cenozoic ice rafting history of the central arctic ocean terrigenous sands on the lomonosov ridge the cenozoic ice rafted debris ird history of the central arctic is reconstructed utilizing the terrigenous coarse sand fraction in iodp 302 cores from 0 to 273 meters composite depth this holocene middle eocene quantitative record of terrigenous sand accumulation on the lomonosov ridge along with qualitative information on grain texture and composition confirms the interpretation that ice initiation sea ice and glacial ice occurred 46 ma in the arctic and provides a long term pattern of arctic ice expansion and decay since the middle eocene ird mass accumulation rates range from 0 to 0 13 g cm2 ka in the middle eocene and from 0 to 0 36 g cm2 ka in the neogene ird mass accumulation rate mar maxima in the miocene and pliocene cooccur with either glacial initiation or intensification in the sub arctic the 46 25 ma ird onset in the central arctic slightly precedes the earliest evidence of ice in the antarctic and compares in timing with a 1000 ppm decrease in atmospheric concentrations of co2 the decline of pco2 in the middle eocene may have driven both poles across the temperature threshold that enabled the nucleation of glaciers on land and partial freezing of the surface arctic ocean especially during times of low insolation

late diagenetic redistribution of uranium and disturbance of the u pb whole rock isotope system in a black shale the middle ordovician llandeilo caradoc formation black shales deposited at about 460 ma on the southwest margin of the welsh basin show evidence of a late diagenetic uranium redistribution event evidence for this redistribution event includes a disturbance in the u pb whole rock isotopic system at about 193 ma marked by a large range in the whole rock 238 u 204 pb between 2 and 90 one explanation for this large range is that individual whole rocks have experienced either a gain or a loss of u at the time of the disturbance this hypothesis is supported by the large range in measured u contents from the llandeilo caradoc formation black shales 0 16 to 6 6 ppm upper crust 2 8 ppm post archean average shale paas 3 1 ppm taylor and mclennan 1985 uranium that was likely sequestered during deposition and early diagenesis has been redistributed on a greater than whole rock scale centimeters to meters the u pb isotope systematics identified in this study and other pb isotope data from the welsh basin evans 1996 constrain a reasonable u concentration of 2 91 ppm for an unaltered llandeilo caradoc shale at the time of deposition 460 ma assuming 2 91 ppm to be an average u content at the time of deposition some rocks in the llandeilo caradoc formation have lost as much as 95 of the u likely present at the time of deposition and early diagenesis whereas others exhibit an almost equal enrichment when the u pb isotopic and elemental data from whole rocks and individual u bearing phases i e carbonate apatite monazite organic matter are examined in conjunction with the paragenetic sequence controls on the distribution of u in the llandeilo caradoc whole rocks and a pattern of open system conditions become apparent despite the presence of potential u rich diagenetic phases such as apatite and monazite most of the u in the relatively enriched samples is associated with a non extractable unidentified diagenetic component uranium mass balance considerations and whole rock u pb isotope systematics require that the non extractable component formed at about 193 ma during a late diagenetic uranium redistribution event the redistribution of u within the llandeilo caradoc formation has important implications for the use of u rich sedimentary minerals as geochronometers and for the use of u as a paleo redox indicator specifically a trace element indicator like uranium may in some cases record information about the postdepositional history of a sedimentary rock rather than document the absolute timing and conditions of deposition moreover this unique history can be properly evaluated only through an integrated petrographic geochemical approach that can discern the distribution and source i e depositional versus diagenetic of u in an individual whole rock

stratigraphic architecture of the cenozoic succession in the mcmurdo sound region antarctica an archive of polar palaeoenvironmental change in a failed rift setting the victoria land basin forms part of the failed west antarctic rift and preserves a cenozoic succession up to 4 km thick that records the onset of cenozoic glaciation and the history of antarctic glaciation over the past 34 myr this succession is relevant both to investigations of modern climate change and to studies of long term palaeoclimate change in general this study provides a sedimentological and stratigraphic review of the victoria land basin succession based on analysis of several continuous drillcores acquired since the 1970s and supported by seismic stratigraphic analysis of a large array of seismic reflection data an array of fifteen lithofacies is recognized within the victoria land basin cenozoic succession including fossiliferous and diversely bioturbated mudrocks and diatomites texturally mature sandstones and conglomerates mixed mudstones and sandstones with dispersed gravel with restricted bioturbation and diamictites and associated lithologies these facies record a variety of marine glaciomarine proglacial and subglacial environments locally volcanic and volcaniclastic deposits are interbedded in the succession lithofacies are arranged in repetitive vertical stacking patterns depositional sequences that record glacial advance retreat cycles with attendant relative sea level changes seven varieties of depositional sequences stratigraphic motifs are recognized within the succession as a whole and interpreted to record a range of depositional settings from rifts unaffected by glacial ice motif 7 through varying degrees of glacial influence with abundant meltwater contributions motifs 6 to 3 to cold polar glaciated environments such as that of today motifs 2 and 1 overall there is a gradual trend upward through the succession from motif 7 at the base towards motif 1 at the top but the trend is not monotonic a significant conclusion of this work is that a record of dynamic climate and glacial conditions is preserved through the entire 34 myr period of the cenozoic icehouse at least in the victoria land basin intervals characterized by consistent stratigraphic style motifs are recognized throughout the victoria land basin succession these intervals are of 1 to 6 myr duration each containing numerous depositional sequences they are one to two orders of magnitude longer than glacial interglacial cycles and record periods during which environmental conditions varied in an internally consistent manner these intervals are considered to reflect convolutions of orbital parameters that remained stable for periods of 106 a and then switched to alternative configurations such intervals are directly analogous to 1 to 8 myr intervals characterized by glaciogenic strata that are preserved within the late palaeozoic of eastern australia among other areas and may be a recurring stratigraphic response to icehouse climate regimes through geological time

evidence for platelet ice accretion in arctic sea ice development moderate quantities of platelet ice are reported in ice cores obtained from floes in the central and western beaufort sea arctic ocean the crystal structure characteristics include a fabric of long thin ragged edged crystals with randomly oriented c axes the cellular substructure that is characteristic of congelation ice is not evident in individual platelet ice crystals but they do occur together with congelation ice in layers ranging from 0 05 to 0 6 m thick platelet ice crystals are observed primarily in second year and multiyear floes the structural characteristics of arctic platelet ice are similar to those of antarctic platelet ice the platelet ice layers have a minimum 18o value of 5 3 and in some cases the platelet ice layers have more negative 18o values than the ice layers above and below them the salinity of platelet ice layers is not significantly different from other ice layers a number of platelet ice growth mechanisms and sources are discussed processes associated with the ellesmere ice shelves nearshore processes such as anchor ice growth in shallow waters off the north coast of alaska and ice growth in freshwater impounded behind grounded ice dams might be locally important but are unlikely to contribute significant quantities of platelet ice to pack ice floes two processes probably account for the presence of platelet ice the first is growth in underice melt ponds which form in inverted depressions at the base of floes when meltwater floes off the ice surface the second is the operation of ice pumps in which ice that is melted off the deeper parts of floes and ridges is deposited as platelet ice at a higher level in either case initially loose accumulations of platelet crystals are entrained in the floes by the growth of congelation ice the widespread occurrence of platelet ice in the central and western beaufort sea suggests that ice growth in both underice melt ponds and associated with the operation of ice pumps might be more common than was previously realized

neodymium isotopic composition of ordovician conodonts as a seawater proxy testing paleogeography 1 to evaluate recent ordovician paleogeographic reconstructions end values were determined in conodonts as a proxy for the isotopic variations in ancient seawater using samples from the major cratons and microplates isotopic variations reveal the existence of distinct oceanic masses and epeiric seas that constrain the position of plates and terranes relative to these water masses and hence constrain models of regional and global paleogeography the isotopic patterns show a consistent picture of the changes in the ordovician oceans the end values for water masses associated with laurentia are strongly negative 28 to 18 in the early ordovician evolving over time to higher values in the range 13 to 5 the early ordovician signature of laurentia is in marked contrast to other cratons and microplates which have a range of values from 10 to 5 samples from south china show interesting signals that reflect a greater similarity to laurentia than other peri gondwana terranes the isotopic variations are a function of both regional geology and global tectonic processes the most obvious being the taconic orogeny and onset of the closure of the iapetus ocean regional and global models of paleogeography are considered in light of these proxy signals this study also reveals that conodonts are powerful geochemical tools for obtaining information on ancient water masses the use of the nd isotopic signatures from conodonts provides a method independent of paleomagnetism and biogeography to test paleogeographic models by integrating such information a more multidisciplinary approach is possible

field observations of slush ice generated during freeze up in arctic coastal waters abstract in some years large volumes of slush ice charged with sediment are generated from frazil crystals in the shallow beaufort sea during strong storms at the time of freeze up such events terminate the navigation season and because of accompanying hostile conditions little is known about the processes acting the water saturated slush ice which may reach a thickness of 4 m exists for only a few days before freezing from the surface downward arrests further wave motion or pancake ice forms movements of small vessels and divers in the slush ice occurs only in phase with passing waves producing compression and rarefaction and internal pressure pulses where in contact with the seafloor the agitated slush ice moves cobble size material generates large sediment ripples and may possibly produce a flat rampart observed on the arctic shoreface in some years processes charging the slush ice with as much as 1000 m 3 km 2 of sediment remain uncertain but our field observations rule out previously proposed filtration from turbid waters as a likely mechanism sedimentary particles apparently are only trapped in the interstices of the slush ice rather than being held by adhesion since wave related internal pressure oscillations result in downward particle movement and cleansing of the slush ice this loss of sediment explains the typical downward increase in sediment concentration in that part of the fast ice canopy composed largely of frazil ice the congealing slush ice in coastal water does not become fast ice until grounded ridges are formed in the stamukhi zone one to two months after freeze up begins during this period of new ice mobility long range sediment transport occurs the sediment load held by the fast ice canopy in the area between the colville and sagavanirktok river deltas in the winter of 1978 1979 was 16 times larger than the yearly river input to the same area this sediment most likely was rafted from canada more than 400 km to the east during a brief time period in the previous fall ocean turbulence is greatly reduced while the congealing slush ice drifts about therefore new ice then forming in intervening open water areas is clean these events explain the patchy appearance of the fast ice after the summer snowmelt more work on the important phenomena reported here is needed to close a major gap in the knowledge of the arctic marine environment

dust transport from patagonia to antarctica a new stratigraphic approach from the scotia sea and its implications for the last glacial cycle abstract we studied two deep sea cores from the scotia sea to reconstruct past atmospheric circulation in the southern hemisphere and to resolve a long standing debate on the interpretation of magnetic susceptibility ms records in southern ocean so sediment high sedimentation sites md07 3134 0 2 1 2 m kyr and md07 3133 0 3 2 1 m kyr cover the last 92 5 kyr and 36 kyr respectively both exhibit a one to one coupling of the ms and ca2 signal to the non sea salt nss ca2 signal of the edml ice core clearly identifying atmospheric circulation as means of distribution comparison of additional proxies also excludes major influence by volcanic sources sea ice icebergs or oceanic current transport the close resemblance of the dust proxies over the last glacial cycle in turn allows for the establishment of an age model of unprecedented resolution and precision for so deep sea sediment because atmospheric transport involves no major leads or lags this is of particular importance because ms is routinely measured on deep sea cores in the so but the sediments usually lack biogenic carbonate and therefore had only limited stratigraphic control so far southern south america ssa is the likely source of eolian material because site md07 3133 located closer to the continent has slightly higher ms values than site md07 3134 and also the ms record of patagonian site salsa shows comparable variability patagonia was the dust source for both the scotia sea and east antarctica dust fluxes were several times higher during glacial times when atmospheric circulation was either stronger or shifted in latitude sea level was lowered shelf surfaces were exposed and environmental conditions in ssa were dominated by glaciers and extended outwash plains hence ms records of so deep sea sediment are reliable tracers of atmospheric circulation allowing for chronologically constrained reconstructions of the circum antarctic paleoclimate history

origin of late paleozoic multiple glacially striated surfaces in northern parana basin brazil some implications for the dynamics of the parana glacial lobe abstract four stratigraphically repeated closely spaced striated surfaces on late paleozoic sandstone at the base of the itarare subgroup in northern parana basin were generated by subglacial erosion during advances of the grounding zone of the tidewater terminus of the parana glacial lobe on unconsolidated sand the sandstone corresponds to a channelized sheet like proglacial outwash fan accumulated sub aquatically in front of the tidewater terminus of a temperate warm based glacier at the margin of the marine flooded parana basin sandy siltstone beds intercalated with the sandstone and resting on top of the striated surfaces represent aggradational mud deposited from settling of fine debris plumes overflows erosion was mostly by abrasion wear of the sand bed under a glacier sliding over an unfrozen substratum evidence of ploughing is minimal the glacier bed is thought to have behaved rheologically as a rigid essentially undeformable substratum discontinuities in the distribution of striations on the surfaces indicate that ice may have at places decoupled from its bed the section studied documents an upward fining and deepening deglacial sequence comprising four stratigraphic cycles of accumulation of sand formation of a striated surface followed by deposition of mud cycles are correlated with short lived probably fast seasonal advances of the tidewater terminus during general retreat of the parana lobe ice advances were not associated with deposition of subglacial diamicton or lodgement of clasts but to erosion of sand probably by ice protuberances under the sliding glacier

a global synthesis of the marine and terrestrial evidence for glaciation during the pliocene epoch abstract the pliocene climate is globally warm and characterised by high atmospheric carbon dioxide concentrations yet the terrestrial and marine scientific communities have gathered considerable evidence for substantial glaciation events in both the northern and southern hemisphere prior to the quaternary evidence on land is fragmentary but marine records of glaciation present a more complete history of pliocene glaciation here we present a global compilation of the terrestrial and marine glacial evidence for the pliocene and demonstrate four glaciation events that can be identified in the southern and or northern hemisphere prior to the latest pliocene intensification of northern hemisphere glaciation there are two globally recognisable glacial events in the early pliocene c 4 9 4 8 ma and c 4 0 ma one event around the early late pliocene transition c 3 6 ma and one event during marine isotope stage m2 c 3 3 ma long term climate cooling decreasing carbon dioxide concentrations in the atmosphere and high climate sensitivity in the pliocene probably facilitated each glaciation event however the mechanisms behind the early pliocene glacial events are unclear the global glaciation at c 3 3 ma may be caused by changes in ocean gateways whereas the decline in carbon dioxide concentrations is important for the latest pliocene intensification of northern hemisphere glaciation

history of ice rafting and water mass evolution at the northern siberian continental margin laptev sea during late glacial and holocene times the late glacial and holocene history of environmental changes in the western laptev sea is reconstructed on the basis of continuous records of ice rafted debris ird and atlantic water indicative subpolar planktic foraminifers and benthic foraminifer cassidulina neoteretis from the two ams14c dated sediment cores one from the upper continental slope and another from the khatanga paleoriver valley on the outer shelf since seasonal sea ice cover is a permanent feature in this high arctic region the prominent ird rich intervals in the oldest 15 4 ka and youngest 7 2 ka sediment units are attributed to iceberg rafting rock types like phyllites are used as indicators of sediment material supplied by icebergs from local ice caps of the severnaya zemlya archipelago authigenic concretions of vivianite and rhodochrosite found in the basal ird rich core section on the slope point to strong water stratification likely caused by meltwater inputs the oldest late glacial ird peaks provide evidence for iceberg production by the local ice caps on severnaya zemlya subsequent meltwater influence is tentatively related to the freshwater release from a retreating barents kara ice sheet in the northeastern kara sea already prior to 15 4 ka atlantic derived waters intermittently reached the western laptev sea continental slope probably facilitated by upwelling in coastal polynyas while subsurface atlantic derived waters were constantly present at the continental slope between 15 4 and 12 ka the disappearance of c neoteretis together with reduced abundance of subpolar planktic foraminifers after 12 ka suggests establishment of a freshened shelf water mass on the flooded outer shelf which affected the water mass structure on the continental slope after 7 ka climate cooling and enhanced atlantic derived water inflow caused re growth of ice caps on severnaya zemlya leading to a recurrence of ird peaks of this renewed ird input are centered at 7 2 6 4 5 4 3 and 2 ka implying that this millennial scale variability in the ird input might be related to an overregional changes in atmospheric circulation patterns

importance of lateral transport processes to 210pb budget in the eastern chukchi sea during summer 2003 chinese ipy research program national natural science foundation of china 41125020 fujian natural science foundation 2009j06026 state oceanic administration of china 201105022 4 ministry of education of china

coastal retreat and shoreface profile variations in the canadian beaufort sea the coastline of the southern canadian beaufort sea consists primarily of unconsolidated bluffs although the sea is ice free for 3 months of the year and wave energy is restricted by pack ice the coast is undergoing regional retreat with erosion rates as high as 10 m a 1 in some locations simple and multiple regression analyses were carried out to determine the degree of correlation between the mean retreat rate measured at various locations and the different parameters that may control shoreline recession sediment texture ground ice content cliff height wave energy and shoreface gradient revealed medium to poor correlation with erosion rates showing that the recessive evolution of the coastline can not be explained solely by wave induced and subaerial processes the comparison of nearshore echo sounding records from 1987 with bathymetry from 1971 showed substantial erosion up to 1 m of the submarine profile between 12 and 15 m of water there is strong evidence that this erosion has been caused by sea ice gouging on the seafloor from depths of 5 to 9 m accretion has taken place possibly induced by ice push processes and inshore of the 5 m isobath wave and current erosion of the shoreface has occurred these results suggest that the erosion of the inner shelf by ice gouging drives the erosion observed inshore on the coastal bluffs and nearshore zone as the shoreface profile strives for a state of dynamic equilibrium

spatial and temporal patterns of iceberg rafting ird along the east greenland margin ca 68 n over the last 14 cal ka twelve 1 2 m 10 cm diameter gravity cores collected in 1988 and 1991 from the continental shelf and fjords of east greenland near kangerlussuaq fjord trough ca 68 n 32 w have distinct changes in lithofacies and in the quantity of iceberg rafted ird sediments these changes are readily observed in x radiographs of the split cores we quantify the ird contribution through grain size analyses and counting the number of clasts 2 mm from the x radiographs chronological control is provided by acclerated mass spectroscopy 14c dates on foraminifera during deglaciation after 14 cal ka there was one interval of ird accumulation ca 12 13 cal ka followed by a brief return to ird conditions centred at 9 cal ka thereafter a prominent feature of most cores on the shelf is an increase in ird accumulation that started ca 5 6 cal ka and which has increased toward the present indicators of iceberg rafting such as the net sand flux and numbers of clasts 2 mm ka 1 follow a power law distribution when graphed against distance from the present east greenland coast a measure of the position of the glacier margins the form of the relationship indicates that there is a dramatic decrease in the supply of sediment from the fjords to the shelf these relationships are used to estimate changes in the location of the ice margin during the late quaternary based on a site on the east greenland slope denmark strait and to discuss factors that can negate such a simple transfer function 1997 by john wiley sons ltd

experimental studies of sediment enrichment of arctic ice covers due to wave action and frazil entrainment two processes are investigated that are believed to contribute to the sediment enrichment of ice covers in coastal arctic waters one process results from wave action which pumps sediment rich underlying water into the surface cover the other enriching mechanism is produced by rising frazil that entrains suspended sediment which subsequently becomes incorporated in the surface ice layer in both processes the sediment enrichment of the ice cover is found to depend upon the sediment size and concentration in the underlying water column in the wave dependent process the rate of sediment enrichment is influenced by the period amplitude and duration of the wave action as well as the size of the ice particles and motion of the cover frazil rising through sediment laden water was found to entrain particles of sand far more effectively than silt sand laden frazil floe would often become so loaded with sediment that the floe would eventually settle to the floor of the water column

provenance of the pre devonian sediments of england and wales sm nd isotopic evidence nd values and clast petrography of the longmyndian sediments of shropshire indicate a provenance dominated by juvenile high nd t uriconian volcanic sources but with an increasing detrital contribution from older low nd t metamorphic sources up section by contrast most lower palaeozoic strata of england and wales have low nd t values typical of sediments derived from long established continental crust the sm nd isotopic evidence suggests that avalonia received sediment from an adjacent large continent in the cambrian to lower ordovician and in the silurian ordovician and silurian volcanicity supplied juvenile detritus only during and shortly after active volcanism

sediment transport by sea ice in the chukchi and beaufort seas increasing importance due to changing ice conditions abstract sediment laden sea ice is widespread over the shallow wide siberian arctic shelves with off shelf export from the laptev and east siberian seas contributing substantially to the arctic ocean s sediment budget by contrast the north american shelves owing to their narrow width and greater water depths have not been deemed as important for basin wide sediment transport by sea ice observations over the chukchi and beaufort shelves in 2001 02 revealed the widespread occurrence of sediment laden ice over an area of more than 100 000 km2 between 68 and 74 n and 155 and 170 w ice stratigraphic studies indicate that sediment inclusions were associated with entrainment of frazil ice into deformed multiple layers of rafted nilas indicative of a flaw lead environment adjacent to the landfast ice of the chukchi and beaufort seas this is corroborated by buoy trajectories and satellite imagery indicating entrainment in a coastal polynya in the eastern chukchi sea in february of 2002 as well as formation of sediment laden ice along the beaufort sea coast as far eastward as the mackenzie shelf moored upward looking sonar on the mackenzie shelf provides further insight into the ice growth and deformation regime governing sediment entrainment analysis of radarsat synthetic aperture sar imagery in conjunction with bathymetric data help constrain the water depth of sediment resuspension and subsequent ice entrainment 20 m for the chukchi sea sediment loads averaged at 128 t km 2 with sediment occurring in layers of roughly 0 5 m thickness mostly in the lower ice layers the total amount of sediment transported by sea ice mostly out of the narrow zone between the landfast ice edge and waters too deep for resuspension and entrainment is at minimum 4 106 t in the sampling area and is estimated at 5 8 106 t over the entire chukchi and beaufort shelves in 2001 02 representing a significant term in the sediment budget of the western arctic ocean recent changes in the chukchi and beaufort sea ice regimes reduced summer minimum ice extent ice thinning reduction in multi year ice extent altered drift paths and mid winter landfast ice break out events have likely resulted in an increase of sediment laden ice in the area apart from contributing substantially to along and across shelf particulate flow an increase in the amount of dirty ice significantly impacts sub ice algal production and may enhance the dispersal of pollutants

characteristics of the active layer and shallow subsea permafrost a seasonal active layer associated with subsea permafrost was found in the sediments near the seabed of the beaufort sea near prudhoe bay alaska the active layer existed where sea ice was frozen to the seabed and also in shallow water where the under ice seawater salinities exceeded open water values initial freezing of the active layer was about coincident with the formation of new sea ice within 400 m of shore it appeared to freeze to an underlying ice bonded permafrost table ibpt farther offshore where this table is deeper the active layer thickness decreased with distance offshore and the layer was underlain by a talik relative ice contents in the active layer generally decreased with distance offshore were a few hundred parts per thousand ppt in the fall and ranged to more than 800 ppt in the spring seasonal changes in the bulk soil solution salinity showed that the partially frozen active layer redistributed salts during freezing was infiltrated by concentrated brines derived from the growth of sea ice and affected the timing of brine drainage to lower depths in the sediments these brines provide the salts required for thawing the underlying subsea permafrost in the presence of negative sediment temperatures the region near shore had a partially frozen transition layer just above the ibpt where the ice content increased and the brine content decreased with depth temperature at the ibpt is nearly constant beyond about 412 m to at least 3 5 km offshore at about 2 41 c implying relatively constant soil solution salinities there

a semianalytical algorithm for quantitatively estimating sediment and atmospheric deposition flux from modis derived sea ice albedo in the bohai sea china quantitative estimates of particulate matter pm concentration in sea ice using remote sensing data is helpful for studies of sediment transport and atmospheric dust deposition flux in this study the difference between the measured dirty and estimated clean albedo of sea ice was calculated and a relationship between the albedo difference and pm concentration was found using field and laboratory measurements a semianalytical algorithm for estimating pm concentration in sea ice was established the algorithm was then applied to modis data over the bohai sea china comparisons between modis derived and in situ measured pm concentration showed good agreement with a mean absolute percentage difference of 31 2 from 2005 to 2010 the modis derived annual average pm concentration was approximately 0 025 g l at the beginning of january after a month of atmospheric dust deposition it increased to 0 038 g l atmospheric dust deposition flux was estimated to be 2 50 t km 2 month similar to 2 20 t km 2 month reported in a previous study the result was compared with on site measurements at a nearby ground station the ground station was close to industrial and residential areas where larger dust depositions occurred than in the sea but although there were discrepancies between the absolute magnitudes of the two data sets they demonstrated similar trends

lower palaeozoic and precambrian igneous rocks from eastern england and their bearing on late ordovician closure of the tornquist sea constraints from u pb and nd isotopes the u pb isotope ages and nd isotope characteristics of asuite of igneous rocks from the basement of eastern england show that ordovician calc alkaline igneous rocks are tectonically interleaved with late precambrian volcanic rocks distinct from precambrian rocks exposed in southern britain new u pb ages for the north creake tuff zircon 449 13 ma moorby microgranite zircon 457 20 ma and the nuneaton lamprophyre zircon and baddeleyite 442 3 ma confirm the presence ofan ordovician magmatic arc tectonically interleaved precambrian volcanic rocks within this arc are verified by new u pb zircon ages for tuffs at glinton 612 21 ma and orton 616 6 ma initial end values for these basement rocks range from 4 to 6 consistent with generation of both c 615 ma and c 450 ma groups of rocksin continental arc settings the u pb and sm nd isotope data support arguments for an ordovician fold thrust belt extending from england to belgium and that the ordovician calc alkaline rocks formed in response to subductionof tornquist sea oceanic crust beneath avalonia

ice rafting of fine grained sediment a sorting and transport mechanism beaufort sea alaska abstract the presence of turbid sediment rich fast ice in the arctic is a major factor affecting transport of fine grained sediment turbid ice was found to be present in a zone 10 to 20 km wide along the coast of the beaufort sea sediment concentrations observed in cores taken in seasonal fast ice ranged from 3 to more than 1 600 g m3 finely disseminated silt and clay sized particles dominated discoloring the upper segments of the cores in a layer up to 1 m thick in almost all of the cores the upper most 10 cm of ice was relatively less turbid and the relief at the base of the turbid layer was 10 to 20 cm over distances of 1 to 2 m observers have documented the widespread sporadic occurrence of sediment rich fast ice in both the beaufort and bering seas the known sources a d transport relations of suspended sediment did not explain this distribution of turbid ice the occurrence of sediment in only the upper part of the seasonal fast ice indicates that sediment rich ice forms early during ice growth the most likely mechanism for the formation of sediment laden ice and preferential sorting of fine sediments requires resuspension of nearshore bottom sediment during storms accompanied by formation of frazil ice and subsequent lateral advection before the fast ice is stabilized we estimate that the sediment incorporated in the beaufort ice canopy formed a significant proportion of the seasonal influx of terrigenous fine grained sediment the dominance of fine grained sediment suggests that in the arctic and sub arctic these size fractions may be ice rafted in greater volumes than the coarse fraction of traditionally recognized ice rafted sediment the incorporation and transport mechanism may be a significant factor in the transport of fine grained sediments in the arctic basin

upper crustal recycling in southern britain evidence from nd and sr isotopes analyses of representative rocks from southern britain are used to examine in detail the evolution of this segment of continental crust the vast majority of late precambrian basement rocks have unradiogenic 87sr 86sr ratios and model tdmnd ages of 1 3 ga although locally the rosslare complex and rushton schists have model tdmnd ages 1 7 ga identifying for the first time an old component in the basement of southern britain following the closure of the iapetus ocean sediments exhibit a progressive increase in model tdmnd ages 1 35 ga in the lower palaeozoic to 1 75 ga in the jurassic this variation demonstrates the southerly transport of detritus tdmnd 2 0 ga from the mixed archaean proterozoic terrains of northern europe and america the granitoids have significantly higher end than those of contemporaneous sediments and thus yield a different nd isotope evolution curve when considered in isolation the majority of rocks analysed have model tdmsr ages in the range 1 2 to 0 46 ga with youngest sediments generally recording the lowest model ages therefore with time the sediments record a striking increase in the ratio of model nd to model sr age the data suggest that the rb sr ratios of the crustal rocks is increased by a factor of approximately 2 every 900 ma implying that on average the british upper crust was reworked by erosion and sedimentation every 600 ma

interdecadal variation in an antarctic sponge and its predators from oceanographic climate shifts during the 1960s there was extensive formation of anchor ice to depths of 30 meters at mcmurdo station antarctica during this period the sponge homaxinella balfourensis was rare as were its predators in that depth zone most of the existing sponges were killed by anchor ice during the 1970s anchor ice formation was reduced and there was a massive recruitment of homaxinella which covered as much as 80 percent of the substrata in that zone many predators appeared but did not control the sponge population and it continued to grow through that decade the early 1980s were characterized by ice formation and almost all of the homaxinella were eliminated leaving an order of magnitude more predators in that zone the interdecadal increases in anchor ice probably result from local upwelling of extremely cold deep water possibly in response to shifts in the strengths of regional currents

a critical assessment of subglacial mega floods a case study of glacial sediments and landforms in south central alberta canada the existing subglacial megaflood explanation of glacial sediment deposition and landform production in south central alberta relies upon four sets of observations and associated interpretations 1 a subglacial genesis for all glacilacustrine sediments lying stratigraphically below a local melt out till or ice stagnation facies 2 a melt out genesis for the ice stagnation facies 3 a syn depositional status for the glacitectonic disturbance visible in most exposures due to periodic ice bed re coupling and 4 a subglacial megaflood origin for a truncation surface and clast lag that occurs at the top of the sedimentary exposures and the carving of hummocky terrain and flutes in the area we provide alternative interpretations of the sediment landform assemblages of the area and demonstrate that alternative simpler interpretations of the evidence can be proposed specifically we propose 1 a proglacial rather than subglacial origin of glacilacustrine sediments 2 a glacilacustrine origin for the melt out till and its subsequent glacitectonic disturbance by minor glacier readvances 3 postdepositional rather than syn depositional glacitectonic disturbance due to a significant advance by glacier ice after the accumulation of a thick sequence of glacilacustrine sediments 4 that some linear chains of hummocks are the morphological expression of glacitectonic folding and thrusting 5 that the use of the truncation surfaces to propose a subglacial fluvial origin for hummocky moraine is flawed logic because they do not constitute the tops of hummocks but rather occur on the interfluves that separate the numerous small coulees incised into the valley sides during postglacial time truncation surfaces and clast lags occur locally on the beds of spillway tracts and can be explained as the products of erosion by subaerial spillway water the mega flood explanation of flutings and hummocky moraine in the region is also questioned because these landforms record a regional ice flow imprint of mis aligned and cross cutting flow sets terminating at series of inset and locally cross cutting and lobate transverse ridges moraines these landform associations preclude a subglacial flood origin for the flutings and demonstrate that the transverse ridges are more appropriately interpreted as recessional push moraines the similarity of the glacial landforms of this region to the active temperate glacial landsystem produced by historical glacier recession in modern glacierized catchments where sheetfloods have not been influential in subglacial landform production allows us to apply a modern analogue to landscape interpretation that does not include subglacial sheetflooding

geochemical and isotope composition of pebbles from the caban conglomerate formation and their bearing on the source of welsh palaeozoic sedimentary rocks major trace and ree geochemistry together with nd isotope determinations provide new insights into the provenance of seven pebbles of igneous origin from an early silurian facies of the caban conglomerate formation from central wales the geochemical composition of the pebbles supports formation in a subduction related environment on an active continental margin biotite whole rock rb sr systematics constrain the age of a granite pebble to 650 38 ma the pebbles provide discrete examples of avalonian basement which contributed to the isotope composition of sedimentary rocks in the welsh basin and one granite pebble provides a rare example from the welsh basin of an igneous rock with a palaeoproterozoic depleted mantle model age

anchor ice seabed freezing and sediment dynamics in shallow arctic seas diving investigations confirm previous circumstantial evidence of seafloor freezing and anchor ice accretion during freeze up storms in the alaskan beaufort sea these related bottom types were found to be continuous from shore to 2 m depth and spotty to 4 5 m depth spotty anchor ice occurred as pillow shaped crystal aggregates on buried slabs of frozen sand surrounded by unfrozen sand considerations of required conditions for ice bonding and anchor ice growth allows regional extrapolation and suggests the possibility of anchor ice growth out to 20 m depth the estimated maximum depth of supercooling during fall storms anchor ice and seabed freezing apparently do not develop during a calm freeze up because of the abrupt growth of anchor ice during a freezing storm and its release soon after formation of a surface ice cover this ice type has not been documented before the concretelike nature of frozen bottom where present should prohibit sediment transport by any conceivable wave or current regime during the freezing storm but elsewhere particularly where the bonded crust is broken by grounded ice anchor ice lifts coarse material off the bottom and incorporates it into the ice canopy thereby leading to significant ice rafting of shallow shelf sediment and likely sediment loss to the deep sea

arctic ice export events and their potential impact on global climate during the late pleistocene 1 ice sheets in the north american arctic and to a lesser extent those in northern eurasia calved large quantities of icebergs that drifted through fram strait into the greenland sea several times during the late pleistocene these icebergs deposited fe oxide grains 45 250 m and coarse lithic clasts 250 m matched to specific circum arctic sources four massive arctic iceberg export events are identified from the laurentide and the innuitian ice sheets between 14 and 34 ka calendar years in a sediment core from fram strait these relatively short duration 1 4 kyr events contain 3 5 times the background levels of fe oxide grains they began suddenly as indicated by a steep rise in the number of grains matched to an ice sheet source suggesting rapid purges of ice through fram strait due perhaps to collapse of ice sheets the larger events from the northwestern laurentide ice sheet are preceded by events from the innuitian ice sheet despite the chronological uncertainties the arctic export events appear to occur prior to heinrich events

sediments in arctic sea ice implications for entrainment transport and release despite the arctic sea ice cover s recognized sensitivity to environmental change the role of sediment inclusions in lowering ice albedo and affecting ice ablation is poorly understood sea ice sediment inclusions were studied in the central arctic ocean during the arctic 91 expedition and in the laptev sea east siberian arctic region expedition 1992 results from these investigations are here combined with previous studies performed in major areas of ice ablation and the southern central arctic ocean this study documents the regional distribution and composition of particle laden ice investigates and evaluates processes by which sediment is incorporated into the ice cover and identifies transport paths and probable depositional centers for the released sediment in april 1992 sea ice in the laptev sea was relatively clean the sediment occasionally observed was distributed diffusely over the entire ice column forming turbid ice observations indicate that frazil and anchor ice formation occurring in a large coastal polynya provide a main mechanism for sediment entrainment in the central arctic ocean sediments are concentrated in layers within or at the surface of ice floes due to melting and refreezing processes the surface sediment accumulation in central arctic multi year sea ice exceeds by far the amounts observed in first year ice from the laptev sea in april 1992 sea ice sediments are generally fine grained although coarse sediments and stones up to 5 cm in diameter are observed component analysis indicates that quartz and clay minerals are the main terrigenous sediment particles the biogenous components namely shells of pelecypods and benthic foraminiferal tests point to a shallow benthic marine source area apparently sediment inclusions were resuspended from shelf areas before and incorporated into the sea ice by suspension freezing clay mineralogy of ice rafted sediments provides information on potential source areas a smectite maximum in sea ice sediment samples repeatedly occurred between 81 n and 83 n along the arctic 91 transect indicating a rather stable and narrow smectite rich ice drift stream of the transpolar drift the smectite concentrations are comparable to those found in both laptev sea shelf sediments and anchor ice sediments pointing to this sea as a potential source area for sea ice sediments in the central arctic ocean sea ice clay mineralogy is significantly different from deep sea clay mineral distribution patterns the contribution of sea ice sediments to the deep sea is apparently diluted by sedimentary material provided by other transport mechanisms

a shift in heavy and clay mineral provenance indicates a middle miocene onset of a perennial sea ice cover in the arctic ocean during the arctic coring expedition acex a 428 m thick sequence of upper cretaceous to quaternary sediments was penetrated the mineralogical composition of the upper 300 m of this sequence is presented here for the first time heavy and clay mineral associations indicate a major and consistent shift in provenance from the barents kara western laptev sea region characterized by presence of common clinopyroxene to the eastern laptev east siberian seas in the upper part of the section characterized by common hornblende amphibole sea ice originating from the latter source region must have survived at least one summer melt cycle in order to reach the acex drill site if considering modern sea ice trajectories and velocities this shift in mineral assemblages probably represents the onset of a perennial sea ice cover in the arctic ocean which occurred at about 13 ma thus suggesting a coeval freeze in the arctic and antarctic regions

modern dirty sea ice characteristics and sources the role of anchor ice extensive dirty ice patches with up to 7 kg m 2 sediment concentrations in layers of up to 10 cm thickness were encountered in 2005 and 2007 in numerous areas across the central arctic the fe grai

how normal faulting and sedimentation interact to produce listric fault profiles and stratigraphic wedges abstract in a series of scale experiments we generated listric normal faults by extending models composed of colored sand layers deposited at regular time intervals throughout deformation during syntectonic sedimentation progressive bulk extension along a single set of faults caused domino type tilting of fault blocks underlying tilted faults propagated upwards with constant dips into newly sedimented layers hence fault profiles become progressively more listric tilting of the free surface resulted in asymmetrical depressions and in fan shaped deposits stepwise or continuous geometric models of domino tilting and synchronous sedimentation yield the same structural and stratigraphic features as observed in the sand models the continuous geometric model shows that a critical parameter governing fault curvature is the ratio r between rates of bulk strain and sedimentation both types of models reveal that synchronous sedimentation and bulk extension are capable by themselves of generating listric normal faults

orogenesis vs diagenesis can we use organic rich shales to interpret the tectonic evolution of a depositional basin abstract black shales from the southern appalachian basin and the southwest welsh basin have anomalous u pb and nd model ages suggesting syn and post depositional resetting of the sm nd and u pb isotopic systems this alteration to the primary detrital signature of these two shale sequences is indicative of black shale diagenetic depositional processes that obscure paleo environmental and provenance information recorded prior to and during deposition the trace element and isotopic signatures of these two shale sequences reveal a syn post depositional history that is de coupled from the coeval orogenic history of the region making it difficult to reconstruct the tectonic and oceanographic conditions present at the time of deposition both the ordovivian welsh basin and the devonian appalachian basin sequences host ree and u bearing diagenetic phosphate minerals that play a critical role in the whole rock ree and u budgets in the welsh basin shales early diagenetic apatite and a later monazite phase dominate the ree budget and cause the redistribution of ree early in the basin s history ca 460 ma this redistribution is recorded by the sm nd system 450 90 ma and the nd model ages that are anomalously old by as much as 20 t dm 2 0 ga this early history is complicated by a permo triassic fluid event affecting the whole rock u budget and resetting the u pb isotopic system at 193 45 ma the appalachian basin sequence appears to have a much less complicated history yet still records a significant disturbance in both the sm nd isotopic system 392 76 ma and the pb isotopic system 340 50 ma at about the time of deposition ca 365 ma these two sequences suggest a pattern of diagenetic disturbance common to black shales these processes are unique to black shales and must be considered when interpreting provenance and paleo environmental information from the black shale sequences although these rocks are susceptible to alteration the alteration may provide extensive information on the post depositional history of the basin while still retaining some primary depositional information if black shale processes are considered during the interpretation of isotopic and trace element signatures from organic rich shales it may be possible to recover an extensive basin history

dating the transition of smectite to illite in palaeozoic mudrocks using the rb sr whole rock technique the interpretation of mudrock rb sr whole rock regression ages using stratigraphically well constrained samples from the ordovician and silurian of central wales is re examined two new rb sr whole rock regressions are presented along with k ar and rb sr data from the

chitinozoa and nd isotope stratigraphy of the ordovician rocks in the ebbe anticline nw germany chitinozoa and nd isotope stratigraphy of the ordovician rocks in the ebbe anticline nw germany

lipid distribution in surface sediments from the eastern central arctic ocean abstract during the arctic 91 expedition with rv polarstern numerous short multicorer and long cores kastenlot cores including surface sediments were recovered along a transect crossing the eastern part of the arctic ocean in this paper we present data on the concentration and distribution of short c17 c19 and long chain c27 c29 c31 n alkanes as well as fatty acids 16 0 16 1 18 0 18 1 in the surface sediments from this transect these compounds among others have been used to distinguish between autochthonous marine organic matter and allochthonous terrigenous organic matter supply changes in short chain n alkane as well as fatty acid contents of the sediments allow us to distinguish between regions characterized by higher or lower marine productivity organic carbon contents of the surface sediments are generally high and vary between 0 3 and 2 in general the high organic carbon content of the sediments is derived from a high input of terrigenous organic matter marine productivity in the arctic ocean is mainly controlled by reduced sea ice cover which allows a higher production rate of phytoplankton regions with a higher marine organic matter content are the area nw of svalbard the yermak plateau a part of the lomonosov ridge and makarov basin and the morris yesup rise the pattern of distribution of long chain n alkanes in arctic ocean surface sediments is mainly controlled by sea ice and or direct transport from the adjacent shelf areas although dilution by turbidites influences the deep basins

langmuir circulation driving sediment entrainment into newly formed ice tank experiment results with application to nature lake hattie united states kara sea siberia 1 langmuir circulation lc was generated under freezing conditions in saltwater tank experiments through surface wind stress and cross waves interacting with subsurface return flow fine grained sediments distributed in the tank prior to frazil crystal formation were aligned in parallel streaks in lc bottom convergence zones downwelling at lc surface convergence zones aligned floating frazil in wind parallel rows and individual crystals rotated on helical paths down to the tank bottom and up again to the surface the crystals interacted with suspended particles in the water column and with sediment on the tank bottom preferentially collecting fine grained particles and enhancing their entrainment into new ice evidence includes higher sediment concentrations in ice and ice interstitial water ice pore water as compared to the tank water both tank ice and ice interstitial water contain more silt sized particles than tank water suspension load and tank bottom sediment sand is reduced in the ice and clay is about the same concentration in all samples this points to preferential entrainment of fine particles in newly formed ice supported by lc driven circulation comparable results of lc supported ice particle entrainment were found in lake hattie comparison of ice sediment from tank experiments run with kara sea material to ice particles from the natural kara setting showed both types of ice sediment have very similar grain size distributions and mineralogical compositions results from experiments and nature help to better understand the potentially lc driven entrainment of sediment into ice formed in shallow freezing waters

benthic and planktic community changes at the north siberian margin in response to atlantic water mass variability since last deglacial times the eastward penetration of atlantic derived water adw into the eurasian basin of the arctic ocean was investigated at the western laptev sea continental margin for the time since c 17 6 ka using a high resolution investigation of the lithology geochemistry planktic and benthic foraminifers and ostracods on a sediment core from 270 m water depth major steps in the environmental evolution of the region are recognized in general adw was continuously present in the study area between 17 6 and 15 4 ka adw manifested itself through open water polynyas and associated upwelling events comparison between the laptev sea and northern svalbard shelf using cassidulina neoteretis allows assuming an unmodified subsurface inflow of adw within its northern branch between 15 4 and 13 2 which was strongest after 14 7 ka and in line with the overall climate amelioration a local freshwater event at 13 ka followed by shelf flooding and the establishment of a freshened shelf water mass resulted in an off shelf displacement of adw from the studied site as suggested by the disappearance of c neoteretis between 12 and 7 ka as evidenced by an abundance peak in nonion labradoricum the sea ice marginal zone was located at the site around 12 11 ka but then shifted northward during the early holocene warming enhanced adw inflow since 7 ka correlated with climate cooling and southward retreat of the seasonal drift ice margin the inflow of adw during mid late holocene differed from deglacial times because of the combined influence of northern and eastern adw branches

reprint of benthic and planktic community changes at the north siberian margin in response to atlantic water mass variability since last deglacial times abstract the eastward penetration of atlantic derived water adw into the eurasian basin of the arctic ocean was investigated at the western laptev sea continental margin for the time since c 17 6 ka using a high resolution investigation of the lithology geochemistry planktic and benthic foraminifers and ostracods on a sediment core from 270 m water depth major steps in the environmental evolution of the region are recognized in general adw was continuously present in the study area between 17 6 and 15 4 ka adw manifested itself through open water polynyas and associated upwelling events comparison between the laptev sea and northern svalbard shelf using cassidulina neoteretis allows assuming an unmodified subsurface inflow of adw within its northern branch between 15 4 and 13 2 which was strongest after 14 7 ka and in line with the overall climate amelioration a local freshwater event at 13 ka followed by shelf flooding and the establishment of a freshened shelf water mass resulted in an off shelf displacement of adw from the studied site as suggested by the disappearance of c neoteretis between 12 and 7 ka as evidenced by an abundance peak in nonion labradoricum the sea ice marginal zone was located at the site around 12 11 ka but then shifted northward during the early holocene warming enhanced adw inflow since 7 ka correlated with climate cooling and southward retreat of the seasonal drift ice margin the inflow of adw during mid late holocene differed from deglacial times because of the combined influence of northern and eastern adw branches

the distribution of dissolved and total dissolvable aluminum in the beaufort sea and canada basin region of the arctic ocean 1 vertical profiles of the concentrations of dissolved al d al and total dissolvable al t al are reported from a transect extending from the continental shelf of the beaufort sea into the canada basin in the arctic ocean sampling was performed in late summer and early autumn 2007 a year of historically extensive sea ice melt vertical profiles of d al displayed surface maxima 1 3 nmol kg 1 subsurface minima 300 m depth suggest that al is likely lost through particle scavenging in the interior of the canada basin concentrations of t al show that particulate al 0 2 m is the dominant form of al in the water column except at greater depths at the most offshore stations lateral transport of d al and t al off the shelf likely results from the offshore progression of cyclonic eddies spawned inshore oscillating upwelling and downwelling favorable winds and brine rejection during sea ice formation that can drive currents sufficiently energetic to resuspend shelf sediments

petrology and geochemistry of the rhobell volcanic complex amphibole dominated fractionation at an early ordovician arc volcano in north wales

arctic perennial ice cover over the last 14 million years knowledge of the long term history of the perennial ice is an important issue that has eluded study because the cenozoic core material needed has been unavailable until the recent arctic coring expedition acex detrital fe oxide mineral grains analyzed by microprobe from the last 14 ma 164 m of the acex composite core on the lomonosov ridge were matched to circum arctic sources with the same mineral and 12 element composition these precise source determinations and estimates of drift rates were used to determine that these sand grains could not be rafted to the acex core site in less than a year thus the perennial ice cover has existed since 14 ma except for the unlikely rapid return to seasonal ice between the average sampling interval of about 0 17 ma both north america and russia contributed significant fe grains to the acex core during the last 14 ma

initiation of salt diapirs with frictional overburdens numerical experiments we have studied the initiation of salt diapirs with frictional overburdens under lateral compression and extension the overburden is assumed to be elasto plastic with mohr coulomb yield criterion and non associated flow rule plastic flow localizes into narrow shear bands which may represent faults the geometry and the evolution of these shear zones are simulated for various rheological parameters the dilational and frictional properties of frictional overburdens are found to be important controls on the types of shear zones formed in lateral compression and extension the friction and dilation angles influence the angle of shear and the width dip spacing and development history of conjugate zones of shear plus dilation fault zones that define wedges and grabens

application of portable free fall penetrometer for geotechnical investigation of arctic nearshore zone the arctic is currently undergoing rapid changes with regard to sea ice extent permafrost thaw and coastal erosion in addition to hydrodynamic processes the sediments in the arctic nearshore zon

investigations on physical and textural properties of arctic first year sea ice in the amundsen gulf canada november 2007 june 2008 ipy cfl system study we report sea ice temperature and bulk salinity measurements as well as textural analysis from 33 first year drift and fast ice stations sampled between november 2007 and june 2008 in the southern beaufort sea amundsen gulf canadian arctic during the international polar year circumpolar flaw lead ipy cfl system study we use this significant dataset to investigate the halo thermodynamic evolution of sea ice from growth to melt a strong desalination phase is observed over a small time window in the spring using calculated proxies of sea ice permeability brine volume fraction and of the intensity of brine convection rayleigh number we demonstrate that this phase corresponds to full depth gravity drainage initiated by a restored connectivity of the brine network with warming in the spring most stations had a textural sequence typical of arctic first year ice with granular ice overlying columnar ice unusual textural features were observed sporadically sandwiched granular ice platelet ice and draped platelet ice we suggest that turbulence in leads and double diffusion in strong brine plumes following the refreeze of cracks are plausible mechanisms for the formation of these textures

suspension freezing of bottom sediment and biota in the northwest passage and implications for arctic ocean sedimentation ice observations and sediment collected in a summer transit through the northwest passage provide insights on suspension freezing the most important sediment entrainment mechanism for the arctic ocean no evidence was seen for entrainment by bottom adfreezing bluff slumping river flooding dragging ice keels or significant eolian transport from land to sea lack of eolian sediment loading in the northwest passage together with that already reported for northern alaska eliminates wind as an important source for fine sediment in the pack of the beaufort gyre and related parts of the transpolar drift muddy sediment with pebbles and cobbles algae with holdfasts ostracodes with appendages and well preserved mollusks and sea urchins were collected from two sites in a 50 km long stretch of turbid ice these materials indicate that suspension freezing reaching to a water depth of 25 30 m during the previous fall was responsible for entrainment this mechanism requires rapid ice formation in open shallo

deposition of organic carbon in arctic ocean sediments terrigenous supply vs marine productivity during the arctic 91 expedition with rv polarstern several kastenlot cores were recovered along a profile crossing the eastern part of the arctic ocean in this paper we present results of detailed sedimentological and organic geochemical investigations on three of these cores which have yielded a wide range of data for the interpretation of the flux and type of organic matter in general the high organic carbon content of the sediments is derived from a high input of terrigenous organic matter the variation in content and composition of the organic carbon in the sediments of core ps2174 5 reflect glacial interglacial changes interglacial stages 7 and 5e reveal a low organic carbon content 0 5 and as indicated by high hydrogen indices low c n ratios higher content of n alkanes c 17 and c 19 and a high opal content reflect higher marine productivity during the glacial stages stages 6 upper 5 and 4 organic carbon values are significantly higher 0 7 1 3 low hydrogen indices high c n ratios low short chain n alkanes and low opal contents provide evidence for a higher input of terrigenous organic matter and reduced marine productivity changes in the content and composition of the organic carbon are believed to vary with the fluctuations in sea level and sea ice coverage

interaction of sea ice sediments and surface sea water in the arctic ocean evidence from excess 210pb 1 we measured the activities of 210pb 226ra 238u and 137cs in a suite of ice rafted sediments irs from the arctic ocean in an attempt to assess the interaction of sea ice sediments and surface water the concentrations of these nuclides were compared to those of the benthic sediments in the coastal and shelf regions of the arctic ocean which are believed to be the major source region for the irs the concentration factors cf activity of a nuclide in irs average activity in benthic sediments are 1 and 4 92 for 137cs and 210pb respectively the cf values for 137cs are comparable to the values that can be obtained from the previously published data while we report the first set of high cf values of 210pb a major portion of 210pb in some irs samples is likely derived from surface waters and thus the concentrations of 210pb combined with another particle reactive radionuclide such as 7be 234th in irs might provide information on the residence time and transit time of sea ice laden sediments

anchor ice formation and ice rafting in southwestern lake michigan u s a abstract anchor ice i e ice attached to the bed in a lake stream or ocean is common in the nearshore zone of southwestern lake michigan during winter lacustrine anchor ice has at least four distinct morphologies and was observed on sand pebble and boulder substrates in water depths to 4 m the limit of diving traverses the maximum depth of anchor ice formation may be much greater anchor ice is released from the lake bed on mornings following formation events released floating anchor ice carries sediment to the water surface this sediment is ice rafted along shore and offshore under the influence of prevailing winds we estimate that 0 85 m3 of sand per meter of beach is being removed from the nearshore zone of southwestern lake michigan by anchor ice annually melting ice drops this sand in deep water far from shore this is a significant loss of sand from the sediment starved nearshore zone of southwestern lake michigan

sedimentation during marine isotope stage 3 at the eastern margins of the glacial lake humber basin england the stratigraphic sequence at north cave on the eastern margins of the lake humber basin records the deposition of a fluvioperiglacial fan lfs 1 4 with early sedimentation lf1 dating to marine isotope stage mis 3 optically stimulated luminescence date range 41 8 38 6 ka and 14c dates 41 6 49 ka bp three phases of permafrost and ice wedge development during mis 3 are evident and indicate possible fan abandonment and hence periods of reduced nival runoff involution structures dated to 11 1 ka with large boulders and fine grained sorted circles in lf4b are interpreted as periglacially cryoturbated littoral deposits with boulders derived from anchor ice initially deposited at the margins of lake humber up to an altitude of 8 m od during mis 2 the style and age of fluvioperiglacial fan deposition at north cave is compatible with several mid devensian sites around britain characterized by significant nival melt and run off from steeply incised valleys in permafrozen cuesta landscapes this phase of fluvioperiglacial fan aggradation to near or below 0 m od is recorded around the glacial lakes humber and fenland basins and indicates that no glacial lakes existed at that time

crustal growth and late precambrian early palaeozoic plate tectonic evolution of england and wales comparison of the basement rocks of britain reveals major contrasts to the n and s of the iapetus suture solway shannon line north of the suture polymetamorphic high grade basement schists and gneisses and igneous rocks date from about 2900 ma to c 400 ma the latter age corresponding to closure of the iapetus ocean by contrast s of the suture in england and wales the basement is dominantly low grade metamorphic rock together with intrusive and extrusive igneous and sedimentary rocks there is little geological or geochemical evidence for the presence of basement older than c 900 ma below this area and the predominant expression of crustal growth in england and wales is indicated by radiometric ages between c 700 ma and 450 ma reflecting late precambrian palaeozoic magmatism and metamorphism palaeomagnetic data from scotland demonstrate that the crust in northern britain developed as an integral part of the laurentian shield during mid proterozoic times 1600 1000 ma the palaeomagnetic record from the pre ordovician rocks of england and wales shows that this area was unrelated to the laurentian shield prior to closure of the iapetus ocean the apparent polar wander a p w path is that of a distinct microplate involved in rapid growth of iapetus during early cambrian times and emplaced in its present configuration adjacent to northern britain as a result of subduction of the ocean basin between cambrian and silurian times we conclude that whereas the basement to the north of the iapetus suture formed an essentially continental unit from 2900 to 400 ma the basement of england and wales is a result of crustal growth from about 900 ma to 400 ma and formed by accretion of island arcs associated accretionary prisms and fore arc basin sediments within the iapetus ocean

rb sr whole rock isochron ages δ18o values and geochemical data for the sarn igneous complex and the parwyd gneisses of the mona complex of llŷn n wales the mona complex exposed on the ll n peninsula includes the sarn complex which is a suite of variably deformed plutonic igneous rocks originally mapped partly as gneisses ranging from gabbro to granite and an inlier of high grade paragneisses geochemical data for samples from the sarn complex may be divided into two distinct populations the rb sr data for samples from these geochemical groups define significantly different ages the older age 549 19 ma initial 87 sr 86 sr 0 7096 3 is identified as the age of intrusion in late precambrian to cambrian times while a younger age of 458 16 ma may approximate to the age of a resetting event the parwyd paragneisses yield an rb sr whole rock isochron age of 542 17 ma concordant with the age of intrusion of the sarn complex with an initial 87 sr 86 sr of 0 7069 4 for the sarn complex 18 o values range from 9 5 to 12 0 per mil smow and in the parwyd metasediments from 9 4 to 13 3 per mil we conclude that the earliest magmatism and metamorphism in the mona complex of ll n occurred during late precambrian to cambrian times broadly contemporaneous with similar events in anglesey the high initial 87 sr 86 sr and high 18 o values for the sarn complex are most simply interpreted as reflecting either a crustal source region or incorporation of a significant proportion of crustal material such as the parwyd gneisses into a mantle derived magma

contrasts in arctic shelf sea ice regimes and some implications beaufort sea versus laptev sea the winter ice regime of the 500 km from the mainland than in the beaufort sea as a result the annual freeze up does not incorporate old deep draft ice and with a lack of compression such deep draft ice is not generated in situ as on the beaufort sea shelf the laptev sea has as much as 1000 km of fetch at the end of summer when freezing storms move in and large 6 m waves can form also for the first three winter months the polynya lies inshore at a water depth of only 10 m turbulence and freezing are excellent conditions for sediment entrainment by frazil and anchor ice when compared to conditions in the short fetched beaufort sea we expect entrainment to occur yearly different from the intensely ice gouged beaufort sea shelf hydraulic bedforms probably dominate in the laptev sea corresponding with the large volume of ice produced more dense water is generated in the laptev sea possibly accompanied by downslope sediment transport thermohaline convection at the midshelf polynya together with the reduced rate of bottom disruption by ice keels may enhance benthic productivity and permit establishment of open shelf benthic communities which in the beaufort sea can thrive only in the protection of barrier islands indirect evidence for high benthic productivity is found in the presence of walrus who also require year round open water by contrast lack of a suitable environment restricts walrus from the beaufort sea although over 700 km farther to the south we could speculate on other consequences of the different ice regimes in the beaufort and laptev seas but these few examples serve to point out the dangers of exptrapolating from knowledge gained in the north american arctic to other shallow arctic shelf settings

controls on strain localization in a two dimensional elastoplastic layer insights into size frequency scaling of extensional fault populations 1 we use a two dimensional 2 d finite element code to investigate how mechanical properties and boundary conditions influence progressive strain localization during extension of a 2 d elastoplastic layer the deforming medium is modeled using a strain softening von mises rheology with a gaussian heterogeneity in yield strength distributed randomly in space specifically we examine the effects of changing 1 the thickness of the deforming layer 2 the basal boundary condition 3 the range of strengths in the deforming layer 4 the strength loss on failure and 5 the total accommodated strain discrete zones of plastic shear strain are observed to nucleate and grow progressively during each experiment in order to quantify and thus discriminate between the deformation patterns produced under differing conditions we calculate the size frequency distributions of the shear band populations size is defined as the total plastic strain represented by each discrete structure a wide range of size frequency distributions is observed including both power law and exponential as well as distributions that show breaks in scaling with a transition from power law at small sizes to exponential at large sizes we show that these variations in population statistics are directly reflecting a change in strain localization in space and time caused by changing model parameters furthermore by making an analogy between the model shear bands and tectonic faults we provide insights into key features of fault size frequency distributions that have been measured in continental and oceanic extensional settings and also observed in analogue experiments

a framework for estimating anchor ice extent at potential formation sites in mcmurdo sound antarctica a distinctive feature of polar regions is the formation of ice clusters attached to the seabed known as anchor ice anchor ice plays an important role in mobilizing bed sediments and serves ecological roles providing habitats or as an agent of disturbance creating potentially fatal environments to benthic fauna the sublittoral zone associated with the landward margin represents the most likely environment for anchor ice formation where conditions conducive to the advection of supercooled water from sub ice shelf cavities are favourable we develop a framework to estimate the areal extent of anchor ice formation assuming a northerly flow of 75m deep supercooled water plumes from the ross and mcmurdo ice shelf cavities antarctica in mcmurdo sound our results indicate that regions beneath the mcmurdo ice shelf extending along brown peninsula and white and black islands are likely conducive to anchor ice formation anchor ice may also form along the hut point peninsula and around ross island and in pockets along the southern victoria land coast the limitations of our approach include an imposed northerly flow of ice shelf water poorly constrained sub ice shelf bathymetry and temporal variability in supercooled water depth production particularly in the

influence of uniform basement extension on faulting in cover sediments abstract numerical predictions are compared with the results obtained from sandbox experiments intended to reproduce the effects of uniform basement extension for mechanically homogeneous or uniformly layered sediments that are not strain softened faults are not expected to develop during uniform basement extension even in heterogeneous or strain softening sediments subject to uniform basement extension the only faults to develop reveal an irregular and uncharacteristic distribution of displacements along the fault plane it is inferred that minor and inevitable gradients in strain rate are the most important reason why faulting was observed in the sandbox models irregularities such as topographic variation can also lead to faulting numerical experiments show that with increasing thickness of a basal elastic layer rubber membranes in sandbox models faulting of the cover sediments can cause the strain in the underlying elastic basement layer to become non uniform faulting during uniform basement extension is controlled by irregularities particular to each example and thus does not give rise to a characteristic structural style in the overlying sediments thus sandbox experiments of this type cannot be used as templates for structural interpretation except for the rare case when the initial distribution of sediment and basement material properties are known and their influence is explored from extensive numerical experimentation

the emergence of asymmetric normal fault systems under symmetric boundary conditions abstract many normal fault systems and on a smaller scale fracture boudinage often exhibit asymmetry with one fault dip direction dominating it is a common belief that the formation of domino and shear band boudinage with a monoclinic symmetry requires a component of layer parallel shearing moreover domains of parallel faults are frequently used to infer the presence of a decollement using distinct element method dem modelling we show that asymmetric fault systems can emerge under symmetric boundary conditions a statistical analysis of dem models suggests that the fault dip directions and system polarities can be explained using a random process if the strength contrast between the brittle layer and the surrounding material is high the models indicate that domino and shear band boudinage are unreliable shear sense indicators moreover the presence of a decollement should not be inferred on the basis of a domain of parallel faults alone

is ice rafted sediment in a north pole marine record evidence for perennial sea ice cover ice rafted sediments of eurasian and north american origin are found consistently in the upper part 13ma bp to present of the arctic coring expedition acex ocean core from the lomonosov ridge

numerical model of frazil ice and suspended sediment concentrations and formation of sediment laden ice in the kara sea a one dimensional vertical numerical model of currents mixing frazil ice concentration and suspended sediment concentration has been developed and applied in the shallow southeastern kara sea the objective of the calculations is to determine whether conditions suitable for turbid ice formation can occur during times of rapid cooling and wind and wave induced sediment resuspension although the model uses a simplistic approach to ice particles and neglects ice sediment interactions the results for low stratification shallow 20 m freeze up conditions indicate that the coconcentrations of frazil ice and suspended sediment in the water column are similar to observed concentrations of sediment in turbid ice this suggests that wave induced sediment resuspension is a viable mechanism for turbid ice formation and enrichment mechanisms proposed to explain the high concentrations of sediment in turbid ice relative to sediment concentrations in underlying water may not be necessary in energetic conditions however salinity stratification found near the ob and yenisey rivers damps mixing between ice laden surface water and sediment laden bottom water and probably limits incorporation of resuspended sediment into turbid ice until prolonged or repeated wind events mix away the stratification sensitivity analyses indicate that shallow 20 m unstratified waters with fine bottom sediment settling speeds of 1 mm s 1 or less and long open water fetches 25 km are ideal conditions for resuspension

particulate matter in pack ice of the beaufort gyre ice observations and sediment samples were collected in the beaufort gyre in 1988 fine sediment occurred in very small patches of turbid ice as thin spotty surface layers in mud pellets or in old snowdrifts the latter were widespread south of 74 n containing an estimated 22 tonnes of silt and clay km 2 average particle concentration in sea ice 40 mg l 1 was much higher than in sea water 0 8 mg l 1 or in new snow but the sediment load was significantly smaller and of finer texture compared to that observed in a shelfal source area after a major entrainment event

microfeatures of modern sea ice rafted sediment and implications for paleo sea ice reconstructions distinguishing sea ice rafted debris sird from iceberg rafted debris is crucial to an interpretation of ice rafting history however there are few paleo sea ice proxies this study characterizes quartz grain microfeatures of modern sird from the arctic ocean and compares these results with microfeatures from representative glacial deposits to potentially differentiate sird from ice rafted sediments which have been recently subjected to glacial processes this allows us to evaluate the use of grain microfeatures as a paleo sea ice proxy sird grains were largely subrounded with medium relief pervasive silica dissolution and a high abundance of breakage blocks and microlayering the glacial grains were more angular with lower relief and higher abundances of fractures and striations gouges discriminate analysis shows a distinct difference between sird and glacial grains with 7 of the sird grains containing typical glacial microtextures suggesting this method is a useful means of inferring paleo sea ice presence in the marine record we propose that differences in microfeatures of sird and glacial ice rafted debris reflect differences in sediment transport and weathering histories sediment transported to a coastal setting and later rafted by sea ice would be subject to increased chemical weathering whereas glaciers that calve icebergs would bypass the coastal marine environment thus preserving their glacial signature

tracking nutrient and productivity variations over the last deglaciation in the arctic ocean we have reconstructed the surface water environment of the arctic ocean over the last 50 000 years using measurements of the organic nitrogen and carbon isotope ratios carbonate and total organic carbon concentrations toc and terrestrial biomarkers lignin and long chain n alkanes in four multicores variations in nitrogen isotope ratios that are concordant with toc and carbonate concentrations representing foraminifera and excluding ice rafted debris reflect differences in relative nutrient utilization of phytoplankton in the surface waters however 15n variations also appear to be dependent on the stratification of the water column and therefore potentially track the exchange of nutrients between deep and surface waters low last glacial maximum lgm 15n values and higher holocene values are opposite to those recorded in the southern ocean the arctic ocean with higher nutrient utilization today compared to the lgm therefore acts as a counterpart to the southern ocean although the global impact on carbon dioxide variations compared to the southern ocean is probably low

okhotsk sea ice coverage and kamchatka glaciation over the last 350ka evidence from ice rafted debris and planktonic δ18o high resolution records of ice rafted debris ird and oxygen isotope records spanning an e w trending transect across the okhotsk sea unravel the marine and terrestrial cryogenic history of ne siberia over the last 350 kyr ird predominantly dispersed basin wide by sea ice shows lowest fluxes during interglacial periods implying a reduced and seasonal sea ice coverage highest ird accumulation rates are observed during glacial and deglacial periods with a more extended but highly dynamic ice cover although being rather synchronous ird fluxes are on average higher in the western okhotsk sea than in the eastern part pointing to a persistent but mobile particle supplying sea ice cover even during full glacial conditions presumably less dense in the eastern parts mis 6 is exceptional in this respect asynchronous fluxes of ird which vary spatially reflect rapid paleoclimatic and paleo glaciomarine changes ird accumulation rates were by factor 2 3 higher during mis 6 as compared to the last glacial maximum and the ird depositional center shifted from the western okhotsk sea early mis 6 toward kamchatka late mis 6 synchronous to a distinct change in the ird mineral composition both the characteristic composition of late mis 6 ird originating from the sredinny mountain range of kamchatka and their significantly enhanced accumulation rates refer to intensified iceberg dispersal across the eastern part of the okhotsk sea at 138 ka 135 ka 129 ka and 128 ka bp this scenario affords the presence of extended mountain glaciers protruding down to sea level on the western side of kamchatka anomalously light planktonic stable oxygen isotopes during mis 6 3 termination ii and mis 5 5 5 4 suggest significant freshwater supply related to the westward drainage of kamchatka glaciers the intensified kamchatka glaciation observed during late mis 6 was repeated during mis 3 iceberg discharges into the eastern okhotsk sea are observed at 60 ka 51 ka 42 ka 38 ka 36 ka and 31 ka and may partly correspond to n atlantic heinrich events

the origin and sedimentary diagenetic and metamorphic evolution of chlorite mica stacks in llandovery sediments of central wales u k chlorite mica stacks in the llandovery sedimentary rocks of central wales have been studied both within cleaved turbidite mudrocks and within early diagenetic apatite carbonate and monazite concretions stacks show a graded distribution within turbidite units indicating an origin as detrital particles concretions provided an arrested diagenetic environment which restricted subsequent deformation and so revealed the nature of the stack precursor minerals these included detrital mica and also probable pyroxenes amphiboles and volcanic rock particles relic textures of which can be seen preserved within the concretions diagenetic alteration to chlorite probably with some white mica intergrowth occurred most probably via smectite and then mixed layer or swelling chlorite intermediates subsequent modification during the caledonian cleavage forming episode determined the present shape and mineralogy of the stacks outside concretions chlorite pseudomorphs were rotated by tectonic compression crushed at their margins and pulled apart along 001 cleavage and slip planes growth of at least two generations of secondary mica infillings has been recognized and this was probably accompanied by the growth of secondary chlorite this resulted in barrel shaped stacks elongated parallel with cleavage and with the 001 plane rotated from the bedding towards the perpendicular to the cleavage within early diagenetic concretions it is evident that some stacks had formed prior to lithification however these have a relatively simple morphology and the original bedding parallel grain shapes are largely preserved

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

a field and laboratory study of wave damping by grease ice in a field and laboratory study we discuss the formation growth and wave absorption properties of grease ice our field observations show that grease ice formation occurs under cold windy conditions in both leads and polynyas in leads grease ice forms in the open water then is herded to the down wind edge of the lead in polynyas a langmuir circulation herds the grease ice into long plumes parallel to the wind in the laboratory we grow grease ice in a wave tank and measure its wave absorption properties for single frequency two dimensional waves on a large scale we find that the thickness of the grease ice which increases away from the paddle is determined by a balance between the wave momentum flux and the free surface tilt on a small scale our photographs show that the crystals which make up the grease ice consist of discs measuring about 1 mm in diameter and 1 10 m thick which at low rates of shear sinter together into larger clumps yielding a viscosity increase to measure this non linear viscosity we study the decay of wave amplitude between two critical distances measured inwards from the leading edge the first occurs when the depth of grease ice exceeds k 1 where k is the wave number the second further distance is a line of transition from liquid to solid behavior which we call the dead zone between these two distances the wave amplitude decays with a linear slope which increases as a 0 k 2 where a0 is the wave amplitude in open water concurrent measurements of ice concentration show that it increases from values of 18 22 at the leading edge to a local maximum of 32 44 at the dead zone while the values at the dead zone increase non linearly with a0k finally comparison of the observed to that calculated from a yield stress viscosity model shows if the yield stress coefficient is proportional to the incident wave momentum flux the model predicts the observed

effect of ductile and frictional decollements on style of extension abstract scaled analogue models were used to study the effect of frictional and ductile detachments on thin skinned extension models consisted of two halves one half is the ductile and the other has a frictional detachment extension occurred above two different basal configurations a stretchable rubber sheet and a folded banded sheet intended to produce homogeneous and heterogeneous extension respectively model parameters varied systematically and included the brittle ductile thickness ratio rheologies and bulk strain structures in the two halves are compared in profiles and plan views a series of graben developed above both halves of models extended above a banded sheet although there were differences in style propagation rate and width of the deformation zone between the two halves different rates of propagation of structures in the two halves led to the formation of an accommodation or transfer zone parallel to the extension direction most relay ramps and inflection of normal faults in this zone indicate differential extension between the two halves in contrast in models extended above a stretchable rubber sheet extensional structures such as horst and graben developed only above the ductile detachment model results indicate that heterogeneous mechanical stratigraphy and displacement rate have no effect on extensional structure above a rubber sheet however above 20 bulk extension deformation becomes heterogeneous along multiple sets of conjugate faults oblique to the extension direction

entrainment and export of laptev sea ice sediments siberian arctic sea ice sediments sis sediments rafted by ice and shelf surface deposits from the siberian laptev sea were analyzed to study turbulent entrainment processes this study focused on the silt and clay fractions on average representing 63 4 and 30 4 total 93 7 of the bulk sis respectively generally the sis contains 50 more silt than the shelf deposits while the clay percentages in both sample groups are similar sand sized particles are less abundant in sis than in bottom sediment although sis is clearly enriched in silt no evidence was found for preferential ice entrainment of any silt subfraction coarse medium fine statistical tests of sis and shelf silt parameters and the similar clay mineral compositions of both sample groups provide evidence for entrainment of laptev bottom deposits into newly forming ice the entrainment is related to the mechanism known as suspension freezing accordingly coarser clasts sand and plant debris may be lifted upward by buoyant anchor ice while coarse silt particles are supposed to be transported to the surface by rising frazil aggregates additionally turbulent interaction of convergent langmuir circulation and near surface frazil ice streaks is proposed to support ice entrainment of the finest particles 6 4 phi 12 m entrainment and export of sis from the laptev sea were assessed for ten individual flaw leads extended narrow polynyas separating fast and drifting ice using particle concentrations in ice samples and new ice formation rates the results show that roughly 20 mt of sis can be annually exported from the laptev sea by lead ice only thus formation and export of sediment laden lead ice may play a major geological role in siberian arctic shelf erosion and coastal retreat

assessing patterns of annual change to permafrost bluffs along the north slope coast of alaska using high resolution imagery and elevation models abstract coastal permafrost bluffs at barter island on the north slope beaufort sea coast of alaska are among the most rapidly eroding along alaska s coast having retreated up to 132 m between 1955 and 2015 here we quantify rates and patterns of change over a single year using very high resolution orthophotomosaics and co registered surface elevation models derived from a survey grade form of structure from motion photogrammetry from a fixed wing manned aircraft the resulting elevation models were validated with over 10 000 ground check points and found that 95 agreed to within 20 cm before accounting for real differences in the ground surface due to seasonality vegetation and checkpoint acquisition errors this data set provides the most detailed and accurate measurements of coastal change to date along the alaskan coast and the method is scalable to more extensive coastlines between july 2014 and july 2015 the bluffs retreated an average of 1 3 m and a maximum of 8 1 m with an associated net volume loss of 38 100 300 m3 1 3 m3 m this average retreat over this single year was slightly less than the 60 year mean rate of change of 1 5 0 1 m yr suggesting the 2014 2015 year represented relatively typical to slightly below average conditions most of the bluff material 70 was lost during the 3 summer months july to sept of 2014 and the remaining 30 between the late summer and following winter spring the pattern of change was predominantly landward retreat of the top of the bluffs removal of the debris apron and subsequent niching at the base of the bluffs during mid to late summer july to sept followed by erosion of the bluff face and deposition of debris at the base of the bluff through the remainder of the year sept to the following july drivers of the observed change are likely a combination of thermal erosion on the bluff face throughout the summer and episodic thermo mechanical removal of material niching and undercutting of the base associated with high water levels driven by low pressure storms and westerly winds these patterns and high rates of change are believed to be broadly representative of coastal permafrost bluffs found along many high latitude coastlines worldwide

effects of strain gradients on asymmetry of experimental normal fault systems abstract sandbox experiments were carried out to investigate the influence of horizontal strain gradients on the asymmetry of normal fault systems in regions of crustal extension during the experiments faults facing in the direction of higher strain were preferentially developed the results show that the horizontal strain gradient is an important factor in controlling the asymmetry of normal fault systems the experiments also relate the degree of asymmetry to the horizontal strain gradient the results may be applicable to the formation of asymmetric normal fault systems on either side of the axes of mid oceanic ridges extensional back arc regions and continental rifts

a shape and compositional analysis of ice rafted debris in cores from iodp expedition 323 in the bering sea abstract sediment cores recovered during iodp expedition 323 in the bering sea northern pacific contained numerous ice rafted debris ird clasts up to 85 mm in length the physical properties including roundness and sphericity of 136 clasts from the working half of the cores a subsample of the total clast number were analysed and their composition determined using standard petrographic techniques after removal of pumice and possible fall in derived material from the clast population a total of 86 clasts from the original collection were considered to be ird while roundness and sphericity vary greatly in the clast population the ird are predominately discoid in shape with oblate prolate indices typically between 5 and 5 there are four time periods over the approximately 4 5 ma sample interval 0 36 0 67 ma 0 82 1 06 ma 1 54 1 77 ma and 3 28 ma where there are no ird in the sample set for sites of the bering slope suggesting that these times may have been ice free most clasts show some rounding and are likely to have spent time on beaches with wave action wave action on beaches suggests periods of no ice or only seasonal sea ice the low roundness values of other clasts however suggest they underwent little working and therefore the presence of glaciers or more permanent sea ice at times in those locations the abundance of rounded and unfaceted clasts as ird suggests a lack of large ice sheets in the area during cool periods clast composition of the ird is divided into four broad groups basalt and andesite granite and metamorphic sedimentary and felsic volcanic the granite and metamorphic and more mature sedimentary lithologies are most likely derived from the alaskan continental margin while the extrusive igneous clasts could be derived from a variety of volcanic sources surrounding the bering sea both emergent now or emergent at times of lower sea level there is only a poor correlation with ird abundance and marine isotope stages mis for the time period 2 mm transported by sea ice may not be a good indicator of past climate conditions