chironomid based lateglacial climatic reconstruction for southeast scotland this paper presents the first chironomid based climatic reconstruction for the uk lateglacial obtained from a lake basin in southeast scotland whitrig bog comparison of chironomid lithological geochemical and pollen data reveals a marked vegetation lag behind the warming following deglaciation warm water chironomid taxa e g chironomus had replaced cold water chironomid taxa e g paracladius prior to the arrival of shrubs and trees and when local soils were still poorly developed in addition to clear evidence for the younger dryas stadial chironomid data also reveal two short term cold episodes that punctuate the lateglacial interstadial both of which are also reflected in pollen and lithological data as reversals from open birch scrub woodland to open herbaceous tundra coinciding with inwash of minerogenic matter into the basin 1997 john wiley sons ltd

geodetic constraints on postseismic deformation following the 1990 ms 7 8 luzon earthquake and implications for luzon tectonics and philippine sea plate motion 1 we have obtained three epochs of high quality dual frequency gps data at 15 stations in the luzon philippines region since the july 16 1990 ms 7 8 earthquake from which we generate horizontal velocity fields at the earth s surface for the 1993 1996 and 1996 1998 periods we use these velocities plus 1996 1998 gps velocity results reported elsewhere from 13 additional stations to show that present day deformation in luzon is dominated by strike slip motion along the philippine fault system the measured strike slip rate across central luzon is faster than the expected long term slip rate on the fault which we attribute to postseismic deformation following the 1990 earthquake the 1993 1996 and 1996 1998 deformation patterns cannot be statistically distinguished within the 10 uncertainties of the data if the observed deformation is interpreted using an elastic half space model with uniform slip below a subsurface locking depth we find a fault slip rate of 40 mm yr and a locking depth of 15 km this is too fast to be a steady interseismic rate as it disagrees with what is known from paleoseismic and other evidence about earthquake recurrence and long term slip rate on the philippine fault system in central and northern luzon also a 15 km locking depth for steady interseismic slip is probably too shallow compared to the depth of rupture in the 1990 earthquake if the deformation is instead interpreted with two types of viscoelastic model we find that the observed velocities can be fit well for a range of values of lower lithosphere viscosity and long term slip rate using a two dimensional 2 d viscoelastic coupling model the minimum allowable lower lithosphere viscosity is 0 5 1019 pa s with an associated long term slip rate of 15 22 mm yr faster long term slip rates also fit well with correspondingly higher values of viscosity with a possibly more realistic model that includes 3 d viscoelastic effects we find preferred long term velocities in the range 20 35 mm yr and viscosities in the range 2 6 1019 pa s our preferred viscosities correspond to maxwell times on the order of 7 20 of the typical earthquake recurrence interval and are several times higher than values found for a number of californian strike slip earthquakes other implications of our 1993 1998 surface velocities are that the philippine sea eurasia ph eu euler vector of seno et al 1993 is a better description of the ph eu convergence rate than a euler vector recently estimated from gps velocities in the northern ph and that the great majority of the normal component of ph eu plate convergence is taking place west of luzon presumably largely at the manila trench we also find that luzon is rotating counterclockwise relative to ph at 1 2 myr only 25 of the rate recently suggested by other workers on the basis of limited gps data

accelerator mass spectrometer ages for the younger dryas event in atlantic canada abstract in atlantic canada bulk sediment dates for the onset of a late glacial cooling widely regarded as the younger dryas event are highly variable ranging from 14 300 270 to 10 800 100 yr b p we present the first accelerator mass spectrometer ams 14c dates from atlantic canada at or close to the boundaries of this event from six sites in new brunswick and nova scotia the mean of five dates places the onset of this cooling at ca 10 770 yr b p the inclusion of a sixth perhaps anomalously old date changes the mean to 10 880 yr b p the termination averages three dates ca 10 000 yr b p these dates place the timing of the younger dryas event in atlantic canada closer in line with the traditional chronozone boundaries of 11 000 and 10 000 yr b p in northwest europe

younger dryas interval and outflow from the laurentide ice sheet a boxmodel of the great lakes is used to estimate meltwater flow into the north atlantic between 8000 and 14 000 calendar years b p controls on the model include the oxygen isotopic composition of meltwaters and lake waters as measured in the shells of ostracodes outflow rates are highest when oxygen isotopic values of the lake waters are most negative denoting a maximum glacial meltwater component flow rates reach maximum values before the onset of the younger dryas and after it ends these maxima appear to be correlative with the major meltwater pulses mwp 1a and 1b although the resumption of north atlantic deep water formation may be tied to the reduction in ice sheet melting neither the onset nor the end of the younger dryas as recorded in the greenland ice sheet project gisp2 records appear tied to maxima in meltwater outflow from the laurentide ice sheet

source mechanism of the luzon philippines earthquake of july 16 1990 the luzon philippines earthquake of july 16 1990 with ms 7 8 was generated by left lateral faulting in the central luzon island ground breakage was observed along a linear trace extending 110 km the maximum horizontal offset as measured on the fault was as much as 6 m a fault area of 120 20 km2 was inferred from a field study and aftershock data this event is one of the largest strike slip earthquakes ever recorded in the world for long period surface waveform analysis we used very broadband records from 14 stations of the gdsn geoscope iris and erios networks the centroid moment tensor cmt solution from surface waves represents almost pure left lateral strike slip faulting on a steep fault with strike 155 dip 88 and rake 7 the seismic moment is 3 9 1020 nm 1027 dyn cm which gives mw 7 7 the average dislocation on the fault is 5 4 m and the stress drop is 5 2 mpa 52 bars teleseismic p and sh waves from 14 stations are used to model the spatiotemporal distribution of subevents five subevents are detected in an interval of 44 sec their sequence indicates a bilateral rupture the mean velocity of rupture toward the north is 2 7 km sec the total seismic moment of the subevents is 3 6 1020 nm the largest aftershock ms 6 6 occurred on july 17 near the recognized northern end of the main fault the cmt solution for the aftershock represents a reverse faulting with moment of 6 4 1019 nm mw 6 5 this aftershock was probably caused by compression produced by block motion of the eastern block of the main fault

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

origin and consequences of cyclic ice rafting in the northeast atlantic ocean during the past 130 000 years deep sea sediment cores recovered from the northeast atlantic ocean were examined in order to elucidate the influence of the earth s orbital parameters on major ice rafting analyses of coarse grained ice rafted debris and planktonic foraminifers revealed a strong reaction to the precession signal since 130 000 yr b p dropstone layers have been deposited each half period of a precessional cycle 11 000 1000 yr ice rafting occurs during times of winter minimum summer maximum insolation and summer minimum winter maximum insolation in the first case high summer insolation forces meltwater discharge from the ice sheets into the polar seas which subsequently enhances formation of sea ice during the winter in the second case growth of continental ice enhances iceberg production which also leads to a salinity reduction of surface seawater both situations result in a southward penetration of polar water thus the marine record of dropstones documents ice rafting not only during weichselian stades but also during cold events within interstades the regularity of ice rafting yields a useful framework to calibrate and elucidate climatic changes not only in the region of the north atlantic ocean but also in remote areas such as the pacific ocean and the antarctic

sub pixel mapping of alunite and jarosite using aster data a case study from north of semnan north central iran abstract a widespread series of volcanic rocks and younger intrusive bodies are exposed in the north and northeastern semnan north central iran they show an intermediate to felsic composition which have undergone various types of alteration including alunite and jarosite in this research aster data were used for sub pixel mapping of these typical minerals using the mixtured tuned matched filtering mtmf algorithm the spectral properties of field samples were measured by an asd spectroradiometer and their spectra were analyzed through a visual comparison to the usgs spectral library however the z profile method was used for extraction of target spectra from pixels in which the occurrence of desired minerals were verified by other methods the mtmf output results revealed pixels with the highest fractions of alunite and jarosite dominantly near the altered rhyolitic and andesitic tuffs as well as in adamelites it is suggested that an integration of mtmf method and the aster data is a powerful approach for sub pixel mapping of alunite and jarosite which could be applicable in mineral exploration projects

climate correlations between greenland and antarctica during the past 100 000 years the ice cores recovered from central greenland by the grip1 2 and gisp23 projects record 22 interstadial warm events during the part of the last glaciation spanning 20 105 kyr before present the ice core from vostok east antarctica records nine interstadials during this period4 5 here we explore links between greenland and antarctic climate during the last glaciation using a high resolution chronology derived by correlating oxygen isotope data for trapped o2 in the gisp2 and vostok cores we find that interstadials occurred in east antarctica whenever those in greenland lasted longer than 2 000 years our results suggest that partial deglaciation and changes in ocean circulation are partly responsible for the climate teleconnection between greenland and antarctica ice older than 115 kyr in the gisp2 core shows rapid variations in the 18o of o2 that have no counterpart in the vostok record the age depth relationship and thus the climate record in this part of the gisp2 core appears to be significantly disturbed

crustal thickness variation from a continental to an island arc terrane clues from the gravity signatures of the central philippines abstract offshore and ground gravity data were utilized to estimate crustal thickness across the central philippines where a transition from continental to island arc terrane occurs significant differences in gravity anomalies were observed between the palawan microcontinental block pcb and the philippine mobile belt pmb two major terranes that came together through arc continent collision islands of the pcb mindoro tablas romblon sibuyan and western panay made up of an assortment of continent derived sedimentary and igneous rocks and slivers of ophiolitic bodies register lower bouguer anomalies compared to that displayed by masbate island in the pmb the calculated crustal thickness of this region exhibits a complex moho topography of non uniform depth across the collision zone with the thickest parts 32 km corresponding with ophiolitic units emplaced consequent to arc continent collision on the other hand relatively thinner crust 21 km within the collision zone coincides with areas surmised to have undergone attenuation following intra arc rifting the same characteristics are observed offshore of western mindoro and within the marinduque basin areas known to have experienced crustal thinning following regional tectonic rearrangements that triggered riftings and intra basin openings

interseismic deformation and moment deficit along the manila subduction zone and the philippine fault system we examine interseismic coupling of the manila subduction zone and fault activity in the luzon area using a block model constrained by gps data collected from 1998 to 2015 estimated long term slip rates along the manila subduction zone show a gradual southward decrease from 90 100 mm yr at the northwest tip of luzon to 65 80 mm yr at the southern portion of the manila trench we provide two block models models a and b to illustrate possible realizations of coupling along the manila trench which may be used to infer future earthquake rupture scenarios model a shows a low coupling ratio of 0 34 offshore western luzon and continuous creeping on the plate interface at latitudes 18 19 n model b includes the north luzon trough fault and shows prevalent coupling on the plate interface with a coupling ratio of 0 48 both models fit gps velocities well though they have significantly different tectonic implications the accumulated strain along the manila subduction zone at latitudes 15 19 n could be balanced by earthquakes with composite magnitudes of mw 8 8 9 2 assuming recurrence intervals of 500 1000 years gps observations are consistent with full locking of the majority of active faults in luzon to a depth of 20 km inferred moments of large inland earthquakes in luzon fall in the range of mw 6 9 7 6 assuming a recurrence interval of 100 years

icing the north atlantic there is debate over the causes of the large and abrupt climate changes that the north atlantic region has experienced in the past and may do in the future the driving forces of such changes might originate in the north atlantic itself or could be transmitted to the region from elsewhere new evidence on the extent and movement of the british ice sheet around the end of the last ice age supports the first contention and in particular implicates the advance and retreat of the laurentide ice sheet in causing some of the big climate jumps of the past

alluvial response to differential subsidence sedimentological analysis aided by remote sensing willwood formation eocene bighorn basin wyoming usa a colour landsat thematic mapper image was used to identify and to map on a regional scale alluvial facies in the lower eocene willwood formation each facies covers a distinct geographical area of several hundred square kilometres in the bighorn basin of wyoming usa comparison of the image with laboratory spectra from willwood formation rocks and field exposures shows that the image provides information regarding the colour of mudstones their relative abundances and the relative abundance of sandstones facies were further characterized from field study and published descriptions on the basis of sandbody geometry the types of nodules present in the mudstones and the abundance and geometry of carbonaceous mudstones this information helps to interpret the fluvial environments represented and types of alluvial palaeosols found in the willwood formation four facies have been distinguished the first facies is dominated by sheet sandbodies associated with immature palaeosols the sheets mark the locations of major channels which tend to occur in topographic lows the second facies is characterized by more mature moderately drained soils that required relatively lengthy periods of non deposition facies three and four dominantly consist of drab mudstones and abundant carbonaceous units both formed in poorly drained areas although minor red mudstones demonstrate that drainage conditions periodically improved in facies three facies four underwent prolonged saturation the geographical facies distribution suggests that east west faults previously mapped in the bighorn mountains extend westward into the bighorn basin and were active during early eocene time the lithological heterogeneity of the willwood formation rocks is attributed to warping associated with movement along these basement controlled faults fault activity created topographic gradients which influenced the position of major channel systems and helped produce variable drainage conditions that affected eocene soil development

new constraints on the motion of the fairweather fault alaska from gps observations 1 gps velocities from sites near to the fairweather fault in southern alaska are combined with line length data from geodetic surveys by the u s geological survey usgs to estimate the slip rate and locking depth of the fairweather fault using dislocation theory we perform a weighted least squares inversion of the geodetic data and obtain a best fitting slip rate of 45 6 2 0 mm yr and locking depth of 9 0 0 8 km the slip rate we estimate is one of the highest observed across any strike slip fault we also include the dalton creek segment of the denali fault in our model and estimate a slip rate of 3 8 1 4 mm yr for this section of the fault this is substantially lower than the rate observed for the denali fault segment to the northwest which ruptured in the november 3 2002 mw 7 9 denali fault earthquake

abrupt increase in greenland snow accumulation at the end of the younger dryas event the warming at the end of the last glaciation was characterized by a series of abrupt returns to glacial climate the best known of which is the younger dryas event1 despite much study of the causes of this event and the mechanisms by which it ended many questions remain unresolved1 oxygen isotope data from greenland ice cores2 4 suggest that the younger dryas ended abruptly over a period of about 50 years dust concentrations2 4 in these cores show an even more rapid transition 20 years this extremely short timescale places severe constraints on the mechanisms underlying the transition but dust concentrations can reflect subtle changes in atmospheric circulation which need not be associated with a large change in climate here we present results from a new greenland ice core gisp2 showing that snow accumulation doubled rapidly from the younger dryas event to the subsequent preboreal interval possibly in one to three years we also find that the accumulation rate change from the oldest dryas to the bo11ing allerod warm period was large and abrupt the extreme rapidity of these changes in a variable that directly represents regional climate implies that the events at the end of the last glaciation may have been responses to some kind of threshold or trigger in the north atlantic climate system

ice sheet variability around the north atlantic ocean during the last deglaciation millennial scale variability in the flux of ice rafted detritus to north atlantic sediments during the last glacial period has been interpreted to reflect a climate forced increase in the discharge of icebergs from ice sheet margins surrounding the northern north atlantic ocean 1 but the relationship between ice sheet variability and climate change is not clear as both the sources of ice rafted detritus and the ice marginal processes are varied and complex 2 4 terrestrial records are helpful in unravelling this complexity because they can demonstrate the scale of ice sheet oscillations and whether the ice sheet or sector was advancing or retreating with respect to climate change here we constrain the age and anatomy of a prominent readvance of the british ice sheet in the northern irish sea region at similar to 14 14 c kyr bp similar to 16 4 calendar kyr bp the analysis indicates that the british ice sheet participated in an iceberg discharge episode known as heinrich event 1 comparison with other terrestrial and marine ice sheet records suggests that the dynamic collapse of the laurentide ice sheet beginning at 14 6 15 0 c 14 kyr bp1 4 similar to 17 2 17 6 calendar kyr bp 5 initiated varied responses from other ice sheet margins around the northern north atlantic region these observations support the argument that the release of icebergs and meltwater during heinrich event 1 disrupted the north atlantic thermohaline circulation 6 8 leading to a delay or reversal of deglaciation of the northern hemisphere and at least as far south as 40 degrees s for two to three thousand years 5 9 10 suggesting a climate forcing and response similar to that of the ensuing younger dryas cold snap 11 12

the determination of displacement fields from geodetic data along a strike slip fault observations of angles or distances between stations of a geodetic network are commonly used to infer information about the movement of the surface of the earth the absence of any observations external to the network leads to an ambiguous displacement field existing techniques for eliminating this ambiguity are all unsatisfactory in some respect the best technique an inner coordinate solution is not appropriate for networks located in a strike slip fault environment the inner coordinate solution zeros the rotation of all stations about their center of mass along a strike slip fault like the san andreas however motion normal to the fault is less likely than motion parallel to the fault the solution presented here an outer coordinate solution finds the rotation of the network that minimizes the components of displacement normal to the fault since motion along a strike slip fault is generally expected to be parallel to the fault the displacements obtained with the outer coordinate solution are more reasonable than those obtained with other techniques examination of a trilateration network near san francisco bay demonstrates the large effect that the choice of adjustment technique can have on the inferred relative motion of the two sides of the fault the inner coordinate solution gave a rate of about 1 mm yr whereas the preferred outer coordinate solution rate was 36 mm yr

plate convergence and deformation north luzon ridge philippines abstract marine geophysical and earthquake seismology data indicate that the north luzon ridge a volcano capped bathymetrie ridge system that extends between luzon and taiwan is presently undergoing deformation in response to the relative motion between the asian and philippine sea plates plate motion models predict convergence along the western side of the philippine sea plate from japan in the north to indonesia in the south and most of this plate margin is defined by active subduction zones however the western boundary of the philippine sea plate adjacent to the north luzon ridge shows no evidence of an active wnw dipping subduction zone this is in marked contrast to the presence of both the philippine trench east luzon trough subduction zones to the south and the ryukyu trench subduction zone to the north crustal shortening in response to ongoing plate convergence in the north luzon ridge region apparently takes place through a complex pattern of strike slip and thrust faulting rather than by the typical subduction of oceanic lithosphere along a discreet zone the curvilinear bathymetrie trends within the north luzon ridge represent the traces of active faults the distribution of these faults mapped by both multichannel and single channel seismic reflection methods and earthquake seismicity patterns and focal mechanism solutions suggest that right lateral oblique slip faulting occurs along ne trending faults and left lateral oblique slip faulting takes place on n and nnw trending faults the relative plate convergence accommodated by the deformation of the north luzon ridge will probably be taken up in the future by the northward propagating east luzon trough subduction zone

holocene climatic instability a prominent widespread event 8200 yr ago the most prominent holocene climatic event in greenland ice core proxies with approximately half the amplitude of the younger dryas occurred 8000 to 8400 yr ago this holocene event affected regions well beyond the north atlantic basin as shown by synchronous increases in windblown chemical indicators together with a significant decrease in methane widespread proxy records from the tropics to the north polar regions show a short lived cool dry or windy event of similar age the spatial pattern of terrestrial and marine changes is similar to that of the younger dryas event suggesting a role for north atlantic thermohaline circulation possible forcings identified thus far for this holocene event are small consistent with recent model results indicating high sensitivity and strong linkages in the climatic system

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

detection of creep along the philippine fault first results of geodetic measurements on leyte island central philippine geodetic trilateration gps measurements were acquired from experiments conducted in 1991 and 1993 in the central part of the philippine fault on leyte island displacement vectors deduced from two least squares adjustments indicate a mean slip rate of 26 10 mm yr at an azimuth of about n130 e these values are consistent with the tectonic and kinematic data our results indicate that the displacements are 1 almost parallel to the philippine fault and 2 related to creep along the fault because no moderate seismic events occurred between the two observation epochs

late glacial allerod younger dryas buried organic deposits nova scotia canada a contribution to the north atlantic seaboard programme of igcp 253 termination of the pleistocene abstract numerous deposits of organic shallow pond sediments and wetland peat accumulations buried by minerogenic sediments have been discovered throughout nova scotia they are interpreted as representing a late glacial climatic oscillation correlative with the allerod younger dryas event of europe and the north atlantic ocean the organic deposits began forming during the warm or warming interval following deglaciation and often record a transition to colder conditions the climatic reversion recorded in many deposits began about 10 8 ka bp and continued or sustained cooling culminated in the burial of the organic deposits by minerogenic sediments indicative of solifluction and mass wasting processes some deposits provide strong evidence for regeneration or rejuvenation of local glaciers as the organic deposits are not as susceptible as lake sediments to contamination by old carbon they provide a more reliable chronological framework for deglaciation and late glacial vegetational history palynological evidence shows that pioneer herb tundra communities colonized some areas shortly after 13 ka bp willow and birch shrubs followed soon after spruce woodlands had migrated into the region prior to 10 8 ka bp but had not yet reached the northeast mainland and cape breton island cooling after 10 8 ka bp decimated tree populations and favoured a return to shrub and herb communities the record in the buried deposits was then truncated by deposition of minerogenic sediments and lake sediment sequences from deeper basins with continuous sedimentation are required to complete the record

abrupt climate oscillations during the last deglaciation in central north america evidence from stable isotopes and a variety of proxies from two ontario lakes demonstrate that many of the late glacial to early holocene events that are well known from the north atlantic seaboard such as the gerzensee killarney oscillation also known as the intra allerod cold period younger dryas and preboreal oscillation also occurred in central north america these results thus imply that climatic forcing acted in the same manner in both regions and that atmospheric circulation played an important role in the propagation of these events

wisconsinan late glacial environmental change in southern new england a regional synthesis a synthesis of vegetational and climatic history during the wisconsinan late glacial 13 9 ka bp is presented for the southern new england region the interpretations are based on a number of pollen stratigraphical investigations supported by plant macrofossil data chronology is based partly on ams dates of plant macrofossils reference is made briefly to the controversial nature of the evidence for deglaciation in the region a curve representing mean july temperature changes in the region during the period 13 9 ka bp is provided

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

variations of younger dryas atmospheric radiocarbon explicable without ocean circulation changes the concentration of radiocarbon 14c in the atmosphere depends on its production rate by cosmic rays and on the intensity of carbon exchange between the atmosphere and other reservoirs for example the deep oceans for the holocene the past 11 500 years it has been shown that fluctuations in atmospheric radiocarbon concentrations have been caused mostly by variations in the solar magnetic field1 2 3 recent progress in extending the radiocarbon record backwards in time4 5 6 7 8 9 10 has indicated especially high atmospheric radiocarbon concentrations in the younger dryas cold period between 12 700 and 11 500 years before the present these high concentrations have been interpreted as a result of a reduced exchange with the deep ocean reservoir caused by a drastic weakening of the deep ocean ventilation7 8 9 11 12 here we present a high resolution reconstruction of atmospheric radiocarbon concentrations derived from annually laminated sediments of two polish lakes lake go ciaz and lake perespilno these records indicate that the maximum in atmospheric radiocarbon concentrations in the early younger dryas was smaller than previously believed and might have been caused by variations in solar activity if so there is no indication that the deep ocean ventilation in the younger dryas was significantly different from today s

a multiproxy investigation of late glacial climate and vegetation change at pine ridge pond southwest new brunswick canada abstract pollen plant macrofossil chironomid and lithological analyses of late glacial sediment from pine ridge pond all indicate that the warming following deglaciation was punctuated on two separate occasions by a return to colder climes initially by a brief and moderate cold episode the killarney oscillation followed shortly by the younger dryas the killarney oscillation ams 14 c dated at between 11 290 and 10 960 yr b p is characterized by abrupt and simultaneous increases in betula birch pollen and betula glandulosa dwarf birch macrofossils and a decline in tree pollen the younger dryas is distinguished by the reversion of a short lived closed picea spruce forest to a prolonged forest tundra stage ca 10 820 to 9500 yr b p during which macrofossils of arctic alpine plants such as salix herbaces cassiope hypnoides armeria maritima and thalictrum alpinum make their sole late glacial appearance chironomid inferred summer surface water temperatures indicate a cooling of approximately 8 and 12 c during the killarney oscillation and younger dryas respectively and coarse sand analysis indicates increased erosion on the landscape during these same intervals

abrupt changes in north american climate during early holocene times recent studies of the greenland ice cores have offered many insights into holocene climatic dynamics at decadal to century timescales1 2 3 despite the abundance of continental records of holocene climate few have sufficient chronological control and sampling resolution to compare with the greenland findings4 butannually laminated sediments varves from lakes can provide high resolution continental palaeoclimate data with secure chronologies here we present analyses of varved sediments from deep lake in minnesota usa trends in the stable oxygen isotope composition of the sedimentary carbonate indicate a pronounced climate cooling from 8 9 to 8 3 kyr before present probably characterized by increased outbreaks of polar air decreased precipitation temperatures and a higher fraction of the annual precipitation falling as snow the abrupt onset of this climate reversal over several decades was probably caused by a reorganization of atmospheric circulation and cooling of the arctic airmass in summer that resulted from the final collapse of the laurentide ice near hudson bay and the discharge of icebergs from the quebec and keewatin centres into the tyrell sea the timing and duration of this climate reversal suggest that it is distinct from the prominent widespread cold snap that occurred 8 200 years ago in greenland and other regions1 5 6 no shifts in the oxygen isotope composition of sediment carbonate occurred at 8 2 kyr before present at deep lake but varve thickness increased dramatically probably as a result of increased deposition of aeolian dust taken together our data suggest that two separate regional scale climate reversals occurred between 9 000 and 8 000 years ago and that they were driven by different mechanisms

intensity gradients and reversals in late glacial environmental change in east central north america abstract radiocarbon dated pollen sites from the allegheny plateau east and the till plains west document significant vegetational and climatic change between 15 000 and 9000 14 c bp south of the great lakes although limited by the problems of no analog vegetation pollen transfer functions tf and response surfaces rs quantify the climatic changes including a cold oscillation chronologically equivalent to the european younger dryas phase i before ca 13 000 14 c bp conditions across the region were similar january 20 to 16 c july 12 c rs or 19 c tf mean annual precipitation 80 to 90 cm year 1 phase iia between ca 13 000 and 11 000 14 c bp n s and e w climate gradients were initiated till plains temperatures increased by ca 8 c in january and by 8 c rs or 2 3 c tf in july plateau increases for january were 3 6 c and for july were 8 c rs or 1 2 c tf precipitation generally increased somewhat phase iib ca 11 000 to 10 000 14 c bp gradients became less pronounced the western sites show a climate reversal january drop of ca 5 to 2 c july drop to ca 1 2 c becoming more like the plateau sites which show a brief small fluctuation this is followed by an abrupt 10 to 20 cm year 1 reduction in precipitation january warming of ca 3 c and continued cooler julys phase iii after 10 000 14 c bp gradients similar to those of today developed the changes in phases iib and iii are probably linked to the drainage history of the great lakes and via that history to the changes on the european continent

allerod younger dryas lake temperatures from midge fossils in atlantic canada remains of freshwater midges are abundant in lake sediments and their species distributions are closely related to the surface water temperature of lakes their distributions thus provide a powerful tool for paleoclimatology the distribution of species in a core from splan pond in atlantic canada indicates that there were abrupt transitions in late glacial temperatures between warm and cold states the transitions are correlative with the well known warm allerod and cold younger dryas events in europe these data thus confirm the inference from palynological data that these events affected regions on both sides of the atlantic

geodetic constraints on coseismic rupture during the 1990 ms 7 8 luzon philippines earthquake 1 we analyze single frequency gps measurements taken before and after the july 16 1990 ms 7 8 luzon earthquake to constrain the faulting parameters of this major strike slip event the geodetic data imply fairly uniform left lateral slip of 5 5 6 5 m along the well mapped part of the fault trace in agreement with field mapping of the rupture and in general accord with seismological estimates of the fault parameters in addition we find that substantial slip of about 4 5 m magnitude continued about 40 50 km northward or northwestward into the cordillera central beyond the end of the mapped rupture this fault segment includes a substantial thrust component in addition to left lateral slip the geodetic data favor a faulting depth of at least 20 km along the central part of the rupture unusually deep for a major continental strike slip earthquake

timing is everything in a game of two hemispheres what causes ice ages and other episodes of violent climate change one clue comes from a new study of ice cores which unexpectedly seems to show rapid warming events happening first in the southern hemisphere

climatic effects of glacial lake agassiz in the midwestern united states during the last deglaciation stable isotope and pollen analyses of a sediment core from deep lake minnesota provide new information on the climatic effects of glacial lake agassiz in minnesota and insights into the cause of the prominent picea recurrence during the younger dryas in the southern great lakes region bulk carbonate 18o exhibited large fluctuations between 12 0 and 9 1 ka dates are in calendar years throughout this paper unless indicated otherwise probably reflecting the effects of glacial lake agassiz superimposed on climatic warming related to large scale climatic controls in particular a 3 decrease in 18o 11 2 10 2 ka interrupted the 18o enrichment of 1 from 12 0 to 11 2 ka and 3 5 from 10 2 to 9 1 ka this 18o decrease coincided with the expansion of lake agassiz we interpret this decrease as a result of decreased summer temperature and increased precipitation derived from the cold and isotopically light meltwaters of lake agassiz during this 18o decline pinus pollen continued to increase at the expense of picea pollen at deep lake as at other minnesota sites providing evidence that climatic cooling induced by lake agassiz did not cause a reversal to a picea dominated vegetation the absence of such a vegetational response implies that the prominent picea recurrence during the younger dryas in the southern great lakes region was not caused solely by climatic cooling due to increased flux of meltwater from lake agassiz into the great lakes instead the picea recurrence might have been driven primarily by the westward penetration of the younger dryas cooling

irregular glacial interstadials recorded in a new greenland ice core the greenland ice sheet offers the most favourable conditions in the northern hemisphere for obtaining high resolution continuous time series of climate related parameters profiles of 18o 16o ratio along three previous deep greenland ice cores1 3 seemed to reveal irregular but well defined episodes of relatively mild climate conditions interstadials during the mid and late parts of the last glaciation but there has been some doubt as to whether the shifts in oxygen isotope ratio were genuine representations of changes in climate rather than artefacts due to disturbed stratification here we present results from a new deep ice core drilled at the summit of the greenland ice sheet where the depositional environ ment and the flow pattern of the ice are close to ideal for core recovery and analysis the results reproduce the previous findings to such a degree that the existence of the interstadial episodes can no longer be in doubt according to a preliminary timescale based on stratigraphic studies the interstadials lasted from 500 to 2 000 years and their irregular occurrence suggests complexity in the behaviour of the north atlantic ocean circulation

lateglacial environmental changes in the netherlands spatial and temporal patterns a contribution to the north atlantic seaboard programme of igcp 253 termination of the pleistocene abstract the history of vegetational changes during the weichselian lateglacial in the netherlands is based primarily on pollen records derived from lacustrine sediments they provide a fairly consistent picture of progressive followed by retrogressive vegetation succession through time problems arise however when we try to match pollen records obtained from terrestrial peat sequences with those obtained from lacustrine deposits this is especially the case at around about 12 000 bp conditions seem to have varied significantly depending on the geomorphological position of individual site terrestrial sites are more prone to hiatuses in response to episodes of pronounced reductions in effective precipitation the spread of pinus from ca 11 300 bp which has been interpreted traditionally as a successive phase in vegetational development coincides with changes in the local vegetation that indicate more intense freeze thaw conditions more continental conditions are assumed implying more severe winters by comparison with the preceding time interval at ca 10 850 bp both vegetation and coleopteran evidence indicate a distinct drop in the average july temperature from 18 15 c to 11 10 c consequently the mean annual temperature was also lowered estimated to between 2 and 5 c and conditions approximated those of permafrost environments simultaneously effective precipitation increased considerably resulting in a pronounced rise in lake levels and large scale floodings of rivers soon after at ca 10 500 bp summer temperatures appear to have risen while effective precipitation declined considerably resulting in a fall in lake levels and periodic exposure of river beds which provided sources for the accumulation of large inland dunes

effects of lichens on the reflectance spectra of granitic rock surfaces abstract the objective of this study was to determine the effect of lichen cover on the spectral reflectance characteristics of granitic rocks rock samples collected from bedrock exposures and talus slopes were granodiorite tonalite granite and quartz diorite the lichens found on these rocks varied in color i e black dark brown medium gray olive green yellow green green orange and orange red the visible and near infrared reflectance spectra 400 1100 nm of the rock and lichen samples show that lichens can affect the rock s spectra these changes are dependent on the reflectance contrast between the rock surface and the lichen covering

crustal motion and block behaviour in se asia from gps measurements results acquired using global positioning system gps data taken over a large part of se asia indicate that sundaland i e indochina along with the western and central part of indonesia constitutes a stable tectonic block moving approximately east with respect to eurasia at a velocity of 12 3 mm yr 31 with respect to india and australia this block moves due south significant motion has not been detected along the northern boundary to south china i e along the red river fault whereas nearly 50 mm yr 31 of right lateral motion has to be accommodated between india and sundaland in the andaman burma region fl 2001 elsevier science b v all rights reserved

use of landsat multispectral scanner data for the definition of limonitic exposures in heavily vegetated areas digital enhancement techniques were found to be ineffective for defining exposed limonite in a landsat scene covering the heavily vegetated butte and dillon montana idaho area use of statistical by derived mixing models has shown that maximum separability between limonitic rocks and vegetation can be accomplished through the use of a compound 4 5 6 7 ratio this ratio utilizes the spectral information present in all four mss bands and is particularly sensitive to the spectral contrasts between nonlimonitic rocks limonitic rocks and vegetation modified journal abstract

stratigraphy and paleolimnologic record of lower holocene sediments in northern lake huron and georgian bay seismic reflection profiling and piston coring identified seismic reflectors in northern lake huron and georgian bay linked with unconformities caused by at least six reductions in lake level in ascending stratigraphic order these lowstands occurred at about 11 200 bp associated with the kirkfield outlet from early lake algonquin 10 200 9900 bp associated with the post algonquin lake level fall 9800 9050 bp the most extreme lowstand associated with the main stanley hough draw down and 7800 7450 bp the concomitant highstands are lake algonquin from about 11 200 10 200 bp early lake mattawa between 9600 and 9350 bp the main mattawa phase 9050 7800 bp and the nipissing highstand at about 4700 bp isotopic and paleoecological data show that all of the lowstands are characterized by cold dilute and isotopically very light 20 waters from the melting laurentian ice cap highstands on the other hand are characterized by higher dissolved solid concentrations and a much smaller

late weichselian environmental change in southern sweden and denmark a synthesis is presented of the envronmental and climatic variations that are inferred to have occurred in southern sweden up to latitude 59 n and denmark during the weichselian late glacial 14 9 ka bp the chronology and characteristics of the main phases of deglaciation sea level change periglacial activity soil development vegetation cover and climate change are summarised a curve representing the main changes in temperature including quantitative estimates based upon beetle data and using the mutual climatic range method is presented

sudden changes in north atlantic circulation during the last deglaciation sudden changes in the flow of warm atlantic surface waters into the norwegian sea occurred frequently during the last deglaciation typically involving shifts in sea surface temperature of 5 c in fewer than 40 years these led to equally large and rapid changes in atmospheric temperatures and to shifts in atlantic deep thermo haline circulation and ice sheet melting rates

the relationship between seismic and aseismic slip on the philippine fault on leyte island bayesian modeling of fault slip and geothermal subsidence delineating seismic and aseismic slip on faults allows the exploration of the complex relationship between these different modes of slip further quantifying them helps in the assessment of seismogenic potential we present a distributed slip model of the rate of aseismic slip along the leyte island section of the philippine fault and make comparisons with the extent of seismic slip from the latest significant earthquakes in july 2017 we derived both coseismic and aseismic slip distributions from kinematic inversions of synthetic aperture radar interferometric insar observations using a probabilistic bayesian framework velocity maps from stacking and time series analysis of alos interferograms spanning 4 years 2007 2011 show a step change in ground deformation right on the fault inverting for slip at depth reveals along strike variations of aseismic slip rate over 100 km aseismic slip on the surface reaches rates of more than 3 cm yr equivalent to the long term slip rate 3 3 0 2 cm yr over the same period a 20 km segment in tongonan appears to be locked this segment ruptured in mw 6 5 and mw 5 8 earthquakes on 6 and 10 july 2017 respectively as constrained by sentinel 1 and alos 2 insar data seismic slip appears to be restricted within the tongonan segment with up to 152 21 cm of left lateral displacement the slip budget and complementarity between the extents of interseismic and coseismic slip suggest that a seismogenic asperity exists in tongonan the presence of active hydrothermal systems and rate strengthening materials provide physical conditions that can promote aseismic slip

philippine fault a key for philippine kinematics on the basis of new geologic data and a kinematic analysis we establish a simple kinematic model in which the motion between the philippine sea plate and eurasia is distributed on two boundaries the philippine trench and the philippine fault this model predicts a velocity of 2 to 2 5 cm yr along the fault geologic data from the visayas provide an age of 2 to 4 ma for the fault an age in good agreement with the date of the beginning of subduction in the philippine trench the origin of the philippine fault would thus be the flip of subduction from west to east after the locking of convergence to the west by the collision of the philippine mobile belt with the eurasian margin

earthquake deformation cycle on the san andreas fault near parkfield california six moderate earthquakes are thought to have ruptured the parkfield segment of the san andreas fault since 1857 the similar characteristics of the three seismically recorded events together with the quasi regular 22 year recurrence interval have led to the forecast of a similar event in 1988 5 years in this study the potential for the hypothesized earthquake is assessed by estimating the time required for interseismic straining to recover the strain energy released by the most recent june 1966 parkfield earthquake for a simple model of the earthquake cycle this interval is proportional to the ratio of the 1966 seismic moment to the interseismic moment deficit rate baseline lengths measured before and after the 1966 earthquake are inverted to estimate the magnitude and distribution of the combined coseismic and transient postseismic slip although the geodetic data determine only broad spatial averages of the fault slip they do require that slip at depth exceeded the surface offsets measured in 1966 inversions with extreme prior models are calculated to assess the range of seismic moment and moment deficit rates consistent with the available geodetic data inversions assuming only that the slip distributions are to some degree smooth yield strain energy recovery intervals of 14 25 years extreme values range from as little as 6 years to as much as 29 years in comparison historic recurrence intervals of parkfield earthquakes range from 12 to 32 years these results are consistent with the expectation of a magnitude 5 6 earthquake near parkfield by 1993

evidence for massive discharges of icebergs into the north atlantic ocean during the last glacial period sediments in the north atlantic ocean contain a series of layers that are rich in ice rafted debris and unusually poor in foraminifera1 here we present evidence that the most recent six of these heinrich layers deposited between 14 000 and 70 000 years ago record marked decreases in sea surface temperature and salinity decreases in the flux of planktonic foraminifera to the sediments and short lived massive discharges of icebergs originating in eastern canada the path of the icebergs clearly marked by the presence of ice rafted detrital carbonate can be traced for more than 3 000 km a remarkable distance attesting to extreme cooling of surface waters and enormous amounts of drifting ice the cause of these extreme events is puzzling they may reflect repeated rapid advances of the laurentide ice sheet perhaps associated with reductions in air temperatures yet temperature records from greenland ice cores appear to exhibit only a weak corresponding signal moreover the 5 10 000 yr intervals between the events are inconsistent with milankovitch orbital periodicities raising the question of what the ultimate cause of the postulated cooling may have been

analysis of crustal deformation in luzon philippines using geodetic observations and earthquake focal mechanisms we utilize regional gps velocities from luzon philippines with focal mechanism data from the harvard centroid moment tensor cmt catalog to constrain tectonic deformation in the complex plate boundary zone between the philippine sea plate and eurasia the sundaland block processed satellite imagery and digital elevation models are used with existing gravity anomaly seismicity and geologic maps to define a suite of six elastic blocks geodetic and focal mechanism data are inverted simultaneously to estimate plate rotations and fault locking parameters for each of the tectonic blocks and faults comprising luzon major tectonic structures that were found to absorb the plate convergence include the manila trench 20 100 mm yr 1 and east luzon trough 9 15 mm yr 1 philippine trench 29 34 mm yr 1 which accommodate eastward and westward subduction beneath luzon respectively the left lateral strike slip philippine fault 20 40 mm yr 1 and its northward extensions the northern cordillera fault 17 37 mm yr 1 transtension and the digdig fault 17 27 mm yr 1 transpression the macolod corridor a zone of active volcanism crustal thinning extension and extensive normal and strike slip faulting in southwestern luzon is associated with left lateral transtensional slip of 5 10 mm yr 1 the marikina fault which separates the central luzon block from the southwestern luzon block reveals 10 12 mm yr 1 of left lateral transpression our analysis suggests that much of the philippine fault and associated splays are locked to partly coupled while the manila and philippine trenches appear to be poorly coupled luzon is best characterized as a tectonically active plate boundary zone comprising six mobile elastic tectonic blocks between two active subduction zones the philippine fault and associated intra arc faults accommodate much of the trenchparallel component of relative plate motion 2006 elsevier b v all rights reserved