a self regulating model of bedrock river channel geometry 1 the evolution of many mountain landscapes is controlled by the incision of bedrock river channels while the rate of incision is set by channel shape through its mediation of flow the channel shape is itself set by the history of bedrock erosion this feedback between channel geometry and incision determines the speed of landscape response to tectonic or climatic forcing here a model for the dynamics of bedrock channel shape is derived from geometric arguments a normal flow approximation for channel flow and a threshold bed shear stress assumption for bedrock abrasion the model dynamics describe the competing effects of channel widening tilting bending and variable flow depth transient solutions suggest that channels may take 1 10 ky to adapt to changes in discharge implying that channel disequilibrium is commonplace if so landscape evolution models will need to include bedrock channel dynamics if they are to probe the effects of climate change

uranium distribution as a proxy for basin scale fluid flow in distributive fluvial systems we infer system scale fluid flow in the late jurassic salt wash fluvial succession sw usa by plotting uranium deposit distribution against sedimentological data using uranium distribution as a proxy for subsurface fluid flow more than 90 of uranium deposits in the salt wash occur where sandstone forms 40 55 and sand rich channel belts form 20 50 of the succession which coincides with changes in channel belt connectivity and gross scale architecture the paucity of uranium below these cut off values suggests that fluid flow is related directly to predictable downstream fining and facies variations in distributive fluvial systems supplementary material a summary table of location data key trends and the amalgamation ratio method is available at https doi org 10 6084 m9 figshare c 2849581

was the black sea catastrophically flooded in the early holocene abstract a catastrophic flooding of the black sea basin was proposed to have occurred during its reconnection to the ocean in the early holocene possible cultural consequences of the flood include the migration of neolithic farmers from around the black sea towards central europe as well as the creation of flood myths stratigraphic and paleo geomorphologic information from danube delta aided by radiocarbon ages on articulated mollusks constrain the level in the black sea before the marine reconnection to ca 30 m below the present sea level rather than 80 m or lower if the flood occurred at all the sea level increase and the flooded area during the reconnection were significantly smaller than previously proposed

the last reconnection of the marmara sea turkey to the world ocean a paleoceanographic and paleoclimatic perspective during the late glacial marine isotope stage 2 the marmara sea transformed into a brackish lake as global sea level fell below the sill in the dardanelles strait a record of the basin s reconnection to the global ocean is preserved in its sediments permitting the extraction of the paleoceanographic and paleoclimatic history of the region the goal of this study is to develop a high resolution record of the lacustrine to marine transition of marmara sea in order to reconstruct regional and global climatic events at a millennial scale for this purpose we mapped the paleoshorelines of marmara sea along the northern eastern and southern shelves at cekmece prince islands and imrali using data from multibeam bathymetry high resolution subbottom profiling chirp and ten sediment cores detailed sedimentologic biostratigraphic foraminifers mollusk diatoms x ray fluorescence geochemical scanning and oxygen and carbon stable isotope analyses correlated to a calibrated radiocarbon chronology provided evidence for cold and dry conditions prior to 15 ka bp warm conditions of the bolling allerod from 15 to 13 ka bp a rapid marine incursion at 12 ka bp still stand of marmara sea and sediment reworking of the paleoshorelines during the younger dryas at 11 5 to 10 5 ka bp and development of strong stratification and influx of nutrients as black sea waters spilled into marmara sea at 9 2 ka bp stable environmental conditions developed in marmara sea after 6 0 ka bp as sea level reached its present shoreline and the basin floors filled with sediments achieving their present configuration

catastrophic early holocene sea level rise human migration and the neolithic transition in europe abstract the collapse of the laurentide ice sheet and release of freshwater 8740 8160 years ago abruptly raised global sea levels by up to 1 4 m the effect on human populations is largely unknown here we constrain the time of the main sea level rise and investigate its effect on the onset of the neolithic across europe an analysis of radiocarbon ages and palaeoshoreline reconstruction supports the hypothesis that flooding of coastal areas led to the sudden loss of land favoured by early farmers and initiated an abrupt expansion of activity across europe driven by migrating neolithic peoples

lithologic and tectonic controls on bedrock channel form at the northwest himalayan front 1 recognition that channel form reflects a river s ability to erode rock and transport material has spawned stream power models that estimate incision patterns by approximating energy dissipation within a channel these models frequently assume that channel width scales as a power law with drainage area partly because drainage area is easily extracted from digital elevation models dems however this assumption is often confounded by local variations in rock strength and rock uplift rate that can cause channel constriction downstream here we investigate the morphological response to spatial changes in rock strength and rock uplift rate of 10 bedrock channels traversing the mohand range along the northwest himalayan front we present a new method to continuously measure and compare channel width slope and other hydraulic parameters that integrate satellite imagery and dem analysis our method corrects for an 13 overestimation of average channel gradient from a 90 m resolution dem that arises from short circuits of fine scale meanders we find that channels 1 narrow 1 km upstream from knickpoints formed by an increase in rock strength 2 adjust laterally more than vertically in response to downstream decreases rock erodibility and uplift rate and 3 meander where shear stresses are high and channel widths are low we attribute these results to a high ratio of sediment supply to transport capacity which enhances lateral erosion relative to vertical incision our results suggest that substrate strength and sediment supply substantially influence channel form and that channel width should be explicitly measured when interpreting tectonic signals from bedrock channel morphology

further evidence of abrupt holocene drowning of the black sea shelf a 1999 survey of the black sea continental shelf off the north central turkish seaport of sinop using a side scan sonar small remotely operated vehicles and a series of dredge lowerings located inspected and sampled an exposed high energy paleoshoreline at a depth of 155 m radiocarbon dating of mollusk shells collected from this ancient beach revealed that the marine flooding of the black sea took place between 7460 and 6820 yr b p all ages are reported in radiocarbon years not calendar years without correction for reservoir age or dendro calibration changing it from a lacustrine to marine environment this relic surface remained in contact with the bottom waters of the black sea for a long period of time before being draped by a thin layer of sapropel mud wood samples recovered from this same location were very well preserved and yielded dates as old as 3580 yr b p q 2000 elsevier science b v all rights reserved

the effect of spatial heterogeneities on geomorphic expression in a model of basin evolution spatial variability is a basic component of all natural systems the system being studied here is the topography of an evolving drainage basin spatially heterogeneous erosivity within the drainage basin influences the structure of the drainage network the roughness of small scale features and the overall appearance of the simulated topography the presence of heterogeneities does not simply blur and smear analytical relationships the heterogeneities themselves introduce new structure to the organization of the drainage basin three measures the slope area relationship the cumulative area relationship and the hypsometric distribution are all systematically affected by spatial heterogeneity we will demonstrate how and why these relationships are affected and also how different structures in the heterogeneities themselves are manifested in the resulting simulated topography

compilation of geophysical geochronological and geochemical evidence indicates a rapid mediterranean derived submergence of the black sea s shelf and subsequent substantial salinification in the early holocene abstract our knowledge of rate and processes in which semi enclosed environments alternate from lacustrine to marine is commonly limited because of the paucity of specific proxies for sea level and salinity here we investigate the timing rate and key mechanisms involved in the transformation of the previously isolated black sea lake to the modern partly enclosed marine sea using a suite of geophysical geochemical and geochronological methods cores were collected in transects across shelves of ukraine romania bulgaria and turkey biogenic carbonate from these cores was analyzed for radiocarbon and strontium oxygen and carbon isotopes strontium results indicate that the submergence of the black sea shelf at 9300 calendar years bp was caused by the ingress of mediterranean water and was abrupt taking radiocarbon years are calibrated to calendar years by tuning the oxygen and carbon isotope composition of the mollusk record to that of the u th dated sofular cave stalagmites the match shows a reduction of the lake s prior high reservoir age accompanying the inflow of the mediterranean water in 900 years the salinity reached a threshold that excluded all previous black sea lacustrine fauna these results imply that any substantial postglacial submergence of the black sea shelves did not occur prior to entry of mediterranean water

major shifts in nutrient and phytoplankton dynamics in the north pacific subtropical gyre over the last 5000 years revealed by high resolution proteinaceous deep sea coral δ15n and δ13c records abstract the north pacific subtropical gyre npsg is the largest continuous ecosystem on earth and is a critical component of global oceanic biogeochemical cycling and carbon sequestration we report here multi millennial scale sub decadal resolution records of bulk stable nitrogen 15 n and carbon 13 c isotope records from proteinaceous deep sea corals data from three kulamanamana haumeaae specimens from the main hawaiian islands extend the coral based time series back 5000 yrs for the npsg and bypass constraints of low resolution sediment cores in this oligotrophic ocean region we interpret these records in terms of shifting biogeochemical cycles and plankton community structure with a main goal of placing the extraordinarily rapid ecosystem biogeochemical changes documented by recent coral records during the anthropocene in a context of broader late holocene variability during intervals where new data overlaps with previous records there is strong correspondence in isotope values indicating that this older data represents a direct extension of anthropocene records these results reveal multiple large isotopic shifts in both 15 n and 13 c values similar to or larger in magnitude to those reported in the last 150 yrs this shows that large fluctuations in the isotopic composition of export production in this region are not unique to the recent past but have occurred multiple times through the mid to late holocene however these earlier isotopic shifts occurred over much longer time intervals millennial vs decadal timescales further the 15 n data confirm that the extremely low present day 15 n values recorded by deep sea corals 8 are unprecedented for the npsg at least within the past five millennia together these records reveal centennial to millennial scale oscillations in npsg biogeochemical cycles further these data also suggest a number of independent biogeochemical regimes during which 15 n and 13 c trends were synchronous similar to recent coral records or distinctly decoupled we propose that phytoplankton species composition and nutrient source changes are the dominant mechanisms controlling the coupling and de coupling of 15 n and 13 c values likely primarily influenced by changing oceanographic conditions e g stratification vs entrainment the decoupling observed in the past further suggests that oceanographic forcing and ecosystem responses controlling 15 n and 13 c values of export production have been substantially different earlier in the holocene compared to mechanisms controlling the present day system

slip rate at the north eastern front of the qilian shan china terra nova 22 180 187 2010 abstract we constrain the slip rate for the frontal thrust of the qilian shan north eastern tibet by combining structural investigations satellite imagery topographic profiling and 10be exposure dating we surveyed two terrace levels and from each we took 6 7 samples in profiles dug to depths of 2 m these constrain inheritance and determine the precise ages of abandonment of the terraces 29 9 7 8 ka for the upper terrace and 16 3 4 4 ka for the lower one topographic profiles with a determination of burial of the footwall by sediment yield offsets of the surfaces of 96 4 4 4 and 40 1 2 8 m the average vertical rate is 2 8 1 3 mm a 1 with a horizontal slip rate of 2 5 mm a 1 this rate is higher than those determined farther north on similar structures but is consistent with the gps velocity field and accounts for roughly half of the geodetic shortening across the qilian shan

coastal barium cycling at the west antarctic peninsula barium cycling in the ocean is associated with a number of processes including the production and recycling of organic matter freshwater fluxes and phenomena that affect alkalinity as a result the biogeochemical cycle of barium offers insights into past and present oceanic conditions with barium currently used in various forms as a palaeoproxy for components of organic and inorganic carbon storage and as a quasi conservative water mass tracer however the nature of the oceanic barium cycle is not fully understood particularly in cases where multiple processes may be interacting simultaneously with the dissolved and particulate barium pools this is particularly the case in coastal polar regions such as the west antarctic peninsula where biological drawdown and remineralisation occur in tandem with sea ice formation and melting glacial meltwater input and potential fluxes from shelf sediments here we use a high precision dataset of dissolved barium bad from a grid of stations adjacent to the west antarctic peninsula in conjunction with silicic acid si oh 4 the oxygen isotope composition of water and salinity measurements to determine the relative control of various coastal processes on the barium cycle throughout the water column there is a strong correlation between bad and si oh 4 present in deeper samples but nevertheless persists significantly in surface waters this indicates that the link between biogenic opal and barium is not solely due to barite precipitation and dissolution at depth but is supplemented by an association between bad and diatom tests in surface waters possibly due to barite formation within diatom dominated phytodetritus present in the photic zone sea ice meltwater appears to exert a significant secondary control on barium concentrations likely due to non conservative biotic or abiotic processes acting as a sink for bad within the sea ice itself or sea ice meltwater stimulating non siliceous productivity that acts as a bad sink meteoric water input conversely exerts little or no control on local barium levels indicating that glacial meltwater is not a significant coastal source of barium to the west antarctic peninsula shelf waters

channel changes in badlands stripping of the vegetation and soil from a 13 hectare site in virginia underlain by coastal plain sediments created a rapidly evolving badland topography two types of channels developed 1 sand bed alluvial channels were graded to transport the bed material load supplied from slope erosion with available runoff but they also generally eroded their beds slowly and 2 steeper bedrock floored channels incised rapidly in bedrock channels the erosion rate was proportional to the 4 9ths power of drainage area and the 2 3rds power of gradient these exponents are consistent with a model in which the erosion rate is proportional to the bed shear during high flows due to rapid mass wasting and reduced runoff the alluvial channels became as much as 50 steeper during the winter than the summer with an attendant yearly cycle of winter aggradation and summer entrenchment the gradients their seasonal variability and their downstream hydraulic geometry were consistent with the predictions of total load transport formulas for sand beds and high loads the hydraulic geometry of alluvial channels in the virginia badlands were similar to that on the morrison formation in the western united states

late glacial to holocene paleoenvironmental evolution of the black sea reconstructed with stable oxygen isotope records obtained on ostracod shells high resolution stable oxygen isotope d 18 o on ostracod shells xrf scanning and bulk grain size data obtained on a transect of 6 gravity cores from the continental slope in the northwestern black sea give new insight into the hydrological evolution of the black sea since the last glacial maximum lgm stable climatic conditions during the lgm were followed by a series of meltwater pulses between 18 and 15 5 kyr bp that resulted in temporary isotopic depletion of the black sea waters subsequently steadily increasing d 18 o values in all cores are mainly caused by isotopically enriched precipitation at the onset of the allerod bolling warm period a comparison of the major trends in d 18 o at different water depths suggests evaporation driven deep water formation since 14 5 kyr bp while the two shallowest cores from 168 and 465 m water depth were under the influence of increased warming in the upper water column since 14 5 and 12 5 kyr bp respectively the core from 168 m depth seems to be additionally influenced by freshwater input of the danube this core provides a high resolution record from the younger dryas allerod boundary and suggests that a nao like climate mode was governing the interannual variability in the run off of the danube which implies that this climate mode has been a persistent climatic feature over central europe the inflow of saline mediterranean waters occurs between 9 and 8 kyr bp where a merging of all d 18 o records signals an initial homogenisation of the water column

a post younger dryas black sea regression identified from sequence stratigraphy correlated to core analysis and dating the north western black sea shelf is the widest continental shelf of the black sea where the danube delta prodelta system includes important records on the black sea water level fluctuations this study integrates newly acquired high resolution single channel seismic reflection profiles and calypso piston cores recovered along a transect extending from the danube delta deep into its deep sea fan the correlated results provide information on the late quaternary architecture of the danube black sea shelf and on the role of global glacio eustatic fluctuations on the building of the danube delta prodelta the sedimentary sequences in the black sea are strongly affected by water level changes for the whole duration of late glacial holocene period the level of the black sea was controlled by the regional climate modifications rather than the global eustatic changes the seismic sequences recognized on a very high resolution seismic profile were dated by two calypso piston cores based on the obtained data during the last glacial maximum the black sea was a land locked lake with the level below 120 m in the course of the deglaciation the lake level rose up to 40 m which is confirmed by occurrence of the prodelta lobes formed after the rise in water level originated from the melt water following the younger dryas 11 000 8500 c 14 bp there occurred a new level lowering to the level of 100 m identified by the forced regression deposits recorded on the romanian shelf this last lowstand previously recognized by a pronounced shoreline with a characteristic beach profile and a belt of coastal dunes is also indicated by the prodelta at 100 m depth all these coastal features as well as the incised anastomosed channel system remained preserved on the shelf resulting from a rapid ultimate transgression starting immediately after 8500 c 14 bp c 2010 elsevier ltd and inqua all rights reserved

climate warming during antarctic ice sheet expansion at the middle miocene transition during the expansion of the antarctic ice sheet about 14 million years ago sea surface temperatures in the southern ocean rose climate model simulations suggest that this short lived warming was related to changes in ocean atmosphere circulation induced by the growth of the ice sheet

an abrupt drowning of the black sea shelf abstract during latest quaternary glaciation the black sea became a giant freshwater lake the surface of this lake drew down to levels more than 100 m below its outlet when the mediterranean rose to the bosporus sill at 7 150 yr bp 1 saltwater poured through this spillway to refill the lake and submerge catastrophically more than 100 000 km2 of its exposed continental shelf the permanent drowning of a vast terrestrial landscape may possibly have accelerated the dispersal of early neolithic foragers and farmers into the interior of europe at that time

orographic precipitation and the relief of mountain ranges 1 the influence of climate on the relief of mountain ranges has long been supposed but has received little quantitative investigation the simplified system of a longitudinal river profile in a bedrock channel coupled to a physically based model of orographic precipitation is used to explore how orographically influenced patterns of precipitation affect the relief of fluvially sculpted mountain ranges it is shown that the impact on the orography depends on the nature of the precipitation regime significant changes in relief also occur for imposed temperature changes of realistic magnitude although the ability of the relief to respond to any given change depends sensitively on its response time and the timescale of the forcing

paleo evolution of the black sea watershed sea level and water transport through the bosporus straits as an indicator of the lateglacial holocene transition the paleo evolution of the black sea level during the lateglacial holocene transition is still unclear which motivates us to provide new estimates for that period based on the analysis of water budget hydrological conditions in the black sea catchment area are reconstructed here using water balance equation available data and constraints based on simple theory relating the runoff ratio with climatic characteristics in order to estimate the impact of the aridity of climate we consider two alternative scenarios 1 climate change under constant in time gradient in precipitation and evaporation over land and sea and 2 climate change accounting for changes in the horizontal distribution of precipitation and evaporation hydrological data are compiled from available present day data and paleo observations a number of sensitivity experiments is carried out revealing that the hydrological conditions in the black sea watershed should have evolved towards a very arid climate similar to the present day climate in the caspian sea area in order to initiate a drop of sea level of 100 m below the sill depth of the bosporus straits as speculated in some recent research estimates of sea level changes reveal a qualitative agreement with the coast line evolution inferred from paleo observations the younger dryas draw down of the black sea starts at about 13 3 to 13 kyr bp with a maximum low stand of 104 m at 11 5 kyr bp in an arid climate scenario the sea level reaches the outlet at about 8 8 to 7 4 kyr bp approximately at that time mediterranean sea level was about 10 m higher making flooding events of the black sea possible however the nature and exact timing of the holocene reconnection depends also on other not well known factors one of them is the bosporus sill depth motivating further research in this field estimates of the water transport through the bosporus straits are also provided for the time of lateglacial holocene transition

the late holocene evolution of the black sea a critical view on the so called phanagorian regression abstract throughout its geologic history the black sea experienced major sea level changes accompanied by severe environmental modifications including geomorphologic reshaping the most spectacular changes were driven by the quaternary glaciations and deglaciations that reflect responses to milankovitch cycles of 100 and 20 ky periodicity major sea level changes were also considered for a shorter and more recent cyclicity the concept of the phanagorian re and transgression cycle supposedly with a minimum sea level stand of 5 6 m below its present position in the middle of the 1st millennium bc was established in 1963 by fedorov for the black sea region it was based on archaeological and palaeogeographical research conducted around the ancient greek colonies of the cimmerian bosporus in particular at the name giving site of phanagoria where underwater prospection had revealed the presence of a large number of submerged relics of the classical greek era analyses of sediment cores as well as 14c dated fossil coastal bars in the western and southern parts of taman peninsula show that contemporary coastal bars are related to different sea levels the dissymmetry can reach up to 6 m around 500 bc this and more evidence from drill cores confirms that on taman peninsula many of the apparent sea level changes are tectonically induced the subsidence may have been initiated by the release of gas from mud volcanoes inherited along anticline axes other observations around the black sea confirm that submerged archaeological sites correspond to areas where subsidence has taken places while the so called holocene highstand said to have been located above the present day sea level is associated with uplift areas triggered by the ongoing caucasus orogeny recent oceanographic research carried out in the black sea area shows that since the black sea was reconnected with the mediterranean sea i e 7500 14c bp at the latest both marine water bodies have been in equilibrium this fact and arguments from archaeology history hydrodynamics etc lead us to question the existence of the phanagorian regression it is important to note that none of the sea level curves established for the eastern mediterranean shows a comparable regression transgression cycle of several metres during the 1st millennium bc

northeastward growth of the tibet plateau deduced from balanced reconstruction of two depositional areas the qaidam and hexi corridor basins china we address the problem of late cenozoic uplift erosion and growth of northeastern tibet by reconstructing from isopach maps and drill holes the volumes and masses of sediments deposited in the qaidam and hexi corridor basins since 35 myr ago the mass budget is based on simple geometrical assumptions such as regional similarity of the thickness ratios between strata of different ages in the qaidam where our record extends back to the oligocene the budget shows a huge rise of the accumulation rates after the beginning of the pliocene 5 3 ma the early pliocene seems to be the period of maximum deposition with accumulation rates in excess of 1 mm yr 1 2 7 kg m 2 yr 1 of compacted rocks throughout the basin there also seems to be a southeastward shift of the largest depocenters between the upper pliocene 3 4 1 6 ma and the quaternary in the hexi corridor sedimentation is confined to small foreland flexural depressions associated with the frontal thrusts of the qilian shan and occurs at an average rate one order of magnitude smaller than in the qaidam basin the accumulation rate is maximum in the quaternary the sedimentation history appears to support a plateau building mechanism resulting from the combination of two geologicallly common processes crustal scale thrusting and sedimentary basin infilling the time needed to completely fill the qaidam basin and make its catchment a plateau closely resembling that of the highest part of tibet qangtang is of the order of 9 myr the mechanism now at work north of the kunlun which involves rapid infilling of broad flat areas separated by relatively narrow mountain ranges has thus probably been important in producing the high smooth topography that characterizes much of central tibet

quaternary paleoclimatic paleoceanographic and tectonic evolution of the marmara sea and environs strabo 63 bc 21 ad book 1 3 4 jones 1954 themarmarasea fig 1 hasalwaysattractedinterestasagreatgatewaylinkingtheblackseato the eastern mediterranean sea through a net work of narrow straits with shallow sills straitsof bosphorus istanbul and dardanelles c anakkale forthepast2500 3000yr informa tion about surface and bottom currents depthsoundings and sea level variation were crucialforsafenavigationacrossthesestraitsbysea far ingpeopleandexplorers thusconstitutingama jorstrategicassetandyieldingenormouseconom icandpoliticaladvantages throughoutantiquity sailors knew that the bottom waters across thestraits of dardanelles and bosphorus owednorthward and utilized this knowledge to sailintothemarmaraseaandblackseabyloweringlargebasketswithweightsintothenorth owingmediterranean water to counteract the strongsouth directed surface out ow from the blacksea systematic scienti c investigations in the mar marasearegionstartedinthelate19thcentury the rstbathymetricsurveyrevealedthepresenceof three deep basins and their intervening ridges andrussow 1901 p nar 1943 subsequentlyproposedthatasinglefaulttransectedthesethreebasins extending from the izmit bay in the eastto the gulf of saros in the west pfannensteil 1944 noted the rhombohedric shape of thedeepmarmaraseabasinsandproposedthattheridgesseparatingthebasinsrepresenthorstblocksbounded by normal faults healsosuggested inadditiontothestraitofbosphorus thepresenceofasecondchannel thesakaryabosphorus fig 1 which connected the black sea to the mar mara sea during the quaternary in 1948 ketinpublished his renowned paper revealing the truenatureofthenorthanatolianfaultasoneoftheworld slargest active intra continental strike slipfaults ketin 1948 pavoni 1961 and kopp etal 1969 proposedthataseriesofsyntheticand

rotating hydraulics and upstream basin circulation the flow in a source fed f plane basin drained through a strait is explored using a single layer reduced gravity shallow water numerical model that resolves the hydraulic flow within the strait the steady upstream basin circulation is found to be sensitive to the nature of the mass source uniform downwelling localized downwelling or boundary inflow in contrast the hydraulically controlled flow in the strait is nearly independent of the basin circulation and agrees very well with the gill theory solution obtained using the strait geometry and the numerically determined average potential vorticity in the strait entrance region this gill solution however gives a unique value of the upstream boundary layer flux splitting that does not agree with any of the full numerical solutions the coupled basin strait system is shown to select an average overflow potential vorticity corresponding to the gill solution with maximum fluid depth on the strait boundaries this state also corresponds to one of maximal upstream basin potential energy this result is robust to changes in the basin geometry strait characteristics the dissipation parameter linear drag and the net mass flux the nonunique relation between basin conditions and overflow transport is significant with regard to deep overflow transport monitoring it is shown that the potential vorticity selection leads to overflow or weir transport relations that are well approximated by the zero potential vorticity theory however accurate estimates of the transport can only be obtained if conditions within the strait entrance region and not the basin are used

young danube delta documents stable black sea level since the middle holocene morphodynamic paleogeographic and archaeological implications new radiocarbon and optical dates show that the holocene danube delta started to build out of a black sea embayment 5200 yr ago delta lobe development phases differ by as much as 5 k y from previously proposed ages the new chronology allows for a better understanding of the danube delta paleogeography includ ing the demise of istria the main ancient greek roman city in the region prior reconstructions of sea level in the black sea inferred fluctuations to 15 m in range however stratigraphy of beach ridg es in the delta shows that the relative black sea level for the past 5 k y was stable in the danube delta region within 2 m and 1 5 of the current level hydroisostatic effects related to a proposed catastrophic reconnection of the black sea to the world ocean in the early holocene may have been responsible for the sea level reaching the highstand earlier than estimated by models the new sea level data suggest that submergence at several ancient settle ments around the black sea may be better explained by local fac tors such as subsidence rather than by basin wide sea level fluctuations

postglacial connection of the black sea to the mediterranean and its relation to the timing of sapropel formation the opening of the connection between the mediterranean and black seas as sea level rose above the bosporus sill has long been associated with the formation of the most recent holocene sapropel deposit s1 in the eastern mediterranean but the mechanism has remained elusive we present a model for the opening of the black sea based on hydraulics arguments which demonstrates that increased freshwater flux out of the black sea began 500 1000 years after sea level reached sill depth and that the timescale for the increased freshwater flux that drained the freshwater reservoir of the black sea is about 2500 3500 years we argue that the increased freshwater discharge out of the black sea would lead to decreased deep water formation and higher productivity in the surface waters in the eastern mediterranean two conditions generally associated with sapropel formation the delay in increased freshwater flux after the opening of the black sea and the period of increased freshwater discharge appear to match the onset and duration of sapropel deposits in the eastern mediterranean

bedrock channels response to differential rock uplift in eastern qilian mountain along the northeastern margin of the tibetan plateau abstract the response of bedrock channels to differential rock uplift in eastern qilian mountain significantly dictates the topographic evolution of the northeastern margin of the tibetan plateau our ability to extract tectonic information directly from channel profiles mainly depends on the calibration of incision processes laws here we assess the degree and nature of channels response to differential rock uplift in eastern qilian mountain base on an empirical calibration of the shear stress incision model utilizing field survey data lithologic resistance sediment flux discharge and channel width parameters calibration indicates that channels developed in the high mountain zone hmz show an approximate 1 1 1 3 times increase in erosion coefficient k than in the low mountain zone lmz mainly attributing to the adjustments of channel width and discharge moreover profiles analysis reveals a systematic geographic distribution of steepness indices and concavity in this area the regions of high and low steepness indices are spatially associated with the higher high rock uplift rates and lower low rock uplift rates parts of landscape respectively suggesting that the spatial distribution pattern of channel steepness mainly reflects the differential rock uplift channels with abnormal high concavity values apparently associate with the major thrust faults suggesting that the differential rock uplift is controlled by the thrusting of major active faults combining parameters calibration with profile analysis between the two zones the possible increase in rock uplift rates is 2 4 times in the hmz than in the lmz indeed

geomorphic limits to climate induced increases in topographic relief recognition of the potential for strong dynamic coupling between atmospheric and tectonic processes has sparked intense cross disciplinary investigation and debate on the question of whether tectonics have driven long term climate change or vice versa it has been proposed that climate change might have driven the uplift of mountain summits through an isostatic response to valley incision because isostasy acts to compensate mean elevations the debate hinges on the question of whether climate change can significantly increase topographic relief or more precisely increase the volume of missing mass between summits and ridges here we show that in tectonically active mountain ranges geomorphic constraints allow only a relatively small increase in topographic relief in response to climate change thus although climate change may cause significant increases in denudation rates potentially establishing an important feedback between surficial and crustal processes neither fluvial nor glacial erosion is likely to induce significant isostatic peak uplift

northern sourced water dominated the atlantic ocean during the last glacial maximum increased carbon sequestration in the ocean subsurface is commonly assumed to have been one of the main causes responsible for lower glacial atmospheric co2 concentrations remineralized carbon must have been stored away from the atmosphere for thousands of years yet the water mass structure accommodating such increased carbon storage continues to be debated here we present new sediment derived bottom water neodymium isotope records that allow fingerprinting of water masses and provide a more complete picture of the atlantic meridional overturning circulation geometry during the last glacial maximum these results suggest that the vertical and meridional structure of the atlantic water mass distribution only experienced minor changes since the last ice age in particular we find no compelling evidence supporting glacial southern sourced water substantially expanding to shallower depths and farther into the northern hemisphere than today which had been previously inferred from stable carbon isotope 13c reconstructions we argue that depleted 13c values observed in the deep northwest atlantic do not necessarily indicate the presence of southern sourced water instead these values may represent a northern sourced water mass with lower than modern preformed 13c values that were further modified downstream by increased sequestration of remineralized carbon facilitated by a more sluggish glacial deep circulation corroborating previous evidence

evaluating the controls of shear stress sediment supply alluvial cover and channel morphology on experimental bedrock incision rate 1 we explored the dependence of experimental bedrock erosion rate on shear stress bed load sediment flux alluvial bed cover and evolving channel morphology we isolated these variables experimentally by systematically varying gravel sediment flux qs and water discharge qw in a laboratory flume gradually abrading weak concrete bedrock all else held constant we found that 1 erosion rate was insensitive to flume averaged shear stress 2 erosion rate increased linearly with sediment flux 3 erosion rate decreased linearly with the extent of alluvial bed cover and 4 the spatial distribution of bed cover was sensitive to local bed topography but the extent of cover increased with qs qt where qt is flume averaged transport capacity once critical values of bed roughness and sediment flux were exceeded starting from a planar geometry erosion increased bed roughness due to feedbacks between preferential sediment transport through interconnected topographic lows focused erosion along these zones of preferential bed load transport and local shear stresses that depended on the evolving bed morphology finally continued growth of bed roughness was inhibited by imposed variability in discharge and sediment flux due to changes in spatial patterns of alluvial deposition and impact wear erosion was preferentially focused at lower bed elevations when the bed was cover free but was focused at higher bed elevations when static alluvial cover filled topographic lows natural variations in discharge and sediment flux may thus stabilize and limit the growth of roughness in bedrock channels due to the effects of partial bed cover

hydraulic calculations of postglacial connections between the mediterranean and the black sea a series of simple hydraulic calculations has been performed to examine some of the questions associated with the reconnection of the black sea to the mediterranean through the turkish strait system during the holocene ryan et al s catastrophic flood scenario whereby the erosive power of the marine in fluxes initiated after eustatic sea level reached the sill depth opened up the bosphorus allowing saline water to pour into the black sea and filling it on a short time scale is examined the calculations show that although it might be possible to fill the palaeo black sea within the order of a decade a 1 2 year filling time scale is not physically possible a hydraulic model is also used to examine the more traditional connection hypothesis of near continuous freshwater outflow from the black sea with a slowly increasing saline inflow from the mediterranean beginning around 8 9 kyr bp the model considers two forms for the structure of the bosphorus a shallow sill as seen today and a deep sill associated with no sediments filling the 100 m gorge above the bedrock in the strait sensitivity experiments with the hydraulic model show what possible strait geometric configurations may lead to the black sea reaching its present day salinity of 18 psu salinity transients within the black sea are shown as a function of time providing for values that can be validated against estimates from cores to consider a deep non sediment filled bosphorus 100 m deep the entry of mediterranean water into the sea of marmara after 12 0 kyr bp is examined a rapid entry of marine water into the sea of marmara is only consistent with small freshwater fluxes flowing through the turkish strait system smaller than those of the present day by a factor of at least 4 such a small freshwater flux would lead to the salinification of the black sea being complete by an early date of 10 2 9 6 kyr bp thus the possibility of a deep bosphorus sill should be discounted

constraints on black sea outflow to the sea of marmara during the last glacial interglacial transition new cores from the upper continental slope off romania in the western black sea provide a continuous high resolution record of sedimentation rates clay mineralogy calcium carbonate content and stable isotopes of oxygen and carbon over the last 20 000 yr in the western black sea these records all indicate major changes occurring at 15 000 12 800 8400 and 7100 yr before present these results are interpreted to reflect an evolving balance between water supplied by melting glacial ice and other river runoff and water removed by evaporation and outflow the marked retreat of the fennoscandian and alpine ice between 15 000 and 14 000 yr is recorded by an increase in clays indicative of northern provenance in black sea sediments a short return toward glacial values in all the measured series occurs during the younger dryas cold period the timing of the first marine inflow to the black sea is dependent on the sill depths of the bosporus and dardanelles channels the depth of the latter is known to be 80 5 m which is consistent with first evidence of marine inundation in the sea of marmara around 12 000 yr the bedrock gorge of the bosporus reaches depths in excess of 100 m relative to present sea level though it is now filled with sediments to depths as shallow as 32 m two scenarios are developed for the connection of the black sea with the sea of marmara one is based on a deep bosporus sill depth effectively equivalent to the dardanelles and the other is based on a shallow bosporus sill less than 35 m in the deep sill scenario the black sea s surface rises in tandem with the sea of marmara once the latter connected with the aegean sea and black sea outflow remains continuous with inflowing marine water gradually displacing the freshwater in the deep basin the increase in the 18 o of mollusk shells at 12 800 yr and the simultaneous appearance of inorganic calcite with low 18 o is compatible with such an early marine water influx causing periodic weak stratification of the water column in the shallow sill scenario the black sea level is decoupled from world sea level and experiences rise and fall depending on the regional water budget until water from the rising sea of marmara breaches the shallow sill in this case the oxygen isotope trend and the inorganic calcite precipitation is caused by increased evaporation in the basin and the other changes in sediment properties reflect climate driven river runoff variations within the black sea watershed the presence of saline ponds on the black sea shelf circa 9600 yr support such evaporative drawdown but a sensitive geochemical indicator of marine water one that is not subject to temperature salinity or biological fractionation is required to resolve whether the sill was deep or shallow

dating of erosion surface and terraces in the eastern qilian shan northwest china the actively deformed foreland of eastern qilian shan mountains contains well preserved geomorphic features such as erosion surfaces river terraces and tectonically uplifted alluvial fans providing suitable archives for research on regional tectonic activities and palaeoclimatic changes these geomorphic surfaces are well dated by using a combination of magnetostratigraphy electron spin resonance thermoluminescence infra red stimulated luminescence radiocarbon dating and correlation with the well established loess palaeosol sequences of china our results show that the erosion surface formed about 1 4 ma ago and the age of river terraces is 1 24 ma 820 860 ka 780 ka 420 440 ka 230 250 ka 140 ka 60 ka and 10 ka respectively valley incision rates of e 0 09 0 25 m ka 1 have been identified the repetitive stratigraphic and geomorphic pattern of these terraces indicates the fluvial sedimentation incision cycles are tightly associated with the 100 ka glacial interglacial climatic cycles copyright c 2006 john wiley sons ltd

flow water mass changes and hydraulics in the bosphorus 1 using average sections along the bosphorus taken in september 1994 with a loosely tethered profiler and an acoustic doppler current profiler gregg et al 1999 found the exchange flow between the sea of marmara and the black sea to be quasi steady but far from satisfying the hydraulic control conditions for two layered flows here we examine synoptic sections and use images from an acoustic backscatter system to provide the first detailed look at the flow and water mass changes in the bosphorus and to assess how well the flow satisfies the hydraulic assumptions thirty kilometers long 28 100 m deep and 0 75 3 km wide the bosphorus has bathymetry for more complex than that used in analytic or numerical models of exchange flows the particulars affect dynamics in important ways for instance owing to changes in channel shape the narrowest section known as the contraction is not also the minimum in cross sectional area rather it is a transition between the wider northern half and the narrower southern half of the strait and some places south of the contraction have slightly smaller areas sharp bends occur throughout the strait and often produce flow separations as well as directing upper and lower flows to opposite sides of the channel never 28 of the water column the interface thickens to 75 in the southern half of the strait as a result of intense mixing downstream of the contraction as a consequence of the strong mixing and numerous flow separations we conclude that the exchange flow may be at least partly controlled by friction instead of being a simple hydraulic flow

mathematical modeling of black sea level change for the last 20000 years abstract a mathematical model of the black sea level change for the last 20 000 years is presented in this paper based on the equations of viscous incompressible fluid motion according to navier stokes sen venans and the equation of water balance in the sea the solution of the differential equations shows that the black sea level has been generally rising due to glacier melting and increase of freshwater balance in the late pleistocene water which was flowing into the black sea did not have time to fully flow into the marmara sea because water was flowing through the long and very narrow canyon which the bosphorus strait was then water accumulating in the black sea increased the sea level and increased the slope of the surface of river in the strait towards the marmara sea when the level of the world ocean rose above river level the strait began to form increasing depth caused excessive water to flow from the black sea as a result of regression the black sea level approached the marmara sea level and the global oceanic transgression of the two seas began continuing to the present when the depth of the strait was 12 15 m the penetration of the marmara sea s dense water into the black sea occurred water discharge in the counterflow was increasing when the ocean level was rising the calculations showed that secondary fluctuations of the black and marmara seas levels greater than 50 cm were theoretically impossible during the holocene as the deep strait allowed the possibility of intensive flow toward either the black or marmara sea when the value of the freshwater balance is positive the regression of the black sea level below marmara sea level is theoretically impossible vertical movement of earth crust can modify the shape of the eustatic sea level curves a method allows calculation of the eustatic sea level course using the known local curves the eustatic mediterranean sea level change and world ocean level change are calculated using nine local mediterranean sea level change curves tectonic components of the nine local curves were calculated an assessment of the method s accuracy was made

testing the physical oceanographic implications of the suggested sudden black sea infill 8400 years ago 1 we apply a shock capturing numerical model based on the single layer shallow water equations to an idealized geometry of the black sea and the sea of marmara in order to test the implications of a suggested sudden black sea infill 8400 years ago the model resolves the two dimensional flow upstream and downstream of the hydraulic jump provoked by the cascade of water from the sea of marmara into the black sea which would occur during a sudden black sea infill the modeled flow downstream of the hydraulic jump in the black sea would consist of a jet that is in part constrained by bathymetric contours guided by the bosporus canyon the modeled jet reaches depths of up to 2000 m and could explain the origin of the sediment waves observed at this depth at a late stage of the infill the modeled jet is attached to the coast and might account for the course of a submerged channel at the mouth of the bosporus the preservation of continuous barrier washover lagoonal fill systems occurring on the black sea shelf is however not easily reconcilable with the large flows over the southwest black sea shelf predicted by the model intensified flow in the upstream basin sea of marmara is restricted to the immediate vicinity of the bosporus suggesting that a sudden reconnection need not have disturbed sediments in the wider sea of marmara

earth science river incision revisited a data set compilation suggests that measurements of river erosion into rock depend on the observation timescale casting doubt on whether terraces and other incised landforms faithfully record changes in climate and tectonics

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

hemispherically asymmetric trade wind changes as signatures of past itcz shifts abstract the atmospheric hadley cells which meet at the intertropical convergence zone itcz play critical roles in transporting heat driving ocean circulation and supplying precipitation to the most heavily populated regions of the globe paleo reconstructions can provide concrete evidence of how these major features of the atmospheric circulation can change in response to climate perturbations while most such reconstructions have focused on itcz related rainfall here we show that trade wind proxies can document dynamical aspects of meridional itcz shifts theoretical expectations based on angular momentum constraints and results from freshwater hosing simulations with two different climate models predict that itcz shifts due to anomalous cooling of one hemisphere would be accompanied by a strengthening of the hadley cell and trade winds in the colder hemisphere with an opposite response in the warmer hemisphere this expectation of hemispherically asymmetric trade wind changes is confirmed by proxy data of coastal upwelling and windblown dust from the atlantic basin during heinrich stadials showing trade wind strengthening in the northern hemisphere and weakening in the southern hemisphere subtropics in concert with southward itcz shifts data from other basins show broadly similar patterns though improved constraints on past trade wind changes are needed outside the atlantic basin the asymmetric trade wind changes identified here suggest that itcz shifts are also marked by intensification of the ocean s wind driven subtropical cells in the cooler hemisphere and a weakening in the warmer hemisphere which induces cross equatorial oceanic heat transport into the colder hemisphere this response would be expected to prevent extreme meridional itcz shifts in response to asymmetric heating or cooling understanding trade wind changes and their coupling to cross equatorial ocean cells is key to better constraining itcz shifts and ocean and atmosphere dynamical changes in the past especially for regions and time periods for which few paleodata exist and also improves our understanding of what changes may occur in the future

deltas south of the bosphorus strait record persistent black sea outflow to the marmara sea since 10 ka at the southern exit of the bosphorus strait in the northeastern marmara sea high resolution seismic profiles reveal two lobate progradational delta lobes in modern water depths of v40 65 m the younger delta was active from v10 to 9 ka based on radiocarbon dates of equivalent prodelta deposits and the elevation of its topset to foreset transition the topset to foreset transition climbs in the seaward direction because the delta prograded into a rising sea low abundances of marine fauna and flora in the 10 9 ka interval support a deltaic interpretation there are no rivers in the area that could have fed the delta instead all evidence points to the strait itself as the source of sediment and water when this outflow was strongest v10 6 6 0 ka sapropels accumulated in basinal areas of both the aegean and marmara seas benthic foraminiferal and dinoflagellate cyst data from contemporary deposits elsewhere in the marmara sea point to the continual presence through the holocene of a surface layer of brackish water that we ascribe to this same outflow from the black sea through the bosphorus strait by v9 1 8 5 ka two layer flow developed in the bosphorus strait as global sea level continued to rise and the sediment supply to the younger delta was cut off because the outflowing black sea water ceased to be in contact with the floor of the strait the older delta lobe lies below a prominent lowstand unconformity and is tentatively interpreted to have formed from v29 5 to 23 5 ka oxygen isotopic stage 3 when the marmara sea stood at v355 m and a second sapropel accumulated in deep basinal areas crown copyright 2002 elsevier science b v all rights reserved

a signature of transience in bedrock river incision rates over timescales of 10 4 10 7 years measured rates of river incision into bedrock are commonly interpreted as proxies for rates of rock uplift see refs 1 and 2 for example and indices of the strength of climatic forcing of erosion over time see refs 3 and 4 for example this approach implicitly assumes that river incision rates are in equilibrium with external forcings over a wide range of timescales here we directly test this assumption by examining the temporal scaling of bedrock river incision from 155 independent measurements of river incision compiled from 14 sites of these sites 11 exhibit a negative power law dependence of bedrock river incision rate on measurement interval a relationship that is apparent over timescales of 10 4 10 7 years and is independent of tectonic and geomorphic setting thus like rates of sediment accumulation rates of river incision into bedrock exhibit non steady state behaviour even over very long measurement intervals non steady state behaviour can be explained by episodic hiatuses in river incision triggered by alluvial deposition if such hiatuses have a heavy tailed length distribution regardless of its cause the dependence of incision rate on measurement interval complicates efforts to infer tectonic or climatic forcing from changes in rates of river incision over time or from comparison of rates computed over different timescales

chemostratigraphy and magnetic susceptibility of the late devonian frasnian famennian transition in western canada and southern china implications for carbon and nutrient cycling and mass extinction we investigate the late devonian frasnian famennian extinction interval in western alberta and south china to shed light on the palaeoecological and palaeoceanographic conditions that characterize this biotic crisis both the lower and upper kellwasser events are documented in western canada only the upper kellwasser event has been evaluated in south china our multi proxy geochemical approach reveals that these events are characterized by positive d 13 c and d 15 n excursions and increasing magnetic susceptibility canada china and increases in detrital al si ti zr productivity cu ni zn and redox mo u v elemental proxies canada we interpret these trends as part of a systemic palaeoecological shift associated with the development of wide spread terrestrial forests and their alteration of chemical mechanical weathering patterns increase in detrital proxies is thus interpreted as resulting from pedogenically driven weathering on the con tinents that nutrified epeiric and continental margin seas high biological productivity led to eutro phication and development of suboxic to anoxic conditions during both events and probably euxinic conditions during the upper kellwasser event in western canada positived 13 c excursions are the telltale signature of excessive carbon burial while redox proxies and d 15 n records indicate

transient channel incision along bolinas ridge california evidence for differential rock uplift adjacent to the san andreas fault 1 the rates and spatial distribution of active deformation provide critical constraints on the geodynamics of deforming lithosphere yet such data are often difficult to acquire in eroding landscapes where poor preservation of geomorphic or stratigraphic markers hinders strain reconstruction recent advances in understanding of the relationship between bedrock channel profile form and erosion rate have led to their use as an index of rock uplift rate in steady state landscapes here we extend this analysis to landscapes experiencing a transient increase in erosion rate using an example from the marin county region of northern california we characterize channel and hillslope gradients in a series of small watersheds along a monolithologic portion of the franciscan terrane in marin county channel steepness indices vary strongly from north to south along the ridge and correspond with the progressive development of relief on threshold hillslopes along valley walls these patterns argue that recent channel incision has engendered a transient adjustment of hillslope gradient as incision outpaces soil production rates these differences in landscape form and inferred incision rate are explained by differential rock uplift within the region east of the san andreas fault relationships between channel gradient and incision rate suggest a threefold to fivefold difference in incision rate across the region and place a minimum bound on differential rock uplift rates our study highlights how landscape analysis can place bounds on the distribution of earth deformation in both space and time and thus lends insight into the processes driving that deformation

early holocene marine flooding of the black sea abstract echo sounding data recorded in the black sea in 1969 imaged a chain of hills 5 to 150 m high at a depth of 2000 2200 m that resemble hills on the lower continental rise like those hills the features in the western black sea may have been created by bottom currents the easterly flowing currents inferred to have formed the hills may be related to a catastrophic flood of the black sea from the sea of marmara 7150 yr ago

incision and channel morphology across active structures along the peikang river central taiwan implications for the importance of channel width river morphology and dynamics are strongly influenced by active tectonics we report channel dynamics for the peikang river which flows through the hsuehshan range in central taiwan using a digital elevation model and field surveys we constrain channel morphology for an 90 km stretch of river to calculate unit stream power and boundary shear stress along the river path incision rates are estimated with optically stimulated luminescence dating of sand deposited on strath terraces we find a strong correlation between unit stream power shear stress and incision rate but only if variation in channel width is considered a calibrated river incision rule implies river incision rates of 9 13 5 mm yr upstream of the meiyuan and tili faults and suggests that one or both of these structures are presently active our results indicate that the shuilikeng fault is also actively deforming as incision rates increase to 6 10 mm yr across it compared to 1 4 mm yr in adjacent reaches prominent narrowing across the shuilikeng fault and the absence of significant gradient variation indicate that channel width is a first order morphological adjustment to differential incision only when the channel width to depth ratio reaches a minimum does the channel slope significantly adjust to local changes in base level as is the case upstream of the meiyuan and tili faults

fluvial incision and tectonic uplift across the himalayas of central nepal the pattern of fluvial incision across the himalayas of central nepal is estimated from the distribution of holocene and pleistocene terraces and from the geometry of modern channels along major rivers draining across the range the terraces provide good constraints on incision rates across the himalayan frontal folds sub himalaya or siwaliks hills where rivers are forced to cut down into rising anticlines and have abandoned numerous strath terraces farther north and upstream in the lesser himalaya prominent fill terraces were deposited probably during the late pleistocene and were subsequently incised the amount of bedrock incision beneath the fill deposits is generally small suggesting a slow rate of fluvial incision in the lesser himalaya the terrace record is lost in the high range where the rivers are cutting steep gorges to complement the terrace study fluvial incision was also estimated from the modern channel geometries using an estimate of the shear stress exerted by the flowing water at the bottom of the channel as a proxy for river incision rate this approach allows quantification of the effect of variations in channel slope width and discharge on the incision rate of a river the determination of incision rates requires an additional lithological calibration the two approaches are shown to yield consistent results when applied to the same reach or if incision profiles along nearby parallel reaches are compared in the sub himalaya river incision is rapid with values up to 10 15 mm yr it does not exceed a few millimeters per year in the lesser himalaya and rises abruptly at the front of the high range to reach values of 4 8 mm yr within a 50 km wide zone that coincides with the position of the highest himalayan peaks sediment yield derived from the measurement of suspended load in himalayan rivers suggests that fluvial incision drives hillslope denudation of the landscape at the scale of the whole range the observed pattern of erosion is found to closely mimic uplift as predicted by a mechanical model taking into account erosion and slip along the flat ramp flat geometry of the main himalayan thrust fault the morphology of the range reflects a dynamic equilibrium between present day tectonics and surface processes the sharp relief together with the high uplift rates in the higher himalaya reflects thrusting over the midcrustal ramp rather than the isostatic response to reincision of the tibetan plateau driven by late cenozoic climate change or late miocene reactivation of the main central thrust

solutions of the stream power equation and application to the evolution of river longitudinal profiles 1 erosion by bedrock river channels is commonly modeled with the stream power equation we present a two part approach to solving this nonlinear equation analytically and explore the implications for evolving river profiles first a method for non dimensionalizing the stream power equation transforms river profiles in steady state with respect to uniform uplift into a straight line in dimensionless distance elevation space second a method that tracks the upstream migration of slope patches which are mathematical entities that carry information about downstream river states provides a basis for constructing analytical solutions slope patch analysis explains why the transient morphology of dimensionless river profiles differs fundamentally if the exponent on channel slope n is less than or greater than one and why only concave up migrating knickpoints persist when n 1 at migrating knickpoints slope patches and the information they carry are lost a phenomenon that fundamentally limits the potential for reconstructing tectonic histories from bedrock river profiles stationary knickpoints which can arise from spatially varying uplift rates differ from migrating knickpoints in that slope patches and the information they carry are not lost counterparts to migrating knickpoints called stretch zones are created when closely spaced slope patches spread to form smooth curves in distance elevation space these theoretical results are illustrated with examples from the california king range and the central apennines

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

a physical explanation for an observed area slope elevation relationship for catchments with declining relief a general relationship between the contributing area slope and mean elevation of catchments with relief declining after a tectonic uplift event is presented this relationship is based on the continuity equation for runoff and erosion processes in the catchment the key hypothesis underlying this relationship is that as a catchment declines the nondimensionalized catchment approaches a constant form this hypothesis is verified for computer simulated catchments the area slope elevation relationship covers several cases catchments declining toward a peneplain catchments declining from a high slope dynamic equilibrium resulting from a high rate of tectonic uplift to a low slope one resulting from a lower rate of tectonic uplift and catchments declining from an elevated initial condition as for example in the decline of a mine spoil heap a previously published relationship between slope and area for catchments in dynamic equilibrium and based on runoff and erosion physics is shown to be a special case of this general relationship the new area slope elevation relationship is compared with data from simulated catchments and a field catchment it is thus shown that for declining catchments the area slope elevation relationship is a good predictor of catchment form for catchments with declining relief it is argued that the slope area elevation relationship is sufficient with the planiform drainage pattern to completely define the elevation properties of the catchment such as for instance the hypsometric curve

a hydrological model of the black and caspian seas in the late pleistocene and early middle holocene abstract this topic area has been a controversial one since the concept of a catastrophic black sea flood was first proposed and there is still considerable disagreement between experts as to the exact sequence of events this paper describes a numerical model of the caspian and black sea basins together with flows through the manych spillway and the bosphorus strait the model has been calibrated against the deductions made by various researchers concerning past water levels and parameters such as river flow volumes and evaporation rates have been assigned to give reasonable agreement with these deductions the model successfully predicts flow through the manych spillway during the early khvalynian transgression of the caspian sea between 15 2 and 12 3 ky bp and not thereafter the black sea is predicted to reach a lowstand of 163 m in about 11 ky bp and then to fill relatively rapidly due to increased river inflow combined with a breakthrough of mediterranean water across the bosphorus sill in about 10 5 ky bp this is followed by a period of high outflow through the bosphorus and between 9 3 and 8 ky bp by rapidly rising salinity due to marine inflow at depth the model also highlights two significant points of conflict with the physical evidence these concern the lack of apparent reason for the sudden onset of sapropel formation in the black sea in 7 6 ky bp and the significant erosion that has apparently occurred across the manych sill

mathematical model of the late pleistocene and holocene transgressions of the black sea abstract although the late pleistocene holocene fluctuations in the black sea have been studied over many years no overall picture of this difficult natural phenomenon has as yet been developed and described moreover in the literature many researchers have provided mutually exclusive opinions about many of the processes occurring within this time interval the variation in conceptualizations about the filling of the black sea basin is explained by the following reasons 1 fluctuations of sea level in the basin were never properly studied as physical processes under conditions of increased freshwater runoff change in bosporus strait depth increase in world ocean level etc therefore some conclusions about sea level changes were not verified by appropriate calculations and have not been physically substantiated 2 the study of sea level fluctuations are conducted according to modern sea depth markers and sediment age but as the sediment was formed under varying depth conditions and could have moved relative to modern markers by the agency of various geological processes it is possible that that every core may give a different level curve 3 processes of sedimentation erosion and redeposition of sediment occurring in the sea have been studied insufficiently for this reason the same geological material has been interpreted differently by various researchers therefore mathematical modeling of sea level fluctuations based on various physical laws seems to be of great importance in this paper the value and sign for the black sea freshwater balance during the upper pleistocene holocene are discussed the hypothesis suggests that during the specified period of time the freshwater balance of the sea was always positive the sea was filled with water up to the sill mark in the bosporus strait and a river flowed into the sea of marmara along the strait bottom in the present paper geologic evidence of the river flow in the strait during the glacial age and later is presented other points of view about the sea s freshwater balance change are considered a mathematical model of the black sea basin filling with freshwater in the upper pleistocene holocene is suggested it considers that change in water volume inflowing to the black sea to be a result of ablation neotectonic processes in the strait bottom erosion and sediment accumulation black sea level change calculations have shown the following as a result of repeated increases in river runoff during glacial melting the level of the black sea started to rise from 80 m probably to 20 30 m making in the process numerous secondary fluctuations the reason for this phenomenon was the circumstance that the water volume brought by the rivers could not flow to the sea of marmara through the narrow canyon of the bosporus strait at the time therefore water collected in the sea raising its level at approximately 12 ka bp the world ocean level rose to the river surface and began to increase its depth as a result of the increase in strait depth the accumulated water in the black sea flowed out thereby lowering its level to a mark close to the ocean level according to calculations this occurred ca 11 ka bp thereafter the black sea level rose together with the ocean level water within the sea of marmara has flowed to the black sea since approximately 9 ka bp in the form of a bottom counterflow with a small time delay theoretical change in the black sea level practically corresponds to data obtained from geological investigations the theory offered here of fluctuations in black sea level is self sufficient it explains all processes from the melting of the glaciers by physical laws and does not demand the application of any additional hypotheses in the conclusion of this paper the debatable questions about the black sea s possible lowering and the subsequent flooding of the basin are considered

the flooding of the san matias gulf the northern patagonia sea level curve abstract northern patagonia is characterised by tectonic depressions below present sea level some of them are today flooded by the sea others remain emerged although they are at altitudes of 50 m bajo del gualicho 35 m salinas grandes and 7 m salina la piedra san matias gulf also was such an emerged depression below contemporary mean sea level during the late pleistocene it flooded between 11 500 and 11 000 years ago when the sea level surpassed the sill of the gulf today 50 m below mean sea level during postglacial sea level rise in those days shrublands extended on the slopes of the tectonic depression in situ pieces of woods dredged from the bottom of the gulf at depths of 70 m gave a conventional age of 11 310 150 years bp we used the wood together with dated shells from the continental shelf and shells and organic matter dated from the san blas negro and chubut coastal plains to construct a sea level curve sea level rise surpassed the present level somewhat before 6000 years bp reaching a maximum stand of 6 m it has since gently diminished towards present sea level

prompt transgression and gradual salinisation of the black sea during the early holocene constrained by amino acid racemization and radiocarbon dating abstract the restricted environment of the black sea is particularly sensitive to climatic and oceanographic fluctuations owing to its connection with the mediterranean sea via the narrow bosphorus strait the exact mechanism and timing of the most recent connection between these water bodies is controversial with debate on the post glacial history of the black sea being dependent on radiocarbon dating for numerical ages here we present new 23 accelerator mass spectrometer ams radiocarbon ages on peat and bivalve molluscs supported by the first amino acid racemization aar dating of bivalve molluscs n 66 in the black sea these data indicate infilling of the black sea during the early holocene from an initial depth 107 m below sea level and 72 m below that of the bosphorus sill these data combined with a review of previous radiocarbon ages has enabled a unique perspective on the post glacial black sea a sea level curve based on conventional and ams radiocarbon ages on peat and ams based ages on dreissena sp shells indicate the water level in the earlier lake phase continued until the early holocene to be lower than the bosphorus sill after the younger dryas ended however the absence of ams dated mollusc ages from the shelves of this basin older than the younger dryas is suggestive of sub aerial exposure of the shelves and comparatively lower water levels when the younger dryas began thus post glacial outflow from the black sea occurred through a lowered or open bosphorus seaway basin wide radiocarbon ages on peat indicate a prompt increase in water level from that of the pre existing and unconnected palaeo lake during the earliest holocene 9600 9200 cal a bp mass colonisation of the black sea by mediterranean taxa did not occur until salinity had risen sufficiently a process which took 1000 a or more from the initial transgressive event this gradual change in salinity contrasts with the prompt transgression which would have taken 400 a to occur

oceanography noah s flood did a great flood once surge into the black sea forming the basis of a biblical tale quirin schiermeier investigates a computer model that has added weight to the idea

paleo tsushima water and its effect on surface water properties in the east sea during the last glacial maximum revisited abstract the semi enclosed deep marginal east sea is known by limited sill flow and low sea surface salinity during the last glacial maximum lgm when sea level was about 130 m lower than the present level although three straits the tsugaru the soya and the tartar with shallower than 130 m sills were completely closed the korea strait with a maximum sill depth of 140 m seems to have persisted as a partial connection to the east sea allowing a sill flow the volume transport at the korea strait during the lgm is estimated at approximately 0 3 1 1 1012 m3 yr by using bathymetry seismic reflection profiles and current data the low sea surface salinity has been explained by the east china sea coast water ecscw and high precipitation however the existing geological observations indicate that precipitation was reduced in the glacial east sea the high resolution numerical simulation results predict that evaporation 2 16 mm day exceeded precipitation 1 43 mm day further suggesting net evaporation evaporation minus precipitation rates 0 2 1012 m3 yr over the lgm east sea this signifies that the precipitation was not the factor lowering surface paleosalinity and that the paleo tsushima water carried a huge amount of freshwater from the ecscw than previously expected the calculated surplus evaporation 0 2 1012 m3 yr and sill flow 0 3 1 1 1012 m3 yr are not identical but they could be oceanographically considered as similar the comparison between both values implies that most of the throughflow ultimately escaped the east sea through the evaporation process during the lgm the regional sea level in the almost isolated east sea might be largely maintained by a rough balance between incoming throughflow and outgoing evaporation during the lgm the geographic restriction due to lowered sea level and lower surface salinity by limited vertical mixing in the glacial east sea are analogous to modern oceanographic features in the black sea

distribution of active rock uplift along the eastern margin of the tibetan plateau inferences from bedrock channel longitudinal profiles 1 current models of long term river incision into bedrock suggest that the local rate of differential rock uplift should exert a primary control on the gradient of channel longitudinal profiles however discrimination of this effect from the influence of variations in substrate erodibility sediment flux precipitation and transient changes in profile shape has proved difficult in practice here we investigate the controls on the spatial distribution of bedrock channel gradients adjacent to the sichuan basin in an effort to assess the degree and nature of active deformation along this margin of the tibetan plateau analysis of river longitudinal profiles utilizing a channel steepness index a measure of profile gradient normalized for drainage area reveals a zone of anomalously steep channels adjacent to the topographic front of the plateau margin channel profiles are systematically less steep in their headwater reaches on the plateau and in their lower reaches east of the plateau margin comparison of steepness indices to mapped lithologic variations reveals that lithology has only a limited influence on channel gradient in this field area we observe no systematic relationship between steepness indices and upstream drainage area channels of all size are steeper near the plateau margin we argue that these systematic changes are not readily explained as a consequence of increased sediment flux or of orographic precipitation we are led to conclude that steep channel profiles along the topographic front of the plateau reflect active differential rock uplift between this region and the foreland

modeling the influence of rainfall gradients on discharge bedrock erodibility and river profile evolution with application to the big island hawai i motivated by convex concave bedrock river profiles developed across a climate gradient on the wetside of the kohala peninsula of the big island of hawai i we numerically model how rainfall gradients may influence longitudinal fluvial incision patterns first we model transient profile adjustment with two tectonic boundary conditions subsidence and uplift in this generalized analysis we assume that rainfall gradients only influence incision by modifying the relation between upstream drainage area and local discharge using a detachment limited model downstream increases in rainfall lead to profile convexities during transient adjustment in both tectonic settings and this is the opposite of the predicted increase in profile concavity that would develop in a steady state uplifting profile a transport limited erosion model develops only concave channel profiles without clear signatures of the rainfall pattern second we model the development of convex concave transient profiles and incision patterns on kohala using a detachment limited model if rainfall gradients only influence incision through the local discharge reasonable rainfall gradients can only develop channel convexities that are much smaller than those observed instead we hypothesize that local bedrock erodibility increases with the degree of rainfall dependent chemical weathering when local erodibility is assumed to scale with local rainfall rate the model can produce convex concave profiles similar to those observed in kohala our results suggest that changes in local bedrock erodibility due to local climate dependent weathering may be an important mechanism by which climate influences landscape form and rates of evolution this hypothesis requires further testing in this study area and beyond

the last sea level changes in the black sea evidence from the seismic data abstract high resolution shallow seismic data collected from the southwestern shelf of the black sea indicate five different seismic stratigraphical units the lower three of them belong to the upper cretaceous eocene oligocene miocene and early quaternary prior to holocene sediments respectively these units are considered as a basement for the recent sediments deposited related to the latest connection of the black sea and the mediterranean the surface of these units are truncated to form an etchplain developed before the flandrian transgression the fourth unit covers the older units by an onlap its contact with the older units seen at 105 m is the shoreline of the black sea prior to the last major sea level change the fifth unit has been deposited since drowning of the black sea shelf the principal cause of drowning of the black sea shelf is not only the last sea level rise as it is at the shelves of the sea of marmara but also the opening of the strait of istanbul it is also realised by the comparison of the shelf area and the catalca kocaeli etchplain that the present continental part of this etchplain has been considerably uplifted with respect to the shelf area along the present shoreline this uplifting must have also reactivated the faults around the strait of istanbul foundering the strait valley and thus permitting the mediterranean waters to pass into the black sea and initiating the sudden drowning of the black sea shelf

climatic control of bedrock river incision bedrock river incision drives the development of much of earth s surface topography and thereby shapes the structure of mountain belts and modulates earth s habitability through its effects on soil erosion nutrient fluxes and global climate although it has long been expected that river incision rates should depend strongly on precipitation rates quantifying the effects of precipitation rates on bedrock river incision rates has proved difficult partly because river incision rates are difficult to measure and partly because non climatic factors can obscure climatic effects at sites where river incision rates have been measured here we present measurements of river incision rates across one of earth s steepest rainfall gradients which show that precipitation rates do indeed influence long term bedrock river incision rates we apply a widely used empirical law for bedrock river incision to a series of rivers on the hawaiian island of kaua i where mean annual precipitation ranges from 0 5 metres to 9 5 metres ref 12 over 70 per cent of the global range and river incision rates averaged over millions of years can be inferred from the depth of river canyons and the age of the volcanic bedrock both a time averaged analysis and numerical modelling of transient river incision reveal that the long term efficiency of bedrock river incision across kaua i is positively correlated with upstream averaged mean annual precipitation rates we provide theoretical context for this result by demonstrating that our measurements are consistent with a linear dependence of river incision rates on stream power the rate of energy expenditure by the flow on the riverbed these observations provide rare empirical evidence for the long proposed coupling between climate and river incision suggesting that previously proposed feedbacks among topography climate and tectonics may occur