millennial scale sea surface temperature and patagonian ice sheet changes off southernmost chile 53 s over the past 60 kyr 1 glacial millennial scale paleoceanographic changes in the southeast pacific and the adjacent southern ocean are poorly known due to the scarcity of well dated and high resolution sediment records here we present new surface water records from sediment core md07 3128 recovered at 53 s off the pacific entrance of the strait of magellan the alkenone derived sea surface temperature sst record reveals a very strong warming of ca 8 c over the last termination and substantial millennial scale variability in the glacial section largely consistent with our planktonic foraminifera oxygen isotope 18o record of neogloboquadrina pachyderma sin the timing and structure of the termination and some of the millennial scale sst fluctuations are very similar to those observed in the well dated sst record from odp site 1233 41 s and the temperature record from drowning maud land antarctic ice core supporting the hemispheric wide antarctic timing of sst changes however differences in our new sst record are also found including a long term warming trend over marine isotope stage mis 3 followed by a cooling toward the last glacial maximum lgm we suggest that these differences reflect regional cooling related to the proximal location of the southern patagonian ice sheet and related meltwater supply at least during the lgm consistent with the fact that no longer sst cooling trend is observed in odp site 1233 or any sst chilean record this proximal ice sheet location is documented by generally higher contents of ice rafted debris ird and tetra unsaturated alkenones and a slight trend toward lighter planktonic 18o during late mis 3 and mis 2

insights into deglaciation of the largest ice free area in the south shetland islands antarctica from quantitative analysis of the drainage system abstract a quantitative geomorphic analysis of the drainage system on byers peninsula livingston island has been carried out in order to study the relief evolution glacial history and possible neotectonic influence on the largest ice free area of the south shetlands archipelago aerial photographs sar data from radarsat 2 satellite field work a digital elevation model and gis spatial analysis have been used to identify map and study the existing drainage basins a series of morphometric parameters have been studied in 30 selected basins in order to characterize their shape as well as the drainage network results in morphometric parameters reveal elongation trends in the shape of basins and a limited hierarchical network common of a youthful stage of landscape evolution models several morphometric indexes hypsometric integral hypsometric curves sl index transverse topographical drainage basin asymmetry t factor have been used to study possible controls on drainage development results have been discussed in relation to relief and drainage evolution linked to the spatial distribution of lithological units and structural framework t factor shows an apparently disorganized pattern and absence of tectonic influence however there are local values of second order basin asymmetry directions and magnitudes which could reflect a succession of master rills through time related to the changes in water supply during the deglaciation history of byers peninsula hypsometric values and curves of basins are also mainly related to a young stage of landscape evolution analysis of hypsometric integrals together with t factor index has allowed us to establish a possible deglaciation model on byers peninsula which successfully explains the results areas of different landscape evolution stage are linked in space and support the hypothesis of local glacial centers during the ice cover retreat process sl index results do not show the same pattern in results which could be due to differences between incision and lateral shifting ratios quantitative geomorphic analysis indicates that during the deglaciation of byers peninsula at least three areas acted as local glacial centers nw central and rotch dome area changes in index results clearly show a different behavior between two areas distal areas and proximal areas close to the glacial centers morphometric indexes have demonstrated their being useful tools to provide information on the glacial history in recently deglaciated antarctic areas

tectonic geomorphology of the southeastern mississippi embayment in northern mississippi usa we analyzed drainage basin geometry in part of the southeastern mississippi embayment near the new madrid seismic zone in order to detect areas of lateral stream migration that could indicate recent tectonism toward this goal a field of drainage basin asymmetry vectors was generated from a digital terrain model and compared to geologic structure lithofacies seismicity remotely sensed lineaments and major drainage divides transverse topographical drainage basin asymmetry t index results define geomorphic domains in northern mississippi 33 to 35 n 88 5 to 90 25 w that may reflect deep crustal blocks bounded by active faults or flexures t index measurements a proxy for lateral stream migration of more than 4500 second order drainage basins produced a two dimensional field of 282 spatially averaged vectors from which we interpreted 12 domains some domain boundaries correspond to mapped faults of two paleozoic fault systems in our study area the northeast striking mississippi valley graben system and the northwest striking ouachita thrust belt and foreland faults several other prominent domain boundaries may be previously unmapped faults flexures parallel to these systems this interpretation is supported by satellite image analysis of the northeastern study area which reveals lineaments consistent with our domain boundaries that have strikes that reflect the regional subsurface structural grain

central costa rica deformed belt kinematics of diffuse faulting across the western panama block fault kinematics seismicity and geodetic data across central costa rica reveal a diffuse fault zone here named the central costa rica deformed belt ccrdb the ccrdb defines the western margin of the panama block and links the north panama deformed belt npdb along the caribbean coast with the middle america trench mat along the pacific coast the junction of the ccrdb and the mat coincides with an abrupt transition from smooth to rough crust on the subducting cocos plate rough smooth boundary shallow subduction of rough thickened oceanic crust associated with the cocos ridge shifts active shortening into the volcanic arc along faults of the ccrdb variable fault kinematics along this zone may reflect three combined deformation mechanisms horizontal shortening and shear from oceanic ridge indentation basal traction from shallow subduction and localized block uplift from subducting seamount roughness within the forearc domain 1 mesoscale faults express transtension where steep ne striking regional scale faults intersect the pacific coast across the volcanic arc domain 2 mesoscale faults exhibit mostly sinistral and dextral slip on ne and nw striking conjugate faults respectively approaching the npdb in the back arc domain 3 transcurrent faulting is modified by transpression and crustal thickening fault kinematics are consistent with earthquake focal mechanisms and global positioning system gps measurements radiometric age constraints confirm that faulting postdates the late neogene onset of shallow subduction the ensuing deformation front has propagated northward into the volcanic arc to its present position along the seismically active ccrdb within the forearc the effect of shallow subduction is overprinted by local uplift related to underthrusting seamounts

iceberg scours along the southern u s atlantic margin rapid climate fluctuations associated with ice sheet oscillations have resulted in pulses of iceberg discharge that are recorded by iceberg scour marks along continental shelves and ice rafted debris deposits across the north atlantic iceberg transport is largely controlled by ocean surface currents therefore iceberg trajectories can serve as a proxy for paleo circulation studies records of iceberg transport from ice rafted debris i e heinrich layers in the north atlantic suggest that most icebergs released during quaternary glaciations were entrained in a cyclonic subpolar gyre restricted to polar and mid latitudes however new data suggest that there may have been an additional southerly component of transport along the western atlantic margin here we present evidence of extensive iceberg scouring across the upper slope offshore of south carolina 1000 km south of the proximal ice margin during quaternary glacial maximums the location and orientation of the keel marks suggest that icebergs were entrained in a southwestward flowing coastal current at present warm waters of the rapid northeastward flowing gulf stream bathe the upper slope off the southeastern united states an offshore shift in the gulf stream axis during sea level lowstand may have allowed glacially fed coastal currents to penetrate farther south this may be the first evidence of iceberg rafting to subtropical latitudes in the north atlantic

characteristic features of pockmarks on the north sea floor and scotian shelf this paper presents the results of a comparative study of pockmarks and associated features appearing on both sides of the north atlantic on the scotian shelf off nova scotia and in the northern north sea pockmarks are formed in seabed material consisting of soft silty clay the seismic sonar and lithologic characteristics of the sediments on the scotian shelf are remarkably similar to those found in the northern north sea sediment clouds suspended in the water column immediately over the seabed have previously been observed on side scan records associated with gas charged sediments on corresponding shallow seismic records these and similar observations strongly suggest that most pockmarks are caused by gas efflux through the seafloor however the detailed mechanism of formation and the origin of the gas in the sediments is still unknown

a community based geological reconstruction of antarctic ice sheet deglaciation since the last glacial maximum a robust understanding of antarctic ice sheet deglacial history since the last glacial maximum is important in order to constrain ice sheet and glacial isostatic adjustment models and to explore the forcing mechanisms responsible for ice sheet retreat such understanding can be derived from a broad range of geological and glaciological datasets and recent decades have seen an upsurge in such data gathering around the continent and sub antarctic islands here we report a new synthesis of those datasets based on an accompanying series of reviews of the geological data organised by sector we present a series of timeslice maps for 20 ka 15 ka 10 ka and 5 ka including grounding line position and ice sheet thickness changes along with a clear assessment of levels of confidence the reconstruction shows that the antarctic ice sheet did not everywhere reach the continental shelf edge at its maximum that initial retreat was asynchronous and that the spatial pattern of deglaciation was highly variable particularly on the inner shelf the deglacial reconstruction is consistent with a moderate overall excess ice volume and with a relatively small antarctic contribution to meltwater pulse 1a we discuss key areas of uncertainty both around the continent and by time interval and we highlight potential priorities for future work the synthesis is intended to be a resource for the modelling and glacial geological community

geomorphology and shallow structure of a segment of the atlantic patagonian margin abstract we study an area little known of the atlantic patagonian margin from 44 30 s to 47 40 s and from 59 w to nearly 61 w the multi beam bathymetry coupled with high resolution seismic reflection profiles has provided details on the morphology and shallow acoustic structure on this area the main morphological characteristics of the seafloor features on the shelf and middle slope are described the atlantic patagonian continental shelf north of 45 40 s is located at a depth of 170 200 m south of this latitude the shelf edge is at 128 to 200 m the shelf surface is marred by circular depression and ridges oriented oblique to the shelf edge the upper slope and upper middle slope are plowing by icebergs from antarctica in pleistocene and local reefs of cold water coral further enhance the topography of the area in the middle slope there are two terraces the 20 to 60 km wide nagera and the 15 to 60 km wide perito moreno terraces showing moats hollows pot holes sediment drifts and sediment waves the terraces may have been formed in late miocene whereas the other forms are of pleistocene age other features are a sediment swell south of 47 s and seven submarine canyons on the middle slope these incipient canyons have been developed in the middle slope by retrogressive erosion some terminating on the upper middle slope and others on the upper slope and the canyon 6 breaching the shelf edge individual seafloor features existing on the atlantic patagonian margin have been classified into two main groups according to their origin along and across slope processes these primary agents were supplemented by endogenic processes such as expulsion of gas water diapirism of high pressure mud and folding faulting the results suggest that today down slope processes on the slope are practically non existent and that the morphology of the upper and middle slope is slowly being remolded by along slope bottom currents

seismic stratigraphy sedimentary architecture and palaeo glaciology of the mackenzie trough evidence for two quaternary ice advances and limited fan development on the western canadian beaufort sea margin abstract a comprehensive grid of high resolution 2 d seismic reflection data from the western canadian beaufort sea margin is used to reconstruct past ice stream dynamics within the mackenzie trough eight seismic facies and five sequences divided into two megasequences are identified from the mackenzie trough stratigraphy evidence for two quaternary ice advances to the shelf break is provided by two sequences of acoustically chaotic to semi transparent facies interpreted as subglacial till buried landforms interpreted as lateral moraines and a grounding zone wedge record the positions of still stands or re advances in the ice margin the continental slope beyond the trough is characterised by canyons separated by inter canyon ridges and thin glacigenic debris flows correlation with the onshore record suggests that the older of the two ice advances which excavated the mackenzie trough probably occurred during the illinoian or early wisconsinan glaciations the younger ice stream advance is interpreted to have occurred during the last late wisconsinan glaciation the onset of cross shelf glaciation on the western canadian beaufort sea margin is inferred to have been initiated significantly later than on the eastern beaufort sea and eastern canadian arctic margins which have a longer history of ice advance and were less peripheral to the ice sheet centre the architecture of the slope beyond the mackenzie trough reflects this comparatively short history of ice advance and lacks the progradational architecture and major glacial sedimentary depocentre or trough mouth fan that is characteristic of slopes seaward of cross shelf troughs on formerly glaciated margins

minimal change in antarctic circumpolar current flow speed between the last glacial and holocene relatively little is known about the dynamics of the antarctic circumpolar current during the last glacial period estimates of current speeds over the past 20 000 years based on sediment grain size suggest that average flow speeds during the last glacial were comparable to modern speeds but not in the areas with overlying winter sea ice

seismic and bathymetric evidence for four different episodes of iceberg scouring on the new jersey outer shelf possible correlation to heinrich events abstract re analysis of dense chirp seismic surveys on the outer new jersey shelf reveals two sets of shallowly buried incisions the incisions are linear to slightly sinuous oriented ne sw and exhibit cross cutting relationships we interpret both sets as paleo iceberg scours one set cuts into the r horizon a regional unconformity that formed 45 40 ka and which was subsequently buried by the finer grained outer shelf sediment wedge osw the second set is part of an erose boundary between a layered lower unit of the osw and an upper more transparent unit the erose boundary scours are deeper and have steeper slopes than the r horizon scours the latter often exhibit bermed edges whereas the former do not these differences in cross sectional morphology are likely determined by the material properties of the sediments being scoured sand at the r horizon and clay at the erose boundary the orientation of both sets of scours is consistent with previously recognized iceberg scours in stratigraphically younger seafloor on the outer new jersey shelf in 110 150 m water depths located 40 km to the northeast we argue that heinrich events recurring periods of massive iceberg flux into the north atlantic represent the most likely times for transporting icebergs to these latitudes based on stratigraphic relationships a recently published ambient sea level curve and radiocarbon age constraints we attribute the r horizon scours to heinrich event h4 37 cal ka the erose boundary scours to h3 30 cal ka and the seafloor scours to h2 23 cal ka and or h1 17 cal ka facies changes immediately following the r horizon and erose boundary scours may be related to heinrich event forced climate changes perhaps the onset of interstadial conditions and associated melt water pulses floods these pulses floods repeatedly carried fine grained rock flour produced by widespread glacial erosion to the new jersey shelf

stone run block stream formation in the falkland islands over several cold stages deduced from cosmogenic isotope 10be and 26al surface exposure dating cosmogenic isotope 10be and 26al surface exposure dating has been applied to valley axis and hillslope stone runs relict periglacial block streams and their source outcrops in the falkland islands south atlantic the data indicate that stone runs are considerably older landforms than previously envisaged and afford no evidence that they are a product of the last glacial maximum the samples range in apparent 10be age from 42k to 731k yr bp but some of these are minima the results indicate that valley axis stone runs may be up to 700 800k yr old have simple exposure histories and are composite landforms that developed over several cold stages analyses of some hillslope and outcrop samples also demonstrate simple exposure histories with 10be ages from 42k to 658k yr bp in contrast isotopic ratios from other hillslope and outcrop samples reveal they have had a complex exposure history involving periods of burial or shielding the samples range in 10be age from 59k to 569k yr bp and these are regarded as minimum age estimates larger stone runs may be older than smaller runs and there is a possibility that stone runs older than 800k yr exist in other parts of the falklands the assertion that glaciation in the falklands was restricted to the highest uplands is supported by the data and the potential for age determination of other boulder strewn and bedrock landforms using cosmogenic isotope analysis in order to extend the geochronology of quaternary events and processes is noted

effect of subducting sea floor roughness on fore arc kinematics pacific coast costa rica fault kinematics and uplift in the costa rican fore arc of the middle america convergent margin are controlled to a large extent by roughness on the subducting cocos plate along the northwest flank of the incoming cocos ridge seafloor is characterized by short wavelength roughness related to northeast trending seamount chains onland projection of the rough subducting crust coincides with a system of active faults oriented at high angles to the margin that segment the fore arc thrust belt and separate blocks with contrasting uplift rates trunk segments of pacific slope fluvial systems typically follow these margin perpendicular faults regionally developed marine and fluvial terraces are correlated between drainages and across faults along the costa rican pacific coast terrace separations across block bounding faults reveal a pattern of fore arc uplift that coincides roughly with the distribution of incoming seamounts magnitude and distribution of quaternary uplift along the costa rican pacific coast suggests that despite a thin incoming sediment pile the inner fore arc shows an accumulation of mass a characteristic that may be due to underplating of seamounts beneath the fore arc high

kinematics associated with late cenozoic deformation in central costa rica western boundary of the panama microplate we present kinematic data for late cenozoic deformation in central costa rica that marks the western margin of the panama microplate i e the caribbean panama boundary this boundary extends from the north panama deformed belt west through the valle central in costa rica and then southwest along the east nicoya fracture zone to intersect the middle america trench terrace correlation and basin asymmetry indicate a major change in tectonic evolution across the boundary where three regional northeast striking faults intersect the pacific coast mesoscopic fault populations are consistent with transtension across these north east striking faults and with transpression within the east trending valle central this late tertiary and quaternary transcurrent deformation links the north panama deformed belt to the east with the middle america trench to the west earthquake focal mechanisms are consistent with mesoscopic fault data suggesting that fault populations characterize the present day stress field this deformation marks the western extent of the panama microplate a fragment of volcanic arc that separated from the caribbean plate in the late tertiary or early quaternary and is currently advancing northward due to collisions with south america to the east and the indenting cocos ridge on the cocos plate to the south

pedosediments of karstic sinkholes in the eolianites of ne yucatan a record of late quaternary soil development geomorphic processes and landscape stability abstract the pedogenetic and geomorphic processes controlling soil development in tropical karstic landscapes are still poorly understood we have discovered and studied thick pedosediments in karst pockets developed in late pleistocene lithified calcareous dunes eolianites in the ne coast of the yucatan peninsula the morphological geochemical and mineralogical characteristics of the pocket fills were interpreted as a record of pedogenesis and geomorphic dynamics that shaped the soil mantle during the holocene sand fraction mineralogy and the zr ti ratio indicated a mixed origin of the soil parent material volcanic and granitic metamorphic components redeposited in the lithoral and coastal environments were identified within the soil matrix primary minerals were transformed by weathering and caused desilicification accumulation of clay hydroxy interlayered vermiculite and kaolinite and dithionite citrate bicarbonate extractable iron oxides fed reworked pedofeatures indicative of clay illuviation and redoximorphic processes were observed this set of processes points to a continuous phase of humid pedogenesis several thousand years long in the early middle holocene however the development of thick recalcified pedosediments in the pockets contrasting with the thin background rendzinas requires active soil redeposition during a late phase of geomorphic activity the available accelerator mass spectrometry ams radiocarbon date indicates that the switch of the erosion sedimentation processes could be related to ancient maya land use impact

internal structure of a contourite drift generated by the antarctic circumpolar current 1 we describe the internal structure and stratigraphy of a well imaged contourite drift from the southern ocean this drift which we have named the south falkland slope drift lies on the northern flank of the falkland trough due south of the falkland islands drifts which occur directly in the path of the antarctic circumpolar current acc downstream of the drake passage gateway are of considerable paleoceanographic significance since their detailed stratigraphic record will help to constrain the history of the acc we have reprocessed a grid of seismic reflection profiles generously provided by westerngeco ltd in order to enhance imaging of the south falkland slope drift and of drift deposits within the trough the resultant high quality images enable us to map the internal architecture of these drifts in unprecedented detail by combining seismic stratigraphic mapping with measured sedimentation rates from nearby boreholes we have inferred ages of the principal mappable horizons with minor adjustments to sedimentation rates through time we can show that these ages correspond to significant southern ocean events we propose that the south falkland slope drift initiated at 24 5 20 5 ma in accordance with some but not all published estimates of acc establishment a highly reflective horizon with an estimated age of 14 5 ma corresponds to growth of the east antarctic ice sheet which led to a period of significant global cooling a similarly bright reflective horizon with an estimated age of 9 ma is thought to be related to a reorganization of bottom current flow which just predated establishment of grounded ice sheets on the antarctic peninsular shelf finally a prominent early pliocene unconformity at 4 5 ma may be linked with the onset of major northern hemisphere glaciation or with antarctic ice sheet expansion we conclude that this well imaged drift is an important and largely continuous stratigraphic record of acc activity and suggest that it would be an excellent drilling target

active thrusting landscape evolution and late pleistocene sector collapse of baru volcano above the cocos nazca slab tear southern central america in this paper stratigraphy geochronology and geologic mapping are used to characterize a sequence of quaternary deposits associated with edifice failure of baru volcano which together with balanced cross sections illustrate the upper plate s response to along strike variations in subduction properties that occur across the tear in the subducting slab located at the panama fracture zone the subducting panama fracture zone is an active transform that separates disparate styles of subduction between the thick rapid and flat subduction of the cocos plate to the west and the thinner more oblique and steeper subduction of the nazca plate to the east we focus on the arc forearc region above the cocos nazca slab tear where both the fila costena inner forearc fold and thrust belt and the exhumed cordillera de talamanca terminate along strike to the southeast the fila costena thrust belt imbricates an eocene late miocene forearc basin sequence with up to 40 km of shortening inboard of cocos plate subduction and crosscuts a sequence of pleistocene and younger volcano sedimentary units on the southwestern flanks of the active baru volcano at its southeastern termination these units constrained in age by radiocarbon dating n 11 soil color and 40 ar 39 ar n 5 data include a sequence of late pleistocene to holocene debris avalanche and lahar deposits landscape morphology the areal distribution of units and new shortening estimates from balanced cross sections collectively suggest that the southeastern termination of the fila costena thrust belt actively propagates to the southeast coeval with migration of the panama triple junction the prevailing map pattern suggests that the forearc s response to southeastward migration of the slab tear varies with distance to the trench in contrast to deformation patterns in the outermost forearc plate boundary tractions associated with shallow subduction and cocos caribbean convergence are more influential in the development of arc forearc deformation than either oblique subduction of the 2 km bathymetric scarp or right lateral shear which both occur astride the subducting panama fracture zone

stabilization of glaciers terminating in closed water bodies evidence and broader implications 1 the behavior of glaciers terminating in deep water is determined by the interaction of buoyancy iceberg production and the sensitivity of ice flow to subtle changes in resistance at the glacier bed modeling efforts assume rapid evacuation of icebergs but some glaciers terminate in closed basins where icebergs may accumulate multibeam bathymetric survey of a glacial lake in iceland that received outlet glaciers during the little ice age document near parallel flow of narrow ice fingers that extended up to 1 km beyond the grounding line these previously unseen features apparently occurred when iceberg production exceeded iceberg melt resulting in iceberg buttressing of the ice margin similar stabilization of ice flow may resolve long standing debates about past continental ice sheet behavior including the rapid readvance of the laurentide ice sheet into lake superior ca 11 ka and the genesis of glacial flutes observed in the central arctic ocean basin

climatic inferences from glacial and palaeoecological evidence at the last glacial termination southern south america there is uncertainty about the interhemispheric timing of climatic changes during the last glacial interglacial transition different hypotheses relying on different lines of evidence point variously to the northern hemisphere leading the southern hemisphere and vice versa or to synchrony between the hemispheres southern south america is well placed to test the various alternatives using both glacial and palaeoecological evidence we argue here from a synthesis of key proxy records that there was a sudden rise in temperature that initiated deglaciation sychronously over 16 of latitude at 14 600 14 300 14 c yr bp 17 500 17 150 cal yr there was a second step of warming in the chilean lake district at 13 000 12 700 14 cy r bp 15 650 15 350 cal yr which saw temperatures rise to close to modern values a third warming step particularly clear in the south occurred at ca 10 000 14 c yr bp 11 400 cal yr the latter achieving holocene levels of warmth following the initial warming there was a lagged response in precipitation as the westerlies after a delay of ca 1600 yr migrated from their northern glacial location to their present latitude which was attained by 12 300 14 cy r bp 14 300 cal yr the latitudinal contrasts in the timing of maximum precipitation are reflected in regional contrasts in vegetation change and in glacier behaviour the large scale of a 80 km glacier advance in the strait of magellan at 12 700 10 300 14 c yr bp 15 350 12 250 cal yr which spans the antarctic cold reversal and the younger dryas was influenced by the return of the westerlies to southern latitudes the delay in the migration of the westerlies coincides with the heinrich 1 iceberg event in the north atlantic the suppressed global thermohaline circulation at the time may have affected sea surface temperatures in the south pacific and the return of the westerlies to their present southerly latitude only followed ocean reorganisation to its present interglacial mode copyright 2000 john wiley sons ltd

the mw 6 4 damas costa rica earthquake of 20 november 2004 aftershocks and slip distribution the earthquake of 20 november 2004 was located north of damas island in the pacific coast of costa rica within the costa rica deformed belt the earthquake was located at 24 km depth and reported with a magnitude m w of 6 4 and a strike slip mechanism with a large normal dip slip motion this mechanism agrees with mapped faults in the area that suggest transtensional deformation on the forearc and the entire western boundary of the panama microplate aftershock locations do not delineate a preferable plane to distinguish between the two nodal planes and are distributed between 15 and 25 km depth the slip distribution during the mainshock modeled after teleseismic and local data pictured a circular rupture 8 km in radius and 0 25 m of average displacement the fault plane cannot be distinguished from the two nodal planes from the slip distribution because of the lack of directivity and resolution for this magnitude earthquake weak evidence from empirical green s function analysis suggests that the dextral northwest oriented fault could be the causative fault depth to the top of the slab hypocenter location of the mainshock its slip distribution depth distribution of the aftershocks and quaternary fault activity at the surface suggest that deformation takes place throughout the whole thickness of the crust this extended deformation might be caused by seamount subduction and strong basal friction on the upper plate due to subduction of a thick young and buoyant oceanic plate rough seafloor and underplating of large seamounts

glacial geomorphology and chronology of deglaciation south georgia sub antarctic we mapped and dated the glacial geomorphology of north east south georgia in the maritime sub antarctic the aim was to examine the timing of deglaciation of the island in the context of inter hemispheric phasing of climate change former glacier limits are restricted to the inner fjords and our detailed mapping of them has demonstrated a consistent geomorphological pattern that is similar across several different glacier types and sizes the pattern comprises three suites of moraines categories a c not all of which are represented at every site because the outer suite is often overridden by younger suites category a is an outer wide low amplitude moraine ridge category b comprises 2 4 sharp crested bouldery moraines that are often located close to or even over riding a and category c is a series of lower amplitude moraines with overprinted streamlined landforms such as flutings analysis of in situ cosmogenic 10be in boulders on these moraines has allowed us to determine a deglacial chronology for the older two moraine groups the age of the inner youngest group has been estimated from soil development the cosmogenic nuclide ages show that the outermost moraine was deposited ca 12 2 1 5 ka bp but that a subsequent readvance in the mid holocene ca 3 6 1 1 ka bp reached and in places over rode this earlier moraine this latter advance coincides with the mid holocene hypsithermal a final late holocene advance reached closely similar limits to the previous two fluctuations and is estimated from soil data to have an age of ca 1 1 ka bp we suggest that the close concordance of late glacial and interglacial limits in this case associated with warming can be explained by a change in dominant forcing during glacials extensive sea ice limits precipitation availability and so glaciers are restricted to the inner fjords during interglacials precipitation is not limited in the same way by sea ice cover and so during warming precipitation increases and tidewater glaciers on the island have responded by advancing this study emphasises the importance of a clear understanding of geomorphology in order to interpret chronological information

comparison of trends of iceberg scour marks with iceberg trajectories and evidence of paleocurrent trends on saglek bank northern labrador shelf high resolution seismic and sidescan sonar surveys on saglek bank indicate extensive areas of iceberg scoured sea bottom and provide data for an analysis of 6075 iceberg scour marks in 537 samples each of 0 25 km by 2 0 km area the general trends of iceberg scours measured on sidescan sonographs are comparable to iceberg trajectories which are mostly controlled by currents on saglek bank iceberg scour and iceberg drift directions are generally northwest southeast straight scours predominate on the shelf edge reflecting the influence of unidirectional oceanic labrador currents bank top scours are commonly curved reflecting the influence of slower moving water more subject to the effects of rotary tidal currents and storms this difference in dispersion of scour trends between the bank top and shelf edge is due to the relative strengths of variable tidal and storm driven currents and unidirectional oceanic currents pack ice forces may also influence iceberg movement modern icebergs scour the she

keel depths of modern antarctic icebergs and implications for sea floor scouring in the geological record abstract icebergs affect the geological record through the scouring or ploughing action of their keels reworking sediments where they contact the sea floor satellite radar altimeter measurements of the surface elevation of the marine margins of the antarctic ice sheet are inverted to produce ice thickness values these data are assumed to represent the keel depths of newly calved icebergs there are three peaks in the frequency distribution of antarctic iceberg keel depths a about 140 200 m in thickness associated with smaller ice shelves fringing antarctica e g wilkins george vi and brunt ice shelves b about 250 300 m from large ice shelves e g ross ronne amery and c approximately 500 600 m from fast flowing ice sheet outlet glaciers e g pine island and dibble glaciers together with the filchner ice shelf controls on iceberg keel depth are ice thickness at the grounding line creep thinning and the rate of melting freezing at the floating ice shelf base with distance to the calving margin the distribution of sea floor scours produced by iceberg grounding is dependent on the changing form and flow of the glaciers and ice sheets from which icebergs are derived and on berg drift tracks and melt rates sea floor evidence for icebergs with particularly deep keels has sometimes been interpreted to indicate the presence of extensive former ice shelves however the largest modern antarctic ice shelves do not produce large numbers of icebergs thicker than about 350 m implying that sea floor scours found in deeper water are unlikely to be an indicator of extensive past ice shelf development iceberg scours found at water depths in excess of about 500 m in the geological record are instead probably indicative of either a the former presence of fast flowing ice sheet outlet glaciers b ice shelves fed from major interior basins where lateral spreading is constrained topographically or c a pulse of large icebergs released during major deglaciation or ice sheet collapse

late miocene to recent plate tectonic history of the southern central america convergent margin new plate reconstructions constrain the tectonic evolution of the subducting cocos and nazca plates across the southern central american subduction zone from late miocene to recent because of the strong relationships between lower and upper caribbean plate dynamics along this margin these constraints have wide ranging implications for the timing and growth of upper plate deformation and volcanism in southern central america the reconstructions outline three important events in the neogene history of this margin 1 the coeval development of the panama triple junction with the initiation of oblique subduction of the nazca plate at 8 5 ma 2 the initiation of seamount and rough crust subduction beginning at 3 4 ma and 3 cocos ridge subduction from 2 to 3 ma a comparison of these events with independent geologic geomorphic volcanic and stratigraphic data sets reveals that the timing rates and origin of subducting crust directly impacted the neogene growth of upper plate deformation and volcanism in southern central america these analyses constrain the timing geometry and causes of a number of significant tectonic and volcanic processes including rapid plio quaternary arc fore arc contraction due to cocos ridge subduction the detachment of the panama microplate at 1 3 ma and the late miocene cessation of mantle wedge derived volcanism across 300 km of the subduction zone

relict sea floor ploughmarks record deep keeled antarctic icebergs to 45 s on the argentine margin abstract this paper reports ploughmarks on the argentine continental margin up to 44 50 s the most northerly morphological evidence of giant icebergs in the southern atlantic more than 2500 ploughmarks up to 32 km long 685 m wide and more than 20 m deep have been observed at modern water depths up to 646 m taking into account these iceberg sizes and ocean current directions which appear to have remained similar from the last full glacial to the present interglacial the icebergs that produced the ploughmarks are interpreted to be calved from fast flowing ice streams draining huge basins of the west antarctic ice sheet and the western antarctic peninsula during the last glacial maximum lgm about 20 000 years ago ploughmarks at the deepest water depths correspond to icebergs more than 500 m thick and at least 2 km wide given a sea level rise of 120 m since the lgm the icebergs after having drifted northeast in the antarctic circumpolar current were transported northward by the falklands malvinas current a total distance of 2000 to 4000 km the waters north of the falkland islands in particular were probably several degrees colder than today to prevent rapid iceberg melting and deterioration

bulls eye pockmarks and polygonal faulting in the lower congo basin relative timing and implications for fluid expulsion during shallow burial abstract this study describes a new type of pockmark association from the lower congo basin offshore west africa consisting of up to 8 stacked paleopockmarks separated by intervals of drape and onlap fill the stacked paleopockmarks occur within the depocentres of polygonally faulted plio pleistocene sediments and are distributed evenly in the downslope parts of two salt mini basins the majority of the stacked pockmarks initiated synchronously in the late pliocene 3 ma with a subordinate initiation phase in the mid pliocene 4 ma the primary agents in pockmark formation are interpreted to be pore water expelled during early stage compaction together with biogenic methane bottom simulating reflections bsrs associated with free gas overlain by gas hydrates are currently found in the area it is speculated that biogenic methane accumulated within and below a clathrate cap which was repeatedly breached forming pockmarks at discrete horizons separated by intervals of draping sedimentation the mid and late pliocene pockmark initiations appear to coincide with sea level falls following periods of relatively stable highstand conditions several subsequent pockmark horizons may similarly correlate with subsequent sea level falls during the late pliocene and early pleistocene the stacked paleopockmarks are completely surrounded by polygonal faults and consistently occur within polygonal fault cells that crosscut the succession containing the stacked pockmarks early stage compaction and dewatering of the pliocene sediments thus preceded polygonal faulting providing a constraint on the conditions leading to polygonal faulting of the fine grained host sediments the relationship documented here is interpreted as due to the presence of a hydrate cap in the plio pleistocene mini basins which may have retarded the normal compaction processes and facilitated pockmark formation by allowing the build up of gas hydrate and free gas in the basin centres the relative timing and spatial relationships implies that fluids expelled due to polygonal faulting were not implicated in pockmark formation in this area

relict iceberg keel marks on the new jersey outer shelf southern hudson apron swath sonar bathymetry reveals sinuous furrows 400 m wide kilometers long and 4 m deep inscribed in semilithified clays on the southern hudson apron we interpret these as keel marks created by floating icebergs detached from the retreating laurentide ice sheet since ca 25 ka keel mark orientations suggest two phases of iceberg rafting these phases could correlate with heinrich meltwater events h2 and h1 ca 25 and 17 ka bracketing the late wisconsinan glacial maximum ca 22 ka during holocene transgression some keel marks were reworked and reformed into oblique ridges where older sandier sediments crop out at the seafloor relict glacial features on the new jersey outer shelf provide a tie between the timing of laurentide glacial retreat and the evolution of shallow stratigraphy on this mid latitude shelf during the last global sea level cycle ca 120 ka to present

antarctic peninsula ice sheet evolution during the cenozoic era the antarctic peninsula region is currently undergoing rapid environmental change resulting in the thinning acceleration and recession of glaciers and the sequential collapse of ice shelves it is important to view these changes in the context of long term palaeoenvironmental complexity and to understand the key processes controlling ice sheet growth and recession in addition numerical ice sheet models require detailed geological data for tuning and testing therefore this paper systematically and holistically reviews published geological evidence for antarctic peninsula ice sheet variability for each key locality throughout the cenozoic and brings together the prevailing consensus of the extent character and behaviour of the glaciations of the antarctic peninsula region major contributions include a downloadable database of 186 terrestrial and marine calibrated dates an original reconstruction of the lgm ice sheet and a new series of isochrones detailing ice sheet retreat following the lgm glaciation of antarctica was initiated around the eocene oligocene transition in east antarctica palaeogene records of antarctic peninsula glaciation are primarily restricted to king george island where glacigenic sediments provide a record of early east antarctic glaciations but with modification of far travelled erratics by local south shetland island ice caps evidence for neogene glaciation is derived primarily from king george island and james ross island where glaciovolcanic strata indicate that ice thicknesses reached 500 850 m during glacials this suggests that the antarctic peninsula ice sheet draped rather than drowned the topography marine geophysical investigations indicate multiple ice sheet advances during this time seismic profiling of continental shelf slope deposits indicates up to ten large advances of the antarctic peninsula ice sheet during the early pleistocene when the ice sheet was dominated by 40 kyr cycles glacials became more pronounced reaching the continental shelf edge and of longer duration during the middle pleistocene during the late pleistocene repeated glacials reached the shelf edge but ice shelves inhibited iceberg rafting the last glacial maximum lgm occurred at 18 ka bp after which transitional glaciomarine sediments on the continental shelf indicate ice sheet retreat the continental shelf contains large bathymetric troughs which were repeatedly occupied by large ice streams during pleistocene glaciations retreat after the lgm was episodic in the weddell sea with multiple readvances and changes in ice flow direction but rapid in the bellingshausen sea the late holocene epoch was characterised by repeated fluctuations in palaeoenvironmental conditions with associated glacial readvances however this has been subsumed by rapid warming and ice shelf collapse during the twentieth century

a new bathymetric compilation highlighting extensive paleo ice sheet drainage on the continental shelf south georgia sub antarctica a grid derived from a new compilation of marine echo sounding data sets has allowed us to visualize and map the geomorphology of the entire continental shelf around south georgia at an unprecedented level of detail the grid is the first continuous bathymetric data set covering south georgia to include multibeam swath bathymetry and represent them at a subkilometer resolution large and previously undescribed glacially eroded troughs linked to south georgia s modern day fjords radiate from the island marking the former pathways of large outlet glaciers and ice streams a tectonic or geological influence is apparent for the major troughs where glaciers have exploited structural weaknesses on the continental block bed forms lining the troughs give some first insights into glacial dynamics within the troughs suggesting arteries of fast flowing ice occupied these topographic depressions in the past and operated over both bedrock and sedimentary substrates on the outer shelf and within the troughs large ridges and banks are also common interpreted as terminal lateral and recessional moraines marking former positions of ice sheets on the shelf and their subsequent reorganization during deglaciation a small trough mouth fan has developed at the mouth of at least one of the cross shelf troughs demonstrating a focused sediment delivery to the margin slides and slide scars are also present on parts of the margin showing that margin stability perhaps also related to glaciation has been an important factor in depositional processes on the continental slope implications of the new observations are that ice sheets have been more extensive on south georgia than any previous studies have reported their age may date back to late miocene times and evolution of the shelf system has probably involved numerous late cenozoic glacial episodes however relatively fresh seafloor geomorphology coupled with evidence from other maritime antarctic islands heard island and kerguelen island indicating extensive glaciation at the last glacial maximum raises the possibility that the extent of sub antarctic glaciation for the last glacial period has until now been underestimated

description and numerical model of pleistocene iceberg scours and ice keel turbated facies at toronto canada near toronto in southern ontario canada glaciolacustrine muds and shoreface sands of late pleistocene age early wisconsin glaciation 45 ka were deformed by icebergs ploughing the floor of an ancestral ice dammed lake ontario outcrop mapping and a ground penetrating radar survey identify ice scour structures up to 4 m deep up to 10 m wide and at least several hundred metres long with high standing lateral margins berms ploughing of lake floor sediment is also recorded by ice keel turbated facies in which storm deposited shoreface sands have been mechanically mixed with underlying muds palaeoenvironmental information for one prominent scour such as water depths estimates of the mass and draft of the ice mass and scouring forces can be determined using a simple finite element numerical model a mass of 0 04 million tonnes a keel draft of between 10 and 30 m and a scouring force of 5 103 kn is consistent with scouring by a small iceberg bergy bit or pressure ridged lake ice the former is preferred because of the considerable depth of the scour and the overall glacial depositional setting estimates of ice mass dimensions agree with independent reconstructions of palaeobathymetry no greater than 20 m derived from storm deposited hummocky and swaley cross stratified facies that fill the scour data presented here aid the identification of ice scour structures and turbated sediment in the ancient record despite being a common process on modern high latitude shelves descriptions of ancient structures and facies are few

geophysical evidence of deep keeled icebergs on the rockall bank northeast atlantic ocean high resolution multibeam swath bathymetric data acquired from the rockall bank reveal an abundance of linear to slightly sinuous seabed incisions these features interpreted as relict iceberg scours provide for the first time evidence that the rockall bank was intensively scoured by iceberg keels while the shallower portion of the rockall bank lacks evidence of iceberg scouring on the western and southern flanks between 250 and 450 m water depth the seabed is almost completely covered by thousands of cross cutting scours more isolated scours up to 800 m wide and 25 km long are also observed down to nearly 600 m water depth based on a full glacial sea level low stand of 120 m these isolated scour marks must have been carved bygigantic icebergs with keels up to 500 m deep and able to create incisions up to 15 m deep in the seabed analysis of scour orientation length width and depth indicates that these mega icebergs were likely calved from large fast flowing ice sheet outlets draining circum north atlantic ice sheets prevailing scour orientations suggest a number of possible ice sheet sources including southeast and southern greenland and the donegal barra ice stream of the last british irish ice sheet the bimodal distribution of the scour depth observed across the rockall bank suggest either different icebergs provenances or physical and climatic controlson icebergs draft

identification of possible quaternary deformation in the northeastern mississippi embayment using quantitative geomorphic analysis of drainage basin asymmetry to investigate neotectonism in the mississippi embayment east of the new madrid seismic zone we identified geomorphic domains that show evidence of ground tilting during quaternary time transverse basin profiles were converted to two dimensional vectors that denote channel position with respect to basin divides these basin asymmetry vectors record the net direction and degree of lateral migration of trunk streams more than 2500 vectors were measured and spatially averaged within 400 km 2 bins this field of 300 mean vectors delineates several domains that show preferred directions of stream migrations possibly driven by ground tilting the timing of stream migration was interpreted using across valley distributions of quaternary alluvial terraces comparison of our mean vector field with subsurface structures suggests that some domain boundaries may be related to reactivated faults late quaternary activity is suggested for two northeast striking faults of the southeastern reelfoot rift margin we acquired two seismic profiles showing near surface faulting beneath scarps that follow the domain boundary associated with one of these northeast striking faults big creek fault zone reelfoot thrust seismicity ends on the south against this fault suggesting that the rift margin has dextral slip accommodating northeastward movement of the thrust hanging wall our vector field also suggests late quaternary movement on the reelfoot thrust and on two other northwest striking faults here termed the hatchie river fault and the wolf river fault several other weak domains may imply minor elements of neotectonism our results demonstrate that morphometric analysis of drainage basin asymmetry can be an effective reconnaissance tool within neotectonic settings

simultaneous inversion for earthquake location and velocity structure beneath central costa rica we have imaged the complex crustal and upper mantle structure beneath central costa rica using p wave arrival times from locally recorded earthquakes thurber s 1983 iterative inversion method is used to simultaneously estimate velocities along a three dimensional grid and hypocentral parameters of local earthquakes our data consist of over 12 000 arrival times from more than 1300 earthquakes recorded by stations of a permanent seismographic network in costa rica our resulting velocity model correlates well with mapped geologic units at very shallow depth and with tectonic features at greater depth we find low velocities 4 0 to 4 8 km sec in the shallow crust above 10 km near the active volcanoes and associated with a nw se trending late cretaceous to late tertiary sedimentary basin southeast of herradura peninsula high velocities 5 4 to 5 7 km sec in the shallow crust correlate with outcrops of late jurassic to early tertiary ultramafic ophiolitic units and with basic tertiary volcanic units at depths between 20 and 30 km high velocities 6 8 to 7 2 km sec are associated with the subducting cocos plate under costa rica and two prominent low velocity bodies 6 3 to 6 5 km sec are present about 30 km trenchward of the volcanic arc and along the projection of the aseismic cocos ridge as it subducts beneath costa rica the thickened oceanic crust of the cocos ridge is most likely responsible for its low velocities the deep low velocity anomaly located trenchward of the axis of the volcanoes may indicate the presence of a low density intrusive resulting from an earlier phase of magmatism possibly the late miocene episode that produced the talamanca intrusive complex

the antarctic ice sheet during the last glacial maximum and its subsequent retreat history a review abstract an emerging body of evidence from studies of the last glacial interglacial cycle suggests that the east and west antarctic ice sheets have not advanced and retreated in concert the west antarctic ice sheet advanced to the outer shelf in most regions during the last glacial maximum lgm the retreat from the shelf commenced shortly after the lgm and continued into the late holocene the west antarctic ice sheet in ross and amundsen seas slid across a deforming bed at least during the final phases of extended glaciation this implies that at this time the ice sheet had a low profile differences in the number and locations of grounding zone wedges and smaller grounding zone features from trough to trough imply that individual west antarctic ice sheet ice streams retreated episodically details concerning the expansion retreat and behavior of the east antarctic ice sheet eais are more sparse the picture emerging is that the eais did not expand to the continental shelf edge during the lgm rather it achieved a maximum extent of a mid shelf position in some locations while in other areas the ice terminus was situated near its present location the timing of retreat along sectors within the eais appears diachronous and in places occurred prior to the lgm the antarctic peninsula shelf contained considerably more ice during the lgm than previously proposed the results presented in this paper support more recent published ice sheet models that call for greater contributions of melting ice from west antarctica including the antarctic peninsula to the post glacial rise in sea level

buried iceberg ploughmarks in the early quaternary sediments of the central north sea a two million year record of glacial influence from 3d seismic data abstract buried linear to curvilinear depressions interpreted as iceberg ploughmarks were identified through most of the 2 ma long and about 700 m thick early quaternary sedimentary record in two 3d seismic cubes from the central north sea basin 56 58 n 2 3 e the mean width of 402 features measured at 6 time slices in cube c08 was between 49 and 63 m and mean length was 2 5 to 3 7 km mapping the

can glacial erosion limit the extent of glaciation kaplan m r hein a s hubbard a 2009 can glacial erosion limit the extent of glaciation geomorphology 103 2 172 179

repeated fluid expulsion through sub seabed chimneys offshore norway in response to glacial cycles abstract focused fluid flow through sub seabed sediments is a common phenomenon on continental margins worldwide however the governing controls and timing of this fluid release have been difficult to understand in particular for fluid flow features buried beneath sub surface sediments a link between fluid flow activity ensuing pockmark formation and the last glacial maximum has been hypothesized on the formerly glaciated norwegian margin new high resolution p cable 3d seismic data from the nyegga area on the mid norwegian margin reveal at least two more periods of fluid expulsion from sub seabed sediments the 3d seismic data show depositional patterns within chimney features expressed as truncations of seismic horizons against the flanks of the chimneys the truncations are interpreted by analogy with present day observations as evidence for buried carbonate mounds and or sediment wash out during formation of pockmarks in the past the truncations are hence an indicator and a chronological marker for fluid expulsion in the past the classification of chimneys results in three major groups 1 chimneys that have been formed and consecutively reactivated one or two times during the last 200 kyr and that have a fluid flow expression at the present seafloor 2 chimneys that are approx 125 160 ka bp old without any associated fluid flow expression at the present day seafloor 3 chimneys with no stratigraphical evidence for reactivation formed after the last glacial maximum 18 25 ka bp the observations suggest that each activity period was likely related to the last stages of maximum glaciations in the region the emplacement of thick sequences of glacigenic debris flow deposits during these maximum stages most likely caused rapid increase in overpressure and subsequently the formation of focused fluid flow features piercing through sediments of the naust formation at nyegga

subtropical iceberg scours and meltwater routing in the deglacial western north atlantic during the last deglaciation northern hemisphere ice sheets discharged ice and meltwater seafloor scours and numerical modelling suggest that freshwater and icebergs from the laurentide ice sheet reached the subtropical north atlantic

terrestrial and submarine evidence for the extent and timing of the last glacial maximum and the onset of deglaciation on the maritime antarctic and sub antarctic islands this paper is the maritime and sub antarctic contribution to the scientific committee for antarctic research scar past antarctic ice sheet dynamics pais community antarctic ice sheet reconstruction the overarching aim for all sectors of antarctica was to reconstruct the last glacial maximum lgm ice sheet extent and thickness and map the subsequent deglaciation in a series of 5000 year time slices however our review of the literature found surprisingly few high quality chronological constraints on changing glacier extents on these timescales in the maritime and sub antarctic sector therefore in this paper we focus on an assessment of the terrestrial and offshore evidence for the lgm ice extent establishing minimum ages for the onset of deglaciation and separating evidence of deglaciation from lgm limits from those associated with later holocene glacier fluctuations evidence included geomorphological descriptions of glacial landscapes radiocarbon dated basal peat and lake sediment deposits cosmogenic isotope ages of glacial features and molecular biological data we propose a classification of the glacial history of the maritime and sub antarctic islands based on this assembled evidence these include type i islands which accumulated little or no lgm ice type ii islands with a limited lgm ice extent but evidence of extensive earlier continental shelf glaciations type iii seamounts and volcanoes unlikely to have accumulated significant lgm ice cover type iv islands on shallow shelves with both terrestrial and submarine evidence of lgm and or earlier ice expansion type v islands north of the antarctic polar front with terrestrial evidence of lgm ice expansion and type vi islands with no data finally we review the climatological and geomorphological settings that separate the glaciological history of the islands within this classification scheme

the antarctic circumpolar current between the falkland islands and south georgia abstract hydrographic and lowered acoustic doppler current profiler data along a line from the falkland islands to south georgia via the maurice ewing bank are used to estimate the flow of circumpolar water into the argentine basin and to study the interaction of the antarctic circumpolar current with the falkland plateau the estimated net transport of 129 21 sv sv 106 m3 s 1 across the section is shared between three major current bands one is associated with the subantarctic front saf 52 6 sv and the other two with branches of the polar front pf over the sill of the falkland plateau 44 9 sv and in the northwestern georgia basin 45 9 sv the latter includes a local reinforcement 20 sv by a deep anticyclonic recirculation around the maurice ewing bank while the classical hydrographic signature of the pf stands out in this eastbound branch it is less distinguishable in the northbound branch over the plateau other circulation features are a southward entrainment of diluted nor

evidence of a widespread paleo pockmarked field in the orange basin an indication of an early eocene massive fluid escape event offshore south africa abstract the detailed interpretation and seismic attribute analysis of 2d and 3d seismic reflection data sets revealed the presence of a distinct seismic horizon displaying circular and elongated depressions in early eocene sediments along the northwestern slope of the orange basin on the southwest african margin their occurrence within a single seismic horizon indicates a contemporaneous formation process we interpret the depressions as paleo pockmarks which occur as single pockmarks predominantly nne ssw aligned pockmark trains and coalescing elongated pockmarks the paleo pockmarked surface covers an area of 2800 km 2 and has been mapped by integrating the 3d dataset with industrial 2d seismic grids the spatial and temporal occurrence of the paleo pockmarks is associated to two episodes of rapid sedimentation during the late maastrichtian to paleocene comprising fine grained shelf eroded material we propose that they were formed during the early eocene by the seepage of both 1 overpressured pore fluids from disequilibrium compaction of upper maastrichtian sediments and 2 thermogenic gas from underlying cretaceous mature source rocks we show that the location of the pockmarks is controlled by the underlying faults system of the paleo slope the paleocene eocene transition is known for its series of hyperthermal events characterized by negative excursions of the carbon isotope curve the early eocene widespread event of fluid and thermogenic gas escape identified in this work can be an example of the type of carbon release processes occurring in hydrocarbon prone sedimentary basins during this time

iceberg scours pits and pockmarks in the north falkland basin abstract glaciation in the southern hemisphere is limited by the availability of land from which to seed ice sheets the extents of the antarctic patagonian and new zealand ice sheets at the last glacial maximum lgm are relatively well known although the rates and styles of their retreat after the lgm are poorly constrained particularly in antarctica offshore records of glaciation are relatively sparse in the southern hemisphere despite the potential ocean climate insights that can be gained from records of glaciation that are preserved offshore in this study we document the occurrence of iceberg scours and accompanying pits within the north falkland basin c 50 s and discuss their origin the cross sectional shapes of scours are u to v shaped and occur in present day water depths of 280 to 460 m individual scours are up to 38 km long 1 km wide and up to 10 m deep the scours are observed as erosional linear to curvilinear depressions showing only one point of contact between the iceberg and seafloor often with raised berms composed of excavated material identified either side of the main depression undulating width of scours is interpreted as an effect of rotation of the iceberg keel during scour excavation the elongate morphology of the scours differentiates them from asymmetrical pits interpreted to represent iceberg impact pits and symmetrical pockmarks interpreted to form due to fluid expulsion in cross section the differentiation is highly interpretative but the 3d bathymetric expression is unequivocal the sinusoidal character of the scours suggests the interaction between local tidal currents and the east falkland malvinas currents in the north falkland basin at the time of formation offshore and onshore landscape analysis is used to determine potential sources of icebergs and suggests that they were most likely sourced from the antarctic peninsula these results inform our understanding of southern hemisphere ocean climate interactions during the last glacial cycle and suggest that the east falklands malvinas current a key current in the southern hemisphere bringing cold low salinity antarctic derived waters into the south atlantic was in operation during the last glacial cycle the accumulation of icebergs west of the falkland islands would also result in further cooling from fresh meltwater perturbations enhancing the development of a potential ice bridge along the argentinian coast

multi stream order analyses in basin asymmetry a tool to discriminate the influence of neotectonics in fluvial landscape development madrid basin central spain morphometric analysis of the tajo drainage network using a dem was carried out in order to determine neotectonic influence on the development of the madrid basin since the pliocene statistical analysis of digitally derived transverse topographical drainage basin asymmetry t factor was used to infer directions of ground tilting a crustal block pattern was interpreted from a mean basin asymmetry vector field that was computed using a new approach based on a gridded running average of the raw vector field measurement of r factor for different order channels allows investigation of evolution rates of different order rivers and at the same time reveals possible factors controlling basin evolution the vector data show clear differences between high and low orders high order asymmetry is consistent with fluvial terrace distribution as it reflects channel migration and incision within the main valleys and shows a general trend toward a central basin axis running sw ne a sw ne trend is also defined by other morphographical approaches such as drainage density and relief analysis both approaches point toward the presence of two uplifted areas running sw ne and a subsided zone between them which is in agreement with previous crustal flexure models in contrast low order asymmetry shows a clear trend indicating eastward tilting which could be driven by recent changes in maximum principal stress direction and its influence on fault reactivations in general large rivers generating fluvial terraces are controlled by basement structure with positive and negative crustal flexures driving their migration direction and thus controlling the spatial distribution of terraces because the position of main streams is controlled by large tectonic lineaments that favor groundwater flow convergence on the other hand small tributaries have low capabilities to attain equilibrium and t factor values of low order basins may reflect more recent block tectonics due to variations in stress fields or may reflect local controls like lithology

ice sheet extent of the antarctic peninsula region during the last glacial maximum lgm insights from glacial geomorphology we present marine geological and geophysical data for the antarctic peninsula that call for a larger ice sheet reconstruction during the last glacial maximum lgm than suggested by previous studies such glacial reconstructions are important for quantifying post lgm sea level rise and providing boundary conditions for general circulation models megascale glacial lineations on the continental shelf surrounding antarctica provide documentation for grounded ice that was streaming swath bathymetry data nbp02 01 reveal lineations in each of the major glacial troughs except for smith trough which features grooves and bedrock drumlins 0 5 3 km spacing 1 20 elongation ratios on crystalline bedrock we place the maximum extent of ice at the seaward limit of the lineations at or near megascale glacial lineations imaged in this study and other areas surrounding antarctica including the ross sea pine island bay have a consistent morphology with elongation ratios of 80 1 and spacings of 200 600 m mode of 300 m in contrast lineations bundles canals et al 2000 in the gerlache boyd trough exhibit larger spacing 1 5 km and the upstream portions 7 km are carved directly into bedrock rather than till as suggested by previously unpublished air gun 120 hz seismic data these features have yet to be dated however they are believed to have been active during the lgm radiocarbon dates in glaciomarine sediments foraminifera and organic matter from seven glacial troughs indicate that megascale glacial lineations were formed during the lgm other geomorphic features such as the grounding zone wedge in the northwestern weddell sea formed when the ice sheet was retreating the initial retreat of the grounded ice from the outer shelf occurred by 18 500 cal yr b p the inner shelf was mostly ice free by 13 000 cal yr b p this is significantly earlier than numerical models which suggest antarctic deglaciation began at 12 000 cal yr b p this also suggests the peninsula area contributed to global sea level rise associated with meltwater pulse mwp 1a

active thrusting in the inner forearc of an erosive convergent margin pacific coast costa rica 1 structural and geomorphic analyses of the fila costena thrust belt in southwest costa rica indicate active thrusting within the inner forearc the fila costena exposes three major thrust faults that imbricate the late tertiary forearc basin sequence of the terraba basin the frontal thrust of the fila costena marks the boundary between an uplifting inner forearc and a subsiding outer forearc with only local uplift astride the indenting cocos ridge on the basis of surface constraints a cross section across the thrust belt suggests that all three thrusts flatten into parallelism with a low angle decollement horizon near the contact between the basement and the cover sequence of the terraba basin this decollement lies at a depth of 4 km the minimum shortening recorded by restoration of fault related folds is 17 km or 45 observations of late tertiary marine sediments tilted and faulted late quaternary fluvial terraces and raised holocene marine terraces indicate that fila costena uplift was likely initiated in the quaternary and is ongoing given that the coastal mountains are separated from the talamanca range by a valley the decollement that delaminates the forearc basin from the underthrusting forearc must continue as a flat beneath the valley but must link with the plate boundary along a crustal scale ramp system a structural geometry that has resulted in uplift of the talamanca range the highest peaks in central america the dichotomy between uplift in the inner forearc and subsidence in the outer forearc is explained in terms of the response of an arcward thickening wedge to rough subducting crust index terms 8150 tectonophysics plate boundary general 3040 8123 tectonophysics dynamics seismotectonics 8010 structural geology fractures and faults 8015 structural geology local crustal structure 8005 structural geology folds and folding

a 70 kyr sea surface temperature record off southern chile ocean drilling program site 1233 1 we present the first high resolution alkenone derived sea surface temperature sst reconstruction in the southeast pacific ocean drilling program site 1233 covering the major part of the last glacial period and the holocene the record shows a clear millennial scale pattern that is very similar to climate fluctuations observed in antarctic ice cores suggesting that the southern hemisphere high latitude climate changes extended into the midlatitudes involving simultaneous changes in air temperatures over antarctica sea ice extent extension of the antarctic circumpolar current and westerly atmospheric circulation a comparison to other midlatitude surface ocean records suggests that this antarctic millennial scale pattern was probably a hemisphere wide phenomenon in addition we performed sst gradient reconstructions over the complete latitudinal range of the pacific eastern boundary current system for different time intervals during the last 70 kyr the main results suggest an equatorward displaced subtropical gyre circulation during marine isotope stages 2 and 4

a new bathymetric compilation for the south orkney islands region antarctic peninsula 49 39 w to 64 59 s insights into the glacial development of the continental shelf we present a new high resolution 300 m bathymetric grid of the continental shelf surrounding the south orkney islands northeast of the antarctic peninsula the new grid derived from a compilation of marine echo sounding data improves previous regional bathymetric representations and helps to visualize the morphology of the shelf in unrivalled detail the compilation forms important baseline information for a range of scientific applications and end users including oceanographers glacial modelers biologists and geologists in particular due to the limited understanding of glacial history in this region the bathymetry provides the first detailed insights into past glacial regimes the continental shelf is dominated by seven glacially eroded troughs marking the pathways of glacial outlets that once drained a former ice cap centered on the south orkney islands during previous glacial periods grounded ice extended to the shelf edge north of the islands a large 250 km long sediment depocenter interpreted as a maximum former ice limit of one or more cenozoic glaciations suggests that ice was only grounded to the 300 350 m contour in the south hypsometric analyses support this interpretation indicating that a significant proportion of the shelf has been unaffected by glacial erosion using these observations we propose a preliminary ice cap reconstruction for maximum glaciation of the south orkney plateau suggesting an ice coverage of about 19 000 km2 the timing of maximum ice extent number of past advances and pattern of subsequent deglaciation s remain uncertain and will require further targeted marine geological and geophysical investigations to resolve

contribution of giant icebergs to the southern ocean freshwater flux 1 in the period 1979 2003 the mass of giant icebergs icebergs larger than 18 5 km in length calving from antarctica averaged 1089 300 gt yr 1 of ice under half the snow accumulation over the continent given by the intergovernmental panel on climate change 2246 86 gt yr 1 here we combine a database of iceberg tracks from the national ice center and a model of iceberg thermodynamics in order to estimate the amount and distribution of meltwater attributable to giant icebergs by comparing with published modeled meltwater distribution for smaller bergs we show that giant icebergs have a different melting pattern an estimated 35 of giant icebergs mass is exported north of 63 s versus 3 for smaller bergs although giant bergs spend more of the earlier part of their history nearer to the coast we combine both estimates to produce the first iceberg meltwater map that takes into account giant icebergs the average meltwater input is shown to exceed precipitation minus evaporation p e in certain areas and is a nonnegligible term in the balance of freshwater fluxes in the southern ocean the calving of giant icebergs is however episodic this might have implications for their impact on the freshwater budget of the ocean it is estimated that over the period 1987 2003 the meltwater flux in the weddell and ross seas has varied by at least 15 000 m3 s 1 over a month because of the potential sensitivity of the production of deep waters to abrupt changes in the freshwater budget variations in iceberg melt rates of this magnitude might be climatologically significant

icebergs rework shelf sediments to 500 m off antarctica icebergs and sea ice rework the sediments of high latitude shelves producing modern diamicts ice keel turbates unrelated to glacial proximity off antarctica sidescan sonar data indicate the presence of ice gouge features formed by the physical interaction between ice keels and the sea bed these are recognized as incisions a few metres deep and tens of metres wide in water depths up to 500 m on the submarine bank tops and slopes off wilkes land and in the weddell sea subcircular depressions 30 to 150 m in diameter a washboard pattern and hummocky bed features also represent iceberg resting sites the freshness of sea bed morphology nearby holocene sediment ponding and active hydraulic sedimentary processes indicate that the sea floor is being reworked by iceberg keels tabular iceberg drafts in excess of 330 m have been measured and modeling studies suggest that nontabular iceberg drafts of 500 m are possible we conclude that a modern ice keel turbate deposit in the form of a poorly stratified diamicton is probably widespread on that part 54 of the antarctic shelf less than 500 m deep

iceberg scouring in scoresby sund and on the east greenland continental shelf modern and relict scours produced by iceberg keels have been reported from a number of high latitude continental shelves in the northern hemisphere and antarctica but observations are largely absent from the east greenland shelf about 18 km3 yr 1 of icebergs are calved into the scoresby sund fjord system east greenland these icebergs have submarine keels with drafts up to 550 m modern iceberg contacts with the sea floor are inferred from calculated keel depths and stationary icebergs identified on sequential landsat imagery acoustic profiles parasound 3 5 khz of the sea floor show that scouring is a significant process in water depths 550 m iceberg scouring intensity varies inversely with water depth the most intense scouring occurs at depths of 300 400 m iceberg scours were observed on over 25 000 km2 of the east greenland shelf at 69 72 n and 75 n scours are being actively produced on the modern shelf but relict scours probably dating back to the late weichselian are also present the rate of iceberg production from greenland ice sheet outlet glaciers and iceberg drift tracks on the shelf suggests that iceberg scouring is important over a significant proportion of the 500 000 km2 area above the shelf break around greenland

seamount ridge and transform subduction in southern central america understanding the factors that control subduction zone processes is a first order goal in the study of convergent margins in southern central america a growing body of research reveals strong links between the character of the subducting slab and the mechanics of important processes that include subduction erosion fluid flow deformation and seismogenesis in this paper i evaluate the role that seamount ridge and transform subduction have in the development of upper plate deformation and volcanism by summarizing previous work across a 500 km long region of central america where each of these three scenarios are present along strike the data show that the subduction of short wavelength bathymetry e g seamounts and faults on the seafloor produces short wavelength deformation that persists for relatively short timescales 104 105 years whereas the subduction of longer wavelength bathymetry e g the aseismic cocos ridge results in longer wavelength deformation that endures over a longer time scale 106 years the timing and distribution of upper plate deformation are consistent with subhorizontal cocos ridge subduction driving upper plate deformation and the increased crustal thickness 20 km of the subducting cocos ridge is likely one of the most important factors in the production of upper plate contraction and crustal thickening the data illustrate a fundamental connection between lower plate properties and upper plate deformation and highlight the profound influence that bathymetry and crustal thickness have in the localization and kinematics of upper plate strain and volcanism in middle america

sea level changes at the lgm from ice dynamic reconstructions of the greenland and antarctic ice sheets during the glacial cycles abstract new experiments were performed with three dimensional thermomechanical models of the greenland and antarctic ice sheets to simulate their behaviour during the glacial cycles to reconstruct their thickness and extent at the last glacial maximum lgm and to estimate their glacio eustatic contribution to the global sea level stand the calculations used improved ice dynamic and isostatic treatments updated datasets on higher grid resolutions and refined climatic treatments based on newly calibrated transfer functions between ice core records and climatic perturbations results are discussed from a reference run with standard parameters that is compared with available glacial geological observations and from a series of sensitivity experiments focusing on isostatic adjustment thermomechanical coupling climatic forcing mass balance changes and basal melting rates and viscosity changes of antarctic ice shelves for the antarctic ice sheet we find that volume changes are closely linked with grounding line changes of the west antarctic ice sheet at the lgm the grounding line extended close to the continental shelf break almost everywhere ice over central east antarctica was generally thinner than today and varied mainly in accordance with accumulation fluctuations for the greenland ice sheet melting is important only during interglacial periods and the most sensitive period concerns the size of the ice sheet during the eemian at the lgm the greenland ice sheet extended beyond the present coastline to cover at least the inner continental shelf and thinned by up to several hundred meters in central areas for a plausible range of parameters the experiments indicate that at the time of maximum sea level depression 21 kyr bp the antarctic ice sheet contributed 14 18 m to the sea level lowering and the greenland ice sheet 2 3 m significantly less than the older climap reconstructions whereas both ice sheets were at 21 kyr bp close to their maximum extent the experiments also indicate that their maximum volumes were reached only by 16 5 kyr bp greenland and 10 kyr bp antarctica equal to an additional sea level lowering of respectively 0 4 and 3 7 m holocene retreat was essentially complete by 5 kyr bp in greenland but is found to still continue today in west antarctica before reversing to growth during the next millenium the models were found to reproduce gross features of the ice sheet s history since the lgm in reasonably good agreement with available glacial geological data although observational control on ice thickness changes remains very limited

electrical resistivity in support of geological mapping along the panama canal abstract dredging and widening of the panama canal is currently being conducted to allow larger vessels to transit to and from the americas asia and europe dredging efficiency relies heavily on knowledge of the types and volumes of sediments and rocks beneath the waterway to ensure the right equipment is used for their removal to aid this process a waterborne streaming electrical resistivity survey was conducted along the entire length of the canal to provide information on its geology within the confines of the canal a total of 663 line kilometers of electrical resistivity data were acquired using the dipole dipole array the support of the survey data for dredging activities was realized by calibrating and qualitatively correlating the resistivity data with information obtained from nearby logged boreholes and geological maps the continuity of specific strata was determined in the resistivity sections by evaluating the continuity of similar ranges of resistivity values between boreholes it was evident that differing geological units and successions can have similar ranges of resistivity values for example quaternary sandy and gravelly alluvial fill from the former river channel of the chagres river had similar resistivity ranges generally from 40 to 250 m to those characteristic of late miocene basalt dikes from 100 to 400 m but for quite different reasons similarly competent marine based sedimentary rocks of the caimito formation were similar in resistivity values ranging from 0 7 to 10 m to sandstone conglomerate of the bohio formation consequently it would be difficult to use the resistivity data alone to extrapolate more complex geotechnical parameters such as the hardness or strength of the substrate a necessary component for such analyses requires detailed objective information regarding the specific context from which the geotechnical parameters were derived if these data from cored boreholes and detailed geological surveys are taken into account however then waterborne streaming resistivity surveying can be a powerful tool in this case it provided inexpensive and highly resolved quantitative information on the potential volume of loose suctionable material along the gamboa sub reach which could enable large cost savings to be made on a major engineering project involving modification of one of the most important navigable waterways in the world

iceberg crater marks on the sea floor labrador shelf abstract sidescan sonograms of the labrador seabed show evidence of numerous subcircular iceberg generated impact craters some of these craters are found in linear associations crater chains having been formed by a single iceberg keel alternately impacting and rotating free of the seabed a three degrees of freedom iceberg model is used to generate crater chain configurations an unstable trapezoid shaped iceberg of 6 million t with a draft of 140 m in a water depth of 160 m is used in the simulations soil pressures acting on the penetrating keel introduce a vertical heave motion which depending on phase relationships with the swinging motions of the iceberg results in a variety of noncoherent crater depths and crater chain morphologies including chains with skips where craters appear to be missing on sidescan sonograms depending on the position of the final static orientation of the iceberg keel it may generate a crater chain if the keel comes to rest above the seabed or a crater chain may lead into a normal scour if the keel remains below the seabed both configurations are observed in nature

transport and variability of the antarctic circumpolar current in drake passage the baroclinic transport of the antarctic circumpolar current acc above 3000 m through drake passage is 107 3 10 4 sv and has been steady between 1975 and 2000 for six hydrographic sections 1993 2000 along the world ocean circulation experiment woce line sr1b the baroclinic transport relative to the deepest common level is 136 7 7 8 sv the acc transport is carried in two jets the subantarctic front 53 10 sv and the polar front pf 57 5 5 7 sv southward of the acc the southern antarctic circumpolar current transports 9 3 2 4 sv we observe the pf at two latitudes separated by 90 km this bimodal distribution is related to changes in the circulation and properties of antarctic bottom water three realizations of the instantaneous velocity field were obtained with lowered adcps from these observations we obtain near bottom reference velocities for transport calculations net transport due to these reference velocities ranges from 28 to 43 sv consistent with previous estimates of variability the transport in density layers shows systematic variations due to seasonal heating in near surface layers volume transport weighted mean temperatures vary by 0 40 c from spring to summer a seasonal variation in heat flux of about 0 22 pw finally we review a series of papers from the international southern ocean studies program the average yearlong absolute transport is 134 sv and the standard deviation of the average is 11 2 sv the error of the average transport is 15 to 27 sv we emphasize that baroclinic variability is an important contribution to net variability in the acc

the timing and cause of glacial advances in the southern mid latitudes during the last glacial cycle based on a synthesis of exposure ages from patagonia and new zealand abstract glacier advances in the southern mid latitudes during the last glacial cycle ca 110 10 ka were controlled by changes in temperature and precipitation linked to several important ocean climate systems as such the timing of glacial advance and retreat can yield important insights into the mechanisms of southern hemisphere climate change this is particularly important given that several recent studies have demonstrated significant glacial advances prior to the global last glacial maximum glgm in patagonia and new zealand the cause of which are uncertain the recent increase in chronological studies in these regions offers the opportunity to compare regional trends in glacial activity here we compile the first consistent 10be exposure dating chronologies for patagonia and new zealand to highlight the broad pattern of mid latitude glacial activity over the last glacial cycle our results show that advances or still stands culminated at 26 27 ka 18 19 ka and 13 14 ka in both patagonia and new zealand and were broadly synchronous but with an offset between regions of up to 900 years that cannot be explained by age calculation or physically plausible erosion differences furthermore there is evidence in both regions for glacial advances culminating from at least 45 ka during the latter half of marine isotope stage mis 3 glacial activity prior to the glgm differed from the large northern hemisphere ice sheets likely due to favourable southern hemisphere conditions during late mis 3 summer insolation reached a minimum seasonality was reduced winter duration was increasing and sea ice had expanded significantly inducing stratification of the ocean and triggering northward migration of oceanic fronts and the southern westerly winds glacial advances in patagonia and new zealand during the glgm were probably primed by underlying orbital parameters however the precise timing is likely to have been intrinsically linked to migration of the coupled ocean atmosphere system which may account for the small offset between patagonia and new zealand due to differences in oceanic frontal migration during deglaciation advances or still stands occurred in both regions during the southern antarctic cold reversal ca 14 5 12 9 ka rather than the northern younger dryas ca 12 9 11 7 ka our findings suggest that major rearrangements of the southern hemisphere climate system occurred at various times during the last glacial cycle with associated impacts on the position and intensity of the southern westerly winds and oceanic fronts as well as wind driven upwelling and degassing of the deep southern ocean thus reconstructing the timing of glacial advance retreat using our compilation is a powerful way to understand the mechanisms of past interhemispheric climate change

pliocene holocene contourite deposition under the antarctic circumpolar current western falkland trough south atlantic ocean the eastward flowing antarctic circumpolar current acc has influenced sedimentation on the slope and floor of the western falkland trough where the axis of the current is topographically constrained deep water flow below 3000 m has produced a symmetrical sediment drift on the trough floor with non depositional margins indicating higher current velocities at the base of slope to the southeast of the falkland islands there is a gap in the north scotia ridge north of which the floor of the trough is swept clean of sediment by the acc both echo character mapping and gloria side scan data indicate that currents follow the bathymetric contours along the slope redistributing sediment and locally eroding furrows from six cores on the drift and on the northern slope two styles of contourite deposition have been identified on the drift holocene biogenic sandy contourites overlie last glacial maximum muddy contourites and fine grained diatomaceous hemipelagites sedimentation rates here average 3 4 cm ka 1 the sandy contourites present in four of the cores from the sediment drift are sharply underlain by the finer grained diatomaceous hemipelagites the lack of a coarsening upward sequence commonly associated with an increase in current velocity may be indicative of high current activity eroding away the finer negative sequence pliocene and mid pleistocene glaucony rich sandy contourites containing radiolaria characterise the falkland plateau and the floor of the trough near the gap in the north scotia ridge we suggest that the glaucony is derived from a combination of authigenic formation and erosion of locally outcropping cretaceous and tertiary strata this is supported by dinoflagellate analysis sedimentation rates in these current swept areas average 1 cm ka 1

holocene forearc block rotation in response to seamount subduction southeastern peninsula de nicoya costa rica the southeastern tip of the peninsula de nicoya costa rica on the caribbean plate margin lies inboard of the rough bathy metric terrain on the subducting cocos plate and along the land ward projection of the convergence vector for the fisher seamount group the southern tip of the peninsula has nearly orthogonal coastlines and extensive well preserved holocene marine terraces

quaternary uplift and seismic cycle deformation peninsula de nicoya costa rica differing rates and styles of quaternary deformation along the costa rican fore arc reflect segmentation of the trench corresponding with three contrasting domains of subducting sea floor offshore rapid upward flexure of the southern fore arc segment results from the subduction of the buoyant cocos ridge whereas moderate deformation along the central fore arc segment reflects the subduction of buoyant seamounts in contrast the northern costa rican fore arc deforms in response to the subduction of relatively dense sea floor devoid of major bathymetric anomalies quaternary geomorphic evidence and earthquake oral histories from the peninsula de nicoya within the northern costa rican fore arc demonstrate arcward tilting of the fore arc crust with discrete uplift events occurring during large subduction earthquakes uplift rates calculated from the late holocene cabuya terrace along the peninsula s trench perpendicular southeastern coast decrease systematically toward the arc from 4 5 m k y at cabuya to 1 7 m k y at montezuma 8 km to the northeast an uplifted carbonate beachrock horizon radiocarbon age 4500 5200 yr b p correlated between cabuya and montezuma is tilted 0 1 downward toward the arc although quaternary uplift is evident as far arcward as tambor 10 km northeast of montezuma uplifted terraces are absent between tambor and the golfo de nicoya a submerged archaeological site radiocarbon age 2500 yr b p located along the golfo de nicoya coast 30 km northeast of montezuma demonstrates late holocene subsidence of 0 5 m k y these data indicate net late holocene arcward tilting of the peninsula at an angular rotation rate of between 0 01 and 0 02 k y oral histories describing the m 7 7 nicoya subduction earthquake of 5 october 1950 provide evidence of seismic cycle deformation along the peninsula s southwestern coast between puerto carrillo and nosara interviews with 48 residents show that coseismic uplift of at least 1 m affected this coastline and that a significant fraction of this uplift has subsequently been reversed during four decades of gradual subsidence the coseismic deformation pattern estimated from a uniform slip dislocation model for the 1950 earthquake is consistent with both geomorphic and oral history evidence these observations suggest that seismic cycle deformation functions as an important mechanism of vertical tectonism within the costa rican fore arc arcward rotation and doming of the peninsula de nicoya during the quaternary may reflect repeated cycles of sudden coseismic deformation followed by gradual postseismic and or interseismic crustal movement

overpressure within upper continental slope sediments from cptu data gulf of lion nw mediterranean sea data from in situ piezocone tests cptu and laboratory analyses are utilized for the interpretation of the stress history of quaternary sedimentary sequences in the upper continental slope of the gulf of lion northwestern mediterranean sea a cptu based preconsolidation pressure profile referenced to the current effective stress indicates that the deposit is underconsolidated from 12 meters below the seafloor mbsf down to at least 150 mbsf excess pore pressure below 12 mbsf is further supported by results from oedometer and dissipation tests subseafloor pockmarks and indications of free gas in seismic reflection profiles reveal four main overpressure sources si siv with overpressure ratios 0 3 at subseafloor depths coinciding with levels where the dominantly silty clayey sediment contains increased proportions of sand we relate the excess pore pressure related to free gas due to gas exsolution processes and sea level variations driven by pleistocene sea level changes

quaternary glaciations in the southern ocean and antarctic peninsula area abstract there are three main difficulties in constructing detailed time series for late quaternary glacier fluctuations in the southern ocean sub antarctic region sea level control on ice extent differential tectonics and lack of material for radiometric dating south of 60 s the glacial equilibrium line altitude is low enough for glaciers to expand without a decrease in temperature if sea level falls thus most tidewater glaciers in this region are not reliable indicators of small scale fluctuations in climate tectonic uplift during the quaternary may explain why the falkland islands did not develop most of their glacial and nivoglacial features until the last glaciation the south shetland islands have a unique assemblage of raised marine features in the sub antarctic possibly because the crustal block overlies a zone of magmatism and may respond sensitively to isostatic changes imposed by fluctuating ice masses despite the lack of vegetation some radiometric dates have been obtained from peat seaweed and fossil remains of marine shells and bones associated with glacial and raised beach deposits together with relative weathering criteria and drift distribution these suggestthat glaciers in the southern ocean and sub antarctic region have fluctuated synchronously with glaciers elsewhere in the southern hemisphere during the last 100 ka the last glaciation maximum culminated after 26 ka bp and glacier advances are inferred for the late glacial intervals 15 14 ka and 12 10 ka bp and the neoglacial interval last 5 ka

regulation of ice stream flow through subglacial formation of gas hydrates localized subglacial zones of high traction help to regulate ice sheet flow geophysical data from a palaeo ice stream suggest that methane gas accumulation and hydrate formation beneath ice sheets can produce such high traction sticky spots

c swithinbank 1988 satellite image atlas of glaciers of the world antarctica washington dc united states government printing office united states geological survey professional paper 1386 b