morphologic variability of the coccolithophorid calcidiscus leptoporus in the plankton surface sediments and from the early pleistocene abstract on a global scale morphological variability of the extant coccolithophorid calcidiscus leptoporus murray and blackman 1898 loeblich and tappan was investigated in surface sediments and plankton samples and from an early pleistocene time slice 1 8 ma to 1 6 ma in the bivariate space coccolith diameter versus number of rays in the distal shield holocene samples follow a single unimodal morphocline sample means of coccolith size and number of elements group in three clusters i ii and iii which are of biogeographic significance clusters ii and iii coccoliths mean coccolith size of 5 0 m and 20 9 elements and 6 6 m and 25 6 elements respectively are found in a tropical belt extending from 11 n to 17 s with an annual minimum sea surface temperature above 23 5 c cluster i coccoliths 5 8 m 20 7 elements are found in samples outside that belt the distribution of coccoliths in the surface sediments is tentatively interpreted to be a result of mixing to a varying degree of at least three different morphotypes small intermediate and large which were identified in the living plankton and which are separated from each other at 5 m and 8 m mean coccolith diameter respectively a comparison of the surface sediments with the early pleistocene assemblages revealed that between 1 6 ma and 1 8 ma two morphoclines a and b existed the first of which persisted until the holocene in the form of c leptoporus while the second comprises only extinct morphotypes including calcidiscus macintyrei as one end member during the early pleistocene morphocline a was more homogeneous and no clusters were evident morphocline b shows a clear bimodality with a separation of morphotypes at 9 5 m our observations suggest that morphoclines are subsets within the total stratigraphical range of a single species and represent the global variability of that species in a particular time interval morphotypes which belong to a morphocline represent the infra specific variability of that species within the biogeographic and stratigraphic limits of that species

centroid moment tensor solutions for july september 1998 abstract centroid moment tensor solutions are presented for 214 earthquakes that occurred during the third quarter of 1998 the solutions are obtained using corrections for aspherical earth structure represented by a whole mantle shear velocity model sh8 u4l8 of dziewonski and woodward dziewonski a m woodward r l 1992 acoustic imaging at the planetary scale in emert h harjes h p eds acoustical imaging plenum new york 19 785 797 a new model of anelastic attenuation of durek and ekstrom durek j j ekstrom g 1996 a radial model of anelasticity consistent with long period surface wave attenuation bull seism soc am 86 144 158 is used to predict the decay of the waveforms

evidence of 550 year and 1000 year cyclicities in north atlantic circulation patterns during the holocene sedimentological colour data obtained from north atlantic deep sea sediment core neap15k pro vide a continuous climate record for the last 11500 yr with a mean sampling interval of 15 yr variations in sediment lightness a proxy for changes in north atlantic deep water nadw circulation are characterized by high frequency fluctuations with periodicities equivalent to 550 and 1000 yr as well as a 1600 yr cyclicity comparable to that reported in other studies of holocene climate cross spectral analysis suggests that the 550 yr and 1000 yr cyclical variations in nadw circulation were coherent with fluctuations in atmospheric con ditions over greenland where both these periodicities have been identified previously in the holocene gisp2 d18o record stuiver et al 1995 a similar statistical comparison provides evidence that high frequency 550 yr variability in nadw circulation patterns may have been linked to short term variations in atmospheric 14c values during the holocene in general nadw pro

rapid determination of global moment tensor solutions in an effort to improve data services the national earthquake information center has begun a program in cooperation with the incorporated research institutions for seismology data management center iris dmc to produce rapid estimates of the seismic moment tensor for most earthquakes with a body wave magnitude of 5 8 or greater although this program is still undergoing testing and fine tuning an estimate of the moment tensor can usually be produced within 20 minutes of the arrival of the broadband p waveform data from the iris dmc although the speed with which this data can be obtained varies in many cases a solution can be obtained within two hours of the earthquake these solutions do not vary significantly from the final solutions determined using the entire network because of the manner in which the data and the synthetic seismograms are aligned the method is insensitive to the effects of timing errors epicentral mislocation and lateral heterogeneity in earth structure this procedure was implemented in may 1993 the results from that month are presented here

t waves from the 1998 papua new guinea earthquake and its aftershocks timing the tsunamigenic slump t waves recorded at hydrophone and seismic stations following the papua new guinea earthquake of 17 july 1998 and its aftershocks show that a small event at 09 02 gmt featured source properties incompatible with an elastic dislocation of appropriate body wave magnitude m b 4 4 these include an exceptional duration 47 s at the wake island hydrophone station wk31 a spectrum rich in high frequencies 7 to 12 hz and a generally low spectral amplitude these characteristics can be explained by the model of an underwater slump accelerating from a standstill and eventually slowing down the relocation of the 09 02 event is compatible with its location within an amphitheater inside which shipboard cruises in 1998 and 1999 documented the presence of a 4 c km3 geologically fresh slump we propose that the slump took place at 09 02 on 17 july 1998 i e 13 minutes after the mainshock and that it generated the locally catastrophic tsunami whose properties amplitude and distribution of runup timing could not be explained by a dislocation model

primary productivity variability on the atlantic iberian margin over the last 70 000 years evidence from coccolithophores and fossil organic compounds 1 this study analyzes coccolithophore abundance fluctuations e g emiliania huxleyi gephyrocapsa specimens and florisphaera profunda in core md01 2444 sediment strata retrieved at the iberian margin northeastern atlantic ocean coccolithophores are calcareous nannofossils a major component of the oceanic phytoplankton which provide information about past ecological and climatological variability results are supported by data on fossil organic compounds sea surface temperatures alkenones and n hexacosan 1 ol index and geochemical analyses benthic 13ccc and planktonic 18occ isotopes three scenarios are taken into account for this location at centennial scale resolution over the last 70 000 years the holocene and the stadial and interstadial modes the different alternatives are described by means of elements such as nutrients upwelling phenomena temperatures at surface and subsurface level or the arrival of surface turbid fresh and cold waters due to icebergs low sea level increased aridity and dust during the holocene moderate primary productivity was observed mainly concentrated in e huxleyi specimens surface temperatures were at maxima while the water column was highly ventilated by northern sourced polar deep waters and warmer subsurface nutrient poor subtropical waters over most of the last glacial stadials surface productivity weakened higher f profunda and reworked specimen percentages and lower diunsaturated and triunsaturated c37 alkenones the arrival of cold arctic surface waters traced by tetraunsaturated c37 peaks and large e huxleyi together with powerful ventilated southern sourced polar deep waters disturbed in all likelihood the delicate vertical equilibrium while preventing significant upwelling mixing finally during the last glacial interstadials lower f profunda percentages nonreworked material and higher diunsaturated and triunsaturated c37 alkenones a combined signal is observed warm surface temperatures were concurrent with generally low oxygenation of the deep sea floor moderate arrival of northern sourced deep waters and subsurface cold nutrient rich recently upwelled waters probably of polar origin these particular conditions may have promoted vertical mixing while enhancing surface primary productivity mainly of gephyrocapsa specimens

numerical modelling of tsunami generation and propagation from submarine slumps the 1998 papua new guinea event summary deep and large submarine slumps may generate tsunamis as disastrous as tsunamis of tectonic origin such a landslide is likely to be the origin of the 1998 july 17 tsunami of papua new guinea the deadliest tsunami in the last 50 years water waves devastated a 20 km stretch of coastline wiping out three villages and killing more than 2200 people a numerical model has been developed to study the efficiency of deep slumps in producing tsunamis and has been applied to the papua new guinea event the landslide is treated as the flow of a homogeneous gravity driven continuum governed by a rheological law water waves are generated by sea bottom displacements induced by the landslide the shallow water approximation is adopted for both the landslide and the associated water waves the resulting differential equations are solved by a finite difference method based on shock capturing the shallow water hypothesis is tested by comparison with a model solving navier stokes equations for a mixture of water and sediments sensitivity tests carried out for a 2 d simplified geometry show that the water surface profile depends strongly on the constitutive law of the landslide the 1998 event is simulated numerically by the shallow water model testing different friction laws the observed inundation height distribution is well reproduced by the model for a volume of 4 km3 with its top located at a water depth of 550 m and sliding with a coulomb type friction law over a distance of 5 km

ocean surface water response to short term climate changes revealed by coccolithophores from the gulf of cadiz ne atlantic and alboran sea w mediterranean the response of coccolithophore assemblages to short term millennial and centennial climatic changes over the last 50 kyr is studied in core m39029 7 from the gulf of cadiz atlantic ocean and core md95 2043 from the alboran sea western mediterranean sea the nannoplankton data are compared with oxygen isotopes u37k sst and other biogeochemical and sedimentological proxies to obtain a new perspective of the paleoceanography and paleoecology of the area during these short term climatic changes coccolithophores indicate that heinrich events he were characterised by the presence of cold low salinity and turbid water masses on both sides of the strait of gibraltar high abundances of the lower photic zone lpz species florisphaera profunda in the gulf of cadiz synchronous with he are interpreted as being an evidence of upper water column stratification on the atlantic side these episodes coincided with input of terrigenous material especially during h2 surface waters during dansgaard oeschger do stadials were also cold and turbid while most of do interstadials were characterised by warm water flora the increase in small placoliths small gephyrocapsa and emiliania huxleyi 4 m which is considered here as a cold water indicator the sharp decrease in large specimens of e huxleyi related to the warming trend in the last deglaciation can be used as a biostratigraphic reference level that marks at least approximately the deglaciation and the beginning of the holocene peaks of f profunda are observed during termination 1 t1 in the alboran sea they are isochronous with the organic rich layer 1 recognised in the western mediterranean in this interval the water column of the region was stratified as a consequence of the global increase in the sea level following the deglaciation quantitative analyses of the coccolithophore assemblage allow us to interpret that coccolithophore production has been higher in the alboran sea than in the gulf of cadiz during the holocene

spatial analysis of the la paca se spain 2005 seismic series through the relative location of multiplets and principal component analysis abstract on 29 january 2005 a m w 4 8 i max vi vii earthquake occurred near the village of la paca se spain the aftershock sequence shows distinct heterogeneity manifested in a non uniform temporal decay of activity and different source mechanisms for the main shock and the largest aftershocks we analysed 262 earthquakes of the seismic series in order to characterize the active seismic structures moving window cross correlation of the p and s waveforms recorded at local broad band stations and the application of a selection algorithm have allowed to identify events with similar waveforms multiplets and to classify them into 16 clusters of 3 25 earthquakes each in each multiplet cluster events have been relocated with respect to a master event by the linear inversion of cross correlation time lags for p and s waves clusters show epicentral alignments with a predominant direction n145 e and two secondary directions n6 e and n40 e spatio temporal patterns of the seismicity have been analysed using principal component analysis pca upon the relocated epicentre distribution and we have obtained three trends n42 e n14 e and n145 e present during all the sequence these directions inferred from relative location and pca are coincident with nodal planes of moment tensor solutions for the larger events within the series they can be interpreted as the simultaneous activity of conjugate strike slip faults under a n160 170 e orientation of the principal compressive stress 1

tectonic interpretation of aftershock relocations in eastern papua new guinea using teleseismic data and the arrival pattern method summary the arrival pattern ap method and teleseismic data have been used to relocate aftershocks following three major mw 7 8 interplate earthquakes that occurred in eastern papua new guinea in 2000 november the first event was an mw 8 0 strike slip earthquake that ruptured the weitin fault over a length of 100 km no aftershocks were located in the upper 15 km suggesting that the accumulated strain was fully released in this event the two subsequent mw 7 8 thrust events occurred on the new britain trench wadati benioff zones dipping 20 define the locations of the thrust events at 152 e and 153 e on fault planes with strikes of 75 and 65 respectively the plot of aftershocks defines a complex seismic zone beneath new ireland where events have occurred in the overriding pacific and south bismarck plates above the deeper zone of subduction of the solomon sea plate these events cluster in a broad zone to the northeast of the weitin fault rather than defining a linear feature that might have been expected following a near vertical major strike slip event

late quaternary insolation forcing on total organic carbon and c37 alkenone variations in the arabian sea we here present records of total organic carbon toc and c37 alkenones used as indicators for past primary productivity from the western was and eastern arabian sea eas new data from an open ocean site of the was upwelling area are compared with similar records from ocean drilling program odp site 723 from the continental margin off oman and md 900963 from the eas these records together with other proxies used to reconstruct upwelling intensity indicate periods of high productivity in tune with precessional forcing on the basis of their phase relationship to boreal summer insolation they can be divided into three groups in the was differences between monsoonal proxies 1 and productivity 2 document a combined signal of moderate sw monsoon winds and of strengthened and prolonged ne monsoon winds whereas in the eas phasing indicates maximum productivity 3 at times of stronger ne monsoon winds associated with precession related maxima in ice volume

response of nannoplankton to major changes in sea surface temperature and movements of hydrological fronts over site dsdp 594 south chatham rise southeastern new zealand during the last 130 kyr abstract a high resolution history of paleoceanographic changes in the subpolar waters of the southern margin of the subtropical convergence zone during the last 130 kyr is present in foraminiferal assemblages of dsdp site 594 the foraminifera indicate that sea surface temperatures during the last interglacial climax were warmer than today and that between substage 5d through to the end of isotope stage 2 temperatures were mostly cooler than holocene temperatures the paleotemperatures suggest that 1 the subtropical convergence was located over the site during substage 5e later moving further north then moving southwards to near the site during the holocene and 2 the polar front was positioned over the site during glacial stages 6 4 2 and possibly parts of stage 3 several major events are indicated by the nannofloral assemblages during these large changes in sea surface temperature and associated reorganization of ocean circulation first the time progressive trends between e huxleyi and medium to large gephyrocapsa are unique to this site with e huxleyi dominating over medium gephyrocapsa during stages 5c a middle part of stage 4 and after the middle point of stage 3 this unusual trend may at least partly be caused by the shift of the polar front across the site second upwelling flora e huxleyi and small placoliths increase in abundance during stages 1 3 and 5 suggesting that upwelling or disturbance of water stratification took place during the interglacials thirdly there are no significant differences between the distribution patterns of the various morphotypes of medium to large gephyrocapsa and the combined value of all medium gephyrocapsa increases in abundance during glacials stages 2 and 4 and the end of stage 6 similar to the abundance trends in benthic foraminifera finally subordinate nannofossil taxa also show distinctive climatic trends during the last glacial cycle 1 syracosphaera spp are present in increased abundance during warmer extremes in climate substages 5e 5a and stage 1 2 coccolithus pelagicus and calcidiscus leptoporus dominate the subordinate nannofossil taxa and their relative proportions seem to provide a useful paleoceanographic index with c pelagicus dominating when the polar front zone is over the site stages 6 4 and 2 whilst c leptoporus is relatively more abundant when the stc is positioned over the site stages 1 and 5e increased abundance of c pelagicus also can indicate intensified coastal upwelling

the 1998 papua new guinea earthquake and its fault plane estimated from relocated aftershocks the 1998 papua new guinea earthquake of m w 7 0 occurred near the wewak trench where the north bismarck plate is subducting beneath the australian plate its mechanism is thrust type and one of the nodal planes is almost parallel to the plate interface to determine which of the two nodal planes of the main shock is the fault plane we relocated the main shock and aftershocks using a method of modified joint hypocenter determination we combined and employed two types of data in this study firstly we used data reported by the national earthquake information center neic of the u s geological survey usgs which includes three stations at the northeastern edge of irian jaya and one station in northern papua new guinea from which the epicentral distances are less than 2 degrees secondly in addition to the above permanent station data we used data from temporary aftershock observations near the epicentral area around the sissano lagoon carried out by tsuji et al 1998 using three component seismometers they carried out observations from august 2 to october 2 1998 at three sites although the network did not record the main shock and immediate aftershocks the data obtained by temporary observation sites can clearly assist in identifying their absolute locations since it is possible to apply the joint hypocenter determination jhd method hypocenters were relocated between the coastline and the wewak trench distributed along a nodal plane dipping shallowly to the southwest therefore we can conclude that this nodal plane is the main shock fault and that the 1998 papua new guinea earthquake was an interplate earthquake between the north bismarck and australian plates

evidence for active subduction at the new guinea trench 1 recent seismic tomography imaging shows clear evidence for southwestward subduction along the entire length of the new guinea trench ngt in indonesia and papua new guinea viewed in conjunction with the occurrence of large mw 7 thrust earthquakes that are known to have occurred on the trench this confirms conclusions of earlier studies that the ngt is an active inter plate boundary the 650 km long slab is visible to a depth of about 300 km and subducts with a dip angle that varies from 30 at 136 e to 10 at 143 e the improved clarity of the seismic tomography in this region stems from the use of a more accurate data set of p and s wave arrival times and hypocentral locations

the last 100 000 years in the western mediterranean sea surface water and frontal dynamics as revealed by coccolithophores a quantitative analysis was carried out on coccolith assemblages from two pleistocene cores k1 and k10 from the western mediterranean the distribution of selected coccolithophore species provides new paleoclimatic and paleoceano graphic data a continuous sequence from the top of isotope stage 5 to the holocene was recorded the reversal in dominance between gephyrocapsa muellerae and emiliania huxleyi was dated in both cores at ca 73 ka at about 47 ka e huxleyi shows a regular increase whereas g muellerae progressively decreases in abundance during interglacial periods high concentrations of coccoliths are observed whereas in glacial times coccoliths are more diluted and the percentage of reworked forms increases as a consequence of the higher terrigenous input after taking careful account of the dilution factor we conclude that the production of coccolithophores was higher during warm periods maxima in coccolith concentrations coincide with highstand episodes probably as a result of the intensification of the atlantic flux into the mediterranean across the gibraltar strait this intensification could have produced an increase in nutrient content in the surface mediterranean waters during cold periods the western mediterranean front underwent a reduction in activity probably due to an increase in the saline and or thermal gradients between the superficial waters and intermediate waters in the liguro provencal basin

synchroneity between marine and terrestrial responses to millennial scale climatic variability during the last glacial period in the mediterranean region land sea climatic proxies have been obtained from the last glacial section of images core md95 2043 western mediterranean sea vegetation and alkenone derived sst curves indicate rapid 150 years and synchronous terrestrial and marine climatic changes paralleling the dansgaard oeschger d o climatic variability over greenland this frequency of climate change can be related to shifts between the two modes of operation of the north atlantic oscillation nao transfer functions applied to the pollen data indicate that there was an amplification of the climatic signal during heinrich events hes in comparison with other d o stadials the development and persistence of both scandinavian and atlantic mobile polar highs over southwestern europe may explain the extreme cooling 10 c and dryness 400 mm during heinrich events 5 and 4 in the mediterranean region comparison of the results of core md95 2043 with similar climatic data from images core md95 2042 located off portugal indicates that thermal and precipitation gradients occurred between the mediterranean and the atlantic sides of iberia within hes hes 4 and 5 are associated with more humid conditions in the atlantic by 200 mm than in the mediterranean site as is the case at the present time this comparison also illustrates the different behaviour of these areas during the d o stadials in contrast with the mediterranean site the atlantic site shows similar precipitation and temperature drops for all the d o stadials including those related to the hes here we propose the operation of different mobile polar highs mph as the driving mechanism for this difference in behaviour between the atlantic and mediterranean sides of iberia hes are related to a stronger influence of the scandinavian mph forcing a severe aridification and cooling of the full iberian peninsula the atlantic mph may have been dominant during the other stadials which would preferentially affect southwestern iberia

the aitape 1998 tsunami reconstructing the event from interviews and field mapping on the evening of 17 july 1998 on the aitape coast of papua new guinea a strongly felt earthquake was followed some 10 25 minutes later by a destructive tsunami the tsunami comprised three waves each estimated to be about 4 m high the second of the three waves rose to a height of 10 15 m above sea level after it had crossed the shoreline and caused most damage maximum wave heights and the greatest damage were recorded along a 14 km sector of coast centered on sissano lagoon in this sector the wavefronts moved from east to west along the coast all structures were destroyed and in the two main villages 20 40 percent of the population was killed partial destruction extended 23 km to the southeast and 8 km to the northwest and effects of the tsunami were felt as far as 250 km to the west northwest beyond the international border more than 1600 people are known to have died with some estimates as high as 2200 1000 were seriously injured and 10 000 survivors were displaced this paper presents information from interviews with eye witnesses and from mapping of damage and inundation and includes new information on the height shape and timing of the waves on the possible escape of petroleum and other gases from beneath the seafloor before and during the tsunami on unusual sound effects that preceded the waves and lighting effects that followed on possible deep circulation to 250 m of sea water in the waves on subsidence of the order of 50 70 cm at the coastal sand barrier and on the resilience and potential protective capacity of certain species of trees eye witness accounts indicate that the tsunami reached the shore at between 09 00 and 09 08 ut which is earlier than is proposed in published models of the timing and location of the source of the tsunami

variations of terrestrial input and marine productivity in the southern ocean 48 s during the last two deglaciations various biomarkers n alkanes n alcohols and sterols have been studied in a piston core tsp 2pc taken from the southern ocean to reconstruct the paleoenvironmental changes in the subantarctic region for the last two deglaciations mass accumulation rates of terrestrial higher molecular weight n alkanes and n alcohols and marine dinosterol and brassicasterol biomarkers increased significantly at the last two glacials and stayed low during interglacial peaks early holocene and the eemian these records indicate that the enhanced atmospheric transport of continental materials and the increased marine biological productivity were synchronously linked in the southern ocean at the last two glacials this suggests that increased glacial dust inputs have relieved iron limitation in the subantarctic southern ocean these two processes however were not linked at the cooling phase from the eemian to marine isotope stage mis 5d during this period paleoproductivity may have been influenced by the latitudinal migration of the high production zone associated with the antarctic polar front

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

coccolith evidence for instabilities in surface circulation south of iceland during holocene times abstract the coccolith based micropaleontological investigation of an exceptionally thick deep sea holocene sediment core was conducted in order to document the pattern and timing of surface circulation changes south of iceland over the gardar contour drift during the last 12 000 years fluctuations in bulk carbonate content at the core location are primarily driven by the coccolith fraction the observed overall correlation between bottom flow speed as given by the sortable silt mean size index and the bulk coccolith concentration abundance g dry sediment suggests that the accumulation of this fine carbonate fraction is as a first order controlled by processes of sediment redistribution by bottom current the down core variations in coccolith assemblage structure species indicate that changes in properties of surface waters south of iceland occurred as two distinct steps at ca 11 2 and 6 ka the onset of north atlantic drift water influence over the gardar drift after 11 2 ka was associated with excess export flux of coccolith carbonate in the vicinity of an active frontal system the period from 10 to 6 ka saw the progressive warming of the study area which culminated between 6 and 7 ka cooling of the surface waters after 6 ka as indicated changes in the relative abundances of the dominant coccolith species took place in two phases the present hydrological regime being only established after a last cooling step between 3 5 and 2 8 ka these long term reorganisations of the surface hydrology are interpreted as the response of the north atlantic to the combined force of the solar insolation and the waning laurentide ice sheet millennial scale perturbations of the surface hydrology are documented by changes in accumulation of the species emiliania huxleyi these successive decreases in the export fluxes of e huxleyi exhibit a distinct millennial pacing in phase with previously recorded holocene advection of cool ice bearing waters from the greenland iceland seas to the british islands from a clear analogy with the most recent extreme variation in global ocean climate we argue that mechanisms responsible for these observed millennial scale perturbations might be found in long term modulations of the atmospheric processes associated with the north atlantic oscillation nao

the last 3000 years in the ria de vigo nw iberian margin climatic and hydrographic signals the hydrographic evolution of the r o a de vigo nw spain during the last 3000 years has been reconstructed using benthic foraminiferal assemblages stable oxygen isotopes molecular biomarkers and sea surface temperatures sst reconstructed from the u k9 37 index benthic oxygen isotopes and sst records provide evidence of episodic salinity contrasts between surface and bottom waters the comparison of ssts with other climate records for the northern hemisphere has allowed the inference of oceanographic and climatic signals which describe the changes in hydrographic conditions of the r oa in general two different periods can be recognized from 975 cal bc to cal ad 1000 the organic carbon is mainly of continental origin benthic foraminiferal assemblages are typical of environments that are poorly oxygenated rich in organic matter and dominated by eurihaline taxa percentages of planktonic foraminifera are low and ssts are warmer than today these data suggest a restricted environment where the exchange with open ocean waters was diminished at cal ad 1000 an important hydrographic change in the r oa circulation involved an intensie cation of coastal upwelling processes as ree ected in colder ssts and increases in the contribution of marine organic carbon and planktonic and opportunistic benthic foraminifera in these conditions the sediments of the r oa recorded not only local factors but also several well known northern hemisphere climate signals

climate change and coastal hydrographic response along the atlantic iberian margin tagus prodelta and muros ria during the last two millennia the tagus prodelta w portugal and the muros ro a nw spain are areas of high deposition rates registering high resolution palaeoclimatic records for western iberia we compare the climatic conditions of the two areas over the last two millennia based on proxies of temperature sea surface temperatures and oxygen isotopes continental input grain size iron and magnetic susceptibility and productivity inorganic and organic carbon carbon isotopes benthic foraminifera and diatoms biogeochemical changes in the tagus prodelta reflect widely recognized north atlantic climatic periods encompassing the roman period ad 0 350 the dark ages ad 400 700 the mediaeval warm period mwp ad 800 1200 and the little ice age lia ad 1300 1750 the atmospheric north atlantic oscillation nao drives the tagus prodelta multidecadal long term variability in precipitation river input during cold periods negative nao and marine upwelling during warmer periods positive nao a scheme that is reversed in the galician region the muros ro a shows only local hydrodynamics until ad 1150 including a suboxic event in the inner ro a around ad 500 700 since ad 1150 atlantic warm upwelled waters have ventilated the outer ro a but only reach the inner ro a at ad 1750 the twentieth century records are also interpreted as a reflex of the inverse nao mode in both areas resulting in amplification of the lia biogeochemical water conditions centennial scale solar activity appears to be another important forcing mechanism or the only one if solar activity drives the nao and bond cycles behind changes in the hydrography of the tagus prodelta and primary production bottom ventilation and organic carbon degradation in the muros ro a

appraising the cohesion of palaeoenvironmental reconstructions in north west spain since the mid holocene from a high temporal resolution multi proxy peat record investigation of abrupt palaeohydrological regime change remains challenging due to site specific noise ratios and the limitations of dating control and spatial resolution of multi proxy records s

millennial surface water dynamics in the ria de vigo during the last 3000 years as revealed by coccoliths and molecular biomarkers a combined study of coccolith assemblages and biomarkers in a gravity core collected from the ria de vigo nw spain allowed us to reconstruct the paleoenvironmental conditions for the last 3000 years the quantitative distribution of coccolithophore species points to three different intervals within the core dated by ams radiocarbon measurements the first interval ca 975 bc 252 ad characterized by high abundances of calcidiscus leptoporus and gephyrocapsa muellerae i s thought to represent moderate water temperatures suggesting a transition from a warmer to a cooler period the second interval ca 252 1368 ad characterized by the dominance of coccolithus pelagicus helicosphaera carteri and syracosphaera spp and a high concentration of hexacosanol linked to terrestrial input is interpreted as having been a humid period with fluvial input the third interval ca 1368 ad 1950 is characterized by a high abundance of gephyrocapsa oceanica high alkenone values and low values of hexacosanol and is thought to represent a period dominated by oceanic conditions within the ria taking into account the ocean atmospheric system affecting the region studied here we propose an alternation in the mean state of north atlantic oscillation nao at millennial time scales awell developed upwelling system and an active ria ocean connection during the warmer interval i suggest a nao phase influenced by a hypsithermal period the occurrence of the humid and relatively warm interval ii is consistent with a negative phase in the nao as well as a relative restriction in ocean ria exchange interval iii which was drier and more productive again suggests the dominance of a positive phase in the nao with a more intense oceanic connection and more energized upwelling d 2004 elsevier b v all rights reserved

snow avalanche formation 1 snow avalanches are a major natural hazard endangering human life and infrastructure in mountainous areas throughout the world in many countries with seasonally snow covered mountains avalanche forecasting services reliably warn the public by issuing occurrence probabilities for a certain region however at present a single avalanche event cannot be predicted in time and space much about the release process remains unknown mainly because of the highly variable layered character of the snowpack a highly porous material that exists close to its melting point the complex interaction between terrain snowpack and meteorological conditions leading to avalanche release is commonly described as avalanche formation it is relevant to hazard mapping and essential to short term forecasting which involves weighting many contributory factors alternatively the release process can be studied and modeled this approach relies heavily on snow mechanics and snow properties including texture while the effect of meteorological conditions or changes on the deformational behavior of snow is known in qualitative or semiquantitative manner the knowledge of the quantitative relation between snow texture and mechanical properties is limited but promising developments are under way fracture mechanical models have been applied to explain the fracture propagation and micromechanical models including the two competing processes damage and sintering have been applied to explain snow failure there are knowledge gaps between the sequence of processes that lead to the release of the snow slab snow deformation and failure damage accumulation fracture initiation and fracture propagation simultaneously the spatial variability that affects damage fracture initiation and fracture propagation has to be considered this review focuses on dry snow slab avalanches and shows that dealing with a highly porous media close to its melting point and processes covering several orders of scale from the size of a bond between snow grains to the size of a mountain slope will continue to be very challenging

high resolution holocene palynological record from the scotian shelf abstract because of their location at the confluence of polar and subtropical airmasses and near a transition zone between the cold labrador current and the gulf stream the atlantic provinces experience some of the most dynamic climate conditions in canada major climate changes occurred during the holocene as shown by pollen records from lakes but previous paleoceanographic studies based on low resolution proxy data records do not show major changes during the past 8000 years therefore the holocene history of canada s atlantic region was examined using a high resolution palynological record from the scotian shelf la have basin sea surface conditions were reconstructed using proxy data from dinoflagellate cysts and paleobioclimatic transfer functions ocean atmosphere interactions are determined by onshore offshore correlation of marine and pollen records from nova scotia results show a succession of major paleoceanographic events sea surface temperatures sst february and august up to 5 c higher than today s average and slightly higher salinity are reconstructed between 10 5 and 8 5 ka the last pulse of meltwater from the residual ice sheet affected the shelf waters between 8 5 and 6 5 ka by lowering the sst in february and the salinity most previous studies failed to record this event since 6 5 ka august temperature generally remained around today s value while february temperature was generally 2 c above it except for recurring colder and lower salinity intervals these cold intervals have a recurrence of about 1000 years a slight cooling of summer sst is recorded in the last 500 years comparison with climatic reconstructions from nova scotia pollen records shows a difference in timing between ocean and atmosphere the onset of the climatic optimum hypsithermal in nova scotia lags by about 2000 years until 8 ka relative to the ocean but it lasted longer the neoglacial cooling in atlantic canada however started earlier 2 ka than the late holocene ocean cooling la have basin s holocene paleoceanography presents some differences from most other studies from the region 1 the hypsithermal started earlier 2 the last pulse of meltwater is recorded 3 the last 6500 years are punctuated by colder intervals increased productivity and blooms of toxic algae in the early holocene are probably due to a combination of factors increased nutrients and a greater stability of the water column because of meltwaters higher sst and increased upwelling or storm activity

the effect of bathymetry on tsunami characteristics at sisano lagoon papua new guinea the 1998 papua new guinea tsunami was greater than expected from its earthquake magnitude the area of significant impact was small approximately a 30 km stretch near the mouth of sissano lagoon papua new guinea to explain the localized nature of the event a submarine landslide has been conjectured to be responsible our study indicates that offshore bathymetry is critical to predicting tsunami coastal behavior model runs with newly obtained bathymetric data indicate that an earthquake fault source combined with the existing seafloor geometry may also explain the concentrated tsunami although the definitive cause of the papua new guinea tsunami remains uncertain local bathymetry had a notable effect on the wave behavior

marsh benthic foraminifera response to estuarine hydrological balance driven by climate variability over the last 2000 yr minho estuary nw portugal abstract a high resolution study of a marsh sedimentary sequence from the minho estuary provides a new palaeoenvironmental reconstruction from nw iberian based on geological proxies supported by historical and instrumental climatic records a low salinity tidal flat dominated by trochamminita salsa haplophragmoides spp and cribrostomoides spp prevailed from ad 140 1360 roman warm period dark ages medieval climatic anomaly this sheltered environment was affected by high hydrodynamic episodes marked by the increase in silt clay ratio decrease of organic matter and poor and weakly preserved foraminiferal assemblages suggesting enhanced river runoff the establishment of low marsh began at ad 1380 this low salinity environment marked by colder and wet conditions persisted from ad 1410 1770 little ice age when foraminiferal density increased significantly haplophragmoides manilaensis and trochamminita salsa mark the transition from low to high marsh at ad 1730 since ad 1780 the abundances of salt marsh species jadammina macrescens trochammina inflata increased accompanied by a decrease in foraminiferal density reflecting climate instability when droughts alternate with severe floods sw europe marsh foraminifera respond to the hydrological balance controlled by climatic variability modes e g nao and solar activity thus contributing to the understanding of ne atlantic climate dynamics

new insights into the glacial latitudinal temperature gradients in the north atlantic results from uk 37 sea surface temperatures and terrigenous inputs abstract sea surface temperatures sst and input of continental materials have been reconstructed from the study of the long chain alkenones and n alkanes respectively in a core located in the western side of the mid atlantic ridge md952037 37 05 n 32 02 w 2630 m depth both the long and short term variability recorded by the temperatures and the planktonic 18o are basically the same over the last 280 kyr showing a clear glacial interglacial evolution comparison with core su90 08 located only 6 north and directly influenced by the cold polar waters associated with the polar front during glacial times revealed different climatic conditions during glacial periods at both locations whereas core md952037 recorded similar sst values during the last two glacial periods ca 14 15 c the northern core displayed colder conditions during isotopic stage 2 8 10 c than in stage 6 13 15 c these results indicate the existence of a well developed steep north south gradient between 37 and 43 n during the last glacial period but not during stage 6 which suggests a southern expansion of the polar front during the last glacial maximum

pleistocene calcareous nannofossil stratigraphy for odp leg 177 atlantic sector of the southern ocean abstract seven ocean drilling program odp sites recovered during odp leg 177 in the atlantic sector of the southern ocean were analyzed to study the pleistocene calcareous nannofossil record calcareous nannofossil events previously described from intermediate and low latitudes were identified and calibrated with available geomagnetic and stable isotope stratigraphic data in general pleistocene southern high latitude calcareous nannofossil events show synchronicity with those observed from warm and temperate latitudes the first occurrence fo of emiliania huxleyi and the last occurrence lo of pseudoemiliania lacunosa are observed in marine isotope stages mis 8 and 12 respectively a reversal in abundance between gephyrocapsa muellerae and e huxleyi is observed at mis 5 mis 6 is characterized by an increase in g muellerae and mis 7 features a dramatic decrease in the proportion of gephyrocapsa caribbeanica this latter species began to increase its proportions from mis 14 to 13 the lo of reticulofenestra asanoi is observed within subchron c1r 1r and the fo of r asanoi occurs at the top of c1r 2r a re entry of medium sized gephyrocapsa can be identified in some cores during subchron c1r 1n the lo of large morphotypes of gephyrocapsa is well correlated through the studied area and occurs during the middle low part of subchron c1r 2r synchronous with other oceanic regions the fo of calcidiscus macintyrei and fo of medium sized gephyrocapsa occur in the studied area close to 1 6 ma

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

revealing climatic variability of the last three millennia in northwestern iberia using pollen influx data climatic variability of the last 3 millennia in nw iberia has been documented using high resolution pollen analysis of vir 18 core retrieved from the ria de vigo 42degrees14 07 n 8degrees47 37 w the depth age model is based on two accelerator mass spectrometry c 14 dates and three historically dated botanical events in galicia the expansion of juglans and pinus as well as the introduction of eucalyptus during the last 3000 years the relative pollen record demonstrates the occurrence of an open deciduous oak forest indicating a humid and temperate climate in northwestern iberia two step forest reduction since 975 cal bc suggests climate as the main cause rather than major socio economic changes documented in historical archives absolute pollen influx has been compared with instrumental summer and winter temperatures and tentatively used as a proxy of short decadal scale and low amplitude similar to 1degreesc temperature variations this new approach allows us to detect for the first time in nw iberia the millennial scale climatic cyclicity suggested by north atlantic records challenging the apparent climatic stability reflected by the relative pollen record the little ice age is recorded as low pollen influx values between 1400 and 1860 cal ad with a cold maximum at 1700 cal ad maunder minimum the roman and medieval warm periods are detected through high pollen influx values at 250 cal bc 450 cal ad and 950 1400 cal ad respectively c 2003 elsevier science b v all rights reserved

palaeoproductivity changes and upwelling variability in the galicia mud patch during the last 5000 years geochemical and microfloral evidence theholocenepalaeoclimatichistoryofthegaliciancontinentalshelfhasbeeninvestigatedthrough theanalysesofdiatomremains othersiliceouscompounds biogenicsilica bsi andmetalscontentinamul tiproxyapproachtoagravitycorerecoveredfromthegaliciamudpatch nwiberianpeninsula coveringthe last 5000 years downcore changes in diatom assemblages composition and abundance reflect changes in diatomproductionrelatedtolong short termvariationsinclimate regionaloceanography upwellingstrength and river influx off the coast of nw spain and portugal palaeoclimatic variability was related to the relative strengths and position of the azores high and iceland low pressure cells metals and microflora fluctuations are interpreted as changes in the riverine influence and upwelling intensity paced by oceanographic atmos pheric and climatic changes lack of diatoms between 4700 3300 and 1800 1200 cal yr bp could be linked to early diagenetic processes taking place in the sediment after burial biogenic barium baexcess metals and diatomassemblages showageneralincreaseofmarineproductivityforthelast1200cal yrbp between800 and500cal yrbphighproductionofthemicrofloraistriggeredbyinfluxofriver derivednutrientsundercon ditionsofswwindsandstormsresultingfromanaonegative likephase thebiosiliceousandgeochemical signatures of sediments from the last 500 cal yr bp indicate conditions of enhanced upwelling and increased

subducting oceanic crusts of the philippine sea and pacific plates and weak zone normal compression in the kanto district japan summary oceanic crusts subducting into the mantle were detected by analyses of mantle earthquakes in the kanto district central japan earthquakes in a depth range of 30 80 km in the southwestern ibaraki prefecture were relocated by a modified method of joint hypocentre determination we obtained a good distribution map of hypocentres and focal mechanisms a boundary layer between the eurasian and philippine sea plates was found where thrust earthquakes with p axes in the nw se direction and of which low angle nodal planes dip northward occurred in a layer with a thickness of about 4 km the p wave velocity in this layer is estimated to be less than about 7 0kms l another boundary layer between the philippine sea and pacific plates exists about 15 km beneath the above boundary layer thrust earthquakes with p axes in the ew direction and of which low angle nodal planes dip westward occurred in this layer that also has a thickness of about 4km furthermore normal faulting earthquakes of which the p axes are almost perpendicular to the boundary layers were found immediately outside the boundary layers combining these results we can conclude that the boundary layers are oceanic crusts that exist at the top of the subducting philippine sea and pacific plates weak zone normal compression was proposed to result from the existence of low velocity oceanic crusts at plate boundaries this hypothesis can be explained because only stress caused by relative motion of the two plates is consumed inside the weak oceanic crust the remnant stress after subtracting the above stress from the tectonic one applied at the plate boundary is the stress of which the p axis is normal to the plate boundary

quick aftershock relocation of the 1994 shikotan earthquake and its fault planes the 1994 shikotan earthquake of mw 8 2 occurred near the western kurile trench where the pacific plate is subducting beneath the north american plate although its mechanism is thrust type it is not a typical low angle thrust event with a nodal plane parallel to the plate boundary that occurs at the plate boundary in order to determine which of the two nodal planes of the main shock was the fault plane we relocated the main shock and all aftershocks with m 5 3 using a modified joint hypocenter determination method earthquakes on the northwestern side of the aftershock area including the main shock are located along a plane dipping east southeastward with a dip of 70 this plane is about 80 to 150 km long and 70 km wide the main shock occurred at the north northeastern bottom of this plane which is almost parallel to one of the two nodal planes of the main shock determined by harvard university which has a strike of n51 e and a dip of 76 thus we conclude that this plane is the fault plane that the fault broke at the northeastern bottom of the fault plane and that the rupture propagated to the surface and also to the southeast in addition to the aftershocks aligned with this fault plane there is a secondary alignment which is subparallel to the main fault plane and about 50 km east where the largest aftershock of mw 7 3 occurred on oct 9 since several aftershocks occurred on this secondary fault plane on the same day as the main shock it seems reasonable to suppose that this secondary fault plane was generated together with the main fault plane at the time of the main shock

global and regional factors controlling changes of coastlines in southern iberia spain during the holocene the interaction between global glacio eustatic sea level rise and regional factors oceanographic and tectonic has controlled the evolution of coastline during the holocene in southem iberia at ca 10 000 14c years bp a deceleration of relative sea level rise took place both in the atlantic and mediterranean littorals with a maximum transgression at 6450 14c years bp in subsiding areas present tidal flats estuaries illustrate a clear marine influence recorded both in sediments and the fauna while in uplifting areas prograding spit bar systems developed two phases of major progradation are distinguished in these systems the first one between 6450 and 3000 14c years bp with a sedimentary gap at ca 4000 14c years bp and the second one from 2750 14c years bp up to present with an intervening gap between 1200 and 1050 14c years bp these progradation phases develop during stillstands followed by relative sea level fall while the sedimentary gaps represent relative high sea level in the mediterranean areas with a higher uplift rate marine terraces almost coeval to those gaps occur the most pronounced modifications in littoral dynamics occurred at between 3000 and 2750 14c years bp represented by changes in the direction of longshore drift and prevailing winds and in the predominance of progradation over aggradation processes at ca 1000 14c years bp the estuaries record a greater fluvial than marine influence and at 500 years ago an extraordinary increase in coastal progradation took place in all littoral zones the european medieval warm period is characterized at least during its initial phase by low pressure climate conditions while during the little ice age anticyclonic conditions gave rise to a strong coastal progradation

analysis of the far field tsunamis generated by the 1998 papua new guinea earthquake the tsunami generated by the 1998 papua new guinea earthquake was observed at several tide gauges and ocean bottom pressure gauges in japan the fault model of the 1998 papua new guinea earthquake was estimated using those tsunami waveforms observed in japan and coseismic subsidence observed along the coast of papua new guinea near the source region the numerical simulation of the tsunami using the linear boussinesq equation was carried out the tsunami waveforms in japan are explained by the fault model which is consistent with the harvard cmt solution including the seismic moment of 3 7 1019 nm the additional tsunami source such as a sediment slump is not needed to explain the observed tsunami in japan the mechanism of the earthquake was likely to be a steeply dipping reverse fault the 1998 papua new guinea earthquake was likely to occur within a small accretionary prism near the new guinea trench

empirical constraints on magnitude distance relationships for seismically induced submarine tsunamigenic landslides abstract seismically induced submarine landslide tsunamis here called silts attract growing attention due to their unique setting damage potential and short warning time a question of key importance especially for tsunami early warning is how far can an earthquake trigger a tsunamigenic slump here we investigate the relationships between earthquake magnitude and the maximal distance between the seismogenic fault and the tsunamigenic slumps rf and between the earthquake epicenter and the slump re and propose empirical constraints on these magnitude distance m d relations the 49 identified silts are spread in various seismotectonic and bathymetric settings in different seas around the globe we found that the maximal distance of the tsunamigenic submarine landslide from the parent earthquake grows with the magnitude and is bounded by an envelope constrained by mw as low as 4 9 for several kilometers the 1968 liguria coast italy and as far as 250 km for mw 7 7 the 1819 rann of kachchh india higher earthquake magnitudes also produce silts seemingly distances lower than 250 km however it is suspected that the available data is limited and unable to reflect the true nature of silt s generation generalized empirical relations between the earthquake magnitude mw and the maximal distance from the seismogenic fault to its generated silt rf in km are log rf 1 17 0 49 mw r2 0 78 the empirical distance between the earthquake epicenter and the corresponding tsunamigenic slump re in km is log re 0 87 0 45 mw r2 0 83 although many earthquakes within the m d bounding envelope did not produce tsunamis the successful events still enable the delineation of the m d zone vulnerable to tsunami generation which in turn can be applied to tsunami early warning procedures this is particularly important for near coast inland earthquakes as their tsunamigenic potential might be overlooked

estimation of current plate motions in papua new guinea from global positioning system observations plate tectonic motions have been estimated in papua new guinea from a 20 station network of global positioning system sites that has been observed over five campaigns from 1990 to 1996 the present velocities of the sites are consistent with geological models in which the south bismarck woodlark and solomon sea plates form the principal tectonic elements between the pacific and australian plates in this region active spreading is observed on the woodlark basin spreading centre but at a rate that is about half the rate determined from magnetic reversals the other major motions observed are subduction on the new britain trench seafloor spreading across the bismarck sea seismic lineation convergence across the ramu markham fault and left lateral strike slip across the papuan peninsula these motions are consistent with a 8 2 myr 1 clockwise rotation of the south bismarck plate about a pole in the huon gulf and a rotation of the woodlark plate away from the australian plate second order deformation may also be occurring in particular manus island and northern new ireland may be moving northward relative to the pacific plate at 5 8 mm yr 1 significant at the 95 but not at the 99 confidence level which may suggest the existence of a north bismarck plate

the july 1998 papua new guinea earthquake mechanism and quantification of unusual tsunami generation the unusual tsunami generated by the july 17 1998 papua new guinea earthquake was investigated on the basis of various geophysical observations including seismological data tsunami waveform records and on land and submarine surveys the tsunami source models were constructed for seismological high angle and low angle faults splay fault and submarine slumps far field and near field tsunamis computed from these models were compared with the recorded waveforms in and around japan and the measured heights along the coast around sissano lagoon respectively in order to reproduce the far field tsunami waveforms small sources such as splay fault or submarine slump alone were not enough and a seismological fault model was required relocated aftershock distribution and observed coastal subsidence were preferable for the low angle fault but the low angle fault alone could not reproduce the large near field tsunamis the low angle fault with additional source possibly a submarine slump is the most likely source of the 1998 tsunami although other possibilities cannot be excluded computations from different source models showed that the far field tsunami amplitudes are proportional to the displaced water volume at the source and the comparison with the observed tsunami amplitudes indicated that the displaced water volume at the 1998 tsunami source was 0 6 km3 the near filed tsunami heights on the other hand are determined by the potential energy of displaced water and the comparison with the observed heights showed that the potential energy was 2 x 1012 j

a biomarker approach to the organic matter deposited in the north atlantic during the last climatic cycle abstract the study of the composition of total organic carbon toc c37 alkenones and c23 c33 n alkanes in the north atlantic ocean cores su90 08 and su90 39 has allowed the development of a model for the differentiation of marine and terrigenous toc this model gives rise to results in good agreement with inorganic markers such as magnetic susceptibility ms and non carbonate content according to this model the terrigenous toc accounts for most of the organic matter in the glacial sediments thus the higher toc of the glacial periods 0 1 0 45 vs 0 05 0 15 in the interglacials is due to the increase in terrigenous toc the changes in marine toc those associated to sea surface productivity are independent of the glacial interglacial evolution the terrigenous toc is more important at higher latitudes probably due to higher terrigenous detrital inputs associated with iceberg transport in this respect the correlation between n alkanes and ms strongly suggests that the main source of these hydrocarbons are ice rafted materials and that aeolian inputs only represent minor contributions the four peaks of reworked n alkanes in the su90 08 core that are coincident with the heinrich layers h1 h2 h4 and 115 are in agreement with this hypothesis on the other hand the abrupt marine toc peaks of su90 08 show a 23 ka periodicity indicating that the marine productivity at 43 n in the north atlantic ocean was precessionally driven the productivity maxima in this core correlate with low latitude oceanographic processes such as periods of enhanced trade wind intensity and equatorial upwelling which are also tuned to precession and independent of the global glacial interglacial evolution

molecular stratigraphy a new tool for climatic assessment variations in sea surface temperatures over the past 500 000 years are inferred from the relative abundance behaviour of two organic compounds c37 alkenones over the upper 8 metres of a sediment core from the eastern equatorial atlantic this molecular record ascribed to contributions from prymnesiophyte algae correlates well with the variations in the 18 signal for the calcareous skeletons of certain planktonic foraminifera thus providing the first demonstration of a new stratigraphical technique which may be especially valuable where methods based on carbonate 18 fail

sea surface dynamics and palaeoenvironmental changes in the north atlantic ocean iodp site u1313 during marine isotope stage 19 inferred from coccolithophore assemblages abstract coccolithophore assemblages recovered from integrated ocean drilling program iodp site u1313 are investigated to reconstruct the palaeoceanographic evolution of a sector of the north atlantic during marine isotope stage mis 19 790 760 ka at orbital suborbital and millennial time scales the end of the glacial mis 20 is marked by the arrival of cold waters deriving from ice melting at higher latitudes as recorded by coccolithus pelagicus pelagicus the mis 19c is characterised by an extension of warmer north atlantic transitional waters natw reflecting the intensification of subtropical gyre influence on site u1313 identified by an increase in warm species umbilicosphaera sibogae the influence on the site of cooler natw is inferred from higher percentages of gephyrocapsa margereli which starts increasing from 779 ka finally the transition from mis 19a to mis 18 is characterised by a southward shift of the palaeoceanographic system due to a southward extension of the subpolar front as indicated by an increase of cold subspecies c pelagicus pelagicus the evolution of the palaeoproductivity proxy records number of coccoliths g of sediment and nannofossil accumulation rate nar and the abundances of small gephyrocapsa g margereli u sibogae and c pelagicus pelagicus show that fluctuations in sea surface productivity and alternations between cooling and warming phases occurred on the precessional timescale spectral analyses of u sibogae number of coccoliths g of sediment and nar indicate a significant concentration of variance close to half precession 10 kyr this reflects a nonlinear response of the mid latitude north atlantic surface ocean to low latitude insolation forcing furthermore millennial to multi centennial instability in sea surface dynamics is highlighted by spectral and wavelet analyses of u sibogae g margereli and c pelagicus pelagicus percentages number of coccoliths g of sediment and nar which reveal the occurrence of rapid events related to stadial and interstadial type conditions

near field modeling of the july 17 1998 tsunami in papua new guinea modest earthquakes may trigger large submarine landslides responsible for disastrous tsunami waves as demonstrated by the papua new guinea event of july 17 1998 the relatively small earthquake was followed by unexpectedly high waves up to 15 m wiping out 3 villages and killing more than 2200 people numerical simulations show that seismic dislocation sources are not energetic enough to reproduce the observed tsunami along the coast tsunami generation by a submarine landslide has been simulated by a finite difference model assimilating the landslide to a flow of granular material long wave approximation is adopted for both water waves and the slide numerical results show that observed inundation heights are well reproduced for a volume of 4 km located 20 km offshore sliding downslope with a coulomb type friction

coccolithus pelagicus a productivity proxy related to moderate fronts off western iberia abstract the traditional interpretation of coccolithus pelagicus as a cold water proxy is examined based on its distribution patterns in the water column off the portuguese coast using data from eleven cruises and in holocene surface sediment samples and quaternary cores from the same region coccolithus pelagicus is common in the portuguese upwelling system an area where surface waters are predominantly of subtropical origin although revealing an affinity for low temperature upwelled waters the species was found in waters up to 18 c associated with riverine plume and shelf break fronts c pelagicus seemed to consistently occupy a particular ecological niche between other phytoplankton groups related to moderate turbulence conditions combined with nutrient availability from this behaviour it is proposed that c pelagicus can be used as a tracer of the periphery of areas of enhanced productivity coccolithus pelagicus preferences for fronts of moderate temperature and salinity gradients are tentatively used to explain particular features of its sedimentary record the repeated increase of c pelagicus in thanatocoenoses surface sediment assemblages close to three river mouths on the portuguese shelf are interpreted as a positive response to the development of riverine plumes on the other hand inconsistencies in the correlation between sea surface cooler glacial and warmer interglacial isotope stages and the relative abundance pattern of c pelagicus during the late quaternary as registered in two galicia bank piston cores 42 n are tentatively explained in terms of shifts in the extent of the outer limit of the local palaeoproductivity belt off the iberian peninsula

flood frequencies reveal holocene rapid climate changes lower moulouya river northeastern morocco current high resolution palaeoenvironmental records reveal short term holocene cool ings one of these major holocene rapid climate changes occurred between 3 2 and 2 7 cal ka bp the sensitivity of river systems vis a vis slight and short term holocene climatic variations is a subject of controversy in the scientific community in this paper we present a 4 0 to 1 4 cal ka bp palaeoflood record from the lower moulouya river northeastern morocco to demonstrate the high sensitivity of semiarid rivers in the southwestern mediterranean towards holocene environmental changes the lower moulouya flood deposits are characterised by thick well stratified predominantly clayey to silty overbank fine sediments these cohesive sediments show evidence of excellent preservation conditions against fluvial erosion and contain a continuous record of mid to late holocene flood sequences the moulouya palaeoflood record can be interpreted in the context of regional and global high resolution proxy data revealing a strong coupling with holocene rapid climate changes the centennial scale moulouya palaeohydrological history will be discussed with palaeoenvironmental data from the same record palaeomagnetics sedimentary charcoal record anthracological analyses snail analyses to generate new ideas about the mid to late holocene hydrological cycle in the southwestern mediterranean the deduced features of pronounced lower moulouya flooding and the decreased fire recurrence during holocene cooling remain somewhat inconsistent with the interpret ation of other palaeohydrological and paleaoecological records from the southwestern mediterranean however enhanced lower moulouya flood frequencies between 3 2 and 2 7 cal ka bp agree with increased floodplain aggradation in other major river systems of mediterranean north africa copyright 2009 john wiley sons ltd

millennial scale coccolithophore paleoproductivity and surface water changes between 445 and 360 ka marine isotope stages 12 11 in the northeast atlantic abstract a high resolution coccolithophore study was carried out in order to improve the understanding of the paleoceanographic evolution and changes in paleoproductivity occurring off the iberian margin im between 445 and 360 ka i e during late marine isotope stage 12 to 11 coccolithophore assemblages allowed reconstructing surface water changes characterized by millennial scale oscillations 1 5 kyr cycles involving portugal or iberian poleward currents pc and ipc prevalence changes in paleoproductivity possibly related to the upwelling of eastern north atlantic central waters enacw of sub tropical enacwst or sub polar origin enacwsp were also recognized this study also permitted detecting abrupt events stadial interstadial type oscillations and revealed that changes in paleoproductivity are related to opposite dynamics during glacial and interglacial stages with the reversed setting being established during the deglaciation furthermore a possible control of half and fourth precessional cycle components on the occurrence of abrupt changes within the assemblages structure during the deglaciation is proposed on the basis of wavelet analysis results applied to selected taxa