the january 1998 earthquake swarm at axial volcano juan de fuca ridge hydroacoustic evidence of seafloor volcanic activity on january 25 1998 at 11 33z an intense swarm of earthquakes began within the summit caldera of axial volcano central juan de fuca ridge jdfr the earthquake swarm was detected using the u s navy hydrophones in the northeast pacific ocean the earthquake swarm lasted 11 days and produced 8247 detected 1037 located earthquakes during the first two days of the swarm earthquake activity migrated from the summit caldera 50 km along the south rift zone of axial volcano at rates of 0 92 0 13 and 0 23 0 09 m s 1 earthquake epicenter migration is characteristic of a lateral magma dike injection the largest three swarm earthquakes occurred within the caldera their timing and mechanisms are consistent with adjustment of the caldera floor as magma is removed from beneath the summit earthquakes with short t wave rise times shallow focal depths cluster at two spots along the summit and south rift zone and are considered possible seafloor eruption sites in situ ground deformation and hydrothermal plume monitors and later shipboard observations confirmed the occurrence of a seafloor volcanic eruption at the volcano s summit

glacier fluctuations in the southern peruvian andes during the late glacial period constrained with cosmogenic 3he the occurrence of pronounced climate reversals during the last glacial termination has long been recognised in palaeoclimate records from both hemispheres and from high to low latitudes accurate constraint of both the timing and magnitude of events such as the younger dryas and antarctic cold reversal is vital in order to test different hypotheses for the causes and propagation of abrupt climate change however in contrast to higher latitude regions well dated records from the tropics are rare and the structure of late glacial tropical climate remains uncertain as a step toward addressing this problem we present an in situ cosmogenic 3 he surface exposure chronology from nevado coropuna southern peru documenting a significant fluctuation of the ice margin during the late glacial period ten tightly clustered ages from a pair of moraines located halfway between the modern glacier and the last glacial maximum terminus range from 11 9 to 13 9ka and give an arithmetic mean age of 12 8 0 7ka 1s these data constitute direct evidence for a readvance or prolonged stillstand of glaciers in the arid andes of southwestern peru copyright 2011 john wiley sons ltd

lithospheric stress states predicted from long term tectonic models influence of rheology and possible application to taiwan abstract the long term stress state of the lithosphere results from a combination of boundary forces surface loads and tractions from mantle flow here we have employed a numerical technique which allows for the self consistent treatment of the interaction between the lithosphere and mantle and takes into account the deformation of the free surface we have used this to study lithospheric dynamics in order to gain insights on the present day conditions of stress and deformation of the lithosphere our numerical approach takes the observed topography and far field plate velocities as input and computes the resultant deformation as a function of the rheological stratification our model application is inspired by taiwan tectonics stress data and earthquake focal mechanisms indicate that the upper crust in taiwan may be predominantly under compression the recent pingtung earthquake in 12 26 2006 however suggests that the sub moho mantle lithosphere under southern taiwan may be under extension if this earthquake indeed represents the local state of stress this raises the question as to why extension and compression can occur simultaneously in this region for addressing this issue we have performed a number of numerical simulations in which we studied the effects of rheological stratification boundary conditions and geometry on the stress state and lithospheric dynamics we have employed both layered viscosity models and models in which we use laboratory based non newtonian and temperature dependent creep laws results show that the rheological stratification plays an important role in lithospheric deformation the relatively hot lithospheric thermal state in taiwan makes it likely that part of the lower crust is relatively weak which results in decoupling from surface near deformation with deformation at depth bending of a subducting slab underneath taiwan causes an extensional stress state in the sub moho mantle lithosphere whereas the collision of the philippine sea plate with the eurasian margin is responsible for a compressional state of stress in the crust it is demonstrated that models with a weak lower crust are also in reasonable agreement with available gps data as well as with constraints on uplift rates from long term geodynamic modelling studies

long term seismicity and ground deformation at axial volcano juan de fuca ridge seismicity along the juan de fuca ridge jdfr has been monitored since august 1991 using u s navy hydrophones in the northeast pacific ocean during this time the focus of jdfr seismicity has been axial volcano where a total of 9055 earthquakes have been detected 1669 located this activity occurred within 48 discrete swarms along the summit caldera and flank rift zones from august 1991 to may 1996 axial volcano exhibited only one swarm with 50 earthquakes from may 1996 to november 1997 swarm activity increased significantly with five swarms of 50 earthquakes activity culminated at the volcano in january 1998 with an 11 day 8247 event swarm that was the result of a major eruption along the summit and southern flank seafloor deformation sensors indicated pre eruption swarms in october 1995 may 1996 and june 1996 coincided with subsidence of the caldera floor the 1996 1997 swarm activity increase also coincided with horizontal extension of the north rift zone consistent with pre eruption deformation of the volcano following the 1998 eruption swarm activity dramatically decreased and no earthquakes have been detected since april 1998 this is the longest aseismic period 1 yr observed at the volcano since acoustic monitoring began suggesting the january 1998 swarm marked the end of an eruptive cycle at axial volcano

late pleistocene glacial sequence in the area of the high plain of bogota eastern cordillera colombia abstract four main glacial events could be reconstructed on the basis of morphologic and 14c evidence in the parano regions surrounding the high plain of bogota eastern cordillera colombia in the area four distinct morainic levels were recognized between ca 2750 3000 m and ca 3750 m radiocarbon dates in combination with climatological data derived from palynological evidence indicate that morainic complex 4 was formed between ca 13 000 12 400 yr b p complex 3 between ca 18 000 14 000 yr b p complex 2 between ca 22 500 19 500 yr b p whereas complex 1 may be of middle last glacial age or of penultimate glacial age the spatial distribution of moraines throughout the area clearly shows that limits of former glacier systems were strongly influenced by local climatological conditions

the june july 1993 seismo acoustic event at coaxial segment juan de fuca ridge evidence for a lateral dike injection the coaxial segment juan de fuca ridge was the site of an intense swarm of earthquakes that began at 21 43 gmt on june 26 1993 julian day 177 the swarm started near 46 15 n and migrated northward over the next 40 hours to 46 36 n where the majority of 676 events occurred during the following 3 weeks of activity the earthquakes propagated nne at a velocity of 0 3 0 1 m s 1 from the southern to northern swarm sites the activity went undetected by land based seismic networks along the oregon and washington coasts suggesting that the earthquakes were all m 4 0 the character of this earthquake swarm is very similar to dike injections observed at krafla and kilauea volcanoes the earthquake activity and subsequent migration probably represent a lateral dike injection into faults and fissures comprising the coaxial segment the reservoir acting as the dike s source likely resides beneath or to the south of the initial southern swarm of earthquakes the large magma supply at axial volcano cannot be ruled out as the source for the coaxial dike even though axial volcano exhibited no earthquake activity related to the coaxial swarm the t wave earthquake swarm reported here is the first deep ocean observation of volcanic seismicity associated with what most likely was a mid ocean ridge dike injection event

response of interior north america to abrupt climate oscillations in the north atlantic region during the last deglaciation several broad scale climatic oscillations during the last deglaciation are well documented in regions around the north atlantic ocean this paper reviews empirical evidence for these deglacial climatic oscillations from non coastal north america and discusses implications for testing climatic simulations and for understanding the cause and transmittal mechanisms paleoclimatic interpretation of oxygen isotope records from several small sites in the eastern great lakes region indicates a classic deglacial climatic sequence that is comparable with records from europe and greenland the climatic events as interpreted from crawford lake oxygen isotopes include the bolling allerod boa warming at 12 700 14c bp a warm boa at 12 500 10 920 14c bp an intra allerod cold period shortly before 11 000 14c bp a cold younger dryas yd climate reversal at 10 920 10 000 14c bp the holocene warming at 10 000 14c bp a brief preboreal oscillation pb at 9650 14c bp and an early holocene cold event at 7500 14c bp 8200 cal bp some of these events were also evident from changes in upland and aquatic vegetation and sediment lithology the pronounced yd climatic reversal has been documented from pollen records along the ecotones at this time and from glacier readvances in the great lakes region along the rocky mountains from alberta to colorado the yd event is indicated by alpine glacier advance and or shift in timberline vegetation in minnesota and upper new york early holocene climatic instability is also suggested by oxygen isotope records and or varve thickness the regional variations in evidence for the yd and other events in north america suggest that climatic oscillations may have different expressions in paleo records depending on geographic location and characteristics of a particular site the extent and magnitude of these climatic oscillations across north america suggest that these oscillations are an expression of climatic change that was probably widespread rather than locally induced by a nearby glacier the location of these sites implies that climatic signals were likely carried over the northern hemisphere through the atmosphere as indicated by general circulation models we hypothesize that the lack of evidence for a cold yd in interior north america west of the great lakes region and east of the rocky mountains was caused by the trapping of cold arctic air mass north of the laurentide ice sheet and by uninterrupted northward expansion of warm caribbean air this strongly contrasted climate also produced non analogous biological assemblages

five years of ground deformation monitoring on axial seamount using a bottom pressure recorder the results of five years of pressure measurements collected by a bottom pressure recorder deployed within the summit caldera of axial seamount on the central juan de fuca ridge are interpreted for monotonic offsets related to vertical seafloor movements results indicate five significant subsidence events during the observation period 3 7 years or an average of 1 35 events per year the displacements range from 3 10 cm with durations of 10 14 days these results indicate an active volcanic system and can be viewed as positive evidence for future attempts at seafloor volcanic observatories and response to active events on oceanic ridge crests advanced instrumentation based on multiple sensors has been deployed at the site to reinforce the results of this pilot experiment

southeast indian ocean ridge earthquake sequences from cross correlation analysis of hydroacoustic data summary parameters of earthquake sequences for instance location and timing of foreshocks and aftershocks are critical for understanding dynamics of mid ocean ridge and transform faults whole sequences including small earthquakes in the ocean cannot be well recorded by land based seismometers due to large epicentral distances recent hydroacoustic studies have demonstrated that t waves are very effective in detecting small submarine earthquakes because of little energy loss during propagation in sound fixing and ranging channel for example an mw 6 2 2006 march 6 40 11 s 78 49 e transform fault earthquake occurred at the southeastern indian ocean ridge but national earthquake information center only reported three aftershocks in the first following week we applied cross correlation method to hydroacoustic data from the international monitoring system arrays in the indian ocean to examine the whole earthquake sequence we detected 14 aftershocks and none foreshock for the earthquake and locations of these aftershocks show an irregular pattern from the observation we suggest that the feature could be caused by complicated transcurrent plate boundary dynamics between two overlapped spreading ridges that is possibly explained by the bookshelf faulting model

evidence of a recent magma dike intrusion at the slow spreading lucky strike segment mid atlantic ridge 1 mid ocean ridge volcanic activity is the fundamental process for creation of ocean crust yet the dynamics of magma emplacement along the slow spreading mid atlantic ridge mar are largely unknown we present acoustical seismological and biological evidence of a magmatic dike intrusion at the lucky strike segment the first detected from the deeper sections 1500 m of the mar the dike caused the largest teleseismic earthquake swarm recorded at lucky strike in 20 years of seismic monitoring and one of the largest ever recorded on the northern mar hydrophone records indicate that the rate of earthquake activity decays in a nontectonic manner and that the onset of the swarm was accompanied by 30 min of broadband 3 hz intrusion tremor suggesting a volcanic origin two submersible investigations of high temperature vents located at the summit of lucky strike seamount 3 months and 1 year after the swarm showed a significant increase in microbial activity and diffuse venting this magmatic episode may represent one form of volcanism along the mar where highly focused pockets of magma are intruded sporadically into the shallow ocean crust beneath long lived discrete volcanic structures recharging preexisting seafloor hydrothermal vents and ecosystems index terms 3035 marine geology and geophysics midocean ridge processes 7280 seismology volcano seismology 8419 8149 tectonophysics planetary tectonics 5475 4259 oceanography general ocean acoustics 9325 information related to geographic region atlantic ocean keywords mid atlantic ridge earthquake hydroacoustic

high resolution studies of the summit of axial volcano sea beam bathymetry sea marc i side scan 30 khz towed camera and submersible data from axial volcano juan de fuca ridge jdfr have been integrated to produce detailed maps of the volcano s summit region in order to elucidate its volcanic and tectonic evolution the proximity of axial volcano the youngest edifice of the cobb eickelberg seamount chain to the jdfr superposes a hotspot derived radial stress pattern onto the linear stress field of a mid ocean ridge spreading center the morphology of the summit of axial volcano reflects the differing eruptive styles produced from this superposition long rift zones begin at the edges of the caldera and extend as much as 75 km to the north and south axial volcano has a distinct summit plateau similar to those found on many other submarine volcanos the process by which summit plateaus are constructed is illustrated by the lava flows originating from the south rift zone which have partially filled the southern half of the caldera and have smoothed the flanks the summit plateau contains penetrative ne sw fracturing that is approximately parallel to the jdfr the unusual rectangular caldera is 3 8 km in size and its trend is about 160 three possible mechanisms are discussed for the caldera s formation 1 canary island type trapdoor formation 2 overlapping spreading center interaction and 3 magma source migration although none of these models is fully compatible with the present data base the overlapping spreading center model is preferred postcaldera volcanism probably began with the formation of the central caldera eruptive complex which was characterized by relatively low volume high viscosity flows the most recent volcanism has apparently taken place along the northern and southern rift zones which have erupted more fluid lavas resulting in areally extensive flows covering up to 60 of the caldera floor extensive low temperature venting and areas of high temperature venting near the northern and southern rift zones and caldera walls suggest a shallow magmatic source beneath the summit of axial volcano

evidence of the younger dryas in central america abstract three sites provide records that address whether the younger dryas was manifest in central america marine records from barbados and the cariaco basin are discussed as well as possible climatic forcing mechanisms sequences from montane la chonta bog costa rica and lowland lake quexil guatemala record a temperature decline of 1 5 2 5 c dated between 11 070 10 400 14c years bp and ca 12 000 10 300 14c years bp respectively the record from lake la yeguada panama does not include cooling although significant reorganization of local communities occurred during the younger dryas chronozone colder tropical ssts throughout deglaciation contributed to sub regional climatic variation more intense monsoonal activity and cooler air temperatures however the temperature reversals are not associated with the coldest tropical ssts which occurred during meltwater pulses the temperature reversals appear to be a response to extra tropical conditions presumably in the north atlantic which suggests that younger dryas cooling extended as far south as costa rica in panama monsoonal conditions may have blocked cooler temperatures precipitation continued to increase throughout deglaciation due to strong forcing by seasonal solar insolation in central america while desiccation events occurred to the north and south

a high resolution speleothem record of climatic variability at the allerod younger dryas transition in missouri central united states stable isotopic analysis and 234 u 230 th mass spectrometry dating of a single calcite stalagmite from onondaga cave east central missouri reveal climatic variability between 13 200 and 12 400 yr bp coincident with the aller d younger dryas transition in the gisp2 greenland ice cores n 18 o values of speleothem calcite mark decreasing temperatures between 13 200 and 13 000 yr bp while more rapidly decreasing n 13 c values record a sharp shift toward c3 vegetation at approximately 13 100 yr bp because of uncertainties in the chronological control of both this speleothem and the gisp2 record and the brevity of this speleothem record v800 years direct comparison of the two sequences is difficult the interval preserved by this speleothem may span the inter aller d cold period iacp alone both the iacp and the start of the younger dryas or only the first half of the younger dryas in any case these data demonstrate that the climate of the north american interior deteriorated significantly and rapidly during the interval associated with the aller d younger dryas transition fl 2001 elsevier science b v all rights reserved

the el abra stadlal in the eastern cordillera of colombia south america abstract the el abra stadial is a climatic cooling event defined in the eastern cordillera of colombia which corresponds both in timing and intensity to the younger dryas climatic oscillation of the northern north atlantic region the stadial was preceded by the relatively warm guantiva interstadial and followed by the warm holocene colder climatic conditions during the el abra stadial caused a 400 m lowering of the upper andean forest limit below its altitudinal location during the preceding guantiva interstadial translated in temperature change this represents a drop in mean annual temperature of approximately 2 to 3 c the lowering of the upper forest limit and inferred temperature change for the el abra stadial compared to late holocene conditions are in the order of 600 m and 4 c respectively the transition of the guantiva interstadial to the el abra stadial has been radiocarbon dated at 11 210 90 bp and 10 820 60 bp climatic warming may have started shortly after 10 380 90 bp and near present day temperatures were reached at least as early as 8920 100 bp maximum cooling was probably attained between 10 800 bp and 10 300 bp further ams radiocarbon dating is planned to establish more exactly the timing of the el abra stadial a glacial advance of el abra age the bocatoma stade has been recognized in the highest part of the colombian eastern cordillera the sierra nevada del cocuy during this advance glaciers extended some 700 m lower than at present a climatic cooling event of el abra age associated with shifts of the upper andean forest limit and glacial advances has also been recognized in other parts of andean colombia including the central cordillera and the sierra nevada de santa marta

recent eruptions on the coaxial segment of the juan de fuca ridge implications for mid ocean ridge accretion processes the 1993 seismic swarm and volcanic eruption on the coaxial segment of the juan de fuca ridge was the first verified mid ocean ridge accretion event monitored by the national oceanic and atmospheric administration u s navy sound surveillance system sosus ambiguity in the location of the initial seismicity resulted in an uncertainty as to whether the dike intruded from the summit and north rift zone of the adjacent axial volcano or whether it arose locally within the coaxial segment however analyses of multibeam side scan sonar towed camera submersible and geochemical data show that the coaxial segment is morphologically structurally and geochemically distinct from the north rift zone of axial volcano there is no geologic or geochemical evidence that dike injections from axial volcano have extended north of 46 18 n in the past whereas the 1993 eruption site is at 46 31 n furthermore all seafloor manifestations of the 1993 dike injection lie along the central neovolcanic zone of the coaxial segment analyses of repeat seabeam surveys combined with seafloor observations show that two other eruptions of approximately the same volume as the 1993 eruption occurred along the coaxial segment in the 1981 1991 interval these three diking events may have relieved decades of accumulated stress over 35 km or more of this segment the spatial pattern and hydrothermal history of the 1993 event is consistent with a dike with a significant lateral component of injection

a younger dryas icecap in the equatorial andes abstract morphologic and stratigraphic evidence shows that a late glacial ice cap existed on part of the eastern cordillera of ecuador lat 0 20 s on ground with a mean elevation of 4200 m where none exists now an outlet glacier from an ca 800 km 2 ice cap terminated at 3850 m altitude in the papallacta valley on the eastern side of the plateau radiocarbon dates show that moraines formed by this advance were ice free by 13 200 14 c yr b p tephras and the age of organic deposits at the plateau edge indicate ice free conditions before 11 800 14 c yr b p this interval was followed by the expansion of an ca 140 km 2 ice cap that discharged glaciers into adjacent valleys where terminal moraines were built at 3950 m altitude ams and conventional radiocarbon dates from macrofossils peat and gyttja above and below till of the readvance indicate that the ice cap formed between ca 11 000 and 10 000 14 c yr b p and was thus coeval with the european younger dryas event the ice cap developed in response to a surface temperature cooling of at least 3 c in the tropical andes a finding that is consistent with a coupled equatorial high latitude north atlantic climate system operating at the late glacial holocene transition these results are further evidence that younger dryas cooling may have been a global event

1998 eruption of axial volcano multibeam anomalies and sea floor observations lava flows erupted during the january february 1998 seismic swarm at axial volcano on the juan de fuca ridge have been identified by differencing of pre and post event multibeam bathymetric surveys and by seafloor observations a sheet flow more than 3 km in length and 500 800 m wide erupted from the uppermost south rift is the site of a robust hydrothermal system 1998 lavas occur over about 9 km of the upper south rift zone or about 20 of the along axis length of the seismicity event 50 km the estimated volume of lava erupted is 18 76 106 m for the extrusion and 100 106 m for the intrusion the total volume is consistent with the volume from modeling of seafloor strain measurements recorded during the event

temporal geographical meltwater influences on the north atlantic conveyor implications for the younger dryas the temporal and geographical roles of meltwater discharge from the laurentide ice sheet on north atlantic deep water nadw production are investigated utilizing a global realistic geometry coupled climate model which does not require the use of flux adjustments model results suggest that preconditioning by meltwater discharge to the mississippi prior to the younger dryas yd is capable of pushing nadw beyond the limit of its sustainability the diversion of meltwater to the st lawrence then merely serves to completely inhibit nadw production the modeled change in surface air temperature generally agrees with the global pattern and magnitude of temperature change seen in paleoclimatic reconstructions of the yd and is intimately linked to changes in nadw formation the global thermohaline circulation provides an interhemispheric teleconnection with the southern oceans while changes in the atmospheric heat transport reacting to a global redistribution of oceanic heat transport provide a mechanism for interbasin teleconnection although the primary thermodynamic and hydrological cycle feedback processes are included within the atmospheric model in the absence of additional feedbacks an equilibrium without the presence of nadw is possible the inclusion of the wind stress speed feedback is found to significantly contribute to the resumption of nadw production as suggested by previous studies contrary to these same studies however the coupled model indicates an advective spin up timescale is required for resumption of nadw production and hence the termination of the modeled yd like climate event as opposed to a decadal century timescale the reason for the discrepancy is unclear but may be associated with the use of fixed salt flux fields applied in previous studies or the duration strength and geographical location of the imposed meltwater applied

evidence for deformation associated with the 1998 eruption of axial volcano juan de fuca ridge from acoustic extensometer measurements acoustic extensometer instruments capable of making precise daily measurements of horizontal distance were deployed across the north rift zone of axial volcano in june 1996 and were in place when a submarine eruption began on axial s south rift zone in january 1998 the instruments recorded a gradual 9 cm extension over a 405 m baseline leading up to the eruption and then an abrupt 4 cm contraction at the time of the eruption an elastic point source deformation model shows that deflation of axial s summit can explain both the 4 cm distance decrease at the extensometer array and a 3 2 m subsidence measured by another instrument in the caldera if the pressure source is located at a depth of 3 8 km below the center of the caldera the 9 cm distance increase may represent pre eruption spreading across the rift zone

paleoenvironment of the folsom archaeological site new mexico usa approximately 10 500 14c yr b p as inferred from the stable isotope composition of fossil land snail shells abstract well preserved aragonitic land snail shells vallonia from late pleistocene eolian sediment in the folsom archaeological site in new mexico exhibit an overall decrease of 18opdb from maximum values of 2 7 more positive than modern to younger samples with lower average values of about 3 6 within the modern range the age of the samples approximately 10 500 14c yr b p suggests that the decrease in 18o may manifest climatic changes associated with the younger dryas some combination of increased relative humidity and cooler temperatures with decreased 18o of precipitation during the times of snail activity can explain the decrease in shell 18o a well known paleoindian bison kill occurred at the folsom site during this inferred environmental transition average 13c values of the aragonite shells of the fossil vallonia range from 7 3 to 6 0 among different archaeological levels and are not as negative as modern values this suggests that the proportion of c4 vegetation at the folsom site approximately 10 500 14c yr b p was greater than at present a result which is consistent with other evidence for higher proportions of c4 plants in the region at that time

the role of ocean atmosphere reorganizations in glacial cycles abstract a case is made that glacial to interglacial transitions involve major reorganizations of the ocean atmosphere system such reorganizations constitute jumps between stable modes of operation which cause changes in the greenhouse gas content and albedo of the atmosphere only in this way can the rapidity of glacial terminations the hemispheric synchroneity and symmetry of mountain glaciation and the large polar air temperature and dustiness variations be accounted for if these reorganizations are driven in some fashion by orbitally induced seasonal insolation changes then the connection between insolation and climate is most likely through impacts of fresh water transport on the ocean s salinity distribution

climatic change during the younger dryas chron in northern south america a test of the evidence abstract new ams and palynological data are presented from the colombian andes to assess vegetational and climatic change during the lateglacial holocene transition with special emphasis on the younger dryas yd chronozone the new evidence is compared and discussed with other colombian cores and with data from other countries in the region the lateglacial climatic reversal in colombia known as the el abra stadial has an estimated lower boundary of 11 200 conventional and 10 900 interpolated 14 c yr bp respectively although the el abra stadial is assumed to be the equivalent of the european yd the present data suggest that the el abra stadial is a biostratigraphical signal representing both the yd chronozone and the earliest holocene 11 000 9000 14 c yr bp on the basis of new ams dates and a re evaluation of the pollen zones we divided the colombian el abra biozone into two phases from ca 11 000 to ca 10 500 14 c yr bp there is a sharp increase of subparamo and paramo pollen reflecting a relatively cool phase during the yd chronozone zone y1 after ca 10 500 14 c yr bp a slight increase of arboreal pollen and the presence of cactaceae zone z1 point toward a relatively milder but drier phase extending to ca 9000 14 c yr bp in the earliest holocene our conclusions add detail to the concept of astronomical forcing of contrasting rainfall changes in northern south america between 12 400 and 8800 14 c yr bp we propose an environmental drought during the el abra biozone with subsequent erosion of the sediments deposited during that period as a major factor explaining the poor presence of yd evidence in northern south america we conclude that at hydrologically sensitive sites without a clear lithological change around 11 000 9000 14 c yr bp a hiatus during the yd chronozone can only be detected if other cores are available with bracketed time control we state that the start of the temperature decline in central america and northern south america is related to the global yd cooling event however much work is still required to understand the duration and amplitude of the climatic reversal during the yd chronozone in this part of the globe

termination of a 6 year ridge spreading event observed using a seafloor seismic network on the endeavour segment juan de fuca ridge 1 we present automatically determined epicenters and magnitudes for 36 523 earthquakes recorded along the endeavour segment between august 2003 and october 2006 using a local ocean bottom seismometer obs network the catalog is dominated by two swarm sequences in january and february 2005 in the vicinity of the endeavour overlapping spreading center which included earthquakes in west valley the northern portion of the endeavour segment southwest endeavour valley and the endeavour vent fields these swarms are attributed to volcanism including a dike intrusion on the northern endeavour in february 2005 and smaller diking events on the propagating tip of the west valley segment in both swarms the dike on the northern endeavour propagated to the south which is inconsistent with magma sourced from the axial magma chamber beneath the elevated central portion of the segment following the swarms seismic activity on the endeavour segment decreased on average to 15 of pre swarm values and almost ceased at the segment ends we infer that a 6 year non eruptive event that started with a swarm in 1999 and finished with the 2005 swarms ruptured the entire segment and relieved plate spreading stresses the inferred coupling between the 1999 and 2005 events the observation of extensive precursory activity prior to the 2005 swarms and the interaction between seismically active regions during the swarms is consistent with static triggering with delays influenced by viscoelastic relaxation hydraulic diffusion and magma withdrawal and replenishment

tropical climatic variation on the pacific slopes of the ecuadorian andes based on a 25 000 year pollen record from deep sea sediment core tri 163 31b marine sediments from 3 37 s 83 58 w yield a well dated pollen record of equatorial andean vegetation moderate development of podocarpus high montane rainforest 34 000 28 000 yr b p and increase of high andean grassland pollen 28 000 16 000 yr b p imply an extended dry cool glacial period following a brief interstade rapid stepwise expansion in coastal and montane forest pollen characterizes the deglacial interval the general correspondence between pollen and oxygen isotope variations in tri 163 31b suggests that tropical climatic variations in the northern andes were basically coherent with northern hemisphere glacier variations

tropical south america during the last glacial maximum evidence from glacial periglacial and fluvial records abstract the records of the lgm climates of tropical south america are still sparse compared to the vast region under consideration nevertheless a number of records hold up to critical evaluation early attempts to reconstruct the lgm temperature and precipitation conditions for the lgm around 21 14 c ka bp have suggested that relative to present lowland temperatures were on average only a few c cooler whereas in the andes the temperature depression was in the range of 6 8 c these reconstructions further suggested that tropical precipitation was more limited in both the lowlands and in the andes although recent pollen evidence supports significantly cooler tropical lowland temperatures during the lgm additional alkenone evidence from sea surface temperatures and model analysis are contradictory the data from tropical south america suggest that the late quaternary climatic changes of the lowlands as well as of the andean mountains reflect a response 1 to environmental changes in the source area of the moisture and 2 to global temperature fluctuations based on glacial periglacial and pollen evidence a lgm temperature depression of 5 6 c can be assumed for both tropical lowland south america and the andes these lgm values for the cooling correspond with recent coral records from barbados and the southwestern pacific ice core records from peru noble gas measurements in brazil and ocean core records from the western equatorial atlantic no difference in the value of lgm cooling can be recognised between the tropical lowlands and the high mountains of south america furthermore in all regions the lgm climates were more arid than the present day climates terrestrial records have not yet yielded records of younger dryas age apart from the tropical andes of ecuador where the younger dryas time is characterised by a cooler and drier climate pollen evidence for cooler younger dryas conditions comes from the bolivian andes

a 135 000 year record of vegetational and climatic change from the bandung area west java indonesia sedimentological and palynological analyses of sediment cores from the intramontane bandung basin west java indonesia provide a first palaeoclimatic record for the indonesian region covering continuously the last 135 000 years our data on palaeosol development indicate anomalously dry conditions for the final part of the penultimate glacial period around 135 000 yr b p and very warm and humid interglacial conditions from 126 000 to 81 000 yr b p during the transition to the last glacial period around 81 000 yr b p freshwater swamp forest of the bandung plain was replaced by an open swamp vegetation dominated by grasses and sedges indicating a change to considerably drier conditions possibly related to reduced moisture uptake by the nw monsoon as a consequence of lower sea levels at the onset of glacial conditions a strong reduction in asplenium ferns from 81 000 to 74 000 yr b p suggests that drier conditions may also have occurred in the mountains of the bandung area while increased numbers indicate that from 74 000 to 47 000 yr b p it was slightly wetter again inferred depression of montane vegetation zones and reduced fern percentages suggests distinctly cooler and possibly drier climatic conditions prevailed in the bandung area from 47 000 to approximately 20 000 yr b p for the last glacial maximum 4 7 c lower temperatures are recorded

in situ ground deformation measurements from the summit of axial volcano during the 1998 volcanic episode since september 1987 seafloor instrumentation monitoring ground deformation has been maintained on the summit of axial volcano on the central juan de fuca ridge during a january 1998 volcanic episode pressure records from the central caldera showed a significant increase in pressure indicating caldera subsidence of over 3 m this observed subsidence is interpreted to represent volcanic deflation as magma is erupted and or injected into the volcanic flanks temperature anomalies of nearly 0 45 c were also observed a comparison of the subsidence record with hydroacoustic recordings indicates a continuous volcanic tremor signal coincident with the subsidence event the time coincidence of subsidence of the summit caldera with migration of epicenters into the volcanic rift zones confirms that during the 1998 episode the volcanic flanks were supplied by lateral dike injection from a central magma body rather than locally derived magma sources

establishing a new era of submarine volcanic observatories cabling axial seamount and the endeavour segment of the juan de fuca ridge abstract at least 70 of the volcanism on earth occurs along the 65 000 km network of mid ocean ridge mor spreading centers within these dynamic environments the highest fluxes of heat chemicals and biological material from the lithosphere to the hydrosphere occur during volcanic eruptions however because underwater volcanoes are difficult and expensive to access researchers are rarely if ever in the right place at the right time to characterize these events therefore our knowledge is limited about the linkages among hydrothermal chemical and biological processes during seafloor formation and crustal evolution to make significant advancements in understanding the evolution of mor environments the united states and canada have invested in the first plate scale submarine cabled observatory linked through the global internet spanning the juan de fuca tectonic plate these two networks include 1700 km of cable and 14 subsea terminals that provide 8 10 kw power and 10 gbs communications to hundreds of instruments on the seafloor and throughout the overlying water column resulting in a 24 7 365 presence in the oceans data and imagery are available in real to near real time the initial experimental sites for monitoring volcanic processes include the mor volcanoes called axial seamount and the endeavour segment that are located on the juan de fuca ridge axial a hot spot influenced seamount is the most robust volcano along the ridge rising nearly 1400 m above the surrounding seafloor and it has erupted twice in the last 15 years in contrast the endeavour segment is characterized by more subdued topography with a well defined axial rift and it hosts one of the most intensely venting hydrothermal systems known a non eruptive spreading event lasting 6 years was documented at endeavour between 1999 and 2005 hydrothermal venting intensity chemistry and temperature as well as associated biological communities at both sites were significantly perturbed by the magmatic and intrusive events this paper presents the similarities and differences between the axial and endeavour volcanic systems and identifies reasons why they are ideal candidates for comparative studies the u s has made a 25 year commitment for sustained observations using the cabled infrastructure the highly expandable nature of submarine optical networking will allow for the future addition of novel experiments that utilize ever evolving advancements in computer sciences robotics genomics and sensor miniaturization comprehensive modeling of the myriad processes involved will continue to assimilate and integrate growing databases yielding a new understanding of integrated processes that create the seafloor in the global ocean basins

the plio pleistocene climatic record of the tropical andes sequences of lake sediments on the high plains of the colombian cordillera oriental at an altitude of c 2500 m represent some 5 or 6 ma the last glacial interglacial cycle is well documented in the sediments of lake fuquene very long sequences up to 350 m long cores were collected in the high plain of bogota representing more than 3 5 ma pollen diagrams are now available covering that time and representing the longest known continuous terrestrial record available they were dated using potassium argon and fission track methods on material from intercalated volcanic ash layers the pollen diagrams can be interpreted in terms of shifting vegetation zones and these in turn enable us to draw approximate temperature and humidity curves the temperature curve for the last 3 5 ma can be correlated with deep sea curves oxygen isotopes temperature an important change in rhythm and intensity seems to take place at approximately 3 1 ma and a cold period that should correspond in time with the pre tiglian of western europe is conspicuous

vegetation and climate change in west java indonesia during the last 135 000 years abstract sedimentological and palynological analyses of two sediment cores from the intramontane bandung basin java indonesia provide the first palaeoclimatic record for the indonesian region covering the last 135 000 years our data indicate anomalously dry conditions for the penultimate glacial and very warm and humid conditions during the last interglacial during the last glacial period fresh water swamp forests of the bandung plain were replaced by open swamp vegetation dominated by grasses and sedges indicating a change to considerably drier climatic conditions possibly as a consequence of lower sea levels at the onset of glacial conditions for the last glacial maximum temperatures 4 7 c lower than at present are recorded

a lateglacial climatic reversion in hokkaido northeast asia inferred from the larix pollen record abstract at present larix gmelini is a main component of taiga developed in north sakhalin northeast china and east siberia during the interval from 11 8 to 12 4 ka bp pollen assemblages from north hokkaido japan are dominated by larix pollen assemblages of this lateglacial climatic reversal known as the kenbuchi stadial are similar to pollen assemblages from the last glacial maximum in north hokkaido vegetation of hokkaido inferred from these pollen assemblages open taiga composed of larix gmelini pinus pumila and picea jezoensis and or picea glehnii may have been like that of north sakhalin today comparison of these fossil pollen assemblages from hokkaido with pollen assemblages from modern surface samples in sakhalin suggests that 11 8 to 12 4 ka bp temperatures relative to today were at least 9 c lower in january and 7 c lower in august and that annual precipitation was at least 735 mm lower than present

the el abra stadial a younger dryas equivalent in colombia abstract a survey of radiocarbon dated palynological stratigraphical and glacio morphological evidence from colombia is presented showing a cold climatic fluctuation most likely between 10 900 and 10 100 bp immediately preceding the initiation of the holocene this fluctuation called the el abra stadial is characterized by lower temperatures and less precipitation and occurs after the late glacial guantiva interstadial average annual temperature during the guantiva interstadial may have been 2 c lower than today and during the el abra stadial from 4 to 6 c lower than today the upper forest line during the el abra stadial was some 400 to 500 m lower than during the guantiva interstadial and some 600 to 800 m lower than today the guantiva interstadial el abra stadial early holocene sequence is radiocarbon dated by some 45 dates and evidence is shown from 14 areas mostly located at high elevations 2000 4000 m in the eastern and central cordillera and in the sierra nevada de santa marta but some from the tropical low lands although more precise dating of the boundaries is desirable we interpret the guantiva el abra climatic fluctuations as equivalents in time and climatic phenomena to the allerod younger dryas sequence in europe

vertical deformation monitoring at axial seamount since its 1998 eruption using deep sea pressure sensors pressure measurements made on the seafloor at depths between 1500 and 1700 m at axial seamount an active submarine volcano on the juan de fuca ridge in the northeast pacific ocean show evidence that it has been inflating since its 1998 eruption data from continuously recording bottom pressure sensors at the center of axial s caldera suggest that the rate of inflation was highest in the months right after the eruption 20 cm month and has since declined to a steady rate of 15 cm year independent campaign style pressure measurements made each year since 2000 at an array of seafloor benchmarks with a mobile pressure recorder mounted on a remotely operated vehicle also indicate uplift is occurring in the caldera at a rate up to 22f1 3 cm year relative to a point outside the caldera the repeatability of the campaign style pressure measurements progressively improved each year from f15 cm in 2000 to f0 9 cm in 2004 as errors were eliminated and the technique was refined assuming that the uplift has been continuous since the 1998 eruption these observations suggest that the center of the caldera has re inflated about 1 5f0 1 m thus recovering almost 50 of the 3 2 m of subsidence that was measured during the 1998 eruption this rate of inflation can be used to calculate a magma supply rate of 1410 6 m 3 year if this rate of inflation continues it also suggests a recurrence interval of 16 years between eruptions at axial assuming that it will be ready to erupt again when it has re inflated to 1998 levels d 2005 elsevier b v all rights reserved

middle and late quaternary vegetational and climatic history of the paramo de agua blanca eastern cordillera colombia abstract the results of a palynological study of a 13 m deep bore hole of lake deposits from the paramo de agua blanca colombian eastern cordillera 5 n elev 3250 m are reported by means of 14 c dates and an indirect dating method based on pollen densities it was possible to provide the pollen diagram with an approximate time scale the section representing some 465 000 years gives a continuous record of the middle and late pleistocene and holocene vegetational and climatic sequences the sequence of glacial and interglacial periods in combination with their age and duration according to the indirect time determinations could be tentatively correlated with the european chronostratigraphic sequence

data model comparison of the younger dryas event the younger dryas cooling event is well established in the north atlantic region through numerous climate proxy records although the climatological controls vary from site to site it is considered to have taken place between about 10 000 and 11 000 bp radiocarbon years 11 500 13 000 calendar years ago outside the north atlantic region climate proxy records and chronology commonly become problematic because of weaker signals and less dating control in addition to this evidence oceanic records reveal conflicting evidence for younger dryas forcing mechanisms and the timing of events we compare proxy evidence with the results from an ocean general circulation model coupled to the energy moisture balance atmospheric model the model results reveal a global pattern and regional magnitude which generally agree with temperature changes interpreted from paleoclimate reconstructions the model also supports the general duration of global cooling of the younger dryas although proxy data can be controversial outside of the north atlantic region the authors believe that there is enough evidence to support the younger dryas event on a global scale they also recognize however that more concrete evidence is needed before the question can be unequivocally answered

lapse rates and other variables applied to estimating paleoaltitudes from fossil floras abstract a previous method for determining paleoaltitude from fossil floras has used the difference between sea level and upland paleotemperatures which is then multiplied by the reciprocal of a normal lapse rate the present study examines other variables that can significantly influence such results terrestrial lapse rates have been calculated for 39 areas of the world based upon mean annual temperature mat mean warm month temperature mat and mean cold month ttemperature cmt these show regional and seasonal variability that is explained by factors including continentality elevation of large massifs or high base levels cold air drainage fog mountain barrier effects and the location of the subtropical high pressure zone lapse rates and projected sea level temperatures based on data from the western united states show distinct regional patterns these indicate that within this region the highest lapse rate and temperature values are correlated with 1 continental climates in the subtropical high pressure zone and 2 areas having relief where the lowest elevation land surfaces base levels occur at high altitude the data are applied to evaluate and revise the methodology for estimating paleoaltitudes variables of climatic change sea level fluctuation and paleogeography are also considered limitations in application of the method are emphasized the method is exemplified by application to the latest eocene florissant flora of colorado u s a although the results are conjectural they strongly suggest that the late eocene erosion surface in the southern rocky mountains occurred at a much higher paleoaltitude than previously thought this high elevation may have resulted from earlier laramide crustal thickening

a cooling event during the younger dryas chron in costa rica abstract a fossil pollen record from the costa rican cordillera de talamanca presents the first ams radiocarbon dated evidence of a temperature decrease during the younger dryas chron this cooling event is named la chonta stadial after the bog at 2310 m altitude located at the actual lower to upper montane forest boundary high resolution pollen analysis revealed that between 11 070 130 ams 14c age and 10 400 yr b p interpolated age vegetation comparable to present day subalpine forest occurred about 300 400 m lower than in the previous warmer interval and 600 to 700 m lower than at present time the radiocarbon dates are close to the earlier estimated ages of 11 080 10 500 yr b p for this interval based on interpolation and pollen concentration rates hooghiemstra et al 1992 the downslope shift of the upper forest line indicates an estimated temperature drop of 2 3 c during the la chonta stadial the local vegetation development is indicative of a drier climate from 10 400 to 9800 120 yr b p ams 14c age subalpine rain forest was replaced by upper montane forest a transitional period to holocene environmental conditions