submarine landforms and shallow acoustic stratigraphy of a 400 km long fjord shelf slope transect kangerlussuaq margin east greenland kangerlussuaq fjord is a relatively uniform steep walled basin whose floor has an almost smooth surface debris is supplied mainly from icebergs from the fast flowing kangerlussuaq glacier sedimentation after iceberg release from multi year sea ice is mainly by rain out of fine grained englacial debris streamlined glacial lineations and drumlins were produced at the sedimentary bed of an ice sheet that expanded into kangerlussuaq trough at the last glacial maximum lgm bedrock channels and crescentic overdeepenings indicate warm based ice and free water beneath parts of the former ice sheet cross cutting iceberg scour marks which characterise outer kangerlussuaq shelf were produced not only during deglaciation but also occasionally through the holocene by deep keeled icebergs from further north in east greenland the outward convex contours of the shelf edge and slope beyond kangerlussuaq trough and debris flows on the slope suggest a glacier influenced high latitude fan the distribution of streamlined subglacial landforms demonstrates that the greenland ice sheet extended throughout kangerlussuaq fjord and reached at least 200 km across the shelf in kangerlussuaq trough at the lgm streamlined landform orientation indicates ice flow from the interior of greenland down the axis of kangerlussuaq trough there is little evidence for discrete sedimentary depocentres in the trough implying that ice probably retreated rapidly from the outer and mid shelf during deglaciation

structural and stratigraphic controls on petroleum seeps green canyon and ewing bank northern gulf of mexico implications for petroleum migration abstract numerous petroleum seeps and chemosynthetic communities are present on the continental slope in the northern gulf of mexico these features are associated with faults and salt highs and indicate recent petroleum migration thirty three known petroleum seep and or chemosynthetic communities in green canyon and ewing bank were studied in a sub regional context to understand their stratigraphic and structural controls and their significance to the overall petroleum system results indicate that surface seeps occur associated with all different allochthonous salt systems present ramp fault systems roho systems stepped counterregional systems and counterregional systems and all four systems are efficient of the thirty five fields and discoveries in the area only six occur near 4 8 km seeps suggesting that the seeps are indicative of an efficient and mature petroleum system but not necessarily of proximal reservoirs petroleum seeps may be more related to poor trap and or seal development the relative rates of vertical migration of petroleum can be estimated based on the timing of salt weld formation these estimates range from 0 0015 to 0 025 m y

correlation of reservoired gases using the carbon isotopic compositions of wet gas components the carbon isotopic compositions of the wet gas components particularly propane isobutane and normal butane have been found to be particularly valuable for correlating one reservoired gas with another the usefulness of these components for correlation results from their carbon isotopic compositions reflecting both the nature of their source and their maturity this source control is strongest for gases derived from the more highly structured types of kerogen i e woody coaly type iii although the wet gas components carbon isotopic compositions of most gases are at least partly controlled by their source for levels of maturity below the point at which thermal destruction of the wet components occurs as a result the wet gas components are found to provide more ositive correlations than is methane alone three exploration examples illustrate the use of the carbon isotopic compositions of the wet gas components for correlation the leduc reef trend of alberta canada the sleipner area in the north sea and the lena field offshore louisiana united states the three examples also illustrate the need to integrate geochemical interpretations with regional geology to obtain a good understanding of the hydrocarbon source

hydrography and energetics of a cold subpolar fjord andvord bay western antarctic peninsula abstract fjords along the western antarctic peninsula contain rich marine ecosystems and tidewater glaciers potentially sensitive to ocean change but much is unknown about the physical oceanography of these fjords this paper presents a comprehensive description of the physical environment of andvord bay a glacial fjord located in the gerlache strait on the northern end of the peninsula measurements were collected as part of the fjordeco program between november 2015 and march 2017 including during three research cruises and from a number of fixed installations sub surface moorings time lapse cameras and automatic weather stations andvord bay is located just north of a sill in the gerlache strait this sill inhibits the direct influence of warm upper circumpolar deep water from the shelf and deep waters in the fjord are therefore relatively cold as a result glaciers in andvord bay are not subject to the substantial ocean driven retreat observed farther south on the peninsula instead mass flux from the glaciers occurs mainly through calving the influence of meltwater in andvord bay is small compared to glacial fjords in the arctic and in the south shetland islands although summer freshening is evident in the fjord near surface layer likely as a result of glacial inputs the combination of surface freshening and the absence of strong mean wind forcing in the fjord results in salinity stratification extending well into the euphotic zone providing advantageous conditions for phytoplankton blooms andvord bay is generally dynamically quiet compared to the ambient ocean with the exception of during local katabatic wind events exchange with the gerlache strait is weak although the deep waters of the fjord are replenished on an annual scale through slow lateral exchange with the outside in addition deep convection may play a role in ventilating subsurface waters in winter

anisotropy beneath the pyrenees range from teleseismic shear wave splitting results from a test experiment we have investigated the seismic anisotropy from sks and skks wave splitting along a n s profile perpendicular to the pyrenean mountain belt the line crossed the north pyrenean fault npf which probably represents the plate boundary between the european and the iberian plates we observed large delay times t 1 3 to 1 5 s and uniform fast polarization directions n100e at three stations located on the iberian plate on the other hand t are smaller 0 5 1 0 s and the scattered at stations located north of the npf the small scale variability the relation with surface geology and the correlation of the t with lithospheric thickness suggest that the anisotropy could be predominantly of lithospheric origin however an asthenospheric contribution cannot be ruled out in the north pyrenean zone an important thermal event before the pyrenean compression has likely erased the former mantle fabric the observed anisotropy is then likely related to the pyrenean orogeny on the iberian plate our splitting parameters are similar to those obtained at two stations located on hercynian structures in central spain this suggests that two contributions are likely superposed to that of the pyrenean built up one related to the hercynian orogeny and the other one related to the rotation of the iberian plate

decrease in natural marine hydrocarbon seepage near coal oil point california associated with offshore oil production prolific natural hydrocarbon seepage occurs offshore of coal oil point in the santa barbara channel california within the water column above submarine vents plumes of hydrocarbon gas bubbles act as acoustic scattering targets using 3 5 khz sonar data seep distribution offshore of coal oil point was mapped for august 1996 july 1995 and july 1973 comparison of the seep distributions over time reveals more than 50 decrease in the areal extent of seepage accompanied by declines in seep emission volume in a 13 km 2 area above a producing oil reservoir declines in reservoir pressure and depletion of seep hydrocarbon sources associated with oil production are the mechanisms inferred to explain the declines in seep area and emission volume

evaluation of possible gas microseepage mechanisms petroleum microseepage anomalies over petroleum accumulations are commonly explained by rapid vertical migration of colloidal gas bubbles through fracture networks this article is a theoretical anal ysis of this mechanism and of continuous gas phase flow in frac tures the gas bubble ascent mechanism is much slower than re ported microseepage velocities so it cannot account for observed microseepage in contrast continuous gas phase flow through frac tures can equal or exceed reported microseepage velocity while maintaining total flux low enough so that petroleum accumulations can exist for geological lengths of time fracture entry pressure for bubbles is more than twice that of a continuous gas phase so con tinuous gas phase migration also requires a lower pressure threshold before initiating seepage vertical microseepage is therefore best explained by the same mechanism interpreted for macroseepage although this article provides a theoretically justified mecha nism for microseepage it also shows why interpretation of surface microseepage signals is problematic fracture geometry controls seepage velocity and flux so geochemical anomalies may indicate an increase in fracture aperture as well as possible subsurface ac cumulations larger fractures require very low gas capillary entry pressures so in some settings surface seepage could result from fractures over stratal migration pathways as well as over petroleum accumulations

origin and consequences of cyclic ice rafting in the northeast atlantic ocean during the past 130 000 years deep sea sediment cores recovered from the northeast atlantic ocean were examined in order to elucidate the influence of the earth s orbital parameters on major ice rafting analyses of coarse grained ice rafted debris and planktonic foraminifers revealed a strong reaction to the precession signal since 130 000 yr b p dropstone layers have been deposited each half period of a precessional cycle 11 000 1000 yr ice rafting occurs during times of winter minimum summer maximum insolation and summer minimum winter maximum insolation in the first case high summer insolation forces meltwater discharge from the ice sheets into the polar seas which subsequently enhances formation of sea ice during the winter in the second case growth of continental ice enhances iceberg production which also leads to a salinity reduction of surface seawater both situations result in a southward penetration of polar water thus the marine record of dropstones documents ice rafting not only during weichselian stades but also during cold events within interstades the regularity of ice rafting yields a useful framework to calibrate and elucidate climatic changes not only in the region of the north atlantic ocean but also in remote areas such as the pacific ocean and the antarctic

variable methane fluxes in shallow marine systems over geologic time abstract carbon cycling is an important but poorly understood process on passive continental margins in this study we use the ionic and stable isotopic composition of interstitial waters and the petrology mineralogy and stable isotopic composition of authigenic carbonates collected from ocean drilling program odp leg 174a sites 1071 and 1072 to constrain the origin of the carbonates and the evolution of methane on the outer new jersey shelf the pore fluids of the new jersey continental shelf are characterized by 1 a fresh brackish water plume and 2 organic matter degradation reactions which proceed through sulfate reduction however only minor methanogenesis occurs the oxygen isotopic composition of the pore fluids supports a meteoric origin of the low salinity fluids authigenic carbonates are found in nodules thin 1 cm layers and carbonate cemented pavements siderite is the most common authigenic carbonate followed by dolomite and calcite the oxygen isotopic composition of the authigenic carbonates i e 1 3 6 5 peedee belemnite pdb indicates an origin in marine pore fluids the carbon isotopic composition of dolomite cements range from 16 4 to 8 8 pdb consistent with formation within the zone of sulfate reduction siderite 13c values show a greater range 17 67 16 4 but are largely positive mean 2 8 and are interpreted to have formed throughout the zone of methanogenesis in contrast calcite 13c values are highly negative as low as 41 7 and must have formed from waters with a large component of dissolved inorganic carbon derived from methane oxidation pore water data show that despite complete sulfate reduction methanogenesis appears not to be an important process presently occurring in the upper 400 m of the outer new jersey shelf in contrast the carbon isotopic composition of the siderites and calcites document an active methanogenic zone during their formation the methane may have been either oxidized or vented from shelf sediments perhaps during sea level fluctuations if this unaccounted and variable methane flux is an areally important process during neogene sea level fluctuations then it likely plays an important role in long term carbon cycling on passive continental margins

iceberg discharges into the north atlantic on millennial time scales during the last glaciation high resolution studies of north atlantic deep sea cores demonstrate that prominent increases in iceberg calving recurred at intervals of 2000 to 3000 years much more frequently than the 7000 to 10 000 year pacing of massive ice discharges associated with heinrich events the calving cycles correlate with warm cold oscillations called dansgaard oeschger events in greenland ice cores each cycle records synchronous discharges of ice from different sources and the cycles are decoupled from sea surface temperatures these findings point to a mechanism operating within the atmosphere that caused rapid oscillations in air temperatures above greenland and in calving from more than one ice sheet

geophysical and geochemical evidence for subsurface hydrocarbon leakage in the bering sea alaska abstract geophysical and geochemical surveys were conducted on the bering sea shelf to investigate whether hydrocarbons found in the surficial sediment particularly in association with certain geophysical events indicate the presence and nature of more deeply reservoired oil and gas deposits surface sediment samples were obtained at 1000 sites where high resolution seismic data indicated the presence of gas seepage and or surface faulting in addition sites for background measurements were occupied away from areas of gas seepage results of the geophysical survey show seismic wipeout zones to be present throughout the bering sea shelf sediment samples obtained within the shallow wipeout zones confirm that these features are caused by gas in addition compositional and isotopic analyses indicate that the gas is of biogenic and thermogenic origins the thermogenic leakage appears to be related to localized faulting and shallow structuring the high resolution seismic data therefore provide an excellent tool for locating leakage points thereby enhancing the opportunity of finding migrated thermogenic hydrocarbons in surficial sediments an examination of vertical variability shows the hydrocarbon concentrations to be strongly related to various processes occurring in the surficial sediments core samples must be taken from below the zone of maximum disturbance to obtain unaltered hydrocarbon samples

a new greenland deep ice core the polar ice sheets are rich sources of information on past atmospheric conditions including paleoclimates a new deep ice core has been drilled in south greenland comparison of the oxygen isotopic profile with that from camp century and with a deep sea foraminifera record indicates that the new core reaches back to about 90 000 years before present in a continuous sequence the details in the wisconsin part of the ice core records seem to be climatically significant and the general trends reveal all of the relevant emiliani stages recorded in deep sea cores the redated camp century record suggests a dramatic termination of the eem sangamon interglacial

behavior of a glacier derived suspended sediment plume in a small arctic inlet the changing configuration of a glacier derived turbid surface meltwater plume was observed over a 40 hr period in a small marine inlet in spitsbergen factors controlling plume position tides winds and melt stream discharge were also monitored tidal forcing was the dominant control on plume behavior over the study period when winds were calm or light the plume spread over much of the inlet on the flood and around high tide and was restricted to the north side on the ebb and at low water winds were generally 5 kts and only influenced plume position when reaching over 12 kts coriolis effects were unimportant sediments on the inlet floor fined progressively with distance from glacier fed stream effluxes short cores showed that deposition was mainly in the form of structureless sands and silts

evidence of episodic fluid gas and sediment venting on the northern gulf of mexico continental slope surficial sediments and sea floor features of the northern gulf of mexico continental slope record dramatic episodic venting and slower seepage of formation fluids brines crude oil gases and fine grained sediments faults activated by massive sediment input during periods of plio pleistocene falling to low sea levels accompanied by compensating salt movement provide avenues of vertical transport to the continental slope surface many of these faults cut thick sedimentary sequences that frequently contain geopressured zones which provide the driving force for fluid and gas expulsion flux rate and fluid characteristics are interpreted as important determinants of modern sea floor geology and biology qualitatively under conditions of rapid flux of sediment rich fluids mud volcanoes up to 1 km wide and 50 m high and extensive sheets of extruded mud result these sediments contain old and displaced microfaunas muds are frequently extruded with large volumes of crude oil and gas both biogenic and thermogenic in water depths greater than approximately 500 m rapid to moderate vertical flux of hydrocarbon gases and fluids results in the construction of relief features composed of gas hydrates ejected mud and authigenic carbonates areas with near surface hydrates frequently support complex chemosynthetic communities with associated hardgrounds containing calcareous remains of mussels clams and associated gastropods slow flux seeps promotes the formation of 13 c depleted carbonate hardgrounds stacked carbonate slabs and moundlike carbonate buildups frequently 20 m relief barite along with carbonate has been found in areas where rapid flux of sediment carrying fluids has waned in the recent past and mineral rich brines are now being ejected crests chimneys and cones of these minerals are found in such settings both recent numerical simulations of fluid release from geopressured zones and direct observations at the sea floor support a pattern of episodic venting short term episodes of venting are probably regulated by fault movement perhaps controlled by local salt adjustment destabilization of gas hydrates by oceanographic processes also causes short term episodic gas expulsion these events occur with interannual to intra annual frequencies longer gas hydrate stabilization destabilization cycles in continental margin settings are forced by hydrostatic loading and unloading at the frequency of sea level change radiometric dating suggests that other long term episodes of venting and major venting expulsion events are also probably modulated by sea level change time scales of thousands of years in response to low stand sedimentary loading results of this summary of vent seep related phenomena suggest that sediment input from the shelf margin associated with cyclic plio pleistocene falling to low sea level periods followed by major listic fault and salt adjustments to a new sediment load have activated venting seepage throughout this period and perhaps longer

shallow sediment deformation styles in north western campeche knolls gulf of mexico and their controls on the occurrence of hydrocarbon seepage during german r v meteor m67 2 expedition to campeche knolls southern gulf of mexico a set of 2d high resolution seismic data was acquired to study the near surface sediment structure and its relationship with hydrocarbon seepages in this salt province the comprehensive survey covered 20 individual bathymetric highs or ridges and identified three principle structural types passive type chaopopte type and asymmetric flap type the first type is the result of passive diapirism whereas the latter two were initialized by a regional compressional event in the miocene but are later differently modified by salt tectonism chapopote type structures appear as symmetrical domes with uplifted coarse grained miocene sediments in their cores and rather thin syn kinematic sediments covering the crests asymmetric flap type structures are also first folded as domes or ridges but one flap later subsided together with salt evacuation resulting in single uplifted monoclines with the coarse grained pre kinematic sediments as reservoir units both structural types can focus and accumulate hydrocarbons the geometries of the structures suggest that hydrocarbons are accumulated in the center of the chapopote type structures and in the subsided flaps of the asymmetric flap type structures hydrocarbon leakage from these thinly sealed reservoirs is regarded as the principle mechanism for the seepage in the study area and accordingly the most seepage prone positions are above these reservoirs the seep locations suggested by analysis of sea surface oil slick images of sar satellite data are also examined in this study these independently derived seep locations confirm the seepage prone positions to be above the shallow buried reservoirs this study suggest that the shallow sediment structures control the distribution of the hydrocarbon seeps of the north western campeche knolls although the hydrocarbons are sourced from the greater depth

partitioning effects from ocean and atmosphere on the calving stability of kangerdlugssuaq glacier east greenland we use the 7 km retreat of kangerdlugssuaq glacier kg east greenland to examine the mechanisms interactions and relative significance of atmospheric forcing and ice ocean interactions hydrographic data from 1991 1993 and 2004 show that subtropical waters are common in kangerdlugssuaq fjord kf and that surface waters were warm in 2004 relative to 1991 and 1993 the main water column was nonetheless warmest in 1991 we contend that while flow of subtropical waters into fjords provides a setting in which rapid glacier retreat can occur the triggering of retreat depends on additional environmental factors the climatic variables standing out in our study of kg and kf are air temperature and katabatic winds both had strong positive anomalies during winter 2004 05 when kg retreated we show that proglacial ice melange was absent and that fjord freeze up did not occur until 11 april 2005 due to warm and windy conditions we demonstrate that this setting is unusual and hypothesize that exposure to open water in winter months caused the retreat calculation of ice front melt rates shows that discharge of basal meltwater first from runoff and subsequently from frictional basal heating should intensify the interaction between glacier and fjord

association of oil seeps and chemosynthetic communities with oil discoveries upper continental slope gulf of mexico abstract geochemical fingerprinting of many upper gulf slope oils indicates an origin from deeply buried mesozoic carbonate source rocks substantial vertical migration 6 km 19 680 ft along salt and fault migration conduits must be invoked to explain the emplacement of mesozoic sourced oils in shallow miocene to pleistocene reservoirs gulf slope seeps provide evidence of oil and gas charge in a rapidly subsiding salt basin where oil and gas migration is a geologically recent or ongoing event sea floor oil and gas seeps gas hydrates chemosynthetic communities authigenic carbonate derived from hydrocarbon oxidation and natural oil slicks are diagnostic indicators of charge there is a regional association between seeps and the upper gulf slope oil province offshore louisiana and texas there is also a subregional relationship between seeps and the localized charge systems that give rise to individual oil accumulations key case histories include marquette field jolliet field and the gc 228 discovery in northwest green canyon as well as the cooper and auger discoveries in northeast garden banks

transport of suspended particulate matter in an antarctic fjord abstract vertical profiles of temperature salinity and light attenuation were used in conjunction with underwater photography and water samples to characterize the nature and dynamics of particle transport in an antarctic fjord most of the particles are sand sized 0 1 2 mm floccules comprised of individual grains in the 5 to 50 m size range the quartz silt grains are derived from basal debris laden meltwater originating from beneath the submerged valley glacier the meltwater buoyantly rises to form cold water interflows at mid water depths turbulent mixing near the seafloor also plays a role in the transport and break up of floccules together the midwater cold tongues and near bottom turbidity account for 87 of the total sediment load thus attesting to the importance of non surface transport mechanisms in polar fjords

reducing the risk of finding a working petroleum system using sar imaging sea surface slick sampling and geophysical seafloor characterization an example from the eastern black sea basin offshore georgia abstract as new plays emerge in deepwater settings sea surface slicks are often overlooked as a source of geochemical information to help define potential petroleum systems to demonstrate how sea surface hydrocarbon slicks can be used a case study is presented from the eastern black sea in the rioni basin offshore republic of georgia there source rocks of oligo miocene age maikop are suspected of charging upper miocene deepwater channel levee sands in fold and thrust system traps to reduce exploration risk direct evidence of hydrocarbon generation and migration was sought using sea surface slicks observed there to provide confirmation of charge a collection of diverse data was used first synthetic aperture radar satellite images were utilized to verify the presence of large recurring sea surface slicks over prospective structures these slicks were then sampled for later analysis during the acquisition of 3 d seismic data to verify that the slicks were related to the subsurface expulsion seafloor bathymetric and amplitude data were extracted from the 3 d seismic volume and used to identify potential seafloor features consistent with hydrocarbon seepage some of these seafloor features were found to be coincident with the apparent sea surface origins of the slicks seismic imaging was also used to demonstrate potential migration pathways which may link suspected deep subsurface traps and the seafloor and finally geochemical analysis showed that the compositional characteristics of the slicks hydrocarbons were similar to known maikop sourced oils in the region this combination of data provided a high level of confidence that the seismically imaged traps in offshore republic of georgia are charged suggesting a working petroleum system was present what it cannot tell us is how much petroleum may be in these structures that question can only be answered by the drill bit

petroleum related hydrocarbon seep age in a recent north sea sediment abstract in the summer of 1985 unocal carried out a 55 day surface geochemical survey in the norwegian sector of the north sea the program was set up to include a variety of geochemical techniques to aid evaluation of their effectiveness for detecting hydrocarbon seepages in the marine environment the ship was equipped with both bottom water and bottom sediment sampling devices and an analytical laboratory and computer network so that onboard measurements and real time data interpretation could be made during the survey 4100 line kilometers of bottom water data 11 000 sites and 320 sediment cores were obtained a major hydrocarbon gas anomaly was defined during part of the bottom water sampling program a set of sediment cores was taken in the vicinity of this anomaly the data from these cores are used to illustrate the fate of hydrocarbon migration through unconsolidated marine sediment migration by bubble ebullition transports hydrocarbons through the near surface sediment and produces gas plumes in the bottom water trapping of bubbles in the sediment will produce patchy temporal hydrocarbon anomalies in the sediment however extensive sediment anomalies such as those proposed to be developed by microseepage can only be formed at depth in the sediment below the level where sulfate is depleted from the pore water these anomalies result because vertical migration by molecular diffusion creates a steady state hydrocarbon oxidation zone sulfate reduction zone at depth in the sediment which efficiently eliminates hydrocarbon transport further to the surface

influence of glacial water and carbonate minerals on wintertime sea ice biogeochemistry and the co2 system in an arctic fjord in svalbard the effect of freshwater sources on wintertime sea ice co2 processes was studied from the glacier front to the outer tempelfjorden svalbard in sea ice glacier ice brine and snow march april 2012 was mild and the fjord was mainly covered with drift ice in contrast to the observed thicker fast ice in the colder april 2013 this resulted in different physical and chemical properties of the sea ice and under ice water data from stable oxygen isotopic ratios and salinity showed that the sea ice at the glacier front in april 2012 contained on average 54 of frozen in glacial meltwater this was five times higher than in april 2013 where the ice was frozen seawater in april 2012 the largest excess of sea ice total alkalinity at carbonate ion co32 and bicarbonate ion concentrations hco3 relative to salinity was mainly related to dissolved dolomite and calcite incorporated during freezing of mineral enriched glacial water in april 2013 the excess of these variables was mainly due to ikaite dissolution as a result of sea ice processes dolomite dissolution increased sea ice at twice as much as ikaite and calcite dissolution implying different buffering capacity and potential for ocean co2 uptake in a changing climate

modeled glacial north atlantic ice rafted debris pattern and its sensitivity to various boundary conditions an iceberg drift and decay model is used to compute the ice rafted debris ird flux to the glacial north atlantic under steady iceberg discharge from the greenland and laurentide ice sheets i investigate the sensitivity of modeled ird distribution pattern to formulation of glacial iceberg decay meltwater drainage of laurentide ice sheet at its southern margin and the choice of ocean current and wind fields used as model boundary conditions modeled ird patterns are compared with the observed basic glacial mode ird pattern ruddiman 1977 and the last five heinrich layer patterns grousset et al 1993 model results show that the first order control on ird deposition pattern is the prevailing ocean currents and the choice of current fields is critical in determining the results winds can have significant effect when they exert drag in concert with ocean currents formulation of glacial iceberg decay directly affects its survival and the expanse of ird distribution but the formulation is perhaps one of the largest uncertainties in the model drainage of the southern margin of the laurentide ice sheet through the laurentian channel by meltwater instead of glaciers predicts no significant ird deposition in the open north atlantic in contrast to observations suggesting that glacier i e iceberg drainage through the laurentian channel was significant during the times of observed ird deposition in most experiments the model predicts a high ird deposition band that roughly coincides with the latitudinal band of high heinrich layer deposition but are measurably south of the basic glacial mode high ird deposition band this discordance suggests either that the flow fields used as model boundary conditions are inaccurate or that much of the basic glacial mode ird was not delivered by icebergs but perhaps sea ice

distribution of subsurface hydrocarbon seepage in near surface marine sediments hydrocarbon seeps in surficial marine sediments are of two types active and passive active seeps occur where gas bubbles pockmarks or bright spots are visible on seismic profiles and where chemosynthetic communities are present in conjunction with large concentrations of migrated hydrocarbons macroseeps these generally occur where generation and migration of hydrocarbons from source rocks are ongoing today at maximum burial or where significant migration pathways have developed from recent tectonic activity passive seeps occur where concentrations of migrated hydrocarbons are usually low microseeps with few or no geophysical anomalies these occur typically in areas where generation and expulsion is relict no longer at maximum burial or regional seals prevent significant vertical migration the type of seepage controls the distribution of migrated hydrocarbons in the near surface sediments and should dictate the sampling equipment and approach used to detect seeps active seeps are usually detected near the water sediment interface in the water column or at the sea surface and at relatively large distances from major leak points most conventional sediment and water samplers can capture active seeps the gulf of mexico santa barbara channel and parts of the north sea have active hydrocarbon seeps passive seeps can only be detected relatively far below the water sediment interface and require samples to be collected near leak points sampling equipment must penetrate the zone of maximum disturbance or any shallow migration barriers in areas where surficial sediments are coarse grained or compacted conventional gravity corers will not work other options for subsurface sampling include vibracores jet cores and rotary cores precise location of samples site specific using seismic profiles to locate leak points is critical to detect passive hydrocarbon seeps the beaufort and bering seas offshore alaska and parts of the north sea contain passive seeps

the quantification of diffusive hydrocarbon losses through cap rocks of natural gas reservoirs a reevaluation discussion 1 a calculation scheme is presented to estimate the quantities of diffusive gas loss through the water saturated cap rock of natural gas reservoirs over geologic time reexamination of earlier calculations in a 1982 paper by leythaeuser et al revealed that the estimate of the rate of diffusive hydrocarbon losses through the cap rock of the harlingen netherlands natural gas reservoir was based on oversimplified assumptions concerning the boundary conditions at the reservoir cap rock interface according to this recalculation the time required to reduce the present day methane content of the harlingen gas field by one half is approximately 70 m y not the previously published value of 4 5 m y consequently diffusion losses through the cap rock appear to affect the long erm stability of natural gas reservoirs to a lesser extent than suggested by the earlier results

sediment thicknesses and holocene glacial marine sedimentation rates in three east greenland fjords ca 68 n we compared measured and estimated sediment budgets in heavily glaciated fjords in east greenland mass balance calculations and regional glacio climatic conditions suggest that the sediment flux to the seafloor in kangerdlugssuaq and nansen fjords should be dominated by iceberg rafting and not by the rain out of suspended particulates in meltwater as the glacier calving flux is estimated at 15 and 2 km 3 yr compared to meltwater volumes of 4 4 and 1 7 km 3 yr respectively gravity cores in the three fjords indicate that the uppermost 1 2 5 m of sediment consists of diamictons or fine grained laminated muds ams radiocarbon dates on calcareous foramininfera or shells 16 total indicate sedimentation rates of 110 to 340 cm ka within the fjords over the last 1 ka and 10 20 cm ka during the holecene on the inner and middle shelf annual sediment discharge is around 0 67 times 10 6 tonnes yr within the kangerdlugssuaq fjord and trough system which translates into an average basin wide rate

patterns of ice rafted detritus in the glacial north atlantic 40 55 n the observation by heinrich 1988 that during the last glacial period much of the input of ice rafted detritus to the north atlantic sediments may have occurred as a succession of catastrophic events rekindled interest on the history of the northern ice sheets over the last glacial period in this paper we present a rapid method to study the distribution of these events both in space and time using whole core low field magnetic susceptibility we report on approximately 20 cores covering the last 150 to 250 kyr well defined patterns of ice rafted detritus appear during periods of large continental ice sheet extent although these are not always associated within their maxima most of the events may be traced across the north atlantic ocean for the six most recent heinrich layers hl two distinct patterns exist hl1 hl2 hl4 hl5 are distributed along the northern boundary of the glacial polar front over most of the north atlantic between 40 and 50 n hl3 is more restricted to the central and eastern part of the northern atlantic the nd sr isotopic composition of the material constituting different heinrich events indicates the different provenance of the two patterns hl3 has a typical scandinavia arctic icelandic young crust signature and the others have a large component of northern quebec and northern west greenland old crust material these isotopic results obtained on core su 9008 from the north american basin are in agreement with the study by jantschik and huon 1992 who used k ar dating of silt and clay size fractions of an eastern basin core me 68 89 these data confirm the large spatial scale of these events and the enormous amount of ice rafted detritus they represent

oceanographic and physiographic controls on modern sedimentation within antarctic fjords physical oceanographic data and modern surface sediments were collected from eleven fjords along the western side of the antarctic peninsula and south shetland islands surface sediment samples 62 were analyzed for texture and total organic carbon content the distribution of biogenic and terrigenous facies within the fjords is controlled by bay geometry and oceanographic regime climate plays a secondary role but along with ice drainage basin size controls the rate of terrigenous supply to the glacial marine environment specifically fjords along the danco coast and palmer archipelago with a high length to width ratio tend to have bottom sediments that are arenaceous where ice rafted sediment is released preferentially at the head of the fjord biogenic facies are favored where the bay geometry is complex where such complexity exists separate oceanographic regimes develop that lead to separation of terrigenous and biogenic sediments processes of interflow mid and deep water turbid cold tongues and coriolis deflection produce terrigenous facies along the inner fjord and western edges of a fjord system warm outer bay waters tend to develop a stable eddy circulation pattern that favors the productivity of phytoplankton in the surface layers outer bays are therefore floored with organic rich siliceous muds and ice rafted material only in the south shetland islands is melt water input significant enough to generate estuarine circulation within the fjord but here strong bottom currents result in arenaceous bottom sediments with no biogenic facies ice rafted diamictons are produced proximal to the edges of small tide water glaciers in the south shetlands the facies relationships established in this study provide a strong reference for paleoclimatic studies that utilize downcore measurements of texture and organic carbon

ice induced vertical circulation in an arctic fiord ctd and nutrient data taken in south cape fiord next to a glacier face show strong evidence of upwelling in addition a region of down welling is found from 0 5 km to 5 km from the ice intruding layers with thicknesses consistent with lab measurements are found near the ice a phytoplankton bloom is found to be going on in the fiord and an upwelling velocity of 2 5 10 4 m s 1 is calculated by assuming that all the nitrogen required by these cells is up welled from the deep water within 10 2 m of the glacier mechanisms to drive the downwelling are discussed

influence of melting icebergs on distribution characteristics and transport of marine particles in an east greenland fjord a detailed study of distribution of suspended sediments in an east greenland fjord with a high iceberg production rate reveals the existence of intermediate nepheloid layers inls observed inls extended from the head to the mouth of the fjord at water depths between 100 and 400 m particulate organic carbon and nitrogen chlorophyll a and nutrient measurements and observation by microscope and energy dispersive x ray analyses were used to characterize marine particles particles in the inls are composed of glacial flour including 50 m quartz and feldspar grains with angular and sharp edges considered to be released from melting icebergs in situ photographs show large aggregates 1 mm at high concentration 300 particles per liter in and below inls these aggregates in comparison with the dispersed particle size distribution demonstrate that smaller size particles e g clay settle effectively along with larger single size grains in kangerlugssuaq fjord the mass transport of marine particles was governed by the subsurface iceberg melting producing observed inls rather than the surface meltwater plume this suggests that the subsurface water temperature controls release of iceberg debris and the existence of warm subsurface water as well as the spread of cold and fresh water in the surface layer needs to be considered to evaluate the occurrence of ice rafted debris layers including heinrich layers this study provides the field evidence of a modern analogue on ocean conditions that could form iceberg rafted layers

tidal motion ice velocity and melt rate of petermann gletscher greenland measured from radar interferometry over a floating glacier ice tongue or an ice shelf the glacier motion measured by a single repeat pass radar interferogram is difficult to analyze because the long term steady motion of the ice is intermixed with its cyclic downward motion induced by tidal forcing multiple interferograms and a quadruple difference technique are necessary to separate the tidal signal from the long term steady motion of the ice an example of application of this technique is given here using ers 1 radar images of petermann gletscher a major outlet glacier of northern greenland tidal displacements are measured with 5 mm statistical noise the long term ice velocity is measured with a precision of 1 m a 1 the inferred tidal displacements agree well with model predictions from a fixed elastic beam with an elastic damping factor of 0 47 0 01 km 1 the hinge line is mapped with a precision of 20 80 m combining the interferometric ice velocities with ice thickness data the glacier ice discharge is calculated at and below the hinge line at the hinge line the ice flux is 12 1 1 km3 a 1 at the ice front calf ice production is only 0 59 km3 a 1 meaning that 95 of the ice that crosses the grounding line melts before it reaches the calving front assuming steady state conditions the melt rate of the glacier tongue averages 12 1 m a 1 with peak values exceeding 20 m a 1 near the hinge line this high melt rate cannot be accommodated by surface ablation alone only about 2 3 m a 1 and is attributed to pronounced basal melting of the ice tongue basal melting often assumed to be negligible in greenland is the dominant process of mass release from the floating section of petermann gletscher

surface sediment hydrocarbons as indicators of subsurface hydrocarbons field calibration of existing and new surface geochemistry methods in the marco polo area gulf of mexico multiple methods are currently used to collect prepare extract and analyze near surface migrated hydrocarbons from marine sediments to evaluate subsurface petroleum generation and entrapment few have been rigorously tested to evaluate their effectiveness a gulf of mexico field calibration survey over the marco polo field was undertaken as part of an industry funded research project to better understand previously published and unpublished seabed geochemical results and determine which gas and liquid hydrocarbon extraction methods best characterize migrated hydrocarbons in near surface sediments the marco polo calibration data set demonstrates the importance of targeted coring and sampling depth to improve the detection of seabed migrated thermogenic hydrocarbons core samples should be collected along major migration pathways cross stratal leakage features identified by conventional deep seismic and high resolution sea floor imaging not all targeted cores hit the designated feature and thus collecting replicates along key migration features is critical collecting sediment samples below the near surface transition zone known as the zone of maximum disturbance is also important to avoid possible alteration effects and interference by recent organic matter geochemical analysis should include a full range of hydrocarbon types light hydrocarbon gases c1 c5 gasoline range c5 c10 and high molecular weight hmw hydrocarbons c15 the interstitial sediment gas data should be plotted on a total hydrocarbon gas c1 c5 versus wet gas fraction c2 c5 c1 c5 chart to identify background fractionated and anomalous populations compound specific isotopic analysis on selected anomalous samples is critical to correctly identify migrated subsurface gases from near surface generated microbial gases microdesorption bound gases did not provide gas compositions or compound specific isotope ratios similar to the marco polo reservoir gases and thus the bound gas extraction is not recommended a gasoline range analysis provides a new range of hydrocarbons rarely examined in surface geochemical studies that assist in identifying thermogenic hydrocarbons extraction gas chromatography and total scanning fluorescence tsf maximum fluorescence intensity provided information on the presence of thermogenic hmw hydrocarbons but did not work as well with the low level microseepage samples the tsf fluorogram signature was similar for both seep and regional reference background samples and did not help to identify migrated thermogenic hydrocarbons the marco polo calibration study provides a framework to better understand how best to collect targeted deep cores and extract migrated hydrocarbons from near surface marine sediments and to evaluate the results

marine seepage variability and its impact on evaluating the surface migrated hydrocarbon seep signal abstract detection of chemically identifiable hydrocarbon oil and gas seepage is an important tool in offshore exploration generated and or trapped oil and gas can leak to near surface sediments and ocean in detectable concentrations the seepage surface expression is controlled by hydrocarbon generation regional pressure regimes and migration pathways the migrated hydrocarbon concentration and composition varies due to seepage rates and near surface physical and biological processes that can alter the signal a seepage continuum exists from large volume oil and gas seeps known as macro seepage to lower volume seeps known as micro seepage only detectible with special sampling and analysis understanding the impact of migrated hydrocarbon concentration relative to in situ organic material and locally derived microbial hydrocarbons is critical this paper describes factors that control the near surface geochemical signal as well as the challenges in deciphering the migrated hydrocarbon signature to evaluate subsurface hydrocarbon generation and entrapment

surface sediment gases as indicators of subsurface hydrocarbons examining the record in laboratory and field studies abstract near surface sediment gases are commonly examined in surface geochemistry surveys to evaluate subsurface hydrocarbon generation and entrapment sediment gases reside in interstitial spaces bound to mineral or organic surfaces and or entrapped in carbonate inclusions characterizing migrated sediment gases with minimal compositional and isotopic fractionation is challenging and different methods are currently in use to extract and analyze surface sediment gases these methods have not been compared in controlled laboratory experiments the key to calibration experiments is to know the charge gas composition and thus have a basis to evaluate the sediment gas extraction procedure for this laboratory study marine sediments were homogenized and cleansed of in situ light hydrocarbons and bacteria replicate sediment samples were prepared and charged with two different hydrocarbon gas compositions and two concentration levels along with the requisite blank control samples the sediment gases were characterized by four laboratories using a variety of gas extraction procedures three headspace interstitial two adsorbed acid extraction and one ball mill occluded the results have been compared to the charge gases and each method evaluated the laboratory calibration experiments demonstrated that selected interstitial gas extraction methods examined do provide sediment gas compositions and compound specific isotopes similar to the charge gases however some of the results indicate that systematic sampling and or laboratory procedures associated with the adsorbed and ball mill gas extraction methods have altered the original charge gas compositions thus it is our recommendation to use a headspace interstitial gas extraction method in conjunction with a tight sealing storage container and water preparation procedure to best extract and analyze migrated sediment gases

role of diffusion in primary migration of hydrocarbons the following effective diffusion coefficients d cm2 sec were determined for the diffusion of light hydrocarbons through the water saturated pore space of shales methane 2 12 10 6 ethane 1 11 10 6 propane 5 55 10 7 iso butane 3 75 10 7 n butane 3 01 10 7 n pentane 1 57 10 7 n hexane 8 20 10 8 n heptane 4 31 10 8 and n decane 6 08 10 9 on the basis of these new data a deterministic dynamic model was set up to simulate the diffusive transport of light hydrocarbons c1 to c10 from source rocks for eight documented source rock units representing a wid range of geologic conditions maturities of 0 40 to 1 35 mean vitrinite reflectance oil to gas prone kerogens the cumulative amounts of hydrocarbons escaping with time were calculated thus it was shown that diffusion represents an effective process for primary migration of gas but not for oil the rate of mass transport for gas from source rocks with geologic time can be sufficiently high to account for the origin of commercial size gas fields for example a cumulative amount of 109 kg of methane 1 5 109 std m3 or 5 3 1010 scf has escaped by diffusion in 540 000 years from a certain volume 1 000 km2 by 200 m thick of a high mature gas prone mesozoic source rock in western canada the origin of hydrocarbon accumulations with high gas to oil ratios in low mature sediments in geologically young basins early gases and condensates can be explained by an early phase of primary migration predominantly based on diffusion during the initial stages of the accumulation history of those fields extending up to millions of years under certain conditions the reservoir gas changes with geologic time from a methane rich to a wet gas composition at low maturity levels below about 0 6 rm even oil prone source rocks yield methane rich light hydrocarbon mixtures by migration through diffusion compositional trends among reservoir gases of several multiple pay gas fields in louisiana represent evidence for diffusive transport of hydrocarbons the variation in gas composition between the individual pay zones is controlled by increasing distances of diffusive transport of the hydrocarbons from a uniform source rock at depth to their present accumulation sites in the shallow pay zones compounds of high diffusivity are enriched for example in the sligo gas field of louisiana the methane ethane and the iso butane n butane ratios increase from 10 2 to 36 0 and from 0 86 to 1 13 respectively from the deepest to the shallowest of the five productive reservoir sands which are spread over a a depth interval of 5 500 ft 1 676 m diffusion of light hydrocarbons in the subsurface can also have economically adverse effects for example existing gas accumulations can be destroyed by dissipation the rate of this destruction was calculated for the harlingen gas field holland by diffusive loss through 400 m of shale cap rock the initial amount of methane in place of 1 93 109 std m3 6 8 1010 scf is reduced by one half over a period of 4 5 million years this leads us to propose the concept that large gas accumulations can persist through extended periods of geologic time only as dynamic systems reaching some kind of steady state equilibrium between diffusive loss through the cap rock and continuous replenishment from the source rock

deglacial meltwater discharge north atlantic deep circulation and abrupt climate change high resolution paleogeochemical data from the north atlantic ocean indicate that in the interval 15 000 to 10 000 14c years before present b p north atlantic deep water nadw production was decreased or eliminated four times at about 14 500 and probably older 13 500 12 000 and 10 500 years b p each of these changes occurred at the same time as abrupt events of meltwater discharge to the surface ocean inferred from oxygen isotope studies of planktonic foraminifera and from glacial geological studies on land in addition each of these times may be associated with brief episodes of cooler climate in the north atlantic region the best example of which is the younger dryas cooling of 10 500 years ago these results support models linking meltwater discharge decreased nadw production and decreased north atlantic heat flux

high export of dissolved silica from the greenland ice sheet silica is an essential element for marine life and plays a key role in the biogeochemistry of the ocean glacial activity stimulates rock weathering generating dissolved silica that is exported to coastal areas along with meltwater the magnitude of the dissolved silica export from large glacial areas such as the greenland ice sheet is presently poorly quantified and not accounted for in global budgets here we present data from two fjord systems adjacent to the greenland ice sheet which reveal a large export of dissolved silica by glacial meltwater relative to other macronutrients upscaled to the entire greenland ice sheet the export of dissolved silica equals 22 10 gmol si yr 1 when the silicate rich meltwater mixes with upwelled deep water either inside or outside greenland s fjords primary production takes place at increased silicate to nitrate ratios this likely stimulates the growth of diatoms relative to other phytoplankton groups

turbine tent measurements of marine hydrocarbon seeps on subhourly timescales 1 three turbine seep tents simultaneously measured marine seep gas fluxes with high time resolution 0 2 s at multiple locations tents were inverted polyvinyl cones 2 m diameter 1 m tall and weighted on their lower skirt edges rising gas bubbles induce vertical fluid motions which were measured by laboratory calibrated turbines in chimneys on top of the tents initial deployment was at an active seep area in the coal oil point seep field in the santa barbara channel california the three tents simultaneously collected data for continuous time periods of 2 hours in both the morning and afternoon seabed temperature and pressure were acquired every 3 s over the same time periods as the flux measurements from a conductivity temperature depth ctd mounted on one tent results strongly suggest that oceanic swell had a significant forcing effect on the flux at a subhourly timescale there was an inverse relationship between effect of swell height on the flux and flux swells from 1 to 4 m height and periodicities of 7 and 12 s caused variations of 1 to 4 from the average flux proposed mechanisms to explain the observations are diffusion with surrounding sediments termed gas charging swell induced changes in fracture size termed fracture forcing and swell induced vent activation deactivation termed pore activation on the basis of the seep frequency response we propose pore activation was dominant

geological controls on focused fluid flow associated with seafloor seeps in the lower congo basin a synthesis of backscatter imagery coupled with a large 3d seismic dataset in the lower congo basin lcb reveals a patchy distribution of features interpreted to be associated with fluid seepage from 300 m to 2500 m water depth with the exception of one region of anomalous backscatter positive relief mounds all inferred seep sites occur in negative relief pockmarks the extensive 3d seismic dataset in the lcb offers a unique opportunity to study the plumbing system that is feeding surface cold seep systems and in general to reconstruct the relationship between tectonics and fluid flow in continental margins the fluid seeps in the lcb are associated with morphologically stratigraphically or tectonically controlled focused fluid flow the integration of the geophysical datasets backscatter imagery coupled to 3d seismic clearly indicates that fluid seeps are not randomly distributed but their seabed organization reflects 1 the location of the underlying structure reservoir or trap where the fluids are coming from 2 the geometry and morphology of the reservoir trap and 3 the discontinuities in the sedimentary column along which fluids have migrated in the lcb seafloor pockmarks are always associated with underlying tectonic structures fault zones salt diapirs polygonal faults or buried sedimentary bodies turbiditic channels erosional surfaces whereas they never occur above sub horizontal parallel stratified fine grained sediments even if triggering processes can not be clearly defined here we propose a model of seafloor fluid seep organization which represents a new tool for identifying the geometry of flow pathways and the underlying buried bodies where the fluids are originating from this qualitative 3d model provides insight into the geohydrologic processes of continental margins

the origin of massive diamicton facies by iceberg rafting and scouring scoresby sund east greenland almost 90 of 39 m of core material recovered from scoresby sund and the adjacent east greenland shelf is massive diamicton interpreted to be formed predominantly by the release of iceberg rafted debris and reworking by iceberg scouring there is also likely to be a contribution from suspension settling of fines derived from glaciofluvial sources model calculations suggest that the 14c derived holocene sedimentation rate of 0 1 0 3 m 1000 yr 1 in scoresby sund can be accounted for mainly by iceberg rafting of debris a further 4 of core material is of gravel or coarse sand lenses interpreted to reflect iceberg dumping of debris intensive iceberg scouring which reworks sea floor sediments is observed on acoustic records from over 30 000 km2 of the scoresby sund fiord system and the adjacent east greenland shelf 69 72 n and 75 n the rate of iceberg production from greenland ice sheet outlet glaciers and iceberg drift tracks on the shelf suggests that iceberg rafting and scouring may be important over a significant proportion of the 500 000 km2 area above the shelf break the relatively extensive modern occurrence of massive diamicton formed by iceberg rafting and scouring together with suspension settling of fines suggests that it may also be a significant facies in the glacier influenced geological record the recognition in the geological record of the massive diamicton facies described above may also indicate the former presence of fast flowing ice sheet outlet glaciers

spatial distribution and geochemistry of the nearshore gas seepages and their implications to natural gas migration in the yinggehai basin offshore south china sea abstract about 120 gas seepage vents were documented along the west and southwest coast of the hainan island south china sea in water depths usually less than 50 m the principal seepage areas include the lingtou promontory the yinggehai rivulet mouth yazhou bay the nanshan promontory and the tianya promontory they occur along three major zones reflecting the control by faults and lateral conduits within the basement it is estimated that the total gas emission from these seepage vents is 294 956 m 3 year the seepage gases are characterized by a high ch 4 content 76 heavy 13 c 1 values 38 to 33 and high c 1 c 1 5 ratios 0 95 1 0 resembling the thermogenic gases from the diapiric gas fields of the yinggehai basin hydrocarbon source correlation shows that the hydrocarbons in the sediments from seepage areas can be correlated with the deeply buried miocene source rocks and sandstone reservoirs in the central depression the 2d basin modeling results based on a section from the source rock center to the gas seepage sites indicate that the gas bearing fluids migrated from the source rocks upward through faults or weak zones encompassed by shale diapirism or in up dip direction along the sandstone rich strata of huangliu formation to arrive to seabed and form the nearshore gas seepages it is suggested that the seepage gases are sourced from the miocene source rocks in the central depression of the yinggehai basin this migration model implies that the eastern slope zone between the gas source area of the central depression and the seepage zone is also favorable place for gas accumulation

the sizes frequencies and freeboards of east greenland icebergs observed using ship radar and sextant the scoresby sund fjord system east greenland contains the most productive fast flowing outlet glaciers draining east from the greenland ice sheet calving 18 km3 a 1 of icebergs the sizes frequencies and freeboards of 1900 icebergs were measured from f s polarstern using ship x band radar and sextant radar beam spreading exaggerates iceberg width by 60 m per nautical mile of range beyond the first mile data sets on iceberg size e g that collated for antarctic icebergs collected using ship radars which do not take this effect into account will overestimate iceberg dimensions significantly the location and concentration of icebergs within the fjord complex can be explained by 1 the locations of the principal source glaciers and 2 fjord topography and bathymetry iceberg concentration maximum 0 6 icebergs km 2 declines with distance from the major iceberg sources we found that 69 of icebergs within the fjord system are 1 km in length the largest is 2 7 km long icebergs become spread more evenly over the range of size classes in the outer fjord and shelf modal iceberg keel depth calculated from freeboard measurements is 4 500 m in the inner fjords shifting to lower values in the outer fjords reflecting shallower bathymetry radar measurements of iceberg width cannot be used to infer keel depths accurately because width and keel depth are only weakly correlated comparison between freeboards and keel depths for icebergs from east greenland and the barents sea indicates that the iceberg source i e floating or grounded exerts a fundamental control on iceberg dimensions the drift pattern of icebergs is from the head to the mouth of the fjord system although fjord bifurcations bathymetry and currents provide additional complications the trends in observed iceberg size and frequency and in inferred keel depth in the scoresby sund region are likely to be applicable to other fjords and shelves around greenland

control of hydrocarbon seepage intensity on level of biodegradation in sea bottom sediments offshore surface geochemical surveys which target the surface expression of potential migration pathways for sampling such as fault scarps or diapiric features have become a commonly applied approach in the petroleum industry results of such surveys help to reduce risk on key exploration play elements and are used to evaluate prospects and to predict hydrocarbon phase and expected properties based on geochemical surveys conducted by exxonmobil in many basins worldwide there is an interrelation of the seep intensity concentration and level of biodegradation results from offshore west africa where many active macroseeps show moderate to severe biodegradation and a frontier basin offshore united kingdom rockall trough where active microseeps show no evidence of biodegradation are compared the specific biochemical controls on the difference in biodegradation proneness are not known although it appears that a certain threshold of oil concentration is needed to sustain an active bacterial community or to exceed clay adsorption capacities that may protect microseeps from biodegradation it is notable that the 25 norhopane series often considered an indication of severe biodegradation in reservoir oils has not been recognized in even ultra severely biodegraded seeps this suggests that different biodegradation pathways may be followed in marine surface seeps versus those in subsurface hydrocarbon accumulations a likely scenario in light of the fact that physiologically diverse bacterial communities are prevalent under different physiochemical conditions

hydrocarbon migration pathway and methane budget for a gulf of mexico natural seep site green canyon 600 abstract hydrocarbon seeps occur worldwide along continental margins and act as conduits for fluid discharge from the lithosphere to the overlying hydrosphere atmosphere the dynamics and rates of hydrocarbon release at cold seeps remain poorly constrained seepage enables a variety of processes that alter the seafloor morphology and affect the geochemistry of substrata supporting diverse and important chemosynthetic communities here we merge complementary geochemical oil fingerprinting geophysical deep seismic subbottom backscatter multibeam and video imaging video time lapse camera dsv alvin video rov video auv photo surveys data sets to constrain the pathways and magnitudes of methane fluxes from the source reservoir to the seafloor at a well studied prolific seep site green canyon gc 600 in the northern gulf of mexico oil samples from the reservoir an active vent and the sea surface showed compositional similarities consistent with the plumbing system structure identified in seismic data spatial distribution of seep indicators such as bacterial mats microbial communities methane derived carbonates and hydrate outcrops were then used to quantify the total magnitude of methane potentially sequestered in the study domain using a systems approach we combined published values for methane fluxes with data we collected across various scales and resolutions to compile a methane budget for gc600 the system considered for the methane budget is defined as the movement of methane from the salt ridge to the seafloor water interface for each seep domain birthday candles and mega plume total estimated input of methane was 2 8 10 8 2 2 10 9 mol yr in the birthday candles domain and 2 7 10 8 2 3 10 9 in the mega plume domain the combined total output of the system ranged from 3 2 10 5 8 2 10 5 and 3 2 10 6 5 2 10 6 mol yr respectively for birthday candles and mega plume domains leaving a potential surplus input minus output of 2 6 10 8 2 3 10 9 mol yr processes that could balance this budget include accumulation of gas hydrate and sediment free gas and the underestimated potential of biological sinks such as methane oxidation

relationships between seepage tectonics and subsurface petroleum reserves abstract the relationship between visible petroleum seepage and commercial subsurface reserves has been investigated by a study of the distribution of documented seeps in south east asia this is accompanied and integrated with a broader global study the intensity of flowing seepage is controlled largely by present day tectonics and by the timing of petroleum migration when such influences are reduced by isolating sets of tectonically similar basins correlations are found between numbers of seeps and basin reserves at a sub basinal scale seeps are observed to concentrate over tectonic features such as active diapirs active faults and uplifted basin margins it is relatively rare for seeps to directly overlie major fields although many seeps may be linked to downdip accumulations by long tortuous paths the best seep accumulation relationships are observed in active compressional and diapiric settings particularly those involving shallow reservoirs seeps are rare where traps are buried beneath thick undisturbed overburdens the prime value of visible seeps in most frontier basins lies at the regional level in the clues they give to the nature extent and quantitative hydrocarbon potential of a basin s source system

migration of c1 c8 hydrocarbons in marine sediments abstract light hydrocarbon c 1 c 8 profiles are compared for three wells of varying maturities two immature dsdp wells site 397 near the canary islands and site 530a near the walvis ridge in the south east atlantic and a mature well the east cameron well in the texas gulf coast primary migration of c 1 and c 2 appears to be occurring in all of the sedimentary rocks examined primary migration of c 3 components becomes important only as fine grained sedimentary rocks enter the catagenetic hydrocarbon generation zone or over short distances in more permeable sections lateral migration along bedding planes was more important than vertical migration in sedimentary rocks of all maturities the lightest methane ethane and propane gases hydrocarbon show greater fractionation than do the c 4 c 8 alkanes which generally show minimal fractionation during the migrational process subsurface diffusion coefficients for these p p b quantities of c 2 c 5 alkanes from immature sediments from dsdp site 530 are estimated to be several orders of magnitude less than values reported in the literature for diffusion of much larger amounts of these compounds from mature water wet sediments into air or sandstones since our calculations suggest light hydrocarbons are present in amounts less than their reported solubilities in pure water at 25 c we postulate that the sediment organic matter has a substantial effect on retarding the movement of these light hydrocarbons

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

iceberg production debris rafting and the extent and thickness of heinrich layers h 1 h 2 in north atlantic sediments the pattern of heinrich layer distribution for the last two events h 1 14 5 and h 2 21 1 ka mapped from magnetic susceptibility analysis of more than 50 north atlantic ocean cores provides the most detailed information to date on their extent and thickness an integrated spatial average thickness for the layers is 10 15 cm and there is a strong distance decay eastward the pattern of deposition over the north atlantic is similar for events h 1 and h 2 indicating that icebergs followed similar drift tracks rates of iceberg production and sediment flux from the hudson strait drainage basin of the north american laurentide ice sheet the major iceberg source for the events were calculated by using a mass balance approach this provides an envelope of sedimentation rates and the prediction that it would take between 50 and 1250 yr of iceberg sediment delivery to accumulate a heinrich layer averaging 10 cm thick over the north atlantic depending on the model assumptions used the most likely duration of heinrich events is 250 1250 yr

dynamics of the gas flux from shallow gas hydrate deposits interaction between oily hydrate bubbles and the oceanic environment decomposition of methane hydrates on the continental margins is a potentially significant source of atmospheric methane but the input depends upon the poorly understood fate of the hydrocarbon bubbles rising from the sea floor during a field trip to the gulf of mexico three different seepages were imaged and analyzed three different imaging techniques were tried side front and back illumination of which back illumination produced the best results the images were analyzed and the size dependent bubble distribution mass flux and rise speeds determined the total observed gas flux was 62 3 10 3 mol s 1 primarily methane of which a single vent produced seven times the next largest vent of this major vent 50 of the bubble mass was contained in the largest bubbles r 5500 m the vertical velocities demonstrated that these bubbles were heavily contaminated with oil which was also corroborated by bubble shape and oscillation observations

mapping tide water glacier dynamics in east greenland using landsat data landsat multispectral scanner and thematic mapper images were co registered for the kangerdlugssuaq fjord region in east greenland and were used to map glacier drainage basin areas changes in the positions of tide water glacier termini and to estimate surface velocities of the larger tide water glaciers statistics were compiled to document distance and area changes to glacier termini the methodologies developed in this study are broadly applicable to the investigation of tide water glaciers in other areas the number of images available for consecutive years and the accuracy with which images are co registered are key factors that influence the degree to which regional glacier dynamics can be characterized using remotely sensed data three domains of glacier state were interpreted net increase in terminus area in the southern part of the study area net loss of terminus area for glaciers in upper kangerdlugssuaq fjord and a slight loss of glacier terminus area northward from ryberg fjord local increases in the concentrations of drifting icebergs in the fjords coincide with the observed extension of glacier termini positions ice surface velocity estimates were derived for several glaciers using automated image cross correlation techniques the velocity determined for kangerdlugssuaq gletscher is approximately 5 0 km a 1 and that for kong christian iv gletscher is 0 9 km a 1 the continuous presence of icebergs and brash ice in front of these glaciers indicates sustained rates of ice front calving

modeling iceberg rafted sedimentation in high latitude fjord environments 1 an iceberg model sedberg has been developed to simulate sedimentation in high latitude glaciated fjords sediments deposited in fjords provide an important record of glaciological response to changing climatic conditions the model simulates the formation drift and melt of a population of icebergs utilizing monte carlo based techniques with a number of underlying parametric probability distributions to describe the stochastic behavior of iceberg formation and dynamics the model captures iceberg dynamics and melt in fjord environments and has been applied to kangerdlugssuaq fjord in east greenland as an example of an iceberg dominated sedimentary environment sedimentation has been simulated over the past 1500 years encompassing the climatic intervals of the medieval warm period mwp and the little ice age lia model results have been compared with the observed sedimentary record the model demonstrates that the glaciological regime e g basal debris thickness mean annual calving rate mean iceberg size plays a more important role than the direct influence of climate ocean and air temperatures on iceberg sedimentation rate although often changes in climate result in changes to the glaciological regime

holocene variations in mineral and grain size composition along the east greenland glaciated margin ca 67 70 n local versus long distance sediment transport quantitative x ray diffraction qxrd analysis of the 2 mm sediment fraction from surface sea floor samples and marine sediment cores that span the last 10 12 cal ka bp are used to describe spatial and temporal variations in non clay mineral compositions for an area between kangerlussuaq trough and scoresby sund 67 70 n east greenland bedrock consists primarily of an early tertiary alkaline complex with high weight of pyroxene and plagioclase farther inland and to the north the bedrock is dominantly felsic with a high fraction of quartz and potassium feldspars principal component pc analysis of the non clay sediment compositions indicates the importance of quartz and pyroxene as compositional end members with an abrupt shift from quartz and k feldspar dominated sediments north of scoresby sund to sediments rich in pyroxene and plagioclase feldspars offshore from the early tertiary basaltic outcrop coarse 2 mm or 1 mm ice rafted sediments are largely absent from the trough sediments between 8 and 5 cal ka bp but then increase in the last 4 cal ka bp compositional unmixing of the sediments in grivel basin and kangerlussuaq trough indicate the dominance of local over long distance sediment sources with pulses of sediment from tidewater glaciers in kangerlussuaq and nansen fjords reaching the inner shelf during the neoglaciation the change in ird is more dramatic in the sediment grain size proxies than in the quartz wt forty to seventy percent of the variance in the quartz records from either side of denmark strait is explained by low frequency trends but the data from the grivel basin east greenland are distinctly different with an approximate 2500 yr periodicity

tracking an oil slick from multiple natural sources coal oil point california oil slicks on the ocean surface emitted from natural marine hydrocarbon seeps offshore from coal oil point in the santa barbara channel california were tracked and sampled over a 2 h period the objectives were to characterize the seep oil and to track its composition over time using a new sampling device a catamaran drum sampler catdrums the sampler was designed and developed at ucsb chromatograms showed that oil originating from an informally named very active seep area shane seep primarily evolved during the first hour due to mixing with oil originating from a convergence zone slick surrounding shane seep

evidence for massive discharges of icebergs into the north atlantic ocean during the last glacial period sediments in the north atlantic ocean contain a series of layers that are rich in ice rafted debris and unusually poor in foraminifera1 here we present evidence that the most recent six of these heinrich layers deposited between 14 000 and 70 000 years ago record marked decreases in sea surface temperature and salinity decreases in the flux of planktonic foraminifera to the sediments and short lived massive discharges of icebergs originating in eastern canada the path of the icebergs clearly marked by the presence of ice rafted detrital carbonate can be traced for more than 3 000 km a remarkable distance attesting to extreme cooling of surface waters and enormous amounts of drifting ice the cause of these extreme events is puzzling they may reflect repeated rapid advances of the laurentide ice sheet perhaps associated with reductions in air temperatures yet temperature records from greenland ice cores appear to exhibit only a weak corresponding signal moreover the 5 10 000 yr intervals between the events are inconsistent with milankovitch orbital periodicities raising the question of what the ultimate cause of the postulated cooling may have been

focused hydrocarbon migration in shallow sediments of a pockmark cluster in the niger delta off nigeria the niger delta is one of the largest hydrocarbon basin offshore africa and it is well known for the presence of active pockmarks on the seabed during the guineco mebo cruise in 2011 long cores were taken from a pockmark cluster in order to investigate the state of its current activity gas hydrates oil and pore water were sampled for geochemical studies the resulting dataset combined with seismic data reveal that shallow hydrocarbon migration in the upper sedimentary section was focused exclusively within the pockmarks there is a clear tendency for gas migration within the hydrate bearing pockmarks and oil migration within the carbonate rich one this trend is interpreted as a consequence of hydrate dissolution followed by carbonate precipitation in the course of the evolution of these pockmarks we also demonstrate that anaerobic oxidation of methane aom is the main process responsible for the depletion of pore water sulfate with depths of the sulfate methane transition zone smtz ranging between 1 8 and 33 4 m in addition a numerical transport reaction model was used to estimate the age of hydrate layer formation from the present day sulfate profiles the results show that the sampled hydrate layers were formed between 21 and 3750 years before present overall this work shows the importance of fluid flow on the dynamics of pockmarks and the investigated cluster offers new opportunities for future cross site comparison studies our results imply that sudden discharges of gas can create hydrate layers within the upper sedimentary column which can affect the seafloor morphology over few decades this article is protected by copyright all rights reserved

model for hydrocarbon microseepage and related near surface alterations despite recent advances in surface and near surface geochemical methods there continues to be a need for improved understanding of the scientific basis relating these methods to petroleum deposits we have reviewed the literature pertinent to the several methods we have used and integrated that information with some 100 man years of our experience to contribute to that end evidence indicates that hydrocarbon micro seepage from reservoirs most probably involves buoyant colloidal size microbubbles of light hydrocarbons principally methane through the butanes ascending relatively rapidly through a water filled network of fractures joints and bedding planes bacterial consumption of these hydrocarbons creates carbon dioxide and hydrogen sulfide which may alter sediments producing detectable modifications in geomorphic seismic magnetic and radiometric properties we have used combinations of 1 airborne microwave sensing and laboratory analyses of soil gas hydrocarbons 2 shallow source aeromagnetic and soil magnetic susceptibility measurements 3 aerial and surface gamma ray measurements and 4 geomorphology to find productive oil and gas deposits results suggest that using these methods can substantially increase the probability of wildcat success and reduce finding costs in selected geologic settings however these surface methods cannot reveal depth size or quality of reservoirs or even if producible hydrocarbons will be found

thermohaline steps induced by melting of the erebus glacier tongue a vertically stable step like thermohaline structure is observed throughout a continuous 400 m conductivity temperature depth ctd profile taken near the erebus glacier tongue mcmurdo sound antarctica the pattern is best developed between the sea surface and 250 m depth the interval corresponding to that of the irregular underwater profile of the glacier tongue the steps average 17 m in thickness and typically display discontinuities of 0 1 c in temperature 0 04 in salinity and 3 5 10 4 g cm 3 in density the observations are compared with theory and laboratory experiments of cell development and lateral flow near ice melting into vertically stratified salt water at this location subsurface seawater is inferred to remain above the in situ freezing point year round and contains sufficient heat to account for much of the glacier tongue thinning by basal melting an adequate volume of meltwater would result to produce the measured salinity steps we discuss related observations and some implications of this process for ocean circulation and biological productivity in the antarctic

ice sheet and ocean interactions margin of the east greenland ice sheet 14 ka to present diatom evidence seven marine sediment cores were collected from the kangerdlugssuaq trough off the southeast coast of greenland the trough cuts across the continental shelf from the fjord mouth to the upper slope in denmark strait and provides a sedimentary environment sheltered from the east greenland current flowing along the shelf the cores have been 14c dated accelerator mass spectroscopy dates and analyzed for diatom accumulation rates and changes in floral composition it was found that the shelf probably was not glaciated by grounded ice but occupied by an ice shelf and or permanent sea ice between 14 000 years b p and the present average retreat rates of glacial permanent sea ice were circa 60 m yr between circa 13 500 and 11 000 years b p the retreat rates increased to about 150 m yr between 11 000 to 10 000 years b p the increase is unexpected because this correlates with fairbanks 1989 projected low glacial meltwater discharge for the same time which is coeval with the younger dryas several events of sea surface warming cooling took place on the outer shelf from 12 000 to 9000 years b p followed by cooling to the present with a possible warming between 3000 4000 years bp on the inner shelf pulses of warm cool surface water occurred from 9000 to 6000 years b p which was succeeded by surface water cooling until present