late quaternary history of the mackenzie beaufort region arctic canada from modelling of permafrost temperatures 2 the mackenzie delta tuktoyaktuk coastlands in the mackenzie beaufort region maximum permafrost thickness is 750 m in the pleistocene tuktoyaktuk coastlands less than 100 m in the holocene mackenzie delta and 500 m and anomalously warm in the big lake delta plain between the two areas numerical modelling has been used to derive surface temperature histories that fit ground temperatures and permafrost conditions at 12 wells in the unipkat kumak and taglu hydrocarbon fields the models indicate that the present holocene mackenzie delta was built by fluvial processes into a submarine trough the delta front passed a site presently some 20 km from the coast about 4 5 ka and subsequently 58 m of ice bonded permafrost has aggraded in contrast the big lake delta plain was a subaerial platform for much of the wisconsinan it experienced several thousand years of inundation in the holocene probably due to widespread development of thermokarst lakes at sites 8 12 km from the coast the present subaerial conditions were established 0 5 1 5 ka throu

the δ15n of nitrate in the southern ocean nitrogen cycling and circulation in the ocean interior we report analyses of the nitrogen isotopic composition of nitrate in the eastern indian and pacific sectors of the southern ocean in this paper we focus on the subsurface data as well as data from the deep waters of other ocean basins nitrate 15n is relatively invariant in much of the abyssal ocean i e below 2 5 km with a value of 4 8 0 2 observed in lower circumpolar deep water north atlantic deep water and central pacific deep water the isotopic invariance of deep ocean nitrate stems fundamentally from the completeness of nitrate utilization in most of the global surface ocean the southern ocean surface being an important exception in the subantarctic zone north of the polar frontal zone the nitrate 15n of upper circumpolar deep water is 0 7 greater than that of lower circumpolar deep water this isotopic enrichment appears to result from denitrification in the low latitude water masses with which upper circumpolar deep water communicates the isotopic enrichment of upper circumpolar deep water is diminished in the antarctic probably because of the remineralization of sinking organic n which has a low 15n in the antarctic relative to the other water masses of the southern ocean the subantarctic thermocline has a very low nitrate 15n for its nitrate concentration because of exchange with the low latitude thermocline where this isotopic signature appears to originate this signature of the low latitude thermocline has two probable causes 1 mixing with low nitrate surface water and 2 the oxidation of newly fixed n

influence of open ocean nitrogen supply on the skeletal δ15n of modern shallow water scleractinian corals abstract the isotopic composition of skeleton bound organic nitrogen in shallow water scleractinian corals hereafter cs 15 n is an emerging tool for studying the marine nitrogen cycle in the past the cs 15 n has been shown to reflect the 15 n of nitrogen n sources to corals with most applications to date focusing on the anthropogenic terrestrial n inputs to reef environments however many coral reefs receive their primary n sources from the open ocean and the cs 15 n of these corals may provide information on past changes in the open ocean regional and global n cycle using a recently developed persulfate denitrifier based method we measured cs 15 n in modern shallow water scleractinian corals from 8 sites proximal to the open ocean at sites with low open ocean surface nitrate concentrations typical of the subtropics and tropics measured cs 15 n variation on seasonal and annual timescales is most often less than 2 in contrast a broad range in cs 15 n of 10 is measured across these sites with a strong correlation between cs 15 n and the 15 n of the deep nitrate supply to the surface waters near the reefs while cs 15 n can be affected by other n sources as well and can vary in response to local reef conditions as well as coral symbiont physiological changes this survey indicates that when considering corals proximal to the open ocean the 15 n of the subsurface nitrate supply to surface waters drives most of the cs 15 n variation across the global ocean thus cs 15 n is a promising proxy for reconstructing the open ocean n cycle in the past

equatorial pacific 13 c water eddies in the eastern subtropical south pacific ocean abstract argo float profile data are used to analyze warm salty weakly stratified subthermocline eddies of tropical origin in the eastern subtropical south pacific ocean these eddies contain anomalous signatures of the equatorial pacific 13 c water that is carried poleward within the peru chile undercurrent pcu as it flows along the west coast of south america from their source along the chilean coast between 29 and 39 s the eddies spread westward and slightly northward likely at least partly advected by the subtropical gyre the eddy water properties contrast strongly with the colder fresher more strongly stratified waters of subantarctic origin being carried northward then westward by the gyre near the eddy source about 6 of argo profiles sample eddies that are above selected thresholds for both salinity and potential vorticity anomalies relative to maps of the mean distributions of these properties on and around the core isopycnal for the eddies the proportion of such profiles dimini

tertiary quaternary drainage of the pre glacial mackenzie basin abstract pre glacial drainage in the northwestern mackenzie region was established in early tertiary time with the uplift of the mountains during the laramide orogeny and persisted until near the end of the pleistocene rivers arose in the mackenzie and richardson mountains and followed a generally eastward direction across piedmont surfaces from the mountains towards the plains the evidence to support this hypothesis includes geomorphology provenance of sediments reconstruction of paleo surfaces and stratigraphy two major drainage systems developed one to the atlantic ocean and another to the arctic ocean the atlantic drainage is composed of the northwestern tributaries of an integrated drainage system that flowed towards hudson bay traces of this drainage are found in the canyon ranges of the mackenzie mountains iroquois upland and in the norman range of the franklin mountains the arctic drainage included two main basins the porcupine basin that drained from west to east across the richardson mountains and the anderson basin that included the peel and snake rivers as its tributaries late wisconsinan laurentide glaciation deranged these drainage systems establishing the porcupine river as a tributary of the yukon river and integrating the tertiary drainage systems into the mackenzie river system flowing to the arctic ocean

significance of interdune deposits and bounding surfaces in aeolian dune sands bounding surfaces and interdune deposits provide keys for detailed interpretations of the development shape type wavelength and angle of climb of aeolian bedforms as well as overall sand sea conditions current alternate interpretations of bounding surfaces require very different but testable models for sand sea deposition two perpendicular traverses of jurassic entrada sandstone utah reveal relations among cross strata first order bounding surfaces and horizontal strata these field relations seem explicable only as the deposits of downwind migrating climbing enclosed interdune basins horizontal strata and dune bodies consisting of superimposed smaller crescentic dunes cross stratified deposits a 1 7 km traverse parallel to the palaeowind direction provides a time transgressive view showing continuous cosets of cross strata first order bounding surfaces and interdune deposits climbing downwind at an angle of a few tenths of a degree changes occur in the angle of climb cross strata structure and interdune deposits these reflect changes in depositional conditions through time a 1 5 km traverse perpendicular to the palaeowind direction provides a view at an instant in geological time showing first order bounding surfaces and interdune deposits forming flat laterally discontinuous lenticular bodies the distribution of interdune sedimentary structures in this traverse is very similar to that of some modern interdune basins such as those on padre island texas hierarchies of bounding surfaces in an aeolian deposit reflect the bedform development on an erg the presence of three orders of bounding surfaces indicates dune bodies consisting of smaller super imposed dunes the geometry of first order bounding surfaces is a reflection of the shape of the inter dune basins second order bounding surfaces originate by the migration of the superimposed dunes over the larger dune body and reflect individual dune shape and type third order bounding surfaces are reactivation surfaces showing stages in the advance of individual dunes the presence of only two orders of bounding surfaces indicates simple dunes modern and entrada interdune deposits show a wide variety of sediment types and structures reflecting deposition under wet damp and dry conditions interdune deposits are probably the best indicators of overall erg conditions and commonly show complex vertical sequences reflecting changes in specific depositional conditions

the fall recovery orbit and composition of the tagish lake meteorite a new type of carbonaceous chondrite the preatmospheric mass of the tagish lake meteoroid was about 200 000 kilograms its calculated orbit indicates affinity to the apollo asteroids with a semimajor axis in the middle of the asteroid belt consistent with a linkage to low albedo c d and p type asteroids the mineralogy oxygen isotope and bulk chemical composition of recovered samples of the tagish lake meteorite are intermediate between cm and ci meteorites these data suggest that the tagish lake meteorite may be one of the most primitive solar system materials yet studied

a sea level curve for the canadian beaufort shelf radiocarbon dated peat and peaty clay samples from geotechnical boreholes in the canadian beaufort continental shelf have been used to reconstruct a late quaternary relative sea level rsl curve the samples were carefully selected and evaluated using palynological techniques to ensure that reasonable age error limits could be given to each sample the dated samples were then related to the local geological setting using seismic profiles to determine the environment of deposition the resulting data show a rise of 140 m in rsl since 27 000 years bp a minor lowering of rsl at some time between 20 000 and 10 000 years bp is inferred from acoustic data contributions from basin subsidence sediment loading and consolidation account for 35 m of the total rsl rise the rsl curve is interpreted in the light of recent models of the isostatic and eustatic responses of the earth s crust at the laurentide ice sheet margin ice may have been more extensive during the middle wisconsinan than previously thought a

mid wisconsinan eolian deposits of the kittigazuit formation tuktoyaktuk coastlands northwest territories canada the kittigazuit formation is a late quaternary sand unit commonly observed throughout the tuktoyaktuk coastlands and in subbottom sediments of the southern beaufort shelf stratigraphic and sedimentology data including sedimentary structures grain surface characteristics and heavy and light mineralogy assist in characterizing the deposit and indicate that it is eolian in origin plant and arthropod macrofossils suggest that although the summer climate during deposition was as warm or slightly warmer than today conditions were likely more arid permafrost is interpreted as being widespread during deposition accelerator mass spectrometry radiocarbon dates indicate that the kittigazuit formation was deposited between 37 and 33 ka bp the unit is therefore interpreted as a mid wisconsinan eolian dune deposit formed by reworking of underlying alluvial sediments of the kidluit formation under nonglacial conditions glaciogenic sediments overlying the kittigazuit formation indicate that glacial ice cover

late glacial drainage systems along the northwestern margin of the laurentide ice sheet abstract the evolution of drainage systems along the retreating northwestern laurentide ice sheet was complex the interaction of ice margin configuration topography and glacioisostasy resulted in a network of meltwater rivers that variably overflowed to the arctic and pacific oceans and to the gulf of mexico glacial lakes also changed dramatically in size and location during the period of deglaciation at the last and all time glacial maximum the ice sheet extended into the eastern cordillera blocking northward and eastward drainage to the arctic ocean some meltwater and most non glacial runoff were diverted through the mountains to the yukon river basin into alaska and the pacific ocean retreat from the glacial maximum prior to 21 ka bp allowed proglacial drainage from the western margin of the ice sheet to flow into the beaufort sea arctic ocean deglaciation was rapid after about 13 ka bp with the present route of the lower mackenzie river established between 13 and 11 5 ka bp continued ice retreat led to significant southward expansion of the mackenzie beaufort drainage basin at about 11 5 ka bp through drainage capture of glacial lake peace which previously had drained southeastward into the missouri river and to the gulf of mexico very rapid ice retreat between 10 5 and 10 ka bp allowed glacial lake mcconnell to expand down slope in contact with the ice margin numerous glacial lakes occurred along the northwestern margin of the ice sheet during the maximum and retreat phases these include ice dammed glacial lake old crow which occupied unglaciated terrain of the northern yukon and glacial lake peace which utilized a number of outlets as it migrated eastward with the ice front along the peace valley the largest glacial lakes in the region were the result of glacioisostatic depression reversing the regional drainage the mackenzie phase of glacial lake mcconnell was the second largest pleistocene lake in north america 215 000 km 2 late glacial and post glacial changes in drainage systems were largely in response to isostatic rebound

nitrogen isotope ratios of nitrate and n anomalies in the subtropical south pacific nitrogen isotopic ratios of nitrate 15n no3 were analyzed above 1000 m water depth along 17 s in the subtropical south pacific during the revisit woce p21 cruise in 2009 the 15n no3 and n values were as high as 17 and as low as 18 mol n l 1 respectively at depths around 250 m east of 115 w but were as low as 5 and as high as 1 mol n l 1 respectively in subsurface waters west of 170 w the relationships among no3 concentrations n values 15n no3 values and oxygen and nitrite concentrations suggest that a few samples east of 90 w were from suboxic and nitrite accumulated conditions and were possibly affected by in situ water column denitrification most of the high 15n no3 and negative n waters were probably generated by mixing between subantarctic mode water from the southern ocean and oxygen deficit zone water from the eastern tropical south pacific with remineralization of organic matter occurring during transportation moreover the relationship between 15n no3 and n values as well as trichodesmium abundances and size specific nitrogen fixation rates at the surface suggest that the low 15n no3 and positive n subsurface waters between 160 e and 170 w were generated by the input of remineralized particles created by in situ nitrogen fixation mainly by trichodesmium spp therefore the 15n values of sediments in this region are expected to reveal past changes in nitrogen fixation or denitrification rates in the subtropical south pacific

stratigraphy and glaciotectonic structures of permafrost deformed beneath the northwest margin of the laurentide ice sheet tuktoyaktuk coastlands canada the upper 5 20 m of ice rich permafrost at three sites overridden by the northwest margin of the laurentide ice sheet in the tuktoyaktuk coastlands western arctic canada comprise massive ice beneath ice rich diamicton or sandy silt the diamicton and silt contain 1 truncated ice blocks up to 15 m long 2 sand lenses and layers 3 ice veins dipping at 20 30 4 ice lenses adjacent and parallel to sedimentary contacts and 5 ice wedges the massive ice is interpreted as intrasedimental or buried basal glacier ice and the diamicton and silt as glacitectonite that has never thawed deformation of frozen ground was mainly ductile in character deformation was accompanied by sub marginal erosion of permafrost which formed an angular unconformity along the top of the massive ice and supplied ice clasts and sand bodies to the overlying glacitectonite after deformation and erosion ceased postglacial segregated ice and ice wedge ice developed within the deformed permafrost

luminescence dating of mid to late wisconsinan aeolian sand as a constraint on the last advance of the laurentide ice sheet across the tuktoyaktuk coastlands western arctic canada luminescence dating of pre glacial sand in the tuktoyaktuk coastlands northwest territories discounts an early wisconsinan age for the last laurentide glaciation to cross the arctic coastal plain and supports a late wisconsinan age aeolian dune sand from the kittigazuit formation near cliff point on the southern shore of liverpool bay predates till deposited during the toker point stade potassium rich feldspar from three stratigraphic sections 35 km up ice from the toker point glacial limit provides thermoluminescence age estimates that range from 18 7 2 0 to 9 1 1 0 ka and infrared stimulated luminescence age estimates of 23 8 5 1 to 11 0 2 1 ka quartz from four of the same samples provides optically stimulated luminescence age estimates of 16 5 1 0 to 13 7 0 9 ka collectively these estimates reject the early wisconsinan age for the toker point stade glaciation inferred hitherto from radiocarbon dating a review of pre glacial and post glacial age estimates from the region indicates

revisiting nutrient utilization in the glacial antarctic evidence from a new method for diatom bound n isotopic analysis holocene in the indian sector is smaller than in previous measurements these data suggest no change in the degree of nitrate utilization in the atlantic sector and at most a 20 increase from 25 to 45 in the indian sector the new measurements suggest that during the last ice age in the atlantic sector of the antarctic the atmospheric source of biologically available iron was not so great as to become significant relative to the iron supply from below given the apparent spatial variability in the degree of nitrate drawdown more work is required to develop an adequate picture of the glacial antarctic nutrient field index terms 4806 oceanography biological and chemical carbon cycling 4845 oceanography biological and chemical nutrients and nutrient cycling 4894 oceanography biological and chemical instruments and techniques 9310 information related to geographic region antarctica

coupled nitrate nitrogen and oxygen isotopes and organic matter remineralization in the southern and pacific oceans 1 the difference between nitrate 15n and 18o or 15 18 is sensitive to organic matter remineralization and tracks the modification of nitrate as it passes from the deep pacific ocean through the southern ocean surface and into the intermediate depth pacific circumpolar deep water cdw is upwelled with a nitrate 15 18 of 3 0 and appears unaltered by nitrate assimilation in the antarctic surface however within subantarctic mode water samw the primary conduit of deep sea nutrients to the lower latitudes nitrate 15n and 18o are both higher than cdw while nitrate 15 18 is as low as 1 5 the lower samw nitrate 15 18 results from the production of low 15n organic matter during partial assimilation of the surface nitrate pool followed by its sinking and remineralization back to nitrate lowering the 15n of thermocline nitrate more than its 18o as samw flows toward the lower latitudes nitrate 15 18 is expected and observed to increase because complete surface ocean nitrate consumption produces sinking nitrogen with a 15n similar to that of the nitrate supplied from below such that remineralization lowers the 18o of nitrate but not its 15n nitrate 15 18 is also used to estimate a surprisingly high low latitude sinking nitrogen 15n of 9 0 suggesting a major effect of 14no3 loss by tropical denitrification on middepth nitrate basin wide the remineralization of this high sinking nitrogen 15n increases nitrate 15 18 as deep as the southward moving pacific deep water which supplies cdw this relatively high 15 18 is then lowered to the observed cdw value by the remineralization of southern ocean sinking nitrogen with a low 15n

late quaternary variability of sedimentary nitrogen isotopes in the eastern south pacific ocean 1 we present high resolution bulk sedimentary 15n data from the southern edge of the present day oxygen minimum zone of the eastern south pacific the record is interpreted as representing changes in water column nitrogen removal during the last 70 000 years we found significant fluctuations in the isotopic signal that suggest major reorganizations of the oxygen minimum zone at millennial timescales these fluctuations were not related to other millennial scale changes like the northern hemisphere s dansgaard oeschger climate swings or local changes in primary productivity so appear to be dictated by the southern hemisphere s climate rhythm this is preliminarily corroborated by an overall agreement between our 15n data and the sedimentary proxy of ice sheet dynamics in patagonia which is in turn correlated with surface water properties at the midlatitude subduction region of the eastern south pacific intermediate waters finally potential implications on late quaternary changes in atmospheric co2 concentrations are discussed

modeling how surface nitrogen fixation influences subsurface nutrient patterns in the north atlantic 1 we represented mechanistically the process of nitrogen n fixation and associated n anomalies in the atlantic ocean using a three dimensional coupled physical biogeochemical model available direct measurements of n fixation rates in the atlantic ocean are compiled and these along with observed n anomalies constrain the model the model n fixation rate for the whole atlantic domain is 2 1 1012 moln yr 1 the model generated n anomaly shows the observed feature of a subsurface maximum when plotted on isopycnal surfaces the model generated n anomaly bears little relation to the pattern of n fixation at the surface however the highest n fixation rates should be spatially related to n distribution if particulate export is remineralized at depths in the same region where the n fixation occurred we performed case studies varying remineralization and advection to clarify the genesis of the n anomaly and to determine the reasons underlying differences between n anomalies and n fixation rate patterns these studies indicated that the difference between these two patterns was created by both horizontal advection of excess n compared to phosphorus p and preferential remineralization of p compared to n n fixation and preferential p remineralization create high n anomalies both at the surface and in subsurface waters in the tropical atlantic which are transported into the northwestern north atlantic by western boundary currents and subsequently subducted as a result the highest n anomalies are located not in the tropics but in the northwestern north atlantic

nitrogen isotopic composition of organic matter from a 168 year old coral skeleton implications for coastal nutrient cycling in the great barrier reef lagoon abstract ongoing human activities are known to affect nitrogen cycling on coral reefs but the full history of anthropogenic impact is unclear due to a lack of continuous records we have used the nitrogen isotopic composition of skeleton bound organic matter cs 15 n in a coastal porites coral from magnetic island in the great barrier reef as a proxy for n cycle changes over a 168 yr period 1820 1987 ad the magnetic island inshore reef environment is considered to be relatively degraded by terrestrial runoff given prior cs 15 n studies from other regions there was an expectation of both secular change and oscillations in cs 15 n since european settlement of the mainland in the mid 1800s surprisingly cs 15 n varied by less than 1 5 despite significant land use change on the adjacent mainland over the 168 yr measurement period after 1930 cs 15 n may have responded to changes in local river runoff but the effect was weak we propose that natural buffering against riverine nitrogen load in this region between 1820 and 1987 is responsible for the observed stability in cs 15 n in addition to coral derived skeletal 15 n we also report for the first time 15 n measurements of non coral derived organic n occluded within the coral skeleton which appear to record significant changes in the nature of terrestrial n inputs in the context of previous cs 15 n records most of which yield cs 15 n changes of at least 5 the magnetic island coral suggests that the inherent down core variability of the cs 15 n proxy is less than 2 for porites

controls on sedimentary nitrogen isotopes along the chile margin chilean margin sedimentary n isotope records have been the focus of paleoceanographic studies examining the extent of water column denitrification in the eastern south pacific in the past here we use 15n 14n of nitrate and surface sedimentary n along the chilean coast to investigate the relative contributions of water column denitrification and surface nitrate assimilation by phytoplankton to the sedimentary n isotope record off northern and central chile subsurface enrichment of 15no3 is associated with the lowest oxygen concentrations and maximum nitrate deficits the product of water column denitrification locally at 21 s and through the transport of denitrified waters to the south while elevated the 15n of pycnocline nitrate shows no distinct trend with distance from the omz and is nearly homogenous within the shallow subsurface layer presumably due to lateral circulation along the margin moreover an isotopically depleted and relatively uniform layer exists within the shallow subsurface possibly as a result of the remineralization of newly fixed nitrogen that may work to further homogenize the 15n of the upwelling nitrate whereas the high 15n of sedimentary n in the region is clearly a product of denitrification and its isotopic imprint on nitrate along the margin the northward increase in sedimentary 15n from higher southern latitudes also reflects the degree of surface layer nitrate consumption by phytoplankton the northward increase in sedimentary 15n corresponds to a regional decrease in the surface nitrate concentration and isotopic fractionation during nitrate assimilation is apparent in shallow nitrate 15n a comparison of the 15n in shallow subsurface nitrate and sedimentary n suggests that north of 30 s nearly complete nitrate consumption causes the 15n of sediments to converge on that of the nitrate supply such that denitrification should be the dominant signal in downcore 15n records from these latitudes moreover the lateral homogeneity of the denitrification signal in the subsurface within this region suggests that such records will provide robust reconstructions of denitrification intensity