coherence of western boundary pressure at the rapid wave array boundary wave adjustments or deep western boundary current advection this study investigates the coherence between ocean bottom pressure signals at the rapid climate change programme rapid west atlantic variability experiment wave array on the western north atlantic continentalslope includingthewoodsholeoceanographicinstitutionlinew highlycoherentpressuresignals propagate southwestward along the slope at speeds in excess of 128 m s 21 consistent with expectations of barotropic kelvin like waves coherent signals are also evidenced in the smaller pressure differences relative to 1000 m depth which are expected to be associated with depth dependent basinwide meridional transport variations or an overturning circulation these signals are coherent and almost in phase for all time scales from 3 6 years down to 3 months coherence is still seen at shorter time scales for which group delay estimates are consistent with a propagationspeedofabout1 m s 21 over990 kmofcontinentalslopebutwithlargeerrorboundsonthespeed this is roughly consistent with expectations for propagation of coastally trapped waves though somewhat slower than expected a comparison with both eulerian currents and lagrangianfloat measurements shows that the coherence is inconsistent with a propagation of signals by advection except possibly on time scales longer than 6 months

accelerator mass spectrometer ages for the younger dryas event in atlantic canada abstract in atlantic canada bulk sediment dates for the onset of a late glacial cooling widely regarded as the younger dryas event are highly variable ranging from 14 300 270 to 10 800 100 yr b p we present the first accelerator mass spectrometer ams 14c dates from atlantic canada at or close to the boundaries of this event from six sites in new brunswick and nova scotia the mean of five dates places the onset of this cooling at ca 10 770 yr b p the inclusion of a sixth perhaps anomalously old date changes the mean to 10 880 yr b p the termination averages three dates ca 10 000 yr b p these dates place the timing of the younger dryas event in atlantic canada closer in line with the traditional chronozone boundaries of 11 000 and 10 000 yr b p in northwest europe

iceland scotland overflow water transport variability through the charlie gibbs fracture zone and the impact of the north atlantic current the charlie gibbs fracture zone cgfz a deep and wide gap in the mid atlantic ridge near 52 n is a gateway between the eastern and western subpolar regions for the atlantic meridional overturning circulation amoc in 2010 2012 an eight mooring array of current meters and temperature salinity sensors was installed across the cgfz between 500 m and the sea floor to measure the mean transport of westward flowing iceland scotland overflow water isow and investigate the impact of the eastward flowing north atlantic current nac on isow transport variability the 22 month record mean isow transport through the cgfz 1 7 0 5 sv 95 confidence interval is 30 lower than the previously published estimate based on 13 months of current only measurements 2 4 sv 1 2 sv saunders 1994 the latter mean estimate may have been biased high due to the lack of continuous salinity measurements although the two estimates are not statistically different due to strong mesoscale variability in both data sets empirical orthogonal function analysis and maps of satellite derived absolute dynamic topography show that weak westward isow transport events and eastward reversals are caused by northward meanders of the nac with its deep reaching eastward velocities these results add to growing evidence that a significant fraction of isow exits the iceland basin by routes other than the cgfz

on the deep western boundary current south of cape cod abstract using ctd oxygen data from eight cruises in the decade from 1994 2003 we have constructed a mean section of properties across the deep western boundary current dwbc south of cape cod near 70 w since all sections included direct velocity measurements our composite section enables us to portray the flow field as well as the mean water mass structure inshore of the gulf stream between the 2500 and 4000 m isobaths the flow is to the southwest along the bathymetry and is remarkably barotropic the equatorward flowing labrador sea water is shown to have high dissolved oxygen low salinity and low potential vorticity while the underlying overflow water is high in oxygen transport estimates for the cold limb of the thermohaline circulation give a range of 14 to 19 sv for the n atlantic deep water found on the section the greatest uncertainty is due to the presence of a warm core ring on one of the sections which apparently completely reversed the flow in the dwbc offshore of the dwbc some of the deep source waters are returned to the north in the deep gulf stream the section is compared to two other widely separated locations abaco and 55 w that have markedly different dwbc characteristics

potential vorticity structure in the north atlantic western boundary current from underwater glider observations abstractpotential vorticity structure in two segments of the north atlantic s western boundary current is examined using concurrent high resolution measurements of hydrography and velocity from gliders spray gliders occupied 40 transects across the loop current in the gulf of mexico and 11 transects across the gulf stream downstream of cape hatteras cross stream distributions of the ertel potential vorticity and its components are calculated for each transect under the assumptions that all flow is in the direction of measured vertically averaged currents and that the flow is geostrophic mean cross stream distributions of hydrographic properties potential vorticity and alongstream velocity are calculated for both the loop current and the detached gulf stream in both depth and density coordinates differences between these mean transects highlight the downstream changes in western boundary current structure as the current increases its transport downstream upper layer potential vorticity is generall

andean tectonics as a cause for changing drainage patterns in miocene northern south america newdatafromneogenestratainnorthernsouthamericasuggestthatmiocenetectonisminthenortheasternandeswasresponsible for the genesis of the amazon river and changes in the drainage patterns of other major rivers such as the magdalena and the orinoco here we present a new model for the paleogeographic evolution of northern south america during the miocene in the early miocene a large part of the drainage of northwest amazonia was directed northward along the paleo orinoco river system to a deltainlakemaracaibo upliftoftheeasterncordillerainthelate middle miocene caused thefirst development of the amazon river however no connection with the atlantic was established and the amazon fed the paleo orinoco river system which drained toward the caribbean substantial andean uplift in the late miocene resultedinmajorchangesinpaleogeography theorinocochangedits course the amazon established a connection to the atlantic causing the drowning of carbonate platforms and the amazon caribbeanconnectionwasclosed thusthedrainageandpaleogeography ofnorthernsouthamericainthemiocenewerestronglycontrolled by tectonic movements in the northeastern andes

surface climate variations over the north atlantic ocean during winter 1900 1989 abstract the low frequency variability of the surface climate over the north atlantic during winter is described using 90 years of weather observations from the comprehensive ocean atmosphere data set results are based on empirical orthogonal function analysis of four components of the climate system sea surface temperature sst air temperature wind and sea level pressure an important mode of variability of the wintertime surface climate over the north atlantic during this century is characterized by a dipole pattern in ssts and surface air temperatures with anomalies of one sign cast of newfoundland and anomalies of the opposite polarity off the southeast coast of the united states wind fluctuations occur locally over the regions of large surface temperature anomalies with stronger than normal winds overlying cooler than normal ssts this mode exhibits variability on quasi decadal and biennial time scales the decadal fluctuations are irregular in length averaging 9 years before 1945 and 1

a 60 million year cenozoic history of western amazonian ecosystems in contamana eastern peru abstract we provide a synopsis of 60 million years of life history in neotropical lowlands based on a comprehensive survey of the cenozoic deposits along the quebrada cachiyacu near contamana in peruvian amazonia the 34 fossil bearing localities identified have yielded a diversity of fossil remains including vertebrates mollusks arthropods plant fossils and microorganisms ranging from the early paleocene to the late miocene pliocene 20 successive levels this cenozoic series includes the base of the huchpayacu formation fm early paleocene lacustrine fluvial environments charophyte dominated assemblage the pozo fm middle late eocene marine then freshwater environments most diversified biomes and complete sections for the chambira fm late oligocene late early miocene freshwater environments vertebrate dominated faunas the pebas fm late early to early late miocene freshwater environments with an increasing marine influence excellent fossil record and ipururo fm late miocene pliocene fully fluvial environments virtually no fossils preserved at least 485 fossil species are recognized in the contamana area 250 plants 212 animals and 23 foraminifera based on taxonomic lists from each stratigraphic interval high level taxonomic diversity remained fairly constant throughout the middle eocene miocene interval 8 12 classes ordinal diversity fluctuated to a greater degree and family species diversity generally declined with a drastic drop in the early miocene the paleocene pliocene fossil assemblages from contamana attest at least to four biogeographic histories inherited from i mesozoic gondwanan times ii the panamerican realm prior to iii the time of south america s cenozoic splendid isolation and iv neotropical ecosystems in the americas no direct evidence of any north american terrestrial immigrant has yet been recognized in the miocene record at contamana

widespread evidence of 1500 yr climate variability in north america during the past 14 000 yr there is debate concerning the spatial extent and magnitude of the recently identified 1500 yr climate oscillation existing evidence is largely restricted to the north atlantic and adjacent landmasses the spatial extent magnitude and effects of these climate variations within the terrestrial environment during the holocene have not been established we show that millennial scale climate variability caused changes in vegetation communities across all of north america with a periodicity of 1650 500 yr during the past 14 000 calendar years cal yr times of major transitions identified in pollen records occurred at 600 1650 2850 4030 6700 8100 10 190 12 900 and 13 800 cal yr b p consistent with ice and marine records we suggest that north atlantic millennial scale climate variability is associated with rearrangements of the atmospheric circulation with far reaching influences on the climate

response of interior north america to abrupt climate oscillations in the north atlantic region during the last deglaciation several broad scale climatic oscillations during the last deglaciation are well documented in regions around the north atlantic ocean this paper reviews empirical evidence for these deglacial climatic oscillations from non coastal north america and discusses implications for testing climatic simulations and for understanding the cause and transmittal mechanisms paleoclimatic interpretation of oxygen isotope records from several small sites in the eastern great lakes region indicates a classic deglacial climatic sequence that is comparable with records from europe and greenland the climatic events as interpreted from crawford lake oxygen isotopes include the bolling allerod boa warming at 12 700 14c bp a warm boa at 12 500 10 920 14c bp an intra allerod cold period shortly before 11 000 14c bp a cold younger dryas yd climate reversal at 10 920 10 000 14c bp the holocene warming at 10 000 14c bp a brief preboreal oscillation pb at 9650 14c bp and an early holocene cold event at 7500 14c bp 8200 cal bp some of these events were also evident from changes in upland and aquatic vegetation and sediment lithology the pronounced yd climatic reversal has been documented from pollen records along the ecotones at this time and from glacier readvances in the great lakes region along the rocky mountains from alberta to colorado the yd event is indicated by alpine glacier advance and or shift in timberline vegetation in minnesota and upper new york early holocene climatic instability is also suggested by oxygen isotope records and or varve thickness the regional variations in evidence for the yd and other events in north america suggest that climatic oscillations may have different expressions in paleo records depending on geographic location and characteristics of a particular site the extent and magnitude of these climatic oscillations across north america suggest that these oscillations are an expression of climatic change that was probably widespread rather than locally induced by a nearby glacier the location of these sites implies that climatic signals were likely carried over the northern hemisphere through the atmosphere as indicated by general circulation models we hypothesize that the lack of evidence for a cold yd in interior north america west of the great lakes region and east of the rocky mountains was caused by the trapping of cold arctic air mass north of the laurentide ice sheet and by uninterrupted northward expansion of warm caribbean air this strongly contrasted climate also produced non analogous biological assemblages

introduction to atlantic meridional overturning circulation amoc a striking conclusion of the intergovernmental panel on climate change 2007 report is the crucial role that the atlantic meridional overturning circulation amoc may play in anthropogenic climate change however these ipcc coupled climate simulations show a broad range of uncertainty in the magnitude and timing of amoc transport change ranging from none to nearly complete collapse within the 21st century the potential consequences of large changes in the characteristics of amoc have motivated the creation in the united states of an interagency program and implementation plan to develop monitoring and prediction capabilities for the amoc this program parallels the development of substantial monitoring efforts by european south american and african countries notably the uk rapid and rapid watch programs the papers contained in this volume are derived from presentations at the first u s atlantic meridional overturning circulation amoc meeting held 4 6 may 2009 to review the us implementation plan and its coordination with other monitoring activities the atlantic meridional overturning circulation consists of multiple components illustrated in an attached figure water enters the south atlantic at upper and intermediate depths through both western and eastern routes where eddy transport is especially important and is transported northward across the equator where it recirculates within the northern subtropical and subpolar gyres the northern end is defined by the sinking regions of the nordic seas and the labrador sea where the waters that eventually form the upper and lower branches of north atlantic deep water are conditioned high surface salinities the result of high net evaporation in the tropics and subtropics including the mediterranean sea and presence of regions of the arctic ocean that remain ice free even in winter allow for the rapid cooling and thus densification of surface water this dense surface water becomes the source of deep water formation in the sinking regions in addition to transporting mass the amoc transports roughly half of the total amount of heat carried northward through the northern subtropics down the temperature gradient by the ocean in contrast in the southern hemisphere amoc transports heat up gradient from the cool circumpolar current to the warm tropics paleoevidence suggests that amoc heat transport in the two hemispheres has varied over time in ways intimately tied to millennial changes in the earth s climate in one example the abrupt younger dryas spell of cold weather over the north atlantic which began 13 000 years ago has generally been linked to a millennial shutdown of the amoc as a result of massive freshwater discharge from the north american continent the current amoc monitoring array consists of a series of instrumented transects located across key passages see cunningham et al 2010 for a recent review in the arctic and sub arctic transects cross fram strait denmark strait and the faroe channel connecting greenland iceland and the united kingdom as well as the entrance to the labrador sea further south and extending outwards from the east coast of north america there are a series of monitoring arrays including arrays of the canadian atlantic zone monitoring program deployments of the rapid western atlantic variability experiment wave line w at 39 n as well as the rapid moc moored array the latter spans the entire atlantic basin along 26 5 n at tropical latitudes we have the meridional overturning variability experiment move array at 16 n while in the southern hemisphere a corresponding basin spanning transect is being established at the latitude of cape of good hope complemented by arrays at drake passage

fluvial palaeoenvironments in the intracratonic amazonas basin early miocene early middle miocene colombia abstract based on a detailed study of early miocene to early middle miocene sediments in the caqueta river area amazonas basin colombia a reconstruction of the palaeoenvironmental and palaeogeographical history is made sediment composition sedimentary sequences and transport directions indicate that the succession was deposited by a low sinuosity fluvial system with an anastomosing character that originated from the guyana shield basin subsidence precambrian and palaeozoic palaeorelief and a changing base level controlled deposition in this fluvial system sedimentary environments such as channels abandoned channels crevasse splays backswamps and palaeosoils characterized this system where fluvial flooding was common the early miocene to early middle miocene sequences have been truncated by a more recent fluvial system probably of pliocene to pleistocene age representing the precursor of the present caqueta river palynological analysis suggest that the sediments are part of the retitricolporites and the psiladiporites crototricolpites pollen zones fifteen new species are described which belong to the genera psilatricolpites retitricolpites retitricolporites bombacacidites syncolporites and psilastephanocolporites the palynological assemblages indicate that the area was characterized by palm swamps riparian vegetation and a rather diverse tropical forest intervals rich in marine palynomorphs accompanied by high concentrations of mangrove pollen grains zonocostites suggest periods of marine influences and mangrove development it is thought that the marine intervals are related to the late burdigalian transgression

marine incursions and the influence of andean tectonics on the miocene depositional history of northwestern amazonia results of a palynostratigraphic study abstract new palynological and sedimentological data permit the age of neogene sediments in northwestern amazonia to be established more precisely and indicate that major environmental changes occurred in the area during this time based on a study of borehole samples the age of the solimoes formation solimoes basin northwestern brazil is determined as miocene and five pollen zones are distinguished which are correlated with existing zonations for northern south america in addition 30 new sporomorphs are described which belong to the following 12 genera psilamonocolpites retimonocolpites retitricolpites retibrevitricolpites psilatriporites nov gen bombacacidites psilatricolporites retitricolporites rugutricolporites psilastephanoporites nov gen psilastephanocolporoties and heterocolpites a correlation is made between the brazilian wells and some of the studied outcrops in colombian and peruvian amazonia based on palynological marker species the presence of coastal elements such as mangroves zonocostites indicates that during the miocene this area was influenced by marginal marine conditions caused by several marine incursions these incursions may be related to global sea level fluctuations miocene marine phases also are known from sites elsewhere in northern south america which at present like northwestern amazonia are entirely ruled by continental conditions sediment composition shows that during the early miocene the guyana shield was the major source area of sediment input in the basins of northwestern amazonia in the interval from early to middle miocene the andes became the major sediment source area the change in provenance is related to the uplift of the eastern cordillera this event caused a major change in palaeoenvironment and palaeogeography in northwestern amazonia which was characterized by the reverse of a northwestward directed fluvial system into an eastward directed fluvial lacustrine system with an estuarine character

vegetation et fluctuations climatiques postglaciaires sur la cote septentrionale gaspesienne quebec the postglacial ca 13 000 bp vegetational and climatic history is reconstructed from the pollen analytical study of the sediments of two lakes located in coastal northern gaspe peninsula j arrive lake altitude 56 m was submerged by the goldthwait sea until about 11 400 bp euloge lake 83 m in altitude and less than 1 km from the shore escaped the marine invasion before 10 400 bp the vegetation very scarce at first evolved to a herb tundra that lasted for over a millenium a cold climatic oscillation correlative with the younger dryas is identified at both sites between 10 700 and 10 400 bp during this herb tundra phase after 10 400 bp dwarf birch and willows colonized the sites leading to a shrub tundra the afforestation of the area began only around 9300 bp with the late arrival of spruce and aspen this phase was interrupted at 8650 bp by the upsurge of green alder in response to another cold oscillation since 7250 bp the present forested landscape finally developed in three steps characterized by i a high diversity of forest species until 2500 bp ii a loss of diversity until 1000 bp that favoured spruce and balsam fir and iii an increase of heliophilous trees shrubs and herbs these reconstructions contribute to the late glacial palaeogeography of eastern north america through the unravelling of conditions close to the retreating ice

precise radiocarbon dating of late glacial cooling in mid latitude south america abstract variability of atmospheric 14c content often complicates radiocarbon based chronologies however specific features such as periods of constant 14c age or steep changes in radiocarbon ages can be useful stratigraphic markers the younger dryas event in the northern hemisphere is one of those periods showing conspicuous 14c wiggles although the origin of those variations is not fully understood we can make practical use of them and determine i whether the younger dryas was global in extent if so ii were the initial cooling and the final warming synchronous worldwide and iii what are the implications of these similarities differences here we report high resolution ams 14c chronologies from the mid latitudes of south america that pinpoint a cool episode between 11 400 and 10 20014c yr b p the onset of the final cool episode of the late glacial in the southern mid latitudes i e the huelmo mascardi cold reversal preceded the onset of the younger dryas cold event by 550 calendar years both events ended during a radiocarbon age plateau at 10 20014c yr b p thus the huelmo mascardi cold reversal encompasses the younger dryas as well as a couple of short term cool warm oscillations that immediately preceded its onset in the north atlantic region

circulation and deep water export at the western exit of the subpolar north atlantic the current system east of the grand banks was intensely observed by world ocean circulation experiment woce array acm 6 during 1993 95 with eight moorings reaching about 500 km out from the shelf edge and covering the water column from about 400 m depth to the bottom more recently a reduced array by the institut fur meerskunde ifm at kiel germany of four moorings was deployed during 1999 2001 focusing on the deep water flow near the western continental slope both sets of moored time series each about 22 months long are combined here for a mean current boundary section and both arrays are analyzed for the variability of currents and transports a mean hydrographic section is derived from seven ship surveys and is used for geostrophic upper layer extrapolation and isopycnal subdivision of the mean transports into deep water classes the offshore part of the combined section is dominated by the deep reaching north atlantic current nac with currents still at 10 cm s 1 near the bottom and a total northward transport of about 140 sv sv 106 m3 s 1 with the details depending on the method of surface extrapolation used the mean flow along the western boundary was southward with the section mean north atlantic deep water outflow determined to be 12 sv below the 27 74 kg m 3 isopycnal however east of the deep western boundary current dwbc the deep nac carries a transport of 51 sv northward below 27 74 kg m 3 resulting in a large net northward flow in the western part of the basin from watermass signatures it is concluded that the deep nac is not a direct recirculation of dwbc water masses transport time series for the dwbc variability are derived for both arrays the variance is concentrated in the period range from 2 weeks to 2 months but there are also variations at interannual and longer periods with much of the dwbc variability being related to fluctuations and meandering of the nac a significant annual cycle is not recognizable in the combined current and transport time series of both arrays the moored array results are compared with other evidence on deep outflow and recirculation including recent models of different types and complexity

climatic changes in areas adjacent to the north atlantic during the last glacial interglacial transition 14 9 ka bp a contribution to igcp 253 this paper presents a summary of the evidence for climatic changes during the last glacial interglacial transition 14 9 ka bp in land areas adjacent to the north atlantic it is a synthesis of the results of the 12 regional summaries compiled by contributors to the north atlantic seaboard programme of igcp 253 that are published separately in this issue of journal of quaternary science eighteen palaeotemperature curves are compared and arranged in three transects one from southern europe to spitsbergen a second from ireland to poland and the third from southern new england to the labrador baffin shelf area ten maps are presented that summarise the synoptic climatic conditions of the region in 500 year time periods the purpose of the exercise is to examine the extent to which any emerging patterns support the ruddiman and mclntyre model of large scale shifts in the position of the oceanic polar front during the last glacial interglacial transition some broad agreement emerges although the influence of oceanic changes is diminished in areas that lay in close proximity to the laurentide and fennoscandian ice sheets attention is drawn to limitations in the compilations and to the potential for improved models in the future

spreading of denmark strait overflow water in the western subpolar north atlantic insights from eddy resolving simulations with a passive tracer abstractthe oceanic deep circulation is shared between concentrated deep western boundary currents dwbcs and broader interior pathways a process that is sensitive to seafloor topography this study investigates the spreading and deepening of denmark strait overflow water dsow in the western subpolar north atlantic using two eddy resolving atlantic simulations including a passive tracer injected into the dsow the deepest layers of dsow transit from a narrow dwbc in the southern irminger sea into widespread westward flow across the central labrador sea which remerges along the labrador coast this abyssal circulation in contrast to the upper levels of overflow water that remain as a boundary current blankets the deep labrador sea with dsow farther downstream after being steered around the abrupt topography of orphan knoll dsow again leaves the boundary forming cyclonic recirculation cells in the deep newfoundland basin the deep recirculation mostly driven by the meandering pathway of the up

how do high latitude north atlantic climate signals the crossover between the deep western boundary current and the gulf stream 1 a simple model is used to examine how the presence of a continental slope along the western boundary and wind driven gyres especially the gulf stream gs jet affect the pathways of water mass flow and wave propagation in the abyssal ocean two types of forcing an interior source and a boundary inflow to mimic the labrador sea water and the marginal sea overflow are considered here both topography and wind driven gyres considerably alter how the water mass spreads from the source in the steady state case and how transient signals propagate to the unforced regions sloping bathymetry near the western boundary allows for meridional propagation of topographic waves the gs jet creates a strong meridional pv gradient which could partially block the southward water mass transport and wave propagation the effectiveness of the crossover to disrupt the lower layer response depends on the type of high latitude water mass forcing

climatic and limnological changes associated with the younger dryas in atlantic canada pollen diatom and chironomid fossils from the sediments of a core from brier island bog lake nova scotia were studied in an attempt to relate changes in microfossil composition to a climatic cooling in atlantic canada correlative with the european younger dryas ca 10 to 11 ka our paleolimnological data were then compared to similar types of data from splan pond new brunswick to determine if there were any significant differences between a coastal and a more inland site nonarboreal pollen was dominant throughout the brier island core and the interval 10 0 11 0 ka did not show the typical decline in picea and increases in tundra like vegetation characteristic of many sites in atlantic canada however the limnological indicators did undergo marked changes in taxon composition the chironomid assemblage was initially dominated by shallow water warm adapted chironomid taxa followed by abundant sergentia a cold stenotherm during 10 11 ka sergentia disappeared in the post younger dryas interval and the warm adapted genera resumed dominance chironomid inferred paleotemperature reconstructions revealed that at both brier island bog lake and splan pond summer surface water temperatures dropped abruptly to between 13 and 17 c during the 10 11 ka interval suggesting that a cooler climate was present in atlantic canada correlative with the european younger dryas diatom assemblage changes during the same period corroborate the occurrence of limnological fluctuations

observations inferences and mechanisms of the atlantic meridional overturning circulation a review this is a review about the atlantic meridional overturning circulation amoc its mean structure temporal variability controlling mechanisms and role in the coupled climate system the amoc plays a central role in climate through its heat and freshwater transports northward ocean heat transport achieved by the amoc is responsible for the relative warmth of the northern hemisphere compared to the southern hemisphere and is thought to play a role in setting the mean position of the intertropical convergence zone north of the equator the amoc is a key means by which heat anomalies are sequestered into the ocean s interior and thus modulates the trajectory of climate change fluctuations in the amoc have been linked to low frequency variability of atlantic sea surface temperatures with a host of implications for climate variability over surrounding landmasses on intra annual timescales variability in amoc is large and primarily reflects the response to local wind forcing meridional coherence of anomalies is limited to that of the wind field on interannual to decadal timescales amoc changes are primarily geostrophic and related to buoyancy anomalies on the western boundary a pacemaker region for decadal amoc changes is located in a western transition zone along the boundary between the subtropical and subpolar gyres decadal amoc anomalies are communicated meridionally from this region amoc observations as well as the expanded ocean observational network provided by the argo array and satellite altimetry are inspiring efforts to develop decadal predictability systems using coupled atmosphere ocean models initialized by ocean data

decline of subpolar north atlantic circulation during the 1990s observations of sea surface height reveal that substantial changes have occurred over the past decade in the mid to high latitude north atlantic ocean topex poseidon altimeter data show that subpolar sea surface height increased during the 1990s and the geostrophic velocity derived from altimeter data exhibits declining subpolar gyre circulation combining the data from earlier satellites we find that subpolar circulation may have been weaker in the late 1990s than in the late 1970s and 1980s direct current meter observations in the boundary current of the labrador sea support the weakening circulation trend of the 1990s and together with hydrographic data show that the mid to late 1990s decline extends deep in the water column analysis of the local surface forcing suggests that the 1990s buoyancy forcing has a dynamic effect consistent with altimetric and hydrographic observations a weak thermohaline forcing allows the decay of the domed structure of subpolar isopycnals and weakening of circulation

classification and analysis of palynodebris from the palaeocene sediments of the forties field sedimentary organic matter behaves as sedimentary particles and this study attempts to interpret its occurrence in the palaeocene sands and mudstones of the forties field of the north sea new nomenclature and classification of this palynodebris are presented and are used to make quantitative counts of the palynodebris from nearly 600 samples of known sedimentary character the new categories are further refined by objective testing of the data by principal components analysis and cluster analysis it is argued that two types of sedimentary organic matter are of particular value because they are preferentially deposited in different environments palynowafers are most commonly deposited in the submarine fan lobes and channel complexes and amorphous matter occurs mostly in the lower energy basin plain sediments

temporal variability of the meridional overturning circulation at 34 5 s results from two pilot boundary arrays in the south atlantic data from two boundary arrays deployed along 34 5 s are combined to produce the first continuous in situ time series observations of the basin wide meridional overturning circulation moc in the south atlantic daily estimates of the moc between march 2009 and december 2010 range between 3 sv and 39 sv 1 sv 106 m3 s 1 after a 10 day low pass filter is applied much of the variability in this 20 month record occurs at periods shorter than 100 days approximately two thirds of the moc variability is due to changes in the geostrophic baroclinic plus barotropic volume transport with the remainder associated with the direct wind forced ekman transport when low pass filtered to match previously published analyses in the north atlantic the observed temporal standard deviation at 34 5 s matches or somewhat exceeds that observed by time series observations at 16 n 26 5 n and 41 n for periods shorter than 20 days the basin wide moc variations are most strongly influenced by ekman flows while at periods between 20 and 90 days the geostrophic flows tend to exert slightly more control over the total transport variability of the moc the geostrophic shear variations are roughly equally controlled by density variations on the western and eastern boundaries at all time scales captured in the record the observed time mean moc vertical structure and temporal variability agree well with the limited independent observations available for confirmation

palynofacies prediction of distance from sediment source a case study from the upper cretaceous of the pyrenees quantitative variations in the size shape and preservation state of microscopic plant debris assemblages correlate with the actual distance of the sample site from the coastal siliciclastic sediment source a case study from a shelf to basin transect in the upper cretaceous of the spanish pyrenees reveals that 1 the diameter of equant black wood phytoclasts 2 the ratio of equant to lath shaped black wood phytoclasts and 3 several other parameters show predictable changes over a 55 km onshore offshore transect these parameters primarily reflect sedimentological sorting based on particle size and density rather than paleoecological gradients when only samples from the transgressive systems tract are considered multiple regression models predict the distance from the source with a standard error of 5 km r 2 0 84 0 93 these parameters also allow the maximum flooding surface to be more precisely located within mudstone dominated sections by applying the lateral regression relationship to stratigraphic data a quantitative estimate can also be made for the scale of lateral facies shifts through depositional sequences here 10 km

midlatitude equatorial dynamics of a grounded deep western boundary current part i midlatitude flow and the transition to the equatorial region abstracta comprehensive theoretical study of the nonlinear hemispheric scale midlatitude and cross equatorial steady state dynamics of a grounded deep western boundary current is given the domain considered is an idealized differentially rotating meridionally aligned basin with zonally varying parabolic bottom topography so that the model ocean shallows on both the western and eastern sides of the basin away from the equator the flow is governed by nonlinear planetary geostrophic dynamics on sloping topography in which the potential vorticity equation can be explicitly solved as the flow enters the equatorial region it speeds up and becomes increasingly nonlinear and passes through two distinguished inertial layers referred to as the intermediate and inner inertial equatorial boundary layers respectively the flow in the intermediate equatorial region is shown to accelerate and turn eastward forming a narrow equatorial jet the qualitative properties of the solution presented are consistent wi

the interaction of recirculation gyres and a deep boundary current abstractmotivated by the proximity of the northern recirculation gyre and the deep western boundary current in the north atlantic an idealized model is used to investigate how recirculation gyres

new geological framework for western amazonia brazil and implications for biogeography and evolution abstract although many of the current hypotheses to explain the origin and distribution of the amazon biodiversity has been based directly or indirectly on geological data the reconstruction of the geological history of the amazon region is still inadequate to analyze its relationship with the biodiversity this work has the main goal to characterize the sedimentary successions formed in the brazilian amazon in the neogene quaternary discussing the evolution of the depositional systems through time and analyzing their main controlling mechanisms in order to fill up this gap radar image interpretation sedimentological studies and radiocarbon dating allowed the mapping of plio pleistocene to holocene units along the solimoes amazonas river brazil this integrated work led to the characterization of five sedimentary successions overlying miocene deposits of the solimoes pebas formation which include the following ica formation plio pleistocene deposits q1 37 400 43 700 14c yr b p deposits q2 27 200 14c yr b p deposits q3 6730 2480 14c yr b p and deposits q4 280 130 14c yr b p these deposits occur mostly to the west of manaus forming nw se elongated belts that are progressively younger from sw to ne indicating a subsiding basin with a depocenter that migrated to the ne the reconstruction of the depositional history is consistent with significant changes in the landscapes hence the closure of a large lake system at the end of the miocene gave rise to the development of a plio pleistocene fluvial system this was yet very distinct from the modern drainage with shallow energetic highly migrating braided to anastomosed channels having an overall northeast outlet this fluvial system formed probably under climatic conditions relatively drier than today s during the early pleistocene there was pronounced erosion followed by a renewed depositional phase ca 40 000 14c yr b p with the development of prograding lobes and or crevasse splays associated with a lake system i e fan delta and or fluvial flood plain areas after a period of erosion a fluvial system with eastward draining channels started to develop at around 27 000 14c yr b p the fluvial channels were overflooded in mid holocene time this flooding is attributed to an increased period of humidity with a peak between 5000 and 2500 14c yr b p the data presented herein support that rather than being a monotonous area the amazonia was a place with frequent changes in landscape throughout the neogene quaternary probably as a result of climatic and tectonic factors we hypothesize that these changes in the physical environment stressed the biota resulting in speciation and thus had a great impact on modern biodiversity

miocene drainage reversal of the amazon river driven by plate mantle interaction northern south america experienced significant changes in drainage patterns during the opening of the south atlantic ocean disappearance of a mega wetland in the western amazonian basins was followed by the formation of the eastward draining amazon river which has been attributed to andean uplift however south america s westward motion over cold dense subducted slabs implies that regional subsidence and uplift east of the andes may have been driven by mantle convection here we use a coupled model of mantle convection and plate kinematics to show that dynamic subsidence of up to 40 m myr 1 initially formed the amazonian mega wetland in our model the sustained westward motion of continental south america over subducted slabs resulted in rebound of the amazonian mega wetland region at rates of up to 40 m myr 1 after 30 million years ago paired with continued subsidence of the eastern amazonian sedimentary basins at 10 20 m myr 1 the resulting progressive tilt of northern south america to the east enabled the establishment of the amazon river suggesting that mantle convection can profoundly affect the evolution of continental drainage systems

exceptionally steep north south gradients in lake temperatures during the last deglaciation during the transition from the last glacial to the present interglacial climate late glacial period high summer insolation1 combined with the presence of the laurentide ice sheet is thought to have promoted the development of strong summer thermal gradients in north america south of the ice margin2 here we use palaeoecological methods to obtain quantitative evidence for the existence of these gradients our palaeoclimate reconstructions are based on water temperatures inferred from fossil assemblages of aquatic midge larvae in five lakes along a 240 km transect extending from central new brunswick canada to southeastern maine usa we show that the temperature gradient shifted during the killarney oscillation ko and younger dryas yd cooling events and that water temperature differences of 9 and 11 c existed over distances of 55 and 240 km respectively during parts of the late glacial period these gradients are much stronger than the current north south trends of lake summer surface water temperatures for these five lakes and for lakes across the northern tree line the rapid motion of such steep temperature gradients may have affected the progressive development of aquatic and terrestrial ecosystems in the region

an ocean model s response to north atlantic oscillation like wind forcing the response of the atlantic ocean to north atlantic oscillation nao like wind forcing was investigated using an ocean only general circulation model coupled to an atmospheric boundary layer model a series of idealized experiments was performed to investigate the interannual to multi decadal frequency response of the ocean to a winter wind anomaly pattern overall the strength of the sst response increased slightly with longer forcing periods in the subpolar gyre however the model showed a broad response maximum in the decadal band 12 16 years

miocene paleoenvironmental changes in the solimoes basin western amazon brazil a reconstruction based on palynofacies analysis abstract we report palynofacies from two sections of miocene solimoes formation of the solimoes basin western amazon brazil to better understand paleoenvironmental evolution based on cluster analysis five palynofacies associations were recognized dominated by either opaque non opaque algae miospores and structureless marine organic matter the distribution of palynofacies associations reflects a complex depositional system with fluvial lacustrine estuarine and shallow marine environments a high abundance of woody material indicates a fluvial lacustrine dominated environment three marine incursions were recognized indicated by the presence of dinoflagellate cysts and microforaminifera test linings marine influence was more evident during the late middle late miocene interval when transgressions occurred over a greater extent of the amazon region

advection of north atlantic deep water from the labrador sea to the southern hemisphere recently formed labrador seawater lsw and overflow water from denmark strait dsow are main components of the atlantic meridional overturning circulation both exhibit a distinct chlorofluorocarbon cfc maximum here we use 25 years of cfc observations in the atlantic to study the main features of the circulation of lsw and dsow from the cfc data the age and fraction of young deep water are inferred due to the superior spatial data resolution compared to former attempts regional differences in the spreading velocity and pathways of young deep water become evident dependent on the regional circulation the observed distributions of young lsw and dsow showed that the dwbc is the fastest pathway to reach the southern hemisphere the downstream decrease of the fractions of young lsw in the dwbc is slower compared to model studies from 47 n to 42 n dwbc transports of young lsw and dsow decrease by 44 and 49 respectively at 26 n the dwbc transport of young water is still 39 of the lsw formation rate and 44 of the dsow overflow transport interior pathways also exist especially in the subpolar north atlantic and in the transition zone between the subpolar and subtropical gyre compared to dsow the distributions indicate a higher tendency for lsw to follow additional interior pathways north of 45 n the major part of lsw is younger than 20 years the general weakening of new lsw formation since the 1990s worked toward a homogenization between the lsw in the western and the eastern subpolar north atlantic

in situ observation of contour currents in the northern south china sea applications for deepwater sediment transport deepwater currents and related suspended sediment concentration were obtained by an acoustic doppler current profiler adcp mooring system in the northern south china sea from september 2011 to may 2013 to characterize the occurrence of contour currents and to evaluate their sediment transport capacity magnitude of the current velocity generally varied in the range of 0 2 cm s with a dominant flow direction of 250 southwestward the observed contour current defined as the along slope component of the deepwater currents has a tunnel like vertical structure with the largest velocity occurring in the middle of the tunnel and decreasing outwards both the magnitude and the depth range of the maximum velocity display evident inter seasonal variations with the strongest velocity in summer and the weakest in spring while the thickness of the contour currents was the highest in winter and the lowest in spring we also found that passing through of the deep reaching mesoscale eddies significantly affected the magnitude and direction of the contour currents the suspended sediment concentration ssc estimated from echo intensities of the adcp is the highest at the near bottom 400 g l and decreases upwards to 10 g l at water depth shallower than 1750 m high ssc is mostly observed during periods of low magnitude of the contour currents suggesting resuspension of sediment from the seafloor is not the major controlling factor of these high ssc events our observation also suggests that the major role that contour currents play is to transport sediment from the sources through keeping sediment suspended above the lower continental slope of the south china sea

interdecadal variations in north atlantic sea surface temperature and associated atmospheric conditions abstract evidence is presented for a distinct pattern of ocean atmosphere relationship associated with interdecadal variability in the north atlantic region using a century of surface marine observations it is shown that middle and high latitude sea surface temperature sst display a long term fluctuation with negative anomalies before 1920 and during the 1970s and 1980s positive sst conditions prevailed from about 1930 to 1960 the pattern of interdecadal sst variability is constructed by subtracting the average field during 15 cold years from that during a similar interval of warm years the early century warming and the more recent cooling display a similar spatial pattern in both cases the pattern is basin scale and largely of one polarity with maxima in the vicinity of iceland in the labrador sea and northeast of bermuda the corresponding differences in surface atmospheric conditions are determined by averaging and subtracting in the same manner fields of sea level pressure slp and surf

reconciling tracer and float observations of the export pathways of labrador sea water for more than fifty years it has been generally accepted by oceanographers that the deep western boundary current dwbc is the principal conduit of recently convected labrador sea water lsw exported from the high latitude north atlantic to the equator supporting this supposition is observational evidence that the waters of the dwbc have consistently greater equatorward velocities higher concentrations of passive tracers and younger ages compared to ocean interior waters however recent observations and simulations of floats launched in the dwbc in the labrador sea show that most water parcels are quickly ejected from the dwbc and follow instead interior pathways to the subtropics here we show that tracer observations from the last three decades are compatible with the existence of both dwbc and basin interior export pathways from analyses of observational data and model output we find that equatorward transport in the basin interior is consistent with the large scale vorticity balance at mid depth furthermore from the modeling analysis we show that despite higher localized concentrations of tracer and particles in the dwbc only 5 of particles released in the labrador sea are transported from the subpolar to subtropical gyre via a continuous dwbc pathway thus the interior pathway is a significant contributor to lsw export highlights lagrangian observations of labrador sea water match eulerian observations there is deep equatorward flow in the basin interior this interior pathway is significant compared to the pathway along the boundary

palynofacies as indicators of paleoenvironmental changes in a cretaceous succession from the larsen basin james ross island antarctica abstract in order to reconstruct the paleoenvironment of one of the most extensive marine cretaceous successions in the southern hemisphere palynofacies analyses were conducted on 83 samples from the whisky bay albian turonian hidden lake coniacian and santa marta santonian campanian formations in the larsen basin james ross island antarctica categories of particulate organic matter were counted and investigated by cluster analysis the trends and parameters of palynofacies constituents were used to reconstruction paleoenvironments based on the existing sedimentological interpretation the stratigraphic distribution of the four identified palynofacies associations a d reflects a continuous terrestrial influx throughout the succession from base to top a conspicuous increase in woody elements especially non opaque particles is observed this increase in continental elements occurs despite the presence of marine elements this finding corroborates the sedimentological interpretation of a deeper water paleoenvironment during deposition of the whisky bay formation and initiation of a shallowing upward trend in the hidden lake formation culminating with shallow marine shelf environment of the santa marta formation

the dynamics of a simple baroclinic model of the wind driven circulation the authors study the dynamics of a two layer approximation to the steadily forced baroclinic circulation in a closed ocean basin with the aim of understanding its temporal variability and the onset of low frequency variability it is found that for a range of dissipation that includes values used in a number of ocean modeling studies in the past five years if one waits a sufficient length of time the asymptotic behavior of the system is characterized by only a very small number of degrees of freedom by varying the dissipation as a control parameter the authors identify abrupt transitions in the form of the long term circulation exhibited by the model one type of transition from a time varying circulation dominated by two frequencies to a chaotic circulation is accompanied by the appearance of low frequency variability this constitutes an internal mechanism for the production of variability at climatological timescales the model used is a two layer quasigeostrophic model forced by a steady wind stress with a uniform cyclonic curl dissipation is modeled by a lateral diffusion of momentum with a uniform eddy viscosity in two sets of experiments with two internal deformation radii and layer depth ratios the eddy viscosity is varied and the types of circulation that result are reported the stable steady circulation seen in the viscous limit gives way to time dependent circulations of increasing temporal complexity spatially the circulations fall into two types those dominated by large recirculating gyres in the western part of the basin and those with a strong and strongly meandering peripheral current reminiscent of that seen in the black sea from an examination of the linear eigenmodes of the steady circulation the initial transition to time dependence may be characterized as a baroclinic instability of the western recirculation gyre

dynamics of the gulf stream deep western boundary current crossover part ii low frequency internal oscillations abstract a low frequency oscillation in the gulf stream deep western boundary current dwbc system is identified and its influences on several important aspects of the basin scale circulation are investigated an eddy resolving regional primitive equation model is used to demonstrate that feedbacks between the gulf stream with its associated northern and southern recirculation gyres and the upper core of the dwbc can lead to self sustaining large amplitude internal oscillations of roughly decadal frequency the oscillator cycle is described as follows the upper core of the dwbc is entrained under the gulf stream through interaction with the eddy driven northern and southern recirculation gyres as described in part i of this study once entrained the low potential vorticity dwbc water stabilizes the gulf stream and suppresses the eddy fluxes that maintained the interior recirculation gyres this causes the upper dwbc to switch to a southward path along the western boundary thus removing the source o

late quaternary records of vegetation and fire in southeastern north carolina from jones lake and singletary lake abstract we conducted fossil pollen charcoal and geochemical analyses of sediment cores from jones lake and singletary lake spanning the last 50 000 cal yr b p to examine the linkages between climate vegetation and fire activity on the atlantic coastal plain and particularly emphasize changes since the last glacial maximum application of the modern analog technique mat to fossil pollen data allowed for quantitative estimates of holocene climate but pleistocene assemblages had no modern analogues preempting their use for quantitative reconstructions the mat data indicate markedly lower mean annual precipitation and temperatures during the late pleistocene relative to the holocene increased charcoal accumulation during interstadials indicates increased fire activity during these warm intervals geochemical data 13c 15n c n and pollen concentrations indicate a sparsely vegetated pleistocene landscape that produced few fires followed by an increase in biomass and fire activity around the lakes during the holocene transition a quercus spp maximum in the early holocene is associated with low charcoal abundances while increased dominance of pinus spp during the middle holocene is associated with dramatic increases in charcoal it is unclear if the quercus pinus transition was the result of changing fire regimes or if the fire regime changed in response to vegetation the regional asynchronicity of the quercus pinus transition may indicate another forcing mechanism besides climate change such as prehistoric human activity is responsible for the ecological change macroscopic charcoal and c n ratios reach unprecedented values during the late holocene possibly as a result of deforestation by both prehistoric native americans and later immigrant populations

dilution of the northern north atlantic ocean in recent decades declining salinities signify that large amounts of fresh water have been added to the northern north atlantic ocean since the mid 1960s we estimate that the nordic seas and subpolar basins were diluted by an extra 19 000 5000 cubic kilometers of freshwater input between 1965 and 1995 fully half of that additional fresh water about 10 000 cubic kilometers infiltrated the system in the late 1960s at an approximate rate of 2000 cubic kilometers per year patterns of freshwater accumulation observed in the nordic seas suggest a century time scale to reach freshening thresholds critical to that portion of the atlantic meridional overturning circulation

abrupt changes in marine conditions sunneshine fiord eastern baffin island nwt during the last deglacial transition younger dryas and h 0 events

the nature of miocene amazonian epicontinental embayment high frequency shifts of the low gradient coastline a sedimentological and ichnological data set that covers the lower upper miocene sedimentary series of western amazonian foreland basin indicates that widespread restricted marine ingressions shaped western amazonia throughout the miocene the late lower early upper miocene sedimentary series pebas formation consists of stacked 3 to 10 m thick tidally influenced brackish to freshwater bay margin sequences the overlying upper miocene post pebas strata bear tidally influenced low salinity channel deposits that are interbedded with continental deposits the data suggest that several tens of high frequency ingressions reached the basin during the miocene the ingressions were shallow and restricted and were interspersed with rapid progradation along with the prograding shorelines the continental environments swamps lagoons floodplains and forests constrained the extent of the marginal marine embayment consequently the miocene marginal marine and continental strata are closely interbedded throughout the basin these results refine the recent depositional models for miocene amazonia and challenge the theory that marine ingressions shaped the area only during one brief time interval late middle early late miocene during the epoch much of recent literature has documented fossils of mangrove pollen brackish euryhaline fish and brackish water ostracods brackish water trace fossil assemblages and tidal deposits from various miocene stratigraphic levels commonly these data sets are collected from the same outcrops as those for which data sets imply freshwater conditions we propose that these seemingly contrasting data sets can be unified if the repetitive nature of the ingressions is considered and all the paleoenvironmental data are presented in a detailed lithological and stratigraphical context

the biogeochemical cycling of zinc and zinc isotopes in the north atlantic ocean zinc zn is a marine micronutrient with an overall oceanic distribution mirroring the major macronutrients especially silicate seawater zn isotope ratios 66zn are a relatively new oceanographic parameter which may offer insights into the biogeochemical cycling of zn to date the handful of published studies of seawater 66zn show the global deep ocean to be both remarkably homogeneous approximately 0 5 and isotopically heavier than the marine sources of zn 0 1 to 0 3 here we present the first high resolution oceanic section of 66zn from the u s geotraces ga03 north atlantic transect from lisbon to woods hole throughout the surface ocean biological uptake and release of isotopically light zn together with scavenging of heavier zn leads to large variability in 66zn in the ocean below 1000 m 66zn is generally homogeneous 0 50 0 14 2 sd though deviations from 0 5 allow us to identify specific sources of zn the mediterranean outflow is characterized by 66zn of 0 1 to 0 3 while margin sediments are a source of isotopically light zn 0 5 to 0 8 which we attribute to release of nonregenerated biogenic zn mid atlantic ridge hydrothermal vents are also a source of light zn close to 0 5 though zn is not transported far from the vents understanding the biogeochemical cycling of zn in the modern ocean begins to address the imbalance between the light 66zn signature of marine sources and the globally homogeneous deep oceans 66zn of 0 5 on long timescales with overall patterns pointing to sediments as an important sink for isotopically light zn throughout the oceans

cooling in the gulf of st lawrence and estuary region at 9 7 to 7 2 14c ka 11 2 8 0 cal ka palynological response to the pbo and 8 2 cal ka cold events laurentide ice sheet air mass circulation and enhanced freshwater runoff abstract an examination of post younger dryas yd pollen stratigraphies in the gulf of st lawrence and st lawrence estuary region reveals features in the pollen records that represent breaks in the normal vegetation succession widespread vegetation suppression and a delay in migration of plant taxa between 9 7 and 7 2 14 c ka 11 2 and 8 0 cal ka the domination of alnus crispa at sites bordering the st lawrence estuary gulf region in gaspesie and northern new brunswick within this timeframe represents a diversion from the typical vegetation progression from picea and or populus or picea betula to pinus and or betula and signifies a shift to a cooler drier climate coinciding with the a crispa expansion and domination in that region was the contraction of picea populations in other areas in southwestern new brunswick and eastern and southeastern nova scotia picea was replaced by the first appearance of tree birch b papyrifera whereas in western and southwestern newfoundland picea gave way to a resurgence of shrub birch betula glandulosa the picea contraction and immediate resurgence of betula represents cooling and is reliably dated at 9720 110 14 c bp 10 800 11 240 cal bp in southwest newfoundland this first post yd episode of widespread cooling is correlated with the north atlantic preboreal oscillation pbo centered around 9650 14 c bp 10 900 11 180 cal bp in the adjacent great lakes region sites exposed to winds from the gulf of st lawrence in eastern new brunswick prince edward island and northern nova scotia show a lingering persistence of picea and delay in arrival of pinus to 8 0 and 7 7 14 c ka 9 0 and 8 4 cal ka yet pinus was dominant as early as 9 4 14 c ka 10 6 cal ka in southwestern new brunswick at the same time tundra vegetation persisted at high elevations in western and southwestern newfoundland only to be replaced by upslope migration of shrub birch heath by 8 14 c ka prolonged broad scale cooling to 8 14 c ka and to as late as 7 7 14 c ka extended up to 200 km inland in areas exposed to the st lawrence estuary and gulf region and was in response to strong cold dry anticyclonic winds coming off the retreating laurentide ice sheet in combination with enhanced freshwater runoff through the gulf of st lawrence the end of the period of prolonged cooling and onset of regional warming coincided with the diversion of western canada runoff and agassiz ojibway drainage to hudson bay and reduced effect or final break up of the laurentide ice sheet several sites document a subsequent cold shift that interrupted regional warming at 7650 to 7200 14 c bp 8400 to 8000 cal bp and which is variously represented by the suppression of pinus and resurgence of picea sometimes with a crispa quebec maritime region or by an abrupt decrease of picea and resurgence of betula western newfoundland this second post yd cool interval is equated with the 8200 cal bp cold event registered in the greenland ice isotopic record

tracking labrador sea water property signals along the deep western boundary current observations of the deep western boundary current dwbc at line w on the western north atlantic continental slope southeast of cape cod from 1995 to 2014 reveal water mass changes that are consistent with changes in source water properties upstream in the labrador sea this is most evident in the cold dense and deep class of labrador sea water dlsw that was created and progressively replenished and deepened by recurring winter convection during the severe winters of 1987 1994 the arrival of this record cold fresh and low potential vorticity anomaly at line w lags its formation in the labrador sea by 3 7 years complementary observations along the path of the dwbc provide further evidence that this anomaly is advected along the boundary and indicate that stirring between the boundary and the interior intensifies south of the flemish cap finally the consistency of the data with realistic advective and mixing time scales is assessed using the waugh and hall 2005 model framework the data are found to be best represented by a mean transit time of 5 years from the labrador sea to line w with a leading order role for both advection by the dwbc and mixing between the boundary flow and interior waters

transport of the north atlantic deep western boundary current about 39 n 70 w 2004 2008 abstract begun in spring 2004 a sustained measurement program line w is returning high resolution observations of the north atlantic s deep western boundary current dwbc southeast of new england the study focuses on the cold limb of the atlantic meridional overturning circulation near the boundary between the subpolar and subtropical gyres the field study consists of a 6 element continental slope spanning moored array on a line underlying an altimeter satellite ground track and periodic reoccupations of a full depth hydrographic section along the line extending from the continental shelf towards bermuda here data from the first 4 years of the array may 10 2004 april 9 2008 are analyzed along with 9 realizations of the section the array a mix of moored profiler and discrete fixed depth instrument moorings returned temperature salinity and horizontal velocity data with various temporal and depth resolutions after averaging to filter inertial tidal and other high frequency motions the combined moored data set was binned to the lowest common temporal resolution of 5 days the nominal burst sample interval of the moored profilers and interpolated to 2 dbar vertical resolution temperature salinity dissolved oxygen tracer chemical concentrations and direct velocity data were acquired on the hydrographic cruises the present work focuses on the 4 year mean and time varying meridional transport in 4 layers bounded by neutral density surfaces upper and classical labrador sea waters iceland scotland overflow waters and denmark strait overflow waters the 5 d 4 layer summed meridional transport estimates range between 3 5 and 79 9 sv with a record mean average transport of 25 1 sv and standard deviation of 12 5 sv bias adjustment to account for the finite width of the moored array increases the 4 layer mean transport estimate to 28 7 sv at time scales longer than about 1 month the variations in equatorward dwbc transport appear correlated with meridional position of the gulf stream north wall with stronger transport observed when the stream is displaced south

rapid freshening of the deep north atlantic ocean over the past four decades the overflow and descent of cold dense water from the sills of the denmark strait and the faroe shetland channel into the north atlantic ocean is the principal means of ventilating the deep oceans and is therefore a key element of the global thermohaline circulation most computer simulations of the ocean system in a climate with increasing atmospheric greenhouse gas concentrations predict a weakening thermohaline circulation in the north atlantic as the subpolar seas become fresher and warmer1 2 3 and it is assumed that this signal will be transferred to the deep ocean by the two overflows from observations it has not been possible to detect whether the ocean s overturning circulation is changing but recent evidence suggests that the transport over the sills may be slackening4 here we show through the analysis of long hydrographic records that the system of overflow and entrainment that ventilates the deep atlantic has steadily changed over the past four decades we find that these changes have already led to sustained and widespread freshening of the deep ocean

a heinrich like event h 0 dc 0 source s for detrital carbonate in the north atlantic during the younger dryas chronozone in the north atlantic we define h 0 as a heinrich like event which occurred during the younger dryas chron on the se baffin shelf prior to 11 ka surface water productivity was reasonably high as measured by the numbers of diatom and planktic foraminifera per gram but an abrupt increase in detrital carbonate dc 0 event from approximately 15 up to 50 carbonate by weight occurred at 11 14c ka and continued to circa 10 ka these deposits 2 6 m thick are dominated by detrital calcite and silt and clay sized sediments during this event dc 0 h 0 ice extended onto the inner shelf but did not reach the shelf break and probably originated from a center over labrador ungava as a consequence the pattern of ice rafted debris and sediment provenance shown by h o in the north atlantic is different from that during h 1 14 5 ka or h 2 20 ka when the ice sheet extended along the axis of hudson strait and may have reached the shelf break for example there is no concrete evidence for dc o is cores on the floor of the labrador sea due east of hudson strait hu75 55 56 but h o has been noted in cores off newfoundland and west of ireland a coeval carbonate event to dc 0 but this one dominated by dolomite occurs in hu82 su5 on the west side of davis strait with a source either from northern baffin bay or cumberland sound although other sources for north atlantic detrital carbonate cannot be totally excluded our evidence suggests that h 0 represents the expression of glaciological instability of the laurentide ice sheet within the general region of hudson strait and probably to the north cumberland sound and northernmost baffin bay there is one younger dc event dated circa 8 4 ka present in sediments along the labrador margin and in hudson strait which represents the final collapse of the ice sheet within hudson strait and hudson bay

holocene vegetation dynamics of anticosti island quebec and consequences of remoteness on ecological succession abstract the postglacial vegetation history of anticosti island in the gulf of st lawrence quebec was reconstructed from pollen analysis of three sites providing the first paleoecological data for the island the earliest plant communities 8550 7770 14c yr b p 9500 8500 cal yr b p were characterized by a high representation of green alder alnus crispa indicating an open environment with sparse spruce picea between 7770 and 3700 14c yr b p 8500 4000 cal yr b p the island was colonized by mixed deciduous and coniferous forests dominated by paper birch betula papyrifera and spruce a major increase in the abundance of balsam fir abies balsamea occurred ca 3700 14c yr b p 4000 cal yr b p indicating development of the closed fir spruce forests as they exist today the island s remoteness from continental seed plant sources influenced plant colonization afforestation and ecological succession the gulf of st lawrence slowed plant migration and tree species had to spread from the gaspe peninsula repeated drops in fir pollen percentages during the last 4 000 years may reflect the activity of defoliating insects

long term coordinated changes in the convective activity of the north atlantic the north atlantic is a peculiarly convective ocean the convective renewal of intermediate and deep waters in the labrador sea and greenland iceland sea both contribute significantly to the production and export of north atlantic deep water thus helping to drive the global thermohaline circulation while the formation and spreading of 18 degree water at shallow to intermediate depths off the us eastern seaboard is a major element in the circulation and hydrographic character of the west atlantic for as long as time series of adequate precision have been available to us it has been apparent that the intensity of convection at each of these sites and the hydrographic character of their products have been subject to major interannual change as shown by aagaard 1968 clarke et al 1990 and meincke et al 1992 for the greenland sea in the ows bravo record from the labrador sea eg lazier 1980 et seq and at the panulirus hydrostation s site in the northern sargasso off bermuda eg jenkins 1982 talley and raymer 1982 this paper reviews the recent history of these changes showing that the major convective centres of the greenland and labrador seas are currently at opposite convective extrema in our postwar record with vertical exchange at the former site limited to 1000 m or so but with labrador sea convection reaching deeper than previously observed to over 2300 m as a result greenland sea deep water has become progressively warmer and more saline since the early 70 s due to increased horizontal exchange with the arctic ocean through fram strait while the labrador sea water has become progressively colder and fresher over the same period through increased vertical exchange most recently convection has become deep enough there to reach into the more saline nadw which underlies it so that cooler but now saltier and denser lsw has resulted

quasigeostrophic dynamics of the western boundary current abstract a local model is used to investigate the dynamics of the western boundary current in a midlatitude wind driven gyre this current is important for the gyre as a whole and its local instability is correlated with structural changes of the separated eastward jet and the interior gyres in particular the eastward jet can be disrupted and broadened in the regime with a strong local instability in the western boundary current such a regime occurs with a no slip lateral boundary condition alternatively in the absence of local instability the eastward jet is narrow and penetrates farther in the basin interior this behavior is typical with free slip boundary condition both the linear stability and nonlinear time dependent behavior of the western boundary current are analyzed for a wide range of parameters the current loses stability at moderate reynolds numbers and the stability threshold strongly depends upon the vertical stratification profile the nonlinear time dependent flow contains wel

slow variations in mean path of the gulf stream east of cape hatteras the gulf stream between cape hatteras and the new england seamounts varies in position over a wide range of time scales we present evidence that interannual path changes may be governed by a time varying outflow of waters from the labrador shelf region when the shelf and slope waters south of new england turn cold and fresh the stream frequently assumes a more southerly track and conversely when the waters are warm and saline these changes in path and surface water properties most likely result from large variations in shelf transport and thus greater or less dilution of the warm saline gulf stream waters that continually leak from the current into the slope sea these observations point to a thermohaline rather than winddriven mechanism for governing the path of the gulf stream after it leaves the coast

paleoenvironmental reconstruction based on palynofacies analysis of the aptian albian succession of the sergipe basin northeastern brazil abstract palynofacies analyses were carried out on 272 core samples from two wells gtp 17 se and gtp 24 se in the sergipe basin with the aim of reconstructing the paleoenvironments of the upper aptian middle albian for the palynofacies analysis the kerogen categories were counted and subjected to cluster analyses for detailed environmental analysis kerogen distribution trends and parameters were applied based on percentages of kerogen categories total organic carbon analysis was also used the stratigraphic distribution of palynofacies associations that defined eight palynofacies units in well gtp 17 se and ten in well gtp 24 se reflects a continuous terrestrial influx throughout the succession amorphous organic matter aom and palynomorph groups show moderate to high percentages especially in well gtp 24 se the increase in relative abundance of these groups suggests that a long term a transgression and or a decreasing terrestrial influx occurred in the area from the bottom to top six depositional environments were identified in wells gtp 17 se and gtp 24 respectively and they reflect the progressive increase in marine influence as the basin evolved brackish lagoon conditions changed to more open marine conditions as sea level changed during the separation of south america from africa

facies analysis and basin architecture of the neogene subandean synorogenic wedge southern bolivia foreland sedimentation in the subandean zone of south central bolivia spans from the upper oligocene to present it records sediment dispersal patterns in an initially distal and later proximal retroarc foreland basin and thereby contains stratigraphic information on the tectonic evolution of the adjacent andean fold thrust belt within the neogene orogenic wedge individual siliciclastic dominated depositional systems formed ahead of an eastward propagating deformation regime we defined described and interpreted eight architectural elements and 24 lithofacies from 15 outcrop locations representing the neogene foreland basin in the subandean zone and the chaco plain these are combined to interpret depositional settings the up to 7 5 km thick neogene wedge is subdivided in five stratigraphic units on the basis of facies associations and overall architecture 1 the basal oligocene miocene up to 250 m thick petaca formation consists dominantly of calcrete reworked conglomeratic pedogenic clasts and fluvial sandstone and mudstone this unit is interpreted to represent extensive pedogenesis under an arid to semiarid climate with subordinate braided fluvial processes 2 the overlying upper miocene up to 350 m thick yecua formation records numerous small scale transgressive regressive cycles of marginal marine tidal and shoreline facies of sandstone ooid limestones and varicoloured mudstone 3 the upper miocene up to 4500 m thick tariquia formation principally consists of sandstone with interbedded sandstone mudstone couplets representing frequent crevassing in anastomosing streams with an upsection increasing degree of connectedness 4 the up to 1500 m thick lower pliocene guandacay formation represents braided streams and consists principally of granule to cobble conglomerate interbedded with sandstone and sandy mudstone 5 the upper pliocene up to 2000 m thick emborozu formation consists predominantly of alluvial fandeposited cobble to boulder conglomerate interbedded with sandstone and sandy mudstone the coarsening and thickening upward pattern and eastward progradation coupled with the variable proportions of overbank facies channel size and degree of channel abandonment in the tariquia guandacay and emborozu formations reflect a distal through proximal fluvial megafan environment this long lived megafan grew by high sedimentation rates and a northeast through southeast radial paleoflow pattern on large coarse grained sediment lobes the marked overall

influence of peruvian flat subduction dynamics on the evolution of western amazonia convection in the earth s mantle is mainly driven by cold dense subducting slabs but relatively little is known about how 3d variations in slab morphology and buoyancy affect mantle flow or how the surface above deforms in response i e dynamic topography we investigate this problem by studying the dynamics of an active region of flat slab subduction located in peru in south america here the slab geometry is well known based on the regional seismicity and we have observations from the local geological record to validate our models of particular interest is the widespread subsidence and deposition of the solimoes formation across western amazonia that coincided with the development of the peruvian flat slab during the mid late miocene this formation covers an extensive area from the foredeep to the purus arch located view the mathml source 2000km away from the trench close to the andes the preservation of several kilometers of sedimentary thicknesses can be easily accounted for by flexure based on an estimate of the andean loading we predict 2 8 to 3 6 km of accommodation space that spans 100 km the spatial and temporal history of the solimoes formation however particularly the thick distal foreland accumulations up to 1 2 km deep can only be matched with the addition of a longer wavelength dynamic source of topography following the transition from normal to flat subduction we predict over 1 km of dynamic subsidence view the mathml source 1500km wide that propagates over 1000 km away from the trench tracking the subduction leading edge this is followed by a pulse of dynamic uplift over the flat segment behind it we therefore propose that a combination of uplift flexure and dynamic topography during slab flattening in peru is responsible for the sedimentation history and landscape evolution of western amazonia that eventually led to the configuration of the amazon drainage basin we know today

sedimentologic and palynologic records of the last deglaciation and holocene from ballston lake new york continuous pollen and sediment records from two 8 5 m long cores document late pleistocene and holocene sedimentation and vegetation change in the ballston lake basin eastern new york state pebbles at the base of both cores and the geomorphology of the watershed reflect the presence of the mohawk river in the basin prior to 12 900 70 cal yr b p ballston lake formed at the onset of the younger dryas yd by an avulsion of the mohawk river the transition from clay to gyttja with low magnetic susceptibility ms low bulk density and high organic carbon indicates rapid warming and increased lake productivity beginning 11 020 cal yr b p ms measurements reveal that the influx of magnetic particles associated with pre holocene clastic sedimentation ceased after 10 780 cal yr b p the pollen record is subdivided into six zones bl1 12 920 to 11 020 cal yr b p is dominated by boreal forest pollen bl2 11 020 to 10 780 cal yr b p by pine pinus forest pollen bl3 10 780 to 5290 cal yr b p by hemlock tsuga and mixed hardwood pollen bl4 5290 to 2680 cal yr b p by mixed hardwood pollen bl5a 2680 cal yr b p to 1030 cal yr b p by conifer and mixed hardwood pollen and bl5b 1030 cal b p to present by increasing ragweed ambrosia pollen a 62 decrease in spruce picea pollen in 320 cal years during bl1 reflects rapid warming at the end of the yd holocene pollen zones record more subtle climatic shifts than occurred at the end of the yd one of the largest changes in the holocene pollen spectra began 5300 cal yr b p and is characterized by a marked decline in hemlock pollen this has been noted in other pollen records from the region and may record preferential selection of hemlock by a pathogen or parasites

wisconsinan late glacial environmental chage in new brunswick a regional synthesis a synthesis is presented of the history of deglaciation vegetation cover and climate in new brunswick canada during that part of the wisconsinan late glacial period 12 9 ka bp for which detailed records exist curves of inferred temperature variations in the region during this period are presented based upon qualitative interpretations of plant records and quantitative estimates based upon fossil chironomid assemblages

paleogeography of miocene western amazonia isotopic composition of molluscan shells constrains the influence of marine incursions strontium oxygen and carbon isotope compositions of well preserved mollusks bivalves indicate a dominantly freshwater depositional setting for the lower miocene upper miocene pebas formation in western amazonia molluscan 87sr 86sr ratios identify different freshwater sources andean runoff was the dominant water source in miocene western amazonia though there was occasional influx of waters from cratonic catchments at only one stratigraphic level isotope signals indicate increased mesohaline aquatic salinities in concert with a clearly more saline molluscan faunal assemblage strontium isotope based salinity estimates are surprisingly low when compared to other paleosalinity estimates based on the interpretation of ichno faunal assemblages and sedimentological structures we propose that these seemingly contrasting observations can be unified if miocene western amazonia was occupied by a long lived lacustrine wetland system with a restricted connection via the los llanos basin to the caribbean sea abundant runoff supplied fresh water to this system which effectively blocked the influx of saline waters through the restricted marine connection to the north much like modern lake maracaibo such a system could have been the site of microtidal currents and thus could have hosted brackish water fauna in a dominantly freshwater depositional system

patterns of low frequency monthly sea level pressure variability 1899 1986 and associated wave cyclone frequencies abstract spatial patterns of low frequency sea level pressure slp variability are identified by performing rotated principal component analysis rpca on a long term 1899 1986 northern hemisphere gridded dataset the analysis is limited to the region 160 e eastward to 40 e due to missing data early in the century the objective is to identify a comprehensive set of highly recurrent slp teleconnection patterns to examine some aspects of their seasonality and to identify the associated mean winter pressure fields and cyclone frequencies occurring at times of opposite eigenvector polarity the results are further described in the context of the southern oscillation and known midtropospheric teleconnection patterns four low frequency variability patterns are identified over the atlantic european sector including i the north atlantic 0scillation nao and spatial patterns with slp variability centers over ii the eastern atlantic eatl iii southern europe and the northern mediterranean basin s

marine connections of amazonia evidence from foraminifera and dinoflagellate cysts early to middle miocene colombia peru abstract species composition in the present day amazonian heartland has an imprint of past marine influence the exact nature timing and extent of this marine influence however are largely unresolved here we use calcareous tests of foraminifera and marine palynomorphs from miocene sediments in northwestern amazonia to extend on current estimates for salinity ranges paleoenvironments and paleogeography our samples mostly contain tests and or organic linings of euryhaline tolerant to a wide range of salinity foraminifera of the genera ammonia trochammina and elphidium with ammonia being by far the dominant genus at all locations organic walled dinoflagellate cysts dinocysts such as spiniferites brigantedinium and tuberculodinium vancampoae are also common at a number of sites this association of foraminifera and dinocyst taxa points at varying salinities with aberrant forms of ammonia indicating lower limits of 0 10 psu practical salinity units whereas dinocyst associations suggest more marine conditions such regional heterogeneity is common at the interface of shallow marine to freshwater environments like estuaries we conclude that during the early and middle miocene marginal marine conditions reached at least 2000 km inland from the caribbean portal global high sea level and fast subsidence in the sub andean zone are thought to be the controlling mechanisms of the marine incursions lowering of global sea level and a change in tectonic regime terminated the incursions in the course of the plio pleistocene

an event stratigraphy for the last termination in the north atlantic region based on the greenland ice core record a proposal by the intimate group it is suggested that the grip greenland ice core should constitute the stratotype for the last termination based on the oxygen isotope signal in that core a new event stratigraphy spanning the time interval from ca 22 0 to 11 5 k grip yr bp ca 19 0 10 0 k 14 c yr bp is proposed for the north atlantic region this covers the period from the last glacial maximum through termination 1 of the deep ocean record to the pleistocene holocene boundary and encompasses the last glacial late glacial of the traditional northwest european stratigraphy the isotopic record for this period is divided into two stadial episodes greenland stadials 1 gs 1 and 2 gs 2 and two interstadial events greenland interstadials 1 gi 1 and 2 gi 2 in addition gi 1 and gs 2 are further subdivided into shorter episodes the event stratigraphy is equally applicable to ice core marine and terrestrial records and is considered to be a more appropriate classificatory scheme than the terrestrially based radiocarbon dated chronostratigraphy that has been used hitherto 1998 john wiley sons ltd

ocean gyre circulation changes associated with the north atlantic oscillation abstract observational evidence is presented for interannual to interdecadal variability in the intensity of the north atlantic gyre circulation related to the atmospheric north atlantic oscillation nao patterns a two point baroclinic pressure difference between the subtropical and subpolar gyre centers an oceanic analogue to the much used sea level pressure slp based atmospheric nao indices is constructed from time series of potential energy anomaly pea derived from hydrographic measurements in the labrador basin and at station s near bermuda representing the upper 2000 db eastward baroclinic mass transport between the two centers the transport index indicates a gulf stream and north atlantic current that gradually weakened during the low nao period of the 1960s and then intensified in the subsequent 25 years of persistently high nao to a record peak in the 1990s the peak to peak amplitude difference was 15 20 megatons per second mt s 1 with a 43 yr mean of about 60 mt s 1 a change of 25 33

temporal variability of the atlantic meridional overturning circulation at 26 5 n the vigor of atlantic meridional overturning circulation moc is thought to be vulnerable to global warming but its short term temporal variability is unknown so changes inferred from sparse observations on the decadal time scale of recent climate change are uncertain we combine continuous measurements of the moc beginning in 2004 using the purposefully designed transatlantic rapid climate change array of moored instruments deployed along 26 5 n with time series of gulf stream transport and surface layer ekman transport to quantify its intra annual variability the year long average overturning is 18 7 5 6 sverdrups sv range 4 0 to 34 9 sv where 1 sv a flow of ocean water of 106 cubic meters per second interannual changes in the overturning can be monitored with a resolution of 1 5 sv

meridional overturning transports at 7 5n and 24 5n in the atlantic ocean during 1992 93 and 2010 11 abstract transatlantic hydrographic sections along latitudes 7 5n and 24 5n have been repeated with about 20 years difference at the beginning of the 1990s and 2010s for each period an inverse model is applied to the closed box bound by both sections the model imposes mass conservation for individual layers defined by isoneutral surfaces and the whole water column using surface ekman transport and several transport constraints for specific ranges of longitudes and depths as a result the velocities at the reference layer for each station pair and the dianeutral velocities between layers are estimated and the horizontal velocity fields and the water heat and freshwater transports are calculated in particular we find that mass transport per stratum at 24 5n in 2011 is in good agreement with the transport estimates from the rapid watch array during both realizations the dianeutral velocities downwell from the upper north atlantic deep water unadw to the lower north atlantic deep water lnadw strata resulting in the merging of the two southward flowing strata at 24 5n into one deep southward moving stratum at 7 5n at 24 5n there is an increase in southward unadw transport between 1992 and 2011 compensated by a decrease of southward lnadw transport a descent in the upper limit of the antarctic bottom water aabw from 1992 to 2011 is also inferred the atlantic meridional overturning circulation amoc is larger in 1992 93 than in 2010 11 decreasing from 24 7 1 7 to 20 1 1 4 sv at 24 5n and from 29 2 1 7 to 16 9 1 5 sv at 7 5n much of this decrease arises because of the northward flow of antarctic intermediate water aaiw which was much more intense in 1992 93 than in 2010 11 as a consequence heat transport at 24 5n is not significantly different in 1992 1 4 0 1 pw and 2011 1 2 0 1 pw the estimation of heat transport at 7 5n strongly depends on the magnitude of the north brazil current over the american continental platform the freshwater flux into the box bounded by the two transoceanic sections decreases significantly from 1992 93 0 45 0 05 sv to 2010 11 0 36 0 3 sv meaning a decrease in net evaporation over this same area

variability of the deep western boundary current east of the grand banks the deep western boundary current east of the grand banks has been observed during 1999 2005 by moored current meter stations and shipboard current profiling sections these recent observations can be compared with those of a woce moored array deployed during 1993 95 at the same location overall the observations of deep water currents east of the grand banks reported here do not support suggestions of a basin wide slowdown of the atlantic meridional overturning circulation

variability in the slope water and its relation to the gulf stream path 1 sea surface temperature sst and sea surface height ssh data for 1993 2007 for the north atlantic are combined with hydrographic data at 69w to investigate the relation between the gulf stream gs position and the slope water properties sst anomalies north of the gs are correlated with changes in its path the lag of this correlation is such that positive temperature anomalies precede northward shifts of the gs and suggests that sst anomalies move westward with speeds of several cm s eof analysis of the sst and ssh fields shows that cooling and strengthening of the sw flow are in phase over the slope water which is mirrored in the vertical structure of these fields at 69w indicating larger transports in the deep western boundary current lead to southward shifts of the mean gs path this relation between the slope water and the gs path provides some predictability for the latter

gulf stream structure transport and recirculation near 68 w an analysis of the structure and transport of the gulf stream is undertaken using direct current meter observations from a 13 mooring array deployed near 68 w from june 1988 to august 1990 the analysis is based on a stream coordinate approach in which velocities are rotated into a local downstream coordinate frame and averaged according to their relative cross stream location within the current the picture so obtained represents the average synoptic structure of the gulf stream rather than the eulerian averaged structure in which the current is weakened and broadened by lateral meandering of the current and adjacent recirculations many familiar features of the gulf stream are reproduced in the analysis including an asymmetric velocity profile with larger shear on the cyclonic shoreward side of the current an offshore displacement of the velocity core with depth and a subsurface velocity maximum on the offshore side of the current westward recirculations are also seen on both sides of the gulf stream maximum downstream speeds at the axis of the gulf stream reach approximately 2 0 m s at the surface and 0 7 m s at 1000 m roughly twice the corresponding eulerian averaged values the analysis also reveals a deep extension of the gulf stream at 3500 m depth with a width of 130 km and average speeds of 3 4 cm s the transport of the gulf stream in the stream coordinate frame is 113 8 sv approximately 30 larger than the eulerian averaged transport of 88 sv on the basis of these results and other recent studies the downstream transport increase of the gulf stream and the inflow structure to the gulf stream are reconsidered it is concluded that approximately 30 sv or over half of the transport increase between cape hatteras and 68 w is fed by inflow from the northern side of the gulf stream and that this inflow is concentrated near cape hatteras and 68 w where the gulf stream flows steeply across isobaths converging from the north