propagation of the great salinity anomaly of the 1990s around the northern north atlantic 1 time series of t and s extending through 2001 are used to describe propagation of the great salinity anomaly of the 1990s gsa 90s comparison of the distance time relations for the gsa 70s 80s and 90s reveals a substantial intensification of the large scale circulation in the northern north atlantic especially in the subarctic gyre between newfoundland and the faroes the advection rate of the gsa 70s 80s and 90s between newfoundland and the faroe shetland channel is conservatively estimated to have been 3 5 10 and 10 cm s respectively the circulation intensification apparently occurred within a decade between the gsa 70s and 80s during the next decade the advection rate increased from 10 to 13 cm s between newfoundland and iceland basin the gsa 90s was advected towards the faroe shetland channel by the northern iceland basin s branch of the north atlantic current whereas the contribution of the southern branch via the rockall trough was minimal

interpentadal variability of temperature and salinity at intermediate depths of the north atlantic ocean 1970 1974 versus 1955 1959 we have composited historical hydrographic observations for the world ocean for two pentads 1955 1959 and 1970 1974 and have objectively analyzed these data for the purpose of studying the temporal variability of temperature and salinity in the north atlantic ocean the subtropical gyre 500 1300 m of the north atlantic was colder and fresher during 1970 1974 compared to 1955 1959 the relatively large changes in temperature and salinity on constant depth surfaces in the subtropical gyre were due to upward displacements of isopycnal surfaces at intermediate depths the eastern portion of the subarctic gyre was also colder and fresher during the 1970 1974 pentad in contrast the western portion of the subarctic gyre exhibited higher temperatures and salinities during 1970 1974 compared to 1955 1959 characteristic differences in temperature and salinity for both gyres were 0 5 c and 0 025 respectively analysis of changes in potential vorticity indicates that in the subtropical gyre potential vorticity increased in all density layers above the 26 5 surface suggesting that convection in this region may have been shallower in 1970 1974 compared to 1955 1959 below the 26 5 surface potential vorticity decreased through the 27 3 surface indicating that deeper than normal convection may have formed the water masses in these layers at 250 m depth relatively large changes in temperature and salinity occurred along the line of maximum climatological mixed layer depth that extends northeast to southwest across the north atlantic ocean

climatic variability in upper ocean ventilation rates diagnosed using chlorofluorocarbons the chlorofluorocarbon cfc 12 ccl2f2 distributions from two occupations of a meridional hydrographic section in the eastern north atlantic are used to describe the oceanic penetration of cfcs and change in the integrated ventilation patterns over the five years from 1988 to 1993 the cfc 12 water column inventories increased by 30 40 despite a slowing atmospheric growth rate 14 because of continuing uptake by undersaturated subsurface water masses whose response is lagged by the ventilation time scales after removing the long term cfc temporal trend using a tracer age based normalization technique we observe a distinct dipole pattern in upper ocean ventilation with reduced convection in the subpolar gyre and enhanced production of saline subtropical underwater in 1993 these differences are discussed in relation to interannual variability in atmospheric surface forcing upper ocean anomalies and convection patterns associated with the north atlantic oscillation

wind effects on a front over the continental shelf slope a continuously stratified two dimensional vertical and seaward model is used to study the effects of alongshore wind on a front between lighter water over the continental shelf and heavier water in the offshore ocean the model produces three components of alongshore flows one component associated with the horizontal density front and two wind driven components one near the coast and one over the shelf break the cross shore circulation has two near surface features a seaward component resulting from the offshore density gradient and a shoreward seaward component resulting from the right hand left hand alongshore wind stress which has the coast to the right left facing downstream these two components contribute to the maintenance of the front with no wind low density water over the shelf tends to move toward the offshore ocean associated with the near surface seaward flow resulting in flatter isopycnal surfaces a moderate right hand alongshore wind suppresses the density driven surface flow and constrains the shelf water while a strong wind in the same direction pushes the front shoreward and makes isopycnal surfaces steeper resulting in increased exchange of the shelf water a left hand alongshore wind contributes to more rapid frontal relaxation and a seaward shift in its position these results are applied to the labrador shelf

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

upper ocean variability between iceland and newfoundland 1993 1998 we investigate the variability of upper ocean temperature and surface salinity between iceland and newfoundland along world ocean circulation experiment line ax2 in 1993 1998 north of 54 n as well as close to newfoundland deviations from the seasonal cycle indicate upper ocean warming from 1994 to 1998 with largest anomalous warming during late 1995 early 1996 and during the winter 1997 1998 north of 54 n surface salinity increases after mid 1996 the winter of 1995 1996 is the first winter of weak westerlies after more than 20 years of strong westerly conditions in the subarctic gyre and the ocean loses less heat during that winter than during a normal year the magnitude of upper ocean heat content change is at least twice as large as what results from the change in air sea fluxes which indicates a complementary contribution to heat content change by advection altimetric sea level data indicate also an increase of sea level of the order of 6 5 cm during that year out of which more than 4 cm is contributed by the steric change associated with the temperature increase a principal component analysis of the sea level data suggests that the increase sensed along line ax2 west of the reykjanes ridge is found in most of the subpolar gyre although to a lesser extent in most other areas

marine climate variability during the last millennium the loch sunart record scotland uk abstract the first decadal scale reconstruction of british coastal temperature anomalies spanning the last millennium is presented from a sea loch fjord basin loch sunart nw scotland based on modern observation and the results of previous numerical modeling of fjord circulation benthic foraminiferal oxygen isotope records are interpreted as a record of summer temperature a significant climate transition apparently driven by large scale reorganization of northern hemisphere atmospheric circulation occurs in the record around ad 1400 an abrupt but relatively short lived climate warming occurs between ad 1540 1610 when the bottom water temperature anomalies are 1 1 c above the long term average which is warmer than most of the 20th century and the late medieval warm period a long term cooling occurs throughout the little ice age culminating in the coldest recorded temperature anomalies between the late 1920s and 1940s the warmest reconstructed temperatures of the past millennium occurred in the last 5 years of the record which ends in 2006 a replicated post ad 1900 shift in benthic foraminiferal 13 c of ca 0 6 provides evidence of the oceanic 13 c suess effect this feature provides an independent test of the age model and demonstrates the value of benthic foraminifera as palaeo proxies in the loch sunart record

the long term hydrographic record at bermuda abstract a long by oceanographic standards time series of hydrographic observations at bermuda was begun in 1954 and continues to the present analysis of this dataset has shown the temperature and salinity variations on interannual timescales to be largely independent in the surface layer 0 200 dbar where integral timescales for salinity are 50 longer than for temperature and surface salinity changes are correlated with decadal changes in the 18 c water production temperature salinity anomalies are highly correlated in the thermocline where the interannual variability at that level is accountable to either vertical oscillations of the thermocline with amplitudes of 50 m or meridional oscillations of the horizontal gradient set up at the southern edge of the recirculation gyre of 300 kim salinity changes in the deepest layer observed at bermuda station s 1500 2500 dbar are uncorrelated with temperature masked by measurement errors in the early years of the time series inclusion of earlier

a comparison of the isostatic response of bathymetric features in the north pacific ocean and philippine sea summary this paper concerns the calculation and analysis of admittance functions from large and uniform data sets of gravity and topography in four regions of the northern and western pacific ocean the purpose is to separate and describe possible differences in isostatic compensation between several type regions of oceanic crust a mid ocean ridge juan de fuca a mid plate seamount chain hawaiian ridge fracture zone topography on old crust north of hawaii and a marginal basin philippine sea results suggest that there are significant differences in the degree to which long wavelength topography has been compensated which can be distinguished between regions these differences are set in the perspective of three simple compensation mechanisms two of these consider local airy models in which raised topography is compensated at depth either by crustal roots or low density mantle a third considers the effects of an elastic plate of variable thickness supporting crustal variations conclusions are that a a thick plate possibly in excess of 30 km supports the hawaiian ridge b a much thinner plate of 5 to 15 km existed when the fracture zone topography was formed c the juan de fuca ridge is compensated either regionally by a plate 5 to 10 km thick or locally by sub crustal low densities at depths of 15 to 20 km and d the philippine sea shows no evidence for regional support ridges are compensated locally by differences in crustal thickness whereas the basins are underlain by density variations at depths comparable to those of the much younger juan de fuca ridge the major difference between admittance functions for the philippine sea and comparably aged regions of the north pacific ocean adds further new evidence of possible evolutionary differences between it and normal ocean basins

interdecadal variability of the thermohaline circulation in box ocean models forced by fixed surface fluxes intrinsic modes of decadal variability are analyzed using box geometry ocean models forced by constant surface fluxes an extensive parameter sensitivity analysis of the oscillatory behavior is carried out with respect to the spherical cartesian geometry the b effect the coriolis parameter the parameterization of momentum dissipation and associated boundary conditions the vertical and horizontal diffusivities the convective adjustment algorithm the horizontal and vertical model resolution the forcing amplitude and the basin width the oscillations stand out as a robust geostrophic feature whose amplitude is mainly controlled by the horizontal diffusivity unsuccessful attempts to reproduce the variability in zonally averaged 2d models suggest that the 3d adjustment processes are necessary however the b effect is not necessary for decadal variability to occur and therefore classical rossby waves play no fundamental role in the mechanism various experiments with different geometry and forcing are conducted and do not support the necessity of viscous numerical boundary waves or any boundary in sustaining the oscillations the models show two types of oscillatory behavior 1 temperature anomalies propagating geostrophically westward in the eastward jet northern part of the basin and inducing an opposite anomaly in their wake and 2 stationary temperature anomalies in the northwest quarter that respond to the western boundary current transport changes and reinforce geostrophically this change until the opposite temperature anomaly built on the east finally reverses the meridional overturning anomaly the analysis of the transition from steady to oscillatory states using heat fluxes diagnosed at the equilibrium under restoring boundary conditions and the comparison of the variability under various forcing fields suggest that the oscillations are triggered in the regions of strongest surface cooling finally a simple box model analogy is proposed that captures the crucial phase shift between meridional overturning and north south density gradient anomalies on these decadal timescales

persistent cold climatic episodes around greenland and baffin island links to decadal scale sea surface temperature anomalies two unusually persistent cold episodes around greenland and baffin island in 1971 1972 and 1982 1984 are described in terms of their severity atmospheric circulation variability and changes in sea surface conditions the episodes are significant due to the sizeable station temperature departures many exceeding one standard deviation and their persistence in both episodes unusually persistent cold pools of water developed in the northern atlantic and intensified near davis strait close to the onset of the cold climatic events and then migrated out of the region as the episodes came to a close anomalous northerly surface air flow occurs in most months during the two episodes

temporal variability of the subarctic front near the charlie gibbs fracture zone we document temporal variability of the northernmost branch of the north atlantic current known as the north subarctic front nsaf for the period 1976 1985 the front s location and temperature salinity t s parameters were determined from 120 repeat transects along three standard sections occupied by russian ships 1 ocean weather station ows c 52 75 n 35 5 w to st john s newfoundland 2 along 35 w from 52 n to 36 5 n and 3 ows c to cape st vincent portugal the nsaf exhibits significant interannual variability of its location shifting 200 km to 300 km in a few months along the ows c st john s section the front reached its southernmost location in 1976 1977 then experienced two 250 to 300 km northward shifts in 1978 1979 and 1980 1981 all of the three shifts peaked in wintertime these events nearly coincide with events of the opposite sign along the ows c cape st vincent section the northernmost location in 1976 1977 and two 200 km southward shifts in 1978 1979 and 1980 1981 the nsaf s behavior is thus coherent near the charlie gibbs fracture zone at the 500 km scale frontal time series associated with the moving front of t and s at the 200 m level for the cold side of the nsaf reveal two events an s200 minimum in the winter of 1976 1977 which might be a manifestation of the great salinity anomaly of the 1970s and a sharp drop of s200 in early 1984 which might signal the arrival of another large salinity anomaly the great salinity anomaly of the 1980s

evidence for stability enhancement of sea ice in the greenland and labrador seas malmberg proposed in 1969 that anomalously low surface upper 200 m salinities in the iceland seas during the late 1960s could increase the stability of the water column sufficiently to prevent deep convection the increased stability would then enhance the formation of sea ice during winter in this region because even at the freezing point 1 8 c the surface water density is sufficiently low to prevent mixing with the water below hence only a small portion of the water column need be cooled before freezing can occur and ice formation is enhanced here we explore this concept further by examining hydrographic data from three locations bordering greenland and iceland and then compare these with colocated sea ice concentrations for the period 1953 1980 it is shown that the lag correlations between surface salinity and sea ice anomalies show a common structure for the case where salinity anomalies lead sea ice anomalies it is shown that this correlation structure can be reproduced by a simple statistical feedback model using a nonstationary negative feedback coefficient to account for salinity forcing of ice anomalies the data presented are all consistent with the concept of stability enhancement of sea ice formation

quasi decadal salinity fluctuations in the labrador sea abstract the quasi decadal salinity fluctuations in the upper 300 m of the labrador sea are investigated by partitioning all available salinity station data since 1948 by region and bottom depth there are major freshwater anomalies in the early 1970s the great salinity anomaly mid 1980s and early 1990s these vary in amplitude throughout the region being least on the shelf and greatest over the slope region near the labrador current the labrador sea cannot be considered a simple conduit for freshwater anomalies originating in the east greenland current there is evidence that local processes modulate the anomaly the freshwater anomalies in the labrador current are approximately twice as large as those in the east greenland current the baffin island current flowing southward through the western davis strait is the only local source of freshwater with sufficient volume to account for this increase the propagation speed 2 3 cm s 1 of the anomaly along the labrador sea margin is much less than the

interannual to interdecadal variability of sea surface salinity in the atlantic and its link to the atmosphere in a coupled model 1 the interannual to interdecadal variability of sea surface salinity sss in the atlantic is investigated using 200 years of a control simulation of the bergen climate model after verifying that the model behaves realistically we show that most centers of sss variability are located near the mouths of the main rivers of the basin this variability is due primarily to anomalous runoff except in the st lawrence area and to anomalous ekman and geostrophic currents while fluctuations in the freshwater flux play a somewhat lesser role away from the coast sss variability is strong in the northern tropics due largely to anomalous advection and freshwater exchanges regression analysis and a lagrangian technique show that the sss anomalies are advected by the mean oceanic circulation and can be followed along the gyres for several years the link between sss anomalies and the dominant modes of variability of the atmosphere is also investigated the sss response to the north atlantic oscillation nao is dominated by relatively small scales that are forced by anomalous ekman currents but the relative influence of the large scale freshwater fluxes increases at long timescales the nao induced sss anomalies are also strongly advected and distorted by the mean currents so that their pattern at the interannual timescale only reflects in part that of the atmospheric forcing the link between sss anomalies and the east atlantic pattern is similar

contrasting response of the eastern and western north atlantic circulation to an episodic climate event abstractregional observational studies in the north atlantic have noted significant hydrographical shifts in 1997 98 because of the episodic drop in the north atlantic oscillation nao during 1996 investigation using a basin scale model finds that although the western north atlantic wna witnessed unusually low salinity water by 1997 the eastern north atlantic ena simultaneously evidenced intrusions of high salinity water at intermediate depths this study shows that a major source of high salinity in the ena is from the northward penetration of mediterranean outflow water mow that occurred concurrently with a westward shift of the subpolar front the authors confirm that the low salinity intrusion in the wna is from enhanced labrador current flow results from climatological high and low nao simulations suggest that the nao induced circulation changes that occurred in 1997 98 are a characteristic north atlantic basin response to different forcing conditions during characteristic high and low n

on the early response of the climate system to a meltwater input from greenland theearlyresponseoftheatmosphere oceansystemtomeltwaterrunofforiginatingfromthegreenlandice sheet is studied using a coupled atmosphere ocean general circulation model aogcm for this purpose aogcm ensemble simulations without and with associated ocean freshening around greenland are compared for freshwater perturbations initiated in northern winter the mean response for the first three months shows the emergence of negative sea surface temperature sst anomalies in the denmark strait in association with enhanced oceanic advection by the east greenland current the response also shows negative sst anomalies in the north atlantic associated with enhanced westerlies at the ocean surface additionally the baroclinic atmospheric cyclonic circulation east of greenland intensifies and anticyclonic circulations with equivalent barotropic structures develop over western europe and the north pacific ocean simulations by the atmospheric component of the aogcm indicate that atmosphere ocean interactions contribute significantly to enhance the response the sensitivity of the coupled system response to the timing of freshwater perturbation is also studied for freshwater perturbations initialized in northern summer the response during the following winter is similar but stronger in magnitude in the northern hemisphere the atmospheric response resembles the arctic oscillation ao mode of variability the association between anomalies in the denmark strait ssts and in the atmosphere east of greenland is consistent with that observedduring previous great salinityanomaly gsa events the results obtainedhighlight the importance ofatmosphere oceaninteractionintheearlyclimateresponsetogreenlandmelting theteleconnectionswith the north pacific and the contribution of gsa events to north atlantic oscillation nao variability

low frequency temperature fluctuations off bermuda twenty four years of hydrographic stations made by the r v panulirus southeast of bermuda at approximately semi monthly intervals have been used to construct temperature time series at 10 depths ranging from the surface to 2000 m the data contain no significant seasonal signal at depth 250 m subsurface temperature spectra have a broad peak in the eddy containing band at periods 0 100 days and drop rapidly at high frequencies at very low frequencies the spectra indicate some redness down to the largest resolvable time scales most of the energy in the temperature fluctuations is concentrated into two vertical modes which resemble the first two baroclinic normal modes and explain 60 and 23 of the variance respectively the observed spectrum of sea surface temperature sst anomalies has substantially more variance at periods of a year and less than sst anomaly spectra estimated from ship reports on 5 5 grid it is suggested that the excess variance is due to the advection of the sea surface temperature pattern by the underlying field of smaller scale eddies consistently with the observed coherences between surface and deeper temperature records

arctic contribution to upper ocean variability in the north atlantic abstract because much of the deep water of the world s oceans forms in the high latitude north atlantic the potential climatic leverage of salinity and temperature anomalies in this region is large substantial variations of sea ice have accompanied north atlantic salinity and temperature anomalies especially the extreme and long lived great salinity anomaly of the late 1960s and early 1970s atmospheric pressure data are used hem to show that the local forcing of high latitude north atlantic ocean fluctuations is augmented by antecedent atmospheric circulation anomalies over the central arctic these circulation anomalies are consistent with enhanced wind forcing of thicker older ice into the transpolar drift stream and an enhanced export of sea ice fresh water from the arctic into the greenland sea prior to major episodes of ice severity in the greenland and iceland seas an index of the pressure difference between southern greenland and the arctic asian coast reached its highest value of the twe

influence of the north atlantic oscillation on the canary islands precipitation abstract the aim of this paper is to investigate the relationship between the canary island rainfall and the atlantic large scale circulation characterized by the north atlantic oscillation nao index the canary islands are located in the atlantic subtropical belt under the direct influence of the azores high and the trade winds their steep orography makes the islands very sensitive to small variations in a synoptic situation thus providing an excellent natural observatory for the north atlantic variability associated with changes in pressure patterns a significant relationship between rainfall and the nao is found for five of the seven canary islands in order to characterize the physical mechanisms involved a set of automatic objective techniques for identification and detection of disturbances is applied to the 1000 and 500 hpa geopotential from the ncep ncar reanalysis for the period from 1955 to 1998 this method allows for the identification and detection of four main synoptic systems either

subsurface quasi decadal fluctuations in the north atlantic abstract analysis of hydrographic time series data at ocean station 5 panulirus and along the labrador continental margin is used to investigate the subsurface structure associated with the north atlantic quasi decadal sst fluctuation quasi decadal fluctuations of both temperature and salinity are confined to the upper water column that is ventilated by the seasonal cycle in the subtropical gyre they are independent of the variations of the gyre baroclinic transport on the labrador continental margin the quasi decadal fluctuations are confined to the upper portion of the labrador current the quasi decadal fluctuation appears to be surface forced in the subtropical gyre this is predominantly by latent heat flux in the subpolar gyre latent and sensible heat flux alone cannot account for the in phase variation of temperature and salinity instead the variation involves upper ocean convective mixing whose strength is modulated by the density of the winter cooled surface water it has been noted t

warm and saline events embedded in the meridional circulation of the northern north atlantic 1 ocean state estimates from 1958 to 2005 from the simple ocean assimilation system soda system are analyzed to understand circulation between subtropical and subpolar atlantic and their connection with atmospheric forcing this analysis shows three periods 1960s around 1980 and 2000s with enhanced warm saline waters reaching high latitudes alternating with freshwater events originating at high latitudes it complements surface drifter and altimetry data showing the subtropical subpolar exchange leading to a significant temperature and salinity increase in the northeast atlantic after 2001 the warm water limb of the atlantic meridional overturning cell represented by soda expanded in density salinity space during these warm events tracer simulations using soda velocities also show decadal variation of the gulf stream waters reaching the subpolar gyre and nordic seas the negative phase of the north atlantic oscillation index usually invoked in such variability fails to predict the warming and salinization in the early 2000s with salinities not seen since the 1960s wind stress curl variability provided a linkage to this subtropical subpolar gyre exchange as illustrated using an idealized two layer circulation model the ocean response to the modulation of the climatological wind stress curl pattern was found to be such that the northward penetration of subtropical tracers is enhanced when amplitude of the wind stress curl is weaker than normal in this case both the subtropical and subpolar gyres weaken and the subpolar density surfaces relax hence the polar front moves westward opening an enhanced northward access of the subtropical waters in the eastern boundary current

sea ice anomalies observed in the greenland and labrador seas during 1901 1984 and their relation to an interdecadal arctic climate cycle two independent ice data sets from the greenland and labrador seas have been analyzed for the purpose of characterizing interannual and decadal time scale sea ice extent anomalies during this century sea ice concentration data for the 1953 1984 period revealed the presence of a large positive anomaly in the greenland sea during the 1960s which coincided with the great salinity anomaly an upper ocean low salinity water mass that was observed to travel cyclonically around the northern north atlantic during 1968 1982 this ice anomaly as well as several smaller ones propagated into the labrador sea and then across to the labrador and east newfoundland coast over a period of 3 to 5 years a complex empirical orthogonal function analysis of the same data also confirmed this propagation phenomenon an inverse relation between sea ice and salinity anomalies in the greenland labrador sea region was also generally found an analysis of spring and summer ice limit data obtained from danish meteorological institute charts for the period 1901 1956 indicated the presence of heavy ice conditions i e positive ice anomalies in the greenland sea during 1902 1920 and in the late 1940s and generally negative ice anomalies during the 1920s and 1930s only limited evidence of the propagation of greenland sea ice anomalies into the labrador sea was observed however probably because the data were from the ice melt seasons on the other hand several large ice anomalies in the greenland sea occurred 2 3 years after large runoffs in the early 1930s and the late 1940s from northern canada into the western arctic ocean similarly a large runoff into the arctic during 1964 1966 preceded the large greenland sea ice anomaly of the 1960s these facts together with recent evidence of climatic jumps in the northern hemisphere tropospheric circulation suggest the existence of an interdecadal self sustained climate cycle in the arctic in the greenland sea this cycle is characterized by a state of large sea ice extent overlying an upper layer of cool relatively fresh water that does not convectively overturn which alternates every 10 15 years with a state of small sea ice extent and relatively warm saline surface water that frequently overturns

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

multidecadal variability of north atlantic temperature and salinity during the twentieth century abstract substantial changes occurred in the north atlantic during the twentieth century here the authors demonstrate through the analysis of a vast collection of observational data that multidecadal fluctuations on time scales of 50 80 yr are prevalent in the upper 3000 m of the north atlantic ocean spatially averaged temperature and salinity from the 0 300 and 1000 3000 m layers vary in opposition prolonged periods of cooling and freshening warming and salinification in one layer are generally associated with opposite tendencies in the other layer consistent with the notion of thermohaline overturning circulation in the 1990s widespread cooling and freshening was a dominant feature in the 1000 3000 m layer whereas warming and salinification generally dominated in the upper 300 m except for the subpolar north atlantic where complex exchanges with the arctic ocean occur the single signed basin scale pattern of multidecadal variability is evident from decadal 1000 3000 m temperature and salin

convective activity in the labrador sea preconditioning associated with decadal variability in subsurface ocean stratification 1 the decadal variability of the convective activity in the labrador sea is investigated using 43 years of model output from a prognostic coupled ice ocean model that simulates both the arctic and the north atlantic oceans the fields of the surface density and the mixed layer depth indicate that the center of the convective activity is located in western labrador sea the decadal variations of the convective depth are controlled to large extent by the oceanic preconditioning associated with changes in subsurface stratification the intensity of the convective mixing varies from year to year depending upon how strong the isopycnal doming is at the preconditioning stage at the center of the convective region the variations of the subsurface stratification seem to be related to the subsurface temperature changes

on the nature of decadal anomalies in north atlantic sea surface temperature north atlantic sea surface temperature data from the comprehensive ocean atmosphere data set were used to investigate the behavior of temperature anomalies on multiple year timescales during the period 1948 1992 monthly anomaly time series for each 2 square from the equator to 70 n were low pass filtered at 4 years and normalized by the local standard deviation attention is focused on the extreme events the upper and lower deciles of the anomaly time series a 45 year sequence of january maps shows the already familiar phenomena of generally cold conditions prior to 1951 a long warm interval from 1951 through 1967 and again a cold period from 1968 through 1977 the years 1978 through 1982 were largely devoid of persistent strong anomalies but moderate cold conditions returned during 1983 1986 warm conditions dominated the north atlantic from 1987 onward within these thermal epochs however a total of five cold anomaly features and nine warm anomaly features have been identified these features have individual lifetimes of 3 to 10 years a typical size is 20 of latitude or longitude but they range from barely detectable to spanning the width of the basin the latter especially in lower latitudes most of the anomalies move long distances along certain preferred paths these paths generally follow the routes of the subarctic and subtropical gyres anomalies originating off north america along the boundary between the gyres move northeastward toward the norwegian sea along the approximate route of the north atlantic current midlatitude anomalies originating at the eastern boundary tend to spread both northward and southward along the coast the speed of these movements 1 3 km d 1 is generally less than the expected speed of the near surface ocean circulation simple ideas about the effects of beta dynamics and air sea heat exchanges are briefly considered but do not provide a satisfactory explanation for the movements of the anomalies the long timescale of these extreme events and the continuity of their movements suggest a useful degree of predictability of sea surface temperature based on persistence and propagation of features

freshening of the labrador sea surface waters in the 1990s another great salinity anomaly 1 the observed labrador sea surface salinities for 1951 2001 in region 55w 40w 45n 55n show freshening in the 1990s which may rival the great salinity anomaly gsa of the 1970s dickson et al 1988 the 1990s freshening is distinct in the lowest range of salinity values associated with the coastal waters the variability of the highest salinity values provided by the north atlantic current entering the labrador sea shows that the high salinity atlantic waters were not widely present in the 1970 s and 1990s this can be interpreted as weakened transport of saline waters to the area this explanation is consistent with an arctic north atlantic model results forced by ncep ncar reanalysis data for 1958 2001 which suggest that these periods are associated with a reduced meridional overturning the model also associates the coastal freshening with southward current anomalies which are well correlated with the number of icebergs crossing 48n

millennial scale variations of the holocene north atlantic mid depth gyre inferred from radiocarbon and neodymium isotopes in cold water corals abstract variations in north atlantic ocean mid depth circulation during the holocene are poorly understood it is believed that they had a significant influence on the properties of water entering the nordic sea by redistributing heat and freshwater potentially affecting deep water formation and climate to improve our knowledge of the ne atlantic mid depth circulation radiocarbon and neodymium isotope analyses have been then carried out on precisely dated u th l pertusa and m oculata coral fragments from two sediment cores taken at 750 m water depth on the sw rockall trough margin cold water coral cwc end values vary between 12 2 0 3 and 16 6 0 4 and result from variable contributions of unradiogenic mid depth subpolar gyre mid spg water 15 and more radiogenic eastern north atlantic water enaw 11 which is transported northward to the rockall trough by boundary currents along the european margin increased coral end reflects a westward contraction of the mid spg water and a higher proportion of enaw the mid holocene from 8 8 to 6 8 ka bp is marked by unradiogenic coral end from 16 6 0 4 to 14 6 0 5 indicating a greater eastward extension of the mid spg this is followed by a shift from 6 8 to 5 ka bp toward more radiogenic end values from 15 4 0 3 to 13 3 0 2 suggesting a westward contraction of the mid spg and a higher proportion of enaw the mid holocene long term change in end is characterized by millennial variations of up to 2 5 epsilon units well marked during the late holocene indicating that eastward extension of the mid spg coeval with warm periods in northern europe e g the medieval climatic anomaly and the roman warm period most of the cwc derived 14c values match the global ocean values indicating that the water masses bathing the corals were generally well ventilated the exceptions are a few short intervals of eastward extension of the mid spg which are characterized by lower 14c during the late holocene we propose that these minor 14c fluctuations in the rockall trough may be related to local changes in the mixed layer depth or to variability in the advection of water from the labrador sea where deep convection gives rise to thermocline waters that are relatively depleted in terms of 14c the eastward extension of the mid spg between 8 8 and 6 8 ka bp is associated with the holocene climatic optimum concurrent with a maximum strength of the iceland scotland overflow water isow which is indicative of an increase in the atlantic meridional overturning circulation amoc this period is followed by a transition in the north atlantic circulation which occurred around 6 8 ka bp and coincides with the onset of labrador sea water formation a decrease of the isow strength and a contraction of the mid spg leading to a greater intrusion of saline subtropical water into the subpolar atlantic

on the interannual variability of surface salinity in the atlantic the mechanisms controlling the interannual variability of sea surface salinity sss in the atlantic are investigated using a simulation with the echam4 opa8 coupled model and for comparison the ncep reanalysis and an observed sss climatology anomalous ekman advection is found to be as important as the freshwater flux in generating sss anomalies in contrast to sea surface temperature sst anomalies which are primarily caused by surface heat flux fluctuations since the surface heat flux feedback does not damp the sss anomalies but generally damps existing sst anomalies sss anomalies have a larger characteristic time scale as a result they are more influenced by the mean currents and the geostrophic variability which dominate the sss changes at low frequency over much of the basin the link between sss anomalies and the dominant patterns of atmospheric variability in the north atlantic sector is also discussed it is shown that the north atlantic oscillation generates sss anomalies much more by ekman advection than by freshwater exchanges at least in the coupled model there is little one to one correspondence between the main atmospheric and sss anomaly patterns unlike what is found for sst anomalies

decadal variations in labrador sea ice cover and north atlantic sea surface temperatures 1 the spatial and temporal evolution of winter sea ice anomalies in the labrador sea and associated sea surface temperature sst variations in the north atlantic are documented for three periods of above normal ice cover 1972 1974 1983 1985 and 1990 1992 these events are notable for their winter to winter persistence despite the fact that the ice margin retreats to northern baffin bay each summer and for their spatial evolution progressing from the northern labrador sea to the southern tip of newfoundland over a 3 year period above normal sea ice is consistently accompanied by below normal ssts in the subpolar atlantic the latter persist 1 3 years after the decay of the ice anomalies and in some cases exhibit a tendency for eastward movement across the gyre spring summer freshwater anomalies at 100 m depth in the west greenland current are found to precede by 8 months the initial occurrence of above normal ice cover in the northern labrador sea the role of atmospheric forcing in the joint evolution of anomalous sea ice and sst is assessed by means of an ice ocean mixed layer model forced with observed air temperature and wind fields the model results indicate that thermodynamic atmospheric forcing accounts for much of the winter to winter persistence and spatial evolution of the ice and concurrent sst anomaly patterns however the subsequent persistence of sst anomalies in the subpolar region is not well simulated suggesting that oceanic processes omitted from the simple slab mixed layer formulation play a contributing role

the role of sea ice and other fresh water in the arctic circulation salinity stratification is critical to the vertical circulation of the high latitude ocean we here examine the control of the vertical circulation in the northern seas and the potential for altering it by considering the budgets and storage of fresh water in the arctic ocean and in the convective regions to the south we find that the present day greenland and iceland seas and probably also the labrador sea are rather delicately poised with respect to their ability to sustain convection small variations in the fresh water supplied to the convective gyres from the arctic ocean via the east greenland current can alter or stop the convection in what may be a modern analog to the halocline catastrophes proposed for the distant past the north atlantic salinity anomaly of the 1960s and 1970s is a recent example it must have had its origin in an increased fresh water discharge from the arctic ocean similarly the freshening and cooling of the deep north atlantic in recent years is a likely manifestation of the increased transfer of fresh water from the arctic ocean into the convective gyres finally we note that because of the temperature dependence of compressibility a slight salinity stratification in the convective gyres is required to efficiently ventilate the deep ocean

characteristics of winter precipitation variation over northern central eurasia and their connections to sea surface temperatures over the atlantic and pacific oceans abstract this study reveals spatial and temporal characteristics of precipitation variability and their teleconnections to sea surface temperatures ssts over the atlantic and pacific oceans by analyzing 68 yr of recent precipitation records over the former soviet union in addition to a general increasing trend of about 0 4 mm yr 1 or 6 decade 1 over much of the study region three major modes of precipitation variation are identified a quasi biennial variation of 2 3 yr is found over the region surrounding the caspian and aral seas an el nino timescale precipitation variation of 4 5 yr is present over southern central siberia and is associated with eastern tropical pacific ssts a quasi decadal timescale variation of about 11 12 yr is evident over central european russia this quasi decadal precipitation variation is closely linked to a major sst anomaly pattern of alternating latitudinal belts over the atlantic and sst variations over the equatorial pacific ocean these associations to ssts are str

a study of temperature changes in the upper north atlantic 1950 94 in this paper decadal evolution of warm and cold anomalies in the subtropical and subpolar gyres of the north atlantic in the 300 500 m and 100 250 m depth ranges is described a series of pentadally averaged objective maps of upper ocean thermal anomalies from bathythermograph data are presented warm and cold anomalies in the western subtropical gyre are succeeded by similar anomalies in the subpolar gyre and the east atlantic and subtropical return flow major warm and cold anomalies in the 1950s and 1970s respectively are similar to those described previously in ssts although there is more temporal continuity in the subsurface anomalies two very strong events in the subtropical gyre are identified a cold anomaly in 1966 72 and an intense warm anomaly in 1988 94 that show the greatest temperature anomalies in the north atlantic during the period of the study interisotherm thickness anomalies are shown for the subtropical gyre during these periods in the warm period mode waters are both warmer 188 198c and of greater volume than on average and lie in a narrow band south of the gulf stream above a depressed thermocline with warm temperature anomalies to at least 800 m depth in the cold period the predominant mode water temperature is closer to 178c but there is reduced water formation overall with a raised thermocline and cold temperature anomalies down to 600 m depth the bowl of the gyre is flat during the cold period and the implied recirculation may be weaker and extend farther to the south the changes appear to be consistent with the intensification of the subtropical gyre in the warm period and a spindown in the cold period although the relative roles of wind stress and air sea heat fluxes in these changes need to be determined

mg ca ratios in coralline algae record northwest atlantic temperature variations and north atlantic oscillation relationships climate variability in the north atlantic has been linked in part to the north atlantic oscillation nao the nao influences marine ecosystems in the northwestern atlantic and transport variability of the cold labrador current understanding historic patterns of nao variability requires long term and high resolution climate records that are not available from instrumental data here we present the first century scale proxy record of sea surface temperature sst variability from the newfoundland shelf a region from which other annual resolution shallow marine proxies are unavailable the 116 year record was obtained from three sites along the eastern newfoundland shelf using laser ablation inductively coupled mass spectrometry determined mg ca ratios in the crustose coralline alga clathromorphum compactum the alga is characterized by a high mg calcite skeleton exhibiting annual growth increments and a century scale lifespan results indicate positive correlations between interannual variations in mg ca ratios and both station based and gridded instrumental sst in addition the record shows high spatial correlations to sst across the newfoundland shelf and the gulf of st lawrence before 1950 the mg ca proxy record reveals significant departures from gridded temperature records while the newfoundland shelf is generally considered a region of negative correlations to the nao the algal time series as well as a recent modeling study suggest a variable negative relationship with the nao which is strongest after 1960 and before the mid 1930s

sea surface temperature and salinity variability at bermuda during the end of the little ice age 1 we use geochemical and isotope measurements on a 225 year old brain coral diploria labyrinthiformis from the south shore of bermuda 64 w 32 n to construct a record of decadal to centennial scale climate variability the coral was collected alive and annual density bands visible in x radiographs delineate cold and warm seasons allowing for precise dating coral skeletons incorporate strontium sr and calcium ca in relative proportions inversely to the sea surface temperature sst in which the skeleton is secreted previous studies on this and other coral colonies from this region document the ability to reconstruct mean annual and wintertime sst using sr ca measurements goodkin et al 2007 2005 the coral based records of sst for the past 2 centuries show abrupt shifts at both decadal and centennial timescales and suggest that sst at the end of the little ice age between 1840 and 1860 was 1 5 0 4 c colder than today 1990s coral reconstructed sst has a greater magnitude change than does a gridded instrumental sst record from this region this may result from several physical processes including high rates of mesoscale eddy propagation in this region oxygen isotope values 18o of the coral skeleton reflect changes in both temperature and the 18o of seawater ow where ow is proportional to sea surface salinity sss we show in this study that mean annual and wintertime 18o of the carbonate oc are correlated to both sst and sss but a robust quantitative measure of sss is not found with present calibration data in combination however the sr ca and oc qualitatively reconstruct lower salinities at the end of the little ice age relative to modern day temperature changes agree with other records from the bermuda region radiative and atmospheric forcing may explain some of the sst variability but the scales of implied changes in sst and sss indicate large scale ocean circulation impacts as well

late holocene sea surface conditions offshore newfoundland based on dinoflagellate cysts dinoflagellate cysts and xrf core scanning data from two marine sediment cores from embayments north bonavista bay and south placentia bay of newfoundland show significant changes in ocean and atmospheric conditions of the sw labrador sea region during the last 5700 years fresh and cold conditions probably accompanied by seasonal sea ice prevailed both north and south of newfoundland from c 5 7 to 4 0 cal kyr bp this may be linked to intensified labrador current export of cold meltwater and or sea ice from the arctic presumably related to warmer conditions in the northernmost latitudes and the prevalence of strong north westerly winds after c 4 0 cal kyr bp sea surface conditions warmed up and sea ice decreased northeast of newfoundland but conditions were still cold south of newfoundland this suggests a decrease in arctic meltwater export and westerly wind strength after 2 9 2 5 cal kyr bp only minor changes in sea surface conditions affected the study sites sea surface temperatures

decadal variability of hydrography in the upper northern north atlantic in 1948 1990 we investigate the variability of the north atlantic subarctic gyre in recent decades from time series of station temperature and salinity decadal variability stronger at the surface is identified which exhibits vertical coherence over a layer deeper than the late winter mixed layer in the northwestern atlantic it corresponds to the layer with a component of water from the arctic ocean or from the canadian arctic the spatial coherence of the signal is investigated an empirical orthogonal function decomposition of lagged time series indicates that a single pattern explains 70 of the variance in upper ocean salt content corresponding to a propagating signal from the west to the northeast in the subarctic gyre the most likely interpretation is that the salinity signal originates in the slope currents of the labrador sea and is diffused advected eastward of the grand banks over the near western atlantic in the northwestern atlantic temperature fluctuations are strongly correlated to salinity fluctuations and are aligned along the average t s characteristics this signal suggests large variations in the outflow of fresh cold water in the slope current and is strongly correlated with ice cover a basin scale atmospheric circulation of weakened westerlies at 55 n weaker northwesterlies west of greenland and weaker southerlies over the central and eastern north atlantic is associated with the high salinity and warm water phase of the first principal component this circulation pattern leads fluctuations in the northeast atlantic and lags those in the northwestern part of the basin the wind indices also suggest that the fluctuations of the fresh water outflow occur during intervals of anomalously northerly winds either east of greenland 1965 1968 1969 or off the canadian archipelago 1983 1984

on the mechanism of north atlantic decadal variability abstract north atlantic decadal climate variability is studied with a coupled atmosphere ocean sea ice model ecbilt after having reached an approximate statistical equilibrium in coupled mode without applying flux corrections a subsequent 1000 yr integration is performed and analyzed compared to the current climate the surface temperatures are 2 c warmer in the tropics to almost 8 c warmer in the polar regions the covariability between the atmosphere and ocean is explored by performing a singular value decomposition svd of boreal winter sst anomalies and 800 hpa geopotential height anomalies the first svd pair shows a red variance spectrum in sst and a white spectrum in 800 hpa height the second mode shows a peak in both spectra at a timescale of about 16 18 yr the geopotential height pattern is the model s equivalent of the north atlantic oscillation nao pattern the sst anomaly pattern is a north south oriented dipole additional experiments have revealed that the decadal oscillation in ec

great salinity anomalies in the north atlantic abstract we revisited the great salinity anomaly of the 1970s gsa 70s dickson et al 1988 and documented the newly identified great salinity anomaly of the 1980s hence termed gsa 80s both propagated around the north atlantic in a similar fashion the advective mechanism initially proposed to explain the observed sequence of low salinity low temperature events during the gsa 70s apparently holds also for the gsa 80s the latter was successively observed in the west greenland current 1982 the labrador current 1983 the flemish pass 1984 near the charlie gibbs fracture zone 1984 1985 in the rockall channel 1985 south of iceland 1985 1988 in the north sea 1986 1987 norwegian sea 1987 1988 barents sea 1988 1989 and iceland sea 1989 1990 the advection speed of the gsa 80s seems to be greater than the one of the gsa 70s the 1980s anomaly reached the barents sea 6 to 7 years after peaking in the west greenland current while the 1970s anomaly traveled the same route in 8 to 10 years these anomalies however seem to be of different origin the gsa 70s was apparently boosted remotely by a freshwater sea ice pulse from the arctic via fram strait consequently the gsa 70s was accompanied by a large sea ice extent anomaly in the greenland and iceland seas which propagated into the labrador sea in contrast the gsa 80s was likely formed locally in the labrador sea baffin bay mainly because of the extremely severe winters of the early 1980s but supplemented with a possible contribution of the arctic freshwater outflow via the canadian archipelago facilitated by strong northerly winds which would have enhanced stability and ice formation this anomaly was also associated with a positive sea ice extent anomaly in the labrador sea baffin bay which however had no upstream precursor in the greenland sea thus the gsas are not necessarily caused solely by an increased export of freshwater and sea ice from the arctic via fram strait these results are corroborated by the early 1990s data when a new fresh cold anomaly was formed in the labrador sea and accompanied by a large positive sea ice extent anomaly the harsh winters of the early 1990s were however confined to the labrador sea baffin bay area while the atmospheric and oceanic conditions in the greenland iceland and irminger seas were normal the labrador sea baffin bay area appears therefore to play a key role in formation of gsas as well as in propagation of the gsas formed upstream a likely contribution of the enhanced canadian archipelago freshwater outflow to the gsa formation also seems to be significant two major modes of the gsa origin are thus identified remote generated by an enhanced arctic ocean freshwater export via either fram strait or the canadian archipelago and local resulting from severe winters in the labrador sea baffin bay both modes should be taken into account to model decadal variability of the coupled ocean ice atmosphere system in the north atlantic arctic basin

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

the great salinity anomaly in the northern north atlantic 1968 1982 the widespread freshening of the upper 500 800m layer of the northern north atlantic which this paper describes represents one of the most persistent and extreme variations in global ocean climate yet observed in this century though a range of explanations have been advanced to explain this event including in situ changes in the surface moisture flux this paper describes the great salinity anomaly as largely though not entirely an advective event traceable around the atlantic subpolar gyre for over 14 years from its origins north of iceland in the mid to late 1960s until its return to the greenland sea in 1981 1982 the overall propagation speed around this subpolar gyre is estimated at about 3cm s 1 of the total salt deficit associated with the anomaly as it passed south along the labrador coast in 1971 1973 about 72 109 tonnes a deficit equivalent to about two thirds of this figure 47 109 tonnes ultimately passed through the faroe shetland channel to the barents sea arctic ocean and greenland sea during the mid 1970s possible effects on deep water formation and on the representativeness of historical section data are discussed

the different nature of the interdecadal variability of the thermohaline circulation under mixed and flux boundary conditions the differences between the interdecadal variability under mixed and constant flux boundary conditions are investigated using a coarse resolution ocean model in an idealized flat bottom single hemisphere basin objective features are determined that allow one type of oscillation to be distinguished versus the other first by performing a linear stability analysis of the steady state obtained under restoring boundary conditions it is shown that the interdecadal variability under constant flux and mixed boundary conditions arises respectively from the instability of a linear mode around the mean stratification and circulation and from departure from the initial state based on the budgets of density variance it is shown next that the two types of oscillations have different energy sources under the constant flux boundary condition the thermal mode the downgradient meridional eddy heat flux in the western boundary current regions sustains interdecadal variability whereas under mixed boundary conditions the salinity mode a positive feedback between convective adjustment and restoring surface heat flux is at the heart of the existence of the decadal oscillation furthermore the positive correlations between temperature and salinity anomalies in the forcing layer are shown to dominate the forcing of density variance in addition the vertical structure of perturbations reveals vertical phase lags at different depths in all tracer fields under constant flux while under mixed boundary conditions only the temperature anomalies show a strong dipolar structure the authors propose that these differences will allow one to identify which type of oscillation if any is at play in the more exhaustive climate models

north atlantic oscillation induced changes of the upper layer circulation in the northern north atlantic ocean 1 hydrographic data of the 1990s along world ocean circulation experiment sections a1e greenland ireland and a2 newfoundland france indicate a redistribution of cold low saline subarctic waters and warm saline subtropical waters in the upper layer of the northern north atlantic within about 2 years after the north atlantic oscillation had turned from a period with strong westerlies until 1995 to a period with weak westerlies in 1996 and 1997 in the latter period subarctic waters spread preferably southward along the continental slope east of newfoundland rather than eastward with the north atlantic current nac into the irminger iceland and west european basins as a consequence the subarctic front and the associated nac shifted eastward in the newfoundland basin where subarctic waters accumulate and westward in the iceland basin where a large warm and saline anomaly was found in 1996 and 1997 indicating a contraction of the subpolar gyre in the irminger basin the anomaly occurred in 1998 and 1999 whereas the cyclonic circulation in the irminger and iceland basins weakened it intensified in the newfoundland basin where a strengthened labrador current retroflection joined the nac this and the increased anticyclonic recirculation of subtropical waters in the newfoundland and west european basins caused a considerable reduction of the northward heat transport across 47 n in the upper layer in 1997 the anticyclonic circulation occurring in the west european basin suggested a northward expansion of the subtropical gyre

seismic hazard in the northwestern apennines a study of the seismic hazard for the northwestern apennines based on seismotectonic and seismicity data is presented

high resolution holocene record in the southeastern bay of biscay global versus regional climate signals abstract core ks10b north east atlantic 43 50 n 2 03 w water depth 550 m was recovered at a location of high sediment deposition and hence includes a high resolution palaeoclimatic record for the southeastern bay of biscay over the last 9000 cal yr bp the effect of global and regional climatic forcing factors e g orbital forcing north atlantic oscillation nao and their subsequent control on water temperature sea level hydrology and continental influence were investigated by studying planktic and benthic foraminiferal faunas 150 m sedimentology and stable isotopes results indicate probable episodic long term incursions of the warm and salty iberian poleward current ipc into the bay of biscay during the holocene by the intermittent presence of subtropical globigerinoides ruber in the otherwise temperate fauna these incursions seem to be triggered by negative nao like conditions our data show five main climatic periods which are in general agreement with the literature data on the climatic variability in the north atlantic and the iberian peninsula the early holocene 9000 7400 cal yr bp is characterized by low sea level significant downslope transport eutrophic benthic settings and high surface water productivity these environmental characteristics are probably due to the general wet and warm climate under a prevailing negative nao increasing precipitation and river runoff and favouring the incursion of the ipc into the bay of biscay the climatic optimum appears between 7400 and 6000 cal yr bp under a generally positive nao index in the following 6000 3500 cal yr bp surface water cooling is matching a steep decline of the northern hemisphere summer insolation meanwhile benthic settings are changing progressively towards present day trophic conditions the time interval from 3500 to 1800 cal yr bp encompasses the iberian roman humid period characterized by warm and humid conditions and increasing primary production under a prevailing negative nao index the last 1800 years were characterized by stable cool conditions reflecting a change towards a positive nao state

a mechanism for the recurrence of wintertime midlatitude sst anomalies abstract in the early 1970s namias and born speculated that ocean temperature anomalies created over the deep mixed layer in winter could be preserved in the summer thermocline and reappear at the surface in the following fall or winter this hypothesis is examined using upper ocean temperature observations and simulations with a mixed layer model the data were collected at six ocean weather stations in the north atlantic and north pacific concurrent and lead lag correlations are used to investigate temperature variations associated with the seasonal cycle in both the observations and the model simulations concurrent correlations between the surface and subsurface temperature anomalies in both the data and the model indicate that the penetration of temperature anomalies into the ocean is closely tied to the seasonal cycle in mixed layer depth high correlations extend to relatively deep shallow depths in winter summer lead lag correlations in both the data and the model at some of the stations

variability of the northeast atlantic sea surface δ14c and marine reservoir age and the north atlantic oscillation nao abstract we compiled new 14 c analyses of mollusc shells bivalves and gastropods of known age from the collection of the museum national d histoire naturelle de paris and previously published data to investigate changes in the sea surface 14 c and reservoir age in the northeast atlantic sector nea between 1823 and 1952 ad the mollusc shells are mainly located off the atlantic margin between 45 n and 60 n downstream of the north atlantic current nac we show that the temporal variability of the nea 14 c is independent of the mollusc species depth habitat diet and latitudinal distribution the quasi null difference between mollusc 14 c and the marine model indicate that the mollusc 14 c reflects the 14 c values of open marine conditions between 1823 and 1850 ad the pre anthropogenic mean of 14 c is 45 5 corresponding to a reservoir age of 380 60 years and a r value of 7 50 years in agreement with previous estimates the 14 c values show a significant long term decrease of 12 from 1823 to 1952 ad attributed to changes in 14 c production between 1823 and 1900 ad and the suess effect between 1900 and 1952 ad between 1885 and 1950 ad 14 c fluctuations of 10 up to 18 occurred in the northeast atlantic corresponding to reservoir age variations of 90 years up to 170 years these fluctuations are very similar to changes of 14 c in the southern norwegian sea spectral analyses of the nea 14 c exhibit quasi periodic cycles of about 7 4 years almost equivalent to the quasi periodic cycles of the winter index of the north atlantic oscillation nao with a period around 6 5 years we find that changes of nea 14 c cannot be attributed to changes in river runoff or the precipitation evaporation budget the 14 c lows or high reservoir ages correspond to the more intense phase of the winter nao with a time lag of 1 3 years such a time lag may reflect the eastward transit time of upstream changes originating in the labrador sea then entrained within the nac along with the subpolar gyre into the northeast atlantic sector during these events we estimate that about 70 of the total transport in the nac was due to water originating in the labrador sea

temperature and salinity variability on the scotian shelf and in the gulf of maine 1945 1990 examination of temperature and salinity data from the scotian shelf gulf of maine gulf of st lawrence and the adjacent continental slope has shown that the dominant low frequency event over the last 45 years was a cooling and subsurface freshening of the water masses from 1952 to 1967 followed by a rapid reversal of these trends the largest temperature and salinity changes 1952 1967 were 4 6 c and 0 7 respectively and occurred at about 100 m over the slope exchanges with shelf waters and vertical mixing gave rise to the surface manifestation of this variability the westward transport of the labrador current was found to have similar variability increasing from about 1 106 m3 s 1 in the early 1950s to about 4 106 m3 s 1 in the mid 1960s a simple model that accounts for this variation of transport and has a constant entrainment of north atlantic water indicates that changes of the westward flow of the labrador current could contribute significantly to the t s fluctuations

interpentadal variability of salinity in the upper 150 m of the north atlantic ocean 1970 1974 versus 1955 1959 we have composited and objectively analyzed historical hydrographic observations for the north atlantic ocean for two pentads 1955 1959 and 1970 1974 our purpose is the study of the temporal variability of salinity in the upper layers of the north atlantic ocean upper ocean 0 150 m salinity differences between the two pentads exhibit statistically significant changes the subarctic gyre east and north of newfoundland freshened by as much as 0 5 the northern portion of the subtropical gyre increased in salinity by as much as 0 4 while the interior of this gyre decreased in salinity

spatial patterns of atmosphere ocean interaction in the northern winter abstract the variability of monthly mean sea surface temperature sst anomalies over the extratropical north atlantic and pacific and its relation to atmospheric circulation anomalies over the northern hemisphere during wintertime is investigated by applying eigenvector analysis to a 39 year dataset and correlating the time series of the resulting expansion coefficients with the hemispheric 500 mb height and sea level pressure fields in agreement with previous studies the simultaneous correlation between the tone series of the expansion coefficient of the first empirical orthogonal function eof 1 of north pacific sea surface temperature sst and the hemispheric 500 mb height field resembles the pacific north american pattern and the corresponding pattern for atlantic sst resembles the north atlantic oscillation in the vicinity of the conters of action of thew patterns the sst fluctuations associated with these modes explain on the order of half the variance of 500 mb height and slightly less of

imprints of the north atlantic oscillation on four unusual atmospheric parameters abstract using data for 41 yr 1958 1998 from the national center for environmental prediction national center for atmospheric research reanalysis the authors study the impact of the north atlantic oscillation nao on four atmospheric parameters these four parameters have three common characteristics their previous limited use as climate diagnosis tools their high dependence on changes in atmospheric circulation and their relationship with variables associated with the development of synoptic perturbances they are 1 relative angular momentum from 500 hpa to 200 hpa and from 55 n to 90 n 2 advection of temperature at 500 hpa 3 equivalent temperature at 850 hpa and 4 distribution of upper level low systems ull the most significant results are 1 a significant positive correlation between the relative angular momentum from 500 hpa to 200 hpa and from 55 n to 90 n with the nao index computed as the normalized pressure difference between ponta delgada azores and reykjavik iceland 2 the nao affects 500 hpa temperature advection from 45 n to 70 n and a positive nao index is alternatively related to positive or negative anomalies of advection the relationship is positive over the atlantic asia and western america and negative over europe the pacific and eastern america 3 the correlation pattern between nao index and the equivalent temperature at 850 hpa shows a semiannular structure with negative correlations over the arctic and positive correlations over midlatitudes with the exception of the pacific area and 4 the distribution of ull systems is only influenced by nao over both sides of the atlantic ocean and for the latitude belt from 20 n to 50 n

causes of decadal changes of the freshwater content in the arctic ocean abstractdecadal changes of the liquid freshwater content in the arctic ocean are studied with a suite of forward and adjoint model simulations adjoint sensitivities show that freshwater volume changes in the norwegian atlantic current north of the lofoten basin and a salinity maximum in the fram strait and in the canadian archipelago lead to an enhanced northward transport of freshwater the dynamical sensitivities indicate that stronger freshwater export from the arctic is related to an enhanced cyclonic circulation around greenland with an enhanced export through the canadian archipelago and a stronger circulation within the fram strait associated with this circulation around greenland is a large scale cyclonic circulation in the arctic cyclonic wind stress anomalies in the arctic ocean as well as over the nordic seas and parts of the subpolar atlantic are optimal to force the freshwater transport changes results from a simulation over the period 1948 2010 corroborate the result that arctic freshwat

a modelling and observational study of the relationship between sea surface temperature in the north west atlantic and the atmospheric general circulation results from four pairs of 50 day wintertime integrations of the meteorological office s 5 level general circulation model with warm and cold sea surface temperature s s t anomalies of about 3 k in the northwest atlantic are described difference fields between the warm and cold integrations are statistically significant at the 1 level with positive geopotential height over the central north atlantic and weaker negative height over europe the storm track over the atlantic is displaced from its normal position results from four further pairs of integrations with halved s s t anomalies are also described the response is approximately linear with systematic differences in 500 mb geopotential height over the atlantic parts of which are just significant at the 10 level with half the full s s t anomaly overall however the model s response is weaker than could be obtained with tropical s s t anomalies of the same magnitude results from the model integrations are compared with results from an observational study of the relationship between wintertime s s t in the north west atlantic and mean sea level pressure and 500mb height two independent 30 year periods were chosen for study thus minimizing the influence of long term trends in s s t over the atlantic and europe the model results compared well with the observations with s s t data lagging the atmosphere by one month the observational study appears to show that the s s t anomalies are initially forced by perturbations in the atmospheric circulation with s s t data leading the atmosphere by one month results show that atmospheric and s s t anomalies are most persistent in the period october to december throughout the winter these lagged relationships are much weaker and not statistically significant diagnostics of e vector divergence from the gcm experiments are used to suggest that anomalous baroclinic wave activity over the atlantic is important as a momentum forcing for the anomalous time mean flow pattern on the other hand the role of thermal forcing provided by anomalous diabatic heating and transient eddy heat flux convergence may be important to substantiate this statement a simple linear steadystate two layer model of the response to extratropical thermal forcing is described with a suitable basic state flow and a mid tropospheric heat source given mainly by the transient eddy heat flux convergence the response is shown to be equivalent barotropic with a downstream ridge and ascent over the thermal source conversely results from an ocean mixed layer model are discussed which suggest that warm s s t anomalies could be maintained by a positive surface pressure perturbation positioned downstream of the anomaly through anomalous northward advection of warm ocean water by ekman drift currents this northward advection would balance the sensible and latent heat loss into the atmosphere over the s s t anomaly hence it is possible that some positive ocean atmosphere feedback may account for the persistence of such atmospheric and oceanic anomalies

exotic pollen as an indicator of variable atmospheric circulation over the labrador sea region during the mid to late holocene variability in the abundance of exotic non native pollen in sediment cores has long been considered as a potential proxy for changing atmospheric circulation but the difficulty of gaining sufficient total exotic pollen and the incomplete under standing of atmospheric pollen transport patterns has hindered its application in light of recent advances in the study of pollen transport we present an exotic pollen record from two fjord sediment cores taken from the west placentia bay newfoundland and east narsaq sund greenland labrador sea as a basis for studying variations in regional atmospheric circulation the two cores cover the last ca 5500 years and indicate a shift in dominant spring summer air masses at ca 2000 southern greenland and 3000 cal a bp newfoundland transporting reduced concentrations of pollen from southerly and south westerly vegetation zones this may suggest a shift away from more dominantly zonal atmospheric circulation a feature of positive north atlantic oscillation years to more frequent meridional circulation these results support sea ice sea surface temperature proxy reconstructions from newfoundland investigated as part of the same project which also suggest increased winter atmospheric circulation during the early part of the time period studied in this region more positive north atlantic oscillation years and therefore more zonal atmospheric circulation are associated with increased atmospheric circulation in both the winter and the summer seasons copyright 2011 john wiley sons ltd