freeboard and mass extraction of the disintegrated mertz ice tongue with remote sensing and altimetry data abstract in february 2010 the mertz ice tongue mit collapsed and generated a giant iceberg however parameters about this iceberg have not been calculated and published in detail in this study the freeboard map of this iceberg was generated for the first time using a time series icesat glas data methods for producing the freeboard map of this iceberg are suggested field data for ice velocity were used to relocate the footprints collected by different campaigns cross validation was conducted with freeboards extracted from crossovers observed within 30 days of each other the precision of the freeboard extraction is approximately 0 50 m when taking one standard deviation as the precision the freeboard varied from 23 m to 59 m with the mean of 41 m with assumption of hydrostatic equilibrium assuming a snow layer depth of 1 m a snow density of 360 kg m 3 an ice density of 915 kg m 3 and a sea water density of 1024 kg m 3 the minimum maximum and average ice thickness were calculated as 210 m 550 m and 383 m respectively the total ice loss is approximately 8 96 10 11 tons over an area 34 km in width and 75 km in length or approximately 2560 5 km 2 these parameters extracted from remote sensing and altimetry data will provide additional information for studies of the evolution of iceberg especially in iceberg tracking system

the distribution and speciation of iron along 6 e in the southern ocean abstract the distribution and speciation of iron was determined along a transect in the eastern atlantic sector 6 e of the southern ocean during a collaborative scandinavian south african antarctic cruise conducted in late austral summer december 1997 january 1998 elevated concentrations of dissolved iron 0 4 nm were found at 60 s in the vicinity of the spring ice edge sie in tandem with a phytoplankton bloom chiefly dominated by phaeocystis sp this bloom had developed rapidly after the loss of the seasonal sea ice cover the iron that fuelled this bloom was mostly likely derived from sea ice melt in the winter ice edge wie around 55 s dissolved iron concentrations were low 0 2 nm and corresponded to lower biological productivity biomass in the antarctic polar front at approximately 50 s a vertical profile of dissolved iron showed low concentrations 0 2 nm however a surface survey showed higher concentrations 1 3 nm and considerable patchiness in this dynamic frontal region the chemical speciation of iron was dominated by organic complexation throughout the study region organic iron complexing ligands l ranged from 0 9 to 3 0 nm fe equivalents with complex stability log k fe l 21 4 23 5 estimated concentrations of inorganic iron fe ranged from 0 03 to 0 79 pm with the highest values found in the phaeocystis bloom in the sie a vertical profile of iron complexing ligands in the wie showed a maximum consistent with a biological source for ligand production and near surface minimum possibly consistent with loss via photodecomposition this work further confirms the role iron that has in the southern ocean in limiting primary productivity

terrigenous sediment supply in the scotia sea southern ocean response to late quaternary ice dynamics in patagonia and on the antarctic peninsula geochemical and mineralogical compositions of modern and late quaternary marine sediments from the scotia sea trace sources and transport paths of terrigenous sediment we discuss downcore variations of compositional data of two sediment cores from the northern and southern scotia sea that correlate with fluctuations in magnetic susceptibility sediments were derived from very different sources at both localities as revealed by contrasting clay mineral assemblages however a common feature is the input of more basic and undifferentiated crustal material with the potential of high magnetic susceptibility during glacial periods indicated by variable quartz feldspar ratios and major trace and rare earth elements terrigenous sediments mainly originate from nearby terrestrial sources or are introduced through interbasinal sediment transfer from adjacent seas the observed temporal compositional variations have to be attributed to changes in the relative detrital contributions from the diverse source areas ice mass extensions in southern patagonia on the antarctic peninsula and adjacent islands likely control the supply of glaciogenic detritus to the open ocean during times of glacial expansion diluting the sediment input of interbasinal origin current transport is mainly responsible for sediment dispersal to the pelagic scotia sea and may amplify the glaciological source signals during glacial climate periods because of a stronger wind forcing of the antarctic circumpolar current

the distribution of fe in the antarctic circumpolar current abstract the large scale distributions of dissolved and total fe in surface and deep waters of the antarctic circumpolar current exhibit strong relationships with hydrography and biological processes the mean dissolved fe concentrations are low in surface waters of the antarctic circumpolar current 0 31 0 49 nm with a minimum of 0 17 nm and higher averaging 1 11 9 nm in the polar frontal region enhanced dissolved surface water concentrations in the polar frontal region are attributed to input from the continental shelf and coincide with phytoplankton spring blooms of large diatoms the effects of sea ice melting and iceberg melting on the fe concentrations were relatively small dissolved deep water concentrations 400 m in the antarctic circumpolar current ranged from 0 4 to 2 8 nm circumpolar deep water has relatively high dissolved fe concentrations in the polar frontal region 0 4 2 8 nm compared with deep waters further to the south 0 6 1 1 nm similarly total dissolvable unfiltered fe concentrations in the upper circumpolar deep water tend to decrease southward from the polar frontal region in the lower circumpolar deep water total dissolvable fe concentrations are higher than in the upper circumpolar deep water due to the existing nepheloid layer and sources on the mid atlantic ridge dissolved and total dissolvable fe concentrations in the antarctic bottom water are higher than those of other water masses in the antarctic circumpolar current consistent with the nepheloid layer as well as diagenetic input from shelf sediments the high nutrient low chlorophyll areas of the antarctic ocean and northeast pacific ocean have different major fe input sources of similar magnitude in the antarctic circumpolar current upward transport of fe is the main input source whereas in the north pacific ocean aerosols are the dominant source

iceberg trajectory modeling and meltwater injection in the southern ocean this is the first large scale modeling study of iceberg trajectories and melt rates in the southern ocean an iceberg model was seeded with climatological iceberg calving rates based on a calculation of the net surface accumulation from each snow catchment area on the antarctic continent in most areas modeled trajectories show good agreement with observed patterns of iceberg motion though discrepencies in the weddell sea have highlighted problems in the ocean general circulation model output used to force the iceberg model the coriolis force is found to be important in keeping bergs entrained in the coastal current around antarctica and topographic features are important in causing bergs to depart from the coastal regions the modeled geographic distribution of iceberg meltwater joining the ocean has been calculated and is found in many near coastal regions to be comparable in magnitude to the excess of precipitation over evaporation p e

dissolved iron in the southern ocean atlantic sector abstract we report a comprehensive dataset of dissolved iron fe comprising 482 values at 22 complete vertical profiles along a 1 latitudinal section at the zero meridian in addition a shorter high resolution 00 09 surface section of the southernmost part of the transect 66 00 69 35 s is presented within the upper surface mixed layer the concentrations of dissolved fe vary between 0 1 and 0 3 nm an inverse trend versus fluorescence suggests significant fe removal by plankton blooms vertical mixing and upwelling are the most important supply mechanisms of iron from deep waters to the upper surface mixed layer at lower latitude 42 s there is a distinct maximum of 0 6 0 7 nm in the 2000 3000 m depth range due to inflow of north atlantic deep water in one region 55 s elevated dissolved fe found in the surface mixed layer is ascribed to the recent deposition of aeolian dust originating from south america close to the antarctic continent there is an indication of fe supply in surface waters from icebergs in the deep waters there is a strong indication of a hydrothermal plume of dissolved fe and mn over the ridge in the bouvet region 52 56 s in the weddell gyre basin the dissolved fe in the deep water is 0 47 0 16 nm in the eastward flow at 56 62 s and is lower with a value of 0 34 0 14 nm in the westward flow at high 62 69 s latitude at the edge of the continental ice sheet on the prime meridian the continental margin of the antarctic continent appears to be lesser source of dissolved fe than in any other place in the world this is likely because it is unique in being overlain by the extending continental ice sheet that largely prevents biogeochemical cycling

provenance and transport of terrigenous sediment in the south atlantic ocean and their relations to glacial and interglacial cycles nd and sr isotopic evidence sr and nd isotopic compositions of late quaternary surface sediment and sediment cores from the south atlantic and southeast pacific sectors of the southern ocean are used to constrain the provenance and transport mechanisms of their terrigenous component we report isotopic and mineralogical data for core samples from three localities the mid atlantic ridge at 41 s and the northern and southern scotia sea in addition data for surface sediment samples from the south atlantic and southeast pacific sectors of the southern ocean are presented the variations of sr and nd isotopic compositions of the bulk sediment samples in all cores were correlated with the magnetic susceptibility of the sediment and with the inferred glacial interglacial stages the isotopic data indicate that during glacial periods sediment was delivered from continental crust with a shorter residence time than that supplying material during interglacial periods at the core site near the mid atlantic ridge nd isotopic combined with mineralogical evidence indicates interglacial period deposition of a relatively high amount of kaolinite and silt with low nd values 4 5 probably derived from southern south america was indicated the glacial interglacial shift in sources may be due to either a decreasing influence of north atlantic deep water during glacial times or by a larger contribution of glaciogenic detritus from southern south america at the core site in the northern scotia sea sediment of interglacial periods is dominated by smectite with nd 4 we suggest that smectite was derived from the falkland shelf and silt was derived from the argentinian shelf during glacial periods the argentinian shelf was an important source for silt and chlorite with nd 4 the contribution from the falkland shelf seems to have remained similar during glacial and interglacial periods hydrographic transport by bottom currents and turbidites could account for the high glacial detrital flux an evaluation of the significance of an aeolian contribution to deep sea sediment suggests that it plays only a minor role in the southern scotia sea the antarctic peninsula is considered an important source for young material with nd 4 in particular during glacial periods during interglacial periods sediment supply from the antarctic peninsula was lower than during glacial times resulting in a relatively high contribution of old material nd 8 from east antarctica deep water currents and icebergs could account for the transport of the old component to the southern scotia sea the accumulation rates of material from the various source regions for glacial times are in agreement with an increase in the strength of the antarctic circumpolar current the production rate and the circulation pattern of bottom water in the weddell sea appear to have remained similar over most of the last 150 kyr

subsurface melting of a free floating antarctic iceberg abstract observations near a large tabular iceberg in the weddell sea in march and april 2009 show evidence that water from ice melting below the surface is dispersed in two distinct ways warm salty anomalies in t s diagrams suggest that water from the permanent thermocline is transported vertically as a result of turbulent entrainment of meltwater at the iceberg s base stepped profiles of temperature salinity and density in the seasonal thermocline are more characteristic of double diffusive processes that transfer meltwater horizontally away from the vertical ice face these processes contribute comparable amounts of meltwater o 0 1 m3 to the upper 200 m of a 1 m2 water column but only basal melting results in significant upwelling of water from below the winter water layer into the seasonal thermocline suggesting that these two processes may have different effects on vertical nutrient transport near an iceberg

benthic community structure on the u s south atlantic slope off the carolinas spatial heterogeneity in a current dominated system faunal communities of the continental slope and rise seaward of north and south carolina u s a are strongly influenced by the gulf stream the western boundary undercurrent and an increasingly steep declination of the slope toward cape hatteras sixteen stations in depths of 600 3500 m were sampled to characterized the sediment and benthic macrofauna box cores were taken along four transects cape hatteras cape lookout cape fear and charleston on the cape hatteras transect infaunal densities at the 600 m station were as high as those typical of shallower waters and the dominant organisms were species that are more characteristic of continental shelf depths there is high nearly continuous sedimentation of terrigenous fine sandy sediments that are funneled over the cape hatteras slope by southerly flowing long shelf currents we postulate that organic material is transported rapidly over the site and the high depositional rates are enhanced by scavenging activities of filter feeding organisms large deep burrowing deposit feeders serve to carry organic material deep into the sediments the shallow stations on the charleston transect were dominated by sand waves generated by the gulf stream while deeper stations were enriched by macroalgae transported downslope transects off cape lookout and cape fear were more typical of those found elsewhere in the western north atlantic macrofaunal analysis yielded 1202 species 520 of which were new to science annelids were the dominant taxa in terms of density and numbers of species a partial zoogeographic barrier was identified between cape lookout and cape fear species diversity was high at most stations with the highest at an 800 m site off charleston where 436 species were taken from nine cores 0 81 m2 diversity data from off the carolinas support previously stated views that the deep sea is a resource of high species richness and biodiversity densities of macrofauna from all depths were generally higher than in previously published accounts the faunal assemblage at each station was consistent over 2 years in that samples from one station were always more similar to one another than to any other station stations grouped into upper slope middle slope lower slope and continental rise assemblages the upper slope stations were the most variable both in density and community composition transect differences in types of sediment and macrofaunal communities along and across isobaths indicated considerable regional heterogeneity

tracking large tabular icebergs using the seawinds ku band microwave scatterometer abstract knowledge of iceberg locations is important for safety reasons as well as for understanding many geophysical and biological processes originally designed to measure wind speed and direction over the ocean seawinds is a microwave scatterometer that operates at 13 4 ghz ku band on the quikscat satellite radar measurements from seawinds are collected and processed on a daily basis using resolution enhancement techniques to produce daily radar images because icebergs scatter microwave energy more than sea ice and sea water icebergs are detected as high backscatter targets surrounded by lower backscatter regions in daily seawinds images as a result iceberg positions are determined in real time and a time series of iceberg positions is maintained in an antarctic iceberg database by brigham young university s microwave earth remote sensing mers laboratory since seawinds operates independent of both solar illumination and cloud cover and has a large daily spatial coverage this paper demonstrates that seawinds is an excellent platform to detect and track large tabular icebergs these icebergs are generally larger than 5 km and are typically characterized as a rough ice plateau above the surrounding sea water or sea ice the number of icebergs tracked in the mers antarctic iceberg database is found to be generally greater than the number of icebergs tracked by the national ice center the movement patterns of all icebergs detected by seawinds are also analyzed and 90 of icebergs are found to travel a counter clockwise path around antarctica and accumulate in the weddell and scotia seas iceberg detection and tracking is demonstrated via multiple case studies that highlight icebergs c 19a and a 22a using the mers database and through real time operational support of the 2005 2008 and 2009 nsf antarctic cruises iceberg positions are validated by using collocated high resolution satellite imagery and by navigating the nsf ships to physically intercept several large tabular icebergs in the weddell and scotia seas

recent antarctic ice mass loss from radar interferometry and regional climate modelling observed estimates of ice losses in antarctica combined with regional modelling of ice accumulation in the interior suggest that east antarctica is close to a balanced mass budget but large losses of ice occur in the narrow outlet channels of west antarctic glaciers and at the northern tip of the antarctic peninsula

a modeling study of the episodic cross frontal water transport over the inner shelf of the south atlantic bight abstract physical processes that control the episodic cross frontal transport over the inner shelf of the south atlantic bight were examined using a 3d primitive turbulent closure equation model the model results showed that significant cross frontal water exchange occurred under upwelling favorable wind conditions through the detachment of isolated low salinity lenses at the outer edge of the front the formation of isolated lenses was a 3d feature associated with complex nonlinear processes it depended on 1 the amount of multiple river discharges 2 direction and magnitude of the wind and 3 tidal mixing as the total amount of river discharges increased stronger winds were required to form the isolated lenses when the river discharges were larger tidal mixing tended to delay the occurrence of isolated lenses through 1 increasing the cross shelf gradients of density and surface elevation and thus enhancing the along shelf current and reducing the along shelf variation of salinity and 2 streng

pliocene shallow water paleoceanography of the north atlantic ocean based on marine ostracodes abstract middle pliocene marine ostracodes from coastal and shelf deposits of north and central america and iceland were studied to reconstruct paleotemperatures of shelf waters bordering portions of the western boundary current system including the gulf loop current florida current gulf stream and north atlantic drift factor analytic transfer functions provided pliocene august and february bottom water temperatures of eight regions from the tropics to the subfrigid the results indicate 1 meridional temperature gradients in the western north atlantic were less steep during the pliocene than either today or during late pleistocene isotope stage 5e 2 tropical and subtropical shelf waters during the middle pliocene were as warm as or slightly cooler than today 3 slightly cooler water was on the outer shelf off the southeastern and mid atlantic coast of the u s possibly due to summer upwelling of gulf stream water 4 the shelf north of cape hatteras north carolina may have been influenced by warm water incursions from the western edge of the gulf stream especially in summer 5 the northeast branch of the north atlantic drift brought warm water to northern iceland between 4 and 3 ma evidence from the iceland record indicates that cold east greenland current water did not affect coastal iceland between 4 and 3 ma 6 middle pliocene north atlantic circulation may have been intensified transporting more heat from the tropics to the arctic than it does today

iceberg hosted nanoparticulate fe in the southern ocean mineralogy origin dissolution kinetics and source of bioavailable fe abstract sediments from icebergs and glaciers contain nanopartculate fe iii oxyhydroxides including ferrihydrite which form in aqueous oxic micro environments where fe ii bearing rock minerals oxidise and high degrees of supersaturation are promoted by freezing and thawing an ascorbic acid extraction dissolves only labile fe present in fresh loosely aggregated ferrihydrite that is directly or indirectly bioavailable glacial and iceberg sediments contain ferrihydrite aggregates that provide 0 04 to 0 17 fe soluble in ascorbic acid rather larger than the concentrations in a limited suite of atmospheric dusts the dissolution behaviour of labile fe from glacial and iceberg sediments by ascorbic acid is controlled by the access of reactant or removal of solute through micropores to or from active sites in the interior of ferrihydrite aggregates a first order kinetic model is presented to examine the rates at which bioavailable fe can be supplied by melting icebergs in the weddell sea the model utilizes rate constants from the literature for the processes which solubilise fe from nanoparticulate ferrihydrite dissolution photochemical reduction and grazing and the processes that remove fe nanoparticulates sinking scavenging and incorporation in faecal material and render them less reactive transformation aging model results demonstrate that icebergs can supply bioavailable fe to the weddell sea by the dissolution of nanoparticulate ferrihydrite despite loss removal of nanoparticles by sinking aging transformation scavenging and incorporation into faecal pellets at rates that are comparable to atmospheric dust dissolution enhanced by photochemical reduction and grazing provides the most rapid rates of bioavailable fe production

input composition and potential impact of terrigenous material from free drifting icebergs in the weddell sea abstract the hypothesis that fe fertilization of the southern ocean could account for at least part of the glacial interglacial difference in atmospheric co2 has lead to a search for the fe source iron fertilization in the open ocean can occur naturally through increased dust input cross shelf export upwelling of fe replete deep water and release of terrigenous fe from icebergs however the relative importance of these mechanisms in terms of the flux and bioavailability of the fe is the source of much interest and debate an unambiguous tracer of terrigenous material excess 224ra was used to show that free drifting icebergs are a significant fe source to surface waters in the southern ocean activity of 224ra half life 3 7 days was measured in the weddell sea in surface waters surrounding three free drifting icebergs and in iceberg alley inventories of excess 224ra indicate a local terrigenous input 1 3 orders of magnitude greater than estimates of aeolian dust fluxes to the southern ocean burdens of fine terrigenous material associated with current rates of iceberg ejection are estimated to be on the order of 90 106 tons per year for antarctica yielding a total fe input of 3 106 tons per year chemical and mineralogical composition of the terrigenous material confirms that 0 04 0 4 exists as labile fe in ferrihydrite that is potentially bioavailable on the order of 4 40 104 tons of per year these results suggest that free drifting icebergs can contribute significantly to atmospheric co2 drawdown though fe fertilization in the southern ocean

glacial interglacial co2 change the iron hypothesis several explanations for the 200 to 280 ppm glacial interglacial change in atmospheric co2 concentrations deal with variations in southern ocean phytoplankton productivity and the related use or nonuse of major plant nutrients an hypothesis is presented herein in which arguments are made that new productivity in today s southern ocean 7 4 1013g yr 1 is limited by iron deficiency and hence the phytoplankton are unable to take advantage of the excess surface nitrate phosphate that if used could result in total southern ocean new production of 2 3 1015 g c yr 1 as a consequence of fe limited new productivity holocene interglacial co2 levels preindustrial are as high as they were during the last interglacial 280 ppm in contrast atmospheric dust fe supplies were 50 times higher during the last glacial maximum lgm because of this fe enrichment phytoplankton growth may have been greatly enhanced larger amounts of upwelled nutrients may have been used and the resulting stimulation of new productivity may have contributed to the lgm drawdown of atmospheric co2 to levels of less than 200 ppm background information and arguments in support of this hypothesis are presented

eustatic controls on carbonate facies in reservoirs and seals associated with mesozoic hydrocaron fields of the arabian gulf and the gulf of mexico abstract abundant subsurface data for mesozoic and cenozoic sections of the us gulf coast and the middle east make it possible to track the relationship of shelf carbonates and evaporites associated with minor amounts of clastics to eustasy our contention is that because the sedimentary deposition for both regions was in part controlled by gentle tectonic subsidence punctuated by eustatic variations the major hydrocarbon fields which occur here can be related to sea level behaviur at the time of deposition of the reservoir sections and their early diagenesis with the exception of chalks most of these carbonate hydrocarbon fields can be related to highstand system tracts and include the following 1 1 keep up reservoirs with sheet like geometry formed when carbonate accumulation matched sea level rise aggrading to form shoaling upward cycles during sea level highstands 2 2 give up and catch up reservoirs with lense like carbonate geometry formed on drowned shelves during and following rapid sea level rises often downslope from carbonate margins give up reservoirs occur when carbonate accumulation was unable to match sea level rise and catch up reservoirs form where carbonate accumulation was initially unable to keep pace with the sea level rise but then aggraded to sea level 3 3 reservoirs with the prograded discontinuous clinoform geometry of the platform margin formed during stillstands by carbonate accumulation that not only kept up with the sea level rise but also advanced in a seaward direction source rocks for these carbonate reservoirs are often formed during rapid sea level rises while the reservoir seals are usually transgressive shales dense transgressive limestones and or highstand evaporites

spatial scales in czcs chlorophyll imagery of the southeastern u s continental shelf1 a 1 yr time series of coastal zone color scanner czcs imagery of continental shelf waters off the southeastern u s was statistically analyzed to determine dominant scale lengths in the range from 2 to 100 km for near surface chlorophyll chl variability for each image we extracted two dimensional matrices of czcs chl concentrations from each of 10 study areas variograms structure functions were calculated for both the along and across shelf dimension of each data matrix although we designed the study areas to focus on along shelf variability the variograms were used to determine whether the images contained nonrandom structure and if so to estimate its scale lengths outer shelf czcs chl distributions lacked apparent spatial structure in about 50 of the data matrices vs 10 for the inner shelf matrices in general scale length increased with distance offshore and did not change with season for example the mean scale length n 30 images for along shelf czcs chl variability on the inner shelf off georgia was 32 km vs 84 km n 18 images for the outer shelf wc propose that gulf stream frontal eddies are the principal determinants of outer shelf scale length and that topographic effects on the position of a coastal salinity front determine scale length on the inner shelf off georgia and south carolina

liquid hydrocarbon bearing inclusions in modern hydrothermal chimmeys and mounds from the southern trough of guaymas basin gulf of california abstract liquid hydrocarbon bearing inclusions of variable shape e g spherical bowling pin rod and highly irregular occur in hydothermal minerals of chimneys and mounds in the southern trough of guaymas basin central gulf of california the inclusions are preferentially trapped in amorphous silica which occurs as spherules and 0 01 mm thick encrustations on sulfides sulfates and carbonates the inclusions are primary and pseudosecondary and were trapped during not after mineral growth the inclusions are both two phase liquid hydrocarbon and vapor gas and three phase liquid hydrocarbon aqueous fluid and vapor and range from 2 to 50 m in diameter the large range in liquid hydrocarbon and acqueous fluid contents indicates that the hydrothermall fluid and liquid hydrocarbon were never a homogeneous solution but that hydrocarbons were transported as immiscible and possibly solvated forms the liquid hydrocarbon varies in color from deep to pale orange brown and fluoresces a yellow color during excitation by u v light indicating a condesate mainly c 1 to c 10 hydrocarbons composition measurable quantities of hydrocarbons from the inclusions could not be isolated by mineral dissolution by pyrolsis and decrepitation analyses suggest that the more volatile components predominate two phase hydrocarbon inclusions homogenized with the liquid at temperatures ranging from 75 to 190 c excluding one high measurement to obtain true trapping temperatures an unknown pressure correction is required however the trapping temperature of these hydrocarbon inclusions was estimated by measuring trapping temperatures for adjacent aqueous inclusions which range from 116 to 226 c geochemical modelling using these trapping temperatures indicates that the amorphous silica precipitated from the hydrothermal fluid due to conductive cooling in addition to mixing with ambient sea water the temperatures required for the formation of petroleum and its transport to the seafloor in the guaymas basin coincide with those necessary for the precipitation of amorphous silica in the guaymas basin hydrothermal system

the fate of river discharge on the continental shelf 2 transport of coastal low salinity waters under realistic wind and tidal forcing a three dimensional numerical simulation of shelf circulation is presented we employ realistic forcing for the southeast u s continental shelf during the spring season we show that the strongest offshore transport of river induced coastal low salinity waters and associated materials occurs near the surface the preferred mean pathway is in the northeastward direction and it takes about 2 months to cross the entire shelf owing to the mean direction of surface transport and the topography of the south atlantic bight shelf the preferred location for springtime removal is off charleston south carolina and presumably in the vicinity of the charleston bump the transport and fate of the river induced coastal low salinity waters during the spring season are determined by 1 the stratification of nearshore waters which is due to the high river runoff and causes the decoupling between near surface and near bottom layers 2 the prevailing northeastward winds which cause significant offshore transport within the shallow near surface ekman layer and 3 the tidally induced bottom stirring m2 tides comparison of model and data time series of currents shows very good agreement standard deviations of the model and data computed empirical orthogonal functions are almost identical while the respective variance conserving spectra agree both in amplitude and phase

accumulation of biogenic and lithogenic material in the pacific sector of the southern ocean during the past 40 000 years the 230th normalization technique was applied to surface sediments and down core records from the pacific sector of the southern ocean between 120 w and 170 w in order to reconstruct vertical rain rates corrected for lateral redistribution of sediment preserved rain rates of opal organic carbon and biogenic ba all indicate that biological productivity south of the antarctic polar front apf was much lower than today during the last glacial maximum lgm probably in response to increased ice cover however by analogy with modern opal fluxes south of the acc we show that year round ice cover is not a prerequisite for very low rates of opal accumulation available records from north of the apf indicate little to no change in opal export in contrast to records from the indian and atlantic sectors which show enhanced opal export north of the apf during the lgm glacial records from north of 66 s in the pacific all show lithogenic fluxes that were greater than today but significantly lower than lithogenic fluxes in the glacial atlantic and indian sectors together these new records from the pacific sector show that during the lgm the three basins of the southern ocean were significantly more differentiated than today the observed inter basin distribution of lithogenic fluxes and opal burial and the presumed geographical distribution of increased dust input to the southern ocean during the lgm are consistent with an atlantic indian pacific gradient in the degree of iron stimulated diatom productivity within the zone lying between the apf and the subantarctic front previous studies which focused primarily on the atlantic sector may have overestimated the glacial increase in the strength of the biological pump in the southern ocean

natural iron fertilization of the atlantic sector of the southern ocean by continental shelf sources of the antarctic peninsula in large parts of the southern ocean primary production is limited due to shortage of iron fe we measured vertical fe profiles in the western weddell sea weddell scotia confluence and antarctic circumpolar current acc showing that fe is derived from benthic fe diffusion and sediment resuspension in areas characterized by high turbulence due to rugged bottom topography our data together with literature data reveal an exponential decrease of dissolved fe dfe concentrations with increasing distance from the continental shelves of the antarctic peninsula and the western weddell sea this decrease can be observed 3500 km eastward of the antarctic peninsula area downstream the acc we estimated dfe summer fluxes into the upper mixed layer of the atlantic sector of the southern ocean and found that horizontal advection dominates dfe supply representing 54 15 of the total flux with significant vertical advection second most important at 29 13 horizontal and vertical diffusion are weak with 1 2 and 1 1 respectively the atmospheric contribution is insignificant close to the antarctic continent but increases to 15 10 in the remotest waters 1500 km offshore of the acc translating southern ocean carbon fixation by primary producers into biogenic fe fixation shows a twofold excess of new dfe input close to the antarctic continent and a one third shortage in the open ocean fe recycling with an estimated fe ratio of 0 59 is the likely pathway to balance new dfe supply and fe fixation

accelerated antarctic ice loss from satellite gravity measurements accurate quantification of antarctic ice sheet mass balance and its contribution to global sea level rise remains challenging gravity recovery and climate experiment data spanning the period april 2002 to january 2009 confirm earlier estimates of ice loss for antarctica and indicate that east antarctica started losing mass in about 2006

algal communities attached to free drifting antarctic icebergs abstract disintegration of the antarctic peninsula s eastern ice shelves has increased the population of icebergs traversing the weddell sea but until recently little was known about their ecological impact on the pelagic environment here we describe a class of algal communities that occur on the submerged flanks of large free drifting glacially derived tabular icebergs we used remotely operated vehicles to examine these icebergs directly for the first time to survey the algal communities and collect material for shipboard laboratory studies the communities principally diatoms were associated with a characteristic cupped configuration of the ice surface and they served as feeding sites for aggregations of antarctic krill production rate measurements indicate that these communities are providing a substantial contribution to regional primary production in summer as the number of icebergs grows the number of algae communities may also be increasing along with their cumulative contribution to organic carbon flux

depositional diagenetic thermal and maturation histories of cretaceous mishrif formation fateh field dubai rudist reef associated limestones comprising the cretaceous mishrif formation are the major reservoirs in fateh field a giant oil field in offshore dubai in this study mishrif cores from four wells on the western flank of the field were examined to gain insights into the depositional diagenetic thermal and maturation histories of the mishrif formation in this area the wells lowest on the west flank contain relatively deep water lower fore reef facies bounded by two erosional unconformities the upper unconformity marks the laffan mishrif contact and extends over fateh field throughout the region in fateh field the lower intra mishrif unconformity has been identified only on the western flank but is probably present in other locations low on the fateh structure the identification of the lower unconformity indicates two cycles of mishrif sedimentation the cycles are related to deep seated salt movement and epeiric sea level changes fluid inclusion data maturation calculations and burial history modeling indicate that the timing of cementation by blocky calcite spar and oil migration were approximately synchronous and occurred during the oligocene to miocene

dissolved fe and al in the upper 1000 m of the eastern indian ocean a high resolution transect along 95 e from the antarctic margin to the bay of bengal a high resolution section of dissolved iron dfe and aluminum dal was obtained along 95 e in the upper 1000 m of the eastern indian ocean from the antarctic margin 66 s to the bay of bengal 18 n during the u s climate variability and predictability clivar co2 repeat hydrography i08s and i09n sections february april 2007 in the southern ocean low concentrations of dal

terrigenous input and paleoproductivity in the southern ocean the geochemistry of several sites along the polar front zone of the southern ocean revealed significant changes in terrigenous input and productivity on glacial timescales our records indicate concentrations and fluxes of terrigenous elements i e fe al and ti are low during interglacials and increase tenfold to twentyfold during glacials phosphorus accumulation reactive p concentrations and p ti ratios exhibit similar trends as the terrigenous components suggesting increased export production during glacials in all cores elemental ratios remain relatively constant indicating terrigenous sources at each site have not likely varied over the past 250 kyr iron accumulation rates for these sites are 10 times higher during glacials than interglacials and exceed the estimated regional eolian fluxes by 50 times the source of this terrigenous material is thus likely to be hemipelagic rather than direct eolian input or ice rafting and we speculate fe upwelled from this source may have stimulated glacial productivity in the southern ocean

a numerical analysis of shipboard and coastal zone color scanner time series of new production within gulf stream cyclonic eddies in the south atlantic bight eddy induced upwelling occurs along the western edge of the gulf stream between cape canaveral florida and cape hatteras north carolina in the south atlantic bight sab coastal zone color scanner images of 1 km resolution spanning the period april 13 21 1979 were processed to examine these eddy features in relation to concurrent shipboard and current temperature measurements at moored arrays a quasi one dimensional z time dependent biological model using only nitrate as a nutrient source has been combined with a three dimensional physical model in an attempt to replicate the observed phytoplankton field at the northward edge of an eddy the model is applicable only to the sab south of the charleston bump at 31 5 n since no feature analogous to the bump exists in the model bathymetry the modeled chlorophyll nitrate and primary production fields of the euphotic zone are very similar to those obtained from the satellite and shipboard data at the leading edges of the observed eddies south of the charleston bump the horizontal and vertical simulated fluxes of nitrate and chlorophyll show that only 10 of the upwelled nitrate is utilized by the phytoplankton of the modeled grid box on the northern edge of the cyclone while 75 is lost horizontally with the remainder still in the euphotic zone after the 10 day period of the model loss of chlorophyll due to sinking is very small in this strong upwelling region of the cyclone the model is relatively insensitive to variations in the sinking parameterization and the external nitrate and chlorophyll fields but is very sensitive to a reduction of the maximum potential growth rate to half that measured given the success of this model in simulating the new production of the selected upwelling region other upwelling regions for which measurements or successful models of physical and biological quantities and rates exist could be modeled similarly

a note on the charleston gyre the deflection of the gulf stream caused by a topographic feature the charleston bump located offshore of savannah georgia results in a quasi stationary cyclonic eddy the charleston gyre which is situated over the continental slope east of charleston and cape romain occasionally the upwelling associated with this eddy produces an enhancement in the surface layer primary production that is great enough to be detected by the nimbus 7 coastal zone color scanner czcs in this note a czcs image with simultaneous hydrography current and wind observations is presented that documents an unusual manifestation of the gyre in addition to the czcs image a seasat synthetic aperture radar sar image is included that clearly indicates the presence of the eddy adjacent to the gulf stream front

seasonal fluctuations in sea level on the south carolina shelf and their relationship to the gulf stream near bottom pressure measurements obtained over a 9 month period in 1978 on the outer continental shelf off south carolina document that sea level rose 35 to 50 cm between july and october records of coastal sea level showed a similar rise when the pressure and coastal sea level records were corrected for the effects of wind stress and temperature the largest portion of the rise in the two variables remained the amplitude of the change in residual sea level was largest at the shelf break 28 cm and decayed to 22 cm at the coast the relatively small magnitude of the decay suggests that alongshelf pressure gradients imposed at the shelf break have minimum alongshelf wavelengths of 2000 km the changes in residual sea level were seasonal and associated with seasonal changes in the transport of the gulf stream the 3 years of residual sea level records examined here indicate that the amplitude of a typical decrease in transport of the gulf stream off south carolina between july and october has a strong interannual variability the change in transport can be 50 lower to over 100 higher than the historical average the residual sea level records also suggest that a change in transport of the gulf stream is not strongly related to the onshore offshore position of the gulf stream

carbon export associated with free drifting icebergs in the southern ocean abstract enrichment of the pelagic ecosystem associated with the proliferation of free drifting icebergs prompts questions about increased productivity and the export flux of organic carbon to the deep ocean with continued climate warming lagrangian sediment traps lst were deployed autonomously beneath a large tabular free drifting iceberg c 18a in the nw weddell sea during march and april 2009 to collect sinking particles at a depth of 600 m three lst deployments associated with c 18a within a 30 km radius collected sinking diatom frustules dominated by corethron pennatum and fragilariopsis nana euphausiid fragments crustacean and fish fecal material detrital aggregates and mineral grains one lst deployment at a control site 74 km away in open water devoid of icebergs collected diatom frustules euphausiid molts crustacean fecal material and detrital aggregates phytoplankton abundance microbial abundance and biomass were significantly higher in the lst samples than in open water collections at 500 m depth the mean mass flux and organic carbon flux associated with iceberg c 18a were twice as high 124 mg m 2 d 1 and 5 6 mg corg m 2 d 1 respectively than at the control site a similar trend was observed in corg 234th activity being highest near c 18a and lowest at the control site extrapolation of the area of enrichment to 30 km radius around c 18a 2826 km2 produces an estimated mass flux of 350 tons d 1 and carbon flux of 15 8 tons corg d 1 five similar sized icebergs to c 18a were identified in satellite images in a surrounding 47 636 km2 area at the same time of sampling assuming a 30 km radius as the area of influence around each of these five icebergs 46 of the total area would be enhanced with an export flux at 600 m of 122 4 tons corg d 1 the large numbers of smaller icebergs identified visually in this area would only increase this area of influence icebergs serve as areas of local enrichment and with increased proliferation must be considered in the cycling of carbon in the southern ocean

the signature of river and wind borne materials exported from patagonia to the southern latitudes a view from rees and implications for paleoclimatic interpretations abstract riverine and wind borne materials transferred from patagonia to the sw atlantic exhibit a homogeneous rare earth element ree signature they match well with the ree composition of recent tephra from the hudson volcano and hence this implies a dominance of material supplied by this source and other similar andean volcanoes due to the trapping effect of proglacial and reservoir lakes the larger patagonian rivers deliver to the ocean a suspended load with a slightly modified andean signature that shows a ree composition depleted in heavy rees in this paper we redefine patagonia as a source of sediments which is in contrast with other sources located in southern south america quaternary sediments deposited in the northern and to a lesser extent in the southern scotia sea and most of the dust in ice cores of east antarctica have ree compositions very similar to the loess from buenos aires province and to patagonian eolian dust however we rule out buenos aires province as a holocene major source of sediments similarly to buenos aires loess a proximal facies it is likely that the ree compositions of most sediment cores of the scotia sea and antarctica reflect a distal transport of dust with an admixed composition from two main sources a major contribution from patagonia and a minor proportion from source areas containing sediments with a clear upper crustal signature e g western argentina or from bolivia s altiplano evidence indicates that only during the last glacial maximum patagonian materials were the predominant sediment source to the southern latitudes

southern ocean bioproductivity during the last glacial cycle new detection method and decadal scale insight from the scotia sea we present biogenic opal flux records from two deep sea sites in the scotia sea md07 3133 and md07 3134 at decadal scale resolution covering the last glacial cycle in addition to conventional and time consuming biogenic opal measuring methods we introduce new biogenic opal estimation methods derived from sediment colour b wet bulk density si ti count ratio and fourier transform infrared spectroscopy ftirs all methods capture the biogenic opal amplitude however ftirs a novel method for marine sediment yields the most reliable results 230th normalization data show strong differences in sediment focusing with intensified sediment focusing during glacial times at md07 3134 230th normalized biogenic opal fluxes vary between 0 2 and 2 5 g cm22 kyr21 our biogenic opal flux records indicate bioproductivity changes in the southern ocean strongly influenced by sea ice distribution and also summer sea surface temperature changes south of the antarctic polar front lowest bioproductivity occurred during the last glacial maximum when upwelling of mid depth water was reduced and sea ice cover intensified around 17 ka bioproductivity increased abruptly corresponding to rising atmospheric co2 and decreasing seasonal sea ice coverage

imaging and sampling beneath free drifting icebergs with a remotely operated vehicle abstract a commercially available small less than 100 kg remotely operated vehicle rov was modified to image and sample the marine ecosystem surrounding free drifting icebergs east of the antarctic peninsula during three field expeditions in 2005 2008 and 2009 modifications included fitting the vehicle with an accessory tool sled additional thrusters flotation and significant changes to internal wiring to support a wide array of sensors and samplers the rov was re configured aboard the r v nathaniel b palmer to perform either general exploration and biological sampling bio dives or water sampling chemistry dives in situ sensors and a suction sampler were used for bio dives while a suction pump and hose were fastened along the full length of the rov tether to enable continuous water sampling adjacent to each iceberg during chemistry dives details of the rov system are presented along with a discussion of the 18 dives that explored the sides and bottoms of six different icebergs during the 2009 field expedition

evidence against dust mediated control of glacial interglacial changes in atmospheric co2 the low concentration of atmospheric co2 inferred to have been present during glacial periods is thought to have been partly caused by an increased supply of iron bearing dust to the ocean surface1 this is supported by a recent model2 that attributes half of the co2 reduction during past glacial stages to iron stimulated uptake of co2 by phytoplankton in the southern ocean but atmospheric dust fluxes to the southern ocean even in glacial periods are thought to be relatively low and therefore it has been proposed that southern ocean productivity might be influenced by iron deposited elsewhere for example in the northern hemisphere3 4 which is then transported south via ocean circulation similar to the distal supply of iron to the equatorial pacific ocean5 6 7 here we examine the timing of dust fluxes to the north atlantic ocean in relation to climate records from the vostok ice core in antarctica around the time of the penultimate deglaciation about 130 kyr ago two main dust peaks occurred 155 kyr and 130 kyr ago but neither was associated with the co2 rise recorded in the vostok ice core this mismatch together with the low dust flux supplied to the southern ocean suggests that dust mediated iron fertilization of the southern ocean did not significantly influence atmospheric co2 at the termination of the penultimate glaciation

diagenesis thermal maturation and burial history of the upper cambrian bonneterre dolomite southeastern missouri an interpretation of thermal history from petrographic and fluid inclusion evidence abstract in this report fluid inclusion thermal alteration index tai and petrographic data are used to interpret thermal maturation and burial history of the bonneterre formation of southeastern missouri tai visual estimates based on indigenous upper cambrian acritarchs indicate maximum thermal exposure into the mid upper peak gas window this interpretation is in agreement with maximum fluid inclusion homogenization temperatures which average 235 c 455 f or an approximate vitrinite equivalent of 1 7 r0 thin section petrography and fluid inclusion evidence further indicate that three separate episodes of burial have occurred initial burial of unknown depth or thermal exposure culminated in a period of uplift and karstic subaerial exposure possibly during late ordovician time maximum burial and thermal exposure to the mid upper peak gas window followed and is represented in the rock by a high temperature 235 c randomly oriented two phase fluid inclusion population in matrix dolomite subsequent uplift possibly coincident with ouachita overthrusting resulted in a variety of diagenetic fabrics including late burial cements and fractures secondary two phase fluid inclusions within these late calcite cements and those occurring in linear trains that cut across matrix dolomite record lower average homogenization temperatures than their unoriented precursors average th 170 c or an approximate equivalent of 1 3 r0 further indicating that a significant amount uplift has occurred since maximum burial present day bottom hole temperatures of only 74 c an approximate equivalent of 0 7 r0 indicate that uplift has occurred after this second burial episode this event probably coincides with the development of the new madrid fault system during the tertiary which still active today these results demonstrate the utility of fluid inclusion microthermometry complex burial thermal histories

distributions sources and transformations of dissolved and particulate iron on the ross sea continental shelf during summer we report water column dissolved iron dfe and particulate iron pfe concentrations from fifty stations sampled across the ross sea during austral summer january february of 2012 concentrations of dfe and pfe were measured in each of the major ross sea water masses including the ice shelf water and off shelf circumpolar deep water despite significant lateral variations in hydrography macronutrient depletion and primary productivity across several different regions on the continental shelf dfe concentrations were consistently low 0 1 nm in surface waters with only a handful of stations showing elevated concentrations 0 20 0 45 nm in areas of melting sea ice and near the franklin island platform across the study region pfe associated with suspended biogenic material approximately doubled the inventory of bioavailable iron in surface waters our data reveal that the majority of the summertime iron inventory in the ross sea resides in dense shelf waters with highest concentrations within 50 m of the seafloor higher dfe concentrations near the seafloor are accompanied by an increased contribution to pfe from authigenic and or scavenged iron particulate manganese is also influenced by sediment resuspension near the seafloor but unlike pfe is increasingly associated with authigenic material higher in the water column together these results suggest that following depletion of the dfe derived from wintertime convective mixing and sea ice melt recycling of pfe in the upper water column plays an important role in sustaining the summertime phytoplankton bloom in the ross sea polynya

the physical environmental conditions for biogeochemical differences along the antarctic circumpolar current in the atlantic sector during late austral summer 2012 the physical and biological carbon pumps in the different hydrographic and biogeochemical regimes of the atlantic sector of the southern ocean are controlled by a series of coupled physical chemical and biological processes and a project named eddy pump was designed to study them the eddy pump field campaign was carried out during rv polarstern cruise ant xxviii 3 between january and march 2012 particular emphasis was laid on the differences which occur along the axis of the antarctic circumpolar current acc with its associated mesoscale eddy field the study sites were selected in order to represent 1 the central acc with its regular separation in different frontal jets investigated by a meridional transect along 10 e 2 a large scale bloom west of the mid atlantic ridge which lasted several months with conspicuous chlorophyll poor waters to its immediate east studied by a three dimensional mesoscale survey centred at 12 40 w and 3 the georgia basin north of the island of south georgia which regularly features an extended and dense phytoplankton bloom was investigated by a mesoscale survey centred at 38 12 w while eddy pump represents an interdisciplinary project by design we here focus on describing the variable physical environment within which the different biogeochemical regimes developed for describing the physical environment we use measurements of temperature salinity and density of mixed layer turbulence parameters of dynamic heights and horizontal current vectors and of flow trajectories obtained from surface drifters and submerged floats this serves as background information for the analyses of biological and chemical processes and of biogeochemical fluxes addressed by other papers in this issue the section along 10 e between 44 s and 53 s showed a classical acc structure with well known hydrographic fronts the subantarctic front saf at 46 5 s the antarctic polar front apf split in two at 49 25 s and 50 5 s and the southern polar front spf at 52 5 s each front was associated with strong eastward flows the west mid atlantic ridge survey showed a weak and poorly resolved meander structure between the apf and the spf during the first eight days of the survey the oceanographic conditions at the central station at 12 40 w remained reasonably constant however after that conditions became more variable in the thermocline with conspicuous temperature inversions and interleavings and also a decrease in temperature in the surface layer at the very end of the period of observation the conditions in the thermocline returned to being similar to those observed during the early part of the period with however the mixed layer temperature raised the period of enhanced thermohaline variability was accompanied by increased currents the georgia basin survey showed a very strong zonal jet at its northern edge which connects to a large cyclonic meander that itself joins an anticyclonic eddy in the southeastern quadrant the water mass contrasts in this survey were stronger than in the west mid atlantic ridge survey but similar to those met along 10 e with the exception that the warm and saline surface water typical of the northern side of the saf was not covered by the georgia basin survey mixed layers found during eddy pump were typically deep but varied between the three survey areas the mean depths and standard variations of the mixed layer along the 10 e were 77 2 24 7 m at the west mid atlantic ridge 66 7 17 7 m and in the georgia basin 36 8 10 7 m

cooling dilution and mixing of ocean water by free drifting icebergs in the weddell sea abstract iceberg c 18a 35 7 0 184 km was studied repeatedly by five circumnavigational surveys in march april 2009 during the period of the surveys c 18a travelled 109 nautical miles in 23 days covering an area of 8 1 10 3 km 2 this iceberg was formed from iceberg c 18 76 7 km that originated from the ross ice shelf in may 2002 ship based measurements show that this iceberg produced fresh meltwater above the seasonal pycnocline that diluted and chilled the water it passed through from the surface to a depth of approximately 50 m summer mixed layer the surface meltwater effects were detectable as far away as 19 km and persisted for at least 10 days we also found evidence that this iceberg was disrupting the weddell deep water to depths up to 1500 m if we include these deep effects through the water column the estimate of ocean water altered by this single iceberg reaches 3 10 12 m 3 over 23 days chemical and biological effects were detected at the same space and time scales as the physical properties with decreasing partial pressure of carbon dioxide pco 2 close to the iceberg and lower particle and chlorophyll concentration ten days after the passage of c 18a chlorophyll a had increased by 15 these results are consistent with alternative hypotheses regarding the role of icebergs as mediators of a localized geophysical disturbance h 1 as well as promoters of chlorophyll a production h 2

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

impacts on phytoplankton dynamics by free drifting icebergs in the nw weddell sea abstract glacier ice released to the oceans through iceberg formation has a complex effect on the surrounding ocean waters we hypothesized that phytoplankton communities would differ in abundance composition and production around or close to an iceberg this paper tests the influence of individual icebergs on scales of meters to kilometers observed through shipboard oceanographic sampling on march april 2009 surface waters integrated 0 100 m depth within the euphotic zone sampled close to the iceberg c 18a 10 m and the salps on smaller cells 3 10 m the iceberg s main influence in the austral fall is measured not so much by phytoplankton accumulation but by reactivation of the classic antarctic food chain facilitating diatom growth and sustaining high antarctic krill populations

near field zooplankton ice face biota and proximal hydrography of free drifting antarctic icebergs abstract a small rov was used to collect plankton make video surveys and take hydrographic measurements in close proximity to six free drifting antarctic icebergs the icebergs studied ranged in size from 32 km in length large icebergs have a greater scale of influence than do smaller ones and iceberg mediated differences in the hydrographic characteristics of their surrounding water depend on the scale sampled irrespective of size temperature generally decreased in close proximity to an iceberg while salinity increased chlorophyll a was often lower in the surface waters near the iceberg relative to the surface waters further away tabular icebergs typically had 3 distinct underwater features shelf side and bottom ablation pockets were a common feature of subsurface ice the ice itself is a dynamic and seemingly harsh environment with relatively few macrofauna living on it those that do inhabit the ice face are either highly specialized or highly mobile species composition of zooplankton within 40 m of an iceberg did not change relative to distance however biomass was generally greater within 5 m of an iceberg than it was 15 to 40 m distant

applications of fluid inclusion studies to reservoir diagenesis and petroleum migration smackover formation u s gulf coast and fateh field dubai abstract the smackover trend of the united states gulf coast is a prolific producer of oil and gas the distribution of porosity is partly controlled by precipitation of late void filling calcite the timing of the formation of these cements is interpreted from fluid inclusion geothermometry in general the fluid inclusion filling temperatures closely approximate those of the formation of the calcite and indicate that cementation occurred near the maximum depth of burial the trapped fluid is a dense calcium rich brine consistent with modern formation fluids the geochemistry of the fluid inclusions reflects the environment of diagenesis for example h2s rich inclusions occur in cements from deep dolomitic reservoirs the fateh field offshore dubai has estimated petroleum reserves of 2 3 billion bbl of oil production is principally from the mishrif formation an upper cretaceous rudist reef complex late coarse grained calcite cements partly occlude porosity these cements contain both aqueous and oil bearing fluid inclusions fluid inclusion geothermometry indicates temperatures consistent with the geothermal gradient indicating a miocene age for cement deposition since oil was trapped during growth of the calcite cement petroleum generation and migration are also miocene in age preliminary analyses of the oil trapped in inclusions show it to be different than the oil in the reservoir the oil trapped in the inclusions may be an early generated less mature oil end of article last page 957

dissolved fe in the upper waters of the pacific sector of the southern ocean the concentration of dissolved fe was determined in upper ocean waters along 170 degreesw between 53 and 72 degreess during four cruises between october 1997 and march 1998 as part of the us jgofs southern ocean antarctic polar frontal zone cruises fe concentrations were extremely variable in both space and time as a result of advection of meso scale eddys through the region observed values ranged from a maximum of 0 34 nm at 64 degreess in november next to the retreating ice edge to 0 075 nm in march at 71 degreess in the northern ross sea gyre in general the highest average mixed layer fe concentrations and the largest seasonal changes were observed in the two frontal zones at similar to 60 degreess and similar to 64 degreess formation of deep mixed layers during winter and the entrainment of sub surface waters enriched in fe is the primary source of this element to surface waters in this region of the southern ocean additionally upwelling of circumpolar deep water in the circumpolar current along its northern boundary at the polar front and its southern boundary at the southern antarctic circumpolar current front is an important mechanism supplying fe to surface waters in these areas throughout the summer comparison of integrated fe concentrations and th derived poc export and n drawdown all suggest that the maximum changes in these properties are comparable to those that would be predicted by fe availability fe concentrations determined by shipboard flow injection analysis measures et al mar chem 50 1995 3 were significantly higher than those found in replicate samples determined by shored based flameless atomic absorption spectrophotometry after preconcentration by chelation solvent extraction johnson et al mar chem 57 1997 137 the concentration differences which appear to be restricted to the upper 200 300 m do not appear to arise from different sampling or handling processes but instead are believed to result from the different sensitivity of the methods to organic fractions of fe in seawater c 2001 elsevier science ltd all rights reserved

iron fluxes from the shelf regions near the south shetland islands in the drake passage during the austral winter 2006 abstract spatial distributions of dissolved iron fe manganese mn and aluminum al in the upper 500 m of the water column near the antarctic peninsula ap during the 2006 austral winter are consistent with diagenetically produced sedimentary sources and are somewhat higher than data obtained in this region during the 2004 austral summer in contrast surface phytoplankton abundances were 6 7 times lower relative to the 2004 austral summer near the south shetland islands elevated levels of dissolved al fe and mn were found corresponding to high loads of resuspended material above the shelf as indicated by the transmissometer signal despite these high levels of trace metals phytoplankton abundances in this area were lower than in the offshore antarctic circumpolar current acc waters offshore acc stations had low concentrations of fe but up to five times greater abundance of phytoplankton the difference in phytoplankton abundance between the regions seems largely driven by light availability as indicated by mixed layer depths the elevated trace metal concentrations near king george island in the bransfield strait bs correspond to the flow path of the bransfield current this enriched plume can also be seen exiting the bs between clarence and elephant islands into the ona basin where it mixes with high nutrient low trace metal concentration acc waters leading to high productivity in this region and further downstream in the scotia sea during the growing season

provenance and dispersal of glacial marine surface sediments in the weddell sea and adjoining areas antarctica ice rafting versus current transport abstract mineralogical and granulometric properties of glacial marine surface sediments of the weddell sea and adjoining areas were studied in order to decipher spatial variations of provenance and transport paths of terrigenous detritus from antarctic sources the silt fraction shows marked spatial differences in quartz contents in the sand fractions heavy mineral assemblages display low mineralogical maturity and are dominated by garnet green hornblende and various types of clinopyroxene cluster analysis yields distinct heavy mineral assemblages which can be attributed to specific source rocks of the antarctic hinterland the configuration of modern mineralogical provinces in the near shore regions reflects the geological variety of the adjacent hinterland in the distal parts of the study area sand sized heavy minerals are good tracers of ice rafting granulometric characteristics and the distribution of heavy mineral provinces reflect maxima of relative and absolute accumulation of ice rafted detritus in accordance with major iceberg drift tracks in the course of the weddell gyre fine grained and coarse grained sediment fractions may have different origins in the central weddell sea coarse ice rafted detritus basically derives from east antarctic sources while the fine fraction is discharged from weak permanent bottom currents and or episodic turbidity currents and shows affinities to southern weddell sea sources winnowing of quartz rich sediments through intense bottom water formation in the southern weddell sea provides muddy suspensions enriched in quartz the influence of quartz rich suspensions moving within the weddell gyre contour current can be traced as far as the continental slope in the northwestern weddell sea in general the focusing of mud by currents significantly exceeds the relative and absolute contribution of ice rafted detritus beyond the shelves of the study area

sea surface temperature control on the distribution of far traveled southern ocean ice rafted detritus during the pliocene the flux and provenance of ice rafted detritus ird deposited in the southern ocean can reveal information about the past instability of antarctica s ice sheets during different climatic conditions here we present a pliocene ird provenance record based on the 40ar 39ar ages of ice rafted hornblende grains from ocean drilling program site 1165 located near prydz bay in the indian ocean sector of the southern ocean along with the results of modeled sensitivity tests of iceberg trajectories and their spatial melting patterns under a range of sea surface temperatures ssts our provenance results reveal that ird and hence icebergs in the prydz bay area were mainly sourced from i the local prydz bay region and ii the remote wilkes land margin located at the mouth of the low lying aurora subglacial basin a series of ird pulses reaching up to 10 times background ird flux levels were previously identified at site 1165 between 3 3 and 3 0 ma our new results reveal that the average proportion of ird sourced from distal wilkes land margin doubles after 3 3 ma our iceberg trajectory melting models show that slower iceberg melting under cooling ssts over this middle pliocene interval allowed wilkes land icebergs to travel farther before melting hence declining ssts can account for a large part of the observed ird provenance record at site 1165 in early pliocene ird layers sampled at suborbital resolution around 4 6 ma we find evidence for significant increases in icebergs derived from wilkes land during very warm interglacials this is suggestive of large scale destabilization of the east antarctic ice sheet in the aurora subglacial basin as far traveled icebergs would have to overcome enhanced melting in warmer ssts our results highlight the importance of considering ssts when interpreting ird flux and provenance records in distal locations

persistent iceberg groundings in the western weddell sea antarctica abstract we use the time average of a series of satellite synthetic aperture radar sar images from 2005 to 2007 to identify grounded icebergs in the western weddell sea satellite laser altimetry along repeated ground tracks confirms that regions of high mean backscatter are associated with stationary tabular icebergs the altimeter data also provide iceberg freeboard from which we infer maximum ice draft assuming the lightly grounded limit and a two layer density model consistent with a source at filchner ronne ice shelf the maximum iceberg draft agrees very well with the ocean depth at a point where the bathymetry is well constrained by ship soundings however for an extensive region near 71 s south of larsen c ice shelf the maximum grounding depth for several icebergs reveals the ocean to be locally more than 200 m shallower than in bathymetry products this previously uncharted bank is expected to have a profound effect on the northward flow of the western weddell gyre and the cross slope transport of offshore warm deep water towards the eastern antarctic peninsula ice shelves passive microwave data also show that sea ice concentration is reduced in the vicinity of this group of grounded icebergs indicating an iceberg influence on ocean atmosphere heat and freshwater exchanges

initial observations of the subsurface structure and short term variability of the seaward deflection of the gulf stream off charleston south carolina a recurring seaward deflection of the surface layer of the gulf stream has been observed near 32 n latitude off the coast of the southeastern united states it has been suggested that a ridge and trough bottom feature the so called charleston bump on the upper continental slope off the georgia south carolina coast produces the deflection through a bottom steering effect present data indicate that the deflection is great enough to direct the gulf stream s shoreward surface thermal front to the east and even south of east about 70percnt of the time air deployed expendable bathythermograph surveys have been made with sufficient coverage to provide several synoptic three dimensional views of the gulf stream s thermal frontal zone in the region between savannah georgia and cape hatteras north carolina these views show the subsurface structure of the seaward deflection to exhibit large short term variability during wintertime conditions february 1979 the greatest deflection 090 true of the near surface front occurred at a time when the deeper front was more aligned 080 true with local topography within the few days following this observation the deflection angle at all depths decreased to near or below 070 true two large amplitude gulf stream meanders progressed northeastward away from the deflection region during this time period deflection angles at all levels during late summertime conditions november 1979 were observed to be near 070 true a simple kinematical model which incorporates growing propagating gulf stream meanders is proposed to explain the deflection s short term variability a dome shaped volume of cold water was observed to be located over the upper continental slope immediately downstream of the deflection the existence and persistence of this cold dome suggest that upwelling is important in its maintenance a hypothesis consistent with its hydrographic properties

dissolved iron in the vicinity of the crozet islands southern ocean the annual phytoplankton bloom occurring north of the crozet plateau provides a rare opportunity to examine the hypothesis that natural iron fertilization can alleviate high nutrient low chlorophyll hnlc conditions normally associated with the southern ocean therefore during crozet natural iron bloom and export experiment crozex a large multidisciplinary study performed between november 2004 and january 2005 measurements of total dissolved iron dfe0 2 m were made on seawater from around the islands and atmospheric iron deposition estimated from rain and aerosol samples dfe concentrations were determined by flow injection analysis with n n dimethyl p phenylenediamine dihydrochloride dpd catalytic spectrophotometric detection dfe concentrations varied between 0 086 and 2 48 nm with low values in surface waters enrichment of dissolved iron 1 nm at close proximity to the islands suggests that the plateau and the associated sediments are a source of iron waters farther north also appear to be affected by this input of coastal and shelf origin although dissolved iron concentrations decrease as a function of distance to the north of the plateau with a gradient of 0 07 nm km 1 at the time of sampling using lateral and vertical diffusion coefficients derived from ra isotope profiles and also estimates of atmospheric inputs it was then possible to estimate a dfe concentration of 0 55 nm to the north of the islands prior to the bloom event which is sufficient to initiate the bloom the lateral island source being the largest component a similar situation is observed for other sub antarctic islands such as kerguelen south georgia that supply dissolved iron to their surrounding waters thus enhancing chlorophyll concentrations

the cold core eddy and strong upwelling off the coast of new south wales in early 2007 abstract during the austral summer of 2006 07 a series of extreme oceanic events occurred in the tasman sea following a series of strong wind driven upwelling events an intense cold core eddy developed off sydney australia a data assimilating eddy resolving ocean model is used to create a three dimensional time varying reanalysis of these events the reanalysis indicates that the cold anomalies associated with the upwellings were in excess of 5 c near the coast where sea level decreased by as much as 0 2 m the reanalysed three dimensional structure of the cold core eddy shows the eddy leaning to the west north west in towards the continental shelf the diameter of the eddy is about 100 km and the sea level anomaly at the eddy centre peaks at around 1 m with an associated sub surface temperature anomaly in excess of 8 c at 200 m depth corresponding to an upward isotherm excursion of 600 m the circulation around the cyclonic eddy is ageostrophic with upwelling in the southern sector of the eddy where flow is onshore and climbing the continental slope and downwelling in the northern sector where flow is descending off the slope three dimensional trajectories of water parcels around the eddy involve 50 100 m vertical excursions based on the reanalysed circulation and composite satellite images of chlorophyll a we hypothesise that the circulation around the eddy led to significant nutrient enrichment in the euphotic zone around the perimeter of the eddy

weddell sea iceberg drift five years of observations since 1999 52 icebergs have been tagged with gps buoys in the weddell seato enable monitoring of their position the chosen icebergs were of small tomedium size with a few icebergs larger than 10 km associatedwith the calving of icebergs a38 and a43 from the ronne ice shelf the majority of icebergs were tagged off neumayer station 8e 70s it was found that smaller bergs with edges shorter than 200 m had the shortestlife cycle 0 5 yr iceberg and thus freshwater export out of theweddell sea was found to be highly variable in one year the majority of buoysdeployed remained in the weddell sea constituting about 40 of the ncep p efreshwater input whereas in other years all of the tagged icebergs were exported the observed drifts of icebergs and sea ice showed a remarkably coherent motion the analysis of an iceberg sea ice buoy array in the western weddell seaand an iceberg array in the eastern weddell sea showed a coherent sea iceiceberg drift in sea ice concentrations above 86 dynamic kinematic parameter dkp during the course of coherent movement were low and deviations from the meancourse associated with the passage of low pressure system the length scale ofcoherent movement was estimated to be less than 250km about half the value found forthe arctic ocean

cape romain and the charleston bump historical and recent hydrographic observations a review and analysis of historical and new hydrographic data are presented for the charleston bump region an area of doming isotherms is identified primarily between 31 5 sup 0 and 34 5 sup 0 n and the 200 and 400 m isobaths the highest incidences of doming are found off long bay 86 cape fear 38 and cape romain 25 evidence suggests that low salinity shelf water collects in the doming area off long bay in july and that seasonal fluctuations in the depth of the main thermocline layer in this area are linked to gulf stream transport and local winds at times there is a gradual offshore onshore movement of the gulf stream opposite long bay roughly following the 400 m isobath and at other times an abrupt eastward movement near 32 sup 0 n much of the time there appears to be a direct seasonal relationship between historical seasonal velocity fields and offshore deflection with higher lower velocities corresponding to greater lesser deflection

iron and manganese speciation and cycling in glacially influenced high latitude fjord sediments west spitsbergen svalbard evidence for a benthic recycling transport mechanism abstract glacial environments may provide an important but poorly constrained source of potentially bioavailable iron and manganese phases to the coastal ocean in high latitude regions little is known about the fate and biogeochemical cycling of glacially derived iron and manganese in the coastal marine realm sediment and porewater samples were collected along transects from the fjord mouths to the tidewater glaciers at the fjord heads in smeerenburgfjorden kongsfjorden and van keulenfjorden along western svalbard solid phase iron and manganese speciation determined by sequential chemical extraction could be linked to the compositions of the local bedrock and hydrological weathering conditions below the local glaciers the concentration and sulfur isotope composition of chromium reducible sulfur crs in kongs and van keulenfjorden sediments largely reflect the delivery rate and isotope composition of detrital pyrite originating from adjacent glaciers the varying input of reducible iron and manganese oxide phases and the input of organic matter of varying reactivity control the pathways of organic carbon mineralization in the sediments of the three fjords high reducible iron and manganese oxide concentrations and elevated metal accumulation rates coupled to low input of fresh organic matter lead to a strong expression of dissimilatory metal oxide reduction evidenced in very high porewater iron up to 800 m and manganese up to 210 m concentrations in kongsfjorden and van keulenfjorden sediment reworking by the benthic macrofauna and physical sediment resuspension via iceberg calving may be additional factors that promote extensive benthic iron and manganese cycling in these fjords on going benthic recycling of glacially derived dissolved iron into overlying seawater where partial re oxidation and deposition occurs facilitates the transport of iron across the fjords and potentially into adjacent continental shelf waters such iron dominated fjord sediments are likely to provide significant fluxes of potentially bioavailable iron to coastal waters and beyond by contrast low delivery of reducible iron oxyhydr oxide phases and elevated organic carbon mineralization rates driven by elevated input of fresh marine organic matter allow organoclastic sulfate reduction to dominate carbon remineralization at the outer smeerenburgfjorden sites which may limit iron fluxes to the water column

the application of fluid inclusions to migration of oil and diagenesis in petroleum reservoirs abstract fluid inclusions can be used to interpret thermal history and petroleum maturation and migration relative to burial history temperature pressure and composition data collected from fluid inclusions are used to determine the environment of diagenesis and the timing of cementation and migration cements in petroleum reservoirs contain both oil and aqueous fluid inclusions fluorescence spectroscopy is used to identify oil inclusions and to determine the maturity of entrapped oil the lifetime of fluorescence induced by a pulsed laser is related to the api gravity of entrapped oil interpretation of fluid inclusion data depends on knowing the origin of fluid inclusions and the probability that they survive in the burial environment those aspects of fluid inclusion study are investigated by synthesizing oil and aqueous inclusions in calcite crystals in laboratory experiments examples of how fluid inclusions are used to determine the physico chemical environments of diagenesis in petroleum reservoirs and the timing of cementation and migration are given for the wealden basin england the mishrif formation dubai the smackover formation gulf coast u s a and jurassic sandstones offshore norway in the wealden basin temperature data from fluid inclusions are used to determine that oil migration occurred in the cretaceous and that the reservoir rocks have been uplifted to varying degrees at a time after migration distribution of oil inclusions indicates that generation and migration of oil was principally in the western part of the basin the geochemistry of oil inclusions in calcite cements from the mishrif formation dubai are used to determine the type and maturity of entrapped oil temperature data from oil and water inclusions are used to relate reservoir diagenesis to burial history and the migration of oil in deep smackover reservoirs oil contains h 2 s the origin of the h 2 s is examined by study of fluid inclusions containing h 2 s in jurassic sandstones offshore norway fluid inclusion studies show that silica cementation is related to burial depth whereas a later calcite cementation originated from invasion of a hot fluid

response of south carolina continental shelf waters to wind and gulf stream forcing during winter of 1986 the south carolina shelf water response to strong winter atmospheric forcing and gulf stream variations over the slope is discussed with the aid of a comprehensive set of atmospheric and oceanic observations made during project gale genesis of atlantic lows experiment a mixed response is observed to wind and gulf stream forcing subtidal variability of inner and middle shelf waters is primarily a barotropic forced response to coherent synoptic scale alongshore winds this response is not trapped over the shelf as has been found for other wide non equatorial shelves but is also significant at the shelf edge possibly because of the comparable widths of the shelf and slope the outer shelf also shows a significant gulf stream influence the gulf stream appears to have two preferred position modes either onshore with the stream flowing over the charleston bump and along the shelf break or offshore when the stream can be located up to 100 km east of the shelf break transition between the two states is rapid subtidal variability in the outer shelf is dominated by weekly period frontal eddies and meanders when the stream is in an onshore mode and by persistent southward flow when the stream is offshore this southward flow is produced by enlarged cyclonic eddies with upwelled centers located over the slope between the offshore stream and the shelf edge sometimes referred to as the charleston gyre positive mean alongshore sea level slopes at the shelf edge due to the persistence of the cyclonic gyres are geostrophically balanced by mean onshore flow which transports upwelled waters onto the shelf enhancing the biological productivity of the area relative to other regions of the south atlantic bight

large flux of iron from the amery ice shelf marine ice to prydz bay east antarctica the antarctic continental shelf supports a high level of marine primary productivity and is a globally important carbon dioxide co2 sink through the photosynthetic fixation of co2 via the biological pump sustaining such high productivity requires a large supply of the essential micronutrient iron fe however the pathways for fe delivery to these zones vary spatially and temporally our study is the first to report a previously unquantified source of concentrated bioavailable fe to antarctic surface waters we hypothesize that fe derived from subglacial processes is delivered to euphotic waters through the accretion fe storage and subsequent melting fe release of a marine accreted layer of ice at the base of the amery ice shelf ais using satellite derived chlorophyll a data we show that the soluble fe supplied by the melting of the marine ice layer is an order of magnitude larger than the required fe necessary to sustain the large annual phytoplankton bloom in prydz bay our finding of high concentrations of fe in ais marine ice and recent data on increasing rates of ice shelf basal melt in many of antarctica s ice shelves should encourage further research into glacial and marine sediment transport beneath ice shelves and their sensitivity to current changes in basal melt currently the distribution volume and fe concentration of antarctic marine ice is poorly constrained this uncertainty combined with variable forecasts of increased rates of ice shelf basal melt limits our ability to predict future fe supply to antarctic coastal waters

gulf stream bimodality and variability downstream of the charleston bump gulf stream mean flow and variability have been studied in the gulf stream deflection and meander energetics experiment damex this study was conducted between september 1981 and april 1982 in the area of the charleston bump off the coast of the southeastern united states using data from an array of current meters and satellite imagery it has been shown that the seaward deflection of the gulf stream by the bump has a bimodal character and that the gulf stream meander field downstream of the bump differs between the two states of deflection the two deflection conditions have been termed the weakly deflected state and the strongly deflected state in this paper a weakly deflected gulf stream flows past the charleston bump and close enough to the edge of the continental shelf that its shoreward sea surface temperature sst front remains inshore of the 600 m isobath between charleston and cape hatteras a strongly deflected gulf stream turns sharply eastward at the bump and flows seaward far enough to have its shoreward sst front offshore of the 600 m isobath for several tens of kilometers along the continental slope downstream of the bump the transitions between deflection states may occur very rapidly and once in a strongly deflected state the gulf stream may remain so for up to several months two transitions were observed during damex one from a weakly to a strongly deflected state and one in the other direction the transition from weakly to strongly deflected state took only a few days at a given site while the signatures of the other transition were not as definite in the data records the strongly deflected state occurred during the fall and winter in damex october through january and satellite observations from earlier years suggest that it is this time of year in which the strongly deflected state preferentially occurs it was not clear from the damex data alone how the transition from a weakly deflected to a strongly deflected state may be induced but path or transport changes in the gulf stream as it approaches the bump and interactions between the current and rings or eddies are candidate mechanisms the bimodal character of the stream s path affects the low frequency variability of the current between the charleston bump and cape hatteras in the following manner typical meander frontal eddy patterns dominate the mesoscale fluctuation field during times of weak deflection while larger amplitude meanders of the gulf stream jet which can have very sharp curvature and strong anticyclonic circulations in their crests exist during times of strong deflection furthermore these larger amplitude meanders which we call the damex biweekly meanders have generally slower phase propagation speeds than do the typical meander frontal eddy events about 20 25 km day compared with 35 60 km day as well as longer periods about 16 days compared to 1 week

dissolved iron and iron ii distributions beneath the pack ice in the east antarctic 120 e during the winter spring transition distributions of dissolved iron dfe and its reduced form fe ii to a depth of 1000 m were investigated under the seasonal pack ice off east antarctica during the sea ice physics and ecosystem experiment sipex 2 sea ice voyage in september october 2012 concentrations of dfe were elevated up to five fold relative to southern ocean background concentrations and were spatially variable the mean dfe concentration was 0 44 0 4 nm with a range from 0 09 to 3 05 nm profiles of dfe were more variable within and among stations than were macronutrients suggesting that coupling between these biologically essential elements was weak at the time of the study brine rejection and drainage from sea ice are estimated to be the dominant contributors to elevated dfe concentrations in the mixed layer but mass budget considerations indicate that estimated dfe fluxes from brine input alone are insufficient to account for all observed dfe melting icebergs and shelf sediments are suspected to provide the additional dfe fe ii was mostly below the detection limit but elevated at depth near the continental shelf implying that benthic processes are a source of reduced fe in bottom waters the data indicate that dfe builds up under the seasonal sea ice cover during winter and that reduction of fe may be hampered in early spring by several factors such as lack of electron donors low biological productivity and inadequate light below the sea ice the accumulated dfe pool in the mixed layer is expected to contribute to the formation of the spring bloom as the ice retreats

ocean glider observations of iceberg enhanced biological production in the northwestern weddell sea icebergs affect local biological production around antarctica we used an ocean glider to observe the effects of a large iceberg that was advected by the antarctic slope current along the continental slope in the northwestern weddell sea in early 2012 the high resolution glider data reveal a pronounced effect of the iceberg on ocean properties with oxygen concentrations of 13 4 mol kg 1 higher than levels in surrounding waters which are most likely due to positive net community production this response was confined to three areas of water in the direct vicinity of the iceberg track each no larger than 2 km2 our findings suggest that icebergs have an impact on antarctic production presumably through local micronutrient injections on a scale smaller than typical satellite observations of biological production in the southern ocean

contributions from glacially derived sediment to the global iron oxyhydr oxide cycle implications for iron delivery to the oceans estimates of glacial sediment delivery to the oceans have been derived from fluxes of meltwater runoff and iceberg calving and their sediment loads the combined total 2900 tg yr 1 of the suspended sediment load in meltwaters 1400 tg yr 1 and the sediment delivered by icebergs 1500 tg yr 1 are within the range of earlier estimates high resolution microscopic observations show that suspended sediments from glacial meltwaters supraglacial and proglacial sediments and sediments in basal ice from arctic alpine and antarctic locations all contain iron oxyhydr oxide nanoparticles which are poorly crystalline typically 5 nm in diameter and which occur as single grains or aggregates that may be isolated or attached to sediment grains nanoparticles with these characteristics are potentially bioavailable a global model comparing the sources and sinks of iron present as oxyhydr oxides indicates that sediment delivered by icebergs is a significant source of iron to the open oceans beyond the continental shelf iceberg delivery of sediment containing iron as oxyhydr oxides during the last glacial maximum may have been sufficient to fertilise the increase in oceanic productivity required to drawdown atmospheric co2 to the levels observed in ice cores

ice core evidence for the extent of past atmospheric co2 change due to iron fertilisation 1 an extended high resolution ice core record of dust deposition over the past 60 ka from dome c antarctica is presented the data are in conflict with the idea that changes in aeolian iron input into the southern ocean were the major cause for the 80 ppm glacial interglacial co2 increase during the deglaciation the co2 increase shows a linear relationship with the fall of the logarithm of the nss ca2 flux a proxy for dust deposition however the very large variations in the nss ca2 flux related to the glacial antarctic warm events a1 to a4 were accompanied by small co2 variations only our data based analysis suggests that decreased southern ocean dust deposition caused at most a 20 ppm increase in co2 at the last glacial interglacial transition rapid decreases in dust deposition to the northern pacific could have been responsible for a maximum of 8 ppm in addition

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