deep crustal structure of northwestern part of turkey abstract the deep crustal structure of the polatli nallihan karasu nw turkey area was investigated by magnetotelluric and transient electromagnetic measurements all measurements were acquired as part of a national project called crustal structures of turkey undertaken by the general directorate of mineral research and exploration of turkey mta magnetotelluric data were collected from 44 stations located along a 250 km northwest to southeast profile crossing in succession the istanbul zone intra pontid suture sakarya continent izmir ankara suture tavsanli zone the tauride anatolide belt intra pontid suture and sakarya continent after decompositional analysis and strike direction estimation static shift is corrected by using transient electromagnetic data from mt apparent resistivity data the processed mt data were inverted to derive a two dimensional geoelectrical model the estimated model is interpreted with the help of gravity data observed along the mt lines and using earthquake epicenter which occurred around mt measurement lines four layers with distinctive resistivity values dominate the geoelectrical section the uppermost layer having resistivity values of 5 35 ohm m can be interpreted as the sedimentary fill this layer reaches down to about 10 km depth in haymana basin the second layer has resistivity values higher than 110 ohm m and reaches 27 km depth the first and second layers can be inferred as constituting the upper crust in the general model of the earth s lithosphere the third layer underlying the upper crust has resistivity values of 10 30 ohm m corresponding to the lower crust the fourth layer having high resistivity values 225 ohm m can be considered as the upper mantle the depth of the boundary separating the crust from the upper mantle moho varies between 20 and 40 km high conductive zones between the istanbul zone and sakarya continent sakarya continent and tavsanli zone coincide with high bouguer gravity anomaly values it can be inferred from these properties that these zones correspond to the intra pontide suture and the izmir ankara suture noticeable differences in tectonic characteristics are observed between the southern and northern part of sakarya continent in the geoelectrical section the northern part of the continent is separated by high dip slip faults while the faults in the southern part do not affect the high resistive zone in the deeper part of the section these faults controlled the development of the haymana basin but they do not alter the high resistive zone to form separate blocks the majority of these faults which are clearly seen in the geoelectrical section are not evident in the sedimentary fill these buried faults have not been studied in detail prior to the present study

forms and processes of two highly contrasting rivers in arid central australia and the implications for channel pattern discrimination and prediction tooth s nanson g c 2004 forms and processes of two highly contrasting rivers in arid central australia and the implications for channel pattern discrimination and prediction geological society of america bulletin 116 7 8 802 816 rae2008

distribution transport and production of volatile halocarbons in the upper waters of the ice covered high arctic ocean 1 volatile halogenated compounds chbr3 ch2br2 chbr2cl and ch2cli were measured in the water column and in sea ice brine across the arctic ocean from barrow alaska to svalbard during the beringia 2005 expedition august september with rv ib oden high concentrations of brominated compounds up to 42 pmol kg 1 of bromoform were found under multiyear ice in the surface waters over the makarov basin and the lomonosov ridge near the north pole even higher concentrations bromoform up to 160 pmol kg 1 were found in sea ice brine we propose that the high load of riverine dissolved organic matter that is transported in the transpolar drift is a main factor responsible for the high concentration of brominated volatile compounds found in sea ice brine and upper waters and that cycles of freezing and thawing during the transport enhance the transfer of halocarbons to the seawater the iodinated compound ch2cli showed a completely different distribution with highest concentrations in water of pacific origin in the mixed layer and upper halocline of the northern canada basin and over the alpha ridge in the southern canada basin low concentrations of halocarbons were found in upper waters higher concentrations in water of pacific origin especially on the continental shelf indicate production in the shelf regions likely in the chukchi sea and the east siberian sea

an environmental gradient of vegetative controls upon channel planform in the source region of the yangtze and yellow rivers abstract alluvial reaches in the source region of the yangtze and yellow rivers located atop the qinghai tibetan plateau and mostly at elevations that are typically higher than 3500 m have similar slope and valley setting conditions however alluvial reaches in the source region of the yangtze river exhibit predominantly braided channel planforms while equivalent reaches in the source region of the yellow river have more diverse planform morphologies including anastomosing braided anabranching braided and anabranching anastomosing reaches the regional gradient of variation in riparian vegetation and interactions between vegetation development and hydrologic process are shown to be major factors influencing this difference in channel planforms a short period above freezing coincident with recurrent yet pulsed flows in the source region of the yangtze river suppress riparian vegetation growth promoting the development of braided channel morphologies in contrast a milder climate coincident with less variable flows in the source region of the yellow river permit the establishment of different forms of riparian vegetation thereby supporting the development of a wider range of channel planform morphologies

hydrological and sedimentary controls over fluvial thermal erosion the lena river central yakutia abstract water regime and sedimentary features of the middle lena river reach near yakutsk central yakutia were studied to assess their control over fluvial thermal erosion the lena river floodplain in the studied reach has complex structure and embodies multiple levels varying in height and origin two key sites corresponding to high and medium floodplain levels were surveyed in 2008 to describe major sedimentary units and properties of bank material three units are present in both profiles corresponding to topsoil overbank cohesive and channel fill noncohesive deposits thermoerosional activity is mostly confined to a basal layer of frozen channel fill deposits and in general occurs within a certain water level interval magnitude frequency analysis of water level data from tabaga gauging station shows that a single interval can be deemed responsible for the initiation of thermal action and development of thermoerosional notches this interval corresponds to the discharges between 21 000 and 31 000 m 3 s 1 observed normally during spring meltwater peak and summer floods competence of fluvial thermal erosion depends on the height of floodplain level being eroded as it acts preferentially in high floodplain banks in medium floodplain banks thermal erosion during spring flood is constrained by insufficient bank height and erosion is essentially mechanical during summer flood season bank retreat rate is argued to be positively linked with bank height under periglacial conditions

hydrographic conditions during the 2002 sbi process experiments abstract a review of the hydrographic data from the 2002 western arctic shelf basin interactions sbi process cruises permits the following conclusions 1 temperature salinity relationships were similar to canonical descriptions but at five stations in the outer shelf slope region warm high salinity atlantic layer water appeared to have risen displaced the lower halocline and mixed with shelf upper halocline water 2 primary production in the sbi study region was strongly influenced by the advection of dissolved inorganic nitrogen din entering via bering strait this import of din ammonium nitrate nitrite is modified by local processes but without the bering strait inflow biological productivity in the sbi region would be much lower 3 in comparison to the inflowing atlantic waters din urea phosphate and din urea silicate ratios in the pacific waters that dominated the upper 150 m of the water column were low they were also low relative to redfield uptake ratios for phytoplankton 4 microbial processes continue to destroy din in significant quantities as the pacific waters transit the sbi region 5 nitrate and ammonium were the principal contributors to din nitrite concentrations were always

optical properties in waters around the mendeleev ridge related to the physical features of water masses abstract irradiance profiles were measured during the korean 2012 summer arctic ocean cruise and optical properties were studied the optical attenuation coefficient in all surface waters was low as the nutrients in the surface layers became exhausted and phytoplankton growth was only possible at the subsurface where optimal conditions of nutrients and sufficient illumination existed this high attenuation zone was at about 40 60 m the attenuation properties were categorized to three types type 1 waters had weaker maximum attenuation coefficients and were located at the chukchi plateau and the north margin of the study region type 2 water had an intense maximum of attenuation coefficient up to 0 56 m located on west flank of mendeleev ridge and continental slope of east siberian sea two integral parameters attenuation depth and optical thickness were mapped by spatial distribution the attenuation depth was basically shallower 40 m to the west and deeper to the east 100 m the averaged optical thickness at the level of 30 60 m was the main zone of high attenuation both the optical attenuation property and the physical features of the water indicated two subsurface water masses one is the cold shelf water well mixed with river water and transported to the east by a subsurface current along the east siberian slope the other is the warmer water from the pacific with lower nutrients and transported to the northwest along the north margin of the observed region a cyclonically re circulated branch of shelf water passing over the chukchi abyssal plain was described in this study

circulation of the chukchi sea shelfbreak and slope from moored timeseries abstract data from a year long mooring array across the shelfbreak upper slope of the chukchi sea are used to describe and quantify the circulation and water masses of the region the timeseries revealed the year round existence of the eastward flowing shelfbreak jet and seaward of this the westward flowing chukchi slope current in the mean the slope current is estimated to transport 0 57 0 04 sv of pacific water while the bottom intensified shelfbreak jet transports 0 009 0 003 sv towards barrow canyon the slope current is surface intensified in summer and fall and in winter and spring it becomes middepth intensified moves shoreward and weakens two extreme states of the circulation were identified 1 an enhanced slope current and reversed westward flowing shelfbreak jet and 2 a strong eastward flowing shelfbreak jet and weak slope current the former state occurs when the wind stress curl on the chukchi shelf is positive and the latter state occurs when the curl is negative a simple theoretical model is used to determine the changes in sea surface height due to such wind stress curl forcing which is consistent with the observed changes in flow seaward of the shelf both in amplitude and phase via geostrophic set up shelfbreak upwelling occurred throughout the year but there was no correlation between the regional wind conditions and the upwelling furthermore there was no apparent relationship between upwelling and the extreme slope current shelfbreak jet events a comparison of water mass signals between the chukchi slope array and a mooring at the head of barrow canyon supports the notion that the slope current is fed by the outflow of pacific water from the canyon

pathways timing and evolution of pacific winter water through barrow canyon abstract observations from a ship based campaign in july august 2009 combined with idealized numerical simulations are used to investigate the seasonal delivery of pacific winter water to barrow canyon and the subsequent adjustment of the flow down the canyon as the current advects dense water it transitions from a nearly barotropic structure near the canyon head to a strongly baroclinic flow with a subsurface maximum near the canyon mouth both the data and model indicate that the transit times along the three chukchi shelf pathways feeding barrow canyon a coastal pathway a southern hanna shoal pathway and a northern hanna shoal pathway modulate the mode of winter water that occupies the canyon at a given time in particular remnant pacific winter water carried along the rapid coastal pathway can precede the arrival of newly ventilated pacific winter water carried along the two interior pathways the observations and model indicate that the transition between water types draining from the canyon can occur rapidly over time scales of days to weeks we also demonstrate that mixing along the path of the current is unlikely to result in the observed down canyon transition from newly ventilated pacific winter water to remnant winter water further supporting the dominant role of advection while the focus here is on the transition of winter water modes the implication that seasonality within barrow canyon is tied to seasonality of the bering strait inflow together with the relative transit times along advective pathways should hold for other water types as well

holocene variability in sea ice cover primary production and pacific water inflow and climate change in the chukchi and east siberian seas arctic ocean in this study we present new detailed biomarker based sea ice records from two sediment cores recovered in the chukchi sea and the east siberian sea these new biomarker data may provide new insights on processes controlling recent and past sea ice changes the biomarker proxy records show i minimum sea ice extent during the early holocene ii a prominent mid holocene short term high amplitude variability in sea ice primary production and pacific water inflow and iii significantly increased sea ice extent during the last ca 4 5k cal a bp this late holocene trend in sea ice change in the chukchi and east siberian seas seems to be contemporaneous with similar changes in sea ice extent recorded from other arctic marginal seas the main factors controlling the millennial variability in sea ice and surface water productivity are probably changes in surface water and heat flow from the pacific into the arctic ocean as well as the long term decrease in summer insolation the short term centennial variability observed in the high resolution middle holocene record is probably related to solar forcing our new data on holocene sea ice variability may contribute to synoptic reconstructions of regional to global holocene climate change based on terrestrial and marine archives

dissolved methane concentrations in the water column and surface sediments of hanna shoal and barrow canyon northern chukchi sea abstract current estimates of methane ch 4 flux suggest that arctic shelves may be a significant source of atmospheric ch 4 a potent greenhouse gas however little information is known about the ch 4 flux from most arctic shelves other than the east siberian arctic shelf we report here dissolved ch 4 concentrations in the water column and within surface sediments of the northern chukchi sea we hypothesized that this area contains high concentrations of ch 4 because it receives nutrient rich waters through the bering strait promoting primary production that enhances an organic rich material flux to the seafloor and eventual microbial methanogenesis in the sediments in august 2012 as part of the chukchi sea offshore monitoring in drilling area comida project fourteen stations were sampled on hanna shoal a shallow feature on the shelf and ten stations across the undersea barrow canyon on hanna shoal water column ch 4 concentrations ranged from 14 to 74 nm and surface concentrations were up to 15 times supersaturated in ch 4 compared to equilibrium with the average atmospheric concentrations 3 nm ch 4 concentrations at the sediment water interface were around 1 500 nm and typically increased with depth in the sediment at the head of barrow canyon water column ch 4 concentrations ranged from 5 to 46 nm with the highest concentrations in the deepest waters that were sampled 118 m overall the calculated fluxes to the atmosphere ranged from 1 to 80 mol ch 4 m 2 d 1 for hanna shoal and 4 to 17 mol ch 4 m 2 d 1 across the barrow canyon stations although there was a large range in these fluxes the average atmospheric flux 20 mol ch 4 m 2 d 1 across hanna shoal was 12 times lower than the flux reported from the east siberian arctic shelf in summer we conclude that while there is a positive flux of ch 4 to the atmosphere this part of the chukchi sea is not a significant source of atmospheric ch 4 compared to the east siberian sea shelf

channel patterns braided anabranching and single thread a new channel pattern classification is presented based on theoretically derived channel pattern discriminant functions the thresholds are formulated as power laws that relate the critical slope associated with a change in channel pattern to dimensionless discharge and relative bank strength one threshold demarcates the boundary between stable single thread channels both straight and meandering and stable multiple thread channels anabranching another threshold separates anabranching from braided channels where braided channels are considered to be fundamentally unstable the exponents of the thresholds are nearly identical to that in the threshold equation originally proposed by leopold and wolman 1957 and the coefficients are quite similar as well an analysis of their data set using our dimensionless approach reveals that no fundamental difference exists between meandering and straight patterns and thus data from both types are grouped together under the more general heading of single thread channels furthermore we demonstrate that over a limited range of conditions an unstable single thread channel can form stable multiple threads but that for systems far from the threshold bounding the single thread channels the number of divisions required to produce stable anabranches grows geometrically this motivates a separation of multiple thread channels into anabranching and braided types our theoretical thresholds are then compared against several large data sets of field data and the results broadly confirm our proposed thresholds

recent channel adjustments in alluvial rivers of tuscany central italy drastic channel adjustments have affected the main alluvial rivers of tuscany central italy during the 20th century bed level adjustments were identified both by comparing available topographic longitudinal profiles of different years and through field observations changes in channel width were investigated by comparing available aerial photographs 1954 and 1993 98 bed incision represents the dominant type of vertical adjustment and is generalized along all the fluvial systems investigated the arno river system is the most affected by bed level lowering up to 9 m whereas lower incision generally less than 2 m is observed along the rivers of the southern part of the region human disturbances appear to be the dominant factors of adjustments the main phase of vertical change occurred during the period 1945 80 in concomitance with the phase of maximum sediment mining activity at the regional scale the second dominant type of adjustment that involved most of the rivers in the region consists of a narrowing of the active channel based on measurements of channel width conducted on aerial photographs 38 of the reaches analysed experienced a narrowing greater than 50 of the initial channel width the largest values of channel narrowing were observed along initially braided or sinuous with alternate bars morphologies in the southern portion of the region a regional scheme of channel adjustments is derived based on initial channel morphology and on the amounts of incision and narrowing different styles of channel adjustments are described rivers that were originally sinuous with alternate bars to braided generally became adjusted by a moderate incision and a moderate to intense narrowing in contrast sinuous meandering channels mainly adjusted vertically with a minor amount of narrowing copyright 2003 john wiley sons ltd

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

channel changes due to river regulation the case of the piave river italy this paper deals with the channel changes of the piave river in the eastern alps italy which have occurred during this century in response to human interventions in the fluvial system the flow regime and the sediment supply of the river have been considerably altered by hydroelectric dams flow diversions and gravel mining in addition river dynamics have been affected by the construction of streambank protection structures to document these changes a historical analysis was performed using maps and aerial photographs morphological features that were examined included planform configuration channel width braiding index and bed elevation the results indicate that as a consequence of decreases in the flows and sediment supply remarkable channel changes have occurred in the river during this century especially during recent decades the channel has undergone a general narrowing with a decrease in average width to 35 per cent of its initial value while the braiding index has decreased from about 3 to 1 5 in several reaches the planform pattern has changed from braided to wandering the observed trends of channel change suggest that the river has not yet reached a new equilibrium condition and it may therefore be predicted that reductions in width and braiding intensity are likely to continue in the immediate future copyright 1999 john wiley sons ltd

why some alluvial rivers develop an anabranching pattern anabranching rivers have been identified globally but a widely accepted and convincing theoretical explanation for their occurrence has remained elusive using basic flow and sediment transport relations this study analyzes the mechanisms whereby self adjusting alluvial channels can anabranch to alter their flow efficiency sediment transport capacity per unit of stream power it shows that without adjusting channel slope an increase in the number of channels can produce a proportional decrease in flow efficiency a finding particularly relevant to understanding energy consumption in some braided rivers however anabranching efficiency can be significantly increased by a reduction in channel width as occurs when vegetated alluvial islands or between channel ridges form the counteracting effects of width reduction and an increasing number of channels can cause with no adjustment to slope an otherwise unstable system underloaded or overloaded to achieve stability as with other river patterns anabranching can be characterized by stable equilibrium or accreting disequilibrium examples copyright 2007 by the american geophysical union

assessment of downstream trends in channel gradient total and specific stream power a gis approach geographic information systems gis analyses of digital elevation models dems coupled with catchment area based discharge estimation techniques provide a relatively simple means of modelling contiguous downstream trends in channel gradient total stream power and in riverscapes conducive to regime analysis also specific stream power for a small high relief coastal catchment in se australia good agreement was obtained between channel gradients derived from a 25 m cell size dem and field survey equivalents over distances of several kilometres indicating that channel gradients derived from dems can have a reasonable degree of absolute as well as relative accuracy over multi kilometre reach scales assessment of downstream rates of change in channel gradient and specific stream power across four river systems suggests that some of the river reaches most responsive to high magnitude floods occur in zones where these variables rapidly decrease downstream modelling of downstream trends in channel gradient total and specific stream power from catchment wide dems has potential to provide a framework with which to investigate conceptual and empirical models between channel gradient stream power and the form and dynamics of river systems

the meandering braided river threshold a reappraisal abstract the concept of a threshold discharge slope q s combination that separates braided from meandering streams is critically re examined partly by review of previous data and partly by analysis of new data from south island new zealand it is argue d that discriminant functions that use mean annual discharge provide a poor physical basis for interpretations based on natural processes while bankfull discharge is also deficient because it is not a fully independent variable the common use of channel rather than valley slope adds a further misleading component because channel slope is partly dependent on channel pattern sinuosity most previous studies have inadequately treated the role of bed particle size in pattern discrimination failing to recognize that active gravel streams must plot higher on a q s chart than sand bed channels irrespective of pattern because of the greater power requirements for bed material movement within any one size class of bed material there is no evidence to indicate a clear discrimination between braiding and meandering only a weak statistical association between pattern and slope discharge values while this association may be explicable in terms of the high shear stress and stream power that accompany high qs values promoting braiding the real prerequisite for braiding appears to be high loads of bed calibre material producing wide shallow channels a factor that is only partly controlled by stream power accordingly the search for a pattern threshold based on discharge and slope seems to be a futile exercise an interpretation of existing pattern discriminant functions from the perspective of the threshold shear stress for particle movement is made it is concluded that in effect these functions merely state that gravel bed streams are more likely to be braided than channels in finer sediment statistically this appears to be valid and reasons for that difference are offered based on the balance between imposed bed material load and channel capacity

nutrient supply and biological response to wind induced mixing inertial motion internal waves and currents in the northern chukchi sea a fixed point observation station was set up in the northern chukchi sea during autumn 2013 and for about 2 weeks conductivity temperature depth ctd water samplings 6 h and microstructure turbulence measurements 2 to 3 times a day were performed this enabled us to estimate vertical nutrient fluxes and the impact of different types of turbulent mixing on biological activity there have been no such fixed point observations in this region where incoming low salinity water from the pacific ocean river water and sea ice meltwater promote a strong pycnocline halocline that stabilizes the water column previous studies have suggested that because of the strong pycnocline wind induced ocean mixing could not change the stratification to impact biological activity however the present study indicates that a combined effect of an uplifted pycnocline accompanied by wind induced inertial motion and turbulent mixing caused by intense gale force winds 10 m s 1 did result in increases in upward nutrient fluxes primary productivity and phytoplankton biomass particularly large phytoplankton such as diatoms convective mixing associated with internal waves around the pycnocline also increased the upward nutrient fluxes and might have an impact on biological activity there for diatom production at the fixed point observation station it was essential that silicate was supplied from a subsurface silicate maximum a new feature that we identified during autumn in the northern chukchi sea water mass distributions obtained from wide area observations suggest that the subsurface silicate maximum water was possibly derived from the ventilated halocline in the canada basin

seasonal and decadal shifts in particulate organic matter processing and sedimentation in the bering strait shelf region abstract we present data on the quality and quantity of particulate organic material deposited to the benthos in the chukchi sea this analysis is undertaken by using 7 be a short lived radiotracer which is associated with particle deposition the stable carbon isotopic composition of organic material and its c n ratio in the water column and within the sediments and the inventories of chlorophyll a present in surface sediments using previously published data we show that sedimentation processes in the regional bering strait ecosystem may have shifted in the past decade surface sediments collected in 2004 adjacent to the russian coastline in the chukchi sea are less refractory in terms of carbon isotope ratios and c n ratios than was observed for surface sediments at similar locations in 1995 and 1988 based upon sediment 7 be and chlorophyll a inventories short term sedimentation on the shelf occurs immediately north of bering strait and within and downstream of barrow and herald canyons seasonal differences i e ice covered versus open water conditions in the quality of particulate organic carbon reaching the benthos appear to be small in the most productive waters such as barrow canyon however in less productive waters c n ratios and 13 c values show seasonal variations once on the bottom 13 c values in the organic fractions of the sediments are less negative than observed in settling material in the water column which is commonly thought to result from biological processing within the sediments

braided channel pattern and palaeohydrology using an index of total sinuosity abstract channel patterns are commonly represented as discrete types e g straight meandering braided separated by threshold values of slope and discharge however for gravel bed river patterns an index of total sinuosity p can be defined which varies continuously with both stream power per unit channel belt length represented as the product of mean annual flood and valley gradient and median bed material diameter an empirical relationship between p and these controlling variables can be used to provide palaeo hydrological reconstructions for braided stream traces on terrace fragments as an alternative to methods based on bed material sizes and criteria for the threshold of grain motion

seasonal to mesoscale variability of water masses and atmospheric conditions in barrow canyon chukchi sea abstract twenty four repeat hydrographic transects occupied across barrow canyon from 2010 to 2013 are used to study the seasonal evolution of water masses in the canyon from july october as well as the occurrence of upwelling the mean sections revealed that the alaskan coastal water is mainly confined to the eastern flank of the canyon corresponding to a region of sloped isopycnals indicative of the surface intensified alaskan coastal current which advects the water the pacific origin winter water is found at depth banked against the western flank of the canyon its isopycnal structure is consistent with a bottom intensified flow of this dense water mass out of the canyon for the months that were sampled the alaskan coastal water is most prevalent in august and september while the coldest winter water is observed in the month of august it is argued that this newly ventilated winter water is delivered to the canyon via pathways on the central chukchi shelf as opposed to the coastal pathway roughly a third of the hydrographic sections were preceded by significant up canyon winds and hence were deemed to be under the influence of upwelling during these periods anomalously salty water is found throughout the eastern flank of the canyon and on occasion atlantic water fills the deepest part of the section using atmospheric reanalysis data it is shown that upwelling occurs when the beaufort high is strengthened and the aleutian low is deepened two modes of storm tracks were identified northward progressing storms mode 1 and eastward progressing storms mode 2 both of which can drive upwelling mode 1 is prevalent in july august while mode 2 is more common in september october these seasonal patterns appear to be dictated by regional variations in blocking highs

phytoplankton blooms beneath the sea ice in the chukchi sea in the arctic ocean phytoplankton blooms on continental shelves are often limited by light availability and are therefore thought to be restricted to waters free of sea ice during july 2011 in the chukchi sea a large phytoplankton bloom was observed beneath fully consolidated pack ice and extended from the ice edge to 4100 km into the pack the bloom was composed primarily of diatoms with biomass reaching 1291 mg chlorophyll a m 2 and rates of carbon fixation as high as 3 7 g c m 2 d 1 although the sea ice where the bloom was observed was near 100 concentration and 0 8 1 2 m thick 30 40 of its surface was covered by melt ponds that transmitted 4 fold more light than adjacent areas of bare ice providing sufficient light for phytoplankton to bloom phytoplankton growth rates associated with the under ice bloom averaged 0 9 d 1

wintertime variability of the beaufort gyre in the arctic ocean derived from cryosat 2 siral observations we processed the sea surface height measured by the sar synthetic aperture radar interferometric radar altimeter siral on board cryosat 2 cs 2 and successfully estimated the monthly dynamic ocean topography dot of the arctic ocean the cs 2 monthly dot showed the interannual and monthly variability of the beaufort gyre bg during winter between 2010 2011 and 2014 2015 the northward flow at the western edge of the bg was primarily estimated over the chukchi borderland cbl however the bg extended across the cbl and the northward flow was estimated over the mendeleev ridge in the winter of 2012 2013 our analyses revealed a significantly variable bg in response to changes in the sea surface stress field our analysis indicated that 1 sea ice motion driven by wind fields acts as a driving force for the bg when sea ice motion was intensified during winter and 2 sea ice motion can also act as an inhibiting force for the bg when sea ice motion is weakened during winter in addition the relationship between the dot steric height and ocean bottom pressure implied that the dot during winter responded to varying wind stresses through baroclinic and barotropic adjustments according to a tracer experiment we inferred that in the winter of 2012 2013 the pacific origin water carried into the bg through the barrow canyon was transported to the northern shelf and shelf break of the chukchi sea rather than the cbl which is where the pacific origin water had been transported in the other years of the observation period

localized accumulation and a shelf basin gradient of particles in the chukchi sea and canada basin western arctic transparent exopolymer particles tep particulate organic carbon poc and particles size range 5 2 119 m as determined by laser in situ scattering and transmissometry lisst were measured in the water column from the chukchi sea to the canada basin in the western arctic ocean during the late summer of 2012 in general the percentages of tep carbon to poc were high the mean values for the shelf and slope basin regions were 135 4 58 0 standard deviation n 36 and 187 6 73 3 n 58 respectively relative to the corresponding values reported for other oceanic regions suggesting that tep play an important role in regulating particle dynamics a hotspot extremely high concentration of particles accompanied by high prokaryote abundance and production was observed near the seafloor depth 50 m of the shelf region localized accumulation of particles was also found in the thin layer near the pycnocline depth 10 30 m and on the slope over a broader spatial scale particle concentration gradients were identified from the shelf to the basin in the upper water column 50 m the particle size distribution analysis indicated that relatively small particles were dominant in the shelf region compared to the slope basin region these results suggest that particles containing large amounts of tep are produced in the shelf region and are potentially delivered to the slope basin region along the pycnocline which might support productivity and material cycles in the nutrient depleted basin region of the western arctic ocean

spatial patterns of primary production on the shelf slope and basin of the western arctic in 2002 in the spring and summer of 2002 primary production in the chukchi sea was measured using 14 c uptake experiments our cruise track encompassed the shelf and continental slope area of the chukchi and beaufort seas progressing into deep water over the canada basin the study area experienced upwards of 90 ice cover during the spring with ice retreating into the basin during the summer production in the spring was light limited due to ice cover with average euphotic zone production rates of o0 3 g c m 2 d 1 values of 8 g c m 2 d 1 were observed in association with surface bloom conditions during the initial ice breakup considerable nutrient reduction in the surface waters took place between the spring and summer cruise and although not observed this was attributed to a spring bloom decreased ice cover and increased clarity of surface waters in the summer allowed greater light penetration the highest rates of production during the second cruise were found at 25 30 m coincident with the top of the nutricline daily euphotic zone productivity in the summer averaged 0 78 g c m 2 d 1 on the shelf and 0 32 g c m 2 d 1 on the edge of the canada basin these data provide an estimated annual production of 90 g c m 2 yr 1 in the study area

processes of multibathyal aragonite undersaturation in the arctic ocean during three years of study 2010 2012 the western arctic ocean was found to have unique aragonite saturation profiles with up to three distinct aragonite undersaturation zones this complexity is produced as inflow of atlantic and pacific derived water masses mix with arctic derived waters which are further modified by physiochemical and biological processes the shallowest aragonite undersaturation zone from the surface to 30 m depth is characterized by relatively low alkalinity and other dissolved ions besides local influence of biological processes on aragonite undersaturation of shallow coastal waters the nature of this zone is consistent with dilution by sea ice melt and invasion of anthropogenic co2 from the atmosphere a second undersaturated zone at 90 220 m depth salinity 31 8 35 4 occurs within the arctic halocline and is characterized by elevated pco2 and nutrients the nature of this horizon is consistent with remineralization of organic matter on shallow continental shelves bordering the canada basin and the input of the nutrients and co2 entrained by currents from the pacific inlet finally the deepest aragonite undersaturation zone is at greater than 2000 m depth and is controlled by similar processes as deep aragonite saturation horizons in the atlantic and pacific oceans the comparatively shallow depth of this deepest aragonite saturation horizon in the arctic is maintained by relatively low temperatures and stable chemical composition understanding the mechanisms controlling the distribution of these aragonite undersaturation zones and the timescales over which they operate will be crucial to refine predictive models this article is protected by copyright all rights reserved

anastomosis and the continuum of channel pattern anastomosing rivers are characterized by multiple channels separated by islands excised from the floodplain their status relative to the continuum concept of channel pattern is assessed with channel pattern defined in terms of three variables flow strength bank erodibility and relative sediment supply using an ordinal scaling l ow m oderate h igh the traditional forms of straight meandering and braided have respective representations of l l l m l m l m and h h m h in terms of those variables the anastomosing pattern is on average represented by l l m h but not so definitively as other forms specification of the third element sediment supply is particularly hampered by the paucity of data but aggradation a characteristic of many anastomosing rivers can be thought of as symptomatic of a moderately high rate of supply relative to the ability for onward transport a sufficiently high rate of supply to a channel with low flow strength and resistant banks would induce shoaling and or lateral constriction that locally forces flow out of the main channel and ultimately leads to the cutting of anabranches a flow regime characterized by concentrated floods of relatively large magnitude is also regarded as highly conducive to the formation of new channels where low bank erodibility constrains channel capacity anastomosis may in certain cases represent a transitional form of channel pattern but there is no denying the longevity of some anastomosing systems

the morphology and formation of floodplain surface channels cooper creek australia floodplain surface channels are prominent features of the floodplain of cooper creek a low energy anastomosing river in semi arid southwest queensland three distinct floodplain surface environments and corresponding pedological variations are identified braided patterns characterized by large scale braid bars separating wide shallow channels occupy 44 of floodplain area gilgai undulations of the soil surface characteristic of many vertisol soils are subdued or absent from the braided areas the reticulate pattern occupies 39 of the floodplain surface and is characterized by densely developed networks of small channels with angular planforms the prominently developed gilgai in these areas play a significant role in the formation of the reticulate pattern high rarely inundated areas of the floodplain are unchannelled and occupy the remaining 17 of the floodplain surface analysis of the distribution of the patterns over a 370 km long reach of the river reveals that sensitive feedbacks between fluvial and pedogenic processes determine pattern expression the energy of inundating flows is controlled by floodplain width transmission losses and subtle floodplain topography variations the patterns are distributed along an energy continuum braided patterns occur in higher energy areas in which fluvial erosion prevents gilgai expression reticulate patterns are confined to intermediate energy areas in which inundation frequencies are sufficient to provide wetting and drying frequencies necessary for gilgai formation and flow energy sufficiently low to allow gilgai expression unchannelled areas are neither inundated frequently enough to cause gilgai formation nor with sufficient energy to cause channel formation

types of river channel patterns and their natural controls river channel patterns are thought to form a morphological continuum this continuum is two dimensional defined by plan features of which there are three straight meandering branching and structural levels of fluvial relief of which there are also three floodplain flood channel low water channel combinations of these three categories define the diversity of patterns one of the most important factors in channel development is stream power defined by water discharge and river slope the greater the stream power the stronger the branching tendency but threshold values of stream power are different for the three different hierarchical levels of channel relief the critical stream power values and hydrological regime together define the channel pattern and analysis of the pattern type can be undertaken using effective discharge curves 1998 john wiley sons ltd

defining large river channel patterns alluvial exchange and plurality abstract large rivers have anabranching channels with components that may be defined as braided meandering or straight this paper shows that application of such holistic terminologies is complicated by recognition of within type and transitional type variety a confusingly varied use of terms and a coverage of pattern characteristics that for many large rivers is incomplete in natural states big rivers can be plural systems in which main accessory tributary and floodplain channels and lakes differ functionally and vary in terms of morphological dynamics a distinction is drawn between the hydrological and geomorphological connectivity of components in big river plural systems at any one time even at flood stage only some channels are geomorphologically active six types of geomorphological connectivity are described that range from coupled through to partially coupled and decoupled the interplay between geomorphological and hydrological connectivity in large rivers is shown to determine habitat status and therefore ecological diversity for improved understanding of the dynamics as well as the forms of these large composite systems it is helpful to 1 adopt element level specification not only for sediment bodies but also for functioning channels 2 track the sediment transfer processes and exchanges that produce channel forms over the highly varied timescales operating within large rivers and 3 recognise the ways in which partially coupled and connected geomorphological systems produce naturally a composite set of forms at different rates such augmenting information will provide an improved platform for both river management and ecological understanding