turbulent mixing near the yermak plateau during the coordinated eastern arctic experiment during the ice camp component of the coordinated eastern arctic experiment cearex in march april 1989 1500 profiles of temperature conductivity and velocity shear microstructure were obtained near the yermak plateau the dominant signal in isopycnal displacements was the diurnal variability near the plateau consistent with the enhanced diurnal currents found in this region previously from the fram iii and fram iv ice camps the dissipation rate of turbulent kinetic energy e reached maximum values of about 10 6 w kg 1 in two distinct regions the surface mixing layer and the pycnocline between 120 and 220 m there was a significant component of diurnal variability in e in each region in the surface layer e was proportional to the cube of the ice relative current speed at 30 m below the ice and it decayed approximately exponentially with increasing depth major mixing events in the pycnocline were correlated with large amplitude short duration isopycnal displacements the lowest dissipation rates were recorded over the deep nansen basin north of the plateau and in the subsurface core of a submesoscale baroclinic eddy in northern fram strait the time averaged vertical eddy diffusivity near the slope of the plateau was about 2 5 10 4 m2 s 1 in the pycnocline above the atlantic layer implying an upward heat flux of 25 w m 2 although only a small fraction of this heat reached the base of the mixed layer the results confirm that current interactions with steep topography are critical to the modification of atlantic water in the eastern arctic ocean

cryosphere fire and ice ice sheet stability is affected by a complex interplay between meltwater and the geological characteristics of the bedrock under the ice the identification of a recently active subglacial volcano in antarctica adds uncertainty to this system

laboratory experiments on internal solitary waves in ice covered waters internal solitary waves isws propagating in a stably stratified two layer fluid in which the upper boundary condition changes from open water to ice are studied for cases of grease level and nilas ice the isw induced current at the surface is capable of trans porting the ice in the horizontal direction in the level ice case the transport speed of relatively long ice floes non dimensionalised by the wave speed is linearly dependent on the length of the ice floe non dimensionalised by the wave length measures of turbulent kinetic energy dissipation under the ice are comparable to those at the wave density interface moreover in cases where the ice floe protrudes into the pycnocline interaction with the ice edge can cause the isw to break or even be destroyed by the process the results suggest that interaction between isws and sea ice may be an important mechanism for dissipation of isw energy in the arctic ocean

vertical mixing at intermediate depths in the arctic boundary current microstructure and hydrographic observations during september 2007 in the boundary current on the east siberian continental slope document upper ocean stratification and along stream water mass changes a thin warm surface layer overrides a shallow halocline characterized by a 40 m thick temperature minimum layer beginning at 30 m depth below the halocline well defined thermohaline diffusive staircases extended downwards to warm atlantic water intrusions found at 200 800 m depth observed turbulent eddy kinetic energy dissipations are extremely low epsilon 10 6 w m 3 such that double diffusive convection dominates the vertical mixing in the upper ocean the diffusive convection heat fluxes f dc h 1 w m 2 are an order of magnitude too small to account for the observed along stream cooling of the boundary current our results implicate circulation patterns and the influence of shelf waters in the evolution of the boundary current waters

effective diffusivities within oceanic thermohaline staircases a scale for the thickness of layers in regular diffusive type thermohaline staircases derived from dimensional analysis is found to collapse oceanic data combining this scale with laboratory derived double diffusive flux laws we formulate effective diffusivities for salt heat and density the diffusivities depend on the turner number r but are independent of the brunt vaisala frequency for r near 1 the diffusivities for salt and heat are approximately equal 10 4 m2 s 1 they decrease roughly as r 4 and r 2 respectively over the oceanic range 1 r 10

tide mediated warming of arctic halocline by atlantic heat fluxes over rough topography atlantic water brings heat to the subsurface arctic ocean pan arctic microstructure measurements of energy dissipation suggest that vertical mixing is substantial over the continental slopes tidally induced and insensitive to sea ice cover

variations in the thermal output of the subglacial grimsvotn caldera iceland a 69 year record 1922 1991 of heat release has been obtained from the subglacial geothermal system of the grimsvotn caldera within the vatnajokull ice cap the data were derived from in situ measurements of the volume of meltwater accumulated in the caldera lake subtracting climatically induced melting the overall fluctuations in the heat flux are closely related to volcanic activity and are dominated by a main pulse of 11 600 mw caused by a major eruption in 1938 gradually declining to 1600 mw in 1976 1982 heat extracted from the roof of a magma chamber with the aid of hydrothermal convection may have given a basic contribution to the heat flux of 1500 to 2000 mw an upper bound the variable part of the heat flux from 0 to 10 000 mw was released from magma erupted at the base of the glacier and from shallow intrusions the total heat released over the period 1922 to 1991 was 8 1 1 6 1018j equivalent to the energy released by the solidification and cooling of 2 1 0 4 km of basaltic magma the contribution to the total heat flux was 45 max from a magma chamber 35 min from shallow intrusions and 20 from eruptions this implies that magma at the roof of a chamber solidified and cooled at the rate of 1 2 1 6 107 m a 1 or about 1 km over the last 69 years heat release at grimsvotn was probably more intense in the 19th century when volcanic eruptions were more frequent

dynamics stratigraphy and proximal dispersal of supraglacial tephra during the ice confined 2004 eruption at grimsvotn volcano iceland the basaltic phreatomagmatic eruption of grimsvotn volcano iceland in november 2004 g2004 lasted for 5 days during which time two separate vents were active significant deposition of tephra occurred in the first 45 h only we have subdivided the deposit into seven units a g on the basis of differences in texture grain size and componentry and the presence of sharp contacts between the layers the distribution of tephra lobes was used to infer the vent of origin for each unit the g2004 deposit is poorly sorted overall and consists of non vesicular to highly vesicular juvenile components units a and b comprise almost exclusively non to poorly vesicular glass fragments whereas units c g contain at least 30 vol highly vesicular pumice the proportion of non juvenile fragments increases significantly in the final unit unit f of the main phase non juvenile fragments are restricted to the coarse 0 fraction of the deposit main phase units c and e account for 80 of the total deposit volume including the entire distal portion and are interpreted to represent a mixture of 1 a widely dispersed component that fell from the upper margins of a strongly inclined 45 6 10 km high plume and 2 a locally dispersed 3 km from source component originating from pyroclastic density currents and minor tephra jets

greater role for atlantic inflows on sea ice loss in the eurasian basin of the arctic ocean arctic sea ice loss is a leading indicator of climate change and can be attributed in large part to atmospheric forcing here we show that recent ice reductions weakening of the halocline and shoaling of the intermediate depth atlantic water layer in the eastern eurasian basin have increased winter ventilation in the ocean interior making this region structurally similar to that of the western eurasian basin the associated enhanced release of oceanic heat has reduced winter sea ice formation at a rate now comparable to losses from atmospheric thermodynamic forcing thus explaining the recent reduction in sea ice cover in the eastern eurasian basin this encroaching atlantification of the eurasian basin represents an essential step toward a new arctic climate state with a substantially greater role for atlantic inflows

penetration of water into hot rock boundaries of magma at grimsvotn the grimsvotn geothermal area is located within one of the most active caldera volcanoes in iceland in the interior of the ice cap vatnajokull at an altitude of 1 400 m fig 1 its setting oilers unique conditions for calorimetric measurement of the heat release from the subglacial geothermal system the melting of ice due to the geothermal activity creates a depression in the surface of the ice cap ice and water are diverted towards the depression from a 300 km2 drainage basin the meltwater accumulates in a 30 km2 subglacial lake periodic outbursts of water jokulhlaups drain the lake subglacially down to the skeidararsandur plain we propose here that penetration of water into hot rock is the primary reason for the intense heat release 5 000 mw thermal of the subglacial grimsvotn geothermal area injection of water into boundary rocks of magma should be considered as a method of heat exploitation

the effect of the 2002 glacial flood on dissolved and suspended chemical fluxes in the skafta river iceland abstract this study describes the chemical composition of dissolved degased and suspended fluxes of the 2002 skafta glacial flood which emerged from one of the skafta subglacial lake due to geothermal activity beneath the icelandic vatnajokull glacier the dissolved and suspended fluxes during the flood are compared with those normally observed in the skafta river to determine the effect of such floods on the annual fluxes of material delivered to the coastal waters concentrations of most dissolved elements during the flood were significantly higher than those normally observed in the skafta river in addition dissolved concentrations of nutrients such as sio 2 fe and v increased more than an order of magnitude during the flood these will affect biological processes on a local scale the 34 s composition in the flood water suggests that the dissolved so 4 was derived from the oxidation of h 2 s and the geothermal fluid the total suspended particulate load measured in the skafta river during the 8 day 2002 flood was approximately half of the non flood total annual skafta suspended load as particles carry the bulk of limiting nutrients to the oceans this demonstrates the importance of glacial floods for primary production of coastal waters the composition of the flood water and the skafta subglacial lake together with reaction path modelling suggest that substantial degasing of co 2 and h 2 s occurred at the glacial outlet during the flood this degasing may have released as much as 262 000 and 7 980 tonnes of co 2 and h 2 s respectively to the atmosphere having a considerable impact on the local carbon and sulphur cycles during the flood event

observed atlantification of the barents sea causes the polar front to limit the expansion of winter sea ice abstractbarents sea water bsw is formed from atlantic water that is cooled through atmospheric heat loss and freshened through seasonal sea ice melt in the eastern barents sea the bsw and fresh

modeled subglacial water flow routing supports localized intrusive heating as a possible cause of basal melting of mars south polar ice cap the discovery of an 20 km wide area of bright subsurface radar reflections interpreted as liquid water beneath the martian south polar layered deposits spld in data from the mars advanced radar for subsurface and ionosphere sounding marsis instrument and the discovery of two geologically recent potential eskers landforms produced by subglacial melt associated with viscous flow features in martian midlatitudes has suggested recent basal melting of martian ice deposits may be feasible possibly due to locally elevated geothermal heating locations of terrestrial subglacial lakes and major drainage axes have been successfully predicted from subglacial hydraulic potential surfaces calculated from surface topography and ice thickness here we use surface topography from the mars orbiter laser altimeter and spld bed elevations derived from marsis data to calculate the subglacial hydraulic potential surface beneath the spld and determine whether the observed high reflectance area coincides with predicted subglacial lake locations given the sensitivity of terrestrial predictions of lake locations to basal topography we derive over 1 000 perturbed topographies using noise statistics from the marsis data to infer the most likely locations of possible subglacial water bodies and drainage axes our results show that the high reflectance area does not coincide with any substantial predicted lake locations three nearby lake locations are robustly predicted however we interpret this result as suggesting that the high reflectance area assuming the interpretation as liquid is correct is most likely a hydraulically isolated patch of liquid confined by the surrounding cold based ice rather than a topographically constrained subglacial lake

seasonal and regional manifestation of arctic sea ice loss abstractthe arctic ocean is currently on a fast track toward seasonally ice free conditions although most attention has been on the accelerating summer sea ice decline large changes are also occu

glacier volcano interactions in the north crater of mt wrangell alaska glaciological and related observations from 1961 to 2005 at the summit of mt wrangell 62 008 n 144 028 w 4317 m a s l a massive glacier covered shield volcano in south central alaska show marked changes that appear to have been initiated by the great alaska earthquake mw 9 2 of 27 march 1964 the 4 6 km diameter ice filled summit caldera with several post caldera craters on its rim comprises the summit region where annual snow accumulation is 1 2 m of water equivalent and the mean annual temperature measured 10 m below the snow surface is 208c precision surveying aerial photogrammetry and measurements of temperature and snow accumulation were used to measure the loss of glacier ice equivalent to about 0 03 km 3 of water from the north crater in a decade glacier calorimetry was used to calculate the associated heat flux which varied within the range 20 140 w m 2 total heat flow was in the range 20 100 mw seismicity data from the crater s rim show two distinct responses to large earthquakes at time scales from minutes to months chemistry of water and gas from fumaroles indicates a shallow magma heat source and seismicity data are consistent with this interpretation

source and dispersal of jokulhlaup sediments discharged to the sea following the 1996 vatnajokull eruption the october 1996 gjalp eruption beneath vatnajokull glacier led to one of the largest jokulhlaups glacial floods in iceland in the twentieth century a catastrophic discharge of meltwater and sediment swept across the skeidararsandur flood plain to the sea tephra from the eruption consists of vesicular sideromelane shards with a basaltic andesite composition 53 sio 2 3 mgo 0 8 k 2 o after the flood sediment samples were collected from the flood plain and off the southeast coast of iceland where a major sediment plume had been created by the discharge compositions of glass shards from flood plain and seafloor deposits do not match those of the gjalp magma flood plain samples consist primarily of blocky to poorly vesicular sideromelane clasts with compositions that are characteristic of grimsvotn volcanic products 50 sio 2 5 5 mgo 0 4 k 2 o marine samples collected near the jokulhlaup outflow into the sea also consist primarily of blocky to poorly vesicular sideromelane clasts with compositions that are for the most part similar to products of the grimsvotn volcanic center distal marine samples have more vesicular sideromelane clasts with compositions that are similar to products of the katla volcanic center e g 48 sio 2 4 5 mgo 0 8 k 2 o significant deposition to the seafloor was apparently limited to an area just offshore of the skeidararsandur there is no indication that juvenile volcanic material from the gjalp eruption was carried by the 1996 jokulhlaup onto the flood plain or into the ocean instead the jokulhlaup carried primarily older volcaniclastic material eroded by the flood

observations of a diapycnal shortcut to adiabatic upwelling of antarctic circumpolar deep water in the southern ocean small scale turbulence causes diapycnal mixing which influences important water mass transformations in turn impacting large scale ocean transports such as the meridional overturning circulation moc a key controller of earth s climate we present direct observations of mixing over the antarctic continental slope between water masses that are part of the southern ocean moc a 12 h time series of microstructure turbulence measurements hydrography and velocity observations off elephant island north of the antarctic peninsula reveals two concurrent bursts of elevated dissipation of o 10 6 w kg 1 resulting in heat fluxes 10 times higher than basin integrated drake passage estimates this occurs across the boundary between adjacent adiabatic upwelling and downwelling overturning cells ray tracing to nearby topography shows mixing between 300 and 400 m is consistent with the breaking of locally generated internal tidal waves since similar conditions extend to much of the antarctic continental slope where these water masses outcrop diapycnal mixing may contribute significantly to upwelling

free drifting icebergs as sources of iron to the weddell sea abstract in recent years glaciers on the antarctic peninsula have retreated resulting in loss of mass from ice shelves and increased supply of icebergs to the southern ocean free drifting icebergs may serve as an important source of fe to surrounding waters we measured concentrations of dissolved fe and fe content of suspended particulate material via flow injection chemiluminescence and icp ms respectively in the waters surrounding several icebergs during cruises to the scotia and weddell seas in june 2008 and march 2009 surface dissolved fe dfe concentrations varied from 0 58 to 2 92 nm and were elevated up to 60 at some stations 10 km from the icebergs indicating general fe enrichment in the lower salinity surface layer however surface dfe within 1 km of the iceberg was similar to that measured at depths below the draft of the iceberg a feature that may result from upwelling of circumpolar deep water caused by basal melting at the face of the iceberg iron concentrations in ice collected following calving events were highly variable 4 600 nm but were elevated above concentrations in seawater particulate fe normalized to particulate p in suspended particulate material was up to 20 fold higher within 0 6 km of two large tabular icebergs but no enrichment was observed at two smaller icebergs iron phosphorus ratios of suspended particulate material were also higher in deeper 40 m waters compared to shallow ca 15 m waters at the iceberg face iron release appeared to be episodic producing a spatially heterogeneous environment around icebergs this source term may increase in coming years as antarctic ice shelves degrade further potentially impacting the ecology and biogeochemistry of low fe waters of the southern ocean

retreat of the cold halocline layer in the arctic ocean we present a comparison of arctic ocean hydrographic data sets from the 1990s with a focus on changes in the upper few hundred meters of the eurasian basin the most recent observations discussed here were collected during the spring 1995 scientific ice expedition scicex 95 the second in a series of scientific cruises to the arctic ocean aboard u s navy nuclear submarines although the 1990s have seen an abundance of synoptic cruises to the arctic this was the only one to take place in winter spring conditions other data considered here were collected during the first scicex cruise in summer 1993 scicex 93 and during an icebreaker cruise to the eurasian basin in summer 1991 oden 91 a new russian american winter climatology is also used as a reference these comparisons reveal that the eurasian basin cold halocline layer has retreated during the 1990s to cover significantly less area than in previous years specifically we find a retreat from the amundsen basin back into the makarov basin the latter is the only region with a true cold halocline layer during scicex 95 changes are also seen in other halocline types and in the atlantic water layer heat content and depth since the cold halocline layer insulates the surface layer and thus the overlying sea ice from the heat contained in the atlantic water layer this should have profound effects on the surface energy and mass balance of sea ice in this region using a simple mixing model we calculate maximum ice ocean heat fluxes of 1 3 w m 2 in the eurasian basin where during scicex 95 the surface layer lay in direct contact with the underlying atlantic water layer the overall cause of water mass changes in the 1990s might have been a shift in the atmospheric wind forcing and resulting sea ice motion during the late 1980s which we speculate influenced the location where fresh shelf waters flow into the deeper basins of the arctic ocean finally we discuss two different mechanisms that have been proposed for cold halocline water formation and we propose a compromise that best fits these data

winter convection transports atlantic water heat to the surface layer in the eastern arctic ocean a 1 yr 2009 10 record of temperature and salinity profiles from ice tethered profiler itp buoys in the eurasian basin eb of the arctic ocean is used to quantify the flux of heat from the upper pycnocline to the surface mixed layer the upper pycnocline in the central eb is fed by the upward flux of heat from the intermediate depth 150 900m atlanticwater aw layer thisfluxisestimatedtobe 1wm 22 averaged over one year release of heat from the upper pycnocline through the cold halocline layer to the surface mixed layer is however seasonally intensified occurring more strongly in winter this seasonal heat loss averages 3 4wm 22 between january and april reducing the rate of winter sea ice formation this study hypothesizes that the winter heat loss is driven by mixing caused by a combination of brine driven convection associated with sea ice formation and larger vertical velocity shear below the base of the surface mixed layer sml enhanced by atmospheric storms and the seasonal reduction in density difference between the sml and underlying pycnocline

bathymetry heat output and convection in ruapehu crater lake new zealand abstract bathymetric observations of ruapehu crater lake show that it became shallower and its volume decreased by 3 10 6 m 3 between 1965 and 1970 it is likely that this was due to lava moving upwards in the region under the lake from the regular measurements of crater lake temperature outflow and chloride and magnesium ion concentrations the inflows of steam cold water and chloride and magnesium ions were calculated using the 1970 volume only about half the precipitation falling on and around the lake mixes with the lake water since the cold fresh water floats on top of the denser lake water and travels to the outlet without mixing with the main body of water in the lake the chloride content of the input steam appears to vary with time in a similar fashion to that of white island fumaroles temperature and density profiles of the lake in 1965 and 1966 indicated that convection was occurring the temperature profile of the top 175 m of the lake agreed with a model of turbulent convection in small cells giving a temperature gradient at any level in the lake proportional to the heat flux at that level the convection model predicted that the temperature at depth would exceed the local boiling point if the thermal power input reached a value which would sustain a surface temperature approaching 60 c this prediction of instability was not inconsistent with observations convection in the present crater lake probably occurs in the form of thermal plumes from small sources

circulation and thermodynamics in a subglacial geothermal lake under the western skafta cauldron of the vatnajokull ice cap iceland 1 the subglacial geothermal lake beneath the western skafta cauldron depression in the vatnajokull ice cap iceland was accessed by hot water drilling through the overlying 300 m thick ice shelf most of the ca 100 m water column was near 4 7 c but was underlain by a distinct 10 m deep water mass at 3 5 c the sensible heat content of the lake water is approximately twice the potential energy dissipated in outburst floods and the temperature of the lake may be an important factor in the development of subglacial water courses of jokulhlaups from the lake the lake temperature is higher than the temperature of maximum density implying that convective heat transfer can take place in the lake the vertical temperature structure suggests a large scale recirculating flow in the lake the rate of which was estimated from the lake temperatures and the chemical composition of a water sample

formation erosion and exposure of early amazonian dikes dike swarms and possible subglacial eruptions in the elysium rise utopia basin region mars hundreds of narrow linear ridge segments are found in the transition zone between the elysium rise and the utopia basin occurring as both single and multiple ridges the ridges are distinctive because of their very linear steep sided nature their often sharp ridge crest which sometimes is fractured their association with stubby flows their continuity over long distances and their cross cutting of different terrain the linear ridges are interpreted to be single dikes and dike swarms either emplaced as normal dikes or as dikes emplaced subglacially feeding an explosive or effusive eruption five dike swarms are identified having lengths ranging from 10 45 km and being between 1 7 km wide while single ridges are up to 20 km long and 100 500 m wide in the areas of dike swarms crustal dilatation is estimated to vary from 15 60 dikes emplaced en echelon suggest that variations in the local stress field caused rotation during dike emplacement and dikes crosscutting flow units imply that dike emplacement can account for some of the observed linear fractures in the area the ridges both modify and constrain early amazonian flows and flood plain deposits suggesting intense dike emplacement in the early amazonian the association with different stages of inverted craters as well as some features of ice related origin possible ice cauldron and tindar like features indicate that the dikes may have been exposed due to eolian erosion and loss of volatile rich units subsequent to their emplacement

observations of flooding and snow ice formation in a thinner arctic sea ice regime during the n ice2015 campaign influence of basal ice melt and storms seven ice mass balance instruments deployed near 83 n on different first year and second year ice floes representing variable snow and ice conditions documented the evolution of snow and ice conditions in the arctic ocean north of svalbard in january march 2015 frequent profiles of temperature and thermal diffusivity proxy were recorded to distinguish changes in snow depth and ice thickness with 2 cm vertical resolution four instruments documented flooding and snow ice formation flooding was clearly detectable in the simultaneous changes in thermal diffusivity proxy increased temperature and heat propagation through the underlying ice slush then progressively transformed into snow ice flooding resulted from two different processes i after storm induced breakup of snow loaded floes and ii after loss of buoyancy due to basal ice melt in the case of breakup when the ice was cold and not permeable rapid flooding probably due to lateral intrusion of seawater led to slush and snow ice layers at the ocean freezing temperature 1 88 c after the storm the instruments documented basal sea ice melt over warm atlantic waters and ocean to ice heat flux peaked at up to 400 w m 2 the warm ice was then permeable and flooding was more gradual probably involving vertical intrusion of brines and led to colder slush and snow ice 3 c the n ice2015 campaign provided the first documentation of significant flooding and snow ice formation in the arctic ice pack as the slush partially refroze snow ice formation may become a more frequently observed process in a thinner ice arctic

changes in jokulhlaup sizes in grimsvotn vatnajokull iceland 1934 91 deduced from in situ measurements of subglacial lake volume a record of volumes of jokulhlaups from the subglacial grimsvotn lake vatnajokull iceland has been derived for the period 1934 91 the change in lake volume during jokulhlaups is estimated from the lake area ice cover thickness and the drop in lake level the jokulhlaup volumes have decreased gradually during this period of low volcanic activity and declining geothermal power the two jokulhlaups in the 1930s each discharged about 4 5 km peak discharge 25 30 10 3 m 3 s 1 in the 1980s jokulhlaup volumes were 0 6 1 2 km 3 peak discharge 2 10 3 m 3 s 1 the lake level required to trigger a jokulhlaup has risen as an ice dam east of the lake has thickened water flow in a jokulhlaup ceases when the base of a floating ice shelf covering grimsvotn settles to about 1160 m a s l apparently the jokulhlaups are cut off when the base of the ice shelf collapses on to a subglacial ridge bordering the lake on its eastern side the decline in melting rates has resulted in a positive mass balance of the 160 170 km grimsvotn ice drainage basin comparison of maps shows that the average positive mass balance rate was 0 12 km 3 a 1 25 of the total accumulation in the period 1946 87 a gradually increasing positive mass balance has prevailed since 1954 reaching 0 23 km 3 a 1 in 1976 86 48 of total accumulation

geothermal activity in the subglacial katla caldera iceland 1999 2005 studied with radar altimetry the katla caldera is located under the myrdalsjokull ice cap and is one of the most hazardous volcanoes in iceland due to major jokulhlaups that accompany eruptions subglacial geothermal activity is manifested in several 10 50 m deep depressions ice cauldrons within and at the caldera rim and the total geothermal heat output is of the order of a few hundred megawatts a short lived but powerful pulse in geothermal heat output took place in 1999 probably including a minor subglacial eruption when new ice cauldrons formed in three places and an unexpected jokulhlaup occurred following these events a comprehensive monitoring program was set up for katla including ice surface elevation profiling from aircraft to monitor variations in geothermal heat and detect signs of subglacial water accumulation a radar altimeter coupled with a kinematic gps is used achieving an absolute elevation accuracy of 3 m and internal consistency of 1 2 m profiles across the caldera are flown twice a year an annual accumulation ablation cycle in surface elevation with amplitude of 5 10 m is observed by removing this cycle from the data changes due to subglacial geothermal activity are obtained after the events in 1999 a decline in geothermal activity was observed in 2001 03 some ice cauldrons expanded and deepened by 10 15 m indicating renewed increase in geothermal activity this trend is also apparent for 2003 05 the increase in geothermal power amounts to a few tens of megawatts it is likely that the increased thermal output is related to increased seismicity and caused by magma inflow

fluid volcano interaction in an active stratovolcano the crater lake system of poas volcano costa rica rowe g l jr brantley s l fernandez m fernandez j f borgia a and barquero j 1992 fluid volcano interaction in an active stratovolcano the crater lake system of po is volcano costa rica j volcanol geotherm res 49 2351 seismic and geochemical data collected at po is volcano costa rica since 1978 suggest that temperature and chemical variations recorded in subaerial fumaroles and the crater lake are related to episodic release of heat and volatiles associated with hydrofracturing of the upper margin of the shallow magma body power outputs associated with these events approach 600 mw and are superimposed on a baseline energy flux of approximately 200 mw the baseline heat flux suggests a magma solidification rate of 0 012 km3 yr and background volatile release rates of 1000 t d h20 66 t d s 13 t d ci and 0 5 t d f these fluxes are comparable to fluxes of f c1 and s exiting the magmatic hydrothermal system through acidic flank springs and are about a factor of five less than estimated volatile fluxes through summit fumaroles during the high temperature event of 1981 1983 mass balance considerations suggest that heat released at the lake surface is primarily supplied by the ascent of heated brines supplemented by condensation of fumarolic steam calculated average seepage rates out of the lake 450 kg s indicate rapid convection of acidic lake brine through underlying lake sediments and pyroclastic deposits circulation of the extremely corrosive lake brine through the volcanoclastic material beneath the lake may enhance subsurface permeabilities fluxes of rock forming elements observed in the rio agrio basin on the northwest flank of po is suggest that dissolution and removal of volcano elastic material occurs at a rate of approximately 1650 m3 yr however estimated sulfur fluxes from the cooling magma body suggest that porosity created by this dissolution could quickly be filled by the deposition of native sulfur finally analysis of heat and water budgets for the crater lake over the period 1978 1989 indicates that the recent decline and disappearance of the lake was caused by variations in summit rainfall combined with an increase in subsurface heat flow to the lake in 1987 1988 the increase in heat flow is related to continued degassing of high temperature volatiles following a hydrofracturing magma ascent episode that occurred in 1986

candidate subglacial volcanoes in the south polar region of mars morphology morphometry and eruption conditions 1 a number of isolated mountains mapped in the south polar region of mars are documented using mars global surveyor mgs mars orbiter laser altimeter mola and mars orbiter camera moc data these mountains have average separation distances of 175 km they are typically 30 40 km in diameter and 1000 1500 m high and their bases fall near an elevation of 1200 m a significant number of the population are located on or very close to a 660 km long line extending toward the south pole the summits of a number of these mountains have unusual shapes flat topped flat topped with a cone and large summit craters relative to the summit diameter sinuous channels are found in association with the margins of several of the mountains several modes of origin are considered for these mountains including impact tectonic and volcanic these mountains occur in intimate association with the hesperian aged dorsa argentea formation a unit containing features and structures interpreted to be related to a thick areally extensive ice sheet on the basis of these observations and analyses it is concluded that the most plausible origin for these mountains is volcanic and that they represent extrusion of lava from vents many of which lay underneath an ice sheet the unusual shape of many of the mountains is consistent with construction of a volcanic edifice underneath an ice sheet and melting of adjacent ice rich material sometimes forming drainage channels the topography of these mountains suggests that the ice sheet averaged at least 1 4 km thick at the time of eruption these features appear to be associated with early hesperian aged ridged plains hr

influences of the ocean surface mixed layer and thermohaline stratification on arctic sea ice in the central canada basin 1 variations in the arctic central canada basin mixed layer properties are documented based on a subset of nearly 6500 temperature and salinity profiles acquired by ice tethered profilers during the period summer 2004 to summer 2009 and analyzed in conjunction with sea ice observations from ice mass balance buoys and atmosphere ocean heat flux estimates the july august mean mixed layer depth based on the ice tethered profiler data averaged 16 m an overestimate due to the ice tethered profiler sampling characteristics and present analysis procedures while the average winter mixed layer depth was only 24 m with individual observations rarely exceeding 40 m guidance interpreting the observations is provided by a 1 d ocean mixed layer model the analysis focuses attention on the very strong density stratification at the base of the mixed layer in the canada basin that greatly impedes surface layer deepening and thus limits the flux of deep ocean heat to the surface that could influence sea ice growth decay the observations additionally suggest that efficient lateral mixed layer restratification processes are active in the arctic also impeding mixed layer deepening

internal waves and mixing in the marginal ice zone near the yermak plateau observations were made of oceanic currents hydrography and microstructure in the southern yermak plateau in summer 2007 the location is in the marginal ice zone at the arctic front northwest of svalbard where the west spitsbergen current wsc carries the warm atlantic water into the arctic ocean time series of approximately 1 day duration from five stations upper 520 m and of an 8 day duration from a mooring are analyzed to describe the characteristics of internal waves and turbulent mixing the spectral composition of the internal wave field over the southern yermak plateau is 0 1 0 3 times the midlatitude levels and compares with the most energetic levels in the central arctic dissipation rate and eddy diffusivity below the pycnocline increase from the noise level on the cold side of the front by one order of magnitude on the warm side where 100 m thick layers with average diffusivities of 5 3 10 25 m 2 s 21 lead to heat loss from the atlantic water of 2 4 w m 22 dissipation in the upper 150 m is well above the noise level at all stations but strong stratification at the cold side of the front prohibits mixing across the pycnocline close to the shelf at the core of the svalbard branch of the wsc diffusivity increases by another factor of 3 6 here nearbottom mixing removes 15 w m 22 of heat from the atlantic layer internal wave activity and mixing show variability related to topography and hydrography thus the path of the wsc will affect the cooling and freshening of the atlantic inflow when generalized to the arctic ocean diapycnal mixing away from abyssal plains can be significant for the heat budget around the yermak plateau it is of sufficient magnitude to influence heat anomaly pulses entering the arctic ocean however diapycnal mixing alone is unlikely to be significant for regional cooling of the wsc

coherent intrusion complexes in large basaltic volcanoes a new structural model abstract highly concentrated coherent intrusion complexes consisting of thousands of small mafic intrusions occur in probably all major basaltic volcanoes and play an important role in volcano development magma excursions from the high level chamber travel laterally along a surface of neutral buoyancy at the margin of a complex and cause the complex to grow the limited distance however that narrow intrusions can propagate before becoming blocked causes complexes to be wedge like intrusive dike complexes underlie rift zones and asymmetric growth of the dike wedge causes rift zones of shield volcanoes to become non collinear and may initiate a third rift zone in the obtuse angle downbowing of stress trajectories across complexes causes dikes to be non vertical and results in axial subsidence intrusive sheet complexes form instead of dike complexes in volcanic systems that have a restricted ability to expand laterally and accommodate intrusions by expanding vertically instead downbowing of stress trajectories causes sheets to be non horizontal and this combined with subsidence increasing toward the thicker part of the sheet wedge produces the inward and inwardly increasing dip that characterizes cone sheet complexes this mechanism for cone sheets differs considerably from previously proposed mechanisms successive injections of sheets at the top of a sheet complex probably offers the most efficient means of powering a high intensity geothermal field such as the 5000 mw grimsvotn system in iceland it is inferred that similar mechanisms to those in major basaltic edifices operate in spreading ridges study of basaltic edifices has the potential to contribute significantly to the understanding of spreading ridges

eastern arctic ocean diapycnal heat fluxes through large double diffusive steps abstractthe diffusive layering dl form of double diffusive convection cools the atlantic water aw as it circulates around the arctic ocean large dl steps with heights of homogeneous layers of

one more step toward a warmer arctic this study was motivated by a strong warming signal seen in mooring based and oceanographic survey data collected in 2004 in the eurasian basin of the arctic ocean the source of this and earlier arctic ocean changes lies in interactions between polar and sub polar basins evidence suggests such changes are abrupt or pulse like taking the form of propagating anomalies that can be traced to higher latitudes for example an anomaly found in 2004 in the eastern eurasian basin took 1 5 years to propagate from the norwegian sea to the fram strait region and additional 4 5 5 years to reach the laptev sea slope while the causes of the observed changes will require further investigation our conclusions are consistent with prevailing ideas suggesting the arctic ocean is in transition towards a new warmer state

cavi angusti mars characterization and assessment of possible formation mechanisms received 26 august 2002 revised 5 february 2003 accepted 20 february 2003 published 24 may 2003 1 cavi angusti represent a series of large irregular depressions localized in part of the south circumpolar area previously mapped as the hesperian aged dorsa argentea formation their origin has primarily been interpreted to be due to eolian deflation or subglacial melting we use mgs mola and moc data to analyze the largest of these features 100 50 km and up to about 1500 m deep these data reveal terraced interiors centrally located equidimensional and elongated edifices and lava flow like structures that strongly suggest that this basin formed as a result of magmatic intrusion and extrusion causing heating and melting of a volatile rich substrate and drainage and loss of the liquid water volume estimates and heat transfer calculations are consistent with a mechanism involving a combination of intrusion and extrusion very similar to that observed to be responsible for icelandic subglacial eruptions and meltwater generation mounds and ridges in the floors of other depressions suggest that this mechanism may have operated in at least several other features of the cavi eolian activity sublimation and solution are also likely to have played a role in further modification of these features meltwater from basin formation appears to have drained laterally and may also have reentered the regional subsurface groundwater system index terms 6225 planetology solar system objects mars 5480 planetology solid surface planets volcanism 8450 5462 planetology solid surface planets polar regions 5416 planetology solid surface planets glaciation keywords mars cavi angusti dorsa argentea formation