mesoscale model experimental forecasts of the haar of northeast scotland abstract a mesoscale model is used to simulate the diurnal evolution of sea fog off the northeast scottish coast observed on 27 april 1984 it is shown that the accuracy of the early part of the forecast is very dependent on the specification of the initial conditions if the initial description of the fog is sufficiently good the model can accurately erode it during the day and reform it in the following evening the dependence of the accuracy of the forecasts on vertical resolution is also discussed

submarine landforms and shallow acoustic stratigraphy of a 400 km long fjord shelf slope transect kangerlussuaq margin east greenland kangerlussuaq fjord is a relatively uniform steep walled basin whose floor has an almost smooth surface debris is supplied mainly from icebergs from the fast flowing kangerlussuaq glacier sedimentation after iceberg release from multi year sea ice is mainly by rain out of fine grained englacial debris streamlined glacial lineations and drumlins were produced at the sedimentary bed of an ice sheet that expanded into kangerlussuaq trough at the last glacial maximum lgm bedrock channels and crescentic overdeepenings indicate warm based ice and free water beneath parts of the former ice sheet cross cutting iceberg scour marks which characterise outer kangerlussuaq shelf were produced not only during deglaciation but also occasionally through the holocene by deep keeled icebergs from further north in east greenland the outward convex contours of the shelf edge and slope beyond kangerlussuaq trough and debris flows on the slope suggest a glacier influenced high latitude fan the distribution of streamlined subglacial landforms demonstrates that the greenland ice sheet extended throughout kangerlussuaq fjord and reached at least 200 km across the shelf in kangerlussuaq trough at the lgm streamlined landform orientation indicates ice flow from the interior of greenland down the axis of kangerlussuaq trough there is little evidence for discrete sedimentary depocentres in the trough implying that ice probably retreated rapidly from the outer and mid shelf during deglaciation

hydrography and energetics of a cold subpolar fjord andvord bay western antarctic peninsula abstract fjords along the western antarctic peninsula contain rich marine ecosystems and tidewater glaciers potentially sensitive to ocean change but much is unknown about the physical oceanography of these fjords this paper presents a comprehensive description of the physical environment of andvord bay a glacial fjord located in the gerlache strait on the northern end of the peninsula measurements were collected as part of the fjordeco program between november 2015 and march 2017 including during three research cruises and from a number of fixed installations sub surface moorings time lapse cameras and automatic weather stations andvord bay is located just north of a sill in the gerlache strait this sill inhibits the direct influence of warm upper circumpolar deep water from the shelf and deep waters in the fjord are therefore relatively cold as a result glaciers in andvord bay are not subject to the substantial ocean driven retreat observed farther south on the peninsula instead mass flux from the glaciers occurs mainly through calving the influence of meltwater in andvord bay is small compared to glacial fjords in the arctic and in the south shetland islands although summer freshening is evident in the fjord near surface layer likely as a result of glacial inputs the combination of surface freshening and the absence of strong mean wind forcing in the fjord results in salinity stratification extending well into the euphotic zone providing advantageous conditions for phytoplankton blooms andvord bay is generally dynamically quiet compared to the ambient ocean with the exception of during local katabatic wind events exchange with the gerlache strait is weak although the deep waters of the fjord are replenished on an annual scale through slow lateral exchange with the outside in addition deep convection may play a role in ventilating subsurface waters in winter

hydrothermal mounds and young ocean crust of the galapagos preliminary deep sea drilling results leg 70 a total of 32 holes at 5 sites near 1 n 86 w drilled on deep sea drilling project dsdp leg 70 november december 1979 provide unique data on the origin of the hydrothermal mounds on the south flank of the galapagos spreading center hydrothermal sediments primarily mn oxide and nontronite are restricted to the immediate vicinity of the mounds 100 m and are probably formed by the interaction of upward percolating hydrothermal solutions with sea water and pelagic sediments above locally permeable zones of ocean crust mounds as much as 25 m in height form in less than a few 10 5 yrs and geothermal and geochemical gradients indicate that they are actively forming today the lack of alteration of upper basement rocks directly below the mounds and throughout the galapagos region indicates that the source of the hydrothermal solutions is deeper in the crust

origin and consequences of cyclic ice rafting in the northeast atlantic ocean during the past 130 000 years deep sea sediment cores recovered from the northeast atlantic ocean were examined in order to elucidate the influence of the earth s orbital parameters on major ice rafting analyses of coarse grained ice rafted debris and planktonic foraminifers revealed a strong reaction to the precession signal since 130 000 yr b p dropstone layers have been deposited each half period of a precessional cycle 11 000 1000 yr ice rafting occurs during times of winter minimum summer maximum insolation and summer minimum winter maximum insolation in the first case high summer insolation forces meltwater discharge from the ice sheets into the polar seas which subsequently enhances formation of sea ice during the winter in the second case growth of continental ice enhances iceberg production which also leads to a salinity reduction of surface seawater both situations result in a southward penetration of polar water thus the marine record of dropstones documents ice rafting not only during weichselian stades but also during cold events within interstades the regularity of ice rafting yields a useful framework to calibrate and elucidate climatic changes not only in the region of the north atlantic ocean but also in remote areas such as the pacific ocean and the antarctic

numerical simulation of the stratus to cumulus transition in the subtropical marine boundary layer part i boundary layer structure abstract a stratus to cumulus transition sct that resembles observations occurred in lagrangian numerical simulations of the subtropical marine boundary layer over the northeastern pacific ocean southwest of california the lagrangian approach involves translating the domain along the climatological boundary layer trajectory at a rate equal to the observed surface wind speed the sst is increased at a corresponding rate the simulations did not include drizzle the diurnal cycle divergence changes or mesoscale circulations and thus demonstrate that these processes are not essential for an sct a 2d numerical cloud model that can explicitly represent large convective eddies is used turbulence at scales smaller than the large eddies is parameterized using a third moment turbulence closure this type of model requires no cloud regime specific input and is computationally economical for multiday simulations the results suggest that there are four stages in the transition from the stratus topped boundary

lagrangian evolution of the northeast pacific marine boundary layer structure and cloud during cset abstractflight data from the cloud system evolution over the trades cset campaign over the pacific stratocumulus to cumulus transition are organized into 18 lagrangian cases suitable for study an

influence of glacial water and carbonate minerals on wintertime sea ice biogeochemistry and the co2 system in an arctic fjord in svalbard the effect of freshwater sources on wintertime sea ice co2 processes was studied from the glacier front to the outer tempelfjorden svalbard in sea ice glacier ice brine and snow march april 2012 was mild and the fjord was mainly covered with drift ice in contrast to the observed thicker fast ice in the colder april 2013 this resulted in different physical and chemical properties of the sea ice and under ice water data from stable oxygen isotopic ratios and salinity showed that the sea ice at the glacier front in april 2012 contained on average 54 of frozen in glacial meltwater this was five times higher than in april 2013 where the ice was frozen seawater in april 2012 the largest excess of sea ice total alkalinity at carbonate ion co32 and bicarbonate ion concentrations hco3 relative to salinity was mainly related to dissolved dolomite and calcite incorporated during freezing of mineral enriched glacial water in april 2013 the excess of these variables was mainly due to ikaite dissolution as a result of sea ice processes dolomite dissolution increased sea ice at twice as much as ikaite and calcite dissolution implying different buffering capacity and potential for ocean co2 uptake in a changing climate

wrf hindcasts of cold front passages over the arm eastern north atlantic site a sensitivity study abstractthe present study explores the ability of the weather research and forecasting wrf model to accurately reproduce the passage of extratropical cold fronts at the doe arm eastern north atlantic ena observation site on the azores an analysis of three case studies is performed in which the impact of the wrf domain size position of the model boundary relative to the ena site grid spacing and spectral nudging conditions are explored the results from these case studies indicate that model biases in the timing and duration of cold front passages change with the distance between the model domain boundary and the ena site for these three cases if the western model boundary is farther than 1500 km from the site the front becomes too meridional and fails to reach the site making 1000 or 1500 km the optimal distances in contrast integrations with small distances e g 500 km between the site and domain boundaries have inadequate spatial spinup i e the domain is too small for the model to pr

sediment thicknesses and holocene glacial marine sedimentation rates in three east greenland fjords ca 68 n we compared measured and estimated sediment budgets in heavily glaciated fjords in east greenland mass balance calculations and regional glacio climatic conditions suggest that the sediment flux to the seafloor in kangerdlugssuaq and nansen fjords should be dominated by iceberg rafting and not by the rain out of suspended particulates in meltwater as the glacier calving flux is estimated at 15 and 2 km 3 yr compared to meltwater volumes of 4 4 and 1 7 km 3 yr respectively gravity cores in the three fjords indicate that the uppermost 1 2 5 m of sediment consists of diamictons or fine grained laminated muds ams radiocarbon dates on calcareous foramininfera or shells 16 total indicate sedimentation rates of 110 to 340 cm ka within the fjords over the last 1 ka and 10 20 cm ka during the holecene on the inner and middle shelf annual sediment discharge is around 0 67 times 10 6 tonnes yr within the kangerdlugssuaq fjord and trough system which translates into an average basin wide rate

patterns of ice rafted detritus in the glacial north atlantic 40 55 n the observation by heinrich 1988 that during the last glacial period much of the input of ice rafted detritus to the north atlantic sediments may have occurred as a succession of catastrophic events rekindled interest on the history of the northern ice sheets over the last glacial period in this paper we present a rapid method to study the distribution of these events both in space and time using whole core low field magnetic susceptibility we report on approximately 20 cores covering the last 150 to 250 kyr well defined patterns of ice rafted detritus appear during periods of large continental ice sheet extent although these are not always associated within their maxima most of the events may be traced across the north atlantic ocean for the six most recent heinrich layers hl two distinct patterns exist hl1 hl2 hl4 hl5 are distributed along the northern boundary of the glacial polar front over most of the north atlantic between 40 and 50 n hl3 is more restricted to the central and eastern part of the northern atlantic the nd sr isotopic composition of the material constituting different heinrich events indicates the different provenance of the two patterns hl3 has a typical scandinavia arctic icelandic young crust signature and the others have a large component of northern quebec and northern west greenland old crust material these isotopic results obtained on core su 9008 from the north american basin are in agreement with the study by jantschik and huon 1992 who used k ar dating of silt and clay size fractions of an eastern basin core me 68 89 these data confirm the large spatial scale of these events and the enormous amount of ice rafted detritus they represent

tidal motion ice velocity and melt rate of petermann gletscher greenland measured from radar interferometry over a floating glacier ice tongue or an ice shelf the glacier motion measured by a single repeat pass radar interferogram is difficult to analyze because the long term steady motion of the ice is intermixed with its cyclic downward motion induced by tidal forcing multiple interferograms and a quadruple difference technique are necessary to separate the tidal signal from the long term steady motion of the ice an example of application of this technique is given here using ers 1 radar images of petermann gletscher a major outlet glacier of northern greenland tidal displacements are measured with 5 mm statistical noise the long term ice velocity is measured with a precision of 1 m a 1 the inferred tidal displacements agree well with model predictions from a fixed elastic beam with an elastic damping factor of 0 47 0 01 km 1 the hinge line is mapped with a precision of 20 80 m combining the interferometric ice velocities with ice thickness data the glacier ice discharge is calculated at and below the hinge line at the hinge line the ice flux is 12 1 1 km3 a 1 at the ice front calf ice production is only 0 59 km3 a 1 meaning that 95 of the ice that crosses the grounding line melts before it reaches the calving front assuming steady state conditions the melt rate of the glacier tongue averages 12 1 m a 1 with peak values exceeding 20 m a 1 near the hinge line this high melt rate cannot be accommodated by surface ablation alone only about 2 3 m a 1 and is attributed to pronounced basal melting of the ice tongue basal melting often assumed to be negligible in greenland is the dominant process of mass release from the floating section of petermann gletscher

deglacial meltwater discharge north atlantic deep circulation and abrupt climate change high resolution paleogeochemical data from the north atlantic ocean indicate that in the interval 15 000 to 10 000 14c years before present b p north atlantic deep water nadw production was decreased or eliminated four times at about 14 500 and probably older 13 500 12 000 and 10 500 years b p each of these changes occurred at the same time as abrupt events of meltwater discharge to the surface ocean inferred from oxygen isotope studies of planktonic foraminifera and from glacial geological studies on land in addition each of these times may be associated with brief episodes of cooler climate in the north atlantic region the best example of which is the younger dryas cooling of 10 500 years ago these results support models linking meltwater discharge decreased nadw production and decreased north atlantic heat flux

cloud top entrainment instability mixing processes at cloud boundaries are thought to play a critical role in determining cloud lifetime spatial extent and cloud microphysical structure high fidelity direct numerical simulations by mellado j fluid mech 2010 this issue vol 660 pp 5 36 show for the first time the character and potency of a curious instability that may arise as a result of molecular mixing processes at cloud boundaries an instability which until now has been thought by many to control the distribution of climatologically important cloud regimes

on the growth of colloform textures a case study of sphalerite from the galmoy ore body ireland abstract colloform textures have been described from many of the world9s sulphide ore deposits and involve formation of distinct microcrystalline layers these textures provide information related to sequential stages of ore formation yet their mechanism of growth is poorly understood this study has analysed a series of colloform samples from the galmoy zn pb mine ireland results indicate that the growth sequence is not always intuitive and layers that appear stratigraphic upon cursory observation may not be the crystal preferred orientation cpo of discrete colloform layers abruptly switches between different orientation axes examination of the same layers using in situ laser sulphur isotope analysis reveals equally striking changes in 34 s signature between end member bacteriogenic 25 and hydrothermal 10 sources although these results combined with petrographic observation allow the determination of a probable growth history there is no correlation between shifting cpo and 34 s signature trace element analysis reveals changes in trace element sequestration between colloform layers cadmium and chlorine rich layers correspond to a hydrothermal sulphur source whereas iron rich layers correspond to a bacteriogenic sulphur source in the absence of alternative mechanisms we suggest that the most likely factors influencing cpo changes are temperature and degree of supersaturation during two fluid mixing

an extreme cold air outbreak over the labrador sea roll vortices and air sea interaction abstract observational data from two research aircraft flights are presented the flights were planned to investigate the air sea interaction during an extreme cold air outbreak associated with the passage of a synoptic scale low pressure system over the labrador sea during 8 february 1997 this is the first such aircraft based investigation in this remote region both high level dropsonde and low level flight level data were collected the objectives were twofold to map out the structure of the roll vortices that cause the ubiquitous cloud streets seen in satellite imagery and to estimate the sensible and latent heat fluxes between the ocean and atmosphere during the event the latter was achieved by a lagrangian analysis of the flight level data the flights were part of the labrador sea deep convection experiment investigating deep oceanic convection and were planned to overpass a research vessel in the area the aircraft observed roll vortices had a characteristic wavelength of 4 5 km particular

a new parameterization for shallow cumulus convection and its application to marine subtropical cloud topped boundary layers part i description and 1d results abstract a new parameterization of shallow cumulus convection is presented the parameterization consists of a mass flux scheme based on a buoyancy sorting entrainment detrainment plume model the mass flux scheme is coupled to a 1 5 order turbulence closure model with an entrainment closure for convective boundary layers model performance is verified using single column model simulations at relatively high vertical resolution of pure trade cumulus convection and a cumulus to stratocumulus transition mixing rates cloud cover and vertical flux profiles as deduced from previously published large eddy simulation studies are well reproduced by the parameterization the model is used to demonstrate that height variations of lateral mixing rates can be successfully captured by a simple implementation of a buoyancy sorting mechanism in the updraft cloud model a companion paper describes the implementation of the scheme in a mesoscale model

a continental outbreak of air during the second aerosol characterization experiment ace 2 a lagrangian experiment a mesoscale meteorological model is used to simulate the continental outbreak of air that occured over north atlantic ocean during the second aerosol characterization experiment ace 2 comparison with meteosat 6 visible images shows that the model is able to reproduce most of the observed cloud features in the entire modeling domain including a frontal system orographic clouds over the pyrenees and the iberian peninsula boundary layer clouds in the ace 2 region and cloud free areas in the dry air outflow off the portuguese coast the model reproduces correctly the temperature humidity wind speed and direction cloud water content and light precipitation events observed by the aircraft during the lagrangian experiment while following a tagged boundary layer air parcel over a 28 hour long period a passive tracer introduced in the model at the time corresponding to the balloon launch followed the balloon track with an error in position that is smaller than 1 after 24 hours with about 20 higher speed an estimate of the boundary layer entrainment velocity is obtained based on observed boundary layer growth rates and modeled vertical wind speed the average entrainment velocity of 1 28 cm s for the 28 hour lagrangian period agrees with experimentally derived entrainment velocities

steady state large eddy simulations to study the stratocumulus to shallow cumulus cloud transition abstractthis study presents a series of steady state large eddy simulations less to study the stratocumulus to shallow cumulus cloud transition to represent the different stages of what can be interpreted as an eulerian view of the transition each simulation is assigned a unique sea surface temperature sst and run until statistically steady the les runs are identical in every other aspect these idealized boundary driven steady state less allow for a simple parametric assessment of cloud controlling factors in isolation from initial conditions and time lag effects inherent in the lagrangian view of the transition the analysis of the thermodynamic energy budget reveals that as the cloud regime transitions from stratocumulus to shallow cumulus changes in the cloud radiative cooling term are balanced by changes in the subsidence warming term this leads to a linear regression between the cloud fraction cf and an integral that scales to a first order approximation as the lower tropospheric stabi

evidence for massive discharges of icebergs into the north atlantic ocean during the last glacial period sediments in the north atlantic ocean contain a series of layers that are rich in ice rafted debris and unusually poor in foraminifera1 here we present evidence that the most recent six of these heinrich layers deposited between 14 000 and 70 000 years ago record marked decreases in sea surface temperature and salinity decreases in the flux of planktonic foraminifera to the sediments and short lived massive discharges of icebergs originating in eastern canada the path of the icebergs clearly marked by the presence of ice rafted detrital carbonate can be traced for more than 3 000 km a remarkable distance attesting to extreme cooling of surface waters and enormous amounts of drifting ice the cause of these extreme events is puzzling they may reflect repeated rapid advances of the laurentide ice sheet perhaps associated with reductions in air temperatures yet temperature records from greenland ice cores appear to exhibit only a weak corresponding signal moreover the 5 10 000 yr intervals between the events are inconsistent with milankovitch orbital periodicities raising the question of what the ultimate cause of the postulated cooling may have been

submersible observations of hydrothermal manganese deposits on the kaikata seamount izu ogasawara bonin arc abstract during dive 408 of shinkai 2000 on the flank of the kaikata seamount located on the volcanic front of the izu ogasawara bonin arc possibly recent hydrothermal manganese deposits were observed on sandy volcanic sediments at water depths of between 800 and 1200 m the deposits cover almost the entire surface sediment across the manganese belt on the northwestern flank on the seamount on a scale of kilometers the occurrence of the deposits seafloor morphology and temperature of the sediments together with previous shipboard results lead to a possible model for the formation of the manganese deposits a low temperature hydrothermal solution ascends through fractures or faults in the volcanic substrate into permeable volcanic sands and precipitates manganate minerals which cement several centimeters of surface sand as hardpan more intense and probably intermittent discharge of hydrothermal solution follows and forms many typical ridge like vents and mounds on the seafloor subsequently pure dense manganate layers developed beneath the semi consolidated volcanic sandstone and act as a cap to the ascending fluids the proposed mechanism may be the dominant type of low temperature hydrothermal mineralization in submarine island arc volcanoes and rifts similar hydrothermal manganese deopsits most probably occur in other active areas of the modern seafloors and in inactive island arcs

iceberg discharges into the north atlantic on millennial time scales during the last glaciation high resolution studies of north atlantic deep sea cores demonstrate that prominent increases in iceberg calving recurred at intervals of 2000 to 3000 years much more frequently than the 7000 to 10 000 year pacing of massive ice discharges associated with heinrich events the calving cycles correlate with warm cold oscillations called dansgaard oeschger events in greenland ice cores each cycle records synchronous discharges of ice from different sources and the cycles are decoupled from sea surface temperatures these findings point to a mechanism operating within the atmosphere that caused rapid oscillations in air temperatures above greenland and in calving from more than one ice sheet

cloudiness and marine boundary layer dynamics in the astex lagrangian experiments part i synoptic setting and vertical structure abstract a goal of the atlantic stratocumulus transition experiment astex southeast of the azores islands in the east central atlantic ocean during june 1992 was to examine the coupled evolution of cloud dynamical and thermodynamical vertical structure in a marine boundary layer mbl air mass as it advected from cold to warm water in the trade winds in two lagrangian observation periods during astex an unprecedentedly complete view of mbl and cloud evolution was achieved by nearly continuous aircraft coverage of such an air mass for 36 48 hours using three boundary layer aircraft supplemented by satellite ship and balloon observations during the first lagrangian period an accelerated stratocumulus to trade cumulus transition occurred in a clean marine air mass in the second lagrangian period a 200 hpa deep decoupled modified continental mbl persisted with almost no change in structure cumulus rising into intermittent stratocumulus were observed throughout the period the two contrasting a

ice distal upper miocene marine strata from inland antarctica abstract glacimarine strata of the battye glacier formation 130 m thick pagodroma group exposed in the amery oasis of east antarctica provide a record of late miocene palaeoenvironmental conditions in an ice distal setting the formation overlies the amery erosion surface 300 m to 270 m above sea level that formed during an advance of the lambert glacier into prydz bay odp site 739 at least 750 km further north than today two lithological members a grey and muddier lower member and a brown sand rich upper member reflect variation in proximity to the terminus of the lambert glacier ice distal glacimarine diatom bearing mud up to 12 biogenic silica and in situ articulated molluscs occur in the lower member the battye glacier formation is significant because of its inland location which indicates that ice distal marine conditions existed 250 km inland from the current amery ice shelf edge similar neogene strata are known on land only from the pliocene sorsdal formation in the vestfold hills near the antarctic coast three stratigraphic intervals of diatom bearing mud are recognized from glacially reworked clasts and from in situ strata informally referred to as the mcleod beds and bed a the diatom bearing mud also contains sponge spicules and minor silicoflagellates and ebridians marine diatom biostratigraphy constrains the age of the beds to between 10 7 and 9 0 ma late miocene abundant benthic diatoms suggest deposition within shallow euphotic waters the high abundance of intercalary valves of eucampia antarctica from an interval of the mcleod beds suggests that there was less winter sea ice than in prydz bay today it is unlikely that sea ice was perennial because the presence of thalassionema spp and stellarima stellaris roper hasle et sims suggests that summer sea surface temperatures were too warm 0 c and 3 c respectively the palaeoclimate at the time of deposition appears to have been analogous to that in modern fjords of east greenland e g kangerdlugssuaq fjord which is consistent with the depositional model proposed previously for the pagodroma group the three diatom bearing mud intervals were deposited in the amery oasis 250 km inland of the current amery ice shelf edge when the east antarctic ice sheet was reduced in size relative to today

the structure of gradually transforming marine stratocumulus during the astex first lagrangian experiment summary an analysis of the mean and turbulent structure of the planetary boundary layer is presented using aircraft data obtained during the atlantic stratocumulus transition experiment e rst lagrangian experiment the analysis of the mean vertical structure relies mostly on slant proe le data however part of the analysis also uses socalled porpoise runs in the vicinity of the cloud top the analysis of the turbulence structure utilizes all of the data horizontal eight legs as well as slant proe les and presents both scaled turbulence statistics and a spectral analysis the purpose is to investigate details in the temporal development of the e rst lagrangian experiment and to study the turbulent structure in order to e nd scale relations that can be utilized in improved modelling of the stratocumulus capped boundary layer the hypothesis is that so called cloud decoupling has a signie cant impact on the turbulence scaling the measured cloud water is corrected to become consistent between the two participating aircraft the corrected maximum cloud water is more constant in time than in previous studies of the erst lagrangian it is suggested that previously analysed temporal variability may be an artefact of using two different instruments to measure cloud water the cloud top jump in equivalent potential temperature is positive in the erst three eights sufe ciently large for a stable cloud top but decreases and becomes negative for the last two eights in line with the breaking up of the cloud eeld the upper part of the boundary layer warms and dries more rapidly than the lower suggesting entrainment to be a dominant factor in the development of the cloud the analysis of the porpoise e ight legs illustrates how sharp features at the cloud top inversion are smoothed out while analysing several proe les eight legs or even entire eights rather than normalizing each proe le with the height to the local cloud top scaling of the turbulent e uxes and the velocity variances shows that the cloud layer is decoupled throughout almost the entire erst lagrangian it is also shown that while surface layer scaling is appropriate for the marine atmospheric boundary layer mabl the cloud layer turbulence scales with convective scaling the lowfrequency spectrum has no spectral gap with the exception of the vertical velocity and continues to increase with decreasing frequency with only a change in slope this indicates the presence of mesoscale motions the cospectra of the turbulent euxes are very noisy throughout when averaging several spectra into height intervals the scales of the turbulence as indicated by the peak in the averaged spectra appear to vary with height above the surface in the mabl but to be height independent in the cloud layer an attempt to calculate a dissipation length scale shows scatter but is consistent with a dissipation length scale increasing linearly with height in the mabl but being roughly constant or possibly parabolic with height in the cloud layer

diagnosing monthly mean boundary layer properties from reanalysis data using a bulk boundary layer model abstract the mixed layer approach to modeling the planetary boundary layer pbl is particularly well suited to inversion topped pbls such as the stratocumulus topped boundary layer found off the west coast of america in the subtropical pacific ocean at northern and southern latitudes however a strong temperature inversion near 850 hpa the trade wind inversion is not confined to the stratocumulus regimes but has been observed over most parts of the subtropical tropical pacific ocean in this paper the authors test the ability of a simple bulk boundary layer model bblm to diagnose entrainment velocity cumulus mass flux and surface latent heat flux from monthly mean reanalysis data the pbl depth is estimated from geoscience laser altimeter system data the model is based on the conservation equations for mass total water mixing ratio and moist static energy the bblm diagnoses entrainment velocities between 1 and 8 mm s 1 in the stratocumulus and trade wind regions with increasing rates towar

comparative mineralogy and geochemistry of gold bearing sulfide deposits on the mid ocean ridges a comparative study of the mineralogy and geochemistry of sulfide deposits on mid ocean ridges in the northeast pacific and the mid atlantic reveals common characteristics associated with primary gold enrichment average gold contents of 0 8 to 5 ppm au occur in sulfides from southern explorer ridge and axial seamount northeast pacific and from the tag hydrothermal field and snakepit vent field mid atlantic ridge the enrichment of gold in these deposits is consistently related to a phase of late stage low temperature 1 ppm au occur exclusively in pyritic assemblages and commonly with abundant fe poor sphalerite and a suite of complex pb sb as sulfosalts amorphous silica and locally barite or carbonate are important constituents of the gold rich precipitates but do not contain gold themselves high temperature 350 c black smoker assemblages consisting dominantly of pyrite chalcopyrite pyrrhotite isocubanite and abundant anhydrite are uniformly gold poor 0 2 ppm au to the extent that individual sulfides can be mechanically separated chemical analyses by neutron activation indicate that gold is most abundant in sphalerite up to 5 7 ppm au but also occurs in pyrite and marcasite samples of sphalerite with abundant inclusions of fine grained sulfosalts locally contain up to 18 ppm au suggesting that sulfosalts may be repositories for gold no free gold has been observed at 4000 magnification of polished specimens indicating that the gold is present only as submicroscopic inclusions or as a chemical constituent within the sulfides samples from gold rich deposits in the northeast pacific and mid atlantic are compared with similar but relatively gold poor sulfides from the galapagos rift and 13 n on the east pacific rise epr and with barren sulfides from 11 n epr 21 n epr the endeavour ridge and the southern juan de fuca ridge trace element analyses of more than 170 samples show that gold enrichment in almost all of the deposits is associated with high concentrations of ag as sb pb and zn and locally with high cd hg tl and ga in contrast gold is typically depleted in samples with high co se and mo the close association of au with ag as sb and pb may reflect the common behavior of these metals as aqueous sulfur complexes e g au hs 2 at low temperatures similar mineralogical and geochemical associations are observed in sulfide deposits from modern back arc settings and in the ancient geologic record

oceanographic and physiographic controls on modern sedimentation within antarctic fjords physical oceanographic data and modern surface sediments were collected from eleven fjords along the western side of the antarctic peninsula and south shetland islands surface sediment samples 62 were analyzed for texture and total organic carbon content the distribution of biogenic and terrigenous facies within the fjords is controlled by bay geometry and oceanographic regime climate plays a secondary role but along with ice drainage basin size controls the rate of terrigenous supply to the glacial marine environment specifically fjords along the danco coast and palmer archipelago with a high length to width ratio tend to have bottom sediments that are arenaceous where ice rafted sediment is released preferentially at the head of the fjord biogenic facies are favored where the bay geometry is complex where such complexity exists separate oceanographic regimes develop that lead to separation of terrigenous and biogenic sediments processes of interflow mid and deep water turbid cold tongues and coriolis deflection produce terrigenous facies along the inner fjord and western edges of a fjord system warm outer bay waters tend to develop a stable eddy circulation pattern that favors the productivity of phytoplankton in the surface layers outer bays are therefore floored with organic rich siliceous muds and ice rafted material only in the south shetland islands is melt water input significant enough to generate estuarine circulation within the fjord but here strong bottom currents result in arenaceous bottom sediments with no biogenic facies ice rafted diamictons are produced proximal to the edges of small tide water glaciers in the south shetlands the facies relationships established in this study provide a strong reference for paleoclimatic studies that utilize downcore measurements of texture and organic carbon

influence of melting icebergs on distribution characteristics and transport of marine particles in an east greenland fjord a detailed study of distribution of suspended sediments in an east greenland fjord with a high iceberg production rate reveals the existence of intermediate nepheloid layers inls observed inls extended from the head to the mouth of the fjord at water depths between 100 and 400 m particulate organic carbon and nitrogen chlorophyll a and nutrient measurements and observation by microscope and energy dispersive x ray analyses were used to characterize marine particles particles in the inls are composed of glacial flour including 50 m quartz and feldspar grains with angular and sharp edges considered to be released from melting icebergs in situ photographs show large aggregates 1 mm at high concentration 300 particles per liter in and below inls these aggregates in comparison with the dispersed particle size distribution demonstrate that smaller size particles e g clay settle effectively along with larger single size grains in kangerlugssuaq fjord the mass transport of marine particles was governed by the subsurface iceberg melting producing observed inls rather than the surface meltwater plume this suggests that the subsurface water temperature controls release of iceberg debris and the existence of warm subsurface water as well as the spread of cold and fresh water in the surface layer needs to be considered to evaluate the occurrence of ice rafted debris layers including heinrich layers this study provides the field evidence of a modern analogue on ocean conditions that could form iceberg rafted layers

finescale structure and microphysics of coastal stratus observations were made of unbroken marine stratus off the coast of oregon using the combined capabilities of in situ probes and a 95 ghz radar mounted on an aircraft reflectivity and doppler velocity measurements were obtained in vertical and horizontal planes that extend from the flight lines data from three consecutive days were used to examine echo structure and microphysics characteristics the clouds appeared horizontally homogeneous and light drizzle reached the surface in all three cases radar reflectivity is dominated by drizzle drops over the lower two thirds to four fifths of the clouds and by cloud droplets above that cells with above average drizzle concentrations exist in all cases and exhibit a large range of sizes the cells have irregular horizontal cross sections but occur with a dominant spacing that is roughly 1 2 1 5 times the depth of the cloud layer doppler velocities in the vertical are downward in all but a very small fraction of the cloud volumes the cross correlation between reflectivity and vertical doppler velocity changes sign at or below the midpoint of the cloud indicating that in the upper parts of the clouds above average reflectivities are associated with smaller downward velocities this correlation and related observations are interpreted as the combined results of upward transport of drizzle drops and of downward motion of regions diluted by entrainment the in situ measurements support these conclusions

high export of dissolved silica from the greenland ice sheet silica is an essential element for marine life and plays a key role in the biogeochemistry of the ocean glacial activity stimulates rock weathering generating dissolved silica that is exported to coastal areas along with meltwater the magnitude of the dissolved silica export from large glacial areas such as the greenland ice sheet is presently poorly quantified and not accounted for in global budgets here we present data from two fjord systems adjacent to the greenland ice sheet which reveal a large export of dissolved silica by glacial meltwater relative to other macronutrients upscaled to the entire greenland ice sheet the export of dissolved silica equals 22 10 gmol si yr 1 when the silicate rich meltwater mixes with upwelled deep water either inside or outside greenland s fjords primary production takes place at increased silicate to nitrate ratios this likely stimulates the growth of diatoms relative to other phytoplankton groups

simulating the transition from drizzling marine stratocumulus to boundary layer cumulus with a mesoscale model a case of coastal california summer season boundary layer cloud has been simulated with the u s navy coupled ocean atmosphere mesoscale prediction system and the results analyzed in the context of consistency with conclusions derived from large eddy simulation based les studies results show a pronounced diurnal cycle and fair agreement with satellite derived observations of liquid water path when drizzle processes are included a significant degree of mesoscale organization emerges in the form of cloud bands accompanied by a transition from a well mixed boundary layer topped by unbroken stratocumulus cloud into a more potentially unstable convective boundary layer regime the transition and the subsequent development of mesoscale variability is analogous to the drizzle induced cloud breakup produced in large eddy simulation studies the dynamics of the pure stratocumulus cloud are dictated by the model s subgrid parameterization while the more convective regime exhibits appreciable vertical velocities characteristic of an ensemble of cumulus updrafts the existence of convective updrafts is tied to a weak drizzle induced decoupling of the cloud and subcloud layer after which air of higher equivalent potential temperature ue can pool at the surface some similarities to the propagation of deep convection are also noted

numerical simulations and a conceptual model of the stratocumulus to trade cumulus transition abstract a two dimensional eddy resolving model is used to study the transition from the stratocumulus topped boundary layer to the trade cumulus boundary layer the 10 day simulations use an idealized lagrangian trajectory representative of summertime climatological conditions in the subtropical northeastern pacific the sea surface temperature is increased steadily at 1 5 k day 1 reflecting the southwestward advection of the subtropical marine boundary layer by the trade winds while the free tropospheric temperature remains unchanged results from simulations with both a fixed diurnally averaged shortwave radiative forcing and a diurnally varying shortwave forcing are presented a two stage model for the boundary layer evolution consistent with these simulations is proposed in the first stage decoupling is induced by increased latent heat fluxes in the deepening boundary layer after decoupling cloud cover remains high but the cloudiness regime changes from a single stratocumulus layer to sporadic

a moist pbl parameterization for large scale models and its application to subtropical cloud topped marine boundary layers abstract a new general purpose boundary layer parameterization that permits realistic treatment of stratocumulus capped boundary layers scbls with coarse vertical resolution is described it combines a 1 5 order turbulent closure model with an entrainment closure at the boundary layer top three different implementations of the entrainment closure in which the boundary layer height is respectively prognosed reconstructed from thermodynamic values at the grid points or restricted to lie on a flux level of the host model grid are tested in a single column modeling framework at both fine and coarse vertical resolution the first two approaches permit a stratocumulus top and base to lie between grid levels and evolve continuously with time but are more complicated to implement in a three dimensional model the model performs very well in cases of dry convection whatever the inversion implementation and the vertical resolution with 15 mb or better vertical resolution all approaches properly simulate

stabilization of 10a manganates by interlayer cations and hydrothermal treatment implications for the mineralogy of marine manganese concretions abstract experimental substitutions of transition and alkaline earth cations into synthetic 10a na manganate show that cation uptake and the stability of the cation substituted mineral increase with stability of the hydroxide of the cation hydrothermal treatment of synthetic 10a manganates with different metal contents as well as marine diagenetic and hydrothermal 10a manganates shows that the stabilities of their structures are enhanced with increasing temperature the stabilization is due to reinforcement of the tunnel walls supporting the mn4 o2 6 octaheral layers the diagenetic 10a manganates have initially unstable buserite like structures with each interlayer wall composed of two mn2 o2 3 x oh 3 x octahedra 0 x 3 with either a na o2 2x oh n 2x unit n 6 and or 8 or less frequently a mn2 o2 2x oh 2 2x octahedron in between some of these cations in the walls are post depositionally substituted by highly hydrated divalent metal cations particularly cu2 and ni2 while some of the mn2 ions are slowly oxidized to mn4 these interlayer changes result in higher crystal field stabilization energy and shifts from interlayer van der waal s forces and weak coordination links to strong coordination links which stabilize the mineral structures low temperature hydrothermal 10a manganates have todorokite like structures with tunnel walls constructed predominantly of mn2 o2 3 x oh 3 x and mn2 o2 2x oh 6 2x octahedra high temperature hydrothermal 10a manganates have stable todorokite structures with the walls constructed of mn4 o2 6 octahedra the positive correlation between the formation or post depositional alteration temperatures and the mineral stability is due to the increase in oxidation rate of interlayer mn2 ions with increasing temperature of the hydrothermal fluids marine 10a manganates can be used as genetic indicators for manganese concretions and the sediments in which they occur and as a geothermometer in the search of ancient and modern hydrothermal vents where massive sulphide deposits are often found

the relationship between boundary layer stability and cloud cover in the post cold frontal region using nasa aqua modis and airs data the relationship between low level cloud cover cloud top below the 700 hpa level and boundary layer stability is explored in post cold frontal conditions a linear relationship is found between seasonal cloud cover and two separate measures of inversion strength the lower tropospheric stability lts and the estimated inversion strength eis for two specific regions in the north atlantic and pacific in quiescent and weakly subsiding conditions the relationship barely changes when considering dynamically active and subsiding post cold frontal conditions for the same regions to explore the generality of this result and increase sample size cold front centered composites of cloud cover and stability are constructed the northern and southern hemisphere seasonal cloud cover and stability distributions in the post cold frontal regions are then compared a fairly good correlation between cloud cover and eis is found in both hemispheres across all seasons suggesting that a linear relationship between cloud cover and inversion strength proposed for quiescent conditions exists also in more dynamically active subsiding post cold frontal conditions however for a given season and hemisphere the correlation between cloud cover and eis degrades in post cold frontal regions especially in the northern hemisphere at these scales other large scale factors tend to correlate better with cloud cover

cloud aerosol and boundary layer structure across the northeast pacific stratocumulus cumulus transition as observed during cset abstractduring the cloud system evolution in the trades cset field study 14 research flights of the national science foundation g v sampled the stratocumulus cumulus transition between northern

neogloboquadrina pachyderma sinistral coiling as paleoceanographic tracers in polar oceans evidence from northeast water polynya plankton tows sediment traps and surface sediments the abundance and chemistry of the planktonic foraminifera neogloboquadrina pachyderma sinistral coiling have long been used as tools for monitoring polar surface ocean changes and for correlating these changes to atmospheric and thermohaline circulation fluctuations however due to its remote habitat very little is known about how modern n pachyderma s respond to changing environmental conditions in the polar seas modern samples of n pachyderma s from the northeast water polynya provide a means for studying how environmental conditions affect the vertical distribution and chemistry of this species highest abundances of n pachyderma s were associated with the chlorophyll maximum in the surface 20 80 m where they are exploiting their primary food source evidence suggests that the addition of a calcite crust modifies the calcite tests of some n pachyderma s between 50 and 200 m increasing shell density and modifying shell chemistry the shell mass of encrusted forms is 3 4 times greater than the nonencrusted forms between 50 and 200 m the oxygen isotope composition of n pachyderma s shells increase by 1 5 in response to local water column gradients the 13c values of n pachyderma s are basically invariant with depth in this region are consistently 1 0 depleted in comparison with the 13c for equilibrium calcite and remain basically constant during the shell thickening process mass balance calculations suggest that encrustation occurs at all depths but abundance counts suggest that the process occurs mostly at the depth of the main pycnocline sediment fluxes of n pachyderma s occur during a 2 week bloom event and decrease to almost zero below complete ice cover the decoupling of the processes controlling abundances and shell chemistry explain the discrepancies between transfer function and isotopically derived paleotemperature estimates of surface conditions in some oceanic settings the ability of 18o to record surface ocean conditions will depend on vertical water column gradients as evidenced by the differences in core top calibrations between the north and south atlantic

buoyancy reversal decoupling and the transition from stratocumulus to shallow cumulus topped marine boundary layers the transition in a marine boundary layer mbl from stratocumulus topped to shallow cumulus topped is investigated by using a large eddy simulation les model the experiments performed aim to examine the influence on the transition of 1 the probability of buoyancy reversal at the mbl top i e situations in which the mixture of two air parcels becomes denser than either of the original parcels due to phase change or other nonlinear processes involved in the mixing and 2 the degree of decoupling in the mbl i e the strength of a shallow stably stratified layer near cloud base our results suggest that a stratocumulus topped mbl is most likely to transit to a cumulus topped one when 1 there exists high probability of buoyancy reversal at the mbl top and 2 the mbl is decoupled due to large surface evaporation we argue that a parameterization that includes representation of those two effects combined has the potential to provide a simple way of predicting the mbl transition in climate models

modeling iceberg rafted sedimentation in high latitude fjord environments 1 an iceberg model sedberg has been developed to simulate sedimentation in high latitude glaciated fjords sediments deposited in fjords provide an important record of glaciological response to changing climatic conditions the model simulates the formation drift and melt of a population of icebergs utilizing monte carlo based techniques with a number of underlying parametric probability distributions to describe the stochastic behavior of iceberg formation and dynamics the model captures iceberg dynamics and melt in fjord environments and has been applied to kangerdlugssuaq fjord in east greenland as an example of an iceberg dominated sedimentary environment sedimentation has been simulated over the past 1500 years encompassing the climatic intervals of the medieval warm period mwp and the little ice age lia model results have been compared with the observed sedimentary record the model demonstrates that the glaciological regime e g basal debris thickness mean annual calving rate mean iceberg size plays a more important role than the direct influence of climate ocean and air temperatures on iceberg sedimentation rate although often changes in climate result in changes to the glaciological regime

a new parameterization for shallow cumulus convection and its application to marine subtropical cloud topped boundary layers part ii regional simulations of marine boundary layer clouds abstract the impact of physical parameterizations on simulations of cloud topped marine boundary layers is investigated using the fifth generation pennsylvania state university ncar mesoscale model mm5 three month mm5 simulations of the northeast and southeast pacific during june august 1987 are boundary forced with time varying ecmwf analyses runs with four planetary boundary layer pbl parameterizations already implemented in mm5 are compared with runs using new parameterizations of boundary layer turbulence and shallow cumulus convection shcu described in a companion paper numerous modifications to the mm5 that allow it to be used as a regional climate model are described the simulated 3 month mean shortwave cloud radiative forcing swcf and vertical structure of cloud topped boundary layers in the northeast pacific are sensitive to the pbl shallow convection schemes all four current mm5 pbl schemes the blackadar medium range forecast mrf burk thompson and gayno seaman schemes produc

ice sheet and ocean interactions margin of the east greenland ice sheet 14 ka to present diatom evidence seven marine sediment cores were collected from the kangerdlugssuaq trough off the southeast coast of greenland the trough cuts across the continental shelf from the fjord mouth to the upper slope in denmark strait and provides a sedimentary environment sheltered from the east greenland current flowing along the shelf the cores have been 14c dated accelerator mass spectroscopy dates and analyzed for diatom accumulation rates and changes in floral composition it was found that the shelf probably was not glaciated by grounded ice but occupied by an ice shelf and or permanent sea ice between 14 000 years b p and the present average retreat rates of glacial permanent sea ice were circa 60 m yr between circa 13 500 and 11 000 years b p the retreat rates increased to about 150 m yr between 11 000 to 10 000 years b p the increase is unexpected because this correlates with fairbanks 1989 projected low glacial meltwater discharge for the same time which is coeval with the younger dryas several events of sea surface warming cooling took place on the outer shelf from 12 000 to 9000 years b p followed by cooling to the present with a possible warming between 3000 4000 years bp on the inner shelf pulses of warm cool surface water occurred from 9000 to 6000 years b p which was succeeded by surface water cooling until present

mesoscale shallow convection in the atmosphere this paper is a review of the observational experimental theoretical and numerical studies of mesoscale shallow convection msc in the atmosphere typically msc is 1 to 2 km deep has a horizontal length scale of a few to a few tens of kilometers and takes distinctive planforms linear and hexagonal the former is called a cloud street roll or band while the latter is called mesoscale cellular convection mcc comprising three dimensional cells msc is characterized by its shape horizontal extent convective depth and aspect ratio the latter is the ratio of the horizontal extent to that in the vertical for cells the horizontal extent is their diameter whereas for rolls it is their spacing rolls usually align along or at angles of up to 10 from the mean horizontal wind of the convective layer with lengths from 20 to 200 km widths from 2 to 10 km and convective depths from 2 to 3 km the typical value of aspect ratio ranges from 2 to 20 rolls may occur over both water surface and land surfaces mesoscale convective cells may be divided into two types open and closed open cell circulation has downward motion and clear sky in the cell center surrounded by cloud associated with upward motion closed cells have the opposite circulation both types of cell have diameters ranging from 10 to 40 km and aspect ratios of 5 to 50 and both occur in a convective layer with a depth of about 1 to 3 km both the magnitude and direction of horizontal wind in the convective layer change little with height msc results from a complex and incompletely understood mix of processes these processes are outlined and their interplay is examined through a review of theoretical and laboratory analyses and numerical modeling of msc

the galapagos rift at 86 w 5 variations in volcanism structure and hydrothermal activity along a 30 kilometer segment of the rift valley a 30 km segment of the galapagos rift near 86 w has been mapped in detail using the angus towed camera system the submersible alvin and multi narrowbeam sonar data recent volcanic activity and active hydrothermal circulation are evident along the entire length of the segment mapped there are however clear along strike variations in these processes which render previous two dimensional models obsolete although alternate explanations are possible eruptive sequences appear to begin with the outpouring of surface fed sheet flows and end with more channelized pillow flows in the western portion of the rift studied sheet flows dominate with the entire valley floor covered by recent flows associated with a broad shield volcano the eastern portion on the other hand is narrower consisting primarily of less voluminous pillow flows of apparently the same youthful age three possible models for the volcanic evolution of this rift segment are presented according to the first model the extrusive portion of the crust is formed by a distinct volcanic episode followed by a long period of volcanic quiescence the volcanic phase begins with voluminous sheet flows emerging from numerous eruptive fissures which in time evolve into a narrow pillow ridge farther along strike where the flows are smaller and the extrusive zone narrow the marginal portions undergo continued fissuring and subsequent uplift to form marginal highs and lows this deformational activity also affects the extrusive zone once volcanic activity ends converting the distinctly lobate topography of the active period into highly lineated fault controlled terrain according to the second model extension and voleanism can be viewed as a continuous process without major periods of volcanic quiescence the initial lava flows of a new eruptive sequence fill low areas frequently spilling over local sills and flooding much of the rift valley these sheet flows are then capped by pillow ridges but from an areal view sheet flows dominate since they can flow over much greater distances in the third model along strike differences in flow type arise from ephemeral differences in spreading rate along adjacent segments of the rift separated by transient transform faults or adjacent segments of en echelon spreading segments in this third model eruptions dominated by sheet flows are associated with a faster spreading element than eruptions dominated by pillow flows active hydrothermal vent fields were found throughout the study area as well as numerous yellow and ocher accumulations of what appear to be massive sulfide deposits these latter deposits are not associated with active venting apparently reflecting previous active hydrothermal phases when the exiting temperatures were sufficently high to permit surficial sulfide deposition the active vent fields exhibit along strike variations in their exiting temperatures either due to ephemeral differences in spreading rate or variations in the volcanic flow sequences

partitioning effects from ocean and atmosphere on the calving stability of kangerdlugssuaq glacier east greenland we use the 7 km retreat of kangerdlugssuaq glacier kg east greenland to examine the mechanisms interactions and relative significance of atmospheric forcing and ice ocean interactions hydrographic data from 1991 1993 and 2004 show that subtropical waters are common in kangerdlugssuaq fjord kf and that surface waters were warm in 2004 relative to 1991 and 1993 the main water column was nonetheless warmest in 1991 we contend that while flow of subtropical waters into fjords provides a setting in which rapid glacier retreat can occur the triggering of retreat depends on additional environmental factors the climatic variables standing out in our study of kg and kf are air temperature and katabatic winds both had strong positive anomalies during winter 2004 05 when kg retreated we show that proglacial ice melange was absent and that fjord freeze up did not occur until 11 april 2005 due to warm and windy conditions we demonstrate that this setting is unusual and hypothesize that exposure to open water in winter months caused the retreat calculation of ice front melt rates shows that discharge of basal meltwater first from runoff and subsequently from frictional basal heating should intensify the interaction between glacier and fjord

dynamics of cumulus rising into stratocumulus as observed during the first lagrangian experiment of astex the atlantic stratocumulus transition experiment took place during june 1992 in the eastern atlantic ocean in an area extending south east of the azores to madeira one of the goals of this experiment was to study the physical processes responsible for the transition from stratocumulus to shallow cumulus clouds the cloud type most frequently observed was cumulus rising into stratocumulus two lagrangian experiments were carried out to study the evolution of the boundary layer and to observe any transition in the cloud characteristics downstream here we concentrate on the last flight of the first lagrangian experiment during which cumulus cloud was penetrating thin and broken stratocumulus from below the immediate cause of the cumulus convection was condensation at the top of the well mixed surface based boundary layer the lifting condensation level was observed to be at about 500 m and above this height there was a conditionally unstable layer up to 1600 m in the upper part of the conditionally unstable layer the horizontally averaged thermodynamical variables showed that the air was very close to saturation indicating that the upper part of the cloud deck consisted of broken clouds the vertical structure of mean variables variances fluxes and turbulent kinetic energy budget is discussed one of the findings is that the cumulus convection is an important factor in counteracting the gradual dissipation of the stratocumulus deck in that it supplies moisture to the latter furthermore the net longwave radiative loss at cloud top was observed to be about 40 15 w m 2 which tended to destabilize the cloud layer from above the skewness factor s showed that the upward convection was quite intense owing to the rising cumuli the factor s reaching a maximum of about 2 0 7 in the middle of the cloud layer the skewness was found to be slightly negative near the cloud top

modeled glacial north atlantic ice rafted debris pattern and its sensitivity to various boundary conditions an iceberg drift and decay model is used to compute the ice rafted debris ird flux to the glacial north atlantic under steady iceberg discharge from the greenland and laurentide ice sheets i investigate the sensitivity of modeled ird distribution pattern to formulation of glacial iceberg decay meltwater drainage of laurentide ice sheet at its southern margin and the choice of ocean current and wind fields used as model boundary conditions modeled ird patterns are compared with the observed basic glacial mode ird pattern ruddiman 1977 and the last five heinrich layer patterns grousset et al 1993 model results show that the first order control on ird deposition pattern is the prevailing ocean currents and the choice of current fields is critical in determining the results winds can have significant effect when they exert drag in concert with ocean currents formulation of glacial iceberg decay directly affects its survival and the expanse of ird distribution but the formulation is perhaps one of the largest uncertainties in the model drainage of the southern margin of the laurentide ice sheet through the laurentian channel by meltwater instead of glaciers predicts no significant ird deposition in the open north atlantic in contrast to observations suggesting that glacier i e iceberg drainage through the laurentian channel was significant during the times of observed ird deposition in most experiments the model predicts a high ird deposition band that roughly coincides with the latitudinal band of high heinrich layer deposition but are measurably south of the basic glacial mode high ird deposition band this discordance suggests either that the flow fields used as model boundary conditions are inaccurate or that much of the basic glacial mode ird was not delivered by icebergs but perhaps sea ice

seasonal simulations of the planetary boundary layer and boundary layer stratocumulus clouds with a general circulation model abstract the ucla general circulation model gcm has been used to simulate the seasonally varying planetary boundary layer pbl as well as boundary layer stratus and stratocumulus clouds the pbl depth is a prognostic variable of the gcm incorporated through the use of a vertical coordinate system in which the pbl is identified with the lowest model layer stratocumulus clouds are assumed to occur whenever the upper portion of the pbl becomes saturated provided that the cloud top entrainment instability does not occur as indicated by arakawa and schubert cumulus clouds are assumed to originate at the pbl top and tend to make the pbl shallow by drawing on its mass results are presented from a three year simulation starting from a 31 december initial condition obtained from an earlier run with a different version of the model the simulated seasonally varying climates of the boundary layer and free troposphere are realistic the observed geographical and seasonal variations of stratocumulus cloudi

ore paragenesis of recent hydrothermal deposits at the cocos nazca plate boundary galapagos rift at 85 51 and 85 55 w complex massive sulfide mineralizations non sulfidic mineralizations and mineralized basalts complex massive sulfide ores black smokers as well as mineralized basalts and unconsolidated sediments were sampled during the german research expedition garimas 1 in the eastern portions of the galapagos rift at 85 50 w longitude the massive sulfide ores are characterized by a porous layered compositional texture with typical colloidal and or gel textures local occurrences of organism remains worm tubes which are embedded in the ore were also found the composition of the massive sulfide ores exhibits a considerable range from iron sulfide ores pyrite melnikovite pyrite marcasite to copper rich ores chalcopyrite and or zinc dominated ores sphalerite wurtzite schalenblende additional new types of hydrothermal mineralizations were found which consist primarily of manganese hydroxide limonite or fe rich smectite fe rich protosmectite together with limonite and opaline silica hydrothermally altered basalts may be characterized by significant sulfide contents primarily pyrite and locally by hematite sediments in the vicinity of the black smokers frequently contain fragments of complex massive sulfide ores with increasing distance from the black smokers these massive sulfide fragments exhibit complete replacement and pseudomorphism by limonite some replacement and pseudomorphism of microorganisms in unconsolidated sediments by limonitic material is also observed in places the unconsolidated sediments contain manganese hydroxide mineralizations of hydrothermal origin

the obduction of equatorial 13 c water in the pacific identified by a simulated passive tracer the obduction of equatorial 13 degrees c water in the pacific is investigated using a simulated passive tracer of the consortium for estimating the circulation and climate of the ocean ecco the result shows that the 13 degrees c water initialized in the region 8 degrees n 8 degrees s 130 degrees 90 degrees w enters the surface mixed layer in the eastern tropical pacific mainly through upwelling near the equator in the costa rica dome and along the coast of peru approximately two thirds of this obduction occurs within 10 years after the 13 degrees c water being initialized with the upper portion of the water mass reaching the surface mixed layer in only about a month the obduction of the 13 degrees c water helps to maintain a cool sea surface temperature year round equivalent to a surface heat flux of about 6 0 w m 2 averaged over the eastern tropical pacific 15 degrees s 15 degrees n 130 degrees w eastern boundary for the period of integration 1993 2006 during el nino years when the thermocline deepens as a consequence of the easterly wind weakening the obduction of the 13 degrees c water is suppressed and the reduced vertical entrainment generates a warming anomaly of up to 10 w m 2 in the eastern tropical pacific and in particular along the coast of peru providing explanations for the warming of sea surface temperature that cannot be accounted for by local winds alone the situation is reversed during la nina years

structural stability of marine 10 a manganates from the ogasawara bonin arc implication for low temperature hydrothermal activity abstract hydrothermal 10 a manganate deposits with distinct differences in structural stability when exposed to air were found on the kaikata seamount of the ogasawara arc western pacific the most stable 10 a manganates are concentrated near the center of the hydrothermal field while the unstable ones occur towards the field margins all manganates are characterized by very high mn fe ratios and extremely low contents of transition elements such as cu co and ni the variation in 10 a stability of the hydrothermal manganates is not regulated by mineral chemistry or aging but appears to be determined by other factors e g the hydrothermal fluid temperature at mineral deposition we propose a structural model for marine manganates showing two continuous series of increasingly stabilized 10 a manganates one series is of hydrothermal origin structurally similar to todorokite with a tunnel structure fixed at deposition and the other is a buserite like series of diagenetic origin comprising phyllomanganates all the marine 10 a manganates can be progressively stabilized in two different manners the todorokite like series by the establishment of smaller tunnels and the buserite like series by post depositional uptake of 10 a stabilizing interlayer cations both series are linked together with a common end member the most unstable 10 a manganate which appears to be formed at low temperature and easily transforms to a 7 a manganate in air

mixed layer mode simulation of eastern north pacific stratocumulus abstract the cloud topped mixed layer theory developed by lilly 1968 is employed in a slightly generalized form to simulate stratocumulus in the eastern north pacific the radiation parameterization involves cloud top longwave cooling and mixed layer shortwave heating long wave emissivity and shortwave absorption are functions of cloud thickness the model is integrated along climatological trajectories which traverse the area bounded by 145 w 115 w 20 n and 40 n the results of the integration include fields of cloud top and cloud base height mixed layer thermodynamic structure and convective and radiative fluxes where it is possible to compare model generated fields with the observations of neiburger et al 1961 general agreement is found the model predicted location of the southern limit due to cloud top instability of stratocumulus clouds is in agreement with observations

effect of glacial drainage water on the co2 system and ocean acidification state in an arctic tidewater glacier fjord during two contrasting years in order to investigate the effect of glacial water on the co2 system in the fjord we studied the variability of the total alkalinity at total dissolved inorganic carbon ct dissolved inorganic nutrients oxygen isotopic ratio d18o and freshwater fractions from the glacier front to the outer tempelfjorden on spitsbergen in winter 2012 january march and april and 2013 april and summer fall 2013 september the two contrasting years clearly showed that the influence of freshwater mixing and haline convection affected the chemical and physical characteristics of the fjord the seasonal variability showed the lowest calcium carbonate saturation state x and ph values in march 2012 coinciding with the highest freshwater fractions the highest x and ph were found in september 2013 mostly due to co2 uptake during primary production overall we found that increased freshwater supply decreased x ph and at on the other hand we observed higher at relative to salinity in the freshwater end member in the mild and rainy winter of 2012 1142 lmol kg21 compared to at in 2013 526 lmol kg21 observations of calcite and dolomite crystals in the glacial ice suggested supply of carbonate rich glacial drainage water to the fjord this implies that winters with a large amount of glacial drainage water partly provide a lessening of further ocean acidification which will also affect the air sea co2 exchange

iceberg production debris rafting and the extent and thickness of heinrich layers h 1 h 2 in north atlantic sediments the pattern of heinrich layer distribution for the last two events h 1 14 5 and h 2 21 1 ka mapped from magnetic susceptibility analysis of more than 50 north atlantic ocean cores provides the most detailed information to date on their extent and thickness an integrated spatial average thickness for the layers is 10 15 cm and there is a strong distance decay eastward the pattern of deposition over the north atlantic is similar for events h 1 and h 2 indicating that icebergs followed similar drift tracks rates of iceberg production and sediment flux from the hudson strait drainage basin of the north american laurentide ice sheet the major iceberg source for the events were calculated by using a mass balance approach this provides an envelope of sedimentation rates and the prediction that it would take between 50 and 1250 yr of iceberg sediment delivery to accumulate a heinrich layer averaging 10 cm thick over the north atlantic depending on the model assumptions used the most likely duration of heinrich events is 250 1250 yr

boundary layer depth entrainment and decoupling in the cloud capped subtropical and tropical marine boundary layer abstract estimates of marine boundary layer mbl depth and degree of decoupling for two regions of the subtropical and tropical east pacific are presented using satellite observations from the moderate resolution imaging spectroradiometer modis and the tropical rainfall measuring mission trmm microwave imager tmi these data are combined in a novel way with ncep reanalysis data and a mixing line parameterization to estimate the mean entrainment rate we over the two regions mean entrainment rates vary geographically and have maxima just downwind of the californian coast we 4 5 mm s 1 and also in the core of the equatorial east pacific cold tongue where mean we exceeds 6 mm s 1 entrainment exceeds subsidence by 30 or less in the subtropical stratocumulus regions north of the equatorial cold tongue entrainment greatly exceeds subsidence producing a rapid deepening of the mbl as air flows over a marked sst gradient shallow mbls zi 500 700 m are found to be well mixed in general the deco

mapping tide water glacier dynamics in east greenland using landsat data landsat multispectral scanner and thematic mapper images were co registered for the kangerdlugssuaq fjord region in east greenland and were used to map glacier drainage basin areas changes in the positions of tide water glacier termini and to estimate surface velocities of the larger tide water glaciers statistics were compiled to document distance and area changes to glacier termini the methodologies developed in this study are broadly applicable to the investigation of tide water glaciers in other areas the number of images available for consecutive years and the accuracy with which images are co registered are key factors that influence the degree to which regional glacier dynamics can be characterized using remotely sensed data three domains of glacier state were interpreted net increase in terminus area in the southern part of the study area net loss of terminus area for glaciers in upper kangerdlugssuaq fjord and a slight loss of glacier terminus area northward from ryberg fjord local increases in the concentrations of drifting icebergs in the fjords coincide with the observed extension of glacier termini positions ice surface velocity estimates were derived for several glaciers using automated image cross correlation techniques the velocity determined for kangerdlugssuaq gletscher is approximately 5 0 km a 1 and that for kong christian iv gletscher is 0 9 km a 1 the continuous presence of icebergs and brash ice in front of these glaciers indicates sustained rates of ice front calving

the arditurri pb zn f ba deposit cinco villas massif basque pyrenees a deformed and metamorphosed stratiform deposit stratiform banded and massive pb zn f ba mineralizations in metasediments of the westphalian cinco villas formation basque pyrenees show several features related to hercynian deformation and low grade regional metamorphism however some primary depositional textures and structures are preserved minerals like pyrite reveal preregional metamorphic textures framboidal colloform pyrite with automorphic overgrowths dendritic and atoll textures typical of rapid precipitation from supersaturated solutions during hydrothermal sedimentary activity deformation and subsequent micro and mesoscale remobilization have caused morphological and textural changes in the mineralizations producing folding mineral foliation transposition boudinages piercements etc as well as the development of veinlike orebodies pyrite shows a general tendency toward cataclasis whereas sphalerite galena and chalcopyrite exhibit a variety of microstructures subgrains twining recrystallization etc indicative of ductile deformation microscopy suggests the deformation of more plastic sulfide occurred mainly by a dislocation type mechanism at low temperatures 350 c which are compatible with the regional metamorphism recorded in the host rocks

summertime post cold frontal marine stratocumulus transition processes over the eastern north atlantic abstractmarine boundary layer mbl cloud morphology associated with two summertime cold fronts over the eastern north atlantic ena is investigated using high resolution simulations from the weat

hydrothermal activity and sulphide formation in axial valleys of the east pacific rise crest between 18 and 22 s abstract deep grabens some 90 m in depth occur on the crest of the east pacific rise between 17 9 and 18 6 s and between 21 1 and 21 7 s and are found within the topographic highs in these regions along the rise axis these axial valleys mark areas of recent faulting and intensive hydrothermal activity which is associated with the formation of metalliferous sediments and of massive sulphides of iron copper and zinc most iron and manganese released from the ore fluids continues to be deposited outside the grabens preferentially on the western flank of the rise a tendency which can be recognised also in older sediments of this area

estimation of entrainment rate in simple models of convective clouds a method for estimating lateral entrainment rate in clouds is suggested linking its magnitude to buoyant production of vertical kinetic energy within a cloud updraught in single column model studies the formulation captures the high values of entrainment seen in shallow convection and the values an order of magnitude lower in cases of deep convection as suggested by observational studies and large eddy model simulations together with a realistic vertical variation comparison is made with other recent attempts to parametrize entrainment

behavior of a glacier derived suspended sediment plume in a small arctic inlet the changing configuration of a glacier derived turbid surface meltwater plume was observed over a 40 hr period in a small marine inlet in spitsbergen factors controlling plume position tides winds and melt stream discharge were also monitored tidal forcing was the dominant control on plume behavior over the study period when winds were calm or light the plume spread over much of the inlet on the flood and around high tide and was restricted to the north side on the ebb and at low water winds were generally 5 kts and only influenced plume position when reaching over 12 kts coriolis effects were unimportant sediments on the inlet floor fined progressively with distance from glacier fed stream effluxes short cores showed that deposition was mainly in the form of structureless sands and silts

a new greenland deep ice core the polar ice sheets are rich sources of information on past atmospheric conditions including paleoclimates a new deep ice core has been drilled in south greenland comparison of the oxygen isotopic profile with that from camp century and with a deep sea foraminifera record indicates that the new core reaches back to about 90 000 years before present in a continuous sequence the details in the wisconsin part of the ice core records seem to be climatically significant and the general trends reveal all of the relevant emiliani stages recorded in deep sea cores the redated camp century record suggests a dramatic termination of the eem sangamon interglacial

metabasalts axial hot springs and the structure of hydrothermal systems at mid ocean ridges knowledge of the chemical transfer and mineralogical transformations that occur when sea water reacts with basalt at elevated temperatures and pressures can be used along with geological and geophysical data to deduce the typical structure and evolutionary sequence for hydrothermal systems within the oceanic crust along the axis of a mid ocean ridge studies of metabasalt and metadiabase dredged from fault scarps along the axial valley of the mid atlantic ridge reveal consistent relationships among the bulk chemistry of the altered rocks and their secondary mineralogy mineral abundances and mineral compositions especially for chlorite these relationships can be interpreted in terms of the distribution of alteration with respect to time temperature and water rock ratio in young crust assemblages of chl ab ep act chl ab ep act qtz chl ab qtz and chl qtz are produced at successively higher effective sea water to rock ratios within the temperature range of the greenschist facies 250 to 450 c toward higher ratios chlorites tend to become more mg rich pillow basalts of layer 2 are commonly altered under these conditions by sea water on the descending rather than the ascending limb of a convection system this type of alteration which reflects moderately high water rock ratios may characteristically occur above a still partially molten magma chamber as the magma chamber solidifies and is then penetrated more pervasive alteration of the deeper part of layer 2 and of layer 3 occurs at lower water rock ratios producing solutions such as those recovered from springs on the galapagos rift and the east pacific rise at 21 n localized upwelling limbs of the convection system can produce veins filled with quartz sulfides and fe rich chlorite

direct observations of atmospheric boundary layer response to sst variations associated with tropical instability waves over the eastern equatorial pacific tropical instability waves tiws with a typical wavelength of 1000 km and period of 30 days cause the equatorial front to meander and result in sst variations on the order of 18 28c vertical soundings of temperature humidity and wind velocity were obtained on board a japanese research vessel which sailed through three fully developed sst waves from 1408 to 1108w along 28n during 21 28 september 1999 a strong temperature inversion is observed throughout the cruise along 28n capping the planetary boundary layer pbl that is 1 1 5 km deep temperature response to tiw induced sst changes penetrates the whole depth of the pbl in response to an sst increase air temperature rises in the lowest kilometer and shows a strong cooling at the mean inversion height as a result this temperature dipole is associated with little tiw signal in the observed sea level pressure slp the cruise mean vertical profiles show a speed maximum at 400 500 m for both zonal and meridional velocities sst based composite profiles of zonal wind velocity show weakened intensified vertical shear within the pbl that is consistent with enhanced reduced vertical mixing causing surface wind to accelerate decelerate over warm cold ssts taken together the temperature and wind soundings indicate the dominance of the vertical mixing over the slp driving mechanism based on the authors measurements a physical interpretation of the widely used pbl model proposed by lindzen and nigam is presented

transport of suspended particulate matter in an antarctic fjord abstract vertical profiles of temperature salinity and light attenuation were used in conjunction with underwater photography and water samples to characterize the nature and dynamics of particle transport in an antarctic fjord most of the particles are sand sized 0 1 2 mm floccules comprised of individual grains in the 5 to 50 m size range the quartz silt grains are derived from basal debris laden meltwater originating from beneath the submerged valley glacier the meltwater buoyantly rises to form cold water interflows at mid water depths turbulent mixing near the seafloor also plays a role in the transport and break up of floccules together the midwater cold tongues and near bottom turbidity account for 87 of the total sediment load thus attesting to the importance of non surface transport mechanisms in polar fjords

simulation of seasonal variation of marine boundary layer clouds over the eastern pacific with a regional climate model abstractthe seasonal cycle of marine boundary layer mbl clouds over the eastern pacific ocean is studied with the international pacific research center iprc regional atmospheric model iram the results show that the model is capable of simulating not only the overall seasonal cycle but also the spatial distribution cloud regime transition and vertical structure of mbl clouds over the eastern pacific although the modeled mbl cloud layer is generally too high in altitude over the open ocean when compared with available satellite observations the model simulated well the westward deepening and decoupling of the mbl the rise in cloud base and cloud top of the low cloud decks off the peru and california coasts and the cloud regime transition from stratocumulus near the coast to trade cumulus farther to the west in both the southeast and northeast pacific in particular the model reproduced major features of the seasonal variations in stratocumulus decks off the peru and california coasts includin

ice induced vertical circulation in an arctic fiord ctd and nutrient data taken in south cape fiord next to a glacier face show strong evidence of upwelling in addition a region of down welling is found from 0 5 km to 5 km from the ice intruding layers with thicknesses consistent with lab measurements are found near the ice a phytoplankton bloom is found to be going on in the fiord and an upwelling velocity of 2 5 10 4 m s 1 is calculated by assuming that all the nitrogen required by these cells is up welled from the deep water within 10 2 m of the glacier mechanisms to drive the downwelling are discussed

metalliferous sediments within lava sequences of the sumail ophiolite oman mineralogical and geochemical characterization origin and evolution abstract lens shaped siliceous pelagic sediments and metalliferous deposits sampled in the wadi salahi block of the sumail ophiolite are interbedded within the successive lava flows of the extrusive sequence petrological mineralogical and geochemical characteristics of these sediments allow their oceanic environment of deposition and their early diagenetic and later hydrothermal transformations to be defined the sediments are primary radiolarian oozes deposited in a highly productive and open equatorial pelagic realm the biogenic components are mixed with hydrothermal metallic compounds similar to those found in the axial zone of modern active ridges the deposits are subsequently transformed by various oceanic hydrothermal events which are expressed by specific secondary parageneses the sedimentary lenses from the lower lava sequence are epidotized whereas the uppermost lenses from the upper lava unit contain pumpellyite some peculiar lenses are not affected by these oceanic metamorphisms for instance the deposits closely associated with the zuhan orebody which are fe and silica rich with scarce sulfates or the manganiferous sediments located at the top of the lower lava sequences which were earlier lithified by the deposition of the overlying lava flows nowhere in the whole sedimentary section described were detrital or volcaniclastic remains found disproving the possibility that these sediments may have been deposited in a seamount or island arc environment

sea floor massive sulfide deposits from 21 degrees n east pacific rise juan de fuca ridge and galapagos rift bulk chemical composition and economic implications

controls of bathymetric relief on hydrothermal fluid flow at mid ocean ridges we present quantitative modeling results for the effects of surface relief on hydrothermal convection at ocean spreading centers investigating how vent site locations and subsurface flow patterns are affected by bathymetry induced sub seafloor pressure variations the model is based on a 2 d fem solver for fluid flow in porous media and is used to simulate hydrothermal convection systematically in 375 synthetic studies the results of these studies show that bathymetric relief has a profound effect on hydrothermal flow bathymetric highs induce subsurface pressure variations that can deviate upwelling zones and favor venting at structural highs the deviation angle from vertical upwelling can be expressed by a single linear dependence relating deviation angle to bathymetric slope and depth of the heat source these findings are confirmed in two case studies for the east pacific rise at 9 30 n and lucky strike hydrothermal fields in both cases it is possible to predict the observed vent field locations only if bathymetry is taken into account our results thereby show that bathymetric relief should be considered in simulations of submarine hydrothermal systems and plays a key role especially in focusing venting of across axis hydrothermal flow onto the ridge axis of fast spreading ridges

the impact of vertical resolution upon gcm simulations of marine stratocumulus the impact of increased vertical resolution in the hadley centre climate model upon the simulation of stratocumulus is investigated in experiments using single column scm and general circulation gcm model configurations a threefold enhancement of vertical resolution in the boundary layer leads to improvements in the vertical structure of the cloud topped boundary layer produced by the scm and gcm in both well mixed and decoupled situations however single and decoupled mixed layers in the marine stratocumulus subsidence regions are still too shallow and despite increasing layer cloud amounts remain generally too low moreover closer examination of gcm data and scm timeseries reveals an underlying sensitivity to vertical resolution in model interactions between boundary layer and convection processes which appears unrealistic stratocumulus simulation is thus unlikely to improve significantly as a result of enhanced resolution alone and further work is being undertaken to improve the hadley centre model s boundary layer scheme and in particular its interaction with the convection scheme nevertheless this study shows that the full benefit of an improved boundary layer scheme will not be realized if the boundary layer structure is constrained by the rather poor lower troposphere resolution of the standard 19 level climate model future hadley centre model versions will seek to combine the added flexibility of a better resolved structure with improvements to the subgrid boundary layer parametrizations

the origin of massive diamicton facies by iceberg rafting and scouring scoresby sund east greenland almost 90 of 39 m of core material recovered from scoresby sund and the adjacent east greenland shelf is massive diamicton interpreted to be formed predominantly by the release of iceberg rafted debris and reworking by iceberg scouring there is also likely to be a contribution from suspension settling of fines derived from glaciofluvial sources model calculations suggest that the 14c derived holocene sedimentation rate of 0 1 0 3 m 1000 yr 1 in scoresby sund can be accounted for mainly by iceberg rafting of debris a further 4 of core material is of gravel or coarse sand lenses interpreted to reflect iceberg dumping of debris intensive iceberg scouring which reworks sea floor sediments is observed on acoustic records from over 30 000 km2 of the scoresby sund fiord system and the adjacent east greenland shelf 69 72 n and 75 n the rate of iceberg production from greenland ice sheet outlet glaciers and iceberg drift tracks on the shelf suggests that iceberg rafting and scouring may be important over a significant proportion of the 500 000 km2 area above the shelf break the relatively extensive modern occurrence of massive diamicton formed by iceberg rafting and scouring together with suspension settling of fines suggests that it may also be a significant facies in the glacier influenced geological record the recognition in the geological record of the massive diamicton facies described above may also indicate the former presence of fast flowing ice sheet outlet glaciers

the sizes frequencies and freeboards of east greenland icebergs observed using ship radar and sextant the scoresby sund fjord system east greenland contains the most productive fast flowing outlet glaciers draining east from the greenland ice sheet calving 18 km3 a 1 of icebergs the sizes frequencies and freeboards of 1900 icebergs were measured from f s polarstern using ship x band radar and sextant radar beam spreading exaggerates iceberg width by 60 m per nautical mile of range beyond the first mile data sets on iceberg size e g that collated for antarctic icebergs collected using ship radars which do not take this effect into account will overestimate iceberg dimensions significantly the location and concentration of icebergs within the fjord complex can be explained by 1 the locations of the principal source glaciers and 2 fjord topography and bathymetry iceberg concentration maximum 0 6 icebergs km 2 declines with distance from the major iceberg sources we found that 69 of icebergs within the fjord system are 1 km in length the largest is 2 7 km long icebergs become spread more evenly over the range of size classes in the outer fjord and shelf modal iceberg keel depth calculated from freeboard measurements is 4 500 m in the inner fjords shifting to lower values in the outer fjords reflecting shallower bathymetry radar measurements of iceberg width cannot be used to infer keel depths accurately because width and keel depth are only weakly correlated comparison between freeboards and keel depths for icebergs from east greenland and the barents sea indicates that the iceberg source i e floating or grounded exerts a fundamental control on iceberg dimensions the drift pattern of icebergs is from the head to the mouth of the fjord system although fjord bifurcations bathymetry and currents provide additional complications the trends in observed iceberg size and frequency and in inferred keel depth in the scoresby sund region are likely to be applicable to other fjords and shelves around greenland

surface based observations of mesoscale cumulus stratocumulus interaction during astex abstract data obtained from the island of santa maria in the azores during the atlantic stratocumulus transition experiment astex are used to describe cloud and boundary layer structure for a 24 h period on 15 june 1992 over the east central atlantic 37 n 25 10 w the evolution of the mesoscale cloud structure during a 24 h period in the vertical column above the surface site was characterized using a 94 ghz radar a laser ceilometer 3 h radiosonde ascents and surface micrometeorological instrumentation mesoscale circulations and drizzle were found to be key elements of the boundary layer clouds observed in this region during the late night and predawn hours of the study period a single layer of stratocumulus that averaged 200 m in thickness topped a well mixed marine boundary layer mesoscale cellular convection mcc which had ascending regions with horizontal dimensions of 7 km was observed during this period at sunrise decoupling was imposed on this mcc and extreme mesoscale variatio

observed lagrangian transition of stratocumulus into cumulus during astex mean state and turbulence structure aircraft measurements made during the first lagrangian of the atlantic stratocumulus transition experiment astex between 12 and 14 june 1992 are presented during this lagrangian experiment an air mass was followed that was advected southward by the mean wind five aircraft flights were undertaken to observe the transition of a stratocumulus cloud deck to thin and broken stratocumulus clouds penetrated by cumulus from below from the horizontal aircraft legs the boundary layer mean structure microphysics turbulence structure and entrainment were analyzed the vertical profiles of the vertical velocity skewness are shown to illustrate the transition of a cloudy boundary layer predominantly driven by longwave radiative cooling at the cloud top to one driven mainly by convection due to an unstable surface stratification and cumulus clouds during the last flight before the stratocumulus deck was observed to be broken and replaced by cumuli the total water flux the virtual potential temperature flux and the vertical velocity variance in the stratocumulus cloud layer were found significantly larger compared with the previous flights to analyze the cloud top stability the mean jumps of conserved variables across the inversion were determined from porpoising runs through the cloud top these jumps were compared with cloud top entrainment instability criteria discussed in the literature it is suggested that enhanced entrainment of dry air is a key mechanism in the stratocumulus cumulus transition

holocene variations in mineral and grain size composition along the east greenland glaciated margin ca 67 70 n local versus long distance sediment transport quantitative x ray diffraction qxrd analysis of the 2 mm sediment fraction from surface sea floor samples and marine sediment cores that span the last 10 12 cal ka bp are used to describe spatial and temporal variations in non clay mineral compositions for an area between kangerlussuaq trough and scoresby sund 67 70 n east greenland bedrock consists primarily of an early tertiary alkaline complex with high weight of pyroxene and plagioclase farther inland and to the north the bedrock is dominantly felsic with a high fraction of quartz and potassium feldspars principal component pc analysis of the non clay sediment compositions indicates the importance of quartz and pyroxene as compositional end members with an abrupt shift from quartz and k feldspar dominated sediments north of scoresby sund to sediments rich in pyroxene and plagioclase feldspars offshore from the early tertiary basaltic outcrop coarse 2 mm or 1 mm ice rafted sediments are largely absent from the trough sediments between 8 and 5 cal ka bp but then increase in the last 4 cal ka bp compositional unmixing of the sediments in grivel basin and kangerlussuaq trough indicate the dominance of local over long distance sediment sources with pulses of sediment from tidewater glaciers in kangerlussuaq and nansen fjords reaching the inner shelf during the neoglaciation the change in ird is more dramatic in the sediment grain size proxies than in the quartz wt forty to seventy percent of the variance in the quartz records from either side of denmark strait is explained by low frequency trends but the data from the grivel basin east greenland are distinctly different with an approximate 2500 yr periodicity

observed microphysical structure of midlevel mixed phase clouds abstract this paper analyzes airborne measurements of six midlevel clouds observed over the great plains of the united states in late 1999 and early 2000 during the fifth of the complex layered cloud experiments clex 5 data show that these innocuous looking clouds display complicated microphysical and thermodynamic structures five of the six cases exhibit mixed phase conditions in temperatures ranging from near 0 to 31 c at altitudes of 2400 to 7200 m msl four of the cases consist of a single cloud layer while the other two are multilayered systems in the thin mixed phase single layered clouds that the authors observed there is an increase of liquid water content with altitude whereas the ice water content maximizes in the mid to lower part of the clouds this contrasts the two multilayered systems the authors observed in which significant amounts of ice occur in the top as well as the bottom of the individual layers of each system a lack of significant temperature inversions or wind shea

sub sea floor hydrothermal alteration in the galapagos spreading center abstract oceanic crust was drilled at hole 504 b on the southern crest of costa rica rift galapagos spreading center this is the first hole that contains hydrothermally altered rocks containing secondary minerals of greenschist facies in d s d p holes drilled at the typical mid oceanic ridges altered rocks under high temperature water rock interaction are recovered below 890 m subbottom depth based on the secondary minerals the distribution of veins and the trace element contents the cores are classified into three zones zone 1 from 274 to 890 m zone 2 from 890 to 1050 m and zone 3 from 1050 to 1350 m in zone 1 the rocks remain fresh or are partly altered to secondary minerals smectite and saponite etc while in zones 2 and 3 laumontite chlorite epidote quartz and actinolite appear veins are more frequent in zone 2 than in zone 3 some samples in zone 2 are enriched in mn and zn part of zones 2 and 3 is considered to be the discharge zone in a hydrothermal convection system based upon the chemical composition of actinolite whole rock composition and sr isotope data the estimated alteration temperature changes sharply between zones 2 and 3 it is lower than 100 c in zone 1 while it is higher than 200 c in zones 2 and 3 this gap corresponds to the sharp change of hydrothermal alteration and other geophysical properties the most plausible mechanism for the formation of this gap is the time lag intensive hydrothermal activity occurred during the formation of oceanic crust in the rift valley another lava flow covered the rocks in zones 2 and 3

thermohaline steps induced by melting of the erebus glacier tongue a vertically stable step like thermohaline structure is observed throughout a continuous 400 m conductivity temperature depth ctd profile taken near the erebus glacier tongue mcmurdo sound antarctica the pattern is best developed between the sea surface and 250 m depth the interval corresponding to that of the irregular underwater profile of the glacier tongue the steps average 17 m in thickness and typically display discontinuities of 0 1 c in temperature 0 04 in salinity and 3 5 10 4 g cm 3 in density the observations are compared with theory and laboratory experiments of cell development and lateral flow near ice melting into vertically stratified salt water at this location subsurface seawater is inferred to remain above the in situ freezing point year round and contains sufficient heat to account for much of the glacier tongue thinning by basal melting an adequate volume of meltwater would result to produce the measured salinity steps we discuss related observations and some implications of this process for ocean circulation and biological productivity in the antarctic