neogene caribbean plate rotation and associated central american tectonic evolution during the neogene the caribbean plate moved eastward with respect to the north and south american plates reconstructing this motion by closing the cayman trough along its bounding transform faults creates a gore of ocean between northern central america and southern mexico we present instead a reconstruction which juxtaposes these two continental areas by strike slip motion using geological evidence from around the cayman trough the strike slip fault zones of northern central america and the continental margin of southern mexico as our constraints we propose that seafloor spreading began in the cayman trough at 30 5 ma and that subsequently there was 1100 km of relative plate displacement at an average rate of 3 7 0 6 cm yr this neogene plate motion cannot be achieved by rigid plate rotation about a single pole which implies that central america must have rotated anticlockwise relative to the rest of the plate there is evidence for internal plate deformation in central america consistent with such a sense of rotation our suggestion of an originally easterly trending arc in southern central america is more consistent with the timing and geometry of the collision of panama with northern colombia and the resultant deformation than were earlier models that depicted collision of a northerly trending arc

the apparent effects of the mt pinatubo eruption on the greenland ice sheet melt extent the indirect climatological effects of major volcanic eruptions can be of great importance because of the complex feedbacks that exist in the global climate system one such effect is the melt area reduction on the greenland ice sheet using passive microwave satellite data for the period 1979 1995 the melt conditions of the ice sheet before and after the 1991 mt pinatubo eruptions are examined statistical tests indicate that an observed drop following the eruptions has a 97 to 99 probability of being outside the limits of undisturbed variability furthermore this anomaly diminishes as the time from the eruption increases these characteristics in conjunction with an observed increasing melt trend prior to the eruptions indicate that mt pinatubo has had a significant effect on the melt conditions and consequently the energy balance characteristics of the greenland ice sheet

two phytoplankton blooms near luzon strait generated by lingering typhoon parma two phytoplankton blooms near luzon strait triggered by typhoon parma in 2009 were investigated using remote sensing data and in situ observations parma was slow moving a translation speed of similar to 2ms 1 and relatively weak a maximum sustained wind of similar to 30ms 1 during its lingering path northwest of luzon island after it reached a point 120 5 degrees e 20 3 degrees n west of luzon strait parma turned sharply back toward the northern philippines along approximately the same course such long similar to 7days lingering typhoons are rather rare in the south china sea scs before parma low chl a concentrations 0 6mgm 3 appeared west of the central luzon strait a nearshore phytoplankton increase was also observed north of luzon island together with high cdom color dissolved organic matter during and after the typhoon sea surface cooling similar to 3 degrees c stronger wind 20ms 1 and heavy rainfall 100mmday 1 were seen in the above regions the offshore bloom occurred where parma s translation speed was the slowest similar to 1ms 1 it may be caused primarily by the ekman pumping which brought nutrients upward to the euphotic zone and also by the entrainment mixing the nearshore bloom may be triggered by the heavy typhoon induced rainfall which supplied nutrients for the coast region north of luzon island the rapid increase of cdom in the nearshore region implied that terrestrial input may be the source of nutrients

an alternative interpretation of the cayman trough evolution from a reidentification of magnetic anomalies magnetic data were collected during the wilkes 1973 and seacarib ii 1987 cruises to the cayman trough a new interpretation of magnetic data is carried out an isochron pattern is drawn up from our anomaly identifications an early eocene age 49 ma ypresian for cayman trough opening is proposed instead of the late oligocene or middle eocene ages suggested by previous studies our plate tectonic reconstruction is simpler and fits the on land geology jamaica and cuba and the tectonics our reconstruction shows a southward propagation of the spreading centre between magnetic anomalies 8 and 6 26 and 20 ma the trough width increases by 30 km in this period the southward propagation of the cayman spreading centre from the middle oligocene to the early miocene induced the development of the restraining bend of the swan islands the formation of a 1 km high scarp on the eastern trace of the cayman trough transform fault walton fault and the formation of a pull apart basin hendrix pull apart magnetic anomalies and magnetization maps give information about the deformation and the rocks the proposed evolutionary model of the cayman trough from the inception of seafloor spreading to the present configuration is presented in relation to the tectonic escape of the northern boundary of the caribbean plate from the maastrichtian to the present

structural and tectonic evolution of the eastern cayman trough caribbean sea from seismic reflection data the eastern cayman trough preserves a record of the late cretaceous to paleogene caribbean history that is largely affected by neogene strike slip tectonics of the current plate boundary we conducted an analysis of seismic data within the eastern cayman trough based upon single and multichannel seismic reflection profiles collected during the seacarib ii cruise in 1987 and the casis cruise in 1992 these data show that the basement of the eastern cayman trough can be divided into four domains from east to west with distinct morphologic and sedimentary character and inferred older to younger ages 1 a province of rifted mesozoic continental crust exhibiting seven parallel horst blocks striking northeast southwest 2 a continent ocean transition bet een provinces 1 and 3 that exhibits seamounts small hills and sedimentary basins 3 an eocene oceanic crust with rough basement but smoother relief than the rifted crust basement trends are roughly north south and oblique to the northwest trend in domain 1 and 4 the northern jamaica slope which forms an east west trending slope with northward dipping strata that flank the three deeper water domains of the cayman trough the domains are interpreted to be the product of the eocene east west opening of the cayman trough as a pull apart basin in a left lateral strike slip setting closure of the 1100 km of eocene and younger oceanic crust of the cayman trough places the fault block province adjacent to the belize margin of central america restoration of normal faults in the fault block province places an additional 190 km of left lateral offset along the cayman trough a neogene phase of transpression has reactivated structures in the four domains along with on land structures described by previous authors in jamaica the proximity of the eastern margin of the cayman trough to petroliferous continental rocks in central america suggests an improved possibility of hydrocarbon potential unfortunately s diment thicknesses of less than 1 km probably are not conducive to hydrocarbon formation

numerical simulations of tropical cyclone ocean interaction with a high resolution coupled model the tropical cyclone ocean interaction was investigated using a high resolution tropical cyclone ocean coupled model the model design consisted of the noaa geophysical fluid dynamics laboratory tropical cyclone prediction model which was coupled with a multilayer primitive equation ocean model coupling between the hurricane and the ocean models was carried out by passing into the ocean model the wind stress heat and moisture fluxes computed in the hurricane model the new sea surface temperature sst calculated by the ocean model was then used in the tropical cyclone model a set of idealized numerical experiments were performed in which a tropical cyclone vortex was embedded in both easterly and westerly basic flows of 2 5 5 and 7 5 m s 1 with a fourth experiment run with no basic flow specified initially the profile of the tangential wind for hurricane gloria at 1200 utc 22 september 1985 was used as the initial condition of the tropical cyclone for each of the experiments the model ocean was initially horizontally homogenous and quiescent to clarify the impact of the ocean response to the hurricane s behavior analogous experiments were also carried out with the sst kept constant control cases the experiments indicated that the cooling of the sea surface induced by the tropical cyclone resulted in a significant impact on the ultimate storm intensity due to the reduction of total heat flux directed into the tropical cyclone above the regions of decreased sst the sea surface cooling produced by the tropical cyclones was found to be larger when the storms moved slower in the experiments run without an initial basic flow the maximum sst anomaly was about 5 6 c with a resulting difference in the minimum sea level pressure and maximum surface winds of 16 4 hpa and 7 m s 1 respectively in contrast in the experiments run with the 7 5 m s 1 basic flow the maximum sst anomalies ranged from about 2 6 to 3 0 c with a difference in the minimum sea level pressure and maximum surface winds of about 7 3 hpa and 2 7 m s 1 the tropical cyclone ocean coupling significantly influenced the storm track only for the case with no basic flow and the 2 5 m s 1 easterly flow in these cases the storm with the ocean interaction turned more to the north and east no basic flow or the north 2 5 m s 1 easterly flow of the experiments with constant sst in the first case the storm by 72 hours was located over 70 km to the east southeast of the control case a possible explanation for this track deviation is related to a systematic weakening of the mean tangential flow at all radii of the storm due to the interaction with the ocean and resulting alteration of the beta drift

detection of snowmelt regions on the greenland ice sheet using diurnal backscatter change snowmelt regions on greenland ice are mapped daily with the seawinds wideswath ku band 13 4 ghz scatterometer on the quikscat satellite the approach exploits the high temporal resolution of seawinds quikscat data for the melt mapping using diurnal backscatter change independent of the absolute calibration the results reveal several pronounced melting and refreezing events and effects of topography are evident in the melt patterns the spatial resolution is sufficient to identify melt features on the sukker toppen iskappe west of the main ice sheet an anomalous warming event caused by downward mixing of warm air is detected in late september 1999 over the west flank of the southern greenland ice sheet time series images of melt regions are presented over the period from summer to the fall freeze up the satellite observations are verified with in situ measurements from the greenland climate network stations

measurement and parameterization of albedo variations at haut glacier d arolla switzerland spatial and temporal variations of surface albedo on haut glacier d arolla switzerland during the 1993 and 1994 ablation seasons are described correlation and regression analyses are used to explain the albedo variations in terms of independent meteorological and surface property variables parameterizations are developed which allow estimation of albedo variation in surface energy balance models snow albedo is best estimated from accumulated daily maximum temperatures since snowfall on deep snow 0 5 cm w e depth a logarithmic function is used while on shallow snow 0 5 cm w e depth an exponential function is used to enable the albedo to decay to the underlying ice or debris albedo the transition from deep to shallow snow is calculated as a function of decreasing snow depth combined r 2 0 65 this new parameterization performs better than earlier schemes because accumulated daily maximum temperatures since snowfall correlate strongly with snow grain size and impurity concentration the main physical controls on snow albedo ice albedo may be parameterized by its relationship to elevation r 2 0 28 but this approach results in only a small improvement over the assumption of a constant mean ice albedo

geologic evaluation of plate kinematic models for the north american caribbean plate boundary zone heubeck ch and mann p 1991 geologic evaluation of plate kinematic models for the north american caribbean plate boundary zone tectonophysics 191 l 26 four published plate kinematic models for the present day north american caribbean plate boundary predict significantly different fault behavior along this dominantly strike slip plate boundary zone pbz using a computer graphics system we compare the deformational pattern predicted by the four kinematic models with geologic and seismic observations along the entire length of the pbz from central america to the northern lesser antilles our results indicate that none of the kinematic models predict all the geologic and seismic observations across the entire pbz however all four models predict mapped fault character and observed earthquake focal mechanisms along certain segments of the pbz we conclude that the present day deformation within the north american caribbean plate boundary zone cannot be described by rotation about a single pole instead the caribbean plate appears to be segmented into at least three major sub plates or blocks each of which requires an individual pole of rotation to describe its motion relative to the north american plate sub plate boundaries correspond to two poorly studied zones of diffuse deformation within the caribbean plate honduras depression of central america and beata ridge of the caribbean sea

time of sinistral slip along the polochic fault of guatemala abstract the polochic fault of guatemala and chiapas mexico was a neogene transform segment of the north american caribbean plate boundary with a total sinistral slip of 130 km principal activity was within the interval from about 10 3 to 6 6 m y b p or less a time bracket based upon k ar ages from volcanic rock clasts in the colotenango beds of northwest guatemala earliest possible movement was established from ages of volcanic rock constituents of the older colotenango conglomerates deposited by streams that flowed north from a terrane now in central guatemala and onto terrane that was subsequently offset along the polochic fault it is believed that the selegua river was connected to the chixoy river of central guatemala this river system deposited the older part of the colotenango conglomerate now in western guatemala about 130 km west of its source area two volcanic clasts from the conglomerate yield ages of 12 3 1 0 and 10 3 1 0 m y the younger age is believed to set the maximum age of sedimentation of this older part of the conglomerate and is probably close in time to initiation of fault activity distinctive brown serpentinite clasts in the conglomerate have been shown to be petrographically mineralogically and geochemically similar to serpentinite from the presumed source area north of salama guatemala a youngest age of major offset is established by the younger part of the colotenango beds a volcaniclastic deposit which fills much of the ancient polochic fault controlled cuilco river valley our studies of volcanic clasts of the younger colotenango conglomerate reveal pristine glass attesting to its relatively young age k ar determination establishes an age of 6 6 0 3 m y b p for these clasts the youngest age of movement has not been established with certainty it lies between the 6 6 m y age and the age of the uppermost volcaniclastic valley fill the synchroneity of spreading in the cayman trough macdonald and holcombe 1978 with transform activity along the polochic suggests strongly that the two were genetically related the earliest data in the bracketed time interval correlates with the age of ongoing spreading for the mid cayman rise the mid miocene to pliocene volcanic arc 9 19 m y b p of mexico and its probable continuation in guatemala 8 19 m y b p sinistrally offset across the polochic fits well with the chronology discussed above for the polochic

on the response of the ocean to a moving storm the nonlinear dynamics abstract a novel and efficient numerical method is used to investigate the nonlinear equations of motion for the upper layer of a two layer ocean in which the lower layer is infinitely deep and at rest the efficiency is achieved by seeking solutions that are in a steady state translating in equilibrium with the storm oscillations are found in the wake of the storm two features of the response are attributed to the nonlinear terms in the equation of motion 1 a rapid transition from a maximum in the downwelling phase to a maximum in the upwelling phase of each oscillation followed by a gradual relaxation to the next downwelling maximum and 2 a displacement of the maximum response usually to the right of the storm track by 40 km it is shown that the horizontal pressure gradient terms can be neglected from the momentum equations for fast large storms in which case a lagrangian integration can be performed following fluid particles this enables feature 1 to be attributed to the along tra

neotectonic evolution of the isthmus of tehuantepec southeastern mexico abstract the isthmus of tehuantepec of southeastern mexico is located near the triple junction of the north american cocos and caribbean plates a neotectonic study including fault tectonic analysis and study of sub surface data was performed in order to understand the tectonic evolution of this complex zone the plio quaternary fault pattern is described and the brittle structures are interpreted in terms of palaeostress orientations we propose a model of tectonic evolution of the isthmus of tehuantepec since the late miocene 6 ma characterized by extensional tectonics the present structure of the isthmus results from the superimposition of three distinct types of tectonism 1 a tilting of the eastern isthmus during the late miocene early pliocene along a major n s trending normal fault zone the isthmus fault zone as a consequence of the deformation of the subducting slab of the cocos plate along the subducted part of the tehuantepec fracture zone 2 the subsidence of the southern isthmus in relation to n s extension associated with the eastward displacement of the western caribbean plate with respect to the southern north american plate along the polochic motagua fault system and 3 extensions that develop in the northern half of the isthmus related to the evolution of the passive margin of the gulf of mexico

seismic stratigraphic evidence for glacial expanse during glacial maxima in the yakutat bay region gulf of alaska 1 modern shelf bathymetry bordering the gulf of alaska exhibits shelf crossing sea valleys that suggest focused pathways for ice flow during glacial conditions using an integrated seismic data set between the present yakutat and alsek sea valleys we investigate the glacial stratigraphic record in order to improve our understanding of the regional glacial system during maximum glacial conditions our investigations reveal four glacial unconformities of which the latter two are overlain by sediment packages hundreds of meters thick we suggest that these unconformities are indicative of ice advance phases during the little ice age lia the last glacial maxima lgm and two pre lgm advances with glacial retreat sequences preserved from the youngest two the advances were dominated by ice expanse from the malaspina glacial system and alsek river districts rather than the hubbard glacial system and only show distinctive morainal bank development near the shelf edge and near the mouth of or within modern bays fjords or river valleys this observation strongly supports rapid and continuous retreat from glacial maxima conditions during climatic warming all except the inferred lia sequence transgress the shelf and exhibit concentrated erosion in overdeepened troughs analogous to cross shelf troughs similar to those observed on other high latitude glaciated shelves the two alaskan troughs discussed here may be end member examples of high sediment flux systems due to the temperate glacial setting combined with an actively exhuming orogen

rotation of the chortis block causes dextral slip on the guayape fault the chortis block is undergoing deformation as a direct result of large magnitude sinistral strike slip faulting on the north america caribbean plate boundary we have studied the chortis block using geologic mapping remote imagery and earthquake seismology to evaluate the effect that large magnitude strike slip faulting has on an adjacent microcontinental block in the eastern part of the chortis block recent geologic mapping has shown that the northeast striking guayape fault is dextral instead of sinistral as previously assumed because this is a major fault that cuts most of the central america isthmus the new evidence for dextral slip necessitates a reinterpretation of the active tectonics of the chortis block the presence of several north trending rifts in the western part of the chortis block has led previous workers to propose that the chortis block is divided into smaller independently rotating blocks we use earthquake seismology and remote imagery data to extend this interpretation to the central portion of the chortis block however we have modified their model to account for dextral slip on the guayape fault we believe that rotation of the chortis block causes dextral slip on the guayape fault even though central america is undergoing large sinistral displacement with respect to north america

earthquakes of the holocene geologic studies of earthquakes involve mapping of coseismic surface faulting and secondary deformation from historical events trenching and geomorphic analysis to define the timing and size of past earthquakes and investigations of fault zone structure and geometry in both unconsolidated sediments and bedrock this research is now being referred to as paleoseismology seismic geology and earthquake geology since the mid 1970s it has led to some of the most exciting and important contributions to the understanding of earthquake behavior in space and time hanks 1985 allen 1986 the present report is the first of what is hoped will become a regularly contributed summary of the geologic aspects of the study of earthquakes

response of sea surface properties to hurricane dennis in the eastern gulf of mexico 1 sea surface reflectance ssr and sea surface temperature sst were assessed in the eastern gulf of mexico in early july 2005 after passage of hurricane dennis a category 4 storm using data from the modis seawifs and avhrr satellite sensors historical hydrographic and nutrient surveys and a simple vertical water column mixing model the bathymetric gradient across the shelf break the offshore deep nutricline and nearby loop current eddies led to unique ssr and sst changes after the passage of dennis in waters shallower than 50 m a strong sediment resuspension event led to higher ssr in the visible and an increase in the modis fluorescence line height flh these variables returned to pre storm conditions after about 10 days the flh change indicates increasing biomass in the short response time 50 m deep cooled down significantly but there was no apparent change in ssr presumably because the nutricline was too deep to be affected by vertical mixing due to the storm the three dimensional hydrographic and nutrient structure in waters near the west florida shelf defines what changes may be detected at the surface with remote sensing

beyond the motagua and polochic faults active strike slip faulting along the western north america caribbean plate boundary zone abstract i investigate the role of two strike slip faults in the tectonics of the western north america caribbean plate margin the ixcan fault located in guatemala north of the polochic fault is seismically active with earthquakes of magnitude up to 5 7 reported recently fault plane solutions along this curvilinear but generally e w trending fault indicate left lateral strike slip displacement several historic earthquakes appear to have taken place along the ixcan fault since 1728 the largest one being the 1816 event m 7 5 the nw se trending concordia fault in southeastern mexico appears to be the site of the great m 7 6 earthquake of 1902 isoseismals for this event suggest shallow left lateral strike slip faulting i propose a seismotectonic model in which both faults are part of the deformation associated to the north america caribbean plate boundary zone transpressive structures are found in the fault steps between strike slip fault systems

depth and age in the cayman trough abstract caribbean plate boundaries are almost everywhere either strike slip or convergent so oceanic crust accreted at the spreading axis within the cayman trough provides information critical to determining the relative motions and tectonic interactions among the caribbean and surrounding plates the tectonic evolution of the trough as inferred from magnetic anomaly identifications is not entirely compatible with either its crustal subsidence or the geological evidence for time of opening and rate of offset movement along the north american caribbean plate boundary a close examination of basement topography and depth within the trough suggests that the total opening of the cayman trough is about 1100 km and that this opening occurred in two stages crust generated by the present ongoing stage of very slow spreading has extensive relief and shows a distinct increase of crustal depth with increasing distance from the spreading center crust generated by an earlier episode of faster spreading is characterized by reduced topographic relief and no appreciable differential subsidence and is separated from the younger crust by distinct topographic breaks the rate of spreading of the current slow spreading episode is15 5mm yr based upon a new crustal subsidence curve which accommodates lateral as well as vertical cooling of the accreting slab the trough has opened at this rate for about 30 ma the rate of opening prior to 30 ma cannot be determined with any reliability from crustal subsidence a reexamination of magnetic anomalies in the central part of the trough shows that these anomalies can be generated at a much slower spreading rate than previously thought this revised interpretation of cayman trough evolution brings magnetic subsidence and geological evidence into much better agreement

a three dimensional numerical simulation of typhoon holly in the northwestern pacific ocean 1 a three dimensional primitive equation model the princeton ocean model often called pom has been implemented for simulating typhoon holly generated in the tropical pacific ocean this is the first time that a study of this type previously used mostly for coastal regional simulations has been implemented for the northwestern pacific ocean from 24 n to 52 n including the east china sea the yellow sea and the east japan sea in the open ocean the model circulation sea surface elevation and temperature distribution with the passage of holly are described the results are in part compared with observation in the korea tsushima strait the model reproduces well several prominent features obtained in the observation such as a rapid increase of temperature in the korea strait during the passage of typhoon holly in august 1984 and reasonably explains how they happened around the vicinity of the typhoon center the model temperature field successfully presents sea surface cooling in the open ocean having been frequently observed in the past the model also suggests that a coastal jet around the korea strait and a cyclonic eddy field behind holly in the east china sea play an important role in the oceanic conditions although they have not yet been identified by observations

radiative fluxes and their impact on the energy balance of the greenland ice sheet a meteorological experiment was carried out during the summer months of 1990 and 1991 near the mean equilibrium line altitude ela on the western slope of the greenland ice sheet eth camp 69 34 n 49 17 w 1155 m a s l as a part of the project the energy fluxes at the surface including all components of the radiation balance atmospheric profiles with a tower and radiosondes and the cloud conditions were investigated in detail results from the radiative fluxes are compared with observations made at other locations in order to derive general characteristics of the radiation conditions on the greenland ice sheet and their relation to the climate of the ice sheet at eth camp albedo values obtained at ground level 2 m and from a high tower 27 m are similar during the melt season late may to mid august and slightly different during pre and post melt seasons due to the interplay of inhomogeneous surface conditions and solar elevation during the melt period the decrease in global radiation due to increasing cloud amount is compensated for by an increase in longwave incoming radiation because of the steady values of longwave outgoing radiation net radiation at the surface is characterized mainly by the albedo and its variation the regional net radiation for summer months on the greenland ice sheet is determined mainly by three facts 1 a strong increase in albedo from the ablation area to the ela and a smaller increase from the ela to the accumulation area 2 a large increase in longwave outgoing radiation in the ablation area and at the ela in june and july compared to the accumulation area 3 a larger amount of cloud of the stratus type at lower areas

satellite measurements of sea surface cooling during hurricane gloria hurricanes and other strong storms can cause important decreases in sea surface temperature by means of vertical mixing within the upper ocean and by air sea heat exchange here we use satellite derived infrared images of the western north atlantic to study sea surface cooling caused by hurricane gloria 1985 significant regional variations in sea surface cooling are well correlated with hydrographic conditions the greatest cooling up to 5 c occurred in slope waters north of the gulf stream where the seasonal thermocline is shallowest and most compressed moderate cooling up to 3 c occurred in the open sargasso sea where the thermocline is deeper and more diffused little or no cooling occurred in shallow coastal waters bottom depth less than 20 m which were isothermal before the passage of hurricane gloria there is a pronounced right side asymmetry of sea surface cooling with stronger by a factor of 4 and more extensive by a factor of 3 cooling found on the right side of the hurricane track these qualitative results are consistent with the notion that vertical mixing within the upper ocean is the dominant sea surface cooling mechanism of hurricanes

tectonic wedges and offset laramide structures along the polochic fault of guatemala and chiapas mexico reaffirmation of large neogene displacement fault wedges along the polochic fault of northern guatemala and chiapas mexico record left lateral slip of from 20 to 65 km that accompanied documented neogene slip of 130 km across this north american caribbean plate boundary fault wedges can be correlated to source areas consistent with left lateral displacement along the polochic fault they occur adjacent to restraining bends in three areas where changes in strike of the fault have been mapped these wedges which have been previously interpreted as allochthons emplaced along low angle reverse faults are bounded by high angle faults folds that terminate against the polochic fault are part of a regional fold belt that originated during the campanian through paleocene laramide orogenic event a previous contention that some of these major folds are secondary and related to fault movement is shown to be incorrect the 130 km model of left lateral offset across the polochic fault is reviewed along with evidence for and against a neogene time of major displacement additional evidence for the model is presented 1 late cretaceous granitoid rocks from near motozintla chiapas mexico northern fault block are correlated with granitic rocks of the santa maria batholith in the region of huehuetenango guatemala southern block 2 mineralization at the contacts of the granitoid intrusives of the two areas is correlated 3 points of deflection of laramide structural axes are correlated across the fault 4 a major thrust sheet similar to that of the sierra de santa cruz in eastern guatemala is reassembled by reversing 130 km of left lateral slip which has offset serpentinites north of the fault in western guatemala and those south of the fault in central guatemala

neogene north american caribbean plate boundary across northern central america offset along the polochic fault abstract the polochic fault was a segment of the north american caribbean plate boundary across central america in the neogene its 130 km of left slip was previously determined by matching structures and stratigraphie outcrop patterns of northwest and central guatemala across the fault additional support for the model and the youthfulness of the recorded offset comes from an essentially perfect match of major geomorphic features across the fault a reconstruction process which eliminates 123 km of left slip brings together rivers and drainage divides that existed before the polochic became active with the reconstruction carried across the isthmus on an east west fault the regional structural geology assumes the coherent pattern of a continuous orogenic belt whose geometry is compatible with the model of collisional tectonics centered on the motagua suture zone confined within this belt narrowed to some 60 km by the reconstruction lie the major laramide thrusts folds and tectonically emplaced serpentinites of guatemala crystalline rocks of guatemala re join the chiapas massif and paleozoic sedimentary rocks exposed in the core of an almost continuous anticlinorium extend from southern chiapas to lake izabal the polochic does not bend in eastern guatemala but continues eastward to the motagua fault where it dies westward drift of the northern block resulted in rifting which extended from eastern guatemala into the caribbean along the cayman trough the honduras depression may represent an element of a triple junction along with the polochic and izabal cayman rift the polochic continues westward into the pacific ocean and offsets the middle america trench the polochic has offset the miocene volcanic belt of northern central america confirming the previous estimate of a neogene time of movement about 300 km of relative east west neogene displacement has been recorded on the mid cayman rise only 130 km of which can be accounted for across the polochic it is suggested that cumulative extension on north south faults south of the motagua fault zone between the trench and the honduras depression might make up that difference

areal melt and discharge modelling of storglaciaren sweden a grid based glacier melt and discharge model was applied to storglaciaren a small valley glacier 3 km 2 in northern sweden for the melt seasons of 1993 and 1994 the energy available for melt was estimated from a surface energy balance model using meteorological data collected by automatic weather stations on the glacier net radiation and the turbulent heat fluxes were calculated hourly for every grid point of a 30 m resolution digital terrain model using the measurements of temperature humidity wind speed and radiative fluxes on the glacier two different bulk approaches were used to calculate the turbulent fluxes and compared with respect to their impact on discharge simulations discharge of storglaciaren was simulated from calculated meltwater production and precipitation by three parallel linear reservoirs corresponding to the different storage properties of firn snow and ice the performance of the model was validated by comparing simulated discharge to measured discharge at the glacier snout depending on which parameterization of the turbulent fluxes was used the timing and magnitude of simulated discharge was in good agreement with observed discharge or simulated discharge was considerably underestimated in one year

neotectonics of hispaniola plate motion sedimentation and seismicity at a restraining bend abstract the pattern of neogene faulting volcanism and sedimentation in hispaniola helps to resolve a problem that arises in attempting to determine the direction of caribbean plate motion from earthquakes alone namely how well do earthquake mechanisms define plate motion hispaniola occupies a compressional north step or restraining bend in the generally east west trending motagua cayman trough puerto rico trench fault system which marks an active plate boundary zone pbz of left lateral strike slip motion between the north america and caribbean plates four areas are distinguishable in hispaniola from field mapping and from the interpretation of satellite imagery and conventional aerial photographs two of these areas consist of active left lateral strike slip fault systems that roughly define the northern and southern coasts of the island the structure of both fault systems suggest a roughly east west trending direction of relative plate motion consistent with previous findings the intervening area consists of en echelon mountain ranges thrust up at the restraining bend from the early miocene a pleistocene volcanic province within this area is interpreted as defining a diffuse extensional fault termination of the southern strike slip fault zone the fourth area in eastern hispaniola is interpreted as being underthrust by discontinuous fragments of lithosphere in response to convergence at the restraining bend it appears possible that thinner young island arc lithosphere may be more prone to subduction than to escape or flaking processes that are more important in older more buoyant lithosphere

the mid rivera transform discordance morphology and tectonic development to better define the morphotectonic elements and tectonic development of the mid rivera transform discordance multibeam bathymetric seafloor backscatter multichannel seismic reflection and total field marine magnetic data were collected along the entire rivera transform west of 107 w during the bart and famex campaigns of the n o l atalante conducted in 2002 these data show that although the transform tectonized zone of the rivera transform west of 107 30 w is a single continuous morphologic basin this basin consists of two distinct morphotectonic domains an eastern domain which morphologically is a deep rhombochasm within which organized seafloor spreading has occurred and a western leaky transform domain these new data in conjunction with the results of previous studies support the idea that the rivera pacific euler pole is migrating southward towards the eastern half of the rivera transform and further indicate a recent 0 14 ma and most likely ongoing clockwise reorganization of the principle transform displacement zones of the rivera transform west of 108 w we propose that the mid rivera transform discordance owes its origin to this eastward progressing clockwise reorganization of the transform segments that is occurring in response to recent changes in rivera pacific relative plate motion

reply to comment on late cretaceous allochthons and post cretaceous strike slip displacement along the cuilco chixoy polochic fault guatemala

comment on late cretaceous allochthons and post cretaceous strike slip displacement along the cuilco chixoy polochic fault guatemala by t h anderson r j erdlac and m a sandstrom

variations of ablation albedo and energy balance at the margin of the greenland ice sheet kronprins christian land eastern north greenland a meteorological and glaciological experiment was carried out in july 1993 at the margin of the greenland ice sheet in kronprins christian land eastern north greenland within a small area about 100 m 2 daily measurements were made on ten ablation stakes fixed in light and dark ice and were compared to each other simultaneously the components of the energy balance including net radiation sensible heat flux latent heat flux and conductive heat flux in the ice were determined global radiation longwave incoming radiation and albedo were measured and longwave outgoing radiation was calculated by assuming that the glacier surface was melting sensible and latent heat fluxes were calculated from air temperature humidity and wind speed conductive heat flux in the ice was estimated by temperature profile measurements in the uppermost ice layer net radiation is the major source of ablation energy and turbulent fluxes are smaller energy sources by about three times while heat flux into the ice is a substantial heat sink reducing energy available for ice melt albedo varies from 0 42 to 0 56 within the experimental site and causes relatively large differences in ablation at stakes close to each other small scale albedo variations should therefore be carefully sampled for large scale energy balance calculations

reconnaissance study of glacier energy balance in north greenland 1993 94 reconnaissance energy balance studies were made for the first time at two sites in north greenland to compare with conditions in west greenland the field expe e planned to save weight because it is expensive operate in north greenland the larger energy components incoming radiation and ablation were measured for 55 days altogether and the smaller components were evaluated by indirect methods c g turbulent fluxes are calculated from air temperature humidity and w ind speed to save the weight of inst ruments the energy balance model is tuned by choosing surface roughness and albedo to reduce the mean error between measured ablation and modelled daily melting the error standard deviation for ablation is only 5 kg m 2 d 1 which is much lower than found in west greenland due to better instruments and modelling in the presen study net radiation is the main energy source for melting in north greenland but ablation is is relatively low because sublimation and conductive heat fluxes use energy that would otherwise be available for melting there is a strong diurnal variation in ablation mainly forced by variations in shortwave radiation and reinforced by nocturnal cooling of the ice surface by outgoing longwave radiation and sublimation the model frequently predicts a frozen glacier surface at night even when air temperatures are positive

the chixoy polochic fault and its associated fractures in western guatemala in western guatemala post cretaceous volcanic and sedimentary rocks locally cover the trace of the chixoy polochic fault no single throughgoing fault cuts these units however a complicated series of en echelon lineations identified from aerial photographs and field mapping represent the accommodations of displacements along the underlying fault comparison of fracture trends in the chixoy polochic fault zone with models from experimental studies and field examples of strike slip faults suggest that left lateral displacement along the chixoy polochic fault in this area is probably no more than a few kilometres since the accumulation of the overlying beds of probable post mid tertiary age earlier lateral displacements of large magnitude are not precluded although none have been documented by field study

near inertial ocean response to tropical cyclone forcing on the australian north west shelf the regional ocean modeling system roms was applied to the australian north west shelf nws to hindcast the ocean response to four intense historical tropical cyclones tcs while the four cyclones had very different trajectories across the nws all passed within 150 km of a long term vertical mooring located on the continental shelf in 125 m depth the observed ocean response at this relatively shallow southern hemisphere shelf site was characterized by the development of a peak in the counter clockwise ccw near inertial kinetic energy mixed layer deepening and subsequent restratification strong near inertial isotherm oscillations were also observed following two of the cyclones roms reproduced these features and also showed that the peak in the near inertial ccw kinetic energy was observed on the left side of each cyclone trajectory the time rate of change of near inertial kinetic energy depended strongly on the storm rossby number i e defined based on the storm speed the storm length scale and the coriolis frequency the shallow water depth on the nws resulted in first a more rapid decay of near inertial oscillations than in the deep ocean and second a generation efficiency the ratio of near inertial power to the rate of wind work of up to 10 smaller than found for cyclones propagating across deeper water the total energy put into near inertial motions is nevertheless large compared to the background tidal energy the rapid decay of near inertial motions emphasizes the importance of frictional effects in characterizing the response to cyclone forcing in shallow seas

age and spreading history of the cayman trough as determined from depth heat flow and magnetic anomalies the opening of the cayman trough records aspects of relative motion between the north american and caribbean plates essential to accurate reconstruction of caribbean evolution assessment of opening rates based upon basement subsidence analysis as well as magnetic anomaly interpretation shows that the trough may have opened at one third to one half previously proposed rates depths to basement show that the crust has subsided away from the present axis in two stages a younger stage characterized by substantial and asymmetric greater to the east subsidence preceded by an older stage of slight increases of depth with distance depth to age relations calculated from subsidence curves which accommodate lateral as well as vertical cooling of the accreting slab indicate that the trough has opened at an overall rate of less than 15 mm yr since 25 30 ma and at 20 30 mm yr prior to 30 ma marine magnetic anomalies show lineations perpendicular to the trough including a distinct central anomaly but the pattern is neither well defined nor symmetrical about the present axis however partial anomaly sequences can be identified on both sides of the axis and the distribution of these sequences indicates that spreading may have involved frequent short ridge jumps mostly eastward the overall rate of opening as indicated by this interpretation of the magnetics is about 15 and 30 mm yr since and prior to 26 ma both subsidence and magnetics indicate that the trough opened by at least 45 50 ma

post miocene cayman trough evolution a speculative model the cayman trough exhibits cross trough lineations which we interpret as crustal fabric formed parallel to the spreading center at the time of crustal generation alignment and variations of the spreading fabric are roughly symmetrically distributed about the mid cayman spreading center as are variations in the cross trough width of the cayman trough these suggest to us a simple eight stage model of stepwise varying spreading directions and rates for this model it is assumed that 1 tectonic spreading fabric is perpendicular to spreading direction 2 cross trough extension both widens the trough and lengthens the spreading center and 3 cross trough compression narrows the trough but does not shorten the spreading center combining the spreading fabric lineation data with these assumptions we predict a cross trough width variation that is essentially that of the cayman similar variations in spreading direction should be evidenced elsewhere on the plate boundary if the variations we observe do in fact record the history of changes in relative motion between the north american and caribbean plates

sedimentary architecture structural setting and late cenozoic depocentre migration of an asymmetric transtensional basin lake izabal eastern guatemala abstract lake izabal located in eastern guatemala lies in an ew trending basin located along the transform margin between the north american and caribbean plates this plate boundary consists of two main left lateral strike slip faults known as the polochic and motagua fault system pmfs the basin is a 100 20 km lens shaped depression in which the lake occupies its eastern half to the north the basin is confined by a principal deformation zone pdz which is recognized in this area as the most important upper crustal branch of the polochic fault the eastern part of the basin has been uplifted and dissected exposing the basin infill along the slopes of the montana del mico analysis of a set of multichannel seismic reflection profiles most of them acquired within the lake combined with well and outcrop information allowed to outline the structure and evolution of the basin and its stratigraphic architecture the basin is strongly asymmetrical both in cross and along strike directions and is filled up by neogene to quaternary sediments with the deepest side of the basin being to the north close and parallel to the pdz the base of the infill is a mid tertiary unconformity whose differential subsidence through time brought the basin to its present structural setting five main evolutionary stages are recognized based on seismo stratigraphic and structural features which are related to the development and activity of the bordering faults development of the basin began in its easternmost sector a small half graben tilted to the south developed in response to the activity of an oligocene or early middle miocene growth fault in the second stage late miocene the basin tilts to the north causing the sedimentary sequences to thicken towards the northern pdz this stage is dominated by oblique extension and by progressive migration of the basin depocenter towards the west the third stage early pliocene records a strong acceleration of the strike slip activity which causes a rapid westward migration of the depocenter the fourth stage late pliocene although still dominated by regional transtension is related to the development of a transpressional event along the eastern side of the basin as evidenced by the occurrence of folds and reverse faults parallel to the northern bend of the polochic fault during the fifth stage quaternary the eastern part of the basin remains relatively quiescent while the western part undergoes subsidence with localized transtension still related to the activity in this sector of the polochic fault left lateral movement along the polochic fault caused the depocenter to migrate 75 80 km at different velocities with slip rates ranging between 2 1 and 16 3 mm yr this study suggests that the polochic fault developed in the early middle miocene in connection to the deposition of the early sediments of the izabal basin even though an older age oligocene could also be possible to our knowledge this is one of the best examples of sedimentary architecture documenting depocentre migration due to fault movement along a transform system

neotectonics of the caribbean a compilation of earthquake focal mechanism solutions together with the interpretation of inclined intermediate depth seismic zones neogene strike slip faults fault controlled basins and volcanism is used to test three existing models for the neotectonic i e neogene or post oligocene development of the caribbean the current models although based on different hypotheses using different data sets are similar and suggest varying degrees of convergence between the caribbean and either north or south american plates or convergence between the caribbean plate and continental fragments of the northwestern corner of south america using model 1 previous workers have interpreted the disposition of fracture zones and magnetic anomalies in the central and south atlantic as indicating that the caribbean plate is being compressed by north south convergence between the americas with the result that it is being driven eastward relative to the americas along strike slip faults while producing east west trending subductionlike convergent zones along northern and southern plate margins using model 2 previous workers have interpreted the azimuths of active strike slip faults and focal mechanism solutions and closure of three plate velocity circuits as indicating that the south american plate converges in a west northwesterly direction on the southern margin of the caribbean plate and has produced compressional features while strike slip motion dominates along the northern boundary using model 3 previous workers have interpreted focal mechanism solutions and the pattern of strike faulting and basin development in northwestern south america to suggest right lateral displacement of the northwestern corner of south america relative to the craton with convergence and compression in the south central caribbean our integration of geologic information on faults basins and volcanism considerably extends the limited record of plate interactions known from historical reports of the past few hundred years and recorded earthquakes and suggests that 1 relative motion between the north american and caribbean plates is dominantly east west strike slip motion although areas of complex internal deformation associated with restraining bend or compressional strike slip fault segments have been identified in jamaica hispaniola and central america 2 relative motion between the south american and caribbean plates is dominantly east west strike slip motion although an area of restraining bend deformation has been identified in the araya peninsula of venezuela 3 relative motion between a triangular continental fragment of northwestern south america the maracaibo block ranges from northwest to northeast along the south central margin of the caribbean and appears to be driven mostly by the late miocene pliocene collision of the panama arc although additional driving forces may include the collision of the carnegie ridge and or oblique subduction to the northeast in ecuador and 4 relative motion internal deformation may be occurring at a very slow rate between fault bounded blocks within the caribbean plate as a result of the convergence of the maracaibo block and or eastward motion of the caribbean plate relative to a continental promontory of north america in northern central america because the caribbean margins are composed mainly of anisotropic easily deformed continental and arc lithosphere plate boundaries are zones of diffuse deformation and it is difficult to assess the degree of convergence between the americas although data from the caribbean itself suggest that it may be smaller than the amount inferred by some workers using model 1 fracture zone and magnetic anomalies in the atlantic some of the compressional features cited as evidence for the relative convergence of the americas may be instead related to the convergence between the maracaibo block relative to the southern margin of the caribbean many aspects of caribbean neotectonics remain less than completely understood but more integration of seismic and geologic studies particularly exploratory fault trenching of onshore faults and seismic profiling of offshore faults should lead to rapid advances

estimate of ocean mixed layer deepening after a typhoon passage over the south china sea by using satellite data abstractthe ocean responses to typhoon cimaron which influenced the south china sea scs from 1 to 8 november 2006 are analyzed based on satellite observed sea surface temperature sst and climatological temperature profiles in the scs mixed layer deepening an important parameter characterizing turbulent mixing and upwelling driven by strong typhoon winds is derived corresponding to the sst drop of 4 4 c on 3 november 2006 the mixed layer deepened by 104 5 m relative to the undisturbed depth of 43 2 m which is consistent with a simulation result from a mixed layer model furthermore baroclinic geostrophic velocity and vorticity are calculated from the surface temperature gradient caused by the typhoon the negative vorticity associated with the typhoon cooling indicated an anticyclonic baroclinic circulation strongest at the base of the mixed layer and at the depth of 50 m the geostrophic speed reached as high as 0 2 m s 1 typhoon cimaron proceeded slowly 1 7 m s 1 when it was making a s

an investigation of the influences of mesoscale ocean eddies on tropical cyclone intensities abstractthe impact of mesoscale ocean eddies on tropical cyclone intensities is investigated based on a combination of observations and atmosphere ocean coupling simulations a statistical analysis reveals that the tropical cyclone eddy interactions occur at very high frequencies over 90 of the recorded tropical cyclones over the western north pacific have encountered ocean eddies from 2002 to 2011 the chances of confronting a cold core eddy cce are slightly larger than confronting a warm core eddy wce the observational sea surface temperature data have statistically evidenced that cces tend to promote the sea surface temperature decrease caused by tropical cyclones while wces tend to restrain such ocean responses the roles of cces are statistically more significant than those of wces in modulating the sea surface temperature response it is therefore proposed that cces should be paid no less attention than wces during the tc ocean interaction process the cce induced changes in sea surface tempe

tectonic evolution of the north pacific during the cretaceous quiet period the cretaceous quiet period ended with a significant reorganization of the plate tectonics of the north pacific the farallon plate broke into three primary pieces 1 the kula plate 2 a large fragment transferred to the pacific plate and 3 the continued farallon plate the time of the rearrangement is constrained to just before magnetic anomaly 34 by its presence contrasts in tectonic spreading fabric tsf the emperor trough and the chinook trough our model is based on 1 a complete reevaluation of primary bathymetric and magnetic data 2 the distribution of major troughs emperor chinook hokkaido and krusenstern 3 mapping and analysis of tsf orientation and amplitude on quiet zone crust and 4 available deep sea drilling project drill hole data east west trending magnetic reversal lineations and tsf south of the aleutian trench are bounded on the west by the buldir fracture zone at 175 e the major troughs mark the abandonment and initiation of spreading in the reorganization their absence elsewhere precludes other long distance boundary relocations emperor trough is the abandoned pacific farallon spreading center rift initiation and early slow spreading have created the high amplitude topography of the chinook trough we believe that the hokkaido trough is the initiation site of a failed oceanic rift the incorporation of large amounts of farallon plate into the pacific plate obviates the need for the very rapid pacific farallon spreading rates of previous models and significantly alters the interpretation of mid pacific geology

multisatellite observation on upwelling after the passage of typhoon hai tang in the southern east china sea 1 the serial remote sensing based imageries clearly revealed large scale of upwelling within large regional enhancement of chlorophyll a chl a concentration in the southern east china sea ecs after the passage of super typhoon hai tang in july 2005 after the typhoon on 22 july the upwelling area 3 0 mg m3 appeared in the shelf region where the high chl a pattern matched the upwelling in terms of location and time on the other hand a large offshore sst cooling was also observed mainly to the right of typhoon track on 20 july it lasted in a period of 2 3 days this paper provides clear and high resolution evidence that typhoon significant increased upwelling and chl a concentration in the southern ecs

quaternary seismo tectonic activity of the polochic fault guatemala 1 the polochic motagua fault system is part of the sinistral transform boundary between the north american and caribbean plates in guatemala and the associated seismic activity poses a threat to 70 of the country s population the aim of this study is to constrain the late quaternary activity of the polochic fault by determining the active structure geometry and quantifying recent displacement rates as well as paleo seismic events slip rates have been estimated from offsets of quaternary volcanic markers and alluvial fan using in situ cosmogenic 36cl exposure dating holocene left lateral slip rate and mid pleistocene vertical slip rate have been estimated to 4 8 2 3 mm y and 0 3 0 06 mm y respectively on the central part of the polochic fault the horizontal slip rate is within the range of longer term geological slip rates and short term gps based estimates in addition the non negligible vertical motion participates in the uplift of the block north of the fault and seems to be a manifestation of the regional far field stress regime we excavated the first trench for paleo seismological study on the polochic fault in which we distinguish four large paleo seismic events since 17 ky during which the polochic fault ruptured the ground surface

new precipitation and accumulation maps for greenland annual total precipitation and the annual accumulation on the greenland ice sheet are evaluated and presented in two maps the maps are based on accumulation measurements of 25 1 pits and cores obtained from the upper accumulation zone and precipitation measurements made at 35 meteorological stations in the coastal region to construct the accumulation map the annual precipitation was split into solid and liquid precipitation components annual total precipitation exceeding 2500 mm w e occurs on the southeastern tip of greenland while the minimum precipitation is estimated to occur on the northeastern slope of the ice sheet the mean annual precipitation for all of greenland is 340 mm w e the largest annual accumulation of about 1500 mm w e is found on the glaciers in the southeastern corner of greenland while the smallest accumulation is found on the northeastern slope of the ice sheet west of danmarkshavn the mean accumulation on the greenland ice sheet is estimated at 310 mm w e the regional difference in accumulation is examined with respect to the 850 hpa m bar level circulation the present surface topography is found to play an important role in determining regional accumulation on the ice sheet

the caribbean north america cocos triple junction and the dynamics of the polochic motagua fault systems pull up and zipper models the polochic motagua fault systems pmfs are part of the sinistral transform boundary between the north american and caribbean plates to the west these systems interact with the subduction zone of the cocos plate forming a subduction subduction transform triple junction the north american plate moves westward relative to the caribbean plate this movement does not affect the geometry of the subducted cocos plate which implies that deformation is accommodated entirely in the two overriding plates structural data fault kinematic analysis and geomorphic observations provide new elements that help to understand the late cenozoic evolution of this triple junction in the miocene extension and shortening occurred south and north of the motagua fault respectively this strain regime migrated northward to the polochic fault after the late miocene this shift is interpreted as a pull up of north american blocks into the caribbean realm to the west the pmfs interact with a trench parallel fault zone that links the tonala fault to the jalpatagua fault these faults bound a fore arc sliver that is shared by the two overriding plates we propose that the dextral jalpatagua fault merges with the sinistral pmfs leaving behind a suturing structure the tonala fault this tectonic zipper allows the migration of the triple junction as a result the fore arc sliver comes into contact with the north american plate and helps to maintain a linear subduction zone along the trailing edge of the caribbean plate all these processes currently make the triple junction increasingly diffuse as it propagates eastward and inland within both overriding plates

marine tectonics processes at mid ocean ridges the use of multibeam echo sounders and various side looking sonar systems has greatly increased our knowledge and understanding of mid ocean ridge mor processes since the last iugg review on mid ocean ridge research macdonald 1983 the extensive use of swath mapping tools such as sea beam deep tow seamarc i and ii the application of multichannel seismic reflection techniques to the detection of axial magma chambers and the use of satellite data in the study of oceanic lithosphere have rejuvenated marine tectonics and have generated and stimulated a large number of important contributions this review will focus on what we feel were the major developments in marine tectonics with an emphasis on mid ocean ridges in the last four years certain topics such as marine seismicity and satellite studies are only briefly mentionned for reference and will be covered in greater detail in other reviews because of the exponential growth in the number of publications related to mors during 1982 1986 only a few references pertinent to each of the major research topics will be quoted in the text as examples but the reader will find an extensive bibliography at the end of the text references published prior to 1982 were added only where appropriate

concordant paleomagnetic directions from the tehuantepec isthmus constraints on the neogene evolution of the north american caribbean plate boundary we report paleomagnetic data for miocene igneous rocks of the southeastern tehuantepec isthmus region mexico thermal and alternating field demagnetization reveal predominantly norma polarity magnetization interpreted as primary trm the overall mean direction dee 355 6 inc 3 y k 36 4 ag5 9 3 n 8 sites is statistically indistinguishable from the expected direction calculated using the north american reference pole this result indicates that significant rotation or displacement of the tehuantepec region relative to the craton has not occurred since 13 ma

satellite observations of sea surface cooling by hurricanes sea surface cooling associated with 13 hurricanes in the western north atlantic between september 1981 and december 1984 is examined using satellite derived sea surface temperature fields some surface cooling is observed in all cases however because of cloud cover and the fairly weak signal in some cases we see pronounced cooling along an extensive and continuous portion of the storm path for only three strong hurricanes the persistence of cooling following the passage of a hurricane varies from a few days to at least 16 days the amplitude of cooling is moderately well correlated with hurricane strength and is as large as 3 5 c when the hurricanes move rapidly the maximum cooling occurs well to the right of the track approximately 70 km whereas for slowly moving hurricanes the maximum cooling occurs near or on the track because western north atlantic hurricanes are often found in close proximity to high pressure systems daytime satellite images must be made with some care because of diurnal warming

a hierarchical tectonic model of the gulf of mexico and caribbean region abstract a quantitative computer graphic methodology hierarchical tectonic analysis has been used to model the tectonic evolution of the gulf of mexico and caribbean region this method employs a highly structured hierarchical description of the relative motions of pairs of tectonic elements in order to quantify the timing and style of plate interactions the main features described in this model are 1 1 a revised fit of pangea 2 2 the opening of the gulf of mexico in the middle late jurassic 3 3 the formation of a proto caribbean ocean due to the separation of north and south america during the early cretaceous 4 4 the formation of the greater antilles arc along the western margin of the proto caribbean ocean 5 5 the insertion of the farallon plate between north and south america during the middle cretaceous resulting in the northeastward advance of the greater antilles arc and the subduction of proto caribbean oceanic crust 6 6 the complete subduction of the proto caribbean ocean and the collision of the greater antilles arc with the bahamas platform in the late cretaceous 7 7 the truncation of the caribbean section of the farallon plate from its pacific counterpart and the formation of the panama arc latest cretaceous and 8 8 the westward movement of north and south america with respect to the caribbean plate resulting in the opening of the yucatan basin paleocene and subsequently in the evolution of the cayman trough and e w zone of strike slip

climate at the equilibrium line of glaciers the relationships between temperature precipitation and radiation on glacier equilibrium lines are investigated using 70 glaciers for which the mass balance and meteorological observations have been carried out for sufficiently long periods it is found that the characteristic climate at glacier equilibrium lines can be described using the summer 3 months temperature in a free atmosphere annual total precipitation and the sum of global and long wave net radiation all of these are measured at or very near the equilibrium line altitudes then it is shown how the shift of the equilibriumline will occur as a result of a climatic change finally the effect of the shift of the equilibrium line on the annualmean specific mass balance is analytically derived and compared with observations the present results make it possible to identify the altitudes in climate models where glacierization should begin and to evaluate the mass balance changes as a result of possible future changes in the climate

accretionary margin of north western hispaniola morphology structure and development of part of the northern caribbean plate boundary abstract broad range side scan sonar gloria images and single and multi channel seismic reflection profiles demonstrate that the margin of north western hispaniola has experienced compression as a consequence of oblique north american caribbean plate convergence two principal morphological or structural types of accretionary wedges are observed along this margin the first type is characterized by a gently sloping 4 sea floor and generally margin parallel linear sets of sea floor ridges that gradually deepen towards the flat hispaniola basin floor to the north the ridges are caused by an internal structure consisting of broad anticlines bounded by thrust faults that dip southwards beneath hispaniola anticlines form at the base of the slope and are eventually sheared and underthrust beneath the slope in contrast the second type of accretionary wedge exhibits a steeper 6 16 sea floor slope characterized by local slumping and a more abrupt morphological transition to the adjacent basin the internal structure appears chaotic on seismic reflection profiles and probably consists of tight folds and closely spaced faults we suggest that changes in sea floor declivity and internal structure may result from variations in the dip or frictional resistance of the decollement or possibly from changes in the cohesive strength of the wedge sediments the observed pattern of thickening of hispaniola basin turbidites towards the insular margin suggests differential southwards tilting of the hispaniola basin strata probably in response to north america caribbean plate interactions since the early tertiary based upon indirect age control from adjacent parts of the northern caribbean plate boundary we infer a late eocene to early miocene episode of transcurrent motion i e little or no tilting an early miocene to late pliocene period of oblique convergence i e increased tilt during which the accretionary wedge began to be constructed and a late pliocene to recent episode of increased convergence i e twice the miocene to pliocene tilt which has led to rapid uplift and erosion of sediment sources on the margin and on hispaniola generating a submarine fan at the base of the insular slope

spatial and temporal characterization of sea surface temperature response to tropical cyclones abstractthe spatial structure and temporal evolution of the sea surface temperature sst anomaly ssta associated with the passage of tropical cyclones tcs as well as their sensitivity to tc characteristics including tc intensity and translation speed and oceanic climatological conditions represented here by latitude are thoroughly examined by means of composite analysis using satellite derived sst data the magnitude of the tc generated ssta is larger for more intense slower moving and higher latitude tcs and it occurs earlier in time for faster moving and higher latitude storms the location of maximum ssta is farther off the tc track for faster moving storms and it moves toward the track with time after the tc passage the spatial extension of the cold wake is greater for more intense and for slower moving storms but its shape is quite independent of tc characteristics consistent with previous studies the calculations show that the mean ssta over a tc centered box nearly linearly corre

spatial and temporal variations in albedo on storglaciaren sweden extensive albedo data from storglaciaren sweden during nine summers are analyzed focusing on the effect of surface slope on measurements and on the influence of clouds on albedo of both snow and ice surfaces on clear sky days albedo continuously dropped throughout the day by 0 3 when derived from measurements in a horizontal plane over the slightly sloping surface when we correct for the tilt effect over frozen surfaces the apparent decrease in albedo largely disappeared while over melting surfaces it became significantly less pronounced this emphasizes the need to correct horizontally measured data for slope when they are used for example as ground truth for satellite derived albedo or in high resolution glacier melt runoff models albedo varied by 0 1 due to cloud fluctuations to quantify cloud effects albedo changes between successive half hourly and daily data were regressed against corresponding changes in cloudiness expressed by the ratio of global radiation to top of atmosphere solar radiation the resulting relationship over snow explains 66 of oberved albedo changes using hourly and 4 using daily time steps over ice the corresponding values arc 28 and 0 hence cloudiness is a dominating factor in determining short term variability of albedo over snow whereas over ice the observed large day to day variability 20 is mainly attributed to changes in the physical characteristics of the weathering crust results suggest that cloud effects should be incorporated into models treating snow and ice surfaces separately

oceanic core complex development at the ultraslow spreading mid cayman spreading center roughly a third of the global mid ocean ridge system spreads at 6 km spreading centers and thought to accrete some of the thinnest 3 km crust the mcsc generates end member mid ocean ridge basalt compositions and hosts recently discovered hydrothermal vents multibeam bathymetric data reveal that axial depth varies along the mcsc with intraridge rift walls defined by kilometer scale escarpments and massifs dredging and near bottom work has imaged and sampled predominantly basaltic lavas from the greatest axial depths and 15 peridotite surrounded by gabbroic rocks from the prominent massifs the gabbroic rocks exhibit wide compositional variation troctolites to ferrogabbros and in many places contain high temperature amphibolite to granulite facies shear zones gabbroic compositions primarily reflect the accumulation of near liquidus phases that crystallized from a range of basaltic melts as well as from interactions with interstitial melts in a subaxial mush zone magnetization variations inverted from aeromagnetic data are consistent with a discontinuous distribution of basaltic lavas and structurally asymmetric spreading these observations support an oceanic core complex model for mcsc seafloor spreading potentially making it a type example of ultraslow seafloor spreading through mush zone and detachment fault crustal processes

seismic investigation of an active ocean continent transform margin the interaction between the swan islands fault zone and the ultraslow spreading mid cayman spreading centre

the evolution of middle america and the gulf of mexico caribbean sea region during mesozoic time a plate tectonic model for the evolution of middle america and the gulf of mexico caribbean sea region is presented the model which is based upon the existence of the mojave sonora megashear incorporates into the triassic pangea reconstruction three microplates between north and south america thus avoiding the overlap of the bullard fit these plates are the yaqui bounded on the north by the mojave sonora megashear the east and west maya plates bounded on the north by the mexican volcanic zone and on the south by a predecessor of the motagua fault zone and the chortis plate parts of guatemala and honduras during late jurassic time as north america split away from europe africa and south america shear with left lateral sense of displacement occurred along the transform faults that bounded the micro plates if 800 km of left lateral displacement along the mojave sonora megashear 300 km along the mexican volcanic belt and 1 300 km along a proto motagua megashear are restored and if yucatan and cuba are rotated to fit against northern south america then 1 a curvilinear belt of late paleozoic rocks that show lithologic as well as paleontologic similarities extends across the reconstruction and links outcrops in texas eastern mexico nuclear central america and colombia 2 a mediterranean like sea is delineated that was a precursor of most of the present gulf of mexico 3 correlation is implied between the distinctive quartzose san cayetano formation of cuba and the caracas and juan griego groups of venezuela geometric constraints suggest that probably shear initially occurred along the mexican volcanic zone near the end of the middle jurassic subsequently probably about 160 m y ago displacements that total 800 km began along the mojave sonora megashear contemporaneously yucatan and fragments of pre cretaceous rocks that compose parts of central and western cuba migrated northward toward their present positions rotation of yucatan was facilitated by considerable displacement along the proto motagua zone and along a zone that is probably coincident with the modern salina cruz fault accumulation of widespread major salt units of late jurassic callovian to early oxfordian age in the gulf basin probably occurred contemporaneously with the arrival of these blocks at their present positions clastic units that interfinger with some of the youngest salt units and rim the gulf of mexico have not recorded major recognized translations since their accumulation clockwise rotation of south america and the chortis plate occurred during early cretaceous time this movement which was manifested by subduction of jurassic ocean floor against the previously rifted precursor of the island of cuba and under parts of hispaniola and puerto rico is recorded by circum caribbean orogeny abrupt changes in the relative motions between north and south america during late cretaceous time may have resulted in extension and outpourings of basalt upon the jurassic rocks of the ocean floor of the venezuelan basin west of beata ridge sea floor spreading formed the colombian basin related subduction occurred as the chortis plate including part of central america the nicaraguan rise and southeastern cuba was sutured against the maya east plate along the present motagua fault and cayman trench our model is constrained by published geologic data the relative positions of north and south america from atlantic sea floor magnetic anomalies and the requirement that the major transform faults be compatible with the poles of rotation for the appropriate relative motions between north and south america paleomagnetic data from middle america are sparse but do not conflict with the predicted motions of some of the microplates especially chortis

air sea coupling during the tropical cyclones in the indian ocean a case study using satellite observations in the years 1999 and 2001 three intense tropical cyclones formed over the northern indian ocean two over the bay of bengal during 15 19 and 25 29 october 1999 and one over the arabian sea during 21 28 may 2001 we examined the thermal salinity and circulation responses at the sea surface due to these severe cyclones in order to understand the air sea coupling using data from satellite measurements and model simulations it is found that the sea surface temperature sst cooled by about 0 5 0 8 c in the bay of bengal and 2 c in the arabian sea in the bay of bengal this cooling took place beneath the cyclone center whereas in the arabian sea the cooling occurred behind the cyclone only a few days later this contrasting oceanic response resulted mainly from the salinity stratification in the bay of bengal and thermal stratification in the arabian sea and the associated mixing processes in particular the cyclones moved over the region of low salinity and smaller mixed layer depth with a distinct mixed layer deepening to the left side of the cyclone track it is envisaged that daily satellite estimates of sst and sea surface salinity sss using outgoing longwave radiation olr and model simulated mixed layer depth would be useful for the study of tropical cyclones and prediction of their path over the northern indian ocean

a distributed surface energy balance model for complex topography and its application to storglaciaren sweden a grid based surface energy balance mass balance model has been developed to simulate snow and ice melt in mountainous regions with an hourly resolution the model is applied to storglaciaren a valley glacier in sweden using a 30 m resolution digital elevation model emphasis is directed towards computing the radiation components these are modelled individually considering the effects of slope angle aspect and effective horizon a new parameterization for snow albedo is suggested modifying the albedo of the preceding hour as a function of time after snowfall air temperature and cloudiness the model is used to provide the meltwater input for discharge modelling and to assess the influence of the individual components on melt results are validated by means of observed melt rates patterns of snow line retreat and proglacial discharge in general simulations are in good agreement with observations in particular the diurnal and seasonal fluctuations of discharge are simulated remarkably well

an enhanced temperature index glacier melt model including the shortwave radiation balance development and testing for haut glacier d arolla switzerland an enhanced temperature index glacier melt model incorporating incoming shortwave radiation and albedo is presented the model is an attempt to combine the high temporal resolution and accuracy of physically based melt models with the lower data requirements and computational simplicity of empirical melt models represented by the degree day method and its variants the model is run with both measured and modelled radiation data to test its applicability to glaciers with differing data availability five automatic weather stations were established on haut glacier d arolla switzerland between may and september 2001 reference surface melt rates were calculated using a physically based energy balance melt model the performance of the enhanced temperature index model was tested at each of the four validation stations by comparing predicted hourly melt rates with reference melt rates predictions made with three other temperature index models were evaluated in the same way for comparison the enhanced temperature index model offers significant improvements over the other temperature index models and accounts for 90 95 of the variation in the reference melt rate the improvement is lower but still significant when the model is forced by modelled shortwave radiation data thus offering a better alternative to existing models that require only temperature data input

preservation of contrasting geothermal gradients across the caribbean north america plate boundary motagua fault guatemala 1 strike slip plate boundaries juxtapose crustal blocks that may have different geodynamic origins and therefore different thermal structures thermo kinematic modeling of this type of strike slip plate boundary predicts an asymmetric signature in the low temperature thermochronologic record across the fault age elevation profiles of zircon u th he ages across the motagua fault a 500 km long segment of the transform boundary between the north american and caribbean plates document a sharp cooling age discontinuity across the fault this discontinuity could be interpreted as a difference in denudation history on each side of the fault however a low relief miocene erosional surface extends across the fault this surface has been uplifted and incised and provides a geomorphic argument against differential denudation across the fault by integrating magmatic volcanic and heat flow data age elevation profiles and thermo kinematic modeling we propose that large horizontal displacement along the motagua fault has offset a persistent geothermal asymmetry across the fault and explains both the age discontinuities and the age elevation patterns this study illustrates how thermochronology can be used to detect large strike slip displacements and more generally opens new perspectives in understanding the impact of nonuniform thermal structures on thermochronologic results

hurricane forced upwelling and chlorophyll a enhancement within cold core cyclones in the gulf of mexico 1 clear skies subsequent to hurricane ivan s passage across the gulf of mexico in september 2004 provided a unique opportunity to investigate upper ocean responses to a major hurricane oceanic cyclonic circulation was rapidly intensified by the hurricane s wind field 59 62 m s 1 maximizing upwelling and surface cooling 3 7 c in two large areas along ivan s track upward isothermal displacements of 50 65 m computed from wind stress and sea surface height changes caused rapid ventilation of thermoclines and nutriclines leading to phytoplankton blooms with peak concentrations 3 4 days later wind speed changes along ivan s track demonstrated that the cool waters 20 26 c provided immediate negative feedback to the hurricane s intensity although our study focused on a relatively small ocean area it revealed that mesoscale cyclones in addition to warm anticyclones may play an important role in producing along track hurricane intensity changes

sea surface cooling caused by typhoons in the tohoku area in august 1989 a remarkable sea surface cooling event was observed in the north western pacific off japan coast which is known as the tohoku area by using well calibrated satellite sea surface temperature images when typhoons t8914 and t8915 passed over the tohoku area in august 1989 the sea surface cooling maximum reached up to 9 c which is much larger than that reported in the previous studies the corresponding hydrographic data show that the sea surface cooling state is closely related with the ocean structure in the tohoku area the larger sea surface cooling occurs in the oyashio area the numerical experiments taking account of the ocean structure show that the surface cooling maximum is 3 4 times larger in case of the oyashio profile than that of the kuroshio profile and clarify the mechanism of the sea surface cooling

late cretaceous allochthons and post cretaceous strike slip displacement along the cuilco chixoy polochic fault guatemala the disposition of allochthonous masses emplaced in late cretaceous to early tertiary time along the cuilco chixoy polochic strike slip fault zone in western guatemala constrains the amount of tertiary displacement the absence of major disruption of the allochthons argues against lateral displacements of hundreds of kilometers during the tertiary in westernmost guatemala along the flank of the cuilco chixoy polochic fault granite volcaniclastic and volcanic rocks minor carbonate and phyllite comprise a sequence of south dipping allochthons these tilted slabs lie against almost horizontal jurassic and cretaceous beds to the north field relations indicate that the slides were emplaced across the cuilco chixoy polochic fault from south to north probably during late cretaceous or early tertiary time other fault bounded masses which crop out tens of kilometers eastward near san sebastian huehuetenango probably were emplaced contemporaneously with those to the west locally these allochthons lie astride the active trace of the cuilco chixoy polochic fault along which offset streams record about 1 km of left lateral motion total displacement recorded by the apparent offset of allochthonous sheets is no more than several kilometers farther east along much of the cuilco chixoy polochic fault zone a throughgoing strike slip trace has not been identified we postulate that the pre tertiary tectonic record is obscured by an extensive series of allochthons composed of regional stratigraphic suites emplaced during late cretaceous time in western guatemala stratigraphic relationships between serpentinized peridotite and carbonate beds of late cretaceous age indicate turonian as a maximum age for initial emplacement of allochthonous material regional relationships indicate that deformation culminated during latest cretaceous earliest tertiary time the emplacement of thrust sheets along the cuilco chixoy polochic fault is a likely product of contemporaneous cretaceous convergence along the motagua zone to the south collision of the chortis terrane against southern yucatan resulted in crustal shortening uplift and consequent northward directed emplacement of slides allochthons composed of ultramafic rocks sedimentary cover and less commonly granitic rocks were probably derived from the suture zone and the uplifted region between the cuilco chixoy polochic and motagua faults

upper ocean response to hurricane gilbert the evolving upper ocean response excited by the passage of hurricane gilbert september 14 19 1988 was investigated using current and temperature observations acquired from the deployment of 79 airborne expendable current profilers axcps and 51 airborne expendable bathythermographs from the national oceanic and atmospheric administration wp 3d aircraft in the western gulf of mexico the sea surface temperatures ssts mixed layer depths and bulk richardson numbers were objectively analyzed to examine the spatial variability of the upper ocean response to gilbert net decreases of the ssts of 3o 4oc were observed by the profilers as well as by the airborne infrared thermometer airt along the flight tracks and advanced very high resolution radiometer avhrr imagery the axcps indicated a marked cooling from 29oc to about 25 5oc on september 17 1988 which was about 1 2 inertial periods ip following storm passage this pool of cooler water 3 5 o was located further downstream in the hurricane wake by september 19 2 7 ip following the storm as a result of the near inertial currents in the mixed layer while there was a bias of about 0 6oc and 1 7oc between the in situ and avhrr derived ssts respectively both the avhrr images and the objectively analyzed fields indicated a rightward bias in the upper ocean cooling that extended from the storm track to about 4rmax where rmax the radius of maximum winds is equal to 50 km the larger sst offset of 1 7oc was due to the difference between the time of the avhrr image and the time of the aircraft experiment on september 19 the ssts derived from the avhrr images and the airt also indicated large gradients between the cold wake and the warm eddy in the central gulf of mexico the mixed layer deepened by about 30 35 m on the right side of the track during the storm and 1 2 ip later with little evidence of continued deepening afterward the mixed layer current vectors demonstrate that a strong near inertially rotating current was excited by the passage of gilbert with maxima of about 1 1 4 m s 1 the currents observed during and subsequent to 1 2 ip the storm diverged from the storm track whereas the mixed layer current vectors 2 7 ip after storm passage converged toward the track with relative maxima of 0 8 1 m s 1 this alternating pattern of convergence and divergence of the mixed layer current was associated with the upwelling and downwelling cycles of the baroclinic response considerable current shear existed between the mixed layer and the thermocline currents in the cool wake between the storm track and the 4rmax estimates of the bulk richardson numbers ranged between 0 2 and 1 0 during gilbert and at 1 2 ip which suggests that enhanced current shears were responsible for some of the mixed layer deepening