the juan de fuca ridge hot spot propagating rift system new tectonic geochemical and magnetic data underway geophysics deep tow camera work and preliminary geochemical and magnetic studies from a 1980 cruise to the juan de fuca ridge allow the following interpretations 1 the central third between 45 5 n and 46 5 n of the ridge is now actively spreading from a zone which is 10 to 20 km west of the axis bisecting the brunhes matuyama magnetic reversal boundary 2 the apparent terminus of surficial igneous activity at the northern tip of the active cobb propagator has been identified by dredging and camera work the tip appears curved or offset slightly to the west does not correspond to the northernmost tip of the central magnetic anomaly elvers et al 1974 and spreading has been initiated beneath sediments farther north and 3 iron and titanium in fresh glasses from the active volcanic zone exhibit a progressive enrichment northward then a pronounced reversal to more normal concentrations in the vicinity of the cobb offset

reworked tsunami deposits by bottom currents circumstantial evidences from late pleistocene to early holocene in the gulf of cadiz abstract younger sand layers ysls have been identified in drill cores of a late glacial to early holocene muddy contourite succession from the gulf of cadiz in this study we evaluate the grain size characteristics of the ysl which display bi gradational grading with inverse grading from silt to fine or medium grained sand followed by normal grading from fine or medium grained sand to silt radiocarbon dating shows that the ysl formed at three distinct times 1 the bolling allerod sites u1387 and u1386 2 the younger dryas site u1390 and 3 the beginning of the boreal site u1389 ichnological analyses and radiocarbon dating of cores from drill site u1389c indicate that the ysls consist of reworked materials deposited at a high sedimentation rate the results of sedimentological analyses ichnological treatment spatial distributions and radiocarbon dating of the ysls suggest that the possibility of an origin of the ysls is tsunami related but later reworked by bottom current however the source areas of the sandy sediments remain unclear although our results show them to be variable and area dependent some sandy deposits are transported by the mediterranean outflow water mow from the proximal sector of the gulf of cadiz contourite depositional system cds which is close to the strait of gibraltar however in other cases it is more probable that local gravity flows which are the result of instability on adjacent margins provide the sandy material

hydrocarbon source rock potential and elemental composition of lower silurian subsurface shales of the eastern murzuq basin southern libya abstract a shallow borehole was drilled in lower silurian rhuddanian lower aeronian tanezzuft formation siliciclastic sediments at the eastern margin of the murzuq basin shale samples were retrieved from the borehole to study their source rock potential and trace element geochemical composition thirty shale samples analysed from borehole cdeg 2a reveal three geochemically distinct intervals shales from the top 23 38 m interval are weathered and have negligible organic content shales from the middle 38 42 m interval have moderate to good organic richness 0 6 1 7 wt toc with hydrogen index hi values up to 443 mg s2 g toc shales from the bottom 42 51 m interval have poor to moderate organic richness 0 07 0 8 wt toc with hi values up to 277 mg s2 g toc all samples have limited source rock potential and are immature to early mature for hydrocarbon generation it is unlikely that they have ever been buried deeper than 2 km low toc values inorganic geochemical redox proxies ce anomaly authigenic u th u v cr ni co and v sc indicate that the lower silurian tanezzuft formation shales from borehole cdeg 2a were deposited under oxic bottom waters explaining their relatively low toc values deposition took place in a shallow marine environment in a proximal position with regard to an early silurian palaeo shoreline this combined rock eval pyrolysis and whole rock geochemical study provides new insights into the silurian source rock distribution and hydrocarbon prospectivity in central north africa

trace metal fronts in european shelf waters the hebrides shelf edge area is characterized by strong horizontal salinity gradients fronts which mark the boundary between scottish coastal and oceanic waters1 2 the results presented here obtained in summer 1981 on a transect between the open north atlantic and the german bight fig 1 confirm that the hydrographical front is accompanied by dramatic increases in inorganic nutrients phosphate silicate and dissolved trace elements such as cd cu mn and 226ra figs 2 and 3 these data together with measurements from north sea regions suggest that the trace metals are mobilized from partly reduced organic rich sediments and vertically mixed into the surface waters3 the regional variations evident from the transect are interpreted as being the result of the hydrography prevailing in waters around the british isles4

a model for the deposition of hydrothermal manganese near ridge crests a two stage scavenging model is used to describe the transport of hydrothermal mn to the sediments adjacent to ridge crests dissolved mn is hypothesized to be scavenged by slowly settling metal depositing capsuled bacteria which in turn are incorporated into rapidly settling macroaggregates upon reaching the seafloor the mn is subject to resuspension in particulate form and to remobilization within the sediment column and release back into the water column as dissolved mn measured mn distributions in the vicinity of the southern juan de fuca ridge and estimated values of process rate constants are used to limit the range of possible model outcomes the results present a picture of water column distributions and fluxes of dissolved fine particulate and large particle associated mn in a plume advecting off axis the model and best available parameter values suggest that more than 80 of the hydrothermal mn is deposited within several hundred kilometers of the ridge crest though dissolved mn concentrations beyond that distance exceed background levels by many times the residence time of hydrothermal mn in the water column is of the order of several years an off axis component of advection of the order of 0 1 0 3 cm s is needed to make similar the model and measured distributions of mn depositing in the sediments

evidence of high energy events in shelly layers interbedded in coastal holocene sands in cadiz bay south west spain in some present day coastal areas recent inactive deposits now outside the reach of sea agents can be observed these deposits although formed under different climatic and sea level conditions often show similar facies to current littoral deposits they are frequently interpreted as old dunes and beach ridges or as abandoned spit bars representative of previous dynamic stages nevertheless in coastal areas which have been subjected to highly energetic events similar deposits can also be found when a dynamic event acts on several adjacent environments the transported and re deposited sediments can create homogeneous deposits with similar facies that are easily confused in this work shelly layers interbedded in relict littoral sands located in the la algaida pinewood on the edge of the rio san pedro tidal channel in cadiz bay south west spain have been studied the main constituents of the shelly beds are glycimeris valves organisms which are no longer found as live specimens in the present day sea bed of cadiz bay from their appearance the origin of these shelly beds could be related to sea washovers generated by tidal or storm action but their disposition and height over the present sea level implies that even higher energy agents were involved in their formation such as major storms or tsunami waves the most significant process was the mobilization of the sub tidal and littoral sediments and their dispersal and re sedimentation both lengthways and widthways of the coast giving way to homogeneous sandy deposits in all littoral environments some of which are now outside the reach of current sea agents the exception is the present day shore of the san pedro tidal channel where the sediments are being reworked by tidal and small wave action if the proximity of the study zone to the limit of the african and iberian plates is considered where several historical earthquakes and tsunamis have taken place it is possible to think that these deposits could be a consequence of sporadic and successive washovers generated by tsunamis occurring between ad 800 and ad 1200 sedimentological and historical data indicate an increase in seismic and tsunami activity during this period of time while the shelly layers would be the consequence of the most intense pulses occurring during these high energy events copyright 2009 john wiley sons ltd

trace metal distributions within a sitka eddy in the northern gulf of alaska in the northern gulf of alaska mesoscale anticyclonic eddies have been implicated as a mechanism of the cross shelf exchange of iron fe replete coastal waters with fe deplete subarctic alaskan gyre waters based on existing hydrography and macronutrient distributions a sitka eddy sampled during august 2007 is divided into a surface eddy core a shallow subsurface eddy core and a deeper subsurface eddy core the distributions of aluminum al manganese mn and fe in the eddy are examined and compared to distributions at shelf stations similar to where the eddy formed as well as basin stations representative of the fe limited subarctic alaskan gyre relative to basin stations dissolved and particulate al and dissolved mn were elevated in eddy core waters reactive fe concentrations within the shallow subsurface eddy core were nearly seven times greater than reactive fe concentrations at similar densities at the basin stations this shallow subsurface eddy core is likely mixed into the euphotic zone during storm induced mixing as well as mixing during isopycnal relaxation as an eddy dies out the flux of reactive fe to surface waters from the shallow subsurface core of eddies in the gulf of alaska is a significant source compared to both remote and local atmospheric dust deposition it is hypothesized that fe supply from eddies in the eastern gulf of alaska shifts the core of the high nutrient lower than expected chlorophyll water farther west in conjunction with an eddy desert in that same region

recent estuarine sedimentation rates from shallow inter tidal environments in western scotland implications for future sea level trends and coastal wetland development during the mid late holocene large sections of the scottish coastline have been characterized by falling relative sea levels resulting from differential glacio isostatic uplift of this region of northern britain the complex interplay between crustal and sea level movements continues to influence the morphological development of the scottish coast a number of geophysical models predict ongoing uplift of the scottish landmass however a number of recent studies based upon the analysis of satellite altimetry data indicate a late 20th century acceleration in the rate of eustatic sea level rise detailed geochemistry radiometric dating and diatom analysis on selected sediment cores from four mature coastal marsh environments in argyll western scotland provides an opportunity to investigate the linkages between twentieth century crustal movements eustatic sea level rise and recent rates of sedimentation recorded within marsh sediments across the proposed scottish glacio isostatic uplift dome solid phase major and trace element geochemistry has been used to examine the extent to which post depositional physical disturbance and or chemical reactions may have influenced the reliability of the radiometric dating methods geochemical data indicate that the evolution of these marsh environments has not been significantly influenced by physical disturbance and overall the supply of minerogenic material to the marshes has been quite uniform vertical distributions of 210pbexcess and 137cs activity have been measured and used to develop models of recent marsh vertical accretion dating of the cores reveals subtle variations in the rates of sediment accumulation over the last c 70 years between sites for much of the last hundred years or so sedimentation rates have been in good overall agreement with various estimations for sea level rise although at the more easterly sites these estimates are generally exceeded however quasi equilibrium between marsh sedimentation and sea level rise for much of the twentieth century is indicated from the diatom analysis over the most recent period of marsh development 10 years a significant increase in the rate of surface sedimentation is recorded at all sites across the study area diatom analysis of these surface layers reveals an increase in the relative abundance of marine polyhalobous taxa in the near surface sediments this signifies a very recent increase in the rate of regional relative sea level rise indicating that a regional threshold in coastal forcing has now been exceeded these findings provide clear evidence that recent relative sea level rise is now outpacing estimated rates of glacio isostatic adjustment gia across the proposed scottish uplift dome

cliff top storm deposits on banneg island brittany france effects of giant waves in the eastern atlantic ocean this study is based on the morphosedimentary analysis of the cliff top storm deposits accumulated on the coast of banneg island located in the archipelago of molene brittany france these ctsds comprise large tabular clasts quarried from the upper part of the cliff and the backing scoured platform by giant oceanic storm waves impacting directly the western coast of the island an analysis of the distribution and the geomorphology of these accumulations were carried out using the dgps topographic surveys most of the clasts are organised into imbricate boulder clusters or ridges deposited between 7 5 and 14 5 masl 52 accumulations were inventoried from the north to the south of the island representing a global volume of 1000 m3 the median size of the clasts calculated is equivalent to 0 8 0 6 0 4 m and a weight of 0 6 t the largest one measuring 5 3 3 9 0 5 m 32 t is located in the centre of the island ridge 28 it has been deposited 14 m inland from the edge of the cliff at the elevation of 9 m sediment analysis shows that clast sizes become smaller with increasing distance from the shoreline but there is no relationship between the sorting and the distance inland a study of the hydrodynamic conditions inducing clast transport was undertaken by an analysis of the wave data from the 1989 to the 1990 winter storms models of wave runup indicate that their highest water levels may have reached up to 19 masl 5 to 10 m higher than the top of the cliff submersion by giant storm waves has been more important and frequent in the centre and the south of the island wave data over the 1979 to the 2007 period shows that no events as powerful as those of the 1989 to the 1990 winter were recorded during the last 30 years yet it appears that the 1979 1990 decade was characterized by important morphogeneous events while the following period 1990 2007 has experienced a sharp decrease in storm events these variations could be attributed to the inversion from a negative towards a positive phase in the north atlantic oscillation index

different tdm ch4 hydrothermal plume signatures tag site at 26 n and serpentinized ultrabasic diapir at 15 05 n on the mid atlantic ridge as a part of the 1988 noaa vents program ch4 and mn tracers were used to identify and compare hydrothermal plumes found above the tag field 26 n and in the rift valley at 15 n close to the eastern intersection of the ridge axis with the 15 20 n fracture zone at the mid atlantic ridge mar active hydrothermal venting was confirmed at tag based on elevated concentrations of total dissolved mn tdm up to 30 nmol kg high ch4 concentrations up to 200 nl l and elevated nephelometry signals plumes of a different composition were identified at 15 n with high ch4 concentrations up to 400 nl l low total dissolved mn concentrations tdm 1 nmol kg and no significant nephelometry signal the different properties of these tracers and the different tracer ratios can be used to deduce vent fluid characteristics and compare one hydrothermal area to another tdm ch4 and nephel ch4 ratios at tag are of the same order of magnitude as those observed at other spreading axis hydrothermal fields at 15 n the low tdm ch4 ratio provides evidence of fluid circulation into ultrabasic rocks and offers a potentially useful and single method of exploring for hydrothermal activity associated with serpentinization mantle degassing through hydrothermal activity associated with serpentinization is an important process with respect to chemical and thermal exchanges between the upper mantle and the ocean different ratios of hydrothermal tracers i e tdm ch4 provide a useful framework for identifying subseafloor processes along mid oceanic ridges

evidence for storegga tsunami run up at the head of nordfjord western norway numerical simulations show that the storegga tsunami 8 150 cal a bp penetrated into fjords and sounds along the norwegian coast because of its large wavelengths of about 600 800 km despite this deposits from the tsunami have not previously been reported from the innermost fjord district probably because suitable sedimentary archives are lacking in the steep fjord landscape here we describe a persistent and well defined depositional unit up to 3 m thick found in a lake sequence at the head of the 106 km long nordfjord which we interpret as a deposit from the storegga tsunami the unit is identified and mapped in seismic profiles as a continuous semi transparent unit which in places cut deeply into the underlying strata in sediment cores the unit consists of grey silt with sub units containing shell or plant fragments gravel and sand clasts and redeposited lake mud radiocarbon ages date the deposit to the time of the storegga tsunami 8 150 cal a bp we estimate a minimum run up of 1 7 5 m for the tsunami based on the inferred elevation of the lake outlet relative to sea level at that time

the contrasting biogeochemistry of iron and manganese in the pacific ocean abstract vertical and horizontal distributions of dissolved and suspended particulate fe and mn and vertical fluxes of these metals obtained with sediment traps were determined throughout the pacific ocean in general dissolved fe is low in surface and deep waters 0 1 to 0 7 nmol kg with maxima associated with the intermediate depth oxygen minimum zone 2 0 to 6 6 nmol kg vertical distributions of dissolved mn are similar to previous reports exhibiting a surface maximum a subsurface minimum a mn maximum layer coincident with the oxygen minimum zone and lowest values in deep waters near shore removal processes are more intense for dissolved fe than for dissolved mn dissolved mn in the surface mixed layer remains elevated much farther offshore than dissolved fe elevated near surface dissolved mn concentrations occur in the north pacific equatorial current suggesting transport from the eastern boundary near surface mixed layer dissolved mn concentrations are higher in the north pacific gyre reflecting enhanced northern hemisphere aeolian sources residence time estimates for the settling of refractory paniculate fe and mn from the upper water column are 62 220 days fe and 105 235 days mn in contrast residence times for the scavenging of dissolved fe and mn are 2 13 years fe and 3 74 years mn scavenging residence times for dissolved mn based on horizontal mixing in the surface mixed layer of the northeast pacific are 0 4 years nearshore to 19 years 1000 km offshore there is no evidence for in situ fe redox dissolution within sub oxic waters in the eastern tropical north pacific dissolved fe appeared to be controlled by dissolution from sub oxic sediments with oxidative scavenging in the water column or upper sediment layers however in situ mn dissolution within the oxygen minimum zone was evident

comments to dawson a g and stewart i 2007 tsunami deposits in the geological record sedimentary geology 200 166 183

crustal movements and geodynamics in fennoscandia abstract morner n a 1981 crustal movements and geodynamics in fennoscandia in p vyskocil r green and h malzer editors recent crustal movements 1979 tectonophysics 71 241 251 the fennoscandian shield the classical area of glacial isostasy has been subjected to a complex sequence of motions throughout the late cenozoic still the geometry of the areas deformed has been roughly the same an asthenosphere of low viscosity 1020 1021 poises and a lithosphere of high flexural rigidity are established the present uplift represents an other mechanism than the rapid glacial isostatic readjustment of the low viscosity asthenosphere and seems to originate from mesospheric motions at around 1900 1910 there was a distinct geodynamic change which seems to be controlled by changes in the earth s rate of rotation the postglacial uplift of fennoscandia is found to be associated with intensive neotectonism faulting fracturing and seismicity

x ray tomography of tsunami deposits towards a new depositional model of tsunami deposits x ray computed microtomography is used to obtain high resolution imagery of a historical tsunami deposit in andalusia spain 1755 lisbon tsunami the technique allows characterization of grain size distribution structures component analysis and sedimentary fabric of fine grained unconsolidated tsunami deposits at resolutions down to particle scale the results are validated by comparing to data obtained using other techniques such as laser diffraction anisotropy of magnetic susceptibility and x ray microfluorescence on the same deposits specific technical details such as sampling scanning and image processing methods and further improvements are addressed the use of x ray computed microtomography provides new insights into the stratigraphy of the deposits and gives access to significantly more detailed view of key sedimentary features such as mudlines rip up clasts crude laminations convolutions floating outsized clasts and contacts between successive units this analysis of the 1755 tsunami deposits using x ray computed microtomography allows the proposal of new hypotheses for the sedimentary processes forming tsunami deposits deposition by settling is limited and the section analysed here is dominated by a high shear stress leading to the development of traction carpets with laminated mudlines corresponding to the basal frictional region of these carpets the onset of the tsunami backwash is marked by a micro vortex resembling kelvin helmoltz instabilities

control of sulfate pore water profiles by sedimentary events and the significance of anaerobic oxidation of methane for the burial of sulfur in marine sediments abstract gravity driven mass flow deposits proven by sedimentary and digital echosounder data are indicative for prevailing dynamic sedimentary conditions along the continental margin of the western argentine basin in this study we present geochemical data from a total of 23 gravity cores pore water so 4 is generally depleted within a few meters below the sediment surface by anaerobic oxidation of methane aom the different shapes of so 4 profiles concave kink and s type can be consistently explained by sedimentary slides possibly in combination with changes in the ch 4 flux from below thus mostly representing transient pore water conditions since slides may keep their original sedimentary signature a combined analysis and numerical modeling of geochemical physical properties and hydro acoustic data could be applied in order to reconstruct the sedimentary history we present first order estimates of the dating of sedimentary events for an area where conventional stratigraphic methods failed to this day the results of the investigated sites suggest that present day conditions are the result of events that occurred decades to thousands of years ago and promote a persisting mass transport from the shelf into the deep sea depositing high amounts of reactive compounds the high abundance of reactive iron phases in this region maintains low hydrogen sulfide levels in the sediments by a nearly quantitative precipitation of all reduced sulfate by aom for the total region we estimate a so 4 or ch 4 flux of 6 6 10 10 moles per year into the zone of aom projected to the global continental slope and rise area this may sum up to about 2 6 10 12 moles per year provided that the sulfur is completely fixed in the sediments it is about twice the global value of the recent global sulfur burial in marine sediments of 1 2 10 12 moles per year as previously estimated thus aom obviously contributes very significantly to the regulation of global sulfur reservoirs which is hitherto not sufficiently recognized this finding may have implications for global geochemical models as sulfur burial is an important control factor in the development of atmospheric oxygen levels over time

evidence of early flandrian tidal surges in lower strathearn scotland detailed stratigraphic palaeobotanical diatom and pollen and radiometric evidence from a sequence of buried estuarine deposits buried peat and overlying estuarine carse deposits at wester rhynd in lower strathearn suggests the occurrence of two brief marine incursions between the abandonment by the sea of a buried estuarine flat probably the low buried beach at about 8765 75 bp and c 8500 bp the first incursion shortly after 8565 85 bp caused bottom living marine diatoms to be thrown without clastic material onto the rapidly accumulating terrestrial peat the second bracketed by dates of 8485 80 and 8510 85 bp deposited an extremely thin 1 mm layer of fine sand that interrupts an otherwise unbroken buried peat succession covering the period 8765 75 to 7710 70 bp the marine diatom lithostratigraphic and 14c evidence together are consistent with a storm storm surge or tsunami origin for these events which are recognised principally from the diatom evidence having left no mark in the pollen record

holocene relative sea level changes on the margin of a glacio isostatically uplifted area an example from northern caithness scotland evidence is presented for holocene relative sea level changes on the margin of a glacio isostatically uplifted area the lower wick river valley northern caithness scotland lithostratigraphic b

holocene relative sea level changes in harris outer hebrides scotland uk evidence for relative sea level changes during the middle and late holocene is examined from two locations on the atlantic coast of harris outer hebrides scotland using morphological mapping and survey stratigraphical grain size and diatom analysis and radiocarbon dating the earliest event identified is a marine flood which occurred after 7982 8348 cal a 7370 80 14c a bp when the sea crossed a threshold lying at 0 08 m ordnance datum newlyn od 2 17 m mean high water springs mhws before withdrawing this could have been due to a storm or to the holocene storegga slide tsunami by 6407 6122 cal a 5500 60 14c a bp relative sea levels had begun to fall from a sandflat surface with an indicated mhws level of between 0 08 and 1 96 m 2 01 to 4 05 m this fall reached between 0 30 and 2 35 m 2 39 to 4 44 m after 5841 5050 cal a 4760 130 14c a bp but was succeeded by a relative sea level rise which reached between 0 54 and 1 57 m 1 55 to 3 66 m by 5450 4861 cal a 4500 100 14c a bp this rise continued possibly with an interruption until a second sandflat surface was reached between 2 34 and 0 26 m 0 25 to 2 35 m between 2952 3375 cal a 3000 80 14c a and 1948 2325 cal a 2130 70 14c a bp before present levels were reached the regressive episode from the earliest sandflat is correlated with the abandonment of the main postglacial shoreline it is maintained that the fluctuations in relative sea level recorded can be correlated with similar events elsewhere on the periphery of the glacio isostatic centre and may therefore reflect secular changes in nearshore sea surface levels despite published evidence from trim lines of differential ice sheet loading across the area no evidence of variations in uplift between the locations concerned could be found copyright 2009 john wiley sons ltd

hydrodynamic modeling of lake ontario an intercomparison of three models 1 the solutions of three lake hydrodynamic models namely princeton ocean model pom canadian version of diecast model and estuary lake and coastal ocean model are compared with each other and with observations in lake ontario the models have the same horizontal resolution and are forced with meteorological observations during mid april to early october of 2006 the three models obtained qualitatively similar results although they have differences in physical parameters numerical scheme and vertical discretization comparison with observations shows that the models can reproduce the time evolution of lake surface temperature reasonably well all the models produced shallower mixed layers than observations at midlake stations causing significant errors in simulating the temperatures in the thermocline but performed better near the coast all the models also reproduced the characteristics of the time variability of the surface currents but quantitatively had substantial errors at subsurface levels the three models all reproduced the observed spatial pattern of the summer mean near surface temperatures with upwelling colder temperatures along the north shore and downwelling warmer temperatures along the southeastern shore the models simulated a lake wide cyclonic circulation occupying a large portion of the lake consistent with the observed climatology but showed distinct differences in simulating the smaller gyre in the western corner of the lake although pom has half vertical layers compared to z level models its performance is comparable or slightly better than other models in most of the measures during a strong easterly wind event the performances of the models are similar in simulating the upwelling and downwelling processes in the lake and agree with the expected dynamic response to the strong wind forcing

lateglacial and holocene relative sea level changes and first evidence for the storegga tsunami in sutherland scotland we reconstruct one of the longest relative sea level rsl records in northwest europe from the north coast of mainland scotland using data collected from three sites in loch eriboll sutherland that we combine with other studies from the region following deglaciation rsl fell from a late glacial highstand of 6 8 m od ordnance datum c mean sea level at c 15 k cal a bp to below present then rose to an early holocene highstand and remained at c 1 m od between c 7 and 3 k cal a bp before falling to present we find no evidence for significant differential holocene glacio isostatic adjustment between sites on the northwest lochinver loch laxford north loch eriboll and northeast wick coast of mainland scotland this suggests that the region was rapidly deglaciated and there was little difference in ice loads across the region from one site at the head of loch eriboll we report the most westerly sedimentary evidence for the early holocene storegga tsunami on the scottish mainland the presence of the storegga tsunami in loch eriboll is predicted by a tsunami wave model which suggests that the tsunami impacted the entire north coast of scotland and likely also the atlantic coastline of northwest scotland

trace metal remobilization in the interstitial waters of red clay and hemipelagic marine sediments interstitial water samples from the guatemala basin and the coast of baja california have been analyzed for manganese iron copper nickel and nitrate the data provide a systematic look at changes in trace metal diagenesis proceeding from red clay to highly reducing nearshore sediments in red clay sediments the nitrate concentrations suggest that only aerobic respiration is occurring manganese and iron are below detection nickel concentrations remain the same as in bottom seawater but copper shows a pronounced maximum just at the sediment water interface proceeding to hemipelagic sediments denitrification becomes increasingly important and manganese and iron remobilization occur in the sediments the linear manganese and nitrate profiles suggest regions of production or consumption separated by zones of diffusion this differs from the conventional picture of a continuous series of reactions within the sediments manganese reduction always occurs before iron reduction the pore water nickel correlates well with manganese in these sediments suggesting that nickel is associated with mno2 in the solid phase the pore water flux ratio of manganese and nickel agrees well with the ratio in solid phase authigenic oxides copper still displays a core top concentration maximum as well as a second maximum associated with the remobilized manganese the calculated ratio of the cu c flux ratios support the argument for copper remobilization during organic carbon oxidation comparison of the upward and downward diffusive fluxes with the rate of copper buried by sedimentation shows that at least half of the copper buried must be of diagenetic origin and less than 25 of the copper reaching the sediments is buried

a model of the vertical mixing in lake erie in summer a vertical one dimensional model is proposed to describe the vertical mixing in the central portion of the central basin of lake erie in summer the model explicitly describes the various mechanisms which operate in the well mixed upper and bottom layers the model predictions are in good agreement with the observed thermal structure over the entire water column during a month long simulation period the central basin of lake erie has been the subject of intensive investigation in recent years due in large part to concern over the depletion of dissolved oxygen in the hypolimnion during the stratified summer period burns and ross 1972 burns 1976 the central basin encompasses an area about 80 km wide and 200 km long but with a mean depth of only 18 m and a maximum depth of 26 m during summer the lake is strongly stratified and is characterized by an upper mixed layer uml a strong temperature gradient region and a near isothermal bottom mixed layer bml see

vertex manganese transport through oxygen minima abstract manganese transport through a well developed oxygen minimum was studied off central mexico 18 n 108 w in october november 1981 as part of the vertex vertical transport and exchange research program refractory leachable and dissolved mn fractions associated with particulates caught in traps set at eight depths 120 1950 m were analyzed particles entering the oxygen minimum had relatively large mn loads however as the particulates sank further into the minimum total mn fluxes steadily decreased from 190 nmol m 2 day 1 at 120 m to 36 nmol m 2 day 1 at 400 m manganese fluxes then steadily increased in the remaining 800 1950 m reaching rates of up to 230 nmol m 2 day 1 at 1950 m manganese concentrations were also measured in the water column dissolved mn levels 1 were consistently observed within the 150 600 m depth interval in contrast suspended particulate leachable mn amounts were especially low at those depths and never exceeded 0 04 nmol kg 1 the combined water column and particle trap data clearly indicate that mn is released from particles as they sink through the oxygen minimum rate of change estimates based on trap flux data yield regeneration rates of up to 0 44 nmol kg 1 yr 1 in the upper oxygen minimum 120 200 m however only 30 of the dissolved mn in the oxygen minimum appears to be from sinking particulate regeneration the other 70 probably results from continental slope release horizontal transport processes dissolved mn scavenges back onto particles as oxygen levels begin to increase with depth scavenging rates ranging from 0 03 to 0 09 nmol kg 1 yr 1 were observed at depths from 700 to 1950 m these scavenging rates result in mn residence times of 16 19 years and scavenging rate constants on the order of 0 057 yr 1 manganese removal via scavenging on sinking particles below the oxygen minimum is balanced by mn released along continental boundaries and transported horizontally via advective diffusive processes manganese appears to be very weakly associated with particulates nevertheless the amounts of mn involved with sinking biogenic particles are large and the resulting fluxes are on the same order of magnitude as those necessary to explain the excess mn accumulating on the sea floor the overall behavior of mn observed in this and other studies strongly suggests some type of equilibrium occurring between dissolved and particulate phases this equilibrium appears to shift in direct or indirect response to dissolved oxygen levels

patterns of isostatic land uplift during the holocene evidence from mainland scotland preliminary results of a lengthy and detailed investigation into middle and late holocene raised shorelines in mainland scotland indicate that three shorelines are sufficiently widely distributed to permit an examination of their extent and of the patterns of uplift which they indicate the shorelines are the storegga tsunami shoreline reached at c 7100 14c years bp at the culmination of the main postglacial transgression and the blairdrummond shoreline reached after the main postglacial shoreline at c 2000 4200 14c years bp at the time of a tsunami believed to have been caused by the second storegga submarine slide the main postglacial shoreline reached at c 5800 6850 14c years bp the main postglacial shoreline previously believed to be the highest holocene raised shoreline in scotland is now believed to be overlapped around the periphery of the uplifted area by the later blairdrummond shoreline isobase models based upon quadratic trend surface analysis of available comparable height dat

dissolved manganese in the north atlantic ocean 0 35 n abstract dissolved manganese was measured in samples taken from vertical profiles at 13 stations between 0 and 35 n in the atlantic ocean concentrations of dissolved manganese were highest in the surface waters 1 10 to 3 17 nmol l and decreased rapidly over the top few hundred metres to generally low less than 0 5 nmol l and uniform levels for the remainder of the water column highest concentrations in surface waters occurred in latitudes which have particularly high loadings of atmospheric dust of saharan origins and it is suggested that eolian inputs are the most significant source of manganese to the upper water column in this area in the sections of profiles affected by advection of mediterranean water the concentrations of dissolved manganese were similar to those found generally for the atlantic water masses and are consistent with recent data for the mediterranean the generally low concentrations in deep water indicate that in the areas studied there are no major influences of advection of dissolved manganese from sources on the slope or the mid ocean ridge

mid holocene environmental changes in the bay of skaill mainland orkney scotland an integrated geomorphological sedimentological and stratigraphical study a detailed multidisciplinary investigation of intertidal freshwater sediments exposed in the north of the bay of skaill mainland orkney scotland have revealed a complex sedimentary sequence this provided evidence for dynamic coastal environmental changes in the area since the mid holocene freshwater ponds developed on glacial sediments ca 6550 80 yr bp cal bc 5590 5305 from ca 6120 70 yr bp cal bc 5040 4855 these were infilled by blown sand from the distal edge of a dune ridge located to the west thereafter a series of sand blow events alternating with periods of quiescence occurred until ca 4410 60 yr bp cal bc 3325 2900 between ca 5240 160 and 4660 80 yr bp cal bc 4370 3115 pollen and charcoal records show evidence of anthropogenic activities associated with the nearby neolithic settlement of skara brae agriculture was probably affected by recurrent sand movement and widespread deposition of calcium carbonate in the hinterland of the bay machair development between ca 6100 and 5000 yr bp cal bc 5235 3540 corresponds to a mid holocene phase of dune formation recorded elsewhere in northwest europe the more recent and progressive formation of the bay has probably been related to increasing external forcing via storminess long term relative sea level change and sediment starvation within this exposed environment copyright 2000 john wiley sons ltd

the geochemistry of manganese in the northeast pacific ocean off washington1 2 water collected along a transect normal to the coast of washington was analyzed for dissolved co 4 pm and total dissolvable manganese tdm the vertical profiles exhibit the same general features observed elsewhere in the pacific but a horizontal section of the transect shows that concentrations increase markedly toward the continental margin a surface maximum ranging from 0 57 nmol kg in offshore waters to 5 24 over the continental slope is probably due to fluvial inputs especially from the columbia river another possible source is the upwelling of manganeseenriched bottom water over the shelf horizontal gradients are also observed in the oxygen minimum as manganese concentrations decrease from 4 75 nmol kg l near the continental slope to 0 7 1 in open ocean water porewater and solid phase data suggest that manganese is being actively remobilized under reducing conditions in the slope sediments and is diffusing into the overlying seawater at a rate sufficient to balance losses by vertical mixing and particulate scavenging two stations on opposite sides of the juan de fuca ridge have deep concentration maxima that are almost certainly due to injections of hydrothermal vent fluid along the ridge

late devensian and holocene relative sealevel changes at loch nan eala near arisaig northwest scotland pollen diatom radiocarbon and lithostratigraphical data from isolation basins in northwest scotland are used to quantify the reference water tide level indicative range and age of differenty types of isolation and connection contacts tendencies of sea level movement and relative sea level changes from the mid lateglacial interstadial 11 8 ka bp to the late holocene are constructed from these data relative sea level fell continuously from 17 8 m od at 11 8 ka bp to ca 5 2 m od at 10 1 ka bp from an unkown minimum between 10 ka and 9 ka bp relative sea level then rose to 6 3 m od at 8 3 ka bp the maximum holocene sea level occurred within the range 6 6 m od to 9 3 m od between 6 6 ka bp and 4 0 ka bp before falling to present isobase age altitude and quantitative rebound models for northwest scotland are tested using these sealevel data but none of the published models shows close agreement with the new results

inflow and outflow facies from the 1993 tsunami in southwest hokkaido abstract we describe in detail the sedimentary facies provenance and grain size distributions of the 1993 tsunami deposits in the lower reaches of usubetsu river only two lithofacies were recognized a gravel lobe facies glf and a sand sheet facies ssf the gravel lobe facies was deposited rapidly by a hydraulic jump in contrast the sand sheet facies which contains both current ripples and dunes was deposited by a traction current under subcritical flow conditions we identified four stratigraphic units unit 1 unit 2 unit 3 and unit 4 in ascending order we interpreted units 1 and 2 as having been deposited by the inflow and outflow events of the first run up and units 3 and 4 by the inflow and outflow events of the second run up respectively units 3 and 4 were more widely distributed and coarser grained than units 1 and 2 because the second run up was larger than the first run up furthermore unit 4 was more widely distributed than unit 3 because the outflow eroded the inflow deposits grain size distributions of the inflow and outflow deposits were clearly different unit 4 deposits had a peak at 2 5 phi p 1 population in contrast unit 3 deposits had a bimodal distribution with peaks at 0 5 1 5 phi p 2 population and at 2 5 phi p 1 population a comparison of the tsunami deposits with other sedimentary deposits near the study area showed that the tsunami deposits were mainly derived from the seabed at depths below 5 5 m in the offshore area where the marine sands are about 2 2 5 phi in size and thus are the source of the p 1 population the p 2 population is derived from coarse 0 5 2 phi fluvial materials eroded during the tsunami run up according to our calculations benthic foraminiferal tests were entrained from the comparatively deep seabed at depths up to 100 m during the tsunami run up and included in the tsunami deposits

the 1994 shikotan earthquake tsunamis the 1994 shikotan earthquake was one of the greatest earthquakes in recent years with a magnitude of m s 8 0 a tsunami survey was conducted by russian and u s geophysicists from october 16 30 1994 less than two weeks after the earthquake the survey results and a numerical hindcast simulation are reported tsunami focusing effect at locations supposedly sheltered by the island chain is discussed based on the obtained data tsunamis which attacked shikotan island are characterized as long waves the order of 10 20 min wave period with a positive leading wave possible consequences of the positive leading wave form are discussed in relation to the observed minimal destruction of beach vegetation and relatively small transport of marine sediment onto the shore the high quality tide gage record in malokurilskaya bay indicates the occurrence of a 53 cm subsidence at the site

expanding the proxy toolkit to help identify past events lessons from the 2004 indian ocean tsunami and the 2009 south pacific tsunami article i nfo some of the proxies used to identify palaeotsunamis are reviewed in light of new findings following the 2004 indian ocean tsunami and the 2009 south pacific tsunami and a revised toolkit provided the new application of anisotropy of magnetic susceptibility ams to the study of tsunami deposits and its usefulness to determine the hydrodynamic conditions during the emplacement of tsunami sequences together with data from grain size analysis are presented the value of chemical proxies as indicators of saltwater inundation associated marine shell and or coral high energy depositional environment and possible contamination is demonstrated and issues of preservation addressed we also provide new findings from detailed studies of heavy minerals new information gathered during the unesco international oceanographic commission ioc international tsunami survey of fine onshore sediments following the 2009 south pacific tsunami is presented and includes grain size chemical diatom and foraminifera data the tsunami deposit varied ranging from fining upward sand layers to thin sand layers overlain by a thick layer of organic debris and or a mud cap grain size characteristics chemical data and microfossil assemblages provide evidence for marine inundation from near shore and changes in flow dynamics during the tsunami

living with sand a record of landscape change and storminess during the bronze and iron ages orkney scotland abstract palaeoenvironmental analyses of an exposed sequence of interbedded sand and peat overlying glacial till on stronsay orkney has revealed evidence of dynamic landscape change during the holocene ams radiocarbon and osl dating are used to identify periods of minerogenic and organic sediment accumulation a lengthy period of stability during the early holocene is inferred from the development of a deeply weathered till surface with pollen and soil micromorphological evidence suggesting prolonged woodland cover during the mid to late holocene phases of wind blown sand that inundated the landscape are defined from the sedimentary record and are interpreted as periods of increased storminess between c 3400 3100 cal bp and c 2800 2260 cal bp the palaeoecological evidence points to continuity of human exploitation despite the phases of increased storminess during the bronze age and into the iron age rising sea levels and a severe storm event at c 650 years bp inundated the site with massive sands and truncated the record these storm events recorded on stronsay are part of a regionally synchronous record for periods of increased storminess across the north atlantic region during the holocene

patterns of holocene relative sea level change in the north of britain and ireland temporal and spatial patterns of relative sea level rsl change in the north of britain and ireland during the holocene are examined four episodes each defined by marked changes in the rsl trend are identified each episode is marked by a rise to a culminating shoreline followed by a fall episode hrsl 1 dates from the younger dryas to early in the holocene hrsl 2 to hrsl 4 occurred later in the holocene there is extensive evidence for each episode and on this basis the spatial distribution of the altitude data for three culminating shorelines and a shoreline formed at the time of the holocene storegga slide tsunami ca 8110 100 cal bp is analysed ordinary kriging is used to determine the general pattern following which gaussian trend surface analysis is employed recognising that empirical measurements of rsl change can be unevenly distributed spatially a new approach is introduced which enables the developing pattern to be identified the patterns for the most widely occurring shorelines were analysed and found to be similar and common centre and axis models were developed for all shorelines the analyses described provide models of the spatial pattern of holocene rsl change in the area between ca 8100 cal bp and ca 1000 cal bp based on 2262 high resolution shoreline altitude measurements these models fit the data closely no shoreline altitude measurement lying more than 1 70 m or 1 82 m from the predicted value the models disclose a similar pattern to a recently published glacial isostatic adjustment model for present rsl change across the area indicating that the overall spatial pattern of rsl change may not have varied greatly during the last ca 8000 years

a 7600 year sedimentary record of climatic instability in dunnet bay north scotland abstract we present a partial reconstruction of ne atlantic climatic variability the first based on stratigraphic evidence obtained from a vegetated dune system of the northern scottish coast the dune system at dunnet bay is fringed by prominent submerged peat deposits exposed only at low tide which record stable climatic periods when lower energy wind regimes prevailed allowing the formation of organic soils by contrast periods of sand influx are associated with high energy conditions the majority of sand material tested had a narrow range of particle sizes and major element composition supporting the interpretation of a common aeolian origin sand layers were dated with optically stimulated luminescence osl and peat layers were 14 c dated in four cores c1 c4 and seven sample sections s1 s7 the results from the two master sections s1 and s2 1 km apart indicate synchronous episodes of climatic stability 7650 6310 4340 4000 2690 2290 100 0 cal a bp and instability 6310 4340 4000 2690 2290 2000 170 100 cal a bp in spite of very different mean accumulation rates at the two sites 1 mm a 1 at s1 and 0 2 mm a 1 at s2 phases of sand deposition i e aeolian activity at dunnet tend to be associated with high average levels of chloride in the greenland ice sheet project 2 ice core gisp2 phases of peat development show a fairly good correspondence with low ice rafting activity in the ne atlantic and with indicators of wetness measured from a peat bog in sw sweden by contrast comparison of the dunnet depositional timeline with other regional studies e g hebrides and orkney shows little synchronicity this suggests that a local scale variables have a strong effect on regional patterns of dune instability and b the geological and geographic settings of dunnet bay mean that only large climatic regime shifts in the ne atlantic are capable of triggering instability and being preserved in the depositional record

on the distribution of copper nickel and cadmium in the surface waters of the north atlantic and north pacific ocean concentrations of copper nickel and cadmium have been determined for about 250 surface water samples nonupwelling open ocean concentrations of these metals are cu 0 5 1 4 nmol kg ni 1 2 nmol kg and cd less than 10 pmol kg in the equatorial pacific upwelling zone concentrations of ni 3 nmol kg and cd 80 pmol kg are higher than in the open ocean but cu 0 9 nmol kg is not significantly enriched metal concentrations are higher in cool nutrient rich eastern boundary currents cu 1 5 nmol kg ni 3 5 nmol kg and cd 30 50 pmol kg copper is distinctly higher in the coastal waters of the gulf of panama 3 4 nmol kg and also higher in the shelf waters north of the gulf stream 2 5 nmol kg these copper enrichments may be caused by copper remobilized from mildly reducing shelf sediments and maintained by a coastal nutrient trap in the open ocean events of high cu water 1 5 3 5 nmol kg are seen on scales up to 60 km presumably these are due to the advection of coastal water into the oceanic interior the lowest copper concentrations in the north pacific central gyre 0 5 nmol kg bruland 1980 are lower than in the sargasso sea 1 3 nmol kg while for nickel the lowest concentrations are 2 nmol kg in both the north pacific and the north atlantic nickel and cadmium while generally correlated with the nutrients in surface waters show distinct regional changes in their element nutrient correlations the residual concentrations of trace metals in the surface waters of the ocean can be explained if biological discrimination against trace metals relative to phosphorus increases as productivity decreases

erratum holocene coastal environmental changes on the periphery of an area of glacio isostatic uplift an example from scapa bay orkney uk the first detailed investigation of a deep coastal sedimentary basin in orkney reveals a complex holocene history of back barrier morphodynamics at scapa bay the sea flooded a freshwater marsh after ca 9400 yr bp at ca 5 4 m od before ca 7800 bp abundant sediment from nearby cliffs was mobilised inland into a series of gravel barriers across the valley mouth by ca 7500 bp direct marine influence was restricted in the back barrier area although saltmarsh persisted until ca 5900 bp by then at least four gravel ridges had enclosed the backing lagoon where freshwater inputs became dominant as terrestrial sediments filled the basin another freshwater marsh developed the multiple barrier complex demonstrates progradation resulting from continuous sediment supply in a sheltered embayment the progressively rising height of the barrier crests seawards probably resulted from a combination of factors such as barrier morphodynamics increased storminess and long term rising relative sea levels the dominant vegetation surrounding scapa bay changed from open grassland to scrub ca 9400 bp then to deciduous woodland ca 7800 bp and to dwarf shrub heath ca 2600 bp the latter probably a response to a combination of climate change and human activity copyright 2007 john wiley sons ltd

evaluation of holocene crustal movement in the ako plain western japan holocene sea level observations have been obtained from the ako plain in western japan in this coastal area the holocene crustal movements have been evaluated except the crustal response due to the last deglaciation by comparing observations and theoretical predictions of relative sea level rsl variations analyses of diatom assemblages and sedimentary sulphur in core sediments were used along with radiocarbon dates to derive the rsl variations a crustal movement rate between 0 2 mm and 0 2 mm per year corrected for the prediction fits well with the observed rsl index points owing to the constraint of the reconstructed palaeo mean sea level pmsl at 7300 cal bp the coast of the ako plain may have the best estimate of a tectonic subsidence rate of 0 0 2 mm yr the tectonic uplift rates along the tectonically active coast of western kobe were derived to be 0 3 0 7 mm yr and 0 11 0 45 mm yr for tarumi and tamatsu respectively relative to ako over the period concerned the relative uplift along the traverse from ako to western kobe is primarily the result of the crustal movement resulting from the active faulting of the rokko awaji fault system rfs

late devensian and holocene records of relative sea level changes in northwest scotland and their implications for glacio hydro isostatic modelling raised tidal marshes and isolation basins lakes that were once connected to the sea in northwest scotland record changes in relative sea level following deglaciation during the late devensian to the present the kentra to arisaig area which was covered by relatively thick ice c 900 m at the last glacial maximum lgm shows a regression from a marine limit between 36 5 m od and 40 m od at c 15 9 kyr cal bp range 15 6 16 3 kyr cal bp through to an early holocene minimum a range of sites in the same area record a mid holocene maximum indicative of mean sea level c 6 5 m above present the maximum is not a well developed and short duration highstand as predicted by a number of models but is an extended period 8 0 5 0 kyr cal bp with sea level within c 1 m of the maximum sites to the north in kintail show no late devensian record because much of the area lies within the younger dryas ice limit the altitude of the mid holocene maximum in kintail is not well constrained but occurred 7 9 8 1 kyr cal bp further north sites on the applecross peninsula record a late devensian fall in sea level and a holocene maximum for mean sea level no higher than c 3 0 m above present in coigach the furthest north of the new sites and well outside the younger dryas ice limit there is no evidence recorded of late devensian sea levels above present the holocene maximum here was around c 2 5 m above present these observations of sea level change all standardised to change in mean sea level relative to present constrain the glacio hydroisostatic rebound model parameters earth models comprising three mantle layers with lateral viscosity and elastic parameters give a satisfactory description of rebound the parameters h lithosphere thickness 65 km g 6 upper mantle viscosity 4 1020 pa 14c seconds and g lower mantle viscosity 1022 pa 14c seconds give the best overall agreement but discrepancies between observations and predictions remain an increase of 10 in ice thickness north of the great glen compared to the previous optimum ice model provides good agreement for many sites but important discrepancies remain for the northern sites and indicate inadequacies in the model of the british ice sheet several alternative ice models are examined but the various combinations of earth and ice model illustrate the non uniqueness of the solution a combination of more extensive ice limits especially onto the hebridean shelf and west shetland shelf and some changes to ice thicknesses over the mainland should produce a better agreement but the spatial coverage of observations remains a limitation to producing a unique solution the characteristics of the holocene highstand age duration and amplitude at the di erent sites refutes the assumption that globally deglaciation ceased abruptly 7000 yr ago the observations are consistent with an ice model that includes c 3 m of melting over the last 7000 yr 2000 elsevier science ltd all rights reserved

late devensian and holocene relative sea level changes on the isle of skye scotland uk detailed litho and biostratigraphical analyses from three coastal sites in contrasting coastal settings on the isle of skye scotland uk reveal evidence for several changes in relative sea level during the late devensian and holocene at the start of the record relative sea level in the area was high at ca 12 500 14c ca 14 800 cal yr bp but then fell reaching a low point during the younger dryas at ca 11 000 10 000 14c ca 13 000 11 600 cal yr bp when a rock platform correlated with the main rock platform was formed in the early middle holocene relative sea level was rising by ca 8000 14c ca 8800 cal yr bp and in northeast skye a lagoonal surface correlated with the main postglacial shoreline was formed at ca 6600 14c ca 7500 cal yr bp by the late holocene relative sea level was again falling but a rise registered at at least two sites began probably before ca 4000 14c ca 4500 cal yr bp and a second lagoonal surface in northeast skye correlated with the blairdrummond shoreline was formed although by ca 3000 14c ca 3200 cal yr bp relative sea level in the area had resumed its downward trend the pattern of relative sea level changes disclosed is compared with evidence elsewhere in scotland

glacial rebound and sea level change in the british isles observations of sea levels around the coastline of the british isles for the past 10 000 15 000 years exhibit a major regional variation and provide an important data base for testing models of glacial rebound as well as models of the late devensian ice sheet a high resolution rebound model has been developed which is consistent with both the spatial and temporal patterns of sea level change and which demonstrates that the observations are the result of i the glacio isostatic crustal rebound in response to the unloading of the ice sheet over britain and to a lesser degree of the ice sheet over fennoscandia and ii the rise in sea level from the melting late pleistocene ice sheets including the response of the crust to the water loading the hydro isostatic effect the agreement between model and observations is such that there is no need to invoke vertical crustal movements for great britain and ireland of other than glacio hydro isostatic origin the rebound contributions are important throughout the region and nowhere is it sufficiently small for the sea level change to approximate the eustatic sea level rise the observational data distribution around the periphery as well as from sites near the centre of the former ice sheet is sufficient to permit constraints to be established on both earth model parameters specifying the mantle viscosity and lithospheric thickness and the extent and volume of the ice sheet at the time of the last glaciation preliminary solutions are presented which indicate an upper mantle viscosity of 3 5 1020 pas a lithospheric thickness of about 100 km or less and an ice model that was not confluent with the scandinavian ice sheet during the last glaciation and whose maximum thickness over scotland is unlikely to have exceeded about 1500 m

manganese flux from continental margin sediments in a transect through the oxygen minimum the flux of manganese from continental margin sediments to the ocean was measured with a free vehicle benthic flux chamber in a transect across the continental shelf and upper slope of the california margin the highest fluxes were observed on the shallow continental shelf manganese flux decreased linearly with bottom water oxygen concentration and the lowest fluxes occurred in the oxygen minimum zone at a depth of 600 to 1000 meters although the flux of manganese from continental shelf sediments can account for the elevated concentrations observed in shallow coastal waters the flux from sediments that intersect the oxygen minimum cannot produce the subsurface concentration maximum of dissolved manganese that is observed in the pacific ocean

the holocene storegga slide tsunami in the united kingdom all currently known sites in the united kingdom with evidence for the holocene storegga slide tsunami are described information on the altitude distribution stratigraphical context age particle size profile and microfossil characteristics of the deposits is presented the tsunami involved a greater area than previously described reaching a coastline over 600 km long the ubiquitous sand layer which forms the main deposit associated with the event is shown to exhibit a consistent morphology and a particle size profile marked by fining upwards sequences an analysis of new and previously published radiocarbon dates indicates that from evidence in the united kingdom the event took place sometime around 7100 radiocarbon years bp 7900 calibrated years bp a new isobase model for mainland scotland and adjacent areas providing a preliminary estimate of land uplift since the tsunami is presented the model estimates contemporary sea surface level offshore at 14 m below the present day mean high water spring tides tsunami sediment run up is greatest in inlets where it reaches at least 25 m on shetland and at least 5 m along the mainland coastline to the south and run up of the tsunami would have exceeded these values the tsunami sediments identified here are considered particularly valuable as a synchronous marker horizon

the sedimentology of middle holocene tsunami facies in northern sutherland scotland uk abstract lagoonal sediments attributed to the main holocene marine transgression in strath halladale northern sutherland contain a complex coarser layer believed to have been deposited during the tsunami associated with the second storegga slide off south west norway the coarser sequence is dated at between 7590 50 and 7290 50 radiocarbon years bp 6507 6260 cal bc and 6228 6029 cal bc detailed stratigraphical analysis has determined a distinctive suite of sedimentary sub units within the coarser layer in marked contrast to the sediments which occur above and below a pronounced erosional unconformity with the underlying sediments is recorded with the base of the tsunami layer characterised by eroded material from the underlying peat the presence of a mixed diatom assemblage although fragmentary indicates a chaotic accumulation of the deposit with all habitats represented variations in particle size within the sequence disclose striking similarities with those from contemporary tsunami deposits the run up of the tsunami sediments is calculated at a minimum of 4 6 m this is the first occasion on which a deposit of the second storegga slide tsunami has been found outside the north sea basin and indicates that the area affected by the tsunami may have been larger than has been previously described

low sea level stand emplacement of megaturbidites in the western and eastern mediterranean sea piston cores from the balearic and herodotus abyssal plains in the mediterranean sea show that the late pleistocene to holocene sedimentary sequence is dominated by turbidite muds on each plain one turbidite bed is conspicuous by its thickness and this bed can be correlated basinwide on the basis of geochemical compositional analysis and its apparent correspondence with a distinct acoustically transparent layer on high resolution seismic records these megabeds on the two plains represent megaturbidites of very large volume 300 600 km3 each and are shown by ams radiocarbon dating to have been emplaced during the last low stand of sea level at the height of the last glacial maximum the megabed on the balearic abyssal plain is derived from the southern european margin and is the main sedimentation event over the last 120 ka it emplaced as much material as was deposited by smaller flows during the previous 25 ka sedimentation rate curves for the balearic abyssal plain show that falling sea level correlates with increased terrigenous deposition and that gross sedimentation rates in the basin increased as sea level fell from 120 18 ka due to more frequent emplacement of distal turbidites the herodotus abyssal plain megabed is derived from the libyan egyptian continental shelf west of the nile delta and was the dominant sedimentation event in this basin during the past 60 kyr high resolution seismic profiles from the ionian and sirte abyssal plains in the central mediterranean also suggest possible low sea level emplacement of megabeds in these regions available evidence suggests widespread emplacement of megaturbidites throughout the mediterranean at the last glacial maximum although the triggering mechanisms for these events remain speculative catastrophic destabilisation of the margin after a long period of accumulation with an increased rate of sediment supply is suggested

feasibility of bubble plume destratification of central lake erie abstractthe central basin of lake erie has chronic hypoxia that is exacerbated by strong seasonal temperature stratification near the lake bed a computational study was conducted to determine the feasibility of mechanically mixing the water column by using a bubble plume system to reduce stratification thus facilitating vertical transport of oxygen the most efficient design delivered an air flow rate of 0 4 0 5 m3 s 1 through 40 50 non interacting plumes which only mix the watercolumn during the late summer hypoxic events the optimal efficiency was computed using a new metric which neglects changes in stratification resulting from meteorologically induced mixing relative to those from artificial mixing

holocene uplift derived from relative sea level records along the coast of western kobe japan abstract mid to late holocene sea level observations have been obtained from tamatsu and tarumi in western kobe japan in this tectonically active area we evaluate the local tectonic effect during the holocene by comparison between observations and predictions of sea level variations for the purpose of this study we analysed the diatom assemblages and carried out sulphur analysis of sediments these were used along with radiocarbon dates to derive relative sea level variations for the sites a rate of tectonic uplift of between 0 1 and 0 3 mm per year corrected for the prediction fits well with relative sea level rsl index points of tamatsu at 6415 5320 cal bp depending on the altitude of the rsl index point at about 5700 cal bp the best estimate of the rate of tectonic uplift for tamatsu is calculated as 0 11 0 25 mm yr over the period concerned a rate of tectonic uplift between 0 3 and 0 5 mm per year is derived for tarumi at about 7300 and 3835 3365 cal bp these values may explain the height distributions of the late pleistocene marine terraces along the coast of the western kobe providing a first approximation for rates of local crustal movements during the late quarternary

holocene coastal evolution and uplift mechanisms of the northeastern raukumara peninsula north island new zealand abstract the coastal geomorphology of the northeastern raukumara peninsula new zealand is examined with the aim of determining the mechanisms of holocene coastal uplift elevation and coverbed stratigraphic data from previously interpreted coseismic marine terraces at horoera and waipapa indicate that despite the surface morphology there is no evidence that these terraces are of marine or coseismic origin early holocene transgressive marine deposits at hicks bay indicate significant differences between the thickness of preserved intertidal infill sediments and the amount of space created by eustatic sea level rise therefore uplift did occur during early holocene evolution of the estuary the palaeoecology and stratigraphy of the sequence shows no evidence of sudden land elevation changes beach ridge sequences at te araroa slope gradually toward the present day coast with no evidence of coseismic steps the evolution of the beach ridges was probably controlled by sediment supply in the context of a background continuous uplift rate no individual dataset uniquely resolves the uplift mechanism however from the integration of all evidence we conclude that holocene coastal uplift of this region has been driven by a gradual aseismic mechanism an important implication of this is that tectonic uplift mechanisms do vary along the east coast of the north island this contrasts with conclusions of previous studies which have inferred holocene coastal uplift along the length of the margin was achieved by coseismic events this is the first global example of aseismic processes accommodating uplift at rates of 1 mm yr 1 adjacent to a subduction zone and it provides a valuable comparison to subduction zones dominated by great earthquakes

oceanic ridge crest processes oceanic ridge crest processes constitute a vigorous frontier of multidisciplinary research with global ramifications in the earth atmospheric and biologic sciences this deep ocean frontier is gradually opening in response to investigations which are elucidating the role of these processes in the lithosphere hydrosphere atmosphere and biosphere and the application of advanced instrumental and interpretive techniques which are increasing the quality and quantity of data these techniques include crustal drilling with borehole logging deep sea drilling project reports high resolution bathymetry sea beam etc side scan sonar seamarc i and ii gloria etc imagery with video and photography multichannel seismics determination of water column properties ctd with rosette sampler etc and submersible applications

enhanced particle scavenging in deep water of the aleutian basin revealed by 210po 210pb disequilibria the high sedimentation rate but low primary production in surface ocean raised a question whether particles from local upper water column could support high deposition in the aleutian basin here we first present large 210po 210pb disequilibria in deep water of the aleutian basin dissolved 210po and 210pb were depleted relative to 210pb and 226ra respectively in deep water below 1000 m as well as decreased with depth suggesting enhanced particle scavenging in the deep water the 210po residence times 1 2 a in deep water were comparable to those in the upper water column indicating that 210po scavenging rates were high in deep water of the aleutian basin the export fluxes of 210po from the upper 100 m were estimated to be 0 2 0 8 bq m2 d much lower than those in the deep water 7 8 bq m2 d similarly poc export fluxes in deep water 24 80 mmolc m2 d were higher than those in the upper 100 m 1 mmolc m2 d such a large discrepancy between the upper and deep water suggested that particles from local upper water column could not totally meet the enhanced scavenging in the deep water based on mass balance calculations the extra fluxes of 210pb and poc imported to deep water were estimated to be 8 12 bq m2 d and 22 79 mmolc m2 d respectively the ratio of poc to particulate 210pb i e poc ppb in the extra source was estimated to be 6 5 mmol bq which was lower than that in the bering shelf with a mean poc ppb ratio of 10 9 mmol bq implying that particles in the bering shelf could be a potential source for the enhanced particle scavenging in deep water of the aleutian basin however quantitative and detailed role of ridges and manganese from sediments in particle scavenging in the deep water was unclear and further studies are necessary

distribution of hydrothermal manganese over the juan de fuca ridge bottom waters from five hydrographic stations spaced equally along a 400 km section of the juan de fuca ridge north of the blanco fracture zone contain anomalously high concentrations of total dissolvable manganese tdm the two bottom most bottles from each hydrocast approx 100 to 200 m above bottom range from 8 3 to 108 9 nmol kg sup 1 with a median value of 12 0 nmol kg sup 1 this median is nearly a factor of 10 higher than similar near bottom samples obtained from two off axis locations analogy to work on the east pacific rise implies that hydrothermal activity along the ridge axis is contributing substantially to the manganese content of the water column in this portion of the northeastern pacific

distribution geomorphology and lithofacies of cliff top storm deposits examples from the high energy coasts of scotland and ireland abstract cliff top storm deposits ctsds occur on cliffs at elevations of up to 50 m above sea level at exposed sites on the deep water coasts of the british isles this study examines the distribution geomorphology and lithofacies of ctsds at sites from shetland orkney caithness and the outer hebrides in scotland and from the aran islands in galway bay in ireland ctsds are generated largely by the quarrying of blocks from the cliff top and transported by green water bores across cliff top platforms and ramps to be deposited in backing ridges or as debris spreads maximum boulder sizes reach 48 m 3 but it is likely that much larger blocks can be quarried prior to disintegration during transport eye witness accounts and field mapping demonstrate that formation and modification of ctsds has continued during major storms over recent decades recent ctsds bury a range of man made debris but older deposits lack this and instead show weathering effects that indicate a longer residence time in shetland osl dates on intercalated sands suggest that the oldest ctsds date from 800 ad radiocarbon dates on shell buried inside ctsd ridges relate to major storms between 1700 and 1900 ctsds represent an overlooked archive of storm sedimentation that has great potential for the elucidation of local storm chronologies ctsds also provide evidence of wave impacts on any part of the cliff face or top in fundamental contrast to the concentration of wave action at the cliff foot implicit in traditional models of the erosion of rock coasts

processes controlling the distribution and cycling of manganese in the oxygen minimum zone of the arabian sea abstract vertical and horizontal distributions of dissolved and particulate manganese were investigated in the arabian sea northwestern indian ocean during the 1995 spring intermonsoon period march april us jgofs process cruise 2 tn045 the region is characterized by an intense basin wide oxygen minimum zone omz that strongly influences the manganese distribution in the omz two distinct dissolved mn d mn maxima were observed at depths of 200 300 m and 600 m respectively the latter peak displayed concentration maxima of approximately 6 nanomolar and was largely confined to stations north of 19 n latitude stations n2 n7 this mid depth maximum was associated with the low oxygen core of the omz o 2 saager et al 1989 geochimica et cosmochimica acta 53 2259 2267 this signal was largely absent at stations along the southern transect likely due to oxidative scavenging of d mn to the suspended particulate phase mid depth particulate mn maxima at some southern stations stations s4 s11 appear to be remnants of this feature the upper d mn maximum 200 300 m depth was more widely distributed than the 600 m peak with d mn concentrations of 3 to as high as 8 nm at most stations east of about 62 e longitude the signal was everywhere correlated with the secondary nitrite maximum at stations within the main denitrification zone delineated by naqvi 1991 nepheloid layers presumably bacterial also were associated with this depth interval particulate mn profiles displayed corresponding concentration minima and low mn al and reactive refractory mn ratios for this same depth interval suggesting reductive dissolution of mn oxyhydroxides these observations imply that in situ microbially mediated processes may be the predominant source of d mn in the upper omz while horizontal advection is more important deeper in the water column

towards improved empirical isobase models of holocene land uplift for mainland scotland uk a new approach to modelling patterns of glacio isostatic land uplift during the holocene in mainland scotland uk is described the approach is based upon altitude measurements at the inner margin or locally highest point of raised estuarine surfaces dated by radiocarbon assay supported by microfossil analyses 2241 altitudes have been analysed by a technique new to studies of former sea levels gaussian trend surface analysis and isobase models for four holocene shorelines the holocene storegga slide tsunami shoreline abandoned rapidly circa 7900 sidereal years bp the main postglacial shoreline abandoned during circa 6400 7700 sidereal years bp the blairdrummond shoreline abandoned during circa 4500 5800 sidereal years bp and a speculative fourth shoreline the wigtown shoreline abandoned during circa 1520 3700 sidereal years bp are shown in a series of maps the implications of the shoreline patterns for glaicio isostasy in the area are discussed it is maintained that the statistical technique used enables broad estimates to be made of nearshore sea surface change

flandrian relative sea level changes in the ythan valley northeast scotland relict flandrian estuarine deposits in the ythan valley are confined to an area in the lower valley around the present estuary they rest upon a discontinuous layer of peat over an irregular surface of sand and gravel and consist for the most part of a grey silty clay or carse deposit which forms terraces or small areas of carseland at the seaward end of the estuary the grey silty clay contains a layer of grey micaceous silty fine sand which tapers into the basal peat whilst in places the surface of the grey silty clay is covered by peat and or blown sand the vegetational context and age of these deposits have been determined at waterside near the mouth of the present estuary here the grey silty clay accumulated as the result of a marine transgression which began in the early flandrian and culminated between about 6189 95 and some time prior to 4000 80 radiocarbon years b p the carseland surface produced by this phase of accumulation is the highest flandrian estuarine surface in the valley at about 4 5 m o d and is correlated with the main postglacial shoreline elsewhere in eastern scotland withdrawal of the sea from this level may have been interrupted by the formation of a lower carseland surface before present levels were reached though this is far from certain the grey micaceous silty fine sand layer is dated at approximately 6850 140 radiocarbon years b p and is correlated with similar layers that may have been deposited following a storm surge the paper concludes with some considerations on the age and distribution of the main postglacial shoreline in eastern scotland

on the postglacial isostatic adjustment of the british isles and the shallow viscoelastic structure of the earth summary observations of postglacial relative sea level rsl history at sites beyond the margins of the main accumulations of wu rm wisconsin devensian ice may be invoked to test the accuracy of global models of the glacial isostatic adjustment process the existing database of rsl time series for the british isles forms a continuous network of sites that sample the coasts of scotland england and wales fairly uniformly and which may be especially important in this regard not only are these 14c data for the holocene epoch of very high quality in terms of our knowledge of the coastal environment and relationship to palaeo sea level of each age measurement but they are especially numerous and relate to an island that was itself partly glaciated in the north essentially ice free in the south and located well outboard of the massive ice sheet that covered fennoscandia at the last glacial maximum lgm taken together the time series from 55 distinct locations allow us to perform a fairly stringent test of the recently formulated ice 4g vm2 global model of the isostatic adjustment process even without modification this model has been shown to fit most of the time series in the uk data set rather well in order to satisfy very recently published a priori constraints on the maximum thickness of the scottish ice sheet however we find that the lithospheric thickness the feature of the radial viscoelastic structure to which the rebound data from scotland are most sensitive must be somewhat reduced whereas the assumed thickness of the lithosphere in ice 4g vm2 was near to 120 km best fits to the scottish data require a lithospheric thickness near to 90 km this reduced value for lithospheric thickness agrees exceedingly well with the latest estimates of this earth property based on the inversion of oceanic geoid and topography data as the asymptotic thickness characteristic of the oldest ocean floor this would appear to be the best possible a priori estimate for the thickness of the cratonic lithospheres upon which the largest ice sheets of the late pleistocene are known to have rested we also demonstrate explicitly that inferences of the shallow viscoelastic structure beneath the british isles are strongly influenced by the details of the history of deglaciation at remote locations at antarctica in particular

archaeology of the continental shelf marine resources submerged landscapes and underwater archaeology we provide a critical review of the evidence for the long term use of marine resources and coastal environments in human evolution and later development we emphasise the importance of the coastal archaeological record in understanding patterns of human settlement and dispersal and draw attention to the large potential biases introduced by the destructive or obscuring effects of pleistocene sea level change we note that lowered sea levels have been the norm for most of the pleistocene and that periods of high sea level have been too short lived to provide other than a fragmentary coastal record and one that is beset with ambiguities and uncertainties we examine the geological processes of coastal uplift and underwater preservation that may help to mitigate these biases coastlines elevated by isostatic and tectonic processes or with very steep offshore drop offs at plate boundaries are important in providing a potential window into coastal landscapes and archaeology formed during periods of lowered sea level however we conclude that the opportunities afforded by these geological factors are too limited to obviate the need for underwater exploration we review the evidence now available from submerged landscapes across the africa eurasia interface from the atlantic coastlines of northwest europe to the southern red sea we show that geomorphological conditions for the preservation of archaeological and palaeoenvironmental data are commonly present that much material has already been discovered and that new techniques technologies and projects are providing the momentum for a rapidly expanding field of investigation the results do not simply add to what we already know from sites on land but are likely to produce qualitatively different evidence for coastal adaptations and landscapes that have no analogue on present day coastlines we note the strong probability that many coastal landscapes exposed at lowered sea level provided relatively fertile and productive refugia for plants land mammals and humans at a time when increased aridity would have reduced or deterred hinterland occupation we conclude that underwater investigation is essential if hypotheses of early human adaptation and dispersal are to be fully tested

rapid holocene relative sea level changes in gruinart isle of islay scottish inner hebrides litho and biostratigraphic analyses undertaken in the gruinart estuary central islay reveal a detailed sedimentary record of holocene relative sea level changes and high energy flood events during the last 10 000 years during the lateglacial holocene transition relative sea level had fallen to below c 0 5 m od and remained at this depth until c 8830 14c years bp thus the early holocene minimum sea level is here relatively well constrained altitudinally a sustained and largely uninterrupted rise in relative sea level took place after c 8500 14c years bp reaching a maximum altitude of c 4 5 m od and remained at an elevation of c 4 m od until c 2000 14c years bp both the recorded maximum altitude of the main holocene transgression and the late age of the relative marine regression are incompatible with published shoreline uplift isobase models for this area

the storegga slides evidence from eastern scotland for a possible tsunami abstract the second storegga slide on the continental slope off western norway has been dated at between 8000 and 5000 yrs b p a prominent sand layer in flandrian holocene deposits along the coast of eastern scotland and dated at approximately 7000 yrs b p may have been deposited by a tsunami generated by the slide the altitude and stratigraphy of the layer allow estimates to be made of the magnitude of the earthquake which initiated the slide

sedimentologic and geomorphologic tsunami imprints worldwide a review abstract tsunami events with extreme effects on sedimentary transport or considerable alterations of the coastal configuration are rather rare regarding human history but considering geological timescales they occur frequently at least 100 megatsunami in different parts of the world have been recorded in the past 2000 years but presumably far more have failed to be noticed during historical times and are not mentioned either in written or oral ancient records therefore the topic of paleotsunami requires inevitable sedimentological and geomorphological research however field research concerning paleotsunami is astonishingly rare within the scientific approach and only 5 of the existing tsunami literature is related to this subject future efforts in paleotsunami research should focus on the geological evidence of these mega events to clarify their contribution to coastal forming processes this paper reviews the state of the art knowledge of sedimentologic and geomorphic imprints of tsunami along the world s coastlines in order to highlight the need for more detailed studies of paleotsunami depositional and geomorphological traces

holocene relative sea level changes in a glacio isostatic area new data from south west scotland united kingdom abstract this paper contributes to knowledge of holocene relative sea level change along the mainland ayrshire coast and offshore isle of bute sw scotland uk where few such studies have previously been undertaken morphological studies mapping and altitude survey together with stratigraphical and biostratigraphical studies pollen and diatom analyses and radiocarbon dating disclose evidence for mid and late holocene relative sea level changes the main postglacial and blairdrummond displaced shorelines previously identified widely in mainland scotland are dated in the area at c 6800 calibrated years c 6000 14c years and c 4200 calibrated years c 3800 14c years bp respectively this information is compared with previously published information for scotland against the classical theoretical model of relative sea level change in areas of glacio isostasy for the mid and late holocene in conformity with the model a falling sequence of relative sea level changes near the centre of uplift is replaced by a rising sequence towards the periphery in which later shorelines overlap earlier ones in particular the blairdrummond shoreline which overlaps the earlier main postglacial shoreline is identified as the highest holocene shoreline over much of the coastline of scotland

paleomagnetic rock magnetic and geochemical study of the 1755 tsunami deposit at boca do rio algarve portugal abstract a multiproxy study combining paleomagnetic rock magnetic magnetic susceptibility anhysteretic remanent magnetization arm isothermal remanent magnetization irm anisotropy of magnetic susceptibility ams and geochemical xrf data was carried out on trench sediments collected in the area of boca do rio algarve south portugal known to have been stricken by a tsunami wave related to the 1755 lisbon earthquake the magnetic mineral assemblage is dominated by multidomain ferrimagnetic grains with a significant contribution 5 9 of ultra fine magnetic particles related to the presence of pedogenetic magnetite the variable amount of this post depositional magnetite plays a role on the characteristic remanent magnetization chrm of the sediment the primary magnetization recorded at t1 located farthest from the coast is representative of the paleosecular variation of the earth s magnetic field and a comparison of the results with the regional model for the geomagnetic field in europe scha dif 3k was used to constrain the erosional signature of the tsunami layer the result indicates that less than eighty years could be missing in the sedimentary column the eroded sediment thickness 27 40 cm was incorporated in the tsunami layer that is characterized by a low magnetic content and a large increase in the ca content representing allochthonous material sedimentological geochemical magnetic and ams data show that the signature of the tsunami layer reflects at least two waves with an erosive capacity that is controlled by the distance from the shore

cobalt in ferromanganese crusts as a monitor of hydrothermal discharge on the pacific sea floor ferromanganese oxide crusts which accumulate on unsedimented surfaces in the open ocean1 6 derive most of their metal content from dissolved and particulate matter in ambient bottom water7 8 in proportions modified by the variable scavenging efficiency of the oxide phase for susceptible ions9 they differ in this respect from abyssal nodules much of whose metals are remobilized from host sediments here we present maps of cobalt concentration and inferred accumulation rate of ferromanganese crusts from the pacific ocean we propose that depletion of cobalt in pacific crusts measures the location and intensity of submarine hydrothermal discharge use of the cobalt chronometer an algorithm inversely relating cobalt content and crust growth rate permits mapping of the accumulation rate of ferromanganese crusts with only indirect recourse to radioactivity based dating methods these maps show that crusts in hydrothermal areas grow from two to more than four orders of magnitude faster than in the central pacific ocean cobalt enriched crusts are found where water masses are most isolated from continental coastal and hydrothermal sources of metals now and in the past this relationship can resolve the problem of cobalt enrichment in crusts without recourse to hypotheses invoking special cobalt sources or enrichment mechanisms

relative sea level change and evidence for the holocene storegga slide tsunami from a high energy coastal environment cocklemill burn fife scotland uk a site in the cocklemill burn valley on the north shore of the firth of forth scotland provides evidence of relative sea level changes during the holocene from ca 7970 to ca 5090 radiocarbon years bp and of the holocene storegga slide tsunami dated here as having taken place after ca 7215 radiocarbon years bp marine sediments associated with two shorelines widely present in mainland scotland the main postglacial shoreline and the blairdrummond shoreline are recorded the holocene storegga slide tsunami deposits are unique here in the record of such sediments in eastern scotland in that they occur within marine sands of which the upper horizons are intertidal sandflat deposits the tsunami deposits probably accumulated shortly after a period of accelerated relative sea level rise the pattern and timing of which could have played a role in triggering the holocene storegga slide

pleistocene development of the se nordic seas margin abstract throughout the pleistocene the sedimentary environment on the se nordic seas continental slope outer shelf off western norway has been strongly controlled by variability in the norwegian atlantic current nwac glaciations of the shelf areas and sea level changes acoustic and core data from the southern voring plateau show a pleistocene sequence characterised by hemipelagic sediments interfingered by diamictons on the upper slope the area of the 7 25 14 c ka bp storegga slide shows evidence of a long history of pleistocene mega slides during the last interglacial and most likely also during previous interglacials the slide region has been the locus of rapid deposition between water depths of 800 and 1200 m as a result of nwac winnowing along the upper slope the north sea fan region is strongly influenced by glacigenic debris flows gdfs deposited during glacial advances reaching the shelf edge when the norwegian channel was occupied by the norwegian channel ice stream it appears that gdf activity was initiated at ca marine isotope stage 12 interbedded between the debris flow sequences mega slide events such as the more and tampen slides have been identified during glaciations when the entire se nordic seas continental shelf was covered by extensive grounded ice sheets basal till were transported to the shelf edge from where subsequent mass movement occurred during late glaciation early deglaciation meltwater plumes were released at the time of disintegration of ice streams in the norwegian channel as is evidenced from the last deglaciation of the margin at ca 15 14 c ka bp the plume material was transported northwards by currents before rapidly deposited as a thick package within the storegga slide area and on the south voring plateau based on identification and dating of iceberg scourings glacial erosion surfaces and delta deposits on the shelf subsidence rates between 0 7 and 1 2 m ky have been calculated for the last ca 250 ka

late devensian and holocene relative sea level changes in northwestern scotland new data to test existing models abstract pollen diatom lithostratigraphic and radiocarbon data from five sites in northwestern scotland provide new data from an area previously devoid of reliable and precise information on late devensian and holocene sea level changes the sites cover a range of palaeoenvironments indicative of diversity in coastal evolution since deglaciation for each site and palaeoenvironment the reference water tide level indicative range age and tendency of sea level movement of all sea level index points are quantified to enable correlation of the diverse coastal environments the data record patterns of relative sea level change and tendencies of sea level movement from 12 ka bp to 1 ka bp this is the longest and most comprehensive published record of relative sea level change from the area the information is used to test the accuracy of existing models of relative sea level change the results are only broadly consistent with a quantitative rebound model and there is significant disagreement with empirical models during the late devensian and the early holocene

the altitude and age of the main postglacial shoreline in eastern scotland abstract this paper discusses the patterns of altitude and age variation of the main postglacial shoreline in eastern scotland from the firth of forth to the dornoch firth for reasons of comparability attention is confined to the carseland areas the mean altitude of the shoreline declines eastwards from 14 8 m to 6 1 m od in the forth area from 11 2 m to 8 1 m in the earn tay area and northwards up the coast from the tay area to ca 6 4 m in the montrose basin area ca 3 9 m around the ythan estuary and ca 2 0 m near fraserburgh in the beauly firth inner moray firth area it declines northeastwards from ca 9 m to 7 1 7 9 m and declines to 5 7 m in the dornoch firth the isobase pattern for eastern scotland as represented by a quadratic trend surface conceals a significant regional variation in the tay area the age of the shoreline has been investigated at 14 sites grouped in 8 locations at varying distances from the centre of uplift the ages range from ca 6800 14c years bp in the upper forth carselands to 6095 75 5700 90 bp near fraserburgh with the exception of one site the data are consistent with the hypothesis that the shoreline is measurably diachronous having been abandoned progressively later with increasing distance from the centre of uplift the implications of these findings for understanding isostatic eustatic relationships are discussed

linking tsunami deposits submarine slides and offshore earthquakes abstract the recognition that many tsunamis are associated with coastal sedimentation has been of great value in the study of tsunamis prehistorically geological investigation of such sediments has resulted in the identification of a series of palaeotsunamis that appear to have taken place in different areas of the world in most cases however it has proved difficult to link former tsunamis to specific source mechanisms studies of modern tsunamis have also faced difficulties in the recognition of the specific source mechanisms for example offshore earthquakes may trigger submarine slides that combine to produce complex patterns of tsunami flooding at the coast

a tsunami ca 6300 years bp and other holocene environmental changes northern hawke s bay new zealand abstract sediment cores collected in a coastal lagoon a few kilometres east of wairoa northern hawke s bay new zealand were examined using sedimentological geochemical palynological and micropaleontological analyses a distinct short lived catastrophic saltwater inundation csi about 6300 years bp and possibly other minor marine incursions are preserved in the coastal estuarine to lagoonal freshwater sedimentary sequences which have been deposited in the last 6500 years the csi is characterised by a gravel unit that thins landward and decreases in particle size to sand within a sequence consisting mainly of brackish estuarine muds diatom assemblages indicate a marked change from the shallow brackish estuarine muds to marine gravels and sands to brackish estuarine muds the marine influence in the gravel and sand is also shown by the presence of marine dinoflagellates and a peak in na rb sedimentological chemical and paleontological in particular diatoms evidence indicates it is a csi we conclude that this was a tsunami and propose the most likely propagating mechanisms marine influence decreases upcore and totally freshwater conditions are evident in the upper section of the cores the geochemistry of the sediments mainly reflects the change in stratigraphy with distinct signatures for tephra na fe cr organic rich and peat units as br and the coarse gravel sand csi unit na rb cr fe but it is also indicative of changes in depositional environment the change in chemistry na rb in the csi event is indicative of a saltwater influence whereas a marked change in s content suggests a sudden change from brackish to freshwater conditions shortly after 4800 years bp another peak in s and br content about 3200 years bp may indicate another temporary change to brackish conditions

manganese fluxes from mississippi delta sediments abstract massive sediment deposition on the mississippi river delta establishes reducing conditions sufficient to bring about mn dissolution in the top millimeters of sediment as a result significant fluxes of dissolved mn pass from the delta sediments to the overlying water column this process is examined by study of chemical partitioning of mn in river particulates and delta sediments and from interstitial water chemistry remobilized mn is actively transported away from the delta area with aluminosilicate detritus thereby providing excess mn to the deep gulf of mexico at the expense of the delta sediments

hydrothermal methane venting between 12 n and 26 n along the mid atlantic ridge hydrographic surveys along the mid atlantic ridge mar between 12 n and 26 n carried out from 1984 to 1990 show a variable pattern of ch4 rich water column plumes the vertical distribution of ch4 at stations located every 20 40 km is presented along this 1200 km long section of the mar ch4 venting is clearly demonstrated ch4 enriched fluids rise from vents as plumes spreading is confined to the axial valley due to the topography of the mar ch4 contents from 45 nmol to 675 nmol kg are measured in the buoyant plumes above the two active hydrothermal sites mark 23 n tag 26 n known at present whereas ch4 anomalies up to 3 6 nmol kg are typically observed in plumes emitted either on the inner floor on the walls and or at the top of the rift mountains along the studied ridge section ch4 concentrations 45 mol to 144 mol kg in mark and tag vent fluids are of the same order of magnitude as those found in the east pacific rise fluids even though ch4 is known to be unstable with respect to oxidation by dissolved oxygen and in spite of its microbial oxidation in plumes these results confirm ch4 to be a good indicator to track hydrothermal plumes and to map the variation of hydrothermal activity along mid oceanic ridges moreover between 12 and 26 n along the mar ch4 results show that while hydrothermal activity is present everywhere along the ridge it is predominant near fracture zones fz kane fz 15 20 n fz comparison of ch4 tracer with total dissolvable manganese tdm tracer in plumes allows us to differentiate subseafloor hydrothermal processes the high tdm ch4 found above tag and mark areas is indicative of basalt seawater interaction while at 15 n the low tdm ch4 provides evidence of fluid circulation in ultrabasic rocks ch4 data confirm the association between mantle degassing hydrothermal activity and serpentinization along this 12 26 n section of the mid atlantic ridge

holocene land and sea level changes in great britain analysis of more than 1200 radiocarbon dated samples that constrain relative sea levels in great britain over the past 16 000 yr provides estimates of current land level changes negative of relative sea level change maximum relative land uplift occurs in central and western scotland ca 1 6 mm yr 1 and maximum subsidence is in southwest england ca 1 2 mm yr 1 sediment consolidation arising from autocompaction as the sediment accumulates and from land drainage increases the subsidence in areas with thick sequences of holocene sediments with an average effect equivalent to at least an extra ca 0 2 mm yr 1 land subsidence but more in parts of southeast england 0 5 1 1 mm yr 1 modelled changes in tidal range during the mid to late holocene in eastern england suggest that the calculated rate of land subsidence is overestimated unless such changes are quantified the effect is most significant for large coastal lowlands the fenland and humber ca 0 5 and 0 6 mm yr 1 that were tidal embayments during the mid to late holocene

holocene relative sea level changes in the inner solway firth abstract bio and lithostratigraphic data from four sites from the inner solway firth allow an accurate reconstruction of holocene rsl changes in the estuary radiocarbon assays give eleven new sea level index points providing a total of 24 reliable index points for the inner solway firth these data show a consistent pattern of rapid rsl rise during the early holocene culminating in a mid holocene sea level maximum then a gradual fall to the present day level detailed analysis of this dataset quantifies for the first time differential crustal movement between the north and south shores of the solway firth these data are used to test the accuracy of quantitative isostatic rebound models of lambeck and peltier and show there is good general agreement between the data and the models especially during the early holocene the models predict the mid holocene sea level peak slightly later than shown by the data c 500 and c 2000 yr this may be partly due to lack of resolution in the models and for the south solway the maximum altitude at this peak is 1 and 2 5 m too high in the two models the data are also compared to the isobase models of the main postglacial shoreline showing slight diachroneity between the north and south shore but otherwise general agreement with the postulated age and indicating that the altitude of this feature is 1 3 m higher than suggested by the models

sea level change in the irish sea since the last glacial maximum constraints from isostatic modelling models of glacio hydroisostatic sea level change have been published for the british isles that are broadly consistent with the observational evidence as well as with glaciological constraints it has been argued however that the models fail to represent sea level change along the irish sea margins and in southern ireland for the post deglaciation period the argument rests on the interpretation of the depositional environment of the elevated irish sea drift on both sides of the irish sea whether this is terrestrial or glaciomarine the isostatic models for the british isles are consistent with the former interpretation in that sea levels on either side of the irish sea south of about the isle of man are not predicted to have risen above present sea level at any time since the deglaciation of the irish sea this implies that ice over both the irish sea and ireland was relatively thin ca 600 700 m over ireland if the glaciomarine interpretation of the elevated irish sea drift is correct then the maximum ice thickness over central and southern ireland would have to reach 2000 m exceeding that over scotland furthermore for the resulting sea level change to be consistent with the holocene evidence this thick ice sheet could not have extended to the eastern side of the irish sea nor could it have been very thick at its northern and western limits if such an ice model is extreme and incompatible with glaciological observations then the alternative is to accept the interpretation of the irish sea drift as terrestrial in origin copyright 2001 john wiley sons ltd