topographically induced baroclinic eddies near a coastline with application to he northeast pacific abstract a mathematical model is developed to describe the interaction between variable bottom topography and a steady horizontally sheared baroclinic coastal current the topography modeled in this study consists of an offshore seamount and a seaward protrusion of the continental slope the fluid motions are assumed to conserve potential vorticity on the f plane and expressions for the pressure density velocity and mass transport fields are obtained using a normal mode analysis and the appropriate green s function for the horizontal problem the theory is applied to the northeast pacific ocean in an attempt to model the anticyclonic eddy which has been observed by tabata west of sitka alaska the numerical calculations of the model and the observed location dimensions velocities and transports of the sitka eddy are in good agreement the axial velocities and dimensions of the calculated eddy field are largest for upstream surface and bottom currents of approximately 5 7 and 1 2 cm s 1 respectivel

magnetotelluric imaging of upper crustal convection plumes beneath the taupo volcanic zone new zealand 1 broadband mt magnetotelluric data were recorded that form an array of measurements at the south eastern margin of the tvz taupo volcanic zone in the central north island of new zealand these array data are used to investigate mechanisms by which the tvz s extraordinarily high heat flux is transported to the surface taken together with seismological data these mt data show compelling evidence that support a model of hydrothermal convection within the brittle upper 6 7 km part of the crust both 2 d and 3 d inversion models of these mt data show vertical low resistivity zones that connect surface geothermal fields to an inferred magmatic heat source that lies below the brittle ductile transition

three dimensional electrical resistivity image of magma beneath an active continental rift taupo volcanic zone new zealand 1 magmatic activity in regions of continental extension may result in huge 400 km 3 explosive eruptions of viscous gas rich silicic magma geochemical and geological data suggest that the large volumes of magma erupted are produced by extracting interstitial liquid from a long lived mush zone a mixture of solid crystals and liquid melt that accumulates in liquid dominated lenses at the top of a much thicker region of lower melt fraction mush such lenses will be highly electrically conductive compared with normal mid crustal rocks here we use results of 220 magnetotelluric mt soundings to construct a 3 d electrical resistivity image of the northern silicic part of new zealand s taupo volcanic zone a young continental rift associated with very high heat flow and intense silicic volcanism the electrical resistivity image shows a plume like structure of high conductivity interpreted to be a zone of interconnected melt rising from depths 35 km beneath the axis of extension

glider observations of kinematics in a gulf of alaska eddy 1 the depth radial structure of a gulf of alaska goa eddy is investigated using observations from an autonomous winged buoyancy driven glider drifters and satellite altimeters the eddy formed when sitka and yakutat eddies merged in june 2005 sitka and yakutat eddies form in the northeastern goa and travel westward carrying anomalous energy temperature and chemical properties the glider crossed the eddy seven times from mid august to late october 2005 a temperature maximum at 130 m depth near the eddy s center is indicative of coastal water the strongest azimuthal current is 0 35 m s 1 occurring at 270 m depth and 17 5 km radius the eddy s rossby burger number is 0 16 0 47 using a model with nonzero constant potential vorticity anomaly only within each depth s radius of strongest current a function is fit to azimuthal current the fit explains a large percentage of the current s radial variance with a squared correlation coefficient of 0 9 at the depths of strongest current 270 m and weakest stratification 360 m temporal trends in azimuthal volume transport rate and depth mean potential vorticity are not observed during the glider survey

volatile emission during the eruption of baitoushan volcano china north korea ca 969 ad magma volume dre 24 5 km3 the main phase ca 95 vol is represented by comenditic tephra deposited dominantly as widespread fallout blankets and proximal ignimbrites the eruption column is estimated to have reached ca 25 km and thus entered the stratosphere a late phase 5 vol is represented by trachyte emplaced chiefly as moderately welded ignimbrites the comendites contain 3 and the trachytes 10 20 vol phenocrysts mainly anorthoclase hedenbergite and fayalite primary glassy melt inclusions with no signs of leakage were found only in phenocrysts in the comenditic tephra whereas those in phenocrysts in the trachytes are devitrified the comendite magma is interpreted to have been generated by fractional crystallization from a trachyte magma represented by melt inclusions in the phenocrysts in the comendite tephra the mass of volatiles emitted to the atmosphere during the eruption was estimated using the petrologic method the average h2o concentration of the comenditic matrix glass is 1 5 wt probably largely secondary and of the corresponding melt inclusions 5 2 wt melt inclusions in feldspar and quartz present the highest halogen concentrations with a calculated average for chlorine of 4762 ppm and for fluorine of 4294 ppm the comenditic matrix glasses are represented by a fluorine rich 3992 ppm f and fluorine poor group 2431 ppm f averaging 3853 ppm for chlorine only 20 of all sulfur analyses of the comenditic matrix glasses and melt inclusions are above the detection limit of 250 ppm s the difference between pre and post eruptive concentration of h2o is at least 3 7 0 6 wt h2o taking into consideration re hydration of the matrix glass and possible leakage of melt inclusions the difference between pre and post eruptive concentrations of the halogens amounts to 909 90 ppm cl and 1863 280 ppm and 302 40 ppm f the difference for s was estimated based on the average of the maximum s concentrations in the melt inclusions 455 ppm s and the detection limit resulting in 205 40 ppm s the calculated mass of volatiles injected into the atmosphere based on the erupted magma volume and volatile data is 1796 453 megatons for h2o 45 10 megatons for chlorine 42 11 megatons for fluorine and 2 0 6 megatons for sulfur the 969 20 ad eruption of baitoushan volcano one of the largest eruptions of the past 2000 years is thought to have had a substantial but possibly short lived effect on climate

laboratory measurements of electrical conductivity of hydrous and dry silicic melts under pressure an interpretation of the electrical signature of molten rocks within the earth s interior in terms of nature and temperature conditions of magma requires additional laboratory data on the electrical conductivity of silicate melts this paper describes an experimental setup and presents measurements of the electrical impedance of dry and hydrous 1 3 wt h2o metaluminous obsidians determined in an internally heated pressure vessel in the range of 50 400 mpa and 350 1325 c it is shown that the temperature and pressure dependences of electrical conductivity of both hydrous and dry obsidian can be fitted by an arrhenius law applying in the melt and the glass regions this suggests that a similar transport mechanism operates in both melt and glass the determined activation energies are 70 kj mol for the dry obsidian and 65 and 61 kj mol for the 1 and 3 wt h2o melts respectively the activation volume is 20 cm3 mol combination of tracer diffusion and electrical conductivity reveals that sodium is the dominant charge carrier in the hydrous and dry obsidians the temperature and pressure effects on conductivity are therefore interpreted in terms of activation energy and activation volume for na mobility in dry and hydrous rhyolites an increase in conductivity associated with addition of water was observed and is shown to reflect the effect of water incorporation in melts on the mobility of sodium as a prospective it is anticipated that both the mobility and content of sodium could control the electrical conductivity of most terrestrial silicate melts magma under differentiation becomes more conductive due to sodium and water enrichment associated with fractional crystallization therefore its electrical signature must reveal its nature and maturity

petrology of the 1991 1995 eruption at unzen effusion pulsation and groundmass crystallization abstract effusive eruption of dacite magma 2 1 108 m3 during 1991 1995 formed a lava dome at the summit of unzen volcano japan the effusion rate was highest at the beginning 4 0 105 m3 day 4 6 m3 s and decreased roughly with time to almost zero before this pattern was repeated with a second pulse of magma supply the whole rock chemistry of lavas shows significant variation attributable to variations in phenocryst abundance the more mafic the more abundant the phenocrysts the pattern of chemical variation with time shows some difference from that of the effusion rate all phenocrysts in dacite plagioclase hornblende biotite quartz and magnetite show evidence of disequilibrium with melt although a glomerophyric aggregation of phenocrysts suggests coexistence with each other phenocrysts are isotopically heterogeneous from species to species the calculated initial melt composition was rhyodacite and was nearly constant throughout the activity in contrast the bulk phenocryst population is andesite a model explaining the textures and the isotopic heterogeneity is the capture of diorite fragments or xenocrysts by parental rhyodacite magma it is suggested that when effusion rate was high less viscous crystal poor magma exited from the reservoir groundmass glass and plagioclase microlite rims show temporal chemical variations correlating with the effusion rate the higher the effusion rate the more evolved the compositions groundmass crystallinity increased with decreasing effusion rate from 33 to 50 textures in dome lavas suggest that groundmass crystallization had been mostly completed when magma reached the conduit top the fe ti oxide temperature 880 780 c was low when the crystallinity was high micropumice erupted before dome growth provided a sample recording magmatic foam in the conduit porosity of dome lavas was lower at lower effusion rates collapse of foam magma and simultaneous escape of volatiles through the conduit top were probably responsible for the accompanying low frequency earthquakes phenocrysts were broken and the breakdown rims on hornblende phenocrysts were torn off during collapse and successive compaction when effusion waned degassing and the resultant crystallization proceeded more completely so that the magma became too viscous to flow in the conduit top and behaved as a plug resulting in a temporary halt of effusion in turn groundmass crystallization in magma below the plug increased excess pressure in the upper parts of conduit due to slow cooling the plug was scavenged when rising excess pressure overcame its effective strength then the second pulse of magma supply began strong endogenous growth and extrusion of a lava spine in the later stage probably occurred for the same reason

seismic observations from a yakutat eddy in the northern gulf of alaska recent works show that the seismic oceanography technique allows us to relate water column seismic reflections to oceanic finescale structures in this study finescale structures of a surface anticyclonic eddy have been unveiled by reprocessing two seismic transects acquired in the northern gulf of alaska using an 8 km hydrophone streamer and 6600 cu in linear airgun array in september 2008 the eddy was a typical bowl like structure with around 55 km width and 700 m depth it has two fringes around the eddy base and a spiral arm at the ne edge the in situ sea surface temperature and salinity data from a shipboard thermosalinograph help to confirm our interpretations of a spiral arm shed from the warm eddy and the entrained cold water from elsewhere nearby the eddy and offshore the shelf break there is a strong frontal feature probably the alaska current the eddy likely formed offshore yakutat shelf and transported along the offshore shelf break by tracking the sea level anomalies its equivalent diameter of 65 km was measured using the along track altimeter and the seismic constraints it was comparable with results from the representative conventional algorithms of eddy detection geostrophic velocities of the eddy were estimated from the dipping seismic reflections under the assumptions of approximate isopycnals and geostrophic balance measured water properties including sea surface temperature salinity and chlorophyll revealed that eddy translation transports coastal water to the pelagic regions structures synthesized from ctd profiles that sampled an earlier eddy suggest that thin striae around the base might be a common feature in gulf of alaska eddies

evolution of an oceanic anticyclone in the lee of madeira island in situ and remote sensing survey island wakes are areas of a strong eddy activity influencing the availability and transport of organic matter in the ocean which in turn impact biological productivity despite this eddy formation in the lee of north atlantic tropical islands is scarcely documented except for the canary islands moreover the occurrence of anticyclones leeward of madeira has seldom been detected during the summer of 2011 a multiplatform approach combining satellite data with in situ measurements was used to study an anticyclonic eddy generated in the lee of the madeira island the main objective was to confirm recent numerical evidence suggesting that orographically perturbed winds can induce anticyclonic eddies leeward of madeira particularly during summer months the high resolution sampling of the eddy s interior shows a strong downwelling of 100 m of the isopycnal layer below the mixed layer typical of intrathermocline eddies the 25 km radius of this anticyclonic structure exceeds the local deformation radius by a factor of 2 the vortex rossby number remained moderate ro 0 26 even if the relative core vorticity reached a finite value f 0 7 the occurrence of strong trade winds 10 15 m s 1 prior to the detection of the first surface eddy signatures july 2011 concurrent with opposite flowing geostrophic currents shows that the orographic wind forcing is the main mechanism for generating this mesoscale long lived eddy after leaving the shelter of the island the eddy traveled northwesterly following a perpendicular net ekman transport pathway at a speed of 5 km d for at least 2 months an interaction with a cyclonic partner generated in the area helped precipitate the northward trajectory this study presents the first clear evidence of a wind induced mesoscale anticyclone in the lee of madeira

imaging the laguna del maule volcanic field central chile using magnetotellurics evidence for crustal melt regions laterally offset from surface vents and lava flows abstract magnetotelluric mt data were collected at the laguna del maule volcanic field ldmvf located in central chile 36 s 70 5 w which has been experiencing unprecedented upward ground deformation since 2007 these data were used to create the first detailed three dimensional electrical resistivity model of the ldmvf and surrounding area the resulting model was spatially complex with several major conductive features imaged at different depths and locations around laguna del maule ldm a near surface conductor c1 0 5 m approximately 100 m beneath the lake is interpreted as a conductive smectite clay cap related to a shallow hydrothermal reservoir at 4 km depth a strong conductor c3 0 3 m is located beneath the western edge of ldm the proximity of c3 to the recent pleistocene to holocene vents in the northwest ldmvf and nearby hot springs suggests that c3 is a hydrous 5 wt h2o rhyolitic partial melt with melt fraction 35 and a free water hydrothermal component c3 dips towards and is connected to a deeper conductor c4 1 m c4 is located to the north of ldm at 8 km depth below surface and is interpreted as a long lived rhyolitic to andesitic magma reservoir with melt fractions less than 35 it is hypothesized that the deeper magma reservoir c4 is providing melt and hydrothermal fluids to the shallower magma reservoir c3 a large conductor directly beneath the ldmvf is not imaged with mt suggesting that any mush volume beneath ldm must be anhydrous 10 km as it moves from the deep magma reservoir c4 to create small ephemeral volumes of eruptible melt c3 it is hypothesized that there may be a north south contrast in physical processes affecting the growth of melt rich zones since major conductors are imaged in the northern ldmvf while no major conductors are detected beneath the southern vents the analysis and interpretation of features directly beneath the lake is complicated by the surface conductor c1 which attenuates low frequency signals the attenuation from c1 does not affect c3 or c4 at 1 km depth directly beneath ldm a weak conductor c2 50 silicic reservoir with 5 wt h2o at 2 to 5 km depth beneath the inflation center is not supported by the mt data however a smaller 10 km3 eruptible volume could go undetected even with relatively high melt fraction 50 the location of large melt regions to the north has important implications for long term volcanic hazards at ldmvf as well as other volcanoes as it raises the possibility that the vent distribution is not always indicative of the location of deeper source regions of melt

the north pacific climatology of winter mixed layer and mode waters abstract a climatology of the winter mixed layer in the north pacific ocean was constructed using hydrographic data from historical archives and recent observational programs including the world ocean circulation experiment the main aim was to provide better knowledge about source areas of upper water masses the authors have endeavored to preserve water properties near the frontal regions by keeping the smoothing scale as small as possible the resulting climatology shows considerable differences in the mixed layer depth and its water properties from those derived from the world ocean atlas woa maps of the potential vorticity field of the north pacific pycnocline are presented using the isopycnally averaged climatology hydrobase three distinct lateral minima of potential vorticity are identified as subtropical mode water stmw central mode water cmw and eastern subtropical mode water estmw in the western central and eastern parts of the subtropical gyre respectively the hydrobase isopy

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

submesoscale features and turbulent mixing of an oblique anticyclonic eddy in the gulf of alaska investigated by marine seismic survey data

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

diffusion in magmas at depth in the earth the effects of pressure and dissolved h2o abstract experimental data on cation diffusion in silicate melts and glasses at atmospheric pressure cannot be quantitatively applied to diffusion in magmas at depth because pressure and dissolved h2o have significant effects diffusivities of ca and cs in soda lime aluminosilicate melt are reduced by roughly an order of magnitude as pressure increases from 1 to 30 kbar at 1100 c in the case of calcium the pressure effect is smaller at higher temperatures the influence of dissolved h2o is opposite to and for some ions far more important than that of pressure at 700 c cs diffusion in granitic obsidian is enhanced by four orders of magnitude by the addition of 6 wt h2o and ca diffusivity increases by 2 5 orders of magnitude sodium diffusion on the other hand is relatively immune to changes in h2o content the retarding effect of pressure on diffusion in deep seated magmas is largely compensated by higher magmatic temperatures such that overall depth effects on diffusion are of secondary importance diffusion rates in mantle melts are probably well approximated by 1 atm near liquidus values diffusion rates in crustal magmas however are extremely sensitive to h2o content so that models of rate controlled processes in hydrous magmas may be grossly in error if 1 atm diffusivity values are used

gravity waves and turbulence associated with cumulus convection observed with the uhf vhf clear air doppler radars vertical wind disturbances are frequently observed during midsummer afternoons in association with cumulus convection to examine the relation of these wind disturbances to atmospheric stability and turbulence intensity we carried out intensive observations of wind temperature and humidity over a large vertical region extending from the boundary layer to the lower stratosphere using uhf vhf radars and radiosondes at shiga japan 35 n 136 e the wind disturbances propagate quickly into the upper troposphere just after 1500 local standard time lst when the level of free convection lfc descends below the top of the mixed layer while before that the disturbances are confined in the mixed layer however strong turbulence is largely confined to the region below 3 km even after 1500 lst suggesting that the height of 3 km corresponds to the top of cumuli while the wind disturbances above are due to gravity waves generated in association with cumulus convection in addition stratospheric disturbances were examined for 12 cases of midsummer disturbances using routine observational data taken with a vhf radar in a height region of 5 24 km wind disturbances are observed in the lower stratosphere when turbulence as well as wind disturbances are strong in the whole troposphere the stratospheric disturbances are dominant in two regions below and above a height of 18 km where the background horizontal wind is weak long period disturbances are observed only in the lower region this fact suggests that the height of 18 km is a critical level for the long period gravity waves the existence of a strong turbulent layer around 18 km is consistent with this inference

impact of haida eddies on chlorophyll distribution in the eastern gulf of alaska mesoscale haida eddies influence the distribution of surface phytoplankton in the eastern gulf of alaska through two processes enhanced productivity in central eddy water and seaward advection of highly productive coastal waters in the outer rings of eddies these two processes were observed in a sequence of monthly images over five years for which images of seawifs derived chlorophyll distributions were overlaid by contours of mesoscale sea surface height anomaly derived from topex and ers 2 satellite observations satellite measurements were supplemented with ship based chlorophyll observations through one of the eddies haida eddies are deep anticyclonic mesoscale vortices that normally form in winter and early spring near the southwest coast of the queen charlotte islands high levels of chlorophyll observed in eddy centres indicated that they supported phytoplankton blooms in spring of their natal years with timing of these blooms varying from year to year and exceeding in magnitude the chlorophyll concentrations of surrounding water elevated chlorophyll levels also were observed in eddy centres in late summer and early autumn of their natal year enhanced chlorophyll biomass is attributed to higher levels of macro nutrients and higher levels of iron enclosed within eddies than in surface deep ocean water by late spring and summer when coastal water supported higher chlorophyll biomass than did oceanic offshore regions eddies that straddled the continental margin entrained high chlorophyll coastal water into their outer rings and carried it several hundred kilometres into the gulf of alaska along their southern sides on some occasions a deep ocean eddy would entrain chlorophyll from an adjacent eddy located closer to the coast forming a conveyor belt transport process to inject coastal biota into the deep sea region of the gulf this process extended the coastal region of high chlorophyll surface water and therefore phytoplankton rich water several hundred kilometres seaward and dominated the shelf to deep ocean exchange of chlorophyll from late winter to the following autumn

forecasting etna eruptions by real time observation of volcanic gas composition it is generally accepted but not experimentally proven that a quantitative prediction of volcanic eruptions is possible from the evaluation of volcanic gas data by discussing the results of two years of real time observation of h2o co2 and so2 in volcanic gases from mount etna volcano we unambiguously demonstrate that increasing co2 so2 ratios can allow detection of the pre eruptive degassing of rising magmas quantitative modeling by the use of a saturation model allows us to relate the pre eruptive increases of the co2 so2 ratio to the refilling of etna s shallow conduits with co2 rich deep reservoir magmas leading to pressurization and triggering of eruption the advent of real time observations of h2o co2 and so2 combined with well constrained models of degassing represents a step forward in eruption forecasting

factors influencing physical structure and lower trophic levels of the eastern bering sea shelf in 2005 sea ice tides and winds abstract in spring and fall 2005 cross and along shelf transects were sampled to evaluate the influence of physical forcing including sea ice tides and winds on the lower trophic levels of the bering sea ecosystem the hydrography nutrients chlorophyll and zooplankton abundance and species composition were all affected by the presence or absence of sea ice on a north south transect along the 70 m isobath in may shelf waters between 59 n and 62 n were cold and relatively fresh and benthic invertebrate larvae and chaetognaths were a significant fraction of the zooplankton community while to the south the water was warmer saltier and the zooplankton community was dominated by copepods the position of the transition between ice affected and ice free portions of the shelf was consistent among temperature salinity nutrients and oxygen this transition in the hydrographic variables persisted through the summer but it shifted 150 km northward as the season progressed while a transition also occurred in zooplankton species composition it was farther north than the physical chemical transition and did not persist through the summer mooring data demonstrated that the change in the position of the transition in physical and chemical properties was due to northward or eastward advection of water onto and across the shelf from south to north along the 70 m isobath tidal energy decreased resulting in a less sharply stratified water column on the northern portion of the middle shelf as opposed to a well defined two layered system in the southern portion this more gradual stratification in the north permitted a greater response to mixing from winds which were homogeneous from north to south thus the physical and biological structure at any one location over the middle shelf is dynamic over the course of a year and results from a combination of in situ processes and climate mediated regional forcing which is dominated in most years by sea ice

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

studies of quasi horizontally propagating gravity waves in the troposphere using the piura st wind profiler vhf profiler observations of the troposphere obtained over a flat desert in northern peru show the presence of strong quasi sinusoidal oscillations in the vertical wind velocity with periods of around 8 18 min these oscillations are a very typical feature of the vertical velocities over piura this paper presents an overview of the wave characteristics obtained at piura until this point including results obtained using two additional antennas built a few hundred meters to the west and south of the main antenna to measure horizontal wavelengths and phase velocities briefly the piura waves appear to have horizontal wavelengths of 1 3 km with either westward or eastward phase velocities in a ground based reference frame of 0 5 4 m s 1 their occurrence appears to be causally related to the magnitude of the easterly wind which blows over the andean cordillera some 60 km to the east of the site

a study of mountain lee waves using clear air radar the tropospheric and lower stratospheric response to flow over complex terrain is investigated using observations of vertical and horizontal motions made by a clear air doppler radar stationed at toulon in southern france analysis of the data has disclosed that episodic enhancements in the variability of vertical and horizontal velocities are due to lee waves excited by obstacles located within 5 km of the radar three separate cases of lee wave activity are studied two dimensional linear perturbation theory and existing three dimensional simulation results for appropriate parameter values are used as guides to check against the vertical structure observed by radar the magnitudes of vertical velocities observed during lee wave incidence are well within the range reported in previous observational and numerical simulation studies from a detailed examination of one of the cases of trapped waves the time variation observed by the radar of timescales of less than an hour has emerged as the likely result of small directional changes in the upstream winds causing a bodily rotation of the downstream three dimensional wave pattern centred on the wave generating obstacle the observed tendency of the vertical velocity perturbation to change sign with time above the radar location follows as a consequence of the presence of large horizontal gradients in the motion field which are inherent in the structure of three dimensional lee waves the temporal variability of the lee wave pattern has allowed the radar to sweep out a partial horizontal cross section revealing vertical circulation features that are broadly consistent with gravity wave behaviour however analysis of the effects of finite antenna beam spacing on the sampled data indicates that a spurious phase shift might have been introduced between the vertical and horizontal velocity perturbations observed in the cross section in contrast the measured vertical velocities are not seriously affected by finite beam width effects the lee waves examined in this study are quite moderate nevertheless this circumstance has provided a favourable opportunity to conduct a critical evaluation of the capabilities and limitations of this radar technique for observing lee wave phenomena in general we have been able to show clearly how the incidence and vertical structure of the waves respond to the synoptic scale situation in particular we have been able to distinguish between trapped and vertically propagating waves and to relate a transition between these wave types to synoptic scale changes in the static stability structure

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

interannual variability of the gulf of alaska eddy field 1 regions of high eddy kinetic energy eke in the gulf of alaska goa calculated from altimetry data denote formation regions and translation pathways for eddies high eke is observed along the shelf break in winter and spring with lower values in summer and autumn three regions of high eke are examined in detail in the eastern goa particularly high eke occurred in 1998 in the northwestern goa eddies were observed quasi annually between 1999 and 2004 but were less frequent prior to that time or in 2005 and 2006 eddies northeast of kodiak island have been implicated in high offshelf chlorophyll concentrations observed from ocean color satellites correlations between eke and chlorophyll concentration are significant there suggesting that eke may be valuable for predicting phytoplankton blooms in this region

currents and transport on the eastern bering sea shelf an integration of over 20 years of data abstract more than 20 years of data from moorings satellite tracked drifters and hydrographic surveys are integrated to provide a comprehensive view of currents and transport on the eastern bering sea shelf the major sources of water onto the eastern bering sea shelf are north pacific water flowing through unimak pass and bering slope water flowing onto the shelf usually via the canyons that intersect the shelf break absolute geostrophic transport through unimak pass varies from an average of 0 25 106 m3 s 1 sv in the warm months to 0 43 sv in the cold months flow along the 50 m isobath is weak with a transport of 13 months and from amukta pass to bering strait via the bering slope current is 8 months consequently the source of most of the heat transported into the arctic through bering strait is a result of air sea interactions local to the northern bering sea analysis of the currents and water properties on the southern shelf indicates that 50 of the shelf water is exchanged with slope water during october january each year this exchange elevates the october mid shelf average nitrate level from 6 m to 14 16 m by the end of january

a high electrical conductive zone at lower crustal depth beneath the betic chain spain abstract magnetotelluric data with periods of up to 2000 s were collected and the conductivity structure of the crust and upper mantle was imaged in the central betic chain interpretation of the impedance tensor components and the geomagnetic transfer functions was made in terms of a two dimensional resistivity model along a nw se profile from the guadalquivir foreland basin and across the boundary between the external and the internal betics elongated high conductivity zones in the upper and middle crust related to fluid circulation along both sediments and faults were detected the conductors in the upper crust coincide with the areal distribution of the cenozoic and mesozoic sedimentary rocks from the guadalquivir basin and the external betics and the conductors in the middle crust with the major miocene extensional detachments affecting the basement rocks of the internal betic zone a high conductivity zone at lower crustal levels beneath the outer internal betics was also detected next to an area where earlier seismic reflection data had imaged a duplication of the reflective moho this conductor was interpreted as partial melting of a southeast dipping subducted iberian lower crust the geodynamic significance of this subduction depends mainly on whether the overthrusting lower crust belongs to the alboran domain or to the iberian plate in the former case it would correspond to a major plate boundary and in the latter to an intraplate feature

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

physical characteristics and dynamics of the coastal latex09 eddy derived from in situ data and numerical modeling 1 we investigate the dynamics of a coastal anticyclonic eddy in the western part of the gulf of lion gol in the northwestern mediterranean sea during the latex campaign in the summer 2009 latex09 the sampling strategy combines sea surface temperature satellite imagery hull mounted acoustic doppler current profiler data conductivity temperature depth casts and drifter trajectories our measurements reveal an anticyclonic eddy latex09 eddy with a diameter of 23 km and maximum depth of 31 m centered at 3 34 e 42 33 n we use a high resolution three dimensional primitive equation numerical model to investigate its generation process and evolution the model is able to reproduce the observed eddy in particular its size and position the model results suggest that the latex09 eddy is induced by a large anticyclonic circulation in the northwestern part of the gol pushed and squeezed toward the coast by a meander of the northern current this represents a new generation mechanism that has not been reported before the post generation dynamics of the eddy is also captured by the model the collision of the latex09 eddy with cape creus results in a transient structure which is depicted by the trajectories of two lagrangian drifters during latex09 the transient structure and its advection lead to a transfer of mass and vorticity from the gol to the catalan shelf indicating the importance of mesoscale structures in modulating such exchanges in the region

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

3 d water properties and geostrophic circulation on the eastern bering sea shelf abstract the national oceanic and atmospheric administration s noaa alaska fisheries science center bottom trawl survey samples demersal fish at over 350 sites on the eastern bering sea continental shelf each summer on a 37 37 km 2 grid rugged conductivity temperature depth sensors ctds were added to the net hauls to obtain gridded data sets of temperature and salinity measurements for 2008 2010 results reveal the three dimensional thermohaline structure of the shelf including the cold pool and areas of fresher water around st matthew island and in bristol bay horizontal gradients are often strongest roughly along the 50 m and 100 m isobaths that traditionally separate the inner and outer shelf from the middle shelf centered along the 70 m isobath the summer mixed layer depth is less than 30 m over much of the region it reaches the bottom along the alaska peninsula in water depths greater than 70 m showing that the boundary of the well mixed inner shelf is not always at the 50 m isobath the greatest upper to lower layer density difference is found across the shelf north of 59 n the salinity difference is the main contributor to this density difference over most of the region in 2008 and 2010 but the temperature difference dominates in 2009 due to decreased ice melt and reduced freshening near st matthew island the geostrophic velocity relative to the bottom shows northwestward flow seaward of the 100 m isobath and northwestward transports integrated across the shelf of 0 10 0 25 10 6 m 3 s in 2008 and 2010 there was clockwise circulation in a region of less saline water around st matthew island in 2009 that fresher lens did not exist and flow was more concentrated along the 100 m isobath bringing saltier water across the shelf

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

melt distribution beneath a young continental rift the taupo volcanic zone new zealand 1 taupo volcanic zone tvz is a zone of intense volcanism and rifting associated with the subduction of the pacific plate beneath the continental crust of new zealand s north island an image of the conductivity structure beneath the central part of the tvz has been constructed using 2 d inverse modeling of magnetotelluric data a rapid increase in conductivity at a depth of 10 km beneath the tvz 3 km beneath the base of the seismogenic zone but well above the base of the quartzo feldspathic crust 16 km is interpreted to mark the presence of an interconnected melt fraction 4 within the lower crust beneath the quartzo feldspathic crust the model shows a zone of increased conductivity on the eastern side of the tvz consistent with an increased concentration of melt at deeper levels the pacific plate is resistive compared with the overlying mantle

a synoptic survey of young mesoscale eddies in the eastern gulf of alaska eddies in the gulf of alaska are important sources of coastal water and associated nutrients iron and biota to the high nutrient low chlorophyll central gulf of alaska three primary eddy formation regions along the eastern boundary of the gulf have been identified from south to north haida sitka and yakutat in the spring of 2005 three eddies one of each type were sampled soon after their formation the subsurface eddy core water in all three eddies was defined by high iron concentrations and low dissolved oxygen compared with surrounding basin water the sitka and yakutat core waters also exhibited a subsurface temperature maximum mesothermal water coincident in depth with the iron maximum suggesting that eddies may play a role in the formation of temperature inversions observed throughout the gulf of alaska the data suggest different formation regions with the yakutat eddy forming in shallow shelf water with riverine input while the sitka and haida eddies appear to form in deeper water

dynamics and energetics of trapped diurnal internal kelvin waves around a midlatitude island abstractthe generation of trapped and radiating internal tides around izu oshima island located off sagami bay japan is investigated using the three dimensional stanford unstructured nonhydrostatic terrain following adaptive navier stokes simulator suntans that is validated with observations of isotherm displacements in shallow water the model is forced by barotropic tides which generate strong baroclinic internal tides in the study region model results showed that when diurnal k1 barotropic tides dominate resonance of a trapped internal kelvin wave leads to large amplitude internal tides in shallow waters on the coast this resonance produces diurnal motions that are much stronger than the semidiurnal motions the weaker freely propagating semidiurnal internal tides are generated on the western side of the island where the m2 internal tide beam angle matches the topographic slope the internal wave energy flux due to the diurnal internal tides is much higher than that of the semidiurnal tides

a regression modeling approach for studying carbonate system variability in the northern gulf of alaska 1 the northern gulf of alaska goa shelf experiences carbonate system variability on seasonal and annual time scales but little information exists to resolve higher frequency variability in this region to resolve this variability using platforms of opportunity we present multiple linear regression mlr models constructed from hydrographic data collected along the northeast pacific global ocean ecosystems dynamics globec seward line the empirical algorithms predict dissolved inorganic carbon dic and total alkalinity ta using observations of nitrate no3 temperature salinity and pressure from the surface to 500 m with r2s 0 97 and rmse values of 11 mol kg 1 for dic and 9 mol kg 1 for ta we applied these relationships to high resolution no3 data sets collected during a novel 20 h glider flight and a globec mesoscale seasoar survey results from the glider flight demonstrated time space along isopycnal variability of aragonite saturations arag associated with a dicothermal layer a cold near surface layer found in high latitude oceans that rivaled changes seen vertically through the thermocline the seasoar survey captured the uplift to 100 m of dense high pco2 waters at the shelf break that had been forced by the passage of a yakutat eddy during this event the aragonite saturation horizon depth where arag 1 shoaled to a previously unseen depth in the northern goa this work is similar to recent studies aimed at predicting the carbonate system in continental margin settings albeit demonstrates that a no3 based approach can be applied to high latitude data collected from platforms capable of high frequency measurements

an examination of the physical variability around the pribilof islands in 2004 the pribilof islands form a unique ecosystem an anti cyclonic oceanic flow exists around the islands nutrients are introduced into this circulation from two sources 1 the flow along the 100 m isobath with intrusions of nutrient rich water in pribilof canyon and 2 the westward transport and vertical mixing of middle shelf water which contains nutrient rich bottom water enhanced tidal mixing around the pribilofs introduces this deeper nutrient rich water into the euphotic zone and thus supports prolonged production around the islands further the middle shelf water that is advected into the region causes the upper 50 m of the water column around the islands to freshen throughout the summer this enhances the frontal structure and strengthens the baroclinic flow along the 100 m isobath the strengthening of the frontal structure can moderate ecosystem productivity by limiting the intrusion of slope water rich in nutrients and oceanic copepods

stratification on the eastern bering sea shelf revisited abstract the timing and magnitude of stratification can have profound influences on the marine ecosystem on the eastern bering sea shelf in the absence of strong wind mixing stratification can be initiated by the melting of seasonal sea ice or by springtime warming of the surface temperature and salinity both influence the stratification of the eastern bering sea shelf with their relative importance varying spatially and temporally in the northern middle shelf domain north of 60 n salinity stratification is often as important as temperature stratification on the southern middle shelf while the influence of temperature on stratification dominates during summer the influence of salinity stratification plays a role in the interannual variability mooring 2 m2 56 9 n 164 1 w has been deployed at 70 m depth in the southern middle shelf domain since 1995 data from this mooring show that stratification typically begins to set up in may and to break down in september october but these dates can vary by 30 d while no trend is found in the timing of the spring setup the fall stratification breakdown exhibited a trend toward later breakdown 2 d later per year from 1996 to 2009 results suggest that it may be difficult to forecast stratification on the eastern bering sea shelf from climate models as simple indices of wind mixing or heat fluxes are not correlated with stratification contrary to intuition the strength of summer stratification is not correlated with depth averaged temperature warm years such as 2000 and 2001 can have low stratification and cold years such as 2007 can have very high stratification this decoupling of stratification and temperature has implications for forecasting the ecosystem in the face of climate change as we cannot assume that projections of a warmer climate simply imply higher stratification in the future

patterns of flow in the canyons of the northern gulf of alaska abstract the continental shelf around kodiak island is incised with numerous submarine canyons which play an important role in the cross shelf transport of heat salt and nutrients and the transport of ichthyoplankton of deep spawning fish from the slope region into the shallow nursery grounds surrounding kodiak island to explore the pathways and variability of flow and the extent of tidal mixing within the canyons moorings were placed in the chiniak barnabas and amatuli troughs and off the shelf from resurrection bay seward line and the kenai peninsula gore point in the troughs intensified flow was evident near the trough walls and flow was directed by bathymetry with inflow along the upstream northern side and outflow along the downstream southern side the presence of mesoscale eddies in the gulf had no unique influence on currents or salinity in the troughs tidal mixing was strongest in chiniak trough and this introduced cold nutrient rich bottom waters into the upper water column intensified bottom flow associated with the alaskan coastal current was evident along the seward line and gore point and directed toward the kennedy stevenson entrances which are also regions of strong tidal mixing observations of tidal mixing were consistent with model results and satellite images showing cooler phytoplankton rich water in summer in the nursery grounds that surround kodiak island patterns of flow within the troughs and in shelikof strait were consistent with the springtime advance of ichthyoplankton across the shelf

coupled nitrification denitrification in sediment of the eastern bering sea shelf leads to 15n enrichment of fixed n in shelf waters 1 we studied the nitrogen biogeochemistry of the ice covered eastern bering sea shelf using the isotope ratios 15n 14n and 18o 16o of no3 and other n species the 15n 14n of late winter no3 on the shelf decreases inshore and is inversely correlated with bottom water nh4 consistent with an input of low 15n 14n no3 from partial nitrification of nh4 remineralized from the sediments an inshore 15n 14n increase in total dissolved n tdn suggests that 1 the sediment derived nh4 is elevated in 15n due to the same partial nitrification that yields the low 15n 14n no3 and 2 15n deplete no3 from partial nitrification within the sediments is denitrified to n2 the proportion of newly nitrified no3 on the shelf evidenced by an inshore decrease in no3 18o 16o is correlated with the n deficit further implicating nitrification coupled to denitrification however a simple n isotope budget indicates a comparable rate of denitrification supported by diffusion of no3 into the sediments the isotopic impact of benthic n loss is further demonstrated by a correlation between the 15n 14n of shelf surface sediment and the n deficit of the overlying water column both of which increase inshore and northward as well as by arctic no3 isotope data indicating that the fixed n transported through bering strait has a 15n 14n higher than is found in the open bering sea the significant net isotope effect of benthic n loss on the bering shelf 6 8 is at odds with previous assumptions regarding the global ocean s n isotope budget

recent unrest of changbaishan volcano northeast china a precursor of a future eruption 1 over 12 years of continuous monitoring of changbaishan volcano in the border region of china and north korea by means of volcanic seismicity ground deformation and volcanic gas geochemistry yields new evidence for magmatic unrest of the volcano between 2002 and 2006 in this so called active period the frequency of volcanic earthquakes increased by about 2 orders of magnitude compared to that of the background inactive periods the active period was also accompanied by ground inflation high values of co2 he h2 and high ratios of n2 o2 and 3he 4he in volcanic gases released from three hot springs near the caldera rim the monitoring evidence implies pressurization of the magma chamber possibly caused by incremental magma recharge the ground deformation data from both gps and precise leveling are modeled to suggest the corresponding deformation source is at 2 60 km depth beneath the volcano s summit where earthquake swarms were detected in 2002 and 2003 our findings suggest that the magma chamber beneath changbaishan volcano has awakened and resumed activity after remaining dormant since ad 1903 there is an urgent need to keep close watch on this active and very hazardous volcano in northeast china

bias in mean vertical wind measured by vhf radars significance of radar location relative to mountains abstract measurements by vhf wind profiling radars worldwide have for many years shown long term downward atmospheric motion in most of the troposphere various explanations have been proposed some atmospheric and some caused by the radar measurement method at many sites except those in the tropics the authors suggest a new model in which the long term downward vertical wind w is real and atmospheric a consequence of radars being constructed on low ground near or within mountain ranges so that they tend to view on average the same phase of mountain waves a coincidence consisting of five factors low lying radar locations near mountains the upwind slope of untrapped mountain wave phase lines with height the inability of wind profiling radars to measure both the lowest few kilometers of the troposphere and far into the stratosphere decreasing tropospheric static stability with height and increasing tropospheric wind speed with height has led to downward w measurements in most of the troposphe

modification of a kenai eddy along the alaskan stream 1 a kenai eddy was studied through analyses of satellite altimeter data and hydrographic data from shipboard and argo float observations this eddy formed in december 2006 south of the kenai peninsula and propagated southwestward along the alaskan stream the eddy held horizontally uniform warm core water in january 2007 in late winter 2007 this core water was cooled from the top and a subsurface temperature maximum was formed around 26 5 two years later in summer 2009 warm and low dissolved oxygen low do water characterized by a temperature maximum around 26 5 was observed again in the eddy core and was likely the remnant of original core water at the same time cold and high do water intrusions occurred in the eddy core suggesting that strong modification of core water was ongoing after summer 2009 the core water was fully changed through interaction with another eddy

observation of mesoscale ocean features in the northeast pacific using geosat radar altimetry data in this paper geosat altimetry data from the northeast pacific are examined the data are 1 binned data on 1 latitude by 2 longitude blocks and 2 collinear track data the binned data cover the region from 20 n to 60 n from the north american coast westward to 150 w and span from december 15 1986 to june 1 1989 to examine the data for evidence of westward propagation of sea level anomalies three zonal transects 45 n 49 n and 57 n are made complex empirical orthogonal function analysis of the data transects at these latitudes reveals phase speed and amplitude information the first eigenmode at each latitude has a very strong annual signal two dimensional spectral analysis of the first eigenmode at 45 n and 57 n shows westward propagation of sea level anomalies at 45 n only the propagating features are annual in period and of order 1000 km in length at 57 n westward propagation is evident as at 45 n but there is also an eastward component to examine the variability of the coastal sea level signal collinear track data from three ascending tracks crossing the gulf of alaska are analyzed revealing mesoscale features of the order of 100 km that parallel the canadian and alaskan coast the most notable feature is the sitka eddy westward propagation of several of these features is observed the results from the analysis of both types of geosat data are compared with other observational data

the proportion of remineralized nitrate on the ice covered eastern bering sea shelf evidenced from the oxygen isotope ratio of nitrate 1 we present measurements of nitrate and its natural abundance oxygen isotope composition 18o 16o in the water column of the broad and shallow eastern bering sea shelf in the late winter and early spring of 2007 and 2008 in both years nitrate concentrations showed a characteristic decrease from 25 m at the slope to 5 m inshore the 18o 16o ratio of nitrate 18ono3 versus smow also decreased from 3 2 at the slope to 1 5 inshore in 2007 and to as low as 1 inshore in 2008 indicating that nitrate inshore was nitrified at least once since having been entrained as nitrate from the slope the shoreward decrease was less pronounced in 2007 due to 18o enrichment of nitrate from incident phytoplankton assimilation in the ice covered water column whereas little to no algal growth in the water column was evident in 2008 by comparing the 18o of nitrate to that of ambient water in spring 2008 we estimate the fraction of nitrate that was remineralized in situ rather than recently advected from the slope these estimates indicate that 20 100 of the nitrate in winter water of the middle and inner shelves derives from regeneration directly on the shelf rather than from the seasonal entrainment of slope waters with recycling being the dominant mode of seasonal nitrate recharge from the 70 m isobath shoreward these observations indicate substantial nutrient recycling on the shallow shelf which has direct implications for the extent of fixed n loss to benthic denitrification and the fertility of the eastern shelf

long term observations of alaska coastal current in the northern gulf of alaska abstract the alaska coastal current is a continuous well defined system extending for 1700 km along the coast of alaska from seward alaska to samalga pass in the aleutian islands the currents in this region are examined using data collected at 20 mooring sites and from 400 satellite tracked drifters while not continuous the mooring data span a 30 year period 1984 2014 using current meter data collected at a dozen mooring sites spread over four lines seward gore point kennedy and stevenson entrances and the exit to shelikof strait total transport was calculated transport was significantly correlated with alongshore winds although the correlation at the seward line was weak the largest mean transport in the alaska coastal current occurred at gore point 1 4 10 6 m 3 s 1 in winter and 0 6 10 6 m 3 s 1 in summer with the transport at the exit to shelikof strait 1 3 10 6 m 3 s 1 in winter and 0 6 10 6 m 3 s 1 in summer only slightly less the transport was modified at the seward line in late summer and fall by frontal undulations associated with strong river discharge that enters onto the shelf at that time of year the interaction of the alaska coastal current and tidal currents with shallow banks in the vicinity of kodiak archipeligo and in kennedy stevenson entrance results in mixing and prolonged primary production throughout the summer

integrating magnetotelluric and seismic images of silicic magma systems a case study from the laguna del maule volcanic field central chile

a mantle magma reservoir beneath an incipient mid ocean ridge in afar ethiopia the buoyancy of magma should cause it to rise into the crust preventing it from ponding in the uppermost mantle magnetotelluric data from the dabbahu rift segment ethiopia identify a magma reservoir that extends well into the mantle beneath the rift and is so large that it should persist for thousands of years

magnetotelluric imaging of upper crustal partial melt at tendaho graben in afar ethiopia we report on a recent magnetotelluric mt survey across the manda hararo magmatic segment mhms within the tendaho graben in the afar depression in northeastern ethiopia twenty two broadband mt sites with 1 km station spacing were deployed along a profile with the recorded data covering a period range from 0 003 s to 1000 s a two dimensional 2 d resistivity model reveals an upper crustal fracture zone fault and partial melt with resistivity of 1 10 m at a depth of 1 km the partial melt has a maximum horizontal width of 15 km and extends to a depth of 15 km within the afar stratoid series basalts we estimate a melt fraction of about 13 based on geochemical and borehole data and bulk resistivity from the 2 d mt inversion model the interpreted upper crustal partial melt may have been formed by either a magma intrusion from mantle sources or a large volume of continental crust that has been fluxed by a small amount of mantle melt and heat within the mhms and tendaho graben a magma intrusion is a plausible explanation for the upper crustal conductor the inferred presence of a conductive fracture zone or fault with hydrothermal fluid and shallow heat sourcing magma reservoir also makes the tendaho graben a promising prospect for the development of conventional hydrothermal geothermal energy

upwelling and convergence in the middle atlantic bight shelfbreak front convergent and upwelling circulation within the shelfbreak front in the middle atlantic eight are detected using a dye tracer injected into the bottom boundary layer at the foot of the front from the three day displacement and dispersion of two dye injections within the front we infer lagrangian isopycnal diapycnal velocities and diffusivities of 2 x 10 2 m s 4 x 10 6 m s and 9 m 2 s 6 x 10 6 m 2 s these results substantiate model predictions of chapman and lentz 1994 and previous dye tracer observations by houghton 1997

probing the status of felsic magma reservoirs constraints from the p t h 2 o dependences of electrical conductivity of rhyolitic melt electrical conductivity of rhyolitic melts combined with magnetotelluric data can provide important constraints for the physicochemical conditions of active felsic magma reservoirs previous experimental investigations are limited to low h2o concentration 3 wt h2o and low pressure 0 2 gpa for hydrous melts we here report new results from electrical conductivity measurements of peralkaline rhyolitic melts with 4 7 wt na2o and 0 1 7 9 wt h2o at 868 1665 k and 0 5 1 0 gpa in piston cylinder apparatuses using sweeping frequency impedance analyses logarithmic electrical conductivity is found to correlate linearly with h2o concentration and reciprocal temperature and the influence of h2o has been considerably underestimated by previous work the negative pressure effect on electrical conductivity appears to attenuate with increasing h2o concentration based on the new data we develop the following electrical conductivity model for peralkaline rhyolitic melts under conditions up to 1665 k 1 0 gpa and 8 wt h2o log 2 983 0 0732w 3528 233 8w 763 7 5w2 pt where is electrical conductivity in s m t is temperature in k w is h2o concentration in wt and p is pressure in gpa according to the nernst einstein relation this conductivity model can also be applied to metaluminous and peraluminous rhyolitic melts by scaling down according to the diffusivity and concentration of na the primary charge carrier with the new model we suggest that the highest electrical anomaly beneath the tianchi volcano corresponds to a melt fraction of 9 if the melt contains 5 wt h2o or to a melt fraction of 32 for 2 wt h2o similarly the magma reservoir beneath the taupo volcanic zone new zealand is inferred to contain a fully molten rhyolite with 7 5 wt h2o or 36 water saturated melt with 10 wt h2o

tomography from 26 years of seismicity revealing that the spatial extent of the yellowstone crustal magma reservoir extends well beyond the yellowstone caldera the yellowstone volcanic field has experienced three of earth s most explosive volcanic eruptions in the last 2 1 ma the most recent eruption occurred 0 64 ma forming the 60 km long yellowstone caldera we have compiled earthquake data from the yellowstone seismic network from 1984 to 2011 and tomographically imaged the three dimensional p wave velocity vp structure of the yellowstone volcanic system the resulting model reveals a large low vp body interpreted to be the crustal magma reservoir that has fueled yellowstone s youthful volcanism our imaged magma body is 90 km long 5 17 km deep and 2 5 times larger than previously imaged the magma body extends 15 km ne of the caldera and correlates with the location of the largest negative gravity anomaly a 80 mgal gravity low this new seismic image provides important constraints on the dynamics of the yellowstone magma system and its potential for future volcanic eruptions and earthquakes

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

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

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

imaging the magmatic system beneath the krafla geothermal field iceland a new 3 d electrical resistivity model from inversion of magnetotelluric data

evidence for a persistent magma reservoir with large melt content beneath an apparently extinct volcano abstract most active volcanoes display eruption frequencies of 10 1000s years but a class of volcanic systems has extremely long repose time 10 s kyr and are deemed as extinct yet some reawaken posing a particular threat because little is known about the way they endure and stir back to life reawakening primarily depends on the nature of the subvolcanic magma reservoir especially the presence and distribution of melt here we integrate petrology thermobarometry thermomechanical models geophysics and in situ electrical conductivity measurements to show that the magma storage beneath ciomadul a seemingly inactive volcano in eastern central europe that last erupted 30 ka may still hold 20 to 58 km3 of water rich silicic melt constituting up to 20 58 in parts of the upper crustal crystal mush body such a melt volume exceeds the volume of erupted lava over the entire history of the volcano this illustrates the important longevity of a magmatic reservoir at temperature above the solidus which implies that there is still a potential for rapid mush rejuvenation that a seemingly dead volcano like ciomadul is actually capable of erupting in the future calls for renewed attention to inactive volcanoes worldwide and perhaps for a redefinition of their activity inactivity status

electrical conductivity of dry and hydrous naalsi 3 o 8 glasses and liquids at high pressures we report the first study of electrical conductivities of silicate melts at very high pressures up to 10 gpa and temperatures up to 2 173 k impedance spectroscopy was applied to dry and hydrous albite naalsi3o8 glasses and liquids with 0 02 5 7 wt h2o at 473 1 773 k and 0 9 1 8 gpa in a piston cylinder apparatus using a coaxial cylindrical setup measurements were also taken at 473 2 173 k and 6 10 gpa in two multianvil presses using simple plate geometry the electrical conductivity of albite melts is found to increase with temperature and water content but to decrease with pressure however at 6 gpa conductivity increases rapidly with temperature above 1 773 k so that at temperatures beyond 2 200 k conductivity may actually increase with pressure moreover the effect of water in enhancing conductivity appears to be more pronounced at 6 gpa than at 1 8 gpa these observations suggest that smaller fractions of partial melt than previously assumed may be sufficient to explain anomalously high conductivities such as in the asthenosphere for dry melt at 1 8 gpa the activation energy at t 1 073 k is higher than that at t 1 073 k and the inflection point coincides with the rheological glass transition upon heating at 6 10 gpa dry albite glass often shows a conductivity depression starting from 1 173 k due to crystallization followed by rapid conductivity enhancement when temperature approaches the albite liquidus for hydrous melts at 0 9 1 8 gpa the activation energies for conductivity at 1 373 k are lower than those at 973 k with a complex transition pattern in between electrical conductivity and previously reported na diffusivity in albite melt are consistent with the nernst einstein relation suggesting the dominance of na transport for electrical conduction in albite melts

electrical conductivity of hydrous andesitic melts pertinent to subduction zones andesitic magmatism and rocks are widespread at convergent plate boundaries electrically conductive bodies beneath subduction zone arc volcanoes such as the uturuncu volcano bolivia may correspond to active reservoirs of h2o bearing andesitic magma laboratory measurements of electrical conductivity of hydrous andesitic melts are required to constrain the physicochemical conditions of these magma reservoirs in combination with magnetotelluric data this experimental study investigates electrical conductivity of andesitic melts with 0 01 5 9 wt of h2o at 1164 1573 k and 0 5 1 0 gpa in a piston cylinder apparatus using sweeping frequency impedance spectroscopy electrical conductivity of andesitic melt increases with increasing temperature and h2o concentration but decreases with pressure across the investigated range of h2o concentration electrical conductivity varies by 1 2 2 4 log units indicating stronger influence of h2o for andesitic melt than for rhyolitic and dacitic melts using the nernst einstein equation the principal charge carrier is inferred to be na in anhydrous melt but divalent cations in hydrous andesitic melts the experimental data are regressed into a general electrical conductivity model for andesitic melt accounting for the pressure temperature h2o dependences altogether modeling results show that the conductive layer at 20 km depths beneath the surface of the uturuncu volcano could be interpreted by the presence of less than 20 vol of h2o rich andesitic melt with 6 9 wt h2o

variability of physical and chemical characteristics along the 70 m isobath of the southeastern bering sea abstract from observations of ice cover temperature salinity currents and nitrate it is evident that along shelf variability was significant over the middle shelf of the eastern bering sea but less distinct than that observed in the cross shelf domains along the 70 m isobath three zones were evident in the summer the southeastern cold pool centered at 57 n an intermediate zone consisting of warmer water with weaker stratification and the northern cold pool extending northward from 58 n small scale 20 km horizontal features that persisted for months were common nutrient concentrations were related to salinity and were replenished more uniformly over the southern shelf than north of the pribilof islands although mean currents were weak 1 cm s 1 short energetic advective events impacted the temperature and salinity structure

investigations of internal gravity waves using three vertically directed closely spaced wind profilers a network of three wind profilers spaced about 5 km apart was operated in southern france during the alpine experiment alpex program the wind profilers measured vertical motions and the experiment was designed to study traveling internal waves by comparing the vertical velocity fluctuations observed at each station the measured phase velocities together with the observed periods were used to deduce the horizontal wavelength of the waves only a relatively few cases of monochromatic waves could be identified using this array most of the waves that were detected had phase velocities opposite to the prevailing wind and had the speeds required to cause trapping as the intrinsic frequency was doppler shifted upward to the brunt vaisala frequency

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

supercritical fluids at subduction zones evidence formation condition and physicochemical properties abstract there is a general consensus that at subduction zones mass transfer from the subducted slab to the overlying mantle wedge is mediated by a hydrous mobile phase however it is under intense debate whether this phase is an aqueous fluid hydrous silicate melt or supercritical fluid with intermediate composition h 2 o concentration in the range of 30 wt 70 wt supercritical fluids with fluid like viscosity and melt like wetting and element carrying capability are an ideal agent for chemical transport at subduction zones after clarifying the phase relations of silicate h 2 o systems and the definition of supercritical fluids this contribution reviews existing evidence for the presence of supercritical fluids at subduction zones mostly from experimental investigation of phase relations of mineral h 2 o and rock h 2 o systems and the atomic structure and physicochemical properties of supercritical fluids h 2 o rich multi phase solid inclusions from continental subduction zones once their bulk water contents can be confirmed may provide a direct record of supercritical fluids experimental results generally indicate that supercritical fluids can derive from the slab at 160 km depth but there is still significant discrepancy between different studies on h 2 o saturated solidus fluid melt critical curve and the second critical end point scep some novel experimental methods are proposed to resolve the controversies over the formation condition of supercritical fluids the special physicochemical properties of supercritical fluids arise fundamentally from their intermediate composition and intermediate degree of polymerization that are distinctive from aqueous fluids or silicate melts probing the structure and properties of supercritical fluids which are required for understanding of their petrological and chemical behavior and geophysical characteristics relies mainly on in situ spectroscopy but first principles molecular dynamics is becoming a potentially powerful alternative approach

vertical wind variability observed by vhf radar in the lee of the colorado rockies abstract during march 1981 the sunset and platteville vhf clear air radars located in colorado to the east of the continental divide observed vertical winds continuously over a three week period the vertical winds at these locations contain fluctuations with periods from a few minutes to several hours and with magnitudes ranging up to a few meters per second the sunset radar which is located in the foothills observed systematically larger vertical velocities than the vertical velocities observed by the platteville radar which is located on the plains some 60 km to the east although periods of enhanced vertical wind activity were observed to occur at the same time at both sites attempts to correlate vertical wind structures over the two sites in detail were generally not successful the magnitude of vertical velocity fluctuations seen by both radars show large day to day variations with active periods alternating with quiet periods an examination of upper level maps reveals that the occurrence

mechanisms for vertical nutrient transport within a north atlantic mesoscale eddy abstract prompted by observational evidence for an enhanced source of surface nutrients within an anticyclonic eddy in the ne atlantic we investigate vertical transport processes that may produce such a phenomenon for the eddy investigated the dominant mechanism is found to be ageostrophic circulation resulting from a perturbation of the circular flow of the eddy this can produce upwelling velocities of order 10 m d 1 ekman pumping due to wind stress on the eddy also produces upwelling within but on a smaller scale of 0 5 m d 1 there is no evidence that self propagation of the eddy leads to an enhanced nutrient flux by displacement upwards of nutrient laden deeper isopycnals over the core of the eddy deeper winter mixing within the eddy relative to the surroundings however may contribute to the elevated nutrient levels

magnetotelluric image of transcrustal magmatic system beneath the tulu moye geothermal prospect in the ethiopian rift

anticyclonic eddies in the alaskan stream abstract anticyclonic eddies propagating southwestward in the alaskan stream as were investigated through analysis of altimetry data from satellite observations during 1992 2006 and hydrographic data from profiling float observations during 2001 06 fifteen long lived eddies were identified and categorized based on their area of first appearance three eddies were present at the beginning of the satellite observations another three formed in the eastern gulf of alaska off sitka alaska and four were first detected at the head of the gulf of alaska near yakutat alaska the other five eddies formed along the as between 157 and 169 w and were named as eddies while the eddies that formed in the gulf of alaska mainly decayed before exiting the gulf of alaska the as eddies mostly crossed the 180 meridian and reached the western subarctic gyre four of five as eddies formed under negative or weakly positive wind stress curls which possibly caused as separation from the coast comparison of eddy propag

characteristics and variability of the inner front of the southeastern bering sea the inner front of the southeastern bering sea shows marked spatial variability in frontal characteristics created by regional differences in forcing mechanisms differences in forcing mechanisms sea ice advance retreat and storm strength and timing and early spring water properties result in strong interannual variability in biological chemical and physical features near the front we have developed a simple model based on surface heat flux and water column mixing to explain the existence of cold belts cont shelf res 19 14 1999 1833 associated with such fronts hydrography fluorescence and nutrient observations show that pumping of nutrients into the euphotic zone occurs and this can prolong primary production at the inner front the effectiveness of this process depends on two factors the existence of a reservoir of nutrients in the lower layer on the middle shelf and the occurrence of sufficient wind and tidal energy to mix the water column

observations of a kenai eddy and a sitka eddy in the northern gulf of alaska 1 mesoscale eddies in the gulf of alaska are thought to contribute to the shelf slope exchange of nutrients and plankton enhancing biological production we report on a study of two anticyclonic mesoscale eddies in this region observed through in situ sampling during august and september 2007 both eddies exhibited in their cores s profiles with warmer fresher water relative to the properties of the ambient basin water between 150 and 300 m depths hydrographic properties and satellite altimetry data were analyzed to identify likely formation regions for each feature one eddy sampled near yakutat alaska originated in the sitka formation region 221 223 e the second eddy sampled south of kodiak island originated near the kenai peninsula southeast of the kennedy and stevenson entrances to cook inlet an area not previously studied as a formation region subsequent analysis of 16 years of satellite altimeter data from 1992 to 2008 with an algorithm designed to identify and track eddies revealed approximately six kenai eddies that have formed in this region although this number constitutes only 3 2 of the 188 eddies identified by the algorithm during this period it represents 15 4 of the 39 eddies that formed in or propagated westward into the alaskan stream

average vertical motions in the tropical atmosphere observed by a radar wind profiler on pohnpei 7 n latitude 157 e longitude abstract average vertical profiles of the vertical wind obtained under clear sky conditions as weal as under conditions of both light to moderate and heavy rainfall am presented from data obtained using a radar wind profiler located on the island of pohnpei latitude 7 n longitude 157 e the average profiles for the precipitation conditions were obtained insofar as possible under conditions similar to those present within the stratiform and convective regions of tropical mesoscale convective complexes comparison between the vertical wind profiles obtained from the wind profiler and vertical wind profiles obtained earlier by wore conventional methods i e deduced from the convergence divergence of mesoscale horizontal winds shows that while the general features of the profiles obtained by both techniques are similar the profiler results exhibit somewhat more detail the profiler is able to resolve long term average vertical motions down to the cm s 1 subsidence that occurs under clear air condi

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

southeast alaskan shelf from southern tip of baranof island to kayak island currents mixing and chlorophyll a abstract during 2011 and 2013 an integrated ecosystem study was undertaken on the southeast alaska shelf and slope as part of that study a total of 8 moorings were deployed each year along the coast of baranof and chichagof islands in cross sound and at icy point in addition 18 satellite tracked drifters were deployed during the two field years the goals of this manuscript are to describe the coastal currents in southeastern alaska the processes affecting them and how the physics modify the nutrients and primary production in the region mixing in cross sound is an important source of nutrients for the shelf north of the sound resulting in prolonged production during summer while the alaska coastal current is not a continuous feature along the entire gulf of alaska coast it does exist from southern tip of baranof island to cross sound and again northwest of yakutat the narrowness of this shelf coupled with the meanders and eddies in the alaska current result in large amounts of on shelf flow of slope water and off shelf flow of coastal water while local currents and summer winds were similar in 2011 and 2013 2011 was characterized by low chlorophyll a concentrations throughout the spring summer while chlorophyll concentrations in 2013 were typical the cause of this difference remains unclear but bottom up processes likely contributed to the low chlorophyll a concentrations in 2011

a note on cross shelf exchange in the northern gulf of alaska the continental shelf of the gulf of alaska goa is a complex system characterized by large freshwater runoff and strong winds the goa supports one of the world s richest ecosystems including numerous species of fishes marine mammals and sea birds the mechanisms that provide nutrients to support this ecosystem are not well understood the rivers and streams that provide freshwater to the shelf are low in nitrate and the regional winds favor downwelling high concentrations of nitrate are available in the deep basin of the goa but these must be introduced to the shelf in order to support the high productivity we present evidence for cross shelf exchange due to three different mechanisms episodes of downwelling relaxation result in a flux of saline nutrient rich water onto the shelf at depth eddies formed in the northeastern goa propagate along the shelf break influencing cross shelf exchange by carrying shelf origin water from the formation region into the basin and by interacting with the shelf break circulation bathymetric steering in the many canyons that incise the goa shelf results in flow into the canyons where strong tidal mixing results in cross isobath movement of water properties

low frequency isopycnal variability in the alaska gyre from argo abstract the deployment of a large number of argo floats in the northeast pacific ocean since 2001 has led to a great increase in the volume of data available to study the regional variability on interannual to decadal time scales in this paper gridded fields of hydrographic data from argo are used to examine the low frequency variability of representative isopycnal surfaces over the alaska gyre in the eastern subpolar north pacific anomalies in the depth of isopycnal surfaces and spice anomalies on these surfaces are considered over the 14 year period 2004 2017 an eof analysis is used to characterize the variability occurring at large scales over the region the leading mode of isopycnal depth anomalies through the upper 1000 m of the water column is found to be related to the pacific decadal oscillation the response of a stochastic climate model driven by local ekman pumping is shown to give a reasonable account of variability in the depth of the shallow main pycnocline over the alaska gyre although ocean dynamics must play a role in shaping the spatial response to the wind forcing evidence is presented for counter propagating isopycnal depth anomalies in the subarctic current at the depth of the main pycnocline propagation is dominated by disturbances that are advected eastward by the mean flow at greater depths isopycnal depth anomalies propagate westward at approximately twice the speed of first mode long baroclinic rossby waves consistent with the propagation of rossby waves seen in altimetric observations of sea surface height variability the eastward advection of spice anomalies is also evident in the upper ocean however the dominant signal in the record is a large scale positive spice anomaly that forms locally on subsurface isopycnals evidence is presented that this anomaly arises mainly from the downward diffusion across the pycnocline of heat associated with the marine heatwave of 2013 14 over the northeast pacific the extent to which anomalies are generated locally may limit the potential for decadal prediction of upper ocean conditions over the region