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

recent thermohaline trends of the atlantic waters inflowing to the mediterranean sea 1 a total of 5077 argo float profiles in the period 01 2002 05 2010 have been used to analyze salinity and temperature trends in the atlantic waters adjacent to the strait of gibraltar in order to identify the source of recent changes observed in the inflow to the mediterranean sea positive salinity trends of 0 038 0 009 year 1 and 0 013 0 003 year 1 have been found for the surface atlantic water and the eastern north atlantic central water respectively for temperature no significant trend is observed in the surface layer while positive trend of 0 05 0 02 c year is obtained for the thermocline waters the mediterranean water layer does not show any significant trend for the entire period but a switch from positive to negative trends is observed in year 2006 in contrast to previous findings these thermohaline variations are driven by intrinsic water masses changes instead of isopycnal vertical displacements probably related to an enhancement of the net freshwater losses in the area

the atlantic water boundary current north of svalbard in late summer data from a shipboard hydrographic velocity survey carried out in september 2013 of the region north of svalbard in the nansen basin are analyzed to characterize the atlantic water aw boundary current as it flows eastward along the continental slope eight meridional transects across the current spanning an alongstream distance of 180 km allow for a detailed description of the current and the regional water masses during the survey the winds were light and there was no pack ice the mean section reveals that the boundary current was o 40 km wide surface intensified with a maximum velocity of 20 cm s its mean transport during the survey was 3 11 0 33 sv of which 2 31 0 29 sv was aw this suggests that the two branches of aw entering the arctic ocean via fram strait the yermak plateau branch and the svalbard branch have largely combined into a single current by 30 e at this location the boundary current meanders with a systematic change in its kinematic structure during offshore excursions a potential vorticity analysis indicates that the flow is baroclinically unstable consistent with previous observations of aw anticyclones offshore of the current as well as the presence of a near field cyclone in this data set our survey indicates that only a small portion of the boundary current is diverted into the kvitoya trough 0 17 0 08 sv and that the aw temperature salinity signal is quickly eroded within the trough

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

detection and attribution of atlantic salinity changes 1 an analysis of observed and modeled oceanic salinity changes shows that significant changes of salinity which are predicted in the world s oceans as a result of human influence are beginning to emerge a significant increase in salinity has been observed in recent decades in the 20n 50n latitude band of the atlantic ocean although changes at sub polar latitudes of the atlantic and in other ocean basins are not found to be significant compared to modeled internal variability an optimal detection analysis of spatial patterns of salinity trends detects a human influence on the observed salinity increases in the atlantic ocean these results indicate the growing potential for using observations to constrain important properties of the climate system s response to anthropogenic forcing

apparent changes in the climatic state of the deep north atlantic ocean determination of any long term changes in the large scale characteristics of the deep ocean circulation would be an important clue in understanding the climatic interactions of the ocean and atmosphere in the summer of 1981 the rv atlantis ii reoccupied two transatlantic sections at nominal latitudes of 24 30 n and 36 16 n with a conductivity temperature depth instrument ctd one purpose of the work was to make a comparison with previous surveys conducted during the international geophysical year igy 1 when sections were obtained in october 1957 and april may 1959 we report here that significant warming occurred in an ocean wide band from 700 m to 3 000 m with a maximum temperature difference of 0 2 c these changes are sufficient to expand the water column by several centimetres the historical temperature salinity curve was apparently unchanged interannual changes in local water mass characteristics have been proposed previously2 3 perhaps it would be most surprising if no changes were seen to occur what remains obscure is the significance of these changes and the extent to which they represent long term climate trends or merely the minor and random fluctuations to be expected in any complex fluid system

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

forcing of oceanic heat anomalies by air sea interactions in the nordic seas area 1 hydrographic data and atmospheric reanalysis from 1982 to 2005 are used to show a strong link of the atlantic water temperature awt anomalies observed in the transition zone between the norwegian atlantic current and the west spitsbergen current in summer to the surface heat flux shf anomalies observed over the barents sea open water in the preceding late winter a mechanism proposed for this link is formation of ocean temperature anomalies in a deep mixed layer and their subsequent westward export by a branch of atlantic water recirculating in the western barents sea the shf anomalies over the barents sea are due to advection of temperature and humidity by anomalous winds across the arctic ice edge and do not strongly depend on the north atlantic oscillation nao correlations of up to about 0 9 between the awt anomalies and indices of atmospheric variability over the barents sea open prospects for seasonal awt predictability it is also shown that the wind forcing responsible for positive awt anomalies is involved in a cyclonic perturbation of the atmospheric circulation over the nordic seas this perturbation generates through influence on the sea ice distribution a lobe of shf anomalies in the marginal ice zone miz on the eastern barents sea and western greenland sea sides of the nordic seas which has the opposite sign to the open water lobe in contrast to the barents sea miz the diabatic heating of the atmosphere by upward shf anomalies in the greenland sea miz competes with cold advection

multidecadal climate variability in the greenland sea and surrounding regions a coupled model simulation pronounced oscillations of ocean temperature and salinity occur in the greenland sea in a 2000 year integration of a coupled ocean atmosphere model the oscillations involving both the surface and subsurface ocean layers have a timescale of approximately 40 80 years and are associated with fluctuations in the inten sity of the east greenland current the greenland sea temperature and salinity variations are preceded by large scale changes in near surface salinity in the arctic which appear to propagate out of the arctic through the east greenland current these anomalies then propagate around the subpolar gyre into the labrador sea and the central north atlantic these oscillations are coherent with previously identified multi decadal fluctuations in the intensity of the north atlantic thermohaline circula tion the oscillations in the g eenland sea are related to atmospheric variability negative cold anomalies of surface air temperature are associated with negative cold sea surface temperature sst anomalies in the greenland sea with amplitudes up to 2oc near green land declining to several tenths of a degree c over north western europe the c01d sst anomalies and intensified east greenland current are also associated with enhanced northerly winds over the greenland sea

interpentadal variability of temperature and salinity in the deep north atlantic 1970 1974 versus 1955 1959 historical hydrographic observations have been composited and objectively analyzed for the north atlantic ocean for two pentads 1955 59 and 1970 74 for the purpose of studying the temporal variability of the thermohaline structure of the deep north atlantic ocean statistically significant differences between the two pentads are found in the deep ocean at 1750 m depth most of the north atlantic increased in temperature approximately 0 1 c and salinity 0 025 from the earlier to the later period an exception to this was a region in the eastern atlantic between 33 n and 50 n where a cooling 0 1 c and freshening 0 025 occurred changes at other depths as evidenced by difference fields of temperature along 24 5 n and 36 5 n are in agreement with differences found by roemmich and wunsch 1984 who described changes at these latitudes between sections taken in the late 1950 s and sections taken in 1981

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

decadal changes in water mass characteristics at 24 n in the subtropical north atlantic ocean abstract three transatlantic hydrographic sections across 24 n through the center of the subtropical gyre are analyzed for evidence of decadal changes in water mass characteristics in the main thermocline there has been a steady increase in salinity from 1957 to 1981 to 1992 the salinity at a given potential temperature between 12 c and 17 c has increased at a nearly constant rate of 0 010 per decade at constant potential density salinity and temperature both increased at rates of 0 018 per decade and 0 065 c per decade in the intermediate waters between 800 and 1500 dbar salinity has increased as well on average by as much as 0 025 from 1981 to 1992 either on constant potential temperature or constant density surfaces these changes cannot be due to vertical heaving of a constant water mass structure and they cannot be easily explained in terms of horizontal shifts in the subtropical gyre water mass structure throughout the water column down to 2000 dbar and across the zonal extent of the 24 n

recent eurasian river discharge to the arctic ocean in the context of longer term dendrohydrological records 1 mapped correlations between annual discharges ad 1938 1990 of the major eurasian rivers entering the arctic ocean severnaya dvina pechora ob yenisey lena and kolyma demonstrate a positive relationship between discharge and the palmer drought severity index pdsi within the individual basins and more distant areas the relationship between recent discharge and pdsi supports the application of dendrohydrological modeling to produce reconstructions of discharge extending back before the 20th century the dendrohydrologic models explain from 41 yenisey to 55 pechora of the observed variability of flow in the individual basins and 39 of the total combined discharge discharge reconstructions for the period ad 1800 1990 indicate that there is no long term monotonic trend toward higher discharge over the past 200 years reconstructed annual discharge for the individual rivers and the total discharge from all the rivers experienced in the 20th century are within the bounds of natural variability experienced over the past 200 years the s dvina pechora ob and kolyma reconstructions do display significant multidecadal variability in discharge similar to that observed in the north atlantic north pacific and northern hemisphere climatic parameters although the translation of such variability to the river discharges remains uncertain the presence of multidecadal variability makes it more difficult to detect or ascribe annual discharge changes that may be attributable to global warming

the effect of the coarse aeolian sand on siltation of the inner mongolian reach of the yellow river the yellow river flows through an extensive aeolian inner mongolian plateau with a total length of 673 km owing to the high erodibility of the wulanbuhe and kubuqi deserts and the impacts of its upstream reservoirs the siltation of the inner mongolian reach of the yellow river is caused essentially by the aeolian particles larger than 0 1 mm which are very different from the sediment 0 05 mm of the lower yellow river coming from the loess plateau during the period 1954 2000 the total accumulated sediment of this area was about 20 1 108 t the coarse sediment larger than 0 1 mm as about 15 2 108 t and the fine sediment less than 0 1 mm fs about 4 9 108 t in particular there was 6 1 108 t as coming from the wulanbuhe desert and 5 82 108 t as from the kubuqi desert deposited in the river channel of the inner mongolian reach representing 78 6 of the total coarse sediment larger than 0 1 mm

climatic warming of atlantic intermediate waters abstract interdecadal temperature variability of the atlantic ocean is investigated by differencing hydrographic sections taken from the 1920s through the 1990s a comprehensive reanalysis of north atlantic sections and the inclusion of south atlantic sections show that warming seen previously in the north atlantic extends to the south atlantic the largest statistically significant changes occur on pressure surfaces between 1000 and 2000 decibars db over this pressure range and for latitudes between 32 s and 36 n temperatures have warmed by 0 5 c century 1 at 48 n a cooling of 3 c century 1 occurred between the 1950s and 1980s these isobaric temperature trends are decomposed into ones along surfaces of constant neutral density and ones due to the vertical movement of neutral surfaces the two components are associated with different processes in the southern north atlantic 8 36 n the subthermocline warming between the 1950s and 1980s appears to be due primarily to downward displacements of n

cooling and freshening of the subpolar north atlantic ocean since the 1960s little is known of the interdecadal variability in the thermohaline circulation of the world s oceans yet such knowledge is essential as a background to studies of the effects of natural and anthropogenic climate change the subpolar north atlantic is an area of extensive water mass modification by heat loss to the atmosphere lying as it does at the northern limit of the global thermohaline conveyor belt 12 changes in this region may ultimately have global consequences here we report that in august 1991 the waters between greenland and the united kingdom were on average 0 08 c and 0 15 c colder than in 1962 and 1981 respectively and slightly less saline than in 1962 the cause appears to be renewed formation of intermediate water in the labrador sea from cooler and fresher source waters and the spreading of this water mass from the west variations in the source characteristics of labrador sea water can be traced across the north atlantic with a circulation time of 18 19 years between the labrador sea and rockall trough more recently formed labrador sea water with even lower temperature and salinity should cool and freshen the north atlantic still further as it circulates around the ocean in the coming decade

a twentieth century reanalysis forced ocean model to reconstruct the north atlantic climate variation during the 1920s the observed north atlantic multi decadal variability for the period 1872 2009 is reconstructed with the max planck institute ocean model which is forced with an ensemble of the atmospheric twentieth century reanalysis special emphasis is put on the early part of the experiments which includes a prominent climate variation during the 1920s the experiments are in agreement with selected hydrographic records indicating a transition from cold and fresh north atlantic water properties prior to the 1920 climate variation towards warm and saline waters afterwards examining the variation reveals that sea level pressure slp anomalies prior to the 1900s resemble a negative phase of north atlantic oscillation and associated weak winds result in a weak north atlantic current nac and sub polar gyre spg this leads to a reduced transport of warm and saline waters into the higher latitudes simultaneously arctic freshwater release results in the accumulation of cold and fresh water properties which cover the upper layers in the labrador sea and subsequently suppress convection from the 1910s the arctic freshwater export is reduced and nac and spg are strengthened as a result of an increased slp gradient over the north atlantic concurrently labrador sea convection and atlantic meridional overturning circulation amoc increase the intensified nac spg and amoc redistribute sub tropical water into the north atlantic and nordic seas thereby increasing observed and modelled temperature and salinity during the 1920s

changes in river regime after the construction of upstream reservoirs this article presents and analyses many years of investigations in china on the fluvial processes downstream of impounding and detention reservoirs the study covers the change in hydrograph the recovering of sediment concentration along the river course the degradation of stream bed the adjustment of longitudinal profile the coarsening of bed material the change in channel width and the trend of channel pattern variation for alluvial streams downstream of impounding reservoirs without confluence of major tributaries the degradation may extend to a great distance below the dam in the process of reducing the sediment carrying capacity of the flow to match the diminished sediment supply the coarsening of bed material is a factor of equal if not greater importance as compared with the flattening of channel gradient in places where the flow has not been sufficiently cut down and the bank is erosive non resistant a receding of banklines may take place in concurrence with the deepening of the river bed below detention reservoirs even if the total runoff and sediment supply remain essentially unchanged the modification of the hydrograph is sufficient to enhance the deterioration of the downstream channel

large scale atlantic salinity changes over the last half century a model observation comparison abstract large scale freshening of the northern atlantic and concurrent salinity increases in the low latitude atlantic upper layers have been widely reported for the second half of the twentieth century the role of anthropogenic and or unforced variability processes in these changes and the potential for the high latitude freshening to slow the atlantic meridional overturning circulation moc have been the subject of debate these issues are investigated by comparing observed and simulated changes using the third hadley centre coupled model hadcm3 this analysis suggests that a substantial part of the observed trends could be related to multidecadal variability of the moc using an sst derived proxy for historical moc changes in conjunction with model internal variability relationships suggests that much of the observed evolution of northern atlantic freshwater content can be explained as being driven by unforced moc variability hadcm3 simulations with external historical time varying forci

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

north atlantic warming and the retreat of greenland s outlet glaciers mass loss from the greenland ice sheet quadrupled over the past two decades contributing a quarter of the observed global sea level rise increased submarine melting is thought to have triggered the retreat of greenland s outlet glaciers which is partly responsible for the ice loss however the chain of events and physical processes remain elusive recent evidence suggests that an anomalous inflow of subtropical waters driven by atmospheric changes multidecadal natural ocean variability and a long term increase in the north atlantic s upper ocean heat content since the 1950s all contributed to a warming of the subpolar north atlantic this led in conjunction with increased runoff to enhanced submarine glacier melting future climate projections raise the potential for continued increases in warming and ice mass loss with implications for sea level and climate

linear trends of temperature at intermediate and deep layers of the north atlantic and the north pacific oceans 1957 1981 abstract using all available hydrographic station data on ocean temperature observations from world data center b obninsk russia investigation of temperature changes in the north atlantic and north pacific oceans within the depth range of 300 to 3000 m has been carried out for the period 1957 1981 results of statistical data analysis show that in the upper layer to about 500 m depths of both oceans on average seawater temperature declined deeper than 500 600 m in the north pacific ocean no significant temperature changes have been revealed for this 25 year time interval on average for the north atlantic ocean a statistically significant temperature rise about 0 1 c 25 yr 1 is observed in the 800 to 2500 m layer

long term hydrographic changes at 52 and 66 w in the north atlantic subtropical gyre caribbean abstract in july september 1997 two hydrographic lines were done in the western n atlantic along longitudes of 52 and 66 w as part of the woce one time hydrographic survey of the oceans each of these two lines approximately repeated earlier ones done during the international geophysical year s igy and the mid 1980s because of this repeated sampling long term hydrographic changes in the water masses can be examined in this report we focus on temperature and salinity changes within the subtropical gyre mainly between latitudes of 20 and 35 n and compare our results to those presented by bryden et al 1996 who examined changes along a zonal line at 24 n most recently occupied in 1992 since this most recent 24 n section in 1992 substantial changes have occurred in the western part of the subtropical gyre at the depths of the labrador sea water lsw in particular we see clear evidence for colder fresher labrador sea water throughout the gyre on our two recent sections that was not yet present in 1992 at similar longitudes along 24 n at shallower depths inhabited by waters that are an admixture of mediterranean mw and antarctic intermediate waters aaiw our recent survey shows an increase in salinity which can only be attributed to changes in water masses on potential temperature or neutral density surfaces furthermore waters above the mw aaiw layer and into the deeper part of the main pycnocline have continued to become saltier and warmer throughout the 40 year period spanned by our sections these latter changes have been dominantly due to a vertical sinking of density surfaces as t s changes in density surfaces are small but depths of individual t s horizons have increased with time the net change since the igy shows a mean temperature increase between 800 and 2500 m depth at a rate of 0 57 c century with a corresponding steric sea level rise of 1 mm yr and a net downward heave with small values near the top and bottom and a maximum rate of 2 7 m yr at 1800 m depth changes in the deep caribbean indicate a warming since the igy due to temperature increases of the inflowing source waters in the subtropical gyre at 1800m depth but no significant change in the deep salinity

seasonality of the north atlantic oscillation abstract monthly sea level pressure slp data from the national centers for environmental prediction reanalysis for 1948 99 are used to develop a seasonally and geographically varying mobile index of the north atlantic oscillation naom naom is defined as the difference between normalized slp anomalies at the locations of maximum negative correlation between the subtropical and subpolar north atlantic slp the subtropical nodal point migrates westward and slightly northward into the central north atlantic from winter to summer the naom index is robust across datasets and correlates more highly than eof coefficients with historical measures of westerly wind intensity across north atlantic midlatitudes as measured by this mobile index the nao s nodes maintain their correlation from winter to summer to a greater degree than traditional nao indices based on fixed stations in the eastern north atlantic azores lisbon iceland when the naom index is extended back to 1873 its annual values during

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

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

marine calcium carbonate preservation vs climate change over the last two millennia in the fram strait implications for planktic foraminiferal paleostudies abstract we present a high resolution study of planktic foraminiferal distribution patterns in a deep sea core from the eastern fram strait position 78 55 n 06 46 e water depth 1497 m the sediment core is located below atlantic water masses flowing into the arctic ocean and spans the last 2400 years the investigation is based on planktic foraminiferal species distribution stable isotopes and sedimentological data the mean shell weight of neogloboquadrina pachyderma fragmentation organic and inorganic carbon content and the presence of benthic organic linings were also investigated as an indication of preservation changes the results indicate that the planktic foraminifera are affected by dissolution and point to five periods of especially poor preservation at 200 bce 300 650 ce 700 850 ce 1400 1500 ce and from 1800 ce to present in the last century small and fragile subpolar species turborotalita quinqueloba and globigerinita uvula are preserved the increased percentage of these subpolar species together with increases in the caco 3 toc and total foraminiferal flux would point to surface water warming however our data suggest that these fragile species may not have been preserved in sediments older than 1900 ce due to selective dissolution consequently the magnitude of the previously recorded recent surface water warming in the fram strait may be overestimated

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

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

interpentadal variability of steric sea level and geopotential thickness 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 periods 1955 1959 and 1970 1974 difference fields of steric sea level and geopotential thickness for the north atlantic ocean in the 0 to 1500 m depth range between the 1955 1959 and 1970 1974 pentads were computed we find that in the central portion of the subtropical gyre steric sea level decreased by up to 17 5 dyn cm whereas in the western subarctic gyre north of the gulf stream steric sea level increased by an amount up to 7 5 dyn cm from the earlier to the later pentad a decrease in steric sea level 5 dyn cm occurred along the eastern boundary of the north atlantic

subannual seasonal and interannual variability of the north atlantic meridional overturning circulation abstract an eddy permitting numerical ocean model is used to investigate the variability of the meridional overturning circulation moc both wind stress and fluctuations of the seawater density contribute to moc changes on subannual and seasonal time scales whereas the interannual variability mainly reflects changes in the density field even on subannual and seasonal time scales a significant fraction of the total moc variability is due to changes of the density field in the upper 1000 m of the ocean these changes reflect perturbations of the isopycnal structure that travel westward as rossby waves because of a temporally changing phase difference between the eastern and western boundaries the rossby waves affect the moc by modifying the basinwide east west density gradient both the numerical model used in this study and calculations based on rossby wave theory suggest that this effect can account for an moc variability of several sverdrups sv 106 m3 s 1 these results have implications for t

a tree ring based reconstruction of the atlantic multidecadal oscillation since 1567 a d 1 we present a tree ring based reconstruction of the atlantic multidecadal oscillation amo which demonstrates that strong low frequency 60 100 yr variability in basin wide 0 70 n sea surface temperatures ssts has been a consistent feature of north atlantic climate for the past five centuries intervention analysis of reconstructed amo indicates that 20th century modes were similar to those in the preceding 350 yr and wavelet spectra show robust multidecadal oscillations throughout the reconstruction though the exact relationships between low frequency sst modes higher frequency 7 25 yr atmospheric modes e g north atlantic oscillation arctic oscillation and terrestrial climates must still be resolved our results confirm that the amo should be considered in assessments of past and future northern hemisphere climates

atlantic multidecadal variability and associated climate impacts initiated by ocean thermohaline dynamics abstractthe sea surface temperature sst signature of atlantic multidecadal variability amv is a key driver of climate variability in surrounding regions low frequency atlantic meridional overt

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

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

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

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

north atlantic interdecadal variability oceanic response to the north atlantic oscillation 1865 1997 abstract in contrast to the atmosphere knowledge about interdecadal variability of the north atlantic circulation is relatively restricted it is the objective of this study to contribute to understanding how the north atlantic circulation responds to a forcing by the north atlantic oscillation nao on interdecadal timescales for this purpose the authors analyze observed atmospheric and sea surface temperature sst data along with the response of an ocean general circulation model to a realistic monthly surface flux forcing that is solely associated with the nao for the period 1865 1997 in agreement with previous studies it is shown that the relationship between the local forcing by the nao and observed sst anomalies on interdecadal timescales points toward the importance of oceanic dynamics in generating sst anomalies a comparison between observed and modeled sst anomalies reveals that the model results can be used to assess interdecadal variability of the north atlantic circulation the observed

linear trends in salinity for the world ocean 1955 1998 1 quality controlled oceanographic profile salinity measurements from the world ocean database 2001 wod01 were used to calculate linear trends of zonally averaged salinity anomalies for running five year periods from 1955 1959 through 1994 1998 for the world ocean and the atlantic pacific and indian ocean basins from the surface to 3000 meters depth each basin exhibits large scale coherent trends most of the pacific is freshening with the exception of the subtropical south pacific the atlantic exhibits a deep freshening in the subpolar gyre and a shallower more intense increase in salinity in the tropics and subtropics the indian ocean is becoming more saline at all latitudes in the upper 150 meter layer with a subsurface freshening between 40 s and the equator in the 250 1000 meter layer there is freshening in both the weddell and ross seas

deuterium excess record from a small arctic ice cap in this paper we present a deuterium excess d record from an ice core drilled on a small ice cap in svalbard in 1997 the core site is located at lomonosovfonna at 1255 m asl and the analyzed time series spans the period 1400 1990 a d the record shows pronounced multidecadal to centennial scale variations coherent with sea surface temperature changes registered in the subtropical to southern middle latitude north atlantic during the instrumental period we interpret the negative trend in the deuterium excess during the 1400s and 1500s as an indication of cooling in the north atlantic associated with the onset of the little ice age consistently positive anomalies of d after 1900 peaking at about 1950 correspond with well documented contemporary warming yet the maximum values of deuterium excess during 1900 1990 are not as high as in the early part of the record pre 1550 this suggests that the sea surface temperatures during this earlier period of time in the north atlantic to the south of approximately 45 degrees n were at least comparable with those registered in the 20th century before the end of the 1980s we examine the potential for a cold bias to exist in the deuterium excess record due to increased evaporation from the local colder sources of moisture having isotopically cold signature it is argued that despite a recent oceanic warming the contribution from this local moisture to the lomonosovfonna precipitation budget is still insufficient to interfere with the isotopic signal from the primary moisture region in the midlatitude north atlantic