glider observations of the dotson ice shelf outflow abstract the amundsen sea is one of the most productive polynyas in the antarctic per unit area and is undergoing rapid changes including a reduction in sea ice duration thinning ice sheets retreat of glaciers and the potential collapse of the thwaites glacier in pine island bay a growing body of research has indicated that these changes are altering the water mass properties and associated biogeochemistry within the polynya unfortunately difficulties in accessing the remote location have greatly limited the amount of in situ data that has been collected in this study data from a teledyne webb slocum glider was used to supplement ship based sampling along the dotson ice shelf dis this autonomous underwater vehicle revealed a detailed view of a meltwater laden outflow from below the western flank of the dis circumpolar deep water intruding onto the shelf drives glacial melt and the supply of macronutrients that along with ample light supports the large phytoplankton blooms in the amundsen sea polynya less well understood is the source of micronutrients such as iron necessary to support this bloom to the central polynya where chlorophyll concentrations are highest this outflow region showed decreasing optical backscatter with proximity to the bed indicating that particulate matter was sourced from the overlying glacier rather than resuspended sediment this result suggests that particulate iron and potentially phytoplankton primary productivity is intrinsically linked to the magnitude and duration of sub glacial melt from circumpolar deep water intrusions onto the shelf

annual changes in sea ice and phytoplankton in polynyas of the amundsen sea antarctica abstract two coastal polynyas in the amundsen sea amundsen polynya and pine island polynya were studied as part of the dynalife project because of their unusually high rates of biological production and close association with melting ice shelves in this component of the study satellite imagery of ocean color using reprocessing r2009 1 and passive microwave sea ice distributions were used to characterize interannual changes in polynya dynamics and phytoplankton bloom development between 1997 and 2010 interannual differences in sea ice cover were large in both polynyas but especially so in the smaller pine island polynya and were related to synoptic scale wind patterns rather than climate state enso or sam open water season lasted 10 days longer in the amundsen polynya 132 days than in the pine island polynya 122 days the phytoplankton bloom in the amundsen polynya lasted approximately two weeks longer and was 30 more productive per unit area than the bloom in the pine island polynya because pine island polynya was lower in both mean open water area and annual net primary production npp per unit area total annual npp averaged over the 13 year time series was only 60 of that in the amundsen polynya 1 96 and 3 26 tg c yr 1 respectively given the high interannual variability and the short time series duration we did not observe a secular trend in primary production or any relationship with climate indices such as the southern annular mode however with increased iron addition from melting ice shelves into the surface waters of the polynyas we expect that primary production could be enhanced in the future

kimberlite exploration at serra da canastra province brazil kimberlite and lamproite pipes are the only economically significant source rocks forming primary diamond deposits brazil the world s seventh largest diamond producer has all of its production from alluvial deposits the quest for a primary deposit has continued over several decades with very few positive results to that end airborne magnetic data from the serra da canastra diamondiferous province was used to identify kimberlite signatures serra da canastra is located in the central portion of the brazilian province in a low magnetic latitude region the main tectonic feature of the area is a northwest southeast major crustal fracture zone that extends for more than 3000 km within the territory the interpretation strategy was based on joint analysis of analytic signal and euler deconvolution a selected kimberlite target should typically have a roughly circular analytic signal anomaly coincident with a depth 0 200 m and structural n 2 constrained euler solution the proposed approach led to rec

convective mixing in a tropopause fold we present a case study of the passage of a tropopause fold over the uk behind a cold front with emphasis on the mixing caused by convection extending into the fold the event took place on 15 16 january 1999 and was the subject of intensive observations using the met office c130 aircraft and the mesosphere stratosphere troposphere mst radar at aberystwyth here we concentrate on radar and satellite observations during the afternoon of 16 january when the surface cold front had passed over the uk a tongue of moist air moved north eastwards over wales at 700 hpa at this time which because of the very dry air in the fold above resulted in potential instability the resulting convection was clearly observed in noaa satellite images the mst radar depicted the passage of the cold front and tropopause fold as a layer of high echo power and vertical wind shear ascending with time spectral widths showed the fold to be free of turbulence until 1200 utc on 16 january when convection was observed reaching into the frontal zone and generating turbulence eddy dissipation and diffusivity rates of 8 6 mw kg 1 and 8 5 m2s 1 respectively were derived for this event to place these figures in context they are compared with corresponding rates derived for sixteen other passages of tropopause folds over the radar each resulting from shear rather than convective instability the convective event is found to be comparable to the strongest shear events and to correspond to moderate turbulence as experienced by an aircraft this process is of potential importance for atmospheric chemistry because it mixes boundary layer air directly with stratospheric air over a timescale of 1 2 hours copyright 2004 royal meteorological society

the interdisciplinary marine system of the amundsen sea southern ocean recent advances and the need for sustained observations the southern ocean exerts a profound influence on the functioning of the earth system in part because its location and unique bathymetric configuration enable direct linkages to the other major ocean basins ganachaud and wunsch 2000 and lumpkin and speer 2007 it is the site of the world s largest current system the antarctic circumpolar current acc which transfers waters and climatically ecologically important tracers between the atlantic indian and pacific oceans rintoul et al 2001 in addition to the strong horizontal connectivity the acc is also characterized by a vigorous overturning circulation which upwells warm nutrient rich waters from intermediate depth to the surface where they are modified by interactions with the atmosphere and cryosphere to form new water masses some of which are lighter and others more dense marshall and speer 2012 this overturning circulation structures the southern ocean both horizontally and vertically dictates the levels of its communication with the rest of the global ocean and is a fundamental control on the sequestration of carbon from the atmosphere into the ocean interior sallee et al 2012 in some locations the upwelled waters can intrude onto the antarctic shelves supplying heat and nutrients to the shallower regions this is believed to be especially effective in west antarctica where the southern edge of the acc moves close to the shelf break martinson 2011 orsi et al 1995 and thoma et al 2008

break up of a stratospheric streamer observed by mst radar the break up of a stratospheric streamer over the british isles is described using satellite mesosphere stratosphere troposphere mst radar and in situ observations together with european centre for medium range weather forecasts analyses the streamer started as a thin ribbon of high potential vorticity to the west of the british isles as this was strained by the background flow it broke up into a series of mesoscale vortices mst radar and ozonesonde observations delineated a tropopause fold to the west of the initial streamer taking the form of a thin layer of stratospheric air embedded in a deep layer of descending upper tropospheric air the fold appears to have been mixed out by small scale turbulence as the streamer broke up this break up also generated strong inertia gravity waves which broke just above the tropopause introducing extensive mixing to the lowermost stratosphere one of the mesoscale vortices returned over the mst radar showing a very indistinct tropopause typical of a synoptic scale cut off low this vortex was also responsible for the development of a rain band on its eastern flank which brought significant rainfall to the british isles at a time when the synoptic flow pattern was strongly anticyclonic

climatology of tropopause folds at midlatitudes a statistical analysis of a 25 years time series of routine ozone soundings at uccle 51 48 n 4 21 e reveals that the frequency of tropopause folds is within the limits of uncertainty similar for all seasons on the average 4 8 of the ozone profiles show the presence of a fold whereas a shorter time series of soundings 1985 1993 obtained at the observatoire de haute provence 43 54 n 5 45 e yields only a 2 fraction of folds the difference between both stations is however riot entirely statistically significant the average wet and dry artificial radioactivity deposition in the sixties and early seventies was at a maximum at uccle around june in good agreement with global sr 90 wet deposition measurements volchok and kleinman 1971 suggesting that stratosphere troposphere exchange is more important during spring compared to the rest of the year this leads to the hypothesis that if tropopause folds are the major agent of stratosphere troposphere exchange ste they may be more efficient in spring than in autumn

the tropopause in the polar regions abstract the polar and subpolar tropopause in both hemispheres is investigated using the ecmwf reanalysis era data from 1979 to 1993 and radiosonde data from 1989 to 1993 both the thermal and the dynamical criteria are applied to each dataset the tropopauses derived from the radiosonde data are used to validate the era derived tropopauses and to investigate the sharpness of the tropopause the validation reveals that the era data are well suited for the determination of the tropopause a comparison between the thermal and the dynamical tropopause shows a very good agreement except for polar winter and there is clear evidence that the dynamical criterion is more appropriate in winter the results show that the annual cycle of the polar tropopause can be classified into three different patterns a single wave with a tropopause pressure maximum in winter and a minimum in summer is typical for the subpolar parts of eastern siberia and north america a double wave with pressure maxima in spring and autumn

tropopause folds in era interim global climatology and relation to extreme weather events tropopause folds are intimately linked to upper level frontogenesis and jet stream dynamics they play an important role for stratosphere troposphere exchange the dynamical coupling of upper and lower tropospheric levels and for generating severe weather events this study presents a global climatology of tropopause folds using era interim reanalysis data from 1979 to 2012 and a refined version of a previously developed 3 d labeling and fold identification algorithm this algorithm objectively separates stratospheric and tropospheric air in complex situations e g in regions with strong low level inversions and in extratropical cyclones where diabatically generated potential vorticity anomalies typically occur three classes of tropopause folds are defined shallow medium and deep and their geographical distribution vertical extent and seasonal cycle are investigated most shallow folds occur along the subtropical jet stream in agreement with previous studies hot spots of medium and deep tropopause folds are found west of australia and along the coast of antarctica in the southern hemisphere and around the east coast of north america in the northern hemisphere seasonal cycles show maxima in winter for all fold classes medium and deep folds are frequently associated with surface wind gust and precipitation extremes as quantified for folds over the southern indian ocean wind gust extremes occur mainly in an elongated band upstream and equatorward of folds whereas precipitation extremes occur mainly east and poleward of folds overall in the considered region about 20 of medium folds and 33 of deep folds are associated with surface wind or precipitation extremes in the vicinity of the fold

iron deficiency limits phytoplankton growth in antarctic waters enrichment experiments were performed in the ross sea to test the hypothesis that iron deficiency is responsible for the phytoplankton s failure to use up the luxuriant major nutrient supplies found in these and all other offshore antarctic ocean waters nitrate uptake rates in the controls without added trace elements ranged from 0 58 to 1 22 mol kg 1 d 1 the addition of 1 to 5 nmol of unchelated fe per liter resulted in rates that were 2 to 10 times higher 2 54 to 6 00 mol no3 kg 1 d 1 rates in bottles with 2 nmol mn added were identical to those in the controls 0 57 to 1 04 mol no3 kg 1 d 1 total decreases in no3 were balanced by increases in particulate organic n these results suggest that fe deficiency is the primary reason that the present day southern ocean biological pump is shut off in contrast iron was 50 times more abundant during the last glacial maximum greater fe availability may have stimulated the biological pump and contributed to the ice age drawdown of atmospheric c02 these results also imply that large scale southern ocean fe fertilization is feasible at least in terms of the total amounts of fe required i e 100 000 to 500 000 tons yr 1

oceanic heat transport onto the amundsen sea shelf through a submarine glacial trough glaciers which drain the west antarctic ice sheet wais into the amundsen sea are accelerating and thinning rapidly these observations have been attributed to the regional oceanography whereby heat contained within circumpolar deep water cdw drives the basal melting of floating glaciers on the basis of new data we calculate that 2 8 terra watts 1012 of oceanic heat flow onto the continental shelf and toward the glaciers via a submarine glacial trough this is enough to account for most of the basal melting in the entire region suggesting the ocean is supplying an excess of heat toward the antarctic continent

climatology of tropopause folds over a european arctic station esrange 1 eleven years september 1996 to august 2007 of continuous measurements of three dimensional wind and backscattered signal strength observed with esrange radar esrad have been utilized to study the annual and interannual variation of tropopause folds over an arctic station two typical tropopause fold events one is associated with a streamer type of system and the other with a cutoff low are selected and are characterized with the help of synoptic charts and potential vorticity pv analysis typical characteristics of radar parameters during the passage of folds are identified such as the sudden rise in the tropopause altitude high reflectivity layer sloping downward from the tropopause beneath the jet stream and intensification of the jet stream these characteristics are utilized to discern the tropopause fold in the radar data the climatology of tropopause folds exhibits a pronounced annual cycle with a large number of folds in winter and fewer in summer the annual cycle of folds is more or less similar in all the years however significant interannual variation is observed with winter periods exhibiting maximum interannual variability the climatology of folds and its annual cycle are compared and contrasted with similar climatological studies available in the literature the differences in the climatologies are discussed in light of differences in the algorithms and the spatial variability of fold frequency

numerical modeling of ocean ice interactions under pine island bay s ice shelf 1 a two dimensional numerical model is used to simulate the dynamics of buoyant meltwater rich plumes flowing beneath the ice shelf occupying much of pine island bay west antarctica recent studies have shown that this ice shelf along with all others fringing the amundsen sea is thinning rapidly in the model both the coriolis effect and subshelf topography are important in controlling plume dynamics and the spatial distribution of ice melt melt is concentrated in a narrow zone within 20 km of the grounding line where steep subshelf slopes and access to warm ambient water allow melt rates to exceed 100 m yr 1 the plume generated by entrainment of ambient water into the meltwater in these areas is guided by the topography of the ice shelf underside and exits the ice shelf at three distinct outflow locations melt rates generated along the course of the plume are higher approximately 2 5 than rates elsewhere the model suggests that the observed ice shelf thinning rates could have resulted from a hypothetical instantaneous 0 25 c warming of the ambient water entrained by the plume a context for this value is provided by the 40 year warming trend documented by jacobs et al 2002 for circumpolar deep water in the nearby ross sea

a five year radar based climatology of tropopause folds and deep convection over wales united kingdom abstracta five year 2006 10 radar based climatology of tropopause folds and convective storms was constructed for wales united kingdom to determine how deep moist convection is modulated by tropopause folds based on the continuous high resolution data from a very high frequency vhf wind profiling radar located at capel dewi wales 183 tropopause folds were identified tropopause folds were most frequent in january with a secondary maximum in july based on data from the u k weather radar network a climatology of 685 convective storms was developed the occurrence of convective storms was relatively high year round except for an abrupt minimum in february april multicellular lines 43 5 were the most common morphology with a maximum in october followed by isolated cells 33 1 with a maximum in may september and nonlinear clusters 23 4 with a maximum in november january convective storms were associated with 104 56 8 of the tropopause folds identified in this study with the associ

chemical and physical characteristics of iron oxides in riverine and glacial meltwater sediments abstract the speciation and grain size distribution of iron have been examined in several riverine and glacial sediments in order to evaluate controls on the concentrations and modes of occurrence of iron oxides in weathering derived particulates three operationally defined fractions have been recognised relating to the reactivity of iron towards dissolved sulphide 1 highly reactive iron fe hr consisting of ferric oxides 2 poorly reactive iron fe pr consisting of magnetite and some sheet silicate iron and 3 unreactive residual silicate iron fe u the finer fractions of each riverine and glacial suite are enriched in fe hr and usually also have higher fe hr fet ratios however coarser fractions may also have elevated fe hr contents and relationships of fe hr to both surface area and al indicate that iron oxides dominantly occur in association with the surfaces of aluminosilicate minerals which are common in finer grained fractions but may also be relatively enriched in coarser fractions a similar range of fe hr surface loadings is evident in the riverine and glacial meltwater suites from 0 6 to 1 8 mg fe m 2 for the riverine sediments and 0 5 to 1 5 mg fe m 2 for the glacial meltwater sediments despite wide variations in catchment bedrock lithology and climatic conditions significantly lower iron oxide loadings 0 1 mg fe m 2 were found in subglacial sediments most fe hr is closely associated with organic c although the latter occurs as blebs or smears rather than continuous coatings e g ransom et al 1997 ransom b bennett r h baerwald r shea k 1997 tem study of in situ organic matter on continental margins occurrence and the monolayer hypothesis mar geol 138 1 9 electron microscope observations show that iron oxides may occur as nanoparticulate 10 20 nm spheres at the edges of sheet aluminosilicate minerals as crystalline oxides infilling surface pits in coarser grained aluminosilicate minerals and occasionally as discrete crystalline oxides the similar occurrences of iron oxides in both riverine and glacial environments indicates that the delivery of reactive iron oxides to the oceans during glacial interglacial cycles will be affected by the masses and grain size characteristics of sediments delivered by glacial and riverine fluxes rather than by differences in iron mineralogy these delivery rates will be modified by behaviour of the oxide nanoparticles during transport from the continents

physical forcing of phytoplankton dynamics in the southwestern ross sea coastal zone color scanner czcs imagery of phytoplankton pigments and passive microwave imagery of sea ice distributions in the southwestern ross sea are presented for three different seasons 1978 1989 1979 1980 and 1981 1982 and were analyzed in conjunction with meteorological data obtained from a series of automatic weather stations aws dynamics of the phytoplankton bloom in terra nova bay differed from those in the ross sea owing to spatial differences in katabatic wind fields which determine when the surface waters stratify interannual variation in the timing of formation of the ross sea polynya appears to be controlled by winter temperatures which determine sea ice thickness and integrity rather than variability or intensity in wind stress together czcs aws and passive microwave data suggest that when the ross sea polynya forms early stronger and more frequent katabatic winds result in increased advective losses of phytoplankton in surface waters and a delay in the phytoplankton bloom if polynya formation is delayed until after the winds diminish in frequency the phytoplankton bloom will develop earlier the observation that diatoms dominate both the marginal ice zone and terra nova bay which are hydrographically similar while phaeocystis antarctica is found in unstable waters north of the ross ice shelf suggests that stratification plays an important role in determining species composition in the ross sea

phytoplankton biomass and pigment responses to fe amendments in the pine island and amundsen polynyas nutrient addition experiments were performed during the austral summer in the amundsen sea southern ocean to investigate the availability of organically bound iron fe to the phytoplankton communities as well as assess their response to fe amendment changes in autotrophic biomass pigment concentration maximum photochemical efficiency of photosystem ii and nutrient concentration were recorded in response to the addition of dissolved free fe dfe and fe bound to different model ligands analysis of pigment concentrations indicated that the autotrophic community was dominated by the prymnesiophyte phaeocystis antarctica throughout most of the amundsen sea although diatoms dominated in two experiments conducted in the marginal ice zone few significant differences in bulk community biomass particulate organic carbon nitrogen and chlorophyll a w ere observed relative to the controls in treatments with fe added alone or bound to the ligand phytic acid in contrast when fe was bound to the ligand desferrioxamine b dfb decreases in the bulk biomass indices were observed the concentration of the diatom accessory pigment fucoxanthin showed little response to fe additions while the concentration of the p antarctica specific pigment 19 0 hexanoyloxyfucoxanthin 19 0 hex decreased when fe was added alone or bound to the model ligands lastly

iron from melting glaciers fuels the phytoplankton blooms in amundsen sea southern ocean iron biogeochemistry dissolved iron dfe and total dissolvable fe tdfe were measured in january february 2009 in pine island bay as well as in the pine island and amundsen polynyas amundsen sea southern ocean iron fe has been shown to be a limiting nutrient for phytoplankton growth even in the productive continental shelves surrounding the antarctic continent however the polynyas of the amundsen sea harbor the highest concentrations of phytoplankton anywhere in antarctica here we present data showing the likely sources of fe that enable such a productive and long lasting phytoplankton bloom circumpolar deep water cdw flows over the bottom of the shelf into the pine island bay where dfe and tdfe were observed to increase from 0 2 to 0 4 nm dfe and from 0 3 4 0 to 7 14 nm tdfe respectively at the southern end of pine island bay the cdw upwelled under the pine island glacier bringing nutrients including fe to the surface and melting the base of the glacier concentrations of dfe in waters near the pine island glacier and the more westward lying crosson dotson and getz ice shelves varied between 0 40 and 1 31 nm depending on the relative magnitude of upwelling turbulent mixing and melting these values represent maximum concentrations since associated ligands which

tropopause folds and cross tropopause exchange a global investigation based upon ecmwf analyses for the time period march 2000 to february 2001 1 a new methodology is proposed to identify folds of the dynamical tropopause taken as the 2 potential vorticity pv units pvu isosurface from global analysis data sets from the european centre for medium range weather forecasts ecmwf it consists of a three dimensional subdivision of the atmosphere into stratospheric and tropospheric parts and a subsequent examination of multiple tropopause crossings in vertical profiles of the analyses the method is applied to a 1 year period starting in march 2000 seasonal mean fold frequency distributions show that folds occur preferentially in the subtropics with maximum frequencies of about 30 pronounced maxima are located in the subtropical bands that extend from 20 e to 120 e on both hemispheres during summer generally subtropical folds are comparatively shallow deep folds occur most frequently in midlatitudes during winter over eastern north america and the western north atlantic with maximum frequencies of about 1 detailed investigation of the relationship between individual folds and cross tropopause exchange events reveals that on the average individual folds in the extratropics are associated with larger exchange mass fluxes compared to the subtropics however due to the much higher frequency of subtropical folds the percentage of exchange events that are associated with tropopause folds is larger near 20 40 latitude 50 70 than further poleward 20 30 during winter and 10 20 during summer this indicates that tropopause folds are the key feature for cross tropopause exchange in the subtropics whereas in the extratropics other tropopause structures are at least of equal importance

historical sam variability part i century length seasonal reconstructions seasonal reconstructions of the southern hemisphere annular mode sam index are derived to extend the record before the reanalysis period using station sea level pressure slp data as predictors two reconstructions using different predictands are obtained one jones and widmann jw based on the first principal component pc of extratropical slp and the other fogt on the index of marshall a regional based sam index visbeck is also considered these predictands agree well post 1979 correlations decline in all seasons except austral summer for the full series starting in 1958 predictand agreement is strongest in spring and summer hence agreement between the reconstructions is highest in these seasons the less zonally symmetric sam structure in winter and spring influences the strength of the sam signal over land areas hence the number of stations included in the reconstructions reconstructions from 1865 were therefore derived in summer and autumn and from 1905 in winter and spring this paper examines the skill of each reconstruction by comparison with observations and reanalysis data some of the individual peaks in the reconstructions such as the most recent in austral summer represent a full hemispheric sam pattern while others are caused by regional slp anomalies over the locations of the predictors the jw and fogt reconstructions are of similar quality in summer and autumn while in winter and spring the marshall index is better reconstructed by fogt than the pc index is by jw in spring and autumn the sam shows considerable variability prior to recent decades

magnetic mapping of majhgawan diamond pipe of central india magnetic response over kimberlite lamproite pipes can be used to map their horizontal and vertical cross sections a published ground magnetic vertical intensity contour map is used to map the majhgawan kimberlite pipe near panna in central india using barnett s 1976 method we obtained a reasonable match between the computed and observed fields with three separate bodies the model suggests a possible later intrusion into the main pipe geological studies using drill hole data imply a nearly concentric vertical lithological zoning within the pipe and thus support the hypothesis of multiple intrusions indicated by magnetic data the multiple intrusion hypothesis is of interest to exploration because specific intrusions within one composite pipe may differ markedly in the incidence of diamonds the higher incidence of diamonds reported in the central part of the majhgawan pipe as compared to the outer part also supports the possibility of a later intrusion into the main pipe

observations beneath pine island glacier in west antarctica and implications for its retreat thinning ice in west antarctica is currently contributing about 10 of the observed rise in global sea level observations obtained from an autonomous underwater vehicle operating beneath pine island glacier west antarctica reveal that the glacier was recently grounded on a transverse ridge in the sea floor but now warm sea water flows through the widening gap above the ridge thinning ice in west antarctica resulting from acceleration in the flow of outlet glaciers is at present contributing about 10 of the observed rise in global sea level1 pine island glacier in particular has shown nearly continuous acceleration2 3 and thinning4 5 throughout the short observational record the floating ice shelf that forms where the glacier reaches the coast has been thinning rapidly6 driven by changes in ocean heat transport beneath it as a result the line that separates grounded and floating ice has retreated inland7 these events have been postulated as the cause for the inland thinning and acceleration8 9 here we report evidence gathered by an autonomous underwater vehicle operating beneath the ice shelf that pine island glacier was recently grounded on a transverse ridge in the sea floor warm sea water now flows through a widening gap above the submarine ridge rapidly melting the thick ice of the newly formed upstream half of the ice shelf the present evolution of pine island glacier is thus part of a longer term trend that has moved the downstream limit of grounded ice inland by 30 km into water that is 300 m deeper than over the ridge crest the pace and ultimate extent of such potentially unstable retreat10 are central to the debate over the possibility of widespread ice sheet collapse triggered by climate change11 12

ice sheet record of recent sea ice behavior and polynya variability in the amundsen sea west antarctica investigation of how regional sic is recorded in the ice sheet stratigraphy over the period 2002 2010 we find that the ice sheet chemistry is significantly correlated with sic variability within the as and pine island bay polynyas based on this result we evaluate the use of icecore chemistry as a proxy for interannual polynya variability in this region one of the largest and most persistent polynya areas in antarctica msa concentrations correlate strongly with summer sic within the polynya regions consistent with msa at this site being derived from marine biological productivity during the spring and summer cl concentrations correlate strongly with winter sic within the polynyas as well as some regions outside the polynyas consistent with cl at this site originating primarily from winter sea ice formation spatial correlations were generally insignificant outside of the polynya areas with some notable exceptions ice core glaciochemical records from this dynamic region thus may provide a proxy for reconstructing as and pine island bay polynya variability prior to the satellite era

key role of organic complexation of iron in sustaining phytoplankton blooms in the pine island and amundsen polynyas southern ocean primary productivity in the amundsen sea southern ocean is among the highest in antarctica the summer phytoplankton bloom in 2009 lasted for 470 days in both the pine island and amundsen polynyas such productive blooms require a large supply of nutrients including the trace metal iron fe the organic complexation of dissolved fe was investigated in the amundsen sea during the spring of 2009 to better understand the potential role of ligands in enhancing the local stock of dissolved fe the main sources of fe and ligands to the amundsen sea are thought to be melting sea ice and the circumpolar deep water cdw which is modified mcdw on the continental shelf and upwells beneath the coastal glaciers and ice shelves upwelling of relatively warm mcdw is also responsible for the rapid melting of the pine island glacier pig and surrounding ice shelves resulting in additional release of fe into surface waters at upwelling stations near ice shelves organic ligands were nearly saturated with fe thus enhancing the stock of fe and its availability to the phytoplankton community however ligands had little capacity to buffer additional fe input from glacial melt in these coastal upwelling regions much of the glacial fe supply is lost due to vertical export of fe via scavenging and precipitation conversely within the phytoplankton bloom in the nearby coastal polynyas the uptake of fe combined with the production of organic matter enhanced the abundance of relatively unsaturated organic ligands capable of stabilizing additional fe supplied from glacial melt these unsaturated dissolved organic ligands combined with the continuous input of fe dissolved and particulate from glacial melt appear to favor the solubilization of fe thus increasing the stock of bioavailable fe and fueling the phytoplankton bloom

inflow of warm circumpolar deep water in the central amundsen shelf the thinning and acceleration of the west antarctic ice sheet has been attributed to basal melting induced by intrusions of relatively warm salty water across the continental shelf a hydrographic section including lowered acoustic doppler current profiler measurements showing such an inflow in the channel leading to the getz and dotson ice shelves is presented here the flow rate was 0 3 0 4 sv 1 sv 10 6 m 3 s 21 and the subsurface heat loss was estimated to be 1 2 1 6 tw assuming that the inflow persists throughout the year it corresponds to an ice melt of 110 130 km 3 yr 21 which exceeds recent estimates of the net ice glacier ice volume loss in the amundsen sea the results also show a 100 150 m thick intermediate water mass consisting of circumpolar deep water that has been modified cooled and freshened by subsurface melting of ice shelves and or icebergs this water mass has not previously been reported in the region possibly because of the paucity of historical data

the effect of atmospheric forcing resolution on delivery of ocean heat to the antarctic floating ice shelves abstractoceanic melting at the base of the floating antarctic ice shelves is now thought to be a more significant cause of mass loss for the antarctic ice sheet than iceberg calving in this study a 10 km horizontal resolution circum antarctic ocean sea ice ice shelf model based on the regional ocean modeling system roms is used to study the delivery of ocean heat to the base of the ice shelves the atmospheric forcing comes from the era interim reanalysis 80 km resolution and from simulations using the polar optimized weather research and forecasting model 30 km resolution where the upper atmosphere was relaxed to the era interim reanalysis the modeled total basal ice shelf melt is low compared to observational estimates but increases by 14 with the higher resolution winds and just 3 with both the higher resolution winds and atmospheric surface temperatures the higher resolution winds lead to more heat being delivered to the ice shelf cavities from the adjacent ocean and an increase in the

iron from melting glaciers fuels phytoplankton blooms in the amundsen sea southern ocean phytoplankton characteristics and productivity the phytoplankton community composition and productivity in waters of the amundsen sea and surrounding sea ice zone were characterized with respect to iron fe input from melting glaciers high fe input from glaciers such as the pine island glacier and the dotson and crosson ice shelves resulted in dense phytoplankton blooms in surface waters of pine island bay pine island polynya and amundsen polynya phytoplankton biomass distribution was the opposite of the distribution of dissolved fe dfe confirming the uptake of glacial dfe in surface waters by phytoplankton phytoplankton biomass in the polynyas ranged from 0 6 to 14 mg chl a l 1 with lower biomass at glacier sites where strong upwelling of modified circumpolar deep water from beneath glacier tongues was observed phytoplankton blooms in the polynyas were dominated by the haptophyte phaeocystis antarctica whereas the phytoplankton community in the sea ice zone was am ix ofp antarctica and diatoms resembling the species distribution in the ross sea water column productivity based on photosynthesis versus irradiance characteristics averaged 3 00 g c m

stronger ocean circulation and increased melting under pine island glacier ice shelf the ice shelf buttressing antarctica s pine island glacier has been melting rapidly observations taken between 1994 and 2009 show that meltwater production has increased by about 50 since 1994 as a result of a stronger circulation below the ice shelf

rbsr ages of proterozoic kimberlites of india evidence for contemporaneous emplacement abstract rb sr analyses of leached phlogopite macrocrysts from kimberlite pipes 1 2 5 and 7 in south india give concordant ages of 1091 20 1092 15 1093 20 and 1091 10 ma respectively indicating contemporaneous emplacement of these pipes the present results are in contradiction with earlier measurements groundmass mineral assemblages with low rb sr ratios give a tight set of initial sr ratios at 0 7029 2 0 7019 2 0 7029 2 and 0 7030 4 suggesting derivation of the primary kimberlite magma from a relatively uniform and depleted mantle source a similar age and initial sr isotopic ratio of one sample of the majhgawan lamproite from central india imply that the proterozoic kimberlite lamproite activities in india though widely separated in space were nearly contemporaneous

ice shelf changes in pine island bay antarctica 1947 2000 aerial photographs from 1947 and 1966 satellite optical imagery from 1973 and 1980 and interferometric synthetic aperture radar insar data from 1992 1996 and 2000 are employed to detect ice shelf changes in pine island bay antarctica the front position of the fast flowing central ice shelf did not migrate discernibly over the past 50 years new cracks and rifts appeared in the 1990s however that reveal a major weakening of the ice shelf at the grounding line center the ice shelf thinned 21 m in 8 years the northern slow moving ice shelf also shows signs of decay 1 its calving front is retreating at an accelerating rate and 2 the ice shelf is slowly unpinning from its bedrock anchors these changes are taking place in a region well beyond the temperature dependent limit of viability of ice shelves and hence differ from those observed along the antarctica peninsula they are likely due to a change in oceanic forcing not to a change in air temperature one possibility is that the documented intrusion of warm circumpolar deep water on the continental shelf has increased basal melting compared to that required to maintain the ice shelf in a state of mass balance and that this has triggered a general retreat of ice in this sector

evidence of minimal carbon sequestration in the productive amundsen sea polynya the amundsen sea polynya asp is reportedly the most productive among the coastal polynyas around antarctica however observational constraints limit our understanding of the biological pump and carbon cycle in the asp we measured various carbon related parameters such as primary production bacterial production sinking flux of particulate organic carbon poc and accumulation of organic carbon in the sediment as well as hydrographic parameters during field observations and by instrument moorings over 95 of the photosynthetically produced poc was converted to suspended poc and or dissolved carbon forms in the upper 400 m layer we postulate that most of the carbon transported to the water column by the biological pump in the asp was flushed out of the shelf without being sequestered for long term storage in sediments lack of bottom water formation due to intrusion of circumpolar deep water in the lower layer reduces carbon sequestration efficiency

coastal southern ocean a strong anthropogenic co2 sink 1 large scale estimates of the southern ocean co2 sink do not adequately resolve the fluxes associated with antarctic continental shelves using a mechanistic three dimensional biogeochemical model of the ross sea we show that antarctic shelf waters are a strong sink for co2 due to high biological productivity intense winds high ventilation rates and extensive winter sea ice cover net primary production npp in these waters is 0 055 pg c yr 1 some of this carbon sinks to depth driving an influx of co2 of 20 50 g c m 2 yr 1 although currently unaccounted for the total atmospheric co2 sink on the ross sea continental shelf of 0 013 pg c yr 1 is equivalent to 27 of the most recent estimate of the co2 sink for the entire southern ocean given these results these and other highly productive waters around the antarctic continent need to be included in future budgets of anthropogenic co2