on the origin of the warm inflow to the nordic seas abstract warm and saline waters enter the nordic seas from the south as part of the warm to cold water transformation of the thermohaline circulation of the northern north atlantic one explanation for the origin of the nordic seas inflow is a shallow source hypothesis under which the inflow waters are a modification of upper ocean subtropical waters warm waters from the subtropical gyre are carried to the eastern north atlantic by the north atlantic current and branch northwards joined by poleward upper thermocline flow along the upper continental slope to provide the nordic seas inflow along this pathway the upper water column is progressively cooled and freshened by winter convection the subpolar mode water transformation process and this sets the inflow characteristics a deep source hypothesis provides an alternative explanation for the characteristics of the nordic seas inflow and the pathway delivering the waters to the inflow under this hypothesis inflow waters originate from the core of the mediterranean overflow waters in the gulf of cadiz carried northward at mid depth by the eastern boundary undercurrent in the subtropics continuing into the subpolar gyre along the eastern boundary and rising from depths near 1200m in the rockall trough to less than 600m to cross the wyville thomson ridge into the faroe shetland channel and thence to the nordic seas the deep source hypothesis focus is on lower thermocline source waters beneath the sill depth for the nordic seas inflow in contrast to the shallow source hypothesis focus of transformation of upper thermocline waters above the sill depth on the basis of regional water mass distributions geostrophic shear and direct current measurements we reject the deep source hypothesis in favor of the shallow source hypothesis rather than a flow of deep mediterranean overflow water along the eastern boundary rising from depth to feed the nordic seas the inflow is supplied directly by transformed north atlantic current waters from the same depth range as the inflow mediterranean overflow water is a constituent of the inflow but only through its contribution to defining the temperature salinity relationship of the interior of the subtropical gyre from which the north atlantic current draws its water rather than by direct northward advection of mediterranean outflow water via the eastern boundary undercurrent crossing from the subtropics into the subpolar domain instead the eastern boundary undercurrent wholly expels its transport of mediterranean overflow water into the eastern edge of the subtropical gyre creating the mid depth westward extending subtropical salinity plume for the lower thermocline isopycnal range of the core of the mediterranean overflow water measurements show that at the wyville thomson ridge the flow is southward and descending rather than northward and rising representing cold spillover from the faroese channels entraining warm upper ocean waters as the spillover plume descends and warms into the northern rockall trough no evidence is found in rockall trough northward of 54 n porcupine bank for direct advection of mediterranean overflow waters via an eastern boundary undercurrent extension and the very dilute mediterranean overflow waters in the trough reflect the interaction of the wyville thomson ridge plume descending into the trough from the north and lower thermocline waters delivered to the trough from the south

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

interannual variability of the altimetry derived eddy field and surface circulation in the extratropical north atlantic ocean in 1993 2001 abstract the distribution of surface eddy kinetic energy eke depicts main oceanic surface circulation features the interannual variability of eke and associated geostrophic velocity anomalies in the north atlantic ocean were analyzed to describe the variations in oceanic currents between 1993 and 2002 the sea level anomaly maps of the combined topex poseidon ers 1 2 and topex poseidon alone satellite altimetry data were used to derive eke the study focused on the areas of the gulf stream extension gs north atlantic current nac azores current ac and the northeastern rockall channel and iceland basin and northwestern irminger basin and labrador sea north atlantic the interannual variability of the altimetry derived eke field in the gs extension area reflected the meridional displacements of the gs core described in earlier studies the interannual change of eke in the ac was characterized by high values in 1993 95 followed by lower eke in subsequent years the interannual variability of

multidecadal variability of potential temperature salinity and transport in the eastern subpolar north atlantic the extended ellett line eel hydrographic section extends from scotland to iceland crossing the rockall trough hatton rockall basin and iceland basin with 61 full depth stations at a horizontal resolution of 10 to 50 km the eel samples the upper limb of the atlantic meridional overturning circulation flowing across the iceland scotland ridge into the nordic seas the rockall trough has been sampled nearly four times per year from 1975 to 1996 and the full section annually since 1996 the eel is an exceptionally long timeseries of deep ocean temperatures and salinities this study extends prior work in the rockall trough and examines for the first time 18 year records in the iceland and hatton rockall basins we quantify errors in the timeseries from two sources observational errors and aliasing the data quality and annual sampling are suitable for observing interannual to decadal variability because the variability exceeds our error estimates the upper waters of all 3 basins are cooler fresher from 1997 to 2001 warmer more saline 2001 to 2006 and cooler fresher from 2006 to 2014 a reference level for geostrophic shear is developed heuristically and by comparison with sea surface altimetry the mean northward transport in the upper waters is 6 7 3 7 sv and there is a 6 1 2 5 sv southward flow below the thermocline although the magnitude of the iceland basin overturning circulation 4 3 1 9 sv is greater than in the rockall trough 3 0 3 7 sv the variability is greater in the rockall trough we discuss the results in the context of our understanding of drivers of variability this article is protected by copyright all rights reserved

on the variability of the mediterranean outflow water in the north atlantic from 1948 to 2006 1 recent work has shown that variability in the properties and or transport of mediterranean seawaters spilling across the strait of gibraltar into the north atlantic have had little impact on the variability of mediterranean outflow water mow in the that basin over the past fifty years here we investigate whether circulation changes are the dominant source of mow variability in the north atlantic between 1948 and 2006 using a 1 3 north atlantic configuration of the hybrid coordinate ocean model combined with the marginal sea boundary condition model two simulations forced by either climatological or interannual atmospheric fields are performed the interannual simulation reproduces the observed mow variability without mediterranean seawater changes thus we conclude that mow variability in the last 60 years is a consequence of circulation changes in the north atlantic a series of simulations that separate the mechanical effect of the wind from the impact of buoyancy forcing show that mow variability can be attributed to shifts between its dominant northward and westward pathways the pathway shifts from predominantly northward between 1950 and 1975 to predominantly westward between 1975 and 1995 and finally back to northward after 1995 though these pathway shifts appear to be wind induced the property changes are caused by the combined impact of wind and buoyancy forcing on the circulation of the north atlantic

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

growth of north east atlantic cold water coral reefs and mounds during the holocene a high resolution u series and 14c chronology we investigated the holocene growth history of the mingulay reef complex a seascape of inshore cold water coral reefs off western scotland using u series and radiocarbon dating methods both chronologies revealed episodic occurrences of the reef framework forming scleractinian coral lophelia pertusa during the late holocene downcore u series dating revealed unprecedented reef growth rates of up to 12 mm a 1 with a mean rate of 3 4 mm a 1 our study highlighted a persistent hiatus in coral occurrence from 1 4 ka to modern times despite present day conditions being conducive for coral growth the growth history of the complex was punctuated at least twice by periods of reduced growth rates 1 75 2 8 ka 3 2 3 6 ka and to a lesser extent at 3 8 4 ka and at 4 2 ka timing of coral hiatuses and reduced reef growth rates at mingulay were synchronous with those occurring across the wider northern european region which suggests a close relationship between these ecosystems and large scale shifts in palaeoenvironmental regimes associated with changes to the north atlantic subpolar gyre

on the mechanisms behind decadal heat content changes in the eastern subpolar gyre historical and modern hydrographic data show substantial decadal variability in the heat content hc of the eastern subpolar north atlantic those changes are here investigated in an eddy permitting simulation orca025 g70 forced by reanalysis products for the period 1965 2004 the observed and simulated decadal signal is characterized by a strong cooling in the 1960 s and 1970 s a period of minor changes in the 1980 s and a strong warming in the 1990 s and 2000 s a heat budget calculation is performed within a box bounded by the greenland scotland sills and the cape farewell greenland portugal a25 ovide section the decadal variability of hc is mainly governed by the integrated effect of anomalous oceanic heat transport across a25 ovide hta25hta25 with local air sea heat fluxes playing a damping role the impact of temperature changes acting upon the mean oceanic circulation is shown to dominate the long term behavior of hta25hta25 through lagrangian experiments we show that temperature anomalies advected by the mean circulation across a25 ovide are mostly created by the gyre circulation anomalies upstream of a25 ovide and the associated changes in the relative proportion of cold subpolar and warm subtropical waters feeding the northern and southern branches of the north atlantic current these temperature anomalies induce large scale changes in the pycnocline slope east of reykjanes ridge along a25 ovide when the nac is relatively cold warm the main pycnocline moves upward downward in the iceland basin and on top of reykjanes ridge thereby increasing decreasing the pycnocline slope the resulting velocity anomalies lead to heat transport changes that strongly oppose the thermally driven heat transport anomalies

reversal of the 1960s to 1990s freshening trend in the northeast north atlantic and nordic seas hydrographic time series in the northeast north atlantic and nordic seas show that the freshening trend of the 1960s 1990s has completely reversed in the upper ocean since the 1990s temperature and salinity have rapidly increased in the atlantic inflow from the eastern subpolar gyre to the fram strait in 2003 2006 salinity values reached the previous maximum last observed around 1960 and temperature values exceeded records the mean properties of the atlantic inflow decrease northwards but variations seen in the eastern subpolar gyre at 57 n persist with the same amplitude and pattern along the pathways to fram strait time series correlations and extreme events suggest a time lag of 3 4 years over that distance this estimate allows predictions to be made the temperature of atlantic water in the fram strait may start to decline in 2007 or 2008 salinity a year later but both will remain high at least until 2010

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

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

interannual thermohaline changes in the northern north atlantic 1991 1996 abstract in the period 1991 1996 the woce hydrographic section a1e ar7e between greenland and ireland was repeated five times the observed thermohaline changes altered the baroclinic structure along the eastern margin of the subpolar gyre significantly between june 1995 and august 1996 an overall increase of the temperature and thickness and a decrease of the density of the subpolar mode water spmw layer were observed accompanied by an increase of its salinity east of the reykjanes ridge and a decrease of its salinity in the irminger sea the changes were most pronounced in the iceland basin where the subarctic front retreated westwards coinciding with a strong weakening of the westerlies as determined by the north atlantic oscillation they are related to a local reduction of the ekman upwelling and the ocean to atmosphere heat flux on the one hand and to the advection of anomalies from the subtropics on the other hand the eastward spreading of the different labrador sea water lsw vintages led to a corresponding cooling of the lsw in the irminger sea and in the iceland basin in the period 1991 1996 the renewal of the lsw in the rockall trough occurred more sporadically indicating that the north atlantic current nac impedes the southward spreading of lsw in the eastern atlantic the changes in 1996 seem to have also counteracted this spreading

late holocene intermediate water variability in the northeastern atlantic as recorded by deep sea corals abstract the nd isotopic composition of the aragonite skeleton of fossil deep sea corals lophelia pertusa madrepora oculata and desmophyllum dianthus located in the northeastern atlantic at water depths between 635 and 1300 m was investigated to reconstruct changes in the atlantic mid depth gyre circulation during the past millennium the coral end values varied systematically from 11 8 to 14 4 during the past 1500 years reflecting variations in seawater end and thus water mass provenance low end values end 14 occurred during the warm medieval climatic anomaly mca between 1000 ad and 1250 ad and during the most recent period 1950 ad to 2000 ad interrupted by a period of significantly higher end values 12 5 during the little ice age lia between 1350 ad and 1850 ad one long lived branching coral even recorded an abrupt systematic rise from low to high end values around 1250 ad over the course of its 10 year growth period these variations are interpreted to result from variable contributions of the subpolar and subtropical atlantic intermediate water masses which today are characterized by end values of 15 and 11 respectively the low end values observed during the warm mca and during recent times imply a strong eastward extension of the mid depth subpolar gyre spg induced by a dominant positive phase of the north atlantic oscillation nao during the lia water from the subtropical gyre stg and potentially from the mediterranean sea water msw propagated further northward as indicated by the higher coral end values this pattern suggests a negative mean state of the nao during the lia with weaker and more southerly located westerlies and a westward contraction of the spg variations in the contributions of the two gyres imply changes in the heat and salt budgets at intermediate depths during the past millennia that may have contributed to changes in the properties of north atlantic inflow into the nordic seas and thus deep water formation

implications for ocean mixing of internal wave scattering off irregular topography abstract earlier work has suggested that internal wave reflection off sloping bottoms may cause significant diapycnal mixing in the deep ocean and may also represent an important sink of internal wave energy most theories have been limited however by the representation of the bottom as an infinite plane slope in this paper the scattering of internal waves off irregular topography is studied for a few idealized bottom shapes we pay special attention to the critical case which occurs when the bottom slope dh dx locally matches the wave ray slope s analytical solutions for bottom shapes such that dh dx s at a single point are discussed for both locally convex and concave topography and are compared with the results of specular reflection theory they lead to the important conclusion that one is more likely to observe energy enhancement at the critical frequency above locally convex rather than concave topography this suggests that energy dissipation rates associated with the breaking of internal

atmospheric response to mid holocene warming in the northeastern atlantic implications for future storminess in the ireland uk region abstract there is increasing evidence that accelerated warming at high latitudes is associated with increased climate variability at mid latitudes including the frequency and intensity of storms however due to short instrumental records our understanding of how ocean atmosphere dynamics operate during warmer than present climates remains limited here we present a palaeoceanographic investigation of the transition between the middle holocene intervals of the northgrippian 8 2 4 2 ka and the late holocene interval of the meghalayan 4 2 0 ka to test the hypothesis of an eastward shift of the icelandic low under warmer than present climate scenarios reconstructions of bottom water temperatures bwt and stable oxygen isotopes mg ca 18o using the benthic foraminifera hyalinea balthica reveal warmer than present bwt of up to 2 6 0 7 c on the irish continental shelf until circa 4 2 ka the results suggest that atlantic waters of subtropical origins were more prevalent in the eastern subpolar gyre spg and on the irish continental shelf we link this oceanographic signature to an eastward shift of the icelandic low we then place our local temperature record into an extra regional context using a combination of modern observations and existing palaeo datasets which enables us to assess the impact of changing atmospheric modes on ocean atmosphere climate linkages within the north atlantic region the enhanced influence of warm subtropical atlantic waters recirculating along the boundaries of the spg under this scenario would potentially have enhanced melt rates of marine terminating glaciers on the east greenland shelf during the northgrippian

on the temporally varying northward penetration of mediterranean overflow water and eastward penetration of labrador sea water abstract historical hydrographic data in the eastern north atlantic are used to suggest a connection between the northward penetration of mediterranean overflow water mow and the location of the subpolar front the latter of which is shown to vary with the north atlantic oscillation nao during persistent high nao periods when the subpolar front moves eastward waters in the subpolar gyre essentially block the northward flowing mow preventing its entry into the subpolar gyre conversely during low nao periods the subpolar front moves westward allowing mow to penetrate past porcupine bank into the subpolar gyre the impacts of an intermittent penetration of mow into the subpolar gyre including the possible effect on water mass transformations remain to be investigated

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

reconstructions of surface ocean conditions from the northeast atlantic and nordic seas during the last millennium we undertake the first comprehensive effort to integrate north atlantic marine climate records for the last millennium highlighting some key components common within this system at a range of temporal and spatial scales in such an approach careful consideration needs to be given to the complexities inherent to the marine system composites therefore need to be hydrographically constrained and sensitive to both surface water mass variability and three dimensional ocean dynamics this study focuses on the northeast ne north atlantic ocean particularly sites influenced by the north atlantic current a composite plus regression approach is used to create an inter regional ne north atlantic reconstruction of sea surface temperature sst for the last 1000 years we highlight the loss of spatial information associated with large scale composite reconstructions of the marine environment regional reconstructions of ssts off the norwegian and icelandic margins are presented along with a larger scale reconstruction spanning the ne north atlantic the latter indicates that the medieval climate anomaly warming was most pronounced before ad 1200 with a long term cooling trend apparent after ad 1250 this trend persisted until the early 20th century while in recent decades temperatures have been similar to those inferred for the medieval climate anomaly the reconstructions are consistent with other independent records of sea surface and surface air temperatures from the region indicating that they are adequately capturing the climate dynamics of the last millennium consequently this method could potentially be used to develop large scale reconstructions of ssts for other hydrographically constrained regions

seasonal temperature variability of the neoglacial 3300 2500 bp and roman warm period 2500 1600 bp reconstructed from oxygen isotope ratios of limpet shells patella vulgata northwest scotland abstract seasonal sea surface temperature variability for the neoglacial 3300 2500 bp and roman warm period rwp 2500 1600 bp which correspond to the bronze and iron ages respectively was estimated using oxygen isotope ratios obtained from high resolution samples micromilled from radiocarbon dated archaeological limpet patella vulgata shells the coldest winter months recorded in neoglacial shells averaged 6 6 0 3 c and the warmest summer months averaged 14 7 0 4 c one neoglacial shell captured a year without a summer which may have resulted from a dust veil from a volcanic eruption in the katla volcanic system in iceland rwp shells record average winter and summer monthly temperatures of 6 3 0 1 c and 13 3 0 3 c respectively these results capture a cooling transition from the neoglacial to rwp which is further supported by earlier studies of pine history in scotland pollen type analyses in northeast scotland and european glacial events the cooling transition observed at the boundary between the neoglacial and rwp in our study also agrees with the abrupt climate deterioration at 2800 2700 bp also referred to as the subboreal subatlantic transition and therefore may have been driven by decreased solar radiation and weakened north atlantic oscillation conditions

nonlinear motions at the internal tide source 1 oceanic internal tidal wave generation is commonly modeled via interaction of a sinusoidal barotropic vertical velocity w with topography however general w above slopes are predominantly nonlinear as appears in some nonhydrostatic models here 1 2 hz sampled observations are presented from 2 84 m above the bottom mab at 1400 m at the bay of biscay continental slope fronts are observed that all propagate upslope having heights 50 mab and more or less 5 occurring at the tidal periodicity they are accompanied by o 10 min pulses of w 0 10 m s 1 w and irregular small scale waves superimposed on an asymmetric tidal signal this nonlinearity is further exemplified by variations in frontal arrival and steepness height form and is causing i internal tidal intermittency of 10 tidal periods ii nonlinear generation of internal tidal higher harmonics at the source the observations suggest internal tide generation in a broadband instead of a monochromatic beam

decadal water mass variations along 20 w in the northeastern atlantic ocean abstract water mass variations in the northeastern atlantic ocean along 20 w are analyzed with pentadal resolution over the past 15 years using data from four repeat occupations of a meridional hydrographic section running south from iceland the section was sampled in 1988 1993 1998 and 2003 the results are interpreted in the context of changes in air sea forcing ocean circulation and water properties associated with the north atlantic oscillation nao the nao index oscillated around zero from 1984 to 1988 was strongly positive from 1989 to 1995 after which it shifted to lower positive and occasionally negative values from 1996 to 2003 previously published studies suggest that after the 1995 1996 shift of the nao the subpolar gyre largely retreated to the northwest in the northeastern atlantic ocean resulting in an increasingly southeastern character of local water masses with time water property changes extending from the subpolar mode water spmw just below the seasonal pycnocline through the density range shared by mediterranean outflow water and subarctic intermediate water saiw along 20 w are consistent with changes in wind driven ocean circulation and air sea heat flux associated with shifts in the nao especially after accounting for ocean memory after periods of lower nao index the spmw is warmer saltier and lighter at these same times large increases of apparent oxygen utilization aou and potential vorticity are found at the spmw base consistent with spmw ventilation to lighter densities during lower nao index periods deeper and denser in the water column the cold fresh and dense saiw signature within the permanent pycnocline that was most strongly present in 1993 near the culmination of a period of high nao index is much reduced in 1988 and 1998 in 2003 after a prolonged period of lower nao index increasing influence of warmer saltier subtropical waters is clear within the permanent pycnocline the deep penetration of the changes implies that they are caused primarily by circulation changes resulting from nao associated wind shifts but changes in air sea heat flux could also have played a role

air sea interaction and circulation changes in the northeast atlantic the upper ocean of the rockall trough exhibits coherent interannual variations in temperature and salinity over the past 26 years with highs in the mid 1980s and late 1990s and lows in the late 1970s and early 1990s and with ranges of 0 5 c and 0 05 in salinity the origins of the interannual changes are discussed covering three potential influencing factors the propagation of anomalies developed upstream of the basin the effect of local air sea interaction and the result of changes of regional circulation bringing different water masses into the region the changes in heat and freshwater content of the upper ocean are directly compared to observed variations in air sea heat and freshwater fluxes over the period of the time series it is shown that the role of the atmosphere in locally altering the oceanic properties particularly salinity is relatively small and insufficient to explain the changes two recent hydrographic surveys are analyzed to ascertain how the distribution of water masses to the south of the basin may influence the properties of the northern rockall trough upper ocean and the results are reviewed in the context of historical analyses it is found that the critical factor in determining the properties is the varying amount of relatively cool and fresh north atlantic current water mixing with the dominant water mass the warm saline eastern north atlantic central water at the entrance to the basin variations of inflowing water masses are caused by east west changes in the location of the subpolar front and the relationship of these changes in regional circulation to the north atlantic wind stress field is discussed

late holocene 0 2 4 ka bp surface water temperature and salinity variability feni drift ne atlantic ocean abstract planktonic foraminiferal mg ca ratios and oxygen isotopic compositions of a spliced sediment record from feni drift ne atlantic ocean box core m200309 and piston core enam9606 trace late holocene sea surface temperature sst and salinity changes over the past 2400 years at this location the variability of sst and oxygen isotopic composition of seawater 18 o w reflects variable northward advection of warm and saline surface waters which appears linked to climate variability over the adjacent european continent our records reveal a general long term cooling trend superimposed on this overall trend partly higher temperatures and salinities from 180 to 560 ad and 750 to 1160 ad may be ascribed to the roman and medieval warm periods respectively subsequently our record displays highly variable surface water conditions the main little ice age sst minimum is restricted to the 15th and 16th centuries ad pervasive multidecadal to centennial scale variability throughout the sedimentary proxy records can be partly attributed to solar forcing and or variable heat extraction from the surface ocean caused by shifts in the prevailing state of the north atlantic oscillation nao high salinities in the 17th and 18th centuries are considered to reflect tropical anomalies linked to a southward shift of the intertropical convergence zone propagating across the north atlantic ocean

vivaldi 1991 a study of the formation circulation and ventilation of eastern north atlantic central water abstract a synoptic hydrographic data set comprising 32 full depth ctd casts and 2500 ctd seasoar profiles to 500 m is used to describe the s properties and circulation of central water east of the mid atlantic ridge and between 39 n and 54 n eastward transport of 20 10 6 m 3 s 1 in the north atlantic current turns entirely northwards to the west of 54 n 20 w this transport consists in the upper layers of western north atlantic water freshened at temperatures below 10 c by mixing with subarctic intermediate water northern and southern branches of the north atlantic current are well defined and both turn northwards west of 20 w a further 10 10 6 m 3 s 1 of eastern north atlantic water forms and recirculates anticyclonically to the west of spain south of the north atlantic current and north of 40 n eastern north atlantic water is most weakly stratified east of 20 w and there is clear correlation between weakly stratified pycnostads and positive salinity anomalies relative to western north atlantic water thus eastern north atlantic water is a winter mode water in which strong winter cooling has increased the density and hence also the salinity anomaly at a given temperature near the southern entrance to the rockall trough there is evidence that salinities are also increased by mediterranean water influence circulation south of the north atlantic current is complex there is no evidence for direct ventilation southwards across 40 n where water properties s potential vorticity and cfc 113 and historical data all indicate westward ventilation east of 24 w with weak southward ventilation occurring further west in the vicinity of the azores the circulation pattern suggested is remarkably similar to that proposed by helland hansen and nansen in 1926 the eastern north atlantic geophysiske publicajoner 4 1 76 with anticyclonic circulation of colder eastern north atlantic water north of 40 n meeting warmer water from south of 40 n circulating cyclonically north of the azores current the distribution of pycnostads and s properties between 20 w and 35 w north of the azores indicates alternate bands of western and eastern north atlantic water moving eastward and westward respectively including evidence for westward motion immediately south of the southern branch of the north atlantic current possibly by westward propagation of anticyclonic eddies containing deep pycnostads

interannual variability in the hydrography of the norwegian atlantic current frontal versus advective response to atmospheric forcing 1 the warm and saline inflow of the north atlantic current to the nordic seas is highly relevant for the region and the global climate north of the greenland scotland ridge the norwegian atlantic current consists of two 40 60 km wide branches situated at the slope and 150 200 km offshore respectively to interpret changes in these branches in terms of climate variability in the northern north atlantic it is important to understand their spatiotemporal response to both atmospheric forcing and advection we analyzed three decades of synoptic hydrographic observations of the branches variability with particular focus on the response to the north atlantic oscillation nao and related wind stress curl changes in the nordic seas to do so we separated the effect of fluctuating position and thickness of the branches from the variability in temperature and salinity in the spatially fluctuating cores as a rapid response to the nao we find a deflection of both branches toward the coast which is consistent with an enhanced basin wide cyclonic circulation while the immediate correlation between hydrographic properties and the nao is weak we find a significant negative correlation when the nao leads temperature and salinity by 4 6 years we attribute the overall delayed response to the advection of anomalies generated in the northwestern north atlantic through nao induced air sea interaction and changes in the position of the subpolar front

the synchronization of palaeoclimatic events in the north atlantic region during greenland stadial 3 ca 27 5 to 23 3 kyr b2k two high resolution marine sediment cores located 83 km apart in the ne atlantic have been studied md95 2006 barra fan 57 01 82 n 10 03 48 w 2120 m water depth and md04 2822 rockall trough 56 50 54 n 11 22 96 w 2344 m water depth the records are anchored to the ngrip ice core stratigraphy and gicc05 chronology by the presence of geochemically characterized fugloyarbanki tephra and further tested by radiocarbon age control replicated sea surface temperature sst records show evidence for an abrupt and short lived warming within greenland stadial gs 3 to which we tentatively assign an age of ca 25 6 24 8 kyr gicc05 b2k based on these and another marine palaeoclimate record link17 from the faroe shetland channel we propose a new three fold event stratigraphy for gs 3 within the north east atlantic region the recognition of this warming event within gs 3 in ne atlantic sst records demonstrates that such events may not readily be identified within the coldest stadials of the greenland ice cores highlights the need for carefully constructed event stratigraphies independently tested by the use of tephra isochrones and radiocarbon and illustrates pervasive millennial scale climate variability of the north atlantic region dansgaard oeschger d o events is deeply embedded in the dynamics of atlantic meridional overturning circulation amoc

reorganization of the upper ocean circulation in the mid holocene in the northeastern atlantic a micropaleontological investigation was conducted on two sediment cores from the reykjanes ridge rr core lo09 14 59 12 30 n 31 05 94 w and the faroe shetland channel fsc core hm03 133 25 60 06 55 n 06 04 18 w to document hydrographical changes of the north atlantic current nac during the holocene dinocyst and coccolith assemblages were analyzed and quantitative reconstructions of sea surface temperatures ssts and sea surface salinities ssss were conducted based on dinocyst assemblages both proxies suggest a major reorganization of surface circulation patterns in the northeastern north atlantic between 7 and 5 4 ka bp at both sites ssss before 6 5 7 ka bp were lower than during the mid late holocene suggesting dispersal of meltwater through the nac long term trends of ssts however show higher than present summer ssts on the rr from 9 3 to 6 ka bp and lower than present ssts in the fsc until ca 5 4 ka bp the contrasted sst trends at the two sites suggest that decreasing summer

observed variability of the north atlantic current in the rockall trough from 4 years of mooring measurements the rockall trough is one of the main conduits for warm atlantic water to the nordic seas ocean heat anomalies originating from the eastern subpolar gyre are known to influence arctic sea ice ex

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

seasonal and interannual changes in the north atlantic subpolar gyre from geosat and topex poseidon altimetry sea surface slopes from the altimetric satellites geosat and topex poseidon are used to calculate eddy kinetic energy of the north atlantic subpolar gyre 40 65 n 60 5 w using two years of data from each satellite december 1986 to december 1988 and october 1992 to september 1994 respectively interannual differences in the north atlantic current nac are revealed in regions of strong currents the eddies are driven by baroclinic instability of the mean flow are not seasonally varying and may therefore be used as a surrogate for the mean flow itself wind stress curl fields for the same periods show that the northward and southward shifts in the current branches across the mid atlantic ridge are related to interannual differences in the winter wind stress curl pattern when the zero in wind stress curl is well defined and wind stress is at a maximum outside the nac the eddies are driven primarily by wind stress indicated by a significant seasonality time series of eddy kinetic energy and wind stress are generated for the 4 years and the magnitude phase and significance of annual and semiannual signals are determined interannual changes in the timing of the maximum eddy kinetic energy are associated with that of the maximum wind stress with each being shifted by a month or two later or earlier throughout much of the northern north atlantic a significant annual signal in eddy kinetic energy is observed lagging the wind stress by on average 6 weeks a negligible lag is found in the region of the east greenland current and irminger sea whereas the greatest lag about 2 months is found in the labrador sea

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

response of the eastern north atlantic subpolar gyre to the north atlantic oscillation 1 the salinity changes in the subpolar gyre spg in response to the north atlantic oscillation nao are studied in idealized numerical experiments in the eastern spg anomalies of similar amplitude as those observed during the 1995 1996 shift of the nao are mainly driven by the local response to the wind stress through the set up of an anticyclonic intergyre anomaly in positive nao this anomalous circulation advects altogether i fresh cold water from the western to the eastern spg contributing there to the formation of negative salinity anomalies and ii warm saline subtropical water to the south of newfoundland forming positive anomalies there the latter are subsequently transported with the north atlantic current to the eastern spg where they could act to weaken the low salinity signal the occurrence of this signal is concomitant with the acceleration of the gyre but in contrast to earlier findings is not subject to it

relation between the wind stress curl in the north atlantic and the atlantic inflow to the nordic seas 1 in this study an isopycnic coordinate ocean model has been used to investigate the relationships between the north atlantic wind stress curl wsc and the inflow of atlantic water to the nordic seas for the period 1995 2001 there is a maximum in the correlation between the zonally averaged wsc at 55 n and the inflow with a 15 month time lag capturing a relation already found in observational data in the model this relation is linked to the mixing along the western flank of the rockall bank 56 n 15 w for the period 1995 2001 the atmospheric forcing in the northeastern north atlantic is relatively weak and the depth of the mixed layer is shallower than the sill depths of the greenland scotland ridge gsr slowly moving baroclinic disturbances caused by anomalies in the wind forcing will then be transmitted into the nordic seas where they are recorded as anomalous volume transports in the norwegian atlantic current in contrast for the pentad prior to this period the atmospheric forcing is much more intense and generates mixing well below sill depths of the gsr for all winters baroclinic disturbances forced by variations in the atmospheric forcing will then tend to follow f h contours that do not enter the nordic seas and the 15 month lagged relations between the wind and the volume transports will vanish recent observational data support this view

influence of the atlantic subpolar gyre on the thermohaline circulation during the past decade record high salinities have been observed in the atlantic inflow to the nordic seas and the arctic ocean which feeds the north atlantic thermohaline circulation thc this may counteract the observed long term increase in freshwater supply to the area and tend to stabilize the north atlantic thc here we show that the salinity of the atlantic inflow is tightly linked to the dynamics of the north atlantic subpolar gyre circulation therefore when assessing the future of the north atlantic thc it is essential that the dynamics of the subpolar gyre and its influence on the salinity are taken into account

evolution of subpolar north atlantic surface circulation since the early holocene inferred from planktic foraminifera faunal and stable isotope records abstract past changes in the surface flow regime of two main eastern north atlantic warm water pathways toward the nordic seas were reconstructed based on faunal analyses in combination with carbon and oxygen stable isotope measurements in planktic foraminifera the investigated sites in the surroundings of the faroe islands are located in the transitional area where surface waters of subpolar and subtropical origin mix before entering the arctic mediterranean in these areas large amplitude millennial variability in the characteristics of the upper water column appears modulated by changes in the intensity of the subpolar gyre circulation from 7 8 to 6 ka bp faunal records indicate a deep mixed layer which in conjunction with lighter 18 o values suggest that the inflowing atlantic waters were dominated by a relatively cooler and fresher water mass reflecting a strengthening of the subpolar gyre under conditions of enhanced positive nao like forcing and reduced meltwater input a shift in the hydrographic conditions occurred during the mid holocene centered at 5 ka bp at this time increasing upper water column stratification and the incipient differentiation of the stable isotopic signal of the iceland faroe and faroe shetland surface water masses suggest increasing influx of warmer more saline surface waters from the subtropical gyre as subpolar gyre circulation weakened the mid holocene decline in subpolar gyre strength is presumably related to a shift toward a low state of the nao like forcing associated with decreased solar irradiance later in the holocene from 4 ka bp to present the increased frequency and reduced amplitude of the surface hydrographic changes reflect corresponding fluctuations in subpolar gyre circulation these high frequency oscillations in subpolar gyre strength suggest increased surface circulation sensitivity to moderate freshwater fluxes to the labrador irminger sea basin highlighting the importance of the salinity balance in modulating subpolar gyre dynamics particularly under conditions of low nao atmospheric forcing

the water masses of the central north atlantic in 1983 84 abstract hydrographic surveys carried out in 1983 84 along both sides of the mid atlantic ridge between 24 and 53 n provide a detailed description of the well known north atlantic water masses with particular emphasis on their meridional distribution and zonal dissymetry in the upper layers the dense horizontal sampling resolves the several narrow gulf stream extensions into the ocean interior giving the image in the central water density range of a mosaic of mode waters separated by fronts at intermediate depths a vertical shear in the distributions of the mediterranean water and labrador sea water stands out both water masses having their lower part displaced southwards relative to their upper parts bottom waters containing nearly 20 percent of pure antarctic bottom water are observed at 50 n in the eastern basin in contrast with the western basin where proportions greater than 10 percent were found only south of 36 n along our section this water mass analysis also gives indications that stron

assessing variability in the size and strength of the north atlantic subpolar gyre recent studies on the size and strength of the north atlantic subpolar gyre spg offer contrasting assessments of the gyre s temporal variability studies that use empirical orthogonal function eof analyses of satellite sea surface height ssh report a rapid decline in spg size and strength since 1992 20 per decade while concurrent in situ observations report either no trend or a slight decline here we investigate this discrepancy by analyzing the size and strength of the spg with satellite ssh from 1993 to 2015 with two separate methods indirectly via eof analysis and more directly through measurements of the gyre center and boundary we define the boundary of the gyre as the largest closed contour of ssh the center as the minimum ssh and the strength as the difference between the ssh at the boundary and the center we identify a linear decline over the study period in the spg strength 5 1 per decade but find no statistically significant trend in the spg area the trend in the gyre strength is weaker than the eof based trend and is most likely below the level of detection of the in situ measurements we conclude that the variability previously identified as a sharp decline in spg circulation can be more appropriately attributed to basin wide sea level rise during the satellite altimetry period in addition we find that the properties of the eastern spg do not co vary with the spg size suggesting that spg dynamics do not control the strength of the inter gyre throughput

neodymium isotopic composition of deep sea corals from the ne atlantic implications for past hydrological changes during the holocene the nd isotopic composition of deep sea corals lophelia pertusa and madrepora oculata located on the rockall bank at a depth of 747 m was investigated to reconstruct past hydrological changes of the north atlantic the coral 3nd values ranged from 15 4 to 11 9 and demonstrate strong and systematic changes during the holocene most likely reflecting changes in seawater 3nd the 3nd record displays a general trend with a small decrease from 14 1 to 15 2 during the time interval from 9400 to 6000 yrs followed by an abrupt increase in 3nd towards more radiogenic 3nd values ranging from 13 9 to 11 9 these variations imply strong changes in the relative proportions of upper intermediate waters originating in the subtropical and subpolar atlantic which are characterised today by 3nd of 10 4 11 5 and 15 respectively therefore we suggest that the 3nd of reef frameworks forming deep sea corals reveals strong evidence of systematic mid holocene changes in mid depth subpolar gyre circulation a wider eastward extension of the subpolar gyre induced by stronger westerlies and a less intense deepwater formation in the labrador sea occurred during the early mid holocene supposedly larger amounts of freshwater from the subpolar gyre were carried eastward underneath the nordic seas similar to today a freshening of the subpolar gyre may have been offset by a reinforcement of the nac and higher salinities of water masses contributing to the nordic inflow beyond 6000 yrs a weakening of the subpolar gyre triggered an extension of saline subtropical water masses to the eastern north atlantic increasing the potential for labrador sea deep convection and reducing the contribution of subpolar atlantic waters to the basin scale re circulation at the upper intermediate depth and to the nordic seas inflow such modifications could have affected deep water convective activity in the northern hemisphere through a redistribution of freshwater from the early holocene melting of northern hemisphere ice sheets

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

diurnal and semidiurnal internal tide energy flux at a continental slope in the south china sea 1 barotropic surface and baroclinic internal tides were measured at four mooring sites during a field investigation of acoustic propagation characteristics and physical oceanography in the northern south china sea the mooring positions were in a line moving up the shallow portion of a continental slope at water depths between 350 and 85 m using time series of temperature and velocity at several depths 1 month series of semidiurnal and diurnal species internal tidal energy flux vectors were computed for three sites with a 14 day series computed for the fourth shallow site the internal tides had a temporal signature that was not in complete accord with the barotropic tides showing an enhancement of diurnal internal tides with respect to semidiurnal bathymetric slope barotropic tidal fluid particle trajectories and scale of generation site versus internal tide wavelength are investigated as possible causes of the differing response of the species

origin formation and variability of the subpolar mode water located over the reykjanes ridge the origin and formation of the subpolar mode water spmw located over the reykjanes ridge in the north atlantic ocean and the variability of its properties over the period 1966 2004 are investigated through the use of a global eddy permitting 1 4 degrees ocean sea ice model and a lagrangian analysis tool the spmw is fed by subtropical and subpolar waters advected by the branches of the north atlantic current the spmw acquires its properties when its source waters enter the winter mixed layer in the iceland basin the spmw temperature variability is mainly explained by variations of the relative contributions of the subtropical and subpolar water transports to the total transport compared to the 1966 2004 mean lower higher subtropical water relative transport contribution leads to colder warmer spmw in the early 1990s in the late 1960s and late 1990s the intensity of the winter convection in the iceland basin also influences the spmw temperature through the amount of relatively cold intermediate waters of subtropical origin integrated in the spmw layer strong convection partly explains the cold spmw of the early 1990s the large increase in the spmw temperature in the late 1990s is due to both a decrease in the winter convection and an increase in the relative transport of the subtropical waters

interannual variability of the subpolar mode water properties over the reykjanes ridge during 1990 2006 combining hydrographic data from the ovide observatoire de la variabilite interannuelle a decennale observatory of the interannual to decadal variability section greenland portugal with argo and historical ctd data over the period 1990 2006 we estimate the variability of the core properties of a variety of subpolar mode water spmw observed on the eastern flank of the reykjanes ridge this spmw acquires its core properties in the winter mixed layer along the eastern side of the reykjanes ridge we find that the february sea surface temperature along the ridge is a proxy for its core temperature the sources of this mode water are water masses advected by the mean cyclonic circulation in the iceland basin a density compensated tendency for cooling and freshening of the spmw core properties is observed in the early 1990s it stops in 1996 and is followed by an increase in temperature and salinity 1 41 c and 0 11 psu and a decrease in density 0 12 kg m 3 until at least 2003 during the entire period the data do not show any significant modification in the depth of the mode water core while they suggest that the thickness of the layer shrank the variability of the local air sea freshwater and heat fluxes cannot explain the observed salinity and temperature variations they are most likely related to the modifications of the properties of the spmw sources due to the recently evidenced changes driven by the north atlantic oscillation in the relative contributions of subtropical waters and subpolar waters in the iceland basin

simulated decadal variability of the meridional overturning circulation across the a25 ovide section andhighlatitudes 12sv 1sv 10 6 m 3 s 1 and a cellinternal to the subpolar gyre 4sv the decadal moc variability is associated with synchronized transport changes of the subtropical and subpolar inflow within the north atlantic current nac the varying strength of the moc is further related to changes in the upper horizontal transport distribution when the moc is in a strong phase early 1990s the northern branch of the nac in the iceland basin is strong while the southern branch at the rockall trough entrance is relatively weak the inverse situation holds for a persistent weak moc state 1970s contrary to the conclusions of earlier studies variability in the strength and shape of the subpolar gyre does not stand as the main driver of the changing nac structure which is largely induced by the horizontal variability of the subtropical inflow additionally the recently shown intrusion of subtropical waters into the northeastern atlantic late 1960s early 1980s and 2000s are shown to primarily occur during periods of weak moc circulation at a25 ovide

archaeological evidence for village abandonment associated with late holocene earthquakes at the northern cascadia subduction zone abstract geologic evidence suggests that great magnitude 8 or larger earthquakes or series of such earthquakes occurred six times in the past 3000 yr at the northern cascadia subduction zone the archaeological record and native oral traditions demonstrate that native villages along the adjacent coasts of southern british columbia and washington state were occasionally abandoned in the late holocene as a result of these earthquakes and associated tsunamis we infer the temporal pattern of village occupation and abandonment from midden stratigraphy and from an activity index based on the probability distributions of radiocarbon ages at 30 archaeological sites in three regions of northern cascadia deposits of probable tsunami origin are interbedded with or bound cultural strata at several sites earthquakes probably predate hiatuses in occupation or periods of low inferred human activity at many sites the strongest correlation between earthquake incidence and site abandonment occurs in the nootka sound region effects of tsunamis vary with village location coastal morphology and late holocene sea level history