images of jupiter from the pioneer 10 and pioneer 11 infrared radiometers a comparison with visible and 5 μm images all of the data acquired at jupiter by the infrared radiometers on board pioneers 10 and 11 are presented in the form of images with geometric control the images are compared with 5 m and visible images taken in the same time frame the association of dark blue or brown and light white or red areas with warm and cool areas at 5 20 and 45 m respectively extends to nearly all features observed on the planet where the normal association of light and dark visible markings with the zonal velocity breaks down e g at the latitude of the south equatorial belt during the pioneer encounters the infrared emission seems to follow the visible cloud structure rather than the zonal velocity structure exceptions to the general rule involve 20 m radiation which reflects conditions in the altitude range 0 1 0 3 bar for example a comparison between pioneer 10 and 11 images suggests that the south equatorial belt became brighter at 20 m but remained constant at other wavelengths between the two encounters

observed sources and variability of nordic seas overflow the overflows from the nordic seas maintain the deep branch of the north atlantic circulation that is an important part of the global climate system an analysis of observed ocean temperatures and salinities between 1950 and 2005 shows that the atlantic water circulating in the nordic seas is the main source for change in the overflow waters

on the role of eddies and surface forcing in the heat transport and overturning circulation in marginal seas the factors that determine the heat transport and overturning circulation in marginal seas subject to wind forcing and heat loss to the atmosphere are explored using a combination of a high resolution ocean circulation model and a simple conceptual model the study is motivated by the exchange between the subpolar north atlantic ocean and the nordic seas a region that is of central importance to the oceanic thermohaline circulation it is shown that mesoscale eddies formed in the marginal sea play a major role in determining the mean meridional heat transport and meridional overturning circulation across the sill the balance between theoceaniceddyheatfluxandatmosphericcooling ascharacterizedbyanondimensionalnumber isshownto be the primary factor in determining the properties of the exchange results from a series of eddy resolving primitive equation model calculations for the meridional heat transport overturning circulation density of convective waters and density of exported waters compare well with predictions from the conceptual model over a wide range of parameter space scaling and model results indicate that wind effects are small and the mean exchange is primarily buoyancy forced these results imply that one must accurately resolve or parameterize eddy fluxes in order to properly represent the mean exchange between the north atlantic and the nordic seas and thus between the nordic seas and the atmosphere in climate models

interannual changes in the overflow from the nordic seas into the atlantic ocean through denmark strait the global thermohaline circulation is an important part of earth s climate system cold dense water formed in the nordic seas enters the atlantic ocean as overflows across the sills of the greenland scotland ridge the denmark strait overflow dso is one of the main sources of north atlantic deep water until now the dso has been believed to be stable on interannual timescales here for the first time evidence is presented from a 4 year program of observations showing that overflow transports in 1999 2000 were approximately 30 higher than previous estimates later transports decreased remarkably during the observation period coincident with a temporary temperature increase of about 0 5 c

dynamics of downwelling in an eddy resolving convective basin the mean downwelling in an eddy resolving model of a convective basin is concentrated near the boundary where eddies are shed from the cyclonic boundary current into the interior it is suggested that the buoyancyforced downwelling in the labrador sea and the lofoten basin is similarly concentrated in analogous eddy formation regions along their eastern boundaries use of a transformed eulerian mean depiction of the density transport reveals the central role eddy fluxes play in maintaining the adiabatic nature of the flow in a nonperiodic region where heat is lost from the boundary current the vorticity balance in the downwelling region is primarily between stretching of planetary vorticity and eddy flux divergence of relative vorticity althougha narrowviscous boundarylayeris ultimately importantin closingtheregionalvorticitybudget this overall balance is similar in some ways to the diffusive viscous balance represented in previous boundary layer theories and suggests that the downwelling in convective basins may be properly represented in lowresolution climate models if eddy flux parameterizations are adiabatic identify localized regions of eddy formations and allow density to be transported far from the region of eddy formations

consistent fluctuations in intermediate water temperature off the coast of greenland and norway during dansgaard oeschger events abstract rapid warmings epitomize the dansgaard oeschger events that are recorded in greenland ice cores and imprinted in ocean sediment cores while the abrupt climate changes appear connected to perturbations in sea ice and ocean circulation it is unclear how the water masses within the nordic seas responded and were influenced by the inflowing atlantic water in the absence or presence of sea ice high resolution reconstructions of benthic mg ca together with stable isotopes of carbon and oxygen 13c and 18o show a recurring warming 2 5 0 5 c occurring consistently at the inflow and outflow of the nordic seas at intermediate depths down to 1500 m during greenland stadials 9 6 using idealized numerical simulations with an eddy resolving ocean model we investigate the impact of an isolating sea ice cover and freshwater lid in the nordic seas with the presence of an extensive sea ice cover the warm atlantic water entering the nordic seas in the east retains its heat as it exits in the west the depth of the recirculating warm atlantic water increases when including an external freshwater source at the surface of the nordic seas these findings support the view that cold stadials are accompanied by pervasive intermediate water warming across the nordic seas given the current rates of arctic sea ice loss these results provide a potential mechanism for water column destabilization and inception of abrupt climate change

boundary currents and watermass transformation in marginal seas the properties of watermass transformation and the thermohaline circulation in marginal seas with topography and subject to a spatially uniform net surface cooling are discussed the net heat loss within the marginal sea is ultimately balanced by lateral advection from the open ocean in a narrow boundary current that flows cyclonically around the basin heat loss in the interior is offset by lateral eddy fluxes originating in the boundary current the objectives of this study are to understand better what controls the density of waters formed within the marginal sea the temperature of the outflowing waters the amount of downwelling and the mechanisms of heat transport within the marginal sea the approach combines heat budgets with linear stability theory for a baroclinic flow over a sloping bottom to provide simple theoretical estimates of each of these quantities in terms of the basic parameters of the system the theory compares well to a series of eddy resolving primitive equation model calculations the downwelling is concentrated within the boundary current in both a diffusive boundary layer near topography and an eddy driven region on the offshore edge of the boundary current for most high latitude regions the horizontal gyre is expected to transport more heat than does the overturning gyre

causes of changes in the denmark strait overflow abstract the warming nordic seas potentially tend to decrease the overflow across the greenland iceland scotland ridge gisr system recent observations by macrander et al document a significant drop in the intensity of outflowing denmark strait overflow water of more than 20 over 3 yr and a simultaneous increase in the temperature of the bottom layers of more than 0 4 c a simulation of the exchange across the gisr with a regional ocean circulation model is used here to identify possible mechanisms that control changes in the denmark strait overflow and its relations to changed forcing condition on seasonal and longer time scales the authors establish links of the overflow anomalies to a decreasing capacity of the dense water reservoir caused by a change of circulation pattern north of the sill on annual and shorter time scales the wind stress curl around iceland determines the barotropic circulation around the island and thus the barotropic flow through denmark strait for the overlapping time sc

synoptic sections of the denmark strait overflow we report on a rapid high resolution survey of the denmark strait overflow dso as it crosses the sill the first such program to incorporate full water column velocity profiles in addition to conventional hydrographic measurements seven transects with expendable profilers over the course of one week are used to estimate volume transport as a function of density our observations reveal the presence of a strongly barotropic flow associated with the nearly vertical front dividing the arctic and atlantic waters the seven section mean transport of water denser than 27 8 is 2 7 0 6sv while the mean transport of water colder than 2 0 c is 3 8 0 8 sv although this is larger than the 2 9 sv of 2 c water measured by a 1973 current meter array we find that a sampling of our sections equivalent to the extent of that array also measures 2 9sv of cold water both the structure and magnitude of the measured flow are reproduced well by a high resolution numerical model of buoyancy driven exchange with realistic topography

on the nature and variability of the east greenland spill jet a case study in summer 2003 abstractresults from a high resolution 2 km numerical simulation of the irminger basin during summer 2003 are presented the focus is on the east greenland spill jet a recently discovered component of the circulation in the basin the simulation compares well with observations of surface fields the denmark strait overflow dso and the hydrographic structure of typical sections in the basin the model reveals new aspects of the circulation on scales of o 0 1 10 days and o 1 100 km the model spill jet results from the cascade of dense waters over the east greenland shelf spilling can occur in various locations southwest of the strait and it is present throughout the simulation but exhibits large variations on periods of o 0 1 10 days the spill jet sometimes cannot be distinguished in the velocity field from surface eddies or from the dso the vorticity structure of the jet confirms its unstable nature with peak relative and tilting vorticity terms reaching twice the planetary vorticity term the

the east greenland spill jet high resolution hydrographic and velocity measurements across the east greenland shelf break south of denmark strait have revealed an intense narrow current banked against the upper continental slope this is believed to be the result of dense water cascading over the shelf edge and entraining ambient water the current has been named the east greenland spill jet it resides beneath the east greenland irminger current and transports roughly 2 sverdrups of water equatorward strong vertical mixing occurs during the spilling although the entrainment farther downstream is minimal a vorticity analysis reveals that the increase in cyclonic relative vorticity within the jet is partly balanced by tilting vorticity resulting in a sharp front in potential vorticity reminiscent of the gulf stream the other components of the irminger sea boundary current system are described including a presentation of absolute transports

yes some of the mediterranean outflow does come from great depth in 1973 stommel et al predicted that the western mediterranean deep water wmdw contributes directly to the mediterranean outflow through the strait of gibraltar strommel et al 1973 hydrographic data obtained in november 1985 showed unambiguous evidence of wmdw west of the major gibraltar sill thus confirming the prediction

significant role of the north icelandic jet in the formation of denmark strait overflow water the largest dense water plume feeding the lower limb of the atlantic meridional overturning circulation from the nordic seas comes from denmark strait overflow water measurements of hydrography and water velocity north of iceland and ocean model simulations indicate that a significant part of this water is supplied by the north icelandic jet

structure and transports of the east greenland current at 75 n from moored current meters the east greenland current runs from 80 n to 60 n from the fram strait to the denmark strait via the nordic seas it transports waters from the arctic and the nordic seas into the atlantic and also acts as a western intensified southward return flow for waters recirculating within the greenland sea gyre itself an area important for deep water formation data from current meters moored across the current at 75 n in 1994 1995 show a large seasonal variation in the current the annual mean transport is 21 3 sv taking 9 w as the eastern boundary varying from 11 sv in summer to 37 sv in winter errors approximately 5 sv no significant seasonal signal has been observed in the fram or denmark straits suggesting that the seasonal transport is confined within the greenland sea using temperature and velocity data we split the flow at 75 n into two parts a mainly wind driven circulation annual mean of order 19 sv which is trapped within the greenland sea gyre and exhibits a large seasonal cycle transporting predominantly the waters of the greenland sea and a steadier throughflow probably thermohaline driven of order 8 sv in the annual mean with very little seasonal variation data from previous years 1987 1994 indicate the interannual variability of the current is low assuming a spatially coherent structure to the current we extend the time series of the transport back to 1991 and suggest it may be possible to monitor the total transport with one suitably placed mooring

faroe bank channel overflow 1995 2005 abstract the faroe bank channel fbc is the deepest passage across the greenland scotland ridge and there is continuous overflow of dense water through the channel which provides a substantial contribution to the global thermohaline circulation since november 1995 acoustic doppler current profilers adcps have been moored at the sill of the channel continuously except for short annual servicing periods in addition to this ctd sections have regularly been occupied across the channel and instruments recording temperature and salinity have been moored for short periods these observations demonstrate that the channel due to its small width can be monitored fairly well with only one adcp mooring and they allow the generation of a time series of overflow volume flux for the 1995 2005 period the kinematic overflow flux defined solely from the velocity field was found to have an average value of 2 1 0 2 sv with a seasonal and with inter annual variations of approximately 10 amplitude but with no discernible trend for the whole period the average flux of water with potential density exceeding 27 8 kg m 3 was found to be 1 9 0 3 sv with average properties 0 25 c s 34 93 28 01 kg m 3 for this period no evidence was found for a weakening overflow flux but the salinity of the fbc overflow especially the warmer parts has increased substantially during the period which implies an increased average density on the order of 0 01 kg m 3 previous observations of a helical cross channel circulation are confirmed and may explain the thin pycnocline layer but shear instability induces intensive mixing that puts a lower limit on the layer thickness critical control at one point of the sill cross section rather than friction seems to govern the overflow dynamics and simple layered models can explain much of the observed features as well as the seasonal variation but potential vorticity as defined for a single overflow layer is not conserved a previously suggested 1950 2000 weakening of the fbc overflow which was partly based on a subset of the data presented here is not supported by the full dataset

on the cascading of dense shelf waters in the irminger sea abstracthydrographic data collected in the irminger sea in the 1990s 2000s indicate that dense shelf waters carried by the east greenland current south of the denmark strait intermittently descend cascade down the continental slope and merge with the deep waters originating from the nordic seas overflows repeat measurements on the east greenland shelf at 200 km south of the denmark strait 65 66 n reveal that east greenland shelf waters in the irminger sea are occasionally as dense 0 27 80 as the overflow derived deep waters carried by the deep western boundary current dwbc clear hydrographic traces of upstream cascading of dense shelf waters are found over the continental slope at 64 3 n where the densest plumes 0 27 80 originating from the shelf are identified as distinct low salinity anomalies in the dwbc downstream observations suggest that dense fresh waters descending from the shelf in the northern irminger sea can be distinguished in the dwbc up to the latitude of cape farewell

a new path for the denmark strait overflow water from the iceland sea to denmark strait 1 denmark strait overflow water dsow is one of the main components of the thermohaline circulation there has been no consensus on where it is formed and by which way it is brought to the denmark strait it is shown here that it is brought to the sill by a hitherto unknown current that is traced from the sill back into the iceland sea north of iceland the transport of this current is sufficient to account for a major part of the transport of dsow as it has been measured at the sill if some entrainment of ambient water is assumed this supports theories suggesting that the iceland sea is the main source for the dsow and this has consequences for the way in which climate change affects the thermohaline circulation

mesoscale variability in denmark strait the pv outflow hypothesis abstract the outflow through denmark strait shows remarkable mesoscale variability characterized by the continuous formation of intense mesoscale cyclones just south of the sill these cyclones have a diameter of about 30 km and clear signatures at the sea surface and in currents measured near the bottom they have a remnant of arctic intermediate water aiw in their core the authors hypothesis is that these cyclones are formed by stretching of the high potential vorticity pv water column that outflows through denmark strait the light upper layer of the outflow the east greenland current remains on the surface in the irminger sea while the dense overflow water descends the east greenland continental slope the midlevel waters mostly aiw could thus be stretched by more than 100 which would induce very strong cyclonic relative vorticity the main test of this new hypothesis is by way of numerical experiments carried out with an isopycnal coordinate ocean model configured to have a marginal sea

the production of north atlantic deep water sources rates and pathways updating an earlier account by dickson et al 1990 this paper reviews the initial development phase of north atlantic deep water nadw production from the points where the dense inflows from nordic seas cross the greenland scotland ridge to the point off south greenland where the buildup of new production appears almost complete in particular three long term current meter arrays totaling 91 instruments and set at 160 km intervals south from the denmark strait sill are used to validate earlier short term arrays by others and in combination with these earlier arrays to describe the downstream evolution of mean speed depth and entrainment the variability of the overflow current in space and time and the likely contribution of the other three main constituents of nadw production at densities greater than 27 8 from the points of overflow 5 6 sv the transport within this range increases by entrainment and confluence with other contributory streams to around 13 3 sv at cape farewell while recirculating elements prevent us from determining the net southgoing transport a nadw transport of this order appears consistent with recent estimates of net abyssal flow passing south through the north and south atlantic

amino acid abundances and stereochemistry in hydrothermally altered sediments from the juan de fuca ridge northeastern pacific ocean amino acid abundances and stereochemistry in hydrothermally altered sediments from the juan de fuca ridge northeastern pacific ocean