impact of eastern arctic shelf waters on the nansen basin intermediate layers the eurasian shelves supply water to the nansen basin intermediate layers in two ways as buoyancy driven plumes of dense winter water and as permanent inflow of the barents sea branch of atlantic water while the plumes are local and seasonal phenomena the barents sea flow is part of the large scale circulation both interact with atlantic water which enters the arctic ocean through fram strait and moves as a subsurface boundary current eastward along the continental slope during the polarstern cruise ark ix 4 in summer 1993 the fram strait branch was observed as a narrow core within tens of kilometers of the barents sea shelf edge here several patches of cold low salinity water spread across the slope down to about 500 m depth their origin is assumed to be the northern barents sea they mix with the warm saline fram strait branch water fsbw so that the core properties of the latter become modified downstream in the eastern nansen basin the fram strait branch is displaced toward the inner basin by inflow of the barents sea branch of atlantic water bsbw this inflow appears as a broad 200 km wedge extending from 200 to 1300 m depth bsbw is colder and less saline than water of the fram strait branch and it is less dense and less stratified than the ambient water both branches appear to undergo vigorous mixing while spreading eastward so that any eastward continuation of the boundary flow transports about 50 bsbw and 50 fsbw above 600 m and about 80 bsbw and 20 fsbw below that level toward the canadian basin according to available observations the barents and kara seas are the only source areas for shelf waters ventilating the nansen basin below the halocline and these waters constitute a freshwater input rather than a salt input winter shelf water from the laptev sea cannot contribute to layers deeper than the upper halocline

sedimentary response to milankovitch type climatic oscillations and formation of sediment undulations evidence from a shallow shelf setting at gela basin on the sicilian continental margin abstract a multi proxy chronological framework along with sequence stratigraphic interpretations unveils composite milankovitch cyclicity in the sedimentary records of the last glacial interglacial cycle at ne gela basin on the sicilian continental margin chronostratigraphic data including foraminifera based eco biostratigraphy and 18 o records tephrochronological markers and 14 c ams radiometric datings was derived from the shallow shelf drill sites geob14403 54 6 m recovery and geob14414 27 5 m collected with both gravity and drilled mebo cores in 193 m and 146 m water depth respectively the recovered intervals record marine isotope stages and substages mis from mis 5 to mis 1 thus comprising major stratigraphic parts of the progradational deposits that form the last 100 ka depositional sequence calibration of shelf sedimentary units with borehole stratigraphies indicates the impact of higher frequency 20 ka sea level cycles punctuating this 100 ka cycle this becomes most evident in the alternation of thick interstadial highstand hst wedges and thinner glacial forced regression fsst units mirroring seaward shifts in coastal progradation albeit their relatively short lived depositional phase these subordinate hst units form the bulk of the 100 ka depositional sequence two mechanisms are proposed that likely account for enhanced sediment accumulation ratios sar of up to 200 cm ka during these intervals 1 intensified activity of deep and intermediate levantine intermediate water liw associated to the drowning of mediterranean shelves and 2 amplified sediment flux along the flooded shelf in response to hyperpycnal plumes that generate through extreme precipitation events during overall arid conditions equally the latter mechanism is thought to be at the origin of undulated features resolved in the acoustic records of mis 5 interstadials which bear a striking resemblance to modern equivalents forming on late holocene prodeltas of other mediterranean shallow shelf settings

architecture of late orogenic quaternary basins in northeastern mediterranean sea abstract in the northeastern mediterranean sea pliocene to quaternary depocentres have formed in extensional basins bounded by splays of the east anatolian transform fault this tectonic regime is superimposed on a miocene and older back arc environment that experienced late miocene compression along the misis kyrenia thrust which now lies in the middle of the extensional zone the thrust zone is now represented by a narrow horst that appears to be bounded by strike slip faults pliocene quaternary extension took place on listric fault fans that are orthogonal to the bounding transform splays and sole at a messinian evaporite horizon and on some deeper soling listric faults parallel to and near the bounding faults the rapid extension has resulted in progressive landward migration of paleoshorelines and low depositional gradients glacio eustatic fluctuations in shoreline positions strongly influenced sediment distribution most sediment dispersion was from deltaic plumes with turbidites of minor significance depocentres landward of the maximum seaward extent of paleoshorelines were formed almost entirely by tectonic subsidence minor deep water depocentres controlled by halokinesis accumulated mud turbidites during extreme low stands of sea level

polynya dynamics a review of observations and modeling 1 polynyas are nonlinear shaped openings within the ice cover ranging in size from 10 to 105 km2 polynyas play an important climatic role first winter polynyas tend to warm the atmosphere thus affecting atmospheric mesoscale motions second ocean surface cooling and brine rejection during sea ice growth in polynyas lead to vertical mixing and convection contributing to the transformation of intermediate and deep waters in the global ocean and the maintenance of the oceanic overturning circulation since 1990 there has been an upsurge in polynya observations and theoretical models for polynya formation and their impact on the biogeochemistry of the polar seas this article reviews polynya research carried out in the last 2 decades focusing on presenting a state of the art picture of the physical interactions between polynyas and the atmosphere sea ice ocean system observational and modeling studies the surface heat budget and water mass transformation within these features are addressed

the nutrient salinity and stable oxygen isotope composition of bering and chukchi seas waters in and near the bering strait seawater nutrient salinity and oxygen 18 data collected from 1990 to 1993 in the bering and chukchi seas were used to identify potential sources of nutrients and water masses that result in formation of the arctic ocean upper halocline and its associated nutrient maximum water matching the delta sup 18 o values of the arctic ocean upper halocline and containing sufficient or a nearly sufficient nutrient and salinity concentration was collected in subsurface waters in the summer in portions of the bering sea particularly the gulf of anadyr however nutrient concentrations significantly declined in this north flowing water over the shallow continental shelf before it reached the bering strait as a consequence of biological utilization and dilution with nutrient poor and oxygen 18 depleted fresh water therefore it does not appear likely that the flow of unaltered water through the bering strait in the summer plays a critical role in the formation of the arctic ocean upper halocline the role of other mechanisms for contributing pacific derived waters to the arctic ocean nutrient maximum is considered copyright 1997 american geophysical union

on the bering sea ice edge front an oceanographic field program was carried out along the bering sea ice edge in winter 1982 83 to investigate the temperature salinity front associated with and paralleling the winter ice edge currents were measured using taut wire moorings that were in place over winter and an intensive ctd survey was carried out of the frontal structure in midwinter february march the midwinter front separated cold 0 c more saline 32 5 outer shelf water the front had northwestward baroclinic currents paralleling the front ice edge with near surface speeds of 5 6 cm s and an associated transport of about 0 3 106 m3 s these baroclinic currents were superimposed on a regional barotropic along isobath flow resulting in north westward midwinter upper layer flows with monthly mean speeds exceeding 10 cm s an upper layer flow component was directed beneath the ice and provided heat adequate to melt the ice and limit advance of the edge the resulting low salinity meltwater was mixed vertically to maintain the front by wind acting across a highly mobile hydrodynamically rough ice cover subtidal fluctuations were not significantly affected by the front or the ice cover and local winds accounted for less than one quarter of the observed current variability the remainder being probably due to regional variations in the barotropic flow

architecture of stacked quaternary deltas correlated with global oxygen isotopic curve a distinctive pattern of quaternary stacked prograded deltas and intervening transgressions on a rapidly subsiding continental margin in the eastern mediterranean has been dated from offshore wells simple modeling using the quaternary oxygen isotope record as a proxy sea level curve has demonstrated that this pattern is a consequence of sea level change the progradational pattern is dependent principally on the amount of time that is available between successive highstands to provide accommodation space by subsidence on rapidly subsiding continental margins the standard pattern of stacked deltas can be used as a chronological tool in undated quaternary seismic sequences

coupled wind forced controls of the bering chukchi shelf circulation and the bering strait throughflow ekman transport continental shelf waves and variations of the pacific arctic sea surface height gradient abstract we develop a conceptual model of the closely co dependent bering shelf bering strait and chukchi shelf circulation fields by evaluating the effects of wind stress over the north pacific and western arctic using atmospheric reanalyses current meter observations satellite based sea surface height ssh measurements hydrographic profiles and numerical model integrations this conceptual model suggests bering strait transport anomalies are primarily set by the longitudinal location of the aleutian low which drives oppositely signed anomalies at synoptic and annual time scales synoptic time scale variations in shelf currents result from local wind forcing and remotely generated continental shelf waves whereas annual variations are driven by basin scale adjustments to wind stress that alter the magnitude of the along strait meridional pressure gradient in particular we show that storms centered over the bering sea excite continental shelf waves on the eastern bering shelf that carry northward velocity anomalies northward through bering strait and along the chukchi coast the integrated effect of these storms tends to decrease the northward bering strait transport at annual to decadal time scales by imposing cyclonic wind stress curl over the aleutian basin and the western subarctic gyre ekman suction then increases the water column density through isopycnal uplift thereby decreasing the dynamic height sea surface height and along strait pressure gradient storms displaced eastward over the gulf of alaska generate an opposite set of bering shelf and aleutian basin responses while ekman pumping controls canada basin dynamic heights proshutinsky et al 2002 we do not find evidence for a strong relation between beaufort gyre sea surface height variations and the annually averaged bering strait throughflow over the western chukchi and east siberian seas easterly winds promote coastal divergence which also increases the along strait pressure head as well as generates shelf waves that impinge upon bering strait from the northwest

thermal regimes in the chukchi sea from 1941 to 2008 the summer june october temperature observations in the surface 0 m and subsurface 20 mbottom chukchi sea layers collected from 1941 to 2008 have been analyzed using the self consistent data recovery procedure based on correlation analysis and iterative empirical orthogonal function eof decomposition the analysis of the surface and subsurface eofs identified cold normal and warm thermal states with variability of 2 3 years and also 4 7 years we found that the chukchi sea water temperature has gradually increased since 1941 warming in the surface layer since 1941 has been minimal in the bering strait 0 012 1 cy r 1 total 0 8 1c and maximal in long strait 0 030 0 036 1 cy r 1 total 2 0 2 4 1c in the subsurface layer temperatures have increased about half as much minimal 0 0030 0 0075 1 cy r 1 total 0 2 0 5 1c in long strait and rather uniform 0 010 0 015 1 cy r 1 total 0 7 1 0 1c for the remaining chukchi sea analysis of the satellite sea surface height anomaly data shows that during the warm periods there is a stronger flow through the bering strait and intensification of the northwestward currents in the central chukchi sea extensive correlation analysis shows that the thermal state of the chukchi sea agrees well with the flow of pacific water through the bering strait and by an increase of the global atmospheric temperature in addition typical circulation during warm and cold periods was reconstructed using four dimensional variational 4dvar data assimilation into the ocean model and estimates of volume and heat fluxes in the chukchi sea during cold and warm periods were derived which are consistent with eof and correlation analyses

middle upper pleistocene record of 100 ka depositional cycles on the southern tuscany continental margin tyrrhenian sea italy abstract five unconformity bounded depositional sequences have been seismically defined on the tyrrhenian margin offshore southern tuscany italy the set of sequences encompasses a 500 ka interval each sequence recording a 100 ka orbitally driven climate eustatic cycle similarly to most of quaternary continental margins sequences on the southern tuscany margin show an overall regressive motif reflecting shelf sediment progradation basically during the prolonged phases of sea level fall that characterise the middle upper pleistocene 100 ka cyclicity on seismic profiles however progradational units within each sequence display a variable clinoform geometry interpreted as a record of the alternation of highstand falling and lowstand intervals within 100 ka cycles the observed geometric variability is thus used as a key for separating systems tracts otherwise merging into a general progradational regressive sedimentary body composing the bulk of each sequence on a longer term the interplay between sea level changes modulated by 100 ka cycles and regional subsidence controls the stratigraphic architecture and the growth pattern of the continental margin this effect is documented by the overall aggradational retrogradational stacking pattern of sequences superimposed on shelf margin progradation and reflecting the renewal of accommodation space landward of the shelf margin and its exploitation at each cycle

deltas of the lake malawi rift east africa seismic expression and exploration implications high resolution air gun sourced seismic reflection surveys over the offshore regions of five river deltas in lake malawi in the east african rift system reveal considerable variability in acoustic facies and stratigraphic architecture this variability can largely be attributed to the influences of different structural settings and to a lesser degree to high amplitude 100 400 m and high frequency 1000 to 100 000 yr fluctuations in lake level deltas on flexural and axial margins in the rift lake show well developed progradational geometries in contrast a delta on a steep accommodation zone margin distributes coarse sediments over a broad depositional apron rather than concentrating sediment in discrete progradational lobes as on the other deltas a large border ault margin river delta displays the most complex tectonic and stratigraphic architecture of all the deltas studied it contains several delta associated facies including prograding clinoform packages fan deltas stacked against a boundary fault and extensive subaqueous fans flexural margin lowstand deltas may be the most prospective for hydrocarbon exploration due to their large internally well organized progradational lobes and their close proximity to deep water high total organic carbon lacustrine source facies

uniform basin growth over the last 500 ka north anatolian fault marmara sea turkey abstract much of the northern strand of the north anatolia fault system in the marmara sea the main marmara fault is a seismic gap posing a high risk for istanbul deep bathymetric and sedimentary basins are structurally associated with the main marmara fault basin growth including tilting of their margins is thus linked to fault slip through releasing and restraining segments of this and other branches of the north anatolian fault system whether this system has been steady state through at least the last half of the quaternary or whether the main marmara fault more recently propagated through and deactivated pull apart basins is one of the main controversies a published age model and stratigraphic framework for these basins has been lacking and tectonic history models for the marmara sea have relied on extrapolating present deformation rates back through time over 3000 km of new high resolution multichannel seismic reflection combined with existing lower resolution seismic reflection and multibeam bathymetric data make possible a detailed regional stratigraphic interpretation in particular a stack of shelf edge deltas are imaged and interpreted as glacial period deposition during low sea lake levels reflections from the tops of these deltas and from unconformities were correlated across much of marmara sea basins and highs providing critical stratigraphic control we correlate the low stand deltas with known eustatic sea level minima by developing proxies for time from vertical separation of strata across normal faults tilts and sedimentary volumes a preferred age model is proposed at least back to oxygen isotopic stage 14 at 536 ka during this time interval tilting of basin margins vertical separation across the main marmara fault adjacent to western istanbul and tilt related slow collapse on the south flank of the cinarcik basin all indicate steady state basin growth and fault slip

forced regression systems tracts on the bengal shelf a vertical succession of five composite sequences has been identified within the upper 100 m of the outer bengal shelf by means of high resolution multi channel seismic data each sequence consists predominantly of up to 100 km long and some 10 m thick forced regression systems tracts the internal reflection pattern of the regressive units show mainly prograding oblique clinoforms intervening transgressive systems tracts are represented by seismically transparent or chaotic layers on the outer shelf three of the sequences cause shelf aggradation and retrogradation and two of them cause mainly shelf progradation based on the hierarchy of systems tracts their calibration by comparison with eustatic sea level curves and reconstructed paleoshoreline positions the composite sequences are interpreted as eccentricity driven eustatic 4th order milankovitch cycles with a periodicity of about 100 ky internal unconformities mark cycles of 5th or higher order an average subsidence of the outer shelf is estimated to be less than 0 4 mm year during the last 345 ky the correlation between the shelf growth pattern and sea level fluctuations is consistent with the enhanced deposition on the eastern bengal submarine fan from 465 to 125 ky b p as was observed by other authors

comment on the timing and evolution of the post glacial transgression across the sea of marmara shelf south of istanbul by eris et al marine geology 243 57 76 abstract in their recent paper eris and co authors attempt to refute much of our work on deltaic sediments at the southern exit of the bosphorus strait turkey first their age model is completely inconsistent with the well constrained chronology of our cores mar02 110 and mar02 111 their calypso core md 2750 must have seriously oversampled the holocene section giving an erroneous impression of true thicknesses and ties to seismic data and therefore leading to an incorrect assessment of the timing of deltaic sedimentation second they have ignored evaporative drawdown in the marmara sea from 14 7 11 3 ka lowering of the sea surface by evaporation is a better explanation for a lowstand shoreline at 83 m elevation than their proposal that the dardanelles sill was this deep at the time of reconnection with the global ocean third we contest their conclusion that the uppermost delta in this area was sourced from the kurbagalidere river the sediment flux of this river is too little it cannot account for the strong upward climb of the topset to foreset transition into a rapidly rising ocean and eris et al make no attempt to explain the absence of a precursor shelf edge delta that would be mandatory if this river had the water and sediment discharge that they suggest

delta progradation and sediment fluxes since the last glacial in the thermaikos gulf and the sporades basin nw aegean sea greece abstract late quaternary sedimentary cover in the thermaikos gulf consists of three seismic units i the uppermost unit a that represents delta progradation during the last 6000 yr when the sea surface almost reached the present level highstand systems tract hst ii unit b that includes relatively coarse grained sediments deposited in a shallow high energy estuarine environment during the post glacial transgression transgressive systems tract tst and iii the lowest unit c which may represent late glacial prodeltaic deposits and slope to basin turbidites lowstand systems tract lst seismic units a and b overlay a well defined unconformity which resulted from sub aerial erosion during the late glacial sea level fall subtracting the thickness of unit a from the present bathymetry the paleo relief of the late holocene times ca 6000 yr bp sea level up to 20 m was assessed similarly the paleo relief 24 000 yr bp sea level 100 to 120 m was estimated the main morphological feature is the incised valley of a major river that resulted from the confluence of the axios aliakmon loudias gallikos and possibly pinios rivers sediment fluxes in the nw aegean sea were estimated for three time spans of the late quaternary interval i 6000 yr bp present interval ii 18 000 6000 yr bp and interval iii 24 000 18 000 yr bp the terrestrial sediment load supplied by the axios aliakmon pinios and smaller rivers was estimated at 35 4 10 9 t for interval i 93 of this material was deposited on the continental shelf whereas the remaining 7 was transported to the adjacent basin the mean annual terrestrial flux was estimated at 5 5 10 6 t yr 1 during interval ii more than 79 10 9 t of terrestrial sediment were discharged into the area terrestrial flux 6 6 10 6 t yr 1 of which 86 was deposited on the shelf during interval iii the terrestrial load was 40 6 10 9 t terrestrial flux 6 8 10 6 t yr 1 and sediments were predominantly deposited on the slope and basin based on the sediment s carbonate content the biogenic loads and fluxes were also determined the biogenic flux during intervals ii and iii was found to be 2 5 times higher than during interval i

east west differences in water mass nutrient and chlorophyll a distributions in the sea ice reduction region of the western arctic ocean 1 the r v mirai conducted hydrographic surveys in the western arctic ocean during summer 2004 across a front between cold arctic water and warm water from the pacific ocean where sea ice cover has been largely reduced in recent summers the hydrographic data indicate a new type of vertical temperature minimum water west of the front along isohaline surfaces with approximate salinity s of 32 which is fresher than the typical temperature minimum s 33 caused by spreading of pacific winter water pww mainly to the east of the front both of the temperature minimum waters are characterized by low potential vorticity with near freezing temperature suggesting that they are formed by winter convection with sea ice formation a difference between the waters results from a large contribution of sea ice meltwater to the fresh temperature minimum frtmin water of s 32 the distributions of the sea ice meltwater contribution and nitrogen deficit suggest that summer shelf water largely influenced by the sea ice melt in the chukchi sea is modified by winter convection on its way to the chukchi abyssal plain to form the frtmin water this water supplies nutrients through the water distribution to the west of the front at depths shallower than the nutrient maximum layer caused by the pww spreading the shallower nutrient supply by the frtmin water combined with light penetration without sea ice cover could produce a prominent chlorophyll a maximum layer west of the front

modeling ice dynamics of coastal seas a coupled sea ice barotropic ocean model with a 1 km resolution and a seaward domain of 200 km quantifies three coastal processes coupling of ice motion to wind driven coastal currents ice thickness redistribution under compaction at the coast and formation of coastal shear zones the model consists of an ice momentum balance mass concentration and two parameter ice thickness distribution and equations for horizontal water motion and continuity using vertical structure functions an appropriate constitutive law appears to be a hardening plastic based on qualitative observations from alaskan continental shelves for first year sea ice strength is taken to be proportional to the square of ice thickness a north wind example of 10 m s with the coastline to the west shows the depth dependence of rotational shear in the sea ice ocean boundary layer and sea surface tilt which contributes an alongshore slope current there is slight convergence of sea ice over the shelf a coastal shear zone of 4 km and an alongshore ice speed seaward of the shear zone of 6 of the wind speed caused by the combination of an under ice shear layer and an alongshore slope current for an onshore wind ice is near free drift at 3 of the wind seaward of a ridging front which propagates seaward a square dependence of ice strength on thickness is required for the rubble field to approach a limiting thickness consistent with observations the hardening plastic interpretation of the rubble field has the stress state at the yield limit in contrast with a rigid plastic of high constant strength that yields only at the coast we conclude that 1 ice thickness motion feedback is important on scales less than 10 km 2 the observational base to discriminate between mesoscale constitutive laws is not yet available and 3 the relation of ice velocity to wind stress is variable because the ocean slope current responds only to the alongshore component of the wind

reconstruction of late quaternary sea and lake level changes in a tectonically active marginal basin using seismic stratigraphy the gulf of cariaco ne venezuela abstract the gulf of cariaco is a marginal basin located between the cariaco basin and the paria gulf offshore ne venezuela along a system of active right lateral strike slip faults it is connected to the caribbean sea via a shallow 58 m deep sill implying that the gulf was disconnected from the global ocean during eustatic lowstands a dense grid of high resolution reflection seismic profiles has been used to determine the overall tectonic structure of the gulf and to establish the seismic stratigraphy of its sedimentary infill six unconformity bounded seismic stratigraphic units were identified in the upper 200 m of the sedimentary infill detailed seismic stratigraphic and seismic facies analysis allowed defining a series of sedimentary features that can be used as indicators of past sea or lake level in the gulf of cariaco i delta offlap breaks ii evaporites and iii erosional unconformities using accurate measurements of these various indicators at several locations in the gulf and a simple total subsidence model a relative sea lake level history encompassing the last 130 kyr could be reconstructed in periods of connection with the open ocean reconstructed relative sea level correlates well with eustatic sea level in times of disconnection distinct lake level fluctuations occurred which sometimes resulted in total dessication of the gulf lake level fluctuations appear to correlate with major heinrich events stadials and interstadials mis 4 the lgm and the younger dryas were thus identified in the gulf of cariaco sedimentary record the last reconnection to the caribbean sea occurred during mwp1b around 11 5 kyr the very good fit of the cariaco sea lake level curve with the eustatic sea level curves both in terms of amplitude and of timing underscores potential for future paleoclimate research of the sedimentary record contained in this marginal basin despite its active tectonic setting

a 1 ma record of sediment flux south of the grand banks used to infer the development of glaciation in southeastern canada abstract a 20 m long piston core from a basement ridge on the continental rise off southeastern canada provides a 0 9 ma record of distal continental margin sedimentation sediment sources are distinguished by sand and clay sized mineralogy and detrital palynomorphs they include detritus eroded from a northern canadian shield and lower paleozoic rocks transported southward through the labrador sea b the grand banks and c the gulf of st lawrence and newfoundland isotopic stratigraphy allows correlation of glacial and interglacial stages with changes in sources and flux rates via different transport processes nepheloid layer ice rafting and distal turbidity currents the glacial history of southeastern canada is interpreted from variation in the flux and type of detrital material and correlation with other data from the continental margin from stages 27 to 15 the grand banks formed a forested coastal plain limited local glaciation may have occurred in stages 18 and 16 tertiary regolith and cretaceous clays were stripped from land areas in stages 14 and 12 culminating in the excavation of the laurentian channel late in stage 12 extensive cold based ice sheets are inferred for glacial stages 10 8 and 6 with less severe glaciation in stages 4 and 2 extent of this local appalachian ice correlates poorly with global ice volumes

a note on the extent of glaciation throughout the himalaya during the global last glacial maximum abstract quantitative chronologies for the impressive glacial successions that occur throughout the himalaya have until recently been almost totally lacking within the last decade two new techniques have promised to remedy this situation these techniques optically stimulated luminescence and cosmogenic nuclide surface exposure dating enable the age of many glacial features to be determined and have allowed us to study the extent and timing of himalayan glaciation in the late quaternary new data show that the local last glacial maximum lgm occurred during the early part of the last glacial cycle in most areas during marine isotope stage 3 mis 3 mis 3 was a time of increased insolation when the south asian summer monsoon strengthened and penetrated further north into the himalaya the concomitant increased precipitation occurring as snow at high altitudes produced positive glacier mass balances thereby allowing glaciers to advance on the other hand during the global lgm 18 24 ka himalayan glaciation was very restricted in extent generally extending

chronology of quaternary shoreline progradational sequences related to eustatic sea level changes sedimentation and subsidence in saronikos gulf greece abstract the stacking pattern of shoreline progradational sequences in subsiding basins have been used as a chronologic tool in the mediterranean region most previous studies have used a few key seismic lines seaward of deltas where the record is complicated by deltaic distributary switching southeastern saronikos gulf in the western aegean sea at the northwestern end of the south aegean arc lacks large river input of sediment the ene wsw and nw se trending neotectonic aegina and methana basins lie between the tectonically active gulf of corinth and the relatively stable cyclades plateau new high resolution seismic profiles from southeastern saronikos gulf have been interpreted according to the principles of seismic and sequence stratigraphy alpine basement and marine pliocene sediments have been recognized in the surrounding basin margins and more than 300 m and 150 m of unconsolidated sediments have been mapped in aegina and methana basin respectively progradational clinoforms that toplap against transgressive surfaces have been traced along strike leading to the establishment of a robust chronostratigraphic framework further controlled by sedimentation rates as extracted from cores southeastern saronikos gulf poses an outstanding example of development of progradational wedges formed within a microtidal wave dominated regime of low sedimentation rates between 2 8 cm ka and 3 2 cm ka within the framework of low subsiding basins with rates between 0 03 and 0 31 m ka in this environment more than 180 well preserved shoreline progradational units with attributes similar to the ones reported from the aegean and eastern mediterranean seas have been mapped and correlated to sea level lowstands back to 866 ka deeper mid pleistocene progradational units are also recognized tentatively back to 1 4 ma subsidence rate shows a dramatic decrease in the last 1 ma and significant numbers of faults became inactive during the last 130 ka in early middle quaternary methana basin was an isolated lake and extended terrestrial areas were shaped in the poros agios georgios plateau during sea level lowstands aegina basin was continuously connected to the aegean through the agios georgios fault valley this study demonstrates the robustness of chronology based on stacked shoreline progradational sequences and its applicability to determining rates of tectonic subsidence

sedimentary sequences in the gulf of lion a record of 100 000 years climatic cycles abstract the wide continental shelf of the gulf of lion up to 70 km has been the object of numerous investigations since the early days of oceanography yet the question of sequences duration the mechanisms of deposition and factors implied remained unanswered a study of a very dense grid of very high resolution vhr seismic reflection sparker data associated with surficial cores both collected by ifremer between 1992 and 2001 on the outer shelf and upper slope offshore of sete in the languedoc region gives a new insight into these issues analysis of the 3d geometry of the sedimentary record reveals a basic depositional pattern consisting of a pair of horizontally juxtaposed and downlapping prisms prism pi with low angle clinoforms results obtained from integrating lithology palynology micropaleontology seismic stratigraphy stratigraphic simulation support the hypothesis that the basic depositional pattern records a 100 000 years glacioeustatic interglacial glacial cycle as previously suggested by aloisi aloisi j c 1986 sur un modele de sedimentation deltaique contribution a la connaissance des marges passive these de doctorat d etat universite de perpignan 162 pp prisms pi corresponds to deposition at high sea level and prisms pii to deposition during low sea level at glacial maxima five sequences of paired prisms capped by five major erosion surfaces have been identified and modelled showing that the corresponding glacioeustatic cycles the last five cycles at least are recorded on the shelf of the western part of the gulf of lion

dense water formation in the laptev sea flaw lead 1 two primitive equation based models are used to estimate the formation of total volumes either of arctic cold halocline water chw intermediate water imw or deep water dw through freeze related salt rejection in the siberian laptev sea flaw lead system model a assumes that the rejected salt remixes with surface mixed water smw beyond the leads until salinities allow for contribution to the midlayers of either the chw the imw or the dw model b simulates direct salt rejection to the upper layer of the cold halocline and after remixing here further contribution to the midlayers of chw imw or dw averaging both model estimates laptev leads contribute either 0 161 sv of chw 0 075 sv of imw or 0 065 sv of dw which represents as much as 23 16 or 30 of arctic wide lead derived dense water contribution to the appropriate layer respectively northwestern laptev leads produce the greatest amount of dense water these lead sections show very short buoyancy equilibrium timescales 6 to 13 days and local dense water production may potentially be amplified by lateral brine injection into the cold halocline through bottom eddies central southern and southeastern leads generally produce little salt due to low surface water salinities as definite separation mechanisms and proportion distributions of rejected lead brines into chw iwm and dw are still unidentified in nature a combination of lead salt rejection and remixing model a and direct downward expulsion of brine packages model b is assumed to steer laptev lead dense water production

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

circulation on the north central chukchi sea shelf abstract mooring and shipboard data collected between 1992 and 1995 delineate the circulation over the north central chukchi shelf previous studies indicated that pacific waters crossed the chukchi shelf through herald valley in the west and barrow canyon in the east we find a third branch through the central channel onto the outer shelf the central channel transport varies seasonally in phase with bering strait transport and is 0 2 sv on average although some of this might include water entrained from the outflow through herald valley a portion of the central channel outflow moves eastward and converges with the alaskan coastal current at the head of barrow canyon the remainder appears to continue northeastward over the central outer shelf toward the shelfbreak joined by outflow from herald valley the mean flow opposes the prevailing winds and is primarily forced by the sea level slope between the pacific and arctic oceans current variations are mainly wind forced but baroclinic forcing associated with upstream dense water formation in coastal polynyas might occasionally be important winter water mass modification depends crucially on the fall and winter winds which control seasonal ice development an extensive fall ice cover delays cooling limits new ice formation and results in little salinization in such years bering shelf waters cross the chukchi shelf with little modification in contrast extensive open water in fall leads to early and rapid cooling and if accompanied by vigorous ice production within coastal polynyas results in the production of high salinity 33 shelf waters such interannual variability likely affects slope processes and the transport of pacific waters into the arctic ocean interior

summertime synoptic variability of frontal systems in the northern bering sea hydrographic observations in the northern bering sea during august and september 1987 indicate the presence of a front dividing relatively warm fresh bering shelf water from relatively cool saline anadyr water along the western and northern coasts of st lawrence island near anadyr strait a buoyant layer 20 m thick with surface salinities as low as 29 5 practical salinity units and a maximum temperature of 10 c was present adjacent to the island the surface outcrop of the front migrated 80 km north during the nine day time period of the hydrographic observations surface thermal patterns suggest that this front may extend the length of the northern coastline of st lawrence island during the summer the front veers north and passes through the bering strait where temperature differences as large as 6 c exist across the strait an examination of the water mass properties of the bering sea suggests that the buoyant water north of st lawrence island is bering shelf water which has been carried northward through anadyr strait the baroclinic transport assuming no flow at the bottom associated with the front is 0 07 sv which is roughly a third of the seasonal increase in transport through the bering strait in the summer

on the wind driven variability of the flow through bering strait analysis of time series from 1981 to 1982 near bering strait shows the meridional wind component the current and the oceanic pressure gradient to be well correlated we argue that because of the constraining coastal geometry there are wind driven flow divergences which perturb the oceanic pressure field and account for most of the current variability for example northerly winds cause a pronounced set down of sea level southeast of bering strait and if the winds are strong enough they will reverse the mean slope downward to the north through the strait winds during 1976 1977 were also well correlated with the bering strait transport estimates of coachman and aagaard 1981 and we therefore use the calculated winds from 1946 to 1982 to examine the low frequency transport variability there is a marked seasonal cycle with summer transport about 50 greater than during winter the long term mean transport is calculated as less than 0 6 sv which is much lower than earlier estimates abnormally large transports apparently occurred during a number of years from 1948 to 1967 but during the past 15 years transports have tended to be considerably less corresponding to the stronger northerly winds during these years the interannual wind variability near bering strait together with the corresponding variability in the transport through the strait is in fact part of the large scale variability of the atmospheric circulation over the north pacific and its oceanic effects

oceanographic conditions in the marginal ice zone north of svalbard in early fall 1979 with an emphasis on mesoscale processes during september october 1979 the norwegian remote sensing experiment was carried out in the marginal ice zone north of svalbard convergence of the ice cover is correlated with along ice edge winds with the ice to the right while divergence occurs during office winds or calm conditions a wind driven ice edge jet is observed wind driven upwelling of the pycnocline of up to 7 m was present along the ice edge during a 10 to 15 m s easterly wind event the upwelling is due to ekman divergence at the ice edge caused by higher wind stress over ice than over open water the ice edge meanders with a scale of 20 40 km and sheds eddies with a scale of 5 to 15 km into the open water this scale is of the same order as the rossby radius of deformation eddies with the same scale are also seen in the conductivity temperature and depth observations conditions during the experiment were such that barotropic instabilities could have generated these eddies

influence of the st lawrence island polynya upon the bering sea benthos the influence of a polynya a persistent ice free region on water column production and subsequent transport to the shallow continental shelf benthos of the bering sea was evaluated by studying spatial patterns of organic material deposition benthic biomass community sediment metabolism benthic population structure and other potential indicators of enhanced organic carbon transport to benthic communities underlying the st lawrence island polynya despite suggestions that polynyas may be important localized centers of primary production in polar waters we found that the st lawrence island polynya does not obviously enhance the biomass of benthic communities directly below the polynya however southward flowing baroclinic currents generated as a result of brine injection at the polynya edge do appear to have an influence on the biomass and ecological structure of bering sea benthic communities south of st lawrence island these currents appear to affect mean sediment oxygen consumption surface organic carbon nitrogen ratios total organic content and bottom water ammonia by sweeping phytodetrital matter south and to the west of the island a particle reactive short lived natural radioisotope 7be used as an indicator of rapid days to weeks deposition of particulate material from the water column was detected only in surface sediments to the southwest of the island indicating enhancement of particle deposition to the southwest of the island finally the 18o content of tunicate cellulose was highest in the polynya region consistent with increased filter feeding in the late winter when the polynya is present and presumably promoting primary production in the open water the anadyr current consisting of nutrient rich deeper bering sea water that is upwelled onto the shelf in the gulf of anadyr flows west to east in the region south of st lawrence island throughout the year and is the major forcing function for high production in the region the interaction of anadyr water with the winter spring ephemeral polynya and associated baroclinic currents combine to positively influence benthic communities

aleutian basin of the bering sea thermohaline oxygen nutrient and current structure in july 1993 an overview is given of the surface to bottom thermohaline oxygen nutrient and baroclinic flow structures in the aleutian basin of the bering sea and the adjacent north pacific based on high resolution field measurements in july 1993 a basic four layer vertical structure is observed in the upper 1500 m the 30 m top layer is warm low in salinity and nutrients and high in oxygen beneath it a 100 to 150 m thick temperature minimum layer is found believed to be a remnant of winter convection this is followed by a 300 m thick warm layer in which the main halocline oxycline and nutricline are located below it lies a layer of minimum oxygens and maximum nitrates and phosphates centered at a depth of 900 m in the bering sea but rising to 400 m south of the aleutians this basic structure is disrupted in the vicinity of amchitka pass due to strong tidal mixing the deep and abyssal waters of the aleutian basin differ substantially from those at comparable depth in the adjacent pacific by being warmer 0 1 c less saline 0 01 less dense 0 01 kg m3 poorer in oxygen 50 mol kg and richer in silicates 80 mol kg nitrates 1 0 mol kg and phosphates 0 3 mol kg the highest silicate concentrations 240 mol kg occur at the foot of the bering shelf unusual hydrographic conditions exist in an isolated tidal mixing basin in amchitka pass where the bottom mixed layer is 600 m thick 0 7 c warmer 0 14 less saline and 21 mol kg less oxygenated than at comparable depths outside baroclinic currents indicate strong deep jetlike flows on both sides of the aleutian ridge weak shallow eddies in the middle of the aleutian basin and somehat enhanced flows near the bering shelf edge the alaska stream in july 1993 was 100 km wide had a double core with a top speed of 0 54 m s and had a westward volume transport of 38 sv with 14 sv below 1000 dbar the north aleutian current had a speed of 0 2 m s and an eastward transport of 10 sv with 4 sv below 1000 dbar off the bering slope both eastward and westward flows were observed with volume transports near 7 sv

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

late quaternary sea level change sedimentation and neotectonics of the gulf of gokova southeastern aegean sea abstract the sedimentary and tectonic late quaternary evolution of the gulf of gokova located at the southwest anatolia southeastern aegean sea region has been interpreted from 800 line km of 3 5 khz and single channel airgun seismic reflection profiles the older part of the gokova basin is formed by mainly e w trending faults and filled by the latest miocene pliocene quaternary hemipelagic sediments with thickness up to 2 5 km the lycian nappes which primarily cover extreme southwestern anatolia represent the basement rocks for the gokova region younger active faulting so called gokova transfer fault gtf which has not been previously discussed in the literature trends ne in the central part of the gulf of gokova basin and records sinistral strike slip motion broadly parallel to the convergence direction of the aegean anatolian and african plates the continental shelf of the northeastern gulf of gokova is mostly formed by numerous superimposed deltaic successions depositional sequences separated by major erosional unconformities during times of lowered sea level associated with late quaternary glaciations deltas prograded more than 40 km seaward from their present positions foreset progradation terminated with the rise of sea level in interglacial and post glacial times and deltas were relocated far inland these major transgressions resulted in unconformities that are correlated with the beginning of oxygen isotope stages 9 7 5 and 1 and provide chronostratigraphic markers for a detailed analysis of sedimentation patterns in the late quaternary all seismic lines show that the topset to foreset transition of the youngest pleistocene delta system developed around 145 150 ms below present sea level thus the maximum pleistocene sea level lowering 18 000 years bp was about 110 m the positions of maximum regression for isotopic stages 6 8 and 10 were found as 160 190 and 215 m below present sea level respectively paleo shoreline positions during isotopic stages 2 6 and 8 suggest an overall gradual subsidence of gokova basin during the last 0 5 ma in the southeastern aegean sea the seismic sedimentary chronology suggests that the gokova basin is subsiding at 0 3 0 4 mm year three bathymetric low and e w wnw ese directed two main ridges in the gulf area are noticeable from the bathymetric data and are well correlated to the seismic data while the main orientation of the gulf is e w more recent ene wsw and wnw ese structures are remarkable in the western and the mid eastern part of the gulf respectively subsidence rates are greatest in the southern center of the basin and decrease northward so that the northern area is being tilted southward

the role of sea ice and other fresh water in the arctic circulation salinity stratification is critical to the vertical circulation of the high latitude ocean we here examine the control of the vertical circulation in the northern seas and the potential for altering it by considering the budgets and storage of fresh water in the arctic ocean and in the convective regions to the south we find that the present day greenland and iceland seas and probably also the labrador sea are rather delicately poised with respect to their ability to sustain convection small variations in the fresh water supplied to the convective gyres from the arctic ocean via the east greenland current can alter or stop the convection in what may be a modern analog to the halocline catastrophes proposed for the distant past the north atlantic salinity anomaly of the 1960s and 1970s is a recent example it must have had its origin in an increased fresh water discharge from the arctic ocean similarly the freshening and cooling of the deep north atlantic in recent years is a likely manifestation of the increased transfer of fresh water from the arctic ocean into the convective gyres finally we note that because of the temperature dependence of compressibility a slight salinity stratification in the convective gyres is required to efficiently ventilate the deep ocean

holocene sedimentation in the tectonically active tekirdag basin western marmara sea turkey abstract the effects of various depositional conditions and active tectonics on the late holocene sedimentation in the tekirdag basin west of the marmara sea were investigated in 11 gravity cores and on 3 seismic profiles representing shelf to slope to deep basin floor environments except for the two coarser grained avg 60 sand and gravel and calcareous avg 25 caco 3 shelf cores sediments in the slope and basin floor cores constitute low calcareous avg 12 caco 3 and terrigenous mud 90 silt and clay the occurrences of relatively higher total organic carbon contents in sediments from the southern slope 1 14 1 38 compared to that from the northern slope 0 37 1 2 indicate significant input from the southern rivers the presence of silty sandy laminations within the mud matrix of the cores and chaotic and mounded reflection configurations on the seismic profiles from the slope and basin floor environments all suggest the effects of gravity mass movements of sediments slides slumps turbidites most likely due to seismotectonic events earthquakes however it was difficult to establish a basin wide correlation between the historical earthquake events in the region and the positions of silty sandy laminations in dated deep sea sediment cores due to complicated other events such as repeated river run off and floods increased sediment load and slope failure the water contents of sediments from the basin floor avg 10 30 are significantly lower than those from the slope sediments avg 32 46 the former can be explained by the influences of synsedimentation with tectonics and compaction between the north and south boundary sub faults of the naf system whereas the latter shows fluidization of slope sediments during sliding and slumping radiocarbon dated base sections from three cores revealed that sediment deposition at these sites commenced about 4700 bp when the late holocene depositional conditions changed from the formation of upper sapropels to the present state the increases of organic carbon contents at or near the base sections of the cores support this contention

the active submarine nw termination of the south aegean active volcanic arc the submarine pausanias volcanic field abstract methana peninsula shows the longest recorded volcanic history at the western end of the south aegean active volcanic arc including volcanic products from the upper pliocene to recent times the volcanic rocks comprise widespread dacite domes and andesite lava flows from several small volcanic centers and are only imprecisely dated in this paper the integrated analysis of swath bathymetry side scan sonar data and high resolution seismic reflection profiles correlated with core samples has allowed detailed mapping characterization and precise chronological identification of the pausanias submarine volcanic field activity offshore northern methana six volcanic cones or domes are recognized typically 1 3 km in diameter some elongated ne sw and some with a small central crater on their flanks the acoustically reflective volcanic rocks pass laterally into incoherent transparent seismic facies interpreted as volcaniclastic deposits possibly including hyaloclastites that interfinger with the regional basin sediments a sea bottom hummocky field is interpreted as volcanic avalanche and appears to be the submarine continuation of the volcaniclastic apron of northern methana peninsula a robust chronostratigraphic framework has been established based on the recognition of shoreline progradational units and their connection with quaternary eustatic sea level cycles relative dating of the different phases of submarine volcanic activity during the upper quaternary has been achieved by correlating the imaged volcaniclastic flows interlayered within the chronostratigraphically dated sediments dating by stratigraphic position relative to 2d imaged eustatic sea level clinoform wedges appears to be more precise than radiometric methods on land three main submarine volcanic events ve are recognized ve3 at 450 ka a less precisely dated interval at 200 130 ka ve2 and ve1 at 14 ka based on chronostratigraphic constraints subsidence rates of 0 16 0 008 m ka in between marine isotopic stages 6 and 12 and 0 19 0 009 m ka in between marine isotopic stages 12 and 16 were estimated for the marine basin north of methana the morphological similarity to the onshore volcanoes of methana peninsula implies that magmatic constructive processes were dominant regardless of whether in air or in water the upper quaternary submarine volcanic rocks of methana differ from those known from stratovolcanoes elsewhere in the mediterranean e g kos nisyros stromboli and in other volcanic arcs e g montserrat st vincent in the submarine development of domes or small cones the paucity of volcano flank failure deposits and the lack of explosive events pausanias volcanic products date the onset of ne sw faulting as well as the following tectonic phase of e w striking faults possibly related to basin inversion caused by a major rifting phase that also affected most of the south aegean arc and the adjacent gulfs of corinth and argolikos

thermohaline circulation in the arctic mediterranean seas the renewal of the deep north atlantic by the various overflows of the greenland scotland ridges is only one manifestation of the convective and mixing processes which occur in the various basins and shelf areas to the north the arctic ocean and the greenland iceland and norwegian seas collectively called the arctic mediterranean the traditional site of deep ventilation for these basins is the greenland sea but a growing body of evidence also points to the arctic ocean as a major source of deep water this deep water is relatively warm and saline and it appears to be a mixture of dense brine enriched shelf water with intermediate strata in the arctic ocean the deep water exits the arctic ocean along the greenland slope to mix with the greenland sea deep water conversely very cold low salinity deep water from the greenland sea enters the arctic ocean west of spitsbergen within the arctic ocean the lomonosov ridge excludes the greenland sea deep water from the canadian basin leaving the latter warm saline and rich in silica in general the entire deep water sphere of the arctic mediterranean is constrained by the greenland scotland ridges to circulate internally therefore it is certain of the intermediate waters formed in the greenland and iceland seas which ventilate the north atlantic these waters have a very short residence time in their formation areas and are therefore able to rapidly transmit surface induced signals into the deep north atlantic

sea ice and water column structure on the eastern bering sea shelf abstract seasonal sea ice is a defining characteristic of the eastern bering sea shelf and plays a critical role in determining the vertical structure of temperature and salinity over this shelf ice movement relative to local winds ice composition and the impact of both arrival and retreat of ice on the water column at four mooring sites over the middle shelf are examined ice forms primarily in coastal regions and is advected over the southern and outer shelves ice drift from satellite data for two representative years 2003 and 2007 was 2 of local ncep wind speed and oriented 44 to the right of the winds r 2 0 25 measurements from 30 ice cores collected in 2006 2009 gave an average salinity of 5 62 0 88 and an average nitrate concentration of 0 99 0 83 m time series data collected at the biophysical moorings in the bering sea 1995 2012 were used to explore the evolution of the water column under ice at the northern mooring m8 the water column had mixed and cooled to 1 c prior to the arrival of ice little melt occurred after ice arrival at the other three moorings the ocean temperature was 2 4 c when ice arrived resulting in extensive melt melting ice freshened and cooled the upper water column resulting in stratification which persisted for 10 25 days wind induced water column mixing occurred more slowly under the ice than in ice free waters an estimated 1 4 m of ice melted with the first arrival of ice at the three southern moorings where the latent heat of fusion accounted for approximately half the observed cooling during ice retreat there appeared to be little ice melt around the southern two moorings but an estimated 0 8 m at m5 and m8 the extent of ice melt sets up the water column for the following summer

emergent marine record and paleoclimate of the last interglaciation along the northwest alaskan coast the last interglacial high sea level stand the pelukian transgression of isotope substage 5e is recorded along the western and northern coasts of alaska by discontinuous but clearly traceable marine terraces and coastal landforms up to about 10 m altitude the stratigraphy indicates that sea level reached this altitude only once during the last interglacial cycle from the type area at nome to st lawrence island in the bering sea to the eastern limit of the beaufort sea pelukian deposits contain extralimital faunas indicating that coastal waters were warmer than present amino acid ratios in molluscs from these deposits decrease to the north toward barrow consistent with the modern regional temperature gradient fossil assemblages at nome and st lawrence island suggest that the winter sea ice limit was north of bering strait at least 800 km north of its present position and the bering sea was perennially ice free microfauna in pelukian sediments recovered from boreholes indicate that atlantic water may have been present on the shallow beaufort shelf suggesting that the arctic ocean was not stratified and the arctic sea ice cover was not perennial for some period in coastal regions of western alaska spruce woodlands extended westward beyond their modern range and in northern alaska on the arctic coastal plain spruce groves may have entered the upper colville river basin the flaxman member of the gubik formation on the alaskan arctic coastal plain was deposited during marine isotope substage 5a and records the breakup of an intra stage 5 ice sheet over northwestern keewatin

a numerical study of dense water formation and transport on a shallow sloping continental shelf the circulation and transport of dense water generated by an idealized coastal polynya is studied using a three dimensional primitive equation model starting with a homogeneous quiescent ocean a constant negative buoyancy flux is imposed at the surface over a half elliptical region adjacent to the coastal boundary on a gently sloping continental shelf the flow response can be divided into the following three phases geostrophic adjustment instability and offshore eddy transport during geostrophic adjustment the fluid within the forcing region becomes denser and the flow at the edge of the forcing region accelerates in response to the strong density gradient there eventually the flow at the leading edge of the forcing region relative to kelvin wave propagation becomes unstable and a train of counterrotating eddies develops these eddies then form a complex three dimensional flow field and rapidly transport dense water offshore across isobaths the density within the forcing region reaches a maximum which remains fairly constant after the eddies begin to transport the dense fluid offshore the results are qualitatively insensitive to weakening of the negative buoyancy forcing and to changing the bottom slope eddy scales and velocities are consistent with observations in the arctic the results suggest that instability processes and eddy fluxes are important in transporting dense water off continental shelves and into marginal seas

stable isotope profiles of last interglacial pelukian transgression mollusks and paleoclimate implications in the bering strait region abstract the marine paleoclimate during the last interglaciation in the bering strait region is inferred from the stable oxygen and carbon isotope profiles of fossil bivalve mollusks specimens were collected from the marine highstand deposits of the pelukian transgression from the arctic alaskan coastal plain the nome coastal plain st lawrence island and the val katlen suite on the chukotka peninsula as a calibration modern mollusks were obtained from the major water masses in the bering chukchi seas system and from coastal environments near the fossil localities the 18 o composition of the modern mollusks accurately reflects the seawater 18 o differences among the water masses and the ambient temperature range at each site seasonal paleotemperature ranges are estimated from the 18 o profiles of the fossils by comparison with those of the modern specimens a simple model is developed to correct the paleotemperature ranges for the influence of differences in seawater 18 o between water masses and seasonal variations caused by freshwater discharge paleotemperatures calculated for the skull cliff site alaskan arctic coastal plain are close to but slightly cooler than those of modern specimens from peard bay and icy cape the isotopic composition of a pelukian specimen collected near wainwright shows the obvious influence of locally reduced salinities with a correction for lower seawater 18 o this profile yields a summer temperature of 13 c which is 3 c warmer than that from the modern icy cape specimen the isotope records of two specimens from the nome coastal plain suggest salinities that were 3 5 psu lower than the modern eastern bering shelf the paleotemperature range of 0 15 c is consistent with modern conditions in norton sound the character of the isotope profiles of the pelukian specimens from st lawrence island is very different than that of modern specimens near the island but matches the 18 o values of shells from deeper sites in anadyr water this suggests that the fossil mollusks were living in anadyr strait and were transported by a glacial advance from the chukotka peninsula the last interglacial specimens from the val katlen suite have isotope profiles with large seasonal 18 o ranges and the clear influence of a reduced salinity coastal water mass calculated paleotemperatures from the val katlen specimens range from 0 to 13 c differences in the 13 c of shell carbonate between sites appears to reflect the regional distribution of the 13 c of sedimentary organic matter som which is a mixture between terrestrial organic matter mean 13 c of 24 and marine phytoplankton 21 partitioning of 13 c between shallow and deep waters by phytoplankton productivity and remineralization may also affect the regional distribution differences in shell 13 c between taxa may relate to feeding mode and the type and isotopic composition of ingested particles the filter feeders mya and astarte typically have 13 c values 1 2 more positive than the deposit feeders macoma and serripes this effect is attributed to a 13 c difference between marine phytoplankton and som with a component of terrestrial organic carbon

oscillating quaternary water levels of the marmara sea and vigorous outflow into the aegean sea from the marmara sea black sea drainage corridor abstract detailed interpretation of single channel air gun and deep tow boomer profiles demonstrates that the marmara sea turkey experienced small amplitude 70 m fluctuations in sea level during the later quaternary limited in magnitude by the sill depth of the strait of dardanelles moderate subsidence along the southern shelf and quaternary glacio eustatic sea level variations created several stacked deltaic successions separated by major shelf crossing unconformities which developed during the transitions from global glacial to interglacial periods near the strait of dardanelles a series of sand prone deposits are identified beneath an uppermost holocene transparent mud drape the sandy deposits thicken into mounds with the morphology and cross sectional geometries of barrier islands sand waves and current generated marine bars all cross stratification indicates unidirectional flow towards the dardanelles prior to the deposition of the transparent drape which began 7000 years bp in strong support of the notion that the marmara sea flowed westwards into the aegean sea through the dardanelles at times of deglaciation in northern europe the global sea level curve shows that at 11 000 and 9500 years bp sea level rose to the sill depths of the straits of dardanelles and bosphorus respectively the effect from 11 000 to 9500 years bp was seawater incursion into the marmara sea drowning and formation of algal serpulid bioherms atop lowstand barrier islands and transgression of shelves and lowstand deltas at 9500 years bp glacial meltwater temporarily stored in the black sea lake developed into a vigorous southward flow toward the aegean sea forming west directed sandy bedforms in the western marmara sea and initiating deposition of sapropel s1 in the aegean sea this strong outflow persisted until 7000 years bp after which a mud drape began to accumulate in the marmara sea and euryhaline mediterranean mollusks successfully migrated into a progressively more saline black sea where sapropel deposition began most eastern mediterranean sapropels from s1 to s11 appear to correlate with periods of rising sea level and breaching or near breaching of the bosphorus sill these events are believed to coincide with times of vigorous outflow of low salinity fresh surface waters transiting the black sea marmara sea corridor and ultimately derived from melting of northern european ice sheets

lowstand terraces on tyrrhenian sea steep continental slopes abstract wave built terraces formed during sea level stillstands at depths lower than present are found along margins with fairly steep morphology and no to ill developed continental shelf for instance the margin of volcanic islands terraces deposits are up to 20 30 m thick and are flat topped with well defined edges they extend up to 1 km in dip section the deposits are composed of intrabasinal sediments mainly bioclastic sand and silt and are probably due to deposition below the storm wave base during large scale energy episodes two areas of the tyrrhenian sea have been analysed one in a volcanic context the pontine archipelago and the other in a highly active structural context the calabrian arch similar wave built terraces were found in both areas with a main terrace placed at a depth of 100 150 m which is thought to be wurmian older terraces are also present emplaced during the preceding lowstands in the late pleistocene a possible present day terrace is found at about 20 m depth in the pontine archipelago a mechanism of subsequent formation below wave base level and removal because of sea level lowering has been hypothesised during long lasting periods of late pleistocene sea level falls terraces are thus thought to preserve only at the minimum lowstand position and to remain relict on the slope during sea level rise and highstand the analysis of the distribution and depths of these terraces allows some neotectonic interpretation for example in the volcanic archipelago whose western sector has probably risen at an average rate of 2 5 mm yr over the last 20 000 years

constraints from geochemistry and sr nd isotopes for the origin of albitite deposits from central sardinia italy major and trace element contents and sr nd isotope ratios were determined in albitite albitized and unaltered late variscan granitoid samples from the world class na feldspar deposits of central sardinia italy the albite deposit of high economic grade has geological textural and chemical features typical of metasomatic alteration affecting the host granitoids albitization locally accompanied by chloritization and epidotization was characterized by strong leaching of mg fe k and geochemically similar trace elements and by a significant increase of na ca and p were moderately leached in the most metasomatized rocks other major si ti ca and trace elements u th y and zr along with light lree and middle mree rare earth elements behaved essentially immobile at the deposit scale the nd isotope ratios 0 512098 to 0 512248 do not provide information on the emplacement age of the unaltered late variscan granitoids on the other hand their sr isotope ratios fit an errorchron of 274 29 ma 1 error in fair agreement with all published ages of sardinian variscan granitoids the very low rb content of albitized rocks precludes application of the rb sr radiometric system to determine the age of albitization the sm nd system is not applicable either because the 143nd 144nd ratios of albitized rocks and unaltered granitoids overlap the overlap confirms that sm and nd were substantially immobile during albitization on the other hand the measured 87sr 86sr ratios of the albitized rocks are appreciably lower than those of the unaltered host granitoids whereas their initial sr isotope ratios are higher this seems to suggest that a albitization was induced by non magmatic fluids rich in radiogenic sr and b albitization occurred shortly after the granitoid emplacement this conclusion is supported by nd isotopes because unaltered granitoids and albitites fit the same reference isochron at 274 ma the fluids acquired radiogenic sr by circulation through the lower paleozoic metasedimentary basement specifically it is estimated that sr supplied by the non carbonatic basement represents about 22 wt of total sr in albitite

the combined effect of sea level and supply during milankovitch cyclicity evidence from shallow marine δ18o records and sequence architecture adriatic margin the combination of sequence stratigraphy and multiproxy chronostratigraphic data including 18 o records unravels the record of milankovitch cyclicity through the past 400 ka on the adriatic margin chronostratigraphic data and stable isotope records from planktic and benthic foraminifera are derived from borehole prad1 2 a 71 m continuous core drilled on the western adriatic slope the cored interval encompasses the distal parts of stacked progradational wedges that are the main building blocks of 100 ka depositional sequences these sequences and their internal progradational units reflect a cyclic interplay between sea level and oceanographic circulation with relevant feedbacks on sediment supply fluctuations and regional long shore sediment dispersal calibration of slope units with isotope stratigraphy and direct slope shelf correlation indicates that two types of progradational clinoforms alternate in phase with the pattern of composite climate and sea level changes figured by 18 o records changes in clinoform geometry of the kind observed in the adriatic are consistent with a mechanism of switching supply from dominant advection on a flooded shelf during highstands to overall sediment starvation on a narrowed shelf during lowstands seismic and core data document that this mechanism is related to 100 and 20 ka cyclicity reflecting rearrangement of the oceanographic setting and sediment pathways during the last four glacial interglacial cycles

tidal currents in the st lawrence island region 1 vertical and spatial variability of tidal currents in the northern part of the bering sea near st lawrence island were examined using observations made at 17 new and historical current meter mooring locations the semidiurnal currents dominate over the diurnal currents semidiurnal currents exhibit a seasonal modulation with currents being somewhat stronger during the summer and fall when the density structure displays two layer stratification diurnal currents exhibit a weak semiannual modulation examination of the vertical structure of tidal currents shows that maximum semidiurnal currents are observed in the upper or middle layers down to a depth of about 20 m and below this depth the energy of the semidiurnal currents decreases rapidly however the energy of diurnal band currents remains almost constant with depth decreasing only in close proximity to the bottom rotary spectral analysis applied to the records shows further differences the m2 clockwise cw component of rotation dominates in the upper and middle water column but the counterclockwise component ccw dominates near the bottom interpretation of these observed results points to the different bottom boundary layers bbl for the cw and ccw motions in addition to the role of density stratification in organizing the bbl we compare results of a vertically averaged two dimensional model to the observationally derived tidal ellipse parameters and show that the barotropic formulation provides a first order description of the tidal regime within the domain

northward flow in the bering and chukchi seas the ocean circulation on the bering and chukchi sea shelves is investigated using a barotropic numerical model in the presence of the winter seasonal wind stress from the northeast observed northward transport through bering strait of 0 6 sv for the 8 month winter season 1981 1982 can be driven by a sea level difference of 0 4 m between the pacific and arctic oceans this sea level difference between basins is in agreement with hydrographic estimates in the absence of wind stress a 0 4 m sea level difference drives a northward transport through bering strait of 1 1 sv maximum transport through bering strait is geostrophically limited not frictionally or inertially limited major qualitative circulation features of the region are evident in the simulations westward intensification of the northward transport across the bering sea shelf is confirmed with the major transport occurring in the relatively deep gulf of anadyr in the absence of wind anadyr strait contributes 72 of the northward transport through bering strait with northeasterly winds there is a net clockwise circulation around saint lawrence island within the 20 m isobath norton and kotzebue sounds are little influenced by the general circulation northward transport in the chukchi sea bifurcates in the vicinity of point hope the predominant branch is directed toward the northwest in a broad canyon feature south of herald shoal and the balance becomes the alaskan coastal current between cape lisburne and point barrow

sea ice drift near bering strait during 1982 six argos ice stations were deployed in the northeastern bering sea in january and february 1982 four moved north through bering strait and made between one and five passes through the strait before they sank or were crushed by the ice and two remained in western norton sound and shpanberg strait net winds in the region were directed toward the southwest and were relatively uniform geographically net currents were northward and both mean velocity and mean speed were greater at bering strait than at shpanberg strait norton sound contributed ice northward through bering strait in the mean during winter and spring there was also a net divergence of ice near cap lisburne a theory for open shelf shallow water ice drift is developed that adds terms for bottom drag and stress feedback from the water column a stress analysis for a station that remained in western norton sound and shpanberg strait showed that bottom drag did not contribute significantly but that stress feedback from the accelerated shallow water current can be of the same order as the coriolis force however the analysis contained a residual possibly associated with internal ice stress coastal setup or unknown measurement error which was of roughly the same order as the wind and current stress

sedimentary response to climate and sea level changes during the past 400 ka from borehole prad1 2 adriatic margin 1 borehole prad1 2 was drilled in 186 m water depth on the upper slope of the central adriatic in the frame of profiles across mediterranean sedimentary systems promess1 european union funded project the borehole penetrated 71 2 m through a stratigraphic interval characterized by subparallel seismic reflections and uniform seismic units according to an age depth model based on several independent proxies including foraminifera and nannoplankton stratigraphy 18o curves and magnetostratigraphy the cored interval records marine isotope stages and substages mis from mis1 to the top of mis11 thus encompassing the past 370 ka prad1 2 therefore represents an unprecedented continuous record through the last four glacial interglacial cycles from a proximal continental margin setting where depositional sequences are typically composed of progradational units these progradational units record dominantly interglacial intervals mis5 mis7 and mis9 and appear composed of thicker highstand deposits hst formed during interstadials and thinner forced regression units fsst deposited during stadials above distinctive downward shift surfaces the development of thicker highstand deposits with a distinctively thicker bottomset reflects enhanced shore parallel advection any time sea level rise leads to the drowning of the adriatic shelf triggering the formation of dense water and vigorous cyclonic circulation this advection mechanism persisted in each cycle throughout the early phases of the sea level fall but progressively decreased as sea level fall proceeded approaching the maximum lowstand position when most of the shelf became exposed relative sea level falls punctuating interglacials within each 100 ka cycle were thus accompanied by a dearth in sediment flux on the outer shelf the alternation of hst and fsst progradational wedges with markedly different thickness and downlap geometry of their bottomsets is the most evident stratigraphic signature within each 100 ka depositional cycle of the impact on the shelf of higher frequency 20 ka sea level cycles and concomitant supply fluctuations

stratigraphic architecture and spatio temporal variability of high frequency milankovitch depositional cycles on modern continental margins an overview abstract this study is a review of quaternary milankovitch cycles as recorded on modern continental shelves worldwide on the background of the many existing examples we focus on selected case studies from mediterranean adriatic and tyrrhenian seas and atlantic gulfs of mexico and cadiz margins that represent general and peculiar characters of middle upper pleistocene sequences forming under the control of composite 100 and 20 ka milankovitch cycles the most pervasive stratigraphic pattern displayed by shelf deposits is referred to the 100 ka sea level cycle and consists of fairly uniform depositional sequences mostly composed by regressive deposits forming during the falling limb of the sea level curve these are generally classified as falling stage systems tract fsst and display a regressive facies architecture reflecting the dominant control of sea level on many margins fsst units may show slight though significant differences with respect to highstand systems tract hst and lowstand systems tract lst regressive units more closely reflecting environmental changes and the local variability of depositional systems in contrast with the theoretical and overall scale independent model developed to predict composite stratigraphic cycles and sequences the middle upper pleistocene stratigraphic record from numerous shelf settings shows a subdued signature of the higher frequency 20 ka milankovitch cyclicity however when detectable the 20 ka architectural pattern is characterized by a relatively greater spatial and temporal variability compared to 100 ka sequences this fact likely reflects the increasing importance of factors controlling the depositional environment e g seafloor morphology oceanographic regime sediment input and dispersal etc with respect to sea level change during the shorter intervals encompassed by 20 ka cycles on this basis two end member cases have been distinguished depending on the generation or not of high frequency sequence boundaries a prerequisite to qualify the higher frequency motifs as depositional sequences these two end members are comprehensive of the highly variable patterns displayed by middle upper pleistocene shelf sequences which in turn reflect the interplay between the geological setting the dominant sea level control and the effective response of sedimentary systems the variable stratigraphic patterns of milankovitch cycles represent conceptual and practical constraints as to the classification of high frequency quaternary sequences under the general schemes of the standard sequence stratigraphy model

seismic stratigraphy of late quaternary deposits from the southwestern black sea shelf evidence for non catastrophic variations in sea level during the last 10 000 yr abstract detailed interpretation of single channel seismic reflection and huntec deep tow boomer and sparker profiles demonstrates that the southwestern black sea shelf formed by a protracted shelf edge progradation since the miocene pliocene five seismic stratigraphic units are recognized unit 1 represents the last phase of the progradational history and was deposited during the last glacial lowstand and holocene it is divided into four subunits subunit 1a is interpreted as a lowstand systems tract 1b and 1c are interpreted as a transgressive systems tract and subunit 1d is interpreted as a highstand systems tract the lowstand systems tract deposits consist of overlapping and seaward prograding shelf edge wedges deposited during the lowstand and the subsequent initial rise of sea level these shelf edge wedges are best developed along the westernmost and easternmost segments of the study area off the mouths of rivers the transgressive systems tract deposits consist of a set of shingled shore parallel back stepping parasequences deposited during a phase of relatively rapid sea level rise and include a number of prograded sediment bodies including barrier islands beach deposits and thin veneers of seismically transparent muds showing onlap onto the flanks of older sedimentary features a number of radiocarbon dates from gravity cores show that the sedimentary architecture of unit 1 contain a detailed sedimentary record for the post glacial sea level rise along the southwestern black sea shelf these data do not support the catastrophic refilling of the black sea by waters from the mediterranean sea at 7 1 ka postulated by ryan pitman major shimkus maskalenko jones dimitrov gorur sakinc yuce mar geol 138 1997 119 126 ryan pitman touchstone book 1999 319 pp and ballard coleman rosenberg mar geol 170 2000 253 261

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

the changing architecture of sea level lowstand deposits across the mid pleistocene transition south evoikos gulf greece abstract on subsiding continental shelves the style of stacked coastal and deltaic progradational packages is directly dependent on relative sea level changes in the past 0 6 ma sea level change has been dominated by asymmetric 100 ka eustatic sea level cycles whereas the record of sea level changes in earlier pleistocene progradational sequences is less clear in a steadily subsiding basin in which accommodation balances sediment flux the depth of a eustatic lowstand determines the paleo depth of the deepest clinoform inflection point and the seaward limit of the erosional transgressive surface whereas the duration of a lowstand controls the amount of progradation that takes place we report high resolution seismic profiles of an exceptionally preserved coastal progradational sequence from a coastal embayment in the aegean sea that is subsiding at 100 m ma the seismic profiles show clinoforms of smaller amplitude and volume that were deposited before the 100 ka cyclic progradational units this contrasts with literature reports of complexity in progradational sequences at that time we assume that published stacked benthic foram o isotope records are a good proxy for the duration and a reasonable proxy for the amplitude of pleistocene eustatic sea level cycles the mis 6 5 eustatic sea level rise is recognised based on sedimentation rates from cores the underlying major progradational units are correlated with the long duration extreme lowstand 100 ka cycles of mis 6 12 and 16 changes in the elevation of lowstand inflection points in clinoforms are used to tentatively extend the record back to mis 38 by comparison with the benthic foram proxy the deposits of the higher and longer highstands of mis 25 31 and 37 are also recognised this record provides a testable template for future studies of short early pleistocene sections on land and raises questions of detail about parts of the published 18 o records it independently supports the recent evidence that the mid pleistocene transition was an abrupt event with an extreme lowstand in mis 22

seismic stratigraphy and quaternary sedimentary history of the northeast aegean sea abstract seismic profiles show that the upper quaternary recent stratigraphic architecture of the ne aegean sea is characterized by several vertically stacked depositional sequences which are developed within three ne sw trending basins the depositional sequences are separated from one another by prominent shelf crossing unconformities formed during periods of falling and low sea level and reworked further during the subsequent sea level rise by shoreface erosion each depositional sequence consists of a lower mainly parallel stratified subunit and an upper oblique to sigmoid oblique prograded subunit the lower subunit represents hemipelagic and prodeltaic deposition of the transgressive and early highstand systems tracts the upper subunit represents deltas of the forced regressive systems tract the chronology of the depositional sequences is constrained by radiocarbon and u th dates on cores an average sedimentation rate of 30 cm ka is calculated for basinal muds of the region correlations with global sea level curves based on oxygen isotope stratigraphy reveal that the seaward prograded delta sequences developed on a rapidly subsiding shelf during successive glacio eustatic sea level falls associated with late quaternary glaciations a set of paleogeographical maps shows changing basin configuration since 330 ka volumes of the depositional sequences compare well with the volumes of sediment estimated to have been eroded from the incised valleys of the tuzla karamenderes and dumbek rivers draining the biga peninsula

fault related fold growth and isostatic subsidence california channel islands in the northern channel islands of california preservation of paleo shoreline features both as uplifted landforms onshore and subsided depositional features offshore has allowed precise measurement of late quaternary fold growth relative to sea level and has helped to disentangle the relative contributions of tectonic forcing and isostatic response we precisely measured several hundred points on uplifted pleistocene coastal terraces of santa cruz and anacapa islands the elevations of which document anticlinal growth of the islands since at least 400 ka we also interpreted a dense grid of seismic reflection profiles that image a complex of eustatic lowstand deltas that record regional subsidence surrounding the uplifting structure we combined onshore uplift with offshore subsidence measurements to produce a quantitative mass balance of structural growth since 400 ka the data outlined above were then used to test the hypothesis that subsidence around the northern channel islands represents the flexural isostatic response to tectonic loading of the islands calculations of cumulative uplifted mass and cumulative subsided mass across the structure closely match the values predicted for density driven isostatic compensation and local flexural support although the wavelength of flexure predicted for the study area suggests that an additional component of flexural support may extend distally 10s of kilometers into the surrounding offshore basins in the northern channel islands isostatic subsidence is explicitly manifested because erosional mass removal is small because the crust here is relatively thin and weak and most importantly because sea level provides an absolute datum against which to measure vertical deformation an explicit treatment of the interplay between crustal thickening erosional denudation surface uplift and isostatic response helps to illustrate the conditions under which isostatic subsidence may or may not be a significant process where surface denudation rates approach the rate of rock uplift for example isostatic subsidence will approach zero in contrast failure to recognize isostatic subsidence in earthquake hazard studies can lead to order of magnitude errors in slip rate and hazard estimates

eustatic and tectonic control on deposition and lateral variability of quaternary regressive sequences in the adriatic basin italy abstract during the late pleistocene sea level variations related to glacio eustatic cycles induced the deposition of four regressive sequences on the western continental shelf of the adriatic basin the four sequences are bounded by erosion surfaces that formed during sea level fall sub aerial exposure of the shelf and subsequent sea level rise and erosional reworking the sequences and the erosion surfaces at their top numbered 1 4 top down are correlated on distances in the order of 300 km in the central and south adriatic core control on deposits of the most recent depositional sequence sequence 1 suggests that each sequence records a fourth order ca 100 120 kyr cyclicity of sea level change within each depositional sequence progradational units representing highstand to forced regression are dominant whereas transgressive deposits are absent or reduced in both thickness and lateral extent sequences are thus referred to as regressive sequences deposition during sea level fall occurred on an overall subsiding shelf through the dispersal of fine grained sediment supplied from the adjacent alpine and apennine chains this resulted in stacked forced regression deposits thick enough to survive complete removal during subsequent phases of sub aerial and marine erosion erosion and or non deposition were enhanced only where tectonic uplift and morphological highs further reduced the remaining accommodation space resulting in local thickness reduction or in the non preservation of the regressive sequences at larger scale thickness variability and depocenter distribution north and south of the gargano promontory an uplifted block bisecting the adriatic foreland reflect differential deposition and preservation of regressive deposits as a function of contrasting tectonic setting and resulting physiography of the shelf and upper slope

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

evolution and chronology of late pleistocene shelf perched lowstand wedges in the korea strait abstract detailed interpretation of high resolution seismic profiles from the korea strait has shown the existence of a complex of three stacked sedimentary sequences on the outer shelf the individual sequences consisting of prograding wedge are interpreted from internal structure and sediment data as a shelf perched lowstand wedge system related to alternating episodes of successive regression and transgression although the entire sequences have not been fully dated it is believed that the sequences were deposited during late pleistocene sea level lowstands repeated falls of sea level isotopic stages 8 6 and 2 resulted in the formation of lowstand sedimentary sequences during subsequent episodes of sea level rise isotopic stages 8 7 6 5 and 2 1 the sequences were reworked and draped by thin transgressive sands

observations of ice thickness and frazil ice in the st lawrence island polynya from satellite imagery upward looking sonar and salinity temperature moorings 1 for the 1999 winter this paper examines the behavior of the bering sea st lawrence island polynya using a combination of advanced very high resolution radiometer avhrr radarsat synthetic aperture radar sar meteorological data over winter moored upward looking sonars uls and seabird salinity temperature sensors we define a thermal ice thickness from the avhrr retrieval of ice surface temperature combined with meteorological observations and a heat flux model south of the island we compare the uls and thermal thicknesses for congelation and frazil ice when the satellites observe congelation ice over the ulss the uls and thermal ice thicknesses generally agree when sar observes langmuir plumes over the ulss which indicate frazil ice formation the ulss show scatterers at 5 20 m depths in the water column and the seawater temperatures are either within 0 01 c of freezing or are slightly supercooled this suggests that during frazil events crystals either nucleate at depth or are transported to depth by the langmuir circulation the combination of the sar imagery and uls observations also allow measurement of the pack ice advection velocity the polynya width and the downwind frazil accumulation thickness giving widths of 10 to 30 km and thicknesses of 0 1 0 2 m substitution of these observed values with the heat flux into the pease polynya model yields polynya widths that approximately agree with the observed