estimates of surface roughness length in heterogeneous under ice boundary layers 1 measurements obtained in the under ice ocean boundary layer by two autonomous buoys deployed in 2004 and 2005 are used to estimate the roughness length z0 of the underside morphology of arctic ocean pack ice two techniques are used to estimate z0 the first uses an extension of the law of the wall and directly measured turbulent shear stress and velocity at a single point near the ice ocean interface the second uses a one dimensional numerical boundary layer model that is matched to measured velocity profiles in the outer part of the boundary layer with z0 as an adjustable parameter the stress based estimates are sensitive to local morphological features and the effect of nearby ice ridge keels on the roughness estimates is evident averaged over flow direction there is a significant difference in floe roughness between the 2004 and 2005 deployments velocity profile based z0 estimates are more uniform with direction than the stress based estimates and the average value of the profile based estimates lies within the range of the stress based estimates averaged over flow direction both techniques yield z0 estimates of about 100 mm for the 2005 data set a central question is how to best estimate a z0 that can be applied to an individual grid cell in large scale numerical models the profile based estimates are promising in this regard because they are less affected by local morphology than stress based measurements which must be made fairly close to the interface in order to be interpretable using a framework based on the law of the wall

on the hydrography of the northeast water polynya the water masses and circulation in the area of the northeast water polynya located on the east greenland shelf north of 79 n are described on the basis of an r v polarstern cruise during spring and summer 1993 the baroclinic flow shows northward components close to the east greenland coast and eastward components at the northern limit of the polynya an anticyclonic half circle is formed by this and the southward flowing east greenland current in the south the circle is not closed the upper water column occupied by polar water is affected by this circulation pattern while deeper waters in the trough system of the area seem to spread independently different types of deep waters are found in different troughs all being of atlantic origin though they seem not to be directly connected to return atlantic water it is shown that what is called polar water must be formed at least partly on the greenland shelf and that deepwater formation does not occur in the investigated area

autonomous underwater vehicles auvs and investigations of the ice ocean interface in antarctic and arctic waters limitations of access have long restricted exploration and investigation of the cavities beneath ice shelves to a small number of drillholes studies of sea ice underwater morphology are limited largely to scientific utilization of submarines remotely operated vehicles tethered to a mother ship by umbilical cable have been deployed to investigate tidewater glacier and ice shelf margins but their range is often restricted the development of free flying autonomous underwater vehicles auvs with ranges of tens to hundreds of kilometres enables extensive missions to take place beneath sea ice and floating ice shelves autosub2 is a 3600 kg 6 7 m long auv with a 1600 m operating depth and range of 400 km based on the earlier autosub1 which had a 500 m depth limit a single direct drive d c motor and five bladed propeller produce speeds of 1 2 m s 1 rear mounted rudder and stern plane control yaw pitch and depth the vehicle has three sections the front and rear sections are free flooding built around aluminium extrusion space frames covered with glass fibre reinforced plastic panels the central section has a set of carbon fibre reinforced plastic pressure vessels four tubes contain batteries powering the vehicle the other three house vehicle control systems and sensors the rear section houses subsystems for navigation control actuation and propulsion and scientific sensors e g digital camera upward looking 300 khz acoustic doppler current profiler 200 khz multibeam receiver the front section contains forward looking collision sensor emergency abort the homing systems argos satellite data and location transmitters and flashing lights for relocation as well as science sensors e g twin conductivity temperature depth instruments multibeam transmitter sub bottom profiler aqualab water sampler payload restrictions mean that a subset of scientific instruments is actually in place on any given dive the scientific instruments carried on autosub are described and examples of observational data collected from each sensor in arctic or antarctic waters are given e g of roughness at the underside of floating ice shelves and sea ice

measurements beneath an antarctic ice shelf using an autonomous underwater vehicle the cavities beneath antarctic ice shelves are among the least studied regions of the world ocean yet they are sites of globally important water mass transformations here we report results from a mission beneath fimbul ice shelf of an autonomous underwater vehicle the data reveal a spatially complex oceanographic environment an ice base with widely varying roughness and a cavity periodically exposed to water with a temperature significantly above the surface freezing point the results of this the briefest of glimpses of conditions in this extraordinary environment are already reforming our view of the topographic and oceanographic conditions beneath ice shelves holding out great promises for future missions from similar platforms

remote sensing searching for new islands in sea ice coastlines concealed in polar seas are now more accessible to cartography tobias island discovered in 1993 by the german research vessel rv polarstern is a system of low lying banks and shoals hidden in sea ice 70 km off the northeastern coast of greenland here we use satellite radar interferometry and airborne laser scanning to show that this island is 2 km long and 35 m high much larger than was originally reported1 we have also been able to pinpoint the exact location of a stable area where a new group of small islands may be hidden this demonstrates that satellite radar interferometry is an effective tool for finding ice covered islands as well as for mapping them

circulation and water masses of the east greenland shelf the water masses and circulation over the northern greenland continental shelf are described based on two cruises to the region during the summers of 1979 and 1984 the cold polar water over the shelf was found to increase notably in salinity toward the shelf break and the east greenland polar front a colder more saline and relatively isolated fraction of the polar water was identified just above the atlantic intermediate water of the front a middepth layer stable in time indicates little vertical heat exchange warm atlantic intermediate water was found to intrude close to the coast via a newly defined system of troughs in the shelf the polar water was found to circulate over the shelf in a clockwise gyre baroclinic transports northward near the coast with 0 58 sv mean flow and southward elsewhere with 1 47 sv mean flow yielded a net southward transport in the east greenland current of 0 89 sv

ice sheets viewed from the ocean the contribution of marine science to understanding modern and past ice sheets over the last two decades marine science aided by technological advances in sediment coring geophysical imaging and remotely operated submersibles has played a major role in the investigation o

sea ice thickness measurement based on the dispersion of ice swell the dispersion of flexural waves propagating in the arctic sea ice cover is exploited in order to locally measure the ice thickness the observed dispersion for waves filtered in the 4 20 s period interval at up to 4 broad band seismometers deployed in spring 2007 near the north pole is compared to a parameterized model that accounts for a complex wavefield made of a superposition of independent plane waves with different amplitudes and back azimuth angles the parameterization that includes finding the best modeled ice thickness is performed by using the cross correlation functions between the seismometers the ice thickness is estimated to 2 5 0 2 m for the 1 km large floe the seismic stations were deployed on which is coherent with other independent measurements at this site this study thus demonstrates the feasibility of using broad band seismometers deployed on the sea ice in order to passively measure the ice thickness without requiring active sources nor human intervention

on the frequency distribution of turbidite thickness the frequency distribution of turbidite thickness records information on flow hydrodynamics initial sediment volumes and source migration and is an important component of petroleum reservoir models however the nature of this thickness distribution is currently uncertain with log normal or negative exponential frequency distributions and power law cumulative frequency distributions having been proposed by different authors a detailed analysis of the miocene marnoso arenacea formation of the italian apennines shows that turbidite bed thickness and sand interval thickness within each bed have a frequency distribution comprising the sum of a series of log normal frequency distributions these strata were deposited predominantly in a basin plain setting and bed amalgamation is relatively rare beds or sand intervals truncated by erosion were excluded from this analysis each log normal frequency distribution characterizes bed or sand interval thickness for a given basal grain size or basal bouma division measurements from the silurian aberystwyth grits in wales the cretaceous great valley sequence in california and the permian karoo basin in south africa show that this conclusion holds for sequences of disparate age and variable location the median thickness of these log normal distributions is positively correlated with basal grain size the power law exponent relating the basal grain size and median thickness is different for turbidites with a basal a or b division and those with only c d and e divisions these two types of turbidite have been termed thin bedded and thick bedded by previous workers a change in the power law exponent is proposed to be related to i a transition from viscous to inertial settling of sediment grains and ii hindered settling at high sediment concentrations the bimodal thickness distribution of thin bedded and thick bedded turbidites noted by previous workers is explained as the result of a change in the power law exponent this analysis supports the view that a and b divisions were deposited from high concentration flow components and that distinct grain size modes undergo different depositional processes summation of log normal frequency distributions for thin and thick bedded turbidites produces a cumulative frequency distribution of thickness with a segmented power law trend thus the occurrence of both log normal and segmented power law frequency distributions can be explained in a holistic fashion power law frequency distributions of turbidite thickness have previously been linked to power law distributions of earthquake magnitude or volumes of submarine slope failure the log normal distribution for a given grain size class observed in this study suggests an alternative view that turbidite thickness is determined by the multiplicative addition of several randomly distributed parameters in addition to the settling velocity of the grain sizes present

modelling the spread of oil under fast sea ice using three dimensional multibeam sonar data 1 a substantial portion of the world s remaining oil and gas reserves are found in the arctic exploration pressure will intensify as sea ice thinning and retreat continue and the subsequent production could involve spills or blowouts under various kinds of sea ice existing models for the spread of oil under ice are inadequate because they are unable to replicate the complexity or uniqueness of different ice regimes through the novel combination of 3 d under ice imagery from an autonomous under water vehicle auv and oil trajectory modelling we demonstrate that it is possible to overcome these deficiencies results suggest that we are presently underestimating the spread of oil under sea ice by an order of magnitude this is an important result with wide ranging ramifications as it suggests that our present ability to contain and recover oil under ice is limited

influence of ice thickness and surface properties on light transmission through arctic sea ice the observed changes in physical properties of sea ice such as decreased thickness and increased melt pond cover severely impact the energy budget of arctic sea ice increased light transmission leads to increased deposition of solar energy in the upper ocean and thus plays a crucial role for amount and timing of sea ice melt and under ice primary production recent developments in underwater technology provide new opportunities to study light transmission below the largely inaccessible underside of sea ice we measured spectral under ice radiance and irradiance using the new nereid under ice nui underwater robotic vehicle during a cruise of the r v polarstern to 83 n 6 w in the arctic ocean in july 2014 nui is a next generation hybrid remotely operated vehicle h rov designed for both remotely piloted and autonomous surveys underneath land fast and moving sea ice here we present results from one of the first comprehensive scientific dives of nui employing its interdisciplinary sensor suite we combine under ice optical measurements with three dimensional under ice topography multibeam sonar and aerial images of the surface conditions we investigate the influence of spatially varying ice thickness and surface properties on the spatial variability of light transmittance during summer our results show that surface properties such as melt ponds dominate the spatial distribution of the under ice light field on small scales 1000 m2 while sea ice thickness is the most important predictor for light transmission on larger scales in addition we propose the use of an algorithm to obtain histograms of light transmission from distributions of sea ice thickness and surface albedo

limit on slip rate and timing of recent seismic ground ruptures on the jinghong fault se of the eastern himalayan syntaxis abstract quantifying slip rates and earthquake occurrence of active faults on the shan plateau southeast of the eastern himalayan syntaxis is critical to assessing the seismic hazard and understanding the kinematics and geodynamics of this region most previous estimates of slip rates are averaged over either many millions of years using offset geological markers or decades using gps well constrained millennial slip rates of these faults remain sparse and constraints on recurrence rates of damaging earthquakes exist only for a few faults here we investigate the millennial slip rate and timing of recent earthquakes on the jinghong fault one of the geomorphically most significant sinistral slip faults on the central shan plateau we map and reconstruct fault offset 18 5 m of alluvial fan features at manpa on the central jinghong fault using a 0 1 m resolution digital surface model obtained from an unmanned aerial vehicle survey we establish a slip rate 2 5 0 7 mm yr over the past 7000 years using pit exposed stratigraphy this millennial slip rate is consistent with rates averaged over both decadal and million year timescales excavations at three sites near the town of gelanghe on the northeastern jinghong fault demonstrate 1 that the last seismic ground rupture occurred between 482 and 889 cal yr bp most likely in the narrower window 824 767 cal yr bp if the lack of large earthquakes in the historical earthquake record is reliable and 2 that multiple fault ruptures have occurred since 3618 cal yr bp combining this finding with a lack of large earthquakes in the 800 year long chinese historic record in this region we suggest an average recurrence interval of seismic ground ruptures on the order of 1000 years this recurrence interval is consistent with the slip rate of the jinghong fault and the size and earthquake frequency on other sinistral faults on the shan plateau

the underside of arctic sea ice imaged by sidescan sonar despite extensive submarine operations in the arctic little is yet known about the three dimensional morphology of the ice underside several studies have been done using upward looking sonar1 7 which yields a linear profile of ice draft from which the distributions of features such as pressure ridges and leads may be derived such a profile gives no information about the spatial morphology or appearance of the ice bottom surface in contrast the upper ice surface has been well documented from airborne and satellite borne sensors such as synthetic aperture radar passive microwave infrared and visual imaging here i report the first extensive set of imagery of the underside of sea ice in the arctic ocean sidescan sonar images show a distinct difference between the appearance of first year ice and of multi year ice first year ice has a smooth bottom except for a network of cracks while multi year ice is covered with an array of blisters or bulges the clear discrimination between ice types enables sidescan sonar to be used as a means of validating airborne passive microwave data

a new bathymetry of the northeast greenland continental shelf constraints on glacial and other processes a new digital bathymetric model dbm for the northeast greenland neg continental shelf 74 n 81 n is presented the dbm has a grid cell size of 250 m 250 m and incorporates bathymetric data from 30 multibeam cruises more than 20 single beam cruises and first reflector depths from industrial seismic lines the new dbm substantially improves the bathymetry compared to older models the dbm not only allows a better delineation of previously known seafloor morphology but in addition reveals the presence of previously unmapped morphological features including glacially derived troughs fjords grounding zone wedges and lateral moraines these submarine landforms are used to infer the past extent and ice flow dynamics of the greenland ice sheet during the last full glacial period of the quaternary and subsequent ice retreat across the continental shelf the dbm reveals cross shelf bathymetric troughs that may enable the inflow of warm atlantic water masses across the shelf driving enhanced basal melting of the marine terminating outlet glaciers draining the ice sheet to the coast in northeast greenland knolls sinks and hummocky seafloor on the middle shelf are also suggested to be related to salt diapirism north south orientated elongate depressions are identified that probably relate to ice marginal processes in combination with erosion caused by the east greenland current a single guyot like peak has been discovered and is interpreted to have been produced during a volcanic event approximately 55 ma ago

beds comprising debrite sandwiched within co genetic turbidite origin and widespread occurrence in distal depositional environments co genetic debrite turbidite beds occur in a variety of modern and ancient turbidite systems their basic character is distinctive an ungraded muddy sandstone interval is encased within mud poor graded sandstone siltstone and mudstone the muddy sandstone interval preserves evidence of en masse deposition and is thus termed a debrite the mud poor sandstone siltstone and mudstone show features indicating progressive layer by layer deposition and are thus called a turbidite palaeocurrent indicators ubiquitous stratigraphic association and the position of hemipelagic intervals demonstrate that debrite and enclosing turbidite originate in the same event detailed field observations are presented for co genetic debrite turbidite beds in three widespread sequences of variable age the miocene marnoso arenacea formation in the italian apennines the silurian aberystwyth grits in wales and quaternary deposits of the agadir basin offshore morocco deposition of these sequences occurred in similar unchannellized basin plain settings co genetic debrite turbidite beds were deposited from longitudinally segregated flow events comprising both debris flow and forerunning turbidity current it is most likely that the debris flow was generated by relatively shallow few tens of centimetres erosion of mud rich sea floor sediment changes in the settling behaviour of sand grains from a muddy fluid as flows decelerated may also have contributed to debrite deposition the association with distal settings results from the ubiquitous presence of muddy deposits in such locations which may be eroded and disaggregated to form a cohesive debris flow debrite intervals may be extensive 26 x 10 km in the marnoso arenacea formation and are not restricted to basin margins such long debris flow run out on low gradient sea floor 0 1 may simply be due to low yield strength 50 pa of the debris water mixture this study emphasizes that multiple flow types and transformations between flow types can occur within the distal parts of submarine flow events

digital terrain mapping of the underside of sea ice from a small auv 1 in april 2007 the first three dimensional digital terrain mapping of the underside of sea ice to be done from an ice launched autonomous underwater vehicle auv was carried out at an ice camp in the beaufort sea using the gavia vehicle which could be launched and recovered through 3 1 m holes gavia was equipped with a geoswath 500 khz interferometric sonar system which yielded swaths of typical width 80 m the imagery showed the morphological distinctions between first year fy and multi year my ice undersides the contrast between the shapes of fy and my ridges and the appearance of refrozen leads ice drafts were validated by drilling and it was found that ridge slope statistics and local probability density functions pdfs of draft could be derived with high precision the special opportunities offered by access to 3 d mapping are pointed out

warm water pathways toward nioghalvfjerdsfjorden glacier northeast greenland nioghalvfjerdsfjorden glacier 79ng is the largest of three marine terminating outlet glaciers draining the northeast greenland ice stream to understand how atlantic waters supply waters in the cavity beneath the floating 79ng we analyze historic and recent bathymetric hydrographic and velocity observations obtained on the northeast greenland continental shelf the bathymetry is characterized by a trough system consisting of the westwind trough and the norske trough in the northern and southern part of the continental shelf respectively atlantic waters recirculating in fram strait cross the shelf break and enter the trough system at its southeastern inlet toward the inner shelf warm atlantic intermediate water aiw present below 200 m in the norske trough shows large contributions of the recirculating atlantic water we found that the bathymetry is sufficiently deep to provide a direct subsurface pathway for warm aiw between the shelf break and the 79ng cavity via the norske trough likewise based on the hydrographic data we show that the norske trough supplies aiw warmer than 1 c to the 79ng which is not present in the westwind trough our moored and lowered velocity measurements indicate that a boundary current carries warm aiw along the northeastern slope of norske trough toward the 79ng we suggest that anomalies in atlantic water temperatures in fram strait could reach 79ng within less than 1 5 years thereby modifying the glacier s basal melt rates

a new view of the underside of arctic sea ice the autosub ii autonomous underwater vehicle auv operating off ne greenland in august 2004 obtained the first successful swath sonar measurements under sea ice showing in unprecedented detail the three dimensional nature of the under ice surface the vehicle operated from rrs james clark ross obtained more than 450 track km of under ice multibeam data we show imagery from first and multiyear ice including young ridges old hummocks and undeformed melting ice in addition we show how the combination of other on board sensors enabled the vehicle to obtain detailed information about seabed topography water structure and current fields in an exploratory mode within a region which is seldom visited because of difficult year round ice conditions this included identification of a new current regime in the norske trough

thick and deformed antarctic sea ice mapped with autonomous underwater vehicles satellites have documented trends in antarctic sea ice extent and its variability for decades but estimating sea ice thickness in the antarctic from remote sensing data remains challenging in situ observations needed for validation of remote sensing data and sea ice models are limited most have been restricted to a few point measurements on selected ice floes or to visual shipboard estimates here we present three dimensional 3d floe scale maps of sea ice draft for ten floes compiled from two springtime expeditions by an autonomous underwater vehicle to the near coastal regions of the weddell bellingshausen and wilkes land sectors of antarctica mean drafts range from 1 4 to 5 5 m with maxima up to 16 m we also find that on average 76 of the ice volume is deformed ice our surveys indicate that the floes are much thicker and more deformed than reported by most drilling and ship based measurements of antarctic sea ice we suggest that thick ice in the near coastal and interior pack may be under represented in existing in situ assessments of antarctic sea ice and hence on average antarctic sea ice may be thicker than previously thought