identification et distribution des grandes masses d eau dans les mers du labrador et d irminger the main deep water masses present at the time of the css hudson cruises in labrador and irminger seas in june 1990 and october november 1991 have been identified using characteristic temperatures t and salinities s the purpose of this study was to establish the transfer functions between micropaleontological assemblages of top sediments and thermohaline characteristics of water masses the water mass at the top of the labrador sea labrador sea water lsw is formed after intense movements of winter convection in the first 900 m depth of the water column below that depth the lsw parameters reach a double minimum s 34 80 and t 2 9 c only the sediments located on the continental slopes of greenland and labrador between depths of 500 and 1500 m are in contact with the lsw below the lsw the superior fraction of the north east atlantic deep water neadw1 is characterized by a temperature maximum 3 3 c and as such is distinguishable from the inferior fraction neadw2 the latter is ch

diatoms as hydrographic tracers example from bering sea sediments variations in the distribution of diatom species in surface sediments mirror distinct hydrographic regimes on the bering shelf spring salinity fronts divide the water column into four zones with different vertical structures and different productivity patterns four assemblages of diatoms can be distinguished in sediments underlying the zones

palynomorph distribution in recent sediments from the labrador sea surface sediments from the labrador sea and baffin bay have been examined for their palynomorph content pollen and spore assemblages reflect the vegetation zones of eastern canada although long distance atmospheric transport results in over representation of pinus and spores a linear decrease of pollen input is observed with distance from the source vegetation the abyssal domain receives less than 2 of the initial input the abundance of dinoflagellate cysts reflects a relatively high primary productivity in surface water masses which seems proportional to the benthic productivity as shown by the concentrations of organic linings of foraminifers the relative abundance of dinoflagellate cyst taxa and principal component analysis led to the definition of three assemblages that can be related to sea surface conditions and current pattern the modern distribution of dinoflagellate cysts was used to interpret assemblages recovered in five box cores from the deep labrador sea results reveal important ch

halide systematics in comparison with nutrient distributions in sites 1033b and 1034b saanich inlet odp leg 169s abstract the entire suite of halogens was measured in the pore fluids of hole 1033b and 1034b from saanich inlet odp leg 169s the fast sedimentation rates and large amount of organic carbon burial coupled with anoxia of the overlying waters promotes an advanced stage of diagenesis within the sediment column chloride interstitial water profiles suggest salinity variations within the waters of saanich inlet concentration profiles for iodide and bromide support the argument that they are produced through the degradation of organic matter although the concentration increases in i and br indicate that these halides are not regenerated in similar proportions to marine organic matter it appears that iodide and bromide are regenerated to similar degrees within the sediment column and in similar proportions to the sediment halide concentrations fluoride porewater values show a complicated pattern most likely caused by secondary reactions involving complexation with mg2 carbonate fluorapatite precipitation carbonate mineral diagenesis and or uptake into alumino silicate minerals

estimating trajectory of free overfall nappe the upper surface profile of a rectangular free overfall is modeled using the free fall parabolic equation empirical and semiempirical relationships for the unknown quantities in this equation are presented it was found that the resulting simple and straightforward method adequately predicts the position of the upper nappe surface a relationship for establishing the vertical thickness of the nappe due to another researcher is given thus enabling the entire nappe profile from the brink to be described the equations are of use in the design of spillways and diversionary structures utilizing a free overfall

living coccolithophore communities in the norwegian greenland sea and their record in sediments abstract investigation of epipelagic coccolithophore communities along a transect from the voring plateau off norway to scoresbysund east greenland and comparison with coccolith assemblages in underlying surface sediments reveal that sedimentation of coccoliths is dependent on the following factors 1 composition of the coccolithophore communities and their bloom phases 2 grazing and selective destruction by zooplanktonic organisms 3 type of vertical flux in fecal pellets and 4 varying carbonate dissolution in different water masses dissolution increases towards the boundaries of carbonate sedimentation as a result the original composition of the living communities becomes increasingly obscured in the impoverished taphocoenoses however differential resistance to dissolution of the two primary calcareous nannoplankton species emiliana huxleyi and coccolithus pelagicus is such that occurrence and ratio of the two species in surface sediments reflect the various water masses in the norwegian greenland sea

high molecular weight polycyclic aromatic hydrocarbons in hydrothermal petroleums from the gulf of california and northeast pacific ocean hydrothermal petroleums and heavy tars have been analyzed for polycyclic aromatic hydrocarbons pah with molecular weights greater than that of coronene 300 da samples from the hydrothermal systems in the guaymas basin gulf of california and in the escanaba trough and middle valley northeastern pacific were analyzed by gas chromatography mass spectrometry and high pressure liquid chromatography with diode array absorbance detection mass spectra and fluorescence spectra were used to characterize the compounds several large pahs with six and more rings were identified among the heavy pah production routes via one ring build up and scholl condensation are proposed to explain the observed structures the variations in pah concentrations and distributions between samples from different locales are a consequence of the hydrothermal conditions of generation migration and post depositional alteration

chlorine stable isotopes and halogen concentrations in convergent margins with implications for the cl isotopes cycle in the ocean abstract chlorine stable isotopes 37cl and halogen concentrations e g br cl in 168 pore fluids and 23 serpentines and other solids from three subduction zones the nankai trough costa rica and mariana forearc provide critical information on fluid sources flow paths and reaction conditions the 37cl values of pore fluids at the nankai and costa rica subduction zones are significantly more negative minimum 7 8 2 0 3 than seawater value 0 at nankai trough the minimum 37cl value is situated below the decollement and evolves laterally from 7 8 at the most arcward odp site 808 to 7 1 at site 1174 2 km seaward from site 808 and to 5 8 at the reference site 1173 at costa rica along the decollement the minimum 37cl value evolves from 5 5 at the most arcward odp site 1040 1254 to 3 2 at site 1043 1255 1 km seaward and to 0 at the reference site 1039 1253 at both subduction zones the br cl ratios are higher than the seawater value 1 5 10 3 and also show seaward evolutions these pore fluids originate from greater depth arcward at 250 c from hydrous mineral formation that preferentially incorporates 37cl and excludes br in contrast the 37cl values in the pore fluids at the mariana serpentine mud volcanoes are higher than the seawater value 0 3 to 1 8 and the br cl ratios are lower these pore fluid values and the high cl concentrations with positive 37cl values 1 2 to 6 0 in the serpentines support that the upwelling pore fluid originates from dehydration of the subducting slab that releases water enriched in 37cl into the fluid phase the constancy of the ocean 37cl over the past 200 ma suggests that the isotopically fractionated chlorine in serpentinites and the cl exchanged in subduction zones are efficiently recycled back into seawater if the efficiency is

sea ice switch mechanism and glacial interglacial co2 variations 1 a physical mechanism is proposed for the glacial interglacial variations in the rate of vertical mixing and in sea ice cover in the southern ocean such variations were postulated without an explanation by toggweiler 1999 and stephens and keeling 2000 who used them to explain the glacial interglacial co2 variations in the physical mechanism explored here initially given by gildor and tziperman 2001b changes in the stratification of the southern ocean due to the cooling of north atlantic deep water nadw during glacial maxima reduce the rate of vertical mixing of the surface water with the deep water the changed temperature of the nadw arriving to the southern ocean and the reduced vertical mixing there also increase the southern ocean sea ice cover during glacial maxima these vertical mixing and sea ice cover changes are shown to be a natural result of the sea ice switch mechanism of the glacial cycles a box model of the climate system is used to demonstrate the above physical mechanism and its effect on the atmospheric co2 because of the uncertainties in the exact dependence of the vertical mixing on vertical stratification it is impossible to quantify the exact separate contribution of reduced vertical mixing and larger sea ice cover to the glacial co2 variations the co2 variations are not essential to the existence of the glacial cycles in the sea ice switch mechanism yet they are shown to amplify the glacial interglacial variability consistent with the view of the role of co2 deduced from proxy observations

millennial scale ice rafting events and hudson strait heinrich like events during the late pliocene and pleistocene a review abstract various types of abrupt millennial scale climate variability such as dansgaard oeschger and heinrich events characterized the last glacial period over the last decade a number of studies demonstrated that such millennial scale climate variability was not limited to the last glacial but inherent to quaternary climate here we review the occurrence and origin of millennial ice rafting events in the north atlantic during the late pliocene and pleistocene last 3 4 ma with a special focus on north atlantic hudson strait hs heinrich like events we show that heinrich layers 5 4 2 and 1 in marine sediment cores from across the north atlantic all bear the organic geochemical fingerprint of the hudson area using this framework and combining previously published results detailed investigations into the organic and inorganic chemistry of ice rafted debris ird found across the north atlantic demonstrate that prior to mis 16 650 ka ird in the north atlantic did not originate from the hudson area of northern canada the signature of this early ird is distinctly different compared to that of hs heinrich layers rather ice rafting events during the late pliocene and early pleistocene predominantly emanated from the calving of the greenland and fennoscandian ice sheets and possibly minor contributions from local ice streams from the north american and british ice sheets compared to north atlantic hs heinrich events these early pleistocene ird events had a limited impact on surface water characteristics in the north atlantic north atlantic hs heinrich like events first occurred during mis 16 at the same time the dominant frequency in silicate rich ird accumulation shifted from the obliquity 41 ka to a 100 ka frequency across the north atlantic iceberg survivability or a change in iceberg trajectory likely did not control this change in ird regime these results lend further support for the existing hypothesis that an increase in size thickness of the laurentide ice sheet controls the occurrence of north atlantic hs heinrich events favoring an internal dynamic mechanism for their occurrence

benthic foraminiferal assemblages in labrador sea sediments relations with deep water mass changes since deglaciation surface sediment samples from the labrador sea and the irminger and iceland basins have been analysed for their benthic foraminiferal content to define the relationship between benthic foraminiferal assemblages and bottom water characteristics on the shelf 301 530 m and the upper slope 1364 and 1980 m the distribution of assemblages is complex and appears related to diversified microhabitats in the deep sea domain 2600 m three main assemblages have been identified the first dominated by epistominella exigua is related to the north east atlantic deep water neadw the second characterized by the co dominance of cibicides wuellerstorfi and e exigua seems to characterize the north west atlantic bottom water nwabw the third marked by the occurrence of nuttalides umbonifera is recorded at depths greater than 3500 m and is associated with the northern extent of the antarctic bottom water aabw microfaunal and isotopic analyses of two cores from the greenland slope 90 013 011 2800 m and

a 200 ka geomagnetic chronostratigraphy for the labrador sea indirect correlation of the sediment record to specmap abstract a chronostratigraphic framework for the last 200 ka based on relative variations of geomagnetic paleointensity has been derived for the labrador sea where 18o stratigraphies are compromised by lack of benthic foraminifera and environmental perturbations of the planktic record relative paleointensity records derived from three labrador sea piston cores are correlated to a recently developed 200 ka paleointensity composite sint 200 y guyodo j p valet earth planet sci lett 143 1996 23 36 the chronology for sint 200 was derived by correlating oxygen isotope stratigraphies from individual paleointensity records to the specmap chronostratigraphy the correlation of sint 200 to labrador sea paleointensity records allows the specmap chronology to be imported into the labrador sea although comparisons of the chronostratigraphy based on paleointensity correlations with those derived from ams 14c dates and 18o data indicate significant discrepancies support for the new chronostratigraphic framework is provided by 1 consistent correlation of labrador sea detrital layers to north atlantic heinrich layers 2 general consistency between planktic 18o values and the specmap reference curve and 3 feasible prediction for the age of ash layer 2 as the new chronostratigraphy is tied to specmap labrador sea sediment cores can now be directly compared with any specmap dated record

the magnetic signature of rapidly deposited detrital layers from the deep labrador sea relationship to north atlantic heinrich layers rock magnetic parameters from deep labrador sea piston core p 094 are useful for recognizing rapidly deposited detrital layers some of which correlate with north atlantic heinrich layers variations in magnetic properties and lithology distinguish two classes of rapidly deposited detrital layers during the last ice age 1 seven detrital carbonate dc layers have high carbonate content and mean magnetite grain diameters about 4 times greater than the background sediments 2 six low detrital carbonate ldc layers have very similar magnetic properties to dc layers but low carbonate content similar to the background sediments the magnetite associated with dc and ldc layers is well sorted and relatively uniform within and between layers ice rafted detritus ird recognized by increased percentage of the 125 micron grain size fraction and by high magnetic susceptibility is associated with most dc and ldc layers but is not the dominant detrital constituent the correspondence of dc and ldc layers with increased grain size of well sorted magnetite but not with coarse fraction content precludes ice rafting as the primary depositional mechanism dc and ldc layers may have been deposited from suspended sediment derived from turbidite activity in the nearby northwest atlantic mid ocean channel namoc this interpretation is supported by a piston core p 013 from a greenland rise site largely but not completely outside the influence of the namoc the association of dc layers with ird and the apparent age correlation of dc layers to north atlantic heinrich layers suggest that the ice advances which produced the ird in p 094 and in correlative north atlantic heinrich layers also triggered turbiditic flows down the namoc several dc and ldc layers however do not correlate with recognized heinrich layers but appear to be coeval with recently discovered high frequency ird rich layers in the north atlantic

geochemistry of fluid phases and sediments relevance to hydrothermal circulation in middle valley odp legs 139 and 169 geochemical and isotopic studies of pore fluids and solid phases recovered from the dead dog and bent hill hydrothermal sites in middle valley ocean drilling program leg 169 have been compared with similar data obtained previously from these sites during ocean drilling program leg 139 although generally the hydrothermal systems reflect non steady state conditions the data allow an assessment of the history of the hydrothermal processes sediment k al ratios as well as the distribution of anhydrite in the sediments suggest that the dead dog hydrothermal field has been and still is active in contrast similar data in the bent hill hydrothermal field indicate a waning of hydrothermal activity pore fluid and hydrothermal vent data in the dead dog hydrothermal field are similar in nature to the data collected during odp leg 139 in the area of the bent hill sulfide deposit however the pore water data indicate that recent wholesale flushing of the sediment column with relatively unaltered seawater has obliterated a previous record of hydrothermal activity in the pore fluids data from the deepest part of hole 1035a in the bent hill locality show the presence of hydrothermal fluids at greater depths in this area this suggests the origin of the hydrothermal fluids found to be emanating from hole 1035f which constitutes one of the first man made hydrothermal vents in the middle valley hydrothermal system similarly corked hole 858g because of seal failures has acted as a hydrothermal vent with sulfide deposits forming inside the cork

turbidite megabeds in an oceanic rift valley recording jokulhlaups of late pleistocene glacial lakes of the western united states abstract escanaba trough is the southernmost segment of the gorda ridge and is filled by sandy turbidites locally exceeding 500 m in thickness new results from ocean drilling program odp sites 1037 and 1038 that include accelerator mass spectrometry ams 14c dates and revised petrographic evaluation of the sediment provenance combined with high resolution seismic reflection profiles provide a lithostratigraphic framework for the turbidite deposits three fining upward units of sandy turbidites from the upper 365 m at odp site 1037 can be correlated with sediment recovered at odp site 1038 and deep sea drilling program dsdp site 35 six ams 14c ages in the upper 317 m of the sequence at site 1037 indicate that average deposition rates exceeded 10 m k yr between 32 and 11 ka with nearly instantaneous deposition of one 60 m interval of sand petrography of the sand beds is consistent with a columbia river source for the entire sedimentary sequence in escanaba trough high resolution acoustic strat

hydrothermal petroleum at the seafloor and organic matter alteration in sediments of middle valley northern juan de fuca ridge abstract sediments from high heat flow areas of middle valley northern juan de fuca ridge contain traces of bitumens with insignificant amounts of thermogenic components and mainly lipid material which has experienced accelerated diagenesis these sediments have been exposed to mild hydrothermal conditions 50 120 c based on their bitumen compositions the hydrothermal bitumen in a barite alteration products the aliphatic fraction represents the mildly transformed and immature matter and the major polynuclear aromatic hydrocarbons are the high temperature constituents 300 c the 14c age of this bitumen is about 29 000 abp reflecting rapid organic carbon cycling

the escanaba trough gorda ridge hydrothermal system temporal stability and subseafloor complexity abstract the composition and temperature of vent fluids sampled from the active hydrothermal system in escanaba trough gorda ridge in 2000 and 2002 remain unchanged from the only time this field was previously sampled in 1988 odp leg 169 drilled nine bore holes at this site in 1996 some within meters of the vents yet this disturbance has not impacted the measured compositions or temperatures of the fluids exiting at the seafloor the fluids have maximum measured temperatures of 218 c and contain 20 more chloride than local ambient seawater our interpretation is that the fluid compositions are generated by supercritical phase separation of seawater with much of the water rock reaction occurring within the 400m thick sedimentary section that overlies the basalt at this site the odp drilling results provide information on the mineralogy and composition of materials below the seafloor as well as direct constraints not typically available on the physical conditions occurring below the seafloor hydrothermal system calculations utilizing geochemical modeling software suggest the fluids are close to saturation with a suite of minerals found subsurface suggesting equilibrium between the fluids and substrate these results provide an explanation for why the fluids have remained chemically stable for 14 yrs the pore water data from drilling suggest that the hydrology and chemistry of the hydrothermal system are much more complex within the sediment cover than would be expected from the surface manifestations of the hydrothermal system while the pore waters have chloride contents both greater and less than the local seawater only fluids with higher chloride contents vent at the seafloor our calculations suggest that at the current conditions the brines fluids with chlorinity greater than seawater are actually less dense than the vapors fluids with chlorinity less than seawater these density relationships may provide an explanation for why the brines are now venting preferentially to the vapors a situation opposite to what is usually observed or inferred

surface oceanographic changes in the eastern labrador sea nannofossil record of the last 31 000 years abstract calcareous nannofossils in two ams 14c dated piston cores from the eastern labrador sea yield oceanographic information of the last 31 kyr moderate nannofossil productivity and abundance of north atlantic warm water taxa in the southern labrador sea core 91 045 094p suggest cool surface ocean condition between 31 and 26 thousand years ago ka the irminger current was absent in this interval thus we attribute this cool condition to weak advection of north atlantic water from the southeast we found evidence of cold and or seasonally ice covered surface conditions between 26 and 13 ka in the southern labrador sea and between 31 and 12 6 ka in the northeastern labrador sea core 90 013 013p increase of nannofossil productivity and abundance of north atlantic taxa at about 10 7 ka in core 91 045 094p suggests that the southern labrador sea was influenced by warm north atlantic surface water the polar water of the labrador current had little or no influence on the surface ocean in this area before 9 ka the labrador current started to flow or intensify after 9 ka and became strong by 8 4 ka the northeastern labrador sea remained cold until 8 4 ka perhaps because of discharge of cold meltwater from the greenland ice sheet at this time productivity increased sharply and the assemblage of nannofossils changed these suggest a significant improvement in surface ocean conditions and the establishment of the warm irminger current which marked the onset of the modern circulation pattern characterized by warm west greenland current and strong labrador current

hydrothermally derived petroleum examples from guaymas basin gulf of california and escanaba trough northeast pacific ocean petroleum is associated with sulfide rich sediment at two active oceanic spreading axes in the northeast pacific ocean in the guaymas basin a spreading axis in the gulf of california petroleum having a wide range of compositions forms by hydrothermal alteration of organic matter in quaternary sediment composed mainly of marine diatomaceous ooze and muddy turbidites in escanaba trough at the southern end of the gorda ridge spreading axis offshore northern california petroleum is formed by hydrothermal processes acting on mainly terrigenous organic material in quaternary turbiditic river derived sediment comparisons of the distributions of hydrocarbons n alkanes isoprenoids terpanes steranes and aromatics show that chemical differences among four petroleum samp es are such that two samples from guaymas basin can be distinguished from two samples from escanaba trough distinguishing characteristics resulting from differences in sources include n alkane distributions and certain sterane ratios distinguishing characteristics resulting from differences in thermal histories of the organic matter include hopane and sterane epimer ratios and various distributions of polycyclic aromatic hydrocarbons these oils differ from conventionally derived petroleum in that they are admixtures of products generated over a wide range of thermal regimes and their generation expulsion and migration occurred simultaneously over an instantaneous geological time period the potential economic significance of hydrothermally derived petroleum is uncertain but the act that petroleum can form at active oceanic spreading axes adds a new facet to understanding the processes of petroleum generation expulsion and migration

the connection between iron ore formations and mud shrimp colonizations around sunken wood debris and hydrothermal sediments in a lower cretaceous continental rift basin mecsek mts hungary in the early cretaceous the continental rift basin of the mecsek mts hungary was situated on the southern edge of the european plate the opening of the north atlantic ocean created a dilatational regime that expanded to the southern edge of the european plate where several extensional basins and submarine volcanoes were formed during the early cretaceous epoch permanent seaquake activity caused high swell events during which a large amount of terrestrial wood fragments entered into submarine canyons from rivers or suspended woods which had sunk into the deep seafloor these fragments created extended wood fall deposits which contributed large scale flourishing of numerous burrowing thalassinid crustaceans twelve different thalassinid coprolite ichnospecies can be found in the berriasian hauterivian volcano sedimentary formations

bacterial response to contrasting sediment geochemistry in the central indian basin in order to investigate whether geochemical physiographic and lithological differences in two end member sedimentary settings could evoke varied microbe sediment interactions two 25 cm long sediment cores from contrasting regions in the central indian basin have been examined site tvbc 26 in the northern siliceous realm 10 s 75 5 e is organic c rich with 0 3 0 09 total organic carbon site tvbc 08 in the southern pelagic red clay realm 16 s 75 5 e located on the flank of a seamount in a mid plate volcanic area with hydrothermal alterations of recent origin is organic c poor 0 1 0 07 significantly higher bacterial viability under anaerobic conditions generally lower microbial carbon uptake and higher numbers of aerobic sulphur oxidizers at the mottled zones characterize core tvbc 26 in the carbon poor environment of core tvbc 08 a doubling of the 14 c uptake a 250 times increase in the number of autotrophic nitrifiers a fourfold lowering in the number of aerobic sulphur oxidizers and an order higher of denitrifiers exist when compared to core tvbc 26 this suggests the prevalence of a potentially autotrophic microbial community in core tvbc 08 in response to hydrothermal activity microbial activity at the northern tvbc 26 is predominantly heterotrophic with enhanced chemosynthetic activity restricted to tangreen mottled zones the southern tvbc 08 is autotrophic with increased heterotrophic activity in the deepest layers notably the bacterial activity is generally dependent on the surface productivity in tvbc 26 the carbon rich core and mostly independent in tvbc 08 the carbon poor hydrothermally influenced core the northern sediment is more organic sink controlled and the southern more hydrothermal source controlled hydrothermal activity and associated rock alteration processes may be more relevant than organic matter delivery in these deep sea sediments thus this study highlights the relative importance of hydrothermal activity versus organic delivery in evoking different microbial response in the central indian basin sediments

helium and carbon gas geochemistry of pore fluids from the sediment rich hydrothermal system in escanaba trough abstract ocean drilling program odp leg 169 which was conducted in 1996 provided an opportunity to study the gas geochemistry in the deeper part of the sediment rich hydrothermal system in escanaba trough gas void samples obtained from the core liner were analyzed and their results were compared with analytical data of vent fluid samples collected by a submersible dive program in 1988 the gas geochemistry of the pore fluids consisted mostly of a hydrothermal component and was basically the same as that of the vent fluids the he isotope ratios r ra 5 6 6 6 indicated a significant mantle he contribution and the c isotopic compositions of the hydrocarbons 13c ch4 43 13c c2h6 20 were characterized as a thermogenic origin caused by hydrothermal activity on the other hand the pore fluids in sedimentary layers away from the hydrothermal fields showed profiles which reflected lateral migration of the hydrothermal hydrocarbons and abundant biogenic ch4 helium and c isotope systematics were shown to represent a hydrothermal component and useful as indicators for their distribution beneath the seafloor similarities in he and hydrocarbon signatures to that of the escanaba trough hydrothermal system were found in some terrestrial natural gases which suggested that seafloor hydrothermal activity in sediment rich environments would be one of the possible petroleum hydrocarbon generation scenarios in unconventional geological settings

initiation of the european deglaciation as recorded in the northwestern bay of biscay slope environments meriadzek terrace and trevelyan escarpment a multi proxy approach three cores retrieved on the northwestern slope of the bay of biscay are described and discussed in the light of the european last deglaciation history this integrated sedimentological and micropalaeontological study provides a detailed evolution scheme for the deep and sea surface conditions of the bay during the final deglacial step with a direct link with the continental palaeoenvironments as early as 15 ka 14c bp a european precursor melting event is recorded as a purge of the channel and irish sea palaeoriver systems pleni heinrich event conditions occurred in the bay of biscay between 14 4 and 13 ka 14c bp with a typical canadian signature only recorded at 14 ka 14c bp namely 1 ka later than the first evidence of melting of the british ice sheet our data demonstrate that following heinrich event 2 the last glacial maximum was characterised by a gradual warming accompanied by at least two pulses of the north atlantic drift these north atlantic drift heat northward penetrations are supposed to have primarily forced the heinrich event 1 collapse

sources and occurrence of c12c22n alkane distributions with even carbon number preference in sedimentary environments abstract the occurrence of c12 c22n alkanes with a strong even carbon number preference is reported in recent and miocene sediments encompassing marine and freshwater systems deposited under oxic and anoxic conditions it is therefore shown that these n alkanes can be found in a wider type of sedimentary environment than those previously described the occurrence in some cases of a parallel distribution of c14 c20n alk 1 enes is also illustrated a variety of biological sources including both marine and freshwater bacteria as well as fungi and yeast species is suggested to account for such distributions

stress induced smectite dehydration ramifications for patterns of freshening and fluid expulsion in the n barbados accretionary wedge abstract presented is new experimental evidence that smectites can partially dehydrate from 18 5 a to 15 4 a hydrates when they are subjected to effective mineral framework stresses above 1 3 0 3 mpa we show here that this process can substantially freshen saline pore fluids and impact our understanding of the hydrogeologic processes in convergent margins where smectites are abundant the general anomalous freshening of pore fluids in the n barbados accretionary wedge was previously proposed to relate to the widespread lateral expulsion of fluids derived from mineral dehydration reactions at great depth in contrast our analysis suggests that a significant part of the widespread anomalous freshening relates to stress induced smectite dehydration that occurred during the ocean drilling program odp pore water extraction process clear evidence for long distance lateral flow appears to be limited to localized chloride and isotopic anomalies developed in a 20 m thick locally mineralized region at the top of decollement horizon at site 948 our reinterpretation is consistent with the fluid flow in the decollement zone being 1 highly transient on time scales of several hundreds of years and 2 channeled laterally into heterogeneous finger like flow paths that are apparently not intersected and or sampled by drilling in most regions at the toe of the wedge the incipient stress induced dehydration of smectite may also be buffering in situ fluid pressures in the wedge maintaining the effective stresses at 1 3 mpa

dinocyst based reconstructions of sea ice cover concentration during the holocene in the arctic ocean the northern north atlantic ocean and its adjacent seas abstract sea ice cover extent expressed in terms of mean annual concentration was reconstructed from the application of the modern analogue technique to dinocyst assemblages the use of an updated database which includes 1492 sites and 66 taxa yields sea ice concentration estimates with an accuracy of 1 1 10 holocene reconstructions of sea ice cover were made from dinocyst counts in 35 cores of the northern north atlantic and arctic seas in the canadian arctic the results show high sea ice concentration 7 10 with little variations throughout the interval in contrast in arctic areas such as the chukchi sea and the barents sea the reconstructions show large amplitude variations of sea ice cover suggesting millennial type oscillations with a pacing almost opposite in western vs eastern arctic other records show tenuous changes with some regionalism either in trends or sea ice cover variability during the mid holocene and notably at 6 0 5 ka minimum sea ice concentration is recorded in the eastern fram strait northern baffin bay and labrador sea however this minimum cannot be extrapolated at the scale of the arctic and circum arctic the comparison of recent observations and reconstructions suggests larger variations in the arctic sea ice cover during the last decades than throughout the holocene

elusive isotopic properties of deglacial meltwater spikes into the north atlantic example of the final drainage of lake agassizthis article is one of a series of papers published in the special issue on the theme polar climate stability network the impact of the final drainage of lake agassiz some 8 4 ka ago on the atlantic meridional overturning circulation is still debated the lack of isotopic response in planktic foraminifer records at the outlet of the drainage channel constitutes a puzzling element in this debate to estimate the response of the 18o salinity relationship in ocean surface waters to drainage we use a core raised from southeast hudson bay to document 18o values of lake waters immediately prior to drainage valves of candona sp an ostracod from lacustrine varved sediments underlying marine clays yielded 18o values clustered around 20 5 versus vpdb vienna peedee belemnite assuming a lake bottom temperature of about 0 c an isotopic composition of 25 versus vsmow vienna standard mean ocean water is calculated for paleolake waters not unlike values reported for earlier stages of lake agassiz this value is only slightly more negative than those estimated for laurentide ice sheet lis meltwaters during the

dinoflagellate cyst distribution in high latitude marine environments and quantitative reconstruction of sea surface salinity temperature and seasonality a data base of 179 reference sites documents the relations between the assemblages of organic walled dinoflagellate cysts and sea surface temperature salinity and seasonality throughout the north atlantic adjacent subpolar basins labrador sea baffin bay irminger and iceland basins and epicontinental environments off eastern canada estuary and gulf of st lawrence hudson bay principal component analyses show close relationships between dinoflagellate cyst data and sea surface conditions the first component 71 1 of the variance correlates with the winter temperature salinity and seasonal duration of sea ice cover whereas the second component 11 3 of the variance appears mainly related to summer temperature transfer functions using the best analogue method were tested by reconstructing modern sea surface conditions on the basis of the reference dinoflagellate cyst assemblages the correlation coefficient between instrumental averages and reconstructed values ranges from 0 87 august tem

simmax a modern analog technique to deduce atlantic sea surface temperatures from planktonic foraminifera in deep sea sediments we present a data set of 738 planktonic foraminiferal species counts from sediment surface samples of the eastern north atlantic and the south atlantic between 87 n and 40 s 35 e and 60 w including published climate long range investigation mapping and prediction climap data these species counts are linked to levitus s 1982 modern water temperature data for the four caloric seasons four depth ranges 0 30 50 and 75 m and the combined means of those depth ranges the relation between planktonic foraminiferal assemblages and sea surface temperature sst data is estimated using the newly developed simmax technique which is an acronym for a modern analog technique mat with a similarity index based on 1 the scalar product of the normalized faunal percentages and 2 a weighting procedure of the modern analog s ssts according to the inverse geographical distances of the most similar samples compared to the classical climap transfer technique and conventional mat techniques simmax provides a more confident reconstruction of paleo ssts correlation coefficient is 0 994 for the caloric winter and 0 993 for caloric summer the standard deviation of the residuals is 0 90 c for caloric winter and 0 96 c for caloric summer at 0 m water depth the sst estimates reach optimum stability standard deviation of the residuals is 0 88 c at the average 0 to 75 m water depth our extensive database provides sst estimates over a range of 1 4 to 27 2 c for caloric winter and 0 4 to 28 6 c for caloric summer allowing sst estimates which are especially valuable for the high latitude atlantic during glacial times an electronic supplement of this material may be obtained on adiskette or anonymous ftp from kosmos agu org login toagu s ftp account using anonymous as the username and guestas the password go to the right directory by typing cd append typels to see what files are available type get and the name of the file toget it finally type exit to leave the system paper 95pa01743 simmax a modern analog technique to deduce atlantic sea surfacetemperatures from planktonic foraminifera in deep sea sediments uwepflaumann josette duprat claude pujol and laurent d labeyrie diskette may be ordered from american geophysical union 2000florida avenue n w washington dc 20009 payment mustaccompany order

hydrothermal geochemistry of sediments and pore waters in escanaba trough odp leg 169 geochemical studies of pore fluids and solid phases in two ocean drilling program odp drill sites sites 1037 and 1038 in the escanaba trough off northern california have provided further data on the hydrothermal processes associated with the spreading of the gorda ridge previous work in the area of odp site 1038 includes the discovery of a hydrothermal system and associated sulfide deposits centered around an uplifted sediment hill in this sedimented extensional environment this earlier work provided some insights into the present nature of venting however only deep drilling investigations can provide the means to fully understand the genesis and evolution of this system and associated hydrothermal deposits odp leg 169 is the third deep drilling operation to explore the magnitude genesis and evolution of hydrothermal systems on sedimented ridges previous studies centered on the guaymas basin in the gulf of california and the middle valley in the ne pacific ocean pore water studies in the reference odp site 1037 and in the hydrothermally active area of odp site 1038 have revealed the presence of a complex system of hydrothermally originated fluids whereas the data in the reference site indicate recent hydrothermal activity in the basal part of the drill site the evidence in site 1038 suggests that fluids of hydrothermal origin spread out at shallow depths around the central hill causing substantial sediment alteration as well as deposition of hydrothermal sulfides in the near surface zone of the sediments a second major discovery at site 1038 was the evidence for fluid phase separation at depth at temperatures possibly in excess of 400 c this conclusion is based on the presence of both low cl and high cl fluids the latter appear to be advected rapidly towards the surface presumably along cracks and faults the low cl fluids however appear to be transported laterally along sandy horizons in the sediments thus signifying two very different migration pathways for high cl and low cl hydrothermally phase separated fluids studies of the organic geochemistry of dissolved gases and matured organic matter corroborate these findings of extensive hydrothermal alteration of the sediments

mechanisms of abrupt climate change of the last glacial period 1 more than a decade ago ice core records from greenland revealed that the last glacial period was characterized by abrupt climate changes that recurred on millennial time scales since their discovery there has been a large effort to determine whether these climate events were a global phenomenon or were just confined to the north atlantic region and also to reveal the mechanisms that were responsible for them in this paper we review the available paleoclimate observations of abrupt change during the last glacial period in order to place constraints on possible mechanisms three different mechanisms are then reviewed ocean thermohaline circulation sea ice feedbacks and tropical processes each mechanism is tested for its ability to explain the key features of the observations particularly with regard to the abruptness millennial recurrence and geographical extent of the observed changes it is found that each of these mechanisms has explanatory strengths and weaknesses and key areas in which progress could be made in improving the understanding of their long term behavior both from observational and modeling approaches are suggested finally it is proposed that a complete understanding of the mechanisms of abrupt change requires inclusion of processes at both low and high latitudes as well as the potential for feedbacks between them some suggestions for experimental approaches to test for such feedbacks with coupled climate models are given

productivite et flux de carbone dans la mer du labrador au cours des derniers 40 000 ans geochemical and micropaleontological analyses of labrador sea sediments allowed us to intercalibrate indicators of paleoproductivity and paleofluxes of carbon and to reconstitute biogeochemical fluxes notably in relation to deep sea circulation changes western boundary undercurrent and north atlantic deep water linear or logarithmic relations are observed between the subrecent fluxes of paleoproductivity indicators coccoliths diatoms dinocysts 230th the 13c content of left coiling or sinistral neogloboquadrina pachyderma the modern surface water carbon production and the rates of organic and inorganic carbon corg cinorg burial all indicators increase by a factor of 102 to 103 in response to the evolution of paleosea surface conditions since the last glacial maximum correlations are observed between authigenic cinorg 230th coccoliths and 13c content left coiling or sinistral neogloboquadrina pachyderma and also between authigenic corg dinocysts uranium and sulfur relative cinorg

impact of shallow living radiolarian flux variations on north atlantic cycladophora davisiana percentages abstract the cause of high cycladophora davisiana percentages a deep living maximum abundance 200 m radiolarian species in high latitude 45 late pleistocene deep sea sediments has been much debated in this paper we show that in four subpolar north atlantic cores these late pleistocene high percentages 20 result more from a reduction of other radiolarian flux predominantly shallow living species c davisiana flux relative to holocene flux these findings are similar to those reported from the north pacific hays et al 2013 in both oceans the late pleistocene to holocene shallow living species flux increase is larger than the concomitant decrease of c davisiana flux similarly high c davisiana percentages 20 found today in okhotsk sea holocene sediments kruglikova 1975 robertson 1975 morley and hays 1983 result from low radiolarian concentrations in the overlying dicothermal layer 20 150 m where year round temperatures are near 0 c it is likely that the high c davisiana percentages in north atlantic late pleistocene sediments were caused by a similar overlying stratification that had important biological consequences for radiolarians and other plankton a more significant time transgressive increase in shallow and others radiolarian assemblage flux occurs initially in the southernmost core in mid holocene ultimately recorded at the northernmost site during the late holocene here flux of the deep assemblage and c davisiana also increases

neogloboquadrina pachyderma sinistral coiling as paleoceanographic tracers in polar oceans evidence from northeast water polynya plankton tows sediment traps and surface sediments the abundance and chemistry of the planktonic foraminifera neogloboquadrina pachyderma sinistral coiling have long been used as tools for monitoring polar surface ocean changes and for correlating these changes to atmospheric and thermohaline circulation fluctuations however due to its remote habitat very little is known about how modern n pachyderma s respond to changing environmental conditions in the polar seas modern samples of n pachyderma s from the northeast water polynya provide a means for studying how environmental conditions affect the vertical distribution and chemistry of this species highest abundances of n pachyderma s were associated with the chlorophyll maximum in the surface 20 80 m where they are exploiting their primary food source evidence suggests that the addition of a calcite crust modifies the calcite tests of some n pachyderma s between 50 and 200 m increasing shell density and modifying shell chemistry the shell mass of encrusted forms is 3 4 times greater than the nonencrusted forms between 50 and 200 m the oxygen isotope composition of n pachyderma s shells increase by 1 5 in response to local water column gradients the 13c values of n pachyderma s are basically invariant with depth in this region are consistently 1 0 depleted in comparison with the 13c for equilibrium calcite and remain basically constant during the shell thickening process mass balance calculations suggest that encrustation occurs at all depths but abundance counts suggest that the process occurs mostly at the depth of the main pycnocline sediment fluxes of n pachyderma s occur during a 2 week bloom event and decrease to almost zero below complete ice cover the decoupling of the processes controlling abundances and shell chemistry explain the discrepancies between transfer function and isotopically derived paleotemperature estimates of surface conditions in some oceanic settings the ability of 18o to record surface ocean conditions will depend on vertical water column gradients as evidenced by the differences in core top calibrations between the north and south atlantic

marine reservoir corrections for bowhead whale radiocarbon age determinations twenty two pairs of radiocarbon dates on driftwood and bowhead whale balaena mysticetus bones from raised beaches dates on whale bone and terrestrial plant detritus from a stratigraphie section and 25 additional dates on whale bones from the lowest 1 ka bp raised beaches in the eastern canadian arctic suggest that a marine reservoir correction of about 200 years is appropriate for normalized age determinations on bone collagen from the bowhead whale in this region this is less than the correction 400 years normally applied to carbonate shells of marine molluscs from this region the carbon in bowhead collagen appears to be derived from the whales zooplankton food rather than from marine bicarbonate

structure of the upper water column in the northwest north atlantic modern versus last glacial maximum conditions 1 during the last glacial maximum the northwestern north atlantic constituted a major conduit for labrador and greenland ice sheet meltwaters vertical density gradients in its upper water masses have been reconstructed by combining information from transfer functions based on dinocysts and from oxygen isotope measurements 18o in planktonic foraminifera transfer functions yield temperature and salinity and thus potential density for the warmest august and coldest february months in the photic zone the 18o values in different size fractions of epipelagic globigerina bulloides and mesopelagic neogloboquadrina pachyderma left coiled npl foraminifera allow us to assess gradients through the pycnocline between surface and intermediate waters based on the calibration of a versus 18o relationship from transfer function reconstructions the size and density of npl shells provide further constraints on these gradients the results show the development of a very strong pycnocline during the lgm with a difference of about 3 summer to 1 5 winter units between surface and underlying waters they indicate conditions unfavorable for vertical convection and support the hypothesis of the spreading of a shallow low salinity buoyant layer over the northern north atlantic this layer depicted a strong e w gradient with maximum seasonal contrast and minimum absolute values westward

distribution patterns of dinoflagellate cysts and other organic walled microfossils in recent norwegian greenland sea sediments dinoflagellate cysts and other organic walled microfossils have been studied in recent surface sediments from the entire norwegian greenland sea more than 30 taxa have been recognized of which only few show a distinct distribution pattern and allow description of four assemblages the occurrence of most taxa is related to the relatively warmer waters of the norwegian sea algidaspaeridium minutum s 1 brigantedinium simplex and impagidinium pallidum are the only species showing a preference for colder water masses two species i pallidum and nematosphaeropsis labyrinthus are mainly restricted to the oceanic environment whereas the other species have also been reported from neritic environments in previous studies due to the limited knowledge of the ecological and sedimentological factors influencing the occurrence of dinoflagellate cysts in oceanic environments their distribution in recent sediments can be only related to surface water masses in a broad sense although the distribution of assemblages correlates with specific surface water masses comparison with assemblages recovered from sediment traps deployed basinwide in the norwegian greenland sea dale and dale 1992 revealed some major discrepancies in species composition and percentage abundances the differences cannot be explained with certainty at the moment although there is some evidence that transport of dinoflagellate cysts and other fossilizable microplankton in water masses by currents in sea ice and sediments may modify the assemblages found in recent oceanic surface sediments from the norwegian greenland sea

paleoceanographic reconstructions of surface ocean conditions in the greenland iceland and norwegian seas through the last 14 ka based on diatoms prior reconstructions of the last glacial maximum and the holocene did not include detailed paleoclimate data from the greenland iceland and norwegian gin seas which cover sensitive areas for oceanographic boundaries sea ice distribution and deep water formation in order to fill this gap we studied nine well dated sediment cores from this area and reconstructed the paleoceanographic conditions of the surface gin seas at 2000 year intervals since 13 400 bp based on the diatom record results show that a n s extending sea ice free corridor had opened along norway already at 13 400 bp indicating a northward flow of a branch of the north atlantic drift possibly caused by a change in the jet stream flow due to the decreased height of the north american ice sheet a major change of climatic conditions occurred over the gin seas as the insolation anomaly reached its maximum around 9000 bp when the sea ice cover and the oceanic fronts retreated to a northwesterly position along greenland and the ocean temperatures rose the first half of the holocene is recorded as the warmest period during the last 13 400 bp in the gin seas the duration of this climatic optimum decreased both toward the north and toward the margins of the area the second half of the holocene is characterized by a cooling trend in step with the decreasing insolation these results support the proposal of imbrie et al 1992 that the gin seas region acts as an initial responder to insolation changes

late quaternary climate change from δ18o records of multiple species of planktonic foraminifera high resolution records from the anoxic cariaco basin venezuela seasonal trade wind induced upwelling along the southern margin of the caribbean sea occurs in response to the annual migration of the intertropical convergence zone laminated high deposition rate sediments of the cariaco basin a small anoxic basin on the venezuelan continental shelf clearly record large changes in the past intensity of this upwelling because sediments of the cariaco basin are largely unbioturbated they offer a natural opportunity to study the stable isotopic records of multiple planktonic foraminiferal taxa and to evaluate their sensitivity to both the modern hydrography and temporal changes in upwelling intensity and climate oxygen isotope data 18o from four dominant foraminiferal taxa are presented for the time period covering the last 28 kyr the 18o data from globigerina bulloides after correction for nonequilibrium precipitation are used as a monitor of sea surface conditions during the winter spring upwelling season the 18o data from white globigerinoides ruber are used as a measure of annual average conditions in the near surface while pink g ruber data are consistent with use as an index of endmember conditions during the summer fall nonupwelling season data from the deeper dwelling neogloboquadrina dutertrei yield information on conditions near the base of the local thermocline during the last glacial 18o data from g ruber and generally reduced interspecific differences indicate cooling of surface waters over the cariaco basin by up to 4 c this longer term cooling does not appear to be related to changes in upwelling intensity along the coast but may instead reflect more regional cooling of the larger caribbean superimposed on this pattern between 12 6 and 10 ka is a convergence of 18o data between g bulloides and n dutertrei implying much stronger upwelling during the last deglaciation this scenario is consistent with other evidence for high productivity at this time at 14 ka a sharp 18o depletion event observed in all taxa seems to have been produced by increased freshwater discharge to the southern caribbean suggesting either higher regional rainfall or the influence of glacial melting in the andes minimum 18o values of pink g ruber around 6 7 ka record warmer summer sea surface temperatures and or decreased salinity in the mid holocene

hydrothermal effects on organic matter high vs low temperature components abstract hydrothermal activity and sea bed mounds have been explored in guaymas basin central gulf of california by the deep sea drilling project piston coring dredging and diving with the d s r v alvin the deep seated magmatic heat flow causes extensive thermal alteration of both organic and mineral matter especially in the case of the south rift of guaymas basin this results in hydrothermal circulation with concomitant migration of organic pyrolysate to the seabed the bitumen at depth of dsdp sites 477 and 481 contained thermogenic components such as primary olefins thermodynamically stabilized molecular markers 17 h hopanes and elemental sulfur with traces of polynuclear aromatic hydrocarbons pah the major components were n alkanes with no carbon number predominance and unresolvable complex branched and cyclic hydrocarbons hump which are typical of mature petroleum and were generated by the heat from the intrusives and magma dredge samples recovered from a mound in guaymas basin contained petroleum of a thermogenic origin as confirmed by the presence of gasoline range hydrocarbons a broad distribution of n alkanes c13 c33 no carbon number predominance hump pristane and phytane olefins and pah and large amounts of aromatic naphthenic and asphaltic material similar petroleums subsequently recovered from other active mounds in the southern rift by the d s r v alvin had analogous compositions ranging from volatile to heavy oils in pyrrhotite chimneys the extractable organic matter consisted of mainly higher molecular weight pah these petroleums are derived from the immature primarily marine organic matter at depth by thermal alteration rapid quenching by hydrothermal removal and migration followed by condensation at the sea bed results in the manifestations of oil as part of the sulfide formations exterior exposed oil samples are degraded and leached whereas interior samples are essentially unaltered the pah are high temperature resynthesis aromatization products that condense in the hottest parts of the vent systems

isotope stratigraphy sedimentation rates deep circulation and carbonate events in the labrador sea during the last 200 ka high resolution stable isotope and accelerator mass spectrometry 14c measurements in 25 box and piston cores from the labrador sea allow the reconstruction of major paleoceanographical changes during the last 200 ka in this basin and also document the links between the interior of the laurentide ice sheet and the north atlantic ocean during this interval two deep circulation regimes are indicated by contrasting sedimentation rates on the slopes i the modern situation is characterized by a gyre of the north atlantic deep water nadw components into the basin which is responsible for the high energy western boundary undercurrent this regime also prevailed during the former true interglacials and possibly during shorter warm intervals e g bolling allerod ii a more frequent nadw free situation during glacial and interstadial intervals is marked by the presence of a vertically homogeneous water mass in the basin sedimentological records also indicate that carbonate events i e pulses of

late quaternary lithofacies provenance and depositional environments 12 30 cal ka north and south of the denmark strait this paper describes the lithofacies and chronology of cores from north and south of the denmark strait for a period when ice sheets flanked both sides of the strait a wide range of sediments have been recovered indicating a complex of depositional processes jm96 1229ggc1 1047 m water depth is from the base of the nw iceland slope at the southern edge of the blosseville basin whereas jm96 1226ggc4 retrieved sediments south of the sill in 1519 m of water additional information is based on jm96 1220ggc2 and 1221ggc2 which were recovered from the upper w iceland slope at 500 m water depth below the latra moraine of possible last glacial maximum age and upslope of jm96 1226 ams 14c dates indicate that jm96 1226 and 1229 span the last 10 to 27 32 ka bp whereas jm96 1220 and 1221 recovered sediments dated between ca 8 and 18 ka bp closely spaced radiocarbon dates on jm96 1229 indicate an erosional hiatus of 7 ky between 12 and 19 cal ka lithofacies descriptions are based on visual descriptions and x radiographs jm96 1229 consists of fine grained sediments sometimes graded with scattered ice rafted debris whereas jm96 1226 consists largely of beds of matrix supported diamicton provenance indicators mass magnetic susceptibility and geochemistry for jm96 1229 support the delivery of sediments from nw iceland but there is a substantial difference in these properties between sediments from the w iceland upper slope and the sediments in jm96 1226 south of the denmark strait this indicates that the diamictons on the floor of the strait did not derive entirely from the iceland ice sheet and adjacent upper slope the general absence of sediments 12 cal ka on the slopes and floor of the denmark strait indicates that denmark strait overflow waters inhibited sediment accumulation during the holocene between ca 12 and 30 cal ka however a combination of more proximal sediment sources ice sheets and reduced thermohaline activity resulted in the accumulation of sediments on the slopes and basin floors

changes in the western boundary undercurrent outflow since the last glacial maximum from smectite illite ratios in deep labrador sea sediments high resolution mineralogical studies were performed on late glacial and deglacial sediments from two deep piston cores from the labrador sea located at the inlet sw greenland rise and outlet labrador rise of the western boundary undercurrent wbuc gyre at the two sites smectites transported from the eastern iceland and irminger basins by the wbuc are observed clay mineral changes are used as proxies for the paleointensity reconstruction of the wbuc on the greenland rise a clay mineral index smectite illite s i ratio is defined a s i ratio of 1 characterized the last glacial maximum it increased after 17 ka and reached a maximum value of 4 during the early holocene the mineralogical changes are gradual and do not show any reversal during the younger dryas this pattern which is confirmed by first order estimations of smectite and illite fluxes suggests gradually increasing sedimentary fluxes and wbuc intensity since the last glacial maximum a peak in the velocity of the wbuc at 9 ka as recorded by clay assemblages is consistent with other regional studies based on pollen foraminifera or grain size measurements a massive dilution of smectites by illite and chlorite s i 3 occurs at 8 5 ka it corresponds to a period of rapid sediment accumulation and reflects an intensified illite rich detrital supply by meltwaters from the southern greenland ice margin on the labrador rise the smectite content varies between 20 and 60 with no obvious trend through time the mineralogical composition is strongly influenced by ice rafted deposition and by the abundance of fast deposit units cf heinrich layers in the north atlantic which contain abundant detrital carbonates spilled over from the north west atlantic mid ocean channel in such layers smectites are present but are diluted by the addition of illites chlorites and kaolinites this provides evidence for a discrete and continuous wbuc supply of fine particles from the irminger and iceland basins as far as the southeastern part of the labrador basin early deglacial smectite rich layers up to 60 are also observed at this site they indicate an increase in the outflow of the wbuc at 13 5 ka bolling allerod as previously reported from grain size or foraminiferal assemblage studies

hydrothermal petroleum genesis migration and deposition in guaymas basin gulf of california hydrothermal activity and seabed mounds have been explored in guaymas basin by the deep sea drilling project dsdp piston coring dredging and diving with the deep submersible research vessel dsrv alvin sedimentary organic matter derived primarily from immature degraded microbial detritus is easily converted to petroleum under the hydrothermal regime these petroleums are mature and migrate in the fluids and by diffusion to the seabed the fluid migration is aided by near critical aqueous solution and supercritical carbon dioxide and hydrocarbons petroleum compositions vary from condensates to naphthenic to waxy all with significant amounts of asphaltenes and hydrothermal products such as olefins and toxic polynuclear aromatic hydrocarbons pah the heavy ends condense at the seabed depositing mainly as a cement with the sulfides and other minerals and to a lesser extent as entrapped oil and crystalline wax in vugs and conduits of the mounds the pah are high temperature resynthesis aromatiza

modern distribution of diatoms in sediments from the george v coast antarctica abstract currently little information exists concerning high frequency climate change in the antarctic data that are essential to gaining a more complete understanding of global climate change sediments from the george v coast continental margin potentially contain a high resolution record of the late holocene the relatively high rate of sedimentation 3 mm year and the presence of laminated intervals which contain undisturbed sequences make these sediments valuable for future downcore work in order to utilize diatom assemblages as proxies of paleoclimatic and paleoceanographic parameters a preliminary study of the surface sediment distribution of diatoms from the george v coast continental margin was completed nitzschia curta van heurck hasle and nitzschia kerguelensis o meara hasle present great potential for tracking the holocene retreat of ice across the continental shelf of this region concentrations of n curta an ice related form decreases in an offshore direction whereas n kerguelensis an oceanic species associated with circumpolar flow displays an increase in sediments offshore the genus thalassiosira cleve displays a clear association with areas of open water primary production as has been noted in others parts of the antarctic downcore variability in relative abundance of this genus will be useful in understanding the history of sea ice versus open water production on the george v coast shelf in contrast the distribution of chaetoceros ehrenberg resting spores appears to be more complex but may be related to the position of the stationary ice edge associated with the annual minimal extent of sea ice finally an understanding of the downcore variability of thalassiothrix antarctica schimper ex karsten a species which is very abundant in the laminated sections of the sediment cores will have to rely on studies of its distribution in other areas of the antarctic as it is sparsely distributed along the george v coast today

halide systematics in interstitial waters of ocean drilling sediment cores abstract the distribution of dissolved halides cl br i in interstitial waters of deep drill holes in the ocean is discussed for a number of environments hemi pelagic sediments hydrate containing sediments sediments affected by halide brines and also in hydrothermal environments the importance of the diagenesis of organic c in the production of i and br is discussed with reference to the observations of dissolved so 4 2 and nh 4 in the pore fluids more importantly in the zone of methano genesis below the so 4 2 reduction zone and usually associated with high organic c accumulation rates increases in i and br are of importance and usually are much higher than the increases observed in the so 4 2 reduction zone in pore fluids affected by dissolution of evaporites the br cl is often a strong indicator of the degree of evaporation of seawater demonstrated from results obtained in the mediterranean sea dissolution of halites on the other hand leads to br cl much lower than those of sea water in hydrothermal sediments there is no doubt that i and br contents of the fluids are influenced by hydrothermal alteration of the sediments and their organic c but signals are not clear the present study provides an overview of previous dsdp and odp studies of halide distributions in sedimentary pore waters in addition to other contributions on halide distributions in sedimentary pore waters in this symposium volume

diatom distribution and paleoceanographic reconstruction in the southern ocean present and last glacial maximum abstract diatom assemblage and preservational data are used to reconstruct paleoceanographic conditions at the last glacial maximum 18 000 yrs bp in the southern ocean from these data the following points can be made about the last glacial maximum in this region 1 contraction and slight northern shift of the belt of well preserved diatoms appears to be related to the northward shift of late spring early summer sea ice cover 2 presence of open ocean though poorly preserved diatom assemblages to the south of this belt strongly suggest that during many summers large areas of the southern ocean were ice free 3 the distribution of thenitzschia kerguelensis factor both in surface sediments and at the last glacial maximum indicates that the gyre systems particularly the weddell gyre were intensified during glacial times 4 although data are sparse in the higher latitude south atlantic there is an indication that the weddell polynya also existed during glacial times although it was shifted a few degrees northward

stable isotope clue to episodic sea ice formation in the glacial north atlantic sea ice is a determinant parameter of the climate system which acts as amplifier through positive ice albedo feedbacks and induces deep water formation through brine production it is also one of the most elusive parameters in the paleoclimate record most proxies of sea ice provide information on its presence and extent of e g diatoms or dinocysts but do not permit assessment on its rate of formation however seemingly off equilibrium low 18o values in mesopelagic planktic foraminifer species as observed today in the arctic ocean are thought to relate to the production of isotopically light brines during sea ice formation and might thus provide a clue on the rate of sea ice growth with reference to the isotopic properties of modern planktic foraminifers in the arctic ocean and using multi proxy data sets from the last glacial stage in the northwest north atlantic we re examined some of the current interpretations of planktic isotope records in the glacial nw north atlantic the large amplitude light isotopic excursions recorded in neogloboquadrina pachyderma left coiling during heinrich events 1 for example correspond to extensive sea ice cover as reconstructed from dinocysts and do not seem unequivocally linked to low salinity pulses such light isotopic excursion more likely responded to enhanced rates of sea ice formation resulting in the production and sinking of isotopically light brines on the contrary the isotopically heavy planktic foraminifers of the last glacial maximum lgm interval stricto sensu would rather suggest relatively low rates of brine production thus low sea ice growth rates in the area this would imply that the lgm distribution of sea ice in the north atlantic was primarily linked to spreading and drifting from marginal and nordic source areas and not from enhanced in situ production at the scale of glacial interglacial cycles isotopic distillation processes relating to sea ice production at high latitudes could be one of the factors controlling the 18o salinity relationship in deep ocean water masses that might deserve closer examination as it would be independent of continental ice volume changes

spatial analysis of early warning signals for a north atlantic climate transition in a coupled gcm the climate system can potentially switch from one stable state to another the closer a system is to a bifurcation point i e tipping point the more likely it is that even small perturbations can force the system to experience a state shift e g a collapsing atlantic meridional overturning circulation amoc and associated cooling in parts of the north atlantic here we present an abrupt state transition from a warm to a cold north atlantic climate state with expanded sea ice during an orbitally forced transient holocene simulation performed with the community climate system model version 3 the state transition is associated with a weakening of the amoc by about 33 in this simulation the changing background climate induced by slow external orbital forcing plays an important role for the abrupt climate shift the model allows the identification of regions and variables that play a key role for a potential climate transition and show early warning signals increase in autocorrelation and standard deviation as well as trends in skewness especially for sea surface salinity in the northern north atlantic are identified as robust early warning signals whereas no early warning signals are found in the time series of the amoc stream function

reconstruction of sea surface temperature salinity and sea ice cover in the northern north atlantic during the last glacial maximum based on dinocyst assemblages past sea surface conditions over the northern north atlantic during the last glacial maximum were examined from the study of 61 deep sea cores the last glacial maximum time slice studied here corresponds to an interval between heinrich layers h2 and h1 and spanningabout 20 16 ka on a 14c time scale transfer functions based on dinocyst assemblages were used to reconstruct sea surface temperature salinity and sea ice cover the results illustrate extensive sea ice cover along the eastern canadian margins and sea ice spreading only during winter over most of the northern north atlantic on the whole much colder winter prevailed despite relatively mild conditions in august 10 15 c at most offshore sites thus suggesting a larger seasonal contrast of temperatures than today lower salinity than at present is reconstructed especially along the eastern canadian and scandinavian margins likely because of meltwater supply from the surrounding ice sheets these reconstructions contrast with those established by climap on the basis of planktonic foraminifera these differences are discussed with reference to the stratigraphical frame of the last glacial maximum which was not the coldest phase of the last glacial stage the respective significance of dinocyst and foraminifer records is also examined in terms of the thermohaline characteristics of surface waters and the vertical structure of upper water masses which was apparently much more stratified than at present in the northern north atlantic thus preventing deep water formation

smnd signature of modern and late quaternary sediments from the northwest north atlantic implications for deep current changes since the last glacial maximum abstract nd isotopes and sm nd concentrations have been investigated in the clay size fraction of surface and late quaternary sediments of the northern north atlantic four sources of nd have been identified in the surface sediments 1 a radiogenic nd typical of the iceland volcanism 2 a pan african nd issued from eastern greenland 3 a variscan nd derived from the arctic ocean 4 an old unradiogenic nd related to the north american shield in the iceland and irminger basins the major sources of nd are the variscan nd derived from the arctic ocean and the iceland nd except in the western irminger basin where the pan african nd originating from eastern greenland is dominant and labels sedimentary supplies linked to the denmark strait overflow water nd derived from icelandic volcanism is never clearly dominant even on the reykjanes ridge and the nd derived from the american shield becomes dominant only in the labrador sea sediments lying in the pathway of the western boundary undercurrent have nd isotopic compositions which are shifted towards more radiogenic values indicating an input of material from the eastern basins carried by this deep current late quaternary sediments were cored from the southern greenland rise core 90 013 013 and eastern labrador rise orphan knoll core 91 045 094 in core 90 013 013 nd values during the last glacial maximum are as low as 20 but subsequently rose to 9 in the modern sediments indicating that the sedimentary material during the last glacial maximum was dominated by unradiogenic nd from the north american shield this may be related to a lesser outflow of the western boundary undercurrent in core 91 045 094 located along the labrador current trajectory a dominant supply of north american shield nd is recorded perhaps originating at least partially from the hudson strait the sm nd data are compatible with smectite vs illite studies at the same sites which suggest a continuous but more modest western boundary undercurrent supply during last glacial maximum

holocene north atlantic surface circulation and climatic variability evidence from diatom records diatom analyses have been performed on a 425cm long holocene marine sediment sequence from the north atlantic south of iceland and a 920cm sediment core spanning the last c 7500 years from skalafjord faeroe islands additional core data include stable isotopes and results from magnetic susceptibility measurements while chronostratigraphic control has been provided by ams 14c measurements the diatom records reveal distinct changes in north atlantic surface circulation and climate that have been correlated with published terrestrial and marine records initial holocene warming is dated at 9900 14c years bp and after a preboreal cold spell enhanced north atlantic current activity and warming prevailed from 9600 to 8800 14c years bp from 8800 to 8000 4c years bp the advection of warm atlantic water masses weakened presumably under atmospheric circulation conditions characterized by a dominating negative nao prior to the holocene climatic optimum 6000 5000 14c years bp distinct hydrographic gradient

sediments sedimentation rates and environments southeast baffin shelf and northwest labrador sea 8 26 ka ten 14c dated cores are described from the labrador sea continental slope and hatton and resolution basins on the southeast baffin shelf based on sharply defined detrital carbonate layers in the labrador sea cores we propose that the laurentide ice sheet reached the shelf break at both 20 and 15 14c ka 24 3 and 18 2 sidereal ka and contributed significant sediment to the northwest labrador sea both times the flux was 720 kg m2 ka during these periods of maximum ice extent the laurentide ice sheet retreated from its 15 ka position at the shelf break to the inner shelf between 14 and 12 14c ka ice proximal conditions recognized by relatively light 18o on near surface planktonic foraminifera high detrital carbonate and benthic foraminiferal faunas dominated by elphidium excavatum forma clavata cassidulina reniforme prevailed until at least 10 14c ka the ice readvanced toward resolution basin and across part of hatton basin at 11 14c ka accelerator mass spectrometry dates on core tops i

reduced meltwater outflow from the laurentide ice margin during the younger dryas the cause of the younger dryas cold event which interrupted the last deglaciation is still a matter of debate1 a prevalent hypothesis proposed by broecker et al 2 is that the abrupt climate change was driven by a decrease in the rate of north atlantic deep water production triggered by a sudden dilution of north atlantic surface water in response to the diversion of laurentide icesheet melt water from the mississippi drainage system to that of the st lawrence river here we investigate the feasibility of this triggering mechanism by reconstructing sea surface temperature salinity and sea ice cover records for the outlet of the gulf of st lawrence into the north atlantic ocean these reconstructions based on dinoflagellate cyst assemblages3 4 in sediment cores from the region show reduced meltwater runoff low temperatures and extensive sea ice cover during the younger dryas dated here between 10 800 and 10 300 bp meltwater pulses did occur before and after the younger dryas event as early as 11 700 bp during the development of the champlain sea in the st lawrence lowland and afterwards until 10 100 bp at the resolution of our salinity proxy 0 7 the meltwater pulses preceding the younger dryas did not affect sea surface salinity off the shelf break these constraint on the meltwater outflow through the st lawrence drainage system do not support the triggering mechanism of the broecker et al hypothesis2 unless the north atlantic thermohaline circulation is more sensitive to small salinity changes than most models suggest23

flow measurement in sloping channels with rectangular free overfall this technical note describes an experimental study of the free overfall from a rectangular channel with differing slopes and bed roughnesses the relationship between the upstream critical depth and brink depth is explored and found to be influenced by both slope and channel bed roughness with roughness having a greater effect at steeper slopes two empirical equations are proposed for calculating this relationship the first requiring only the channel slope to be known and the second requiring a knowledge of channel slope and roughness the accuracy of the two equations when used in a method for flow measurement are compared the first relationship in which the effects of slope and roughness are aggregated provides a useful estimate of channel discharge if only the channel slope is known if both bed roughness and slope are known then the second relationship can be used to calculate channel discharge with greater accuracy

li and li isotopic composition of hydrothermally altered sediments at middle valley juan de fuca li and li isotopes have been measured in the clay fraction of sediments recovered from the middle valley hydrothermal site on the juan de fuca ridge the li content of pure detrital clays is 51 ppm while hydrothermal clays and carbonates have lower li 22 11 ppm however there is no clear relationship between the mineralogy of the hydrothermal alteration products and their li content the 7li value of the detrital clays is 5 8 hydrothermal clays and carbonates have 7li in the range of 3 9 to 7 8 these values do not seem to be dependent on the temperature at which they formed modelling of the li and li isotope systematics indicates that the fluid from which the alteration products form is significantly enriched in li higher than 10 000 mol kg 1 relative to pore fluids recovered from within the sediments up to 589 mol kg 1 wheat c g m j mottl 1994 data report trace metal composition of pore water from sites 855 through 858 middle valley juan de fuca ridge in mottl m j davis e e fisher a t slack j f eds proc odp sci res 139 749 755 and that this li is derived from sediment thus the alteration products are not in equilibrium with their conjugate pore fluids rather the alteration minerals formed at lower water sediment ratios this suggests that fluid flow pathways at middle valley were more diffuse in the past than they are today

application of modern analog technique to marine antarctic diatoms reconstruction of maximum sea ice extent at the last glacial maximum modern analog technique mat applied to antarctic diatoms is a new approach for quantitative sea ice paleoreconstructions in the southern ocean in a first step we show that mat is a better approach than the imbrie and kipp method to reconstruct the modern sea ice pattern we then use this approach to reconstruct sea ice presence in number of months per year during the last glacial maximum lgm at this time sea ice presence was greater than today leading to a shorter diatom growing season the maximum sea ice extent inferred from quantitative values of sea ice presence was located 5 8 north of its actual position leading to double the surface of modern winter sea ice this greater sea ice extent may have played a significant role on atmospheric and surface oceanic circulations and therefore on southern mid latitude and high latitude climates it may also have reduced the amount of heat moisture and co2 from the ocean to the atmosphere thus participating in the lowering of atmospheric co2 during the lgm

petroleum associated with polymetallic sulfide in sediment from gorda ridge a sediment sample impregnated with asphaltic petroleum and polymetallic sulfide was dredged from the southern end of gorda ridge the escanaba trough off northern california within the offshore exclusive economic zone of the united states the molecular distributions of hydrocarbons in this petroleum show that it was probably derived from terrestrial organic matter in turbidite sediment filling the escanaba trough hydrothermal activity at the gorda ridge spreading center provided the heat for petroleum formation and was the source of fluids for sulfide mineralization

distribution of coccoliths in surface sediments in the norwegian greenland sea abstract the distribution of coccoliths has been examined in 20 surface sediment samples along an east west transect in the norwegian sea based on the abundance and species richness of coccoliths three biogeographic zones have been established along this transect the distribution of coccolith assemblages in the surface sediments appears to match closely with the locations of the different surface water masses in the norwegian greenland sea

ice age paleotopography a gravitationally self consistent theory of postglacial relative sea level change is used to infer the variation of surface ice and water cover since the last glacial maximum lgm the results show that lgm ice volume was approximately 35 percent lower than suggested by the climap reconstruction and the maximum heights of the main laurentian and fennoscandian ice complexes are inferred to have been commensurately lower with respect to sea level use of these ice age boundary conditions in atmospheric general circulation models will yield climates that differ significantly from those previously inferred on the basis of the climap data set

palynological evidence of climatic and oceanographic changes in the north sea during the last deglaciation abstract palynological analyses performed on cores from the norwegian channel troll 8903 led to reconstruction of the late glacial variations in sea surface conditions using dinoflagellate cyst data and permitted direct correlation with the vegetation history of northwestern europe derived from pollen assemblages by 15 000 yr b p ice rapidly receded from the norwegian shelf and relatively warm summer conditions prevailed in surface waters a first late glacial cooling marked by extensive seasonal sea ice cover is dated at ca 13 600 13 00014c yr b p which coincides with the oldest dryas interval during the bolling allerod interval a rise in sea surface temperature both in february up to 3 c and august up to 15 c led to the establishment of ice free conditions in the northern north sea while pollen data reveal a densification of the vegetation cover the beginning of the younger dryas interval is marked by an increase in nonarboreal pollen input indicative of the opening of the forest vegetation cover concomitant with a cooling of surface waters during winter and development of sea ice cover however sea surface conditions remained relatively warm in summer until about 10 300 yr b p when extremely cold conditions and extensive sea ice cover developed up to 7 months yr improving conditions are recorded in surface waters by 10 100 yr b p a few hundred years before the development of forest cover onshore as shown by the pollen record such a discrepancy between marine and terrestrial indicators at the end of younger dryas time suggests a delayed response of the vegetation to regional climate warming

sea ice cover sea surface salinity and halo thermocline structure of the northwest north atlantic modern versus full glacial conditions abstract seasonal sea ice develops along the eastern continental margins in the northern north atlantic where freshwater and or meltwater outflow are responsible for relatively low salinity in surface waters and very pronounced water mass stratification sea ice constitutes a major parameter in the marine ecosystem since the duration and extent of its seasonal spreading constrain the plankton distribution and the related microfossil assemblages on the sea floor organic walled dinoflagellate cysts that are highly resistant to dissolution were recovered from surface sediments of the northern north atlantic and used to develop transfer functions best analogue method for the reconstruction of the seasonal spreading and duration of sea ice cover in addition to salinity and temperature of the warmest month of the year application of the best analogue approach to cores from the labrador sea reveals large variations in sea ice cover and sea surface conditions throughout the last glacial stage and during the early holocene isotopic analyses in epipelagic and mesopelagic planktonic foraminifers also suggest important changes in salinity and temperature gradients between the surface and sub surface water masses specific study of the last glacial maximum lgm time slice 16 20 ka on a 14 c time scale in the northwestern north atlantic shows much more extensive sea ice than at present with perennial sea ice lying along the continental margins of eastern canada seasonal spreading of the cover of sea ice offshore was accompanied by large seasonal contrasts in temperature with very cold winters but relatively warm summers a pattern linked to strong stratification between a buoyant low saline surface layer having a low thermal inertia and the underlying intermediate oceanic waters

wisconsin holocene paleoenvironment of the bering sea evidence from diatoms pollen oxygen isotopes and clay minerals abstract a core from the southeastern bering sea contains a depositional record of the wisconsin glacial interval and the holocene four lithologic units show distinctive changes in diatom species palynomorphs oxygen isotopes in diatom silica and clay minerals unit 4 the oldest probably represents the glacial advance of the early wisconsin and records extensive sea ice cover and a soggy herbaceous tundra on the exposed continental shelf unit 3 represents the stades and interstades of the middle wisconsin including an early period of high seasonal variability and a later period with expansion of winter sea ice in the basin and of tundra onshore unit 2 represents the late wisconsin glacial maximum and subsequent deglaciation with a tundra covered shelf sea ice cover increased to a maximum during which the surface waters were probably covered by sea ice throughout the year subsequent to the sea ice maximum the isotope ratios record a major meltwater event unit 1 represents the holocene with expansion of shrub tundra or scrub forest in the coastal upland and waters of increased temperature and salinity in the bering sea

micropaleontology and palynology of core par87a 10 a 23 000 year record of paleoenvironmental changes in the gulf of alaska northeast north pacific micropaleontological data of core par87a 10 reveal that the last glacial interval prior to 13 ka was marked by low biogenic fluxes and poor caco3 preservation quantitative estimates of sea surface conditions based on dinocyst assemblages suggest that cold temperatures and freezing winter conditions existed during this period the glacial to interglacial transition i e the 13 8 ka interval was characterized by an increase in fluxes of microfossils indicating enhanced productivity in surface waters a higher biogenic carbonate production probably resulted in better preservation of caco3 this interval was marked by relatively low salinity and by sea surface temperatures increasing toward modern values relatively high pollen flux during the transition suggests nutrient inputs through atmospheric and or fluvial transport from the adjacent north american continent after 8 ka diminished fluxes of plankton concomitant with a decline in pollen input are associated with decreasing nutrient supply as predominantly eastward winds became established over the north pacific

late quaternary paleoceanography of the western baffin bay region evidence from fossil diatoms seven marine cores from the east coast of baffin island were examined for variations in diatom content the cores have good age control and were used for holocene paleoceanographic reconstruction

sensitivity of the northern hemisphere climate system to extreme changes in holocene arctic sea ice the extent of seasonal and perennial sea ice changed dramatically through the late quaternary and these changes influenced both the ocean and atmosphere by controlling the exchange of energy moisture and gases between them and by altering the planetary albedo reconstructing the changing patterns of sea ice distribution in the recent past remains one of the outstanding challenges to the paleo community to evaluate the importance of these reconstructions we performed sensitivity tests using ncar s community climate model ccm3 and a series of prescribed sea ice extents designed to capture the full range of arctic sea ice variability under interglacial holocene and full glacial last glacial maximum boundary conditions our simulations indicate that surface temperatures and sea level pressures in winter djf are most sensitive to changes in sea ice and that these changes are propagated over the surrounding land masses in the north atlantic but that equivalent changes in sea ice produce smaller corresponding changes in temperature or sea level pressure in the north pacific region a comparison between climap map chart series mc 36 geological society of america boulder co 1981 and a more realistic assessment of lgm sea ice yields dramatic changes in winter temperatures and precipitation patterns across eurasia these differences forced only by changed sea ice conditions reinforce the need to develop accurate maps of past sea ice to correctly simulate late quaternary environments such reconstructions also will be essential to validate the next generation of sea ice models

submerged and unsubmerged natural hydraulic jumps in a bedrock step pool mountain channel high resolution digital elevation models dems for natural submerged and unsubmerged jump regions were tested against the classical hydraulic jump chj and engineering analogues that have dominated previous geomorphic and engineering research dems were compared for two discharge conditions the data showed bed and water surface features of the natural jump regions differ significantly from chj conditions and engineering analogues with respect to boundary conditions roughness elements were highly irregular in frequency spacing size and orientation and were comprised of form obliquity and bed scour in boulder bed and pure bedrock conditions the data also showed bed and water surface features of natural jump regions have similarities and deviations from chj conditions and engineering analogues with respect to hydraulic characteristics several variations were observed in the hydraulic characteristics between the ballistic and sloping jets revised conceptual models based on idealized corollaries were developed for the natural jump regions based on upstream energy head relative to the downstream tailwater depth and step geometry the dems highlight the importance of recognizing the interrelationship between spatial transcritical flow structures and localized topographic heterogeneities in bedrock channels

the alkali element and boron geochemistry of the escanaba trough sediment hosted hydrothermal system a suite of conjugate pore fluid and sediment samples were collected during leg 169 of the odp from within the clastic sedimentary sequences which host massive sulphides at central hill escanaba trough odp site 1038 we report the alkali element and boron and li and b isotope data for these samples relative to a reference site site 1037 located outside the zone of high heat flow pore fluids from site 1038 show a wide variation in cl 300 800 mm and have far higher concentrations of li up to 6 2 mm b up to 9 7 mm cs up to 5 0 m and rb up to 97 m we show that the pore fluids are derived from hydrothermal circulation that has extended into the basement oceanic crust with input of the alkali elements and b as the rising hydrothermal fluids interact geochemically with the overlying clastic sediments there is however no marked depletion of these elements in the conjugate sediments suggesting that there has been advective transport of fluids away from the primary hydrothermal reaction site this is supported by modelling of the li and b isotope systematics of the pore fluids which shows that they record extensive formation of secondary minerals during cooling of the fluids from 350 to 20 c precipitation of metal rich sulphides would have occurred prior to the formation of these minerals thus the pore fluid li and b isotope data can place important constraints on the locus of sulphide deposition beneath the seafloor at escanaba

the prism pliocene palaeoclimate reconstruction time for a paradigm shift global palaeoclimate reconstructions have been invaluable to our understanding of the causes and effects of climate change but single temperature representations of the oceanic mixed layer for dat

deep sea sedimentary record of the late wisconsin cataclysmic floods from the columbia river new results from ocean drilling program site 1037 and u s geological survey high resolution seismic reflection profiles confirm the great thickness fast deposition rate distant source and convolute path of turbidites that fill the escanaba trough the rift valley of the southernmost segment of the gorda ridge accelerator mass spectrometry 14 c measurements provide the first direct dating of the escanaba trough turbidites demonstrating an average deposition rate faster than 10 m k y between 32 and 11 ka and as fast as 15 m k y during the oxygen isotope stage 2 lowstand in the upper 60 m of sediment the petrology of turbidite sand beds which are as much as 12 m thick show that the dominant source for the turbidites is from the columbia river which is more than 800 km to the north rather than from the much closer rivers of northern california new high resolution seismic reflection profiles show that except for areas of very recent volcanism the entire escanaba trough below 3200 m water depth is floored by the turbidite sequence that was cored in the upper 60 m at site 1037b the ages of the upper 120 m of turbidites correspond with the ages of channeled scabland deposits associated with latest quaternary jokulhlaups from glacial lake missoula the age and source characteristics suggest that these megaturbidite beds in escanaba trough are most likely deposits formed by hyperpycnally generated turbidity currents as the largest of the lake missoula floods entered the sea

glacial north atlantic sea surface conditions reconstructed by glamap 2000 the response of the tropical ocean to global climate change and the extent of sea ice in the glacial nordic seas belong to the great controversies in paleoclimatology our new reconstruction of peak glacial sea surface temperatures ssts in the atlantic is based on census counts of planktic foraminifera using the maximum similarity technique version 28 simmax 28 modern analog technique with 947 modern analog samples and 119 well dated sediment cores our study compares two slightly different scenarios of the last glacial maximum lgm the environmental processes of the ice age land oceans glaciers epilog and glacial atlantic ocean mapping glamap 2000 time slices the comparison shows that the maximum lgm cooling in the southern hemisphere slightly preceeded that in the north in both time slices sea ice was restricted to the north western margin of the nordic seas during glacial northern summer while the central and eastern parts were ice free during northern glacial winter sea ice advanced to the south of iceland and faeroe in the central northern north atlantic an anticyclonic gyre formed between 45degrees and 60degreesn with a cool water mass centered west of ireland where glacial cooling reached a maximum of 12degreesc in the subtropical ocean gyres the new reconstruction supports the glacial to interglacial stability of sst as shown by climap project members climap 1981 the zonal belt of minimum sst seasonality between 2degrees and 6degreesn suggests that the lgm caloric equator occupied the same latitude as today in contrast to the climap reconstruction the glacial cooling of the tropical east atlantic upwelling belt reached up to 6degrees 8degreesc during northern hemisphere summer differences between these simmax based and published u37 k and mg ca based equatorial sst records are ascribed to strong sst seasonalities and sst signals that were produced by different planktic species groups during different seasons

depth averaged model of open channel flows over an arbitrary 3d surface and its applications to analysis of water surface profile a new set of depth averaged equations is introduced to study the flow over an arbitrary three dimensional 3d surface these equations are derived based on a generalized curvilinear coordinate system attached to the 3d bed surface therefore it allows us to include the effect of centrifugal force due to the bottom curvature these general equations make it possible to analyze flows over complex terrain without the limitation of mild slope assumption used in conventional depth averaged models this new model is then applied to calculate the water surface profiles of 1 flow over a cylindrical surface 2 flow over a circular surface and 3 flow with an air core vortex at a vertical intake a simple hydraulic experiment is conducted in the laboratory to observe the water surface profile of flow over a circular surface the results obtained from the model are in good agreement with experimental measurements and calculation by an empirical formula consequently it demonstrates the applicability of the model in cases of flow over a highly curved bottom

late quaternary sea surface conditions at dsdp hole 594 in the southwest pacific ocean based on dinoflagellate cyst assemblages investigation of organic walled dinoflagellate cyst distribution in 118 surface sediments from the southern ocean documents the relatively high diversity of cyst taxa 46 species and distinct cyst assemblages in relation to surface water masses and temperature gradient the antarctic water is characterised by the dominance of selenopemphix antarctica accompanied by brigantedinium spp and impagidinium pallidum the subantarctic water association consists mainly of nematosphaeropsis labyrinthus impagidinium paradoxum and impagidinium sphaericum whereas the subtropical water association is dominated by operculodinium centrocarpum and spiniferites membranaceus multivariate analyses non metric multidimensional scaling demonstrate the relationships with sea surface conditions and enable the application of the best analogue method on the southern ocean dinoflagellate cyst data base for reconstructing past sea surface conditions the dinoflagellate cyst record from dsdp 594 45 31 41 s 174 56 88 e 1204 m southern margin of the chatham rise shows important fluctuations in species composition from glacial to interglacial over the last 140 000 yr reconstruction of winter and summer ssts reveals much lower temperature than present by 6 to 10 c during marine oxygen isotope stages 6 4 and 2 and higher temperature by 2 3 c during substage 5e copyright 2001 john wiley sons ltd journal of quaternary science

a novel chemical fossil of palaeo sea ice ip25 a unique and novel organic compound has been detected in sea ice samples from three locations in the canadian arctic thousands of kilometers apart it is likely that this biomarker is produced by diatoms living in the sea ice and we provide evidence which suggests that the compound a c25 monounsaturated hydrocarbon ip25 may be a specific sensitive and stable proxy for sea ice in sediments over at least the holocene since it has not been reported before we confirmed its identity by synthesis and used the synthesized compound as a reference for quantifying ip25 in a range of sediments from an east west transect in the canadian arctic the recent sediments are either seasonally covered with ice or have permanent ice cover older sediments containing ip25 have been dated using radiocarbon methods to at least 9000 yr if the concept proves generally applicable monitoring ip25 in further sediment cores along with other accepted proxies should allow movements in the position of the ice edge throughout the holocene at least to be better determined which is essential for accurate calibration of climate prediction models a similar approach for antarctic samples of ice and sediments would also seem worthwhile

the north atlantic atmosphere sea surface 14c gradient during the younger dryas climatic event abstract we attempt to quantify the 14c difference between the atmosphere and the north atlantic surface during a prominent climatic period of the last deglaciation the younger dryas event yd our working hypothesis is that the north atlantic may have experienced a measurable change in 14c reservoir age due to large changes of the polar front position and variations in the mode and rate of north atlantic deep water nadw production we dated contemporaneous samples of terrestrial plant remains and sea surface carbonates in order to evaluate the past atmosphere sea surface 14c gradient we selected terrestrial vegetal macrofossils and planktonic foraminifera neogloboquadrina pachyderma left coiling mixed with the same volcanic tephra the vedde ash bed which occurred during the yd and which can be recognized in north european lake sediments and north atlantic deep sea sediments based on ams ages from two norwegian sites we obtained about 10 300 yr bp for the atmospheric 14c age of the volcanic eruption foraminifera from four north atlantic deep sea cores selected for their high sedimentation rates 10 cm kyr 1 were dated by ams 21 samples for each core the raw 14c ages assigned to the ash layer peak is significantly older than the 14c age obtained on land part of this discrepancy is due to bioturbation which is shown by numerical modelling nevertheless after correction of a bioturbation bias the mean 14c age obtained on the planktonic foraminifera is still about 11 000 11 100 yr bp the atmosphere sea surface 14c difference was roughly 700 800 yr during the yd whereas today it is 400 500 yr a reduced advection of surface waters to the north atlantic and the presence of sea ice are identified as potential causes of the high 14c reservoir age during the yd

hydrothermal alteration of organic matter in sediments of the northeastern pacific ocean part 2 escanaba trough gorda ridge samples from the ocean drilling program leg 169 in escanaba trough gorda ridge ne pacific ocean were analyzed to study maturation by accelerated diagenesis and or by catagenesis of the sedimentary organic matter to hydrothermal petroleum at site 1038 the hydrothermal petroleums have migrated after generation to shallower horizons the n alkane maturation was indicated by the strong even c number preference i e cpi 1 0 as in the case of middle valley all samples contained admixed organic matter of terrigenous and marine components as indicated by the distributions of the biomarkers the biological precursors were catagenetically altered to their equivalent mature compounds the presence of high molecular weight pahs in some sediment sections at site 1038 reflected the high temperature alteration and reworking of organic matter into mature hydrothermal petroleum at site 1037 the reference hole in the escanaba trough the n alkanes with a strong predominance of odd c number homologs reflected immature non marine lipid components essentially throughout the hole maturation of organic matter was only observed below 450 mbsf with n alkanes showing a cpi 1 0 the strong even c number predominance in those intervals was attributed to initial maturation by high heat flow during the early rifting process

millennial scale glacial meltwater pulses and their effect on the spatiotemporal benthicδ18o variability 1 ratios of oxygen isotope values obtained from foraminiferal calcite are one of the most established paleoceanographic proxies they are used in the context of estimating variations in ice volume ocean temperature and salinity and provide a means to date marine sediment cores across different ocean basins our study addresses the question how the 18o of the deglacial meltwater signal propagates into the interior ocean when large scale millennial scale reorganizations of the atlantic meridional overturning circulation amoc are present analyzing a series of idealized tracer injection experiments conducted with an earth system model we find that a substantial weakening of the amoc leads to a massive delay in the export of the glacioeustatic oxygen isotope signal into the deep ocean whereas the atlantic pacific lag in benthic oxygen isotope signals is not increased furthermore it is shown that an amoc cessation causes a decoupling of 18o propagation time and water mass age in particular in the deep pacific our results lend further support to the notion that benthic oxygen isotope records obtained from stacks are not a useful global chronostratigraphic tool during periods of millennial scale global ocean circulation changes the regionally varying delay effect of the deglacial sea level signal studied here adds onto existing uncertainties in the interpretation and decomposition of benthic oxygen isotope in terms of sea level temperature and hydrographic variations