interpentadal variability of temperature and salinity at intermediate depths of the north atlantic ocean 1970 1974 versus 1955 1959 we have composited historical hydrographic observations for the world ocean for two pentads 1955 1959 and 1970 1974 and have objectively analyzed these data for the purpose of studying the temporal variability of temperature and salinity in the north atlantic ocean the subtropical gyre 500 1300 m of the north atlantic was colder and fresher during 1970 1974 compared to 1955 1959 the relatively large changes in temperature and salinity on constant depth surfaces in the subtropical gyre were due to upward displacements of isopycnal surfaces at intermediate depths the eastern portion of the subarctic gyre was also colder and fresher during the 1970 1974 pentad in contrast the western portion of the subarctic gyre exhibited higher temperatures and salinities during 1970 1974 compared to 1955 1959 characteristic differences in temperature and salinity for both gyres were 0 5 c and 0 025 respectively analysis of changes in potential vorticity indicates that in the subtropical gyre potential vorticity increased in all density layers above the 26 5 surface suggesting that convection in this region may have been shallower in 1970 1974 compared to 1955 1959 below the 26 5 surface potential vorticity decreased through the 27 3 surface indicating that deeper than normal convection may have formed the water masses in these layers at 250 m depth relatively large changes in temperature and salinity occurred along the line of maximum climatological mixed layer depth that extends northeast to southwest across the north atlantic ocean

influence of pore pressure on the event size distribution of induced earthquakes 1 during an enhanced geothermal system egs experiment fluid is injected at high pressure into crystalline rock to enhance its permeability and thus create a reservoir from which geothermal heat can be extracted the fracturing of the basement caused by these high pore pressures is associated with microseismicity however the relationship between the magnitudes of these induced seismic events and the applied fluid injection rates and thus pore pressure is unknown here we show how pore pressure can be linked to the seismic frequency magnitude distribution described by its slope theb value we evaluate the dataset of an egs in basel switzerland and compare the observed event size distribution with the outcome of a minimalistic model of pore pressure evolution that relates event sizes to the differential stress d we observe that the decrease of b values with increasing distance of the injection point is likely caused by a decrease in pore pressure this leads to an increase of the probability of a large magnitude event with distance and time

carbon isotopic composition of hydrocarbons in ocean transported bitumens from the coastline of australia abstract bitumens stranding along the coastlines of the northern territory western australia south australia victoria and tasmania often have biomarker signatures which closely match those of oils of s e asian origin a suite of these bitumens was studied to determine the isotopic signatures of their alkanes and to compare them to similar oils from the central sumatra basin saturated hydrocarbons were separated into a fraction containing n alkanes and isoalkanes and one containing the multibranched cyclic components using adduction into silicalite gas chromatography isotope ratio mass spectrometry gc irms of the n alkanes revealed 13 c signatures covering a wide range of values from 25 5 to 29 pdb but generally falling between those of the botryococcane containing minas and duri oils from the central sumatra basin n alkanes of the minas oil are 3 4 lighter than their duri counterparts the isotopic compositions of pristane and phytane cover a similar range 13 c 24 to 27 botryococcane is consistently heavy with 13 c values in the range 11 to 14 one bitumen sample with no botryococcane but abundant bicadinanes showed n alkane 13 c values in the range 28 to 29 at the light extreme for waxy bitumens in our sample suite sample to sample differences in carbon isotopic signatures of n alkanes are attributed mainly to variations in primary source with weathering and biodegradation as minor causes instances of low precision for replicate analyses 2 are caused by the relative abundance of co eluting isoalkanes overall the isotopic patterns of waxy bitumens from the australian coastline provide independent confirmation of their similarity to central sumatran lacustrine oils on the other hand asphaltic bitumens from the southern australian coastline are isotopically light with n alkane 13 c values in the range 31 5 to 33 this distinctive feature may assist identification of their source

interdecadal variability of the thermohaline circulation in box ocean models forced by fixed surface fluxes intrinsic modes of decadal variability are analyzed using box geometry ocean models forced by constant surface fluxes an extensive parameter sensitivity analysis of the oscillatory behavior is carried out with respect to the spherical cartesian geometry the b effect the coriolis parameter the parameterization of momentum dissipation and associated boundary conditions the vertical and horizontal diffusivities the convective adjustment algorithm the horizontal and vertical model resolution the forcing amplitude and the basin width the oscillations stand out as a robust geostrophic feature whose amplitude is mainly controlled by the horizontal diffusivity unsuccessful attempts to reproduce the variability in zonally averaged 2d models suggest that the 3d adjustment processes are necessary however the b effect is not necessary for decadal variability to occur and therefore classical rossby waves play no fundamental role in the mechanism various experiments with different geometry and forcing are conducted and do not support the necessity of viscous numerical boundary waves or any boundary in sustaining the oscillations the models show two types of oscillatory behavior 1 temperature anomalies propagating geostrophically westward in the eastward jet northern part of the basin and inducing an opposite anomaly in their wake and 2 stationary temperature anomalies in the northwest quarter that respond to the western boundary current transport changes and reinforce geostrophically this change until the opposite temperature anomaly built on the east finally reverses the meridional overturning anomaly the analysis of the transition from steady to oscillatory states using heat fluxes diagnosed at the equilibrium under restoring boundary conditions and the comparison of the variability under various forcing fields suggest that the oscillations are triggered in the regions of strongest surface cooling finally a simple box model analogy is proposed that captures the crucial phase shift between meridional overturning and north south density gradient anomalies on these decadal timescales

a 20 year coupled ocean sea ice atmosphere variability mode in the north atlantic in an aogcm in order to understand potential predictability of the ocean and climate at the decadal time scales it is crucial to improve our understanding of internal variability at this time scale here we describe a 20 year mode of variability found in the north atlantic in a 1 000 year pre industrial simulation of the ipsl cm5a lr climate model this mode involves the propagation of near surface temperature and salinity anomalies along the southern branch of the subpolar gyre leading to anomalous sea ice melting in the nordic seas which then forces sea level pressure anomalies through anomalous surface atmospheric temperatures the wind stress associated to this atmospheric structure influences the strength of the east greenland current across the denmark strait which in turn induces near surface temperature and salinity anomalies of opposite sign at the entrance of the labrador sea this starts the second half of the cycle after approximatively 10 years the time scale of the cycle is thus essentially set by advection of tracers along the southern branch of the subpolar gyre and by the time needed for anomalous east greenland current to accumulate heat and freshwater anomalies at the entrance of the labrador sea the atlantic meridional overturning circulation amoc does not play a dominant role in the mode that is confined in the subpolar north atlantic but it also has a 20 year preferred timescale this is due to the influence of the propagating salinity anomalies on the oceanic deep convection the existence of this preferred timescale has important implications in terms of potential predictability of the north atlantic climate in the model although its realism remains questionable and is discussed

oceanic control of multidecadal variability in an idealized coupled gcm idealized ocean models are known to develop intrinsic multidecadal oscillations of the meridional overturning circulation moc here we explore the role of ocean atmosphere interactions on this low frequency variability we use a coupled ocean atmosphere model set up in a flat bottom aquaplanet geometry with two meridional boundaries the model is run at three different horizontal resolutions 4 2 and 1 in both the ocean and atmosphere at all resolutions the moc exhibits spontaneous variability on multidecadal timescales in the range 30 40 years associated with the propagation of large scale baroclinic rossby waves across the atlantic like basin the unstable region of growth of these waves through the long wave limit of baroclinic instability shifts from the eastern boundary at coarse resolution to the western boundary at higher resolution increasing the horizontal resolution enhances both intrinsic atmospheric variability and ocean atmosphere interactions in particular the simulated atmospheric annular mode becomes significantly correlated to the moc variability at 1 resolution an ocean only simulation conducted for this specific case underscores the disruptive but not essential influence of air sea interactions on the low frequency variability this study demonstrates that an atmospheric annular mode leading moc changes by about 2 years as found at 1 resolution does not imply that the low frequency variability originates from air sea interactions

bidecadal sea level modes in the north and south atlantic oceans the relationship between the north and south atlantic bidecadal sea level sl oscillations during the twentieth century is investigated for the first time using simple ocean data assimilation reanalysis complex empirical orthogonal function analysis of the bidecadal band gives two dominant modes the first dominating from 1915 to 1965 and the second from 1970 onward the long term time dependent change of mode dominance suggests a structural type regime shift the first mode is characterized by states with north and south atlantic subtropical gyres in phase while tropical and subpolar regions are in opposite phase relative to them the second mode is characterized by the subpolar gyre and north subtropical gyre almost in quadrature with north and south subtropical gyres out of phase thermal rossby waves are very clear only in the second mode these waves seem to be influenced by bottom topography known atlantic meridional overturning circulation amoc sea level fingerprints and amoc strength indices are discussed in the bidecadal oscillations context

a new velocity field for africa from combined gps and doris space geodetic solutions contribution to the definition of the african reference frame afref 1 we analyzed 16 years of gps and 17 years of doppler orbitography and radiopositioning integrated by satellite doris data at continuously operating geodetic sites in africa and surroundings to describe the present day kinematics of the nubian and somalian plates and constrain relative motions across the east african rift the resulting velocity field describes horizontal and vertical motion at 133 gps sites and 9 doris sites horizontal velocities at sites located on stable nubia fit a single plate model with a weighted root mean square residual of 0 6 mm yr maximum residual 1 mm yr an upper bound for plate wide motions and for regional scale deformation in the seismically active southern africa and cameroon volcanic line we confirm significant southward motion 1 5 mm yr in morocco with respect to nubia consistent with earlier findings we propose an updated angular velocity for the divergence between nubia and somalia which provides the kinematic boundary conditions to rifting in east africa we update a plate motion model for the east african rift and revise the counterclockwise rotation of the victoria plate and clockwise rotation of the rovuma plate with respect to nubia vertical velocities range from 2 to 2 mm yr close to their uncertainties with no clear geographic pattern this study provides the first continent wide position velocity solution for africa expressed in international terrestrial reference frame itrf2008 a contribution to the upcoming african reference frame afref except for a few regions the african continent remains largely under sampled by continuous space geodetic data efforts are needed to augment the geodetic infrastructure and openly share existing data sets so that the objectives of afref can be fully reached

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

simulated decadal oscillations of the atlantic meridional overturning circulation in a cold climate state the significance of the atlantic meridional overturning circulation moc for regional and hemispheric climate change requires a complete understanding using fully coupled climate models here we present a persistent decadal oscillation in a coupled atmosphere ocean general circulation model while the present study is limited by the lack of comparisons with paleo proxy records the purpose is to reveal a new theoretically interesting solution found in the fully coupled climate model the model exhibits two multi century long stable states with one dominated by decadal moc oscillations the oscillations involve an interaction between anomalous advective transport of salt and surface density in the north atlantic subpolar gyre their time scale is fundamentally determined by the advection in addition there is a link between the moc oscillations and north atlantic oscillation nao like sea level pressure anomalies the analysis suggests an interaction between the nao and an anomalous subpolar gyre circulation in which sea ice near and south of the labrador sea plays an important role in generating a large local thermal anomaly and a meridional temperature gradient the latter induces a positive feedback via synoptic eddy activity in the atmosphere in addition the oscillation only appears when the nordic sea is completely covered by sea ice in winter and deep convection is active only near the irminger sea such conditions are provided by a substantially colder north atlantic climate than today

optimal excitation of amoc decadal variability links to the subpolar ocean this study describes the excitation of variability of the atlantic meridional overturning circulation amoc by optimal perturbations in surface temperature and salinity our approach is based on a generalized stability analysis within a realistic ocean general circulation model which extends the conventional linear stability analysis to transient growth unlike methods based on singular value decomposition our analysis invokes an optimization procedure using lagrangian multipliers which is a more general approach allowing us to impose relevant constraints on the perturbations and use linear measures of the amoc meridional volume and heat transports we find that the structure of the optimal perturbations is characterized by anomalies in surface temperature or salinity centered in the subpolar regions of the north atlantic off the east coasts of greenland and canada south of the denmark strait the maximum impact of such perturbations on the amoc is reached after 7 9 yr this is a robust result independent of the perturbations type the optimization measures the model surface boundary conditions or other constraints the transient growth involves the following mechanism after the initial positive surface density perturbation reaches the deep ocean it generates a cyclonic geostrophic flow that extracts a zonally varying temperature anomaly from the mean temperature field in the upper ocean in turn the anomalous zonal temperature gradient induces by thermal wind balance a northward flow in the upper ocean and a southward flow in the deep ocean thus strengthening the amoc subsequently the transient growth gives way to a decaying oscillation corresponding to a damped oceanic eigenmode with a period of about 24 yr this mode is controlled by westward propagating large scale thermal rossby waves modifying the density field in the north atlantic and hence the amoc simple estimates show that realistic changes in salinity or temperature in the upper ocean such as those due to the great salinity anomaly can induce amoc variations of several sverdups via this mechanism or 10 20 of the mean overturning an idealized model is formulated to investigate the transient growth and highlight the role of mean convection in communicating surface density anomalies to the deep ocean 2014 published by elsevier ltd

simultaneous evolution of gyre and atlantic meridional overturning circulation anomalies as an eigenmode of the north atlantic system abstractthe authors identify an interdecadal oscillatory mode of the north atlantic atmosphere ocean system in a general circulation model gfdl cm2 1 via a linear inverse model lim the oscillation mechanism is mostly embedded in the subpolar gyre anomalous advection generates density anomalies in the eastern subpolar gyre which propagate along the mean gyre circulation and reach the subpolar gyre center around 10 years later when associated anomalous advection of the opposite sign starts the other half cycle as density anomalies reach the labrador sea deep convection region atlantic meridional overturning circulation amoc anomalies are also induced both the gyre and amoc anomalies then propagate equatorward slowly following the advection of density anomalies the oscillation is further demonstrated to be more likely an ocean only mode while excited by the atmospheric forcing in particular it can be approximated as a linearly driven damped oscillator that is partly excited by the north atla

convective mixing and the thermohaline circulation abstract an idealized three dimensional model of buoyancy driven flow in a single hemisphere is used to investigate the relationship between the meridional overturning and the efficiency by which convective mixing eliminates static instability in the fast limit mixing timescale hours to weeks the meridional overturning is not rate limited by the efficiency of convective mixing if convective mixing is made less efficient the model s meridional overturning strength increases moreover the dominant downwelling occurs not at the highest surface density hence the deep ocean is relatively buoyant the numerical results are explained by the different influences of convective mixing and downward advection on the deep ocean heat budget they underscore the fundamentally three dimensional nature of the meridional overturning in addition the narrowness of deep downwelling is related to the geostrophic dynamics of deep temperature anomalies near the eastern wall the model results presented here are in con

polymethylsqualanes from botryococcus braunii in lacustrine sediments and crude oils abstract a novel hydrocarbon 3 7 18 22 tetramethylsqualane has been identified in extracts from the maniguin 2 well on maniguin island philippines the duri oil from sumatra indonesia and the maoming oil shale from china a related hydrocarbon tentatively assigned the structure 3 7 11 14 tetramethylsqualane occurs in the maniguin samples like c34 botryococcane the tetramethylsqualanes are unusually enriched in 13c compared to co occuring n alkanes and c16 20 acyclic isoprenoids polymethylsqualanes extend the range of distinctive hydrocarbons produced by botryococcus braunii and its fossil counterparts

complex patterns of steroidal biomarkers in tertiary lacustrine sediments of the biyang basin china gas chromatography gc gas chromatography mass spectrometry gc ms and gas chromatography mass spectrometry mass spectrometry gc ms ms with co injected synthetic standards were used to analyse the biomarker patterns of some tertiary lacustrine clayey dolomites from the biyang basin china the lithology low pr ph ratio and high gammacerane content of these sediments indicated that high salinity prevailed during their deposition the distributions of steroidal hydrocarbons were particularly unusual and several pseudohomologous series including regular steranes c27 c29 4 methyl steranes c28 c30 including dinosteranes 3b ethyl steranes c29 c31 lanostanes c30 c32 and a variety of other 3b alkylated steranes were identified 3b n propylcholestane 3b n propylstigmastane and 4 4 dimethylcholestane were identified using authentic standards and this is the first time these compounds have been unambiguously characterised in sediments crown copyright 2001 published by elsevier science ltd all rights reserved

temporal and three dimensional spatial analyses of the frequency magnitude distribution near long valley caldera california summary the 3 d distribution of the b value of the frequency magnitude distribution is analysed in the seismically active parts of the crust near long valley caldera california the seismicity is sampled in spherical volumes containing n 150 earthquakes and centred at nodes of a grid separated by 0 3 km significant variations in the b value are detected with b ranging from b 0 6 to b 2 0 high b value volumes are located near the resurgent dome and at depths below 5 km at mammoth mountain b values are found to be much lower south of the long valley caldera we interpret this to indicate that an active magma body has advanced from depths below 8 km to depths of 4 to 5 km beneath mammoth mountain in 1989 and that anomalous crust either highly fractured or containing unusually high pore pressure such as is the case in the vicinity of active magma bodies exists north of the seismically active area beneath the resurgent dome at all depths we also investigate the spatial distribution of temporal variations of the frequency magnitude distribution by introducing diverential b value maps b values increased from b 0 8 to b 1 5 underneath mammoth mountain at the onset of the 1989 earthquake swarm and remained high thereafter this suggests that an intrusion permanently altered the average distribution of cracks at 5 10 km depth or that the pore pressure permanently increased we propose that high b values are a necessary but not suycient condition near a magmatic body and therefore spatial b value mapping can be used to aid in the identification of active magma bodies

the mechanisms of the atlantic meridional overturning circulation slowdown induced by arctic sea ice decline abstractwe explore the mechanisms by which arctic sea ice decline affects the atlantic meridional overturning circulation amoc in a suite of numerical experiments perturbing the arctic sea ice ra

paleoreconstruction by biological markers abstract during diagenesis and conversion of the original lipid fraction of biological systems to petroleum hydrocarbons the following four basic events needed for paleoreconstruction can be monitored by biological markets 1 sourcing 2 maturation 3 migration and 4 biodegradation actual cases of applying biological markers to petroleum exploration problems in different parts of the world are demonstrated cretaceous and phosphoria sourced oils in the wyoming thrust belt can clearly be distinguished from one another by high quality source fingerprinting of biomarker terpanes using gas chromatography mass spectrometry identification of recently discovered biological markers head to head isoprenoids allows subtle source differentiation between oils from sumatra the degree of crude oil maturation in basins from california alaska russia wyoming and louisiana can be assessed by specific novel biomarker ratios 20s 20r sterane epimers field evidence from such interpretation is confirmed by laboratory pyrolysis of the rock an example of immature sumatra rock is given extensive migration is documented by biomarkers in several oils the effect of biodegradation on biomarker steranes and terpanes is exemlified in a california basin all biological marker results are consistent with the geological setting and add a new dimension in assisting the petroleum explorationist toward paleo reconstruction

meridional density gradients do not control the atlantic overturning circulation a wide body of modeling and theoretical scaling studies support the concept that changes to the atlantic meridional overturning circulation amoc whether forced by winds or buoyancy fluxes can be understood in terms of a simple causative relation between the amoc and an appropriately defined meridional density gradient mdg the mdg is supposed to translate directly into a meridional pressure gradient here two sets of experiments are performed using a modular ocean model coupled to an energy moisture balance model in which the positive amoc mdg relation breaks down in the first suite of seven model integrations it is found that increasing winds in the southern ocean cause an increase in overturning while the surface density difference between the equator and north atlantic drops in the second suite of eight model integrations the equation of state is manipulated so that the density is calculated at the model temperature plus an artificial increment dt that ranges from 238 to 98c an increase in dt results in increased sensitivity of density to temperature gradients the amoc in these model integrations drops as the mdg increases regardless of whether the density difference is computed at the surface or averaged over the upper ocean traditional scaling analysis can only produce this weaker amoc if the scale depth decreases enough to compensate for the stronger mdg five estimates of the depth scale are evaluated and it is found that the changes in the amoc can be derived from scaling analysis when using the depth of the maximum overturning circulation or estimates thereof but not from the pycnocline depth these two depth scales are commonly assumed to be the same in theoretical models of the amoc it is suggested that the correlation between the mdg and amoc breaks down in these model integrations because the depth and strength of the amoc is influenced strongly by remote forcing such as southern ocean winds and antarctic bottom water formation

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

basinwide response of the atlantic meridional overturning circulation to interannual wind forcing an eddy resolving ocean general circulation model for the earth simulator ofes and a simple wind driven two layer model are used to investigate the role of momentum fluxes in driving the atlantic meridional overturning circulation amoc variability throughout the atlantic basin from 1950 to 2010 diagnostic analysis using the ofes results suggests that interior baroclinic rossby waves and coastal topographic waves play essential roles in modulating the amoc interannual variability the proposed mechanisms are verified in the context of a simple two layer model with realistic topography and only forced by surface wind the topographic waves communicate high latitude anomalies into lower latitudes and account for about 50 of the amoc interannual variability in the subtropics in addition the large scale rossby waves excited by wind forcing together with topographic waves set up coherent amoc interannual variability patterns across the tropics and subtropics the comparisons between the simple model and ofes results suggest that a large fraction of the amoc interannual variability in the atlantic basin can be explained by wind driven dynamics

oceanic isopycnal mixing by coordinate rotation abstract current numerical models of oceanic circulation differentiate between the eddy diffusion and viscosity transport along the geopotential horizontal and vertical directions only in order to model the effect of anisotropic turbulence as diffusive transport along and across density surfaces the isopycnal mixing tensor has been transformed from a diagonal second rank tensor in the isopycnal coordinate system to a tensor containing off diagonal elements in the geopotential coordinate system

baroclinic instability an oceanic wavemaker for interdecadal variability numerical simulations of coarse resolution idealized ocean basins under constant surface heat flux are analyzed to show that the interdecadal oscillations that emerge naturally in such configurations are driven by baroclinic instability of the mean state and damped by horizontal diffusion when the surface heat fluxes are diagnosed from a spinup in which surface temperatures are strongly restored to apparent atmospheric temperatures the most unstable regions diagnosed by large downgradient eddy heat fluxes are located in the basin northwest corner where the surface heat losses are largest the long wave limit of the baroclinic instability of idealized mean flows in a three layer model with vertical shears as observed in the gcms demonstrates that growth rates of order one cycle per year can be produced locally large enough to amplify thermal anomalies in the face of lateral diffusion the proposed instability mechanism that favors surface intensified perturbations also explains the lack of oscillations if the restoring to a surface climatology is too strong to assess whether this instability process of oceanic origin is robust enough to cause interdecadal variability of coupled ocean atmosphere models a four box ocean atmosphere model is constructed given the large heat capacity of the ocean as compared to the atmosphere the dynamical system that governs the model evolution is reduced to only two degrees of freedom the oceanic overturning thermohaline circulation and the interior north south temperature gradient the authors show that when the baroclinic instability growth rate exceeds the overall dissipation caused by turbulent eddy diffusion in the atmosphere and ocean and infrared back radiation the dynamical system undergoes a hopf bifurcation and interdecadal oscillations emerge through a limit cycle

multiple equilibria as a possible mechanism for decadal variability in the north atlantic ocean decadal climate variability in the north atlantic has received increased attention in recent years because modeling results suggest predictability of heat content and circulation indices several years ahead however determining the applicability of these results in the real world is challenging because of an incomplete understanding of the underlying mechanisms here the authors show that recent attempts to reconstruct the decadal variations in one of the dominant circulation systems of the region the subpolar gyre spg are not always consistent a coherent picture is partly recovered by a simple conceptual model solely forced by reanalyzed surface air temperatures this confirms that surface heat flux indeed plays a leading role for this typeofvariability ashasbeensuggestedinpreviousstudies theresultsfurthersuggestthatlargevariationsin the spg correspond to the crossing of a bifurcation point that is predicted from idealized experiments and an analytical solution of the model used herein performance of this conceptual model is tested against a statistical stochastic model hysteresis and the existence of two stable modes of the spg circulation shape its response to forcing by atmospheric temperatures the identification of the essential dynamics and the reduction to a minimal model of spg variability provide a quantifiable basis and a framework for future studies on decadal climate variability and predictability

coherent multidecadal variability in north atlantic sea level 1 tide gauge records from around the north atlantic are examined and found to show variability on 20 30 year time scales sea surface height variability along the western boundary of the north atlantic shows a particularly strong and coherent signal similar variability is also found in an ensemble of runs using a state of the art climate model gfdl cm2 1 this sea surface height variability is linked to variability of temperatures in the upper layers of the ocean and thence to the atlantic multidecadal oscillation the variability is consistent with the excited internal ocean mode mechanism of multidecadal variability derived from idealised models and the timescale is consistent with that derived from observations of sub surface temperature variability

present day kinematics and fault slip rates in eastern iran derived from 11 years of gps data we analyze new gps data spanning 11 years at 92 stations in eastern iran we use these data to analyze the present day kinematics and the slip rates on most seismogenic faults in eastern iran the east lut west lut kuhbanan anar dehshir and doruneh faults are confirmed as the major faults and are found to currently slip laterally at 5 6 0 6 4 4 0 4 3 6 1 3 2 0 0 7 1 4 0 9 and 1 3 0 8 mm yr respectively slip is right lateral on the ns striking east lut west lut kuhbanan anar and dehshir faults and left lateral on the ew doruneh fault the ns faults slice the eastern iranian crust into five blocks that are moving northward at 6 13 mm yr with respect to the stable afghan crust at the eastern edge of the collision zone the collective behavior of the ns faults might thus allow the arabian promontory to impinge northward into the eurasian crust the ns faults achieve additional ns shortening by rotating counterclockwise in the horizontal plane at current rates up to 0 8 ma modeling the gps and available geological data with a block rotation model suggests that the rotations have been going on at a similar rate 1 0 4 ma over the last 12 ma we identify large strains at the tips of the rotating east lut west lut and kuhbanan faults which we suspect to be responsible for the important historical and instrumental seismicity in those zones

on multidecadal variability of the atlantic meridional overturning circulation in the community climate system model version 3 abstract multidecadal variability of the atlantic meridional overturning circulation moc is investigated diagnostically in the ncar community climate system model version 3 ccsm3 present day simulations using the highest t85 1 resolution version this variability has a 21 yr period and is present in many other ocean fields in the north atlantic in moc the oscillation amplitude is about 4 5 sv 1 sv 106 m3 s 1 corresponding to 20 of the mean maximum moc transport the northward heat transport nht variability has an amplitude of about 0 12 pw representing 10 of the mean maximum nht in sea surface temperature sst and sea surface salinity sss the peak to peak changes can be as large as 6 7 c and 3 psu respectively the labrador sea region is identified as the deep water formation dwf site associated with the moc oscillations in contrast with some previous studies temperature and salinity contributions to the total density in this dwf region are almost equal and in phase the he

sub surface signatures of the atlantic multidecadal oscillation 1 sub surface signatures of the atlantic multidecadal oscillation amo are identified using expendable bathythermograph xbt measurements of temperature from the surface down to a depth of 400 m basin averaged temperature anomalies in the north atlantic at different depths display multidecadal variability with a phase shift between temperature anomalies at the surface and at depth westward propagation of temperature anomalies is observable at depth and there is a lag correlation between east west and north south temperature gradients with the east west temperature gradient leading these sub surface characteristics of the amo agree with those expected from the noise driven internal ocean mode view of the amo as derived from a hierarchy of ocean atmosphere models

energetics of multidecadal atlantic ocean variability abstractoscillatory behavior of the atlantic meridional overturning circulation moc is thought to underlie atlantic multidecadal climate variability while the energy sources and sinks driving the mean moc have received intense scrutiny over the last decade the governing energetics of the modes of variability of the moc have not been addressed to the same degree this paper examines the energy conversion processes associated with this variability in an idealized north atlantic ocean model in this model the multidecadal variability arises through an instability associated with a so called thermal rossby mode which involves westward propagation of temperature anomalies applying the available potential energy ape framework from stratified turbulence to the idealized ocean model simulations the authors study the multidecadal variability from an energetics viewpoint the analysis explains how the propagation of the temperature anomalies leads to changes in ape which are subsequently converted into t

the internal generation of the atlantic ocean interdecadal variability abstractnumerical simulations of a realistic ocean general circulation model forced by prescribed surface fluxes are used to study the origin and structure of intrinsic interdecadal variability of

the leading interdecadal eigenmode of the atlantic meridional overturning circulation in a realistic ocean model abstractvariations in the strength of the atlantic meridional overturning circulation amoc are a major potential source of decadal and longer climate variability in the atlantic this study analyzes continuous integrations of tangent linear and adjoint versions of an ocean general circulation model ocean parallelise opa and rigorously shows the existence of a weakly damped oscillatory eigenmode of the amoc centered in the north atlantic ocean and controlled solely by linearized ocean dynamics in this particular gcm the mode period is roughly 24 years its e folding decay time scale is 40 years and it is the least damped oscillatory mode in the system its mechanism is related to the westward propagation of large scale temperature anomalies in the northern atlantic in the latitudinal band between 30 and 60 n the westward propagation results from a competition among mean eastward zonal advection equivalent anomalous westward advection caused by the mean meridional temperature gradient and westw

influences of tropical extratropical interaction on the multidecadal amoc variability in the ncep climate forecast system we have examined the mechanisms of a multidecadal oscillation of the atlantic meridional overturning circulation amoc in a 335 year simulation of the climate forecast system cfs the climate prediction model developed at the national centers for environmental prediction ncep both the mean and seasonal cycle of the amoc in the cfs are generally consistent with observation based estimates with a maximum northward volume transport of 16 sv 106 m3 s near 35 n at 1 2 km the annual mean amoc shows an intermittent quasi 30 year oscillation its dominant structure includes a deep anomalous overturning cell referred to as the anomalous amoc with amplitude of 0 6 sv near 35 n and an anomalous subtropical cell stc of shallow overturning spanning across the equator the mechanism for the oscillation includes a positive feedback between the anomalous amoc and surface wind stress anomalies in mid latitudes and a negative feedback between the anomalous stc and amoc a strong amoc is associated with warm sea surface temperature anomaly ssta centered near 45 n which generates an anticyclonic easterly surface wind anomaly this anticyclonic wind anomaly enhances the regional downwelling and reinforces the anomalous amoc in the mean time a wind evaporation sst wes feedback extends the warm ssta to the tropics and induces a cyclonic wind stress anomaly there which drives a tropical upwelling and weakens the stc north of the equator the stc anomaly in turn drives a cold upper ocean heat content anomaly hca in the northern tropical atlantic and weakens the meridional heat transport from the tropics to the mid latitude through an anomalous southward western boundary current the anomalous stc transports cold hca from the subtropics to the mid latitudes weakening the mid latitude deep overturning

a comparative study of fossil and extant algaenans using ruthenium tetroxide degradation in this study the chemical structure of algaenans isolated from the freshwater algae tetraedron minimum pediastrum boryanum and botryococcus braunii are compared with their fossil counterparts by means of ruo4 oxidation the results show that the algaenans investigated are preserved in sediments with only minor structural alterations however product mixtures from ruo4 degradation of the fossil algaenans exhibit a broader distribution of oxidation products than freshly isolated algaenans indicating that the fossil biopolymers contain a greater proportion of ether cross links which maybe an effect of diagenetic alteration or different algal strains despite these differences fossil algaenans can still be recognised chemically on the basis of the specific ruo4 oxidation products even after 50 ma of sediment burial

reconstructing extreme amoc events through nudging of the ocean surface a perfect model approach while the atlantic meridional overturning circulation amoc is thought to be a crucial component of the north atlantic climate past changes in its strength are challenging to quantify and only limited information is available in this study we use a perfect model approach with the ipsl cm5a lr model to assess the performance of several surface nudging techniques in reconstructing the variability of the amoc special attention is given to the reproducibility of an extreme positive amoc peak from a preindustrial control simulation nudging includes standard relaxation techniques towards the sea surface temperature and salinity anomalies of this target control simulation and or the prescription of the wind stress fields surface nudging approaches using standard fixed restoring terms succeed in reproducing most of the target amoc variability including the timing of the extreme event but systematically underestimate its amplitude a detailed analysis of the amoc variability mechanisms reveals that the underestimation of the extreme amoc maximum comes from a deficit in the formation of the dense water masses in the main convection region located south of iceland in the model this issue is largely corrected after introducing a novel surface nudging approach which uses a varying restoring coefficient that is proportional to the simulated mixed layer depth which in essence keeps the restoring time scale constant this new technique substantially improves water mass transformation in the regions of convection and in particular the formation of the densest waters which are key for the representation of the amoc extreme it is therefore a promising strategy that may help to better constrain the amoc variability and other ocean features in the models as this restoring technique only uses surface data for which better and longer observations are available it opens up opportunities for improved reconstructions of the amoc over the last few decades

multidecadal variability of the overturning circulation in presence of eddy turbulence at low resolution idealized ocean circulation models forced by prescribed differential surface heat fluxes show spontaneous multidecadal variability depending critically on eddy diffusivity coefficients the existence of this critical threshold in the range of observational estimates legitimates some doubt on the relevance of such intrinsic oscillations in the real ocean through a series of numerical simulations with increasing resolution up to eddy resolving ones 10 km and various diapycnal diffusivities this multidecadal variability proves a generic ubiquitous feature at least in model versions with a flat bottom the mean circulation largely changes in the process of refining the horizontal grid along with the associated implicit viscosity and diffusivity and the spatial structure of the variability is largely modified but there is no clear influence of the resolution on the main oscillation period the interdecadal variability appears even more robust to low vertical diffusivity and overturning when mesoscale eddies are resolved the mechanism previously proposed for these oscillations involving westward propagating baroclinically unstable rossby waves in the subpolar region and its feedback on the mean circulation appears unaffected by mesoscale turbulence and is simply displaced following the polar front

are north atlantic multidecadal sst anomalies westward propagating the westward propagation of sea surface temperature sst anomalies is one of the main characteristics of one of the theories of the atlantic multidecadal oscillation here we use techniques from complex network modeling to investigate the existence of the westward propagation in the north atlantic sst observations we construct climate networks cns by using a linear pearson correlation measure resulting in pearson correlation climate network pccns and a nonlinear mutual information measure resulting in mutual information climate network micns of spatial correlations between sst variations analysis of the topological properties of both types of cns shows that the micns are better in capturing the main features of propagating patterns from the noisy sst data than pccns and that westward propagation of multidecadal sst anomalies indeed seems to occur in the north atlantic

glacial interglacial environmental changes inferred from molecular and compound specific δ13c analyses of sediments from sacred lake mt kenya abstract molecular stratigraphic analyses including lipid distributions and compound specific 13c measurements have been performed at 15 levels in a sediment core from sacred lake mt kenya a high altitude 2350 m a s l freshwater lake with a record extending from the last glacial 40 000 cal yr bp through the present interglacial terrestrial and aquatic organic matter sources were independently assessed using source specific biomarkers 13c values of long chain n alkyl lipids from terrestrial higher plants exhibit large glacial to interglacial shifts those from the last glacial maximum lgm 20 to 18 indicate a terrestrial vegetation dominated by c4 grasses or sedges whereas those from the early holocene 34 to 27 reflect recolonization of the catchment area by c3 plants consistent with a rapid rise in the upper treeline specific algal biomarkers including five unsaturated hydrocarbons of novel structure ascribed to the microalga botryococcus braunii were abundant as confirmed by scanning electronic microscopy sem an extreme 13c shift of over 25 is displayed by the algal biomarkers an elevated value of 5 1 at the last glacial maximum lgm contrasting with a minimum value of 30 3 at the beginning of the holocene a major change in the molecular distributions of the algal biomarkers parallels this large 13c shift with acyclic isoprenoid hydrocarbons dominating the last glacial and cyclic isoprenoid hydrocarbons the holocene the low atmospheric partial pressure of co2 pco2 at the lgm would favour photosynthetic organisms possessing co2 concentrating mechanisms including terrestrial c4 grasses and freshwater green algae hence glacial interglacial changes in pco2 and in the co2 o2 ratio in particular had a significant impact on both terrestrial and aquatic ecosystems on mt kenya in addition to the effects of climate and local environmental factors

isopycnal mixing in ocean circulation models abstract a subgrid scale form for mesoscale eddy mixing on isopycnal surfaces is proposed for use in non eddy resolving ocean circulation models the mixing is applied in isopycnal coordinates to isopycnal layer thickness or inverse density gradient as well as to passive scalars temperature and salinity the transformation of these mixing forms to physical coordinates is also presented

the different nature of the interdecadal variability of the thermohaline circulation under mixed and flux boundary conditions the differences between the interdecadal variability under mixed and constant flux boundary conditions are investigated using a coarse resolution ocean model in an idealized flat bottom single hemisphere basin objective features are determined that allow one type of oscillation to be distinguished versus the other first by performing a linear stability analysis of the steady state obtained under restoring boundary conditions it is shown that the interdecadal variability under constant flux and mixed boundary conditions arises respectively from the instability of a linear mode around the mean stratification and circulation and from departure from the initial state based on the budgets of density variance it is shown next that the two types of oscillations have different energy sources under the constant flux boundary condition the thermal mode the downgradient meridional eddy heat flux in the western boundary current regions sustains interdecadal variability whereas under mixed boundary conditions the salinity mode a positive feedback between convective adjustment and restoring surface heat flux is at the heart of the existence of the decadal oscillation furthermore the positive correlations between temperature and salinity anomalies in the forcing layer are shown to dominate the forcing of density variance in addition the vertical structure of perturbations reveals vertical phase lags at different depths in all tracer fields under constant flux while under mixed boundary conditions only the temperature anomalies show a strong dipolar structure the authors propose that these differences will allow one to identify which type of oscillation if any is at play in the more exhaustive climate models

global observations of large oceanic eddies 1 ten years of sea surface height ssh fields constructed from the merged topex poseidon t p and ers 1 2 altimeter datasets are analyzed to investigate mesoscale variability in the global ocean the higher resolution of the merged dataset reveals that more than 50 of the variability over much of the world ocean is accounted for by eddies with amplitudes of 5 25 cm and diameters of 100 200 km these eddies propagate nearly due west at approximately the phase speed of nondispersive baroclinic rossby waves with preferences for slight poleward and equatorward deflection of cyclonic and anticyclonic eddies respectively the vast majority of the eddies are found to be nonlinear

biomarker evidence for botryococcus and a methane cycle in the eocene huadian oil shale ne china the saturated and unsaturated hydrocarbons of two samples hd 19 and hd 21 from the same section of the middle eocene lacustrine huadian oil shale in ne china were identified and shown to be mainly from algal and bacterial sources comparison of the two samples provided an opportunity to explore the contribution from telalginite to the hydrocarbon profiles cells identified from microscopy as botryococcus in the telalginite of hd 21 were confirmed as belonging to the l race of b braunii from the presence of monoaromatic lycopane derivatives and small amounts of several lycopadienes lycopane was abundant and was probably derived from biohydrogenation of lycopadienes and related lipids on the basis of d 13 c values hopane distributions showed a dominance of those with the biological 17b 21b stereochemistry as expected for an immature shale with low amounts of 17b 21a hopanes moretanes and 17a 21bhopanes two hopenes were also abundant and assigned as c29 and c30 neohop 13 18 enes which occurred together with the c29 and c30 hop 17 21 enes these had depleted carbon isotope values 43 7 to 50 8 indicative of production by methane oxidizing bacteria methanotrophs the high proportion of hopanoids with carbon numbers c32 indicates extensive post depositional diagenetic alteration of bacteriohopanepolyols as well as a direct input of c30 hopanoids the data clearly indicate that there was active utilization of methane in this lacustrine depositional setting but isoprenoid hydrocarbon biomarkers for methanogens such as pentamethylicosane pmi and squalane were in surprisingly low abundance it is possible that these bacterial contributions were present as polar lipids the origins of an unusual c38 isoprenoid alkane assigned as bipristane are uncertain but may be from methanogens steranes and sterenes were relatively minor components but abundant diasterenes and 4 methyldiasterenes were present reflecting significant conversion of the original lipid composition by way of clay catalysed diagenesis the biomarker data suggest that the bottom waters in the original depositional environment had low o2 content but the sediments were probably neither sulfidic nor strongly reducing the high content of organic matter in the shale likely reflects both high but fluctuating productivity due to eutrophic conditions in the overlying water and good preservation in the sediments

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

theoretical investigation of the atlantic multidecadal oscillation a weakly damped mode of variability corresponding to the oceanic signature of the atlantic multidecadal oscillation amo was found through the linear stability analysis of a realistic ocean general circulation model a simpletwo level model wasproposed torationalize bothits period and damping rate this model isextended heretothree levelstoinvestigate how the modecan draw energy fromthe mean flow as found in various ocean and coupled models a linear stability analysis in this three level model shows that the positive growth rate of the oscillatory mode depends on the zonally averaged isopycnal slope this mode corresponds to a westward propagation of density anomalies in the pycnocline typical of large scale baroclinic rossby waves the most unstablemodecorrespondstothelargestscaleone atleastforlowisopycnalslope themodecanbedescribed in four phases composing a full oscillation cycle 1 basin scale warming of the north atlantic amo positive phase 2 decrease in upper ocean poleward transport hence a reduction of the atlantic meridional overturning circulation amoc 3 basin scale cooling negative amo and 4 amoc intensification a criterion is developed to test in oceanic datasets or numerical models whether this multidecadal oscillation is an unstable oceanic internal mode of variability or if it is stable and externally forced consistent with the classical theory of baroclinic instability this criterion depends on the vertical structure of the mode if the upper pycnoclinesignatureisinadvanceofthedeeper pycnoclinesignaturewith respecttothewestwardpropagation the mode is unstable and could be described as an oceanic internal mode of variability

evidence of the amoc interdecadal mode related to westward propagation of temperature anomalies in cmip5 models climate models show a broad diversity in the simulations of the atlantic meridional overturning circulation amoc with its leading modes of variability having different amplitudes periods and driving mechanisms theoretical considerations and computations using ocean gcms suggest that on interdecadal timescales this variability can be controlled by an internal weakly damped oceanic mode associated with westward propagation of large scale density anomalies in the north atlantic ocean these anomalies are dominated by temperature with some compensation from salinity the quadrature phases of this mode include the strengthening of the amoc followed a quarter period later by the development of a broad warm temperature anomaly in the northern atlantic extending to about 1000 m then followed by the weakening of the amoc and then the upper ocean cooling here we investigate whether this mode is present in the simulations of coupled model intercomparison project 5 cmip5 out of the 25 models investigated we find that more than half of the models exhibit variability consistent with this mode some of the relevant modal features includes statistically significant spectral peaks in the band between 15 and 35 years the westward propagation of density anomalies in the 40 circ n 60 circ n latitudinal band which sets the period of the mode the existence of the distinct quadrature phases of the amoc variability and the predominant effect of temperature on density anomalies

large scale baroclinic instability of the mean oceanic circulation a local approach abstractlarge scale baroclinic instability is investigated as a potential source of rossby waves and large scale variability in the ocean this baroclinic instability is first reviewed in a 2 5 layer model as already noticed by several authors the instability arises in westward surface mean flow when the phase velocities of the two vertical modes are made equal by mean flow influence this large scale instability is stronger at low latitudes and thus is likely to happen in the westward return flow of the subtropical gyres further investigations with a continuous stratification quasigeostrophic model show that the instability is stronger where the mean flow projects negatively on the second baroclinic mode imposing positive vertical modes at the surface the linear stability calculation is then performed on argo derived mean flow along with mean stratification data the results show that the unstable regions are situated at low latitudes in every oceanic basin in western boundary currents and in som

biomarker evidence for the co occurrence of three races a b and l of botryococcus braunii in el junco lake galapagos in spite of the fact that individual races of botryococcus braunii are widely distributed in lakes reports of the co exis tence of different chemical races are rare here we report biomarker evidence for the co occurrence of three different races of b braunii a b and l in the water column and sediments of el junco lake a freshwater crater lake at 700 m elevation on san cristobal island galapagos we also show the existence of lycopadienes and lycopatrienes in suspended particles and sediments biomarker indicators of the three races were cis and trans c25 c31 n alkadienes and a c29 triene for race a a series of c34h58 botryococcenes for race b and a c40h78 hydrocarbon trans trans lycopadiene accompanied by minor amounts of isomers for race l epoxides derived from n alkadienes and trans trans lycopadiene specific to races a and l respectively were also detected several previously unreported lycopadienes and lycopatrienes were identified in both the water column and sediment and are believed to represent by products and intermediates respectively of trans trans lycopadiene synthesis botryococcene and lycopadiene concentrations reached 16 7 and 0 8 mg g dry sediment in near surface sediments and varied over more than three orders of magnitude while n alkadienes were present in trace quantities pyrolysates from the kerogen fraction of sediment contained lycopadiene and alkadiene related lipids along with chemically resistant polymers of b braunii cell walls apparently n alkadienes botryococcenes and lycopadienes and trienes can survive in oxic sedi ments for several decades and the down core variation in these lipids likely reflects changes in lake hydrology alternately favoring the bloom or near extinction of b braunii race b 2007 elsevier ltd all rights reserved

the significance of 24 norcholestanes 4 methylsteranes and dinosteranes in oils and source rocks from east sirte basin libya abstract the present paper involves a detailed evaluation of specific steroid biomarkers by gas chromatography mass spectrometry gc ms and gc metastable reaction monitoring mrm analyses of several crude oils and source rocks from the east sirte basin 24 norcholestanes dinosteranes 4 methyl 24 ethylcholestanes and triaromatic steroids have been identified in both source rocks and crude oils of the east sirte basin diatoms dinoflagellates including those potentially associated with corals and or their direct ancestors are amongst the proposed sources of these biomarkers these biomarker parameters have been used to establish a mesozoic oil source correlation of the east sirte basin hydropyrolysis of an extant coral extract revealed a similar distribution although immature of dinosteranes and 4 methyl 24 ethylcholestanes also observed in the sirte oils and source rocks this is consistent with the presence of dinoflagellates present during the deposition of the mesozoic aged east sirte basin formations a good data correlation for the rock extracts revealed a similar distribution of 3 24 dimethyl triaromatic steroids 3 methyl 24 ethylcholestanes 4 methyl 24 ethylcholestanes and 2 methyl 24 ethylcholestanes observed in one of the oil families and associated source rocks for the east sirte basin

chemical molecular and isotopic differentiation of organic facies in the tertiary lacustrine duaringa oil shale deposit queensland australia abstract total organic matter extractable organic matter bitumen and pyrolysates released on low temperature sealed tube pyrolysis of kerogen were analysed chemically and isotopically based on bulk bitumen and biomarker parameters the sediments are immature to a depth of approx 1300 m within the terrestrial and lacustrine depositional environments of the tertiary duaringa basin various organic facies have been classified according to inorganic input and maceral abundances of organic matter derived from land plant and algal sources the latter derived mainly from pediastrum and with a varying botryococcus content the lacustrine upper lamosite is chemically and isotopically distinct from the lower lamosite due to a changing algal community relative contributions from allochthonous land plants and for the lower lamosite a slightly more saline and restricted lake environment the lower lamosite is associated with the highest concentrations of c 28 c 30 4 methylsteranes and 13 c depletion in toc in the upper lamosite there is a strong positive correlation between botryococcus content and 13 c enrichment the organically lean claystones have sources nearly identical to the lamosites but the organic matter is diluted due to rapid influx of siliciclastics the terrestrial facies the cannel coal and carbonaceous shales are mainly distinguished from the lacustrine facies by higher relative proportions of c 29 steranes c 30 4 methylsteranes and 13 c values for the pyrolysed hydrocarbons intermediate between the two lamosite facies the carbonaceous oil shale has a composite geochemical signature intermediate between the two end members lamosite and cannel coal oleanane and ring a degraded triterpanes derived from lupane arborane and oleanane skeletons are distributed throughout all organic facies representing both autochthonous and allochthonous higher plant inputs higher concentrations of oleanane and des a lupane are associated with the terrestrial facies hopanes dominate over steranes in all organic facies and their concentration ranges are independent of facies for the lamosites the aliphatic biopolymer algaenan is implicated as the dominant source for n alkanes from analysis of their yields homologue abundances and individual 13 c values in the terrestrial facies resinites are paraffinic and are a major source for the n alkanes released on pyrolysis compound specific analysis of extractable and pyrolysate hydrocarbons allowed deconvolution of different source inputs to free lipids and kerogen for the lamosites low molecular weight n alkanes in the bitumen are derived mainly from a pediastrum source while botryococcus is associated with waxy n alkanes however the situation is reversed in the kerogen pediastrum algeanan has a longer average alkyl chain length than botryococcus algaenan the magnitude of the isotopic differences between single n alkanes released at different temperatures is useful in determining multiplicity of sources

on the relationship between decadal buoyancy anomalies and variability of the atlantic meridional overturning circulation abstractowing to the role of the atlantic meridional overturning circulation amoc in ocean heat transport amoc variability is thought to play a role in climate variability on a wide range of time scales this paper focuses on the potential role of the amoc in climate variability on decadal time scales coupled and ocean only general circulation models run in idealized geometries are utilized to study the relationships between decadal amoc and buoyancy variability and determine whether the amoc plays an active role in setting sea surface temperature on decadal time scales decadal amoc variability is related to changes in the buoyancy field along the western boundary according to the thermal wind relation buoyancy anomalies originate in the upper ocean of the subpolar gyre and travel westward as baroclinic rossby waves when the buoyancy anomalies strike the western boundary they are advected southward by the deep western boundary current leading to latitudinally coherent amoc variability the amoc i

biological marker compounds as indicators of the depositions history of the maoming oil shale abstract the eocene maoming oil shale from guangdong province occurs as a laterally uniform stratigraphic section typically 20 25 m thick from which the aliphatic hydrocarbon constituents of six representative samples were investigated using gc and c gc ms the sediments evaluated included the basal lignite a vitrinite lens from the overlying claystone and four intervals from the massive oil shale bed as expected the lignite and vitrinite differ markedly from the oil shales the lignite is dominated by bacterial hopanoids and components of higher plant origin including c 29 steroids and triterpenoids such as oleanenes visually the oil shale samples show corroded and degraded phytoclasts spores wispy particles of fluorescent organic material attributable to dinoflagellates and especially in the uppermost sample colonial algal bodies the distributions of biological markers in the oil shales show many features in common notably a dominance of dinoflagellate derived 4 methylsteroids and a significant proportion of higher plant derived n alkanes with marked odd over even carbon number predominance overall they exhibit several features that resemble characteristics of the messel shale the hydrocarbons of the lowest shale horizon suggest that there may have been a gradual transition between deposition of the original peat and the subsequent oil shales the aliphatic hydrocarbons of the uppermost shale are dominated by a number of c 31 and c 33 botryococcane homologues and other unusual branched alkanes possibly derived from green algae all of the samples are immature overall molecular and microscopic examination of the stratigraphic succession of the maoming oil shale suggests a shallow lacustrine environment within which peats were deposited this lake subsequently deepened to support abundant algal populations especially dinoflagellates culminating in a dominance of botryococcoid algae

interpentadal variability of salinity in the upper 150 m of the north atlantic ocean 1970 1974 versus 1955 1959 we have composited and objectively analyzed historical hydrographic observations for the north atlantic ocean for two pentads 1955 1959 and 1970 1974 our purpose is the study of the temporal variability of salinity in the upper layers of the north atlantic ocean upper ocean 0 150 m salinity differences between the two pentads exhibit statistically significant changes the subarctic gyre east and north of newfoundland freshened by as much as 0 5 the northern portion of the subtropical gyre increased in salinity by as much as 0 4 while the interior of this gyre decreased in salinity

geometry of the pamir hindu kush intermediate depth earthquake zone from local seismic data 1 we present new seismicity images based on a two year seismic deployment in the pamir and sw tien shan a total of 9532 earthquakes were detected located and rigorously assessed in a multistage automatic procedure utilizing state of the art picking algorithms waveform cross correlation and multi event relocation the obtained catalog provides new information on crustal seismicity and reveals the geometry and internal structure of the pamir hindu kush intermediate depth seismic zone with improved detail and resolution the relocated seismicity clearly defines at least two distinct planes one beneath the pamir and the other beneath the hindu kush separated by a gap across which strike and dip directions change abruptly the pamir seismic zone forms a thin approximately 10 km width curviplanar arc that strikes east west and dips south at its eastern end and then progressively turns by 90 to reach a north south strike and a due eastward dip at its southwestern termination pamir deep seismicity outlines several streaks at depths between 70 and 240 km with the deepest events occurring at its southwestern end intermediate depth earthquakes are clearly separated from shallow crustal seismicity which is confined to the uppermost 20 25 km the hindu kush seismic zone extends from 40 to 250 km depth and generally strikes east west yet bends northeast toward the pamir at its eastern end it may be divided vertically into upper and lower parts separated by a gap at approximately 150 km depth in the upper part events form a plane that is 15 25 km thick in cross section and dips sub vertically north to northwest seismic activity is more virile in the lower part where several distinct clusters form a complex pattern of sub parallel planes the observed geometry could be reconciled either with a model of two sided subduction of eurasian and previously underthrusted indian continental lithosphere or by a purely eurasian origin of both pamir and hindu kush seismic zones which necessitates a contortion and oversteepening of the latter

assembly of the pamirs age and origin of magmatic belts from the southern tien shan to the southern pamirs and their relation to tibet 1 magmatic rocks and depositional setting of associated volcaniclastic strata along a north south traverse spanning the southern tien shan and eastern pamirs of kyrgyzstan and tajikistan constrain the tectonics of the pamirs and tibet the northern pamirs and northwestern tibet contain the north facing kunlun suture the south facing jinsha suture and the intervening carboniferous to triassic karakul mazar subduction accretion system the latter is correlated with the songpan garze hoh xi system of tibet the kunlun arc is a composite early paleozoic to late paleozoic triassic arc arc formation in the pamirs is characterized by 370 320 ma volcanism that probably continued until the triassic the cryptic tanymas suture of the southern northern pamirs is part of the jinsha suture a massive 227 ma batholith stitches the karakul mazar complex in the pamirs there are striking similarities between the qiangtang block in the pamirs and tibet like tibet the regional structure of the pamirs is an anticlinorium that includes the muskol and sares domes like tibet the metamorphic rocks in these domes are equivalents to the karakul mazar songpan garze system granitoids intruding the qiangtang block yield 200 230 ma ages in the pamirs and in central tibet the stratigraphy of the eastern pshart area in the pamirs is similar to the bangong nujiang suture zone in the amdo region of eastern central tibet but a triassic ocean basin sequence is preserved in the pamirs arc type granitoids that intruded into the eastern pshart oceanic basin arc sequence 190 160 ma and granitoids that cut the southern qiangtang block 170 160 ma constitute the rushan pshart arc cretaceous plutons that intruded the central and southern pamirs record a long lasting magmatic history their zircons and those from late miocene xenoliths show that the most distinct magmatic events were cambro ordovician 410 575 ma triassic 210 250 ma likely due to subduction along the jinsha suture middle jurassic 147 195 ma subduction along rushan pshart suture and mainly cretaceous middle and late cretaceous magmatism may reflect arc activity in asia prior to the accretion of the karakoram block and flat slab subduction along the shyok suture north of the kohistan ladakh arc respectively before india and asia collided the pamir region from the indus yarlung to the jinsha suture was an andean style plate margin our analysis suggests a relatively simple crustal structure for the pamirs and tibet from the kunlun arc in the north to the southern qiangtang block in the south the pamirs and tibet likely have a dominantly sedimentary crust characterized by karakul mazar songpan garze accretionary wedge rocks the crust south of the southern qiangtang block is likely of granodioritic composition reflecting long lived subduction arc formation and cretaceous cenozoic underthrusting

identification of the mechanism of interdecadal variability in the north atlantic ocean the aim of this paper is to identify the physical mechanism of interdecadal variability in simulations of the north atlantic ocean circulation with the modular ocean model of the geophysical fluid dynamics laboratory to that end a hierarchy of increasingly complex model configurations is used the variability in the simplest case that of viscous purely thermally driven flows in a flat bottom ocean basin with a box shaped geometry is shown to be caused by an internal interdecadal mode the westward propagation of temperature anomalies and the phase difference between the anomalous zonal and meridional overturning that characterize the interdecadal mode are used as fingerprints of the physical mechanism of the variability in this way the variability can be followed toward a less viscous regime in which the effects of continental geometry and bottom topography are also included it is shown that although quantitative aspects of the variability like period and spatial pattern are changing the physical mechanism of the interdecadal variability in the more complex simulations can be attributed to the same processes as in the simplest model configuration

a theory for the surface atlantic response to thermohaline variability abstract the response of the upper warm limb of the thermohaline circulation in the north atlantic to a rapid change in deep water formation at high latitudes is investigated using a reduced gravity ocean model changes in deep water formation rate initiate kelvin waves that propagate along the western boundary to the equator on a timescale of months the response in the north atlantic is therefore rapid the southern hemisphere response is much slower limited by a mechanism here termed the ldquo uatorial buffer since to leading order the flow is in geostrophic balance the pressure anomaly decreases in magnitude as the kelvin wave moves equatorward where the coriolis parameter is lower together with the lack of sustained pressure gradients along the eastern boundary this limits the size of the pressure field response in the southern hemisphere interior adjustment is by the westward propagation of rossby waves but only a small fraction of the change in thermohaline circulation strength is commun

spatial variation in the frequency magnitude distribution of earthquakes under the tectonic framework in the middle east abstract spatial variations of seismic energy released and b value over the middle east region are investigated based on a seismicity catalog from 1995 to 2007 the goal is to use these seismic parameters and based on other geodetic and geophysical observations such as gps measurements strain rate model fault distribution focal mechanism crustal model q model and gravity measurements etc to uncover spatial patterns that seem anomalous areas of high energy released cumulative seem to correspond to the areas of relatively high b values areas of high energy released and high b values seem to correspond very well with the location of continental collision where earthquake activities are high the divergent boundary between arabia and african plates and subduction zone at makran seem to correspond to low to moderate energy release northern pamir azerbaijan caucasus the lower part of zagros mountains eastern turkey owen fracture zone strait of bob el mandeb and south of the sulaiman shear zone seem to correspond to high cumulative energy released high strain rate high b values and high fault density while the central and eastern iran southern zagros northern pakistan gulf of aden alborz southwest of the caspian sea western caucasus and kopeh dagh seem to correspond with lower b values the cross section map for hindu kush shows general decreasing of the b values with depth however a region of high b value is observed underneath pamir at depths from 170 to 230 km this anomaly region can be due to dehydration of pamir crustal slab at depth