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

the link between the north atlantic oscillation and arctic sea ice export through fram strait abstract recently hilmer and jung have shown that the wintertime link between the north atlantic oscillation nao and the sea ice export through fram strait changed from zero correlation 1958 77 to about 0 7 1978 97 during the last four decades in the current study the authors focus on the question of how the two phenomena are linked in a long term context during wintertime december march this is done on a statistical basis using data from a century scale control integration of the coupled general circulation model echam4 opyc3 along with historical sea level pressure data for the period 1908 97 from the results of this study there is less indication that a significant link on interannual and decadal timescales between the nao and the sea ice export through fram strait is a characteristic property of the climate system at least under present day climate conditions this missing link can be explained by a vanishing net impact of the nao on sea ice thickness as well as sea ice drift near fram st

on the role of the nao in the recent northeastern atlantic arctic warming 1 studies such as those by zhang et al 1998 and peterson et al 2003 suggest that the northeastern atlantic arctic warmed in the early 1990s and that regional sea level pressure slp variations and the nao may be responsible sea surface temperature changes in fram strait and the barents sea depend respectively on slp variations over the barents sea and norwegian sea since winter 1972 slp over the barents and norwegian seas has been unusually low during nao winters little pressure field change occurred during nao winters or around the denmark strait the normal location of the icelandic low simultaneously the nao mode became highly persistent on a month to month basis throughout the nao winters and ultimately throughout all seasons during a multiyear episode in which the arctic reached peak warming a similar nao persistence episode is shown to have occurred from 1920 1925 during another notable arctic warming event

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

hysteresis behavior of the atlantic ocean circulation identified in observational data abstract on the basis of the multidecadal component of a fram strait sea ice export reconstruction and on a sea surface temperature proxy for changes in the ocean circulation a bifurcation diagram for two cycles of the atlantic ocean multidecadal oscillation is constructed it suggests a hysteresis behavior that is consistent with nonlinear convective adjustment to changes in deep water formation in the north atlantic and with the meridional overturning circulation bistability associated with two distinct configurations of the north atlantic subpolar gyre simulated in response to idealized carbon dioxide increase the nonlinear dynamics of the atlantic ocean circulation emphasized here on the basis of observational data adds to the hysteresis behavior shown in theoretical and numerical studies

a simulation of thermohaline effects of a great salinity anomaly abstract model simulations of an idealistic great salinity anomaly gsa demonstrate that variability in the sea ice export from the arctic when concentrated to short pulses can have a large influence on the meridional heat transport and can lead to an altered overturning state one single freshwater disturbance resulting from excess ice export as in 1968 can disrupt the deep mixing process the critical condition for a large oceanic response is defined by the intensity duration and timing of the ice pulse in particular as it exits through the denmark strait a recovery from this event takes several years for advection and diffusion to remove the salinity anomaly concurrently the influence of the gsa propagates to the subtropics via the boundary currents and baroclinic adjustment as a result of this adjustment there are large up to 20 changes in the strength of the overturning cell and in the meridional heat transport in the subtropics and subpolar areas simulations show a temperature sali

two circulation regimes of the wind driven arctic ocean the major goal of this paper is to demonstrate the existence in the arctic ocean of two regimes of wind forced circulation we simulated the vertically averaged currents sea level heights and ice drift in the arctic ocean from 1946 to 1993 using a two dimensional wind forced barotropic model that includes frictional coupling between the ocean and ice the model has a spatial resolution of 55 5 km and is driven by winds river runoff and an imposed but realistic sea level slope between the pacific and the atlantic oceans there is a good agreement between velocities from observed buoy motions and velocities of modeled ice drift even though the model lacks ocean baroclinicity and ice thermodynamics the results indicate that wind driven motion in the central arctic alternates between anticyclonic and cyclonic circulation with each regime persisting for 5 7 years based upon our analysis of the modeled sea level and ice motion anticyclonic wind driven motion in the central arctic appeared during 1946 1952 1958 1963 1972 1979 and 1984 1988 and cyclonic motion appeared during 1953 1957 1964 1971 1980 1983 and 1989 1993 shifts from one regime to another are forced by changes in the location and intensity of the icelandic low and the siberian high the two regimes may help explain the significant basin scale changes in the arctic s temperature and salinity structure observed recently the great salinity anomaly and the variability of ice conditions in the arctic ocean

source to sink statistical identification of regional variations in the mineralogy of surface sediments in the western nordic seas 58 n 75 n 10 w 40 w the non clay and clay mineralogies of the 2 mm sediment fraction from 157 seafloor samples in the western nordic seas is calculated by quantitative x ray diffraction analysis our sample coverage includes the iceland shelf the ice impacted east greenland margin and the greenland iceland and irminger seas the bedrock geology of source areas includes precambrian basement rocks devonian red beds and younger marine and fluvial sediments and large outcrops of early tertiary to recent flood basalts and other volcanic facies sediment erosion and transport in the area are associated with ice sea ice and icebergs and glacial meltwater and fluvial sediment plumes we use principal component analysis fuzzy k means clustering and discriminant function analysis to reduce the original 31 minerals 157 sites matrix to more manageable 5 regional coherent clusters of sites which are well discriminated by the weight of six minerals namely quartz pyroxene illites magnetite and maghemite amorphous silica e g glass and muscovite the close spatial relationship between bedrock geology and discrete cluster membership stresses the importance of this variable and indicates that far distant sediment transport by sea ice icebergs or other mechanisms although occurring does not radically change the mineral composition of present day sea floor sediments our improved knowledge of the regional mineral assemblages allows for tracking distinct eastern greenland and icelandic sources

a mechanism of decadal variability of the sea ice volume in the northern hemisphere a long term simulation performed with a coarse resolution global atmosphere ocean sea ice model displays strong decadal variability of the sea ice volume in the northern hemisphere with a significant peak at about 15 18 years this model results from the coupling of ecbilt a spectral t21 3 level quasi geostrophic atmospheric model and clio a sea ice ocean general circulation model first the mechanism underlying the variability of ice volume in the model was studied by performing correlation analyses between the simulated variables in a second step a series of additional sensitivity experiments was performed in order to illustrate the role of specific physical processes this as allowed us to identify a feedback loop in the ice ocean system which proceeds as follows an increase in at tic sea ice volume induces an increase in the salinity there this salinity anomaly is transported to the greenland sea where it promotes convective activity this warms up the surface oceanic layer and the atmosphere in winter and induces a decrease of the ice volume completing half a cycle the changes in ice volume are driven by a geopotential height pattern characterised by centres of action of opposite signs over greenland and the barents kara central arctic area thermodynamic feedback between the ice and the atmosphere appear also to be very important for the persistence of the oscillation the dynamical response of the atmosphere to sea ice and temperature anomalies at surface plays a smaller role

satellite archives reveal abrupt changes in behavior of helheim glacier southeast greenland rapid changes in helheim glacier and other greenland outlet glaciers since 2000 are well known but knowledge on earlier decades is fragmentary here we exploit the satellite image archives to produce and analyze a monthly to seasonal record of helheim glacier front position 1980 2011 statistical analysis identifies decadal periods with abrupt changes in variability and mean the record also reveals evidence of volatile advance retreat behavior in the 1980s in one of several cases of large amplitude subannual changes the glacier front surged forward in 1984 85 advancing 6 km within a few months surpassing its little ice age maximum position and afterward retreated 5 km within a few weeks these findings challenge the prevailing view of front position stability in the decades before the multi year retreat in the early 2000s cold conditions including rigid ice melange appear to be a factor in the high amplitude seasonal advances in the 1980s however the magnitude and abruptness of the changes in the record cannot be explained solely as a climatic response such that glacio dynamics must be invoked further the volatile advance retreat behavior in the cold 1980s resulted in increased dynamic ice loss complicating the interpretation of increased calving activity as a response to warming

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

fram strait ice export during the nineteenth and twentieth centuries reconstructed from a multiyear sea ice index from southwestern greenland abstract historical observations of multiyear ice called storis in the southwest greenland waters exist from the period 1820 2000 obtained from ship logbooks and ice charts it is argued that this ice originates in the arctic ocean and has traveled via the fram strait southward along the greenland coast in the east greenland current and around the southern tip of greenland therefore it is hypothesized that these observations can be used as proxies for reconstructing the fram strait ice export on an annual basis an index describing the storis extent is extracted from the observations and a linear statistical model formulated relating this index to the fram strait ice export the model is calibrated using ice export values from a hindcast study with a coupled ocean ice model over the period 1949 98 subsequently the model is used to reconstruct the fram strait annual ice export in the period 1820 2000 the model has significant skill calculated on independent data based on this reconstruction

a comparison between multiproxy and historical data ad 1990 1840 of drift ice conditions on the east greenland shelf 66 n the reduction in sea ice along the se greenland coast during the last century has severely impacted ice rafting to this area in order to reconstruct ice rafting and oceanographic conditions in the area of denmark strait during the last 150 years we conducted a multiproxy study on three short 20 cm sediment cores from outer kangerdlugssuaq trough 300 m water depth the proxy based data obtained have been compared with historical and instrumental data to gain a better understanding of the ice sheet ocean interactions in the area a robust chronology has been developed based on 210pb and 137cs measurements on core po175gkc 9 66 2 n 32 w and expanded to the two adjacent cores based on correlations between calcite weight percent records our proxy records include sea ice and phytoplankton biomarkers and a variety of mineralogical determinations based on the 2 mm sediment fraction including identification with quantitative x ray diffraction ice rafted debris counts on the 63 150 m sand fraction

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

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

investigations of the mass balance of the southeastern ronne ice shelf antarctica data from the filchner v campaign were used to investigate the mass balance conditions in the southeastern ronne ice shelf ris antarctica radio echo sounding and seismic measurements over this area show a maximum ice thickness of 2000 m close to the grounding line of foundation ice stream the measurements also revealed that the position of this grounding line is 40 km further south than previously thought new mass flux calculations result in an estimate or 51 km 3 a 1 for the ice stream transport from the ice sheet into the eastern ice shelf the mollereisstrom mes west of foundation ice stream shows a maximum ice thickness of 1100 1200 m in the grounding line area and a mass flux of 23 km 3 a 1 assuming steady state conditions mass balance calculations based on the new data result in a mean melt rate of about 1 m a 1 at the ice shelf base for the entire southeastern part of the ris the melt rate in the grounding line area of foundation ice stream exceeds 9 m a 1 in contrast other ice streams draining into the filchner ronne ice shelf show maximum melt rates from 1 2 m a 1 mes to 4 m a 1 rutford ice stream our calculations indicate that nearly all of the ice deposited in the drainage area of the eastern ris on the ice sheet does not reach the ice shelf front as original meteoric ice but is melted at the ice shelf base

has arctic sea ice rapidly thinned abstract reports based on submarine sonar data have suggested arctic sea ice has thinned nearly by half in recent decades such rapid thinning is a concern for detection of global change and for arctic regional impacts including atmospheric time series ocean currents and river runoff into an ocean ice snow model show that the inferred rapid thinning was unlikely the problem stems from undersampling varying winds that readily redistribute arctic ice create a recurring pattern whereby ice shifts between the central arctic and peripheral regions especially in the canadian sector timing and tracks of the submarine surveys missed this dominant mode of variability although model derived overall thinning from the 1960s to the 1990s was less than hitherto supposed there is also indication of accelerated thinning during the early mid 1990s

a hemispheric mechanism for the atlantic multidecadal oscillation abstract the physical processes associated with the 70 yr period climate mode known as the atlantic multidecadal oscillation amo are examined based on analyses of observational data a deterministic mechanism relying on atmosphere ocean sea ice interactions is proposed for the amo variations in the thermohaline circulation are reflected as uniform sea surface temperature anomalies in the north atlantic these anomalies are associated with a hemispheric wavenumber 1 sea level pressure slp structure in the atmosphere that is amplified through atmosphere ocean interactions in the north pacific the slp pattern and its associated wind field affect the sea ice export through fram strait the freshwater balance in the northern north atlantic and consequently the strength of the large scale ocean circulation it generates sea surface temperature anomalies with opposite signs in the north atlantic and completes a negative feedback the authors find that the time scale of the cycle is associated with the

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

monitoring ice thickness in fram strait time series of ice thickness in fram strait are evaluated together with ice drift for estimation of the ice flux from the arctic ocean ice draft was measured from moored sonars every 4 min suggesting a nominal sampling interval of 30 m on the basis of these data the annual cycle of many statistics can be resolved the modal ice thickness shows a maximum of 3 15 m in may and a minimum in september of 2 43 m indicating an annual variation range of 0 72 m this compares with model results comprehensive drillings and most of the submarine observations during the last 2 3 decades indicating no significant long term ice thickness change this is also concurrent with the lack of significant temperature changes in the arctic ocean during the same period the mean ice thickness in the central core of the ice stream shows an annual amplitude of 1 m with a minimum in september of 2 25 m and a maximum in april may of 3 25 m the mean thickness of ice only open water excluded is 3 27 m and compares with 3 29 m which is the mean thickness of ice only from 17 submarine tracks in the arctic ocean 1960 1982 the mean annual ice export which is equal to the mean annual net production of ice in the arctic ocean is 2850 km 3 yr 1 for the period 1990 1996 this efflux shows significant variations from year to year with a minimum in 1990 1991 of 2050 km 3 yr 1 and a maximum in 1994 1995 of 4700 km 3 yr 1 this significant variation of nearly 130 is mainly caused by an increased atmospheric forcing and to a lesser degree by an increase in the annual mean ice thickness of 20 over the same period

solar forcing as an important trigger for west greenland sea ice variability over the last millennium abstract arctic sea ice represents an important component of the climate system and the present reduction of sea ice in the arctic is of major concern despite its importance little is known about past changes in sea ice cover and the underlying forcing mechanisms here we use diatom assemblages from a marine sediment core collected from the west greenland shelf to reconstruct changes in sea ice cover over the last millennium the proxy based reconstruction demonstrates a generally strong link between changes in sea ice cover and solar variability during the last millennium weaker or stronger solar forcing may result in the increase or decrease in sea ice cover west of greenland in addition model simulations show that variations in solar activity not only affect local sea ice formation but also control the sea ice transport from the arctic ocean through a sea ice ocean atmosphere feedback mechanism the role of solar forcing however appears to have been more ambiguous during an interval around ad 1500 after the transition from the medieval climate anomaly to the little ice age likely to be driven by a range of factors

variability of fram strait ice flux and north atlantic oscillation we estimate the winter sea ice export through the fram strait using ice motion from satellite passive microwave data sea ice motion october may is obtained by tracking the displacement of common features in sequential 85 and 37 ghz brightness temperature fields the average winter area flux over the 18 year record 1978 1996 is 670 000 km2 7 of the area of the arctic ocean the winter area flux ranges from a minimum of 450 000 km2 in 1984 to a maximum of 906 000 km2 in 1995 the daily monthly and interannual variabilities of the ice area flux are high there is an upward trend in the ice area flux over the 18 year record the average winter volume flux over the winters of october 1990 through may 1995 is 1745 km3 ranging from a low of 1375 km3 in the 1990 flux to a high of 2791 km3 in 1994 the sea level pressure gradient across the fram strait explains more than 80 of the variance in the ice flux over the 18 year record we use the coefficients from the regression of the time series of area flux versus pressure gradient across the fram strait and ice thickness data to estimate the summer area and volume flux the average 12 month area flux and volume flux are 919 000 km2 and 2366 km3 we find a significant correlation r 0 86 between the area flux and positive phases of the north atlantic oscillation nao index over the months of december march correlation between our 5 years of volume flux estimates and the nao index gives r 0 56 during the high nao years a more intense icelandic low increases the gradient in the sea level pressure by almost 1 mbar across the fram strait thus increasing the atmospheric forcing on ice transport correlation is reduced during the negative nao years because of decreased dominance of this large scale atmospheric pattern on the sea level pressure gradient across the fram strait

evidence for a recent change in the link between the north atlantic oscillation and arctic sea ice export evidence for a recent change in the link between the north atlantic oscillation nao and arctic sea ice export through fram strait during wintertime djfm is presented from the analysis of simulated arctic sea ice and observations for the period 1958 1997 whereas no correlation between the two time series is found from 1958 to 1977 r 0 1 the correlation increased significantly thereafter r 0 7 1978 1997 the increased coherency between the nao and arctic sea ice export through fram strait during the last two decades resulted from anomalous meridional wind components near fram strait which were associated with the more easterly position of the nao s centers of interannual variability compared to 1958 1977

sea ice transport a highly variable link between arctic and north atlantic the variability of the ice volume flux into the northeast atlantic is investigated with an optimized dynamic thermodynamic sea ice model using 40 years 1958 1997 of atmospheric forcing fields derived from the ncep ncar reanalysis project the simulated sea ice export from the arctic exhibits considerable interannual to decadal variability and is primarily a linear response to sea level pressure anomalies over greenland and over the barents and kara seas our model results suggest that ice export anomalies such as in 1968 which supposedly caused the so called great salinity anomaly in the northern north atlantic are not unique but rather frequent events as part of the variability of the arctic climate system

paleoenvironments during younger dryas early holocene retreat of the greenland ice sheet from outer disko trough central west greenland paleoenvironments during the late younger dryas through early holocene retreat of the greenland ice sheet from the outer shelf in the disko trough system of central west greenland were investigated via lithofacies foraminifera dinocysts and sediment provenance analyses in radiocarbon dated sediment cores from the upper slope jr175 vc35 and outer shelf jr175 vc20 and hu2008029 070cc core data show that the ice margin retreated rapidly from the outer shelf by calving beginning by 12 2k cal a bp under cold paleoceano graphic conditions with up to 11 months of sea ice ice retreat into disko bugt was well underway by 10 9k cal a bp enhanced ice sheet ablation in disko bugt and elsewhere along the west greenland coast is inferred from cold glacial marine conditions associated with high sedimentation rates between 10 9 and 9 5k cal a bp on the outer shelf glacial marine conditions are recorded on the outer shelf until 7 8k cal a bp detrital carbonate bearing sediments rich in 2 mm clasts deposited between 11 6 and 10 6k cal a bp indicate that icebergs calved from northern baffin bay ice margins were melting and releasing sediments along west greenland while the greenland ice sheet margin was retreating into disko bugt copyright 2013 john wiley sons ltd

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

simulation of the interannual variability of the wind driven arctic sea ice cover during 1958 1998 a thermodynamic dynamic sea ice model based on a granular material rheology developed by tremblay and mysak is used to study the interannual variability of the arctic sea ice cover during the 41 year period 1958 98 monthly wind stress forcing derived from the national centers for environmental prediction ncep reanalysis data is used to produce the year to year variations in the sea ice circulation and thickness we focus on analyzing the variability of the sea ice volume in the arctic basin and the subsequent changes in sea ice export into the greenland sea via fram strait the relative contributions of the fram strait sea ice thickness and velocity anomalies to the sea ice export anomalies are first investigated and the former is shown to be particularly important during several large export events the sea ice export anomalies for these events are next linked to prior sea ice volume anomalies in the arctic basin the origin and evolution of the sea ice volume anomalies are then related to the sea ice circulation and atmospheric forcing patterns in the arctic large sea ice export anomalies are generally preceded by large volume anomalies formed along the east siberian coast due to anomalous winds which occur when the arctic high is centered closer than usual to this coastal area when the center of this high relocates over the beaufort sea and the icelandic low extends far into the arctic basin the ice volume anomalies are transported to the fram strait region via the transpolar drift stream finally the link between the sea ice export and the north atlantic oscillation nao index is briefly discussed the overall results from this study show that the arctic basin and its ice volume anomalies must be considered in order to fully understand the export through fram strait

the interpretation of the icelandic sea ice record the representativeness of the icelandic sea ice record one of the longest climate indicators for the north atlantic sector is assessed by statistical analysis correlation of the sea ice index with ice concentration data for the adjacent seas suggests that the index is a reasonable measure of the ice cover of a large area of the northern north atlantic sector associations with surface air temperature and sea level pressure are strong but regional rather than hemispheric in scale the immediate causes of the variable advance of ice onto the icelandic coasts are clear in the analysis of the atmospheric circulation data severe ice conditions are associated with enhanced anticyclonicity in the icelandic region and stronger northerly and westerly winds over the greenland sea it is concluded that the icelandic index is a useful indicator of the state of the atmospheric flow north of iceland and of the character of the east greenland current one of the major avenues of meridional heat exchange in the climate system

a well verified multiproxy reconstruction of the winter north atlantic oscillation index since a d 1400 abstract a new well verified multiproxy reconstruction of the winter north atlantic oscillation nao index is described that can be used to examine the variability of the nao prior to twentieth century greenhouse forcing it covers the period a d 1400 1979 and successfully verifies against independent estimates of the winter nao index from european instrumental and noninstrumental data as far back as 1500 the best validation occurs at interannual timescales and the weakest at multidecadal periods this result is a significant improvement over previous proxy based estimates which often failed to verify prior to 1850 and is related to the use of an extended reconstruction model calibration period that reduced an apparent bias in selected proxies associated with the impact of anomalous twentieth century winter nao variability on climate teleconnections over north atlantic sector land areas although twentieth century nao variability is somewhat unusual comparable periods of persistent positive phase

late holocene paleoceanography and climate variability over the mackenzie slope beaufort sea canadian arctic abstract late holocene paleoceanography and climate variability of the southeastern beaufort sea canadian arctic have been investigated on the basis of sedimentary cores collected over the mackenzie slope piston trigger and box cores were sampled at station 803 in 2004 aboard the ccgs amundsen at 218 m water depth the chronology of the piston core is constrained by 4 ams 14 c dates as the sedimentation rate in the box core is assessed from 210 pb data we obtain a continuous composite sequence covering the last 4600 years with a sedimentation rate of 140 cm kyr 1 transfer functions modern analogue technique based on dinoflagellate cyst dinocyst assemblages were used to reconstruct the evolution of sea surface conditions over the time period covered by the cores palynological data reveal that dinocyst assemblages are dominated by operculodinium centrocarpum sensu lato mean of 43 3 throughout the core with the accompanying taxa brigantedinium spp 19 6 islandinium minutum 15 6 and cysts of pentapharsodinium dalei 13 7 four zones have been established on the basis of dinocyst relative abundances dinocyst assemblage zone 1 d1 from 4600 to 2700 cal years bp is dominated by o centrocarpum mean of 49 0 in zone d2 2700 1500 cal years bp the relative abundances of o centrocarpum decrease 34 4 in favour of the opportunistic heterotrophic taxa brigantedinium spp 28 8 and cysts of polykrikos sp var arctic quadratus 2 8 dinocyst zone d3 1500 30 cal years bp or 450 1920 ad is characterised by the high relative abundance of the peridinioid taxa i minutum 19 9 the last zone d4 spanning from 1920 to 2004 ad is again dominated by o centrocarpum 44 5 and shows low relative abundances of brigantedinium spp and cf echinidinium karaense quantitative reconstructions of past sea surface parameters august sea surface temperature sst august sea surface salinity sss and duration of sea ice cover indicate relatively stable conditions over the last 4 6 kyr with episodic cooling events sst of 1 5 c below the modern value of 6 c that took place between 700 and 1820 ad we associate the last and the longest of these cooling events 1560 1820 ad with the little ice age reconstructed sss shows decadal oscillations since 1920 ad that we tentatively associate with the accumulation of freshwater by the beaufort gyre and the subsequent great salinity anomalies our data suggest that similar salinity anomalies could have occurred ca 1860 and 1790 ad stable isotopic data show a slight increase in 13 c values from 27 1 at the base to 25 8 at the top over the last 4 6 kyr that we associate with the gradual increase in atmospheric co 2 concentration as recorded by antarctic ice cores variations in the 15 n profile suggest variations in pacific water influence from 4600 to 1300 cal years bp associated with centennial scale shifts of the arctic oscillation phases

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

a record of holocene sea ice variability off west greenland and its potential forcing factors abstract we present a reconstruction of holocene sea ice variability from sediment core ga306 gc3 from the holsteinsborg dyb off west greenland which provides an index of palaeoceanographic and palaeoenvironmental conditions within this climatically sensitive region during the last 6700 yr the reconstructed sea ice record combined with previously published proxy data suggests that relatively warm conditions with reduced sea ice extent prior to 5000 cal yr bp were associated with the holocene thermal maximum subsequent cooling and extensive sea ice cover between ca 5000 and 4000 cal yr bp was followed by even colder conditions and persistent sea ice cover during the neoglacial cooling phase particularly after ca 1500 cal yr bp there is a positive correlation between west greenland sea ice cover and solar activity over the past 5000 yr but the correlation is much weaker prior to 5000 cal yr bp in addition there is a strong link between west greenland sea ice and changes in the abundance of arctic benthic foraminifera species related to different water masses of the west greenland current during the entire interval even prior to 5000 cal yr bp our findings indicate that sea ice variability off west greenland was driven not only by solar activity but also by ocean circulation the strength of cold polar water from the east greenland current and warm atlantic water from the irminger current

a freshwater jet on the east greenland shelf in august 1997 rrs discovery cruise 230 world ocean circulation experiment woce section a25 ran a hydrographic section into cape farewell on the southern tip of greenland the closest approach to the shore was 2 nm in a water depth of 160 m over the east greenland shelf analysis of the hydrographic data conductivity temperature depth ctd vessel mounted acoustic doppler current profiler and thermosalinograph has revealed a current flowing southwestward 15 km wide 100 m deep and centered 10 km offshore we believe it to be driven by meltwater runoff from greenland this feature which we call the east greenland coastal current egcc carries a little less than 1 sv 106 m3 s 1 with peak current speeds of 1 m s 1 at the surface the center of the egcc lies on a salinity front with maximum salinity contrast 4 practical salinity units psu between coast and shelf break and between surface and bottom a spot value of freshwater transport is 0 06 sv 1800 km3 yr 1 which is equivalent to 30 of the arctic freshwater gain the presence of the egcc and its continuity up the east greenland coast as far as denmark strait is confirmed in satellite sea surface temperature images and surface drifter tracks we estimate the sensitivity of its freshwater flux to changes in melt season mean surface air temperature to be 25 per 1 c

thinning of the arctic sea ice cover comparison of sea ice draft data acquired on submarine cruises between 1993 and 1997 with similar data acquired between 1958 and 1976 indicates that the mean ice draft at the end of the melt season has decreased by about 1 3 m in most of the deep water portion of the arctic ocean from 3 1 m in 1958 1976 to 1 8 m in the 1990s the decrease is greater in the central and eastern arctic than in the beaufort and chukchi seas preliminary evidence is that the ice cover has continued to become thinner in some regions during the 1990s

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

further evidence of ice thinning in the arctic ocean a sea ice thickness profile obtained in september 1996 from the eurasian basin of the arctic ocean between fram strait and the north pole was compared with a profile obtained in the same region in september october 1976 a decline in mean ice draft of 43 was observed over the 20 year interval in agreement with changes observed in other parts of the arctic ocean by rothrock et al 1999

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

climatic and environmental changes during the middle to late holocene in southern south america a sclerochronological approach using the bivalve retrotapes exalbidus dillwyn from the beagle channel abstract little is known about the effects of holocene climate variability on marine environments and their biota in southern south america fossil shells of the aragonitic bivalve retrotapes exalbidus dillwyn offer the possibility of investigating climate variability and particularly the seasonal dynamics of sea water temperature in the beagle channel during different parts of the middle to late holocene we compared three specimens of different geological age determined by 14 c i e 5190 bp 3839 bp and 431 bp these shells respectively refer to a cooling period at ca 5000 bp a climate optimum at ca 4000 bp and a further cooling at ca 500 bp all three shells showed clear annual growth bands with a distinct intra annual 18 o cycle 18 o ranges clearly indicate higher summer temperatures in the 3839 bp shell 1 53 1 16 compared with the 5190 bp shell 1 29 0 72 and the 431 bp shell 1 55 0 44 which correspond to maximum ssts of 17 73 c 9 61 c and 10 81 c respectively apparently r exalbidus shells are suitable bioarchives that allow comparing seasonal patterns through the holocene thus constituting another proxy for evaluating paleoclimatic and paleoenvironmental changes in this region

evolution of the freshwater coastal current at the southern tip of greenland abstractshipboard hydrographic and velocity measurements collected in summer 2014 are used to study the evolution of the freshwater coastal current in southern greenland as it encounters cape farew

subtropical coral reveals abrupt early twentieth century freshening in the western north pacific ocean instrumental climate observations provide robust records of global land and ocean temperatures during the twentieth century unlike for temperature continuous salinity observations in the surface ocean are scarce prior to 1970 and the magnitude of salinity changes during the twentieth century is largely unknown surface ocean salinity is a major component in climate dynamics as it influences ocean circulation and water mass formation here we present an annually resolved reconstruction of salinity variations in the surface waters of the western subtropical north pacific ocean since 1873 based on bimonthly records of 18o sr ca and u ca in a coral from the ogasawara islands the reconstruction indicates that an abrupt regime shift toward fresher surface ocean conditions occurred between 1905 and 1910 observational atmospheric data suggest that the abrupt freshening was associated with a weakening of the winds that drive the kuroshio current system and the associated subtropical gyre circulation we note that the abrupt early twentieth century freshening in the western subtropical north pacific precedes abrupt climate change in the northern north atlantic by a few years the potential for abrupt regime shifts in surface ocean salinity should be considered in climate predictions for the coming decades

holocene variations in mineral and grain size composition along the east greenland glaciated margin ca 67 70 n local versus long distance sediment transport quantitative x ray diffraction qxrd analysis of the 2 mm sediment fraction from surface sea floor samples and marine sediment cores that span the last 10 12 cal ka bp are used to describe spatial and temporal variations in non clay mineral compositions for an area between kangerlussuaq trough and scoresby sund 67 70 n east greenland bedrock consists primarily of an early tertiary alkaline complex with high weight of pyroxene and plagioclase farther inland and to the north the bedrock is dominantly felsic with a high fraction of quartz and potassium feldspars principal component pc analysis of the non clay sediment compositions indicates the importance of quartz and pyroxene as compositional end members with an abrupt shift from quartz and k feldspar dominated sediments north of scoresby sund to sediments rich in pyroxene and plagioclase feldspars offshore from the early tertiary basaltic outcrop coarse 2 mm or 1 mm ice rafted sediments are largely absent from the trough sediments between 8 and 5 cal ka bp but then increase in the last 4 cal ka bp compositional unmixing of the sediments in grivel basin and kangerlussuaq trough indicate the dominance of local over long distance sediment sources with pulses of sediment from tidewater glaciers in kangerlussuaq and nansen fjords reaching the inner shelf during the neoglaciation the change in ird is more dramatic in the sediment grain size proxies than in the quartz wt forty to seventy percent of the variance in the quartz records from either side of denmark strait is explained by low frequency trends but the data from the grivel basin east greenland are distinctly different with an approximate 2500 yr periodicity

global scale modes of surface temperature variability on interannual to century timescales using 100 years of global temperature anomaly data we have performed a singular value decomposition of temperature variations in narrow frequency bands to isolate coherent spatio temporal modes of global climate variability statistical significance is determined from confidence limits obtained by monte carlo simulations secular variance is dominated by a globally coherent trend with nearly all grid points warming in phase at varying amplitude a smaller but significant share of the secular variance corresponds to a pattern dominated by warming and subsequent cooling in the high latitude north atlantic with a roughly centennial timescale spatial patterns associated with significant peaks in variance within a broad period range from 2 8 to 5 7 years exhibit characteristic el nino southern oscillation enso patterns a recent transition to a regime of higher enso frequency is suggested by our analysis an interdecadal mode in the 15 to 18 years period range appears to represent long term enso variability this mode has a sizeable projection onto global average temperature and accounts for much of the anomalous global warmth of the 1980s a quasi biennial mode centered near 2 2 years period and a mode centered at 7 to 8 years period both exhibit predominantly a north atlantic oscillation nao temperature pattern a potentially significant decadal mode centered on 11 to 12 years period also exhibits an nao temperature pattern and may be modulated by the century scale north atlantic variability

surface sea floor and near surface box cores sediment mineralogy in baffin bay as a key to sediment provenance and ice sheet variations to better understand the glacial history of the ice sheets surrounding baffin bay and to provide information on sediment pathways samples from 82 seafloor grabs and core tops and from seven box cores were subjected to quantitative x ray diffraction weight percent wt analysis of the 2000 m all show an abrupt drop in calcite wt post 5 cal ka bp following a major peak in detrital carbonate mainly dolomite this dolomite rich detrital carbonate dc event in jr175bc06 is possibly coeval with the younger dryas cold event four possible glacial sourced end mem bers were employed in a compositional unmixing algorithm to gain insight into down core changes in sediment provenance at the deep central basin estimates of the rates of sediment accumulation in the central basin are only in the range of 2 to 4 cm cal ka surprisingly low given the glaciated nature of the surrounding land

sea ice and marine climate variability for nw iceland denmark strait over the last 2000 cal yr bp md99 2263 is a 46 cm box core collected from djupall a trough that cuts across the nw iceland shelf and ends above denmark strait we provide a multiproxy record that documents changes in the regional marine climate over the last 1700 yr the depth age model is based on seven calibrated radiocarbon dates on mollusk shells and on 210pb and 137cs sediment accumulation rates were variable 0 2 0 8 mm yr but increased dramatically ad 1500 grain size magnetic properties quantitative mineral composition of the 2 mm sediment fraction benthic foraminiferal composition benthic and planktic 18o ratios and abundances fluxes of the sea ice biomarker ip25 were determined to better compare the various proxies 12 of the critical climate proxies were co ordinated into 100 yr sample time series which were examined by principal component analysis the 1st axis explained 49 of the variance and the 2nd axis explained an additional 17 the variables most strongly associated with the 1st axis were sediment pr

a signal of persistent atlantic multidecadal variability in arctic sea ice satellite data suggest an arctic sea ice climate system in rapid transformation yet its long term natural modes of variability are poorly known here we integrate and synthesize a set of multicentury historical records of atlantic arctic sea ice supplemented with high resolution paleoproxy records each reflecting primarily winter spring sea ice conditions we establish a signal of pervasive and persistent multidecadal 60 90 year fluctuations that is most pronounced in the greenland sea and weakens further away covariability between sea ice and atlantic multidecadal variability as represented by the atlantic multidecadal oscillation amo index is evident during the instrumental record including an abrupt change at the onset of the early twentieth century warming similar covariability through previous centuries is evident from comparison of the longest historical sea ice records and paleoproxy reconstructions of sea ice and the amo this observational evidence supports recent modeling studies that have suggested that arctic sea ice is intrinsically linked to atlantic multidecadal variability this may have implications for understanding the recent negative trend in arctic winter sea ice extent although because the losses have been greater in summer other processes and feedbacks are also important