a global view of martian surface compositions from mgs tes thermal emission spectrometer tes data from the mars global surveyor mgs are used to determine compositions and distributions of martian low albedo regions two surface spectral signatures are identified from low albedo regions comparisons with spectra of terrestrial rock samples and deconvolution results indicate that the two compositions are a basaltic composition dominated by plagioclase feldspar and clinopyroxene and an andesitic composition dominated by plagioclase feldspar and volcanic glass the distribution of the two compositions is split roughly along the planetary dichotomy the basaltic composition is confined to older surfaces and the more silicic composition is concentrated in the younger northern plains

monitoring and analysis of ocean swell fields from space new methods for routine observations 1 satellite synthetic aperture radar sar observations can provide a global view of ocean swell fields when using a specific wave mode sampling a methodology is presented to routinely derive integral properties of the longer wavelength swell portion of the wave spectrum from sar level 2 products and both monitor and predict their evolution across ocean basins sar derived estimates of swell height and energy weighted peak period and direction are validated against buoy observations and the peak directions are used to project the peak periods in one dimension along the corresponding great circle route both forward and back in time using the peak period group velocity the resulting real time data set of great circle projected peak periods produces two dimensional maps that can be used to monitor and predict the spatial extent and temporal evolution of individual ocean swell fields as they propagate from their source region to distant coastlines the result is found to be consistent with the dispersive arrival of peak swell periods at a midocean buoy the simple great circle propagation method cannot project the swell heights in space like the peak periods because energy evolution along a great circle is a function of the source storm characteristics and the unknown swell dissipation rate a more general geometric optics model is thus proposed for the far field of the storms this model is applied here to determine the attenuation over long distances for one of the largest recorded storms observations of 15 s period swells are consistent with a constant dissipation rate that corresponds to a 3300 km e folding scale for the energy in this case swell dissipation is a significant term in the wave energy balance at global scales

spectral evidence for weathered basalt as an alternative to andesite in the northern lowlands of mars mineral abundances derived from the analysis of remotely sensed thermal emission data from mars have been interpreted to indicate that the surface is composed of basalt surface type 1 and andesite surface type 2 1 the global distribution of these rock types is divided roughly along the planetary dichotomy which separates ancient heavily cratered crust in the southern hemisphere basalt from younger lowland plains in the north andesite 1 but the existence of such a large volume of andesite is difficult to reconcile with our present understanding of the geological evolution of mars here we reinterpret martian surface rock lithologies using mineral abundances from previous work1 and new mineralogies derived from a spectral end member set representing minerals common in unaltered and low temperature aqueously altered basalts our results continue to indicate the dominance of unaltered basalt in the southern highlands but reveal that the northern lowlands can be interpreted as weathered basalt as an alternative to andesite the coincidence between locations of such altered basalt and a suggested northern ocean basin implies that lowland plains material may be composed of basalts weathered under submarine conditions or weathered basaltic sediments transported into this depocentre

searching for the source regions of martian meteorites using mgs tes integrating martian meteorites into the global distribution of igneous materials on mars the objective of this study was to identify and map possible source regions for all 5 known martian meteorite lithologies basalt lherzolite clinopyroxenite orthopyroxenite and dunite using data from the mars global surveyor thermal emission spectrometer mgs tes we deconvolved the tes data set using laboratory spectra of 6 martian meteorites los angeles zagami alh a77005 nakhla alh 84001 and chassigny as end members along with atmospheric and surface spectra previously derived from tes data global maps 16 pixels degree of the distribution of each meteorite end member show that meteorite like compositions are not present at or above tes detectability limits over most of the planet s dust free regions however we have confidently identified local scale 100s1000s km2 concentrations of olivine and orthopyroxene bearing materials similar to alh a77005 chassigny and alh 84001 in nili fossae in and near ganges chasma in the argyre and hellas basin rims and in eos chasma nakhla like materials are identified near the detection limit throughout the eastern valles marineris region and portions of syrtis major basaltic shergottites were not detected in any spatially coherent areas at the scale of this study martian meteorite like lithologies represent only a minor portion of the dust free surface and thus are not representative of the bulk composition of the ancient crust meteorite like spectral signatures identified above tes detectability limits in more spatially restricted areas tens of km are targets of ongoing analysis

pyroxene spectroscopy revisited spectral compositional correlations and relationship to geothermometry the authors wish to thank the various agencies which have provided the necessary support for this project including grants in aid of research from sigma xi the scientific research society to e a c the geological society of america grant 3741 87 to e a c and nasa planetary geology and geophysics grant nagw 642 to m j g

storm waves focusing and steepening in the agulhas current satellite observations and modeling strong ocean currents can modify the height and shape of ocean waves possibly causing extreme sea states in particular conditions the risk of extreme waves is a known hazard in the shipping routes crossing some of the main current systems modeling surface current interactions in standard wave numerical models is an active area of research that benefits from the increased availability and accuracy of satellite observations we report a typical case of a swell system propagating in the agulhas current using wind and sea state measurements from several satellites jointly with state of the art analytical and numerical modeling of wave current interactions in particular synthetic aperture radar and altimeter measurements are used to show the evolution of the swell train and resulting local extreme waves a ray tracing analysis shows that the significant wave height variability at scales 100 km is well associated with the current vorticity patterns predictions of the wavewatch iii numerical model in a version that accounts for wave current interactions are consistent with observations although their effects are still under predicted in the present configuration from altimeter measurements very large significant wave height gradients are shown to be well captured and also associated with the current vorticity patterns at global scale

olivine and pyroxene diversity in the crust of mars datafromthe observatoire pour la mineralogie l9eau les glaces et l9activite omega on the mars express spacecraft identify the distinct mafic rock forming minerals olivine low calcium pyroxene lcp and high calcium pyroxene hcp on the surface of mars olivine and hcp rich regions are found in deposits that span the age range of geologic units however lcp rich regions are found only in the ancient noachian aged units which suggests that melts for these deposits were derived from a mantle depleted in aluminum and calcium extended dark regions in the northern plains exhibit no evidence of strong mafic absorptions or absorptions due to hydrated materials

results from the ism experiment the imaging spectrometer ism operating in the near infrared is the first ever flown in space for planetary observation with a spectral range of 0 76 3 14 m its main goals were to obtain information on the mineralogical composition of the surfaces of mars and phobos and on the composition spatial and temporal variations of the martian atmosphere the infrared imaging spectrometer ism acquired 40 000 spectra of mars and phobos here we present the first results on the surface mineralogy of mars and phobos and the atmospheric composition of mars

outer organic layer and internal repair mechanism protects pteropod limacina helicina from ocean acidification scarred shells of polar pteropod limacina helicina collected from the greenland sea in june 2012 reveal a history of damage most likely failed predation in earlier life stages evidence of shell fracture and subsequent re growth is commonly observed in specimens recovered from the sub arctic and further afield however at one site within sea ice on the greenland shelf shells that had been subject to mechanical damage were also found to exhibit considerable dissolution it was evident that shell dissolution was localised to areas where the organic periostracal sheet that covers the outer shell had been damaged at some earlier stage during the animal s life where the periostracum remained intact the shell appeared pristine with no sign of dissolution specimens which appeared to be pristine following collection were incubated for four days scarring of shells that received periostracal damage during collection only became evident in specimens that were incubated in waters undersaturated with respect to aragonite ar 1 while the waters from which the damaged specimens were collected at the greenland sea sea ice margin were not ar 1 the water column did exhibit the lowest ar values observed in the greenland and barents seas and was likely to have approached ar 1 during the winter months we demonstrate that l helicina shells are only susceptible to dissolution where both the periostracum has been breached and the aragonite beneath the breach is exposed to waters of ar 1 exposure of multiple layers of aragonite in areas of deep dissolution indicate that as with many molluscs l helicina is able to patch up dissolution damage to the shell by secreting additional aragonite internally and maintain their shell we conclude that unless breached the periostracum provides an effective shield for pteropod shells against dissolution in waters ar 1 and when dissolution does occur the animal has an effective means of self repair we suggest that future studies of pteropod shell condition are undertaken on specimens from which the periostracum has not been removed in preparation

effects of glass content and oxidation on the spectra of snc like basalts applications to mars remote sensing 1 we have investigated the effects of crystallization and oxidation on the visible and near infrared visnir and mid infrared mid ir spectra of materials with a shergotty nakhla chassigny snc basaltic composition in order to investigate potential links between martian visnir spectra martian mid ir spectra and snc meteorite data snc basalt samples of varying crystallinities were synthesized and subsequently oxidized in air at 700 c for 1 7 days and reflectance spectra of both fine 75 m and coarse 75 500 m basalt samples were obtained before and after oxidation the effects of crystallization on the spectral properties are readily observed in the unoxidized products in the visnir increasing crystallization is accompanied by an increasing influence of pyroxene absorptions and decreasing influence of glass absorptions in the mid ir changes in spectral properties with crystallization are due to the variations in relative amounts of glass pyroxene and plagioclase oxidation alters the glass and pyroxenes within the samples leading to changes in visnir and mid ir spectral shapes although distinct signatures of oxidation products are not always observed both spectral and electron microscopy data indicate that hematite is the dominant oxidation product in the pigeonite and glass of the samples in pigeonite hematite is present in nanophase form and leads to the diminishment of the diagnostic 1 and 2 m pyroxene absorptions in the visnir as well as pyroxene absorptions expressed between 800 and 1100 cm 1 in the mid ir in glass hematite forms a near surface layer that is detected with varying efficiencies in the visnir and mid ir depending on the crystallinity and particle size of the analyzed sample oxidized snc basalt samples of various crystallinities and fine grain sizes provide the best analogs to mars remote sensing data in the visnir and mid ir in the visnir partially crystalline oxidized snc basalts can reproduce martian dark region characteristics in the mid ir similarities exist between the spectra of a partially crystalline oxidized snc basalt and the basalt lithology detected by the thermal emission spectrometer tes the andesite lithology detected by tes is best matched by the spectrum of a fully crystalline oxidized snc basalt these results imply that plagioclase rich lithologies are not required by tes data and that observed variations in spectral character of dark regions across the martian surface can be explained by snc basalts influenced by oxidation coupled with variations in degree of crystallization

the rocks of mars from far and near award of the meteoritical society 2001 h y mcsween jr the leonard medal address the rocks of mars from far and near

seeing through the dust martian crustal heterogeneity and links to the snc meteorites through the application of new analytical techniques to high spatial resolution imaging spectrometer data the ferrous mineralogy of major volcanic terrains on mars is shown to consist of significant fractions of both low and high calcium pyroxene changes in the relative abundances of these pyroxenes are observed for units of different age and morphology even in regions with higher degrees of alteration and contamination from dust volcanic rocks with these characteristics are uncommon on earth but are typical of the basaltic snc meteorites shergottites nakhlites and chassignites thought to be from mars thus it is possible to infer even through the veil of dust that the snc meteorites have mineralogic affinities to major volcanic provinces on mars and are therefore truly representative of the heterogeneity observed on the surface of the red planet

ocean wave directional spectra and wave current interaction in the agulhas from the shuttle imaging radar b synthetic aperture radar sir b synthetic aperture radar ocean wave spectra for a 200 km pass crossing the agulhas current off the coast of africa are analyzed a significant enhancement of one spectral peak along the northern edge of the current is attributed both to amplification of the waves by refraction dominated wave current interaction and to transient specular backscatter contributions spatially correlated to the waves

mantled and exhumed terrains in terra meridiani mars 1 hematite bearing deposits in the terra meridiani region of mars constitute the top stratum of a partially eroded layered complex that covers dissected noachian aged cratered terrain the hematite unit consists of dark plains and dunes covering a bright substrate this substrate is fully exposed beyond the borders of the hematite bearing deposit and consists of polygonal ground separated by ridges or valleys together with layered deposits that have been eroded into a variety of landforms the complex is partially covered by a regional scale aeolian mantle that thickens toward the north the hematite bearing stratum exhibits low albedoes pulse widths and intermediate thermal inertias whereas the underlying unit exhibits high values of these parameters both units have spectral emissivity signatures similar to those for the low albedo cratered terrain to the south with the addition of hematite for the top stratum the complex is interpreted to consist of extensive plains forming lava flows and tephra deposits emplaced during an extensional regime and at least partially buried by an aeolian mantle aeolian stripping of the mantle exposed much of the complex and differentially eroded the deposits to produce the landforms existent today exploration of the hematite bearing deposits by the 2003 mars exploration rover opportunity will allow testing of the hypotheses presented since this stratum has been locally reworked into dunes that only partially cover the underlying brighter portion of the complex in particular the rover based measurements will allow us to test the extent to which the unusual remote sensing properties of the units indicate aqueous alteration

mars surface diversity as revealed by the omega mars express observations the observatoire pour la mineralogie l eau les glaces et l activite omega investigation on board the european space agency mars express mission is mapping the surface composition of mars at a 0 3 to 5 kilometer resolution by means of visible near infrared hyperspectral reflectance imagery the data acquired during the first 9 months of the mission already reveal a diverse and complex surface mineralogy offering key insights into the evolution of mars omega has identified and mapped mafic iron bearing silicates of both the northern and southern crust localized concentrations of hydrated phyllosilicates and sulfates but no carbonates and ices and frosts with a water ice composition of the north polar perennial cap as for the south cap covered by a thin carbon dioxide ice veneer

in situ compositions of martian volcanics implications for the mantle the primary objective of this analysis is to determine the mineralogic composition of relatively pristine terrains exposed on the surface of mars this analysis is conducted using imaging spectrometer data acquired in 1989 by the imaging spectrometer for mars ism instrument that was onboard the phobos ii spacecraft the ism instrument acquired some of the highest spectral 64 channels between 0 77 and 3 14 m and spatial resolution 22 km pixel observations to date of mars focused on the equatorial region relatively unaltered surfaces were identified in these data on the basis of their spectral properties low albedo weak spectral slope absence of ferric absorptions and were found in volcanic terrains of syrtis major valles marineris ophir planum and sinus meridiani oxia palus spectra representative of the diversity among terrains were extracted for detailed analysis using the modified gaussian model to determine the primary mafic mineralogy it was determined that the mafic mineralogy of the regions investigated is dominated by low calcium and high calcium pyroxene lcp hcp and that there was homogeneity within a given region but some heterogeneity between regions in the relative abundance of lcp to hcp the two pyroxene mineralogy is consistent with the mineralogies of the basaltic snc meteorites believed to have originated on mars two pyroxene volcanic mineralogies are indicative of large degrees of partial melting e g komatiites or a mantle source depleted in aluminum integration of these findings with previous studies of mars and the snc meteorites indicates that 1 the snc mineralogies are representative of large volcanic regions of mars with surface ages as old as 2 3 ga 2 the martian mantle was depleted in aluminum at least as long ago as the oldest terrain analyzed ophir planum and 3 there has been little evolution in the composition of mantle source regions as the 180 ma snc mineralogies are comparable to those of the oldest terrains analyzed

relation of the spectroscopic reflectance of olivine to mineral chemistry and some remote sensing implications using high resolution visible and near infrared diffuse spectral reflectance we have systematically investigated apparent wavelength shifts as a function of mineral chemistry in the fe mg olivine series from fo11 to fo91 the study also shows that trace amounts of nickel can be spectrally detected in the olivine structure we show that significant compositional information can only be extracted at relatively high resolution because the overall spectral characteristics of the olivines change only subtly as a function of the fe mg ratio significant spectral variation as a function of grain size is also demonstrated adding a further complication to the interpretation of remotely sensed data from olivine rich surfaces this laboratory study is expected to aid in the interpretation of remotely sensed data from both terrestrial and extraterrestrial bodies terrestrial applications may include the recognition of ultramafic ultrabasic and basaltic terrains which in themselves may have mineral potential among extraterrestrial applications the asteroids are obvious candidates for further examination if instrumentation can provide the necessary wavelength coverage resolution and signal to noise ratio so that spectra can be compared to those laboratory data discussed here some permutations of fe mg ni relations in olivines are discussed as they apply to the interpretation of asteroid surfaces and other extraterrestrial bodies

analysis of terrestrial and martian volcanic compositions using thermal emission spectroscopy 2 application to martian surface spectra from the mars global surveyor thermal emission spectrometer atmospherically corrected thermal infrared spectra of large regions of the martian surface from the mars global surveyor thermal emission spectrometer mgs tes previously have been interpreted to represent two general spectral classes one class represents a basalt to basaltic andesite composition and the other class represents a basaltic andesite to andesite composition we have performed new linear deconvolutions of the two martian surface type spectra with an end member set tailored to represent volcanic rock types our preparatory study of laboratory spectra of terrestrial volcanic rocks acquired at 2 cm 21 sampling convolved to tes spectral sampling 10 cm 21 shows little degradation in deconvolution results when compared to results acquired using the higher spectral resolution data indicating that the deconvolution technique is valid for analyzing data at tes resolution our spectral fits to the martian data agree well with previous models and do not exhibit any notable deviations from the martian spectra that would indicate the absence of any significant end members in our model modal mineralogies obtained with these new spectral fits also compare favorably within the previously stated uncertainties to prior results the newly derived modal mineralogies are used with new and traditional classification schemes for volcanic igneous rocks introduced in a companion paper wyatt et al this issue to classify the martian compositions our results substantiate the previously proposed hypothesis that these two spectral classes on the martian surface represent volcanic compositions with distinguishable differences in silica content ranging from basalt to andesite

a new insight from space into swell propagation and crossing in the global oceans a half century ago it was recorded that ocean swells can propagate up to halfway around the globe however from a global perspective how ocean swells propagate in the global oceans has yet to be depicted to date synthetic aperture radar sar is the only available remote sensing instrument to measure the two dimensional information of ocean surface waves here a 10 year 2002 2012 global wave data set of the spaceborne advanced sar on board the european space agency s satellite envisat and the global wind data set of the windsat were used to 1 depict the propagation routes of ocean swells in the global oceans 2 identify four distinguished crossing swell pools and 3 interpret how these pools are formed together these findings yield a new insight into ocean swells propagation and the consequent occurrence of crossing swells on a global ocean scale from space which will further deepen our understanding of nature of ocean

extensive dissolution of live pteropods in the southern ocean as a result of ocean acidification aragonite may become undersaturated by 2050 in the upper layers of the southern ocean analyses of sea snail specimens extracted live from the southern ocean in january and february 2008 show that the shells of these organisms are already dissolving

sun glitter imagery of surface waves part 2 waves transformation on ocean currents under favorable imaging conditions the sentinel 2 multi spectral instrument msi can provide spectacular and novel quantitative ocean surface wave directional measurements in satellite sun glitter imagery ssgi owing to a relatively large swath with high spatial resolution 10 m ocean surface roughness mapping capabilities changes in ocean wave energy and propagation direction can be precisely quantified at very high resolution across spatial distances of 10 km and more this provides unique opportunities to study ocean wave refraction induced by spatial varying surface currents as expected and demonstrated over the grand agulhas current area the mesoscale variability of near surface currents documented and reconstructed from satellite altimetry can significantly deflect in coming south western swell systems based on ray tracing calculations and unambiguously revealed from the analysis of sentinel 2 msi ssgi measurements the variability of the near surface current explains significant wave current refraction leading to wavetrapping phenomenon and strong local enhancement of the total wave energy in addition to its importance for wave modeling and hazard prediction these results open new possibilities to combine different satellite measurements and greatly improve the determination of the upper ocean mesoscale vorticity motions

small scale open ocean currents have large effects on wind wave heights tidal currents and large scale oceanic currents are known to modify ocean wave properties causing extreme sea states that are a hazard to navigation recent advances in the understanding and modeling capability of open ocean currents have revealed the ubiquitous presence of eddies fronts and filaments at scales 10 100 km based on realistic numerical models we show that these structures can be the main source of variability in significant wave heights at scales less than 200 km including important variations down to 10 km model results are consistent with wave height variations along satellite altimeter tracks resolved at scales larger than 50 km the spectrum of significant wave heights is found to be of the order of 70 hs 2 g2 tm0 1 2 times the current spectrum where hs is the spatially averaged significant wave height tm0 1 is the energy averaged period and g is the gravity acceleration this variability induced by currents has been largely overlooked in spite of its relevance for extreme wave heights and remote sensing

discovery of olivine in the nili fossae region of mars we have detected a 30 000 square kilometer area rich in olivine in the nili fossae region of mars nili fossae has been interpreted as a complex of grabens and fractures related to the formation of the isidis impact basin we propose that post impact faulting of this area has exposed subsurface layers rich in olivine linear mixture analysis of thermal emission spectrometer spectra shows surface exposures of 30 olivine where the composition of the olivine ranges from fo30 to fo70

impact of sea ice processes on the carbonate system and ocean acidification at the ice water interface of the amundsen gulf arctic ocean 1 from sea ice formation in november 2007 to onset of ice melt in may 2008 we studied the carbonate system in first year arctic sea ice focusing on the impact of calciumcarbonate caco3 saturation states of aragonite xar and calcite xca at the ice water interface uiw based on total inorganic carbon ct and total alkalinity at and derived ph co2 carbonate ion co3 22 concentrations and x we investigated the major drivers such as brine rejection caco3 precipitation bacterial respiration primary production and co2 gas flux in sea ice brine frost flowers and uiw we estimated large variability in seaice ct at the top mid and bottom ice changes due to caco3 and co2 gas flux had large impact on ct in the whole ice core from march to may bacterial respiration was important at the bottom ice during all months and primary production in may it was evident that the sea ice processes had large impact on uiw resulting in a five times larger seasonal amplitude of the carbonate system relative to the upper 20 m during ice formation co2 increased by 30 mmol kg 21 co 3 22 decreased by 50 mmol kg 21 and the xar decreased by 0 8 in the uiw due to co2 enriched brine from solid caco3 conversely during ice melt co3 22 increased by 90 mmol kg 21 in the uiw and x increased by 1 4 between march and may likely due to caco3 dissolution and primary production we estimated that increased ice melt would lead to enhanced oceanic uptake of inorganic carbon to the surface layer

retracking ers 1 altimeter waveforms for optimal gravity field recovery summary we have reprocessed ers 1 radar altimeter waveforms using an algorithm designed to minimize sea surface slope error and decouple it from significant wave height swh error standard waveform retracking estimates three parameters arrival time swh and amplitude we show that errors in retracked estimates of arrival time and swh are inherently correlated because of the noise characteristics of the returned waveform this suggests that some of what is called sea state bias in the literature may be caused by correlated errors rather than true electromagnetic or skewness bias we have developed a retracking algorithm that reduces this error correlation and makes the resolution of sea surface slope signals independent of sea state the main assumption is that the swh varies smoothly along the satellite track over wavelengths of 90 km this approach reduces the rms error in sea surface slope to only 62 per cent of that of standard retracking methods while our method is optimized for gravity field recovery it may also improve the resolution of sea surface height signals of interest to physical oceanographers

impact of biogeochemical processes and environmental factors on the calcium carbonate saturation state in the circumpolar flaw lead in the amundsen gulf arctic ocean 1 we report on measurements across an annual cycle of carbon dioxide system parameters in the polar mixed layer pml of the circumpolar flaw lead in the amundsen gulf arctic ocean from these and other properties nitrate s t of the pml we found that biological processes photosynthesis and respiration accounted for about 50 of the monthly variations in the carbonate ion concentration co32 and the saturation state of these waters with respect to calcite ca and aragonite ar vertical mixing and salinity changes had equal impacts over the annual cycle the impact of sea ice meltwater resulted in decreasing values in summer but most of this change was offset by the increase as a result of co2 drawdown during biological photosynthesis

physical and biogeochemical controls on the variability in surface ph and calcium carbonate saturation states in the atlantic sectors of the arctic and southern oceans polar oceans are particularly vulnerable to ocean acidification due to their low temperatures and reduced buffering capacity and are expected to experience extensive low ph conditions and reduced carbonate mineral saturations states in the near future however the impact of anthropogenic co2 on ph and will vary regionally between and across the arctic and southern oceans here we investigate the carbonate chemistry in the atlantic sector of two polar oceans the nordic seas and barents sea in the arctic ocean and the scotia and weddell seas in the southern ocean to determine the physical and biogeochemical processes that control surface ph and high resolution observations showed large gradients in surface ph 0 10 to 0 30 and aragonite saturation state ar 0 2 to 1 0 over small spatial scales and these were particularly strong in sea ice covered areas up to 0 45 in ph and 2 0 in ar in the arctic sea ice melt facilitated bloom initiation in light limited and iron replete dfe 0 2 nm regions such as the fram strait resulting in high ph 8 45 and ar 3 0 along the sea ice edge in contrast accumulation of dissolved inorganic carbon derived from organic carbon mineralisation under the ice resulted in low ph 8 05 and ar 1 1 in areas where thick ice persisted in the southern ocean sea ice retreat resulted in bloom formation only where terrestrial inputs supplied sufficient iron dfe 0 2 nm such as in the vicinity of the south sandwich islands where enhanced ph 8 3 and ar 2 3 were primarily due to biological production in contrast in the adjacent weddell sea weak biological uptake of co2 due to low iron concentrations dfe 0 2 nm resulted in low ph 8 1 and ar 1 6 the large spatial variability in both polar oceans highlights the need for spatially resolved surface data of carbonate chemistry variables but also nutrients including iron in order to accurately elucidate the large gradients experienced by marine organisms and to understand their response to increased co2 in the future

sentinel 3a views ocean variability more accurately at finer resolution this is the first multiplatform evaluation involving data from the new sentinel 3a altimeter an experiment was undertaken in the algerian basin employing an ocean glider and a ship mission along the same track and synchronous with an overpass of the sentinel 3a mission this provided three independent views of the ocean velocity field along a section that encompassed three different oceanographic regimes the results demonstrate the capacity of sentinel 3a to retrieve fine scale oceanographic features 20 km the intercomparison with in situ platforms showed a significant improvement order 30 in resolution and 42 in velocity accuracy using a synthetic aperture radar mode with respect to lower resolution mode of conventional altimetry in addition the three platform view provided valuable insight into the variability of evolving oceanographic features in an area of the mediterranean that remains chronically under sampled