landslides and climate change in the italian dolomites since the late glacial abstract the paper deals with the relationship between the temporal occurrence of landslides and climatic changes in the italian dolomites since the late glacial after an introduction on the state of the art with particular reference to the alpine region the results of recent investigations in the two study sites are illustrated at cortina d ampezzo several landslides were dated mainly by the radiocarbon method the most ancient landslide event there involved large rock slides which affected the dolomitic slopes following the withdrawal of glaciers after the last glacial maximum lgm and also slides and flows mainly occurring in pelitic materials of the valley floors from 13 000 to 10 000 cal bp a later series of flows occurred between 5500 and 2500 cal bp in the upper badia valley alta badia the most ancient events go back to 10 000 and 9000 cal bp and correspond with earth flows that followed vast rotational slides affecting the bedrock up to a depth of about 50 m more recent earth flows involving more modest amounts of material took place between 6500 and 2300 cal bp by analysing the dates from the two study areas it was possible to correlate the recorded increase of landslide activity with the climatic changes occurring at the boundary between the late glacial and the holocene and between the atlantic and the subboreal and to compare the results with those derived from other european regions the types and causes of landslides taking place in these two periods were substantially different reflecting the different morphoclimatic conditions that existed in the two areas when these mass movements were triggered finally notwithstanding the importance of non climatic causes such as geological structural factors and possible human influences it is concluded that many of the dated landslides can be considered as indicators of climatic change

fluid budgets at convergent plate margins implications for the extent and duration of fault zone dilation faults at convergent plate boundaries are important conduits for fluid escape and recent evidence suggests that fluid expulsion along them is both transient and heterogeneous for the nankai and barbados convergent margins we have used numerical models to investigate the long term partitioning of expelled fluids between diffuse flow and flow along connected high permeability fault conduits for a simple case of spatial heterogeneity we estimated the extent of high permeability conduits necessary to maintain a balance between incoming and expelled fluids for the case of transient expulsion we constrained the duration of elevated permeability required to balance the fluid budgets comparison of modeled and observed geochemical profiles suggests that the initiation of connected flow conduits is delayed with respect to the time of accretion into each accretionary complex and may be related to burial below a critical depth either where the overlying wedge is sufficiently thick to prevent fluid escape to the sea floor or where sediments behave brittlely

high frequency of super cyclones along the great barrier reef over the past 5 000 years understanding long term variability in the occurrence of tropical cyclones that are of extreme intensity is important for determining their role in ecological disturbances1 2 3 4 5 for predicting present and future community vulnerability and economic loss6 and for assessing whether changes in the variability of such cyclones are induced by climate change7 our ability to accurately make these assessments has been limited by the short less than 100 years instrumented record of cyclone intensity here we determine the intensity of prehistoric tropical cyclones over the past 5 000 years from ridges of detrital coral and shell deposited above highest tide and terraces that have been eroded into coarse grained alluvial fan deposits these features occur along 1 500 km of the great barrier reef and also the gulf of carpentaria australia we infer that the deposits were formed by storms with recurrence intervals of two to three centuries8 9 10 11 and we show that the cyclones responsible must have been of extreme intensity central pressures less than 920 hpa our estimate of the frequency of such super cyclones is an order of magnitude higher than that previously estimated which was once every several millennia12 13 14 and is sufficiently high to suggest that the character of rainforests and coral reef communities were probably shaped by these events

synchronous high frequency oscillations in tropical sea surface temperatures and north atlantic deep water production during the last glacial cycle stable isotopic measurements of g sacculifer and c wuellerstorfi in a core from the western equatorial atlantic imply that there are parallel suborbital oscillations in surface water hydrography and deep water circulation occurring during oxygen isotope stages 2 and 3 low values of g sacculifer 18o accompany high values of c wuellerstorfi 13c linking warmer sea surface temperatures ssts in the tropics with increased production of lower north atlantic deep water nadw the amplitude of the 18o oscillations is 0 6 or 2 3 c which is superimposed on a glacial interglacial amplitude of about 2 1 using the g sacculifer 18o data we calculate that surface waters were colder during stage 2 than calculated by climap 1976 1981 the longer period 2 kyr oscillations in air temperature recorded in the greenland and antarctic ice cores appear to correlate with oscillations in sea surface temperature in the equatorial atlantic the magnitude of these oscillations in tropical sst is too large to have resulted from changes in meridional heat transport caused by the global conveyor alone the apparent synchroneity of equatorial sst and polar air temperature changes as well as the amplitude of the sst changes at the equator are consistent with the climate effects expected from changes in the atmosphere s greenhouse gas content h2ovapor co2 and ch4

palaeoflood and floodplain records from spain evidence for long term climate variability and environmental changes abstract palaeoflood chronologies from seven spanish river basins and floodplain aggradation chronologies from thirteen rivers are analysed these fluvial records were divided in to two sub sets namely atlantic 10 ka record and mediterranean 3 ka record river basins which represent distinct modern hydroclimatic conditions in atlantic basins floods result from intense widespread rainfalls associated with atlantic frontal systems transported by westerly airflow mediterranean river flooding is related to heavy rainfall induced by mesoscale convective systems mcss during autumn months evidence from radiocarbon dates in slackwater flood deposits shows six periods of flood clusters at 10 750 10 240 9550 9130 4820 4440 2865 2350 960 790 and 520 290 cal bp despite the different flood producing weather conditions in atlantic and mediterranean rivers the radiocarbon sample clusters overlap and indicate changes in large scale atmospheric circulation and climatic conditions in the iberian peninsula comparison with proxy records of mean temperature for the northern hemisphere demonstrates a relationship between the period of slackwater flood deposition and cold climatic phases e g the 2650 yr bp climatic event or ad 1590 1650 period of the little ice age radiocarbon dates from aggraded floodplain sediments were clustered at 2710 2320 2000 1830 and 910 500 cal bp the first cluster period is in phase with the timing of slackwater deposition whereas the third 910 500 cal bp occurs in between two periods of increased flood frequency as indicated by the palaeoflood and documentary flood records it is argued that the 910 500 cal bp floodplain aggradation period reflects the first post roman evidence of environmental change related to generalised land use changes at the catchment scale which produced high sediment load transported to overbank areas during high flows

evidence for changes in the north atlantic deep water linked to meltwater surges during the heinrich events abstract deep sea sediment records from north atlantic cores 40 n 55 n provide evidence of several massive iceberg discharges known as heinrich events during the last glacial period high resolution benthic 18 o and 13 c records from north atlantic sediment cores were used to monitor the impact of heinrich events on thermohaline circulation and to estimate the sensitivity of deep oceanic circulation to changes in freshwater input to the north atlantic surface waters our data indicate that major rearrangements of deep water masses were directly associated with these massive iceberg discharges to trace in detail the deep water conditions in the north atlantic benthic 13 c values in several cores were used to generate time slices before during and after heinrich event 4 dated at 35 ka bp although north atlantic deep water continued to form during the oxygen isotope stage 3 at 37 ka bp deep circulation was characterized by an increased incursion of deep waters of southern origin which reduced the 13 c composition of north atlantic deep waters particularly in the eastern atlantic basin north atlantic deep water production was reduced during heinrich layer 4 hl4 at 35 ka bp synchronously with the changes in the surface water hydrology deep convection processes may have occurred in areas not affected by the salinity decrease soon after hl4 33 ka bp the 13 c distribution was similar to that before the event similarly a rapid return to initial 13 c values was observed at the end of the most clearly defined heinrich events hl5 hl4 and hl1 comparison between deep circulation patterns corresponding to hl4 the last glacial maximum and heinrich event 1 indicates that each of these periods was characterized by a different circulation state associated with changes in convection sites

distinguishing allogenic from autogenic causes of bed elevation change in late quaternary alluvial stratigraphic records abstract allogenic and autogenic mechanisms both cause changes in the bed elevation of rivers and thereby influence the characteristics of alluvial stratigraphic records asrs allogenic forcing mechanisms can be grouped into five categories whose relative influence varies with timescale climate tectonism base level land use land cover and direct human modification of channels late quaternary asrs are influenced by the greatest range of allogenic forcing variables with climate among the most important autogenic mechanisms of bed elevation change are ubiquitous throughout fluvial systems and are always time transgressive autogenic bed elevation change propagates through drainage networks at predictable rates and results in a time space envelope within which its effects are capable of operating asrs that can be correlated over geographical areas large enough and time intervals small enough to exist outside this envelope most likely result from allogenic forcing this formulation represents a quantitative and geographic set of threshold criteria for distinguishing between autogenic and allogenic mechanisms over late quaternary timescales 10 2 to 10 5 years in tectonically stable regions climate change is the dominant allogenic mechanism and therefore the first order control on the morphology sedimentology pedologic characteristics and chronology of alluvial stratigraphic records that meet or exceed the threshold criteria for demonstrating allogenic causality

correlated millennial scale changes in surface hydrography and terrigenous sediment yield inferred from last glacial marine deposits off northeastern brazil abstract the stable isotope composition of planktonic foraminifera correlates with evidence for pulses of terrigenous sediment in a sediment core from the upper continental slope off northeastern brazil stable oxygen isotope records of the planktonic foraminiferal speciesglobigerinoides sacculiferandglobigerinoides ruber pink reveal sub milankovitch changes in sea surface hydrography during the last 85 000 yr warming of the surface water coincided with terrigenous sedimentation pulses that are inferred from high xrf intensities of ti and fe and which suggest humid conditions in northeast brazil these tropical signals correlate with climatic oscillations recorded in greenland ice cores dansgaard oeschger cycles and in sediment cores from the north atlantic heinrich events trade winds may have caused changes in the north brazil current that altered heat and salt flux into the north atlantic thus affecting the growth and decay of the large glacial ice sheets

the timing of alluvial sedimentation and floodplain formation in the lowland humid tropics of ghana sierra leone and western kalimantan indonesian borneo abstract temporal patterns in floodplain genesis and alluvial sedimentation in lowlands tropical rain forest zones of ghana sierra leone and western kalimantan indonesian borneo based upon 14 c age determinations are described alluvial low terraces or buried sediments in west africa yielded ages of 36 21 ka in west kalimantan a widespread episode of alluviation has yielded dates of 54 51 ka the 20 13 ka interval was characterised by channel incision with valley floor erosion and neither region records sedimentation holocene alluvial sedimentation and floodplain construction in west africa occurred during two temporal intervals 10 7 ka and 4 ka to present and in western kalimantan in response to early holocene sea level rise followed by late holocene regression and coastal outgrowth the clustering of 14 c dates closely corresponds to regional lake level fluctuations and vegetational changes and to global indications of climatic change we propose that periods of more frequent episodes of accelerated floodplain erosion and reconstitution channel morpho sedimentary activity and alluvial accumulation 1 are responses to interstadial and interglacial periods of higher precipitation following intervening periods of cooler and drier conditions and 2 may be synchronous during the last 60 ka throughout the african and asian inner humid lowland tropics

the flickering switch of late pleistocene climate change polar ice contains a unique record of past climate variations previous greenland ice cores have documented relatively warm interstadial periods during the last glaciation and short centuryscale returns to colder conditions during the glacial to interglacial warming see for example ref 1 these climate features have also been observed to varying degrees in ocean sediment cores2 4 and terrestrial pollen and insect records5 7 here we report electrical conductivity measurements from a new greenland ice core which confirm these previous observations and also reveal a hitherto unrecognized mode of rapid climate variation fluctuations in ice conductivity on the scales of 5 20 years reflect rapid oscillations in the dust content of the atmosphere this flickering between two preferred states would seem to require extremely rapid reorganizations in atmospheric circulation

the holocene fluvial chronology of spain evidence from a newly compiled radiocarbon database abstract a critical analysis of 74 radiocarbon dates selected from a total of 102 published and unpublished dates from holocene fluvial environments in spain has identified a number of periods of increased fluvial activity in spain namely 11 170 10 230 9630 8785 7980 6860 5800 4800 3880 3085 2895 1820 1300 0 cal bp the latter period reflecting sustained fluvial response to increased human impact the radiocarbon samples were classified according to type of depositional environment a alluvial overbank b flood basin c alluvial channel gravels d fluvio torrential deposits and e slackwater flood deposits palaeofloods dates from slackwater flood deposits indicated at least five phases of increased frequency of large magnitude floods during the holocene 10 855 10 230 9530 8780 2880 2430 975 790 and 520 265 cal yr bp flood basin type deposition occurred from 7980 to 4830 cal yr bp the main clusters of dates from alluvial floodplain deposits occurred at 2750 2150 and 930 520 cal yr bp the record is discussed in relation to other palaeoenvironmental archives including pollen records of holocene vegetation change and palaeoclimatic proxies such as the north atlantic drift ice record comparison with the latter indicates that major holocene flooding coincided with cold climate phases during 9530 9280 2880 2430 and 520 265 cal yr bp a cooling phase at 10 855 10 230 and warming phases at 9030 8780 and 975 790 cal yr bp

enormous ganges brahmaputra sediment discharge during strengthened early holocene monsoon rivers are the main source of terrigenous sediment delivered to continental margins and thus exert a major control on coastal evolution and sequence development however little is known about past changes in fluvial sediment loads despite the recognition of significant variation under changing climatic regimes in this study we present the first quantified estimate of sediment discharge for a major river system under conditions of an intensified early holocene monsoon development of the ganges brahmaputra river delta began ca 11000 yr b p when rising sea level flooded the bengal basin thereby trapping most of the river s discharge on the inner margin chronostratigraphic data from these deltaic deposits are used to calculate the rates of sediment storage on the margin which provide a minimum estimate of the river s past sediment load results reveal that 5 1012 m3 of sediment was stored in the bengal basin from ca 11000 to 7000 yr b p which corresponds to a mean load of 2 3 109 t yr in comparison modern sediment load of the ganges brahmaputra is 1 109 t yr ranking it first among the world s rivers and underscoring the significance of a two fold increase sustained over 4 k y furthermore the timing of immense discharge in the early holocene strongly suggests its relation to a stronger than present southwest monsoon in south asia similar patterns of high monsoon related sediment discharge have been noted throughout the tropics and subtropics suggesting a widespread fluviosedimentary response the potential magnitude of which is showcased by the ganges brahmaputra system

the gisp2 δ18o climate record of the past 16 500 years and the role of the sun ocean and volcanoes measured 18o 16o ratios from the greenland ice sheet project 2 gisp2 ice core extending back to 16 500 cal yr b p provide a continuous record of climate change since the last glaciation high resolution annual 18o 16o results were obtained for most of the current millennium a d 818 1985 and record the medieval warm period the little ice age and a distinct 11 yr 18o 16o cycle volcanic aerosols depress central greenland annual temperature 1 5 c maximally and annual 18o 16o for about 4 yr after each major eruptive event on a bidecadal to millennial time scale the contribution of solar variability to holocene greenlandic temperature change is 0 4 c the role of thermohaline circulation change on climate problematic during the holocene is more distinct for the 16 500 10 000 cal yr b p interval analogous to 14c age calibration terminology we express time in calibrated cal yr b p a d 1950 0 cal yr b p the oldest dryas bolling older dryas allerod younger dryas sequence appears in great detail bidecadal variance in 18o 16o but not necessarily in temperature is enhanced during the last phase of lateglacial time and the younger dryas interval suggesting switches of air mass transport between jet stream branches the branched system is nearly instantaneously replaced at the beginning of the bolling and holocene at 14 670 and 11 650 cal yr b p respectively by an atmospheric circulation system in which 18o 16o and annual accumulation initially track each other closely thermodynamic considerations of the accumulation rate temperature relationship can be used to evaluate the 18 o 16o temperature relationship the gisp2 ice layer count years of major gisp2 climate transitions also support the use of coral 14c ages for age calibration

late holocene 1500 yr climatic periodicities and their implications fourier and nonlinear regression analysis of a 4000 yr paleoclimate proxy record in western canada shows strong periodicities of 1500 yr and several weaker century to millenial scale periodicities in conjunction with the 23 708 yr milankovitch periodicity these produce a model of climate fluctuation through the postglacial consistent with recognized paleoclimatic fluctuations of the past 15 000 yr in the northern mid latitudes these results suggest that postglacial climatic anomalies such as the little ice age and the younger dryas were at least in part periodic phenomena rather than the result of unique aperiodic events projecting these periodicities into the future suggests that even in the absence of anthropogenic climate forcing a natural warming trend will continue until ca a d 2400

multi process late quaternary landscape evolution modelling reveals lags in climate response over small spatial scales landscapes evolve in complex non linear ways over quaternary timespans integrated geomorphological field studies usually yield plausible hypotheses about timing and impact of process activity landscape evolution models lems have the potential to test and falsify these landscape evolution hypotheses despite this potential lems have mainly been used with hypothetical data and rarely to simulate the evolution of an actual landscape in this paper we use a lem lapsus landscape process modelling at multi dimensions and scales to explore if it is possible to test and falsify conclusions of an earlier field study on 50 ka landscape evolution in okhombe valley kwazulu natal south africa in this lem five landscape processes interact without supervision water driven erosion and deposition creep solifluction biological weathering and frost weathering calibration matched model results to three types of qualitative fieldwork observations individual process activity over time relative process activity over time and net landscape changes over time results demonstrate that landscape evolution of the okhombe valley can be plausibly simulated a particularly interesting and persistent feature of model results are erosional and depositional phases that lag climatic drivers both by decades and by several ka within a few hundred meters the longer lag has not been reported for this spatial scale before and may be an effect of slow landscape soil vegetation feedbacks the combined modelling and fieldwork results allow a more complete understanding of these responses to climate change and can fill in hiatuses in the stratigraphical record suggestions are made for methodological adaptations for future lem studies

paleoenvironmental dynamics of low order paleovalleys in the late quaternary palmas cacador summit surface southern brazil abstract the quaternary dynamics of landscapes in the subtropical continental region of brazil is not still well understood pedostratigraphic records of low order paleovalleys paleovalley heads and 1st and 2nd order paleovalleys of the palmas cacador summit surface serve as important resources for the identification of landscape component responses relief soil sediment and vegetation of plateau areas of southern brazil in the light of environmental changes driven by climatic variations of the late quaternary we integrated litho pedo allo and chronostratigraphic descriptions with carbon stable isotope analysis phytoliths indices and 14c and osl dating we found that at 44 86 ky bp there was a change in the hydrodynamics of 2nd order perennial channels humid climate controlled possibly by tectonics at 28 35 to 23 69 to 28 ky bp regressive pedogenesis in dry climate began with a predominance of erosion by overland flows at 2 60 to 23 69 ky bp full regressive pedogenesis occurred under a continuous climate regime of drier characteristics punctuated by millenary climatic fluctuations to a wetter regime of between 4 60 and 19 77 ky bp echoing the results postulated by the knox s model during this period the most pronounced modifications to the landscape were made with a change in vegetation from campo cerrado to campo limpo with changes in erosion patterns caused first by overland flows and then earthflows debris flows and with the gradual silting filling and burying of gullies valley heads and 1st and 2nd order valley bases since 2 60 ky bp the area returned to a predominance of progressive pedogenesis in wet and cold climates finally we found that at the local scale low order basins

after the deluge mediterranean stagnation and sapropel formation in an east mediterranean marine core the upper sapropel begins soon after the start of a global event a very heavy precipitation which occurred in the equatorial latitudes during the late glacial early holocene this heavy precipitation in africa channelled by the nile river across 35 of latitude produced a low salinity surface layer in the east mediterranean in this confined basin with high bottom salinity the steep salinity gradient stratified the water column the stagnant bottom waters triggered the sapropel formation cretaceous sapropels in the tropical oceans may result from the same chain of events in warm humid climates with contrasting wet and dry seasonal rhythm

simulated climate and biomes of africa during the late quaternary comparison with pollen and lake status data new compilations of african pollen and lake data are compared with climate ccm1 ncar boulder and vegetation biome 1 2 gsg lund simulations for the last glacial maximum lgm and early to mid holocene emh the simulated lgm climate was ca 4 c colder and drier than present with maximum reduction in precipitation in semi arid regions biome simulations show lowering of montane vegetation belts and expansion of southern xerophytic associations but no change in the distribution of deserts and tropical rain forests the lakes show lgm conditions similar or drier than present throughout northern and tropical africa pollen data indicate lowering of montane vegetation belts the stability of the sahara and a reduction of rain forest the paleoenvironmental data are consistent with the simulated changes in temperature and moisture budgets although they suggest the climate model underestimates equatorial aridity emh simulations show temperatures slightly less than present and increased monsoonal precipitation in the eastern sahara and east africa biome simulations show an upward shift of montane vegetation belts fragmentation of xerophytic vegetation in southern africa and a major northward shift of the southern margin of the eastern sahara the lakes indicate conditions wetter than present across northern africa pollen data show an upward shift of the montane forests the northward shift of the southern margin of the sahara and a major extension of tropical rain forest the lake and pollen data confirm monsoon expansion in eastern africa but the climate model fails to simulate the wet conditions in western africa

stratigraphy of near valley head quaternary deposits and evidence of climate driven slope channel processes in southern brazilian highlands abstract during the past 40 years colluvial and alluvial deposits have been used in brazil as good indicators of regional landscape sensitivity to quaternary environmental changes in spite of the low resolution of most of the continental sedimentary record geomorphology and sedimentology may favor palaeoenvironmental interpretation when supported by independent proxy data this paper presents results obtained from pedostratigraphic sequences in near valley head sites of southern brazilian highlands based on geomorphologic sedimentologic micromorphologic isotopic and palynologic data results point to environmental changes with ages that coincide with marine isotopic stages mis 5b 3 2 and 1 during the late pleistocene although under temperatures and precipitation lower than today the local record points to relatively wet local environments where shallow soil water saturated zones contributed to erosion and sedimentation during periods of climatic change as during the transition between mis 2 and mis 1 late pleistocene events with ages that coincide with the northern hemisphere younger dryas are also depicted during the mid holocene slope wash deposits suggest a climate drier than today probably under the influence of seasonally contrasted precipitation regimes the predominance of overland flow related sedimentary deposits suggests an excess of precipitation over evaporation that influenced local palaeohydrology this environmental condition seems to be recurrent and explains how slope morphology had influenced pedogenesis and sedimentation in the study area due to relative sensitiveness resilience and short source to sink sedimentary pathways near valley head sites deserve further attention in quaternary studies in the humid tropics

a general model of paraglacial landscape response a unifying attribute of all forms of paraglacial response is that deglaciation results in the exposure of unstable or metastable sediment sources that are subsequently tapped by a wide variety of processes over a wide range of timescales the paraglacial period in different geomorphological contexts is therefore con ditioned by two variables glacially conditioned sediment release and rate of sediment reworking under steady state conditions the latter may be approximated by an exhaustion model in which sediment yield is related to the amount of remaining available sediment by a negative exponential function this model offers an approximation for the behaviour of primary paraglacial systems in which glacigenic sediment sources are not replenished the long term behaviour of secondary primarily uvial paraglacial systems in which sediment inputs include both in situ and reworked glacigenic sediment appears intrinsically more complex but consistent with an exhaustion model if initial sediment avai

climate controls on late pleistocene landscape evolution of the okhombe valley kwazulu natal south africa hillslopes in central and western parts of kwazulu natal south africa are often mantled by colluvial sediments of the masotcheni formation these sediments have accreted in response to several cycles of deposition pedogenesis and incomplete erosion climatic controls on these cycles are incompletely known results from fieldwork micromorphology stable carbon isotope analysis and optically stimulated luminescence dating of masotcheni formation sediments from okhombe valley in the drakensberg foothills are combined deposition in the area had at least 11 phases starting before 42 ka and ending before 0 17 ka the first six deposits from before 42 ka to after 29 ka resulted from the interplay between slope processes and fluvial redistribution under cold conditions solifluction was the most important slope process no deposits have been found from the last glacial maximum arguably because this period was too dry the last five deposits from about 11 ka to before 0 17 ka resulted from fluvial redistribution of upslope material and older deposits under increasing precipitation current extreme gully erosion in the masotcheni formation indicates a lack of available upslope material leaving downslope deposits as the only sediment source for fluvial redistribution this model for landscape response to climate change may be able to explain how climate controlled landscape processes in other masotcheni formation sites in kwazulu natal in the research area and elsewhere this proposition may be tested with numerical landscape evolution models

geomorphic and paleoclimatic implications of latest pleistocene radiocarbon dates from colluvium mantled hollows california radiocarbon analyses of charcoal from basal colluvium in 11 california hollows show a clustering of dates between 9000 and 15 000 b p an indication that changes in the storage and discharge of colluvium from hillslopes accompanied the pleistocene holocene transition hollows are sites of topographically induced convergence and deposition of colluvial debris and evacuation of this debris was apparently more thorough and possibly more frequent in the latest pleistocene perhaps due to a combination of changes in vegetation and rainfall characteristics one hypothesis is that greater storm intensities occurred in the latest pleistocene and induced a higher frequency of landslides in hollows and a regional extension of channel heads upslope relative to the holocene during the last pleistocene california hollows apparently contained smaller volumes of colluvium in storage the increased storage of debris during the holocene may have resulted in a diminished supply of sediment to stream channels

rock varnish microlamination dating of late quaternary geomorphic features in the drylands of western usa abstract varnish microlamination vml dating is a correlative age determination technique that can be used to date and correlate various geomorphic features in deserts in this study we establish a generalized late quaternary i e 0 300 ka varnish layering sequence for the drylands of western usa and tentatively correlate it with the specmap oxygen isotope record we then use this climatically correlated varnish layering sequence as a correlative dating tool to determine surface exposure ages for late quaternary geomorphic features in the study region vml dating of alluvial fan deposits in death valley of eastern california indicates that during the mid to late pleistocene 5 15 ky long aggradation events occurred during either wet or dry climatic periods and that major climate shifts between glacial and interglacial conditions may be the pacemaker for alteration of major episodes of fan aggradation during the holocene interglacial time however 0 5 1 ky long brief episodes of fan deposition may be linked to short periods of relatively wet climate vml dating of alluvial desert pavements in death valley and the mojave desert reveals that pavements can be developed rapidly

geomorphic changes in ras al subiyah area kuwait the ras al subiyah area is considered one of the most promising areas in kuwait for future development this development will include a new town called subiyah and its associated infrastructure this area is also being considered as the location for connection between boubyan island which is now undergoing major development and the kuwait mainland the present study investigates the geomorphology of the ras al sabiyah area in the northern sector of kuwait the study area is generally flat and it is located west of the jal az zor escarpment it is bordered on the east by the khor al sabiyah tidal channel and on the south by kuwait bay the area receives sediments from several sources currently the most important are aeolian sediments and the deposition of mud delivered through the khor al sabiyah from the iraqi marshes the study area has been subjected to severe environmental changes due to the gulf wars and the drainage of iraqi marshes and the associated artificial changes in fluvial system twenty two surface sediments were collected from the ras al subiyah area samples were collected to include the main geomorphologic characteristic features of the study area field observations and remote sensing images from 1990 and 2001 were used to produce an updated geomorphologic map for the ras al subiyah and a map showing geomorphic changes between 1990 and 2001 grain size of the surface sediment ranges from gravel to medium sand in general grain size statistical analysis indicates that most of the areas are composed of two or more classes of sands transported and deposited from different sources including aeolian sabkhas river and the bays the variability in the grain size statistical parameters may be attributed to the complexity of surface morphology as well as the diversity in the type of depositional environment in the ras al subiyah area the total area subjected to change during the 12 year period 1990 2001 is about 32 km2 as calculated using gis techniques

how did rivers in the wet tropics ne queensland australia respond to climate changes over the past 30 000 years the nature and timing of fluvial response and coincident changes in climate as inferred from multiple independent proxies are examined in the wet tropics of north eastern australia chronostratigraphic data provide evidence for regionally synchronous fluvial aggradation at 30 13 ka 8 5 ka and again from 1 ka terrace incision and removal occurred at 13 8 ka and 5 1 ka a new synthesis of regional palaeoenvironmental proxy records spanning the last 30 ka highlights key periods of environmental change comparison of the records of fluvial and environmental change reveals the relationship is complex with no clear relationship between river aggradation incision and wetter drier conditions the nature and timing of fluvial response in the wet tropics also shows broad similarities with coastal valleys in south eastern new south wales suggesting continental scale controls on fluvial response to changing climate during the late quaternary in australia copyright c 2017 john wiley sons ltd

a 100 ka record of fluvial activity in the fitzroy river basin tropical northeastern australia this study reports the nature and timing of quaternary fluvial activity in the fitzroy river basin which drains a diverse 143 000 km 2 area in northeastern queensland before discharging into the

landscape sensitivity to rapid environmental change a quaternary perspective with examples from tropical areas abstract a millennial scale of rapid change during the quaternary is recorded in grip and gisp2 ice core records and is also found in tropical oceans rapid warming episodes followed by gradual cooling associated with sub milankovich cycles implies an asymmetry in the behaviour of climate that is likely to be reflected in landscape responses slope failures floods colluvial alluvial sedimentation may reflect short term changes in the record but reorganisation of slope and fluvial systems involves significant time lags or delays often on a millennial scale and requiring changes to the vegetation cover while some records of sedimentation indicate major landscape instability during last 20 ky or in the early holocene others indicate pulses of activity throughout the last glacial cycle lgc these differences may reflect regional patterns of climate change but also illustrate the importance of landscape sensitivity to our understanding of the impacts of rapid environmental change methodological problems arise in attempting correlations between site specific records of sedimentation and integrated signals of hydrologic change found in deltaic and off shore fans

the holocene younger dryas transition recorded at summit greenland analysis of ice from dye 3 greenland has demonstrated that the transition between the younger dryas and holocene climate periods occurred over a 40 year period a near annually resolved multiparameter record of the transition recorded in the gisp2 core from summit greenland shows that most of the transition occurred in a series of steps with durations of about 5 years some climate proxies associated with mid latitude sources appear to have changed about 15 years before climate proxies associated with more northern regions changes in atmospheric water vapor are likely to have played a large role in the climate transition

dating of debris flow fan complexes from lantau island hong kong china the potential relationship between landslide activity and climate change five debris flow fan complexes bordering the coastal foothills of western lantau island hong kong have been the subject of a stratigraphic and dating study to explore the potential relationship between past periods of climate change and landslide activity luminescence osl ages from the fan complexes supported by a few calibrated radiocarbon 14c ages on duplicate samples suggest six main periods of accumulation 28 000 20 000 ka 14 500 10 500 ka 5800 5000 ka 4370 4230 ka 3560 3320 ka and 1350 1050 ka the younger periods 10 000 ka appear to be dominated by relatively thin 0 5 1 5 m units deposited mainly by debris flood events whereas the older periods are dominated by thicker 1 0 3 5 m units deposited by debris flow events we hypothesise that immediately prior to the last glacial maximum lgm i e 21 000 ka the climate was cool and dry upland areas were probably devoid of vegetation providing favourable conditions for sediment production in source areas these debris laden source areas are likely to have been mobilised during periodic rainstorm activity rapidly channelised over relatively short drainage courses and then deposited as thick sediment rich debris flow deposits along the coastal foothills during the early to middle holocene the climate was warmer and more humid pluvial conditions dominated forests occupied the upland source areas leading to possibly reduced sediment yields more frequent flash floods and deposition dominated by debris floods compared with recent studies on the weathering and erosion history of the pearl river delta our landslide age data are indicative of a potential link between increased landslide activity and intensification of the east asian monsoon during the early to middle holocene

geomorphic response to rapid climatic and hydrologic change during the late pleistocene and early holocene in the humid and sub humid tropics abstract the data base concerning late quaternary environmental change in the humid tropics is dependent on records from scattered sites the intensity and duration of wet dry oscillations remain speculative and the responses of hillslopes and river systems are based on over simplified models however available evidence indicates that prolonged aridity affected all but a few favoured core areas of equatorial climate after 20 000 bp lasting 5 7 ka dry conditions at the lgm were marked by semi arid landforms and reduced steam activity large palaeofloods occurred after 13 000 be but dry conditions returned after 11 000 bp before the early holocene pluvial led to abundant sedimentation lasting nearly 2 ka after 9500 bp in africa amazonia and australasia erosion channel cutting and flood deposition occurred at the pleistocene holocene transition followed by multiple shifts from lateral to vertical accretion fill cut episodes during the early holocene while thick overbank deposits formed during the later holocene re establishment of the lowland rainforests was delayed until after 9000 bp in africa australia and brazil and several wet dry oscillations followed in the mid holocene period hillslope activity at the lgm was marked by local sediment transfers and fan formation at the termination sediment fluxes increased rapidly but mass movement probably peaked after 10 000 bp sediment delivery to stream channels was not immediate and large sediment stores remain on the landscape today many in areas of potential sensitivity of erosion

lacustrine fluvial interactions in australia s riverine plains climatic forcing of fluvial systems has been a pre occupation of geomorphological studies in australia since the 1940s in the riverine plain southeastern australia the stable tectonic setting and absence of glaciation have combined to produce sediment loads that are amongst the lowest in the world surficial sediments and landforms exceed 140 000 yr in age and geomorphological change recorded in the fluvial fluvio lacustrine and aeolian features have provided a well studied record of quaternary environmental change over the last glacial cycle the region includes the willandra lakes whose distinctive lunette lakes preserve a history of water level variations and ecological change that is the cornerstone of australian quaternary chronostratigraphy the lunette sediments also contain an ancient record of human occupation that includes the earliest human fossils yet found on the australian continent to date the lake level and palaeochannel records in the lachlan willandra system have not been fully integrated making it difficult to establish the regional significance of hydrological change here we compare the willandra lakes environmental record with the morphology and location of fluvial systems in the lower lachlan an ancient channel belt of the lachlan willandra creek acted as the main feeder channel to willandra lakes before channel avulsion caused the lakes to dry out in the late pleistocene electromagnetic surveys geomorphological and sedimentary evidence are used to reconstruct the evolution of the first new channel belt following the avulsion single grain optical dating of floodplain sediments indicates that sedimentation in the new middle billabong palaeochannel had commenced before 18 4 1 1 ka a second avulsion shifted its upper reaches to the location of the present lachlan river by 16 2 0 9 ka the timing of these events is consistent with palaeohydrological records reconstructed from willandra lakes and with the record of palaeochannels on the lachlan river upstream willandra lakes shows high inflows during the last glacial maximum 22 ka but their subsequent drying between 20 5 ka and 19 ka was caused by river avulsion rather than regional aridity this case study highlights the benefits of combining fluvial with lacustrine archives to build complementary records of hydrological change in lowland riverine plains

understanding the impacts of late quaternary climate change in tropical and sub tropical regions abstract the understanding of climate impacts on tropical rivers and catchments has developed in part from models developed for temperate landscapes and a common rhythm is often apparent when millennial scale studies are compared at this level issues arising from the complex response of rivers to internal and external factors appear less important than the climate driven signal understanding the fluvial record however depends on the availability and interpretation of other sources of proxy data such as pollen spectra lake levels and ocean cores in many rainforest areas few pollen records exist and many of these reveal a hiatus at the time of the last glacial maximum examples of fluvial archives from africa indonesia and tropical queensland australia are discussed in relation to independent records of vegetation change and inferences are made concerning critical episodes in fluvial history focusing on the transitions from oxygen isotope stage ois 3 towards glacial conditions in ois2 and the pleistocene holocene transition to modern climates links between climate vegetation change and fluvial activity are presented as descriptive models

late quaternary stream sedimentation in the humid tropics a review with new data from ne queensland australia there is now a wide agreement that temperature depression in the humid tropics during the last glacial maximum lgm was at least 5 c most estimates of precipitation reduction at the lgm range from 25 30 to 50 65 based on proxy data but the recent ccm1 model envisages only around 12 dates obtained from river sediments indicate major changes to fluvial activity in the late quaternary isotope zone 3 sediments 58 28 ka bp are widespread and possibly indicate cooler conditions post 28 ka bp and certainly post 21 ka bp river regimes altered radically towards fan building braiding or major reduction in all activity this paper reports on fan formation in ne queensland between 26 and 14 ka bp and reviews evidence for comparable changes in humid tropical areas of s america w africa and se asia including records of holocene sedimentation within a global rhythm of major changes to river regimes in the humid tropics during the late quaternary it is now possible to detect regional variations in stream response to climatic change at the lgm reductions in stream power may have led to fan formation in ne queensland while vegetation changes may have contributed to increased sediment loads and braiding in some forest marginal areas but in w africa greater aridity may have been responsible for enfeebled streams leaving few records channel cutting then deposition of coarse sediment in braided rivers marked the transition to the early holocene in w africa and fans became entrenched in ne queensland this regime persisted until forest recovery was complete by 9 5 8 5 ka bp when widespread overbank deposition occurred and a change towards meandering channels took place widely across the humid tropical zone followed by several cut and fill episodes in the middle and late holocene

the timing and environmental significance of late quaternary linear dune development in western zambia optical luminescence dates for 19 samples from the degraded linear dune field of western zambia indicate multiple periods of regional dune building for the late quaternary 32 000 27 000 16 000 13 000 10 000 8000 and 5000 4000 yr ago these dates show that the last glacial maximum was not the only time when dune construction commonly linked to marked aridity occurred in central southern africa during the late quaternary whereas rainfall significantly less than today s ca 1400 mm yr 1 is a prerequisite for dune construction in the area adequate sediment supply also determines dune construction and preservation so that dune building cannot be simply and singularly linked to marked aridity the zambezi river system is proposed as an important source of dune sediments with the nature of linear dune activity explaining why stacked sediments preserve several phases of dune formation chronologies of dune construction in western zimbabwe and the southwest kalahari are in broad agreement with our zambian chronology and support a model of rainfall shifts along a sw ne gradient with some notable disparities these are probably a function of interregional sediment supply differences the number of samples used to delimit constructional periods and the multicausal nature of forcing mechanisms

the last glacial cycle from the humid tropics of northeastern australia comparison of a terrestrial and a marine record a detailed pollen record from the ocean drilling program site 820 core located on the upper part of the continental slope off the coast of northeast queensland was constructed to compare with the existing pollen record from lynch s crater on the adjacent atherton tableland and allow the production of a regional picture of vegetation and environmental change through the last glacial cycle some broad similarities in patterns of vegetation change are revealed despite the differences between sites and their pollen catchments which can be related largely to global climate and sea level changes the original estimated time scale of the lynch s crater record is largely confirmed from comparison with the more thoroughly dated odp record conversely the lynch s crater pollen record has assisted in dating problematic parts of the odp record in contrast to lynch s crater which reveals a sharp and sustained reduction in drier araucarian forest around 38 000 yrs bp considered to have been the result of burning by aboriginal people the odp record indicates most likely a stepwise reduction dating from 140 000 yrs bp or beyond the earliest reduction shows lack of a clear connection between araucaria decline and increased burning and suggests that people may not have been involved at this stage however a further decline in araucarian forest possibly around 45 000 yrs bp which has a more substantial environmental impact and is not related to a time of major climate change is likely at least partially the result of human burning the suggestion from the odp core oxygen isotope record of a regional sea surface temperature increase of around 4 degrees c between about 400 000 and 250 000 yrs bp may have had some influence on the overall decline in araucaria and its replacement by sclerophyll vegetation c 2000 elsevier science b v all rights reserved

disequilibrium of holocene sediment yield in glaciated british columbia it is generally supposed that specific sediment yield the quantity of sediment passing a monitored river cross section per unit area drained upstream of that section declines as the area drained increases1 3 part of the sediment mobilized from the land surface is supposed to go back into storage at field edges and on footslopes and floodplains in contrast we show here that data from british columbian rivers reveal a pattern of increasing specific sediment yield at all spatial scales up to 3 104 km2 this results from the dominance of secondary remobilization of quaternary sediments along river valleys over primary denudation of the land surface the result controverts the conventional model which has been derived from studies of small highly disturbed agricultural catch ments the rivers are still responding to the last glaciation giving a landscape relaxation time greater than 10 kyr this holds pro found implications for geomorphological theory and for studies of erosion