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

iron and manganese diagenesis in deep sea volcanogenic sediments and the origins of pore water colloids abstract volcanogenic sediments are typically rich in fe and mn bearing minerals that undergo substantial alteration during early marine diagenesis however their impact on the global biogeochemical cycling of fe and mn has not been widely addressed this study compares the near surface 0 20 cm below sea floor cmbsf aqueous no 3 and solid phase reactive fe distributions between two volcanogenic sediment settings 1 a deep sea tephra rich deposit neighbouring the volcanically active island of montserrat and 2 mixed biosiliceous volcanogenic sediments from abyssal depths near the volcanically inactive crozet islands archipelago shallow penetration of o2 aq into montserrat sediments was observed 5 cmbsf and largely controlled by the oxidation of organic matter dissolved fe and mn distributions in montserrat pore waters were lowest in the surface oxic layer 0 3 m fe 32 m mn with maxima 20 m fe 200 m mn in the upper 1 15 cmbsf unlike montserrat fe and mn in crozet pore waters were ubiquitously partitioned between 0 2 m and 0 02 m filtrations indicating that the pore water distributions of fe and mn in the traditionally termed dissolved size fraction are dominated by colloids with respective mean abundances of 80 and 61 plausible mechanisms for the origin and composition of pore water colloids are discussed and include prolonged exposure of crozet surface sediments to early diagenesis compared to montserrat favouring nano particulate goethite formation and the elevated dissolved si concentrations which are shown to encourage fine grained smectite formation in addition organic matter may stabilise authigenic fe and mn in the crozet pore waters we conclude that volcanogenic sediment diagenesis leads to a flux of colloidal material to the overlying bottom water which may impact significantly on deep ocean biogeochemistry diffusive flux estimates from montserrat suggest that diagenesis within tephra deposits of active island volcanism may also be an important source of dissolved mn to the bottom waters and therefore a source for the widespread hydrogenous mnox deposits found in the caribbean region

extinction survival and recovery of corals from the triassic to middle jurassic time recognizing extinction events and determining their cause at the triassic jurassic t j transition and near the pliensbachian toarcian lower jurassic boundary is a field of growing interest we provide arguments for these events through a literature based new evaluation of coral diversity from triassic to dogger and a new palaeobiogeographical map the t j extinction of corals is clearly related to the breakdown of reef environments origination curves show that hettangian the lowest jurassic stage was not only a survival phase but already rather a recovery phase post extinction evolution of reefs and their survival only in the northernmost margin of the tethys support the hothouse hypothesis for the t j extinction event during pliensbachian many new taxa appear but mostly solitary corals not really framebuilders many of these taxa do not occur anymore during the following stages the new increase in diversity is related to the development of bajocian middle jurassic reefs

factors regulating the great calcite belt in the southern ocean and its biogeochemical significance the great calcite belt gcb is a region of elevated surface reflectance in the southern ocean so covering 16 of the global ocean and is thought to result from elevated seasonal concentrations of coccolithophores here we describe field observations and experiments from two cruises that crossed the gcb in the atlantic and indian sectors of the so we confirm the presence of coccolithophores their coccoliths and associated optical scattering located primarily in the region of the subtropical agulhas and subantarctic frontal regions coccolithophore rich regions were typically associated with high velocity frontal regions with higher seawater partial pressures of co2 pco2 than the atmosphere sufficient to reverse the direction of gas exchange to a co2 source there was no calcium carbonate caco3 enhancement of particulate organic carbon poc export but there were increased poc transfer efficiencies in high flux particulate inorganic carbon regions contemporaneous observations are synthesized with results of trace metal incubation experiments 234th based flux estimates and remotely sensed observations to generate a mandala that summarizes our understanding about the factors that regulate the location of the gcb

glacial interglacial variability in diatom abundance and valve size implications for southern ocean paleoceanography antarctic sea ice extent along with southern ocean biological productivity varied considerably during glacial interglacial periods and both are known to have played a considerable role in regulating atmospheric co2 variations in the past here we present data on diatom absolute abundance valves g of sediment and size over the past 42 ka b p and how they link to glacial interglacial changes in antarctic sea ice extent southern ocean frontal systems and aeolian dust flux our records of sea ice and permanent open ocean zone diatom abundances suggest a shift in the antarctic winter sea ice limit and polar front respectively up to the modern day polar frontal zone during marine isotopic stages mis 2 and late mis 3 in addition to glacial shifts in the polar front diatom assemblages also recorded a plausible northward shifts in polar front during few intervals of mis 1 glacial periods north of the polar front in the indian sector of the southern ocean were characterized by higher total diatom abundance larger fragilariopsis kerguelensis apical length and thalassiosira lentiginosa radius this is probably a consequence of 1 a northward expansion of the opal belt a region characterized by high production and export of biogenic silica 2 an increase in terrigenous input via erosion of crozet islands and 3 the alleviation of iron deficit by high input of fe bearing dust the larger and highly silicified diatoms such as f kerguelensis and t lentiginosa may have mainly contributed in transporting biogenic silica and organic carbon to the seabed for the last 42 ka in the northern polar frontal zone of the indian sector of the southern ocean

a quasi synoptic view of the frontal circulation in the crozet basin during the antares 4 cruise abstract with the major objective of estimating the secondary vertical circulation a fine grid survey of hydrographic and current fields across the crozet basin frontal zone was made as a physical component of the multidisciplinary antares 4 cruise this frontal zone forms the boundary of the antarctic circumpolar current and the agulhas return current with the quasi permanent existence of strong eddy activity prior to any quantitative diagnosis of the vertical circulation from the fine grid data it is necessary to place the mesoscale circulation and its time variability of the survey area within the basin wide context we give a quasi synoptic view of the ambient frontal circulation during the cruise period using satellite derived chlorophyll concentrations and sea surface temperature particular emphasis is placed on evaluation of the degree of synopticity of our fine grid measurements by comparing mesoscale features on satellite images the limited survey area 1 5 latitude 2 longitude lies precisely within the southernmost and easternmost convergent zone of the two current systems cutting across mesoscale meanders having typical wavelengths of 400 km and periods of 4 months both these satellite images and topex poseidon sea surface height data indicate little temporal variability of the survey area during the 14 days of measurement although fortuitous this quasi steady state of circulation enables us to use the ensemble of fine grid data as a set of synoptic data for diagnosing the vertical circulation using quasi geostrophic dynamics preliminary analysis of the horizontal and vertical hydrographic structure of the fine grid hints at the existence of wave like cross frontal intrusions having a mean along front wavelength of about 30 km

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

physical controls on biogeochemical zonation in the southern ocean the primary control on the n s zonation of the southern ocean is the wind induced transport of the antarctic circumpolar current acc the acc divides the southern ocean into three major zones the subantarctic zone saz north of the acc the acc transport zone and the zone south of the acc saccz the zone of acc transport is most often subdivided into two zones the polar frontal zone pfz and the antarctic zone aaz but it may be appropriate to define more subzones or indeed only one at some longitudes to maintain geostrophic balance isopycnals must slope upwards to the south across the acc thus raising nutrient rich deep water closer to the surface as one goes polewards in addition silicate concentrations increase polewards along isopycnals because of diapycnic mixing with silicate rich bottom water surface silicate concentrations therefore decrease northwards from high levels in the saccz to low levels in the saz within the saz and pfz and even in the northern part of the aaz silicate levels may drop to limiting levels for siliceous phytoplankton production during summer nitrate concentrations also decrease northwards but only become limiting in the subtropical zone north of the saz the second circumpolar control is the changing balance of stratification with temperature dominating near surface stratification in the saz and salinity dominating further south because of fresh water input to the surface from melting ice this results in circumpolar features such as the subsurface 2 c temperature minimum and the subduction of the salinity minimum of antarctic intermediate water which are often but not always associated with frontal jets and large transports the transport of the acc is dynamically constrained into narrow bands the number and latitudinal location of which are controlled by the bathymetry and so vary with longitude thus it is not the fronts that are circumpolar but the total acc transport and scalar properties of the salinity and temperature fields evidence of summer silicate and nitrate uptake in all zones saz pfz and aaz shows that there is productivity despite their high nutrient low chlorophyll status blooms covering large areas say 400 km across in the pfz and aaz are found in the vicinity of submarine plateaux which suggest benthic iron fertilizatio

fluxes of particulate iron from the upper ocean around the crozet islands a naturally iron fertilized environment in the southern ocean despite a large macronutrient reservoir the southern ocean has low levels of chlorophyll primarily due to low iron availability exceptions to this situation are island systems where natural terrestrial iron inputs allow the development of large blooms particulate organic carbon poc and particulate labile and refractory iron analyses were performed on large 53 m particles collected at the base of the mixed layer within such a system the crozet islands and in adjacent high nutrient low chlorophyll hnlc waters biogenic iron was obtained by removal of estimated lithogenic fe from the total fe present we combine these data with 234th measurements to determine downward particulate fe fluxes fluxes of fe ranged from 4 to 301 nmol m 2 d 1 labile not detectable to 50 mol m 2 d 1 biogenic and from 3 to 145 mol m 2 d 1 total and on average were approximately four times larger below the highly productive naturally iron fertilized region than below the adjacent hnlc area downward labile iron fluxes are close to the sum of dissolved terrestrial atmospheric and upwelled iron calculated from the planquette et al 2007 model refractory iron fluxes are 2 orders of magnitude larger and these can only have come from particles advected from the plateau itself the biogenic fe is a substantial fraction 0 76 mean 23 of the total particulate fe to the north of the islands the origin of this fe pool must be dominantly biological conversion from the lithogenic fraction as other supply terms including aeolian deep mixing and lateral advection of dissolved fe are inadequate to account for the magnitude of this fe inclusion of the offshore biologically available fraction of the lithogenic iron flux is therefore required to calculate fully the yield of carbon exported per unit iron injected

quantifying export production in the southern ocean implications for the ba xs proxy the water column and sedimentary baxs distribution around the crozet plateau is used to decipher the controls and timing of barite formation and to evaluate how export production signals are recorded in sediments underlying a region of natural fe fertilization within the fe limited southern ocean export production estimated from preserved vertical sedimentary baxs accumulation rates are compared with published export fluxes assessed from an integrated study of the biological carbon pump to determine the validity of baxs as a quantitative proxy under different fe supply conditions typical of the southern ocean detailed assessment of the geochemical partitioning of ba in sediments and the lithogenic end member allows appropriate correction of the bulk ba content and determination of the baxs content of sediments and suspended particles the upper water column distribution of baxs is extremely heterogeneous spatially and temporally organic carbon baxs ratios in deep traps from the fe fertilized region are similar to other oceanic settings allowing quantification of the inferred carbon export based on established algorithms there appears to be some decoupling of poc and ba export in the fe limited region south of the plateau the export production across the crozet plateau inferred from the baxs sedimentary proxy indicates that the fe fertilized area to the north of the plateau experiences enhanced export relative to equivalent southern ocean settings throughout the holocene and that this influence may also have impacted the site to the south for significant periods this interpretation is corroborated by alternative productivity proxies opal accumulation 231paxs 230thxs baxs can be used to quantify export production in complex settings such as naturally fe fertilized volcanoclastic areas providing appropriate lithogenic correction is undertaken and sediment focusing is corrected for along with evaluation of barite preservation

oldest scleractinian coral reefs on the north american craton upper triassic carnian northeastern british columbia canada abstract bioclastic accumulations composed of crinoids brachiopods molluscs spongiomorphs and scleractinian corals occur within upper triassic strata of the lower baldonnel formation at pardonet hill in northeastern british columbia canada these small buildups 100 to 500 m3 have planar bases and broadly convex tops these mounds are interpreted as small patch reefs composed of packstone bioclastic floatstone rudstone and carbonate breccia intercalated with mixed siliciclastic carbonate sediments deposited in a shallow subtidal setting i e above fairweather wave base amalgamated hummocky cross stratified to current ripple laminated quartz dominated sandstone beds and numerous sharp based normally graded bioclastic commonly encrinitic packstone grainstone quartz sandstone couplets characterize inter reef lithologies conodont biostratigraphy indicates that the pardonet hill patch reefs occur within strata dated as earliest upper carnian lower nodosus zone the pardonet hill patch reefs originated and developed during an interval of regional sea level lowstand strata within which these patch reefs occur represent the westernmost migration of the triassic shoreline in western canada disappearance of coral reefs in the study area may have been affected by rapid marine transgression and failure of reef faunas to recolonize the new shore zone further to the east the pardonet hill locality occurred on the western margin of the north american craton during the triassic prior to their discovery reef like structures dominated by corals in the western panthalassa were limited to allochthonous terranes now part of the cordillera the pardonet hill patch reefs occur at approximately 30 triassic paleolatitude in modern settings this is at the extreme latitudinal margin of subtropical zooxanthellate reef development the presence of benthic faunas characteristic of low paleolatitude settings on the northwestern coast of pangea has significant implications in paleotectonic and paleoenvironmental reconstructions

early history of scleractinian corals and its geological consequences conventional views have implied that scleractinian corals were hermatypic and thus were potentially reef building from the onset of their appearance in early mesozoic time in shallow shelf carbonate environments however for almost 25 m y they held rather subordinate positions and generally did not participate in extensive ecologic reef framework evidence from both north america and europe demonstrates that triassic corals had ecologic preferences quite different from those in the cenozoic a key step in the evolutionary success of these corals may have been the advent of a symbiotic association with algae this association believed to have developed at the end of the triassic could have been responsible for thrusting scleractinians into prominent positions as reef builders and may account for their dramatic radiation in mesozoic time

potential contributions of ancient oceanic islands to evolutionary theory before much was known about the geology of continental margins and the occurrence of oceanic islands in suspect terranes tests of theories related to island biogeography were undertaken mostly by ecologists and in paleontological investigations of non insular biota a significant new source of paleontological data with which to test models for species equilibrium over evolutionary versus ecological time scales and other important problems in evolutionary theory exists within circum oceanic belts where ancient oceanic islands are preserved as allochthonous terranes research on faunas from these areas simplifies attempts to apply the theory of island biogeography to the fossil record and to trace the history of island populations over evolutionary time scales paleontologic data from a paleozoic island arc alexander terrane show significant fluctuations in the taxonomic diversity of brachiopods and thus question one of the main assertions of the dynamic equilibrium model these data also support the con

fe and h2o2 distributions in the upper water column in the indian sector of the southern ocean total dissolvable iron tdfe particulate iron pfe and hydrogen peroxide h2o2 measurements were performed along a n s transect in the upper 250 m in the southern ocean 62 00e 66 42s 49 00s antares ii cruise february 1994 tdfe was organically extracted apdc dddc chloroform and analysed by graphite furnace atomic absorption spectrometry gfaas pfe was analysed by gfaas following a strong mixed acid leach and h2o2 was analysed on board by fluorometry the respective detection limits are equal to 0 13 nmol kg 0 02 nmol kg and 3 0 nmol kg tdfe concentrations vary from 0 4 to 6 2 nmol kg and profiles are not completely depleted in the surface pfe concentrations vary from 0 02 to 0 2 nmol kg iron carbon fe c uptake ratios for phytoplankton were calculated either from seawater or particle measurements they are variable along the transect but are consistent when they could be compared all the observed ratios are within the range of values proposed for the fe c uptake ratios by phytoplankton using our uptake ratio calculated in the permanent open ocean zone 4 10 6 mol mol we estimate that the primary production which can be supported by the iron input flux into the surface waters is two times higher than the measured primary production in the same area in the surface waters h2o2 concentrations vary from 5 0 to 19 7 nmol kg such low concentrations are due to strong vertical mixing low dissolved organic matter concentrations and the latitude of the site

modern coral reefs of western atlantic new geological perspective contrary to popular belief of the late 1960s western atlantic holocene reefs have a long history and are not feeble novice nearshore veneers that barely survived postglacial temperatures rather the growth of these reefs kept pace with the rising seas of the holocene transgression and their development was for the most part controlled by offshore wave energy conditions and the relationship between changing sea levels and local shelf topography thus the outer shelves of the eastern caribbean in areas of high energy have relict reefs consisting predominantly of acropora palmata a robust shallow water coral the flooding of adjacent shelves during the postglacial transgression introduced stress conditions that terminated the growth of these reefs when about 7 000 r ago shelf water conditions improved scattered deeper water coral communities reestablished themselves on these stranded shelf edge reefs and fringing and bank barrier reefs began to flourish in shallow coastal areas at the same time the fragile and rapidly growing acropora cervicornis and other corals flourished at greater depths on the more protected shelves of the western caribbean and the gulf of mexico as a result late holocene buildups more than 30 m thick developed in those areas

island arc carbonates characterization and recognition in the ancient geologic record abstract carbonates of island arc origin that are preserved in paleozoic mesozoic terranes of the north american cordillera exhibit a distinctive suite of paleontologic and lithologic features and share a fundamental similarity with limestones forming in modern volcanic arcs this study provides the first detailed synthesis of carbonate depositional systems in island arcs and documents primary sedimentary constituents based on facies relationships and faunal communities models are developed that show patterns in the long term evolution of shallow marine organisms and the construction evolution and demise of carbonate platforms in island arcs a suite of criteria is identified that may be used to differentiate island arc carbonates from limestones that accumulated in other platform settings biogeographic isolation prolonged subsidence steep submarine slopes and tectonic instability of volcanic edifices contribute to the development of relatively high levels of species endemism impoverished normal marine faunas complex provincial affinities and relict biotas in limestones that are characterized by exceptionally thick platform and periplatform sequences fringing and barrier reefs at the shelf margin extensive lagoonal deposits and rapid lateral and vertical facies changes although destructive tectonic and geologic processes in island arcs may hinder determining the original size and extent of the carbonate platform and particular facies types may not be represented e g fringing and barrier reefs may be replaced by sand shoals at the platform margin many characteristics have potential value for identifying carbonates of island arc origin in the ancient rock record apart from being associated with calc alkaline volcanic and volcaniclastic assemblages the most valuable suite of features for recognizing island arc carbonates is marine biotas that exhibit elevated levels of endemism and mixed paleobiogeographic affinities extraordinary thicknesses of platform shallow marine and periplatform carbonates and rapid facies changes between volcanic and carbonate rocks and between shallow and deep water limestones recognizing that an ensemble of features is distinctive within island arc carbonates considerably enhances identification of volcanic arcs in the ancient geologic record and thus improves the likelihood of successfully unraveling the complex geologic history of ocean basins

fluxes and distribution of dissolved iron in the eastern sub tropical north atlantic ocean aeolian dust transport from the saharan sahel desert regions is considered the dominant external input of iron fe to the surface waters of the eastern sub tropical north atlantic ocean to test this hypothesis we investigated the sources of dissolved fe dfe and quantified dfe fluxes to the surface ocean in this region in winter 2008 surface water dfe concentrations varied between 1 5 nm correlated positively with apparent oxygen utilization aou and showed the importance of organic matter remineralization as an dfe source as a consequence vertical diffusive mixing formed an important fe flux to the surface ocean in this region even surpassing that of a major dust event

occurrence of 1 o monoalkyl glycerol ether lipids in ocean waters and sediments the occurrence of 1 o monoalkyl glycerol ethers mages in marine sediments is typically attributed to the presence of sulfate reducers however little is known about other possible sources within the marine realm we have examined the concentrations and distributions of mages in suspended particulate organic matter from surface water and underlying sediments of the southern ocean and the eastern south atlantic ocean mages including monounsaturated diunsaturated and branched were found in surface water from both settings suggesting a planktonic source likely aerobic bacteria supporting this we found a significant correlation between the concentrations of phytoplankton biomarkers and mages mage distributions in southern ocean and south atlantic surface water differed with longer chain length and more unsaturated components in southern ocean water which we suggest could be an adaptation to lower surface temperature sedimentary mage distributions were significantly different from those of overlying water which we propose to be the result of an additional sedimentary source however mages were present in both oxic and nitrogenous ferruginous sediments suggesting other bacterial sources besides sulfate reducers

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

dissolved trace metals ni zn co cd pb al and mn around the crozet islands southern ocean a phytoplankton bloom shown to be naturally iron fe induced occurs north of the crozet islands southern ocean every year providing an ideal opportunity to study dissolved trace metal distributions within an island system located in a high nutrient low chlorophyll hnlc region we present water column profiles of dissolved nickel ni zinc zn cobalt co cadmium cd lead pb aluminium al and manganese mn obtained as part of the nerc crozex program during austral summer 2004 2005 two stations m3 and m1 were sampled downstream north of crozet in the bloom area and near the islands along with a control station m2 in the hnlc zone upstream south of the islands the general range found was for ni 4 64 6 31 nm zn 1 59 7 75 nm co 24 49 pm cd 135 673 pm pb 6 22 pm al 0 13 2 15 nm and mn 0 07 0 64 nm vertical profiles indicate little island influence to the south with values in the range of other trace metal deprived regions of the southern ocean significant removal of ni and cd was observed in the bloom and zn was moderately correlated with reactive silicate si indicating diatom control over the internal cycling of this metal higher concentrations of zn and cd were observed near the islands pb al and mn distributions also suggest small but significant atmospheric dust supply particularly in the northern region

conductive structures under the canadian rocky mountains the paper reports results from an array of 33 three component magnetometers that recorded time varying fields in 1981 over an area of some 56 000 km2 in the canadian cordillera the array was centr

iron and other transition metals in patagonian riverborne and windborne materials geochemical control and transport to the southern south atlantic ocean abstract the bulk of particulate transition metals transported by patagonian rivers shows an upper crustal composition riverine particulate 0 5 n hcl leachable trace metal concentrations are mainly controlled by fe oxides complexation of fe by dissolved organic carbon doc appears to be an important determinant of the phases transporting trace metals in patagonian rivers in contrast aeolian trace elements have a combined crustal and anthropogenic origin aeolian materials have fe mn and al contents similar to that found in regional topsoils however seasonal concentrations of some metals e g co pb cu and zn are much higher than expected from normal crustal weathering and are likely pollutant derived we estimate that patagonian sediments are supplied to the south atlantic shelf in approximately equivalent amounts from the atmosphere 30 10 6 t yr 1 and coastal erosion 40 10 6 t yr 1 with much less coming from the rivers 2 0 10 6 t yr 1 low trace metal riverine fluxes are linked to the low suspended particulate load of patagonian rivers inasmuch most of it is retained in pro glacial lakes as well as in downstream reservoirs based on our estimation of aeolian dust fluxes at the patagonian coastline the high nutrient low chlorophyll sub antarctic south atlantic could receive 1 0 to 4 0 mg m 2 yr 1 of leachable 0 5 n hcl fe past and present volcanic activity in the southern andes through the ejection of tephra must be highlighted as another important source of fe to the south atlantic ocean based on the 1991 hudson volcano eruption it appears that volcanic events can contribute several thousand fold the mass of leachable fe to the ocean as is introduced by annual patagonian dust fallout

electromagnetic images of crustal structures in southern and central canadian cordillera data from more than 400 magnetotelluric soundings made since the early 1980 s in the canadian cordillera over a 300 000 km2 area between 49 and 53 5 n are used to image qualitatively regional three dimensional crustal variation in electrical conductivity by means of phase maps phase frequency sections and maps of resistivity at depth two hundred of the soundings were acquired as part of lithoprobe southern canadian cordillera transect activities and their locations were coordinated with the seismic reflection and refraction experiments the lower crust has a generally pervasive low resistivity 1 100 m throughout the cordillera west of the foreland belt within this canadian cordilleran regional conductor the magnetotelluric data reveal both two dimensional structures with highest conductivities along the coast belt and omineca belt and three dimensional variation along geological strike this conductor mapped over a volume in excess of 106 km3 is most probably caused by fluids saline wat

theory and observations of ekman flux in the chlorophyll distribution downstream of south georgia 1 a large phytoplankton bloom occurs downstream of south georgia an island on the northern edge of the scotia sea atlantic sector of the southern ocean this is due to natural iron fertilisation being advected downstream in the antarctic circumpolar current mapping of seawifs chl a in dynamic height longitude space reveals the trajectory of surface water under the dual influences of geostrophic flow and ekman flux a theoretical estimate of the trajectory shows good agreement with observations the trajectory is dependent on the wind stress mixed layer depth ratio but independent of the latitudinal separation of dynamic height contours the chl a distribution suggests that iron reaches 20 w below the mixed layer away from the effects of ekman flux but beyond the iron is confined to the surface layer chl a reduces monotonically east of south georgia with the signal detectable to 15 e over 3500 km downstream indicating the basin scale biogeochemical influence of the iron supply

a tale of three islands downstream natural iron fertilization in the southern ocean iron limitation of primary productivity prevails across much of the southern ocean but there are exceptions in particular the phytoplankton blooms associated with the kerguelen plateau crozet islands and south georgia these blooms occur annually fertilized by iron and nutrient rich shelf waters that are transported downstream from the islands here we use a highresolution 1 12 ocean general circulation model and lagrangian particle tracking to investigate whether inter annual variability in the potential lateral advection of iron could explain the inter annual variability in the spatial extent of the blooms comparison with ocean color data 1998 to 2007 suggests that iron fertilization via advection can explain the extent of each island s annual bloom but only the inter annual variability of the crozet bloom the area that could potentially be fertilized by iron from kerguelen was much larger than the bloom suggesting that there is another primary limiting factor potentially silicate that controls the inter annual variability of bloom spatial extent for south georgia there are differences in the year to year timing of advection and consequently fertilization but no clear explanation of the inter annual variability observed in the bloom s spatial extent has been identified the model results suggest that the kerguelen and crozet blooms are terminated by nutrient exhaustion probably iron and or silicate whereas the deepening of the mixed layer in winter terminates the south georgia bloom therefore iron fertilization via lateral advection alone can explain the annual variability of the crozet bloom but not fully that of the kerguelen and south georgia blooms this article is protected by copyright all rights reserved

distributions of dissolved and particulate iron in the sub antarctic and polar frontal southern ocean australian sector this paper presents iron fe profiles in the upper 1000 m from nine short term transect stations and three long term process stations occupied in the australian sector of the southern ocean during the saz sense expedition in austral summer january february 2007 strong vertical and horizontal gradients in fe concentrations were observed between the 18 sampled profiles i e 0 09 0 63 nmol l dissolved fe dfe average dfe concentrations in surface gggwaters in the northern sub antarctic zone saz n west station p1 were 0 2770 04 nmol l this is lower in the saz n east region station p3 and around where average dfe values in the mixed layer were 0 4870 10 nmol l the polar front pf station p2 exhibited the lowest average surface fe values i e 0 2270 02 nmol l iron concentrations in deep waters down to 1000 m were more uniform 0 25 0 37 nmol l dfe which is in accordance with values reported elsewhere in remote waters of the southern ocean but lower than those observed in the north atlantic and north pacific basins a strong decoupling was observed between dfe and nutrient cycles at all stations particulate fe levels were generally very low for all saz stations o0 08 1 38 nmol l with higher values observed at stations collected near tasmania and in the saz n east region the intrusion of subtropical waters enriched with fe from sediments or dust further north is thought to mediate fe input to the saz n and stz areas while input from below would be the main source of fe in the pf region we applied the tracer fen fen dfe rfe p po4 3 where rfe p is the algal uptake ratio to estimate the degree to which the water masses were fe limited in this study fen tended to be negative and decreased with increasing depths and latitude positive fen values indicating fe sufficiency were observed in the near surface waters collected in the saz n east and near continental sources where primary production was higher and ultimately limited by the lack of macro nutrients not fe micro organisms residing in the saz n west and pf on the other hand experienced negative fen indicating a strong co limitation by low silicic acid concentration and fe supply and light in the case of pf

biosedimentology of the early jurassic post extinction carbonate depositional system central high atlas rift basin morocco this study documents a liassic example of the long ranging effects of mass extinction on carbonate systems biohistoric constraints inherent in the liassic carbonate depositional system are deciphered from normal marine sub tidal deposits of the central high atlas rift basin morocco through hettangian sinemurian to early toarcian times the integration of results from the analysis of lithofacies depositional geometries microfacies macrobenthos carbonate build ups carbon and oxygen stable isotopes and rare earth element yttrium distribution patterns allows the intrinsic or biohistoric control on the central high atlas deposits to be separated from extrinsic factors such as basin development and palaeoclimate the survival interval in the aftermath of the end triassic mass extinction persisted until the early sinemurian indicated by a severely depleted carbonate system impoverished in skeletal organisms a tectonic pulse at the early to late sinemurian boundary interval caused a basin widening with immigration of a marine fauna however until the latest sinemurian macdonelli subzone of the raricostatum zone the deposits were dominated by filter feeding benthic heterotrophs sponges brachiopods polychaetes and crinoids during this stage primary production within the enlarged basin must have been largely planktonic and there was a net flux of organic matter to the sea floor oxygen minimum zone a regional radiation of organic walled phytoplankton is inferred to explain the selective success of the filter feeding community and the occurrence of sponge mounds thus significant effects of the end triassic mass extinction are still present during the late sinemurian through almost the entire pliensbachian a highly productive shoal rimmed carbonate platform existed it developed subsequent to tectonic reorganization and a marine recirculation event radiolarian facies 13c 1 1 strongly negative ce anomaly photosymbiotic sediment producers mainly large bivalves now state the success of specialists and environmental equilibrium conditions in the latest pliensbachian the climax stage was reached with the development of a coralgal reef rimmed carbonate platform the liassic carbonate depositional system experienced a terminal multicausal early toarcian drowning event during which most of the large bivalves became extinct

redox conditions and trace metal cycling in coastal sediments from the maritime antarctic abstract redox sensitive trace metals mn fe u mo re nutrients and terminal metabolic products no 3 nh 4 po 4 3 total alkalinity were investigated for the first time in pore waters of antarctic coastal sediments the results of this study reveal a high spatial variability in redox conditions in surface sediments from potter cove king george island western antarctic peninsula particularly in the shallower areas of the bay the significant correlation between sulphate depletion and total alkalinity the inorganic product of terminal metabolism indicates sulphate reduction to be the major pathway of organic matter mineralisation in contrast dissimilatory metal oxide reduction seems to be prevailing in the newly ice free areas and the deeper troughs where concentrations of dissolved iron of up to 700 m were found we suggest a combination of several factors to be responsible for the domination of metal oxide reduction over sulphate reduction in these areas these include the increased accumulation of fine grained material with high amounts of reducible metal oxides a reduced availability of metabolisable organic matter and an enhanced physical and biological disturbance by bottom water currents ice scouring and burrowing organisms based on modelled iron fluxes we calculate the contribution of the antarctic shelf to the pool of potentially bioavailable iron feb to be 6 9 103 to 790 103 t yr 1 consequently these shelf sediments would provide an feb flux of 0 35 39 5 mg m 2 yr 1 median 3 8 mg m 2 yr 1 to the southern ocean this contribution is in the same order of magnitude as the flux provided by icebergs and significantly higher than the input by aeolian dust for this reason suboxic shelf sediments form a key source of iron for the high nutrient low chlorophyll hnlc areas of the southern ocean this source may become even more important in the future due to rising temperatures at the wap accompanied by enhanced glacier retreat and the accumulation of melt water derived iron rich material on the shelf

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

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

seismic reflectors conductivity water and stress in the continental crust the uppermost 10 15 km of the earth s continental crust differs in several geophysical properties from the lower crust the upper crust is electrically resistive seismically transparent contains nearly all intracontinental earthquake hypocentres and responds to stress elastically with brittle fracture the lower crust is electrically conductive contains many seismic reflectors is aseismic and shows ductile response to stress i show here that the characteristics of both regions can be explained if the entire crust contains saline water in separated cavities in the compressively stressed rocks of the upper crust but in the lower crust forming an interconnected film on the crystal surfaces the model may apply principally to technically active parts of the continental crust beneath shields the lower crust may be dry

changes in micronutrient supply to the surface southern ocean atlantic sector across the glacial termination major deepwater masses upwell and reach the surface in the southern ocean forming an important conduit supplying nutrients and micronutrients to the surface and playing a key role in the regulation of global climate through ocean atmosphere gas exchange here we reconstruct changes in micronutrient distribution in this region in response to past changes in upwelling oceanic mixing and sea ice seasonality we present two downcore zn si opal records from the scotia sea and drake passage region which we interpret in the context of micronutrient distribution in the atlantic sector of the southern ocean over the last glacial termination previous work shows that micronutrient availability in the surface waters in the south atlantic appear to be controlled dominantly by upwelling and mixing of micronutrient rich deepwaters which are additionally fuelled by the terrestrial sediment sources of the scotia arc and south georgia this is supported by our reconstructions which show micronutrient availability to the west of the scotia arc and south georgia are consistently lower than to the east over the last glacial termination due to downstream transport and mixing into surface waters of continentally derived material in the antarctic circumpolar current micronutrient availability in this region was at a minimum from 20 to 25 ky bp coinciding with maximum sea ice coverage and increased due to an expansion of the seasonal sea ice zone and increased mixing of subsurface waters our findings are consistent with largely diminished upwelling of micronutrients during the maximum glacial extent and reduced mixing due to the presence of persistent sea ice during the deglacial there was an increase in micronutrient availability as well as other nutrients and inorganic carbon within the antarctic circumpolar current as a result of an increase in deep oceanic upwelling mixing and strengthened zonal transport

timing and tectonic setting of stikine terrane magmatism babine takla lakes area central british columbia new bedrock mapping completed as part of the nechako natmap project indicates that the area between babine and takla lakes in central british columbia is underlain by rocks of the early permian asitka late triassic takla and early to middle jurassic hazelton volcanic arc assemblages of the stikine terrane these are cut by large composite stocks of quartz diorite granodiorite and quartz monzonite previously mapped as the late triassic to early jurassic topley intrusions new u pb n 6 and laser 40ar 39ar n 10 isotopic age dates reported in this paper suggest there are two distinct ages of plutons the topley intrusive suite with isotopic ages between 218 and 193 ma and east of babine lake the new spike peak intrusive suite with isotopic ages ranging from 179 to 166 ma west of the main plutonic belt is a thick volcanic succession of subaerial porphyritic andesite flows volcanic breccias and rhyolitic ash flow tuffs that have isotopic ages between 185 and 174 ma these rocks are assigned t

analysis of horizontal and vertical processes contributing to natural iron supply in the mixed layer in southern drake passage abstract horizontal advection vertical mixing and mixed layer entrainment all affect iron concentrations and biological productivity in the ona basin near the shackleton transverse ridge str in southern drake passage trace metal sampling in the region indicates that dissolved iron concentrations are significantly higher on the continental shelf near the antarctic peninsula and the south shetland islands than they are in the deep waters away from the shelf comparisons between satellite derived sea surface height ssh and chlorophyll a chl a levels in the ona basin show 95 correlation between chl a concentrations and horizontal advection of these iron rich shelf waters during the months of november and december for the years 1997 2010 however no significant correlations are found for january april while high chl a concentrations in the ona basin persist through march enhanced vertical diapycnal mixing and mixed layer entrainment are considered as alternative mechanisms for delivering iron into the ona basin mixed layer and sustaining the high chl a concentrations estimates of iron flux based on in situ measurements of dissolved iron concentrations suggest that diapycnal mixing alone can supply iron to the base of the mixed layer at a rate of 64 2 nmol m 2 day 1 during the summer in addition the summer mixed layer in the ona basin deepens from january to april allowing for iron rich water to be steadily entrained from below estimates based on monthly mixed layer climatologies produce average daily entrainment rates ranging from 5 to 25 nmol m 2 day 1 while neither diapycnal mixing nor entrainment alone is always sufficient to meet the estimated iron demand for the ona basin bloom numerical simulation suggests that the combined effect of the two processes can consistently supply sufficient iron to sustain the bloom

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

a coral reef in the telkwa range british columbia the earliest jurassic example an end triassic mass extinction profoundly affected reef ecosystems that flourished in the late triassic tethys seaway the collapse of late triassic coral sponge reefs was followed by an early jurassic hettangian sinemurian perturbation interval with a near global absence of reefs and sharp reductions in diversity a jurassic sinemurian reef in the hazelton group of central british columbia appears to fill the gap its paleoecology and composition show it to be the first large framework example in north america and perhaps the world it demonstrates that the reef building triassic coral phacelostylophyllum survived the extinction event and was constructing reefs in early jurassic time during a global reef eclipse the reef is a 48 m thick bioherm that grew within the island arc complex of stikinia following a decrease in volcanism reef building began with bivalves growing upon water lain tuffs the reef was dominated by large dendroid phaceloid corals primarily phacelostylophyllum rugosum a spe

magnetometer array studies earth structure and tectonic processes this review presents results from magnetovariation fields recorded by two dimensional arrays of magnetometers the emphasis is on the conductive structures mapped and studied and their tectonic implications eleven arrays were operated in north america between 1967 and 1985 a region of highly conductive uppermost mantle and or lower crust extending at least from 33 n to 54 n has been shown to extend beneath much of the continent west of the rocky mountains two recent investigations are discussed in more detail those of conductive structures under the canadian rockies and emslab electromagnetic sounding of the lithosphere and beyond array results for washington and oregon including a conductive strip beneath the cascades volcanoes correlations with high heat flow and seismic parameters make it reasonable to attribute these regional conductors to partial melting and or hot saline water within the craton the north american central plains conductor is discussed this narrow crustal feature is associated with a major fracture zone and age boundary which may be a plate boundary of proterozoic time an array beneath the auroral electrojet for study of the external currents is noted results from four array studies in southern africa are considered two of these relate to the southern cape conductive belt which correlates not with high heat flow but with a large static magnetic anomaly the magnetovariation magnetic and gravity anomalies and geological data can be accounted for if an accumulation of ophiolitic rocks including serpentine is present in the lower crust such an accumulation may have formed at a subduction in proterozoic time two other arrays delineated a conductive belt associated with the southwestern end of the african rift system in namibia subsequent resistivity soundings located a conductor of resistivity 10 ohm m at less than 4 km depth two array studies in india follow one in the north and one in the south the array in the himalayan foothills and indo gangetic plain mapped a conductor transverse to the regional strike this may be a fracture zone produced in the interplate collision with a rise of asthenospheric material such as fluids into the fractures the southern indian array reveals crustal conductors under the indo sri lankan graben and another under the comorin ridge southwest of the tip of the subcontinent array studies in central and southeastern australia and in fennoscandia in regions without large local conductivity anomalies have been used to study conductivity variation with depth a note on the carpathian crustal anomaly is included as an example of combination of response parameters secured at different times to form a virtual array

dust deposition in the eastern indian ocean the ocean perspective from antarctica to the bay of bengal atmospheric deposition is an important but still poorly constrained source of trace micronutrients to the open ocean because of the dearth of in situ measurements of total deposition i e wet dry deposition in remote regions in this work we discuss the upper ocean distribution of dissolved fe and al in the eastern indian ocean along a 95 e meridional transect spanning the antarctic margin to the bay of bengal we use the mixed layer concentration of dissolved al in conjunction with empirical data in a simple steady state model to produce 75 estimates of total dust deposition that we compare with historical observations and atmospheric model estimates except in the northern bay of bengal where the ganges brahmaputra river plume contributes to the inventory of dissolved al the surface distribution of dissolved al along 95 e is remarkably consistent with the large scale gradients in mineral dust deposition and multiple source regions impacting the eastern indian ocean the lowest total dust deposition fluxes are calculated for the southern ocean 66 60 mg m 2 yr 1 and the highest for the northern end of the south indian subtropical gyre up to 940 mg m 2 yr 1 at 18 s and in the southern bay of bengal 2500 570 mg m 2 yr 1 our total deposition fluxes which have an uncertainty on the order of a factor of 3 5 are comparable with the composite atmospheric model data of mahowald et al 2005 except in the south indian subtropical gyre where models may underestimate total deposition using available measurements of the solubility of fe in aerosols we confirm that dust deposition is a minor source of dissolved fe to the southern ocean and show that aeolian deposition of dissolved fe in the southern bay of bengal may be comparable to that observed underneath the saharan dust plume in the atlantic ocean

inversion of magnetovariation event to causative current iii test of channelled current model sabc conductor inverted as chennelled currents and structure evaluation abstract algorithms developed in an earlier paper for the inversion of fields of channelled currents are tested with models the deepening effect of the inverted model expected from the spreading of current is found to be slight the same algorithms are then applied to 1983 magnetometer array data which appear to be dominated by current channelling the model space is explored with different models and constraints on models and with inversion from different data sets some features are consistent with all best fitting 3 d line and sheet current models inverted these are a the conductor plunges east of the canadian rocky mountains and b it makes a sharp bend towards the east with the plunge the inversion results are compatible with other geophysical data from the same area the conductive structure is located crossing the rocky mountains in the depth range 30 120 km it is either in the upper mantle or in the lower crust and may be related to a seismic low velocity zone

discovery of triassic phylloid algae possible links with the paleozoic triassic phylloid algae have recently been discovered in a reef in the southern yukon these plate like algae are the primary frame builders in a few small patches in the upper section of the reef where they are associated with fossils and sedimentary structures suggesting deposition in very shallow water a vague porous microstructure in some of the algae suggests affinities with paleozoic codiacean phylloid algae but preservation is too poor to permit definite classification nevertheless the indication that phylloid algae did not become extinct at the end of the paleozoic as formerly supposed increases the possibility of finding missing evolutionary links between paleozoic phylloid algae and their modern counterparts

inputs of glacially derived dissolved and colloidal iron to the coastal ocean and implications for primary productivity 1 glacial meltwaters draining shield bedrock under the greenland ice sheet gis contain 0 4 m total dissolved fe tdfe with an average flow weighted concentration of 53 nm the concentrations of 0 03 and 0 03 0 4 m fe vary over the ablation period with weighted means for each of these fractions being respectively 22 4 nm and 30 8 nm these concentrations are lower estimates as an adjacent larger glacier a more representative source of glacial meltwater had higher dissolved fe concentrations and reactions of meltwaters with proglacial sediments could also enhance dissolved fe concentrations this source of tdfe is additional to the reactive oxyhydr oxide phases identified by raiswell et al 2006 that are also introduced to adjacent polar seas from glaciers the fe concentrations in the shield bedrock underlying the gis are lower than those of other crustal rocks 4 0 cf 6 2 but we argue that these fe concentrations are not limiting on the total dissolved fe concentrations we measure the biogeochemical weathering processes operating on the subglacial debris and suspended sediment in our catchment are likely to be similar to those in other glaciated catchments therefore the meltwater fe concentrations reported here can be used to give a first estimate of global fluxes of meltwater dissolved fe to coastal polar waters a lower estimate of the global flux of tdfe from glacial meltwaters is 75 106 moles fe a this glacial meltwater input of fe to adjacent polar waters will be greatest around greenland where there are highest annual meltwater discharges however the greatest impact of this source of glacial meltwater fe is anticipated to be in antarctic high nutrient low chlorophyll hnlc waters where phytoplankton productivity is typically limited by availability of fe for antarctic waters the estimated meltwater fe tdfe input is about 10 of that suggested to come from sea ice melting but glacial inputs continue throughout the austral summer ablation period after sea ice melt is complete

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

contribution of resuspended sedimentary particles to dissolved iron and manganese in the ocean an experimental study abstract a number of trace metals play essential roles in marine ecosystem structure and biological productivity until recently it has been argued that phytoplankton access primarily dissolved iron while particulate iron was considered a refractory material with little use biologically and limited interaction with the dissolved pool in order to assess the transfer mechanisms between sediment sourced particulate trace metals and the dissolved pool we conducted a 14 month incubation that reacted resuspended sediments with natural seawater both originating from the kerguelen area keops cruises southern ocean in the dark and at concentrations replicating natural conditions three types of sediments were investigated named biosi biosi ca and basalt mostly composed of i biogenic silica bsio2 ii bsio2 and calcite and iii basaltic fragments respectively the release of dissolved silicon dsi iron dfe and manganese dmn was monitored regularly throughout the incubation as well as living bacteria density and fe organic ligands depending on the origin and composition of the sediment unique dfe and dmn fluxes were observed including a strong decoupling between dfe and dmn the basaltic sediment released up to 1 09 0 04 nmol l 1 of dfe and 0 28 0 09 nmol l 1 of dmn while the biogenic sediments released a higher 3 91 0 04 nmol l 1 and 8 03 0 42 nmol l 1 of dfe and dmn respectively several factors influencing the release and removal of dfe and dmn were discernable at the temporal sampling resolution of the incubation including the structural composition of the sediment bacterial abundance and the formation of manganese oxides the regular sampling over short timescales and the extended sampling over one year proved to be critical to constrain the processes and exchanges that govern the contribution of the particulate to the dissolved pools overall this incubation provides a strong basis for reassessing the role of resuspended sedimentary particles in the marine biogeochemical cycles of fe and mn indeed we show that biogenic silica calcite rich and basaltic particles can contribute substantial dissolved fe and mn to the overlying water column in the future the global extent of this previously overlooked external metal source should be quantified through further process studies and biogeochemical models this article is part of a special issue entitled cycles of trace elements and isotopes in the ocean geotraces and beyond edited by tim m conway tristan horner yves plancherel and aridane g gonzalez

shelf derived iron inputs drive biological productivity in the southern drake passage water entrainment while fe 228 ra ratios were used to calculate the fe flux in the summer of 2006 we found rapid mixing and significant lateral iron export namely a dissolved iron flux of 1 1 10 5 mol d 1 and total acid leachable iron flux of 1 1 10 6 mol d 1 all of which is transported in the mixed layer from the shelf region offshore this dissolved iron flux is significant especially considering that the bloom observed in the offshore region 0 5 2 mg chl a m 3 had an iron demand of 1 1 to 4 10 5 mol fe net vertical export fluxes of particulate fe derived from 234 th 238 u disequilibrium and fe 234 th ratios accounted for only about 25 of the dissolved iron flux on the other hand vertical upward mixing of iron rich deeper waters provided only 7 of the lateral dissolved iron flux we found that similarly to other studies in iron fertilized regions of the southern ocean lateral fluxes overwhelm vertical inputs and vertical export from the water column and support significant phytoplankton blooms in the offshore regions of the drake passage

canadian cordilleran displacement palaeomagnetic results from the early jurassic hazelton group terrane i british columbia canada summary the early jurassic telkwa formation comprising the base of the hazelton group was sampled at three areas in the central part of the stikine terrane british columbia detailed alternating field and thermal step demagnetization on samples from nine sites from the red canyon area and 10 sites from the zymoetz river area both of which are in the bulkley ranges and eight sites from the telkwa range area isolate stable remanence magnetization components the components are interpreted to be primary magnetizations because of the presence of two polarities and the much improved agreement of their inclinations after full tilt correction of the sites from the bulkley ranges within locality declinations agree well between locality declinations are discordant the expected cratonic declination is 340 whereas declinations from this study are 265 227 and 328 for the red canyon zymoetz river and telkwa range areas respectively these results are similar to those of monger irving 1980 and we concur that the discordant declinations are the result of differential rotation about vertical axes between sample localities our observed mean inclination of 52 is in good agreement with monger irving s 1980 result of 54 they interpreted this to indicate 1300 km of northward displacement since the early jurassic and their interpretation was substantiated by several later studies however with revisions to the geologic time scale and the early jurassic reference pole for north america the early jurassic canadian cordillera palaeomagnetic data base appears latitudinally concordant this indicates that terrane i and southern wrangellia were in much the same latitudinal position relative to the north american craton as they are now tectonic displacement models developed in view of discordant cretaceous palaeomagnetic data from the canadian cordillera must now consider latitudinally concordant permian to early jurassic data and middle eocene to recent data this tectonic senario appears more reconcilable with the regional tilt hypothesis however this hypothesis cannot account for discordant cretaceous data from bedded volcanic rocks in terrane i it is therefore probable that cretaceous cordilleran tectonics were characterized by both regional tilting and moderate latitudinal displacement

trace element composition of suspended particulate matter along three meridional clivar sections in the indian and southern oceans impact of scavenging on al distributions abstract we present the trace element composition al si p ca fe and zn of suspended particulate matter spm samples collected in the upper 1000 m along u s clivar co2 repeat hydrography meridional section i09n i08s from the southern ocean to the bay of bengal at 95 e and in surface waters along meridional section i06s from the south african margin to the antarctic shelf edge at 30 e a band of elevated surface ocean pca 0 5 0 3 m over 30 60 s is consistent with the global pattern of high coccolithophore production encircling the southern ocean suggested by remote sensing over 50 60 s both sections exhibit a sharp transition from ca rich to si rich particulate matter up to 2 8 6 5 m indicating a change from coccolithophore to diatom communities in waters with low residual nitrate along i08s diatom blooms display elevated pzn concentrations and zn p ratios 14 9 5 7 mmol mol 1 reflecting cellular zn stoichiometry of southern ocean diatoms regions of high primary productivity in the southern ocean are coincident with unexpectedly high surface ocean pal concentrations max 12 6 26 5 nm compared to background concentrations typically 50 of surface ocean pal in these regions originates from adsorptive scavenging of dissolved al onto biogenic particles along i08s dissolved al reservoirs likely originate from transport of al enriched waters by the agulhas return current local dust deposition and seasonal ice melt along i06s pal distributions suggest larger inputs of dust to the surface mixed layer than have previously been described by contrast pfe concentrations remain low in both surface this article is part of a special issue entitled cycles of trace elements and isotopes in the ocean geotraces and beyond

secular oscillations in the carbonate mineralogy of reef building and sediment producing organisms driven by tectonically forced shifts in seawater chemistry the primary mineralogy of oolites and early marine carbonate cements led sandberg nature 305 1983 19 22 to divide the phanerozoic eon into three intervals of aragonite seas and two intervals of calcite seas hardie geology 24 1996 279 283 has shown that these oscillations together with synchronous oscillations in the mineralogy of marine potash evaporites can be explained by secular shifts in the mg ca ratio of seawater driven by changes in spreading rates along mid ocean ridges the hardie model also predicts that high mg calcite should precipitate along with aragonite as it does in today s aragonite sea we have uncovered oscillations in the carbonate mineralogy of hypercalcifying organisms ones that have produced massive skeletons large reefs or voluminous bodies of sediment that correspond to sandberg s aragonite seas and calcite seas and that are predicted by the hardie model particular groups of corals sponges and algae appear to have been dominant reef builders only when favored by an appropriate mg ca ratio in seawater in early and middle paleozoic calcite seas calcite i reefs were dominated by calcitic tabulate heliolitid and rugose corals and calcitic stromatoporoids in contrast during the period of late paleozoic early mesozoic aragonite seas aragonite ii aragonitic groups of sponges scleractinian corals and phylloid algae as well as high mg calcitic red algae were principal reef builders during late cretaceous time at the acme of calcite ii massive rudists displaced aragonitic hermatypic corals in today s aragonite sea aragonite iii scleractinian corals are again dominant reef builders along with high mg calcitic coralline algae major sediment producing algae exhibit temporal patterns similar to those of reef builders calcitic receptaculitids flourished during calcite i whereas aragonitic dasycladaceans did not become dominant rock formers until aragonite ii during calcite ii calcitic nannoplankton formed massive coccolith chalks in warm shallow seas of the late cretaceous after the mg ca ratio of seawater had reached a very low value and calcium concentration a very high value as the mg ca ratio of seawater rose and calcium concentration fell during the cenozoic era individual coccoliths on average became less massive and encrusted cells less thickly by pliocene time during aragonite iii the prominent genus discoaster secreted only narrow rayed coccoliths that covered less than 25 of the cell surface also during aragonite iii the aragonitic green alga halimeda emerged as the dominant skeletal sediment producer in reef tracts the influence of seawater chemistry on skeletal secretion appears to have been especially strong for morphologically simple taxa that exert relatively weak control over their own calcification such groups include algae sponges corals and bryozoans morphological simplicity also permits these groups to adopt vegetative or colonial modes of growth that confer success in competition for space on reefs this linkage in addition to the basic chemical demands of hypercalcification has given the mg ca ratio of seawater strong control over the success of individual reef building taxa more generally this ratio appears to have strongly influenced evolutionary changes in the skeletal mineralogy of sponges and cheilostome bryozoans throughout their history we conclude that throughout phanerozoic time a chain of causation has extended from mid ocean ridge processes via seawater chemistry to the mineralogical and biological composition of reef communities and bioclastic carbonate deposits

the influence of shelf processes in delivering dissolved iron to the hnlc waters of the drake passage antarctica abstract dissolved trace element distributions near elephant island in the drake passage show extremely high levels of dissolved fe and mn in waters above the shelf the entrainment of this enriched shelf water by the fe poor antarctic circumpolar current acc as it passes through the shackleton gap delivers an estimated 2 8 106 mol yr 1 dissolved fe to the offshore waters of the drake passage the magnitude and spatial distribution of dissolved fe mn and al over the shelf are consistent with a diagenetically produced sedimentary source but are inconsistent with eolian or upwelling sources the systematics of the mn and fe concentrations suggest that there are two distinct sources of dissolved fe to the surface waters of this region the highest fe concentrations are associated with bransfield strait water which can be identified by its characteristic temperature and salinity t s properties both inside the bransfield strait and in the bransfield current outflow between elephant and clarence islands most of the shelf area is dominated by a second water type with t s properties that are typical of modified antarctic surface water which while also enriched has a lower fe mn ratio the predominantly linear relationships between the fe and mn concentrations at the stations in each of these water mass types suggest that the distribution of these elements is largely controlled by physical mixing processes and that biological removal of fe on the shelf while certainly occurring is limited perhaps as a result of rapid physical flushing processes and relatively slow biological growth rates the consequent export of large quantities of this shelf derived fe into the acc is likely responsible for the extensive regions of enhanced primary production seen in satellite imagery downstream of the drake passage

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

atmospheric deposition fluxes of 26 elements over the southern indian ocean time series on kerguelen and crozet islands 1 atmospheric deposition of dust is suspected to have a significant impact on biogeochemical processes in high nutrient low chlorophyll waters of the open ocean in this study we report time series of atmospheric deposition samples collected over two years at three different sites on kerguelen and crozet islands in the southern indian ocean total atmospheric deposition fluxes were measured for a large suite of elements al as ba ca ce co cr cu fe k la li mg mn na nd ni pb rb s si sr ti u v and zn most of them are identified as coming from sea salt or crustal sources but enrichment factor variabilities of pb as cr cu and v highlight an anthropogenic contribution during the austral winter for these five elements for al fe mn and si deposition fluxes are similar for both kerguelen and crozet islands fluxes for the other non sea salt elements exhibit differences below a factor of five with a decreasing gradient from crozet to kerguelen

circulation pathways and transports of the southern ocean in the vicinity of the southwest indian ridge circulation pathways and transports of the antarctic circumpolar current acc and agulhas return current arc around the complex bathymetry of the southwest indian ridge and del cano rise have been established from two hydrographic surveys and two year long moorings after crossing the southwest indian ridge in a 110 sv 1 sv 106 m3s 1 flow concentrated at 48 s the acc fragments before being reconcentrated into several branches by the bathymetry in particular 30 40 sv turns north around the eastern flank of the del cano rise turns west as part of anticyclonic flow round the del cano rise finally returning eastward as part of the crozet front eddy variability from both satellite data and moorings is low over the bathymetry of the del cano rise so the strong currents found between the del cano rise and the crozet plateau are believed to be permanent features this largely barotropic time independent transport is the major pathway for the acc to enter the crozet basin the anticyclonic flow also transfers water from the mozambique basin across the southwest indian ridge to the south side of the del cano rise given the evidence for fragmentation of the acc where it crosses the southwest indian ridge and the concentration of several jets into the crozet front from the acc subtropical front and agulhas return current it is misleading to relate standard frontal definitions such as the polar front and subantarctic front to the major transport pathways

the hettangian corals of the isle of skye scotland an opportunity to better understand the palaeoenvironmental conditions during the aftermath of the triassic jurassic boundary crisis at ob lusa isle of skye scotland six distinct coral beds were observed in a modern outcrop where a hettangian succession is exposed the coral associations are monogenic belonging to lepidophyllia a massive cerioid genus the lowest bed has relatively well developed colonies that form small bioconstructions whereas the other beds have small and dispersed colonies that are completely drowned in the matrix their morphology and size can vary but the general growth fabric is dominated by platy colonies this type of growth fabric is defined as a platestone the most surprising characteristic of these specimens especially for the platy corals is their growth pattern many samples do not exhibit the classical growth polarity because they are bifacial geochemical analyses 180 13c were conducted on oyster shells that were associated with the corals the results indicate that the mean palaeotemperature was approximately 22 c sedimentological analysis revealed shallow settings where the hydrodynamic energy and siliciclastic inputs fluctuated the general faunal assemblage of the outcrop had low diversity and was mainly composed of allochthonous bioclasts the corals at ob lusa clearly did not live under ideal environmental conditions for the development of corals

two abyssal sites in the southern ocean influenced by different organic matter inputs environmental characterization and preliminary observations on the benthic foraminifera abstract the abundance and diversity of the deep sea benthos are intimately linked to inputs of organic matter from the euphotic zone however it is often difficult to isolate the influence of surface productivity on benthic ecosystems from other environmental factors to this end two abyssal sites 4200 m water depth located under contrasting productivity regimes around the crozet plateau in the indian ocean sector of the southern ocean were sampled during the austral summer of 2004 2005 one site m5 east of the crozet isles was located beneath an area where there was an enduring seasonal phytoplankton bloom the second site m6 was located in an oligotrophic high nutrient low chlorophyll hnlc region to the south of the islands organic fluxes to the seafloor at these sites are thought to reflect the overlying productivities so that the benthic environment to the east of the islands was more eutrophic than at the southerly station all other environmental variables were similar at the two sites which are located just 460 km apart the concentrations of chlorophyll a and total organic carbon in the surficial sediments were significantly greater at the relatively eutrophic site east of the islands m5 than at the southerly site m6 total nitrogen however was similar at both sites significantly higher phytopigment concentrations were observed in the surficial sediments at the eutrophic site in particular the concentration of chlorophyll a was 3 times greater than at the southern site although the freshness of the labile component as measured by chlorophyll a to pheophorbide ratio was not different between sites these results confirm that fluxes of organic matter to the seafloor were higher at the site located beneath the bloom region this was reflected in the abundance and diversity of live stained and dead benthic foraminifera 125 m which were greater at the eutrophic site the species composition of the dead foraminiferal assemblages were similar at both sites however and were dominated by nuttallides umbonifera pullenia bulloides and melonis pompiloides an exception was the phytodetritus species epistominella exigua which was more abundant at the eutrophic site indicating a larger seasonal component to the export under the bloom region differences in the organic matter input regimes at the two sites appear to influence the abundance and diversity but not the overall species composition of the foraminiferal assemblages

upper triassic sponges sphinctozoa from southern yukon stikinia terrane the first tethyan type upper triassic sponge reefs in north america have recently been discovered in the southern yukon in stikinia terrane sphinctozoa from these reefs and inter reef limestones are represented by 18 species and 12 genera belonging to six families the genus yukonella with one species y rigbyi and the species polytholosia ramosa and polycystocoelia norica are described for the first time some of the yukon sponges were previously known only from the tethyan realm colospongia dictyocoelia polycystocoelia and uvanella others from tethyan and north american localities ascosymplegma follicatena paradenigeria and salzburgia one polytholosia cylindrica is probably endemic to north america the mixed affinities of the yukon sponges may reflect the paleogeographic origin of stikinia as an island in the ancestral pacific ocean between tethys and the north american craton

the island mass effect and biological carbon uptake for the subantarctic crozet archipelago marine productivity is often higher downstream than upstream of islands this so called island mass effect was tested and quantified with respect to biological carbon uptake and air sea exchange of carbon dioxide co2 at the crozet plateau between november 2004 and january 2005 during two crozex cruises the remote plateau is situated at 45 5 47 0 s 49 0 53 0 e south of the subantarctic front saf in the polar frontal zone pfz surface waters upstream south of the plateau had high nutrient and low chlorophyll hnlc concentrations the fugacity of carbon dioxide fco2 in surface water was just below the atmospheric value and oceanic co2 uptake was small 0 2 0 1 mol m 2 throughout crozex the mixed layer concentration of dissolved inorganic carbon dic decreased by 15 mol kg 1 from november to january in these hnlc waters indicating significant biological carbon uptake extensive phytoplankton blooms occurred downstream north of the plateau in austral spring these reduced surface water fco2 by 30 70 atm and dic by 30 60 mol kg 1 and created an important oceanic sink for atmospheric co2 of 0 6 0 8 0 4 mol m 2 corresponding to a total uptake of 1 3 0 8 tg c 1 tg 1012 g the reduction of dic in the upper 100 m was much larger downstream 2 3 mol m 2 than upstream 1 mol m 2 of the plateau in january further confirming the existence of the island mass effect for the crozet archipelago an additional finding is the sizeable dic deficit in the hnlc waters upstream south of the plateau suggesting that some hnlc waters of the pfz are more productive than commonly thought deep mixed layers of 60 90 m may hide such sustained modest marine productivity from detection by satellite

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

oceanic iron supply mechanisms which support the spring diatom bloom in the oyashio region western subarctic pacific 1 multiyear 2003 2008 time series observations along the a line provided information on the temporal variability of the dissolved iron diss fe concentration in the oyashio region of the western subarctic pacific and the data indicated that there was an annual cycle in the concentration of surface diss fe occurring every year diss fe was supplied into the surface water in this region every winter and supports the spring phytoplankton bloom after development of the thermocline the diss fe concentration was drawn down during the phytoplankton bloom period and was depleted in summer in some water masses then diss fe increased from autumn to winter with the increasing depth of the surface mixed layer the high diss fe concentrations in the surface layer in winter were controlled by mesoscale oceanic intrinsic processes such as vertical winter mixing and horizontal fe rich intermediate water transport difference in magnitude of the winter mixing processes among different water masses caused the heterogeneous distribution of diss fe concentration in the surface layer moreover the vertical section profiles along a cross oyashio transect showed the occurrence of fe rich intermediate water and upward transport of materials from the intermediate water to the surface layer via tidal and winter mixing processes are important mechanisms to explain the high winter surface diss fe concentrations additionally the substantially higher diss fe no3 ratio in the winter surface layer in this studied area other than the high nutrient low chlorophyll region indicates that the winter surface water in the oyashio and the oyashio kuroshio transition zone has a high potential to stimulate phytoplankton growth

inversion of magnetovariation event to causative current i current sheet model abstract electromagnetic induction in a horizontally layered medium is formulated in matrix form the observed magneto variation event is inverted to a horizontal current sheet in a conducting earth after the separation of the fields into internal and external parts in wave number domain two frequency components of magnetovariation events t 69 and 23 min recorded in southern alberta and british columbia canada are inverted to their internal current sheet source the current concentration across the canadian rocky mountains is found in a narrow band of 70 80 km width the maximum depth of this current is estimated at 55km near the base of the thick crust in this area

study of the phytoplankton plume dynamics off the crozet islands southern ocean a geochemical physical coupled approach the crozet archipelago in the indian sector of the southern ocean constitutes one of the few physical barriers to the antarctic circumpolar current interaction of the currents with the sediments deposited on the margins of these islands contributes to the supply of chemical elements including iron and other micro nutrients to offshore high nutrient low chlorophyll hnlc waters this natural fertilization sustains a phytoplankton bloom that was studied in the framework of the keops 2 project in this work we investigated the time scales of the surface water transport between the crozet island shelves and the offshore waters a transport that contributes iron to the phytoplankton bloom we report shelf water contact ages determined using geochemical tracers radium isotopes and physical data based on in situ drifter data and outputs of a model based on altimetric lagrangian surface currents the apparent ages of surface waters determined using the three independent methods are in relatively good agreement with each other our results provide constraints on the time scales of the transport between the shelf and offshore waters near the crozet islands and highlight the key role played by horizontal transport in natural iron fertilization and in defining the extension of the chlorophyll plume in this hnlc region of the southern ocean

radium isotopes as tracers of iron sources fueling a southern ocean phytoplankton bloom elevated levels of productivity in the wake of southern ocean island systems are common despite the fact that they are encircled by high nutrient low chlorophyll hnlc waters in the crozet plateau region it has been hypothesized that iron from island runoff or sediments of the plateau could be fueling the austral summer phytoplankton bloom here we use radium isotopes to quantify the rates of surface ocean iron supply fueling the bloom in the crozet plateau region a 1d eddy diffusion mixing model applied to a 228 ra profile t1 2 5 75 years at a station north of the islands suggests fast vertical mixing in the upper 300 m kz 11 100 cm 2 s 1 with slower mixing between 300 and 1000 m kz 1 5 cm 2 s 1 this estimate is discussed in the context of kz derived from the ctd ladcp data in combination with the dissolved fe profile at this location we estimated a vertical flux of between 5 6 and 31 nmol fe m 2 d 1 the cross plateau gradients in the short lived radium isotopes 224 ra t1 2 3 66 d and 223 ra t1 2 11 4 d yielded horizontal eddy diffusivities kh o f 39 and 6 6 m 2 s 1 respectively if we assume that the islands surface runoff alone were supplying dissolved fe to the bloom region then the flux estimates range from 2 3 to 14 nmol fe m 2 d 1 if the plateau sediments are considered a source of fe and conveyed to the bloom region through deep winter mixing combined with horizontal transport then this flux may be as high as 64 390 nmol fe m 2 d 1 combined these fe sources are sufficient to initiate and maintain the

seismic studies of the crust under the williston basin the seismic refraction method was used in 1981 to study the crust under the northern half of the williston basin in saskatchewan a new method of spatial seismic recording based on a triangular arrangement of receivers was used for the first time to obtain three dimensional structure and velocity information the broadside seismic refraction and wide angle reflection data obtained by the technique were of particular value in defining several faulted blocks these blocks are also characterized by aeromagnetic anomalies trending in a northerly direction the crustal thickness in the southern part of the western provinces shows large variation ranging from 35 to 50 km much of the area is also notable for the presence of one or more low velocity layers and a high velocity lower crust there is good evidence for significant lateral heterogeneity and detailed deep seismic reflection and refraction studies would likely yield information on dips and strikes of beds and faults around the basin as well as defi

dissolved manganese in the atlantic sector of the southern ocean the first comprehensive dataset 492 samples of dissolved mn in the southern ocean shows extremely low values of 0 04 up to 0 64 nm in the surface waters and a subsurface maximum with an average concentration of 0 31 nm n 20 s d 0 08 nm the low mn in surface waters correlates well with the nutrients po4 and no3 and moderately well with si oh 4 and fluorescence furthermore elevated concentrations of mn in the surface layer coincide with elevated fe and light transmission and decreased export th 234 u 238 deficiency and fluorescence it appears that mn is a factor of importance in partly explaining the hnlc conditions in the southern ocean in conjunction with significant controls by the combination of fe limitation and light limitation no input of mn from the continental margins was observed this is ascribed to the protruding continental ice sheet that covers the shelf and shuts down the usual biological production microbial breakdown and sedimentary geochemical cycling the low concentrations of mn in the deep ocean basins 0 07 0 23 nm were quite uniform but some elevations were observed the highest deep concentrations of mn were observed at the bouvet triple junction region and coincided with high concentrations of fe and are deemed to be from hydrothermal input the deep basins on both sides of the ridge were affected by this input in the deep weddell basin the input of weddell sea bottom water appears to be the source of the slightly elevated concentrations of mn in this water layer c 2010 elsevier ltd all rights reserved

large scale circulation around the crozet plateau controls an annual phytoplankton bloom in the crozet basin the circulation in the vicinity of the crozet plateau in the southwest indian ocean sector of the southern ocean is examined using hydrographic sections argo floats surface drifters and satellite altimetry all four techniques confirm that a major branch of the antarctic circumpolar current the subantarctic front saf flows anticyclonically round the del cano rise west of the crozet plateau i e eastward to the south of the del cano rise then northward and sometimes northwestward into the crozet basin before turning back eastward in a combined front with the agulhas return current and the subtropical front this s bend in the saf is a permanent feature controlled by the bathymetry as has been inferred previously by pollard and read pollard r t read j f 2001 circulation pathways and transports of the southern ocean in the vicinity of the southwest indian ridge journal of geophysical research 106 c2 2881 2898 similar but much weaker anticyclonic flow is found round the crozet plateau itself with no more than 5 10 106 m3 s 1 turning north to the east of the crozet islands circulation north of the crozet plateau between the plateau and the s bend of the saf is extremely weak fed only by anticyclonic meanders breaking off the saf into the area from the west or north and occasional input from the northward partially wind driven i e ekman flow south and east of the islands in consequence of the weak circulation dissolved iron from the land or sediments of the crozet plateau and islands can build up during the winter in the polar frontal zone between crozet and the saf which gives rise to an annual bloom in this area biological evidence from satellite images and from phytoplankton and zooplankton distributions supports the circulation pattern we develop this pattern confirms that patchiness of productivity in the bloom area results from close juxtaposition of water that has entered the area from the west from the saf and from the south and east after flowing past the islands flow from the south and east has had a chance to entrain iron from the islands and sediments whereas flow from the west has not