large scale bedforms sediment distribution and sand mobility in the eastern north sea off the danish west coast abstract two side scan sonar surveys were carried out 9 months apart in a 24 km2 off thorsminde at the danish west coast were water depth is 12 18 m sediment samples were systematically collected in the same area using a 250 m sampling grid the north sea study area is exposed to strong wind induced coastal currents and high waves and thereby characterized by significant sediment transport the seabed data were used to analyse the large scale dynamical bedforms found in the area the mobility of the bedforms the areal variation of the seabed mean grain size and the grain size variation across the large bedforms the compilation of side scan sonar mosaics revealed very large bedforms with a mean wavelength of approximately 500 m and heights of 1 3 m these bedforms indicate a north going net sediment transport caused by the jutland coastal current large dunes l 10 100 m and smaller bedforms were also recorded as well as large shoreface connected ridges with a spacing of 3 4 km the bedform configuration appears to be relatively stable only small changes having been observed between the two surveys even though a 100 yr cyclone and several storms occurred between the two surveys the small changes observed also indicate a net northerly sediment transport the surface sediments reveal a remarkably high positive correlation between the mean grain size and the position across the very large flow transverse bedforms from coarse sand in the troughs to fine sand at the crest and lee side slope of the bedforms

storm influences on a tidal sandbank s surface middelkerke bank southern north sea the results are presented of two types of pre storm and post storm surveys carried out on the middelkerke bank southern north sea the first type of survey was planned to detect detailed morphological changes in two selected areas of the bank totalling 3 km2 for the survey in these shallow waters to be completed in a fast and accurate way use was made of a special hovercraft based hydrographic system the other type of survey concerned grab samplings covering the sandbank in order to study spatial variations in surficial grain size the pre storm and post storm morphological surveys showed that small and medium dunes disappear under stormy conditions a 5 m westerly displacement of most of the large and very large dunes has been interpreted as the result of bedform migration under normal fair weather locally dominant ebb flow the lowering of the large dunes crests by up to 1 2 m is considered an effect of the storms the accretion of the lower part of the northwestern flank is attributed to the deposition of sand derived from shallow parts of the sandbank during storms the grain size surveys showed that especially the central and northern parts of the sandbank were affected by grain size changes the northwestern flank showing a clear coarsening and the landward southeastern flank a fining with respect to the fair weather situation it is put forward that the waves approaching from the north cause an extra winnowing on the exposed flank of the bank on the southeastern flank of the bank which is better protected against the wave action fine particles are then deposited

formation mechanisms for self organized kilometer scale shoreline sand waves the feedbacks between morphology and waves through sediment transport are investigated as a source of kilometer scale shoreline sand waves in particular the observed sand waves along srd holmslands tange denmark are examined we use a linear stability model based on the one line approximation linking the bathymetry to the perturbed shoreline previous models that consider the link by shifting the equilibrium profile and neglecting the curvature of the depth contours predict a positive feedback only if the offshore wave incidence angle c is above a threshold c 42 considering curvilinear depth contours and using a linearly decaying perturbation in bed level we find that c can vary over the range 0 90 depending on the background bathymetric profile and the depth of closure dc associated to the perturbed wave refraction there are two sources of instability the alongshore gradients in wave angle wave angle mechanism and the alongshore gradients in wave energy induced by wave crest stretching wave energy mechanism the latter are usually destabilizing but the former are destabilizing only for large enough dc steep foreshores and gently sloping shorefaces the critical angle comes out from the competition between both mechanisms but when both are destabilizing c 0 in contrast with earlier studies the model predicts instability for the holmslands tange coast so that the observed sand waves could have emerged from such instability the key point is considering a larger dc that is reasonably supported by both observations and wave climate which brings the wave angle mechanism near the destabilizing threshold

lichenometric and radiocarbon dating of holocene glaciation cordillera blanca peru hfeasurements of rliizocurpoii subgenus rliizocurpo r thalli on moraines the ages of which are constrained by six radiocarbon dates two pre colombian structures and one historically dated flood dep6sit indicate that lichenometry can be used to estimate the age of stabilization of glacial deposits that date to the last c 7 ka on the west side of the cordillera blanca perlj 8 40 9040 s 77 00 77 40 w the preliminary growth curve for subgenus rtiizocurpan resembles those derived for alpine areas in alaska and colorado and can be subdivided into an initial rapid phase of growth c 0 4 mm yr that lasts c 100 years a c 500 to 1000 year long phase of decelerating growth and a period of slow linear growth 0 016 mm yr that commences after c loo0 years size clustering of subgenus riiizocurpoir thalli supports a four fold subdivision of cirque moraines at altitudes between 4200 and 4650 m the oldest moraines stabilized between c 7000 and 6ooo bp and the three younger groups between c 3350 and 1600 bp between c 1250 and 400 bp and within the last 100 years this subdivision is supported by limiting radiocarbon dates from the cordillera blanca and from several cordilleras in southern peni and indicates that the holocene glacial chronology of the cordillera blanca is the most complete heretofore recognized in the tropical andes

broad synchrony of a late glacial glacier advance and the highstand of palaeolake tauca in the bolivian altiplano the morphology and sedimentology of glacially influenced fan deltas on massifs at the margin of the southern altiplano bolivia suggest a broadly synchronous expansion of glaciers and palaeolake tauca during the late glacial interval this is shown by sedimentary successions of glacigenic glacifluvial and glacideltaic facies linking palaeoglaciers with palaeolake tauca on the flanks of cerro azanaques and cerro tunupa at altitudes of 3770 3720 m radiocarbon dates from peat overlain by glacial diamict and glacifluvial outwash indicate that glaciers in this area reached their last glacial maximum extent after ca 13 300 14 c yr bp glacifluvial fan deltas contiguous with the moraines confirm that the advance coincided with a highstand of palaeolake tauca radiocarbon dated to the interval ca 13 500 11 500 yr bp modeling of climatic controls on this glacier advance suggests the primary forcing was increased summer wet season moisture possibly amounting to 600 mm above the modern values of 200 400 mm greater cloud cover probably depressed local temperatures and reduced the evaporation rate the consequent rise in effective annual moisture p e comfortably accommodates a palaeolake 48 50 10 3 km 2 in area and up to 100 m deep in the southern altiplano because the palaeoglacier equilibrium line altitudes rose toward the south and west like the gradient of modern precipitation totals we conclude that the increased late glacial moisture was brought by weather systems similar to those of the present but that atmospheric conditions were cloudier and cooler 1997 john wiley sons ltd

middle to late holocene environmental changes in bajo de la quinta ne patagonia inferred by palynological records and their relation to human occupation the north patagonian region between 38 and 42 s extends along the proximity of two major atmospheric circulation features in south america the northern border of the southern westerly circulation belt and the northeast trade wind circulation associated with the subtropical south atlantic anticyclone the influence of this westerly wind system determines the annual and seasonal precipitation regimen in north patagonia while the influence of the south atlantic anticyclone is more pronounced towards the east the changing strength of either of these circulation systems has had a strong influence on holocene environmental change in the region palaeoenvironmental changes are inferred from a 500 cm long core from bajo de la quinta 40 55 42 s 64 20 19 w by means of pollen sediment and geomorphological analyses a dry phase with westerly winds during the middle holocene at around 7000 6600 cal yr bp is indicated by xerophytic psammophytic vegetation and patagonian steppe components between 6600 and

pollen sequence from the chilean lake district during the llanquihue glaciation in marine oxygen isotope stages 4 2 pollen stratigraphy of a core taken from a fen at fundo nueva braunau 40 17 499s 73 04 839w situated 2 km beyond the western border of llanquihue age glacial drift spans an age range from an estimated 60 000 70 000 bp to about 14 000 14 c yr bp marine oxygen isotope stages 4 2 the location at present is in the contact zone of valdivian evergreen forest and lowland deciduous beech forest early and late in the pollen record as indicated by assemblages of southern beech nothofagus dombeyi type and grass gramineae the site was located in subantarctic parkland intervening assemblages represent expansion of valdivian north patagonian evergreen forest 49 355 to about 40 000 14 c yr bp and north patagonian evergreen forest subantarctic parkland approximately 40 000 to 30 000 14 c yr bp climate over the time span was under the storm regime of the southern westerlies and apparently uninterruptedly wet when subantarctic parkland expanded cold conditions with summer temperatures estimated at 8 9 c 7 c lower than present resulted in episodes of glacier maxima climate moderated during the period of forest expansion at which time glaciers were in a state of recession contrasting with the continuously wet climate of the lake district for the period of record climate in semi arid arid subtropical chile underwent extended intervals of precipitation data from both the terrestrial and marine realm implicate the southern westerlies as the cause of intensified storm activity at lower latitudes copyright 2000 john wiley sons ltd

variations in soil carbonate formation and seasonal bias over 4 km of relief in the western andes 30 s revealed by clumped isotope thermometry abstract carbonate clumped isotope thermometry provides a new method for investigating long standing questions regarding seasonal biases in soil carbonate formation and the relationship between soil carbonate formation temperatures recorded by clumped isotopes t 47 and surface temperatures we address these questions by comparing c o and clumped isotope data from holocene soil carbonates to meteorological and in situ soil monitoring data along a 170 km transect with 4 km of relief in chile 30 s this arid transect experiences a winter wet season and a 20 c range in mean annual air temperature we test the hypothesis that regardless of soil moisture conditions soil carbonates from arid regions record warm season biases and form in isotopic equilibrium with soil water and soil co2 below 3200 m precipitation falls as rain and soil carbonate t 47 values at depths 40 cm resemble summer soil temperatures above 3200 m precipitation falls as snow and t 47 values resemble mean annual soil temperatures soil carbonates from the highest site yield anomalous 18 o 13 c and t 47 values indicative of kinetic isotope effects consistent with cryogenic carbonate formation our findings 1 demonstrate that soil carbonate t 47 values from shallow 40 cm 3 highlight the role of the soil moisture regime in modulating the timing of soil carbonate formation which affects the resulting carbonate t 47 values and 4 show that soil carbonates from high elevation or high latitude sites may form under non equilibrium conditions these findings underscore the importance of understanding past soil moisture conditions when attempting to reconstruct paleotemperatures using carbonate clumped isotope thermometry

extractable fe and al in late pleistocene and holocene paleosols on niwot ridge colorado front range summary surface and buried paleosols on niwot ridge in the front range of colorado were analyzed for extractable fe and al to determine if their distributions would assist in the interpretation of past and present soil forming environments extractable fe and al distributions in surface and buried paleosols suggest that leaching is more pronounced in the older paleosols with a considerable difference in soil forming environment between pleistocene interstadial later pleistocene and postglacial paleosols using radiocarbon dated buried a horizons it appears that little pyrophosphate extractable fe and al have been translocated downward into these middle latitude alpine buried paleosols there is no evidence that the na pyrophosphate extractable fe and al were affected by degradation of organic matter following burial however the data suggest that some amorphous fe and al might have been affected by soil water movement over permafrost and by redistribution of preweathered sediments

a 350014c yr high resolution record of water level changes in lake titicaca bolivia peru abstract sediment cores collected from the southern basin of lake titicaca bolivia peru on a transect from 4 6 m above overflow level to 15 1 m below overflow level are used to identify a new century scale chronology of holocene lake level variations the results indicate that lithologic and geochemical analyses on a transect of cores can be used to identify and date century scale lake level changes detailed sedimentary analyses of subfacies and radiocarbon dating were conducted on four representative cores a chronology based on 60 accelerator mass spectrometer radiocarbon measurements constrains the timing of water level fluctuations two methods were used to estimate the14c reservoir age both indicate that it has remained nearly constant at 25014c yr during the late holocene core studies based on lithology and geochemistry establish the timing and magnitude of five periods of low lake level implying negative moisture balance for the northern andean altiplano over the last 3500 cal yr between 3500 and 3350 cal yr b p a transition from massive inorganic clay facies to laminated organic matter rich silts in each of the four cores signals a water level rise after a prolonged mid holocene dry phase evidence of other significant low lake levels occurs 2900 2800 2400 2200 2000 1700 and 900 500 cal yr b p several of the low lake levels coincided with cultural changes in the region including the collapse of the tiwanaku civilization

late quaternary glacial history in the encierro valley northern chile 29 s deduced from 10be surface exposure dating abstract the late pleistocene glacial and climate history in the dry central andes is not well known so far mainly because of the lack of suitable material for radiocarbon dating in order to establish a glacial chronology we applied surface exposure dating using in situ produced cosmogenic 10be for 11 boulders from moraines in the encierro valley 29 s northern chile we discuss sample specific effects topographic shielding sample geometry rock surface erosion inheritance and post depositional geomorphological instability and systematic uncertainties production rate of 10be latitude and altitude scaling minor glacial advances probably occurred around 11 6 1 2 ka bp whereas major advances are recorded at 14 0 1 4 ka bp and eventually at 24 1 2 4 ka bp this may indicate synchrony of some late pleistocene glacial advances south and north of the so called arid diagonal 25 s increased precipitation plays a dominant role for the observed late pleistocene glacial advances in the absence of further glacial chronologies south and north of the research area it remains difficult to disentangle the influence of the complex and in space and time variable westerlies and the tropical summer precipitation regime

late holocene environmental changes as recorded in the sediments of high andean laguna chepical central chile 32 s 3050 m a s l abstract we present a reconstruction of environmental changes from sediments of high altitude laguna chepical in the subtropical andes of central chile 32 16 s 70 30 w 3050 m a s l for the past 3100 years based on subfossil pollen microscopic charcoal and diatoms we inferred changes in moisture related to precipitation and ice cover ice free season related to summer temperature at decadal to millennial scales sustained wetter and colder summer temperatures than today prevailed between 1100 bc and ca ad 1 afterward decreasing pollen accumulation rates and increased fire activity suggest drier conditions and possibly enhanced seasonality and or inter annual climate variability frequent changes between cold and warm summers were observed particularly for the last 1000 years about ad 1250 during the medieval climate anomaly wet years and early break up of ice cover occurred in central chile which is today typical for el nino like mean conditions conversely and with the exception of a few wet pulses a generally dry period with extended ice cover cool summers was observed between ad 1400 and ad 1850 little ice age this can be interpreted as a trend toward more la nina like mean conditions recent climate change and human disturbances during the last 100 years have prompted changes in diatom and plant communities that are unprecedented in the late holocene first planktonic diatoms increased as a result of hydraulic interventions in the lake during the late 19th century and secondly the andean vegetation shifted upward as result of recent warming and the frequency of arboreal taxa was significantly reduced at the same time peaks of fire activity were observed

mid and late holocene limnogeology of laguna del negro francisco northern chile and its palaeoclimatic implications lacustrine sediments from the high elevation endorheic saline lake negro francisco 27 28 s 69 14 w 4125 m provide a detailed mid and late holocene environmental history of the southern chilean altiplano mineralogy chemical composition and sedimentary facies analyses of the deposits confirm the regional significance of mid holocene aridity between 6000 and 3800 bp precipitation rates were signifi cantly lower than the c 250 mm yr 1 of today fully arid conditions were interrupted by short term moist spells with an average return period of about 200 years effective moisture increased after 3800 bp and peaked between 3000 and 2600 bp and between 2200 and 1800 bp in two phases with conditions more humid than today comparison with regional palaeodata suggest that these two late holocene humid spells were most likely related to pacific moisture sources salinity levels increased again in laguna del negro francisco after 1800 bp the onset of modern climatic conditions was a stepwise nonlinear proce

morphology and maintenance of steep dunes near dune asymmetry transitional areas on the shallow shelf beibu gulf northwest south china sea abstract symmetrical dunes can be found in areas where dune asymmetry changes sense but in areas where dunes are not expected to be moving the development and maintenance of symmetrical dunes are poorly understood in the southeastern beibu gulf we have identified five typical dune asymmetry transitions at the depths of shallower than 50 m basing on the latest bathymetric data those regions are separated into two classes according to their different shapes and locations sand transport directions are deduced by dune migrations between surveys simulated regional currents and sand size trends the two classes of the regions are found to experience opposing net sand transports from the north and south around the asymmetry transitions the dunes have impressive steep sections relatively symmetrical shapes and almost straight crests they have a general height length h l relation h 0 0575 l1 0836 r2 0 834 which is steeper than dunes in other seas some of the dunes have extraordinary large heights exceeding a quarter of water depth which is attributed to the preserved sand body bidirectional sand accretion erosion in troughs and absence of significant erosion on crests the steepness and straight crests of dunes adapt to the nearly symmetrical or weak asymmetrical reversing currents which induce flow separations and reversals on both flanks of the dunes it also suggests that dunes develop differently under sufficient and limited sand supply dunes will gradually grow in size when being continually supplied with sand however if sand supply is restricted dunes may separate or turn into more isolated individuals to sustain the h l relation the h l relation of dunes can be maintained during either growth or separation overall the nearly symmetrical or weak asymmetrical reversing currents maintain the steep shapes of dunes while variations in sand supply affect their sizes to work out the detailed transports of sediment future observations of flow structures and related models of such two sided steep dunes are still required

subdivision of late pleistocene moraines in the cordillera blanca peru based on rock weathering features soils and radiocarbon dates abstract the progressive development of unusual rock weathering features and soils and minimum limiting radiocarbon dates provide a basis for subdividing four groups of late pleistocene moraines on the west side of the cordillera blanca northern peru 9 20 1 000 s 77 10 77 30 w boulders on the youngest late pleistocene moraines have 10 to 14 cm tall weathering posts soils on these moraines yield mean profile development index pdi values of 0 05 0 04 1 these moraines date between ca 13 500 and 9700 500 yr b p older than previously postulated the next older moraines have boulders with weathering post heights between 20 and 25 cm and soils with pdi values of 0 08 0 07 and were deposited prior to 13 280 190 yr b p probably during the last glacial maximum marine isotope stage 2 moraines from an older glaciation have boulders with weathering posts between 39 and 50 cm high soils that yield pdi values of 0 21 0 07 and are older than 19 700 340 yr b p boulders on moraines from a still older glaciation have lost ca 50 of their above ground volume and have weathering posts between 62 and 70 cm high pdi values for soils on these moraines are 0 32 0 06 linear and logarithmic models of weathering post and soil development with time are used to estimate minimum and maximum ages for the two oldest moraine groups linear models suggest that the second oldest moraines are between ca 20 500 and 46 500 yr b p and that the oldest moraines are between ca 29 000 and 72 000 yr b p in contrast logarithmic models suggest ages of greater than ca 75 500 yr b p and greater than ca 500 000 yr b p respectively

effect of wave topography interactions on the formation of sand ridges on the shelf 1 the role of wave topography interactions in the formation of sand ridges on microtidal inner shelves is investigated with an idealized morphodynamic model the latter uses the two dimensional shallow water equations to describe a storm driven flow on an inner shelf with an erodible bottom and a transverse slope both bed load and suspended load sediment transport are included new are the incorporation of a wave module based on physical principles and a critical shear stress for erosion a linear stability analysis is used to study the initial growth of bed forms by analyzing the initial growth of small perturbations evolving on an alongshore uniform basic state which describes a storm driven flow on a microtidal inner shelf model simulations show that wave topography interactions cause the ridges to become more trapped to the coast both growth and migration of the ridges are controlled by suspended load transport the physical mechanism responsible for ridge growth is related to transport by the stormdriven current of sediment that is entrained due to wave orbital motions induced by bed forms this new mechanism even acts in absence of a transverse bottom slope the orientation spacing and shape of the modeled ridges agree well with field observations from different shelves

climate variability over the last 9900 cal yr bp from a swamp forest pollen record along the semiarid coast of chile abstract we present a fossil pollen analysis from a swamp forest in the semiarid coast of chile 32 05 s 71 30 w at the northern influence zone of southern westerly wind belt a 10 000 cal yr bp calendar years before 1950 palynological sequence indicates a humid phase characterized by dense swamp forest taxa dated between 9900 and 8700 cal yr bp the presence of pollen starved sediments with only scant evidence for semiarid vegetation indicates that extreme aridity ensued until 5700 cal yr bp the swamp forest recovered slowly afterwards helped by a significant increase in moisture at 4200 cal yr bp a new swamp forest contraction suggests that another slightly less intense drought occurred between 3000 and 2200 cal yr bp the swamp forest expansion begins again at 2200 cal yr bp punctuated by a highly variable climate comparisons between the record presented here with other records across the region imply major variations in the extent of the southern westerlies during the holocene this variability could have been caused either by latitudinal displacements from the present mean position of southern westerlies wind belt or by changes in the intensity of the south pacific subtropical anticyclone both of which affect winter precipitation in the region

observations and analysis of giant sand wave fields on the taiwan banks northern south china sea abstract understanding sand wave dynamics is of importance in marine science and also has relevance in engineering giant sand wave fields wave heights up to 10 m are not common and thus have been relatively rarely studied this paper presents the first study on bedform changes related to giant sand wave geomorphology on the taiwan banks using data from three repeated multi beam bathymetric surveys 2011 2012 and 2013 and a spatial cross correlation method different sand transport patterns are obtained classical crest perpendicular migration is observed in the small sand waves with migration rates of 1 5 m a and migration is parallel with the current direction however the giant sand waves are immobile over the observed periods and along crest transport sand transport has been observed that is perpendicular to the predominant current direction statistical results support these findings and thus illustrate a type of sediment transport pattern that differs from other sand wave fields around the world it is concluded that the giant sand waves act as a bathymetric obstacle thus changing the direction of bottom currents flowing over them resulting in a change in sediment transport pattern on the taiwan banks

the cerro bayo district chilean patagonia late jurassic to cretaceous magmatism and protracted history of epithermal ag au mineralization the cerro bayo low sulfidation epithermal district is located in the aysen region chilean patagonia at the western tip of the deseado massif epithermal silver gold province mineralization is hosted in the mainly rhyolitic fragmental successions of the jurassic ibanez formation new biotite 40ar 39ar and zircon u pb ages together with published ages constrain the eruption of this unit to between 158 and 144 ma rhyolitic domes and dikes including cerro bayo proper aligned on the prominent n s striking cerro bayo fault and intruding rocks of the ibanez formation were dated by u pb on zircon at 146 5 0 2 and 146 3 0 2 ma dacitic domes of 83 0 0 2 and 82 6 0 2 ma u pb on zircon are present in the western part of the district at laguna verde silver and gold mineralization is hosted by steeply dipping dominantly n to nw and subordinate w striking quartz veins and to a lesser extent in breccias which on the basis of new adularia 40ar 39ar ages were emplaced in three main episodes 1 mallines ca 144 to 142 ma 2 bahia jara and brillantes ca 137 to 124 ma and 3 laguna verde 114 to 111 ma overall spanning 33 m y most ag au has been produced from veins emplaced in the latter two episodes veins at mallines and bahia jara are spatially related to the cerro bayo fault the oldest episode of mineralization in the district is similar in age to the youngest epithermal deposits in the deseado massif whereas the economically most important veins are age equivalent to skarn and polymetallic vein mineralization in the patagonian andes of southern chile the protracted history of epithermal processes at cerro bayo records the evolution from continental scale extension related to the gondwana breakup to the establishment of andean type arc and back arc environments the largely extensional tectonics throughout this period resulted in similar epithermal mineralization styles emplaced episodically over a large time interval

late pleistocene early holocene paraglacial and fluvial sediment history in the turbio valley semiarid chilean andes abstract the transitional character of climatic conditions confers great relevance to paleoclimate studies in the semiarid region where glacial and holocene geomorphologic records are scarce here we present the paraglacial and fluvial evolution of the turbio valley 30 s using both field observations and 14 c ams chronology two key sites at the uppermost turbio valley show glacial margins which likely formed during the 17 12 ka central andean pluvial event and earlier 37 27 ka episodes associated with glacial advances reported elsewhere in the semiarid andes likewise two episodes of subsequent paraglacial response are identified a first episode corresponds to early holocene fine grained deposits 11 500 7800 cal yr bp extending far downstream 40 km from the glacial margins these deposits and coeval debris cones 11 000 5500 cal yr bp are the result of arid conditions with occasional runoffs that were unable to export sediments along the trunk valley the second episode corresponds to disconformably overlying fluvial gravels extending 70 km downstream from the glacial margin indicative of an increase in the fluvial transport capacity occurring not long after 5500 cal yr bp fluvial transport increase resulted from a late holocene shift to wetter climate conditions representing a forcing factor which enhanced the paraglacial response

episodic dynamics of a sand wave field abstract the morphodynamics of a sand wave field in a flood dominant channel inside moriches inlet was monitored for eight weeks during the summer of 2005 bathymetric data show sand waves on average are 15 m long and 39 cm high with shallow slip faces the sand waves remained stationary over the eight week study the maximum peak current speeds recorded during this study only reached 60 cm s this velocity was not sufficient to cause measurable sand wave migration analysis based on work by van rijn suggests that the sand waves of this size would be created when the current velocity exceeds 80 cm s conditions not observed during this study water level data from sandy hook nj and shinnecock inlet ny show that large tidal ranges occur when a drop in barometric pressure increases the elevation of high tide and strong north winds decrease the low tide elevation during these events the current velocity may reach 80 cm s which is predicted to be strong enough to produce these sand waves this study demonstrates that high energy episodic events may control sand wave morphology at moriches inlet

evolution of lascar volcano northern chile lascar volcano in the central andes is an ese wnw elongate composite stratocone stage i 3 at 26 45 ka producing the soncor ignimbrite no caldera formed laharic and alluvial fan deposits and a debris avalanche formed from 26 45 to 19 2 ka indicating a humid climatic period the dacitic and andesitic western stratocone stage iii developed over the soncor vent stage iii culminated in the 9 2 ka tumbres eruption which formed andesitic scoria flow fans and a summit collapse crater stage iv activity switched to the east forming an andesite lava three nested summit craters which repeatedly filled with lava and collapsed absence of significant erosion since 9 2 ka is due to the much drier holocene climate activity since 1984 displays cycles of lava dome formation in the summit crater lava dome subsidence with crater collapse vulcanian to plinian explosive eruptions culminating in the major explosive eruption of 19 20 april 1993 the total volume of magma erupted from lascar over a 43 ka period is estimated at 30 to 40 km 3

geomorphology internal structure and successive development of a glacier foreland in the semiarid chilean andes cerro tapado upper elqui valley 30 08 s 69 55 w we use geomorphological analysis sedimentological survey remote sensing and ground penetrating radar gpr in order to understand the complex landform assemblage found in front of the cerro tapado glacier in the upper elqui river catchment semiarid andes of chile the geomorphological analysis highlights prominent boundaries dividing the landform assemblage into from the upper part to the lower part an upper latero frontal moraine complex an upper debris covered glacier a lower debris covered glacier two rock glaciers and a lower morainic complex the sedimentological survey highlights the rather small size of the surface debris in general 400 m receding of the glacier occurred along with downslope displacements dm m y 1 of most of the landform units and a significant evolution of the thermokarst features on the debris covered glaciers considerable surface lowering occurred in the upper part of the assemblage while localized bulging is seen along the morphological boundaries in the lower units the gpr profiles highlight spectacular internal structure in the upper debris covered glacier with up to 80 m of buried ice in the other landform units the internal structure is less visible and more heterogeneous the analysis of the radar wave velocity along the gpr profiles reveals the occurrence of air filled and moist zones in the internal structure the geomorphological assemblage is fundamentally characterized by its morphological structural and dynamical boundaries and defined as a young probably 2000 years polygenetic construction with landform units having added to overlapped one another the rock glaciers do not derive from the present debris covered glacier but preexist to it

tidal sand wave formation influence of graded suspended sediment transport 1 the influence of graded suspended sediment transport on the formation of tidal sand waves is investigated hereto in the framework of a linear stability analysis we examine the time development of small amplitude perturbations superimposed to a flat heterogeneous seabed in a shallow tidal sea dominated by one tidal constituent the heterogeneous bottom material is modeled by a bimodal sediment mixture and the transport of sediment close to the bottom as well as in suspension is considered the active layer concept is employed and hiding exposure effects are taken into account the mechanisms giving rise to the sediment sorting process along the bed forms are found to be unaffected by the fractional transport of sediment in suspension on the other hand the formation of sand waves is quantitatively substantially affected by the graded suspended sediment transport and the wavelength of the most amplified mode is found to depend strongly on the characteristics of the sediment mixture in particular the graded suspended sediment transport largely affects the contribution to the amplification rate related to the sorting process this leads to the growth of bed forms characterized by a smaller wavelength compared with that predicted for a uniform sediment when the mean grain size of the sediment mixture is relatively coarse on the other hand longer bed forms appear when the sediment mixture is characterized by a relatively fine mean grain size moreover a destabilizing effect is identified in the former case while the flat bed configuration is stabilized in the latter case a comparison of the theoretical predictions with field observations seems to support the model even though it cannot be considered conclusive

high resolution marine record of climatic change in mid latitude chile during the last 28 000 years based on terrigenous sediment parameters abstract marine sediment cores from the continental slope off mid latitude chile 33 s were studied with regard to grain size distributions and clay mineral composition the data provide a 28 000 yr14c accelerator mass spectrometry dated record of variations in the terrigenous sediment supply reflecting modifications of weathering conditions and sediment source areas in the continental hinterland these variations can be interpreted in terms of the paleoclimatic evolution of mid latitude chile and are compared to existing terrestrial records glacial climates 28 000 18 000 cal yr b p were generally cold humid with a cold semiarid interval between 26 000 and 22 000 cal yr b p the deglaciation was characterized by a trend toward more arid conditions during the middle holocene 8000 4000 cal yr b p comparatively stable climatic conditions prevailed with increased aridity in the coastal range the late holocene 4000 0 cal yr b p was marked by more variable paleoclimates with generally more humid conditions variations of rainfall in mid latitude chile are most likely controlled by shifts of the latitudinal position of the southern westerlies compared to the holocene the southern westerly wind belt was located significantly farther north during the last glacial maximum less important variations of the latitudinal position of the southern westerlies also occurred on shorter time scales

late pleistocene climate conditions in the north chilean andes drawn from a climate glacier model a climate glacier model was used to reconstruct late glacial climate conditions from two case study glaciers at 18 and 22 s in the arid sub tropical western andes of northern chile the model uses i the geometry of the late glacial maximum glaciation ii modern diurnal and annual cycles amplitudes and lapse rates of the climate iii empirical statistical sublimation melt and accumulation models developed for this area and iv dynamic ice flow through two known cross sections for steady state conditions the model is validated with modern conditions and compares favorably with the glaciological features of today the mass balance model calculates the modern equilibrium line altitude at 18 s as high as 5850 m field data 5800 m whereas no glaciers exist in the fully arid southern area at 22 s despite altitudes above 6000 m and continuous permafrost for late glacial times the model results suggest a substantial increase in tropical summer precipitation ap 840 50 10 mm a 1 for the northern test area 1000 10 30 mm a 1 for the southern test area and a moderate temperature depression t 4 4 0 1 0 2 c at 18 s 3 2 0 1 c at 22 s extratropical frontal winter precipitation june september was 15 of the total annual precipitation a scenario with higher winter precipitation from the westerlies circulation belt does not yield a numerical solution which matches the observed geometry of the glaciers therefore we conclude that an equatorward displacement of the westerlies must be discarded as a possible explanation for the late pleistocene glaciation in the andes of northern chile

changes of sedimentological patterns and morphological features due to the disposal of dredge spoil and the regeneration after cessation of the disposal activities abstract the interaction of dumped sediments with the morphology and sedimentology of a coastal environment and the recovery of the seafloor after cessation of dumping activities is still poorly known especially from a longer term perspective this paper presents a quantitative impact study of the dumping of dredged material on two overlapping disposal sites situated on different morphological entities an old disposal site located on a sandy shoal was closed in 1999 afterwards a new disposal site was designated mainly located in a tidal gully the approach included the interpretation of chrono sequential single beam echosoundings high resolution multibeam bathymetrical and backscatter data ground truthed with boxcores dumping has caused the formation of a large scale dump mound on both the old and new disposal site on the new disposal site the dump mound is superposed by individual disposal mounds and depressions that are probably formed by scouring events on the old disposal site also small depressions occur which are likely associated with the former dumping process the disposal has led to the accumulation of sand both on the old and new disposal site regardless of the high mud content of the dredge spoil for the new disposal site dumping efficiency has been estimated as 30 40 which would lead to a yearly growth of 380 000 m 3 a different sedimentation pattern was revealed for the old and new disposal site which is ascribed to the difference in morphological setting and differences in dredge spoil nature after cessation of the disposal of dredged sediments on the old disposal site a morphodynamic equilibrium was fairly quickly restored bedforms were formed within less than one year and their distribution and surficial sediments are again representative for the belgian coastal zone the consistent ebb dominated asymmetry of the very large dunes their sw migration and sediment accretion extending beyond the sw limit of the new disposal site suggest an important bedload transport in the direction of the navigation channels these findings contrast to the overall flood dominated residual current transport direction

monitoring underwater nourishments using multibeam bathymetric and backscatter time series natural and man induced coastal erosion endanger life and environment in coastal areas worldwide for sedimentary barrier coasts beach and underwater nourishments are an efficient coastal protection strategy to optimize nourishments and to understand their impact on the marine environment monitoring strategies are required in this study we investigate the potential of multibeam echosounder mbes data providing both bathymetry and backscatter bs for monitoring the evolution of the nourished sediment and morphodynamics over time a time series of seven mbes measurements as well as two sets of box cores vibrocores and seismic data were acquired of a channel side nourishment near the wadden sea island ameland the netherlands between april 2017 and may 2019 in general a high confidence of the acoustic reliability of the bs time series measurements is demonstrated the unsupervised bayesian classification method supported by ground truthing is employed to produce a time series of sediment maps revealing sediments ranging from sandy mud to sand with varying amounts of shell fragments based on the sediment maps the nourished sediment could be distinguished from the natural sediment within one year the shell rich pre nourishment seabed is recreated by washing out finer sediments which are deposited towards the main tidal channel using the seismic data and vibrocores the shell rich pre nourishment seabed could be identified in the subsurface after being buried by the nourishments supporting the general findings furthermore a rapid development of steep bedforms with increasing sediment sorting is observed in parts of the nourished areas this study shows that high resolution sediment maps obtained from a time series of mbes bs together with bathymetry reveal morphodynamic and sedimentary processes of nourishment evolution and can advance underwater nourishment strategies

holocene evolution and geochronology of a semiarid fluvial system in the western slope of the central andes ams 14 c data in el transito river valley northern chile abstract in this paper we discriminate the contribution of the different sediment sources into a river situated in the semiarid region of northern chile differentiating the ones driven by the paraglacial response from the ones yielded to the tributary junction alluvial fans or the ones coming from the hillslopes the sedimentary infilling is accurately described in the main landforms such as alluvial fans alluvial terraces and landslides in the current valley floor where twenty six 14c ams samples were picked up the 14c age data indicate that the aggradation in the uppermost part of the valley immediately postdates the glacial retreat at 15 000 14c years cal b p and spans the whole holocene starting at 11 ka b p and finishing about 2 ka b p the main sources for lateral inputs are debris flows from tributary catchments in the portion where the river is embedded in between 1000 and 2000 m a s l as well as catastrophic landslides additionally an extensive detailed geomorphological mapping is provided to discuss the meaning of the ages together with an assessment of where the samples came from finally the dataset and field criteria provided in this work contribute to better perform paleoclimatological interpretations for the semiarid fluvial systems of northern chile these interpretations usually consider the increased influence of the westerlies during the holocene and the span of time that the paraglacial response delivers glacigenic sediments into the system

development of a pleistocene calcrete over a sequence of marine terraces at tongoy north central chile and its paleoenvironmental implications abstract the importance of the norte chico region in north central chile has long been recognized for the paleoclimates recorded in its soils this area lies in an extreme climate gradient between the hyper arid atacama desert in the north and a mediterranean climate in the south which has made it very sensitive to past climate changes nevertheless few paleoclimate studies have been undertaken in the region and these were mostly concentrated on the holocene we studied pleistocene climate changes recorded in soils that formed over a series of marine terraces near tongoy about 60 km south of la serena the calcrete and soil development took place on four marine terraces associated with marine isotope stages mis 11 mis 7e mis 5e and mis 1 the different types of calcretes that developed on the three oldest terraces containing calcareous material indicate that they developed during different periods and that climatic conditions favorable for the development of these soils existed in the area at least from mis 11 412 ka until post mis 5e 125 ka the calcrete horizons show well defined development stages recording cyclic climate changes varying between arid and more humid during the late pleistocene these climate changes recorded in the tongoy soils are reflected by sedimentological geomorphological and pedogenic processes climate cycles have only been recorded previously for the post mis 5e stage in the area this study being the first to include climate variations reaching mis 11

late holocene climate variability on the eastern flank of the patagonian andes chile a δ18o record from mollusks in lago cisnes 47 s stable isotopes in mollusk shells have been widely used for hydrological balance reconstructions however their use is restricted to lakes that preserve the calcareous material of the shells lago

the southern westerlies in central chile during the two last glacial cycles as documented by coastal aeolian sand deposits and intercalating palaeosols abstract changes in the position and intensity of the southern westerly winds sww and related causal processes during the quaternary are controversial and not well understood here we present a record from continental central chile based on coastal aeolian sand and dunes with intercalated palaeosols reaching back 190 ka in time sixteen samples for luminescence dating and additional samples for geochemical procedures were analysed from three locations in the norte chico la serena los vilos las ventanas besides the recent bw horizons four palaeosols btb1 btb2 btb3 btb4 are identified they formed in periods with stable surface conditions and a relatively dense vegetation cover whereas sand accumulation reflects increased aeolian activity under dry conditions and in parts glacial sea level lowering three of these soils are well bracketed by luminescence data to

mobile sand deposits and shoreface sediment dynamics in the inner german bight north sea abstract this paper presents a conceptual model for the net bedload transport regime on the shoreface of the german bight the model is based on the spatial distribution of the surficial sediment cover north sea sands which is identical to the uppermost layer in the seismic recordings sediment thickness was measured using very high resolution seismic profiling chirp sonar and vibrocoring the three dimensional sediment distribution was estimated using geostatistical methods cokriging the results demonstrate a longshore sand distribution with three distinct zones in zone 1 0 10 m water depth the sediments attain their maximum thickness of 10 2 5 m between 10 and 15 m water depth a relatively thin sand layer of 0 4 1 5 m is observed within zone 2 the seaward adjacent zone 3 15 20 m water depth is characterized by an averaged sand thickness of 2 3 m with local maxima of 5 6 m further offshore the sand layer decreases to about 1 2 m thickness the net bedload transport directions inferred from this sediment zonation comprise a longshore sediment bypassing in zone 1 which results in a substantial sediment supply to the innermost part of the german bight due to bedload convergence shore normal bedload transport shifts sand to and fro across the coastal profile although the net directional transport is seawards this results in sediment depletion between the 10 and 15 m isobaths zone 2 and an adjacent sediment accumulation in deeper waters zone 3

self organized kilometer scale shoreline sand wave generation sensitivity to model and physical parameters the instability mechanisms for self organized kilometer scale shoreline sand waves have been extensively explored by modeling however while the assumed bathymetric perturbation associated with the sand wave controls the feedback between morphology and waves its effect on the instability onset has not been explored in addition no systematic investigation of the effect of the physical parameters has been done yet using a linear stability model we investigate the effect of wave conditions cross shore profile closure depth and two perturbation shapes p1 cross shore bathymetric profile shift and p2 bed level perturbation linearly decreasing offshore for a p1 perturbation no instability occurs below an absolute critical angle c0 40 50 for a p2 perturbation there is no absolute critical angle sand waves can develop also for low angle waves in fact the bathymetric perturbation shape plays a key role in low angle wave instability such instability only develops if the curvature of the depth contours offshore the breaking zone is larger than the shoreline one this can occur for the p2 perturbation but not for p1 the analysis of bathymetric data suggests that both curvature configurations could exist in nature for both perturbation types large wave angle small wave period and large closure depth strongly favor instability the cross shore profile has almost no effect with a p1 perturbation whereas large surf zone slope and gently sloping shoreface strongly enhance instability under low angle waves for a p2 perturbation finally predictive statistical models are set up to identify sites prone to exhibit either a critical angle close to c0 or low angle wave instability

an advance of soler glacier north patagonian icefield at c ad 1222 1342 soler glacier is a temperate outlet glacier on the eastern side of the north patagonian icee eld in chile the glacier is currently receding from its little ice age maximum position attained sometime between ad 1600 and 1900 across the snout and foree eld of the glacier is an arcuate belt of well sorted granule gravel and coarse sand containing tree remains these sediments are interpreted as reworked glaciolacustrine material elevated to the glacier surface by thrusting and folding radiocarbon dating of samples of tree remains in these reworked glaciolacustrine sediments demonstrates that the glacier overrode this lake bed sometime between ad 904 and ad 1334 in situ tree remains plastered onto a large boulder in front of the glacier constrain this advance to the period between ad 1222 and ad 1342 this advance precedes by several hundred years the maximum little ice age extent of other north patagonian icee eld outlet glaciers suggesting either an early age for the onset of little ice age conditions or a previously unrecognized period of glacier advance prior to the advance at c ad 1222 to ad 1342 soler glacier was more recessed than at present cone rming the dynamic response of patagonian glaciers to holocene climatic e uctuations

late quaternary glacier response to humidity changes in the arid andes of chile 18 29 s abstract today no glaciers exist between 18 30 s and 27 s even on mountains much higher than 6000 m these dry high mountain environments are very sensitive to changes in climatic boundary conditions particularly humidity since temperatures are far below freezing here we present a reconstruction of climatic changes since the last glacial maximum for the chilean dry andes of the southern hemisphere we reconstructed regional equilibrium line altitudes ela for three different moraine stages representing extensive past glaciations in this currently unglaciated region comparison of the regional pattern of the ela with modern climate conditions allows us to draw implications about the paleoclimatic conditions during the best preserved moraine stage ii glaciations in the northern as well as in the southern part of the research area our results suggest humid conditions in the northern part 18 24 s during late glacial times with strongly increased convective precipitation during austral summer the temporal coincidence of glaciers in the mountains and high lake levels on the altiplano tauca phase is evident to the south no simple shift of the westerlies is implied by our glacier reconstructions the northern limit of effective moisture for glacier formation did not shift significantly but stayed in the area of the present day northernmost glaciers of the westerlies at about 27 s but further south precipitation increased significantly accompanied by at least 2 3 c colder conditions the age of this glaciation is uncertain but probably of late glacial or last glacial maximum lgm times overall glaciers in the dry andes of south america clearly responded to large changes in the humidity not primarily the temperature regime with all its consequences on the environment hydrology vegetation etc illustrating the different regional responses to global climatic change

horizontal and vertical sediment sorting in tidal sand waves modeling the finite amplitude stage the bed of coastal seas displays a large number of rhythmic bed features of which sand waves are relevant to study from an engineering perspective sediments tend to be well sorted over these bed forms which is so far poorly understood in terms of modeling of finite amplitude sand waves using delft3d we employ bed stratigraphy and consider four different grain size classes which are normally distributed on the phi scale the standard deviation sortedness is then varied whereas the geometric mean grain size is kept constant the results show that typically the crests of sand waves are coarser than the troughs residual flow causes net sedimentation on the lee side of the crest and consequently the general sorting pattern is distorted since larger grains experience a larger settling velocity they are deposited on the upper lee slope whereas the smaller grains are found on the lower lee slope due to sand wave migration also the internal structure of the sand wave is revealed which follows the same sedimentation pattern as the lee slope surface these results qualitatively agree with sorting patterns observed offshore the sorting processes lead to longer wavelengths and lower wave heights as a function of standard deviation this relates to the dampening effect of suspended sediment transport for fine grains finally it appears that the modeled wave heights fall in the same range as observations in the north sea these results are valuable for e g predicting the morphological response after engineering activities and determining suitable aggregates for sand extraction

interrogating the time and processes of development of the las liebres rock glacier central chilean andes using a numerical flow model the las liebres rock glacier is a large 2 2 km long andean rock glacier whose internal composition and kinematics are known from previous studies we investigate its development by posing and testing the following null hypothesis the rock glacier has developed from a constant supply of debris and ground ice in periglacial conditions and resulting creep of the ice rock mixture a rheological model was formulated based on recent advances in the study of ice rock mixture rheology and calibrated on the known surface velocities and internal composition of the rock glacier we show that the rock glacier viscosity is inversely related to both water and debris fractions in agreement with recent field and theoretical studies of ice rock mixture rheology taking into account the possible variations in water fraction the model was used to estimate the time spans of development 0 91 7 11 ka rates of rock wall retreat 0 44 4 18 mm a and rates of ground ice formation 0 004 0 026 m a for the rock glacier these results support the null hypothesis of a periglacial origin of the las liebres rock glacier copyright 2016 john wiley sons ltd

dominant enso frequencies during the little ice age in northern patagonia the varved record of proglacial lago frias argentina abstract the global character of the time interval known as the little ice age lia is at present relatively well established however the forcing mechanisms behind this cooling interval are still elusive investigations in annually laminated sediments have shown that varved sediments are among the best climate archives to tackle these questions proglacial lago frias in northern patagonia is fed by the tronador ice cap 3554 m previous investigations have shown that this glacier has reacted sensitively to climate change during the lia with well identified major glacial advances between ad 1800 1850 results of a multiproxy study of lago frias sediments reflect variations in the transport of glacially derived clay and silt to the basin that can be directly linked to changes in climate sedimentological evidence combined with a chronological model indicate variations in varve thicknesses showing two frequencies centered at 16 4 and 10 5 years that have been previously attributed to the solar cycles and the tropical atlantic sea surface dipole tad respectively the main frequency is however located between 2 5 and 3 0 years pointing towards a dominant el nino southern oscillation enso signal thus the lago frias record provides new insights about the complexity of the various forcing mechanisms behind the cooling during the lia in an area with a paucity of high resolution climate records

a late holocene 2600 bp glacial advance in the south central andes 29 s northern chile radiocarbon dates and relative ages of soils on moraines provide evidence of a substantial late holocene 2600 bp readvance of glaciers in the western part of the arid andes at 29 s the glacier in the encierro valley northern chile reached about 60 of its late pleistocene extent the equilibrium line altitude ela during this advance remained between 4250 and 4500 m which is above the modern 0 c isotherm of the free atmosphere during summer it is suggested that given the specific climate at high elevations in the extremely arid andes a substantial increase in effective moisture is sufficient to explain this advance whereas no significant temperature depression was needed this compares favourably with the regional late holocene climatic history when lake levels were higher and effective moisture greater than today between 3000 and 1800 bp judging from regional palaeodata we suggest that this late holocene humid spell was most likely related to increased westerly moisture sources from the pacific

sandwaves and other large scale bedforms as indicators of non tidal surge currents in the skagerrak off northern denmark abstract results from side scan sonar surveys made at two sites in the skagerrak off hanstholm and hirtshals show that transverse and longitudinal current induced bedforms are widespread in both areas down to a water depth of 70 m a maximum sandwave height of 7 m is found off hanstholm comet marks have a maximum length of near 50 m off hanstholm wave action markedly affects the seabed at depths of less than 25 m this can cause significant deformation of current induced bedforms the bedforms are not relict structures they demonstrate that maximum bottom flow velocities associated with the jutland current can locally reach a magnitude of at least 70 100 cm s bedform configuration and sediment distribution off hansholm indicate continuation of the jutland current bottom flow axis in a northeast direction diverging from the coastline this may favour sand transport in greater water depths than is usually found elsewhere in the area as an exception at one occasion at the site off hirtshals megaripples were found to have southwest facing leeside slopes and small comet marks were also directed towards the southwest this must have resulted from exceptional outflow conditions with bottom current speed in excess of 60 cm s

detecting shifts of submarine sediment boundaries using side scan mosaics and gis analyses abstract detecting changes of sediment boundaries on the seafloor is important for a better understanding of sediment dynamics and related impacts to benthic habitats side scan sonars sss perform more cost effectively in shallow waters than other acoustic systems because of their larger swath widths and the resolution of its images does not change with varying water depth however as they are generally towed behind the survey vessel they tend to have lower positioning accuracy which makes them unreliable for change detection analyses in this study we present a workflow that processes sss data in a way that makes them fit for change detection analyses to test the capacity of sss mosaics for change detection we used a free software called digital shoreline analysis system which was developed by the united states geological survey for arcgis version 10 4 onwards the methods were applied in three areas in the sylt outer reef german bight north sea our results showed that with appropriate processing sss mosaics could be used for change detection of sharp sediment boundaries we found a common trend in the sediment distribution patterns of coarse sediments by monitoring the movement of their boundaries the boundaries moved in northeast southwest direction and boundary movements of less than 20 m were typically observed the methods presented here are semi automated repeatable and replicable which has potential for wide scale monitoring of sediment distribution patterns

sedimentology and stratigraphy of tidal sand ridges southwest florida inner shelf abstract detailed investigation of linear shelf sand ridges located off the southwest coast of florida shows them to be tide dominated sand bodies these ridges are remarkably similar to the large sand ridges of the north sea and they have abundant apparent analogs in the stratigraphic record many of which are important petroleum producers the florida ridges are asymmetric in profile about 10 km long 1 km wide with relief of 3 4 m with the adjacent sea bed extensive tidal current monitoring sediment distribution patterns and side scan sonar surveys permit characterizing their morphodynamics tidal currents show distinct bidirectional patterns with speeds up to 70 cm s there is slight flood dominance and currents show much higher velocities in the troughs as compared to the crests of he ridges megaripples and sand waves are widespread and migrate obliquely across the ridges at opposite directions on the gentle and steep sides of the ridge shallow high resolution seismic data and 39 vibracores in the area of the ridges show a consistent sequence characterized by three ascending holocene lithofacies 1 muddy quartz sand with limestone clasts 2 bioturbated muddy shelly quartz sand and 3 well sorted cross stratified quartz sand that characterizes the sand ridges themselves each of the tidal sand ridges displays a coarsening upward sequence of fine well sorted sand small scale multidirectional cross stratification dominates the stratigraphy of the cores in this facies but megaripple cross stratification is also present all data indicate that these tidal ridges are good modern analogs for many of the shelf sand bodies in the ancient record especially the mesozoic of the mid continent area

extractable al and fe in early to middle quaternary paleosols in gorges valley mount kenya east africa summary two of the oldest paleosols on mount kenya east africa in the gorges moraine of early pleistocene age were studied to determine if extractable fe and al might prove useful in the interpretation of present and past soil forming environments using documented paleomagnetic ages for the tills and loesses we attempted to determine if extractable crystalline fe and al could provide information on relative age paleomagnetic dating places the tills as slightly younger than the olduvai subchron the data indicate that no pyrophosphate extractable fe and al normalized against fe d and al d have been translocated downward in the two paleosols further the amount of dithionite extractable fe is greater in the paleosol solum under hagenia forest which is in accordance with its older relative age early brunhes established by paleomagnetic methods the activity ratio fe 0 fe d for the sola aeolian sediments in the two paleosols shows overall lower values in the paleosol under hagenia forest suggesting greater conversion to crystalline fe as well as advanced age

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

southern westerlies during the holocene deduced from geomorphological and pedological studies in the norte chico northern chile 27 33 s abstract in the norte chico precipitation is controlled by atmospheric perturbations and frontal systems associated with the belt of westerly wind circulation the holocene climatic history of the region can be reconstructed from geomorphic and pedologic investigations in comparison to modern climatic conditions increased influence of the westerlies is deduced for the time periods prior to 7300 yr b p between 5000 3700 yr b p 3000 1800 yr b p and around 270 yr b p it remains uncertain whether the increased influence of the westerlies was the consequence of northward shifts of the westerlies as a whole of a meridional expansion of the westerly belt or only of intensity changes of the atmospheric dynamics almost synchronous with changes in the westerlies the coastal fogs in the region were apparently reduced or the fog belt in the coastal range was elevated probably due to a weakened upwelling and warmer water conditions in the eastern pacific in general the climate of the norte chico has become more variable since 5000 yr b p especially since 3000 yr b p with frequent changes of the geoecological conditions

tide induced bedload transport pathways in a multiple sand ridge system offshore of hainan island in the beibu gulf northwest south china sea modern sand transport pathways in a multiple sand ridge system are elusive and have rarely been studied in recent years we report herein a field with four en echelon linear sand ridges offshore of hainan island in the beibu gulf and describe the distribution and morphology of these sand ridges in detail for the first time dune crest comparisons and seismic profiles are also interpreted to assess sand transport over the dunes based on a delft 3d model regional tidal currents and tide induced bedload transport in the multiple sand ridge system were simulated to provide insights into the related bedload transport paths the results show that bedload transport and residual flows are mostly directed to the south on the east side of the sand ridges and to the north on the west side and these differences coincide with dune asymmetries and migrations cross ridge transport is weak and mostly converges on the crests of sand ridges from the two flanks the bedload transport is unbalanced on either flank of the sand ridges thus leading to the asymmetry and crest kinks of the sand ridges a distinct correlation is not observed between the net cross ridge sand transport and sand ridge asymmetry in this system cross swale transport is significant between the neighboring sand ridges and helps construct the bedload transport circulation in the swales sand accretion also occurs in the swales and benefits from the southwestward bedload transport from the north end of sand ridge 3 distinct evidence has not been found for closed bedload transport circulation around sand ridges in this multiple sand ridge system although limited clockwise current vortices develop on several sand ridges additional field observations and simulations are required to characterize the suspended load transport in a multiple sand ridge system and the effects of local sand supply conditions on sand transport also need further evaluation copyright c 2018 john wiley sons ltd

early to mid holocene aridity in central chile and the southern westerlies the laguna aculeo record 34 s abstract central chile 32 35 s lies at the northern border of strong westerly influence and thus exhibits a steep precipitation gradient therefore the palaeoclimatic archives in the region are suitable for detecting past moisture changes the study of laguna aculeo 33 50 s 70 54 w presents a multiproxy holocene lake record including sedimentology geochemistry mineralogy pollen diatoms and radiocarbon dating 17 dates results indicate an arid early to mid holocene period about 9500 5700 cal yr b p after 5700 cal yr b p effective moisture increased progressively and around 3200 cal yr b p modern humid conditions were established numerous intercalated clastic layers reflect flood deposition during rainy winters a fluvial unit was deposited shortly before 9000 cal yr b p subsequently flood events were absent until 5700 but have become frequent since 3200 cal yr b p the frequency of flood layers possibly points to weak or no el nino activity during the early and mid holocene with a subsequent increase during the late holocene during the early and mid holocene the westerlies were probably blocked and hence deflected southward by the subtropical high pressure cell higher precipitation during the last 3200 yr seems strongly related to a weakened subtropical high pressure cell with intensified westerlies and possibly increased el nino activity

speleothem master chronologies combined holocene 18o and 13c records from the north island of new zealand and their palaeoenvironmental interpretation the stable isotope records of four stalagmites dated by 19 tims uranium series ages are combined to produce master chronologies for delta 18 o and delta 13 c the delta 18 o records display good overall coherence but considerable variation in detail variability in the delta 13 c records is greater but general trends can still be discerned this implies that too fine an interpretation of the structure of individual isotopic records can be unreliable speleothem delta 18 o values are demonstrated to show a positive relationship with temperature by comparing trends with other proxy records but also to respond negatively to rainfall amount speleothem delta 13 c is considered to be most influenced by rainfall the postglacial thermal optimum occur red around 10 8 ka bp which is similar in timing to antarctica but up to 2000 years earlier than most northern hemisphere sites increasingly negative delta 18 o values after 7 5 ka bp indicate that temperatures declined to a late mid holocene minimum centred around 3 ka bp but more positive values followed to mark a warm peak about 750 years ago which coincided with the mediaeval warm period of europe low 5110 values at 325 years bp suggest cooling coincident with the little ice age a marked feature of the delta 13 c record is an asymmetric periodicity averaging c 2250 years and amplitude of c 1 9parts per thousand it is concluded that this is mainly driven by waterbalance variations with negative swings representing particularly wet intervals the 5110 record shows a higher frequency cyclicity with a period of c 500 years and an amplitude of c 0 25 parts per thousand this is most likely to be temperature driven but some swings may have been amplified by precipitation

assessing decadal scale changes to a giant sand wave field in eastern long island sound three digital precision bathymetric data sets spanning 16 1 yr enabled a long term analysis of the geometric migration and volumetric changes to large bedforms in a 1 km2 region of eastern long island sound whereas a 1 yr study of sand wave mechanics during 1987 provided indirect evidence of long term southwestward transport this study adds a june 2003 data set and conclusively demonstrates a basinward southwestward progression of sand waves between 7 and 17 m in height in addition the modus operandi of sand wave migration during various temporal scales involves crestal flexing crestal rotation and differential migration along the crest a volumetric analysis suggests that the sand waves are in a waning phase of migration and early stage of preservation as sea level rises into the basin and flood dominant tidal currents decrease in strength

climatic variations in the argentine plains during the last 18 000 years the last deglacial hemicycle was characterized by a general increase in temperature and precipitation in the region with a few significant departures from this general trend the present ne sw climatic gradient was maintained throughout the entire period except in the upper holocene the following sequence of events is apparent if the present climate is taken as a reference base 1 a 18 000 8500 yr b p arid and cool with aeolian sand ad loess deposition patagonian fauna climatic isolines temperature precipitation etc were located some 750 km northeast of their present positions 2 b 8500 3500 yr b p humid subtropical with brazilian fauna pedogenesis and fluvial dynamics climatic limits migrated about 800 900 km southwest of their former positions 3 c 3500 1000 yr b p dry subtropical aeolian dynamics the normal latitudinal climatic gradient was interrupted by the occurrence of an anticyclonic centre which stabilized the climate over an area of some 1 600 000 km2 4 d 1000 yr b p little ice age climate was similar to the present one over much of the plains but the northeastern extremity was warmer 5 e little ice age climatic deterioration in the southern belt was characterized by generalized aeolian activity and migration of isolines more than 150 km to the northeast in that area 6 f present climate 19th and 20th centuries subtropical humid in the east and dry in the west

lateglacial and holocene cosmogenic surface exposure age glacial chronology and geomorphological evidence for the presence of cold based glaciers at nevado sajama bolivia comparisons of palaeo equilibrium line altitudes between the western and eastern cordilleras in the central andes are commonly based on the assumption that the tall outermost moraines visible in remotely sensed images of the western cordillera date to the last glacial maximum lgm however field investigation and geomorphic mapping at nevado sajama bolivia indicates the tall moraines are relic features with shorter moraines overlying and in some cases extending beyond them 36cl exposure ages from the shorter moraines suggest that they date to lateglacial times ca 16 9 10 2 ka although lateglacial deposits have been found throughout the central andes the extent of these deposits relative to lgm deposits varies both between the western and eastern cordilleras and north to south along the western cordillera in the western cordillera in the zone of easterly winds the lateglacial appears to be the most extensive glacial advance of the last glacial cycle geomorphic evidence also suggests that some lateglacial moraines were deposited by cold based ice a previously unreported finding in the tropical andes retreat from other glacial features occurred at about 7 0 4 4 ka and 4 7 3 3 ka these are the first directly dated holocene glacial deposits in the western cordillera of bolivia and their presence suggests that the mid holocene may not have been as warm and dry as previously thought copyright 2008 john wiley sons ltd

holocene glacier chronology of valenzuela valley mendoza andes argentina glacial geologic evidence and radiocarbon dated glacial deposits provide evidence of glacier fluctuations during the last 5 ka years in the andes radiocarbon dated moraines morphological and stratigraphical studies permit the reconstruction of glacier fluctuations during the holocene in the valenzuela area of the mendoza andes valley located at 35s in the upper rio grande basin the holocene record in this part of the andes is mostly unknown so this research is relevant for palaeoclimatic reconstructions in south america in the rio valenzuela glacier variations were dated in the el azufre and el pefion valleys the first neoglacial advance occurred at c 5700 yr bp and a very close re advance of similar magnitude occurred at 4700 4300 yr bp which formed well preserved lateral terminal moraines the first neoglacial advance occurred in the el pefion valley at c 4400 yr bp and a well preserved terminal moraine is observed a second neoglacial advance reached its maxima at c 2500 2200 yr bp in the el

mid to late holocene climate change an overview the last 6000 years are of particular interest to the understanding of the earth system because the boundary conditions of the climate system did not change dramatically in comparison to larger glacial interglacial changes and because abundant detailed regional palaeoclimatic proxy records cover this period we use selected proxy based reconstructions of different climate variables together with state of the art time series of natural forcings orbital variations solar activity variations large tropical volcanic eruptions land cover and greenhouse gases underpinned by results from general circulation models gcms and earth system models of intermediate complexity emics to establish a comprehensive explanatory framework for climate changes from the mid holocene mh to pre industrial time the redistribution of solar energy due to orbital forcing on a millennial timescale was the cause of a progressive southward shift of the northern hemisphere nh summer position of the intertropical convergence zone itcz this was accompanied by a pronounced weakening of the monsoon systems in africa and asia and increasing dryness and desertification on both continents the associated summertime cooling of the nh combined with changing temperature gradients in the world oceans likely led to an increasing amplitude of the el nin o southern oscillation enso and possibly increasingly negative north atlantic oscillation nao indices up to the beginning of the last millennium on decadal to multi century timescales a worldwide coincidence between solar irradiance minima tropical volcanic eruptions and decadal to multi century scale cooling events was not found however reconstructions show that widespread decadal to multi century scale cooling events accompanied by advances of mountain glaciers occurred in the nh e g in scandinavia and the european alps this occurred namely during the little ice age lia between ad w1350 and 1850 when the lower summer insolation in the nh due to orbital forcing coincided with solar activity minima and several strong tropical volcanic eruptions the role of orbital forcing in the nh cooling the southward itcz shift and the desertifi cation of the sahara are supported by numerous model simulations other simulations have suggested that the fingerprint of solar activity variations should be strongest in the tropics but there is also evidence that changes in the ocean heat transport took place during the lia at high northern latitudes with possible additional implications for climates of the southern hemisphere sh

recent glacial history and paleoclimate of the peruvian bolivian andes abstract radiocarbon dates of glacial deposits in the peruvian bolivian andes are used to place the observed phases of glaciation in a common chronological framework the climatic conditions that may determine modern snowline are examined in order to understand the types of climatic forcing to which glaciers may have been sensitive in the past also considered are independent proxies of climatic change including pollen sequences lake level history and ice core data late pleistocene glaciation in central peru between 24 ka and 12 ka bp appears to have occurred during colder and perhaps drier conditions in bolivia a glacial maximum is dated to phases of late holocene glaciation in peru that correspond in part to the little ice age in the northern hemisphere appear to have been caused by a combination of colder and wetter conditions an overall warming trend may be the cause for the retreat of many glaciers in the region since the mid 19th century

late quaternary glaciation of the cordillera real bolivia glacial geological studies in tropical mountain areas of the southern hemisphere can be used to address two issues of late pleistocene climate change the global synchroneity of deglaciation and the magnitude of temperature reduction in the tropics radiocarbon dates from the cordillera real and from other areas in peru and bolivia suggest that late pleistocene glaciation culminated between 14 000 and 12 000 yr bp followed by rapid deglaciation because deglaciation was apparently synchronous with that in northern hemisphere regions insolation change at high latitudes may not have been the only factor that produced global deglaciation at this time late pleistocene glaciation in the cordillera real culminated when precipitation was 200 mm yr 1 higher and temperatures were 3 5 1 6 c lower than today this produced an equilibrium line altitude depression of about 300 100 m on the western side of the cordillera prior to this conditions were drier and probably at least as cold however the lack of moraines in the cordillera real dated to the last glacial maximum ca 18000 yr bp precludes using the equilibrium line altitude method to quantitatively evaluate the discrepancy between warm sea surface temperatures and cold terrestrial conditions reconstructed with other proxies for this time period

patagonian ash on sub antarctic south georgia expanding the tephrostratigraphy of southern south america into the atlantic sector of the southern ocean

paleoenvironmental changes in the semiarid coast of chile 32 s during the last 6200 cal years inferred from a swamp forest pollen record pollen analysis of two sediment records from a coastal swamp forest site in the chilean semiarid region 31 50 s 71 28 w shows an alternation of dry and wet phases during the past 6100 cal yr b p the most prominent vegetation changes occur at 4200 cal yr b p with the expansion of the swamp forest taxa luma chequen and escallonia sp followed by a regression of the forest beginning at 3200 cal yr b p and ending with its replacement by a xerophytic scrub between 1800 and 1300 cal yr b p the swamp forest reexpanded after 1300 cal yr b p and persisted with minor variation until the present we interpret the establishment of the swamp forest at the study site to be the result of a rising watertable in response to increased rainfalls from 4200 cal yr b p onward our results indicate that in north central chile the second half of the holocene was climatically more variable than previously thought suggesting significant changes in the position and or intensity of the westerlies wind belt and possibly in the frequency of el nino southern oscillation events

late quaternary glacier advances and palaeolake highstands in the bolivian altiplano abstract recent study of late quaternary moraines and pluvio lacustrine features around the southern altiplano of bolivia suggests they developed more or less synchronously during the last glacial cycle the stratigraphy of lacustrine and deltaic sediments can be linked to outwash and moraines on glaciated massifs e g cerro condor iquina cerro azanaques and cerro tunupa which border the poopo uyuni and coipasa salt basins uranium series and radiometric dating of lake carbonates by previous workers suggests that major palaeolakes developed during the intervals 72 68 ka bp 44 34 ka bp and 15 4 9 5 ka bp radiocarbon dating of peat associated with glacifluvial and glacial sediments indicates that the most extensive glacier advance of the later part of the last glacial cycle culminated after 13 3 ka bp and that a smaller readvance may have occurred between 12 and 10 ka bp as the highest palaeolake stand the tauca phase has been dated to ca 13 8 ka bp it is concluded that increased effective moisture and cool climatic conditions during the interval ca 14 13 ka bp forced the simultaneous expansion of glaciers and lakes in and around the southern altiplano a palaeolake may have been present on the southern altiplano for much of the interval ca 15 4 9 5 ka bp its surface reaching different levels at different times

glaciation in the andes during the lateglacial and holocene this review updates the chronology of andean glaciation during the lateglacial and the holocene from the numerous articles and reviews published over the past three decades the andes which include some of the world s wettest and driest mountainous regions offer an unparalleled opportunity to elucidate spatial and temporal patterns of glaciation along a continuous 68 degree meridional transect the geographic and altitudinal extent of modern glaciers and the sensitivity of both modern and former glaciers to respond to changes in specific climatic variables reflect broad scale atmospheric circulation and consequent regional moisture patterns glaciers in the tropical andes and in the mid latitude andes are likely to have been far more sensitive to changes in temperature than glaciers in the dry subtropical andes broad scale temporal and spatial patterns of glaciation during the lateglacial are apparent in the southernmost andes the lateglacial chronology appears to have a strong antarctic signature with the best dated moraines correlating closely with the antarctic cold reversal the southernmost andes do not appear to have experienced a significant ice advance coeval with the younger dryas yd climatic reversal at the other end of the andes from w 0t o 9 n a stronger yd connection may exist but critical stratigraphic and geochronologic work is required before a yd ice advance can be fully demonstrated in the central andes of peru well dated moraines record a significant ice readvance at the onset of the yd but ice was retreating during much of the remaining yd interval the spatial temporal pattern of holocene glaciation exhibits tantalizing but incomplete evidence for an early to mid holocene ice advance s in many regions but not in the arid subtropical andes where moraines deposited during or slightly prior to the little ice age lia record the most extensive advance of the holocene in many regions there is strong evidence for neoglacial advances in the interval between 1 0 and 2 5 ka moraines that correlate with the lia of the northern hemisphere are seen in all presently glacierized mountain ranges most of these date to within the past 450 years outboard of these moraines in many regions are moraines of a slightly more extensive advance that occurred several hundred years prior to the onset of the lia priorities for future work include filling in several prominent spatial gaps in the distribution of chronologic studies for the lateglacial these gaps include the arid regions of northern chile and argentina the southern peruvian andes between 11 5 and 13 5 s and the andes of northern peru and

the role of non uniform roughness in the formation of sand ribbons abstract sand ribbons typically are shallow water sedimentary features characterized as thin elongate bands of sand overlying a coarser lag sediment which is exposed between them the ribbons are oriented along the direction of the dominant current and are formed by a secondary circulation pattern that includes a small component of the boundary shear stress directed toward the center of the sand ribbons a perturbation expansion coupled with flume experiments indicates that this circulation pattern is linked to differences in the bottom roughness between the sand ribbons and the adjacent coarser strips the non uniform turbulence field arising from this roughness distribution drives a secondary helical flow the expansion indicates that there is a preferred ratio of sand ribbon spacing to water depth 4 1 for unstratified channel flow conditions the secondary flow pattern forces the downstream flow to readjust so that the boundary shear stress over the smooth sand strips is considerably smaller than the mean stress this serves to retard the movement of sand through such a system

palynological evidence for increased aridity on the central chilean coast during the holocene abstract the late quaternary vegetation of the semiarid coast of central chile is inferred from the palynological analysis of profiles from quereo 31 55 s and quintero 32 47 s prior to 11 400 yr b p wet conditions are suggested by the abundance of pollen indicators of swamp and aquatic taxa such as cyperaceae and myriophyllum and by the presence of traces of arboreal pollen since ca 10 000 yr b p a trend toward increasingly drier conditions is implied by the almost complete absence of arboreal and aquatic taxa and a general decrease in the diversity of the semiarid shrubland indicators from 3000 yr b p onward the pollen records show the reappearance of swamp and aquatic taxa presumably associated with wetter conditions which led to recolonization by forest taxa at 1720 yr b p in quintero the drier climate detected along the semiarid coast of central chile during most of the holocene extended inland to the andean foot hills within the present mediterranean type climate zone of chile and also affected the distribution of the winter deciduous nothofagus forests and the northern boundary of the temperate rain forests

facies architecture in depositional systems resulting from the interaction of acidic springs alkaline springs and acidic lakes case study of lake roto a tamaheke rotorua new zealand the facies architecture in hot spring systems tends to become more varied and complicated as the degrees of freedom in the system increase discharge aprons fed by waters from a single vent will for example be characterized by predictable downslope facies changes that reflect downslope changes in water chemistry and temperature the facies architecture however becomes exponentially more intricate when more factors start to impact the system this phenomenon is readily apparent in the geothermal area around lake roto a tamaheke located in the whakarewarewa thermal village rotorua new zealand where the facies architecture developed in response to the interactions between acid lake acid hot spring and alkaline hot spring depositional regimes with additional extraneous sediment being brought into the area by volcanic ash clouds wind blown pollen and surface run off from the surrounding drainage basin much of the complexity in the facies architecture of this system stems from the temporal varianc