the pribilof islands temperature salinity and nitrate during summer 2004 abstract the pribilofs comprised of st paul and st george islands and two smaller islands are a highly productive area on the western edge of the eastern bering sea shelf proximity to both the slope and more shallow shelf waters and the confluence of multiple physical domains differentiates conditions in this region from those in other areas on this shelf this is a unique domain in the bering sea that we refer to as the pribilof domain hydrographic and biological data were collected during a 2004 summer research cruise in this region the study undertook testing the hypothesis that on shelf intrusion of slope waters supplies nutrients to this multi domain area thereby seasonally influencing new primary production and consequently the entire marine ecosystem the pribilof domain is characterized by enhanced mixing particularly the area between st paul and st george islands organized anti cyclonic flow around st paul island around st george island and around the island group strong tidal currents and is a location where nutrient rich water from the bottom layer of the middle shelf and deeper water from the slope are vertically mixed to sustain production throughout the summer

high grade magnetite mineralization at 1 86 ga in neoarchean banded iron formations gongchangling china in situ u pb geochronology of metamorphic hydrothermal zircon and monazite

fluid inclusions as tectonothermobarometers relation between pressure temperature history and reequilibration morphology during crustal thickening results of experimental reequilibration studies of natural primary aqueous inclusions in quartz under conditions of hydrostatic compressive loading at 1 2 3 4 and 5 kbar and 500 c indicate that the intensity of reequilibration features is inversely proportional to inclusion volume the smallest inclusions show the first evidence of reequilibration dissolution of inclusion walls after 1 8 kbar of effective pressure for effective pressures less than 3 8 kbar decrepitation of inclusions is probably controlled by the corrosive action of water on the inclusion walls at higher effective pressures decrepitation is related to high compressive stress and is less dependent on fluid interaction with the inclusion walls the observed correlation between inclusion size intensity of reequilibration features and amount of loading combined with paragenetic and microthermometric data for the inclusions may be used to determine the pressure temperature history of the inclusions and their host rocks

seasonal cross shelf distribution of major zooplankton taxa on the northern gulf of alaska shelf relative to water mass properties species depth preferences and vertical migration behavior the cross shelf distribution of major zooplankton species was examined on the northern gulf of alaska goa shelf during the production season for four years between october 1997 and october 2001 the zooplankton community on the northern goa shelf consisted of oceanic and neritic species of the north pacific subarctic species complex cross shelf distribution of the major zooplankton species was influenced by their depth preferences vertical migration behavior salinity temperature preferences and by cross shelf water mass distribution and movement the neritic community dominated by pseudocalanus spp metridia pacifica and calanus marshallae had highest abundances on the inner shelf in the alaska coastal current and in the adjacent fjords in late spring and early summer the oceanic community which contained primarily neocalanus cristatus and eucalanus bungii was observed in the alaskan stream and adjacent waters near the shelf break a mid shelf transition zone contained a mixture of oceanic and neritic species prince william sound pws contained a unique species complex of large mesopelagic copepods amphipods and shrimp neocalanus flemingeri and oithona similis were abundant in all four regions during spring and early summer the transition zone commonly crossed much of the shelf between the shelf break and the acc but satellite images and ctd data indicate that occasionally a narrow shelf break front can form in which case distinct zooplankton species groups are observed on either side of the front satellite data also revealed numerous large and small eddies which probably contribute to cross shelf mixing in the transition zone

precise u pb titanite age constraints on the emplacement of the bushveld complex south africa the c 2 06 ga bushveld complex intrudes the transvaal supergroup south africa calcsilicate xenoliths within the mafic phase of the bushveld complex rustenburg layered suite or rls preserve calcsilicate xenoliths with high temperature c 1200 c mineralogies that were later metasomatized by hydrous retrograde c 600 700 c fluids whose timing has been unconstrained new u pb isotope data from newly grown titanite within a completely retrogressed xenolith indicates that retrogression occurred at 2058 9 0 8 ma this suggests that retrogression was due to hydrothermal circulation associated with the cooling rls and not slightly later bushveld related granites the new data place a tight constraint on the minimum age of emplacement of the rls

sea ice response to atmospheric and oceanic forcing in the bering sea abstract a coupled sea ice ocean model is developed to quantify the sea ice response to changes in atmospheric and oceanic forcing in the bering sea over the period 1970 2008 the model captures much of the observed spatiotemporal variability of sea ice and sea surface temperature sst and the basic features of the upper ocean circulation in the bering sea model results suggest that tides affect the spatial redistribution of ice mass by up to 0 1 m or 15 in the central eastern bering sea by modifying ice motion and deformation and ocean flows the considerable interannual variability in the pattern and strength of winter northeasterly winds leads to southwestward ice mass advection during january may ranging from 0 9 1012 m3 in 1996 to 1 8 1012 m3 in 1976 and averaging 1 4 1012 m3 which is almost twice the january may mean total ice volume in the bering sea the large scale southward ice mass advection is constrained by warm surface waters in the south that melt 1 5 1012 m3 of ice in mainly t

structural controls on fe mineralization at thabazimbi mine south africa abstract chemical sedimentary rocks of the transvaal supergroup along the northern margin of the transvaal basin were imbricated during formation of the mohlapitsi fold and thrust belt between ca 2 55 and 1 93 ga high grade 63 fe stratiform fe ore bodies occur at or close to the base of the banded ironstone dominated penge formation which forms a distinct e w trending mountain range in the area the penge formation is separated from underlying malmani dolostone by a thin laterally continuous rheologically weak carbonaceous shale layer that has been intensely sheared this horizon denotes the position of a regional top to n low angle detachment that has been variably deformed during progressive development of the mohlapitsi belt several of kumba s thabazimbi iron ore deposits including kwaggashoek east donkerpoort west kumba donkerpoort west and buffelshoek west are confined to a zone directly above this detachment recent studies of ore petrography fluid alteration fluid composition and stable isotope geochemistry link economic iron ore mineralization to hydrothermal or hypothermal processes along with localized high grade mineralization a structural control on fluid flow has been suggested although a lack of structural data has hampered more concise mineralization models thus far in this study we present and analyse data from detailed structural mapping over a protracted period of mining across four opencast pits this mapping is combined with drillhole data to produce accurate intergrated 3d models of these deposits which reveal the true geometry of these ore bodies data and resultant models indicate that enhanced hydrothermal fluid flow associated with significant iron mineralization is linked to thrusting shearing in response to 1 fold amplification and flexural flow along the e w trending detachment between the malmani dolostone and banded iron formation 2 subsidiary fold accommodation structures such as conjugate shear joints normal and reverse faults and thrusts associated with inner and outer arc shortening and extension respectively 3 localization of fe at the intersections of major reverse faults the detachment and stratigraphically higher low angle thrusts which are preferentially developed at the contacts between diabase and banded iron formation collectively these features both aided and compartmentalized regional pervasive fluid flow along the detachment and in stratigraphically higher sites subsequent ore preservation was enhanced by reactivation of nw to nnw trending mesozoic normal faults and concomitant downthrow of fault bounded blocks structural relationships and timing of high grade iron ore mineralization further suggest that associated top to n kinematic fold and thrust formation of the mohlapitsi belt and subsequently the main detachment between malmani dolostone and banded iron formation of the penge formation could have been active during and immediately after intrusion of the bushveld complex at ca 2 05 ga

major influences on the evolution of the 2 67 2 1 ga transvaal basin kaapvaal craton abstract the transvaal is one of three structural basins of the transvaal supergroup preserved on the kaapvaal craton the evolution of the neoarchaean palaeoproterozoic transvaal basin is ascribed predominantly to magmatism palaeoclimate and eustasy with plate tectonics playing a sporadic role the supergroup comprises basal protobasinal rocks followed by the black reef formation chuniespoort group and uppermost pretoria group immature siliciclastic and bimodal volcanic rocks of the protobasinal unit reflect a wide zone of rifting related to the c 2 7 ga ventersdorp supergroup mantle plume individual protobasinal successions were laid down in separate fault bounded basins controlled at least partially by greenstone belt orientations in the kaapvaal basement post magmatic post rifting thermal subsidence accommodated black reef fluvial sheet sandstones and the subsequent thick carbonate bif epeiric platform succession of the chuniespoort group subordinate mechanical subsidence accompanied this long lived thermal relaxation intense weathering due to neoarchaean atmosphere composition greatly reduced clastic sedimentation and the greenhouse palaeoclimate further encouraged carbonate sedimentation globally enhanced sea levels due to enhanced mid ocean ridge growth consequent upon either global magmatic events or supercontinent break up also played a pivotal role in chuniespoort epeiric basin evolution pretoria group sedimentation is ascribed to two cycles of rifting and subsequent thermal subsidence the first cycle appears to reflect plate tectonically induced rifting with an epeiric sea drowning the rift basin despite reduced sea levels due to the first major global glaciation the second pretoria cycle is most likely related to a major continental flood basalt event with thermal subsidence allowing a second and probably larger epeiric sea to advance onto the northern kaapvaal craton evaluation of the inferred relatively minor importance of plate tectonics in the evolution of the essentially intracratonic transvaal basin depends to a large degree on the age assigned to the limpopo orogeny during which the zimbabwe and kaapvaal cratons collided recent evidence for a c 2 0 ga collision supports the concept that catastrophic global magmatic events gradually gave way to plate tectonics during transvaal basin evolution

coupling primary production and terrestrial runoff to ocean acidification and carbonate mineral suppression in the eastern bering sea water column ph and carbonate mineral saturation states were calculated from dissolved inorganic carbon dic and total alkalinity data collected over the eastern bering sea shelf in the spring and summer of 2008 the saturation states of the two most important carbonate minerals calcite calcite and aragonite aragonite were strongly coupled to terrestrial runoff from the yukon and kuskokwim rivers primary production in the surface waters and remineralization of organic matter at depth over the shelf in spring before ice melt occurred ph over the shelf was largely confined to a range of 7 9 8 1 and calcite and aragonite ranged from 1 5 to 3 0 and 0 8 to 2 0 respectively at the stations closest to river outflows aragonite was undersaturated in the water column from the surface to the bottom during the summer sea ice retreat high rates of primary production consumed dic in the mixed layer which increased ph and calcite and aragonite however calcite and aragonite decreased by 0 3 in the bottom waters over the middle and outer shelf over the northern shelf where export production is highest aragonite decreased by 0 35 and became highly undersaturated the observed suppression and undersaturation of calcite and aragonite in the eastern bering sea are correlated with anthropogenic carbon dioxide uptake into the ocean and will likely be exacerbated under business as usual emission scenarios therefore ocean acidification could threaten some benthic and pelagic calcifying organisms across the bering sea shelf in the coming decades

coastal atmospheric forcing in the northern gulf of alaska a comparison of winds over the northern gulf of alaska found measured winds to be significantly weaker than calculated geostrophic winds the latter required more than the standard 30 reduction to correct for frictional effects in the maritime boundary layer an additional 11 is calculated based on principal axis analysis a counterclockwise rotation of the instantaneous geostrophic wind vectors of 44 59 total beyond the standard 15 was required to align them with those measured at a coastal weather station however events in these two wind sets were well correlated throughout the year and the rotary coherence was significant for frequencies lower than 0 895 cpd on the basis of empirical orthogonal function analysis most of the seasonal variability in this coastal current is associated with wind changes freshwater discharge is also important in driving the alongshore baroclinic flow and a secondary cross shelf flow

package fluids 1 computer programs for analysis of fluid inclusion data and for modelling bulk fluid properties the computer package fluids contains five sets of computer programs written in c for the calculation of fluid properties both model fluids and data from fluid inclusions can be analysed in the programs bulk density molar volume and composition of fluid inclusions are calculated with the program bulk which uses microthermometric data micro raman spectroscopic data cation ratios and volume fraction estimations as input the program offers a broad variety of equations of state which are selected according to the fluid system or the temperature and pressure conditions of interest the isochores that correspond to the output or test v x properties of fluid inclusions are calculated by the program isoc in calculating the isochores this program takes account of the compressibility and expansion of selected host minerals the program test allows different equations of state to be compared directly with experimental data thereby facilitating selection of the most adequate model in the programs bulk and isoc loner is a group of programs that handle individual equations of state eos for all fluid systems presented in the programs bulk and isoc aqso is a group of programs that allows purely empirical modelling of electrolyte bearing aqueous solutions henry s law for dilute gas bearing aqueous solutions and osmotic coefficients for dilute electrolyte bearing aqueous solutions the programs are available on the university of leoben web site at http www unileoben ac at buero62 minpet ronald

trace element and upb isotope compositions of pyrite types in the proterozoic black reef transvaal sequence south africa implications on genesis and age abstract the proterozoic black reef is in most cases indistinguishable from the gold uranium and pyrite bearing archaean witwatersrand reefs however the prevailing opinion that the black reef gold mineralization was largely derived from reworking of the underlying kimberley reef is not supported by the morphology trace element geochemistry and u pb isotope data on detrital pyrite in these reefs the grade of metamorphism recorded in the black reef quartzite formation is significantly lower than the 300 400 c that has been proposed for the sediments of the witwatersrand supergroup the u pb isotope and trace element geochemical signatures in pyrite have therefore been preserved in the black reef the morphological and compositional differences retained by the detrital and synsedimentary pyrite types both occurring together in the black reef imply that they were formed by different processes and in contrasting geochemical environments in the black reef the data for the detrital pyrite are consistent with their derivation from a 3000 2800 ma granitic probably hydrothermally altered source region by contrast the geochemical and pb isotopic composition of the concretionary pyrite is interpreted to reflect its synsedimentary formation in a lagoonal or tidal flat environment prior to 2500 ma the morphology primary mineral inclusions and the unradiogenic pb isotopic compositions preserved in the black reef detrital pyrite are irreconcilable with models proposed for the formation of witwatersrand pyrite by a process of pyritization of fe bearing detrital minerals fluids present in the black reef depositional diagenetic environment were anomalously enriched in radiogenic pb and any transformation process would not be able to escape acquiring this enriched pb isotopic signature

factors influencing physical structure and lower trophic levels of the eastern bering sea shelf in 2005 sea ice tides and winds abstract in spring and fall 2005 cross and along shelf transects were sampled to evaluate the influence of physical forcing including sea ice tides and winds on the lower trophic levels of the bering sea ecosystem the hydrography nutrients chlorophyll and zooplankton abundance and species composition were all affected by the presence or absence of sea ice on a north south transect along the 70 m isobath in may shelf waters between 59 n and 62 n were cold and relatively fresh and benthic invertebrate larvae and chaetognaths were a significant fraction of the zooplankton community while to the south the water was warmer saltier and the zooplankton community was dominated by copepods the position of the transition between ice affected and ice free portions of the shelf was consistent among temperature salinity nutrients and oxygen this transition in the hydrographic variables persisted through the summer but it shifted 150 km northward as the season progressed while a transition also occurred in zooplankton species composition it was farther north than the physical chemical transition and did not persist through the summer mooring data demonstrated that the change in the position of the transition in physical and chemical properties was due to northward or eastward advection of water onto and across the shelf from south to north along the 70 m isobath tidal energy decreased resulting in a less sharply stratified water column on the northern portion of the middle shelf as opposed to a well defined two layered system in the southern portion this more gradual stratification in the north permitted a greater response to mixing from winds which were homogeneous from north to south thus the physical and biological structure at any one location over the middle shelf is dynamic over the course of a year and results from a combination of in situ processes and climate mediated regional forcing which is dominated in most years by sea ice

the structural setting of mineralisation at kolomela mine northern cape south africa based on fully constrained implicit 3d modelling abstract kolomela mine formerly known as the sishen south project is located approximately 9 km from postmasburg in the northern cape province of south africa iron ore is primarily concentrated near the top of the asbesheuwels or asbestos hills subgroup within the kuruman formation high grade hematite rich iron ore deposits in south africa have been addressed in the literature although much of this work focusses on their geochemical or isotopic signatures and the role of paleosinkholes in ore preservation recent work on high grade bif hosted fe deposits in south africa and elsewhere emphasizes the role of deformation in iron mineralisation and upgrading of bif over a sequence of events either punctuated by supergene enrichment or terminating with a supergene overprint the proximity of the kheis orogenic front the protracted tectonic history of the area a recently resolved local structural framework and an emerging set of literature on superimposed hypogene metasomatic hydrothermal hypothermal and deformation induced processes justify a re examination of the kolomela deposits closely spaced drillhole data pit mapping over a period of four years and re interpretation of the tectonic setting from high resolution geophysical data have been incorporated into fully constrained 3d models of the five principle kolomela deposits which are presented here and analysed in terms of their geometry tectonic setting relationship to major structures the geometry of the underlying dolomite contact and the possible role of gabbroic intrusions a strong spatial correlation between thicker ore and thicker underlying gabbroic bodies in the forms of sills is evident we propose that protracted multi phase tectonic evolution complete with several compressional extensional events at this margin of the kaapvaal craton provided an ideal setting for preparation of bif by early low grade metamorphism deformation and porosity creation followed by fluid movement along interconnected contacts unconformities gabbro contacts and major structures

trapped motion around the pribilof islands in the bering sea observations in the region of the pribilof islands and canyon pic reveal a clockwise circulation around the group of islands and around each of the two largest islands st paul and st george six current meters deployed around st paul island revealed a steady clockwise flow around the island which was strongest south of the island and weakest to the east we use a high resolution tidal model in the pic region to show that this flow pattern results from tidal rectification over the shallow topography tides tidal residual currents of 10 15 cm s were predicted by the model compared to mean currents of 5 20 cm s observed at the mooring sites both diurnal and semidiurnal tidal oscillations contribute to the clockwise circulation around the islands in the diurnal band the enhanced currents occur also at the shelf slope where a tidal wave generates a shelf wave due to resonance with topography in the pic region the main shelf wave occurs in the pribilof canyon where both observations and measurements show enhancement of the diurnal tidal currents

coastal fresh water discharge in the northeast pacific very high annual rates of precipitation in the coastal mountains that border the northeast pacific ocean produce large fresh water discharges 23000 m3 s 1 this discharge has been ignored previously since it does not enter the ocean in the form of large rivers but instead the water enters by way of numerous small rivers and streams thus it acts as a line source instead of a point source this coastal discharge contributes at least 40 of the fresh water that enters the northeast pacific from the atmosphere the discharge is comparable to the mean annual discharge of the mississippi river system the fresh water creates a cross shelf density gradient that drives an alongshore baroclinic jet the width of this jet is less than 25 km with speeds in excess of 100 cm s 1 it extends along the coast from southeast alaska to at least kodiak island apparently the flow is maintained as a narrow current adjacent to the coast by wind stress that causes downwelling conditions here throughout most of the year

physical forcing and nutrient conditions associated with patterns of chl a and phytoplankton productivity in the southeastern bering sea during summer abstract measurements of nutrients primary 14 c productivity and new nitrate productivity collected in the southeastern bering sea in july and august 2004 together with measurements from july 1981 are used to characterize the regional production system during summer and to analyze the major physical and nutrient factors controlling biological patterns the patterns of surface productivity suggested by the two different summers were remarkably similar in the regions of data overlap and agree with recent compilations of summer conditions from remotely sensed data summer was characterized by low production in the middle and outer shelf associated with surface mixed layers that were stabilized by heat elevated productivity was restricted to regions associated with the surface expression of thermohaline fronts as well as to tidally mixed regions adjacent to and between the pribilof islands based on chl a and productivity measurements the biological impact of the shelf break front of the southeastern bering sea extends at least as far inshore as the pribilof islands the existence of elevated summer productivity associated with a recently identified shelf partition front between the pribilof domain and the middle shelf domain east of st paul island was confirmed and its thermohaline nature resulting from cumulative intrusions of slope derived water is described yearly estimates of new and primary productivity compiled for the various biophysical regimes range from 1800 mmol n m 2 yr 1 and 170 g c m 2 yr 1 at the shelf break front to less than 700 mmol n m 2 yr 1 and 100 g c m 2 yr 1 in oceanic and coastal waters we hypothesize that trace metals rather than macronutrients or grazing likely restrict the seaward extent of elevated production at the shelf break front iron may be supplied to the front by isopycnal mixing from deeper shelf waters that were in contact with sediments by extending elevated production throughout the summer the thermohaline and tidal fronts enhance the coupling of primary production to epipelagic food webs for the large populations of fish birds and mammals in the region changes in the intensity or location of these frontal systems may impact populations that forage in them from the nearby pribilof islands

the importance of freshwater to spatial variability of aragonite saturation state in the gulf of alaska high latitude and subpolar regions like the gulf of alaska goa are more vulnerable than equatorial regions to rising carbon dioxide co2 levels in part due to local processes that amplify the global signal recent field observations have shown that the shelf of the goa is currently experiencing seasonal corrosive events carbonate mineral saturation states 1 including suppressed in response to ocean acidification as well as local processes like increased low alkalinity glacial melt water discharge while the glacial discharge mainly influences the inner shelf on the outer shelf upwelling brings corrosive waters from the deep goa in this work we develop a high resolution model for carbon dynamics in the goa identify regions of high variability of and test the sensitivity of those regions to changes in the chemistry of glacial melt water discharge results indicate the importance of this climatically sensitive and relatively unconstrained regional freshwater forcing for variability in the nearshore the increase was nearly linear at 0 002 per 100 mol kg increase in alkalinity in the freshwater runoff we find that the local winds biological processes and freshwater forcing all contribute to the spatial distribution of and identify which of these three is highly correlated to the variability in given that the timing and magnitude of these processes will likely change during the next few decades it is critical to elucidate the effect of local processes on the background ocean acidification signal using robust models such as the one described here

chlorite thermometry in the witwatersrand basin constraints on the paleoproterozoic geotherm in the kaapvaal craton south africa a series of post depositional alteration events can be distinguished in the late archean witwatersrand basin they range from thrust controlled metamorphism during pre transvaal crustal thickening burial metamorphism and hydrothermal infiltration during crustal thinning and associated deposition of the 2 6 2 1 ga transvaal supergroup sediments thermal metamorphism related to the 2 06 ga bushveld igneous complex and hydrothermal alteration as a consequence of the 2 023 ga vredefort impact event the relative importance of these events varies locally with different events responsible for the maximum temperatures achieved in different parts of the basin the pre transvaal metamorphism affected the northern margin of the basin whereas the syn bushveld thermal metamorphism is particularly pronounced in the lower parts of the witwatersrand supergroup chlorite geothermometry in conjunction with fluid inclusion microthermometry and the thermodynamic modeling of equilibrium mineral assemblages was applied

rapid shifts in subarctic pacific climate between 138 and 70 ka during the past decades remarkable changes in sea surface temperature sst and sea ice extent have been observed in the marginal seas of the subarctic pacific however little is known about natural climate variability at millennial time scales far beyond instrumental observations geological proxy records such as those derived from marine sediments offer a unique opportunity to investigate millennial scale natural climate variability of the artic and subarctic environments during past glacial interglacial cycles here we provide reconstructions of sea ice variability inferred from ip25 ice proxy with 25 carbon atoms sea ice biomarker and sst fluctuations based on alkenone unsaturation index graphic of the subarctic pacific realm between 138 and 70 ka warmest sea surface conditions were found during the early eemian interglacial 128 to 126 ka exceeding modern ssts by 2 c the further north pacific climate evolution is marked by pronounced oscillations in sst and sea ice extent on millennial time scales which correspond remarkably well to short term temperature oscillations known from greenland and the north atlantic these results imply a common forcing which seems to be closely coupled to dynamics of the atlantic meridional overturning circulation however immediate propagation of such climate fluctuations far beyond the north atlantic basin suggests a rapid circumpolar coupling mechanism probably acting through the atmosphere a prerequisite to explain the apparent synchronicity of remote climatic reorganizations in the subarctic pacific

2 05 ga isotopic ages for transvaal mississippi valley type deposits evidence for large scale hydrothermal circulation around the bushveld igneous complex south africa abstract the known dimensions of hydrothermal fluid circulation associated with emplacement of the 2 055 ga bushveld igneous complex bic are extended with new isotopic ages for paleoproterozoic mineral deposits in wallrocks transvaal supergroup surrounding the bic a fluorite rich mississippi valley type mvt deposit in the zeerust district dated at 2 05 ga sm nd isochron age has nd isotopic compositions that are identical to coeval f rich lebowa granite late in the bic intrusive sequence suggesting transport of magmatic fluids 100 km beyond the present margins of the bic hydrothermal illite from the zn pb mvt bushy park deposit dated at 2 05 ga by k ar geochronology links widespread mvt deposits of the kaapvaal craton to large scale basinal brine circulation associated with emplacement of the bic these data in combination with gold vein phosphate mineral and paleomagnetic resetting ages indicate a regional scale bushveld age hydrothermal system circulating 700 km outward from the prese

the black reef quartzite formation in the western transvaal sedimentological and economic aspects and significance for basin evolution a sedimentological study of the early proterozoic black reef quartzite formation in the south western parts of the transvaal province of south africa was undertaken with the primary aim of examining the sedimentological controls of gold mineralization in the black reef placer which occurs at the base of this formation a second aim of the study was to investigate the early history of the basin in which the transvaal sequence of south africa was deposited the thin siliciclastic black reef quartzite formation which is informally subdivided into a lower conglomerate unit and an upper quartzite unit is underlain by archaean rocks belonging to the basement complex and the witwatersrand and ventersdorp supergroups and is overlain by a thick succession of carbonate rocks of the malmani subgroup the pre transvaal palaeosurface is characterised by elongated northeast to southwest trending grabens and partly eroded horst blocks the black reef quartzite formation which has a maximum thickness of about 30 m in the study area typically comprises a succession of interbedded arenites and mudstones with a sporadically developed basal conglomerate unit thickness trends are similar to the dominant structural trend of the pre transvaal palaeosurface at localities where the conglomerate unit is absent the formation invariably overlies quartzites of the witwatersrand supergroup directly the palaeocurrent distribution of the conglomerate unit is unimodal with modes towards the southwest in the southern parts of the study area and towards the north in the northern regions most of the palaeocurrent distributions of the quartzite unit are unimodal too but bimodal distributions were found at three localities pebble size of the black reef placer is largest in the northeastern parts of the study area but no orderly lateral size variation was found pebble roundness too varies greatly and apparently randomly the composition of the pebble assemblage is not constant but no systematic lateral change could be detected a petrographic study of the arenites of the formation reveals a remarkable textural and mineralogical maturity especially for the upper beds it is concluded that the pre transvaal palaeosurface had a palaeorelief of up to 30 m and that the topography of the palaeo landscape was the dominant factor controlling early sedimentation in the basin the palaeo grabens probably constituted the valleys of shallow braided stream systems that drained south westwards and northwards from a palaeo drainage divide in the northern parts of the study area sediment including detrital gold was derived from erosion of witwatersrand rocks and fed to the graben valleys via several alluvial fans during a subsequent transgression the fluvial systems became drowned and transgressive estuarine conditions ensued during the final stages of siliciclastic sedimentation the upper quartzite beds of the formation were probably reworked by shallow marine processes before carbonate precipitation commenced the cause of the marine transgression is not known beyond doubt it is suggested however that lithospheric rifting which initiated the extrusion of the underlying ventersdorp lavas resumed during early transvaal times resulting in complete severing of the continental crust and the creation of a linear sea

temporal changes in benthic ostracode assemblages in the northern bering and chukchi seas from 1976 to 2010 abstract we analyzed living ostracode assemblages from the northern bering sea collected between 1976 and 2010 and from the chukchi sea collected in 2009 and 2010 to examine how climatic and oceanographic changes are affecting modern ostracode species distributions totals of 21 and 28 ostracode species were identified respectively from bering and chukchi sea surface sediment samples the bering sea assemblage is largely transitional in species composition between those inhabiting western arctic continental shelves and the subarctic gulf of alaska temporal changes in the bering sea assemblage provide evidence that decadal temperature changes have affected species composition for example the proportion of normanicythere leioderma a predominantly arctic species decreased from 70 of the total assemblage population in 1999 to 15 by 2006 this decrease coincided with a shift in the arctic oscillation toward a positive mode and warmer bering sea surface temperatures sst beginning in the early 2000s in contrast the more temperate species pectocythere janae also known as kotoracythere arctoborealis made up less than 4 of the bering assemblage prior to 2000 but increased in abundance to as much as 30 as bering sea temperatures rose from 2001 to 2006 this pattern has reversed since 2006 when cooler temperatures led to a decline in p janae and return in the prominence of n leioderma our results support the idea that recent ocean temperature changes and a reduced sea ice season in the bering chukchi sea region are changing species composition in benthic ecosystems

tectonic and geochronological constraints on late archaean and palaeoproterozoic stratigraphic correlation within and between the kaapvaal and pilbara cratons recent radiometric dating of carbonates and banded iron formations on the kaapvaal craton southern africa has suggested that late archaean and palaeoproterozoic carbonate sedimentation was diachronous across the craton we present new shrimp u pb zircon ages of 2583 5 ma and 2588 7 ma for two samples of a tuff bed 320 km apart in the upper oak tree formation transvaal supergroup these ages in conjunction with published data support previously established sequence stratigraphic correlations that show the temporal equivalence of late archaean carbonates in the region a review of the sequence stratigraphy and geochronology of the mount bruce megasequence set on the pilbara craton western australia and the newly named highveld megasequence set on the kaapvaal craton indicates a remarkably similar geohistory both cratons are characterized by a divergent megacycle hamersley range and vaal megasequences followed by a convergent megacycle chichester range and drakensberg megasequences our data show that the megasequence boundary is marked by drowning of both cratons at approximately the same time c 2590 ma which permits more meaningful geotectonic correlations between them

on the recent warming of the southeastern bering sea shelf abstract during the last decade the southeastern bering sea shelf has undergone a warming of 3 c that is closely associated with a marked decrease of sea ice over the area this shift in the physical environment of the shelf can be attributed to a combination of mechanisms including the presence over the eastern bering sea shelf of a relatively mild air mass during the winter especially from 2000 to 2005 a shorter ice season caused by a later fall transition and or an earlier spring transition increased flow through unimak pass during winter which introduces warm gulf of alaska water onto the southeastern shelf and the feedback mechanism whereby warmer ocean temperatures during the summer delay the southward advection of sea ice during winter while the relative importance of these four mechanisms is difficult to quantify it is evident that for sea ice to form cold arctic winds must cool the water column sea ice is then formed in the polynyas during periods of cold north winds and this ice is advected southward over the eastern shelf the other three mechanisms can modify ice formation and melt and hence its extent in combination these four mechanisms have served to temporally and spatially limit ice during the 5 year period 2001 2005 warming of the eastern bering sea shelf could have profound influences on the ecosystem of the bering sea from modification of the timing of the spring phytoplankton bloom to the northward advance of subarctic species and the northward retreat of arctic species

the third arctic climate pattern 1930s and early 2000s 1 persistent near surface warm temperature anomalies have occurred in two localized areas eastern siberia east siberian sea and northeastern canada baffin bay during winter and spring in recent years 2000 2005 in contrast to previous decades the proximate cause in winter was a northward displacement and strengthening of the aleutian low and a weakening of the icelandic low spring showed a dipole pattern with higher sea level pressure slp on the north american side of the arctic and lower pressures over eurasia phase space trajectories of arctic climate for 1951 2005 based on the first two eofs of slp the arctic oscillation and a pacific north american like pna pattern show multi annual variability leading to lower slp and warmer temperatures in the last decades of the 20th century recent winters have some projection onto pna but the slp dipole in recent springs does not strongly project onto either of the two basic climate patterns the period from 1928 1935 also had a dipole structure in slp which contributed to the interdecadal arctic wide warm temperature anomalies in the first half of the 20th century recognition of the recent persistent and somewhat unique arctic climate pattern is important as it contributes to the ongoing reorganization of arctic ecosystems

structural evolution of the mount wall region in the hamersley province western australia and its control on hydrothermal alteration and formation of high grade iron deposits abstract the discovery of two relatively small but high grade iron ore deposits near mt wall an intensely faulted part of the southwestern hamersley province provides unique insights into the structural control on ore formation in this region the deposits have many geological features typical of the high grade microplaty hematite group which also contains the much larger mt tom price paraburdoo and mt whaleback deposits the deposits are structurally controlled along early normal faults and contain abundant microplaty hematite and martite and are largely confined to the dales gorge member of the brockman iron formation in addition to the microplaty hematite martite ore there are martite goethite ores and rare magnetite goethite or magnetite hematite ores below the modern weathering surface hydrothermally altered zones in wallrock bif from the lower dales gorge member contain magnetite hematite and carbonate talc bearing mineral assemblages a staged ore genesis model involving early extension and fluid circulation along normal faults hypogene silica leaching and carbonate alteration followed by deep meteoric oxidation with microplaty hematite formation and finally weathering can explain most features of the mt wall deposits the role of deformation was to provide pathways for mineralising fluids and initiate the seed points for the mineralised systems high grade iron in the wellthandalthaluna deposit is situated between the nw to nnw trending boolgeeda creek fault and a synthetic joining splay the northern fault both are high angle normal faults and formed during early extension in this part of the province faults are characterised by localised small scale deformation and brecciation deep carbonate alteration and oxidation recent weathering has penetrated deeply into the fault zones converting the carbonate rich assemblages into goethite mineralisation in the arochar deposit is situated in the overlap or relay zone between two segments of the mt wall fault zone a moderately to steeply southerly dipping normal fault system which at arochar is intruded by dolerite dykes at both locations the ore controlling faults are offset by later nw trending dextral and normal faults fault relay zones or fault splay zones were likely zones of increased permeability and fluid flow during fault development or reactivation and may also have been important in initiating mineralisation in larger deposits such as mt tom price and mt whaleback however structural controls on the largest iron ore deposits are often obscured due to the intensity and scale of ore development whereas they are better preserved in the smaller deposits recognition that carbonate bearing protores at mt wall survived for nearly two billion years until intense recent weathering converted them to martite goethite or magnetite goethite ores may imply that more of the giant hematite goethite deposits of the hamersley province had hydrothermal precursors and were not formed by supergene processes alone

the bif hosted high grade iron ore deposits in the archean koolyanobbing greenstone belt western australia structural control on synorogenic and weathering related magnetite hematite and goethite rich iron ore the koolyanobbing banded iron formation bif hosted iron ore deposits total premining resources 150 million metric tons mt indicated reserves 32 mt are located in the mesoarchean lower succession bif of the koolyanobbing greenstone belt younami terrane yilgarn craton in western australia in the koolyanobbing greenstone belt a deformation sequence that broadly correlates with the proposed deformation history of most greenstones belts within the southern cross domain includes d 1 structures mainly small scale f 1a and f 1b folds formed in a north south to northwest southeast compressional regime a ductile to brittle deformation sequence d 2 to d 4 generated during east west compression and a late stage brittle segmentation of bif and reactivation of faults attributed to d 5 the formation of the seven known medium 45 58 wt fe to high grade 58 68 wt fe magnetite martite specularite and goethite bearing orebodies can be subdivided into four archean stages and one weathering related upgrade from the permian and or mesozoic to recent times the archean ore forming stages comprise 1 early fe mg ca metasomatism causing local ferroan carbonate and ferroan talc alteration of the metamorphosed quartz magnetite bif protolith 2 sequential syn d 2a coaxial to syn d 4 transpressional tight folding driven removal of carbonate quartz and minor ferroan talc by solution and mechanical transfer producing residual enrichment of medium to high grade magnetite ore 3 magnetite mineralization in syn d 2b and syn d 4 breccias and fractures forming medium grade ore zones or overprint magnetite in bif and first stage magnetite ore and 4 mineralization of hydrothermal specularite and locally associated ferroan dolomite quartz alteration and local oxidation of magnetite in and near brittle d 4 faults fractures and reactivated f 1 and f 2a fold cores modern weathering related leaching of carbonate and minor quartz pseudomorphic goethite replacement of existing iron oxides and gangue and coeval or subsequent to oxidation in the vadose zone formed goethite martite ore with local relics of specularite or magnetite and or kenomagnetite the intensity and localization of this supergene modification is in most deposits at koolyanobbing controlled by existing hypogene magnetite specularite rich medium to high grade ore zones and or carbonate altered bif at depth the existence of high grade ore below the weathering horizons suggests the possibility of further concealed magnetite and or specularite rich orebodies within the deposits and region

genesis of high grade hematite orebodies of the hamersley province western australia a reply sir we are very thankful for the constructive comments provided by kneeshaw and kepert unfortunately the competitive ownership structure of the iron ore mining industry in the hamersley province limits our personal knowledge of the mount whaleback deposit to occasional mine visits and to the available literature published and unpublished we do however have access to the data on the smaller giles mini and lido deposits 50 and 10 km west of mount whaleback respectively and to extensive exploration mapping in the ophthalmia ranges to the north direct proof for rotation of the orebody as it is preserved at paraburdoo in the approximately 50 dip of the overlying proterozoic hematite conglomerates of the mount mcgrath formation is not preserved at mount whaleback however we believe that there is sufficient information available in the literature to think that a rotational model for a large part of the deposit is perfectly plausible first and above all as stated in taylor et al 2001 f2 folds are more upright with axial planes dipping about 50 s in the southern and western part of the deposit away from the whaleback fault e g as shown on section no 315120e fig 4 in powell et al 1999 interestingly the ore controlling faults are also more upright in this part of the deposit which suggests an intimate link between the dip of these fault planes and dip of the axial planes of f2 folds secondly

recent shifts in the state of the north pacific 1 the winters of 1999 2002 for the north pacific were characterizedbyspatialpatternsinsealevelpressureanomaly slpa and sea surface temperature anomaly ssta with little resemblance to those of the leading pattern of north pacific climate variability the pacific decadal oscillation pdo in essence the southeastern northern portion of the north pacific was subject to atmospheric forcing characteristic of that before after the major regime shift of 1976 77 recent major changes in the ecosystems off the west coast of the united states and continued conditions similar to those of the early 1990s in the gulf of alaska bering sea and sea of okhotsk are consistent with these slpa and ssta patterns our result illustrates that a single indicator such as the pdo is incomplete in characterizing north pacific climate index terms 1635 global change oceans 4203 1610 global change atmosphere 0315 0325 4215 oceanography general climate and interannual variability 3309 3339 meteorology and atmospheric dynamics ocean atmosphere interactions 0312 4504 citation bond n a j e overland m spillane and p stabeno recent shifts in the state of the north pacific geophys res lett 30 23 2183 doi 10 1029 2003gl018597 2003

modern distribution of dinocysts from the north pacific ocean 37 64 n 144 e 148 w in relation to hydrographic conditions sea ice and productivity abstract palynological analyses were performed on 53 surface sediment samples from the north pacific ocean including the bering and okhotsk seas 37 64 n 144 e 148 w in order to document the relationships between the dinocyst distribution and sea surface conditions temperatures salinities primary productivity and sea ice cover samples are characterized by concentrations ranging from 18 to 143 816 cysts cm3 and the occurrence of 32 species a canonical correspondence analysis cca was carried out to determine the relationship between environmental variables and the distribution of dinocyst taxa the first and second axes represent respectively 47 and 17 8 of the canonical variance axis 1 is positively correlated with all parameters except to the sea ice and primary productivity in august which are on the negative side results indicate that the composition of dinocyst assemblages is mostly controlled by temperature and that all environmental variables are correlated together the cca distinguishes 3 groups of dinocysts the heterotrophic taxa the genera impagidinium and spiniferites as well as the cyst of pentapharsodinium dalei and operculodinium centrocarpum five assemblage zones can be distinguished 1 the okhotsk sea zone which is associated to temperate and eutrophic conditions seasonal upwellings and amur river discharges it is characterized by the dominance of o centrocarpum brigantedinium spp and islandinium minutum 2 the western subarctic gyre zone with subpolar and mesotrophic conditions due to the kamchatka current and alaska stream inflows assemblages are dominated by nematosphaeropsis labyrinthus pyxidinopsis reticulata and brigantedinium spp 3 the bering sea zone depicting a subpolar environment influenced by seasonal upwellings and inputs from the anadyr and yukon rivers it is characterized by the dominance of i minutum and brigantedinium spp 4 the alaska gyre zone with temperate conditions and nutrient enriched surface waters which is dominated by n labyrinthus and brigantedinium spp and 5 the kuroshio extension north pacific subarctic current zone characterized by a subtropical and oligotrophic environment which is dominated by o centrocarpum n labyrinthus and warm taxa of the genus impagidinium transfer functions were tested using the modern analog technique mat on the north pacific ocean 359 sites and the entire northern hemisphere databases 1419 sites results confirm that the updated northern hemisphere database is suitable for further paleoenvironmental reconstructions and the best results are obtained for temperatures with an accuracy of 1 7 c

on the seasonal variability of the alaska coastal current current measurements of the alaska coastal current were analyzed for their mean structures and seasonal cycles the current is westward alongshore at the surface 25 to 175 cm s 1 with a baroclinic shear of 30 cm s 1 in the upper 70 m the amplitude of the seasonal variation of the flow decreases with depth and its maximum phase delay of 3 months occurs at 175 m relative to the surface the amplitude of the seasonal cycle of the north south cross shore flow is a minimum at mid depth the phase of this seasonal cycle is also delayed at deeper depths but the maximum shift relative to the surface occurs at 110 m rather than at the bottom 175 m empirical orthogonal function analysis indicates that the first mode of the alongshore flow has nearly constant amplitude with depth barotropic variations and is related to the east west wind the second mode explains significant variance of the surface current and the freshwater discharge the cross shore flow analysis shows that the first mode is again nearly barotropic and is principally related to the east west wind with increased southward flow when the winds are increased westward the second mode of the cross shore flow fluctuates with runoff such that the offshore flow at the surface and the onshore flow near to the bottom coincide with increased freshwater discharge

comparison of warm and cold years on the southeastern bering sea shelf and some implications for the ecosystem the southeastern middle shelf of the bering sea has exhibited extreme variability in sea ice extent temperature and the distribution and abundance of species at multiple trophic levels over the past four decades from 1972 2000 there was high interannual variability of areal extent of sea ice during spring march april in 2000 this shifted to a 5 year 2001 2005 period of low ice extent during spring which transitioned to a 4 year 2007 2010 period of extensive sea ice high low areal extent of sea ice in spring was associated with cold warm water column temperatures for the following 6 7 months the ocean currents also differed between warm and cold years during cold years the monthly mean currents over the shelf were largely westward while in warm years the direction of currents was more variable with northward flow during december february and relatively weak flow during the remainder of the year the types and abundance of zooplankton differed sharply between warm and cold years this was especially true during the prolonged warm period 2001 2005 and cold period 2007 2010 and was less evident during the years of high interannual variability during the warm period there was a lack of large copepods and euphausiids over the shelf however their populations rebounded during cold period small crustacean zooplankton taxa did not appear to vary between and warm and cold years for both walleye pollock and pacific cod year class strength recruitment was low during the prolonged warm period but improved during the following cold period year class strength did not appear to vary as a function of warm and cold years during the period of high year to year variability also recruitment of arrowtooth flounder a predator of pollock and cod did not appear influenced by the warm or cold years finally the distribution and relative abundance of fin whales appeared to differ in warm and cold years with fewer whales on the southeastern middle shelf during warm years

an examination of the physical variability around the pribilof islands in 2004 the pribilof islands form a unique ecosystem an anti cyclonic oceanic flow exists around the islands nutrients are introduced into this circulation from two sources 1 the flow along the 100 m isobath with intrusions of nutrient rich water in pribilof canyon and 2 the westward transport and vertical mixing of middle shelf water which contains nutrient rich bottom water enhanced tidal mixing around the pribilofs introduces this deeper nutrient rich water into the euphotic zone and thus supports prolonged production around the islands further the middle shelf water that is advected into the region causes the upper 50 m of the water column around the islands to freshen throughout the summer this enhances the frontal structure and strengthens the baroclinic flow along the 100 m isobath the strengthening of the frontal structure can moderate ecosystem productivity by limiting the intrusion of slope water rich in nutrients and oceanic copepods

transport through unimak pass alaska we examined inflow through unimak pass 200 m deep which is the only major connection between the shelves of the north pacific ocean and the eastern bering sea geostrophic transport was generally northward from the gulf of alaska into the bering sea the flow through the pass appeared to be modulated by the seasonal cycle of freshwater discharge on shorter time scales transport also was affected by semi daily variations in tidal mixing this effect was significant and not anticipated near bottom currents measured from moorings were maximum during winter and significantly correlated r 0 7 with the alongshore winds although the flow through unimak pass transported some nutrients from the north pacific ocean the gulf of alaska shelf is not the major source of nutrients to the bering sea shelf

stratification on the eastern bering sea shelf revisited abstract the timing and magnitude of stratification can have profound influences on the marine ecosystem on the eastern bering sea shelf in the absence of strong wind mixing stratification can be initiated by the melting of seasonal sea ice or by springtime warming of the surface temperature and salinity both influence the stratification of the eastern bering sea shelf with their relative importance varying spatially and temporally in the northern middle shelf domain north of 60 n salinity stratification is often as important as temperature stratification on the southern middle shelf while the influence of temperature on stratification dominates during summer the influence of salinity stratification plays a role in the interannual variability mooring 2 m2 56 9 n 164 1 w has been deployed at 70 m depth in the southern middle shelf domain since 1995 data from this mooring show that stratification typically begins to set up in may and to break down in september october but these dates can vary by 30 d while no trend is found in the timing of the spring setup the fall stratification breakdown exhibited a trend toward later breakdown 2 d later per year from 1996 to 2009 results suggest that it may be difficult to forecast stratification on the eastern bering sea shelf from climate models as simple indices of wind mixing or heat fluxes are not correlated with stratification contrary to intuition the strength of summer stratification is not correlated with depth averaged temperature warm years such as 2000 and 2001 can have low stratification and cold years such as 2007 can have very high stratification this decoupling of stratification and temperature has implications for forecasting the ecosystem in the face of climate change as we cannot assume that projections of a warmer climate simply imply higher stratification in the future

spring and fall phytoplankton blooms in a productive subarctic ecosystem the eastern bering sea during 1995 2011 abstract the timing and magnitude of phytoplankton blooms in subarctic ecosystems often strongly influence the amount of energy that is transferred through subsequent trophic pathways in the eastern bering sea spring bloom timing has been linked to ice retreat timing and production of zooplankton and fish a large part of the eastern bering sea shelf 500 km wide is ice covered during winter and spring four oceanographic moorings have been deployed along the 70 m depth contour of the eastern bering sea shelf with the southern location occupied annually since 1995 the two northern locations since 2004 and the remaining location since 2001 chlorophyll a fluorescence data from the four moorings provide 37 realizations of a spring bloom and 33 realizations of a fall bloom we found that in the eastern bering sea if ice was present after mid march spring bloom timing was related to ice retreat timing p n 11 a fall bloom also commonly occurred usually in late september average day 274 se 4 2 n 33 and its timing was not significantly related to the timing of storms p 0 88 df 1 27 or fall water column overturn p 0 49 df 1 27 the magnitudes of the spring and fall blooms were correlated p 0 011 df 28 the interval between the spring and fall blooms varied between four to six months depending on year and location we present a hypothesis to explain how the large crustacean zooplankton taxa calanus spp likely respond to variation in the interval between blooms spring to fall and fall to spring

coupled nitrification denitrification in sediment of the eastern bering sea shelf leads to 15n enrichment of fixed n in shelf waters 1 we studied the nitrogen biogeochemistry of the ice covered eastern bering sea shelf using the isotope ratios 15n 14n and 18o 16o of no3 and other n species the 15n 14n of late winter no3 on the shelf decreases inshore and is inversely correlated with bottom water nh4 consistent with an input of low 15n 14n no3 from partial nitrification of nh4 remineralized from the sediments an inshore 15n 14n increase in total dissolved n tdn suggests that 1 the sediment derived nh4 is elevated in 15n due to the same partial nitrification that yields the low 15n 14n no3 and 2 15n deplete no3 from partial nitrification within the sediments is denitrified to n2 the proportion of newly nitrified no3 on the shelf evidenced by an inshore decrease in no3 18o 16o is correlated with the n deficit further implicating nitrification coupled to denitrification however a simple n isotope budget indicates a comparable rate of denitrification supported by diffusion of no3 into the sediments the isotopic impact of benthic n loss is further demonstrated by a correlation between the 15n 14n of shelf surface sediment and the n deficit of the overlying water column both of which increase inshore and northward as well as by arctic no3 isotope data indicating that the fixed n transported through bering strait has a 15n 14n higher than is found in the open bering sea the significant net isotope effect of benthic n loss on the bering shelf 6 8 is at odds with previous assumptions regarding the global ocean s n isotope budget

shifts in the physical environment in the pacific arctic and implications for ecological timing and conditions abstract the northern bering sea and chukchi sea represent the gateway from the pacific to the arctic this contiguous marine system encompasses one of the largest continental shelves in the world and serves as the sole point of connection between the north pacific and arctic ocean this region has unique attributes and complex dynamics driven by the convergence of distinct water masses dynamic currents advection between pacific and arctic systems and important latitudinal gradients relevant to stratification and water mass structure water temperature and seasonal ice cover many processes and interactions in the region appear to be changing with important implications for both hydrography and ecology our analyses access remote and local data sources in us and russian waters to characterize oceanographic conditions and analyze the implications of dramatic shifts in recent years previously this region appeared resistant to trends apparent elsewhere in the greater arctic now the pacific arctic also appears to be in rapid transition the conditions observed in 2017 2019 are unprecedented we note important shifts in the phenology and magnitude of physical variables including sea ice extent concentration and duration as well as extreme reduction in the extent and intensity of the related bering sea cold pool we also note distinct regional dynamics in sea surface temperature in the bering chukchi system distinguishing western eastern and northern areas of the bering sea specifically our analyses distinguish the northern bering sea as an important transition zone between the pacific and arctic with higher frequency variability in sea surface temperature anomalies our results suggest that the strength and position of the aleutian low may be linked to warm and cold phases in the bering sea and has an important role in large scale circulation while cold winds out of the north are necessary to form ice in the northern bering sea strong winds may be associated with weak sea ice as wind action may break ice and enhance vertical mixing counteracting enhanced sea ice production from the advection of cold air research in this important region is complicated by international borders but may be enhanced through international collaboration this analysis represents an attempt to integrate data across russian and us waters to more fully represent system wide processes to contrast regional trends and to better understand physical interactions

the genadendal zn pb mn mineralization south africa a possible early proterozoic alkaline hydrothermal system a complex hydrothermal system is described in a 2 3 ga sedimentary succession it comprises an epigenetic part developed just below an uncomformity characterized by intense desilicification of cherty dolostone and by mineralization forming the matrix of a breccia probably representing a collapsed paleocave horizon two facies can be identified in this desilicification zone a blue facies that is characterized by replacement of chert by coarsely crystallized mn fe rich dolomite and a breccia matrix filled in by the same dolomite plus some galena and sphalerite and a red facies that is characterized by chert replacement by a similar dolomite which is only mn rich rubefaction of dolostone and deposition of primary mn fe oxides zn pb the syngenetic part immediately overlies the uncomformity and forms zn shale interpreted as former metalliferous mud deposited in a paleosinkhole flooded by hydrothermal solutions theoretical calculations suggest that the desilicification of the dolostone can be best explained by mixing of warm relatively dilute hydrothermal solutions with cold alkaline surficial brines it is proposed that the latter resulted from surface evaporation of deep bicarbonated solutions which then descended into the substratum where mixing occurred the genadendal occurrence is part of a local group of pb zn deposits in a cherty dolostone sequence these deposits have not been controlled by igneous intrusions and may be related to the mississippi valley type comparisons are made with other mineral deposits such as kombat namibia and franklin furnace new jersey which also may have formed under alkaline conditions

multiyear sea ice export through the bering strait during winter 2011 2012 1 six ice beacons deployed in the beaufort sea during august 2011 tracked the anomalous export of multiyear sea ice from the chukchi sea through the bering strait to the bering sea between november 2011 and may 2012 these are the first observations in 34 years of ice beacon export through the bering strait using 34 years of passive microwave derived ice motion fields we find that during 2011 2012 southward ice motion in the chukchi sea persisted for a record six of seven months and that sea ice speeds were significantly faster than the long term mean the combination of increased ice speeds and reduced likelihood of ice arch development through the strait culminated in the record export of 13 5 103 km2 of sea ice through the bering strait monthly sea level pressure fields dominated by an aleutian low and siberian high show anomalies in december and january played a role in initiating this event and forced multiyear ice into the southern chukchi sea however these variations were small and typical of this area yet we find no evidence of a similar export event in the last 34 years even though the forcing was similar to the climatology this leads us to attribute this event to a change in the responsiveness of the arctic ice pack to typical forcing mechanisms

hydrothermal origin for the 2 billion year old mount tom price giant iron ore deposit hamersley province western australia giant iron ore deposits such as those in the hamersley province of northwestern australia may contain more than a billion tonnes of almost pure iron oxides and are the world s major source of iron it is generally accepted that these deposits result from supergene oxidation of host banded iron formation bif accompanied by leaching of silicate and carbonate minerals new textural evidence however shows that formation of iron ore at one of those deposits mount tom price involved initial high temperature crystallisation of magnetite siderite iron silicate assemblages this was followed by development of hematite and ferroan dolomite bearing assemblages with subsequent oxidation of magnetite leaching of carbonates and silicates and crystallisation of further hematite preliminary fluid inclusion studies indicate both low and high salinity aqueous fluids as well as complex salt rich inclusions with the range of fluid types most likely reflecting interaction of hydrothermal brines with descending meteoric fluids initial hematite crystallisation occurred at about 250 c and high fluid pressures and continued as temperatures decreased although the largely hydrothermal origin for mineralisation at mount tom price is in conflict with previously proposed supergene models it remains consistent with interpretations that the biosphere contained significant oxygen at the time of mineralisation

integrated assessment of the carbon budget in the southeastern bering sea abstract during the primary field program for the bering ecosystem study 2008 2010 independent seasonal estimates of net primary production npp net community production ncp vertical export production cexp and benthic carbon consumption bcc were used to construct a shelf wide carbon budget for the southeastern bering sea here we quantify the annual production utilization and transport of npp for the southeastern shelf region of the bering sea spatially partitioned into outer middle and coastal domains we observed that approximately 25 and 30 of npp on the shelf is exported horizontally from the middle and outer domains respectively this horizontal transport was the dominant mode of carbon export in the outer domain exceeding cexp by more than 30 g c m 2 yr 1 99 g c m 2 yr 1 compared to 67 g c m 2 yr 1 respectively in the middle domain cexp was more prominent than lateral transport 65 g c m 2 yr 1 and 46 g c m 2 yr 1 respectively and vertically exported carbon was more efficiently recycled in this domain than in the outer domain 53 and 32 of cexp respectively in the coastal domain lateral transport was a source of carbon to the bottom layer with estimated input of carbon exceeding npp by as much as 54 g c m 2 yr 1 while the source of this additional carbon is unknown one possible source is transport from the middle domain during wind events that induce coastal convergence overall the combined carbon reservoir attributed to burial and transport in the middle and outer domains is similar to a previous budget for this region 47 walsh and mcroy 1986 although some qualitative differences are apparent the data presented here indicate a more pelagic character in the outer domain relative to the middle domain and that the middle and coastal domain carbon budgets are balanced only when combined

excess 210pb and 137cs concentrations mass accumulation rates and sedimentary processes on the bering sea continental shelf abstract we used 210pb and 137cs concentrations in twelve cores from the continental shelf and slope of the bering sea to investigate recent mass accumulation rates in sediments and sedimentation processes no decreases in exogenic 210pb concentrations with depth were observed in sediments from the shallow shelf area suggesting that there has been considerable mixing of the sediments there however we calculated mass accumulation rates from 210pbex profiles for several cores collected from the outer shelf and the slope mass accumulation rates in the sediments from these cores ranged from 0 11 to 0 44 g cm 2 y 1 for the cores with a mixed surface layer we showed that sediments that accumulated over the last 50 78 years were mixed the 210pbex inventories in the sediment cores suggested deposition of 210pb particles was focused in the slope area 137cs was observed in the sediments collected from the northern to western shelf areas the 137cs inventories showed higher values in the shelf area which suggests that fine grained particles from the yukon river have contributed to sedimentation there

variability in modern sea surface temperature sea ice and terrigenous input in the sub polar north pacific and bering sea reconstruction from biomarker data in order to study the modern sea surface characteristics of the sub polar north pacific and the bering sea i e sea surface temperature sst and sea ice cover surface sediments recovered during the rv sonne expedition 202 in 2009 were analysed to distinguish between marine and terrestrial organic carbon hydrogen index values long chain n alkanes and specific sterols have been determined the results show that in the bering sea especially on the sea slope the organic carbon source is mainly caused by high primary production in the north pacific on the other hand the organic material originates predominantly from terrestrial higher plants probably related to dust input from asia sst has been reconstructed using the modified alkenone unsaturation index calibration from muller et al 1998 offers the most reliable estimate of mean annual temperature in the central north pacific but does not correlate with mean annual temperature throughout the study area in the eastern north pacific and the bering sea the sikes et al 1997 calibration seems to be more accurate and matches summer sst the distribution of the novel sea ice proxy ip25 highly branched c25 isoprenoid alkene in surface sediments is in accord with the modern spring sea ice edge and shows the potential of this proxy to track past variation in sea ice cover in the study area

cetacean distribution and abundance in relation to oceanographic domains on the eastern bering sea shelf 1999 2004 abstract visual line transect surveys for cetaceans were conducted on the eastern bering sea shelf in association with pollock stock assessment surveys aboard the noaa ship miller freeman in june and july of 1999 2000 2002 and 2004 transect survey effort ranged from 1188 km in 1999 to 3761 km in 2002 fin whales balaenoptera physalus were the most common large whale in all years except 2004 when humpback whales megaptera novaeangliae were more abundant dall s porpoise phocoenoides dalli were the most common small cetacean in all years abundance estimates were calculated by year for each oceanographic domain coastal middle and outer slope the middle and outer slope domains were divided into two strata north and south because of variable survey effort the distribution and abundance of baleen whales changed between the earlier colder and later warmer survey years fin whales consistently occupied the outer shelf and secondarily the middle shelf and their abundance was an order of magnitude greater in cold compared to warm years humpback whales lived on the margin of the northern alaska peninsula eastern aleutian islands and bristol bay their preferred habitat is possibly associated with areas of high prey availability due to nutrient upwelling and aggregation mechanisms minke whales balaenoptera acutorostrata occur shoreward of fin whales in the outer and middle shelf and in coastal habitats along the alaska peninsula the highest abundance for this species was observed in a cold 1999 year no clear relationship emerged for odontocetes with regard to warm and cold years dall s porpoise occupied both outer and middle domains and harbor porpoise phocoena phocoena were more common in middle and coastal domains this study provided a unique broad scale assessment of cetacean distribution and abundance on the eastern bering sea shelf and a baseline for future comparisons

the proportion of remineralized nitrate on the ice covered eastern bering sea shelf evidenced from the oxygen isotope ratio of nitrate 1 we present measurements of nitrate and its natural abundance oxygen isotope composition 18o 16o in the water column of the broad and shallow eastern bering sea shelf in the late winter and early spring of 2007 and 2008 in both years nitrate concentrations showed a characteristic decrease from 25 m at the slope to 5 m inshore the 18o 16o ratio of nitrate 18ono3 versus smow also decreased from 3 2 at the slope to 1 5 inshore in 2007 and to as low as 1 inshore in 2008 indicating that nitrate inshore was nitrified at least once since having been entrained as nitrate from the slope the shoreward decrease was less pronounced in 2007 due to 18o enrichment of nitrate from incident phytoplankton assimilation in the ice covered water column whereas little to no algal growth in the water column was evident in 2008 by comparing the 18o of nitrate to that of ambient water in spring 2008 we estimate the fraction of nitrate that was remineralized in situ rather than recently advected from the slope these estimates indicate that 20 100 of the nitrate in winter water of the middle and inner shelves derives from regeneration directly on the shelf rather than from the seasonal entrainment of slope waters with recycling being the dominant mode of seasonal nitrate recharge from the 70 m isobath shoreward these observations indicate substantial nutrient recycling on the shallow shelf which has direct implications for the extent of fixed n loss to benthic denitrification and the fertility of the eastern shelf

long term observations of alaska coastal current in the northern gulf of alaska abstract the alaska coastal current is a continuous well defined system extending for 1700 km along the coast of alaska from seward alaska to samalga pass in the aleutian islands the currents in this region are examined using data collected at 20 mooring sites and from 400 satellite tracked drifters while not continuous the mooring data span a 30 year period 1984 2014 using current meter data collected at a dozen mooring sites spread over four lines seward gore point kennedy and stevenson entrances and the exit to shelikof strait total transport was calculated transport was significantly correlated with alongshore winds although the correlation at the seward line was weak the largest mean transport in the alaska coastal current occurred at gore point 1 4 10 6 m 3 s 1 in winter and 0 6 10 6 m 3 s 1 in summer with the transport at the exit to shelikof strait 1 3 10 6 m 3 s 1 in winter and 0 6 10 6 m 3 s 1 in summer only slightly less the transport was modified at the seward line in late summer and fall by frontal undulations associated with strong river discharge that enters onto the shelf at that time of year the interaction of the alaska coastal current and tidal currents with shallow banks in the vicinity of kodiak archipeligo and in kennedy stevenson entrance results in mixing and prolonged primary production throughout the summer

sea ice and water column structure on the eastern bering sea shelf abstract seasonal sea ice is a defining characteristic of the eastern bering sea shelf and plays a critical role in determining the vertical structure of temperature and salinity over this shelf ice movement relative to local winds ice composition and the impact of both arrival and retreat of ice on the water column at four mooring sites over the middle shelf are examined ice forms primarily in coastal regions and is advected over the southern and outer shelves ice drift from satellite data for two representative years 2003 and 2007 was 2 of local ncep wind speed and oriented 44 to the right of the winds r 2 0 25 measurements from 30 ice cores collected in 2006 2009 gave an average salinity of 5 62 0 88 and an average nitrate concentration of 0 99 0 83 m time series data collected at the biophysical moorings in the bering sea 1995 2012 were used to explore the evolution of the water column under ice at the northern mooring m8 the water column had mixed and cooled to 1 c prior to the arrival of ice little melt occurred after ice arrival at the other three moorings the ocean temperature was 2 4 c when ice arrived resulting in extensive melt melting ice freshened and cooled the upper water column resulting in stratification which persisted for 10 25 days wind induced water column mixing occurred more slowly under the ice than in ice free waters an estimated 1 4 m of ice melted with the first arrival of ice at the three southern moorings where the latent heat of fusion accounted for approximately half the observed cooling during ice retreat there appeared to be little ice melt around the southern two moorings but an estimated 0 8 m at m5 and m8 the extent of ice melt sets up the water column for the following summer

changes in the distribution and abundance of albatrosses in the eastern bering sea 1975 2010 abstract a number of marine species are showing poleward shifts in their distributions in response to climate warming three albatross species frequent the bering sea the laysan phoebastria immutabilis the black footed phoebastria nigripes and the endangered short tailed albatross phoebastria albatrus to determine if albatrosses changed their distribution or abundance in the eastern bering sea between 1975 and 2010 we examined at sea survey data using the north pacific pelagic seabird database within our study area all three species of albatross occurred most frequently in the waters of the aleutian islands in the eastern bering sea all three species were most abundant near the shelf break and in particular in the vicinity of the major submarine canyons in the shelf slope starting in the 1990s population densities increased for all three albatross species with a marked increase in the 2000s in the 2000s there was also an increase in the frequency at which albatrosses were recorded in the central and northern bering sea both black footed and short tailed albatrosses shifted the centers of their bering sea distributions northward the laysan albatross center of distribution shifted southward due to increased numbers along the southern shelf break but densities also increased northward we suggest that the observed changes in distribution and abundance of the three albatross species in the eastern bering sea may have been responses to an increase in the availability of squid their primary prey there additionally the expansion of the distribution of the short tailed albatross in the eastern bering sea may represent the reclamation of its previous range now that the population is beginning to recover from near extinction caused by over harvesting we suggest that predicted increases in ocean temperatures and northward movement of prey could result in albatrosses and other marine apex predators foraging farther north along the bering sea shelf and staying later in fall

the influence of several factors controlling the interactions between prince william sound alaska and the northern gulf of alaska abstract interactions between the circulation of prince william sound pws alaska and that of the continental shelf region of the northern gulf of alaska are studied numerically the focus is on the flow structure at hinchinbrook entrance he and montague strait ms and the associated pws interior circulation under various initial state and forcing configurations bottom topography inhibits flow into pws under barotropic conditions while stratification very much facilitates flow into pws layered flow develops at he and ms under baroclinic conditions with two four layers under march september stratification conditions in both baroclinic cases the top layer transports inflow and a cyclonic eddy develops over the central basin of pws westward wind the predominant direction enhances this upper layer inflow and the lower layer outflow eastward wind completely reverses the flow direction not only at he but also inside pws remarkably the total outflow through ms is consistently less than the

chronological correlations between the pilbara and kaapvaal cratons abstract the early geological development of the pilbara and kaapvaal cratons has many features in common attempts have been made to correlate geologically similar features of the two cratons and it has been postulated that they originated as contiguous components of a single continent vaalbara during this time the early geological histories of the pilbara and kaapvaal cratons are here compared in detail and the evidence that they were initially contiguous is assessed these comparisons indicate significant differences in the chronologies of magmatic events within the granite greenstone crusts of the pilbara and kaapvaal cratons in addition igneous correlatives emplaced during ca 2985 and 2782 ma magmatic events on the kaapvaal craton have not been identified on the pilbara craton and a well defined 2760 ma magmatic event manifest as widespread emplacement of granitic rocks into the pilbara granite greenstone basement and eruption of flood basalts of the lower part of the fortescue group is absent from the kaapvaal craton furthermore similarities in first and second order transgression regression cycles within the sedimentary supracrustal sequences may be attributable to global sea level fluctuations and thus may be irrevelant to the question of former contiguity however similarities in some aspects of the geological development of the pilbara and kaapvaal cratons imply that there were periods extending for between 60 and 200 ma of the archaean era during which the style of crust formation intensity of volcanism and subaerial erosion and magnitude of sea level fluctuations may have varied on a global scale such similarities include the overall duration of formation of the granite greenstone crusts from ca 3650 to 3100 ma the onset of craton wide erosion in the interval ca 3125 to 3000 ma the major episodes of flood basaltic volcanism between 2760 and 2680 ma the predominance of chemical carbonate and banded iron formation sedimentation between ca 2630 and 2440 ma and the transition to widespread clastic sedimentation within the interval 2440 to 2200 ma

hydrothermal controls on iron and lead mineralization on the farms leeuwbosch and cornwall thabazimbi district south africa abstract the paleoproterozoic malmani subgroup and penge formation transvaal supergroup exposed on the farms leeuwbosch and cornwall north of thabazimbi limpopo province south africa host hydrothermal pb ag cu zn and high grade hematite iron ore deposits which include the historic leeuwbosch lead mine based on ore petrography fluid inclusion and stable isotope analyses and geochemical modeling the structurally controlled stratabound leeuwbosch pb ag cu zn fe deposits formed from high salinity nacl cacl2 rich basinal brines with total salinities from 18 to 24 wt nacl equivalent which are similar to those found in the mississippi valley type mvt pb zn deposits the minimum formation temperatures homogenization temperatures for the lead deposits range between 120 and 185 c and the estimated formation conditions are 200 c at 1 kbar pressure stable isotope analyses of gangue siderite and calcite indicate that the deposits formed from base metal enriched brines derived from recycled seawater with 13cvs pdb from 0 46 to 3 17 and 18ovs smow from 2 95 to 1 79 hydrothermal transport of lead and silver as pbcl3 and agcl2 respectively took place at mildly acidic ph and elevated fo2 in the so42 predominance field extensive host rock interaction neutralized and reduced the ore fluid to precipitate galena hosting ag with chalcopyrite and sphalerite fluid inclusions in gangue quartz and calcite in the extensive structurally controlled and pervasive stratabound hydrothermal iron ore deposits on the farms leeuwbosch and cornwall chiefly consisting of high grade hematite with rare relict magnetite show a wide compositional variability due to episodic fluid mixing and successive hydrothermal activity in the presence of several distinct fluid end members total salinities of fluid inclusions in quartz from the hematite deposits range from 9 2 to 39 9 wt nacl eq with highly variable proportions of nacl and cacl2 and minimum formation temperatures are between 100 and 190 c the estimated formation conditions for the iron ore deposits are 175 c and 1 kbar stable isotopes of gangue calcite indicate that diagenetic fluids with 13cvs pdb from 3 33 to 2 09 and 18ovs smow from 2 52 to 5 60 and a second fluid with 13cvs pdb of 7 45 and 13cvs pdb of 17 45 were controlling the formation of the hematite deposits in agreement with oxidized conditions during hematite formation and characteristic host rock alteration patterns traced by carbon and oxygen isotopes the second low salinity fluid was derived from the overlying waterberg group sandstones and played an important role in the formation of the iron ore deposits in addition to high salinity diagenetic brines iron was leached from the bifs of the penge formation transported as fecl under mildly acidic conditions and likely deposited in response to the oxidation of the iron bearing fluids the lead and iron ore deposits formed by combinations of structural controls which influenced the regional fluid flow patterns and fluid compositions and fluid rock interaction with reactive carbonate lithologies of the malmani subgroup which acted as a sink for metals transported in acidic hydrothermal solutions

geochemistry of precambrian carbonates iv early paleoproterozoic 2 25 0 25 ga seawater in an effort to narrow down the first and second order variations in isotopic composition of the early paleoproterozoic 2 25 0 25 ga seawater we report a comprehensive study of mineralogy chemistry and isotopic composition of the malmani dolomite transvaal supergroup south africa duck creek dolomite wyloo group australia and bruce limestone member of the espanola formation huronian supergroup canada based on trace element data their diagenetic rank increases in the order duck creek bruce malmani the interpolation of alteration trends to best values yields an estimate of 0 70550 for 87sr86sr comparable to our previously published value of 0 70496 for 13c the measured range of 0 1 5 pdb is similar to that observed for phanerozoic marine carbonates in contrast the best 18o value for dolostones is 5 pdb depleted in 18o relative to phanerozoic counterparts but comparable to the estimates obtained by similar approach for archean facies the isotope geochemistry and mineralogy of bruce limestone member is consistent with the proposition that the sequence may have been deposited in a lacustrine environment possibly related to the recession of the brace glaciers if such interpretation proves unacceptable from a sedimentological standpoint the origin of the unusual isotopic signatures must be sought despite the above trace element interpretation in as yet unspecified post depositional alteration phenomena in contrast to phanerozoic carbonates the early paleoproterozoic as well as the previously described archean counterparts are enriched in mn and fe

origins of the subsurface ammonium maximum in the southeast bering sea abstract in the bering sea it has long been argued that ammonium rich bottom water from the middle shelf of bristol bay is tidally diffused seaward resulting in a mid depth ammonium tongue over the outer shelf weak horizontal mean flows in the region relative to an especially strong tidal component support this contention we examined the distribution of ammonium further north in the vicinity of the pribilof islands on the middle shelf bottom waters had concentrations of 4 7 mol kg 1 and over the outer shelf there was a mid depth ammonium tongue optimal multiparameter analysis of hydrographic data suggested that bottom waters from the middle shelf were prevalent across the outer shelf and could account for this ammonium tongue drifter tracks demonstrated that middle shelf water was incorporated into a westward flow along the shelf break south of st george island and mean flows derived from several decades of drifter tracks also show prominent cross shelf advection in the region this was consistent with a scalar argument suggesting that in the vicinity of the pribilof islands the seaward movement of middle shelf water and loss of nitrogen over the middle shelf was the result of advection rather than tidally driven lateral diffusion

an overview of the geology of the transvaal sequence and bushveld complex south africa the late archaean early proterozoic transvaal sequence is preserved within the transvaal kanye and griqualand west basins with the 2050 ma bushveld complex intrusive into the upper portion of the succession within the transvaal basin both transvaal and bushveld rocks are extensively mineralized the former containing large deposits of iron manganese asbestos andalusite gold fluorine lead zinc and tin ores and the latter some of the world s major occurrences of pge chromium and vanadium ores transvaal sedimentation began with thin predominantly clastic sedimentary rocks black reef vryburg formations which grade up into a thick package of carbonate rocks and bif chuniespoort ghaap taupone groups these lithologies reflect a carbonate bif platform sequence which covered much of the kaapvaal craton in reaction to thermal subsidence above ventersdorp aged rift related fault systems an erosional hiatus was followed by deposition of the clastic sedimentary rocks and volcanics of the pretoria postmasburg segwagwa groups within the three basins under largely closed basin conditions an uppermost predominantly volcanic succession rooiberg group loskop formation is restricted to the transvaal basin a common continental rift setting is thought to have controlled pretoria group sedimentation rooiberg volcanism and the intrusion of the mafic rocks of the rustenburg layered suite of the bushveld complex the dipping sheets of the rustenburg magmas cut across the upper pretoria group stratigraphy and lifted up the rooiberg lithologies to form the roof to the complex subsequent granitic rocks of the lebowa and rashoop suites of the bushveld complex intruded both upper rustenburg rocks and the rooiberg felsites

synthetic fluid inclusions xv tem investigation of plastic flow associated with reequilibration of fluid inclusions in natural quartz the nature and abundance of dislocations in quartz surrounding fluid inclusions were studied to obtain a better understanding of processes associated with fluid inclusion reequilibration synthetic fluid inclusions containing 10 wt nacl aqueous solution were formed in three samples at 700 c and 5 kbar one of the samples was quenched along an isochore to serve as a reference sample the other two samples were quenched along a p t path that generated internal pressures in excess of the confining pressure the two samples were held at the final reequilibration p t conditions of 625 c and 2 kbar for 30 and 180 days respectively following the experiments microstructures associated with fluid inclusions were examined with the tem quartz in healed fractures in the reference sample that was quenched isochorically shows a moderate dislocation activity quartz adjacent to reequilibrated fluid inclusions in the other two samples however showed a marked increase in dislocation activity compared to the un reequilibrated sample deformation of the inclusion walls occurred anisotropically by expansion of mobile dislocations in their slip systems dislocation expansion was controlled by glide in the rhombohedral planes 1 0 1 1 that was restricted to narrow zones 3 m in the immediate vicinity of the fluid inclusion walls outside of the healed fracture plane these plastic zones were observed after both short term 30 days and long term 180 days experiments and are attributed to hydrolytic weakening of quartz around fluid inclusions owing to diffusion of water into the quartz matrix during the experiment the close spatial association of submicroscopic water bubbles with dislocations and the rarity of water bubbles in the reference sample show clearly that in both the 30 and 180 day experiments reequilibration involves water loss from the fluid inclusions our results indicate that synthetic fluid inclusions in this study recover chemically and volumetrically even at relatively fast experimental loading rates such that internal stresses never reach the point of brittle failure the driving force for fluid inclusion deformation involves two related mechanisms plastic deformation of hydrolytically weakened wet quartz in the healed fracture and water leakage associated with preexisting and strain induced dislocations

evidence for platy hematite grains in sinus meridiani mars 1 midinfrared 1600 200 cm 1 spectral data received from the mars global surveyor thermal emission spectrometer mgs tes have provided evidence for a large hematite bearing fe2o3 deposit in sinus meridiani mars we report here the results of a laboratory spectroscopic investigation of 24 hematite samples including polycrystalline hand samples massive and schistose textures single crystal hand samples and particle size fractions single crystal and polycrystalline discrete particles laboratory midinfrared analyses of crystallographically oriented hematite samples suggest that the hematite emission in sinus meridiani sm is predominantly from the crystallographic c face of hematite this observation implies the presence of platy hematite particles with the plate face being the crystallographic c face the observations are consistent with a formational model where the platy gray hematite originated as an iron oxide chemically precipitated from fe rich aqueous and or hydrothermal solutions on early mars that was buried recrystallized to platy hematite and subsequently reexposed as lenses of schistose hematite in a friable consolidated stratigraphic unit unconsolidated platy hematite particles are also likely to be present as a physical weathering product of the schistose hematite lenses

recent climate variation in the bering and chukchi seas and its linkages to large scale circulation in the pacific the thermal state of the bering sea exhibits interdecadal variations with distinct changes occurred in 1997 1998 after the unusual thermal condition of the bering sea in 1997 1998 we found that the recent climate variability 1999 2010 in the bering sea is closely related to pacific basin scale atmospheric and oceanic circulation patterns specifically warming in the bering and chukchi seas in this period involves sea ice reduction and stronger oceanic heat flux to the atmosphere in winter the atmospheric response to the recent warming in the bering and chukchi seas resembles the north pacific oscillation npo pattern further analysis reveals that the recent climate variability in the bering and chukchi seas has strong covariability with large scale climate modes in the pacific that is the north pacific gyre oscillation and the central pacific el nino in this study physical connections among the recent climate variations in the bering and chukchi seas the npo pattern and the pacific large scale climate patterns are investigated via cyclostationary empirical orthogonal function analysis an additional model experiment using the national center for atmospheric research community atmospheric model version 3 is conducted to support the robustness of the results

sea ice impacts on spring bloom dynamics and net primary production in the eastern bering sea 1 in the eastern bering sea changes in sea ice have been implicated in recent major upper trophic level shifts however the underlying relationships between sea ice and primary producers have not been well tested here we combine data from multiple satellite platforms reanalysis model results and biophysical moorings to explore the dynamics of spring and summer primary production in relation to sea ice conditions in the northern bering sea sea ice consistently retreated in late spring leading to ice edge phytoplankton blooms in cold 0 1 c waters however in the southeastern bering sea sea ice retreat was far more irregular although this did not significantly alter bloom timing late retreat led to blooms at the ice edge while early retreat led to blooms in open waters that were warmer 5 4 c and 70 more productive early sea ice retreat also led to higher productivity in summer likely due to weaker thermal stratification overall annual net primary production during warm years of early sea ice retreat was enhanced by 40 50 compared to years with late sea ice retreat in the southeastern bering sea these findings suggest the potential for future sea ice loss to enhance overall carrying capacity of the southeastern bering sea ecosystem consistently warm blooms in the future may also channel more energy flow toward the pelagic rather than benthic environment to date however neither sea ice extent nor the timing of its retreat have undergone long term changes in the eastern bering sea

sedimentary records of bulk organic matter and lipid biomarkers in the bering sea a centennial perspective of sea ice variability and phytoplankton community abstract in this study organic geochemical analyses of two sediment cores bl16 and lv63 23 recovered from the western bering sea were carried out to examine the sea ice variability and its relationship to phytoplankton community evolution over the past century bulk stable organic carbon isotopic composition 13ctoc showed pronounced depletion on the northern shelf since the late 1970s indicating greater terrigenous organic matter om under warming during recent decades variation in sedimentary om in the southward core was closely associated with marine primary productivity and regional deposition processes arctic sea ice proxy ip25 throughout the two cores with different temporal profile patterns demonstrated sea ice presence with the spatio temporal variability across the study area over the past century the phytoplankton marker ip25 index pip25 a proxy for estimating semi quantitatively sea ice concentrations reflected a decreased sea ice cover with more distinct interannual fluctuations between 0 7 and 0 2 especially in core bl16 after the late 1970s coinciding with the recent warming scenario increased concentrations of phytoplankton biomarkers brassicasterol and dinosterol and their ratios as well as the pip25 record in core bl16 indicated a synchronous variability of reduced sea ice cover with the enhancement of phytoplankton productivity since the late 1970s these results suggested a coupled interaction of the sea ice condition and planktonic ecosystem in the north bering shelf our results also revealed recent since the 2000s spatial heterogeneity in sea ice coverage between the northern and southern parts of the bering sea

experimental evidence for non redox transformations between magnetite and hematite under h2 rich hydrothermal conditions abstract transformations of magnetite fe ii fe 2 iii o 4 to hematite fe 2 iii o 3 and vice versa have been thought by many scientists and engineers to require molecular o 2 and or h 2 thus the presence of magnetite and or hematite in rocks has been linked to a specific oxidation environment however the availability of reductants or oxidants in many geologic and industrial environments appears to have been too low to account for the transformations of iron oxides through redox reactions here we report the results of hydrothermal experiments in mildly acidic and h 2 rich aqueous solutions at 150 c which demonstrate that transformations of magnetite to hematite and hematite to magnetite occur rapidly without involving molecular o 2 or h 2 fe 3 o 4 mt 2h aq fe 2 o 3 hm fe aq 2 h 2 o the transformation products are chemically and structurally homogeneous and typically occur as euhedral single crystals much larger than the precursor minerals this suggests that in addition to the expected release of aqueous ferrous species to solution the transformations involve release of aqueous ferric species from the precursor oxides to the solution which reprecipitate without being reduced by h 2 these redox independent transformations may have been responsible for the formation of some iron oxides in natural systems such as high grade hematite ores that developed from banded iron formations bifs hematite rich deposits formed on mars corrosion products in power plants and other industrial systems

variability of physical and chemical characteristics along the 70 m isobath of the southeastern bering sea abstract from observations of ice cover temperature salinity currents and nitrate it is evident that along shelf variability was significant over the middle shelf of the eastern bering sea but less distinct than that observed in the cross shelf domains along the 70 m isobath three zones were evident in the summer the southeastern cold pool centered at 57 n an intermediate zone consisting of warmer water with weaker stratification and the northern cold pool extending northward from 58 n small scale 20 km horizontal features that persisted for months were common nutrient concentrations were related to salinity and were replenished more uniformly over the southern shelf than north of the pribilof islands although mean currents were weak 1 cm s 1 short energetic advective events impacted the temperature and salinity structure

carbon and oxygen isotopic covariations in hydrothermal calcites isotopic covariations of carbon and oxygen in hydrothermal calcites are quantitatively modeled in terms of the following three mixing processes 1 mixing between two different fluids which leads to the precipitation of calcite 2 mixing between fluid and rock a calcite precipitation due to fluid rock interaction b secondary alteration of primary calcite by interaction with a subsequent fluid the models are derived from mass balance equations a distinction among the three mixing processes can be made on a 13c vs 18o diagram which places important constraints on the genesis of hydrothermal mineralization the variables which control the ultimate isotopic composition of hydrothermal calcites include the composition of the initial fluid and the wallrock temperature and dissolved carbon species owing to significant temperature dependent fractionation effects during equilibrium precipitation of calcite from a hydrothermal fluid the mixing processes may be distinguished by telltale patterns of isotopic data in 13c vs 18o space in particular caution must be exercised in postulating the fluid mixing as the cause for mineral deposition this is demonstrated for hydrothermal pb zn deposits in the western harz mountains germany a positive correlation between 13c and 18o values is observed for calcites from the bad grund deposit in the upper harz two sample profiles through calcite veins show similar correlations with the lowest values at the center of the veins and the highest values at the vein margins because the correlation array has a greater slope than for calcite precipitation at equilibrium in a closed system and because fluid mixing may not proceed perpendicular to the vein strike it is assumed that a fluid rock interaction is responsible for the observed correlation and thus for the precipitation of calcite a deep seated fluid is inferred with a 13c value of 7 and a 18o value of 10 as well as h2co3 as the dominant dissolved carbon species precipitation temperatures of the calcites are estimated to be about 280 170 c quite different isotopic distributions are observed for calcites from the st andreasberg deposit in the middle harz an alteration model is suggested based mainly on the isotopic distribution through a calcite vein in addition to a primary fluid which has the same isotopic composition as that in the bad grund deposit and thus seems to be responsible for the precipitation of calcite associated with sulfides an evolved hco 3 dominant subsurface fluid with 13c about 20 15 and 18o 0 is deduced to alter the primary calcite at low temperatures of 70 40 c

sedimentation rates basin analysis and regional correlations of three neoarchaean and palaeoproterozoic sub basins of the kaapvaal craton as inferred from precise u pb zircon ages from volcaniclastic sediments abstract calculation of sedimentation rates of neoarchaean and palaeoproterozoic siliciclastic and chemical sediments covering the kaapvaal craton imply sedimentation rates comparable to their modern facies equivalents zircons from tuff beds in carbonate facies of the campbellrand subgroup in the ghaap plateau region of the griqualand west basin transvaal supergroup south africa were dated using the perth consortium sensitive high resolution ion microprobe ii shrimp ii dates of 2588 6 ma and 2549 7 ma for the middle and the upper part of the nauga formation indicate that the decompacted sedimentation rate for the peritidal flat to subtidal below wave base stratifera and clastic carbonate facies southwest of the ghaap plateau at prieska was of up to 10 m ma when not corrected for times of erosion and non deposition dates of 2516 4 ma for the upper gamohaan formation and 2555 19 for the upper monteville formation indicate that some 2000 m of carbonate and subordinate shale sedimentation occurred during 16 ma to 62 ma on the ghaap plateau for these predominantly peritidal stromatolitic carbonates decompacted sedimentation rates were of 40 m ma to over 150 m ma bubnoff units the mixed siliciclastic and carbonate shelf facies of the schmidtsdrif subgroup and monteville formation accumulated with decompacted sedimentation rates of around 20 b for the kuruman banded iron formation a decompacted sedimentation rate of up to 60 b can be calculated thus for the entire examined deep shelf to tidal facies range archaean and phanerozoic chemical and clastic sedimentation rates are comparable four major transgressive phases over the kaapvaal craton followed by shallowing upward sedimentation can be recognized in the prieska and ghaap plateau sub basins in griqualand west and partly also in the transvaal basin and are attributed to second order cycles of crustal evolution first order cycles of duration longer than 50 ma can also be identified the calculated sedimentation rates reflect the rate of subsidence of a rift related basin and can be ascribed to tectonic and thermal subsidence comparison of the calculated sedimentation rates to published data from other archaean and proterozoic basins allows discussion of general precambrian basin development siliciclastic and carbonate sedimentation rates of archaean and palaeoproterozoic basins equivalent to those of younger systems suggest that similar mechanical chemical and biological processes were active in the precambrian as found for the phanerozoic particularly for stromatolitic carbonates matching modern and neoarchaean sedimentation rates are interpreted as a strong hint of a similar evolutionary stage of stromatolite building microbiota the new data also allow for improved regional correlations across the griqualand west basin and with the malmani subgroup carbonates in the transvaal basin the nauga formation carbonates in the southwest of the griqualand west basin are significantly older than the gamohaan formation in the ghaap plateau region of this basin but are in part correlatives of the oaktree formation in the transvaal and of parts of the monteville formation on the ghaap plateau

the early proterozoic mississippi valley type pb zn f deposits of the campbellrand and malmani subgroups south africa pb zn f deposits occur in the very late archaean 2 55 ga shallow marine dolostone of the relatively undeformed campbellrand and malmani sub groups which are overlain unconformably by the lower proterozoic postmasburg and pretoria group siliciclastics they consist of stratiform deposits formed by replacement and porosity filling as well as pipes ring shaped and irregular bodies associated with collapse breccia in the transvaal basin the latter were generated during the karst denudation period between the deposition of the chuniespoort group ending at 2 4 ga and of the pretoria group starting at 2 35 ga a part of these mineralisations were overprinted by the metamorphism of the bushveld complex intrusion at 2 06 ga in the transvaal basin the age of the mineralisation is constrained between the start of the pretoria group deposition and the bushveld intrusion it is concluded that although most of the mineralisations are characteristic of the mississippi valley type some of the northernmost occurrences rich in siderite are less typical a classic genetic model is proposed in an environment characterised by tensional tectonics and basin development brines of basinal origin were heated by circulation into pre chuniespoort rocks leached metals from the rocks they permeated and rose as hydrothermal plumes at relatively shallow depth they deposited minerals after mixing with water of surficial origin

the thabazimbi murchison lineament of the kaapvaal craton south africa 2700 ma of episodic deformation the thabazimbi murchison lineament is a prominent tectonic feature extending for approximately 500 km in a nne ssw direction across the kaapvaal craton the lineament has a tectonic history of more than 2 5 ga because it appears to form and or influence the boundary between the archaean granite greenstone terrain of the kaapvaal craton and the southern margin of the high grade terrain of the limpopo mobile belt the northern margin of the archaean proterozoic transvaal basin the southern margin of the mesoproterozoic waterberg basin and has probably also influenced the emplacement of the mesoproterozoic bushveld complex mesozoic karoo basalts and sediments formed the springbok flats these lavas erupted into half graben structures formed by the normal reactivation of the previously strike slip zebedelia fault part of the thabazimbi murchison relay system the lineament is cut by a mesozoic dyke swarm associated with the break up of gondwana

effects of el nino southern oscillation and north pacific weather patterns on interannual variability in the subarctic bering sea extraordinary interannual variability in ice cover air and sea surface temperatures sst and surface winds in the eastern bering sea have been observed over recent years to investigate the causes of this interannual variability long term 20 30 years time series of air ocean and ice parameters from the bering sea were cross correlated with the southern oscillation index soi an index of el nino southern oscillation enso events in the tropical southern hemisphere as well as with an index of pacific north american pna events in the north pacific five to thirty percent of the interannual variability linear regression with various smoothing in the bering sea data sets with the exception of surface winds is explained by the soi when the bering sea data lags the soi for comparison 29 52 of the variability in the sst off south america can be explained by the soi the signs of the correlations all suggest that warming in the bering sea follows negative anomalies in the soi that is enso events positive anomalies in the soi which tend to precede el nino events were found to precede cooling in the bering sea significant correlation persists for 18 20 months higher order polynomial regressions between the soi and bering sea data can explain up to 40 of the bering sea variability the mechanism for the connection between enso events and bering sea interannual variability appears to be of atmospheric nature and is associated with the winter position and intensity of the aleutian low the aleutian low is intensified and eastward of normal in association with el nino i e warm events but is weaker and westward of normal during cool events it is the regional winds associated with the variable position of the aleutian low that cause the regional warming and cooling events this seesaw in the aleutian low is also used to explain the out of phase ice conditions between the bering sea and the sea of okhotsk pna events are also associated with an intensified aleutian low as well as 700 mbar ridging over northwestern north america causing southerly flow over alaska however while correlation between enso events and pna was significant the correlation between the bering sea and pna was marginal except for surface winds here surface winds from the north were significantly correlated with the pna this apparent inconsistency as well as the lack of correlation of surface winds with the soi is explained by the lack of preferred site of the aleutian low during enso events this lack of preferred site helps explain why the major el nino event of 1982 1983 had little apparent effect on the bering sea

the mount gibson banded iron formation hosted magnetite deposit two distinct processes for the origin of high grade iron ore the mount gibson banded iron formation lies within the windanning formation of the luke creek group which is found in almost all greenstone belts throughout the murchison province the banded iron formation bif typically consists of alternating bands of magnetite and microcrystalline quartz chert with rare carbonaceous and iron silicate rich shale partings and layers and rare thin fine grained tuff bands owing to repetition by isoclinal folding and attenuation by faulting the true thickness of the mount gibson bif is unknown but appears to be on the order of 100 m although the mount gibson bif is typical of many algoma type iron formations situated within a greenstone belt on an archean craton it is also similar to hamersley type bif in petrology areal extent and ore genesis high grade hematite deposits formed within bif were thought to have formed by the supergene leaching of chert from typical cherty bif recent evidence suggests that at least some of these deposits are formed by hypogene replacement of chert by carbonates with subsequent supergene leaching of the carbonate and accessory minerals and oxidation of magnetite to hematite magnetite carbonate bif in which there is clear evidence of hydrothermal replacement of chert by carbonate forms distinctive magnetite goethite ore with magnetite locally persisting to the surface mount gibson shows clear evidence of the formation of high grade ore by this process but also contains high grade hematite ore and chert free bif that show no evidence of the hypogene replacement of chert high grade hematite occurrences up to 1 km in strike length are found within the weathered zone overlying the magnetite bif at mount gibson and continue into unweathered chert free bif at depth that show no evidence of hydrothermal carbonate or supergene enrichment the cherty bif shows sharp contacts against chert free bif and high grade ore even when strongly weathered this suggests that deep saprolitic in situ high grade ore may be produced by different processes including hydrothermal replacement of chert mesobands by carbonates with subsequent supergene leaching of the carbonate and by the oxidation of chert free bif in which chert bands either never developed or were apparently removed during diagenesis neither model requires supergene selective leaching of quartz chert during deep weathering

regional scale metasomatism in the fortescue group volcanics hamersley basin western australia implications for hydrothermal ore systems mafic to intermediate volcanic rocks of the fortescue group form the lowermost stratigraphic unit of the 100 000 km2 hamersley basin on the southern margin of the archaean pilbara craton western australia these represent one of the oldest 2 8 2 7 ga known examples of a continental flood basalt sequence a regional burial metamorphic gradient extends across the basin from prehnite pumpellyite facies in the north to epidote actinolite greenschist facies in the south and west superimposed on this metamorphic gradient regional scale metasomatism has affected extensive areas of the fortescue group metasomatized mafic lavas are characterized by well developed assemblages dominated by pumpellyite quartz or epidote quartz associations the mineral associations of metasomatic domain types broadly match the distribution of metamorphic isograd indicator minerals with a southward and westward increase in the proportion of epidote a continuum exists between least altered rocks that preserve the regional metamorphic signature and the most intensely altered metasomatized rocks metasomatism is essentially continuous over a stratigraphic strike length of 100 km and across a strike width of 20 km regionally metasomatically altered volcanic rocks occur widely across the hamersley basin and its outliers over an area of some 450 km by 200 km metasomatic alteration is most conspicuous in the lower grade metamorphic zones because pumpellyite and epidote rich rocks are green to yellow green in outcrop whole rock geochemical data indicate that metasomatism is associated with strong depletions in alkalis na k li rb alkali earths mg sr be ba and heavy first transition series metals mn fe co ni cu zn with a significant enrichment in si calcium shows more variable mobility such geochemical trends particularly depletions in fe mn and base metals co ni cu zn together with the metasomatic mineral assemblages are comparable with those associated with the sub sea floor circulation of seawater particularly in relation to the metal depleted root zones of base metal deposits petrographic features indicate that the development of metasomatic mineral associations post dates the formation of regional metamorphic assemblages consequently it is interpreted that the hydrothermal fluid flowed through the buried pile after sufficient time to allow for the metamorphic mineral assemblages to approach equilibrium with ambient p t conditions the hydrothermal depletion in fe observed across the fortescue group mafic lavas is intriguing given the abundance of iron ore in the overlying hamersley group and a possible connection cannot be ignored furthermore the scale of fluid flow observed in the fortescue group which occurred through zones of inherent permeability such as vesicular and brecciated lava flow tops without the aid of major cross cutting structures has significant implications for the size of metasomatic systems in other mafic volcanic terranes with potential consequences for the exploration for hydrothermal mineral deposits

circulation of prince william sound alaska the circulation of prince william sound alaska is described using hydrographic 1974 1989 current meter 1977 1979 and acoustic doppler current profiler 1986 1990 observations from both the sound and the adjacent gulf of alaska ancillary data include data for winds freshwater runoff and satellite tracked drifters prince william sound is a small inland sea in that it is wide enough to have appreciable horizontal cyclonic circulation it is also a fjord in that it has basin depths to 700 m but is stilled at 180 m to the open ocean the general circulation pattern is defined by a portion of the westward flowing alaska coastal current on the gulf of alaska shelf that enters prince william sound through hinchinbrook entrance and transits the sound from east to west before exiting through montague strait and rejoining the coastal current however there is much variability in this circulation especially in the transport through hinchinbrook entrance in addition some of the water entering the sound becomes involved in the cyclonic circulation in the northern sound and so has a longer residence time the circulation is strongly mediated by seasonal and interannual variations in winds and freshwater runoff as well as by local topography both inside and outside the sound in winter the strong cyclonic winds over the gulf of alaska cause coastal downwelling and strong flow in the upper layers into prince william sound through hinchinbrook entrance and out through montague strait in summer the downwelling ceases allowing subsurface denser water to rise above the sill and flow into the sound through the bottom layers of hinchinbrook entrance we conclude that the best transport data came from montague strait from which we estimate that 40 of the volume of prince william sound is flushed in summer may september this estimated volume rises to about 200 in winter october april

tracking the arctic s shrinking ice cover another extreme september minimum in 2004 1 satellite passive microwave observations document an overall downward trend in arctic sea ice extent and area since 1978 while the record minimum observed in september 2002 strongly reinforced this downward trend extreme ice minima were again observed in 2003 and 2004 although having three extreme minimum years in a row is unprecedented in the satellite record attributing these recent trends and extremes to greenhouse gas loading must be tempered by recognition that the sea ice cover is variable from year to year in response to wind temperature and oceanic forcings

the carbonates of the transvaal and griqualand west sequences of the kaapvaal craton with special reference to the lime acres limestone deposit the campbell group carbonates were deposited in a basin transgressing from southwest to the east and to northeast at the southwestern margin of the kaapvaal craton in griqualand west mainly tidal flat carbonates and shallow marine deposits are found to be followed by subtidal carbonates marking the slow transgression north of the griquatown fault where the center of the griqualand west sub basin developed continuous subsidence matched by stromatolitic carbonate growth led to accumulation of the thickest carbonate pile 2000 m there the largest limestone deposits of south africa are located the deposit at lime acres and mining operations of the ppc lime ltd are described and discussed in respect to diagenetic processes that permitted limestone preservation

organic geochemistry applied to environmental assessments of prince william sound alaska after the exxon valdez oil spill a review abstract organic geochemistry played a major role in the environmental assessments conducted following the exxon valdez oil spill which occurred on march 24 1989 and released about 258 000 bbls 41 million liters of alaska north slope crude oil into prince william sound geochemical analyses of more than 15 000 sediment tar and biological samples and about 5000 water samples provide the largest database yet collected on oil spill chemistry and we review the results here the marine environment of the sound has a complex background of petrogenic pyrogenic and biogenic hydrocarbons from natural and anthropogenic sources geochemical evaluation of the fate and effects of the spilled oil required that this oil and its residues be distinguished from the background a variety of molecular and isotopic techniques were employed to identify various hydrocarbon sources and to distinguish quantitatively among mixed sources in the samples although the specific criteria used to distinguish multiple sources in the region affected by the exxon valdez spill are not necessarily applicable to all spill situations the principles that governed their selection are distributions of polycyclic aromatic hydrocarbons pah and dibenzothiophenes distinguish exxon valdez oil and its weathered residues from background hydrocarbons in benthic sediments ratios of c 2 dibenzothiophene c 2 phenanthrene and c 3 dibenzothiophene c 3 phenanthrene were particularly useful carbon isotopes and terpane distributions distinguished exxon valdez residues found on shorelines from tars from other sources diesel and diesel soot were identified by the absence of alkylated chrysenes and a narrow distribution of n alkanes whereas pyrogenic products were distinguished by the dominance of 4 to 6 ring pah over 2 to 3 ring pah and by the dominance of non alkylated over alkylated homologues of each pah series the presence of 18 h oleanane in benthic sediments coupled with its absence in exxon valdez oil and its residues confirm another petrogenic source results of geochemical studies suggest that the petrogenic component in the background of benthic sediments is derived from oil seeps in the eastern gulf of alaska in 1990 and 1991 exxon valdez residues generally forming a small increment to the pre spill background were found to be only sporadically distributed in some shallow near shore sediments adjacent to shorelines that had been heavily oiled in 1989 in 1994 occurrences of exxon valdez tars on shoreline surfaces were rare although residues could be found buried in shoreline sediments at some isolated locations along the spill path where they were protected from wave action spilled oil residues collected 16 months after the spill were degraded on average by nearly 50 shoreline residues from sources other than the spill were also identified and are widespread throughout the sound these residues include 1 geochemically distinct tars and oils imported from california oil fields to alaska for fuel and construction purposes prior to the discovery of the cook inlet and north slope oil fields 2 diesel and diesel soot and 3 more highly refined products of the more than 2700 chemical analyses of biological samples of higher life forms fish birds and mammals about 150 6 indicate recognizable residues of exxon valdez oil which were identified by their distribution of polycyclic aromatic hydrocarbons pah most of these samples 138 were collected in 1989 and most were associated with external surfaces or the gastrointestinal tract rarely do internal tissues or fluids contain recognizable fingerprints of spilled oil this observation includes samples from marine mammals that were visibly oiled externally other hydrocarbon sources including diesel and a non petroleum artifact that occurs when concentrations of individual pah are at or near their method detection limit are also identified in biological samples

evidence of prolonged aragonite undersaturations in the bottom waters of the southern bering sea shelf from autonomous sensors abstract the southeastern shelf of the bering sea is a dynamic area that experiences seasonal variability in primary production and remineralization of organic matter both of which control the carbon biogeochemistry of the water column surface water partial pressure of carbon dioxide p co 2 is greatly reduced in summer by biological production which increases carbonate mineral saturation states in contrast the export of large quantities of organic matter from surface blooms drives an active remineralization loop that sharply increases p co 2 near the bottom lowering ph and suppressing new observations from moored biogeochemical sensors in 2011 showed that seasonal net community production lowers surface water p co 2 causing large gradients between the ocean and atmosphere that are sustained throughout the summer confirming that these waters likely remain supersaturated with respect to aragonite throughout the open water season on the other hand moored sensors deployed near the bottom showed that p co 2 levels exceed 500 atm by early june and remain at these high levels well into the autumn months indicating that the bottom waters are likely continuously undersaturated in aragonite for at least several months during each year only a small fraction of the increased p co 2 can currently be attributed to the intrusion of anthropogenic co 2 from the atmosphere while the majority is due to natural respiration processes the biological impacts along with the timing and duration of these undersaturation events could play a role in the development of larval and juvenile calcifiers in the region and will change as anthropogenic co 2 concentrations continue to rise