evolution of the eastern volcanic ridge of the canary islands based on new kar data the results of 64 new k ar age determinations together with 32 previously published ages show that after a period of erosion of the basal complex miocene volcanic activity started around 20 ma in fuerteventura and 15 ma in lanzarote forming a tabular succession of basaltic lavas and pyroclastics with a few salic dykes and plugs this series includes five separate volcanic edifices each one with its own eruptive history in fuerteventura several miocene eruptive cycles have been identified in the central edifice one around 20 17 ma followed by two others centred around 15 and 13 ma in the southern edifice the maximum of activity took place around 16 14 ma whereas in the northern one the main activity occurred between 14 and 12 ma in lanzarote a first cycle of activity took place in the southern edifice between 15 5 and 14 1 ma followed by another between 13 6 and 12 3 ma in the northern edifice three pulses occurred 10 2 8 3 6 6 5 3 and 3 9 3 8 ma an important temporal gap greater in fuerteventura than in lanzarote separates series i from the plio quaternary series ii iii and iv formed by multi vent basaltic emissions in fuerteventura the following eruptive cycles have been identified 5 2 9 2 4 1 8 1 7 0 8 0 4 and 0 1 ma in lanzarote the activity was fairly continuous from 2 7 ma to historic times with a maximum in the lower pleistocene eruptive rates in the series i edifices were on the average 0 1 0 01 km3 ka comparable but slightly smaller than in similar edifices in tenerife and la gomera but much lower than in gran canaria average post miocene eruptive rates were about 0 013 0 027 km3 ka in lanzarote and 0 003 0 007 km3 ka in fuerteventura all these volcanic edifices show a similar general sequence fissural eruptions erosion multi vent volcanism repeated at different periods in different parts of the eastern islands of the canaries the model of growth of the series i edifices is comparable to those in tenerife and la gomera long periods of activity sometimes greater than 6 m y with pulses separated by gaps however salic and intermediate differentiates frequent in tenerife and la gomera are very scarce in these islands the fuerteventura lanzarote ridge shows a decrease in volcanic activity with time and also a certain ssw nne polarity in the temporal development of volcanism

fractal clustering of induced seismicity in the geysers geothermal area california summary we analyse earthquakes recorded at the geysers geothermal field in california an area where industrial activity induces seismicity the seismicity is characterized by the seismic b value and d the fractal dimension of earthquake hypocentres measured from sliding windows containing 200 events we study a group of events strongly clustered around an injection well over most of the time period examined we find a positive correlation between b and d however during the initiation of injection into a new well we find instead a negative correlation the diverences in correlation are statistically significant at the 1s level but only marginally so at the 2s level these results provide evidence for a transient change in the seismic mechanisms operating and may be explained by a change from conditions of slow stress loading to rapid loading as a result of the build up of the rate of water injection into the reservoir

the role of partial melting in the 15 ma geochemical evolution of gran canaria a blob model for the canary hotspot the subaerial portion of gran canada canary islands was built by three cycles of volcanism a miocene cycle 8 5 15 ma a pliocene cycle 1 8 60 ma and a quaternary cycle 1 8 0 ma only the pliocene cycle is completely exposed on gran canaria the early stages of the miocene cycle are submarine and the quaternary cycle is still in its initial stages during the miocene sio2 saturation of the mafic volcanics decreased systematically from tholeiite to nephelinite for the pliocene cycle sio2 saturation increased and then decreased with decreasing age from nephelinite to tholeiite to nephelinite sio2 saturation increased from nephelinite to basanite and alkali basalt during the quaternary in each of these cycles increasing melt production rates sio2 saturation and concentrations of compatible elements and decreasing concentrations of some incompatible elements are consistent with increasing degrees of partial melting in the sequence melilite nephelinite to tholeiite the mafic volcanics from all three cycles were derived from co2 rich garnet lherzolite sources phlogopite ilmenite sulfide and a phase with high partition coefficients for the light rare earth elements lree u th pb nb and zr possibly zircon were residual during melting to form the miocene nephelinites through tholeiites phlogopite ilmenite and sulfide were residual in the source of the pliocene quaternary nephelinites through alkali basalts highly incompatible element ratios e g nb u pb ce k u nb pb ba rb zr hf la nb ba th rb nb k nb zr nb th nb th la and ba la exhibit extreme variations in many cases larger than those reported for all other ocean island basalts but these ratios correlate well with degree of melting survival of residual phases at higher degrees of melting during the miocene cycle and differences between major and trace element concentrations and melt production rates between the miocene and pliocene tholeiites suggest that the miocene source was more fertile than the pliocene quaternary source s we propose a blob model to explain the multi cycle evolution of canary volcanoes and the temporal variations in chemistry and melt production within cycles each cycle of volcanism represents decompression melting of a discrete blob of plume material small degree nephelinitic and basanitic melts are derived from the cooler margins of the blobs whereas the larger degree tholeiitic and alkali basaltic melts are derived from the hotter centers of the blobs the symmetrical sequence of mafic volcanism for a cycle from highly undersaturated to saturated to highly undersaturated compositions reflects melting of the blob during its ascent beneath an island in the sequence upper margin corelower margin volcanic hiatuses between cycles and within cycles represent periods when residual blob or cooler entrained shallow mantle material fill the melting zone beneath an island

coastal ice core record of recent northwest greenland temperature and sea ice concentration coastal ice cores provide an opportunity to investigate regional climate and sea ice variability in the past to complement hemispheric scale climate reconstructions from ice sheet interior ice cores here we describe robust proxies of baffin bay temperature and sea ice concentration from the coastal 2barrel ice core collected in the thule region of northwest greenland over the 1990 2010 record 2barrel annually averaged methanesulfonic acid msa concentrations are significantly correlated with may june baffin bay sea ice concentrations and summer temperatures higher msa is observed during warmer years with less sea ice indicative of enhanced primary productivity in baffin bay similarly 2barrel annually averaged deuterium excess d excess values are significantly correlated with annual baffin bay sea ice concentrations and summer and annual temperatures warm cool years with anomalously low high sea ice concentration are associated with proportionally more less low d excess baffin bay moisture at the ice core site multilinear regression models incorporating 2barrel msa d excess and snow accumulation account for 38 51 of the baffin bay sea ice and temperature variance the annual temperature model is significantly correlated with temperatures throughout most of greenland and eastern arctic canada due to the strong influence of the north atlantic oscillation and atlantic multidecadal oscillation

long range connective sandpile models and its implication to seismicity evolution abstract we propose a new variant of the sandpile model the long range connective sandpile model by means of introducing randomly internal connections between two separated distant cells the long range connective sandpile model demonstrates various self organized critical states with different scaling exponents in the power law frequency size distributions we found that a sandpile with higher degree of randomly internal long range connections is characterized by a higher value of the scaling exponent for the distribution whereas the nearest neighbor sandpile is possessed of a lower scaling exponent our numerical experiments on the long range connective sandpile models imply that higher degree of random long range connections makes the earthquake fault system more relaxant that releases accumulated energy more easily and produces fewer catastrophic events whereas lower degree of long range connections possibly caused by fracture healing very likely motivates accelerating seismicity of moderate events

block model of earthquake sequence abstract a model of interaction of lithospheric blocks is suggested dynamics of the lithosphere is described as an alternation of slow deformations and ruptures earthquakes the model is used to produce an artificial catalog of seismicity and the properties of this catalog are compared with and contrasted to the properties of real seismicity catalogs by this means it is possible to determine which properties of earthquake sequences can be derived from simple assumptions about the processes that occur in the lithosphere we consider both the instability of the process and possibility that large earthquakes might be predicted

deep crustal structure and magmatic processes the inception of seafloor spreading in the norwegian greenland sea summary an extensive investigation into the deep crustal structure of the conjugate norwegian and e greenland margins utilizing two ship expanded spread and wide aperture cdp profiling has led to the identification of a unique suite of crustal structures developed during the onset of seafloor spreading on both margins a region of low velocity crust was found proximal to marginal escarpments immediately seaward of the low velocity crustal block seaward dipping reflectors occur within thick crust that is interpreted to be wholly igneous a product of voluminous melt production enhanced by convective partial melting processes this earliest formed oceanic crust is actually several kilometres thicker than the low velocity crust or the adjacent continental crust normal oceanic crustal thicknesses are not produced until about 5 my after the initiation of spreading when convective partial melting has abated and the magma budget has reduced the extrusive unit reduces to normal thicknesses long before the intrusive and plutonic section indicating that the thickening or thinning of oceanic crust is accomplished primarily by variations in the latter

the correction for sediment loading on the seafloor available measurements of sediment velocity and density indicate that a factor of 600 m s 1 of two way sediment reflection time will correct seafloor depth to yield basement depth in the absence of sediment loading this simple linear relation is derived from the results of six deep drill holes in abyssal sediments of the north and south atlantic oceans the relation predicts the sediment correction with an accuracy of about 50 m regardless of the lithology sampled down to a depth of 1 5 s of reflection time the cost wells on the u s continental shelf and empirical relations among velocity density porosity and depth provide estimates of the deeper behavior of abyssal sediments and suggest that the 600 m s 1 factor continues to provide a satisfactory sediment correction to a depth of 3 s

1 fβ fluctuations and self similarity in earthquake dynamics observational evidences in southern italy abstract recently it has been determined that many statistical features of earthquakes are scale invariant with universal values for exponents the analysis of scaling laws has led to the development of a wide variety of physical models of seismogenesis involving nonlinear dynamics and it can be used to better characterize the seismicity pattern in this work the presence of scale invariance properties in the seismicity of a selected area of the southern appennine chain is revealed 1 f fluctuations are detected from the analysis of earthquake sequences using the counting statistics and at the spatial scale a self similar structure in the epicentre aggregate is determined by the estimation of its fractal dimension finally correlations between temporal exponent fractal dimension and b value variations are described

postdepositional losses of methane sulfonate nitrate and chloride at the european project for ice coring in antarctica deep drilling site in dronning maud land antarctica nitrate and typically 51 20 of msawere lost while for chloride no significant depletion could be observed in firn older than one year assuming a first order exponential decay rate the characteristic e folding time for msais 6 4 3 years and 19 6 years for nitrate it turns out that for nitrate and msathe typical mean concentrations representative for the last 100 years were reached after 5 4 and 6 5 years respectively indicating that beneath a depth of around 1 2 1 4 m postdepositional losses can be neglected in the area of investigation only msaconcentrations and postdepositional losses showed a distinct dependence on snow accumulation rate consequently msa concentrations archived at this site should be significantly dependent on the variability of annual snow accumulation and we recommend a corresponding correction with a simple approach we estimated the partial pressure of the free acids msa hno3 and hcl on the basis of henry s law assuming that ionic impurities of the bulk ice matrix are localized in a quasi brine layer qbl in contrast to measurements this approach predicts a nearly complete loss of msa n o3 and cl index terms 0322 atmospheric composition and structure constituent sources and sinks 0330 atmospheric composition and structure geochemical cycles 0365 atmospheric composition and structure troposphere composition and chemistry 1827 hydrology glaciology 1863 1863 hydrology snow and ice 1827 keywords postdepositional loss snow chemistry methane sulfonate

an ice core indicator of antarctic sea ice production 1 the sea ice surface not open water is the dominant source of sea salt to aerosol and ice cores in coastal antarctica here we show that it may also form the dominant source for central antarctica we can then explain higher concentrations in the winter and last glacial maximum lgm as being due to increased sea ice production this suggests that ice core sea salt can indicate at least the timing of changes in antarctic sea ice production the pattern of sea salt in ice cores is consistent with marine evidence about sea ice changes in the holocene and lgm sea salt shows no change at the initial co2 increase out of the last glacial making it unlikely this was primarily due to changing sea ice cover the sea salt record should not be treated as an indicator of meridional transport

relationships between the interannual variability of antarctic sea ice and the southern oscillation abstract a climatology of antarctic sea ice extent based on 20 years of data 1973 1992 is presented including measures of interannual variability and extrema in the first half of the year the greatest variability is found in the western hemisphere particularly in the weddell and ross sea regions while in the second semester the variability displays a considerable degree of zonal symmetry we have used this dataset to explore the possible links between antarctic sea ice extent and the southern oscillation index soi to do this we have calculated their correlation for all pairings of calendar months as well as with the soi taken from the year before and subsequent to that of the time of the sea ice data most of the correlations assume their largest magnitude when the soi leads the anomalies in the sea ice but these differ considerably between the three ocean basins the extent of indian ocean sea ice in the months april through july is positively correlated with the soi during most of the previou

the effect of hot spots on the oceanic age depth relation hot spots located both midplate and on midocean ridges can bias the empirical age depth relation ocean floor bathymetry for seafloor greater than 80 m y b p in age has been previously used to determine if the oceanic lithosphere behaves as a cooling half space or as a cooling plate however large areas of the ocean basins do not fit a simple age depth relation anomalously shallow swells approximately 1000 km wide and 1 km high surround hot spots such as iceland the azores and the cape verde islands by sorting seafloor depth data by distance to the nearest hot spot track we show that the along isochron variation in depth in the north atlantic correlates with distance from a hot spot track due to the absence in the north atlantic of seafloor both old and far from hot spots we compare depth versus age at constant distance and do not observe flattening of the age depth relation in any distance range the age depth relation depth meters 2700 295 t m y 1 2 derived for seafloor 1200 to 1800 km from a hot spot track represents our best estimate of the age depth relation appropriate to seafloor unaffected by a hot spot track in the north atlantic the previously inferred flattening of the age depth relation appears to be caused by the inclusion of hot spot swells this implies that hot spots may be the primary means of heat transfer from the deeper mantle to the base of the lithosphere

glaciochemistry of polar ice cores a review human activities have already modified the chemical composition of the natural atmosphere even in very remote regions of the world the study of chemical parameters stored in solid precipitation and accumulated on polar ice sheets over the last several hundred thousand years provides a unique tool for obtaining information on the composition of the preindustrial atmosphere and its natural variability over the past this paper deals with the chemistry of polar ice focused on the soluble mineral na nh4 k ca mg h f cl no3 so4 and h2o2 and organic methanesulfonate ch3so3 formate hcoo acetate ch3coo and formaldehyde hcho species and their interpretation in terms of past atmospheric composition aerosols and water soluble gaseous species we discuss ice core dating the difficulties connected with trace measurements and the significance of the ionic composition of snow we examine temporal from the last decades back to the last climatic cycle and spatial including examples from coastal as well as central areas of greenland and antarctica variations in the ionic budget of the precipitation and evaluate ice core studies in terms of the chemical composition of our past atmosphere we review 1 how greenland and antarctic ice cores that span the last few centuries have provided information on the impact of human activities and 2 how the chemistry of deep ice cores provides information on various past natural phenomena such as climatic variations glacial interglacial changes el nino volcanic eruptions and large boreal forest fires

comparison of sediment sound velocity functions from conjugate margins a comparison of velocity functions from 15 regions within the conjugate margins of the norwegian greenland sea southeast indian ocean north atlantic and south atlantic ocean shows that velocity functions are not significantly different across most conjugate margins one major exception is the segment from the blake plateau to new england in the western north atlantic and its counterpart in northwest africa here the velocity gradients are consistently steeper on the african side compared with those on the north american side the reason for this unexpected difference was sought in the geologic literature of the two margins published studies of these two margins show that although total subsidence and sediment thickness of each of the margins are about equal the older beds pre cenozoic are much thicker on the african side this fundamental difference in depositional history seems to be the major cause of the difference in velocity profiles possible differences in the distribution of salt along the margins of africa and north america are not considered a likely source for the trans atlantic differences in the velocity functions the north atlantic data therefore illustrate that velocity increases more rapidly with depth in sections biased toward greater proportions of older beds that is sedimentation rates decrease as the basin ages these studies also reveal that sound velocity profiles are sensitive to the early conditions of deposition on passive margins

seismic activity on neighbouring faults as a long term precursor to large earthquakes in the san francisco bay area activity in moderate size earthquakes accelerated in the several decades before the large california earthquakes of 1989 1906 and 1868 this type of precursor seems to require the presence of several major faults in close enough proximity to one another that moderate size shocks are selectively triggered on surrounding faults during the latter stages of the cycle of strain buildup to large earthquakes it may be possible to use quantitative aspects of similar seismic precursors to make predictions of large earthquakes on timescales of a few years to one decade

seismic quiescence before the 1999 chi chi taiwan mw 7 6 earthquake the chi chi taiwan earthquake of 20 september 1999 was preceded by a notable decrease of the regional seismicity rate the anomalous period started in january 1999 and lasted about 9 months up to the occurrence of the mainshock as revealed from analyzing the taiwan catalog data from 1 january 1994 to 20 september 1999 our results indicate that the mean seismicity rate is 435 events per month with a standard deviation of 78 events for earthquakes with magnitude above 2 0 during the anomalous period seismicity rates fell outside the range of one standard deviation with a mean value of 314 events per month there was also a consistent trend of decreasing regional b value as well as notable increases of seismic activity in areas surrounding the chi chi earthquake source region via the z test map zmap analysis

volcanic evolution of the island of tenerife canary islands in the light of new k ar data new age determinations from tenerife together with those previously published 93 in all provide a fairly comprehensive picture of the volcanic evolution of the island the oldest volcanic series with ages starting in the late miocene are formed mainly by basalts with some trachytes and phonolites which appear in anaga teno and roque del conde massifs in anaga ne three volcanic cycles occurred one older than 6 5 ma a second one between 6 5 and 4 5 ma with a possible gap between 5 4 and 4 8 ma and a late cycle around 3 6 ma in teno nw after some undated units the activity took place between 6 7 and 4 5 ma with two main series separated by a possible pause between 6 2 and 5 6 ma in the zone of roque del conde s the ages are scattered between 11 6 and 3 5 ma between 3 3 and 1 9 ma the whole island underwent a period of volcanic quiescence and erosion the large canadas volcano made up of basalts trachytes and phonolites was built essentially between 1 9 and 0 2 ma to the ne of this central volcano linking it with anaga is a chain of basaltic emission centers with a peak of activity around 0 8 ma the canadas caldera had several collapse phases associated with large ignimbrite emissions there were at least an older phase more than 1 ma old on the western part of the volcano and a younger one less than 0 6 ma old in the eastern side the two large valleys of guimar and la orotava were formed by large landslides less than 0 8 ma ago and probably before 0 6 ma ago the present canadas caldera was formed by another landslide less than 0 2 ma ago this caldera was later filled by the huge teide volcano which has been active even in historic times during the same period a series of small volcanoes erupted at scattered locations throughout the island the average eruptive rate in tenerife was 0 3 km3 ka with relatively small variations for the different eruptive periods this island and la gomera represent a model of growth by discontinuous pulses of volcanic activity separated by gaps often coinciding with episodes of destruction of the edifices and sometimes extended for several million years the neighbouring gran canaria on the other hand had an initial rapid shield building phase during which more than 90 of the island was built and a series of smaller pulses at a much later period a comparison between these three central islands indicates that the previously postulated westward displacement in time of a gap in the volcanic activity is valid only as a first approximation several gaps are present on each island overlapping in time and not clearly supporting either of the models proposed to explain the evolution of the canaries

the 2011 2012 submarine eruption off el hierro canary islands new lessons in oceanic island growth and volcanic crisis management forty years after the eruption of the teneguia volcano on la palma 1971 the last volcanic event in the canary islands a submarine eruption took place in 2011 off shore el hierro the smallest an

west antarctica s sensitivity to natural and human forced climate change over the holocene the location and intensity of the austral westerlies strongly influence southern hemisphere precipitation and heat transport with consequences for human society and ecosystems with future warming global climate models project increased aridity in southern mid latitudes related to continued poleward contraction of the austral westerlies we utilize antarctic ice cores to investigate past and to set the stage for the prediction of future behaviour of the westerlies we show that holocene west antarctic ice core reconstructions of atmospheric circulation sensitively record naturally forced progressive as well as abrupt changes we also show that recent poleward migration of the westerlies coincident with increased emission of greenhouse gases and the antarctic ozone hole has led to unprecedented penetration compared with 100 000 years ago of air masses bringing warmth extra antarctic source dust and anthropogenic pollutants into west antarctica copyright 2012 john wiley sons ltd

patterns of seismic activity preceding large earthquakes we analyze the patterns of seismic activity which precede large events in a mechanical model of a fault the model generates a statistical distribution of events similar to that observed for a single fault with a scaling region consistent with the gutenberg richter law at small and moderate magnitudes and an excess of events at large magnitudes we find only slight variation in the scaling behavior during a loading cycle however we do observe systematic variations in space and time of the overall rate of activity in the model the activity accelerates dramatically preceding a large event and is usually a maximum hi the neighborhood of the future epicenter these results are compared to california seismicity data where we find that activity patterns vary regionally looking at patterns of activity in the san francisco bay area since 1948 we find an increase of activity on the calaveras fault near san jose beginning in the 1980s which if our model is relevant would forecast a large earthquake in that region the 1989 loma prieta earthquake occurred on the san andreas fault within 30 km of the section of the calaveras fault showing increased activity

k ar chronology of the volcanic eruptions in the canarian archipelago island of la gomera a geochronological study of the island of la gomera canaries has been carried out by the k ar method the 26 new ages obtained together with the 17 previous determinations show that above the main unconformity of the island separating the basal complex from the later volcanic series there is a unit of lower old basalts more than 10 m y old polymictic volcanic breccias were emplaced between 10 and 9 m y ago the upper old basalts above them were formed between 9 and 6 m y ago with a peak of activity around 7 m y after a period of erosion 6 5 m y a thick series of young basalts associated with trachytic and phonolitic domes and flows were rapidly emplaced between 4 5 4 m y ago finally local basaltic activity took place 2 8 m y ago the age of the basal complex is not well known although three ages 14 6 15 5 and 19 3 m y have been obtained for some alkaline intrusives which seem to represent the youngest events in the complex

fractal dimension and b value on creeping and locked patches of the san andreas fault near parkfield california we tested the hypotheses 1 that the fractal dimension d of hypocenters are different in a locked and a creeping segment of the san andreas fault and 2 that the relationship d 2b holds approximately where b is the slope of the frequency magnitude relationship the test area was the 30 to 50 km fault segment north of park eld for which two earthquake catalogs exist the borehole high resolution seismic network data and the u s geological survey data which have a minimum magnitude of completeness of mc 0 4 and mc 1 0 1 2 respectively the relative location errors in the two catalogs are estimated as 0 25 km and less than 1 km respectively the periods of high quality data available extend from 1987 to 1998 5 and 1981 to 2000 2 respectively furnishing 2609 and 3775 events for analysis in the two catalogs in the locked part 0 5 b 0 7 and 0 96 d 1 14 whereas in the creeping segment 1 1 b 1 6 and 1 45 d 1 72 however the spatial distribution of the hypocenters in the creeping segment is not well approximated by a fractal distribution we conclude 1 that the frequency magnitude distribution as described by b as well as the fractal dimension d are different in the locked and creeping segments near park eld 2 that the spatial distribution in the creeping segment is not well approximated by a fractal distribution and 3 that the relationship d 2b holds in the locked segment where both parameters can be measured accurately thus we propose that the heterogeneity of seismogenic volumes lead to differences in d and b and that these differences where established by high quality data may furnish clues concerning properties of fault zones

post depositional movement of methanesulphonic acid at law dome antarctica and the influence of accumulation rate a series of ice cores from sites with different snow accumulation rates across law dome east antarctica was investigated for methanesulphonic acid msa movement the precipitation at these sites up to 35 km apart is influenced by the same air masses the principal difference being the accumulation rate at the low accumulation rate w20k site 0 17 m ice equivalent msa was completely relocated from the summer to winter layer moderate movement was observed at the intermediate accumulation rate site 0 7 m ice equivalent dome summit south dss while there was no evidence of movement at the high accumulation rate de08 site 1 4 m ice equivalent the main dss record of msa covered the epoch ad 1727 2000 and was used to investigate temporal post depositional changes co deposition of msa and sea salt ions was observed in the surface layers outside of the main summer msa peak which complicates interpretation of these peaks as evidence of movement in deeper layers a seasonal study of the 273 year dss record revealed msa migration predominantly from summer into autumn in the up core direction but this migration was suppressed during the tambora 1815 and unknown 1809 volcanic eruption period and enhanced during an epoch 1770 1800 with high summer nitrate levels a complex interaction between the gradients in nss sulphate nitrate and sea salts which are influenced by accumulation rate is believed to control the rate and extent of movement of msa

evolving towards a critical point a review of accelerating seismic moment energy release prior to large and great earthquakes there is growing evidence that some proportion of large and great earthquakes are preceded by a period of accelerating seismic activity of moderate sized earthquakes these moderate earthquakes occur during the years to decades prior to the occurrence of the large or great event and over a region larger than its rupture zone the size of the region in which these moderate earthquakes occur scales with the size of the ensuing mainshock at least in continental regions a number of numerical simulation studies of faults and fault systems also exhibit similar behavior the combined observational and simulation evidence suggests that the period of increased moment release in moderate earthquakes signals the establishment of long wavelength correlations in the regional stress field the central hypothesis in the critical point model for regional seismicity is that it is only during these time periods that a region of the earth s crust is truly in or near a self organized critical soc state such that small earthquakes are capable of cascading into much larger events the occurrence of a large or great earthquake appears to dissipate a sufficient proportion of the accumulated regional strain to destroy these long wavelength stress correlations and bring the region out of a soc state continued tectonic strain accumulation and stress transfer during smaller earthquakes eventually re establishes the long wavelength stress correlations that allow for the occurrence of larger events these increases in activity occur over longer periods and larger regions than quiescence which is usually observed within the rupture zone of a coming large event the two phenomena appear to have different physical bases and are not incompatible with one another

potential and limitations of marine and ice core sea ice proxies an example from the indian ocean sector diatom assemblages in marine cores and sea salt deposition fluxes in ice cores have been used as sea ice proxies in the southern hemisphere here a marine and an ice core proxy record for the indian ocean covering the last two glacial cycles are compared in order to illustrate their potential and limitations the marine core was extracted in a location completely ice free under present day conditions and therefore was unable to record changes to the recent sea ice extent similarly no sea ice was recorded at that location during the previous interglacial period during the last glacial period however the site was seasonally covered by sea ice and the diatom assemblages allowed an estimation of average seasonal sea ice presence the ice core data originated from the east antarctic plateau the marine sodium present in the ice core was used as a proxy of the sea ice coverage and on average a larger sea ice surface led to an increased sea salt aerosol flux seen e g at the last glacial inception however the response of the sea salt flux to increasing sea ice extent diminished during peak glacial conditions when only minimal variability was recorded in the ice core record a first order approximation is used to take this non linear response of the ice core sea ice proxy into account based on the ice core proxy record sea ice extent was reduced considerably during the warm episodes of the previous two interglacial periods compared to modern sea ice extent in particular during the peak warmth of the last interglacial the ice core proxy also showed a very strong precessional variability pronounced spectral peak at 23 ka period over the past 240 ka the advantage of combining the two proxy records lies in the complementary nature of their response while the ice core proxy showed limited sensitivity during full glacial conditions the marine proxy recorded the seasonal sea ice coverage once the sea ice retreated south of the location of the marine core the ice core proxy responded to changes in sea ice extent a composite of marine and ice core records may thus provide a data basis for a more detailed reconstruction of sea ice around antarctica over the last few glacial interglacial cycles

earthquakes as self organized critical phenomena a cellular automation model with threshold elements previously proposed by bak et al 1988 which generates 1 f noise and self organizes into a critical state is studied as a model for earthquake occurrence the model explains some of fractal features of earthquakes such as the power law distribution of the size of the earthquake the model is modified so that every earthquake may trigger aftershocks the modified trigger model explains other fractal features of earthquakes such as the power law decay of aftershock frequency and the power law decay of aftershock frequency and the power law correlation of the hypocenter distribution

sea ice albedo climate feedback mechanism abstract the sea ice albedo feedback mechanism over the arctic ocean multiyear sea ice is investigated by conducting a series of experiments using several one dimensional models of the coupled sea ice atmosphere system in its simplest form ice albedo feedback is thought to be associated with a decrease in the areal cover of snow and ice and a corresponding increase in the surface temperature further decreasing the areal cover of snow and ice it is shown that the sea ice albedo feedback can operate even in multiyear pack ice without the disappearance of this ice associated with internal processes occurring within the multiyear ice pack e g duration of the snow cover ice thickness ice distribution lead fraction and melt pond characteristics the strength of the ice albedo feedback mechanism is compared for several different thermodynamic sea ice models a new model that includes ice thickness distribution the ebert and curry model the maykut and untersteiner model and the semtner level 3 an

interpretation of recent antarctic sea ice variability 1 trends in the satellite derived antarctic sea ice concentrations 1979 2002 show pronounced increase decrease in the central pacific sector bellingshausen western weddell sector by 4 10 per decade confidence levels for these regional trends exceed 95 positive polarities of the antarctic oscillation aao lead to more less ice in the eastern ross amundsen sector bellingshausen northern weddell sector which are qualitatively opposite to the impacts of positive polarities of the el nino southern oscillation enso the mechanisms responsible for the covariability between the ice and the a aao and b enso are demonstrated over the last 24 years a positive aao trend and a slightly negative enso trend produce a spatial pattern of ice changes similar to the regional ice trends however the magnitude of the ice changes associated with the aao and enso is much smaller than the regional ice trends more local or less understood large scale processes should be investigated for the explanations

seismic quiescence before the landers m 7 5 and big bear m 6 5 1992 earthquakes the landers earthquake of 28 june 1992 was preceded by a seismicity rate decrease of 75 in a volume approximately 11 by 23 by 15 km located adjacent to and north of the epicenter this anomaly started for all magnitude bands in january 1988 lasting 4 5 yr up to the mainshock a smaller volume 7 by 14 by 15 km to the south of the epicenter showed a seismicity rate decrease of 75 starting in november 1989 the big bear earthquake of the same day was preceded by a 100 decrease of the seismicity rate within a volume of approximately 13 by 22 by 15 km around the hypocenter this volume contained 192 earthquakes of m 1 6 during the background period of 9 yr but none during the 1 6 yr from december 1990 to 27 june 1992 the standard deviate z values characterizing these rate changes are very high 6 3 and 12 3 respectively and the anomalies are unique not surpassed in significance by any other rate decrease in portion of the southern california earthquake catalog examined 117 06 w to 115 40 w and 33 45 n to 35 10 n no seismicity rate change was found in the vicinity of the m 6 1 joshua tree earthquake of 23 april 1992 based on magnitude signatures and frequency magnitude analyses we conclude that the two quiescence anomalies could not have been due to a shift or a compression of the magnitude scale and we interpret them as precursor anomalies this analysis was carried out using the declustered earthquake catalog for the landers area with corrections of 0 2 and 0 1 august 1985 and may 1990 for two suspected magnitude shifts with a new visualization technique we can investigate the stability and changes of the seismicity rate as a function of time and space by mapping z values for rate changes at every time interval and in volumes centered on a dense grid of points latitude longitude this computer code furnishes an almost continuous sequence of smooth contour maps of the degree of rate changes any anomalies artificial or real may thus be defined accurately

southern ocean sea ice extent productivity and iron flux over the past eight glacial cycles sea ice and dust flux increased greatly in the southern ocean during the last glacial period palaeorecords provide contradictory evidence about marine productivity in this region but beyond one glacial cycle data were sparse here we present continuous chemical proxy data spanning the last eight glacial cycles 740 000 years from the dome c antarctic ice core these data constrain winter sea ice extent in the indian ocean southern ocean biogenic productivity and patagonian climatic conditions we found that maximum sea ice extent is closely tied to antarctic temperature on multi millennial timescales but less so on shorter timescales biological dimethylsulphide emissions south of the polar front seem to have changed little with climate suggesting that sulphur compounds were not active in climate regulation we observe large glacial interglacial contrasts in iron deposition which we infer reflects strongly changing patagonian conditions during glacial terminations changes in patagonia apparently preceded sea ice reduction indicating that multiple mechanisms may be responsible for different phases of co2 increase during glacial terminations we observe no changes in internal climatic feedbacks that could have caused the change in amplitude of antarctic temperature variations observed 440 000 years ago

sea ice variability and primary productivity in the ross sea antarctica from methylsulphonate snow record 1 the ross sea contains the most biologically productive continental shelf in antarctica and is a region where the annual formation of sea ice drives substantial amounts of bottom water formation we present snow pit chemistry data from mt erebus saddle that provide a quantitative proxy to reconstruct summer sea ice conditions and rates of marine primary production the methylsulphonate ms record is strongly correlated with changes in the area of open water r2 0 903 p 0 05 caused by differences in atmospheric circulation and the sea ice damming effect of large icebergs b 15 and c 19 which calved from the ross ice shelf in 2000 and 2002 respectively furthermore ms and phytoplankton net primary production correlate significantly r2 0 927 p 0 01 our results demonstrate the potential of the mt erebus saddle ice core to reconstruct sea ice and primary productivity variability in the ross sea beyond the observational record

a giant landslide on the north flank of tenerife canary islands the extent of mass wasting along the north flank of tenerife has been mapped using swath bathymetry gloria side scan sonar and 3 5 khz echo sounder data the marine surveys show that north of tenerife a giant landslide is exposed over an area of 5500 km2 of the seafloor more than twice the surface area of the island the landslide truncates an older ridge and valley topography that is associated with the shield building basalts on tenerife we interpret the ridge and valley topography as the result of subaerial erosion the landslide is estimated to have a length of 100 km a width of up to 80 km and a volume of about 1000 km3 it extends onshore into the orotava and icod valleys which have been interpreted as of landslide origin k ar dating of basaltic flows in the steep headwall of orotava suggests an age of formation for the valley is younger than 0 78 ma and may even be younger than 0 27 ma the icod valley is located immediately to the north of the most recent volcano on tenerife las canadas and has been associated with the collapse of its caldera between 1 2 and 0 2 ma a young age for the landslide is supported by the 3 5 khz echo sounder data which show that the landslide is draped by a thin 10 m layer of younger sediment the landslide did not form however during a single catastrophic event but represents the amalgamation of a number of separate landslides the occurrence of the ridge and valley topography in water depths of up to 2 5 km suggests that the shield building basalts have subsided by at least this amount since they formed 3 3 8 0 ma we speculate that this subsidence is caused by some form of stress relaxation that occurs in the underlying lithosphere the giant landslide imaged in our sonar data is associated with the late stages in the development of the most recent volcano on tenerife las canadas which only began at about 1 8 ma thus landsliding may be a particular feature of the time soon after emplacement when because of incomplete isostatic adjustment oceanic volcanoes have their greatest elevations above sea level and therefore are most susceptible to slope failure

hotspot tracks and the early rifting of the atlantic abstract many hotspot tracks appear to become the locus of later rifting as though the heat of the hotspot weakens the lithosphere and tens of millions of years later the continents are split along these weakened lines examples are the west coast of greenland east coast of labrador madeira hotspot the south coast of mexico north coast of honduras guyana hotspot and the south coast of west africa north coast of brazil st helena hotspot a modern day analog of a possible future rift is the snake river plain where the north american continent is being pre weakened by the yellowstone hotspot track this conclusion is based on reconstructions of the motions of the continents over hotspots for the past 200 million years the relative motions of the plates are determined from magnetic anomaly isochrons in the oceans and the motion of one plate is chosen ad hoc to best fit the motions of the plates over the hotspots however once the motion of this one plate is chosen the motions of all the other plates are prescribed by the relative motion constraints in addition to the correlation between the predicted tracks and sites of later continental breakup exposed continental shields correlate with the tracks their exposure may be the result of hotspot induced uplift which has led to erosion of their former platform sediment cover

covariation of sea ice and methanesulphonic acid in wilhelm ii land east antarctica sea ice plays an important role in ocean atmosphere heat exchange global albedo and the marine ecosystem knowledge of variation in sea ice extent is essential in order to understand past climates and to model possible future climate scenarios this paper presents results from a short firn core spanning 15 years collected from near mount brown wilhelm ii land east antarctica variations of methanesulphonic acid msa at mount brown were positively correlated with sea ice extent from the coastal region surrounding mount brown 60 1208 e and from around the entire antarctic coast 0 3608 e previous results from law dome identified this msa sea ice relationship and proposed it as an antarctic sea ice proxy curran and others 2003 with the strongest results found for the local law dome region our data provide supporting evidence for the law dome proxy at another site in east antarctica but a deeper mount brown ice core is required to confirm the sea ice decline suggested by curran and others 2003 results also indicate that this deeper record may also provide a more circum antarctic sea ice proxy

antarctic sea ice relationships with indices of the atmospheric circulation of the southern hemisphere a link between the antarctic sea ice extent and low frequency atmospheric variations particularly enso has been suggested by recent modeling and empirical studies this question is examined here using a high resolution by week by region data base of antarctic sea ice extent for the 1973 1982 period although of relatively short duration by northern hemisphere standards such a data base offers an opportunity rare in southern hemisphere climate studies the seaice variations are examined in the context of longer term indices of the large scale atmospheric circulation these are a southern oscillation index soi and an index of sea level pressure slp wavenumber one in the southern hemisphere extratropics the indices are updated through 1982 and their associations with regional scale pressure indices in the australia new zealand sector are also examined the 1973 1982 period is anomalous when compared with the period 1951 1972 correlation analysis of the monthly sea ice and circulation index values reveals that much of the apparent link between the ice and the soi suggested in previous studies arises from autocorrelations present in both data sets and the strong annual cycle of sea ice extent removing these effects from the data and re running the correlations reveals that most of the resulting significant associations between the ice and one or other of the circulation indices can probably be explained on the basis of chance in order to reconcile these findings with previous studies that show some strong ice circulation interactions on regional scales only those months in which significant correlations occur between both largescale circulation indices and the sea ice are examined further these occur preferentially in the ross and weddell sectors which constitute the regions contributing most to the variability of antarctic sea ice the analysis suggests that the sea ice extent changes lag the soi by several months but may precede changes in extratropical slp wavenumber one confirmation of these tentative regional ice extent circulation teleconnections necessarily awaits the forward extension of the high resolution sea ice data base beyond the 10 years available here

frequency magnitude statistics and spatial correlation dimensions of earthquakes at long valley caldera california summary intense earthquake swarms at long valley caldera in late 1997 and early 1998 occurred on two contrasting structures the first is defined by the intersection of a northnorthwesterly array of faults with the southern margin of the resurgent dome and is a zone of hydrothermal upwelling seismic activity there was characterized by high b values and relatively low values of d the spatial fractal dimension of hypocentres the second structure is the pre existing south moat fault which has generated largemagnitude seismic activity in the past seismicity on this structure was characterized by low b values and relatively high d these observations are consistent with lowmagnitude clustered earthquakes on the first structure and higher magnitude divuse earthquakes on the second structure the first structure is probably an immature fault zone fractured on a small scale and lacking a well developed fault plane the second zone represents a mature fault with an extensive coherent fault plane

sources and transport pathways of marine aerosol species into west antarctica sixteen high resolution marine aerosol na so4 records from spatially distributed international trans antarctic scientific expedition itase ice cores spanning the last 200 years from the pine island thwaites and ross drainage systems and the south pole are used to examine sources sea spray and frost flowers and transport pathways of marine aerosols into west antarctica factors contributing to the amount of marine aerosols transported inland include sea ice extent the presence of open water features polynyas leads wind strength and direction and the strength and positioning of low pressure systems analysis of so4 na ratios indicates that frost flowers can contribute significantly 40 to the na budget of antarctic ice cores higher na concentrations in the ross drainage system may result from greater production of marine aerosols related to frost flowers in the ross sea region in association with greater sea ice extent and larger open water areas significant positive correlations of sea ice extent and the na time series exist in some regions of west antarctica higher wind speeds in winter and higher na concentrations when slp is

a 200 year sub annual record of sulfate in west antarctica from 16 ice cores sixteen high resolution ice core records from west antarctica and south pole are used to examine the spatial and temporal distribution of sulfate for the last 200 years the preservation of seasonal layers throughout the length of each record results in a dating accuracy of better than 1 year based on known global scale volcanic events a dual transport source for west antarctic sea salt ss so4 2 and excess xs so4 2 is observed lower tropospheric for areas below 1000 m elevation and mid upper tropospheric stratospheric for areas located above 1000 m our xsso4 2 records with volcanic peaks removed do not display any evidence of an anthropogenic impact on west antarctic so4 2 concentrations but do reveal that a major climate transition takes place over west antarctica at 1940 global scale volcanic eruptions appear as significant peaks in the robust spline residual xsso 4 2 records from sites located above 1000 m elevation but do not appear in the residual records from sites located below 1000 m

ice core evidence for antarctic sea ice decline since the 1950s the instrumental record of antarctic sea ice in recent decades does not reveal a clear signature of warming despite observational evidence from coastal antarctica here we report a significant correlation p

precursory seismic activation and critical point phenomena in this paper we relate the behavior of seismicity prior to a characteristic earthquake to the excitation in proximity to a spinodal instability we illustrate the spinodal instability as the upper limit of superheated water prior to a steam explosion we draw an analogy between the steam explosion and a characteristic earthquake and show that the power law activation associated with the spinodal instability is essentially identical to the power law increase in benioff strain observed prior to characteristic earthquakes we find that theory and actual data give very similar results

morphology and structure of loihi seamount based on seabeam sonar mapping loihi seamount has been mapped using seabeam multibeam sonar and the resulting data have been processed to produce bathymetric maps with a 10 m contour interval and shaded relief perspective images analysis of morphological and structural data recorded in the maps and images indicates that constructional volcanism on loihi has been localized predominantly along its southern and northern rift zones and that these rifts have been active since early in the seamount s history the distinct asymmetry between loihi s eastern and western slopes the eastern slopes are steeper is attributed to mass wasting of large sections of the volcano s west flank two large amphitheater valleys on the seamount s west flank are believed to have resulted from repeated mass wasting events triggered by earthquakes associated with an early rift zone whose core now lies buried beneath the block feature present on loihi s southwest flank the prominent kink in the present south rift zone of loihi may represent a fundamental readjustment of along rift magma conduits that was caused by gravitational slumping on the southwest flank of the volcano lava cones and constructional volcanic ridges are present along the rims of summit pit craters and form a continuous chain of volcanic constructs around the periphery of the summit platform the concentric arrangement of young eruptive vents pn loihi s summit may be caused by ring dikes the morphology and structural interrelationships of pit craters on loihi s summit suggest that the southeastern pit is the youngest the formation of a summit platform on loihi may have been caused by repeated collapse of pit craters and the southward migration of primary magma conduits that underlie the pits this model predicts a north to south age progression for volcanism on loihi s summit

case 23 nomination of precursory seismic quiescence as a significant precursor several cases of extremely strong quiescences have been investigated in great detail and it was found that they are statistically highly significant and that they cannot be reasonably explained by catalog heterogeneity several additional cases of quantitatively measured quiescence have been documented the method of measuring quiescence has progressed from using visual means to using a quantitative approach and the understanding of the noise sources has significantly advanced during the last few years therefore i feel that quiescence is a real phenomenon and the method to detect it has matured to a point that is acceptable for the list of significant precursors although considerably more work needs to be done to understand this parameter and its role in the earthquake generation process

the 1999 chi chi taiwan earthquake as a typical example of seismic activation and quiescence 1 the pattern informatics algorithm which has recently shown promising performance for earthquake forecasting in southern california has been used to detect the locations where precursory seismic activity occurred preceding the 1999 chi chi taiwan earthquake using the pattern informatics method as presented in this paper the epicenter of the chi chi main shock was found to exhibit signatures of anomalous activity related to the seismic activation and quiescence in the taiwan region over a time span of about 6 years before the main shock a strategy of making intermediate term earthquake hazard assessment by means of pattern informatics is therefore proposed on the basis of retrospective analysis of the chi chi earthquake

frost flowers implications for tropospheric chemistry and ice core interpretation 1 this paper discusses the chemical composition of frost flowers and their accompanying slush layers and the evidence for their role as a salt source in processes important to atmospheric chemistry and ice core interpretation analysis of antarctic frost flowers shows that they are highly saline and fractionated in sea salt ions with sulfate being depleted strongly relative to sodium because frost flowers give a bright return on satellite scatterometer images the times and places of their formation can be identified when winds blow towards an aerosol sampling station from areas identified by the scatterometer as covered with flowers the collected aerosol is also depleted in sulfate because the flowers have a large salinity bromide concentrations are elevated in frost flowers relative to seawater with their high surface area it is possible that bromine is released to the atmosphere from frost flowers with consequent implications for tropospheric ozone depletion the finding that quantities of fractionated sea salt are available at the sea ice interface in the winter months and may be transported inland as aerosol also has implications for the interpretation of ice core records analysis of one near coastal core shows that the majority of the sodium comes from a fractionated source rather than from open water hitherto strong sea salt signals in ice cores have been attributed to increased open water and more efficient transport inland perhaps due to stormier weather at least in coastal regions however these signals may be related instead to the increased formation of sea ice and frost flowers

reflection seismic investigations in the volcaniclastic apron of gran canaria and implications for its volcanic evolution high resolution reflection seismic data obtained around gran canaria allow a detailed and consistent correlation of seismic reflectors of the northern and southern canary basins with the lithology drilled by dsdp leg 47a sse of gran canaria as well as with major phases of volcanic activity on gran canaria as mapped onshore two prominent reflectors were chosen as marker horizons and correlated with the drilled lithology the results indicate that reflector r7 above the miocene volcaniclastic debris flows v1 v3 reflects the shield building phase of gran canaria reflector r3 is interpreted as corresponding with the pliocene roque nublo formation the top of the massive island flank of gran canaria defined by seismically chaotic facies extends 44 to 72 km off the coast of gran canaria west of gran canaria the flank of tenerife onlaps the steeper and older flank of gran canaria which in turn is onlapping the older flank of fuerteventura to the east in a similar way erosional channels which can also be traced up to 50 km from the area between gran canaria and fuerteventura into the deeper northern basin have been identified in the bathymetry the data presented provide new detailed information for modelling the submarine and subaerial evolution of the central canary islands of gran canaria and tenerife i e the timing of their shield building phases and later stages of major volcanic activity as reflected by the position of prominent seismic reflectors in the seismic stratigraphy

correlation of seismotectonic variables and gps strain measurements in western turkey period extending from 1981 to 1998 are examined in the eastern mediterranean and western turkey area this analysis was conducted in three tectonic subdivisions corresponding to regions dominated by shear extensional and compressional deformation the region of shear coincides with the northern anatolian fault zone nafz the region of extension with the aegean back arc region and the region of compression to the aegean subduction zone between the african and anatolian plates the median b value in the region of extension is larger than those observed in the regions of shear and compression and suggests that large magnitude earthquakes are less probable in this region than along the nafz and aegean subduction zone a significant correlation is observed between d2 and d15 with dilatation over the 10 40 km range in the back arc region of extension a marginal correlation between gps derived strain and b value is observed only in the region of compression where it correlates negatively with shear and positively with dilatation a significant positive correlation is observed between d and b along the nafz a clear relationship between d and b does not exist in regions deformed by extension and compression the relationship between d and b along the nafz may also be an indicator of increased seismic hazard since the positive relationship between d and b is a recent characteristic of the nafz observed only in the 20 year period preceding the izmit earthquake index terms 7215 seismology earthquake parameters 7209 seismology earthquake dynamics and mechanics 7223 seismology seismic hazard assessment and prediction 7230 seismology seismicity and seismotectonics keywords gps strain fractal dimension b value

las hijas seamounts the next canary island volcanic structures on the seafloor off the nw african coast between 25 n and 32 n were imaged by gloria side scan sonar and simrad em12 multibeam bathymetry the newly discovered las hijas seamounts located 70 km south east of hierro are interpreted as young volcanic edifices their location is consistent with the spacing and timing of propagation of volcanism of the canary archipelago and may represent future sites of volcanic islands

the polar expression of enso and sea ice variability as recorded in a south pole ice core an annually dated ice core recovered from south pole 2850ma s l in 1995 that covers the period1487 1992 was analyzed for the marine biogenic sulfur species methanesulfonate ms empirical orthogonal function analysis is used to calibrate the high resolution ms series with associated environmental series for the period of overlap 1973 92 utilizing this calibration we present a 1500 year long proxy record of the polar expression of the el ni o southern oscillation enso and southeastern pacific sea ice extent variations these records reveal short term periods of increased 1800 50 1900 40 and decreased sea ice extent 1550 1610 1660 1710 1760 1800 in general increased decreased sea ice extent is associated with a higher lower frequency of el ni o events

climate variability in west antarctica derived from annual accumulation rate records from itase firn ice cores thirteen annually resolved accumulation rate records covering the last 200 years from the pine island thwaites and ross drainage systems and the south pole are used to examine climate variability over west antarctica accumulation is controlled spatially by the topography of the ice sheet and temporally by changes in moisture transport and cyclonic activity a comparison of mean accumulation since 1970 at each site to the long term mean indicates an increase in accumulation for sites located in the western sector of the pine island thwaites drainage system accumulation is negatively associated with the southern oscillation index soi for sites near the ice divide and periods of sustained negative soi 1940 42 1991 95 correspond to above mean accumulation at most sites correlations of the accumulation rate records with sea level pressure slp and the soi suggest that accumulation near the ice divide and in the ross drainage system may be associated with the mid latitudes the post 1970 increase in accumulation coupled with strong slp accumulation rate correlations near the coast suggests recent intensification of cyclonic activity in the pine island thwaites drainage system

effects of canary hotspot volcanism on structure of oceanic crust off morocco analysis of over 6400 km of multichannel seismics mcs and 50 sonobuoy reflection and refraction experiments reduced both in the domain of x t and tau p shows that a region within the jurassic quiet zone off morocco underwent dramatic changes as a result of the passage of the lithosphere over the canary hotspot commencing approximately 60 ma a seismic unit ucf interpreted as volcanic in origin is observed within the sediments in a region characterized by a broad bathymetric swell it shows diffractions from its upper surface and an internally chaotic seismic facies and pinches out between sedimentary units of continuous subparallel facies a velocity inversion is noted between the ucf 4 7km s and the underlying sediment 3 1 km s the ucf is time transgressive it lies near the cretaceous s tertiary boundary in the northern portion of the study area and is younger to the south kinematic studies of the movement of the canary hotspot relative to africa show that the hotspot first appeared off nw africa about 60 ma and was located beneath oceanic crust in the region where the ucf is observed depth to basement measurements in areas not effected by the hotspot show a consistent linear trend of increased depth with age in areas effected by the hotspot the thermal rejuvenation is evident as basement depths shoal with increased proximity to the present hotspot the reheating of the crust resets the thermal age of the lithosphere with many of the properties of crust of a younger age subsidence curves of the reheated crust off morocco show good correlation to subsidence curves of other reheated crust on a global basis a zone characterized by high crustal velocities 7 1 7 4 km s and greater crustal thicknesses by 1 2 km is observed in an area that corresponds to the bathymetric swell the region of the ucf and the reelevated basement the high velocities and increased crustal thickness are interpreted to be the result of underplating and assimilation of existing oceanic crust caused by the canary thermal anomaly the presence of high crustal velocities coupled with a thickened crustal section has been noted on various passive margins of the world they have generally been attributed to the thermal processes associated with continental rifting off morocco we believe that similar thermally induced phenomena have occurred but that here the heat anomaly was the midplate volcanism associated with the canary hotspot

an emerging technique multi ice core multi parameter correlations with antarctic sea ice extent using results stemming from the international trans antarctic scientific expedition itase ice core array plus data from ice cores from the south pole and siple dome we investigate the use of sodium na non sea salt sulfate nssso4 2 and methylsulfonate ms as proxies for antarctic sea ice extent sie maximum and mean annual chemistry concentrations for these three species correlate significantly with maximum mean and minimum annual sie offering more information and clarification than single ice core and single species approaches significant correlations greater than 90 exist between na and maximum sie nssso4 2 with minimum and mean sie and ms with mean sie correlations with sie within large geographic regions are in the same direction for all ice core sites for na and nssso4 2 but not ms all ice cores display an sie correlation with nssso4 2 and ms but not all correlate with na this multi core multi parameter study provides the initial step in determining which chemical species can be used reliably and in which regions as a building block for embedding other ice core records once established the resulting temporal and spatial matrix can be used to relate ice extents atmospheric patterns biological productivity and site conditions

ice core records as sea ice proxies an evaluation from the weddell sea region of antarctica 1 ice core records of methanesulfonic acid msa from three sites around the weddell sea are investigated for their potential as sea ice proxies it is found that the amount of msa reaching the ice core sites decreases following years of increased winter sea ice in the weddell sea opposite to the expected relationship if msa is to be used as a sea ice proxy it is also shown that this negative msa sea ice relationship cannot be explained by the influence that the extensive summer ice pack in the weddell sea has on msa production area and transport distance a historical record of sea ice from the northern weddell sea shows that the negative relationship between msa and winter sea ice exists over interannual 7 year period and multidecadal 20 year period timescales national centers for environmental prediction national center for atmospheric research ncep ncar reanalysis data suggest that this negative relationship is most likely due to variations in the strength of cold offshore wind anomalies traveling across the weddell sea which act to synergistically increase sea ice extent sie while decreasing msa delivery to the ice core sites hence our findings show that in some locations atmospheric transport strength rather than sea ice conditions is the dominant factor that determines the msa signal preserved in near coastal ice cores a cautious approach is thus required in using ice core msa for reconstructing past sea ice conditions including the need for networks of ice core records and multiproxy studies to assess the significance of past msa changes at different locations around antarctica

ice sheet record of recent sea ice behavior and polynya variability in the amundsen sea west antarctica investigation of how regional sic is recorded in the ice sheet stratigraphy over the period 2002 2010 we find that the ice sheet chemistry is significantly correlated with sic variability within the as and pine island bay polynyas based on this result we evaluate the use of icecore chemistry as a proxy for interannual polynya variability in this region one of the largest and most persistent polynya areas in antarctica msa concentrations correlate strongly with summer sic within the polynya regions consistent with msa at this site being derived from marine biological productivity during the spring and summer cl concentrations correlate strongly with winter sic within the polynyas as well as some regions outside the polynyas consistent with cl at this site originating primarily from winter sea ice formation spatial correlations were generally insignificant outside of the polynya areas with some notable exceptions ice core glaciochemical records from this dynamic region thus may provide a proxy for reconstructing as and pine island bay polynya variability prior to the satellite era

evidence for precursory changes in the frequency magnitude b value summary a clear case has been established for a significant increase in the slope of the frequency magnitude relation for periods of up to six years before a number of earthquakes in new zealand and california in a region of about 200 km diameter in central new zealand the b value increased from near unity to more than 2 0 at the end of 1968 and remained abnormally high until the beginning of 1975 an earthquake of magnitude 6 0 followed in 1977 january within 50 km of the location which had registered the highest b value the anomaly was detected in contour maps of b values windowed in space and time then resolved more precisely in time using the cusum technique it was statistically significant at a level higher than 99 99 per cent compared with the average rate of moment release in this region there was a deficit of 1 3 x 10 nm during the anomalous period which is equivalent to an earthquake of magnitude 6 08 this phenomenon of a high b value has been found before all shallow new zealand earthquakes of magnitude 6 0 or more since 1965 wherever the seismicity rate and detection threshold were adequate to resolve it further the only statistically significant occurrences of high b value were those which were followed by large earthquakes two of magnitude 6 8 and 6 0 and a swarm of equivalent magnitude 5 3 the phenomenon has also been found before the san fernando and coalinga earthquakes in california both of which were thrust events but it is not apparent before two large californian earthquakes with strike slip mechanisms observations of high b value are consistent with reported instances of quiescence in background seismicity in fact what has been interpreted as quiescence may probably be more accurately described as a localized high b value the duration of the anomaly is not a simple function of magnitude different strain rates in the regions examined may account for this the available data suggest that careful monitoring of the b value may provide a tool for medium term earthquake prediction although perhaps not in all tectonic environments

k ar ages and magnetic stratigraphy of a hotspot induced fast grown oceanic island el hierro canary islands abstract the combined use of accurate radiometric dating and magnetic stratigraphy can be applied to define the main stages of the building of oceanic volcanic islands this method has been successfully applied on the island of el hierro the westernmost island of the canaries archipelago for the emerged part of this island built in the last 1 2 ma magnetic stratigraphy and mapping show the presence of four consecutive subchrons k ar dating of eighteen samples in stratigraphic sequences using an unspiked technique produced ages consistent with the general volcanic stratigraphy the ages show that the magnetic polarity zones correlate to the upper part of the matuyama and to the brunhes chrons the jaramillo normal polarity subchron of the upper part of the matuyama reverse polarity chron is recorded in one of the lava sequences the lower limit of this event is constrained by two ages of 1 04 0 02 ma and one of 1 05 0 02 ma close to the value deduced from the astronomically tuned magnetic polarity time scale apts the volcanic history can be summarised by two consecutive main basaltic volcanic edifices the el tinor active during the upper part of the matuyama chron and the el golfo edifice constructed during the brunhes chron

convective partial melting 1 a model for the formation of thick basaltic sequences during the initiation of spreading stretching and thinning of continental lithosphere during rifting and initiation of seafloor spreading cause upwelling of mantle rocks into a pressure temperature environment where partial melting occurs the amount of melt liberated is however insufficient to account for the thickness of igneous crust emplaced near the continent ocean boundary at some passive margins these igneous structures are known from seismic reflection and deep refraction studies on numerous passive margins worldwide seismic studies also suggest that the transition from continental to oceanic crust on these volcanic margins is relatively abrupt their evolution apparently does not include a prolonged extensional phase preceding the inception of spreading to account for these observations we propose a model for the generation of partial melt in which the lateral temperature contrasts evoked by rifting and asthenospheric upwelling drive convection in the upper mantle deep hot mantle material is transported upward by the convection and hence much larger volumes flow through the region where partial melting occurs than during passive upwelling numerical calculations show that convective partial melting can provide substantial additions to melting due to passive upwelling alone using this model we propose an evolutionary scheme for volcanic passive margins emphasize the contrast with nonvolcanic margins and describe conditions which might lead to the development of both types

simulation of the frictional stick slip instability a lattice solid model capable of simulating rock friction fracture and the associated seismic wave radiation is developed in order to study the origin of the stick slip instability that is responsible for earthquakes the model consists of a lattice of interacting particles in order to study the effect of surface roughness on the frictional behavior of elastic blocks being rubbed past one another the simplest possible particle interactions were specified corresponding to radially dependent elastic brittle bonds the model material can therefore be considered as round elastic grains with negligible friction between their surfaces although breaking of the bonds can occur fracturing energy is not considered stick slip behavior is observed in a numerical experiment involving 2d blocks with rough surfaces being rubbed past one another at a constant rate slip is initiated when two interlocking asperities push past one another exciting a slip pulse the pulse fronts propagate with speeds ranging from the rayleigh wave speed up to a value between the shear and compressional wave speeds in agreement with field observations and theoretical analyses of mode ii rupture slip rates are comparable to seismic rates in the initial part of one slip pulse whose front propagates at the rayleigh wave speed however the slip rate is an order of magnitude higher in the main part of pulses possibly because of the simplified model description that neglected intrinsic friction and the high rates at which the blocks were driven or alternatively uncertainty in slip rates obtained through the inversion of seismograms particle trajectories during slip have motions normal to the fault indicating that the fault surfaces jump apart during the passage of the slip pulse normal motion is expected as the asperities on the two surfaces ride over one another the form of the particle trajectories is similar to those observed in stick slip experiments involving foam rubber blocks bruneet al 1993 additional work is required to determine whether the slip pulses relate to the interface waves proposed by brune and co workers to explain the heat flow paradox and whether they are capable of inducing a significant local reduction in the normal stress it is hoped that the progressive development of the lattice solid model will lead to realistic simulations of earthquake dynamics and ultimately provide clues as to whether or not earthquakes are predictable

a review of sea ice proxy information from polar ice cores sea ice plays an important role in earth s climate system the lack of direct indications of past sea ice coverage however means that there is limited knowledge of the sensitivity and rate at which sea ice dynamics are involved in amplifying climate changes as such there is a need to develop new proxy records for reconstructing past sea ice conditions here we review the advances that have been made in using chemical tracers preserved in ice cores to determine past changes in sea ice cover around antarctica ice core records of sea salt concentration show promise for revealing patterns of sea ice extent particularly over glacial interglacial time scales in the coldest climates however the sea salt signal appears to lose sensitivity and further work is required to determine how this proxy can be developed into a quantitative sea ice indicator methane sulphonic acid msa in near coastal ice cores has been used to reconstruct quantified changes and interannual variability in sea ice extent over shorter time scales spanning the last 160 years and has potential to be extended to produce records of antarctic sea ice changes throughout the holocene however the msa ice core proxy also requires careful site assessment and interpretation alongside other palaeoclimate indicators to ensure reconstructions are not biased by non sea ice factors and we summarise some recommended strategies for the further development of sea ice histories from ice core msa for both proxies the limited information about the production and transfer of chemical markers from the sea ice zone to the antarctic ice sheets remains an issue that requires further multidisciplinary study despite some exploratory and statistical work the application of either proxy as an indicator of sea ice change in the arctic also remains largely unknown as information about these new ice core proxies builds so too does the potential to develop a more comprehensive understanding of past changes in sea ice and its role in both long and short term climate changes

a 340 year record of biogenic sulphur from the weddell sea area antarctica detailed records of methanesulphonic acid msa and non sea salt sulpha te nss so have been obtained from ice cores drilled on dolleman island on the east coast of the antarctic peninsula i0 35 2 s 60 55 5 w annual average concentrations of msa arc presented for the period i 652 1992 over this lime span the mean ann ual concen tration of msa is 0 69 eq 1 1 cr 0 33 n 340 the range is 0 13 2 35 eq 1 1 a nd the msa nss s04 2 ratio is 0 22 the high msa concentration reflects the proximity of the weddell sea believed to be a region of high marine phyt0plankton production t he overa ll mean nss so concentration is about 66 of the total sulphate d eposited in the snowfall low frequency variations of msa and oxygen isolope signals correla te closely indicat ing that they may be modulated by similar atmospheric processes positive correlations are observed between the oxygenisotope signature and both l 1sa r 0 4 1 and nss s04 2 r 0 50 signilicant at the 99 level a small negative correlation can be seen between both species and the annual duration or sea ice a t scoria bay laurie island in the south orkneys since 1902 msa r 0 23 and nss so r 0 29 significant at 95 confidence no significant link between high msa concentrations and el nino even ts is observed at this location

depth and geoid anomalies over oceanic hotspot swells a global survey the broad depth and geoid anomalies associated with 23 hotspot swells in oceanic areas have been analyzed maximum height and geographical extent of the topographic swell and of the geoid anomaly as well have been measured for each hotspot the results indicate a clear increase of the topographic swell height with age of the underlying lithosphere from values in the range 300 500 m at young ages to values in the range 1 500 2 000 m at ages larger than 100 ma the geoid anomaly amplitude also increases with plate age from nearly zero close to mid ocean ridges to 6 8 m over old plates on the other hand the geographical extent of the swell does not show any clear relationship with plate age the mean lateral extent of swells range from 1 000 to 1 500 km swells located close to spreading ridges show a significant non zero depth anomaly but are associated with negligible geoid signal these results complete those of a previous study where the apparent compensation depth of oceanic hotspot swells was showed to increase linearly with the square root of plate age and coincide roughly with the base of the thermal lithosphere this trend may either be interpreted in terms ofmore lithospheric thinning or dynamical support besides both seem necessary to explain the observed bathymetry in proportion evolving with aging of the lithosphere less

accelerating seismicity of moderate size earthquakes before the 1999 chi chi taiwan earthquake testing time prediction of the self organizing spinodal model of earthquakes summary seismic activation of moderate size earthquakes for the 1999 chi chi taiwan earthquake has been found a self organizing spinodal sos model can explain some observations concerning seismic activation but the equal time durations of the mid and precursory periods during an earthquake cycle conjectured in the original published sos model have not been supported in this case the chi chi test presented here shows unequal time durations of the mid and precursory periods of an earthquake cycle this in turn makes the possibility of time prediction of a characteristic earthquake impossible in the context of the sos model in addition comparisons with numerical simulations of the sliding block model suggest the change in the system s stiffness is a potential mechanism of seismic activation

self organized fractal seismicity of reservoir triggered earthquakes in the koyna warna seismic zone western india analysis of the koyna warna earthquake catalog 1968 1996 shows that on an average there is a positive correlation between the b value decrease and fractal dimensions decrease in both d2s and d2t of earthquake epicenters 0 5 and 2 5 years prior to 1973 m5 2 and 1980 m5 5 events respectively except a negative correlation for about five years 1988 1993 prior to the 1993 1994 sequence m5 4 this positive correlation indicates a weaker clustering or that the epicenters tend to fill the two dimensional plane while the origin of the negative correlation seems to be that during periods of large events low b value there is strong clustering around the main shock epicenter high fractal dimension interestingly during the last year 1995 1996 of the studied period both the b value and correlation dimensions rose significantly suggesting that stress release occurs through increased levels of low magnitude and increasingly scattered seismicity suggesting an increased risk of larger magnitude events incidentally during 2000 three earthquakes of magnitude m 5 0 one earthquake of m 4 0 45 earthquakes of magnitude m 3 0 3 9 and several thousand earthquakes of m 3 have occurred in the region thus it can be inferred that at local scales the relationship yields both positive and negative correlation that appears to be controlled by different modes of failure within the active fault complex

horizontal plate motion a key allocyclic factor in the evolution of the great barrier reef the great barrier reef complex of northeastern australia thins dramatically and becomes younger from north to south these variations are a consequence of the cenozoic northward movement of the indian australian plate the temperate climatic conditions that applied off northeast australia during the early tertiary were progressively replaced by tropical conditions the present day south to north facies distribution along the eastern australian continental margin mimics the cenozoic vertical facies sequence through the northern part of the great barrier reef region

high resolution ice cores from us itase west antarctica development and validation of chronologies and determination of precision and accuracy shallow ice cores were obtained from widely distributed sites across the west antarctic ice sheet as part of the united states portion of the international trans antarctic scientific expedition us itase program the us itase cores have been dated by annual layer counting primarily through the identification of summer peaks in non sea salt sulfate nssso4 2 concentration absolute dating accuracy of better than 2 years and relative dating accuracy better than 1 year is demonstrated by the identification of multiple volcanic marker horizons in each of the cores tambora indonesia 1815 being the most prominent independent validation is provided by the tracing of isochronal layers from site to site using high frequency ice penetrating radar observations and by the timing of mid winter warming events in stable isotope ratios which demonstrate significantly better than 1 year accuracy in the last 20 years dating precision to 1 month is demonstrated by the occurrence of summer nitrate peaks and stable isotope ratios in phase with nssso4 2 and winter time sea salt peaks out of phase with phase variation of 1 month dating precision and accuracy are uniform with depth for at least the last 100 years

prodigious submarine landslides on the hawaiian ridge the extensive area covered by major submarine mass wasting deposits on or near the hawaiian ridge has been delimited by systematic mapping of the hawaiian exclusive economic zone using the side looking sonar system gloria these surveys show that slumps and debris avalanche deposits are exposed over about 100 000 km2 of the ridge and adjacent seafloor from kauai to hawaii covering an area more than 5 times the land area of the islands some of the individual debris avalanches are more than 200 km long and about 5000 km3 in volume ranking them among the largest on earth the slope failures that produce these deposits begin early in the history of individual volcanoes when they are small submarine seamounts culminate near the end of subaerial shield building and apparently continue long after dormancy consequently landslide debris is an important element in the internal structure of the volcanoes the dynamic behavior of the volcanoes can be modulated by slope failure and the structural features of the landslides are related to elements of the volcanoes including rift zones and fault systems the landslides are of two general types slumps and debris avalanches the slumps are slow moving wide up to 110 km and thick about 10 km with transverse blocky ridges and steep toes the debris avalanches are fast moving long up to 230 km compared to width and thinner 0 05 2 km they commonly have a well defined amphitheater at their head and hummocky terrain in the lower part oceanic disturbance caused by rapid emplacement of debris avalanches may have produced high level wave deposits such as the 365 m elevation hulopoe gravel on lanai that are found on several islands most present day submarine canyons were originally carved subaerially in the upper parts of debris avalanches subaerial canyon cutting was apparently promoted by the recently steepened and stripped slopes of the landslide amphitheaters

physical basis for statistical patterns in complex earthquake populations models predictions and tests understanding the physics of earthquakes and the space time patterns they produce is illuminated by the use of coarse grained models and simulations that capture the basic physical processes and that are amenable to analysis we present a summary of ideas that describe the nucleation growth and arrest of earthquakes on individual faults under shear loading we find that faults reside in a metastable state near a classical spinodal that governs the nucleation and growth of slip events the roughness of an associated stress distribution field x t determines whether slip events are confined within the initial high stress patch or break away and grow to become very large we find a critical value of roughness that is associated with a first order order disorder transition we also give a number of predictions examples and applications of these ideas and indicate how they might be tested through systematic observational programs

seismicity in north eastern brazil fractal clustering and the evolution of the b value summary we analyse a catalogue of earthquakes recorded near joao camara brazil an intraplate area with a simple velocity structure and low attenuation the evolution of seismicity is characterized by the seismic b value and the fractal dimension of earthquake epicentre locations measured from sliding 100 event windows the events are divided into a number of spatial clusters using a nearest centroid sorting technique and two of these clusters are examined in detail one cluster characterized by intense activity shows a clear negative correlation between b value and fractal dimension of epicentre locations as has been predicted from simple mechanical models a second cluster shows a weak positive correlation and it is suggested that this might be explained in terms of fluid flow in the fault zone

a 200 year sulfate record from 16 antarctic ice cores and associations with southern ocean sea ice extent chemistry data from 16 50 115m deep sub annually dated ice cores are used to investigate spatial and temporal concentration variability of sea salt ss so4 2 and excess xs so4 2 over west antarctica and the south pole for the last 200 years low elevation ice core sites in western west antarctica contain higher concentrations of so4 2 as a result of cyclogenesis over the ross ice shelf and proximity to the ross sea polynya linear correlation analysis of 15 west antarctic ice core so4 2 time series demonstrates that at several sites concentrations of ssso4 2 are higher when sea ice extent sie is greater and the inverse for xsso4 concentrations of xsso4 2 from the south pole site east antarctica are associated with sie from the weddell region and west antarctic xsso4 2 concentrations are associated with sie from the bellingshausen amundsen ross region the only notable rise of the last 200 years in xsso4 around 1940 is not related to sie fluctuations and is most likely a result of increased xsso4 2 production in the mid low latitudes and or an increase in transport efficiency from the mid low latitudes to central west antarctica these high resolution records show that the source types and source areas of ssso4 2 and xsso4 2 delivered to eastern and western west antarctica and the south pole differ from site to site but can best be resolved using records from spatial ice core arrays such as the international trans antarctic scientific expedition itase

dimethylsulphide and dimethylsulphoniopropionate in the south west indian ocean sector of east antarctica from 30 to 80 e during broke west abstract we investigated the spatial and vertical variations of dimethylsulphide dms dissolved particulate and total dimethylsulphoniopropionate dmspd dmspp and dmspt in the south west indian ocean sector of east antarctica between 30 80 e and south of 62 s from january to march 2006 twenty seven sites were examined and mean concentrations in the upper 150 m of the water column were for dms 8 nm range nd 63 nm dmspd 5 nm nd 36 nm dmspp 11 nm nd 38 nm and dmspt 16 nm nd 54 nm the highest concentrations of the sulphur compounds occurred in the western sector of the study area on the antarctic shelf and across the antarctic slope front region asf of the eastern weddell gyre ewg in the cosmonaut sea concentrations were lower north of the asf region of the ewg and in the eastern sector of the antarctic circumpolar current acc and the greater prydz bay gyre pbg circulation in the cooperation sea the influence of melting pack ice on dms and dmspd concentrations was apparent in this study but was predominantly restricted to a few stations in the cosmonaut sea early in the voyage dms concentrations were extremely high at stations in the western sector of the marginal ice zone miz in the early part of the study mean 25 nm reaching concentrations as high as 63 nm at station 42 decreasing to a mean concentration of 5 5 nm in the reduced miz to the east in the seasonal mixed layer sml water 4 50 m from the acc and ewg mean dms concentrations were 5 nm whilst very low concentrations of dms occurred under forming sea ice 0 5 nm mean dmspp concentrations in the top 50 m of the miz stations across the survey were closely similar 18 20 nm and slightly higher than sml waters 13 14 nm whilst mean dmspd concentrations were 275 and 100 higher in samples from the miz stations 8 15 nm compared with sml waters 4 nm in the eastern sector the coastal region across the shelf break and asf region was largely free of ice and there was generally no elevation of dmspd mean 4 nm this suggests that biological processes associated with the pack or fast ice in the asf region of the western sector of the survey in conjunction with the oceanography of the region may have caused the high concentrations of dms and dmspd observed at latitudes 67 s whilst filtration affects did influence dmspd concentrations at a few sites it was clear that elevated dms and dmspd concentrations occurred in the top 50 m and winter water ww layers of miz stations and in high salinity shelf water hssw at specific locations on the antarctic shelf and likely reflected melting sea ice dms and dmspp were also detected below the euphotic zone in modified circumpolar deep water mcdw on the antarctic slope with dmspp possibly transported there in sedimenting detritus and faecal material the significant concentrations of dms detected in lower mcdw 0 42 1 1 nm and antarctic bottom water aabw 2 7 nm were likely to have been transported to these depths in wintertime as dense shelf water overflows from the cape darnley and prydz bay source regions the high concentrations of dms and dmspd observed in the surface waters of the miz further support the importance of the antarctic region and the sea ice zone to the global sulphur cycle

sea level pressure variability in the amundsen sea region inferred from a west antarctic glaciochemical record using european center for medium range weather forecasts ecmwf numerical operational analyses sea ice extent records and station pressure data we investigate the influence of sea level pressure variability in the amundsen sea region on a west antarctic siple dome glaciochemical record empirical orthogonal function analysis of the high resolution siple dome multivariate ice core chemical time series record sdeof1 documents lower tropospheric transport of sea salt aerosols to the site during 1985 1994 the sdeof1 record of high low aerosol transport corresponds to anomalously low high sea level pressure slp in the amundsen sea region spatial correlation patterns between ecmwf monthly slp fields and the annual sdeof1 record suggest that a majority of sea salt aerosol is transported to siple dome during spring september october and november analysis of zonal and meridional wind fields supports the slp sdeof1 correlation and suggests the sdeof1 record is sensitive to changes in regional circulation strength no relationship is found between sea ice extent and the sdeof1 record for the period 1973 1994 to investigate the sdeof1 record prior to ecmwf coverage a spring transpolar index stpi is created using normalized slp records from the new zealand and south america antarctic peninsula sectors and is significantly correlated at least 95 c l with the sdeof1 record on an annual r 5 0 32 p 0 001 and interannual 3 years r 5 0 51 p 0 001 basis dominant periodicities 3 3 and 7 1 years in the annual sdeof1 record 1890 1994 a d suggest that a portion of the recorded interannual variability may be related tropical extratropical enso teleconnections changes in the periodic structure of the full 850 1994 a d siple dome record suggests a shift in slp forcing during the little ice age 1400 1900 a d interval

an ice core record of antarctic sea ice extent in the southern indian ocean for the past 300 years the differing response of ice extent in the arctic and antarctic to global average temperature change over approximately the last three decades highlights the importance of reconstructing long term sea ice history here using high resolution ice core records of methanesulfonate ms from the east antarctic ice sheet in princess elizabeth land we reconstruct southern indian ocean sea ice extent sie for the sector 62 92 e for the period ad 1708 2000 annual ms concentration positively correlates in this sector with satellite derived sie for the period 1979 2000 r 2 0 25 p 0 02 the 293 year ms record of proxy sie shows multi decadal variations with large decreases occurring in two warm intervals during the little ice age and during the 1940s it is very likely that the global temperature is the controlling factor of antarctic sea ice variation at the centennial scale although there has been a change in phase between them in recent decades