the origin of low δ18o granites and related rocks from the seychelles the 750 ma seychelles granites have whole rock 18o values that range from 1 2 to 7 5 differences in 18o values between quartz feldspar and whole rock for samples that have a range of 18o values suggest that these minerals are in magmatic equilibrium and that the whole rock 18o values were little affected by post crystallization interaction with fluids two suites of granites the mahe type and the praslin type have previously been recognized on the basis of chemical and radiogenic isotope composition the former have a mean whole rock 18o value of 5 25 0 65 1 whereas the latter are much more variable with a mean whole rock 18o value of 3 00 3 27 biotite and amphibole separates from both granite types range in d from 69 to 116 and show a positive correlation with whole rock 18o values dolerite dykes that intruded the granites during or shortly after their crystallization also have whole rock 18o values mean 2 24 1 93 lower than that expected for mantle derived basaltic rocks but these values appear to be the result of fluid rock interaction we suggest that the mahe type granites are derived mainly from juvenile mafic to intermediate crust with normal d and 18o values whereas the praslin type granites are mixtures of this source and older crust that acquired its low d and 18o values by extensive interaction with meteoric water at high temperature it is unlikely that meteoric water sufficiently depleted in d and 18o was available at 750 ma because of the relatively low latitude of the region at that time we suggest that alteration of the source took place significantly before production of the granite magmas depletion in 18o of the seychelles granites does not necessarily require a regional extensional tectonic setting at 750 ma as has been proposed

the link between climate warming and break up of ice shelves in the antarctic peninsula a review of in situ and remote sensing data covering the ice shelves of the antarctic peninsula provides a series of characteristics closely associated with rapid shelf retreat deeply embayed ice fronts calving of myriad small elongate bergs in punctuated events increasing flow speed and the presence of melt ponds on the ice shelf surface in the vicinity of the break ups as climate has warmed in the antarctic peninsula region melt season duration and the extent of ponding have increased most break up events have occurred during longer melt seasons suggesting that meltwater itself not just warming is responsible regions that show melting without pond formation are relatively unchanged melt ponds thus appear to be a robust harbinger of ice shelf retreat we use these observations to guide a model of ice shelf flow and the effects of meltwater crevasses present in a region of surface ponding will likely fill to the brim with water we hypothesize building on weertman 1973 hughes 1983 and van der veen 1998 that crevasse propagation by meltwater is the main mechanism by which ice shelves weaken and retreat a thermodynamic finite element model is used to evaluate ice flow and the strain field and simple extensions of this model are used to investigate crack propagation by meltwater the model results support the hypothesis

modis based mosaic of antarctica moa data sets continent wide surface morphology and snow grain size abstract we present digital image mosaics of surface morphology and optical snow grain size for the antarctic continent and surrounding islands assembled from 260 moderate resolution imaging spectroradiometer modis images the products are derived from modis band 1 red light 647 nm and band 2 infrared 857 nm orbit swath data acquired during the 2003 2004 austral summer multiple images of all areas are combined in a data cumulation scheme to improve spatial resolution and increase radiometric content of the mosaics the component images were de striped geo registered and re sampled to the projection grid using the modis swath to grid toolbox ms2gt software a 125 m ground equivalent polar stereographic projection was used identical to previous radar image mosaics and similar to several other continent wide data sets geo location accuracy of the final mosaics is better than 125 m swath acquisition times were limited to the range 05 00 13 30 ut to provide broad but uniform mosaic illumination regions of cloud cover blowing snow and intense forward scattering were masked prior to compositing the moa snow grain size data set image provides the first continent wide semi quantitative map of mean summer snow firn and blue ice grain size optical grain size radius was determined using a normalized difference index derived from modis band 1 and band 2 rad values atmospheric correction adjustments for directional reflectance variation and snow grain size estimation were accomplished by a look up table generated by a combination of published models of snow spectral reflectance and atmosphere radiative transfer validation of the snow grain size image is provided by in situ spectra of snow covered sea ice made in october 2003 we use the new data sets to determine major ice shelf areas and shelf edge coastline and ice grounding line vector files and determine areas of selected blue ice regions these data sets are available for download at http nsidc org data moa

polynya dynamics drive primary production in the larsen a and b embayments following ice shelf collapse 1 the climate driven collapses of the larsen a and b ice shelves have opened up new regions of the coastal antarctic to the influence of sea ice resulting in increases in seasonal primary production in this study passive microwave remote sensing of sea ice concentration and satellite imagery of ocean color are employed to quantify the magnitude of and variability in open water area and net primary productivity npp in the larsen embayments between 1997 and 2011 numerical model output provides context to analyze atmospheric forcing on the coastal ocean following ice shelf disintegration the embayments function as coastal sensible heat polynyas the larsen a and b are as productive as other antarctic shelf regions with seasonally averaged daily npp rates reaching 1232 and 1127 mg c m 2 d 1 and annual rates reaching 200 and 184 g c m 2 yr 1 respectively a persistent cross shelf gradient in npp is present with higher productivity rates offshore contrasting with patterns observed along the west antarctic peninsula embayment productivity is intimately tied to sea ice dynamics with large interannual variability in npp rates driven by open water area and the timing of embayment opening opening of the embayment is linked to periods of positive southern annular mode and stronger westerlies which lead to the vertical deflection of warm maritime air over the peninsula and down the leeward side causing increases in surface air temperature and wind velocity high productivity in these new polynyas is likely to have ramifications for organic matter export and marine ecosystem evolution

biodiversity change after climate induced ice shelf collapse in the antarctic the marine ecosystem on the eastern shelf of the antarctic peninsula was surveyed 5 and 12 years after the climate induced collapse of the larsen a and b ice shelves an impoverished benthic fauna was discovered that included deep sea species presumed to be remnants from ice covered conditions the current structure of various ecosystem components appears to result from extremely different response rates to the change from an oligotrophic sub ice shelf ecosystem to a productive shelf ecosystem meiobenthic communities remained impoverished only inside the embayments on local scales macro and mega epibenthic diversity was generally low with pioneer species and typical antarctic megabenthic shelf species interspersed antarctic minke whales and seals utilised the larsen a b area to feed on presumably newly established krill and pelagic fish biomass ecosystem impacts also extended well beyond the zone of ice shelf collapse with areas of high benthic disturbance resulting from scour by icebergs discharged from the larsen embayments

satellite observations of antarctic sea ice thickness and volume 1 we utilize satellite laser altimetry data from nasa s ice cloud and land elevation satellite icesat combined with passive microwave measurements to analyze basin wide changes in antarctic sea ice thickness and volume over a 5 year period from 2003 2008 sea ice thickness exhibits a small negative trend while area increases in the summer and fall balanced losses in thickness leading to small overall volume changes using a 5 year time series we show that only small ice thickness changes of less than 0 03 m yr and volume changes of 266 km3 yr and 160 km3 yr occurred for the spring and summer periods respectively these results are in stark contrast to the much greater observed losses in arctic sea ice volume and illustrate the different hemispheric changes of the polar sea ice covers in recent years the uncertainties in the calculated thickness and volume trends are large compared to the observed basin scale trends this masks the determination of a long term trend or cyclical variability in the sea ice cover it is found that lengthening of the observation time series along with better determination of the interannual variability of sea ice and snow densities will allow for a more statistically significant determination of long term sea ice thickness and volume trends in the southern ocean

katabatic wind forcing of the terra nova bay polynya the terra nova bay polynya is a perennial winter feature in the western ross sea antarctica which occupies roughly 1000 km2 it is formed and maintained by the combined influence of persistent katabatic winds which advect newly formed bay ice eastward and the drygalski ice tongue which prevents northward drifting pack ice from entering terra nova bay existence of anomalously strong katabatic drainage along this coast is predicted by parish s 1982 simulation of wintertime airflow which reveals a pronounced confluence of surface winds upslope from the reeves glacier where the winds are further focused by local topography the simulation is strongly supported by regional sastrugi orientations average wintertime atmospheric conditions and ice sheet topography which control surface air drainage are stable on a climatic time scale therefore persistent wintertime katabatic winds should be an annual phenomenon further evidence comes from multi year landsat images which consistently show windswept snowfree areas on the reeves glacier in marked contrast to typical antarctic katabatic winds strong persistent winter winds are observed at sea level 25 km beyond the coastal slope break air probably descends as bora type winds and is likely to be significantly denser than the air at sea level conditions are not favorable for hydraulic jumps apparently typical of other katabatic regimes the horizontal density difference is maintained during airflow across the nansen ice sheet because relatively little air mass modification occurs there in contrast to situations where air moves over an ice laden ocean observations thus suggest that katabatic winds maintain their identity for some distance seaward of the coast qualitative trajectory calculations indicate that for representative geostrophic conditions this distance is on the order of the observed polynya width estimated ice freezing rates are 20 cm day 1 but wind generated waves and currents prevent ice from consolidating the blocking effect of the drygalski ice tongue is a consequence of its orientation with regard to western ross sea ice drift patterns ice tongue length controls polynya width absence of such blocking along other coasts experiencing strong katabatic outflow partly explains why similar polynyas do not form there

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

regulation of algal blooms in antarctic shelf waters by the release of iron from melting sea ice during summer 1995 96 we measured iron in the water column and conducted iron enrichment bottle incubation experiments at a station in the central ross sea 76 30 s 170 40 w first in the presence of melting sea ice and 17 days later in ice free conditions we observed a striking temporal change in mixed layer dissolved iron concentrations at this station from 0 72 2 3 nm with sea ice present to 0 16 0 17 nm in ice free conditions these changes were accompanied by a significant drawdown in macronutrients and an approximate doubling of algal diatom biomass our incubation experiments suggest that conditions were iron replete in the presence of sea ice and iron deficient in the absence of sea ice we surmise that bioavailable iron was released into seawater from the melting sea ice stimulating phytoplankton production and the biological removal of dissolved iron from the mixed layer until iron limited conditions developed these observations suggest that the episodic release of bioavailable iron from melting sea ice is an important factor regulating phytoplankton production particularly ice edge blooms in seasonally ice covered antarctic waters

northern larsen ice shelf antarctica further retreat after collapse changes of larsen ice shelf antarctica and the surrounding glaciers after its collapse in 1995 were investigated using satellite radar imagery with emphasis onchanges in the glaciers which previously nourished the ice shelf north of seal nunataks the large glaciers retreated several kilometres inland of the previousgrounding line the velocity field of drygalski glacier the largest glacier in this area was mapped by means of interferograms derived from pairs of ers syntheticaperture radar images from 1995 and 1999 the main part of the glacier showed significant acceleration of flow over these 4 years with an increase of veocity upto three fold at the terminus similar accelerations were observed by means of interferometry on several other grounded glaciers suggesting that the removal ofice shelves could lead to an effect on eustatic sea level for larsen b the northernmost surviving part of larsen ice shelf the retreat of the ice front to october2000 is documented

polynya signature simulation method polynya area in comparison to amsr e 89 ghz sea ice concentrations in the ross sea and off the adelie coast antarctica for 2002 05 first results the polynya signature simulation method pssm is applied to special sensor microwave imager observations from different defense meteorological satellite program spacecraft for 2002 05 to analyze the polynya area in the ross sea ross ice shelf polynya risp and terra nova bay polynya tnbp and off the adelie coast mertz glacier polynya mgp antarctica on a sub daily scale the risp and the mgp exhibit similar average total polynya areas major area changes 10 000 km 2 tnpb 2000 km 2 occur over a range of 2 3 to 20 days in all regions sub daily area changes are largest for the mgp 5800 km 2 and smallest for the tnbp 800 km 2 underlining the persistence of the forcing of the latter artist sea ice asi algorithm concentration maps obtained using 89 ghz advanced microwave scanning radiometer amsr e data are compared to pssm maps yielding convincing agreement in the average similarly detailed winter polynya distribution average asi algorithm ice concentrations take values of 25 40 and 65 80 for the pssm open water and thin ice class respectively the discrepancy with expected values 0 and 100 can be explained by the different spatial resolution and frequency used by the methods a new land mask and a mask to flag icebergs are introduced comparison of pssm maps with thermal ice thickness based on avhrr infrared temperature and ecmwf era 40 data suggests an upper thickness limit for the pssm thin ice class of 20 25 cm

the relationship between the southern hemisphere annular mode and antarctic peninsula summer temperatures analysis of a high resolution model climatology abstract the large regional summer warming on the east coast of the northern antarctic peninsula ap which has taken place since the mid 1960s has previously been proposed to be caused by a trend in the southern hemisphere annular mode sam the authors utilize a high resolution regional atmospheric model climatology 14 km grid spacing to study the mechanisms that determine the response of the near surface temperature to an increase in the sam t sam month to month variations in near surface temperature and surface pressure are well represented by the model it is found that north of 68 s t sam is much larger on the eastern lee side than on the western windward side of the barrier this is because of the enhanced westerly flow of relatively warm air over the barrier which warms and dries further as it descends down the lee slope the downward motion on the eastern side of the barrier causes a decrease in surface mass balance and cloud cover south of 68 s vertical deflection across

strong surface melting preceded collapse of antarctic peninsula ice shelf 1 during the austral summer of 2001 02 melting at the surface of larsen ice shelf in the antarctic peninsula was three times greater than the average of five previous summers this exceptional melt event lasted for three months and was followed by the collapse of larsen b ice shelf during which 3 200 km2 of ice shelf surface was lost the strong melting was caused by a persistent atmospheric circulation anomaly which depleted sea ice concentrations in front of larsen ice shelf and transported warm air to the ice shelf throughout the 2001 02 summer this supports the theory that large meltwater fluxes accelerate the retreat of antarctic peninsula ice shelves

meltwater movement in a deep snowpack 2 simulation model a numerical simulation model is developed describing the one dimensional flow of meltwater in a snowpack based on established methods of modeling unsaturated groundwater flow the results of field observations of snowmelt and meltwater flow are used to determine parameters describing the hydraulic properties of the snowpack and surface energy balance measurements are used as input to the model tests of the performance of the model show a high sensitivity to the saturated hydraulic conductivity of the snowpack and to liquid water content of the snow saturated hydraulic conductivity can be measured with acceptable precision by simple field methods however measurement of liquid water content is more difficult and constitutes the major limitation affecting calibration of the model the model is relatively insensitive to exponents in the power law equations relating conductivity capillary pressure and liquid water content meltwater wave speeds predicted by the model are somewhat slower than those observed in the field observations of snowpack layering and horizontal inhomogeneity of flow suggest that these features affect transient storage of meltwater and consequently cause meltwater wave speeds to differ from those predicted by a one dimensional model

glacier acceleration and thinning after ice shelf collapse in the larsen b embayment antarctica 1 ice velocities derived from five landsat 7 images acquired between january 2000 and february 2003 show a two to six fold increase in centerline speed of four glaciers flowing into the now collapsed section of the larsen b ice shelf satellite laser altimetry from icesat indicates the surface of hektoria glacier lowered by up to 38 6 m in a six month period beginning one year after the break up in march 2002 smaller elevation losses are observed for crane and jorum glaciers over a later 5 month period two glaciers south of the collapse area flask and leppard show little change in speed or elevation seasonal variations in speed preceding the large post collapse velocity increases suggest that both summer melt percolation and changes in the stress field due to shelf removal play a major role in glacier dynamics

estimation of equivalent permeability of snowpack using a snowmelt lysimeter at patsio northwest himalaya the meltwater percolation process through the snowpack greatly influences its physical and mechanical properties the percolation process is important for understanding the spring avalanche phenomenon as well as the meltwater runoff for basin hydrology studies the permeability of individual snow layers depends on parameters such as porosity pore connectivity and the geometrical shape of the pores snowpack equivalent permeability plays an important role in governing the transmission of meltwater through the different layers of the snowpack in this paper we present the design fabrication and installation of a snowmelt lysimeter at patsio field research station himachal pradesh india and determine the snowpack equivalent permeability using lysimeter discharge data the snowmelt lysimeter having a collector area of 6 25 m 2 and a high capacity snowmelt measuring tipping bucket was installed on flat ground near the observatory with a data acquisition system snowmelt discharge measurements were made for two melt seasons 2006 07 and 2007 08 snow and meteorological data were collected at 15 min intervals using a semi automatic weather station the hourly surface snowmelt was estimated using an energy balance approach the maximum daily discharge was 2 mm w e h 1 for most of the observation period the daily mean wave speed of the meltwater front varied from 109 to 285 mm h 1 for a daily mean discharge range of 0 6 1 8 mm w e h 1 while wave speeds for a particular melt flux of 2 mm w e h 1 varied between 113 and 486 mm h 1 the pore size distribution index was estimated using the power fit relation between wave speed and discharge the equivalent permeability of the snowpack was found to vary between 3 4 x 10 8 and 9 9 x 10 12 m 2

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

the impact of a changing southern hemisphere annular mode on antarctic peninsula summer temperatures since the mid 1960s rapid regional summer warming has occurred on the east coast of the northern antarctic peninsula with near surface temperatures increasing by more than 2 degrees c this warming has contributed significantly to the collapse of the northern sections of the larsen ice shelf coincident with this warming the summer southern hemisphere annular mode sam has exhibited a marked trend suggested by modeling studies to be predominantly a response to anthropogenic forcing resulting in increased westerlies across the northern peninsula observations and reanalysis data are utilized to demonstrate that the changing sam has played a key role in driving this local summer warming it is proposed that the stronger summer westerly winds reduce the blocking effect of the antarctic peninsula and lead to a higher frequency of air masses being advected eastward over the orographic barrier of the northern antarctic peninsula when this occurs a combination of a climatological temperature gradient across the barrier and the formation of a fohn wind on the lee side typically results in a summer near surface temperature sensitivity to the sam that is 3 times greater on the eastern side of the peninsula than on the west sam variability is also shown to play a less important role in determining summer temperatures at stations west of the barrier in the northern peninsula similar to 62 degrees s both at the surface and throughout the troposphere this is in contrast to a station farther south similar to 65 degrees s where the sam exerts little influence

rapid collapse of northern larsen ice shelf antarctica in january 1995 4200 square kilometers of the northern larsen ice shelf antarctic peninsula broke away radar images from the ers 1 satellite complemented by field observations showed that the two northernmost sections of the ice shelf fractured and disintegrated almost completely within a few days this breakup followed a period of steady retreat that coincided with a regional trend of atmospheric warming the observations imply that after an ice shelf retreats beyond a critical limit it may collapse rapidly as a result of perturbated mass balance

from ice shelf tributary to tidewater glacier continued rapid recession acceleration and thinning of rohss glacier following the 1995 collapse of the prince gustav ice shelf antarctic peninsula glasser n f scambos t a bohlander j truffer m pettit e davies b j 2011 journal of glaciology 57 203 397 406

2001 2009 elevation and mass losses in the larsen a and b embayments antarctic peninsula we investigate the elevation and mass balance response of tributary glaciers following the loss of the larsen a and b ice shelves antarctic peninsula in 1995 and 2002 respectively our study uses modis imagery to track ice extent and aster and spot5 digital elevation models dems plus atm and icesat laser altimetry to track elevation changes spanning the period 2001 09 the measured larsen b tributary glaciers hektoria green evans punchbowl jorum and crane lost up to 160 m in elevation during 2001 06 and thinning continued into 2009 elevation changes were small for the more southerly flask and leppard glaciers which are still constrained by a larsen b ice shelf remnant in the northern embayment continued thinning of 3 m a 1 on drygalski glacier 14 years after the larsen a ice shelf disintegrated suggests that mass losses for the exposed larsen b tributaries will continue for years into the future grounded ice volume losses exceed 13 km 3 for crane glacier and 30 km 3 for the hektoria green evans glaciers the combined mean loss rate for 2001 06 is at least 11 2 gt a 1 our values differ significantly from published mass budget based estimates for these embayments but are a reasonable fraction of grace derived rates for the region 40 gt a 1

interpretation of recent southern hemisphere climate change climate variability in the high latitude southern hemisphere sh is dominated by the sh annular mode a large scale pattern of variability characterized by fluctuations in the strength of the circumpolar vortex we present evidence that recent trends in the sh tropospheric circulation can be interpreted as a bias toward the high index polarity of this pattern with stronger westerly flow encircling the polar cap it is argued that the largest and most significant tropospheric trends can be traced to recent trends in the lower stratospheric polar vortex which are due largely to photochemical ozone losses during the summer fall season the trend toward stronger circumpolar flow has contributed substantially to the observed warming over the antarctic peninsula and patagonia and to the cooling over eastern antarctica and the antarctic plateau

foehn winds in the mcmurdo dry valleys antarctica the origin of extreme warming events abstract foehn winds resulting from topographic modification of airflow in the lee of mountain barriers are frequently experienced in the mcmurdo dry valleys mdvs of antarctica strong foehn winds in the mdvs cause dramatic warming at onset and have significant effects on landscape forming processes however no detailed scientific investigation of foehn in the mdvs has been conducted as a result they are often misinterpreted as adiabatically warmed katabatic winds draining from the polar plateau herein observations from surface weather stations and numerical model output from the antarctic mesoscale prediction system amps during foehn events in the mdvs are presented results show that foehn winds in the mdvs are caused by topographic modification of south southwesterly airflow which is channeled into the valleys from higher levels modeling of a winter foehn event identifies mountain wave activity similar to that associated with midlatitude foehn winds these events are found to be caused by str

testing the foodbancs hypothesis seasonal variations in near bottom particle flux bioturbation intensity and deposit feeding based on 234th measurements abstract naturally occurring 234th 24 d half life was used on the west antarctic continental shelf to evaluate temporal variations in the flux of particulate material reaching the seabed bioturbation intensity the seasonal continuity of feeding by benthic fauna and trends in particle selection during ingestion for six common detritivores four surface deposit feeders and two subsurface deposit feeders these measurements were made at three stations during the five foodbancs cruises december 1999 march june and october 2000 and march 2001 to assess the nature of pelagic benthic coupling on the shelf and to evaluate the seabed as a potential food bank for deposit feeders when surface primary production is minimal two summer regimes were sampled march 2000 and march 2001 with the latter exhibiting a distinct 1 2 cm thick phytodetritus layer in nearly all sediment core samples at site b the 234th fluxes into the near bottom 150 170 mab sediment traps were indistinguishable for the december march 2000 march june 2000 and june october 2000 sampling intervals fluxes ranging from 170 to 280 dpm m 2 d 1 however the sediment trap 234th flux measured for the october 2000 march 2001 interval 1000 dpm m 2 d 1 was 5 fold greater than during the other three sampling periods consistent with the deposition of a phytodetritus layer the steady state 234th fluxes derived from seabed inventories at site b were 2 4 2 7 times greater than the sediment trap 234th fluxes indicating substantial scavenging of this particle reactive radiotracer in the bottom 150 m of the water column and or lateral transport near the seabed the seabed 234th inventories at the three stations showed no variation during the first four cruises but were significantly greater during cruise fb v march 2001 when the phytodetritus layer occurred based on 234th distributions in the seabed bioturbation intensities quantified using the diffusive mixing coefficient db varied from 0 5 to 97 cm2 yr 1 mixing coefficients were significantly lower during fb ii than during fb iii but no other time comparisons were statistically significant p 0 05 234th dbs showed no distinct seasonality and no correlation with either organic carbon flux into the sediment traps or 234th inventory in the seabed the four surface deposit feeders examined an echiuran worm and three holothurians protelpidia murrayi bathyplotes fuscivinculum and peniagone vignoni exhibited greater particle selection for recently deposited sediment during ingestion than the two subsurface deposit feeders studied a head down deposit feeding holothurian molpadia musculus and an irregular urchin amphipneustes lorioli all six deposit feeders contained excess 234th activity in gut sediments during all five cruises indicating sediment ingestion year round even during the austral winter the lack of seasonal variation in bioturbation intensity and the demonstration of year round feeding in deposit feeders are consistent with the hypothesis that the seafloor sediments accumulate labile organic matter produced during periods of high primary production and that deposit feeders utilize this food source as a food bank on a year round basis

recent atmospheric warming and retreat of ice shelves on the antarctic peninsula in 1978 mercer1 discussed the probable effects of climate warming on the antarctic ice sheet predicting that one sign of a warming trend in this region would be the retreat of ice shelves on the antarctic peninsula analyses of 50 year meteorological records have since revealed atmospheric warming on the antarctic peninsula2 3 and a number of ice shelves have retreated4 8 here we present time series of observations of the areal extent of nine ice shelves on the antarctic peninsula showing that five northerly ones have retreated dramatically in the past fifty years while those further south show no clear trend comparison with airtemperature data shows that the pattern and magnitude of ice shelf retreat is consistent with the existence of an abrupt thermal limit on iceshelf viability the isotherm associated with this limit having been driven south by the atmospheric warming ice shelves therefore appear to be sensitive indicators of climate change

a low level explanation for the recent large warming trend over the western antarctic peninsula involving blocked winds and changes in zonal circulation 1 we demonstrate a mechanism whereby the impact of stronger circumpolar westerly winds on the mountains of the antarctic peninsula contributes significantly to the enhanced warming trend observed over its western side in the last 50 years numerical and laboratory meteorological modelling demonstrate how when westerly winds impinge on this side warm air below the height 1 5 2 0 km of the peninsula is advected in a southerly direction the strength of the annual mean westerly winds has increased by about 15 20 since the 1960s while the modelling results indicate that contemporaneously the air advected to its western side originates from an increasingly northerly and warmer location this gives rise to increased northerlies and a greater transport of warm air into this region consequently there is a reduction in the sea ice extent further amplifying the local warming this low level orographic mechanism for the local climate trend is supported by observational evidence

phytoplankton biomass and photosynthetic competency in the summertime mertz glacier region of east antarctica abstract vertical profiles of water temperature salinity beam transmission density pressure wind speed wind direction phytoplankton biomass chlorophyll a chl a plus phaeophytin a and photosynthetic competency by fast repetition rate fluorometry are presented for the mertz glacier region east antarctica for a 3 week period during the austral summer 2000 2001 injection of low salinity water from the melting of the ice pack formed a shallow ca 25 m mixed layer offshore two distinct deep mixing features were observed associated to varying degrees with high chlorophyll levels and high photosynthetic competency along the adelie land coast a deep mixing layer 1400 m with chl a concentrations of 386 mg m 2 and elevated fv fm 0 5 was observed at the eastern end of the study area along a seaward extension of fast ice a bloom of phaeocystis antarctica bloom formed within a shallow 24 m mixed layer with surface chl a concentrations of ca 8 mg m 3 and elevated fv fm 0 5 this feature also had high surface salinity 34 and was contiguous with a deep mixing feature 236 m frrf parameters fv fm and psii were strongly suppressed in surface waters

regions of rapid sea ice change an inter hemispheric seasonal comparison this bi polar analysis resolves ice edge changes on space time scales relevant for investigating seasonal iceocean feedbacks and focuses on spatio temporal changes in the timing of annual sea ice retreat and advance over 1979 80 to 2010 11 where arctic sea ice decrease is fastest the sea ice retreat is now nearly 2 months earlier and subsequent advance more than 1 month later compared to 1979 80 resulting in a 3 month longer summer ice free season in the antarctic peninsula and bellingshausen sea region sea ice retreat is more than 1 month earlier and advance 2 months later resulting in a more than 3 month longer summer icefree season in contrast in the western ross sea antarctica region sea ice retreat and advance are more than 1 month later and earlier respectively resulting in a more than 2 month shorter summer ice free season regardless of trend magnitude or direction and at latitudes mostly poleward of 70 n s there is strong correspondence between anomalies in the timings of sea ice retreat and subsequent advance but little correspondence between advance and subsequent retreat these results support a strong ocean thermal feedback in autumn in response to changes in spring sea ice retreat further model calculations suggest different net ocean heat changes in the arctic versus antarctic where autumn sea ice advance is 1 versus 2 months later ocean atmosphere changes particularly in boreal spring and austral autumn i e during march may are discussed and compared as well as possible inter hemispheric climate connections

mass loss of larsen b tributary glaciers antarctic peninsula unabated since 2002 ice mass loss continues at a high rate among the large glacier tributaries of the larsen b ice shelf following its disintegration in 2002 we evaluate recent mass loss by mapping elevation changes between 2006 and 2010 11 using differencing of digital elevation models dems the measurement accuracy of these elevation changes is confirmed by a null test subtracting dems acquired within a few weeks the overall 2006 2010 11 mass loss rate 9 0 2 1 gt a 1 is similar to the 2001 02 2006 rate 8 8 1 6 gt a 1 derived using dem differencing and laser altimetry this unchanged overall loss masks a varying pattern of thinning and ice loss for individual glacier basins on crane glacier the thinning pulse initially greatest near the calving front is now broadening and migrating upstream the largest losses are now observed for the hektoria green glacier basin having increased by 33 since 2006 our method has enabled us to resolve large residual uncertainties in the larsen b sector and confirm its state of ongoing rapid mass loss

the permeability of a melting snow cover data from snow lysimeters in california and vermont are used to find the saturated permeability of a melting snow cover in the range of 10 40 10 10 m2 depending on snow density the unsaturated permeability increases as about the third power of liquid saturation the gravity flow theory is shown to be an accurate representation of meltwater drainage from snow covers in two diverse areas even though the snow covers are treated as homogeneous units the variation of saturated permeability with snow density occurs about as predicted by shimizu s formula for dry snow although ice layers decrease the permeability somewhat

coastal landfast sea ice decay and breakup in northern alaska key processes and seasonal prediction 1 seasonal breakup of landfast sea ice consists of movement and irreversible ice detachment in response to winds or oceanic forces in the late stages of ice decay the breakup process of landfast sea ice in the chukchi sea at barrow alaska was analyzed for the years 2000 through 2010 on the basis of local observations of snow and ice conditions weather records image sequences obtained from cameras coastal x band marine radar and satellite imagery we investigated the relation of breakup to winds tides and nearshore current measurements from a moored acoustic doppler current profiler two breakup modes are distinguished at barrow on the basis of the degree of ice decay mechanical breakup due to wind and oceanic forces follows ablation and weakening of the ice thermal breakup is the result of ice disintegration under melt ponds requiring little force to induce dispersion grounded pressure ridges are pivotal in determining the breakup mode the timing of thermal breakup of the nearshore ice cover was found to correlate with the measured downwelling solar radiation in june and july this linkage allows for the development of an operational forecast of landfast ice breakup results from forecasts during 2 years demonstrate that thermal breakup can be predicted to within a couple of days 2 weeks in advance the cumulative shortwave energy absorbed by the ice cover provides for a measure of the state of ice decay and potential for disintegration discriminating between the two modes of breakup bears the potential to greatly increase forecasting skill

antarctic sea ice parameters from amsr e data using two techniques and comparisons with sea ice from ssm i 1 we use two algorithms to process advanced microwave scanning radiometer for the earth observing system amsr e data in order to determine algorithm dependence if any on the estimates of sea ice concentration ice extent and area and trends and to evaluate how amsr e data compare with historical special sensor microwave imager ssm i data the monthly ice concentrations derived from the two algorithms from amsr e data the amsr e bootstrap algorithm or aba and the enhanced nasa team algorithm or nt2 differ on average by about 1 3 with data from the consolidated ice region being comparable for aba and nt2 retrievals while data in the marginal ice zones and thin ice regions show slightly higher values when the nt2 algorithm is used the iceextents and areas derived separately from amsr e using these two algorithms are however in good agreement with the differences aba nt2 being about 0 07 106 km2 on average for ice extents and 0 07 106 km2 for ice area which are small compared with mean seasonal values of 10 5 106 and 9 8 106 for ice extent and area respectively likewise extents and areas derived from the same algorithm but from amsr e and ssm i data are consistent but differ by about 0 24 106 km2 and 0 14 106 km2 respectively the discrepancies are larger with the estimates of extents than area mainly because of differences in channel selection and sensor resolutions trends in extent during the amsr e era were also estimated and results from all three data sets are shown to be in good agreement within errors

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