cooling trend over the past 4 centuries in northeastern hong kong waters as revealed by alkenone derived sst records abstract the climate history over the past few centuries is important to be used to assess how regional climate responds to global forcing here we report three high resolution alkenone based sea surface temperature sst records over the past 4 centuries from three sediment cores collected in the mirs bay northeastern hong kong all three sst records consistently show a general cooling trend toward the present with most of cooling occurring over the last century alkenone derived sst values stayed around 26 5 27 c at the three sites prior to 1900s and decreased into the range of 25 26 c the magnitude of cooling approximately from the little ice age lia to present tends to be dampened from 2 c nearshore to 1 c offshore the cooling trend as identified in all three sst records is thus opposite to the global temperature rise over the last century assisted with modern observations we interpret that the alkenone derived sst reflects increasing upwelling in the mirs bay which likely results from the strengthened east asian summer monsoon in the context of global warming over the last century

behavior of rare earth elements in a paleoweathering profile on granodiorite in the front range colorado usa abstract a paleoweathering profile on the boulder granodiorite in northern colorado provides an opportunity to trace the behavior of rees from parent rock through a weathering profile into unconformably overlying permian sediments with progressive upward weathering of the granodiorite na2o cao sio2 ta hf co th cr sc cr th zr hf la sc zr y and la th decrease al2o3 and fe2o3t increase and tio2 mgo k2o p2o5 rb zr sc cr co hf nb ta y th u ree ti nb and zr nb increase to maximum values and then either level off or decrease lree enrichment is less in the weathering profile than in the parent granodiorite and although the parent does not have an eu anomaly or only a slight positive anomaly all samples from the weathering profile and overlying sediments have significant negative eu anomalies this observation is especially important in that it shows conclusively that a negative eu anomaly can be produced during chemical weathering of granitoids we suggest these eu anomalies are due to relative enrichment of the other rees and partial loss of eu during the breakdown of plagioclase the boulder weathering profile also has a very minor negative ce anomaly that is within error of a ce anomaly in the parent in the unweathered parent 50 of the ree are contained in sphene and in the case of la also in allanite from 10 20 of the ree are contained in apatite and biotite hornblende and from 7 10 of the hrees are in zircon with exception of eu for which feldspars contribute about 8 negligible amounts of rees occur in the feldspars in weathered samples 75 of the rees are contained in clay minerals the crossover between sphene and clay control of rees occurs over a distance of 1 m near the contact with fresh rock except for their small negative eu anomalies the clay minerals have ree patterns very similar to those of the parent rock isocon plots suggest apparent enrichments of many elements in the boulder weathering profile result from losses of na ca and si during plagioclase weathering in addition variable amounts of sr eu ta nb p and ba were lost during weathering although th u zr y th sc zr hf lu hf and ti zr may have been transferred relatively unchanged from granodiorite parent to the bulk weathering profile most other element ratios and ree distributions were significantly changed during weathering this observation implies that caution needs to be exercised when using ree patterns and element ratios to trace sediment provenance the fact that most element ratios and ree distributions also differ between fountain sediments and the bulk weathering profile may be related to one or a combination of four factors listed in order of probable decreasing importance contribution of other sources to the fountain sediments sorting of minerals during sediment deposition remobilization of elements during diagenesis and leaching of elements by water flow through the upper meter of the weathering profile

facies mosaics across the persian gulf and around antigua stochastic and deterministic products of shallow water sediment accumulation abstract among broadly different types of sedimentary successions those that accumulate in nearshore settings are perhaps unique in that a very wide range of rock types recurs with high frequency over relatively short stratigraphic intervals this vertical lithofacies heterogeneity suggests that deposition of any sedimentary unit at any site was short lived that many different sediment types existed within a complex mosaic over the depositional surface and that this facies montage repeatedly moved across surfaces of accumulation in response to eustatic sedimentologic and or tectonic forcing data on numbers and thicknesses of lithofacies units from several dozen such sequences define the size frequency distribution expected if horizons of lithologic change occur randomly within sedimentary successions walther s law suggests that the amount of vertical lithologic heterogeneity manifest in a sedimentary sequence should reflect the degree of lateral heterogeneity in sediment composition that existed across depositional surfaces if so this repetition should also be manifest in sizes and areal distributions of sediment patches constituting the depositional mosaic in order to examine size frequency relations of sediment bodies across surfaces of sediment accumulation we tabulated numbers and areal extents of lithotopes across two rather dissimilar settings across the persian gulf and around the caribbean island of antigua although compositions and lateral extents of different sediment types exhibit broad lateral variation across interior to margin transects in either area lithotope abundances and areal extents define frequency distributions that are in excellent agreement with those anticipated for a facies mosaic of elements whose mean linear widths constitute an exponential frequency distribution these are the size frequency distributions one would expect if mosaic element boundaries occur randomly across regions of sediment accumulation and suggest that distributions of lithotope areas from holocene surfaces are directly analogous to lithofacies thickness frequencies from ancient successions in addition to the fact that both of the size frequency distributions attest to the importance of stochastic processes during sediment deposition they also afford numerical descriptors of abundances and areal extents of holocene lithosomes that can then be used as controlling parameters in computational models of sediment accumulation importantly results derived from such simulations are based not on inference of water depth varying in response to change in subsidence sea level and rate of sediment accumulation but on statistical attributes intrinsic to modern and ancient marginal marine successions

turf banked terrace treads and risers turf exfoliation and possible relationships with advancing treeline fine scale geomorphic pedogenic processes at alpine treeline may facilitate the initial stages of conifer invasion of alpine tundra turf banked terraces and turf exfoliation associated with solifluction may provide both the topographic protection and the seedbed necessary for conifer establishment above treeline the morphometry stoniness and surface penetrability of turf banked terraces were recorded whereas differences among sites exist due to topographic constraints differences in soil penetrability depend on turf exfoliation exfoliated turf risers are significantly more penetrable than non exfoliated solifluction risers and adjacent treads these penetrable microsites provide favorable conditions for seed germination the process of turf exfoliation may play a role in conifer advance into tundra during climatic change d 2004 elsevier b v all rights reserved

relationships between climate and soil hydrological and erosional characteristics along climatic gradients in mediterranean limestone areas an investigation was undertaken to determine the relationships between climate and soil hydrological and erosional characteristics rainfall simulation experiments were carried out along three climatological gradients on similar limestone lithologies in the mediterranean region standard experiments were used to characterize each site so that an objective comparison could be made at each of the eleven south facing slopes three experiments were carried out a total of 33 plots were selected for the experiments located in the galilee and carmel mountains israel crete greece and alicante spain simulated rainfall was used in order to measure time to ponding and runoff steady state infiltration rate runoff coefficient runoff sediment concentration and the erosion rate at each of the 33 selected plots the mean annual rainfall is not directly correlated with soil erodibility infiltration and runoff the effect of climate on geomorphological processes does not have a great impact on runoff and infiltration at pedon scale during the wet seasons studied the local thunderstorms discourage any kind of soil moisture trends along the climatic gradients and thus on hydrological processes human impacts mainly grazing and fires seem to be the most relevant factors for soil hydrological and erosional response in the mediterranean region

a 22 000 year record of vegetation change in the north central sonoran desert abstract plant macrofossils from eleven packrat neotoma sp middens provide a history of vegetation change over the last 22 140 years at eagle eye mountain near the northern border of the sonoran desert in arizona this site is located in the arizona upland subdivision departures and arrivals of various perennial plant species during the holocene were similar to other records from more southerly sites and support earlier generalizations of van devender van devender t r 1990 late quaternary vegetation and climate of the sonoran desert united states and mexico in betancourt j l van devender t r martin p s eds packrat middens the last 40 000 years of biotic change university of arizona press tucson pp 134 165 regarding the tempo and mode of late quaternary changes in the arizona upland evergreen woodland containing pinus monophylla singleleaf pinyon juniperus osteosperma utah juniper and quercus turbinella shrub live oak occupied the site during full glacial times the latter two species but not p monophylla persisted into the early holocene and were joined by a limited number of desertscrub species including acacia greggii catclaw carnegiea gigantea saguaro and several other succulents with the arrival of many other species during the middle holocene a desertscrub community that differed considerably from the modern vegetation developed acacia greggii and cercidium floridum blue paloverde were the principal large woody species on exposed hillslopes assemblages similar in composition to the modern desertscrub did not appear until approximately 4000 years ago when the more xerophytic cercidium microphyllum foothills paloverde arrived and c floridum disappeared from hillslopes the delayed arrival of c microphyllum in comparison to other sonoran desertscrub species with similar climatic tolerances is attributed to the limited dispersal distance of its seeds by seed eating heteromyid rodents at 4540 and 6425 yr b p the cold intolerant shrub encelia farinosa was present on northeasterly aspect exposures where it is absent today suggesting slightly warmer winter conditions during the middle holocene the presence of the tree cercidium floridum and the perennial c 4 grass setaria leucopila on exposed slopes during the middle holocene indicates substantially moister conditions during that time than in the late holocene or today at sites on the xeric limits of the modern distributions of both species average annual precipitation is from 50 to 100 greater than that presently received at eagle eye mountain in particular the responses of s leucopila and cacti during the middle holocene indicate substantial increases in warm season precipitation

effects of direct and indirect heating on the validity of rock weathering simulation studies and durability tests rock surface and subsurface temperature responses in samples exposed to direct heating insolation under natural hot desert conditions reveal considerable variability between lithologies related to differences in thermal properties especially albedo and thermal conductivity however when the same samples are heated indirectly by air in an oven based environmental cabinet lithological differences in temperature response disappear and all samples attain temperatures similar to the air temperature within the cabinet rates and patterns of rock decay produced in such environmental cabinets may not therefore reflect those encountered under natural conditions where breakdown is related to micro environmental conditions at the rock air interface and where rock temperature is one of the most important controlling factors in addition to implications for assessment of weathering effectiveness use of only indirect forms of heating affects the determination of comparative rock durability because all rock types are cycled through the same temperature regimes because temperature exerts such a major control on rock breakdown through its control on physical and chemical weathering processes all significant factors influencing it must be included in the design of weathering simulations and durability tests

controls on links between geomorphical and surface sedimentological variability aitutaki and maupiti atolls south pacific ocean abstract isolated carbonate platforms and atolls occur throughout the geologic record from archean to present although the roles of sea level change tectonics and sediment supply on large scale changes in stratigraphical architecture of these systems are relatively well understood the details of the nature and controls on sedimentological variability between and within individual geomorphic elements on platforms and atolls are less well constrained the purposes of this study are 1 to describe compare and contrast geomorphological and sedimentological characteristics of surficial holocene sediments from two south pacific atolls aitutaki and maupiti representing different physical and chemical oceanographic settings and 2 to explore possible causes for sedimentological heterogeneity by contrasting the patterns with those present on other platforms and regions both atolls include annular shelf edge reef systems with a red algal rim and reef flat flanked lagoonward by reef sand aprons up to 1 500 m wide these aprons consist of moderately sorted coarse sand and gravel with an abundance of halimeda coral and red algal fragments broadly sediments become finer and better rounded away from margins water depths increase abruptly inboard of these reef sand aprons into platform interiors with depths up to 25 m maupiti and 9 m aitutaki although patch reefs dot these lagoons sediment is commonly poorly sorted with bimodal and polymodal size distributions and includes a mix of whole and fragmented skeletal grains peloids and ooids mud and fine sand are abundant up to 80 on maupiti 85 on aitutaki the occurrence of peloids fine ooid sand and oolitically laminated skeletal grains on maupiti atoll as previously documented on aitutaki is consistent with interpretations of the impact of elevated regional ocean total alkalinity ta and ph levels in this part of the pacific on these wave dominated atolls open ocean waves impinging on the platform margins generate currents that transport sediment from the reef across the sand apron and towards the platform interior unlike the tide dominated platforms of the bahamas however weak tides preclude strong daily agitation and circulation so ooids do not grow large and mud and fine sand transported into the atoll interiors is sequestered there in the interiors both sediment produced in situ and fine allochthonous sediment are more influenced by biological processes than by physical transport processes so bioturbated muddy sand is most common collectively the comparative analysis provides actualistic process based conceptual models for the nature and controls on variability of shelf margin reef and reef apron systems and platform interiors within and among atolls

high resolution unsaturated alkenones sea surface temperature records in the yellow sea during the period of 3500 1300 cal yr bp abstract high resolution sea surface temperature records based on long chain unsaturated alkenones u 37 k sst in the south yellow sea ys during the period of 3500 1300 cal yr bp were reconstructed in sediment core z8 from the shandong mud wedge the sst records show broad variations between 14 3 and 16 9 c 15 6 c on the average with a high sst phase at 3500 2750 cal yr bp a low and intense fluctuating sst period at 2500 2000 cal yr bp and a sharp cooling period at 1750 1300 cal yr bp superimposed on this trend five cooling periods occurred in 3360 3250 cal yr bp 3150 3050 cal yr bp 2750 2650 cal yr bp 2350 2150 cal yr bp and 1750 1300 cal yr bp variation pattern of the sst records is similar to the fluctuations of the kuroshio current kc indicating a close relationship between the yellow sea warm current yswc and the kc the general u 37 k sst curve fluctuates with the local air temperature variations the intensity of the east asia winter monsoon eawm could be a key factor affected the prevailing relationship between the cold coastal current and the warm yswc and dominated the sst variation in core site z8 during 3500 1300 cal yr bp furthermore our temperature records within age uncertainty coincides with the changes of the solar irradiance changes suggesting a possible link between solar forcing and climate variability

molecular 13c and 14c evidence for the allochthonous and ancient origin of c16c18 n alkanes in modern soils the heterogeneous isotopic composition of c3 and c4 plants can be used to to follow the fate of plant carbon into soil organic molecules thus after 23 years of cropping of maize c4 on a soil which was previously under c3 vegetation c25 c33 soil n alkanes are 13c enriched up to 9 relatively to the initial c3 soil reflecting the input of 13c enriched n alkanes from maize waxes in sharp contrast c16 c18 soil n alkanes do not show any significant 13c 12c variation over the same time interval this absence of isotopic variation along with consideration of their relative concentration absolute concentration and biodegradability demonstrate that these substances must represent a regular input from an external source evidence of a large contribution of an ancient source amounting to more than 65 of the alkane fraction is given by a 14c age of 8510 yrs bp moreover short chain n alkanes from soils diesel fuel diesel automobile exhaust and petroleum products exhibit similar distributions and 13c values these findings suggests that c16 c18 soil n alkanes represent a non point source pollution of ancient hydrocarbons either carried by aerosols or entering the soil via continuous hydrocarbon seepage from the deep sedimentary rocks of the paris basin

holocene paleoenvironment changes in the northern yellow sea evidence from alkenone derived sea surface temperature abstract a well dated high resolution sea surface temperature sst record based on long chain unsaturated alkenones from a northern yellow sea nys sediment core is present in this study variations in linear sedimentation rate alkenone content and sst clearly reveal five distinct stages consistent with changes in local sea level as well as the evolution of the yellow sea warm current yswc before 8 9 cal kyr bp the marine transgression might not reach to the northern part of the nys a shallow coastal environment was formed from 8 9 to 8 5 cal kyr bp with a subsequent fast transgression during 7 8 to 6 5 cal kyr bp after 5 8 cal kyr bp the nys was dominated by a relatively constant marine environment sst records reveal that the yswc was likely to have started since 7 0 cal kyr and strengthened progressively in period of 7 0 5 5 cal kyr bp after 5 5 cal kyr bp the sst elevated about 1 5 c which correlated well to salinity changes along the yswc indicating that the formation time of the modern yswc was at about 5 5 cal kyr bp the sst variation shows a millennial period of 1500 yr and centennial periods of 131 yr and 113 yr the 1 5 kyr cycle dominated the period of 8 9 5 5 cal kyr bp suggesting a tele connection between the yellow sea sst and global climate changes might through the kuroshio current centennial periods dominated almost all of cold periods recorded in core by14 implying the signature of solar irradiance cycles by means of the strengthened east asia winter monsoon eawm

effects of drying heating annealing and roasting on carbonate skeletal material with geochemical and diagenetic implications abstract carbonate skeletons subjected to drying heating annealing or roasting at elevated temperatures as part of routine sample preparation for chemical analyses or geochemical experiments differ significantly from skeletal materials as they occur in nature heating of skeletal samples can degrade organic material expel h2o and oh reduce the concentration of some trace elements and change the mineralogy and texture of the material thermal degradation of organics and expulsion of water in inclusions which can occur at temperatures of 100 105 c cause fracturing and pitting of skeletal samples areas of pitting reflect original concentrations of volatile phases within the skeleton coralline aragonites are partially or completely altered to calcite at temperatures of 150 c or higher the degree of alteration varies with temperature and duration of heating and genus of the coral high mg calcites hmcs tend to form calcian dolomite and multiple hmcs of lower mg content on heating but the rate of alteration is related to the taxonomic group rather than the mg content echinoids alter very rapidly dolomite detectable by x ray diffraction formed in clypeaster heated for 6 h at 200 c while the coralline red alga neogoniolithon showed no alteration after heating at 400 c for 23 h mineralogical alteration of coralline aragonites and echinoid hmcs is positively correlated with water loss skeletal carbonates comprise a very diverse and heterogeneous suite of materials and their diversity and heterogeneity are reflected in their responses to heating variations in rate and degree of alteration on heating in many cases between different subsamples of material produced by the same organism make it difficult to obtain a consistent product from heat treatment many workers have used high temperature experiments to model diagenetic processes and the results of this study have implications for diagenetic alteration as well as for laboratory analyses and experiments

westward shift of the yellow sea warm salty tongue 1 the accumulated in situ hydrographic survey as well as the satellite observed sea surface temperature sst show consistent westward shifting of the yellow sea warm salty tongue yswst in winter a 2 d thermal model is used to show the westward shifting of the yswst due to cooling and advection the mitgcm is applied to simulate the circulation in the yellow and east china seas under the northern monsoon wind in winter the sea surface height ssh is adjusted to have a ridge in the channel and a trough in the 50 70 m iso bath in the yellow sea the barotropic transport of ssh and baroclinic transport of horizontal density gradient play the major role for the shifting of the yswst while the ekman wind drift plays a minor role

complex decapod burrows and ecological relationships in modern and pleistocene intertidal carbonate environments san salvador island bahamas abstract burrowing by thalassinidean shrimp in modern tropical shallow subtidal to intertidal carbonate environments is widespread and a powerful agent of bioturbation particularly within sandy substrates deep and intense burrowing by callianassids commonly occurs along the intertidal margins of hypersaline lagoons throughout the bahamas such as pigeon creek on san salvador island where the sediments of extensive sand flats are thoroughly bioturbated by glypturus acanthochirus in addition to dominating the deep tier infauna g acanthochirus is a true ecosystem engineer and its prodigious burrowing activity results in a highly mounded topography on sand flats individual sediment cones commonly coalesce with time to form large composite mounds with surfaces stabilized by the development of microbial mats this unique biogenetically produced topography sets the stage for colonization by shallow tier burrowers particularly the upogebiid shrimp upogebia vasquezi and several species of fiddler crabs burrow systems of u vasquezi are distinctive and complex they typically consist of a pair of u shaped burrows in close proximity or criss crossing with knobs or short tunnels at their bases the entire u burrow pair is lined by a thick externally pelleted wall inside burrow diameters range from 0 2 to 1 cm and burrow depths are 10 15 cm in contrast to the much deeper callianassid burrows these complex upogebiid burrows also occur as trace fossils in late pleistocene lagoon margin facies of the grotto beach formation on san salvador initially reported as fragmentary burrow fills whole burrow systems virtually identical to the modern upogebiid burrows recently have been found at several localities these fossil burrows are most abundant in beds lying immediately below a terra rossa paleosol that marks the late pleistocene holocene stratigraphic boundary and the beds likely were deposited with sea level stillstand and regression associated with the onset of wisconsinan glaciation with their high potential for preservation these complex upogebiid trace fossils may prove useful as both paleoenvironmental and sea level position indicators in the study of quaternary carbonate sequences throughout the bahamas and other geologically similar regions

patterns of sediment composition of jamaican fringing reef facies recent carbonate sediments from jamaican north coast fringing reefs were collected along three parallel traverses in the vicinity of discovery bay each traverse extended from near shore across the back reef reef crest and fore reef to a depth of 75 m relative abundances of the biotic constituents vary between sites reflecting general patterns of reef community composition the sediment is dominated by highly comminuted coral fragments 27 1 to 63 1 plates of the calcareous green alga halimedu 0 4 to 38 7 coralline algae 4 7 to 16 2 and the encrusting foraminiferan homotremu rubrum 0 7 to 9 5 with lesser amounts of other taxonomic groups non encrusting foraminifera 1 3 5 5 molluscs 1 4 7 0 echinoderms 0 9 5 0 coral fragments coralline algae and particles of homotrema rubrum dominate the sediments of the shallow portions of the fore reef 5 15 m whereas plates of hulimedu are most abundant in sediments from the back reef and deeper portions of the fore reef 2 24 m q mode cluster analysis using sediment constituent data resulted in the delineation of four reef biofacies over the depth range of this study 1 75 m

analyzing spatial patterns in modern carbonate sand bodies from great bahama bank abstract three carbonate sand bodies on great bahama bank which show a range of depositional facies patterns typifying modern deposits as well as their ancient counterparts are quantitatively interrogated to broaden our perspective of the types of information that can be derived from studies of modern environments rimming the southern end of tongue of the ocean toto is the broadest expanse of high energy sands found in the bahamas characterized by narrow sandbars separated by wide deep channels and a lack of islands a variation of the tidal bar motif with broader and more irregular sandbars relatively narrow channels and few small islands occurs at the northern end of exuma sound schooners sands associated with tidal channels and the numerous islands of the exumas chain along the western edge of exuma sound occur primarily as flood tidal deltas the geometry of sandbars that inhabit the three sand bodies is quantified using landsat remote sensing and assembled along with optically derived bathymetric surfaces into a gis this database is quantitatively examined using a suite of morphometric tools to compare and contrast geometric character of sandbars within and between the three sand bodies considered are properties such as the size shape complexity distribution orientation and topography of the individual sandbars profiles and spatial analysis tools enable sandbar and channel spacing position relative to the platform margin connectedness separation distances and density to be characterized as has been previously reported for reef dominated environments certain aspects of the geometry of the three systems are found to behave in a systematic and hence predictable manner though important mathematical differences are revealed between the scaling of reefal landscapes and the grainy geobodies considered by this study because the three sand bodies are disparate in their overall extent and depositional settings e g orientation prevalence of islands this predictable behavior has the potential to impart considerable insight to the characterization of grainstone systems

extensive boulder erosion resulting from a range fire on the type pinedale moraines fremont lake wyoming abstract in july 1988 the flatfish range fire burned over the type pinedale moraines at fremont lake wyoming and caused extensive exfoliation of exposed boulder surfaces the mass of exfoliated material from 130 of 1030 boulders investigated was measured and recorded with information concerning factors that could influence the extent of fire induced exfoliation the range in thickness of material removed from 98 randomly selected boulders within the burn area averaged over the entire exposed boulder surface area is 6 1 to

poisson processes of carbonate accumulation on paleozoic and holocene platforms abstract cambro ordovician carbonate lithofacies units in the elbrook and conococheague formations exposed at wytheville virginia as well as those in many other phanerozoic peritidal sequences exhibit exponential thickness frequency distributions that is occurrence frequency decreases exponentially with linear increase in unit thickness such distributions are characteristic of waiting times between independent poisson events this relative frequency of spaces of different size between horizons of lithologic change is what one would expect if the horizons were distributed randomly throughout carbonate successions abundances of different lithologies both as net stratigraphic thickness and as number of occurrences also decreases exponentially among successively rare sediment types with each lithology being about 60 as plentiful as the next more abundant rock type relations between net thickness and number of occurrences for each facies define a linear trend coincident with a mean thickness for all wytheville units of 0 48 m a relation indicating that thickness distribution is independent of facies type similar relations are apparent for the horizontal extent of carbonate sediment bodies from the holocene florida bahama platform areal extents of individual facies units lithotopes are described by a frequency distribution in agreement with that anticipated for a population of equidimensional facies elements whose diameter distribution follows an exponential frequency distribution although regional gradients in sediment texture and composition are also apparent along most transects from platform margin to interior such frequency distributions indicate that lateral extents of individual sediment reflect a largely stochastic distribution of facies boundaries across this holocene surface lithotope abundances also yield trends of exponentially decreasing dominance among successively subordinate facies with each being about 70 as extensive the next more abundant sediment type relations between areas and abundances for all lithotopes define a covariant trend corresponding to a mean area of 2 2 103 km2 for all florida bahamas lithotopes we consider several numerical models of stochastic carbonate accumulation although not demonstrably unique scenarios incorporating the sequential superposition of randomly placed coniform lithotopes result in thickness and area frequency distributions that are the same as those observed in ancient and modern platform deposits such simulations of poisson processes of sediment accumulation are in general agreement with stochastic models of lithologic heterogeneity that have been more widely applied to petroleum reservoirs and groundwater aquifers to the as yet unknown degree that peritidal lithofacies area and thickness are correlated data from paleozoic and holocene platforms suggest that carbonate units should exhibit length height ratios of approximately 105 given the decimeter scale over which facies are designated in most paleozoic peritidal successions these relations predict mean lateral extents on the order of several tens of kilometers a value in general agreement with the few data that exist on spatial continuities of peritidal lithotopes in paleozoic carbonate sequences

evidence for paleoclimate changes from lignin records of sediment core a02 in the southern yellow sea since 9 5 cal kyr b p abstract sediment core a02 collected from the central yellow sea mud cysm was analyzed for various lignin parameters to provide evidence for the paleoclimate changes in the southern yellow sea sys area during the holocene the results showed that the variations of various lignin parameters were dominated by the hydrodynamic sorting process driven by climate factors and in turn lignin records can well reflect paleoclimate changes during the holocene the paleovegetation of the yellow river basin was dominated by nonwoody angiosperms and the terrestrial organic matter in core a02 was highly degraded and mainly came from peat and surface soils compared with climate records in previous studies we found that terrestrial organic matter indicator 8 marine organic matter indicator p phenols and vegetation parameters s v c v ratios had the similar variation trends with the el nino southern oscillation enso on the millennial time scale and correlated well with the bond events 0 to 6 and the east asian winter monsoon eawm on the multidecadal to centennial time scale enso events dominated the long term trends of the biomarkers in the sys during the holocene while eawm for the shorter time scale lignin records of core a02 responded not only to the regional climatic factors such as the eawm but also to the global climatic factors such as bond events and enso in addition to the global cold climate events it also recorded other regional cold events at around 3 7 cal kyr b p 6 5 cal kyr b p and 7 0 cal kyr b p and coincided well with previous related records in the east asian these proved that the paleoclimate in sys area was controlled by both regional and global climatic factors

the effects of fire on rock weathering some further considerations of laboratory experimental simulation fire in the natural environment is a widespread agent of geomorphological and biological change temperatures can exceed 1000 c there is often a rapid rise from ambient conditions through a steep thermal gradient promoting rock disintegration laboratory simulation studies have established that temperature changes which are representative of natural fires affect rock material properties which can then be related to weathering susceptibility this study extends previous work by more closely replicating the natural environment a through the simulation of rainfall and b by encasing samples to reflect the exposure of a single rock face to a passing fire event rock samples collected on cyprus were prepared and tested following previously reported procedures change in modulus of elasticity was monitored using a non destructive ultrasonic method the data corroborate previous work but with somewhat different degrees of change the new results are more likely to be representative of natural conditions and real world change the rate of rock disintegration and effects such as case hardening appear to be a function of rock thermal characteristics material properties and environmental constraints such as diurnal temperature range copyright 1999 john wiley sons ltd

the significant role of sediment bio retexturing within a contemporary carbonate platform system implications for carbonate microfacies development abstract assessments of carbonate platform reef lagoon sediments and benthic habitats around rodrigues island south west indian ocean have been undertaken in order to examine carbonate sediment textural properties and the controls on texturally defined sediment fabrics reef lagoon sediments sampled from across the expansive 8 km wide carbonate dominated windward platform principally comprise poorly sorted medium to coarse grained bioclastic sands composed of a low diversity of grain constituents predominantly non geniculate coralline algal bioclasts despite a marked homogeneity in sediment compositional and grain size properties eight distinct sediment textural groups can be identified that form a heterogeneous mosaic across the contemporary reef lagoon system only along the narrow outer platform margins reef crest sand apron and outermost lagoon environments do we observe consistent predictable transitions in sediment textural groups where physical processes are the primary drivers of selective sediment transport and sorting in contrast across the main expanse of the lagoon the sediment substrates are characterised by an irregular mosaic of texturally defined sediment groups formed primarily as a function of sediment bio retexturing the burrowing activities of alpheid and callianassid shrimps are particularly important in this respect and impart a distinctly unique textural fabric to the upper sediment horizons in the environments in which the respective organisms occur the consequence of this is that at the platform system scale individual texturally defined sediment groups are relatively poor indicators of prevailing hydrodynamic regimes or of local sediment production reflecting more the biological action of organisms inhabiting the substrate this has important implications for understanding the development of carbonate sediment fabrics in the context of palaeoenvironmental reconstructions and for interpreting a key diagnostic criteria of carbonate microfacies

coral reef sedimentation on rodrigues and the western indian ocean and its impact on the carbon cycle coral reefs in the southwest indian ocean cover an area of ca 18530 km2 compared with a global reef area of nearly 300000 km2 these regions are important as fishing grounds tourist attractions and as a significant component of the global carbon cycle the mass of calcium carbonate stored within holocene neritic sediments is a number that we are only now beginning to quantify with any confidence in stark contrast to the mass and sedimentation rates associated with pelagic calcium carbonate which have been relatively well defined for decades we report new data that demonstrate that the reefs at rodrigues like those at reunion and mauritius only reached a mature state reached sea level by 2 3 ka thousands of years later than most of the reefs in the australasian region yet field observations show that the large lagoon at rodrigues is already completely full of carbonate detritus typical lagoon depth less than 1 m at low spring tide the presence of aeolian dunes at rodrigues indicates periodic exposure of past lagoons throughout the pleistocene the absence of elevated pleistocene reef deposits on the island indicates that the island has not been uplifted most holocene reefs are between 15 and 20 m in thickness and those in the southwest indian ocean appear to be consistent with this observation we support the view that the co2 flux associated with coral reef growth acts as a climate change amplifier during deglaciation adding co2 to a warming world southwest indian ocean reefs could have added 7 10 to this global flux during the holocene

boulder weathering and erosion associated with a wildfire sierra ancha mountains arizona an april may 2000 coon creek fire burned 37 5 km 2 of the sierra ancha mountains 32 3 km miles north of globe az including 25 sandstone and 19 diorite boulders surveyed in 1989 and resurveyed after the burn after the summer 2000 monsoon season and after the winter 2001 season when viewed from the perspective of cumulative eroded area both sandstone and diorite displayed bimodal patterns with 79 of sandstone boulder area and 93 of diorite boulder area undergoing either no fire induced erosion or fire induced erosion 76 mm when stretched over cumulative boulder areas erosion due to the fire averaged 26 mm for sandstone and 42 mm for diorite post fire erosion from thunderstorm summer rains averaged i mm for 5 diorite and i mm for 10 sandstone boulders while only a single diorite boulder eroded an average of 1 2 mm after the winter winter erosion removed an average of 5 5 mm from 14 sandstone boulders thus fire appears to increase a rock s susceptibility to post fire weathering and erosion processes as predicted by goudie et al earth surf process landf 17 1992 605 in contrast to experimental research indicating the importance of size in fire weathering no statistically significant relationship exists between erosion and boulder height or boulder surface area a result similar to zimmerman et al quat res 42 1994 255 these data exclude 12 original sites and 85 boulders at sites impacted by the fire that could not be relocated with a reasonable cause for the lack of relocation being boulder obliteration by the fire given evidence from 1 0 be and 2 6 al cosmogenic nuclides earth planet sci lett 186 2001 269 supporting the importance of boulders in controlling evolution of nonglaciated bouldered landscapes geol soc amer bull 76 1965 1165 fire obliteration of boulders could be an important process driving drainage evolution in nonglaciated mountains

bio retexturing early diagenetic fabric modifications in outer ramp settings a case study from the oligo miocene of the central mediterranean abstract bioturbation is ubiquitous in cenozoic outer ramp settings the oligo miocene ramp carbonate sequences of se sicily and the maltese islands provide specific examples to illustrate the effects of sediment retexturing by burrowers and provide significant conclusions which must be taken into account by sedimentologists when interpreting palacoenvironments thalassinoidean burrow systems may penetrate several metres into the underlying beds with evidence of concentrated activity at selected levels the general intra bed process of this crustacean dominated bioturbation is well documented however the effects when several beds are involved can be dramatic 1 a buried homogeneous wackestone beds can be depleted in lime mud by gallery excavation the dumping of this mud at the sediment surface leads to lime mud enrichment of the contemporary accumulating layer and might be a major factor in the development of the tabular outer ramp bedforms 2 b vertical reworking of unlithified sediment between beds both upwards and down is capable of homogenising two distinctly dissimilar lithologies producing a third which in no way reflects the surface processes of the depositional setting 3 c bioturbation often continues during incipient near seafloor lithification this produces random lateral variations in lithology within single beds the degree of lateral dissimilarity is proportional to the intensity longevity of the bioturbation episode bio retexturing destroys primary depositional fabrics and masks inorganic process related structures it can be as effective a remodelling agent as tidal energy it can texturally remodel areas of high primary permeability into irregular interconnected zones of low permeability as the outer ramp provides a potential fluid migration route from basin to shallow water clearly bio retexturing must exert a major influence on longer term formation wide diagenetic processes

bathymetric effect on the winter sea surface temperature and climate of the yellow and east china seas 1 whether and how the atmosphere reacts to changes in extratropical sea surface temperature sst is under intense debate and this lack of understanding has been a major obstacle in the study of non el nino climate variability using new satellite measurements we detect clear ocean to atmospheric feedback in the yellow and east china yec seas that is triggered by the submerged ocean bottom topography under intense surface cooling in winter water properties are well mixed up to 100 m deep ocean depth thus has a strong influence on sst of the continental shelf leading to a remarkable collocation of warm tongues and deep channels high winds and increased cloudiness are found over these warm tongues one such band of ocean atmospheric co variation meanders through the basin following a deep channel for an amazing distance of 1000 km in addition to these climatic effects the kuroshio front where the warm current meets the much colder shelf water strengthens the growth of storms

the effect of ash and needle cover on surface runoff and erosion in the immediate post fire period abstract hillslopes are thought to be most susceptible to enhanced surface runoff and erosion immediately following wildfire due to removal of protective vegetation and litter cover and in many cases a fire induced reduction in soil wettability this enhanced susceptibility declines as vegetation and litter layer recover for logistical reasons however few studies have been able to examine the responses of burnt terrain immediately following burning and little is therefore known about the effect of the wettable ash layer that often covers the ground until it is redistributed or removed by wind or water erosion here we quantify the effects of ash and needle cast ground cover on surface runoff generation and soil erodibility in the immediate post fire period 2 10 days following a severe wildfire in an aleppo pine forest over calcareous soils in mediterranean eastern spain a homogenous vegetation cover and lack of wind during the fire resulted in 100 ash cover 36 mm mean depth across the study area the ground fire did not consume the tree crowns but its high intensity caused complete tree mortality leading to subsequent needle fall hydrological and erosional responses were measured for fifteen 1 hour rainfall simulations 55 mm h 1 on 0 25 m2 circular plots for each of three terrain types i ash and needle covered ii ash only covered and iii bare furthermore ash and needle cast cover were monitored over an eleven week period on otherwise undisturbed terrain to examine its evolution during the first critical months following burning the soils exhibited no or slight post fire water repellency the overlying wettable ash layer had a porosity of 83 providing a water storage capacity of 30 mm a third of the plots with ground cover did not generate any surface runoff ash needle and ash only plots showed 25 and 18 fold reductions in surface runoff respectively compared to bare terrain mean sediment yield from covered plots was more than two orders of magnitudes lower than from bare plots the ash cover remained unchanged during the first two weeks while overlying needle cast more than doubled heavy rainfall 153 mm over a subsequent six day period removed the ash almost entirely where no needle cast was present whereas on ash and needle covered ground only a limited redistribution and accumulation into litter dams occurred the results quantify the potential importance of ash deposits on the susceptibility of hillslopes to surface runoff and erosion immediately following fire the combination of ash and needle cast appears particularly effective in reducing hillslope responses the outcomes demonstrate clearly that the widely held notion of landscapes being most susceptible to surface runoff and erosion directly after burning is not correct where a fire has resulted in substantial ash deposition instead the susceptibility will be greatest following a storm event of sufficient severity to remove this protective layer and before the onset of vegetation recovery

rock fragments in top soils significance and processes this introductory paper reviews various aspects of rock fragments in top soils such information is required for various reasons and in particular for predicting the impact of climatic or landuse changes on the response of these soils particular attention is paid to the definition and measurement of rock fragment content in top soils the density of soils containing rock fragments the spatial distribution and movement of rock fragments in top soils the effects of rock fragments on some key hydrological processes thermal properties of top soils physical soil degradation soil erosion and soil productivity

shallowing upwards sedimentation in a coral reef lagoon great barrier reef of australia abstract sediments in the 5 25 m deep lagoon of davies reef a typical mid shelf reef in the central great barrier reef are described based on data gleaned from 19 soft sediment cores 75 mm diameter up to 7 5 m penetration 22 surface sediment samples and air lift surveys the holocene sediment pile which averages 5 10 m thickness is entirely skeletal in origin and has a very poorly sorted coral gravel rich base which grades up into poorly sorted muddy sands with infaunal molluscan gravel these muddy sands mainly derived from the reef rim as opposed to being produced in situ on the lagoon floor have been intensely bioturbated by callianassid shrimps leaving the infaunal molluscan gravel patchily distributed and the bivalves disarticulated and preferentially oriented sub hori ontally concave up there are no vestiges of primary depositional sedimentary structures such as bedding or cross bedding radiocarbon dating suggests that significant accumulation of muddy sand in the center of the lagoon did not begin until about 2 500 3 000 yr bp and that sediment accumulation rates have increased through time from an average of 1 4 mm yr between 2 400 and 640 yr bp to 3 4 mm yr over the past 640 years interpreting these data the coral gravel rich base to the sediment pile represents a period of prolific coral growth across the top of davies reef platform following flooding by the holocene transgression but before the outer reef rim caught up with sea level to form a lagoon when the rim did reach sea level about 3 000 4 000 yr bp it started to shed large qua tities of mud and sand grade sediment into the center of the reef platform and this combined with decreased water circulation led to the demise of coral growth in the newly formed lagoon as the area of reef rim at sea level increased so too did the supply of sediment to the lagoon which explains the observed increase in sediment accumulation rate through time using previously published data to aid speculation into the future development of the lagoon a shallowing upwards model for reef lagoon sedimentation is developed in this model a complete sequence consists of a fining upwards base reflecting the gradation from coral gravel up into bioturbated muddy sands and a coarsening upwards top reflecting a gradation from bioturbated muddy sands up into a zone of shallow subtidal co al rubble and patch reefs then inter and supratidal windward storm shingle ramparts and leeward sand cays

contemporary sedimentation in the cocos keeling islands indian ocean interpretation using settling velocity analysis abstract textural parameters of grain size distributions derived from sieve analysis and component analysis have been used to the exclusion of other methods to examine sedimentary processes in modern reef environments however because these methods do not reflect the hydraulic behaviour of bioclastic sediment this study uses settling velocity analysis accounting for grain size density and shape variability and component analysis of separated settling velocity fractions to describe and differentiate bioclastic deposits and infer transport pathways in the cocos keeling islands an indian ocean atoll principal component and cluster analysis of settling 251 samples and component 90 samples characteristics discriminated eight settling velocity and five component classes a derived settling velocity classification reflecting the hydraulic properties of the sediments describes a lagoonward gradient from those with fast settling characteristics on the outer reef flat to those with moderate settling character on sand aprons the active sediment transport system is constrained between these zones component analysis of bulk samples identifies two broad sediment types 1 those with reef derived components found throughout the active transport zone reef flat to sand aprons and 2 those characterised by greater proportions of gastropod and halimeda fragments which are produced and deposited in situ in the lagoon component analysis of settling fractions further resolves details of sediment movement in the active transport zone sediment is transported from the productive reef flat to passage entrances which form initial depositional environments slower settling material is selectively transported from the entrances through the passage conduits to passage exit environments these form the main depositional areas under mean energy conditions during moderate to high energy events sediment is flushed from the passage to sand apron zones with slower settling grains deposited in the deep lagoon sinks results show that settling velocity analysis and component analysis of settling fractions can resolve the nature of sediment transport patterns in reef environments at a much finer scale than studies in which analysis is based on grain size distributions

persistent intensification of the kuroshio current during late holocene cool intervals abstract the kuroshio current kc which redistributes heat and moisture from the tropics toward mid latitudes considerably affects ocean atmosphere land interactions along its pathways however our knowledge about the kc strength and associated forcing based on investigations of instrumental data and model simulations is controversial impeding assessment of its possible change in the near future in this study we investigated kc strength over the past 4400 yr by analyzing alkenone u 37 k sea surface temperature sst signal in a sediment core under the influence of the yellow sea warm current yswc a branch of the kc in the western north pacific along with a coastal sst record over the last 1000 yr outside of the yswc effect our sst record in the warm current pathway opposite to the patterns of coastal sst and solar irradiance changes at multi centennial timescales effectively manifests variations of yswc strength in conjunction with published records we show a remarkably intensified yswc and probably the kc as well during the cool interval between 1400 1850 ad the little ice age lia we suggest that cold climate conditions perhaps in relation to strengthened east asian winter monsoon and pacific walker circulation were more favorable for kc enhancement

the himalayas organic carbon burial and climate in the miocene cooling ages of rock in the himalayas imply that rapid exhumation between the main central thrust system and the south tibetan detachment system occurred between 21 and 17 ma the generation of relief and enhanced weathering which followed this event may have resulted in a pronounced increase in the delivery of dissolved strontium carbon phosphorus and other chemical weathering products to the ocean richter et al 1992 the increased supply of nutrients stimulated productivity in oceanic upwelling zones and expansion of the oxygen minimum zone leading to enhanced burial and preservation of organic matter in the monterey formation and other deposits from this interval a downdraw of atmospheric co2 associated with enhanced chemical weathering rates and organic matter burial may have led to global cooling and the expansion of the antarctic ice sheet by 15 ma the above scenario differs from the monterey hypothesis of vincent and berger in that co2 downdraw is primarily via silicate weathering rather than organic carbon burial and that organic carbon burial is driven by increased delivery of nutrients to the ocean rather than by stronger upwelling a carbon mass balance calculation which assumes that river fluxes have been increasing over the last 40 ma predicts that absolute organic carbon burial increased over this interval while at the same time the fraction of carbon buried as organic matter versus carbonate decreased this implies that the organic carbon cycle has acted as a net source of co2 to the atmosphere over the late cenozoic

uk 37 temperature estimates from eemian marine sediments in the southern coast of hainan island tropical china abstract this study concerns high resolution sea surface temperature sst changes for the eemian interglacial period reconstructed from the southern coast of hainan island china the lower marine unit in the sediment core is composed of monotonous mud 31 m thick dated to be from the eemian interglacial period or lower part of marine isotope stage 5 mis 5 determined by optically stimulated luminescence osl the high sedimentation rate and the richness of organic matter and marine fossils provide good opportunity for the study of palaeo environments in the northern margin of the south china sea scs sediment grain size foraminifer sediment color index and long chain alkenone were used to reveal the near shore sedimentary environments and temperature at millennial scale specifically a high resolution uk 37 sst record was reconstructed for the eemian interglacial period the new evidence in northwestern margin of scs shows that the maximum value of sst during the eemian interglacial is approximately 29 c and the lowest is 26 5 c the trend of decreasing sst from 29 c throughout the marine sequence is consistent with the variations in sediment grain size reflecting the cooling trend of sst and sea level lowering tendency during the last interglacial period this new eemian sst result agrees with other records in the region of scs showing a coherent descending trend but spatial heterogeneity exists in timing and amplitude the insolation changes might be the main force for initiating the sst evolution during the penultimate interglacial period

ecological perspectives on rock surface weathering towards a conceptual model a wide range of information is now available on the ecology of rock surface microorganisms including bacteria fungi and algae and lichens and their role in weathering in particular locations external environmental conditions as well as rock characteristics determine the type of rock surface community and thus the style of biological weathering a simple preliminary conceptual model can be drawn which relates biological weathering activity to an environmental stress gradient and which is applicable at a range of scales further research needs carrying out to test and extend this model in order to make some progress towards the important goal of assessing the overall importance of biological weathering to geomorphology

sediments of the dry tortugas south florida usa facies distribution on a ramp like isolated carbonate platform abstract four sedimentary facies may be delineated based on quantitative analysis of texture and composition of modern surface sediments on the dry tortugas carbonate platform these include 1 mollusk halimeda wackestone 2 mollusk packstone to grainstone 3 coralgal halimeda grainstone and 4 coralgal grainstone even though the tortugas platform is characterized by an open circulation due to deep broad marginal channels and a lack of a continuous surface breaking marginal reef facies are not distributed at random and show bathymetrical zonation also facies appear to cover wide belts rather than forming a mosaic mollusk halimeda wackestone occurs in protected platform interior areas ca 10 18 m deep mollusk packstone to grainstone occurs in more open platform interior settings adjacent to channels and in deeper outer reef areas of 14 25 m water depth coralgal halimeda grainstone is found on shallow marginal shoals 1 11 m deep and coralgal grainstone on the somewhat deeper 3 16 m seaward edges of these shoals however there is bathymetrical overlap of facies in intermediate depths of ca 5 17 m this limitation has implications for the interpretation of the fossil record because changes in water depth are commonly thought to be reflected in facies changes e g in sequence stratigraphy comparison with previous sediment studies of the 1930s 1960s and 1970s in the area exhibit a decrease in coral fragments and increases in coralline algal and mollusk shell fragments these observations might be a result of environmental changes such as coral decline and die outs during temperature events disease and the increase in macroalgae due to the ecological extinction of the echinoid diadema the results suggest that more long term studies are needed that further explore the influence of environmental change on reef sediment composition dry tortugas surface sediments consist of lower portions of halimeda plates and mollusk shell fragments and higher percentages of coralline algal fragments as compared to sediments of the adjacent florida reef tract possibly as a consequence of differences in platform morphology and exposure to waves and currents

low latitude climate control on sea surface temperatures recorded in the southern okinawa trough during the last 13 3 kyr abstract paleotemperature records were reconstructed for the past 13 3 kyr using the alkenone unsaturation index uk 37 and the tetraether index of 86 carbon atoms tex86 proxies measured in sediment core oki 151 which was collected in the southern okinawa trough the uk 37 and tex86 derived temperatures for the top sample are close to the modern mean annual sea surface temperature sst changes in ssts in the southern okinawa trough were primarily controlled by the western tropical pacific ocean low latitude winter insolation and sea level rise unlike previous studies we found that the high latitude north atlantic played no significant role in the sst variations in this area moreover ssts in the southern okinawa trough decoupled from the east asian summer monsoon system in the last 13 3 kyr the uk 37 and tex86 based ssts dropped significantly at 7 6 6 9 kyr bp centered on 7 3 kyr bp these findings suggest that the cold event at 7 3 kyr bp was widely recorded in the okinawa trough however the tex86 based ssts dropped approximately 14 c during this period for an unknown reason

holocene hydrological and sea surface temperature changes in the northern coast of the south china sea abstract in order to reconstruct the holocene environmental history of a coastal site in the northern south china sea this study analysed the organic carbon isotope ratios 13corg and alkenone unsaturation ratios uk 37 from a 36 5 m long sediment core drilled at seabed in the mouth region of the pearl river estuary and generated a coupled hydrological and temperature record this record reveals changes of monsoon induced sediment discharge and sea surface temperature of the holocene in four stages in stage i the site was under fluvial conditions prior to postglacial marine transgression stage ii saw an increase of sea surface temperature from c 23 0 c to 27 0 c associated with a strengthened summer monsoon from c 10 350 to 8900 cal years bp this was also a period of rapid sea level rise and marine transgression during which the sea inundated the palaeo incised channel i e the lower part of the t shape accommodation space created by the rising sea in these 1500 years fluvial discharge was strong and concentrated within the channel and the high sedimentation rate 11 8 mm year was very close to the rate of sea level rise in the subsequent 2000 years stage iii sea level continued to rise and the sea flooded the broad seabed above the palaeo incised channel resulted in fluvial discharge spreading thinly across the wide accommodation space and a much reduced sedimentation rate 1 8 mm year sea surface temperature in this stage reached 27 3 c initially but dropped sharply to 26 1 c towards c 8200 cal years bp the final stage covers the last 7000 years and the site was under a stable sea level sedimentation in this stage varied a little but averaged at 1 8 mm year whilst fluvial discharge and sea surface temperature didn t change much two short periods of hydrological and temperature change were observed which are related to the climatic cooling events of c 4200 cal years ago and the little ice age

cosmogenic nuclides topography and the spatial variation of soil depth abstract if the rate of bedrock conversion to a mobile layer of soil depends on the local thickness of soil then hillslopes on uniform bedrock in a landscape approaching dynamic equilibrium should be mantled by a uniform thickness of soil conversely if the depth of soil varies across an actively eroding landscape then rates of soil production will also vary and consequently the landscape will not be in morphologic equilibrium the slow evolution of hillslopes relative to the tempo of climatic variations and tectonic adjustments would suggest that local morphologic disequilibrium may be expected in many landscapes here we explore this issue of equilibrium landscapes through a previously developed model that predicts the spatial variation in thickness of soil as a consequence of the local balance between soil production and erosion first we confirm the assumption in the model that soil production varies inversely with the thickness of soil using two independent methods one method uses the theoretical prediction that at local steady state soil production equals removal the depth of soil should vary inversely with hillslope curvature the second method relies on direct measurements of in situ produced concentrations of cosmogenic 10 be and 26 al in bedrock at the base of the soil column for our study site in northern california the two methods agree and yield the expression that the rate of soil production declines exponentially with the thickness of soil from 0 077 mm year with no soil mantle to 0 0077 mm year under 1 m of soil we then use this function of soil production in a coupled production and diffusive model of sediment transport to explore the controls on the spatial variation of the depth of soil on four separate spur ridges noses where we measured the data for the function of soil production model predictions are sensitive to boundary conditions grid scale and run time nonetheless we found good agreement between predicted and observed depths of soil as long as we used the observed function of soil production the four noses each have spatially varying curvature and consequently have varying depths of soil implying morphologic disequilibrium we suggest that our study site has been subjected to a wave of incision and varying intensities of erosion because of tectonic and climatic oscillations that have a frequency shorter than the morphologic response time of the landscape

late holocene variation in vertical thermal gradient from the coastal east china sea links to monsoon climate and coastal upwelling the evolution history of coastal upwelling systems in the east china sea over the late holocene are important yet difficult to be characterized here we present 3000 year temperature records based on both alkenones uk 37 and glycerol dialkyl glycerol tetraethers texh86 from a sedimentary core in the coastal upwelling site of the southern east china sea by examining the similarity and difference between the down core texh86 derived temperature and records of sea surface temperature summer monsoon and winter monsoon we suggest that the texh86 mainly reflects temperature in the subsurface water in the studied site in this sense paired temperature records from both surface uk 37 and subsurface texh86 water would yield an estimation on the vertical thermal gradient which provides insight into the upwelling strength in the summer season weak upwelling periods occurred at 2600 2800 yr bp 2000 2400 yr bp 1200 1550 yr bp 350 750 yr bp and the recent 100 years positive correlations among the

sea surface temperature variability in southern okinawa trough during last 2700 years 1 most of the temperature reconstructions for the past two millennia are based on proxy data from various sites on land here we present a bidecadal resolution record of sea surface temperature sst in southern okinawa trough for the past ca 2700 years by analyzing tetraether lipids of planktonic archaea in the odp hole 1202b a site under the strong influence of kuroshio current and east asian monsoon the reconstructed sst anomalies generally coincided with previously reported late holocene climate events including the roman warm period sui tang dynasty warm period medieval warm period current warm period dark age cold period and little ice age however the medieval warm period usually thought to be a historical analogue for the current warm period has a mean sst of 0 6 0 8 c lower than that of the roman warm period and sui tang dynasty warm period despite an increase since 1850 ad the mean sst in the 20th century is still within the range of natural variability during the past 2700 years a close correlation of sst in southern okinawa trough with air temperature in east china intensity of east asian monsoon and the el nino southern oscillation index has been attributed to the fluctuations in solar output and oceanic atmospheric circulation

a currents of removal approach for interpreting carbonate sedimentary processes abstract this study develops a currents of removal methodology to examine and quantify the nature of physical transport processes affecting the formation of bioclastic deposits in the cocos keeling islands an indian ocean atoll this approach is based on the hydraulic settling and threshold of entrainment characteristics of bioclastic deposits and measured current energy potential mobility pm analysis of 157 samples quantifies the proportion of deposits able to be transported in each geomorphic zone results show that under mean energy conditions wave induced currents entrain and transport sediment within the atoll and show that transport of sediment is not solely reliant on storm energy conditions gradients of pm values are used to reconstruct sediment transport pathways from the reef flat 85 100 pm through shallow passages 75 100 pm to sand aprons 50 75 pm and shallow 0 20 pm and deep lagoon 0 pm comparison of settling velocity distributions of bed material and sediment retained in sediment trap experiments show that actual mobility levels correspond with pm estimates potential mobility analysis also identifies the immobile portions of deposits which increase lagoonward constituent analysis of immobile fractions and analysis of settling frequency distributions are used to differentiate the importance of physical and biological processes in the formation of deposits throughout cocos and identify the role of each geomorphic zone in the transport system the pattern of sediment is controlled by physical processes between the reef flat the primary sediment production zone with sediment transported through the shallow passage conduits to the sand aprons the formation of shallow and deep lagoon deposits is controlled by autochthonous sediment production and storm deposition potential mobility analysis is a powerful tool enabling physical transport processes within bioclastic sedimentary environments to be quantified the ability to examine an individual deposit s hydraulic behaviour and development also enables depositional processes to be examined at a much finer resolution than previously attempted using conventional textural approaches

debris flows as geomorphic agents in the huachuca mountains of southeastern arizona abstract numerous debris flows occurred in the huachuca mountains of southeastern arizona during the summer rainy season of 1988 in areas that were burned by a forest fire earlier in the summer debris flows occurred following a major forest fire in 1977 as well suggesting a causal link between fires and debris flows abundant evidence of older debris flows preserved along channels and in mountain front fans indicates that debris flows have occurred repeteadly during the late quaternary in this environment soil development in sequences of debris flow deposits indicates that debris flows probably recur over time intervals of several hundred to a thousand years in individual drainage basins in the study area surface runoff in the steep drainage basins of the huachuca mountains is greatly enhanced following forest fires as the hillslopes are denuded of their vegetative cover water and sediment eroded from the hillslope regolith are rapidly introduced into the upper reaches of tributary channels by widespread rilling and slope wash during rainfall events this influx of water and sediment destabilizes regolith previously accumulated in the channel triggering debris flows that scour the channel to bedrock in the upper reaches following a debris flow the scoured trapezoidally shaped channel gradually assumes a swale shape and the percentage of exposed bedrock declines as material is introduced from the slopes debris flows do a tremendous amount of work in a very short time however and are the major channel forming events where the tributary channels enter larger trunk channels the debris flows serve as the main source of very coarse sediment the local slope and coarse particle distribution of the trunk channel depend on the competence of water flows in the channel to transport the material introduced by debris flows where the smaller channels drain directly to the mountain front debris flows create extensive alluvial fans which dominate the morphology of the basin range boundary time intervals between debris flows in the drainage basins of the huachuca mountains are probably controlled by complex interactions among climate forest fires and slope processes fires destroy the protective vegetation that stabilizes the upper catchment slopes and inhibits erosion however not every fire that burns a catchment causes debris flows because sufficient weathered material must accumulate in the upper channel reaches to initiate a large debris flow if such accumulation has not occurred the material introduced to a channel following a forest fire will move only a short distance down the channel thus the episodic nature of debris flows probably depends on rates of slope weathering and erosion which are in turn controlled by climate both directly and through vegetation and forest fires

effects of fire on geomorphic factors and seedling site conditions within the alpine treeline ecotone glacier national park mt abstract this paper evaluates the geomorphic effects of fire on the alpine treeline ecotone and how those effects influence post fire seedling establishment conditions forest fires are becoming more common in high elevations and ecosystem responses in these areas are not well studied results indicated that burned areas experienced increased soil loss complete loss of the duff layer less compact soils larger clast sizes and increased rock spalling and altered seedling site conditions seedlings showed distinct preferences for micro sites with deeper less compact soils and a greater cover of rock the effects of fire within the alpine treeline ecotone will affect treeline position and geomorphic processes within these higher elevations

the incidence of microscopic charcoal in late glacial deposits abstract microscopic charcoal is not routinely counted by those investigating late glacial deposits it is largely the domain of those pursuing anthropogenic questions relating to the holocene interglacial 23 sites dating to the devensian late glacial ca 13 000 10 000 14c yr bp in scotland have charcoal records and seven of these can be shown to have a high charcoal content a phenomenon that has passed largely unremarked we discuss patterns of charcoal representation and explore possible explanations for high charcoal abundances especially in the loch lomond stadial including taphonomy e g secondary erosion of charcoal bearing deposits long distance transport aridity especially during the loch lomond stadial warmth and effective precipitation especially during the late glacial interstadial and humanly caused fires upper palaeolithic available data do not allow the establishment of clear relationships between vegetation types and charcoal abundance it is suggested that patterns of burning may need to be considered in the context of arid wet shifts in climate it is probable that combinations of factors are responsible for the late glacial charcoal records but the difficulty remains that too few data are routinely collected or available for study

the transient nature of the empty bucket model of reef sedimentation abstract the geometry of modern reefs has been likened to an empty bucket with the narrow reef rim comprising the container pail that encloses the water filled bucket while the analogy is valid the assumption that this constitutes a final geometry is not examples from the indian pacific and atlantic oceans individually and collectively demonstrate current filling of the lagoons by reef perimeter sand aprons since sea level only approximated its present position 3 to 6 ky ago it follows that the observed extent of modern highstand lagoon filling is minimal if the filling process was to continue unabated the result would be a flat topped bank but during the pleistocene low stands of sea level aborted the filling process extrapolating these relationships to the geologic record suggests that the empty bucket model of unfilled reef lagoon space is greatest during icehouse high frequency glacial fluctuations of sea level alternatively filled buckets in which cycle thickness approximates accommodation space are probably largely restricted to greenhouse time intervals the co occurrence of quaternary high amplitude frequency sea level changes with rapidly growing scleractinian corals probably enhanced the occurrence of empty bucket morphologies

global temperature calibration of the alkenone unsaturation index uk 37 in surface waters and comparison with surface sediments in this paper we compile the current surface seawater c37 alkenone unsaturation uk 37 measurements n 629 1 to 30 c temperature range to derive a global field based calibration of uk 37 with alkenone production temperature a single nonlinear global surface water calibration of uk 37 accurately predicts alkenone production temperatures over the diversity of modern day oceanic environments and alkenone synthesizing populations t 0 957 54 293 uk 37 52 894 uk 37 2 28 321 uk 37 3 r2 0 97 n 567 the mean standard error of estimation is 1 2 c with insignificant bias in estimated production temperature among the different ocean regions sampled an exception to these trends is regions characterized by strong lateral advection and extreme productivity and temperature gradients e g the brazil malvinas confluence in contrast to the surface water data the calibration of uk 37 in surface sediments with overlying annual mean sea surface temperature anno is best fit by a linear model anno 29 876 uk 37 1 334 r2 0 97 n 592 the standard error of estimation 1 1 c is similar to that of the surface water production calibration but a higher degree of bias is observed among the regional data sets the sediment calibration differs significantly from the surface water calibration uk 37 in surface sediments is consistently higher than that predicted from anno and the surface water production temperature calibration and the magnitude of the offset increases as the surface water anno decreases we apply the global production temperature calibration to the coretop uk 37 data to estimate the coretop alkenone integrated production temperature coretop ipt and compare this with the overlying annual mean sea surface temperature anno we use simple models to explore the possible causes of the deviation observed between the coretop temperature signal as estimated by uk 37 and anno our results indicate that the deviation can best be explained if seasonality in production and or thermocline production as well as differential degradation of 37 3 and 37 2 alkenones both affect the sedimentary alkenone signal

on the interpretation of shallow shelf carbonate facies and habitats how much does water depth matter abstract many stratigraphic studies of ancient shallow water carbonate platforms focus interpretation on the primacy of changes in accommodation inferred by assuming a direct and deterministic link between depositional facies and water depth the purpose of this study is to test this assumption explicitly and quantitatively by exploring relations between substrate type classified on the basis of both habitats and facies and the water depth at which they occur on a modern well studied shallow rimmed shelf margin gis analysis of digital benthic habitat and bathymetry maps of the shallow 8 m south florida shelf illustrate that most substrate types occur across a range of water depths similarly at greater water depths habitats and facies are more constrained more dominance of one class more deterministic with generally decreasing dominance more diversity at shallower water depths at a scale of shelf to basin transects facies and habitats clearly are related to water depth yet on this narrower 10 km shallow shelf margin at the scale of this study water depth and habitats and facies are not uniquely related or linked this general lack of correspondence between bottom type and water depth may be a manifestation of landscape disequilibrium a state in which habitats and facies do not fully reflect ambient environmental conditions perhaps recording the influence of rapid change in sea level alternatively it may reflect the impact of variables other than water depth although more general consequences of these results for other depositional settings remains to be evaluated they do emphasize the fact that variables other than bathymetry may significantly influence the ecological and sedimentologic attributes of depositional surfaces they do allow for the quantification of some of the potential uncertainties inherent in the interpretation of analogous ancient platforms and can serve to focus future observations on the causes and consequences of vertical and lateral heterogeneity in ancient stratigraphic sequences

the middle eocene seeb formation of oman an investigation of acyclicity stratigraphic completeness and accumulation rates in shallow marine carbonate settings abstract the middle eocene seeb formation represents deposition on one of the earliest modern style carbonate platforms i e influenced by seagrasses and mangroves and presents an opportunity to explore controls on the preservation of cenozoic carbonate lithofacies in the study area the seeb fm is dominated by an anomalously thick approximately 250 m and uniform package of shallow marine platform interior sediments these nodular indistinctly bedded shallow subtidal sediments display no evidence for relative sea level change such as subaerial exposure features and lack the shallowing upwards cyclothems that have characterized carbonate sediments deposited in platform interior settings throughout much of the rock record particularly during greenhouse periods we conclude that this is a consequence of thorough bio retexturing of the sediment by burrowing organisms and the roots of marine vegetation which destroyed primary fabrics facies diversity evidence for cyclicity and missing time horizons such as cycle bounding exposure surfaces it seems possible that the remarkable thickness of apparently acyclic seeb fm sediment that built up may reflect increased bio disturbance of the shallow marine environment following the late cretaceous expansion of seagrasses and mangroves a similar lack of peritidal cyclothems may be common to many cenozoic shallow marine carbonate deposits missing time horizons in limestones reflecting erosion or nondeposition have been identified by some authors to explain discrepancies between low calculated accumulation rates of ancient sediments and higher rates measured in comparable modern environments however our studies of the seeb fm suggest that the significance of such missing time horizons in ancient sediments may have been overstated and that apparent differences between modern and ancient accumulation rates are a consequence of the extrapolation of unrepresentative localized high rates of modern sediment production to large platform scale areas our study reinforces the idea that modern sediment production and accumulation rates may be much lower than previously thought because they are typically measured in highly productive areas such as seagrass beds and do not take into account the highly variable nature of carbonate production storage erosion and destruction across platforms therefore far less missing time needs to be inferred for ancient sediments to account for any imbalance between modern and ancient sediment accumulation rates

summer monsoon induced upwelling dominated coastal sea surface temperature variations in the northern south china sea over the last two millennia the south china sea scs situated to the north of the indo pacific warm pool ipwp is under the strong influence of the asian monsoon system however coastal sea surface temperature sst reco

dating fluvial terraces with and profiles application to the wind river wyoming abstract fluvial strath terraces provide a record of river incision and the timing of climatic perturbations to the fluvial system dating depositional surfaces like terraces that are older than the range of 14 c however is difficult we employ a cosmogenic radionuclide crn profile technique that addresses a major problem of crn dating on such surfaces nuclide inheritance by measuring 10 be and 26 al profiles we constrain the exposure age and the mean crn inheritance for the deposit the crn profile also yields a self check on the assumptions underlying the method we report our attempts to date terraces along the wind river wy like many sequences of western north american fluvial terraces these are inferred to reflect oscillation between glacial and interglacial conditions in the headwaters previous dating of some of these terraces and the associated terraces and glacial deposits makes this a unique location to compare dating methods dates from five sites along the bull lake glacial correlative terrace wr 3 are 118 125 ka which agrees with dates on bull lake age moraines and independent age estimates on the terrace and is consistent with the model of terrace glacial relationship crn inheritance is significant and highly variable requiring it be considered despite the additional sampling complexity assuming all inheritance in wr 3 deposits arises during exhumation in the headwaters we obtain minimum mean rates of exhumation of 13 130 m my for the source rocks alternatively assuming the crns are inherited during clast transport the time of fluvial transport from source to terrace is 10 ka it increases downstream and is lower for sand than cobbles the crn ages for older terraces wr 7 300 ka and wr 15 510 ka are lower by 50 than previous estimates based on tephrochronology the most plausible explanation is eolian deflation of a once thicker loess cover on the terrace surfaces mean thicknesses of loess of 0 5 1 5 m are required to reconcile these concentrations of crn with the previous estimates of age difficulty in dating the older terraces emphasizes that geologic caution independent estimates of age and multiple sample sites should still be part of dating depositional surfaces with crns even when employing the inheritance correction technique

centennial scale winter monsoon variability in the northern east china sea during the holocene the east china sea ecs responds to changes in the strength of the kuroshio and east asian monsoon activity multidecadal resolution records of the palaeotemperature indices and from core ky07 04 pc 1 show that the hydrology of the ecs responded to variability in the east asian winter monsoon unlike mg ca derived sea surface temperatures which show neither warming nor cooling trends during the holocene the record showed a general warming trend at a rate of 0 2 c ka 1 this warming was attributable to shrinkage of the yellow sea central cold water and or weaker winter cooling of the surface water the record indicated a centennial scale variability with an 1 c amplitude superimposed on the warming trend that reflected changes in the east asian winter monsoon and or the kuroshio temperature minima appeared at ca 3 0 4 7 6 2 7 9 and 9 0 ka and spectral analysis of the last 7 ka revealed significant peaks with periodicities of approximately 210 250 and 440 years that were close to those observed in solar radiation the reconstructed winter monsoon variability is consistent with chinese documentary records for the last two millennia copyright 2012 john wiley sons ltd

the effects of callianassa bioturbation on the preservation of carbonate grains in davies reef lagoon great barrier reef australia abstract coring air life excavation and tracer sediment experiments in the lagoon floor sediments of davies reef revealed that callianassid shrimp had produced during their feeding a 5 60 cm thick surface layer of moderately to poorly sorted gravel free sediment above very poorly sorted gravelrich sediment the subsurface gravel is epilithic in origin close to reef framework but consists predominantly of infaunal molluscs through most of the lagoon these infaunal skeletons tend to be buried rapidly in a well preserved state escaping the microboring that attacks all grains on the surface two geologically significant points emerge first the surface layer will not get preserved in its present form and any analyses of surface samples can give a false impression of the accumulating sedimen pile and the prevailing hydraulic regime and second the combination of continuous fine sediment recycling and surface microboring can lead to a bias in the fossil reefal limestone record with epilithic organisms seemingly subordinate to infaunal molluscs

weakened yellow sea warm current over the last 2 3 centuries abstract variations of oceanic currents beyond the instrumental period are often difficult to characterize although sea surface temperature sst changes along current pathways could provide some indirect information here we reconstruct four u 37 k based annual sst records over the past 2 3 centuries from muddy areas in the yellow sea ys and the northern east china sea ecs to characterize the regional sst variation patterns and to assess whether such patterns could be used to infer current changes three offshore sites are located along the pathway of the yellow sea warm current yswc and an additional coastal site near the yangtze river mouth with the minimal yswc influence the records show ssts dropped 3 6 c over the last 2 3 centuries at the three offshore sites and a warming trend toward the present at the coastal site the cooling sst trend observed at the three offshore sites is at odds with the average northern hemisphere temperature and solar irradiance changes strongly suggesting that regional processes or drivers in the ys and northern ecs regions overturned the global temperature signal accordingly we propose that the yswc weakened over the last 2 3 centuries which might be linked to the east asian winter monsoon variability

molecular stratigraphy a new tool for climatic assessment variations in sea surface temperatures over the past 500 000 years are inferred from the relative abundance behaviour of two organic compounds c37 alkenones over the upper 8 metres of a sediment core from the eastern equatorial atlantic this molecular record ascribed to contributions from prymnesiophyte algae correlates well with the variations in the 18 signal for the calcareous skeletons of certain planktonic foraminifera thus providing the first demonstration of a new stratigraphical technique which may be especially valuable where methods based on carbonate 18 fail

holocene reef accretion on the rodrigues carbonate platform an alternative to the classic bucket fill model carbonate platform evolution around the island of rodrigues southwestern indian ocean is reconstructed from cores recovered across the platform9s windward margin in contrast to the classic bucket fill model of carbonate platform evolution whereby platform filling occurs predominantly as a function of the lagoonward transport of sediment from the reef rim data from rodrigues demonstrate that the primary mode of platform filling was through reef progradation from the platform interior seaward indeed radiocarbon dates indicate that much of the platform interior had filled by 2000 cal calibrated yr b p data also indicate that the reef rim probably caught up with sea level only in the past 1000 yr and subsequent export of sediment from those areas into the lagoon has probably only become important during the final stages of the platform9s evolution we interpret this as a function of the platform margin reef9s catch up growth mode this would have allowed significant marine circulation within the platform interior thus promoting active reef growth prior to sea level being attained given that such catch up growth modes are widely recognized on many reef platform margins we suggest that this novel platform evolutionary model may have widespread applicability sounder resolution 10 cm were made at each core site and water depths were normalized to the tide curves and corrected to mean sea level msl is 1 872 m above chart datum all core depth measurements were uncompacted and were normalized to msl

slope form and associations with ground boulder cover in arid environments northeast jordan abstract many studies of slope form and sediment transfer dynamics use either bounded field plots or laboratory physical hardware models to study associations between morphology and process results are presented here of a study which examines spatial variations in slope form changing ground surface boulder cover between sites and at different points along slope profiles and evidence for the movement of fine grained sediments which underlie the boulder cover the study site is located in northeast jordan an arid landscape characterised by a late tertiary to early quaternary basalt plateau spreading across the foot slopes of the druz mountains basalt age ranges from approximately 8 9 ma to recent scoracious deposits from local eruptive centres which are no more than 100 000 years old the study considers whole slope profiles rather than a representative section of a slope and accounts for form differences by quantifying slope shape using a length height integral slope form differs with basalt age gradually changing from concave to convex shapes the boulder cover can be used to examine the mobility and redistribution of underlying fine grained sediment by establishing the degree of clast burial at points along slope profiles twenty five slope profiles were surveyed and five plots distributed between crest and toe located at similar points on thirteen the axial dimensions of boulders within each plot were recorded sorting and the preferential movement of smaller clasts is a characteristic of the steepest part of slopes while mean clast size increases downslope for older basalts and decreases downslope for younger basalts the degree of wadi network evolution and the development of sediment pans known as qa and marab varies with flow age links can be established between the age and physical nature of individual lava flows differences in slope form and their spatial distribution associations also exist between changes in boulder dimensions basalt type and the extent of clast burial between topographic highs and lows

precipitation in the yellow river drainage basin and east asian monsoon strength on a decadal time scale abstract paleomonsoon strength is difficult to reconstruct the strength of the east asian monsoon and precipitation over large areas correlate well on a decadal time scale thus monsoon strength can be reconstructed through proxies of sediments originating from large areas in the present study we investigated the characteristics of a sediment core from the northern yellow sea mud the results showed that sedimentary characteristics are mainly controlled by discharge changes of the yellow river the relationships between median grain size mz magnetic susceptibility ms and the sio2 al2o3 ratio of sediments and spatially averaged precipitation around the yellow river drainage basin reveal that changes in mz and ms are correlated with variation in precipitation the agreement of temporal trends in mz ms and the monsoon strength index confirm that spatially averaged precipitation changes in the yellow river drainage basin on decadal time scale are driven by the monsoon strength these characteristics of marine sediments from the northern yellow sea mud can thus be used as proxies for monsoon strength

north pacific and north atlantic sea surface temperature variability during the holocene holocene climate variability is investigated in the north pacific and north atlantic realms using alkenone derived sea surface temperature sst records as well as a millennial scale simulation with a coupled atmosphere ocean general circulation model aogcm the alkenone sst data indicate a temperature increase over almost the entire north pacific from 7 cal kyr bp to the present a dipole pattern with a continuous cooling in the northeastern atlantic and a warming in the eastern mediterranean sea and the northern red sea is detected in the north atlantic realm similarly sst variations are opposite in sign between the northeastern pacific and the northeastern atlantic a 2300 year long aogcm climate simulation reveals a similar sst seesaw between the northeastern pacific and the northeastern atlantic on centennial time scales our analysis of the alkenone sst data and the model results suggests fundamental inter oceanic teleconnections during the holocene

high resolution palaeofire signals from christina lake alberta a comparison of the charcoal signals extracted by two different methods abstract two high resolution palaeofire signals were extracted from the annually laminated sediment of christina lake in the boreal forest of alberta canada a charcoal curve focusing on large charcoal fragments 125 m was extracted by the sieving method described by whitlock and millspaugh a carbon curve which includes all size fractions of charcoal was extracted by a method modified from winkler s chemical assay method modifications included increasing the duration of nitric acid treatment to 2 h and using a total carbon analyser tca rather than standard loss on ignition these adjustments resulted in a carbon curve which is unaffected by clay water losses and subtle changes in sedimentology which were problematic in the original gravimetric technique the sensitivity of the tca allowed subtle shifts in carbon i e charcoal abundance to be detected in lake sediments with low levels of charcoal when compared with the known fire history near the lake since 1900 the sieved charcoal curve was most responsive to fires known to burn near the shore of the lake and less responsive to fires burning elsewhere in the watershed the tca carbon curve was somewhat more sensitive than the sieved charcoal curve for detecting fires in the drainage basin which did not burn to the lake edge the tca carbon curve was strongly correlated with sediment influx suggesting stream inputs of charcoal are the dominant influence on this signal the peak in response of the tca curve to known fire events was sometimes lagged by several years suggesting that it can take several seasons for the bulk of stream transported charcoal to make its way from the watershed to its final deposition site in the lake very large fires burning just outside the drainage basin of the lake were not detected by either method suggesting that both of the methods used are sensitive only to fires burning in the watershed and that long distance aerially dispersed charcoal is insignificant at this site

hillslope gradient particle size relations evidence for the formation of debris slopes by hydraulic processes in the mojave desert this study is concerned with debris slopes free of superincumbent cliffs or basal stream channels and developed on closely jointed and or mechanically weak rocks in the mojave desert analyses of the relation between hillslope gradient s and mean particle size bar d reveal that the slope coefficient of the relation varies with debris slope plan form and where plan form is constant the intercept varies with rock type a theoretical model is developed which shows that the observed pattern of variation in the slope of the s bar d relation with plan form is consistent with the debris slopes being formed by and adjusted to hydraulic processes debris slopes in the mojave desert appear to lie along a continuum at one end are debris slopes underlain by closely jointed and or mechanically weak rocks such as those examined in this study that are transport limited well adjusted to present hydraulic processes and exhibit a strong relationship between s and bar d at the other end are debris