millennial scale changes in north atlantic circulation since the last glaciation ocean circulation is closely linked to climate change on glacial interglacial and shorter timescales extensive reorganizations in the circulation of deep and intermediate depth waters in the atlantic ocean have been hypothesized for both the last glaciation1 2 3 4 5 6 and the subsequent younger dryas cold interval3 6 7 8 9 10 but there has been little palaeoceanographic study of the subtropical gyres11 12 13 these gyres are the dominant oceanic features of wind driven circulation and as such they reflect changes in climate and are a significant control on nutrient cycling and possibly atmospheric co2 concentrations here we present cd ca ratios in the shells of benthic foraminifera from the bahama banks that confirm previous suggestions11 12 that nutrient concentrations in the north atlantic subtropical gyre were much lower during the last glacial maximum than they are today up to 50 lower according to our data these contrasting nutrient burdens imply much shorter residence times for waters within the thermocline of the last glacial maximum below the glacial thermocline nutrient concentrations were reduced owing to the presence of glacial north atlantic intermediate water a high resolution cd ca record from an intermediate depth indicates decreased nutrient concentrations during the younger dryas interval as well mirroring opposite changes at a nearby deep site3 9 together these observations suggest that the formation of deep and intermediate waters north atlantic deep water and glacial north atlantic intermediate water respectively wax and wane alternately on both orbital and millennial timescales

tropical pacific atlantic ocean interactions at multi decadal time scales analysis of sea surface temperature sst observations suggests a pan oceanic interaction between the tropical pacific and the atlantic ocean at multi decadal time scales such that periods of anomalously high ssts in the tropical pacific are followed by a basin wide sst dipole in the atlantic ocean with a time delay of a few decades the sst anomaly structure in the atlantic ocean is reminscent of variations in the north atlantic thermohaline circulation the two ocean basins are linked through an atmospheric bridge involving anomalous fresh water fluxes based on the observational findings the atlantic thermohaline circulation may strengthen during the next decades in response to the strong decades long increase in tropical pacific sst which will have strong impacts on the climates of north america and europe through changes in the north atlantic oscillation nao

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

major features and forcing of high latitude northern hemisphere atmospheric circulation using a 110 000 year long glaciochemical series the greenland ice sheet project 2 glaciochemical series sodium potassium ammonium calcium magnesium sulfate nitrate and chloride provides a unique view of the chemistry of the atmosphere and the history of atmospheric circulation over both the high latitudes and mid low latitudes of the northern hemisphere interpretation of this record reveals a diverse array of environmental signatures that include the documentation of anthropogenically derived pollutants volcanic and biomass burning events storminess over marine surfaces continental aridity and biogenic source strength plus information related to the controls on both high and low frequency climate events of the last 110 000 years climate forcings investigated include changes in insolation of the order of the major orbital cycles that control the long term behavior of atmospheric circulation patterns through changes in ice volume sea level events such as the heinrich events massive discharges of icebergs first identified in the marine record that are found to operate on a 6100 year cycle due largely to the lagged response of ice sheets to changes in insolation and consequent glacier dynamics and rapid climate change events massive reorganizations of atmospheric circulation that are demonstrated to operate on 1450 year cycles changes in insolation and associated positive feedbacks related to ice sheets may assist in explaining favorable time periods and controls on the amplitude of massive rapid climate change events explanation for the exact timing and global synchroneity of these events is however more complicated preliminary evidence points to possible solar variability climate associations for these events and perhaps others that are embedded in our ice core derived atmospheric circulation records

teleconnections between the subtropical monsoons and high latitude climates during the last deglaciation the major deglacial intensification of the southwest monsoon occurred at 11 450 150 calendar years before present synchronous with a major climate transition as recorded in greenland ice an earlier event of monsoon intensification at 16 000 150 calendar years before present occurred at the end of heinrich layer 1 in the atlantic and parallels the initial rise in global atmospheric methane concentrations and the first abrupt climate changes in the antarctic thus the evolution of the monsoonal and high latitude climates show teleconnections but hemispheric asymmetries superimposed on abrupt events the monsoonal climate shows high frequency variability of 1785 1450 and 1150 year oscillations and abrupt climate change seems to occur when at least two of these oscillations are in phase

a reconstruction of the north atlantic oscillation using tree ring chronologies from north america and europe tree ring records six from eastern north america and four from northwestern europe are used to develop the first reconstruction of the winter north atlantic oscillation nao the reconstructed series spans the interval ad 1701 1980 and explains 41 of the variance in the nao over the ad 1874 1980 calibration period the reconstruction also captures the spectral properties of this index suggesting that the oscillatory character of the nao is a long term feature of the north atlantic climate system

beryllium 10 in the greenland ice core project ice core at summit greenland concentrations of the cosmogenic isotope 10be have been measured in more than 1350 samples from the greenland ice core project grip ice core drilled at summit greenland although a dust associated component of 10be retained by 0 45 m filters in some of the samples complicates the interpretations the results confirm that the first order origin of 10be concentration variations is changes in precipitation rate associated with different climate regimes this effect is seen not only between glacial and interglacial periods but also during the shorter dansgaard oeschger interstadials by contrast the 10be data do not support the interpretation of rapidly varying accumulation i e climate during the last interglacial they can however be used to help place limits on the origin of the ice in these events after taking into account variable snow accumulation effects variations in the 10be flux are observed probably caused by solar and geomagnetic modulation but possibly also by primary cosmic ray variations the most dramatic is a 10be peak 40 000 years ago similar to that found in the vostok ice core thus permitting a very precise correlation between climate records from arctic and antarctic ice cores the 36cl 10be ratio considering either total or only ice associated 10be shows significant variability over the whole core depth thus confirming the difficulty in using this parameter for dating ice cores

comparison between instrumental observational and high resolution proxy sedimentary records of late holocene climatic change a discussion of possibilities abstract variability of the north atlantic region is a key factor in the workings of global climate changes related to orbital factors and to the thermohaline circulation thc occur on timescales ranging from 1000 to 100 000 years whereas subdecadal decadal and multidecadal trends are associated with changes in atmospheric circulation sea surface temperature sst and salinity long term changes are known only from proxies whereas shorter periodicities are identified in instrumental and other observational data between lies a range of less well known centennial periodicities too long to be recorded observationally and too short for all but the highest resolution proxy records such as tree rings atmospheric 14c and varved lake sediments numerous investigations of such periodicities involve comparisons between the proxy and the observational record however results depend on the length of the datasets being analysed the relative strength of the periodicities present whether data are stationary or non stationary the degree to which they have been smoothed in order to remove particular fluctuations and the methods of analysis employed ideally comparisons should be between datasets of equal length and of similar properties but these criteria are not always easy to fulfill a search for periodicities in a range of well known multidecadal datasets reveals that whilst some frequencies previously identified in the central england temperature cet record and in the koch sea ice index are statistically significant those found by several authors in the index of the north atlantic oscillation nao are not as the index approximates to white noise instead decadal periodicity of the nao described by several authors appears to be result of smoothing of the raw data periodicities of 6 1 33 9 and 213 years identified in a proxy record from laminated sediments from loch ness scotland appear respectively to be related to a subdecadal variations in sst and salinity in the north atlantic ocean b multidecadal interactions between the nao and the north atlantic thc and c a well known centennial solar periodicity

the gisp2 δ18o climate record of the past 16 500 years and the role of the sun ocean and volcanoes measured 18o 16o ratios from the greenland ice sheet project 2 gisp2 ice core extending back to 16 500 cal yr b p provide a continuous record of climate change since the last glaciation high resolution annual 18o 16o results were obtained for most of the current millennium a d 818 1985 and record the medieval warm period the little ice age and a distinct 11 yr 18o 16o cycle volcanic aerosols depress central greenland annual temperature 1 5 c maximally and annual 18o 16o for about 4 yr after each major eruptive event on a bidecadal to millennial time scale the contribution of solar variability to holocene greenlandic temperature change is 0 4 c the role of thermohaline circulation change on climate problematic during the holocene is more distinct for the 16 500 10 000 cal yr b p interval analogous to 14c age calibration terminology we express time in calibrated cal yr b p a d 1950 0 cal yr b p the oldest dryas bolling older dryas allerod younger dryas sequence appears in great detail bidecadal variance in 18o 16o but not necessarily in temperature is enhanced during the last phase of lateglacial time and the younger dryas interval suggesting switches of air mass transport between jet stream branches the branched system is nearly instantaneously replaced at the beginning of the bolling and holocene at 14 670 and 11 650 cal yr b p respectively by an atmospheric circulation system in which 18o 16o and annual accumulation initially track each other closely thermodynamic considerations of the accumulation rate temperature relationship can be used to evaluate the 18 o 16o temperature relationship the gisp2 ice layer count years of major gisp2 climate transitions also support the use of coral 14c ages for age calibration

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

western north atlantic evidence for millennial scale changes in ocean circulation and climate two late quaternary series of high resolution percent carbonate data from western north atlantic sediment drifts bermuda rise and bahama outer ridge show millennial scale oscillations superimposed on the familiar longer period oscillations of orbital origin the dominant high frequency oscillation in these records has a quasi period of about 4000 years these percent caco3 changes most likely result from the influence of climate change on the flux of terrigenous material from eastern canada the resuspension of continental margin sediment by deep eddy kinetic energy and carbonate dissolution sediment is transported to the bermuda rise by deep recirculating gyres and to the bahama outer ridge by the deep western boundary current system stable isotope results on foraminifera across several of these oscillations from interstadial climate conditions and from a glacial inception display variability similar to that of percent caco3 oxygen isotope ratios of planktonic foraminifera suggest large variations in near surface temperature and or salinity and carbon isotope ratios of benthic foraminifera indicate that there were significant oscillations in the flux of north atlantic deep water nadw these data support models which couple surface ocean conditions in the north atlantic production of nadw north atlantic heat flux and evidence for temperature oscillations in ice cores

the laminated sediments of loch ness scotland preliminary report on the construction of a chronology of sedimentation and its potential use in assessing holocene climatic variability abstract two sediment cores ca 6 m long have been recovered from the north basin of loch ness scotland each consists of ca 4 5 m of laminated gyttja terminating in a basal grey unlaminated clay a suite of three 14c ams dates have been obtained and place the base of the gyttja at ca 9500 yr b p investigations into the structure composition and formation of the laminae are in progress analysis by backscatter scanning electron microscopy bsem has demonstrated that they consist of couplets comprising dark clay rich sediments thought to be deposited from spring to autumn and pale silt rich layers believed to represent sedimentation through winter the laminae are thus thought to record incidence and intensity of streamflow into the loch over the past nine millennia and thus illustrate environmental change over the region for most of the holocene x ray densitometry has been utilised in order to count the laminations and test the hypothesis that they are varves it has however proved difficult to obtain a continuous sequence of countable laminations although it has been possible to construct a fragmented floating chronology which indicates that the hypothesis may be correct examination of lamination thickness reveals that although the average rate of sedimentation throughout the time periods studied seems to have remained fairly constant significant variations have occurred as loch ness is located on the northwest oceanic fringe of europe any climatic signal which the laminations contain will be closely related to even larger scale events over and within the north atlantic ocean which is a major controller of global climate preliminary statistical investigation of sequences of laminae is being carried out in order to search for periodicity of sedimentation which may then be related to appropriate climatic indices

late holocene 1500 yr climatic periodicities and their implications fourier and nonlinear regression analysis of a 4000 yr paleoclimate proxy record in western canada shows strong periodicities of 1500 yr and several weaker century to millenial scale periodicities in conjunction with the 23 708 yr milankovitch periodicity these produce a model of climate fluctuation through the postglacial consistent with recognized paleoclimatic fluctuations of the past 15 000 yr in the northern mid latitudes these results suggest that postglacial climatic anomalies such as the little ice age and the younger dryas were at least in part periodic phenomena rather than the result of unique aperiodic events projecting these periodicities into the future suggests that even in the absence of anthropogenic climate forcing a natural warming trend will continue until ca a d 2400

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

interdecadal variations in north atlantic sea surface temperature and associated atmospheric conditions abstract evidence is presented for a distinct pattern of ocean atmosphere relationship associated with interdecadal variability in the north atlantic region using a century of surface marine observations it is shown that middle and high latitude sea surface temperature sst display a long term fluctuation with negative anomalies before 1920 and during the 1970s and 1980s positive sst conditions prevailed from about 1930 to 1960 the pattern of interdecadal sst variability is constructed by subtracting the average field during 15 cold years from that during a similar interval of warm years the early century warming and the more recent cooling display a similar spatial pattern in both cases the pattern is basin scale and largely of one polarity with maxima in the vicinity of iceland in the labrador sea and northeast of bermuda the corresponding differences in surface atmospheric conditions are determined by averaging and subtracting in the same manner fields of sea level pressure slp and surf

coastal groundwater dynamics off santa barbara california combining geochemical tracers electromagnetic seepmeters and electrical resistivity this paper presents repeat field measurements of 222 rn and 223 224 226 228 ra electromagnetic seepage meter derived advective fluxes and multi electrode stationary and continuous marine resistivity surveys collected between november 2005 and april 2007 to study coastal groundwater dynamics within a marine beach in santa barbara california the study provides insight into magnitude and dynamics of submarine groundwater discharge sgd and associated nutrient loadings into near shore coastal waters where the predominant sgd drivers can be both spatially and temporally separated rn 222 and 223 224 226 228 ra were utilized to quantify the total and saline contribution respectively of sgd the two short lived 224 223 ra isotopes provided an estimate of apparent near shore water mass age as well as an estimate of the ra derived eddy diffusion coefficient kh 224 ra 2 86 0 7 m 2 s 1 223 ra 1 32 0 5 m 2 s 1 because 222 rn t 3 8 day and 224 ra t

holocene periodicity in north atlantic climate and deep ocean flow south of iceland climate fluctuations during the past millennium are relatively well documented1 on a longer timescale there is growing evidence of millennial scale variability of holocene climate at periodicities of 2 500 and 950 years possibly caused by changes in solar flux 2 3 and 1 500 years maybe related to an internal oscillation of the climate system 4 5 6 but the involvement of deep water masses in these holocene climate changes has yet to be established here we use sediment grain size data from the iceland basin to reconstruct past changes in the speed of deep water flow the study site is under the influence of iceland scotland overflow water isow the flow of which is an important component of the thermohaline circulation that modulates european climate flow changes coincide with some known climate events the little ice age and the mediaeval warm period and extend over the entire holocene epoch with aquasi periodicity of 1 500 years the grain size data indicate afaster isow flow when the climate of northern europe is warmer however a second mode of operation is observed in the early holocene when warm climate intervals are associated with slower isow flow at that time the melting remnant of land based glacial age ice may have provided a sufficient source of fresh water to the ocean to reduce isow flow south of iceland

climate and solar variability recorded in holocene laminated sediments a preliminary assessment comparison of the properties of the laminated sediments of loch ness scotland with a range of climatic and palaeoclimatic indices shows that in a short core spanning the period 1321 1963 ad the signal of lamination thickness is significantly correlated p 0 01 with data on the number of ice weeks off iceland the index of the north atlantic oscillation nao and with zurich sunspot number power spectra identified in lamination thickness data for both short and long cores indicate the presence of peaks at low frequencies compatible with the nao the 11 year sunspot cycle the hale or double sunspot cycle and the gleissberg 88 year solar cycle several peaks also occur at intermediate and at higher periodicity however and general spectral density is weak so that these results are regarded as preliminary the sediments of loch ness appear however to contain a record of the influence of the north atlantic ocean and via that solar variability upon the climate of northern scotland spanning recent centuries

the north atlantic oscillation and its imprint on precipitation and ice accumulation in greenland interannual to decadal fluctuations in net precipitation and ice accumulation are examined over greenland it is shown that in western greenland these fluctuations are correlated with the north atlantic oscillation the analysis is based on two complementary data sources a highly resolved net precipitation and accumulation history over 15 years derived form the reanalysis data of the european centre for medium range weather forecasts and a composite ice accumulation record representative for the western part of central greenland it is suggested that western greenland snow accumulation is a good proxy for the nao index with the potential for the reconstruction of a long time series

depositional processes of alluvial fans along the hilina pali fault scarp island of hawaii abstract a series of previously unstudied alluvial fans are actively forming along the hilina pali escarpment on the south flank of k lauea volcano on the island of hawaii these fans are characterized by their steep slopes coarse grain sizes and lobate surface morphology fans are fed by bedrock channels that drain from the ka desert but sediment is mostly sourced from deeply eroded alcoves carved into the hilina pali examination of recent deposits indicates that the fans are dominantly constructed from gravel and larger sized sediment flow discharges calculated using field measurements of channel geometries and the manning equation indicate that events inducing sediment transport are of high magnitude and occur during high intensity precipitation events including kona storms the fans along the hilina pali appear to be a rare example of fans formed predominately from sieve lobe deposition owing to the area s high slopes high discharge coarse bedload and limited supply of fine grained sediment given such conditions sieve lobe deposition can form large lobes consisting of boulder sized material which may have implications for the identification of depositional processes when interpreting the stratigraphic record

high frequency paleovariability in climate and co2 levels from vostok ice core records the high resolution of the vostok records provides a unique look at the causes of paleoclimatic variability during the last complete glacial cycle the records present strong evidence for the interaction between orbital forcing and internal physico chemical mechanisms of variability this interaction appears to account for the great wealth of spectral features found in the records

gulf stream shifts following enso events over the past three decades the annual mean latitude of the gulf stream off the coast of the united states has been forecastable from the intensity of the north atlantic oscillation nao 1 the predictions accounting for more than half the variance here we show that much of the unexplained variance can be accounted for by the southern oscillation in the pacific the gulf stream being displaced northwards following el nino southern oscillation enso events this provides a link between events in the equatorial pacific and the circulation and weather conditions of the north atlantic

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

long term coordinated changes in the convective activity of the north atlantic the north atlantic is a peculiarly convective ocean the convective renewal of intermediate and deep waters in the labrador sea and greenland iceland sea both contribute significantly to the production and export of north atlantic deep water thus helping to drive the global thermohaline circulation while the formation and spreading of 18 degree water at shallow to intermediate depths off the us eastern seaboard is a major element in the circulation and hydrographic character of the west atlantic for as long as time series of adequate precision have been available to us it has been apparent that the intensity of convection at each of these sites and the hydrographic character of their products have been subject to major interannual change as shown by aagaard 1968 clarke et al 1990 and meincke et al 1992 for the greenland sea in the ows bravo record from the labrador sea eg lazier 1980 et seq and at the panulirus hydrostation s site in the northern sargasso off bermuda eg jenkins 1982 talley and raymer 1982 this paper reviews the recent history of these changes showing that the major convective centres of the greenland and labrador seas are currently at opposite convective extrema in our postwar record with vertical exchange at the former site limited to 1000 m or so but with labrador sea convection reaching deeper than previously observed to over 2300 m as a result greenland sea deep water has become progressively warmer and more saline since the early 70 s due to increased horizontal exchange with the arctic ocean through fram strait while the labrador sea water has become progressively colder and fresher over the same period through increased vertical exchange most recently convection has become deep enough there to reach into the more saline nadw which underlies it so that cooler but now saltier and denser lsw has resulted

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

multiproxy reconstructions of the north atlantic oscillation multiproxy composite reconstructions of north atlantic oscillation nao indices are presented spanning the last three centuries these composite time series draw on four nearly independent reconstructions derived from different combinations of global and north atlantic sector climate proxy data e g tree rings and ice cores as well as long instrumental records a composite reconstruction based on all four series r4 extends from 1750 to 1979 while another version based on only three series r3 extends from 1701 to 1979 both composite reconstructions outperform the individual series based on correlation and verification statistics these results suggest that each individual series reflects different aspects of the nao such that when combined they yield more robust reconstructions as to be expected these composite reconstructions based on both proxy and long instrumental data yield more optimal results than individual or composite reconstructions based on proxy data alone the reconstructions presented here provide an improved means of addressing features evident in the instrumental record with respect to those of prior centuries one such feature evident in the reconstructions is an apparent increase in variance in the instrumental period relative to the past record

time scales and trends in the central england temperature data 1659 1990 a wavelet analysis we have applied the standard wavelet and the adaptive wavelet transform algorithms to the record of the central england temperature cet from 1659 1990 peaks in the cet spectra include 7 5 1 0 yr 14 4 1 0 yr 23 5 2 0 yr as well as a previously unreported variation at 102 15 yr our wavelet analysis of cet agrees with previous results from singular spectrum analysis ssa by plaut et al 1995 and gives additional results of variability on longer timescales the interdecadal and century scale variability in cet is strongly dependent on the interval of analysis estimates of a data trend are also shown to be sensitive to the cutoff timescale of the filter a cooling of 0 3 c during 1659 1720 is found relative to the temperatures during the 1800s the complex time dependence of the actual data cautions against using model derived representations of natural variability on such long timescales

patterns of low frequency monthly sea level pressure variability 1899 1986 and associated wave cyclone frequencies abstract spatial patterns of low frequency sea level pressure slp variability are identified by performing rotated principal component analysis rpca on a long term 1899 1986 northern hemisphere gridded dataset the analysis is limited to the region 160 e eastward to 40 e due to missing data early in the century the objective is to identify a comprehensive set of highly recurrent slp teleconnection patterns to examine some aspects of their seasonality and to identify the associated mean winter pressure fields and cyclone frequencies occurring at times of opposite eigenvector polarity the results are further described in the context of the southern oscillation and known midtropospheric teleconnection patterns four low frequency variability patterns are identified over the atlantic european sector including i the north atlantic 0scillation nao and spatial patterns with slp variability centers over ii the eastern atlantic eatl iii southern europe and the northern mediterranean basin s

nao and sea surface temperature signatures in tree ring records from the north atlantic sector temperature sensitive tree ring chronologies from scandinavia and labrador are respectively analyzed for their response to two major features of north atlantic climate variability 1 the north atlantic oscillation nao and 2 coastal and near coastal surface air and sea surface temperatures ssts 1 nao using superposed epoch analysis sea below above average ring width departures from scandinavian scots pine pinus sylvestris l were found to follow positive negative anomalies in winter december february sea level pressure slp related to the icelandic low pressure cell a key element of the nao in addition to a documented summer temperature relationship these trees show a positive correlation with winter temperatures for oslo norway oslo data are used to define the northwest european end of the winter temperature seesaw another major feature of the nao below above average tree growth departures tend to follow greenland above ga or greenland below gb seesaw winters which are associated with high low pressure and cold warm conditions over scandinavia 2 ssts growing season april september land sea temperatures were reconstructed for three 5 5 gridcells 50 55 n 50 65 w near the coast of labrador for the period from 1813 to 1988 the tree ring data used in this case were four maximum latewood density chronologies of white spruce picea glauca moench voss from sites in southern and central labrador an alternative model based on only two chronologies allows extension of these reconstructions back to 1713 the reconstructions explain about 45 of the temperature variance from 1915 1988 and pass several tests for model validation with high levels of statistical significance they primarily provide information on short period

on sharp spectral lines in the climate record and the millennial peak the existence of a narrow spectral line in the internal oscillations of the climate system would be a physical discovery of the first order thus the appearance of such a spectral peak with a q 20 near 1500 years period in the physical properties of the greenland ice core is intriguing bandwidth less than two cycles in 110 000 years apparently similar phenomena exist in some deep sea cores it is shown however that the peak appears at precisely the period predicted as a simple alias of the seasonal cycle inadequately under the nyquist criterion sampled at integer multiples of the common year if this peak is therefore discounted climate variability appears as expected to be a continuum process in the millennial band more generally however aliasing of high frequencies must be a concern in any core analysis