channel axis overbank and drift sediment waves in the southern hikurangi trough new zealand abstract in the southern apex of the hikurangi trough east of new zealand swath bathymetry and backscatter seismic profiles and cores from the proximal part of the 2000 km long hikurangi channel show different types of sediment waves in the channel axis and on the levee backslopes these represent different responses to large turbidity currents locally backslope sediment waves merge into sediment waves formed by a deep geostrophic flow in the channel axis and on channel walls sediment waves that have wavelengths of 1 4 km and heights of less than 6 m occur where cores show gravelly and coarse sandy turbidites they are not apparent in layering below the channel axis they are inferred to be thin transitory surface sand bodies migrating across coarser substrates and may have formed in a recent perhaps the last turbidity current their geometry suggests that they probably formed as antidunes in high velocity flows that were much thicker than the channel depth overbank sediment waves also have similar wavelengths of 1 4 km but heights of up to 45 m they have conspicuous sub seabed layering to a depth of at least 400 m beneath the seabed seismic stratigraphy indicates that they have developed for most of the last 2 ma during near vertical aggradation of the channel its levees and overbank slopes at average rates of 0 4 0 7 m ka the sediment waves migrate up levee backslopes towards the levee crest at rates of 3 20 m ka and are inferred to be formed beneath lee waves initiated in overbank flows by the linear perturbation of the levee they are best developed on the outsides of bends where centrifugal outflow of upper overspill parts of large turbidity currents might be concentrated they are particularly well developed at right hand bends on the left bank where centrifugal and southern hemisphere coriolis effects combine poorly developed sediment waves on the inside of some left hand bends may be the result of coriolis effects only overbank sediment waves decrease in height and wavelength away from the channel and continue into a depression along the slope toe deformation front at the landward edge of the turbidite plain where the channel intersects the slope toe depression the absence of a left bank levee suggests that overbank flows re enter the channel along the toe of the chatham rise sediment waves up to 5 m high and 2 5 km in wavelength migrate away from the channel and towards a slope toe moat they are inferred to be part of a drift deposit perhaps associated with a branch of the pacific deep western boundary current

submarine canyons and channels in the lower st lawrence estuary eastern canada morphology classification and recent sediment dynamics abstract series of submarine canyons and channels observed in the lower st lawrence estuary lsle provide an opportunity to analyze in great detail the morphology spatial distribution and modern activity of such systems in a relatively shallow 300 m semi enclosed basin based on their geomorphology and physical settings the canyons and channels were classified into four categories according to their feeding sources ancient or recent glacially fed river fed longshore drift fed and sediment starved systems their activity was interpreted based on geomorphological characteristics such as the presence of bedforms related to gravity flows backscatter intensity axial incision and the presence of rapidly deposited layers in surficial sediments river fed deltas were interpreted as inactive mainly because suspended sediment concentrations at river mouths are low preventing the generation of hyperpycnal currents or delta lip failures related to high sediment supply longshore drift fed canyons present where the coastal shelf narrows were found to be episodically active probably due to earthquakes or extreme storm events unlike other longshore drift fed canyons observed elsewhere in the world they are active infrequently because of the modern low rates of sediment supply to their heads the most active canyons are the sediment starved type and were observed near pointe des monts their activity is probably due to slope failures and to the presence of strong hydrodynamic processes therefore sediment supply is not the main mechanism responsible for modern canyon and channel activity in the lsle however sediment supply has been an important factor during the formation of the submarine channels and canyons their quasi exclusive occurrence on the quebec north shore is attributed to its larger watershed and important sedimentary delivery during deglaciation the quebec north shore watershed is 20 times greater than the quebec south shore watershed which favored the transport of greater volumes of sediment during the early holocene moreover the slope proximity to the shore led to the formation of longshore drift fed systems on the north shore when sediment supplied to rivers were transferred on a narrow shelf

structure and paleoearthquake records of active submarine faults cook strait new zealand implications for fault interactions stress loading and seismic hazard 1 a new interpretation of active faulting in central cook strait new zealand reveals tectonic structures associated with the spatial transition from subduction to continental transform faulting marine seismic reflection profiles and multibeam bathymetric data indicate that there are no throughgoing crustal faults connecting the north island dextral fault belt and the marlborough fault system in south island the major faults terminate offshore associated with 5 20 km wide step overs and a change in regional fault strike this structure implies that propagation of strike slip earthquake ruptures across the strait is not probable faulted sedimentary sequences in the wairau basin marlborough shelf correlated to glacioeustatic sea level cycles provide a stratigraphic framework for fault analysis a high resolution study of the postglacial 20 ka vertical displacement history of the cloudy and vernon faults reveals up to six and five paleoearthquakes since 18 ka respectively these long timescale records indicate variable recurrence intervals and possibly variable stress drop thus conforming to the variable slip model of earthquake behavior integration of these data with other submarine and terrestrial paleoearthquake records indicates the presence of clustered earthquake sequences involving multiple faults different sequences do not always involve the same faults it appears that earthquake clustering is driven by fault interactions that lead to specific loading conditions favoring the triggering of earthquakes on major faults in relatively short time intervals present day regional coulomb stress distribution has been calculated in two scenarios considered to represent minimum and maximum loading conditions the models incorporating secular tectonic loading and stress changes associated with major crustal earthquakes indicate high stress loading in a large part of central cook strait these conditions may favor the triggering of future damaging earthquakes in this region

the bering sea and paleoceanography abstract this paper serves as an introduction to the bering sea preceding the 14 contributed papers contained in this volume several parts of the paper are allocated for current reviews of the bering sea included in the review topics are geomorphology surface water circulation and the importance of the formation of intermediate waters representative results of previous paleoceanographic studies are also presented in particular focusing on spatial and temporal distributions of biosiliceous microfossils as well as isotopic analyses of carbon and nitrogen concerning changes in productivity and nutrients motivations behind the scientific expeditions conducted which resulted in the many papers included here are briefly discussed in order to illustrate the recent trend in paleoceanography in the bering sea and the adjacent regions brief summaries or highlights of each of the contributed papers are given in order to provide an overview of the volume

ploughing the deep sea floor bottom trawling is a fishing technique whereby heavy nets and gear scrape along the sea bed and is shown here to disturb sediment fluxes and modify the sea floor morphology over large spatial scales the direct impact of bottom trawling on local fish populations has received much attention but trawling also affects other aspects of the ocean environment this paper shows that bottom trawling a commercial practice in which heavy nets and gear are dragged along the ocean floor induces sediment reworking and erosion causing the gradient of the sea floor to become smoother over time this reduces the morphological complexity of deep sea environments the authors draw parallels between the effects of bottom trawling at sea and intensive agriculture on land with the important difference that on land ploughing takes place once or twice a year whereas at sea bottom trawling can be a frequent occurrence bottom trawling is a non selective commercial fishing technique whereby heavy nets and gear are pulled along the sea floor the direct impact of this technique on fish populations1 2 and benthic communities3 4 has received much attention but trawling can also modify the physical properties of seafloor sediments water sediment chemical exchanges and sediment fluxes5 6 most of the studies addressing the physical disturbances of trawl gear on the seabed have been undertaken in coastal and shelf environments7 8 however where the capacity of trawling to modify the seafloor morphology coexists with high energy natural processes driving sediment erosion transport and deposition9 here we show that on upper continental slopes the reworking of the deep sea floor by trawling gradually modifies the shape of the submarine landscape over large spatial scales we found that trawling induced sediment displacement and removal from fishing grounds causes the morphology of the deep sea floor to become smoother over time reducing its original complexity as shown by high resolution seafloor relief maps our results suggest that in recent decades following the industrialization of fishing fleets bottom trawling has become an important driver of deep seascape evolution given the global dimension of this type of fishery we anticipate that the morphology of the upper continental slope in many parts of the world s oceans could be altered by intensive bottom trawling producing comparable effects on the deep sea floor to those generated by agricultural ploughing on land

deepwater source variations during the last climatic cycle and their impact on the global deepwater circulation the degree of similarity of the 13c records of the planktonic foraminiferal species n pachyderma and of the benthic foraminiferal genus cibicides in the high latitude basins of the world ocean is used as an indicator of the presence of deepwater sources during the last climatic cycle whereas continuous formation of deep water is recognized in the southern ocean the norwegian sea stopped acting as a sink for surface water during isotope stage 4 and the remainder of the last glaciation however deep water formed in the north atlantic south of the norwegian sea during the last climatic cycle as early as isotope substage 5d and this area was also the only active northern source during stages 4 2 a detailed reconstruction of the geographic distribution of 13c in benthic foraminifera in the atlantic ocean during the last glacial maximum shows that the most important deepwater mass originated from the southern ocean whereas the glacial north atlantic deep water cannot be traced south of 40 n at shallower depth an oxygenated 13c rich intermediate water mass extended from 45 n to 15 s in the pacific ocean a ventilation higher than the modern one was also found in open ocean in the depth range 700 2600 m and is best explained by stronger formation of intermediate water in high northern latitudes

effect of commercial trawling on the deep sedimentation in a mediterranean submarine canyon abstract in order to study sediment accumulation rates in the palamos submarine canyon northwestern mediterranean during the last century three sediment cores were extracted from the canyon axis at depths of 450 1200 and 1750 m respectively where instrumented moorings were previously located estimated sedimentation rates based on 210 pb and 137 cs profiles suggest that the contemporary trends of sediment transfer and accumulation in the canyon may be different from secular trends during the seventies a two fold increase of the sediment accumulation rate took place at the 1750 m depth site this change has been associated to trawling activities and is attributed to the rapid technical development that the local trawling fleet underwent during the seventies the surroundings and rims of submarine canyons are frequently targeted by commercial trawling fisheries an activity that may enhance the input of resuspended particles into canyons and eventually trigger sediment gravity flows our results suggest that the effects of trawling over the dynamics of the seafloor may extend further and deeper from the fishing grounds eventually extending to bathyal depths hence the anthropogenic influence on the sedimentary budget of some deep submarine environments may be more important than previously thought

holocene sedimentary activity in a non terrestrially coupled submarine canyon cook strait canyon system new zealand abstract the cook strait canyon system located between the north and south islands of new zealand is a large 1800 km 2 multi branching shelf indenting canyon on an active subduction margin the canyon comes within 1 km of the coast but does not intercept fluvial or littoral sediment systems and is therefore defined as a non terrestrially coupled system sediment transport associated with a strong tidal stream and seafloor disturbance related to numerous high activity faults is known from previous studies little is known however about the rates of sedimentary activity in the canyon and the processes driving it a substantial dataset of em300 multibeam bathymetry gravity cores 3 5 khz seismic reflection profiles camera and video transects and current meter data have been collected across the region between 2002 and 2011 the canyon system therefore provides an excellent study area for understanding sediment transport in a non coupled submarine canyon system analysis of the data reveals a two staged sediment transport system where 1 oceanographic tidal processes mobilise sediment from the continental shelf and transport it to depocentres in the upper central canyons and 2 tectonic earthquake processes remobilise sediment that is transported through the lower canyon to the deep ocean tidal boundary layer currents within the canyon reach velocities up to 0 53 m s and are capable of mobilising fine sand in the central reach of the upper canyons the velocity is higher at the canyon rim and capable of mobilising coarse sand sediment depocentres resulting from this tidally forced sediment transport have a well formed geomorphology within the mid upper canyon arms of cook strait and nicholson canyons pseudo static stability modelling supported by sediment core analysis indicates that sediment accumulated in the upper canyons fails during seismic events approximately every 100 years the 100 year return period ground shaking level peak ground acceleration ignoring the effect of the water column above the seabed at this site is estimated to be 0 23 g fresh rock outcrops and bed scour in the lower canyon floor indicate that remobilised material is transported to the deep ocean the processes identified here are likely to be analogous to those occurring in many non coupled shelf indenting canyons on active margins globally and provide a framework within which the biological response to geomorphic processes in submarine canyons can be assessed

on the upscaling of process based models in deltaic applications abstract process based numerical models are increasingly used to study the evolution of marine and terrestrial depositional environments whilst a detailed description of small scale processes provides an accurate representation of reality application on geological timescales is restrained by the associated increase in computational time in order to reduce the computational time a number of acceleration methods are combined and evaluated for a schematic supply driven delta static base level and an accommodation driven delta variable base level the performance of the combined acceleration methods is evaluated by comparing the morphological indicators such as distributary channel networking and delta volumes derived from the model predictions for various levels of acceleration the results of the accelerated models are compared to the outcomes from a series of simulations to capture autogenic variability autogenic variability is quantified by re running identical models on an initial bathymetry with 1 cm added noise the overall results show that the variability of the accelerated models fall within the autogenic variability range suggesting that the application of acceleration methods does not significantly affect the simulated delta evolution the time scale compression method the acceleration method introduced in this paper results in an increased computational efficiency of 75 without adversely affecting the simulated delta evolution compared to a base case the combination of the time scale compression method with the existing acceleration methods has the potential to extend the application range of process based models towards geologic timescales

trawling induced daily sediment resuspension in the flank of a mediterranean submarine canyon abstract commercial bottom trawling is one of the anthropogenic activities causing the biggest impact on the seafloor due to its recurrence and global distribution in particular trawling has been proposed as a major driver of sediment dynamics at depths below the reach of storm waves but the issue is at present poorly documented with direct observations this paper analyses changes in water turbidity in a tributary valley of the la fonera palamos submarine canyon whose flanks are routinely exploited by a local trawling fleet down to depths of 800 m a string of turbidimeters was deployed at 980 m water depth inside the tributary for two consecutive years 2010 2011 the second year an adcp profiled the currents 80 m above the seafloor the results illustrate that near bottom water turbidity at the study site is heavily dominated both in its magnitude and temporal patterns by trawling induced sediment resuspension at the fishing ground resuspended sediments are channelised along the tributary in the form of sediment gravity flows being recorded only during working days and working hours of the trawling fleet these sediment gravity flows generate turbid plumes that extend to at least 100 m above the bottom reaching suspended sediment concentrations up to 236 mg l 1 close to the seafloor 5 m above bottom a few hours after the end of daily trawling activities water turbidity progressively decreases but resuspended particles remain in suspension for several hours developing bottom and intermediate nepheloid layers that reach background levels 2 mg l 1 before trawling activities resume the presence of these nepheloid layers was recorded in a ctd turbidimeter transect conducted across the fishing ground a few hours after the end of a working day these results highlight that deep bottom trawling can effectively replace natural processes as the main driving force of sediment resuspension on continental slope regions and generate increased near bottom water turbidity that propagates from fishing grounds to wider and deeper areas via sediment gravity flows and nepheloid layer development

last glacial holocene change in intermediate water ventilation in the northwestern pacific abstract the modern north pacific is the terminus for deep water circulation while no deep water mass is formed today the region is the source of north pacific intermediate water 300 800 m formed primarily in the sea of okhotsk however the source and strength of intermediate water in the glacial north pacific was likely different from the present intermediate water here we present microfossil evidence of late quaternary ventilation changes associated with changes in intermediate water intermediate water ventilation decreased drastically at the glacial termination when it switched to the modern circulation system the ventilation change appears to have been widespread and synchronous in the north pacific glacial microfossil assemblages indicate that there was relatively strong ventilation of intermediate water which seems to have been cold and well oxygenated as if produced by brine rejection during the formation of sea ice on the basis of the glacial distribution of microfossils in the north pacific we suggest that intermediate water was derived from the bering sea during the glacials rather than the sea of okhotsk

southern gulf of mexico wilcox source to sink investigating and predicting paleogene wilcox reservoirs in eastern mexico deep water areas source to sink analyses show that northern gulf of mexico gom wilcox group siliciclastic deep water systems are linked to transport of sediments from the laramide tectonic belt into the deep basin less is known however about southern gom sedimentation new drilling and discoveries in the mexican deep water have generated considerable interest since the opening of mexico to international exploration to investigate paleogene deposition in mexico s offshore areas a three phased approach was employed 1 seismic mapping of deep water depocenters 2 regional stratigraphic analysis of potential basin entry points and 3 prediction of submarine fan dimensions using empirical scaling relationships isochore and structural mapping of the wilcox depocenters used available well and seismic data potential basin entry points were identified by evaluation of wilcox fluvial deltaic systems and tectonic elements empirical scaling relationships previously established between fluvial and deep water segments provide first order predictions of submarine fan dimensions paleogene wilcox source to sink systems of the greater gom basin change north to south as a function of varied tectonics and sedimentary accommodation the united states sector was a passive margin continental scale drainage systems fed a broad gently dipping shelf by contrast the southern gom basin was a tectonically active margin smaller scale fluvial systems sourced from the hidalgoan uplands flowed directly into foreland basins located on the slope results presented here indicate that several systems rimming the southern gom were able to effectively transfer sediment from the mountain belt into the basin regional observations and semiquantitative predictions of fan dimensions provide a context for future detailed work based on new well and seismic information

morphodynamics in sediment starved inner shelf submarine canyons lower st lawrence estuary eastern canada abstract the contemporaneous activity and sedimentary processes in a series of inner shelf submarine canyons located in the lower st lawrence estuary were examined using high resolution multibeam bathymetry and backscatter data the presence of crescent shaped bedforms csbs displaced upslope at the bottom of the canyons between 2007 and 2012 indicates that they are currently active through the remobilization of sediment by gravity flows however the shelf and shores of the region are characterized by the absence of sediment our results indicate that gravity flows currently eroding the canyon floors do not transport new material downslope coming from the shelf but rather remobilize in situ deglacial sediments within the canyon thalweg we suggest that slope failures and internal tides waves are responsible for sediment remobilization in these canyons although their role in the upslope migrating csbs is unclear this paper provides evidence that sediment supply is not a prerequisite for the modern activity of inner shelf submarine canyons when processes such as slope failures and internal tides waves are frequent enough to remobilize in situ sediments

the contribution of alaskan siberian and canadian coastal polynyas to the cold halocline layer of the arctic ocean numerous arctic ocean circulation and geochemical studies suggest that ice growth in polynyas over the alaskan siberian and canadian continental shelves is a source of cold saline water which contributes to the maintenance of the arctic ocean halocline the purpose of this study is to estimate for the 1978 1987 winters the contributions of arctic coastal polynyas to the cold halocline layer of the arctic ocean the study uses a combination of satellite oceanographic and weather data to calculate the brine fluxes from the polynyas then an oceanic box model is used to calculate their contributions to the cold halocline layer of the arctic ocean this study complements and corrects a previous study of dense water production by coastal polynyas in the barents kara and laptev seas recurrent polynyas form on the canadian and alaskan coasts from banks island to the bering strait and on the siberian coast from the bering strait to the new siberian islands in the bering sea polynyas form in norton sound south and west of st lawrence island and in the gulf of anadyr two regions that account for almost 50 of the total dense water production are the siberian coastal polynyas in the adjacent regions of the gulf of anadyr and anadyr strait and the alaskan coastal polynyas which occur along the coast from cape lisburne to point barrow for all of the western arctic coastal regions examined the mean annual total brine flux is 0 5 0 2 sv combination of this flux with the contribution from the barents kara and laptev seas which is recalculated from data in the earlier study shows that over the entire arctic coastal polynyas generate about 0 7 1 2 sv of dense water this compares well with the theoretical estimates of 1 1 5 sv because an unknown fraction of the barents kara and laptev brine flux must go to the eurasian basin deep water the coastal polynyas alone cannot renew the halocline layer other potential brine generation mechanisms include overall freezing on the shelves and the response of the ice to infrequent violent storms for example during february 1982 an intense storm generated a large region of low ice concentration in the eastern chukchi sea over barrow canyon the refreezing of the region was followed by the flow of a dense plume down barrow canyon although the ocean dynamical response to this refreezing needs to be established the possible response of a barrow canyon flow to this refreezing event suggests that the overall refreezing in response to infrequent violent storms may be a potential source of the additional brine needed to maintain the arctic ocean halocline

derivation of direct on fault submarine paleoearthquake records from high resolution seismic reflection profiles wairau fault new zealand direct on fault submarine paleoearthquake records can be derived from high resolution seismic reflection profiles of active fault growth sequences coseismic vertical increments of displacement are best preserved in the architecture of the growth sequence when the long term rate of sedimentation exceeds the rate of fault vertical displacement postseismic stratigraphic intervals can be recognized on vertical displacement history curves from which estimates of the earthquake timing and vertical displacements can be made the strike slip wairau fault is a major seismic hazard in central new zealand and is partially submarine analysis of 10 high resolution seismic profiles spanning a 20 km section of the offshore fault trace reveals two types of postseismic growth sequences and a composite paleoearthquake record with up to eight surface rupturing earthquakes since 18 ka the recurrence intervals range from 0 9 to 3 8 ka mean is 2 2 ka while the coseismic vertical displacements range from 0 5 to 5 3 m mean is 2 5 m these data conform to the variable slip model of earthquake behavior the vertical coseismic displacement is not always predictable from the recurrence interval preceding the event the data indicate that the seismic moment release has not been constant between earthquakes or that the ratio of horizontal to vertical coseismic displacement at a given site has varied over multiple earthquake cycles the offshore data are consistent with onshore paleoearthquake records long term dextral slip rate of 2 mm yr compared to 3 5 mm yr 40 km in land and paleoearthquakes of mw 7 5 the last earthquake occurred on the fault 2 0 0 3 kyr ago indicating that significant elastic strain has now accrued

origin of the deep bering sea nitrate deficit constraints from the nitrogen and oxygen isotopic composition of water column nitrate and benthic nitrate fluxes 1 on the basis of the normalization to phosphate a significant amount of nitrate is missing from the deep bering sea bs benthic denitrification has been suggested previously to be the dominant cause for the bs nitrate deficit we measured water column nitrate 15n 14n and 18o 16o as integrative tracers of microbial denitrification together with pore water derived benthic nitrate fluxes in the deep bs basin in order to gain new constraints on the mechanism of fixed nitrogen loss in the bs the lack of any nitrate isotope enrichment into the deep part of the bs supports the benthic denitrification hypothesis on the basis of the nitrate deficit in the water column with respect to the adjacent north pacific and a radiocarbon derived ventilation age of 50 years we calculate an average deep bs 2000 m water depth sedimentary denitrification rate of 230 mol n m 2 d 1 or 1 27 tg n yr 1 more than 3 times higher than high end estimates of the average global sedimentary denitrification rate for the same depth interval pore water derived estimates of benthic denitrification were variable and uncertainties in estimates were large a very high denitrification rate measured from the base of the steep northern slope of the basin suggests that the elevated average sedimentary denitrification rate of the deep bering calculated from the nitrate deficit is driven by organic matter supply to the base of the continental slope owing to a combination of high primary productivity in the surface waters along the shelf break and efficient down slope sediment focusing along the steep continental slopes that characterize the bs

north pacific deep water formation during the latest glaciation for at least 20 years palaeoceanographers have speculated about the existence of a source of young nutrient depleted deep water in the north pacific npdw during glaciations proof of its existence has eluded researchers because the present deep north pacific is very corrosive to calcium carbonate thus it has been difficult to obtain a long time series of oxygen isotope data on benthic foraminifera for dating the sediment and carbon isotope data for use as a proxy for deep water nutrient content i report here on a stable isotope record from a western subarctic pacific core taken at 3 km water depth the carbon isotope ratios in the benthic foraminifera cibicidoides show no evidence of nutrient depleted npdw from glacial to holocene time

estimation of sea ice production in the bering sea from amsr e and amsr2 data with special emphasis on the anadyr polynya

postglacial after 18 ka deep sea sedimentation along the hikurangi subduction margin new zealand characterisation timing and origin of turbidites recent sedimentation along the hikurangi subduction margin off northeastern new zealand is investigated using a series of piston cores collected between 2003 and 2008 the active hikurangi margin lies along the pacific australia subduction plate boundary and contains a diverse range of geomorphologic settings slope basin stratigraphy is thick and complex resulting from sustained high rates of sedimentation from adjacent muddy rivers throughout the quaternary turbidites deposited since c 18 ka in the poverty ruatoria and matakaoa re entrants are central to this study in that they provide a detailed record of the past climatic conditions and tectonic activity here alternating hemipelagite turbidite debrite and tephra layers reflect distinctive depositional modes of marine sedimentation turbidity current debris flow and volcanic eruption respectively turbidites dominate the record ranging in lithofacies from muddy to sandy turbidites and include some basal reverse graded turbidites inferred to be derived from hyperpycnal flows stacked turbidites are common and indicate multiple gravity flows over short time periods the chronology of turbidites is determined by collating an extremely dense set of radiocarbon ages and dated tephra which facilitate sedimentation rate calculation and identification of the origin of turbidites sedimentation rates range from 285 cm ka during late glacial time 18 5 17 ka to 15 to 109 cm ka during postglacial time 17 0 ka turbidite deposition is controlled by 1 the emplacement of slope avalanches reorganising sediment pathways 2 the postglacial marine transgression leading to a five fold reduction in sediment supply to the slope due to disconnection of river mouths from the shelf edge and 3 the holocene pleistocene boundary climate warming resulting in a drastic decrease in the average turbidite grain size flood induced turbidites are scarce nine hyperpycnites are recognised since 18 ka and the youngest is correlated to the largest enso related storm event recorded onland lake tutira other turbidites contain a benthic foraminiferal assemblage which is strictly reworked from the upper slope and which relates to large earthquakes over the last c 7 ka they yield a shorter return time 270 430 years than the published coastal records for large earthquakes c 670 years but the offshore record is likely to be more complete the deep sea sedimentation along the new zealand active margin illustrates the complex interaction of tectonic and climate in turbidite generation climate warming and glacio eustatic fluctuations are well recorded at a millennial timescale 18 ka while tectonic deformation and earthquakes appear predominant in fostering turbidite production at a centennial timescale 270 430 years

threshold of erosion of submarine bedrock landscapes by tidal currents since sea level stabilized 7000 yr bp shelf seas experiencing semi diurnal tides will have been affected by streaming four times per day if tidal erosion of bedrock were even only marginally efficient the 10 million streamings since then should have left geomorphological imprints we examine high resolution multibeam sonar data from three areas with extreme tidal currents the minas passage bay of fundy experiencing 8 knot surface tidal currents was surveyed in 2007 with a multibeam sonar in an area near to transverse dunes which are evidence for bedload transport the data show local overhanging surfaces near to the sediment rock contact potentially created by abrasion by saltating particles however they are uncommon in the straits of messina where surface currents reach 10 knots surveying revealed ridges lying oblique to the flow that are not obviously broken into separate outcrops by erosion in the bristol channel uk sonar data collected where currents reach 3 4 knots at 1 5 m above the bed reveal outcrops of limestone with superimposed sand dunes but only minor rounding of blocks holocene tidal currents have apparently been generally ineffective at eroding bedrock we examine this issue further by compiling extreme tidal streams around the uk and from them estimate shear stresses representing a macro tidal environment where peak surface currents reach 9 7 knots those data are compared with shear stresses in mountainous rivers where long term rates of erosion are comparable with tectonic uplift rates and are thus geomorphologically significant whereas river stresses reach 102 103 pa the largest tidal stresses are generally 101 and only rarely approach 102 pa too small for quarrying to operate generally however the vertical faces in the minas passage may represent the onset of abrasion given this limited evidence for abrasion we explore conditions in the geological past for tides that may have locally eroded bedrock

motion and rigidity of the pacific plate and implications for plate boundary deformation 1 using up to 11 years of data from a global network of global positioning system gps stations including 12 stations well distributed across the pacific plate we derive present day euler vectors for the pacific plate more precisely than has previously been possible from space geodetic data after rejecting on statistical grounds the velocity of one station on each of the pacific and north american plates we find that the quality of fit of the horizontal velocities of 11 pacific plate pa stations to the best fitting pa euler vector is similar to the fit of 11 australian plate au velocities to the au euler vector and 20 better than the fit of nine north american plate na velocities to the na euler vector the velocities of stations on the pacific and australian plates each fit a rigid plate model with an rms residual of 0 4 mm yr while the north american velocities fit a rigid plate model with an rms velocity of 0 6 mm yr our best fitting pa au relative euler vector is located 170 km southeast of the nuvel 1a pole but is not significantly different at the 95 confidence level it is also close 70 km in position and 3 in rate to a pole derived from transform faults identified from satellite altimetry suggesting that the vector has not changed significantly over the past 3 myr our relative euler vector is also consistent with all known geological and geodetic evidence concerning the au pa plate boundary through new zealand the gps sites offshore of southern california are presently moving 4 5 1 mm yr relative to predicted pacific velocity with their residual velocities in approximately the opposite direction to pa na relative motion likewise the easternmost sites in south island new zealand are moving 3 1 mm yr relative to predicted pacific velocity with the residuals in approximately the opposite direction to pa au relative motion these velocity residuals are in the same sense as predicted by elastic strain accumulation on known plate boundary faults but are of a significantly higher magnitude in both southern california and new zealand implying that the plate boundary zones in both regions are wider than previously believed index terms 1206 geodesy and gravity crustal movements interplate 8155 1208 geodesy and gravity crustal movements intraplate 8110 1243 geodesy and gravity space geodetic surveys 8158 tectonophysics evolution of the earth plate motions present and recent 3040 8159 tectonophysics evolution of the earth rheology crust and lithosphere keywords pacific plate motion plate rigidity plate boundary deformation

storm induced sediment gravity flows at the head of the eel submarine canyon northern california margin 1 as part of the strataform program a bottom boundary layer bbl tripod was deployed at 120 m depth in the northern thalweg of the eel canyon during winter 2000 increases of the near bottom suspended sediment concentrations ssc recorded at the canyon head were not directly related to the eel river discharge but were clearly linked to the occurrence of storms bbl measurements revealed that during intensifications of the wave orbital velocity sediment transport at the head of the canyon occurred as sediment gravity flows directed down canyon observational evidence for near bed sediment gravity flow transport included an increase toward the bed of the down canyon component of wave averaged velocity and high estimated ssc at higher sampling frequencies 1 hz the current components during these events fluctuated at the same periodicity as the pressure reflecting a clear influence of the surface wave activity on the generation and maintenance of the sediment gravity flows the origin of such flows is not related to the formation of fluid muds on the shelf or to intense wave current sediment resuspension around the canyon head region rather liquefaction of sediment deposited at the head of the canyon induced by wave load excess pore water pressures during storms combined with elevated slopes around the canyon head appear to be the mechanisms initiating sediment transport the resulting fluidized sediment layer can easily be eroded entrained into the water column and transported down canyon as a sediment gravity flow results from this study reveal that storm induced sediment gravity flows occur periodically in the eel canyon head and suggest that this kind of sediment transport process can occur in other submarine canyons more frequently than previously expected

late pliocene to early pleistocene 2 4 1 25 ma paleoproductivity changes in the bering sea iodp expedition 323 hole u1343e abstract late pliocene to early pleistocene paleoproductivity changes in the bering sea were reconstructed using geochemical concentrations and mass accumulation rates mars of caco 3 biogenic opal and total organic carbon toc and sedimentary nitrogen isotope ratios 15 n at iodp expedition 323 hole u1343e drilled in the northern slope area 1956 m deep of the bering sea caco 3 concentration is generally low but prominent caco 3 peaks occur intermittently due to subseafloor authigenic carbonate formation rather than biogenic accumulation regardless of glacial interglacial variations biogenic opal concentrations reflect orbital scale glacial interglacial variations however toc concentration did not show clear glacial interglacial variation probably due to poor preservation the sedimentary 15 n values vary synchronously with biogenic opal concentration on orbital timescales the co varying pattern of opal productivity and 15 n values at hole u1343e is a result of nutrient utilization controlled by diatom productivity in the bering slope area where fe is not a limiting factor biogenic opal and toc mars showed a temporal shift at around 1 9 ma from a high productivity period under nutrient enriched conditions to a low productivity period under relatively nutrient depleted conditions high diatom productivity with low 15 n values before 1 9 ma is associated with abundant nutrient supply by upwelling in relation to strong surface current system this productivity decrease at about 1 9 ma was also found in the southern bering sea site u1341 and may be related to global opal reorganization

the opening of cook strait interglacial tidal scour and aligning basins at a subduction to transform plate edge abstract cook strait the central seaway through the axial ranges of new zealand has many inferred origins a compilation of marine geological and geophysical datasets suggests that cook strait developed when five sedimentary basins at a rapidly changing obliquely convergent plate boundary were moved into line and were linked by strong tidal scour in middle pleistocene times the basins relate partly to oblique subduction north of cook strait and partly to intercontinental transform to the south prior to opening muddy subduction pull down and foreland basins in the northwest were separated from equally quiet water rotating forearc to transform basins in the southeast the land barrier between them narrowed and was finally breached as subduction related basins migrated southwards and transform related basins extended northwards in response to rotation and divergent branching of a major transcurrent fault following breaching a history of alternating scour and quiet water deposition is recorded by a series of deep irregular unconformities in muddy basin fill scour is correlated with interglacial periods of high sea level when land barriers were submerged and strong tides caused by a 140 phase difference at either end of the strait eroded muddy sediments deposited in glacial periods when an emergent landbridge limited tidal exchange

cadmium and delta13c paleochemical ocean distributions during the stage 2 glacial maximum changes in heat and salt transport by ocean currents have been implicated in ice age climate cycles weyl 1 968 newell 1 974 broecker et al 1 990b in addition to the direct physical effects of the ocean on climate the ocean carbon system controls atmospheric co2 and the co2 fluctuations documented in ice core bubbles barnola et a1 1 987 neftel et a1 1 988 are thought to be a significant factor in climate oscillations hansen et al 1 984 dramatic changes in oceanic circulation patterns and carbon system chemistry have occurred during the late quaternary glacial interglacial global climate cycles boyle keigwin 1 982 curry lohmann 1 983 shackleton pisias 1 984 boyle keigwin 1 987 duplessy et al 1 988 curry et al 1 988 broecker et al i 990a these changes in the ocean system may be significant driving forces in the progression of ice age co2 cycles toggweiler sarmiento 1 985 ennever mcelroy 1 985 wenk siegenthaler 1 985 boyle 1 988a b broecker peng 1 990 the oceanic distributions of c513c cd and other carbon system linked properties are controlled by the interaction between biological uptake and decomposition with the general circulation of the ocean because records of past oceanic cd and c5 1 3c are preserved in shells of planktonic and benthic foraminifera

effects of a shelf polynya on flow and water properties in the northern bering sea we present long term 230 day measurements from three moorings in the vicinity of saint lawrence island on the northern bering sea shelf one mooring was deployed near the polynya which often exists south of the island these data confirm the existence of strong 0 15 m s 1 flow toward bering strait northwest of the island in anadyr strait and suggest that regional circulation results in a moderate 0 03 5 m s 1 mean flow eastward along the southern coast of saint lawrence island coherent variations in the regional circulation and variations in the geostrophic wind account for much of the low frequency current fluctuation south of saint lawrence island however there were 11 events when offshore northerly winds coincided with the temperature following the freezing point increasing salinity and reversal of the current this suggests that ice formation and the ensuing brine rejection affect flow in the vicinity of the polynya scaling of a simplified momentum equation indicates that the cross shelf density gradient was a possible mechanism for some of the reversals salinity data show a seasonal cycle as well as individual events of brine rejection during an average event time of 65 hours the salinity increased by 8 10 3 g kg 1 h 1 the heat flux can be estimated as 535 wm 2 these fluxes correspond to an ice production of 5 m during winter 1981 extrapolation of our results and comparison with the freshwater cycle suggest that brine rejection is an important component of the regional salt budget

probabilistic hazard of tsunamis generated by submarine landslides in the cook strait canyon new zealand cook strait canyon is a submarine canyon that lies within ten kilometres of wellington the capital city of new zealand the canyon walls are covered with scars from previous landslides which could have caused local tsunamis palaeotsunami evidence also points to past tsunamis in the wellington region furthermore the canyon s location in cook strait means that there is inhabited land in the path of both forward and backward propagating waves tsunamis induced by these submarine landslides pose hazard to coastal communities and infrastructure but major events are very uncommon and the historical record is not extensive enough to quantify this hazard the combination of infrequent but potentially very consequential events makes realistic assessment of the hazard challenging however information on both magnitude and frequency is very important for land use planning and civil defence purposes we use a multidisciplinary approach bringing together geological information with modelling to construct a probabilistic tsunami hazard assessment of submarine landslide generated tsunami although there are many simplifying assumptions used in this assessment it suggests that the cook strait open coast is exposed to considerable hazard due to submarine landslide generated tsunamis we emphasise the uncertainties involved and present opportunities for future research

recent sediment transport and deposition in the lisbon setubal and cascais submarine canyons portuguese continental margin abstract recent sediment transport and deposition in the lisbon setubal and cascais submarine canyons portuguese continental margin were investigated on the basis of water column profiles of suspended particulate matter records of near bottom currents and settling fluxes of particulate matter obtained with benthic landers and analysis of surface sediments the results show that fine grained predominantly lithogenic sediment derived from adjacent shelf areas accumulates in the upper reaches of the canyons sediment deposited further down in the middle and lower reaches of the canyons is essentially similar to the hemipelagic sediment found on the adjacent continental slope indicating that down canyon transport of sediment from the upper to the lower canyon is limited tidal currents measured at various depths in the lisbon setubal canyon appear sufficiently strong to resuspend and transport sediment but net up canyon flow of the bottom water may retain shelf derived lithogenic sediment in the upper canyon sediment gravity flows which in the nearby nazare canyon are an effective mechanism for down canyon sediment transport appear rare in the lisbon setubal canyon and probably also in the cascais canyon turbidity current events recorded in the sedimentary record of the canyons may correspond to seismic events of 1969 and 1755 ad

event driven sediment flux in hueneme and mugu submarine canyons southern california vertical sediment fluxes and their dominant controlling processes in hueneme and mugu submarine canyons off south central california were assessed using data from sediment traps and current meters on two moorings that were deployed for 6 months during the winter of 2007 the maxima of total particulate flux which reached as high as 300 g m 2 day in hueneme canyon were recorded during winter storm events when high waves and river floods often coincided during these winter storms wave induced resuspension of shelf sediment was a major source for the elevated sediment fluxes canyon rim morphology rather than physical proximity to an adjacent river mouth appeared to control the magnitude of sediment fluxes in these two submarine canyon systems episodic turbidity currents and internal bores enhanced sediment fluxes particularly in the lower sediment traps positioned 30 m above the canyon floor lower excess 210 pb activities measured in the sediment samples collected during periods of peak total particulate flux further substantiate that reworked shelf rather than newly introduced river borne sediments supply most of the material entering these canyons during storms published by elsevier b v

present deep submarine canyons activity in the bay of biscay ne atlantic present sedimentation in three canyons of the bay of biscay audierne blackmud and capbreton is studied by the combined analysis of cores and current meter data collected over a 7 month period at the current meter mooring locations interface cores were collected to characterize the recent sedimentation processes in the two canyons located in the northern part of the bay of biscay audierne and blackmud there is no evidence of recent sedimentary deposits canyons are by passing or erosive areas in the southern part of the bay of biscay capbreton recent turbidite are deposited in the three canyons current meters recorded energetic currents with velocities showing alternating upslope and downslope motions and a period corresponding to the semi diurnal component m2 these currents are supposed to be related to deep internal tides the high speed of the current 1 m s in audierne and blackmud is consistent with the lack of preservation of recent sediments on the canyon floors in capbreton canyon the magnitude of currents is less and recent turbidites are preserved in addition to periodical current motion small magnitude gravity event corresponding to a low concentration turbulent surge or a high concentration nepheloid layer initiated during a storm was recorded during the mooring period these results suggest that deep sea canyons in the bay of biscay have behaviour at present varying between by passing or erosion areas and sediment trapping these examples suggest that sediments are moved up and down by low energy tide initiated hydrodynamic events during most of the time during higher magnitude short duration gravity events the sediments are transferred down canyon towards the deep sea

national seismic hazard model for new zealand 2010 update a team of earthquake geologists seismologists and engineering seis mologists has collectively produced an update of the national probabilistic seismic hazard psh model for new zealand national seismic hazard model or nshm the new nshm supersedes the earlier nshm published in 2002 and used as the hazard basis for the new zealand loadings standard and numerous other end user applica tions the new nshm incorporates a fault source model that has been updated with over 200 new onshore and offshore fault sources and utilizes new new zealand based and international scaling relationships for the parameterization of the faults the dis tributed seismicity model has also been updated to include post 1997 seismicity data a new seismicity regionalization and improved methodology for calculation of the seismicity parameters probabilistic seismic hazard maps produced from the new nshm show a similar pattern of hazard to the earlier model at the national scale but there are some significant reductions and increases in hazard at the regional scale the national scale differences between the new and earlier nshm appear less than those seen between much earlier national models indicating that some degree of consis tency has been achieved in the national scale pattern of hazard estimates at least for return periods of 475 years and greater online material table of fault source parameters for the 2010 national seismic hazard model

chlorofluorocarbon evidence for recent ventilation of the deep bering sea the pattern of the global thermohaline circulation of today s oceans is controlled by deep water formation at the northern and southern limits of the atlantic the apparent lack of deep water formation in the north pacific on the other hand suggests that this ocean plays only a minor role in the global circulation but it is unclear whether this was also the case during periods of glaciation there is conflicting evidence in the sedimentary record for the existence of a deep water source in the north pacific during the last glacial maximum1 4 here we report the detection of anthropogenic chlorofluorocarbons in the bottom waters of the aleutian basin in the eastern bering sea which suggests that a small amount of bottom water has formed in this region during the past 40 years although the small volumes of water involved are unlikely to play a significant role in determining present day global circulation patterns the results lend credence to the possibility that this sea was an important source of deep water for the northwestern pacific ocean during the last glacial maximum

the relationship of undrained shear strength and porosity with depth in shallow 50 m marine sediments abstract in this paper we review the relationship between undrained shear strength and porosity with depth of marine sediments in the upper 50 m below the seafloor based on a compilation of data from 46 ocean drilling program odp legs we find that only about half of the drill sites show the anticipated increase in strength 59 and associated decrease in porosity 49 down hole moreover a significant correlation coefficient for both strength and porosity with depth is found at only 31 of the sites four categories of sediments are distinguished based on the significance of correlation coefficients we observe an influence of sediment composition and texture on the relationship between strength and porosity with depth fine grained siliciclastic sediments clayey and silty sediments and nannofossil oozes with less than 50 carbonate frequently show significant correlation coefficients for strength and porosity with depth while fine grained carbonates with high carbonate concentrations calcareous muds and nannofossil oozes with an average carbonate content of 87 as well as reef facies carbonates lack significant trends down hole moreover correlation patterns vary considerably with geological or tectonic setting for instance delta deposits of the amazon fan and sediments from the atlantic passive continental margins frequently show significant correlation coefficients for both properties extensional arcs often show significant correlation only for one property shear strength or porosity correlation patterns are discussed in the light of sediment composition geological and tectonic setting the methods used for shear strength measurement and previous work published on compaction behaviour

sediment transport processes at the head of halibut canyon eastern canada margin an interplay between internal tides and dense shelf water cascading abstract to investigate the processes by which sediment is transported through a submarine canyon incised in a glaciated margin the bottom boundary layer quadrapod ralph was deployed at 276 m depth in the west halibut canyon off newfoundland during winter 2008 2009 two main sediment transport processes were identified throughout the deployment firstly periodic increases of near bottom suspended sediment concentrations ssc were recorded associated with the up canyon propagation of the semidiurnal internal tidal bore along the canyon axis carrying fine sediment particles resuspended from deeper canyon regions the recorded ssc peaks lasting less than 1 h were observed sporadically and were linked to bottom intensified up canyon flows 40 cm s 1 concomitant with sharp drops in temperature secondly sediment transport was also observed during events of intensified down canyon current velocities that occurred during periods of sustained heat loss from surface waters but were not associated with large storm waves high resolution velocity profiles throughout the water column during these events revealed that the highest current speeds 1 m s 1 were centered several meters above the sea floor and corresponded to the region of maximum velocities of a gravity flow such flows had associated low ssc and cold water temperatures and are interpreted as dense shelf water cascading events channelized along the canyon axis sediment transport during these events was largely restricted to bedload and saltation producing winnowing of sands and fine sediments around larger gravel particles analysis of historical hydrographic data suggests that such gravity flows are not related to the formation of coastal dense waters advected towards the outer shelf that reached the canyon head rather the dense shelf waters appear to be generated around the outer shelf where convection during winter is able to reach the sea floor and generate a pool of near bottom dense water that cascades into the canyon during one or two tidal cycles a similar transport mechanism is likely to occur in other submarine canyons along the eastern canadian margin as well in other canyoned margins where winter convection can reach the shelf edge