latitudinal structure of the meridional overturning circulation variability on interannual to decadal time scales in the north atlantic ocean abstractthe latitudinal structure of the atlantic meridional overturning circulation amoc variability in the north atlantic is investigated using numerical results from three ocean circulation si

decadal variability of subpolar gyre transport and its reverberation in the north atlantic overturning 1 analyses of sea surface height ssh records based on satellite altimeter data and hydrographic properties have suggested a considerable weakening of the north atlantic subpolar gyre during the 1990s here we report hindcast simulations with high resolution ocean circulation models that demonstrate a close correspondence of the ssh changes with the volume transport of the boundary current system in the labrador sea the 1990s decline of about 15 of the long term mean appears as part of a decadal variability of the gyre transport driven by changes in both heat flux and wind stress associated with the north atlantic oscillation nao the changes in the subpolar gyre as manifested in the deep western boundary current off labrador reverberate in the strength of the meridional overturning circulation moc in the subtropical north atlantic suggesting the potential of a subpolar transport index as an element of a moc monitoring system

observed basin scale response of the north atlantic meridional overturning circulation to wind stress forcing abstractthe response of the north atlantic meridional overturning circulation moc to wind stress forcing is investigated from an observational standpoint using four time series of overturning transports below and relative to 1000 m overlapping by 3 6 yr these time series are derived from four mooring arrays located on the western boundary of the north atlantic the rapid western atlantic variability experiment wave array 42 5 n the woods hole oceanographic institution line w array 39 n rapid moc mocha 26 5 n and the meridional overturning variability experiment move array 16 n using modal decompositions of the analytic cross correlation between transports and wind stress the basin scale wind stress is shown to significantly drive the moc coherently at four latitudes on the time scales available for this study the dominant mode of covariance is interpreted as rapid barotropic oceanic adjustments to wind stress forcing eventually forming two counterrotating ekman overturning cells c

effect of mineralogy and pedoclimatic variations on ni and cr distribution in serpentine soils under temperate climate abstract part of the soils occurring in the serpentinite szklary massif sw poland have developed in quaternary under temperate climate on the parent rock not affected by chemical weathering in studied parent ultrabasite ni occurs in cr magnetite up to 0 96 wt of nio forsterite up to 0 55 wt of nio iddingsite up to 0 99 wt of nio and serpentine up to 0 55 wt of nio while cr is bounded with cr magnetites up to 21 77 wt of cr 2 o 3 and clinochlores up to 1 68 wt of cr 2 o 3 cr magnetites are highly resistant to weathering while other primary minerals more susceptible to weathering release parts of ni and cr which are trapped in authigenic phases the latter however contain less ni and cr than corresponding primary minerals clayous matrix 0 37 wt of nio and 0 08 wt of cr 2 o 3 smectites 0 30 wt of nio and 0 07 wt of cr 2 o 3 and mixture of oxy hydroxides and clay minerals 0 36 wt of nio and 0 14 wt of cr 2 o 3 at the mineral scale smectite plays an important role in the trapping of ni at the profile scale ni and cr are moderately diluted upwards the soil profile and cr is generally less mobile than ni the soil formed in szklary is chemically different than the analogous serpentine soils occurring more to the south in europe french massif central vosges mountains and ligurian apennines nw italy the difference is due to participation of fluvioglacial material produced by quaternary continental glaciacion in poland however similar vertical relative variations of ni and cr were found in all compared soils in spite of differences in parent rock composition allogenic contaminations and degree of soil development comparison with other well drained pedons located in similar uphill positions shows a climatic control of the cr and ni vertical distribution in serpentine soils humid mountainous variant of temperate climate induces leaching of mg and subsequent lack in smectite neoformation which lead to the release of ni ni is less mobile in the colder and dryer climate of poland moreover some primary minerals which are generally considered as not stable under soil conditions olivine serpentine and chlorite are still present even in the a horizon of the studied polish pedon their resistance is due to slower rates of weathering related to the climate but also due to former hydrothermal processes affecting the parent rock fabric

year round measurements of the irminger current variability of a two core current system observed in 2014 2016 the irminger current ic flowing northeastward along the western flank of the reykjanes ridge is an important component in the overturning of the north atlantic subpolar gyre a 2 year 2014 2016 time series from moored observations shows that the ic consists of two highly variable current cores a subsampling experiment using an ocean reanalysis showed that this current s variability is adequately captured by the array the two current cores contribute nearly equally to the mean volume transport the total 2 year mean transport was found to be 10 6 sv with a standard deviation of daily monthly values of 9 2 sv 4 4 sv and a standard error of 1 4 sv mean heat and freshwater transport were 0 21 pw and 22 5 msv respectively sref 34 92 the volume transport is strongest in spring and the average over the first year 8 6 sv was lower than that of the second year 12 4 sv coinciding with an increase in the density gradient over the array in the second year the variability of the total transport is dominated by variations in the western core while the warmer saltier eastern core contributes more to the heat and negative freshwater transport during the two observed winters which were marked by exceptional deep convection in the central irminger sea mixed layer deepening down to 400 m depth and outcropping of the 27 7 kg m3 isopycnal were observed within the ic

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

magma sponge hypothesis and stratovolcanoes case for a compressible reservoir and quasi steady deep influx at soufriere hills volcano montserrat 1 we use well documented time histories of episodic gps surface deformation and efflux of compressible magma to resolve apparent magma budget anomalies at soufriere hills volcano shv on montserrat wi we focus on data from 2003 to 2007 for an inflation succeeded by an episode of eruption plus deflation we examine mogi type and vertical prolate ellipsoidal chamber geometries to accommodate both mineralogical constraints indicating a relatively shallow pre eruption storage and geodetic constraints inferring a deeper mean pressure source an exsolved phase involving several gas species greatly increases andesite magma compressibility to depths 10 km i e for water content 4 wt crystallinity 40 and this property supports the concept that much of the magma transferred into or out of the crustal reservoir could be accommodated by compression or decompression of stored reservoir magma i e the magma sponge our results suggest quasi steady deep mainly mafic magma influx of the order of 2 m3s 1 and we conclude that magma released in eruptive episodes is approximately balanced by cumulative deep influx during the eruptive episode and the preceding inflation our magma sponge model predicts that between 2003 and 2007 there was no evident depletion of magma reservoir volume at shv which comprises tens of km3 with radial dimensions of order 1 2 km in turn implying a long lived eruption

breaking the linkage between labrador sea water production and its advective export to the subtropical gyre abstractdeep water formation in the northern north atlantic has been of long standing interest because the resultant water masses along with those that flow over the greenland scotland ridge constitute the lower limb of the atlantic meridional overturning circulation amoc which carries these cold deep waters southward to the subtropical region and beyond it has long been assumed that an increase in deep water formation would result in a larger southward export of newly formed deep water masses however recent observations of lagrangian floats have raised questions about this linkage motivated by these observations the relationship between convective activity in the labrador sea and the export of newly formed labrador sea water lsw the shallowest component of the deep amoc to the subtropics is explored this study uses simulated lagrangian pathways of synthetic floats produced with output from a global ocean sea ice model it is shown that substantial recirculation of newly formed lsw in the

impact of labrador sea convection on the north atlantic meridional overturning circulation abstract the overturning and horizontal circulations of the labrador sea are deduced from a composite vertical section across the basin the data come from the late spring early summer occupations of the world ocean circulation experiment woce ar7w line during the years 1990 97 this time period was chosen because it corresponded to intense wintertime convection the deepest and densest in the historical record suggesting that the north atlantic meridional overturning circulation moc would be maximally impacted the composite geostrophic velocity section was referenced using a mean lateral velocity profile from float data and then subsequently adjusted to balance mass the analysis was done in depth space to determine the net sinking that results from convection and in density space to determine the diapycnal mass flux i e the transformation of light water to labrador sea water the mean overturning cell is calculated to be 1 sv 1 sv 106 m3 s 1 as compared with a horizontal gyre of 18 sv the

decadal evolution of ocean thermal anomalies in the north atlantic the effects of ekman overturning and horizontal transport basin scale thermal anomalies in the north atlantic extending to depths of 1 2km are more pronounced thanthebackgroundwarmingover thelast 60years a dynamicalanalysis basedonreanalyses ofhistorical data from1965to2000suggeststhat thesethermalanomaliesare formedbyocean heat convergences augmented by the poorly known air sea fluxes the heat convergence is separated into contributions from the horizontal circulation and the meridional overturning circulation moc the latter further separated into ekman and moc transport minus ekman transport moc ekman cells the subtropical thermal anomalies are mainly controlled by wind induced changes in the ekman heat convergence while the subpolar thermal anomalies are controlled by the moc ekman heat convergence the horizontal heat convergence is generally weaker only becoming significant within the subpolar gyre these thermal anomalies often have an opposing sign between thesubtropicalandsubpolargyres associatedwithopposingchangesinthemeridionalvolumetransportdriving the ekman and moc ekman heat convergences these changes in gyre scale convergences in heat transport are probably induced by the winds as they correlate with the zonal wind stress at gyre boundaries

wind forced variability of the remote meridional overturning circulation abstractthe mechanisms by which time dependent wind stress anomalies at midlatitudes can force variability in the meridional overturning circulation at low latitudes are explored it is shown that

latitudinal dependence of atlantic meridional overturning circulation amoc variations 1 amoc variations are often thought to propagate with the kelvin wave speed resulting in a short time lead between high and low latitudes amoc variations however as shown in this paper using a coupled climate model gfdl cm2 1 with the existence of interior pathways of north atlantic deep water nadw from flemish cap to cape hatteras as that observed recently amoc variations estimated in density space propagate with the advection speed in this region resulting in a much longer time lead several years between subpolar and subtropical amoc variations and providing a more useful predictability the results suggest that amoc variations have significant meridional coherence in density space and monitoring amoc variations in density space at higher latitudes might reveal a stronger signal with a several year time lead

interdecadal variations of the thermohaline circulation in a coupled ocean atmosphere model abstract a fully coupled ocean atmosphere model is shown to have irregular oscillations of the thermohaline circulation in the north atlantic ocean with a time scale of approximately 50 years the irregular oscillation appears to be driven by density anomalies in the sinking region of the thermohaline circulation approximately 52 n to 72 n combined with much smaller density anomalies of opposite sign in the broad rising region the spatial pattern of see surface temperature anomalies associated with this irregular oscillation bears an encouraging resemblance to a pattern of observed interdecadal variability in the north atlantic the anomalies of sea surface temperature induce model surface air temperature anomalies over the northern north atlantic arctic and northwestern europe

basinwide response of the atlantic meridional overturning circulation to interannual wind forcing an eddy resolving ocean general circulation model for the earth simulator ofes and a simple wind driven two layer model are used to investigate the role of momentum fluxes in driving the atlantic meridional overturning circulation amoc variability throughout the atlantic basin from 1950 to 2010 diagnostic analysis using the ofes results suggests that interior baroclinic rossby waves and coastal topographic waves play essential roles in modulating the amoc interannual variability the proposed mechanisms are verified in the context of a simple two layer model with realistic topography and only forced by surface wind the topographic waves communicate high latitude anomalies into lower latitudes and account for about 50 of the amoc interannual variability in the subtropics in addition the large scale rossby waves excited by wind forcing together with topographic waves set up coherent amoc interannual variability patterns across the tropics and subtropics the comparisons between the simple model and ofes results suggest that a large fraction of the amoc interannual variability in the atlantic basin can be explained by wind driven dynamics

variability of the simulated meridional heat transport in the north atlantic for the period 1951 1993 a 43 year ocean model simulation for the period 1951 1993 is analyzed with a focus on the meridional heat transport mht as a proxy for the strength of meridional overturning cell moc at 25 n the surface heat flux forcing associated with the north atlantic oscillation nao pattern is related to the variability in mht both on interannual and longer timescales the manifestation of the interannual and decadal oceanic response to nao is nonlocal as evidenced by the concentrated heat content and sea level variability at the gulf stream and north atlantic current regions and shown by the comparison of the model sea level variability to the altimeter data between low mht years in mid 1980s and high mht years in early 1990s the same area is singled out by empirical orthogonal function analysis in the leading mode of the sea level mht and time series of the leading sea level mode are highly correlated which reflects the importance of the moc in determining the variability of the heat content of the whole basin also the model suggests that the mht moc has entered a very strong phase since the mid 1980s and this trend has continued up to the end of 1993 this behavior follows the general trend in the nao index

dynamics of eddy driven low frequency dipole modes part iii meridional displacement of westerly jet anomalies during two phases of nao abstract in this paper the north south variability of westerly jet anomalies during the two phases of the north atlantic oscillation nao is examined in a theoretical model it is found that the north south variability of the zonal mean westerly anomaly results from the interaction between the eddy driven anomalous stationary waves with a dipole meridional structure nao anomalies and topographically induced climatological stationary waves with a monopole structure which is dependent upon the phase of the nao the westerly jet anomaly tends to shift northward during the positive nao phase but southward during the negative phase synoptic scale eddies tend to maintain westerly jet anomalies through the excitation of nao anomalies but the climatological stationary wave and its position relative to the eddy driven anomalous stationary wave appear to dominate the north south shift of westerly jet anomalies on the other hand it is shown that when the climatological stationary wave ridge is located downs

opposing decadal changes for the north atlantic meridional overturning circulation hydrographic properties of the north atlantic ocean have changed significantly over the past decades a combination of changes in seawater density calculated from observed properties of sea water and a numerical ocean model reveals that the strength of the meridional overturning circulation has changed in different directions in the subpolar and subtropical basins respectively

deciphering the pathways for the deep limb of the meridional overturning circulation for the past 50 years it has been assumed that the principal pathway for the deep limb of the atlantic meridional overturning circulation amoc is the deep western boundary current dwbc however recent observations of lagrangian floats have shown that the dwbc is not necessarily a unique dominant or continuous pathway for these deep waters a significant portion of the deep water export from the subpolar to the subtropical gyres follows a pathway through the interior of the newfoundland and subtropical basins which is constrained by the western boundary and the western flank of the mid atlantic ridge the hypothesis that deep eddy driven recirculation gyres are a mechanism for partitioning the deep limb of the amoc into the dwbc and this interior pathway is investigated here eulerian and lagrangian analyses of the output of ocean general circulation models at eddy resolving eddy permitting and non eddy permitting resolutions are used to test this hypothesis eddy driven recirculation gyres simulated in the eddy resolving and eddy permitting models and similar to recirculations inferred from hydrographic data are shown to shape the export pathways of deep water from the subpolar to the subtropical gyres

on the relationship between the meridional overturning circulation alongshore wind stress and united states east coast sea level in the community earth system model large ensemble

the origins of late twentieth century variations in the large scale north atlantic circulation abstractsurface forcing perturbation experiments are examined to identify the key forcing elements associated with late twentieth century interannual to decadal atlantic circulation variability as simulated in an ocean sea ice hindcast configuration of the community earth system model version 1 cesm1 buoyancy forcing accounts for most of the decadal variability in both the atlantic meridional overturning circulation amoc and the subpolar gyre circulation and the key drivers of these basin scale circulation changes are found to be the turbulent buoyancy fluxes evaporation as well as the latent and sensible heat fluxes these three fluxes account for almost all of the decadal amoc variability in the north atlantic even when applied only over the labrador sea region year to year changes in surface momentum forcing explain most of the interannual amoc variability at all latitudes as well as most of the decadal variability south of the equator the observed strengthening of southern ocean westerly wi

wind forced interannual variability of the atlantic meridional overturning circulation at 26 5 n the observed atlantic meridional overturning circulation amoc at 26 5 n shows interannual variability consisting of an increase from early 2004 to late 2005 and a following downtrend which reaches a minimum in the winter of 2009 2010 these interannual amoc fluctuations are dominated by changes in the upper mid ocean geostrophic flow except during the winter of 2009 2010 when the anomalous wind driven ekman transport also has a significant contribution the physical mechanisms for the interannual changes of the amoc are proposed and evaluated in a two layer model while the ekman transport is linked to the north atlantic oscillation nao the anomalous geostrophic transport involves the oceanic adjustment to surface wind forcing in particular the intensification and weakening of the southward interior geostrophic flow is modulated by the internal rossby wave adjustment to the surface wind forcing the gulf stream on the other hand is controlled by both topographic waves along the us coast and westward propagating planetary waves our study suggests that a large part of the observed amoc interannual variability at 26 5 n can be explained by wind driven dynamics

temperature salinity structure of the north atlantic circulation and associated heat and freshwater transports abstractthis study investigates the circulation structure and relative contribution of circulation components to the time mean meridional heat and freshwater transports in the north atlantic using numerical results of a high resolution ocean model that are shown to be in excellent agreement with the observations the north atlantic circulation can be separated into the large scale atlantic meridional overturning circulation amoc that is diapycnal and the subtropical and subpolar gyres that largely flow along isopycnal surfaces but also include prominent gyre scale diapycnal overturning in the subtropical mode water and labrador sea water integrals of the meridional volume transport as a function of potential temperature and salinity s yield streamfunctions with respect to and to s and heat functions these argue for a significant contribution to the heat transport by the southward circulation of north atlantic deep water at 26 5 n the isopycnic component of the subtropical gyre is colder and fr

the coherence and impact of meridional heat transport anomalies in the atlantic ocean inferred from observations abstractobservations of thermosteric sea level tsl from hydrographic data equivalent water thickness ewt from the gravity recovery and climate experiment grace and altimetric sea surface height ssh are used to infer meridional heat transport mht anomalies for the atlantic ocean an unknown control version of a kalman filter in each of eight regions extracts smooth estimates of heat transport convergence htc from discrepancies between the response to monthly surface heat and freshwater fluxes and observed mass and heat content two models are used model a using only the heat budget for 1993 2010 and model b using both heat and mass budgets for 2003 10 based on the small contributions of mass to ssh model a is rerun using ssh in place of tsl to improve temporal resolution and data consistency estimates of mht are derived by summing the htc from north to south assuming either negligible anomalies at 67 n or setting mht to observed values near 40 n both methods show that mht is highly coh

phenocryst hosted melt inclusions record stalling of magma during ascent in the conduit and upper magma reservoir prior to vulcanian explosions soufriere hills volcano montserrat west indies the mechanics of explosive eruptions influence magma ascent pathways vulcanian explosions involve a stop start mechanism that recurs on various timescales evacuating the uppermost portions of the conduit during the repose time between explosions magma rises from depth and refills the conduit and stalls until the overpressure is sufficient to generate another explosion we have analyzed major elements cl s h2o and co2 in plagioclase hosted melt inclusions sampled from pumice erupted during four vulcanian events at soufriere hills volcano montserrat to determine melt compositions prior to eruption using fourier transform infrared spectroscopy we measured values up to 6 7 wt h2o and 80 ppm co2 of 42 melt inclusions 81 cluster between 2 8 and 5 4 wt h2o 57 to 173 mpa or 2 7 km suggesting lower conduit to upper magma reservoir conditions we propose two models to explain the magmatic conditions prior to eruption in model 1 melt inclusions were trapped during crystal growth in magma that was stalled in the lower conduit to upper magma reservoir and during trapping the magma was undergoing closed system degassing with up to 1 wt free vapor this model can explain the melt inclusions with higher h2o contents since these have sampled the upper parts of the magma reservoir however the model cannot explain the melt inclusions with lower h2o because the timescale for plagioclase crystallization and melt inclusion entrapment is longer than the magma residence time in the conduit in model 2 melt inclusions were originally trapped at deeper levels of the magma chamber but then lost hydrogen by diffusion through the plagioclase host during periodic stalling of the magma in the lower conduit system in this second scenario which we favor the melt inclusions record re equilibration depths within the lower conduit to upper magma reservoir

density compensated overturning in the labrador sea the atlantic meridional overturning circulation a key constituent of the climate system is projected to slow down in the twenty first century due to a weakening of the labrador sea convection itself a response to greenhouse gas warming and or enhanced freshwater flux from the arctic however the first observations from the overturning in the subpolar north atlantic program reveal a minimal response of the meridional overturning circulation to the strong labrador sea convection during the winters of 2015 2016 from an analysis of the observational and reanalysis data we show here that this weak response can be explained by a strong density compensation in the labrador sea although convection induces important changes of temperature and salinity in the basin interior the export of the thermal and haline anomalies to the boundary current largely takes place along density surfaces as a result the transformation across density surfaces that is the imprint on the overturning circulation is relatively small this finding highlights the critical relationship between temperature and salinity in determining the overturning strength in the labrador sea and underlines the necessity of accurate freshwater flux estimates for improved meridional overturning circulation predictions compensation of the effects of salt and temperature changes on water density in the labrador sea can explain the minimal response of the atlantic overturning circulation to convection according to analyses of observations and reanalysis data

a sea change in our view of overturning in the subpolar north atlantic to provide an observational basis for the intergovernmental panel on climate change projections of a slowing atlantic meridional overturning circulation moc in the 21st century the overturning in the subpolar north atlantic program osnap observing system was launched in the summer of 2014 the first 21 month record reveals a highly variable overturning circulation responsible for the majority of the heat and freshwater transport across the osnap line in a departure from the prevailing view that changes in deep water formation in the labrador sea dominate moc variability these results suggest that the conversion of warm salty shallow atlantic waters into colder fresher deep waters that move southward in the irminger and iceland basins is largely responsible for overturning and its variability in the subpolar basin

a reversal of climatic trends in the north atlantic since 2005 the mid 1990s warming of the north atlantic subpolar gyre was probably related to strengthened overturning observations and numerical models suggest that a climate reversal to a cooling trend occurred around 2005

signal propagation related to the north atlantic overturning 1 changes of the meridional overturning circulation moc due to surface heat flux variability related to the north atlantic oscillation nao are analyzed in various ocean models i e eddying and non eddying cases a prime signature of the forcing is variability of the winter time convection in the labrador sea the associated changes in the strength of the moc near the subpolar front 45 n are closely related to the nao index leading moc anomalies by about 2 3 years in both the eddying and non eddying simulation further south the speed of the meridional signal propagation depends on model resolution with lower resolution non eddying case 4 3 resolution the moc signal propagates equatorward with a mean speed of about 0 6 cm s similar as spreading rates of passive tracer anomalies eddy permitting experiments 1 3 show a significantly faster propagation with speeds corresponding to boundary waves thus leading to an almost in phase variation of the moc transport over the subtropical to subpolar north atlantic

mechanisms of interannual variations of the meridional overturning circulation of the north atlantic ocean abstract the authors investigate the nature of the interannual variability of the meridional overturning circulation moc of the north atlantic ocean using an estimating the circulation and climate of the ocean ecco assimilation product for the period of 1993 2003 the time series of the first empirical orthogonal function of the moc is found to be correlated with the north atlantic oscillation nao index while the associated circulation anomalies correspond to cells extending over the full ocean depth model sensitivity experiments suggest that the wind is responsible for most of this interannual variability at least south of 40 n a dynamical decomposition of the meridional streamfunction allows a further look into the mechanisms in particular the contributions associated with 1 the ekman flow and its depth independent compensation 2 the vertical shear flow and 3 the barotropic gyre flowing over zonally varying topography are examined ekman processes are found to dominate the shorter time

local and downstream relationships between labrador sea water volume and north atlantic meridional overturning circulation variability abstractwhile it has generally been understood that the production of labrador sea water lsw impacts the atlantic meridional overturning circulation moc this relationship has not been explored

observed interannual variability of the atlantic meridional overturning circulation at 26 5 n the atlantic meridional overturning circulation moc plays a critical role in the climate system and is responsible for much of the heat transported by the ocean a mooring array nomianally at 26 circ n between the bahamas and the canary islands deployed in apr 2004 provides continuous measurements of the strength and variability of this circulation with seven full years of measurements we now examine the interannual variability of the moc while earlier results highlighted substantial seasonal and shorter timescale variability there had not been significant interannual variability the mean moc from 1 apr 2004 to the 31 march 2009 was 18 5 sv with the annual means having a standard deviation of only 1 0 sv from 1 april 2009 to 31 march 2010 the annually averaged moc strength was just 12 8 sv representing a 30 decline this downturn persisted from early 2009 to mid 2010 we show that the cause of the decline was not only an anomalous wind driven event from dec 2009 mar 2010 but also a strengthening of the geostrophic flow in particular the southward flow in the top 1100 m intensified while the deep southward return transport particularly in the deepest layer from 3000 5000 m weakened this rebalancing of the transport from the deep overturning to the upper gyre has implications for the heat transported by the atlantic

magma chamber properties from integrated seismic tomography and thermal modeling at montserrat it is widely believed that andesitic magmas erupted at arc volcanoes are stored in shallow reservoirs prior to eruption but high resolution images of focused regions of magma in the shallow crust are rare we integrate seismic tomography with numerical models of magma chamber growth to constrain the magma chamber beneath soufriere hills volcano montserrat our approach reveals the characteristics and dynamics of the magmatic system with a level of detail that no single method has yet achieved the integrated analysis suggests that a magma chamber of 13 km3 with over 30 melt fraction formed between 5 5 and at least 7 5 km depth a significantly higher melt fraction than inferred from the seismic data alone the magma chamber may have formed by incremental sill intrusion over a few thousand years and is likely to be a transient geologically short lived feature these volume and geometry estimates are critical parameters to model eruption dynamics which in turn are key to hazard assessment and eruption forecasting

exploring mechanisms of variability and predictability of atlantic meridional overturning circulation in two coupled climate models abstractmultidecadal variability in the atlantic meridional overturning circulation amoc of the ocean is diagnosed in the ncar community climate system model version 3 ccsm3 and the gfdl coupled model cm2 1 common diagnostic approaches are applied to draw out similarities and differences between the two models an index of amoc variability is defined and the manner in which key variables covary with it is determined in both models the following is found i amoc variability is associated with upper ocean top 1 km density anomalies dominated by temperature on the western margin of the basin in the region of the mann eddy with a period of about 20 years these anomalies modulate the trajectory and strength of the north atlantic current the importance of the western margin is a direct consequence of the thermal wind relation and is independent of the mechanisms that create those density anomalies ii density anomalies in this key region are part of a larger scale pattern that propagates ar

variability of the atlantic meridional overturning circulation in ccsm4 abstractatlantic meridional overturning circulation amoc variability is documented in the community climate system model version 4 ccsm4 preindustrial control simulation that uses nominal 1 horizontal resolution in all its components amoc shows a broad spectrum of low frequency variability covering the 50 200 yr range contrasting sharply with the multidecadal variability seen in the t85 1 resolution ccsm3 present day control simulation furthermore the amplitude of variability is much reduced in ccsm4 compared to that of ccsm3 similarities as well as differences in amoc variability mechanisms between ccsm3 and ccsm4 are discussed as in ccsm3 the ccsm4 amoc variability is primarily driven by the positive density anomalies at the labrador sea ls deep water formation site peaking 2 yr prior to an amoc maximum all processes including parameterized mesoscale and submesoscale eddies play a role in the creation of salinity anomalies that dominate these density anomalies high nordic sea densi

a theory for the surface atlantic response to thermohaline variability abstract the response of the upper warm limb of the thermohaline circulation in the north atlantic to a rapid change in deep water formation at high latitudes is investigated using a reduced gravity ocean model changes in deep water formation rate initiate kelvin waves that propagate along the western boundary to the equator on a timescale of months the response in the north atlantic is therefore rapid the southern hemisphere response is much slower limited by a mechanism here termed the ldquo uatorial buffer since to leading order the flow is in geostrophic balance the pressure anomaly decreases in magnitude as the kelvin wave moves equatorward where the coriolis parameter is lower together with the lack of sustained pressure gradients along the eastern boundary this limits the size of the pressure field response in the southern hemisphere interior adjustment is by the westward propagation of rossby waves but only a small fraction of the change in thermohaline circulation strength is commun

on mapping the diapycnal water mass transformation of the upper north atlantic ocean abstractdiapycnal water mass transformation is the essence behind the atlantic meridional overturning circulation amoc and the associated heat freshwater transports existing studies have mostly

on the relationship between decadal buoyancy anomalies and variability of the atlantic meridional overturning circulation abstractowing to the role of the atlantic meridional overturning circulation amoc in ocean heat transport amoc variability is thought to play a role in climate variability on a wide range of time scales this paper focuses on the potential role of the amoc in climate variability on decadal time scales coupled and ocean only general circulation models run in idealized geometries are utilized to study the relationships between decadal amoc and buoyancy variability and determine whether the amoc plays an active role in setting sea surface temperature on decadal time scales decadal amoc variability is related to changes in the buoyancy field along the western boundary according to the thermal wind relation buoyancy anomalies originate in the upper ocean of the subpolar gyre and travel westward as baroclinic rossby waves when the buoyancy anomalies strike the western boundary they are advected southward by the deep western boundary current leading to latitudinally coherent amoc variability the amoc i

on the currents and transports connected with the atlantic meridional overturning circulation in the subpolar north atlantic results from an interannually forced 0 08 degrees eddy resolving simulation based on the hybrid coordinate ocean model in conjunction with a small but well determined transport database are used to investigate the currents and transports associated with the atlantic meridional overturning circulation amoc in the subpolar north atlantic spna the model results yield a consistent warming in the western spna since the early 1990s along with mean transports similar to those observed for the trans basin amoc across the world ocean circulation experiment hydrographic section ar19 16 4 sv and boundary currents at the exit of the labrador sea near 53 degrees n 39 0 sv and east of the grand banks near 43 degrees n 15 9 sv over a 34 year integration the model determined amoc across the ar19 section and the western boundary current near 53 degrees n both exhibit no systematic trend but some long term interannual and longer variabilities including a decadal transport variation of 3 4 sv from relatively high in the 1990s to low in the 2000s the decadal variability of the model boundary current transport near 53 degrees n lags the observed winter time north atlantic oscillation index by about 2 years and leads the model amoc across the ar19 section by about 1 year the model results also show that the long term variabilities are low compared to those on shorter time scales thus rapid sampling of the current over long time intervals is required to filter out high frequency variabilities in order to determine the lower frequency variabilities of interest