pacific and atlantic multidecadal variability in the kiel climate model pacific decadal variability pdv and atlantic multidecadal variability amv the two leading decadal modes of observed northern hemisphere sea surface temperature sst variability are investigated in a multi millennial control integration of the kiel climate model kcm it is shown that the two phenomena are independent modes in the model and can be easily separated by principal oscillation pattern pop analysis of model sst pdvrelated variability covers the whole north pacific with strong signals in both the mid latitude north pacific and the western tropical pacific strong signals are also simulated in the eastern indian ocean sector pdv s memory however resides in the north pacific and is linked to the subtropical gyre the amv mechanism is related to the atlantic meridional overturning circulation amoc a stochastic mechanism applies to both pdv and amv

combined influences of seasonal east atlantic pattern and north atlantic oscillation to excite atlantic multidecadal variability in a climate model the physical processes underlying the internal component of the atlantic multidecadal variability amv are investigated from a 1 000 yr pre industrial control simulation of the cnrm cm5 model the low frequency fluctuations of the atlantic meridional overturning circulation amoc are shown to be the main precursor for the model amv the full life cycle of amoc amv events relies on a complex time evolving relationship with both north atlantic oscillation nao and east atlantic pattern eap that must be considered from a seasonal perspective in order to isolate their action the ocean is responsible for setting the multidecadal timescale of the fluctuations amoc rise leading to a warm phase of amv is statistically preceded by wintertime nao and eap from lag 40 20 yrs associated wind stress anomalies induce an acceleration of the subpolar gyre spg and enhanced northward transport of warm and saline subtropical water concurrent positive salinity anomalies occur in the greenland iceland norwegian seas in link to local sea ice decline those are advected by the eastern greenland current to the labrador sea participating to the progressive densification of the spg and the intensification of ocean deep convection leading to amoc strengthening from lag 10 yrs prior an amoc maximum opposite relationship is found with the nao for both summer and winter seasons despite negative lags nao at that time is consistent with the atmospheric response through teleconnection to the northward shift intensification of the inter tropical convergence zone in link to the ongoing warming of tropical north atlantic basin due to amoc rise amv build up nao acts as a positive feedback for the full development of the model amv through surface fluxes but at the same time prepares its termination through negative retroaction on amoc relationship between eap and amoc is also present in summer from lags 30 10 yrs while winter eap is favored around the amv peak based on additional atmospheric forced experiments both are interpreted as the local seasonal dependent atmospheric response to warmer north atlantic finally advection of fresher water from the tropical basin created by local atmosphere ocean anomalous circulation on one hand and from the arctic on the other hand due to large scale sea ice melting leads to decrease of density in the spg and contributes terminating the model amoc amv events all together the combined effects of nao and eap their intertwined seasonal forcing forced role upon by the ocean and the primary role of salinity anomalies associated with oceanic dynamical changes acting as an integrator are responsible in cnrm cm5 for an irregular and damped mode of variability for amoc amv that takes about 35 40 15 20 years to build up dissipate

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

middle and late jurassic radiolarian palaeoecology versus carbon isotope stratigraphy abstract jurassic radiolarians are sensitive to palaeoclimatic palaeoceanographic changes recorded by the stable carbon isotope curve carbon isotopic variations have been linked to changes in ocean structure productivity and concentrations of greenhouse gases in the atmosphere in the middle upper jurassic terminilletto section of the umbria marche sabina apennines central italy well preserved radiolarians are present in a sequence of cherty limestones interbedded with platform derived carbonates the 13 c curve in the aalenian kimmeridgian interval indicates three main positive 13 c events in the lower bajocian late bathonian lower callovian and middle oxfordian the positive 13 c shifts are correlated to increases in visible chert in the outcrop and may represent periods of increased biological productivity of surface sea water spumellaria nassellaria ratios and the fluctuations of relative abundance of selected genera tend to correlate with 13 c and chert abundance values and seem to be related to episodes of high nutrient mobilisation from the base of the bajocian the radiolarian associations show a slight tendency towards diversification coincident with increasing 13 c values in the upper part of the middle bajocian last appearances prevail over first appearances associated with the peak of the 13 c event this may indicate maximum eutrophic conditions coincident with the late bathonian early callovian positive 13 c shift the radiolarian associations record a different trend with respect to the bajocian event when the 13 c values are increasing to a maximum radiolarian associations tend to be reduced in species diversity followed by a small diversification trend when the 13 c values are decreasing we speculate that during the callovian a more stressful palaeoenvironment due to high level of eutrophication is indicated by the combination of high productivity of biogenic silica and low carbonate input although varying preservational conditions may have influenced the observed trends in the radiolarian associations the good correlation between changes of sedimentation patterns radiolarian assemblages and 13 c positive anomalies open interesting avenues for further investigations concerning the palaeoecology of mesozoic radiolarians

long submarine lava flows observations and results from numerical modeling long 100 km lava flows are relatively common on mars and venus and have been identified on the moon but they are rarely documented on earth however although 75 of the earth s surface is covered by water only a small percentage of the ocean floor has been investigated at a resolution sufficient to unequivocally identify the boundaries of long submarine lava flows even so basaltic lava flows as long as 110 km have been identified on the deep 1500 m seafloor near hawaii and the east pacific rise ambient conditions on the deep ocean floor may favor the development of long lava flows for the following reasons first high pressures 15 mpa keep volatiles dissolved in basaltic lavas preventing viscosity increases associated with exsolution and vesiculation second seawater rapidly quenches the surface of submarine basalt flows so that an insulating glass layer 1 5 cm thick encases submarine flows within seconds after their emplacement this glass rind effectively insulates the molten flow interior from additional heat loss making submarine basalt flows behave as well insulated subaerial tube fed flows thus for identical basalt flows emplaced on the deep seafloor and subaerially a submarine flow could advance farther before stopping results of numerical modeling indicate that thin 1 m submarine basalt flows behave similarly to identical subaerial flows but thicker submarine flows may advance significantly farther than their subaerial counterparts

climate and oceanographic variability in the sw barents sea during the holocene the holocene section of the marine sediment core psh 5159n located in the sw barents sea has been studied at high resolution with a multiproxy approach a well stratified water column occurred at the site 11 9 8 ka bp the stratification was probably a result of a winter sea ice cover and or fresh warm surface waters during summer stratification and resultant reduction in air sea interaction allowed for warmer bottom water temperatures the general situation 11 9 8 ka bp could have been associated with an anomalous high pressure system over the nordic seas and the arctic ocean during the 11 10 5 ka bp interval the polar front was located close to the barents sea margin the polar front moved towards the site from 10 5 ka bp and from 9 8 to 7 5 ka bp it was probably located close to the site at 7 5 ka bp the polar front retreated eastwards as the present day oceanographic pattern established the mid holocene was in general characterized by rather stable conditions in contrast highly variable cond

a three thousand year record of north atlantic climate annual band counting on three radiometrically dated stalagmites from nw scotland provides a record of growth rate variations for the last 3000 years over the period of instrumental meteorological records we have a good historical calibration with local climate mean annual temperature mean annual precipitation regional climate north atlantic oscillation and sea surface temperature sst strongest at 65 70 n 15 20 w although the correlation with the latter breaks down prior to the instrumental record this suggests that the climatic factors that force nw scottish climate and therefore our stalagmite growth varied through time and include winter nao strength the strength of the thermohaline circulation and possibly solar output spectral analysis was performed on the stalagmite growth rate time series a spectral frequency of 50 70 years is predominant in two stalagmites that were deposited from 1000 to 3000 bp a slightly longer frequency of 72 94 years is dominant from 1000 bp to present these are the same as that observed in ocean gcm output for the north atlantic region ssts our stalagmites provide high resolution precisely dated evidence of a similar periodicity predominating over the last 3000 years in a climate proxy record known to be sensitive to changes in forcing functions relevant to the north atlantic sector

acid processing of pre tertiary radiolarian cherts and its impact on faunal content and biozonal correlation the numbers of radiolarians visible in thin sections of chert rich rocks are commonly an order of magnitude greater than the numbers observed on the surfaces of fragments etched by hydrofluoric acid hf and typically orders of magnitude greater than the numbers of individuals found in hf processed residues destruction of radiolarians during both diagenesis and hf processing severely reduces faunal abundance and diversity and affects the taxonomic and biostratigraphic utility of chert residues the robust forms that survive the processing represent only a small fraction of the death assemblage and delicate skeletal structures used for species differentiation commonly preserved in limestone radiolarian faunas are either poorly preserved or dissolved in many coeval chert residues first and last occurrences of taxa in chert sequences are likely to be coarse approximations of their true stratigraphic ranges precise correlation is difficult between biozonations based solely on index species from cherts and those constructed from limestone faunas careful selection of samples in sequence use of weaker hf solutions and study of both chert and limestone faunas should yield better biostratigraphic information

patterns of biotic change in middle jurassic to early cretaceous tethyan radiolaria abstract the rate of taxic turnover of nearly 400 radiolarian species subspecies is analyzed in order to document long term biotic change of plankton during the middle jurassic to early cretaceous aalenian to aptian the pattern and dynamic of diversity change is described using four indices rate of species first and last occurrence rate of diversification and rate of turnover plots of cumulative sampling effort suggest that the analyzed data represent an adequate sample of total standing diversity for most examined stages rates of species first occurrence exceed rates of last occurrence for most of the middle jurassic except for the middle bajocian in contrast the late jurassic was a time of decreasing radiolarian diversity and the kimmeridgian records the lowest rate of diversification it is followed by a dramatic increase in first occurrences near the jurassic cretaceous boundary with as a result the highest rate of diversification recorded in the late tithonian regional radiolarian diversity was stable throughout most of the early cretaceous a stratigraphic permutation test was performed to assess the influence of uneven sampling on the observed pattern of taxic turnover and identified the intervals for which randomly obtained patterns are significantly different from the observed pattern the kimmeridgian and late tithonian events coincide with substantial climate derived perturbations in water cycling nutrient supply and oceanic productivity they point to a negative relationship between radiolarian macroevolution and changes in the state of nutrient availability although further work is needed to refine the temporal resolution of this relationship and to explore ecological aspects of its causal link with respect to radiolarian evolution

what is the thermohaline circulation the term thermohaline circulation is widely used in the context of past and future climate change in his perspective wunsch argues that there are many different and inconsistent definitions for this term he defines ocean circulation in terms of mass fluxes which are largely driven by surface forces such as wind and tides and argues that thermohaline circulation should only refer to the separate transport of heat and salinity in the ocean

multidecadal and multicentennial variability of the meridional overturning circulation the variability of the meridional overturning circulation moc simulated in a multimillenial control integration of the kiel climate model kcm displays enhanced variability relative to the red background at decadal and centennial timescales the multidecadal variability is the model s version of the atlantic multidecadal variability amv often referred to as atlantic multidecadal oscillation amo while multidecadal variability originates in the north atlantic multicentennial variability is driven in the southern ocean both multidecadal and multicentennial variability are associated with considerable changes in sea ice extent this may be important to understand the different evolution of sea ice cover in the northern and southern hemisphere during the most recent decades with a strong decline observed in the north and almost no trend in the south

the role of north brazil current transport in the paleoclimate of the brazilian nordeste margin and paleoceanography of the western tropical atlantic during the late quaternary abstract reconstructions of surface paleoceanographic conditions of the western equatorial atlantic and past climates of the adjacent northeast brazilian the nordeste continental margin were undertaken by analyzing sediments from a piston core and associated gravity and box cores recovered from 3107 meter water depth at 0 20 n on the equatorial brazilian continental slope the record is dated by radiocarbon analysis and oxygen isotopic stratigraphy of planktonic foraminifers and spans from near modern to approximately 110 ka high resolution xrf analysis provides insight into the paleoclimate history of the nordeste during the last glacial interval several large amplitude and abrupt peaks are observed in the time series of ti ca and are usually accompanied by peaks of fe k together these record periods of increased precipitation and intense weathering on the adjacent continent and increased terrestrial sediment discharge from nordeste rivers into the atlantic within the limits of dating accuracy most ti ca peaks correlate with heinrich events in the north atlantic this record thus corroborates and extends back in time the previous record of arz et al 1998 determined on sediment cores from farther southeast along the nordeste margin stable oxygen isotopic analysis and mg ca paleothermometry on the near surface dwelling planktonic foraminiferal species globierinoides ruber find that mean sea surface temperature sst during glacial time 20 55 ka n 97 was 23 89 0 79 c and the mean sst during the late holocene 0 5 ka n 14 was 26 89 0 33 c ssts were 0 5 2 c higher and inferred sea surface salinities were lower during most of the periods of elevated ti ca thus as observed in previous studies the western equatorial atlantic was warm at least locally and the adjacent southern tropical continent was wet at the same time that the high latitude north atlantic was cold using the syntrace ccsm3 fully coupled climate model with transient forcing for the period 22 ka to present we find that decreased transport of the north brazil current co occurs with reduced atlantic meridional overturning circulation and colder than normal ssts in the north atlantic region these simulated conditions are invariably associated with significantly increased precipitation in the nordeste region

solidification and morphology of submarine lavas a dependence on extrusion rate the results of recent laboratory experiments with wax extruded beneath relatively cold water may be extrapolated to predict the surface morphology of submarine lavas as a function of the extrusion rate and melt viscosity the experiments with solidifying wax indicated that the surface morphology was controlled by a single parameter the ratio of the time taken for the surface to solidify and a time scale for lateral flow for submarine basalts a solution of the cooling problem which is dominated by conduction in the lava but convective heat transfer in the water and estimates of lava viscosities place this parameter within the empirically determined pillowing regime over a wide range of extrusion rates this result is consistent with the observation that pillow basalts are the most common products of submarine eruptions smoother surfaces corresponding to the various types of submarine sheet flows are predicted for sufficiently rapid extrusions of basaltic magma still higher eruption rates in regions of low topographic relief may produce submarine lava lakes minimum emplacement times can be calculated for submarine volcanic constructs of a single lava flow type

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

low latitudinal standard permian radiolarian biostratigraphy for multiple purposes with unitary association graphic correlation and bayesian inference methods abstract the ideal goal of biostratigraphic studies is to make stratigraphic ranges of all species clear and to fix globally synchronous biohorizons as age controls however it is difficult to achieve this goal in simple traditional ways and so a new solution is proposed for permian radiolarian biostratigraphy to achieve this goal including to establish a globally applicable biostratigraphy to estimate the numerical age of biohorizons and to determine stratigraphic ranges at species level all 400 known permian radiolarian species approximately 70 stratigraphic sections and 1560 samples from 350 previously published papers about the low latitude tethys and panthalassa oceans were analyzed issues of permian studies are summarized and a solution is proposed from the cenozoic point of view considering traditional methods as well as successful methods in cenozoic radiolarian studies here we implement newly proposed methods that have never been used for permian radiolarian studies unitary association method uam minimum disordered biohorizon algorithm mdba graphic correlation gc and reiteration estimation rounds rer of these our proposed rer is a new method to predict the probability of the estimated age for a sample by bayesian inference and joint probability both statistical methods as these four methods are applicable to any biostratigraphic study the principals and practical applications of these methods are carefully explained so non specialists can understand the logical procedure as a result 15 unitary association zones uazs are established for the entire permian biostratigraphic scheme by uam the numerical ages of 42 first occurrences fos are estimated from non parametric data from the middle guadalupian middle permian to the uppermost lopingian uppermost permian by mdba and gc and the statistical likelihood uaz ranges of 165 species in the entire permian were obtained using the rer procedure a usability test of our uazs shows that 97 96 of the 933 tested samples from previously published papers are well correlated and without contradiction within the statistical error of cenozoic synchronous biohorizons at 1 4 myr 23 of 42 fos are potentially regarded as synchronous events as the statistical likelihoods of uaz ranges are estimated by bayesian inference these ranges can be updated by anyone

a description of coads surface meteorological fields and the implied sverdrup transports for the atlantic ocean from 30 s to 60 n abstract using coads data spanning 1947 1988 we describe the regional nature of the atlantic ocean wind driven circulation between 30 8 and 60 n and its annual and interannual variability the sverdrup streamfunction defines the circulation gyres our focus is on three central gyres the northern hemisphere anticyclonic subtropical gyre the cyclonic tropical gyre just north of the equator and the clockwise equatorial gyre straddling the equator this rendition of the sverdrup streamfunction computed with constant drag coefficient and air density compares favorably with that from other climatologies in the straits of florida analyses suggest that differences between the annual cycle in sverdrup transport and observations may be due to regional winds farther north in the tropical gyre the sverdrup circulation argues against a continuous western boundary current transporting water from the equatorial region into the caribbean in boreal winter bringing to question the mechanisms for the known interh

decadal changes in the thermohaline circulation of the north atlantic abstract a set of repeated full depth and mostly ocean wide hydrographic sections is used to describe the temporal and spatial changes of temperature and salinity at the intermediate layers of the north atlantic over the past 40 years they cover three distinct periods namely the late 1950s the early 1980s and the early 1990s but do not constitute a time series most parts of the recently observed changes in the subpolar and subtropical gyres are attributed to the changes of the labrador sea water lsw properties the latter is formed in the labrador sea and spreads into the north atlantic the spreading time of the lsw from the source region is evaluated it takes less than two years for the lsw to arrive in the newfoundland basin and 18 20 yr to reach the deep western basin interior at 24 5 n changing characteristics of the lsw are related to the varying intensity of the meridional overturning circulation moc and the meridional heat transport mht the intensification of the moc and mht around 1981 coincides with the rapid decrease of the lsw production the increase of the lsw production that began just after 1987 and resulted in a dramatic cooling and densification of this water mass was accompanied by a reduction of both moc and mht two scenarios of the moc interaction with the full depth circulation of the north atlantic are suggested these scenarios indicate that the development of the moc is governed by the changing transports of the deep waters of arctic origin the direct contribution of the lsw to the intensity of the moc is negligible the lsw is seen as an important part of the feedback loop in the north atlantic moc system

millennial to centennial scale changes in sea surface temperature in the tropical south atlantic throughout the holocene abstract we performed 18oc globigerinoides ruber 250 300 m white and sst modern analogue technique paleoceanographic reconstructions for the western tropical south atlantic ocean at the northeast brazilian margin to assess millennial to centennial scale climatic shifts that may be propagated by the thermohaline circulation the results show a progressive sst increase 1 c over the holocene with a prominent shift occurring during the mid holocene that may be linked to changes in insolation distribution furthermore spectral and coherency analyses reveal several centennial to millennial scale modes of variability that are similar in both proxy records 4 1 3 8 kyr 1 5 1 0 kyr 700 yr 570 560 yr 390 yr 350 yr and 330 yr such variability could be the result of 1 solar induced atmospheric changes at northern high latitudes possibly propagated southward by the meridional overturning circulation and hence inducing shifts in tropical 18oc and sea surface temperature and or 2 salinity anomalies propagated from the southern atlantic ocean and transmitted to the study site through the agulhas leakage these climate oscillations may have had substantive effects on the holocene climate system especially over the tropical western south atlantic ocean and the south american continent our data show that the western tropical south atlantic may respond to multi centennial to millennial oscillations that are possibly triggered by external solar and internal northern and southern high latitudes climate forcing further investigations are necessary to illuminate the role of the western tropical south atlantic in inter hemispheric heat transfer

effects of regional slope on viscous flows a preliminary study of lava terrace emplacement at submarine volcanic rift zones to understand how large submarine lava terraces form and why they are not commonly observed on land we developed an isoviscous gravity flow model on an inclined surface to simulate the evolution and emplacement of lava flows under submarine conditions by solving this preliminary model using a finite difference method we are able to quantify how lava viscosity pre existing topographic slope effusion rate and lava volume affect meso scale lava morphology our simulations show that in general high lava viscosity gentle regional slope and low effusion rate favor the formation of large terraces but environmental conditions also play an important role a gravity flow spreads more slowly underwater than subaerially we also conclude that for low viscosity basaltic lava the cooling of the lava body is one of the most critical factors that affect its shape this study shows that the isoviscous model though oversimplified provides a quantitative tool to relate lava morphology to eruption characteristics to gain a better understanding of the controls on submarine lava terrace formation future models must take into account the temporal and spatial variation of lava viscosity especially the effects of a brittle outer shell

evolution of mid cretaceous radiolarians in response to oceanic anoxic events in the eastern tethys southern tibet china abstract oceanic anoxic events oaes are well known from their widespread black shale and carbon isotopic excursions in the western and eastern tethys and atlantic ocean however the weakest link in the studies of the oaes is biological evolution sedimentological biostratigraphical and geochemical data from albian to coniacian strata in southern tibet recorded turnover events and fluctuations in diversity of the radiolarian fauna within the eastern tethys during oae 1d and oae 2 abundant radiolarian fossils were obtained from the gyabula formation with 93 species from 43 genera identified and assigned to the mid to upper cretaceous acaeniotyle umbilicata archaeospongoprunum tehamaensis crucella cachensis alievium superbum and dictyomitra formosa zones the association of carbon isotopic excursions black shale and radiolarian turnover indicates extensive changes in the ocean climate system nutrients are made increasing available to the marine plankton through submarine volcanic activity and rising sea level which were a likely cause of radiolarian turnover at or near the oaes active submarine tectonism volcanism leads to the expansion of the hypoxic zone and may cause many deeper dwelling forms to become extinct whereas most of the shallower dwelling radiolarians survive radiolarian evolution thus provides a useful record with which to seek understand relationships between climate paleoceanographic processes and plankton evolution

radiolarian diversity patterns in the latest jurassic earliest cretaceous abstract the global diversity patterns of latest jurassic earliest cretaceous tithonian berriasian radiolarian faunas were analyzed based on samples from the european alps oman philippines and antarctica and an extensive literature survey several measures of diversity were applied to faunas from tropical oman mexico pacific subtropical alps california philippines japan and subpolar antarctic peninsula new zealand northern russia localities original diversity patterns are obscured by taxonomic sedimentological and preservational biases qualitative and quantitative corrections of these biases indicated a significant diversity gradient from tropical subtropical to subpolar latitudes but no significant difference between tropical and subtropical assemblages the latitudinal diversity gradient was apparently asymmetrical being steeper in the northern hemisphere than in the southern hemisphere in the southern hemisphere the diversity gradient was similar to the one observed in modern radiolarian sedimentary assemblages considering the more equable climate of the tithonian berriasian it appears unlikely that temperature was the only control of the observed diversity patterns the results substantiate the notion of latitudinal diversity gradients as a time invariant feature of the earth possibly driven by gradients in biome size

the impact of labrador sea temperature and salinity variability on density and the subpolar amoc in a decadal prediction system labrador sea density variability is important for atlantic meridional overturning circulation amoc dynamics and hence decadal variability in the atlantic we investigate whether temperature or salinity dominate top 500m interannual labrador sea density variability in gridded observations an assimilation of the observations and a set of multi annual hindcasts we find that salinity dominates in the observations and assimilation in the hindcasts salinity remains dominant for the first year but from year three these revert to the same temperature dominance seen in the underlying climate model this is due to damping of the interannual salinity variability possibly caused by unrealistically large convection that develops crucially the hindcasts have high correlation skill in temperature salinity throughout but no skill in density dynamic sea level or the subpolar amoc due to the incorrect drivers this highlights the importance of correctly simulating both the sign and magnitude of temperature salinity variability in a prediction system

stochastically forced multidecadal variability in the north atlantic a model study observations show a multidecadal signal in the north atlantic ocean but the underlying mechanism and cause of its timescale remain unknown previous studies have suggested that it may be driven by the north atlantic oscillation nao which is the dominant pattern of winter atmospheric variability to further address this issue the global ocean general circulation model nucleus for european modelling of the ocean nemo is driven using a 2 000 years long white noise forcing associated with the nao focusing on key ocean circulation patterns we show that the atlantic meridional overturning circulation amoc and sub polar gyre spg strength both have enhanced power at low frequencies but no dominant timescale and thus provide no evidence for a oscillatory ocean only mode of variability instead both indices respond linearly to the nao forcing but with different response times the variability of the amoc at 30 n is strongly enhanced on timescales longer than 90 years while that of the spg strength starts increasing at 15 years the different response characteristics are confirmed by constructing simple statistical models that show amoc and spg variability can be related to the nao variability of the previous 53 and 10 winters respectively alternatively the amoc and the spg strength can be reconstructed with auto regressive ar models of order seven and five respectively both statistical models reconstruct interannual and multidecadal amoc variability well while on the other hand the ar 5 reconstruction of the spg strength only captures multidecadal variability using these methods to reconstruct ocean variables can be useful for prediction and model intercomparision

interdecadal north atlantic meridional overturning circulation variability in ec earth the atlantic meridional overturning circulation amoc in a 600 years pre industrial run of the newly developed ec earth model features marked interdecadal variability with a dominant time scale of 50 60 years an oscillation of approximately 2 sverdrup 1 sv 106 m3 s 1 is identified which manifests itself as a monopole causing the overturning to simultaneously strengthen weaken and deepen shallow as a whole eight years before the amoc peaks density in the labrador irminger sea region reaches a maximum triggering deep water formation this density change is caused by a counterclockwise advection of temperature and salinity anomalies at lower latitudes which we relate to the north south excursions of the subpolar subtropical gyre boundary and variations in strength and position of the subpolar gyre and the north atlantic current the amoc fluctuations are not directly forced by the atmosphere but occur in a delayed response of the ocean to forcing by the north atlantic oscillation which initiates intergyre gyre fluctuations associated with the amoc is a 60 year sea surface temperature variability in the atlantic with a pattern and timescale showing similarities with the real world atlantic multidecadal variability this good agreement with observations lends a certain degree of credibility that the mechanism that is described in this article could be seen as representative of the real climate system

paleoclimate proxy perspective on caribbean climate since the year 1751 evidence of cooler temperatures and multidecadal variability 1 annually resolved coral 18o and sr ca records from southwestern puerto rico are used to investigate caribbean climate variability between 1751 and 2004 c e mean surface ocean temperatures in this region have increased steadily by about 2 c since the year 1751 with sr ca data indicating 2 1 0 8 c and 18o data indicating 2 7 0 5 c coral geochemical records from across the tropics demonstrate that regional variability is important for understanding climate variations at centennial time scales a strong multidecadal salinity signal in the oxygen isotope data correlates with observed multidecadal temperature variations in the northern hemisphere instrumental wind and precipitation data indicate that the most recent coral isotopic variations are caused by expansion and contraction of the steep regional salinity gradient forced by trade wind anomalies through meridional ekman transport the timing of the fluctuations suggests that the multidecadal scale wind and surface circulation anomalies might play a role in atlantic temperature variability and meridional overturning circulation but further work is needed to confirm this suggestion

solidifying bingham extrusions a model for the growth of silicic lava domes in a previous study of the effects of cooling and solidification on flows issuing onto a horizontal plane and spreading under gravity we considered the case of a viscous fluid that solidifies to form a thin surface crust with a finite yield strength in that case the coupling of solidification and viscous stresses in the flow led to a sequence of flow regimes or styles of flow and crustal deformation here we study the spreading from a small source of a plastic material having a yield strength before cooling in this case the fluid again begins to freeze as it spreads radially under gravity and forms a dome having a surface crust which is stronger than the extruded fluid if cooling is sufficiently rapid compared to gravity driven spreading the flow is found to be controlled by solidification the flow again takes on one of a number of flow regimes depending on the pace of solidification relative to the rate of lateral flow or extrusion rate however these flow regimes are quite different from those for the viscous extrusions implying that the internal yield stress has a strong influence on the behaviour styles of flow ranged from inflation of an axisymmetric dome to irregular extrusion of lateral lobes and vertical spines these qualitatively different regimes have much in common with the eruption styles of volcanic lava domes produced by effusion of extremely viscous silicic magmas which may possess a yield strength and the model provides information about the factors influencing the morphology and hazards of such volcanic flows

development of palaeozoic mesozoic radiolaria in the northwestern pacific rim abstract investigations of radiolaria allow us to trace the evolutionary trends and rates of these siliceous microorganisms within the northwestern pacific there are several phases or megacycles in the development of radiolarian fauna in northeastern and eastern russia in ascending order these are ordovician silurian devonian carboniferous early permian late permian triassic middle jurassic middle callovian barremian aptian early campanian late campanian early paleocene and late paleocene to recent no evidence has been found for mass extinction at higher taxonomic levels or for instantaneous catastrophic extinction several of the cycles are characterised by increased diversity and morphological specialization immediately prior to extinction recognition of megacycles permits us to hypothesize a close relationship between radiolarian events and palaeoceanographic palaeoclimatic and tectonic changes which took place in the pacific probably a sharp change of palaeohydrography and the opening of the new submarine seaways led to the appearance and radiation of new higher taxa including the order nassellaria in the early mesozoic

atlantic multidecadal oceanic variability and its influence on the atmosphere in a climate model the mechanisms controlling the decadal to multidecadal variability of the atlantic meridional overturning circulation moc and its influence on the atmosphere are investigated using a control simulation with the ipsl cm4 climate model the multidecadal fluctuations of the moc are mostly driven by deep convection in the subpolar gyre which occurs south of iceland in the model the latter is primarily influenced by the anomalous advection of salinity due to changes in the east atlantic pattern eap which is the second mode of atmospheric variability in the north atlantic region the north atlantic oscillation is the dominant mode but it plays a secondary role in the moc fluctuations during summer the moc variability is shown to have a significant impact on the atmosphere in the north atlantic european sector the moc influence is due to an interhemispheric sea surface temperature sst anomaly with opposite signs in the two hemispheres but largest amplitude in the northern one the sst pattern driven by the moc mostly resembles the model atlantic multidecadal oscillation amo and bears some similarity with the observed one it is shown that the amo reflects both the moc influence and the local atmospheric forcing hence the moc influence on climate is best detected using lagged relations between climatic fields the atmospheric response resembles the eap in a phase that might induce a weak positive feedback on the moc

early paleozoic radiolarian biozonation current knowledge of early paleozoic radiolarians permits the recognition of faunal assemblages and zones that constitute a biozonation this new zonation utilizes robust and relatively common easily recognized morphotypes it will facilitate rapid acquisition of previously unavailable age constraints for marine siliceous sedimentary successions in hitherto poorly understood early paleozoic orogenic collages

atlantic subsurface temperatures response to a shutdown of the overturning circulation and consequences for its recovery abstract using the coupled climate model of intermediate complexity climber 3 changes in the vertical thermal structure associated with a shutdown of the atlantic meridional overturning circulation amoc are investigated when north atlantic deep water formation is inhibited by anomalous freshwater forcing intermediate depth ventilation can remain active and cool the subsurface water masses i e the cold case however if intermediate ventilation is completely suppressed relatively warm water coming from the south penetrates to a high northern latitude beneath the halocline and induces a strong vertical temperature inversion between the surface and intermediate depth i e the warm case both types of temperature anomalies emerge within the first decade after the beginning of the freshwater perturbation the sign of subsurface temperature anomaly has a strong implication for the recovery of the amoc once the anomalous freshwater forcing is removed while the amoc recovers from the cold case

atlantic meridional overturning circulation response to idealized external forcing the response of the atlantic meridional overturning circulation amoc to idealized external solar forcing is studied in terms of the internal unforced amoc modes with the kiel climate model kcm a coupled atmosphere ocean sea ice general circulation model the statistical investigation of kcm s internal amoc variability obtained from a multi millennial control run yields three distinct modes a multi decadal mode with a period of about 60 years a quasi centennial mode with a period of about 100 years and a multi centennial mode with a period of about 300 400 years most variance is explained by the multi centennial mode and the least by the quasi centennial mode the solar constant varies sinusoidally with two different periods 100 and 60 years in forced runs with kcm the amoc response to the external forcing is rather complex and nonlinear it involves strong changes in the frequency structure of the variability while the control run depicts multi timescale behavior the amoc variability in the experiment with 100 year forcing period is channeled into a relatively narrow band centered near the forcing period it is the quasi centennial amoc mode with a period of just under 100 years which is excited although it is heavily damped in the control run thus the quasi centennial mode retains its period which does not correspond exactly to the forcing period surprisingly the quasi centennial mode is also most strongly excited when the forcing period is set to 60 years the period of the multi decadal mode which is rather prominent in the control run it is largely the spatial structure of the forcing rather than its period that determines which of the three internal amoc modes is excited the results suggest that we need to understand the full modal structure of the internal amoc variability in order to understand the circulation s response to external forcing this could be a challenge for climate models we cannot necessarily expect that the response to external forcing is realistically captured by a model even if only strongly damped modes are not well represented that do not account for much variance under present day conditions

east atlantic pattern drives multidecadal atlantic meridional overturning circulation variability during the last glacial maximum the variability of the atlantic meridional overturning circulation amoc and its governing processes during the last glacial maximum lgm is investigated in the kiel climate model kcm under lgm conditions multidecadal amoc variability is mainly forced by the surface heat flux variability linked to the east atlantic pattern eap in contrast the multidecadal amoc variability under preindustrial conditions is mainly driven by the surface heat flux variability associated with the north atlantic oscillation nao stand alone atmosphere model experiments show that relative to preindustrial conditions the change in amoc forcing under lgm conditions is tightly linked to the differences in topography key points multidecadal amoc variability during the lgm and its associated physical processes have been investigated by means of a climate model multidecadal amoc variability during the lgm is mainly driven by surface heat flux variability linked to the east atlantic pattern as opposed to the north atlantic oscillation under preindustrial conditions change in topography during the lgm is responsible for the change in amoc forcing

a 4500 year reconstruction of sea surface temperature variability at decadal time scales off north iceland marine paleo records acquired at high temporal resolution provide critical data for testing numerical climate models and help to understand processes underlying ocean variability this study presents a unique 4500 year reconstruction of sea surface temperature sst obtained from alkenones in the north atlantic polar front area off north iceland at an average temporal resolution of 4 5 years spectral analysis of this signal shows dominant multidecadal oscillations which occurred with a stronger amplitude between 2500 and 4200 years bp hand in hand with fluctuations of bottom currents indicated by paleomagnetic proxies contemporaneous large excursions of the inter tropical convergence zone itcz are also recorded by the distant cariaco titanium time series suggesting a link with low latitude atlantic climate we speculate that the oscillations reflect changes of the meridional overturning circulation moc induced by increased enso activity

volcanic eruption of the mid ocean ridge along the east pacific rise crest at 9 45 52 n direct submersible observations of seafloor phenomena associated with an eruption event in april 1991 in april 1991 we witnessed from the submersible alvin a suite of previously undocumented seafloor phenomena accompanying an in progress eruption of the mid ocean ridge on the east pacific rise crest at 9 45 n 52 n the volume of the eruption could not be precisely determined although comparison of pre and post eruption seabeam bathymetry indicate that any changes in ridge crest morphology resulting from the eruption were 10 m high effects of the eruption included 1 increased abundance and redistribution of hydrothermal vents disappearance of numerous vent communities and changes in characteristics of vent fauna and mineral deposits within the eruption area since december 1989 2 murkiness of bottom waters up to tens of meters above the seafloor due to high densities of suspended mineral and biogenic particulates 3 destruction of a vent community by lava flows mass wasting and possible hydrovolcanic explosion at a site known as tubeworm barbecue in the axial summit caldera asc at 9 50 6 n 4 near critical temperatures of hydrothermal vent fluids ranging up to 403 c 5 temporal variations over a 2 week interval in both temperatures and chemical isotopic compositions of hydrothermal fluids 6 unusual compositions of end member vent fluids with ph values ranging to a record low of 2 5 salinities ranging as low as 0 3 wt nacl one twelfth that of seawater and dissolved gases reaching high concentrations 65 mmol l for both co2 and h2s 7 venting at temperatures above 380 c of visually detectable white vapor that transformed to plumes of gray smoke a few centimeters above vent orifices 8 disorganized venting of both high temperature fluids black and gray smoke and large volumes of cooler diffuse hydrothermal fluids directly from the basaltic seafloor rather than from hydrothermal mineral constructions 9 rapid and extensive growth of flocculent white bacterial mats species unknown on and under the seafloor in areas experiencing widespread venting of diffuse hydrothermal fluid and 10 subseafloor downslope migration of magma normal to the ridge axis in a network of small scale 1 5 m diameter lava tubes and channels to distances at least 100 200 m outside the asc we suggest that in april 1991 intrusion of dikes in the eruption area to 200 m beneath the asc floor resulted in phase separation of fluids near the tops of the dikes and a large flux of vapor rich hydrothermal fluids through the overlying rubbly cavernous lavas low salinities and gas rich compositions of hydrothermal fluids sampled in the eruption area are appropriate for a vapor phase in a seawater system undergoing subcritical liquid vapor phase separation boiling and phase segregation hydrothermal fluids streamed directly from fissures and pits that may have been loci of lava drainback and or hydrovolcanic explosions these fissures and pits were lined with white mats of a unique fast growing bacteria that was the only life associated with the brand new vents the prolific bacteria which covered thousands of square meters on the ridge crest and were also abundant in subseafloor voids may thrive on high levels of gases in the vapor rich hydrothermal fluids initially escaping the hydrothermal system white bacterial particulates swept from the seafloor by hydrothermal vents swirled in an unprecedented biogenic blizzard up to 50 m above the bottom the bacterial proliferation of april 1991 is likely to be a transient bloom that will be checked quickly either by decline of dissolved gas concentrations in the fluids as rapid heat loss brings about cessation of boiling and or by grazing as other organisms are re established in the biologically devastated area

formation of submarine flat topped volcanic cones in hawai i high resolution bathymetric mapping has shown that submarine flat topped volcanic cones morphologically similar to ones on the deep sea floor and near mid ocean ridges are common on or near submarine rift zones of kilauea kohala or mauna kea mahukona and haleakala volcanoes four flat topped cones on kohala were explored and sampled with the pisces v submersible in october 1998 samples show that flat topped cones on rift zones are constructed of tholeiitic basalt erupted during the shield stage similarly shaped flat topped cones on the northwest submarine flank of ni ihau are apparently formed of alkalic basalt erupted during the rejuvenated stage submarine postshield stage eruptions on hilo ridge mahukona hana ridge and offshore ni ihau form pointed cones of alkalic basalt and hawaiite the shield stage flat topped cones have steep 25 sides remarkably flat horizontal tops basal diameters of 1 3 km and heights 300 m the flat tops commonly have either a low mound or a deep crater in the center the rejuvenated stage flat topped cones have the same shape with steep sides and flat horizontal tops but are much larger with basal diameters up to 5 5 km and heights commonly greater than 200 m the flat tops have a central low mound shallow crater or levees that surrounded lava ponds as large as 1 km across most of the rejuvenated stage flat topped cones formed on slopes 10 and formed adjacent semicircular steps down the flank of ni ihau rather than circular structures all the flat topped cones appear to be monogenetic and formed during steady effusive eruptions lasting years to decades these and other submarine volcanic cones of similar size and shape apparently form as continuously overflowing submarine lava ponds a lava pond surrounded by a levee forms above a sea floor vent as lava continues to flow into the pond the lava flow surface rises and overflows the lowest point on the levee forming elongate pillow lava flows that simultaneously build the rim outward and upward but also dam and fill in the low point on the rim the process repeats at the new lowest point forming a circular structure with a flat horizontal top and steep pillowed margins there is a delicate balance between lava heat supply to the pond and cooling and thickening of the floating crust factors that facilitate construction of such landforms include effusive eruption of lava with low volatile contents moderate to high confining pressure at moderate to great ocean depth long lived steady eruption years to decades moderate effusion rates probably ca 0 1 km3 year and low but not necessarily flat slopes with higher effusion rates sheet flows flood the slope with lower effusion rates pillow mounds form hawaiian shield stage eruptions begin as fissure eruptions if the eruption is too brief it will not consolidate activity at a point and fissure fed flows will form a pond with irregular levees the pond will solidify between eruptive pulses if the eruption is not steady lava that is too volatile rich or that is erupted in too shallow water will produce fragmental and highly vesicular lava that will accumulate to form steep pointed cones as occurs during the post shield stage the steady effusion of lava on land constructs lava shields which are probably the subaerial analogs to submarine flat topped cones but formed under different cooling conditions

reconciling two alternative mechanisms behind bi decadal variability in the north atlantic understanding the preferential timescales of variability in the north atlantic usually associated with the atlantic meridional overturning circulation amoc is essential for the prospects for decadal prediction however the wide variety of mechanisms proposed from the analysis of climate simulations potentially dependent on the models themselves has stimulated the debate of which processes take place in reality one mechanism receiving increasing attention identified both in idealized models and observations is a westward propagation of subsurface buoyancy anomalies that impact the amoc through a basin scale intensification of the zonal density gradient enhancing the northward transport via thermal wind balance in this study we revisit a control simulation from the institut pierre simon laplace coupled model 5a ipsl cm5a characterized by a strong amoc periodicity at 20 years previously explained by an upper ocean atmosphere sea ice coupled mode driving convection activity south of iceland our study shows that this mechanism interacts constructively with the basin wide propagation in the subsurface this constructive feedback may explain why bi decadal variability is so intense in this coupled model as compared to others

a high resolution study of holocene paleoclimatic and paleoceanographic changes in the nordic seas 1 high resolution records from images core md95 2011 in the eastern norwegian sea provide evidence for relatively large and small scale high latitude climate variability throughout the holocene during the early and mid holocene a situation possibly driven by consistent stronger westerlies increased the eastward influence of arctic intermediate and near surface waters for the late holocene a relaxation of the atmospheric forcing resulted in increased influence of atlantic water the main changes in holocene climate show no obvious connection to changing solar irradiance and spectral analysis reveals no consistent signature for any periodic behavior of holocene climate at millennial or centennial timescales there are however indications of consistent multidecadal variability

southward migration of the intertropical convergence zone through the holocene titanium and iron concentration data from the anoxic cariaco basin off the venezuelan coast can be used to infer variations in the hydrological cycle over northern south america during the past 14 000 years with subdecadal resolution following a dry younger dryas a period of increased precipitation and riverine discharge occurred during the holocene thermal maximum since approximately 5400 years ago a trend toward drier conditions is evident from the data with high amplitude fluctuations and precipitation minima during the time interval 3800 to 2800 years ago and during the little ice age these regional changes in precipitation are best explained by shifts in the mean latitude of the atlantic intertropical convergence zone itcz potentially driven by pacific based climate variability the cariaco basin record exhibits strong correlations with climate records from distant regions including the high latitude northern hemisphere providing evidence for global teleconnections among regional climates

a multimodel comparison of centennial atlantic meridional overturning circulation variability a mechanism contributing to centennial variability of the atlantic meridional overturning circulation amoc is tested with multi millennial control simulations of several coupled general circulation models cgcms these are a substantially extended integration of the 3rd hadley centre coupled climate model hadcm3 the kiel climate model kcm and the max plank institute earth system model mpi esm significant amoc variability on time scales of around 100 years is simulated in these models the centennial mechanism links changes in the strength of the amoc with oceanic salinities and surface temperatures and atmospheric phenomena such as the intertropical convergence zone itcz 2 of the 3 models reproduce all aspects of the mechanism with the third mpi esm reproducing most of them a comparison with a high resolution paleo proxy for sea surface temperatures ssts north of iceland over the last 4 000 years also linked to the itcz suggests that elements of this mechanism may also be detectable in the real world

toarcian radiolaria from mt mangart slovenian italian border and their paleoecological implications abstract diverse and well preserved toarcian radiolarians have been recovered from a succession of organic rich shale with intercalations of siliceous limestone the succession is located at the slovenian italian border in the julian alps and was deposited on a subsided block pertaining to the south tethyan passive continental margin twenty spumellarian and 17 nassellarian genera were found in total thirty six taxa were identified to species level and one new species bistarkum mangartense n sp is described the assemblages show a high predominance of spumellarians over nassellarians spongy spumellarians especially orbiculiforma are markedly abundant pantanelliidae are generally rare but reach a pronounced peak of 13 in one stratigraphic level among nassellarians parahsuum is the most abundant but members belonging to syringocapsidae are scarce to absent in addition to paleolatitude and water column depth ecological conditions accompanying the early toarcian global anoxic event may have to a considerable extent determined the specific taxonomic composition of these radiolarian faunas

temporal variability of the atlantic meridional overturning circulation at 26 5 n the vigor of atlantic meridional overturning circulation moc is thought to be vulnerable to global warming but its short term temporal variability is unknown so changes inferred from sparse observations on the decadal time scale of recent climate change are uncertain we combine continuous measurements of the moc beginning in 2004 using the purposefully designed transatlantic rapid climate change array of moored instruments deployed along 26 5 n with time series of gulf stream transport and surface layer ekman transport to quantify its intra annual variability the year long average overturning is 18 7 5 6 sverdrups sv range 4 0 to 34 9 sv where 1 sv a flow of ocean water of 106 cubic meters per second interannual changes in the overturning can be monitored with a resolution of 1 5 sv

indications for a north atlantic ocean circulation regime shift at the onset of the little ice age a prominent characteristic of the reconstructed northern hemisphere temperature signal over the last millennium is the transition from the medieval climate anomaly to the little ice age lia here we report indications for a non linear regime shift in the north atlantic ocean circulation at the onset of the lia specifically we apply a novel statistical test based on horizontal visibility graphs to two ocean sediment august sea surface temperature records from the norwegian sea and the central subpolar basin and find robust indications of time irreversibility in both records during the lia onset despite a basin wide cooling trend we report an anomalous warming in the central subpolar basin during the lia that is reproduced in ensemble simulations with the climate model of intermediate complexity climber 3 as a result of a non linear regime shift in the subpolar north atlantic ocean circulation the identified volcanically triggered non linear transition in the model simulations provides a plausible explanation for the signatures of time irreversibility found in the ocean sediment records our findings indicate a potential multi stability of the north atlantic ocean circulation and its importance for regional climate change on centennial time scales