and 200 m in diameter sulfide mounds formed at a fast spreading ridge 12 cm yr despite an overlap in composition between axial and off axial deposits the general trend reflects real differences in compositions off axis deposit differs from axial deposits by the scarcity of zinc sulfides and cobalt and selenium enrichment sulfur isotope variation is minimal for the off axis seamounts and suggests that sulfides precipitated from unmodifed end member hydrothermal solutions axial sulfides have a broader range due to reduction of seawater sulfate at mixing fronts between hydrothermal and seawater solutions along the axial graben fault system lead isotopic compositions of sulfides are in two overlapping but distinct fields indicating different pb sources and separate convective systems for the seamount and the axial deposits our observations suggest that the plumbing system is stable and centred on a shallow localised magma chamber under the seamount this configuration is by far more efficient than unstable axial processes to create during several hydrothermal episodes major sulfide deposits near a fast spreading ridge off axis seamounts are localised areas with high magmatic budget able to drive and focus hydrothermal systems at the same place for a long time other known occurrences of sulfides related to seamounts are at less than 11 km from the ridge axis thus we suggest that off axial volcanoes close to the ridge are first order targets to discover active or inactive large deposits along fast to medium spreading ridges

heat and fresh water transport by eddies into the gulf of alaska abstract anticyclonic mesoscale eddies form in winter along the continental margin of canada and southeast alaska between the latitudes of 51n and 60n and drift westward into the gulf of alaska carrying warmer fresher water away from the continental margin detailed measurements of temperature and salinity between 1995 and 2001 were examined to determine the amount of heat and fresh water transported seaward by several eddies that formed west of the queen charlotte islands eddies formed in a typical winter carry about 30 10 18 j of heat into the gulf which is about 35 to 60 of the heat transported northward each winter along the continental margin toward this region the observed range of eddy heat transport is 10 19 to 10 20 j largest observed eddy heat transport coincided with increased northward heat flow along the continental margin during the el nino winter of 1997 1998 fresh water volume was determined by evaluating the amount of fresh water required to reduce the salinity from a reference level to that observed in eddies this volume varied from 0 to 70 km 3 and was largest during the 1997 1998 el nino winter eddies formed in a typical winter transport 50 km 3 of fresh water seaward which is about 15 of the estimated fresh water input to the continental margin in winter between the columbia river and 54n attributed to local runoff plus direct rainfall and flow in major rivers

whole rock and sulfide lead isotope data from the hydrothermal jade field in the okinawa back arc trough the mineralization of the active hydrothermal jade field resembles in many aspects the kuroko type mineralization the jade field is located in a back arc graben and is associated with a bimodal volcanism lead isotope data from igneous rocks sediments and ores further emphasize the similarities with the kuroko ores and suggest that both sediments and volcanic rocks contributed comparable amounts of lead to the deposit when compared to the sediments a much larger volume of volcanic rocks must have contributed lead to the deposit because of the considerably lower lead concentration of volcanic rocks in contrast to the crustal type lead of the jade field and the kuroko type sulfide deposits the lead isotope signatures of vms type deposits at mid ocean ridges is distinctly different in the absence of a sedimentary cover it reflects the composition of the mantle source whereas in the presence of a sedimentary cover it is either a mixture of mantle and sedimentary lead or it may even be completely dominated by the latter

near vent chemical processes in a hydrothermal plume insights from an integrated study of the endeavour segment support from onc for sample collection is gratefully acknowledge as is the analytical expertise of jody spence bruno keiffer and maureen soon who helped generate the data set reported here funding for sample analysis came from an nserc discovery grant to l a c ocean networks canada is supported through the canadian foundation for innovation all data are provided in the supporting information or through onc at http dmas uvic ca datasearch

zinc copper and lead in mid ocean ridge basalts and the source rock control on zn pb in ocean ridge hydrothermal deposits the contents of zn cu and pb in mid ocean ridge basalts morb and the morb source rock control on zn pb in ocean ridge hydrothermal deposits are examined the values of zn cu and pb for submarine mid ocean ridge basalts morb are respectively in ppm average morb 75 75 and 0 7 west valley juan de fuca ridge jfr 87 64 and 0 5 southern jfr 120 and 0 5 and 21 n east pacific rise epr 73 78 and 0 5 values of zn pb range from about 100 240 and cu pb from 100 156 in this study zn is found to correlate positively with tio2 feo mean square of weighted deviates mswd of 1 6 for jfr basalt and inversely with mg number mswd of 3 5 therefore contrary to statements in the literature that zn should be compatible in morb zn is a mildly incompatible element and must be enriched in the glass phase relative to olivine as zn does not fit into the other major phenocryst phase plagioclase in the source of morb zn likely is most enriched in oxides spinel magnetite and titanomagnetite copper generally does not correlate well with other elements in most morb data examined when differentiation is dominated by olivine cu has a tendency to behave incompatibly e g at mg numbers 70 but overall cu shows some tendency towards being a compatible element particularly along the mid atlantic ridge a behavior presumably due to separation of sulfides in which cu but not zn is markedly enriched copper thus may be in dispersed sulfides in the source of morb ocean ridges provide important data on source rock controls for sulfide deposits because in sediment starved ridges much is known about the possible source rocks and mineralization is presently occurring in contrast to zn pb 5 in continental hot cl rich brines zn pb in the hottest sediment starved ridge black smoker hydrothermal fluids at 21 n epr is about 110 similar to local morb 145 but cu pb is closer to 30 possibly due to subsurface deposition of cu at the jfr the best value of zn pb in the hydrothermal fluids is about 175 again similar to local morb 240 but cu is very low in the fluids that are at temperatures less than 300 c the large morb like zn pb in the hottest black smoker fluids suggests a source rock control for the metals that prohibits significant galena in the black smoker deposits of sediment starved ridges in contrast exhalative deposits on sediment swamped ridges have significant galena its presence is suggestive of pb derivation from sediments an origin supported by pb isotope studies of lehuray and colleagues in 1988

petrogenesis of alkaline basalts from socorro island mexico trace element evidence for contamination of ocean island basalt in the shallow ocean crust postcaldera mafic volcanism on socorro island mexico an island located in the eastern pacific ocean on a segment of a mid ocean ridge spreading center abandoned at 3 5 ma dominantly comprises alkalic basalt hawaiite and mugearite with subordinate mildly alkalic transitional basalt most major element data are consistent with differentiation of alkalic basalt to hawaiite and mugearite by up to 50 fractionation of plagioclase clinopyroxene olivine fe ti oxides high field strength element abundances are consistent with this interpretation and the narrow range in zr nb suggests that parental magmas formed by similar degrees of partial melting of a relatively homogeneous mantle source sr and nd isotopic ratios exhibit relatively narrow ranges 0 7031 0 7032 0 5128 0 5130 respectively despite this a subset of the alkalic basalts has negative ce anomalies and abundances of p2o5 ba y and some rare earth elements in excess of those predicted by fractional crystallization models these chemical features require open system processes the observed heterogeneities are perhaps best explained by assimilation of ocean crustal components by basalt in a shallow magma reservoir regional mantle heterogeneity is evident from elemental and isotopic data for mildly alkalic transitional basalt from socorro island mugearite from san benedicto island and submarine basalts from near socorro island evidence presented here indicates that compositional variations in ocean island basalts can be introduced by ocean crustal contamination and underscores the importance of considering this source of chemical heterogeneity in basalts before characterizing associated mantle

pb isotope compositions of galena in hydrothermal deposits obtained by drillings from active hydrothermal fields in the middle okinawa trough determined by la mc icp ms abstract the pb isotope compositions of galena in hydrothermal deposits obtained by drillings from two hydrothermal fields in the middle okinawa trough were studied one of the study fields was the iheya north field located on a volcanic complex and the other was the izena field located in the sediment filled caldera structure la mc icp ms was applied to directly measure pb isotope compositions in individual galena grains which highlighted variations not only in regional scale but also in microscopic scale so that changes of pb isotope compositions within a galena grain can be tracked homogeneous pb isotope compositions were found within the same hydrothermal site irrespective of the mineral assemblage texture and sampling depth beneath the seafloor in contrast the isotope compositions varied significantly between the two hydrothermal fields the pb isotope composition from the iheya north field was isotopically close to the volcanic rocks of the okinawa trough whereas that from the izena field was more radiogenic with values intermediate between sediments and volcanic rocks of the okinawa trough within the iheya north field intra field variation of pb isotope compositions was recognized between two active sites 2 5 km apart from each other the intra field variation was recognized also in the izena field the sub seafloor massive sulfide layer has a more sediment like pb isotope composition compared to the inactive sulfide mound these results illustrate that the pb mineralizing hydrothermal fluids originate from their local host rocks with without sediment and that the isotope compositions of the galena grains reflect their metal sources either the volcanic rocks and or the sediments via water rock interactions

multi year meanders and eddies in the alaskan stream as observed by topex poseidon altimeter the birth life and decay of long lived anticyclonic eddies or meanders in the alaskan stream are observed from topex poseidon t p satellite their surface height anomalies approach 72 cm average diameter is about 160km and they live for 1 to 3 years propagating along the stream with mean speed of 2 5 km d 1 of the six observed the last three were formed after the first t p observations in september 1992 of these two evolved from eddies near alaskan panhandle in winter drifting across the northern gulf of alaska before entering the alaskan stream while another formed in the stream west of shelikof strait

low frequency variability in the gulf of alaska from coarse and eddy permitting ocean models 1 an eddy permitting ocean model of the northeast pacific is used to examine the ocean adjustment to changing wind forcing in the gulf of alaska goa at interannual to decadal timescales it is found that the adjustment of the ocean model in the presence of mesoscale eddies is similar to that obtained with coarse resolution models local ekman pumping plays a key role in forcing pycnocline depth variability and to a lesser degree sea surface height ssh variability in the center of the alaska gyre and in some areas of the eastern and northern goa westward rossby wave propagation is evident in the ssh field along some latitudes but is less noticeable in the pycnocline depth field differences between ssh and pycnocline depth are also found when considering their relationship with the local forcing and leading modes of climate variability in the northeast pacific in the central goa pycnocline depth variations are more clearly related to changes in the local ekman pumping than ssh while ssh is marginally correlated with both pacific decadal oscillation pdo and north pacific gyre oscillation npgo indices the pycnocline depth evolution is primarily related to npgo variability the intensity of the mesoscale eddy field increases with increasing circulation strength the eddy field is generally more energetic after the 1976 1977 climate regime shift when the gyre circulation intensified in the western basin where eddies primarily originate from intrinsic instabilities of the flow variations in eddy kinetic energy are statistically significant correlated with the pdo index indicating that eddy statistics may be inferred to some degree from the characteristics of the large scale flow

organic rich sediment alteration an experimental and theoretical study at elevated temperatures and pressures organic rich diatomaceous ooze was reacted with sea water at 200 and 300 c 500 bars and an initial fluid sediment mass ratio of 4 to evaluate the role of organic matter in sediment alteration processes at elevated temperatures and pressures decomposition of organic matter during the early stages of reaction dominated alteration and resulted in increased dissolved co2 corganic nh4 and h2s car ylic acids were identified as reaction intermediaries during the transformation of organic matter to ch4 and co2 extensive so42 reduction was observed at 300 c but not at 200 c sediment alteration at 300 c resulted in recrystallization of calcic plagioclase and diatoms to an assemblage containing albite pyrrohotite and quartz in addition to minor anhydrite and mg smectite in contrast sediment alteration at 200 c resulted in only minor anhydrite and mg smectite formation and there was no indication of recrystallization of diatoms to quartz rapid mg fixation during the early stages of alteration resulted in the complete removal of mg from solution at 300 c and partial removal at 200 c production of acidity associated with mg metasomatism was efficiently titrated by thermolytic and oxidative degradation of organic matter resulting in conspicuously low dissolved metal concentrations during the experiments in the later stages of sediment alteration at 300 c albitization of calcic plagioclase caused the continuous release of ca to solution while at 200 c fluid chemistry remained relatively constant speciation calculations for the 300 c experiment indicate an in situ ph of 5 11 and a highly reduced redox state likely controlled by organic matter decomposition experimental results permit us to evaluate fluid mineral equilibria in complex fluids containing high concentrations of dissolved organic species co2 and h2s and constrain better alteration processes in sub sea floor hydrothermal systems at sediment covered spreading centers such as the guaymas basin gulf of california

metal sources in the middle valley massive sulphide deposit northern juan de fuca ridge pb isotope constraints abstract massive sulphides drilled from the bent hill deposit during ocean drilling program leg 139 at middle valley northern juan de fuca ridge have 206 pb 204 pb 18 43 18 86 207 pb 204 pb 15 43 15 63 208 pb 204 pb 38 08 38 60 these span 35 of the total pb isotope range measured in hydrothermal sulphides from the east pacific ocean 206 pb 204 pb ratios overlap the range of local basalts but 208 pb 204 pb and 207 pb 204 pb require a contribution from a more radiogenic source that is similar to the overlying sedimentary sequence three samples have lower 207 pb 204 pb ratios than the mean basalt value which may reflect the preservation of heterogeneities in the local basalts the pb isotopic compositions of primary pyrrhotites are indistinguishable from the secondary pyrite dominated assemblage which recrystallised from low temperature hydrothermal fluids this may be explained by the importance of the sulphosalts as a host for pb in the deposit clastic sulphides from sediments at bent hill are at the radiogenic end of the massive sulphide range suggesting that surficial sulphides may not provide an unbiased sample of the past hydrothermal circulation responsible for massive sulphide deposition if the pb content of sediment is 100 times greater than the basalts the sulphide pb isotopes imply that the hydrothermal fluids have extracted pb from 60 to 900 times more basalt than sediment lead in the massive sulphide deposit has been extracted from 2 10 8 3 10 8 m 3 of oceanic crust demonstrating the local nature of hydrothermal circulation at mid ocean ridges the 3 he 4 he of hydrothermal fluids in the sulphides 6 2 10 6 7 8 10 6 show only half the variation between the sediment and basalt end members displayed by pb isotopes this is consistent with volatile acquisition from magma degassing while the pb is leached during hydrothermal fluid interaction with crystallised oceanic crust

sr nd and pb isotope constraints on the formation of the metalliferous sediments in the nereus deep red sea previous chemical analyses of sediments from nereus deep core 412 located in the northern part of the red sea at about 23 20 n have demonstrated the occurrence of v rich authigenic magnetites associated with fe zn and cu sulphides mostly located at the bottom of the core the evolutionary stage of nereus deep is intermediate between that of the immature shaban deep and the more evolved atlantis ii deep previous studies have proposed either morb basalts by analogy with east pacific rise sulphide deposits or sediments as possible sources of the metals in the red sea metalliferous sediments sr nd and pb isotope systematics observed at ten levels in nereus core 412 lead us to distinguish three types of sediments 1 with predominantly basaltic fragments associated with loose titanomagnetite crystals 0 70413 87sr86sr 0 70622 0 51271 143nd144nd 0 51300 18 618 206pb204pb 18 673 2 detrital or biogenic sediments with a continental isotopic imprint 0 70938 87sr86sr 0 71323 0 51242 143nd144nd 0 51262 18 848 206pb204pb 18 890 and 3 v rich metalliferous sediments 0 70872 87sr86sr 0 70895 0 51260 143nd144nd 0 51274 18 717 206pb204pb 18 851 on sr nd and pb pb isotope diagrams this last group of sediments defines a field located between the fields of the first two groups our data suggest that the sr nd and pb in the studied metalliferous sediments were derived from overlying sedimentary beds in which the two main constituent detrital components show very distinct origins red sea morb and continental arabo nubian shield these data clearly support a model of convective circulation within the nereus deep sedimentary pile this model involves leaching two main components from the upper sedimentary layers of the core and a downward circulation of a hot fluid promoting the growth of v rich magnetites and fe zn and cu sulphides when the fluid cooled by mixing with the pore water of sediments from the lower part of the core a driving force represented by magmatic activity located near the 412 core in the nereus deep is required to explain the presence of hot convective fluids these data also suggest that for sedimented ridges the isotopic imprint of a basaltic source in metalliferous sediments or a hydrothermal ore deposit may result by interaction of a hot fluid with detrital sediments that are enriched in basaltic clasts and loose magmatic crystals

pb isotopes in sulfides from mid ocean ridge hydrothermal sites the authors report pb isotope ratios of sulfides deposited at seven recently active mid ocean ridge mor hydrothermal vents sulfides from three sediment starved sites on the juan de fuca ridge contain pb with isotope ratios identical to their local basaltic sources lead in two deposits from the sediment covered escanaba trough gorda ridge is derived from the sediments and does not appear to contain any basaltic component there is a range of isotope ratios in a guaymas basin deposit consistent with a mixture of sediment and mor basalt pb lead in a galapagos deposit differs slightly from known galapagos basalt pb isotope values the faithful record of pb isotope signatures of local sources in mor sulfides indicates that isotope ratios from ancient analogues ca be used as accurate reflections of ancient oceanic crustal values in ophiolite hosted deposits and continental crustal averages in sediment hosted deposits the preservation of primary ophiolitic or continental crustal pb isotope signatures in ancient mor sulfides provides a powerful tool for investigation of crustal evolution and for fingerprinting ancient terranes

altimeter derived surface circulation in the large scale ne pacific gyres part 1 seasonal variability abstract the seasonal variability of sea surface height ssh and currents are defined by analysis of altimeter data in the ne pacific ocean over the region from central america to the alaska gyre the results help to clarify questions about the timing of seasonal maxima in the boundary currents as explained below the long term temporal mean of the ssh values must be removed at each spatial point to remove the temporally invariant and large signal caused by the marine geoid we refer to the resulting ssh values which contain all of the temporal variations as the residual ssh our main findings are 1 the maximum surface velocities around the boundaries of the cyclonic alaska gyre the alaska current and the alaska stream occur in winter at the same time that the equatorward california current is weakest or reversed forming the poleward davidson current the maximum surface velocities in the california current occur in summer these seasonal maxima are coincident with the large scale atmospheric wind forcing over each region 2 most of the seasonal variability occurs as strong residuals in alongshore surface currents around the boundaries of the ne pacific basin directly connecting the boundaries of the subpolar gyre the subtropical gyre and the equatorial current system 3 seasonal variability in the surface velocities of the eastward north pacific current west wind drift is weak in comparison to seasonal changes in the surface currents along the boundaries 4 there is an initial appearance next to the coast and offshore migration of seasonal highs and lows in ssh alongshore velocity and eddy kinetic energy eke in the alaska gyre similar to the previously described seasonal offshore migration in the california current 5 the seasonal development of high ssh and poleward current residuals next to the coast appear first off central america and mainland mexico in may june prior to their appearance in the southern part of the california current in july august and their eventual spread around the entire basin in november december similarly low ssh and equatorward transport residuals appear first off central america and mexico in january february before spreading farther north in spring and summer 6 the maximum values of eke occur when each of the boundary currents are maximum

observations from a yakutat eddy in the northern gulf of alaska 1 the impingement of deep basin eddies on the shelf in the gulf of alaska has been implicated as an important mechanism for cross shelf exchange the influence of eddies on biological processes has been confirmed with data from the sea viewing wide field of view sensor showing elevated chlorophyll associated with eddies altimetry data suggest that an eddy formed in the winter of 2003 near yakutat alaska and propagated along the shelf break reaching the head of the gulf by spring this eddy was sampled during may and september of 2003 the eddy core water was warm salty and high in nitrate relative to basin water of the same density but was similar to historical water properties from the shelf near yakutat this suggests a shelf origin for the eddy core water

lagrangian study of mesoscale circulation in the alaskan stream area and the eastern bering sea abstract the alaskan stream is the western boundary current in the subarctic north pacific the alaskan stream area is characterized by a significant temperature salinity and density differences between the coastal and open ocean waters and strong mesoscale dynamics in this paper we demonstrate the transport pathways of the alaskan stream water in the eastern subarctic pacific and its extension into the eastern bering sea from 1 october 1994 to 12 september 2016 with the help of altimetry based lagrangian maps mesoscale eddy activity along the boundary between the shelf and deep basin in the alaskan stream region and the eastern bering sea is shown to be related to the wind stress curl in the northern north pacific in winter a significant correlation is found between the concentration of chlorophyll a in the alaskan stream area and eastern bering sea in august september and the wind stress curl in the northern north pacific in november march the mesoscale dynamics forced by the wind stress curl in winter may influence not only lower trophic level organism biomass but also salmon abundance and catch in the study area

a dual origin for the hydrothermal component in a metalliferous sediment core from the mid atlantic ridge a highly metalliferous sediment core collected from tag 26 n mid atlantic ridge has been analyzed for uranium series isotopes rare earth elements ree and radiogenic isotopes two types of deposition of hydrothermal material have been identified and characterized the first is sulfide material which has been rapidly deposited and is sometimes clearly turbiditic this material exhibits high u fe and eu sm ratios and low 230th fe and ree fe ratios it is proposed that u is incorporated into the sulfides by diffusion through the oxidized coating with reductive fixation near the sulfide oxide boundary the second hydrothermal component is particulate fallout from the neutrally buoyant plume which is diluted by the background pelagic sedimentation this component exhibits u fe ratios around 2 10 5 an order of magnitude greater than reported plume particulate levels but the 230th fe ree fe and eu sm ratios are similar to plume values nd and pb isotopes have been used to differentiate the hydrothermal and pelagic end members within this sediment core

eddies in the eastern gulf of alaska from topex poseidon altimetry eddy activity in the gulf of alaska goa is evidenced to fluctuate with the el nino southern oscillation enso cycle altimetry from topex poseidon is used to study eddy formation along a single descending track in the far eastern goa from late 1992 through late 1998 the track is sampled between 45 n and 60 n where it is roughly parallel to the eastern boundary the geoid and mean currents are removed from the data through extraction of the temporal mean at each point the resulting anomalies are passed through a matched filter designed to detect gaussian signals embedded in noise the filter is optimized to detect eddies with amplitude 10 cm and diameters roughly 50 350 km both anticyclonic and cyclonic structures are examined the distribution of eddies in space is similar for both anticyclonic and cyclonic eddies with most occurring between 50 n and the northern limits of the goa few eddies of either sign were found south of 50 n anticyclonic eddies are stronger and have a broader distribution of amplitudes typically 5 30 cm compared to cyclonic features which are more symmetrically distributed over 5 15 cm the detection of weak 15 cm eddies is sensitive to the filter threshold but detection of larger amplitude eddies is robust the average amplitude of anticyclonic eddies increases following the 1993 1994 1995 and 1998 el nino events eddy amplitude appears to vary with enso strength the strongest eddies detected form in early 1998 these results support previous numerical studies of eddy development in the eastern goa

iron transport by mesoscale haida eddies in the gulf of alaska abstract a two year study of the iron distributions in anticyclonic mesoscale haida eddies of the eastern north pacific ocean has shown that such eddies are a major source of iron to the high nitrate low chlorophyll hnlc waters of the central gulf of alaska basin these eddies which are typically about 100 km in diameter form off the west coast of canada in winter and then track roughly westward into the open ocean therefore they carry large quantities of iron rich coastal waters into iron limited waters of the oligotrophic gyre when the eddies had first formed their dissolved iron concentrations were nearly two orders of magnitude higher than is typically observed at station papa 50 n 145 w 3 n m versus less than 0 05 n m and the total iron in the eddies surface waters 10 40 m was more than 13 n m higher than open ocean waters of the alaska gyre 14 n m versus 0 5 n m while the overall iron content of the eddies decreased rapidly during the first year after they formed the eddy we were able to track the longest still contained 1 5 2 times more iron than the surrounding waters 16 months after its formation therefore although iron concentrations in the surface mixed layers of the eddies drop to levels observed outside very rapidly within 4 months upward transport along isopycnals and upwelling due to eddy decay as well as vertical advective and diffusive transports typical of north pacific waters probably provide steady fluxes of iron into the euphotic zone from the still iron rich eddy core waters throughout the lifetime of the eddy

pb isotope systematics of a fossil hydrothermal system from the troodos ophiolite cyprus evidence for a polyphased alteration history pb isotopic ratios have been determined on massive sulphides from the troodos ophiolite and their inferred source rocks epidosites and greenschist altered dikes the latter have distinctly higher pb isotope ratios than the sulphides the high 207 pb 204 pb ratios for the whole rocks indicate the involvement of an old sedimentary pb component extensive leaching of three epidosite samples shows that the radiogenic pb can be removed and the resulting trend for the leached samples is consistent with a pb pb age of 95 ma for these rocks inferred initial pb isotope ratios are similar to those of the sulphides this study and fresh glasses from the akaki canyon in cyprus therefore the pb incorporated in the massive sulphides may originate from these greenschist facies hydrothermally altered rocks the isotopic composition of the leachate pb points toward a sedimentary origin calculation of the pb isotopic ratios for 90 ma old average troodos sediment shows that the foreign pb in the epidosites may very well be derived from this source this pb probably does not reside within the mineral lattices of these metamorphic rocks but rather is adsorbed on mineral surfaces or is present in microscopic particulate matter that may have been filtered from the circulating seawater unmodified seawater is considered an unlikely pb source because of the extremely small dissolved pb contents of seawater furthermore no seawater or sedimentary signature is evident in the sulphides several models of pb transport from different sources into these rocks may be envisaged such as dissolution of miocene evaporites and brine formation equilibration of pore waters to the pb isotope ratios of host sediments and direct infiltration of deep sea particulate matter from the nepheloid layer with the limited amount of data presently available it is impossible to critically determine the most likely processes of pb transport copyright 2000 elsevier science ltd high temperature convectively driven submarine hydrother mal systems at sea floor spreading centres are believed to be of major importance to the heat transport from the newly formed oceanic crust these seawater fed hydrothermal systems are also believed to have major impacts on the chemical mineral ogical and physical properties of the oceanic lithosphere one of the most eminent processes is the formation of sulphide deposits by precipitation of sulphides from upwelling hot hy drothermal fluids upon mixing with cold circulating seawater in the more permeable portions in the upper parts of the oceanic lithosphere present day knowledge of these submarine hydrothermal systems comes partly from their most accessible component the hot springs that emanate hydrothermal fluids at or near the ridge axis but also from seawater basalt and seawater diabase interaction experiments and petrologic and geochemical studies on both in situ oceanic crust and ophiolites because the in ferred source rocks from these hydrothermal systems are lo

multi scale modeling of the north pacific ocean assessment and analysis of simulated basin scale variability 1996 2003 1 a primitive equation ocean general circulation model is used to investigate climate impacts in the north pacific ocean in the 1996 to 2003 period the objective is to assess the model ability to reproduce observed modes of variability and study their impact in the northeast pacific this work is done within the framework of the u s global ecosystem globec northeast pacific program studying the links between climate variability and ecosystem dynamics three large scale events are considered the 1997 1998 el nino the 1999 regime shift and the 2002 cold fresh subsurface anomalous water mass that was observed in the gulf of alaska and off the coast of oregon the circulation model is shown to generate the correct seasonal to interannual large scale variability and is able to represent the climatic signals of interest in the eastern pacific we show that the influence of the 1997 1998 el nino reached the coastal gulf of alaska and induced an increase in the upper ocean heat content along the coast of north america an analysis of the sea surface temperature for the model years shows agreement between model and data in the representation of the 1999 shift to a cold phase in the eastern and northern north pacific finally using the model results we speculate that the origin of the 2002 cold fresh anomaly in the northeast pacific was due to enhanced mixing during the preceding winter in the center of the alaska gyre owing to anomalous changes in the density structure of the upper ocean this water was able to move geostrophically toward the coast and it persisted in the northeast pacific below the mixed layer the following year

intrinsic and forced interannual variability of the gulf of alaska mesoscale circulation abstract the response of the gulf of alaska goa circulation to large scale north pacific climate variability is explored using three high resolution 15 km regional ocean model ensembles over the period 1950 2004 on interannual and decadal timescales the mean circulation is strongly modulated by changes in the large scale climate forcing associated with pdo and enso intensification of the model gyre scale circulation occurs after the 1976 1977 climate shift as well as during 1965 1970 and 1993 1995 from the model dynamical budgets we find that when the goa experiences stronger southeasterly winds typical during the positive phase of the pdo and enso there is net large scale ekman convergence in the central and eastern coastal boundary the geostrophic adjustment to higher sea surface height ssh and lower isopycnals lead to stronger cyclonic gyre scale circulation the opposite situation occurs during stronger northwesterly winds negative phase of the pdo along the eastern side of the goa basin interannual changes in the surface winds also modulate the seasonal development of high amplitude anticyclonic eddies e g haida and sitka eddies large interannual eddy events during winter spring are phase locked with the seasonal cycle the initial eddy dynamics are consistent with a quasi linear rossby wave response to positive ssh anomalies forced by stronger downwelling favorable winds e g southwesterly during el nino however because of the fast growth rate of baroclinic instability and the geographical focusing associated with the coastal geometry most of the perturbation energy in the rossby wave is locally trapped until converted into large scale nonlinear coherent eddies coastally trapped waves of tropical origin may also contribute to positive ssh anomalies that lead to higher amplitude eddies however their presence does not appear essential the model ensembles which do not include the effects of equatorial coastally trapped waves capture the large haida and sitka eddy events observed during 1982 and 1997 and explain between 40 and 70 of the tidal gauges variance along the goa coast in the western side of the goa basin interannual eddy variability located south of the alaskan stream is not correlated with large scale forcing and appears to be intrinsic a comparison of the three model ensembles forced by ncep winds and a multi century long integration forced only with the seasonal cycle shows that the internal variability alone explains most of the eddy variance the asymmetry between the eddy forced regime in the eastern basin and the intrinsic regime in the western basin has important implications for predicting the goa response to climate change if future climate change results in stronger wintertime winds and increased downwelling in the eastern basin then increased mesoscale activity perhaps more or larger eddies might occur in this region conversely the changes in the western basin are not predictable based on environmental forcing eastern eddies transport important biogeochemical quantities such as iron oxygen and chlorophyll a into the gyre interior therefore having potential upscale effects on the goa high nutrient low chlorophyll region

formes figures et facies sedimentaires glaciels des estrans vaseux des regions froides abstract frost and drift ice are two important processes creating distinctive features in tidal flats of cold regions original sedimentary forms figures and structures and a particular facies characterized by two opposite grain sizes fine and coarse together result from ice action in muddy tidal flats grooves or furrows polished and striated surfaces tracks and trails various drag roll and skip marks circular depressions chaotic microreliefs pushed ridges polygonal nets monroes lenticular bedding and deformations are common to intertidal zones along the st lawrence and the james hudson bay area canada they also occur elsewhere in most tidal flats and on continental shelves dominated by ice a better knowledge of drift ice features in modern tidal flats is needed it is a prerequisite to the discovery of similar features in consolidated rocks the finding of such indicators should improve greatly any interpretation of the paleoenvironmental conditions of deposition

bathymetric prediction from dense satellite altimetry and sparse shipboard bathymetry the southern oceans south of 30 s are densely covered with satellite derived gravity data track spacing 2 4 km and sparsely covered with shipboard depth soundings hundreds of kilometers between tracks in some areas flexural isostatic compensation theory suggests that bathymetry and downward continued gravity data may show linear correlation in a band of wave lengths 15 160 km if sediment cover is thin and seafloor relief is moderate at shorter wave lengths the gravity field is insensitive to seafloor topography because of upward continuation from the seafloor to the sea surface at longer wavelengths isostatic compensation cancels out most of the gravity field due to the seafloor topography we combine this theory with wiener optimization theory and empirical evidence for gravity noise to signal ratios to design low pass and band pass filters to use in predicting bathymetry from gravity the prediction combines long wavelengths 160 km from low pass filtered soundings with an intermediate wavelength solution obtained from multiplying downward continued band pass filtered 15 160 km gravity data by a scaling factor s s is empirically determined from the correlation between gravity data and existing soundings in the 15 160 km band by robust regression and varies at long wave lengths we find that areas with less than 200 m of sediment cover show correlation between gravity and bathymetry significant at the 99 level and s may be related to the density of seafloor materials in these areas the prediction has a horizontal resolution limit of 5 10 km in position and is within 100 m of actual soundings at 50 of grid points and within 240 m at 80 of these in areas of very rugged topography the prediction underestimates the peak amplitudes of seafloor features images of the prediction reveal many tectonic features not seen on any existing bathymetrie charts because the prediction relies on the gravity field at wavelengths 160 km it is insensitive to errors in the navigation of sounding lines but also cannot completely reproduce them therefore it may be used to locate tectonic features but should not be used to assess hazards to navigation the prediction is available from the national geophysical data center in both digital and printed form

basement geology and tectonic evolution of ireland as deduced from pb isotopes in ireland lead isotope data collected on carboniferous hosted zn pb deposits can and has been interpreted to indicate that lead and other metals were derived from the underlying basement rocks in order to test this hypothesis whole rock lead isotope measurements were made on greywackes from the longford down inlier which represent the along strike continuation of the northern part of the caledonian basement underlying the base metal deposits the lead isotope data define a linear array on a 207 pb 204 pb versus 206 pb 204 pb plot with end points at 207 pb 204 pb 15 542 206 pb 204 pb 18 456 and 207 pb 204 pb 15 461 206 pb 204 pb 17 973 no evidence of lead isotope overprinting by the mineralizing event could be found in the samples studied when the lead isotope data are corrected for addition of radiogenic lead since the time of base metal mineralization c 350 ma ago there is a 1 1 correlation between the lead isotopic composition of galenas in the base metal deposits and the longford down grewyackes these results support the hypothesis that lead and other metals were derived from the greywackes underlying the base metal mineralization on a 208 pb 204 pb versus 206 pb 204 pb plot neither whole rock greywacke nor galena lead isotope data define a linear array the 208 pb 204 pb 206 pb 204 pb trend is best explained by tectonic or sedimentological mixing of three isotopically distinct lead isotope end members these end members are 1 old unradiogenic basement in nw ireland lewisian complex precursor 2 ordovician arc material from nw ireland and 3 ordovician arc material form se ireland isotopic modelling of these end members shows that the present day mixing line seen in the ordovician and silurian sediments can be calculated back to values inferred for the ordovician arc end members using the same values of as were used to back calculate the lead isotopic composition of the greywackes to the time of mineralization this information is further confirmation of the sediment mixing model presented a tectonic model developed from these and established geological data suggest a late ordovician closure of the iapetus ocean and that the silurian greywackes are a by product of eroded ordovician arc material from nw and se of the iapetus suture

equilibrium structure and dynamics of the california current system this paper addresses the structure and dynamical mechanisms of regional and mesoscale physical variability in the subtropical northeast pacific ocean using the regional oceanic modeling system roms the model is configured with a u s west coast domain that spans the california current system ccs with a mesoscale horizontal resolution up to as fine as 3 5 km its mean seasonal forcing is by momentum heat and water fluxes at the surface and adaptive nudging to gyre scale fields at the open water boundaries its equilibrium solutions show realistic mean and seasonal states and vigorous mesoscale eddies fronts and filaments the level of eddy kinetic energy eke in the model is comparable to drifter and altimeter estimates in the solutions with sufficiently fine resolution because the model lacks nonseasonal transient forcing the authors conclude that the dominant mesoscale variability in the ccs is intrinsic rather than transiently forced the primary eddy generation mechanism is the baroclinic instability of upwelling alongshore currents there is progressive movement of meanseasonal currents and eddy energy offshore and downward into the oceanic interior in an annually recurrent cycle the associated offshore eddy heat fluxes provide the principal balance against nearshore cooling by mean ekman transport and upwelling the currents are highly nonuniform along the coast with important influences by capes and ridges in both maintaining mean standing eddies and launching transient filaments and fronts

modelling the generation of haida eddies abstract a numerical model forced with average annual cycles of climatological winds surface heat flux and temperature and salinity along the open boundaries is used to demonstrate that haida eddies are typically generated each winter off cape st james at the southern tip of the queen charlotte islands of western canada annual cycles of sea surface elevation measured at coastal tide gauges and topex poseidon crossover locations are reproduced with reasonable accuracy model sensitivity studies show that haida eddies are baroclinic in nature and are generated by the merging of several smaller eddies that have been formed to the west of cape st james the generation mechanism does not require the existence of instability processes and is associated with the mean advection of warmer and fresher water masses around the cape from hecate strait and from the southeast these advected water masses generate plumes of buoyant flow which intensify and sustain small patches of anticyclonic circulation immediately to the northwest of the cape when the flow is stronger several of these smaller eddies can merge to generate a larger eddy the haida eddy similar to observations a typical generation shedding cycle for larger haida eddies in the model is 3 4 months consistent with previous in situ water property measurements these experiments show that the eddies are generally comprised of mixed layer water from hecate strait queen charlotte sound and the continental shelves off northern vancouver island their vertical extent during the mature stage is roughly 1000 m

the interannual variability of the surface eddy kinetic energy in the labrador sea abstract the variability of the surface eddy kinetic energy eke in the labrador sea is investigated with a suite of numerical integrations using a regional ocean model simulations are performed over the period 1980 2001 and are compared to satellite observations over the last 9 years the surface eke pattern in the basin is dominated by a region along the west coast of greenland where eddies mainly anticyclonic are formed by instability of the main currents flowing over the continental slope consistent with previous idealized results here the interannual changes are linked to the shear of the incoming boundary current system imposed as boundary condition to the model domain the highly variable strength of the east greenland current at the northeast boundary derived from the simple ocean data assimilation soda reanalysis strongly influences the vortex formation in the center of the labrador sea where deep convection occurs a statistically significant portion of the modeled interannual surface eke variability is correlated with the local atmospheric forcing and both heat and wind fluxes play an important role and can be adopted as predictors at a lag of 2 3 months the arctic oscillation index can also be used as a remote indicator of the atmospheric fluxes but with lower skill than local measurements in contrast the north atlantic oscillation index does not correlate significantly with the surface eke at intraseasonal and interannual scales the analysis of altimeter data over the 1993 2001 supports the existence of this asymmetry between the regime locally forced by the atmosphere in the central basin and the regime remotely forced by the incoming boundary current along the west greenland coast those results have important implications for monitoring and predicting the surface eddy kinetic energy variability in the labrador sea

metal mobility in sediment covered ridge crest hydrothermal systems experimental and theoretical constraints abstract the presence of sedimentary organic matter blanketing midocean ridge crests has a potentially strong impact on metal transport in hydrothermal vent fluids to constrain the role of organic matter in metal mobility during hydrothermal sediment alteration we reacted organic rich diatomaceous ooze from guaymas basin gulf of california and organic poor hemipelagic mud from middle valley northern juan de fuca ridge with seawater and a na ca k cl fluid of seawater chlorinity at 275 to 400 c 350 to 500 bars and initial fluid sediment mass ratios ranging from 1 6 to 9 8 reaction of these fluids with both sediment types released co2 and high concentrations of ore forming metals fe mn zn pb to solution relatively low concentrations of cu were observed in solution and likely reflect the reducing conditions that resulted from the presence of sedimentary organic matter both the concentrations of co2 and dissolved metals were lower in fluids reacted with middle valley sediment compared with aqueous concentrations in fluids reacted with guaymas basin sediment during alteration of both sediment types metal concentrations varied strongly as a function of temperature increasing by up to an order of magnitude over the 75 c range of each experiment major element fluid chemistry and observed alteration assemblages suggest that during hydrothermal alteration of organic lean sediment from middle valley a feldspar quartz illite mineral assemblage buffered in situ ph in contrast data from the experimental alteration of organic rich guaymas basin sediment suggest that a calcite plagioclase quartz assemblage regulated in situ ph fluid speciation calculations suggest that in situ ph during guaymas basin sediment alteration was lower than during alteration of middle valley sediment and accounts for the substantially greater metal mobility at a given temperature and pressure during the former experiment comparison of our results with the results of basalt alteration experiments indicate that except for cu hydrothermal sediment alteration results in equal or greater concentrations of ore forming metals at a given temperature and pressure accordingly the presence of ore forming metals in fluids currently venting from sediment covered hydrothermal systems at concentrations substantially lower than in fluids from bare rock systems may reflect chemical reequilibration during subsurface cooling within the sediment pile

low frequency pycnocline variability in the northeast pacific abstract the output from an ocean general circulation model ogcm driven by observed surface forcing is used in conjunction with simpler dynamical models to examine the physical mechanisms responsible for interannual to interdecadal pycnocline variability in the northeast pacific ocean during 1958 97 a period that includes the 1976 77 climate shift after 1977 the pycnocline deepened in a broad band along the coast and shoaled in the central part of the gulf of alaska the changes in pycnocline depth diagnosed from the model are in agreement with the pycnocline depth changes observed at two ocean stations in different areas of the gulf of alaska a simple ekman pumping model with linear damping explains a large fraction of pycnocline variability in the ogcm the fit of the simple model to the ogcm is maximized in the central part of the gulf of alaska where the pycnocline variability produced by the simple model can account for 70 90 of the pycnocline depth variance in the ogcm evidence of westward

interdecadal variations in the alaska gyre abstract climatic dynamic topography variations in the alaska gyre during the period 1968 1990 are described with an objective analysis of more than 12000 std and xbt stations and coads wind stress data interannual dynamic height and sst variations were correlated and were consistent with recently described large scale climatic shifts in the north pacific the gyre was cantered more to the east circulation appeared stronger and sst was lower during the early to mid 1970s than during the 1980s the aleutian low np and pna indices intensified during the interim but the response did not appear as a gyre spinup instead the associated wind stress anomalies forced a slowly varying dynamic height anomaly across the eastern and northern part of the gyre through ekman convergence which had the effect of displacing the gyre s low somewhat to the wsw in the 1980s the wind curl spectrum was white and the slow oceanic response was modelled as stochastic forced climate variability with a simple first order m

lead and strontium isotopes in metalliferous and calcareous pelitic sediments of the red sea axial trough lead and strontium isotope compositions have been determined in sediments from depressions in the axial graben zone of the red sea outside the atlantis ii deep hydrothermal metal rich precipitates are intercalated between normal calcareous pelitic sediments or alternate in thin strata with the latter in these deeps the pb isotope composition of both the normal and hydrothermal sediments of the red sea lies within narrow limits with less variation than in recent basalts from the depressions while the normal calcareous pelitic sediments are isotopically similar to corresponding sediments with continental characteristics in other oceans the hydrothermally influenced deposits bear an obvious mantle signature with respect to pb isotopes the sr isotope composition of the red sea graben sediments is mainly controlled by seawater sr derived from miocene evaporites may be incorporated to different degrees in sediments of brine filled deeps the silicate fractions of the sediments have sr isotope characteristics of continental debris mixed with volcanic glass

mesoscale eddies dominate surface phytoplankton in northern gulf of alaska abstract the hnlc waters of the gulf of alaska normally receive too little iron for primary productivity to draw down silicate and nitrate in surface waters even in spring and summer our observations of chlorophyll sensed by seawifs north of 54 n in pelagic waters 500 m depth of the gulf found that on average more than half of all surface chlorophyll was inside the 4 cm contours of anticyclonic mesoscale eddies the ratio approaches 80 in spring months yet these contours enclosed only 10 of the total surface area of pelagic waters in the gulf therefore eddies dominate the chlorophyll and phytoplankton distribution in surface pelagic waters we outline several eddy processes that enhance primary productivity eddies near the continental margin entrain nutrient and fe rich and chlorophyll rich coastal waters into their outer rings advecting these waters into the basin interior to directly increase phytoplankton populations there in addition eddies carry excess nutrients and iron in their core waters into pelagic regions as they propagate away from the continental margin as these anticyclonic eddies decay their depressed isopycnals relax upward injecting nutrients up toward the surface layer we propose that this transport brings iron and macro nutrients toward the surface mixed layer where they are available for wind forced mixing to bring them to surface these mesoscale eddies decay slowly but steadily perhaps providing a relatively regular upward supply of macro nutrients and iron toward euphotic layers they might behave as isolated oases of enhanced marine productivity in an otherwise iron poor basin we note that much of this productivity might be near or just below the base of the surface mixed layer and therefore poorly sampled by colour sensing satellites it is possible then that eddies enrich phytoplankton populations to a greater extent than noted from satellite surface observations only

the anticyclonic baroclinic eddy off sitka alaska in the northeast pacific ocean abstract among the many mesoscale eddies found in the northeast pacific ocean is a well developed anticyclonic baroclinic eddy situated within a few hundred kilometers of sitka alaska 57 n 138 w it has definitely been observed during spring and summer 1958 summer 1960 and summer 1961 observations made at other times show some evidence of its occurrence also the trajectories of three norpax drifting buoys for april may 1977 also indicated the probable presence of an eddy there the eddy whose diameter ranges from 200 to 300 km and whose depth extends to 100 m and probably to as much as 2000 m recurs at the same location the center of the eddy is characterized by the following features the surface water is less saline and only somewhat warmer than at its periphery at depths within and below the halocline it is warmer less saline and contains more dissolved oxygen than at the periphery and a warm core is situated within the halocline the halocline is usually depressed by less than 100 m but

on the redistribution of pb in the oceanic crust during hydrothermal alteration abstract major and trace element as well as pb isotope data are presented for greenschist to amphibolite facies greenstones from two locations 1 metabasalt breccias from the galapagos rift at 100 w and 2 metabasalt breccias and unbrecciated greenstones from the chile ridge at 38 s greenstone breccias from both locations display stockwork like sulfide mineralizations related to the upflow portion of a hydrothermal convection system whereas galapagos rift stockwork sulfides belong to the normal type containing cu fe sulfides chile ridge stockwork sulfides are galena rich pb zn cu sulfides and represent a previously unknown type of sulfide mineralisation in a morb environment geochemically the greenstones can be divided into two types 1 1 the unbrecciated galena free greenstones from both chile ridge and galapagos rift show at least a 10 20 fold pb enrichment compared to fresh morb with respect to similar pb enrichment measured in greenstones from two other locations i e dsdp hole 504b and galapagos rift near 86 w we suggest that this may be a general feature of all stockwork mineralised oceanic greenstones 2 2 the galena and quartz rich metabasalt breccias from the chile ridge are up to 3000 fold enriched in pb up to 1000 g g pb in the whole rock analyses compared to morb and indicate pb mineralisation two orders of magnitude higher than that of the normal greenstone type a mass balance calculation carried out using crustal column thickness of 3000 m with a 200 m thick greenstone layer and 0 15 m of galena bearing breccias shows that at the chile ridge 42 of the entire pb is concentrated in the greenstones this suggests that the rest of the crustal column is depleted in 58 of its primary pb content this degree of depletion matches well with previous calculations that a 56 depletion of pb in oceanic crust subjected to mantle recycling via subduction would be necessary to yield a himu mantle source within 2 ga despite the need for future investigations into the extent and volume of the pb enrichment in chile ridge greenstones we believe that this process of major pb redistribution is capable of creating huge volumes of oceanic crust that on average are extremely pb depleted and which when recycled would produce the himu source

improved extended reconstruction of sst 1854 1997 abstract an improved sst reconstruction for the 1854 1997 period is developed compared to the version 1 analysis in the western tropical pacific the tropical atlantic and indian oceans more variance is resolved in the new analysis this improved analysis also uses sea ice concentrations to improve the high latitude sst analysis and a modified historical bias correction for the 1939 41 period in addition the new analysis includes an improved error estimate analysis uncertainty is largest in the nineteenth century and during the two world wars due to sparse sampling the near global average sst in the new analysis is consistent with the version 1 reconstruction the 95 confidence uncertainty for the near global average is 0 4 c or more in the nineteenth century near 0 2 c for the first half of the twentieth century and 0 1 c or less after 1950

altimeter derived surface circulation in the large scale ne pacific gyres part 2 1997 1998 el nino anomalies abstract changes in the sea surface heights ssh and geostrophic transports in the ne pacific are examined during the 1997 1998 el nino using altimeter data sea level pressure slp fields proxy winds and satellite sea surface temperature sst most of the signal occurs along the boundaries of the basin from panama to the alaska peninsula changes in the ssh and alongshore transports along the boundaries are caused both by propagation of signals from the south stronger between the equator and the gulf of california and by local and basin scale winds stronger between the pacific northwest and the alaska peninsula two periods of high ssh occur at the equator may july 1997 and october 1997 january 1998 the first coastal ssh signal moved quickly polewards to approximately 24 n in early june then stalled and moved farther north during transient events in july september large scale wind forcing combined with the equatorial signals during the second period of high equatorial ssh fall 1997 to move the high ssh and poleward transports quickly around the alaska gyre a connection between the boundary currents and the interior north pacific developed as part of the large scale response to the basin scale winds after changes in the boundaries decreases in anomalies of ssh and poleward transports began in january 1998 south of 40 n and in february 1998 farther north

the instability of rossby basin modes and the oceanic eddy field abstract low frequency large scale baroclinic rossby basin modes resistant to scale dependent dissipation have been recently theoretically analyzed and discussed as possible efficient coupling agents with the atmosphere for interactions on decadal time scales such modes are also consistent with evidence of the westward phase propagation in satellite altimetry data in both the theory and the observations the scale of the waves is large in comparison with the rossby radius of deformation and the orientation of fluid motion in the waves is predominantly meridional these two facts suggest that the waves are vulnerable to baroclinic instability on the scale of the deformation radius the key dynamical parameter is the ratio z of the transit time of the long rossby wave to the e folding time of the instability when this parameter is small the wave easily crosses the basin largely undisturbed by the instability if z is large the wave succumbs to the instability and is largely destroyed before making a c

seawater metasomatism in hydrothermal sediments escanaba trough northeast pacific abstract hydrothermal sediments from the nesca vent field escanaba trough are enriched in a number of typical vent fluid metals for which fluid data for the same sediment hosted site exhibit anomalous depletion these results are consistent with cooling of rising fluids and precipitation of various metal sulphide sulphate and oxide phases in situ within the sediment column prior to expulsion of the fluids from the seabed significant enrichments of mg and u elements which are quantitatively removed from high temperature vent fluids are also observed in the escanaba trough sediments however enrichments of these elements cannot derive from simple conductive cooling of the rising vent fluids but instead are believed to result from extensive seawater metasomatism as relatively fresh unreached seawater is heated from below by hot sediments and or percolating vent fluids in the upper levels of the circulation system calculated seawater sediment interaction ratios range from 5 1 to 2500 l of seawater per gram of sediment pb sr and nd isotope distributions for the escanaba sediments are consistent with combined sediment fluid and seawater sediment interactions pb isotope ratios for hydrothermal and background sediments coincide with local sulphide deposits but are much more radiogenic than local morb this indicates not only that complete isotopic re equilibration must occur between the hot rising fluids and the host sediments but in addition that sediment composition appears to dominate the pb isotopic composition of these fluids sr and nd isotope ratios in the hydrothermally altered sediments which are distinct from background ratios coincide closely with modern seawater values providing confirmatory evidence that extensive interactions must also have occurred between these hydrothermal sediments and relatively fresh unreacted seawater

the middle valley sulfide deposits northern juan de fuca ridge radiogenic isotope systematics the bent hill and the ore drilling program massive sulfide deposits in middle valley the sediment filled rift valley at the northern juan de fuca ridge are among the largest and richest sulfide deposits on the modern sea floor drilling during ocean drilling program leg 169 allowed a complete hydrothermal system to be sampled for the first time representative samples from this leg were analyzed for radiogenic isotopes sr nd and pb with the objectives of determining the sources of metals in the deposits and the nature of fluid circulation and evolution of the hydrothermal systems samples were chosen both from the sulfide deposits and host units the latter including sediments basaltic flows and sills sr nd and pb isotope compositions of the basalts and sills below the bent hill massive sulfide deposit confirm that both were highly altered by hydrothermal solutions the data also show that the sills are cogenetic petrologically with the underlying basaltic basement pb isotope compositions of the massive sulfides in both sulfide deposits vary within narrow ranges i e 206 pb 204 pb ranges of 18 83 18 89 and 18 77 18 89 for bent hill and ore drilling program respectively which could reflect remobilization replacement and recrystallization of sulfides during formation of the sulfide mounds but also mixing and homogenization during hydrothermal circulation of fluids below the sea floor data for the massive sulfides form elongate clusters between the basalts and the sediment clusters in pb isotope diagrams the most simple explanation for these patterns involves the mixing of pb from a basaltic source 206 pb 204 pb range of 18 64 18 74 with pb from isotopically heterogeneous sediments comprising a hemipelagic component with relatively higher 207 pb 204 pb and 208 pb 204 pb values and a clastic component turbidite with relatively higher 206 pb 204 pb values a third potential source is represented by hydrothermal sulfides present in both the sediments and basalts that have relatively unradiogenic pb isotope ratios 206 pb 204 pb range of 17 83 18 36 implying an old crustal source possibly older than 1 5 ga the overlapping pb isotope compositions of the massive sulfides in the two deposits suggest that the same sources were involved and in similar proportions to form the deposits ore drilling program massive sulfide is extremely enriched in zn compared to bent hill massive sulfide if the metal sources are the same for the two deposits other parameters must have produced the differences between them such as different fluid chemistry temperature or factors at the depositional site pb isotope data for sulfides of the bent hill massive sulfide feeder zone and the stratiform deep copper zone 206 pb 204 pb range of 18 59 18 82 are both much less radiogenic than the massive sulfides and overlap with the field for the underlying basalts the pb isotope ratios a high cu zn ratio and intense alteration of the basalts strongly suggest that the basalts were the main source for the metals in the deep copper zone and related feeder zones rather than a higher sediment influence in the overlying massive sulfides this conclusion is also supported by positive correlations between the pb isotope value and zn cu ratio contents of pb and mo a silicified zone immediately above the deep copper zone may have played a major role in the formation of the deposits by serving as an efficient seal preventing the deep seated fluids to escape to the sea floor as observed even today when the seal formed the fluids were forced to circulate in the lower part of the sedimentary sequence and in the basalts the seal would have insulated this hydrothermal system leading to higher temperatures in the fluids and subsequently to more efficient leaching of metals this model offers an explanation for differences in the pb isotope compositions of the massive sulfides and the underlying deep copper zone and feeder zones

satellite and hydrographic observations of eddy induced shelf slope exchange in the northwestern gulf of alaska 1 satellite and hydrographic observations of oceanographic conditions in the northwestern gulf of alaska indicate that anticyclonic eddies propagating adjacent to the continental shelf alter the structure of the shelf break front and in doing so influence the shelf slope exchange of biota and water mass properties eddies typically form in the northern gulf of alaska during fall and winter and propagate southwestward within an 200 km wide corridor along and above the continental slope eddy activity within this corridor diminishes in the downstream direction the trajectories of faster propagating 4 km day eddies tend to lie closer to the shelf break than do the trajectories of slower propagating 1 5 km day eddies the interaction between azimuthal eddy currents and the shelf break frontal jet 1 establishes an upwelling zone associated with the leading flank of the eddy that strengthens cross slope gradients 2 weakens cross slope gradients and promotes shelf slope exchange where the eddy is adjacent to the shelf and 3 reestablishes a weak upwelling zone associated with the trailing flank of the eddy

mineralogy geochemistry and sr pb and in situ s isotopic compositions of hydrothermal precipitates from the tangyin hydrothermal field southern okinawa trough evaluation of the contribution of magmatic fluids and sediments to hydrothermal systems abstract the okinawa trough ot is a back arc basin where rifting is in its initial stages and where hydrothermal fields htfs have developed above terrigenous sediments and volcaniclastics layers of variable thickness the source of ore forming materials within the hydrothermal systems of the ot is complex and may include seawater magmatic rock magmatic fluid and sediments the contribution of magmatic fluids and sediments to the hydrothermal systems of the ot is still uncertain at least 10 modern seafloor htfs have been reported from the ot including the jade hakurei iheya north knoll clam tangyin yonaguni knoll iv hatoma and irabu here we report results of mineralogical geochemical and whole rock sr pb and in situ s isotopic analyses of hydrothermal precipitates from the tangyin htf in the southern ot this field was discovered during the hobab3 cruise in 2014 and contains four types of hydrothermal precipitates fe zn and zn pb rich massive sulfides silica rich precipitates and native sulfur rich samples sulfates in zn pb fe zn and silica rich samples have 87sr 86sr ratios of 0 71068 0 71750 which are higher than those of modern seawater and magmatic rocks and indicate that the sr is derived mainly from seawater and sediments the zn pb fe zn and silica rich samples have 206pb 204pb 18 5129 18 5307 207pb 204pb 15 6374 15 6489 and 208pb 204pb 38 8759 38 9113 ratios that are intermediate between sediments and magmatic rocks suggesting the pb is a mixture of sediment and magmatic rock derived pb the in situ s isotopic data indicate that the ore forming fluids associated with all sample types had low 34s values with the fe zn mean 34s 1 27 1 38 sd n 12 and zn pb rich mean 34s 0 93 0 32 n 36 massive sulfides and silica rich precipitates mean 34s 2 85 1 14 n 58 having lower 34s values than those of native sulfur rich samples mean 34s 4 23 0 72 n 5 the zn pb and fe zn rich massive sulfides and silica rich precipitates represent the medium high temperature 120 c early middle stages of mineralization formed under reducing conditions at low sulfur fugacity fs2 based on the occurrence of low fs2 mineral assemblages e g high fe sphalerite isocubanite pyrrhotite the low 34s values of these three types of samples and of the hakurei and clam htfs with low fs2 mineral assemblages and low concentrations of cu bi and au most likely reflect the incorporation of biological sulfur previously formed by msr within the sediments the native sulfur rich samples of the tangyin htf formed at low temperatures

gold enrichment and the bi au association in pyrrhotite rich massive sulfide deposits escanaba trough southern gorda ridge high gold contents to 10 1 ppm avg 1 4 ppm n 34 occur in pyrrhotite rich massive sulfide samples from the sediment covered floor of the escanaba trough the slow spreading southernmost segment of gorda ridge these concentrations reflect the presence of primary gold formed during high temperature hydrothermal activity in mounds and chimneys and secondary gold deposited during sea floor weathering of massive sulfide primary gold occurs as fine grained 2 m secondary gold grains have a porous flaky morphology and occur in samples in which pyrrhotite is oxidized and replaced by fe oxyhydroxides fe sulfate and sulfur mounds and chimneys dominated by pyrrhotite and containing lesser amounts of isocubanite chalcopyrite and fe rich sphalerite were formed by high temperature estimated range 325 275 c reduced low sulfur vent fluids the mineral and fluid compositions during this main stage of hydrothermal venting reflect subsurface interaction between circulating hydrothermal fluids and turbiditic sediment containing as much as 1 1 percent organic carbon as the deposition of pyrrhotite cu fe sulfides and sphalerite waned a volumetrically minor suite of sulfarsenide arsenide bi and au minerals was deposited from highly reduced late main stage fluids diffusing through mounds and chimneys the low solubility of au as a bisulfide complex and the absence of fluid mixing during this stage of hydrothermal activity apparently inhibited the precipitation of gold directly from solution instead gold precipitation is thought to be linked to elevated concentrations of bi in the late main stage fluids the textural relationships of au and bi minerals in pyrrhotite rich samples low melting point of native bismuth 271 4 c and recent experimental results on au and bi in hydrothermal fluids contribute to the hypothesis that gold was effectively scavenged from the escanaba trough vent fluids by coexisting droplets of liquid bismuth additional phase relationships of alloys in the au bi system indicate that deposition of native bismuth and maldonite occurred at temperatures as low as 241 c bismuth droplets trapped in void space between main stage mineral grains scavenged gold from ambient hydrothermal fluid to a greater extent than bismuth enclosed by late forming pyrrhotite the limited solid solution of au in bi can explain the apparent exsolution texture in which gold blebs are hosted by native bismuth the electrum native bismuth with gold inclusions and galena represent the last traces of gold mineralization from late main stage fluids during sea floor weathering and the oxidation of pyrrhotite in the mounds and chimneys secondary gold formed as aggregates of colloidal particles along ph gradients between acidic pore waters and ambient seawater gold was mobilized from earlier formed primary gold minerals and transported as aqueous chloride complexes the reduction of au iii by residual fe2 in partly altered pyrrhotite and adsorption of colloids by fe oxyhydroxides may have influenced the location of secondary gold grains within the alteration front solubility differences between gold and silver chloride complexes at low temperature account for the low ag content of secondary gold grains the high concentrations of bi and thus the association of au and bi minerals in pyrrhotite rich massive sulfide can be ascribed to the extensive interaction of hydrothermal fluids with sediment in the escanaba trough in contrast the absence of the au bi association in massive sulfides at other ridges including other sediment covered sites at middle valley and the guaymas basin reflects the predominantly basaltic source rocks

on the existence of storm tracks abstract given that middle latitude weather systems transport heat in a manner such as to weaken the baroclinicity that is thought to be crucial to their growth it is perhaps surprising that concentrated regions of such eddy activity i e storm tracks are found in the northern hemisphere winter the existence and possible self maintenance of storm tracks is investigated using a linear stationary wave model with storm track region forcings taken from data averaged over a number of winters it is found that the direct thermal effect of the eddies does indeed act against the existence of the storm track their vorticity fluxes lead to some reduction of this effect it is argued that the mean diabatic heating in the storm track region is an indirect eddy effect this heating is found to maintain the mean maximum in baroclinicity in the region further the mean low level flow induced by the eddy effects is such as to enhance the warm western oceanic boundary currents that are crucial to the existence of t

generation of low frequency spiciness variability in the thermocline abstract the generation of variance by anomalous advection of a passive tracer in the thermocline is investigated using the example of density compensated temperature and salinity anomalies or spiciness a coupled markov model is developed in which wind stress curl forces the large scale baroclinic ocean pressure that in turn controls the anomalous geostrophic advection of spiciness the double integration of white noise atmospheric forcing by this markov model results in a frequency spectrum of large scale spiciness proportional to 4 so that spiciness variability is concentrated at low frequencies an eddy permitting regional model hindcast of the northeast pacific 1950 2007 confirms that time series of large scale spiciness variability are exceptionally smooth with frequency spectra 4 for frequencies greater than 0 2 cpy at shorter spatial scales wavelengths less than 500 km the spiciness frequency spectrum is whitened by mesoscale eddies but this eddy forced variability can be fi

submarine hydrothermal venting related to volcanism in the lesser antilles evidence from ferromanganese precipitates 1 radiogenic isotope compositions sr nd pb hf and os of sediment hosted seafloor ferromanganese crusts and sediments incrusted with ferromanganese oxyhydroxides from the lesser antilles island arc were measured to distinguish between hydrogenous seawater derived and hydrothermal metal sources the ages of the precipitates range between recent last few thousand years and a few 100 kyr as deduced from 10be and co concentrations evidence from the presence of bladed todorokite and nontronite together with the major element and ree composition suggests that a significant proportion of these sediment hosted precipitates formed at relatively low temperatures from a mixture of seawater and hydrothermal fluids associated with island arc volcanism the radiogenic isotope compositions of all metals mentioned above except pb show large differences in hydrothermal versus hydrogenous contributions over space and time in contrast to precipitates of high temperature fluids which mainly scavenge their ree contents from seawater the crusts of this study show 143nd 144nd of up to 0 512817 nd 3 5 this is close to the signature of the nearby island arc rocks and far above the expected local seawater ratio of 0 51209 nd 10 7 these crusts also show high 176hf 177hf up to 0 283102 low 87sr 86sr up to 0 7069 and low 187os 188os up to 0 16 compared with local seawater as expected from hydrothermal island arc derived metal contributions in contrast the pb isotope signatures of the crusts cannot be explained by mixing between seawater and hydrothermal sources it is suggested that pb was either removed from the ascending fluids within the sediment column before they reached seawater or the temperatures were too low to leach significant amounts of pb from the rocks or sediments external sources such as saharan dust particulate inputs from the orinoco river or even incongruent release of pb isotopes from the island arc rock derived particles must have contributed to the observed pb isotope variability our results suggest that submarine hydrothermalism originating from intraoceanic island arc volcanism creates distinct geochemical environments for the dispersion of hydrothermal fluids and may be an important mechanism to supply metals of hydrothermal origin to seawater

an eddy resolving model of circulation on the western gulf of alaska shelf 2 comparison of results to oceanographic observations currents generated by an eddy resolving semispectral primitive equation model are compared with those measured by moored current meters 1989 and 1991 and satellite tracked drifting buoys 1987 from shelikof strait alaska the model reproduced many of the dominant circulation features including the cross sectional spatial structure of the alaskan coastal current the estuarine inflow at the bottom of the sea valley and the mean transport the first mode empirical orthogonal functions of the model and of the observed data represent similar spatial structures and were significantly correlated in time while the model produced eddies 20 km diameter at a similar rate as observed the timing did not generally match the observations as a result correlations between the measured currents and model generated currents usually were not significant correlations between modeled and measured transport through the sea valley however were significant for both years

a basin scale oceanic instability event in the gulf of alaska a composite noaa 14 satellite advanced very high resolution radiometer image of the gulf of alaska for early march 1995 reveals a sequence of six anticyclonic oceanic eddies spanning more than 1500 km of the continental margin of north america from central british columbia to central alaska although isolated mesoscale eddies have previously been documented for this eastern boundary region the composite image provides the first evidence that trains of such eddies can develop simultaneously along the entire coast the 80 km radius and 250 km spacing of these warm core eddies are consistent with a baroclinic instability event in the poleward coastal current that prevails along the northwest continental margin of north america in winter roughly october through march wind data from offshore meteorological buoys combined with partial cloud free thermal images for january and february suggest that the event was triggered in mid january by an abrupt coast wide reversal in the prevailing poleward wind the instability event disrupted the alongshore transport of relatively warm high salinity water and presumably resulted in a greatly enhanced cross shore flux of brackish nutrient rich coastal water into the open ocean on the basis of its basin scale extent and more than 2 month duration it is feasible that the event had a major impact on the early spring recruitment and survival of zooplankton and pelagic fish within the highly productive fishery zones of coastal british columbia and alaska less extensive eddy sequences found in several earlier satellite images for the region suggest that these instability events are fairly common if so this indicates that the poleward current that forms over the eastern pacific continental slope in late fall herein the northeast pacific coastal current is marginally stable and likely to deform into a series of mesoscale eddies following abrupt basin scale reversals in the seasonally dominant wind provided these wind events occur early enough in the season the coastal current could reform with the onset of poleward winter winds

geochemistry of basalt from escanaba trough evidence for sediment contamination mid ocean ridge basalts morbs erupted in escanaba trough introduction the southernmost segment of the gorda ridge have greater isotopic crustal contamination of basaltic magmas is generally and geochemical variability than those from the remainder of the recognized for continental volcanoes e g taylor 1980 ridge samples from the sediment free northern sites in the trough leeman hawkesworth 1986 glazner et al 1991 the are depleted normal morb similar to those from the northern composition thickness and low melting temperatures of gorda ridge however samples from the sediment covered portion continental crustal rocks facilitate assimilation that can of the trough are significantly enriched in incompatible elements be easily identified however the extent to which basaltic and sr nd and pb isotopic ratios are shifted toward the composition magmas are contaminated by oceanic crust is a topic of of local sediments pb isotopic ratios in particular lie on a mixing intense debate e g bohrson reid 1995 clague et al line with local sediments assimilation fractional crystallization 1995 eiler et al 1996 bohrson et al 1996 and references afc calculations suggest that 25 40 fractional crystallization therein thirlwall et al 1997 the debate has focused coupled with assimilation of 1 2 of local sediments can produce on distinguishing the chemical characteristics magmas the enrichment observed for some escanaba basalts variations in acquire during ascent crustal storage and emplacement the amount of enrichment of elements with similar incompatibility from those that have been used to identify heterogeneous for comparably differentiated basalts and uncorrelated isotopic mantle sources for most ocean island volcanoes the ratios suggest variable amounts of assimilation of compositionally crustal components available to serve as contaminants heterogeneous assimilants by parental magmas assimilation of are poorly characterized but include the underlying sediment by morb magmas probably resulted when laccolithic altered oceanic crust pelagic to hemipelagic sediment intrusions ponded at the sediment basement interface beneath the and the hydrothermally altered volcanic edifice thick sediment cover in the southern part of escanaba trough mid ocean ridge basalts morbs are relatively unigeochemical and isotopic evidence for contamination can be detected form geochemically with depleted incompatible element in these lavas because of the strong compositional contrast between and radiogenic isotope compositions compared with lavas the parental magma and assimilant the depleted morb magma from ocean island or continental volcanoes however and highly enriched sediment assimilant are end member comexcess chlorine content and cl k ratios in fresh morb positions that provide a sensitive indicator for the smallest amount glasses support the idea that morb magmas may also of contamination of oceanic magma by crustal processes be affected by assimilation of hydrothermally altered oceanic crust e g michael schilling 1988 michael cornell 1996 chlorine like other incompatible elements shows the greatest enrichment in strongly frac