model and field observations of effects of circulation on the timing and magnitude of nitrate utilization and production on the northern gulf of alaska shelf abstract the globec program was tasked with understanding the mechanistic links between climate forcing and the ocean ecosystem response on the northern gulf of alaska goa shelf to address this task samples were collected five to six times times annually along the seward line between 1998 and 2004 however interpreting seward line field observations in space and time is complicated by the complex circulation on the goa shelf the alaska current alaskan stream and alaska coastal current produce eddies and meanders which mix the iron limited small cell oceanic community with the iron rich large cell coastal community thus observations at any point in space and time are the result of the degree of mixing of the oceanic and coastal water masses the roms circulation model with an embedded ecosystem model was used to extend globec observations in space and time on the goa shelf the timing of the spring bloom in simulations was related to shallowing of the pycnocline the spring bloom began in late march april on the inner shelf and in may on the mid and outer shelf the simulations suggest that the magnitude of shelf production is a balance between the amount of iron from freshwater runoff and nitrate with iron limitation on the outer shelf and adjacent ocean and nitrate limitation on the inner shelf simulated shelf break eddies form near yakutat have elevated iron concentrations relative to surrounding waters and propagate westward influencing production and nitrate concentrations on the outer shelf and in the adjacent ocean during spring and summer simulated primary production in the seward line region was about 100 130 g cm 2 y 1 but production of up to 300 g cm 2 y 1 is predicted for regions in lower cook inlet and around kodiak

the troodos cyprus and kizildag s turkey ophiolites as structural models for slow spreading ridge segments the troodos cyprus and kizildag southern turkey ophiolites in the eastern mediterranean region represent remnants of the neotethyan ocean which evolved as a result of seafloor spreading north of afro arabia in mesozoic time both ophiolites display numerous planar to listric normal faults and structural grabens in their sheeted dike complexes suggestive of tectonic extension and complex intrusive relations in their plutonic units indicate recurring and intermittent magmatic activities detachment surfaces within the lower crustal sequence troodos or at the boundary between the crustal and mantle sequences kizildag define a brittle plastic transition zone along which tectonic thinning and extension within the crustal units above was accommodated by mylonitization and denudation in lower crustal units or mantle rocks below the variation in depth to these accommodation zones is inferred to be a function of the vertical temperature gradient in the oceanic lithosphere which may in turn point to the

size fractionated iron distribution on the northern gulf of alaska 1 concentrations of soluble 0 4 m and colloidal 0 025 0 4 m fe size fractions were removed from surface waters within the inner and mid shelf as a result the contribution of soluble fe to the total fe concentration increased from the inner shelf to the shelf break slope waters surface water dissolved fe concentrations on the northern goa continental slope were higher than those previously observed in the central goa gyre variations in surface water fe concentrations from spring through summer appear to result from the changes in freshwater discharge and physical processes on the shelf

birth death and resurrection the life cycle of suprasubduction zone ophiolites 1 suprasubduction zone ssz ophiolites display a consistent sequence of events during their formation and evolution that suggests that they form in response to processes that are common to all such ophiolites this sequence includes the following 1 birth which entails the formation of the ophiolite above a nascent or reconfigured subduction zone this stage is typically characterized by the eruption of arc tholeiite lavas and the formation of layered gabbros and sheeted dike complex 2 youth during which is continued melting of refractory asthenosphere depleted during birth occurs in response to fluid flux from the subducting slab with extensional deformation of the older plutonic suite eruption of refractory lavas and the intrusion of wehrlite pyroxenite 3 maturity with the onset of semistable arc volcanism typically calc alkaline as the subduction zone matures and stabilizes and the intrusion of quartz diorite and eruption of silicic lavas and 4 death which is the sudden demise of active spreading and ophiolite related volcanism which in many cases is linked to collision with an active spreading center and the onset of shallow underthrusting of the buoyant spreading axis expressed as dikes and lavas with oceanic basalt compositions that crosscut or overlie rocks of the older suites 5 resurrection with emplacement by obduction onto a passive margin or accretionary uplift with continued subduction the early stages 1 3 may be diachronous and each stage may overlap in both time and space the existence of this consistent progression implies that ophiolite formation is not a stochastic event but is a natural consequence of the ssz tectonic setting

glacial influence on the geochemistry of riverine iron fluxes to the gulf of alaska and effects of deglaciation riverine iron fe derived from glacial weathering is a critical micronutrient source to ecosystems of the gulf of alaska goa here we demonstrate that the source and chemical nature of riverine fe input to the goa could change dramatically due to the widespread watershed deglaciation that is underway we examine fe size partitioning speciation and isotopic composition in tributaries of the copper river which exemplify a long term goa watershed evolution from one strongly influenced by glacial weathering to a boreal forested watershed iron fluxes from glacierized tributaries bear high suspended sediment and colloidal fe loads of mixed valence silicate species with low concentrations of dissolved fe and dissolved organic carbon doc iron isotopic composition is indicative of mechanical weathering as the fe source conversely fe fluxes from boreal forested systems have higher dissolved fe concentrations corresponding to higher doc concentrations iron colloids and suspended sediment consist of fe hydr oxides and organic complexes these watersheds have an iron isotopic composition indicative of an internal chemical processing source we predict that as the goa watershed evolves due to deglaciation so will the source flux and chemical nature of riverine fe loads which could have significant ramifications for alaskan marine and freshwater ecosystems

the abundance of seafloor massive sulfide deposits the possibility of mining seafl oor massive sulfide deposits has stirred debate about the sustainable use of this new resource and whether commercial development is worth the risk among the outstanding questions is how many deposits might be accessible to deep sea mining more than 300 sites of high temperature hydrothermal venting have been identifi ed since the discovery of black smokers but signifi cant massive sulfide accumulation has been found at only 165 of these sites estimates of the total number of vent fields and associated mineral deposits based on plume studies and deposit occurrence models range from 500 to 5000 we have used new deposit occurrence data from 10 000 km of ridge arc and backarc spreading centers to estimate the amount of massive sulfide in the easily accessible neovolcanic zones of the global oceans the total accumulation in these areas is estimated to be on the order of 6 108 tonnes containing 3 107 tonnes of copper and zinc this is similar to the total discovered copper and zinc in cenozoic massive sulfi de deposits mined on land but is insuffi cient to satisfy a growing global demand for these metals

trace metal distributions within a sitka eddy in the northern gulf of alaska in the northern gulf of alaska mesoscale anticyclonic eddies have been implicated as a mechanism of the cross shelf exchange of iron fe replete coastal waters with fe deplete subarctic alaskan gyre waters based on existing hydrography and macronutrient distributions a sitka eddy sampled during august 2007 is divided into a surface eddy core a shallow subsurface eddy core and a deeper subsurface eddy core the distributions of aluminum al manganese mn and fe in the eddy are examined and compared to distributions at shelf stations similar to where the eddy formed as well as basin stations representative of the fe limited subarctic alaskan gyre relative to basin stations dissolved and particulate al and dissolved mn were elevated in eddy core waters reactive fe concentrations within the shallow subsurface eddy core were nearly seven times greater than reactive fe concentrations at similar densities at the basin stations this shallow subsurface eddy core is likely mixed into the euphotic zone during storm induced mixing as well as mixing during isopycnal relaxation as an eddy dies out the flux of reactive fe to surface waters from the shallow subsurface core of eddies in the gulf of alaska is a significant source compared to both remote and local atmospheric dust deposition it is hypothesized that fe supply from eddies in the eastern gulf of alaska shifts the core of the high nutrient lower than expected chlorophyll water farther west in conjunction with an eddy desert in that same region

volcanic episodicity and a non steady state rift valley along northeast pacific spreading centers evidence from sea marc i sea marc i side looking sonar images and sea beam bathymetry along a 400 km stretch of the juan de fuca ridge crest provide evidence that excessive extrusive volcanism periodically builds a crestal ridge along the axis of seafloor spreading an elongate summit depression esd or rift valley is commonly observed in the spine of this crestal ridge the crestal ridge volcanic landform has a distinctive shape that is recognized in bathymetric contours both along the spreading axis and at least up to 30 km away from the axis the landform has a plan form shape that resembles a side view of an archer s bow with the long dimension of the bow form parallel to the strike of the ridge in cross section the bow form is flat on top and has steep flanks these bow form shapes can be explained by magma that rises into the crust at a discrete center and flows laterally into belts of ridge parallel dikes similar to icelandic fissure eruptions both the variable dimensions of the esd along axis of the juan de fuca ridge and the relationship among volcanic flow morphologies within and beyond the esd suggest the four different segments of the juan de fuca ridge presented in detail here display different stages in a cycle of oceanic crust accretion this cycle includes episodes in which there is 1 extrusive volcanic construction which widen the crestal ridge prior to the collapse of the summit depression 2 collapse within the summit region of the crestal ridge to form an esd during a phase of volcanic inactivity and 3 renewed magmatism in the esd as its floor widens by extension and brittle fracture of the upper crust this episodic model implies that the width of the young seafloor affected by volcanic extrusion or dominated by tectonic stretching varies through time

crustal magnetization reveals subsurface structure of juan de fuca ridge hydrothermal vent fields a near bottom geophysical survey on the endeavour segment of the northern juan de fuca ridge shows that regions of well defined low crustal magnetization are strongly correlated with both active and extinct submarine hydrothermal vent sites in particular at the main endeavour field we find discrete magnetization lows associated with each cluster of vents magnetization lows are directly centered beneath the vent clusters and have diameters of 100 m which implies a near vertical narrow pipe like source region located directly beneath the surface expression of the vent edifices lows are also separated from each other by only 200 m which further implies highly focused zones magnetization lows are also associated with inactive and extinct vent areas which indicates that alteration of the magnetic minerals in the crust rather than necessarily temporary thermal demagnetization is the primary process responsible for the low magnetization these narrow pipe like bodies are highly characteristic of alteration pipes found in ophiolites and are indicative of hydrothermal fluid up flow zones thus each magnetization low may define an individual upwelling zone with distinct subsurface plumbing and thermal structure the crustal magnetization patterns provide important constraints on the geometry of the subsurface plumbing beneath these hydrothermal vent systems at the main endeavour field magnetization lows are distributed along the trend of the rift valley in a semiregular pattern with a spacing of 200 m arguing that upward flow may be partitioned into regularly spaced intervals along the axis of the rift valley

the volcanic stratigraphy and petrogenesis of the oman ophiolite complex the volcanic stratigraphy and trace element geochemistry of the oman ophiolite complex indicate a multistage magmatic origin comprising 1 magmatism due to sea floor spreading in a marginal basin 2 magmatism associated with discrete submarine volcanic centres or seamounts 3 magmatism associated with crustal uplift and rifting and 4 magmatism associated with continent arc collision trace element petrogenetic modelling is used to investigate the nature of the mantle source region and the partial melting and fractional crystallization history for each magmatic event the petrogenetic pathway for the sea floor spreading lavas requires a high degree of melting of a mantle that was depleted in incompatible elements prior to subduction but subsequently selectively enriched in certain elements mostly lil elements and h2o from an underlying subduction zone it also requires magma mixing in an open system magma chamber prior to eruption the seamount lavas were probably derived by a similar degree of partial melting of a similar source but fractional crystallization was restricted to smaller high level magma chambers the rifting lavas were derived from a mantle source that was more depleted than the seamount lavas prior to subduction but which was later modified by a larger subduction zone component the syn collision lavas were however derived from an enriched mantle source which probably underlay the passive continental margin rather than the marginal basin complex results such as these may provide considerable insight into the petrogenetic changes accompanying the transitions from spreading to arc volcanism in a supra subduction zone setting

glacial flour dust storms in the gulf of alaska hydrologic and meteorological controls and their importance as a source of bioavailable iron 1 iron is an essential micronutrient that limits primary productivity in much of the ocean including the gulf of alaska goa however the processes that transport iron to the ocean surface are poorly quantified we combine satellite and meteorological data to provide the first description of widespread dust transport from coastal alaska into the goa dust is frequently transported from glacially derived sediment at the mouths of several rivers the most prominent of which is the copper river these dust events occur most frequently in autumn when coastal river levels are low and riverbed sediments are exposed the dust plumes are transported several hundred kilometers beyond the continental shelf into iron limited waters we estimate the mass of dust transported from the copper river valley during one 2006 dust event to be between 25 80 ktons based on conservative estimates this equates to a soluble iron loading of 30 200 tons we suggest the soluble fe flux from dust originating in glaciofluvial sediment deposits from the entire goa coastline is two to three times larger and is comparable to the annual fe flux to goa surface waters from eddies of coastal origin given that glaciers are retreating in the coastal goa region and in other locations it is important to examine whether fluxes of dust are increasing from glacierized landscapes to the ocean and to assess the impact of associated fe on marine ecosystems

the influence of net community production and phytoplankton community structure on co2 uptake in the gulf of alaska 1 biological productivity is a key factor controlling the ocean s ability to take up carbon dioxide from the atmosphere however the ecological dynamics that drive regions of intense productivity and carbon export are poorly understood in this study we present high spatial resolution estimates of air sea co2 flux net community production ncp rates calculated from o2 ar ratios and phytoplankton population abundances determined by continuous underway measurements on a cruise across the gulf of alaska in may 2010 the highest rates of ncp 79 2 13 mmol c m 2 d 1 and oceanic co2 uptake air sea flux of 14 7 2 4 mmol c m 2 d 1 were observed across a transition zone between the high nitrate low chlorophyll hnlc waters of the alaskan gyre and the coastal waters off the aleutian islands while the transition zone comprises 20 of the total area covered in crossing the gulf of alaska it contributed 49 of the total ncp and 48 of the total co2 uptake observed along the cruise track a corresponding transition zone phytoplankton bloom was dominated by two small celled 20 m phytoplankton communities which were distinct from the phytoplankton communities in the surrounding alaskan gyre and coastal waters we hypothesize that mixing between iron rich coastal waters and iron limited alaskan gyre waters stimulated this bloom and fueled the high ncp and co2 export observed in the region

distribution and lability of dissolved iron in surface waters of marginal seas in southeastern asia abstract more than eighty surface water samples from marginal seas in southeastern asia including the south china sea east china sea western philippine sea and the taiwan strait were collected in order to assess the sources and transport of iron in this region dissolved fe chelex labile and total dissolved concentrations were determined additionally samples were collected from near shore waters along the west coast of taiwan during two different seasons and analyzed for potential lability of fe although total dissolved fe concentrations were in general replete in coastal waters and decreasing seaward the proportions of the dissolved labile chelex extractable and non labile fe fractions showed substantial spatial variability results from dissolved fe distributions indicate that fe in estuarine and coastal regimes forms highly stable non labile complexes which are removed quickly resulting in moderate to low dissolved concentrations offshore most of the fe replete river plumes contain a large proportion of dissolved non labile fe species that also show a low potential bio reactivity and seasonally variable concentrations making biological production in the coastal and adjacent marginal seas temporally dependent on the potential chemical reactivity of the different fe fractions in the source waters regional flow patterns in the study area led to localized supplies of fe enriched waters in the northern taiwan strait and southern east china sea waters

active and relict sea floor hydrothermal mineralization at the tag hydrothermal field mid atlantic ridge the tag hydrothermal field is a site of major active and inactive volcanic hosted hydrothermal mineralization in the rift valley of the slow spreading mid atlantic ridge at 26 degree n the axial high is the principal locus of present magmatic intrusions the tag field contains three main areas of present and past hydrothermal activity 1 an actively venting high temperature sulfide mound 2 two former high temperature vent areas 3 a zone of low temperature venting and precipitation of fe and mn oxide deposits the volcanic centers occur at the intersections between ridge axis parallel normal faults and projected axis transverse transfer faults the intersections of these active fault systems may act as conduits both for magmatic intrusions from sources beneath the axial high that build the volcanic centers and for hydrothermal upwelling that taps the heat sources radiometric dating of sulfide samples and manganese crusts in the hydrothermal zones and dating of sediments intercalated with pillow lava flows in the volcanic center adjacent to the active sulfide mound indicate multiple episodes of hydrothermal activity throughout the field driven by heat supplied by episodic intrusions over a period of at least 140 times 10 sup 3 yr the sulfide deposits are built by juxtaposition and superposition during relatively long residence times near episodic axial heat sources counterbalanced by mass wasting in the tectonically active rift valley of the slow spreading oceanic ridge hydrothermal reworking of a relict hydrothermal zone by high temperature hydrothermal episodes has recrystallized sulfides and concentrated the first visible primary gold reported in a deposit at an oceanic ridge

volcanic growth faults and the origin of pacific abyssal hills the topographic features known as abyssal hills characterize 30 of the ocean floor and yet their origin has been the subject of vigorous debate for over 40 years submersible based investigations show that pacific abyssal hills are created on the flanks of the east pacific rise as horsts and grabens which lengthen with time hills are bounded on one side by ridge facing scarps produced by normal faulting and on the other by more gentle slopes produced by volcanic growth faulting

ophiolitic melange and flyschoidal sediments of the tithonian lower cretaceous in albania ophiolitic melange and flyschoidal sediments of the tithonian lower cretaceous age are widespread in the eastern albanides they lie transgressively or normally on top of the ophiolitic sequence through radiolarian cherts of the kimmeridgian tithonian age or on top of the carbonate sequence of the periphery of the ophiolites through middle liassic dogger malm pelagic limestones with manganese nodules and radiolarian cherts they are overlain by conglomerates or neritic limestones of the lower cretaceous age ophiolitic melange consists of ophiolitic conglobreccias often of homogenous composition serpentinite melange with a sedimentary serpentinite matrix or basaltic sedimentary tuffagglomerate less commonly they have a heterogeneous composition with small amounts of fine grained matrix and marls with calpionellids in other examples the ophiolitic melange contains heterogeneous exotic blocks including all the members of the ophiolite suite serpentinite ophicalcite gabbro plagiogranite diabase basalts dacites amphibolite sulphide and chromite ores as well as blocks of radiolarites limestones etc in the argillic matrix they are overlain by conglomerate sandstone marly flyschoidal deposits with abundant ophiolitic detritus and calpionellids these deposits are linked with tithonian lower cretaceous tectogenesis which led to the fragmentary uplift of ophiolites and partly of their sedimentary periphery and to the formation of the faulted topography the presence of the ophiolitic melange and flyschoidal sediments both over the ophiolites and the associated sedimentary rocks of their periphery indicate that the latter were not the basement of an ophiolite nappe during the late jurassic time

resource assessment of undiscovered seafloor massive sulfide deposits on an arctic mid ocean ridge application of grade and tonnage models abstract norway has started ongoing initiatives related to deep sea mining these include the evaluation of mineral resources within its sovereign territorial waters on the deep ocean floor of the arctic region i e the mohns ridge 71 73 n among the variety of possible seabed resources seafloor massive sulfides sms attract particular interest owing to the significant development potential and the general lack of knowledge of the sms deposits the present study aims at assessing mineral resources i e cu zn au and ag from a number of undiscovered sulfide deposits with the help of a revised model for mafic hosted volcanogenic massive sulfide vms deposits that adequately corresponds to geological settings of slow spreading ridges application of the model requires a priori knowledge of the seafloor terrain to depict favorable geologic environments for the occurrence of sms deposits in such context estimates are conducted for the easily accessible volcanically active parts of the ridge where 11 undiscovered deposits are expected in these areas total metal endowments are calculated to be on average 447 000 tonnes using a monte carlo simulation that combines the probabilistic estimates of number of undiscovered deposits with the grade and tonnage models estimates of in place metal resources are generated in cumulative distribution form to present expected amount of undiscovered metals at 90 confidence intervals

coastal fresh water discharge in the northeast pacific very high annual rates of precipitation in the coastal mountains that border the northeast pacific ocean produce large fresh water discharges 23000 m3 s 1 this discharge has been ignored previously since it does not enter the ocean in the form of large rivers but instead the water enters by way of numerous small rivers and streams thus it acts as a line source instead of a point source this coastal discharge contributes at least 40 of the fresh water that enters the northeast pacific from the atmosphere the discharge is comparable to the mean annual discharge of the mississippi river system the fresh water creates a cross shelf density gradient that drives an alongshore baroclinic jet the width of this jet is less than 25 km with speeds in excess of 100 cm s 1 it extends along the coast from southeast alaska to at least kodiak island apparently the flow is maintained as a narrow current adjacent to the coast by wind stress that causes downwelling conditions here throughout most of the year

discovery of ancient and active hydrothermal systems along the ultra slow spreading southwest indian ridge 10 16 e 1 we report the discovery of active and fossil hydrothermal systems during r v knorr cruise 162 legs vii and ix along a 400 km long segment of the ultra slow southwest indian ridge swir between 10 and 16 e where the effective spreading rate for mantle upwelling is the slowest of any ocean ridge explored to date 8 4 mm yr 1 full rate eight of forty one optical temperature profiles contain hydrothermal plume characteristics that indicate firm evidence for two active vent sites and tentative evidence for as many as three others fossil hydrothermal material was recovered in 6 of the 38 dredge hauls and includes an occurrence of partially oxidized sulfide breccias four deposits ofsepiolite and silica as well as mn oxide and nontronite cemented breccias the massive sulfide deposit likely developed during mixing of upwelling hot fluids with cold seawater within a shallow permeable fault breccia along a deep seated normal fault bounding the southern rift valley wall silica and sepiolite deposits were found mostly on the rift valley walls and likely formed during low to moderate temperature ultramafic hosted hydrothermal activity the abundance of hydrothermal material and the frequency of localized hydrothermal activity is remarkable because the mantle upwelling and magma supply rates and hence the magmatic heat input along this section of the swir are lower than on any other explored segment of the global mid ocean ridge system this observation suggests that high mantle upwelling and magma supply rates are not required to drive mid ocean ridge hydrothermal systems and that a close relationship between magmatic heat input and hydrothermal activity may not be established at the ultra slow end of the ridge spreading spectrum the frequency and distribution of hydrothermal activity in the study area may reflect a largely tectonic control on fluid circulation with hydrothermal vent sites being preferentially associated with long lived faults that provide fluid pathways our results suggest the contribution of magma starved ridge segments to the global ocean lithosphere geochemical budget is potentially much larger than previously thought

some characteristics of yakutat eddies propagating along the continental slope of the northern gulf of alaska abstract data from array for real time geostrophic oceanography argo profiling floats oil tanker thermosalinographs shipboard adcp and towed ctd surveys and satellite altimetry are used to examine properties of two 200 km diameter anticyclonic yakutat eddies that propagated westward at 1 5 km day 1 along the continental slope of the northern gulf of alaska goa in 2001 and 2003 the eddies had lifetimes of up to 5 years remained close to the shelfbreak and had relatively constant size and strength until they encountered the alaskan stream where they appeared to spawn smaller shorter lived anticyclones the azimuthal velocity field was vigorous 25 40 cm s 1 and in gradient wind balance with rossby numbers of 0 05 conservation of salt and azimuthal mass transports between 20 m and the depth of the 32 2 isohaline from shipboard surveys in may and august 2003 suggest little mass exchange occurred between the surface layers of the eddy and ambient waters chlorophyll concentrations were greater in the eddy than in ambient waters in both may and august in may the chlorophyll was patchily distributed while in august dense chlorophyll concentrations occurred in and beneath the seasonal thermocline within 50 km of the eddy center the high august chlorophyll concentrations might have been fostered by a broad and shallow it appears likely that as yakutat eddies approach the shelfbreak non linear processes will modify the slope flow field and the stability and structure of the shelfbreak front leading to cross slope flows and flow reversals this interaction may induce 30 km wide streamers of shelf water to flow around the trailing edge of the anticyclone the role of streamers in the freshwater and nutrient budgets of the goa shelf and basin is unknown but their contribution to these budgets will depend on the trajectory of a yakutat eddy especially its proximity to the shelfbreak as the eddy propagates along the goa continental slope

the importance of freshwater to spatial variability of aragonite saturation state in the gulf of alaska high latitude and subpolar regions like the gulf of alaska goa are more vulnerable than equatorial regions to rising carbon dioxide co2 levels in part due to local processes that amplify the global signal recent field observations have shown that the shelf of the goa is currently experiencing seasonal corrosive events carbonate mineral saturation states 1 including suppressed in response to ocean acidification as well as local processes like increased low alkalinity glacial melt water discharge while the glacial discharge mainly influences the inner shelf on the outer shelf upwelling brings corrosive waters from the deep goa in this work we develop a high resolution model for carbon dynamics in the goa identify regions of high variability of and test the sensitivity of those regions to changes in the chemistry of glacial melt water discharge results indicate the importance of this climatically sensitive and relatively unconstrained regional freshwater forcing for variability in the nearshore the increase was nearly linear at 0 002 per 100 mol kg increase in alkalinity in the freshwater runoff we find that the local winds biological processes and freshwater forcing all contribute to the spatial distribution of and identify which of these three is highly correlated to the variability in given that the timing and magnitude of these processes will likely change during the next few decades it is critical to elucidate the effect of local processes on the background ocean acidification signal using robust models such as the one described here

geomorphic tectonic control of sediment discharge to the ocean the importance of small mountainous rivers analysis of data from 280 rivers discharging to the ocean indicates that sediment loads yields are a log linear function of basin area and maximum elevation of the river basin other factors controlling sediment discharge e g climate runoff appear to have secondary importance a notable exception is the influence of human activity climate and geology on the rivers draining southern asia and oceania sediment fluxes from small mountainous rivers many of which discharge directly onto active margins e g western south and north america and most high standing oceanic islands have been greatly underestimated in previous global sediment budgets perhaps by as much as a factor of three in contrast sediment fluxes to the ocean from large rivers nearly all of which discharge onto passive margins or marginal seas have been overestimated as some of the sediment load is subaerially sequestered in subsiding deltas before the proliferation of dam construction in the latter half of this century rivers

the internal structure of an active sea floor massive sulphide deposit the hydrothermal circulation of sea water through permeable ocean crust results in rock water interactions that lead to the formation of massive sulphide deposits these are the modern analogues of many ancient ophiolite hosted deposits1 4 such as those exposed in cyprus here we report results obtained from drilling a series of holes into an actively forming sulphide deposit on the mid atlantic ridge a complex assemblage of sulphide anhydrite silica breccias provides striking evidence that such hydrothermal mounds do not grow simply by the accumulation of sulphides on the sea floor indeed the deposit grows largely as an in situ breccia pile as successive episodes of hydrothermal activity each form new hydrothermal precipitates and cement earlier deposits during inactive periods the collapse of sulphide chimneys dissolution of anhydrite and disruption by faulting cause brecciation of the deposit the abundance of anhydrite beneath the present region of focused hydrothermal venting reflects the high temperatures 150 c currently maintained within the mound and implies substantial entrainment of cold sea water into the interior of the deposit these observations demonstrate the important role of anhydrite in the growth of massive sulphide deposits despite its absence in those preserved on land

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

moist morb axial magmatism in the oman ophiolite the evidence against a mid ocean ridge origin the oman ophiolite has an axial volcanic suite and associated sheeted dike complex similar in composition to modern mid oceanic ridge basalt morb its internal structure is regarded by many as being directly comparable to ocean lithosphere from the east pacific rise however there has long been controversy over the geodynamic setting in which the ophiolite formed and the extent to which the analogy can be drawn because the morb like axial volcanics are overlain by lavas that include depleted arc tholeiites and boninites to some this implies that the entire ophiolite formed above a subduction zone others maintain that it formed at a true open ocean mor and that the water required to generate the arc like magmas derived from descending near axis hydrothermal fluids or from ancient subduction a popular compromise posits that the axial suite formed at a true mor and the later magmatism documents the initiation of obduction we test these models by reexamining the morb like character of the early axial lavas and dikes we show that fractionation trends require the presence of water at concentrations significantly higher than any open ocean morb instead trends are identical to those of backarc basin and intraoceanic forearc volcanics by showing that the entire ophiolite formed in a hydrous system we rule out all models in which the oman ophiolite was generated at an open ocean mor instead it formed at a submarine spreading center above a probably newly initiated subduction zone

intertidal foraminifera in the macro tidal estuaries of the gulf of cambay implications for interpreting sea level change in palaeo estuaries abstract the gulf of cambay is a macro tidal estuarine embayment lying in an active monsoon zone characterized by a high annual sediment load the present study examines the distribution of foraminifera in the narmada and tapti estuaries of the gulf in order to use these as analogues for the study of palaeo macro tidal estuarine environments and as a means of recording the extent of sea level change in estuarine settings foraminifera are widely distributed in sand flats mud flats and marshes at the mouths of the estuaries the overall foraminiferal assemblage is low diversity comprising epifaunal and infaunal taxa dominated by ammonia murrayinella haynesina quinqueloculina nonion cibicides cibicidoides elphidium trochammina and miliammina the triserial planktonic foraminifer gallitellia vivans an indicator of stressed and up welling areas is also recorded in the intertidal sediments of the estuaries these foraminifera are carried into estuaries up to 50 km up the river mouths by the strong tidal currents in the bay three biofacies are recognized trochammina miliammina biofacies high marsh murrayinella haynesina biofacies low marsh and mud flats and ammonia elphidium quinqueloculina biofacies shallow marine

emplacement of the jurassic mirdita ophiolites southern albania evidence from associated clastic and carbonate sediments sedimentology can shed light on the emplacement of oceanic lithosphere i e ophiolites onto continental crust and post emplacement settings an example chosen here is the well exposed jurassic mirdita ophiolite in southern albania successions studied in five different ophiolitic massifs voskopoja luniku shpati rehove and morava document variable depositional processes and palaeoenvironments in the light of evidence from comparable settings elsewhere e g n albania n greece ophiolitic extrusive rocks pillow basalts and lava breccias locally retain an intact cover of oceanic radiolarian chert in the shpati massif elsewhere ophiolite derived clastics typically overlie basaltic extrusives or ultramafic rocks directly the oldest dated sediments are calpionellid and ammonite bearing pelagic carbonates of latest jurassic berrasian age similar calpionellid limestones elsewhere n albania n greece post date the regional ophiolite emplacement at one locality in s albania voskopoja calpionellid limestones are gradationally underlain by thick ophiolite derived breccias containing both ultramafic and mafic clasts that were derived by mass wasting of subaqueous fault scarps during or soon after the latest stages of ophiolite emplacement an intercalation of serpentinite rich debris flows at this locality is indicative of mobilisation of hydrated oceanic ultramafic rocks some of the ophiolite derived conglomerates e g shpati massif include well rounded serpentinite and basalt clasts suggestive of a high energy shallow water origin the berriasian pelagic limestones at voskopoja experienced reworking and slumping probably related to shallowing and a switch to neritic deposition mixed ophiolite derived clastic and neritic carbonate sediments accumulated later during the early cretaceous mainly barremian aptian in variable deltaic lagoonal and shallow marine settings these sediments were influenced by local tectonics or eustatic sea level change terrigenous sediment gradually encroached from neighbouring landmasses as the ophiolite was faulted or eroded an aptian transgression was followed by regression creating a local unconformity e g at boboshtica a turonian marine transgression initiated widespread upper cretaceous shelf carbonate deposition in the regional context the southern albania ophiolites appear to have been rapidly emplaced onto a continental margin in a subaqueous setting during the late jurassic late oxfordian late tithonian this was followed by gradual emergence probably in response to thinning of the ophiolite by erosion and or exhumation the sedimentary cover of the south albanian ophiolites is consistent with rapid relatively short distance emplacement of a regional scale ophiolite over a local pelagonian korabi microcontinent

the alaska coastal current continuity of transport and forcing current moorings were deployed on the continental shelf at 13 locations in the northwest gulf of alaska they measured the alaska coastal current at three positions along the coast during april october 1991 the strongest currents were in the confined region of shelikof strait mean daily transport was as large as 2 5 106 m3 s 1 mean transport over the 6 month period ranged from 0 85 106 m3 s 1 at the easternmost line off gore point to 0 64 106 m3 s1 at the westernmost section shelikof strait indicating significant transport to the south of kodiak island the transports were well correlated r 0 8 and in phase with each other and were also correlated with wind r 0 6 data suggest that in shelikof strait and off gore point baroclinic flow is 75 and 40 respectively of total transport

metamorphosed pb zn ag ores of the keketale vms deposit nw china evidence from ore textures fluid inclusions geochronology and pyrite compositions abstract the keketale pb zn deposit is located in the devonian volcanic sedimentary maizi basin of the altay orogenic belt the mineralization at keketale is hosted in marbles and deformed volcanic tuffs and biotite garnet chlorite schists folded into a series of overturned synclines formed in multiple deformation events keketale contains economic amounts of pb 0 89 mt 1 51 wt zn 1 94 mt 3 16 wt and ag 650 t 40 g t detailed petrographic studies have defined two main generations of sulfide development the banded pyrite of the early stage a is commonly stratiform with minor galena sphalerite and chalcopyrite stage b is characterized by a large amount of polymetallic sulfides including pyrrhotite chalcopyrite sphalerite and galena with minor pyrite hosted in quartz veins three types of fluid inclusions fis including mixed carbonic aqueous c type pure carbonic pc type and aqueous w type have been recognized in quartz of stage b the c type fis have homogenization temperatures of 150 326 c and salinities of 0 2 16 6 wt nacl equivalent the pc type fis are dominated by co2 with minor ch4 and n2 and have initial ice melting temperatures of 57 5 to 56 7 c co2 homogenization temperatures of 11 14 1 c the w type primary fis were completely homogenized at temperatures of 124 359 c with salinities of 5 0 14 6 wt nacl equivalent such co2 rich fluid inclusions are consistent with those discovered in orogenic type deposits in the altay area and elsewhere muscovite separates from the polymetallic quartz veinlets of stage b yield a well defined 40ar 39ar isotopic plateau age of 259 33 2 56 ma with an isochron age of 259 62 2 65 ma this age is coeval with the closure of the paleo asia ocean and reactivation of the ertix fault system la icp ms analyses of two generations of pyrite indicate that the banded pyrite of stage a is relatively depleted in metallic elements and contains low contents of cu 0 39 ppm ag 0 20 ppm au below the detection limits pb 17 43 ppm and zn 14 38 ppm whereas the pyrite in quartz polymetallic sulfide veinlets of the stage b is relatively rich in metallic elements e g cu 2 56 ppm ag 3 07 ppm au 0 01 ppm pb 1047 ppm and zn 1136 ppm the trace amounts of cu pb zn au and ag are interpreted to have been initially locked in the lattice of type a pyrite and then liberated and precipitated as micromineral inclusions with type b pyrite during subsequent metamorphism and deformation two key factors are considered vital to the formation of economic ores of the keketale pb zn deposit namely the original devonian banded pyrite formed in a vms system and subsequent permian deformation and metamorphic processes that liberated cu pb zn au and ag from the lattice of type a pyrite to form galena sphalerite and chalcopyrite with minor muscovite in quartz veinlets the model provides a new interpretation of vms pb zn deposit occurring in back arc basin environments followed by collision and new insights into the unique regional fe cu pb zn au mineralization in the altay orogenic belt

metamorphic textures and geochemistry of the cyprus type massive sulfide lenses at zurabad khoy iran abstract the upper cretaceous volcanogenic exhalative fe cu massive sulfide lenses at zurabad iran occur within spilitized basalts of the khoy ophiolite both the host rocks and the sulfide lenses are metamorphosed to greenschist facies and have been subjected to weak deformation causing textural changes in the ore the presence of preserved banded pyrite pyrrhotite chalcopyrite and sphalerite in a matrix rich in chlorite indicates that the ore was a primary facies of synvolcanic hydrothermal massive sulfide mineralization similar to those formed in modern seafloor environments and in cyprus type ophiolite deposits coarse grained pyrite porphyroblasts or crystalloblasts recrystallized pyrrhotite and chalcopyrite together with regional silicate sulfide foliation were produced by sub seafloor metamorphism followed by regional metamorphism and ophiolite obduction brittle deformation and shearing produced cataclastic textures in pyrite which were filled by chalcopyrite and pyrrhotite post obduction and or post metamorphic events produced late veinlets of pyrite chalcopyrite and gangue minerals supergene processes related to gossan formation converted pyrite pyrrhotite and chalcopyrite to marcasite and birdseye pyrite primary sphalerite contains an average of 14 mole fes which shows equilibration at temperatures below 240 c and a pressure less than 1 kilobar based on its equilibrated textures with other sulfides and silicates in the foliation pyrrhotite was a primary mineral in the zurabad volcanogenic massive sulfide lenses therefore pyrrhotite can be primary and with pyrite forms a buffer that constrains sulphur fugacity during regional metamorphism on the evidence of textures mineralogy and geochemistry pyrite is stable in the greenschist facies provided that the activity of sulphur remains high of prime importance in exploration of the massive sulfide lenses in the zurabad area has been the recognition of banded gossans and coarse pyrite porphyroblasts which may prove to be a successful exploration tool in the search for further massive sulfide mineralization in the district

deformation partitioning in a slow spreading ridge undergoing oblique extension mohns ridge norwegian sea although oceanic spreading is often perpendicular to the ridge trends in some cases the angle between these two directions can be significantly less than 90 40 50 this occurs because of either a bend of the ridge trend or a change of the spreading direction we here describe oblique spreading in the mohns ridge resulting in deformation partitioning between the valley walls which are dominantly affected by strike slip displacements and the axial valley which is subject to nearly pure extension the axial valley walls are characterized by en echelon normal faults affecting the walls while the axial valley is affected by parallel faults grouped into oblique sets these fault sets define different structures horst or tilted blocks that are regularly spaced inside the axial valley moreover some ridge segments mainly undergo pure extension whereas others are affected by oblique extension we explain this faulting pattern including the along strike and transverse variations as a consequence of depth variations of the brittle ductile transition

distribution of alteration zones in the upper oceanic crust aging of the upper oceanic crust produces alteration zones that have distinct mineralogical and geochemical characteristics five zones are recognized in the troodos ophiolite and in situ oceanic crust 1 a sea floor weathering zone swz 2 a low temperature zone ltz 3 a transition zone tz 4 an upper dike zone udz and 5 a mineralized zone mz the mz may be overlain by the swz ltz or tz but in the known examples it is always underlain by the udz the development of the swz is dependent upon the duration of cold seawater circulation which is dependent upon seafloor topography and the rate and nature of sedimentation the boundary between the low and high temperature zones is largely controlled by permeability contrasts lateral variation in the depth of this boundary indicates that the thermal gradient is not uniform within the crust this along with the evidence for disequilibrium assemblages implies that regional metamorphic zones are not appropriate to describe the distribution of alteration effects

the deglacial transition on the southeastern alaska margin meltwater input sea level rise marine productivity and sedimentary anoxia 1 oxygen isotope data from planktonic and benthic foraminifera on a high resolution age model 44 14c dates spanning 17 400 years document deglacial environmental change on the southeast alaska margin 59 33 32 n 144 9 21 w 682 m water depth surface freshening i e 18o reduction of 0 8 began at 16 650 170 cal years b p during an interval of ice proximal sedimentation likely due to freshwater input from melting glaciers a sharp transition to laminated hemipelagic sediments constrains retreat of regional outlet glaciers onto land circa 14 790 380 cal years b p abrupt warming and or freshening of the surface ocean i e additional 18o reduction of 0 9 coincides with the bolling interstade of northern europe and greenland cooling and or higher salinities returned during the allerod interval coincident with the antarctic cold reversal and continue until 11 740 200 cal years b p when onset of warming coincides with the end of the younger dryas an abrupt 1 reduction in benthic 18o at 14 250 290 cal years b p likely reflects a decrease in bottom water salinity driven by deep mixing of glacial meltwater a regional megaflood event or brine formation associated with sea ice two laminated opal rich intervals record discrete episodes of high productivity during the last deglaciation these events precisely dated here at 14 790 380 to 12 990 190 cal years b p and 11 160 130 to 10 750 220 cal years b p likely correlate to similar features observed elsewhere on the margins of the north pacific and are coeval with episodes of rapid sea level rise remobilization of iron from newly inundated continental shelves may have helped to fuel these episodes of elevated primary productivity and sedimentary anoxia

structural and geophysical expression of the solea graben troodos ophiolite cyprus field studies show that extensional structures in the north central part of the troodos ophiolite including steep normal faults grabens dikes and low angle detachment faults are related to e w present coordinates spreading the solea graben directly north of the mafic ultramafic rock outcrops around mount olympus consists of a 10 to 15 km wide western portion that is underlain by a low angle detachment fault between the sheeted dike complex and the plutonic section structural and paleomagnetic evidence indicates that the sheeted dikes above this detachment have been rotated 40 or more about subhorizontal axes the eastern portion of the graben contains sheeted dike blocks with varying axes of rotation and significantly different style of intrusive activity most structural features in the graben formed simultaneously with or shortly after cessation of spreading at the graben axis based on cross cutting ophiolitic dikes and hydrothermal mineralization timing of the uplift of the central part of the troodos ophiolite is uncertain but is probably related to the tectonic thinning of the upper crust by low angle normal faulting the solea graben spreading center provides a model for the structure of modern mid ocean ridges that are spreading amagmatically

dissolved iron distribution in the western and central subarctic pacific hnlc water formation and biogeochemical processes it is well known that phytoplankton growth is broadly limited by iron fe availability in the subarctic pacific to investigate which fe sources control the amplitude of seasonal variation in biogeochemical parameters in the subarctic pacific we examined the spatial variation in the west to east distribution of dissolved fe dfe across the western and central subarctic pacific through the japanese geotraces program the vertical section profile of the western subarctic pacific gyre showed high dissolved fe concentrations from the bottom of the surface mixed layer to as deep as approximately 3000 m suggesting that fe rich intermediate water is transported laterally and distributed across the western subarctic gyre over 2000 km the section data also indicate that the influence of the western fe rich intermediate water does not reach the alaskan gyre fe index dfe observed po4 observed rfe p distribution clearly indicates that the western fe rich intermediate water is well explained by external sedimentary fe sources and water transport systems from a subpolar marginal sea the sea of okhotsk and the continental margin the spatial pattern of fe to nutrient stoichiometry supplied from the intermediate water to the surface in comparison with reported fe and nutrient demand in surface phytoplankton quantitatively explains the differences in surface macronutrient consumption between the western and eastern gyre as well as the formation of the high nutrient and low chlorophyll region in the whole subarctic pacific

estuarine removal of glacial iron and implications for iron fluxes to the ocean while recent work demonstrates that glacial meltwater provides a substantial and relatively labile flux of the micronutrient iron to oceans the role of high latitude estuary environments as a potential sink of glacial iron is unknown here we present the first quantitative description of iron removal in a meltwater dominated estuary we find that 85 of dissolved fe is removed in the low salinity region of the estuary along with 41 of total dissolvable iron associated with glacial flour we couple these findings with hydrologic and geochemical data from gulf of alaska goa glacierized catchments to calculate meltwater derived fluxes of size and species partitioned fe to the goa iron flux data indicate that labile iron in the glacial flour and associated fe minerals dominate the meltwater contribution to the fe budget of the goa as such goa nutrient cycles and related ecosystems could be strongly influenced by continued ice loss in its watershed

early establishment of seafloor hydrothermal systems during structural extension paleomagnetic evidence from the troodos ophiolite cyprus abstract paleomagnetic data from the troodos ophiolite are used to help constrain models for the relationship between extensional normal faulting and hydrothermal alteration related to production of large tonnage sulfide deposits at oceanic ridges we have sampled dikes from the troodos sheeted complex that have been subjected to variable hydrothermal alteration from greenschist alteration typical of the low water rock mass ratio interactions outside of hydrothermal upflow zones as well as from severely recrystallized rocks epidosites altered within high water rock mass ratio hydrothermal upflow zones in the root zones beneath large sulfide ore deposits these dikes are moderately to highly tilted from their initial near vertical orientations due to rotations in the hangingwalls of approximately dike parallel oceanic normal faults comparison of characteristic remanence directions from these dikes with the late cretaceous troodos reference direction therefore allows a tilt test to determine whether remanent magnetizations were acquired prior to or subsequent to tilting remanence directions for both greenschist and epidosite dikes show similar magnitudes of tilting due to rotational normal faulting and restore to the late cretaceous troodos reference direction upon restoration of dikes to near vertical positions about a nnw trending horizontal axis these data along with field observations of focused alteration along normal faults suggest that epidosite alteration occurred during the early stages of extensional tilting and prior to significant rotation this sequence of events is similar to that observed for creation of large tonnage sulfide bodies at intermediate to slow spreading centers which form soon after cessation of magmatism and during the early stages of structural extension we suggest that the dike parallel normal faults were initiated as extensional fractures during this early stage of crustal extension thus providing the necessary permeability for focused fluid flow and that later slip along these structures during rotational planar normal faulting caused reduction in permeability due to gouge formation

seasonal and spatial variabilities in northern gulf of alaska surface water iron concentrations driven by shelf sediment resuspension glacial meltwater a yakutat eddy and dust phytoplankton growth in the gulf of alaska goa is limited by iron fe yet fe sources are poorly constrained we examine the temporal and spatial distributions of fe and its sources in the goa based on data from three cruises carried out in 2010 from the copper river ak mouth to beyond the shelf break april data are the first to describe late winter fe behavior before surface water nitrate depletion began sediment resuspension during winter and spring storms generated high total dissolvable fe tdfe concentrations of 1000 nmol kg 1 along the entire continental shelf which decreased beyond the shelf break in july high tdfe concentrations were similar on the shelf but more spatially variable and driven by low salinity glacial meltwater conversely dissolved fe dfe concentrations in surface waters were far lower and more seasonally consistent ranging from 4 nmol kg 1 in nearshore waters to 0 6 1 5 nmol kg 1 seaward of the shelf break during april and july despite dramatic depletion of nitrate over that period the reasonably constant dfe concentrations are likely maintained during the year across the shelf by complexation by strong organic ligands coupled with ample supply of labile particulate fe the april dfe data can be simulated using a simple numerical model that assumes a dfe flux from shelf sediments horizontal transport by eddy diffusion and removal by scavenging given how global change is altering many processes impacting the fe cycle additional studies are needed to examine controls on dfe in the gulf of alaska

burial of the mohn knipovich seafloor spreading ridge by the bear island fan time constraints on tectonic evolution from seismic stratigraphy 1 six seismic multichannel profiles and multibeam bathymetric data were collected during 2000 and 2001 from the mohn knipovich spreading ridge bend in the norwegian greenland seas the full spreading rate is slow to ultraslow 15 17 mm a 1 characterized by both magmatic and amagmatic spreading and lack of transform faults the area is covered by sediments from the bear island fan and the proximity of the ridge to a glacial margin with high sedimentation rates provides a unique opportunity to study the timing and tectonic development from seismic data the sediments in the current study have been dated by correlation to the bear island fan seismic stratigraphic network the magma starved northern part of the study area has an asymmetric axial valley which is deepest to the west whereas the axial volcanic ridge in the southern part is more symmetric the western axial mountains are about 600 800 m higher than the eastern and the sedimentary architecture shows that almost all tectonic activity after 1 3 ma occurred on the western side low angle 20 50 typically 25 faults are ubiquitous even at initiation little interaction between sedimentation and block rotation indicates rapid short lived episodes of fault movement at the axial flank detachment and starting core complex development on the western side can explain the asymmetric tectonic development of the axial mountains difference in elevation recent quiescence of the eastern axial mountains and the existence of older corrugated surfaces in the west